MEEDICAL OIBT& -- - .SCHOOL AJSY GIFT OF THE SAN FRANCISCO COUNTY MEDICAL SOCIETY HUMAN ANATOMY The skeleton in relation to the contour of the body. HUMAN ANATOMY INCLUDING STRUCTURE AND DEVELOPMENT AND PRACTICAL CONSIDERATIONS BY THOMAS DWIGHT, M.D., LL.D. PARKMAN PROFESSOR OF ANATOMY IN HARVARD UNIVERSITY CARL A. HAMANN, M.D. PROFESSOR OF ANATOMY IN WESTERN RESERVE PROFESSOR OF ANATOMY IN THE UNIVERSITY OF UNIVERSITY PENNSYLVANIA J. PLAYFAIR McMURRICH, PH.D. PROFESSOR OF ANATOMY IN THE UNIVERSITY OF MICHIGAN GEORGE A. PIERSOL, M.D., SC.D. J. WILLIAM WHITE, M.D., PH.D., LL.D. JOHN RHEA BARTON PROFESSOR OF SURGERY IN THE UNIVERSITY OF PENNSYLVANIA WITH SEVENTEEN HUNDRED AND THIRTY-FOUR ILLUSTRATIONS, OF WHICH FIFTEEN HUNDRED AND TWENTY-TWO ARE ORIGINAL AND LARGELY FROM DISSECTIONS BY JOHN C. HEISLER, M.D. PROFESSOR OF ANATOMY IN THE MEDICO-CHIRURGICAL COLLEGE EDITED BY GEORGE A. PIERSOL PHILADELPHIA & LONDON J. B. LIPPINCOTT COMPANY Copyright, 1906, by J. B. Lippincott Company. Copyright, 1907, by J. B. Lippincott Company. Entered at Stationers' Hall, London, England. All Rights Reserved. ELECTROTYPEO AND PRINTf D 0V J. B. LIPPINCOTT COMPANY, PHILADELPHIA, U.S.A. 6jwy~: PREFACE. THE preparation of this work was undertaken with three chief considerations in mind. i. The presentation of the essential facts of human anatomy, regarded in its broadest sense, by a descriptive text which, while concise, should be sufficiently com- prehensive to include all that is necessary for a thorough understanding not only of the gross appearances and relations of the various parts of the human body, but also of their structure and development. 2. Adequate emphasis and explanation of the many and varied relations of anatomical details to the conditions claiming the atten- tion of the physician and surgeon. 3. The elucidation of such text by illustrations that should portray actual dissections and preparations with fidelity and realism. To the first of these ends the co-operation of several American teachers of anatomy was enlisted, whose contributions have been welded into a homogeneous whole. Dr. Thomas Dwight has written the description of the skeleton, including the joints, and that of the gastro-pulmonary system and of the accessory organs of nutrition. Dr. Carl A. Hamann has contributed the account of the cerebro-spinal and sympathetic nerves. Dr. J. Playfair McMurrich has supplied the systematic description of the mus- cular and of the blood- and lymph- vascular system. Dr. George A. Piersol has written the introductory, histological and embryolog- ical paragraphs throughout the work and contributed the description of the central nervous system, including the deep relations of the cranial nerves, of the organs of special sense, of the carotid, coccygeal and aortic bodies, and of the uro-genital system. The second desideratum adequate consideration of the practical applications of anatomy has been ensured by the co-operation of Dr. J. William White, whose ripe experience, both as a surgeon and as a teacher of surgery, has enabled him to point out with unusual force the relations of anatomy to the requirements of the practitioner, and to associate for the benefit of the student anatomical facts with those conditions, resulting from injury or disease, that these facts elucidate. While no attempt has been made to cover the field of operative surgery, brief descriptions of operative methods have been given when they have seemed necessary to complete the study of an anatomical region or of an important organ. Occasion- ally a relatively rare operation has been included because of the exceptional practical importance of the subject from an anatomical standpoint. The writer of the Practical Considerations has aimed at presenting, in connection with each organ or system, enough facts illustrative of the dependence of the diag- nostician and practitioner upon anatomical knowledge to awaken interest and to com- bat the tendency to regard anatomy as something to be memorized during student days and forgotten when examinations are over. Even when such facts do not seem at a first glance to come within the scope of a text-book of anatomy, it will be found that a careful comparison of this text with the descriptive portion of the book will show a real and practical relation between them a relation which, once established v VI PREFACE. in the minds of the student and the physician, will make it easier for the former to learn his anatomy and for the latter to remember and apply it. Dr. White desires to acknowledge fully his obligations to the existing treatises on applied anatomy and to the various text-books and encyclopedias on surgery and medicine from which many valuable suggestions were gathered. To Drs. Gwilym G. Davis and T. Turner Thomas, his thanks are due for a careful search for possible errors, for friendly criticism, and for help in the selection of illustrations. The illustrations for the anatomy a matter of fundamental importance in a work of this character have received most conscientious attention. The determination to produce a series of original drawings that should faithfully record the dissections and preparations as they actually appear, and not as diagrammatic figures, has involved an expenditure of time and painstaking effort that only those having experience with similar tasks can appreciate. When it is stated that considerably more than two thousand original drawings have been made in the preparation of the figures illus- trating the work, some conception will be had of the magnitude of this feature. In the completion of this labor the editor has been most fortunate in having the assistance of Dr. John C. Heisler, to whose skill and tireless enthusiasm he is indebted for the admirable dissections from which most of the illustrations of the muscles, blood-vessels, nerves, perineum and inguinal region were drawn, as well as for many suggestions for and revision of the drawings themselves. Professor Gwilym G. Davis has also rendered valuable assistance in supplying the dissections for the drawings relating to the Practical Considerations, as well as in supervising that portion of the artist's work. In addition to the numerous dissections and preparations made especially for the illustrations, advantage has been taken of the rich collections in the museums of the Medical Department of the University of Pennsylvania, of the Harvard Medical School and of the Wistar Institute of Anatomy, which were kindly placed at the editor's service. Records of the dissections, in many cases life size, were made in water colors chiefly by Mr. Hermann Faber, whose renditions combine faithful drawing with artistic feeling to a degree unusual in such subjects. The records not made by the last-named artist are from the brush of Mr. Ludwig E. Faber. The translations of the colored records into black and white, from which the final blocks have been made, as well as the original drawings of the bones and of the organs, have been made by Mr. Erwin F. Faber. To the conscientious and tireless efforts of this artist are due the technical beauty that distinguish these illustrations. Mr. J. H. Emerton drew the joints, as well as some figures relating to the gastro-pulmonary system, from dissections and sections supplied by Professor Dwight. The numerous illustrations representing the histological and embryological de- tails throughout the work, and in addition the sections of the brain-stem under low magnification, are by Mr. Louis Schmidt. In all cases sketches with the camera lucida or projection lantern or photographs have been the basis of these drawings, the details being faithfully reproduced by close attention to the original specimens under the microscope. Notwithstanding the unusually generous allotment of drawings from original dissections and preparations, advantage has also been taken of a number of illus- trations which have appeared in special monographs or in foreign journals or works. With very few exceptions such borrowed illustrations have been redrawn and modi- fied to meet the present requirements, due acknowledgment in all cases being given. PREFACE. vii The editor gratefully acknowledges the many kindnesses shown by a number of his associates. Dr. William G. Spiller generously placed at his disposal a large collection of microscopical preparations of the central nervous system, from which drawings of selected sections were made. To Dr. George Fetterolf the editor is indebted for valuable assistance in preparing for and seeing through the press the section on the peripheral nervous system. The collaboration of Dr. Edward A. Shumway very materially facilitated the preparation of the description of the eye, which received only the editor's revision. Likewise, Dr. Ralph Butler, by placing in the editor's hands a painstaking review of the more recent literature on the ear and preliminary account of that organ, greatly lightened the labor of writing the text. Further, Dr. Butler supplied the microscopical preparations from which several of the drawings were made. In addition to assuming the preparation of the index a no insignificant undertaking in a work of this character Dr. Ewing Taylor gave valu- able assistance in the final revision of the first hundred pages of the book. The editor is indebted to Dr. W. H. F. Addison for repeated favors in preparing special microscopical specimens. Dr. T. Turner Thomas kindly assisted in locating cross- references. This opportunity is taken to express full appreciation and thanks to the various authors and publishers, who so kindly have given permission to use illus- trations which have appeared elsewhere. Very earnest consideration of the question of nomenclature led to the conclusion, that the retention, for the most part, of the terms in use by English-speaking anatomists and surgeons would best contribute to the usefulness of the book. While these names, therefore, have been retained as the primary terminology, those adopted by the Basle Congress have been included, trie BNA synonyms appear- ing in the special type reserved for that purpose. The constant aim of the editor has been to use the simplest anatomical terminology and preference has always been given to the anglicized names, rather than to the more formal designations. Although in many cases the modifications suggested by the new terminology have been followed with advantage, consistent use of the Basle nomenclature seems less in accord with the conceded directness of English scientific literature than the enthusi- astic advocates of such adoption have demonstrated. The editor desires to express his appreciation of the generous support given him by the publishers and of the unstinted facilities placed by them at his disposal throughout the preparation of the work. UNIVERSITY OF PENNSYLVANIA, SEPTEMBER, 1907. CONTENTS. INTRODUCTION. Relation of Anatomy to Biology . . Subdivisions of Anatomical Study General Plan of Vertebrate Construction Descriptive Terms THE ELEMENTS Of STRUCTURE. The Elementary Tissues The Cells and Intercellular Sub- stances The Embryonal Cell Vital Manifestations Metabolism Growth Reproduction Irritability The Animal Cell , Structure of the Cytoplasm . , Structure of the Nucleus The Centrosome Division of Cells Mitotic Division . . PAGE I 6 6 7 8 9 10 ii Amitotic Division 14 EARLY DEVELOPMENT. The Ovum 15 The Spermatozoon 16 Maturation of the Ovum 16 Fertilization of the Ovum 18 Segmentation of the Ovum 21 The Blastoderm and the Blastodermic Layers 22 Derivatives of the Blastodermic Layers. . 24 The Primitive Streak and the Gastrula. . 24 The Significance of the Primitive Streak. . 25 The Fundamental Embryological Pro- cesses 26 The Neural Canal 26 The Notochord 27 The Coelom 28 The Somites 29 The Fcttal Membranes 30 The Amnion 30 The Serosa 31 The Vitelline Sac 32 The Allantois and the Chorion 32 The Human Fcetal Membranes 35 The Amnion and Allantois 35 The Chorion 41 The Amniotic Fluid 41 The Umbilical Vesicle 42 The Deciduse 44 The Trophoblast 46 The Decidua Vera 46 The Decidua Placentalis 48 The Placenta 49 The Umbilical Cord 53 The After-Birth 55 Development of Body-Form 56 The Stage of the Blastodermic Ves- icle 56 The Stage of the Embryo 56 The Visceral Arches and Fur- rows 59 The Development of the Face . . 62 The Stage of the Foetus 63 THE ELEMENTARY TISSUES. The Epithelial Tissues 67 Squamous Epithelium 68 Columnar Epithelium 69 Modified Epithelium 70 Specialized Epithelium 70 Endothelium ;..'.. 71 The Connective Tissues 73 The Cells of Connective Tissue 73 The Intercellular Constituents 74 Fibrous Tissue 74 Reticular Tissue 75 Elastic Tissue 76 Development of Connective Tissue.. 77 Tendon 77 Adipose Tissue 79 Cartilage So Hyaline Cartilage 80 Elastic Cartilage Si Fibrous Cartilage 82 Development of Cartilage 82 Bone 84 Chemical Composition 84 Physical Properties 85 Structure of Bone 85 Bone Marrow 90 Red Marrow 91 Yellow Marrow 93 Development of Bone 94 Endochondral Bone 94 Membranous Bone 98 Subperiosteal Bone 98 THE SKELETON, INCLUDING THE JOINTS. The Axial Skeleton 103 The Appendicular Skeleton 104 General Considerations of the Bones. . . . 104 General Considerations of the Joints .... 107 The Spinal Column 114 The Thoracic Vertebrae 115 CONTENTS. The Thoracic Vertebrae Continued The Cervical Vertebra; The Lumbar Vertebra? Peculiar Vertebrae Dimensions of Vertebrae Gradual Regional Changes The Sacrum The Coccyx Development of the Vertebra Variations of the Vertebrae Articulations of the Vertebral Column . . Ligaments Connecting the Bodies . . Ligaments Connecting the Laminae, and the Processes Articulations of the Occipital Bone, the Atlas and the Axis The Spine as a Whole Dimensions and Proportions Movements of the Head Movements of the Spine Practical Considerations : The Spine .... Curvature of the Spine Sprains, Dislocations and Fractures . Landmarks The Thorax The Ribs The Costal Cartilages The Sternum Articulations of the Thorax The Anterior Thoracic Articulations . The Intersternal Joints The Costo-Sternal Joints The Interchondral Joints The Costo- Vertebral Articulations. . The Thorax as a Whole The Movements of the Thorax Practical Considerations : The Thorax . . Deformities Fractures and Disease of the Ribs . . Landmarks . . , The Skull The Cranium The Occipital Bone The Temporal Bone The Tympanic Cavity The Sphenoid Bone The Ethmoid Bone The Frontal Bone The Parietal Bone The Bones of the Face The Superior Maxilla The Palate Bone The Vomer The Lachrymal Bone The Inferior Turbinate Bone The Nasal Bone The Malar Bone The Inferior Maxilla The Temporo-Maxillary Articulation .... The Hyoid Bone The Skull as a Whole The Exterior of the Cranium The Interior of the Cranium The Architecture of the Cranium .... The Face The Orbit The Nasal Cavity The Accessory Pneumatic Cav- ities The Architecture of the Face . . . The Anthropo|ogy of the Skull Practical Considerations : The Skull .... The Cranium. . 116 117 119 122 122 124 I2 7 128 131 132 132 133 135 138 141 142 142 *43 144 144 146 149 149 153 155 '57 158 159 160 160 160 162 165 167 167 169 170 172 172 172 176 183 1 86 191 194 197 199 199 204 205 207 208 209 209 211 214 216 216 218 220 220 222 222 223 226 228 228 235 235 Malformations The Wormian Bones Diseases of the Cranial Bones Fractures Landmarks The Face Deformities and Fractures Dislocation of the Jaw Landmarks The Bones of the Upper Extremity The Shoulder-Girdle The Scapula Practical Considerations Malformations Fractures and Disease Landmarks Ligaments of the Scapula The Clavicle Practical Considerations Malformations Fractures and Disease Landmarks The Sterno-Clavicular Articulation . The Coraco-Clavicular Ligament. . . . Movements of the Clavicle and Scap- ula Surface Anatomy of the Shoulder- Girdle.. Practical Considerations The Sterno-Clavicular Articula- tion The Acromio-Clavicular Articu- lation The Humerus Practical Considerations Malformations Separation of the Epiphyses .... Fractures and Disease The Shoulder-Joint Practical Considerations Dislocations and Diseases Landmarks The Ulna Practical Considerations Malformations Fractures Landmarks The Radius Practical Considerations Malformations Fractures and Disease Landmarks The Radio-Ulnar Articulations The Forearm as a Whole The Elbow-Joint Practical Considerations Dislocations and Disease Landmarks The Bones of the Hand The Carpal Bones The Metacarpal Bones The Phalanges Practical Considerations The Carpus The Metacarpus The Phalanges Landmarks Ligaments of Wrist and Metacarpus Movements and Mechanics of Wrist and Carpo-Metacarpal Articu- lations Surface Anatomy of the Wrist and Hand . 235 236 237 238 240 242 243 246 246 248 248 248 253 253 254 255 256 257 258 259 259 260 261 262 262 263 263 263 264 265 270 270 271 273 274 278 278 280 281 285 285 286 287 287 293 293 294 296 297 299 301 305 305 308 309 309 3U 317 319 319 319 320 320 320 326 328 CONTENTS. XI Practical Considerations: The Wrist- Joint 329 Landmarks 33 The Joints of the Carpus, Metacarpus and Phalanges 630 The Bones of the Lower Extremity 332 The Pelvic Girdle 33 2 The Innominate Bone 332 Joints and Ligaments of the Pelvis. . 337 The Sacro-Iliac Articulation. . . . 338 The Symphysis Pubis 339 The Sacro-Sciatic Ligaments. . . 339 The Pelvis as a Whole 341 Mechanics of the Pelvis 342 Surface Anatomy 345 Practical Considerations: The Pelvis... 345 Malformations 345 Fractures and Disease 346 Landmarks 349 Joints of the Pelvis 350 The Femur 352 Surface Anatomy 360 Practical Considerations: 361 The Epiphyses 361 Fractures and Disease 363 Landmarks 366 The Hip-Joint 367 Practical Considerations 374 Outward or Posterior Luxations .... 375 Inward or Anterior Luxations 377 Congenital Luxation 380 Disease of the Hip- Joint 380 The Framework of the Leg 382 The Tibia 382 Practical Considerations 387 Separation of the Epiphyses 387 Fractures and Disease 389 Landmarks 390 The Fibula 39 1 Practical Considerations 393 Separation of Upper Epiphysis .... 393 Fractures and Disease 394 Landmarks 396 Connections of the Tibia and Fibula. . . . 396 The Bones of the Leg as one Apparatus 397 The Patella 398 The Ligamentum Patellae 400 The Knee-joint 400 Practical Considerations : The Knee- joint 409 Dislocations 409 Subluxation of Semilunar Cartilages 411 Disease of Knee-joint 412 The Patella 416 The Bones of the Foot 419 The Tarsal Bones 419 The Metatarsal Bones 428 The Phalanges 432 Practical Considerations : The Foot- Bones 436 Fracture, Dislocation and Disease . . 437 Landmarks 437 The Ankle-joint 438 The Articulations of the Foot 440 Intertarsal Joints 445 Tarso-Metatarsal Joints 446 Metatarso-Phalangeal Joints 447 Synovial Cavities 447 The Foot as a Whole 447 Surface Anatomy 449 Practical Considerations: The Ankle- joint 450 Dislocations and Disease 450 Tarsal, Metatarsal and Phalangeal Joints 45i Landmarks 453 THE MUSCULAR SYSTEM. Muscular Tissue in general 454 Nonstriated or Involuntary Muscle. . 454 Structure 455 Development 457 Striated or Voluntary Muscle 457 General Structure 458 Structure of the Muscle-Fibre. . 459 Cardiac Muscle 462 Development of Striated Muscle. 465 Myomeres and their Modifica- tions 467 General Consideration of the Muscles .... 468 Attachments 468 Form 469 Fasciae 470 Tendon - Sheaths 470 Bursae 471 Classification 471 Nerve-Supply 473 The Branchiomeric Muscles 474 The Trigeminal Muscles 474 Muscles of Mastication 474 Submental Muscles 477 Trigeminal Palatal Muscle 479 Trigeminal Tympanic Muscle 479 The Facial Muscles 479 Hyoidean Muscles 480 Platysma Muscles 480 Superficial Layer 481 Deep Layer 486 Practical Considerations: Muscles and Fasciae of Cranium 489 The Scalp 489 The Face 492 Landmarks 494 The Vago- Accessory Muscles 495 Muscles of Palate and Pharynx 495 Muscles of Larynx 1824 Trapezius Muscles 499 The Metameric Muscles 502 The Axial Muscles 5 02 Orbital Muscles 502 Fasciae of Orbit ....... 504 Movements of Eyeball 505 Hypoglossal Muscles 506 The Trunk Muscles : 50? The Dorsal Muscles 507 Transverso-Costal Tract 508 Transverso-Spinal Tract 511 The Ventral Muscles 515 Abdominal Muscles 515 Rectus Muscles 516 Obliquus Muscles 517 Ventral Aponeurosis 521 Inguinal Canal 523 Anterior Abdominal Wall. . 525 Hyposkeletel Muscles 526 Practical Considerations : The Abdo- men 526 The Loin ... 53 XII CONTENTS. Practical Considerations Continued Landmarks and Topography o f Abdomen Anatomy of Abdominal Incisions . . Examination of Abdomen. The Thoracic Muscles kectus .Muscles Obliquus Muscles Hyposkeletal Muscles, The Cervical Muscles The Deep Cervical Fascia Rectus Muscles Obliquus Muscles Triangles of the Xeck 1 1 y pi >skeletal Muscles Practical Considerations : The Neck. . . . Cervical Fascia and its Spaces Landmarks The Diaphragm The Pelvic and Perineal Muscles Pelvic Fascia Obturator Fascia Pelvic Muscles Perineal Muscles The Appendicular Muscles The Muscles of the Upper Limb Muscles extending between Axial Skele- ton and Pectoral Girdle Pectoral Fascia Preaxial Muscles Postaxial Muscles The Axilla Muscles passing from Pelvic Girdle to Brachium Preaxial Muscles Postaxial Muscles Practical Considerations : Muscles and Fascia of Axilla and Shoulder. . Fracture of Clavicle Dislocation of Shoulder- Joint The Brachial Muscles Preaxial Muscles. Postaxial Muscles Practical Considerations : Muscles and Fascia of the Arm Fractures of Humerus The Antibrachial Muscles Preaxial Muscles Postaxial Muscles Practical Considerations : The Forearm. The Muscles of the Hand Deep Fascia 531 535 537 538 538 538 542 542 543 546 547 548 55 55i 554 556 558 558 559 559 562 566 568 568 568 568 571 574 575 575 575 579 579 582 585 585 588 589 590 591 592 598 603 606 606 Preaxial Muscles 607 Muscles of First Layer 607 Muscles of Second Layer 610 Muscle of Third Layer ; 610 Muscles of IV and V Layers. ... 611 Postaxial Muscle Practical Considerations : The Wrist and Hand 613 Palmar Abscesses 616 Dislocation of Thumb 617 Surface Landmarks of Upper Extremity . 618 The Muscles of the Lower Limb 623 Muscles extending from Pelvic Girdle to Femur 623 Preaxial Muscles 623 Postaxial Muscles 630 The Femoral Muscles 633 P'ascia Lata 633 Preaxial Muscles 636 Postaxial Muscles 639 Practical Considerations : Muscles and Fascia; 641 The Buttocks 641 The Hip and Thigh 642 Fractures of the Femur 644 The Knee 645 Bursae of Popliteal Region 646 The Crural Muscles 647 The Crural Fascia 647 Preaxial Muscles 648 Superficial Layer 649 Middle Layer 651 Deep Layer 654 Postaxial Muscles 655 The Muscles of the Foot 659 The Plantar Fascia 659 Preaxial Muscles 659 First Layer 660 Second Layer 662 Third Layer 662 Fourth and Fifth Layers 663 Postaxial Muscles 665 Practical Considerations : Muscles and Fascia; 665 The Leg 665 The Ankle and Foot 666 Club- Foot 667 Surface Landmarks of Lower Extremity 669 The Buttocks and Hip '. 669 The Thigh 670 Tin- Kurt- 671 The Leg 671 The Ankle and Foot 672 THE VASCULAR SYSTEM. Tin MM >< >n-Y.\soi.AK SYSTEM. The Structure of Blood- Vessels 673 The Arteries 675 The Veins 677 The Capillaries 678 The Blood 680 General Characteristics 680 Blood-Crystals 680 The Colored MU.d-eYlls 681 The Colorless l',lood-( /ells 684 The Blond-Plaques 685 Development of Blood-Vessels and Cells.. 686 The Heart General Description 689 Position and Relations 692 Chambers of the I leart 693 Architecture of the Heart-Muscle . . . 700 Structure 702 Blood* Vessels and Lymphatics 71.3 Nerves ;i 1 ).-\eli (pinellt ;. -5 Practical Considerations: The Heart. .. . 710 Valvular Disease 711 Rupture and \Vounds 713 The Pericardium 71.} CONTENTS. Xlll Practical Considerations: The Pericar- dium 717 The General Plan of the Circulation .... 719 THE ARTERIES 719 General Plan of Arterial System. .. . 720 The Pulmonary Aorta 722 The Systemic Aorta 723 The Aortic Arch 723 Practical Considerations: Aortic Arch and Thoracic Aorta 726 Surface Relations 726 Aneurisms 727 The Coronary Arteries 728 The Innominate Artery 729 Practical Considerations 729 The Common Carotid Arteries 730 Practical Considerations 731 The External Carotid Artery 733 Practical Considerations 733 Branches of External Carotid Ar- tery 734 The Internal Carotid Artery 746 Practical Considerations.. 747 Branches of Internal Carotid Artery, 748 Anastomoses of Carotid System. .. . 753 The Subclavian Artery 753 Practical Considerations 756 Branches of Subclavian Artery 758 The Axillary Artery 767 Practical Considerations 769 Branches of Axillary Artery 771 The Brachial Artery 773 Practical Considerations 775 Branches of Brachial Artery 777 The Ulnar Artery 778 Practical Considerations 780 Branches of Ulnar Artery 781 The Radial Artery 785 Practical Considerations 786 Branches of Radial Artery 787 The Thoracic Aorta 791 Branches of Thoracic Aorta 792 The Abdominal Aorta 794 Practical Considerations 796 The Visceral Branches. 797 The Parietal Branches 805 The Common Iliac Arteries 807 Practical Considerations 807 The Internal Iliac Artery 808 Practical Considerations 810 Branches of Internal Iliac Artery. .. . 810 The External Iliac Artery 818 Practical Considerations 819 Branches of External Iliac Artery . . . 820 The Femoral Artery 821 Practical Considerations 824 Branches of Femoral Artery 826 Anastomoses of Femoral Artery. ... 831 The Popliteal Artery 831 Practical Considerations 832 Branches of Popliteal Artery 833 The Posterior Tibial Artery 835 Practical Considerations 836 Branches of Posterior Tibial Artery, 838 The Anterior Tibial Artery 842 Practical Considerations 842 Branches of Anterior Tibial Artery, 844 The Dorsal Artery of the Foot 845 Development of the Arteries 846 THE VEINS 850 General Characteristics 850 Classification 852 The Pulmonary System 852 The Pulmonary Veins 852 The Cardinal System 854 The Cardiac Veins 854 The Superior Caval System 857 Vena Cava Superior 857 Practical Considerations 858 The Innominate Veins 858 Practical Considerations 859 Tributaries of Innominate Veins 859 The Internal Jugular Vein 861 Practical Considerations 863 Tributaries of Internal Jugular Vein. 863 The Sinuses of the Dura Mater 867 Practical Considerations 869 The Diploic Veins 874 Practical Considerations 875 The Emissary Veins 875 Practical Considerations 876 The Cerebral Veins 877 Practical Considerations 878 The Ophthalmic Veins 879 Practical Considerations 880 The External Jugular Vein. 880 Practical Considerations 881 Tributaries of External Jugular Vein 882 The Subclavian Vein 884 Practical Considerations 885 Veins of the Upper Limb 886 The Deep Veins 886 The Superficial Veins ' 889 Practical Considerations 891 The Azygos System 893 The Azygos Vein 893 Tributaries 893 Practical Considerations 895 The Hemiazygos Vein 895 The Accessory Hemiazygos Vein. . 895 The Intercostal Veins 896 The Spinal Veins 897 Practical Considerations 898 The Veins of the Spinal Cord 898 The Inferior Caval System 898 Vena Cava Inferior 899 Practical Considerations 900 Tributaries of Inferior Cava. ... 901 Practical Considerations . . . 904 The Common Iliac Veins 905 The Internal Iliac Veins 905 Tributaries of Internal Iliac .... 905 The External Iliac Vein 909 Tributaries of External Iliac. . . . 909 The Veins of the Lower Limb 910 The Deep Veins 910 The Superficial Veins 914 Practical Considerations of Iliac Veins and Veins of Lower Limb .... 917 The Portal System 919 The Portal Vein 919 Tributaries of Portal Vein 920 Practical Considerations 925 Development of the Veins 926 The Foetal Circulation 929 THE LYMPHATIC SYSTEM. General Consideration 931 Lymph-Spaces 93 1 Lymph-Capillaries 933 Lymph-Vessels 934 Lymph-Nodes 935 Structure of Lymphoid Tissue 936 Development of Lymphatic Vessels and Tissues 939 The Thoracic Duct 94* XIV CONTENTS. The Thoracic Duct Continued Practical Considerations 944 The Right Lymphatic Duct 945 The Lymphatics of the Head 945 The Lymph-Nodes 945 The Lymph- Vessels 949 Practical Considerations 955 The Lymphatics of the Neck 957 The Lymph-Nodes 957 The Lymph-Vessels 958 Practical Considerations 959 The Lymphatics of the Upper Limb .... 961 The Lymph-Nodes 961 i The Lymph- Vessels 963 ^ Practical Considerations 965 * The Lymphatics of the Thorax 966 The Lymph-Nodes 966 The Lymph-Vessels 968 Practical Considerations 971 The Lymphatics of the Abdomen 972 The Lymph-Nodes 972 The Lymph- Vessels 976 The Lymphatics of the Pelvis 983 The Lymph-Nodes 983 The Lymph -Vessels 984 Practical Considerations 990 The Lymphatics of the Lower Limb .... 991 The Lymph-Nodes 991 The Lymph-Vessels 993 Practical Considerations 994 THE NERVOUS SYSTKM. General Considerations 996 The Nervous Tissues 997 The Nerve-Cells 997 The Nerve-Fibres 1000 Neuroglia 1003 The Nerve-Trunks 1006 The Ganglia 1007 Development of the Nervous Tissues . . . 1009 Nerve-Terminations 1014 Motor Endings 1014 Sensory Endings 1015 THE CENTRAL NERVOUS SYSTEM. THE SPINAL CORD 1021 Membranes 1022 Cord-Segments 1024 Form of the Spinal Cord 1026 Columns of the Cord 1027 Gray Matter 1028 Central Canal 1030 Microscopical Structure 1030 White Matter 1036 Fibre Tracts 1039 Blood- Vessels of Spinal Cord 1047 Development of Spinal Cord 1049 Practical Considerations : Spinal Cord. . 1051 Malformations 1051 Injuries 1052 Localization of Lesions 1053 THE BRAIN 1055 General Description 1056 General Development 1058 Derivatives from the Rhombencephalon 1063 The Medulla Oblongata 1063 Internal Structure 1068 The Pons Varolii 1077 Internal Structure 1078 The Cerebellum 1082 Lobes and Fissures 1084 Architecture 1088 Internal Nuclei 1088 Cerebellar Cortex 1090 Cerebellar Peduncles 1093 The Fourth Ventricle 1096 Development of the Hind- Brain Deri- vatives 1 100 The Medulla 1 101 The Pons 1 103 The Cerebellum 1 103 The Mesencephalon 1 105 The Corpora Quadrigemina 1106 The Cerebral Peduncles 1 107 The Sylvian Aqueduct 1 108 Internal Structure of the Mid-Brain 1112 The Tegmentum 1112 The Crusta 1115 The Median Fillet 1115 The Posterior Longitudinal Fas- ciculus 1116 Development of Mid-Brain 1117 The Fore-Brain 1 1 19 The Diencephalon 1119 The Thalamus 1119 Structure 1120 Connections 1121 The Epithalamus 1 123 The Trigonum Habenulae 1123 The Pineal Body 1 124 The Posterior Commissure 1125 The Metathalamus 1 1 26 The Hypothalamus 1127 The Subthalamic Region 1127 The Corpora Mammillaria ... . . . 1128 The Pituitary Body 1129 The Third Ventricle 1131 The Telencephalon 1 132 The Cerebral Hemispheres 1 133 Cerebral Lobes and Interlobar Fissures 1135 Lobes of the Hemispheres 1139 Frontal Lobe 1 139 Parietal Lobe 1 143 Occipital Lobe 1 145 Temporal Lobe 1147 Insula 1149 Limbic Lobe 1 150 The Rhinencephalon 1151 The Olfactory Lobe 1151 Architecture of the Hemispheres 1 155 The Corpus Callosum 1155 The Fornix 1158 The Septum Lucidum 1159 The Lateral Ventricles 1160 Internal Nuclei of the Hemisphere 1169 The Caudate Nucleus 1 169 The Lenticular Nucleus 1169 The Claustrum 1172 The Amygdaloid Nucleus 1172 The Internal Capsule 1 173 Structure of the Cerebral Cortex. 1175 The Nerve-Cells of Cortex 1 176 The Nerve-Fibres of Cortex 1179 Variations in Cerebral Cortex 1180 White Centre of the Hemisphere 1 1 s^ The Association Fibres 1182 The Commissnral Fibres 1184 CONTENTS. White Centre of the Hemisphere Continued The Projection Fibres 1187 Development of the Derivatives of Fore- Brain 1189 The Pallium 1189 The Sulci and Gyri 1 190 Histogenesis of Cerebral Cortex. .. . 1192 The Rhinencephalon 1 193 The Corpus Striatum 1 193 The Diencephalon 1193 The Cerebral Commissures 1194 Measurements of the Brain 1195 The Membranes of the Brain 1197 The Dura Mater 1 198 The Pia Mater 1202 The Arachnoid 1203 The Pacchionian Bodies 1205 The Blood -Vessels of the Brain 1206 Practical Considerations : The Brain and Its Membranes 1207 Congenital Errors of Development. . 1207 The Meninges ' 1208 Cerebral Hemorrhage 1209 Cerebral Localization 1210 Cranio-Cerebral Typography 1214 THE PERIPHERAL NERVOUS SYSTEM. THE CRANIAL NERVES The Olfactory Nerve The Optic Nerve The Oculomotor Nerve The Trochlear Nerve The Trigeminal Nerve The Gasserian Ganglion The Ophthalmic Nerve and Branches The Ciliary Ganglion The Maxillary Nerve and Branches The Spheno-Palatine Gang- lion The Mandibular Nerve and Branches The Otic Ganglion The Submaxillary Ganglion Practical Considerations: The Tri- geminal Nerve The Abducent Nerve The Facial Nerve Practical Considerations The Auditory Nerve The Glosso-Pharyngeal Nerve The Vagus or Pneumogastric Nerve Practical Considerations The Spinal Accessory Nerve Practical Considerations The Hypoglossal Nerve Practical Considerations THE SPINAL NERVES The Posterior Primary Divisions The Cervical Nerves The Thoracic Nerves The Lumbar Nerves The Cpccygeal Nerve The Anterior Primary Divisions The Cervical Nerves The Cervical Plexus and Branches 1 220 1220 1223 1225 1228 1230 1232 1233 1236 1237 1240 1242 1246 1247 1248 1249 1250 1254 1256 1260 1265 1272 1274 1275 1275 1277 1278 1279 1281 1282 1282 1284 1284 1285 1286 The Phrenic Nerve 1290 Practical Considerations 1 292 The Brachial Plexus and Branches 1292 The External Anterior Thoracic Nerve 1 297 The Musculo-Cutaneous Nerve 1298 The Median Nerve 1298 Practical Considerations 1301 The Internal Anterior Thoracic Nerve 1303 The Lesser Internal Cutaneous Nerve 1303 The Internal Cutaneous Nerve 1303 The Ulnar Nerve 1303 Practical Considerations 1306 The Subscapular Nerves 1306 The Circumflex Nerves 1307 Practical Considerations 1308 The Musculo-Spiral Nerve 1308 Practical Considerations 1314 The Thoracic Nerves 1314 Practical Considerations 1318 The Lumbar Plexus and Branches 1319 The Ilio-Hypogastric Nerve 1320 The Ilio-Inguinal Nerve 1321 The Genito-Crural Nerve 1322 The External Cutaneous Nerve ..'... 1324 The Obturator Nerve 1324 The Accessory Obturator Nerve. . . . 1324 The Anterior Crural Nerve 1327 Practical Considerations : Lumbar Plexus 1330 The Sacral Plexus and Branches 1331 The Great Sciatic Nerve 1335 The External -Popliteal Nerve 1336 The Anterior Tibial Nerve 1336 The Musculo-Cutaneous 1338 The Internal Popliteal Nerve 1339 The Posterior Tibial Nerve 1342 The Pudendal Plexus and Branches 1345 The Small Sciatic Nerve 1348 The Pudic Nerve 1349 The Coccygeal Plexus 1352 Practical Considerations : Sacral Plexus 1352 THE SYMPATHETIC NERVES 1353 General Constitution and Arrange- ment 1355 The Gangliated Cord 1356 Rami Communicantes 1356 Cervico-Cephalic Portion of Gangliated Cord 1358 The Superior Cervical Ganglion 1359 The Middle Cervical Ganglion 1362 The Inferior Cervical Ganglion 1362 Thoracic Portion of Gangliated Cord . . . . 1364 The Splanchnic Nerves 1364 Lumbar Portion of Gangliated Cord. .. . 1366 Sacral Portion of Gangliated Cord 1367 The Plexuses of the Sympathetic Nerves 1367 The Cardiac Plexus 1367 The Solar Plexus 1368 Subsidiary Plexuses 1369 The Hypogastric Plexus 1374 Subsidiary Plexuses 1374 Practical Considerations : The Sympa- thetic Nerves 1375 Development of the Peripheral Nerves. . 1375 THE ORGANS OF SENSE. THE SKIN. General Description 1381 Structure 1382 The Hairs 1389 XVI CONTENTS. The Hairs Continued Structure ............. The Nails ............................. 1394 The Cutaneous Glands ................. J 397 The Sebaceous Glands ............. : 397 The Sweat Glands ................. 1398 Development of the Skin and its Append- ages ........................ THE NOSE. The Outer Nose Cartilages of the Nose ............. i44 Practical Considerations : The External Nose ....................... 1407 The Nasal Fossa? ...................... 1409 The Vestibule ..................... 1409 The Septum ...................... 1410 The Lateral Wall .................. 1410 The Nasal Mucous Membrane ...... 1413 The Olfactory Region .......... 1413 The Respiratory Region ....... 1415 Jacobson's Organ ................. I4 J 7 Practical Considerations : The Nasal Cavities .................... 1417 The Accessory Air-Spaces ............. 1421 The Maxillary Sinus ............... I4 22 The Frontal Sinus ................. i4 2 3 The Ethmoidal Air-Cells ........... 1424 The Sphenoidal Sinus ............. 1425 Practical Considerations : The Accessory Air-Spaces .................. 1426 Development of the Nose .............. 1429 THE ORGAN OF TASTE The Taste-Buds ....................... 1433 Structure ......................... 1434 Development ..................... 1436 THE EVE'. The Orbit and its Fascke .............. 1436 Practical Considerations ........... 1438 The Eyelids and Conjunctiva .......... 1441 Practical Considerations ........... 1446 The Eyeball .......................... 1447 Practical Considerations ........... 1448 The Fibrous Tunic .................... 1449 The Sclera ........................ 1449 The Cornea ....................... 1450 Practical Considerations ........... 1453 The Vascular Tunic ................... 1454 The Choroid .................... : . 1455 The Ciliary Body .................. 1457 Practical Considerations 1459 The Iris 1459 Practical Considerations 1461 The Nervous Tunic 1462 The Retina 1462 Practical Considerations , 1468 The Optic Nerve 1469 Practical Considerations 1470 The Crystalline Lens 1471 Practical Considerations 14/3 The Vitreous Body 1473 Practical Considerations 1474 The Suspensory Apparatus of the Lens.. 1475 The Aqueous Humor and its Chamber. . 1476 Practical Considerations 1476 The Lachrymal Apparatus 1477 The Lachrymal Gland 1477 The Lachrymal Passages 1478 Practical Considerations 1479 Development of the Eye i4 So THE EAR. The External Ear 1484 The Auricle 1484 The External Auditory Canal 1487 Practical Considerations 1490 The Middle Ear I49 2 The Tympanic Cavity I49 2 The Membrana Tympani 1494 The Auditory Ossicles I49 6 The Mucous Membrane 1500 The Eustachian Tube 1501 The Mastoid Cells 1504 Practical Considerations : The Middle Ear 1504 The Tympanic Cavity I54 The Tympanic Membrane 1505 The Eustachian Tube 1507 The Mastoid Process and Cells 1508 The Internal Ear i5 10 The Osseous Labyrinth 1511 The Vestibule 15" The Semicircular Canals 1512 The Cochlea 1513 The Membranous Labyrinth 1514 The Utricle I5U The Saccule 15*5 The Semicircular Canals 1515 The Cochlear Duct 151? The Nerves of the Cochlea 1521 Development of the Ear 1523 THE GASTRO-PULMONARY SYSTEM. General Considerations 1527 Mucous Membranes 1528 Structure 1528 Glands 1531 Types of ('.lands 1331 Simple Tubular Glands 1532 Compound Tubular (".lands 1532 Tubo- Alveolar Glands 1532 >< TOUS ('.lands 1534 Mucous ( '.lauds 1534 Simple Alveolar 1535 Compound Alveolar < .lands. .. . 1535 Development of < '.lands 1537 THK AIIMI NTARV CANAL. Th<- Mouth. . 1538 The Lips, Cheeks and Vestibule 1538 The Teeth '. '54 2 Description of Individual Forms. . . . 1543 Structure of the Teeth 1548 The Enamel i.S4 s The Dentine 155 The Cementum 1552 The Alveolar Periosteum 1553 Implantation and Relations of the Teeth 1554 Development of the Teeth 1556 First and Second I Jentition 1564 The Gums 1567 The Palate 1567 The Hard Palate 1567 The Soft Palate 1568 CONTENTS. XV11 The Tongue 1573 General Description 1573 The Glands of the Tongue '1575 The Muscles of the Tongue 1577 The Sublingual Space 1581 The Salivary Glands 1582 The Parotid Gland 1582 The Submaxillary Gland '. 1583 The Sublingual Gland 1585 Structure of the Salivary Glands. ... 1585 Development of the Oral Glands. . . . 1589 Practical Considerations: The Mouth. ... 1589 Malformations : Harelip and Cleft Palate 1589 The Lips 159 The Gums 159 The Teeth I59 1 The Roof of the Mouth 1592 The Floor of the Mouth 1593 The Cheeks 1594 The Tongue 1594 The Pharynx 1596 The Naso-Pharynx 1598 The Oro-Pharynx 1598 The Laryngo-Pharynx 1598 The Lymphoid Structures 1599 The Faucial Tonsils 1600 The Pharyngeal Tonsil 1601 Relations of the Pharynx 1601 Development and Growth of Pharynx 1603 Muscles of the Pharynx 1604 Practical Considerations : The Pharynx.. 1606 The (Esophagus 1609 General Description 1609 Course and Relations 1609 Structure 161 1 Practical Considerations : (Esophagus. .. 1613 Congenital Malformations 1613 Foreign Bodies 1613 Strictures 1614 Carcinoma 1614 Extrinsic Disease 1614 Diverticula : 1614 The Abdominal Cavity 1615 The Stomach 1617 General Description 1617 Peritoneal Relations 1619 Position and Relations 1619 Structure 1621 Growth 1629 Variations 1629 Practical Considerations : The Stomach 1629 Congenital Malformations 1629 Injuries of the Stomach 1630 Ulcers and Cancer 1631 Dilatation and Displacement 1631 Operations on the Stomach 1632 The Small Intestine 1633 General Description 1633 Structure 1634 The Duodenum 1644 Duodeno-Jejunal Fossae 1647 Interior of the Duodenum 1648 The Jejuno-Ileum 1649 The Mesentery and Topography .... 1650 MeckePs Diverticulum 1652 Practical Considerations: The Small In- testine 1652 The Peritoneal Coat 1652 The Muscular Coat 1653 The Mucous and Submucous Coats 1653 Ulcers of the Duodenum 1653 Infection 1654 Typhoid Ulcers 1654 Contusion and Rupture 1654 Obstruction 1655 Operations 1656 The Large Intestine 1657 General Description 1657 Structure 1657 The Caecum 1660 The Vermiform Appendix 1664 Peritoneal Relations 1665 Pericaecal Fossae 1666 Retro-Colic Fossae 1667 The Colon 1668 General Description 1668 Peritoneal Relations 1670 The Sigmoid Flexure 1671 Development and Growth 1671 The Rectum 1672 The Anal Canal 1673 The Anus 1673 Muscles and Fasciae of Rectum and Anus 1675 The Ischio-Rectal Fossa 1678 Practical Considerations: The Large In- testine 1680 The Caecum j 680 The Vermiform Appendix 1681 Etiology of Appendicitis 1681 Anatomical Points relating to the Symptoms and to the Treat- ment of Appendicitis 1683 Operations for Appendicitis .... 1685 The Colon and Sigmoid Flexure. . . . 1685 Distention and Rupture 1686 Displacements 1686 Obstruction and Stricture 1687 Wounds 1688 Operations 1688 The Rectum and Anal Canal 1689 Development of the Alimentary Canal . . 1694 Formation of the Mouth 1694 Formation of the Anus 1695 Differentiation of the Body-Cavity. . . 1700 Development of the Peritoneum. ... 1702 The Liver 1705 General Description 1705 Borders and Surfaces 1707 Blood-Vessels 1709 Structure 1712 The Hepatic Duct 1718 The Gall-Bladder 1719 The Common Bile-Duct 1720 Peritoneal Relations of the Liver. ... 1721 Position of the Liver 1722 Development and Growth 1723 Practical Considerations : The Biliary Apparatus 1726 Anomalies in Form and Position of the Liver 1726 Hepatoptosis and Hepatopexy 1726 Obstruction of Hepatic Circulation. . 1727 Wounds and Hepatic Abscess 1727 Malformations of Gall-Bladder 1729 Wounds and Rupture 1729 Distention and Cholecystitis 1729 The Cystic and Common Bile-Ducts. 1731 Operations on Gall-Bladder and Bili- ary Ducts 1732 The Pancreas 1732 General Description 1732 Structure 1734 Pancreatic Ducts 1736 Development 1737 XV111 CONTENTS. Practical Considerations : The Pancreas. 1738 Malformations 1738 Injuries 1738 Pancreatitis 1739 The Peritoneum 1740 General Considerations 1740 The Anterior Parietal Peritoneum.. . 1742 The Anterior Mesentery 1744 The Posterior Mesentery : Part I. . . 1746 The Posterior Mesentery : Part II.. . 1751 The Posterior Mesentery : Part III. . 1753 Practical Considerations : The Perito- neum 1754 Anatomical Routes for Infections. . . 1754 Peritonitis anatomically considered. . 1756 Abdominal Hernia 1759 General Considerations 1759 Predisposing anatomical conditions. 1759 Inguinal Hernia 1763 Anatomy of Inguinal Canal 1763 Anatomy of Indirect Inguinal Hernia 1766 Varieties of Inguinal Hernia. .. . 1767 Anatomy of Direct Inguinal Her- nia 1770 Anatomical Considerations of Treatment 1770 Femoral Hernia 1773 Anatomy of Femoral Canal. . . . 1773 Anatomical Considerations of Treatment 1774 Umbilical Hernia 1775 Ventral Hernia 1776 Lumbar Hernia 1777 Obturator Hernia 1777 Sciatic Herniae 1778 Perineal Herniae 1778 Diaphragmatic Hernise 1778 Intraabdominal Herniae 1779 ACCESSORY ORGANS OF NUTRITION. The Spleen 1781 General Description 1781 Structure 1 783 Peritoneal Relations 1785 Development and Growth 1787 Accessory Spleens 1787 Practical Considerations : The Spleen. . . .1787 The Thyroid Body 1789 General Description 1789 Structure 1791 Development 1793 Accessory Thyroids 1793 Practical Considerations : The Thyroid Body 1794 m\jr. The Parathyroid Bodies 1795 General Description 1795 Structure 1795 The Thymus 1796 General Description 1796 Structure 1798 Development and Changes 1800 The Suprarenal Bodies 1801 General Description 1801 Structure 1802 Development and Growth 1804 Accessory Suprarenals 1805 Practical Considerations: The Suprarenal Bodies 1806 The Anterior Lobe of the Pituitary Body, 1807 Development 1808 The Carotid Body 1809 The Coccygeal Body 1811 The Aortic Bodies 1812 THE ORGANS OF RESPIRATION. The Larynx 1813 Cartilages, Joints and Ligaments. .. . 1813 Form of Larynx and Mucous Mem- brane : 1818 Muscles of the Larynx 1825 Changes with Age and Sex 1828 Practical Considerations : The Larynx.. 1828 The Mediastinal Space 1832 Practical Considerations 1833 The Trachea 1834 General Description 1835 Structure 1835 Relations 1836 Growth and Subsequent Changes 1837 Bifurcation of Trachea and Roots of Lungs 1837 The Bronchi 1838 Practical Considerations : The Air-Pas- sages 1840 The Lungs 1843 General Description 1843 Lobes and -Fissures 1845 Physical Characteristics 1846 The Bronchial Tree 1847 The Lung Lobule 1849 Structure 1851 Blood- Vessels 1853 Relations to Thoracic Walls. . . . 1855 The Pleurae 1858 General Description 1858 Relations to the Surface 1859 Structure 1860 Development of the Respiratory Tract 1861 Practical Considerations : The Lungs and Pleurae 1864 THE URO-GENITAL SYSTEM. THE URINARY ORGANS. The Kidneys 1869 General Description 1869 Position and Fixation 1870 Relations 1873 Architecture 1875 Structure 1877 Practical Considerations: The Kidneys . 1887 Anomalies of Form, Size or Num- ber 1887 Anomalies of Position 1887 Renal Calculus 1890 Injuries and Tumors 1893 Operations 1893 The Renal Ducts 1894 Pelvis of the Kidney 1894 The Ureter 1895 Structure, 1896 Practical Considerations: The Ureters. .. 1898 Congenital Anomalies 1898 Ureteral Calculus 1899 Wounds 1900 Operations 1901 CONTENTS. xix The Bladder I9 01 General Description 1901 Peritoneal Relations 1904 Fixation and Relations 1905 Structure , i9 8 Practical Considerations: The Bladder. . 1910 Congenital Anomalies 1910 Effects of Distention 1911 Retention of Urine 1912 Rupture and Wounds 1913 Cystitis and Vesical Calculus 1914 The Male Perineum 1915 The Triangles 1916 The Perineal Interspaces 1916 Landmarks i9 l8 Lateral Lithotomy 1919 Median Lithotomy 1921 Suprapubic Lithotomy 1921 The Female Bladder 1922 The Urethra I9 22 The Prostatic Portion 1922 The Membranous Portion 1923 The Spongy Portion 1923 The Female Urethra 1924 Structure 1924 Practical Considerations: Male Urethra. . 1927 Congenital Abnormalities 1927 Clinical Division of Urethra 1928 Rupture of Urethra 1930 Anatomical Consideration of Ure- thritis 1930 Stricture of Urethra 1931 l Urethral Instrumentation 1933 Development of the Urinary Organs. .. . 1934 The Pronephros 1934 The Mesonephros (Wolffian Body). . 1935 The Metanephros (Kidney) 1937 The Bladder and Urethra 1938 THE MALE REPRODUCTIVE ORGANS. The Testes 1941 General Description 1941 Architecture 1942 Structure 1942 Spermatogenesis 1944 The Spermatozoa 1946 The Epididymis 1947 General Description 1947 Structure 1947 The Appendages of the Testicle 1949 The Appendix Testis 1949 The Appendix Epididymidis J 949 The Paradidymis 1950 The Vasa Aberrantia 1950 Practical Considerations: The Testicles 1950 Congenital Anomalies 1950 Orchitis 1951 Epididymo-Orchitis 1952 Castration 1952 Hydrocele 1953 The Spermatic Ducts 1953 The Vas Deferens 1954 The Ejaculatory Duct 1955 Structure of Spermatic Duct 1956 The Seminal Vesicles 1956 General Description 1956 Structure 1958 Practical Considerations: The Seminal Vesicles 1959 The Spermatic Cord 1960 Practical Considerations: The Spermatic Cord 1961 The Scrotum 1961 General Description Coverings of the Testicle Practical Considerations: The Scrotum . The Penis General Description The Corpora Cavernosa The Corpus Spongiosum The Glans Penis Structure Practical Considerations: The Penis. .. . Congenital Abnormalities Circumcision Contusions and Wounds Amputation The Prostate Gland General Description Position and Relations Structure Development Practical Considerations : The Prostate Gland Relations to Generative System Injuries Hypertrophy Operations The Glands of Cowper General Description Structure Development 1961 1963 1964 1965 1965 1966 1967 1968 1968 1972 1972 1973 1974 1975 1975 1975 1976 1977 1979 1979 1979 1979 1980 1982 1984 1984 1984 1984 THE FEMALE REPRODUCTIVE ORGANS. The Ovaries General Description Position and Fixation Structure Follicles and Ova The Human Ovum Corpus Luteum Development Variations Practical Considerations : The Ovaries. . The Fallopian Tubes General Description Course and Relations Structure Development and Changes Variations Practical Considerations : The Fallopian Tubes Rudimentary Organs The Epoophoron Gartner's Duct The Paroophoron Vesicular Appendages The Uterus General Description Attachments and Peritoneal Rela- tions The Broad Ligament The Round Ligament Position and Relations Structure Development and Changes Menstruation and Pregnancy Practical Considerations : Uterus and Attachments Compartments of Pelvis Displacements of Uterus The Broad Ligament The Round Ligaments The Vagina General Description Relations. . . 1985 1985 1986 1987 1988 1990 1990 1993 1995 1995 1996 1996 1997 1997 1999 1999 1999 2OOO 2OOO 2OOI 2OO2 2OO2 2003 2003 2004 2OO4 2005 2007 2007 2010 2012 2012 2013 2014 2014 2015 20l6 20l6 20l6 XX CONTENTS. The Vagina Continued Structure 2017 Development 2019 Variations 2019 Practical Considerations: The Vagina. 2019 Relations to Uterine Cervix 2019 Fistulae 2020 The Labia and the Vestibule 2021 The Labia Majpra 2021 The Mons Pubis 2021 The Labia Minora 2022 The Vestibule 2022 The Clitoris 2024 The Bulbus Vestibuli 2025 The Glands of Bartholin 2026 Practical Considerations : The External Genitals 2027 The Mammary Glands 2027 General Description 2027 Structure 2029 Milk and Colostrum Development Variations Practical Considerations : The Mammary Glands The Nipple Paths of Infection Carcinoma Removal of the Breast Development of Reproductive Organs . . General Considerations The Indifferent Stage Differentiation of the Male Type. . . . Descent of the Testis Differentiation of the Female Type . . Descent of the Ovary .* The External Organs In the Female In the Male Summary of Development The Female Perineum . . PAGE 2030 2032 2033 2033 2034 2035 2036 2037 2037 2038 2038 2040 2042 2043 2043 2044 2044 2045 2046 HUMAN ANATOMY. ANATOMY is that subdivision of morphology the science of form as contrasted with that of function or physiology which pertains to the form and the structure of organized beings, vegetal or animal. Phytotomy and Zootomy, the technical names for vegetal and animal anatomy respectively, both imply etymologically the dissocia- tion, or the cutting apart, necessary for the investigation of plants and animals. The study of organized bodies may be approached, evidently, from several stand- points. When the details of the -structure of their various tissues and organs par- ticularly is investigated, such study constitutes General Anatomy or Histology, fre- quently also called Microscopical Anatomy, from the fact that the magnifying lens is used to assist in these examinations. The advantages of comparing the organization of various animals, representing widely different types as well as those closely related, are so manifest in arriving at a true estimate of the importance and significance of structural details, that Comparative Anatomy constitutes a department of biological science of far-reaching interest, not merely for the morphologist, but likewise for the student of human anatomy, since we are indebted to comparative anatomy for an intelligent conception of many details encountered in the human body. Devel- opmental Anatomy, or Embryology, also has been of great service in advancing our understanding of numerous problems connected with the adult organism by tracing the connection between the complex relations of the completed structures and their primitive condition, as shown by the sequence of the phases of development. These three departments of anatomical study general, comparative, and developmental anatomy represent the broader aspects of anatomical study in which the features of the human body are only incidents in the more extended contemplation of organized beings. The exceptional importance of an accurate knowledge of the body of man has directed to human anatomy, or anthropotomy , so much attention from various points of view that certain subdivisions of the subject are conveniently recognized ; thus, the systematic account of the human body is termed Descriptive Anatomy, while when the mutual relations and peculiarities of situation of the organs located in par- ticular parts of the body especially claim attention, such study is spoken of as Topo- graphical or Regional Anatomy. Consideration of the important group of anatomi- cal facts directly applicable to the diagnosis and the treatment of disease constitutes Applied Anatomy. General Plan of Construction. Vertebrate animals, of which man rep- resents the most conspicuous development of the highest class, fishes, amphibians, reptiles, birds, and mammals being the recognized subdivisions of the vertebrata, possess certain characteristics in common which suffice to distinguish the numerous and varied members of the extended group. The fundamental anatomical feature of these animals is the possession of an axial column, or spine, which extends from the anterior or cephalic to the poste- rior or caudal pole and establishes an axis around which the various parts of the elongated body are grouped with more or less symmetry. While this body-axis is usually marked by a series of well-defined osseous segments constituting the ver- tebral column of the higher animals, among certain of the lower fishes, as the sharks or sturgeons, the axial rod is represented by cartilaginous pieces alone ; in fact, the tendency towards the production of a body-axis is so pronounced that the formation HUMAN ANATOMY. of a primitive axis, the notochord, takes place among the early formative processes of the embryo. In addition to the fundamental longitudinal axis, vertebrate animals exhibit a transverse cleavage into somatic or body-segments. While such segmentation is rep- resented in the maturer conditions by the series of vertebrae and the associated ribs, the tendency to this division of the body is most marked in the early embryo, in which the formation of body-segments, the somites, takes place as one of the primary developmental processes. Although these primary segments do not directly corre- spond to the permanent vertebrae, they are actively concerned in the formation of the latter as well as the segmental masses of the earliest muscular tissue. In man not only the skeleton, but likewise the muscular, vascular, and nervous systems are affected by this segmentation, the effects of which, however are most evident in the structure of the walls of the thoracic portion of the body-cavity. Disregarding the many variations in the details of arrangement brought about by specialization and adaptation, the body of every vertebrate animal exhibits a fundamental plan of construction in which bilateral symmetry is a conspicuous fea- ture. Viewed in a transverse section passing through the trunk, the animal body FIG. i. Neural arch Neural tube Spinal cord Vertebral axis Epidermi Coriutn Parietal mesoblast Costal segment Parietal mesoblast Aorta ==3^' Parietal mesothelium ' TTf Visceral mesothelium Entoblastic epithelium Subepithelial mesoblast Visceral mesoblast Diagrammatic plan of vertebrate body in transverse section. (Modified from Wiedersheim.} may be regarded as composed primarily of the axis, formed by the bodies of the vertebrae, and two tubular cavities of very unequal size enclosed by the tissues con- stituting the body-walls and invested externally by the integument (Fig. i). The smaller of these, the neural tube, is situated dorsally, and is formed by the series of the vertebral arches and associated ligaments ; it surrounds and protects the great cerebro-spinal axis composed of the spinal cord and the specialized cephalic extremity, the brain. The larger space, the visceral tube corresponding to the body- cavity, or ccelom, lies on the ventral side of the axis and contains the thoracic and abdominal viscera, including the more or less convoluted digestive-tube with its accessory glandular organs, the liver and the pancreas, and the appended respiratory tract, together with the genito-urinary organs and the vascular and lymphatic appa- ratus. The digestive-tube, which begins anteriorly at the oral orifice and opens posteriorly by the anus, is extended by two ventral evaginations giving rise to the respiratory tract and the liver, a dorsal glandular outgrowth representing the pan- creas. The sexual and urinary glands and their ducts primarily occupy the dorsal wall of the body cavity. The vascular system consists essentially of the ventrally placed contracting dilatation, the heart, divided into a venous and an arterial com- DESCRIPTIVE TERMS. 3 partment, and the great arterial trunk, the aorta, the major part of which occupies the dorsal wall of the space. The elongated typical vertebrate body terminates anteriorly in the cephalic segment, posteriorly in the caudal appendage ; between these two poles extends the trunk, from which project the ventrally directed limbs, when these appendages exist. Just as the axial segments, represented by the bodies of the vertebrae, take part, in conjunction with the neural arches, in the formation of the neural canal, so do these segments also aid in forming the supporting framework of the ventral body-cavity in connection with the series of ribs and the sternum. Descriptive Terms. The three chief planes of the vertebrate body are the sagittal, the transverse, and the frontal. The sagittal plane, when central, passes through the long axis of the body vertically and bisects the ventral or anterior and the dorsal or posterior surfaces. The transverse plane passes through the body at right angles to its long axis and to the sagittal plane. The frontal plane passes vertically but parallel to the anterior or ventral surface, being at right angles to both the sagittal and transverse planes (Fig. 2. ) The vertical position of the long axis in the human body is unique, since man, FIG. 2. FIG. 3. Three principal planes of human body. T, T, transverse; S, S, sagittal ; F, F, frontal. Human embryo showing primary relations of limbs, a, a, preaxial surfaces ; 6, 6, postaxial ; s, s, somitic. segments of trunk. of all animals, is capable of habitually maintaining the erect posture with full exten- sion of the supporting extremities. The lack of correspondence between the actual position of the chief axis of man and the horizontal fore-and-aft axis of vertebrates in general results in discrepancies when the three principal planes of the human body are compared with those of other animals. Thus, the sagittal plane alone retains the relation, as being at right angles to the plane of the support, in all verte- brates, although in man its greatest expansion is vertical. The transverse plane in man is parallel with the suppprting surface, while it is, obviously, at right angles to the corresponding plane in the four-footed vertebrate ; likewise, the frontal plane in man is vertical, while it is horizontal in other animals. The various terms employed in describing the actual position of the numerous parts of the human body and their relations to surrounding structures have been adopted with regard to the erect attitude of man and the convenience of the student of human anatomy ; hence, in many cases, they must be recognized as having a limited specific and technical application and often not directly applicable to other 4 HUMAN ANATOMY. vertebrates. Superior and inferior, upper and lower, as indicating relations towards or away from the head-end of the body, are, probably, too convenient and useful as expressing the peculiar relations in man to readily be relinquished, although when directly applied to animals possessing a horizontal body-axis they refer entirely to relations with the plane of support, the additional terms cephalic and caudal being necessary to indicate relations with the head- and tail-pole. Likewise, "anterior" and "posterior," as referring respectively to the front and back surfaces of the human body, are more logically described as ventral and dorsal, with the advantage that these terms are directly applicable to all vertebrates. ' ' Outer' ' and ' ' inner, ' ' as expressing relations with the sagittal plane, are now largely replaced by the more desirable terms lateral and mesial respectively, external and internal being reserved to indicate relations of depth. Cephalic and caudal, central and peripheral, prox- imal and distal, are all terms which have found extensive use in human anatomy. Preaxial and postaxial, in addition to their general and obvious significance with reference to axes in common, have acquired a specific meaning with regard to the limbs, the appreciation of which requires consideration of the primary relations observed in the embryo. In the earliest stage the limbs appear as flattened buds which project from the side of the trunk and present a dorsal and ventral surface ; subsequently the limbs become folded against the body, the free ends being directed ventrally, while one border looks headward, the other tailward. If an axis corre- sponding to the transverse plane of the body be drawn through the length of the extremities, each limb will be divided into two regions, one of which lies in front of the axis, and is, therefore, preaxial, the other behind, or postaxial. On reference to Fig. 3 it is obvious that the preaxial border or surface of each limb is primarily directed towards the cephalic or head-end of the animal, and, conversely, that the postaxial faces the caudal or tail-end. These fundamental relations are of great im- portance in comparing the skeleton of the upper and lower extremities with a view of determining the morphological correspondence of the several component bones, since the primary relations become masked in consequence of the secondary dis- placements which the limbs undergo during their development. The terms homologue and analogue call for a passing notice, since an exact understanding of their significance is important. Structures or parts are homologous when they possess identical morphological values founded on a common origin ; thus, the arm of a man, the front leg of a dog, and the wing of a bat are homologues, because each represents the fore-limb of a vertebrate, although they differ in individual func- tion. On the other hand, the wing of a bat and that of a butterfly are analogous, since they are structures of functional similarity, although of wide morphological diversity. Homologue, therefore, 'implies structural identity, analogue implies functional similarity. Parts are said to be homotypes when they are serial homo- logues ; thus, the humerus and the femur are homotypes, being corresponding structures repeated in the same animal. Where parts possess both morphological and functional identity, as the wing of a bird and of a bat, they are analogous as we'll as homologous. THE ELEMENTS OF STRUCTURE. WHEN critically examined, the various organs and parts going to make up the complex economy of the most highly specialized vertebrate and, indeed, the same is true of all animals whose organization does not approach the extremely simple uni- cellular type are found to be constituted by the various combinations of a very small number of elementary tissues ; these latter may be divided into four funda- mental groups : Epithelial tissues ; Connective tissues ; Muscular tissues ; Nervous tissues. Of these the nervous tissues are most specialized in their distribution, while the connective tissues are universally present, in one or another form contributing to the composition of every organ and part of the body. The tissues of the circulatory system, including the walls of the blood-vessels and lymph-channels and the corpus- cular elements of their contained fluids, the blood and the lymph, represent special- izations of the connective tissues of such importance that they are often conceded the dignity of being classed as independent tissues ; consideration of the develop- ment of the vascular tissues, however, shows their genetic relations to be so nearly identical with those of the great connective- tissue group that a separation from the latter seems undesirable. Each of the elementary tissues may be resolved into its component morphologi- cal constituents, the cells and the intercellular substances. The first of these are the FIG. 4. Pseudopod Vegetal food- inclusions Entoplasm Exoplasm A, unicellular animal (amceba); B, embryonal cell, leucocyte. descendants of the embryonal elements derived from the division or segmentation of the parent cell, the ovum, and are highly endowed with vital activity ; the intercellu- lar substances, on the other hand, represent secondary productions, comparatively inert, since they are formed through the more or less direct agency of the cells. The animal cell may exist in either the embryonal, matured, or metamorphosed condition. The embryonal cell, as represented by the early generations of the direct off- spring of the ovum, or by the lymphoid cells or colorless blood-corpuscles of the adult, consists of a small, irregularly round or oval mass of finely granular gelati- nous substance the protopla sm in which a smaller and often indistinct spherical body the nucleus lies embedded. In the embryonal condition, when the cell is without a limiting membrane, and composed almost entirely of active living matter, the outlines are frequently undergoing change, these variations in shape being known as amoeboid movements, from their similarity to the changes observed in the outline of an active amoeba, the representative of the simplest form of animal life, in which 6 HUMAN ANATOMY. the single cell constitutes the entire organism, and as such is capable of performing the functions essential for the life-cycle of the animal. As the embryonal cell advances in its life-history, the conditions to which it is subjected induce, with few exceptions, further specializations, since in all but the lowest forms division of labor is associated with a corresponding differentiation and adaptation to specific function. Vital manifestations of the cell include those complex physico-chemical phenomena which are exhibited during the life of the cellular constituents of the body in the performance of the functions necessary for fulfilment of their appointed life-work. These embrace metabolism, growth, reproduction, and irritability. Metabolism, the most distinctive characteristic of living matter, is that process by which protoplasm selects from the heterogeneous materials of food those partic- ular substances suitable for its nutrition and converts them into part of its own sub- stance. Metabolism is of two forms, constructive and destructive. Constructive metabolism, or anabolism, is the process by which the cell converts the simpler com- pounds into organic substances of great chemical complexity; destructive metabolism, or katabolism, on the contrary, is the process by which protoplasm breaks up the complex substances resulting from constructive metabolism into simpler compounds. Vegetal cells possess the power of constructive metabolism in a conspicuous degree, and from the simpler substances, such as water, carbon dioxide, and inorganic salts, prepare food-material for the nutritive and katabolic processes which especially dis- tinguish the animal cell, since the latter is dependent, directly or indirectly, upon the vegetal cell for the materials for its nutrition. Growth, the natural sequel of the nutritive changes effected by metabolism, may be unrestricted and equal in all directions, resulting in the uniform expansion of the cell, as illustrated in the growth of the ovum in attaining its mature condition. Such unrestricted increase, however, is exceptional, since cells are usually more or less intimately related to other structural elements by which their increase is modi- fied so as to be limited to certain directions ; such limitation and influence result in unequal growth, a force of great potency in bringing about the differentiation and specialization of cells, and, secondarily, of entire parts and organs of the body. Familiar examples of the result of unequal growth are observed in the columnar elements of epithelium, the fibres of muscular tissue, and the neurones of the ner- vous system. Reproduction may be regarded as the culminating vital manifestation in the vegetative life-cycle of the cell, since by this process the parent element surrenders its individuality and continues its life in the existence of its offspring. While the details of the process by which new cells arise from pre-existing cells are reserved for consideration in connection with the more extended discussion of the cell to follow (see page 9), it may here be stated that reproduction occurs by two methods, the indirect or mitotic and the direct or amitotic. The first of these, involving the complicated cycle of nuclear changes collectively known as mitosis or karyokinesis, is the usual method ; the second and simpler process of direct division, or amitosis, is now recognized as exceptional and frequently associated with conditions of im- paired vital vigor. Irritability is that property of living matter by virtue of which the cell ex- hibits changes in its form and intimate constitution in response to external impres- sions. These latter may originate in mechanical, thermal, electrical, or chemical stimuli to which the protoplasm of even the lowest organisms responds, or they may be produced in consequence of the obscure and subtle changes occurring within the protoplasm of neighboring elements, as illustrated by the reaction of the neurones in response to the stimuli transmitted from other nervous elements. THE ANIMAL CELL. Ever since the establishment of the Cell Doctrine, in 1838, by the announcement of the results of the epoch-making investigations of Schleiden and Schwann on "The Accordance of Structure and Growth of Animals and Plants," the critical examination of the cell has been a subject of continuous study. Notwithstanding the tireless cnthu- STRUCTURE OF THE CELL. siasm with which these researches have been pursued by the most competent investi- gators and the great advance in our accurate knowledge concerning the intricate problems relating to the morphology and the physiology of the cell, much pertaining to the details of the structure and the life of the cell still remains uncertain, and must be left to the future achievements in cytology. The account here given of the mor- phology of the cell presents only those fundamental facts which at the present time may be accepted as established upon the evidence adduced by the most trustworthy observers. The more speculative and still unsettled and disputed problems of cy- tology, interesting as such theoretical considerations may be, lie beyond the purpose of these pages ; for such discussions the student is referred to the special works and monographs devoted to these subjects. An appreciation, however, of the salient facts of cytology as established by the histologists of the present generation is essen- tial not only for an intelligent conception of the structure of the morphological ele- ments, but likewise for the comprehension of the highly suggestive modern theories concerning inheritance, since, as will appear in a later section, the present views regarding these highly interesting problems are based upon definite anatomical details. FIG. 5. Cytoplasm Spongioplastn Hyaloplasm Metaplastic inclusions Exoplasm Endoplasm Nuclear membrane Nucleolus Centrosome surrounded by centrosphere Cytoplasm Cell-wall Diagram of cell-structure. In the upper part of the figure the granular condition of the cytoplasm is represented ; in the lower and left, the reticular condition. Notwithstanding the great variations in the details of form and structure, cells possess a common type of organization in which the presence of the cell-body or cyto- plasm and the nucleus is essential in fulfilling the modern conception of a cell. The latter may be defined, therefore, as a nucleated mass of protoplasm. The term protoplasm, as now generally employed by histologists, signifies the organized substance composing the entire cell, and with this application includes both the cytoplasm and the nucleus. Structure of the Cytoplasm. The cytoplasm, or the substance of the cell- body, by no means invariably presents the same appearance, since it may be regarded as established that the constituents of this portion of the cell are subject to changes in their condition and arrangement which produce corresponding morphological varia- tions ; thus, the cytoplasm may be devoid of definite structure and appear homoge- neous ; at other times it may be composed of aggregations of minute spherical masses and then be described as granular, or, where the minute spheres are larger and con- sist of fluid substances embedded within the surrounding denser material of the cell, as alveolar ; or, again, and most frequently, the cytoplasm contains a mesh- work of fibrils, more or less conspicuous, which arrangement gives rise to the reticidar con- dition. The recognition of the fact established by recent advances in cytology, that the structure of cytoplasm is not to be regarded as immutable, but, on the contrary, as capable of undergoing changes which render it probable that a cell may appear 8 HUMAN ANATOMY. during one stage of its existence as granular and at a later period as reticular, has done much to bring into accord the conflicting and seemingly irreconcilable views regarding the structure of the cell championed by competent authorities. Whatever be the particular phase of structural arrangement exhibited by the cell, histologists are agreed that the cytoplasm consists of two substances, an act ire and a passive ; while both must be regarded as living, the vital manifestations of con- tractility are produced by the former. Since a more or less pronounced reticular arrangement of the active and passive constituents of cytoplasm is of wide occurrence in mature cells, this condition may serve as the basis for the description of the morphology of the typical cell. Critical examination of many cells, especially the more highly differentiated forms of glandular epithelium, shows the cytoplasm to contain a mesh-work com- posed of delicate fibrils and septa of the more active substance, the spongioplasm ; although conspicuous after appropriate staining, the spongioplastic net-work may be seen in the unstained and living cell, thereby proving that such structural details are not artefacts due to the action of reagents upon the albuminous substances com- posing the protoplasm. The interstices of the mesh-work are filled with a clear homogeneous semifluid material to which the name of hyaloplasm has been applied. Embedded within the hyaloplasm, a variable amount of foreign substances are frequently present ; these FIG. 6. B C Spermatogenic cells, showing variations in the condition and the arrangement of the constituents of the cyto- plasm and the nucleus; the centrosomes are seen within the cytoplasm close to the nucleus. A, from the guinea-pig X 1685 (Afeves) ; , from the salamander X 500 (Meves) ; C, from the cat X 750 (von Lenhossek). include particles of oil, pigment, secretory products, and other extraneous materials, which, while possibly of importance in fulfilling the purposes of the cell, are not among its true morphological constituents. These substances, which are inert and take no part in the vital activity of the cell, are termed collectively metaplasm. Cytoplasm consists, therefore, morphologically, of the spongioplasm and the hyaloplasm ; chemically, cytoplasm consists of certain organic compounds, salts and water. The organic compounds are grouped under the term proteins, which are complex combinations of carbon, hydrogen, nitrogen, and oxygen, with often a small percentage of sulphur. The proteins of the cytoplasm contain little or no phosphorus. Structure of the Nucleus. The nucleus, during the vegetative condition of the cell, or the "resting stage," as often less accurately called, appears as a more or less spherical body whose outline is sharply defined from the surrounding cyto- plasm by a definite envelope, the nuclear membrane. Since the nucleus is the nutritive, as well as reproductive, organ of the cell, the fact that this part of the cell is relatively large in young and actively growing elements is readily explained. The nucleus consists of two parts, an irregular reticulum of nuclear fibres and an intervening semifluid nuclear matri.\\ therein resembling the cytoplasm. Exam ined under high magnification, after appropriate treatment with particular stains, such as hsematoxylin, safranin, and other basic dyes, the nuclear fibres are shown to be composed of minute irregular masses of a deeply colored substance, appropriately STRUCTURE OF THE CELL. called chromatin in recognition of its great affinity for certain stains ; the chromatin particles are supported upon or within delicate inconspicuous and almost colorless threads of linin. The latter, therefore, forms the supporting net-work of the nuclear fibrils in which the chromatin is so prominent by virtue of its capacity for staining. The forms of the individual masses of chromatin vary greatly, often being irregular, at other times thread-like or beaded in appearance. Not infrequently the chromatin presents spherical aggregations which appear as deeply stained nodules attached to the nuclear fibres ; these constitute the false nucleoli, or karyosomes, as distinguished from the true nucleolus which is frequently present within the karyoplasm. Chemi- cally, chromatin, the most essential part of the nucleus, contains nuclein, a com- pound rich in phosphorus. The matrix, or nuclear juice, which occupies the interstices of the net-work, possesses an exceedingly weak affinity for the staining reagents employed to color the chromatin, and usually appears clear and untinted, and is probably closely related to the achromatin. It contains a substance described as paralinin. The micleolus, or plasmosome, ordinarily appears as a small spherical body sometimes multiple lying among, but unattached to, the nuclear fibres ; its color in stained tissues varies, sometimes resembling that of the chromatin, although less deeply stained, but usually presenting a distinct difference of tint, since it responds readily to dyes which, like eosin or acid fuchsin, particularly affect the linin and cytoplasm. Concerning the exact nature, purpose, and function of the nucleolus much uncertainty still exists ; according to certain authorities, these bodies are to be regarded as storehouses of substances which are used in the formation of the chro- matin segments during division, while other cytologists attribute to the nucleolus a passive role, even regarding it as by-product which, at least in some cases, is cast out from the nucleus into the cytoplasm, where it degenerates and disappears. Since trustworthy observations may be cited in support of both of these conflicting views, definite conclusions regarding the exact nature of this constituent of the nucleus must be deferred. The nucleolus is credited with containing a peculiar substance known as pyrenin. The term amphipyrenin, as applied to the substance of the nuclear membrane, is of doubtful value. The Centrosome. In addition to the parts already described, which are con- spicuous and readily seen, the more recent investigations into the structure of cells show the presence of a minute body, the cen- trosome, which plays an important role in elements engaged in active change, as con- spicuously during division and, in a lesser degree, during other phases of cellular activity. Ordinarily the centrosome escapes attention because, on account of its minute size and varia- ble staining affinity, it is with difficulty distin- guished from the surrounding particles. Its usual position is within the cytoplasm, but the exact location of the centrosome seems to de- pend upon the focus of greatest motor activity, since, as shown by Zimmermann, this little body, or bodies, being often double, is always found in that part of the cell which is the seat of greatest change ; thus, in a dividing ele- ment, the centrosome lies immediately related to the actively changing nucleus, while within ciliated epithelium it is removed from the nu- cleus and is found closely associated with the contractile filaments which probably produce the movements of the hair-like ap- pendages. In recognition of the intimate relations between this minute body and the active motor changes affecting the morphological constituents of the cell, the cen- trosome may be regarded physiologically as its dynamic centre ; the name kino- centrum has been suggested by Zimmerman as best expressing this probable function of the centrosome. This little body is frequently surrounded by a clear FIG. Centrosomes (c, c) in human epithelium; A, B, cells from gastric glands; C, from duo- denal glands ; D, from tongue ; /, leucocyte with centrosome X 625: (K. W. Zimmermann.) 10 HUMAN ANATOMY. area or halo, the centrosphere or the attraction sphere, within which it appears as a minute speck, frequently being double instead of single. In recapitulation, the chief constituents of the animal cell may be tabulated as follows : ( Meshwork Spongioplasm. Cytoplasm \ Ground-substance Hyaloplasm, containing inclusions, l\fela- (. plasm. f Linin fibrils. PROTOPLASM { f Nuclear reticulum consisting of I Chromatin (containing Nu- | Centrosome ( clein}. I Nuclear matrix (containing Para/in in}. I Nucleus \ucleolus (containing Pyrenin. I Nuclear membrane. DIVISION OF CELLS. Disregarding for the present, at least, the occurrence of direct fission as a means of producing new elements observed among the simplest forms of animal life, Diagram of mitosis. A, resting: stage, chromatin irregularly distributed in nuclear reticulum; a, centrosphere containing double centrosome; n, nucleolus. B, chromatin arranged as close spirem ; c, r, centrosomes surrounded by achromatic radial striations. C, stage of loose spirem, achromatir figure forming amphiaster (am/>). D, chra segments towards new nude!, as established by centrosomes (c, c) ; < p, <. i|iiatoi ial plate formed by intonningliiig segments. (,. separating groups of daughter chromosomes (rf, rf) united bv connecting threads (c t). //, daughter chrOMOSOmei ('/, /) becoming arranged around daughter c-rntr.>ss whirh have already divided; C, C, beginning cleavage of cytoplasm across plane of equatorial spinale. /, completed daughter nuclei (D, D) ; cytoplasm almost divided into two new cells. (Modi/ltd from H'ilson), or as an exceptional method among effete and diseased cells of the higher types, the production of IH-U generations of cells may be assumed as accomplished for all DIVISION OF CELLS. varieties of elements by a complicated series of changes, collectively known as kar- yokinesis, or mitosis, especially affecting the nucleus. As already pointed out, in addition to presiding over the nutritive and chemical changes, the nucleus is par- ticularly concerned in the process of reproduction ; further, of the several morpho- logical constituents of the nucleus, the chromatin displays the most active change, since this substance is the vehicle by which the characteristics of the parent cell are transmitted to the new elements. So essential is this substance for the perpetuation of the characteristics of each specific kind of cell that the entire complex mitotic cycle has for its primary purpose the insurance of the equal division of the chroma- tin of the mother cell between the two new nuclei, such impartial distribution of the chromatin taking place irrespective of any, or even very great, dissimilarity in the size of the daughter cells, the smaller receiving exactly one-half of the maternal chromatin. Mitotic Division. The details of karyokinesis, or mitosis, sometimes also spoken of as indirect division, include a series of changes involving the centrosome, FIG. 9. ADC \x - - ^i, .? ti D H Chromatic figures in dividing cells from epidermis of salamander embryo. X 960. A, resting stage; B, close spireme ; C, loose spireme; D, chromosomes (*' wreath " ), seen from surface; E, similar stage, seen in profile; F, longitudinal cleavage of chromosomes ; G, beginning migration of segments towards centrosomes ; ff, separating groups of daughter segments ; /, daughter groups attracted towards poles of new nuclei, cytoplasm exhibits begin- ning cleavage. the nucleus, and the cytoplasm, which are conveniently grouped into four stages ; (i) the Prophases, or preparatory changes; (2) the Metaphase, during which the chromatin is equally divided ; (3) the Anaphases, in which redistribution of the chromatin is accomplished ; (4) the Tclophases, during which the cytoplasm under- goes division and the daughter cells are completed. 12 HUMAN ANATOMY. In anticipation of the consideration of the details of mitosis, it should be pointed out that the process includes two distinct, but intimately associated and coinci- dent series of phenomena, the one involving the chromatin, the other the centro- somes and the linin. While as a matter of convenience these two sets of changes are described separately, it must be understood that they take place simultaneously and in coordination. The purpose of the changes affecting the chromatin is the accu- rate and equal division of this substance by the longitudinal cleavage of the chroma- tin segments ; the object of the activity of the centrosomes and the linin is to supply the requisite energy and to produce the guiding lines by which the chromatin segments are directed to the new nuclei, each daughter cell being insured in this manner one-half of the maternal chromatin. The Prophases, or preparatory stages, include a series of changes which involve the nuclear substances and the centrosomes and result in the formation of the karyokinetic figure ; the latter consists of two parts, ( i ) the deeply staining chro- matin filaments, and (2) the achromatic figure, which colors but slightly if at all. The chromatin loses its reticular arrangement and, increasing in its staining affinities, becomes transformed into a closely convoluted thread or threads, constituting the " close skein ;" the filaments composing the latter soon shorten and thicken to form the " loose skein." The skein, or spireme, may consist of a single continuous fila- ment, or it may be formed of a number of separate threads. Sooner or later the skein breaks up transversely into a number of segments or chromosomes, which ap- pear as deeply staining curved or straight rods. A very important, as well as remark- able, fact regarding the chromosomes is their numerical constancy, since it may be regarded as established that every species of animal and plant possesses a fixed and definite number of chromosomes which appear in its cells ; further, that in all the higher forms the number is even, in man being probably twenty-four. During these changes affecting the chromatin the nucleolus, or plasmosome, disappears, and, prob- ably, takes no active part in the karyokinesis ; the nuclear membrane likewise fades away during the prophases, the nuclear segments now lying unenclosed within the cell, in which the cytoplasm and the nuclear matrix become continuous. Coincident with the foregoing changes, the centrosome, which by this time has already divided into two, is closely associated with phenomena which include the ap- pearance of a delicate radial striation within the cytoplasm around each centrosome, thereby producing an arrangement which results in the formation of two stars or asters. The centrosomes early show a disposition to separate towards opposite poles of the cell, this migration resulting in a corresponding migration of the asters. In consequence of these changes, the retreating centrosomes become the foci of t\vo systems of radial striation which meet and together form an achromatic figure known as the amphiaster, which consists of the two asters and the intervening spindle. Notwithstanding the observations which tend to question the universal importance of the centrosome as the initiator of dynamic change within the cell, as held by Van Beneden and Boveri, there seems to be little doubt that the centrosome plays an important role in establishing foci towards which the chromosomes of the new nuclei become attracted. The nuclear spindle, which originates as part of, or secondarily from the amphiaster, often occupies the periphery of the nucleus, whose limiting membrane by this time has probably disappeared. The delicate threads of linin composing the nuclear spindle lie within an area, the polar field, around which the chromosomes become grouped. The chromosomes, which meanwhile have arisen' by transverse division of the chromatin threads composing the loose skein, appear often as V-shaped segments, the closed ends of the loops being directed towards the polar field which they encircle. Owing to this disposition, when seen from the broader surface, the chromosomes constitute a ring-like group, sometimes described as the mother r.vvv//// ; the same segments, when viewed in profile, appear as a radiating group of fibrils known as the mother star \ the apparent differences, therefore, be- tween these figures depend upon the point of view and not upon variations in the arrangement of the 111 ires. The Metaphase includes the most important detail of karyokinesis, namely, the longitudinal cleavage of the chromosomes, whereby the number' of the latter is MITOTIC DIVISION. 13 doubled and the chromatin is equally divided. This division is the first step towards the actual apportionment of the chromatin between the new nuclei, each of which receives exactly one-half of the chromatin, irrespective of even marked inequality in the size of the daughter cells. Meanwhile the centrosomes have continued to separate towards the opposite poles of the cell, where, surrounded by their attraction spheres, each forms the centre of the astral striation that marks either pole of the amphiaster, the nuclear spindle being formed by the junction of the prolonged and opposing striae. The purpose of the achromatic figure is to guide the longitudinally divided chromosomes towards the new nuclei during the succeeding changes. The Anaphases accomplish the migration of the chromosomes, each pair of sister segments contributing a unit to each of the two groups of chromosomes that are passing towards the poles of the achromatic spindle ; in this manner each new nucleus receives not only one-half of the chromatin of the mother nucleus, but also the same number of chromosomes that originally existed within the mother cell, the numerical constancy of the particular species being thus maintained. Anticipating their passage towards the poles of the achromatic figure, the mi- grating chromatic segments, attracted by the linin threads, for a time form a com- pact group about the equator of the spindle known as the equatorial plate. As the receding segments pass towards their respective poles, the opposed ends of the sep- arating chromosomes are united by intervening achromatic threads, the connecting fibres. Sometimes the latter exhibit a linear series of thickenings known as the cell-plate or mid-body. The migration of the chromosomes establishes the essential features of the division of the nucleus, since the subsequent changes are only repe- titions, in inverse order, of the changes already noted. The Telophases, in addition to the final stages in the rearrangement of the chromatic segments of the new nuclei, including the appearance of the daughter wreath, the daughter skeins, the new nuclear membrane, and the nucleolus, witness the participation of the cytoplasm in the formation of the new cells. In these final stages of mitosis the cell-body becomes constricted and then divides into two, the plane of division passing through the equator of the nuclear spindle. Each of the resulting masses of cytoplasm invests a new nucleus and receives one-half of the achromatic figure consisting of a half-spindle and one of the asters with a centro- some. The new cell, now possessing all the constituents of the parent element, usually acquires the morphological characteristics of its ancestor and passes into a condition of comparative rest until called upon, in its turn, to enter upon the com- plicated cycle of mitosis. MITOTIC DIVISION. I. Prophases. A. Changes within the nucleus : Chromatic figure. Chromatin loses reticular arrangement, Close skein, Loose skein, Disappearance of nucleolus, Division of skein into chromosomes, Arrangement around polar field mother wreath, Disappearance of nuclear membrane. B. Changes within the cytoplasm : Achromatic figure. Division of centrosome. Appearance of asters. Migration of centrosomes, Appearance of spindle, . Formation of amphiaster, Appearance of nuclear spindle and polar field. II. Metaphase. Longitudinal cleavage of chromosomes, HUMAN ANATOMY. III. Anaphases. Rearrangement of chromosomes into two groups, Migration of groups towards poles of amphiaster. Appearance of connecting fibres between receding groups, Construction of daughter nuclei. IV. Telophases. Constriction of cell-body appears at right angles to spindle, Chromosomes rearranged in daughter nuclei to form skeins, Reappearance of nuclear membrane, Reappearance of nucleoli, Complete division of cell-body, Daughter nuclei assume vegetative condition, Achromatic striation usually disappears, Centrosomes, single or divided, lie beside new nuclei. AMITOTIC DIVISION. The occurrence of cell reproduction without the foregoing complex cycle of karyokinetic changes is known as amitotic or direct division. That this process does take place as an exceptional method in the reproduction of the simplest forms of ani- mal life, or in the multiplication of cells within pathological growths or tissues of a transient nature, as the fcetal envelopes, may FIG. 10. be regarded as established beyond dispute. The essential difference between amitotic and the usual method of division lies in the fact that, while in the latter the chromatin of the nucleus is equally divided and the number of chromosomes carefully maintained, in direct division the nucleus remains passive and suffers cleavage of its total mass, but not of its indi- vidual components. Since the nucleus re- mains in the vegetative' condition, neither the chromatic nor achromatic figure is pro- duced, the activity of the centrosome, when exhibited, being possibly directly expended in effecting a division of the cytoplasm, and inci- dentally that of the nucleus. In many cases the amitotic division of the nucleus is not ac- companied by cleavage of the cytoplasm, such processes resulting in the production of multi- In general, it may be assumed that cells which undergo direct division are elements destined to surfer premature degeneration, since such cells subserve special purposes and are not capable of perpetuating their kind by normal reproduction. Flemming has pointed out the fact that those leuco- cytes which arise by amitotic division, and therefore deviate from the usual mode of origin of these elements, are cells which are doomed to early death; this form of cell-division among the higher forms must be regarded, probably, as a secondary process. Decidual cells showing amitotic division of nucleus (A-D) ; in E an attempt at mitosis has occurred. X 410. nuclear and aberrant nuclear forms. EARLY DEVELOPMENT. THE human body with all its complex organism is the product of the differentia- tion and specialization of the cells resulting from the union of the parental sexual elements, the ovum and the spermatozoon. The Ovum. The maternal germ-cell is formed within the female sexual gland, the ovary, in which organ it passes through all stages of its development, from the immature differentiation of its early condition to the partially completed matura- tion of the egg as it is liberated from the ovary. The human ovum, in common with the ova of other mammals, is of minute size, being, as it is discharged from the ovary, about . 2 millimetre in diameter. Ex- amined microscopically and after sectioning, the human ovum is seen to be enclosed within a distinct envelope, the zona pellucida, .014 millimetre in thickness, which in favorable preparations exhibits a radial striation, and hence is also named the zona radiata. This envelope at first was confounded with the proper limiting mem- brane of the cell, and for a time was erroneously regarded as corresponding to the FIG. n. Corona radiata Zona pellucida Germinal vesicle (nu- cleus) containing germ- inal spot (nucleolus) Zone rich in deutoplasm Zone poor in deutoplasm fading into homogene- ous peripheral zone * > .^' Human ovum from ripe Graafian follicle. X 170. (Nagel.} cell-wall. The nature of the zona pellucida is now generally conceded to be that of a protecting membrane, produced through the agency of cells surrounding the ovum. The substance of the ovum, the yolk, or vitellus, consists of soft, semifluid pro- toplasm modified by the presence of innumerable yolk-granules, the representatives of the important stores of nutritive materials present in the bird's egg. Critically examined, the vitellus is resolvable into a reticulum of active protoplasm, or obplasm, and the nutritive substance, or deutoplasm. At times the yolk is limited externally by a very delicate envelope, the vitelline membrane, which usually lies closely placed, or adherent, to the protecting zona radiata ; sometimes, however, it is separated from the latter by a perivitelline space. The vitelline membrane is probably absent in the unfertilized human ovum. A large spherical nucleus, the germinal vesicle, approximately .037 millimetre in diameter, usually lies eccentrically within the yolk, surrounded by the distinct nuclear membrane. Within the germinal vesicle the constituents common to nuclei in i6 HUMAN ANATOMY. FIG. 12. Head End-knob Middle-piece Axial filament Tail general are found, including the all-important chromatin fibrils, nuclear matrix, and nucleolus ; the latter, in the original terminology of the ovum, is designated as the germinal spot, and measures about .05 millimetre in diameter. In addition to these more easily distinguished components of the maternal cell, the centrosome must be accepted as a constant constituent of the fully formed, but unmatured, ovum, although its presence may escape detection. The Spermatozoon. The male germ-cell, the spermatic filament, is produced by the specialization of epithelial elements lining the seminiferous tubules within the testicle. The human spermatozoon consists of three parts, the ovoid head, the cylindrical middle-piece, and the attenu- ated, greatly extended tail ; of these the head and middle- piece are the most important, since these parts contain re- spectively the chromatin and the centrosome of the cells from which the spermatic filaments are derived. The centrosome is represented by a minute spherical body, the end-knob, which lies in the middle-piece immediately beneath the head at the extremity of the axial fibre ; the latter extends throughout the spermatozoon from the head to the termination of the tail, ending as an extremely attenuated thread, the terminal fila- ment. The tail corresponds to a flagellum and serves the purposes of propulsion alone, taking no part in the important changes produced in the ovum by the entrance of the male element. It is of interest to note that both the ovum and the spermatozoon are the direct specializations of epithelial tissue, the active elements of the primary indifferent sexual glands being derived from the mesodennic lining of the body-cavity. Maturation of the Ovum. Maturation, or ripening of the ovum, is that process by which the female element is prepared for the reception of the spermatozoon. It takes place, however, entirely independently of the influence of the male or of the probability of fertilization, every healthy ovum un- dergoing these changes before it becomes sexually ripe. About the time that the ovum is liberated from the ovary by the bursting of the Graafian follicle, as the sac which encloses the egg within the ovarian stroma is called, its nucleus en- gages in the complicated cycle already described as mitotic division. The nucleus migrates to the periphery of the ovum, loses its limiting membrane, and undergoes division, one pole of the nuclear spindle being located within the protrusion of protoplasm which has coincidently taken place. With the division of the nuclear chromatin, the protruded protoplasm becomes constricted and finally separated from the ovum ; the minute isolated mass thus formed, containing one-half of the maternal chromatin, is the first polar body. Almost immediately the mitotic cycle is repeated, and again results in the constric- tion and final separation of a minute cell, the second polar body. These two isolated portions of the ovum remain visible for a long time as small, deeply stained cells lying within the perivitelline space beneath the zona pellucida. The chromatin remaining within the ovum after the repeated division becomes collected within a new nucleus, which now takes a non-central position within the egg, and is henceforth known as the female pronnclcus or egg-nucleus. After matu- ration the ovum is prepared for union with the spermatozoon, although in many cases the male sexual element has actually entered the ovum before the completion of the maturation cycle : should, however, impregnation not occur, the ovum passes nliuig the oviduct into the uterus and is firtally lost. The passage of the human egg from the ovary 'to the uterus occupies, probably, about eight days, a period corresponding closely to the length of time that the ovum retains its capability of fertilization. The significance of the extrusion of the polar bodies a process which occurs -Terminal filament Human spermatozoon, semi diagrammatic. X 1650. EARLY DEVELOPMENT. 17 with great constancy in almost all animals, and, indeed, is probably represented in the development of vegetal organisms as well has been the subject of much dis- cussion and speculation. The most satisfactory explanation of the significance of maturation has been proposed by Van Beneden, Boveri, and others, based upon the comparison of the changes which take place in the development of the germ-cells of the two sexes. In order to appreciate the necessity and the meaning of maturation of the ovum, it will be of advantage to take a brief survey of the phenomena attending the devel- opment of the male sexual elements. The seminiferous tubules of the testicle are lined with epithelial cells, certain of which, known as the primary spermatocytes, FIG. 13. -"* Semi-diagrammatic representation of the formation of the polar bodies, based upon observations of invertebrate ova (Ascaris and Physa). n, nucleus; c, c, centrosomes ; J, nuclear spindle; p', />", first and second polar bodies; . \ . , ^ . ^ Inner cells Outer cells Zonapellucida -V^y- V ^ v ^^7^-Trophc X^x _ ^/^- -Zona pellucida Diagram of early mammalian blastodermic vesicle, Diagram of mammalian blastodermic vesicle; inun consisting of trophoblast and inner cell-mass. cells differentiating into ectoblast and entoblast. (After (After Van Reneden.) Van Reneden.} the blastomeres very early exhibit inequality in size and in rapidity of division (Fig. 1 6), the effect of this differentiation being, that the more rapidly multiplying blas- tomeres are smaller than the rnore slowly dividing elements. It is of interest, in this connection, to note that the purest type of total equal segmentation is observed in the ovum of the lowest vertebrate, the amphioxus, an animal whose development has shed much light on many obscure problems in the embryology of the higher forms, including mammals and even man. The meroblastic bird's egg, on the contrary, undergoes cleavage only within a limited circular field at its animal pole ; it is said, therefore, to undergo partial dis- coidal segmentation. In contrast to this, the centrolecithal ova exhibit partial super- ficial segmentation, the peripheral zone of formative material alone undergoing cleavage. The Blastoderm and the Blastodermic Layers. The completion of segmentation in holoblastic ova results in the production of a mass of blastomeres, which is a solid sphere composed of mutually compressed segmentation cells ; to this sphere the older anatomists gave the name of the montla. or the mulberry ma>s. The solidity of the morula is temporary,' since a cavity is soon developed within it. This cavitv, often called the segmentation cavity, increases to such an extent that a THE BLASTODERMIC VESICLE. hollow sac is formed, walled by a single layer of cells, at one point on the inner sur- face of which is attached a small mass of cells. The outer, covering layer of cells is known as the trophoblast ; the small group of cells attached to the inner surface of the trophoblast is known as the inner cell-mass (Fig. 18). Examined from the sur- face, this aggregation of inner cells appears as an opaque circular field, the embryonic area, due to the increased thickness and consequent diminished transparency of the wall of the blastodermic vesicle at the place of attachment of the included cells. In the purest type of the blastodermic vesicle, that seen in the amphioxus (Fig. 26, A), the sac consists of a single layer of blastomeres of almost uniform size ; the mammalian blastodermic vesicle, however, presents greater complexity, due to the unequal rate at which some of the segmentation cells divide and to the rapid increase in the size of the vesicle. The inner mass of germinal cells soon undergoes differentiation (Fig. 19) into two strata, an outer layer, closely applied to the trophoblast, and an inner layer. These layers are respectively the ectoblast and the entoblast, two of the three great primary blastodermic layers from which the embryo is differentiated. Coincidently with the formation of these germinal layers, the mammalian blas- todermic vesicle grows with great rapidity, increasing from a sphere of microscopic size to a vesicle of one or more millimetres in diameter. In consequence of this precocious growth the trophoblast undergoes great expansion, with the result that its cells, in some cases at least, become temporarily reduced to flattened plate-like elements. For a time these flattened trophoblast cells may extend over the embryonic ectoblast, as in the rabbit, and have been called the cells of Raiiber. In such cases, therefore, the ectoblast is overlaid within the embryonic area by the cells of Rauber, but at the margin of the area, the embryonic ectoblast is continuous with the trophoblast forming the outer layer of the wall of the blastodermic vesicle. With the subsequent expansion of the blastodermic vesicle, the cells of Rauber dis- appear from the surface of the embryonic ectoblast, which then lies upon the surface of the vesicle. FIG. 21. Fro. 20. Entoblast Trophoblast Embryonic ectoblast Mesoblast Diagram of mammalian blastodermic vesicle; the entoblast forms an almost complete inner layer. Entoblast Trophoblast Diagram of mammalian blastodermic vesicle ; the mesoblast is just appearing as the third blastodermic layer. The early blastodermic vesicle at first consists of only two primary layers, the ectoblast and the entoblast ; this stage of development is appropriately termed that of the bilaminar blastoderm (Fig. 20); a little later, a third layer, the mesoblast, makes its appearance between the outer and inner blastodermic sheets ; this stage is designated as that of the tri laminar blastoderm (Fig. 21). The early embryo, shortly after the formation of the blastodermic vesicle, con- sists of three layers of cells, the ectoblast, the mesoblast, and the entoblast. The histological characters of the outer and inner of these primary layers differ, almost 24 HUMAN ANATOMY. from the first, from those of the mesoblast, their component elements being more compact in arrangement and early manifesting a tendency to acquire the character- istics of covering cells or epithelium. The mesoblastic elements, on the contrary, soon assume irregular forms and are loosely held together by intercellular substance, thus early foreshadowing the special features which distinguish the subsequently differentiated connective tissues. This early distinction becomes more marked as differentiation proceeds, the epithelial tissues possessing elements of comparatively regular form, separated by minute amounts of intercellular substance ; the latter in the connective tissues, on the con- trary, becomes conspicuous on account of its excessive quantity and the resulting profound modifications in the physical character of the tissue; the cells of the con- nective tissues rapidly assume the irregularly stellate or triangular form so charac- teristic in young tissues of this class. Since the three primary layers give rise to all the tissues of the organism, a brief synopsis presenting these genetic relations here finds an appropriate place. DERIVATIVES OF THE BLASTODERMIC LAYERS. From the ectoderm are derived The epithelium of the outer surface of the body, including that of the conjunc- tiva and anterior surface of the cornea, the external auditory canal, to- gether with the epithelial appendages of the skin, as hair, nails, sebaceous and sweat-glands (including the involuntary muscle of the latter). The epithelium of the nasal tract, with its glands, as well as of the cavities communicating therewith. The epithelium of the mouth and of the salivary and other glands opening into the oral cavity. The enamel of the teeth. The tissues of the nervous system. The retina ; the crystalline lens, and perhaps part of the vitreous humor. The epithelium of the membranous labyrinth. The epithelium of the pituitary and pineal bodies. From the mesoderm are derived The connective tissues, including areolar tissue, tendon, cartilage, bone, den- tine of the teeth. The muscular tissues, except that of the sweat-glands and dilator pupillae. The tissues of the vascular and lymphatic systems, including their endothelium and circulating cells. The sexual glands and their excretory passages, as far as the termination of the ejaculatory ducts and vagina. The kidney and ureter. From the entoderm are derived The epithelium of the digestive tract, with that of all glandular appendages except those portions derived from ectodermic origin at the beginning (oral cavity) and termination of the tube. The epithelium of the respiratory tract. The epithelium of the urinary bladder and urethra. The epithelium of the thyroid and thymus bodies, the atrophic primary epithe- lium of the latter being represented by Hassall's corpuscles. The Primitive Streak and the Gastrula. Examined from the surface during the formation of the primary layers, the mammalian blastodermic vesicle, as represented by that of the rabbit, presents a circular light -colored field, the embryonic area, which corresponds to the expansion of the original embryonic spot, the latter becoming larger with the extension of the ectoblast and the entoblast differentiated from the inner cell mass. At first circular, the embryonic area later becomes oval or pyriform in outline ( Figs, jj, j^), the larger end corresponding with the cephalic THE EMBRYONIC AREA. pole of the future embryo. In consequence of the proliferation of the ectoblastic cells, the embryonic area becomes differentiated into a central field, the embryonic shield, and a peripheral zone, the area pellucida, which by transmitted light appear respectively dark and light, owing to the varying transparency of the thicker cen- tral and thinner peripheral portions of the germinal field. FIG. 22. FIG. 23- Area pellucida -Embryonic shield -Area pellucida -Wall of blastoder- mic vesicle Embryonic area of rabbit of about six and one- half days, seen from the surface by transmitted light. X 26. (Kollmann.} -Embryonic shield -Wall of blastodermic vesicle. Embryonic area of rabbit of about seven days, seen from the surface. X 26. (Kollmann.) FIG. 24. Coincidently with the assumption of the oval or pyriform outline, the caudal border of the embryonic area exhibits a luniform thickening, the embryonic crescent ; from the latter proceeds the formation of a conspicuous, although transient, structure, known as the primitive streak (Fig. 24). The latter appears as a lineal thicken- ing which extends forward well towards the centre of the embryonic area. The pro- liferation of the outer blastodermic layer along the primitive streak is accompanied by the appearance or a narrow longitudinal furrow, the primitive groove, throughout its extent with the exception of its anterior end, at which point the primitive streak termi- nates in a thickened extremity, the node of Hensen. Although indicating the direction of the axis of the future embryo, the primi- tive streak takes no part in the formation of the new organism, being entirely tran- sient in its career. Transverse section of the anterior end of the primitive streak (Fig. 25) shows that in that place all three of the blastodermic layers ectoblast, mesoblast, and entoblast are completely fused, the mesoblast in this situation and here alone forming a continuous sheet interposed between, as well as blended with, the ectoblast and entoblast. The Significance of the Primitive Streak and the mode of formation of the mesoblast are vexed problems in embryology. A brief note on this topic will suffice here. In amphioxus, the lowest vertebrate, the immediate result of segmen- tation is a hollow sphere, the blastula, filled with fluid, lined by a single layer of cells. Invagination at one point of the wall of the blastula occurs, forming eventually a two-layered cup, the gastrula, the outer layer of which is the ectoblast, and the inner one the entoblast. The cavity within the entoblast is the archcnteron or primi- tive gut. The opening into the archenteron is the blastoporc. Cells given off from the entoblast, near the blastopore, form a third layer, the mesoblast. Typical gas- trulation does not occur in the higher mammals, although in the early human embryo a canal appears, known as the neurenteric canal, the opening of which is often regarded as homologous with the blastopore. The primitive streak is regarded by some authorities, notably Hertwig, as an elongated blastopore with lips fused. The mesoblast is commonly thought to arise from the entoblast, although the ecto- blast, in the region of the primitive streak, seems to have a share in the production of the middle germ-layer. -Head process Hensen's node -Primitive streak Embryonic area Extra-embryonic part of blasto- dermic vesicle Embryonic area of rabbit of about eight days, seen from the surface. X 20. (After Van Beneden.) 26 HUMAN ANATOMY. THE FUNDAMENTAL EMBRYOLOGICAL PROCESSES. Shortly after the appearance of the primitive streak a structure, it will be remembered, which is only transient and takes no part in the formation of the embryo proper a series of phenomena mark the earliest stages of the future new being. These changes are known as the fundamental embryological processes, and result in the formation of the neural canal, the notochord, and the somites. While described for convenience as separate processes, they progress to a great extent simultaneously. Ectoblast Mesoblast Transverse section through cephalic end of primitive streak of very young rabbit embryo. X 100. The Neural Canal. The earliest indication of the embryo consists in the appearance of two slightly diverging folds (Fig. 27), enclosing the anterior end of the primitive streak, which are produced by a local proliferation and thickening of the ectoblast. These are the medullary folds and mark the beginning of the formation of the neural canal, from which the great cerebro-spinal nervous axis, together with its outgrowths, the peripheral nerves, is derived. The medullary folds at first border a shallow and widely open furrow (Fig. 28), the medullary groove ; FIG. 26. Blastula and gnstrtila stages in the development of amphioxus, drawn from the model* <>t Hatsclifk. X ago. A, blastula composed of single layer of cells surrounding segmentation cavity; re, <>:, respectively ectoblastic and i-nt'iMastic areas. />', beginning imagination of entpblastic area (en). C, completed gastrula ; ec, en, ectoblast and entoblast ; nt, mcsoblast cell ; b, blastopore, leading into archenteron. the latter becomes rapidly deeper and narrower as the medullary folds increase in height and gradually approach each other. The approximation of the folds ( Fig. 29) and subsequent fusion take place earliest at some distance behind the ivphalic end of the groove, at a point which later corresponds to the upper cervical region of the spinal cord. After the closure of the groove and its conversion into the medullary canal (Fig. 32), the thickened and invaginated ectoblast forming tin- lining of the neural tube becomes separated from the outer layer of the embryo by the ingrowth of the THE NOTOCHORD. 27 FIG. 27. mesoblast. The subsequent differentiation of the walls of the neural tube will be more fully considered in connection with the nervous system ; suffice it here to state that the cephalic portion expands into the brain vesicles, and subsequently becomes the brain with the contained ventricles, while the remainder of the tube becomes the spinal cord, enclosing- the minute central canal. The Notochord. Coinci- de.ntly with the formation of the med- ullary groove the entoblast opposite the bottom of that furrow exhibits Medullary groove proliferation and thickening ; the group of cells thus differentiated be- ~ ~ W mic v f eSjf der " comes separated from the general - Primitive streak mass of the inner layer and takes up a position immediately below the "~~ Embryonic area neural tube (Figs. 30, 31). This isolated column of entoblastic cells constitute the notochord, or chorda dorsalis. the earliest suggestion of c- , ' & & Embryonic area of rabbit of about eight and one-half days the cardinal Vertebrate axis around seen from the surface. X 24. (Kollmann.) which the parts of the early embryo are symmetrically arranged. While for a time constituting the sole longitudinal axis of the embryo, extending from a point near the cephalic pole, which corresponds later Medullary fold FIG. 28. Groove Medullary fold Transverse section of rabbit embryo of about eight and one-half days. X 80. Future neural canal is represented by widely open groove. Amniotic sac FIG. 29. Closing neural canal Somatopleura Body-cavity / / / / Visceral mesoblast Entoblast Chorda Open gut-tube V isceral mesoblast Entoblast Chorda Open gut-tube Splanchnopleura Transverse section of rabbit embryo of about nine and one-quarter days. X 80. Neural canal is just closing. to the base of the skull, to the caudal extremity, the notochord is but a temporary structure, and subsequently is supplanted by the true vertebral column. It is 28 HUMAN ANATOMY. interesting to note, that in the connecting link between the vertebrates and invertebrates, the amphioxus, the notochord remains as the permanent and sole spinal axis. The history of the notochord in man and mammals presents three stages : (a) it exists as an unbroken cord which extends uninterruptedly through the series of cartilaginous vertebrae ; (6) the notochord suffers segmentation in such manner that the breaks in its continuity correspond to the vertebral bodies, conspicuous proliferation and local increase in its substance, on the contrary, marking the FIG. 30. FIG. 31. Transverse sections through axis of early human embryo of about fifteen days, showing formation of notochord from entoblast. High magnification. (After Kollmann.) n, neural canal; ch, cells forming notochord differenti- ating from entoblast (e ) ; tn, mesoblast ; s, early somite ; 6, sections of primitive aortse. position of the intervertebral disks in which the chordal tissue during the first months after birth is represented by a considerable mass of central spongy substance ; (>) atrophy of the remains of the notochord, resulting in the entire disappearance of the chordal tissue within the vertebrae and the reduction of the proliferated intervertebral cell-mass to the pulpy substance existing within the intervertebral disks. The cephalic end of the notochord in man corresponds in position to the dorsum sellae, and marks the division of the skull into two parts, that lying in front of FIG. 32. Paraxial mesoblast Ectoblast Amniotic cavity Somatopleura W '.*&4&!g& \ \ ,-^-^1- *$3&&* * 3 *T* Body-cavity Splanchno- Open Ento- Chorda Neural Visceral Body-cavity pleura gut blast tube mesoblast Transverse section of rabbit embryo of about nine and one-quarter days. X 80. Neural canal is now closed. the termination of the notochord, the prechordal portion, and that containing the notochord, the chordal portion ; the latter is sometimes described as the vertebral segment of the skull. The Coelom. The downward growth of the neural ertoblast and the upward extension of the chordal entoblast effect a division of the mesoblast along the embryonic axis into two sheets ( Fig. 28). These latter undergo further division in consequence of the formation of a cleft within their substance, as the result of which the mesoblast becomes split into two layers enclosing a space, the ccclom, or primary body-cavity (Fig. 29). THE SOMITES. 29 The cleavage of the mesoblast, however, does not extend as far as the mid-line of the embryo, but ceases at some distance on either hand, thus leaving a tract of uncleft mesoblast on either side of the medullary groove and the chorda. The uncleft area constitutes the paraxial mesoblast (Fig. 32), which extends from the head towards the caudal pole and appears upon the dorsal surface of the embryo as two distinct ribbon-like tracts bordering the neural canal. Beyond the paraxial mesoblast, the cleft portions of the middle layer extend on either side as the lateral plates ; each lateral plate consists of two laminae, the one forming the dorsal and the FIG. 33. FIG. 34. Neural canal Intermediate cell- mass Primary gut-tube Parietal mesoblast ' Visceral mesoblast Transverse section of human embryo of about fifteen days, showing early differentiation of somite. X 210. (Kollmann.) -. x :. v Coelom Transverse section of human embryo of about twenty-one days, showing differentiation of somite. X 90. (Kollmann.} FIG. 35. Dorsal border of yotome ;-plate other the ventral boundary of the enclosed primary body-cavity ; in view of their subsequent relations to the formation of the body-walls and the digestive tube respectively, the dorsal mesoblastic lamina is appropriately named the parietal layer and the ventral lamina the visceral layer (Fig. 32). In the separation of these layers, which soon takes place in consequence of the dorsal and ventral folding occurring during the formation of the amnion and the gut-tube, the parietal mesoderm adheres to the ectoblast, in conjunction with which it constitutes the somatopleura (Fig. 29), the ecto-mesoblastic sheet of great importance in the production of the lateral and ventral body- walls. Similarly, the visceral mesoblast unites with the entoblast*to form the splanchnopleura (Fig. 29),' the ento-mesoblastic layer from which the walls of the primary digestive canal are formed. The Somites. The paraxial mesoblast at an early stage about the twentieth in man exhibits indications of transverse division, in consequence of which this band-like area becomes differentiated into a series of small quadrilateral masses, the somites, or protovertebrte. This segmentation of the embryonic mass appears earliest at some distance behind the cephalic end of the embryo, at a point which later corresponds to the beginning of the cervical region. The somites are seen to best advantage in the human embryo at about the twenty-eighth day (Fig. 71). The early somites, on transverse section, appear as irregular quadrilateral bodies, composed of mesoblast and covered externally by ectoblast, lying on either side of the neural canal and the notochord (Fig. 33). Each somite consists of a dorsomesial principal cell-mass, which is connected with the lateral plate by means of an intervening cell-aggregation, the intermediate cell-mass (Fig. 33). Subsequently, Differentiation of myotome of human embryo of about twenty-one days. X 5 2 5- (Kollmann.) 30 HUMAN ANATOMY. the latter becomes separated from the remaining portion of the somite and is probably identified with the formation of the segmented excretory apparatus of the embryo, the Wolffian body, and hence is known as the ncphrotome. The principal mass, including the greater part of the somite proper, consists of an outer or peripheral zone of condensed mesoblast enclosing a core of looser struc- ture. The less dense mesoblastic tissue later breaks through the surrounding zone on the side directed towards the notochord and forms a fan-shaped mass of embryonic connective tissue which envelops the chorda and grows around the neural canal. The cell-mass derived from the core of the myotome constitutes the sclerotomc, and directly contributes the tissue from which the permanent vertebrae and the associated ligamentous and cartilaginous structures arise. The remaining denser part, the myotome, which collectively forms a compressed C-like mass, becomes differentiated into a lateral and a mesial stratum (Fig. 35). The lateral stratum, sometimes called the cutis-plate, consists of several layers of closely packed elements. By some these cells are regarded as concerned in producing the connective tissue portion of the skin ; according to others they are in large part converted into myoblasts, which, with those of the mesial stratum, or muscle-plate, give rise to the voluntary muscles of the trunk. The genetic relations of' the somite, therefore, may be expressed as follows : I Myolome muscle segment. SOMITE -j Sclerotome axial segment. (. Nephrotome excretory gland segment. The number of somites of the human embryo is about thirty-seven, comprising eight cervical, twelve thoracic, five lumbar, five sacral, and from five to seven caudal segments. THE FCETAL MEMBRANES. The Amnion. With the exception of fishes and amphibians, animals whose development takes place in water, the young vertebrate embryo is early enveloped in a protecting membrane, the amnion. Animals possessing this structure, including reptiles, birds, and mammals, are classed, therefore, as amniota, in contrast to the anamnia, in which no such envelope is formed. An additional foetal appendage, the allantois, is always developed as a structure complemental -Embryonic ectobiast to the amnion ; hence the am- ,Mesobiast niota possess both amnion and c Entoblast allailtois. Since the development of the fcetal membranes in man presents certain deviations from the process as seen in other mammals, due to pecu- liarities affecting the early human embryo, it is desirable cavitv of biastodermic l ? examine briefly the forma- vesicie tion of these structures as ob- 'rrophobiast served in animals less highly specialized. ^_^^^ Referring to the early niajjram of mammalian biastodermic vesicle. mammalian embryo, ill which the biastodermic layers are arranged as somatopleura and splanchnopleura on either side of the embryonic axis and the surrounding uncleft mesoderm, and extend as parallel sheets over the en- larging biastodermic vesicle, the first trace of the amnion appears as a duplicature of the somatopleura. The earliest indication of the process is seen slightly in front of the cephalic end of the embryo, the resulting head-fold being, however, soon fol- lowed by the appearance of the lateral and tail-folds. The rapid growth of these THE AMNION. duplicatures of somatopleura from all sides results in the encircling of the embryo within a wall which increases in height until the prominent edges of the folds meet and coalesce over the dorsal aspect of the enclosed embryo. The folds of the ainnion first meet over the head-end, from which point the union extends tailward, where, however, fusion may be delayed for some time. The line along which the junction of the folds takes place is known as the amniotic suture. The amnion thus forms FIG. 37- ^Serosa 'Ectoblast 1 f Amnion rMesoblast) -Exocoelom pen gut-t'ube Splanchnopleura a closed sac completely in- vesting the embryo and con- taining a fluid, the liquor atnnii ; at first closely sur- rounding the embryo, the amniotic sac rapidly expands until its dimensions allow the enclosed foetus to turn freely, practically supported by the amniotic fluid, which pos- sesses a specific gravity of 1003. It has long been known that in certain forms, conspicuously in the chick, the amnion executes rhythmi- cal contractions, at the rate of ten per minute, whereby the embryo is swayed from end to end of the sac. From the manner of its formation, as folds of the somatopleura (Figs. 37 and 38), it is evident that the amnion consists of an inner ectoblastic and an outer mesoblastic layer. The Serosa, cr False Amnion. Coincident with the fusion of the inner layers of the somatopleuric folds to form the closed sac of the amnion, the outer layers of the same folds unite to FIG. 38. Serosa Amnion Trophoblast Vitelline sac Entoblast Diagram showing formation of amniotic folds and of gut-tube ; trans- verse section of axis of embryo. \mniotic sac Gut-tube produce a second external en- velope, the serosa, or false am- nion. The serosa soon becomes separated from the amnion by an intervening space to form the primitive chorion ; the latter, therefore, consists of ectoblastex- ternallyand mesoblast internally, the reverse of the disposition of these layers in the amnion. The outer surface of the mammalian primitive chorion the outer envelope formed of the serosa and the trophoblast is distinguished by prolifera- tion of the epithelial elements, which process results in the production of more or less con- spicuous projections or villi (Fig. 40), this villous condition being particularly well marked in man. The ectoblast of the primitive chorion takes no part in the formation of the body of the embryo, but, on the other hand, assumes an important r61e in establishing the earliest connection between the embryo and the maternal tissues and, later, participates in the formation of the placenta. The ectoblast of the Diagram showing formation of amniotic folds and vitelline sac ; longitudinal section of embryo. HUMAN ANATOMY. primitive chorion is the direct derivative of the original ectodermal layer of the blastodermic vesicle beyond the embryonic region proper, a layer which, on account of this important nutritive function, has been called by Hubrecht the trophoblast. As already noted (Fig. 32), the cleft between the parietal and visceral layers of the mesoblast is the primary body-cavity or ccelom ; with the separation of these layers following the dorsal and the ventral folding associated respectively with the formation of the amniotic sac and the gut-tube, the intramesoblastic space becomes greatly expanded and extends between the amnion and primitive chorion. This large space is appropriated only to a limited extent by the future definite body- cavity, and hence is divisible into an embryonic and an extra-embryonic portion, or exocce/om (Fig. 38), which are temporarily continuous. The Vitelline Sac. While the somatopleura is engaged in producing the protecting amniotic sac, the splanchnopleura, composed of the entoblast and the adherent visceral layer of mesoblast, becomes approximated along the ventral sur- face of the embryo to define the primitive gut-tube by enclosing a part of the blastodermic vesicle ; the remaining, and jar larger, portion of the latter cavity constitutes the vitelline sac, and corresponds to the yolk-sac of the lower forms. The constriction and separation of the gut-tube from the vitelline sac is accom- plished earliest at the F IG - 39- cephalic and caudal ends of the future alimentary canal, the intervening por- tion remaining for a time in widely open communi- cation with the yolk-sac. During the rapid diminu- tion of the latter the com- munication becomes re- duced to a narrow channel, the vitelline duct, which persists as a slender stalk terminating at its distal end in the remains of the yolk- sac. In animals other than mammals in which a pla- centa is developed, the yolk-sac is the chief nutri- tive organ of the embryo ; the mesoblastic tissue of the vesicle becomes vascu- larized by the development of the blood-vessels consti- tuting the vitelline circulation, of which the vitelline or omphalomesenteric arteries and veins form the main trunks. The contents of the yolk-sac as such do not directly minister to the nutrition of the embryo, but only as materials absorbed by the vitelline blood-vessels. In man and other high mammals the nutritive function of the yolk is at best insignificant, the vitelline sac of these animals representing the more important organ of their humbler ancestors. In the lowest members of the mammalian group, the monotremata, in which the large ova are comparatively rich in deutoplasm, the vitelline circulation is of great importance for respiration and nu- trition, since it constitutes the means for the performance of these functions until the immature animals are transferred to the marsupial pouch to complete their develop- ment. In the kangaroo and opossum the yolk-sac at one point forms a disk-like organ, which, from the fact that it becomes provided with vascular villi that lie in contact with the uterine mucous membrane, is termed tin- vitelline placenta. The Allantois and the Chorion. Coincidently with the formation of the amnion, another foetal appendage, the allantois, makes its appearance as an out- Primitive chorion Amnion Amniotic sac Gut-tube Ccelom Allantois Yitelline duct Diagram showing completed amnion and serosa, beginning allantois and vitelline duct. THE VITELLINE SAC. 33 growth from the caudal segment of the primary gut-tract. Although modified in man and certain mammals to such an extent that its typical form and relations are obscured, the allantois, when developed in a characteristic manner, as in the chick, assumes the appearance of a free vesicle connected with the embryo near its caudal pole by means of a narrow pedicle, the allantoic stalk. Since the allantois is an evagination from the primitive gut, its walls are formed by direct continuations of the primary layers enclosing the digestive canal, namely, a lining of entoblastic cells, reinforced externally by a layer of visceral mesoblast. Beginning as a wide bay on the ventral wall of the hind-gut, the allantois elon- gates and appears as a pyriform sac projecting from the embryo behind the attach- ment of the still large vitelline stalk (Fig. 39). It rapidly grows into the exoccelom, and in mammals expands in all directions until it comes into contact with the inner surface of the primitive chorion, with which it fuses to constitute the true chorion. The latter, sometimes spoken of as the allantoic chorion in contrast to the amniotic or primitive chorion, now becomes the most important envelope of the mammalian embryo on account of the role that it is destined to play in establishing the respira- FIG. 40. A 'Primitive chorion -Amnion -Amniotic sac Allantois ^Vitelline sac Diagram showing villous condition of serosa, expanding allantois, and diminishing vitelline sac. tory and nutritive organ of the foetus, the placenta. After the fusion of the allantois with the primitive chorion to form the chorion, the villous projections upon the external surface of the latter become more highly developed, consisting of a core of mesoblastic tissue covered externally by the ectoblast. The primary purpose of the allantois, as a receptacle for the effete materials ex- creted by the Wolffian body of the early foetus, is soon overshadowed by its function as a respiratory organ ; this occurs with the appearance of the rich vascular supply within the chorion following the invasion of its mesoblastic tissue by the blood-vessels constituting the allantoic circulation. The latter includes the two allantoic arteries, which are extensions from the aortic stem of the embryo and convey venous blood, and the two allantoic veins, which return the oxygenated blood to the embryo and become tributary to the great venous segment of the primitive heart. The vascu- larization of the chorion extends to the highly developed villi occupying its outer surface in many mammalian forms, especially man. The vascular villi of the chorion, bearing the terminal loops of the blood-vessels conveying the foetal blood, are important structures on account of their intimate relations with the uterine mucous membrane (Fig. 41), in conjunction with which 3 34 HUMAN ANATOMY. they form a respirative and nutritive apparatus. The intimacy between the uterine mucous membrane and the chorionic tufts presents all degrees of association, from simple apposition, as seen in the sow, where the feebly developed and almost uni- formly distributed vascular projections are received within corresponding depressions in the richly vascular uterine tissue, to the firm and complex attachment found in the highly developed human placenta. FIG. 41. Villi of extraplacental chorion Gut-tube Ectoblast Amniotic meso blast Space between am- nion and chorion Allantois Allantoic blood- vessels Allantoic sac Mesoblast Entoblast "Maternal blood-spaces "Decidua placentalis Diagram showing villous chorion, differentiation of placenta! area, and vascularization of chorion. In contrast with the chorion of those animals in which the nutritive relations between the maternal tissues and the embryo are uniformly distributed are the local specializations seen in the chorion of those types in which a placental area is de- veloped. The animals in which the latter condition obtains are known as placentalia, of which three subgroups are recognized depending upon the multiple (cotyledons), FIG. 42. Diagrams illustrating the various types of development of the chorion. A, uniformly developed villi (hog, horse) ;"/?, multiple placentae or cotyledons (cow, sheep); C, zonular placenta (cat, dog); />, discoidal placenta (monkey, man). A-B comprise non-deciduate ; C-D, deciduate mammals. zonular, or discoidal form of the placenta, man and the apes representing the highest specialization of the last division. In its general plan of development, therefore, the placenta is formed of a fatal and a maternal portion, the former consisting of the vascular villi which are unusually well developed within a particular portion of the chorion, and the latter of the opposed uterine lining which becomes highly special- ized throughout a corresponding area and more or less intimately united with the THE HUMAN FCETAL iMEMBRANES. 35 foetal structures. The mucous membrane of the entire uterine cavity, in many of the higher mammals, suffers profound change, and before the end of gestation becomes inseparably attached to the chorion even in its extent beyond the placental area ; in such animals the fused uterine and chorionic tissue constitute the deciduce which, lined internally by the closely applied amnion, form the membranous envelope en- closing the foetus. After rupture consequent upon the expulsion of the foetus at the termination of pregnancy, the deciduae, including the specialized placental portion, are separated from the uterine wall and expelled as the membranes and the placenta which are known collectively as the after-birth. The foregoing sketch of the general development of the foetal membranes in the higher mammals must be now supplemented by consideration of the peculiarities encountered in the development of these structures in man. THE HUMAN FCETAL MEMBRANES. The young human embryo is distinguished by the very early formation of the amniotic cavity, by the precocious development of the mesoblast and extra- embryonic ccelom, by the presence of the body-stalk and- by the great thickening of the trophoblast. It must be remembered, in considering the formation of the human fcetal membranes, that the earliest stages of development, to wit, fertilization, segmentation, the formation of the blastodermic vesicle, the earliest differentiation of the embryonic area and the formation of the amniotic cavity have not yet been observed on human specimens. Our knowledge of these processes is derived from a study of some of the lower types ; beyond these very early stages, however, the conditions in the human embryo have been subject to direct study. The Human Amnion, Amniotic Cavity and Allantois. The accompany- ing diagrams (Fig. 43) will serve to illustrate the process of formation of the fcetal membranes in man. Of these five diagrams, A alone is purely hypothetical with reference to the human embryo. In diagram A the amniotic cavity is already indicated as a small cleft between the embryonic area below and a covering layer of cells above continuous with the trophoblast. This layer, the trophoblast, forms the outer covering of the entire vesicle. It is presumably already thickened at as early a stage as this diagram represents. Presumably also the surface of the trophoblast shows irregularities, for this tissue it is which comes into direct contact with the uterine mucous membrane and which, by its activities, forces its way into the maternal decidua. This latter process is known as implantation, a process which supposedly is taking place, if not completed, at about the stage of this diagram. Whether the trophoblastic layer in man is originally a thin single sheet of cells, as for instance is the case in the rabbit, or whether it is from the beginning thickened, we do not know. Certainly the thickened condition appears at a very early stage. The embryonic area shows the embryonic ectoblast proper, which is of small extent ; this ectoblast being so distinguished from the trophoblastic ectoblast. The ento- blast beneath is represented as already arranged in the form of a sac. Between the entoblast and ectoblast the mesoblast has made its appearance. It will be noted that in the diagram the entoblastic sac is much smaller than the outer trophoblastic vesicle. We do not know that this is really the condition when the entoblastic sac is first formed or only appears in conjunction with the great development of the extra embryonic ccelom in the mesoblast. It is certainly not unreasonable to suppose that the former case is the true one. The early appearance of the amniotic cavity is to be explained in this way. After the blastodermic vesicle has reached the stage when the inner cell mass is attached to one point on the inner surface of the trophoblast, the formation of a cavity occurs in the region of the inner mass. This cavity, at first very small, has below it the cells of the inner mass, which soon become arranged into the two primary germ layers of the embryonic area, ectoblast and entoblast, while above the cavity is a layer of cells continuous with the trophoblast. Such a method of formation of the amniotic cavity has been observed in some of the lower forms, for instance, by Hubrecht, in the hedge hog, and since the earliest human embryo accurately studied shows a completely closed amniotic cavity, while in 36 HUMAN ANATOMY. a very early stage of development, it is a reasonable inference that in man such a process actually occurs. In diagram B the mesoblast has not only surrounded the entoblastic sac and the inner surface of the trophoblast, so enclosing the large extra-embryonic ccelom, but has invaded the layer of cells above the amniotic cavity, dividing this layer into two parts, the inner part going to form the ectoblast of the amnion, the outer part being a continuation of the trophoblast of the chorion. There is here evidently a very great development of the extra-embryonic ccelom. In explanation of this condition, it may be assumed that the entoblastic sac is at first much smaller than the trophoblastic covering of the vesicle ; that the mesoblast, shortly after its appearance, FIG. 43 am Diagrams illustrating development of human fu-tal membranes. Staged is hypothetical ; others are basrn stages which have been actually observed. Red represents trophoblast; purple, embryonic ectoblast; K r;l > "^" blast; blue, entoblast. ac, amniotic cavity; /, allantois ; am, amnion; f>, body-stalk; r/i, chorion; ee, embryonic ectoblast; en, entoblast; ?, gut-tube; m, mesoblast ; p, placental area; /.trophoblast; v, yolk-sac ; vs, yolk-stalk. around the vesicle ; the splanchnic layer around the entoblast, the somatic layer around the trophoblast, so enclosing between them as they grow, the considerable space which becomes, by this process, extra-embryonic body cavity. This diagram corresponds roughly to the condition of Peters' embryo ( Fig. 44). The trophoblast is greatly thickened ; its outer surface very irregular, showing lacuna- or spaci-s filled with maternal blood. This early intimate contact of the fulal tissue with the maternal blood permits nutrition of the young embryo from the maternal blood to be carried on through the trophoblast cells some time before the allantoic circulation and definite placenta are established. Hence the significance of this term trophoblast. THE HUMAN FCETAL MEMBRANES. 37 In the next diagram, (Fig. 43), C, the extra-embryonic coelom has invaded the sheet of mesoblast above the amniotic cavity to such an extent that the chorion is completely separated from the amnion and the body of the embryo except at one point, the posterior end of the body, where a solid stalk of mesoblast connects the chorion and embryo. This solid band of mesoblast is called the body -stalk. It represents, therefore, a primary and permanent connection between the chorion and the body of the embryo. A small diverticulum from the entoblastic sac growing into the mesoblast of the body-stalk marks the beginning of the allantois. As the diagram shows, the amnion is at first a comparatively small membrane overlying the embryonic area. The ectoblast of the amnion is on the inner side facing the embryo, the mesoblast on the outer side. In the chorion these layers are placed inversely, the mesoblast on the inner side, the ectoblast (trophoblast) outside. The space between amnion and chorion is seen to be a continuation of the extra-embryonic ccelom. In diagram D, the amnion has become considerably expanded in association with the growth of the body of the embryo and the accumulation of amniotic fluid. A constriction in the entoblastic sac has made its appearance, a constriction which separates the gut of the embryonic body from its appendage, the yolk-sac, the narrower connecting piece being known as the yolk-stalk, or sometimes as the vitello-intestinal duct. This constricted area is brought about by the rapid growth of the body of the embryo. In the early condition the entoblastic sac is attached to the embryonic body practically along its entire ventral surface. The body region grows very rapidly, particularly the head end, which comes to project from the entoblastic sac to a marked extent ; the tail end also projects somewhat. There is a corresponding growth of the gut within the body of the embryo. As a consequence of this process of expansion of the body, the area of attachment of the entoblast external to the body becomes relatively much reduced in size, occupying only a small portion of the ventral surface of the body, and a progressively smaller portion as the body increases in bulk. In other words, the narrow area of the yolk-stalk makes its appearance. In the diagram (/?, al ') the allantois projects from the posterior end of the embryonic gut into the body-stalk. It will be noticed that the human allantois is never a free structure as it is in many of the 'lower types, where it grows from the body freely into the extra-embryonic ccelom and only later becomes connected with the chorion to form the placenta, but that in man it grows directly into the body- stalk, where, outside of the body of the embryo, it is an insignificant structure. Inside the body, part of the allantois persists as the bladder. The urachus, a fibrous cord which in the adult passes from the top of the bladder to the umbilicus, is also a remnant of the allantois. The thick irregular projections of the trophoblast have received a core of mesoblast tissue, so forming the early chorionic villi. These villi, at the point of attachment of the body-stalk, the area where the placenta is developing, are increasing in size, while the villi over the remainder of the chorion are diminishing in size. In diagram /?, the amnion has become greatly expanded. It lies closer to the inner surface of the chorion. In close association with this expansion of the amnion, and the accompanying growth of the body of the embryo, the structures which form the umbilical cord are so closely approximated that the area of the cord is clearly defined. These structures are the body-stalk containing the allantois and allantoic vessels, the yolk-stalk, and, bounding the other side of this area, the fold of the amnion from beneath the head. At first the body-stalk projects from beneath the extreme posterior end of the body of the embryo, but as growth in this part of the body advances and the tail projects more and more, the body-stalk is brought to the ventral surface of the abdominal region in close proximity to the yolk-stalk. The allantoic blood-vessels grow from the embryo through the body-stalk to the chorion, where they ramify in the chorionic villi. At first there is an extension of the coelom about the yolk-stalk in the umbilical cord, but the mesoblast tissues of the structures of the cord soon fuse together, obliterating this cavity. The area of attach- ment to the abdomen of the umbilical cord becomes relatively very much reduced in size and is known in the adult, after the separation of the cord, as the umbilicus or navel. HUMAN ANATOMY. The chorionic villi at the point of attachment to the chorion of the body-stalk are enlarged. These villi constitute the foetal portion of the placenta, the so-called chorion frondosuui. They are imbedded in the maternal decidua, more specifically, the decidua basalis or placentalis. It must be remembered that the villi contain a core of mesoblast tissue in the stage represented by diagram E, although this meso- blastic core is not shown in the figure, and that the allantoic bipod -vessels run in FIG. 44. Comf>. Ca . Z. Tr. g. Caf>. K. U. E. B.L. Sy. tissue of uterine mucosa ; E., embryo; g., gland of uterus : Af., mesoblast ; Sv., syncytium ; T. M., covering tissue- over break in uterine surface; Tr., trophoblast. X 50 (Pfters}. this mesoblast : also that the villi are in reality considerably branched, not straight as in the diagram. The remainder of the chorion is acquiring a smooth surface and is commonly known as the clnnion lf t-vt-c.o-r>on/-ir reglldliey. The Amniotic Fluid. - Extraplacental area (Choi ion Iteve) u TV us' U- -^ Placental a i (Chorion frondosum) ^Bi External surface of part of the human chorion of the third month ; the lower portion is covered with the highly developed villi of the placental area. at first lies closely applied to the embryo, but soon becomes separated by the space which rapidly widens to accommodate the increasing volume of the contained liquor amnii. The accumulation of fluid within the amniotic sac, which in man takes place with greater rapidity than in other mam- mals, results in 'the obliteration of the cleft between the chorion and amnion until the latter envelope lies tightly pressed against the inner surface of the chorion. The union between the two envelopes, however, is never very intimate, as even after the expulsion of the membranes at birth the attenuated amnion may be stripped off from the chorion, although the latter is then inseparably fused with the remaining portions cf the deciduae. The amniotic fluid, slightly alkaline in reaction, is composed almost entirely of water ; of the one per cent, of solids found, albumin, urea, and grape-sugar are constituents. The quantity of liquor amnii is greatest during the sixth month of gestation, at which time it often reaches two litres. With the rapid increase in the general bulk of the foetus during the later months of pregnancy, the available space for the amniotic fluid lessens, resulting in a necessary and marked decrease in the quantity of the liquid ; at birth, less than one litre of amniotic fluid is usually present. Sometimes, however, the amount of the liquor amnii may reach ten HUMAN ANATOMY. litres, due to pathological conditions of the foetal envelopes ; such excessive secre- tion constitutes hydramnion. During the later months of pregnancy the foetus swal- lows the amniotic fluid, as shown by the presence of hairs, epithelial cells, etc., within the stomach. In view of the composition of the fluid, consisting almost en- tirely of water, it seems certain that the introduction of the liquor amnii does not serve the purposes of nutrition ; on the other hand, it is probable, as held by Preyer, that the unusual demands of the fcetal tissues for water may be met largely in this manner. The source of the amniotic fluid in man has been the subject of much discus- sion. While it has been impossible to determine accurately the extent to which the mother participates in the formation of this fluid, it may be accepted as established that the maternal tissues are the principal contributors ; it is also probable that the foetus likewise aids in the production of the liquor amnii ; the latter, therefore, orig- inates from a double source, maternal and fcetal. The early amniotic fluid resembles FIG. 49. Umbilical vesicle Umbilical stalk- Inner surface of chorion Umbilical cord - Cut edge of amnion- Masses of chorionic villi- Human embryo of about thirty-three days. X 4. Amnion and chorion have been cut and turned asid in appearance and chemical composition a serous exudate ; later, after the formation of the urogenital openings, the liquor amnii becomes contaminated, as well as aug- mented, by the addition of the fluid derived from the excretory organs of the foetus. During the later weeks of gestation the contents of the digestive tube are discharg into the amniotic sac as meconium. The Umbilical Vesicle. The umbilical vesicle, as the yolk-sac in man is termed, presents a reversed growth-ratio to the amnion and body-stalk since it pro- gressively decreases as these latter appendages become more voluminous. The early human embryo is very imperfectly differentiated from the large and conspicuous yolk-sac, with which its ventral surface widely communicates. With the advances made during the third week in the formation of the primitive gut, the connection between the latter and the vitelline sac becomes more definitely outlined in conse- quence of the Inrlnning constriction which indicates the first suggestion of the later vitelline or umbilical duet ( Fig. 47). By the end of the fourth neek the connection - THE UMBILICAL VESICLE. 43 between the umbilical sac and the embryo has become reduced to a contracted channel extending from the now rapidly closing ventral body-wall to the yolk-sac, which is still, however, of considerable size. The succeeding fifth (Fig. 50) and sixth weeks effect marked changes in the umbilical duct, now reduced to a narrow tube, which extends from the embryo to the chorion, where it ends in the greatly diminished vitelline sac. The lumen of the umbilical duct is conspicuous during the earliest months of gestation, but later disappears, the entoblastic epithelial lining remaining for a considerable time within the umbilical cord to mark the position of the former canal. The chief factor in producing the elongation of the umbilical duct is the rapid expansion of the amnion ; with the increase in the amniotic sac the distance between this envelope and the embryo increases, until the amnion fills the entire space within FIG. 50. Amnion _ Umbilical vesicle, (yolk-sac) Inner surface of chorion,- Chorionic villi of outer surface . Chorionic sac of thirty-five day embryo laid open, showing embryo enclosed by amnion. X 2. the chorion, against which it finally lies. In consequence of this expansion, the attachment between the embryo and the amnion around the ventral opening, which later corresponds to the umbilicus, becomes greatly elongated and narrowed. At this point the tissues of the embryonic body-wall and the amniotic layers are directly continuous. The tubular sheath of amnion thus formed encloses the tissue and structures which extend between the embryo and the chorion, as the constituents of the belly-stalk, together with the umbilical duct and the remains of the vitelline blood-vessels ; the delicate mesoblastic layer of the amnion fuses with the similar tissue of the allantois, the whole elongated pedicle constituting the umbilical cord or funiculus. The latter originates, therefore, from the fusion of three chief com- ponents, the amniotic sheath, the belly-stalk, and the vitelline duct ; the belly-stalk. 44 HUMAN ANATOMY. as already noted, includes the allantois, with its blood-vessels, and diverticulum, while traces of the vitelline circulation are for a time visible within the atrophied walls of the umbilical duct. As gestation advances, the amnion and the chorion become closely related, but not inseparably united ; between these attenuated mem- branes lie the remains of the once voluminous yolk-sac, which at birth appears as an inconspicuous vesicle, from three to ten millimetres in diameter, situated usually several centimetres beyond the insertion of the umbilical cord. In cases in which the closure and the obliteration of the vitelline duct before birth are imperfectly effected, a portion, or even the whole, of the intra-embryonic segment of the canal may persist as a pervious tube. Although in extreme cases of faulty closure a passage may lead from the digestive tube to the umbilicus, and later open upon the exterior of the body as a congenital umbilical anus, the retention of the lumen of the vitelline duct is usually much less extensive, being limited to the prox- imal end of the canal, where it is known as Mecke? s diverticulum. The latter is con- nected with the ileum at a point most frequently about 82 centimetres (thirty-two inches) from the ileo-caecal valve. Such diverticula usually measure from five to 7.5 centimetres in length, and possess a lumen similar to that of the intestine with which they communicate. The foregoing envelopes, the amnion and the chorion, are the product of the embryo itself ; their especial purpose, in addition to affording protection for the deli- cate organism, is to aid in establishing close nutritive relations between the embryo and the maternal tissues, which, coincidently with the development of the foetal envelopes, undergo profound modifications ; these changes must next be considered. The Deciduse. The birth of the child is followed by the expulsion of the after-birth, consisting of the membranes and the placenta, which are separated from the uterine wall by the contractions of this powerful muscular organ. Close inspection of the inner surface of the uterus and of the opposed outer surface of the extruded after-birth shows that these surfaces are not smooth, but roughened, presenting evi- dences of forcible separation. The fact that the external layer of the expelled after- birth consists of the greater portion of the modified mucous membrane which is stripped off at the close of parturition suggested the name deciduce for the mater- nal portion of the foetal envelopes shed at birth. Since the deciduae are directly derived from the uterine mucous membrane, a brief sketch of the normal character of the last-named structure appropriately pre- cedes a description of the changes induced by pregnancy. The normal mucous membrane lining the body of the human uterus (Fig. 51) presents a smooth, soft, velvety surface, of a dull reddish color, and measures about one millimetre in thick- ness. The free inner surface is covered with columnar epithelium (said to be cili- ated) which is continued directly into the uterine glands. The latter, somewhat sparingly distributed, are cylindrical, slightly spiral depressions, the simple or bifur- cated blind extremities of which extend into the deeper parts of the mucosa in close relation to the inner bundles of involuntary muscle ; all parts of the tubular uterine glands are lined by the columnar epithelium. The muscular bundles representing the muscularis mucosae are enormously hypertrophied and constitute the greater part of the inner more or less regularly disposed circular layer of the uterine muscle. The unusual development of the muscular tissue of the mucous membrane reduces the submucous tissue to such an insignificant structure that the submucosa is gener- ally regarded as wanting, the extremities of the uterine glands being described as reaching the muscular tunic. The glands lie embedded in the connective-tissue complex, rich in connective-tissue elements and lymphatic spaces, that forms the tunica propria of the mucosa. With the beginning of pregnancy the uterine mucous membrane undergoes marked hypertrophy, becoming much thicker, more vascular, and beset with nu- merous irregularities of its free surface caused by the elevations of the soft spongy component tissue. These changes take place during the descent of the fertilized ovum along the oviduct and indicate the active preparation of the uterus for the reception of the ovum. According to the classical description of the encapsulation of the ovum (Fig. 52) by the uterine mucous membrane, the embryonic vesicle becomes arrested within THE DECIDtLE. 45 one of the depressions of the uterine lining, usually near the entrance of the ovi- duct, whereupon the adjacent mucosa undergoes rapid further hypertrophy, which results in the formation of an annular fold surrounding the product of concep- tion. This encircling wall of uterine tissue continues its rapid growth until the embryonic vesicle is entirely enclosed within a capsule of modified mucous mem- brane, known as the decidua rcflexa, as distinguished from the decidua vera, the name applied to the general lining of the pregnant uterus. That portion of the uterine mucosa, however, which lies in close apposition to the embryonic vesicle, constituting the outer wall of the decidual sac, is termed the decidua serotina ; later it becomes the maternal part of the placenta. FIG. 51. Duct of gland Spiral portion of gland Process of muscular tissue extending be- tween the glands Muscular tissue -Uterine blood- vessel Ut.erine mucous membrane with part of muscular tissue. X 45. Our knowledge of the details regarding the encapsulation of the ovum has been materially advanced by the recent observations of Peters, who had the rare good fortune of carefully studying the details of the process at an earlier stage than any hitherto accurately investigated. The results of Peters' s observations lead to a somewhat modified conception of the early phases of the encapsulation of the ovum, as well as shed additional light on some of the vexed problems concerning the details of the formation of the placenta. According to these investigations, the embryonic vesicle, on reaching the uterine 4 6 IH'MAN ANATOMY. FIG. 52. cavity and becoming arrested at some favorable point, usually in the vicinity of the oviduct, brings about a degeneration of the uterine epithelium over the area of contact. The disappearance of the epithelial lining is followed by sinking and em- bedding of the embryonic vesicle within the softened mucous membrane, the process being accompanied by erosion of some of the uterine capillaries and consequent hemorrhage into the opening representing the path of the ovum. The extravasated blood escapes at the point of entrance on the uterine surface and, later, forms a mushroom-shaped plug marking the position of the embedded ovum. The latter thus comes into closer relations with the maternal tissues at an earlier period than was formerly recognized. The Trophoblast. The ear- liest human embryonic vesicle that has been accurately studied, that of Peters, while measuring only 1.6 millimetres in its greatest di- Diagrams representing relations of the uterine mucous mem- ameter, Was already enclosed CXter- brane to the embryonic vesicle, or ovum, during the embedding nallv bv a COnsoicUOUS CCtoblastic of the latter, s, v, c, decidua serotina, vera, and reflexa, re- ' J spectively ; o, ovum. envelope, m places .5 millimetre or more in thickness. This thick ectoblastic layer is evidently the proliferated trophoblast (page 31), a membrane so designated to indicate the important nutritive functions which it early assumes. Very early the trophoblast becomes honeycombed by the extension of the maternal vascular channels into the ectoblastic tissue (Fig. 53), which consequently is broken up into irregular epithelial trabeculae separating the maternal blood-spaces. The inner surface of the trophoblastic capsule presents numerous irregular depres- sions into which corresponding processes of the adjacent young mesoblast project ; this arrangement foreshadows the formation of the chorionic villi which soon become so conspicuous in the human embryonic vesicle. Coincidently with the invasion of the trophoblast by the vascular lacuna externally and the penetration of the F-J G . 53. mesoblastic tissue internally, the pe- ripheral portions of the ectoblastic capsule undergo proliferation and extend more deeply into the sur- rounding maternal tissues. In con- sequence of the rapid growth of the embryonic vesicle, that part of the hypertrophied uterine mucosa which overlies the embedded embryonic vesicle soon- becomes elevated and projects into the uterine cavity, thus giving rise to the structure described as the decidua reflexa, or, preferably, the decidua capsularis. The Decidua Vera. The changes which affect the uterine mu- cous membrane, the decidua vera, result in great thickening, so that the mucosa often measures nearly a centimetre ; this thickening, however, is most marked in the immediate vicinity of the embedded ovum, throughout the greater part of the uterus the decidua attaining a much less conspicuous hypertrophy. Towards the cervix the mucosa is least affected, and at the internal orifice of the cervical canal presents its normal appearance. Examina- tion of the decidua shows that the normal constituents of the uterine mucosa undergo hypertrophy which results in enlargement of the uterine glands ( Fig. 54), as well as in increase of the intervening connective-tissue stroma. The enlargement of the glands is not uniform, but is limited to the middle and terminal or deeper parts of Mesoblast Trophohlast Intervillous blood-space Sviu-ytium Diagram showing early stage oi attachment between f, II which constriction the cephalic and the caudal poles of the body become denned and partially separated from the embryonal area ; the middle segment, however, em- bracing the widely open gut-tract, for a time remains closely blended with the vitel- line sac, of which, at first, the embryo appears as an appendage (Fig. 68, i and 2). HUMAN ANATOMY. The more complete differentiation of the digestive tube and the ventral folding in of the body-walls change this relation, the rapidly decreasing umbilical vesicle soon becoming secondary to the embryo. At the close of the stage of the vesicle about the fifteenth day the human embryo possesses a general cylindrical body-form, the dilated cephalic pole being free, while the belly-stalk attaches the caudal segment to the chorion ; the amniotic sac invests the dorsal aspect, the large umbilical vesicle occupying the greater part of the ventral surface. Human FIG. 69. Otic vesicle Second visceral arch X Cephalic flexure Optic Maxillary process 4 -Third visceral arch Fourth visceral arch Heart Upper limb-bud Mandibular process ' of first visceral arch Caudal end ot embryo Umbilical cord in section Lower limb-bud Human embryo of about twenty-three days, drawn from the model of His. X 10. FIG. 70. Otic vesicle embryos of the fourteenth and fifteenth days (Fig. 68, 3 and 4) are distinguished by a conspicu- ous flexure opposite the attach- ment of the umbilical vesicle, the convexity being directed ven- trally, the deep corresponding concavity producing a marked change of profile in the dorsal outline. During these changes the expansion of the cerebral segments outlines the three pri- mary divisions of the cephalic portion of the neural tube, the anterior, the middle, and the posterior brain-vesicles. A little later a series of conspicuous bars, the visceral arches, appears as ob- liquely directed parallel ridges on either side of the head, immediately above the prominent heart-tube, which is now undergoing marked torsion. By the nineteenth day the dorsal concavity, which is peculiar to the human embryo, has entirely disap- peared, the profile of this part of the embryo presenting a gentle convexity ; the cephalic axis, however, exhibits a marked bend, the cephalic flexure, in the vicinity of the middle cerebral vesi- cle, in consequence of which the axis of the anterior cere- bral segment lies almost at right angles to that of the middle vesicle. The com- ... r .v ii j i Cephalic flexure pletion of the third week finds the characteristic de- tails of the cephalic end of the embryo, the cerebral, the optic, and the otic vesi- cles, and the visceral arches and intervening furrows well advanced, with correspond- ing definition of the primitive heart and the umbilical stalk and vesicle. The limb-buds usually appear about this time, those of the upper ex- tremity slightly preceding those of the lower. The period between the twenty-first and the twenty-third days witnesses remarkable changes in the gener appearance of the embryo ; in addition to greater prominence of the visceral arches, the cerebral segments, and the limb-buds, the embryonic- axis, which, with the exceptions already noted, up to this time is only slightly curved, now undergoes flexion to such extent that by the twenty-third day the overlapping cephalic and caudal ends of the embryo are in close apposition, the body-axis describing rat u more than a complete circle (Fig. 69). Optic vesicle Mandibular process of first visceral arch Olfactory pit Umbilical cord- Lower limb-bud' Cervical flexure Second visceral arch Third visceral arch Fourth visceral arch Heart 'pper limb-bud : Human embryo of about twenty-live days, drawn from the model of X 10. THE VISCERAL ARCHES AND FURROWS. 59 From the twenty-third to the twenty- eighth day the excessive flexion gradually disappears, owing to the increased volume of the heart and the growth of the head, and by the end of the fourth week the embryo has acquired the most characteristic development of the embryonic stage (Fig. 71). The reduction in the curvature of the body-axis and the consequent separation of its poles and the raising of the head are accompanied by the appearance of four well-marked axial flexions, the cephalic, the cervical, the dorsal, and the sacral flexures (Fig. 71). The first of these, the cephalic, is an accentuation of the primary flexure, which is seen as early as the eighteenth day, and is indicated by the projection of the midbrain ; it corresponds in position to the future sella turcica. The second and very conspicuous bend, the cervical flexure, marks the caudal limit of the cephalic portion of the neural axis, and agrees in position with the subsequent upper cervical region. The dorsal and sacral flexures are less well defined, the former being situated opposite the upper limb-bud, where the cervical and dorsal series of somites join, the latter, near the lower limb-bud, corresponding with the junction of the lumbar and sacral somites. The cephalic segment at this stage presents numerous prominent details, the FIG. 71. Cervical flexure Otic vesicl Maxillary process of first-- visceral arch Cephalic flexure-l|. Eye-- 5 Olfactory pit Umbilical cord Lower limb Third visceral arch First external visceral furrow Second visceral arch Mandibular process of first visceral arch "Dorsal flexure "Upper limb Heart Sacral flexure Human embryo of about twenty-eight days, drawn from the model of His. X 10. secondary cerebral vesicles, the forebrain, the interbrain, the midbrain, the hind- brain, and the after-brain, the visceral arches and furrows, the optic and otic vesicles, the olfactory pits, and the primitive oral cavity all being conspicuous. The heart ap- pears as a large protrusion, occupying the upper half of the ventral body-wall, on which the primary auricular and ventricular divisions are distinguishable. The somites form a conspicuous longitudinal series of paraxial quadrate areas, about thirty-seven in number ; they correspond to the intervertebral muscles, and may be grouped to accord with the primary spinal nerves, being, therefore, distinguished as eight cer- vical, twelve dorsal, five lumbar, five sacral, and five or more coccygeal somites. THE VISCERAL ARCHES AND FURROWS. Since the visceral arches are best developed in the human embryo during the last half of the third week, a brief consideration of these structures in this place is appropriate. The visceral arches in mammalian embryos constitute a series of five parallel bars separated by intervening furrows, obliquely placed on the ventro-lateral aspect of the cephalic segment, occupying the region which later becomes the neck. They represent, in rudimentary development, the important branchial or gill- 6o HUMAN ANATOMY. apparatus of water-breathing vertebrates, in which the respiratory function is per- formed by means of the rich vascular fringes lining the clefts through which the water passes, thus permitting the exchange between the oxygen of the water and the carbon dioxide of the blood. Each arch is supplied by a blood-vessel, or aortic bow, which passes from the main ventral stem, the truncus arteriosus, through the substance of the visceral arch backward to unite with the similar bows to form the dorsal aortce. In aquatic vertebrates the aortic bows supply an elaborate system of secondary branchial twigs, which form rich capillary plexuses within the gills ; in air-breathing vertebrates, however, in which these structures are only rudimen- tary, the main stems, the aortic bows, are alone represented. With the loss of func- tion which follows the acquisition of aerial respiration in the higher vertebrates, the number of visceral arches is reduced from six, or even seven, as seen in fishes, to five, the fifth arch in man, however, being so blended with the surrounding struc- tures that it is not visible externally as a distinct bar. In their condition of great- est perfection, as in fishes, each visceral arch contributes an osseous bar, whicli forms part of the branchial skeleton ; these bony bars are represented in man and mammals by cartilaginous rods, which temporarily occupy the upper arches, for the most part entirely disappearing. When viewed in frontal section (Fig. 73), the mammalian visceral arches are seen as mesodermic cylinders imperfectly separated by external and internal grooves, the visceral furrows and the pharyngeal pouches respectively ; this arrangement emphasizes another modification following loss of function, namely, the conversion of the true visceral clefts of the lower forms into furrows, since in man and mammals the FIG. 72. fissures are closed by the occluding mem- brane formed by the apposition of the ectoblast and the entoblast at the bottom of the outer and inner furrows. The First or Mandibular Arch c , early becomes differentiated into a short Second arch ' , Third arch upper or maxillary process and a longer lower or mandibular process. The maxil- lary process, in conjunction with its fellow of the opposite side and the fronto-nasal Head of human embryo of about twenty-one days, />vwcf whirri rlp^rprulu a ^ J M Primitive aortse "Neural tube Upper half of human embryo of about eighteen days, drawn from His's models. X 45. A, dorsal wall of primitive oropharynx bounded by visceral arches, external and internal furrows. B, anterior wall of primitive oropharynx, seen from behind. 1-5, sections of aortic arches; I-IV, external visceral furrows. caudal end of the series, where the sinking in of the arches and the included furrows produces a depression or fossa the sinus pracervicalis of His in the lower and lateral part of the future neck region. This recess subsequently entirely disappears on coalescence of the bordering parts ; sometimes, however, such union is defective, the imperfect closure resulting in a permanent fissure situated at the side of the neck, known as cervical fistula, by means of which communication is often established between the pharynx and the exterior of the body. Such communication must, however, be regarded as secondary, as originally the external furrows were sepa- rated from the primitive pharyngeal cavity by the delicate epithelial septum already mentioned as the occluding plate. Where entrance into the pharynx through the fistula is possible, it is probable that the septum has been destroyed as the result of absorption or of mechanical disturbance following the use of the probe. The Inner Visceral Furrows, or pharyngeal pouches, repeat the general arrangement of the external furrows. The first pharyngeal pouch becomes narrowed and elongated, and eventually forms the Eustachian tube ; a secondary 62 HUMAN ANATOMY. FIG. 74. Fronto-nasal process Primitive oral cavity lesial nasal process Maxillary process Mandibular process Head of human embryo of about twenty-seven days, showing boundaries ot primitive oral cavity. X 7. (After His.) dorsal expansion gives rise to the middle ear, while the occluding plate separating the outer and inner furrows supplies the tissue from which the tympanic membrane is formed. The second furrow partially disappears without giving origin to perma- nent structures ; its upper part, however, is probably represented by the fossa of Rosenmiiller, which lies, on each side, as a lateral recess in the pharynx. The third and fourth pouches give rise to ventral entoblastic outgrowths from which the epithelial portions of the thymus and of the thyroid body are developed respectively. The last-named organ has an additional unpaired origin from the entoblast forming the ventral wall of the pharynx in the vicinity of the second visceral arch. The Development of the Face and the Oral Cavity. The earliest suggestion of the primitive oral cavity is the depression, or stomodccum, which ap- Laterai nasal process pears about the thirteenth day on the ventral surface of the cephalic end of the embryo immediately beneath the ex- panded anterior cerebral vesicle. Tire oral pit at first is separated from the ad- jacent expanded upper end of the head- gut by the delicate septum, the pharyn- geal membrane, composed of the opposed ectoblast and the entoblast, which in this location are in contact without the inter- vention of mesoblastic tissue. With the rupture of the pharyngeal membrane, the deepened oral pit opens into the cephalic extremity of the head-gut, now known as the primitive pharynx. The formation of the face is closely associated with the growth and fusion of the upper visceral arches in conjunction with the surrounding parts of the ventral surface of the head. The first visceral arch, as already described, presents two divisions, the maxillary and the mandibular process. The latter grows ventrally and joins in the mid-line its fellow of the opposite side, to form, with the aid of the second visceral arches, the tissues from which the lower boundary and the floor of the mouth are derived. The upper and lateral boundaries of the primitive oral cavity and the differentiation of the nasal region proceed from the modification and fusion of three masses, the two lateral paired maxillary processes of the first visceral arches and the mesial unpaired fronto-nasal process, which descends as a conspicuous projection from the ventral surface of the anterior part of the head. The maxillary processes grow towards the mid-line and, in conjunction with the descending fronto-nasal projection, form the lateral and superior boundary of the primitive oral cavity (Fig. 74). Very soon the development of the future nares is suggested by the appearance of slight depressions, the olfactory pits, one on each side of the fronto-nasal process : these areas constitute part of the wall of the forebrain, a relation which foreshadows the future close association between the olfactory mucous membrane and the cortex of the olfactory lobe. During the fifth week the thickened margins of the fronto-nasal process undergo differentiation into the mesial nasal processes, while coincidently the lateral portions of the fronto-nasal projection grow downward as the lateral nasal processes, these newly developed projections constituting the inner and outer boundaries of the rapidly deepening nasal pits. The line of contact between the lateral nasal process and the maxillary process is marked by a superficial furrow, the uaso-optic groove , FIG. 75. Lateral nasal process Maxillary process First external vis- ci-ral furrow Second visceral arch Third visceral arch Head of human embryo of about thirty-four days. (After Hit.) X5- THE STAGE OF THE FCETUS. which leads from the nasal pit to the angle of the eye ; this furrow, however, merely indicates the position of the naso-lachrymal duct which develops independently at the bottom of the primary groove. Reference to Figs. 74 and 75 emphasizes the fact that the nasal pits and the primitive oral cavity are for a time in widely open com- munication ; towards the close of the sixth week, however, the maxillary processes of the first arch have approached the mid-line to such an extent that they unite with the lateral margins of the fronto-nasal process as well as fuse with the lateral nasal processes above. Owing to this union of the three processes, the nasal pits become separated from the oral cavity, and with the appearance and FIG. 76. completion of the palatal sep- tum the isolation of the nasal fossae from the mouth is ac- complished. The lateral nasal processes contribute the nasal Naso-optic groove Anlage producing nasal tip Nasal groove- Oral surface of maxillary process Dorsum of nose ^-Lateral nasal pro- cess Mesial nasal pro- Maxillary process of first arch Roof of oropharynx Portion of head of human embryo of about thirty-four days, showing roof ot primitive oral cavity. X 10. {After His.} FIG. 77. alae, while from the conjoined .mesial nasal process are devel- oped the nasal septum and the bridge of the nose in addition to the middle portion of the upper lip and the intermaxil- lary segment of the upper jaw, the superior maxillary part of the latter being a derivative of the maxillary process of the first arch. Arrested development and imperfect union between the maxillary processes and the fronto-nasal process result in the congenital defects known as harelip and cleft palate, the degree of the malformation depending upon the extent of the faulty union. The Stage of the Fcetus. The fifth week marks the completion of the period of development during which the product of conception has acquired the characteristic features of its embryonal stage ; beginning with the second month and continuing until the close of gestation, the succeeding stage of the foetus is distin- guished by the gradual assumption of the external features which are peculiar to the young human form. In addition to the already mentioned changes affecting the visceral arches and frontal process in the development of the face, the fifth week witnesses the differentiation of the limbs into segments, the distal division of the upper extremity exhibiting indica- tions of the future fingers, which thus anticipate the appear- ance of the toes. The Hver is already conspicuous as a marked protuberance occupying the ventral aspect of the trunk immediately below the heart. The head by this time has acquired a relatively large size, the prominent cephalic flexure which marks the position of the midbrain being par- ticularly conspicuous. At the end of the fifth week, or the thirty-fifth day, the foetus measures about fourteen millimetres in its longest dimension. The sixth week finds the foetus elongated with greater distinctness of the human form, the large size of the head, on which the cervical flexure is very evident, being highly characteristic when compared with corresponding stages of the lower mammals. The several constituents of the face become more perfectly formed, including the completion of the superior boundary of the oral cavity and its separation from the nasal pits by the septum resulting from the union of the fronto-nasal process with the maxillary processes ; the fusion of the latter with the lateral frontal processes now defines the external boundary of the nostrils of the still, however, broad and flattened nose, which lies immediately above the transverse cleft-like oral opening. The visceral arches are no longer visible as individual bars, having undergone com- plete fusion. The differentiation of the digits on both hands and feet has so far Head of human embryo of about seven weeks. X 5- (After Ecker.) 64 HUMAN ANATOMY. progressed that fingers and toes are distinctly indicated, although the fingers only are imperfectly separated. The first suggestion of the external genitals appears about the end of the sixth week. At this time the foetus measures about nineteen millimetres. During the seventh and eighth weeks the fcetal form of the body and the limbs attain greater perfection, the large head becoming raised from the trunk and the toes, as well as fingers, being now well formed, although the rudiments of the nails do not appear until some time during the third month. At the close of the second month the extra-embryonic protrusion of the intestine through the umbilicus into the umbilical cord reaches its greatest extent. The genito-urinary system is repre- sented by the fully developed Wolffian body, the vesical dilatation of the allantoic duct, the separation of the cloaca into rectum and genito-urinary passage, the indif- FIG. 78. Umbilical vesicle, Umbilical stalk. Inner surface of- amnion Umbilical cord. Human embryo of about thirty-five days. X 4- Amnion and chorion cut and turned aside. ferent sexual gland, and the undifferentiated external genitals, consisting of the tal eminence and the associated genital folds and genital ridges. The external ear has assumed its characteristic form, and the eyelids appear as low folds encircling the conspicuous eye, in which the pigmentation of the ciliary region is visible. Although the face is well formed, the nose is still flat, the lips but slightly prominent, and the palate not completely closed. The rapid growth of the brain results in the dispro- portionate size of the head, which at this stage almost equals the trunk in bulk. It is to be noted that by the close of the second month the permanent organs are so far advanced that the subsequent growth of the foetus is effected by the further de- velopment of parts already formed and not by the accession of new organs. The beginning of the second month marks the period of greatest re/atirc growth ; at the end of this month the foetus measures about thirty millimetres in its longest dimension. STAGE OF THE FCETUS. 65 The third month is characterized by greater perfection of the external form, the rounded head is raised from the trunk so that a distinct neck appears, while the thorax and abdomen are less prominent ; the limbs, which are well developed with completed differentiation of the fingers and toes, provided with imperfect nails, now assume the characteristic foetal attitude. The eyelids become united by the tenth week, remaining closed until the end of the seventh month. The cloacal opening becomes differentiated during the ninth and tenth weeks into the genito-urinary and FIG. 79. Umbilical cord Umbilical stalk Allantoic vessels Umbilical vesicle Human foetus of about eight weeks. X 3 1 A- Amnion has been cut and reflected, but still covers the umbilical vesicle and its stalk. the anal orifice, while during the eleventh and twelfth weeks the external genital organs acquire the distinguishing peculiarities of a definite sex. The greatest length of the foetus, measured in its natural position and excluding the limbs, at the end of the third month, is about eighty millimetres ; its weight approximates twenty grammes. The fourth month witnesses augmented growth in the foetus, which, how- ever, resembles in its general appearance the foetus of the preceding month. The 5 66 HUMAN ANATOMY. extra-foetal portion of the intestinal canal, which at an earlier period passes into the umbilical cord, during the fourth month recedes within the abdomen. The differentiation of sex is still more sharply exhibited by the external organs : in the male the penis is acquiring a prepuce, and in the female the labia majora and the clitoris are becoming well developed. At the close of this period the foetus measures approximately 150 millimetres and weighs about 120 grammes. During the fifth month the first foetal movements are usually observed. . The heart and the liver are relatively of large size. The decidua capsularis fuses with the decidua vera, thereby obliterating the remains of the uterine cavity. The meco- nium within the intestinal canal shows traces of bile. The advent of the fine hair, the lanugo, first upon the forehead and the eyebrows, and somewhat later upon the scalp and some other parts of the body, represents a conspicuous advance. Likewise adipose tissue appears in places within the subcutaneous layer. The approximate length, at the end of the fifth month, is twenty-three centimetres and the average weight about 320 grammes. The sixth month is characterized by complete investment of the body by lanugo and by the appearance of the vernix caseosa, the protecting sebaceous secre- tion which coats the body of the foetus to prevent as far as possible maceration of the epidermis in the amniotic fluid. The latter now reaches the maximum quantity, being contained within the large sac of the amnion. The sixth month is distin- guished by the conspicuous increase both in the size and weight of the foetus, and is known, therefore, as the period of greatest absolute growth. At the close of the sixth month the foetus measures approximately thirty-four centimetres in its longest dimension and weighs about 980 grammes. The seventh month is marked by progressive changes in the various parts of the foetus, whereby the more advanced details become pronounced in the central nervous system and digestive tract. The length of the foetus at the close of the seventh month approximates forty centimetres and its weight about 170x3 grammes. The eighth month is occupied by the continued growth and general develop- ment, as part of which the foetus acquires greater plumpness than before and a brighter hue of the integument, now entirely covered with vernix caseosa. The lanugo begins to disappear, while the scalp is plentifully supplied with hair ; the nails have reached, or project beyond, the tips of the fingers. By the close of the eighth month the foetus has attained a length of about forty-six centimetres and a weight of about 2400 grammes. The ninth month witnesses the gradual assumption of the characteristics of the child at birth, among which are the rounder contours, the extensive, although not complete, disappearance of the lanugo, except from the face, where it largely persists throughout life, the completed descent of the testicles within the scrotum, the approximation of the labia majora, the permanent separation of the eyelids, with well-developed lashes, and the presence of dark greenish meconium within the in- testinal canal. The umbilicus has reached a position almost exactly in the middle of the body. The average length of the foetus at birth is about fifty centimetres, or twenty inches ; its average weight, while included between widely varying extremes, may be assumed as approximately 3100 grammes, or 6.8 pounds. The weight of the foetus at term is materially influenced by the age of the mother, women of about thirty-five years giving birth to the heaviest children. The weight and stature of the mother probably also affect the weight of the child. Repeated pregnancies exert a pronounced effect upon the foetus, since the weight of the child reaches the maximum with the fifth gestation. The purpose of the preceding pages is to present an outline of the general developmental processes leading to the differentiation and establishment of the defi- nite body-form of the human embryo ; .a more detailed account of the development of the various parts of the body is given in connection with the descriptions of the systems and the individual organs, to which the reader is referred. THE ELEMENTARY TISSUES. THE various parts and organs of the complex body may be resolved, in their morphological constitution, into a few component or elementary tissues, of which there are four principal groups, the epithelial, the connective, the muscular, and the nervous tissues. The first two of these may be discussed at this place ; the re- maining groups, the muscular and the nervous tissues, are considered most advan- tageously in connection with the muscular and nervous systems to which they are directly related and under which sections they will be found. THE EPITHELIAL TISSUES. The epithelial tissues include, primarily, the integumentary sheet of protecting cells covering the exterior of the body and the epithelium lining the digestive tube. Secondarily, they embrace the epithelial derivatives of the epidermis, such as the nails, hairs, and glands of the skin and its extensions, and the epithelial lining of the ducts and compartments of the glands formed as outgrowths from the primi- tive gut-tube, as well as the epithelium clothing the respiratory tract which originates as an evagination from the digestive canal. An apparent exception to the usual origin of the epithelial tissues from either the ectoblast or the entoblast is presented by the lining of the genito-urinary tract, since all the epithelium occurring in connection with these organs, as far as the bladder, is of mesoblastic origin, and hence genetically related closely with the extensive mesoblastic group of tissues. It is to be noted in this connection that the epithelium of the bladder and of a part of the urethra is derived from outgrowths of the primary gut, and therefore is entoblastic in origin. The primary purpose of epithelium being protection of the more delicate vascular and nervous structures lying within the subjacent connective tissue of the integument or of the mucous membrane, the protecting cells are arranged as a con- tinuous sheet, the individual elements being united by a small amount of inter- cellular substance. Epithelium contains no blood-vessels, the necessary nutrition of the tissue being maintained by the absorption of the nutritive juices which pass to the cells by way of the minute clefts within the intercellular substance. Likewise, the supply of nerve-fibres within epithelium ordinarily is scanty, although in certain localities possessing a high degree of sensibility, as the cornea or tactile surfaces, the termi- nations of the nerves may lie between the epithelial elements. The epithelial tissues are frequently separated from the subjacent connective tissue by a delicate basement membrane, or membrana propria ; the latter, which may be regarded as a derivative or modification of the connective tissue, usually appears as a delicate subepithelial boundary, being particularly well marked beneath the epithelium of glands. According to the predominating form of the component cells, the epithelial tissues are best divided into two chief groups, squamous and columnar, with sub- divisions as shown in the following table : VARIETIES OF EPITHELIUM. I.- SQUAMOUS : a. Simple, consisting; of a single layer. b. Stratified, consisting of several layers. II. COLUMNAR : a. Simple, consisting of a single layer. b. Stratified, consisting of several layers. III. MODIFIED : a. Ciliated, b. Goblet., c. Pigmented. IV. SPECIALIZED : a. Glandular epithelium, b. Neuro-epithelium. 67 68 HUMAN ANATOMY. Squamous epithelium, when occurring as a single layer, is composed of flattened polyhedral nucleated plates which, when viewed from the surface, present a regular mosaic, sometimes described by the terms ' ' pavement' ' or " tessellated. ' ' Such arrangement of the squamous type is unusual in the human body, the lining of the alveoli of the lungs, the posterior surface of the anterior capsule of the crystalline lens, the membranous labyrinth, and a few other localities being the chief places where a single layer of squamous cells occurs. The far more usual arrangement of such cells is several superimposed layers, this constituting the important group of stratified squamous epithelia. When FIG. 81. FIG. 80. , v *v * -V, Simple squamous epithelium from anterior capsule of crystalline lens. X400. Section of stratified squamous epithelium from anterior surface of cornea. X 500. seen in 'section, the deepest cells are not scaly, but irregularly columnar, resting upon the basement membrane by slightly expanded bases. The surface of the un- derlying connective tissue supporting this variety of epithelium is beset with minute elevations or papillae, which serve as advantageous positions for the terminations of the blood-vessels, as well as specialized nerve-endings. Owing to the more favored nutrition of the deepest stratum, the cells next the connective tissue exhibit the greatest vitality, and often are the exclusive source of the new elements necessary FIG. 82. FIG. 83. , Isolated surface cells from epithe- lium lining the mouth. X 350. Epithelial cells from epider- mis, showing intercellular bridges. X6 75 . to replace the old and effete cells which are continually being removed at the free surface ; this Joss is due not only to mechanical abrasion, but also to the displace- ment of the superficial elements by the new cells formed within the deeper layers. Passing from the basement membrane towards the free surface, the form of the cells undergoes a radical change. The columnar type- belongs to the deepest layer alone ; the superimposed cells assume irregularly polyhedral forms and then gradu- ally expand in the direction parallel to'the free surface to become, finally, converted into the large, thin scales so characteristic of the superficial layers of stratified epithelium. The position of the nucleus also varies with the situation of the cells, EPITHELIUM. 69 since within those next the basement membrane the relatively large nucleus the nutritive organ of the cell occupies the end nearest the subjacent connective tissue ; in the middle and superficial strata, the nucleus, comparatively small in size, is placed about the centre of the cell. The irregularly polyhedral cells of the deep or middle strata frequently are connected by delicate processes which bridge the intervening intercellular clefts ; when such elements are isolated, the delicate connecting threads are broken and the disassociated elements appear beset with minute spines, then constituting the prickle- cells. In certain localities, as in the urinary bladder, the columnar cells of the deepest layer rapidly assume the scaly character of the superficial strata ; such epithelium FIG. 85. Ml FIG. 86. Transitional epithelium from bladder of child. X 300. Simple columnar epi- thelium from intestinal mucosa. X 750. Stratified columnar epithelium from vas deferens. X 500. possesses relatively few layers, and from the readiness with which the type of the cells changes, is often described as transitional epithelium ; the latter cannot be regarded as a distinct variety, but only as a modification of the stratified scaly group. Columnar epithelium, when occurring as a single layer of cells, constitutes the simple columnar variety, which enjoys a much wider distribution than the cor- responding squamous group, the lining of the stomach and of the intestinal tube being important examples. When the single layer of such epithelial tissues is re- placed by several, as in the stratified columnar variety, the superficial cells alone FIG. 87. Stratified ciliated columnar epithelium from trachea of child. X 550. Ciliated epithelial cells. A, from intes- tine of a mollusk (cyclas) ; JS, from nasal cavity of frog. X 750. (Engclniaini.) are typically columnar. The free ends of the columnar elements not infrequently present specializations in the form of a cuticular border or of cilia, while their ends which rest upon the basement membrane are pointed, forked, or club-shaped. The intervals thus formed by irregularities of contour are occupied by the cells of the deeper stratum next the basement membrane. Each cell is provided with a nucleus, which is situated about midway between the ends of the superficial elements and nearer the base within the deeper ones. The surface cells often contain collections of mucous secretion which distend their bodies into conspicuous chalice forms known as goblet-cells, which occur in great profusion in the lining of the large intestine and the respiratory mucous membrane. yo HUMAN ANATOMY. FIG. Goblet-cells from epithelium lining large intestine. X 500. Modified Epithelium. The free surface of the epithelium in many localities, as in the trachea, the inferior and middle nasal meatuses, and the uterus, is pro- vided with minute, hair-like vibratile processes, or cilia, which are produced by the specialization of the cytoplasm of the free end of the cell. The exact relations of the cilia to the cytoplasm are still matters of uncertainty, although the investigations of Engelmann and others on the ciliated epithelium of invertebrates render it prob- able that the hair-like processes attached to the cells of higher animals are also connected with intracellular fibrillse, which appear as delicate striations within the superficial and more highly specialized parts of the cells. In man and the higher mammals ciliated epithelium is limited to the columnar variety. The exact number of individual cilia attached to the free surface of each cell varies, but there are usually between one and two dozen such appendages. Their length, likewise, differs with locality, those lining the epididymis being about ten times longer than those attached to the tracheal mucous membrane. When favorable conditions obtain, including a suffi- cient supply of moisture, oxygen, and heat, ciliary motion may continue for many hours and even days. On surfaces clothed with columnar epithelium certain cells are distinguished by unusually clear cytoplasm and exceptional form and size ; these are the goblet-cells, the peculiar elliptical or chalice form of which results from the accumulation of the mucoid secretion elaborated within their protoplasm. When the distention becomes too great the cell ruptures in the direction of least resistance, and the secretion is poured out upon the surface of the mucous membrane as the lubricating mucus. The goblet-cells, therefore, may be regarded as unicellular glands, and represent the simplest phase in the specialization of glandular tissues. The protoplasm of epithelial cells often becomes invaded by particles of foreign substances ; thus, granules of fatty and proteid matters are very commonly encoun- tered, while the presence of granules of eleidin in certain cells of the epidermis char- acterizes the stratum granulosum. When the invading particles are colored, as when composed of melanin, the affected cells acquire a dark brown tint, and are then known as pigmented epithelium. Examples of such cells are seen in the retina and in the deeper cells of the epidermis in certain races. Specialized Epithelium. Reference has already been made to goblet-cells as representing unicellular glands ; these may be regarded, therefore, as instances of a temporary specialization of epithelium into glandular tissue. When the epithelial elements become permanently modified to engage in the elaboration of secretory substances, they are recognized as glandular epithelium. The cells lining the ducts and the ultimate compartments of glands are modified extensions of the epithelial investment of the adjacent mucous membrane. Their form and condition depend upon the degree of speciali- zation, varying from columnar to spherical and polyhedral, on the one hand, and upon the nature and number of the secre- tion particles on the other. The cells lining parts of certain glands, as those clothing the ducts of the salivary glands, or the irregular portion of the uriniferous tubules, exhibit a more or less pronounced striation ; cells presenting this peculiarity are termed rod-epithelium. The highest, and often exceedingly complex, specializations affecting epithelial tissues are encountered in connection with the neurones supplying the organs of special sense. The epithelium in these localities is differentiated into two groups of elements, the sustentacular and the perceptive; to the latter the name of ncuro- epithelium is applied. Conspicuous examples of such specialization are the rod- and cone-cells of the retina and the hair-cells of Corti's organ in the internal ear. A more detailed description of the glandular tissues is given with the digestive tract ; that of the neuro-epithelia with the organs of special sense. FIG. 90. PigmenU-cl epithelium from human retina. X 435- ENDOTHELIAL TISSUES. Mesothelial cells from omentum of dog. X 300. Intercellular cement-substance stained by argentic nitrate. ENDOTHELIUM. The modified mesoblastic, later connective-tissue, cells that line serous surfaces, including ihose of the pericardial, the pleural, and the peritoneal divisions of the body- cavity, together with those of the blood- and lymph-vessels and the lymphatic spaces throughout the body, constitute endothelium. These spaces, in principle, are intramesoblastic clefts and the elements forming their lining are derivatives of the great connective-tissue layer. The endothelia, therefore, belong to the connective tissues and are properly regarded as modified elements of that class ; as FIG. 91. a matter of convenience, however, they may be considered at this place in connection with the epithelial tis- sues. The most striking difference in situation between the endothelia and the epithelia is found in the fact that the former cover surfaces not com- municating with the atmosphere, while the epithelial tissues clothe mucous membranes all of which are directly or indirectly continuous with the integumentary surface. A further contrast between these tis- sues is presented in their genetic re- lations with the primary blastodermic layers, since the epithelia, with the exception of those lining certain parts of the genito-urinary tracts which are derived from the mesoblast, are the trans- formations and outgrowths from the ectoblast and the entoblast, while the endo- thelia are direct modifications of the mesoblastic cells. The young mesoblastic cells bordering the early body-cavity become differenti- ated into a delicate lining, the mesothelium, and later give rise to the characteristic plate-like elements which constitute the lining of the permanent serous sacs. The name mesothelium is sometimes retained to designate the permanent investment of the great serous cavities, as distinguished from the endothelium which clothes the vascular and other serous spaces. Seen in typical preparations, as ob- tained from the peritoneum after treatment with argentic nitrate and subsequent stain- ing with haematoxylin, the endothelial cells on surface view appear as irregularly polyg- onal areas mapped out by deeply tinted lines. The latter represent the silver- stained albuminous intercellular cement- substance which unites the flattened cells in a manner similar to that observed in simple squamous epithelium ; this superficial likeness is so marked that it has led to much confusion as to the proper classification of endothelium under the connective tissues. The lines of apposition are sinuous and less regular than between epithelial elements, in many cases appearing distinctly dentated. The exact form of the cells and the character of their contours, however, are not constant, since they probably depend largely upon the degree of tension to which the tissue has been subjected. Not infrequently the intercellular substance, at points where several endothelial cells are in apposition, shows irregular, deeply colored areas after silver staining ; FIG. 92. Endothelial cells lining artery of dog, after silver staining. X 500. 72 HUMAN ANATOMY. these figures are described as stigmata or pscudostomata, and by some are interpreted as indications of the existence of openings leading from the serous cavity into the subjacent lymphatics. Critical examination of these areas, however, leads to the conclusion that they are largely accidental, and due to dense local accumulations of the stained intercellular materials ; they are not, therefore, to be regarded as intercellu- lar passages. True orifices or stomata, however, undoubtedly exist in certain serous membranes, as in the septum between the peritoneal cavity and the abdominal lymph-sac of the frog, and, possibly, the peritoneal surface of the diaphragm of mammals. The positions of these stomata are marked by a conspicuous modification in the form and arrangement of the surrounding endothelial plates, which exhibit a radial disposition about the centres occupied by the stomata. The immediate walls of the orifices are formed by smaller and more granular elements, the guard or ger- minating cells, the contraction and expansion of which probably modify the size of the openings. Although the ectoblast and the entoblast are the germ layers which furnish great tracts of epithelium in the adult body, yet the mesoblast, the middle germ layer, also supplies distinct epithelial tissues. As it has been already pointed out, the epidermis, the epithelial portion of the skin, with its derivatives, is a product of the ectoblast. The epithelial lining of the mouth cavity as far back as the region of the palatine arches, and the epithelium of the anus are also of ectoblastic origin, since they are formed as in-pocketings of the outer germ layer during early embryonic life. With the exception of these areas, the epithelium lining the entire digestive tube, and that of its accessory glands, notably the liver and the pancreas, is of entoblastic origin. The same thing is true of the epithelium of the respiratory tract, since this entire tract is an outgrowth from the primitive intestine. But in the case of the uro-genital system, the epithelium there found, or most of it, is derived directly from the mesoblast. To be more specific, the Fallopian tubes (uterine tubes), uterus and vagina of the female, which have, of course, a distinct layer of epithelium on their inner surface, are formed from certain embryonic tubes known as the Miillerian ducts, which are derived from the mesoblast. The vas (ductus) deferens of the male is first represented in the embryo by a tube known as the Wolffian duct, which, with its epithelium, is also derived from the mesoblast. The sex-cells found in the sex -glands, which in the case of the male retain a distinct epithelial character, are apparently of mesoblastic origin. The ureter and part of the kidney are out- growths from the Wolffian duct and therefore mesoblastic, while the rest of the kidney not formed in this way is also of mesoblastic origin. Hence, it is evident that distinct layers of epithelium are formed from all three germ layers, and that in this respect no peculiarity is attributable to any one of them. THE CONNECTIVE TISSUES. THE important group of connective substances the most widely distributed of all tissues, is the direct product of the great mesoblastic tract ; the several members of this extended family are formed by the differentiation and specialization of the intercellular substance wrought through the more or less direct agency of the meso- blastic cells. The variation in the physical characteristics of the connective tissues is due to the condition of their intercellular constituents. During the period of em- bryonal growth these latter are represented by gelatinous, plastic substances ; a little later by the still soft, although more definitely formed, growing connective tissue, which, in turn, soon gives place to the yielding, although strong, adult areolar tissue. Grouped as masses in which white fibrous tissue predominates, the intercellular substance presents the marked toughness and inextensibility of tendon ; where, on the contrary, large quantities of yellow elastic tissue are present, extensibility is conspicuous. Further conden- sation of the intercellular sub- FIG. 93. stance produces the resistance encountered in hyaline carti- lage, intermediate degrees of- condensation being presented by the fibrous and elastic varie- ties. In those cases in which the ground-substance becomes additionally impregnated with calcareous salts, the well-known hardness of bone or dentine is attained. Notwithstanding these variations in the density of the intercellular substance, the cel- lular elements have undergone but little change, the connective- tissue corpuscle, the tendon-cell, the cartilage- cell, and the bone- corpuscle being morphologically identical. The principal forms in which the connective substances occur may be grouped as follows : 1. Immature connective tissue, as the jelly of Wharton in the umbilical cord and the tissues of embryos and of young animals. 2. Areolar tissue, forming the subcutaneous layer and filling intermuscular spaces, and holding in place the various organs. 3. Dense fibro-elastic tissue, found in the fasciae, the sclera, the ligaments, etc. Where white fibrous tissue predominates and yellow elastic tissue is practically wanting, structures of the character of tendon or of the cornea are produced ; where, on the other hand, elastic tissue is in excess of fibrous tissue, highly extensible structures, as the ligamentum nuchae or the ligamenta subflava, result. 4. Cartilage, fibrous, elastic, and hyaline varieties. 5. Bone and dentine, in which impregnation of lime salts contributes character- istic hardness. 6. Reticulated connective tissue, occurring as the supporting framework in the lymphatic tissues, and as the interstitial reticulum of many organs. 7. Adipose tissue. The Cells of Connective Tissue. The cellular elements of the connective 73 Embryonal connective-tissue cells from the umbilical cord. X 500. 74 HUMAN ANATOMY. tissues are usually described as of two kinds, the fixed or connective-tissue cells proper, and the migratory or wandering cells. The latter, while frequently included among the elements of these tissues, are usually only migratory leucocytes which temporarily occupy the lymphatic clefts within the connective substance. FIG. 94. FIG. 95. Young connective-tissue cells from subcutaneous tissue of cat em- bryo. X 680. Granule-cells (mast-cells) from suhmucous tissue of mouth. X 1000. v, v, sections of blood-vessels. The typical connective-tissue cell, in its younger condition, possesses a flattened, plate-like body from which branched processes extend. With the completed growth of the tissue, the expanded, FIG. 96. often irregularly stellate, element contracts to the inconspicuous spindle cell commonly observed in adult areolar tissue. Granule-cells are addi- tional elements occasionally encountered in connective tissues. They are irregularly spherical in form and are dis- tinguished by conspicuous granules within their proto- plasm possessing a strong affinity for dahlia and other basic aniline stains. They include the plasma-cells of Waldeyer and the mast-cells of Ehrlich. Pigment-Cells. The fixed cells sometimes contain accumulations of dark parti- cles within their cytoplasm, the elements then appearing as large, irregularly branched pigment-cells; these are con- spicuous in man within the choroid, the iris, and certain parts of the pia mater. The nucleus usually remains uninvaded, and hence appears as a lighter area within the dark brown, or almost black, cell-body. The Intercellular Constituents of the connective substances occur in three forms, -fibrous tissue, reticular tissue, and clastic tissue. Fibrous tissue consists morphologically of varying bundles of silky fibrils of Migratory leucocytes (Wandering cells) Fibrous tissue Section of subcutaneous tissue, showing the usual constituents of areolar tissue. X 300. FIBROUS TISSUE. 75 such fineness that they possess no appreciable width. The fibrils are united by and embedded within a semifluid ground- sub stance, which may be present in such meagre amount that it suffices only to hold together the fibrillae, or, on the other hand, it may constitute a large part of the entire intercellular tissue, as in the matrix of hya- FIG. 97- FIG. 98. ." :^^l Surface view of portion of omentum. X 130. Fi- brous and elastic tissue are arranged as a fenestrated membrane; the nuclei belong to the connective-tissue and the endothelial cells. Pigrnented connective-tissue cells from choroid. X 400. line cartilage. Depending upon the dis- position of the bundles, fibrous tissue occurs in two principal varieties, areolar and dense connective tissue. The fibrous tissue of the areolar group is arranged in delicate wavy bun- dles which are loosely and irregularly in- terwoven, as seen in the subcutaneous layer, the intervening clefts being largely occupied by the ground-substance. In the denser connective tissues the fibrous tissue is disposed with greater regularity, either as closely packed, parallel bundles, as in tendon and aponeuroses, or as intimately felted, less regularly arranged, bands forming extended sheets, as in fasciae, the cornea, and the dura mater. The ground- substance uniting the fibrillae of dense connective tissues often contains a system of definite interfascicular lymph-spaces, f* IG - 99- which, in suitably stained prepara- tions, appear as irregularly stellate ^fC^J'"--'--^ clefts that form, by union of their JH , - ramifications, a continuous net-work of channels for the conveyance of the tissue-juices throughout the dense connective substances ; in non-vascu- lar structures, as the cornea and the denser parts of bone, these systems of intercommunicating lymph-spaces serve to convey the nutritive sub- stances to the connective-tissue cells which lie within these clefts. Fibrous tissue yields gelatin on boiling in water, and is not digested by pan- creatin ; on the addition of acetic acid this tissue becomes swollen and trans- parent, the individual fibrillae being no longer visible. Reticular Tissue. The in- vestigations of Mall have emphasized the presence of a modified form of fibrous tissue in many localities, especially in organs rich in lymphoid cells. This variety of intercellular substance, known as reticular tissue or reticulum, consists of very fine fibrillae, either isolated or associated Cell-spaces of dense connective tissue from cornea of calf ; the surrounding ground-substance has been stained with argen- tic nitrate. X 525. 7 6 HUMAN ANATOMY. FIG. 100. FIG. 101. as small bundles, which unite in all planes to form delicate net-works of great intri- cacy. In lymphatic tissues, where the reticulum reaches a typical development, the mesh-work contains the characteristic lymphoid elements and, in addition, supports the superimposed stellate connective-tissue cells which formerly were erroneously regarded as integral parts of the fibrillar net-work. Reticular tissue, associated with fibrous and elastic tissue, is also present in many other organs, as the liver, kidney, and lung. This modifica- tion of fibrous tissue differs from the more robustly developed form in the absence of the ground-substance and not yield- ing gelatin upon boiling in water (Mall); like fibrous tissue, the reticulum resists pancreatic digestion. The development of fibrous tissue has been a subject of much discussion re- garding which authorities are still far from accord. Two distinct views are held at the present time ; according to the one, Connective-tissue cells from cornea of calf which t h e fib res appear within the Originally occupy cell-spaces similar to those shown in preceding rr t> j figure, x 525. homogeneous intercellular matrix of the early embryonal connective tissue without the direct participation of the cells, the fibres being formed as the result of a process somewhat resembling coagulation. This conception of the formation of the fibres of connective tissue, known as the indirect mode, is held to account for the earliest production of the fibrils in embry- onic tissue. The other view, held by Hem- ming, Reinke, and others, attributes an active participation of the young connective tissue cell, the peripheral zone of its protoplasm, known as ex- oplasm, being directly transformed into fibrillae. In consideration of the careful observations of Flem- ming, it is now generally believed that the method of formation of the fibres of connective tissue directly from the exoplasm of young con- nective tissue cells is the usual one. It is highly probable that the connective tissue cells are concerned in the production of the fibrous tissue, since these elements become much smaller as the formation of the fibrous tissue advances. Elastic tissue usually occurs as a net-work of highly refracting, homogeneous fibres lying among the bundles of fibrous tissue. The indi- vidual fibres are much thicker than the fibrillae of fibrous tissue and, although differing in width, maintain a constant diameter until augmented by fusion with others. When disassociated, as in teased preparations, the elastic fibres assume a highly characteristic form, being wavy, bowed, or coiled. The proportion of elastic tissue in connective substances is, ordinarily, small ; in certain localities, however, as the ligamenta subflava of man, or especially the ligamentum nuchre of the lower mammals, almost the entire structure consists of bundles of robust fibres of elastic Fibrous and reticular connective tissue from human liver after pancreatic digestion. X 23- ELASTIC TISSUE. 77 tissue held together by a small amount of intervening fibrous tissue. In transverse section of such ligaments (Fig. 104), the individual elastic fibres appear as minute polygonal areas separated by the fibrous fibrillae and the associated connective-tissue cells. Within the walls of the large blood-vessels the elastic tissue is arranged as membranous expansions containing numerous p, G I02 openings of vary ing size : these f ene sir ate d mem- branes, as they are called, are probably formed by the junction and fusion of broad ribbon-like V" / / j' elastic fibres. Elastic tissue yields elastin upon * -^^4^ y =jj/ ,H : iL / FIG. 103. FIG. 104. Reticular connective tissue from lymph- Portions of isolated elastic fibres from ligamen- node. X 35- The cells lie upon the fibrous tum nuc h a o f ox. X 375. tissue at the points of intersection. boiling in water, and disappears upon being subjected to pancreatic digestion, thus differing from fibrous and reticular tissue ; by taking advantage of the especial affinity that elastic tissue possesses for certain stains, as orcei'n, a much wider and more generous distribution of elastic tissue has been established than was formerly appre- ciated. The development of elastic tissue has shared the uncertainty surrounding the mode of production of fibrous tissue, since here, as there, two opposed views have been held, one of a cellular and one of an independent origin. Accord- ing to the view of an independent origin, the older one, the elastic fibres first appear as rows of minute beads in the intercellular matrix. These linearly dis- posed beads gradually fuse, thus produc- ing the primary elastic fibres. According to the view of an intracelhdar origin, the one now generally accepted, the elastic fibres are derived directly from the exoplasm of the young connective tissue cells, as in the case of the white fibrils. The density of connective substances depends upon the amount and arrange- ment of the fibrous tissue ; the extensibility is determined by the proportion of elastic tissue present. When the former occurs in well-defined bundles, felted together into interlacing lamellae, dense and resistant structures result, as fasciae, the cornea, etc. ; in such structures the cement- or ground-substance within the interfascic- ular clefts usually contains the lymph-spaces occupied by the connective-tissue cells. Tendon. Tendon consists of dense connective tissue composed almost en- tirely of white fibrous tissue arranged in parallel bundles. The individual fibrillae Elastic fibres - in section Interfibrillar connective tissue Nucleus of con- nective-tissue cell Transverse section of ligamentum nuchse of ox. X 45- HUMAN ANATOMY. of the fibrous tissue, held together by cement-substance, are associated as compara- tively large primary bundles, which in turn are united by interfascicular ground- G. iu6. Blood-vessel within septa enclosing tertiary bundles Tendon-bundle- Profile view Oblique view Surface view Longitudinal section of tendon from young subject; Tendon-bundles from tail of mouse, showing different the tendon-cells are seen in profile between the bundles views of the cells. X 300. of fibrous tissue. X 300. substance and grouped into secondary bundles. The latter, invested by a delicate areolar sheath and partially covered by endothelial cells, are held together by the septal extensions of the FIG. 107. general connective-tissue envelope which surrounds the entire tendon ; the larger septa support the interfascicular blood-ves- sels and the lymphatics. The flattened connec- tive-tissue elements, here known as the tendon-cells, occur in rows within the clefts between the primary bundles, upon and between which the thin, plate-like bodies and rings of the tendon-cells expand. Seen from the surface, these cells appear as nucleated quadrate bodies (Fig- 106) ; viewed in longitudi- nal profile, the tendon-cells present narrow rectangular areas,, while, when seen in transverse section, the same elements appear as stellate bodies, the extended limbs of which, often stretching in several planes, represent sections of the wing-plates. Examined in cross-section (Fig. 107), the cut ends of the primary tendon-bun- dles appear as light irregular polygonal areas, which, under high amplification, at Primary bundle Transverse section of a tendon, showing grouping of primary, secondary .-Hid tertiary bundles of tendon-tissue. X 85. ADIPOSE TISSUE. 79 times exhibit a delicate stippling due to the transversely sectioned fibrillae. The interfascicular clefts frequently are represented, in such preparations, by stellate figures in which the sections of the tendon-cells, lying upon the primary bundles, can be distinguished ; the remaining portion of the stellate cleft is occupied by the FIG. 108. - ! ' YX/X P*H :'Sa .fiS^ " ^/ : - , ^,-r Adipose tissue from omentum. X 160. The fat-cells are arranged as groups betwee connective tissue. :n the bundles of FIG. 109. coagulated and stained interfascicular cement-substance. The larger divisions of the tendon, composed of the groups of secondary bundles, are separated by the septa prolonged inward from the general sheath investing the entire tendon. Ten- don is composed almost exclu- sively of fibrous tissue, elastic fibres being practically absent. Adipose Tissue. The fatty material contained within the body is to a large extent en- closed within connective-tissue cells in various localities ; these modified elements are known as fat-cells, which, together with the areolar tissue connecting the cells and supporting the rich supply of blood-vessels, consti- tute the adipose tissue. The distribution of adipose tissue includes almost all parts of the body, although accumulations of fat are especially Conspicuous Young fat-cells from subcutaneous tissue. X 550. in certain localities. Among the latter are the subcutaneous areolar tissue, the marrow of bones, the mesentery and the omentum, the areolar tissue surrounding the kidney, the vicinity of the joints, and the subpericardial tissue of the heart. On the other hand, in a few situations, in- cluding the subcutaneous areolar tissue of the eyelids, the penis and the labia minora, the lungs, except near their roots, and the interior of the cranium, adipose Peripheral zone~ of protoplasm enclosing oil- drop Young fat-cell Connective-tissue' cells 8o HUMAN ANATOMY. tissue does not occur even when developed to excess in other parts. As ordinarily seen, adipose tissue is of a light straw color and often presents a granular texture due to the groups of fat-cells within the supporting areolar tissue. Examined microscopically in localities where the fat-cells are not crowded, but occur in a single stratum and hence retain their individual form, adipose tissue is seen to be made up of relatively large, clear, spherical sacs held together by deli- cate areolar tissue. Unless treated with some stain, as osmic acid, Sudan III. or quinoline-blue, possessing an especial affinity for fat, the oily contents of the cells appear transparent and uncolored, and apparently occupy the entire cell-body. Critical study of the fat-cell, however, demonstrates the presence of an extremely thin enveloping layer of protoplasm, a local thickening on one side of the sac mark- ing the position of the displaced and compressed nucleus (Fig. 109). Fat-cells occur usually in groups, supported and held together by highly vas- cular connective tissue. In localities possessing considerable masses of fat, as be- neath the scalp and the skin, the cells are grouped into lobules which appear as yellow granules to the unaided eye ; in such localities the typical spherical shape of the individual fat-cells is modified to a polyhedral form as the result of the mutual pressure of the closely packed vesicles. In connective-tissue elements about to become fat-cells, isolated minute oil- drops first appear within the protoplasm ; these increase in size, coalesce, and grad- ually encroach upon the cytoplasm until the latter is reduced to a thin, almost inappreciable, envelope, which invests the huge distending oil-drop. The nucleus, likewise, is displaced towards the periphery, where it appears in profile as an incon- spicuous crescent embedded within the protoplasmic zone. After the disappearance of the fatty matters, as during starvation, the majority of fat-cells are capable of resuming the usual appearance and properties of connective-tissue corpuscles ; cer- tain groups of cells, the fat-organs of Toldt, however, exhibit an especial tendency to form adipose tissue, and hence only under exceptional conditions part with their oily contents. CARTILAGE. Cartilage includes a class of connective tissue in which the intercellular substance undergoes increasing condensation until, as in the hyaline variety, the intercellular matrix appears homogeneous, the constituent fibres being so closely blended that the fibrous structure is ordinarily no longer appreciable. Depending upon the differences presented by the intercellular matrix, three varieties of cartilage are recognized, hyaline, elastic, andji&roits. Considered in relation to the denser connective tissues, the description of fibrous cartilage, which differs but little from white fibrous tissue, should next follow ; since, however, the term ' ' cartilage' ' is usually applied to the hyaline variety, the latter will first claim attention. Hyaline cartilage, or gristle (Fig. no), enjoys a wide distribution, forming the articular surfaces of the bones, the costal cartilages, the larger cartilages of the larynx and the cartilaginous plates of the trachea and bronchi, the cartilages of the nose and of the Eustachian tube. In the embryo the entire skeleton, with the ex- ception of part of the skull, is mapped out by primary hyaline cartilage. The apparently homogeneous matrix of hyaline cartilage, after appropriate treatment, is resolvable into bundles of fibrous tissue ; ordinarily, however, these are so closely united and blended by the cementing ground-substance that the presence of the component fibrils is not evident. The cartilage-cells, as the connective-tissue elements which lie embedded within the hyaline matrix are called, are irregularly oval or spherical, nucleated bodies. They occupy more or less completely the interfascicular clefts, or lacuna:, within which they are lodged. In adult tissue usually two or more cells share the same compartment, the group representing the descendants from the original occupant of the space. The matrix immediately surrounding the lacunse is specialized as a laver of different density, and is often described as a capsule ; a further differentiation of the ground-substance is presented by the more recently formed matrix, which CARTILAGE. 81 Perichondrium Young cartilage- cells Group cell; of older often stains with greater intensity, thereby producing the appearances known as the cell-areas. The lacunae of hyaline cartilage are homologous with the lymph- spaces of other dense forms of connective tissue ; although canals establishing com- munication between the adjacent lacunas are not demonstrable in the tissues of the higher vertebrates, it is not improbable that minute interfascicular passages exist which facilitate the access of nutritive fluids to the cells enclosed within the lacunae. The free surface of cartilage is covered by an envelope of dense connective tissue, the perichondrium ; the latter consists of an external fibrous layer of dense fibro-elastic tissue and an inner looser stratum or chondrogenetic layer, containing numerous connective-tissue cells. These are arranged in rows parallel to the sur- face of the cartilage and, during the growth of the tissue, gradually assume the characteristics of the cartilage-cells, being at first spindle-shaped and later ovoid and spherical. The young cartilage-cells thus formed become gradually separated by more extensive tracts of the newly deposited intercellular matrix ; as the groups of cells originating from the division of the original occupant of the lacuna recede from the perichondrial surface, they lose their primary parallel dis- FIG. no. position and become irregu- larly arranged and still further separated. Those portions of the ground-substance most re- mote from the perichondrium at times appear granular, this feature being intensified when, as in aged subjects, a deposition of calcareous matter takes place in these situations. In articular cartilage the su- perficial zone contains sparsely distributed groups of small cells arranged parallel to the free surface ; in the deeper strata these groups are replaced by elongated rows of larger ele- ments lying perpendicular to the articular surface. This columnar disposition of the car- tilage-cells is particularly evi- dent towards the underlying zone of calcified matrix. The blood-vessels of normal cartilage are usually limited to the periphery, within the perichondrium or the associated synovial membranes ; the nutrition of the cartilage is maintained by imbibition of the fluids through the matrix into lacunae, the existence of minute interfascicular canals being highly probable. In the thicker masses of the tissue, as in the cartilages of the ribs, nutrient canals exist in those portions most remote from the perichondrium ; these spaces contain a small amount of areolar tissue supporting the blood-vessels, which are, however, limited to the channels, the nutrition of the cartilage tissue being effected here, as at the periphery, by absorption through the matrix. Nerves have never been demonstrated within the cartilages, which fact explains the conspicuous insensibility of these tissues so well adapted to the friction, concus- sion, and compression incident to their function. Elastic cartilage, called also yellow elastic or reticular cartilage (Fig. in), has a limited distribution, occurring principally in the cartilages of the external ear, part of the Eustachian tube, the epiglottis, the cartilages of Wrisberg and of San- torini, and part of the arytenoid cartilages of the larynx. In its physical properties this variety differs markedly from hyaline cartilage, as it is dull yellowish in color 6 Cartilage-cells Lacuna contain- ing nest of cells -Empty lacuna surrounded by hvaline matrix Transverse section of peripheral portion of costal cartilage, X 250. 82 HUMAN ANATOMY. and pliable and tough in consistence, in contrast to the bluish opalescent tint and comparative brittleness of the hyaline variety. The characteristic feature of the structure of the elastic cartilage is the presence of elastic fibres within the intercellular matrix. The cell-nests are immediately sur- rounded by limited areas of hyaline intercellular substance corresponding to the matrix of hyaline cartilage. The matrix intervening between these homogeneous fields, however, is penetrated by delicate, often intricate, net-works of elastic fibres extending in all directions. The connective-tissue cells lie within the lacunae, in the hyaline areas, and closely resemble the elements of hyaline cartilage. Elastic carti- lage possesses a perichondrium of the usual description. Fibrous cartilage, or fibro-cartilage (Fig. 112), as the fibrous variety is usu- ally designated, is found in comparatively few localities, the marginal plates and the interarticular disks of certain joints, the symphyses, the intervertebral disks, sesamoid cartilages, and the lining of bony grooves for tendons being its chief representatives. FIG. IT i. \y" i ' 'l-G> ' "-A, & ;: .- : ... ~.; ; M . - WftA .-< "fc Cartilage-cells |r Hyaline areas ;^ " Mf ilw^i Elastic net-work ; >'>/.' -T^^ of intertx-llular tissue | Lacuna contain- V;V S '.':,^ : ing cell Section of elastic cartilage from the epiglottis. X 450. In its physical properties this tissue resembles both fibrous tissue and cartilage, pos- sessing the flexibility and toughness of the former combined with the firmness and elasticity of the latter. A proper perichondrium is wanting. In structure fibro-cartilage closely resembles dense fibrous tissue, since its prin- cipal constituent is the generally parallel wavy bundles of fibrous connective tissm- : among the latter lie small, irregularly disposed oval or circular areas of hyaline matrix which surround the cartilage-cells, singly or in groups. The number of cells and the proportion of fibrous matrix differ in various localities. The development of cartilage proceeds from the mesoblast, the cells of which undergo proliferation and, forming compact groups, become ^he embryonal cartilage- cells ; at first the latter lie in close apposition, since the matrix is wanting. During the later stages, when the masses of embryonal cartilage map out the subsequent skeletal segments, the cells are separated by a small amount of homogeneous matrix formed through the influence of these elements. DEVELOPMENT OF CARTILAGE. 83 Cartilage grows in two ways : () by the expansion produced by the inter- stitial growth effected by the formation of new cells and the associated matrix and (b) by the addition of the new tissue developed by pcrichon- p, G II2 drial growth at the periphery of the cartilage from the chondro- genetic layer. The latter mode \ ; .\" continues throughout the period of growth, and includes the di- rect Conversion of the COnneC- Hyaline area live-tissue cells of the perichon- cartHage-cefis drium intothecartilage elements, and the accompanying formation of new matrix. The development of the elastic fibres within the elastic cartilage is secondary, the matrix during the early stages of growth ; Fibrous inter- Being hyaline. The elastic tis- cellular sub- /- i r _ '*" X-, A stuncc sue first appears in the form of minute granules, which later \ fuse and become the elastic fibres; this change first appears , ^" ; -Cartilage-ceils in the vicinity of the cartilage- cells, the elastic reticulum sub- sequently invading the more re- -'-' mote portions Of the matrix. In Section of fibrous cartilage from intervertebral disk. X 225. the development of the fibro- cartilage, the fibres appear coincidently with the limited pericellular areas of hyaline substance. CHEMICAL COMPOSITION OF THE CONNECTIVE SUBSTANCES. Connective Tissue. The fibrils of white fibrous connective tissue consist of a substance known as collagen. The interfibrillar ground-substance contains mainly mucoid and the albuminous materials serum globuli and serum albumin. Gelatin is the hydrate of collagen, and is obtained by boiling fibrous tissue with water, when the gelatin separates like a jelly on cooling. In the case of the yellow elastic fibres, elastin is found in place of collagen. In reticular tissue rcticulin is found. The latter substance contains phosphorus. These substances, namely, collagen with its hydrate gelatin, elastin and perhaps reticulin, are among those known as albuminoids, which are closely related to the true albumins, yet differ in some important respects. The albuminoids, for the most part, contain less carbon and more oxygen than the albumins proper. Cartilage. The fibres which are found in the matrix of fibro-cartilage and elastic cartilage are respectively composed of collagen and of elastin, just as they are in the corresponding connective tissues. According to His, the chemical composition of human cartilage is as follows : Costal cartilage. Articular cartilage. Water 67.67 73.59 Solids . 32.33 26.41 Organic matter 30.13 24.87 Mineral salts 2.20 1.54 In the mineral salts there is about 45 per cent, of sodium sulphate. A somewhat smaller percentage of potassium sulphate, and smaller amounts of the phosphates of sodium, calcium and magnesium, as well as of sodium chloride, are present. Adipose Tissue. The fats in the animal body are mainly the triglycerides of stearic, palmitic and oleic acid. There is found in man a comparatively large amount of olein. Small quantities of lecithin, cholesterin and free fatty acids are also found in fat tissue. 8j HUMAN ANATOMY. BONE OR OSSEOUS TISSUE. In the higher vertebrates, osseous tissue forms the bony framework, or skeleton, which gives attachment and support to the soft parts, affords protection to the more or less completely surrounded delicate organs, supplies the passive levers for the exercise of muscular action, insures stability, and maintains the definite form of the animal. In addition to contributing the individual bones composing the principal, and in man the only, framework, or entoskeleton, osseous tissue occurs in the lower ver- tebrates associated with the integument as an exoskeleton. Representatives of the latter are seen in the bony plates present in the skin of certain ganoid fishes, the dermal plates of crocodiles, the dorsal and ventral shields of turtles, or the dermal armor of the armadillo. Osseous tissue also exists within various organs in certain animals and then constitutes the splanchnoskeleton. Examples of the latter are furnished by the bony plates encountered in the sclerotic coat of the eyes of birds, in the diaphragmatic muscle of the camel, in the tongue of certain birds, in the heart of ruminants, in the nose, as the snout-bones of the hog, in the respiratory organs, as the laryngeal, tracheal, and bronchial bones of birds, and in the genital organs, as the penile bone of carnivorous and certain other mammals. True osseous tissue does not occur outside the vertebrates. Many invertebrate animals possess a skeletal framework, usually external but in some cases internal. Such a framework, however, consists of calcareous incrustations, hardened excre- tions or concretions composed principally of calcium carbonate and of silicious structures. These earthy or mineral hard parts of invertebrates are structureless deposits, so differing materially from the bone tissue of the higher vertebrates as well in structure as in chemical composition. Sometimes a deposit of calcareous material occurs in adult cartilage, a process entirely distinct from the formation of bone tissue. Familiar examples of such calcification are seen in the costal and some of the laryngeal cartilages. Chemical Composition. Bone is a dense form of connective tissue, the matrix of which is impregnated with lime salts ; it consists, therefore, of two parts, an animal and an earthy portion, the former giving toughness and the latter hardness to the osseous tissue. The animal or organic part of bone may be removed by calcination, leaving the inorganic constituents undisturbed. If a bone be heated in a flame with free access of air, the animal matter at first becomes charred and the bone black ; continued combustion entirely removes the organic materials, the earthy portion alone remain- ing. After such treatment, while retaining its general form, the bone is fragile and easily crushed, and has suffered a loss of one-third of its weight, due to the destruc- tion and elimination of the animal constituents. The latter, evidently, constitute one-third and the mineral matters two-thirds of the bone. The inorganic constitu- ents include a large amount of calcium phosphate, much less calcium carbonate, with small proportions of calcium fluoride and chloride, and of the salts of magnesium and sodium. The animal portion of the bone, on the other hand, may be separated from the inorganic salts by the action of dilute hydrocnloric acid, which desolves out the earthly constituents ; after such treatment the bone, although retaining perfectly its form and details, is tough and flexible, a decalcified rib or fibula being readily tied into a knot. The animal constituents of bone yield gelatin upon prolonged boiling in water, therein resembling fibrous connective tissue. The composition of bone, according to Berzelius, is as follows : ORGANIC MATTER Gelatin and blood-vessels, 33-3 f Calcium phosphate, 51-04 I Calcium carbonate, 1 1 ;v > INORGANIC MATTER \ Calcium fluoride, 2.00 Magnesium phosphate, 1.16 Sodium oxide and sodium chloride, 1. 20 100.00 PHYSICAL PROPERTIES OF BONE. FIG. 113. Physical Properties. Rauber has shown that a five-millimetre cube of com- pact bone of an ox when calcined will resist pressure up to 298 pounds ; when decal- cified up to 136 pounds ; under normal conditions up to 852 pounds, the pressure being applied in the line of the lamellae. It results from its composition that while bone is very hard and resistant to press- ure, it is also somewhat flexible, elastic, and capable of withstanding a tearing strain. It is remarkable that in many substances the power to resist a crushing strain is very different from that of resisting a tearing one. Thus, cast iron is more than five times as resistant to the former strain as to the latter, and wrought iron is nearly twice as resistant to the latter as to the former. Neither of these materials, therefore, is well fitted to resist both strains, since a much greater quantity must be used than would be needed were either material to be exposed only to the strain it is best able to with- stand. Bone, however, has the property of resisting both strains with approximately equal facility, its tearing limit being to its crushing limit about as 3 is to 4. This has the advantage that strength need not be obtained by great increase of weight, con- sequently the plan of bone structure com- bines lightness and strength. Structure of Bone. On sawing through a bone from which the marrow and other soft parts have been removed by ma- ceration and boiling, the osseous tissue is seen (Fig. 113) to be arranged as a pe- ripheral zone of compact bone enclosing a variable amount of spongy or cancellated bone. In the typical long bones, as the humerus or femur, the compact tissue al- most exclusively forms the tubular shaft enclosing the large marrow-cavity, the can- cellated tissue occupying the expanded extremities, where, with the exception of a narrow superficial stratum of compact bone, it constitutes the entire framework ; the clefts between the lamellae of the spongy bone are direct extensions of the general medullary cavity and are filled with mar- row-tissue. In the flat bones (Fig. 116), as those of the skull, the compact substance consists of an outer and inner plate, or tables, enclosing between them the cancel- lated tissue, or diploe, as this spongy bone is often termed. Short and irregular bones are made up of an inner mass of spongy bone covered by an external shell of compact substance which often presents local thickenings in order to insure additional strength where most needed. The cancellated bone consists of delicate bars and lamellae which unite to form an intricate reticulum of osseous tissue well calculated to insure considerable strength without undue weight ; in many positions, conspicuously in the neck of the femur (Fig. 374), the more robust lamellae are disposed in a definite manner with a view of meeting the greatest strains of pressure and of tension. Although composed of the same structural elements, compact and spongy bone differ in their histological details in consequence of the secondary modifications which take place during the conversion of the spongy bone, the original form, into the compact substance. To obtain the classic picture of osseous tissue, in order to study its general arrangement in the most typical form, it is desirable to examine thin ground sections of the compact substance cut at right angles to the axis of a long bone which has been macerated and dried, and in which the spaces contain air. Section of upper end of humerus, showing the external layer of compact bone surrounding the med- ullary cavity below and the spongy bone above. 86 HUMAN ANATOMY. The compact bone in such preparations, when examined under low ampli- fication (Pig. 114), is seen to be composed of osseous layers arranged as three chief groups : (a) the circumferential lamellcc, which extend parallel to the external and internal surfaces of the compact bone ; (b) the Haversian lamellcc, which are disposed concentrically and form conspicuous annular groups, the Haversian systems. enclosing the Haversian canals ; and (c~) the interstitial or ground lamellcc, which constitute the intervening more or less irregularly arranged bony layers filling up the spaces between the Haversian systems and the peripheral strata. FIG. 114. -External circumferen- tial lamella; . i * 'A~ ->-i\)j'. -Haversian canal sur- rounded by Havci- sian lamella: r-s Interstitial latnclhe ^-v^^V^.- " - *$^l**K'- ^ r O ;* * *-***** x- - < ~ - - <- --. . Jv . S* m^^!!^^; - ~ -i- .^^vc~> ^ Wc^+ %2H : ^ -- ^^^v ^>*V.*r^^*SSs ^ J f -^- - S. "- ir x . - v - / '*"-'/ -*> ~^ > . ,^^=x .__ ^^- ^~7J2'_""t- -~~ *- '-1 .^ ^t : -^^v CTi^ *- -ifc- ' Tra Internal i ii< unilrioti- tial lar insvcrse section of compact bone (metatarsal) ; the section has been ground and dik-d, IK-IKO tin.- lacuna- are filled with air. X 85. Each Haversian system consists of the concentrically disposed lamellae and the centrally situated channel, or Haversian canal, enclosing the ramifications of the medullary blood-vessels and associated marrow-tissue. Between the annularly arranged lamellae are seen small spindle-shaped or oval spaces, the hicnn ., 700. the developing osseous tissue; sinre these cells are concerned in the production of the latter, they are appropriately termed osteoblasts. Later some of them become sur- rounded by the bony matrix, and are thus transformed into bone-cells. The osteo- genetic layer is rich in blood-vessels which, as the bone is formed, are continued into the primary marrow-cavities. The Marrow. The spaces in the interior of bones, whether the large medullary cavities surrounded by the compact substance forming the shaft of the long bones or the irregular interstices between the trabeculae composing the cancel- THE RED BONE-MARROW. 91 lated tissue, are filled with bone-marrow. The latter also extends within the larger Haversian canals. Although originally only of one variety within the bones of the early skeleton, the marrow in the adult consists of two kinds, the yellow and the red. Thus, within the shaft of the long bones it consists of a light yellowish tissue, presenting the char- acteristics of ordinary adipose tissue, while within the spaces of the cancellated tissue at the ends of the same bones the marrow appears of a dull red color. In addition to the ends of the long bones, the localities in which red marrow especially occurs are the bodies of the vertebrae, the ribs, the sternum, the diploe of the cranium, and the short bones. Red Marrow. The ingrowth of the periosteal tissue and blood-vessels con- stitutes the primary marrow within the embryonal skeleton ; from this tissue the red marrow filling the young bones is directly derived. The red marrow is, therefore, FIG. 122. u f . \ ''it \ I Y i ! / i v ' Vs.% < ' I.v'M ^''iulfS^ t\h A A& / . M " -, . ;: ' , vU; v '-' j .IV- ' / / ,i. Dense fibrous layer Last formed lamella of bone Periosteal blood- vessel passing into the bone Bone-cell within lacuna - tt ife'xfljs \v ous with periosteum 'TOffi-V'"i Remains of osteogenetic Y Invpr n Section of young periosteum and subjacent bone. X 275. the typical and first formed variety within the foetus and the young animal ; subse- quently, that situated within the shaft of the long bones becomes converted into yellow marrow by the replacement of the majority of the marrow elements by fat- cells. The red marrow (Fig. 123), when examined in section after fixation and staining, presents a delicate reticulum of connective tissue which supports the numerous medullary blood-vessels and the cellular elements. Next the bone the fibrous tissue forms a thin membrane, the endosteum, lining the medullary cavity and the larger Haversian canals into which the marrow extends. This membrane is highly vascu- lar, its vessels joining those within the osseous canals on the one side and those of the marrow on the other. The delicate fibrous reticulum, in addition to the thin-\valled blood-channels which it supports, contains within its meshes the several varieties of elements char- HUMAN ANATOMY. acteristic of the red marrow ; these are : (i) the marroiv-cells, (2) the eosinophiie cells, (3) the giant cells, and (4) the nucleated red blood-cells. The marrow-cells, or mychcytes, resemble the large lymphocytes of the blood, but may differ from the latter in their slightly larger size and in the possession of a relatively large round or oval nucleus which contains comparatively little chromatin; the presence of neutrophile granules within the cytoplasm of the marrow- cells affords an additional differential characteristic when compared with the large lymphocytes in which these granules are absent. The eosinophiie cells occur in considerable numbers within the red marrow, and appear in varying stages of growth, as evidenced by their round vwnonudear, the indented transitional and segmented polymorphonuclear condition ; the cells con- taining the latter form of nucleus are most abundant and represent, probably, the mature elements. The giant cells, or myeloplaxes, are huge elements of irregular oval form, and contain simple or polymorphous nuclei. They represent specialized myelocytes, FIG. 123. Marrow-cells Young red blood-cells-*-^ Giant cell Blood-Vessel 'mmr^^ Blood-vessel Connective-tissue reticulum Section of red marrow from epiphysis ot young femur. X 300. and during the processes resulting in the removal of osseous tissue they are the. osteoclasts which are actively engaged in effecting the absorption of the bony matrix. Ordinarily the giant cells occupy the central portions of the marrow : when, however, they enter upon the role of bone- destroyers, they lie on the sur- face of the osseous trabeculae within the depressions known as Howship" s lacionr (Fig. 128). The nucleated red blood-cells within the red marrow are concerned in the important function of renewing the colored cells of the blood, the red marrow being the chief seat in which this process takes place after birth ; hence the red marrow is classed as a blood-forming organ. The nucleated red blood-cells exist within the marrow in two forms, an older and a younger. The genetically older cells, the erythroblasts, are the descendants of the embryonal nucleated blood-cells on the one hand and the immediate parents of the younger blood-elements on the other. The erythroblasts possess relatively large nuclei, with chromatin reticulum and cytoplasm tinged with haemoglobin ; they are frequently observed during mitosis, since they give rise to the second generation of nucleated red blood-cells. The latter, the normo- THE YELLOW BONE-MARROW. 93 blasts, are directly converted into the mature, non-nucleated red blood-disks on the disappearance of their nucleus. In addition to a larger amount of haemoglobin in their cytoplasm, the normoblasts differ from the erythroblasts in the possession of a deeply staining nucleus, in which the chromatin no longer appears as a reticul.um. It is usual to find isolated groups of fat-cells distributed within the red marrow, although the amount of adipose tissue is very meagre in localities farthest removed from the medulla of the long bones. The varieties of leucocytes usually seen in the blood are also encountered within the red marrow in consequence of the intimate relations between the latter tissue and the blood-stream conveyed by the medullary capillaries. Yellow Marrow. Since the appearance of the yellow marrow is due to the preponderating accumulation of fat-cells which have replaced the typical elements of the marrow contained within the shaft of certain bones, the formation of this variety is secondary and must be regarded as a regression. Examined in section, yellow marrow resembles ordinary adipose tissue, since it consists chiefly of the large oval fat-cells supported by a delicate reticulum of connective tissue. In localities in which the latter exists in considerable quantity, numerous lymphoid cells represent the remaining elements of the originally typical marrow-tissue. After prolonged fasting the yellow marrow loses much of its oily material and becomes converted into a gelatinous substance containing compara- tively few fat-cells ; upon the re-establishment of normal nutrition this tissue may again assume the usual appearance of yellow marrow. Blood-Vessels. The generous blood-supply of bones is arranged as two sets of vessels, the periosteal and the medullary. The former constitutes an external net-work within the periosteum, from which, on the one hand, minute twigs enter the subjacent compact substance through channels ( Volkmanri s canals} communi- cating with the Haversian canals, within which they anastomose with the branches derived from the medullary system ; additional vessels, on the other hand, pass to the cancellated tissue occupying the ends of the long bones. The medullary artery is often, as in the case of the long bones, a vessel of con- siderable size, which, accompanied by companion veins, traverses the compact sub- stance through the obliquely directed medullary canal to gain the central part of the marrow. On reaching this position the medullary artery usually divides into ascend- ing and descending branches, from which radiating twigs pass towards the periphery. The latter terminate in relatively narrow arterial capillaries, which, in turn, expand somewhat abruptly into the larger venous capillaries. Such arrangement results in diminished rapidity of the blood-stream, the blood slowly passing through the net- work formed by the venous capillaries. The latter vessels, within the red marrow, possess thin walls and an imperfect endothelial lining in consequence of which the blood comes into close relation with the elements of the medullary tissue. During its sluggish course within the blood-spaces of the red marrow, the blood takes up the newly formed red cells, which thus gain entrance into the circulation to replace the effete corpuscles which are continually undergoing destruction within the spleen. It is probable that leucocytes also originate in the bone-marrow. After thus coming into intimate relations with the marrow-tissue, the blood is collected by capillaries which form small veins. In addition to the companion veins accompanying the nutrient artery along the medullary canal, in many instances the larger veins pursue a course independent of the arteries and emerge from the can- cellous tissue by means of the canals piercing the compact substance at the ends of the bones. Although destitute of valves within the medulla, the veins possess an unusual number of such folds immediately after escaping from the bone. Lymphatics. The definite lymphatic channels of the bones are principally associated with the blood-vessels of the periosteum and the marrow as perivascular channels, although it is probable that lymphatic spaces exist within the deeper layers of the periosteum, in close relation to the osseous tissue. The perivascular lym- phatics follow the blood-vessels into the Haversian canals, where, as well as on other surfaces upon which the canaliculi open, the system of intercommunicating juice- channels represented by the lacunae and the canaliculi is directly related with the lymphatic trunks. 94 HUMAN ANATOMY. Nerves. The periosteum contains a considerable number of nerves, the ma- jority of which, however, are destined for the supply of the underlying osseous tissue, since those distributed to the fibrous envelope of the bone are few. The periosteal nerves follow the larger blood-vessels, in the walls of which they chiefly terminate. Medullary nerves accompany the corresponding blood-vessels through the medullary canal, and within the marrow break up into fibrillae to be, probably, distributed to the walls of the vascular branches along which they lie. Regarding the ultimate endings and arrangement of the sensory fibres little is known ; in view of the low degree of sensibility possessed by healthy bones and their periosteum, the number of such nerves present in osseous structures must be very small. FIG. 124. .... DEVELOPMENT OF BONE. The bones composing the human skeleton, with few exceptions, are preceded by masses of embryonal cartilage, which indicate, in a general way, the forms and relations of the subsequent osseous segments, although many details of the model- ling seen in the mature bones appear only after completed development and the pro- longed exercise of the powerful modifying influences exerted by the action of the attached muscles. Since the primary formation of such bones takes place within the cartilage, the process is appropriately termed endochondral development. Certain other bones, notably those forming the vault of the skull and almost all those of the face, are not preceded by cartilage, but, on the contrary, are produced within sheets of connective tis- sue ; such bones are said, therefore, to arise by intra- membranous development. It will be seen, however, that the greater part of the bone formed by endochondral de- velopment undergoes absorption, the spongy substance within the ends of the long and the bodies of the irregu- lar bones representing the persistent contribution of this process of bone-production. Even in those cases in which the intracartilaginous mode is conspicuous, as in the de- velopment of the humerus, femur, and other long bones, the important parts consisting of compact substance are the product of the periosteal connective tissue, and hence ge- netically resemble the intramembranous group. Although both methods of bone-formation in many instances proceed coincidently and are closely related, as a matter of con- venience they may be described as independent processes. Endochondral Bone Development. The pri- mary cartilage, formed by the proliferation and condensa- tion of the elements of the young mesoblastic tissue, grad- ually assumes the characteristics of embryonal cartilage, which by the end of the second month of intra-uterine life maps out the principal segments of the fct-tal cartilaginous skeleton. These segments are invested by an immature form of perichondrium, or primary periosteum , from which proceed the elements actively engaged in the production of the osseous tissue. The primary periosteum consists of a compact outer fibrous and a looser inner osteogcnctic layer; the latter is rich in cells and delicate intercellular fibres. The initial changes appear within the cartilage at points known as centres of ossification, which in the long bones are situated about the middle of the future shaft. These early changes (Fig. 125) involve both cells and matrix, which exhibit con- spicuous increase in si/c and amount respectively. As a further consequence of this activity, the cartilage-cells become larger and more vesicular, and encroach upon the intervening matrix, in which deposition of lime salts now takes place, as evidenced by the gritty resistance offered to the knife when carried through such ossific centres. On acquiring their maximum growth the cartilage-cells soon exhibit indications of impaired vitality, as suggested by their shrinking protoplasm and degenerating Clarified human foetus of about three and one-half months, show- ing the partially ossified skeleton. Two-thirds natural size. DEVELOPMENT OF BONE. 95 Embryonal cartilage nuclei. The enlarged spaces enclosing these cells are sometimes designated as the primarv arcohe. Coincidently with these intracartilaginous changes, a thin peripheral layer of bone has been formed beneath the young periosteum ; from the latter bud-like processes of the osteogenetic layer grow inward from the periphery and invade the embryonal cartilage, by absorption of the cartilage-matrix gaining the centre of ossification and there effecting a destruction of the less resistant cells and inter- vening matrix. In consequence of the penetration of the periosteal processes and the accompanying absorption of the cartilage, a space, the primary marrow-cavity, now occupies the centre of ossification and contains the direct continuation of the osteogenetic laver. This tissue, t\\e primary marrow, which has thus gained access to the interior of the cartilage, contributes the cellular elements upon which a double role devolves, to produce osseous tissue and to remove the embryonal cartilage. The cartilage-matrix closing the enlarged cell-spaces next the pri- FIG. 125. mary marrow-cavity suffers absorp- tion, whereby the cartilage-cells are liberated and the opened spaces are converted into the secondary arcolcz, and directly communicate with the growing medullary cavity. After the establishment of this communi- cation, the cartilage- cells escape from their former homes and undergo dis- integration, taking no part in the direct production of the osseous tissue. Beyond the immediate limits of the primary marrow- cavity the car- tilage-cells, in turn, repeat the pre- paratory stages of increased size and impaired vitality already described, but in addition they often exhibit a conspicuous rearrangement, where- by they form columnar groups sepa- rated by intervening tracts of calci- fied matrix (Figs. 126, 129). This characteristic belt, or zone of calci- fication, surrounds the medullary cavity and marks the area in which the destruction of the cartilage ele- ments is progressing with greatest energy. In consequence of the columnar grouping of the enlarged cartilage-cells and the intervening septa of calcified matrix, an arrange- ment particularly well marked in the ends of the diaphysis of the long bones, a less and a more resistant portion of the cartilage are offered to the attacks of the marrow- tissue by the cell- and matrix-columns respectively ; as a result of this difference, the cells and the immediately surrounding partitions are first absorbed, while the intervening trabeculee of calcified cartilage-matrix remain for a time as irregular and indented processes, often deeply tinted in sections stained with hsematoxylin, which extend beyond the last cartilage-cells into the medullary cavity. These trabeculffi of calcified cartilage-matrix serve as supports for the marrow-cells assigned to pro- duce the true bone, since these elements, the ostcoblasts, become arranged along these trabeculce, upon which, through the influence of the cells, the osseous tissue is formed. Simultaneously with the destructive phase attending the absorption of the car- tilage, the constructive process is instituted by the osteoblasts by which the bone- tissue is formed. These specialized connective-tissue elements, resting upon the Cartilage-cells be- coming enlarged and regrouped Enlarged cartilage- cells at centre of ossification Periosteum Section of tarsal bone of foetal sheep, showing centre of ossifi- cation. X 50. 9 6 HUMAN ANATOMY. irregular trabeculae of the calcified cartilage, bring about, through the influence of their protoplasm, the deposition of a layer of bone-matrix upon the surface of the FIG. 126. Embryonal cartilage Cartilage-cells becoming en- larged and grouped Zone of calcification Osteogenetic layer of perios- teum Central spongy bone en- closing remains of carti- lage ;#; ' .H' . ' &''.?.'i 4 > : ' ?/ I : '.-'' '' '" * ! Longitudinal section of tnetatarsal bone of foetal sheep, showing stages of endochoodral boae-developtneat. X 40. trabeculse, which thus becomes enclosed within the new bone. After the latter has attained a thickness of at least the diameter of the osteoblasts, some of the cells in closest apposition are gradually surrounded by the osseous matrix (Fig. 127), until, ENDOCHONDRAL BONE. 97 FIG. 127. Bone-cell Section of a portion of osseous tra- becula and foetal marrow. X 375- finally, they lie isolated within the newly formed bone as its cells ; the bone-cells are therefore imprisoned osteoblasts, which, in turn, are specialized connective-tissue elements. The bone-cells occupy minute lenticular spaces, the primary lacuna, at this immature stage the canaliculi being still unformed. The early bone-matrix is at first soft, since the deposition of the calcareous materials takes place subsequently. The increase in the thickness of the new bone is attended by the gradual disap- pearance of the enclosed remains of the calcined cartilage, the last traces of which, however, can be seen for some considerable time as irregular patches within the osseous trabeculae (Fig. 131), somewhat removed from the zone of calcification. The cartilage and the bone of the trabeculae stand, therefore, in inverse relations, since the stratum of bone is thinnest where the cartilage is thickest, and, con- versely, the calcified matrix disappears within the robust bony trabeculae. A number of the latter, together with the enclosed remains of the calcified cartilage, soon undergo absorption, with a corresponding enlargement of -the intervening marrow-spaces. The remaining tra- beculae increase by the addition of new lamellae on the surface covered by the osteoblasts, and at some distance from the zone of calcification form a trabecular reticulum, the primary central spongy bone. In the case of the irregular bones, the central spongy bone is represented by the cancellated substance forming the internal frame- work ; in the long bones, on the contrary, the primary cancellated tissue undergoes further absorption within the middle of the shaft simul- taneously with its continued development at the ends of the diaphysis from the car- tilage. As the result of this absorption, a large space the central marrow- cavity is formed (Fig. 129), the growth of which keeps pace with the general expansion of the bone. The absorption of the young osseous tissue to which reference has been made is effected through the agency of large polymorphonucleated elements, the osteo- clasts. These are specialized marrow- FIG. 128. cells whose particular role is the break- _rj^. ing up and absorption of bone-matrix. They are relatively very larg-e, their '.*)- ,;, - irregularly oval bodies measuring from .050 to .100 millimetre in length and from .030 to .040 millimetre in breadth. The osteoclasts (Fig. 128), singly or in groups, lie in close relation to the surface of the bone which they are at- tacking within depressions, or How- ship'' s lacuna, produced in consequence of the erosion and absorption of the osseous matrix which they effect. When not engaged in the destruction of bone, these cells occupy the more central portions of the marrow-tissue, where, in the later stages, they are probably identical with the myeloplaxes or giant cells encountered in the red marrow. The only part of the central spongy bone which persists after the completed development and growth of the long bones is that constituting the cancellated tissue occupying their ends. It will be seen, therefore, in many cases, that the product of the endochondral bone-formation, the primary central osseous tissue, is to a large extent absorbed, and constitutes only a small part of the mature skeleton. The early marrow-cavity, as well as all its ramifications between the trabeculae, is filled with the young marrow-tissue ; the latter gives rise to the permanent red marrow 7 'Osteoclast Bone-cell within lacuna Howship's- lacuna Osteoblasts Portion of trabecula of spongy bone undergoing absorp- tion by osteoclast. X 500. 9 8 HUMAN ANATOMY. FIG. 129. Embryonal cartilage Zone of calci fication in the limited situations where the central spongy bone persists, as in the vertebrae, the ribs, the sternum, and the ends of the long bones. The important fact may be here emphasized that the process sometimes spoken of as the ' ' ossification of cartilage' ' is really a substitution of osseous tissue for car- tilage, and that even in the endochondral mode of formation cartilage is never directly converted into bone. .The ossification of the epiphyses (Fig. 130), which in the majority of cases does not begin until some time after birth, the cartilage capping the diaphysis mean- while retaining its embryonal character, repeats in the essential features the details already described in connection with endochondral bone-formation of the shaft. After the establishment of the primary marrow-cavity and the surrounding spongy bone, ossification extends in two directions, towards the periphery and towards the adjacent end of the diaphysis. As this process continues, the layer of cartilage in- terposed between the central spongy bone and the free surface on the one hand, and between the central bone of the epiphysis and the diaphysis on the other, is gradually reduced until in places it entirely disappears. Over the areas which correspond to the later joint-surfaces the cartilage persists and be- comes the articular cartilage covering the free ends of the bone. With the final ab- sorption of the plates separating the epiphyses from the shaft the osseous tissue of the seg- ments becomes continuous, "bony union" being thus accomplished. Intramembranous Bone-Develop- ment. The foregoing consideration of the formation of bone within cartilage renders it evident that the true osteogenetic elements are contributed by the periosteum when the latter membrane sends its processes into the ossific centre ; the distinction, therefore, be- tween endochondral and membranous bone is one of situation rather than of inherent difference, since in both the active agents in the production of the osseous tissue are the osteoblasts, and in essential features the pro- cesses are identical. Since in the produc- tion of membrane-bone the changes within pre-existing cartilage do not come into ac- count, the development is less complicated and concerns primarily only a formative pro- cess. Although the development of all osseous tissue outside of cartilage may be grouped under the general heading of intramembranous, two phases of this mode of bone- formation must be recognized ; the one, the intramembranous, in the more literal sense, applying to the development of such bones as those of the vault of the skull and of the face, in which the osseous tissue is formed within the mesoblastic shtvts, and the other, the subpcriosteal> contributing with few exceptions to the production of every skeletal segment, in which the bone is deposited beneath rather than within the connective-tissue matrix. In consideration of its almost universal participation, the periosteal mode of development will be regarded as the representative of the intramembranous formation. Subperiosteal Bone. The young periosteum, it will be recalled, consists of an outer and more compact fibrous and an inner looser osteogenetic layer. The latter, in addition to numerous blood-vessels, contains young connective-tissue ele- ments and delicate bundles of fibrous tissue. These cells, or osteoblasts, become more regularly and closely arranged along the fibrillae, about which is deposited the Zone of calci- fication Embryonal cartilage Longitudinal section of phalanx of fretus of five months. X 23. SUBPERIOSTEAL BONE. 99 new bone-tissue, the osteoblasts becoming- enclosed within the homogeneous matrix to constitute the bone-cells. The osseous trabecula thus begins to increase not only FIG. 130. Columns of carti- lage-cells Spongy bone of epiphysis Epiphyseal bone Remains of carti- lage separating bone of epiphysis and diaphysis aphyseal bone Marrow-tissue Longitudinal section including epiphysis and upper end of diaphysis of long bone of cat, just before osseous union of the head and shaft takes place. X 50. in length, by the addition of the last-formed matrix upon the supporting fibres, but also in width, by the deposition of new layers of osseous material by the osteoblasts. IOO HUMAN ANATOMY. These cells cover the exterior of the trabeculae as they lie surrounded by the young marrow-tissue which extends from the osteogenetic layer of the periosteum into the intertrabecular spaces. The union of the young trabeculae results in the production of a subperiosteal net-work of osseous tissue, the peripheral spongy bone. The latter forms a shell surrounding the central endochondral bone, or, where the latter has already disappeared, the central marrow-cavity of the shaft. The two processes, central and peripheral bone-formation, progress simultaneously, so that the produc- tions of both lie side by side, often in the same microscopical field (Fig. 131). -Fibrous layer of periosteum Osteojjenetic . V H .. ' '-L*- _ WSICU^UIKIU - '.'. V,\. % * layer of peri- v-vp ** .'.;"* -* ""**'. ^ " > osteum - /^ / ~ ~~Wa^ - *y t - ; -'.'jy^ ,fe'U't-i : " " - , . Ss?r ,, ', , * .1 . " - '"'" <- ; * i, ffjjfl *:-''; v> hone trabecula A V ^%' '/ J^| < ^ ^ . " 'V^A '" "'-.- ",'..- > '" ^ " ; :> ^^- i"-' : sS Vv.^' ri'- * v-X^^^. Portion of developing humerus of foetal sheep, showing periostea! and central spongy bone. X i The development of compact bone involves the partial absorption of the subperiosteal net-work of osseous trabeculae and the secondary deposition of new bone-tissue. The initial phase in the conversion of the peripheral spongy bone into compact substance is the partial absorption of the trabeculae by the osteoclasts of the primary marrow-tissue ; in consequence of this process the close reticulum of pcrios- teal bone is reduced to a delicate framework, in which the comparatively thin remains of the trabeculae separate the greatly enlarged primary marrow-cavities, which, now known as the Haversian spaces, are of round or oval form. After the destructive work of the osteoclasts has progressed to the required extent, the osteoblastic elements of the young marrow contained within the Havrr- INTRAMEMBRANOUS BONE. 101 sian spaces institute a secondary formative process, by which new bone is deposited on the walls of the Haversian spaces. This process is continued until, layer after layer, almost the entire Haversian space is rilled with the resulting concentrically disposed osseous lamellae ; the cavity remaining at the centre of the new bone per- sists as the Haversian canal, while the concentrically arranged layers are the lamellae of the Haversian system, the extent of the latter corresponding to the form and size of the Haversian space in which the secondary deposit of bone occurs. It is evident from the development of the compact substance that the interstitial or ground- lamellae of the adult tissue correspond to the remains of the trabeculae of the primary spongy bone ; these lamellae are, therefore, genetically older than those constituting the Haversian systems. The details of the formation of the Haversian lamellae, in- cluding the deposition of the matrix and the inclusion of the osteoblasts to form the bone-cells, are identical with those of the production of the trabeculae of the earlier bone. Intramembranous Bone. The development of certain bones, as those con- stituting the vault of the skull and the greater part of the skeleton of the face, differs in its earliest details from that of the subperiosteal bone, although the essen- tial features of the processes are identi- cal. The mode by which these mem- FIG. 132. brane-bones are formed may claim, therefore, a brief consideration. The early roof of the skull consists, except where developing muscle occurs, only of the integument, the dura mater, and an intervening connective-tissue layer in which the membranous bones are formed. The earliest evidences of ossification usually appear about the middle of the area corresponding to the later bone, delicate spicules of the new bone radiating from the ossific centre towards the periphery. As the tra- beculae increase in size and number they join to form a bony net-work (Fig. 132), close and robust at the centre and wide-meshed and delicate towards the margin where the reticulum fades into the connective tissue. With the con- tinued growth of the bony tissue the net-work becomes more and more compact until it forms an osseous plate, which gradually expands towards the limits of the area devoted to the future bone. For a time, however, until the completion of the earliest growth, the young bones are separated from their neighbors by an intervening tract of unossified connective tissue. Subsequent to the earlier stages of the formation of the tabular bones, the continued growth takes place beneath the periosteum in the manner already described for other bones. On examining microscopically the connective tissue in which the formation of membrane-bone has begun, this layer is seen to contain numerous osteogenetic fibres around and upon which are grouped many irregularly oval or stellate cells ; the latter correspond to the osteoblasts in other locations, since through the agency of these elements the osseous matrix is deposited upon the fibres. As the stratum of bony material increases some of the cells are enclosed to form the future bone-cor- puscles. Although the osteogenetic fibres correspond to delicate bundles of fibrous tissue, they are stiffer, straighter, and present less indication of fibrillar structure. Since the fibres forming the ends of the bony spicules generally spread out, they fre- quently unite and interlace with the fibres of adjacent spicules, thus early suggesting the production of the bony net-work which later appears. Growth of Bone. It is evident, since the new bone is deposited beneath the periosteum, that the growth of the subperiosteal bone results in an increased diame- Parietal bone of human foetus of three months, showing trabecular net-work of intramembranous bone. X 5. 102 HUMAN ANATOMY. ter of the shaft as well as in thickening of the osseous wall separating the medullary cavity from the surface. In order, therefore, to maintain the balance between the longitudinal growth of the medullary cavity, effected by the absorption of the endo- chondral bone, and its lateral expansion, the removal of the innermost portions of the subperiosteal bone soon becomes necessary. Absorption of the older internal trabeculae thus accompanies the deposition of new osseous tissue at the periphery ; by this combination of destructive and formative processes the thickness of the cylindrical wall of the compact substance of the diaphysis is kept within the proper limits and the increased diameter of the medullary cavity insured. Throughout the period of early growth the increase in length of the bone is due to the addition of new cartilage at the ends ; later, the cartilaginous increments, contributed by the chondrogenetic layer of the perichondrium, are supplemented by interstitial expansion following the multiplication of the existing cartilage-cells. On attaining the maximum growth and the completion of epiphyseal ossification, a por- tion of the cartilage may persist to form the articular surfaces. After the cessation of peripheral growth and the completion of the investing layer of compact substance, the osteogenetic layer of the periosteum becomes more condensed and less rich in cellular elements, retaining, however, an intimate connection with the last-formed subjacent bone by means of the vascular processes of its tissue, which are in con- tinuity with the marrow-tissue within the intraosseous canals. In addition to being the most important structure for the nutrition of the bone, on account of the blood- vessels which it supports, the periosteum responds to demands for the production of new osseous tissue, whether for renewed growth or repair, and again becomes active as a bone-forming tissue, its elements assuming the r61e of osteoblasts in imitation of their predecessors. THE SKELETON: INCLUDING THE BONES AND THE JOINTS. FIG. 133. THE skeleton forms the framework of the body. In the widest sense it includes, besides the bones, certain cartilages and the joints by which the different parts are held together. The skeleton of vertebrates is divided into the axial and the appendic- ular ; the former constitutes the support- ing framework of the trunk and head ; the latter, that of the extremities. The Axial Skeleton. The general plan of the axial skeleton of the trunk is as follows : a rod composed of many bony disks (the vertebral bodies) connected by fibro-cartilage separates two canals, a dorsal and a ventral. In most vertebrates the rod is in the main horizontal, with the dorsal canal above and the ventral below ; but in man the rod is practically vertical, with the dorsal canal behind and the ventral in front. The former is called the neural, because it encloses the central nervous system ; the latter, the visceral. The vertebral column has developed about the primary axis, the notochord. The neural canal is enclosed by a series of separate arches springing one from each vertebra. The skeletal parts of the anterior, or ventral, canal are less nu- merous ; they are the ribs, the costal carti- lages, and the breast bone. Above is the bony framework of the head, or the skull. This also is divided into a dorsal and a ven- tral portion by a bony element which is apparently a continuation of the bodies of the vertebrae, and, indeed, is actually de- veloped, in part, around the front of the notochord. The cephalic axis, however, is bent at an angle with the vertebral bodies, so that the neural arches, which here en- close the brain, are chiefly no longer be- hind but above. Below and in front of the brain-case is the face, which contains the beginning of the digestive tube, of which the jaws and teeth are special organs. In the head we do not find the separation of the parts enclosing the brain into a series of vertebrae, but they are clearly a continuation of the vertebral arches, the posterior, or occipital, division strongly suggesting a vertebra. The face is far more complicated, the vertebral plan being lost. In short, the axial skeleton consists of a 103 The tinted portions constitute the axial skeleton ; the untinted, the appendicular skeleton. 104 HUMAN ANATOMY. central, many-jointed rod bent forward near the top, with very perfect bony walls behind and above it, enclosing the central nervous system, and very imperfect bony and cartilaginous walls before and below it, enclosing the digestive apparatus and its associates, the circulatory, respiratory, urinary, and reproductive organs. The Appendicular Skeleton has an entirely distinct origin ; it is the frame- work of the limbs. It consists of two girdles, a thoracic and a pelvic, to each of which is attached a series of segments, the terminal one of which expands into five rays, -fingers and toes. According to some anatomists, the true vertebrate plan is of seven terminal rays, but, the question being still undecided, the more usual sys- tem is followed. Each of these rays consists of three or four bones. Proximal to this comes a series of short bones, wrist and ankle ; still nearer, a pair of bones, fore- arm and leg ; then a single bone, aim and thigh ; and lastly a bony arch, the girdle. In man, the thoracic girdle, made up of collar-bone and shoulder-blade, lies external to the chest, while the pelvic girdle fuses on each side into one bone, meets its fellow in front, and unites with the bodies of certain vertebrae. Thus, besides bearing a limb, the pelvic girdle forms a part of the wall of the abdominal and the pelvic cavities and would seem to belong to the axial skeleton, but embryology and comparative anatomy show that it does not. GENERAL CONSIDERATION OF THE BONES. The bones have the physiological function of bearing weight, of affording pro- tection, and especially, by the systems of levers composing the limbs, of effecting movements through the action of the muscles. They must, therefore, be capable of resisting pressure, accidental violence, and the strain caused by the pull of the muscles. The size of the bones must be such that besides serving the obvious needs of support and protection they may be sufficiently large to offer adequate surface for the origin and insertion of muscles, and the shape must be such as to allow this without undue weight. Shapes of Bones. Bones are divided, according to their form, into long, flat, and irregular ; such classification, however, is of little value, since many bones might be variously placed. Long bones form the best-defined group. They consist of a shaft and two extremities, each of which takes part in the formation of a joint, or, as in the case of the last phalanges, is terminal. Flat bones, where very thin, consist of a single plate ; where thicker, they con- sist of two plates separated by spongy substance called diploe. Irregular bones may be regarded as embracing all others. The group of the so-called short bones has no significance. Sesamoid Bones, with the exception of the patella, are not usually included in the description of the skeleton. With the above exception, they are small rounded bones developed, for the most part, in the capsules of joints, but sometimes in ten- dons. Usually one surface is cartilage-covered, and either enters into the formation of a joint or, separated by a bursa, plays on another bone, or on cartilage or liga- ment. Their function is to obviate friction, and, in some cases, to change the direc- tion of the pull of a muscle. The number of sesamoid bones is very variable ; but the usual idea that they are, so to speak, accidental, depending on the mechanics of a certain joint or tendon, must probably be abandoned. They are rather to be con- sidered as real parts of the skeleton, 1 all of which have their places in certain animals, but all of which either are not developed, or, if they do appear, are again lost in others. Thus, certain sesamoid bones of the fingers are very frequent in the foetus and very rare in the adult. Growth of Bones. The microscopical details of bone-growth are given else- where (page 94). Suffice it to say here that each bone has certain so-called centres of ossification from which the formation of the new bone spreads. In the long bones there is one main centre in the shaft, or diaphysis, which appears in the first half of foetal life. Other centres appear, usually some time after birth, in the ends of the 1 Thilenius : Morpholog. Arbeiten, Ikl. \i., 1896. MECHANICS OF BONE. 105 bones. There may be one or several in each end. The part formed around each of these secondary centres is called an epiphysis. Growth takes place chiefly in the cartilage between the epiphyses and the shaft. When, therefore, a joint is resected in childhood the surgeon tries to leave a part of the epiphysis in place. A curious relation exists between the course of the chief medullary artery of the shaft of a long bone and the behavior of the epiphyses. The epiphysis towards which the vessel is di- rected is the last to appear and the first to unite. (The fibula furnishes an exception. ) As a rule, also, the largest epiphyses appear first and unite last. In long bones with an epiphysis at one end only, the nutrient canal leads towards the opposite extremity. Mechanics of Bone. A long bone has a hollow shaft containing marrow, the wall being. of compact bone. The hollowness of the shaft takes from the weight, and, moreover, conforms to the well-known law that a given quantity of matter is much stronger, both lengthwise and crosswise, when disposed as a hollow cylinder than as a solid one of equal length. The proportion of the central or medullary cavity is not the same in all bones. Perhaps, as an average, its diameter may be said to equal one-third of that of the bone. In the shaft this cavity is crossed by a few bony trabeculae, almost all of which are destroyed in maceration. Towards the ends, as the outer wall becomes thinner, large numbers of thin plates spring from its inner surface and incline towards one another in graceful curves, until at last the expanded end of the bone consists of spongy or cancellated tissue enclosed within a delicate wall of compact substance. The arrangement of these plates is distinctly pur- poseful, since it has been shown that they are so disposed as to correspond with the stress-lines an engineer would construct for the special purpose served by the end of the bone. None the less, it would be unwarranted to maintain that mathematical correctness is always to be found, or that there are not other modifying influences. The internal structure of all bones, excepting, perhaps, those of the skull, is of this nature, so that the following remarks apply to spongy bone in general. The delicate cancellated structure is for the most part in thin plates. The sim- plest arrangement occurs in a short bone exposed to pressure only at two opposite surfaces ; in such cases the plates run between these surfaces with few and insignifi- cant cross-pieces. Where severe pressure may come in almost any direction, as in the case of the globular heads of the humerus and femur, the round-meshed pattern predominates, producing a very dense spongy structure which may be represented diagrammatically by drawing lines crossing at right angles and by enlarging every point of intersection. In the midst of this round-meshed type there is very fre- quently a central core with stronger plates and larger spaces. The vaulted system is found at the projecting ends of bones, and between the round-meshed cancellated substance and the shaft. Several special arrangements will be described in connec- tion with the bones in which they occur. An epiphysis, until it has fused, shows the mechanical structure of a separate bone. A process for the attachment of muscles or ligaments generally contains a very light internal structure, the surface of the shaft of the bone being rarely continued under it. The continuation of the fibres of attached tendons is not represented by internal plates of bone, although the oppo- site opinion has supporters. Certain of the bones of the cranium and the face are in parts hollowed out into mere shells bounding a cavity lined with mucous membrane continuous with that of the nose or the pharynx. The elasticity of bones is enhanced by curves. The long bones very usually present a double curve. It has been maintained that these curves form a spiral structure. There are striking instances of it, but the universality of the law is not proved ; although shocks are thus lessened, the passage of one curve to another is a weak point in the bone. The ends of the long bones are enlarged for articulation with their neighbors. The greater part of this enlargement forms the joint, the various shapes of which will be discussed later. Besides this, there are usually at the ends prominences for muscles. The shaft generally bears ridges, which in some cases are made of dense bone and materially add to the strength of the bone. A ridge or prominence usually implies the insertion of a fibrous aponeurosis or a tendon. Muscular fibres, however, may spring from the periosteum over a flat surface. 106 HUMAN ANATOMY. Parts of Bones. The following are some of the names applied to features of bone : A process is a general term for a projection. A spine or spinous process is a sharp projection. A tuberosity is a large rounded one, a tubercle is a small one, either rounded or pointed. A crest is a prominent ridge. A head is an enlargement at the end of a bone, in part articular. A neck is a constriction below a head. A condyle is a rounded articular eminence, generally a modification of a cylinder. A fossa is a pit. A glenoid cavity is a shallow articular depression. A cotyloid cavity is a deep one. A sulcus is a furrow. A foramen is a hole, in the sense of a perforation. A sinus is the cavity of a hollow bone, equivalent to antrum. It is used also to designate certain grooves for veins in the cavity of the cranium. In addition to the cartilage-covered articular surfaces proper, the fresh bones show in some places a plate of cartilage quite like one for a joint ; such plates serve to lessen the friction of a tendon playing over the bone. In other places a look of peculiar smoothness is conferred by the presence of a bursa, although cartilage is wanting. Sex of Bones. The general characteristics of the bones of the female sub- ject are, first, a greater slenderness ; second, a smaller development of processes and ridges for muscular attachment ; third, and most important of all, the small size of the articular surfaces. These guides usually suffice to determine the sex of the chief bones ; some, especially those of the pelvis, possess characteristic sexual differences of form. Age of Bones. At birth the long bones have cartilaginous ends in which, with one or two exceptions, the centres of ossification have not yet appeared. Many- bones at this period still consist of several pieces which ultimately fuse. The shape and proportions are in some cases different from those of the adult. Sexual differ- ences cannot in most cases be determined. During the Jirst years new centres of ossification appear, distinct pieces unite, and the proportions change from the type of the infant to that of the child. Towards puberty important further changes in proportion occur, and sexual differences develop. After puberty the bones present three stages, adolescence, maturity, and senility. In the first the union of the epiphyses is going on ; after this has taken place the line of separation is visible for a time, but gradually disappears. Our knowledge of the time at which these changes occur enables us to determine the age of the skel- eton. The long period of maturity presents little that allows of a precise estimate of age. The separate bones of the vault of the cranium gradually fuse into one. The senile skeleton in its extreme stage is very striking. There is a general atrophy of the bones both within and without, those of the face becoming in parts of papery thinness ; not only the cavities within the cranial bones become larger, but also the spaces within the cancellous tissue inside the bones, due to the partial absorption of the spongy substance. The only bones, however, which show a distinct change of form are the jaws, and this is a secondary result of the loss of the teeth. In many cases, however, senile absorption and atrophy do not occur, except, perhaps, in the head ; it may be, therefore, absolutely impossible to distinguish a long bone of an old subject from one of an individual in early maturity. The periods at which the age of bones is most often a matter of medico-legal inquiry are at the time of birth and in childhood and youth. The dates of the first appearance of ossification in the various bones are the criteria for the first. These are to be used, however, with great caution, since variation is considerable. The information to be derived from consideration of the general development of the body is perhaps of equal value. The same holds good for childhood and adolescence. The particular point on which the writer holds strong views, based on his own observations, differing from those generally accepted, is as to the time of union of the epiphyses at the end of ado- GENERAL CONSIDERATION OF THE JOINTS. 107 lescence. He is convinced, as his statements will show, that this union occurs earlier than is generally taught. Relation of the Bones to the Figure. While it may be said that power- ful muscles leave their imprint on the bones in strong, rough ridges, yet it is impos- sible to give a trustworthy description of the figure from the size and shape of the bones, since these are determined chiefly by prenatal influences. Very delicate, even puny, bodies may have large and strong bones, and great muscular develop- ment may coexist with a light framework. Variations. Besides the great range of individual variation, without departure from the usual type, bones occasionally show greater peculiarities. These may occur through either excess or defect of ossification. Structures which are normally car- tilaginous or fibrous may become replaced by bone, and abnormal foramina may occur in consequence, or to accommodate the aberrant course of blood-vessels or nerves. The most interesting of these variations are such as present an arrangement which is normal in some of the lower animals. Many variations may be plausibly accounted for as reversions, but others cannot be explained in this way according to any conceivable scheme of descent. By speaking of these variations as animal analogies we avoid theories and keep to scientific truth. Number of Bones. The usual enumeration of the bones composing the human skeleton is misleading, for while it is customary in some parts, as the head, to count each bone, in others, like the sacrum and the hyoid, only the ultimate condition, after union of the component segments, is considered. In other cases, like the sternum, there may be grave doubt which course is the proper one to follow ; and finally, as in the coccyx, the number is variable. Bearing these impor- tant facts in mind, it may be stated that the human skeleton in middle life usually comprises, as conventionally reckoned, two hundred separate bones, excluding the sesamoids within the tendons of the short flexor of the thumb and of the great toe and the ear-ossicles, but including the patella and the hyoid bone. Of this number, seventy-four bones belong to the axial and one hundred and twenty-six to the appen- dicular skeleton. The skeleton is advantageously described in the following order : the spine, the thorax, the head, the shoulder-girdle and the arm, the pelvic girdle and the leg. The account of the bones of each region is succeeded by that of the joints and the ligaments holding them together, followed by a consideration of the region as a whole and of its relation to the surface. The applications of anatomical details of the skeleton to the requirements of medicine and surgery are pointed out in appro- priate places. GENERAL CONSIDERATION OF THE JOINTS. A JOINT or articulation implies the union of two or more bones. Joints may be divided, according to their mobility, into three great classes : the FIXED JOINT (Syn- arthrosis), the HALF-JOINT (Amphiarthrosis} , and the TRUE JOINT (Diarthrosis}. Fixed Joints. These allow no motion in the mature condition, and are rep- resented by two subdivisions, the Suture and the Synchondrosis. The suture is the direct union of two bones which at first may be separated by membrane or by fibrous tissue, but which eventually become-firmly united. Several varieties of this form of union are recognized ; thus a serrated suture is one in which the edges are interlocked, as the teeth of two saws ; conspicuous examples are seen in the interparietal and the parieto-occipital junctures. Frequently one bone tends to overlap at one end of the suture and to be overlapped at the other. A squamous suture is one in which a scale-like bone very much overlaps another, as in the relation between the temporal and the parietal bone. An harmonic sutiire is one in which two approximately plane surfaces are apposed, as in the case of the vertical plate of the palate and the maxillary bone. The term grooved suture is sometimes employed to designate a form of union in which one bone is received within the grooved sur- face of another, as the rostrum of the sphenoid and the vomer. Wormian bones are small, irregular ossifications which appear as bony islands in the course of a suture. Familiar examples of these are seen in the line of the parieto-occipital suture. io8 HUMAN ANATOMY. Synchondrosis is the union of two bones by an intervening strip of cartilage, which usually ultimately becomes replaced by bone. Such is the union between the pieces of the body of the sternum and between certain bones of the base of the skull. The term is also applied to the union of the shaft and the epiphyses of long bones. Half-Joints, including Symphysis and Syndcsmosis. From the stand-point of development, there is no fundamental difference between symphyses and the true joints. In both cases a small cavity appears within the intervening mesoblastic tissue connecting the ends of the embryonal bones. This small cavity, in the case of the true joints, rapidly increases, and later is lined by the flattened mesoblastic cells investing the subsequently differentiated synovial membrane. When, on the con- trary, the bones are to become united by dense fibrous and fibro-cartilaginous tissue, as in the case of a symphysis, the interarticular space is always a mere cleft sur- rounded by the interlacing and robust bundles of the dense tissue forming the union in the mature joint. A symphysis implies great strength and very limited and indefinite motion, there being no arrangement of surfaces to determine its nature. The chief function of this form of union seems rather to be to break shocks. The central cavity is not always found. The symphysis pubis (Fig. 361) is a typical half -joint. Those con- necting the bodies of the vertebrae are usually so classed, but it is not certain that they quite agree either in structure or development with the description. A transi- FIG. 134. Diagrams of various forms of suture. A, serrated ; JS, squamous ; C, harmonic ; D, grooved. tional form leading from the symphysis to the true joint is one in which the limited synovial cavity, instead of being in the centre of a mass of fibro-cartilage, lies between two cartilaginous surfaces, somewhat like that of a true joint, but so interlocked and surrounded by short, tense fibres as to preclude more than very slight motion. This arrangement is often seen in the articulation between the sacrum and ilium, some- times improperly called the sacro-iliac synchondrosis. Syndesmosis is to be included among the half-joints. It is the binding together of bones by fibres, either in bundles or as a membrane, without any inter- vening cartilage ; an example of this arrangement is seen in the union effected by the interosseous ligament in the lower tibio-fibular articulation. True Joints. These articulations develop in a similar manner to the half- joints, except that the opposed ends of the developing bones are of hyaline carti- lage, fibro-cartilage being present only at the sides, except in the case of a compound joint, where it forms the intervening plate. The tissue at the sides of the articular cleft differentiates into two layers, the inner, which is the svnvrial membrane, consist- ing of a layer of cells continuous with the superficial layer of the cartilage-cells and secreting a viscid fluid, the synovia, which lubricates the joint ; and the outer part, which becomes a fibrous bag called the eapsiilar ligament. The latter, in its simplest form, consists of only enough fibrous tissue to support the synovial membrane. The capsular ligament is strengthened by accessory ligaments developing in or around it, the arrangement of which depends on the needs of the joint. During development, STRUCTURE OF JOINTS. 109 independent of the influence of motility or of muscular action, the articular ends of the bones assume definite shapes such as will allow the motion peculiar to that joint, and (barring the frequent want of perfect coaptation) no other. The common char- acteristics of true joints are articular surfaces covered by hyaline cartilage, so shaped as to determine the nature of the movement, enclosed by a capsule lined with a synovial membrane. The articular surfaces are not necessarily formed wholly of bone, since very often increased concavity is secured by the addition of a lip of fibro- cartilage to the margin of the bone ; in other cases ligaments coated with carti- lage complete a socket ; or again, disks of fibro-cartilage loosely attached to the periphery may project into a joint and partially subdivide it, following one bone in certain movements and the other in others. Compound joints result from the persistence and differentiation of a portion of the tissue uniting the ends of the embryonal bones into a partition which, in the complete compound joint, separates the two synovial cavities developed, one on either side of the septum. The tissue between the bones becomes a fibre-cartilagi- nous disk, 1 which partially or completely subdivides the cavity. In such a joint, when typical, there are two ends of bone covered with articular cartilage, separated D Diagrams illustrating formation of joints. A, bones are united by young connective tissue; B, appearance of joint-cavity; C, differentiation of joint-cavity and capsule; D, development of two joint-cavities separated by fibrous septum, resulting in a compound joint. by a fibro-cartilaginous disk or meniscus, and two distinct synovial membranes. The movements are, however, still determined to a considerable extent by the shape of the bones, so that these articulations may be classed as true joints. The fibro- cartilaginous meniscus may be replaced by a row of bones as in the wrist. Structure of True Joints. The opposed ends of the bones, and sometimes other tissues, are coated with hyaline articular cartilage, which gives a greater smoothness to the articulating surfaces than is found on the macerated bones. Though following in the main the bony contours, the cartilage does not do so accu- rately ; details are found on the cartilage that are obscure on the bones. It dimin- ishes the force of shocks. Although, as already stated, the shape of the articular ends determines the nature of the motion, it is important to recognize that, as in the case of saddle-joints, the opposed surfaces are not so accurately in apposition that irreg- ular movements cannot and do not occur. Failure to appreciate this fact has given rise to much difficulty in accounting for motions that undoubtedly take place, but which, according to the mathematical conception of the joint, are impossible. Further, the range of individual variation is great ; just as a man may have a long or a short head, so any of the articular ends of his bones may depart considerably from the average proportions. It is even possible in some of the smaller joints that 1 Discus articularis. no HUMAN ANATOMY. FIG. the articular surface of a certain bone may be plane, convex, or concave in different persons. The capsule. Every joint, with possibly some exceptions in the carpus and the tarsus, is enclosed by a capsule? or capsular ligament, which arises from the peri- osteum near the borders of the articular cartilage and surrounds the joint. This envelope consists of a membrane, often containing fat within its meshes, composed of two layers, the inner delicate synovial membrane and the external fibrous layer. The latter, while in some places very thin, is usually strengthened by the incorpora- tion of fibrous bands which, from their position, are known as lateral, anterior, or posterior ligaments. These bands are of strong, non-elastic fibrous tissue which under ordinary circumstances do not admit of stretching. The strength and security of the joint are often materially increased through thickenings of fasciae and expansion of tendons which blend with the underlying capsule. The capsule must be large enough to allow the characteristic movements of the joint ; consequently, when the bone is moved in any particular direction that side of the capsule is relaxed and thrown into folds. These folds are drawn out of the way either by small special muscles situated beneath those causing the chief movement or by fibres from the deeper surfaces of these latter muscles. In the joints of the arches of the vertebrae, there being no muscles inside the spinal canal, a dif- ferent arrangement exists for the inner side of the capsule, elastic tissue there taking the place of muscle. The relation of the insertion of the capsule to the line of the epiphysis is important. Although this point is fully con- sidered in the description of the individual joints, it may be here stated that, as a rule, in the long bones, the capsule arises very near the line of the epiphysis. The synovial membrane which lines the interior of the capsule and other portions of the joint, except the surfaces of the articular cartilages, consists of a delicate connective- tissue sheet, containing many branched and flattened connective-tissue cells. The latter, where numerous, as is the case except at points subjected to considerable pressure, are ar- ranged on the free surface of the synovial mem- brane as a more or less continuous layer, often spoken of as the endothelium of the synovial Since in many places the layer of connective-tissue elements is imperfect and Capsule Synovial membrane Articular cartilage Joint-cavity Reflection of syno- vial membrane Epiphyseal bone. Diagram showing the parts of a typical joint. sac. the component cells retain their stellate form, the cellular investment of the joint- cavity is at best endothelioid, suggesting, rather than constituting, an endothelium. The synovial membrane is in certain places pushed inward by accumulations of fat of definite shape between it and the capsule. It is also prolonged, as the synovial fringes, 2 into any space that might otherwise be left vacant in the various movements. They are alternately drawn in or thrust out, according to circumstances. Some- times pieces of them, or of fibro- cartilage, become detached in the joint, giving rise to much trouble. The cavity which is found when a joint is opened on the cadaver, with the tissues dead and relaxed, easily suggests a false impression. It is to be remembered that the synovial fluid normally is present in quantity little more than sufficient to lubricate the joint, and that in life all the parts are strongly pressed together so that no true cavity exists. This is well shown by frozen sections. Certain so-called intra-articidar ligaments, as the ligamentum teres of the hij>, or the crucial ligaments of the knee-joint, are found in the adult, roughly speaking, inside the joint. The sketch of development given above shows that they Cannot be truly within the articular cavity. In fact, either they wander in from the capsule, carrying with them a reflection of synovial membrane, or they are the remnants of 1 Cnpiuln nrtlcularis. '-' IMicav synovliiles. Ill the capsules separating two distinct joints which have broken down so as to make a common articular cavity. Such ligaments retain their synovial covering and really lie without the joint-cavity. Vessels and Nerves. Important arterial anastomoses surround all the larger joints ; from the larger vessels small branches pass inward to the ends of the bones, to the periphery of the articular cartilages, and to the capsule. The margins of the cartilages are surrounded by vascular loops ; the articulating surfaces are, however, free from blood-vessels. The synovial membrane is usually well supplied with minute branches, a rich net-work being described at the bases of the synovial fringes. The veins form strong plexuses. Lymphatics are found well developed directly beneath the inner surface of the synovial membrane ; while it is certain that they absorb from the joint, direct open- ings into the articular cavity have not been demonstrated. Nerves, presumably sensory and vasomotor, end in the tissues around the syno- vial membrane. In addition to the Pacinian bodies, which are sometimes very numerous, Krause has described special articular end-bulbs outside the synovial membrane surrounding the finger-joints in man. FIG. 137. Blood-vessel Free surface of articular car- tilage Bone Marrow-cavity Synovial mem- brane Union of carti- lage and syno- vial membrane Section through margin of joint, showing articular cartilage and capsule. X 135. Bursae ' are sacs rilled with fluid found in various places where friction occurs between different layers or structures. They are sometimes divided into synovial and mucous bursae. These varieties are distinct in typical instances, but, since the one passes insensibly into the other, it is doubtful whether this subdivision is war- ranted. Some bursse, especially those around the tendons of the fingers, have a true synovial lining reflected over the tendons, and are surrounded by strong fibrous sheaths known as the theca synoviales. 2 Other bursae are placed as capsules around a cartilage-coated facet over which a tendon plays. Both the vaginal and capsular varieties may be classed as synovial bursae. Representatives of the mucous bursae are those within the subcutaneous tissue where the skin is exposed to friction, as at the elbow and the knee. These bursae seem little more than exaggerations of the spaces between layers of areolar tissue. The same may be said of some of those among the muscles. The mucous bursat are provided with more or less of a cellu- lar lining, but the latter is less perfect than in the synovial class. A bursa may be simple or composed of several cavities communicating more or less freely. They often communicate with joints. Their number is uncertain. Many, perhaps most, are present at birth, but new ones may appear in situations exposed in certain 1 Bursae synoviales. - Vaginae raucosae tendinura. ii2 HUMAN ANATOMY. individuals to uncommon pressure or friction, and, under these circumstances, the ones usually present may be enormously enlarged. Modes of Fixation in Joints. Ligaments, muscles, atmospheric pressure, and cohesion are the agents for fixation. Ligaments. A capsular ligament, pure and simple, has little retaining strength. The accessory ligaments, on the contrary, have great influence. Their arrangement differs with the nature of the joint. Thus, a ball-and-socket joint has thickenings at such parts of the capsule as the particular needs of that joint require. A hinge-joint implies strong lateral ligaments ; a rotary joint, some kind of a retain- ing-band that shall not arrest motion. Sometimes certain ligaments are tense, or nearly so, in every position of the joint,' as the lateral ligaments of a hinge-joint. Often a ligament is tense only when a joint is in a particular position, as the ilio- femoral ligament of the hip when the thigh is extended. A strong ligament like the one just mentioned is, when tense, the greatest protection against displace- ment. Muscles. The action of the muscles is of great importance in maintaining the joints in position, in certain instances being the most efficient agency. The con- stant pull of the muscles keeps the more movable bone closely applied to the more fixed in all positions. Muscles which are nowhere in contact with the joint may exercise this function. The tendons of muscles sometimes act as ligaments, which differ from the ordinary ligamentous bands in that they may be made tense or relaxed by muscular action. Sometimes they are intimately connected with the capsule, at other times distinct from it. Some muscles, whose tendons cross several joints, exercise, by their tonicity, an influence on them all. Thus, the peroneus longus is essential to the maintenance of the transverse arch of the foot. Certain muscles passing over more than one joint exert a ligamentous action on one joint determined by the position of the other. This, however, is more properly dis- cussed in connection with the action of muscles. Atmospheric Pressure. Much has been written about the action of this agency in holding joints in place. The atmosphere exerts a certain pressure on all bodies, animate or inanimate, and thus tends to compress them. The joints, as parts of the body, are subject to this general influence. It is by no means very effi- cacious. The shoulder- joint has a capsule long enough to allow very free motion, and consequently too long to hold the humerus in place. This is done chiefly by the muscles. When these are paralyzed the arm falls out of place, atmospheric pressure being inadequate to resist the weight. The most important action of atmospheric pressure is to keep the soft parts closely applied to the bones. Cohesion is the action of the viscid synovial fluid which tends to hold the surfaces together. It is very feeble, but probably has an appreciable influence in the smaller joints. Limitation of Motion. The shape of the joint determines the nature of the movement ; its range depends in part on other factors, such as the tension of liga- ments or of the tendons of muscles and the resistance of the soft parts. Motion in True Joints. It is easy to conceive that an upright rod on the highest point of rather less than half a sphere may FIG. 138. slide to the periphery along an indefinite number of ROTATION^ At/o ^ lines. This is angular motion. The rod on reach - -4^? ing the periphery, or at any point on the way, may travel round in a circle describing the surface of a cone. This is circumduction. Finally, without an}' change of position, the rod may revolve on its own axis. This is rotation. Changes of Position of Parts of the Body. Assuming that the palms are looking forward, an- Uiagram illustrating different kinds of . ^ . , , motion. gular motion ot a limb, or of a part of one, towards the median plane of the body is called adduction ; tin- opposite movement, abduction. A motion bringing the distal end of a limb bone? nearer to the head is called Jlc. \~ion ; the opposite movement, extension. The move- ments of the ankle and the foot, however, present a difficulty, although the above VARIETIES OF TRUE JOINTS. 113 nomenclature is generally accepted, since the digital extensor muscles flex and the flexors extend. It is best with reference to the ankle-joint to speak of plantar flexion and dorsal flexion. Pronation in the arm is turning the front of a limb downward ; supination, the converse. Thus, when the palm rests upon a table the arm is pronated ; when the back of the hand rests upon the same support the arm is supinated. Reference to the skeleton during these movements will show that pro- nation is associated with crossing of the bones of the forearm, while during supina- tion they are parallel. These terms should not be applied to motions of the leg. Rotation is inward or outward, according as it is towards or away from the median line of the body. Varieties of True Joints. The following are the chief kinds of true joints, the nature of the motion being determined by the articular surfaces : Arthrodia, 1 a gliding joint permitting merely a sliding between two nearly plane surfaces, as between the articular processes of the vertebrae. Enarthrosis, 2 a ball-and-socket joint permitting angular motion in any direc- tion, circumduction and rotation. The shoulder- and hip-joints are conspicuous examples, Condylarthrosis,' an egg-shaped joint permitting angular motions more freely on the long axis than on the short one, circumduction but (theoretically, at least) no rotation, as in the radio-carpal articulations. The imaginary axes for the angular motions lie in the convex bone. The Saddle-Joint, 4 is a modification of the above, the end of one bone being convex in one plane and concave in another, at right angles to the first, while the other bone is the converse ; thus in one plane one bone is the receiver and in the other the received. The articulation of the trapezium with the first metacarpel bone is an example. The motions in such joints are precisely the same as those of the preceding form. The two imaginary axes are, however, on opposite sides of the joint, each being at right angles to the convex plane of its own bone. It is clear that if the reciprocal curves of the two bones of a saddle-joint coincide, and that if they fit closely, rotation is out of the question ; but, in point of fact, that is not the case, for there is no very accurate agreement of the surfaces, and the contained curve is smaller than the containing, so that a certain amount of rotation is possible. 5 Ginglymus, 6 a hinge-joint permitting motion only on a single axis approxi- mately transverse to the long axis of the bone, consequently the moving bone keeps in one plane. The ankle-joint is an example. The inclination of the transverse axis may vary, and one end of the joint be larger than the other. If the course of the revolving bone is that of a spiral around the transverse cylinder the articulation constiutes a screw-joint,' 1 as the humero-ulnar articulation. Trochoides, 8 a pivot-joint permitting motion only on one axis coincident with at least a part of the long axis of the bone, namely, rotation, as in the atlanto-axial articulation. Should a part of the bone be so bent as to lie outside of the axis, as in the radius, this part undoubtedly changes position ; nevertheless, there is merely rotation, for the change of position is accidental, depending on the shape of the bone, not on the nature of the motion. Certain complicated joints may combine several of the above forms. 5 Reneclu Rois-Reymond. Archiv fiir Anat. u. Phys., Phys. Abtheil., 1895. 1 Arthrodia. -'Enarthrosis. :l Articulatio cllipsoidea. 4 Articulatio sellaris. 6 Ginglymus. ~ Articulatio cochlearis. " Articulntio trochoidea. THE SPINAL. COLUMN. THE spinal column is the central part of the skeleton. It supports the head, bears the ribs, thus indirectly supporting the arms, and encloses the spinal cord. It gives origin to many muscles, some passing between different parts of the spine, others connecting it with the body. These purposes demand great strength and flexibility. The spine is composed of many pieces united by tough fibro-cartilagi- nous disks, by which the force of shocks is broken and the great range of move- ment is distributed among many joints. It is convex behind in the regions of the thorax and pelvis, so as to enlarge those cavities, and has forward convexities in the neck and loins. The numerous prominences which it presents serve for the support of the ribs, the attachment of muscles, and the interlocking of the various pieces. The spinal column is firmly fixed near the 'lower end between the bones of the pelvis. The bones composing this column are called vertebra, of which in the adult there are thirty-three or thirty-four in all. They are divided into five groups. The FIG. 139. ipinous process Facet for tubercle of rib Transverse process Superior articular process Demi-facet for head of rib Body Sixth thoracic vertebra from above. first seven are the cervical ; the next twelve, which bear ribs, are the thoracic ; the next five are the lumbar, making twenty-four above the pelvis. These are known as the presacral vertebrae. The remainder are in the adult united into two bones, the first five forming the sacrum, the last four or five the coccyx. As many as thirty-eight are seen in the young embryo, but some disappear or are fused. With the exception of the first two, the atlas and the axis, which require a separate description (page 119), the vertebrae above the sacrum present the following features, which are common to all, but which are modified in the different regions : (i) a body 1 or centrum ; ( 2) n. pedicle* springing from the back of the body on either side, supporting (3) the lamina? a plate which meets its fellow in the middle line to form an arch bounding the spinal or vertebral foramen* for the spinal cord. Each vertebra gives origin to several processes. namely, (4) a spinous process? sprin^in^ from the point of union of the laminae ; (5) a transverse process on each side, pro- jecting outward from the junction of the pedicle and lamina ; (6) two articulating 1 Corpus. " Radix arcus vertebrae. ' Arcus. * Foramen vertebrale. ' 1'rorrssus spinoMis.'' I'rm I'XMIS transversus. 114 THORACIC VERTEBRA. processes 1 on each side, one above and one below the lamina, forming true joints with the opposed processes of the neighboring vertebrae ; (7) a rib or costal element, which in the thoracic region is a separate bone, in the cervical region is a part of the vertebra, and in the lumbar FIG. 140. Pedicle Superior articular process-, and facet Articular facet on transverse process Superior demi-facet for rib Inferior demi-facet for rib Inferior articular process Spinous process Sixth thoracic vertebra from the side. region mingles with the trans- verse process. The costal ele- ment is also represented in the sacrum. Thoracic Vertebrae. A vertebra from the middle of the thoracic region is de- scribed first as intermediate in several respects to the others. The body is but a little broader transversely than from before backward. It is a little deeper behind than in front, thereby helping to form the curve of the spine. The upper and lower borders pro- ject a little anteriorly. The upper and lower surfaces, as in all the vertebrae, are rough where the intervertebral disks join them. The posterior surface is concave from side to side, and presents in the middle one or two foramina for the escape of the veins. At the back of the side of the body there is half an articular facet both above and below, which, with the intervening disk, forms an oval, shallow socket for the head of the rib belonging to the lower vertebra. The spinal foramen, en- closed by the arch, is circular. The pedicles, which are much deeper than thick, arise from the upper half of the body. The supe- rior border rises gradually to the articular process. The inferior bor- der is concave, forming the top of the notch? which, when the succeed- ing vertebra is in place, forms the top of the intervertebral foramen? which is wholly behind the lower half of the body. The laminae are broad, each reaching to the level of those of the next vertebra. The spinous process is long, and points strongly downward, over- lapping the one below. It has a narrow under surface which is grooved, and two lateral ones meet- ing above in a ridge continued from the laminae. This arrangement of the laminae and spines completely closes the cavity of the spinal canal. The spinous processes are slightly enlarged at the end for the supraspinous liga- ment and muscles. The transverse processes are strong, having to support the ribs. They pro- Superior articu- lar process and facet Spinous process Sixth thoracic vertebra from behind. 1 Processus articularis. - Incisura vertebral! ' Fissura IntervertebrnHs n6 HUMAN ANATOMY. ject outward and backward, and enlarge at the tip, which anteriorly presents a con cave articular surface for the tubercle of the rib, and is rough behind for muscles. The articular surfaces are in two pairs above and below, each. pair facing in opposite directions, so that the lower ones of one vertebra meet the upper ones of Inferior articular process Superior articular process Transverse foramen Transverse process FIG. 142. Spinous process Posterior limb of transverse process Posterior tubercle 'ostal element Anterior tubercle Body Anterior limb of transverse process Fourth cervical vertebra from above. the next. Each presents a smooth, roughly oval articular surface. The superior ones face backward, a little outward, and a very little upward ; the inferior, con- versely, look forward, inward, and slightly downward. Groove for spinal nerve FIG. 143. Superior articular process Anterior tubercle Posterior tubercle Fourth cervical vertebra from in front. Cervical Vertebrae. A typical cervical vertebra is much smaller than the thoracic. The body is decidedly longer from side to side than from before backwan The upper surface is raised at the sid FIG. 144. so as to embrace the body next above, superior articular process and facet anc j h as its front border rounded for the latter to descend over it ; for this pur- Anterior pose the lower anterior border is pro- t..i,e,vie longed downward. The height of the i'";tenoi body is about the same before and be- tubercle , . hind. The spinal foramen is triangular, v/ith the greatest diameter transverse. The pedicles are short and light, "nerve r and extend backward and outward from the body. The notches above and be- low them are about equal. The intervertebral foramen is opposite the intervertebral disk, and a part of the bodies of two vertebrae. Inferior articular pro- cess and facet Inlet vertebral notcb Fourth cerviral vertebra from the side. LUMBAR VERTEBRA. 117 The laminae are smooth and do not quite meet those of the next vertebra, unless the head be bent backward. The spinous process projects backward and a little downward. It is short and forked at the end, very often unevenly. The transverse processes are often described as double. The posterior limb, which is the true transverse process, projects outward and somewhat forward from the junction of the pedicle and lamina, and ends in a flattened, nearly vertical pro- jection, the posterior transverse tubercle. The anterior limb, a vertical plate spring- ing from the side of the body and extending outward, ends in the anterior transverse tubercle. This limb is the shorter of the two and its tubercle the larger. The limbs are cdnnected by a concave plate or bone, slanting slightly outward, which forms the floor of a gutter 1 in which the spinal nerve lies, and which represents the costal element. A round hole, the transverse foramen, for the vertebral artery and veins, lies internal to this plate ; the artery usually does not pass through the foramen of the seventh vertebra. Since the scalenus anticus muscle springs from the anterior FIG. 145. Spinous process Superior articular facet Mammillary process Third lumbar vertebra from above. tubercles and the scalenus medius from the posterior ones, on leaving the spine the spinal nerves pass between these muscles. The articular processes are placed at the outer ends of the laminae ; the upper face upward and backward, the lower forward and downward. Lumbar Vertebrae. A typical lumbar vertebra is very much larger than the others. The body is broad from side to side, the upper and lower borders projecting especially at the sides. The posterior surface is slightly concave and presents two large venous openings. The spinal foramen is three-sided, with a transverse diameter but slightly exceeding the antero-posterior. The pedicles are short and strong, diverging only slightly. They are very nearly on a level above with the top of the body, so that there is a small notch above and a large one below. The laminae are broad at the sides, but less so near the mid-line, so that in this 1 Sulcus n. spinalis. u8 HUMAN ANATOMY. region there is a large opening into the spinal canal. A considerable part of the arch is lower than the body. The spinous process is a flat projection extending nearly straight backward, with two lateral surfaces and a superior, inferior, and posterior border. The last is rough and thickened below, with occasionally a tendency to become bifid. The transverse processes, which are solely for muscular attachments, and FIG. 146. Superior articular proces Mammillary process Transverse process Accessory process Inferior articular process and facet Third lumbar vertebra from the side. therefore not heavy, project outward and somewhat backward. They are thin, having an anterior and a posterior surface and a blunt end. The articular processes are large, very nearly vertical, and curved. The superior, facing somewhat backward but chiefly inward, are concave and embrace the inferior ones of the vertebra above, which are convex, and face in the opposite direction. Superior articular process and facet Mammillary process Accessory process Inferior articular process Spinous process Lamina Third lumbar vertebra from behind and the side. The mammillary processes form on either side a rounded lateral projection on the posterior border of the superior articular process. Additional tiilu-rcli>s, the accessory processes, appear as inconspicuous elevations at the junction of the posterior border of the transverse with the superior articular processes. The details :m is 1 12 for the white male and 116 for the female. Such a rule is, however, not abso- lute, there being many doubtful cases, but a narrow sacrum is almost invariably male. Another, and very reliable, guide, especially in conjunction with the first, is the curve. There are contradictory statements among authors, but the truth is, as originally shown by Ward, that the male sacrum is the more regularly curved, while the anterior surface of the female bone runs in nearly a straight line from the prom- ontory to the middle of the third piece and then suddenly changes its direction. Variations. The sacrum often consists of six vertebrae. Such a one may be recognized even when the lower part is wanting, so that the vertebrae cannot be counted. If a line across the front, connecting the lowest points of the auricular surfaces, passes below the middle of the third sacral, the sacrum is of six pieces ; if above, of five. 1 Sacra consisting of only four vertebrae are rare. THE COCCYX. This bone is composed of four or five 2 flattened plates representing vertebral bodies. It is an elongated triangle with the apex below. The base, joined by fibro- cartilage to the apex of the sacrum, is oblique, the posterior border being higher than the front, so that the coccyx slants forward from the sacrum. The anterior surface of the coccyx is, moreover, very slightly concave. ^^ first vertebra consists of a thin.foWy, about twice as broad as long, from the back of which on each side the rudiment of an arch extends upward as a straight process, the coccygeal cornu, which FIG. 155. //& (Sa Cornu / iB?r ' ~\ a f .. i Ylk Surface for sacrum^ Transverse P-ess Coccygeus < Gluteus maximus III V Posterior IV Sphincter ani The coccyx. overlaps the back of the body of the last sacral vertebra and joins the sacral cornu. A short lateral projection from the side of the body represents the transverse process; perhaps the costal element also. On the upper border of this process, at its origin, is a notch, which usually forms a foramen with the sacrum for the anterior division of the fifth sacral nerve. Very faint rudiments of these two pairs of processes are sometimes to be made out on the second vertebra, which is much smaller than the first, but also broad and flat. The succeeding ones are much smaller and ill-defined. Constrictions on the surfaces and notches on the edges mark the outlines of the 1 Bacarisse : Le sacrum suivant le sexe et suivant les races. These, Paris, 1873. 2 According to Steinbach, there are five in man and four or five in woman. Die Zahl der Caudalwirbel beim Menschen. Inaugural Dissertation, Berlin, 1899. 128 HUMAN ANATOMY. original pieces, which become less and less flat and more and more rounded. It is rare to see more than four distinct segments, but very often the last is somewhat elongated and shows signs of subdivision. It is not uncommon for the first piece to remain separate, neither fusing with the sacrum nor the next coccygeal plate. STRUCTURE OF THE VERTEBRAE. The shell of compact bone forming the surface is everywhere very thin. The general plan of the internal spongy bone is one of vertical plates which in a frontal section (Fig. 156, A) are bowed somewhat outward from the middle of the bone, and of transverse plates connecting them near together at the ends and farther apart in the FIG. 156. Frontal (A) and sagittal () sections of body of lumbar vertebra, showing the arrangement of the bony lamellae. Natural size. middle third where larger spaces occur. The strongest plates spring from the pedi- cles and diverge through the bone, joining, probably, for the most part the hori- zontal system. In the sacrum the same general plan prevails, but in addition there are series of plates, mainly horizontal, in the lateral parts ; those from the first sacral are the most important. DEVELOPMENT OF THE VERTEBRA. Presacral Vertebrae. These vertebrae ossify from three chief centres and at least five accessory ones. The median one of the three chief centres forms the greater part of the body ; while the other two, one appearing in each pedicle, form the postero-lateral part of the body, the arch, and the greater part of the processes. The oblique neuro-central sutures separate the regions of these centres. The lat- eral centres of the upper thoracic and the cervical vertebrae appear first. It is usually taught that they appear in the sixth or seventh week of fcetal life, but Bade l with the Rontgen rays found no sign of them at eight weeks. The point is unset- tled. The first median centres to appear are those of the lower thoracic and the upper lumbar vertebrae. In this region and below it the median centres precede the lateral ones ; in the upper part of the spine the growth is much more vigorous in the lateral centres. The median centres of the cervical vertebrae appear in order from below upward. The upper ones (judging from Rontgen-ray work and from transparent foetuses) sometimes have not appeared as late as the sixth month, although we have seen them towards the close of the third. . // />/;/// the upper and lower ends of the bodies are still cartilaginous, but the arches are well advanced in ossification, although bone does not cross the median lint- until some months later. The transverse processes of the thoracic vertebrae are farther advanced than those in other regions. The spines are still cartilaginous. The neuro-central suture is lost at from four to six years, disappearing first in the 'Arch, fiir Mikros. An;it., Bel. lv,, 1899. DEVELOPMENT OF THE VERTEBRAE. 129 lumbar region. The tips of the spinous and transverse processes develop from cen- tres which appear about puberty and fuse about the eighteenth year. A thin epi- physeal disk, covering the upper and lower surfaces of each body, grows from a centre seen about the seventeenth year, and joins by the twentieth, the line of union per- sisting a year or two longer. The mammillary processes of the lumbar region arise from separate centres ; so do also the costal elements of the sixth and seventh cer- vicals, and sometimes that of the first lumbar. In cases in which this costal element of the seventh cervical remains free there is a cervical rib and no transverse fora- men ; exceptionally in these cases a foramen persists. According to Leboucq, 1 the development of the anterior limb of the transverse process of the cervical vertebrae is more complicated than is usually taught. There is a slight outward projection from the ventral side of the body rep- resenting the prominence for the head FIG. 157. of the rib to rest upon ; this grows out- ward and meets a growth from the transverse process that grows inward like a hook. This inward growth rep- resents what we commonly call the costal element of a cervical vertebra, but there may be also a separate ossi- fication representing an actual rib, namely, a small piece of bone on the ventral aspect of the tip of the trans- verse process of the seventh cervical vertebra. When a separate ossifica- tion occurs in this region in the fifth or sixth vertebra, it is situated still more externally than in the seventh, and forms the floor of the gutter be- tween the anterior and the posterior tubercles, which is the true costal ele- ment. It is probable that in certain cases of cervical ribs accompanied by a transverse foramen, the latter is en- closed by the hook-like process from the transverse process meeting the growth from the body of the vertebra, and that the rib coming from the separate ossification lies anteriorly to it and distinct from it. At birth the i I , i ii Ossification of the vertebrae. A, cervical vertebra at lumbar articular processes resemble the thoracic. The type changes in early childhood. The Sacrum. Each sacral ver- tebra has the three primary centres of the others, the median ones appearing before the lateral of the same vertebra. Proba- bly the median centres of the first three appear first and then the lateral ones of the first vertebra ; data, however, are wanting for a definite statement. The time of the first appearance of ossification in the sacral vertebrae is very variable ; probably the earliest median centres appear about the beginning of the fourth month and the lateral ones some weeks later. In a skiagraph of a foetus estimated to be about three and a half months old the median centres of the upper three vertebrae and the lateral ones of the first are visible. This is, perhaps, earlier than the rule. Little progress in ossification of the last two sacrals takes place before birth. The lateral centres join the median, in the lower vertebrae, during the second year ; in the upper ones, three or four years later. In the upper three vertebrae a centre appears out- side the anterior sacral foramen, from which a part of the lateral mass is developed. Ossification of the vertebras, birth ; centres for body (a), neural arches (6), and costal ele- ment (c). B, dorsal vertebra at two years; cartilaginous tips of transverse (a) and spinous (b) processes; rf, centre for body. C, lumbar vertebra at two years ; position of ad- ditional later centres for various processes indicated (a, f>, c) ; d, centre for body. 1 Me'moires couronne's, etc., Acad. Royale des Sciences de Belgique, tome lv., 1896. 9 130 HUMAN ANATOMY. This represents a costal clement which fuses with the front of the pedicle. Those of the first two sacrals appear shortly before birth (Bade). The line of union can still be seen at seven years on the top of the first vertebra. The time at which the laminae FIG. 158. C. f (rib) F Costal element Illustrating homology of costal element (c. !' about seventeen years tebral disks. A thin plate appears in the upper and lower parts of these disks which fuses with the bodies before the latter unite. The union of the vertebrae begins below and proceeds upward in a very irregular manner. Probably union generally occurs first in the lateral masses, between the laminae VARIATIONS OF THE VERTEBRA. 131 sooner than between the bodies. By the fifteenth year the lower three vertebrae are generally fused, the second joining them from eighteen to nineteen. The five pieces are united by the twentieth year. In some cases several of the sutures are still to be seen, but all may have disappeared. The union of the bodies, as shown by sections, in the case of the upper ones, may not be complete internally till a much later period. Two thin epiphyses appear on each side of the sacrum about the eighteenth year, one for the aiiricular surface and the other below it. The lines of union of these plates may be visible after twenty-one. The Coccyx. Our data concerning the ossification of the coccyx are very un- satisfactory. Each segment has one centre, but the first may have two, one on each side, and, according to some, secondary centres for the cornua. Ossification begins in the first piece at about birth, and successively in the others, from above down- ward, until puberty. The lower three or four pieces fuse within two or three years after birth, and join the first at perhaps about twenty ; there is, however, great diversity, and frequently the first unites with the sacrum instead of with the others. The Atlas. The atlas is almost wholly formed from two centres which F IG - 161. appear in the seventh week of foetal life in the root of the posterior arches ; from these points ossification spreads most rapidly backward. In the course of the first year a centre is found in the middle of the anterior arch. The lateral masses meet behind in the fourth year and join the median anterior nucleus in the fifth. Sometimes the union of the posterior __ arches does not OCCUr. The anterior nu- Unique case of absence of the anterior arch of the atlas. cleus may be absent, and the front arch may show a median suture or be represented by ligament or cartilage. In one in- stance the anterior arch was wholly wanting, the lateral masses being fastened to the odontoid by ligament 1 (Fig. 161). The Axis. The ossification of the axis begins by two lateral points appearing by the eleventh week. The median one, which does not com'e till the fifth month, is at first double, but the two points speedily fuse. At about the same time two nuclei appear side by side in the odontoid process, which join together before birth, leaving a space between them at the tip. This may be closed by the extension of ossification, or a centre may appear in it at the second year, which fuses by the twelfth. The piece thus formed has been held to represent the epiphyseal plate for the top of the atlas. The odontoid process joins the body at the periphery, the union beginning in the third year and being complete a year or two later ; a piece of car- tilage in the middle of the juncture is said to persist under the odontoid until old age. Very rarely the odontoid remains distinct. The arches join the body in the third year, and usually meet behind at the same time ; the latter union, however, may be delayed. Variations of the Vertebrae. The commonest and most interesting variations are those of number. These are very frequent in the coccyx, since there are originally more elements than persist, and indeed we are not sure even of the normal number in this bone. Numerical varia- tions are also often observed in the sacrum, less so in the lumbar, still less so in the thoracic, and extremely rare in the cervical region. The number of vertebrae above the sacrum (twenty- four) is usually unchanged, but, owing to differences in development of the costal element, one region is not rarely increased or diminished at the expense of the next one. Thus the very com- mon condition of six lumbar vertebra,' is due to the want of development of the costal element (the rib) of the last thoracic, and implies only eleven vertebrae in that region. Conversely, thir- teen thoracics imply an undue development of the costal element of the first lumbar, and con- sequently only four lumbar vertebrae. Often the costal element of the last cervical is free and over-developed, making a cervical rib. But even if this be large enough to reach the aternum, which is exceedingly rare, the number of cervical vertebrae is usually considered unchanged. Other changes are due to variations in development of the costal element in the last lumbar and the first sacral. Transitional forms are here very frequently met with. The last lumbar 1 Dwight : Journal of Anatomy and Physiology, vol. xxi., 1887. 132 HUMAN ANATOMY. may, by an excessive growth of these elements, become sacralized, articulating more or less per- fectly with tlie ilium, and, conversely, the first sacral may have almost freed itself from those below it. Thus we may find a partially sarrali/ed vertebra, which may be either the twenty-fifth or the twenty-fourth. It often happens, particularly in the latter case, that a vertebra appears to be a first sacral on superficial examination, which is found to have little or nothing to do in form- ing the articular surface, in which case it is not a true sacral, for the first sacral is the fnlc rails which has the largest surface for the joint with the ilium. A false promontory may coexist with the normal one. This is probably most frequent when the twenty-fourth vertebra is partly sacralized. Any of the preceding peculiarities may be unilateral, so that sometimes a vertebra may seem from one side to belong surely to one region, and equally surely to the other region when seen from the opposite side. There is, however, another set of variations in which the number of presacral vertebrae is increased or diminished. There may be, for instance, one thoracic or one lumbar vertebra too many or too few, without any compensatory change in the next region. In these cases, more- over, the terminal vertebrae of the region may be very nearly typical ones, and sometimes even the size of the vertebrae will be modified so as to give the region its approximate relative length. Similar changes may be found in the neck, but they are exceedingly rare. Variations of either kind are likely to have an effect on the column as a whole ; thus, if there be a large cervical rib the last thoracic rib is likely to be small, or if the first rib is rudi- mentary the last is apt to be large. It follows that the thorax seems to be in certain cases moved upward or downward ; this change may occur on one side only. Rosenberg's theory, formerly much in vogue, is that there are opposite tendencies at the two ends of the spine. At the upper there is a tendency for the cervical region to encroach on the thoracic, and at the lower for each of the regions to encroach on the one above it. Such changes he considers progressive. On the other hand, the opposite movement by which the thorax encroaches on the neck or loins is considered reversive. Rosenberg has described a spine which he considers archaic, in which there are two extra presacral vertebrae and fifteen pairs of ribs, the first being cervical. There are two spines in the Warren Museum with a simi- lar number of presacrals in which the last is sacralized on one side. As to the way in which anomalies of the lower part of the spine come about, Rosenberg 1 thinks he has shown that in the course of development the sacrum is composed of vertebrae placed farther back than the permanent ones, and that the ilium enters into connection with vertebrae more and more ante- rior. As new ones join it above former ones become detached from it below. If it does not make the usual progress the spine is archaic, having too many presacrals ; if it goes too far the spine is of the future. Rosenberg's theory has been overthrown by Bardeen,* who has shown that the original position of the ilium is opposite the superior part of the lumbar region and that it travels tailwards. Having joined a vertebra at the fifth week, it never leaves it. At this early time the thoracic vertebrae are differentiated. The author 3 and Fischel* believe that numerical variation is the result of an error in segmentation. A want of development of the bodies, which may be only half the normal height, is found almost exclusively in the lumbar region. We have seen (apparently congenital) fusion of the lumbar bodies while all the arches were present, but three of them crowded together. The separation of the pedicles of the fifth lumbar from the body is a very rare anomaly among whites, but not among American aborigines. ARTICULATIONS OF THE VERTEBRAL COLUMN. The ligaments connecting the segments of the spine may be divided, according to the parts of the vertebrae which they vinite, into two groups : 1. Those connecting the Bodies of the Vertebrae ; 2. Those connecting the Laminae and the Processes. LIGAMENTS CONNECTING THE BODIES. Intervertebral Disks 5 (Figs. 162, 163). These form a series of fibro-carti- lages interposed between the bodies of the vertebrae, forming about one-fourth of the movable part of the spine and adding greatly to its strength. They are developed, like the bodies, around the notochord, persisting parts of this structure forming a central core to each disk. The outer part of the disks consists of oblique layers of fibres, slanting alternately in opposite directions, some almost horizontal, which hold the vertebral bodies firmly together ; the centre of the disks is occupied by a spare containing iluid in the meshes of a yellowish pulp. 6 This central core is strongly compressed, so as practically to be a resistant ball within the more yielding fibro- cartilaginous socket. The proportion of the disks to the vertebral bodies varies in the different parts of the spine. They are absolutely largest in the lumbar region, but relatively in the cervical. For many reasons it is difficult to reckon the per- 1 Morph. Jahrbuch, Bd. i. and xxvii. 4 Anatomische Hefte, No. 95, 1906. *Anat. Anzeiger, Bd. xxv., 1904, and American Journal of Anatomy, vol. iv., 1905. 'Ihvi-lit : Memoirs Boston Society of Nat. Hist., vol. v., 1901. 1 l MM.., .11 iM.iiiiiu^ Intervertcbralcs. '''Nucleus pulposus. LIGAMENTS OF THE SPINE. 133 Posterior at- lanto-axial ligament centage very accurately, and there is much variation. The following proportions are, therefore, only approximate. The disks form in the cervical region forty per cent. , in the thoracic, twenty per cent. , and in the lumbar, thirty-three per cent, of the length of the spine. Anterior and Posterior FIG. 162. Common Ligaments. The Odontoid process of axis Transverse ligament bodies are connected by short fibres surrounding the disks, and by long bands which are only partially separable from the general envelope. The an- terior common ligament 1 (Figs. 163, 165) begins at the axis and extends to the sacrum. It consists of shorter and longer fibres blending with the peri- osteum and springing from the edges of the vertebrae and from the disks, to end at similar points on the next vertebra, or on the second, third, fourth, or fifth. The borders are not sharply defined. The posterior common ligament' ( Fig. 164) is a much more distinct struc- ture. It arises from the back of the body of the axis, re- ceiving fibres from the occipito- axial ligament, and runs to the sacrum. It also is attached to the disks and the edges of the bodies, but possesses a dis- tinct margin, which, except in the neck, expands laterally into a series of points at the intervertebral disks. It stands well out from the middle of the bodies, bridging over the veins of the larger ones. Interspinous ligament Seventh cervi- cal spine Intervertebral foramen Lamina Ligamentum subflavum Supraspinous ligament LIGAMENTS CONNECT- ING THE LAMINAE AND THE PROCESSES. The articular processes (Fig. 165) are coated with hyaline articular cartilage and surrounded by loose capsules, with which, especially in the thorax, the ligamenta subflava are inseparably connected, pre- venting by their tension the occurrence of folds. The ligamenta subflava 3 ( Fig. 163) are elastic membranes of considerable strength connecting the laminae from the axis to the sacrum. They are particularly developed in the lumbar region. As just mentioned, they encroach on the side of the capsules towards the canal. They also extend a short distance under the spinous processes. The supraspinous ligament (Figs. 162, 163) extends as a well-marked cord 1 Lig. longitudinalc iinterius. - Liu Inngitudinalc postcrius. '' Ligg flava. Tenth tho-- racic ver- tebra Median section of upper half of spine. 134 HUMAN ANATOMY. along the tips of the spines from the last cervical to the sacrum. The interspinous ligaments are membranes connecting the spinous processes between the tips and the laminae, extending from the ligamenta subflava to the supraspinous ligament. FIG. 163. Tenth thoracic vertebra Ligamentum su.bflavum Intervertebral foramen First lumbar vertebra Posterior common ligament Intervertebral disk Anterior common ligament Fifth lumbar vertebra First sacral vertebra - Supraspinous ligament Fifth lumbar spine Median section of lower half of spim-. The ligamentum nuchae (Fig. 166) represents in the neck a modification of the two last-mentioned ligaments. It is a vertical curtain reaching from the exter- LIGAMENTS OF THE SPINE. 135 FIG. nal occipital protuberance to the spine of the muscles of the two sides. The free border is continuous with the supraspinous ligament, but, instead of touching the cervical spines, it lies in the superficial layer of muscles, and is rein- forced below by radiating fibres from each, of the spinous processes of the cervical region. It is inseparably blended with the origin of the trapezii and with the fasciae between the muscular layers, especially with that covering the semispinalis and the short suboccipital muscles. In the region of the axis it is a thick median membrane ; in the lower cervical region it is of little importance. In man it contains but a small proportion'of elas- tic fibres, in marked contrast to what is found in many quadrupeds in which the structure con- sists principally of elastic tissue, since in these animals the ligamentum nuchae forms an important organ for the support of the head at the end of the horizontal vertebral axis. The intertransverse ligaments (Fig. 162) are trifling collections of fibres between the transverse processes, although occasionally distinct round cords region. FIG. 165. Anterior occipito-atlantal ligament Mastoid process Lateral occipito-atlantal ligament Anterior tubercle of atlas seventh cervical, separating the Posterior common ligament Posterior surface of bodies of vertebrae shown after removal of arches by cutting through the pedicles. in the thoracic Atlanto-axial ligament and joint Anterior common ligament Anterior ligaments of upper end of spine. ARTICULATIONS OF THE OCCIPITAL BONE, THE ATLAS, AND THE AXIS. The arrangement here differs in some points considerably from that of the rest of the spine in order to provide for the security and the free movement of the head. The ligaments effecting this union consist of three groups : i. Those connecting the Atlas and the Axis, including the. Anterior Atlanto- Axial ; Transverse ; Posterior Atlanto-Axial ; Two Capsular. 1 3 6 HUMAN ANATOMY. 2. Those connecting the Occipital Bone and the Atlas, including the Anterior Occipito-Atlantal ; Posterior Occipito-Atlantal ; Accessory Occipito-Atlantal ; Two Capsular. 3. Those connecting the Occipital Bone and the Axis, including the Lateral Odontoid or Check ; Middle Odontoid ; Occipito- Axial. The important peculiarities are the odontoid and the transverse ligaments. The odontoid, or check ligaments 1 ( Fig. 168), are two strong, symmetrical bundles of fibres extending from the slanting surface on each side of the top of the odontoid process outward and a little upward to a roughness on the inner side of each occipital condyle. Some fibres pass directly across from one condyle to the FIG. 166. Ligamentutn nuchse Trapezius muscle Ligamentum nuchae Posterior occipitoatlantal ligament Posterior atlanto-axial ligament Ligaments of back of neck. other. These are occasionally collected into a distinct round, glistening bundle. The space above the odontoid process, between it and the basilar process, is oc- cupied by a mass of dense fibrous tissue reaching to the anterior occipito-atloid ligament, in the midst of which is a more or less distinct median band connecting these parts, the middle odontoid ligament. 2 A supra-odontoid bursa may be developed in this tissue. The transverse ligament 4 (Figs. 167, 168) of the atlas is a strong band passing between the tubercles on the inner side of each lateral mass of the atlas. It does not run straight, but curves backward around the odontoid, from which it is separated by a bursa. A band from the middle of the transverse ligament ; upward to the cerebral side of the basilar process, and another downward to the body of the axis, so* that the whole structure is called the cruciform ligament. ' s Trolard: Journ. tie 1'Anat. et tk- la Physio!., 1897. 1 I.iKK. aliiii.i. I. in. .i|>i< is di'iittv 4 l.ijj. I rarisvcrsum iitliintis. ' l.ij triu iiituni .itl.mtis. OCCIPITO-SPINAL LIGAMENTS. 137 Another bursa lies between the odontoid and the anterior arch of the atlas. The transverse ligament and the two check ligaments are in series with the interarticular ligaments of the heads of the ribs. The other ligaments of this region are in the main simple membranes connect- FIG. 167. Upper end of occipito-axial ligament Lateral odontoid ligament Occipito-atlantal joint Cruciform ligameht Atlas Atlanto-axial joint Axis ; Occipito-axial ligament, fused with dura, turned down Dura Back of occiput and arches removed ; occipito-axial ligament cut and turned down. ing neighboring parts. The anterior occipito-atlantal ligament l ( Fig. 165 ) extends between the front of the foramen magnum and the anterior, arch of the atlas ; the anterior atlanto-axial (Fig. 165) is in serial continuation with it. A distinct rounded, raised band, the accessory occipito-atlantal, passes in the median line from the under side of the occiput to the front tubercle of the atlas (Fig. 165), and thence to the body of the axis, where it joins the anterior common ligament of the spine. The occipito-axial ligament 2 {appa- ratus ligamentosus) (Fig. 167) descends in- side the spinal canal from the basilar process to the body of the axis, where it joins the posterior common ligament and completely conceals the odontoid process and its special ligaments. The posterior occipito-atlantal 3 and the posterior atlanto-axial ligaments 4 lie in the region of the arches (Fig. 166). The former extends between the posterior border removai e of mfddie C of transve?se fig of the foramen magnum and the arch of the P r cess is thrown strongly upward, atlas ; the latter between the arch of the atlas and that of the axis. These are in series with the ligamenta subflava, but differ from them in being non-elastic. In the former of these membranes there is an opening just behind the facets on the atlas for the condyles, bridged over by a band, for the entrance of the vertebral artery. FIG. 168. Front of foramen magnum Lateral odontoid ligament Bursa on back of odontoid =- Atlas Transverse liga- ment, cut Articular facet of axis 1 Mcmbrana atlantooccipitalis anterior. " Mcmbrana tcctoria. ;i Mcmbrana atlantooccipitalis posterior. 4 Membrana atlantoepistrophk-a. 133 HUMAN ANATOMY. Synovial joints, the shapes of which are described with the bones, exist be- tween the occipital bone and the atlas and between the atlas and the axis. The capsule of the upper joint is very thick, especially behind, where it is continuous with the posterior occipito-atloid ligament. The capsule surrounding the articular surfaces of the atlas and axis is strengthened posteriorly by a bundle running upward and outward from the axis. FIG. 169. rior tubercle of atlas cord Posterior bursa Trartsverse process of atlas tebral artery cut obliquely Apparatus ligamentosus Vertebral artery cut in transverse foramen r bursa Transverse ligament Anterior tubercle of atlas Transverse section of spine passing through atlas and odontoid process. THE SPINE AS A WHOLE. Anterior Aspect (Fig. 170). The bodies enlarge, in the main, regularly from above downward. This progression is interrupted only by a slight decrease from the first to the fourth thoracic. . In the cervical region the origin of the costal elements from the sides of the bodies gives the latter a false appearance of breadth. The middle of the thoracic region is particularly prominent in front, owing in part to the aortic depression on the left. A slight curve to the right in this region is generally seen ; it is probably attributable to this cause. Posterior Aspect (Fig. 170). A deep gutter extends on each side of the spinous processes, bounded externally in the neck and loins by the articular pro- cesses and in the back by the transverse. In the latter region the spines which are subcutaneous are often deflected from the median line, and may be arranged in zig- zag. The laminae completely close the spinal canal in the convex thoracic and sacral regions, while it is left open in the neck and loins, except during extension of the former. Lateral Aspect (Fig. 171). The profile view shows best of all the increase in the importance of the bodies from above downward, and coincidently with this the gradual moving backward of the intervertebral foramina. These increase greatly in size from the lower part of the thoracic region. The Curves. The curve of the spine is necessarily an arbitrary one, since it varies not only in individuals and according to age, sex, and occupation, but also with position and the time of day, being longer when lying than standing, and after a night's rest than after a day's work. The difference occasioned by position occurs especially in youth, when it may amount to half an inch or more. It is of little consequence after middle age. Bearing these variations in mind, the following guide to the curve, suggested by Humphry, may be accepted : a line dropped from the middle of the odontoid process passes through the middle of the body of the second thoracic, that of the twelfth thoracic, and the anterior inferior angle of the fifth lumbar. Henle divides the spine into four quarters ; and although this method has the defect of using the unreliable pelvic section, it very often proves remarkably correct. Thus, if we continue Humphry's line to the level of the tip of the coccyx, the middle point is opposite the eleventh thoracic, the end of the first quarter oppo- site the lower border of the third thoracic, and that of the third quarter opposite the lower edge of the fourth lumbar. The development of the curves can hardly be said to have begun at birth. At THE SPINE AS A WHOLE. Anterior FIG. 170. I. Cervical Posterior 139 I. Thoracic I. Lumbar Sacrum r '< - -2 o Coccyx Anterior and posterior views of adult spine. 140 HUMAN ANATOMY. FIG. 171. -I. Thoracic -I. Lumbar Sacral I. Coccygeal I.:iU i.il view of adult spine. that age the infant's spine presents in front one general concavity, slightly interrupted by the promontory of the sacrum. The liga- mentous spine, containing little bone, is ex- ceedingly flexible in any direction : the atlas can be made to touch the sacrum. It is more accurate to say that the general axis of the spine is a curved one than that any per- manent or fixed curve exists. The cervical curve appears as the infant grows strong enough to hold up its head ; it is never, properly speaking, consolidated (Syming- ton), since it is always obliterated by a change in the position of the head. The lumbar curve appears at from one to two years when the child begins to walk. The mechanism of its production is explained as follows. When an infant lies on its back the thighs are flexed and fall apart. If these be held together and pressed forcibly down, the lumbar region will spring upward, owing to the shortness of the ilio-femoral ligaments, which bend the pelvis and, indirectly, the spine. The psoas muscles, moreover, act directly on the spine. When the child first stands, the body is inclined forward ; when the muscles of the back straighten it, the lumbar curve is produced by the same mech- anism, since it is immaterial whether the legs are extended on the trunk or the trunk on the legs. How or when these curves be- come consolidated is very difficult to deter- mine. The influence of differences in thick- ness of the front and back of the various bodies and disks is inappreciable in the neck ; in the lower part of the back and in the first, and perhaps the second, lumbar vertebrae the height is greater behind. In the loins the third vertebra is much thicker in front and, likewise, the fourth and fifth in a less degree. The intervertebral disks are also much thicker in front. How soon actual difference in the diameters of the vertebrae appears is un- certain. A child of about three shows little of it, except in the last lumbar, and, accord- ing to Symington's plates, there is not much more difference at five or even thirteen years. It is certain that throughout the period of growth the curves can be nearly or quite effaced. The restraining influences are the gradually developing differences in the verte- brae and the disks, the effect of the. sternum and the ribs on the thoracic region, the pull of the elastic ligaments of the arches, and perhaps, above all, muscular tonieity. In the latter part of middle age the curves of the back and loins become consolidated; this is, however, distinctly a degenerative process. LENGTH OF PRESACRAL REGIONS. 141 Dimensions and Proportions. The length and the proportions of the dif- ferent presacral regions (including the intervertebral disks), measured along the an- terior surface of the spine, have, in fifty males and twenty-three female bodies, been found by us as stated below. We give for comparison Ravenel' s 1 and Aeby's 2 propor- tions combined. The former measured eleven and the latter eight spines of each sex. Cunningham's 3 proportions, from six male and five female spines, are also added. In the proportions, one hundred represents the total presacral length along the curves. ACTUAL LENGTH OF PRESACRAL REGIONS OF SPINE. Male. Centimetres. (Inches.) Neck 13.3 ( 5.25) Back 28.7 (11-31) Loins 19.9 ( 7.82) 61.9 (24.38) Female. Centimetres. (Inches.) I2.I ( 4-75) 26.5 (10.44) 57-3 _ (22.57) PROPORTIONS OF PRESACRAL REGIONS OF SPINE. Neck Back Loins (Dwight.) Male. (R. & A.) (Cunningham.) 21-5 46.3 21.7 46.7 21.8 46.5 32.2 31-4 31-7 IOO.O 99-8 IOO.O Female. (Dwight.) (R. & A.) (Cunningham.) 21.2 21.7 21.6 46.1 46.5 45.8 32.7 _32.4 32.8 IOO.O IOO.6 IOO.2 Thus, while it is true that the lumbar region is relatively longer in woman, the difference is trifling. ABSOLUTE AND RELATIVE LENGTH OF PRESACRAL REGIONS DURING GROWTH. AGE. OBSERVER. ABSOLUTE LENGTH. (In Millimetres.) RELATIVE LENGTH. (Total = loo.) Neck. Back. Loins. Total. Neck. Back. Loins. At birth Ravenel. Ravenel. Ravenel. Chipault. 4 Chipault. Ravenel. Aeby. Aeby. Dwight. Chipault. Chipault. Chipault. Chipault. Chipault. Ravenel. Aeby. Dwight. Aeby. Chipault. Symington. 5 Ravenel. Symington. Ravenel. Aeby. Symington. Dwight. Aeby. Aeby. Dwight. 50 40 40 40 42 50 52.5 53-5 61 60 69 67 62 68 70 79-5 78 79-9 81 80 80 80 85 9i 95 1 20 IOO 107.5 113 93 IOO 95 80 80 IOO 103 107 125 121 129 08 130 132 140 153-5 162 162 174 170 1 80 175 195 218.7 220 265 221.8 229.5 250 50 50 50 45 44 58 60 61 77 72 83 79 69 79 9 98 101 103.3 102.8 104 135 106 150 153-5 136 183 151 152-5 161 193 190 185 I6 5 1 66 208 215-5 221.5 263 253 281 264 261 279 300 331 34i 345-2 357-8 354 395 36i 430 463.2 45i 568 472.8 489-5 524 25-9 21 21.6 24.2 25-3 24 24-3 24.1 23.2 23-7 24-5 25-2 23-7 24-3 23-3 24 22-9 23.1 22.6 22.5 20.3 22.2 19.8 19.7 21-5 21. 1 21. 1 21-9 21-5 48.2 52.6 51-3 48.4 48.1 48.1 47-5 48.6 47-5 47-8 45-9 44-8 49-7 47-4 46.7 46.4 47-5 46.9 48.9 48 45-6 48-5 45-4 47.2 48.7 46.6 46.9 46.9 47-7 25-9 26.3 27 27.4 26.6 27-9 27.8 27-5 29.2 28.5 29.6 30 26.6 28.3 30 29.6 29.6 29-9 28.5 29.4 34-2 29-3 34-9 33-i 29.1 3 2 -2 3i-9 3i-i 30-7 .At birth ... At birth One month One month Three months Six months . . Six months ... Ten months One year boy One year boy One year and one month, boy . One and a half years, girl . . . One and a half years, boy . . Two years boy Three years girl .... Four and a half years, boy . . Five years boy . . . . Five years boy Six years boy Nine years girl Eleven years, boy Thirteen years, girl Fifteen years boy Sixteen years girl Sixteen years girl Seventeen years girl 1 Zeitschrift fiir Anat. und Entwicklng., 1876. 3 Cunningham : Memoirs, 1886. 6 The Anatomy of the Child. 2 Arch, fiir Anat. und Entwicklng., 1879. 4 Revue d' Orthopedic, 1895. 1 42 HUMAN ANATOMY. It appears from the above that in the adult the neck is a little more than one- fifth of the movable part of the spine and the loins a little less than one-third. In the young embryo these proportions are reversed, biit by the time of birth these two parts are nearly equal. Movements of the Head. Those between the occiput and atlas are almost wholly limited to flexion and extension, of which the latter is much the greater. This is in part due to the reception of the posterior pointed extremities of the articu- lar processes of the atlas into the inner parts of the posterior condyloid fossae. The anterior occipito-atlantal ligament and the odontoid ligaments are tense in extreme extension. In flexion the tip of the odontoid is very close to, if it does not touch, the basilar process. The range of both these motions is much increased by the participation of the cervical region. There may be a little lateral motion between the atlas and head, and there is some slight rotation. The great variation of the shape of the articular facets makes it clear that both the nature and extent of the motions must vary considerably. The joint between the atlas and axis is devoted almost wholly to rotation. The transverse ligament keeps the odontoid in place, and the very strong odontoid liga- ments check rotation alternately. The head is highest when directed straight forward, but the joints are in more perfect adaptation if one condyle be a little anterior to the other, and if the atlas be slightly rotated on the axis. This position, though entail- ing a slight loss of height, is the one naturally chosen, as that of greatest stability. Movements of the Spine. The very extensive range of motion of the whole spine is the sum of many small movements occurring at the intervertebral disks. The whole column is a flexible rod, but this conception is modified by the following peculiarities : ( i ) the motion is not equally distributed, owing to the vary- ing distances between the disks and the differences of thickness of the disks them- selves ; (2) the bodies, which form the essential part of the rod, are not circular, so that motion is easier in one direction than in another ; (3) the rod is not straight but curved ; (4) the kind of motion is influenced by the articular processes, and varies in the different regions. Other modifying circumstances exist, but these suf- fice to show that, while certain general principles may be laid down, an accurate analysis of the spinal movements is absolutely impossible. The incompressible semifluid centre of each disk has been compared to a ball on which the rest of the. disk plays. This would, therefore, be a universal joint were there no restraining apparatus. The motions are flexion and extension, i.e., angular movements on a transverse axis ; lateral motion, i.e. , the same on an antero-posterior axis, and rotation on a vertical axis. It is unlikely that any single one of these motions ever occurs without some mingling of another. Flexion and extension are greatest in the neck and loins. Extension is more free than flexion in the neck, where it is limited by the locking of the laminae, which, when the head is thrown as far back as possible, gives great rigidity to the neck. In the loins and in the region of the last two thoracic vertebrae flexion is the more exten- sive. Before the spine is consolidated, slight flexion is possible throughout the back, but extension is very quickly checked by the locking of the laminae and spines. Lateral motion is greatest in the neck, but it is considerable also in the back and loins. Such motion is always associated with rotation, which is most free in the neck, considerable in the back, and very slight, at most, in the loins. It is to be remembered that motions both in the antero-posterior and in the transverse plane are checked by the tension of the ligaments on the side of the body of the vertebra opposite to the direction of the motion, and also by the resistance to compression of that side of the intervertebral disk towards which the motion occurs. The liga- menta subflava, being elastic, tend continually to bring the bones back into position from the innumerable slight displacements to which they are subject. That this replacement is effected by a purely physical p'roperty of the tissue instead of by muscular action implies a great saving of energy. The amount of all motions, and of rotation in particular, decreases throughout life and varies much in individuals. According to Keen, the rotary motion between the atlas and the axis amounts to twenty-five degrees, that in the rest of the neck to forty-five degrees, and that of the thoracic and lumbar regions to about thirty degrees on each side. PRACTICAL CONSIDERATIONS: THE SPINE. 143 PRACTICAL CONSIDERATIONS. While the number of vertebrae in the neck is almost invariable in man (and indeed in all the mammalia except the sloth and the sea-cow), the length of the cervical region varies greatly in individuals. As it is apparently shortened during full inspiration and lengthened during full expiration, so an actual change in its length is associated with the types of thorax that correspond to these conditions. The long neck is therefore found in persons with chests that are flat above the mammae, with wide upper intercostal spaces and narrow lower ones, and with lack of prominence of the sternum. These conditions are often associated with phthisical tendencies. The short neck is found in persons with chests of the reverse type. Its theoretical association with apoplectic tendencies is very doubtful. The remaining variations both in the length and in the shape of the vertebral column are closely connected with corresponding variations in its curves. The normal curves of the spine are four : the cervical, thoracic, lumbar, and pelvic (or sacro-coccygeal). The cervical and lumbar are concave backward, the thoracic and pelvic convex backward (Fig. 171). These curves are produced and kept up partly by the twenty-three intervertebral disks. They are altered by disease. An additional curve not uncommon in absolutely healthy persons consists in a slight deflection of the thoracic spine to the right ; this asymmetry is usually ascribed to the greater use of the right arm, but it is due to the position of the heart and the aorta. All the vertebral bodies are composed of cancellous tissue, which is more spongy in direct proportion to the size of the vertebrae, and therefore is least so in the neck and most spongy in the lumbar region. This corresponds with the greater succu- lence and elasticity of the lower intervertebral disks and aids in minimizing the effect of jars and shocks such as are received in alighting from a height upon the feet, the lower portion of the column of course receiving the greater weight. If in such falls the calcaneum or tibia is broken, the spine usually escapes injury. If the lower extremity remains intact, the safety of the spine depends largely upon the elasticity given by its curves and by the disks. The fact that the bodies have to bear the chief strain of such shocks and of extreme flexion and extension, the most usual forms of spinal injury, serves, together with their comparative vascularity, to make them the seat of tuberculous infection when it invades the spine. Their spongy texture, once they are softened by inflam- mation, leads to their ready disintegration under the superincumbent weight. In the neck and in the loins the process may at first merely cause a straightening of the column, the normal curves being concave backward. In the thoracic region the most common situation it soon produces kyphosis, an exaggerated backward curve, the sharp projection of the spinous processes of the affected vertebrae causing it to be known as ' ' angular curvature. ' ' The abscesses which result from caries of the vertebrae are governed as to their position and course by the fasciae and muscles that surround them. They will, therefore, be described later (page 643). The suspension of the whole body from the chin and occiput separates the indi- vidual vertebrae so that they are held together mainly by their ligaments. This obviously relieves or removes the pressure of the superincumbent weight on the bodies of diseased vertebrae. The relief of pressure in cases of thoracic caries is continued by the use of appliances which transfer the weight of the head. and shoulders to the pelvis. The simplest of these is the plaster jacket. For cervical caries, the weight of the head is transferred to the trunk beneath the level of disease by means of an apparatus extending from above the head to a band (of leather or plaster) encircling the chest. In cases of kyphosis corrected by the method of "forcible straightening" it is obvious that a gap proportionate to the amount of bone which has previously been destroyed must be left between the bodies of the diseased vertebrae. The ultimate integrity of the spinal column will depend upon the extent and character of the ankylosis which takes place between the separated vertebrae. It is asserted (Calot) that such consolidation does occur between the bodies in moderately severe cases, and between the laminae, transverse processes, and spines in the more serious 144 . HUMAN ANATOMY. ones. It has been shown (Wullstein) that injury to the dura and cord and even fracture of the arches and processes are possible concomitants of forcible rectifica- tion of kyphosis. If the curve forward of the lumbar spine is exaggerated, constituting lordosis, it is usually compensatory, and is acquired in an effort to maintain the erect position, as in cases of high caries, great obesity, pregnancy, ascites, abdominal tumors, etc. Scoliosis or lateral curvature commonly results from faulty positions in young, undeveloped persons with weak muscles, as school-girls, who sit or stand in such atti- tudes that the muscles are relieved and the strain is borne by insensitive structures, like ligaments and fasciae. This results in a deflection of one part of the column generally the thoracic to one side, usually the right, and the formation of a compen- satory curve below, and occasionally of one above also. The bodies of the affected vertebrae are at the same time rotated, partly by the action of the slips of the longis- simus dorsi which are attached to the ribs near the angles and to the tips of the trans- verse processes (Fig. 520), so that in advanced cases the tips of the spinous pro- cesses of the affected segments turn towards the concavity of the curves, while the transverse processes of the vertebrae involved tend to lie in an antero-posterior plane and can often be felt projecting backward. A further explanation of the causes of the rotation may be found in the behavior of a straight flexible rod under similar conditions. Torsion results from any motion in which all particles of a straight flexible rod do not move in parallel columns. Therefore, if it be bent in two planes at the same time torsion must inevitably occur. The vertebral column being bent in the antero-posterior plane by a series of gentle curves, lateral bending must, therefore, inevitably lead to torsion, since it means bending in two planes. A little consideration of the relations of the spine to the ribs, scapula, and pelvis will show that lateral flexion and rotation cannot take place without causing (a) sep- aration of the ribs on the convex side ; () change in the costal angles, making the ribs more horizontal on the convex and more oblique on the opposite side ; (f) undue prominence of their angles on the convex side, the scapula being carried upon them so that it also is more prominent ; (a? ) diminution of the ilio-costal space on the concave side ; (e) elevation of the shoulder on the convex side ; (/") flatten- ing of the chest in front on the convex and undue prominence of the chest on the opposite side ; {g} projection of the ilium on the concave side. Lateral curvature with these secondary deformities may also be produced by unequal length of the lower limbs, one-sided muscular atrophy, hypertrophy, or spasm, sacro-iliac disease, empyema, and asymmetry of either the pelvis or the head. The latter factor is especially interesting from an anatomical stand-point. From what has been said (page 142) of the position of greatest stability of the joints be- tween the head and the atlas and the latter and the axis, it-is evident that the position of greatest ease is with the head slightly turned to one side, the condyles of the occiput not being in their best contact with the superior articular surfaces of the atlas when the head is held straight, but rather when the head is slightly twisted (Dwight). The effects of this are far-reaching. First, there is an instinctive effort to get the eyes on the same plane in looking forward, which is presumably the primary cause of the asymmetry of the face that is usually found. It is also easier to sypport the weight in standing chiefly on one leg, hence the other side of the pelvis is allowed to fall so that the lumbar region slants away from the supporting leg. This must be corrected by a lateral motion of the spine above it, and as this is not pure but mixed with rotation, there occurs a twist in the spine ; one shoulder is higher than the other as well as farther forward. In healthy persons such positions, if not maintained too long, do little harm ; but there is likely to be some spinal asymmetry in all, and there is the danger that it may become pronounced and fixed in the weak. Strains of the spine are most common in the cervical and lumbar regions : in the former because of the greater mobility of the articulation with the cranium, and in both because of their own mobility, the greatest degree of bending in an antero- posterior direction being possible in those two segments of the spine. The thoracic and pelvic curves are primary, form part of the walls of the thorax and pelvis, PRACTICAL CONSIDERATIONS: THE SPINE. 145 appear early, and are chiefly due to the shape of the vertebral bodies. The cervical and lumbar curves are secondary, develop after birth, and depend mainly on the shape of the disks. Greater mobility would naturally be expected under the latter circumstances. The close articulation between the separate vertebrae throughout the whole column, while it renders a slight degree of sprain not uncommon, tends at the same time to diffuse forces applied to the spine and to concentrate them within certain areas. These areas are the points at which fixed and movable portions of the spine join each other, as in the neighborhood of the atlanto-axial, the cervico- thoracic, and the dorso-lumbar regions. If the force is sufficient to cause an injury of greater severity than a sprain it is apt to be a dislocation or a fracture with dislocation at one or other of these localities. The latter accident is usually caused by extreme flexion of the spine, and of the three points mentioned is most often found in the segment including the lower two thoracic and the upper one or two lumbar vertebrae. This is due to the fact that ( i ) this segment has to bear almost as much weight as the lumbar spine, and yet its vertebrae are smaller and weaker. (2) The transverse processes are short, while the longer ones below, together with the crest of the ilium and the ribs above, give a powerful leverage to the muscles that move the region in question. (3) It is the region at which the most concave part of the thoracico-lumbar curve is found, making the " hollow of the back" and corresponding to the " waist" where the circumference of the trunk is smallest. (4) Its nearness to the middle of the column enables a greater length of leverage to be brought to bear against it than against any other part. (5) The different segments of the spine above it are com- paratively fixed (Humphry). These anatomical facts account for the frequency and severity of the injury known as ' ' fracture-dislocation' ' in this region as a result of extreme flexion. A view of the vertebral column from behind (Fig. 170) serves well to illustrate some of these points. Pure dislocations are rare, but are more frequent in the upper than in the lower part of the spine, because the bodies of the cervical vertebrae are small, and the interlocking of the articular processes is less firm than it is lower in the column. The vertebra most commonly dislocated is the fifth cervical, which might be expected from the fact that in the neck flexion and extension are freest between the third and sixth vertebrae. The dislocation is usually anterior, that is, the articular process of one vertebra slips forward and falls down on the pedicle of the vertebra below, resting in the intervertebral notch, this accident being rendered easy by the com- paratively horizontal position of the articular processes in the cervical region. Such dislocation is practically impossible in the thoracic or lumbar region without fracture, while fracture is comparatively rare in the cervical region. The lumen of the spinal canal may be but little, if at all, invaded. As to reduction, experiments show (Walton) that no moderate amount of exten- sion in a direct line would raise the displaced articular processes in the least degree. It was, however, found easy to unlock these processes by retro-lateral flexion, bend- ing the head towards the side to which the face was already turned, an inappreciable amount of force being necessary. Rotation into place completed the reduction. All pure dislocations are really subluxations, as without extensive fracture of the processes and great laceration of ligaments a complete separation of the articu- lar surfaces of two adjoining vertebrae is practically impossible. Pure fracture, not the result of a gunshot wound, is rare. If from flexion, the fracture involves the body ; if from direct violence, usually the laminae. These facts require no explanation. Dislocations and fractures of the upper two cervical vertebrae are especially serious on account of the proximity of the medulla and of their position above the roots of the phrenic nerve and of the nerves supplying the external muscles of respiration. If the accident is from overflexion, it may be a dislocation between the occiput and the atlas, as it is there that the movements of flexion and extension of the head take place. If it arises from extreme rotation, and especially if there is rupture of the check ligaments, it may be a dislocation of the atlas from the axis, as it is there that the rotary movements of the head occur. " A dumb person expresses ' yes' at the 146 HUMAN ANATOMY. occipito-atloid joint and 'no' at the atlo-axoid" (Owen). Painless nodding and rotation of the head aid, therefore, in the exclusion of the occipito-atlantal and atlanto-axial regions in obscure cases of high caries. The axis is more spongy than the atlas, and is weakest about one centimetre below the neck of the odontoid process, and this is one of the most frequent seats of fracture. In fracture-dislocations, which constitute from seventy to eighty per cent, of se- vere spinal injuries, the thoracico-lumbar region suffers most commonly for the reasons above stated. The almost vertical direction of the articular processes of the thoracic vertebrae causes them, when flexion is extreme, as when a weight has fallen on the back, to be frequently fractured, which, together with the accompanying crushing of the vertebral body and rupture of the supra- and interspinous ligaments and the ligamenta subflava, permits the immediate sliding forward of the vertebrae above the crushed one and the compression of the cord often its practical severance between the anterior edge of the posterior arch of the upper vertebra and the poste- rior edge of the body of the lower one. (For the resulting symptoms, see section on Nervous System, page 1053.) It may be mentioned here that the spinal nerves do not arise from the cord opposite the vertebrae after which they are named. Their regions of origin may briefly be stated as follows : 1 i ) Occiput to sixth cervical spine, eight cervical nerves. (2) Seventh cervical to fourth thoracic spine, upper six thoracic nerves. (3) Fifth to tenth thoracic spine, lower six thoracic nerves. (4) Eleventh and twelfth thoracic spines, five lumbar nerves. (5) First lumbar spine, five sacral nerves. Landmarks. To fix the limits of the spine in the living, draw a horizontal line from the anterior nasal spine to the lower edge of the external occipital pro- tuberance and another backward from the top of the symphysis pubis. Seen from the side, the top of the spine is in a line connecting the front of the lobe of each ear, passing behind the neck of the lower jaw. Frozen sections show that the front of the vertebral bodies is much nearer the centre of the body than one is prepared to expect. A vertical transverse, or frontal, plane through the thorax at its greatest breadth strikes the angle of the jaw, the front of the cervical convexity of the spine, and cuts the body of the fourth lumbar (Langer). The relations of the spine anteriorly are considered with the parts in front of it. The parts felt from the surface are the spinous processes and some few of the trans- verse ones. The line of the spines is a good example of the general rule that prominences on the skeleton lie in hollows in the flesh ; a deep furrow between the muscular masses marks their position. Palpation of the normal spine with the soft parts in place gives the following information. The spine of the second cervical can be felt by deep pressure a little below the occiput. The short spines of the succeeding vertebrae are made out with great difficulty. The fifth is longer than those just above it. The sixth is much longer and nearly as long as that of the seventh. The name vertebra prominent conferred on the seventh is misleading, for the spine of the first thoracic is the most prominent in this region. The third, fourth, and fifth cervical spines recede from the surface by reason of the forward curve of the cervical segment and on account of their shortness. This permits of free extension of the head and neck. The liga- mentum nuchae also prevents them from being felt distinctly. The sixth and seventh cervical and first thoracic are easily felt. The remainder, lying in the groove caused by the prominence of the erector spinae muscles, can usually be palpated without much difficulty. The relative sizes vary so much that it is not safe to identify any spine in this way. If the whole series from the second cannot be counted, it is best to start from the fourth lumbar, which is on a level with the highest points of the ilia. \\rt (bra- can also be identified from the lower rrbs by the relations of the heads to the bodies. The relations of the spinous processes to the body vary. Thus, in the cervical region the first five spines pass nearly straight backward. The sixth and seventh, like the upper two or three thoracic spines, descend a little, so that the tip is opposite LANDMARKS OF THE SPINE. FIG. 172. 147 Pons Anterior boundary of foramen magnum Superior laryngeal opening Cricoid cartilage Thyroid gland Upper border of manubrium Left innominate vein Innominate artery Ascending portion of aortic arch Upper border of body of sternum Section of right lung Right auricular appendage Right auricle Lower border of body of sternum Diaphragm Lower end of ensiforn, cartilage Liver Stomach Pancreas Duodenum Transverse colon Sigmoid flexure Bladder Symphysis pubis Medulla Posterior boundary of foramen magnum Odontoid process of axis (Esophagus Division of trachea Right pulmonary artery Left auricle Aorta End of abdominal aorta Left common iliac vein Sacrum Rectum Coccyx Seminal vesicles Prostate Median section of the body of a man aged twenty-one years. (After Braune.) I 4 8 HUMAN ANATOMY. to the body next below it. With the fourth or fifth thoracic they point much more strongly downward, so as to be opposite the disk below the succeeding body. This continues to the tenth, where they are opposite the body below. In the loins the spines have a considerable posterior surface, which is opposite the disk and the upper part of the body below it. The tips of the spines are not always in a straight line, but sometimes describe a zigzag. The transverse process of the atlas can be felt below the tip of the mastoid process, moving with the head when the latter is turned. The transverse processes below this are felt with great difficulty through the muscles of the side of t-he neck. Those of the back and loins are too thickly covered to be felt. The laminae are also thickly covered with muscles, so that the operation of laminectomy necessarily involves a deep wound, and in the thoracic region this difficulty is increased by the backward projection of the ribs. As landmarks the spines of the vertebrae, on account of their accessibility, have great value. These spines have the following relations. The fourth cervical spine corresponds to (i) the opening of the larynx; (2) the bifurcation of the carotid artery, and hence the point of origin of both the external and internal carotid arteries. The sixth cervical indicates the level of the carotid tubercle (transverse process of the sixth vertebra) and the entrance of the vertebral artery into the bony canal. The seventh cervical spine is a guide to ( i ) the lower border of the cricoid cartilage ; the lower opening of the larynx and the beginning of the trachea ; (2) the lower end of the pharynx and the upper opening of the oesophagus ; (3) the crossing of the omo-hyoid over the common carotid ; (4) the level of the apex of the lung and to the summit of the arch'of the subclavian artery. The fourth thoracic spine corresponds to the level at which the aorta reaches the spinal column, the trachea bifurcates, and posteriorly the apex of the lower lobe of the lung is found. It is on the same level as the root of the spine of the scapula. The seventh thoracic lies on a level with the inferior angle of the scapula. The eighth thoracic indicates the lower level of the heart and that of the central tendon of the diaphragm and the level at which the inferior vena cava passes through the diaphragm. The ninth tho- racic marks the level at which the upper edge of the spleen is found in health, and at which also the oesophagus pierces the diaphragm. The tenth thoracic corresponds to the lower edge of the lung, the spot at which the liver comes to the surface poste- riorly. The spines of the third to the ninth thoracic correspond to the heads of the fourth to the tenth ribs respectively. The eleventh thoracic is a guide to the normal situation of the lower border of the spleen and to the upper part of the kidney. The tivelfth thoracic marks the lower limit of the pleura, the passage of the aorta through the diaphragm, and the situation of the pyloric end of the stomach, and is on a level with the head of the last rib. The first lumbar spine is on the line of the renal arteries and the pelvis of the kidney. The second lumbar spine corre- sponds to (i) the termination of the duodenum and the commencement of the jejunum ; (2) the opening of the ductus communis choledochus into the intestine ; (3) the lower border of the kidney ; (4) the lower border of the pancreas ; (5) the upper end of the root of the mesentery ; (6) the point of origin of the superior mesenteric artery 5(7) the commencement of the thoracic duct ; (8) the commence- ment of the vena porta ; (9) the termination of the spinal cord and the origin of the cauda equina ; (10) the upper end of the receptaculum chyli. The third lumbar corresponds to the level of the umbilicus and the origin of the inferior mesenteric artery ; the fourth lumbar spine marks the point of bifurcation of the abdominal aorta into the two common iliac arteries, and lies on a level with the highest part of the ilium ; and, finally, the fifth lumbar spine is a little below the beginning of the inferior vena cava. Direct cocainization of the spinal cord has recently been employed in surgery in operations on the lower abdomen, pelvis, and lower extremities. The injection into the subarachnoid space surrounding the cord is made through the space between the fourth and fifth lumbar vertebrae. To find this space, draw a line connecting the highest points of the crest of the ilium posteriorly. This will pass through the spine of the fourth lumbar vertebra. The point for injection is one centimetre below and one centimetre to the outer side of the point at which the transverse line crosses the vertebral spine in the median line. THE THORAX. THE thorax is that part of the body-cavity separated by the diaphragm from the abdomen below, but without complete separation from the neck above. Its bony walls are formed behind by the thoracic vertebrae, at the sides by the ribs, and in front by their continuations, the costal cartilages, and the sternum. Kic;. 173. The bony thorax, anterior view. THE RIBS. The ribs, arranged as twelve pairs, are flat bars of bone, curved and twisted, which are attached behind to the spine and continued in front by the costal cartilages ; they form the greater part of the bony walls of the thorax. The first seven pairs, 149 150 HUMAN ANATOMY. exceptionally eight, reach the sternum through their cartilages ; hence they are called sternal ribs, 1 as distinguished from the remaining five pairs of asternal ribs. 2 Each cartilage of the next three joins that of the rib above it. The last two pairs have the cartilages ending free, and are termed floating ribs. Their complicated curves are best understood by studying them in place. Each rib (with certain exceptions to be detailed later) has an articular surface, the head, at the posterior end ; followed by a narrower neck, succeeded by an articular facet on the tubercle which rests on the transverse process of the vertebra. The first rib has an .upper and a lower surface, an outer and an inner border ; the second faces in a direction intermediate to this and the following, which have an outer and an inner surface, an upper and a lower border. They are placed obliquely, the front end being lower than the hind one. The outline of the ribs is irregular, so that their declination is not due wholly to their position, but in part also to their shape. Thus, one in the middle of the series slants a little downward as far as the tubercle, then declines more sharply to a roughness near the tubercle known as the angle, and thence more gradually to the end. The main curve of such a rib is backward, outward, and downward as far as the angle, which marks a rather sudden change of direction, the course changing to one forward, slightly outward, and downward, until, as it reaches the front of the chest, it runs forward, downward, and inward. The external surface is vertical at the back and side and slants slightly upward in front. Bearing the declination of the rib in mind, it is evident that to accomplish this the rib must be twisted on itself, otherwise the upper edge would project in front. FIG. 174. Articular facets for bodies of vertebrae . Articular facet on tubercle for transverse process Right fifth rib from behind. The head :i is an enlargement at the posterior end and on the outer surface, i.e., the one farthest from the cavity of the chest. It has an articular surface at the end facing inward and backward, divided into an upper and a lower facet, each for the body of a vertebra, by a transverse ridge, whence a ligament passes to the inter- vertebral disk. The lower facet is the larger, and is generally concave ; the upper is nearly plane. The head increases in size to the ninth rib and then lessens. The neck * is compressed from before backward, smooth in front and rough for ligaments behind. The upper aspect has a sharp border, the crest? for the superior costo-transverse ligament. The neck grows slightly longer in descending the series to the same level. The crest on the top of the neck is most developed in the sixth, seventh, and eighth ribs. The tubercle 6 is an elevation beyond the neck on the posterior surface of the rib, bearing internally a round articular surface facing backward and, in most cases, downward, to rest on the transverse process ; beyond the articular facet is a rough knob for the external costo-transverse ligament. The shaft 7 is smooth inside, the surface being continuous with that of the neck. The subcostal groove* for the intercostal vein is best marked in the middle ribs, begin- ning at the tubercle and running forward, growing fainter, along three-quarters of the rib, just under cover of the lower border. The outer surface is rather irregular. The angle !( at which the shaft changes its direction is marked by a rough line on the posterior surface, some distance beyond the tubercle, receiving muscles from the system of the erector spinae. The angle, which is not found in the first rib, is 1 Coatae verne. 2 Coatae spurine. ^Capitulum. * Colin in ; 'Crista colli. '"' Tulicrculuin "Corpus costac. * Snlcns coatalia. '' Angulu* costae. THE RIBS. very near (one centimetre beyond) the tubercle in the second ; it gradually recedes from the tubercle, being in the ninth and tenth about five centimetres distant. The angle is a little nearer in the eleventh, and is wanting in the last. The twist is greatest from the sixth to the ninth rib. Several of the upper ribs present near FIG. 175. Tuberosity Angle Head __, Articular facets for bodies of vertebrae A Inferior border (external intercostal) Right fifth rib: A, under surface; B, postero-lateral aspect. the middle a rough impression for a point of the serratus magnus. The upper border of the shaft is thick and rounded behind, but thin near the front. The lower border is sharp where it overhangs the subcostal groove ; less so in front. The anterior end of each rib is cupped to receive the costal cartilage. 152 HUMAN ANATOMY. The ribs increase in length from the first to the seventh or eighth, after which they decrease to the last, which is usually the shortest. The length of the last rib is, however, Very uncertain, varying from one centimetre to perhaps fifteen centime- tres or more. It often is longer than the first. The curve is comparatively regular in the- first rib, after which the difference between the two ends becomes more marked, the curve being very pronounced behind and less so in front. The curve is much less throughout in the lower ribs ; in fact, it decreases continually. The first rib is the broadest of all at the anterior end. There is a general, but not regular, increase from the second to the seventh rib, and a subsequent decrease. The fourth rib is relatively broad, the fifth narrow. 1 Exceptional Ribs. Certain of the ribs the first, second, tenth, eleventh, and twelfth present peculiarities which claim mention. FIG. 176. Cervicalis ascendens Serratus posticus superior External intercostal Second (limitation of sen atus itiff>iu Third (limitation of serratus magnus First and second ribs of right side, upper surface. The first rib is flat, not twisted, with an outer and an inner border. The head is small and has but one facet, resting as it does on the first thoracic vertebra. The neck is small and flat like the body. The tubercle is very prominent. The scalene tubercle is a very small but, from its relations, important elevation on the inner margin of the upper surface, at about the middle, for the insertion of the scalenus anticus. It separates two grooves crossing the bone for the subclavian artery and vein. The posterior one for the artery is the more marked. There is a rough impression behind the latter near the outer border for the scalenus medius. There is no subcostal groove. The second rib is intermediate in shape between the first and the rest. The roughness for the serratus magnus is very marked about the middle of the shaft. 1 Anderson : Journal of Anatomy and Physiology, vol. xviii., 1884. EXCEPTIONAL RIBS. 153 The tenth rib has usually only a single articular facet on the head ; it may or may not have a facet on the tubercle. The eleventh rib has a single articular facet on the head ; the tubercle is rudi- mentary and non-articular ; the angle and the subcostal groove are slightly marked. The twelfth rib has also a single articular facet on the head ; the tubercle is at most a faint roughness ; the angle and the subcostal groove are wanting. Development. The first centre for the shaft appears in the ninth week of foetal life, and spreads so rapidly that by the end of the fourth month the perma- nent proportion of bone has been formed. At an uncertain period, probably before puberty, a centre appears for the head and another, except in the last two or three ribs, for the tubercle ; these unite presumably by the twentieth year. Variations. The num- ber of ribs is often increased or FIG. diminished by one, generally by a change at the end of a re- gion, as explained in varia- tions of the spine (page 131). Cervical ribs occur by the cos- tal element of the seventh cer- vical becoming free. In the lowest and most common grade it consists of a head, a neck, a tubercle, and a rudimentary shaft one or two centimetres long, ending free. In the next grade it is longer, and its end, perhaps continued in cartilage, rests on the first rib. Some- times it fuses with the first rib, which then becomes bicipital, as is normal in certain whales. In the third grade, which is very uncommon, it resembles a small first rib, reaching the ster- num. A cervical rib has been seen more than once with the transverse foramen persisting. The explanation of this condition is given under ossification of the vertebrae. When a cervical rib reaches the sternum, the next rib is usually attached to the side of the manubrium by a broad cartilage, fusing with that of the cervical rib. The rib of the eighth vertebra has been seen to end like an ordinary second rib. It is also very rare to have only twelve pairs of ribs, of which the first is cervical. There may be thirteen ribs by the addition of the costal element of the first lumbar. This may be so small as to present no rib-like feature, or it may resemble an ordinary twelfth rib. In cases of an extra rib from this source the twelfth rib is usually uncom- monly long. Very rarely the first true thoracic rib is imperfect, being continued in ligament to the sternum, joining the shaft of the second rib, or even ending free. A bicipital rib may occur also by the fusion of the first thoracic with the second be- yond the tubercles. The resulting plate later subdivides, to be continued by two normal costal cartilages. Ribs sometimes divide, generally near the front. The parts formed by such cleavage are continued by costal cartilages which usually re- unite, so that a foramen is formed which is bounded laterally or externally by bone, mesially by cartilage. This occurs most commonly in the third and fourth ribs, espe- cially in the latter. THE COSTAL CARTILAGES. The costal cartilages ' continue the ribs, the first seven going directly to the ster- num, the next three each to the one above it, and the last two ending free. They grow longer from the first to the seventh, sometimes to the eighth. The last two 1 Cartilagines costalcs. Vertebral ends of tenth, eleventh, and twelfth ribs of right side from below. 154 HUMAN ANATOMY. cartilages are short and pointed. There is occasionally a projection downward from the fifth, at its most dependent point, which articulates with the sixth. Usually there is a similar projection on the latter for the seventh. The eighth, ninth, and FIG. 178. Interclavicular notch Posterior Anterior Surfaces of sternum with coossified ensiform cartilage. tenth cartilages have usually their chief connection with the one above, not through their ends, but through similar facets. As to direction : the first cartilage descends, the second is horizontal, the third rises very slightly, and the fourth is the first to fall and then rise. This change of direction occurs in each to the ninth or tenth carti- THE STERNUM. 155 lage, the falling portion becoming always relatively shorter and the rising longer. The last two cartilages continue the line of their ribs, having no rising portion. It is not uncommon to find eight cartilages joining the sternum. Tredgold found this condition in ten per cent, of white men. It is very much more frequent in negroes and in other dark FIG. 179. It is said to occur more often on the right side. Clavicular races. THE STERNUM. facet First rib-- cartilage Third' BODY FourtJ The adult sternum consists of three flat median plates, the two former being bone, the last largely car- tilage, namely, the presternum or manubrium, the mesosternum, gladiolus, or body, and the metasternum or ensiform cartilage. The manubrium 2 is broad in mammals having clavicles, to which it gives support at the upper angles. MANUBRIUM In man it is irregularly quadrilateral, with the angles cut off, broad above, narrower below, the greatest breadth equalling or exceeding the length. It is con- cave behind, but in front it is convex from side to side second and slightly concave from above down. The upper border is concave in the middle, forming the bottom of the interclavicular notch? On each side of this, in the place of a corner, is a concavity for the sternal end of the clavicle. This depression 4 is more on the top than on the side of the sternum, and usually encroaches more on the back of the bone. It is concave from within outward and may, or may not, be slightly con- cave from before backward. The facet is coated with articular cartilage. Just below the joint, the side of the manubrium projects outward to meet the cartilage of the first rib. This is the widest part of the first piece, the border then slanting inward to the lower angle, which also is cut off by a notch for the second costal cartilage, which is received between it and the body. The lower border, separated from the meso- sternum by fibro-cartilage, projects a little forward into a transverse ridge, always to be felt in life, which in- dicates the level of the second costal cartilage. The oblong body, or gladiolus, 5 ossifying origi- nally in four pieces, one above another, varies con- siderably in shape. It is generally slightly concave behind and nearly plane in front, but it may be convex or even concave. The greatest breadth is below the middle, whence the borders slant inward to the lower end, the narrowest part, where it joins the ensiform cartilage. The sides of the body present alternately smooth concavities opposite the spaces between the costal cartilages and articular facets for the latter. To understand the position of these articular facets, we must recall the composition of the mesosternum as consisting of four pieces. The second cartilage reaches the junction of the manubrium and the body ; the third, that of the first and second pieces of the body ; the fourth, that of the second and third pieces ; the fifth, that of the third and fourth pieces. The two remaining sternal ribs send their cartilages to this fourth piece of the body ; the sixth to the side, and the seventh to the lower angle, or even the 1 Journal of Anatomy and Physiology, vol. xxxi, 1897. Lamb : Nature, 1888. -Manubrium sterni, x Incisura jugularis. 4 Incisura clavicularis. ' Corpus stcrni. Fifth- Sixth- Seventh- Right side of sternum. 156 HUMAN ANATOMY. lower edge. The first and second pieces of the body are about equal in length ; the third is shorter, and the fourth still more so ; hence the fifth, sixth, and seventh cartilages end very close togetluT, especially the two last. The ensiform cartilage, 1 or xiphoid process, more or less bony in middle life, is a flat plate with a rounded end, not rarely bifid. It is fastened to the lower end of the body in such a way that their posterior surfaces are continuous, but that the ensiform, being thinner, is overlapped by the ends of the seventh cartilages ; its front is therefore at a deeper level than that of the body. The size and shape of the ensiform cartilage are very uncertain ; usually the tip projects somewhat forward. Differences due to Sex. The body of the male sternum is both absolutely and relatively longer than that of the female. This is in accordance with the greater development of the male thorax. The following table gives the actual size, accord- ing to the writer 2 and to Strauch. 3 DWIGHT. Men. Centimetres. Manubrium 5.37 Body 11.04 Total 16.41 STRAUCH. Women. Men. Women. Centimetres. Centimetres. Centimetres. 4-94 5-049 5-056 9.19 11.014 9-059 14.13 16.063 14.115 FIG. i 80. . Hyrtl gave a rule for determining the sex, that the manubrium of the female exceeds half the length of the body, while the latter in the male is at least twice as long as the manubrium. A study of 342 sterna, of which 222 were male and 120 female, confirmed Hyrtl's law for the mean ; since, however, approximately forty per cent, of the cases were exceptions, it is clearly worthless to determine the sex in any given case. Probably the law would be correct if we had to do only with well-formed sterna, but the body varies greatly. It is easy to recognize a typical male or female sternum. The former has a long, regular body, the lower pieces of which are well developed, sepa- rating the lower cartilages of the true ribs. The latter has a shorter and relatively broader body, the lower parts of which are poorly developed, so that the carti- lages are near together, and the seventh ones of the two sides almost, or quite, meet below the body in front of the base of the ensiform. Variations. The very rare cases of fissure of the sternum, and the not uncommon ones of perfora- tion in the median line, represent different degrees of arrest of development. The lower half of the sternum is sometimes imperfectly developed. We have de- scribed a case in a negress in which there was but little and irregular ossification below the fourth costal carti- lage. A very rare anomaly is that of the manubrium being prolonged to the insertion of the third costal cartilages, as occurs usually in the gibbons and occa- sionally in other anthropoid apes. The suprasternal bones, very rarely seen in the adult, are a pair of rounded bones compressed later- ally, about the size of peas, placed on the top of the manubrium at the posterior border just internal to the sterno-clavicular joint. They are presumably the tops of the lateral cartilaginous strips forming the sternum, in which they are normally lost. They are regarded as representing the episternum of lower vertebrates. * Journal of Anatomy aixl Physiology, vol. xxiv., 1890. " Inau.y;. Disscr., Porp.it, 1881. 1 rrmc-Miv xipliiiiilcii-. Foramen Sternum, showing foramen due to im- perfect union of lateral parts. DEVELOPMENT OF THE STERNUM. 157 FIG. 181. B Development and Subsequent Changes. The cartilaginous bars repre- senting the ribs in the early embryo end in front in a strip connecting them from the first to the ninth, which approaches its fellow above and recedes from it below. The union of these two strips, which begins above, forms the future sternum as far as the ensiform cartilage. Thus at this early stage there are nine sternal ribs. While the mesosternum is forming by the union of the lower part, a portion of the ninth strip separates itself from the rest to fuse with its fellow for the ensiform cartilage, and the remainder of the ninth joins the eighth, which, as a rule, itself later recedes from the sternum. The original cartilaginous strips having fused, points of ossification first appear in the manubrium about the sixth month of foetal life. There is one chief one and a varying number of small ones variously disposed. Sometimes it ossifies in a larger upper and a smaller lower piece. In the latter months, before birth, several points appear in the mesosternum. The first piece generally has a single centre, those below two in pairs. At birth one usually finds ossification begun in the first three pieces of the body. The centre for the last piece of the body begins to ossify at a very variable time. We have seen bone in it at thirteen days and have found none at seven years. Perhaps three years is not far from the average. The centre, or cen- tres, for this last piece of the body are placed in its upper part. Its cartilage is directly continuous with that of the ensiform, the line of demarcation being determined by the difference in thickness, the ensiform being thinner and continuing the plane of the posterior surface. Thus, the lower part of the last piece may continue cartilaginous for a con- siderable time. A centre in the ensiform is sometimes seen at three, but may not come for several years later. The four pieces of the meso- sternum join one another from be- low upward, the union being com- pleted on the posterior surface first. The process is extremely variable. The only points regarding which we are certain are that it is more rapid than is usually stated and that the body is almost always in one piece at twenty. The fourth piece of the body joins the third at about eight, the third joins the second at about fifteen, and the second unites with the first usually at eighteen or nineteen. We once saw all four pieces distinct at eighteen, but in one or two instances only have we found the body incomplete after twenty. The amount of bone in the ensiform at twenty is still small. The adult condition, except that the ensiform gradually becomes wholly bone, may persist to extreme old age. The ensiform often joins the body after middle age, rarely before thirty. The union of the manubrium and the body is rare, and appears to be the result of a con- stitutional tendency rather than of age, as in our observations we have repeatedly found it under fifty, and have seen all three pieces united at twenty-five. The different pieces are more apt to fuse in man than in woman. ARTICULATIONS OF THE THORAX. The joints uniting the bones taking part in the formation of the bony thorax constitute two general groups, the Anterior and the Posterior Thoracic Articula- tions. The former include the joints between the pieces of the sternum, those be- tween the sternum and the costal cartilages, and those between the costal cartilages ; the latter, or the costo-vertebral articulations, include those between the vertebrae and the ribs. Ossification of the sternum. A, at sixth foetal month ; a, centre for manubrium. B, at birth ; a, for manubrium ; b, c, d, for seg- ments of body. C, at about ten years ; a, manubrium ; b, c, d, seg- ments of body ; e, ensiform cartilage. 158 HUMAN ANATOMY. THE ANTERIOR THORACIC ARTICULATIONS. These include three sets : i. The Intersternal Joints, or those uniting the segments of the sternum ; FIG. 182. Sterno-clavicular joint Anterior intersternal ligament Chondro-sternal ligament Costo-xiphoid ligament Interchondral ligament The sternum and costal cartilages from before. 2. The Costo-Sternal Joints, or those uniting the ribs by means of their cartilaginous extensions with the sternum ; 3. The Interchondral Joints, or those uniting certain of the costal cartilages with one another. INTERSTITIAL ARTICULATIONS. 159 THE INTERSTERNAL JOINTS. While the manubrium and the four pieces of the body, or sternebrse, are still separate ossifications in a common strip of cartilage, the structure is greatly strength- FIG. 183. First rib. MANUBRIUM Interarticular ligament Chondro-sternal joint BODY Interchondral joint ENSIFORM CARTILAGE Interchondral ligament Longitudinal section through sternum and costal cartilages. ened by the thick periosteum, reinforced by the radiating bands from the costal joints and longitudinal fibres before and behind. When the body has become one piece it is separated from the manubrium by the persisting cartilaginous strip. The 160 HUMAN ANATOMY. strengthening bands require no further description. A cavity is often found in the cartilage, making a typical half-joint. At what time it appears is unknown. Some- times it is so developed that the joint is practically a true one, with articular carti- lage ; this exceptional arrangement is more common in women than in men, being especially adapted to the female type of respiration. The cartilage persisting between body and ensiform is strengthened in a similar manner. A cavity rarely occurs in the cartilage, which, on the contrary, often undergoes ossification. THE COSTO-STERNAL JOINTS. The first costal cartilage joins directly, without interruption, the lateral expan- sion of the sternum ; the following costal cartilages articulate at the points already mentioned by synovial joints. Those that come between different sternebrae that is, from the second to the fifth often have the joint subdivided by a band into an upper and a lower half. This is usual in the joint of the second cartilage ; progres- sively rare as we descend. The sixth and seventh cartilages frequently have no true joint. 1 Each of these joints is enclosed by a capsule, the front and back fibres of which radiate over the sternum. THE INTERCHONDRAL JOINTS. The seventh, eighth, ninth, and tenth costal cartilages have each an articulation by a true joint on the projections above described with the one above it. There is a connection between the fifth and sixth cartilages ; usually on the right, very frequently on the left. 2 This is, as a rule, also a true joint, but the cartilages may be merely bound together by bands of fibres. The joint on the right side is almost always a true one. The ends of the eighth, ninth, and tenth cartilages are joined by fibrous tissue to the cartilage above. The costo-xiphoid ligament is a band extending from either side of the base of the ensiform to the lower border and, perhaps, the front of the seventh cartilage near its end. THE COSTO-VERTEBRAL ARTICULATIONS. The joints between the ribs and the spine are in two series : an inner, or Costo- Central, between the heads of the ribs and the bodies of the vertebrae ; an outer, or Costo- Transverse, between the tubercles and the transverse processes. The Costo-Central Joints. The head of the rib is received in a hollow articular fossa formed by a part of two bodies and the disk between them. Although as a whole concave, it may in a typical case be further analyzed. The lower half of the socket is convex from above downward, fitting into the hollow at the lower part of the joint of the rib ; the upper part is about plane, looking downward and out- ward, with the upper border considerably overhanging the joint. These two facets have each a synovial capsule and are separated by an inten>ertebral ligament? a band running from the ridge on the head of the rib to the posterior part of the inter- vertebral disk. In the foetus before term it extends across the back of the disk the head of the opposite rib. The front of the capsules is strengthened by the anterior costo-rcrfcbral ligament, ' which is a series of radiating fibres from the head to both vertebrae and the interven- ing disk, not clearly separable into three bands. These stellate ligaments (Fig. 184) are least developed in the upper part of the thorax. The strongest collection of fibres is to the lower vertebra. The joint of the first and last two ribs is not sub- divided ; that of the tenth is uncertain. Strong fibres pass from the head of the first rib to the seventh cervical vertebra. Few or no fibres from the last rib reach the body of the eleventh thoracic. The lower fibres are made tense when the rib is raised and the upper when it is depressed. The Costo-Transverse Joints. The articular surfaces <>f the tubercles, 'Musgrove: Journal of Anatomy and Physiology, vol. xxvii., 1893. 2 Fawcett: Anat. Anzeiger, Ikl. xv. Bardeleben : ibid. 'tig- cnpltull costne intcrartirul.-irc. ' I. in. rapitnli costnc rndlatum. COSTO-TRANSVERSE ARTICULATIONS. 161 convex vertically, are received into the hollows on the facets of the transverse pro- cesses. The cavities are deepest in the upper part of the thoracic region, but the facet on the first transverse process is nearly plane. In the lower part of the region FIG. 184. VII rib. Superior costo-trans- verse ligament VIII ri Posterior costo-trans- verse ligament IX rib Intervertebral foramen Upper part of stellate ligament Lower part of same Body of ninth thoracic vertebra Ligaments uniting ribs with spine, from before. these cavities are smaller and less concave, allowing freer motion. There is none for the twelfth rib, and but a poor one, if any, for the eleventh. There are three costo-transverse ligaments : the posterior, the middle, and the siiperior. The pos- FIG. 185. Transverse process Lamina of vertebra above of vertebra below- Middle costo- transverse liga- ment Posterior costo- transverse ligament Costo-transverse joint Middle costo-trans- verse ligament Costo-vertebral joint Interarticular liga- ment Intervertebral disk Transverse section through intervertebral disk and ribs. terior 1 are strong bands running outward from the tips of the transverse processes to the rough part of the tubercle beyond the joint. The middle * are strong short fibres connecting the front of the transverse process and the back of the neck of the 1 Lig. costotransvcrsarium posterius. - Lig. colli costae. 162 HUMAN ANATOMY. rib between the head and the tubercle. Those for the last two ribs are small, that for the twelfth springing from the accessory tubercle. The superior costo-transverse ligaments ' are thin bands, passing downward and a little inward from the under side of the transverse processes to the crest on the upper edge of the neck of the rib below. Those of the first and last two ribs are of little account. This band becomes tense when the rib is depressed and carried inward ; the inner fibres are tense when the rib is raised. The outer fibres fuse with the front surface of the posterior inter- costal aponeurosis. Weaker and inconstant bands of the same general direction are described behind these. The fibres of the aponeurosis are particularly strong between the last two ribs. A special band of the same series runs from the transverse process of the first lumbar upward and outward to the last rib. The movements of the ribs are described with those of the thorax (page 165). THE THORAX AS A WHOLE. The thorax is a cage with movable walls capable of expansion. In shape it is an irregular truncated cone, much deeper behind than in front and broader from side to side than from before backward. The thoracic vertebrae form the posterior Tubercle Lamina of VII thoracic vertebra Middle cost o-trans verse ligament Posterior costo-transverse, ligament Superior costo-transverse ligament Ligamentum subflavum Intertransverse ligament '' VII thoracic rib VIII rib IX rib Ligaments uniting ribs with spine, from behind. boundary ; the sternum, including the very beginning of the ensiform cartilage, th anterior. The inlet, or upper boundary, is an imaginary plane slanting downward and forward from the top of the first thoracic vertebra to that of the sternum, and bounded laterally by the inner borders of the first rib. The inferior boundary, made by the diaphragm, does not exist in the skeleton. Suffice it to say that the dome- like disposition of the diaphragm makes the abdomen much larger and the thorax much smaller than one would expect from the skeleton alone. The thorax of the living presents a fairly well-defined posterior surface, while the lateral ones pass in- sensibly into the anterior ; the upper part is hidden by the shoulder-girdle and arm. The line of the angles of the ribs marks the limits of the back and sides. The inside of the thorax is heart-shaped in horizontal section. The spine projects into it behind, and the ribs recede from this on either side. As the bodies of the vertebra are larger in the lower part, the projection into the thorax is greater : but as the area of the section is much larger, the effect is less striking. The distance from front to 1 Lig. costotninsM-i-.ni iiim iintcrlus. THE THORAX AS A WHOLE. 163 back in the median line is least at the top. It increases at once, owing to the back- ward bend of the spine and the forward slant of the sternum, reaching the maxi- mum at about the middle of the thorax. It decreases slightly below, owing to the forward sweep of the spine, but the position of the lower end of the sternum is so uncertain that this is very variable. The breadth of the thorax increases very rapidly, reaching nearly the maximum where the third rib crosses the axillary line. Below this it increases a little, being greatest where the fifth rib crosses the same The bony thorax, lateral view. line. It then continues very nearly the same with some slight diminution below. The greatest length of the thoracic framework is in the axillary line, the lowest point being the cartilage of the tenth or eleventh rib, which in the male may nearly reach the crest of the ilium. The downward slant of the ribs and the rise of most of the cartilages make the study of horizontal sections at first very confusing. The relations at certain levels must be somewhat conventional, for the variations are very great, depending on figure, age, health, position, and the stage of the respiratory movements. Two levels must be taken as standards, subject to these corrections. 164 HUMAN ANATOMY. The top of the sternum is on a level with the disk between the second and third thoracic vertebrae ; the junction of manubrium and body of sternum is on a level FIG. 188. FIG. 189. Transverse section through thorax at level of third thoracic vertebra. (Sraune.) Transverse section at level of fourth thoracic vertebra. (Braune.) "0 -0 Transverse section at level of eighth thoracic vertebra. (Braune.) with the top of the fifth thoracic vertebra. Less accurate, but still useful, is a third level : the lower end of the body of the sternum is opposite the ninth thoracic vertebra. Accompanying diagrams, FIG. 190. taken from Braune, show the varia- C~~_J3 tions of size, form, and relations at different levels (Figs. 188 to 191). The breadth of the intercostal spaces is very different in diverse parts. Between the tubercles and angles it is pretty nearly the same Q 5 throughout, butthelasttwo spaces are a little broader. The first two spaces are much the broader at the sides and in front. They are broad near the sternum as far down as the fifth cartilage. At the sides the ribs are very close together, from the fourth to the ninth often almost in contact. The lowest spaces are again broader. The Thorax in Infancy and Childhood. At birth the thorax is relatively insignificant. The sternum is small and undeveloped in the lower part. The ribs are more horizontal. The top of the sternum is opposite the body FIG. 191. of the first thoracic vertebra. In 7 the course of the first year it lies opposite the upper part of the second, and at five or six has reached its definite level opposite the disk between the second and third thoracic vertebrae. The lower part of the sternum is undeveloped, and the ribs do not fall so low at the sides. The want of breadth is very striking, while in the adult, throughout the chest below the level of the second costal cartilage, the antero-posterior diameter is to the transverse as i to 2*4, or as i to 3 ; at birth it is as 2 to 3. We have found it at probably three years as i to 2 ; at five or six the thorax has nearly reached its permanent shape. Differences due to Sex. The whole structure is lighter in women, but the 'i;;i!is. - I'rotuheriintin occipital)* extcrnn. "Linen rm.li.u- superior. * Linen nuchne supremo. DEVELOPMENT OF THE OCCIPITAL BONE. 175 FIG. 194. Superior median fissure the external occipital crest? runs from the protuberance to the foramen magnum. Above the middle of this crest the inferior curved line' 1 leaves it to extend outward and downward to the border of the bone. The inner part of this line is rough, the outer indistinct. Below this line there is usually a depression on either side of the crest. The internal surface of the squamous portion is divided into four depressions orfosst? ; the upper two lodge the occipital lobes of the cerebrum and the lower two the lateral lobes of the cerebellum. Below the middle is the internal occipital pro- tuberance? approximately opposite to the outer. A ridge runs from the apex of the bone to the protuberance, and is continued as the internal occipital crest* to the foramen magnum. Very often the second part of this ridge divides shortly after its origin, so as to enclose a depression, the vermian fossa, so called because it is below the middle lobe, or vermis, of the cerebellum. A ridge runs transversely from the protuberance to the lateral angle of the bone. The superior vertical ridge may be grooved for the superior longitudinal sinus and the transverse ridge for the lateral sinus. More frequently the longitudinal sinus lies to one side of the vertical ridge and is continued into one of the lateral ones, much larger than its fellow, and usually the right, which lies above the transverse ridge, and shows in the bone no communication with the smaller, which lies in or above the other ridge. There are many variations in this arrangement, of which the rarest is a symmetrical course and division of the supe- rior groove. A single or a bifur- cated groove is sometimes found on the internal crest. Development. Four cen- tres appear in the cartilage around the foramen magnum about the eighth week of fcetal life : one for the basilar, one for each exoccipi- tal, and one (or more probably a pair that speedily fuse) for the lower part of the squamous por- tion, the siip r a- occipital. A week or so later two nuclei appear in the membrane above the latter, from which a strip of bone de- velops which soon joins it. From this upper ossification, the supe- rior occipital, is developed all the upper part of the squamous por- tion, including the external occipital protuberance and the superior curved line. Occasionally still another nucleus appears on each side, anterior and external to the preceding, which probably accounts for certain separate ossifications often found in the lambdoidal suture. The squamous part shows a median cleft above, which quickly disappears, two lateral ones between the ossifications, which persist till birth, and a notch at the posterior border of the foramen magnum. The squa- mous portion joins the exoccipitals in the course of the second or third year. The latter begin to unite with the basilar a year or so later. None of these sutures, es- pecially the latter, is completely closed before the seventh year, or even later. The front parts of the condyles are formed from the basilar, which joins the ex- occipitals at the anterior condyloid foramina. Separate ossifications, large Woimian bones, 6 are found in the suture between the squamous portion and the parietals. Sometimes there is a large median triangular one which is interpreted as the result of a want of union of the usual superior centre of the squamous portion, and said to 5 Consult Stieda : Anatomische Hefte, iv., 1892, and Debirre : Journ. de 1'Anat. et de la Phys., 1895. 1 Linia nuchae raediana. ~ L. nuchae inferior. 3 Protub. occip. interna. 4 Crista occipitalis interna. C 0ssa suturarum. superior oc- cipital Squamous por- tion Fissure be- tween upper and lower portions Supra-occipital Exoccipital Basi-occipital Posterior condyloid foramen Occipital bone at birth, from before. 7 6 HUMAN ANATOMY. be the homologue of the interparietal bone. This interpretation is inconsistent with the history of ossification. Kerkring has described an occasional triangular minute piece of bone which appears during the fifth month in the notch at the back of the foramen magnum, and is fused before birth. We have specimens which imply that it is, or may be, originally double. Improved methods of investigation will prob- ably' show that this bone is not uncommon. The cerebral side of the basilar is fused with the sphenoid by seventeen ; the lower side unites later, probably before twenty. THE TEMPORAL BONE. The plan of the organ of hearing must be known to understand the temporal bone. 1 The external ear, besides the auricle, consists of a cartilaginous and bony tube, the external auditory meatus* leading to the membrane of the tympanum which closes it. The middle ear, the cavity of the tympanum, is a space internal to the FIG. 195. SQUAMOUS PORTION Supramastoid crest Occipitahs Spina suprameatum Splenins capitii Squamo-mastoid suture Sterno-mastoid Mastoid foramen Auricularis posterio Zygoma Masseter Anterior root of zygoma Glenoid fossa APEX OF PETROUS PORTION Glaserian fissure Trachelo-mastoid MASTOID PORTION' Tympano-mastoid fissure Mastoid process / ; External auditory meatus / TYMPANIC PORTION Vaginal process 'Stylo-glossus ' Stylo-hyoid Styloid process Right temporal hone, external aspect. membrane, opening through the Eustachian tube into the throat, and communicating behind with cavities in the bone. It is lined with mucous membrane and is crossed by a chain of small bones, the car ossicles, the embryological importance of which is explained elsewhere. The internal ear is a complicated system of cavities in the substance of the bone containing the organ of hearing connected with the brain by the auditory nerve, which leaves the bone through a canal, the internal auditory meatus. Development shows that the bone consists of the following three parts. ( i ") The petro-mastoid, the petrous part of which is first found surrounding the special apparatus of the organ of hearing, constituting the internal ear, while the mastoid process is a much later outgrowth. (2) The tympanic portion, which at birth is a ring, incomplete above, encloses the membrane of the tympanum as a frame holds a glass. This ring grows out later into a cylinder, still open above, which forms the external auditory meatus. Not all its growth, however, is outward, since a part 1 Os lemporalc. '-' Meatus acuaticus externus THE TEMPORAL BONE. 177 expands forward and deeper than the original ring, making the front part of the tympanic plate, bounding the cavity of the tympanum and the Eustachian tube externally. The tympanic cavity, or the middle ear, lies between the petro-mastoid and the tympanic portion, the roof and floor being developed from the former. (3) The squamou s portion is external and above. It forms a part of the side of the skull, the roof of the external meatus where the tympanic portion is deficient, the articulating surface for the jaw, and a part of the mastoid process. There is also the long, slender styloid process, which is a part of the hyoid bar of the second visceral arch of the embryo. It begins as an ossification of a distinct piece of cartilage, but joins the petro-mastoid. The following description is that of the adult bone. The Squamous Portion. 1 Most of this is a thin vertical layer forming part of the wall of the skull, joined below by a horizontal one which forms a small part of the base of the skull, the articulating surface for the jaw, and the roof of the external FIG. 196. Eminentia articularis Zygoma Glenoid fossa Postglenoid tubercle Fissure of Glaser Tympanic plate External auditory meatus Eustachian tube Carotid canal Cochlea Semicircular canal Facial canal Antrum Groove for lateral sinus Horizontal section through right temporal bone, seen from below. auditory meatus. The edge of the vertical part is convex except below. The upper and posterior borders overlap the parietal bone by a broad bevelled surface. The anterior border joins the great wing of the sphenoid, overlapping above and over- lapped below, where it passes into the horizontal part. The posterior angle of the vertical portion sends downward the postauditory process, from which the upper part of the mastoid, including some of the mastoid cells, is developed. The squamo- mastoid siiture, separating this from the mastoid portion, is usually lost in the second year. When it persists, it shows that the anterior portion of the mastoid down to the lower border of the external meatus, or even lower, is formed from the squamosal. Its surface is smoother than that of the mastoid proper. A small, particularly smooth, but inconstant patch situated on the level of the upper part of the meatus, one centimetre or more behind it, marks the position of the antrum. The thick- ness of the bone at this place, which is that of note-paper in the infant reaches 1 Pars squamosa. 12 I 7 8 IK MAN ANATOMY. six millimetres in the adult. A small, sharp prominence, the spina suprameatum , is found just behind the upper part of the meatus. It is an important landmark in the surgery of the region. Just posterior to it is usually a minute venous foramen. The inner side of the squamous portion, besides the large bevelled articular surface, presents a smooth one, forming part of the wall and floor of the cranial cavity. This is separated from the petrous portion by the petro- squamous suture, which is closed early. Two grooves for branches of the middle meningeal artery diverge from its lower border, one running upward and the other backward. The front of the hori- zontal part forming the floor is rough and thick, joining the great wing of the sphenoid. The zygomatic process J projects forward from the outer surface of the squamosal to complete the zygomatic arch with the malar, which it joins by a serrated end. The free part has an external and an internal surface, a rounded bor- der below and a sharp edge above. The latter, which receives the insertion of the temporal fascia, can be followed back to the origin of the process. The zygoma has two roots. The posterior root passes directly backward above the auditory FIG. 197. SQUAMOUS PORTION Zygoma Groove for meningeal artery Internal auditory meatus Carotid canal PETROUS PORTION , Styloid process Aquaeductus ves- tibuli Groove for lateral sinus MASTOID PORTION Aquaeductus cochleae Right temporal bone, internal aspect. meatus, crosses the squamous portion above the postauditory process, and, curving slightly upward, is lost at the notch between the squamous and mastoid portions. Its hind part is the supramastoid crest, which joins the inferior temporal ridge on the parietal. The anterior root bends sharply inward. It is grooved above for the passage of the fibres of the temporal muscle. Its lower surface forms a semi-cylin- drical transverse elevation, the cniinen/ia articular is? the front part of the articular cavity of the lower jaw. Near its outer end is a tubercle for the external lak-ral ligament. Just in front of the auditory meatus, on the under side of the bone, is the smaller postgUnoid tubercle, sometimes described as a third root. Tlu- glcnoid fossa'' is a deep hollow on the under side of the squamous portion, with its greatest diameter nearly transverse, but passing somewhat forward and outward, bounded externally by the posterior root of the zygoma ; behind, by the fissure of Closer* which separates it from the tympanic portion ; and extends forward and inward to meet the inner end of the eminentia articularis. Both gk-noid fossa and articular eminence are covered with cartilage. The bone separating the glenoid fossa from 1 Procesau* zygnmatlcos. "Tuberculum nrticulnre. ''Fossa innndilmlnris. ' Flssurn pctrntympnnlca. THE TEMPORAL BONE. 179 the interior of the cranium is very thin. Behind the glenoid fossa the horizontal part of the squamosal forms the roof of the external auditory meatus. The Tympanic Portion. 1 The tympanic portion of the temporal bone appears as a trumpet-shaped layer of bone, forming all but the roof of the external auditory meatus. Its edge is thin in front, thick below, and very thin behind, where it curls up before the mastoid to meet the postauricular process of the squamosal. It is separated from the mastoid by the minute tympano-mastoid fissure. The ante- rior part of the tympanic portion, called the tympanic plate, runs obliquely forward, concealing the petrosal. It is separated from the glenoid fossa and from the thick anterior edge of the squamosal by the fissure of Glaser, which opens into the tym- panic cavity. The outer end of the fissure is closed ; the inner part is double, since a thin piece of the petrous, the tegmen tympani, bends down between the squamous and tympanic portions. The lower edge of the tympanic plate ends free. A part covering the base of the styloid process is the vaginal process," 1 which sometimes splits to enclose it. FIG. 198. SQUAMOUS PORTION Eustachiantube Carotid canal Aquaeductus cochleae PETRO-MASTOID PORTION Jugular fossa Joining occipital Zygoma Articular eminence Glenoid fossa Tegmen tympani Glaserian fissure TYMPANIC PORTION Styloid process Stylo-mastoid foramen Mastoid process 1 Digastric groove Occipital groove Right temporal bone from below. The Petro-Mastoid Portion. 1 ' This part of the temporal bone may for convenience of description be subdivided into the mastoid and the petrous. The mastoid subdivision forms a part of the wall of the skull behind the tympanic. It is prolonged downward into a nipple-shaped process, the outside of which is rough and slightly prominent. On its lower surface, under cover of the apex, is the digastric groove^ for the origin of the posterior belly of the digastric muscle. Just internal to this, at the very edge of the bone, is the much smaller occipital groove for the occipital artery. The ridge between the two may be developed into a para- mastoid process. The greater part of the internal surface is occupied by a broad and deep groove? running obliquely downward, forward, and inward for the lateral sinus on its way to the jugular foramen. The direction of this groove is very uncertain. Sometimes it descends gradually ; at others it turns far forward and descends nearly vertically. In the latter case it approaches closer than otherwise to the outer wall of the skull, but the distance in all cases is very variable (Figs. 199, 200). It may be only a few millimetres. As it descends it reaches the inner side of the antrum and the mastoid cells. It is separated from the antrum by a plate some six 1 Pars tympanica. - Vagina processus stytoldeus. ;1 Pars petrosa ct mastoidea. 4 Incisura mastoidea. ; 'Sulcus sigmoideus. i8o HUMAN ANATOMY. millimetres thick in early childhood, and from the antrum or upper mastoid cells by a very thin one in adult life. 1 Behind the groove a small, smooth surface forms a part of the cerebellar fossa. FIG. 199. A B Carotid canal Tympanic cavity Jugular fossa Facial canal External auditory meatus Groove for lateral sinus Tympanic cavity Facial canal External auditory meatus Groove for lateral sinus Mastoid canal U^ Horizontal sections through a right temporal bone with slight development of the mastoid cells. A, just above the floor of the external auditory meatus ; B, near the roof of the same canal. FIG. 200. Tympanic cavity Similar sections of a right temporal l>one with considerable development t tin- mastoid cells and oonsequ removal of the lateral sinus from the surface. A small canal, the mastoid foramen* transmitting a vein, runs from the sinus to the outside of the bone, which it sometimes reaches as far back as the suture between 'Clarke: Journal of Anatomy and Physiology, vol. \\vii, 1893. "Foramen mnstnidcnui. THE TEMPORAL BONE. 181 Facial canal Crista falci- form is Tractus spi- ralis ^-r-Area cribrosa superior r| Cut wall of in- f '"AiJ ternal meatus fe^ - Area cribrosa y media -Foramen singu- lare Bottom of right internal auditory meatus. X 5. the temporal and the occipital. The interior of the mastoid process contains spaces, the mastoid cells, to be described later. The size and shape of the mastoid process are very variable. The rough upper border of the mastoid subdivision forms an entering angle with the squamosal, into which fits a sharp point from the lower bor- der of the parietal, which rests on it above. Behind and below the FIG. 201. mastoid joins the occipital bone. The petrous subdivision is an elongated pyramid running for- ward and inward, presenting four surfaces (besides the base covered by the mastoid), four borders, and an apex. The surfaces are the supe- rior, posterior, inferior, and anterior. The superior surface slants forward and downward in the floor of the middle cerebral fossa. It has the following features. Above the apex there is a depression * for the Gasserian ganglion. Just external to this the bone is excessively thin and often deficient, so as to leave the end of the carotid canal uncovered. Behind the middle of the pyramid is an elevation, nearly at right angles to its long axis, caused by the superior semicircular canal. External to this the surface is made of a very thin plate of bone, the tegmen tympani, which, extending outward from the petrous, forms the roof of the tympanum and of its continuation, the Eustachian tube. Externally, this plate bends down into the Glaserian fissure, so that its edge may appear between the squamosal and tympanic portions (Fig. 198). At the inner border of the tegmen tympani near FIG. 202. its front is a groove leading to a little rent in the bone, the hiatus Fa/lopii, 2 through which passes the great su- perficial petrosal nerve. A minute opening, more external, transmits the smaller superficial petrosal nerve. In youth the outer side of the teg- men is bounded by the petro-sqtia- mous suture. The posterior surface forms a part of the posterior cranial fossa. The chief feature is the internal auditory meatus? a nearly round canal with a slight groove leading to it from the front. Its shorter posterior wall is about five milli- metres long. The canal is closed by a plate of bone, the lamina cribrosa (Fig. 201), which is divided by the falciform crest into a smaller fossa above and a larger one below. The former has an opening by which the facial nerve enters its canal, the aqueduct of Fallopius. Branches of the auditory nerve pass through minute openings in both fossae. About one centi- metre behind the meatus is a little cleft, the aqu&ductus vcstibuli? entering the bone obliquely from below. Higher and nearer to the meatus is a minute depression, the remnant of tib& floccul&r fos&a? which is large in some animals and in the infant. It receives a fold of the dura. The inferior surface of the petrous presents in front a large rough surface for 1 Impressio tegmenti. - Hiatus canalis facialis. 3 Meatus acusticus interims. 4 Apertura cxterna aquaeductus vestibuli. 6 Fossa ubarcuata. Petro-squamous suture Squamous por- tion Internal audi- tory meatus Internal ear Aquaeductus cochleae Tympani External audi- tory canal Tympanic ring Styloid process Frontal section through temporal bone, showing the cavities of the outer, middle, and inner ear and the four sides of the petrous. 182 HUMAN ANATOMY. the origin of the levator palati and tensor tympani muscU-s. Kxtcrnal to the hack of this is the round orifice of the carotid canal 1 ; back of this, and more internal, is the jugular fossa. This presents two extreme types, entirely different, \vith inter- mediate forms. It may be a large thimble-shaped hollow, the edge of which bounds the venous part of the jugular foramen internally, forming a large reservoir for the blood of the lateral sinus as it leaves the skull. On the other hand, it may be a small flat surface. A minute, but very constant, foramen in the ridge between it and the carotid canal transmits the tympanic branch of the glosso-pharyngeal nerve. A minute foramen, usually found in the jugular fossa, transmits the auricular branch of the vagus. The aquadudus cochlece ends at a small triangular opening - in front of the jugular fossa, close to the inner edge. Behind the fossa is a small surface where the temporal bone is united to the occipital, first by cartilage and then by bone. The stylo-mastoid foramen, the orifice of the facial canal for the facial nerve, is near the outer edge of this surface. The stylo-mastoid branch of the posterior auricular artery enters it. FIG. 203. SQUAMOUS PORTION Groove for meningeal artery Foramen for lesser superficial pe- trosal nerve- Hiatus Fallopji Depression for Gasserian ganglion Eustachian tube Carotid canal APEX OF PETROUS Carotid canal (lower end) Tympanic plate- Vaginal process Styloid process Right temporal bone from before. The anterior surface of the petrous is nearly all hidden by the tympanic plate. It forms the inner wall of the cavity of the tympanum and of the bony part of the Eustachian tube, which leaves the bone in the entering angle between this surface of the petrous and the tympanic. The features of this surface are treated in the section on the ear. The -processes cochUariformis* attached like a shelf to this outer wall, divides the canal for the tensor tympani muscle from the Eustachian tube below it. The front of this plate can be seen at the entering angle, where the bony tube ends. The small portion of the outer surface of the petrous which is visible is in front of this point, and rests against the inner edge of the great wing of t' sphenoid. The superior internal border of the petrous is a prominent ridge in the bas< of the skull, separating the middle and the posterior fossae. The tentorium is attached to it. The superior petrosal sinus runs along it in a shallow gnwrc within the attached border of the tentorium. Near the front a groove by which the fifth nerve reaches the Gasserian ganglion crosses this border. The inferior internal border articulates anteriorly with the basilar process of 1 CanalU carotlcus. - Apertura externa atiuaeductus cochleae. ''Septum canalls musculotubarll. THE TEMPORAL BONE. 183 the occipital bone, and is separated posteriorly from the occipital by the jugular foramen. A little spine on the edge of the thimble-shaped fossa, or on the plane surface that may take its place, the intrajugular process, joins the corresponding process of the occipital either directly or by ligament, so as to divide the foramen into two parts, the posterior for the vein, the anterior for nerves. In front of the foramen a small groove on the cerebral edge of this border marks the position of the inferior petrosal sinus. The superior and the inferior external borders are concealed by the other elements of the temporal, except near the front, where they bound the surface which touches the sphenoid. The apex of the petrous is mostly occupied by the opening of the carotid canal. The styloid process is a part of the hyoid bar (from the second branchial arch), which joins the temporal under cover of the vaginal process. It is thick at its origin, but presently becomes thinner and ends in a sharp point. It is usually about an inch long, but varies greatly. It runs downward, forward, and inward, and is con- tinued as the stylo-hyoid ligament to the lesser horn of the hyoid. Three muscles, the stylo-glossus, stylo-hyoid, and stylo-pharyngeus, diverge from it to the tongue, the hyoid bone, and the pharynx. An ill-defined process of the cervical fascia, the stylo-maxillary ligament, passes from it to the back of the ramus of the lower jaw. Canal for tensor tympani CAVITIES AND PASSAGES WITHIN THE TEMPORAL BONE. The Cavity of the Tympanum. 1 The tympanic cavity is a narrow cleft about five millimetres broad at the top, narrowing to a mere line below. It measures about fifteen millimetres vertically and from be- FIG. 204. fore backward. It is bounded internally by the petrous ; above by a projection from it, the legmen tympani ; below by the jugular fossa, or, if this be very small, by the bone external to it ; externally by the tym- panic portion of the bone and the membrane, except at the top, where the squamosal is ex- ternal to it. The part above the level of the membrane is the supra- tympanic space, the attic, or the epitympanum. This is separated from the cranial cavity by a very thin plate, which is sometimes imperfect. In front, the cavity of the tympanum narrows to the Eusta- chian tube. It opens behind through the antrum, which serves as a vestibule, into the mastoid cells. The antrum is a cavity of irregular size and shape, compressed somewhat from side to side, with an antero-posterior diameter of from ten to fifteen millimetres, situated behind the epitympanum in the backward projection of the squamosal, which forms the superficial part of what appears to be the mastoid, and contains some of the so-called mastoid cells. The communication with the tympanum is a narrow one, and a certain number of cells open into the latter independently. The antrum and the cells nearest it are lined with mucous membrane continued from the middle ear. The inside of the mastoid varies greatly. Sometimes it con- 1 The detailed description of this space is given in connection with the ear. Carotid canal (inferior end) Sagittal section through right temporal bone, seen from outer side. 184 HUMAN ANATOMY. tains large pneumatic cavities, sometimes diploe instead of air-cells, and, again, it may be almost solid ; the latter condition is, however, probably always pathological. According to Zuckerkandl's 1 investigations of 250 temporal bones, the mastoid is entirely pneumatic in 36.8 per cent, and wholly diploetic in 20 per cent. The re- maining 43.2 per cent, were mixed, the diploe being at the point of the mastoid and the cells above. Neither size nor shape indicates its internal structure. The relation of the cells to the lateral sinus has been already mentioned. The Facial Canal. The course of the canal 2 for the facial nerve is important. It runs outward from the superior fossa of the internal auditory meatus for some three millimetres, until joined by the canal from the hiatus Fallopii. It then makes a sharp turn (the genu} backward, passing internal to the attic of the tympanum just below the external semicircular canal, which almost always projects a little farther outward. It then curves backward to descend to the stylo-mastoid foramen, passing just above the fenestra ovalis. The descending portion is rarely strictly vertical. Below the genu the facial canal may make a bend either outward or inward, but its general line of descent usually inclines outward, sometimes very strongly. Rarely the descent is tortuous. The lower part may incline forward. The genu is opposite a point on the surface above the external meatus, and the subsequent course of the canal can be indicated in general by a line following the posterior border of the auditory opening. An instrument introduced straight into the front of the mastoid will pass behind the facial canal. 3 The diameter of the latter is about one and one- half millimetres. Just before its lower end a very minute canal, transmitting the chorda tympani nerve, runs upward and forward from it to the cavity of the tympa- num. From the front of the cavity this nerve escapes by the minute canal of Hug uter, which opens near the inner end of the fissure of Glaser, passing between the tym- panic plate and the tegmen tympani. The facial canal has several other minute openings. There are also minute canals for Jacob so ti 1 s nerve from the glosso- pharyngeal, leading to the tympanum, and for Arnold' 's branch of the vagus, which enters the jugular fossa and leaves by the fissure between the mastoid and tympanic portions. The carotid canal 4 is close to the front of the tympanum and just before the cochlea of the internal ear. The internal auditory meatus is almost behind the canal, and the Eustachian tube lies to the outer side of its horizontal portion. The temporal bone is porous in structure, except about the internal ear, where it is very dense. A transverse section, either vertical or horizontal, through the external and internal meatus (the middle and internal ears) shows how nearly the entire bone is pierced (Fig. 202). The carotid canal and the jugular fossa, when deep, are further sources of weakness. The fossa sometimes opens into the middle ear by a small rent. Articulations. The temporal bone joins the occipital by the petro-mastoid portion. These two bones form the entire posterior fossa of the skull, except at the extreme front, in the middle, where it extends along the back of the sphenoid, and at the side, where a small portion of the lateral sinus is made by the posterior inferior angle of the parietal. This latter bone articulates with the squamous and the top of the mastoid. The great wing of the sphenoid fits into the angle between the squamous and petrous portions, articulating at the side of the skull with the front of the foramen. These two bones the sphenoid and the temporal form the entire middle fossa. The malar bone joins the zygoma, completing the arch. The lower jaw articulates with the glenoid fossa by a true joint. Development. The squamous portion is ossified in membrane from one centre, appearing near the end of the second month of foetal life. In the course of the third month a centre appears in the lower part of the future tympanic ring. The ossification of the petro-mastoid portion comes from several nuclei, the number of which probably varies. The process begins towards the end of the fifth month about the membranous labyrinth. The opisthotic nucleus lies at the inner side of the tympanic cavity and spreads to the lower part of the bone. The prootic is near the superior semicircular canal. The cpiotic, arising near the posterior canal, 1 Monatsschrift fiir Ohrenheilkunde, Bd. xiii, 1879. 'Joyce : Journal of Anatomy and Physiology, vol. xxxiv., 1900. 2 Canalls fnclnlla. 4 CnnnlK i.-initunv DEVELOPMENT OF THE TEMPORAL BONE. 185 FIG. 205. Squatnous portion spreads into the mastoid portion. This one is sometimes double. There is also a separate nucleus for the tegmen, but this is not constant. When present, it seems to be the last to fuse with the others, which become one by the end of the sixth month. The carotid artery passes at first along the base of the skull in a groove which is made into a canal by the opisthotic. The separated petrous portion, when ossification has made some progress, shows a very promi- nent superior semicircular canal, and a deep cavity under it, extending back- ward from the inner surface. This is the floccular fossa, which, however, is completely hidden by the dura. The mastoid process becomes fairly distinct in the course of the second year. It Tegmen tympani in Inner wall Glaserian fissure Tympanic ring Malleus of tympanum Temporal bone at about birth, outer aspect. FlG. 206. Petro-squamous suture Position of superior semicircular canal develops greatly about the time of puberty, when it becomes pneumatic. This may occur much earlier. J. J. Clarke has seen it wholly pneumatic several times before the tenth year ; once at three and a half. 1 The squamosal joins the petrous in the course of the first year. At birth the tympanic por- tion consists solely of the im- perfect ring open above. This enlarges trumpet-like from the edges, the front one forming the tympanic plate. The growth is of unequal rapidity, so that the lower part is left behind, presenting a deep notch the outer edges of which meet by the end of the second year, leaving a foramen below, which usually closes Carotid canal- ^ ' \ two or three years later, but exceptionally persists. The tympanic plate fuses almost at once with the petrous, but the Glaserian fissure remains ; the groove showing the line of union of the tympanic and mastoid processes generally disappears in the second year, but occasionally persists through life. Kircher 2 found it present on both sides in five per cent, of 300 skulls. The styloid process consists of two parts. The first joins the petrous at about birth. The second, which represents all but the base, is an ossification of the stylo-hyoid ligament, and does not join till puberty or later. In very early foetal life the chief vein returning the blood from the brain passes through the membrane that is to become the squamosal. This open- ing the foramen jugulare spurium is later of less importance, and is finally Posterior semicir- cular canal Floccular fossa Internal auditory canal Temporal bone at about birth, from above and within. FIG. 207. Malleus Tympanic ring Tegmen tympani in Glaserian fissure Tympanic portion of temporal bone in the second year. closed. In the skull, at birth, a pin-hole representing it may be found at the postglenoid tubercle. later. It is sometimes seen 1 Journal of Anatomy and Physiology, vol. xxvii., 1893. 2 Archiv fur Ohrenheilkunde, Bd. xiv., 1879. 1 86 HUMAN ANATOMY. THE SPHENOID BONE. In the adult this bone ' consists of a cubical body, from the sides of which arise the great wings, from its front the lesser wings, and from below the pterygoid pro- cesses. Both development and comparative anatomy show that these parts represent several bones. The body consists of two parts, a posterior and an anterior. The posterior, the basisphenoid, is the centre of the middle fossa of the base of the skull ; from its sides spread the great wings, or alisphenoids. These with the temporal bones complete the middle fossa. The anterior part, the prcsphenoid, inseparably connected with the basisphenoid, is in both the middle and the anterior fossae. The lesser wings, the orbito-sphenoids, spread out from the presphenoid and cover the apices of the orbits. The pterygoid processes consist each of two plates, the inner of which represents a separate bone of the face, the outer being an expansion from the alisphenoid. Two bones called the cornua sphenoidalia, or sphcnoidal turbinates, of independent origin, ultimately form a part of the body of the sphenoid. Optic foramen FIG. 208. Sphenoidal turbinate Sphenoidal foramen Infratemporai crest External ptery- goid plate Hamular process Pterygoid notch Internal pterygoid plate The sphenoid bone from before. The Body. It is necessary to describe the basisphenoid and the presphenoid together, since they form the roughly cubical body. The superior surface con- tains the deep pituitary fossa? or sella turcica, in which hangs the pituitary body from the brain. Behind it is the dor sum sclla, a raised plate continuous with the surface of the basilar process of the occipital and which completes the posterior fossa. Its outer angles are knobs pointing both forward and backward, the posterior dinoid processes, to which the tentorium is fastened. Beneath these, on either side of the dorsum, is a groove for the sixth nerve. In front of the sella is the olivary eminence' (of the presphenoid), which is usually an oval swelling, though it may be plane or concave. At its sides grooves, often very poorly marked, lead to the optic foramina. The posterior edge of this eminence is sometimes grooved for a vein and sometimes sharp. Its lateral ends may become tubercles, the middle dinoid processes. The olivary eminence is in most cases bounded in front by a transverse elevation con- necting the lesser wings, of which, indeed, it is a part, forming, when present, the separation of the anterior and middle fossae. The front border presents in the median line a triangular point, the cthmoidal spine. At each lateral surface of the body is the carotid groove* for the internal carotid artery. It is well marked only at the posterior edge, where the artery enters 1 Os sphcnuidalc. " Fossa hypophyscos. "Tubvrrulum sellat. 4 Stilcus cnroticus. THE SPHENOID BONE. 187 it from the apex of the petrosal. It is here bounded internally by a little tubercle, the petrosal process, at the base of the dorsum, and externally by a very delicate plate, the lingula, which sometimes projects considerably ; these .two processes touch either side of the end of the carotid canal in the petrous. The rest of the side of the body is hollowed for the cavernous sinus, in which the carotid artery runs. It is covered below by the origin of the great wing. The posterior surface of the body is rough up to puberty for the cartilage that binds it to the basilar process of the occipital ; later these parts coossify, and thereafter the posterior surface is made artificially by the saw. The anterior surface presents in the middle a sharp ridge, the sphenoidal crest ,^ to join the vertical plate of the ethmoid. Just at the sides of this the bone is smooth and aids in forming the wall of the nasal fossa. In each lateral half is an opening, the sphenoidal foramen? into the cavity of the bone. The inferior surface presents in the middle a longitudinal swelling, thick behind, narrow and sharp in front, the rostrum, fitting into the vomer and usually joining the lower edge of the crest without interruption. It may stop short of it. On either side of the rostrum there is a smooth triangular surface made of delicate plate, which extends up onto the front, forming the smooth surface beside the crest, and bound- FIG. 209. Foramen rotundum Carotid groove Scaphoid fossa Pterygoid fossa External pterygoid plate Hamular process The sphenoid bone from behind. ing a large part of the hole into the antrum. These are the bones of Bertin, or sphenoidal spongy bones, of which more is to be said under Development (page 191). The body of the sphenoid is hollow, enclosing two cavities, the sphenoidal sinuses, separated by a septum, which runs obliquely backward from the crest, so that one sinus is usually much larger than the other. These sinuses have irregular ridges partially subdividing them. They are lined by mucous membrane and open into the nasal cavity by the sphenoidal foramina. The opening is reduced when the ethmoid is in place. The great wings 3 have each a cerebral or superior surface forming a large part of the middle fossa, an external surface looking outward into the temporal and downward into the zygomatic fossa, and an orbital surface forming most of the outer wall of that cavity. The superior surface is smooth and concave ; springing from the side of the basisphenoid, it spreads upward and outward and also backward to fill the gap between the petrous and squamosal parts of the temporal. By the side of the body there is a short canal running forward to open on the front of the bone into the spheno-maxillary fossa ; this is the foramen rotundum for the superior max- illary division of the fifth nerve. A little further back and more internal is a pin- 1 Crista sphenoidalis. - Apertura sinus sphcnoidalis. 3 Alac magnae. 1 88 HUMAN ANATOMY. hole, the foramen of Vesalius, for a minute vein. Farther back and outward near the angle is the foramen ovale, transmitting the mandibular division of the fifth cranial nerve to the base of the skull, and admitting the small meningeal branch of the internal maxillary artery. Just beyond this, in the extreme angle, so as some- times to be completed by the temporal, is the foramen spinosum, admitting the middle meningeal artery to supply the bone and the dura. The external surface is divided into a larger, superior, vertical part, looking towards the temporal fossa, and one looking into the zygomatic fossa. These are separated by the infratcm- poral crest, which near the front points downward as a strong prominence, the infra- temporal spine. The inferior surface contains the foramen ovale and the foramen spinosum. Just behind the latter, at the posterior angle, is the spine of the sphenoid, pointing downward, grooved at the inner side by the chorda tympani nerve. The external surface has an anterior border where it meets the orbital surface, which joins the malar. The superior border slants upward, overlapping the frontal and parietal bones. The posterior border is about vertical as far down as the infra- temporal crest, and bevelled, especially above, to be overlapped by the squamous part of the temporal. The lower part of this border runs backward and somewhat overlaps the squamosal. The posterior border of this surface, from the spine to the Articulates with frontal FIG. 210. Ethmoidal crest Sphenoidal fissure Foramen rotun- diini Foramen ovale Foramen spinosum Post, cli process The sphenoid bone from above. body, is slightly rough for the petrous, making with it a groove on the under side for the cartilaginous Eustachian tube. The smooth orbital surface, facing inward and forward, is quadrilateral, broader in front than behind. Almost the whole of it is in the outer wall of the orbit, of which it forms the greater part ; but a small portion, narrow behind and expanding in front, looks into the spheno-maxillary fissure, which bounds this surface below. It joins the malar in front. On the top of the bone there is a rough triangular region in the angle formed by the meeting of the external and orbital surfaces, on which the frontal bone rests. This is above the front half of the orbital plate. The remainder of the upper and the whole of the posterior border of the latter bound the sphcnoidal fissure. ' This cleft is an elongated aper- ture, directed obliquely outward and upward between the great and lesser wings of the sphenoid, completed externally by the frontal. It opens anteriorly into the orbit and transmits the third, the fourth, the ophthalmic division of the fifth and sixth cranial nerves, and the ophthalmic veins. There is a small projection near the middle of the hind border for a ligament crossing the fissure and for the outer head of the external rectus. The lesser wings, 2 forming the back part of the anterior fossa and of the roof of the orbit, arise by two roots. The superior is a plate covering the presphenoid ; the inferior is a strong process from the side of the body. With the latter they 1 I'issur.i orbltallH superior. '' Alne parvae. THE SPHENOID BONE. 189 p IG 2II Sphenoid bone, showing abnormal development of middle clinoid processes, especially on the left side. Re- duced one-half. enclose a canal, commonly called the optic foramen,^ for the optic nerve, which is accompanied by the ophthalmic artery. The length of the canal measured along the inferior root is about five millimetres. The length of the roof is greater, per- haps nearly twice as much, but it is variable from the uncertain development of that part of the bone ; definite dimensions are, therefore, wanting. The vertical diameter, some five millimetres, of the opening into the orbit is a little greater than the transverse. The small wing over- hangs the front of the middle fossa bounding the sphenoidal fissure above, and ends laterally in a sharp point. The anterior clinoid process is a sharp pro- jection backward above the inferior root and towards the posterior clinoid. Sometimes it reaches the latter ; some- times it is connected by a spur with the middle clinoid process, then bridging the carotid groove and making a carotico- flinoid foramen (Fig. 211). The an- terior border of the lesser wings is rough at its inner part and smooth at the outer, where it joins the posterior edge of the horizontal plate of the frontal. The posterior border is smooth, form- ing most of the boundary of the anterior and middle cranial fossae. The pterygoid processes 2 are downward projections which, articulating with the palate bone, form the back of the framework of the upper jaw. Each consists of two plates, an inner and an outer, united in front, diverging behind to form the pterygoid fossa, and separating below on either side of the pterygoid notch. The inner springs from the body, the outer from the great wing. The inner pterygoid plate 3 is the longer. It is nearly vertical, ending in the slender hamular process* which points outward, bounding a deep little notch through which the tendon of the tensor palati plays. At the inner side of its origin the internal plate presents a scale-like curved projection, the vaginal process, above which is an antero-poste- rior groove below the body of the sphe- noid, in which the lateral expansion of the base of the vomer is received. Just external to the vaginal process is an- other small groove, the ptery go-palatine, which the palate bone converts into a canal leading back from the spheno- maxillary fossa. The outer pterygoid plate 5 is broader and flares outward. The anterior surface of the root is nearly smooth, forming the back wall of the spheno-maxillary fossa. It has the openings of two canals : the upper and outer is that of the foramen rotundum ; Portion of sphenoid bone, showing the foramen pterygo- -11 j i 1 11 spinosum. the lower and inner, which is smaller, is the Vidian canal, transmitting the nerve and vessels of that name. There is a vertical ridge between the two, and a slight groove below the latter, forming with the palate bone the beginning of the poste- rior palatine canal which runs from the spheno-maxillary fossa through the hard palate, transmitting a descending palatine nerve and vessels. The lower anterior edges of both plates are rough to articulate with that bone. The outer surface of the external plate is irregular for the origin of the external pterygoid muscle. The inner wall of the inner plate is smooth. It bounds laterally the back of the nasal cavity. The posterior borders of both plates are sharp, excepting that the inner is formed by the union of two lines which enclose the scaphoid fossa where the tensor palati arises. Rather less than half way down the internal plate presents a promi- 1 Foramen opticum. - Processus pterygoidei. :i Lamina mcdialis proc. pteryg. * Hamulus pterygoidei. "' Lamina lateral!.- proc. pteryg. FlG. 212. Spheno-maxillary fossa Foramen ovale External pterygoid plate 190 HI 'MAN ANATOMY. Great win. (alisphenoid) nence bounding a groove below, which supports the Eustachian tube. The posterior border of the outer plate is irregularly scalloped. Near the top a transverse ridge crosses its inner surface ; if well marked, this forms the top of the pterygoid fossa. It may be barely discernible (Waldeyer l ). Just above the scaphoid fossa is the hind end of the Vidian canal opening into the middle lacerated foramen opposite the apex of the petrous. The development of the pterygoid plates varies greatly. The upper part of the outer may be prolonged to the spine of the sphenoid, just outside of the foramen ovale, with a perforation at this point, so that some of the branches of the third division of the fifth cranial nerve may pass on either side of it. This occurs by the ossification of a band of fibrous tissue, connecting the back of the plate with the spine, and thus FIG. 213. forming the foramen ptcrygo- spinosum of Civinini (Fig. 212). This is always behind the fora- men ovale, or internal to it. Just outside of the foramen is found, very rarely, a little canal on the under side of the great wing, transmitting a branch of the mandibular division of the fifth nerve, the porus crotaphit- ico-buccinatorius of Hyrtl. Articulations. Much has been already said incident- ally on this point in the fore- going description. The sphenoid bone joins the occipital behind. The great wings send the spine into the entering angle between the squamous and petrous portions of the temporal. These two bones the sphenoid and the temporal form the entire middle fossa of the skull. The middle lacerated foramen is just behind the carotid groove at the side of the body and in front of the end of the petrous. At the side of the skull the great wings join the squamous behind, the parietal and the frontal above, and the malar in front. The ethmoid covers the front of the body of the sphenoid, its vertical plate joining the crest. The vomer covers the rostrum below. The palate bone fills FIG. 214. Presphenoid xt. pterygoid plate Int. pterygoid plate Sphenoid bone at about birth, seen from before. Jugum sphenoidale Si mall wing- (orbito-sphenoid) Foramen rotundum Great wing (alisphenoid) up the pterygoid notch, com- pleting the fossa, and by its sphenoidal process touches the edge of the body. The frontal bone joins the lesser wings. Development. The presphenoid and basisphenoid each ossify from a pair of nuclei, those of the former appearing at the end of the second month of foetal life and the latter a little later. At about the eighth week a nu- cleus is to be seen in each of the greater wings near the body and extends outward, involving also the external pterygoid plate. The internal pterygoid plate has a nucleus of its own, which is present in the fourth month and joins the outer a month later. Two little gran- ules appear in the fourth month for the lingula and a neighboring piece of Un- bone. The orbito-sphenoids have each two centres, one on either side of the optic foramen. It would seem that the inner may in some cases take the place of those for the presphenoid. In any case the presphenoid and the lesser wings unite before birth. In the seventh or eighth month the presphenoid and basisphenoid unite, but at birth they are still separated by cartilage on their lower surface. At birth the bone con- 1 Sitzungsber. Acad. Wissen., Berlin, 1893. Basisphenoid Lingula Foramen ovale Sphenoid bone at about birth, seen from behind. THE ETHMOID BONE. 191 Crista galli sists of the basisphenoid, the presphenoid, and the lesser wings in one piece, and a lateral one on each side, namely, the greater wing and the pterygoids. The dorsum sellae has a separate epiphysis which appears after birth. In the first year the lesser wings spread across the top of the presphenoid, joining the jugum sphenoidale, so that it does not show in the anterior fossa. The external pterygoid plate is an out- growth of the great wing. The cornua sphenoidalia, bones of Berlin, or sphenoidal turbinate bones, are two thin plates which appear before birth at the front of the presphenoid. They cover both the front and its inferior surface at the sides of the rostrum. At five years they are still free, but have approached their permanent shape of hollow cones. The hollowing out of the body of the sphenoid now begins, and at the same time the upper part of these bones is absorbed, so that the foramina become notches. These bones are ultimately joined to the sphenoid, the ethmoid, and the palate. Though usually reckoned as parts of the sphenoid, there is reason to believe that they are generally fused earlier with the ethmoid. The basisphenoid begins to coossify with the occipital at about the fifteenth year. The process is first completed above. THE ETHMOID BONE. The ethmoid J consists of a median plate forming a part of the nasal septum, of the cribiform plate joining it at the top on either side and forming the roof of the nasal cavity, and of two lateral masses attached to the lateral border of each cribriform plate, and touching the vertical plate very slightly just below its junction with the front of the cribriform plate. These lateral masses are roughly cubical, interposed between the cavities of the nose and of the orbit. They consist of FIG. 215. a series- of delicate plates forming the walls of air-spaces or cells, which are mostly completed by neighboring bones. The vertical or median plate 2 projects near the front into cranial cavity as the crista galli, thicker in front than behind, with an oblique upper border run- ning sinuously downward and backward. Its greatest elevation is about one centimetre. The front part is occasionally hollow, forming a part of the frontal sinus. It gives attachment to the falx cerebri, a fold of dura separating Uncinate process the hemispheres of the brain. A Trie ethmoid bone, outer aspect from the right side. little plate, a/a, 3 facing downward and forward, arises from the front on either side, articulating with the frontal. Just before the crista galli is a pin-hole, the foramen c&cum, usually formed by both ethmoid and frontal, but which may be in either. It is said to transmit a vein in early life, but is closed later. The part of the vertical plate below the horizontal one is five-sided. The upper border runs along the base of the skull ; one in front of it slants downward and forward under the nasal spine of the frontal, sometimes reaching the nasal bones ; another descends nearly vertically along the crest of the sphenoid. Of the two inferior borders, the posterior runs downward and forward along the greater part of the vomer, while the anterior, running downward and backward to meet it, is free in the skeleton, but in life is attached to the triangular cartilage which forms a large part of the septum. The sides, covered with mucous membrane, are smooth except at the upper part, where there are vertical grooves for the olfactory nerves. This plate usually slants to one side. The horizontal or cribriform plate 4 forms the floor of a narrow groove on either side of the crista galli and, farther back, in the middle of the anterior fossa of 1 Os cthmoidale. - Lamina pcrpendicularis. 3 Processus alaris. 4 Lamina cribrosa. Mid. turbinate 192 HUMAN ANATOMY. the skull. The greatest breadth of the groove is about five millimetres. It nar- rows in front to a point, and thus allows the lateral masses to touch the median plate. It supports the olfactory lobe of the brain, and is perforated by holes for the passage of the olfactory nerves. These are arranged rather vaguely in three rows. There are many in front and few behind. Many of the larger ones, which are near the septum or at the outer side, are small perforated pits. At the front a longi- tudinal fissure, close to the crista galli, transmits the nasal branch of the fifth nerve. The lateral masses 1 are two collections of bony plates imperfectly bounding cavities. They are roughly six-sided, the greatest diameter being antero-posterior. The outer surface presents a vaguely quadrilateral plate, the os planum? forming a large part of the inner wall of the orbit. In its upper border are two notches, which become the anterior and posterior ethmoidal foramina when the frontal bone is in place. The former transmits the nasal branch of the fifth nerve from the orbit to the cranial cavity. The os planum is bounded behind by the body of the sphenoid ; below by the palate bone and superior maxilla, the former of which usually, and the latter always, complete some eth- moidal cells which appear along the lower border. There is a large mass of open cells in front of the / / / os planum. Those nearest to it are completed by the lachrymal and the more anterior ones by the Median or perpendicular plate of ethmoid bone in place. The right lateral mass of the ethmoid has been removed. nasal process of the superior maxilla. Posteriorly, the lateral mass rests against the body of the sphenoid, the posterior cells being separated from those of the sphenoid by the cornua sphenoidalia. The open cells on the upper surface of the lateral mass are closed by the imperfect cells on the under side of the horizontal plate of the frontal beside the sphenoidal notch. The few cells that open anteriorly are contin- uous with the lateral ones, and are closed by the nasal process of the upper jaw. The numerous spaces within the ethmoid are, for the most part, completed by the neighboring bones, after which they are named. There are some beneath the os planum, however, entirely within the ethmoid. Tin- fthmoidal ccUs* are divided into anterior and posterior, of which the former open into the nose below the middle turbinate bone and the latter above it. The si/e and shape of the ethmodial cells are very irregular ; sometimes the middle turbinate is hollowed into one, some- 1 Labyrinthii!) ethmoldalis. "Lamina pupyracea. 3 Cellulae cthmoldalcs. THE ETHMOID BONE. 193 Median plate Crista galli Infundibulum Orbital plate The ethmoid bone from above. times they swell out into the cavities of other bones, notably into the frontal sinus. The internal surface of the lateral mass, forming the outer wall of the nasal cavity, cannot be seen on the entire bone. It is best studied on the bisected skull ; but to study the whole bone, further cutting is necessary, since this sur- face is made of a series of con- voluted plates, some of which FIG. 217. conceal others. At least two of these the superior and the mid- dle turbinate bones 1 are evident. They are curled with their con- vexities towards the median plane, so as to overhang two antero-posterior passages, the superior and the middle meatus of the nasal fossa. According to Zuckerkandl, there are three ethmoidal turbinate bones in .more than eighty per cent., and sometimes four. When only two are seen, it is owing either to the absence of the second or to its slight development, so that it is hidden by the upper. It is certain that only two are evident in most cases, and we shall follow the usual method of so describing the bone. 2 The inferior ethmoidal (middle) tur- binate is much the larger, very prominent, and joins the ascending process of the superior maxilla at the crista ethmoidalis or superior turbinate crest. Its general course is backward and downward, to end in a point at the posterior border of the bone. The free edge is so much curled under as to be hidden. The superior turbinate is much smaller, occupying the postero- superior angle. It appears to separate from the turbinate below it at about the middle of this sur- face. The siiperior meatus, which it overhangs, is therefore small. As above implied, an additional ethmoidal turbinate may appear from beneath it, and still another small one may very exceptionally be found above it at the extreme upper posterior angle. At the point at which the middle turbi- nate bone joins the nasal process of the maxilla there is often a slight elevation, the agger nasi, which is supposed to be the an- terior end of another turbinate which passes under the preceding. When the middle turbine is removed, a curved projecting plate, the uncinate process? is seen on the lateral mass, curving downward and backward. It is some two or three millimetres broad and, extending beneath the rest of the bone, joins the inferior turbinate. The uncinate process, together with the agger, is held to represent the 2 There are practically three turbinate bones, the upper two of which are parts of the ethmoid and the lowest a separate bone. These are called superior, middle, and inferior ; hence we speak of the inferior ethmoidal turbinate as the middle one. 1 Concha nasalis superior ct media. 3 Processus uncinatus. 13 FIG. 218. Superior surface Alar process of crista galli Posterior ethmoidal cells Posterior ethmoidal cells Middle turbinate Sup. meatus Median plate The ethmoid bone from behind, showing median plate and lateral masses. 194 HUMAN ANATOMY. FIG. 219. Probe in infundibulum Crista gal!' Cribriform- plate Sup. turbinate Bulla Uncinate process The ethmoid bone, inner aspect from left side, part of the middle turbinate having been removed. naso-turbinal bone of many mammals. Behind this is a globular swelling, the bulla, 1 formed by a plate springing from the os plenum, covering cells, which also is held to represent a turbinate. Between the uncinate process and the bulla is a deep groove, the infundibulum* curving downward and backward, the opening into which from the nasal fossa is known as the hiatus semilunaris. The upper end of the infundibulum opens into the frontal sinus in about half the cases, 3 ending blindly in the others ; it is bounded externally to a varying extent by the lachrymal. A number of anterior ethmoidal cells generally open into this portion. The lower end of the infundibu- lum has an opening on its outer side into the antrum. Articulations. These have already been described incidentally. Briefly recapitulated, however, the articula- tions of the ethmoid are with the frontal, the sphenoid, the palatals, the vomer, the inferior turbinates, the lachrymals, and the nasals. Development. The ethmoid is very small at first and backward in its development. About the middle of foetal life ossification appears in the os planum and the middle turbinate bone. A centre (two, according to Poirier) for the vertical plate occurs in the first year, from which ossification extends into the crista galli. The cribriform ossifies chiefly (perhaps wholly) from the lateral masses. The date of the union of the three pieces is rather uncertain ; it takes place, probably, at about the sixth year. The cells appear first as depressions during foetal life. According to the more generally accepted view, their growth is by absorption of bone. It is hard to believe that this is not, at least, a factor ; Poirier, however, holds that they are due to the course of ossification. THE FRONTAL BONE. This bone, 4 which forms the front of the vault of the skull, most of the floor of its anterior fossa, and bounds the greater part of the orbits and the ethmoidal cells above, is developed into two symmetrical halves which unite in the second year. It is convenient to divide the bone thus formed into a vertical and a horizontal portion, although this division rests on no scientific basis. The vertical portion, 5 convex anteriorly, presents on either side, below its middle, the frontal eminence? which represents the chief centre of ossification of either half. Very prominent in infancy, it diminishes during growth, and is hardly to be made out in most adult skulls. The lower border of the vertical portion grows downward in front between the orbits. At the sides of this projection are the internal angular processes of the orbits. In the middle-line a faint zigzag line marks the remnant of the iutcrfroutal suture. Above this is a smooth, rather prominent surface, called the glabclla, external to which are the superciliary ridges'" or emi- nences, which extend outward, somewhat above the inner ends of the orbits. The development of these varies greatly. On either side of the nasal projection is the orbital arch, extending outward from the internal angular process. At about the s H. A. Lothrop : Annals of Surgery, vol. xxviii., 1898. 1 Knl I. -i cthmuiilnlis. "Infundibulum tthinuidalc. * frontolc. r ' Squama frontalis. 'Iul.it frnntnle. "Arena MijiiTi-illares. THE FRONTAL BONE. 195 inner third of the arch is the supraorbital notch * for the nerve and the artery of the same name. The outer edge of the notch is more prominent than the inner. Very often this is replaced by a foramen, which may be four or five millimetres above the edge of the bone. The arch ends externally in the external angular process? which joins the malar and is very prominent. From it springs the temporal crest? which, curving upward and backward, separates the anterior surface of the bone from the lateral one, which is a part of the temporal fossa. This crest generally, before leaving the bone, divides into two lines, of which one is much more distinct than the other. The vertical part of the bone has a slight point above in the middle and a very jagged posterior border interlocking with the parietal. The latter is slightly overlapped above and overlaps below. The bevelled, though jagged, articular sur- face broadens below to meet a triangular rough space on the inferior surface. At the lower lateral edge the bone is covered by the top of the great wing of the sphenoid. FIG. 220. Temporalis External angular "" / *MBffi^ iyffii'ffiW 1IU - a "K- P IOL ' ess "vyp Supra-orbital foramen Corrugator supercilii Orbicularis palpebrarum Nasal spine The frontal bone from before. The horizontal portion 4 shows in the middle of its lower aspect a rough surface extending onto the front, called the nasal process, which articulates anteriorly with the nasal bones and laterally with the ascending processes of the upper jaw. In the middle projects a thin plate, the nasal spine, behind and between the nasal bones. On either side of this there is often found a small smooth surface forming a small part of the roof of the nasal cavity. Behind this lies the median ethmoidal notch? on either side of which is an irregular space reaching to the inner edge of the orbit, made of imperfect cells, completing the ethmoidal ones. In front of these a cavity extends directly up, hollowing out the bone into \hefrontal sinus, which may extend outward and backward over the orbits. A partition separates the sinuses of the two sides, which are rarely symmetrical. The sinus opens into the middle meatus either directly, under the front of the middle turbinate, or through the infundibulum. When the ethmoid is in place, the cribriform plate and the crista galli fill up the ethmoidal notch ; the ethmoidal cells are then closed, and the ethmoidal foramina 1 Incisura supraorbitalis. - Processus zygomaticus. 3 Linca temporalis. 4 Pars orbitalis. "' Incisura cthiuoidults. 196 HUMAN ANATOMY. and canals are formed. External to this lies the orbital plate, the front of which is overhung by the supraorbital arch. It is slightly concave from side to side. Just under cover of the external angle is an ill-marked depression 1 for the lachrymal gland. Near the internal angular process there may be a small fossa 2 for the cartilaginous pulley for the superior oblique muscle. More frequently there is a minute tubercle. The inner border of the orbital surface runs nearly straight backward. Its sharp edge articulates from before backward with the ascending process of the maxilla, the lachrymal, and the ethmoid. The outer edge runs obliquely inward. External to it, behind the angular process which joins the malar, is a rough triangular surface articulating with the great wing of the sphenoid. The posterior border of the orbital plate is short and serrated to join the small wings of the sphenoid. The internal surface of the frontal presents the frontal crest below in the Groove for longitudinal sinus Pacchionian depressions External angular process Supra-orbital foramen Frontal sinus Frontal crest Foramen caecum Nasal spine Nasal process The frontal bone from behind. median line. It is a slight ridge, to which the falx is attached. A narrow groove runs along it, starting at the foramen c^ci/iu, a hole either in this bone or between it and the ethmoid. This groove is for the superior longitudinal sinus. After a short distance the crest disappears, but the groove broadens and extends to the top of the bone. There are a few grooves for branches of the middle meningeal artery at the side and some small Pacchionian depressions. 3 Below, on either side of the notch, are the orbital plates, which slant strongly downward and inward, so as to leave the ethmoid in a deep gutter. Their upper surfaces are very irregular with so called digital impressions for the opposed cerebral convolutions. It is now evident how the frontal, the ethmoid, and the lesser wings of the sphenoid form the anterior fossa of the skull. 8 See Parietal Rone (pai^e igS). 1 Fossa nl.ni.liil.il' l.u i iin.iliv 2 Foven trochlcnrl*. THE PARIETAL BONE. 197 Articulations. The frontal articulates with the nasal, superior maxillary, lachrymal, malar, ethmoid, sphenoid, and parietal bones. Development and Changes. The only important centres are the two sym- metrical ones appearing in the membrane at the frontal eminences towards the end of the second month of fcetal life. There is a separate point for the nasal spine and one near each angular process of the orbit. These smaller ones are fused in the seventh month of fcetal life. There is a centre for the posterior angle (Gegenbaurj, which also. unites before birth. The median (in'etopic) suture usually closes towards the end of the second year, and a year or two later is hardly to be recognized, except by the rudiment at the lower end. Occasionally the suture persists ; in that case it remains in extreme old age after the others have vanished. Not very rarely in the foetus or infant a dilatation of the fissure, metopic fontanelle, is found near the upper part of its lower third. There are a few cases of traces of this in the adult. 1 The frontal sinuses appear about the seventh year and increase up to adult life. Later they are said to grow again, since in the latter part of life the inner table of the skull follows the shrinking brain. As their size is dependent chiefly on the behavior of the inner table, we can infer little about it from the shape of the fore- head, unless the superciliary eminences are very prominent. THE PARIETAL BONE. The two parietal bones ' complete the vault of the skull. Each is a thin quadri- lateral bone with an inner and an outer table separated by diploe. Near the middle FIG. 222. Parietal foramen Post. sup. angle .< Ant. sup. angle Anterior inferior angle Mastoid Right parietal bone, outer surface. Sphenoid on the convex external surface is \\\z parietal eminence? where ossification begins. It is very prominent in childhood, but, as a rule, is not very evident in the adult. Crossing this surface below the middle are two curved lines * continuous with those 'Schwalbe : Zeitschrift fur Morph. und Anthrop., Bd. iii., 1901. " Ossa parietalia. 3 Tuber parictale. 4 Linac tcmporales 198 HUMAN ANATOMY. into which the temporal crest of the frontal divides. The superior crosses the bone, ending at its posterior border. The inferior turns down towards the posterior part so as to reach the lower border to become continuous with the supramastoid crest of the temporal. In the middle of their course the lines are about two centi- metres apart. The space between them is a little smoother than the surface above and below. It is uncommon to be able to trace both lines throughout. The inferior is usually the better marked. Sometimes a part of each is suppressed. The identity of a single line is shown by its termination. Near the upper posterior angle is a minute pin-hole, the parietal foramen? which transmits a vein. This foramen is very often wanting, and, when visible, may be closed. In very rare cases it is a large hole, which may even admit a finger. It is occasionally double. The internal surface is smooth and glistening, as is the case throughout the inside of the cranium. It is marked by tree-like grooves for the branches of the middle meningeal artery. FIG. 223. Groove for longitudi- nal sinus Post. sup. angle Ant. sup. angle Grooves for middle meningeal artery Anterior inf. angle sterior inferior angle Right parietal bone, inner surface. One of these starts close to the anterior lower angle, being at first very deep and sometimes a canal for a short distance. Its situation is exceedingly constant. One or two other branches appear in the posterior half of the lower border. The superior longitudinal sinus rests in a groove * completed by both bones along the upper border. This groove is rarely symmetrical, being generally largest on the right. At the posterior inferior angle there is a small surface completing the groove 3 of the lateral sinus at the point at which it turns from the occipital into the temporal bone. Pacchi- onian depressions are small pits of varying size and number, found in the upper part of the inner surface, and most commonly near the groove for the longitudinal sinus, which contain the Pacchionian bodies of the arachnoid. The largest might receive the tip of the little finger. The anterior, superior, and posterior borders are all jagged. The anterior border meets the frontal, overlapping it below, overlapped above. The superior border meets that of its fellow. The serrations are most developed in the middle, 1 Foramen parietalc. '* Sulcus sagittal-*. Sulcu* trunsvcrsus. THE SUPERIOR MAXILLA. 199 the end of the suture behind the parietal foramina being nearly straight. The pos- terior border interlocks with the squamous portion of the occipital by a very irregular line of suture. The inferior border, concave in the middle, is bevelled on its outer surface, except behind. It is covered anteriorly by the top of the great wing of the sphenoid, and along the concavity by the squamous part of the temporal. The pos- terior portion presents a point at the back of the concavity which fits into an angle between the squamous and mastoid parts of the temporal. Behind this it is thick and jagged for the top of the mastoid portion. The anterior superior corner is about a right angle. The inferior one is somewhat drawn out. The superior posterior corner is rounded. The inferior is cut off. Parietal impressions is the term applied to depressions which are observed very exceptionally on the outer surface of the parietal bones above the parietal emi- nences and near the upper border. They are usually large, i.e. , some seven centi- metres long by five or six centimetres broad. Some sections have shown that they involve only the outer surface of the bone. A thinning above the sagittal suture has also been observed, and even one over the lambdoidal suture. These latter are generally considered atrophic changes occurring in old age. The same explanation is offered for the parietal impressions proper, and very possibly with justice ; still, the case is reported by Shepherd l of an old woman who remembered having them all her life, and who declared that her father had them likewise. This would point to their being occasionally both congenital and hereditary. The late Professor Sir George Humphry 2 observed them in the orang-outang. Articulations. Each parietal articulates with its mate, the occipital, temporal, sphenoid, and frontal bones. Development. A single centre appears in the membrane at the end of the second fcetal month. According to Toldt {Lotos, 1882), this is double, consisting of an upper and a lower part, which soon fuse. The centre becomes very prominent, and bone-rays extend from it, making the bone very rough till after birth. The fontanelles at the four corners of the bone are discussed in describing the skull as a whole (page 231). The radiating lines of bone leave an interval near the back of the upper border of the bone, called the sagittal fontanelle, which closes during the latter part of foetal life. According to Broca, this can be seen at birth once in four times. The parietal foramen is left as this fissure closes. Its occasional great size is accounted for by irregularities in the process. Very rarely a suture divides the parietal into an upper and a lower portion. THE FACE. The face consists of the orbits, the nose, and the jaws. Portions of the sphe- noid and the ethmoid form a considerable part of it, as has been described. The facial bones are two superior maxillce, two malar, two nasal, two lachrymal, two palate, two inferior turbinates, the vomer, the inferior maxilla, and the hyoid. The future nasal septum, extending in the median plane from the base of the skull to the upper jaw, is very early developed in cartilage. Ossification progresses from superficial centres on either side. These form the vertical plate of the ethmoid and the vomer ; but a considerable part, the triangular cartilage, remains cartilaginous. THE SUPERIOR MAXILLA. The superior maxilla :i is a very irregular bone, which with its fellow forms the front of the upper part of the face, the floor of the orbit, much of the outer wall and floor of the nasal cavity, much of the hard palate, and supports all the upper teeth. It has a body, and malar, nasal, alveolar, and palatal processes. The general shape of the body' is that of a four-sided pyramid ; the base looking towards the nasal cavity, one surface forming the floor of the orbit and the other two the front and back of the bone. These three surfaces meet at the apex, which is the malar process? 'Journal of Anatomy and Physiology, vol. xxvii., 1893. 2 Ibid, vol. viii., 1874. 3 Maxilla. 4 Corpus maxillae. 5 Pfocessus zygomaticus. 2OO HTM AN ANATOMY. This is a rough triangular surface articulating with the malar, often perforated, and sending downward a smooth ridge separating the anterior and posterior surfaces ; the former is in the front of the face, the latter in the zygomatic fossa. The lower border of both is the alveolar process, 1 which is simply a curved row of tooth sockets made of very light plates of bone, which are absorbed after the loss of the teeth. The palatal process 2 joins the inner side of the body like a shelf and supports the anterior part of the alveolar process. The nasal process 3 rises from the anterior inner part to meet the frontal bone. In certain parts of the description it is con- venient to disregard these subdivisions. The anterior surface of the bone forms the lower and outer boundary of the nasal opening, which is finished above by the nasal bone. On the entire skull this aperture resembles an ace of hearts inverted. The lower boundary of the opening is slightly raised and smooth. On the side it is sharp. The pointed anterior nasal spine projects forward where the two bones meet below the opening. 4 There is a slight depression the incisor or my rtiform fossa over the lateral incisor tooth. External to this is a ridge caused by the socket of the canine tooth. Farther outward is a well-marked hollow, the canine fossa. Above Lachrymal groove Lachrymal notch Orbital surface Infra-orbital groove Posterior dental canal Zygomatic surface Masseter Malar process Tuberosity Buccinator Nasal process Orbicularis palpebrarum Lev. lab. sup. alceq. nasi Orbicularis palpsbrarum Infra-orbital foramen Lev. labii sup. Canine fossa Incisor crest Lev. ang, art's Compres. naris Incisor fossa Depres. alee nasi Alveolar process Right superior maxillary bone, outer surface. this, about five millimetres below the edge of the orbit, is the infra-orbital foramen, transmitting the nerve and artery of the same name. This surface is bounded above and externally by the malar process. The zygomatic surface is in the main convex, except for a smooth concavity behind the malar process. The lower posterior portion, the tuber osity? is rough, and presents at its upper part two or three minute posterior dental foramina 6 by which those nerves enter canals in the bone. The smooth superior or orbital surface, slanting a little downward and outward, is triangular. The posterior border is free, forming the lower limit of the spheno-maxillary fissure, and running obliquely forward to the malar process. The anterior border passes outward and backward to the same. The inner border is in the main antero-posterior. The hind end slants outward, articulating with the little triangular orbital surface of the palatal. Anterior to this, the border joins the os planum of the ethmoid ; and anterior to the latter, at the base of the nasal process, lies a semicircular indentation, the lachry- mal notch? the posterior border of which touches the lachrymal bone. The deep infra- orbital groove* runs more than half across the orbital surface from behind, and then 4 For a more detailed account, see the section on the Nasal Cavity. 1 I'rnresMis .-ilvrolarK. '-' I'rm'ussus pulntinus. :l Proccssus frontalis. ''Tuber maxillare. ''Foramina alveolarla. 7 Im iMir:i l:ii i im.iliv Snlrns infraorhltalls. THE SUPERIOR MAXILLA. 201 becomes a canal, opening at the corresponding foramen in front. Occasionally a suture marks the course of the canal. The internal wall of the body presents on the separate bone a very large opening into the antrum, or maxillary sinus, which is much reduced when the other bones are in place. In front of this opening the wall is smooth and concave, forming a part of the lachrymal groove. Near the level of the top of the body there is the rough horizontal inferior turbinate crest for articulation with that bone. The wall at the back of this surface has a vertical groove, which, when the palate bone is in place, forms part of the posterior palatine canal, opening near the back of the hard palate and transmitting the descending palatine artery and the anterior palatine nerve. The malar and the alveolar processes have been incidentally described. The nasal or ascending process rises at the inner side of the orbit. It is thin below, with an outer surface towards the face and an inner towards the nose. The top is thick and rough, joining the frontal. The lachrymal groove^ for the tear-sac and the nasal duct begins on its outer surface and passes down behind it, making a deep notch at the front of the orbital plate. The lower part of the process extends down as far as the inferior turbinate crest, forming, with the lachrymal, the inner side of the groove. The point of junction of the front border of the groove with the orbital plate is usually marked by the lachrymal tubercle. The inner side shows above at the pos- terior border some cellular spaces completing the anterior ethmoidal cells, bounded below by a ridge, the crista ethmoidalis, which articulates with the front of the middle turbinate bone. Below it the bone is concave, forming part of the vestibule of the nose ; above it is plane and marked with vascular grooves. The palatal process projects inward from the anterior two-thirds of the body and joins the alveolar process in front. It is very smooth above, the mucous mem- brane being lightly attached to it. It is slightly concave from side to side, and has a raised edge in front. It is also raised along the median line to form the nasal crest" 1 with its fellow. The front of this ridge, called the incisor crest, suddenly rises to a higher level and juts out below the nose as the anterior nasal spine. The vomer rests on the ridge, except at the front, where its place is taken by the triangular cartilage. The under surface of the palatal process, horizontal behind, slants down- ward in front to the incisor teeth. It is rough for the firm support of the mucous membrane. The median surface of the palate is rough to join with its fellow. A little behind the incisors it shows a groove in the lower part, which becomes a canal in the upper, and opens into the floor of the nasal fossa of either side. Thus there are two canals above and one below, like a Y placed transversely. These are the canals of Stenson, which transmit an artery connecting the vessels of the nose and mouth. Their common orifice is called the anterior palatine canal? Into this open two minute canals, the left anterior to the right, made by the junction of the -bones. These are the canals of Scarpa, and transmit the naso-palatine nerves. They are by no means always to be found. The canals of Stenson represent the anterior palatine canal of lower animals, which in them is generally double throughout. In man the whole opening is usually closed by mucous membrane. The back of the palate process joins the horizontal plate of the palate bone, which completes the palate behind. The antrum or maxillary sinus 4 is a large cavity within the body, the shape of which it follows in the main, although with many variations of size. The large opening on its inner wall is much diminished when the palate, the ethmoid, and the inferior turbinate are in place. It lies near the anterior end of the lateral wall of the middle nasal meatus, covered by the middle turbinate. A small part of the roof of the antrum is often formed by the palate bone, and sometimes the cavity extends into the malar. The inner and most of the posterior and outer walls are generally very thin, as is also the roof, except around the infra-orbital canal, which projects into the antrum. The development outward towards the malar bone varies much, as does the downward and forward growth towards the alveolar process. The lower border of the antrum is usually a trifle below the level of the floor of the nares. According to C. Reschreiter, 5 this is a male characteristic. Be that as it may, it certainly is in 5 Zur Morphologic des Sinus Maxillaris, Stuttgart, 1878. 1 Sulcus lacrlraalis. '- Crista nasalis. 3 Foramen incisivum. * Sinus maxillaris. 202 HUMAN ANATOMY. accord with the larger size of the sinuses in man. The internal surface is largely smooth. Bony ridges springing from various parts tend to subdivide the cavity. They sometimes form little pockets above the teeth. According to Gruber, 1 it may in rare cases be completely subdivided into a smaller posterior chamber and a larger front one, both of which open into the nasal cavity. The lowest part of the antrum is indented by the roots of the molars and of the second bicuspid, at least very frequently. The first and second molars always indent it, but the bicuspid and the wisdom-tooth may not. (For further details, see Teeth, page 1556.) Articulations. All the bones of the face, except the lower jaw and the hyoid, touch the superior maxilla. It has been described as the key to the architecture of the face. The palate bone both completes the palate and lies between this bone and the pterygoids, closing the posterior part of the opening into the antrum. The malar, joining the process of that name, makes the prominence of the cheek and helps to bound the orbit. The nasals complete the anterior nasal aperture. The lachrymals and ethmoid touch the inner side of the orbital plate, and the ethmoid the inner surface of the nasal process. The frontal rests on the nasal process, the FIG. 225. Nasal process -j Ethmoidal crest Middle tneatus Inferior turbinate crest Inferior meatus Incisor crest Anterior nasal spine ( Wi, / ' \ At Mi no ' \ Anterior palatine canal fa Alveolar proc Completes ethmoidal cells Antrum Posterior palatine canal Nasal crest Palatal process Tuberosity Right superior maxillary bone, inner surface. crest inferior turbinate rests on the inner surface of the maxilla, and the vomer on the made by the union of the palate processes. Development and Changes. There are certainly four chief centres, all of which appear at about the end of the sixth week of foetal life. Three of them fuse very rapidly. There is one on either side of the infra-orbital groove, a malar and an orbito-facial, and below and internally a palatine. The fourth, the intermaxillary, stays distinct longer. It comprises the front of the palate as far back as the anterior palatine canal, and represents a very constant separate ossification in vertebrates, the premaxilla, in front of the maxilla, except in certain mammals in which it is between them. It bears the incisor teeth, and at the third foetal month fuses with the maxilla. As the intermaxillary grows, the suture in the roof of the mouth per- sists for a time. It is very plain at birth and often for a year or two later. Some- times it is seen in the adult. At first the posterior suture is very close to the incisors, but as it grows the intermaxillary forms a large part of the palate. If detached, it is seen notched behind, so as to form the inner wall of the upper part of 1 Virchow's Archiv, Bd. Ixiii. THE SUPERIOR MAXILLA. 203 Stenson's canal. The suture is rarely seen above and never in front, being concealed by the plate forming the front of the bone. Albrecht J asserts that each intermaxil- lary is double. In support of this is the fact that in cleft palate the fissure does not always come between the incisor teeth and the canine, but an incisor may be found on its outer side. In reply to this it has been pointed out that three incisors on each side occasionally occur, and that, as anomalies are likely to be found in groups, this is merely an irregular arrangement. Moreover, in cases in which the cleft has but one incisor on each side of it, it is well argued that the original position of the tooth-sacs has no certain relation to the bones (Th. Kolliker 2 ). In sup- port of Albrecht is the occasional presence of a line subdividing the lower surface of the premaxilla ; but, on the other hand, it is not certain that this is really a suture, and there seems no evidence that the premaxilla has two centres of ossifi- cation. While there is much that is plausible in Albrecht' s views, they cannot be considered as established. Sir William Turner 3 thus concludes an excellent discussion of the question : " What is yet wanted, however, to give completeness to the evidence of the division of the intermaxillary bone into an inner and an outer part is the discovery that the intermaxillary bone normally rises from two distinct centres of ossification, one for the inner, the other for the outer part. Of this we have at present no evidence. FIG. 226. Alveolar process FIG. 227. Lachrymal groove Inferior surface of upper jaw at about birth. Antrutn Ant. palatine canal Palatal process Mesial surface of upper jaw at about birth. But, in connection with this matter, we ought not to forget that it is quite recently that the embryological evidence of the origin of the intermaxillary part of the human upper jaw from a centre distinct from that of the superior maxilla has been completed. And yet for nearly a century, on such minor evidence as was advanced by Goethe, viz., the suture on the hard palate extending through to the nasal surface, anatomists have believed and taught that the human upper jaw represented both the superior and intermaxillary bones in any other mammal. Where a question in human embryology hinges upon an examination of parts in a very early stage of development, we often have to wait for many years before an appropriate specimen falls into the hands of a competent observer. The upper and lower sides of the bone are at first very near together. The tooth-sacs are directly below the orbit. In the latter part of foetal life the antrum appears as a slight pouch growing in from the nasal side. As the bone grows, the antrum remains for some time on the inner side of the infra-orbital canal. The outer part of the bone, especially towards the malar, is filled with diploe, which subse- quently is absorbed as the sinus extends outward. By the end of the second year the cavity has extended above the first permanent molar ; by the twelfth or thirteenth year, when the second molar has appeared, the antrum approaches, though it has not yet reached, its definite shape. During the first dentition it is separated by the uncut teeth from the front of the bone. 1 Sur les quatres os intermaxillaires, Soc. d'Antropol. de Bruxelles, 1883. Die morpho- logische Bedeutung der Kiefer-, Lippen-, und Gesichtsspalten, Langenbeck's Archiv, Bd. xxi. 2 Ueber das Os intermaxillare des Menschen. Nova Acta der Leopold. Carol. Akad. der Naturforschen, Bd. xliii., 1882. 3 Journal of Anatomy and Physiology, vol. xix., 1895. 204 HUMAN ANATOMY. Orbital surface Spheno-maxillary fossa Spheno-palatine notch VERTICAL PLATE For ext. pteryg. plate Pterygoid fossa HORIZONTAL PLATE ^ For int. pterygoid plate Right palate bone from behind. TUBEROSITY After the loss of the teeth from old age or otherwise the alveolar process is absorbed. Senile atrophy is particularly marked in this bone. THE PALATE BONE. This 1 consists of a horizontal and a vertical plate and three processes, the py- ramidal, the orbital, and the sphenoidal. The horizontal plate * is quadrilateral. It completes with its fellow the hard FIG. 228. palate, filling the space left vacant be- prbitai process tween the back parts of the superior maxillae. Its superior surface is smooth like the rest of the floor of the riares, and the lower rough, but less so than that of the superior max- illa. The anterior border fits the back of the palatal process of the maxilla ; the inner border is rough to meet its fellow, and raised into a nasal crest meeting the back of the lower edge of the vomer. This is prolonged behind to form with the other the posterior nasal spine. The posterior border is smooth and concave from side to side. The outer border joins the vertical plate. 3 This is very thin, with an outer and an inner sur- face. It is surmounted by two processes, between which is a deep notch which forms three-quarters or more of the spheno-palatine foramen 4 when the bone is in position, so that both processes touch the body of the sphenoid. The outer surface presents near the top a smooth vertical surface forming part of the ptery go-maxillary FIG. 229. For ethmoid Orbital process To complete ethmoidal cells Spheno-palatine foramen Sup. turbinate crest Sphenoidal process Middle nasal meatus Inf. turbinate crest Inferior meatus Tuberosity Posterior nasal spine Nasal crest Inner aspect of right palate bone in place. Part of inferior turbinate removed. fissure. This narrows below into a groove which makes the posterior palatine canal when applied to the corresponding groove in the maxilla. In front of this the surface is at first rough where it rests against that bom-, and more anteriorly smooth where it closes the lower part of the opening of the* antrum by an irregular 1 IK |. ,1 ii mum - I'.n s hot i/iiiii.iliv I'. II-. iu-iiii-iulirnl.il ix. ' 1'iit.iim-ii Nphi>nnpal;i< iiiuiii. Ant. part of inf. turbinate THE PALATE BONE. 205 prolongation. The inner surface, looking towards the nasal cavity, is free and smooth. It is crossed below the middle by a ridge, the inferior turbinate crest 1 for the posterior attachment of the inferior turbinate bone. Nearly on a level with the base of the notch is another ridge faintly marked behind it ; this is the superior turbinate crest * for the middle turbinate bone of the ethmoid. A small part of the top of the vertical plate looks into the superior meatus. The pyramidal process, or tuberosity, is the only solid part of the bone. It projects backward and some- what outward from the lower part of the vertical plate. A smooth, hollowed, triangular surface fits into the space left between the pterygoid plates, completing the floor of the pterygoid fossa ; on one side of this is a groove for the front of the internal pterygoid plate and on the other a rough surface for that of the outer. Thus, through the palate bone, the pterygoids support the back of the upper jaw. The outer side of the process rests against the tuberosity of the maxilla in front of the tip of the external pterygoid plate. The orbital process, is the anterior of the two processes above the vertical plate, the larger and higher, so called because it forms a small part of the floor of the orbit near its apex on the inner side. This little surface, on the outer side of the process, is triangular, one edge articulating with the upper jaw and one with the os planum, the hind edge being free. Another smooth surface looks outward and backward towards the spheno-maxillary fossa. It is separated from the preceding surface by an angle. Three other surfaces rest against other bones. An antero-inferior one joins the maxilla, sometimes helping .to close the antrum ; an anterior one touches the ethmoid, bounding part of a cell ; and a small one, just at the top of the notch, touches the sphenoidal spongy bone. The posterior or sphenoidal process has a narrow upper surface, which, joining the sphenoidal spongy bone near the base of the internal ptery- goid plate, completes the ptery go -palatine canal. This surface reaches the edge of the vomer. The internal surface, slant- FIG. 230. Spheno-maxillary foss; Sphenoida process Tuberosity Orbital surface Orbital process Maxillary surface Antrum Post, pala- tine canal For sup. maxillary Right palate bone, outer aspect. ing a little downward, is free, looking into the nasal fossa. The outer surface is di- vided by a vertical ridge into an anterior part, free and smooth, looking into the spheno-maxillary fossa, and a scale-like pos- terior portion which rests against the external pterygoid plate. The Spheno-Maxillary Fossa. When the palate bone is applied to the sphenoid and the maxilla, the spheno-palatine foramen forms a window between the nasal chamber and a little hollow, the spheno-maxillary fossa , just below and behind the apex of the orbit. The posterior wall of this space, formed by the smooth sur- face of the sphenoid above the pterygoid plates, is pierced by the foramen rotundum and the Vidi an canal. Below, it narrows funnel-like into the posterior palatine canal. Articulations. The palate bone articulates with its fellow, the superior max- illary, sphenoid, ethmoid, vomer, and inferior turbinate bones. Development. Ossification begins from a single centre appearing in mem- brane near the end of the second fcetal month at about the junction of the vertical and horizontal plates. It is very delicate throughout fcetal life, but the posterior free edge of the palate is very early much denser. Originally the horizontal plate is larger than the vertical one ; at birth they are about equal. THE VOMER. The vomer' is a thin, irregularly quadrilateral plate, forming the back and lower part of the nasal septum. The superior border expands laterally into two wings, or alee, which articulate with the under surface of the body of the sphenoid, and enclose a medium groove for the rostrum. Laterally, the wings fit under the vaginal pro- 1 Crista turbinatis. - Crista ethmoidalis. 3 Vomer. 206 HUMAN ANATOMY. cesses of the sphenoid. The posterior border is free. Thick above, just under the alse, it soon narrows and runs downward and forward. The inferior border fits FIG. 231. SUPERIOR BORDER Ala Naso-palatine groove Vomer in place, from left side. FIG. Vomer, superior surface. between the nasal crests of the palatals and maxillae, and anteriorly changes its direc- tion so as to rise over the higher incisor crests as far as the anterior palatine canal. The anterior border is the longest. Its upper part articulates with the back of FIG. 233. the vertical plate of the ethmoid, the A\X lower part with the triangular cartilage of the nasal septum. The latter is received into a groove which may extend behind the vertical plate. The sides of the vomer are covered with mucous membrane. They present a few irregularities, the most important of which is a groove on either side, nearer the front than the back, for the naso-palatine nerve ; and, just anterior to this, a thickening which is normally insignificant, but occasionally is developed to one side or the other, forming a spur which may nearly close the passage. Articulations. The vomer articulates with the sphenoid, ethmoid, palate, and superior maxillary bones and the median triangular cartilage. Development. It is to be remembered that, although the vomer becomes through ossification one of the separate bones of the face, at an early period it is but a portion of the septal car- tilage without any hint of demarcation. A single centre appears before the close of the second foetal month in the membrane at the under border of the cartilage, which then forms the septum. This grows upward on either side of the cartilage until the bone is complete. The young bone shows very clearly its formation in two plates ; but in the adult this appears only in the groove between the wings and in the lower part of the front border, which still receives the triangular cartilage. Groove for rostrum of sphenoid Ant. border for ethmoid Grooved ant. border for septal cartilage Vomer from before and above. THE LACHRYMAL BONE. 207 THE LACHRYMAL BONE. The lachrymal bone l is an exceedingly thin osseous plate, filling the vacancy in the inner wall of the orbit between the orbital plate of the ethmoid and the ascending process of the superior maxilla. It is quadrilateral, the long diameter being vertical, and presents an outer surface directed towards the orbit and an inner surface towards the nasal fossa. The latter rests, in part, against the turbinate process of the eth- moid, which more or less overlaps it. It closes the infundibulum and several anterior FIG. 234. Lachrymal crest Nasal process of sup. max. Lachrymal groove Orbital surface Hamular process Right lachrymal bone in place, outer aspect. FIG. 235. ethmoidal cells. The lower and anterior portion of this surface forms a part of the wall of the middle nasal meatus. The outer surface is subdivided by a vertical ridge, 2 marking off a smaller anterior part, which forms the lachrymal groove ; 3 and, joining the corresponding groove of the superior maxillary, complete the lachrymal canal. The posterior part of the orbital surface is plane. The hamular process 4 is a small tongue of bone curving forward from the lower part of the dividing ridge to form the posterior border of the canal at the floor of the orbit. The descending process is a downward prolongation of the grooved portion, forming part of the wall of the canal, and meeting the lachrymal process of the inferior turbinate. The bone also articulates with the frontal by its upper surface, and with the front of the os planum by its pos- terior border. Articulations. The lachrymal articulates with the eth- moid, frontal, superior maxillary, and inferior turbinate bones. Development. Ossification is from a single centre said to appear in the eighth foetal week, although the variations imply meatus" extra ones. Macalister 5 enumerates six separate ossicles which may occur about the bone. It varies greatly iii size ; it may be wanting, though rarely, and sometimes is very large. A considerable development of the hamular portion, which may be separate, represents the condition of prosimians and platyrhine apes. 6 It may be subdivided or perforated. 7 5 Proc. Royal Society, 1884. fi Gegenbaur : Morph. Jahrbuch, Bd. vii. 7 Le Double : Essai sur la Morphogenie et les Variations du Lacrymal, 1900 ; and Zabel : Varietaten und Vollstandiges Fehlen des Tranenbeins beim Menschen, Anat. Hefte. Bd. xv., Heft i, 1900. 1 Os lacrimalc. " Crista lacrimalis. 3 Sulcus lacrimalis. 4 Hamulus lacrimalis. Right lachrymal bone, inner aspect. Upper part completes anterior ethmoidal cells, lower looks into middle nasal 208 HUMAN ANATOMY. THE INFERIOR TURBINATE BONE. This is an elongated curved bone ' placed in the lateral wall of the nasal cavity below the superior and middle turbinates, which are parts of the ethmoid. The inner convex surface is pitted and grooved by the cavernous tissue beneath the mucous membrane. This condition is continued round the free lower border a little way up the outer side. The rest Ethmoidal process Right inferior turbinate bone in place, inner aspect. FIG. 237. of the outer surface, overhanging the inferior nasal meatus, is nearly smooth. The ends of the bone are pointed. They are connected below by the regular curve of the inferior border. The upper border is thin and irregular. It articuiates in front with the inferior turbinate crest of the max- illa. Behind this rises the lachrymal process * the highest to meet the lachrymal bone. Posterior to this the maxillary process 3 bends outward and downward. It does not, how- ever, usually hook over the upper edge of the plate bounding the entrance of the an- trum, but meets it edge to edge, consider- ably reducing the opening. Still farther back is the ethmoidal process* meeting the uncinate process ; and, finally, the border rests on the inferior turbinate ridge of the palate bone. Articulations. The inferior turbinate articulates with the superior maxillary, ethmoid, palate, and lachrymal bones. Development. Ossification proceeds from a single center which appears about the middle of foetal life. 1 Concha inferior. - 1'roc. lacrimalls. 3 Proc. maxlilarl*. 4 Proc. ethmoidalis. Right inferior turbinate bone, outer aspect. THE NASAL AND MALAR BONE. 209 Crest Groove 10 r nasal nerve Right nasal bone, outer and inner aspects. THE NASAL BONE. The two nasal bones 1 bound the anterior nasal opening above. Each one is a four-sided plate with an outer and an inner surface. The upper end is thick and jagged, articulating with the frontal above and also behind. The anterior border, which articulates with its fellow, is thick above and thin below. When the two bones are in place, the united upper portions of these borders form posteriorly the nasal crest, which articulates with the nasal spine of the FIG. 238. frontal, and sometimes with F "/A TAL the vertical plate of the eth- moid below it. The pos- terior border joins the as- cending process of the maxilla. The thin lower border, slanting downward and outward, has one or two indentations. The outer surface is broader below than above. It is depressed in the upper third, and has there a foramen for a vein. The extreme upper part of the inner surface is rough to join the frontal. Below this it is smooth where it forms the front of the nasal chamber ; the lower part of the Jnner surface sometimes seems hollowed out. A vertical groove for the nasal nerve ends near the notch in the lower border. Articulations. The nasal bone articulates with the frontal, ethmoid, superior maxilla, and the opposite nasal. Development. Ossification spreads from a centre appearing about the eighth week of foetal life. At first the bone is broad and short. Occasionally a little Wormian bone is found in the median line between the nasals and the frontal. The two bones sometimes coossify, after the fashion of apes. Either a vertical or a trans- verse suture may be found. THE MALAR BONE. This bone 2 forms the prominence of the cheek, the outer border of the orbit, most of the wall separating the orbit from the temporal fossa, and completes the zygomatic arch. For simplicity of description it is best to consider it a diamond- shaped bone, with an outer and an inner surface, four angles, four borders, and one important process, the orbital, which is neither an angle nor a border. The outer surface presents a slight prominence, the tuberosity? a little below the middle. The surface is nearly smooth, except that near the lower border there is often a certain roughness extending onto the zygomatic process for the origin of the masseter muscle. The greater part of the inner stirface is smooth, looking towards the temporal and zygomatic fossae ; but a rough space under the front angle joins the malar process or the maxilla. It sometimes helps to close the antrum, in which case a part of it is smooth, being lined with mucous membrane. The superior angle, or frontal process* joins by a rough surface the external angular process of the frontal. The posterior angle, or zygomatic process? more prominent below than above, joins the zygomatic process of the temporal, passing below it. The anterior and the inferior angles have no special names. The postero-superior, or temporal border, is at first vertical, becoming horizontal towards the hind end. Near the beginning there is a posterior projection, the marginal process, which varies considerably. The postero-inferior, or masseteric border, slightly irregular, is free, forming the lower edge of the front of the zygoma. The antero-inferior, or maxillary border, is slightly concave. It articu- 1 Ossa nasalia. - Os zygomaticum. 3 Tuberositas malaris. 4 Processus frontosphenoidalis. D Processus tcmporalis. 14 210 HUMAN ANATOMY. lates with the front of the malar process of the maxilla, bounding externally the rough surface of the inner side of the malar. The antero-superior, or orbital border, is smooth and concave, forming the external and most of the inferior boundary of the orbit. The orbital plate, or process, which forms the front of the outer wall of the orbit, projects inward from this border, joining the bone at nearly a right angle. FIG. 239. Malar canal Tuberosity Right malar bone, outer aspect. It is narrow in front and broad behind, where its anterior surface looks .towards the orbit and its posterior towards the temporal fossa. Its projecting edge is jagged throughout, and in front meets the superior maxilla. Behind that it joins the outer border of the great wing of the sphenoid, and above articulates with the frontal. Be- tween the part meeting the maxilla and that meeting the great wing there is usually a short, smooth surface bound- FIG. 240. ing the end of the spheno- Frontai process maxillary fissure, which lies between these bones in the lower outer angle of the orbit. Two foramina on the orbital surface lead to minute canals. The lower, the malar, 1 ope on the outer surface of th bone ; the upper, the tem- poral? opens on the back of the orbital process. They transmit branches from the superior maxillary division of the fifth nerve. They va greatly. In all mammals the pri- mary function of the malar is to unite the maxilla and the temporal bone. Its union Only in primates does it join the sphe- Temporal canal Malar canal Maxillary surface Orbital process Temppro-zygo- matic surface Right malar bone, inner aspect. with the frontal is a further development. noid and separate the orbit from the temporal fossa. Articulations. Tin- malar bone articulates with the frontal, superior maxillary, temporal, and sphenoid bones. Development and Variations. There are three centres of ossification- -an 1 Foramen zygumaticufacialc. '-' Foramen zyuoinaticotemporale. THE INFERIOR MAXILLA. 211 anterior, a posterior, and an inferior appearing towards the end of the second foetal month. They fuse in the course of the third. Sometimes, but very rarely in the white races, the bone is divided by a fissure as in some apes into an upper and a lower part. This is said to be relatively common (seven per cent.) in the Japanese. A division into three has been seen. The roughness for the masseter sometimes gives a deceptive appearance of a separate piece to this portion. On the other hand, an occasional slight horizontal cleft in the zygomatic process is probably a remnant of a division. THE INFERIOR MAXILLA. The inferior maxilla, 1 mandible, or lower jaw develops in two symmetrical halves, which soon fuse. The bone, as a whole, consists of a central part the body forming the chin and supporting the teeth, and two rami projecting upward from the back on either side and articulating with the glenoid fossa of the temporal. The body is convex in front and concave behind. The line of junction of the original halves is the sywp/iysis, marked by a slight line. There is a forward pro- jection of the lower border of the chin which is a human characteristic. A short FIG. 241. Coronoid process External pterygoid CONDYLE Temporal Sigmoid notch Neck Masseter. ANGLE BODY External oblique line Platysma Inferior maxillary bone, outer aspect. Mental foramen Depressor anguli oris Incisor fossa Levator menti SYMPHYSIS Mental tubercle Depressor labii inf. distance from the median line at the lower border is the mental tubercle* bounding this projection laterally. The alveolar process, above the body, is of the same nature as that of the upper jaw. A slight depression, the incisor fossa, is found below the teeth of that name on the front of the bone. The mental foramen for the terminal branches of the inferior dental nerve and artery is rather below the middle of the bone under the second bicuspid, sometimes just before it. The external oblique line? starting from the mental tubercle, passes below the mental foramen into the front edge of the ramus. Sometimes it seems to spring from the lower border under the molar teeth, and sometimes both these origins may be present at once. On the lower border of the bone, rather to its inner side, there is a rough oval behind each mental tubercle for the anterior belly of the digastric muscle. The inner side of the body is in the main smooth. The superior and inferior genial tubercles* are two pairs of small, sharp spines near the lower part of the inner side of the symphysis for the genio-glossi and genio-hyoid muscles respectively. The internal oblique line begins at first very indistinctly near the genial tubercles, and is lost on the inner side of the ramus. It is particularly prominent under the molars, and gives attach- 1 Mandibula. -Tubcrculum mcntale. ; Linca obliyua. *Spinac incntalcs. " Linca mylohyoidca. 212 HUMAN ANATOMY. ment to the mylo-hyoid, which forms the muscular partition separating the oral cavity from the superficial -region under the chin. There is a faint hollow, the sub- lingual fossa, above it, below the incisors, for the sublingual gland lying beneath the mucous membrane, and a deeper one, the submaxillary fossa, for the submaxillary gland below the line near the junction of the body and ramus. The ramus, which joins the body at an angle of from 110 to 120 in the adult, is a four-sided plate with an outer and an inner surface. The point of union of the posterior and inferior borders is called the angle, and is generally turned out- ward with a lip, which helps to form the under part of the massctcric fossa, on its outer side, for that muscle. When well marked, it represents the fossa which is so striking in the carnivora and some other orders. The fossa is not always present, the muscle being then inserted into a roughness. At the front of this space the lower border of the bone is often grooved by the facial artery crossing it. A projec- tion, known as the lemurine proces-s, may extend from the angle either backward or downward, but is not often large. The lower border of the ramus, where it joins the body, often presents a concavity, which is sometimes very marked, giving a peculiar outline ; it is named the antegonium by Harrison Allen. There is a rough- FIG. 242. Coronoid process Sigmoid notch Fossa for sublin- gual gland Sup. genial tuber. (genio-glossus) Inf. genial tuber. (genio-hyoid) Superior constrictor Alveolar border Int. pterygoid Angle Digastric Mylo-hyoid Submaxillary gland Inferior maxillary bone, inner aspect. ness on the inner side of the ramus at the angle for the internal pterygoid. About on a line with the free edge of the alveolar process is the lowest point of the inferior dental foramen, 1 an opening into the inferior dental canal for the nerve and artery to the teeth ; the foramen is guarded in front by a sharp point, the lingula. A faint groove is continued from this opening below the internal oblique line for the mylo- hyoid vessels and nerve. The front border of the ramus is thick below and narrow above, where it becomes the coronoid process, z pointing upward and outward, into which the temporal muscle is inserted. The outer border of the thick part is made by the external oblique line, which is continued into the thin edge above ; the inner border is continued from the inner edge of the alveolar process, or sometimes from the internal oblique line. It ends on the inner surface of the coronoid process. The posterior border of the ramus slants upward, backward, and a little outward. It is rough at the angle and smooth above, where it widens to form the back of the head or condyle. ' This presents an articular surface convex from before backward and higher at the middle than at the ends. The longest diameter is not quite trans- verse, for the axes, if prolonged, would meet near the front of the foramen magnum. There is a pretty distinct tubercle at the outer and inner ends. The condyle has 1 Foramen imimliliulnrc. - I'roccssus coronoldcin. 'Ciipltulnm mnndlbulac. THE INFERIOR MAXILLA. 213 the appearance of being set rather on the front of the neck,* which is merely a constriction below the head ; the articular surface, however, extends at least as far down behind as in front v There is a depression for a part of the insertion of the external pterygoid on the front of the neck internal to the sigmoid notch? which is the deep depression separating the coronoid process from the condyle. The dental canal' 1 " sweeps downward and forward with a slight curve, and then runs FIG. 244. Alveolar process Coronoid process Condyle Symphysis Dental canal Right inferior maxilla at about birth, inner aspect. Dental canal Section through body of lower jaw, anterior surface. FIG. 245. Condyle horizontally nearer the lower than the upper border of the body of the jaw. 4 It lies at first against the inner wall, but soon is nearer the outer. This relation then varies, but towards the anterior end of its course it is against the inner wall. It divides under the second bicuspid into the mental canal, some five millimetres long, running to the mental foramen, and into the incisive canal, much smaller, for the vessels and nerves of the front teeth, which, after dividing, is lost in the cancellated tissue under the lateral incisor. Structure. The jaw is of very tough bone, especially at the symphysis, where it is almost solid. On section the body shows very thick walls below, before, and behind. The alveolar processes, on the contrary, are made of very light plates that are ab- sorbed rapidly after the loss of the teeth. Development and Growth. The two halves of the inferior maxilla are formed separately, each from six centres. They are at first connected by ligament. Even before birth the union seems very close, but they become coossified only in the course of the first year. The centres appear from the sixth to the eighth week of foetal life in the membrane of Meckel's cartilage, except as otherwise mentioned. They fuse during the third month. The centres are : ( i ) the dentary, which is a line of ossific deposit forming the lower border and the front of the alveolar process ; (2) one in the distal end of Meckel's carti- lage, for the region of the symphysis ; (3) one for the coronoid ; (4) one appearing in cartilage, not that of Meckel, for the condyle and top of the ramus ; (5) one for the angle ; (6) the splenial, for the inner alveolar plate, extending back to include the lingula. This one appears some three weeks later than the others. Still another minute one is said to help to form the mental foramen (Rambaud et Renault). All these, except that for the condyle, which unites at fifteen, fuse shortly after their appearance. The mandible, being at first nothing but a hollow bar to hold tooth-sacs, is very shallow. The ramus is small, the head bent back- ward and the angle very large. At birth it is about 140. With the loss of teeth, from whatever cause, the alveolar process atrophies. In old age the bone is very small and of light structure, and the angle enlarges considerably, so as to mimic the infantile form. *Fawcett : Journal of Anatomy and Physiology, vol. xxix., 1895. 1 Collum mandibulac. - Incisura mandiluilac. :; Canalis maiidibulae. Alveolar process Right half of lower jaw at about birth, from above. HUMAN ANATOMY. Intra-articular fibre-cartilage FIG. 246. Zygoma, cut surface External pterygoid \ THE TEMPORO-MANDIBULAR ARTICULATION. This is a compound joint, the elements of which are the socket, the condyle, and the meniscus, an intra-articular disk of fibro-cartilage, dividing the cavity into an upper and a lower part, both being enclosed by one capsular membrane. The socket includes the glenoid fossa and the articular eminence of the temporal bone. The articu- lar coating of the socket, which is continued onto the front of the articular eminence, is not true cartilage (Langer), though resem- bling it to the naked eye. The socket is bounded behind by the fissure of Glaser. The tympanic plate behind it is covered by areolar tissue and a part of the parotid gland, which extend to the back of the head of the jaw and make the socket much narrower and deeper than it seems on the dry bone. The intra-articular fibro-cartilage^ is oblong trans- versely with rounded angles. It rests more on the front of the condyle than on the top. It is concave both above and below, being moulded on the eminentia articularis and on the condyle. It may be merely one millimetre thick in the middle, and is said to be some- times perforated. The thick posterior border fits into the highest part of the socket. The capsule, lax and weak, is attached to the borders of the articular surfaces and to the edges of the intra-articular fibro-cartilage. The external lateral ligament" 1 is a com- paratively strong collection of fibres, strengthening the capsule externally. The fibres run downward and back- FIG. 247. External lateral ligament The temporo-mandibular articulation ; the joint opened. ward from the tubercle on the zygoma, at the outer end of the articular eminence, to the outer side of the neck as far as the hind border. The effect of this insertion is to place the trans- verse axis of rotation of the jaw, not in the head of the mandible, but in the neck. The capsule receives at the front and inner side two bands of fibrous tissue continuous with the dura mater, which passes through the fora- men ovale around the third di- vision of the fifth nerve. 3 The spheno-mandibular ligament, 4 formerly improperly called the internal lateral, is a weak fibrous structure originally developed around a part of Meckel's car- tilage. It runs from the spine of the sphenoid to the lingula without connection with the joint. The capsule is far too loose to hold the jaw firmly in place, hence it is supplemented by the powerful muscles of mastic -.itum. One of these, the external pterygoid, is inserted into both the head of the lower jaw and the meniscus, which it draws forward, bring incorpo- "Fuwri-U : Journal of Anatomy ami Physiology, vol. x.xvii., 1893. ' hUrus iirtiriilaris. - Llg. tcmporomnnilil>ul:iro. 1 Llg. sphenoinandlhulnre. Ext. auditory meatus Styloid process Stylo- mandihu- lar ligament Stylo-hyoid ligament Hyoid bone The tenipou) maiuliluikir artu-ululion, ouu ' THE ARTICULATION OF THE MANDIBLE. 215 FIG. 248. Carotid canal Spine of sphenoid Spheno- mandibular ligament Capsule The temporo-mandibular articulation from behind. rated with the front of the capsule. The stylo-maxillary ligament is a bundle of fibres of the cervical fascia running from the styloid process to the angle of the jaw. Movements. These occur on both sides of the meniscus, which slides for- ward and backward on the articular eminence. They may be divided into those of opening and closing the mouth and of grinding the teeth. In the former, as the mouth begins to open, the meniscus and the head of the jaw move forward, the condyle at the same time advancing on the former as the lower jaw turns on a transverse axis pass- ing through the neck in both halves of the jaw. This continues as the mouth opens wider, the meniscus descending onto the articular eminence, and probably, when the movement is extreme, rising a little on the other side. This has been graphically demonstrated on the living by an apparatus bearing luminous points at the sym- physis, the condyle, and the angle of the jaw, which were photographed as the mouth opened to various widths. 1 It was shown that the for- ward movement of the meniscus occurs even in a very slight opening of the mouth. The angle of the jaw moves forward at the very beginning of the act, but soon passes backward. The point on it describes some very complex curves. Grinding movements, in which the mouth is not opened, must occur chiefly between the skull and the meniscus ; just what occurs below the latter is uncertain. The lower jaw can be thrust for- ward evenly, as the meniscus of each side de- scends onto the articular eminence ; but in ordinary motions it seems to advance on one side and perhaps to recede on the other. Spec * has shown that the opposed crowns of the molars (and apparently of the premolars also) fall on the arc of a cir- cle that touches the front of the condyle, drawn, when projected on a plane, from a centre on the crest of the lachrymal bone. This allows the teeth of the lower jaw to slide on those of the upper, which the joint would not allow were the line between the teeth a straight one. To this may be added that the inferior incisors rest against the lingual surfaces of the superior, and that the tendency of the edges of the former to make a transverse arch, increased by the wearing away of the outer corners of the lower lateral incisors, implies an alternate rising and falling of either side of the jaw in grinding movements with the mouth closed, though the axis, in the main antero-posterior, can- not be a fixed one. It must be remembered in this connection and in the mechanics of the jaw throughout that the range of variations is great, and that there is frequently a want of symmetry in the joints. This want of precise working is in- creased by the laxity of the ligaments and the num- ber of muscles acting on various parts of the jaw. Development. The tympanic portion of the temporal being at birth nothing but the ring, it is evident that the joint belongs solely to the squamous portion, and is always bounded by the fissure of Glaser. At this age the glenoid fossa is nearly fiat and the eminentia articularis but slightly raised. Even after birth the joint below the meniscus is very slight, so that but little motion can occur in it, while the meniscus 1 Luce : Boston Medical and Surgical Journal, July 4, 1889. * Arch, fur Anat. und Phys., Anat. Abtheil., 1890. FIG. 249. Transverse section of right tempqro-man- dibular articulation from behind. 216 HUMAN ANATOMY. itself can play freely on the flat glenoid. The socket gradually deepens, and as- sumes something like its definite shape apparently in the course of the third year. THE HYOID BONE. This is a U-shaped bone ' not in contact with any other, situated below the jaw and above the larynx, with which its physiological relation is intimate. It gives origin to a large part of the muscular fibres forming the tongue. It consists of a central body, elongated transversely, and of a pair of greater and lesser horns. The convex anterior surface of the body looks forward and upward ; the posterior surface, which is deeply hollowed, faces in the opposite direction. The front surface is divided by a median and a transverse ridge into four spaces, of which the upper are the larger. The greater cornua extend with a curve backward and a little upward. They are broadest at their front, and KIG. 250. as they pass backward are somewhat twisted, so that the upper surface comes to look outward. Each ends in a small knob. They are connected with I Great cornu the body sometimes by fibro-cartilage, occasionally by a synovial joint. The lesser cornua, slender processes some five millimetres long, are the bony ter- minations of the stylo-hyoid ligaments. There is usually a synovial joint be- 5maii comu tween them and the body, which they join at the ends of the upper border. They may be connected by ligament, . Body and are not very rarely wanting, which simply means that ossification has not The hyoid bone from in front. Occurred at the lower ends of the stylo-hyoid ligaments. The outline of the body and greater horns is easily felt from the surface, and the whole bone can be grasped and moved from side to side. Development. As embryology shows, the basihyoid, or body, is connected with the second visceral arch through the stylo-hyoid ligaments, the lower ends of which become the lesser horns, or cerato-hyoids, and with the third arch by the greater horns, the thyro-hyoids. The bone ossifies in cartilage, two nuclei appearing (according to Sutton) in the fourth fcetal month, one on each side of the median line, and speedily fusing. A nucleus appears in each greater horn in the fifth month. Statements as to the time of appearance of ossification in the lesser horns vary from a few months after birth to the end of adolescence. The latter is probably nearer the truth. The greater horns rarely coossify with the body before forty-five, but after that age not infrequently. Indeed, in old age they are generally joined. The lesser horns are rarely consolidated before advanced age. THE SKULL AS A WHOLE. In connection with the description of the skull as a whole, which is not intended to recapitulate the points already mentioned, but to discuss the general features, especially those resulting from the apposition of the distinct parts, let it be remem- bered that the skull is an egg-shaped structure, and that the face is placed under its anterior and middle fossae. The Cranial Sutures. There are three antero-posterior sutures, ;i median and a lateral one on each side, and two transverse ones. The median antero- posterior suture is the sagittal;' 1 it lies between the parietal bones, and is jagged, except at the posterior part, which is usually straight. Occasionally the inctopic suture'' persists between the original halves of the frontal bone. It is rarely in direct continuation with the sagittal. The coronal suture* crosses the top of the head, sep- arating the frontal from tin- parietals. It ends at the top of the great wing of the 1 Os hyoidcum. - Sutura saglttalia. '' S. frontalls. 4 S. coronalls. THE SKULL AS A WHOLE. 217 sphenoid below. Its termination is at a vague region where several sutures approach one another, called the pterion. In the lower races occasionally, but rarely in the higher, the lower end of the coronal is continuous with the suture between the squa- mosal and the great wing, in which case two sutures cross each other at right angles, and the pterion is a definite point, an ape-like feature. If the lower corner of the parietal bone is carried downward, and the suture between the great wing and the lower border of the frontal falls considerably, the general plan is that of an H, the cross-piece being the suture between the parietal and the sphenoid ; but the H is not often very clear. A separate bone, the epipteric, is occasionally found in this FIG. 251. Supra-orbital foramen Frontal Exter. angular process Lesser wing of sphenoid Optic foramen Great wing of sphenoid Lachrymal groove Ethmoid Malar Superior maxillary Infra-orbital foramen Middle turbinate Nasal septum Inferior turbinate Anterior nasal spine Styloid process Corrugator superciHi rbicularis palpebrarum 'endo oculi rbicularis palpebrarum evator labii superiovis alceque nasi Levator labii superiorly Zygomaticus major Zygomaticus minor Masseter evator anguli arts Compressor naris Depressor alee nasi Buccinator Mental foramen Levator nienti Depressor labii inferioris Depressor anguli oris Platysma The skull from in front. region. (See under Growth and Age of the Skull.) The lambdoidal suture l starts from the top of the mastoid on each side to run upward and backward to a point separating the occipital from the parietals, the interlocking teeth being very long. What is practically a continuation of this suture runs downward between the oc- cipital and the mastoid. Wormian bones are often found, and sometimes in great numbers, in the lambdoidal suture. Sometimes there is a very large triangular one occupying the place of the upper part of the occipital. Such a one may be sub- divided. We incline to consider it a Wormian bone rather than a representative of the interparietal. 1 Sutura lambdoidca. 218 HUMAN ANATOMY. The lateral antero-posterior suture begins at the root of the nose and runs through the orbit to the side of the head, ending at the lambdoidal. Its various parts are named from the adjacent bones. Thus, it begins with the fronto-nasal, to continue between the frontal and the following bones : the superior maxilla, the lachrymal, the os planum of the ethmoid, the body, the lesser and greater wings of the sphenoid, the malar, and in the temporal fossa the great wing of the sphenoid again. Then behind the coronal it runs between the parietal above and the sphenoid and temporal below. FIG. 252. Inferior temporal line Coronal suture Sup. temporal line Ext. angu- lar process Great \vin.u of sphenoid .** ^\ ' /' ^ *&&' External occipital protuberance Mastoid process External auditory meat us Styloid process The skull from the side. THE EXTERIOR OF THE CRANIUM. Superior Aspect. 1 This is oval and broader behind than in front, showing the coronal, sagittal, and the top of the lambdoidal sature. On either side is the parietal eminence, and in front the smaller frontal ones. The superior, and perhaps a little of the inferior, curved lines appear laterally. It is rarely quite symmetrical. Posterior Aspect. 2 This is circular in outline, or sometimes five-sided, having an inferior, two lateral (nearly vertical), and two oblique superior borders. Below the middle is the external occipital protuberance, which is beneath the most posterior point of the skull. Lateral Aspect/' This shows nothing of the face that has not been mentioned. The zv^oniatic arch is prominent, bridging over a deep hollow. The part of the hollow above the arch is tin- temporal fossa^ deepest in front, and nearly tilled by tilt- temporal muscle. The inner wall is formed by the squamosal and tin- ^ivat wing of the sphenoid ; the front one chiefly by the orbital plate of tin- malar. Tin- inj'ni- tcniporal crest o\\ the great wing separates the temporal fossa from the -ygomatu fosta below. (The latter fossa is described with the face, page 227.) The two temporal 1 Virniii vertical)*. " Xorinn occipital!*. "' Virma latiT.ili-. THE EXTERIOR OF THE CRANIUM. 219 lines are to be seen in whole or in part. The inferior always ends in the supra- mastoid ridge. The mastoid process varies much in development. Anterior Aspect. 1 The cranial portion of the skull is seen only above the orbits and the root of the nose. Much of its lower part is occupied by the frontal sinuses. Inferior Aspect. 2 (The lower jaw is supposed to be removed.) This aspect may be divided into three regions by two cross-lines, one being at the roots of the pterygoid plates and one at the front edge of the foramen magnum. Passing from behind forward, near the posterior surface, are seen the external occipital pro- FIG. 253. Anterior palatine canal Posterior nasal spine Posterior palatine canal Hamular process Great wing of sphenoid Carotid canal Styloid process Jugular fossa Stylo-mastoid foramen Mastoid proces Digastric fossa Occipital groov Parietal bone Posterior condyloid foramen Posterior nares Vomer Foramen ovate Eminentia articularis Middle lacerated foramen Foramen spino- sum Glenoid fossa Fissure of Glaser Condyle Inferior curved line External occipital protuberance Superior curved line Base of skull from below, the lower jaw removed. tuberance and the superior and inferior curved lines. In front of the latter the occipital bone is convex to the outer side of the foramen magnum. A line con- necting the backs of the condyles halves the foramen magnum. The mastoid pro- cesses appear laterally. Internal to them are the digastric grooves, and just internal to these the occipital grooves, nearly or quite in the suture. Between the mastoid and styloid processes is the stylo-mastoid foramen. The region between the two above-mentioned lines includes the guttural fossa in the middle for the pharynx ; on each side of this are openings for great vessels and nerves, and, externally, the joint of the jaw. The basilar process in front of the foramen magnum forms the 1 Xorma frontalis. - A'orina basalb. 220 HUMAN ANATOMY. roof of the pharynx. On either side of it is a rent separating it from the temporal bone. The back of this rent is \hzjugular foramen ; then comes \.\i& fissure proper ; and, at the apex of the petrous portion, the middle lacerated foramen, which in life is filled with cartilage, as is also the fissure. Outside, in the petrous bone, is the carotid opening, internal to the tympanic plate, which is separated by the fissure of Glaser from the glenoid fossa. The outer border of the petrous forms a gutter with the great wing of the sphenoid for the cartilaginous part of the Eustachian tube. Just outside of this is the foramen spinosum, often in the suture between the sphenoid and temporal, and before it the foramen ovale. In the front part of the base outside of the pterygoid is that part of the great wing which looks downward, overhanging the zygomatic fossa. THE INTERIOR OF THE CRANIUM. The vault 1 of the cranium has the groove for the superior longitudinal sinus in the middle, with Pacchionian depressions on each side of it. The grooves for the middle meningeal artery cover the parietal region. The base of the cranium is divided into three fossae, the anterior, the middle, and the poster io r. The anterior fossa 2 is bounded behind by the line in front of the olivary emi- nence and by the edge of the lesser wings of the sphenoid. It has a deep hollow over the nasal cavity, the floor of the depression being the cribriform plate of the ethmoid. In the median line are the crista galli and the foramen caecum. The lateral part of the anterior fossa slants downward, inward, and backward, and is quite smooth in the middle behind the hollow. The middle fossa 3 is limited in the centre to the sclla turcica, but expands at the sides. It is separated from the posterior fossa by the dorsum sell& and the superior border of the petrous. The middle fossa has the olivary eminence and the optic foramina in front of the sella turcica, at each side of which is the groove for the internal carotid artery and the cavernous sinus. The clinoid processes tend to meet above its sides, and sometimes do so, especially when the middle clinoid is developed. On the anterior border of the fossa, near the middle, is the sphenoidal fissure opening into the orbit. Just behind its inner end is the foramen rotundum ; farther back and outward are the foramen ovale and foramen spinosum, from which latter start the grooves of the middle meningeal artery ; more internal lies the middle lacerated foramen. The depression for the Gasserian ganglion is seen at the apex of the anterior surface of the petrous portion of the temporal bone ; the ganglion is very conveniently placed for its ophthalmic, superior maxillary, and mandibular branches to reach the sphenoidal fissure, the foramen rotundum, and the foramen ovale re- spectively. The posterior fossa 4 is much the larger. In the middle is the foramen Mag- num, with the basilar groove before it. The impression for the superior petrosal sinus is at the top of the petrous. The inferior petrosal sinus lies on the suture between the petrous bone and basilar process. The internal auditory mcatits, the jugular foramen, and the anterior condyloid foramen are very nearly in a vertical line. The impressions for the lateral sinuses run outward from the internal occipital protuberance until they suddenly turn downward, making a deep groove in the tem- poral bone. The course of the second portion of the sinus is straight downward and inward, the highest point of the sinus corresponding with the supramastoid crest above the middle of the mastoid process. This point is sometimes so near to the surface that the bone is translucent. In its descent the sinus may for a time keep near the surface, or leave it at once. There is much variation in many respects ; sometimes the downward turn of the sinus is less sharp. The claim that anything can be predicated of this from the shape of the head is extremely uncertain. Just before reaching the jugular foramen the sinus once more changes its direction, running forward and upward. THE ARCHITECTURE OF THE CRANIUM. The curved vault of the skull is well adapted to break shocks, but the bast- is much weaker ; not only is the bone thin in many places, but it is interrupted by 1 C.-ilviiriii. rn-.;i i-iMiiii :iiiti-riiir. I . iTunii nu-fli.-i. 4 K. criinii posterior. THE ARCHITECTURE OF THE CRANIUM. 221 many openings. The whole of the anterior fossa is very thin ; so is the sella turcica, being just over the sphenoidal sinus. A chain of openings crosses the middle fossa on either side. The temporal bone is practically crossed by the external and internal meatuses and the middle ear, besides containing other cavities. Thus the petrous is brittle, although the bone is very dense. A rim of comparatively firm bone extends around two-thirds of the skull, starting on each side from the occipital protuberance, which may be even two centimetres in thickness, along the line of the lateral sinus to the supramastoid ridge ; it follows the line of origin of the zygoma, FIG. 254. Ethmoidal spine Crista galli Foramen caecum Frontal sinus Cribriform plate Optic foramen Olivary emi- nence Sella turcica Sphenoidal fissure (con- cealed) Lateral sinus Torcular Herophili Base of skull from above. and ends in the infratemporal crest on the great wing of the sphenoid. A median ridge strengthens the skull in both the frontal and occipital regions. The average thickness of the vault is about four millimetres. It is thick through- out the frontal region and at the parietal eminences, a thin area lying behind and below the latter. The Pacchionian depressions may almost perforate the skull. It is very thin in the squamous part of the temporal ; less so in the superior occipital fossae. If the base of a skull be held to the light and examined from within, the 222 HUMAN ANATOMY. translucency of 'the following parts will be very evident : the roofs of the orbits, one or two uncertain points in the great wing of the sphenoid, one in the lower part of the squamous portion just outside of the petro-squamous suture corresponding to the glenoid fossa, the beginning of the basilar process, a varying portion of the descending part of the groove for the lateral sinus, and nearly the whole of the floor of the cerebellar fossa. A little rim of firm bone surrounds the foramen magnum except in front. THE FACE. This consists essentially of the framework of the jaws and of the orbital and nasal cavities, as well as of certain accessory regions, the zygomatic and spheno- maxillary fossa. Apart from features in the bones already described, the front view shows the outline of the orbits, of the nasal opening, of the prominence of the cheek, and of a vacant space left between the upper jaw and the ramus of the lower. The foramina for the escape of the terminal branches of the three divisions of the fifth nerve are very nearly in a vertical line, only the mental foramen is usually a little lateral. The side view shows the zygomatic fossa below the arch and within the ramus. The Orbit. Although the base is quadrilateral, the orbital cavity is conical rather than pyramidal, since its section a little behind the base is almost circular. The upper margin of the entrance is formed by the frontal bone, which slants down- ward to the very prominent external angular process, which affords great protection to the eye. The suture with the malar can easily be felt in life, owing to the greater projection of the upper bone. The outer border and the inner half of the lower are made by the malar, which has a sharp orbital edge throughout. This is continued by an ascending sharp edge of the superior maxillary into the front border of the lachrymal canal, at the top of which it becomes indistinct. This is to be considered the inner boundary ; but there is difficulty in accurately determining this border, for if the upper border be followed down at the inner side, It will be seen to run to the posterior edge of the lachrymal groove made by the ridge in the lachrymal bone. In some skulls this is much the more evident border. The upper part of the inner border is the only one that cannot easily be felt in life. The roof of the orbit is arched from side to side and from before backward. It is overhung by the border, especially at the outer angle, where it lodges the lachrymal gland. The inner wall, composed of part of the ascending process of the maxilla, the lachrymal, the os planum of the eth- moid, and part of the body of the sphenoid, is nearly vertical in front, but farther back slants inward. The inner wall is frequently quite convex in the middle ; if this condition is marked, it is probably pathological. There is an approach to an angle between this surface and the upper. The two ethmoidal foramina are found above the os planum. The inner wall curves gradually into the inferior surface, formed by the maxilla, and presenting the infra-orbital groove and canal. The outer r.W/ slants strongly inward, its lower border being internal to the upper. It is formed by the malar bone in front and the great wing of the sphenoid behind. The back part of the upper angle of the outer wall is occupied by the sphenoidal fissure, which opens into the middle fossa of the skull, and the lower angle by the spheno-maxillary fissure, separating the wing of the sphenoid from the maxilla ; the outer end of this fissure, closed by the malar bone, opens into the zygomatic fossa. The optic fora- men is at the posterior point of junction of the roof and the inner wall. The apc.v of the orbit is at the inner end of the sphenoidal fissure. The axes of the orbits, if prolonged, cross each other at the back of the sella turcica at an angle of from 42 to 44. The orbital axis is, therefore, very differ- ent from the visual axis, which is antero-posterior. The former, moreover, runs downward from the apex to the base, making an angle of from 15 to 20 with tin- horizontal plane. The dimensions of the adult orbit vary with different observers and, no doubt, in different localities. The depth is from forty to forty-five millimetres, the breadth at the base is about forty millimetres, and the height about thirty-five millimetres in males. In females the dimensions are rather less. The roof is thin and separates the orbit from the cranial cavity, except in THE NASAL CAVITY. 223 front, at the inner side, where the frontal sinus intervenes. This sinus extends downward, mesially, almost to the top of the lachrymal groove. The inner and lower walls, separating the orbit from the nasal cavity and the antrum respectively, are very thin and offer little resistance to a tumor or a foreign body. The great wing of the sphenoid in the outer wall is thick, except just at the edge of the sphenoidal fissure ; it separates the orbit from the middle cranial fossa. The outer wall just behind the anterior border is thin, where it cuts off union with the temporal fossa. The Nasal Cavity. The nasal cavity of each side has an anterior and a pos- terior opening, a roof, a floor, an outer wall, and an inner, the septum, which, when FIG. 255. Crista galli Partition sepa- rating frontal sinus from orbit Sup. turbinate Lower part of infundibulum Nasal septum Antrum Inferior turbinate Floor of nasal fossae Inferior meatus Front section of skull through plane of outer border of orbits. Arrows pass through communication between antrum and middle meatus. the cartilage is present, completely separates it from its fellow. The anterior common opening of the two cavities is shaped like an inverted ace of hearts, bounded above by the border of the nasal bones and elsewhere by the superior maxillae. In the middle of the floor of the opening is the anterior nasal spine, resembling closely the bow of a boat. The anterior edge where the two bones meet is the cutwater, and above is a triangular surface, the deck, bounded by a sharp line, which runs outward, forming the lower border of 'the opening. In the adult this line is usually continuous with the lateral border of the opening, but in infants' skulls the line passes from the side onto the anterior surface of the maxillary bone. Another line a little behind this, starting inside the nose at the front of the inferior turbinate crest, runs close to the line from the spine. Though these lines are usually 224 II I'M AX ANATOMY. Probe in infundibulutn t fused in the adult, forming a rather dull inferior border continuous with the lateral sharp one, they may remain distinct and enclose a well-marked fossa on the face just below the nasal opening ; this is the fossa pratnasalis, rarely seen in other than low races. Variations in the arrangement of these lines may occur, and according to Zuckerkandl, 1 the line from the border of the nose may not always form the anterior border of the fossa. The combined nasal openings, though in the main triangular, may be roughly quadrilateral. More or less asymmetry is the rule. The nasal bones and the nasal spine may point sideways, but not necessarily to the same side. The spine points to the side on which the opening is the wider ; the broader aperture usually does not descend so low as the narrower one. The tip of the nose is more often turned to the right. In life the shape' of the nose depends quite as much on the soft parts as on the bones. The posterior openings of the nares, the choance, are remarkably symmet- rical ; bounded above by the wings of the vomer, which conceal the body of the sphenoid, on the sides by the internal pterygoid plates, internally by the vomer, and below by the horizontal plate of the palate, each is much higher than broad. The index of the choanae, showing the proportion of the breadth to the height (~fieTh7^) k ^ * or men anc ^ ^4 ^ or women > showing relatively lower openings in the latter ( Escat). Measuring the combined breadth from one pterygoid process to the other at the hard palate on FIG. 256. ten adult skulls irrespective of sex, we found the average breadth 27.7 centimetres and the average height 28.4 centimetres. The extremes were 24 and 31 centimetres for the breadth and 25 and 31 for the height. 2 The inclination of the posterior border of the vomer is in a general direct ratio to the degree of prognathism, 3 or the forward projection of the face. Each nasal chamber ( Figs. 255, 256) is very narrow, and much higher in the middle than at either orifice. The front part, the vestibule, extends under the bridge of the nose. The roof is extremely narrow except at the posterior end. It is composed of the nasal bones, thin below, thick above ; of a small part of the frontal, a thin plate separating it from the frontal sinus ; the very thin cribriform plate, easily broken ; the vertical anterior surface of the sphenoid, pierced by an opening into the sinus ; and, finally, the wing of the vomer. The floor is a smooth gutter, formed by the palatal processes of the maxillae and palate bones. The lower border of the anterior nasal opening is higher than the floor, so that an instrument has to be tilted over it. The anterior palatine canal opens through the floor near the front on either side of the septum. The floor, except at the posterior part, is of strong bone, and is smooth all over. The median wall is derived from a plate of cartilage, developed at a very early period, from which the vertical plate of the ethmoid and the vomer are also formed. A large quadrilateral space is left vacant in the macerated skeleton, which in life is filled by the unossified portion of the original plate, known as the triangular cartilage. Apparently the process of ossification is excessive along the line of union between the ethmoid and the vomer, since the adult septum is usually bent to one side in its anterio'r two-thirds, thus making one nasal cavity much smaller 1 Normale und pathologische Anatomic der Nasenhohle, 2te Auflage, Vienna, 1893. 1 The development of tin- nasal cavity is described with that of the head. Escat : Cavite" Naso-Pharyngiene, Paris, 1894. Inferior turbinate Anirum Portion of anterior section of preceding skull, seen from be- hind. The arrows occupy the opening from the antrum into the hiatus semilunaris. THE NASAL CAVITY. 225 than the other. A ridge is often found at or near the junction of these two bones on the prominent side, thereby still further reducing the smaller cavity. This ridge may be developed into a shelf, called a spur, which may even touch the opposite wall. The outer wall is the most instructive, as giving the most light on the con- struction of the region. In front is the smooth-walled vestibule, formed by the inner side of the nasal and the ascending process of the maxilla, extending upward under the frontal sinus. The swelling known as the agger may be found near the top of its outer wall. The inferior turbinate is much the larger, reaching forward almost to the opening in the bone. The large inferior meatus which it overhangs is higher in front than behind. The middle turbinate, over the middle meattis, does not extend nearly so far forward. The little superior turbinate with the limited superior meatus below it is still farther back, reaching only half-way along the FIG. 257. Spheno-ethmoidal recess Extension of sphenoidal sinus Pituitary fossa Crista galli Frontal sinus Sup. turbinate Middle turbinate Middle meatus Inf. turbinate Inf. meatus Anterior palatine canal Spheno-palatine foramen Hamular process Palatal plate of sup. maxilla Inner aspect of outer wall of right nasal fossa. middle turbinate. The three turbinates end behind very nearly in a vertical line, the middle sometimes projecting farthest. The lines of attachment of the turbinates all slant downward and backward, but the inclination of the middle one is greatest. The variations in number of the turbinates and the structures concealed by the middle one have been described with the ethmoid. The spheno-ethmoidal recess is a lateral expansion of the cavity behind the superior turbinate and the front of the body of the sphenoid. The posterior portion of the outer wall of the nasal chamber, formed by the palate bone and the internal pterygoid plate, is smooth. The outer wall slants inward, so that the roof of the nasal cavity is narrower than the 'floor and has the following openings: in the superior meatus that of the posterior ethmoidal cells ; farther back is the spheno-palatine foramen communicating with the spheno- maxillary fossa. The middle meatus receives the opening of \\\e frontal sinus either directly under the front of the middle turbinate or through the infundibulum. 15 226 HUMAN ANATOMY. These arrangements are about equally common. It receives also the openings of the anterior ethmoidal cells, the aperture of the antruni into the infundibulum, and a larger opening from the antruni behind the infundibulum. The lachrymal canal opens into the inferior meatus under the fore part of the turbinate. External to the outer wall are the orbit, the antrum, and farther back the spheno-maxillary fossa with- the posterior palatine canal below it. The Accessory Pneumatic Cavities. These include the frontal sinuses, the maxillary antra, the ethmoidal cells, and the sphenoidal sinuses. They have already been described with the separate bones, but may be here further briefly con- sidered in their mutual relations to the nasal fossae and the skull. All of these spaces open into the nasal chambers above the inferior meatus, the sphenoidal cells into the roof, the posterior ethmoidal cells into the superior meatus, the anterior eth- moidals, the antra, and the frontal sinuses into the middle meatus. FIG. 258. Infratemporal crest Spheno-maxillary fissure Spheno-palatine foramen Glenoid fossa Mastoid process External auditory meatus Styloid process Zygoma Inner wall of zygomatic fossa (external ptery- goid plate) Spheno-maxillary fossa seen through pterygo- maxillary fissure Posterior dental canal Hamular process Lateral view of skull with zygomatic arch removed. The sphenoidal sinuses (Fig. 257) are almost invariably unequal, the sep- tum being much to one side. The large openings in the front of the body of the sphenoid are much reduced when the cornua sphenoidalia are in place. The open- ings of the posterior ethmoidal cells are small and irregular. The anterior cells make a part of the floor of the frontal sinuses. They open either into the infundibulum or under the middle turbinate. The frontal sinuses (Figs. 255, 257), when exposed from the front, have a vaguely triangular outline. One side is against the septum, separating it from its fellow, which is rarely symmetrical. The upper border runs from the top of this downward and outward. The lower border bends downward at the inner end, where the cavity runs down to the nose at the inner angle of the orbit. The inner part extends back for a varying distance over the orbit. In about half the cases the cavity opens directly into the middle meatus; in the rest it opens into the top of THE SPHENO-MAXILLARY FOSSA. 227 the canal in the ethmoid, known as the infundibulum. In the former cases one of the cells of the ethmoid is particularly liable to make a projection the frontal bulla into the floor of the sinus. The antrum (Fig. 255) is a four-sided pyramid with an irregular base towards the nasal cavity (Merkel). The apex is at the malar. In addition to the base, an orbital, an anterior, and a posterior surface are recognized. Owing to the irregularity of the base there is a groove instead of an angle below, above the alveolar process. (This relation is described with the upper jaw. ) The large in- ternal aperture in the superior maxilla is divided into two when the other bones are in place. Both are near the top ; the anterior opens into the infundibulum, the pos- terior into the middle meatus. Partial septa project into the antral cavity. An important projection is that of the infra-orbital canal. The zygomatic fossa (Fig. 258) is the space internal to the lower jaw, sepa- rated from the temporal fossa by an imaginary plane at the level of the upper border of the zygoma. It is open below and behind. The front wall is made by FIG. 259. Orbital surface of great wing of sphenoid Frontal process of malar Cut surface of zygoma Tympanic plate of temporal Mastoid process Optic foramen Sphenoidal fissure Sphenoidal sinus Foramen rotundum Vidian canal Probe in pterygo-palatine canal Posterior wall of spheno- maxillary fossa Palate bone -Hamular process of internal pterygoid plate Zygomatic surface of external pterygoid plate Portion of right half of skull, showing posterior wall of spheno-maxillary fossa. The superior maxilla, ethmoid, and part of malar have been removed. the maxilla, what little roof there is by that part of the great wing of the sphenoid internal to the infratemporal crest, and the inner wall by the external pterygoid plate. It "has two important fissures, the spheno-^naxillary ', horizontal, admitting to the orbit, between the sphenoid and maxilla ; the other, the pterygo-maxil- lary, vertical, between the maxillary bone and the front of the united pterygoid plates. The spheno-maxillary fossa (Fig. 259) is a small cavity below and behind the apex of the orbit at the point of junction of the spheno-maxillary and the pterygo-maxillary fissures. The posterior wall is formed by the sphenoid above the roots of the pterygoid plates. The transverse and antero-posterior diameters of the fossa are about fifteen millimetres. It contains the spheno-palatine or Meckel's ganglion. The foramen rotundum opens into it behind, transmitting the superior maxillary division of the trifacial nerve. More internal and lower on the posterior wall is the orifice of the Vidian canal, transmitting the great superficial and deep petrosal nerves and accompanying blood-vessels. Still nearer the median line is 228 HUMAN ANATOMY. the minute pterygo-palatine canal, formed by the palate and sphenoid bones. The spheno-palatine foramen opens through the inner wall into the nasal cavity. The fossa opens below into the posterior palatine canal. The Roof of the Mouth. This comprises the hard palate and the inner aspect of the alveolar process. The proportions, as stated elsewhere (page 229), vary ; as a rule, the broad palate is less vaulted than the narrow one. The oral roof presents the orifices of three canals, the anterior^ and the two posterior palatine. The first is situated in the mid-line in front, the others at the outer posterior angles. The palatine grooves for the anterior palatine nerves and accom- panying blood-vessels extend forward from the posterior palatine foramina. Be- hind, but close to, the latter are the orifices of the accessory palatine canals. The inner side of the alveolar process is rough except opposite the second and third molai* teeth, and the same is true of that part of the palate made by the superior maxillae. An occasional swelling, the torus palatinus, is in the mid-line at the junction of the superior maxillae. Internal to the first molar is a ridge with the groove outside of it at the lateral border of the maxilla. The line separating the superior maxillae from the horizontal plates of the palate bones has a forward curve in the middle in nearly three-quarters of the cases. It is about straight in some twenty per cent, and curved backward in the rest. The fissures are not always symmetrical. 2 The Architecture of the Face. With the exception of the lowef jaw, the structure of the face is extremely light. It is subject to no strain save through that bone, and to some extent through the action of the tongue on the palate ; it has, however, to be protected against occasional violence. There are certain strong and strengthening regions. The hard palate is strong throughout, except at the hind part, and especially strong back of the incisors. Some strength is gained by a thickening just outside of the nasal opening above the canine teeth, running up into the ridge in front of the lachrymal groove. The root of the nose is also very thick. The face is considerably strengthened through the malar bone and its con- nections, especially with the robust external angular process. A little support is probably given to the back of the jaw through the pterygoids. ANTHROPOLOGY OF THE SKULL. There are certain terms and measurements which should be known, especially as some of them come into practical use in the surgery of the skull. Points on the Surface of the Skull. (See also Fig. 265, page 241.) Alveolar point, the lowest point in the mid-line of the upper alveolar process. Asterion, the lower end of the lambdoidal suture ; three sutures diverge from it like rays. Auricular point, the centre of the external auditory nieatus. Basion, the anterior point of the margin of the foramen magnum. Bregma, the anterior end of the sagittal suture. Dacryon, the point of contact of the frontal, maxillary, and lachrymal bones. Glabella, the region above the nose between the superciliary eminences. Glenoid point, the centre of the glenoid fossa. Gonion, the outer side of the angle of the lower jaw. Inion, the external occipital protuberance. Lambda, the posterior end of the sagittal suture. Malar point, the most prominent point of that bone. Mental point, the most anterior point of the symphysis of the lower jaw. Nasion, the point of contact of the frontal bone with both nasals. Obelion, the sagittal suture in the region of the parietal foramina. Occipital point, the most posterior point in the mid-line. (It is above the protuberance.) Ophryon, the point of intersection of the median line with a line connecting the tops of the orbits. Opisthion, the posterior point of the margin of the foramen magnum. Pterion, the region where the frontal, the great \vingof the sphenoid, the parietal, and the temporal bones almost meet. (As, in fact, they very rarely do meet, the term is a \ague one. ) 1 For the description of this canal, see under Superior Maxilla (page 201). 1 Stieda : Arch, fiir Anthropol., 1893. ANTHROPOLOGY OF THE SKULL. 229 Stephanion, the region where the curved lines on the temporal bone cross the coronal suture. Subnasal point, in the median line at the root of the anterior nasal spine. Indices. The cephalic index is the ratio of the breadth to the length of the skull ( I00 ^ n br t e ^ dth j. The length is taken from the glabella to the occipital point, and the breadth is the greatest transverse diameter above the supramastoid ridge. A high index means a short skull ; a low index, a long one. A skull with an index above 80 is brachycephalic ; from 75 to 80, mesaticephalic ; below 75, dolichocephalic. The index of height is the ratio of the line from basion to bregma to the length /TOO x_eig_t\ ^ skull with an index above 75 is hypsicephalic ; from 70 to 75, orthocephalic ; below 70, platycephalic. The facial index is the ratio of the length to the breadth of the face ( '"^^"h *** ) The length is from the nasion to the mental point, and the breadth is the greatest at the zygomatic arches. A high index means a long face. A head with a facial index above 90 is leptoprosopic ; one with a lower one, chamo'prosopic. In the absence of the lower jaw the index of the upper face may be taken, which is almost equally valuable. The only difference is that the length is taken from the nasion to the alveolar point, and that an index above 50 is leptoprosopic, and one below it chaincEprosopic. The nasal index is the ratio of the length of the nose to the breadth ( I0 . x ^".f h ) . The V breadth / length is measured in a straight line from the fronto-nasal suture to the anterior nasal spine. A skull is Icptorhine when the index is below 48 ; when from 48 to 53, mesorhine ; and when above 53, platyrhine. The orbital index is the ratio of the height of the base to the breadth, thus / IooXhe 'g ht \ V breadth / The breadth is a horizontal from the outer border to the point of contact of the frontal with the maxilla and lachrymal. A large index means a high orbit. An orbit with an index below 84 is tnicroseme ; with one from 84 to 89, mesoseme ; with one above 89, megaseme. An index of 70 is low for a Caucasian, and one of 106 very high. The average for English skulls is said to be 88. The index depends considerably on the extent to which the upper border overhangs. The palatal index is the ratio of the breadth to the length. The former is taken from the socket of the second molar of one side to that of the other ; the latter is from the alveolar process in the middle line to the posterior nasal spine ( I0 ^ en rt ^ ) . Prognathism denotes the forward projection of the face. This was formerly expressed by what is known as Camper's facial angle, which was measured on the arc between two lines meeting at the nasal spine, one starting from the auricular point, the other from the most promi- nent part of the forehead in the middle line (avoiding the projecting nose). This has fallen into disuse owing to inherent defects, and perhaps in part to the discordant directions given for drawing the lines. Flower's gnathic index is the ratio of the line from the basion to the 11 A. A.t- \' t ^1. u iU / loo X basi-alveolar line \ . in- alveolar point to the line from the basion to the nasion -PP . A sku 1 is \ basi-nasal line / orthognathous with an index below 98 ; mesognathous with one from 98 to 103 ; prognathous with one above 103. Shape of the Skull. Extreme forms occur in Caucasians. The long, narrow skull, with often a slight prominence along the sagittal suture, the scaphoid form, is due to the early closure of the sagittal suture, and the short, round skull to that of the transverse ones. In support of this theory is the fact that the metopic or median frontal suture is never found in narrow, but only in broad skulls. The high, sugar-loaf, acrocephalic skull shows obliteration of all three sutures on the top of the vault. The great backward occipital projection sometimes seen is usually asso- ciated with many Wormkin bones in the lambdpidal suture. The long type of skull is naturally associated with the long, narrow face, and the round head with the broad face ; but the connection is not absolute. The two types of face deserve a short consideration. The narrow face has the high orbit, the narrow nose, with the aperture pointed above, and a long, narrow palate. The outline of the range of teeth in one jaw to a great extent determines that of the other ; but, in addition to the smaller curve, the lower jaw in this form is rather delicate, is particularly likely to show the constriction in front of the masseter, and has a more obtuse angle. The short and broad face has wide, low orbits, a broad and almost quadrilateral opening of the nose, and a wide pair of jaws, the lower with an approxi- mately square angle. If, as is most probably the case, the head is orthognathous, the edges of the teeth tend to form part of an antero-posterior curve, which is particularly marked in the region of the molars. It is to be noted, however, that some, or any, of these features may be found in a face of the opposite type. Dimensions of the Skull. The actual length of the various diameters is of much less importance than their relations to one another in the science of craniology ; they may, however, be important in medico-legal questions. With the exception of the height, they vary within wide limits, even among Caucasians. In the following table the means of both sexes are from Broca : Males. Females. Mean. Millimetres. Millimetres. Length 182 174 Breadth 145 135 Height 132 125 2 3 o HUMAN ANATOMY. Cranial Capacity. This may vary in all races from 1000 to 1800 cubic centimetres. Welcker gives the following means and extremes for white races : ' Mean. Maximum. Minimum. Cu. cm. Cu. cm. Cu. cm. Males ..................... i45>-> 179 Females ........... ........ A skull with a capacity exceeding 1450 cubic centimetres is mc^accphalic ; one with a capacity from 1350 to 1450, mesocephalic ; one below 1350, microcephalic. Manouvrier has devised a formula for calculating the weight of the brain from the cranial capacity, as follows : weight in grammes is to capacity in cubic centimetres as i to 0.87. Asymmetry. The whole head is almost always asymmetrical. The left side of the cranium, as shown by hatters' models, is larger, especially in the frontal region. The right side of the head is usually the higher. The cause of this is probably to be found in habitual position. The spine is not held symmetrically, but the atlas inclines to the left ; the head, when held most firmly, does not rest evenly on both condyles, but on one, usually the left. The position of the head, thus taken, is not enough to compensate for the obliquity of the base ; but certain changes take place in the relations of the component parts. Thus a face which seems FIG. 260. Anterior fontanelle Anterior lateral fontanelle The skull at birth, from before. , tolerably symmetrical when resting on the left condyle only becomes quite uneven if placed upon both. The right orbit is usually the higher, the right side of the jaw is the stronger, and its teeth are set in a smaller curve. The tip of the nose turns to the right. Moreover, the face lacks symmetry in another direction : the right upper jaw and the malar bone are more promi- nent than the left. More striking differences, depending on these, are seen (luring litV, which are ascribed to the effect of gravity on soft parts habitually held unevenly, the right side being the higher. The right eye is the higher and, apparently, the larger, the lids being farther apart ; while the cleft is narrow on the left and the eye nearer the nose. The left nostril is the larger ; the left fold of the cheek is less marked. In a certain proportion of persons all these peculiarities are reversed, and some of them may be transposed without the others. Growth and Age of the Skull. By the sixth month of fcetal life the skull, though smaller, is in much the same condition as at birth, except that then the occipital region is relatively larger. The most striking points are the insignificance of the face and the flatness of the inferior surface. In the cranium the frontal region is relatively small. The vault, which is developed in mem- Inane, presents marked prominences at the parietal and frontal eminences, and a smaller one at 1 Kxtreme cases occasionally pass these limits. There is in the Warren Museum the skull of a Highlander with a capacity of 1990 cubic centimetres, and one of a tall man, presumably an American, who could read and write, though his intelligence was defective, with a capacity <>f 1225 cubic centimetres. Turner has noted the skull of a female Australian of 930 cubic centi- metres' capacity. GROWTH OF THE SKULL. 231 the external occipital protuberance, from which radiating lines in the bone mark the process of development. The bones of the vault are exceedingly thin. Each is separate, the external periosteum and the dura uniting at the edges, thus limiting the spread of an effusion under the former to one bone. Six places where there are considerable membranous intervals between the developing bones are called fontanelles. They are situated at the four angles of the parietal bones, so that two are median and two are on either side. The median ones, by far the most prominent, are the anterior and posterior fontanelles. The anterior fontane lie, an important landmark in mid- wifery, is a diamond-shaped space between the rounded angles of the parietals and frontals, some thirty-five millimetres long by twenty-five millimetres broad. This one continues to grow after birth, and is not closed till some time in the first half of the second year, or even later. The posterior fontanelle is situated at the apex of the squamous portion of the occipital, extending between the parietals. At an early stage, owing to the median fissure in the occipital, it is diamond-shaped, but later it is triangular. The space is more or less filled up in the last two months before birth, but it may not be truly closed for a month or two after. The anterior lateral fontanelle is a small unimportant space at the lower anterior angle of the parietal, above the great wing of the sphenoid, and extending around it. It usually closes at from two to three months after birth. The part between the sphenoid and squamosal is likely to persist the longest. According to Sutton, 1 in early fcetal life the orbito-sphenoid bone reaches the lateral FIG. 261. Anterior lateral fontanelle Posterior lateral fontanelle The skull at birth, lateral aspect. wall of the skull at this point, and a piece of cartilage belonging to it is found in this fontanelle. It becomes bone in the course of the first year, and may unite with either sphenoid, temporal, frontal, or parietal, or persist as the epipteric bone. It most often joins the parietal. The pos- terior lateral fontanelle, under the corresponding angle of the parietal, extends down between the temporal and the occipital. It is larger than the preceding, and may be very distinct for a month or more after birth. Its complete closure is said never to occur before the twelfth month, and, perhaps, usually not till the second year. 2 The sagittal fontanelle (see Ossification of Parietal) may be present at the seventh month of fcetal life, or later. The oblique fissure at the line of junction of the two parts of the squamous portion of the occipital persists till after birth, and must not be mistaken for an effect of violence. The mastoid process does not exist at birth. The tympanic bone is a mere frame for the ear-drum. The base of the cranium is very flat. The condyles are barely prominent, and the basilar process rises but slightly. In the first year the outer surface of the bones of the vault becomes smooth. The bones gain in thickness, and in the second year the cliploe appears. At the same time the jagged points develop in the sutures, and at the end of that year the metopic suture between the frontals closes. 1 Journal of Anatomy and Physiology, vol. xviij., 1884. 2 Adachi : Ueber die Seitenfontanellen, Zeitschrift fur Morph. und Anthrop., Bd. ii., Heft 2. 232 HUMAN ANATOMY. The/ace, while helping to form the orbit and nasal cavities, is essentially for the jaws, and the jaws for the teeth. The greatest change in the head after birth is the downward growth of the face. According to Froriep, in the infant the face is to the cranium as i to 8 ; at two years as i to 6 ; at five, as i to 4 ; at ten, as i to 3 ; in the grown woman as i to 2.5 ; in the man as i to 2. On contrasting the front view in the infant and adult, counting as "face" all below a line at the top of the orbits and as "cranium" all above it, it will be seen that in the infant the cranium forms about one-half and in the adult much less. The lower border of the nasal opening is at birth but very little below the orbit. A line connecting the lowest points of the malar bones passes at this age midway between the nasal opening and the border of the alveolar process. At birth the nasal aperture is relatively broad ; its lower border is not sharply marked off from the face A line from the nasal spine runs outward to end inside the cavity, and the crest from the outer border is still rudimentary, ending shortly on the front of the face, so that at the outer angle there is no distinct separation between face and nasal cavity. 1 The nasal cavity is shallow, the posterior nares very small. The vomer slants strongly forward. The lower jaw is small and the angle of the ramus very obtuse. The alveolar processes are rudi- mentary. The breadth of the skull at its widest equals or exceeds the combined height of the Fir,. 262. Posterior fontanelle Interparietal suture-H Anterior fontanell The skull at birth, from above. cranium and face in the infant ; in the adult it is but three-quarters of it. The breadth o face is to its height as 10 to 4 at birth, and about as 9 to 8 in the adult. Merkel divides the growth of the head into two periods, with an intervening one of rest. The first ends with the seventh year, and is followed by inactivity till puberty, when tin.- second period begins. Thejtrstperioamay be subdivided into three stages. In the first stag?, reach- ing to the end of the first year, the growth is general, but the face gains on the cranium. At six months the basilar process rises more sharply, which, with the downward growth of the face-, lias an important effect on the shape of the naso-pharynx. The lower part of the nasal cavity gains particularly. The posterior opening doubles its size in the first six months, to re-main stationary till the end of the second year. In the second stage, to the end of the fifth year, the vault grows more than the base, assuming a more rounded and finished appearance. The face still gains relatively, but grows more in breadth than in height. In the third stag?, corresponding roughly to the seventh year, the base grows more and the vault less. The face lengthens considerably, the growth in the nasal chambers being chiefly in the lower part. The head, though small, has lost the infantile aspect. The foramen magnum and the petrous portion of the temporal have reached their full size, and the orbit very nearly. The parietal and frontal eminences are still very prominent. The mastoid is rudimentary. This condition lasts till puberty, when the 1 Macalister : Journal of Anatomy and Physiology', vol. xxxii., 1898. GROWTH OF THE SKULL. 233 second period begins. This is marked by growth in all directions, the gradual rounding off of the eminences of the vault, the progress of the mastoid, the strengthening of ridges, the greater curving of the zygomatic arches, and the increase of the face. This last is due chiefly to the advance of the nose, the gain of the superciliary eminences, and the increase of the lower jaw. The rise of the basilar process increases and the occipital condyles stand out more from the bases at the front edges. These processes are nearly finished in the female by nineteen and in the male one or two years later, though, especially in the latter, they require several years more for their absolute completion. The thickness of the vault is very nearly reached by puberty. At seven the frontal sinus is only as large as a pea. Its development is not completed before the twentieth year. There is no means of knowing whether or not it then entirely ceases. The orbit bears nearly the same proportion to the cranium at all ages ; but at birth it equals about one-half of the height of the face, and in the adult rather less than one-third. At birth the axis of the orbit is horizontal. While sometimes the transverse diameter of the base of the orbit is much the larger, this does not seem to be always so. As the face grows the vertical diameter increases rapidly, so that, according to Merkel, at five the base lacks only two or three millimetres of the adult height, which it gains in the next two years. The full breadth is probably not attained before puberty. The changes in the nasal cavity are important as an essential element in the growth of the face. At birth the line of the hard palate, if prolonged back, would strike near the junction of the basilar process and sphenoid ; at three it strikes near the middle of the basilar ; at six, the front edge of the foramen magnum, which is nearly or quite the condition of the adult. The measurements of the vertical diameter of the choanae are important from their significance with regard to both the nose and the pharynx. At birth the height is from five to six millimetres (seven millimetres is exceptional) and the breadth of each opening very little greater. At from six months to a year both diameters have doubled, their proportions remaining unchanged. There is little change before the end of the second year, when the height increases more rapidly. Thus they change from circular to oblong openings. It is not till after puberty that the height exceeds the distance between the internal pterygoid plates. HEIGHT OF POSTERIOR NARES. Authority. Age. Sex. Millimetres. Disse 4 male 16 Disse 5 female n Escat 5 15 Escat 8 18 Dwight 7 or 8 20 Dwight . . . . 7 or 8 21 Dwight 10 female 22 Dwight ii 22 Dwight. 14 female 22 Escat 14 20 Dwight 15 male 23 Dwight 16^ female 23 Dwight 17 female 19 Dwight. 18 male 29 Dwight . 19 male 24 Escat I5toi8 (9 cases) 25 The Closure of the Sutures. The occipital bone unites with the basisphenoid at the cerebral aspect about seventeen and on the outside of the skull some three years later. The lower end of the suture between the occipital and the mastoid process is one of the first to close. We have seen it lost in a skull of fourteen, of which the other bones were almost falling apart. No doubt this was exceptionally early. The closure of the great sutures of the vault 1 ( to which the term is usually applied ) begins on the inside of the skull, probably before thirty, at the lower ends of the coronal and at the back of the sagittal, and spreads irregularly. The process is generally far advanced before it appears on the outside. The closure of the sutures on one side of the head does not necessarily follow the same course on the other. It has usually begun on the outside by forty, although the sutures are still distinct. They probably are nearly or quite obliterated on the inside by fifty-five. The apex of the lambdoidal suture is one of the last points to persist internally. It is impossible to state with accuracy the time at which the sutures disappear on the outside, as this may never occur, and the process throughout is utterly irregular. All may be gone very early or all may be distinct at an advanced age. When the metopic suture fails to close in early childhood it is one of the very last to disappear. It is unsafe from the sutures alone to draw any conclusions as to the age of a skull. The weight of the skull in both sexes is greatest from twenty to forty-five. 2 The changes in old age are essentially atrophic. The most striking is the absorption of the alveolar processes ; this, however, may occur prematurely from the loss of teeth. The angle of the lower jaw becomes much more obtuse. The thin parts of the face and of the base 1 Dwight : The Closure of the Cranial Sutures as a Sign of Age, Boston Medical and Sur- gical Journal, 1890. Parsons : Anthrop. Institute G. Brit, and Ireland, vol. xxx, 1905. 2 Gurriere and Massetti : Rivista speriment. di Freniatria e de Med. legale, 1895. 234 HUMAN ANATOMY. of the skull become still thinner and may be quite absorbed. The thinning of the vault is less marked. Occasionally, in extreme age, symmetrical depressions appear in the upper parts of the parietals behind the vertex. In the latter part of life the frontal sinuses enlarge, as the inner table follows the shrinking brain. In some rare cases the skull grows heavier in old age, owing to an increase in thickness of the inner table. Differences due to Sex. There is no marked sexual difference in skulls up to puberty. These characteristics appear during the last stage of growth. They may be summed up by saying that the female skull differs less than the male from that of childhood. The parietal and frontal eminences are more prominent ; the superciliary prominences and glabella less marked ; the zygomata, mastoid, occipital protuberance, and muscular ridges less developed. The whole structure is lighter. The face is smaller in proportion to the cranium, owing to the lighter jaws. The lower jaw alone is also relatively lighter to the cranium. 1 The frontal and occipital regions are less developed than the parietal. Two points are of especial value, namely, in the female skull the change of direction from the forehead to the top of the head is more sudden, suggesting a definite angle, while in man the passage is imperceptible ; and, secondly, in man a wedge-shaped growth above the front of the condyle is more developed, so as to throw the face higher up. There is no trouble in recognizing a typical skull of either sex ; but in many cases the decision is difficult, and sometimes impossible. Surface Anatomy. It is convenient for many reasons to settle on what shall be called the normal level of the skull. This should be parallel with the axis of the eye when looking at the horizon. It is expressed by a plane passing through the points above the middle of each external auditory meatus and the lowest points of the anterior border of each orbit. A simple method is to regard the upper border of the zygoma as horizontal, but this is not sufficiently accurate with skulls of low races. The following parts are easily explored by the finger : the whole of the vault as far as the superior occipital line, the occipital protuberance behind, and the supe- rior temporal ridges at the sides. Often the bregma and sometimes the chief sutures can be made out. The possibility of parietal depressions is to be remembered in cases of injury ; also that they may be expected to be symmetrical. The superciliary eminences and the upper borders of the orbits are easily explored. The .prominence of the former is likely to imply a large frontal sinus ; but the converse is not true, for, especially in the latter part of life, there may be a large sinus with no external indication. The sinus always extends downward to the inner side of the orbit, but its expansion outward and backward is very uncertain. The external angular process protects the outer side of the eye, and one or both temporal ridges can be followed from it. The suture between the process and the malar is easily felt through the skin. A line connecting the most prominent points of the zygomatic arches indicates the depth of the orbits. The zygoma is easily followed backward to the auricle. By pressing the latter forward, the supramastoid crest can be made out. Just below this is the spina supra- meatum, close to the cartilaginous meatus. The outside of the mastoid is easily explored. The course of the lateral sinus is in a curved line with the convexity upward from the external occipital protuberance to the upper part of the mastoid, only the lower part of the sinus touching a straight line between those points. According to Birmingham, the descending part follows roughly the line of the attachment of the ear. There is, however, great variation in its course as to the sharpness of its descent and its relation to the surface of the mastoid. It may be exceedingly close, or in no particular relation to it (Figs. 199, 200, and de- scription of the temporal bone, page 179). The antrum leading to the mastoi cells is just back of the upper part of the meatus, often under a small, smoot surface. The antrum of Highmore in the superior maxilla extends upward to the floo of the orbit, outward into the malar prominence, downward to just above the line of reflection of the mucous membrane from the lips to the alveolar process, and inward to the line of attachment of the ala of the nose, which is above the canine eminenc and marks the separation of the antrum from the nasal cavity. The variations of the upper end of the infundibulum are of interest. In the cases (about one-half) in which it drains the frontal sinus it is easy for fluid from the latter to run through the infundibulum both into the nasal cavity through the hiatus scmilunaris and into the antrum through the opening in its outer side. If the 1 Gurriere and Massrtii : Rivista speriment. di I-'n-niatria e de Mt-d. K-gale, 1895. PRACTICAL CONSIDERATIONS : THE SKULL. 235 infundibulum ends blindly, there is less likelihood of inflammation spreading from the frontal sinus to the antrum. The nasal bones and their junction with the nasal cartilages are easily recognized. The ramus and body of the lower jaw are to be examined from the outside. The head and coronoid process are felt more easily if the mouth be opened. PRACTICAL CONSIDERATIONS. The Cranium. In the development of the cranium, provision is made for its continuous enlargement, so that it may accommodate the rapidly growing brain. Accordingly, the first rudiment is a membranous capsule, at the base of which carti- lage is soon formed, giving support to the overlying portions. Then several centres of ossification appear in various portions of the membrane and grow quickly, so as to protect the cerebral mass, the membrane remaining between these centres still permitting the growth and expansion of the contents. Finally, the separate bones become united, first at their edges, then at their angles, to make the complete unyielding bony cranium. Arrest of these processes at various stages produces the equally various forms of malformation, only a few of which need be mentioned here. It is to be observed that, as a rule, they affect that part of the cranium that is of membranous origin, the base (developed from cartilage) being much more rarely involved. Turner (quoted by Allen) states that this is because the areas of the different bones are less precisely defined, and because the process of ossification is more liable to disturbance in mem- brane than in cartilage. In some cases the whole calvaria may be lacking and represented only by a membrane. Fissures extending from the margins of the bones towards the centres may exist, especially in the frontal and parietal bones, and may be mistaken for fractures. Other irregular gaps filled with membrane may be found, and are gen- erally situated at or near the natural foramina for vessels. The ossification of the bones may be so incomplete as to constitute what is called aplasia cranii congenita, a condition in infants due, usually, to maternal cachexia, and characterized by the absence of bone either in localized patches or at points scattered over the entire calvaria. The non-closure of the sutures, or defective development, may be followed by protrusion of the dura mater, either with or without part of the brain, constituting a meningocele if the protrusion consists only of the membranes and cerebro-spinal fluid ; an encephalocele if it contains brain ; or a hydrencephalocele if the contained brain is distended by an excess of ventricular fluid. These protrusions, in the order of frequency, occur (a) in the occipital region ; () at the fronto-nasal junction ; (f) in the course of the sagittal, lambdoidal, and other sutures ; (d) at the anterior or lateral fontanelles, and at the base of the cranium, entering the orbit, nose, or mouth through normal or abnormal openings. In hydrocephalus there are practically always atrophy and thinning of the cranium. "The deformities of hydrocephalus are largely determined by the con- dition of the sutures at the time of the occurrence of the disease. Fixation at the line of the sagittal suture causes bulging at the forehead and the occiput. Fixation at both the lambdoidal and the sagittal sutures causes vertical bulging at the line of the coronal suture and enormous increase of the ascending portion of the frontal bone. Should the intracranial pressure announce itself prior to the closure of any of the sutures of the vertex, the several bones composing it become widely separated and the fontanelles enormously increased in size" (Allen). In microcephalus there is diminution in the size of the cranium and of its cavity, due to premature ossification of the sutures. The subjects of microcephalus are usually idiotic. The operation of "linear craniotomy," by which a strip of bone is excised on either side of the median line of the cranium, was intended to permit of the expansion of the brain in such cases. It has not established itself in surgical favor. The arrested growth of the skull is thought to be due to the arrested development of the brain, and not vice versa. The skulls of idiots, even when not markedly microcephalic, approximate in many ways to those of the lower animals, 236 HUMAN ANATOMY. and form a distinct type characterized by the proportionate largeness of the facial bones, the contraction of the brain-case, especially in front and above, the upward slant of the occipital bone between the foramen magnum and the occipital crest, the projection backward of the frontal bone between the parietals at the situation of the anterior fontanelle, and by many minor peculiarities. In spite of these, however, they are easily referred to the human species by the descent of the cranial cavity below the level of the glenoid fossa, the number of the nasal bones, the shap'e of the jaws, the number and direction of the teeth, etc. Cretinism is said to be associated with initial deformities of the base pertaining to errors of development and trophic changes in the bones arising from cartilage, especially the basilar process of the occipital and the body of the sphenoid. Accessory to these deviations, and in a measure dependent upon them, are the modified facial proportions and dental irregularity of cretins. The Wormian bones, "detached centres of ossification in the marginal area of growing membrane bones, which they aid in occupying intervening spaces among the bones themselves," have been depressed in injuries of the skull, and have resembled fragments of bone pressing against the meninges. The edge of such a bone has been mistaken for a line of fracture. The most frequent cause of the formation of Wormian bones is the stretching of the membranous envelope of the cranial cavity which occurs in hydrocephalus, assistance in the completion of the cranial cavity being supplied by Wormian bones, which may form in numbers, espe- cially along the sagittal, lambdoidal, and squamous sutures. The fact that in development the cranial bones touch first and unite first at the points nearest their centres of ossification explains the formation and situation of the fontanelles. The four sides of each parietal bone, for example, become united to the four surrounding bones earlier in the middle than at the four angles. At the latter, therefore, there remain spaces covered with membrane. The anterior fontanelle, at the junction with the frontal of the antero-superior angles of the parietal, is the largest, and is not closed for from one to two years after birth. In rickets its closure is much retarded. Its condition, as to fulness or the reverse, gives a valuable indication in many of the diseases of children. In a state of health, the opening, while still membranous, is level with the cranial bones or is very slightly depressed. Systemic exhaustion, malnutrition, diseases associated with depletion of the vascular system, gastric catarrh, chronic diarrhoea, and maras- mus, or simple atrophy, all produce a marked depression of the fontanelle, which in the great majority of cases indicates feeding and stimulation. A bruit de souffle of greater or less intensity, and synchronous with the pulse, is often heard over the anterior fontanelle, and was at one time thought to be charac- teristic of rickets and of hydrocephalus, but has little diagnostic significance. The thickness of the skull varies in individuals, in the various portions of the skull, and often even in the two halves of the same skull. Humphry observes that, as he has often found the skull to be thick in idiots, and the several bones to be thickest when the skull is small, i.e., when the brain is small, "the term ' thick-headed,' as a synonym for ' stupid,' derives some confirma- tion from anatomy." Anderson says, however, that the weight of the brain does not seem to have any relation to the thickness of the skull, although this does not affect the truth of the statement that as the brain diminishes with age the skull is apt to thicken, the addition of bone taking place on the interior and giving rise to the irregular surface with close dural adhesions often met with in operations upon the cranium in old persons. The middle cerebral fossa, the centre of the squamous portion of the temporal, and the middle of the inferior occipital fossae arc the thinnest parts of the skull, varying from 1.75 millimetres to .85 of a millimetre, and in exceptional skulls m -as- tiring only . 2 millimetre in thickness. This has an important bearing on the location of fractures (page 239). At the parietal eminence, the posterior superior angle of the parietal, the superior angle of the occipital, and especially at the frontal eminences and the occipital protuberance areas of thickening are found ; at the latter point the skull may measure fifteen millimetres in thickness (Anderson). The average thick- ness of the remaining parts of the calvaria is from five to 7.5 millimetres. PRACTICAL CONSIDERATIONS : THE SKULL. 237 In trephining these general facts should be remembered, as should the occa- sional want of parallelism between the inner and outer tables. The shape of the skull is influenced by race and by disease. The racial pecu- liarities have sometimes a medico-legal significance, but cannot be described here. (See also page 229.) Pathological asymmetry is caused in many ways. In rickets the head is enlarged, and this enlargement seems greater than it really is on account of the retarded growth of the facial bones. All the fontanelles are larger than usual and close later. The anterior fontanelle is sometimes patent at the end of the third or fourth year. In craniotabes the rhachitic softening of the bones favors absorption under pressure. Consequently the regions most affected by the thinning of the bones are the occipital and the posterior half of the parietal, which are between two forces, the expanding and growing brain within and the supporting surface, as the pillow, without. Various peculiar shapes may result. The changes in hydrocephalic and microcephalic skulls have already been described. Syphilis in the young affects especially the fronto-parietal region, producing thickening or nodes of those bones in the vicinity of the anterior fontanelle. This site is probably determined by the vascularity accompanying growth, as this is the last portion of the cranium to become bony. Such nodes are, therefore, analogous to the rings or collars that form in the long bones of syphilitic children near the epiphyses ; the immobility of the cranial bones, however, causing the exudate to harden rather than to take on inflammatory action. The bulging of the forehead in some hereditary syphilitics is due to the catarrh of the frontal sinuses which often accompanies the Schneiderian catarrh, that produces first the so-called "snuffles" and later caries of the nasal bones, with the characteristic flattening of the nose. In adults syphilis of the cranium usually causes necrosis, spreading from the external to the internal table. Necrosis from whatever cause is more apt to affect the external table, which is more exposed to injury and less richly supplied with blood. The calvaria is far more frequently attacked by disease than the base, doubt- less from its greater liability to traumatism. The bones of the cranium are supplied with blood by arteries entering from the pericranium on one side and from the dura mater on the other. The dural supply is the larger ; hence the foramina on the inside of the cranium are larger and more numerous than those on the exterior, and hence also traumatic detachment of the pericranium over considerable areas may not result _ in necrosis. When detached from disease, the latter (as in syphilis), even when originating externally, is apt to spread along the vessels, and thus cause necrosis by finally affecting the dural supply. The meningeal blood-vessels running on the exterior surface of the dura the remnant of the primitive membranous cranium (Humphry) and sending branches to the cranium are not very strong, and consequently do not offer much resistance to the separation of the dura from the skull ; neither do their branches furnish a very large quantity of blood, surgically considered. It follows that a traumatic separation of the dura is not in itself a lesion followed by serious consequences, unless the separation takes place at or about the situation of the main trunks. Hence, when an extradural clot is suspected to be the cause of grave symptoms, it is usually sought for first over the anterior inferior angle of the parietal bone, i.e. , about three centimetres (approximately one inch and a quarter) behind the external angular process on a level with the upper border of the orbit. This will make accessible the region of the main trunk and the anterior branch of the middle meningeal. This latter branch at this point runs through a bony canal on the inner- surface of the cranium, and is therefore frequently torn when fracture occurs in this region. An opening on the same level, but just below the parietal eminence, will permit the posterior branch to be reached. The venous channels (emissary veins) connecting the sinuses within and the superficial veins without the cranium sometimes convey infective disease, such as erysipelas or cellulitis of the scalp, and thus bring about a septic meningitis or sinus thrombosis. FIG. 238 HUMAN ANATOMY. The time-honored custom of blistering or leeching behind the ear in intra- cranial inflammations rests on the fact that the largest emissary vein is the mastoid, traversing the mastoid foramen and connecting the lateral sinus with an occipital vein or with the posterior auricular. (For further discussion of these channels of communication, see the section on the Venous System. ) While the spinal dura mater has no intimate connection with the inner surfaces of the vertebrae (being separated from the arches by adipose tissue and from the bodies by the posterior ligament), the dura mater of the cranium becomes closely attached to the bones, especially at the base, where it adheres tightly to the many ridges and prominences and to the edges of the foramina which transmit the nerves and vessels. To the sides and summit of the skull the dura is less closely attached ; hence in fractures at the base the dura is generally torn, and the risk both of serious hemorrhage and of infection is thereby increased, while in fracture of the calvaria it much oftener escapes. Fractures of the Cranium. That fractures in this region are not vastly more frequent is due to various factors ; among them are the rounded shape of the calvaria, causing blows to glance off ; the division of the separate bones into inner and outer tables, with the comparatively spongy diploe intervening; aud the curved thicken- ings which, like buttresses, strengthen the skull externally, and extend on each side through the supra-orbital ridge and the upper border of the temporal fossa to the mastoid process and thence to the occipital tuberosity. From this latter point on the inner surface other ridges, like the groining of a roof, run forward in the median line to the frontal bone, downward to the foramen magnum, and laterally, on either side of the groove for the lateral sinus, extend to the mastoid. In very young persons the dome of the skull is made up of three dis- tinct arches composed of the occipital, the frontal, and the parietal bones. In child- hood the centre (the most prominent portion) of each of these bones is, on account of early ossification, thicker than the rest, while the edges are connected by mem- brane and are comparatively movable. These mechanical conditions, together with the elasticity of the individual bones in young persons, make fractures of the skull in them comparatively rare. In the adult the membranous layer between the sutures becomes thinner or disap- pears and the bones denser and less elastic ; they are, therefore, more easily fractured. The two tables may be broken separately, although this is rare. In almost all cases in which fracture is complete the inner table suffers more than the outer. This is because (a) it is more brittle ; (<$) the fibres on the side of greatest strain suffer most (as in "green-stick" fracture) ; (c) the material carried inward from without is greater at the level of the inner table than at the point of application of the external force. Agnew explains this diagrammatically as follows : Section of frontal bone, natural size, showing rela- tion of external and internal tables of compact bone to intervening diploe. AB represents a section of the arch of the skull. CD and EF represent the lines of a vertical force applied about G. The effect is to flatten the curve so that it is as HI, while at the same time the vertical lines diverge (JK and LM) and the particles of bone in the external table tend to be forced together at N and separated or burst apart at O. PRACTICAL CONSIDERATIONS : THE SKULL. 239 FIG. 264. Force applied to the vertex would tend to drive apart the lower borders of the parietal bones, but the bases of the great arch formed by these bones are overlapped by the squamous portions of the temporal, and thus this outward thrust is prevented. If the force be applied to the frontal bone, as it overlaps the parietals at the middle of the coronal suture, it is transmitted to them and is resisted by the same mechanism. The occipital bone and the bones at the sides of the skull (beneath the level of the ridges that have been described) break more easily, as they are thinner, the diploe is less developed, and the two tables are more closely united (Humphry); but from their situation they are less exposed to injury, and are protected by a thicker covering of soft parts. Fractures of the base are usually due to indirect violence. They may result from foreign bodies thrust through the nose, orbit, or pharynx ; or from a blow upon the nose acting through the bony septum to produce fracture of the cribriform plate of the ethmoid ; or through a blow or fall upon the point of the chin, driving the condyles of the inferior maxilla into the cranium. As a rule, however, the force traverses the vault or, more rarely, the spinal column (as in falls upon the feet or buttocks). Fractures of the base are very frequent for several reasons. The large expanse of bone forming the vault is contracted at the base into three comparatively narrow por- tions, which descend in successively lower planes from before backward, but which all have relatively thin floors, on which the force received at a distant portion of the cra- nium is ultimately expended. This impact reaches the base by the shortest route, so that a blow of sufficient violence upon the frontal bone will fracture the orbital plates in the anterior cerebral fossa; upon the vertex, the petrous portion of the temporal and the floor of the middle fossa ; and upon the occiput, the floor of the posterior or cerebellar fossa. Furthermore, the base is provided with a series of well-marked ridges which aid in the transmission of force and which fade away into the vault. The anterior ridges are gathered into the lesser wing of the sphenoid and end at the sides of the anterior clinoid process. The middle group, collected into the petrous portion of the temporal bone, passes to the centre of the base of the skull and terminates at the foramen lacerum medium. The ridges of the posterior group, meeting at the torcular Herophili, continue to the foramen magnum, at the posterior limit of which they divide and pass for- ward to meet again in the basilar process, and end in the posterior clinoid process. The region of the sella turcica is therefore the centre of resistance to the transmis- sion of forces from the vault to the base. This is well surrounded by fluid, and the vibrations which are concentrated here may thus become lost in the fluid without injuring the brain-substance. The region of the middle fossa suffers, however, most frequently because : i. It is connected (by the fronto-sphenoidal and petro-occipital sutures) with both the other fossae, and hence often participates in their injuries. 2. It is intrinsically one of the weakest parts of the skull, on account of the presence of the foramina lacera, the carotid grooves, the hollows for the pituitary body, the depression for the sphe- noidal sinus, the petro-sphenoidal suture, and the thin walls of the tympanum, of the external auditory canal, and of the temporal fossa. Moreover, just in front of this region the descending pterygoid processes and the lower jaw reinforce the Base of skull from above, showing lines of fractures. 2 4 o HUMAN ANATOMY. cranium proper, while behind it are the thickening of the basilar process and the posterior clinoid plate (Humphry) (Fig. 254). The differential symptoms of fracture through the floors of these fossae are determined by their anatomical relations. They are as follows : 1. Anterior Cerebral Fossa. (a) Epistaxis when the Schneiderian membrane and the dura and arachnoid are torn. It should not be forgotten that the blood may come from the mucous membrane alone, (b') Loss of smell from injury to the olfactory bulbs resting on the cribriform plate, (c) Subconjunctival ecchymosis. The blood is usually derived from the meningeal vessels over the orbital plates, but in bad cases may come from the ophthalmic artery, ophthalmic vein, or cavern- ous sinus. If the body of the sphenoid is fractured, the blood may find its way through the sphenoidal sinuses into the pharynx and stomach, and then be vomited, giving rise to a mistaken diagnosis of gastric injury. 2. Middle Cerebral Fossa. (a) Hemorrhage from the ear. This may be merely from a torn tympanic membrane. () Escape of cerebro-spinal fluid from the ear. This indicates that the petrous portion of the temporal is broken, the dura mater and the arachnoid torn, and the membrana tympani ruptured. If the latter escapes injury, the fluid may trickle into the throat through the Eustachian tube. (c) In rare and very severe cases the lateral sinus has been opened or the internal carotid torn, (d) There may be deafness or facial paralysis, or both. 3. Posterior or Cerebellar Fossa. (a) Hemorrhage into the pharynx if the basilar process is involved and the pharyngeal mucous membrane torn. (6) Ecchy- mosis at the nape of the neck and about the mastoid. Of course the characteristic symptoms of any two or even of all three of these injuries may be commingled if the fracture is extensive enough. Just as fractures would be more frequent were it not for the mechanism that has been described, so concussion or laceration of the brain would occur far oftener were it not for certain factors, among which may be mentioned the different strata of tissue of varying density intervening between the brain and the scalp. The soft diploe and the dense inner "vitreous" table both tend to diminish shock to the brain, the former by arresting vibrations and the latter by lateralizing them. The eminences on the inner surface of the skull project into the spaces between the great divisions of the brain, where, in places, there is more subarachnoid fluid than else- where ; such elevations are intimately connected at their edges and terminal points with the strong expansions of the dura mater, the falx and the tentorium, which still further take up and distribute the final vibrations. ' ' Thus there is every facility for causing jarring impulses to deviate from the direct line and take a circumferential route, in which they are gradually weakened and rendered harmless" (Humphry). The conditions tending to minimize the effects of violence inflicted upon the skull are thus summarized by Jacobson : "(i) The density and mobility of the scalp. (2) The dome-like shape of the skull. This, like an egg-shell, is calculated to bear hard blows and also to allow them to glide off. (3) Before middle life the number of bones tends to break up the force of a blow. (4) The sutures interrupt the transmission of violence. (5) The internal membrane (remains of foetal peri- osteum) acts in early life as a linear buffer. (6) The elasticity of the outer table. (7) The overlapping of some bones, e.g. , the parietal by the squamous ; and the alternate bevelling of adjacent bones, e.g. , at the coronal suture. (8) The pus ence of ribs or groins, e.g. , (a) from the crista galli to the internal occipital pro- tuberance ; (b} from the root of the nose to the zygoma ; (r) the temporal ridge from orbit to mastoid ; (\ a misplaced third molar. PRACTICAL CONSIDERATIONS : THE FACE. 245 The inferior maxilla has no epiphysis, and, as might therefore be expected, the ends of the bone at and near the articular surfaces are usually exempt from disease, in marked contrast to the long bones, in which those regions especially suffer. The inferior maxilla is not a very vascular bone ; the mucous membrane of the gum is in close contact with it ; it occupies a peculiarly exposed position, and is subject to frequent minor traumatisms ; it is readily infected through carious teeth or tooth-sockets. Such a tooth or an open socket communicates directly with the cancellous tissue of the bone, thus probably permitting in the lower, as in the upper jaw the direct contact of the toxic agent in phosphorus necrosis. Similar conditions are found in no other bones of the skeleton. As a result of the conditions just enumerated, osteitis and necrosis are common, are associated with much pain, and are often very slow in their progress. The excessive pain, dysphagia, dribbling of saliva, and occasional aphasia and marked nervous symptoms are thought to be due to reflex irritation associated with compression of the inferior dental nerve in the dental canal by the products of inflammation. Such irritation of a cranial nerve confined within a bony canal is rare, and associates the above symptoms with those occasioned by pressure from similar causes on the other branches of the fifth pair and on the seventh. Fracture Q{ the lower jaw may occur at any point. The whole bone is to a great extent protected from fracture by its horse- shoe shape, which gives it some of the FlG - 266> properties of a spring, by its density of struc- ture, by its great mobility, and by the buffer- like interarticular cartilages that protect its attached extremities (Treves). The neck of the condyloid process and the coronoid process are so deeply situated and so sheltered in the temporal fossa by the zygomatic arches that they are seldom broken. The ramilS is protected (though tO a Mandible, showing lines of fractures. less extent) by the masseter externally and the internal pterygoid internally, and is not often fractured. The angle and the symphysis are thickened, and thus resist fracture. About three centimetres (approximately one and a quarter inches) laterally to the symphysis the bone is weakened by the presence of the mental foramen and the large socket for the canine tooth. It is most often broken there or thereabouts either by direct or by indirect violence. Most fractures of the body of the bone are compound on account of the firm adhesion of the gum, which is usually torn ; hence necrosis and non-union following infection from the mouth-fluids are not un- common results. (For the displacement accompanying this fracture see section on Muscles, page 493.) The deformity, in so far as it is produced by anatomical forces, is apt to consist of depression of the anterior and larger fragment by the digastric, the genio-hyo-glossus, and the genio-hyoid, and elevation of the posterior and smaller fragment by the temporal, the masseter, and the internal pterygoid. The dental nerve, while escaping injury at the time of the accident, may later be compressed by callus, and, if irritated, may, by reason of its anatomical associa- tions with the regions in front of the pinna or in the external auditory meatus, give rise to " faceache" or to "earache." If paralyzed, and the patient puts a cup to his lips, he feels with his lower lip only half of it ; in paralysis of the fifth nerve itself it seems to him exactly as though it were broken (Owen). The capsule of the temporo-maxillary joint is thinnest anteriorly and strongest externally ; hence suppuration is most likely to extend in a forward direction. The strong external lateral ligament arising from the lower edge of the zygoma and running backward and downward seems to prevent the condyle being pressed back- ward against the bony meatus and the middle ear (Fig. 247). As Treves observes, if it were not for this provision, blows upon the chin would be far more dangerous than they are. In spite of its great mobility and its frequent use, the joint is rarely the subject 246 HUMAN ANATOMY. of acute disease, the intra-articular cartilage being so arranged (page 214) that it acts as an elastic buffer presenting one surface upon which the hinge-like, and another upon which the sliding, movement of the jaw may take place. Suppurative disease of the middle ear may extend to the joint (Barker). Rheumatoid arthritis is perhaps the most common disease of the joint, and may be localized there in subjects otherwise predisposed by the frequent exposure of the joint to cold and wet. The so-called " subluxation," sometimes, perhaps, depending upon relaxation of the ligaments, is more probably in the majority of cases due to rheumatic or gouty changes in the joint. Dislocation of the jaw (discussed in connection with the action of the associ- ated muscles, page 493) occurs only when the mouth is widely open, as in yawning, so that the condyle passes beyond its proper limits, over the summit of the ridge, and is lodged in front. " When the mouth is widely opened the condyles, together with the interarticular fibre-cartilage, glide forward. The fibre-cartilage extends as far as the anterior edge of the eminentia articularis, which is coated with cartilage to receive it. The condyle never reaches quite so far as the summit of that emi- nence. All parts of the capsule save the anterior are rendered tense. The coronoid process is much depressed. Now, if the external pterygoid muscle (the muscle mainly answerable for the luxation) contract vigorously, the condyle is soon drawn over the eminence into the zygomatic fossa, the interarticular cartilage remaining behind. On reaching its new position it is immediately drawn up by the temporal, internal pterygoid, and masseter muscles, and is thereby more or less fixed. A specimen in the Muse"e Dupuytren shows that the fixity of the luxated jaw may sometimes depend upon the catching of the apex of the coronoid process against the malar bone" (Treves). Excision of the inferior maxilla, since it is concerned chiefly with the soft parts, will be considered in connection with the Muscles (page 493). Landmarks. The supra-orbital ridges mark the boundary between the face and the cranium. The supra-orbital notch can be felt at the junction of the inner and middle thirds of the supra-orbital margin. A line from that point to the interval between the two bicuspid teeth in both jaws crosses the infra-orbital and the mental foramina (Holden). The attachment of the nasal cartilages to the superior maxillae and to the nasal bones can easily be felt. The connective tissue between the skin and the cartilages is very scanty. This is a source of difficulty in some of the plastic operations on the nose, and is also a cause of the severe pain felt in cellulitis and in furuncles of that region. The great vascularity of the part and the fact that " the edge of the nostril is a free border and the circulation therefore is terminal" (Treves) favor congestion and engorgement, while the close connection of the skin and cartilage resists the swelling ; hence the nerve-pressure and the excessive pain. The malar prominence, the concavity of the superior maxilla representing the anterior wall of the antrum, its malar process, corresponding to the apex of that cavity, the incisor fossa, and the canine fossa can easily be recognized either through the cheek or, more readily, through the gums with a finger in the mouth. The zygoma can be both seen and felt, the lower border more distinctly than the upper on account of the attachment to the latter of the dense temporal fascia. Wasting diseases cause an apparent increase in the prominence of the zygoma. The condyle of the inferior maxilla can be outlined and its motions observed (Fig. 246) just in advance of the ear. A line drawn from the angle to the condyle indicates the posterior border of the ramus. In making incisions in this region for inflammatory or suppurative conditions this line is to be remembered. Posterior to it important blood-vessels may be injured ; anterior to it deep punctures may be mack' with safety, the only structure of consequence endangered being branches of the facial nerve. From the angle of the jaw forward the outline of the inferior maxilla can be seen and felt both externally and within the mouth. The alignment of the teeth is usually disturbed in fracture, and is often the most easily recognized symptom. With a finger between the cheek and the teeth, the anterior border of the coronoid PRACTICAL CONSIDERATIONS : THE FACE. 247 process may readily be defined. In dislocation this is unnaturally prominent. Be- tween its base and the last molar tooth there is often a space through which liquid food or other fluids can be conveyed by a tube to the pharynx in cases in which fracture- dressing, or trismus, or ankylosis rend-ers the lower jaw immovable. Along the lower border externally, just in advance of the anterior edge of the masseter, the groove for the facial artery may be felt, and in the middle line the ridge which indicates the thickening at the symphysis. On the inner surface of the jaw may be recognized the genial tubercles, some- times in two distinct pairs, indicating the attachments of the genio-hyo- FIG. 267. glossi and genio-hyoidei. The sub- lingual fossae may be located, and just external to them, and at their lower border, the faint beginning of the mylo-hyoid ridge, which runs upward and backward, becoming more evident opposite the last two molars. Above this line the bone is cov- ered by the mucous membrane of the mouth ; hence diseases of this portion find their expression in the oral cavity, while those of the lower portion of the bone are more apt to involve the soft parts and glands of the neck (Fig. 267). The fossae for the submaxillary glands cannot be felt through the mouth, but, as they lie below the ridge, while the sublingual fossae lie above it, the well-known clinical relations of the former glands to the neck and of the latter to the mouth are explained. The familiar change in the shape of the lower jaw in edentulous old persons is due to absorption of the alveolar process. (Most of the landmarks of the face are of more importance in relation to the soft parts, the nerves, and the contents of the cavities of the orbit, nose, and mouth than in connection with the bones themselves. They will, therefore, be further con- sidered in those connections.) Inner surface of lower jaw, showing various areas. THE UPPER EXTREMITY. The Shoulder-Girdle. This consists of the clavicle and scapula. The latter is far the most important morphologically, representing, as it does, both the scapula and the coracoid of the lower classes of vertebrates ; while the clavicle is inconstant in mammals, and seems to be no part of the primitive shoulder-girdle. The scapula bears the socket for the humerus. It has no bony attachment to the trunk save through the clavicle, which, interposed between it and the sternum, is connected with both by joints. THE SCAPULA. Physiologically, the essential part of the scapula is the socket for the shoulder ; a part of this is made by the coracoid element, which in man is an insignificant pro- cess of the shoulder-blade. The secondary functions of the bone are to give origin to some muscles and to afford leverage to others for their action on the arm. In most mammals the scapula may be considered a rod running upward from the joint, from which three plates expand, one towards the head, one towards the tail, and one outward. In man the second of these plates points downward and is excessively developed. It is more convenient in man to speak of one main plate, the body of the scapula, with the spine springing from the dorsal surface. The body is triangular, with two surfaces, a ventral one towards the ribs and a free dorsal one, three borders, and three angles. The posterior or vertebral border, 1 sometimes called the base, is the longest. It is nearly vertical from the lower angle to a triangular space on the dorsum, oppo- site the origin of the spine, above this it, as a rule, slants forward, but at a very varying angle. The upper border 2 slants downward and forward to the supra- scapular notch* at the base of the coracoid process. This notch, transmitting the suprascapular nerve, is sometimes imperceptible, but usually is well marked and sometimes very deep. It is bridged by a ligament, which may be replaced by bone, transforming the notch into a foramen. The anterior or axillary border 4 is the only thick one. Just below the glenoid cavity it begins as a triangular roughness for the long head of the triceps. This is continued as a line which ends on the dorsal surface near the lower angle, a little above an unnamed process curving for- ward and inward from which a part of the teres major arises. This is the analogue of a process much developed in some small monkeys. It is sometimes very large, the increase of size being in no relation to that of the bone nor of the muscle. Above this on the anterior border there is a deep groove for a part of the sub- scapularis muscle just internal to the anterior edge proper. Below the process the border runs downward and backward to the inferior angle. 5 This angle is some- times very sharp, sometimes quite the reverse. The same, in a less degree, may be said of the upper angle, 6 usually sharp, sometimes squarely truncated. The anterior angle 7 is the glenoid cavity. This, with the base of the coracoid process, is called the head of the scapula, the neck being a constricted region behind it, reaching to the suprascapular notch. The glenoid cavity 8 is an oval, slightly hollowed, cartilage-covered surface expanding from a narrower base. The long a\in is vertical and the broad end below. There is often an indentation at the upper part of the inner margin. The edge is a little raised where it bears the glenoid ligament, which deepens the cavity for the reception of the head of the humerus. The top of the edge forms the supraglenoid tubercle, whence starts the long head of the biceps. The coracoid process springs from the top of the head just behind the glenoid cavity and a little to the inner side. The first part, or root, which is compressed from side to side, rises inclining somewhat inward. The second, the free projecting portion, irregularly cylindrical, runs forward, rather outward and downward, to end in a knob near the inner side of the shoulder-joint. The upper and inner surface is 1 Marge vcrtebrnlls. M. superior. :! IncUura scapulae. H M. nxillarls. fl Anifiilus inferior. " A. incdinlis. ~ A. latcrnlis. 8 Cavltas iilrii.iiil.ilis. 248 THE SCAPULA. 249 rough and convex, the under and outer smooth and concave. A rounded promi- nence, the conoid tubercle, for the conoid ligament, is situated on the top of the first part and rather to the inner side, just above the angle formed by the two parts. A ridge from behind this, running outward and forward, separates the two parts dis- tinctly. The trapezoid ridge for the trapezoid ligament runs forward from the conoid tubercle along the inner side. The outer side of the upper aspect has a ridge for FIG. 268. ACROMION PROCESS Root of spine Superior border SUPERIOR ANGLE Long head of triceps Supraglenoid tubercle Conoid tubercle CORACOID PROCESS Riceps and cot aco- brachialis ANTERIOR SURFACE (Siibscapulans) POSTERIOR SURFACE Axillary border INFERIOR ANGLE Right scapula from before. the coraco-acromial ligament. The short head of the biceps and the coraco- brachialis arise from a roughness at the tip of the process, and the pectoralis minor from one at its inner side. The anterior surface, or venter, 1 is concave, forming the subscapular fossa, the deepest hollow being along the origin of the spine. At the very top the bone often takes a turn outward. The serratus magnus is attached to rough surfaces inside the upper and lower angles and to a narrow line connecting them just beside 1 Facies costalis. 250 HUMAN ANATOMY. the vertebral border. These surfaces are separated from the rest of the fossa by well-marked lines, which, with some four ridges running forward and upward from the spinal border, give origin to tendinous septa from which the subscapularis springs. This muscle arises also from the deep groove inside the axillary border. The posterior surface, 1 or dorsum, is divided by the spine into a supraspinous and an infraspinous fossa. The former gives origin to the supraspinatus ; near the back it is often strengthened by a vertical swelling. The infraspinous fossa is chiefly occupied by the infraspinatus, but two other areas are marked off by two lines : one, running forward and upward, separates the dorsal side of the lower angle and of the unnamed process on the axillary border ; from this space springs the teres major. The second line leaves the axillary border near the glenoid cavity and, diverging slightly, strikes the former line near the front, bounding a narrow region for the teres minor, which is crossed high up by a groove for the dorsal scapular artery. FIG. 269. Anterior tubercle ACROMION Coraco-acromial ligament^ ~~^ '^l&iJwx'Metacrorntal tubercle Short head of biceps -7^ CORACOID PROCESS Long head of biceps Suprascapular notch SUPERIOR ANGLE Upper part of vertebral border Right scapula from above. The spine 2 is a triangular plate arising from a small triangular surface at the pos- terior border, running outward and somewhat upward. Its attached border stops at the neck before reaching the glenoid cavity. The spine forms an acute angle with the floor of the supraspinous fossa, and an obtuse one with that of the infraspinous. Its front border is rounded and curves forward, and forms the posterior boundary of the great scapular notch connecting the supra- and infraspinous fossre. The free border is narrow beyond the triangular area, but soon broadens, presenting an upper and a lower lip. The descending fibres of the trape/ius are inserted into the whole length of the former, and of its continuation into the acromion. The lower lip often begins with a tubercle for the ascending and horizontal fibres, a little beyond which it narrows again. It gives origin to the deltoid muscle, which also is continued along the acromion. The acromion 3 is a broad, llat expansion overhanging the shoulder-joint and articulating with the clavicle by an elongated faret slanting slightly upward. A 1 Fades dursulls. - Splna scapulae. ' Acnnuion. THE SCAPULA. 251 short preclavicular border in front of this, receiving the outer end of the coraco- acromial ligament, runs forward and outward to the anterior tubercle. From this the outer border runs backward to the metacromial tiibercle, whence the posterior border runs into the hind edge of the spine. The outer border has three or four irregularities above for the tendinous septa of the deltoid, and is smooth at its lower edge for the same muscle. The lower lip of the spine runs directly into the hind border of the acromion, but often splits so as to enclose a narrow space continued into the back of the process, from which the deltoid springs. The acromion varies much in shape ; according to this description it is quadrate ; often, however, the pre- FIG. 270. SUPERIOR ANGLE Levator anguli scapula; Supraspinatii Trapezius. Rhomboideus minor Coraco-acromial ligament RACOID PROCESS Biceps and coraco- brachialis ACROMION Anterior tubercle eltoid acromial tubercle iceps, long head Groove for dorsal artery ANTERIOR ANGLE Teres major -Occasional origin of latissinms dor si Right scapula from behind. clavicular edge is rudimentary, so that it is three-sided ; or the metacromial tubercle is at the apex of a very obtuse angle, so that it is curved and narrow. There are also intermediate forms. 1 The inclination of the acromion to the horizon is on an average not far from 45, with a variation of probably 15 either way. This may or may not depend on a corresponding variation of slant in the spine. All the details determining the outline of the scapula vary greatly. The hind border may be convex, or the infraspinous portion concave. The bone lying with the dorsum up should rest on the coracoid and the upper and lower angles, with the vertebral edge rising from the table ; but this may be almost straight, or even bend the other way so as to change the usual points of support. The length from the upper to the lower angle ranges from 13.2 centimetres 1 Macalister : Journal of Anatomy and Physiology, vol. xxvii., 1893. 252 HUMAN ANATOMY. or less up to 20. i centimetres. The scapular indi-.v is the ratio of the breadth, measured along the base of the spine, to the length (~y~"e3i~~ ) It ranges from 55 to 82. The following means have been given for Caucasians : Broca, 65.9 ; Flower and Garson, 65.2 ; Dwight, 63.5. A high index means a broad scapula, which is one of a low type. The infraspinous index is the ratio of the breadth to the length of the infraspinous fossa, measured from the lower angle . , e ., . 100 X breadth \ TU- r .!_ to the starting-point of the spine ( fiifai s p inous j^n ) Thls ranges from 72.3 to 100.2. with a mean of about 87. High indices imply a broad scapula, but this method is of small value, as very diverse shapes may have similar indices. It is not possible to predicate anything of the figure during life from the shape of this bone. The most that can be said is that a long arm requires the leverage furnished by a long scapula. Differences due to Sex.. The chief point is the size. From the study of eighty-four male and thirty-nine female bones it appears that of 123 bones, twenty- six measure less than fifteen centimetres in length, of which only three were male ; also that seventy-six measure sixteen centimetres or more, of which only five were FIG. 271. SUPERIOR ANGLE Serratus niafnus Glenoid cavity Triceps (long head) \ Subscap u la ris VERTEBRAL BORDER Ridges for tendi- nous attach- ments Process for teres major - Serratus magnus Right scapula from before. INFERIOR ANGLE female. There was no single instance of a bone measuring less than fourteen centi- metres being male, nor of one measuring seventeen centimetres being female. In doubtful cases the glenoid cavity is very valuable. In woman it is not only smaller, but relatively narrower. Very few male sockets are less than 3.6 centimetres in length, and very few female as long. The typical female scapula is very delicate ; PRACTICAL CONSIDERATIONS : THE SCAPULA. 253 the lower angle is sharp, the process on the front border small ; the hind border straight up to the spine, then slanting forward in another straight line ; the upper border descends sharply ; the coracoid is slight, with the end compressed instead of knobbed ; the acromion is curved and narrow. An expert should be reasonably sure of the sex four times in five. Doubtful bones are almost always male ; so are those of peculiar shape, with the exception of concave vertebral borders. The scapular index has no sexual significance. 1 Structure. The strong parts are seen when the bone is held to the light. The head, neck, coracoid, acromion, and most of the spine are strong. So also are the front border, the lower angle, and, to a less extent, the hind border, which is strongest above the spine. Most of the body is very thin. A section through the socket, along the origin of the spine, shows the bony plates so disposed as to resist pressure in that line. Development. There is one chief centre for the scapula proper and one for the coracoid, besides an indefinite number of accessory ones. The first appears about the eighth week (Rambaud et Renault) at the neck, and forms nearly the FIG. 272. D Ossification of scapula. A, at eighth fcetal month ; S, towards end of first year ; C, from fourteen to fifteen years ; >, from seventeen to eighteen years ; E, about twenty years, a, chief centre ; b, for coracoid process ; c, for acro- mion ; d, for inferior angle ; e, additional for acromion ; /, for vertebral border. whole bone, including the spine and the root of the acromion and the dorsal part of the root of the coracoid. The coracoid centre appears in the first year ; it forms also the top of the glenoid cavity, and fuses with the first at fourteen or fifteen, beginning to unite at the ventral surface. At the earlier age the acromion is carti- lage beyond a line drawn from the back of the clavicular facet to the front of the metacromion. At about fifteen many little nuclei appear in the acromion. The anterior tubercle is formed from a single nucleus ; the others coalesce into two groups, one in the centre, the other at the outer margin. At about eighteen the latter joins the body and the other two fuse. A year later the mass so formed also joins the body. Sometimes this remains connected by fibro-cartilage ; very rarely several pieces persist. A scale-like epiphysis appears at the conoid tubercle of the coracoid about fifteen, and soon fuses. About seventeen or eighteen a nucleus appears in the strip of cartilage along the posterior border and one at the lower angle. Both are generally fused by twenty, but the lower is one of the last to fuse in the skeleton, and the line of union may remain for years. PRACTICAL CONSIDERATIONS. The scapula is rarely absent and rarely malformed. The outer part of the acromion may exist as a distinct bone, as may, but less frequently, the coracoid. Many cases of so-called fracture of the acromion and others of supposed traumatic separation of the acromial epiphysis are probably cases of persistent epiphysis. The centre for the inferior angle sometimes remains distinct, being united to the body 1 Dwight : The Range and Significance of Variation in the Human Skeleton, Proc. Mass. Mecl. Soc., 1894. HUMAN ANATOMY. FIG. 273. Lines ot fracture of the scapula. by a synchondrosis. The possibility of its detachment by excessive action of the latissimus dorsi has been mentioned, but no case of traumatic separation has been recorded. Fracture is rare, in spite of the thinness of much of the bone, because of its mobility, the adaptation of its curves to the underlying thoracic surface, the elasticity and compressibility of that surface, the thickness of the muscles that cover the scapula and of those that lie beneath it, the fragility of the clavicle (which by frac- turing often saves the scapula), and the great range of movement and corresponding weakness of the shoulder- joint, which, in like manner, by undergoing luxation, prevents the force of the traumatism from reaching the scapula. Fracture of the body and of the inferior angle from indirect violence has been reported in a few cases. The arms were fixed, and strong traction was being exer- cised in more than one case. It seems probable that the bone breaks between the opposing forces of the rhomboids and trapezius on the one hand, and the teres muscles, the subscapularis, and the infraspinatus on the other. The most common fracture is that of the body, usually running transversely or obliquely through the subspinous fossa. The attachments of the subscapu- laris beneath and of the infraspinatus above usually prevent any marked displacement. There is pain on lifting the arm to a horizontal position, because, in order that the deltoid may be able to do this, the acromion must become a fixed point, and that necessitates the contraction of the rhomboids and other muscles whose function it is, aided by the leverage afforded by the pro- longation of the scapula downward, to fix the blade of the scapula when the deltoid is in action. Superficial ecchymosis is rare on account of the dense infraspinous fascia which prevents the effused blood from reaching the surface. Fracture of the acromion is attended with slight flattening of the tip of the shoulder, the weight of the arm, acting through the deltoid, dragging the frag- ment downward. There may be the usual symptoms of preternatural mobility, crepitus, etc. Fracture of the coracoid is rare. Before the age of seventeen it may be an epiphyseal separation. Displacement is not common, as the downward pull of the pectoralis Tninor, short head of the biceps, and coraco-brachialis (page 590) is effectually resisted by the coraco-acromial and coraco-clavicular ligaments. Crepitus and preternatural mobility may possibly be recognized by sinking the fingers into the interval between the deltoid and pectoral muscles. The coracoid will be found just beneath the inner deltoid margin. Fractures of the neck of the scapula include, in surgical language, those which begin at the suprascapular notch and run to the axillary border of the bone detach- ing the glenoid cavity and the coracoid process. There is no instance of fracture of the anatomical neck, the constricted part supporting the glenoid cavity. The fragment, with the arm, will drop downward, away from the acromion. This puts the deltoid on the stretch and causes flattening of the shoulder. There will be a depression beneath the edge of the acromion. The arm will be increased in length. These symptoms (which will occur only if the coraco-acromial and coraco-clavicular ligaments are torn) are also found in subglenoid luxation of the luinierus ( page 583); but in the fracture, the presence of crepitus, the downward displacement of the coracoid, the ready disappearance of the deformity on pushing the head of the hunicnis upward, its prompt reappearance when the arm is allowed to hang by the side, and the ease with which the hand may be placed on the opposite shoulder serve clearly to denote the character of the accident. Excision of the scapula itself is not uncommonly indicated on account of malig- PRACTICAL CONSIDERATIONS : THE SCAPULA. 255 nant neoplasm, subperiosteal and central sarcomata especially. The main danger of the operation is hemorrhage. The subclavian should, therefore, be controlled. The dorsalis scapulae, crossing the axillary border of the scapula at a point on a level with the centre of the vertical axis of the deltoid (Treves), and the subscapular run- ning along the lower border of the subscapularis muscle to reach the inferior angle, are the largest vessels that require division, but the suprascapular, posterior scapular, and branches of the acromio-thoracic artery will also be cut. Infectious diseases giving rise to caries and necrosis and to suppuration are rare. When they affect the supraspinous region the pus is directed forward by the fascia covering the supraspinatus, which encloses that muscle in an osseo-fibrous compartment. In the infraspinous region the still denser infraspinous fascia con- ducts the pus in the same direction ; hence abscesses originating in scapular dis- ease are likely to point near the axilla and in the neighborhood of the insertions of the scapular muscles into the humerus. On the under surface of the scapula, between the ridges which give origin to the tendinous fibres that intersect the subscapularis muscle, the periosteum is loose and easily separated. Suppuration following caries of this aspect of the bone may, therefore, cause extensive detachment of the perios- teum, and it has been found necessary to trephine the thin portion of the blade of the scapula to give vent to such a purulent collection. Landmarks. The greatest breadth of the scapula is in a line from the glenoid margin to the vertebral border ; the greatest length in a line from the superior to the inferior angle. The general outlines of the scapula can easily be felt. The bony points most readily recognized by touch are the acromion, the coracoid, the spiae, the vertebral ejdge, and the inferior angle. The edge of the acromion is an important landmark. Measurement from it to the suprasternal notch is the easiest way of determining shortening in fracture of the clavicle. If this measurement is less than on the sound side, and the clavicle itself is unchanged in length, it indicates a dislocation of the acromial end of the latter. Undue prominence of the edge of the acromion is seen in luxation of the humerus (page 582) and in fracture of the neck of the scapula. In these conditions the fingers may be pressed beneath the acromion, as they can in old cases of deltoid paresis or paralysis with atrophy of that muscle, when the weight of the arm drags the humerus downward and increases the space between the greater tuberosity and the acromial edge. The coracoid process may be felt through the inner deltoid fibres, below the inner portion of the outer third of the clavicle, by thrusting the fingers into the space between the pectoral and deltoid. In fracture it may be depressed, as it is in fracture of the scapular neck. The axillary artery can be felt just to the inner side of the coracoid as it passes over the second rib. The spine is least prominent in muscular and most conspicuous in feeble and emaciated persons. This is also true of the inferior angle, which in weak, and especially in phthisical, subjects is not held tightly to the chest, but projects in a wing-like manner (scapulae alatae). This is partly due to general muscular weak- ness, in which the latissimus dorsi and serratus magnus participate, and partly to the shape of the thorax and the direction of the clavicles. The flatter and shallower the chest the more oblique in direction and the lower are the' collar-bones, carrying with them downward and forward the upper and anterior portions of the scapulae, and by that much tending to make the lower and posterior portions more promi- nent. The length of the arm is usually measured from the junction of the spine of the scapula and the acromion the acromial angle to the external condyle of the humerus. The vertebral edge of the scapula lies just at the side of the spinal gutter. When the arm hangs at the side of the body, this edge is parallel with the line of the spinous processes. It can be made prominent (for palpation) by carrying the hand of the patient over the opposite shoulder. The superior angle is made accessible by the same position. The axillary border of the scapula and the inferior angle are best examined with the elbow flexed and the forearm carried behind the 256 HUMAN ANATOMY. back. With the arm at the side, the superior angle is about on the level of the upper edge of the second rib ; the inferior angle is opposite the seventh intercostal space (and hence is a guide in selecting a space for the various operations for em- pyema, page 1867); the inner end of the spine is opposite the spinous process of the third dorsal vertebra. With the shoulders drawn forcibly backward, the vertebral borders of the scapula can be made almost to touch at the level of the spines, and are not more than from two to three inches apart at the angles. With the hands clasped on the vertex, the inferior angles are from sixteen to seventeen inches apart. By crossing the arms on the front of the chest, and leaning forward, the scapulae are also widely separated, and this position is therefore selected for auscultation and percussion. The mobility of the scapula lessens the functional disability in ankylosis of the shoulder-joint. LIGAMENTS OF THE SCAPULA. Two ligaments the transverse and the coraco-acromial pass from one part of the scapula to another. The transverse or suprascapular ligament l (Fig. 289) is a little band on the upper border, 'just behind the root of the coracoid, making a bridge over the supra- scapular notch, under which the suprascapular nerve passes. It may be replaced by bone. The coraco-acromial ligament 2 (Fig. 274) is a triangular structure, broad at its base, along the outer border of the coracoid process, and narrowing to its insertion into the inner side of the end of the acromion just in front of the acromio- clavicular joint. The borders are strong, converging bands with a weak space between, the front one being the stronger and overlapping the other when they Capsule of shoulder-joint Humerus Tendon of biceps Coraco-acromial ligament Coracoid process Coraco-clavicular ligament FIG. 274. Acromio-clavicular joint I 'hivirle Ligaments about the right shoulder from above. meet. The course of the fibres in the weaker part is variable ; sometimes they diverge from near the front of the coracoid to the posterior band, sometimes they are in the main parallel with the latter, sometimes a band passes from this membrane to the front of the clavicle. The weak portion of this ligament is pierced by the pectoralis minor, when, as often happens, this muscle is inserted into the capsule of the shoulder <>r the upper end of the humerus. This ligament is really part of the apparatus of the shoulder-joint, forming a roof over the capsule, from which it is separated by a bursa. Before dissection the hind border of the ligament is not very 1 LIg. transversum scapulae supcrlus. " Llg. coracracromiale. THE CLAVICLE. 257 distinct, since the bursa appears to connect it with the capsule below and a thin fascia with the clavicle above. The spino-glenoid ligament 1 is an occasional little band at the great scapular notch, running from the anterior border of the spine to the posterior edge of the glenoid cavity, crossing the suprascapular vessels and nerve. THE CLAVICLE. The function of the clavicle, 2 or collar-bone, which extends from the top of the sternum to the acromion, is to give support to the shoulder-joint in the wide and varied movements of the arm. It is found in mammals that climb, fly, dig, or swim with movements requiring an outward and backward sweep of the arm. It is absent in those that use the fore-limb simply for progression with movements nearly restricted to one plane. It is present, but imperfectly developed, in some carnivora FIG. 275. T> apezius ACROMIAL END Right clavicle, superior and posterior surfaces. STERNAL END 'ectoralis major whose arms serve, in part, for prehension. In man it has a doubly curved shaft, a thick inner end, and a flattened outer one. The shaft is convex in front through the two inner thirds and concave in the outer one. The former portion has a superior, an inferior, an anterior, and a pos- terior surface ; but in the outer third the two latter surfaces narrow into borders. The superior surface is smooth, except for a slight unevenness at the inner end, FIG. 276. Acromial facet Pectoralis major Sternal facet Sterno-hyoid Trapezoid ridge Conoid tubercle Right clavicle, anterior and inferior surfaces. giving origin to the clavicular head of the sterno-cleido-mastoid. The inferior sur- face has near the inner end an oval roughness, which may or may not be raised, for the rhomboid ligament from the cartilage of the first rib. Beyond this is a longi- tudinal groove, more marked near the outer end, for the insertion of the subclavius muscle. Outside of the middle, near the hind border (sometimes on the hind surface), is the nutrient foramen, directed outward. The anterior surface narrows continu- ally from within outward. The inner two-thirds are rough for the pectoralis major ; 1 Lig. transversum scapulae infcrius. - Clavicula. 258 HUMAN ANATOMY. external to this the rough concave edge gives origin to the deltoid. The beginning of this is often marked by a minute tubercle, which, when exceptionally large, is the deltoid tubercle. The posterior surface is smooth, and narrows gradually till it reaches the outer end, the beginning of which is marked by a tubercle on the under surface. The borders are very ill marked. The sharpest is that separating the anterior from the inferior surface. That between the anterior and superior ones is fairly well marked near the inner end ; but it soon grows indistinct, so that often at the middle of the bone the front surface seems to twist into the upper, and the anterior inferior border becomes the front border of the outer end. Of the posterior borders, the upper, though rounded, is distinct along the middle of the bone ; the lower is very vague, but usually is well defined in the outer part ; when it is not, the posterior surface seems to twist into the lower. The inner or sternal extremity 1 is club-shaped, drawn out downward and somewhat backward. Its inner surface, coated with articular cartilage, is of very variable shape. It is approximately oval, with the long axis slanting downward and backward, and is rough and generally concave, but not always so. The front edge of the inner surface forms an acute angle with the anterior border of the bone, and the hind one an obtuse angle. The outer or acromial extremity - is flattened above and below and curved forward. At the very front of this end is FIG. 277. an articular surface joining the scapula. It A is oval, with the long axis horizontal, and usually faces downward as well as outward. There is generally behind this a rough space for ligament at the end, which gradually slants into the hind border. The conoid tubercle 9 ' is at the posterior border of the lower surface of the outer extremity just at its junction with the shaft. The trapezoid ridge extends from it forward and outward Ossification , of clavicle. A, at birth ; a, , chief cen- across t he bone. Its anterior portion is tre ; b, c, cartilaginous ends. , at about eighteen . . i years ; d, sternal epiphysis. often broad. I his tubercle and ridge are for the insertion of ligaments of correspond- ing names, passing upward from the base of the coracoid. Between the ridge and the end of the bone there is a smooth space, sometimes almost a groove, which lies above the supraspinatus muscle as it crosses the shoulder-joint. The clavicle varies greatly in length, thickness, amount of curve, and in the outline of the ends. Some- times the outer end is but little broader than the shaft. A very rare form is one in which the inner part of the shaft is flat and but slightly thicker than the outer. Differences due to Sex. The male bone is longer, stronger, more curved, and with larger articular facets. Apart from sex, a strong bone is generally more curved. Development. The centre for this bone, evident in the sixth week, precedes all others. It is remarkable as developing in indifferent tissue before any hint of the bone is to be seen. A little later a cartilaginous outline appears, which is shortly involved in the ossifying process. At about seventeen a centre is formed in the epiphysis at the sternal end, and joins the shaft a year or so later. Surface Anatomy. In life the anterior surface and edge, as well as the superior surface, are easily felt through the skin. The joint with the acromion is dis- tinct, the clavicle being higher than the scapula. The position of the bone is nearly horizontal, but in strong men the outer end is often the higher. The bone is highly elastic, owing to its curves. PRACTICAL CONSIDERATIONS. The chief function of the clavicle is to steady the shoulder and keep the upper arm at such a distance from the trunk that the muscles running from tin.- latter to the humiTiis may give it lateral motion. Therefore, in animals, in which no such 1 Extrcmitas stcmalls. " Extremitas ucromialis. 'TutMTMitU coracoidcn. PRACTICAL CONSIDERATIONS: THE CLAVICLE. 259 movement exists, and the fore-limbs are used only in progression, no clavicle, or a mere rudiment of it, is present. Congenital absence of both clavicles is rare. In several reported cases the shoulders could be brought together in front of the body. The congenital absence of both acromial ends is not so uncommon. Theoretically, one would expect, as a result of absence of the clavicle, a weakened upper extremity, some lateral curvature of the spine, interference with the upper chest (from the weight of the arm and scapula), and hence diminished lung capacity with the secondary ill effects upon growth, nutrition, etc. Such consequences were predicated (Maunder) as a result of arrest of growth from epiphyseal separation, but neither in those cases, in non-union after fracture, nor in congenital absence have they been noted. On the contrary, in the four cases of symmetrical absence of the acromial end recorded by Gegenbaur the func- tional disability was slight, the motions of the scapula being unimpaired. The whole bone becomes ossified very early, beginning before any other long bone of the skeleton. Its one epiphysis, at the sternal end, is, on the contrary, the last of the epiphyses of the long bones to ossify, appearing about the seventeenth or eighteenth year and, according to Poland, joining the diaphysis from the twenty- second to the twenty-fifth year. D wight places the time of union somewhat earlier. Separation of this epiphysis is among the rarest of epiphyseal detachments. But five cases have been recorded. Two of them were from muscular action, the pectoralis major and the clavicular fibres of the deltoid being apparently the agencies that carried the sternal end of the diaphysis forward. The age of the patient (from seventeen to twenty-five), the shape of the flattened diaphyseal end (unlike the pointed end of a fractured bone), and the integrity of the shape of the suprasternal notch aid in distinguishing this accident from a forward dislocation or a fracture on the inner side of the costo-clavicular ligament. Fracture of the clavicle is more common than that of any other bone, except possi- bly the radius ; it is, likewise, the most frequent seat of incomplete ( ' ' greenstick' ' ) fracture. About one-half of all clavicular fractures occur during early childhood, This frequency is due ( i ) to the early ossification of the bone, so that it is relatively more brittle than are the other bones ; (2) to the lack of close attachment between the periosteum and the bone ; (3) to the unusual thickness of the periosteum (prob- ably associated with the early ossification), which tends to prevent complete fracture ; and (4) to the common occurrence of falls and minor accidents among children. The amount of disability is often surprisingly slight, and the diagnosis, unless confirmed by skiagraphic testimony, may have to be made on the basis of very trifling deformity with localized tenderness and swelling. Muscular action may produce fracture through the violent contraction of the pectoralis major or of the clavicular portion of the deltoid. Indirect violence (received through falls on the hand, elbow, or shoulder) is the common cause. The frequency with which such falls occur, and the uniformity with which the force is transmitted to a slender bone containing but little cancellous tissue, and held firmly at either end by strong ligamentous attachments, sufficiently explain the common occurrence of clavicular fracture. The break usually occurs about the junction of the middle and outer thirds, because: (i) the outer end (like the inner) is firmly held by the ligamentous connec- tions, the middle of the bone being the most movable ; (2) at the outer end of the middle third the bone is smaller, and therefore weaker ; (3) at this point the sternal curve (convex forward) and the acromial curve (concave forward) meet, and force applied to the extremity of the bone is there expended. Fracture of the clavicle is rarely compound, because, although the bone is sub- cutaneous, the skin is very freely movable over it, and because the usual displace- ment carries the sharp end of the outer fragment backward and the sharp end of the inner fragment upward (Fig. 278). The anatomical causes of the common form of displacement will be considered in connection with the muscles concerned (page 579). The relations of the clavicle to great vessels and nerve-trunks would seem to render frequent complications probable, but as a matter of fact the latter occur with 260 HUMAN ANATOMY. comparative rarity : ( i ) because of the elastic curves of the bone, which enable it to escape fracture in many cases of direct violence ; (2) because of the inter- position of the subclavius muscle between the bone and the nervous and vascular trunks ; (3) because of the situation of the common fracture, the inner end of the outer fragment (the portion most likely to inflict injury) being both above and external to the region of danger. Still, cases of wound of the subclavian vessels, internal jugular vein, and of pressure pa- p IG 2 _ s ralysis of the upper extremity have been reported as complications of fracture of the clavicle. The supraclavicular nerves ( branches of the third and fourth cervical) pass in front of the bone, and may be involved in the callus, giving rise to severe and per- sistent pain. In resection or excision of the clavi- cle, either for disease or as a step in the performance of an interscapulo-thoracic Lines of fracture of the clavicle and acromion process. amputation, the protection afforded the vessels by the subclavius muscle should be remembered. Superficially, the cephalic vein and the supraclavicular nerves may have to be divided. Disease of the clavicle is not uncommon as a result of the various infections, syphilitic, tuberculous, typhoidal, etc. The bone is also the subject of new growths, especially of sarcomata. The anatomical relations already alluded to are those chiefly involved in these cases. Swelling and oedema of the arm may result from pressure on the subclavian vein in the angle between the clavicle and the rib ; gangrene, from pressure upon the artery ; pain or paralysis, from pressure upon the brachial plexus at the outer part of the costo-clavicular space. It is probable that, in view of the subcutaneous position of the clavicle and its consequent exposure to slight traumatisms, osteitis of one form or another would be more frequent if it were not for its great elasticity, which probably limits the effect of minor blows to the superficies of the bone. Ac- cordingly, syphilitic subperiosteal nodes are fairly common, while tuberculosis and septic and post-typhoidal osteitis are relatively rare. Landmarks. The clavicle is subcutaneous through its entire length. When at rest the bone is about on the same level as the spine of the scapula. In inspira- tion it moves forward an inch. The inner end of the bone is its largest portion, and its projection in front of and above the clavicular notch on the sternum should not be erroneously regarded as evidence of disease or injury. The deltoid tubercle at its outer third is sometimes unusually prominent, and should not then be mistaken for an exostosis. The curves of the bone may easily be traced from end to end. The normal curves may be increased in greenstick fracture without any positive angularity being produced ; but in this case careful measurement will show that the distance between the two ends of the bone is slightly lessened as compared with the uninjured side. It should not be forgotten, however, that the curves are apt to be increased in mus- cular persons, and that for the same reason the right clavicle is sometimes more curved, thicker, and a little shorter than the left. In general terms it may be said that the inner third of the bone is in relation below to the first rib, which it crosses obliquely ; the middle third to the axillary vessels and the brachial plexus (and below them to the first intercostal space); and the outer third to the coracoid process and the acromio-clavicular joint (Fig. 274). In the male, and in robust, vigorous persons generally, the clavicles are on a high plane and pass almost horizontally outward, giving the "square-shouldered" appear- ance usually associated with ideas of muscular strength and decreasing the apparent length of the neck. In the strong male the outer end may even be higher than tin- inner. In narrow-chested and in consumptive persons the clavicles are depressed and THE STERNO-CLAVICULAR ARTICULATION. 261 incline downward, and hence the sloping narrow shoulders and long necks so often seen in feeble or in phthisical individuals. In very fat persons, in those suffering from organic heart disease attended with dyspncea, and in emphysematous subjects the clavicles are raised and the neck thereby apparently shortened. THE STERNO-CLAVICULAR ARTICULATION. This is the only joint between the trunk and the upper extremity. The socket on the upper angle of the manubrium is coated with cartilage which often extends a little onto the first costal cartilage. This very shallow socket is made rather more secure by the forward inclination of the manubrium and also by being rather FIG. 279. Clavicle Sterno-clavicular ligament Interclavicular ligament Clavicle First costal cartilage Sternum First costal cartilage Sterno-clavicular articulations from before ; clavicles horizontal. more on the back than on the front of that bone, so that to some extent it over- laps the front of the clavicle. The very irregular end of the clavicle is coated with cartilage, which, however, gives it no regular nor constant shape. As a rule, it is concave from before backward, but there is often a swelling at the posterior lower angle. The interarticular fibre-cartilage l (Fig. 280), a disk subdividing the joint into two, is the chief factor in maintaining the great security of the joint. It is a FIG. 280. Rhomboid ligament Right sterno-clavicular joint opened. Left clavicle raised to show rhomboid ligament. Front view. rounded disk, thinnest in the middle and generally thickest at the upper border, which is attached to the upper edge of the inner end of the clavicle, while the lower border is attached to the first costal cartilage at the outer border of the joint. In the main it faces upward and outward, so that the clavicle rests upon it. It is said to be sometimes perforated. 1 Discus articularis. 262 HUMAN ANATOMY. The capsule (Fig. 280) surrounds the joint, being attached to the borders of the articular surfaces and also to the borders of the interarticular disk. It is strengthened before and behind by bands running upward and outward from the ster- num, of which the posterior are the stronger, and sends some deep fibres to the disk. These bands strengthening the capsule are sometimes described as the anterior and posterior sterno- clavicular ligaments. There are two distinct synovia/ cavities. The interclavicular ligament (Fig. 279) is a fairly well-defined band run- ning from the top of one clavicle across to the other. It is closely connected with the top of the joint and loosely with the top of the sternum, towards which it sinks with a slight curve. This does much towards filling up the deep interclavicular notch. The costo-clavicular 1 or rhomboid ligament (Fig. 280) arises from the costal cartilage just outside of the joint, with which it is loosely connected, and runs upward and outward to the rough rhomboid impression on the under side of the clavicle. It is a layer of strong, short fibres. THE SCAPULO-CLAVICULAR A-RTICULATION. The Acromio-Clavicular Articulation. This joint includes a capsular ligament (Fig. 274) and occasionally an intra-articular fibro-cartilage. The elongated facet on each bone is covered with articular cartilage, that of the clavicle usually overlapping the other. The capsule is weak, except above and behind, where there are strong bands extending outward from the clavicle. Of these the posterior are the longer. The fibro-cartilage, when present, is wedge-shaped, attached by the base to the superior part of the capsule, the thin edge reaching, perhaps, half-way through the cavity of the joint. Sometimes it divides the joint into two. There may be merely a thick pad of fibrous tissue attached to the outer end of the clavicle with only a very rudimentary joint. The coraco-clavicular ligament is an important ligamentous apparatus divided into an outer part, the trapezoid, and an inner, the conoid (Fig. 289). These are continuous behind, but diverge in front. The trapezoid ligament a is a four- sided layer of parallel fibres, springing from the trapezoid ridge and the top of the first part of the coracoid, to run outward to the trapezoid ridge on the under side of the clavicle. The line of attachment to the clavicle is usually the longer, and, as this runs forward and outward, the anterior fibres are almost horizontal. The conoid ligament, 3 or inner part, is less strong. It arises from the posterior border of the conoid tubercle at the root of the acromion, and runs to the tubercle of the same name at the back of the under side of the clavicle. Both these tubercles being prominences of some size, this ligament is not a cord, as might be inferred, but another layer continuous with the trapezoid behind. The inner fibres incline inward as they ascend. The general direction is upward and perhaps a little backward, but this changes with the position of the bones. There may be a synovial bursa in the open angle seen from the front between these two parts of the ligament. Movements of the Clavicle and Scapula. The compound joint at the inner end of the clavicle is practically a universal one. The clavicle can be raised, depressed, carried forward or backward, circumducted, and slightly rotated. The outer and lower end of the disk being attached to the corresponding border of the facet, it follows that the clavicle lies upon it. When the shoulder is raised or depressed the motion is almost wholly between the clavicle and the disk, though the latter slides a little, and in marked falling of the shoulder the top of the disk starts to come out of the socket, but is restrained by the top of the capsule. Forward and backward motions occur chiefly between the disk and the sternum, but there is some displacement of the former. Circumduction, therefore, involves both parts of the joint ; rotation is chiefly in the inner one. It is remarkable that a joint at which there is so much strain, owing to lever.i^e, should be so strong with such apparently imperfect bony arrangements for retention. Part of the safety is due to the subdivision of the joint and a great deal to the assist- ance of muscles. At both ends of the clavicle, as Morris has pointed out, the great muscles are so placed that by their contraction they draw the bones together. 1 Lig. costoclavlcularc. " Llg. trnpezoitleutn. ;1 Llg. conoidcum. MOVEMENTS OF THE CLAVICLE AND SCAPULA. 263 The obvious advantage of a joint between the clavicle and the acromion, apart from breaking shocks and -making the shoulder-girdle much more elastic, is that it allows the angle between the bones to change with the position of the arm, and thus the direction of the glenoid cavity may be modified so as to give the best support to the arm in different positions. The motion at the outer end of the clavicle is con- siderable, but indefinite. The overlapping clavicle can advance a little laterally onto the acromion, except in the cases in which the plane of the joint is vertical. There is also motion on an approximately vertical axis when the shoulder is thrown forward and the outer end of the clavicle advances, the angle between the back of the clavicle and the spine of the scapula being diminished. When the clavicle can advance no farther, the tension of the trapezoid ligament checks the progress of the coracoid. In the withdrawal of the shoulder the reverse occurs, the movement being finally checked by the conoid. In up-and-down movements of the shoulder the motion is on an approximately antero-posterior axis. When it rises the base of the coracoid comes into direct contact with the clavicle and the rhomboid ligament is strained ; when it falls the clavicle rests on the first rib and the conoid is put on the stretch, as are also the interclavicular ligament and the top of the capsule of the sternal end. Probably the freest movement is when the arm is raised vertically, in which case the lower angle of the scapula swings strongly forward so as to direct the glenoid cavity more nearly upward. The clavicle rises from the sternal end, and perhaps slightly rotates. Possibly the lower end of the scapula is withdrawn slightly from the chest. Apart from the movements of the arm the scapula may change its position considerably. It may rotate on either the end of the acromion (as in rais- ing the arm) or on the superior angle, the lower angle being the most movable point. When it is carried far forward a larger portion of the posterior surface of the lungs can be examined. The scapulae may also be raised or brought nearer together. Surface Anatomy of the Shoulder-Girdle. The general shape of the clavicle is easily made out by pressing on its front and superior surfaces with the muscles relaxed. The degree of backward projection of the inner end can be deter- mined. It is placed horizontally in woman ; in man the outer end is slightly raised. The joint with the acromion is easily felt from above, the clavicle being the higher. The outline of the acromion, which slopes somewhat downward, is easily felt. It forms the point of the shoulder-girdle, but not of the shoulder, as the humerus always projects beyond it externally. A plane vertical surface placed against the outside of the shoulder cannot touch the acromion if the head of the humerus is in place. The possibility that the outer epiphysis of the acromion may not unite by bone is to be remembered. The finger can be carried from the acromion along the spine to its triangular origin. The tip of the coracoid is to be felt by manipulation in the infraclavicular fossa at the inner side of the humerus. The posterior border of the scapula is always to be felt ; in thin persons its outline can be traced and the shape of the inferior angle approximately recognized. PRACTICAL CONSIDERATIONS. The Sterno-Clavicular Articulation. The interposition of an elastic buffer in the shape of the interarticular fibro-cartilage, united to both the bones by very strong ligamentous fibres, and completely bisecting the joint (Fig. 280), in fact, converting it into two separate joints, prevents the clavicle from transmitting to the sternum the full force of blows and falls received upon the hand or shoulder, and allows of the varied, though limited, movements of the articulation. Dislocation is rare. The ligaments are stronger than .the clavicle, which is therefore usually broken by any force sufficient to threaten the integrity of the joint. The curves of the clavicle, the mobility of the scapula, and the play of the acromio- clavicular joint all tend to diffuse forces that might otherwise have been expended on this articulation, which is furthermore strengthened by the tendinous origins of the sterno-cleido-mastoid and of the pectoralis major. The most common form of dislocation is the forward one, the anterior sterno- clavicular ligament being the weaker and thinner. Backward luxation is re- 264 HUMAN ANATOMY. sisted by the more powerful posterior ligament and by the rhomboid. Upward displacement the least frequent is resisted by the interarticular cartilage, which is strongly inserted below into the cartilage of the first rib and the sternum, and above into the clavicle itself, by the rhomboid and interclavicular ligaments and by both the anterior and posterior ligaments ; hence the rarity of this luxation. In many displacements of the sternal end of the clavicle the shoulder is carried downward or backward until the clavicle is in contact with the strong first rib, which then acts as a fulcrum, the sternal end of the bone continuing its upward or forward motion until the resisting ligaments are torn and the luxation is produced. In backward dislocation by indirect violence the force has usually pushed the shoulder forward and inward, as when the patient has been caught between two cars or between a wall and a wagon. In this dislocation the sternal end may press upon the trachea, the internal jugular, or the beginning of the innominate vein, and may therefore, if the faulty position has become permanent, require excision. Disease of the sterno-rclavicular joint is not very common, considering its super- ficial position and its constant motion. This is probably due to the fact that the motion is slight and that strains and injury to the synovia! membranes are prevented by the strong and elastic interarticular cartilage and by the strength of the ligaments. Suppuration usually shows itself in front (as the anterior ligament is the thinnest), but may perforate by ulceration the posterior ligament and find its way to the medi- astinum. With the arm at the side the articulation becomes V-shaped, the clavicle touching the joint surface only at its lowest angle. With the arm elevated, the two joint surfaces are brought into closer relation, and the shape of the joint viewed from the front becomes linear ; hence raising of the arm is uniformly productive of pain in disease of the joint. Ankylosis is rare, probably owing to the separation of the diseased joint surfaces by the thick, resistant fibro-cartilage. The Acromio-Clavicular Articulation. This is one of the shallowest of the articulations, the clavicle being merely superimposed, as it were, upon the upper edge of the acromion. The powerful ligaments which bind the clavicle to the cora- coid (the conoid and trapezoid), although they have no direct relation to the joint, are the most important factors in preserving its integrity when force is applied to the point of the shoulder. The movements of the joint are around two axes, an antero-posterior and a vertical one, so that the relations of the glenoid cavity to the humerus may remain relatively unchanged when the arm is elevated or is advanced. The scapula must obviously move backward or forward on the side of the chest in a curve established by the curve of the ribs. It does this on a radius represented by the clavicle, the centre of the rotation being at the sterno-clavicular joint. The acromio-clavicular joint enables this motion to take place, while at the same time the glenoid cavity continues to point obliquely forward. If it were not for this, the act of pushing or striking with the arm advanced, or of falling upon the hand with the arm in a like position, would bring the head of the humerus against the capsule of the joint instead of against the glenoid cavity, and would thus increase the frequency of luxation. Conversely, "rigidity of this little joint may be a cause of insecurity in the articulation of the shoulder and of weakness in certain movements of the limb" (Treves). Dislocation is rare. The dislocation of the acromial end of the clavicle upward (described by some surgical writers, for the sake of uniformity, as dislocation of the scapula downward) is much the more frequent. The capsular ligament is torn or stretched, even in the incomplete forms. In the complete variety the coraco- clavicular ligaments must be torn or ruptured, but their great strength, increased in effectiveness by their distance from the joint, renders this accident uncommon. Dislocation of the clavicle beneath the acromion between it and the coracoid process and dislocation of the clavicle beneath the coracoid are extremely rare accidents. It is not certain that the latter has ever occurred. Both obviously require for their production extensive laceration of all of the ligaments binding together the scapula and the outer portion of the clavicle. THE HUMERUS. 265 THE HUMERUS. The bone of the arm consists of a shaft and two enlarged extremities. The upper extremity includes a globular articular head and two tubcrosities for muscular insertions. The head 1 looks upward, inward, and backward. It is not truly a part of a sphere, for the curve in the horizontal plane is bolder than that in the vertical. The vertical diameter between the edges of the articular surface is longer than the transverse. It is surrounded by a slight groove for the attachment of the capsular ligament at what is called the anatomical neck? The siirgical neck* is just below the whole upper extremity. The tuberosities are separated in front by a deep furrow, the bicipital groove, , 4 through which runs the tendon of the long head of the biceps. The greater tuberosity 5 is a rough enlargement placed externally. Its highest point is at the front, just by the groove. A superior surface of this tuberosity begins here and, passing downward and backward beside the head, broadens as it goes. It bears three smooth facets for the insertion of the supra- spinatus, the infraspinatus, and the teres minor, in this order ; the first being highest and most in front, the last and lowest most behind. The lesser tuberosity, 6 much smaller, is on the front of the bone. It bears a prominent angle, sometimes an actual crest running downward and inward for the subscapularis. The upper aspect of the process, which looks also inward, is smooth for a bursa beneath the tendon. The shaft is roughly cylindrical above and prismatic below. It is convenient to divide it by three borders into three surfaces. The anterior border starts from the greater tuberosity as the outer lip of the bicipital groove, which, growing shallower, can be traced through the first quarter of the shaft. This outer lip becomes thicker and more prominent for some two inches below the surgical neck to receive the insertion of the pectoralis major. Below this it is joined by the lower end of the deltoid eminence, after which, smooth and rounded, it grows fainter, but may be traced downward to a ridge separating the capitellum from the trochlea, where it ends. The internal border starts at the inner side of the neck, often so near the inner lip of the bicipital groove as to be confounded with it, and runs straight down to the very tip of the internal condyle. It is at best very faint in the first quarter, and often barely visible ; but it is distinct in the middle and prominent in the last third, where it is known as the internal supracondylar ridge. The external border begins at the back of the greater tuberosity and runs to the outer condyle, the lower part being the external supracondylar ridge, which has a forward curve. A great exaggeration of this ridge has been seen in the negro. The internal surface bears the inner lip of the bicipital groove, which, starting from the lesser tuberosity, is often very faint ; it receives the tendon of the teres major. The bicipital groove soon becomes shallow, and is lost after two or three inches. The nutrient foramen, running downward into the bone, is rather below the middle of this surface, sometimes being almost in the internal border. The external surface is convex in the upper half and concave in the lower. Its second quarter is occupied by a long, rough elevation, the deltoid eminence? slanting downward and forward against the interior border for the insertion of the deltoid muscle. The posterior surface is twisted, facing somewhat inward above and backward below. 'The upper plane portion gives origin to the outer head of the triceps, and the lower, convex except below, to the inner head. A broad spiral groove beginning on the external surface behind the deltoid eminence, in front of the outer border, twists forward and downward. This is generally improperly called the musculo-spiral groove* The groove truly deserving that name, containing the musculo-spiral nerve and the supe- rior profunda artery, occupies the lower and posterior part of the greater groove, from which it usually is not to be distinguished throughout, though both grooves may be distinct. The musculo-spiral groove is some five millimetres broad, and, when well developed, begins on the posterior surface, separating the areas for the outer and inner heads of the triceps muscle, and interrupts the external border, behind which the broad spiral groove never passes. A second nutrient foramen, also running downward and sometimes the larger of the two, may occur in the groove. The shaft takes a forward bend just at its termination, so that most of the lower end lies in front of the continuation of the axis of the shaft. 1 Caput humeri. 2 Collum anatomicum. 3 C. chirurgicum. 4 Sulcus intertubercularis. 5 Tubcrculura niajus. G Tub. minus. ' Tuberositas deltoidea. * Sulcus radialis. 266 HUMAN ANATOMY. FIG. 281. Greater tu- berositv Head -Lesser tuberosity L Bicipital groove ! Brachio-radialis - Sup ra sp Hiatus \Subscapularis . Pecioralis major Lalissimus dor si , Teres major ^Deltoid Deltoid- Coraco-brachiahs eminence ^Rrachialis anticus External- border - Internal bicipital ridge -External bicipital or pecto- ral ridge Internal border Extensor carp i /I i \ radialis long, y ,A^ ^^^Pronator radii ^; ^T teres Tendon common i W ^i. ^Jjjfl^ j Tendon common to exten. carp. ^A^^^Bjj rod. brev., ex- xaSP^* 1 k JjP*^ \opronator ra- S^p) ilii teres, flex. ten. communis carpi radialis, digitorum, ex- palmaris lon- ten, min. digiti, exten. carpi ul- gns, flex, sub- lim. dig., flex. naris carpi ulnaris External supra- condylar ridge y s Anterior border Internal supracondylar ridge Radial- fossa K\tn iia condyle roronoid fossa I Internal condyle Vommoti u-iulon for flexor muscl CapiU-llum Troclilcii Right hutnerus from before. The outline figure shows the- areas of muscular attachment. Heac Neck THE HUMERUS. FIG. 282. Greater tuber- ositv 26 7 Surgical neck Spiral groove Musculo-spiral groove Internal condyle Groove for ulnar nerve Supraspinatus Inner head of triceps External head of triceps Deltoid Brachialis anticus Brachio-radialis Anconeus Olecranon fossa External condyle Trochlea Right humerus from behind. The outline figure shows the areas of muscular attachment. 268 HUMAN ANATOMY. FIG. 28-1. The lower extremity is broad from side to side, with an articular surface below, and two lateral projections, the condyles. The inner condylc, 1 much the larger, is sharp and prominent, giving rise with a part of the supracondylar ridge to the flexor pronator mus- cles. It is faintly grooved behind by the ulnar nerve, and the lower part of the front often presents a smooth surface. The outer condylc ~ is a slightly raised knob. The articular surface, most of which is at a lower level than the condyles, consists of two parts, an inner pulley-like surface, the trochlea, for the ulna, and an outer convexity, the capitellum, for the radius. The trochlea 11 is bounded internally by a sharp border, forming about three-quarters of a circle, and projecting below the rest of the bone as well as before and behind it. It is bounded externally by a ridge, which is prominent behind where the trochlea forms the whole of the articular surface, but is faint in front where it separates the trochlea from the capitellum. Above the joint this ridge is continuous with the an- terior border of the shaft. The trochlea is convex from before backward. A section through the middle forms almost a complete circle, being broken only above, where a thin plate con- nects it with the shaft. It is concavo-convex from side to side, the convexity being greatest at the inner bor- der. There is a depression above the trochlea both before and behind ; the former, the coronoid fossa, is small and receives the coronoid process of the ulna in flexion ; the posterior depression, triangular and much the larger, is the olecranon fossa, receiving that process in extension. The bone separating these fossae the plate just alluded to is so thin as to be translucent. It may be perforated by the supratrochlear foramen, most frequently found in savage tribes. The joint be- tween the humerus and ulna is commonly called a hinge-joint, but there are serious modifications. First, the axis of the trochlea is not at right angles to that of the shaft, but slants downward and inward ; next, the borders of the trochlea are not at right angles to its axis, but are so placed as to transform it into a spiral or screw-joint ; finally, these borders are not parallel to each other, but the inner slants downward and inward so that the transverse diameter of the joint is greater below than at the top, either before or behind. The capitellum, 4 on which the concave head of the radius plays, is situated on the front of the outer part of the lower end. It is not far from being a por- tion of a sphere, since it is convex and nearly equally so in all directions, but the arc from above downward is the longest. A groove runs between it and the outer ridge of the trochlea ; the outer border is straight : the posterior runs from it obliquely backward and inward. The capitellum is placed so much to the front as to be nearly or quite invisible from behind ; hence the articu- lar surface is much more extensive on the front than the back. The radial fossa, a small depression above the capitellum, receives tin- edge of the head of the radius in extreme flexion. The supracondylar process is a small bony spur occurring in probably two or three per cent., which arises from the front of the bone a little anterior to the 1 Eplcondylus inedialis. '' Epicondylus latcralN. Tin lilc.i. ' Ciipituluui. Longitudinal section of humerus, showing relation of compact and spongy none. THE HUMERUS. 269 internal supracondylar ridge. It is usually connected by a fibrous band to the tip of the inner condyle, thus representing' the supracondylar foramen found very generally among mammals. The median nerve and generally either the brachial or the ulnar artery pass through it. The process, without any completing ligament, has been seen hooking over the nerve alone. We have once seen a bony foramen. The so-called torsion of the humerus is a very complicated problem arising from the theory of the changes necessary to account for the adult condition of the humerus and femur, assuming theni to have been originally symmetrical. The practical point is that the horizontal axis subdividing the articular surface of the head of the humerus, imagined on the same plane as the transverse axis of the elbow, forms an angle with the latter. This angle varies consider- ably ; according to Gegenbaur, it is 12 for the adult European. In the lower races it is greater, and still greater in the lower animals. (This is what Continental anatomists call the supple- mental angle, as they assume that the twisting has approached 180, and that thus the true angle is 168. We give this as the simplest. ) The angle is greater in the foetus. Gegenbaur gives it as 59 at from three to four months, and as 34 at from three to nine months, after birth. This change probably occurs in the epiphyses. It is certain that the shaft of the developing humerus does not actually twist, for the borders are straight, as are all the long nerves with the single exception of the musculo-spiral. No spiral fibres have been found in the bone. Structure. The walls of the shaft are of compact bone enclosing a cavity. At the upper end the head is made of round-meshed tissue of considerable density ; the greater tuberosity is of lighter structure ; both are enclosed by thin bone. The line of union of the upper epiphysis is seen on section after it has disappeared from the surface. Transverse sections at the lower end show a system of strong plates passing obliquely from the front to the back above the inner condyle. Differences due to Sex. The chief guides are the greater delicacy of the female bone, and especially the smaller size of the head. It is generally thought that the female humerus presents a sharper angle between the axis of the shaft and the transverse axis of the trochlea than does the male, but Berteaux's 1 measurements make the difference too slight to be significant, 79 for man and 78 for woman. Development. The primary centre for the shaft appears towards the end of the second fcetal month, and before birth bone has reached to the extremities, which are formed by the union of several centres. There are two or three for the upper, a chief one for the head coming soon after birth and sometimes earlier. It is Ossification of humerus. A, just before birth; II. in the first year; Cat three years; C', sections of ends of preceding ; D, at five years ; /;, at about thirteen years ; F, 1 ', sections of ends of preceding ; /", at about sixteen ; /"', sections of ends of preceding, a, centre for shaft ; f>, for head ; c , for capitellum and part of trochlea ; d, for greater tuberosity ; e, for head and tnberosities in transverse section ; /", for internal condyle ; g, for inner part of trochlea. present at birth in 22.5 per cent, of foetuses weighing seven pounds and over (Spen- cer 2 ). It is almost always present by the end of the third month after birth. In the third year ossification begins in the greater tuberosity, and another point may appear somewhat later in the lesser one. At five all the centres for this end have 1 l.e Humerus et le Femur, Paris, 1891. 2 Journal of Anatomy and Physiology, vol. x\\., 1891. 270 HUMAN ANATOMY. become one, making a cap for the top of the shaft, which latter extends into the head. The largest centre for the lower end is that for the capitellum, which is seen by the end of the first half-year. It forms also a part of the outer side of the trochlea. A centre for the tip of the inner condyle is evident by the fifth year. One or more minute points of ossification for the trochlea appear in the tenth year, and one for the tip of the external condyle in the fourteenth. Although all these epiphyses are originally in the same strip of cartilage, they do not unite into one- piece of bone. The capitellum is joined by the ossification for the trochlea, and joins the shaft at from fourteen to fifteen. We are not sure whether the insignificant centre for the outer condyle, which fuses at about the same time, joins the epiphysis or the shaft. Rambaud and Renault seem to believe the latter. The centre for the internal condyle remains separate after the rest are fused and joins the shaft at about eighteen. The upper end joins at about nineteen, the line of union being lost at twenty or twenty-one. It is usually lost earlier in the female. Surface Anatomy. The external and internal condyles are the only points that are truly subcutaneous. The outer is easily recognized under normal conditions, but is quickly obscured by swelling. The internal is so prominent that it can always be recognized, unless the joint has been utterly broken to pieces. The fact that the inner condyle joins the shaft after the rest of the lower end exposes it to the danger of being broken off before the union has occurred, or while it is still weak. The upper end of the humerus is everywhere covered by muscle, but much of its outline can be explored. The amount of its forward projection varies much ; but it always projects outward beyond the acromion. The lesser tuberosity and the bicipital groove can be recognized on rotating the bone, but indistinctly. The groove is filled by the tendon and still further obscured by the capsule and muscles. The surgical neck is best felt in the axilla, whence, the arm being extended, the head can be examined, though imperfectly. PRACTICAL CONSIDERATIONS. FIG. 285. Head The humerus occasionally fails to develop, either alone or together with the other bones of the extremity. The bone of one arm may be shorter and thicker than the normal bone. Lengthening beyond normal limits is much rarer. The shallowness of the glenoid cavity obviates the necessity for projecting the head of the bone from the shaft, as in the femur ; the "neck" is, therefore, merely a very narrow and superficially shallow constriction of an inward prolongation of the shaft between the tuberosities below and the joint surface above. Both its shortness and its shallowness render it far less liable to fracture than the femoral neck. When, in old age, absorption and fatty degeneration of the cancellous tissue have occurred, fracture does take place, as a result usually of falls upon the shoulder. It is often accompanied by impaction, the head being driven into the broad surface of cancellated tissue on the upper end of the lower fragment (Fig. 285 ). This results in a lessening of the bulk of the upper end, or subacromial portion, of the humerus, and thus in a little flattening of the deltoid and a little increased promi- nence of the acromion. If impaction does not occur, and the capsule of the joint is completely torn through its entire circumference, necrosis of the upper fragment must follow. Usually, through untorn periosteum and through portions of capsule reflected from the inner side of the shaft below the anatomical neck to the edge of the articular cartilage on the head, the blood-supply is maintained so that necrosis is prevented and union results. There is no direct blood-supply to the head of the humerus corresponding to that received by the femoral head through the ligamentum teres. The displacement Shaft Fracture of anatomical neck of humerus, slmwini; mipartiori. PRACTICAL CONSIDERATIONS: THE HUMERUS. 271 is apt to be slight, the muscles inserted into the bicipital groove and acting on the lower fragment being antagonized by those inserted into the greater tuberosity. That tuberosity may be torn off as a rare accident. The displacement theoreti- cally will depend upon the action of the muscles inserted into that portion of the bone (page 590). The large upper epiphysis of the humerus (made up of centres for the head and the tuberosities which begin to coalesce about the' sixth year) is fully formed by the age of puberty. It includes then the two tuberosities, the upper fourth of the bicipi- tal groove, all of the head, the anatomical neck, and a little of the shaft just below it. A line nearly horizontal and crossing the bone beneath the great tuberosity, and therefore considerably below the anatomical neck, represents the epiphyseal line at the twentieth year, when the epiphysis and shaft become united. It is within a half inch of the so-called surgical neck (Fig. 286). The lower surface of the epiphysis is concave and the upper surface of the diaphysis convex or conical (Fig.. 287). FIG. 287. FIG. 286. Upper end of humerus, showing epiphyseal line. A, on surface; , in section. Upper end of humerus, showing cupping 01 epiphysis to receive the pointed end of diaphysis. The traumatic separation of this epiphysis is a not infrequent accident of child- hood and adolescence. It is commonly caused by forcible traction of the arm upward and outward. In such cases three anatomical factors probably enter into the production of the lesion. ( i ) The partial fixation of the epiphysis by the sub- scapularis, supra- and infraspinatus, and the upper fibres of the teres minor. Even on the dead subject, rotation outward with abduction will most readily produce the disjunction. (2) The ease with which the periosteum, strongly attached to the epiphysis but very loosely to the diaphysis, may be separated from the latter. This is illustrated by the fact that in cases of detachment the teres minor, though inserted below the epiphyseal line, is apt to retain its connection with the periosteum covering the epiphysis. (3) The powerful muscles resisting abduction and inserted into the diaphysis just below the epiphyseal line. There may be only separation with little or no displacement ; but if displace- ment occurs, the muscles just alluded to (the latissimus, pectoral, and teres) tend to 272 HUMAN ANATOMY. draw the diaphyseal fragment strongly towards the chest-wall, so that its upper end may be found beneath the coracoid process. The shape of the opposing surfaces of the epiphysis and diaphysis lessens both the frequency and the amount of the dis- placement. The two surfaces usually remain in contact at some point : ( i ) on account of that shape ; (2) because the humerus on the epiphyseal line is broader than at any other part of its upper end. The deformity will be recurred to in connection with that of the conditions which it most closely resembles, fracture of the surgical neck and dislocation of the humerus, which (on account of the importance of muscular action in their production and in their treatment) will be considered after the muscles have been described. It might be expected that, as the chief growth of the humerus takes place from its upper epiphysis, arrest of growth and development should be a usual sequel. The upper epiphysis from the tenth year to adult life will, according to Vogt, add from seven to ten centimetres to the length of the humerus, the lower epiphysis during the same time adding but one-fifth as much. The activity of the upper epiphysis is shown by the frequency of conical stump after amputation through the upper end of the humerus. 1 Despite these facts, in comparatively few cases of disjunction is atrophy or arrest of growth reported as a result. It has been sup- posed, too, that necrosis of the epiphysis should follow this injury on account of deficient blood-supply to the head ; but, through the tuberosities, through the connection of the reflected capsule to the articular cartilage, and through portions of untorn periosteum, the blood-supply is ample. Firm bony union is therefore the usual result in well-treated cases. This is favored by the fact, already alluded to, that the opposing surfaces are nearly always in contact at some point. The portion of the shaft just beneath the head and tuberosities is known as the ' ' surgical neck' ' because it is so often the seat of fracture. It contains, as will be seen on examining a longitudinal section of the humerus (Fig. 283), a considerable quantity of cancellous tissue, the absorption of which in old persons leaves the bone weak at that point. The factors already described as favoring epiphyseal separation are operative in this case (page 271). The upper curve of the bone, beginning on this level, ends inferiorly at about the lower margin of the deltoid tubercle. Its convexity is forward and outward. The' lower curve is concave forward. Both curves may be markedly increased in rickets. The middle of the bone is not only the point of union of these curves, but is also the smallest and hardest and least elastic portion of the shaft ; hence it is most frequently broken, though fractures of the shaft at various levels below and above this point are not uncommon. The deltoid tubercle, when unusually developed, should not be taken for an exostosis. The region is, however, a fre- quent seat of bony outgrowths on account of the insertion and origin, respectively, of the coraco-brachialis and deltoid, and the brachialis anticus and internal head of the triceps. The close attachment of the periosteum to the shaft which is thus necessi- tated favors the development of osteo-periostitis, and thus of osteophytes as a consequence of repeated muscular strains. Other favorite seats of exostoses are near the insertion of the pectoralis major, the latissimus dorsi, and the third head of the triceps. Tumors of a more serious variety, especially the sarcomata, attack the h merus. The central sarcomata are found in the upper extremity chiefly at th< upper end of the humerus and at the lower ends of the radius and ulna. It may be interesting to note that those are the extremities towards which the respective nutrient arteries are not directed, and therefore, in accordance with the general rule, the extremities at which bony union of the epiphyses and diaphyses takes place latest. The close attachment of the periosteum at the middle of the shaft has been said to account for the fact that non-union after fracture occurs in this region more fre- quently than in the shaft of any other long bone of the skeleton. This has also been attributed to interference with the nutrient artery (which enters the bone near its 1 Owen, Lejars, and others, quoted by Poland. PRACTICAL CONSIDERATIONS : THE HUMERUS. 273 FIG. 288. middle) and to imperfect immobilization of the humerus, the elbow being fixed by splints, any motion of the hand or forearm under those circumstances being trans- formed into motion of the upper end of the lower fragment. These may be factors, but the chief reason for non-union is the entanglement of muscular and tendinous fibres of the brachialis anticus and of the triceps between the bony fragments (page 590). Descending the shaft it is not difficult to see why a fracture just above the con- dyles ("at the base of the condyles," " supracondylar" ) should often be met with. The olecranon fossa, the coronoid fossa, the shallower fossa for the radius just above the external condyle, all contribute to weaken the bone at this point. Moreover, in falls upon the elbow (the common cause of this fracture) the tip of the olecranon is frequently driven directly into its fossa and against the very thin lamina at its base, starting a fracture which extends laterally through the supracondylar and supra- trochlear ridges to the border of the bone. If this transverse line of fracture is associated with one running perpendicularly into the joint, it constitutes the so-called " T-fracture" ("inter- condylar' ' ) ; it is produced in the same manner, but usually by a greater degree of force. In the so-called "extension" and "flexion" fractures in this region the same mechanism is probably present, though it is easy to imagine the same result (if the capsule and ligaments of the elbow-joint remain intact) without the agency of the olecranon. It should be noted that the external supracondylar ridge, the strongest and most prominent, springs from the external condyle, ascends in the line of the shaft, and terminates in the head, so that it is well adapted to receive and distribute force applied through the radius, as in falls on the hand, or in pushing or striking strongly. The external is smaller than the internal condyle because the extensors and supinators arising from it are less powerful muscles than the flexors and pronators connected with the former. This makes it less prominent; but in spite of these protective conditions it is at least as frequently broken, es- pecially from indirect violence, because of its direct connection with the hand through the radius and capitellum. On account of the dense triceps fascia covering it, and its connection with the ligaments of the elbow-joint, the displacement is slight. The line of fracture usually passes through the radial fossa and enters the joint through the depression between the capitellum and the trochlear ridge. The internal condyle is more often broken by direct violence, or by the wedge-like action of the olecranon starting a fracture which runs through the thin bone of the olecranon and coronoid fossae, and through the trochlear depression. The displacement is usually upward, is the result of the force causing the break, and is but little influenced by anatomical factors. The brachialis anticus may elevate the fragment, but the ulna remains attached and prevents much displacement. Either epiconclyle may be broken. The line of the lower epiphysis runs obliquely across the bone from just above the external epicondyle to a point just below the internal epicondyle. In infancy both epicondyles (as well as the trochlea and capitellum) enter into the epiphysis ; but at the thirteenth year the internal epicondyle is quite distinct, and the trochlea, capitellum, and external epicondyle are welded into the lower epiphysis proper, which by the fourteenth to the fifteenth year (Dwight), sixteenth year (Treves and Stimson), seventeenth year (Poland), is firmly united to the diaphysis. After the thirteenth year, there- fore, separation of the epiphysis will probably leave the internal epicondyle attached to the diaphysis. "The point of junction of the trochlear and capitellar portions of the lower epiphysis at the middle of the trochlear groove at the sixteenth year 18 Lines of fractures of the humerus. a, through anatomical neck ; b, through tuberosities ; c, through surgical neck ; rf, through shaft; e, T-frac- ture involving condyles. 274 HUMAN ANATOMY. is the narrowest portion of the bone, and much more likely to be broken across, detaching one or other portion of bone rather than the whole epiphysis separating at this age" (Poland). As the synovial membrane is attached on the inner side about five millimetres (three-sixteenths of an inch) below the internal epicondyle, fracture of the latter does not necessarily extend into the joint-cavity. On the outer side it is attached up to the level of the external epicondyle, so that the joint is likely to be involved in traumatic separation of that process. As the capsule of the joint is attached at a higher level than the epiphysis in front, behind, and laterally, the displacement in epiphyseal separations is within the capsule, and therefore likely to be limited. The close relationship of the synovial membrane gives rise, however, to extensive effusion, which affects both diagnosis and treatment. The union to the diaphysis at about the fifteenth year leaves the further growth of the bone dependent upon the upper epiphysis (page 272 ) ; hence injuries involving the epiphysis, or excision of the elbow in which the epiphyseal limits are overstepped, will not be followed by arrest of growth if the patient is more than fifteen years of age. Epiphysitis, on account of the synovial and capsular relations above described, is apt to involve the elbow-joint, and to result in considerable stiffness. The anatomical deformity and diagnosis of epiphyseal separation will be con- sidered in connection with the subjects of supracondylar fracture and luxation of the elbow (page 590). About two inches above the inner condyle there is often found (one per cent, of recent skeletons, Turner) a hook-like process projecting downward and converted into a foramen by a ligamentous band. When it is present the median nerve usually passes through it, which demonstrates that " it is the homologue and rudi- ment of the supracondyloid foramen of the lower animals" (Darwin). The process can sometimes be recognized by the sense of touch. The intercondylar foramen, which is occasionally present in man, occurs, but not constantly, in various anthro- poid apes, and, though it weakens the bone somewhat, is chiefly interesting because it is found in much greater frequency in skeletons of ancient times, and thus illus- trates Darwin's assertion that "ancient races more frequently present structures which resemble those of the lower animals than do modern." THE SHOULDER-JOINT. The ligaments of this articulation are : Capsular ; Glenoid Accessory ligaments : Coraco-Humeral ; Gleno-Humeral. This is a very simple 1 instance of the ball-and-socket joint, the only irregularity being the position of the humeral head somewhat on one side instead of at the top of the bone, so that the axis of rotation does not correspond with tin- axis of the shaft. The shallow socket of the glenoid cavity, lined with articular cartilage, is deepened by the glenoid ligament' (Figs. 290, 292), a fibro-cartilaginous band attached by its base to the border of the cavity and ending in a sharp edge. It is thus triangular on section (Fig. 291), the breadth of the base- being live- millimetres and the height at its greatest about one centimetre. This ligament is composed chiefly of fibres running around the socket. It is directly continuous with the fibres of the long head of the biceps from the insertion of the latter into the top of the socket. The capsular ligament 2 (Fig. 289) is so lax that in the dissected joint the head of the humerus falls away from the socket. In life it is kept in place chiefly by the tonicity of the surrounding muscles. The course of the tilnvs is in the main longitudinal, but they are indistinct. Tin- capsule arises above from tin- edge of the 1 Lalirum ulcnoidalc. "Capsulu artirularis. THE SHOULDER-JOINT. 275 glenoid cavity and the bone just around it, from the outer surface of the glenoid ligament as far as its edge, excepting at the top, where it does not encroach on the ligament, and at the inner side, where its origin is uncertain. It may arise there as FIG. 289. Coracoacromial ligament Bursa Trapezoid ligament Clavicle Capsule Long head of biceps Humerus Conoid ligament Suprascapular ligament Right shoulder-joint from before. described, but very often it arises at some distance from the border of the joint from the anterior surface of the scapula. In exceptional cases this distance may be half an inch, perhaps more. The inferior attachment of the capsular ligament is to the FIG. 290. Acromio-clavicular joint Acromion Tendon of biceps Head of humerus Glenoid ligament Glenoid cavity Spine of scapula sa^<- <>f the median nerve across the brachial artery, and with the departure of the tilnar nerve from its proximity to the vessel. Posteriorly, the middle of the bone is covered by the triceps. Just below the middle the musculo-spiral nerve and the superior profunda wind around in the groove below the deltoid insertion, and the inner head of the triceps arises from the bone. At the junction of the middle and lower thirds the brachial artery from the inner side and the musculo-spiral nerve from the outer side tend to approach the front of the bone. The landmarks at the lower extremity will be considered in relation to the elbow-joint and the bones of the forearm. The surface anatomv and the relations of the soft parts to the humerus will be KM urrod to after those structures have been described. THE ULNA. 281 THE FOREARM. The skeleton of the forearm consists of two bones, an inner, the ulna, and an outer, the radius. The former is large above and small below ; the latter, the con- verse. The ulna plays around the trochlea in flexion and extension, carrying the radius with it. The radius plays on the ulna in pronation and supination, carrying with it the hand. These bones are connected by an interosseous membrane, which gives origin to muscles, adds to the security of the framework, and yet implies a great saving in weight. THE ULNA. The ulna consists of a shaft and two extremities. The upper extremity is devoted to the joint with the humerus, and laterally to that with the head of the radius. The former articular surface is the greater sig- moid cavity hollowed out of the continuous surfaces of the olecranon process behind and above and the coronoid process in front. The olecranon, 1 a cubical piece of bone projecting upward in continuation with the shaft, presents this articular surface in front (to be described later), and a superior, a posterior, and two lateral surfaces. The siiperior surface is pointed in front, with the ooint or beak external to the middle. A slight groove just back of the edge serves for the attachment of the capsular ligament. Behind this are two parts of different texture, the posterior of which is for the insertion of the triceps. The posterior surface is triangular, bounded above by the irregular edge of the top, and laterally by two lines which meet below to make the posterior border of the shaft. It is subcutaneous, and is covered by a bursa (Fig. 294). The outer stirface is bounded in front by the sharp edge of the sigmoid cavity, along which is the groove for the capsule. Behind this is a hollow for the anconeus. The inner surface has in front the inner border of the sigmoid, less sharp than the outer, the capsular groove, and farther back a rough elevation. The coronoid process z rises from the anterior surface of the front of the shaft. It has an upper, articular surface, an anterior, and two lateral ones. The front surface rises to a point nearer the outer side. The capsular groove runs along the border ; and below this, bounded by two lines meeting below, is a rough region for the brachialis anticus. Within the angle formed by the meeting of these two lines is a rough rounded space, the tuberosity of the ulna, from the edge of which arises the oblique ligament. The brachialis anticus is inserted into the lower part of this sur- face and the tuberosity. The inner surface is bounded above by the sharp project- ing border of the sigmoid cavity, at the edge of which is a rough prominence from which certain fibres of the flexor sublimis digitorum take origin. The outer surface presents the lesser sigmoid cavity. The greater sigmoid cavity 3 occupies the anterior surface of the olecranon and the superior one of the coronoid process. There is a constriction in the middle of both borders, but deeper in the outer, where the two processes meet, and the articu- lar surface on the dry bone seems often to be interrupted in a line between them. The sigmoid cavity, concave from above downward, is broader in the upper half than the lower. It is surrounded, except where it is joined by the lesser sigmoid cavity, by an ill-marked groove for the capsular ligament. The articular surface is subdivided by a rounded ridge, running from the point of the olecranon to that of the coronoid, into a larger inner and a smaller outer portion. The course of this ridge is generally somewhat inward as well as downward. This and the cross-line divide the articular surface into four spaces. Of the upper, the inner is concave and the outer convex from side to side. Of the lower, the inner is concave in the same direction and the curve of the outer is uncertain ; probably, as a rule, slightly concave, it may be plane or a little convex. The lesser sigmoid cavity, 4 for the head of the radius, is a concavity on the outer side of the coronoid process, separated from the greater by a ridge, which does not interrupt the cartilage coating both. It generally is an oblong quadrilateral area forming about one-sixth of the circumference of a cylinder, with parallel borders ; 'Olecranon. - Processus coronoideus. 3 Incisura semilunaris. 4 Incisura radialis. 282 HUMAN ANATOMY. FIG. 294. FIG. 295. Triceps Subcutaneou surface Flex, sublim digitorum Aponeurosis of ext. carpi ulnaris, flex, profundus digitorum and flex, carpi ulnaris Lesser sigmoid cavity Posterior border Upper end of right ulna, posterior aspect. Tip of olecranon Greater sigmoid cavity Tuberosity Nutrient canal. Interosseous border- -Anterior border Brachialis anticus Supinator brevi* Flex, profund \ digitorum Flex, sublim. dig. (coronoid head) Pronat. radii teres (lesser head) Flex. long, pollicis (accessory head) J Pronator qttadratus Styloid process Right ulna, inner aspri-t. Tin- nutliin- li^un- sln>\vs tin.- ;uvus ot inusi-tihir ;iti:n. littK-nt. THE ULNA. 283 FIG. 296. ( Olecranon tip Greater sigmoid cavity ) Coronoid process Lesser sigmoid cavity -Supinator ridge nterosseous border Vertical ridge Triceps Anconeus Ext. carpi ulnaris I { Supinator brevis Ext. ossis met. pollicis Ext. long, pollicis Ext. indicis Groove for ext.. carp, ulnar. Styloid process . Right ulna, outer aspect. The outline figure shows the areas of muscular attachment. 284 HUMAN ANATOMY. ...: 'if.'- but sometimes the front border is short and the inferior runs obliquely backward, making it almost triangular. The shaft, 1 which presents three borders and three surfaces, steadily diminishes from above downward. In the- upper part the bone curves slightly backward and outward (i.e. , towards the radius), then inward through the greater part of its extent, till at the lower quarter it again bends outward and, at the same time, for- ward. The posterior border' is formed by the union of the two lines bounding the subcutaneous surface at the back of the olecranon. Following FIG. 297. the curves just described, it runs to the back of the styloid process, being very distinct in the first two-thirds, where it gives origin to the aponeurosis of the flexor carpi ulnaris. The anterior border? springing from the junction of the front and inner sides of the coronoid, runs down to end just above the front of the styloid process. Its last quarter, which is rough to give origin to the pronator quadratus, has a backward slant. The outer or in- terosseous border* is very sharp in the middle two-fourths of the shaft, where it gives origin to that membrane. It begins above by the union of two lines, which, starting from the front and back of the lesser sigmoid cavity, bound a triangular depression. The posterior of these lines, sharp and raised, is the supinator ridge. The depression which gives origin to the supinator brevis receives the bicipital tuberosity of the radius in pronation. The border becomes indistinct below and is lost as it approaches the head of the ulna. The anterior surface is usually concave through- out, though the upper part may be convex. In the third quarter a line often appears which slants downward into the front border, giving origin to the upper fibres of the pronator quadratus. Below this line, when present, there is a depression occupied by that muscle. Above this arises the flexor profundus digitorum. The nutrient foramen running upward is a little above the mid- dle. The inner surface, concave at the side of the upper ex- tremity and convex below, gives further origin in its upper two- thirds to the last-named muscle. The posterior surface has several features which are to be recognized only on a well-marked bone, and are very variable. The oblique line starts from the supinator ridge, or from the hind edge of the lesser sigmoid cav- ity, and runs downward to the posterior border at the end of the first third. It gives origin to a part of the supinator brevis, and helps to mark off a three-sided depression running onto the olecranon for the anconeus. It is sometimes the apparent continuation of the supinator ridge, as in Fig. 296. The region below this is subdivided by a vertical ridge of uncertain beginning and end. Sometimes it springs from the interosseous border, and it is usually lost below in the hind one. The extensor carpi ulnaris springs from the surface internal to it, which is some- times a deep gutter. External to the vertical ridge are areas Longitudinal section of ulna. for the extensor ossis metacarpi pollicis, extensor longus pol- licis, and extensor indicis from above downward in the order named. The lower extremity of the ulna consists of the head and the styloid process. The head' is a rounded enlargement pro- jecting forward and outward, presenting an articular surface on the outer side, which passes onto the front and the back, making at least two-thirds of a circle, around which the radius swings. A ridge marks the upper border of this surface, which overhangs the lower. The latter is rounded, so that the lateral articular surface continues without real interruption into the inferior, which is separated from the wrist-joint by the triangular tibro-cartilage. The under side of the articular surface is somewhat kidney-shaped, the concavity looking towards the styloid process, from which it is separated by a groove for the 1 Corpus ulnnc. - Margo ilnrxilis. \largovotaris. 4 Crlsta intcrossea. '' Ciipitiiluin. I PRACTICAL CONSIDERATIONS : THE ULNA. 285 attachment of the fibre -cartilage. The styloid process is a short, slender process running down from what may be called the posterior internal angle of the lower end. There is a distinct groove between the styloid process and the head on the posterior aspect, and sometimes a faint one in front, transmitting respectively the tendons of the extensor and the flexor carpi ulnaris. Structure. There is much solid bone in the shaft, and altogether the ulna is a strong-walled bone. Many plates near together from the anterior surface pass upward under the coronoid process to the middle of the greater sigmoid notch. The best-marked system of plates in the coronoid is in the main parallel to these. The greater sigmoid notch is bounded by compact substance. Sagittal sections show plates radiating from it, some of which form arches near the top of the olecranon with others from the posterior surface. The head is composed of spongy tissue within thin walls. Development. The centre for the shaft appears in the eighth week, from which practically all the bone except the lower end is developed. At about five, Ossification of ulna. A, at birth ; B, at five years ; C, at ten years ; D, at about sixteen years, a, centre for shaft ; b, c, cartilaginous epiphyses ; d, centre for lower epiphysis ; e, for upper epiphysis. one appears for the head and styloid process ; and at about ten, one for the top of the olecranon. This fuses at about sixteen ; the lower end joins the shaft at eighteen. PRACTICAL CONSIDERATIONS. The ulna may be absent, or may be more or less defective in size or shape. Such deformities are not common. Fracture of the olecranon at its junction with the shaft, where it is narrowed, is frequent. The degree of displacement is largely determined, as in the parallel case of the patella, by the amount of laceration of the enveloping fibrous structure. If this is great, the triceps strongly elevates the fractured process. Occasionally the mere tip of the olecranon, or even a thin portion of the superficies only, may be separated either by muscular action or by direct violence. The epiphyseal line is above- the constriction that marks the union of the olec- ranon with the shaft. The epiphysis is small and includes the upper part of the olecranon with the insertion of the triceps, a part only of the attachment of the pos- terior ligament, and a very small portion of the posterior triangular subcutaneous surface. The epiphyseal line runs from the upper part of the sigmoid cavity in front downward and backward. The epiphysis enters but little into the elbow-joint ; it is largely within the limits of strong periosteal and tendinous and ligamentous expansions, is of small size, and before the fourteenth or fifteenth year is on a 286 HUMAN ANATOMY. FIG. plane anterior to the epicondyles. For these anatomical reasons, neither muscular action (triceps) nor falls on the elbow are so productive of separation of this epipb- ysis in children as of fracture of the olecranon in adults. It is, in fact, one of the rarest of epiphyseal disjunctions. The symptoms are very similar to those of fractured olecranon. The coronoid process is rarely broken except in cases of dislocation of the forearm backward from falls upon the hand. The mechanism is obvious. The force is applied through the medium of the oblique fibres of the interosseous membrane. The line of fracture is nearer the tip than the base of the process. The insertion of the brachialis anticus tendon in the latter region prevents much displacement of the fragment, and the attachment of the capsule of the joint to its edge insures a sufficient vascular supply for pur- poses of repair. Great proneness to recurrence after re- duction in a case of backward dislocation of the forearm should lead to a suspicion of the existence of this fracture. Fracture of the shaft of the ulna alone may occur at any point, and is usually the result of direct violence, as when the arm is raised to protect the head from a blow, or in a fall upon the ulnar side of the forearm. In the lat- ter case, when the ulnar fracture is in the upper third, it is not infrequently associated with forward dislocation of the head of the radius (Fig. 300). ' The subcutaneous position of the ulna renders fracture frequently compound. This accounts for the greater fre- quency of non-union in this bone as compared with the radius. In fracture at the lower third the lower fragment is drawn towards the radius by the pronator quadratus. Fractures associated with those of the radial shaft will be considered in relation to the effect of muscular action upon them (page 604). The lower epiphysis of the ulna comprises the articular surfaces on the radial and inferior aspects and the styloid process. It is concave superiorly to fit the rounded lower end of the diaphysis. The level of the epiphyseal line is about one- sixteenth of an inch above the level of that of the radius. This epiphysis is strongly Lines of fracture of corp- noid, olecranon, and styloid processes of ulna. FIG. 300. Fracture of upperthird of ulna, with dislocation of radius forward. held to the lower epiphysis of the radius by the inferior raclio-ulnar ligaments and also by the triangular fibro-cartilage extending from the root of the styloid pro Ossification of radius. A, at birth ; S, at two years ; C, at five years ; /?, between eighteen and nineteen years. a, centre for shaft ; 6, for lower epiphysis ; c, for upper epiphysis. end of the fifth. The latter unites at about fifteen, the lower at eighteen or nineteen. A scale-like epiphysis for the bicipital tuberosity is said to appear towards eighteen and to fuse very promptly. PRACTICAL CONSIDERATIONS. The radius may be absent or more or less defective, and in either case there is apt to be corresponding absence or deficiency in the hand (Humphry). As might be expected, injuries of the upper end in the adult are extremely rare. Except at one point (just below the external condyle posteriorly), the head is far from the surface and deeply buried beneath the thick supinators and the long and short radial extensors of the carpus. Even at that point, more prominent bony processes the external condyle and the olecranon receive the brunt of the injury in cases of falls or blows. The upper epiphysis does not become fully ossified until the fifteenth year, and is united to the diaphysis at the beginning of the sixteenth year. It is, therefore, among the last of the epiphyses of the long bones to ossify and the first to join its diaphysis. The violence which separates it from the shaft is often direct. In cases of indirect violence the force is applied usually as a combined pull and twist on the forearm of a very young child. As the epiphysis is altogether intra-articular (the synovial membrane lining the whole inner surface of the orbicular ligament), swelling is early and marked. As there is direct communication with the larger synovial cavities of the elbow, the whole joint will participate in the effusion. Although no ligaments or tendons are attached to the epiphysis, the orbicular ligament hugs it closely and holds it in place. If any displacement occurs, the upper part of the diaphysis may go either forward or backward. On movements of pronation and supination, the epiphysis can be felt immovable just below the external condyle. An injury known as "elbow-sprain," or "pulled elbow," and described as a ' ' subluxation of the orbicular ligament' ' and as a " subluxation of the head of the radius," should be mentioned here because, although it has been known for more than two hundred years, has well-defined and constant symptoms, occurs in one 294 HUMAN ANATOMY. FIG. 308. per cent, of all surgical cases in children under six years of age, and is believed to depend on a distinct anatomical lesion, the exact nature of that lesion is still un- known. It is usually caused by traction on the forearm. The most plausible of many theories are : ( i ) that it is due to the head of the radius slipping out from beneath the orbicular ligament, which is pinched between it and the capitellum (Fig. 311) ; and (2) that it is a partial epiphyseal separation. The differential diagnosis is said to depend chiefly on the facts that in the " subluxation" the head of the radius will rotate with the shaft, and that all the symptoms disappear rapidly after forced supination has removed the functional disability. There seems nothing absolutely inconsistent with these symptoms in the view that a slight epiphyseal separation has occurred, the upper end of the diaphysis being displaced forward, but carrying with it the radial head. This theory is strongly favored by the fact that very few cases have occurred in children over five years of age. Ossification of the radial head begins towards the end of the fifth year. It should be remembered that the epiphy- sis includes only the upper part of the head, the lower portion and the neck being ossified from the shaft. The upper end of the diaphysis is therefore approximately of the same size and shape as the head, and may easily have been mistaken for it in many of the cases. The problem pre- sented is so purely an anatomical one that, in spite of the prevalent differences of opinion, it seems proper to make this brief presentation of it. Fractures of the head are uncom- mon. Fractures between the head and the lower end will be considered in refer- ence to the effect of muscular action upon them (page 604). In the neighborhood of the tubercle the thickness of the bone, the ridges that run up towards the head and down towards the outer edge, and the ample covering of muscles render fracture com- paratively uncommon. A little lower the union of the two secondary curves near the point of greatest curvature in the primary curve of the whole shaft renders the bone more vulnerable. Still lower the effects of indirect violence through falls upon the hand, the union near the lower end of the compact tissue of the shaft with the cancellous tissue of the expanded lower extremity, the compara- tively superficial position of the bone, and the projection of the anterior articular lip, into which the anterior carpo-radial ligament is inserted, all very markedly favor fracture. Accordingly, we find that, on account of these anatomical conditions, of one hundred fractures of the radius, approximately- three will be in the upper third, six in the middle third, and ninety-one in the lower third, the large majority of these latter being within from 2.5 to 5 centimetres (one to two inches) of the wrist- joint. Fractures of the lower end of the radius are almost always produced by a cross-breaking strain caused by falls on the hand, and exerted through the strong anterior common ligament. The broad attachment of this ligament to almost the whole anterior lip of the radius brings the strain equally on the bone through its entire width. The fracture is, therefore, usually irregularly transverse. In addition to the force transmitted by means of the ligament, there is an approximately vertical force, due to the weight of the body, which thrusts the sharp lower end of tin- shaft into the lower fragment, made up chiefly of spongy tissue, with merely a thin shell of com- pact tissue holding it together. This vertical force transmitted through the forearm Lines of fracture of neck and of lower end of radius (Colles's fracture). A, dorsal; R, lateral aspect. PRACTICAL CONSIDERATIONS : THE RADIUS. 295 FIG. and hand not only thus impales the lower fragment on the upper, but necessarily carries the former to a higher level. In addition, the ulno-carpal fasciculus of the common ligament drags on the lower end of the ulna, and either causes fracture of the styloid process, into the side and base of which it is attached, or causes the lower end of the ulna to project unduly on the antero-internal aspect of the wrist. The stripping up of the periosteum, the laceration of the tendon sheaths that are so closely applied to the bone, especially the flexor tendons by the jagged edge of the upper fragment, and the consequent effusion are the chief remaining anatomical factors in producing the character- istic deformity of this most common of all fractures. The lower fragment is found on the dorsum of the wrist. The lower end of the upper fragment is found anteriorly beneath the pronator quadratus or under the flexor ten- dons. The styloid process of the radius is on a higher level than that of the ulna ; in dislocation of the wrist this is not the case. The hand is carried towards the radial side (Fig. 309). In cases with but very trifling displacement it is still possible to recognize the absence of the projection of the anterior articular lip of the bone on the front of the wrist, and some slight elevation of the dorsum. The angle between the axis of the forearm and the ground is said (Chiene) to determine whether in such a fall the line of force passes upward in front of the axis of the forearm and the radius is broken, or extends up the forearm itself, resulting in a sprain of the wrist or a dislocation of the bones of the forearm backward at the elbow. The forward sloping of the carpal surface of the radius causes the posterior edge of the bone to receive the greater part of the force ; hence the lower fragment is rotated backward on a transverse axis, and hence the disappearance of the prominence of the anterior articular lip. The carpal surface of the radius also slopes down- ward and outward ; hence the radial edge of the lower fragment receives (through the ball of the thumb) a greater part of the shock than the ulnar edge, which is, moreover, firmly attached by the triangular ligament. This favors the upward displacement of the radial styloid and the radial displacement of the hand. There are almost always some crushing and distortion of the lower spongy fragment, even when it is not materially displaced. Anterior displacement of this fragment may occur when the force is applied in the reverse direction, i.e. , with the hand in forced palmar flexion. The infre- quency of falls on the back of the hand explains the rarity of this accident, but the greater weakness of the posterior ligament and the absence of any projecting articular lip to increase the leverage exerted through the ligament also contribute to make the accident uncommon. The later results of these fractures are much influ- enced by the close proximity of the flexor and extensor tendons to the region of injury, as, even when the sheaths escape laceration origi- nally, they are liable to become adherent during the process of repair. The lower epiphysis of the radius is osseous about the end of the tenth year and is united to the shaft in the nineteenth or twentieth year. The epiphyseal line is almost transverse (Fig. 310), and extends from about nineteen millimetres (three- fourths of an inch) above the apex of the styloid process to six millimetres (one- fourth of an inch) above the lower edge of the sigmoid cavity. The epiphysis is Fracture of lower end of radius, showing hand carried towards the radial side. 296 HUMAN ANATOMY. thinnest in the centre (five millimetres), the line at that point crossing the bone about three millimetres below the tip of the prominent middle thecal tubercle. The need for an accurate conception of this epiphysis is emphasized by the facts: (i) that it is more often separated than any other in the body, with the possible exception of the lower epiphysis of the femur ; (2) that its line has more than once been figured and described as a line of fracture on the basis of skia- graphs. The cause of separation is almost always a fall on the pronated hand. The carpal bones are carried against the posterior border of the radial epiphysis, the pro- nator quadratus and other muscles fix the lower ends of the diaphyses of the radius and ulna, and the epiphysis is forced backward. The anterior carpal ligament and the tendons on the palmar surface of the wrist are put on the stretch and aid in the displacement. The supinator longus is directly attached to the epiphysis and aids in maintaining the deformity. The synovial membrane of the wrist- joint does not reach the level of the epi- physeal line of either the radius or the ulna. That joint is, therefore, not frequently involved. The thinness of the centre of the epiphysis would lead, to the expectation that fracture would often complicate the separation. This is not the case, however. Poland says that the epiphysis is more solid than the lower end of the bone of the adult (which has, of course, become cancellous in structure), and that it thus escapes the fracture, comminution, and impaction which are so frequent in later life. The radius is often the subject of rickets, and of both syphilitic and tuberculous epiphysitis, especially at its lower end, on account of the exceptional 'frequency of falls upon the hand and strains of the epiphyseal joint. Subperiosteal sarcomata are rare. Central sarcomata almost invariably attack the lower end of the bone (page 366). Landmarks. The head of the bone may be felt at the bottom of the dimple or depression just below the external condyle and to the outer side of the olecranon. It lies be- tween the outer border of the anconeus and the muscular swell of the supinator longus and radial extensors of the car- pus. It is covered by the external lateral and orbicular liga- ments. It can readily be felt to move when the forearm is pronated and supinated. Its presence in that position demon- strates that dislocation of the radius or of both bones of the forearm backward the common dislocation at the elbow Its free rotation negatives the existence of a non-impacted FIG. 310. Lower end of left radius, showing epiphyseal line, dorsal aspect. has not occurred, fracture of the radius. The upper edge of the head lies immediately below the elbow-joint. In full supination the tubercle can be indistinctly felt a little below the lower edge of the head. The upper half of the radial shaft cannot be felt, as it lies beneath the bellies of the extensors and the supinator brevis. The lower half is almost subcutaneous and can readily be palpated through or between the tendons and muscles. The expanded lower extremity is partly subcutaneous (at the base of the styloid exter- nally) and is readily felt. The styloid itself, the prominent tubercle at the radial side of the groove for the extensor longus pollicis (middle thecal tubercle), and the sharp tubercle at the base of the styloid can easily be recognized. The latter is the inferior termination of the pronator crest of the diaphysis, marks the ex- ternal termination of the epiphyseal line, and is on a level with the lower and outer part of the pronator quadratus muscle. The posterior end of the- middle thecal tubercle is three millimetres above the epiphyseal line on the posterior aspect of the bone. The styloid process of the radius is lower i.e., nearer the hand than the sty.loid process of the ulna. RADIO-ULNAR ARTICULATIONS. 297 JOINTS AND LIGAMENTS BETWEEN RADIUS AND ULNA. These include, 1. Superior Radio-Ulnar Articulation : Orbicular Ligament ; Capsular Ligament. 2. Inferior Radio-Ulnar Articulation : Triangular Cartilage ; Capsular Ligament. 3. Ligaments uniting the Shafts : Interosseous Membrane ; Oblique Ligament. The superior radio-ulnar joint 1 (Figs. 311, 312) is between the circum- ference of the head of the radius and the lesser sigmoid cavity of the ulna extended into a circle by the orbicular ligament. The articular ends of the bones are coated FIG. 311. External conclyle Orbicular ligament surrounding head of radius Tuberosity of radius \ Internal condyle i Coronoid process Oblique ligament Radius Superior radio-ulnar articulation, anterior aspect. The capsule of the elbow has been removed. with cartilage requiring no particular description. The orbicular ligament 2 (Fig. 311) surrounds the head of the radius, springing from the two ends of the lesser sig- moid cavity and from the lines running down from them. This band embraces the head tightly, but is separated from it by the cavity of the joint, and is lined with 1 Artie, radioulnaris proximalis. - Lig. annularc radii. 298 HUMAN ANATOMY. synovial membrane. It narrows below so as to fold under the projecting head, and is attached, chiefly through fibres from the lower border of the lesser sigmoid cavity, to the inner side of the neck. It is connected above with the capsular ligament of the elbow-joint. That the fibres to the neck limit rotation is easily shown by dividing all bands connecting the bones, excepting the orbicular ligament ; for were it not so, the radius could then be turned continuously, which is not the case. It is doubtful, however, whether these fibres become tense by any movement which can occur in the undissected joint. The inferior radio-ulnar joint 1 is, when seen from the front, an L-shaped cavity, the vertical part being between the head of the ulna and the hollow on the radius, and the horizontal limb between the ulna and the triangular cartilage, which is attached by its base to the border between the inner and lower ends of the radius in such a manner that its distal surface is in the same plane as the lower end of the radius. The apex of the cartilage is attached by a ligament some three millimetres long to the groove between the head and the styloid process of the ulna and to the inner surface and anterior edge of the latter. Strong bands, inseparable from, the ligaments of the wrist, run along its border to the front and back of the articular surface of the radius. The fibro-cartilage 2 is very flexible Front of capsule FIG. 312. Median nerve Radial nerve Coronoid process Inner side of greater sigmoid cavity Ulnar nerve Orbicular ligament Horizontal section through right elbow-joint from above. The trochlea of humerus has been removed. and adapts itself to the surfaces of the lower end of the ulna and of the first row of the carpus. Its inner end, however, is not as broad as the lower end of the ulna. It is in some cases perforated. The membrana sacciformis is the synovial mem- brane of this joint, lining the capsule between the ulna and the triangular cartilage, between the ulna and radius, and extending a little above the level of the top of the apposed articular surfaces of these bones. The capsule enveloping it is delicate, but strengthened in front and behind by ill-marked bands passing between the bones ; these are sometimes described as distinct anterior and posterior ligaments. The connection between the lower ends of the bones is much strengthened by the pronator quadratus. The ligaments between the shafts are the interfesseous membrane and the oblique ligament. The interosseous membrane a (Fig. 315), composed of fibres running downward and inward, closes, except above, the opening between the bones. Beginning from one to two centimetres below the tubercle of the radius on tin- anterior surface of the interosseous riclge, and lower from the sharp edge, it connects the two ridges as far as the lower joint, following the posterior division of the inter- ossemis ridge <>f the radius. The upper fibres are nearly transverse. Some long til ins, particularly on the posterior surface, run from ulna to radius. There are 'Artie, radloulnarls distiilis. '-'hi-nis .11 1 i> uliiris. : Mcmhnuiu inU-ni-*si-;i intcrlir;u Iiii. THE FOREARM AS A WHOLE. 299 several small openings for the passage of vessels and nerves. Pressure transmitted upward from the hand through the radius would tend to stretch the greater number of the fibres, and thus distribute the strain through both bones. While the radius FIG. 313. Capsule of wrist-joint Head of ulna Styloid process of radius Capsule of inferior radio-ulnar joint Ligament of triangular cartilage Triangular cartilage Styloid process of ulna Lower end of right radius in supination. can hardly be enough displaced to bring this about, it is conceivable that the bones might bend sufficiently to make this action effective. The oblique ligament 1 (Fig. 311), an inconstant little band, runs downward arid outward, partly closing the space above the membrane, from the tubercle of the Head of ulna ( Ligament of triangular cartilage-^* Styloid process of ulna FIG. 314. Capsule of inferior radio-ulnar joint tyloid process of radius Triangular cartilage' Capsule of wrist-joint Lower end of right radius in pronation. ulna to the beginning of the oblique line of the radius. It has been plausibly sug- gested that it represents a part of the flexor longus pollicis muscle. THE FOREARM AS A WHOLE, AND ITS INTRINSIC MOVEMENTS. The two bones and the ligaments form an apparatus capable of being moved as a whole on either the arm or the hand, and of greatly changing its own shape by the movements of the radius on the ulna. As these latter are theoretically inde- pendent of the position of the forearm with regard to the arm, it is best to consider them here. The movement of the radius is a very simple one of rotation on an axis coincid- ing with that of the neck of the bone, and then, owing to the outward bend of the shaft, passing down between the bones and finally through the head of the ulna. The amount of rotation probably rarely exceeds 160. Rotation is limited chiefly by the anterior -and posterior radio-ulnar ligaments, the former being very tense at the end of supination and the latter at the end of pronation. The oblique ligament limits forced supination. As above stated, it is unlikely that the fibres of the oroicular ligament to the radius become tense during life. The fact that the lower end of the radius swings round the ulna in no way changes the character of the movement. If the radius were throughout in continuation of the axis of the neck, and the ulna enlarged below to support it, rotation on the axis of the neck would not change the position of the bone. The departure of the greater part of the radius from that line necessitates the swinging round of the lower end, but does not affect the nature of the movement. The changes of relative position of the bones during rotation are very important. It must be remembered that when the ulna is held so that the front of the middle of the shaft is horizontal, the head of the radius is in a plane above that of the main 1 Chorda obliqua. 300 H I'M AN ANATOMY. axis of the ulna. When the radius is brought into semipronation (so that the thumb will point upward) the bones are most nearly parallel and at the greatest possible distance from each other, and the membrane is approximately tense ( Fig. 315). The forearm is broadest at about the middle. The membrane is at the bottom of a moderate hollow seen from either the front or the back. In extreme supination the anterior hollow is effaced and the posterior deepened. The radius approaches the ulna, especially above the middle. In extreme pronation the front hollow is much deepened and the hind one lost. The bones are much nearer together than in any other position. The radius crosses the ulna, and- is above and internal to it at the wrist. Should the capsule be opened from below without disturbing the triangular car- tilage in a specimen from which the hand has been disarticulated, in supination the front of the under side of the head of the ulna will be exposed ; in forced pronation FIG. 315. Supination. Interosseous membrane.. Head of ulna. -Oblique ligament -Interosseous membrane Position of the bones of the forearm in pronation and supination. almost the whole under end will appear (Figs. 313, 314). As the radius passes behind the head, the ligament of the triangular cartilage is relaxed and the band at the back of the joint is made tense. This ligament becomes tense before com- plete supination and is somewhat relaxed when supination is extreme. The motion above described is the only one between the radius and ulna ; nevertheless, in certain movements of twisting the hand and arm the ulna plays a part to be considered later (page 304). Surface Anatomy of the Radius and Ulna. The position of both bones can be felt in a body that is not very muscular, though comparatively little of them is subcutaneous. The triangular space of the back of tin- olecranon, and the pos- terior border of the ulna starting from it and running to the styloid process, can all be traced with the finger. When tin- arm is straight, the top of the olecranon is a little above the level of the internal condyle and behind it ; when the arm is brut at a right angle, the top of the olecranon is in the same vertical plane as the back of THE ELBOW-JOINT. 301 the humerus ; and when it is strongly flexed, the top of the olecranon corresponds to the vertical plane of the internal condyle. The head of the radius and the furrow above it opening into the joint are easily felt at the outside and behind. In the lower third of the forearm the bones can easily be felt. The ulna here is posterior and best felt at the back. ' In supination the styloid process is distinct. It is hidden by the soft parts in pronation, and the head is exposed. The forward sweep of the lower end of the radius is evident. The inferior expansion can be felt both before and behind ; the styloid process is examined best from the outer side. It extends nearly one centimetre lower than that of the ulna. The inequalities on the back can be felt vaguely ; the most evident is the ridge bounding the groove for the long extensor of the thumb. THE ELBOW JOINT. 1 This is a considerably modified hinge-joint, the axis of rotation being oblique to the long axis of both the humerus and the ulna, and the course of the latter at the joint being also a spiral one. It is to be understood that the radius follows the ulna, which is the directing bone of the forearm in the motions of the elbow. The Articular Surfaces. These have been described with the bones ; it remains only to give here a summary. The motions between the forearm and the humerus depend essentially on the trochlea and on the surfaces of the greater sigmoid cavity. This is a modified hinge-joint. As has been shown, the transverse axis of FIG. 316. Triceps Trochlea - Bursa Subcutaneous bursa - Olecranon Coronoid process Ulna Sagittal section of right elbow-joint through the trochlea. the trochlea is not at right angles to the shaft, and it may be added that the same is true of the sigmoid cavity and the axis of the ulna. The effect of this will be noticed later. Again, as already pointed out, the trochlea is not only oblique, but is so shaped that the ulna in turning on it describes a spiral line. It has also been shown that the trochlea is not equally broad throughout, and that there are curious differ- ences of curve in the sigmoid cavity. Finally, the lateral ligaments are not quite tense, "especially when the joint is half flexed. It follows from these facts that the motion is a very complicated one, and that a certain lateral motion of the ulna on 1 Articulatio cubiti. 302 HUMAN ANATOMY. the humerus is possible. The head of the radius plays on the capitellum, but it follows the ulna. The capsular ligament ' surrounding the joint is very weak behind, stronger in front, and very strong at the sides, which last-named parts are usually called the lateral ligaments. The anterior fibres arise from the humerus above the coronoid and radial fossae, and from the front of the bases of both condyles. Behind, they arise from about the middle of the olecranon fossa, which is only partly within the capsule. Transverse fibres bridge it, passing between the highest points of the borders of the trochlea. Below this the posterior fibres arise beyond these borders, so that the trochlea is included in the joint. At the sides the fibres forming the so-called lateral ligaments radiate from points below the tips of the condyles. A little of the external and a large part of the internal condyle are not enclosed. The FIG. 317. Band strengthening front of capsule Fibres of orbicular ligament Thin part of capsule Bursa for tendon of biceps Radius nternal condyle of humerus Cut tendon of biceps Oblique ligament Ulna Capsule of right elbow-joint from before. capsule is inserted below, posteriorly, into the little groove described with the bone at the border of the olecranon. The radiating fibres from the external condyle arc- inserted into the surface of the orbicular ligament, behind, outside, and in front. They are covered by tendinous fibres of the muscles from the condyle, which arc- almost inseparable from them, and which greatly strengthen tin- joint. The fibres radiating from the tip of the inner condyle, or the internal lateral Kgeunent* are in two layers. The posterior, the deeper, is attached to the side of the olecranon ; the anterior is a strong band passing to the side of the coronoid process, which sends fibres backward, overlapping the deeper layer. The anterior fibres go to tin- orbicular ligament and to the coronoid process near its edge. The front part of the capsule is strengthened by delicate oblique fibres from the front of the internal ron- dyle, passing downward and outward. Masses of fat, incorporated in the capsule both before and behind, project into the joint, carrying the synovial membrane before 'Capsula articular!*. '-' Lig. collateralc ulnare. THE ELBOW-JOINT. 303 them. There is a thick pad of fat, which, when large, may bear well-marked synovial folds at the notch on the inner side of the ulna where the olecranon joins the coronoid. Movements. These are of two orders : that of flexion and extension, and those which occur in twisting the forearm. For practical purposes the former may be reduced to those of the ulna, which the radius is forced to follow. The move- ments of the ulna are not far from turning on an oblique axis, which cuts the long axis of the humerus at an angle of approximately 80 externally. When the forearm is fully extended, it therefore forms externally an obtuse angle with the humerus. Were the long axis of the ulna perpendicular to the axis of the joint, the forearm in flexion would cross the humerus, as indeed is often erroneously stated ; in fact, however, the long axis of the ulna also forms an angle of about 80 with the axis of the joint, and, as these angles equal each other, in flexion the forearm is parallel with the humerus. A simple demonstration of this is gained by cutting out a copy of Fig. 320. ' On folding it at the line of the joint (a b} the two parts will lie one on FIG. 318. Olecranon Internal condyle Posterior part of capsule Radius External part of capsule con- ( cealing orbicular ligament Ulna Right elbow-joint, posterior and outer aspect. the other. If then another model be made with the axis of the lower piece at right angles to the joint, it will show that the lower piece crosses the upper. When extension is complete, the tip of the olecranon can go no farther into the fossa on the back of the humerus, and the front of the capsule is tense. In complete flexion of the dissected arm, the tip of the coronoid is in contact with the humerus in front ; but in life the motion may be checked by the soft parts before it has reached its limit. Morris has shown that there is much variation in the range of movement, depending on differences in the upper end of the ulna. The lateral ligaments of a theoretically perfect hinge-joint should always be tense ; in the elbow they are not quite tense in semiflexion. Moreover, the imaginary axis does not remain fixed throughout the motion. Motions of the Forearm on the Humerus in twisting the Hand. The articulation between the concave head of the radius and the convex capitellum of the humerus is practically a ball-and-socket joint ; the radius may glide on the humerus, following the ulna, or it may rotate on a fixed axis, as described above. It is easily shown, however, that the swinging of the lower end of the radius round 1 Potter : Journal of Anatomy and Physiology, vol. xxix., 1895. 304 HUMAN ANATOMY. a motionless ulna is not what actually occurs in life. Let the reader grasp lightly his right wrist with his left thumb and forefinger, so that they nearly meet at the styloid process of the radius, and, pressing the right elbow to the side for steadiness, FIG. 319. Radius Oblique ligament / r I'i, (//" Interosseous membrane Ulna Tendon of biceps Right elbow-joint, inner aspect. Superficial layer of inter, lat. ligament Posterior part of capsule Olecranon Deeper layer of internal lateral ligament FIG. 320. pronate the right arm. The lower end of the radius will occupy the place at the base of the left thumb previously occupied by the ulna, which will have travelled outward along the left forefinger. It is very doubtful whether in this experiment all motion at the shoulder is eliminated ; nevertheless, the ulna undoubtedly changes its place, and with equal certainty it does not ' ' rotate. ' ' To prove this, let the arm of a subject be held in a vice above the elbow, which should be semiflexed, and, the forearm being supine, let a long pin pointing outward be fixed into the outer side of the radius above the wrist, and another pointing inward into a corre- sponding point of the ulna. On pronating the hand, the pin in the radius will describe a large curve and that in the ulna will make no evident movement. On close inspection, aided by placing some object close to the head of the pin in the ulna, it will appear that, though the bone has not rotated, the pin-head has changed its place : it has moved down- ward and outward. If the hand be now disarticulated, and two pins bearing brushes dipped in paint be placed in the end of the head of the ulna and in the lower surface of the radius, pointing downward so as to continue the line of the shafts of these bones, on twisting the forearm, each of these brushes will describe a curve on a sheet of paper held against them ; that in the radius making a large curve upward and inward, and the ulnar pin a small one downward and out- ward. The relative size of these curves mav be varied greatly by the operator. What has occurred is this : besides the rotation of the radius, there has been a lateral movement between the ulna and humerus combined with a slight extension. This movement is less when the arm is nearly straight than when Hexed, for in the latter position the lateral parts of the Diagram showing tin- l:il :umlfs i if tin- lung axes of tin- Imiii-s \\ith iiu- ;i\is ill lln- joint. PRACTICAL CONSIDERATIONS : THE ELBOW-JOINT. 305 capsule are least tense. It is probably assisted by a want of perfect adaptation between the articular surfaces. These experiments on the dead body do not quite fulfil the conditions of the living, because we have no evidence that then the muscles can produce quite the same movement ; moreover, Cathcart has shown that in anky- losis of the shoulder-joint this motion is greatly impaired, thus proving that in life a small amount of motion at that joint is an essential part of free twisting of the hand. Experiments by Hultkrantz on the living subject tend to show that the slight motion of the ulna is in the opposite direction to that described. There is probably much individual variation. l PRACTICAL CONSIDERATIONS. The Elbow-Joint. This joint is dependent for its strength more upon the shape of the bones that enter into it than upon the ligaments or muscles. As the elbow ceased to be useful for support, but became of the utmost importance for prehension, the radius became movable instead of fixed, and the strength of the joint came to depend in much larger proportion upon the ulna. Force applied in the line of the long axis of the limb, as in hanging by the hands (the weight being transferred from the wrist and the radius to the ulna and the elbow, largely by means of the triangular and orbicular ligaments, with very slight help from the oblique ligament), is resisted in the order of effectiveness (a) by the hook of the olecranon over the trochlea ; (b') by the lateral ligaments ; (c) by the biceps, triceps, and brachialis anticus, aided by the flexors, extensors, prona- tors, and supinators. The lower part of the lesser sigmoid cavity of the ulna under- hangs the inner edge of the radial head, and aids in preventing the radius from being drawn away from the ulna. Force applied in the same line, but in the opposite direction, as in falls upon the hands (the thrust being transferred from the radius to the ulna by means of the oblique fibres of the interosseous membrane), is resisted almost exclusively by the coronoid process, aided perhaps by the surface of contact between the radial head and the capitellum, which is diminished in full extension. As the dislocation usually occurs with the forearm hyperextended, the lateral ligaments, particularly the inner one, are often stretched and torn ; the brachialis anticus is drawn tightly over the humerus and is sometimes ruptured. The coronoid process is not infrequently broken. Antero-posterior dislocations are the most frequent, because of () the lesser antero-posterior diameter of the joint as compared with the lateral diameter ; () the varying efficiency of the hold of the ulnar processes the coronoid and olecranon on the humerus in different positions of the elbow ; (c*) the weakness of the anterior and posterior ligaments, and the absence of effective muscular support. Backward dislocation of both bones is far more frequent than forward, be- cause : (i) The capsular ligament is weakest posteriorly. (2) The coronoid, which resists backward displacement, is smaller, less curved, and received in a shallower fossa than the olecranon, which prevents luxation forward. (3) It is in its relation of least effectiveness when the joint is in full extension. (4) Falls upon the hand with the forearm extended greatly outnumber all other causes of dislocation of the elbow. (5) In full extension the already slight surface of contact between the radius and humerus is diminished and the posterior articular edge of the radial head projects behind the capitellum. (6) The ulna and radius are apt to be dislocated together rather than separately because of the strong ligaments which hold them to each other the triangular ligaments below, the interosseous membrane, and the orbicular and oblique ligaments above and because of the absence of any such intimate connection of either bone with the humerus. It is this ligamentous connection with the ulna which enables the radius, in spite of the shallowness of the articular cup upon its head, to resist the powerful forward pull of the biceps. 1 Heiberg : Ueber die Drehung der Hand, 1884 ; contains an exhaustive bibliography. Heiberg : Journal of Anatomy and Physiology', vol. xix., 1885. Cathcart : ibid. Dwight : ibid. Hultkrantz : Das Ellenbogen Gelenk und seine Mechanik, Jena, 1897 ; contains the later bibliography. 306 HUMAN ANATOMY. Lateral dislocations of the separate bones are infrequent for the same reason ; .of both bones because of the great relative width of the joint, its irregular undulating transverse outline, the prominences of the border of the trochlea and of the capi- tellum, the strength of the lateral ligaments, and the presence of the flexor and extensor muscular masses arising from the condyles. Inward dislocation is the rarest on account of the greater projection of the inner border of the trochlea. When either bone is dislocated separately, it is most apt to be the radius, and in the forward direction on account of the slightness of its humeral connection, its mobility, its direct relation with the hand and wrist, and the effect of muscular action (biceps) upon its upper extremity. The orbicular ligament offers the chief, if not the only resistance to this forward pull of the biceps. Therefore, if this is torn, recurrence of the luxation is common, unless the arm is kept in the acutely flexed position. When the ulna is dislocated alone, it is almost always backward for reasons already mentioned. In the common backward dislocation of both bones, the tip of the coronoid may rest upon the posterior surface of the trochlea, or may ascend to the level of the olecranon fossa, which, however, it is prevented from actually entering by the pres- ence of the soft parts and by the tension of the structures on the front of the joint. The most easily recognized symptom of this displacement is the change in the rela- tion of the tips of the condyles and the olecranon, the latter occupying a much higher position in extension, or lying much more posteriorly in flexion (page 287, Fig. 301). In making this measurement it is important to be sure that the line uniting the tips of the condyles, and in full extension in the normal arm, crossing the olec- ranon about one-sixteenth of an inch below its tip, is a straight line at right angles to the long axis of the humerus. Any upward or downward curve given to this line destroys its diagnostic significance. The large majority of cases of dislocation of the elbow occur in young males, usually below the age of twenty. Kronlein has called attention to the fact that at this age fractures of the clavicle are also common and luxation of the shoulder is rarely met with, while after twenty both clavicular fracture and elbow dislocation are comparatively rare and shoulder dislocation is common. He concludes that in childhood fracture of the clavicle is the equivalent of dislocation of the shoulder by direct violence, and dislocation of the elbow is the equivalent of the shoulder dis- location from indirect violence. The anatomical explanation may be that the disproportion between the head of the humerus and the glenoid cavity (page 278) is less marked in childhood, the articular surfaces are therefore not so easily separated, and force applied to the point of the shoulder is more apt to reach and be expended upon the clavicle. As to the elbow, the shallowness in children of the fossae which receive the processes and a corresponding want of prominence in the latter, together with the ease with which the elbow-joint in childhood may be hyperextended (which is not the case in adult life), are possible explanations of the frequency of this dislocation in young persons. Congenital dislocations occur. In some instances they have been associated with deficiency of the capitellum, and have then been accompanied by such elonga- tion of the radial neck as to place the head of that bone on a level with the tip of the olecranon. This affords an illustration of the general law, which may be mentioned here, that the rate of growth of epiphyses is inversely as the pressure upon them. Other examples are to be seen in the overgrowth of the cranial bones in hydrocephalus, when their edges are separated by the pressure of the ventricular fluid ; in the pro- jection of the vomer and intermaxillary bones beyond the level of the alveolar arch in some cases of cleft palate ; in the bony outgrowths that fill up the glenoid cavity or the acetabulum in unreduced luxations of the humerus or femur ; and in many other similar conditions. /V.vw.sr <>f the elbow-joint is most often tuberculous, but may be of any variety. In spite of the constant exposure of the joint to traumatism, it is not attacked by disease with exceptional frequency. This is probably partly due to the firm inter- PRACTICAL CONSIDERATIONS : THE ELBOW-JOINT. 307 locking of its bony constituents, preserving its ginglymoid character and preventing the injurious effect of side strains, partly to the similar protective effect of its strong lateral ligaments, and somewhat to the laxity of its capsule, permitting of moderate distention without undue tension. It is easily and often spontaneously immobilized in the early stages of disease ; it then bears no weight and is but little exposed to harmful increase of intra-articular pressure from muscular spasm ; and finally, as its fixation does not, as in the joints of the lower extremity, interfere greatly with moderate out-door exercise, the general resistant power is not so easily lowered. Swelling first shows itself posteriorly on either side of the olecranon process, and extends to the fossa over the head of the radius. In these directions the capsule is thinnest and most lax and the synovial cavity is nearest the skin. As distention continues there may be a bulging beneath the anconeus to the outer side of the olecranon, or on the front of the elbow beneath the brachialis anticus and extending towards the outer side, as it is limited internally by the thickening of the capsule constituting the internal lateral ligament. Pus is apt to follow the same lines of least resistance, and discharge upon the back of the arm on either side of the triceps, but especially on the outer side on account of the attachment of the dense intermuscular fascia above the internal con- dyle ; over the head of the radius beneath the external condyle ; or in front to the outer side of the tendon of the biceps, a position determined by the resistance of the bicipital aponeurosis on the inner side. The radio-ulnar joint, which is part of the articulation, is often involved, affecting the motions of pronation and supination. The upper radial epiphysis and most of the lower humeral epiphysis are within the limits of the capsule, and may either be the starting-point of joint disease or become secondarily involve'd. The position of semiflexion which gives the greatest ease, and is therefore voluntarily assumed, is that which affords most room for synovial distention and relaxes the muscles most immediately in relation with the joint. Distention of the joint is easily distinguished from disease of the neighboring bursae. The bursa over the olecranon, when enlarged, constitutes a single rounded superficial prominence ; that beneath the triceps tendon, while it causes swelling on either side of that structure, does not extend to or obliterate the fossa over the head of the radius, nor does it cause a ' ; puffiness between the inner condyle and the olecranon process when the arm is bent at a right angle" (Harwell). The bursae beneath the brachialis anticus and between the tubercle of the radius and the biceps tendon, if enlarged, cause a vague fulness over those regions, but none of the charac- teristic appearances of synovitis. Chronic enlargement of the latter bursa, in a case of Agnew, caused pressure paralysis of the muscles supplied by the median and posterior interosseous nerves. The obliquity of the line of the elbow-joint (page 268) should be remembered in the treatment of fractures involving the articulation. In obscure injuries about the joint the position of acute flexion, with the hand upon the front of the chest, is the one least likely to be followed by serious ankylosis, as in that position the full functional value of this obliquity is more apt to be preserved than when the forearm is at a right angle. The position is also the one in which it is easiest to retain in place many fractures in the region of the elbow. Especially in fractures of the lower end of the humerus, if the fragments are at once replaced, the coronoid. process in front and the muscular and tendinous structures behind hold them firmly and prevent recurrence of deformity. If the fracture is intercondylar, or T-shaped, the acutely flexed position not only holds the condyles in position, but tends to prevent by pressure the involvement of the joint line by callus, which later would prove obstructive. If either the coronoid or olecranon fossa, or both, be involved, it is more important to prevent the filling up of the former than of the latter, as full flexion is of far greater functional importance than full extension. If the condyles espe- cially the inner be split off, the position relaxes the muscles that cause displacement. It is also, of course, the most useful position of the limb in case ankylosis does occur. In excision of the elbow-joint the following anatomical points should be remem- bered : (i) The lines of the various epiphyses. (2) The position of the ulnar nerve 3 o8 HUMAN ANATOMY. in the groove between the internal condyle and olecranon. (3) The close relation of the posterior interosseous nerve to the head of the radius. (4) The post-operative value (in extending the forearm) of the outer aponeurotic expansion of the triceps and of the anconeus muscle. These should be carefully protected from injury. Landmarks. The following points may be mentioned in addition to those which may be found under the Humerus, Radius, and Ulna : A line from one condyle to the other will be at right angles with the humeral axis, but will be oblique in relation to the axis of the forearm. The line of the radio-humeral articulation is horizontal. The line of the humero- ulnar articulation is oblique downward and inward ; the tip of the internal condyle is therefore from a quarter to a half inch farther above the articular line than is the tip of the external condyle. The internal condyle points backward rather than inward. The length of the articulation line is about two-thirds of the length of a line joining the tips of the condyles. In semiflexion the external condyle is easily seen ; in acute flexion it disappears, and the rounded capitellum of the humerus, with the outer edge of the triceps stretched over it, can be seen and felt. The Inferior Radio-Ulnar Joint. This articulation has been dislocated in a few instances, in most of which, the cause having been extreme pronation of the wrist, the lower end of the ulna was carried backward, projecting on the back of the wrist and pointing outward, i.e. , towards the middle finger. The backward dis- placement probably involves the tearing of the triangular fibre-cartilage and a rup- ture of the posterior radio-ulnar ligament. The deviation of the ulna to the radial side may be due to the action of the pronator quadratus. The shallowness of the sigmoid cavity on the radius favors recurrence after reduction. But little is known of this injury. THE CARPUS. 309 THE HAND. THE hand is composed of the carpus or wrist, consisting of eight small bones arranged in two rows, which is succeeded by five rays of four segments each, namely, a metacarpal bone and three phalanges, excepting the thumb, in which one phalanx is wanting. THE CARPUS. There are eight carpal bones arranged in two rows of four each. The first row includes, named from the radial towards the ulnar side, the scaphoid, the semilunar, the cuneiform, and the pisiform ; the second row, the trapezium, the trapezoid, the os magnum, and the unciform. Exceptionally, several other bones may occur, due to the persistence of centres laid down in early fcetal life, which normally fuse with other centres or disappear. Thus there is much in favor of the view that the plan of the carpus is more complicated. This point is further considered in the dis- cussion of variations (page 313). The pisiform of the first row, whatever may be its morphological significance, is in man practically nothing but a sesamoid bone in the tendon of the flexor carpi ulnaris, resting on the palmar surface of the cunei- form, and having no share in the mechanics of the wrist excepting as giving attach- ment to a part of the anterior annular ligament. The first row, therefore, consists really of the three first-mentioned bones, which are joined into one flexible piece by interosseous ligaments. The upper end of this combination bears an egg-shaped articular surface for the wrist-joint, to which all three bones contribute. Its lower side has a concavo-convex outline, the concavity receiving the inner two bones and the convexity bearing the outer two of the second row. The latter consists of four bones connected by ligaments : the trapezium, for the thumb ; the trapezoid and os magnum, for the next two fingers ; and the unciform, for the ring and little fingers. The dorsal side of the carpus is slightly convex and the palmar deeply concave, forming by its middle the floor of a deep canal, bridged by the anterior annular ligament, which runs between bony elevations on each side of the carpous. To shorten the description, it may be said that little depressions for ligaments can be seen on well-marked bones near their edges on the dorsal and palmar aspects, especially the former. The scaphoid [os naviculare], or boat-shaped bone, is the largest and most external of the first row. It is a flattened elongated disk placed with the long axis running outward and downward. It receives its name from being convex on the upper and outer side for the radius and concave on the opposite side for the head the os magnum. Nearly corresponding with the long axis is the long and very FIG. 321. For trapezium FIG. 322. For trapezoid Tuberosity Tuberosity For radius Right scaphoid, dorsal aspect. Palmar surface Right scaphoid, inner aspect. narrow dorsal surface. The palmar surface is broader, runs more downward, and the outer end rises into the tuberosity of the scaphoid, from which part of the anterior annular ligament springs. The convex proximal surface for the radius is wholly articular ; the inner edge is straight, the dorsal and palmar converge externally ; it tends to encroach on the dorsal surface. Internally there are two surfaces, both 3io HUMAN ANATOMY. articular : the upper, very narrow, articulates at its lower border with the semilunar and gives attachment above to the fibre-cartilaginous ligament connecting these bones ; the lower is an elongated cavity embracing part of the top and the outer side of the head of the os magnum. The outer surface, continuous with the dorsum, is a small groove for the lateral ligament of the wrist. The distal surface, forming the convexity of the medio-carpal joint, articulates with the trapezium and trapezoid. It is convex in all directions. The scaphoid articulates withy?z ( x. brevis and oppvii. mm. dig. , carpi u/iuu is Opponent win. dig. Palmar interossei Abductor and flex, brevis mi>i. digit i Flex, sublim. digit. Flex, profund. digit Bones of right hand, palmar aspect. and runs to a point on the palmar aspect rather nearer the inner side. A groove for the capsule surrounds the joint, and on the outer side is a tubercle for the tendon of the extensor of the bone. The articular pro.\~hnal end is convex from side to side and concave from above downward, forming a typical saddle-joint with the trupe/.ium. The head is also broader from side to side. The articular surface is carried only a THE PHALANGES. 317 little way onto the dorsum, but bends strongly forward, ending in two lateral pro- longations with a notch between them, on each of which a sesamoid bone plays. The outer of these is the more prominent. The nutrient foramen runs towards the distal end. The second metacarpal has a base which is triangular when seen from the end. and forked to straddle the point of the trapezoid. On the outer side is a small square facet near the dorsum for the trapezium ; on the inner side there is a narrow oblique surface for the os magnum, and in front of it one showing a tendency to subdivide, articulating with the next bone. The third metacarpal has an oblong proximal surface, broadest on the dor- sum, where a tubercle, the stylo id process, projects towards the trapezoid. We have found the third metacarpal touching this bone in forty per cent, of 100 specimens, and sometimes this occurred when the styloid process was not particularly developed. Externally there is a facet like the lower part of the inner one of the second, and internally a double one to meet the next. The fourth metacarpal has a nearly square upper surface articulating with the unciform, and therefore of uncertain nature, sometimes convex, sometimes concave. At the outer dorsal angle of this surface is a small distinct facet for a joint with the os magnum. On the outer side are two facets for the third, and on the inner a long one, concave from dorsum to palm, for the fifth. The fifth metacarpal has a base generally broader than deep, concave from side to side and convex from above downward. A single facet on the outer side has a convexity to meet the concavity on the fourth. The inner side has, of course, no facet, but a tubercle. The dorsal ridge on this bone is twisted, starting from the inner side. Development. Each bone has two centres, a primary one for the shaft, appearing early in the third month of foetal life, and one for an end, appearing in the third year. The secondary centre is for the distal end in the four inner metacarpals and in the proximal of the first, that is, at the end towards which the nutrient artery does not run. They fuse at about eighteen. Rarely smaller epiphyses appear at the other ends also, as in mammals generally. A centre for the styloid process of the third is sometimes seen, and it may become distinct, suggesting an extra carpal bone, or it may fuse with one of the adjoining ones. THE PHALANGES. Features of Each Bone. The phalanges 1 of the first and second row differ (except in size) only in the proximal ends. The dorsum of the shaft is rounded from side to side ; the palmar surface is flat with raised edges for the sheaths which bind down the tendons very closely. It is considerably overhung by the distal and somewhat by the proximal end. The nutrient foramen, when present, runs distally. The proximal end of they?/ row is a concave articular surface, broadest trans- versely. A groove runs round the end, except on the palmar surface, for the cap- sule and for fibres from the extensor tendons of the fingers on the dorsum. Two very slight inequalities in front mark the attachment of the glenoid ligament. There is a rough tubercle on each side, just below the groove for the partial insertion of the interosseous muscles. The distal end in both the first and second rows has an articular surface which curves over two condylar prominences, separated by a median furrow, onto the palmar aspect. This surface is seen on the dorsum only as a small curved median facet which broadens as it passes over the end and continues to expand to its termination. The lateral borders of the joint are well defined. A depression with an overhanging tubercle is on each side of this end ; both depression and tubercle give attachment to the lateral ligament. The pro ximal ends of the second and third rows are essentially the same. They differ from that of the first row because, while the latter fits onto the single rounded end of a metacarpal, those of the two distal rows fit onto double condylar ends. Thus the proximal articular surface presents a median elevation, separating two hollows, continued into a projecting point on the surface front and back. In the phalanges of the second row the dorsal point is the larger ; in the last row the points 1 Phalanges digitorum manus. 3 i8 HUMAN ANATOMY. are about equal. In the last row the palmar point is at a lower level than the rough- ness that succeeds it. There is a transverse ridge in both on the dorsal aspect for extensor tendons ; the flexor tendons are inserted on the palmar side to a slight ridge on the second phalanx and to a roughness spreading considerably on the shaft of the terminal one. The phalanges of the third row are much smaller and flatter than the preceding. The dorsum of the diminutive shaft is convex from side to side and its palmar aspect plane where not encroached upon by roughnesses. The free end is sharp and rounded, with points at each end projecting backward. The dorsal distal border bears a narrow semilunar roughness ; a much broader one on the palmar side sup- ports the pulp of the end of the finger, giving firm attachment to the connective tissue. Peculiarities of Individual Phalanges. Every phalanx of the first row is longer than any of the second row. The first and second phalanges of the middle finger are longer than the corresponding ones of the ring finger, which in turn sur- pass those of the index. Those of the little finger are the smallest. The terminal phalanges are of very nearly the same length. The phalanges of the first row have the following peculiarities. That of the index-finger has a very large external tubercle at the dorsum ; the hollow at the base is deeper than that of any other ; the base is relatively strong compared with the shaft, which is flatter than any other. The phalanx of the middle finger is strong in all its parts ; there is a large external tubercle, often divided into a dorsal and a palmar part ; at the distal end the ulnar condyle is more prominent. The phalanx of the ring finger has the base relatively small and the condyles relatively large, so that the borders are nearly parallel ; the dorsum is more convex transversely than that of the third, and much more so than that of the index ; it is also narrower. The phalanx of the little finger is weak, narrowing rapidly so as to appear pointed ; there is a tubercle at the inner and dorsal side of the base, and the radial condyle is the more projecting. One cannot, therefore, determine to which side the phalanx of the ring finger belongs. In the second row the phalanx of the middle finger is always stronger than that of the ring finger, and the latter than that of the index. According to Pfitzner, 1 the distal ends are the more characteristic. In the second finger the radial condyle is the more prominent ; this is also true in the third, but to a less degree ; the ulnar condyle is the larger in the fourth, and still more so in the fifth. The distal or terminal phalanges can be distinguished more surely by strength than by length ; the third is the strongest ; then comes the fourth ; next the second, which is more or less pointed ; and last the fifth, which is relatively weak. These characteristics are to be used with great caution in drawing differential deductions. Development. The phalanges have each a centre for the shaft and one for the proximal end. The former appears in the latter half of the third month of foetal life at about the same time in the terminal and proximal rows. Probably the termi- nal row shows ossification somewhat earlier than the other (Bade). The centres for the second phalanges appear after a distinct interval about the middle of the fourth month. In both the first and second rows the centre appears nearer the proximal end. It is said that in all the rows ossification begins in the middle finger, next in the index, and later in the ring and little fingers ; there is, however, con- siderable variation. The centre for the second phalanx of the little finger is dis- tinctly later than the others. Ossification begins in the epiphyses in the third year or later. They are fused by eighteen. In addition to the proximal epiphyses, the terminal phalanges have each a distal cap-like ossification of perichondrial origin. which quickly joins the shaft. Sesamoid bones'- occur in the metacarpo-phalangeal joints. In the f cut us of the fourth month they are very numerous, but many disappear by fusion or other- wise during development. A pair is constant in the joint of the thumb. They are t\vo bones of variable si/e, in general rather larger than a small pea, lying on the palmar side of the head of the first metacarpal. The tendon of the long flexor passes. 'Sclmalbi-'s Morpholog. Arbeiten, lid. i. ami ii., 1893. 2 0ssn scsamoidca. PRACTICAL CONSIDERATIONS : THE HAND BONES. 319 between them. They each have one cartilage-covered surface against the bone and are otherwise surrounded by fibrous tissue. A small one on the radial side of the joint of the index-finger occurs in rather less than half the cases, and one on the ulnar side of the little finger in rather more than four-fifths. Pfitzner 1 gives the following table of percentages showing the frequency of the various sesamoid bones, combining his work and that of Thilenius : Number of Hands. Thumb. Index. Middle. Ring. Little. Fourth-month foetus . . Fourteen to ninety years 30 1323 Rad. Uln. IOO IOO 99.9 100 R. L. 46 23 47.8 o.i R. L. 30 15 1-5 R. L. 23 30 O O.I Rad. Uln. 15 63 2.3 82.4 Variations in the number of the fingers are generally regarded as malforma- tions. The most common occurrence is an extra finger, the identification of which is not certain. It seems often as if we should content ourselves with saying that there is an extra finger, but that no particular one has been repeated. Sometimes the thumb has three phalanges. Occasionally any of the terminal phalanges is doubled. A very uncommon condition is that of seven or eight fingers and no thumb. The dissection of such a case revealed the absence of the radius and of the radial side of the wrist, the skeleton of the forearm consisting of two ulnae and that of the hand of the ulnar sides of two opposite ones fused together. PRACTICAL CONSIDERATIONS. The Carpus. Of the carpal bones the scaphoid and semilunar are most fre- quently broken, on account of their more direct relation to the line of transmission of force in falls upon the hand. The diagnosis is difficult, and has been made oftenest by the help of a skiagraph. There is but little displacement. The other bones of the carpus, on account of their shortness, irregular and rounded shape, and compact union by strong ligaments which yet permit slight movements be- tween the bones, usually escape injury except in cases of crush of the whole hand. They are, however, not infrequently the seat of tuberculous disease, as might be expected from their great liability to traumatism of all grades. Their synovial re- lations (Fig. 342) favor the spread of such disease from one bone to the remainder, and render conservative treatment unsatisfactory. The result, too, is affected by the close proximity of the flexor and extensor tendons, which become involved in the tuberculous process or bound down by adhesions. The Metacarpus. The first metacarpal bone, which is morphologically a phalanx, is, like all the phalanges, developed from an epiphysis situated at its proximal end. But one case of disjunction has been recognized during life. It re- sembled a dislocation at the carpo-metacarpal joint, but the seat of abnormal move- ment was below the level of the lower edge of the trapezium. In the remaining metacarpal bones the epiphysis is situated at the distal extremity. Falls upon or striking with the closed fist tend to produce forward displace- ment. As the metacarpal bones of the index-, middle, and ring fingers are the longer, their epiphyses are more likely to be separated in this manner. A fall on the extended fingers and metacarpo-phalangeal region may cause backward displace- ment, though this is rarer. The diagnosis from dislocation of the proximal phalanges is not easy. It is aided by the recognition of " muffled crepitus" (Poland) and by the great tendency of the deformity to recur, due partly to the small articular areas of the separated bones and partly to the action of the flexors and the interossei. Skiagraphy will usually establish the diagnosis. Fracture of the metacarpal bones is usually the result of a blow with the clinched fist. The metacarpals of the thumb and little finger are therefore rarely broken. On account of the mode of application of the force, the seat of fracture is 1 Zeitschrift fur Morph. und Anthropol., Bd. ii., 1901. 320 HUMAN ANATOMY. apt to be near the distal end, although the thinnest and weakest parts of the bones are just above the middle and they sometimes break there. The proximal fragment is held firmly by its ligamentous attachments and is less movable than the phalangeal portion ; its distal end may project on the dorsum. The knuckle of the affected finger sinks and partially disappears. The lumbricales and the interossei aid in producing this deformity, and may cause the proximal end of the distal fragment to become prominent on the dorsum of the hand. In examining for these fractures it should be remembered that the metacarpal bones of the index- and middle fingers are bound tightly to the carpus and possess but little power of independent movement. The others are more movable. In the treatment of these fractures the normal palmar concavity of the metacarpal bones should never be forgotten. The Phalanges. Epiphyseal separation of the phalanges is extremely rare. The epiphyses are all at the upper ends of the bones. The diagnosis from severe sprain or from fracture will usually be made by the X-rays. It is now thought that not a few of the cases of necrosis of the proximal end of a phalanx following acute inflam- mation or whitlow are the result of epiphyseal sprain or disjunction. Of course, necrosis is often the sequel of the spread of infection from the superficial structures of the hand to the closely applied fibro-cellular tissue over the terminal phalanges. Fractures occur most frequently in the proximal and most rarely in the ter- minal phalanges. The relation of the tendons on the dorsal and palmar surfaces usually prevents any marked displacement. Occasionally an anterior angular de- formity of the proximal phalanx is seen after fracture. It is believed to be favored by the action of the interossei. The frequency with which both tuberculous and syphilitic inflammations affect the phalanges is probably due to their exposure to slight injury. They are, how- ever, not often the subject of post-typhoidal infection. The cause of whitlow has already been mentioned, and will be recurred to. The reason for the over- growth of the bony structures of the hand in acromegaly and in hypertrophic pul- monary osteo-arthropathy is not known. In the latter case it has been suggested that the enlargement of the terminal phalanges, like the ' ' clubbing' ' of the fingers in phthisical patients, may be due to an osteogenetic stimulus derived from the pres- ence in the circulation of the secondary products of the pulmonary infection. This would be analogous to the increased rapidity of growth observed in adolescents during convalescence from typhoid. Landmarks. On the inner side of the hand, below the wrist, the pisiform bone can be felt, and when grasped firmly can be given slight lateral movement. Lower and more externally the hook of the unciform can be made out. On the outer side the tuberosity of the scaphoid just below and internal to the radial sty- loid and still lower the ridge of the trapezium may both be felt. With the hand in full flexion, the dorsal prominence of the scaphoid and semilunar and the curved line of their articulation with the radius may be felt ; the anterior and posterior lips of the articular surface of the latter bone can be palpated and the groove or depression beneath them recognized. The projection of the os magnum on the back of the hand, and occasionally of the base of the third metacarpal at its articu- lation with the os magnum, may easily be felt. When an unusual prominence of these bones exists, and is first noticed after a fall or strain, it sometimes leads to a mis- taken diagnosis of exostosis or of ganglion. The metacarpal bones, their concavity, their expanded anterior extremities form- ing the knuckles, the shape and size of the shafts and ends of the phalanges, and of their articulations with the metacarpus and with each other, can all readily be made out through or between the overlying tendons. The surface markings of the hand and of its joints will be considered later (page 621.) LIGAMENTS OF THE WRIST AND METACARPUS. The ligaments and joints of the wrist include three articulations, the radio- carpal, the intracarpal, and the carpo-metacarpat ', which often receive detailed separate description. The simpler and in many ways more desirable conception of these joints is to regard them as parts of a common articulation consisting of a LIGAMENTS OF THE WRIST AND METACARPUS. 321 general capsular ligament enclosing synovial cavities separated by an interarticular fibre-osseous septum composed of the bones of the first row and their interosseous ligaments. Preparatory to the common description which follows, it is necessary to consider the ligaments and relations of the groups of bones which take part in the formation of the subdivisions of the general articulation. The pisiform being practically a sesamoid bone, the upper end of the carpus is an egg-shaped articular surface made chiefly by the convexities of the scaphoid and semilunar and to a small extent by the cuneiform (Fig. 340). These three bones are united into one apparatus by two strong interosseous ligaments situated just below the proximal ends of the bones, covered by synovial membrane and com- FIG. 340. Ulna Triangular cart Semil merit of first row Interosseous carpo-metacarpal ligament Dorsal ligament of second row Dorsal intermetacarpal ligaments Dorsal aspect of right wrist. The joint of ulna is opened and the shaft displaced forward and inward to show under side of head. The radio-carpal, intracarpal, and carpo-metacarpal joints are shown by removing the dorsal ligaments and flexing the hand. pleting the articular surface. They completely shut off the radio-carpal from the in- tracarpal joint. The latter is concavo-convex, the concave part being formed by the cuneiform, the semilunar, and the hollow surface of the scaphoid ; the convexity by the lower surface of the latter bone, which articulates with the trapezium and trape- zoid. The concavity amounts to a socket, of which the side formed by the scaphoid is nearly at right angles to the base, while the inner, formed by the cuneiform, is oblique. The scaphoid is attached to the semilunar much less tightly than is the cuneiform, so that considerable motion occurs between them. The scaphoid, besides sliding in various directions on the semilunar, can turn on an approximately trans verse axis through its proximal part, which permits of flexion and extension, to some degree independent of the rest of the first row. Its lower end may also move 322 HUMAN ANATOMY. somewhat outward and inward, so as to broaden or narrow the socket. The distal row of carpal hones presents a prominence made by the os magnum and the unci- form, which are held firmly together so as to move nearly as one, fitting into the socket presented by the first row. The outer side of this prominence is quite straight, making an entering angle with the trapezoid, receiving the ridge between the concavity and convexity of the scaphoid. At this point near the palmar surface the os magnum receives a ligament from the scaphoid, which may occasionally deserve to be called interosseous. The pisiform has a capsular ligament enclosing the joint between it and the cuneiform. The four bones of the second row are joined by three interosseous ligaments: one FIG. 341. Ulna Interosseous membrane Radius Inferior dorsal radio-ulnar, ligament (relaxed) Dorsal carpo-metacarpal ligaments Dorsal transverse ligament Accessory bands Scapho-metacarpal band Dorsal aspect of right wrist. between the trapezium and trapezoid, near the palm ; one between the trapezoid and os magnum, near the dorsum ; and one between the os magnum and unciform, much the strongest, connecting the palmar halves of the bones at the distal end. None of these interrupt the communication of the synovial cavity of the intracarpal joint and those at the bases of the metacarpals. The scaphoid, semilunar, and cuneiform have very properly been compared to an intra-articular fibro-cartilage or meniscus, subdividing a joint. No muscle of the forearm is inserted into them. (The flexor carpi ulnaris, which has the pisiform as a sesamoid bone in its tendon, has its real termination in the fifth metacarpal. ) Hence this series is never directly moved, but changes position under the pressure of the distal row, which is pulled against it by the muscles moving it. It plays an important part in the movements of the joint LIGAMENTS OF THE WRIST AND METACARPUS. 323 The bases of the metacarpals, except the thumb, articulate with one another by the lateral facets, and just below these joints are held together by strong interosseous ligaments connecting the rough depressions below the bases. The fibres of the Radiu Radio-caipal joint Intracar_ (between scaphoid and os m pal j Joint between trapezium a first metacarpal agn nd Ulna Inferior radio-ulnar joint Triangular fibro-cartilage vIntracarpal joint (between cuneiform and unciform) Carpo-metacarpal joint Carpal synovial sacs seen in longitudinal section. interosseous ligament from the trapezium to the trapezoid are inseparable from some from the trapezium to the second metatarsal. A common description will best serve for the ligaments connecting the forearm, the first row, the second row, and the bases of the metacarpals (Figs. 340, 341). The simplest conception is of a capsule passing from the forearm to the metacarpus and attached to the intervening bones. It is much strengthened by neighboring 324 HUMAN ANATOMY. tendons and their sheaths. It is strong at the sides ; weak in front and behind. The stronger bands are inextricably blended with the rest ; that on the outside, the external lateral ligament? runs from the radial styloid process to the outer side of the scaphoid, thence to the trapezium, and is continuous with the capsule of the carpo-metacarpal joint of the thumb. The internal lateral ligament' 1 ' runs from the styloid process of the ulna to the side of the cuneiform, and to the pisiform, thence to the narrow internal edge of the unciform, and finally to the fifth metacarpal. The dorsal part of the capsule is the weakest, but is much strengthened by the extensor tendons. A continuous layer passes from the radius and ulna to the first row, thence to the second, and thence to the metacarpals. The general direction of the fibres of FIG. 343. Radius Interosseous membrane I'lna Styloid process Radio-carpal ligament Tubercle of scaphoid Ridge of trapezium Anterior carpal ligament Ant. inferior radio-ulnar ligament Styloid process Pisiform ligament Pisiform Int. lateral ligament ciform Tendon of ext. carpi ulnaris Outer end of ant. annular ligament Inner end of ant. annular ligament Anterior aspect of right wrist-joint. A portion oi the anterior annular ligament has been removed and the canal for the flexor carpi radialis opened. the proximal part is transverse, inclining inward from the styloid process of the radius and the scaphoid to the cuneiform. This constitutes the dorsal transverse ligament, which serves to hold the head of the os magnum and the adjoining part of the unci- form in the socket made by the concavity of the first row. It has no definite borders. Tolerably distinct bands pass to the bases of the four inner metacarpals ; those to the second and third are tense and the others lax. Various accessory bands are often found. The anterior part of the capsule in the hollow of the wrist is stronger : it is reinforced by oblique bands converging downward. Many of these fibres are attached to the narrow palmar prominence of the os magnum. Pretty distinct bundles go to the bases of the metacarpals. Very small disks project into both the radio-carpal and tin- intracarpal joints from the dorsum, which are hardly seen 1 Llg. t "1l.-iiri.ili- carpi rudlulc. Lltf. oolluteralv carpi ulnare. LIGAMENTS OF THE WRIST AND METACARPUS. 325 in frozen sections. Their broader bases are attached to the capsule, and the free sharp edges end in the joint fitting in between the bones. The pisiform has a special joint on the palmar side of the cuneiform, with a lax capsule. This is strength- ened internally by a bundle FIG. 344. Palmar fascia Muscles of little finger \ Pisiform Cuneiform Anterior annular ligament Palmar carpal ligaments Tendon of flex, carpi rad. Scaphoid Unciform Os magnum Dorsal carpal ligaments Transverse section through right wrist from above. The flexor tendons have been removed from the canal beneath the annular ligament. Radius Intra-articular disk Semilunar Intra-articular disk Os magnum from the cuneiform run- ning from the dorsal to the palmar side. Two well- marked bands pass down- ward from it on the latter aspect ; the one to the base of the fifth metacarpal is really the end tendon of the flexor carpi ulnaris, the other passes obliquely to the proximal edge of the unciform process. The Anterior An- nular Ligament. This is an extremely strong structure, bridging the hollow of the wrist, and enclosing a canal through which pass the tendons of the long flexors of the thumb and fingers and the median nerve. It springs internally from the process of the unciform and from the pisiform, the latter part being fused with FIG. 345. the band from it to the unciform. It is attached externally to the ridge on the trapezium, and by a deeper process to the tuberosity of the scaphoid and to the inner side of the front surface of the trapezium, thus splitting to allow the passage of the tendon of the flexor carpi radialis through a special canal in the groove of the trapezium. Frozen sections through the wrist, passing through the pisiform (Fig. 344) (but not those through the unciform), show deep fibres from the annular liga- ment passing down under the canal and blending with the front ' of the capsular ligament of the wrist. The proximal and distal borders of the ligament are somewhat artificial, as it is connected with the fascia of the forearm and with the palmar fascia, besides receiving fibres from the flexor carpi ulnaris. This anterior annular ligament holds the sides of the wrist firmly together and prevents them from spreading when pressure is applied from above. Its fibres mingle with the origins of mus- cles of the thumb and of the little finger. The posterior annular ligament is but a thickening of the fascia of the back of the forearm, and has no place among the true ligaments. The Carpo-Metacarpal Articulations. Those of the four inner fingers have been partially described. They connect with the general articular cavity of the wrist. A band from the adjacent edges of the os magnum and unciform to those of the third and fourth metacarpals (Fig. 340) does not completely interrupt the continuity of this cavity, as it does not reach the dorsal surface. The carpus and metacarpus are connected on both front and back by bands which can be fairly distinguished from the capsule. Trans- verse bands run also on both surfaces from the base of one metacarpal to the next. The opposed sides of the bases are partly covered with articular cartilage, Third metacarpa! Frozen section through right middle finger, the hand being straight. 326 HUMAN ANATOMY. Radius Disk Semilunar Os magnum Third metacarpal Same as Fig. 345, the hand being flexed. as has been described. Interosseons metacarpal ligaments connect their sides distally from this. These complete the capsules, which are imperfect only on the carpal side. The articulation of the thumb ( Fig. 342) differs from the others in being complete in itself. It is a saddle-shaped joint. The hand lying supine, the long axis of the joint slants down- FIG. 346. ward and inward. In this direction the trapezium is con- cave ; at right angles to it con- vex. The joint is surrounded by a capsule, which is strongest on the dorsal and palmar sides, where the direction of the fibres is longitudinal ; it is weak at the outer anterior end, where it is strengthened by the tendon of the extensor of the metacarpal bone. The motions are flexion, extension, adduction, abduc- tion, and circumduction. Ro- tation in the flexed position may be possible from the im- perfect adaptation of the ar- ticular surfaces, but can hardly be of practical importance. Flexion is limited by the locking of the palmar projection of the metacarpal against the trapezium ; the other angular motions by the tension of the ligaments. Movements and Mechanics of the Wrist and Carpo-Metacarpal Articulations. It is convenient in studying these movements to imagine that the metacarpus follows the motions of the second row of carpal bones. This is true of the index- and middle fingers, but not of the others. The motions of the wrist in the widest sense are flexion, extension, adduction, abduction, and circumduction. The joint is a compound one, egg-shaped above, the scaphoid, semilunar, and cuneiform acting as a meniscus. The motions are best studied by removing the skin and tendons on the dorsal aspect and inserting long pins into the radius, semi- lunar, and os magnum, and, for some purposes, the scaphoid. The Rontgen rays have been useful chiefly as corroboratory evidence. In flexion the motion begins in the upper joint, where it is most extensive ; as it goes on the lower takes part. In extension, starting with the arm straight, more than half occurs in the lower joint. Adduction (ulnar flexion) (Fig. 348, It), owing to the lesser prominence of the ulna, is more free than abduction. The meniscus glides towards the radial side, and in so FIG. 347. Third metacarpal ( K magnum Same as Fig. 345, the hand being overextended. doing assumes the relation to the radius that it has in extension. The scaphoid touches the radius only by one end, so that its long axis approaches the direction of that of the forearm, and the semilunar leaves the triangular cartilage. The curve of the meniscus broadens, increasing the distance between the ends of the cuneiform and the scaphoid. A small part of the motion occurs in the mid-carpal joint. The unciform, moving with the os magnum, comes nearer to the semilunar. The space LIGAMENTS OF THE WRIST AND METACARPUS. 327 between the neck of the os magnum and the scaphoid enlarges. In abduction (radial flexion) (Fig. 348, A) the second row of the carpus has a larger share in the motion than in adduction. The meniscus moves to the ulnar side and is flexed, while its ends approach each other, narrowing the arch. The lower end of the scaphoid is crowded against the os magnum and the proximal end of the unciform recedes from the semilunar. Lateral motions do not occur when the wrist is either strongly flexed or extended. The screw surfaces of the cuneiform and unciform are important factors in the combination of antero-posterior and lateral motions ; but the os mag- num and unciform, which move together, do not twist in the socket formed by the first row if the latter be fixed. Circumduction is a combination of the preceding motions. Though the meniscus moves as a whole, the scaphoid is less closely attached to the semilunar than is the cuneiform. FIG. 348. Reduced tracings from skiagraphs, showing the position of the carpal bones. A , in radial flexion ; S, in ulnar flexion. 1 Flexion is limited by the tension of the dorsal ligaments ; extension in the upper joint chiefly by the lateral ligaments, in the lower by the locking of the bones of the meniscus against those of the first row. The anterior fibres of the capsule probably assist. Lateral motion is checked in the upper joint by the side liga- ments ; in the lower joint it is limited chiefly by the shape of the bones. The number of joints between the carpal bones divide the force of shocks transmitted through the hand. The motions of the carpo-metacarpal joints of the fingers are almost wanting, except for the ring and little fingers. In both these the motion is essentially flexion, most marked in the latter, and, owing to the dorsal convexity of the carpus, tending to oppose the little finger to the thumb. The metacarpo-phalangeal articulations are surrounded by a rather loose capszile, which is inserted into both bones pretty close to the articular cartilage. It is weakest on the dorsum, where it is supported by the extensor tendons. It 1 In tracings from X-ray photographs it is in places very difficult satisfactorily to outline the separate bones, partly because the contours of both surfaces as well as of thick processes are shown, and partly because some bones lie in front of others, owing to the palmar concavity of the wrist. The greatest difficulty is with the respective outlines of the trapezium and trapezoid. In the above figures the outline of the latter is indicated in dotted lines. This confusion is of little practical importance, since the drawings are to illustrate the changes of position between the first row and the forearm on one side and the second row on the other. 3 28 HUMAN ANATOMY. FIG. 349. Glenoid cartilage Insertion of ext. commun. cligitorum Outer side of right forefinger. The metacarpo- phalangeal joint is opened. springs from little hollows on the sides of the heads of the metacarpals. Longi- tudinal fibres are distinct at the sides, if sought for from within the joint. The cap- sule is strengthened on the palmar surface by fibrous or fibro-cartilaginous plates, the glenoid cartilages, which form the beginnings of the floor of the canals for the flexor tendons (Fig. 350). These plates are firmly fastened to the bases of the phalanges, whose motions they follow, and loosely to the metacarpals. In the thumb the glenoid plate amounts to little or nothing, as the palmar aspect of the joint is chiefly covered by the two sesamoid bones, which are firmly held near together by transverse fibres. When sesamoids are present in the other joints, they are lost in the fibrous tissue at the sides of these plates. The glenoid cartilages of the four inner fingers are attached to one another by a series of bands of little strength, the transverse metacarpal ligament (Fig. 351). The articular surface of the metacarpal is in the main convex and that of the phalanx concave. They do not make a true ball-and- socket joint, for the long axis of the latter is transverse and at right angles to that of the former, which, moreover, is much broader at its palmar than at its dorsal end. As the glenoid disks are parts of the floors of the canals for the tendons diverging from the mid- dle of the wrist, those of the second and fifth fingers are not squarely placed, but incline to the middle of the hand. Movements. When the finger is straight, it can be moved laterally, a little backward, and flexed, as well as circumducted. It can, on the dead hand, be slightly rotated ; but this motion does not occur in life. When it is fully flexed, lateral motion is impossible owing to the tenseness of the capsule, which has occurred in two ways, partly from the fact that in flexion the phalanx rests on the broadest, instead of the narrowest, part of the head, and because, the depressions for the origins of the strongest lateral parts being near the dorsum, these are stretched when the phalanx has travelled round the palmar prominence of the head. The interphalangeal ar- ticulations differ from the pre- ceding by the peculiarities of the articular ends and the greater relative strength of the lateral parts of the capsules. The gle- noid cartilages are small. There is no lateral motion. They are the purest hinge-joints in the body. The Surface Anatomy of the Wrist and Hand. The joint between the forearm and the carpus can be approxi- mately indicated by a line either on the back or the front, but more accurately on the former, starting from the head of the ulna, running nearly transversely, but with a slight upward bend, to near the radial styloid, and then sweeping downward to its tip. The first row of carpal bones can be made prominent on the back by flexing the wrist. The hollow FIG. ii. 350. Transverse metacarpal ligament III. A IV. V. Metacarpals Phalanges Palmar aspect of right metacarpo-plialangeal joints flexor tendons opt'iu-d. Glenoid cartilages Sheaths for PRACTICAL CONSIDERATIONS: THE WRIST-JOINT, 329 Metacarpals on the dorsum of the os magnum is distinct, and some indication of the mid-carpal joint may be felt near it. ' ' Slightly external to the middle of the hand is a promi- nence, sometimes indistinct, but often very well marked, formed by the styloid process on the base of the third metacarpal bone at its articulation with the os magnum" (Thane and Godlee). On the palmar side the pisiform can be felt just at the beginning of the hypothenar eminence. When the hand is flexed and the muscles relaxed, it is easily moved from side to side. The unciform process can be indistinctly felt below it. The tubercle of the scaphoid FIG. 351. is felt with difficulty below and internal to the radial styloid, and at the beginning of the thenar eminence (the ridge on the trapezium) more clearly. The position of the annular ligament may be de- duced from these points, and it may be felt by pressure on the hand. It is a general rule for the joints between the meta- carpals and the phalanges, as well as for those between the latter, that the more distal moves on the proximal, and that, therefore, the promi- nence of the knuckle in flexion is made by the head of the metacarpal. All the meta- carpo-phalangeal joints can be made out from the dorsum. The sesamoid bones of the thumb are felt with difficulty. The web of the fingers lies about thirteen millimetres distal to the palmar aspect of the metacarpo-phalangeal joints. That of the index-finger is about midway between the transverse furrow reaching the radial side of the hand and the first crease on the finger ; those of the other fingers are in the same relation to the second furrow and the respective creases. The interdigital joints are slightly distal to the upper line of the complicated creases of the first joints and to the single line of the creases of the second row. Sheath for flexor tendons opened Transverse metacarpal ligament Palmar aspect of right metacarpo-phalangeal joints. Sheath for flexor tendons on one finger opened ; on adjacent finger still closed. PRACTICAL CONSIDERATIONS. The Wrist-Joint. The radio-carpal has the greatest amount of motion of the three rows of joints that intervene between the metacarpus and the forearm. Its strength is not derived from the shallow concavity on the lower end of the radius, or from the ligaments which, taken together, compose the capsule, but rather from the tough fibrous tissues forming the sheaths of the large number of tendons that pass over the anterior and posterior aspects of the joint and are closely united to the bones. It escapes frequent injury, also, because of the numerous bones that enter into the carpus, which by their gliding motion one upon the other diffuse force received through falls upon the hand ; because of the same effect produced by the movement of the mid-carpal joint (intracarpal of Dwight), which takes up part of the force in overextension of the hand before it reaches the wrist ; and because of the absence of any long rigid lever on the distal side of the joint. Dislocation backward is by fai the most common, on account of the frequency of falls upon the hand. The diagnosis from Colics' s fracture is made by observing that in dislocation : (i) the anterior swelling is nearer the ball of the thumb ; (2) the posterior swelling is more sharply defined at its upper edge ; (3) the styloid process of the radius is nearer the hand than that of the ulna ; (4) the distance from 330 HUMAN ANATOMY. it to the head of the metacarpal bone of the index-finger is shortened ; (5) the antero-posterior diameter of the wrist is increased ; (6) the flexion and immobility of the wrist are greater. In dislocation forward the posterior swelling (the sharp border of the radius and ulna) approaches the hand ; the rounded prominence of the carpus is on the front of the wrist ; the antero-posterior diameter is increased and the stylo-meta- carpal measurement is lessened. Outward (radial) dislocation of the wrist is resisted by the contact of the scaphoid with the styloid process of the radius and by the internal lateral ligament. Inward dislocation would theoretically be easier, as there is no bony obstacle, and as adduction may be effected to a greater extent than abduction, and with greater power, on account of the leverage afforded by the projection of the cuneiform and pisiform bones on the inner side of the wrist. It is for this reason that the hand commonly assumes the position of adduction and the little finger becomes inclined towards the ulna when, from disease or other cause, the muscles lose the influence of volition and exercise an uncontrolled sway over the part (Humphry). Disloca- tion in either lateral direction is, however, very rare. Spontaneous subluxation forward is a condition thought to be associated with hard manual labor in which the strong anterior ligament becomes stretched and the radial side of the carpus is displaced forward and upward. This is followed, in accordance with a general law of growth (page 104), by an overgrowth of the posterior portion of the lower end of the radius, from which the normal opposing pressure of the carpus has been removed. The lower end of the ulna becomes unduly prominent. Disease of the wrist-joint is frequently tuberculous, but may be septic or rheu- matic or gonorrhceal in its origin. As the joint-cavity does not include the epiphyseal lines of either the radius or ulna, the synovial membrane being attached to the margins of the epiphyses, disease and injury of the latter do not of necessity involve the joint. The circumstances already detailed that protect the joint from dislocation also protect it from sprains and lessen the frequency of traumatic synovitis and of the sequelae of traumatism. Disease of any variety once established is apt to extend to the various synovial pouches of the carpus on account of their proximity, to involve the flexor and ex- tensor tendon sheaths for the same reason, and to result, in accordance with its character, in either extensive disorganization or much limitation of motion. The flexors and extensors on the front and back of the wrist act with about equal force, and therefore but little displacement occurs. The swelling usually shows itself first on the dorsum through the thinner pos- terior ligament, the joint being nearer the surface on that aspect. Landmarks. The line of the wrist-joint is convex upward. A straight line drawn between the two styloid processes is oblique downward and outward. It unites the two extremities of the arc which represents the line of the joint. The highest point of that arc is a half-inch above the interstyloid line. If a knife were introduced horizontally below the tip of the styloid process of the ulna, it would open the wrist-joint ; below the styloid of the radius, it would strike the scaphoid. The remaining landmarks are described on page 621. The Joints of the Carpus, Metacarpus, and Phalanges. As the inter- mediate ligaments uniting the separate bones of each row of the carpus are all trans- verse, and do not pass from one row to another, the mid-carpal (intracarpal ) joint permits of considerable motion in both flexion and extension. It undergoes disloca- tion with extreme rarity, and usually only as a result of a degree of force sufficient to stretch or tear tendons and ligaments. Dislocation of the second row of the carpus forward is prevented by the manner in which the concave surfaces of the trapezium and trapeze ml rest upon the posterior convex facet of the scaphoid, as well as by the undulating manner in which the side of the unciform is disposed with regard to the side of the cuneiform. I )is|)lacement backward is prevented by the manner in which the round head of the os magnum and the convex posterior and upper surface of the unciform are let into PRACTICAL CONSIDERATIONS : THE CARPAL JOINTS. 331 the hollow formed in the anterior and inferior surfaces of the bones of the first row (Humphry). The joints between the individual bones of the carpus allow of but little motion, and much force is needed' to produce displacement of those bones. In the order of frequency the os magnum, semilunar, scaphoid, pisiform, trapezium, trapezoid, and unciform have been reported as separately dislocated. It is interesting to note in relation to the order of frequency that the middle finger is the longest, and is the one most exposed to injury and to force applied to the fingers ; its metacarpal bone is the longest ; it articulates directly with the strongest carpal bone, the os magnum, and it, in its turn, with the semilunar, which unites with the scaphoid in connecting the hand with the forearm. In reported cases the pisiform was thought to be dislocated secondarily after the rupture of the tendon of the flexor carpi ulnaris below the bone. The other separate carpal luxations have but little anatomical interest. Disease of the mid-carpal joint is usually tuberculous, and is apt to begin in or extend to the os magnum because i. It is the bone most exposed to traumatism (vide supra), receiving the effects of injury to three metacarpal bones. 2. The joint participates in the movements of flexion and extension of the wrist, which are partly limited by the portion of the oblique fibres (both radial and ulnar) of the anterior annular ligament (page 325) and by some of the radial fibres of the weak posterior ligament, which are attached to the os magnum. 3. The slight rotation permitted in the mid-carpal joint is around a vertical axis drawn through the head of the os mag- num. A very slight enlargement of the bone would tend to pinch and bruise the synovial membrane between it and the trapezoid, those two being more closely bound together than any of the other bones. It has been noticed (Mundell) that the point of greatest tenderness in these cases of carpal tuberculosis was in a line between the index- and middle fingers, corresponding to the junction of the os magnum and the trapezoid. Harwell says that in tuberculosis of the wrist-joint the point of special tenderness is on the outer side of the extensor indicis tendon. This is on the same line, and, in cases in which the carpus has become involved, would correspond to the same point of junction. Dislocations of the metacarpal bones from the carpus usually involve single bones, are incomplete, and are in the backward direction. The wavy, irregular out- line of the distal edge of the carpus, the dovetailing of the metacarpals and carpals by means of the alternating convexities and concavities, and the strength of the interosseous and transverse metacarpal ligaments sufficiently explain the infrequency of dislocation of the metacarpus as a whole. Dislocations of the metacarpo-phalangeal and interphalangeal joints amount to " nearly thirty per cent, of all dislocations" (Stimson). Backward displacement of the proximal phalanx of the thumb is the most frequent and the most important. The cause is usually exaggerated extension of the phalanx, which carries its proximal end up onto the dorsum of the metacarpal bone above the articular surface. The relation to the muscles of the thumb is so important that the luxation will be described in that connection (page 617). Dislocations between the phalanges usually occur at the first phalangeal joint, and in the backward direction, as the cause is common! v a fall upon the palmar surface of the finger in extension. THE LOWER EXTREMITY. The Pelvic Girdle. This consists of the two innominate bones, which join each other in front, and the sacrum behind. While the thoracic girdle is adapted to freedom of motion, the pelvic is fitted for strength and support. The study of the innominate bone should be preceded by a general idea of the pelvis. A plane between the promontory of the sacrum and the top of the pubes divides the pelvis into the false pelvis above, formed chiefly by the ilia, and the true pelvis below. The latter presents the sacrum and coccyx behind, the arch of the pubes in front and below, and the tuberosity of the ischium at the side. Behind this is the sacro-sciatic notch, much reduced by ligaments. On the sides are the hip- joints, and towards the front the obturator or thyroid foramen. THE INNOMINATE BONE. This 1 consists originally of the ilium, pubis, and ischium, each of which forms a part of the hip-joint, but which fuse so completely that the lines of union are not usually to be seen in the adult. The ilium forms the upper and posterior part of the bone, the pubis the front, and the ischium the inferior. The two latter enclose the obturator foramen. The Ilium. The ilium, 2 a plate of bone forming the side of the false pelvis and a part of the true, may be said to have four borders. The superior border, or crest, :! very much the longest, is convex upward and outward. It connects two tubercles, the anterior and posterior superior spines of the ilium, of which the former is a knob overhanging the concave anterior border and giving attachment to Pou- part's ligament and the sartorius, while the latter is less prominent. The crest has a double lateral curve, the front half being convex externally and the posterior inter- nally. It is thicker at the ends than in the middle, and presents also a thickening near the middle of each curve, projecting on the convex side. There is an external lip, from the whole length of which springs the fascia lata of the thigh, an internal lip, and ^n intermediate space. The anterior border i^ short, rounded, and con- cave, descending to the anterior inferior spine, a knob a little above the border of the acetabulum giving origin to the straight head of the rectus femoris and a part of the ilio-femoral band of the capsule of the hip-joint. The posterior border, very short and also concave, ends in the posterior inferior spine, an ill-marked angle at the bottom of the surface that joins the sacrum. The inferior border consists anteriorly of an attached part, which meets the other bones in the acetabulum, and behind this of a free concave part, which bounds the upper part of the great sacro- sciatic notch.* The ilium might also be described as consisting of an expanded por- tion, narrowing below to a stem, which joins the other bones in the acetabulum. Its upper part follows the curves of the crest. The lateral or outer surface is crossed by the three curved or gluteal lines, convex above and behind, all ending at or near the sciatic notch. The superior, much the strongest, arises from the crest at the middle of its second curve and ends a little in front of the posterior inferior spine, marking off a raised rough surface behind its upper two-thirds. The middle begins at the crest, one or two inches from the anterior superior spine, and ends near the top of the notch. The inferior, the faintest, starts a little above the anterior inferior spine and is lost near the front of the notch. The three gluteal muscles, maximus, medius, and minimus arise respectively behind these- three lines in the order given. A slight groov for the reflected tendon of the rectus femoris, starting at the anterior inferior spine, runs backward above the acetabulum. The ventral or inner surface is divided into an upper posterior and a lower anterior part by the ilio-pcctincal Hue ' in front, and a rough border con- tinuing it. The former is a line beginning on the pubis and continued across the 1 ms Adductor magnns Gastrdcttemiusft. (inner head) Inner lip oi linea aspera Groove for femoral vessels _ . W GREATER TROCHANTER Linea Quadrat! Gluteal ridge Outer lip of linea aspera Ext. supracondylar ridge Adductor tubercle Depression for gastrocnemius INTERNAL TUBEHOSITY Depression for gastrocnemius EXTERNAL TUBERO8ITY Popliteal groove Intercondylar notch Right femur from behind. The outline figure shows the areas of muscular attachment. 356 HUMAN ANATOMY. prominence of the linea aspera at the back. The surface on either side of this line may be plane, concave, or convex, perhaps more often concave. The shaft expands slightly above, where it is roughly four-sided with rounded borders. A ridge, which is very variously developed, often runs from the lower side of the neck, separating the anterior and internal surfaces. When strong, it emphasizes the concavity of the former. The lower third of the shaft broadens. The linea aspera 1 is a prominent longitudinal ridge along the back of the middle third of the bone, strengthening the concavity and giving attachment to many muscles. It has two more or less well-defined borders or lips. It is formed from above by the union of three lines : the spiral, a faint intermediate line coming down from the lesser trochanter, and a third external one coming from the back of the greater trochanter. The upper part of the last is called the ghdeal ridge, as it receives fibres of the gluteus maximus. This part may be considerably elevated, especially in muscular subjects, into a rough knob, the spurious third trochanter. The true third trochanter, which is sometimes seen at this point, is a smooth rounded eminence, the analogue of the third trochanter extensively found among mammals and particularly developed in the odd-toed ungulata. This is sometimes best developed on delicate female femurs with no rough muscular ridges. Of course the two forms may coexist. A rough elongated depression, \he fossa hypotrochanterica, also receiving fibres of the gluteus, is sometimes found outside the gluteal ridge. The linea aspera divides somewhat below the middle of the bone into two supra- condylar ridges, which bound a triangular space 2 as they pass down to the tops of the condyles. The outer ridge is at first much the sharper, but it becomes indis- tinct an inch or more above the condyle. The inner is but slightly raised ; it is interrupted above its middle for the passage of the femoral vessels into the popliteal space. It ends in the sharp adductor tubercle above the inner border of the condyle. At its termination the shaft has four surfaces : a posterior one nearly plane, a front one slightly convex, a distinct outer one, and an oblique inner one, passing insensibly backward and inward from the anterior surface. There are usually two nutrient foramina, both directed upward, the larger between the lines converging to the linea aspera, the other near the middle of the bone, a little to the inside of that line. The lower extremity, articulating with the tibia below and the patella in front, presents two backward prolongations, the condyles, along which the tibia travels in flexion. These are compressed from side to side, and separated by the intercondylar fossa? which is beneath the back part of the shaft. The inner condyle'' is the lower when the shaft is vertical, but in life both are in the same plane. The outer 3 is longer from before backward ; it lies in an antero-posterior plane, while the inner extends backward and inward. The lateral outline of each has been well com- pared to a watch-spring partly uncoiled. Each bears a tuberosity near the posterior end of the lateral side, very nearly in continuation with the supracondylar ridges for the so-called lateral ligaments of the knee. A depression on each side for the head of the gastrocnemius is found above and behind the tuberosities. The ex- ternal condyle bears a deep oblique groove for the tendon of the popliteus at the back of the outer surface. The articular \surj "ace for the knee not only covers the lower and posterior aspects of the condyles, but is prolonged upward on the front for the support of the patella, as a groove which is shown by horizontal sections to be concave in the middle and convex at either side. The upper boundary slants upward and outward, the shaft just above it presenting a slight depression. Its outer border is a promi- nent ridge resisting outward dislocation of the knee-pan. The patellar surface is continuous with the articular facets of the condyles, being marked off only by certain lines, which, though distinct on the fresh cartilage, are often obscure on the dried bone, representing the separation of these joints. In some animals the separation is complete. The outer lhn\ usually concave posteriorly, runs obliquely inward to just in front of the intercondylar notch. The inner, less clear and generally straight, begins much farther forward and runs obliquely backward to the inner side of the front of the notch. The outer in particular marks n distinct change of level. Be- hind these lines the articular surfaces extend along the lower and posterior sides of the condyles even onto the upper aspect, so as to allow extreme llexion of the knee. ' Linea aspcra. '' IMiiitiim !><>|>lilcum. 3 Fossa Intcrcondyloiden. 4 Conilylus medialis. ' Cundyliis l.Ucralis. THE FEMUR. 357 Frontal sections through the back part of the condyles show that the inner is nearly symmetrical in its convexity from side to side, while the inferior surface of the outer FIG. 372. Outer head of gastrocnemius External lateral ligament External tibial face Popliteal groove Patellar facet Lower end of right femur, outer aspect. slants upward and inward. The length of the articular surface of the inner condyle from the back to the line marking off the patellar facet is considerably greater (perhaps two centimetres) than that of the outer. FIG. 373. Patellar surfa External tuberositv Limit of patellar surface Internal tuberosity Lower end of right femur from below. Structure. Transverse sections in series through the whole length of the femur are very instructive. They show the great strength of the shaft, the thick- ness of its walls, the smallness of the central canal, and the addition made by the linea aspera ; likewise that the shaft becomes four-sided both above and below, and that in the latter region the greater diameter is transverse. Coincident with these changes are a great diminution of the thickness of the walls and a great increase of the spongy tissue. The weakness of the walls just above the knee is very striking. The architecture of the condyles is well exhibited, consisting of vertical plates run- 358 HUMAN ANATOMY. ning in the main forward and backward, crossed by transverse ones, in part diverging from the solid bone at the bottom of the intercondylar notch. Such sections show also the prominence of the outer border of the patellar surface and the curve of that articulation. At the upper end they display the prominence of the lesser trochanter, the series of strong plates crossing it, which at a higher level are seen diverging from a single plate, Bigelow's true neck 1 (Merkel's calcarfemorale'}, to which we shall return. The greater trochanter, quite free from all pressure, is very light and the head very dense. Frontal sections of the head and neck (Fig. 374) show the series of plates given off successively from both the inner and outer walls forming Gothic FIG. 374. Lesser trochanter Oblique section of right femur parallel to lower border ot neck, through upper end of lesser tro- chanter. Frontal section through upper end ot jciniu , showing aiiangement of pressure and tension lamella-. arches at the top of the bone. The under side of the neck is thick and gives off a series of plates, near together, running obliquely up into the "head in the line of the greatest pressure, especially when the shaft is oblique, as in life. A less distinct & ri.-s of long arches springs from the outer side, curving across, and acting as "ties." The head is of the round-meshed pattern, fitted t< resist pressure in any direction, often presenting an almost solid core at the middle, and generally showing the curved line of union of the epiphysis of the head. The true neck of the femur is a plate, or a series of plates, springing from a thick spur of bone, which leaves the hind wall of the neck to run outward towards the greater trochanter. This is best 1 The Hip. Philadelphia, iS6<) ; also Huston Medical and Surgical Journal, 1875. 1 Virchow's Archiv, Ikl. 1., 1870. THE FEMUR. 359 seen in sections parallel with the lower wall of the neck (Fig. 375) ; it appears also in transverse ones. When strongly developed it can be shown as a real septum by gouging away the spongy tissue of the posterior intertrochanteric ridge beneath which it passes. Sexual and Individual Variations. Apart from general lightness of struc- ture, the female femur presents distinctly smaller articulations than the male. The average diameter of the head of thirty-eight male bones is 4.8 centimetres, and of twenty-six female ones 4.15 centimetres. In only two of the male bones is the diameter less than 4. 5 centimetres, and in only two of the female is it greater. Both of the latter are long ones. In women the size of the head increases with the length, but in men a short femur is about as likely to have a large head as a long one. The breadth of the articular surface of the knee is less conclusive ; the averages are 8.3 centimetres and 7.4 centimetres, but there is much overlapping. The peculiarity of outline in the typical female femur is very characteristic when well marked : the shaft narrows gradually from the condyles till at or above the middle the nar- rowest part is reached, above which there is a much less evident expansion. The typical male bone narrows much more suddenly above the condyles, so that the stouter shaft soon reaches a tolerably uniform thickness. The inclination of the shaft is somewhat greater in woman. The angle with a vertical line in the above series is 9.3 in man and 10. 6 in woman. (According to Bertaux, it is 8.75 and n.) It is naturally greater in shorter femurs, and consequently is of very doubtful value as a sexual characteristic, especially in view of the great individual variation. The angle of the neck with the shaft is of minor significance. In the writer's series it ranges from 110 to 144, the average for men being 125.1 and that for women 125.6. In the male bones there is little connection between the length of the femur and the size of the angle ; in women long bones have a large angle and short bones a small one. The average angle of the longer half of the male bones is 126.5 and that of the shorter 123.6, while the longer and shorter halves of the female series give 129.2 and 121.9 respectively. A long neck gen- erally has a high angle and a short neck a low one. 1 Thus it appears that there are great variations in the angle of the shaft and that of the neck. The same is true of almost every detail. The forward inclination of the neck is in two-thirds of the cases from 5 to 20, and usually from 12 to 14. Its extreme is 37. Very rarely this angle is negative, that is, the neck slants backward. An extreme negative angle of 25 has been observed, but this is extraordinary. 2 The curve and outline of the shaft vary much. An extreme form is the pilastered femur, very convex, with a prominent linea aspera, generally stout, implying strength. An opposite form is nearly straight, has a low linea aspera, and is flattened before and behind in the upper part of the shaft. In extreme forms the depression in the front of the top of the shaft is increased and bounded internally by a sharp ridge running up to the under side of the neck, which usually has a low angle. Though apparently weaker, this form is sometimes found in very powerful men. The index of the shaft is the proportion of the thickness to the breadth, the latter being 100. Thus ( j^-^ 22 ). This is taken at about the middle of the shaft where the linea aspera is most prominent. It is said to be greater on the right than on the left and in men than in women. Bertaux found the average in adults 104.4, an d m a series of young femurs 112.1. The index of the neck is the proportion of the thickness to the height. Thus ( Ul '''^g h * I0 ). The average is 133.05. It is a trifle higher in women, but the difference in unimportant. A strong convexity of the shaft outward as well as forward suggests a patho- logical condition. Development and Changes. The shaft begins to ossify not later than the seventh week of fcetal life. A centre appears in the lower end during the last month of pregnancy. It is rarely wanting at birth, but the precise time of its appearance as well as its size are too variable to make it a very valuable guide to the age of the 1 H. H. Hirsch : Anatomische Hefte, Bd. xxxvii., 1899. Mikulicz : Arch, fiir Anat. uncl Phys., 1878. 360 HUMAN ANATOMY. foetus or infant. Its growth seems to be slight during the first three weeks after birth. The neck grows as a part of the shaft and receives three epiphyses, one for each trochanter and one for the head, which fits over it like a cap. The latter appears in the second half of the first year, 1 and is pretty conclusive evidence that the age of six months at least has been reached. The epiphysis for the greater trochanter comes in the third year (sometimes some years later), and that for the lesser at a time variously stated as from eight to fourteen years. It is probable that FIG. 376. Ossification of femur. A,zA eighth foetal month; ft, at birth; C, during first year; D, at eight years; E,a\. about fifteen years, a, centre for shaft; i>, lower epiphysis; c, for head; d, for greater trochanter; e, for lesser trochanter. the former is much nearer the mark. The head unites with the shaft at about eighteen, the trochanters somewhat later ; probably there are great variations ; but all these superior epiphyses should be joined by nineteen, and at twenty the line of union is indistinct or lost. An epiphysis for the third trochanter has been seen. The lower epiphysis is joined by twenty, and often sooner. At birth the angle of the neck may be 160, but is often less ; it diminishes under the pressure of the weight as the child walks, and by the time of puberty has probably assumed about its permanent angle. There is no reason to believe that the angle diminishes in old age. Surface Anatomy. The greater trochanter can be explored when the muscles about it are relaxed. The lesser trochanter, though deep, can be felt from behind. A large third trochanter can be recognized, and must not be mistaken for a tumor. Owing to the individual variations of the neck and the pelvis, the relations of the trochanter must vary. According to Langer, a horizontal line at the top of the greater trochanter divides the head, touches the top of the symphysis, and about divides the nates. This is particularly true of broad pelves, and therefore of women. We have found from measurements of 118 males and 37 females that the trochanter is i.i centimetres, on the average, higher than the symphysis in the male and three millimetres in the female. Topinard gives as provisional distances in the male the following : the anterior superior spine of the ilium is six centimetres above the head of the femur, the latter two centimetres above the greater trochanter (practically agreeing with Langer), and the greater trochanter two centimetres above the pub.es. The head of the femur lies under a crease beneath the proper fold of the groin, and can sometimes be distinguished at the inner side of the sartorius. Nelaton's line is drawn from the anterior superior spine of the ilium to the most prominent point of the tuberosity of the ischium. It should just touch the top of the greater trochanter. The shaft is too thickly covered to be examined in detail, except near the knee. The sides of both condyles are easily examined ; the lateral tubercles and the adductor 1 Fagerlund : Wiener Med. Presse, 1890. PRACTICAL CONSIDERATIONS: THE FEMUR. 361 tubercle can be felt. The latter marks the line of union of the lower epiphysis with the shaft. When the knee is flexed, the patellar surface, its borders, and part of the articular surface of the condyles can be felt. PRACTICAL CONSIDERATIONS. Before the age of four the upper epiphysis is not distinct, and traumatism is apt to result in separation of the upper cartilaginous end of the bone, i.e. , a fracture through some part of the cartilaginous neck. Later three epiphyses may be affected by injury, viz., those for the head and the two trochanters. FIG. 377. Section through hip-joint, showing epiphyses of head and greater trochanter of femur. The epiphysis for the head is shaped like a hollow hemisphere set upon the convex upper end of the neck. The epiphyseal line slopes downward and inward, and is entirely within the synovial membrane. Separation by indirect violence occurs as a result of extreme extension of the thigh, as in falls backward with the limb fixed, or as when a child carried in the arms of a nurse throws itself violently backward. The force is thus in effect applied at the lower end of the femur, which acts as the long arm of a lever. When it is carried far backward the ilio-femoral ligament is put upon the stretch, and its point of insertion becomes the fulcrum. The resistance (or weight) is at the point where the forward movement of the short arm of the lever the neck and head 362 HUMAN ANATOMY. is resisted, perhaps slightly, by the ligamentum teres, but chiefly by the anterior margin of the acetabulum. Separation is followed by shortening. This may be recognized by Nelaton's line (Fig. 378), by the base line of the " ilio-femoral triangle" (Bryant's) (Fig. 379), or by Robson's line, which is a line dropped vertically from the anterior spine to meet a transverse line drawn forward and inward from the tip of the greater tn>- chanter across the front of the thigh, the patient being in dorsal decubitus. Eversion, from the weight of the limb, is usually present. The toughness of the periosteum and the strength of the cartilaginous bond betweeji the neck and head in childhood may make the epiphyseal line stronger than the thin neck beneath it, and fracture of the neck may therefore occur even in young children or adolescents. The symptoms are very similar to those of epi- physeal separation. The crepitus may be rough instead of ' ' muffled. ' ' The X-rays will sometimes differentiate the two conditions. In a case of injury to the hip in a young person, it is, however, probable that epiphyseal' disjunction will result rather than fracture of the neck; but in youth, on account of the presence of the epiphyseal FIG. 378. FIG. 379. Showing Nelaton's line. Showing Bryant's triangle. joint and the weakness of the neck, both of these lesions are more frequent than dislocation. Either of them will convert the normal obliquity of the neck to a position more nearly horizontal, causing prominence and ascent of the trochanter, and bringing about at once the condition known as coxa vara, which will probably increase later, as whenever the angle of the neck with the shaft is diminished the strain upon the former is increased. Thus,* either epiphyseal separation, fracture of the neck, or slight rhachitis in early childhood may result in coxa vara at the period of adolescence, when the softening incident to rapid growth is taking place, the body weight is increasing, often disproportionately, and laborious occupations are frequently begun. The cpiphysis for the greater trochanter unites at about tin- nineteenth year. It is easily dislocated, almost always from direct violence, and usually between the thirteenth and eighteenth years, because that is the period of greatest exposure to traumatism, and because at the latter date the epiphysis is joined to the shaft. The line of junction with the shaft is on the level of the tubercle for the quadratus on the posterior edge of the greater trochanter ( Fig. 3^3). It is therefore below the level of the capsule of the hip-joint and of the insertions of the ^lutei, obturators, pyrifonnis, PRACTICAL CONSIDERATIONS : THE FEMUR. 363 FIG. 380. and gemelli. Disjunction from indirect violence through the action of these muscles is rare, on account of : (i) The prolongation downward and outward of the fibres of the capsular ligament which extend below the epiphyseal line. (2) The attachment above that line of some of the aponeurotic fibres of origin of the vastus externus. (3) The toughness of the periosteum. For these same reasons, when disjunction does occur, there is usually but little displacement. If it exists, and is marked, the epiphysis is drawn into approxi- mately the same position as that occupied by the head of the bone in a dislocation onto the dorsum of the ilium. The age of the patient (epiphyseal separation being impossible after nineteen and dislocation rare before that age) and the failure of the displaced epiphysis to move with rotation of the femur are aids to diagnosis. The absence of rotation and of shortening of the limb distinguishes this lesion from " extracapsular" fracture of the neck. About fifty per cent, of the recorded cases have died of py- aemia. This is probably because : ( i ) The greater trochanter is an apophysis rather than an epiphysis, and is in contact at its base with cancellous tissue of a lighter and more spongy character than that adjoining the true terminal epiphyses of the long bones. (2) The violence causing the injury is direct and thus associated with much bruising and crushing of that tissue. (3) The disjunction is attended by extensive detachment of the periosteum from the vascular upper end of the bone, as the periosteum over the tro- chanter is very thin and the dense tendinous fibres are almost di- rectly attached to the osseous tissue itself (Poland). The epiphysis for the lesser trochanter can be separated usu- ally only between the thirteenth year and the nineteenth, when it joins the shaft. But one case has been recorded. It was then torn off in a boy of fourteen, as the result of the strain on the ilio- psoas in a fall backward on the feet. Death from pyaemia followed. Fracture of the neck of the femur is common (especially in old age), in spite of its depth and its thick covering of soft parts, because : (i) In falls upon the feet or hip it receives and transmits much of the weight of the body, which, in the former case at least, reaches it in a direction which causes a cross-strain favorable to fracture. (2) It is a comparatively fixed portion of a very long lever into the upper end of which many powerful muscles are inserted. (3) It is of itself lengthened and thus made more vul- nerable, as compared, for example, with the neck of the hu- merus, so as to increase the leverage of these muscles, the degree of mobility of the hip-joint, and the basis of support for the trunk. (4) Its mechanical weakness increases in old age (rum Klenoidale. 3 68 HUMAN ANATOMY. the level of the articular surface. These structures are covered by synovial mem- brane. The head of the femur is covered by articular cartilage, except at the de- pression for the insertion of the round ligament. The bones are connected by the capsule and the round ligament. The capsule 1 (Figs. 385, 386) is a fibrous envelope enclosing the joint, strengthened by certain bands, which are inseparable parts of its substance, though they have names of their own. The capsule is attached to the cotyloid ligament and to the periphery of the acetabulum just outside of the origin of the latter. In this respect there is much uncertainty ; the capsule always rises from the free edge of the transverse ligament, and, as a rule, elsewhere outside the base of the cotyloid ; but it may in parts arise from its edge. This applies to the capsule examined from within ; externally the fibres extend a considerable distance from the border of the joint. They almost conceal the opening at the notch below ; above, they partly bridge over the reflected tendon of the rectus and partly join its deeper fibres. The cap- FIG. 384. Articular surfac Fat in acetabular fossa Tuberosity of ischium Anterior inferior spine of ilium Cotyloid ligament Stump of round ligament Transverse ligament Capsule reflected Socket of right hip-joint. The capsule has been divided near its origin and reflected. sule extends to the base of the anterior inferior spine of the ilium and some distance on the obturator crest. The attachment to the femur, seen from without, runs from the top of the greater trochanter, just above the superior cervical tubercle, down the spiral line to the level of the top of the lesser trochanter, where the line of insertion turns in for about two centimetres, when it passes upward along the back of the neck, less than half-way from the head to the posterior intertrochanteric line, till, reaching the top of the neck, it gradually passes outward to the starting-point. Thus the capsule stops about a finger' s-breadth short of the lesser trochanter, in- cludes less than half the hind side of the neck, and stops short of the digital fossa and of the inner side of the top of the greater trochanter. Posteriorly, it is not truly inserted into the neck, but simply crosses it, its position being determined by the line of reflection of the synovial membrane. The general direction of the fibres is longitudinal ; but the posterior fibres, when the femur is strongly extended, assume the form of a twisted band running from the back of the socket outward 1 Capsuln nrticularls. I I THE HIP-JOINT. 369 and upward across the back of the neck to the top of the greater trochanter (Fig. 387). Moreover, beneath the longitudinal layer there is a sling of circular fibres, the zona orbicularis, starting from the anterior inferior spine of the ilium and pass- ing behind the neck to return to the same point. It lies near the head of the femur, completely concealed by the longitudinal fibres. It is isolated only by a rather artificial dissection. The capsule varies much in thickness in different places ; thus, it is very weak behind and very strong in front. It is strengthened by three collections of accessory FIG. 385. Ilio-femoral ligament Right hip-joint, anterior aspect. fibres. Much the most important is the ilio-femoral ligament ' (Fig. 385), a thick triangular expansion, intimately fused with the capsule, arising by its apex from the lower part of the anterior inferior spine of the ilium and from the bone below and behind it above the lip of the acetabulum, and extending by its base from the superior cervical tubercle to the level of the lesser trochanter. The borders of this are often particularly strong, and are spoken of as the outer and inner limbs of the ligament. A weak space is sometimes seen between them near the insertion, whence it has been called by Bigelow the Y-ligament from a resemblance to an inverted Y. 1 Lig iliofcmorale. 24 370 HUMAN ANATOMY. Striking examples of this are generally artificial productions. The beginning of the ilio-femoral ligament covers the outer part of the head. The capsule is much thinner over the inner part of the head, and is covered by the bursa under the ilio- psoas, which often communicates with the joint. The pubo-femoral liga- ment 1 (Fig. 385) is a slender band of fibres, thickening the under side of the capsule, extending from the lowest point of the capsular insertion on the spiral line to the outer end of the obturator crest. It is rarely very evident. The ischio-femoral ligament 2 (Fig. 387) is a strong but ill-defined bundle at the back of the joint, extending from the ischial origin of the capsule to the top of the digital fossa. The capsule is further supported by muscles and by bands of fibrous tissue, generally expansions from tendons or fasciae. Morris describes a band on the upper FIG. ; V S6. Cotyloid ligament Capsul Z.Fat in acetabular fossa Round ligament Obturator membrane Frontal section through right hip-joint. The femur has been allowed to fall from the socket. anterior aspect, passing between the reflected tendon of the rectus and the highest origin of the vastus externus, which is sometimes very strong, but, in our opinion, inconstant. The relation of the ilio-psoas has been mentioned. Fibres are received at the upper outer part from the gluteus minimus. The obturator internus and the gemelli are close against it behind, and the obturator externus behind and below. We have seen a tendinous band beneath the tendon of the obturator internus quite distinct from the capsule internally and fused with it externally. It may have been n reduplication of that muscle or an extra ischio-fcmoral ligament . :1 The round ligament (/io-anifntmn fcrcs] (Figs. 384, 389) is a weak band of fibrous tissue, containing vessels and nerves, surrounded by synovial membrane, lying under the fat in the deep non-articular hollow of the socket, connecting the ;! Journal of Anatomy and Physiology, vol. viii., 'Li||- pubocnpstilarc " Lig. ischiocapsulare. THE HIP-JOINT. 37i rim of the acetabulum with the head of the femur. The origin is from each edge of the notch and from the deeper fibres of the transverse ligament, the insertion into the deepest part and upper edge of the depression in the femoral head. A fresh specimen, especially from a child, shows the lower half of the depression becoming gradually shallower and forming a groove in which the upper part of the band rests, which, covered with the synovial membrane, completes the spheri- cal shape of the head. Vessels run along the round ligament, which in infancy FIG. Reflected tendon of rectus Back of capsule Tuberosity of ischium Ischio-femoral ligament Right hip-joint, posterior aspect. and early childhood nourish the head, but in the adult they often do not enter the bone. This ligament is sometimes wanting. According to Moser, 1 this defect is only in the o 1 d, and is to be looked upon as a degenerative change. Comparative anatomy teaches that it is the analogue of a part of the capsule. It is remarkable that it is wanting in certain species closely allied to others possessing it. Besides the two extremes of complete freedom within the joint and of total absence, the ligamentum teres of animals is also found in an imperfectly developed condition as a fold along 1 Schwalbe's Morpholog. Arbeiten, Bd. ii., 1893. This paper gives the literature. 372 HUMAN ANATOMY. the side of the cavity between the notch in the acetabulum and the head of the bone. Many of the statements of its absence require confirmation by more observations. Thus, among the anthropoid apes it seems to be generally present in all but the ourang. In this animal, though usually wanting, it has been found in a rudimentary condition. Meckel declared that it was absent in the gibbon, but we believe no other observer has had a similar experience. It is very strongly developed in the ostrich, but is wanting in the rhea (the American ostrich) and probably in the casso- wary. Sutton * considers it as the tendon of the pectineus muscle which has become separated through skeletal modifications. Sutton relies a good deal on the condition in the horse for support in his argument. He found it consisting of two bands, one within the joint, apparently the usual ligament, and another passing out of the cavity to the linea alba at its junction with the pubes, which he calls the pubo- femoral portion. The pectineus muscle arises in part from this latter portion. Sutton gives a table telling the story of the structure according to his theory. In sphenodon (a lizard) the tendon of the ambiens, representing the pectineus, passes FIG. 388. Bursa beneath ilio-psoas I Round ligament Front of capsule Spine of ischium Capsule a tached to neck of femur Tendon of obturator externus Cotyloid ligament Horizontal section through right hip-joint. into the joint to the head of the femur ; in the ostrich the ligament is continuous with the tendon by means of connective tissue ; in the horse the two parts are distinct ; and in man the external part is wanting. The structure is evidently a very variable one. The synovial membrane (Figs. 386, 388) lines the capsule, covers the cotyloid and transverse ligaments, surrounds the ligamentum teres, and covers the fat in the fossa of the acetabulum. It is reflected from the femoral attachment of the capsule onto the neck, which it invests to the border of the articular cartilage. This reflected part presents certain folds caused by fibres from the capsule running up along the neck, called retinacula (Fig. 390). There are generally three chief ones : a superior, starting from the superior cervical tubercle and running along the upper border, or backward across the neck to the head of the femur ; a middle, from near the inferior cervical tubercle along the front of the lower border of the neck ; and an inferior, from near the lesser trochanter along the lower side. Any of these may be more or less free from the neck. 1 Journal of Anatomy and Physiology, vol. xvii., 1883. THE HIP-JOINT. 373 The retinacula l probably strengthen the union of the head and neck before the union of the epiphyses. Movements. As a ball-and-socket joint, the hip permits motion on an indefi- nite number of axes. If the ball were on the end of a straight rod, we could assume that flexion and extension occur on a transverse axis and adduction and abduction on an antero-posterior one, but the inclination of the shaft of the femur and that of the neck in two directions complicates the problem, so that accurate analysis of the FIG. 389. Crest of ilium Head of femur Obturator membrane Symphysis pubis The inner wall of the hip-joint socket has been cut away, exposing the head and round ligament without disturbing the capsule. movements is practically impossible. Rotation is motion on a vertical axis which is generally assumed to pass through the head and the intercondylar notch. This must, of course, vary with the shape of the bone. Although the angular motions in the four conventional planes are far from simple, they may be assumed to be so for practical purposes. Flexion is stopped in life by the contact of the thigh and the trunk before the limits of the motion are reached. Extension is limited by the 1 Fawcett : Journal of Anatomy and Physiology, vol. xxx., 1896. 374 HUMAN ANATOMY. Retinaculum Posterior intertrochanteric ridge resistance of the strong ilio-femoral ligament, excepting the outer band. Abduction is limited, the thigh being extended, by the pubo-femoral ligament and perhaps by the inner limb of the ilio-femoral. FIG. 390. When the thigh is flexed, the latter is Round ligament certainly relaxed, and the strain comes on the pubo-femoral and a part of the capsule behind it, a very weak re- gion. Adduction with a straight thigh is limited by the outer limb of the ilio-femoral, the top of the capsule, and Morris's band from the rectus tendon to the vastus externus, if it be present. After moderate flexion is passed, the ilio-femoral is relaxed. Outward rotation, the thigh being Capsule straight, is checked by the ilio-femoral, especially by its inner band. As the thigh is flexed the inner band is re- laxed and the outer is at first tense, but both are relaxed as flexion reaches about 45. Morris's band now be- comes tense, and -as flexion becomes extreme the round ligament is tense also, unless the thigh be abducted, when it is completely relaxed. In- ward rotation is checked by the ischio- femoral ligament in any position. The most important part of the capsule is the ilio-femoral band, which is extremely strong and prevents over- extension. It is an essential element in maintaining the upright position. The round ligament has probably no mechanical function, though it can be made tense by flexing, and at the same time either adducting the femur or rotating it outward. It is too weak to be of any real use as a restraint. Probably its chief usefulness is to carry vessels to the head of the femur in childhood. PRACTICAL CONSIDERATIONS. The greater security of the hip-joint, as compared with the shoulder-joint, is due to the depth of the acetabular cavity ; to its reinforcement by the cotyloid fibro- cartilage ; to the attachments of the ilio-psoas, gluteus minimus, and vastus externus to the capsule ; but chiefly to the thickenings of the capsule itself, which are described as the ilio-, ischio-, and pubo-femoral ligaments. The greatest pressure upon the capsule in all ordinary positions is in an upward and outward direction, or upon the anterior surface of the capsule, as when, under the influence of the powerful extensors, the pelvis and trunk tend to roll backward upon the thighs in the erect posture. The tension and pressure are, of course, greatest near the pelvic attachment of the capsule where the head will impinge upon it with the most advantage as to leverage. The capsule is especially fitted to resist this pressure. If two lines be drawn, one from the anterior inferior iliac spine to the inner border of the femur near the lesser trochanter, the other from the anterior part of the groove for the external obturator (/.<-'., the upper part of the tuberosity of the ischium) to the digital fossa, all the ligament outside and above these lines is very thick and strong ; whereas, all to the inner side and below, except along the narrow pubo-femoral band, is very thin and weak, so that the head of the bone can be Right femur seen from inner side, showing reflection of synovial membrane onto the neck. PRACTICAL CONSIDERATIONS: THE HIP-JOINT. 375 FIG. 391. Diagram indicating strong and weak portions of capsule of hip- joint. (At/is.) IS seen through it (Morris). Fig. 391 represents this diagrammatically. In addition, the greater elevation and thickness of the upper and outer rim of the acetabulum, and the pressure against the trochanter exerted by the ilio-tibial band of the fascia lata (Allis) in adduction of the thigh (which means an outward movement of the upper extremity of the femur), should be mentioned among the factors that resist displacement. The ligamen- tum teres is of little value, as its bony attachment to the femoral head is easily separated by a force less than that required to rupture the ligament. A line drawn from the anterior spine to the tuber ischii will approxi- mately bisect the acetabulum and will divide each half of the pelvis into two planes, the pubo-ischiatic, inner or anterior, and the ilio-ischi- atic, outer or posterior (Fig. 392). When the head of the femur escapes from the acetabulum it must lie on the surface of one or other of these planes. All dislocations are, there- fore, either (i) outward i.e. , pos- terior or (2) inward i.e., anterior. i. Outward or Posterior Luxations. Traumatisms in which the force expended upon the region of 'the hip result, as a rule, in children in epiphyseal sep- aration (page 361), in old persons in fracture of the neck of the femur (page 363). In 173 cases of dislocation of the hip, 138 were between fifteen and forty-five years of age. In practically all positions of the hip in which luxation is probable the force acts through some form of leverage which brings the short arm of the lever always the head and neck of the femur against a weak portion of the cap- sule. If it does this with the aid of a bony fulcrum, the power is ex- erted to the greatest possible ad- vantage. Thus, in hyperextension of the thigh, the acetabular rim acts as a fulcrum, but the head of the bone is brought against the anterior part of the capsule, the ilio-femoral ligament, which is usually stronger than the bone itself. Hyperflexion is arrested by the contact of the soft parts of the front of the thigh with the abdomen ; hyperadduetion by the contact of the shaft with the pubes. Hyperabduction, however, brings the greater trochanter against the prominent outer lip of the ace- tabulum, while the head is carried downward against the thin inner and lower part of the capsule ; the ilio-femoral and ischio-femoral liga- ments are relaxed, and the weak pubo-femoral ligament offers but little resistance ; the head, being opposite the shallowest part of the acetabulum, projects half its bulk out of that cavity ; the weight i.e., the resistance of the capsule is very close to the fulcrum, greatly increasing the power of the leverage. FIG. 392. Superior spine Diagram showing dividing line (A", )") between outer and inner pelvic planes. (A/Us.) 376 HUMAN ANATOMY. The ilio-femoral ligament may, in cases in which the thigh is adducted and rotated inward at the time of application of the force, take the place of the acetabu- lar rim as a fulcrum. In that position it is wound round the neck of the femur, and FIG. 393. Luxation of the head of the femur onto the dorsum of the ilium. when the flexed leg is used as a crank the head may be made to burst through the lower and posterior part of the capsule. Allis ' has shown that these conditions, easily demonstrated experimentally, are reproduced in many forms of accident. It is obvious that they are all favorable to a downward dislocation, and this, as is the case with the humeral head, is the direc- tion primarily taken in the FIG. 394. vast ma j or it;y o f these luxa- tions. If the thigh has been rotated inward, either in ad- duction or abduction, the head of the bone will pass outward and backward and rest behind the acetabulum on some part of the outer or posterior plane of the pelvis. If it lies upon the ilium, a little above the acetabulum, it constitutes the ' ' iliac' ' dis- location, "above the obtu- rator tendon ;" if upon the ischium, on a level with or a little below the acetabulum, it is the " ischiatic" or "sci- atic" dislocation, " below the obturator tendon.' obturator internus sometimes interposes an stacle to the upward of the head, but its impor- tance in this respect has been exaggerated. The degree of flexion of the limb at the time of the accident is more likely to determine the level at which the head rests. 1 Reduction of Dislocations of the Hip, Philadelphia, 1896. Relation of the head of the femur to the innominate bone in dorsal luxa- This tendon ob- PRACTICAL CONSIDERATIONS: THE HIP-JOINT. 377 In both positions the ilio-femoral ligament, which is almost invariably intact, has now become the fulcrum. As the short arm of the lever the head and neck has moved outward, the long arm the shaft of the femur must move inward ; hence adduction is present in all cases of outward luxation in which the Y-ligament is not lacerated, and is persistent because the head lying in contact with the outer wall of the pelvis cannot be moved inward. Rotation inward, which is also present and persistent, is due to the same tension upon the Y-ligament. This explains the usual position of the limb with the line of the femur crossing that of the opposite thigh a little above the knee and the great toe resting upon the instep of FIG. 395. the sound foot. Flexion of the thigh is maintained partly by the tension on the ilio-psoas. The muscles have a very minor part in the production or maintenance of the characteristic deformity. The external rotators, the glutei and the pectineus, are often lacerated. There is shortening, and the trochanter is above the level of Nelaton's line. In the rare cases in which the Y- ligament or its outer limb is torn, outward luxation with neither adduc- tion nor inversion becomes possible. 2 . Inward or Anterior L uxations. These always occur with the thigh in abduction, and are favored by out- ward rotation, which carries the head towards the lower anterior part of the capsule. If it passes upward and rests on the body of the pubis, it constitutes the "pubic" luxation (Figs. 395, 396) ; if downward, it is in or opposite the thyroid foramen, and is often called an ' ' obturator' ' or " thyroid' ' luxa- tion (Figs. 397, 398). The ilio-femoral ligament again becomes the fulcrum ; the short arm of the lever has been carried inward, necessitating a corre- sponding outward movement of the long arm ; hence abduction is present. The exaggerated rotation outward is maintained by the tension of the liga- ment ; hence the eversion of the limb. Neither abduction nor eversion can be overcome, because the head is held firmly against the pubo-ischiatic pelvic plane. The gracilis, pectineus, and ad- dllCtOrS are apt tO be torn J the Stretch- Luxation of the head of the femur onto the pubis. ing of the ilio-psoas, the glutei, and the muscles inserted into the greater trochanter aids in maintaining both the flexion and the eversion. The ilio-tibial band of fascia will be found relaxed ; the trochanteric prominence disappears as the trochanter approaches the mid-line and is in a measure sunk in the socket. There will be shortening on measurement from the anterior superior spine to the condyle ; the head of the femur will be unduly prominent in the pubic variety. With the patient in dorsal decubitus, it will be evident that the acetabula are situated on a horizontal plane about midway between the pubes and the sacrum. From this level the pelvis slopes upward to the symphysis and downward to the 378 HUMAN ANATOMY. FIG. sacro-iliac junction. It is obvious that no anterior dislocation can be below the bi- acetabular line and no posterior dislocation can be above it. As the femur is about equal in length to the tibia and tarsus, if the head is in the socket the foot will be on the acetabular level when the thigh is vertical and the knee flexed. If the head is dislocated anteriorly, the foot will be on a higher level ; if posteriorly, the foot will be lower, and may even touch the surface on which the patient lies. There will be corresponding changes in the level of the knees (Allis). The femoral vessels are not often injured in hip luxations, because they lie above the joint and luxations are always primarily downward ; and because, as the head approaches them in the inward variety only, and as for the production of that variety abduction is necessary, the muscles beneath them the pectineus and ilio- psoas are put upon the stretch and the vessels are lifted out of harm's way. The relations of the sciatic nerve to these injuries are of great importance. The nerve is in close relation to the hamstring muscles, especially to the biceps. These structures are made tense and are stretched across the neck of the femur pos- teriorly by flexion of the thigh on the pelvis, espe- cially if the leg is also extended on the thigh, so that the origin and inser- tion of the hamstring mus- cles are separated. If, in a dislocation, the head of the femur originally lies on the anterior plane of the pelvis, and either by the force producing the dis- placement (as is commonly the case), by the action of muscles, or during efforts at reduction is made to pass to the posterior plane, it must traverse the narrow space between the sciatic nerve and hamstrings and the edge of the acetabu- lum. The nerve is thus very apt to be bruised and stretched and separated somewhat from the biceps tendon. Later, if replace- ment by " circumduction" is attempted, the head may pass beneath the nerve, which will then be tightly stretched over the front of the neck, will prevent full extension of the thigh, and will cause continued pain and disability. Other com- plications associated with the nerve may occur, and have been fully demonstrated by Allis, whose excellent experimental and clinical work forms the basis for the fore- going summary of the anatomy of hip luxations. In reduction of posterior dislocations by the method of circumduction the thigh, which is already flexed, adducted, and inverted by the agencies above described, is still furtheryfetrd' and adducted and lifted upward to relax the ilio-psoas and to bring the head of the bone near the margin of the acetabulum ; it is then abducted, tightening the inner band of the ligament, and crcrtcd, tightening the outer band and converting the femoral attachment of the whole ligament ( but chiefly of its outer limb) into a fulcrum around which, as a centre, the abduction and eversion being continued into circumduction, the head of the bone sweeps, skirting the lower edge of the acetalniliun, and finally, by extension of the thigh, re-entering Relation of the head of the femur to the innominate bone in pubic luxation. PRACTICAL CONSIDERATIONS: THE HIP-JOINT. 379 that cavity at the point where it emerged. The whole movement is made up of the successive steps of flexion, adduction, abduction, eversion, and extension. In reduction of anterior dislocations some of the steps of the procedure are reversed, i.e., the movement consists of flexion, abduction, adduction, inversion, and extension, in the order mentioned. The inner limb of the ligament is then of chief importance as a fulcrum. The objection to this method in both cases is the danger to the sciatic nerve, already pointed out, and also to the femoral vessels. Allis's methods of reduction are intended to avoid this danger. He endeavors to cause the head to retrace accurately the path by which it left the socket. In a posterior dislocation the head has usually left the FIG. 397. acetabulum in a down- ward direction, has fallen below the socket, and has passed outward around the edge of the acetabu- lum to its new position ; the limb has then fallen into partial extension by its own weight. Thus there are three steps, which, naming them in their reverse order, are : 3, extension ; 2, motion outward ; i, motion downward. The steps of his method are accord- ingly : i, flexion ; 2, ro- tation of the head inward (by carrying the leg out), placing it where it was immediately after leaving the acetabulum ; 3, lifting to bring the head to the level of the socket and extension (using the ilio-femoral ligament, which then be- comes tense, as a ful- crum, and aided by the upward pressure of the thumbs of an assistant), carrying the head up- ward into the socket. In the reduction of anterior dislocations the anatomical and mechani- cal principles involved are the same. In those dislocations the head has left the socket by tearing the capsule on its inner margin, and has passed inward to the pubo-ischiatic plane ; the limb representing the other end of an inflexible lever must move in the opposite direction, or outward ; and as it falls a little downward by its own weight, the head rises slightly. To restore it, reversing these steps, flex to a perpendicular, lowering the head somewhat ; make traction on the limb, drawing the head outward ; and then, the head being fixed by the hands of an assistant, adduct and extend the thigh, causing the head to enter the socket. By these methods reduction of dislocation complicated with fracture of the Luxation of the head of the femur into the obturator foramen. 380 HUMAN ANATOMY. FIG. 398. femur becomes possible because of the firm connection between (a) the base of the neck and the acetabulum through the unruptured portion of the capsule, and (6) the two fragments through the attachment of muscles along the linea aspera. These connections enable the limb to be used for traction, although the fracture quite precludes the employment of circumduction and rotation. Allis summarizes the principles of his method by saying that the cardinal rule applicable to every form of dislocation of the hip is : draw the head in the direction of the socket ; apply a fulcrum at the upper part of the lever ; pry the head into the socket. The old view that the opening in the capsule was often a slit which required enlargement before the head could be replaced has been shown (Allis and Morris) to be fallacious. The inelastic character of the capsular fibres, the globular shape of the femoral head, and the suddenness of application of the force (preventing stretching) make the rent in every case as large as the head ; it is not infrequently larger. If, however, it is situated near the femoral attachment of the capsule, it may leave a cuff of the latter hanging from its pelvic ori- gin over the acetabulum, and offering a serious, if not insuperable, obstacle to reduction. Congenital dislocation of the hip may be unilateral or bilateral, and while occasionally the result of intra- uterine traumatism, is usually due to an arrest of development of the ace- tabulum. The head rests on the dor- sum ilii, either directly upon the bone or on the gluteus minimus. The cap- sule is stretched and thickened to bear the weight of the trunk. The tro- chanters can be seen through the glutei ; they are above N61aton's line ; there is usually lumbar lordosis to compensate for the displacement pos- teriorly of the centre of gravity. The perineum is widened. Disease of the hip-joint is fre- quent and grave. It may begin in the epiphysis for the head, in the synovial membrane, or, much more rarely, in the articular cartilage. It may be of any variety, but tuberculous disease outnumbers all others. Both the frequency and the gravity of disease of the hip-joint are due to : i, the exceptional exposure of the joint to strains or traumatism on account of its im- portance in carrying the weight of the trunk and in progression ; 2, the intra- capsular situation of the upper femoral epiphysis ; 3, the relation of the joint to some of the most powerful muscles of the body, so that great intra-articular pressure- is easily set up and with difficulty overcome ; 4, its enclosure by dense, unyielding fibrous structures that increase tension after disease has begun ; 5, the thinness of the non-articular plate of bone that separates it from the pelvis, and the presence up to puberty of the Y-shaped cartilage which divides the acetabulum into three bony segments (Fig. 353) ; 6, its deep situation, rendering the early symptoms in many cases inconspicuous ; 7, the deprivation of fresh air and exercise, and often of sunlight, involved in the immobilization of the joint. The disease is attended by certain symptoms having a definite anatomical basis : i. Swelling, which is most easily demonstrated (a) at the lower anterior portion of the joint just internal to the ilio-femoral ligament, where the capsule is thin and the Relation of the head of the femur to the innominate bone in obturator luxation. PRACTICAL CONSIDERATIONS: THE HIP-JOINT. 381 joint is nearest the surface ; and (<) at the lower posterior part of the capsule, which is also thin. 2. Tenderness over these points, i.e. , beneath the middle of Pou- part's ligament and behind the trochanter. 3. Alteration in position, the femur being flexed, abducted, and everted. This puts the joint in the position of greatest comfort, which is that of its greatest capacity. In extension the head of the bone presses against the upper anterior portion of the capsule, and the Y-ligament is drawn as a dense band across the front of the joint. Flexion relaxes the superior or main portion of the Y-ligament and the ilio-psoas muscle ; abduction, the outer limb of the ligament and the ilio-tibial band of fascia lata ; eversion, the inner limb. Flexion is, in its effect on tension, the most effective of these motions ; eversion the least. The joint will now hold a larger quantity of fluid than when the limb is in extension. 4. At this stage, to bring the limb parallel with its fellow, to overcome the shortening caused by abduction, and to relieve strain, as the thigh cannot be moved on the pelvis, the lumbar spine is curved with the convexity towards the diseased side and the pelvis is tilted downward on that side. This is the stage of apparent lengthening. The real position of the limb in abduction is shown by straightening the pelvis so that a line drawn between the two anterior superior spines is at right angles to the longitudinal mid-line of the body. 5. With the same object of securing parallelism, i.e., of reducing strain upon the mus- cular and fibrous structures which are holding the limb in its abnormal position, the deformity caused by flexion (maintained by the ilio-psoas, which is in such close relation to the front of the capsule) is met by an arching forward lordosis of the lumbar spine. The real position of the limb in flexion is shown by raising the thigh of the affected side until the lumbar curve is effaced and the lumbar spines touch the surface on which the patient lies. 6. Pain in the knee is often marked. It is due to the association of the nerve-supply to the two joints, both being innervated from the same spinal segments, as they both receive twigs from the anterior crural, obturator, sciatic, and sacral plexus. 7. Rigidity of the joint is due to fixation by (a) the muscles inserted into and passing over the cap- sule ; () all the muscles moving the lower limb on the pelvis. Rotation is the most valuable movement for diagnostic purposes because it is least likely to be interfered with by extra-articular disease. For example, in abscess beneath the gluteus, or in enlargement of the subgluteal bursa, flexion of the thigh is interfered with ; in psoas or iliac abscess extension is limited ; in superficial disease of the upper end of the shaft, or in suppuration of the bursa over the trochanter, adhe- sions of the soft parts may limit both flexion and extension. 8. Muscular wasting is often a very early symptom, and is then due to reflex atrophy from the associa- tion emphasized long ago by Hilton of the nerves supplying a joint with those of the muscles moving that joint ; in this instance both joint and muscles are supplied by the anterior crural, the sciatic, the sacral plexus, the obturator, etc. Later, atrophy of muscles may be due to disuse. The glutei and the thigh muscles are those most obviously affected. The atrophy of the former aids in producing the characteristic obliteration of the gluteo-femoral crease. 9. After softening of the capsule and diminution of tension have occurred, the adductors draw the limb inward. The lumbar spine is now curved so that the concavity is towards the diseased side, thereby drawing up the pelvis on that side so as to relieve strain and secure parallelism of the limb. This is the stage of apparent shortening. The real position of the limb in adduction is shown by bringing the interspinous line to a right angle with the longitudinal axis of the body. The adductors are supplied almost exclusively by the obturator nerve, which enters largely into the supply of the articulation, and act to great advantage when the capsular and ligamentous resistance has partly disappeared. As the shaft and lower end of the femur move inward, the head is necessarily brought more forcibly against the outer fibres of the capsule near its pelvic attachment, and when they soften is partially projected from the acetabulum, against the upper and outer rim of which it rests. 10. During this stage the trochanter on the diseased side is often found to be nearer the middle line of the body than the other trochanter. The cause of this is either absorption of the head and neck of the femur or deepening of the acetabulum with sinking in of the head, and the diagnosis between these may be made by rectal examina- 382 HUMAN ANATOMY. tion, which sometimes shows thickening over the inner surface of the acetabulum in the latter case and not in the former (Cheyne). In dislocation from disease, unless there has been separation of the head or great absorption of the neck, the tro- chanter will be farther away from the middle line on the affected side than on the sound one. This will serve to distinguish shortening of the limb due to this cause from shortening due to acetabular deepening. Abscesses developing within the joint may pass outward through the thin posterior part of the capsule, and under the gluteal muscles, to a point beneath the greater trochanter ; they may make their exit through the cotyloid notch and point in Scarpa's triangle ; they frequently pass out anteriorly, and are found beneath the tensor vaginae femoris at the outer aspect of the thigh ; they may perforate the acetabulum and point within the pelvis. A finger in the rectum may then detect fluctuation through the structures that separate the abscess from the rectal wall, viz. , the anal fascia, the levator ani, the obturator fascia and obturator internus, and the periosteum of the inner surface of the innominate bone. After perforation of the acetabulum, an abscess may extend upward and point above Poupart's ligament on the inner side of the vessels. Excision of the hip may be done either by means of an anterior incision passing between the tensor vaginae and sartorius muscles superficially and the glutei and rectus more deeply, or by a posterior incision in the line of the limb and just back of the greater trochanter, the muscles attached to which being divided as close to the bone as possible. THE FRAMEWORK OF THE LEG. This is formed by the tibia and the fibula and the intero^seous membrane (Fig. 411). The bones are so closely united as to constitute one apparatus, but as they are separable it is necessary to describe them apart. The tibia, very much the larger, is the only one concerned in forming the knee-joint, and bears almost the whole weight. It forms the upper and inner side of the mortise known as the ankle-joint. The fibula, placed externally and posteriorly, is a slender bone. The upper end has a true joint with the tibia, the lower is more closely fastened to it. The interosseous membrane is at the bottom of a hollow between the bones. The arrangement favors lightness, as it gives increased size for the origin of muscles. The joints of the fibula, as well as its elasticity, serve to break shocks. THE TIBIA. The tibia consists of a shaft, an upper and a lower extremity. The upper extremity, or head, composed of an outer and an inner tubcrosity, is very large, expanding laterally from the shaft. The outline of the upper surface is transversely oval, the inner end being the broader. It is chiefly occupied l>y two articular surfaces for the condyles of the femur, separated at the middle by a promi- nence, the spine, 1 with a triangular non-articular surface before and behind it. The former of these is rough, the latter smooth and grooved. The spine itself is com- posed of two lateral parts connected behind, of which the inner is the longer from before backward, rising from the condylar surfaces. The crucial ligaments of the knee-joint are attached to the non-articular surfaces before and behind it. The inner condylar facet is concave ; it has an oval outline and is longer from before backward than transversely. It rises as a ridge on the side of the spine. The outer facet is more nearly circular, being shorter than the inner. It is slightly depressed in the middle. The posterior half is usually a little convex from before backward, and is often prolonged onto the posterior surface of the bone. The convexity is much greater when the semilunar cartilage is intact. The front half may be plane, convex, or concave in the same direction. This facet rises to a point on the outer side of the spine. The tuberosities 2 overhang the back of the tibia. They are separated behind by the popliteal notch* continuous with the groove from the top. Under the back of the outer tuberosity is a small articular facet for the head of the fibula, looking downward and a little backward and outward. Its outline is uncer- tain, being either round or quadrilateral. It may be curved in any direction, and 1 Eminentia iutercondyloidcu. -Comlylus hitcialis i-l nu-ili.ilis. " Fnss;i intvroiimlyloiilcii imstrrior. THE TIBIA. 383 its inclination varies much. In some cases it nearly or quite reaches the superior articular surface. Laterally, this tuberosity is rough for the ligaments of the knee- joint. The same may be said of the side of the inner tuberosity, which towards the back has a broad horizontal groove running along it for the tendon of the semi- membranosus. The tubercle 1 of the tibia is a triangular prominence on the front of the upper end. Its lower part is rough for the tendon of the extensor quadriceps, and its upper smooth for a bursa between this tendon and the bone. The top of the tubercle is about an inch below the top of the bone ; it is lost below in the ridge of the front of the shaft. The shaft 2 has three borders and three surfaces. The anterior border, the crest 3 begins at the outer side of the tubercle, curves as it descends, at first a little inward, then a little the other way through the middle of the shaft, where it is very sharp, and, finally, at the lower third, becoming much less prominent, it sweeps to the front of the inner malleohis. The inner border, the least marked of the three, begins under the inner tuberosity near the back and goes to the back of the inner malleohis. It is most distinct in the middle. The older border, or interosscous ridge,* begins below the facet for the head of the fibula, runs downward and somewhat backward past the middle of the shaft, and then, inclining forward, divides some two or three inches above the lower end into two lines enclosing a space on the outer side of the lower end, to which the fibula is bound by ligaments. The anterior of these divisions is the more evident continuation of the ridge. The internal surface is subcutaneous : generally convex above and concave below ; the outer, bounded behind by the in- terosseous ridge, is at first external, but in the lower third twists to the front. The Posterior, in its upper and lower parts, faces also somewhat outward. It is crossed in the upper third by the oblique linef which, running downward and inward from the back of the fibular facet to the inner border, marks off a triangular space above it which is occupied by the popliteus muscle. A vertical line, generally very faint, running down for some distance from the oblique line partially divides this sur- face into an inner broader and an outer narrower part : the former for the flexor of the toes, the latter for the tibialis posticus. The nutrient foramen, the largest in the body, is on this surface at the junction of the first and second thirds external to the oblique line ; it runs down into the bone. The shaft is triangular on section in the upper and middle thirds, being narrower and sharper in front in the middle one. In the lower third the section becomes quadrilateral as the shaft broadens and the anterior border sinks and turns inward. The lower extremity is thickest transversely. The internal matteolus* is a thick projection downward and inward from the whole of the inner side, to form one boundary of the ankle. Its lower end is thick, reaching farthest down in front, with a depression at the back for the lateral ligament of the ankle. The surface looking towards the joint is articular ; it slants a little away from the median line of the bone. The outer side of the lower end of the shaft is slightly concave, with a tubercle both before and behind. The articular cartilage of the lower end is pro- longed some two or three millimetres onto this outer side. Both in front and behind, but especially in front, the bone presents a swelling, separated by a depression from the lower border, above which the capsule is inserted. On the posterior surface a broad groove for the tendons of the tibialis posticus and the flexor longus digitorum runs obliquely downward and inward onto and along the hind border of the mal- leolus. A faint groove for the flexor longus hallucis is sometimes seen near the outer end of the posterior surface. The lower side forms the top of the ankle- joint and is wholly articular. It is broader before than behind, as the sides converge towards the back. It is concave from before backward. There is a slight antero- posterior elevation in the middle, fitting into a depression on the top of the as- tragalus. Variations. The transverse axes of the knee- and ankle-joints are rarely parallel. The shaft of the tibia is so twisted as to make the foot point outward. The angle between the two axes varies from o to 48, but is usually between 5 and 20. The backward inclination of the top of the tibia varies considerably. When excessive, it seems to imply an aptitude for the squatting position, as among the natives of India, but no inability to assume the upright position. A continuation 1 Tuberositas tibiae. " Corpus tibiae. 3 Crista anterior. 4 Crista interossea. ' Linea poplitea. '' Malleolus medialis. HUMAN ANATOMY. FIG. 399. Spine Ext. condylar surface ,- ._ Int. condylar surface Tubercle- Bursal surface For ligamentum- patellas ' 1 Biceps Ext. long.- digitorum Tibialis anticust ) Internal surface (subcuta- neous) Tendon patella (extensor quadriceps) -Gracilis -Senritendinosus Anterior border- or crest -Internal border External or inter- - osseous border For MtncmhuInternaJ malleolus Riglit tibia from before. Tlie outline figure shows the areas of muscular attachment. THE TIBIA. 385 FIG. 400. Int. condylar surface Spine Internal tuberosity Groove for seminiembranosus Semimembranosus- Popliteus Soleus (tibial head) \ Flex. long, digitorum Soleus (tibial head) Tibialis posttcus Popliteal notch Ext. condylar surface External tuberosity Articular surface for fibula Popliteus Oblique line Groove for tibial. post, andyfc.r. long, digit Internal malleolus 1 - Nutrient foramen Posterior surface External (interosseous) border Posterior division of interosseous border Tibio-fibular ligament Groove ior flex, long. hall. astragalus Right tibia from behind. The outline figure shows the areas of muscular attachment. 386 HUMAN ANATOMY. of the lower articular cartilage onto the front of the tibia, allowing extreme dorsal flexion of the ankle, is often associated with this. The thickness of the tibia is FIG. 401. Spine Ext. fibro-cartilage ,\ Post, crucial ligament Int. fibro-cartilage Ext. condylar surface Ext. fibro-cartilage Anterior crucial ligament Int. condylar surface Int. fibro-cartilage ft Bursal surface Attachment of tendon patella? Upper end of right tibia from above and before. very variable. The very thin, platycnemic^ form is most common in savage races, and is therefore associated with the pilastered femur. It is found not rarely among FIG. 402. FIG. 403. Frontal section of upper end of tibia. Frontal section of lower end of tibia. whites, but the shape of the accompanying femur is uncertain. The tibia/ iinic.i (transverse diameter X ioo\ .1 . r . . j- amero-posterio, a,;,,,,,,,, ) ls tlu> r;ltl of tlu ' transverse t> tlu- antcM-o-postcrior (liameter. PRACTICAL CONSIDERATIONS : THE TIBIA. 387 According to French statistics, this in whites is from 70 to 80 ; in* savage races it is much lower. The method of reckoning it at the level of the nutrient foramen is likely to be superseded by one choosing the middle of the bone. Structure. The shaft has strong walls in the middle, being especially thick under the crest. At both ends the walls become thin. The head contains a large amount of cancellated tissue with comparatively thin walls. The architectural arrange- ment of the trabeculae at the ends is very clear. A frontal section of the upper end shows successive vertical plates springing from the sides to support the expanding tuberosities, with an irregular system in the middle. Sagittal sections show plates from the walls meeting each other in arches. A somewhat similar pattern is seen at the lower end. In a frontal section there are several transverse plates, of which the strongest marks the border of the epiphysis. Several of these from the outer side turn down to join the lower surface at the origin of the malleolus, where there is a distinct thickening of the crust. There is sometimes an imperfect bony canal for the nutrient artery for a short distance after its entrance into the cancellated tissue. Development. There are only three centres of ossification : one for the shaft, appearing in the seventh or eighth foetal week ; one for the upper end, appear- ing usually in the last month of foetal life ; and one in the lower, appearing in the second half-year. 1 These epiphyses correspond to what has been described as the FIG. 404. Ossification of tibia and fibula. A, at eighth foetal month ; S, at birth ; C, at two and one-half years ; >, at four years ; E, at about fifteen years, a, centre for shafts ; &, for upper epiphysis of tibia ; c, for lower epiphysis of fibula ; d, for lower epiphysis of tibia ; e, for upper epiphysis of fibula ; f, for tubercle of tibia. ends of the bone. The upper extends farthest down on the front, including the tubercle, which may have a separate nucleus. According to Rambaud and Renault, this is of usual occurrence, appearing at from eight to fourteen years and quickly joining the epiphysis. The lower end joins the shaft at about eighteen and the upper at nineteen or twenty. PRACTICAL CONSIDERATIONS. The upper epiphysis of the tibia is separated only by traumatism of marked severity because of : (i) its great width; (2) its irregularly cupped surface; (3) the downward projection in which the tibial tubercle is developed, or to which the latter becomes united when it arises from a separate centre ; (4) the protection afforded it (#) on the outer side by the head of the fibula (which is connected exclusively with this epiphysis), the anterior and posterior upper tibio-fibular liga- ments, and indirectly by the external lateral ligament ; () on the inner side by the internal lateral ligament, and (e^> on both sides by the fibres of insertion of the 1 Fagerlund : loc. cit. 3 88 HUMAN ANATOMY. FIG. 405. vasti and semimefnbranosus and of their fascial expansions ; (5) the toughness of the periosteum uniting it with the diaphysis ; and (6) the fact that while there is no possibility of its displacement by muscular action, it does not project enough to be exposed to the effects of direct violence. The possibility of disjunction of this epiphysis complicating an injury to the knee continues up to the twentieth year at least ; in injuries to the elbow epiphyseal separation may be excluded after the eighteenth year. Three-fourths of the recorded cases have occurred in males, as might be expected on account of their more frequent exposure to serious injury. The epiphysis has been displaced forward, and outward and forward. It has never been displaced backward, partly, at least, on account of the tongue-like process con- necting it with the tibial tubercle. Its inward displacement would necessitate the separation of the head of the fibula or the laceration of the superior tibio-fibular ligaments. The attachment of the syno- vial membrane of the knee-joint does not descend to the level of this epiphysis ; hence that articulation is often not involved in these injuries. They should not, when severe, be mistaken for dislocation, or, when slight, for sprains of the knee. They may be distinguished from the former by the age of the patient and the unimpaired mobility of the knee, and from the latter by the situation of the pain or tenderness. Dislocation of the knee is very rare in children. Good union has taken place in some cases ; arrest of growth has followed in others, as might be expected from the fact that the chief increase in length of the tibia takes place from this epiphysis. The tubercle of the tibia has been detached in ten recorded instances, all males : nine from violent action of the quadriceps in powerful young men, eight of whom were between sixteen and eighteen years of age, the age of the remaining two not having been mentioned (Poland). This separation should be carefully distinguished from frac- ture of the patella. In disjunction the latter bone is drawn upward, the patient is unable to extend the leg, and the swell- ing following laceration of the subligamentous bursa may simu- late swelling of the knee-joint. The latter may be involved directly as the synovial membrane is in close proximity to the tubercle or indirectly, through the occasional, though rare, communication with the subligamentous bursa. Fracture of the patella, however, does not occur in children and is very rare in adolescence. In patella fracture the fragments of bone are brought together, so that crepitus may be felt only by pushing the two fragments towards each other; the groove between them can almost always be recognized. In disjunction of the tubercle crepitus can be elicited only by pulling the fragment downward ; the outline of the patella is normal, and can usually be made out. The X-rays would be conclusive. Bony union should be expected. The shaft of the tibia gradually decreases in size to about the junction of the middle and lower thirds, and then expands again to the ankle. At its smallest point on an average about ten centimetres (four inches) above its lower end it has to bear a greater weight on a smaller area than any other bone (Humphry). At this level meet the two independent vertical columns into which, according to Fayel and Duret, the spongy tissue of the tibia is divided (one occupying the upper two-thirds, the other the lower third of the bone), and hence these authorities assert that this spot represents the minimum of resistance (Treves). In some tibiae it is at or near the junction of an ill-defined long upper curve, in which the crest terminates, and a short lower curve. On transverse section the tibia is seen to be cylindrical in its lower third and three-sided above. As it has been demon- strated that if two homogeneous solids present on section equal areas, the one Epiphyseal lines of tibia. PRACTICAL CONSIDERATIONS: THE TIBIA. 389 FIG. 406. triangular and the other circular, the former has the greater power of resistance (Tillaux), the shape of the tibia in this region is thought to be an additional source of weakness. For all these reasons it is the most frequent seat of fracture from indirect vio- lence. As in such cases the breaking strain is usually continued for a moment after the tibia gives way, the weak fibula is apt to be broken also. The line of fracture usually runs from its level on the crest upward and backward, and under the action of the calf muscles and the weight t of the body the sharp lower end of the upper fragment frequently protrudes, making the fracture compound. Fracture at about the same level from direct violence is also very common on account of the exposed position of the bone, and all fractures are apt to be com- pound as a result of the large proportionate area of the bone which is subcutaneous. Fracture of the shaft at the upper end involving the knee-joint is rare, and is usually from either direct violence or a fall from a considerable height, "com- pression fracture." Fracture of the lower end of the shaft involving the ankle-joint is a not infrequent complication of Pott's fracture. Separation of the lower epiphysis is nearly three times as fre- quent as that of the upper. It is caused usually by a considerable degree of violence, and in fifty per cent, of recorded cases has been associated with fracture of the lower end of the fibula or separation of the fibular epiphysis, in which case the displacement is often outward ; usually it is backward. It may be mistaken for dislocation of the ankle. In patients from eleven to seventeen years of age disjunction of the epiph- ysis is more frequent than dislocation ; as the malleolus and the foot go backward with the epiphysis, the inner malleolus preserves its normal relation to the foot, but not to the leg or outer ankle. In dislocation the reverse is the case. The ankle-joint usually escapes, as both anteriorly and pos- teriorly the synovial membrane is below the epiphyseal line. The synovial pouch of the lower tibio-fibular joint that extends upward between these two bones is in close relation to that line, but is sepa- rated by the periosteum which is continuous over the epiphysis, and thus also escapes injury. Arrest of growth is not common, but has occurred, and severe ankle sprains in the young should be treated with especial care on account of the possibility of involvement of the epiphyseal joint and later disease or deformity. Disease of the tibia, if infectious, is most common in the neigh- borhood of its two epiphyses and at the junction of the middle and lower thirds. The region is a favorable one for ' ' juxta-epiphyseal sprain," in which the violence is expended on the spongy tissue of the diaphysis near the epiphyseal line. " Many of the pains called ' growing pains' are due to juxta-epiphyseal sprain or injury. Such a sprain is often nothing but the first degree of an epiphyseal separation, in the same way that an articular sprain is nothing but the first degree of dislocation' ' (Poland). The usual causes strain, traumatism, cold, etc. influence the localization of tuberculous disease in or near the epiphyses. If recognized early, and if the infected focus is removed by operation, the knee- and ankle-joints will usually escape. In the later stages the products of liquefaction may find their way from the upper epiphyseal line to the knee-joint, either directly through the intervening half-inch of bone or by way of the tibio-fibular joint, which is in close relation to the epiphysis (Fig. 425), and then to the subpopliteus bursa, which always communicates with the knee-joint and often with both ; or they may gain the surface of the tibia and extend upward beneath the periosteum. If the lower epiphysis is involved a similar direct or indirect infection of the ankle-joint may occur, the tibio-fibular synovial pouch being sometimes first involved. Lines of fracture of tibia and fibula. 390 HUMAN ANATOMY. Post-typhoidal periostitis and osteitis of the tibia are exceedingly common, an,d affect particularly the subcutaneous area of the bone near the lower third, where there are no muscular attachments. They are probably due, therefore, to slight traumatisms. This same area is peculiarly subject not only to this form of infection and, as has been said, to fracture, but also to tuberculosis (when the epiphyses are spared), to syphilitic nodes and gummata, to softening and deformity from rickets, and to sepsis spreading inward from cutaneous inflammations and ulcers. It is probably so vulnerable by reason of t its exposure to frequent slight injury and to strain disproportionate to its size and strength (vide supra), and because of its dependent position and its distance from the main source of the blood-supply of the bone (the nutrient artery entering it at its upper third), both of which circumstances favor passive hyperaemia and the localization of infection. Sarcoma, in accordance with the general rule already mentioned (page 366), affects chiefly the upper third of the tibia. Landmarks. On the inner side of the knee the internal tuberosity of the tibia is in close relation in extension with the internal condyle of the femur, the two making a uniform rounded prominence. The interval between them can be felt but not seen. If the leg is flexed and the ankle rested upon the opposite knee, the tibial tuberosity becomes visible and lies in advance of the inner condyle. The prominence of the outer tuberosity is distinctly to be seen and felt on the antero- external aspect of the limb about 2.5 centimetres (one inch) below the joint-line. It represents the lowest level of the synovial membrane. Into it is inserted, about half-way between the tip of the patella and the head of the fibula, the important ilio-tibial band of fascia to which illusion has been made in reference to fracture of the neck of the femur and dislocation of the hip (page 377). The posterior edge of the head of the tibia is not accessible to direct examina- tion, and this is true of the external and posterior surfaces throughout. The internal border can be traced from the tuberosity to the malleolus. The antero-internal surface, which is subcutaneous throughout, can be seen and felt. The anterior border or crest constitutes the prominence of the "shin." It is sharp in the upper two-thirds and fades into the shaft at the summit of the lower third. In well-marked tibiae it presents a distinct double curve, the upper part of which has its concavity outward. The tubercle is easily felt and seen. It should be in line with the ligamentum patellae and a point on the front of the ankle mid- way between the malleoli. It is about on a level with the head of the fibula. The inner malleolus is twelve millimetres (half an inch) above and in front of the outer malleolus, but on the same plane posteriorly. Its lower border is rounded. The notch for the internal lateral ligament can be felt. Its tip is twelve millimetres below the joint-line. Its sharp posterior border forms the inner boundary of the groove for the tibialis posticus tendon. THE FIBULA. The fibula is a long, slender bone with a knob-like upper end and a pointed lower one. The upper extremity, called the head, 1 has a rounded or vaguely quadri- lateral articular surface above, looking upward, a little inward and forward, to meet the corresponding one on the tibia. The styloid process, 2 a short prominence, juts upward from its outer posterior angle. The outer part of the head is rough. An ill-marked neck below it is indistinguishable from the shaft. The shaft ' is best described as having four borders, separating four sic Us, though one of the borders joins another near the lower end. The borders, proceeding in regular order round the bone from the front, are (i) the antero-external, (2) the postero-external, (3) the postero-internal, sometimes called the oblique ridge, and (4) the antero-internal or interosseous. The antero-c.vlrnni/ border begins faintly on the front of the shaft, a little below the neck, and becomes very prominent as it descends, twisting slightly outward. In the last quarter it splits into two lines which run to the front and back of the outer malleolus, enclosing a triangular subcutaneous space. The postero-external bonier begins on the outer side of the neck below the styloid 1 Cnpitulum fibulae. "Apex capitull tihuluc. ''Corpus fibulae. THE FIBULA. 39i FIG. 407. Styloid process FIG. 408. Styloid process Head Biceps Biceps Soleus Flex. long, hallucis External malleolus Groove for tendons External malleolus Right fibula from before. Right fibula from behind. The outline figures show the areas of muscular attachment. 392 HUMAN ANATOMY. Tibial facet FIG. 409. -Styloid process Head Neck Anterior surface - Antero-internal border Antero-external border Internal surface^ Posterior surface 'Soieus Tibialis! posticus .Postero-external border -Postero-internal border \ ] }Flex. long, hallucii Inferior interosseous ligament Facet for astragalus j -Fossa ^Ext. lateral ligament Right fibula, inner aspect. The outline figure shows the areas of muscular attachment. PRACTICAL CONSIDERATIONS: THE FIBULA. 393 process. It is strongest at and below the middle of the bone. It twists backward and is lost at the back of the malleolus. The postero-internal border begins at the inner side of the back of the head. It is very strong at about the middle. It ends in the last quarter by joining the interosseous ridge. The latter, or antero-internal border, begins poorly marked at the inner side of the neck, soon becomes sharp, and descends rather straighter than the others to some three inches above the lower end, where it divides into two lines which, ending at the borders of the articular facet for the astragalus, enclose a rough space for ligaments. The interosseous membrane, being attached to this ridge, separates the front of the bone from the back. The anterior surface, between this and the antero-external border, is very narrow. It forms a part of a hollow, of which the membrane is the floor, from which certain extensor muscles arise. The external surface, between the antero-external and the postero-external borders, is a characteristic one, presenting for more than the lower half a shallow groove for the peroneus longus and brevis, which sweeps down to the back of the malleolus behind the subcutaneous space enclosed by the splitting of the antero-external border. The posterior siirface is bounded by the postero- external border and by the postero-internal till that border joins the interosseous ridge, which bounds the surface in its lower part. It faces backward above and inward below. The nutrient foramen, running downward, enters it rather above the middle, usually near the postero-internal border. A roughness on the outer part of this surface is for the origin of the soleus. The internal surface, relatively broad in the greater part of its course, looks inward to the hollow between the two bones. It ends in the last quarter where the oblique ridge joins the interosseous one. The lower extremity of the fibula is pointed, forming the outer malleolus, 1 which projects downward and a little outward. Its outer surface is a continuation of the subcutaneous triangle, and the greatest prominence near its back is in line with the posterior of the borders of the space. Most of the internal surface is occupied by a triangular articular facet for the astragalus, the upper part of which is nearly vertical, while the lower slants outward. Below and behind this, on the inner side of the greatest projection, is a deep hollow for part of the external lateral ligament. The malleolus is broader behind than in front, presenting a groove in continuation of the external surface for the peroneal tendons. Development. The centre for the shaft appears in the eighth fcetal week ; that for the head of the bone, which, according to the usual order of long bones, should develop next, does not come till after that of the malleolus. The latter ap- pears in the second year, the former two or three years later. The lower epiphysis is probably fused with the shaft by eighteen or nineteen and the upper by twenty. PRACTICAL CONSIDERATIONS. The upper epiphysis has a flat lower surface and is about on a level with the most prominent part of the tibial tubercle. It includes, therefore, all that portion of the head of the fibula into which the biceps tendon and external lateral ligament are inserted. Its line of cartilage at and after the thirteenth year is in close relation with the synovial membrane of the tibio-fibular joint. Its disjunction is favored by its situation on the most exposed aspect of the limb, its subcutaneous position, and the insertion into it of the biceps muscle. The attachment of the external lateral ligament also enables a powerful strain to be brought upon it in over-adduction of the leg. In spite of these favorable circumstances, the protection afforded by the slight overhang of the external tubefbsity of the tibia and the fixation given by the strong anterior and posterior upper tibio-fibular ligaments make separation of this epiphysis a very rare occurrence. Boyd says that several cases are known in which it has been pulled off by violent contraction of the biceps in an effort to prevent falling. It is then felt as an easily recognizable fragment the space between which and the diaphysis is increased upon extension of the leg. Fracture of the shaft of the fibula in its upper two-thirds occurs from direct violence and as a secondary result of fracture of the tibia. In spite of the slender- ness of the bone and its position on the outer aspect of the leg, fracture is not very frequent because of {a) its elasticity, which is marked ; () its protective covering 1 Malleolus lateralis. 394 HUMAN ANATOMY. of muscles and fascia ; and (V) its backward curvature, which carries it to a plane posterior to that of the tibia, which thus protects it both internally and anteriorly from direct violence. Fractures about the middle of the lower third of the shaft, and especially those about 7.5 centimetres (three inches) from the ankle, are so commonly produced by leverage that, whatever their exact level, most of them may be grouped as instances of Pott's fracture, although an effort has been made to draw between them distinc- tions that are ordinarily academic rather than practical. These fractures usually result from over-abduction of the foot. When that occurs suddenly, the weight of the body being upon the limb, the tension first comes upon the deltoid ligament. This may stretch slightly or some of its fibres may be torn, or there may be a small detachment from its malleolar origin. As a rule, such a case ends in a more or less severe sprain. If the ligament ruptures, or the tip of the malleolus is torn off, or the malleolus itself is fractured, the abduction of the foot continues, and the astragalus is subluxated and carried against the inner surface of the external malleolus. The fibula is thus converted into a lever of the first order. The force is applied at its lower end ; the fulcrum consists of the stout tibio-fibular ligaments, which are often stronger than the bone itself and which are rarely com- pletely ruptured, though often stretched and lacerated ; the weight or resistance is in the body of the bone, which is prevented from moving inward by the articulation of its Opper end with the tibia. As soon, therefore, as its limit of elasticity is ex- ceeded, it breaks at a weak (if not its weakest) point, and the upper end of the lever i.e. , of the lower fragment is forced in the direction opposite to that of the lower end, i.e., the malleolus (Fig. 410). The impact of the astragalus and the pull of the ligaments may cause, in addition to the fracture of the tip of the malleolus, fracture of the anterior or of the outer articular edge of the tibia. If the tibio- fibular ligaments rupture, the fibula becomes a lever of the second order, the fulcrum shifting to its upper end. The dislocation of the astragalus outward will be more marked. The bone may break at any point, but the fracture is still likely to be within the limits of the lower third. Rose and Carless have adopted the following useful classification based on the injury to the inner side of the foot or to the tibia itself. It divides these fractures into four groups, the term Pott's fracture being correctly applied, according to these authors, to the first two only. i. The internal lateral ligament is torn through ; the intact internal malleolus can be felt projecting beneath the skin (Fig. 410, A). 2. The malleolus is torn off and a distinct sulcus can be felt between it and the lower end of the tibial shaft (Fig. 410, B). 3. The interosseous tibio-fibular ligament is ruptured (or the flake of bone at the tibial attachment is torn off) ; the subluxation outward is very marked ; either the inner malleolus or the deltoid ligament yields, " Dupuytren's fracture" (Fig. 410, C). 4. The tibia fractures transversely just above the base of the malleolus ; the lower end of the upper fragment may be mis- taken for the tip of the malleolus (Fig. 410, Z>). The less frequent accident of forcible over-inversion of the foot, if the external lateral ligament holds, produces by the same mechanism a similar series of occur- rences. The tip of the external malleolus is dragged violently inward, the tibio- fibular ligaments act again as a fulcrum, and the bone is apt to break at about the same level, i.e. , from 5 to 7.5 centimetres (two to three inches) above the joint, the upper end of the lower fragment being carried outward instead of inward. In these cases there is a subluxation of the astragalus inward which not infrequently results in a fracture of the inner malleolus. In all these forms of fracture the lacera- tion of ligamentous structures loosening the connection of the foot to the leg, the upward pull of the calf muscles, and the weight of the foot itself combine to produce a subluxation of the foot backward which is often overlooked. The cardinal symptoms of the common form of Pott's fracture are eversion of the foot, prominence of the inner malleolus, shortening of the distance from the front of the ankle to the web of the great toe, increased width between the malleoli, and tenderness over (a) the space between the til>i;i and the external malleolus anteriorly, i.e., over the strained or torn tibio-fibular ligaments ; (6) over the base or tij> or anterior border of the internal malleolus, i.e., over a ruptured internal lateral PRACTICAL CONSIDERATIONS: THE FIBULA. 395 ligament or a fracture of the malleolus ; and ( l;iUr;ilis. THE KNEE-JOINT. 403 posterior horn, moreover, joins the posterior crucial ligament. There is not more than one centimetre between the two horns, so that this cartilage is almost circular. The internal cartilage l is C-shaped. The anterior horn, thin and fibrous, is in- serted into the rough surface near the anterior border at no very definite point. Sometimes it runs into the transverse ligament without any fixed ending ; some- times the extreme point is free. The posterior horn is attached to the back of the tibial facet of the spine and to the edge of the articular facet behind it. The FIG. 418. Femur Inner head of gastrocnemius Popliteus tendon and opening into joint Long external lateral ligament Tendon of biceps Head of fibula Extensor tendon Subrectal bursa Superficial band to patella Ligamentum patellae Anterior tibio-fibular ligament Right knee-joint, external aspect. The extensor tendon is drawn forward and upward. distance between the horns is about three centimetres. The anterior horn of the internal cartilage may not come into contact with the femur. The vertical diameter of the cartilages at the periphery is from six to eight millimetres. The breadth varies in different joints, ranging from one to nearly two centimetres. 2 The broadest part is near the back of the internal one, but the external is, on the whole, the broader. It is said sometimes to completely divide that half of the joint. The free border is very thin and may present fine prolongations with scalloped edges. 2 For various statistics, consult Higgins : Journal of Anatomy and Physiology, vol. xxix., 1895- 1 Meniscus medialis 404 HUMAN ANATOMY. The lower surfaces of the disks adapt themselves to the top of the tibia, the outer cartilage concealing the convexity at the back of the tuberosity. The upper surfaces form cups to receive the femoral condyles. At the sides of the spine, where the cartilages are wanting, the cups are completed by the upward slope of the tuber- osities. The coronary ligaments (Fig. 420) are parts of the capsule connecting the periphery of the semilunar cartilages with the tibia. They are of little strength and allow more or less motion. Those of the external cartilage are more than two cen- timetres long at the front and 1.3 centimetres at the back, while those of the internal are from four to five millimetres. Thus the external cartilage can move very freely on the tibia, both from the length of these ligaments and from the approximation of its horns, while the internal can move but little. This has an important influence FIG. 419. Shaft of femur P$ Capsule I Alar ligament Anterior crucial ligament External semilunar cartilage -Tendon of popliteus Capsule reflected Bursa of tendon of semimembranosus Anterior wall of right knee-joint seen from behind, the lower end of the femur having been removed. on the mechanics of the joint. The popliteus muscle is attached to the outer, which is significant in the same connection. The transverse ligament ' (Fig. 420) is a band, usually ill-defined and often quite wanting, which connects the cartilages at the front of the knee, running from the convexity of the outer to near the anterior cornu of the inner and sometimes into it. It is closely attached to the capsule in front. The crucial ligaments * (Figs. 419, 420) are two broad, thick bands, the strong- est in the joint. The anterior arises from the depression in front of the spine of the tibia, close to the external semilunar cartilage, and runs upward, backward, and outward to the back of the inner side of the outer condyle. The posterior, the stronger, arises from the back of the groove at the posterior aspect of the top of the bone, and from its outer border, leaving the floor of the groove and the transverse piece of the spine of the tibia free and covered by synovial membrane. It is also closely connected with the external semilunar cartilage. It runs forward, upward, and a little inward to the front of the outer side of the inner condyle and of the 1 l.i transvcrsum uunu. '-' l.iu:mimt,-i cruclata gcnu. THE KNEE-JOINT. 405 intercondylar notch. The fibres from the external semilunar cartilage run along it in a varying position, but usually as a well-defined bundle. When the joint is straight the surface of the anterior ligament looks approximately forward and up- ward, its line of insertion being about vertical ; when it is fully flexed the outer edge is brought forward so that the ligament is somewhat twisted on itself and the upper part looks inward, the line of insertion slanting slightly downward and back- ward. In the former position the posterior crucial has the anterior surface looking outward, forward, and downward, the line of insertion being horizontal, with the front external. With the knee flexed the ligament is closely applied to the internal condyle. The Subpatellar Fat, the Ligamentum Mucosum, and the Ligamenta Alaria (Figs. 419, 423). If the joint be opened by dividing the capsule just above FIG. 420. Patellar surface Capsule reflected External condyle Ant. crucial ligament Ext. semilunar cartilage Transverse ligament 1 Coronary ligament Edge of superior surface of tibia Capsule reflected Post crucial ligament Internal condyle Internal semilunar cartilage Coronary ligament Bursa beneath ligamentum patellae Tuberosity of tibia Right knee-joint, opened and the knee flexed. Seen from before. the patella, or, better, by splitting the patella and turning one-half to either side, a large mass of fat is seen inside the capsule, below the patella and above the front and top of the tibia, covered by the synovial membrane. This mass has a definite shape, though, of course, subject to change by pressure. It is perhaps best described as pyramidal, the base being towards the surface between the knee-pan and the tibia. When the knee is straight it fills the patellar surface of the femur and laterally passes 'under the condyles, filling the space between them and the tibia. It reaches to the semilunar cartilages. Towards the joint it has two free angles, a larger one below entering between the bones as just described and a smaller one above. The lateral halves, including the synovial covering, are called the alar ligaments l (Figs. 419, 423). From the middle of this mass below the patella runs a collection of fat with areolar and elastic tissue, invested by synovial membrane, to the top of the inter- condylar notch. This is the ligamentum mucosum, 2 of little strength and not absolute constancy, which acts as a guy, preventing the mass of fat from falling away from the femur. There are also collections of fat about the crucial ligaments and at the back of the joint between the posterior crucial and the capsule. The synovial membrane lines the capsule in a general way, but is separated 1 Plicae alares. - Plica synovialis patellae. 406 HUMAN ANATOMY. from it by the masses of fat just described. It surrounds the lower halves of the crucial ligaments with the fat in a common envelope, so that there is in nature no interval between them. There is but a small chink between the upper halves, though each has its separate sheath. The back of the posterior crucial is partly un- covered by synovial membrane. Synovial fringes formed by the membrane and more or less underlying tissue project from the folds of the alar ligaments, from the ligamentum mucosum, and from near the borders of the patella. Bursae. ( i ) The most important is a large one under the extensor tendons, just above the capsule, with which it usually communicates. It probably in most cases develops independently of the capsule, which then lies in front of its lowest FIG. 421. Posterior surface of femur Gastrocnemius-, Back of capsule Internal condyle Post, crucial ligament Int. semilunar cartilage Tibia Gastrocnemius Insertion of anterior crucial ligament External condyle Ext. semilunar cartilage Tendon of popliteus Tendon of biceps Fibula Frontal frozen section of right knee-joint passing through condyles and behind shaft of femur. Seen from behind. The superior tibio-hbular joint is opened. part, a communication forming subsequently. Such a communication almost always exists in the adult, less frequently in the infant. The opening may be small and well defined or so large that the cavities of the joint and bursa give no sign of subdivision. This carries the cavity of the joint any part of three finger-breadths above the knee-pan. It is possible that sometimes there is a communication from the beginning. (2) Prepatellar bursce are found on the front of the patella at different depths. Directly below the skin is the superficial fascia, often lamel- lated and adherent to the layer beneath it. According to Bize, 1 (#) a bursa is present in this superficial layer, usually over the lower half of the patella, in eighty- eight per cent, of knees examined. The next layer is an aponeurotic one continu- ous with the fascia lata, beneath which (<) a bursa is found in ninety-five per cent., most commonly at the inner inferior part. A still deeper (c} bursa occurs beneath 1 Journal de 1'Anat. et de la Phys., 1896. THE KNEE-JOINT. 407 the fibrous layers from the tendon of the quadriceps over the lower part of the bone in eighty per cent. (3) A large and constant bursa lies on the smooth anterior surface of the tubercle of the tibia beneath the ligamentum patellae, which is inserted into the lower part. It extends upward to about the level of the top of the tibia, from which it is separated by the fat below the knee. It practically never communi- cates with the knee-joint. As the tendon before it is inserted obliquely, descend- ing lower on the outer side, the shape of the bursa is roughly triangular. The greatest diameter is the transverse one at the top, the outer border is not quite so long, and the inner about half the length of the outer. The breadth is from 3 to 4 centimetres, the outer border from 2.5 to 4, and the inner from 1.5 to 2.5 centi- metres. (4) A subcutaneous bursa is often found over the tuberosity of the tibia Posterior crucial ligament Anterior crucial ligament Capsule Internal semilunar cartilage Fascia lata Fascia lata External semilunar cartilage Capsule \ wMLiiiiiMiiiii'M'ai/aiii^^^u.'Ui.'^ii'^y ill' I'll/ i-.fttn ) Frontal section through middle of right knee-joint. Seen from hehind. and (5) another over the ligament of the patella. At the back of the knee there are several bursae. (6) The largest is that beneath the inner head of the gastrocne- mius (Fig. 426), which later in life often connects with the joint. It is usually prolonged between the gastrocnemius and the tendon of the semimembranosus. (7) A bursa is commonly found between the long lateral ligament and the tendon of the popliteus as it passes beneath it, and another between the ligament and the tendon of the biceps. The relations of the tendon of the popliteus muscle are so important as to re- quire a separate description. The muscular belly is usually separated from the back of the tibia, near the top, by a prolongation of the capsule between the tibia and the back of the external semilunar cartilage, which is described by some as a bursa com- municating with the joint. According to either view, there is a deficiency of the coronary ligament at this point. The muscle is connected beyond this with the outer side of the external semilunar cartilage. Passing above this, it becomes a part 408 HUMAN ANATOMY. of the capsule^ and on reaching its insertion it makes a more or less prominent pro- jection into the joint. There may or may not be a projection of the capsule like a bursa at the point where the two are .fused. On its way the tendon often sends some fibres to the posterior crucial. Movements. The motions between the femur and the patella will be consid- ered after those between the thigh and the leg. The knee cannot be a hinge-joint, for in such the moving part is always at the same distance from the axis of rotation, which is out of the question in the knee, owing to the shape of the condyles. The fact that these are neither of equal length nor parallel complicates the problem. The joints are further subdivided by the semilunar cartilages, which make a slight socket for each condyle. This socket is more or less movable and also compressible and elastic, so that it may change its shape to accommodate itself to the form of FIG. 423. Tendon of extensor quadriceps Capsule Post, crucial ligament Internal condyle Alar ligament Capsule Ligamentum mucosum External condyle Alar ligament Ligamentum patellae Tubercle of tibia Patella removed from right knee, which is strongly flexed to show alar ligaments and ligamentum mucosum. A probe is passed beneath the latter. different parts of the condyle. The external semilunar cartilage, having its horns securely attached near together and having a long coronary ligament, can swing backward and forward pretty freely as a whole. The internal cartilage is more closely fastened to the tibia, excepting the anterior horn, which has no constant arrangement. Not only can the semilunar cartilages change shape, but, as Braune has shown, the cartilage of the joint is capable of compression. For all these reasons accurate mathematical statements are impossible. In extension of the .leg on the thigh, beginning with the knee flexed, the tibia travels along the irregular curve of the condyles, carrying the semilunar cartilages with it. There is practically no movement between the internal cartilage and the tibia, unless at the end, and probably little beneath the external. The external tuberosity of the tibia reaches the front of the shorter condyle before the internal tuberosity has completed its course. The last part of the advance of the latter is accompanied by an outward rotation of the tibia on a vertical axis passing through about the middle of the outer condyle, so that while the inner tuberosity still swings PRACTICAL CONSIDERATIONS: THE KNEE-JOINT. 409 forward, the outer part of the external swings back. This motion occurs below the external semilunar cartilage. Flexion begins with a corresponding inverse rotation of the tibia. While the knee is straight the tibia is firmly fixed, so that in rotation of the limb at the hip the bones move as one. The long lateral ligament and that part of the capsule called the internal ligament are placed so far back that they are relaxed in flexion but become tense in extension. Both the crucial ligaments are always nearly tense, especially the posterior. The anterior is quite tense in exten- sion, the posterior in flexion. The latter prevents forward displacement of the femur on the tibia when, as in alighting from a leap, the whole weight is carried for- ward by the impetus, the knee being flexed. Another rotation on a vertical axis through the middle of the joint may occur when the knee is flexed. The motion is between the femur and the internal semilunar cartilage, and both above and below the external one. This motion is chiefly passive, i.e. , imparted by another person twisting the leg when the muscles are relaxed. It probably, however, can be exe- cuted actively to some extent. It is very slight in less than semiflexion of the knee, and diminishes as flexion becomes more extreme. The precise angle at which it is greatest seems uncertain. Rotation of the tibia outward, tending to untwist the crucial ligaments, is resisted by neither, but by the internal lateral ligament. Rota- tion inward is resisted by both crucials, especially the anterior, and by the external lateral. The posterior ligament is made tense in life in positions in which it would otherwise be lax by the action of the semimembranosus. It is tense in extension. The front part of the capsule is tense in flexion and relaxed in extension, but its condi- tion in the latter state is considerably modified by the degree of contraction of the quadriceps extensor. Movements of the Patella. The patella in the upright position, when the muscles are relaxed, has the lower part of the articular surface resting against the top of that of the femur. When the muscle is contracted the former is drawn entirely above the latter. As flexion begins the lower zone of the articular surface fits into the groove on the femur, the two upper and the internal strip not being in contact with it. In semiflexion the knee-pan has passed below the patellar surface of the femur, and the middle zone rests on the front of the outer condyle and on a small part of the inner. As flexion becomes extreme the patella follows the outer condyle, resting on its under side by its superior zone, the convex portion is in the notch, and only the strip along the inner edge is in contact with the outer side of the internal condyle. In the latter part of the movement the mucous ligament becomes tense, and through it, and still more by atmospheric pressure, the alar ligaments are brought close in to fill the chink between the femur and the tibia. PRACTICAL CONSIDERATIONS. The Knee-joint. The anatomical conditions which should render the knee- joint peculiarly subject to dislocation are as follows : i. Its situation between the longest bones of the skeleton and its consequent exposure to tremendous leverage. 2. Its similar exposure to frequent strain and traumatism. 3. The extensive and varied character of its movements. 4. The absence of bony prominences, which could effectively strengthen the joint, upon either the articular surface of the lower end of the femur or the shallow upper surface of the tibial tuberosities. The ability of the joint to resist dislocation, which is of very rare occurrence, lies in () the strength of the ligaments, especially the crucial ; () the expansions of the quadriceps tendon on the front of the joint ; (>) the reinforcement of the posterior ligament by the semimembranosus tendon ; (d) the similar relation of the internal lateral ligament to the semimembranosus, and of the external lateral to the tendons of the biceps and popliteus ; (e) the power thus conferred upon strong muscles to meet and modify or resist sudden strains by varying the tension of the capsule and even of the ligaments ; (/) the deepening of the tibial cup by the semi- lunar cartilages, and the adaptation of the latter to the varying positions of the bones so that the contact between and pressure upon the joint-surfaces are as extensive and as uniform as the shape of the condyles will permit. Dislocations of the knee may be antero-posterior or lateral in direction. The 410 HUMAN ANATOMY. former usually and the latter invariably are incomplete, owing to the large superficial areas of the joint-surfaces. In the great majority of cases dislocations of the knee are due to indirect violence acting through the femur as a lever, as, for example, in falls forward, the foot and leg being fixed. The weight of the trunk carrying the upper end of the thigh forward, brings the lower end with great power the fulcrum and the resistance, or weight, being so close to each other against the posterior ligament, a rupture of which permits the movement to continue and results in an anterior dislocation of the knee, which is, regarded from an etiological stand-point, a displacement of the femur backward. If the fall is in the opposite direction, the femur may be displaced anteriorly, i.e. , posterior dislocation of the knee may occur. Occasionally the anterior disloca- tion has followed the fall of a weight upon the front of the femur. The application of force to the front of the leg when the knee was flexed has produced a posterior dislocation, the effect of the biceps, popliteus, and semimembranosus in reinforcing the posterior ligament being minimized in that position. Lateral dislocations are caused by adduction or abduction of the leg, the thigh being fixed, or by falls sideways when the foot and leg are fixed. The great width FIG. 424. Vastus internus Patella -_^ , Lateral expansion of quadriceps tendon Tendon of adductor inagnus Tibia' v Internal condyle Tendon of sartorius Inner aspect of right knee-joint, showing expansion of quadriceps tendon. of the joint and the slight resistance offered by the interposition of the tibial spine between the femoral condyles render them rarer than antero-posterior luxations. Forward dislocation is more common, possibly because of the greater laxity of the capsule in front, and is more apt to be complete than the backward. The knee is extended ; the tibial tubercle prominent ; the antero-posterior diameter increased ; the anterior margin of the tibial tuberosities palpable in front ; the rounded condyles may be felt, but less distinctly posteriorly ; the popliteal concavity is obliterated ; the aponeurotic expansion of the quadriceps is loose and lies in folds about the upper border of the patella. The femoral vessels and nerves may be bruised, compressed, or lacerated. In backward dislocation also the knee is in extension and the antero-posterior diameter increased. The displaced bony prominences may be recognized by palpa- tion. This dislocation is even less apt to be complete than the forward variety : but if it is, the vessels and nerves are oftener injured, as shown by the more frequent occurrence of gangrene. This is probably due to the sharpness and prominence of the backward projection of the upper edge of the tibial tuberosities, as compared with the rounded depressed notch between the femoral condyles which receives the vessels in forward dislocation. In lateral dislocation, in accordance with the direction of the displacement, .PRACTICAL CONSIDERATIONS: THE KNEE-JOINT. 411 one or other condyle becomes prominent, as does, on the opposite aspect of the limb, the head of the fibula or the inner tuberosity of the tibia. The patella, owing to the shortness and strength of its ligament, is carried with the tibia. The lateral diameter of the joint is increased. The foot is apt to be rotated in the direction of the luxation owing to the tension of the biceps in the outward and of the popliteus and inner hamstrings in the inward variety. Dislocations by rotation have also occurred. FIG. 425. /// / Femur Internal semilunar cartilage Crucial ligaments External semilunar cartilage Cavity of knee-joint Superior tibio-fibular articulation Tibia . Fibula Frontal section through knee-joint, showing articulating surfaces and epiphyseal lines. In the various forms of luxation the crucial, the lateral, and the posterior liga- ments and the biceps and gastrocnemius muscles suffer most severely ; the popliteus and semimembranosus less so. They are often compound, and may for that reason necessitate amputation. The injury to the ligaments leaves the joint weak and insecure for a long time. Subluxation of the semilunar cartilages occurs usually when the leg is fixed, the knee slightly flexed, and the femur rotated upon the tibia, because the move- ments of flexion and extension take place between the femur and these cartilages, which, therefore, follow the motion of the tibia ; whereas in rotation the move- 4i2 HUMAN ANATOMY. meats then occurring between the tibia and the cartilages one of them is fixed between the corresponding condyle and the tibia which rotates beneath it ; the remaining cartilage, especially if the rotation is marked, may be dragged or squeezed so that it is nipped between the tibia and femur. Thus the contraction of the biceps which effects outward rotation of the leg brings more closely together the external tuberosity of the tibia and the external condyle, and the outer cartilage is held firmly between them. This increases slightly the distance between the internal condyle and the head of the tibia, leaving the internal cartilage freer to move into an abnormal position. When the popliteus, semitendinosus, and semimembranosus contract to rotate the leg inward, they, in like manner, fix the internal cartilage and allow of increased mobility of the external cartilage. Subluxation of the inner cartilage is the more frequent because (i) outward rotation of the leg is far more common than inward rotation ; (2) the muscle chiefly concerned in effecting inward rotation, the popliteus, when it contracts, steadies and supports the external cartilage by pressure against its outer margin (Morris) ; no corresponding support is given the internal cartilage during outward rotation ; (3) the anterior crucial ligament isattached somewhat in front of, and often directly to the inner cornu of the external cartilage, tending to limit its forward motion. It is altogether behind the internal cartilage ; (4) the external cartilage has a strong attachment to the femur through the ligament of Wrisberg posteriorly. The displacement is forward in the majority of cases. The symptoms are pain, from the pressure on the cartilage itself, increased by reflex spasm of the muscles moving the joint, and followed by a synovitis. The edge of the cartilage may often be felt. Disease of the knee-joint is of great frequency on account of its exposure to (a) direct violence and to cold and wet, by reason of its superficial position, and (6*) to strains and wrenches through the leverage of the femur and tibia. The factors competent to resist luxation are not able to protect it from minor injuries. It is a favorite seat, therefore, of traumatic synovitis, and on account also of its complexity, its large size, and the difficulty in keeping it at absolute rest disease, if acute, is apt to be severe and threatening ; if subacute, tends to become chronic or to recur. All the above reasons, combined with its inclusion of the lower femoral epiphysis and its close relation to the upper tibial epiphysis, the seats of the chief growth of the lower limb, make it also one of the joints most commonly subject to tuberculous disease, while gout, rheumatism, and syphilitic and gonococcic infection are often localized in it. Most of the chronic diseases due to infection, as well as those directly following traumatism, begin in the synovial membrane because of the large superficial expanse of that membrane. The intra-articular effusion whether "simple," from hyper- lemia, or inflammatory, from infection causes the knee to assume the position of moderate flexion because ( i ) its capacity is then greater than in full extension or full flexion, and maximum capacity is equivalent to minimum pressure ; (2) flexion, relaxes the densest and most resistant ligaments, the posterior and the lateral (as they are attached behind the centre of the bone) and (if moderate) the posterior crucial. It is resisted only by the ligamentum patellae, which is in less close rela- tion to the joint (being separated by the pad of fat on which it lies), and by the thinner and more extensible anterior portion of the capsule ; (3) the joint is inner- vated in accordance with the general law that the same nerves which supply the interior of an articulation supply also both the muscles moving it and the skin over the insertion of those muscles (Hilton). The knee-joint is acted on by ten muscles, four of which are extensors and six flexors. The latter are not only numerically in excess, but are also the more powerful and the more favorably situated for acting upon the joint. Therefore, when the articular twigs of the obturator, sciatic, and anterior crural nerves are irritated by disease, and both the anterior and posterior groups of muscles contract reflexly, the flexors predominate. The principle is of wide-spread application, and should be considered in reference to the position of most joints, at least in the early stages of disease. Later in knee-joint disease the softening and elongation of the ligaments permit the pull of the flexors to produce posterior displacement of the bones of the leg PRACTICAL CONSIDERATIONS: THE KNEE-JOINT. 413 upon the thigh. This is aided in dorsal decubitus by gravitation, which also favors the outward rotation of the leg that commonly occurs at the same time. The swelling of synovitis, whether acute or chronic, is limited, until the capsule gives way, by the attachments of the synovial membrane, that is, it extends upward beneath the rectus for from two to three finger-breadths or from four to five centi- metres (one and a half to two inches) above the summit of the patella ; laterally, it reaches the same level under the vastus internus, but is not quite so high on the other side, under the vastus externus. Downward, it descends to nearly the middle of the ligamentum patellae, attaining the same level on the inner side, but stopping FIG. 426. Tendon of extensor quadriceps . Suprapatellar bursa Cavity of joint -Patella External condyle Prepatellar bursa External lateral ligament Tendon of popliteus Popliteal bursa Head of fibula - External semilunar cartilage Ligamentum patellae Subpatellar bursa -Tubercle of tibia _ Tibia Rit, r ht knee-joint. The joint-cavity and several bursae have been distended with injection mass before dissection. (Spalteholz.) just above the head of the fibula on the outer side. The patella is separated from the trochlea of the femur " floated up." In testing for this symptom, it is impor- tant to grasp the anterior muscles of the thigh firmly and draw them towards the knee so as to relax the pull of the quadriceps, which is occasionally great enough to hold the patella in contact with the femur, even in the presence of considerable effusion (Fig. 426). The condition is usually unmistakable, but may have to be differentiated from periarticular abscess or haematoma. In the latter cases the swelling will not be uniform ; the inner depression at the side of the patella may be obliterated, and not HUMAN ANATOMY. FIG. 427. the outer, or vice versa ; fluctuation cannot be obtained in every direction, i.e., from side to side under the patella or obliquely ; the patella will lie directly upon the femur. The diagnosis from bursal enlargements will be considered in relation to those structures. Syphilitic disease of the gummatous type is apt to begin in the subcutaneous tissue without the joint, which it involves secondarily. In its earlier stages the swelling would therefore be periarticular, and recognizable by the foregoing symp- toms. Later, as it extends in both directions, there will usually be ulceration of the skin. The knee is more often the seat of the so-called loose bodies than is any other joint. They are sometimes the result of osteo-arthritis (which affects the knee by preference), causing thickening and fibrinous or calcareous change in some of the syno- vial fringes ; or they may be produced in those fringes from embryonic remnants, and are then composed of hyaline cartilage or nbro-cartilage ; or they may result from the organization of inflammatory lymph after an acute arthritis- ; or they may be portions of an interarticular or articular cartilage de- tached by violence, although this is rare. In a case of suppurative arthritis the incisions for drainage should be made on either side of the patella and a little below its middle, and should be placed towards the posterior aspect of the lateral pouches of the synovial membrane. Genu I'algum " knock-knee" in young children may be directly due to rickets, or may follow Charcot's disease, in- fantile paralysis, or any sprain or dislocation of the knee that leaves the internal lateral ligament weak or defective. In children and adolescents without these antecedents its essential cause is still a matter of dispute. There can be no doubt, however, that in the great majority of cases the production of the deformity is favored by static modi- fications of certain anatomical conditions which are probably the cause and not the result of the diaphyseal overgrowth of femur and tibia (Mikulicz), of the contrac- tion of the biceps and tensor vaginae femoris (Duchenne), of the elongation of the in- ternal lateral ligament (Stromeyer), and of the atrophy of the external condyle (Oilier) which are found in most cases of this de- formity, and each of which has been given etiological importance. The angle between the femoral and tibial axes (corresponding to that between the arm and forearm) opens outward at the knee. It results not, as in the upper extremity, from an outward obliquity of the lower segment of the limb, but from the inward slant of the thighs from the pelvis to the knees, the tibiae (like the humerus) being parallel to the longitudinal axis of the body and to each other. That the line of the knee-joint may be hori/oiital, the internal condyle of the femur is longer than the external. In a normal person standing erect in the military attitude of "atten- tion" the weight of the trunk is transmitted downward from the head of the femur in a vertical line which passes through the external condyle (Fig. 427). The erect position must therefore be maintained, not merely through the approximation of the Line of pressure between hip and knee. FIG. 428. PRACTICAL CONSIDERATIONS: THE KNEE-JOINT. 415 bones, as would be the case if the axis of the whole lower limb were a perpendicular running through the acetabulum and the centre of the ankle-joint, but by the help of muscular and ligamentous structures. The tendency (which is so common a factor in the production of deformities) to assume an attitude which will transfer strain from a tired muscle to the neighboring ligaments operates here to cause stretching and elongation of the internal lateral ligament, as the ' ' attitude of rest' ' with the feet separated and everted is the one usually adopted. The evil effects are, of course, favored by much standing, and are most marked in young persons of feeble physique whose weight has increased dis- proportionately to their muscular strength. The outer side of the knee shows the changes due to increased pressure and to long-continued approximation of musculo- tendinous points of origin and insertion, i.e., atrophy of the outer condyle and outer tuberosity ; contraction and shortening of the ilio-tibial band of fascia, of the external lateral ligament, of the tendon of the biceps, and of the tensor vaginae femoris. The inner side shows the effects of removal of normal pressure from grow- ing bones and of chronic strain of fibrous and periosteal tissue, i.e. , overgrowth of the femoral diaphysis just above the inner end of the epiphyseal line and of the tibial diaphysis just below the corresponding level ; lengthening of the internal lateral ligament ; bony outgrowth at its tibial insertion from chronic periostitis. The tibia is apt to be rotated outward, possibly through the action of the short- ened biceps. Talipes valgus (q.v. ) may be either a cause or a result of genu valgum. The disappearance of the deformity when the knees are flexed is probably due to the outward rotation of the femur that ac- companies flexion, and not, as is generally stated, to the fact that the antero-posterior diameter of the condyles is unaffected by the disease. The clinical symptoms and results and the treatment by apparatus cannot be described here. In Maceweri s osteotomy the femur is divided from the inner side of the thigh at a point twelve millimetres (half an inch) above the adductor tubercle and in a line at right angles to the long axis of the femur. Osteotomy may also be done from the outside of the thigh and at the same level. These opera- tions are usually safe, but the popliteal artery, the anastomotica magna, the external peroneal nerve, and other important struc- tures have been accidentally divided. Genu varum " bow-leg" is almost always rhachitic in its origin. A child with rickets and having lumbar lordosis of the spine stands with its thighs slightly flexed, either as a secondary result of the shortening of the ilio-femoral ligaments produced by backward rotation of the pelvis (to compensate for the for- ward rotation of the sacrum) or more simply as an easy method of relaxing the weak ilio-psoas muscles and preserving the centre of gravity. As the thighs flex the knees separate, the femurs rotate outward on their own axes, the line of gravity falls to the inside of the centre of the knee-joint (Fig. 428), the pressure is greatest on the inner condyle and tuberosity, the strain comes upon the external lateral ligament, and the outward bowing begins and is continued by the leverage of the body weight. Genu recurvattim " back-knee" is a deformity in which, as a result of intra- uterine malposition, or of congenital paralysis of the flexors and popliteus, or of pressure brought upon the posterior and crucial ligaments in walking in a case of partial paralysis of the quadriceps, the limb being swung forward, the heel coming to the ground in full extension, and the weight of the body reaching the joint in front of its centre of gravity, the knee is bent backward and the whole limb presents a long curve with its concavity forward. In excision of the knee the lines of the epiphysis should be remembered if the patient is under twenty or twenty-one years of age (page 365), the relation of the femoral vessels to the posterior ligament, the situation and extent of the synovial Showing the form of the bones in bow-legs. 416 HUMAN ANATOMY. pouches (which in infectious cases are usually involved), the direction of the articular line (with which the saw cut should be parallel), and sometimes the possibility of infection of the neighboring bursae. Landmarks. The synovial membrane rises from four to five centimetres (one and a half to two inches) above the upper border of the patella ; it is higher on the inner than on the outer side of the thigh ; its upper limit descends in flexion of the knee. The bony points have been described in connection with the femur and tibia (pages 367, 390) ; the bursae will be described later. The Patella. Congenital absence of the patella on one or both sides has been noted in a number of instances, and has in some cases been observed in several members of the same family. The functional disability was slight or altogether unnoticeable. Fracture by muscular action is more common in this bone than in any bone of the skeleton. It occurs usually with the leg in partial flexion upon the knee. In this position fracture is favored because (i) the ligamentum patellae is then taut and fixes the lower edge of the bone ; (2) the patella is in contact only through the upper third of its convex under surface with the most prominent part of the articu- lar surface of the condyles (Fig. 429); and (3) at this time the quadriceps extensor FIG. 429. Rectus muscle tella Subpatellar tissue Tendo patellae Tibia Femur Showing position of patella in relation to condyles of femur with knee partially flexed. has the greatest advantage of leverage upon the patella, as when the knee is fully bent the muscle gets its leverage for the beginning of extension through the projec- tion of the front of the condyles, and the patella lies on the pad of fat between the femur and tibia (Fig. 430), and when the knee is almost or quite extended, the patella or three-fourths of it occupies the depression of the trochlea, or even that just above it. As a result of the cross-strain brought to bear in the partially flexed position the bone usually breaks transversely a little below its mid-line, i.e., through the area unsupported by the femur beneath (Fig. 429). Occasionally it gives \\av at a higher level. The accident may happen as the result of a fall, but the fall is more apt to follow than to precede the fracture. In ordinary falls upon the knee the force is received upon the tubercle of the tibia, not upon the patella. Direct violence often causes an irregular, comminuted, or stellate fracture. Fracture never occurs in children and is extremely rare before adult lik-. When the bone is broken the fragments arc immediately separated by the action of the quadriceps upon the upper one. The degree of their separation will de- pend upon the amount of laceration of the lateral aponeurotic expansions of the conjoined tendon. Unless that fibrous structure is torn, no great separation of the fragments can occur, as it is inserted into the borders and front of the patella, PRACTICAL CONSIDERATIONS : THE PATELLA. which is thus embedded, as it were, in a hood spread out over the front of the joint and extending to the lateral ligaments and to the oblique lines running up from the tubercle to the tuberosities (Fig. 424). The force causing the fracture in cases of direct violence, or atmospheric pressure on the front of the knee if the fracture was from muscular action, drives in between the fragments, as they separate, in the shape of shreds or of an irregular fringe, portions of that part of the rectus tendon which was inserted into the longitudinal grooves or striae on the anterior surface of the bone. These offer an obstacle to bony union. As the synovial membrane of the knee-joint lies in contact with, and is attached to, the under surface of the patella, it will usually be lacerated, i.e. , the knee-joint will be opened and the fragments surrounded by bloody synovial fluid. The synovial membrane is re- flected from the patella some distance above the apex of the bone ; hence a fracture may occur at that level without involvement of the joint. The pad of fat on which FIG. 430. Patella Subpatellar tissue Showing position of patella in relation to condyles of femur with knee flexed at right angle. the tip of the bone rests, and over which the membrane is reflected, may aid in saving the joint from injury. The common failure to get bony union by non-operative methods is thus seen to be due to (i) separation of the fragments by the quadriceps, (2) the interposition of portions of the capsule, (3) the presence of blood-clot and synovial fluid, and is supposed to be further favored by (4) the sesamoid character of the bone inclining it to unite by fibrous rather than by bony tissue. It has been asserted, however (Wirth), that the patella is a detached portion of the upper tibial epiphysis and not a true sesamoid bone. As non-union is common on account of the above anatomical conditions, oper- ative measures are often resorted to. In the open operations used in old united fractures the fragments are drilled obliquely from a half-inch above and below the line of fracture to just above the cartilaginous under surface, so that the wire used to hold them together does not lie in the joint. 27 418 HUMAN ANATOMY. To approximate the fragments elevation of the limb sometimes suffices, but occasionally partial section of the lateral expansions of the quadriceps, of the rectus tendon, and of the muscle itself will be required as successive steps. In the best of the operations used in recent fractures, and which do not widely open the joint, a silk or silver ligature is carried through an incision at the lower border of the patella behind that bone and between it and the trochlear groove in the femur, is brought out through an incision at the upper border, rethreaded on a needle with an eye near the point, brought down in front of the patella, beneath the skin, and tied or twisted so as to hold the fragments together. The blood-clot and synovial exudate are squeezed out through the two incisions ; the entangled capsular fibres are removed by attrition of the fractured surfaces against each other. These operations are, of course, not applicable to old fractures in which shortening of the muscle has taken place and approximation and forcible rub- bing together of the fragments are impossible. Operations for recent fracture by open arthrotomy permit the direct removal of the fringe of interposed tendinous and capsular fibres and the repair by suture of the rents in the capsule and in the lateral expansions of the quadriceps. The patellar fragments may also be sutured, but this is not always necessary. Dislocation of the patella usually occurs from muscular action and as a conse- quence of sudden contraction of the quadriceps. The displacement is commonly in the outward direction because the long axis of the quadriceps muscle and tendon is inclined to that of the ligamentum patellae in such a way that the bone is situated at the apex of an obtuse angle which opens outward. When the quadriceps contracts the tendency is to straighten this angle, i.e., to carry the patella outward, and this, aided by the greater strength of the vastus externus as compared with that of the inner vastus, is more than suf- ficient to overcome the resistance offered by the greater prominence of the external condyle, as well as the relatively more extensive insertion of the vastus interims into the inner margin of the patella. The bone may even, as in one recorded case, be carried entirely past the condyle, so as to lie behind the centre of motion of the knee when the joint is bent, thus causing the quadriceps extensor to act as a flexor of the leg on the thigh. The external articular facet on the under surface of the patella is larger than the internal. The patella is in relation, therefore, chiefly with the external condyle, and even if dislocation occurs from direct violence, it is more likely to be driven in that direction (Humphry). If it has once passed beyond the edge of the outer condyle a "complete" luxation necessarily attended by laceration of the capsule it is less likely to be replaced than if it had gone in the opposite direction, because of (a) the resistance offered by the prominence of the condyle itself and () the greater comparative strength of the vastus externus. Outward luxation is not very rare in cases of genu valgum, and, per contra, in congenital cases of patella luxation and in unreduced traumatic luxations genu valgum has followed (Makins). The patella may be displaced inward by direct force. It is sometimes turned on edge by a force insufficient to dislocate it completely, and is held in that position by the tension of the soft parts attached to it and by the pressure of the over- lying fascia, "like a stick on end under a tightly stretched sheet" (Stimson). In flexion of the knee the patella lies deeply in the depression between the condyk-s and the quadriceps tendon is on the stretch. The bone is therefore somewhat removed from danger of direct violence, and is steadied and fixed by the quadri- ceps muscle. In extension the patella rests on the trochlear surface of the femur only by its lower margin ; it is more prominent and thus more exposed to force directly applied ; the quadriceps is relaxed, leaving the bone freely movable. For these reasons extension is the position in which dislocation most commonly occurs. THE TARSAL BONES. 419 THE FOOT. The framework of the foot consists of the tarsus, metatarsus, and. phalanges, which differ in their proportionate size from the corresponding divisions of the hand. Thus, in the latter the carpal region is the shortest and that of the phalanges the longest, equalling almost precisely the other two ; in the foot, on the contrary, the region of the phalanges is the shortest and that of the tarsus makes about half the entire length. The tarsus differs also in its arrangement more than the carpus from the primitive type. The tarsal bones may be considered as divided into two lateral divisions : an outer series of two bones bearing the two outer toes, and an inner series of five bearing the three inner toes, so placed that the proximal bone of the inner part rests on top of the proximal of the outer. The outer side of the skeleton of the foot rises but little from the ground, while the inner is highly arched. THE TARSAL BONES. The tarsal bones are the calcaneum, or os calcis, the heel-bone ; the cuboid, which with it forms the outer division ; the astragalus, or talus, which joins the leg ; the scaphoid, placed between the astragalus and the three cuneiform, which bear the three inner metatarsals. THE CALCANEUM. The calcaneum 1 is a narrow elongated bone forming the heel, supporting the astragalus, and joining the cuboid in front. It has six surfaces. The inferior sur- face presents at the back a swelling subdivided into the internal and external plan- tar tubercles, of which the former is much the larger, forming the posterior pier of the foot. These tubercles are continuous at the posterior border, in front of which a deep notch divides them. Each appears on its side of the bone. In front of these the lower surface, convex from side to side, is marked by longitudinal grooves. Near the front is the anterior tubercle, a small swelling, from which and from a depression near it arise calcaneo-cuboid ligaments. The posterior surface is roughly oval with the small end up. The tendo Achillis is attached to a roughness occupying its lower half, above which the bone slants forward and is smooth for a bursa between it and the tendon. The lower part of the posterior surface is con- tinuous with the plantar tubercles. The internal surface is smooth and concave ; for the internal tubercle projects strongly inward, while in front and above there is a shelf-like process, the sustentaculum tali, to support the head of the astragalus, slanting downward and forward. Beneath this is a slight groove for the tendon of the long flexor of the great toe. Lower down near the front border a depression for a ligament to the cuboid runs down in front of the anterior tubercle. The ex- ternal surface is the longest. It presents about its middle a vague tubercle for the middle bundle of the outer lateral ligament of the ankle, and nearer the front a larger one, the peroneal spine. When well marked this is a ridge, covered with cartilage, slanting downward and forward, separating two grooves for the tendons of the peroneus longus and brevis. The outer posterior plantar tubercle projects somewhat on this side. Rather more than the anterior two-thirds of the superior surface are devoted chiefly to the joints with the astragalus ; the posterior portion is convex from side to side and concave from before backward. There are two articular facets : the posterior facet, the larger, a vaguely four-sided swelling, occu- pies the middle of this surface. Its long axis runs forward, downward, and out- ward. It is convex in this direction. The upper inner end is the broader, and near it the facet is very often concave at right angles to the long axis, but in the main it is about plane in that direction and may be even slightly convex. The anterior facet, long and narrow, concave from before backward, runs forward and outward, nearly parallel to the long axis of the former. It begins internally on the top of the sustentaculum and ends at the most anterior point of the bone. In about half the cases this surface is subdivided into two, and, as a rule, when it is not there is a 1 Calcanciis. 420 HUMAN ANATOMY. A FIG. 431. B Bones of right foot, dorsal aspect. A, outer series ; /?, inner series. THE CALCANEUM. 421 notch in the free border just at the end of the sustentaculum. Occasionally the facet in front of the interruption is rudimentary or wanting, in which case, instead of articular cartilage, merely synovial membrane is beneath the head of the astraga- lus. In 200 feet we have found the facet single in 95, divided in 94, and in n the front was wanting. The two chief facets (counting the anterior as one, even if sub- divided) are separated by a deep groove for the interosseous ligament to the astrag- alus. This gutter broadens in front into a rough depression, the sinus tarsi, for ligaments. At its outer part there is a tubercle for the origin of the extensor brevis digitorum. The anterior surface, turned somewhat inward, is wholly articular for the cuboid. It is three-sided with rounded angles. The longest diameter is from above downward and outward, nearly parallel with the inner border. The upper border is straight or convex, overhanging the joint at the inner side. The outer border slants a little inward as it descends. The surface is concave from above downward and convex transversely. Both these curves are most marked at FIG. 432. Cuboid Astragalus Sustentaculum tal Interosseous groov Sinus tarsi Peroneal spine Astragalus Internal tubercle For bursa i Tendo Achillis Right calcaneum from above. the upper inner angle, where they form almost a groove for the plantar process of the cuboid. The general effect is of a screw surface twisting upward and inward. The calcaneum articulates with two bones, the cuboid and the astragalus, and excep- tionally with the scaphoid, to which it may be united by cartilage. Variations. The hind end of the sustentaculum is very rarely a separate piece : os sustentaculi proprium. The inner edge of the front of the bone, which normally comes very near to the scaphoid, may meet it. Sometimes the two bones are fused. The calcaneum secundarium is a small ossicle rarely present on the dorsum between the calcaneum, the cuboid, the scaphoid, and the head of the astragalus. Fusion of the calcaneum and astragalus has been observed at the sus- tentaculum. Structure. The walls are thin, the cancellated tissue filling the bone, with a tendency to the formation of large spaces at the middle. The architectural arrange- ment is very clear in an antero-posterior section, which shows diverging plates from 422 HUMAN ANATOMY. the greater articular facet for the astragalus and a system of loops connecting them. The large spaces are at the neutral point. FIG. 433- Longitudinal section of calcaneum, showing; arrangement of lamellae. Development. The chief nucleus is said to appear in the sixth month of foetal life. We have twice seen it earlier, once at about the fourth month. An epiphysis for the back of the bone and the posterior plantar tubercles appears from the seventh to the tenth year. It begins to fuse by fifteen, completing the process in a year or so. THE CUBOID. The cuboid ' is a six-sided bone, flattened from above downward, interposed between the calcaneum and the fourth and fifth metatarsal bones. It is important to remember that the dorsal surface faces almost as much outward as it does upward. The dorsal surface, slightly rough, has the following outline : an oblique posterior border against the calcaneum, which, though most often convex, may be concave, sinuous, or straight ; a short outer concave one ; an internal one, at first straight when against the scaphoid, and slanting outward when against the external cunei- form ; and an anterior one, slanting outward and backward. The plantar surface FIG. 434. External cuneiform Calcaneum lalcaneum Groove Promontory Right cuboid. For inf. calcaneo-cuboid ligament Promontory A, inner aspect ; B, posterior, outer, and inferior surfaces. has essentially the same shape, only the angle between the posterior and r borders is drawn out. Owing to the oblique position of the bone, this tits into the upper inner an^le >f the anterior surface of the calcaneum. Just below this angle is a prominence, the plantar tubercle. A thick, rounded, oblique ridgi-, the promon- tory or tnbnosity, starting at the back of the outer border, runs forward and inward across the bone behind a groove between it and the anterior border. The tendon of the peroneus longus lies on the smooth anterior slope of the promontory, the outer 1 IK cuboideuin. THE ASTRAGALUS. 423 part of which is coated with cartilage. The external surface of the bone is deeply notched. The internal surface is mostly rough, but presents at about the middle an articular facet for the external cuneiform, broad above, narrow below, and not usu- ally reaching the plantar surface. Commonly another smaller facet for the scaphoid is found behind this one, from which it is separated sometimes completely, but more often merely by a ridge, which makes no real interruption. The anterior surface, articular for the bases of two metatarsals, has an inner, an upper, and a lower border, the two latter meeting at a rounded angle externally. A faint vertical ridge, nearer the inner than the outer border, usually divides this facet into an inner oblong and an outer triangular part for the fourth and fifth bones. The curves of these articu- lations vary greatly : sometimes both parts are concave from above downward ; sometimes both are practically plane. The posterior surface, entirely articular, is the complement of the front of the os calcis. The cuboid articulates with the calcaneum, the external cuneiform, the fourth and fifth metatarsal bones, often with the scaphoid, and at times with the astragalus. Development. There is but one centre, appearing at about birth ; in our experience, more often after than before. For Secondary Cuboid, see Scaphoid. ASTRAGALUS, is a very irregular bone devoted almost wholly to THE The astragalus, ' or talus, articular surfaces. It is enclosed above by the socket of the leg bones. Its main part, or body, rests on the calcaneum, and presents in front a constricted neck bearing a rounded head, projecting forward and inward into the hollow on the back of the scaphoid. The upper surface presents a pulley-like articular facet covering the greater part of the bone, convex from before backward, slightly concave transversely, decidedly broader in front than behind. The cartilage covering it is continued down on either side to meet the articular surfaces of the malleoli. The inner border FIG. 435. Scaphoid FIG. 436. Head For calcaneo- aphoid lig. Calcaneum Internal tubercle External tubercle Groove for tendon of flex. long. hall. Right astragalus from above. Groove for flex, long. hall. External tubercle Right astragalus from below. of the upper articular surface is distinct, but generally not sharp ; the outer, which reaches higher, is better defined in the region just anterior to its middle, but behind on the dry bone it seems rounded. A very well-marked bone shows (what is very striking in the freshly opened joint) that this blunted edge is really a narrow tri- angular area belonging to the superior surface, broadest behind, made apparently by the pressure of the posterior tibio-fibular ligament from the external malleolus to 1 Talus. 424 HUMAN ANATOMY. the back of the tibia. A much smaller similar surface is found at the front, made by the corresponding anterior ligament. The direction of the anterior border of the articular surface is very uncertain. It usually projects forward at the outer end, the rest being either transverse, posteriorly concave, or oblique. Just anterior to it is a deep transverse hollow on the upper surface of the neck, which receives the edge of the tibia in extreme dorsal flexion of the foot. The posterior border of the articular surface is also of uncertain shape. Its inner end is usually somewhat farther back than the outer. Behind it two rough tubercles project backward, slanting down to FIG. 437. Sustentaculum For scaphoid For sustentaculum For ligament Calcaneum Astragalus Type of calcaneo-astragaloid joint with an undivided anterior articular facet on calcaneum. a posterior sharp edge. Between them is a deep groove for the tendon of the flexor longus hallucis, running obliquely downward and inward. The outer tubercle, which is much the larger, is sometimes separated by a suture from the rest of the bone, and is then known as the os trigonum. The inner tubercle may be barely distinguishable. This region behind the superior articular facet is sometimes de- scribed as the posterior surface of the bone. The external surface of the body shows the triangular facet for the outer malleolus, concave from above downward, FIG. 438. Synovial not cartilaginous Sustentaculum For scaphoid For internal cak-aneo- scaphoid ligament For sustentaculum Calcaneum Astragalus Type of calcaneo-astragaloid joint when anterior facet on calcaneum is not only divided but has front portion rudimentary. with the lower end projecting outward, plane or convex from before backward. This is bounded before and behind by a rough strip, with a hollow at the upper ends for the front and back bundles of the external ligament of the ankle. The internal surface has at the top a narrow curved facet for the inner malleolus, with a concave lower border, deepest in front and pointed behind. A part of the intrrnal lateral ligament is inserted into a hollow below it. The inferior surface of the body presents a four-sided facet, concave in the line of its long axis, which is oblique, corresponding to that of the greater surface on the top of the calcaneum. In front of and parallel to this is a di-rp groove for the interosseous ligament, expanding at the outer end into a triangular hollow on the under side of the neck. This is a THE SCAPHOID. 425 constricted portion, much broader transversely than vertically, connecting the head with the body. It often presents a groove along the upper and inner aspect near the articular surface of the head for the insertion of the ligament passing to the scaphoid. The head, which points forward and inward, is articular in front and below. The anterior surface, which fits into the hollow on the back of the scaph- oid, is vaguely oval, with its long axis running downward and inward. The upper edge, parallel with this, is nearly straight. The articular surface of the head ex- tends onto the under side, reaching to the deep groove separating the neck from the posterior facet for the calcaneum. On a fresh bone the cartilage shows the following facets, which are less well marked on a macerated one : a facet on the front of the head to fit into the scaphoid ; one on the lower and inner side to rest on the anterior articular facet of the top of the calcaneum ; one partly between these, which in the dried bones would be free, appearing between the sustentaculum and the scaphoid, but in life resting on the inferior calcaneo-scaphoid ligament, which is partly covered with cartilage and elsewhere with synovial membrane, forming a part of the socket. The cartilage on this surface is distinguished by its thinness. These facets are modified according to the arrangement of those on the calcaneum. If there be but one long anterior facet on both sustentaculum and on the end of the body of the calcaneum, the facet on the head for the anterior facet of the calcaneum reaches that for the concavity of the scaphoid in front, leaving internally a triangular interval between the two, occupied by the facet for the liga- ment (Fig. 437). In the other extreme (Fig. 438), where the anterior facet on the calcaneum does not reach beyond the sustentaculum, the area of the head rest- ing against the ligament completely separates the two others and plays on that part of the calcaneum where the anterior articular cartilage should be. Finally, when the anterior facet on the calcaneum is divided into two, the corresponding facet may be completely subdivided by an interruption of the cartilage, or in less marked forms there may be merely a ridge breaking the surface into two, but without sepa- ration ; such a ridge is often found even when the opposed articular surface is not divided. The lines, however, on the head of the astragalus do not strictly correspond to the boundaries of these surfaces. The astragalus articulates with four bones, the tibia, fibula, calcaneum, and scaphoid. Development. The nucleus probably appears at about the seventh month of fcetal life. When the os trigonum occurs, that implies another centre for the ex- ternal tubercle and the part of the articular surface under it. The deviation of the axis of the neck from that of the long axis of the bone varies considerably among individuals, but, nevertheless, changes during develop- ment. In the adult the angle varies from o to 24, the mean of forty-three bones being 12.32. In the foetus (presumably at term) the angle ranges from 17.5 to 45.5, the mean of twenty-two bones being 35-76 . 1 THE SCAPHOID. The scaphoid, 2 or navicular, may be compared to a disk, concave behind where it fits onto the head of the astragalus, convex in front where it rests on the three cuneiform bones. It is thinner at the outer end, where it touches the cuboid, than at the inner, where it presents the tuberosity. The superior, or dorsal, surface is long transversely. Its posterior border is regularly concave, the anterior slightly scalloped, presenting two small points projecting forward on either side of the mid- dle cuneiform. When in position the highest point on the scaphoid is behind that bone. The greater part of the dorsal surface slants downward on the inner side of the foot. The inferior, or plantar, surface is rough, and in the main transversely concave. The tuberosity at the inner border for the attachment of a part of the tibi- alis posticus muscle is a knob formed by the junction of the dorsal and plantar sur- faces, and projecting downward chiefly into the sole of the foot. The end of the knob is sometimes distinct from the scaphoid, and is known as the tibia le externum. 1 C. L. Scudder : Congenital Talipes Equino-Varus, Boston Med. and Surg. Journ., vol. ii., 1887. Parker and Shattock : The Pathology and Etiology of Congenital Club-Foot, London, 1884. 2 Os naviculare pcdis. 426 HUMAN ANATOMY. Its identity is quite evident in cases in which, though fused, it projects as a hook. It may be represented by the sesamoid bone in the tendon of the tibialis posticus. Near the outer end of the plantar surface there is almost always a slight projection by the side of the cuboid which may be very much developed, extending to near the notch in front of the sustentaculum of the calcaneum, in which case it is known as the secondary cuboid. The external surface is narrow and rough, resting against the cuboid, with which it articulates in about half the cases by a facet near the dor- sum, which rarely extends far towards the sole. 1 The posterior surface is con- cave, in the main oval and completely articular. Usually the regularity of the lower border is interrupted near the outer part by the external knob of the plantar surface. If this be much developed the shape of the posterior surface is changed from oval into quadrilateral, but it is always articular throughout. The anterior surface is slightly convex and entirely articular, except when the process just men- tioned is so large as to appear below it. The articular surface is divided into three FIG. 439. Dorsal surface FIG. 440. Dorsal surface For head of astragalus Right scaphoid from behind, proximal aspect. External Middle Internal Tuberosity cuneiform cuneiform cuneiform Right scaphoid from in front. facets, in the main triangular, corresponding to the outline of the bases of the three cuneiform bones. The character of these facets is not constant : the inner is usually convex and the outer concave. The scaphoid articulates with the astragalus, the three cuneiform bones, often with the cuboid, and exceptionally it touches or joins the calcaneum. The secondary cuboid, above alluded to, has but once been seen isolated, although we have met with one foot in which it seemed possible that it might have been distinct earlier. It is fused with either the cuboid or the scaphoid, but apparently much more frequently with the latter, in which it occupies the position above described, lying at the weak part of the inferior calcaneo-scaphoid ligament. Development. It is generally held that the process begins in the fourth or fifth year, but, according to Gegenbaur, it begins in the first. The tibiale externum exists as a separate cartilage at the second month of foetal life. Usually this fuses with the rest, but it may have a centre of its own. THE THREE CUNEIFORM BONES. These wedge-shaped bones, placed between the scaphoid and the three inner metatarsals, and abutting externally on the cuboid, form an important part of the transverse arch of the foot. The thin edge of the internal cuneiform, which is much the largest, points up, that of the others down. The middle cuneiform is the smallest and shortest, so that the second metatarsal bone lies in a mortise between the inner and outer. THE INTERNAL CUNEIFORM. The internal cuneiform, 2 besides the proximal and distal surfaces, has an internal, an external, and an inferior. The posterior, or proximal surface, rounded below and pointed above, is slightly concave and wholly articular. The anterior, or distal, surface, also articular, is kidney-shaped, with the notch in the outer border. The inner surface has a small ridge in its distal half, pointing upward, which is the 'I'tit/m-r: Morph. Arbritcn, Bel. vi., 1896. 2 cunciforine priniiim. THE CUNEIFORM BONES. 427 highest part of the bone, but almost the whole of this surface is on the inner side of the foot. Its outer border runs obliquely forward and outward with a sinuous course till it reaches the end of the middle cuneiform, when it turns forward. It has a short concave posterior border for the scaphoid and a long, nearly straight one for the first metatarsal bone. It passes without a sharp boundary into the lower surface. It is crossed by a faint groove, which exceptionally is deep, running obliquely downward and forward to a smooth swelling for a bursa under the tendon FIG. 441. FIG. 442. Dorsal Dorsal Mid. cuneiform Scaphoid Right internal cuneiform, outer aspect. Right internal cuneiform, inner aspect. of the tibialis anticus just before its insertion. The inferior surface, rough and round, has a tubercle near the proximal end for a part of the tibialis posticus. The external surface is mostly rough, with a smooth articular strip for the middle cuneiform following its upper and posterior border. The internal cuneiform articu- lates with the scaphoid, middle cuneiform, and first and second metatarsal bones. Development. A centre appears in the third year. Very exceptionally it is double, and the bone is divided by a suture into two, a dorsal and a plantar. THE MIDDLE CUNEIFORM. The middle cuneiform l has a sharp ridge below and an oblong surface above. The latter, or superior surface, is very little longer than broad. The lateral borders of this surface have an outward inclination. The inner of them corresponds to the proximal part of the outer border of the first cuneiform. The outer border, for its proximal two-thirds, rests against the external cuneiform, beyond which there is a small space between the bones. The proximal side of this surface is a little convex and the distal about straight. The posterior surface, wholly articular, FIG. 443. Scaphoid Right middle cuneiform. A, inner aspect ; B, outer aspect. is slightly concave. It is triangular, with the dorsal border rounded, the outer concave, and the inner straight or slightly convex. The anterior surface, ar- ticular for the second metatarsal, is narrower. It has a slight convexity in the upper part in a vertical plane. The internal surface has an articular facet corresponding to that on the internal cuneiform and a rough depression for an interosseous liga- ment. The external surface has a facet along the hind border, broader above than below, and rarely a small one at the front lower angle, both for the external 1 Os cuneifor me secundum. 428 HUMAN ANATOMY. cuneiform. The middle cuneiform articulates with the scaphoid, the internal and external cuneiforms, and the second metatarsal. Development. One centre appears in the fourth year. THE EXTERNAL CUNEIFORM. The external cuneiform, 1 seen from above, is much longer than broad, with a very oblique proximal border slanting outward and backward, an anterior border running less obliquely in the same direction, an inner one close against the middle bone in its proximal third or one-half, then receding from it and extending onto the outer side of the second metatarsal, and an outer border first running forward and outward against the cuboid, and then forward not quite against it, but overlapping the fourth metatarsal. The ridge constituting the inferior surface does not quite reach the proximal end. The posterior surface, wholly articular, is oblong, with the long axis vertical, and often a little convex. The anterior surface, articular for the third metatarsal, is triangular and about plane. Its inner border rises higher than the outer. The internal surface articulates with the second cuneiform bone by FIG. 444. Cuboid Fourth metatarsal Third metatarsal Right external cuneiform. A, inner aspect ; B, outer aspect. one or two corresponding facets, as the case may be, and has, in addition, a facet for the outer side of the base of the second metatarsal at the front upper angle, and often extending down the border ; or the middle portion may be wanting. In the middle of the surface is a roughness for the interosseous ligament. The external surface is chiefly rough, giving origin to an interosseous ligament for the cuboid ; at the upper proximal angle is a large facet for the same bone, and at the distal upper angle there may or may not be a small one for the side of the fourth meta- tarsal. The external cuneiform articulates with the scaphoid, the middle cuneiform, the cuboid, and the second, third, and fourth metatarsals. Development. Ossification begins in the first year. The Intercuneiform Bone. On the dorsum there is a little pit which we have called the intercuneiform fossa, situated between the proximal portions of the internal and middle cuneiform bones, usually more at the expense of the latter than of the former. We have at least twice seen a separate ossicle, the intercuneiform 6one,* in this fossa. The better specimen was wedge-shaped, its length exceeding one centimetre. It clearly was more intimately related to the middle than to the internal cuneiform. Pfitzner has since seen it fused with the former. THE METATARSAL BONES. Of these five bones 3 the first is very much the largest, although the shortest. The second is the longest, and the others of about equal length. The first metatarsal bone has a concave base corresponding to the facet on the internal cuneiform, which is prolonged down into a point (tuberosity} rather to the outer side, on the external aspect of which the prroneus longus is inserted into a round impression. On the inner side of the base is a small prominence for the tibialis anticus. A smooth facet for the second metatarsal is often found on the outer side. A groove for the capsular ligament more or less perfectly encircles the ? Anat. An/eiger, Bel. xx., 1902. 1 Os runcifonnv tcrtiuin. ; '0ssa mctatnrsalin 1-V. THE METATARSAL BONES. 429 base. The strong shaft has three sides : an internal, looking also upward, in the main convex ; an external, concave and nearly vertical ; and an inferior, or plantar, FIG. 445. Grooves for sesamoid bones Internal cuneiform External surface Plantar C Phalangeal surface Head Internal surface Inferior surface Tibialis anticus Impression of peroneus longus Tuberosity Internal cuneiform Right first metatarsal. A, proximal aspect ; B, plantar aspect ; C, dorsal aspect. also concave. The borders bounding the outer surface are the most distinct. One or two nutrient foramina enter this surface, running distally. The enlarged and Lateral ligament Ext. cuneiform Third metatarsal Mid. cuneiform Third metatarsal Ext. cuneiform Plantar Middle cuneiform External cuneiform Right second metatarsal. A, proximal aspect ; B, outer aspect ; C, inner aspect. rounded distal end, the head, is articular except at the sides, where it is flattened. The facet extends farther onto the plantar aspect, where it expands laterally. It 430 HUMAN ANATOMY. has there a median elevation, with a groove on either side for a sesamoid bone. There is a rough surface for ligaments on each side of the head. Middle cuneiform External cuneiform Plantar Fourth metatarsal Second inetatarsa External cuneiform Right third metatarsal. A, proximal aspect ; B, outer aspect ; C, inner aspect. The four outer metatarsal bones are distinguished by their bases. That of the second is concave at the end, and fits the middle cuneiform ; on the inner side a small facet at the top meets the outside of the first cuneiform ; on the outer side there are two, an upper and a lower, with a deep cut between each, resting FIG. 448. Cuboid Plantar Third metatarsal External cuneiform -Fifth metatarsal Cuboid iRht fourth metatarsal. .(, proximal aspect ; /,'. outer aspect ; (.'. inner aspect. Ligament on both the outer cuneiform and the third metatarsal. The occasional facet for the first metatarsal is on the shaft rather than on the end. It is often wanting on the THE METATARSAL BONES. 431 second when present on the first, implying the presence of a bursa rather than of a joint. The base of the third metatarsal fits the outer cuneiform, and is nearly plane. The posterior upper border, seen from the dorsum, is oblique, running Dorsal Tuberosity Cuboid Plantar Fourth metatarsal Cuboi Tuberosity Cuboid Right fifth metatarsal. A, distal aspect ; B, dorsal aspect ; C, plantar aspect. outward and backward. The inner surface has two facets for the second, and the outer surface one at the top for the fourth metatarsal. The base of the fourth metatarsal is also oblique. It has an oblong facet for the cuboid, and a single internal one at the top for the third, FIG. 450. which is separated from the proximal end by a rough space for the insertion of an interosseous ligament from the tarsus. There is externally a triangular facet at the upper angle for the fifth. This last facet is bounded in front by a deep groove which receives the edge of the facet on the fifth. The fifth metatarsal has an even more oblique base, the inner two-thirds of which bear a facet for the cuboid. The outer part is prolonged as the tuberosity beyond the edge of the foot, overhanging the joint. The inner side has a facet for the fourth metatarsal bone. The shafts of the metatarsal bones are flattened lat- erally, but theoretically three-sided, like the first. The second has an external surface looking directly outward ; a superior one at the base, which twists so as to become in- ternal. This is separated from the former in the distal two- thirds of the shaft by a sharp ridge. The third side is internal at the base, but soon becomes inferior. The shaft of the third differs only slightly, the external surface looking some- what upward and there being more of a ridge below. In the fourth it seems as if the proximal part of the shaft had been bent outward on its axis, so that the outer side looks more upward and the other two are less twisted. In the fifth this process has gone farther ; the originally outer side is now the upper, separated by one border from the inner and by another from the inferior. This last border, now external, represents the one that was the inferior of the third metatarsal. The nutrient foramina of the four outer metatarsals are in the external surfaces, running upward. They are not very constant. Fifth metatarsal Cuboid Right fifth metatarsal, inner aspect. 432 HUMAN ANATOMY. FIG. 451. Os intermetatarseum The heads of the metatarsal bones are compressed, like the shafts, from side to side, and have each a pair of lateral tubercles at the dorsal aspect of the end of the shaft, separated by a groove from the articular surface. Lateral ligaments are attached both to the tubercles and the grooves. The ar- ticular surface is oblong, extending well onto the plantar side, where it ends in two lateral prolongations, of which the outer is the more prominent. A line connecting their ends would be oblique to the shaft, especially in the outer toes. Fusion of the outer cuneiform with its metatarsal occurs occasionally at the plantar aspect. It is probably con- genital. Pfitzner has seen it at seventeen and we at nineteen. Development. Centres for the shafts of the meta- tarsals appear towards the end of the third month of foetal life. A proximal epiphysis for the first and distal ones for the others appear in the third year, fusing at about seven- teen. Occasionally the metatarsals, especially the first, have an epiphysis at each end. Os Intermetatarseum. This is an occasional wedge-shaped bone found on the dorsal aspect of the foot, between the internal cuneiform and the first and second metatarsals. It may articulate with all three, or with any of them, or be attached to them by connective tissue. More often it is connected by bone with one of the three neighbors, especially with the internal cuneiform, of which it may seem to be a pro- cess (Fig. 451). It is found in some form once in ten feet (Pfitzner). THE PHALANGES. Intermetatarsal bone fused with right internal cuneiform. FIG. 452. Third, distal or ungual. phalanx Second, or middle, phalanx There are two for the great toe and three for each of the others. Although of very different proportions, they present the features which have been described for those of the hand, especially the shape of the articular sur- faces. The first phalanx of the great toe is about as long as that of the thumb and nearly twice as broad. There is a tubercle for muscular insertion at each side of the pal- mar aspect of the base. The terminal phalanx of the great toe is also very massive. The first, or proximal, pha- langes of the other toes diminish in length from within out- ward. Those of the second row are so short as to be almost cubical, although they are broader than thick. The terminal, or distal, phalanges are very rudimentary. Pfitzner 1 has shown that in about one-third of the cases the terminal phalanx of the little toe is fused with the middle one, even before birth. Presumably they never were distinct in the embryo. As he has found this condition in Egyptian mummies, certain very pessimistic views as to the degener- ation in store for the human foot are probably unwarranted. Sesamoid Bones. Those of the first metatarso-pha- langeal joint are large and constant ; those of the same joint in the other toes very rare. The least uncommon are those of the fifth toe, of which the inner sesamoid is found in 5.5 per cent, and the outer in 6.2 per cent. A sesamoid of the interphalangeal joint of the great toe is found in 50.6 per cent. (Pfitzner*). Development. The first nucleus to appear is that of the distal phalanx of the great toe at the end of the third fcetal month. Those of the other distal phalanges, except the fifth, come some two weeks later. The bones of the proximal row seem to ossify rather later than the 1 Arch, fur Anat. und Entwick., 1890. * Morph. Arbeiten, Bd. i. First, or proximal, phalanx Phalanges of right second toe, plantar surface. THE PHALANGES. 433 distal ones, but this order is not constant. According to Bade, 1 the middle phalanges have begun to ossify in the eighteenth week of foetal life, but we have found bone wanting considerably later. The process of ossification in the fourth and fifth toes is decidedly later than at the inner side of the foot. It does not begin in the middle phalanx of the fifth till near term, and we have sometimes seen no sign of it in the Ossification of bones of tHe foot. A, during sixth fcetal month; B, at eighth foetal month; C, at birth; Z>, during first year ; 7?, between three and four years ; f, at about fifteen years, a, for shaft of metatarsals ; 6, for cal- caneuin c, for proximal phalanges ; d, for distal phalanges ; e, for astragalus \f, for middle phalanges ; g, for cuboid ; h, for external cuneiform ; /, for heads of metatarsal bones and base of first proximal phalanx ; /, for base of first distal phalanx; k, for internal cuneiform ; /, for base of first metatarsal. fifth, and even in the fourth at birth. Proximal epiphyses appear from the fourth to the sixth year, and fuse at about sixteen. The terminal phalanges have distal caps like those of the hand. The fifth toe, according to Pfitzner, has the following pecu- liarities : the proximal epiphysis of the second phalanx and the centre for the shaft of the terminal one are wanting, the proximal epiphysis of the latter being greatly exaggerated. 1 Arch, fur Mik. Anat., Bd. lv., 1900. 28 434 HUMAN ANATOMY. FIG. 454. Abductor hallucis Internal tuberosity Flexor brevis digitorum Groove for tendon of flexor longus hallucis Sustentaculum tali Astragalus ) Scaphoid Tibialis posticus External cuneiform Middle cuneiform Internal cuneiform Tibialis anticus Peroneus longus First metatarsal Sesamoid bones Abductor and flexor brevis hallucis Adductores obliquus et transversus Flexor longus hallucis Postero-inferior surface of calcaneum Abductor minimi digiti External tuberosity Abductor ossis metatarsi quinti Accessorius (outer head) Inferior surface of calcaneum Flexor brevis hallucis Cuboid ridge Groove for pe roneu s longus Abductor ossis metataisi quinti Flexor brevis minimi dijftti Abductor obliquus hallucis Third plantar interosseus Second plantar interosseus First plantar interosseus Abductor brevis minimi digiti Third plantar interosseus Second plantar tnterosseus First plantar interosseus Flexor fi> >" I* digitoi inn Flexor longus digital urn Bones of right foot, plantar aspect. BONES OF THE FOOT. FIG. 455. Tendo Achillis Bursal surface Calcaneum Lateral articular surface for fibula. Groove for peroneus longits Groove for peroneus brevis Extensor brevis digit or um Groove for peroneus longus Peroneus brevis Peroneus tertius Fourth dorsal interosseus Extensor brevis digitorum Extensor longus digitorum Groove for flexor longus hallucis Superior articular surface of astragalus Lateral articular surface for tibia Cuboid Scaphoid External cuneiform Middle cuneiform Internal cuneiform First metatarsal First dorsal interosseus Extensor brevis hallucis Extensor longits hallucis Bones of right foot, dorsal aspect. 436 HUMAN ANATOMY. PRACTICAL CONSIDERATIONS. The union of the foot with the leg at a right angle, while necessitated by the erect attitude of man, makes it essential that the bones of the foot shall be so shaped and united that they may afford a basis for both support and propulsion, all pre- hensile function being sacrificed to those ends. Accordingly, we find the tarsus proportionately much larger, both it and the metatarsus stronger, and the pha- langes much smaller and less mobile than the corresponding parts of the hand. The strength of the foot and its comparative freedom from injury, in spite of its con- stant exposure to traumatisms of various grades of severity, are due to the arrange- ment of its component bones into the form of an arch, which is well adapted not only to sustain weight and to provide leverage for motion, but also to resist and distribute excessive force received, as in falls upon the feet. The posterior pillar of the arch, composed of the os calcis and the hinder portion of the astragalus, has but one joint the calcaneo-astragaloid with a very limited range of motion. The action of the calf muscles upon the heel is thus applied to the elevation of the hinder pillar with the least possible expenditure of force, as there are no unnecessary movements between their point of insertion and the ankle-joint. The anterior pillar beginning at the top of the astragalus the summit of the arch may be said to include practically most of the foot anterior to the ankle and to separate naturally into ( I ) a larger and stronger inner division consisting of the neck and head of the astragalus, the scaphoid, the three cuneiforms, and the three inner metatarsals ; and (2) a weaker and smaller outer division composed of the cuboid and the remaining metatarsals. The anterior pillar thus secures in the wide surface of the distal extremities of the metatarsal bones a broad basis of support ; its inner division carries most of the weight, and is enabled to do this by the thickness and strength of the metatarsal bone of the great toe and by the parallelism of the latter with the great toe ; its outer division bears less weight, but supports the inner division laterally and broadens the surface in contact with the ground. The normal foot thus rests directly upon the os calcis and the anterior extremities of the metatarsals, the outer side of the foot aiding more in preserving balance than in carrying weight. An imperfect transverse arch including the scaphoid, cuboid, and cuneiforms adds to the elasticity of the foot and aids the main arch in affording a pressure-free area for the plantar vessels and nerves. Both arches depend for their integrity not only upon the shape of the bones, but also upon the fasciae, ligaments and tendons, and to some extent upon the small plantar muscles. Still another transverse arch is formed by the bases of the metatarsal bones, and a third, but less distinct one, by their heads. Perhaps the most accurate conception of the foot mechanically is as a semi-dome (Ellis), the whole dome being completed in well-shaped feet when the inner borders are approximated. The epiphysis of the os calcis occupies the posterior rounded extremity of the bone, and has inserted into it the tendo Achillis. No positive clinical evidence of separation exists, but it is probable that the X-rays will show that in young persons lesions heretofore supposed to be fractures of the os calcis from muscular action are actually epiphyseal disjunctions. The epiphyses of the remaining bones of the foot have but little surgical interest. The first metatarsal, like that of the thumb, has its epiphysis at the proximal end, and to that extent resembles a phalanx. The other four metatarsals have their epiph- yses at the distal ends. All the phalangeal epiphyses are at the proximal ends. In the metatarso-phalangeal joints the synovial membrane is in close relation to the epiphyseal lines ; in the phalangeal joints it is not. A knowledge of these farts may occasionally be useful in cases of disease or injury limited to a particular bone. Fracture of the hones of the tarsus is rare, except as a result of crushing injuries or of falls from considerable heights. If the bones of the anterior pillar are broken, it is usually by direct violence, as the numerous joints and ligaments of this region render it so elastic, and so diffuse forces applied, as in jumps or falls, as effectually to PRACTICAL CONSIDERATIONS: THE FOOT BONES. 437 prevent fracture. The bones of the posterior pillar are broken in both ways. In falls the astragalus is apt to break about its neck, the weakest portion ; or if the foot is strongly dorsiflexed, the anterior articular edge of the tibia may act as a wedge and split it across. The os calcis may be broken between the astragalus and the ground, compression fracture ; or it may be broken behind the insertion of the inferior calcaneo-scaphoid ligament, the anterior arch being flattened by the fall, but the ligament resisting rupture. A few cases of fracture of the sustentaculum tali have been reported, the foot having been in forcible inversion, the lesser process (susten- taculum) being broken off against the edge of the astragalus. In each case this was followed by eversion and sinking of the inner border of the foot (valgus), the support given by the internal articulating surface to the astragalus having been removed. Of the metatarsal bones, the first, although the strongest, is most frequently broken because it carries so large a proportion of the body weight and because it receives an undue share of the violence in falls associated with eversion of the foot. The fifth comes next in frequency because of its exposed position on the outer side of the foot and the added violence in cases of inversion. Dislocation of separate bones, especially of the astragalus, is rare. It is always the result of the application of considerable crushing force, is usually associated with other injuries, and is influenced but little by anatomical factors. Disease of the bones of the foot, and especially tuberculous disease of the tarsus, is common because of : (i) the frequency of traumatism ; (2) the exposure to cold and damp and the scanty protection afforded by the superjacent tissues ; (3) the remoteness from the centre of circulation and the dependent position of the part, both favoring congestions ; (4) the preponderance of cancellous tissue in the bones ; and (5) the difficulty in securing perfect rest, especially after minor injuries, which are those most often followed by tuberculous osteitis. It affects most frequently those bones that bear most of the weight of the body, the os calcis, the head of the astragalus, and the base of the first metatarsal. It is more likely to remain localized when situated in the os calcis or in the hinder part of the astragalus ; in the anterior portions of the tarsus the number and complexity of the synovial cavities (often intercommunicating) tend to prolong and to spread the disease. In disease of the tarsal bones excepting the astragalus, to which no muscle is attached the tendon sheaths in the vicinity may be involved by direct extension from the periosteum. Any metatarsal bone may be involved in cases of ' ' perforating ulcer, ' ' the situa- tion of the latter being determined usually by the degree of pressure upon the sole in cases in which anaesthesia is already present ; hence the frequency with which the first metatarsal is involved in this disease. Excision of the separate bones has frequently been performed, especially of the astragalus and os calcis. Landmarks. On the inner side of the foot can be felt : (#) the ridge between the inner and posterior surfaces of the os calcis ; () the tubercle of the os calcis ; (r) the sustentaculum tali, one inch directly below the tip of the malleolus ; (d) from one- half to three-quarters of an inch in front of the latter the head of the astragalus, very noticeable in flat-foot ; (i%".' . FIG. 483. '' ' i Muscle-fibres of human heart. X 375- Diagram showing the form and arrangement of the fibres of heart muscle. (M. Heidenhain.) sesses a relatively large amount of sarcoplasm, as evidenced by the considerable accumulation surrounding the nucleus, as well as the thicker strata separating the muscle-columns. The unusual quantity of sarcoplasm accounts for the conspicuous FIG. 484. Capillary blood-vessel Undifferentiated sarcoplasm Nucleus Fibres of cardiac muscle in transverse section. X 375. longitudinal striation of cardiac muscle and agrees with what may be expected in muscular fibres subjected to such constant activity. 4 6 4 HUMAN ANATOMY. FIG The blood-vessels of striped muscle are very numerous to insure adequate nutrition to a tissue of great functional activity. The larger arteries and accompany- ing veins penetrate the muscle along the septal extensions of the epimysium and divide into smaller branches which run between the fasciculi. These vessels undergo further subdivision into twigs which pass between the finer bundles of muscle-fibres and ultimately break up into the capillaries enclosing the indi- vidual fibres. The capillary vessels of voluntary muscle form a characteristic net-work consisting of nar- row rectangular meshes (Fig. 485), the longer sides of which correspond to the direction of the muscle-fibres between which they run ; the shorter sides of the meshes are formed by the capillaries which extend across or may encircle the individual fibres. The capillaries supplying muscles subjected to prolonged and powerful contractions often exhibit local dilatations, which may serve for temporary reservoirs for the blood during contraction. The closeness of the capil- lary net-work is determined by the size of the muscle-fibres, muscles composed of fine fibres possessing the smallest vascular meshes. The relation of the blood-vessels to cardiac muscle is unusually intimate, the capillaries not only enclosing the muscle-fibres with a rich net- work, but lying within depressions on the surface of the fibres, or even in channels surrounded by the muscular tissue (Meigs). The lymphatics of striated muscular tissue are represented by the interfascicular clefts, which extend within the connective tissue between the muscle-fibres, and the more definite channels within the septa. The larger lymph-vessels formed by the confluence of those lying between the fasciculi pass to the sheath of the muscle and tendon and carry off the lymph from the muscular tissue. The nerves supplying striped muscle include both motor and sensory fibres. The former terminate in specialized arborizations, the motor nerve-endings, which Longitudinal Transverse Injected voluntary muscle, showing arrange- ment of interfascicular vessels and capillaries. FIG. 486. Neural canal Ectoblast Lateral plate of myotome -^f^ . JT Medial plate of myotome -fgffi. Wolffian body fff, Parietal mesoblast of {, somatopleura /'' t ;-% ,' ' ' Wolffian body - Parietal mesoblast b -Umbilical vein Body-cavity Aorta Body-cavity Transverse section of rabbit embryo, showing differentiation of myotomes. X 90. are usually regarded as lying beneath the sarcolemma upon the sarcous substance. The sensory fibres are connected with the neuro-muscular end organs or u __. The designation ' ' cutis-plate, ' ' applied to the compact outer epi- thelioid portion of the myotome, expresses the relation to the in- tegument which has been widely accepted, since this part of the l^ t myotome is generally regarded as concerned in the formation of the connective-tissue portion of the skin. This fate of the ' ' cutis- plate" was long age denied by Balfour, who held that both layers Developing voluntary muscle; the fibres are still unstnated. X 525. of the myotome are Concerned in the formation of muscular tissue. Kaestner l arrived at similar conclusions, and more recently Bardeen 2 has shown that in the pig practically the entire epithelial lamella is converted into muscle. According to this investigator, while some of the epithelial elements of the skin-plate degenerate, the greater number undergo mitosis and give rise to myoblasts which, in turn, become the spindle-cells from which the muscle-fibres are developed. The outer margin of the epithelial lamella is sharply defined by a limiting membrane formed by the adja- cent cells ; a somewhat similar but less pronounced boundary guards the inner con- tour of the lamella. The external limiting membrane persists until the conversion of the epithelioid elements into myoblasts and spindle-cells has been well established, by which time the mesoblastic tissue surrounding the myotomes has grown in between the latter and the adjacent ectoblast ; it is from this source, therefore, and not from the " cutis-plate," that the connective-tissue layer of the integument is derived. The masses of embryonal muscle, or myomeres, derived from the somites are early separated by the ingrowth of intersegmental septa of connective tissue which FIG. 490. , Developing muscle-fibres in which striation is just appearing. X 375. later support the intersegmental blood-vessels and nerves and, in the thoracic region, the costal elements, and, by the ingrowth of a connective-tissue partition, each urn- is further divided into a dorsal and a ventral portion, from which, in a general way, the muscles associated with the spine and the antero-lateral body-walls are derived respectively. In this primitive condition the trunk musculature is represented by a series of 1 Archiv fiir Anat. u. Phys., Suppl. Hd., 1890. 'Johns Hopkins Hospital Reports, vol. ix., 1900. STRIATED OR VOLUNTARY MUSCLE. 467 bands, the myomeres, each of which consists of a dorsal and a ventral portion, and which succeed one another regularly and segmentally throughout the entire length of the trunk. The muscle-fibres of which each myomere is composed extend from the intersegmental septum in front to that behind, having thus a regular antero- posterior direction. In the lower vertebrates this condition persists with but little modification throughout life, producing the flake-like arrangement of the muscles characteristic of the fishes. In the higher vertebrates, however, numerous secondary modifications supervene, whereby the myomeres are broken up into individual mus- cles, their original segmental arrangement becoming at the same time greatly ob- scured, although it still persists in those regions in which the muscles are intimately associated with segmental skeletal structures such as the vertebrae and ribs. These changes are of several kinds, and, as a rule, several varieties of modi- fication cooperate in the differentiation of a muscle. Some of the more important are as follow : 1. An end-to-end fusion of several myomeres or portions of myomeres takes place, producing a muscle-sheet or band which extends 'interruptedly through sev- eral primary segments. Such a modification gives rise to muscles supplied by a number of segmental nerves ; just as many, indeed, as there are myomeres partici- pating in the formation of the muscle. Examples of muscles formed in this way are to be seen in the musculature of the abdominal walls, the oblique muscles, the trans- versalis, and the rectus, for instance, being all polymeric muscles, as are also many of the longitudinal muscles of the back. Not infrequently the origin of these mus- cles by the fusion of portions of successive myomeres is shown, independently of their nerve-supply, by the persistence in their course of some of the intermuscular septa, these forming transverse tendinous bands traversing the muscle in a horizontal direction. Such tendinous inscriptions (inscriptiones tendinecB^, as they are termed, occur normally in the rectus abdominis, and are also frequently found in the internal oblique, the sterno-hyoid, and the sterno-thyroid muscles. 2. A longitudinal division of the myomeres into a number of distinct and origi- nally parallel portions may occur. Examples of this modification combined with the end-to-end fusion of the portions so formed from successive myomeres are very abundant. Thus, the rectus abdominis is the result of the splitting off of the ventral portion of a number of successive myomeres, whose remaining portions are largely represented in the oblique and transverse abdominal muscles. So, too, in the neck, the differentiation of the sterno-hyoid and omo-hyoid is due to the same process, and it has also acted in the differentiation of the various muscles of the transverso- costal group of the dorsal musculature. 3. A tangential splitting of the myomeres is again an occurrence of great fre- quency, producing superposed muscles, and is clearly shown in the dorsal muscula- ture and in the ventro-lateral muscles of the thoracic and abdominal walls. It does not necessarily involve all portions of a myomere when this has already divided longitudinally, but may be confined to only certain of the parts so formed. Thus, while it affects the ventro-lateral abdominal muscles, it does not affect the rectus abdominis, this muscle representing the entire thickness of the ventral borders of a number of successive myomeres. 4. Associated with the change just described there is frequently a modification in the direction of the fibres in one or more of the superposed muscles. Primarily the fibres of each myomere have an antero-posterior direction, a condition which is still retained in the rectus abdominis, for instance. In the ventro-lateral abdominal and thoracic muscles, however, the original direction of the fibres has been greatly altered, those of the superficial layer being directed in general downward and inward, those of the middle layer to a considerable extent downward and outward, while those of the deepest layer are directed almost or quite transversely, that is to say, in a direction which is 90 different from that taken by the fibres of the myomere. 5. An exceedingly interesting modification is that which results from the migra- tion of some of the myomeres over their successors, so that a muscle formed from certain of the cervical myomeres, for example, may in the adult condition be super- posed upon muscles derived from the thoracic segments. In such cases of migration 468 HUMAN ANATOMY. the segmental nerve, or at least those fibres of it which originally supplied the por- tions of the myomeres in question, retains its connection and is consequently drawn out far beyond its usual territory, a ready explanation being thus afforded for the extended course of the long thoracic, long subscapular, and phrenic nerves. The muscles supplied by these nerves, as well as the pectoralis major and minor muscles, are all derived from cervical myomeres, their adult position being due to the process of migration, of whose existence they form convincing examples. 6. Finally, portions of one or several successive myomeres may undergo degen- eration, becoming converted into connective tissue, which may have the form of fascia, aponeurosis, or tendon. Examples of this degeneration are to be found in practically all muscles, since the tendons by which they make their bony attachments have resulted from its action. In the lower vertebrates and in the foetus tendons and aponeuroses are much less developed than in the higher forms or in the adult, being represented by muscular tissue which later becomes converted into tendon or aponeurosis. The intermuscular septa between the muscles of the limbs seem to have arisen in this way, and occasionally relatively large aponeurotic sheets have so arisen, as in the case of the aponeurosis which unites the two posterior serratus muscles. Of especial interest in this connection are the degenerations into liga- ments of muscle-tissue primarily occurring in the neighborhood of many of the joints, the accessory ligaments being in many cases formed in this manner. Thus, the external lateral ligament of the knee-joint, the ligamentum teres of the hip-joint, and even the great sacro-sciatic ligament owe their origin to this process, and many other of the ligaments may also be referred to it. As a result of these various modifications and their combinations the individual muscles of the adult body, together with the aponeurotic sheets which are frequently associated with them, are formed. GENERAL CONSIDERATION OF THE VOLUNTARY MUSCLES. The voluntary or striated muscles constitute a very considerable portion of the entire mass of the body, their weight in an average adult male having been esti- mated at about 43.4 per cent, of the total body weight (Vierordt). Each muscle is a distinct organ composed of a number of contractile fibres united into bundles or fasciculi surrounded by a delicate sheath of connective tissue, the pcrinn'siitin, in which blood-vessels and nerves ramify to the various fasciculi, and which, at the surface of the muscle, is continuous with the fascia which encloses the entire organ. At each extremity of the muscle the contractile tissue is united with dense connective tissue, the general structure of which resembles that of the muscle, its fibres being arranged in distinct bundles separated and enclosed by looser tissue comparable to the perimysium. By means of these tendons, as they may generi- cally be termed, the attachment of the muscle to portions of the skeleton or other structures is effected. The extent to which the tendon is developed varies greatly in different muscles, in some being hardly noticeable, so that the muscle-tissue appears to be directly attached to the bone (Fig. 496), at other times forming a long rounded or flattened band (Fig. 576), to which the term tendon is usually applied, or again forming a broad, flat expansion, termed an aponeurosis (Fig. 525). Both the tendons and aponeuroses are to be regarded as representing portions of the original muscle converted into connective tissue, and, indeed, comparative anatomy shows that many of the ligaments and aponeuroses of the body, even although they may not seem to be directly related to neighboring muscles, are really to be regarded as muscles which have undergone a tendinous degeneration. Attachments. The great majority of the voluntary muscles are attached at either end to portions of the skeleton, passing over one or more joints, in which thcv effect movement by their contraction. Occasionally, however, a muscle may be attached at one of its extremities, in part or entirely, to fascia, as, for instance, the glutens maximus and the tensor fasciae late, or both of its attachments may be to fascia, as is the case with some of the muscles of expression and with the muscles of the palate and the intrinsic musculature of the tongue. Others, again, may have one or both of their attachments to tendons of other muscles, e.g., the accessorius GENERAL CONSIDERATION OF THE VOLUNTARY MUSCLES. 469 and the lumbricales, while others may pass between portions of the skeleton and special organs upon which they act, as is exemplified by the muscles of the eyeball. Whatever may be the nature of the structure to which the attachment is made, it is convenient for 'purposes of description to regard one of the points of attachment of each muscle as the fixed point from which it acts in contraction, and to speak of this as its origin, and to regard the other as the point upon which it acts, speaking of it as the insertion. It must be understood, however, that this distinction between the two attachments is somewhat arbitrary, since what is usually the fixed point may under certain circumstances become the movable one. For instance, in the case of a muscle passing from the pelvis to a leg bone, if the body be erect, the contraction of the muscle will cause an inclination of the trunk on the hip-joint, the attachment to the leg bone being then the fixed point and that to the pelvis the movable one. In other positions of the body, however, the contraction of the muscle will produce a movement of the leg, the fixed and movable points being exactly reversed. Since, however, the movement of the leg may be regarded as the more usual result of the contraction of the muscle, the pelvic attachment is arbitrarily regarded as the origin and the attachment to the femur or tibia the insertion of the muscle in question. FIG. 491. Central portion Tendon o Diagrams showing semi-pinnate (A) and pinnate () arrangement of muscle-fibres, which pass from tendon 01 origin above to that of insertion below. C, compound pinnate arrangement, as in central division of deltoid muscle. (After Poirier.) Form. The muscles assume various forms, dependent to some extent upon the structures to which they are attached. Some are thin sheets with almost parallel fibres, others are more or less band-like, while others may have considerable thick- ness, and be quadrate, triangular, or spindle-shaped. Surrounding certain of the orifices of the body are what are termed orbicular or sphincter muscles (Figs. 495, 499), consisting of a muscular sheet whose fibres have a crescentic course around either side of the orifice, the lips of which will tend to be drawn together by the con- traction of the muscle. Where the surfaces for attachment are considerable, the fibres composing a muscle have a more or less parallel course ; but where a comparatively small area is all that is available for the attachment of a strong muscle, as is the case with many of the limb muscles, it is clear that such an arrangement cannot obtain. The muscle- fibres then converge from either one or both sides to be inserted one above the other into the tendon, forming what is termed a scmipinnate (e. g. , many of the muscles of the leg, Fig. 609), or pinnate muscle (e. g. , mterossei dorsales, Fig. 590.) This convergence may take place towards either one or both tendons of attachment, and occasionally these may spread out over opposite surfaces of the muscle to form apo- neurotic sheets which overlap, so that the muscle-fibres pass obliquely from the sur- face of one tendon to that of the other (e.g. , gastrocnemius, semitendinosus, Fig. 635). Finally, in some of the broader muscles (e.g. , deltoid and subscapularis) the muscle-fibres may arise from and converge to a series of tendinous bands which 470 HUMAN ANATOMY. alternate with one another, the muscle having thus a compound pinnate arrangement (Fig. 491, C). As a rule, the tendons occur in connection with the extremities of the muscle, but occasionally one or more tendinous intersections may occur in the course of the muscle, which thus becomes divided into two or more bellies. This condition may be the result of the end-to-end union of the tendons of attachment of two primarily distinct muscles {e.g., digastric, Fig. 497) or to the persistence of some of the dividing lines which separate the various embryonic segments of which a muscle may be composed {e.g., rectus abdominis, Fig. 523) ; or it may be due to a sec- ondary attachment formed by a muscle in its course, it being bound down to a neighboring bone by a band of fascia {e.g., omo-hyoid). Certain muscles present the peculiarity of possessing two or more separate heads of origin, attached to different bones and uniting to form a common tendon of insertion. In certain cases {e.g., biceps femoris, pronator radii teres) this condition indicates the union of two primarily distinct muscles which had a common insertion, or which were, at all events, originally inserted close together, but in other cases it has resulted from a separation of an original muscle into two portions. The ana- tomical nomenclature is not quite consistent as regards such muscles, since it describes the biceps femoris as a two-headed muscle, although its two heads are fundamentally distinct organs ; while, on the other hand, it usually regards the psoas and iliacus and the gastrocnemius and soleus as distinct muscles, notwith- standing their common insertion. Fasciae. Connecting the various muscles and uniting them into groups, and also surrounding the entire musculature of the body and separating it from the deeper layers of the integument, are sheets of connective tissue known as fascia. These sheets are by no means isolated portions of connective tissue, but are rather to be regarded as parts of the general interstitial connective-tissue net-work which traverses all parts of the body, thickened to form more or less definite sheets stand- ing in relation to the neighboring organs. The density of the sheets varies greatly ; in some regions they are imperfectly developed and may contain considerable amounts of fat, while in others they form dense, glistening sheets resembling the expansions of tendons mentioned above, and termed, like these, aponeuroses. It is convenient to recognize two principal layers of fasciae, the superficial and the deep. The superficial fascia immediately underlies the skin of the entire body, and is sometimes considered a portion of it and termed the panniculus adiposus, since, except in the eyelids, penis, scrotum, and labia minora, it contains considerable quan- tities of fat. It is connected with the subjacent deep fascia by a more or less exten- sively developed layer of areolar tissue, which, however, is lacking in certain regions, such, for instance, as the face, the palmar surface of the hand, and the plantar surface of the foot, where the superficial and deep fasciae are intimately united. The deep fascia, on the other hand, immediately covers and invests the muscles, and in the intervals between them becomes continuous with the periosteal connec- tive tissue enclosing the bones. Those lamellae of the fascia which dip down between the muscles of the limbs the intermuscu'lar septa are frequently of con- siderable firmness and serve for the origin of fibres of the neighboring muscles, and occasionally muscles {e.g., soleus, levator ani) take their origin in part directly from portions of the deep fascia, which then becomes thickened along the line of the origin to form strong bands, termed arcus tendinei, attached at either extremity to neighboring bones. Certain portions of the deep fascia, and especially of the intermuscular septa, represent portions of the muscular system which have undergone tendinous degen- eration, and are represented by muscular tissue in the lower vertebrates. Indeed, the relative amount of aponeurotic and tendinous tissue, as compared with the mus- cular, is very much greater in the higher than in the lower forms, and is appre- ciably greater in the human embryo than in the adult, indicating a transformation of one tissue into the other (hiring the life of the individual. Tendon-Sheaths. Where tendons run in grooves of bones, bands of dense connective tissue extend across between the lips of the grooves, being continuous GENERAL CONSIDERATION OF THE VOLUNTARY MUSCLES. 471 there with the periosteum, and convert the grooves into canals within which the ten- dons are enclosed, although capable of free movement to and fro. These connective- tissue bands are the tendon-sheaths, and the canals which they assist in forming may contain one or more tendons. Each sheath is lined on its deeper surface by a synovial membrane similar to those occurring in the joints, and at either extremity of the sheath this membrane is reflected upon the tendon which it encloses, so that the tendon is contained within a double-walled cylinder whose cavity is filled with a fluid serving to diminish friction during the movements of the tendon (Fig. 492). It is customary to distinguish the synovial portion of a tendon-sheath as the serous or synovial sheath {vagina mucosa) from the fibrous sheath (vagina fibrosa) with which it is always closely con- FIG. 492. nected. Strands of connective tissue pass at intervals across the synovial cavity of the sheath from the floor of the groove on the bone and transmit blood-vessels to the tendon ; these strands constitute what are termed v in- Phalanx cula tendinum, or, from their general similarity to the mesentery, mesotendons. Diagram showing relations of ten- T j i , i don to tendon-sheath as in cross-section In some cases a tendon-sheath may serve to a cer- of finger . tain extent as a pulley, affording a smooth surface over which the tendon changes its direction, as in the case of the extensor tendons of the hand when this is partly extended. A special development of this condition is to be seen in the tendinous loop (trochlea muscularis} over which the tendon of the superior oblique muscle of the eyeball is reflected (Fig. 516). Bursae. The intervals between the various muscles and between these or their tendons and the bone are occupied by loose areolar tissue. In situations in which a muscle or tendon in its movements comes in contact with a bony prominence, or in which two tendons glide upon each other, the spaces of the areolar tissue enlarge and become filled by a fluid resembling that of the synovial cavities, the result -being the formation of what is termed a bursa, whose purpose is to diminish the friction between the muscle or tendon and the bone. Examples of such bursae are to be found abun- dantly in connection with the muscles of the limbs, and some of those which occur in the vicinity of joints frequently fuse with the adjacent synovial cavities ; the bursa of the subscapularis, situated between that muscle and the neck of the scapula, for instance, uniting with the synovial cavity of the shoulder-joint, and the bursa supra- patellaris, between the tendon of the quadriceps femoris and the femur, fusing with the cavity of the knee-joint. Bursae are also developed in the areolar tissue intervening between the superficial and deep fasciae in situations in which the integument rests directly upon a bone, as, for instance, over the olecranon process, and is frequently subjected to pressure in that region. Such bursae are termed subcutaneous burs& to distinguish them from those developed in connection with the muscles. Classification of the Muscles. The muscles may be classified according to three plans : they may be arranged according to their topographical relations, according to their physiological significance, or, finally, upon a morphological basis, their embryological or developmental significance forming the guide for their arrange- ment in groups. In the following pages the last-named plan will be followed as far as possible. Embryologically the skeletal muscles are formed, for the most part, from a series of segmentally arranged masses of mesoblast^-the mesoblastic somites which appear at an early stage of development on either side of the notochord and later extend ventrally towards the mid- ventral line (page 465). That portion of the musculature which has such an origin may be regarded as consisting primarily of a series of plates arranged segmentally along each side of the body, each plate corresponding to and being supplied by one of the segmental nerves and by those fibres of it which arise from the cells of the anterior horn of the spinal cord or their homologues in other portions of the central nervous system. A diagrammatic representation of this mus- culature in its primary condition is shown in Fig. 493, and from this it will be per- ceived that the series of muscle-plates extends throughout the entire trunk and neck HUMAN ANATOMY. FIG. 493. regions of the body and to a certain extent into the head region, there being, how- ever, in this last region a considerable area in which the muscle-plates are unrepre- sented. Throughout this area of the head region muscles occur which arise in relation to the branchial arches and, accordingly, in a much more ventral position than the mesodermic somites. Furthermore, these muscles are supplied by branches from the mixed cranial nerves, arising from cells situated in a portion of the medulla oblongata which is comparable to the lateral horn of the spinal cord and con- stituting what are termed lateral motor roots, in contradistinction to the median or anterior motor roots which supply the muscles derived from the mesodermic somites. There are thus two sharply defined systems of musculature : the one, primarily confined to the cranial region, is supplied by lateral motor nerves, and from its rela- tion to the branchial arches maybe termed the branchiomeric musculature ; the other, supplied by anterior motor nerves, is arranged primarily in a series of segmental (metameric) plates, and may be termed the metameric mus- culature. These two systems constitute the first divisions in the morphological classifica- tion of the musculature. The further subdivision of the branchio- meric muscles is most conveniently made with reference to the various cranial nerves by which they are supplied. For the metameric musculature a more complicated subdivision is both necessary and convenient, and in the first place it may be divided into the axial and the appendiciilar musculature. For the latter group, which includes all the muscles of the limbs, a derivation from the mesodermic so- mites seems probable, outgrowths from certain somites extending into the limb-buds when these develop ; but it has not yet been possi- ble to demonstrate, that this is the case, the limb muscles really making their appearance in an unsegmented mass of mesoblast in the limb-bud which appears to have no connection with the mesoblastic somites, these structures apparently not being continued into the limb- bud, but seeming to stop short at its base. In- deed, it is quite possible that the limb muscles should not be included under the metameric musculature ; but until it is demonstrated that their mode of development is not a secondary condensation of the embryological history, it seems preferable to retain them as members of that group. . The later development of the cranial mes- oblastic somites is somewhat different from that of the others, and it is consequently convenient to group the axial muscles derived from them by themselves. And since the somites form in the embryo two clearly defined groups, it seems well to place the derived muscles in two groups which may be termed respectively the orbital and the hypoglossal groups. The remaining somites, which maybe grouped together as the trunk somites, in their later development undergo numerous modifications, some of which may be regarded as fundamental and primarily affecting all of the series, and thus affording .1 lusis for a further subdivision. The most fundamental of these modifications is a division of each somite into a dorsal and a ventral portion, corresponding respectively to the primary divisions of the spinal nerves, and permitting the recognition of a Diagram showing grouping of head and trunk myotomes. Ill, IV, VI, orbitalgroup (supplied by cranial nerves indicated by Roman numerals) rep- resenting persisting first three cephalic myoloim-s ; XII, hypoglossal group, representing persisting last three cephalic myotomes, intervening ones having disappeared; i, i, i, i. I, first niyotome of cervical, 'thoracic, lumbar, sacral, and coccygeal groups of trunk myotomes. Each niyotome is di- vided into dorsal and ventral segments. GENERAL CONSIDERATION OF THE VOLUNTARY MUSCLES. 473 dorsal and a ventral group of trunk muscles. The portions of the ventral divisions on either side of the mid-ventral line separate to form a subordinate group of mus- cles which may be termed the rec- tus group (Fig. 494), the more FIG. 494. lateral portions giving rise tO a Dorsal division of spinal nerve group which, from the prevailing oblique course of its fibres, may Dorsal group be termed the obliquus group ; ventral divi- ^- ?**-. and, finally, from the more dor- """""- sal portions of the ventral muscu- lature there are developed in cer- tain regions of the body muscles which lie ventral to the bodies or processes of the vertebrae, and may be termed the hyposkeletal muscles, in contrast to the re- maining musculature which ex- tends between the skeletal ele- ments or lies dorsal to them, and N ^^^^~^^^P^- Rectus group hence is termed the episkeletal mus- r il^r irp> Diagrammatic cross-section of body, showing primary groups oJ re - trunk muscles. To sum up the classification proposed it may be represented in the following manner : I. BRANCHIOMERIC MUSCLES. II. METAMERIC MUSCLES. A. Axial Muscles. 1. Orbital muscles. 2. Hypoglossal muscles. 3. Trunk muscles. a. Dorsal, b. Ventral. a. Rectus set. b. Obliquus set. c. Hyposkeletal set. B. Appendicular Muscles. Nerve-Supply. The segmental regularity of the mesodermic somites is but slightly retained in the adult, numerous modifications, such as fusion, tangential and longitudinal splitting, migration, and even obliteration taking place in them to pro- duce the various muscles of the adult. The various modifications have not in all cases been traced, but a study of the nerve-supply of a muscle gives in many, if not all, cases an important clue to its origin. This depends upon the fact that the muscles may be regarded as the end-organs of the motor nerves, and that the seg- mental relation established in the embryo between a nerve and the muscle-tissue derived from a given mesodermic somite is not disturbed in later development, no matter what changes of relation the muscle- tissue may undergo. Thus, when a muscle, such as the rectus abdominis, is found to be supplied by a number of spinal nerves, it is because it has been formed by the fusion of portions of a corresponding number of mesodermic somites ; and when a muscle, such as the latissimus dorsi, lying mainly in the lumbar region, is found to be supplied by a cervical nerve, it is because it has wandered from its original point of formation in the cervical region. Variations in the nerve-supply are occasionally seen, especially in the limb mus- cles; but it seems probable that such variations are only apparent, the nerve-fibres supplying the muscle being in all cases strictly equivalent, arising from the same region of the spinal cord, even although they may pursue in different individuals somewhat different paths in order to reach their destination. Thus, a muscle which normally is supplied by fibres from the median nerve may sometimes be found to be 474 HUMAN ANATOMY. supplied by the ulnar nerve, the nerve-fibres using the ulnar nerve as a pathway by which to reach their destination, instead of the median nerve. It is important, therefore, both from the morphological and clinical stand-points, that not only should the nerve along which the fibres pass to reach their destination be known, but also the nerve-roots by which they issue from the central nervous system. THE BRANCHIOMERIC MUSCLES. The branchiomeric muscles are those skeletal muscles which are derived from the mesoderm associated with the branchial arches, and are supplied by those cranial nerves whose motor fibres constitute what are termed lateral motor roots. These nerves are the trigeminus, facialis, and glosso-pharyngeo-vago-accessorius groups, and the classification of the muscles may well be according to their innervation by these three nerve-groups. I. THE TRIGEMINAL MUSCLES. The trigeminal muscles stand in relation primarily to the first embryonic or jaw- arch, and in the adult to the structures developed in association with this, i.e., to the mandible and the malleus. The mandibular muscles are represented by the muscles of mastication and two muscles, the mylo-hyoid and the anterior belly of the digastric, which extend between the mandible and the hyoid bone, and may be termed the submental muscles. Connected with the malleus is a single muscle, the tensor tympani, and an additional trigeminal muscle is found in association with the soft palate, the tensor palati. (a) THE MUSCLES OF MASTICATION. 1. Masseter. 3. Pterygoideus Externus. 2. Temporalis. 4. Pterygoideus Internus. i. MASSETER (Fig. 495). The masseter is a strong quadrilateral muscle composed of two portions, sep- arated at their origin and posteriorly by a quantity of loose areolar tissue, but united towards their insertion into the mandible. Attachments. The superficial portion arises by a strong aponeurosis from the anterior two-thirds of the lower border of the zygoma, while the deeper part arises directly from the posterior third of the lower border and the whole of the inner surface of the zygoma. The fibres of the superficial portion pass downward and slightly backward to be inserted into the outer surface of the angle of the mandible, while those of the deeper portion pass more directly downward and are inserted into the outer surface of the ascending ramus as high as the bases of the articular and coronoid processes, encroaching to a certain extent upon the insertion of the temporal muscle. Nerve-Supply. By the masseteric branch of the anterior portion of the man- dibular division of the trigeminus. Action. To raise the mandible and, by its superficial portion, to draw it for- ward to a slight extent. Owing to the fibres of the muscle being directed almost perpendicularly to the lever upon which it acts, the masseter works at much less mechanical disadvantage than is usual, and its action is therefore exceedingly powerful. Relations. A considerable portion of the masseter is subcutaneous. Poste- riorly, however, the parotid gland rests upon its outer surface-, and it is crossed by the parotid duct, the transverse facial artery, and branches of the facial nerve. Anteriorly its deep surface is separated from the buccinator muscle by a well-devel- oped mass of fat, the buccal fat-pad ( page 489). The Parotido-Masseteric Fascia. Covering the anterior surface of the masseter is a thin layer of fascia, the masseteric fasti*, attached above to the zygoma THE TRIGEMINAL MUSCLES. 475 and fading out anteriorly beneath the facial muscles. Posteriorly it becomes thicker and divides into two layers to enclose the parotid gland {parotid fascia), the super- ficial layer becoming continuous behind with the layer of the deep cervical fascia which encloses the sterno-mastoid muscle, while the deeper layer is connected inter- nally with the styloid process and joins the deep cervical fascia below. A thickening of this deeper layer forms a flat band, the stylo-mandibular ligament, which passes downward and outward from the styloid process to the angle of the jaw. 2. TEMPORALIS (Fig. 495). The temporal fascia forms a strong aponeurotic membrane attached above to the superior temporal line and the portion of bone between this and the inferior line, being along this attachment continuous with the periosteum. Below it divides into two layers which are separated by a quantity of adipose tissue, through which the FIG. 495. Temporal- fascia (cut) Temporal muscle, partially exposed Buccinator Massi'tt-r. deep portion Masseter, superficial portion Lateral aspect of skull with temporal, masseter, buccinator, and oral muscles in place. middle temporal artery may run, and is attached to the zygoma, its superficial layer inserting into the upper border of the arch and its deeper layer into the inner surface. Attachments. The temporal muscle arises from the upper half of the deep surface of the temporal fascia and from the whole extent of the floor of the temporal fossa. Its fibres converge to an exceedingly strong tendon, which inserts into the coronoid process of the mandible, occupying both its borders, the whole of its inner surface, and a varying amount of its outer surface. Nerve-Supply. By the anterior and posterior deep temporal branches from the anterior portion of the mandibular division of the trigeminus. Action. To raise the mandible. The more posterior fibres serve to retract the jaw, acting thus as an antagonist of the external pterygoid. 476 HUMAN ANATOMY. FIG. 496. i bone (cut) 'uncivil' of mandible Upper head) External ^Lower head j pteryfjoid Relations. - Superficial to the temporal fascia are branches of the superficial temporal vessels and the auriculo-temporal nerve. Beneath the muscle is in relation to the internal maxillary artery and the external pterygoid muscle. 3. PTERYGOIDEUS EXTERNUS (Fig. 496). Attachments. -.-The external pterygoid arises by two heads. The upper head takes its origin from the under surface of the great wing of the sphenoid, inter- nal to the infratemporal crest (pterygoid ridge), while the lower head arises from the outer surface of the lateral pterygoid plate. The two heads are at first separated by a triangular interval through which the internal maxillary artery frequently passes, but, passing backward and outward, they soon unite to be inserted into the anterior border of the interarticular fibro-cartilage of the mandibular articulation and into the neck of the condyloid process oi the mandible. Nerve-Supply. By the exter- nal pterygoid branch of the anterior portion of the mandibular division of the trigeminus. Action. When both muscles act together, they draw the jaw and the interarticular fibro-cartilage for- ward, a movement which always accompanies and assists in the de- pression of the jaw. \Yhen but one muscle acts, the ramus to which it is attached is drawn forward, while the internal pterygoid other pivots in its articular surface, the result being an apparent lateral movement of the jaw towards the pivotal side. Relations. The outer surface of the external pterygoid is in rela- tion to the coronoid process of the mandible and the temporal muscle, its lower head is frequently crossed. by the internal maxillary artery and the buccal nerve, and anteriorly it is separated from the masseter by the buccal fat-pad. The deep surface rests upon the upper part of the internal pterygoid muscle, and is in relation to the internal maxillary artery and the inferior dental and lingual branches of the mandibular division of the trigeminus. 4. PTERYGOIDKl'S IXTERNUS (Fig. 496). Attachments. The internal pterygoid arises from the walls and floor of the pterygoid fossa, the majority of its fibres being attached to the inner surface of the external pterygoid plate and to the tuberosity of the palate bone. A smaller bundle of fibres, forming what may be termed a second head, separated from the main por- tion of the muscle by the lower head of the external pterygoid, frequently arises from the tuberosity of the maxilla and the adjacent portion of the palate bone. From these origins the fibres are directed downward and somewhat outward and backward to be inserted into the inner surface of the angle and ramus of the mandi- ble below the mylo-hyoid groove. Nerve-Supply. By the internal pterygoid branch from the trunk of the mandibular division of the trigeminus. Action. Its chief action is to raise the jaw, having in this respect almost as powerful action as the massrter. Owing to the direction of its fibres, it will also assist the external pterygoid in protruding the jaw and in producing its lateral movements. Relations. The outer surface of the muscle is in relation with tin- ramus of the mandible, the internal maxillary artery, and the inferior dental and lingual nerves Mylo-hyoid, stump External and internal pterygoid muscles, seen from within. THE TRIGEMINAL MUSCLES. 477 passing between the muscle and the bone. Above its larger head is covered by the external pterygoid. Its inner surface is in contact above with the tensor palati, the superior constrictor of the pharynx, and the ascending palatine artery, while towards its insertion it is in relation with the stylo-hyoid and posterior belly of the digastric and with the submaxillary gland. Variations of the Muscles of Mastication. The muscles of mastication are all derivatives of a single muscular mass represented by the adductor mandibulce of fishes, and indications of their common origin are not infrequently to be seen in partial unions of the various muscles. Thus, fibres from the posterior portion of the deeper head of the masseter may join the tem- poral, fibres from both the temporal and masseter sometimes pass to the anterior border of the fibro-cartilage of the mandibular articulation, and connections have also been observed between the temporal and the external pterygoid. Additional independent muscles apparently belonging to this group sometimes occur in the pteiygoideus proprius, which extends from the infratemporal crest of the sphenoid to the posterior edge of the external pterygoid plate, and in the pterygo-spinosus, which has for its attachments the spine of the sphenoid and the posterior border of the external pterygoid plate. The significance of these muscles passing between points which are immovable is somewhat obscure. The close relationship which the pterygo-spinosus bears to the spheno-mandibular ligament seems to indicate that it represents the musculature of that portion of the mandibular arch which has become transformed into the ligament, and that usually it is represented by the connective tissue enclosing the ligament. (6) THE SUBMENTAL MUSCLES, i. Mylo-hyoideus. 2. Digastricus (Anterior Belly). This group of trigeminal muscles contains but two representatives, the mylo- hyoid and the anterior belly of the digastric. This latter muscle, as ordinarily described, consists of two distinct muscles united at their attachment to the hyoid bone, the anterior of the two muscles belonging to the trigeminal group, while the posterior is a member of the facial group. It will be convenient to describe the muscle as a whole, even although it belongs only in part to the group under con- sideration. i. MYLO-HYOIDEUS (Fig. 497). Attachments. The mylo-hyoid arises irom. practically the entire length of the mylo-hyoid ridge of the mandible, from which the fibres pass inward and slightly backward to be inserted for the most part into a median fibrous raphe common to the two muscles of opposite sides, the posterior fibres, however, being attached to the upper border of the body of the hyoid bone. The two muscles, taken together, form a muscular floor for the mouth, the diaphragma oris, upon which the tongue may be said to rest. Nerve -Supply. By the mylo-hyoid from the inferior dental branch of the mandibular division of the trigeminus. Action. To draw the hyoid bone upward and at the same time to raise the floor of the mouth, pressing the tongue against the palate. Relations. The superficial surface of the mylo-hyoid is in relation with the anterior belly of the digastric and with the facial artery. The submaxillary gland curves around its posterior free margin and is thus in relation with both its surfaces, the submaxillary duct running forward upon its deeper surface. This latter surface is also in relation with the genio-hyoid, genio-glossal, hyo-glossal, and stylo-glossal muscles, with the sublingual gland, and with the lingual branch of the trigeminus and the hypoglossal nerve. 2. DIGASTRICUS (Figs. 497, 502). Attachments. The digastric, as its name indicates, consists of two bellies which are united by a strong cylindrical tendon. The anterior belly, which alone belongs to the trigeminal group of muscles, arises from the digastric fossa of the mandible, and is directed downward, backward, and slightly outward to become con- 478 HUMAN ANATOMY. tinuous with the intermediate tendon. This is bound down to the greater horn and body of the hyoid bone by a pulley-like band of the cervical fascia and to a certain extent by the stylo-hyoid muscle, which divides near its insertion into the hyoid into two slips, between which the tendon of the digastric passes. The posterior belly (Fig. 502) takes its origin from the mastoid groove of the temporal bone, and passes downward and forward to become connected with the intermediate tendon. Nerve-Supply. The anterior belly is supplied by the mylo-hyoid nerve from the inferior dental branch of the mandibular division of the trigeminus, the posterior belly by the digastric branch of the facial. Action. The digastric either raises the hyoid bone or depresses the jaw, FIG. 497. Mandible Mylo-hyoid * Hyoid bon Thyro-hyoid membrane Stylo-glossus Internal pterygoid Thyro-hyoid Thyroid cartilagi Stylo-pharyngeu Crico-thyroid- Genio-hyoid (mylo-hyoid removed) Digastric, anterior belly Fascial loop binding tendons to hyoid bone .Stylo-glossus Stylo-hyoid Masseter Digastric, posterior belly ^Thyroid gland Submental muscles from below ; trachea has been displaced downward and backward. according as one or other of the bones is fixed by the antagonizing muscles. By raising the hyoid when the mandible is fixed, it assists the mylo-hyoid in pressing the tongue against the palate during the first portion of the act of deglutition, and in the second portion of that act the posterior belly will assist the stylo-hyoid in drawing the hyoid upward and backward and so help in elevating the larynx. Relations. The anterior belly rests upon the mylo-hyoid muscle. The pos- terior belly is covered by the sterno-mastoid and splenius muscles, and crosses both the external and internal carotid arteries, the internal jugular vein, and the pneumo- gastric and spinal accessory nerves. Variations. A close relationship exists between the mylo-hyoid and the anterior belly of the digastric, and there is usually more or K-ss i-xrhange of fibres between the two muscles, sometimes amounting to a complete fusion. A duplicity of the anterior belly is a rather fre- THE FACIAL MUSCLES. 479 quent variation, and the anterior bellies of opposite sides may be united by the more or less complete conversion of the fascia which typically passes between them into muscular tissue. An independent muscle extending between the body of the hyoid and the symphysis of the mandible, and termed the mento-hyoid, occasionally is found running alongside of the medial border of the anterior belly, and is to be regarded as a separated portion of that muscle. As regards the posterior belly, it may take its origin from any part of the mastoid groove or even from the outer portion of the superior fluchal line, and occasionally it fuses completely with the stylo-hyoid. In certain cases in which there is a failure of the anterior belly to differ- entiate from the mylo-hyoid, the posterior belly is inserted into the angle of the mandible instead of into the hyoid bone, a condition recalling the arrangement typical in the majority of the mammalia, in which the posterior belly of the digastric is represented by a depressor mandibula. (c} THE TRIGEMINAL PALATAL MUSCLE, i. TENSOR PALATI (Fig. 509). Attachments. The tensor palati (tensor veil palatini) takes its origin from the scaphoid fossa and spine of the sphenoid and from the outer surface of the car- tilaginous portion of the Eustachian tube. It descends along the outer surface of the internal pterygoid plate, and, becoming tendinous, bends at right angles around the hamulus and is continued inward to be inserted into the posterior border of the palate bone and into the aponeurosis of the soft palate. Nerve-Supply. By fibres from the mandibular division of the trigeminus, which traverse the otic ganglion. Action. It tends to draw the soft palate to one side. The two muscles acting together will stretch the soft palate. (d) THE TRIGEMINAL TYMPANIC MUSCLE, i. TENSOR TYMPANI (Fig. 1252). Attachments. The tensor tympani is a small bipenniform muscle which lies in a bony canal situated above the Eustachian tube. Its fibres take their origin from the cartilaginous portion of the Eustachian tube, the adjacent portions of the great wing of the sphenoid, and also to a certain extent from the walls of the bony canal. The tympanic end of the Eustachian tube is separated from the opening of the canal for the tensor by a bony ridge, the processus cochleariformis, over which the tendon of the tensor bends almost at right angles and passes outward across the tympanic cavity to be inserted into the manubrium mallei near its attachment to the head of the bone. Nerve-Supply. By fibres from the mandibular division of the trigeminus, which traverse the otic ganglion. Action. The muscle draws the handle of the malleus inward and so tenses the membrana tympani. II. THE FACIAL MUSCLES. The muscles supplied by the facial nerve are readily divisible into two groups. Primarily this musculature is associated with the second branchial or hyoid arch, represented in the adult by the lesser cornu of the hyoid bone, the stylo-hyoid liga- ment, styloid process, and stapes, and a small group of muscles the stylo-hyoid, the posterior belly of the digastric, and the stapedius are still found in relation to these structures. From the surface of the mass from which these muscles differentiate there is separated at an early stage a layer which gradually increases in extent and eventually covers all the neck and head in a cowl, as it were, its progress from the hyoid arch being followed by a branch of the facial nerve, which eventually, with the growth of the muscle, increases to such an extent as to appear to be the main stem of the nerve. From the muscular sheet numerous superficial muscles of the head and neck develop, and the entire group so formed may be termed, from one of its principal members, the platysma group, the group retaining the primary relationships forming the hyoidean group. 480 HUMAN ANATOMY. (a) THE HYOIDEAN MUSCLES. I. Stylo-hyoideus. 2. Digastricus (Posterior Belly). 3. Stapedius. i. STYLO-HYOIDEUS (Figs. 497, 502). Attachments. The stylo-hyoid forms a slender spindle-shaped muscle which arises from the upper portion of the styloid process and passes obliquely downward and forward to be inserted into the base of the greater cornu of the hyoid bone, usually dividing before its insertion into two slips, between which the intermediate tendon of the digastric passes. Nerve-Supply. By a branch from the digastric branch of the facial nerve. Action. To raise and draw backward the hyoid bone. Relations. Above the stylo-hyoid descends along the inner border of the posterior belly of the digastric, passing in front of that muscle below. Internal to it is the stylo-pharyngeus, and below the hyo-glossus and the glosso-pharyngeal and hypoglossal nerves, passing forward between it and the stylo-pharyngeus. 2. DIGASTRICUS (Posterior Belly). See page 478. 3. STAPEDIUS (Fig. 1254). Attachments. The stapedius arises from the walls of the cavity contained within the pyramidal eminence, and its tendon, entering the tympanic cavity through the aperture at the apex of the eminence, is inserted into the neck of the stapes. Nerve-Supply. By a small branch arising from the facial nerve during its course through the lower part of the facial ( Fallopian) canal. Action. By its contraction it draws the head of the stapes towards the pos- terior wall of the tympanic cavity, depressing the posterior part of the foot-plate of the bone while it raises the anterior part, thus tensing the membrane which closes the fenestra ovalis. Variations of the Hyoidean Muscles. A close relationship exists between the stylo-hyoid and the posterior belly of the digastric, the one or the other occasionally failing to separate from the common mass from which they are derived. A bundle of muscle-fibres sometimes passes from the tip of the styloid process to the angle of the mandible, forming what may be termed the stylo-rnandibularis, and recalling by its insertion the condition presented in certain cases by the posterior belly of the digastric (page 479). A duplication of the stylo-hyoid has also been observed, the second slip, which has been termed the stylo-hyo ideus profundus, varying considerably in its insertion, sometimes accompa- nying the stylo-hyoid proper and sometimes inserting into the lesser cornu of the hyoid, and in some cases replacing the stylo-hyoid ligament. The division of the stylo-hyoid near its insertion for the passage of the intermediate tendon of the digastric does not always occur, the insertion being by a single head which may pass either to the outer or the inner side of the tendon. (6) THE (a) SUPERFICIAL LAYER. 1 . Platysma. 2. Occipito-frontalis. 3. Auricularis posterior. 4. Auricularis superior. 5. Auricularis anterior. 6. Orbicularis palpebrarunf. 7. Zygomaticus major. 8. Levator labii superioris alaeque nasi. 9. Depressor labii inferioris. 10. Levator mrnti. PLATYSMA MUSCLES. (6) DEEP LAYER. 1. Orbicularis oris. 2. Nasalis (compressor nasi depressor ala- nasi i. 3. Levator labii superioris. 4. Levator anguli oris. 5. Risorius. 6. Depressor anguli oris. 7. Buccinator. et The comparative and embryological study of the platysma muscles have shown their origin from the musculature of the second or hyoid arch and their extension THE FACIAL MUSCLES. 481 thence over the head and neck. At first they are confined entirely to the neck region, but even in the lower mammals the extension upon the head has begun, and in the higher members of this group two portions can be distinguished in the muscle-sheet. The more superficial of these is situated in the lateral and posterior portions of the neck, and extends thence upon the sides of the face and over the vertex of the skull to the orbital and nasal regions of the face. The deeper one lies more anteriorly in the neck, and extends upward over the jaw to the region around the mouth. In the higher forms a differentiation of both layers to form a number of more or less separate muscles takes place and reaches its highest development in man, whose mobility of facial expression is due to the existence of a considerable number of platysma muscles. These muscles have arisen from the common sheets by the partial conversion of these into connective tissue, by the secondary attachment of portions of the sheets to the skeleton, by various modifications of the primary direc- tion of the fibres, and by the obliteration of certain portions of the sheet found in the FIG. 498. Depressor anguli oris TEJA Mandible - Raphe of mylo-hyoid Sterno-hyoid ^ Platysma-" 1 .Depressor labii inferioris Levator menti Mylo-hyoid Hyoid bone Thyroid cartilage Sterno-mastoid Sterno-thyroid* Inner end of clavicle Superficial muscles of neck. lower animals, the cervical portion of the deep layer, for instance, being normally lacking in man, the layer being represented only by the muscles of the lips. The platysma musculature is characterized for the most part by the pale color of its fibres, by their aggregation to form thin bands or sheets usually more or less inter- mingled with connective-tissue strands, so that their margins are, as a rule, ill-defined, and by their attachment in frequent cases to the integument. These peculiarities, together with a considerable amount of variation which occurs in the differentiation of the various muscles, have brought about not a little difference in the number of muscles recognized in the group by various authorities, some recognizing as distinct muscles what others regard as merely more or less aberrant or unusually developed slips. (a] THE MUSCLES OF THE SUPERFICIAL LAYER. i. PLATYSMA (Figs. 498, 499). Attachments. The platysma takes its origin from the skin and subcutaneous tissue over the pectoralis major and deltoid muscles on a line extending from the car- tilage of the second rib to the tip of the acromion process. Its fibres are directed 482 . HUMAN ANATOMY. upward and inward and are inserted into the body of the mandible from the sym- physis to the insertion of the masseter, the more posterior fibres extending upward upon the face towards the angle of the mouth and becoming lost partly in the fascia of the cheeks and partly among the muscles of the lips. Nerve-Supply. By the inframandibular branch of the facial nerve. Action. The contraction of the platysma results in drawing the lower lip downward and outward and at the same time raising the skin of the neck from the underlying parts. It is one of the most important muscles employed in the expression of horror and intense surprise. It does not seem probable that the muscle has much effect in producing depression of the mandible, an action which it might be expected to possess on account of its upper attachment. Relations. The platysma rests upon the deep fascia of the neck and covers all the structures at the front and sides of that region. Upon its deep surface lie the external jugular vein, the superficial lymph-nodes of the neck, and the superficial branches of the cervical plexus. It covers also the sterno-mastoid muscle and the depressors of the hyoid bone, and, above, the digastric and mylo-hyoid muscles, together with the submaxillary gland and the lower portion of the parotid. Variations. There is usually more or less decussation of the two muscles across the median line, especially in their upper parts, where, indeed, a certain amount of decussation may be considered a normal condition. The muscle is subject to considerable amounts of variation in its development, sometimes forming a very thin, pale layer largely interspersed with connective tissue, and at other times it is composed of strong, deeply colored bundles with much less inter- mixture of connective tissue. Its extension upon the face may also vary considerably, some- times being traceable as high up as the zygoma and extending backward to behind the ear. On the other hand, it may be very considerably reduced in size, especially below, a complete absence of the lower half of the muscle having been observed. 2. OCCIPITO-FRONTALIS (Fig. 499). Attachments. The occipito-frontalis (m. epicranius) is a muscular and aponeu- rotic sheet which covers the entire vertex of the skull from the occipital region to the root of the nose. It consists of two muscular portions, one of which, the occipitalis, arises from the superior nuchal line and inserts after a short course into the posterior border of the epicranial aponeurosis, while the other, thefrontatis, taking its origin from the anterior border of the galea, is inserted into the skin in the neighborhood of the eyebrows, over the glabella, and into the superciliary arches, a portion of it being frequently prolonged downward upon the nasal bone, forming what has been termed the pyramidalis nasi (m. procerus), which is frequently described as a distinct muscle. The epicranial aponeurosis (galea aponeurotica) (Fig. 499) is a dense aponeu- rotic sheet which covers the entire vertex of the cranium and is prolonged laterally over the temporal fascia as a thin layer which extends almost to the zygoma. On its superficial surface it is intimately associated with the integument, being united to its deeper surface by a thin but close and resistant layer of fascia which represents the superficial fascia of other regions of the body and in which are embedded the vessels and nerves of the scalp. The under surface of the galea is, however, smooth, and is connected with the periosteum by a lax layer of connective tissue, so that it is capable of considerable movement to and fro upon the periosteum, the skin being carried with it in such movements. A section through the scalp at the vertex would show from without inward ( i ) the skin, (2) the dense superficial fascia with its vessels and nerves, (3) the epicranial aponeurosis, (4) loose connective tissue, and (5) periosteum (Fig. 504). Nerve-Supply. The occipitalis is supplied by branches from the posterior auricular branch of the facial, the frontalis by branches from the rami temporales of the same nerve. Action. The occipitalis acting alone will draw backward the galea aponeurotica, while the frontalis draws it forward. If, however, the galea be fixed by the occipitales, the action of the frontales is to raise the eyebrows and throw the skin of the forehead into transverse wrinkles, both of these actions being greatly increased by the simul- taneous contraction of both the occipitales and the frontales. It is consequently the THE FACIAL MUSCLES. 483 muscle employed in the expression of interrogation and surprise and also, in con- junction with the platysma, in that of horror. v The transversus micha- is a thin muscular band, frequently present, arising from the occipital protuberance and extending laterally to terminate in various attachments ; sometimes, for instance, uniting with the posterior border of the sterno-cleido-mastoid or with the auricu- laris posterior. It may take its origin either superficial to or beneath the attachment of the trapezius to the superior nuchal line, and in the former case is to be regarded as a portion of the platysma group of muscles, while in the latter it is more probably a relic of the primary con- nection between the trapezius and the sterno-cleido-mastoid and belongs to that group of muscles (page 501). 3. AURICULARIS POSTERIOR (Fig. 499). Attachments. The posterior auricular (retrahens aureni) is composed of a few bundles of fibres which arise from the outer extremity of the superior nuchal line and the base of the mastoid process and pass horizontally forward to be inserted into the posterior surface of the concha. It is frequently imperfectly separated from the occipitalis. Nerve-Supply. By the posterior auricular branch of the facial nerve. Action. To draw the auricle backward. FIG. 499. -Frontalis Auricula ris superior Occipitalis Auricularis anterior Auricularis posterior Zygomaticus m Zygomaticus mil Levator ang Levator labii superioris Buccinator Risorius Co Orb ugator supercilii cularis palpebrarum bital part of same muscle ramidalis nasi Lev. labii sup. alaeque nasi Compressor narium Dilatores naris Depressor alae nasi Orbicularis oris Depressor anguli oris Depressor labii inferioris Levator menti Platysma Superficial dissection of head, showing platysma muscles. 4. AURICULARIS SUPERIOR (Fig. 499). Attachments. The superior auricular (attollens aurem) is a triangular muscle which arises from the lateral portion of the galea aponeurotica or from the temporal fascia and converges to be inserted into the upper part of the cartilage of the auricle. Nerve-Supply. By fibres from the rami temporales of the facial nerve. Action. To draw the auricle upward. 5. AURICULARIS ANTERIOR (Fig. 499). Attachments. The anterior auricular (attrahens aurem} is frequently con- tinuous with the preceding muscle, lying immediately anterior to it. It arises from the lateral part of the galea aponeurotica or from the temporal fascia and is inserted into the upper anterior part of the auricular cartilage or into the fascia immediately anterior to the cartilage. 4*4 HUMAN ANATOMY. Nerve-Supply. By fibres from the rami temporales of the facial nerve. Action. To draw the auricle upward and forward. it 6. ORBICULARIS PALPEBRARUM (Figs. 499, 500). The orbicularis palpebrarum (m. orbicularis oculi) is an elliptical sheet whose fibres have their origin in the neighborhood of the inner angle of the eye and curve thence, some upward and outward and some downward and outward, around the rima palpebralis to terminate in the neighborhood of the external angle. The course of the fibres lies partly in the substance of the upper and lower eyelids and partly over the bones surrounding the margin of the orbit. In accordance with these relations, it is customary to regard the muscle as consisting of two main portions, the pars palpe- bralis and the pars orbitalis. The internal pafpcbral ligament (ligamentum palpebrale mediate). Where the fibres of the orbicularis arise at the inner angle of the eye there is a dense band of fibrous tissue which is attached at one extremity to the frontal process of the maxilla. Thence it is directed outward across the outer surface of the lachrymal sac and bifur- cates to be inserted into the inner border of each tarsal plate. Just before its bifur- cation the ligament gives off from its posterior surface a bundle which is reflected inward over the lachrymal sac and FIG. 500. passes behind this to be attached to the Internal palpebral ligament Orbicularis palpebrarum crest of the lachrymal bone. Tensor tarsi \ Upper tarsal plate --ri_- i- / i t_ 'i i \ This ligament, which is also known it . as the tcnao oath, may be regarded as the tendon of origin of the fibres of the orbicularis oculi. At the outer angle of the eye there is a certain amount of decussation of the fibres of the muscle to form a raphe palpebralis lateralis, N Lower tarsal ^ut there ' s no distinct formation of a \ P late fibrous band comparable to the inter- paT p l ebrarum nal ligament. Orbicularis palpebrarum has been dissected from its deeper "aTS ralpeDrallS. 1 fie palpe- porSon or fen r sor e ta e rsi. inward wkh eyelids ' showing Iachr > mal bral portion of the muscle arises partly from the internal palpebral ligament and partly from the crest of the lachrymal bone. The fibres which take origin from the ligament arch outward in the upper and lower eyelids to terminate in the lateral palpebral raphe, forming a thin, pale sheet in the subcutaneous tissue of the eyelid. Its marginal fibres, sometimes more or less distinct from the others, form what has been termed the pars ciliaris or muscle of Riolan. The fibres which arise from the posterior lachrymal crest are usually regarded as forming either a distinct muscle, which has been termed the tensor tarsi or Homer' s muscle, or else as a separate part of the orbicularis, the pars lacrimalis. It is directed horizontally outward behind the lachrymal sac, resting upon the posterior surface of the reflected bundle of the internal palpebral ligament. Towards its outer end it bifurcates, sending a slip to each eyelid partly to be inserted into the tarsal plates and partly to fuse with the rest of the pars palpebralis. Pars Orbitalis. The orbital portion of the muscle is usually of a deeper color and somewhat thicker than the palpebral, and the fibres towards its periphery tend to scatter themselves among the adjacent platysma muscles and to make numerous connections with these. Some bundles from the lateral and lower parts of the muscle which extend downward and forward upon the cheek have been regarded as a dis- tinct muscle, the malaris. The main muscle arises from the internal palpebral ligament, the frontal process of the maxilla, and the inner portions of the upper and lower margins of tin- orbit. The fibres arch outward to tin- lateral palpebral raphe, a portion of those arising Irom the maxilla inserting into the integument of the eyebrow and forming \\hat has been termed the cor ruga tor snf>ercilii ( Fig. 499). Nerve-Supply. By the rami tempo'-ales and zygomatici of the facial nerv THE FACIAL MUSCLES. 485 Action. The principal action of the orbicularis palpebrarum is to approximate the upper and lower eyelids, closing the palpebral fissure. In addition, the attach- ment of the orbital portion to the skin draws the eyebrow downward and the skin of the cheek upward to form a fold around the margin of the orbit, giving increased protection to the eyeball. The corrugator supercilii draws the eyebrow downward and inward, producing vertical wrinkles of the integument over the glabellaand giving a thoughtful expression. The pars lacrimalis draws the tarsal plates inward and backward and so tenses the internal palpebral ligament, causing it to compress the lachrymal sac. 7. ZYGOMATICUS MAJOR (Figs. 499, 502). Attachments. The zygomaticus major (m. zygomaticus) is a slender muscle which arises above from the outer surface of the zygomatic bone, near its articulation with the zygomatic process of the temporal, and passes obliquely downward and for- ward towards the angle of the mouth. Its fibres interlace with those of the depressor and levator anguli oris, and terminate by blending with the orbicularis oris and by inserting into the subcutaneous tissue of the lips. Nerve-Supply. By fibres from the zygomatic branch of the facial nerve. Action. To draw upward and outward the angles of the mouth, as in smiling and laughing. Variations. A slender muscle is very frequently found arising from the zygomatic bone anterior to the zygomaticus and passing downward to be inserted into the upper lip. It lias been termed the zygomaticus minor, and appears to be a separation of a portion of the zygo- matic muscle. 8. LEVATOR LABII SUPERIORIS AL^EQUE NASI (Figs. 499, 501). Attachments. This muscle takes its origin from the outer surface of the frontal process of the maxilla, and descends along the angle which marks the junction of the nose and the cheek to be inserted into the integument of the upper lip and into the posterior part of the ala nasi. Nerve-Supply. From the rami zygomatici of the facial nerve. Action. The principal action of this muscle is to raise the upper lip, although its insertion into the ala nasi enables it to assist in the dilatation of the nostrils. Variations. This muscle is subject to considerable variation in its development, and frequently comes into continuity with neighboring muscles, especially with the zygomaticus minor, when this is present, and with the levator labii superioris proprius. Indeed, these two muscles are often associated with it to form what is termed the qnadratus labii superioris, of which the levator labii superioris alaeque nasi forms the cap/if angnlare, the levator labii superi- oris proprius the caput infraorbitale, and the zygomaticus minor the capnt zygomaticus. Since, however, the levator labii superioris proprius belongs to the deep layer of the platysma muscles, and therefore to a different group than the other heads of the quadratics, it seems preferable to regard all the heads as distinct muscles. 9. DEPRESSOR LABII INFERIORIS (Figs. 498, 499). Attachments. The depressor of the lower lips (in. quadratus labii inferioris) arises from the body of the mandible beneath the canine and premolar teeth, its origin being covered by the depressor anguli oris. It forms a thin quadrate sheet which is directed upward and forward and is inserted in the skin of the lower lip, its fibres mingling also with those of the orbicularis oris. Nerve-Supply. From the supramandibular branch of the facial nerve. Action. To draw down the lower lip. 10. LEVATOR MENTI (Fig. 498). Attachments. The levator menti (m. mentalis) arises from the body of the mandible below the incisor teeth, and its fibres descend, diverging as they go, to be inserted into the integument above the point of the chin. Nerve-Supply. From the supramandibular branch of the facial nerve. 486 HUMAN ANATOMY. Action. To draw upward the skin of the chin, thereby causing protrusion of the lower lip, as in pouting. When its action is combined with contraction of the depressors of the angles of the mouth, it gives an expression of haughtiness or con- tempt, and has thence been termed the m. superbus. When slightly contracted, it gives an expression of firmness or decision. Belonging to the superficial layer of the platysma musculature are a number of additional more or less rudimentary muscles attached at both extremities to various parts of the cartilage of the concha. These muscles will be considered in connection with the description of the ear (page 1499). (6) THE MUSCLES OF THE DEEP LAYER, i. ORBICULARIS ORIS (Figs. 499, 501, 503). Attachments. The orbicularis oris is a rather strong elliptical muscle whose fibres occupy the thickness of both the upper and lower lips between the skin and the mucous membrane of the mouth. For the most part the fibres composing the muscle are forward prolongations of the buccinator, but mingled with these there are fibres from all the muscles which are inserted in the vicinity of the mouth, such as the zygomaticus, levator anguli oris, levator labii superioris, depressor anguli oris, depressor labii inferioris, and risorius. It possesses, however, some slight attachment to skeletal structures by three groups of fibres which have frequently been regarded as distinct muscles. These groups are : ( i ) the incisivi labii superioris, a series of bundles of fibres which arise from the incisive fossae of the maxillae and pass downward and outward to mingle with the other fibres of the orbicularis at the angles of the mouth ; (2) the incisivi labii inferioris, which arise from the alveolar border of the mandible beneath the canine teeth and unite with the orbicularis at the angles of the mouth ; and (3) the depressor septi, composed of the uppermost fibres of the orbicularis, which bend up- ward from either side in the median line and are inserted into the margin of the septal cartilage of the nose. Nerve-Supply. From the rami buccales and supramandibular branch of the facial nerve. Action. The main action of the orbicularis oris is to bring the lips together, closing the mouth, and if its action be continued, it will press the lips against the teeth. Its more peripheral fibres, aided by FIG. 501. the incisive bundles, will tend to pro- Pyramidalis nasi trude the lips. 2. NASALIS (Fig. 501). m Attachments. The nasalis . . ^K narium ess forms a thin sheet which arises from ;Diiatores naris the maxilla in close association with Levator iabii_ '^B* F M ^jf \/7 the incisive bundles of the upper lip. na p si al na q s u a1 I^* The more medial fibres, the pars alaris portion cut mm <*Lm ) ( depressor alte nasi} , are inserted into away 'Sffw^/ , , , . ILg^f the alar cartilage ot the nose, while BlJaf^nenH^nr^nti the more lateral ones, the pars trans- orbicuiaris oris ^pUP^ versa ( compressor nariuni) , often re- ceiving slips from the adjacent levator labii superioris alaeque nasi and the Muscles of the nose. levator anguli oris, extend forward over the ala of the nose to terminate upon its dorsal surface in a thin aponeurosis which unites it to the muscle of the opposite side. Nerve-Supply. From the zygomatic and buccal rami of the facial nerve. Action. The more median fibres draw the alar cartilage downward and in- ward, while the more lateral ones slightly depress the tip of the nose and at the same time compress the nostril. THE FACIAL MUSCLES. 487 Variations. Fibres from the nasalis sometimes pass upward upon the nasal bones and may enter into the formation of the pyramidalis nasi ( page 482 ) . Frequently the pars alaris and pars transversa are recognized as distinct muscles, the former being termed the depressor alee nasi or myrtiformis, while the latter is named the compressor narium. Uncertain and at best feeble muscular slips on the outer margin of the nostrils are sometimes described as distinct muscles, the dilatores naris anterior et posterior. 3. LEVATOR LABII SUPERIORIS (Fig. 499). Attachments. The elevator of the upper lip (m. levator labii superioris pro- prius) arises above from the infraorbital margin of the maxilla and extends almost vertically downward over the infraorbital vessels and nerve to join with the orbicu- laris oris and also to be inserted into the skin of the upper lip between the insertions of the levator labii superioris alseque nasi and the levator anguli oris. Nerve-Supply. From the zygomatic branches of the facial nerve. Action. To raise the upper lip. Acting in conjunction with the levator labii superioris alaeque nasi, it plays an important part in the expression of grief. 4. LEVATOR ANGULI ORIS (Figs. 499, 502). Attachments. The elevator of the angle of the mouth (m. caninus) arises from the canine fossa of the maxilla by a rather broad origin, from which its fibres con- verge to be inserted into the skin at the angle of the mouth, partly mingling with the fibres of the depressor anguli oris. Nerve-Supply. From the zygomatic branches of the facial nerve. Action. To raise the angle of the mouth. 5. RISORIUS (Fig. 499). Attachments. The risorius is a triangular sheet of muscle which arises from the outer surface of the parotido-masseteric fascia and from the integument of the cheek and passes forward towards the angle of the mouth, where it unites with the triangularis and orbicularis oris. Nerve-Supply. From the rami buccales of the facial nerve. Action. To draw the angle of the mouth outward. Its contraction imparts a tense and strained expression to the face which is termed the risus sardonicus. Variation. The risorius is frequently absent, and may be represented only by some scattered muscular bands. Its intimate association with the depressor anguli oris indicates its derivation from that muscle. 6. DEPRESSOR ANGULI ORIS (Figs. 498, 499). Attachments. The depressor of the angle of the mouth (m. triangularis) takes its origin from the outer surface of the body of the mandible and from the skin and passes upward to the angle of the mouth, where its fibres are inserted into the skin and also mingle with those of the caninus, risorius, and orbicularis oris. Nerve-Supply. From the supramarginal branch of the facial nerve. Action. To draw the angle of the mouth downward and slightly outward, giving an expression of sorrow. Variations. A bundle of fibres not infrequently arises from the anterior border of the depressor anguli oris near its origin and passes obliquely downward and inward towards the median line beneath the chin, either losing itself in the superficial fascia of that region or uniting with its fellow of the opposite side. This slip has been regarded as a distinct muscle and termed the transversus menti. It seems exceedingly probable that both this bundle and the risorius are derivatives of the depressor, and this muscle, notwithstanding its position super- ficial to both the depressor labii inferioris and the platysma, is really a portion of the deeper layer of the platysma musculature, its present position having been acquired by a migration from the region of the upper lip. 488 HUMAN ANATOMY. 7. BUCCINATOR (Fig. 502). Bucco-Pharyngeal Fascia. The buccinator alone of the platysma group of muscles is covered by a distinct layer of fascia which forms the anterior part of the fascia buccopharyngea and is a dense, resistant sheet of connective tissue intimately FIG. 502. Temporal \ Corrugator supercilii Orbic. palp., palpebral part Pyramidalis nasi Orhic. palp., orbital part Lev. labii sup. al. nasi (cut) Levator labii superioris (cut) Compressor narium Levator anguli oris ^ Zygomaticus Buccinator Orbicularis oris Depressor labii inferioris Levator tnenti atysma Tensor palati Levator palati Styloid process ; Hamular process - : Digastric, posterior belly Superior constrictor Stylo-gloss us Pterygo-mandibular ligament Stylo-phyarynneus Stylo-hyoid Mandible (cut) Hyo-glossus Greater hyoid cornu Middle constrictor Thyro-hyoid Inferior constrictor Oral, pharyngeal, and styloid groups of muscles; part of mandible has been removed to show deeper structures. adherent to the outer surface of the muscle. Anteriorly the fascia thins out to disap- pear in the tissue of the lips ; above it is attached to the alveolar portion of the maxilla and to the internal pterygoid plate of the sphenoid, and -thence is continued backward over the superior con- FIG. 503. stricter muscle of the pharynx to meet with its fellow of the opposite side behind the phar- ynx ; below it is attached to the posterior part of the mylo-hyoid ridge of the mandible. Along a line which descends vertically from the tip of the hamulus of the sphenoid to the posterior extremity of the mylo-hyoid ridge of the mandible the fascia is greatly thickened, forming the ptcrygo-fnandibular Hga- nicnt, from which fibres of the buccinator arise anteriorly, while posteriorly it gives origin to a portion of the superior constric- tor of the pharynx. Attachments. The buc- cinator forms a thick quadrilateral muscle lying immediately exterior to the mucous membrane of the cheek. Its line of origin is horseshoe-shaped, extending above along the alveolar border and tuberosity of the maxilla and thenre upon the hamulus Levator anguli oris Buccinator 1 U-pn-ssor anguli oris Diagram showing course ..I <-onipi>nrnt lilurs loiming orbicu' Lilians oris nmsrU-. PRACTICAL CONSIDERATIONS : THE SCALP. 489 of the internal pterygoid plate of the sphenoid. It then descends upon the anterior border of the pterygo-mandibular raphe, whence it passes forward along the body of the mandible, above the mylo-hyoid ridge, as far as the premolar teeth. From this extensive origin its fibres are directed forward to become continuous with those of the orbicularis oris, also inserting to a certain extent into the integument of the lips. Nerve-Supply. From the buccal branch of the facial nerve. Action. The buccinator draws the angle of the mouth laterally, pressing the lips against the teeth. When the cheeks are distended the muscle serves to com- press the contents of the mouth, and plays an important part in mastication in pre- venting the accumulation of the food between the cheek and the jaws, forcing it back between the teeth. Relations. Superficially with the bucco-pharyngeal fascia, which is separated from the anterior part of the masseter and from the zygomaticus and risorius by an extensive pad of fat, the buccal fat-pad. This is prolonged backward into the zygo- matic fossa between the temporal and pterygoid muscles, and is traversed by the facial vessels and the buccal branches of the trigeminal and facial nerves. The buccinator is pierced from without inward by the parotid duct and by the buccal branch of the trigeminal nerve on its way towards its distribution to the mucous membrane of the cheek. PRACTICAL CONSIDERATIONS : MUSCLES AND FASCIAE OF THE CRANIUM. The Scalp. The Occipito- Frontal Region. The layers of the scalp from within outward are : i. The pericranium as the periosteum covering this part of the skull is termed closely invests the underlying bones and is firmly attached at the sutures through which, so long as these remain ununited, it is continuous (intersutural mem- brane) with the outer layer of the dura, the endosteum of the cranium. A similar FIG. 504. Hair-follicle Fibrous septa Outer compact bone- Diplo< Inner compact bone uperficial fascia Aponetirosis Subaponeurotic ssue Pericranium Bone Dura mater Pacchionian bodies Superior longitudinal sinus Portion of frontal section of head hardened in formalin, showing layers of scalp, skull, and meninges. X 2'A and more constant continuity exists through the foramina. As the dura is the chief source of blood-supply of the cranial bones, they rarely necrose after accidents which strip the pericranium from their surface (page 237). Subpericranial effusions of blood, or collections of pus, are limited and outlined by the lines of the sutures. Cephalhaematomata' ' in this situation correspond in shape to that of one bone ; they are commonly congenital, constituting a form of caput succedaneum, following head presentations, and are then apt to be found over a parietal bone, since that region is most exposed to pressure during child-birth. Tillaux suggests that in early life they may be encouraged by the softness and vascularity of the cranial bones and the 490 HUMAN ANATOMY. laxity of the pericranium, and that their greater frequency in male children may depend upon the larger size of the head in the male foetus. The close association of the bloody effusion with the pericranium an osteogenetic membrane sometimes results in the development of bone at the periphery of the swelling. The hard ridge which is usually present at this situation may give rise, through contrast with the relatively depressed centre, to the mistaken diagnosis of fracture of the skull. Occasionally a collection of blood beneath the pericranium communicates with the diploic sinuses, when it will probably be situated to one side of the cranium ; or with the superior longitudinal sinus, when it will be in the mid-line. No traumatic history may be obtainable. The swelling will be soft, reducible, of varying tension, and may receive from the brain a feeble pulsatile impulse. The importance of the emissary veins in transmitting extracranial infection to the venous channels of the dura may be mentioned here, but can better be under- stood after the venous system has been described (page 876). 2. The subaponeurotic connective tissue between the pericranium and the apo- neurosis of the occipito-frontalis. This is so loose, thin, and elastic that the union between these layers is not a close one. The motion of the ' ' scalp' ' upon the skull is a motion of the parts above upon the parts beneath this layer. Movable growths will, therefore, be found to occupy the former region and immovable swellings will probably have deeper attachments. Effusions of blood, suppuration, or infective cellulitis occurring in the subaponeurotic space may extend widely, and may be limited only by the attachments of the musculo-fibrous layer. They may reach, there- fore, posteriorly to the superior curved line of the occipital bone, anteriorly to a little above the eyebrows, and laterally to a level somewhat above the zygoma. Exten- sive haematomata are uncommon, as the vessels in this cellular tissue are few and small. If they are large, they suggest fracture of the skull with laceration of a branch of the middle meningeal artery or of a venous sinus. They may, however, by reason of a hard border and soft centre, be mistaken for depressed fracture when the skull itself is uninjured. Suppuration and cellulitis are often serious on account of the tendency to spread, the possible extension to the meninges, and the difficulty in applying antisepsis, in securing drainage, or, later, in obtaining the rest necessary for rapid healing. In abscess the diffusion of the pus is favored by the density and the vitality of the super- jacent layers, which, in consequence of the former property, do not soften and permit pointing, and, because of the latter, do not slough and thus give exit to the pus, which therefore may extend in the line of least resistance, i.e., along the loose subapo- neurotic layer. Wounds involving either the muscle or its aponeurosis, if transverse to the direction of their fibres, gape widely. Their healing will be hastened by firm bandaging of the whole cranium so as to control and limit the movements of the scalp. 3. The occipito-frontalis muscle and aponeiirosis ; 4, the superficial fascia ; 5, the skin. These three layers are so intimately blended that from the practical stand-point they may be considered together. The thin aponeurosis is tied to the skin (which is here thicker than anywhere else in the body) by dense, inelastic, perpendicular and oblique fibres of connective tissue, enclosing little shot-like masses of fat. This area is very vascular, almost all the vessels of the scalp being found in it adherent to the cellular-tissue walls of the fat-containing compartments. As a result of these anatomical conditions it is found that (i) suppuration is very limited in extent ; (2) superficial infections (such as erysipelatous dermatitis) are accom- panied by but little swelling ; (3) incised wounds do not gape ; (4) lacerated and contused wounds are not followed by sloughing, which is also rare as a result of continuous pressure, as from bandages ; (5) hemorrhage after wounds is abundant and is persistent because of the adherence of the vessel-walls to the subcutaneous layer of fascia, which prevents both their retraction and contraction ; (6) collections of blood after contusions may, like the deeper ones already described, become very firm at the periphery, in this case from an excess of fibrinous exudate and from the presence of particles of displaced fat, while the inelastic fibres of cellular tissue (from among which the fat particles have been driven out by the force of the blow) remain depressed in the centre ; these appearances have not infrequently led to a PRACTICAL CONSIDERATIONS: THE SCALP. 491 mistaken diagnosis of fracture of the skull ; (7) lipomata are rare, as in the only layer in which fat is found its abnormal growth is resisted by the density of the surrounding connective tissue. Baldness affects especially the area $f the scalp which directly overlies the occipito-frontal aponeurosis. It is attributed (Elliott) largely to the lack of muscular fibres in this region, so that the skin is not ' ' exercised' ' and the lymph-current is made to depend chiefly on gravity. The density of the superficial fascia connecting the skin and the aponeurosis allies it with that of the palmar and plantar regions, in both of which similarly dense fascia is found and hair is absent. Dermoids are common over the anterior fontanelle and the occipital protuber- ance because the early contact of the skin and dura mater continues longest in these regions. "Should the skin be imperfectly separated, or a portion remain persist- ently adherent to the dura mater, it would act precisely as a tumor germ and give rise to a dermoid cyst" (Sutton). Wens are also common on account of the presence of large numbers of seba- ceous glands. In removing such growths, if the dissection is carried close to the sac, the subaponeurotic layer will not be opened and all danger, even in case of infection, will be minimized. So-called ' ' horns' ' are found here with relative frequency by reason of the number of sebaceous glands. Emphysema of the scalp may occur as a complication of fractures involving the pharynx, the frontal sinuses, or the ethmoid or nasal bones. The air infiltrates either the subaponeurotic or subcutaneous cellular tissue. Pneumatocele of the frontal region is very rare, but has occurred in a few cases as a result of a communication between the nasal cavity and bony defects in the anterior wall of the frontal sinuses. The swelling is soft, elastic, and resonant, and is made more tense by forced expiration, less so by pressure. The entrance and escape of air may be heard on auscultation. The air is always beneath the pericranium. Syphilis, tuberculosis, carcinoma, and sarcoma may affect the scalp primarily, and are mentioned in the order of frequency of occurrence. Cirsoid aneurism is especially frequent upon the scalp. The Temporal Region. Here the skin is thinner and less intimately adherent to the subcutaneous fascia than in the occipito-frontal region ; that fascia also is somewhat less closely connected to the aponeurosis beneath. Hemorrhage between these layers is therefore .more easily controlled by the usual process of picking up and tying the vessel, the walls of which will be found freer from attachments to the bundles of fascia. The fascia over the temporal muscle itself is of such strength and thickness that abscesses beneath it rarely point above the zygoma, but are directed into the pterygo- maxillary region and thence into the pharynx or into the neck, or along the anterior temporal muscular fibres to the coronoid process and thence into the mouth. Abscesses above it have no special anatomical peculiarities. The fat in the temporal fossa is abundant, and is found in the subcutaneous fascia, between the two layers of the temporal fascia, and directly upon the muscle itself. The disappearance of this fat in diseases attended by emaciation causes the characteristic unnatural prominence of the zygoma and apparent deepening of the temporal fossae. The temporal muscle should be considered with the pterygoids in their relation to fracture of the ramus and coronoid process (pages 245, 493), to dislocation of the inferior maxilla (pages 246, 493), and to resection of that bone. The pericranium of this region is thinner and more adherent than that of the occipito-frontal region, and the subpericranial connective 'tissue is absent ; hence subperiosteal abscess or haematoma is practically unknown. The region may be invaded by tumors originating in the orbit and spreading through the spheno-maxillary fissure or through the thin orbital process of the malar bone. Trephining and other operations in this region are so closely related to intra- cranial diseases and middle-ear disease that they will be considered in that relation (page 1509). 492 HUMAN ANATOMY. The Mastoid Region. For the same reasons the practical anatomy of the soft parts covering the remaining region of the skull the mastoid will be taken up later (page 1508). The Face. The skin of the forehead and cheeks is thin and vascular and the cellular tissue beneath is loose. Therefore wounds bleed freely but unite rapidly ; sloughing is rare ; cellulitis tends to spread ; oedema is common ; superficial infections (favored by the constant exposure of the region) are attended by much redness and swelling and little pain ; if they result in abscess, it is not apt to attain a large size, as the delicacy of the skin permits of early pointing. On the other hand, necrotic processes (as in cancrum oris) once established in the loose cellular tissue and fat of the cheeks, run a rapid and destructive course, and may be followed by great dis- figurement and by limitation of the motions of the inferior maxilla. Abscesses beneath the buccinator aponeurosis, like fatty growths in the same situation, project towards the cavity of the mouth ; they should be opened through the mucous membrane. FIG. 505. Upper cut edge of masseter _ Temporal External pterygoid Internal pterygoid Masseter (cut) Parotid gland partly removed Buccinator 'osterior fragment Line of fracture Anterior fragment Digastric, anterior belly Mylo-hyoid I lyo-glossus Body of hyoid bone Thyro-hyoid Omo-hyoid Sterno-hyoid Dissection of fracture of body of mandible, showing displacement produced by muscular action. Over the lower third of the nose the skin is closely adherent, as it is over the chin, where it is also very dense. Infections in those regions are therefore exception- ally painful (page 246). The vascularity and mobility of the skin of the forehead and of the cheeks make it especially useful in plastic operations upon tin n-gion of the nose and mouth. On account of the rich blood-supply, naevi are common on all parts of the fan , as, by reason of the numerous sweat and sebaceous glands, are acneiform eruptions. Lupus and malignant pustule are frequent and grave forms of local infection : rodent ulcer (epithelioma) is common ; while on the forehead the early syphilitic- roseola or papule (corona veneris) and about the lips and nose the later tubercular syphilide are often seen. Lipomata, in spite of the considerable quantity of fat in the subcutaneous tissue, are very rare. The mass of fat between the buccinator and masseter muscles PRACTICAL CONSIDERATIONS : THE FACE. 493 FIG. 506. Upper joint-cavity Interarticular cartilage Ram us of mandible " boule de Bichat," "sucking cushion" is believed to receive and distribute the increased atmospheric pressure which follows the establishment of a partial vacuum in the mouth during- sucking. It thus aids in preventing the buccinator from being carried in between the alveoli. It is relatively smaller in adults than in infants and in the latter does not much diminish in size, even in the presence of emaciation, when the general subcutaneous fat has largely disappeared ( Ranke) . Sutton says, ' ' The sucking cushions sometimes enlarge in adults and simulate more serious species of tu- mors, and it is curious that in some of the recorded cases the enlargement has been as- sociated with the impaction of a salivary calculus in the duct of the parotid gland. ' ' The importance of avoid- ing conspicuous scars on the face leads the surgeon to make his incisions, whenever possi- ble, either in or parallel with the lines of the natural furrows due to the insertion of some of the facial muscles into the skin itself, or in the shadow of overhanging parts, as beneath the upper brow or the lower edge of the inferior maxilla. For a reason not understood, but possibly associated with the difficulty in securing rest, combined with the large vascular sup- ply, cicatricial overgrowth and true keloid are both relatively common after wounds of the face. In fracture of the inferior maxilla the irregularity in the horizontal planes of the two fragments (the anterior being the lower) is due to (a) the weight of the chin and opposite side of the jaw FIG. 507. Articular eminence Dissection showing relations when mandible rests within glenoid fossa ; outer part of capsular ligament has been cut away, exposing upper and lower joint-cavities. I'pper joint-cavity Tendon of- .7 temporal . ;ji muscle ; V; Coronoid' process < the action on the an- terior fragment of the di- gastric and other depressors of the chin ; and (c) the effect of the posterior fibres of the temporal, the internal pterygoid, and the super- ficial fibres of the masseter in elevating the posterior fragment (Fig. 505). In fracture of the ramus there is little displacement, as the bone lies between the two muscular planes of the masseter and internal ptery- goid and is splinted by them. In fracture of the neck of the condyle the upper fragment is drawn upward and forward by the external pterygoid ; the re- mainder of the jaw is some- what elevated by the masseter, temporal, and internal pterygoid. The difficulty in approximation of the fragments may result in excess of callus, which greatly interferes with the subsequent movements of the temporo-maxillary articulation. The mechanism of dislocation of the lower jaw has already been described (page Ramus of mandible Dissection showing relations when mandible is depressed and carried forward upon articular eminence; capsular ligament is stretched in con- sequence. 494 HUMAN ANATOMY. ..Temporal muscle 'ondyle of jaw 246), but can now be better understood. It should be remembered that the muscles of mastication are exceptionally irritable and are all supplied by the motor branch of the mandibular division of the fifth nerve. When the mouth is opened very widely, as in yawning, or in an effort to take an unusually large bite, the deep posterior ver- tical fibres of the masseter (which are the only ones attached to the ramus and aiding in closing the mouth that do not run forward as well as upward) are carried behind the centre of motion, so that their contraction tends still further to open the mouth or to keep it open. Reflex contraction from overstretching is excited in the general group, and the external pterygoid acting with most advantage in that position, draws the condyle into the zygomatic fossa, where it is held by the masseter and internal pterygoid. ' ' Noisy movement' ' of the temporo-maxillary joint is often due to weakness of the muscles of mastication, permitting the joint surfaces to fall apart as the result of the slight lengthening of the ligaments produced in time by the weight of the jaw. Paralysis and spasm of the facial and masticatory muscles will be considered in relation to the nerves supplying them (pages 1255, 1248). The most frequent congenital defect of the muscles of the face is in connection with harelip, in which deformity FIG. 508. the portion of the orbicularis oris corresponding to the cleft is absent. Dermoids are not infre- quently found at the angles of the orbit, in the cheeks near the corner of the mouth, in the naso-labial furrows, at the root of the nose, and in the mid-line of the chin. Reference to the embryology of the face will show that these are localities in which epiblastic inclusion is likely to occur. Marked congenital asym- metry of the face may occur from failure of developmental processes. Landmarks. Just within the mid-point of a line drawn from the mastoid process to the external occipital protuberance the occipital artery can be felt as, with the great occipital nerve, it enters the scalp on its way to the vertex. The superficial temporal artery can be felt, and often can be seen where it runs over the base of the zygoma in front of the ear. Its vein and the auriculo-temporal nerve are just behind it. The division of the artery into its anterior and posterior branches takes place about 5 cm. (2 in.) above the zygoma. These branches are easily palpable on the firm underlying structures, and thus afford testimony as to the presence or absence of arterial degeneration. In old persons they are often tortuous and plainly visible, especially the anterior branch where it crosses the anterior por- tion of the temporal muscle. The region is a frequent seat of cirsoid aneurism. At the junction of the middle with the inner third of the supra-orbital bony margin the supra-orbital notch may be felt. From this point the supra-orbital nerve and artery pass almost directly upward, crossing the orbital margin. Between that point and the root of the nose the frontal artery and supratrochlear nerve ascend and the frontal vein descends. The movement of the condyle of the inferior maxilla up to the summit of the eminentia articularis when the mouth is open and the external pterygoid contracts, and its return into the glenoid cavity when that muscle is relaxed and the mouth closed, can plainly be felt. Masseter muscle, partly cut away Dissection showint slipped Mandible position of dislocated jaw, condyle having in front of articular eminence. THE VAGO-ACCESSORY MUSCLES. 495 The relation of many of the bony points to the overlying soft parts has been described (page 246). The shape of most of the muscles cannot be separately distinguished. Com- parison of a skull with a partially dissected head will show, however, that over the vault of the cranium from the supra-orbital ridges to the nucha the general shape of the skull determines the surface form during life, the flattened muscles and aponeu- rosis closely conforming to it. In the temporal regions, in spite of the deep bony fossa, the triangular muscle and the accompanying fat (page 491) make the surface in vigorous, well-nourished persons slightly convex. The outlines of the muscle can be seen when it is in contraction, especially the portion anterior to the hairy scalp. On the face the characteristics that distinguish the individual are due largely to the presence of muscles and of subcutaneous fat. The edge of the orbit and the naso-frontal junction are covered and given rounded outlines by the orbicularis palpebrarum and the pyramidalis nasi. The muscles running from the malar bone and maxilla to the upper lip aid the buccinator and the fat of the cheek in rilling up the great hollows beneath the malar prominences. The orbicularis oris gives shape and expression to the mouth. The masseter fills out the posterior portion of the cheek and becomes visible in outline when in firm contraction, especially the vertical anterior border, just in front of which the facial artery crosses the inferior maxilla. As nearly all the facial muscles have fibres of insertion into the facial integument, their influence upon expression and upon the creases and folds that become perma- nent as ' ' wrinkles, " " crows' feejt, ' ' etc. , is apparent. III. THE VAGO-ACCESSORY MUSCLES. The muscles supplied by the glosso-pharyngeal, vagus, and spinal accessory nerves may be grouped together both on account of their relations in the adult and on account of the intimate relations which exist between the three nerves. The glosso-pharyngeal and vagus correspond to the posterior branchial arches, the glosso- pharyngeal to that represented in the adult by the greater cornu of the hyoid bone and the vagus to those represented by the laryngeal cartilages. Consequently we find the muscles supplied by these nerves to be those associated with the pharynx and larynx, one of the muscles of the soft palate, the levator palati, being also included in the group. The pharyngeal muscles, for the most part, are supplied from the pharyngeal plexus, into which fibres from both the glosso-pharyngeal and vagus nerves enter. The laryngeal muscles, however, are supplied by branches coming directly from the stem of the vagus nerve. The spinal accessory nerve stands in such intimate relations with the vagus that its nucleus of origin may well be regarded as an extension of that of the vagus, and by the union of a portion of its fibres with those of the vagus to form a common trunk opportunity is afforded for its fibres to participate in the formation of the pharyngeal plexus, and there is evidence pointing to the origin of the fibres of the inferior laryngeal nerve, which supplies the majority of the laryngeal muscles, from the spinal accessory nucleus. In addition, however, to its participation in the supply of the pharyngeal and, possibly, the laryngeal muscles, the spinal accessory also innervates the trapezius and sterno-mastoid muscles, and these, on account of their relations, must constitute a subgroup distinct from the other vago -accessory muscles. (a) THE MUSCLES OF THE PALATE AND PHARYNX. 1. Stylo-pharyngeus. 5. Palato-pharyngeus. 2. Levator palati. 6. Constrictor pharyngis superior. 3. Azygos uvulae. 7. Constrictor pharyngis medius. 4. Palato-glossus. 8. Constrictor pharyngis inferior. i. STYLO-PHARYNGEUS (Figs. 502, 509). Attachments. The stylo-pharyngeus arises from the inner surface of the styloid process near its base. It is directed downward, the glosso-pharyngeal nerve 496 HUMAN ANATOMY. covering its outer surface, passes between the middle and superior constrictors of the pharynx, and, being joined by fibres from the palato-pharyngeus, is inserted into the posterior border of the thyroid cartilage and the posterior wall of the pharynx. Nerve-Supply. By a branch of the glosso-pharyngeal nerve. Action. To draw upward the posterior wall of the pharynx and the thyroid cartilage. 2. LEVATOR PALATI (Fig. 509). Attachments. The elevator of the soft palate (m. levator veli palatini) arises from the under surface of the apex of the petrous portion of the temporal bone and from the cartilaginous portion of the Eustachian tube. It descends obliquely down- Salpingo- pharyngeus Levator palati- Superior ^ constrictor Palato-pharynge Palato-pharyngeus Stylo-pharyngeus ! FIG. 509. Nasal septum Eustachian tube External pterygoid Posterior crico-arytenoid -(Esophagus Muscles of palate and pharynx, seen from behind ; pharynx laid o'pen. ward and forward, and, broadening out, enters the substance of the soft palate, into the aponeurosis of which it is inserted. Nerve-Supply. From the pharyngeal plexus by fibres which probably have their origin in the anterior part of the nucleus of the spinal accessory nerve. Action. To elevate the soft palate. 3. A/v<;os UVUL^: (Fig. 509). Attachments. The azygos uviihr (m. uvulae"), so named <>n the supposition that it was an unpaired muscle, consists of two narrow slips which arise from the THE VAGO-ACCESSORY MUSCLES. 497 aponeurosis of the soft palate and from the posterior nasal spine. They pass back- ward and downward, almost parallel with each other, into the uvula to be inserted into its aponeurosis. Nerve-Supply. From the pharyngeal plexus. Action. To raise the uvula. 4. PALATO-GLOSSUS (Fig. 1339). Attachments. The palato-glossus (m. glossopalatinus) is a thin sheet which arises from the under surface of the aponeurosis of the soft palate and descends in the anterior pillar of the fauces (arcus glossopalatinus) to be inserted into the sides of the tongue, mingling with the fibres of the stylo-glossus. Nerve-Supply. From the pharyngeal plexus, probably by fibres from the anterior part of the nucleus of the spinal accessory nerve. Action. To raise the back part of the tongue and at the same time to narrow the fauces by causing an approximation of the anterior pillars. Acting from below, it will depress the soft palate. 5. PALATO-PHARYNGEUS (Fig. 509). Attachments. The palato-pharyngeus (m. pharyngopalatinus) arises from the aponeurosis of the soft palate, from the posterior border of the hard palate, and also from the lower portion of the cartilage of the Eustachian tube. It passes downward and backward in the posterior pillar of the fauces (arcus pharyngopalatinus), internal to the superior and middle constrictors of the pharynx, and is inserted into the pos- terior border of the thyroid cartilage and into the posterior wall of the pharynx. That portion of the muscle which arises from the cartilage of the Eustachian tube is often regarded as a distinct muscle which has been termed the salpingo-pharyngeus. Nerve-Supply. From the pharyngeal plexus, probably by fibres from the anterior part of the nucleus of the spinal accessory nerve. Action. It draws the pharynx and thyroid cartilage upward and at the same time approximates the two posterior pillars of the fauces. Acting from below, it will depress the soft palate. 6. CONSTRICTOR PHARYNGIS SUPERIOR (Figs. 501, 510). Attachments. The superior constrictor of the pharynx forms a thin quadri- lateral sheet whose origin is closely associated with part of that of the buccinator, there being usually some interchange of fibres between the two muscles. It arises from the lower part of the posterior border of the internal pterygoid plate and from its hamulus, from the posterior border of the pt'erygo-mandibular ligament, and is thence continued upon the internal oblique line of the mandible, the mucous mem- brane of the mouth, and the side of the tongue. The uppermost fibres pass in a curve backward and upward and are inserted into the pharyngeal tubercle of the occipital bone, while the remainder unite with the muscle of the opposite side in a median raphe on the posterior wall of the pharynx. Nerve-Supply. From the pharyngeal plexus by fibres which probably arise from the anterior portion of the nucleus of the spinal accessory nerve. Action. To compress the pharynx. Relations. Between the uppermost fibres of the muscle and the base of the skull is an interval in which may be seen the levator palati and the Eustachian tube. This interval has been termed the sinus of Morgagni, and is closed by a sheet of connective tissue termed the fascia pharyngobasilaris, which is an upward prolonga- tion to the base of the skull of the pharyngeal portion of the bucco-pharyngeal fascia (page 488). Externally the superior constrictor is in relation above with the internal carotid artery, the vagus nerve, and the cervical sympathetic, and below with the upper part of the middle constrictor and the stylo-pharyngeus. Internally it is lined by mucous membrane throughout the greater part of its extent, being in relation, how- ever, with the tonsil and the palato-pharyngeus muscle. 32 498 HUMAN ANATOMY. Variations. A considerable amount of independence may exist between the bundles of fibres coming from different portions of the line of origin, and the muscle has consequently been described as consisting of various portions to which the terms pterygo-pharyngeus, bucco- pharyngeus, mylo-pharyngeus, and glosso-pharyngeus have been applied. Not infrequently a bundle of fibres is to be found arising from the basilar portion of the occipital bone or even from the inferior surface of the petrous portion of the temporal or the spine of the sphenoid, and passing downward to be inserted along with the pharyngo-palatinus. A bundle which passes from the cartilaginous portion of the Eustachian tube to be inserted with the palato-pharyngeus has been termed the sal ping o-pharyngeus. Internal carotid artery Internal jugular vein Central attachment of pharynx Mastoid f^s process Internal pterygoid Styloid process L Digastric, posterior belly Stylo- pharyngeus Stylo-glossus Stylo-hyoid Stylo-hyoid ligament Lateral expan- sion of pharynx Tip of great cprnu of hyoid bone Thyro-hyoid ligament Superior cornu of thyroid cartilage Middle constrictor ndible Inferior constrictor ongitudinal muscle of oesophagus . Muscles of pharynx from behind ; portion of ink-i ior constrictor has be?n removed. 7. CONSTRICTOR PHARYNGIS Mr.nirs (Fi^. 510). Attachments. The middle constrictor of the pharynx is a fan-shaped sheet which arises from the stylo-hyoid ligament and both cornua of the hyoid bone. The lil. res pass backward to be inserted into the pharyngeul raphe, the upper fibres THE VAGO- ACCESSORY MUSCLES. 499 overlapping the lower part of the superior constrictor and extending in some cases almost to the occipital bone, while the lower fibres are overlapped by the inferior constrictor. Nerve-Supply. From the pharyngeal plexus, probably by fibres from the anterior portion of the spinal accessory nucleus. It is said to be supplied also by the glosso-pharyngeal nerve. Action. To compress the pharynx. Variations. As in the case of the superior constrictor, the fibres from different parts of the origin may have considerable independence. Thus the fibres from the greater cornu of the hyoid have been recognized as a muscle, the cerato-pharyngeus, distinct from the remainder, to which the term chondro-pharyngeus has been applied. 8. CONSTRICTOR PHARYNGIS INFERIOR (Figs. 501, 510). Attachments, Like the middle constrictor, the inferior is also a fan-shaped sheet and arises from the outer surface of the thyroid and cricoid cartilages of the larynx. The fibres radiate backward to be inserted into the pharyngeal raphe, the upper ones overlapping the lower part of the middle constrictor, while the lower ones mingle with the musculature of the oesophagus. Nerve-Supply. From the pharyngeal plexus, probably through fibres from the anterior part of the nucleus of the spinal accessory. It is said to receive also fibres from the vagus through both the superior and inferior laryngeal nerves. Action. To compress the pharynx. The three constrictors of the pharynx play important parts in the final acts of deglutition, forcing the food towards the oesophagus. They are also important agents in producing modulations of the voice, since the pharynx may be regarded as forming a resonator, alterations of whose form will naturally result in modifications of voice. Variations. The portions of the muscle arising from each of the two laryngeal cartilages may be more or less distinct and have been termed the thyro-pharyngeus and crico-pharyngeus. (6) THE MUSCLES OF THE LARYNX. The muscles of the larynx will be considered in connection with the description of that organ (page 1824). (c) THE TRAPEZIUS MUSCLES, i. Sterno-cleido-mastoideus. 2. Trapezius. This group includes but two muscles, the trapezius and sterno-cleido-mastoid, which extend from the skull to the pectoral girdle. Both are in reality compound muscles, formed by the fusion of fibres derived from the branchiomeres supplied by the spinal accessory with portions of the myotomes supplied by the second, third, and fourth cervical nerves. Strictly speaking, therefore, they belong only partially to the series of branchiomeric muscles, but the union of the elements derived from the two sources is so intimate that any attempt to distinguish them in a brief descrip- tion of the muscles would tend to confusion. i. STERNO-CLEIDO-MASTOIDEUS (Fig. 541). Attachments. The sterno-mastoid is attached below by two heads to the sternum and the clavicle. The sterna/ ht ad arises by a strong rounded tendon from the anterior surface of the manubrium sterni, while the clavicular head is more band- like, and takes origin from the upper surface of the sternal end of the clavicle. The two heads are directed upward and backward, the clavicular head gradually passing beneath the sternal one, and the two, eventually fusing, are inserted into the mastoid process of the temporal bone and into the outer part of the superior nuchal line. 5 oo HUMAN ANATOMY. Nerve-Supply. The external branch of the spinal accessory and the second and third cervical nerves. Action. The two muscles of opposite sides, acting together, will draw the head forward, thus bending the neck. Acting singly, each muscle will tend to draw the head towards its own side and at the same time to rotate it towards the opposite side. Relations. Superficially the muscle is covered by the platysma, and is crossed obliquely by the external jugular vein and in varying directions by the superficial branches of the cervical plexus. It covers, FIG. 511. above, the upper part of the posterior belly of the digastric, the splenius capitis, the levator scapulae and the scaleni, and below it crosses the omo-hyoid and covers the lower attach- ments of the sterno-hyoid and sterno-thyroid. It also covers the common carotid artery and the lower portions of the e"xternal and internal carotids, the facial and internal jugular veins, the cervical plexus, and the lateral lobe of the thyroid gland. erno-occipita! Sterno-mastoid, su- perficial and deep Variations. Considerable variation exists in the amount of fusion of the two heads, their complete distinctness being of so frequent occurrence as to be regarded as normal by some authors. But, in ad- dition to these- two portions, the muscle presents fre- quently a separation into other parts, and compara- tive anatomy reveals a primary constitution of the muscle from at least five distinct portions, any one or more of which may appear as distinct bundles (Fig. 511). These portions are arranged in two layers, the superficial one consisting of a superficial sterno-mastoid, a sterno-occipital, and a cleido- occipital portion, while the deep one is formed by a deep sterno-mastoid and a cleido-mastoid portion, the names applied indicating the attachments of the various bundles. Occasionally the lower portion of the muscle is traversed by a tendinous intersection, a peculiarity of interest in connection with the formation of the muscle by the fusion of portions derived from different myotomes. Cleido-occipi- tal, lower part turin-d downward Quadricipital type of sterno-mastoid, showing the components of the muscle. (After Maubrac.) 2. TRAPEZIUS (Figs. 512, 559). Attachments. The trapezius is the most superficial muscle upon the dorsal surface of the body, and is a triangular sheet whose base corresponds with the mid- dorsal line. The two muscles of opposite sides being thus placed base to base, form a rhomboidal sheet which covers the nape of the neck and the upper part of the back and shoulders, resembling somewhat a monk's cowl, whence the name cucnllaris sometimes applied to the muscle. It arises above from the superior nuchal line and the external occipital pro- tuberance, and thence along the ligamentum nuchae and the spinous processes of the seventh cervical and all the thoracic vertebrae, together with the supraspinous ligaments. The upper fibres pass downward and outward, the middle- ones directly outward, and the lower ones upward and outward, and are inserted, the upper ones into the outer third of the posterior border of the clavicle, the middle ones into the inner border and upper surface of the acromion process and the upper border of the spine of the scapula, and the lower ones into a tubercle at the base of the scapular spine. * Throughout the greater part of its length the origin of the muscle is by short tendinous fibres intermingled with muscle-tissue, but from about the middle of the ligamentum imch;r t< > the spinous process of the second thoracic vertebra it is entirely tendinous. Furthermore, throughout the upper half of this portion of the origin the tendinous fibres gradually increase in length and throughout its lower half they again diminish, so that there is formed by the two muscles of opposite sides, in this region, THE VAGO-ACCESSORY MUSCLES. 501 a well-marked oval or rhomboidal tendinous area, which has been termed the oval aponeicrosis. In their course to their insertion the lower fibres pass over the smooth surface at the base of the spine of the scapula, and sometimes a bursa mucosa is developed between the bone and the muscle. Nerve-Supply. From the external branch of the spinal accessory and from the third and fourth cervical nerves. Action. Acting from above, the upper fibres draw upward the point of the shoulder, while, acting from below, they draw the head backward. The middle and lower fibres draw the scapula towards the mid-dorsal line and at the same time rotate it so as to raise the point of the shoulder. Variations. Like the sterno-mastoid, the trapezius is a compound muscle consisting of three distinct portions. That portion of the muscle which inserts into the tuberosity of the FIG. 513. FIG. 512. Sterno-mastoid - Aponeurosis of trapezius .Trapezius -Acromion Scapular spine Infraspinatus omboideus major Teres major o-occipitalis lius Latissimus dorsi Superficial dissection of back, showing trapezius and adjacent muscles. .Cleido-occipitalis cervicalis Clavicle Acromion Dorso-scapularis superior Tuberosity of spine Tendinous slip to infraspinous fascia Dorso-scapularis inferior Latissimus dorsi Components of human trapezius muscle. (Streissler. ) scapular spine represents what is termed in the lower mammals the dorso-scapularis inferior, while the portion which inserts into the spine and acromion process represents the dorso-scap- ularis superior. The clavicular portion, on the other hand, is in the lower forms associated with the cleido-occipitalis element of the sterno-cleido-mastoid, and may therefore be termed the cleido-occipitalis cervicalis. Indications of this triple constitution are to be seen in a more or less distinct separation of the clavicular portion of the muscle from the rest and, less frequently, by a separation of the lower from the middle portion (Fig. 513). Occasionally, too, bundles pass from the anterior border of the clavicular portion to join the cleido-occipitalis portion of the sterno-cleido-mastoid, indicating the common origin of the two muscles. Variations likewise occur in the extent of the spinal attachment of the trapezins, owing to the reduction of one or other of its parts, and it may be remarked that this attachment usually extends lower in the muscle of the right side than in that of the left. Of especial interest from the comparative stand-point is the occasional existence of a bundle of fibres which lies beneath the cervical portion of the trapezius, and is attached at one extremity to the outer end of the clavicle or to the acromion process and above to the transverse processes of some of the upper cervical vertebrae, usually the atlas and axis. It is apparently the equivalent of the omo-transversarius of the lower mammals, a muscle which is closely associated with the members of the trapezius group. 502 HUMAN ANATOMY. THE METAMERIC MUSCLES. A. THE AXIAL MUSCLES. As has been pointed out. the history of the anterior two groups of myotomes, supplied by cranial nerves, differs somewhat from that of the remaining ones, and it is convenient, therefore, to consider the muscles derived from these myotomes separately from the rest. I. THE ORBITAL MUSCLES. 1. Levator palpebrae superioris. 2. Rectus superior. 3. Rectus internus. 4. Rectus inferior. 5. Rectus externus. 6. Obliquus superior. 7. Obliquus inferior. The most anterior of the persistent myotomes are three in number, supplied by the oculo-motor, trochlear, and abducent nerves. They give rise to the muscles situated in the orbit. FIG. 514. i. LEVATOR PALPEBRAE SUPERIORIS (Fig. 516). Attachments. The levator palpebrae superioris is a rather slender muscle which lies in the greater portion of its course immediately beneath the periosteal lining of the roof of the orbit. It arises at the back of the orbit, a short distance above the upper margin of the optic foramen, and is directed forward, broad- ening as it goes, to be in- serted by a broad aponeu- rosis principally into the upper border of the tarsal plate of the upper eye- lid, the uppermost til>iv> mingling somewhat with those of the palpebral portion of the orbicularis oculi. The aponeurosis by which the levator inserts into the tarsal plate is largely composed of non- striated muscular fibres, which constitute what has been termed the orbito- palpcbral muscle. This is triangular in shape. with the truncated apex united to the levator and with the base attached to the external palpebral raphe, the tarsal plate of the upper eyelid, and the internal palpebral ligament. Nerve-Supply. From the oculo-motor nerve. Action. To draw the upper eyelid upward and backward. Relations. Immediately above the levator palpebrae superioris, between it and the periosteum of the roof of the orbit, are the trochlear and frontal nerves and the supra-orbital vessels. Below it rests upon the medial half of the rectus superior. Tendinous loop for sup. oblique Superior oblique, distal part Internal rectus__ Superior oblique._; proximal part Optic nerve, vator palpebrae sup. .tipper tarsal plate Palpebral fissure Superior rectus Inferior oblique External rectus .Stutni) of levator palpebrse superioris Ocular muscles seen from above after removal of roof of orbit ; elevator of uppt-r o\vlid has been rut and reflected forward. THE AXIAL MUSCLES. 2. RECTUS SUPERIOR (Fig. 514). Attachments. The superior rectus arises from the upper portion of a fibrous ring termed the annulus of Zinn (annulus tendincus communis), which surrounds the optic foramen and is formed by a thickening of the orbital periosteum in that region. Thence the muscle is directed forward over the eyeball and is inserted into the sclera a little above the upper margin of the cornea. Nerve-Supply. From the oculo-motor nerve. Action. To rotate the eyeball so that the pupil is directed upward and at the same time somewhat inward. 3. RECTUS INTERNUS (Fig. 514). Attachments. The internal rectus (m. rectus medialis) arises from the inner portion of the annulus tendineus communis and passes forward along the inner wall of the orbit to be inserted into the sclera a short distance behind the inner margin of the cornea. Nerve-Supply. From the oculo-motor nerve. Action. To rotate the eyeball so that the pupil is directed inward. FIG. 515. Superior rectus Levator palpebra; superioris / Superior oblique / Trochlea, tendon of superior Sphenoidal fissure External rectus Optic nerve (cut) __ Spheno-inaxillary fissure. Inferior oblique oblique in place Internal vectus Inferior rectus Right orbit seen from before, showing stumps of ocular muscles attached to common tendinous ring of origin. 4. RECTUS INFERIOR (Fig. 516). Attachments. The inferior rectus arises from the lower portion of the com- mon tendinous ring, its line of origin being continuous with that of the rectus interims. It is inserted into the sclera a short distance below the inferior margin of the cornea. Nerve-Supply. From the oculo-motor nerve. Action. To rotate the eyeball so that the pupil is directed downward and at the same time somewhat inward. 5. RECTUS EXTERNUS (Fig. 514). Attachments. The external rectus (m. rectus lateralis) arises by two heads, one of which is attached to the lower and outer portion of the common tendinous ring and to the spine on the lower border of the sphenoidal fissure, and the other to the upper and outer part of the common tendinous ring. It passes along the outer wall of the orbit and is inserted into the sclera a little behind the outer border of the cornea. Nerve-Supply. From the abducens or sixth nerve. Action. To rotate the eyeball so that the pupil is directed outward. Relations. Between the two heads of the external rectus there pass the oculo- motor, nasal, and abducent nerves and the ophthalmic vein. 504 HUMAN ANATOMY. 6. OBLIQUUS SUPERIOR (Figs. 514, 516). Attachments. The superior oblique muscle of the eyeball arises a little in front of the inner part of the optic foramen and passes forward along the upper and inner wall of the orbit to terminate in a round tendon which passes through a ten- dinous loop, the trochlea, attached to the fovea trochlearis of the frontal bone. Thence it is reflected outward, downward, and backward, and, passing beneath the superior rectus, is inserted into the sclera beneath the outer margin of that muscle and at about the equator of the eyeball. Nerve-Supply. From the trochlearis or fourth nerve. Action. To rotate the eyeball so that the pupil is directed inward and downward. FIG. 516. Levator palpebrae superioris Superior oblique Superior rectus External rectus (cut) Internal rectus Optic nerve Stump of external rectus ,- Insertion of levator palpebra- superioris into upper larval plate Inferior oblique Inferior rectus Lateral view of ocular muscles after removal of outer wall of orbit ; elevator of upper lid has been pulled upward and inward. 7. OBLIQUUS INFERIOR (Fig. 516). Attachments. The inferior oblique muscle arises near the margin of the orbit from a small depression on the orbital surface of the maxilla. It is directed out- ward, backward, and upward, and, passing between the inferior rectus and the floor of the orbit, is inserted into the sclera a little behind the equator of the eyeball and under cover of the external rectus. Nerve-Supply. From the oculo-motor nerve. Action. To rotate the eyeball so that the pupil is directed upward and outward. Fasciae of the Orbit. The muscles, nerves, and vessels of the orbit are em- bedded in a mass of loose areolar tissue which, abundantly intermingled with a soft fat, completely fills the orbital cavity. Around the vessels, nerves, and muscles this areolar tissue condenses to form their sheaths, and a special condensation, the capsule of Tenon (fascia bulbi), surrounds the posterior four-fifths of the eyeball, forming a socket for it. The inner surface of this capsule is smooth and is united to the outer surface of the sclera only by lax and slender bands of fibres which traverse a distinct lymph-space termed the space of Tenon (spatium intcrfasciale), which inter- venes between the capsule and the eyeball, thus facilitating the movements of the latter in the socket. Posteriorly the capsule is continuous with the sheath of the optic nerve and anteriorly it joins with the conjunctiva anterior to the line of insertion of the rectus muscles into the sclera. The tendons of the rectus muscles conse- quently perforate the capsule, which is prolonged backward upon the tendons for a short distance, in the case of the superior oblique as far as the trochlea. and then becomes continuous with the areolar sheaths of the muscles which arc intimately THE AXIAL MUSCLES. 505 adherent to the muscle-tissue and constitute the fasciae rausculares. These fasciae are somewhat thicker in their anterior portions than more posteriorly, and give off pro- longations to neighboring parts. From the fascia of the rectus superior a prolonga- tion passes to join the tendon of the levator palpebrae superioris, and one from the rectus inferior passes to the lower border of the tarsal plate of the lower eyelid, these two recti thus acquiring a certain amount of action upon the eyelids. From the lateral surface of the fascia of the external rectus a rather strong prolongation is given off which attaches to the orbital surface of the zygomatic bone, forming what has been termed the external check ligament of the eyeball, while from the medial surface of the fascia of the internal rectus a similar, although somewhat laxer, prolon- gation passes to the crest of the lachrymal bone and the reflected portion of the internal palpebral ligament. The Movements of the Eyeball. The four recti muscles of the eyeball may be regarded as forming a cone whose apex is at the annulus tendineus communis FIG. 517. Levator palpebrse superioris Fat Superior rectus Capsule of Tenon Superior oblique (cut) \ c-^ \ \ s Fat Optic nerve \ Inferior rectus -ri Septum orbitale Upper tarsal plate Lower tarsal plate Space of Tenon Septum orbitale Inferior oblique Diagrammatic sagittal section through orbit, showing relations of fascia to muscles, eyeball, and orbital wall. and the base at the insertions of the muscles into the sclera. The line joining the insertions of the muscles is not, however, a circle, but rather a spiral, the insertion of the internal rectus being nearest to and that of the rectus superior farthest from the edge of the cornea. The axis of the cone does not correspond in direction with the antero- posterior axis of the eyeball, but, owing to the divergence of the axes of the two orbits, is inclined to it from within outward at an angle of about 20. It follows from this that during the contraction of either the superior or infe- rior rectus the axis of rotation of the eyeball will not coincide with its transverse axis, but will be inclined to it (Fig. 518), and consequently the action of either of these muscles in directing the pupil upward or downward will be complicated by a certain amount of oblique movement, in the one case inward and in the other case outward. In producing purely upward or downward movements of the pupil the rectus muscles are associated with the oblique ones, the coordination of the inferior oblique with the superior rectus producing a purely upward rotation, while that of the superior oblique with the inferior rectus produces a purely downward movement. 5o6 HUMAN ANATOMY. FIG. 518. It has been demonstrated also that the oblique movements of the eyeball are by no means due to the action of the superior and inferior oblique muscles acting alone', but that in every such movement there is a coordination of two of the recti muscles with one of the obliques. Thus, in rotations which direct the pupil upward and inward the superior and internal recti cooperate with the inferior oblique, and in the downward and outward movements the inferior and external recti cooperate with the superior oblique. A purely outward or inward rotation can be produced by the action of the external or internal rectus, as the case may be. But it is to be noted that the movements of the eyeball are always bilateral, and that the in- ward rotation of the one eye is generally as- sociated with the outward rotation of the other, the combined movements thus re- quiring the cooperation of different muscles. In all movements of the eyeballs there is, accordingly, a coordination of various orbital muscles, and when the combined oblique movements are performed this co- ordination becomes somewhat complicated. The direction of both pupils upward and to the right requires the coordination in the right eye of the inferior oblique and the su- perior and external recti and in the left eye of the inferior oblique and the superior and internal recti. Variations. But few variations have been observed in the orbital muscles. Absence of the levator palpebrae superioris has been noted, and a slip from this muscle, termed the tensor trochlece, sometimes passes to the trochlea. E i Diagram showing action of ocular muscles. S, S\, Q,Q\, sagittal and transverse axes of eyeball; di- rection of pull of muscles is indicated by lines ; dotted lines indicate axes around which superior and inferior recti and oblique muscles rotate eye- ball ; vertical axis (O) corresponds to axis of rota- tion of internal and external recti. (Landois.) II. THE HYPOGLOSSAL MUSCLES. 1. Genio-glossus. 2. Hyo-glossus. 3. Stylo-glossus. 4. Lingualis. It is well known that the hypoglossal nerve represents the anterior roots of three spinal nerves which have secondarily been taken up into and consolidated with the cranial region. Corresponding to these three nerves are three myotomes which combine to give rise to muscles connected with the tongue. i. GEMO-GLOSSUS (Fig. 1339). The genio-glossus is described with the tongue (page 1578). 2. HYO-GLOSSUS (Fig. 1339). The hyo-glossus is described with the tongue (page 1578). Variations. The fibres which arise from the lesser cornn of tin- hyoid hone are frequently separate from the rest of the muscle and have been described as the ckottdro-gloSSUS^ and the fibres arising from the body of the hyoid are frequently separated by a distinct interval from those arising from tin- greater cornu, the former constituting a muscle which has been termed the Inixio-g/osstis and the latter the t - t 'ni/i)-^ r /oxxnx. A bundle of fibres, forming what has been termed the /> i/icco-gti>ssns. sometimes arises from the carti'la^o triticea. situated in the lateral hvo-thyroid ligament, and passes upward and forward to insert nloiiii with tin- posterior fibres of the hyo-glossus. THE TRUNK MUSCLES. 507 3. STYLO-GLOSSUS (Fig. 1339). The stylo-glossus is described with the tongue (page 1579). Variations. The stylo-glossus is occasionally absent, and may in such cases be replaced by a mylo-glossus, which arises from the inner surface of the angle of the mandible or from the stylo-mandibular ligament and is inserted into the sides and under surface of the tongue. This muscle is usually present in the form of some small bundles of fibres having the attach- ments described. 4. LINGUALIS (Fig. 1340). The lingualis is described with the tongue (page 1579). III. THE TRUNK MUSCLES. THE DORSAL MUSCLES. In employing the term dorsal to indicate a group of muscles it must be clearly understood that the group does not include all the muscles which, in the adult con- dition, are found upon the dorsal surface of the body. The term, so far as it has a topographic significance, refers to a phylogenetic stage in which the muscles it is intended to designate were the only dorsal muscles, and, as here employed, it indi- cates only those muscles which are derived from the dorsal portions of the embryonic myotomes and are supplied by the posterior divisions (dorsal rami) of the spinal nerves. An examination of the muscles of the back readily shows that they consist of two distinct sets. There is a superficial set, consisting of broad and flat muscles, which are, with few exceptions, attached to the skeleton of the fore-limb, and a deeper set, consisting of elongated and relatively thick muscles, whose attachments are confined to portions of the axial skeleton. The muscles of the former set, which may conveniently be designated the spino-humeral muscles, are all supplied by branches from the ventral rami of the spinal nerves ; they have reached their present position, in which they almost completely cover in the true dorsal muscles, by a secondary migration from the more ventral portions of the trunk, and prop- erly belong to the system of limb muscles, in connection with which they will be described. The true axial dorsal muscles are all included in the deeper set. Viewed from the surface, they appear to form elongated columns of muscle-tissue, extending con- tinuously, more or less parallel with the spinal column, over considerable stretches of the back ; but when the more superficial portions of the columns are removed, it will be seen that the deeper portions are associated with the individual vertebrae, their fibres possessing a more or less distinct segmental arrangement. The columns, indeed, are to be regarded as formed by the fusion of a number of originally inde- pendent muscle-segments, derived from the dorsal portions of a corresponding number of myotomes, a mode of formation also indicated by the fact that the columns are supplied by nerves from a greater or less number of successive spinal nerves, from just as many, indeed, as there are myotomes entering into their composition. Comparative anatomy demonstrates that the dorsal musculature may, further- more, be regarded as consisting of two parallel portions or tracts, a median and a lateral. The former portion, which includes the majority of the dorsal muscles, is composed of those muscles which fundamentally arise from the transverse processes of the vertebrae and are inserted into the spinous processes, and may therefore be termed the transverso-spinal portion ; while the more lateral tract consists of mus- cles which, taking, their origin primarily from the transverse processes, are inserted into the ribs or their homologues, and may accordingly be termed the transverso- costal portion. A certain amount of overlapping of the median tract by the lateral one occurs in man ; indeed, in the lumbar region the two tracts fuse to a certain extent to form the sacro-spinalis ; but throughout the thoracic and cervical regions they are fairly distinct. 5 o8 HUMAN ANATOMY. Psoas magnus Lumbar vertebra Subperitoneal tissue 1 Fascia Peritoneum The deep fascia of the back invests all the muscles of the dorsal group, separating them from the spino-humeral group. Above, the fascia is not especially strong, and in the cervical and upper thoracic regions forms what is termed the fascia nuchae, which lies beneath the trapezius and rhomboid muscles. In the lower thoracic and lumbar regions, however, the fascia becomes considerably thickened, especially that portion which invests the sacro-spinalis (vertebral aponcurosis), form- ing a strong rhomboidal sheet extending from about the level of the sixth thoracic vertebra to the tip of the sacrum, its anterior borders giving attachment to various muscles, while the posterior ones are attached to the posterior portions of the iliac crests, where it becomes contin- FIG. 519. uous with the fascia lata covering the gluteal muscles. This dense layer is termed the fascia lunibo-dorsalis (Fig. 559), and is generally regarded as consisting of two lateral por- tions which are practically united in the mid-dorsal line by their common attachment to the spi- nous processes of the vertebrae and the supraspinous ligaments. Each of these lateral portions is again considered as consisting of two layers which together invest the sacro-spinalis ( Fig. 519), the posterior layer being that which has already been described, while the anterior layer is attached medially to the tips of the transverse processes of the lumbar vertebrae, above to the lower border of the twelfth rib, and below to the crest of the ilium. It passes outward beneath the sacro-spinalis, separating it from the quadratus lumborum, and at the outer border of the former muscle it fuses with the posterior layer to form a strong aponeurotic band, from which the latissimus dorsi and the internal oblique and trans- verse abdominal muscles take partial origin, and which is continued ventrally over the inner surface of the transversus abdominis as \hzfascia transversalis. Lumbar spine Skin .Transversalis fascia; ;. ..'..- Transversalis muscle Internal oblique External oblique /--Triangle of Petit ^Quadratus lumborum Latissimus dorsi Ant. layer of lumbo-dorsal fascia r Superficial fascia Posterior layer of lumbo-dorsal fascia Sacro-spinalis Diagram showing formation and relations of lumbo-dorsal fascia to muscles of body-wall. (a) THE TRANSVERSO-COSTAL TRACT. 1 . Sacro-spinalis. 2. Ilio-costalis. 3. Longissimus. 4. Splenius. i. SACRO-SPINALIS (Fig. 520). Attachments. The sacro-spinalis, sometimes termed the erector spina, forms a large muscular mass occupying the lumbar portion of the vertebral groove. It takes its origin from the under surface of the lumbo-dorsal fascia, the crest of the ilium, the posterior surface of the sacrum, and the spines of the lumbar ver- tebrae. Anteriorly it divides into three separate muscles, two of which, the ilio- costalis and the longissimus, belong to the transverso-costal group, while the third, the spinalis, is a member of the transverso-spinal series. Nerve-Supply. The posterior divisions of the lumbar nerves. 2. ILIO-COSTALIS (Fig. 520). Attachments. The ilio-costalis, also termed the sacro-/u^tba/is, is the most lateral of the three muscles into which the sacro-spinalis divides, and is the forward continuation of the portion of that muscle which arises from the crest of the ilium. The muscle is continued upward in the vertebral groove immediately internal to the angles of the ribs as far as the fourth cervical vertebra, receiving, however, acces- sions from the ribs as it passes over them. The fibres which arise from the iliac THE TRUNK MUSCLES. 509 FIG. 520. Obliquus superior Trachelo-mastoi d Levator anguli scapulae ; colli Cervicalis ascendens Transversalis cervicis Rectus capitis posticus minor Rectus capitis posticus major Obliquus inferior Semispinalis capitis (complexus and biventer) Levator anguli scapulse Semispinalis colli Accessor! us (ilio-costalis dorsi) Spinalis dorsi I.ongissimus dorsi Ilio-costalis (ilio-costalis lumborum) Sacro-spinalis (erector spinae) Quadratus lumborum Multifidus spinae Dissection c>f muscles of back, showing transverso-costal and transverso-spinal tracts. 5 io HUMAN ANATOMY. crest are mainly inserted into the lower six or seven ribs, and form what is termed the ilio-costalis lumborum. With the remainder of the iliac fibres bundles arising from the lower five, six, or seven ribs associate themselves to form the ilio-costalis dorsi, also termed the accessorius, which inserts into the upper five or six ribs ; and, finally, the uppermost portion of the muscle, the ilio-costalis cervicis or cervicalis ascendens, is formed by the union of bundles arising from the upper six or seven ribs, and is in- serted into the posterior tubercles of the transverse processes of the fourth, fifth, and sixth cervical vertebrae. Nerve-Supply. From the posterior divisions of the spinal nerves from the lower cervical to the first lumbar. Action. The various portions of the ilio-costalis tend to bend the spinal column backward in the lower cervical, thoracic, and lumbar regions, and also to draw it somewhat to one side. They may likewise have some action in drawing down the ribs, assisting in forced expiration. 3. LONGISSIMUS (Fig. 520). Attachments. -The longissimus represents the upward prolongation of that portion of the sacro-spinalis which arises from the dorso-lumbar fascia and the lumbar vertebrae. It is continued upward immediately medial to the ilio-costalis to be inserted into the mastoid process of the temporal bone, but, like the ilio-costalis, it receives in its course accessory bundles and also gives off bundles which are inserted into the skeletal parts over which it passes. The fibres which represent the direct continuation of the sacro-spinalis are con- tinued as far upward as the first thoracic vertebra, and are reinforced by short acces- sory bundles from the transverse processes of the lower six thoracic vertebrae to form what is termed the longissimus dorsi. The fibres of this portion of the muscle are inserted along two lines, the medial of which passes along the accessory processes of the lumbar vertebrae and the transverse processes of all the thoracic vertebrae, while the lateral line passes along the transverse processes of the lumbar vertebrae and the angles of the ribs as far forward as the second. From the transverse processes of the upper six thoracic vertebrae bundles arise which unite to form the longissimtis cervicis or transversalis cervicis, which continues the line of the longissimus to an insertion into the posterior tubercles of the transverse processes of the second to the sixth cervical vertebrae ; and, finally, the longissimus capitis or trachelo-mastoid is formed by bundles arising- from the transverse processes of the three upper thoracic vertebrae and the articular processes of the three lower cervical, and passes upward to be inserted into the mastoid process of the temporal bone. Nerve-Supply. From the posterior divisions of the spinal nerves from the third cervical to the second sacral. Action. The thoracic and cervical portions of the longissimus will draw the spinal column backward and to one side ; the longissimus capitis will have a similar action on the head. 4. SPLENIUS (Fig. 520). 10US Attachments. The splenius forms a flat muscle which arises from the spino processes of the upper four or six thoracic and the seventh cervical vertebrae and from the lower half of the ligamentum nuclue. It passes upward and slightly laterally and divides into two portions, the lower of which, curving around the outer edge of the upper portion, passes to an insertion in tin- posterior tubercles of the upper three cervical vertebrae, forming the s/>/cniits cervicis. The upper portion, which is termed the splenius cn/iitis, continues upward, and is inserted by a short tendon into the posterior border of the mastoid process of the temporal bone and into the outer part of the superior nuchal line. Nerve-Supply. From the posterior divisions of the second to the eighth cer- vical nerves. Action. The splenius cervicis will draw the upper cervical vertebra- backward and will rotate the atlas towards the side of the muscle in actiori. The action of THE TRUNK MUSCLES. 511 the splenius capitis upon the head will be similar ; the simultaneous action of the two muscles of opposite sides will bend the head backward, each muscle neutralizing the rotatory effect of the other. (6) THE TRANSVERSO-SPINAL TRACT. 1. Spinalis. 6. Intertransversales. 2. Semispinalis. 7. Rectus capitis posticus major. 3. Multifidus. 8. Rectus capitis posticus minor. 4. Rotatores. 9. Obliquus capitis superior. 5. Interspinales. 10. Obliquus capitis inferior. i. SPINALIS (Fig. 520). Attachments. The spinalis in its lower portion is the continuation of the deeper and innermost fibres of the sacro-spinalis, and, like the longissimus, with which it is partly associated, it is regarded as consisting of a thoracic, a cervical, and a cranial portion. The spinalis dorsi arises from the spinous processes of the upper two lumbar and the lower two or three thoracic vertebrae by tendons common to it and the longissimus dorsi. It forms a thin, flat muscle which passes upward, inserting as it goes into the spinous processes of the thoracic vertebrae from the second to the eighth or ninth, but one vertebra intervening between its uppermost tendon of origin and its lowermost tendon of insertion. The spinalis cervicis arises from the spinous processes of the upper two or four thoracic and the lower two cervical vertebras, and ascends alongside the spinous processes of the cervical ver- tebras to be inserted, into those of the second, third, and fourth vertebras. The spinalis capitis consists of bundles arising from the spinous processes of the upper thoracic and last cervical vertebrae, and passes upward to be inserted with the semi- spinalis capitis. Nerve-Supply. From the posterior divisions of the spinal nerves from the third cervical to the last thoracic. Action. To extend the spinal column. 2. SEMISPINALIS (Fig. 520). Attachments. The semispinalis forms the superficial layer of the muscles lying in the groove between the spinous and transverse processes of the vertebras. Three portions may be recognized in it. The semispinalis dorsi arises from the trans- verse processes of the lower six or seven thoracic vertebrae ; its fibres are directed obliquely upward and medially and are inserted into the spinous processes of the five or six upper thoracic and last two cervical vertebrae. The semispinalis cervicis arises from the transverse processes of the five or six upper thoracic vertebrae and is inserted into the spinous processes of the second, third, fourth, fifth, and sometimes the sixth cervical vertebras. This portion of the muscle is almost concealed beneath the upper- most portion, the semispinalis capitis, which arises from the transverse processes of the upper six thoracic vertebrae and the articular and transverse processes of the lower three or four cervical vertebras. The fibres are directed almost vertically upward, and are joined by the spinalis capitis to form a broad muscle-sheet which is inserted into the under surface of the squamous portion of the occipital bone between the superior and inferior nuchal lines. An intermediate tendinous intersection usually divides the semispinalis capitis into an upper and a lower portion, and is much more distinct in the more medial bundles than in the lateral ones. Frequently these more medial bundles are sep- arated somewhat from the others, and they have been considered a distinct muscle and termed the biventer, the lateral portion of the muscle being named the complexus. Nerve-Supply. From the posterior divisions of the spinal nerves from the second cervical to the last thoracic. Action. The semispinalis dorsi and cervicis extend the vertebral column and rotate it somewhat towards the opposite side. The semispinalis capitis draws the head backward and also rotates it slightly towards the opposite side. 512 HUMAN ANATOMY. 3. MULTIFIDUS (FigS. 520, 52l). Attachments. The multifidus (multifidus spina} constitutes the middle layer of the muscles occupying the groove between the transverse and spinous processes ;. 521 Intertrans poste Interspinales Levatores costarum Rotatores Levatores costarum Interspinales. Intertransversales laterales Deep muscles of kick. Multifidus Multifidus of the vertebra, and is covered, in the thoracic and cervical regions, by tin- si-mi- spinalis. It takes its origin from the dorsal surface of the sacrum and from the trans- THE TRUNK MUSCLES. 513 verse or articulating processes of all the vertebrae as far up as the fourth cervical. The fibres from each vertebra pass over from two to four of the succeeding vertebrae and are inserted into the spinous processes of the third to the fifth, the entire insertion of the muscle extending from the spinous process of the last lumbar vertebra to that of the axis. Nerve-Supply. From the posterior divisions of the spinal nerves from the third cervical to the last lumbar. Action. To bend the spinal column backward and rotate it towards the op- posite side. 4. ROTATORES (Fig. 52l). Attachments. The rotatores (rotatores dorsi) form the deepest layer of the muscles occupying the spino-transverse groove. They form a series of small muscles hardly distinguishable from the bundles of the multifidus, beneath which they lie. They are to be found along the entire length of the spinal column from the sacrum to the axis, arising- from the transverse process of one vertebra and passing, some of the fibres to the base of the spinous process of the next succeeding vertebra {rotatores breves) and the rest to a corresponding point of the second vertebra above {rotatores longi) . Nerve-Supply. From the posterior divisions of the spinal nerves from the third cervical to the last lumbar. Action. To bend the spinal column backward and rotate it towards the op- posite side. 5. INTERSPINALES (Fig. 521). Attachments. The interspinales are relatively small muscles which pass be- tween the spinous processes of succeeding vertebrae. They are usually absent throughout the greater portion of the thoracic region, occurring only in connection with the first and the last two spines, but they are exceptionally well developed in the lumbar region and are usually paired in the cervical region, where they stop at the axis. Nerve-Supply. From the posterior divisions of the spinal nerves from the third cervical to the fifth lumbar. Action. Acting together to bend the cervical and lumbar portions of the spinal column backward. 6. INTERTRANSVERSALES (Fig. 521). Attachments. The name intertransversales (mm. intertransversarii) has been applied to a series of small muscles occurring in the cervical and lumbar regions and extending between the transverse or mammillary processes of successive vertebrae. In each of the regions named two sets of intertransversales are recognized, but it seems probable that only one of the sets in such region belongs to the dorsal group of muscles. This set will alone be considered here, the other (anterior) one being described with the ventral muscles of the regions in which it occurs. The intertransversarii posteriores occur only in the cervical region and extend between the posterior tubercles of the transverse processes of succeeding vertebrae. The intertransversarii mediales occur only in the lumbar region and extend between the mammillary processes of successive vertebrae. Nerve-Supply. Probably by fibres belonging to the posterior divisions of the cervical and lumbar nerves, but it is at present insufficiently determined. Action. To bend the cervical and lumbar portions of the vertebral column laterally. 7. RECTUS CAPITIS POSTICUS MAJOR (Fig. 522). Attachments. The greater straight muscle (m. rectus capitis posterior major) an'ses from the apex of the spinous process of the axis and passes upward and out- ward, broadening as it goes, to be inserted into the middle portion of the inferior nuchal line. 33 5 i4 HUMAN ANATOMY. Nerve-Supply. By a branch from the posterior division of the suboccipital nerve. Action. To draw the head backward and to rotate it towards the same side. 8. RECTUS CAPITIS POSTICUS MINOR (Fig. 522). Attachments. The lesser straight muscle (m. rcctus capitis posterior minor) arises from the posterior tubercle of the atlas and passes upward, broadening as it goes, to be inserted into the inner portion of the inferior nuchal line. Nerve-Supply. By a branch from the posterior division of the suboccipital nerve. Action. To draw the head backward. FIG. 522. Rectus capitis posticus_iL_ minor Rectus capitis posticus 3L- major Obliquus superior Suboccipital triangle 5 Obliquus inferior Supraspinous ligament Posterior tubercle of atlas Transverse process of atlas ilnterspinales Multifidus Deep dissection of neck, showing suboccipital group of muscles. 9. OBLIQUUS CAPITIS SUPERIOR (Fig. 522). Attachments. The superior oblique muscle of the head arises horn the trans- verse process of the atlas and passes upward to be inserted into the squamous portion of the occipital immediately above the outer part of the inferior nuchal line. Nerve-Supply. By a branch from the posterior division of the suboccipital nerve. Action. To draw the head backward and slightly laterally. 10. OBLIQUUS CAPITIS INKKKIOK (Fig. 522). Attachments. The inferior oblique muscle of the head arises from the tip of the spinous process of the axis and is directed outward and upward to be iiiti'rti'd into the transverse process of the atlas. Nerve-Supply. By a branch from the posterior division of the suboccipital nerve. Action. To rotate the axis towards the same side. THE VENTRAL MUSCLES. 515 The Sacro-Coccygeus Posterior. The reduction of the caudal vertebrae in man, indicated by the condition of the coccygeal vertebra;, has brought about a reduction of the terminal portion of the dorsal axial musculature, it being, as a rule, represented only by the ligaments upon the dorsal surface of the coccyx. Quite frequently, however, muscular fibres occur inter- mingled with the connective tissue, and occasionally a distinct muscle, the sacro-coccygeus posterior, may be found, extending from the last sacral vertebra or even from the greater sacro- sciatic ligament to the coccyx. THE VENTRAL MUSCLES. The ventral trunk musculature includes all those axial muscles which are supplied from the anterior divisions (ventral rami) of the spinal nerves. As already indicated (page 473), it is divisible into three subgroups : a group of more median muscles, char- acterized by their fibres retaining more or less perfectly a longitudinal direction and constituting the rcctus group ; a more lateral group, in which the fibres possess a distinctly oblique or transverse direction, and may consequently be termed the obliqiius group ; and, finally, a hyposkcletal group, whose fibres have a longitudinal direction, and which is situated anterior or ventral to the spinal column. Instead of considering the various muscles belonging to each of these groups in succession, it seems more convenient to combine a topographic classification with the morphological one, and to describe the various groups as they occur in the neck, thoracic, abdominal, and perineal regions. It must be understood, however, that the delimitations of these regions are somewhat arbitrarily chosen, and that there is, so far as the muscles are concerned, a considerable amount of overlapping of certain regions, portions of myotomes which strictly belong to the thoracic region, for instance, being found within the limits of what is recognized as the abdominal region. In many cases these overlapping myotomes have united with myotomes of the lower region to form a continuous muscle, and it is consequently impossible to refer them to their proper topographic position without doing violence to the individuality of the muscles which they help to form ; but when they remain practically distinct from the muscles of their adopted region, they will be referred to the region from which they have come. It will be convenient to consider first the muscles of the abdominal region, there- after taking up in succession those of the thoracic and cervical regions, those of the perineal region being left until the last. THE ABDOMINAL MUSCLES. The Superficial Fascia of the Abdomen. The superficial fascia of the abdomen is usually described as consisting of two layers. These, however, are well marked only over the anterior and especially the lower part of the abdominal wall, losing their distinctness laterally and above, where they pass over into the superficial fasciae of the back and thorax. The superficial layer ( Camper s fascia} usually con- tains a considerable amount of fat, except at the umbilicus, and may occasionally reach a great thickness owing to the development of that tissue. The deeper layer immediately underlies the fatty layer, and is a connective-tissue membrane of vary- ing density, containing a considerable amount of yellow elastic tissue. It is con- nected to the deep abdominal fascia which covers the muscles of the abdominal wall by loose areolar tissue, except along the median line, where it is firmly adherent along the linea alba and around the umbilicus. A short distance above the sym- physis pubis it gives off a band which is largely composed of elastic tissue and is inserted below into the fascia of the penis, forming the suspensory ligament of that organ (Fig. 528). In the inguinal region the deep layer of the superficial fascia is especially well defined, forming what has been termed the fascia of Scarpa. Laterally it passes down over Poupart's ligament to unite with the fascia lata of the thigh, the super- ficial vessels and lymph-nodes of this region lying between it and the superficial layer. More medially it is continued down over the spermatic cord, becoming con- tinuous below partly with the deep layer of the superficial fascia of the perineum (fascia of Colles} and partly, after fusing with the superficial layer, which loses its fat, with the dartos of the scrotum. HUMAN ANATOMY. (a) THE RECTUS MUSCLF:S. I. Rectus abdominis. 2. Pyramidalis. i. RECTUS ABDOMINIS (Fig. 523). Attachments. The rectus abdominis forms a flat but strong muscle which traverses the entire length of the ventral abdominal wall immediately lateral to the linea alba. It arises from the anterior surface of the xiphoid process of the sternum and from the cartilages of the fifth, sixth, and seventh ribs, and is inserted by a strong tendon into the crest and symphysis of the pubis. FIG. 523. Pectoralis major Tendon of rectus Rectus, cut and turned up Cut edge of anterior sheath of rectus Posterior sheath of rectus External oblique Semilunar fold Transversalis fascia Deep epigastric artery Rectus, stump Saphenous opening Sheath of rectus, turned over Tendinous intersection Rectus Crest of ilium ^__Anterior superior iliac tioiifs trndincic oecurs about the U-vel of the umbilicus, another, often alfi-ctmg only the medial portion of the muscle, corresponds approximately to the lourr margin of the thorax, and the third lies about midway between tin' two. The fourth, when present, frequently is limited to the lateral portion of the muscle, and occurs about midwav between the level of the umbilicus and the crest of the pubis. THE VENTRAL MUSCLES. 517 Nerve-Supply. From the anterior divisions of the thoracic nerves from the fifth to the twelfth. Action. The recti act as flexors of the thorax upon the pelvis or, acting from above, they flex the pelvis on the thorax. They also aid in the compression of the abdominal viscera in defecation and parturition and in strong expiratory efforts. Variations. The origin of the rectus sometimes ascends to the fourth or third rib or even higher. The tendinous inscriptions are probably the persistent representatives of the connective-' tissue partitions between certain of the myotomes of which the muscle is composed. They are subject to a certain amount of variation in number, five or six occasionally occurring, while, on the other hand, they may be reduced to two. 2. PYRAMIDALIS (Fig. 523). Attachments. The pyramidalis is a somewhat variable muscle which arises below from the upper surface of the body of the pubis and from the symphysis and is inserted above into the linea alba, somewhere between the umbilicus and the sym- physis. Nerve-Supply. From the anterior divisions of the eleventh and twelfth thoracic nerves. Action. To tense the linea alba. Variations. The extent to which the muscle is developed varies greatly, its insertion some- times extending well up towards the umbilicus, while, on the other hand, it is not infrequently absent. This latter condition has been estimated to occur in over 16 per cent, of cases. (6) THE OBLIQUUS MUSCLES. 1. Obliquus externus. 4. Transversalis. 2. Obliquus internus. 5. Quadratus lumborum. 3. Cremaster. 6. Intertransversales lateral es. 1. OBLIQUUS EXTERNUS (Fig. 524). Attachments. The external oblique forms a muscular sheet in the lateral portions of the anterior abdominal wall. It arises by seven or eight fleshy digitations from the corresponding number of lower ribs, the upper digitations alternating with digitations of the serratus magnus, while the lower three alternate with those of the latissimus dorsi. The fibres from the lowest ribs pass vertically downward to be in- serted into the crest of the ilium ; the remainder are directed mainly downward and forward and , above, directly forward to join a broad aponeurotic sheet which con- tributes to the formation of the ventral abdominal aponeurosis. Nerve-Supply. From the anterior divisions of the eighth to the twelfth thoracic nerves and from the ilio-hypogastric and ilio-inguinal nerves. Action. Since the external oblique is a curved sheet which passes from the lateral portions of the abdominal wall towards the mid-ventral line, contraction of its fibres will tend to compress the abdominal contents and so assist in micturition, defe- cation, parturition, and expiration, its action in the last-named process being increased by the power which it possesses of drawing the lower ribs downward. Furthermore, according as it acts from below or above, it will flex the thorax and spinal column upon the pelvis or the pelvis upon the spinal column, at the same time producing a slight rotation of the thorax to the opposite side and the pelvis to the same side. When the two muscles of opposite sides act together, the rotatory action of each will be neutralized. By the most lateral fibres a lateral flexion of the thorax or pelvis will be produced. 2. OBLIQUUS INTERNUS (Fig. 525). Attachments. The internal oblique muscle lies immediately beneath the ex- ternal one. It arises from the outer two-thirds of Poupart's ligament, from the whole length of the middle lip of the crest of the ilium, and from the lumbo-dorsal fascia. From this extended origin its fibres spread out in a fan-shaped manner, the more posterior ones passing upward and slightly forward to be inserted into the HUMAN ANATOMY. lower three ribs, while of the rest the more anterior ones pass forward and upward, those from the neighborhood of the anterior superior iliac spine directly forward, and those from Poupart's ligament forward and downward, all joining in a flat aponeu- rosis which unites with the anterior abdominal aponeurosis at the linea semilunaris. In its lowermost portion the aponeurosis unites with that of the transversalis to form what is termed the conjoined tendon, and by this it is attached to the crest of the pubis. FIG. 524. Serratus magnu Latissimus dorsi - Gluteus maximum External oblique Petit's triangle- Fascia lata Pectoralis major Origin of pectoralis major from sheath of rectus Line of subcostal arch Linea transversa l.inea semilunaris I'mbilicus Anterior superior iliac spine Suspensory ligament of penis Poupart's ligament Spermatic cord Dissection of lateral body-wall, showing external oblique and adjoining muscles. Nerve-Supply. From the anterior divisions of' the eighth to the twelfth thoracic nerves and from the ilio-hypogastric and ilio-inguinal nerves. Action. The internal oblique acts very similarly to the external in compressing the abdominal contents, in drawing the lower ribs downward, and in flexing the thorax or pelvis laterally. It will also Hex the thorax and vertebral column upon the pelvis or the pelvis upon the vertebral column, but in these actions the accompanying rotation will be in a direction contrary to that caused by the external oblique, the thorax being rotated to the same side and the pelvis to the opposite side. It may be remarked that the rotatory action of the external oblique of the one side and the internal oblique of the other will be in the same direction. Variations. The internal oblique may he crossed by one or more tendinous intersections which have probably the same significance as those of the rectus abdoniinis. THE VENTRAL MUSCLES. 3. CREMASTER (Figs. 525, 1671). Attachments. The cremaster muscle consists of a series of somewhat scat- tered loops of muscle-tissue derived from the lower part of the internal oblique and to a slight extent from the transversalis. It is attached laterally to Poupart's liga- ment and medially to the anterior layer of the sheath of the rectus. The loops de- scend through the inguinal canal along with the spermatic cord, the muscle being FIG. 525. Pectoralis major Serratus magnus Latissimus dorsi Edge of cut external oblique Internal oblique Posterior aponeurosis of internal oblique Iliac crest Fascia lata Cut edge of fascia lata Gluteus maximus Edge of cut aponeurosis of external oblique _ Linea alba _ Anterior aponeurosis of internal oblique Anterior superior iliac spine Conjoined tendon Suspensory ligament Cremaster fibres Dissection of lateral body-wall, showing internal oblique muscle. well developed only in the male, and spread out in the tunica vaginalis communis of the testis and spermatic cord. The loops are united by connective tissue which forms part of the cremasteric fascia. Nerve-Supply. By the genital branch of the genito-crural nerve. Action. To draw the testis upward towards the external abdominal ring. 4. TRANSVERSALIS (Fig. 526). Attachments. The transversalis (m. transversus abdominis) is the deepest layer of muscle on the lateral abdominal wall and immediately underlies the internal oblique. It arises from the cartilages of the lower six ribs, from the lumbo-dorsal 520 HUMAN ANATOMY. fascia, the inner lip of the crest of the ilium, and the outer two-thirds of Poupart's ligament. Its fibres pass horizontally inward to join the ventral abdominal aponeu- rosis along the linea semilunaris ; the lower ones, however, bending somewhat down- ward, pass into an aponeurosis which unites with that of the internal oblique to form the conjoined tendon attached to the crest of the pubis. Nerve-Supply. From the anterior divisions of the seventh to the twelfth thoracic nerves and from the ilio-hypogastric and ilio-inguinal nerves. Action. To compress the contents of the abdomen. FIG. 526. Pectoralis major Serratus magnu Latissimus dorsi Edge of cut external oblique Edge of cut internal oblique Lumbo-dorsal fascia Fascia lata Cut edge of fascia lata Gluteus maximus Tensor fasciae latae Edge of aponeurosis of external oolique . of aponeurosis of internal oblique Tjj* Aponeurosis of transversalis Rectus, covered by sheath Conjoined tendon (.'mna^ter fibres Dissection of lateral body-wall, showing transversalis muscle. The fascia transversalis is a thin layer of connective tissue which lines the inner ( deeper ) surface of the transversalis muscle. Posteriorly it is continuous with the strong aponeurotic band formed by the fusion of the superficial and deep layers of the lumbo-dorsal fascia, anteriorly it combines with the deeper layer of the ventral abdominal aponeurosis to form the posterior layer of the sheath of the rectus muscle, and above it unites with the fascia covering the lower surface of the diaphragm. Below its lateral portion is attached to the crest of the- ilium and the outer part of Poupart's ligament where- it becomes continuous with the iliac fascia, but more medially it is continued downward beneath Poupart's ligament to form the anterior wall of the sheath of the femoral vessels, the portion of it immediately above the vessels being THE VENTRAL MUSCLES. 521 thickened somewhat to form the deep crural arch (Fig. 1773). More medially still it is attached to the free edge of Gimbernat's ligament and to the upper surface of the superior ramus and body of the pubis. A little over i cm. above Poupart's ligament, and about half-way between the anterior superior iliac spine and the symphysis pubis, the transversalis fascia is per- forated by the spermatic cord in the male and by the ligamentum teres of the uterus in the female. The fascia is continued downward and forward over the cord or ligament to form a somewhat funnel-like investment for it termed the infundibuliform fascia, the inner margin of the funnel marking the position of the internal abdominal ring. 5. QUADRATUS LUMBORUM (Fig. 527). Attachments. The quadratus lumborum is a flat quadrilateral muscle which lies towards the back part of the ab- dominal wall, extending between the FIG. 527. crest of the ilium and the lower bor- der of the twelfth rib. It consists of i^. i^^toM^AV two layers of fibres which frequently v v v,\\ are distinguishable from each other { ^>^ only with difficulty. The anterior layer, which arises from the trans- verse processes of the lower four lum- bar vertebrae and from the posterior part of the iliac crest, is inserted into the lower border of the twelfth rib ; the posterior layer (Fig. 527) arises from the crest of the ilium and is in- serted into the lower border of the twelfth rib and into the transverse processes of the upper four lumbar vertebrae. Nerve-Supply. By branches from the lumbar plexus. Action. To draw downward the last rib and to bend the lumbar por- tion of the spinal column laterally. Relations. The quadratus lum- borum rests behind upon the deep layer of the fascia lumbo-dorsalis (Fig. 519), which separates it from the spino- sacral muscle. Its anterior surface is in relation to the kidney and the as- cending or descending colon, is crossed by the lumbar arteries, and is covered towards its inner margin by the psoas major. XII rib Quadratus lumborum Iliac crest Dorsal surface of ilium Quadratus iumborum muscle of right side, seen from behind. 6. INTERTRANSVERSALES LATERALES (Fig. 521). Attachments. The lateral intertransversales are a series of small quadrilateral muscles which extend between successive transverse processes of the lumbar vertebrae. Nerve-Supply. Probably from the anterior rami of the lumbar nerves. Action. To bend laterally the lumbar portion of the spinal column. The Ventral Abdominal Aponeurosis (Fig. 528). The broad aponeurotic sheets into which the oblique and transverse muscles of the abdomen are continued at their anterior (medial) edges unite more or less intimately with one another and with the fascia transversalis to form the ventral abdominal aponetirosis. Laterally the various layers of which this aponeurosis is composed are to a certain extent discerni- ble, since the lines along which the fibres of the three muscles pass into the apo- neurosis do not coincide, that of the external oblique extending from the outer border of the rectus muscle above obliquely downward and laterally to the anterior superior spine of the ilium, while those of the internal oblique and transversus follow essen- 522 HUMAN ANATOMY. dally the outer border of the rectus, except below, where they lie a little lateral to that muscle. More medially, however, the layers become intimately associated and can only be separated artificially. At the outer border of the rectus muscle the aponeurosis divides into two layers (Fig. 529, A) which pass one in front and the other behind the rectus, thus forming a sheath for it (vagina musculi recti). The line of the division is indicated on the surface of the abdomen by a slight groove, and constitutes what is termed the linea scmi- lunaris. When they reach the mesial border of the rectus the two layers unite and become continuous in the middle line with the aponeurosis of the opposite side to form a strong fibrous band which extends from the front of the xiphoid process of the sternum above to the FIG. 528. symphysis pubis be- low, and is termed the linea alba. In its upper part this band is fairly broad, but below the umbilicus, which is situated in the band, it suddenly narrows to a thin line which becomes con- tinuous below with the superior pubic liga- ment, behind the in- sertion of the recti, by a triangular expansion which occasionally contains muscle-fibres and is termed the ad* miniculum lineae albac. 7t\\Qposterio r layer of the aponeurosis, which forms the poste- rior wall of the sheath of the rectus, is fairly thick above, but a lit- tle below the level of the umbilicus it sud- denly becomes very Superficial dissection of abdomen, showing ventral aponeurosis. arched line, the con- cavity of which is downward, and may sometimes be represented by a distinct fold. This margin is termed the line or fold of Douglas (linea semicircularis) (Fig. 523). Uncovered^ fibres of exter- v nal oblique Anterior,^ sheath of rec- tus muscle Anterior superior i iliac spine Intercolumnar I fibres External abdomi-_ajB nal ring Spermatic cord \ >Lineae transversae -Linea alba >vered ex- crnal oblique 9 Linea * semilunaris Suspensory \ ligament of penis Various suggestions have been made in explanation of this sudden change in the thickness of the posterior layer of the sheath of the rectus. It has been supposed that it was connected with the passage of the inferior epigastric artery into the substance of the muscle (Henle), a somewhat inack-qnate cause even if the point of passage of the artery through the sheatli cor- responded with the semicircular line. The thinness of tin- portion of the sheath below the line has been explained on the ground that it represents the portion with which the urinary bladder was in contact in fatal life (Gegenbaur), and also by the view that the strain exerted on this portion of the sheath is less than that placed upon the upper part, since the latter is acted on by fibres of the oblique and transverse muscles which have bony attachments drawn upuard during inspiration, while the lower part is in relation to the less active fibres attached to the inguinal ligament (Solgert. Kinally, it may be slated that the immediate cause for the sudden change in thickness lias been assigned to the development of the processus vaginalis peritoncei, the pouch of peritoneum which in the embryo descends into the genital swelling and gives rise in the male to the ttmi.'a vaginalis testis. The formation of this peritoneal pouch is held to prevent the lower portions of the posterior layer of the abdominal aponeurosis which are derived from tin- aponeuroses of the internal oblique and transversalis from passing behind the rectus muscle, the posterior wall of its sheath being formed only by the fascia transversalis (Kisler). THE VENTRAL MUSCLES. 523 In the lower part of the anterior abdominal wall the lowermost fibres of the abdominal aponeurosis those extending between the anterior superior spine of the ilium and the pubic spine form a strong ligamentous band, the ligament of Pou- part (ligamentum injjuinale) (Figs. 524, 530,), the outer portion of which gives rise to some of the fibres of the internal oblique and transversalis muscles, while the fascia lata of the thigh is attached to it below. Near its medial end some of its fibres pass inward to be attached to the ilio-pectineal line of the pubis, forming a horizontal trian- gular sheet whose free concave lateral border forms the medial boundary of ti\e femo- ral ring (annulus fcmoralis) through which the femoral hernias make their exit from the pelvis. This reflection (Fig. 531) is the ligament of Gimbernat (ligamentum lacunare). Furthermore, a sheet of fibres, variable in its development and termed the triangular fascia (ligamentum inguinale reflexum), or ligament of Colles (Fig. 1485), is reflected upward and medially from the inner portions of Poupart's and Gimbernat' s ligaments in front of the lower medial portions of the aponeuroses of the internal oblique and transversalis muscles to the anterior layer of the sheath of the rectus. The Inguinal Canal. At an early stage in the development of the foetus an outpouching of the lower part of the abdominal wall occurs on each side to form the genital swellings, which later become the scrotum in the male and the labia majora FIG. 529. A Transversalis muscle Transversalis fascia Peri- Division of aponeurosis of internal oblique , Rectus , External oblique Internal obliq Skin Aponeurosis of internal oblique Transversalis muscle Internal oblique Linea alba / Anterior sheath of rectus Superficial fascia Aponeurosis of external oblique B Transversalis fascia Peritoneum Rectus fusion Linea alba Rectus \\i. Superfic Skin Aponeurosis of external oblique Anterior sheath of rectus Diagrams showing constitution of sheath of rectus muscle. A, in upper three-fourths; B, in lower fourth. in the female. The points at which the outpouchings occur are those at which the lower ends of a ligament descending from the primitive kidneys (mesonephri) are attached to the abdominal wall, and these ligaments, consequently, are carried through the length of the outpouching beneath its peritoneal lining to attach to the walls of the scrotum or the labia. In the female the ligaments become in part the round ligaments of the uterus, but in the male the relations of the outpouchings become more complicated. Owing to the descent into them of the testes (page 2040), the ligaments are drawn completely into the pouch, forming the gubernacula of the testes, while the vasa deferentia and the vessels and nerves of the testes are also carried into the pouch, uniting to form the spermatic cord. There are, consequently, pass- ing from the abdominal cavity into each pouch, in the female the round ligaments of the uterus and in the male the spermatic cord. At first, and in the male for a considerable time after birth, the communication of the pouch with the abdominal cavity is widely open ; but later, in the upper part of the pouch in the male and throughout its entire length in the female, the lumen becomes reduced, and finally is completely obliterated by the union of its walls to the sper- matic cord or the round ligament, its lower portion persisting in the male as the space which exists between the visceral and parietal layers of the tunica vaginalis testis. 524 HUMAN ANATOMY. As a result of these processes the lower portion of the abdominal wall is traversed on either side by the spermatic cord or by the ligamentum teres of the uterus, and it is customary to regard the space occupied by the one or the other of these structures as a canal, which is termed the inguinal canal. It should be understood, however, that an actual space surrounding the cord or ligament does not exist, the walls of the canal being united to the structure contained within it. Nevertheless, the union is by no means a strong one, the region of the abdominal wall traversed by the ligamentum teres or especially by the spermatic cord being relatively weak and not infrequently the seat of an inguinal hernia. The inguinal canal is somewhat over 3 cm. ( i ^ in. ) in length and is situated immediately above Poupart's ligament, which it crosses obliquely from above down- ward, medially, and forward. Its upper or inner end is about midway between the anterior superior spine of the ilium and the spine of the pubis, and lies about 12 mm. ( l /z in. ) above the line of Poupart's ligament. It is marked by a more or less distinct depression on the posterior surface of the abdominal wall surrounding the spermatic cord or round ligament, termed the internal abdominal ring (annulus inguinalis FIG. 530. Anterior superior iliac spine- Poupart's ligament Falciform process Iliac portion of fascia lata. Saphenous opening Femoral artery-"-" Femoral vein Internal saphenous vein -Aponeurosis of external oblique . Intercolumnar fibres External abdominal ring . External pillar Internal pillar r.inibernat's ligament, inner boundary of femoral ring Pubic portion of fascia lata Spermatic cord Scrotum Dissection of right inguinal region, showing external abdominal ring and saphenous opening. abdominis). The depression (Fig. 532) is due to the transversalis fascia bring pro- longed downward over the spermatic cord as a funnel-like sheath, the infnndibidi- fonn fascia. The lower or medial end of the canal corresponds to the external abdominal ring (annulus abdominnlis subcutaneus) (Figs. 523, 530), and lies just lateral to and a little above the spine of the pubis and is surrounded by the lower nudial portion of the aponeurosis of the external oblique. The fibres of the aponeu- rosis which bound this ring are somewhat thickened, forming what are termed the pillars Centra) of the ring, the uppermost of which, the internal pillar Cents superior ), consists of fibres passing to the symphysis pubis ; the lower one, the external pillar (cms inferior), is formed by the fibres passing to the pubic spine, and corresponds to the medial end of Poupart's ligament. Stretching across between the two crura are numerous obliquely arching intcrcoltannar fibres ( librae interenirales ) which extend laterally almost as far out as the anterior superior spine of the ilium. From the margins of the external ring an attenuated prolongation of the aponeurosis of the external oblique is continued downward over the spermatic cord as a thin membrane known as the intcrcolionnar or external spermatic fascia. THE VENTRAL MUSCLES. 525 Owing to the oblique direction of the canal, that portion of the aponeurosis of the external oblique which is strengthened by the intercolumnar fibres, together with a portion of the internal oblique, forms its anterior wall, while its posterior wall is formed by the aponeurosis of the transversalis, together with the more medial lower portion of that of the internal oblique, these two layers of fascia uniting in this region to form what is termed the conjoined tendon, which is attached below to the body and superior ramus of the pubis, and medially is especially thickened to form a band, the falx inuinalis, firmly attached along its medial border to the tendon of the rectus. More laterally, where it forms the medial boundary of the internal abdominal ring, it is also thickened (Fig. 531), forming the ligament of Hesse/bach (ligamentum inter- foveolare). Between these two thickenings the abdominal wall is weaker (Fig. 1493) and may give way to internal pressure, permitting a hernia, which conies to the sur- face at the external abdominal ring without having traversed the inguinal canal, and is therefore spoken of as a direct hernia, in contradistinction to the more usual oblique hernia which enters the canal at the internal abdominal ring. FIG. 531. Rectui Deep epigastric artery. Interfoveolar or Hesselbach's ligament Weak area. Conjoined tendon Muscular fibres Lower end of Poupart's ligament Urachus Bladder Poupart's ligament Transversalis muscle Spermatic vessels ..External iliac artery -External iliac vein -Deep epigastric artery (cut) -_Vas deferens '^-Femoral ring Gimbernat's ligament Dissection of posterior surface of anterior abdominal wall, showing relations of conjoined tendon and its expansions to internal abdominal ring. A small fasciculus of muscle-tissue is sometimes found close to the medial border of the internal abdominal ring. It is the m. interfoveolaris (Fig. 531), and arises from the superior ramus of the pubis, passing almost directly upward to spread out on the posterior surface of the transversalis. It is generally regarded as an aberrant portion of the transversalis muscle. The Posterior Surface of the Anterior Abdominal Wall. Throughout its entire extent, with the exception of a small area in the median line below, the posterior surface of the anterior abdominal wall is lined by peritoneum. In the exceptional area the peritoneum is kept from actual contact with the wall by a band of fibrous tissue, the urachus, which extends from the apex of the urinary bladder to the umbilicus and supports the peritoneum somewhat in the manner of a ridge-pole of a tent, so that between it and the abdominal wall there is an interval occupied only by loose areolar tissue and termed the prevesical space of Ret z i us (page 1906). Laterally from the urachus a fibrous cord, the lateral ligament of the umbilicus, may be seen on each side, passing from the side of the bladder to the umbilicus and representing the obliterated hypogastric arteries of the foetus ; while still more laterally there may be seen coming from the external iliac artery the inferior or deep epigas- tric artery, which, passing immediately to the inner side of the internal abdominal ring and posterior to the interfoveolar ligament (Fig. 532), extends upward and inward to penetrate the posterior layer of the sheath of the rectus a short distance below the level of the umbilicus. Both these structures produce a slight ridging or told of the peritoneum, that formed by the obliterated hypogastric artery being termed the />//(({ umbilicalis latcralis, while the other is the plica epigastrica. These two tolds, together with the urachus, mark off the lower portion of the abdominal wall 526 HUMAN ANATOMY. into three areas or foveae (Fig. 532). The median of these foveae lies between the urachus and the lateral umbilical fold and forms the supravesical fossa, having for its floor the rectus muscle. Between the lateral umbilical and the epigastric folds is the inner inguinal fossa, having for its floor the conjoined tendon, and being therefore the region in which direct inguinal hernias arise ; ano* lateral to the epi- FIG. 532. Peritoneal surface Plica epigastrica 1 Hesselbach's triangle Vas deferens. External iliac artery. External iliac vein Plica hypogastrica^ Outer edge of rectus muscle Supravesical fossa Outer inguinal fossa Inner inguinal fossa Bladder, somewhat distended Median umbilical ligament Posterior surface of anterior abdominal wall of formalin subject. gastric fold is the outer inguinal fossa, in whose floor is found the internal abdominal ring, just to the outer side of the deep epigastric artery. The triangular area bounded by Poupart's ligament below, the lateral edge of the rectus muscle medially, and the plica epigastrica laterally has been termed the triangle of Hesselbdch. It is almost identical with the middle inguinal fossa, and defines a little more precisely the seat of the direct hernias. (c) THE HYPOSKELETAL MUSCLES. It seems probable that the psoas major and the psoas minor muscles are, in part at least, assignable to the group of abdominal hyposkeletal muscles. The close associatio'n of the psoas major with the iliacus and its attachment to the femur make it convenient, however, to defer their description until later (page 623). PRACTICAL CONSIDERATIONS. THE ABDOMEN. The abdominal cavity is bounded above by the diaphragm ; below by the floor of the pelvis ; laterally by the diaphragm, the lower ribs, the abdominal muscles, and the lateral expansions of the ilia ; posteriorly by the diaphragm, the tenth, eleventh, and twelfth ribs, the lumbar muscles and vertebrae, the posterior portions of the ilia, and the ischial, sacral, coccygeal, and pubic bones ; and interiorly by the levatores ani and coccygei muscles. It should be noted that the roof, the floor, and much of the remaining parietes of the abdomen are made up of muscular tissue- which, by contraction or by relaxation or stretching, can alter the si/.e of the cavity, affect the relations of the contained viscera, and vary the compression to which they are subject. The tonicity of the muscular walls brings about a normal intra-abdominal pressure which serves in health to retain in position and to give support to the viscera. This pressure is increased in inspiration and by straining, lifting, or coughing. It then, by increasing the outward pressure of the viscera upon the internal sur- face of the parietes, favors the production of hernia, the protrusion of the intestine PRACTICAL CONSIDERATIONS : THE ABDOMEN. 527 through a wound, the stretching of scars, and some forms of dystocia and of uterine displacement. The pelvic cavity " a recess leading downward and backward from the abdomi- nal cavity proper" (Cunningham) is divided from the latter by an imaginary plane extending from the promontory of the sacrum to the upper edge of the pubes. It will be considered separately. The general shape of the abdominal cavity is described on page 1615 as are also the regions into which, for convenience, the abdomen proper may be divided by cer- tain arbitrary lines (page 1615). The structures and organs underlying the spaces thus marked out are approxi- mately as follows : RIGHT HYPOCHONDRIAC. Greater part of right lobe of liver, hepatic flexure of colon, and part of right kidney. EPIGASTRIC. Greater part or whole of left lobe and part of right lobe of liver, with gall-bladder, part of stomach, including both ori- fices, first and major portion of the second parts of duo- denum, duodeno-jejunal flex- ure, pancreas, upper or inner end of spleen, parts of kid- neys, and suprarenal bodies. LEFT HYPOCHONDRIAC. Part of stomach, portion of spleen, tail of pancreas, splenic flexure of colon, part of left kidney, and sometimes part of left lobe of liver. RIGHT LUMBAR. Ascending colon, part of right kidney, and sometimes part of ileum. UMBILICAL. Greater part of transverse colon, lower portion of second and much of third part of duo- denum, some convolutions of jejunum and ileum, with por- tions of mesentery and greater omentum, part of right, often of left, and sometimes of both kidneys, and part of both ureters. LEFT LUMBAR. Descending colon, part of jejunum, and sometimes part of left kidney. RIGHT ILIAC. Caecum with vermiform ap- pendix and termination of ileum. HYPOGASTRIC. Convolutions of ileum, blad- der in children, and when dis- tended in adults also, uterus when in the gravid state, and, behind, sigmoid flexure. LEFT ILIAC. Sigmoid colon, convolutions of jejunum and ileum. The contents of the various regions and the structures intersected by the different planes if the arbitrary lines are continued into planes vary considerably within normal limits and greatly in the presence of disease. The shape and size of the abdomen are also extremely variable. In the normal adult male it is irregularly cylindrical, with a central bulging, an antero-posterior flattening, and a greater width near the pelvis than near the ribs. In the adult female the larger relative size of the lower abdomen is due to the greater development of the pelvis, and usually to flabbiness of abdominal muscles and accumulation of fat from want of exercise, and to compression of the upper segment by corsets ; it is increased by the stretching of repeated pregnancies. In infancy and childhood the abdomen is prominent on account of the undeveloped condition of the pelvis, the pelvic viscera being then practically within the abdomen, and is broader above than below by reason of the relatively great bulk of the liver. In obesity the weight of the intra-abdominal and subcutaneous fat carries the lower part of the abdominal wall downward by gravity, stretches it, and produces a pendulous abdomen. This condition is also favored by ascites, pregnancy, etc. In 528 HUMAN ANATOMY. emaciation the whole anterior abdominal wall becomes concave (scaphoid}, especially the upper portion bounded by the ensiform cartilage and the subcostal angle, the scrobiculus cordis (page 171), which, with the patient supine, may appear to rest directly upon the vertebral column, with walls more nearly vertical than horizontal. Congenital deformities of the abdominal wall usually consist in a failure of the ventral plates to unite in the middle line, producing various degrees of umbilical hernia (q. v. ) or leaving the contents of the abdomen uncovered over a considerable area. Contusions of the anterior abdominal wall, bounded laterally by the outer free border of the external oblique, i.e., by a line just external to a vertical line dropped from the lowest part of the ninth rib, are of importance in relation to the effect upon the organs contained within the abdomen. As the skin over the abdomen and the abdominal muscles receive their nerve-supply from the lowest six intercostal nerves and the branches of the anterior division of the first lumbar, the contraction of the muscles upon the approach of danger, if not voluntary, may be reflexly hastened at the moment of external application of force, and a protecting elastic barrier may thus be interposed between the latter and the abdominal contents. The rigidity caused by the contact of a cold hand with the abdominal surface, preventing palpation of the viscera beneath, affords a familiar illustration of the close relation between skin and muscles. The relation of the nerve-supply of the muscles and that of the underlying viscera explains the rigidity of the belly so usually seen in injury or disease of abdominal organs (page 1683). Finally the relation of the cuta- neous and muscular branches of the intercostal nerves is well shown by the sudden inspiratory effort caused by a dash of cold water on the lower thoracic or abdominal region, six of these nerves supplying the intercostal muscles as well as the antero- lateral surface of the chest and belly. The injurious effect of contusions is diminished by the presence of a thick layer of subcutaneous fat or by the interposition of a fleshy omentum. If the abdominal muscles are relaxed, serious injury to the viscera may be done without obvious damage to the parietes. Absence of ecchymosis or other visible sign of injury should therefore not lead to an absolutely favorable prognosis until after the lapse of suffi- cient time to permit of the development of visceral symptoms. Wounds. The thinness and loose attachment of the skin of the abdomen favor the occurrence of cellulitis as a result of infection from superficial wounds. The superficial layer of the superficial fascia contains the greater part of the subcutaneous fat and covers the superficial blood-vessels. The thickness of the abdominal wall depends chiefly upon the thickness of this fatty layer, which may be of several inches. An abdominal wound may therefore be of considerable depth and yet be attended by little or no bleeding and be practically ' ' superficial. ' ' The deeper layer of the super- ficial fascia (page 515) is firmer, is elastic, and in its lower part is the vestige of the " tunica abdominalis," well developed in the horse and some other quadrupeds for reinforcement of the abdominal muscles, on which the weight of the viscera comes more directly than in man. It is attached in the middle line to the deeper struc- tures and to the iliac crest, and below Poupart's ligament blends with the fascia lata of the thigh. It is not attached over the space between the pubic spine and symphysis, but, being carried downward over the spermatic cord, becomes continuous with the dartos layer of the scrotum and with the fascia of Colles. Cellulitis superficial to this layer may therefore spread in all directions, but beneath it is likely to be at least tempo- rarily arrested at the lines of attachment indicated. General emphysema, effusions of blood, and collections of pus have for a time similar limitations. They are apt to be guided by this fascia into the space between the spine and the symphysis and to descend into the scrotum and towards the perineum, where the lateral attachments of Colles's fascia to the margins of the pubic arch and posteriorly to the base of the triangular ligament prevent their spreading in those directions. More usually the extravasa- tion blood, pus, or urine gains this subfascial space below, as from rupture of the urethra anterior (inferior) to the triangular ligament (page 1932), and ascends to the abdomen by the same route, being prevented from crossing the mid-line or descend- ing to the thighs by the attachments of the deep layer of the superficial fascia that have been described. PRACTICAL CONSIDERATIONS: THE ABDOMEN. 529 Wounds involving the muscular layers of the abdominal wall may gape widely, but the differing directions of the fibres of the external oblique, internal oblique, and transversalis tend to limit this just as they lessen the after-risk of ventral hernia and favor certain physiological acts, as the emptying of the bladder, the bowels, or the uterus. This difference of direction is taken advantage of in gaining access to the abdominal cavity in some operations (page 535). Infection in the lateral intcrmuscular spaces usually spreads rapidly on account of the abundance of loose cellular tissue. The cellulitis or resulting abscess (or collection of blood or air) will be limited by the semilunar line in front, by the costo- chondral arch above, by Poupart's ligament and the crest of the ilium below, and by the edge of the erector spinae behind ; in other words, by the attachments of the muscles between which they spread (Treves). Beneath the abdominal wall, practically making a portion of it, lies a layer of loose connective tissue the subperitoneal or subserous areolar tissue which connects the peritoneum with the parietes. ' ' Extraperitoneal connective tissue' ' has been sug- gested (Eccles) as a better name for it. Infection of this tissue, whether from without, as in the case of wounds, or by extension from some of the viscera lying wholly or partly behind the peritoneum, as in perirenal abscess or certain forms of appendiceal abscess, is likely to spread widely. Abscesses, especially if chronic, often gravi- tate into the iliac fossa and are arrested at Poupart's ligament by the junction of the transversalis and iliac fasciae, constituting a form of iliac abscess. If they are incised here, it will usually be necessary to go through only the abdominal muscles and aponeuroses, including the transversalis fascia, as the looseness and abundance of the subserous tissue will have permitted the abscess to dissect off and push upward the peritoneum. If the patient is supine, pus in the iliac fossae i.e., in the shallow lower zone of the abdomen may gravitate into the deep lateral recesses of the middle zone (page 1615), and it often takes this direction in cases in which the source of infection is an appendix situated behind the caecum. It should be noted that a true iliac abscess is beneath the iliac fascia, and is therefore more apt to be guided by that fascia to the lowest point of the ilio-psoas space and to pass with the ilio-psoas muscle into the thigh, pointing at the outer side of the femoral vessels. The laxity of the subserous tissue favors certain retroperitoneal operations e.g. , uretero-lithotomy by permitting the stripping forward of the peritoneum itself. The relatively great resistant power of the side of the peritoneum in contact with this tissue is subsequently described (page 1754). The fat contained in this layer greatest in the lumbar region (perinephric fa) and in front of the bladder in the space of Retzius (the triangular interval defined by the symphysis pubis, the bladder, and the peritoneum), and abundant in the inguinal and iliac regions may serve as a guide in approaching the peritoneum by incision, or may mislead if mistaken for the omental fat. The latter error has resulted, as, for example, in operation for ovarian cyst, in regarding the peritoneum as the cyst-wall, and in detaching it from the parietes over a wide area. This fat occasionally works its way through intervals between the fibres of the overlying fascia or muscles, especially along the linea alba, and constitutes the subserous lipomata, which, if large enough, are sometimes thought to be irreducible ventral herniae. The laxity of the subse- rous areolar layer between the bladder and the posterior surface of the symphysis pubis permits the peritoneum to be carried up on the summit of a distended bladder as it rises into the abdomen and thus facilitates extraperitoneal access to the an- terior vesical wall (page 1912). Its looseness over the iliacus muscle is a factor in the formation of the sac of inguinal hernia (page 1767). Wounds of the abdom- inal wall dividing this subserous layer, but leaving the peritoneum untouched, should practically be classified among non-penetrating wounds, although in a sense the abdominal cavity has been opened. The symptoms and dangers of infec- tion will be as above enumerated. Wounds involving the peritoneum are called penetrating wounds, the dangers of which have been considered in the section on the peritoneum. In the closing of abdominal wounds the irregularities that may result from the differing directions of the muscular fibres involved causing greater retraction at one 34 530 HUMAN ANATOMY. point than at another should be remembered. This may make accurate suturing in layers difficult, but such suturing, together with careful approximation of the edges of the peritoneal layer, is necessary to lessen the risk of ventral hernia. The respiratory movements prevent the attainment of absolute rest during the healing of abdominal wounds, as they do after fractures of ribs ; but in both cases approximate rest, as secured by strapping with adhesive plaster or by abdominal binders, gives excellent average results. THE LOIN. The posterior abdominal wall is in far less intimate association with the peri- toneum or the small intestine, and is, in its relation to injury or disease, of less importance than the antero-lateral walls, but it will be convenient to consider it and the loin here. Contusions, if over the ilio-costal space, the posterior segment of that portion of the abdominal wall which has no bony protection, are apt, if severe enough, to result in injury to the friable kidneys (page 1891') rather than to the rela- tively strong and elastic ascending or descending colon. Wounds, if they pass through the entire thickness of the wall, may involve either of these structures. When they become infected, the resulting cellulitis or abscess will be influenced as to the direction it takes and in its limitations by the various fasciae and muscular sheaths. The subcutaneous connective tissue is loose and abundant, and is frequently the seat of suppuration or of extensive collections of blood which gravitate towards the iliac crest or pass below it. The boundaries of effusion into the intermuscular spaces external to the edge of the erector spinae have already been described (vide supra). Within the musculo-aponeurotic compartments made by the splitting of the strong lumbar fascia into three layers (page 508) and enclosing the erector spirue and quadratus lumborum muscles the products of suppuration may for a time be con- fined. The middle and posterior layers are, however, very dense and resistant, and therefore, as they form the sheath of the erector spinae, that muscle is rarely the scat of abscess of other than vertebral origin ; beginning in caries of the neural arches, however, an abscess may directly penetrate the muscle between its fibres of origin or insertion. The anterior layer, separating the quadratus lumborum from the sub- serous areolar tissue, is very thin and is continuous with the transversalis fascia. For this reason, abscesses originating about the kidney or around the caecum or sigmoid not infrequently perforate this layer and pass either directly through the outer third of the thin quadratus lumborum external to the erector spinae (which buttresses its inner two-thirds) or through the transversalis fascia external to the quadratus. If they are high (perirenal), they may follow the last dorsal nerve, which pierces this fascia and the transversalis muscle just below the last rib, and may then make their way through the internal oblique and appear at the outer border of the erector spime ; or they may gravitate to the triangle of Petit, the interval between the crest of the ilium (its base) and the converging edges of the external oblique and latissimus dorsi, where, as the floor of the triangle is formed by the internal oblique, they will be subcutaneous as soon as they have perforated the latter muscle. An abscess of lower origin (pericaecal, pericolic) may reach the same space by fol- lowing the ilio-hypogastric branch of the first lumbar nerve. Abscesses in the lumbar subserous areolar f issue are more frequent on the right side, on account of the presence of the appendix. Like abscesses of perinephrie origin occupying the same situations, they may open into the colon or sigmoid. As this tissue is continuous below with the corresponding layer in the pelvis, abscesses originating there may ascend and appear at one or other of the various points de- scribed. True iliac abscesses (vide supra) are beneath the iliac fascia, which is con- tinuous with the transversalis fascia at Ponpart's ligament, but encloses the ilio-psoas muscle in a definite compartment, weak below, where the fascia accompanies the muscle beneath Poupart's ligament to become the pectineal fascia. The upper part of this fascia, covering the psoas muscle, is thinner and less resistant than the lower. Abscesses beginning in disease of the lumbar spine may penetrate directly into the muscular substance. Those beginning in the thoracic spine are often so limited an- teriorly by the internal arcuate ligament and posteriorly by the spine and last rib I PRACTICAL CONSIDERATIONS : THE ABDOMEN. 531 that they are diverted into the psoas sheath between those slips of origin of the muscle which come from the bodies of the vertebrae and those which come from the transverse processes. Often the pus descends, as in iliac abscess, to point on the thigh external to the femoral vessels, but not infrequently it passes under the external arcuate ligament or penetrates the psoas sheath at its outer edge and the anterior layer of the lumbar aponeurosis (to which it is there attached) and points in the loin, in which case it may be mistaken for one of the abscesses origi- nating in or spreading through the subserous areolar tissue. In the typical psoas abscess the thigh is flexed to relax the muscle and its sheath and to lessen the compression of the lumbar nerves which are contained within it. It will be observed that a psoas or a true iliac abscess is in close relation to these nerves, but is separated from the iliac vessels and, except at the upper por- tion, from the genito-crural nerve by the thick iliac fascia. Iliac aneurism may, however, by pressure cause flexion of the thigh and pain in the course of the same nerves. LANDMARKS AND TOPOGRAPHY OF THE ABDOMEN. 1. The bony and cartilaginous structures that constitute the apparent limits of the abdomen, and that are either visible or palpable, are as follows : (a) The tip of the ensiform cartilage, on a level with the lower part of the body of the tenth dorsal vertebra. (b) The seventh, eighth, ninth, and tenth costal cartilages, forming the lateral boundaries of the infrasternal fossa (Fig. 173, page 171;. A notch that may be felt on the costal border indicates the point of union of the tip of the tenth to the edge of the ninth cartilage (Woolsey). (el. At the internal abdominal and the femoral rings it has important relations to hernial sacs (page 1493); it lies at first at the side of the rectus in the subserous areolar tissue, then in the transversalis fascia, then within the .sheath of the rectus (above the fold of Douglas) behind the middle of the muscle, and finally in the muscle itself. It therefore runs from without inward and becomes more superficial as it ascends. With the exception of the superior epigastric and ascending lumbar, all the abdominal and pelvic veins empty directly or indirectly into the inferior vena cava and are therefore affected by the conditions that obstruct that vessel ; hence the superficial veins are often varicose. Although their varicosity is usually a result of obstruction in the portal vein or inferior vena cava, it may occur independently of 534 HUMAN ANATOMY. Dytptp, obstructive cause, as do many cases of varicose veins of the lower extremity, and may be very large and extremely tortuous (.capnt mcdus(e). The mechanism of the production of this form of varicosity by portal obstruc- tion will be more readily understood by reference to Fig. 534, which also explains other phenomena associated with that condition. The superficial epigastric vein is often visible. Through its anastomosis with the deep and superior epigastric veins it is connected with the portal and parumbilical veins and may be enlarged as a symptom of hepatic disease (page 1727). The area of redness about the umbilicus seen in some forms of peritonitis is probably due to inflammation extending along the obliterated umbilical veins (page 1757). The surface veins above the umbilicus empty into the axilla and those below that level into the groin, but the venous currents may be reversed by disease. For example, the superficial epigastric and superficial circumflex iliac normally empty into the internal saphenous vein a little below Poupart's ligament. In cases of obstruction of the inferior vena cava the blood-current is reversed (as it is in the corresponding deep veins), they enlarge, and, by anastomosing with the superior epigastric, internal mammary, and thoraco-epigastric veins, carry blood from the lower limbs into the axillary or innominate, and so into the superior vena cava. In hepatic obstruction, although the superficial epigastric may become varicose (through its connection with the parumbilical and portal veins), this reversal of the blood-current does not occur FIG. 534. in it, as may be shown by emptying the vein by press- ure and observing the di- rection of the current as it refills. The superficial lymphatics of the abdominal wall below the umbilical level empty into the nodes at the groin, those above that level into the nodes in the axilla. 6. The nerves of the abdominal wall (page 535) have already been described in their relation to various clinical phenomena (pages 1683,1755). In addition, it should be said here that the definiteness of the relation in nerve-supply between cu- taneous areas and abdominal organs is often of great value in diagnosis. As the sixth to the twelfth thoracic and the first lumbar spinal segments aid in the nerve- supply to the abdominal viscera, and as the corresponding spinal nerves supply the skin of the abdomen, pain due to visceral disease is often referred (through the com- municating branches with the splanchnic and the sympathetic visceral nerves ) to the peripheral terminations on the skin of the abdomen, which may even be sensitive to the touch. It is possible to map out approximately on the surface the area of distribution of the cutaneous branches from each of these segments (Fig. 535). Head has associated as follows these areas ( which are almost identical with the arras of distribution of the corresponding spinal nerves) and the viscera in closest connection with them : The sixth, seventh, eighth, and ninth thoracic segments with the stomach ; tin- ninth, tenth, eleventh, and twelfth thoracic segments with the intestinal tract : tin- seventh, eighth, ninth, and tenth thoracic segments with the liver and gall-bladder ; the tenth, eleventh, and twelfth thoracic and the first lumbar segment with the kid- ney and ureter ; the second, third, and fourth sacral with the rectum. CAPUT MEDUSAE Diagram showing anatomical relations of certain clinical phenomena in cirrhosis of liver. (After Hart and Taylor.) PRACTICAL CONSIDERATIONS : THE ABDOMEN. 535 The distribution to the pelvic organs will be considered later, but it may be said here that the pelvic viscera are supplied from the fifth lumbar to the fourth sacral segment and that no visceral branches emerge from the FIG. 535. second, third, or fourth lum- bar segments. Division of any of the motor nerves interferes with the function and ultimately with the nutrition of that portion of the musculature of the abdominal wall that is supplied by them, giving rise to weakness over that area, favoring the development of ventral hernia, and, if ex- tensive, interfering with the physiological action of those muscles in defecation, urina- tion, or parturition. For clinical purposes these nerves may be divided into three groups (Eads): (a) the seventh and eighth intercostals ascend obliquely and supply the upper third of the abdominal wall ; () the ninth and tenth intercos- tals run horizontally inward and supply the middle third ; (c) the eleventh intercostal, the last thoracic, and the ilio- hypogastric and ilio-inguinal nerves run obliquely down- ward and inward and supply the lower third. It is obvious that verti- cal incisions elsewhere than in the linea alba (the nerves do not cross the mid-line) will divide a larger number of these nerves and result in more extensive atrophy of abdominal wall than will in- cisions more nearly parallel with the nerves and, when possible, with the chief mus- cular fibres of the region in- volved. Diagram of distribution of cutaneous nerves, based on figures of Hasse , ,- .., and of Cunningham. On right side, areas supplied by indicated nerves are 1 He Anatomy OJ /iO- shown; on left side, points at which nerves pierce the deep fascia. V\ dominal Incisions. A dia- grammatic representation of the structures of the abdom- inal wall in their relation to V-, V 3 , divisions of fifth cranial nerve; GA, great auricular; GO, SO, greater and smaller occipital ; SC, superficial cervical ; St, Cl, Ac, sternal, clavicular, and acromial branches of supraclavicular (Scl) ; Ci, circumflex ; MS, musculo-spiral ; Iff, intercosto-humeral ; LIC, 1C, lesser internal and internal cutaneous ; EC, external cutaneous ; IH, ilio-hypogastric ; //, ilio- inguinal ; r 1 -, last thoracic ; GC, genito-crural ; EC, external cutaneous ; MC, middle cutaneous ; 1C, internal cutaneous ; P, pudic ; -S'-S, small sciatic ; the most important incisions O, obturator; C, T,L, and S, cervical, thoracic, lumbar, and spinal nerves. may help to elucidate the practical application of some of the above-mentioned facts. It should be noted that in many of these incisions the approximately parallel fibres of the internal oblique and transversalis (when they are both muscular) may be regarded as one layer and 536 HUMAN ANATOMY. FIG. 536. 8 separated on the same line. No effort has been made, therefore, to show the latter muscle in the diagram. Incisions Nos. i, 2, and 3 are through the linea alba, No. 2 being carried around the umbilicus to the left to avoid the parumbilical vein and the round liga- ment of the liver. The chief advantage is the accessibility to the whole cavity afforded by prolonging the incision. The slight vascularity of the median raphe and the thinness of the abdominal wall, while operative advantages, tend to favor the later production of hernia. Incision No. 4 combines the disadvantages of the incisions through the linea alba with the added interference with the nerve-supply to the rectus. Incision No. 5 (McBurney) has been described (page 1685). It represents merely the separation of the aponeurotic fibres of the external oblique ; the deeper wound separates the internal oblique and transversalis fibres transversely. It may be noted that its inward extension (Weir), even. if it involves division instead of retraction of the rectus (page 1685), would equally avoid nerve-trunks, but might involve ligation of the deep epi- gastric. The resulting scar in the rectus would, however, merely add in effect another linea transversa and would not impair the efficiency of that muscle. Incision No. 6 (Eads) separates the same structures, but affords a bet- ter opportunity for approach to many appendicular abscesses without going through the peritoneal cavity (page 1685). The incision for inguinal colos- tomy (page 1688) may be made on the same lines as those just described. Incision No. 7, after division of the external oblique, permits the sepa- ration of the fibres of the internal ob- lique and of the upper abdominal in- tercostal nerves, which, like the others, run beneath that muscle, and is used to gain access to the gall-bladder region. Incision No. 8 also respects the internal oblique fibres and the seventh and eighth intercostal nerves and, when used for gastrostomy, permits the development of a valvular or sphincteric action about the orifice (page 1633). Incision No. 9 the vertical incision through the rectus recommended for gas- trostomy (Howse) must divide the terminal branches of the intercostal nerves, and consequently that portion of the muscle distal to the line of division will be weakened or paralyzed and unable to contribute to the formation of a sphincter (Eads). The incision for lumbar colostomy has been described (page 1688). The re- maining incisions through the loin may be more appropriately considered in relation to the approach to the kidneys or ureters (page 1894). Anatomical Relations bearing on the It.vamiuation of the Abdomen. Harris lias suggested utilizing the fixed and circuitous route of the colon (Fig. 1383) to subdi- vide the abdominal cavity by taking the inner or mesial layers of the longitudinal mesocolons and the inferior layer of the transverse mesocolon as the dividing lines. We would thus obtain four regions, namely, (i) the central region surrounded by mesocolon, (2) the superior region lying above the transverse mesocolon, (3) the right postero-lateral and (41 the left postero-lateral regions lying external to and behind the longitudinal mesocolons. Tumors of special viscera begin, as a rule, in the region normally occupied by Diagram illustrating relations of various incisions to structures of abdominal walls. PRACTICAL CONSIDERATIONS: THE ABDOMEN. 537 those organs, and often, when they overlap its boundaries, displace the colon in definite directions. The course of the colon being made apparent by inflating it with air, it may therefore be said that : 1. Growth in the central region would include tumors of the omentum, mesen- tery, small intestine, and peritoneum, many retroperitoneal tumors, and such growths affecting the female generative apparatus as rise from the pelvis into the abdomen. In the latter case the caecum and sigmoid would be displaced upward and outward. 2. Tumors beginning in the superior region would include those of the liver, gall-bladder, stomach, lesser omentum, spleen, and pancreas. Harris calls attention to the fact that pancreatic cysts have usually been mistaken for ovarian cysts, although the former almost always displace the transverse colon downward. They also, being retroperitoneal, carry it forward, while tumors of the spleen, although they cause downward displacement of the colon, especially of the splenic flexure, override it and hug the anterior abdominal wall. Enlargement of the gall-bladder similarly tends to depress and to overlap the right half of the transverse colon. 3 and 4. In the postero-lateral or external regions the most common tumors are those of the kidneys ; but as they are all retroperitoneal, they tend to carry the ascending or descending colon forward as well as inward. There are, of course, exceptions to these relations, as, for example, in the case of a movable kidney, which may be displaced so as to carry the inner layer of the mesocolon forward and inward and so have the colon lying to the outer side, but they are rare, and the anatomical relations described are of distinct diagnostic value. Bowlby has formulated the anatomical reasons for first exploring the right lower half of the abdomen in cases of intestinal obstruction of doubtful origin. He says that here are to be found : (a) the appendix ; (d) intestinal diverticula perhaps attached to the umbilicus or to the neighboring mesentery ; (c) a common site for volvulus, that is, the caecum ; (d ) a usual site for the lodgment of an impacted gall- stone, that is, the lower part of the ileum ; (e) a common place for adhesions due to caseous mesenteric glands ; ( f) the sites of right-sided inguinal, femoral, and obturator herniae. Further, if the obstruction is in the small intestine, it is in the right iliac fossa that undistended intestine will be found, and if this can be secured and traced upward, it is the surest guide to the seat of obstruction. A brief resume of some of those symptoms of abdominal disease having a definite anatomical basis will serve to complete the consideration of this important region. The patient being supine with the thighs flexed : 1. Inspection may show : (a) an asymmetrical swelling referable to a particular organ or region (vide supra] ; (6) general distention, which, if due to ascites, will cause bulging of the flanks, the fluid settling in the deep lateral recesses of the middle zone ; if to flatulence or intestinal paresis, a more symmetrical enlargement, usually somewhat emphasized in the central region on account of the presence there of the coils of thin and easily dilatable small intestine ; if to pregnancy, a rounded cen- tral prominence in the lower abdomen ; (_c) retraction, which if extreme (scaphoid), might be due to tuberculous meningitis, to lead poisoning, or to other cause of great emaciation ; (d) cedema of the skin, indicating, if local, an abscess underlying and close to or in the abdominal wall ; ( tin- lateral border of the sterno-cleido-mastoid, where it again divides into two layers to enclose that muscle. The two layers again unite at the medial border o) the muscle and are continued over the anterior triangle of the neck to the median line, where the fascia be.-onx-s continuous with that of the opposite side. This is the superficial layer of the deep cervical fascia. Above it is attached to the superior nuchal line and the mastoid process, whence it is continued along mg THE CERVICAL MUSCLES. 543 the greater cornu and body of the hyoid bone, to which it is firmly attached, and where it becomes continuous above with the deep fascia of the submental region. This fascia covers in the anterior belly of the digastric, the mylo-hyoid, and the submaxillary gland, and is attached above to the lower border of the mandible, where it becomes continuous with the parotido-masseteric fascia. Below the cervical fascia ends over the anterior surface of the clavicle, and, more medially, in the interval between the lower portions of the two sterno-cleido- mastoid muscles, it splits into two lamellae, enclosing what is termed the spatium suprasternale or space of Burns. Both the lamelke pass down to be attached to the upper part of the manubrium sterni, so that the suprasternal space is completely closed. It contains some fatty tissue, usually some lymphatic nodes, and the lower portions of the anterior jugular veins ; a diverticulum from it is prolonged laterally behind the insertion of the sterno-cleido-mastoid along each vein as it passes towards its point of union with the subclavian vein. From the under surface of this superficial layer a deeper or middle layer is given off at the sides of the neck, and, passing forward, assists in the formation of the sheath for the carotid artery and internal jugular vein, and then divides to enclose the omo-hyoideus and the other depressors of the hyoid bone, a special thickening of it extending downward from the intermediate tendon of the omo-hyoid to the clavicle. Above, the middle layer is attached to the greater cornu and body of the hyoid bone along with the superficial layer, but below it is continued down into the thorax in front of the oesophagus and trachea and becomes lost upon the upper part of the pericardium. A third or deep layer of the cervical fascia, also termed the prevcrtcbral fascia, is given off from the under surface of the superficial layer about on the line of the transverse processes of the vertebrae. It passes almost directly inward over the scalene and hyposkeletal muscles of the neck, enclosing the cervical portion of the sympathetic trunk and contributing to the formation of the carotid sheath. It unites with the corresponding layer of the opposite side over the bodies of the vertebrae. This fascia is continued downward into the thorax in front of the verte- bral column and above it extends to the base of the skull. Towards the median line in its upper part it is separated from the pharyngeal portion of the fascia bucco-pharyngea by some loose areolar tissue which occupies the so-called retro- pharyngeal space. This is continued downward in the loose tissue surrounding the esophagus, but is bounded laterally by the union of the pharyngeal and prevertebral fasciae. The carotid sheath is formed by the union of portions from the middle and deep layers of the cervical fascia. It forms an investment for the common carotid artery, the internal jugular vein, and the vagus nerve. (a) THE RKCTUS MUSCLES. 1. Sterno-hyoideus. 3. Sterno-thyroideus. 2. Omo-hyoideus. 4. Thyro-hyoideus. 5. Genio-hyoideus. i. STERNO-HYOIDEUS (Fig. 541). Attachments. The sterno-hyoid is a flat band-like muscle situated in the front of the neck close to the median line. It arises from the posterior surface of the sternal end of the clavicle and from the manubrium sterni and passes upward to be inserted into the lower border of the body of the hyoid bone. A mucous bursa, more constant in the male than in the female, usually occurs beneath the upper part of the muscle, resting upon the hyo-thyroid membrane near the median line and immediately below the hyoid bone. Nerve-Supply. From the first, second, and third cervical nerves, through the ansa hypoglossi. Action. To draw the hyoid bone downward. 544 HUMAN ANATOMY. Variations. The sterno-hyoid may arise entirely from the clavicle or it may extend its origin to the cartilage of the first rib. It is often divided transversely by a tendinous band which may- occur either in its lower part on a line with the intermediate tendon of the omo-hyoid or, more rarely, in its upper part on a level with the insertion of the sterno-thyroid. 2. OMO-HYOIDEUS (Fig. 541). Attachments. The omo-hyoid is a long, flat muscle consisting of two bellies united by an intermediate tendon. The inferior belly arises from the lateral portion of the superior border and the superior transverse ligament of the scapula, and is directed forward, medially, and slightly upward to terminate in the intermediate tendon. This lies behind the clavicular portion of the sterno-cleido-mastoid, and is enclosed by the middle layer of the deep cervical fascia, a specially thickened portion of which binds it down to the posterior surface of the clavicle and to the first rib. The superior belly arises at the medial end of the intermediate tendon and passes upward and slightly medially to be inserted into the lower border of the hyoid bone, lateral to the sterno-hyoid. FIG. 541. Styloid proce Stylo-glossus- Stylo-pharyngeu Stylo-hyoid Digastric, posterior belly. Rectus capitis anticus major. Spleni Sterno-cleido-mastoid Levator anguli scapulae Scalenus anticus Omo-hyoid, posterior " Buccinator Orbicularis oris Depressor anguli Depressor labii inferioris Hyo-glossus Digastric, anterior belly Mylo-hyoid Hyoid bone Inferior pharyngeal constrictor Thyro-hyoid Sterno-hyoid Thyroid body Omo-hyoid, anterior belly Sterno- thyroid Muscles of the neck ; larynx has been drawn forward. NerverSupply. From the first, second, and third cervical nerves, through the ansa hypoglossi. Action. To draw downward the hyoid bone. Acting from above, it will assist slightly in drawing the scapula upward. This muscle may also act as a tensor of the cervical fascia, thereby preventing undue pressure on the great vessels of the neck. Relations. At its attachment to the scapula the inferior belly is coven-d l>y the trapezius and the muscle is crossed in the middle part of its course by the sterno-cleido-mastoid. The inferior belly is in relation posteriorly with the scalene muscles and the roots of the brachial plexus and sometimes with the third portion of the subclavian artery, the transx crsalis colli and transverse scapular arteries, and the -upruscapular nerve. The superior belly crosses the common carotid artery and the internal jugular vein at the level of the cricoid cartilage. THE CERVICAL MUSCLES. 545 Variations. The omo-hyoid and the sterno-hyoid are derived from a muscular sheet which, in the lo\ver vertebrates, invests the anterior portion of the neck region, lying beneath the platysma. This sheet is represented in man by the two muscles and the middle layer of the deep cervical fascia. The omo-hyoid or one or other of its bellies may be absent, or, on the other hand, an accessory omo-hyoid may be developed. The superior belly not infre- quently fuses more or less completely with the sterno-hyoid and the inferior belly has some- times a clavicular origin. Occasionally the band which binds the intermediate tendon to the clavicle remains muscular, and, uniting at the tendon with the superior belly, produces what lias been termed the cleido-hyoideus. 3. STERNO-THYROIDEUS (Fig. 541). Attachments. The sterno-thyroid is a band-like muscle which lies immedi- ately beneath the sterno-hyoid. It arises from the posterior surface of the manu- brium sterni and from the cartilages of the first and second ribs, and passes upward to be inserted into the oblique line of the thyroid cartilage. Nerve-Supply. From the first, second, and third cervical nerves, through the ansa hypoglossi. Action. To draw the larynx downward. Relations. Superficially the sterno-thyroid is covered by the sterno-hyoid. Deeply it is in relation with the inferior constrictor of the pharynx, the crico- thyroid muscle, the cricoid cartilage, the lobes of the thyroid gland, the inferior thyroid veins, the trachea, and the common carotid artery, and it crosses the left vena anonyma. Variations. The lower portion of the muscle is often crossed by a tendinous intersection, and frequently some of its fibres are continued directly into the thyro-hyoid muscle. The two muscles of opposite sides are frequently united in the median line, sometimes throughout the greater portion of their length, at other times merely by scattered bundles. 4. THYRO-HYOIDEUS (Fig. 541). Attachments. The thyro-hyoid lies beneath the upper portion of the omo- hyoid. It arises below from the oblique line of the thyroid cartilage and is inserted above into the lateral portion of the body and into the greater cornu of the hyoid bone. Nerve-Supply. From the first and second cervical nerves, by fibres which run with the hypoglossal nerve. Action. To draw down the hyoid bone, or, if that be fixed, to draw the larynx upward. Relations. As the muscle passes across the hyo-thyroid membrane it covers the superior laryngeal nerve and artery. A bursa, the b. musculi thyro-hyoidei, is interposed between the muscle and the upper part of the hyo-thyroid membrane. Variations. The thyro-hyoid is often practically continuous with the sterno-thyroid. A bundle of fibres is sometimes to be found passing either from the lower border of the hyoid or from the thyroid cartilage to the lobe, isthmus, or pyramid of the thyroid gland. It is termed the levator glandule thyroidece, under which name are also comprised fibres which are exten- sions of the inferior constrictor of the pharynx to the thyroid gland. 5. GENIO-HYOIDEUS (Fig. 497). Attachments. The genio-hyoid is the superior portion of the rectus group of muscles. It is a rather narrow band which arises from the lower genial tubercle of the mandible and extends backward and downward to be inserted into the anterior surface of the body of the hyoid bone. It is situated close to the median line, under cover of the mylo-hyoid and immediately beneath the lower border of the genio-glossus. Nerve-Supply. From the first and second cervical nerves, by fibres which accompany the hypoglossal. Action. If the hyoid bone be fixed, the genio-hyoid depresses the mandible ; if the mandible be fixed, it draws the hyoid bone forward and upward. 35 546 HUMAN ANATOMY. (6) THE OBLIQUUS MUSCLES. 1. Scalenus anticus. 3. Scalenus posticus. 2. Scalenus medius. 4. Rectus capitis lateralis. 5. Intertransversales anteriores. i. SCALENUS ANTICUS (Fig. 542). Attachments. The anterior scalene (m. scalenus anterior) arises by four tendinous slips from the anterior tubercles of the transverse processes of the third to the sixth cervical vertebrae. The four slips unite to form a rather flat muscle which extends downward and forward to be inserted into the scalene tubercle on the upper surface of the first rib. FIG. 542. Levator anguli scapulae. Subscapularis Serratus magnus, middle portion Sterno-mastoid, stump Rectus capitis anticus major Scalenus anticus Scalenus medius Scalenus posticus, Rhomboidei Sternum I rib Serratus magnus, upper portion Dissection of right side of neck, showing scalene and adjacent muscles. Nerve-Supply. By branches from the fourth, fifth and sixth cervical nerves. Action. To bend the neck forward and to the same side and to rotate it to the opposite side. If the cervical vertebrae be fixed, it will then raise the first rib, assisting in inspiration. Relations. The anterior scalenus lies in front of the roots of the brachial plexus, and near its insertion it passes over the second portion of the subclavian artery and under the subclavian vein. The phrenic nerve rests upon its anterior surfac during its course down the neck. 2. SCALENUS MEDIUS (Figs. 541, 542). Attachments. The middle scalene is situated behind the scalenus anterior. It arises by six or seven tendinous slips from the transverse processes of the lower six or of all the cervical vertebrae and extends downward and outward to be inserted THE CERVICAL MUSCLES. 547 into the upper surface of the first rib, behind the groove for the subclavian artery. Some fibres of the muscle may extend across the first intercostal space to be inserted into the outer surface of the second rib. Nerve-Supply. By branches from the anterior divisions of the cervical nerves. Action. To bend the neck laterally, or, if the cervical vertebrae be fixed, to raise the first rib, assisting in inspiration. Relations. As the middle scalene passes downward to its insertion it diverges from the scalenus anterior, so that a triangular interval exists between the two muscles through which the subclavian artery and the brachial plexus pass, these structures lying in front of the insertion of the scalenus medius. 3. SCALENUS POSTICUS (Fig. 542). Attachments. The posterior scalene (ra. scalenus posterior) lies immediately behind the scalenus medius and anterior to the ilio-costalis cervicis. It arises by two or three tendinous slips from the transverse processes of the lower two or three cervical vertebrae and passes downward and laterally to be inserted into the outer surface of the second rib. Nerve-Supply. From the anterior divisions of the lower three cervical nerves. Action. To bend the neck laterally, or, if the cervical vertebrae be fixed, to raise the second rib. Variations of the Scalene Muscles. There is not a little variation in the extent of the upper attachments of the scalene muscles, the origins being increased or, more usually, dimin- ished in number. A certain amount of fusion may also occur, especially between the medius and posterior, so that it is not always possible to distinguish these two muscles. Occasionally the subclavian artery perforates the lower portion of the anterior scalene, and the portion so separated may form a distinct muscle, the scalenus minimus, which lies in the interval between the anterior and middle scalenus, and is attached above to the transverse processes of the sixth or the sixth and seventh cervical vertebrae and below to the upper surface of the first rib and to the dome of the pleura. A muscle occasionally occurs between the upper part of the pectoralis major and the upper external intercostals, from both of which it is separated by a lamella of areolar tissue. It is termed the supracostalis, and takes its origin from the first rib and sometimes also from the fascia which covers the anterior scalene, and passes downward to be inserted into the outer surface of the third and fourth ribs, sometimes attaching also to, the second rib and sometimes descending as low as the fifth. It has been regarded as an aberrant portion of the pectoralis major or rectus abdominis, but it seems to be more probably a portion of the obliquus muscu- lature and is apparently related to the scaleni. 4. RECTUS CAPITIS LATERALIS. Attachments. The rectus capitis lateralis is a short, flat muscle which arises from the transverse process of the atlas and is inserted into the inferior surface of the jugular process of the occipital bone. Nerve-Supply. From the suboccipital nerve. Action. To bend the head laterally. 5. INTERTRANSVERSALES ANTERIORES. Attachments. The anterior intertransversales are a series of small muscles which pass between the anterior tubercles of the transverse processes of the cervical vertebrae. Nerve-Supply. From the anterior divisions of the cervical nerves. Action. To bend the head laterally. The Triangles of the Neck. The sterno-cleido-mastoid muscle, on account of its position somewhat superficial to the remaining muscles of the neck, serves to divide that region into two triangular areas which are of considerable importance from the stand-point of topographic anatomy. 54 HUMAN ANATOMY. - Ster ic, anterior belly Trape ROTID TRIANGLE anterior belly ROTID R) THIANQI F One of these triangles, the posterior, is bounded by the lateral border of the upper part of the trapezius behind and by the lateral border of the sterno- cleicio-mastoid in front, and has for its base the upper border of the clavicle between the insertion of these two muscles. The anterior triangle is reversed with respect to the posterior one, having its apex downward and its base above. Its lateral boundary is the medial border of the sterno-cleido-mastoid, its medial boundary is the median line of the neck, and its base is formed by the lower border of the mandible and a line FIG 543. extending horizontally backward from the an- gle of the mandible to the mastoid process. Each of these two triangles is again di- visible into subordinate triangles by the mus- cles which cross them. Thus the posterior tri- angle is divided by the inferior belly of the omo- hyoid, which crosses it obliquely, into an upper or occipital triangle and a lower or subclavian triangle, while the an- terior triangle is divisi ble into three triangles by the superior belly of the omo-hyoid and tin- posterior belly of the digastric. The lowest of these triangles, termed the muscular 'or inferior carotid triangle, has its base along the median line and its apex directed laterally, its sides being formed by the sterno-cleido- mastoid below and the superior belly of the omo-hyoid above. The superior carotid triangle has its base along the upper part of the sterno-cleido-mastoid and its apex directed medially ; its sides are formed by the superior belly of the omo-hyoid below and the posterior belly of the digastric above. Finally, the submaxillary or digastric triangle is the basal portion of the original anterior triangle, and is bounded below by the two bellies of the digastric muscle and above by the line of the lower border of the mandible and its continuation posteriorly to the sterno-mastoid muscle. (c) THE HYPOSKELETAL MUSCLES. i. Longus colli. 2. Rectus capitis anticus major. 3. Rectus capitis anticus minor. i. LONGUS COLLI (Fig. 544). Attachments. The longus colli forms an elongated triangular band whose base is towards the median line and the wide-angled apex directed laterally. It may be regarded as consisting of three portions. The medial portion consists of fibres which arise from the bodies of the upper three thoracic and lower two cervical vertebra, forming a muscular band which is inserted into the bodies of the three or four upper cervical vertebrae, the slip to the atlas being inserted into its anterior tubercle. From the lower part of the medial portion slips arc ^i\cn off which con- stitute the inferior oblique portion, and are inserted into the transverse processes of the fifth and sixth, and sometimes also of the fourth and seventh, cervical vertebr.e. SUBCLAVIAN TRIANGLE Omo-hyoid, posterior belly- Clavicle Triangles of neck. THE CERVICAL MUSCLES. 549 And, finally, the superior oblique portion is formed by slips arising from the trans- verse processes of the sixth to the third cervical vertebrae and joining the upper part of the medial portion. Nerve-Supply. From the anterior divisions of the second, third, and fourth cervical nerves. Action. To bend the neck ventrally and laterally. FIG. 544. Anterior tubercle of atlas Longus colli, superior oblique portion W I Rectus capltis anticus major 2 Longus colli, median portion ongus colli, inferior oblique portion Scalenus medius j * Jj Scalenus anticus I rib Clavicle_ L_VII cervical vertebra I thoracic vertebra Deep dissection of neck, showing prevertebral muscles. 2. RECTUS CAPITIS ANTICUS MAJOR (Fig. 544). Attachments. The rectus capitis anticus major (m. longus capitis) partly covers the upper part of the longus colli. It arises by four tendinous slips from the transverse processes of the third to the sixth cervical vertebrae, and passes directly upward to be inserted into the basilar portion of the occipital bone, lateral to the pharyngeal tubercle. Nerve-Supply. From the anterior divisions of the second, third, and fourth cervical nerves. Action. To flex the head and rotate it slightly towards the opposite side. 550 HUMAN ANATOMY. 3. RECTUS CAPITIS ANTICUS MINOR. Attachments. The rectus capitis anticus minor (m. rectus capitis anterior) is a short, flat muscle which arises from the anterior surface of the lateral mass of the atlas and is directed obliquely upward and medially to be inserted into the basilar portion of the occipital bone, immediately behind the insertion of the longus capitis. Nerve-Supply. By the first cervical (suboccipital) nerve. Action. To flex the head. PRACTICAL CONSIDERATIONS : THE NECK. The skin of the front and sides of the neck is thin and movable. The platysma myoides is closely connected to it by the thin superficial fascia. The edges of wounds transverse to the fibres of that muscle are therefore often inverted. In the region of the nape of the neck the skin is thicker and much more closely adherent to the deep fascia; it is poorly supplied with blood ; hair-follicles and sebaceous glands are numerous ; it is frequently exposed to minor traumatisms and to changes of surface heat, and is ' often at a lower temperature than the parts immediately above, which are covered with hair, or than those directly below, which are protected by clothing; the nerve-supply is abundant. For these reasons furun- cles and carbuncles are of common occurrence and are apt to be exceptionally painful. The subcutaneous ecchymosis which follows fracture through the posterior cerebral fossa first appears anterior to the tip of the mastoid and spreads upward and back- ward on a curved line ; the blood is prevented from reaching the surface more directly by the cervical fascia, and therefore goes laterally in the intermuscular spaces, being directed towards the mastoid tip by the posterior auricular artery. In the submaxillary region the looseness of the skin makes it available for plastic operations on the cheeks and mouth. In the submental region the accu- mulation of subcutaneous adipose tissue seen in stout persons gives rise to the so-called " double chin." In both the latter regions (covered by the beard in men) furuncles and sebaceous cysts are common. The surgical relations of the fascia of the neck can best be understood by refer- ence to a horizontal section at the level of the seventh cervical vertebra (Fig. 545). The superficial layer (a, a') will then be seen to envelop the entire neck. Pos- teriorly it is attached between the external occipital protuberance and the seventh cervical spinous process to the ligamentum nuchae ; anteriorly it is interlaced with the same layer of fascia from the other side of the neck ; superiorly between the external occipital protuberance and the middle of the chin it is attached on each side to the superior curved line of the occipital bone, the mastoid, the zygoma, and the lower jaw ; inferiorly between the seventh spine and the suprasternal notch it is attached on each side to the spine of the scapula, the acromion, the clavicle, and the upper edge of the sternum. After splitting to enclose the trapezius and covering in the posterior triangle, this fascia divides again at the hinder border of the sterno- cleido-mastoid. The superficial layer continues over the surface of that muscle, covers in the anterior triangle, and blends with its fellow of the opposite side. From its under surface, after reaching the sterno-mastoid, the deeper layer gives off from behind forward () a process prevertebral fascia which begins near the posterior border of the sterno-mastoid, passes in front of the scalenus anticus, the phrenic nerve, the sympathetic nerve, and the longus colli muscle, and behind the great vessels, the pneumogastric nerve, and the oesophagus to the front of the base of the skull and the bodies of the cervical vertebrae. In the mid-line this descends behind the gullet into the thorax. At the sides of the neck it helps to form the pos- terior wall of the carotid sheath, spreads out over the scalene muscles, and passes down in front of the subclavian vessels and the brachial plexus, until it dips beneath the clavicle, ft is then applied closely to the under surface of the costo-coracoid membrane and splits to become the sheath of the axillary vessels. A second process (f), leaving the sterno-mastoid more anteriorly, aids in forming the anterior wall of the carotid sheath, and joins the preceding layer just internal to the vessels. It is PRACTICAL CONSIDERATIONS : THE NECK. usually described as part of (af) a process tracheal which leaves the sterno-mastoid nearer its anterior border, and, running behind the sterno-hyoid and sterno-thyroid muscles, descends in front of the trachea and the thyroid gland to become connected with the fibrous layer of the pericardium. The adhesion of the deep fascia to the blood-vessels, by preventing contraction and collapse of their walls, favors hemorrhage and increases the risk of the entrance of air into divided veins. Tracing the layers of fascia vertically and from the surface inward, it will be useful to remember that the superficial layer (a, Fig. 546) passes to the top of the sternum (sending a slip to be attached to its posterior border) and to the clavicle. The second layer () descends behind the depressors and in front of the thyroid gland and trachea to merge into the pericardium, and farther out to form a sheath for the omo-hyoid and for the subclavian vein, and is lost in the sheath of the subclavius. FIG. 545. Fusion of superficial layer in mid-line Trachea Space 3 a Thyroid body CEsophagu Carotid artery Internal jugular vein Vertebral vessels Space i Extern, jugular vein Spinal nerves, cut obliquely- Spinal cord Trapezius muscle. Vertebral spin i\ M '. n Fascia covering posterior triangle Fascia passing beneath trapezius Ligamentum nuchoe Section across neck at level of seventh cervical vertebra. This relation of the omo-hyoid is of value in enabling that muscle, when the hyoid is fixed, to increase the tension of this layer of fascia, and thus hold open and prevent atmospheric pressure upon the walls of the vessels especially the veins and the soft parts (including the pulmonary apices) at the base of the neck. Hilton uses this function of the muscle which connects it with the act of respiration to illustrate the precision of the nerve-supply to muscles generally. The omo-hyoid arises in close proximity to the suprascapular notch, and therefore to the supra- scapular nerve. Yet it never receives a filament from that nerve, but is supplied by the hypoglossal to associate it with the movements of the tongue, the cervical plexus to bring it in relation to the movements of the other neck muscles, and the pneumogastric to enable it to act as above described during forced respiration, when the rush of air into the thorax might otherwise cause harmful increase of atmospheric pressure in the lower cervical or supraclavicular region. The pretracheal layer is found between the depressors and the trachea passing down to its pericardial insertion. Hilton thus explains this insertion : ' ' The peri- cardium is most intimately blended with the diaphragm, distinctly identified with it, and capable of being acted upon by it at all times. It is also attached above to the deep cervical fascia. It is thus kept tense by the action of the respiratory muscles in the neck attached to the cervical fascia above and the diaphragm attached to it 552 HUMAN ANATOMY. Hyoid bone below ; or, in other words, these two muscular forces are acting on the interposed pericardium in opposite directions, and so render it tense and resisting. And the special object, no doubt, of this piece of anatomy is that during a full inspiration, when the lungs are distended with air and the right side of the heart gorged with blood from a suspension of respiration, the heart should not be encroached upon by the surrounding lungs. ' ' The prevertebral layer (c, Fig. 546) lying between the oesophagus and spine passes in the mid-line directly into the posterior mediastinum; laterally beyond the scalenus anticus it aids in forming the sheath of the subclavian vessels and accom- panies them into the axilla. Another way of elucidating the practical effect of the somewhat complex dis- tribution of the cervical fascia is to regard the three chief layers superficial, middle, and deep as dividing the neck into four anatomical spaces (Tillaux). 1. Subcutaneous (Space i, Fig. 545) : between the skin and the superficial layer. The most important structure in this space is the external jugular vein, which perforates the fascia just above the middle of the clavicle. 2. Intra-aponeurotic (Space 2, Fig. 546) : between the superficial and mid- dle (sterno-clavicular) layers. This FIG. 546. space does not exist in fact at the summit of the neck where the two layers are one, but at the base its depth is equal to the thickness of the sternum. It may be continuous with the space left at the top of the sternum between the two leaflets of the superficial layer attached to the anterior and posterior borders of the sternum, Griiber's ' ' suprasternal intra-aponeurotic space," " Burns' s space." It contains fat and lym- phatic glands, the sternal head of the sterno-mastoid, and the anterior jugular veins. It is not infrequently the seat of abscess. 3. Visceral (Space 3 = $a -\- 3^, Fig. 545): between the pretracheal and prevertebral layers. This in- cludes all the principal structures of the neck. As it communicates di- rectly with the thorax and axilla, suppuration may travel in those di- rections. It is divided into minor spaces (30 and 3^) by a layer of fascia coming from the under surface of the sterno- mastoid muscle and by the bucco-pharyngeal fascia, a thin layer that comes off from the prevertebral fascia where it leaves the carotid sheath, and which lines the constrictors of the pharynx, leaving between it and the layer applied to the spinal column a small but easily distended space retropharyngeal in which infection from pharyngeal lesions occasionally occurs. 4. Retrovisceral (Space 4, Fig. 546): the space between the prevertebral fascia and spinal column, including the longus colli and rectus capitis anticus, the sympa- thetic nerve, etc. It is obvious in a general way that all infections beneath the middle layer of fascia are more likely to be serious than those superficial to it. Hut to summarize in a little more detail the practical relations of the cervical fascia, we may conclude that superficial to the outer layer (a, Fig. 545) there might occur from traumatism a wound of the external jugular, or from infection a spread ing cellulitis. The space is the seat of superficial phlegmons, which tend to spread under the skin only (Space i, Fig. 545), and, in the absence of tension, are unat- tended by throbbing pain or marked constitutional symptoms. Space 2 Burns's space Space 4 Left in nominate vein Aortic arch -44 Diagram showing relations of cervical fascia in longitudinal section. PRACTICAL CONSIDERATIONS : THE NECK. 553 The space between c and b (3^, Fig. 545) is occupied only by the great vessels and the pneumogastric. Infection there i.e., within the sheath may mean de- scending thrombosis from original infection of a cerebral sinus, or may have spread directly .through the sheath from infected tracts of cellular tissue outside. Behind b, Fig. 545 (retrovisceral space), suppuration is not uncommon as a result of verte- bral disease. Direct infection through the pharyngeal wall usually involves the retropharyngeal space. In either case dysphagia and dyspnoea are usual for obvious reasons. Between b and c, Fig. 546 (pretracheal and prevertebral layers), abscess would spread most readily along the line of the trachea and in front of the vessels into the superior mediastinum. In the intra-aponeurotic space (Space 2, Fig. 546) an abscess would probably point superficially, as the fascia in front of it is very thin. If it were influenced by gravity, however, it would follow the hyoid depressors and their intermuscular spaces to the root of the neck, and might enter the superior mediastinum. Two additional and important spaces are formed by extensions or reduplications of the cervical fascia. That portion of the superficial layer above the level of the angle of the inferior maxilla, and passing from that bone to the zygoma, constitutes the parotid fascia, which on the surface is continuous with that over the masseter, while beneath it becomes thickened to constitute the stylo-maxillary ligament, sep- arating the parotid and submaxillary glands and resisting overaction of the external pterygoid muscle. As the outer fascial investment of the gland is dense and resistant, and as internal to this FIG. 547. ligament the inner layer is thinner and weaker than elsewhere, a positive gap existing between the styloid process and the pterygoid muscle, suppuration within the gland may result in extension to the retropharyngeal / ' '^L \ M y io-hyoid muscle region. It may follow the external carotid downward to the chest, or, as the fascial investment is also incomplete above, may extend upward to the base of the skull, or even into the skull. It sometimes follows the branches ~f~/^^^~- H v id b <>"e of the third division of the fifth nerve through the fora- / / Outer layer of fascia men Ovale into the Cranium. / Inner layer of fascia The second space alluded to is formed by that por- Submaxillary gland tion of the superficial layer between the jaw and the Portion of frontal section across 1 . J J mandible, showing relations of cer- hyoid bone and in front of the stylo-mandibular ligament, vicai fascia. As it passes forward from the latter structure it splits and envelops the submaxillary gland, and becomes firmly attached below to the hyoid and above to the lower jaw externally and the under surface of the mylo-hyoid muscle internally (Fig. 547). Infection " Ludwig's angina," "submaxillary phlegmon," "deep cervical phlegmon" in this space, which contains the salivary gland and its attendant lymphatics, is rendered exceptionally grave by the density of these fascial layers. The infecting organisms usually streptococci may gain access through a lesion of the floor of the mouth near the frenum, or from an alveo- lar abscess, or by way of the digastric muscle from a focus of disease in the middle ear. Once established, they, with their secondary products, are forced along the lines of least resistance by the side of the mylo-hyoid usually towards the base of the tongue, involving the cellular tissue about the glottis and along the vessels that perforate the fascia, causing infective venous thrombosis and involving the deeper planes of connective tissue. Under the latter circumstances, if tension is not promptly relieved, large vessels may be opened by the necrotic process. Jacobson long ago called attention to the interesting fact that communications between ab- scesses and deep vessels have usually taken place beneath the cervical fascia and the fascia lata, two of the strongest fasciae of the body. Tumors of the neck may originate in any of the diverse structures of that region. It may be mentioned here that their situation above or beneath the cervical fascia is an important 'factor in determining their mobility, and hence the probable ease or difficulty of their removal. In the latter situation associated pressure- symptoms are common. 554 HUMAN ANATOMY. Lipoma is frequent ; fibroma and enchondroma are occasionally seen in the region of the ligamentum nuchae ; primary carcinoma is rare. Congenital cysts " hydroceles" of the neck are found beneath the deep fascia, usually in the anterior triangle and below the level of the hyoid. They may arise from dilatation of the lymphatic vessels, or, as Sutton suggests, they may originate, as do the cervical air-sacs in some monkeys, especially the chimpanzees, by the formation of diverticula from the laryngeal mucous membrane. In any event, they ramify in the various intermuscular spaces, and their complete removal is therefore very difficult. Branchial cysts and dermoids are not infrequent. They should be studied in connection with the embryology of the region. Congenital tumor of the sterno-mastoid is a condition resulting from either rup- ture of muscular fibres or bruising of the muscle against the under surface of the symphysis during delivery. It may be a cause of torticollis. Torticollis "wry-neck" maybe due to spasm of the sterno-mastoid either alone or associated with a similar condition of the trapezius, especially the clavicular portion, and often of the scaleni or the complexus. Later there is apt to be second- ary contraction of the deep fascia and of the posterior cervical muscles. Tenotomy of the muscle for the relief of this affection is performed at a level just above its sternal and clavicular insertion. The subcutaneous method has been largely dis- carded in favor of division through an open wound. By the former plan, not only were the anterior, and sometimes also the external, jugular veins endangered, but the cervical space described as "visceral" was occasionally opened, and, if infection occurred, with fatal results from septic cellulitis or pleurisy. Section of the spinal accessory nerve may be resorted to when the spasm is limited to the sterno-mastoid and trapezius, or of the posterior primary divisions of the first, second, and third cervical nerves when the posterior muscles are involved. Landmarks. Athough but few organs belong exclusively to the neck, a great many structures of mueh diversity, and connecting the trunk and head, pass through it. The "landmarks" will therefore be found in relation to different systems, vas- cular, nervous, etc., those given here referring chiefly to the muscles and their effect upon surface form. The mid-line posteriorly has already been described in its relation to the spines of the cervical vertebrae (pages 146148). On the sides of the neck the platysma, when in action, produces inconspicuous wrinkling of the skin. Its fibres are in a line from the chin to the shoulder. The sterno-mastoid, running obliquely from the skull to the sternum and clavicle, divides each lateral half of the neck into two triangles. The anterior of these is boundi-d above by the lower border of the inferior maxilla and a line extending from the angle of that bone to the mastoid process ; anteriorly by a straight line between the middle of the chin and the sternum ; posteriorly by the anterior border of the sterno-mas- toid. Its apex is at the middle of the upper edge of the manubrium. The posterior triangle is bounded posteriorly by the anterior edge of the trapezius, the hinder edge of the sterno-mastoid in front, and the middle of the clavicle below. Its apex is just behind the mastoid process. It will be seen that by this the usual description those structures lying imme- diately beneath the sterno-mastoid would be excluded from both triangles. It is cus- tomary, however, to include the common carotid and internal jugular vein in the anterior triangle, although they are both under cover of the anterior edge of the sterno-mastoid. The anterior triangle is divided into three the superior carotid, the inferior carotid, and the submaxillary by the digastric muscle and the anterior belly of the omo-hyoid. The posterior belly of the omo-hyoid divides the posterior triangle into a lower or subclavian and an upper or occipital triangle. The structures included within these various triangles will be described in connection with the vessels, nerves, etc. The dividing line between the two main triangles the sterno-mastoid can be both seen and felt if, with the mouth closed, the chin is depressed and the skull is rotated towards the opposite shoulder. The thick, prominent, rounded anterior bor- PRACTICAL CONSIDERATIONS : THE NECK. 555 der can then be made out from mastoid to sternum, but is more accentuated below, where the sternal head is salient and sharply denned. This thin posterior border may- be felt vaguely at the upper part, but cannot be seen. * At about the lower third it becomes visible and is continued into the broader and flatter clavicular head. The middle of the muscle is seen throughout most of its length as a fleshy, rounded elevation. Over it, and usually plainly visible, is the external jugular vein, running between the platysma and the deep fascia in a line from the angle of the jaw to the centre of the clavicle. In rest the anterior border is still visible. The position of the muscle on the side towards which the head is turned is indicated by a slight furrow in the skin. The muscles partly overlapped by the sterno-mastoid are, from above downward, the splenius, levator scapulae, digastric, omo-hyoid, sterno-thyroid,. and sterno-hyoid. FIG. 548. External jugular vein Submaxillary gland Digastric, anterior belly Hyoid bone Trapezius Acromio-clavicular joint Acromion process Lesser supraclavicular fossa Suprasternal notch (jugular fossa) Coracoid process Omo-hyoid, posterior belly Supraclavicular fossa Infraclavicular fossa Surface markings of neck, from living subject. The interval between the sternal and clavicular heads of the muscle is indicated by a slight depression, the lesser supraclavicular fossa, and is bounded below by the upper edge of the inner third of the clavicle. Beneath it, about on a line with the sternal end of the clavicle, lie on the right side the bifurcation of the innominate artery and on the left the common carotid artery. Between the outer edge of the clavicular head of the sternp-mastoid and the base of the anterior edge of the trapezius is a broad, flat depression, the supracla- vicular fossa, which is made very evident by shrugging the shoulders, and across which the posterior belly of the omo-hyoid runs and can often be seen and felt in thin persons, especially during inspiration or when the head is turned towards the opposite side (Fig. 548). The line of the muscle is from the suprascapular notch, slightly ascending to the anterior margin of the sterno-mastoid at a level with the cricoid cartilage and then rapidly ascending to the body of the hyoid. Below is. 55 6 HUMAN ANATOMY. posterior belly run the brachial plexus, which can often be felt and sometimes seen, and, near the clavicle, the subclavian artery. Farther out the anterior border of the trapezius may be seen passing from the occiput to its insertion at the outer end of the middle third of the clavicle. The triangular interval between it and the posterior border of the sterno-mastoid is filled from below upward by the scalenus medius, the levator anguli scapulae, and the splenius, but none of them is recognizable through the deep fascia. In the mid-line behind, in addition to the bony points already given (pages 146148), the line of origin of the trapezii can be seen as a slight elongated de- pression. None of the deeper muscles can be seen or felt upon the surface. In the mid-line in front the hyoid bone and its cornua can be felt in the angle between the under surface of the chin and the front of the neck. From the hyoid bone on either side the anterior bellies of the digastric run up towards the symphysis and with the subcutaneous fat give convexity to the submental region. Farther out on this level the submaxillary salivary glands can be felt and often seen. The thyro-hyoid depression, the prominence of the thyroid cartilage (pomum Adami}, the crico-thyroid space, the cricoid cartilage, and sometimes the upper rings of the trachea may be felt from above downward. The relations of these parts to important vascular and nervous structures will be considered later. The sterno-thyroid and sterno-hyoid muscles, while not visible, cover over and obscure the outlines of the trachea, as does also the thyroid isthmus. The thyroid lobes may be felt on each side of the larynx. The average distance from the cricoid to the upper edge of the manubrium is about one and a half inches when the head is erect. In full extension three-quarters of an inch additional can be gained. The trachea recedes as it approaches the sternum, so that it is fully an inch and a half behind the upper border of the latter. In this position between the two sternal heads of the sterno-mastoid is the deep, V-shaped suprasternal notch (fossa jugularis), the depth of which is noticeably affected by forced respiration, being much increased in obstructive dyspnoea. All the surface appearances above described differ in different individuals, and vary in the same person in accord with many conditions, as the amount of subcu- taneous fat, the muscular vigor and development, the pulmonary capacity, the state of repose or of violent exertion, etc. This should be remembered in looking for landmarks in this region, which is in that respect one of the most variable of the body, and most unlike that of the cranium, which perhaps typifies the other extreme of unchangeability. DlAPHRAGMA (Fig. 549). The diaphragm is a dome-shaped muscular sheet which separates the thoracic and abdominal cavities. Notwithstanding its position in the adult, it is a derivative of the cervical myotomes. It represents the upper portion of a structure which is termed in embryology the septum transversum (page 1701), a connective-tissue partition which extends between the ventral and lateral walls of the body and the heart, and serves to convey venous trunks to that organ. Like the heart, when first formed it lies far forward in the uppermost part of the cervical region, but I.IUT it descends with the heart until it reaches its final position. As it passes the third and fourth cervical myotomes in its descent, it receives from them some muscle-tissu< which eventually forms all the muscle-tissue of the diaphragm, that structure, so fai as it is to be regarded as a muscle, being a derivative of the cervical myotom< named. The diaphragm is a muscular sheet composed of fibres radiating from the l border of the thorax and from the upper lumbar vertebrae towards a central trndi- nous area, termed the centrum tendineum. According to their origin, the muscle- fibres may be grouped into three portions. The sternal portion consists of, usually, two bands which arise from the posterior surface of the xiphoid process of the sternum and are separated from one another by a narrow interval filled with con- nective tissue. Laterally they are separated by a similar interval, through which the superior epigastric artery enters the sheath of the rectus abdominis, from the THE CERVICAL MUSCLES. 557 costal portion, the fibres of which take their origin from the cartilages of the lower six ribs, interdigitating with the origins of the transversalis abdominis. In conti- nuity with the costal part is the lumbar part, whose fibres take origin (i) from two tendinous arches, the internal and external arcuate ligaments, which pass over the upper portions of the psoas (arcus lurabocostalis medialis) and the quadratus lum- borum muscles (arcus lumbocostalis lateralisj respectively, stretching between the twelfth rib and the transverse process of the first lumbar vertebra, and (2) by two downward prolongations, the crura, from the anterior and lateral surfaces of the upper three or four lumbar vertebra 1 . The right crus usually extends somewhat farther downward than the left, whose attachment does not pass below the second or third vertebra. Each crus has been divided into three portions, medial, intermediate, and lateral, which are not, how- ever, always clearly recognizable, although indicated by the passage of certain struc- tures from the thorax to the abdomen. Thus, between the medial and intermediate FIG. 5/19. Interval between sternal and costal portions Lower end of sternum Inferior vena cava / tight portion of ..(. Right p central tendon Right crus Right greater splanchnic nerve_ XII rib Middle portion of central tendon (Esophagus _ Left portion of central tendon Aorta Thoracic duct Inferior vena cava Bifurcation of aorta, turned forward Left crus XII rib External arcuate ligament Quadratus lumborum Internal arcuate ligament Psoas magnus Diaphragm, viewed from below and the left. crura the greater splanchnic nerve and the azygos (or hemiazygos) veins pass, while between the intermediate and lateral crura is the sympathetic trunk. The two crura, as they pass upward, leave between them an opening, the hiat^ls aorticus, which is bridged over by a tendinous band (median arcuate ligament} and gives passage to the aorta and thoracic duct. Just behind the posterior margin of the centrum tendineum the crural fibres diverge to surround in a sphincter-like manner the hiatus a'sophageus, through which pass the oesophagus and the vagus nerves and oesophageal branches from the gastric artery and veins. The centrum tendineum, into which the fibres of the three portions insert, is situated somewhat nearer the anterior than the posterior margin of the diaphragm, so that the fibres of the sternal muscular portion are considerably shorter than the others. It has a trefoil shape, possessing a central and two lateral lobes, the right one of these being perforated by a somewhat quadrate foramen, the foramen vena: cavce (foramen quadratum), which transmits the vena cava inferior. The centrum tendineum forms the centre of the dome of the diaphragm, and from its borders the muscular fibres slope downward towards their insertion, the slope of the crural fibres being much steeper than those of the other portions. 558 HUMAN ANATOMY. The dome does not, however, form a simple curve, but is divided by a median depression, which traverses it from before backward, into two secondary lateral domes which are unequally developed, that of the right side extending upward as far as the level of the junction of the fourth costal cartilage and rib, while that of the left reaches only to the fifth costo-cartilaginous junction. Nerve-Supply. From the third, fourth, and sometimes the fifth cervical nerves, by the phrenic nerves. Action. To increase the vertical diameter of the thorax, a contraction of the muscle-fibres depressing the summit of the dome. Relations. The upper surface of the diaphragm forms the floor of the thoracic cavity and is in contact with the pleurae and pericardium, the latter being adherent to the centrum tendineum. Below, the diaphragm is largely invested by peritoneum, and is in relation with the liver, stomach, spleen, kidneys, suprarenal bodies, duodenum, pancreas, inferior vena cava, and the branches of the coeliac artery. Variations. Occasionally the diaphragm is incomplete in its posterior portion, a condition which permits the formation of congenital diaphragmatic hernias. Embryologically the pos- terior portion of the diaphragm is the last to form, and in this fact is probably to be found an explanation of the location of this imperfection and also of the course of the phrenic nerves anterior to the roots of the lungs to reach -the earlier formed anterior portion of the diaphragm. Fibres which arise from the crura and pass to neighboring structures are frequently present. Among the more constant of these are fibres which arise from the inner borders of both crura and pass to the lower portion of the oesophagus, mingled with dense connective-tissue fibres, and others which pass from one crus or the other into the mesentery of the upper part of the jejunum. Probably the suspensory muscle of the duodenum, or muscle of Treitz, which passes from the left crus to the terminal portion of the duodenum, belongs to this latter group of fibres, although it has been stated to be formed by non-striated muscle-fibres. THE PELVIC AND PERINEAL MUSCLES. The ventral portions of the myotomes succeeding the first lumbar and from that as far down as the third (or second) sacral are almost entirely unrepresented in the trunk, being devoted to the formation of the musculature of the lower limb. Below FIG. 550. Iliac crest Iliacu Ilio-pectineal line Acetabulum Levator ani Obturator interim Alcock's ca Iliac fascia ternal iliac vessels vie fascia lite line vie fascia Obturator fascia Anal fascia Ischio-rectal fossa Seminal vesirk External sphincter Internal sphincter Rectum Diagrammatic frontal section through pelvis, showing relations of fasdal layers to pelvic wall an \ Fascia endopeh 1'i-K ir fascia Recto-vesical layer the point mentioned, however, the ventral musculature again appears in the trunk in the pelvic, the perineal, and occasionally the coccygeal region. Owing to the conditions under which it appears, it is not possible to refer the muscles derived from it to the various subdivisions into which the ventral musculature of other regions is divisible, and they will therefore be considered in sequence without any attempt at classification other than regional. The Pelvic Fascia. The pelvic fascia is attached above to the promontory of the sacrum and the ilio-pectineal line (linea terminalis) of the pelvis, where it THE PELVIC AND PERINEAL MUSCLES. 559 becomes continuous with the iliac fascia. It descends over the surface of the pyri- formis and laterally over the upper portion of the obturator internus and the pelvic surface of the pelvic diaphragm. In the upper part of its course over the pelvic dia- phragm it is crossed by a curved thickening, the arcus tendinous, which is attached behind to the spine of the ischium and passes in front upon the sides of the prostate gland or, in the female, upon the bladder, and is continued thence to the anterior pelvic wall to be attached on either side of the symphysis pubis, a little above its lower border, as a lateral pubo-prostatic {pubo-vesical} ligament. Along this tendi- nous arch the pelvic fascia gives off a layer which passes inward to the pelvic viscera, and is termed the fascia endopelvina. In its anterior portion this forms an investment of the prostate in the male and of the base of the bladder in the female, and its under surface in this region is in contact with, and indeed may be regarded as being fused with, the superior layer of the triangular ligament (page 563). That portion of the layer which intervenes between the prostate (or bladder) and the posterior surface of the body of the pubis forms'what is termed the median pubo-prostatic (pubo-vesical} ligament. The continuation of the pelvic fascia passes downward over the surface of the pelvic diaphragm, and is termed the superior fascia of that structure (fascia dia- phragmatis pelvis superior). The Obturator Fascia. From the line along which the pelvic fascia leaves the surface of the obturator internus muscle to pass upon the pelvic diaphragm a sheet of fascia is continued downward over the surface of the obturator internus muscle to be attached below to the tuberosity and ramus of the ischium and the ramus inferior of the pubis. This is the obturator fascia. Along its upper border, nearly corresponding with the arcus tendineus of the pelvic fascia, but lying above this thickening and ending anteriorly farther from the median line, is a similar curved thickening extending from the spine of the ischium, or in some cases from the ilio-pectineal line behind to the posterior surface of the body of the os pubis in front. From this thickening the greater portion of the levator ani muscle arises ; it is consequently termed the arcus tendineus m. levatoris ani, or more briefly the white line. From the line a thin layer of fascia is continued inward upon the under surface of the levator ani, forming what is termed the anal fascia (fascia diaphragmatis pelvis inferior). This latter fascia forms the inner and the obturator fascia the outer wall of the ischio-rectal fossa. Near its lower border the obturator fascia splits into two layers to form a canal, the canal of Alcock, along which the pudic vessels and nerve pass towards the perineum. In the above description the term pelvic fascia is applied to the layer of fascia which lines the entire true pelvic cavity, that is to say, the funnel-shaped cavity included between the pel- vic brim and floor. This conception, employed by the German authors, differs somewhat from that usually held by English anatomists, in that the latter restrict the term to that portion of the fascia extending from the ilio-pectineal line to the white line, the continuation down- ward over the pelvic diaphragm being termed the recto-vesical fascia, from which extensions pass to the bladder, prostate gland, and rectum. The term recto-vesical has also been restricted to the portion of the sheet which extends between the rectum and the bladder and encloses the seminal vesicles (Cunningham), and if the term is to be employed at all, this application of it seems to be the preferable one. Confusion has also existed in the application of the term "white line," since it has been made to include both the arcus tendineus proper and the thickened band from which the leva- tor ani takes its origin (arcus tendineus m. levatoris ani}. These two bands are, however, quite distinct, especially anteriorly, as a careful inspection of the subject will demonstrate, and it seems preferable to restrict the term "white line" to that from which the levator ani arises, naming that at which the fascia endopelvina begins the arcus tendineus. (a) THE PELVIC MUSCLES. i. Levator ani. 2. Coccygeus. 3. Pyriformis. The floor of the pelvis is formed by two muscles which constitute an almost complete partition, the pelvic diaphragm, separating the pelvic from the perineal region. The more anterior and larger of these muscles is the levator ani, the coccy- 560 HTM AN ANATOMY. geus lying along its posterior margin. Above the upper margin of the latter, and forming the posterior wall of the pelvis, is the pyriformis. Slight intervals occupied by connective tissue usually exist between the coccygeus and the other two muscles, presenting opportunities for pelvic hernias. i. LEVATOR AM (Fig. 551). Attachments. The levator ani arises from the posterior surface of the body of the os pubis in front, from the spine of the ischium behind, and in the interval between these two points from a thickening of the upper border of the obturator fascia, the white line. From this long line of origin the fibres converge downward and medially to be inserted into the sides and tip of the coccyx, into a tendinous raphe extending in the median line between the tip of the coccyx and the anus, and into the sides of the lower part of the rectum. The fibres from the most anterior portion of the origin pass almost directly backward and downward to reach the sides of the rectum, and between them and the corresponding fibres of the muscle of the opposite side is a FIG. 551- Pyriformis Coccygeus Ischial spine Levator ani Tip of coccyx - Ischial spine ' Rectum (cut) ,- .Obturator inter- ims i-overeit by pelvic fascia -Urethra (cut) Muscular floor of pelvis, viewed from above. space, occupied in the male by the lower part of the prostate gland and in the by the base of the bladder and lower part of the vagina, the fascia enclopelvina in this region coming into contact with the upper surface of the superior layer of the triangular ligament of the perineum. Nerve-Supply. The posterior portion of the muscle is supplied by a special branch from the third and fourth sacral nerves, the anterior portion by twigs from the inferior hemorrhoulal branches of the pudic nerve. Action. To bend the coccyx forward and to raise the pelvic floor and viscera. Variations. The levator ani is always a well-developed muscle, although the extent of its attachment to the sides of the coccyx varies inversely to the attachment of the coccygeus to that bone. There is usually to be found a dividing line extending across the muscle on a level with the junction of the superior ramus of the pubis with the ilium and separating those fibres which are inserted into the coccyx and the posterior portion of the fibrous raphe from those which pass to the anterior part of the raphe and the rectum. Kach of the portions so separated is sup- plied by a separate nerve, and this, combined with the results of comparative anatomy, seems to show that the posterior portion of the levator is really a muscle quite distinct from tin- ante- rior portion. It has been termed the ;//. i/io-cofty^i-iis. Furthermore, it seems probable that THE PELVIC AND PERINEAL MUSCLES. the anterior portion is composed of two morphologically distinct muscles, one of which arises from the pubis and anterior part of the white line and is inserted into the median fibrous raphe, whence it is termed the ;. pubo-coccygeus ; while the other, situated beneath, i.e f , superficial to the pubo-coccygeus, consists of those fibres which arise from the pubis and are inserted into the rectum, and is termed the m. pubo-rectalis, It may be added that in the lower mammals the muscles corresponding to the ilio-coc- cygeus and pubo-coccygeus are inserted into the caudal vertebrae and act as lateral flexors of the tail. 2. COCCYGEUS (FigS. 551, 603). Attachments. The coccygeus, which forms the posterior and lesser portion of the diaphragma pelvis, lies immediately behind the levator ani. It arises from the spine of the ischium and is inserted into the sides of the sacrum and coccyx. Nerve-Supply. From the third and fourth sacral nerves. Action. To assist the levator ani in raising the pelvic floor. It also flexes the coccyx laterally. Variations. Occasionally the insertion of the coccygeus is confined to the sides of the sacrum, in which cases its coccygeal area is occupied by fibres of the levator ani. The muscle is sometimes termed the ischio-coccygeus, and is represented in the lower mammals by a muscle attached to the caudal vertebrae and acting as a lateral flexor of the tail. The Sac ro- Coccygeus Anterior. Occasionally muscular fibres are to be found arising from the ventral surface of the sacrum and inserting into the coccyx. They form what is termed the sacro-coccygeus anterior or curvator coccygis, and apparently belong to the hyposkeletal group of muscles. 3. PYRIFORMIS (Figs. 551, 552, 602.) Attachments. The pyriformis (m. piriformis) arises from the ventral surface of the sacrum, between the first, second, third, and fourth sacral foramina. It passes laterally through the great sciatic fora- FIG. 552. men, receiving a bundle of fibres from the upper margin of the foramen, and is inserted into the summit of the great trochanter, its tendon shortly before its inser- tion becoming closely united with that of the obturator internus. Nerve - Supply. By branches from the sacral plexus from the first and second sacral nerves. Action. To ro- tate the thigh outward and to draw it slightly outward and back- ward. Obturator internus Greater sacrosciatic ligament its Relations. By anterior surface, Greater sacro- sciatic foramen Dorsum of ilium Greater sacro- sciatic foramen Pyriformis Obturator internus Capsule of hip-joint Deep dissection, showing insertion of pyriform, internal and external obturator muscles. while within the pelvis, the pyriformis is in relation to the sacral plexus, the anterior branches of the internal iliac vessels, and the rectum. It lies immediately above the upper border of the coccygeus muscle. Outside the pelvis it is usually separated from the capsule of the hip-joint by the gluteus minimus and is covered by the gluteus medius. Above the upper border of the muscle at its exit from the greater sciatic foramen are the gluteal vessels and the superior gluteal nerve, while below its lower border, between this and the superior gemellus, are the sciatic and internal pudic vessels and the pudic, sciatic, small sciatic, and inferior gluteal nerves. A bursa, the bursa m. pyriformis, inter- venes between the tendon of the muscle and the summit of the great trochanter. 36 562 HUMAN ANATOMY. Variations. The pyriformis is occasionally absent, and it may be more or less fused with the gluteus minimus or medius. Frequently it is divided into two or more portions by being perforated by the sciatic nerve. From the comparative stand-point the pyriformis is to be regarded, in part at all events, as a portion of the musculature extending between the axial skeleton and the pelvic girdle or limb, and is represented in the lower vertebrates by the caudo-femoralis. (6) THE PERINEAL MUSCLES. 1. Sphincter ani externus. 2. Transversus perinaei superficialis. 3. Ischio-cavernosus. 4. Bulbo-cavernosus. 5. Transversus perinaei profundus. 6. Compressor urethrae. In the early stages of development, while the urogenital ducts and the digest- ive tract open into a common terminal cavity, the cloaca, muscle-fibres derived from the second, third, and fourth sacral myotomes arrange themselves in a flat layer around the external aperture of the cavity, forming what is termed the sphincter cloacce. Later, with the division of the cloaca into a urogenital and a rectal portion and the resulting formation of the perineum, this primary sphincter becomes divided into two portions, one of which forms a sphincter ani, while the more anterior portion gives rise to the muscles of the perineum. The fibres of this latter portion undergo various modifications in accordance with the changes which FIG. 553- Urachus. Supravesical space Symphysis pubis Suspensory ligament of penis Triangular ligament, sup. layer Deep perineal interspac Triangular ligam't, inf. layer Urethra Penis, corpus cavernosum Scrotum Rectum Prostate Cowper's gland IViiiK-al centre Colles's fascia Superficial perineal interspace Continuation of Colles's fascia Diagrammatic sagittal section, showing relations of fascia! layers of perineum. take place in the urogenital sinus, and a horizontal separation of the original sphincter into two layers also occurs, whereby the perineal muscles are arranged in two layers separated by the superior fascia of the urogenital trigone. The muscles formed during these changes retain the original sheet-like form of the sphincter cloacae and are for the most part pale in color, resembling not a little in their general character the platysma muscles of the face. They show a considerable amount of difference in their development in different individuals, numerous acces- sory muscles having been described by various authors, some of which will be referred to in the succeeding descriptions. The Superficial Perineal Fascia. The superficial perineal fascia, being continuous anteriorly with the superficial fascia of the lower portion of the anterior abdominal wall, is, like this, composed of two layers. The more superficial layer usually contains a certain amount of fat, and, as in the abdomen, is really the pan- niculus adiposus of the skin. The deeper layer, which has been termed the fascia of Colics, forms a continuous membrane which is attached at the sides to the rami of the pubes and ischia and in front becomes continuous with the dartos of the THE PELVIC AND PERINEAL MUSCLES. 563 scrotum (or fascia of the labia majora) and on either side of this with the corre- sponding layer of the abdomen. Behind it unites with the posterior border of the trigonum urogenitale on a line extending between the two ischial tuberosities, and thence is continued backward, forming a single sheet with the superficial layer, to unite with the superficial fascia of the gluteal region. This posterior portion of the superficial perineal fascia may conveniently be termed the circumanal fascia. By the union of the deep layer of the superficial fascia with the triangular liga- ment behind, an almost completely enclosed space is formed between the two struc- tures ; it is open only anteriorly where it communicates with the areolar spaces between the superficial and deep layers of the abdominal fasciae. This space is the superficial perineal interspace, and contains the bulb and spongy portion of the urethra, the corpora cavernosa, and certain of the perineal muscles. The Trigonum Urogenitale, The trigonum urogenitale, more usually called the triangular ligament of the perineum, is formed by the deep fascia of the peri- neum, and, like the superficial fascia, is composed of two layers, the superior and inferior (fasciae trigoni urogenitalis superior et inferior). At the sides both layers are attached to the rami of the pubes and ischia, in front to either edge of the lower border of the pubis, and behind they unite with each other and with the deep layer of the superficial fascia along a line extending transversely across the perineum between the tuberosities of the ischia. Between the two layers there is a completely closed space, the deep perineal interspace, in which are to be found the membranous portion of the urethra, the bulbo-urethral glands, the pudic vessels and nerves, and, in front, the subpubic or arcuate ligament of the pubis. At their lateral insertions the layers of the trigone are continuous with the obturator fascia, and the superior layer is fused above with the portion of the fascia endopelvina which invests the lower surface of the prostate gland (or the base of the bladder). The trigone is perforated by the urethra and, in the female, by the vagina, and anteriorly the dorsal vein of the penis passes through it immediately behind the subpubic ligament of the pubis, the fibres of the trigone immediately behind the opening for the vein being thickened to form a transverse band known as the trans- verse ligament of the pelvis. i. SPHINCTER ANI EXTERNUS (Fig. 554). Attachments. The external sphincter of the anus consists of a group of fibres which surround the terminal portion of the rectum, the superficial fibres standing in close relationship with the integument. Its fibres arise posteriorly from the coccyx and from the raphe extending from that bone to the anus, and, passing forward around the anus, are inserted into the superficial fascia and the central tendon of the perineum, and may in some cases be continued forward to join with the fibres of the superficial transverse perineal and bulbo-cavernosus muscles. The central tendon of the perineum is situated in the median line about 2. 5 cm. in front of the anus, and is the point of union of five muscles, namely, the external sphincter ani, the two superficial transversi perinei, and the bulbo-cavernosi. Nerve-Supply. From the fourth sacral nerve and the inferior hemorrhoidal branches of the pudic. Action. To close the anal aperture. It also serves to fix the central tendon of the perineum during the contraction of the bulbo-cavernosi. Variations. The common embryological origin of the external sphincter ani and the perineal muscles is indicated by the extension forward of the fibres of the former to join the bulbo-caver- nosus, and occasionally a fasciculus of it extends as far forward as the base of the scrotum, forming what has been termed the retractor scroti. The longitudinal muscle-fibres of the lower portion of the rectum pass below into a sheet of connective tissue, which divides into three more or less distinct layers extending to the integument. The outer two of these layers traverse the substance of the external sphincter ani, a portion of the outermost one being continued backward to the region of the coccyx on each side of the median line as a moderately strong band known as the ano-coccygeal ligament. By these layers of fibrous tissue the external sphincter is divided, sometimes quite distinctly, into three portions which have been regarded as distinct muscles. One of these lies imme- diately beneath the skin surrounding the anus, and has consequently been termed the sphincter 564 HUMAN ANATOMY. subcutaneus. The sphincter superficialis is that portion of the muscle which lies above and to the outer side of the sphincter subcutaneus, while more deeply still, and forming a ring-like mass of fibres closely encircling the rectal wall, is the sphincter profundus. It is from the sphincter subcutaneus that the retractor scroti, when present, is derived, and fibres from the sphincter superficialis are frequently prolonged in front of the anus to various insertions, as, for instance, to the tuber ischii, the lower layer of the trigomim urogenitale, or even the sheath of the corpora cavernosa. This layering of the external sphincter is probably a relic of the separa- tion of the sphincter cloacae into two layers, the subcutaneous and superficial sphincters repre- senting a portion of the superficial layer, while the deeper one is responsible for the sphincter profundus. 2. TRANSVERSUS PERIN^EI SUPERFICIALIS (Fig. 554). Attachments. The superficial transverse perineal muscle is an exceedingly variable sheet of muscle-fibres situated in the posterior portion of the superficial perineal interspace. In its typical form it may be described as a band of fibres which FIG. 554. Bulbo-cavernosus Ischio-cavernosus Trans, perinwi. superficialis Obturator, interims White line- Levator ani_ Coccygeus . Triangular liga- ment, inf. lu\er _ Tendinous perineal centre Tuberpsity of ischium _ Anus _ Obturator fascia l . _ Sphincter externus I Levator ani Gluteus 7 maxitnus (cut) -Greater sacro-sciatic ligament Tip of coccyx Muscles of male perineum and pelvic floor, seen from below. arises from the medial surface of the ischial tuberosity and passes directly medially to be inserted into the central tendon of the perineum. Nerve-Supply. From the perineal branches of the pudic nerve. Action. To assist in fixing the central tendon of the perineum during the contraction of the bulbo-cavernosi. Variations. The muscle may occasionally be entirely absent. It frequently receives fibres from the anterior ( pu bo-recta 1 ) portion of the levator ani and from the external sphincter ani and makes connections with the bulbo-cavernosi. 3. ISCHIO-CAVERNOSUS (Fig. 554). Attachments. The ischio-cavernosus, also named the erector penis (erector c/iforidis), represents the lateral portion of the sphincter cloacae. The two muscles occupy the lateral parts of the superficial perineal interspace, each arising from the base of the tuberosity of the ischium, enclosing the base of the cms penis (clito- ridis) as in a sheath, and passing forward to be inserted into the corpus cavernosu m. The muscle in the female differs from that of the male only in si/e. Nerve-Supply. From the perineal branches of the pudie nerve THE PELVIC AND PERINEAL MUSCLES. 565 Action. To compress the corpus cavernosum and thus assist in producing or maintaining erection of the penis (or clitoris). 4. BULBO-CAVERNOSUS (Fig. 554). Attachments. The bulbo-cavernosus differs somewhat in its relations in the two sexes. In the male, in which it is also termed the accelerator urines, the two muscles of opposite sides are united in a median fibrous raphe which extends forward from the central tendon of the perineum over the bulb and corpus spongiosum. Arising from this raphe, the fibres are directed laterally and forward over the bulb and corpus spongiosum and are inserted into the under surface of the inferior layer of the urogenital trigone and into the fibrous sheath of the corpus cavernosum, some of the more anterior fibres being continued dorsally to insert into the fascia covering the dorsum of the penis and forming what has been termed the muscle of Houston, or compressor vence dor salis penis. In the female, in which the muscle has been termed the sphincter vagina (Fig. 1732), the two muscles of opposite sides are widely separated from each other by the vagina, which they surround. They arise from the central tendon of the perineum, pass forward, investing the bulbi vestibuli, and are lost in the fascia covering the corpora cavernosa and the dorsal surface of the clitoris. Nerve-Supply. From the perineal branches of the pudic nerve. Action. To compress the bulb and corpus spongiosum and so tend to expel any fluid contained in the urethra. The fibres which pass to the dorsum of the penis (or clitoris) may aid slightly in the erection of that organ, either directly or by compressing the dorsal vein. Variations. The posterior portion of the muscle, that surrounding the bulb, is unrepre- sented in the female and is frequently distinctly separable from the anterior part in the male ; it has been termed the compressor biilbi. The deeper fibres of this part of the muscle are sep- arated from the more superficial ones by a thin layer of areolar tissue, and have been regarded as forming a distinct muscle, the compressor hemisphericum bn/bi, which closely surrounds the bulb, the two muscles of either side interlacing above the bulb so as to form practically a single muscle very variable in its development. Finally, fibres may arise from the ischial tuberosities in common with those of the transversi superficiales and pass forward and medially to unite with the bulbo-cavernosi forming what have been termed the ischio-bulbosi. 5. TRANSVERSUS PERIN^I PROFUNDUS (Fig. 1629). Attachments. The deep transverse perineal muscle is situated in the poste- rior part of the deep perineal interspace. It arises from the medial surface of the inferior ramus of the ischium and passes transversely inward to the median line, where it partly unites with its fellow of the opposite side and partly inserts into the central tendon of the perineum. Nerve-Supply. From the perineal branches of the pudic nerve. Action. To assist in fixing the central tendon of the perineum. 6. COMPRESSOR URETHRA (Fig. 1629). Attachments. The compressor or constrictor of the urethra (m. sphincter urethrae membranaceae) in the male is a thin sheet of muscle-tissue situated in the deep perineal interspace anterior to the deep transversus perinaei. It arises from the inner surface of the inferior ramus of the pubis and is inserted by passing medially to sur- round the membranous portion of the urethra, its anterior fibres forming a median raphe with those of the opposite side. The posterior fibres of the muscle enclose the bulbo-urethral gland. In the female the fibres are inserted \x\Xo the walls of the vagina as it traverses the deep perineal interspace. Nerve-Supply. From the perineal branches of the pudic nerve. Action. To constrict the membranous urethra and, in the female, also to flatten the wall of the vagina. The m. ischio-pubicus is a small muscle situated at the side of the deep perineal interspace. It arises from the inferior rami of the ischium and pnbis and passes anteriorly to be attached to the arcuate ligament of the pubis. It is frequently wanting. 566 HUMAN ANATOMY. THE APPENDICULAR MUSCLES. The limbs make their appearance as two pairs of flat buds (Fig. 69), the upper pair being situated in the lower cervical and the lower pair in the lower lumbar and upper sacral regions. Into the buds processes extend from the myotomes of the regions concerned and apparently give rise to the more proximal muscles of the limb, but that they are the source of all the limb musculature is as yet undetermined. The greater mass of this musculature develops from a blastema which occupies the interior of the limb-bud and which cannot at first be distinguished from that which gives rise to the limb skeleton, and whether it represents a condensation of tissue whose fundamental derivation is the myotomes or is a derivative of the ventral mesoderm has not yet been definitely decided. However that may be, the limb musculature stands in relation to the anterior divisions of definite spinal nerves, that of the upper limb being supplied by the lower five cervical and the first thoracic nerves and that of the lower limb by the lower four lumbar and upper three sacral nerves, and, furthermore, there is a distribution of these nerves to the muscles which may well be regarded as segmental. It is also worthy of note that in those regions of the trunk in which the limbs develop the ventral musculature is either very much reduced or, as in the lower limb, practically wanting. An examination of the limb muscles shows that they may be regarded as being arranged in a ventral or pre-axial group and a dorsal or post-axial group, and in harmony with this arrangement the nerve-fibres which pass to the muscles arrange themselves in ventral or pre-axial and dorsal or post-axial groups. In the fore-limb the dorsal group is represented by the posterior fasciculus or cord of the brachial plexus, while the ventral one is distributed between the lateral and medial fasciculi. In the lower limb the correct relationships of the two groups of muscles and their nerves are less readily perceivable, owing to the forward rotation which the limb has undergone in order to bring its axis into a plane parallel with that of the sagittal plane of the body, a rotation which brings it about that in the adult, except in the more proximal portion of the limb, the pre-axial musculature is on the posterior and the post-axial on the anterior surface. The pre-axial nerve-fibres are distributed mainly by the obturator and greater sciatic (internal popliteal) nerves, while the post-axial ones pass to their destinations by way of the anterior crural and greater sciatic (external popliteal) ; and in this connection it is interesting to note that the fibres of the external popliteal or peroneal, if traced to their exit from the spinal foramina, will be found to lie dorsal to those of the internal popliteal or tibial, not- withstanding that the former are supplied to the anterior and the latter to the pos- terior muscles of the leg. In this arrangement into pre-axial and post-axial groups there is, accordingly, to be found a clue to the proper understanding of the relations of the nerves to the muscles of the limbs, and a further examination of the two groups will reveal indica- tions of a segmental distribution of the nerves and muscles in each. This arrange- ment may be most satisfactorily understood by means of a diagram ( Fig. 555) showing the arrangement of the muscles and nerves in what may be regarded as its fundamental condition. The limb-bud may be regarded as a flat plate whose surfaces are directed dorsally and ventrally. Into the upper portion of this plate the upper- most of the spinal nerves which are associated with it is prolonged, its post-axial and pre-axial fibres passing respectively to either side of its frontal plane, and the succeeding nerves are similarly prolonged into it in succession from above downward. The nerves, however, which lie along the upper and in the lower limb also along the lower borders of the bud are not prolonged into it quite so far as the others, the free edge of the plate being, as it were, rounded off, so that it is only the more cen- tral (or upper) nerves of the series that reach that portion of the bud from which the foot (or hand) and digits will be developed. It follows from this arran^< -im-nt that in the adult each spinal nerve concerned supplies a portion of both the pre-axial and post-axial groups of muscles, and, THE APPENDICULAR MUSCLES. 567 furthermore, that the muscle-fibres in succession from one border of the limb to the other are supplied by successive nerves, those supplied by the uppermost and, in the pelvic limb at least, the lowermost nerves extending only to the neighborhood of the knee (or elbow) or even a shorter distance into the limb. Thus, in the fore- limb one may expect to find the more lateral muscles of the shoulder and arm supplied by fibres from the uppermost nerves of the brachial plexus, those lying towards the middle of the shoulder and brachial regions and in the lateral portion of the antibrachium and hand regions by the middle nerves, and those along the medial portion of the limb by the lower ones. In the lower limb, however, owing to the rotation which it has undergone, the arrangement is to a certain extent reversed, and although in the more proximal muscles the fibres are supplied by suc- cessive nerves from above downward, lower down the fibres from the upper nerves are FIG. 555. to be found along the inner side of the leg _^ 3~^r\ x Dorsai muscles and those from the lower nerves along the outer side. T p . . 11 i. 1 8N\ Intermuscular septum If, then, an originally segmental ar- ^rffN^ P^. V rangement of the muscle-fibres of the limbs * ' >^^**' Mesobiastic is to be recognized, the segments must run jg^ 9 *|PPBfc rSfoi^ /"^"post-axial parallel to the long axis of the limb, and - ^ Q < ^ ^JBffi\^&MkX ^muscles this arrangement has permitted their free consolidation to form the various muscles found in the adult, very few indeed of which are supplied by a single nerve, and represent, accordingly, portions of a sin- gle primitive segment. Furthermore, the j J c ,1 i rr . 1 ^&sjS Latero- Pre-axial muscles adaptation of the muscles to act effectively ^Pc/ ventral on the various joints of the limbs has **^\od' muscles brought about a transverse division of the Diagram of ore- and post-axial groups of limb-muscles. segments, and has also led to a complete (Koiimann.) degeneration of the portions of some of the segments in one part of the limb while they are retained in another. Thus, for example, in the pre-axial musculature of the brachial region no trace is to be found of the segments supplied by the eighth cervical and first dorsal nerves, although the eighth cervical is represented in the post-axial musculature and both in the pre-axial musculature of the forearm. On account of the occurrence of both fusion and degeneration, little trace of an original segmental arrangement of the muscle-fibres is to be found in the adult limb muscles, and their classification according to the segments from which they may be derived is not feasible. Comparative anatomy, however, shows that primarily the limb muscles were arranged with relation to the various joints of the limb, each muscle, as a rule, passing over but a single joint, and in this relation may be found a basis for classification. In man the original relations have been modified in many cases by an alteration in one of the original points of attachment of a muscle so that it passes over two joints, or by the end-to-end union of originally distinct muscles so that the same result is brought about. Making allowance for these modifications, however, the muscles of the upper limb may be classified into ( i ) those passing from the axial skeleton to the pectoral girdle, (2) those passing from the girdle to the brachium or arm, (3) those passing from the brachium to the antibrachium or fore- arm, (4) those passing from the antibrachium to the carpus, and (5) the digital mus- cles. Similarly in the lower limb, in which, however, owing to the firm articulation of the pelvis to the sacrum, the first group of muscles is practically unrepresented, or at least may be placed with those of the second group extending from the pelvic girdle to the femur. With this grouping there may be combined a recognition of the pre-axial and post-axial musculature, these terms being used in the lower limb as well as in the upper to indicate the relationships which obtained before the rotation of the limb. 568 HUMAN ANATOMY. THE MUSCLES OF THE UPPER LIMB. THE MUSCLES EXTENDING BETWEEN THE AXIAL SKELETON AND THE PECTORAL GIRDLE. (a) THE PRE-AXIAL MUSCLES. i. Pectoralis major. 2. Pectoralis minor. 3. Subclavius. The Pectoral Fascia. The superficial pectoral fascia is continuous above with the superficial cervical and below with the superficial abdominal fasciae, and covers the entire anterior wall of the thorax. It usually contains a considerable amount of fat and has embedded in it the mammary gland. The deep fascia is attached above to the clavicle, and forms a thin membrane closely adherent to the surface of the pectoralis major, at the lower border of which FIG. 556. t External anterior thoracic nerve Cephalic vein Branch of acromio-thoracic artery Deltoid Distal stump of pectoralis major Cut edge of deep- pectoral fascia Pectoralis minor enclosed in clavi-pectoral fascia Pectoralis major, cut edge of clavicular portion Pectoralis major, cut edge of sterno-costal portion Dissection of thoracic wall after removal of greater part of pectoralis major, showing clavi-pectoral fascia enclosing pectoralis minor and continuous with axillary fascia. it becomes continuous with the axillary fascia. Medially it is attached to the ventral surface of the sternum and laterally it is continuous with the fascia covering the deltoid. Beneath the deep fascia there arises from the clavicle a second sheet of fascia (clavi-pectoral fascia} (Fig. 556) which encloses the subclavius muscle and is then continued downward to the upper border of the pectoralis minor. There it divides into two sheets which enclose the muscle and at its lower margin unite to form a single sheet which becomes continuous with the axillary fascia close to the lower border of the pectoralis major. The portion of this fascia which intervenes between the clavicle and the subclavius muscle and the upper border of the pectoralis minor is termed the coraco-clavic ular fascia or costo-coracoid membrane. It is prolonged laterally along the upper border of the pectoralis minor, over the upper portion of the axillary vessels, to the coracoid process, its outer portion being thickened to form THE PECTORAL MUSCLES. 569 a band, the costo-coracoid ligament (Fig. 560), which passes obliquely downward and laterally from the clavicle to the coracoid process. The coraco-clavicular fascia occasionally contains muscle-fibres (the m. coraco-clavicularis}, and is usually perfo- rated by the cephalic vein on its way to join the axillary, by the thoraco-acromial artery, and by the external anterior thoracic nerve. i. PECTORALIS MAJOR (Fig. 557). Attachments. The pectoralis major is a strong fan-shaped muscle situated on the anterior thoracic wall. It is composed of three portions : (i) the pars da- vicularis, which arises from the inner half of the anterior border of the clavicle ; (2) the pars sterno-costalis , which arises from the anterior surface of the sternum and the upper six costal cartilages ; and (3) the portio abdominalis, which arises from FIG. 557. Deltoid Clavicle Pectoralis major, clavicular portion Brachial fascia Pectoralis major, sterno- costal portion Serratus magnus Sternum Latissimus dorsi Pectoralis major, abdominal portion Dissection of thoracic wall, showing pectoralis major. the upper part of the anterior layer of the sheath of the rectus abdominis. From these origins the fibres are directed laterally to be inserted into the external bicipital ridge which extends downward from the greater tuberosity of the humerus, the lower fibres of the sterno-costal and the abdominal portions of the muscle passing behind those of the clavicular and upper portions, so that the tendon of insertion is U-shaped in section, consisting of two layers separated above but continuous below. A bursa is usually interposed between the posterior surface of the tendon and the anterior surface of the long head of the biceps humeri. Nerve-Supply. From the external and internal anterior thoracic nerves by fibres from the lower four cervical and the first thoracic nerves. 570 HUMAN ANATOMY. Action. When the arm is abducted to a position at right angles to the body, the pectoralis major will draw the arm forward and at the same time will adduct it. As the arm approaches the vertical position, the adductor action becomes more pronounced and the flexor action less so, and a slight amount of internal rotation appears. When the arm is raised above the level of the shoulder and fixed, the muscle will assist in drawing the trunk upward, as in climbing, and it will also assist in raising the ribs in forced inspiration. Variations. In the lower mammals the pectoralis major is represented by a number of distinctly separate portions, a condition which may be indicated in man by a more than usual distinctness of the three portions of the muscle and by the occurrence of accessory slips. The sterno-costal and abdominal portions may be greatly reduced or even absent. The m. sternalis is present in something over 4 per cent, of all cases examined. It is very variable in its development, and consists of fibres which arise anywhere from the third to the seventh costal cartilage, or even from the sheath of the rectus, and extends upward to be attached to the anterior surface of the sternum, the clavicle, or the tendon of the sterno-cleido-mastoid. Usually the fibres are directed vertically, but sometimes they may have a more or less oblique course. The muscle has been variously regarded as a portion of the platysma, a downward pro- longation of the sterno-cleido-mastoid, an upward prolongation of the rectus abdominis, and as a displaced portion of the pectoralis major. The fact that in the majority of cases it is sup- plied by branches from the anterior thoracic nerves indicates clearly its usual derivation from the pectoralis, but it is asserted that in certain cases it received its nerve-supply from the third and fourth intercostal nerves, in which cases it is more probably to be regarded as representing a thoracic portion of the rectus trunk muscles. The chondro-epitrochlearis is a slip derived from the pectoralis major which takes its origin from the lower costal cartilages or the abdominal portion of the pectoralis and is inserted into the brachial fascia or the medial epicondyle of the humerus. 2. PECTORALIS MINOR (Fig. 560). Attachments. The pectoralis minor lies beneath the pectoralis major. It arises from the outer surface of the third, fourth, and fifth ribs and from the ascia covering the intervening intercostal muscles, and passes obliquely upward and later- ally to be inserted into the coracoid process of the scapula. Nerve-Supply. By branches of the external and internal anterior thoracic nerves fronv the seventh and eighth cervical and first thoracic nerves. Action. To draw the lateral angle of the scapula downward and forward ; if the scapula be fixed, to raise the ribs to which it is attached. Relations. The pectoralis minor is completely covered by the pectoralis major. It covers the outer surface of the upper ribs and their intercostal spaces, and near its insertion it passes over the middle portion of the axillary vessels and the cords of the brachial plexus. 3. SUBCLAVIUS (Fig. 560). Attachments. The subclavius is an almost cylindrical muscle attached at one extremity to the anterior surface of the first costal cartilage and at the other to the under surface of about the middle third of the clavicle. Nerve-Supply. By a special nerve from the brachial plexus from the fifth and sixth cervical nerves. Action. To draw the outer end of the clavicle downward and forward. Variations. The subclavius seems to be the persistent representative of a group of muscles more perfectly developed in the lower mammals and especially in those in which tin- clavicle is more or less rudimentary. Muscle-bands, which represent portions of the group normally degenerated, are occasionally found in man, and on account of their variable relations have been described under various names. They may all be grouped, however, under three terms, the stemo-chondro-scapttlaris, the scapuio-cfavuvlaHs, and the stento-clavicularis ( Le Double). In the mammals which lack a clavicle in many Ungulates, for example a strong muscle-band passes transversely across the upper part of the thorax from the sternum and first costal cartilage to the scapula. This is thesterno-chondro-scapnlaris, and it occasionally occurs in man as a baud arising from the points named, or from either one of them, or from the first ril), and inserting into the coracoid process of the scapula. In those mammals which possess a rudimentary clavicle, such as the Rodents, only the terminations of the sterno-chondro-scapnlar persist, each inserting into the clavicle, and forming THE SCAPULAR MUSCLES. 571 the scapulo-clavicularis and the sterno-clavicularis. Each of these may occur as an anomaly in man, the sterno-clavicularis appearing under various forms, and passing either above, behind, or in front of the clavicle. It should be stated, however, that there is a possibility that some of the varieties of the sterno-clavicularis may really represent persisting portions of the muscular sheet which has given rise to the middle layer of the cervical fascia and to the sterno-hyoid and the omo-hyoid (page 545). In the lower mammals a thin muscular sheet invests a greater or less portion of the trunk in intimate association with the integument, resembling in this respect the platysma. It is termed the panniculus carnosits, and in man is normally unrepresented. Occasional traces of it are found, however, and of these the most frequent is the muscle of the axillary arch, a somewhat variable band of muscle-tissue which passes across the anterior portion of the axillary cavity from the lateral border of the latissimus dorsi to the tendon of the pectoralis major. It presents considerable variation in its insertion, being connected sometimes with the biceps, the coraco-brachialis, the pectoralis minor, or the chondro-epitrochlearis, or being united with slips from the abdominal portion of the pectoralis major, or being inserted into the coracoid process of the scapula. It is supplied by branches from the anterior thoracic nerves. (b) THE POST-AXIAL MUSCLES. 1. Serratus magnus. 3. Rhomboideus minor. 2. Levator anguli scapulae. 4. Rhomboideus major. 5. Latissimus dorsi. i. SERRATUS MAGNUS (Fig. 558). Attachments. The serratus magnus (m. serratus anterior) forms a large muscular sheet covering the lateral wall of the thorax. It arises by nine or ten fleshy digitations from the outer surfaces of the eight or nine upper ribs, the second rib giving attachment to two slips. Its fibres may be regarded as arranged in three groups : the uppermost group consists of fibres from the first and second ribs and is inserted into the ventral surface of the medial angle of the scapula ; the middle group, from the second and third ribs, is inserted into the ventral surface of the vertebral border of the scapula ; while the remaining fibres, constituting the strongest portion of the muscle, converge to the inferior angle of the same bone. Nerve-Supply. By the long thoracic nerve from the fifth, sixth, and seventh cervical nerves. Action. It serves to keep the scapula closely applied against the thoracic wall and draws it laterally. Since the portion inserted into the inferior angle is the strongest, a rotation of the scapula is produced whereby its lateral angle is raised. By this action the serratus plays an important part in the elevation (abduction) of the arm, since, in the first place, by fixing the scapula it allows the deltoid to expend all its action on the humerus instead of wasting part of it in tilting the acromion downward, and, in the second place, after the deltoid has completed its action and has raised the arm through about 90, the further elevation through another right angle is accomplished by a rotation of the scapula resulting from the action of the serratus magnus and trapezius. Variations. Absence of a portion or the whole of the muscle has been observed. Its origin may extend as low as the tenth rib, and it may receive slips from the transverse processes of the cervical vertebrae and from the levator scapulae. 2. LEVATOR ANGULI SCAPULAE (Fig. 559). Attachments. This (m. levator scapulae) is an elongated muscle on the lateral surface of the neck. It arises from the transverse processes of the upper four cer- vical vertebrae and passes downward, forward, and laterally to be inserted into the* medial angle and outer surface of the vertebral border of the scapula as far down as the base of the spine. Nerve-Supply. By the dorsal scapular nerve from the fifth cervical nerve. Action. To draw upward the medial angle of the scapula, producing a rota- tion of the bone contrary to that effected by the serratus anterior. If the scapula be fixed, the action is to bend the cervical portion of the spinal column laterally, rotating it slightly to the opposite side. 572 HUMAN ANATOMY. Variations. The origin may extend to the transverse processes of all the cervical ver- tebrae, and may be continued upon the mastoid process above and upon the upper ribs below. Slips may occur connecting the levator with various neighboring muscles, the most interesting of these connections being that with the serratus magnus, since comparative anatomy shows that the levator was primarily continuous with that muscle. A separated portion of the outer part of the muscle is occasionally inserted into the outer end of the clavicle, forming what is termed the levator claviculce. 3. RHOMBOIDEUS MINOR (Fig. 559). Attachments. The rhomboideus minor is a band-like muscle which arises from the lower part of the ligamentum nuchae and from the spinous process of the FIG. 558. Serratus posticus superior Coracoid process Tendon of supraspinatus Acromion process Lesser, tuberosity of humerus Subscapularis Levator anguli scapulae Superior angle of scapula Supraspinatus Scalenus posticus Scalenus medius Scalenus anticus First rib Serratus mag- nus, upper, middle, and lower por- tions Latissimus dorsi, cut edge Dissection of thoracic wall, showing serratus magnus; clavicle has been removed and scapula drawn outward. last cervical vertebra and passes laterally and downward to be inserted into the ver- tebral border of the scapula at the base of the spine. Nerve-Supply. By the dorsal scapular nerve from the fifth cervical nerve. Action. To draw the scapula upward and medially, at the same time rotating it so that the lateral angle is moved downward. 4. RHOMBOIDEUS MAJOR (Fig. 559). Attachments. The rhomboideus major immediately succeeds the rhom- boideus minor, and is a quadrilateral sheet which arises from the spinous processes of the four upper thoracic vertebrae and from the intervening interspinous liga- THE SCAPULAR MUSCLES, FIG. 559. 573 Semispinalis capitis (complexes) Splenius capitis et colli Sterno-cleido-mastoideus Supraspinatus A nfraspinatus Rhomboideus major Vertebral aponenrosis Serratus magnus Serratus posticus inferior Oluteus medius Gluteus maximus Deltoid Infraspinatus Rhomboideus major Teres major Aponeurosis of trapezius Trapezius Levator anguli scapulae Rhomboideus mino Latissimus dorsi Aponeurosis of latissimus dorsi (vertebral aponeurosis) Superficial muscles of the back. 574 HUMAN ANATOMY. ments. It is directed downward and laterally and is inserted into the lower two- thirds of the vertebral border of the scapula. Nerve-Supply. By the dorsal scapular nerve from the fifth cervical nerve. Action. To draw the scapula upward and medially, at the same time rotating it so that the lateral angle is moved downward. Variations of the Rhomboidei. The rhomboidei are sometimes entirely wanting, and the origins of both muscles may be extended beyond the usual limits. The occipito-scapularis is a muscle occasionally present which is intimately associated in its derivation with the rhomboids. It arises from the inner part of the superior nuchal line and passes downward between the trapezius and splenius to join the rhomboideus minor, inserting with it into the vertebral border of the scapula. 5. LATISSIMUS DORSI (Fig. 559). Attachments. The latissimus dorsi is a large triangular muscle which arises from the spinous processes of the last six thoracic vertebrae and the intervening interspinous ligaments beneath the origin of the trapezius, from the lumbo-dorsal fascia, from the posterior portion of the crest of the ilium, and by fleshy digitations from the outer surfaces of the lower three or four ribs. Its fibres pass upward and laterally over the inferior angle of the scapula, from which an additional slip is usu- ally added to the muscle. It then curves around the lower border of the teres major and is inserted, ventrally to that muscle, into the crest of the inner tuberosity of the humerus. A mucous bursa (bursa m. latissimi dorsi ) lies between the tendons of insertion of the latissimus dorsi and teres major. Nerve-Supply. By the long subscapular nerve from the seventh and eighth cervical nerves. Action. To draw the humerus downward, backward, and inward, at the same time rotating it inward, the action being that of the arm in swimming. If the humerus be fixed, as in climbing, it draws the pelvis and lower portion of the trunk upward and forward. Variations. The latissimus dorsi, like the serratus anterior and pectorales, is a muscle which has migrated extensively from the region of its first formation, the lower cervical region, and this migration can be witnessed in the ontogeny of the muscle. Consequently variations may be expected and do occur in the extent of the origin of the muscle, whose descent and backward migration to the vertebral column may be interrupted at various stages. A great amount of variation of this nature is seen in its attachment to the crest of the ilium. In some cases this attachment extends so far forward as to meet the posterior extremity of the attachment of the external oblique of the abdomen, but usually this does not occur, and a tri- angular interval, known as the triangle of Petit, occurs between the borders of the two muscles and above the crest of the ilium. The floor of the triangle is formed by the internal obliquus abdominis, and, since the abdominal wall is here thinner than elsewhere, the triangle may occa- sionally be the seat of a lumbar hernia. Closely allied to the latissimus dorsi is a muscle, the m. dorso-epitrochlearis, which occurs in 18 or 20 per cent, of cases. It takes its origin from the body or tendon of insertion of the latissimus and passes to the brachial fascia or to the medial epicondyle of the humerns. It has been regarded as an aberrant portion of the pectoralis group of muscles, but its supply by tlit- musculo-spiral nerve places it among the post-axial muscles. The Axillary Fascia. The axillary fascia is a firm sheet which extends across from the lower border of the pectoralis major to that of the latissimus dorsi and teres major, forming the floor of the axilla. Laterally it passes over into the deep fascia of the arm, medially into the fascia covering the serratus magnus, and near the border of the pectoralis major it has inserted into it the downward continu- ation of the fascia which encloses the pectoralis minor (Fig. 556). It is pierced by numerous lymphatic vessels, and along its medial edge is considerably thickened to form a curved hand, whose concavity is directed laterally, and which stretches across between the tendons of the pectoralis major and the latissimus, forming what is termed the axillary arch. Muscle-fibres are occasionally found in this arch (page 571). The axilla is a pyramidal space intervening between the upper part of the brachium and the lateral wall of the thorax. Its apex is directed upward and the THE SHOULDER MUSCLES. 575 base, which is formed by the axillary fascia, downward. Its ventral wall is formed by the pectoralis major and pectoralis minor, its dorsal wall by the latissimus dorsi, teres major, and subscapularis, and its medial wall by the serratus magnus. In the angle formed by the junction laterally of its ventral and dorsal walls lies the m. coraco- brachialis, and in the groove between that muscle and the posterior wall are the axillary vessels and the cords of the brachial plexus. The cavity of the axilla con- tains a considerable amount of fat and a variable number of lymphatic nodes ; it is traversed by the thoracic branches of the axillary vessels and by the intercosto- humeral nerve, and the long thoracic nerve passes downward along its medial wall to the serratus magnus. THE MUSCLES PASSING FROM THE PECTORAL GIRDLE TO THE BRACHIUM. PKE-AXIAL. Posx-AxiAL. i. Coraco-brachialis. i. Supraspinatus. 4. Teres major. 2. Infraspinatus. 5. Subscapularis. 3. Teres minor. 6. Deltoideus. (a) THE PRE-AXIAL MUSCLES. i. CORACO-BRACHIALIS (Figs. 560, 570). Attachments. The coraco-brachialis arises from the tip of the coracoid pro- cess of the scapula by a tendon common to it and the short head of the biceps. It extends downward along the humerus and is inserted at about the middle of its medial border. Nerve-Supply. By the musculo-cutaneous nerve from the seventh cervical nerve. Action. To draw the upper arm forward. Relations. It is crossed ventrally by the pectoralis major, and dorsally it is in relation with the tendons of the latissimus dorsi, the teres major, and the subscapu- laris, from the last of which its tendon is separated by a mucous bursa (dursa m, coraco-brachialis^). Laterally the muscle is in contact with the short head of the biceps. It is usually pierced by the musculo-cutaneous nerve, and is in relation medially with the axillary artery and the median and ulnar nerves. Variations. Comparative anatomy shows that the coraco-brachialis is primarily an ex- tensive muscle consisting of three portions, of which only the middle one and a part of the inferior are normally present in man. The variations which occur usually consist in the appearance of one or other of the missing portions. Thus the upper portion is sometimes represented by a coraco-brachialis superior, which arises from the coracoid process and passes laterally to be inserted into the lesser tuberosity of the humerus or into the capsule of the shoulder-joint, while the lower portion may be more completely represented by the insertion of the muscle extending as far down as the medial epicondyle of the humerus. (*) THE POST-AXIAL MUSCLES. i. SUPRASPINATUS (Fig. 561). Attachments. The supraspinatus occupies the supraspinous fossa of the scapula, arising from the inner two-thirds of this and from the supraspinous fascia. Its fibres pass laterally and converge to a tendon which is inserted into the upper facet upon the greater tuberosity of the humerus and into the capsule of the shoulder- joint. Nerve-Supply. By the suprascapular nerve from the fifth and sixth cervical nerves. Action. To abduct the arm. The supraspinous fascia is the layer of connective tissue which covers the supraspinatus muscle. It is attached to the superior border of the scapula above, to the vertebral border medially, to the spine below, and gradually fades out laterally. the vert 576 HUMAN ANATOMY. 2. INFRASPINATUS (Figs. 561, 572). Attachments. The infraspinatus occupies the infraspinous fossa of the scapula and arises from the entire extent of the fossa, with the exception of a portion towards the axillary border of the bone. It also arises from the infraspinous fascia which covers it. The fibres pass laterally and converge to a strong tendon, which is frequently separated from the capsule of the shoulder-joint by a small bursa (bursa FIG. 560. Axillary vein Axillary artery Subclavius -Costo-coracoid ligament Deltoid Long head of biceps Short head of bice; Insertion of pectoralis major Deltoid Biceps 4 Pectoralis minor Serratus magnus Latissimus dorsi Subscapularis Bicipital fascia m. infraspinati) and is inserted into the middle facet of the greater tuberosity of the humerus. Nerve-Supply. By the suprascapular nerve from the fifth and sixth cervical nerves. Action. When the arm is hanging vertically, it is the chief outward rotator of the humerus. When the arm is abducted to a horizontal position, the muscle draws it backward. Variations. The upper portion of the muscle is sometimes distinctly separated from the rest, and has been termed the infras/>hnitus minor. On the other hand, the separation which usually exists between the infraspinatus and the teres minor tuny be entirely wanting. The infraspinous fascia is a strong fascia which covers the infraspinatus and the teres minor, giving origin to some of the fibres of both muscles. It is attached above to the spine of the scapula, medially to its vertebral border, and fades out laterally into the brachial fascia. 3. TERES MINOR (Fig. 561). Attachments. The teres minor arixt-s from the upper two-thirds of tin- dorsal surface of the scapula, close to its axillary border, and from the infraspinous fascia. tion of thoracic wall and imuiior surface of arm. THE SHOULDER MUSCLES. 577 It passes laterally along the lower border of the infraspinatus to be inserted into the capsule of the shoulder-joint and into the lower facet of the greater tuberosity of the humerus. Nerve-Supply. By the circumflex nerve from the fifth and sixth cervical nerves. Action. When the arm is vertical, it rotates the humerus outward ; when it is horizontal, it draws it backward. FIG. 561. Clavicle Supraspinatus Spine of scapula Infraspinatus Subscapularis Sectional surface of acromion i Supraspinatus Greater tuberosity Teres minor uadrilateral space Tendon of latissimus dorsi Triangular space Long (middle) head of triceps Outer head of triceps Teres major Triceps \ Posterior scapular muscles and part of triceps ; outer part of acromion has been removed. 4. TERES MAJOR (Figs. 561, 572). Attachments. The teres major arises from the dorsal surface of the scapula, along the lower third of its axillary border, and passes laterally to be inserted into the crest of the lesser tuberosity of the humerus immediately dorsal to the insertion of the latissimus dorsi. Nerve-Supply. By the lower subscapular nerve from the fifth and sixth cervi- cal nerves. Action. To draw the arm backward and medially, at the same time rotating it inward. Relations. The teres major is in relation below with the latissimus dorsi, which ><-n Is around its under surface so as to lie ventral to it at its insertion. Above it is relation with the teres minor at its origin, but separates from it as it passes later- 37 578 HUMAN ANATOMY. ally, so that a triangular interval, the base of which is the humerus, lies between the two muscles. This interval is crossed by the long head of the triceps, which overlies the dorsal surface of the teres major, and is thus divided into a more medial triangular space, occupied by the dorsal scapular artery, and a more lateral quad- rangular space, through which the posterior circumflex vessels and the circumflex nerve pass. Variations. Considerable variation occurs in the size of the teres major, an increase in the size of that muscle being associated with a diminution of that of the latissimus dorsi, and rice versa. The teres major is, indeed, to be regarded as fundamentally a portion of the latissimus. 5. SUBSCAPULARIS (Fig. 558). Attachments. The subscapularis is a powerful muscle occupying the ventral (costal) surface of the scapula. It arises from the whole of that surface, with the ex- ception of a small portion near the neck of the bone, some fibres also taking origin from the subscapular fascia. The fibres pass laterally, converging to a strong tendon which is inserted into the lesser tuberosity of the humerus and to a certain extent into the capsule of the shoulder-joint. Nerve-Supply. By the upper and lower subscapular nerves from the fifth and sixth cervical nerves. Action. When the arm is vertical, the subscapularis acts as a powerful inward rotator of the humerus ; when the arm is abducted to a right angle with the body, the muscle serves to draw it forward. Relations. The subscapularis forms a considerable portion of the dorsal wall of the axilla, and is in relation, by its ventral surface, with the axillary vessels and the cords of the brachial plexus, and laterally with the coraco-brachialis and short head of the biceps. Its lower border is in contact with the teres major and with the dorsal scapular vessels and the circumflex nerve. Dorsally it is in contact with the long head of the triceps, and is separated from the neck of the scapula by the large subscapular bursa (bursa m. subscapularis) which frequently is continuous with the synovial cavity of the shoulder-joint. Variations. The subscapularis differentiates in the embryo from the same sheet which gives rise to the teres major and the latissimus dorsi. It is occasionally divided into two or more fasciculi, and sometimes there is separated from its lower portion a small muscle, termed the subscapularis minor, which arises from the axillary border of the scapula and is inserted into the crest of the lesser tubercle of the humerus and sometimes into the capsule of the shoulder- joint. The subscapular fascia is a firm sheet of connective tissue which covers the ventral surface of the subscapularis. It is attached above, medially, and below to the border of the scapula and fades out laterally into the brachial fascia. 6. DELTOIDEUS (Fig. 562). Attachments. The deltoid is a large triangular muscle which covers the shoulder as with a pad. It arises from the ventral border of the outer third of the clavicle and from the acromion process and lower border of the spine of the scapula. Its fibres pass downward, and converge to be inserted into the deltoid tubercle of the humerus. Where the muscle passes over the greater tuberosity of the humerus a mucous bursa (bursa subdeltoidea) is interposed between it and that prominence. Nerve-Supply. By the circumflex nerve from the fifth and sixth cervical nerves. Action. To abduct the arm to a position at right angles to the body. Fur- ther abduction is accomplished by a rotation of the scapula by the contraction of the trapezius and the serratus anterior, whereby the lateral angle of the bone is tilted upward. Relations. The deltoid is in relation by its deep surface with the coraroid process and the capsule of the shoulder-joint and with the various muscles attached to or in the neighborhood of these structures. The cephalic vein passes upward along its anterior border. PRACTICAL CONSIDERATIONS : AXILLA AND SHOULDER. 579 Variations. The portion of the deltoid which arises from the clavicle is subject to con- siderable variation, either being greatly reduced in size or even entirely suppressed, or else being more extensively developed than usual, so that it is in contact or even fused with the clavicular portion of the pectpralis major. It may also be distinctly separated from the remain- der of the muscle, and not infrequently a separation of the acromial and spinal portions may also occur, so that the muscle becomes three-headed. FIG. 562. Trapeziu Spine of scapula Acromio Deltoid, spinal portion Deltoid, acromial portion Sterno-cleido-mastoid 'Clavicle Pectoralis major Deltoid, clavicular portion Deltoid muscle viewed from side Accessory bundles of fibres are occasionally found arising from the fascia infraspinata or from some point along the axillary border of the scapula, and either insert with the deltoid (in. basio-dettoideus) or join with the upper part of the muscle, being continued onward as tendinous fibres which pass to the acromion process and lateral extremity of the clavicle (m. costo-deltoideus] . These fibres represent a portion of the deltoid which in the anthropoid apes arises from the borders of the scapula and in some ot the lower mammals forms a distinct muscle. PRACTICAL CONSIDERATIONS: THE MUSCLES AND FASCIA OF THE AXILLA AND SHOULDER. The practical relations of the fascia descending to the superior borders of the clavicle and scapula have been sufficiently described (page 551). Fracture of the Clavicle. The action of the muscles which move the arm and shoulder and of those attached to the clavicle (page 259) should be considered with reference to the common form of displacement in cases of fracture of the latter bone. The acromial fragment, as it moves with the shoulder, is the more markedly affected. It is carried downward by gravity acting on the upper extremity and aided by the two pectoral muscles and the latissimus dorsi. It is drawn inward by HUMAN ANATOMY. the sternal fibres of the pectoralis major and by all the muscles passing from the trunk to the humerus and scapula. It is rotated on a vertical axis so that its inner end points backward and its outer end forward. The cause of the rotation is the action of the two pectorals upon the shoulder and the contraction of the serratus, which (the support of the clavicle having been removed) draws the scapula (and with it the point of the shoulder) inward and forward instead of more directly for- ward, and so causes an anterior projection of the acromial end of the outer fragment. Theoretically the inner fragment is displaced upward by the clavicular fibres of the sterno-mastoid, but this action is so strongly resisted by the costo-clavicular (rhomboid) ligament and by the upper and inner fibres of the pectoralis major, as well as by the subclavius, that it is not often productive of much deformity (Fig. 563). The rationale of the good effect of recumbency with the head slightly elevated is evident. The weight of the upper extremity ceases to drag the outer fragment downward. The vertebral border of the scapula is pressed closely to the thorax by the weight of the trunk. Its outer border, therefore, cannot be drawn forward by the pectorals and serratus, but tends to fall backward and outward, correcting both the rotation and the inward FIG. 563. displacement. The slight ele- vation of the head relaxes the sterno-cleido-mastoid and re- moves whatever influence it may have in raising the outer end of the inner fragment. Fractures within the limits of the rhomboid ligament at the inner end or within those of the conoid and trapezoid ligaments at the outer end are attended by but little displace- ment. Fractures of the scapula have already been dealt with (page 254). Muscular action influences them but little be- yondwhat has been mentioned. The fascia beneath and connected with the clavicle is of much surgical importance. The superficial fascia of the thorax splits to enclose the breast. The processes which pass from it to the skin (Cooper's " ligamenta suspensoria"), by their involvement and contraction in carcinoma, produce the characteristic adhesion and dimpling of the skin. The deep pectoral fascia splits to form the sheath of the pectoralis major muscle. Carcinoma of the mamma will usually be found adherent to this layer on the anterior surface of the muscle. Such adhesion can best be demonstrated by attempting to move the tumor and breast in the direction of the pectoral fibres. Motion trans- verse to that line may, even in cases in which the tumor and muscle are inseparably connected, appear to be free, because the muscle itself is moved on the subjacent structures. Beneath the deep pectoral fascia an additional sheet, the clavi-pectoral fascia. extends as a continuation downward of the sheath of the subclavius, the two layers of which begin above at the two lips of the subclavian groove on the inferior surface of the clavicle and unite into one layer at the lower edge of the subclavius. This layer is continuous towards the sternum with the deep fascia covering in the first and second intercostal spaces ; externally it is attached to the coracoid process ; inferiorly, after splitting to enclose the pectoralis minor muscle, it blends with the axillary fascia. The portion of the clavi-pectoral fascia above the upper border of the pectoralis minor is known as the costo-coracoid membrane. It, together with the subclavius Dissection of fracture of middle of clavicle PRACTICAL CONSIDERATIONS: AXILLA AND SHOULDER. 581 muscle (which it invests), forms the floor of the so-called superficial infradavicular triangle, the roof of which is made by the clavicular fibres of the great pectoral, the base by the anterior fibres of the deltoid, the upper side by the sternal half of the clavicle, and the lower side by a line parallel to the uppermost sternal fibres of the great pectoral. Its apex is at the sterno-clavicular angle of junction. The floor of this space is pierced by the external anterior thoracic nerve, the acromio-thoracic vessels, and the cephalic vein (Fig. 556). Fat containing a few lymphatic glands, often involved in carcinoma of the breast, is found there. It is closed in above by the clavicle, but is continuous below with the space between the two pectoral muscles down to the level where the superficial layer of the deep fascia and the clavi-pectoral fascia (which has invested the pectoralis minor and continued downward as a single layer again) unite at the lower border of the pectoralis major to form the axillary fascia. Effusions of blood or collections of pus occupying this space between the two muscles are therefore prevented from passing upward by the clavicle, forward by the pectoralis major, and backward by the clavi-pectoral fascia and pectoralis minor. FIG. 564. Humeral branch of acromio-thoracic artery Pectoralis minor \ Deltoid Pectoralis major, distal stump Cephalic Axillary artery and vein Cut edge of superficial pec- toral fascia Cut edge of superficial la clavi-pectoral fascia Teres major covered by axillary fascia Pectoralis major, clavicular origin Costo-coracoid membrane Deep layer of clavi-pectoral fascia Thoracic branch of acromio- thoracic artery Pectoralis minor, cut edge Dissection of thoracic wall ; pectoralis minor has been partly removed, exposing deep layer of clavi-pectoral fascia. Consequently they are apt to approach the surface near the anterior axillary margin or in the groove between the great pectoral and deltoid, i.e. , at either the lower border of the sternal portion of that muscle or the upper border of its clavicular fibres. Beneath the costo-coracoid membrane is a region described as the deep infra- clavicular triangle. Although continuous with the axilla, this space is conveniently studied as a separate region on account of the important structures which it contains and the frequency with which it is invaded by disease. Its floor is formed by the first and second ribs and the intercostal, serratus magnus, and subscapularis muscles. Its apex is at the angle made by the line of the upper border of the small pectoral and that of the clavicle at the coracoid process, those two lines constituting its sides. The base is towards the sternum at the line where the costo-coracoid membrane is fused with the deep fascia over the upper intercostal spaces. Through this triangle pass the axillary, superior thoracic, and acromio-thoracic vessels, the cephalic vein, the external and internal anterior thoracic and long thoracic nerves, and the brachial plexus. It contains fat, with numerous lymphatic glands and vessels. It is obvious 582 HUMAN ANATOMY. that it is continuous above with the neck and inferiorly with the axilla. The latter space is shut in below by the continuation of the axillary fascia from the lower bor- der of the pectoralis major backward to the latissimus dorsi, outward to the deep fascia of the arm, and inward to the deep fascia of the thorax. Abscess or effusion of blood, as its progress in all these directions is resisted, may therefore point in the neck, following the vessels and the trunks of the plexus up from the axilla through the deep infraclavicular triangle, to make its appearance above the clavicle. The skin over the fascia at the base of the axilla is thin and richly supplied with hair-follicles and with sebaceous and sudoriparous glands ; hence superficial infections are frequent and secondary glandular abscesses are common. The con- nective tissue of the axillary space is loose and abundant, permitting of free motion of the arm, but also favoring the occurrence of large collections of blood or of pus. FIG. 565. FIG. 566. Acrotnion Coracoid process Glenoid cavity Head of huincrus Shoulder of subject in which subcoracoid lux- ation has been produced, showing characteristic deformity. Showing relation of bones in preceding subcoracoid luxation. The fascia over the scapular muscles supraspinous and infraspinous fascia has already been described in reference to caries, necrosis, and abscess (pag 255. 279). Dislocation of the Shoulder- Joint. The circumstances that favor or resist dislo- cation of the shoulder-joint have been enumerated (pages 278, 279), but the ana- tomical symptoms of that lesion may now be considered with especial reference to the muscles involved. Shoulder dislocation is either subglenoid or subcoracoid in the vast majority of cases, the former being almost invariably the primary form, for reasons previously given (page 278). A luxation, subglenoid primarily, usually becomes subcoracoid from the con- tinuance of the force producing it, aided strongly by the pectoralis major ; hence the subcoracoid is the most common. The subclavicular, in which the head passes farther inward and lies on the second and third ribs beneath the pectoralis major, = PRACTICAL CONSIDERATIONS: AXILLA AND SHOULDER. 583 FIG. 567. Acromion and the supracoracoid , in which, owing to fracture of the coracoid or the acromion, the head is displaced upward, are so uncommon that they need merely be mentioned here. The backward (subspinous) luxation is resisted so strongly by the subscapu- laris, and especially by the long head of the triceps, that it also is a surgical rarity. In the subglenoid and subcoracoid varieties (Figs. 565, 566) it will be found : i. That the normal curve of the shoulder is replaced by a straight line, because of (a} the absence of the head of the bone and the tuberosities beneath the deltoid ; (^) the stretching of that muscle. 2. For the same reasons it will be found that (a) a ruler applied to the outer side of the arm will touch both the acromion and the external condyle at the same time (Hamilton) ; and (<) the edge of the acromion is unnaturally prominent, while beneath it is a palpable depression instead of the nor- mal resistance of the tuberosities. 3. The elbow is abducted because of the tension of the deltoid. 4. The forearm is flexed on account of the tension of the biceps. 5. The vertical measurement of the axilla is increased (Callaway), because of (a) the presence of the head or upper por- tion of the shaft in the line of meas- urement ; and () the lowering of the axillary folds (Bryant), the insertions of the pectoralis major and latissimus dorsi being, of course, carried down- ward with the humerus. 6. The elbow cannot be made to touch the chest-wall while the hand is placed on the oppo- site shoulder (Dugas), because the head of the bone is held in contact with that wall by the tense muscles and overlying structures, and its lower extremity the other end of a straight, inflexible axis cannot be made at the same time to touch at a second point the curve represented by the wall of the thorax. 7. There is rigidity because of the ten- sion or spasm of the muscles moving the humerus, especially of the sub- scapularis, the deltoid, the supra- and infraspinatus, the biceps, and the coraco- brachialis. 8. In the subcoracoid luxa- tion the prominence of the head may be felt beneath the coracoid or outer third of the clavicle where it lies, the anatom- ical neck resting on the anterior border of the glenoid cavity. There is a little real lengthening, i.e. , the distance between the glenoid surface and the lower end of the humerus must be increased, but this may be converted into apparent short- ening by abduction, which approximates the tip of the acromion and the external condyle. 9. In the subglenoid variety the head may be felt low in the axilla, the anterior wall of which is widened. It rests on the upper part of the outer border of the scapula just below the glenoid cavity. Lengthening is apt to be marked, and, when the arm is adducted somewhat, may exceed an inch. The stretching and ' ' hollow tension' ' of the deltoid and, therefore, the abduction of the arm are marked. 10. There is usually (a) pain from direct pressure upon or from stretch- ing of the brachial plexus, and frequently (6) cedema from similar involvement of the axillary vessels. In all luxations, but especially in the subglenoid and subspinous, the circumflex nerve is apt to be injured ; hence obstinate paresis or paralysis of the deltoid is a not infrequent sequel. In all methods of reduction of shoulder luxations the humerus is used as a lever, and in all it is desirable to secure fixation of the scapula by means of (a) the V. ,,- ' Superficial dissection of preceding subcoracoid luxation, showing muscles after removal of skin and fasciae. HUMAN ANATOMY. Clavicle Coracoid process Long head of biceps Supraspinatus Infraspinatus Teres minor Deltoid weight of the trunk in the supine and recumbent position ; () pressure on the acromion and clavicle ; (c) the use of a folded sheet placed high in the axilla, so that it presses upon the axillary border in front and the dorsum posteriorly when the two ends are carried across the body and made taut ; or (d ) by dragging on the opposite arm, "which, by making tense the trapezius of the opposite side, pro- vokes contraction of the muscle on the injured side" (Makins). The use of the heel or foot in the axilla as a fulcrum while manual extension is made the long arm of the lever, the shaft of the humerus, being carried inward so as to move the short arm, the head, outward requires no anatomical explanation. Kocher's method (applicable especially to subcoracoid luxation) is more com- plex in its mode of action. There is some difference of opinion as to its exact mechanism, but it is safe to say that in its various stages it acts approximately as follows, i. The elbow is flexed, relaxing the biceps, and the arm is pressed closely to the side, making tense the untorn posterior portion of the capsule extending between the posterior lip of the glenoid fossa and the under and back part of the neck of the humerus. This FIG. 568. portion of the capsule and the tendons of the posterior scapu- lar muscles are drawn tightly across the glenoid fossa. 2. The arm is rotated outward until the forearm is parallel with the transverse axis of the body, the hand pointing di- rectly outward. This rolls the head of the bone outward on the tense portion of the cap- sule, which is partly wound, as it were, upon the neck, and at the same time relaxes the scapular tendons and removes them from the fossa. 3. The elbow is raised until the arm is parallel with the antero- posterior axis of the body. This relaxes the anterior fibres of the deltoid, the coraco- brachialis, and the upper por- tion of the capsule, and perhaps widens the space between the margins of the rent, although no obstacle to reduction is usu- ally met with there. The lower portion of the capsule is still tense. 4. Rotation inward on this portion as a fulcrum now moves the articular face of the head towards the comparatively free glenoid cavity and relaxes the subscapularis ; as the elbow is then lowered in adduction the lower capsular segment relaxes and the head re-enters through the rent by which it originally emerged. These details can be worked out satisfactorily in i-xprrinu'iital luxations on the cadaver, and have apparently been demonstrated as to the main points by Faraboeuf, Helferich, and others. Recurrent or "habitual dislocation" i.e., dislocation occurring from trifling causes, such as abduction of the arm may be a remote result of the rupture or for- cible separation of the tendons of the supra- and infraspinatus muscles from the cap- sule of the joint, with rupture of the capsule at its upper portion, and the formation of a free communication between the joint-cavity and that of the subcoracoid bursa (Jossel, quoted by Stimson). It is, however, usually due to the injury to the capsule and to the weakness of the shoglder muscles resulting from the original accident. linrs(c. The large subacromial bursa and the subdeltoid bursa have been de- scribed in relation to their possible enlargements (page 279). The subscapular bursa Pectoral is major (cut) Deeper dissection of preceding subcoracoid luxation, showing displacement of head of humerus and muscles involved. THE BRACHIAL MUSCLES. 585 and the bursa beneath the infraspinatus often communicate with the shoulder-joint, and disease of the latter may spread to them. An infraserratus bursa has been described (Terrillon), situated between the infe- rior scapular angle and the chest-wall. Its enlargement gives rise to friction-like crepitation or creaking, which has been mistaken for fracture of ribs or scapula or for an arthritis of the shoulder. Nancrede says that this symptom is due to (a) an exosto.sis on the ribs or scapula which has caused such atrophy of the subscapular and serratus magnus muscles as to allow the two bony surfaces to come in contact ; or (<) a localized projection of the ribs due, for example, to a post-pleuritic con- traction of the chest, and with the same muscular atrophy ; or (c ) a primary atrophy of the muscles, as in ankylosis of the scapulo-humeral joint, which will admit of the normal scapula and ribs becoming apposed. This latter condition especially causes increased movements of the scapula over the thoracic wall and favors the development of this bursa. THE BRACHIAL MUSCLES. PRE-AXIAL. 1. Biceps 2. Brachialis anticus. POST-AXIAL. 1 . Triceps. 2. Anconeus. Cephalic vein Biceps Skin The brachial group includes those muscles which act primarily upon the fore- arm and form the muscular substance of the arm. Some of them, however, take origin in whole or in part from the pectoral girdle and thus have some effect on the movements which occur about the shoulder-joint, although their principal action is upon the forearm. The Brachial Fascia. The deep layer of the fascia of the arm forms a com- plete investment of the muscles of the brachial region. Above it passes over into the thin fascia covering the deltoid muscle, and me- - ... . FlG - 5 6 9- dially it becomes continu- ous with the axillary fascia, while below it is continuous with the fascia of the fore- arm, adhering firmly to the periosteum covering the subcutaneous portions of the humerus and the ole- cranon process, and being reinforced by tendinous prolongations from the bi- ceps and triceps muscles. From its lateral and medial surfaces it sends sheet-like prolongations in- ward to be attached to the humerus. These sheets, termed the intermuscular septa, are of considerable strength and give attach- ment to adjacent muscles. They pass to the humerus between the lateral and medial borders of the triceps and the remaining muscles of the arm, and it is to be noted that, while the medial or inner septum marks the boundary between the pre-axial and post-axial muscles, this is not the case with the lateral or external septum. In the lower part of their extent the septa are attached to the supra- condylar ridges of the humerus and terminate at the condyles, a number of post-axial muscles of the forearm arising from the outer condyle anterior to the external septum. A number of subcutaneous bursse occur between the integument and the bra- chial fascia in those regions in which the fascia is adherent to the subjacent perios- teum covering so-called subcutaneous portions of the skeleton. Thus there is a Superficial fascia^ Deep fascia Musculo- spiral nerve Brachio- radialis External intermuscular septum Humerus Musculo- cutaneous nerve Brachialis anticus Brachial vessels Median nerve Basilic vein i Internal 1 intermuscular septum Dinar nerve Triceps, inner head Triceps, outer head / ^~~~- -'"' Triceps, middle head . Tendon of triceps Section across right arm in lower third. 5 86 HUMAN ANATOMY. bursa acromialis over the acromion process of the scapula, a bursa olecrani over the olecranon process of the ulna, and a bursa may occur over each condyle of the humerus. (a) THE PRE-AXIAL MUSCLES, i. BICEPS (Figs. 560, 570). Attachments. The biceps (m. biceps brachii), as its name indicates,- takes origin by two heads. The long head arises from the upper border of the glenoid cavity of the scapula by a slender round tendon, which traverses the cavity of the shoulder-joint invested by the synovium and then bends downward into the bicipital groove (intertubercular sulcus) of the humerus, accompanied by a prolongation of the joint capsule (vagina mucosa intertubercularis), and then, becoming muscular, unites with the short head, which arises from the tip of the coracoid process of the scapula in common with the coraco-brachialis. By the union of the two heads a strong muscle is formed which descends in front of the humerus and a short distance above the elbow-joint passes over into a flat tendon, which is continued downward to be inserted into the tuberosity of the radius, a mucous bursa (bursa bicipitoradialis) being interposed between the anterior surface of the tuberosity and the tendon. Some of the fibres of the muscle, instead of passing into the tendon, are continued into a flat tendinous expansion, the semilunar or bicipital fascia (lacertus fibrosus), which passes downward and medially to become lost in the fascia of the forearm. Nerve-Supply. By the musculo-cutaneous nerve from the fifth and sixth cervical nerves. Action. To flex the forearm on the brachium, and when the forearm is in pro- nation to supinate it. It will also act to a slight extent in movements of the arm at the shoulder-joint, assisting the coraco-brachialis in drawing the arm forward. Relations. The biceps is crossed on its ventral surface by the tendon of the pectoralis major and is covered above by the lateral portion of the deltoid. Deeply it is in relation with the humerus, the brachialis anticus, and the supinator. Upon its inner side lie the coraco-brachialis above and below, in the groove between it and the triceps (sulcus bicipitalis medialis), the brachial vessels, and the median nerve. Variations. The biceps presents numerous variations. Its long head is occasionally want- ing, but more frequently additional heads occur. Of these the most frequent, occurring in some- thing over 10 per cent, of cases, is a head which arises from the medial surface of the humerus, between the insertions of the deltoid and coraco-brachialis. Other heads may arise from the external tuberosity of the humerus or from the outer border of that bone, between the deltoid and brachio-radial muscles. 2. BRACHIALIS ANTICUS (Fig. 571). Attachments. The brachialis anticus (m. brachialis) occupies the anterior sur- face of the lower part of the humerus and is for the most part covered by the biceps. It arises from the intermuscular septa and the anterior surface of the humerus imme- diately below the insertion of the deltoid, which it partly surrounds. It passes downward, and the fibres converge to a short tendon which is inserted into the anterior surface of the coronoid process of the ulna. Nerve-Supply. The main mass of the muscle is supplied by branches from the musculo-cutaneous nerve. The fibres which arise from the lateral intermuscular septum and are covered by the brachio-radialis are supplied by a branch from the musculo-spiral nerve. The nerve-fibres come in both cases from the fifth and sixth cervical nerves. Action. To flex the forearm. Variations. The nerve-supply shows the brachialis anticus to be a composite muscle the major portion of which is derived from the pre-axial muscle-sheet, while the lateral portion of it conies from the post-axial sheet. In correspondence with this derivation of the muscle, its lateral portion is occasionally separate from the rest and may terminate below on the fascia of the forearm or on the radius. A longitudinal separation of ilk- pre-axial portion of the muscle may also occur, and it seems probable that the most frequently occurring third head of the biceps (see above i is a derivative of this portion of the brachialis. The epitrochteo-anconM$i&a small, usually quadrangular muscle which is present in about 25 per cent, of cases. It arises from the posterior surface of the inner condyle of the humerus THE BRACHIAL MUSCLES. 587 and passes downward and laterally to be inserted into the external surface of the olecranon process of the ulna. Notwithstanding its position upon the posterior surface of the arm, it is a FIG. 570. Clavicle 7 Subclavius Biceps Tendon of in- sertion of pec- toralis major Coraco- brachialis Tendon of latissimus * Pectoralis minor FIG. 571. Brachialis anticus Inner head of triceps Int. intermuscular septum .. , , Brachialis anticus J radius Bicipital tuberosity of radius Insertion of biceps Brachialis anticus Tendon of insertion of biceps Brachio-radialis Supinator Bicipital fascia Coronoid pro- cess of ulna Muscles of anterior surface of arm. Brachialis anticus and supinator, seen from in front. derivative of the pre-axial muscle-sheet and is supplied by the ulnar nerve, whose main stem, as it passes down between the olecranon and the inner condyle, is covered by the muscle. When absent, the muscle is represented by a strong fibrous band. HUMAN ANATOMY. (6) THE POST-AXIAL MUSCLES, i. TRICEPS (Figs. 570, 572). Attachments. The triceps (m. triceps brachii) is a strong muscle which occu- pies the entire dorsal surface of the arm. It arises by three heads. The scapular or FIG. 572. Supraspinatus Spine of scapula Infraspinatus Infraspinatus, cut edge Teres minor (cut) Inferior angle of scapula Teres major. Serratus magnus Acromion process Head of humerus covered by capsular ligament Tendon of insertion of teres minor Axillary border of scapula Pectoralis major Triceps, long head Triceps Latissimus dorsi long head takes its origin by a tendon from the infra- glenoid tuberosity of the scapula ; the inner or medial head, from the posterior (dorsal) surface of the humerus and from both intermuscular septa below and medial to the groove for the musculo-spiral nerve ; and the outer or lateral head, from the external intermuscular septum and the posterior surface of the humerus above and lateral to the groove for the musculo-spiral nerve. The three heads unite to form a strong, broad tendon which is inserted into the olecranon process of the ulna. The common tendon of insertion tfegins as a broad aponeurosis upon the anterior surface of the long head, the fibres of which are attached to the upper border and the upper part of the posterior sur- face of the aponeurosis. The fibres of the lateral head are attached to the lateral border of the aponeurosis, while those of the medial head, which is much stronger than the lateral one, pass to its anterior surface. Nerve-Supply. By the musculo-spiral nerve fn.m the- sixth, seventh, and eighth cervical nerves. Action. To extend the forearm on the upper arm and to draw the entire arm backward. Tricep postt rioi M apular m clt-s ; portions (it infraspinatus and teres minor cut :i\\a> . Variations. The triceps occasionally possesses an additional head arising either from the coracoid process of the scapula or from the capsule of the shoulder-joint. PRACTICAL CONSIDERATIONS : MUSCLES AND FASCIA. 589 2. ANCONEUS (Fig. 581). Attachments. The anconeus is a short muscle which arises from the posterior surface of the external condyle of the humerus. Its fibres diverge to form a triangu- lar sheet which is inserted into the upper part of the posterior surface of the ulna and into the outer surface of the olecranon process. Nerve-Supply. By the musculo-spiral nerve from the seventh and eighth cervical nerves. Action. To assist the triceps in extending the arm. PRACTICAL CONSIDERATIONS: MUSCLES AND FASCIA OF THE ARM. The deep fascia of the arm, continuous above with that over the deltoid and with the clavi-pectoral fascia, closely embraces all the muscular structures and resists the outward passage of subfascial collections of blood or pus, which therefore, under the influence of gravity, tend for a time to follow the intermuscular spaces downward. OZdema and swelling above the elbow are thus not uncommon as a result of disease or injury at a higher level. Blood or pus may reach the surface by following the structures that pierce the fascia, viz., the basilic vein and the internal and external cutaneous nerves. The ecchymosis after fracture sometimes takes this course. The intermuscular septa (page 585) divide the space enclosed by the brachial aponeurosis into an anterior and a posterior compartment extending from the level of the deltoid and coraco-brachialis insertions to that of the two condyles. They, too, have some effect in limiting effusions, but the latter, especially if due to infection, can readily pass from one space to the other by following the musculo-spiral nerve or the superior profunda artery through the outer septum, or the ulnar nerve, inferior profunda artery, or anastomotica magna through the inner septum. In selecting a method of amputation through the arm it should be remembered that above the middle most of the muscles that it would be necessary to divide are free to retract, i.e., the deltoid, the long head of the triceps, the coraco-brachialis, and the biceps. Below the middle the biceps is the only muscle unattached. In the former situation, therefore, the circular method is apt to lead to a "conical stump' ' from the too free retraction of the flaps and from the activity of the upper humeral epiphysis (page 272). In amputation just above the elbow the circular method is applicable, but the incision should be a little lower at the antero-internal aspect of the limb to allow for the greater retraction in the bicipital region. Inward dislocation of the tendon of the long head of the biceps muscle has probably occurred from direct violence as an uncomplicated lesion in a few cases. The symptoms are said to be (White) : (a) the recognition of the bicipital groove empty ; () inward rotation due to the pressure of the tendon on the lesser tuberosity and on the tendon of the subscapularis ; (c~) adduction of the humeral head, leaving a slight depression beneath the tip of the acromion ; (d) obvious tension along the inner edge of the biceps muscle when the forearm is extended ; (al bone. Nerve-Supply. Hy the- ulnar nerve from the eighth cervical and first thoracic ner\ < Action. To flex and adduct the hand. THE ANTIBRACHIAL MUSCLES. 595 Relations. By its deep surface this muscle is in relation with the sublimis and profundus digitorum and with the ulnar vessels and nerve. The ulnar nerve and posterior recurrent ulnar artery pass beneath a tendinous band which stretches across between the two heads of the muscle, and towards the wrist the ulnar artery comes to lie along the lateral border of the tendon. A mucous bursa (bursa m. flexoris carpi ulnaris ) is frequently to be found between the tendon and the upper part of the pisiform bone. Variations. The flexor carpi ulnaris frequently passes distally to be inserted into the base of the fifth metacarpal. The conversion of the ulnar head into connective tissue has been observed. 5. FLEXOR SUBLIMIS DIGITORUM (Fig. 577). Attachments. The superficial flexor (m. flexor digitorum sublimis) arises from the inner condyle of the humerus in common with the neighboring superficial mus- cles, from an oblique line on the anterior surface of the radius, and from the tendi- nous arch extending between these two bony points and beneath which the median nerve and ulnar artery pass. The fibres arising from these origins form four bellies, prolonged below into as many tendons, which at the wrist pass beneath the ante- rior annular ligament and then diverge towards the bases of the second, third, fourth, and fifth fingers and enter the corresponding digital sheaths. Here each tendon divides over the surface of the first phalanx into two slips, which pass one on either side of the subjacent tendon of the flexor profundus digitorum and partially unite beneath it to be inserted into the base of the second phalanx. Slight tendinous bands, vincula tendinum, pass between the tendons of the profundus and the terminal portions of those of the sublimis. Nerve-Supply. By the median nerve from the seventh and eighth cervical and first thoracic nerves. Action. Primarily to flex the second phalanx of the four medial digits, but a continuation of its action will flex the first phalanges of the same digits and eventually the hand. Relations. Superficially the flexor sublimis is covered by the remaining muscles of the superficial layer ; deeply it is in relation with the flexor profundus digitorum, the flexor longus pollicis, the ulnar vessels, and the median nerve. Variations. Occasionally the portion of the muscle which gives rise to the tendon of the fifth digit appears to be wanting, the tendon arising from the palmar fascia, the anterior annular ligament, or the flexor profundus. An explanation of this anomaly is found in the developmental history of the muscle. In the lower vertebrates the superficial flexor inserts into the palmar fascia, which gives origin to a set of superficial digital muscles, whose relations are similar to those of the digital portions of the sublimis tendons. In the mammalia these digital muscles de- generate into tendinous bands, with which the tendon of the antibrachial portion of the muscle becomes continuous. The origin of the tendon for the fifth. digit from the palmar aponeurosis or transverse carpal ligament is, therefore, a persistence of a phyletic stage, as is also its origin from the flexor profundus, since in the lower mammals the antibrachial portions of the two muscles are united to form a single mass (page 597). (bb) THE MIDDLE LAYER. :. Flexor profundus digitorum. 2. Flexor longus pollicis. i. FLEXOR PROFUNDUS DIGITORUM (Fig. 578). Attachments. The deep flexor (m. flexor digitorum profundus) arises from the anterior and outer surfaces of the ulna and from the inner half of the interosseous membrane. Its fibres are directed downward, and at about the middle of the fore- arm are continued into four tendons, which pass beneath the anterior annular liga- ment along with the tendons of the flexor sublimis to enter the digital sheaths of the second, third, fourth, and fifth fingers. Opposite the first phalangeal joint each tendon passes between the two slips of the corresponding tendon of the flexor sub- limis and is inserted into the base of the terminal phalanx. Nerve-Supply. The lateral half of the muscle is supplied by branches from the anterior interosseous branch of the median nerve and the medial half by the 596 HUMAN ANATOMY. FIG. 578. Brachialis anticus r^B Supinator Insertion of pronator radii teres i- Flexor longus pollicis- Flexor carpi ulnaris Abductor minimi digit! Anterior annular ligament Pronator quadratus Tendon of flexor carpi radial is Abductor pollicis, cut Opponens pollici Flexor brevis pollicis Adductor pollicis, / * oblique portion ,/> -- , V Adductor pollicis, transverse portion ulnar ; the fibres come from the seventh and eighth cer- vical and the first thoracic nerves. Action. The primary action of the flexor pro- fundus is to flex the ter- minal 'phalanges of the second, third, fourth, and fifth fingers, but, continu- ing its action, it also flexes the remaining phalanges of those digits and finally the hand. Relations. In the arm the muscle is covered by the flexor sublimis digi- torum and the flexor carpi ulnaris, and has resting upon its anterior surface the ulnar vessels and the median and ulnar nerves. Posteriorly it is in relation to the pronator quadratus digitorum j . i T 4.U and the wrist-joint. In the hand its tendons are cov- ered by those of the flexor sublimis and by the lum- brical muscles ; they rest upon the adductor pollicis and interosseous muscles and cross the deep palmar arch. Flexor profundus Opponens minimi digit! exor brevis linimi digiti Lumliri- cales Tendons of flexor suliliniis digitorutn Dissection of muscles of forearm and hand, anit-i ii Miiia,.-; inusi k's liavt- IK-IMI removed. n l'u i.tl Variations. The flexor profundus frequently receives additional slips from the flexor sublimis and may be united to the flexor longus pollicis. A slip which has been termed the accessorius ad Jie. \~orcm profundnni digitornin not in- frequently occurs, arising from the coronoid process of the ulna and joining with one of the tendons of the profundus. The significance of the varia- tions of the profundus will be considered in connection with those of the flexor longus pol- licis. 2. FLEXOR LONGUS POL- LICIS (Fig. 578). Attachments. The long flexor of the thumb ( m. flexor pollicis Ionics ) lies to the lateral side of the flexor profundus disj- torum and arises from tin- anterior surface of the ra- dius and the adjacent hall THE ANTIBRACHIAL MUSCLES. 597 of the interosseous membrane. It usually possesses also an origin by means of a slender slip from the coronoid process of the ulna or the medial epicondyle of the humerus. The muscle-fibres pass into a strong tendon at the middle of the forearm, and this passes downward beneath the lateral part of the annular ligament and extends along the volar surface of the thumb to be inserted into the base of its ter- minal phalanx. Nerve-Supply. By the anterior interosseous nerve from the eighth cervical and first thoracic nerves. Action. To flex the terminal phalanx of the thumb ; continuing its action, it will also flex the proximal phalanx and assist in the flexion of the hand. Relations. In the forearm it is covered by the flexor sublimis digitorum, the flexor carpi radialis, and the brachio-radialis, and has resting upon it the radial ves- sels. Deeply it is in relation with the pronator quadratus and the wrist-joint. In the hand its tendon is covered by the opponens pollicis and the flexor brevis pollicis, and it rests upon the adductor pollicis. Variations. The head from the coronoid process or medial epicondyle of the humerus is sometimes absent and the muscle is frequently connected with the flexor profundus digitorum or even fused with it. Occasionally there arises from the lower part of the anterior and external surfaces of the radius a muscle which has been termed theyfe.ror carpi radialis brevis. Its insertion varies some- what, being sometimes on one of the carpal bones, at other times on either the second, third, or fourth metacarpals, and at others, again, into the transverse carpal ligament. Although asso- ciated by name with the flexor carpi radialis, it is more probably a derivative of the deeper layer of the flexor musculature and is supplied by the volar interosseous branch of the median nerve. The majority of the variations of the flexor longus pollicis and flexor profundus digitorum find an explanation in the historical development of the muscles. In the lowest group of the mammalia, the mpnotremata, the two muscles are fused with each other and also with the flexor sublimis to form a common long flexor, from the tendon of which the tendons of the flexor sublimis arise. In slightly higher forms this common flexor can be seen to be composed of five portions, which, from their points of origin and relations, may be termed the condylo-ulnaris, condylo-raclialis, centralis, ulnaris, and radialis, and as the scale is ascended one finds at first a part of the condylo-ulnaris and later the whole of that portion separating from the common mass and joining the tendons of the sublimis. In still higher forms the centralis and condylo-radialis portions follow the example of the condylo-ulnaris, the flexor sublimis digitorum in man being composed of these portions of the common mass. The ulnaris and radialis portions remain, as a rule, united and, after the separation of the superficial portions is completed, constitute the flexor profundus. In man and a few other forms the radialis separates from the ulnaris to form the flexor longus pollicis. The connections which occur between the sublimis, profundus, and flexor longus pollicis are consequently to be regarded as relics of the historical development of the muscles, as the incomplete separation of a common flexor mass. In the lower terrestrial vertebrata the superficial and deeper layers, corresponding practi- cally to the sublimis and profundus (plus the flexor longus pollicis), are distinct, their fusion in the monotremes being a secondary condition, which forms the starting-point for the differentia- tion of the mammalian arrangement of the muscles. In these lower forms both layers insert into tin.- palmar aponeurosis, the extension of the deeper layer to the digits being due to the separation of the layer of the aponeurosis to which the deeper muscle-layer is attached and its differentiation into tendons. It may be added that in the lower vertebrates the palmaris longus is not represented as a separate muscle, and it is to be regarded as a portion of the superficial sheet which has retained its original relations to the palmar aponeurosis, its occasional absence being ascribed to its sharing the history of the flexor sublimis and being incorporated in that muscle. (rr) THE DEEP LAYER. i. Pronator quadratus. i. PROXATOR QUADRATUS (Fig. 588). Attachments. The pronator quadratus is a flat quadrangular sheet extending across between the lower portions of the radius and ulna. It arises from the volar surface of the ulna and passes laterally and slightly clistally to be inserted into the lateral and anterior surfaces of the lower end of the radius. Nerve-Supply. By the anterior interosseous branch of the median nerve from the seventh and eighth cervical and the first thoracic nerves. Action. To pronate the forearm. 598 HUMAN ANATOMY. Variations. The pronator quadratus usually occupies about the lower fourth of the fore- arm, but it may be considerably reduced or, on the contrary, may extend as high as the middle of the forearm or even higher. It represents the lower portion of a muscle-sheet which extends in some of the lower mammals almost the entire length of the forearm, the upper portion of this sheet being represented, as already pointed out, by the coronoid head of the pronator teres. (6) THE POST-AXIAL MUSCLKS. The post-axial muscles of the forearm may be regarded as consisting of two layers, the more superficial of which arises from the external condyle of the humerus, while the deeper one is attached to the bones of the forearm. As was the case with the pre-axial muscles, constituents of both layers have extended into the hand to act as extensors of the digits. (aa) THE SUPERFICIAL LAYER. 1. Brachio-radialis. 4. Extensor communis digitorum. 2. Extensor carpi radialis longior. 5. Extensor minimi digiti. 3. Extensor carpi radialis brevior. 6. Extensor carpi ulnaris. i. BRACHIO-RADIALIS (Fig. 576). Attachments. The brachio-radialis, sometimes termed the supinator longus> arises from the external condylar ridge of the humerus and from the lateral inter- muscular septum. Its fibres form a strong muscle which, at about the middle of the forearm, passes into a tendon which is inserted into the base of the styloid process of the radius. Nerve-Supply. By the musculo-spiral nerve from the fifth and sixth cervical nerves. Action. To flex the forearm. If the arm be in a position of complete prona- tion, it will produce a slight amount of supination. Relations. In its upper part it is in contact medially with the brachialis anti- cus, a portion of whose lateral border it covers, and with the radial nerve. Below it rests upon the upper portion of the extensor carpi radialis longior, the supinator, the pronator teres, the flexor sublimis digitorum, and the radial artery and nerve. It is crossed near its insertion by the tendons of the abductor longus pollicis and extensor brevis pollicis. Variations. The brachio-radialis is sometimes wanting. It may be inserted a consider- able distance above the base of the styloid process of the radius, a condition characteristic of the lower mammals, or it may pass as far down as the carpal bones or even to the base of tin- third metacarpal. 2. EXTENSOR CARPI RADIALIS LONGIOR (Figs. 576, 579). Attachments. The longer of the radial carpal extensors (ra. extensor carpi radialis longus ) lies immediately posterior to the brachio-radialis. It arises from tin- lower third of the external supracondylar ridge of the humerus, the external inter- muscular septum, and the extensor tendon common to it and the neighboring super- ficial muscles. About the middle of the forearm it is continued into a tendon which passes beneath the posterior annular ligament in the second compartment, along with the extensor carpi radialis brevior, ana is inserted into the base of the second meta- carpal. Nerve-Supply. By the deep division of the musculo-spiral nerve from the sixth and seventh cervical nerves. Action. To extend and slightly abduct the hand. Variations. The extensor carpi radialis longior is occasionally fused with the extensor carpi radialis brevior. It may send tendinous slips to the first and third metacarpals and to the trapezium. 3. KXTKNSOK CARIM RADIALIS BKKVIOK < l ; i-. 579). Attachments. The shorter radial carpal extensor ( in. extensor carpi radialis lux-vis ) is fused with the neighboring superficial extensors where it arises from tin- THE ANTIBRACHIAL MUSCLES. 599 external condyle of the hu- merus, from the adjacent in- termuscular septa, and from the deep fascia of the fore- arm. Its fibres converge at about the middle of the fore- arm into a flat tendon, which passes with the long exten- sor carpi radialis beneath the posterior annular ligament in the second compartment and is inserted into the base of the third metacarpal, a bursa (bursa m. extensoris carpi radialis) being inter- posed between* the tendon and the bone. Nerve-Supply. By the posterior interosseous branch of the musculo-spiral nerve from the sixth and seventh cervical nerves. Action. To extend the hand. Variations. It may be fused to a greater or less extent with the extensor carpi radialis lon- gior and may be inserted into the bases of both the second and third metacarpals. 4. EXTENSOR COMMUNIS DIGITORUM (Fig. 579). Attachments. The common extensor of the fingers (m. extensor digitorum communis) arises in com- mon with the neighboring superficial extensors from the external condyle of the humerus, from the septa be- tween it and the adjoining muscles, and from the deep fascia of the forearm. At about the middle of the forearm its fibres go over into four tendons, which pass through the fourth compart- ment beneath the posterior annular ligament and diverge to be inserted into the bases of the middle and terminal pha- langes of the second, third, fourth, and fifth fingers. Just before they pass over the metacarpo-phalangeal joints of their digits the four ten- dons are usually united by FIG. 579. Anconeus Brachio-radialis External condyle Extensor carpi radialis longior .Extensor carpi radialis brevior Flexor carpi ulnat Extensor carpi ulnaris Extensor communis digitorum Extensor ossis metacarpi pollicis Extensor brevis pollicis Extensor longus pollicis Tendon of extensor carpi radialis longior Tendon of extensor carpi radialis brevior Abductor pollicis First dorsal interosseus Dissection of posterior surface of forearm and hand, showing superficial extensor muscles. 6oo HUMAN ANATOMY. FIG. 580. Olecranon process Anconeus Extensor carpi radialis longior External condyle Flexor carpi ulnaris Extensor ossis metacarpi pollicis Extensor carpi radi- alis brevior tendon Extensor carpi radi- alis longior tendon Dissection of posterior surface of forearm and hand, showing deep IIIUM ll'S. three obliquely transverse ten- dinous bands (juncturae ten- (linum), the one between the index and median digits being, however, frequently wanting. As each tendon passes upon the dorsum of the first phalanx of its digit it spreads out into a membranous expansion, which receives the insertions of the interosseous and lumbrical muscles and then divides into three more or less well-defined slips. The median slip passes to the base of the second pha- lanx, while tne lateral ones, passing over the first interpha- langeal joint, unite over the dorsum of the second phalanx and are inserted into the base of the first phalanx. Nerve-Supply. By the posterior interosseous branch of the musculo-spiral nerve from the sixth, seventh, and eighth cervical nerves. Action. To extend the phalanges of the second, third, fourth, and fifth fingers and, continuing its action, to extend the hand. Variations. The principal variations of the common extensor consist in the absence of one or other of the tendons, usually that to the fifth digit and more rarely that to the second, or else in the occurrence of additional tendons, due to the division of one or more of those typically occurring, cer- tain of the digits then receiving two or even three tendons. Oc- casionally an additional tendon is present which passes to the thumb to unite with the tendon of its long extensor. 5. EXTENSOR MINIMI Pi<;- m (Fig. 579). Attachments. The ex- tensor of the little finger ( in. extensor diijiti quinti proprius ) arises in common with the preceding muscle from the lat- eral epicondyleof tin- humerus and from the antibrachial fas- cia. Its tendon passes beneath the posterior annular ligament in the fifth compartment and fuses over the fifth metacarpal THE ANTIBRACHIAL MUSCLES. 60 1 Brachialis anticus with the tendon of the extensor communis digitorum which passes to the little finger. Nerve-Supply. By the posterior interosseous branch of the musculo-spiral nerve from the sixth, seventh, and eighth nerves. FIG. 581. Action. To extend the lit- tle finger. Variations. This muscle is some- times absent, probably remaining in- corporated in the extensor communis. Its tendon occasionally sends a slip to the fourth finger. 6. EXTENSOR CARPI ULNARIS (Figs. 577, 579). Attachments. The exten- sor carpi ulnaris arises in common with the adjacent superficial ex- tensors from the external condyle of the humerus, from the deep fascia, and, usually, from the apo- neurosis attached to the posterior border of the ulna common to this muscle, the flexor profundus digitorum, and the flexor carpi ul- naris. Its tendon passes through the sixth compartment beneath the posterior annular ligament and is inserted into the base of the fifth metacarpal bone. Nerve-Supply. By the posterior interosseous branch of the musculo-spiral nerve from the sixth, seventh, and eighth cervical nerves. ' ;>, Radius Action. To extend and ad- duct the hand. Variations. A fibrous band is Often given off from the tendon of the Dissection of arm, showing deep muscles , vicinhy of elbow. muscle to be inserted somewhere over the fifth metacarpal into the sheath of the tendon of the extensor of the little finger ; it has been termed the m. ulnaris quinti digiti. (bb) THE DEEP LAYER. 1. Supinator. 3. Extensor brevis pollicis. 2. Extensor ossis metacarpi pollicis. 4. Extensor longus pollicis. 5. Extensor indicis. i. SUPINATOR (Figs. 580, 581). Attachments. The supinator, also termed the supinator radii brevis, is a flat triangular muscle which arises partly from the outer condyle of the humerus and the orbicular ligament of the elbow-joint, and partly from the upper part of the lateral border of the ulna and the smooth surface beneath the lesser sigmoicl cavity of that bone. Its fibres pass obliquely downward and outward, diverging as they go, and are inserted into the posterior, lateral, and anterior surfaces of the radius, curving around that bone. The insertion extends downward to about the middle of the radius. Head of radius Supinator 6O2 HUMAN ANATOMY. Nerve-Supply. By the posterior interosseous branch of the musculo-spiral nerve from the sixth cervical nerve. Action. To supinate the forearm. Variations. The posterior interosseous nerve perforates the supinator and occasionally marks the line of separation of the muscle into two portions, which correspond to the epicon- dylar and ulnar portions of the muscle. The muscle is indeed a composite one, a portion of it being derived from the superficial extensor layer and the rest of it from the deep layer. 2. EXTENSOR Ossis METACARPI POLLICIS (Fig. 580). Attachments. The extensor of the metacarpal bone of the thumb (m. abduc- tor pollicis longus) arises from the middle third of the posterior surfaces of the ulna, the interosseous membrane, and FIG. 582. the radius. It passes down- ward and laterally, and its ten- don passes through the first compartment beneath the pos- terior annular ligament to be inserted into the outer side of the base of the first metacarpal bone. Nerve-Supply. By the posterior interosseous branch of the musculo-spiral nerve from the sixth, seventh, and eighth cervical nerves. Action. To abduct and slightly extend the thumb and, continuing its action, to abduct the hand. Relations. It is covered by the muscles of the superficial layer and is crossed obliquely by the dorsal interosseous artery. Below it crosses obliquely the tendons of the extensores carpi radiales and the radial artery. Variations. It may be par- tially or wholly fused with the ex- tensorbrevis pollicis. Occasionally it possesses two tendons, one of which may be inserted into the dor- sal carpal ligament, the abductor brevis pollicis, or the trapezium. -Brachio-radialis Flexor sublitnis digitorum Radial artery Extensor ossis jnetacarpi pollicis .Kxtensor brevis pollicis ^ Extensor carpi radialis longior sor longus pollicis arpi radialis brevior al artery First dorsal interosseus Radialis indicis artery Superficial dissection of hand, virwcd from radial side, showing extensor tendons of thumb. 3. EXTENSOR BREVIS POLLI- CIS (Fig. 580). Attachments. The short extensor of the thumb (m. exten- sor pollicis brevis), also termed the extensor print! internodii pollicis, lies along the medial border of the extensor ossis metacarpi pollicis. It arises from the interosseous membrane and the pos- terior surface of the radius, partly under cover of the extensor longus pollicis, and its tendon, after passing with that <>f the abductor through the first compartment of the posterior annular ligament, is inserted into the base of the first phalanx of the thumb. Nerve-Supply. By the posterior interosseous branch of the musculo-spiral ncrvr from the sixth, seventh, and eighth cervical nerves. Action. -To abduct the thumb and extend its first phalanx. PRACTICAL CONSIDERATIONS : THE FOREARM. 603 Relations. The relations of the muscle are essentially the same as those of the extensor ossis metacarpi pollicis. Variations. The extensor brevis and the metacarpal extensor of the thumb are differen- tiations of a common muscle and show indications of this in their partial or complete fusion. The tendon of the extensor brevis is sometimes continued onward to the terminal phalanx of the thumb or may send a slip to the base of the second metacarpal. 4. EXTENSOR LONGUS POLLICIS (Fig. 580). Attachments. The long extensor of the thumb (m. extensor pollicis longus), also known as the extensor sccundi internodii pollicis, is an elongated fusiform mus- cle lying along the medial border of the extensor brevis pollicis, which it partly covers. It arises from the interosseous membrane and posterior surface of the ulna ; its tendon passes downward in the third compartment beneath the posterior annular ligament and, crossing over the tendons of the extensores carpi radiales, is inserted into the base of the terminal phalanx of the thumb. Nerve-Supply. By the posterior interosseous branch of the musculo-spiral nerve from the sixth, seventh, and eighth cervical nerves. Action. To extend the terminal phalanx of the thumb and, continuing its action, to extend and at the same time slightly adduct the thumb. 5. EXTENSOR INDICIS (Fig. 580). Attachments. The extensor of the index-finger (m. extensor indicis proprius) lies along the medial border of the extensor longus pollicis. It arises from the in- terosseous membrane and the dorsal surface of the ulna. Its tendon passes, along with the tendons of the extensor communis digitorum, through the fourth compart- ment beneath the posterior annular ligament, and eventually is inserted with the tendon of the common extensor which passes to the index-finger. Nerve-Supply. By the posterior interosseous branch of the musculo-spiral nerve from the seventh and eighth cervical nerves. Action. To extend the index-finger. Variations. The extensor indicis may be wanting, or its tendon may send slips to the third and fourth digits. Occasionally a muscle arises from the ulna, below the origin of the ex- tensor indicis, and passes to the third or fourth finger, forming what has been termed the extensor digiti niedii (vel annularis} pro firms. This muscle represents an additional portion of the deep extensor layer which normally disappears. PRACTICAL CONSIDERATIONS : THE FOREARM. The fascia descending from the arm to the forearm should be studied anteriorly with relation to the expansion known as the bicipital aponeurosis (Fig. 570), one of the " two inferior tendons of the biceps" of the older anatomists, which becomes continuous with the deep fascia of the forearm, and thus, through the origin from its under surface of fibres of many of the superficial muscles of that region, associates their action with that of the biceps itself. Partly for this reason injuries and diseases affecting the bicipital region are sometimes associated with a certain weakness of grasp and feebleness of wrist flexion. The facts that only this aponeurotic expansion separates the median basilic vein from the brachial artery, and that in persons of poor muscular development it is often so thin as scarcely to constitute a recognizable layer, were of practical importance when phlebotomy of the median basilic was fre- quent. Arterio-venous aneurism from accidental puncture of the artery was then quite common. Posteriorly the outer aponeurotic expansion of the triceps, running over the anconeus to become continuous with the deep fascia of the forearm, is of importance in its relation to the power of extension of the forearm after excision of the elbow (page 308). The fascia of the forearm, besides giving origin to many fibres of the subjacent muscles, as lias been noted above, envelops the forearm completely, being continu- 604 HUMAN ANATOMY. Flexor longus pollicis Median nerve IJlnar artery Flexor sublimis Ulnar nerve kin ous at the wrist with the anterior and posterior annular ligaments. The septa which run in from it to be attached to the sides of the ulna and radius divide the forearm, with the aid of the interosseous membrane, into two musculo-aponeurotic spaces, an antero-external and a posterior (Fig. 583). The former contains numerous muscles and the main vessels and nerves, the latter is almost entirely muscular. The interpenetration of these main septa and of the intermuscular fascia by nervo-vascular structures renders them of slight importance in limiting the spread of infectious disease or of collections of blood or pus. But in the not infrequent cases of incised wounds severing the muscles and tendons of this region it may systematixe the search for and reunion of the divided structures if the somewhat artificial topog- raphy, as described by Tillaux, is borne in mind. The antero-external compart- ment is thus regarded as including four spaces. i. That between the skin and the first muscular layer, the palmaris, flexor carpi ulnaris, pronator radii teres, etc., and containing the internal cutaneous and musculo-cutaneous nerves, the perforating branches of the radial and ulnar nerves, the superficial veins, and sometimes the ulnar artery when there is a high bifurcation of the brachial. 2. That between the first muscular layer and the flexor sublimis, with the brachio-radialis and short supinator externally. This contains FIG. 583. the radial nerve, artery, and veins. 3. That be- tween the flexor sublimis and the flexor profundus and flexor longus pollicis. This contains the median nerve and the ulnar nerve and vessels. 4. That be- tween the last-named mus- cles and the interosseous membrane, containing the anterior interosseous ves- sels and the interosseous nerve. In the posterior com- partment are to be found, in addition to the exten- sors and the anconeus, only the posterior inter- osseous vessels and nerve (Fig. 5X3). Fractures of the neck of the radius (between the head and the tuberosity) are very rare, as it is covered and protected from direct violence by the long and short supinators and the long and short radial extensors. Angular displacement forward is thought to be caused by the action of the biceps on the upper end of the lower fragment. The upper frag- ment is rotated outward by the supinator brevis. Fracture of the' radius below its tubercle and above the insertion of the pronator radii teres (a little above the middle of the outer side of the bone) is followed by supination and flexion of the upper frag- ment by the biceps and supinator brevis. The lower fragment is pronated and drawn towards the ulna by the pronators. It is well to treat cases of this fracture with the forearm in mode-rate supinatio so as to approximate the fragments and preserve the axis of the bone and the tutu use-fulness of the supinators. In fracture of the radius below the insertion of the pronator radii teres the upper fragment is flexed by the biceps, so that its lower end can sometimes !>, seen and felt on the front of the forearm just above the middle, and is sometimes pronated by the pronator radii teres ; the lower fragment is drawn towards the ulna by the pronator quadratus, aided by the action of the brachio-radialis on the styloid process (Fig,5A). In the usual position in which such fractures are treated, the flexion of the elbow Palmaris longus Flexor carpi radialis Pronator radii teres Radial artery Radial nerve Extensor carpi rad. long. Radius Extenso carpi rad. brev. Supinator Extensor cotnmunis I'ust. inteross. vessels and nerve Interosseous membrane \ \ Extensor carpi ulnaris Extensor ossis metacarpi pollicis Extensor longus pollicis Section across middle of right forearm. I PRACTICAL CONSIDERATIONS : THE FOREARM. 605 and the mid-position between pronation and stipulation sufficiently relax the biceps and the pronator radii teres. The weight of the hand in adduction overcomes the pull of FIG. 584. FIG. 585. the brachio-radialis and pronator quadratus. Fracture of both bones, from either direct or indirect violence, usually takes place below the middle of the fore- arm, as there the muscular masses which protect the upper half of the radius from direct violence have largely been replaced by tendons, the ulna is slender and weak, and the opposing forces rep- resented by the biceps and brachialis anticus above and the weight or force applied through the hand expend themselves. Thus Malgaigne (quoted by Agnew) reports a case in which both bones were broken by muscular action alone while the patient was carrying weight in the form of a shovelful of dirt. When the resulting deform- ity is due chiefly to the con- traction of muscles, it is apt to consist in flexion of both upper fragments by the bi- ceps and brachialis anticus, supination of the upper frag- ment of the radius by the biceps and supinator brevis, and approximation of the two lower fragments by the pronator quadratus. Much overlapping and shortening are usually prevented by the untorn fibres of the interosseous membrane. During the period of repair the mid-position between pronation and supination preserves the parallelism of the two bones, maintains the interosseous space at almost its greatest FIG. 586. width, relaxes (in conjunction with the flexion of the elbow) the muscles involved so far as is possible, and by the weight of the hand dropping to the ulnar side over- comes the resist- ance of others, espe- cially of the brachio- radialis. The large pro- portion of the re- turn current of blood that is carried by the superficial veins of the forearm makes it especially impor- tant that the splints used should be so broad that the bandage does not unduly com- Dissection of fracture of radius between the two pronator muscles. Dissection of fracture of ole- cranon process of left ulna ; joint opened from behind. Ext. carpi radialis long. Ext. carpi radialis brev. Lower end of fragment Brachio-radialis Ext. longus pollicis Radial artery Flexor tendons Lower fragment Ext. brevis and ext. ossis met. poll., cut and turned forward Dissection of Colles's fracture of radius, showing relation of tendons and radial artery. 6o6 HUMAN ANATOMY. press the soft tissues ; while the ease with which both veins and arteries may be obstructed at the bend of the elbow should lead to careful avoidance of pressure in that region from the upper end of the palmar splint. The preservation of the interosseous space is favored by the omission of the primary roller bandage and by the avoidance of direct pressure upon the soft parts by the bandage used to retain the splints. THE MUSCLES OF THE HAND. The Deep Fascia of the Hand. The deep fascia of the palmar surface of the hand is usually regarded as being represented by the pa/mar aponeurosis, a firm sheet of connective tissue which occupies the palm of the hand and lies imme- FIG. 587. Thenar eminence covered with lateral portion oi palmar fascia Hypothenar eminence ^ = ~ Palmar fascia, central portion Palmar fascia, lateral portion =- Digital nerves - Superficial transverse ligament Digital arteries Superficial dissection of hand, showing palmar fascia. diately beneath the skin. This structure represents, however, the superficial layer of a thick aponeurosis which occurs in the lower vertebrates, receiving the insertion of the antibrachial flexors and giving origin to the digital flexors. From the proxi- mal portion of this aponeurosis there is formed, however, the anterior annular liga- ment, and this may be considered as a portion of the palmar aponcurosis. The latter (Fig. 587), often called the palmar fascia, is a fan-shaped sheet whose apex is directed proximally, receiving the insertion of the palmaris longusand being to a certain extent continuous with the anterior annular ligament. It reaches THE MUSCLES OF THE HAND. 607 its greatest breadth over the distal portions of the metacarpals, and is continued onward as four more or less distinct bands, which are inserted into the integument at the bases of the second, third, fourth, and fifth fingers. A little below the lower edge of the aponeurosis transverse bands of fascia (fasciculi transversi) stretch across between the same fingers, lying immediately beneath the skin and being connected to a greater or less extent with one another. These bands constitute the superficial transverse metacarpal ligament beneath the webs of the fingers. The anterior annular ligament (ligamentura carpi transversum) (Fig. 578) is a strong band w r hich stretches across from the trapezium and scaphoid bones of the carpus on the radial side to the pisiform and unciform bones on the ulnar side, forming a bridge across the groove on the anterior surface of the carpus which trans- mits the tendons of the long flexors and of the flexor carpi radialis and the median nerve. The canal so formed is divided by a partition into a small radial compart- ment through which the flexor carpi radialis passes, and a large ulnar one which gives passage to the other structures mentioned. The tendons are enclosed within synovial sacs which extend downward to about the middle of the palm and upward to a short distance above the upper edge of the ligament. The sac which surrounds the flexor longus pollicis is usually separate from that which surrounds the remaining tendons of the ulnar compartment ; occasionally the portion surrounding the tendons of the index-finger is also separate. Towards either side of the palmar surface of the hand the palmar fascia forms a thin covering for thenar and hypothenar eminences formed by the superficial muscles of the thumb and the little finger respectively. Upon the dorsal surface the fascia is thin, and is continued downward from the lower border of the posterior annular ligament over the extensor tendons to the fingers, where it unites with the aponeu- roses of the tendons. (a) THE PRE- AXIAL MUSCLES. The pre-axial muscles of the hand are to be regarded, from the comparative stand-point, as being arranged in five layers. Although these layers become con- fused to a certain extent in the human hand, it will, nevertheless, aid in the proper understanding of their relations to group them according to the primary layers from which they are derived. (aa) THE MUSCLES OF THE FIRST LAYER. 1. Palmaris brevis. 4. Flexor brevis pollicis. 2. Abductor pollicis. 5. Abductor minimi digiti. 3. Opponens pollicis. 6. Opponens minimi digiti. 7. Flexor brevis minimi digiti. The most superficial layer of the palmar muscles in the lower vertebrates takes its origin from the palmar aponeurosis. The greater portion of the layer, as has already been pointed out, becomes converted in the mammalia into the palmar por- tions of the tendons of the flexor sublimis digitorum, and it is only towards either margin of the hand that it persists as muscles, which show indications of their primary relations in their origin from the palmar aponeurosis or the anterior annular ligament. i. PALMARIS BREVIS (Fig. 576). Attachments. The palmaris brevis is a thin quadrangular sheet which lies immediately beneath the skin of the hypothenar eminence. It arises from the proximal portion of the ulnar border of the palmar aponeurosis and is inserted into the skin of the ulnar border of the hand. Nerve-Supply. By the superficial division of the ulnar nerve from the first thoracic nerve. Action. To wrinkle the skin upon the ulnar border of the hand, deepening the hollow of the hand. Variations. The muscle may be greatly reduced in size and is occasionally wanting. 608 HUMAN ANATOMY. 2. ABDUCTOR POLLICIS (Fig. 577). Attachments. The abductor of the thumb (m. abductor pollicis brevis) is the most superficial muscle of the thenar eminence. It arises from the anterior annular ligament and from the scaphoid bone or the trapezium and passes distally to be in- serted along with the flexor brevis pollicis into the radial side of the base ot the first phalanx of the thumb and into the sheath of the tendon of the extensor longus pollicis. Nerve-Supply. By the median nerve from the sixth and seventh cervical nerves. Action. To flex and abduct the thumb. Variations. The portion of the muscle arising from the carpus is sometimes separate from that taking origin from the transverse carpal ligament. Slips are occasionally sent to the abduc- tor from the extensores carpi radiales, the extensor ossis metacarpi pollicis, the opponens pol- licis, and the flexor brevis pollicis. 3. OPPONENS POLLICIS (Figs. 578, 588). Attachments. The opponens pollicis is almost completely covered by the abductor pollicis. It arises from the anterior annular ligament and from the trape- zium, and is inserted into the whole length of the radial border of the first metacarpal. Nerve-Supply. By the median nerve from the sixth and seventh cervical nerves. Action. To flex and adduct the thumb, opposing it to the other fingers. 4. FLEXOR BREVIS POLLICIS (Figs. 578, 588). Attachments. The flexor brevis pollicis lies along the lower (ulnar) border of the opponens pollicis. It arises from the lower border of the anterior annular ligament and is inserted, along with the abductor pollicis, into the radial side of the base of the first phalanx of the thumb. The muscle above described is usually regarded by English anatomists as representing t In- cuter or radial head of the flexor brevis, a second inner or ulnar head being included as part of that muscle. Concerning the inner head three views are held : (a) no inner head is recognized, the small slip arising from the ulnar side of the base of the first metacarpal bone and passing downward to be inserted with the adductor pollicis into the base of the first phalanx, which by many English anatomists is regarded as a small inner head of the flexor brevis, being described as an additional (first) palmar interosseus (page 612) ; (6) the small slip just noted is the iniu-r or ulnar head of the flexor brevis ; (r) the small slip and all the fibres described as forming tin- adductor obliquus (page 610) are regarded as the inner head of the flexor brevis. The first view, adopted by German anatomists, is here followed. Nerve-Supply. By the median nerve from the sixth and seventh cervical nerves. Action. To flex the first phalanx of the thumb. Variations. The muscle is sometimes intimately connected with the abductor pollicis and opponens pollicis. 5. ABDUCTOR MINIMI DIGITI (Fig. 577). Attachments. The abductor of the little finger (m. abductor di^iti quinti) occupies the ulnar border of the hand. It arises from the anterior annular ligament and from the pisiform bone and is inserted into the ulnar side of the base of the- fust phalanx of the little finger. Nerve-Supply. By the deep division of the ulnar nerve from the eighth cer- vical and first thoracic nerves. Action. To abduct the fifth finger. 6. OPPONENS MINIMI DIGITI (Fig. 578). Attachments. This muscle (m. opponens digiti quinti ) is almost completely covered by the abductor and short flexor of the little finger. It arises from the anterior annular ligament and the uncinate process of the unciform bone and is in- serted into the whole of the ulnar border of the fifth metacarpal bone. THE MUSCLES OF THE HAND. 609 Nerve-Supply. By the deep division of the ulnar nerve from the eighth cer- vical and first thoracic nerves. Action. To flex and at the same time adduct the fifth metacarpal. 7. FLEXOR BREVIS MIXIMI DIGITI (Figs. 577, 578;. Attachments. The short flexor of the little ringer (m. tlexor brevis diiti quinti) lies along the lateral (radial) border of the abductor minimi digiti. It arises FIG. 588. Radius Anterior interosseous artery _' Cut edge of anterior annular ligament Opponens pollicis Abductor pollicis Flexor brevis pollicis l-'irsi palmar interosseus __ Flexor longus pollicis tendon -Ulna I'ronator quadratus Flexor carpi ulnaris tendon Cut edge of anterior annular ligament I'isilorm Ixmr Adductor pollicis, oblique portion Third palmar interosseus Fourth palmar inU-nisseus _ Fourth dorsal interosseus Deep dissection of wrist and hand, showing pronator quadratus and short muscles of thumb. from the anterior annular ligament and the uncinate process of the uncinate bone and is inserted into the ulnar side of the base of the first phalanx of the little finger. Nerve-Supply. By the de,ep division of the ulnar nerve from the eighth cer- vical and first thoracic nerves. Action. To flex and slightly abduct the first phalanx of the little finger. Variations. The flexor brevis and opponens minimi digiti are often united by muscle- bundles and may even be completely fused. 39 6io HUMAN ANATOMY. (bb) THE MUSCLES OF THE SECOND LAYER. In the lower vertebrates the second layer also arises from the palmar aponeu- rosis, but from its deeper layers. These, as has been stated (page 597), differentiate into the palmar portions of the tendons of the flexor profundus digitorum, and in the mammalia the muscles retain their primary origin and arise from those tendons forming the lumbrical muscles. I. LUMBRICALES (Fig. 578). Attachments. The lumbricals are four slender, band-like muscles, situated in the palm of the hand. Counting from the radial side of the hand, the first and second lumbricals arise from the radial side of the flexor profundus tendons to the index and middle fingers respectively, while the third one arises from the adjacent sides of the tendons to the middle and ring fingers, and the fourth from those of the tendons to the ring and little fingers. The muscles pass distally into slender tendons which are continued to the radial side of the first phalanges of the second, third, fourth, and fifth fingers, and are inserted into the membranous expansions of the tendons of the extensor communis digitorum to those fingers. Nerve-Supply. The first and second lumbricals are supplied by the median nerve from the sixth and seventh cervical nerves ; the third and fourth by the deep division of the ulnar nerve from the eighth cervical and first thoracic nerves. Action. To flex the first phalanges of the second, third, fourth, and fifth fingers. At the same time, by their traction upon the extensor tendons, they will tend to keep the second and third phalanges extended. Variations. Variations in the arrangement of the lumbricals, and especially of the third and fourth, are not uncommon. The tendon of each of these muscles may bifurcate and be in- serted iato the adjacent sides of the third and fourth or fourth and fifth fingers, and more rarely the sole insertions may be into the ulnar sides of the first phalanges of the middle and ring fingers. The third lumbrical is frequently supplied wholly or in part from the median nerve. (cc) THE MUSCLE OF THE THIRD LAYER. In the lower vertebrates the third layer consists of muscles which arise from the carpal and metacarpal bones and pass to each of the digits. In the mammalia they become greatly reduced in number, frequently persisting, however, in connection with the thumb, index, and little fingers, but in man they are represented only by an adductor pollicis. i. ADDUCTOR POLLICIS (Figs. 578, 588). Attachments. The adductor pollicis is a flat triangular muscle which rests upon the metacarpal bones and the interosseous muscles. It may be regarded as consisting of two portions. The portio obliqua (often described as a distinct muscle, the adductor obliquus pollicis} arises from the trapezium, trapezoid, and os magnum and from the bases of the second and third metacarpals. Its fibres are directed dis- tally and radially, and are inserted by a tendon, in which a sesamoid bone is usually developed, into the ulnar side of the base of the first phalanx of the thumb. It also sends off a slip which passes beneath the tendon of the flexor longus pollicis to be inserted into the radial side of the base of the first phalanx of the thumb along with the flexor brevis pollicis. The portio transvcrsa (often described as the adductor transversus poll ids \ arises from the lower two-thirds of the volar surface of the third metacarpal, and its fibres pass almost directly radially to be inserted into the ulnar side of the base of the first phalanx of the thumb. Nerve-Supply. By the deep division of the ulnar nerve from the eighth cervical and first thoracic nerves. Action. To adduct the thumb. Relations. The adductor pollicis is covered by the tendons of the flexor profundus digitorum for the second and third fingers and by the first and second lumbricals. It conceals the interosseous muscles of the two radial intermetacarpal intervals and also the radial artery and the arteria princcps pollicis. The deep palmar arch passes between the two portions of the muscle, near their origins. THE MUSCLES OF THE HAND. 611 Flexor carpi radialis tendon Tuberosity of scaphoid .Flexor carpi ulnaris tendon Pisiform bone _Unciform process of unciform (dd) THE MUSCLES OF THE FOURTH AND FIFTH LAYERS. i. Interossei volares. 2. Interossei dorsales. In the lower vertebrates the musculature of the fourth palmar layer consists of a pair of muscles for each digit, arising from the carpal and metacarpal bones and inserting into either side of the base of the first phalanx. The fifth layer lies dorsal to these, and consists of four muscular bands, which extend slightly obliquely across the four inter- metacarpal spaces. FIG. 589. In the mammalia a shifting of the in- sertion of one of the muscles of the pairs belonging to the first and fifth digits takes place, so that they are attached to the radial and ulnar sides re- spectively of the ad- jacent second and fourth digits, uniting with the correspond- ing members of the pairs belonging to those digits. With the compound mus- cles so formed the first and fourth inter- metacarpal muscles unite to form the first and fourth dorsal in- terossei, these two muscles being com- posed, accordingly, by the fusion of three primary muscles. The second and third intermetacarpal muscles unite with the radial and ulnar mem- bers respectively of the pair belonging to the third digit, and form with these the second and third dor- sal interossei. The remaining members of the pairs belonging to the first, second, fourth, and \J \ .. Deep dissection of hand, showing interosseous muscles as seen in palm. fifth digits persist as independent muscles, forming what are termed the volar interossei, whose arrange- ment is consequently complementary to that of the dorsal interossei. The intermetacarpal muscles occupy the most dorsal position of all the palmar muscles, and it is probably owing to their participation in the formation of the dorsal interossei that these possess an almost dorsal position in the hand. They are clearly, however, of palmar origin and are supplied by pre-axial nerves. 612 HUMAN ANATOMY. i. INTEROSSEI VOLARES (Fig. 589). Attachments. The volar or palmar interossei are four slender muscles situated in the intervals between the metacarpal bones and resting upon the in- terossei dorsales. Thejirst and second muscles, counting from the radial side, arise from the ulnar side of the bases of the first and second metacarpals, and are inserted into the ulnar side of the base of the first phalanx and, in the case of the second muscle, also into the membranous expansion of the long extensor tendon of the FIG. 590. Extensor carpi ulnaris tendon Extensor carpi radialis longior tendon Extensor carpi radialis brevior tendon Extensor longus pollicis tendon Second dorsal interosseus Third dorsal interosseus Fourth dorsal interosseus Extensor communis digitorum tendons Dissection of hack of hand, showing dorsal interossei and insertion of extensorteiuluiis. corresponding digit. The third m& fourth muscles arise from the radial side of the fourth and fifth metacarpals, and are inserted similarly to the second muscle, but into the radial sides of the fourth and fifth digits. Only three palmar interossei are usually described by Kn-lish anatomists, the muscle in- cluded in the series by tin- ( ierman school as the first interosseus ( ;//. interosseus f>i -hints volaris} being regarded as the small ulnar head of the flexor hrevis pollicis (page 608). The inclusion of this muscle in the series of palmar interossei is warranted by its morphological relations. Nerve-Supply. By the deep division of the ulnar nerve from the eighth cervical and first thoracic nerves. Action. To draw the first, second, fourth, and fifth digits towards the middle finger and to flex the first phalanx of the same digits. PRACTICAL CONSIDERATIONS : WRIST AND HAND. 613 Variations. The first volar interosseus is the most slender of the series and is covered by the oblique portion of the adductor pollicis, with which it may be practically incorporated. ( )ccasionally it is so reduced in si/e as to appear to be wanting. 2. INTEROSSEI DORSALES (Fig. 590). Attachments. The dorsal interossei are also four in number and lie in the intervals 'between the metacarpal bones, dorsal to the volar interossei. Each is a bipinnate muscle arising from the adjacent surfaces of the metacarpals which bound the interspace in which the muscle lies. The first and second muscles, counting from the radial side, are inserted into the radial side of the base of the rirst phalanx and into the membranous expansion of the extensor tendons of the second and third fingers, while the third and fourth are inserted similarly into the radial sides of the third and fourth fingers. Nerve-Supply. By the deep division of the ulnar nerve from the eighth cervical and first thoracic nerves. Action. The first and fourth muscles draw the second and fourth fingers away from the third, while the second and third draw the third finger radially or ulnarly, as the case may be. All the muscles flex the first phalanx of the digits to which they are attached. Variations. Occasionally the second dorsal interosseus is inserted into the base of the first phalanx of the index-finger, upon its ulnar side. (*) THE POST-AXIAL MUSCLE. Normally no post-axial muscles exist in the human hand. Occasionally, however, an ex- tensor brevis digitomtn uianus is more or less perfectly developed. It arises from the dorsum of the carpus, or sometimes from the lower end of the radius and ulna, and passes distally into a varying number of tendons. Most frequently the muscle is small and gives rise to but a single tendon, which joins with the tendon of the extensor digitorum communis of either the second or third digit. Sometimes two tendons occur, passing to the second and third digits, and more rarely three have been observed, passing to the second, third, and fourth fingers. In a -single case a fourth tendon was observed which terminated upon the dorsal surface of the fifth metacarpal. PRACTICAL CONSIDERATIONS. The Wrist and Hand. The skin of the wrist and of the back of the hand is thin and freely movable and contains numerous hair-follicles and sebaceous glands. These structures are absent in the palm and on the palmar and lateral surfaces of the fingers, as well as on the dorsal surface of the terminal phalanges. Sudoriparous glands are, on the contrary, relatively more numerous in the palms of the hands than on any other part of the body surface. These anatomical conditions and the existence of the subungual and periungual spaces and irregularities render the sterilization of the hands for surgical purposes very difficult. The absence of hair-follicles and of sebaceous glands explains the freedom of the palm from the superficial furuncular infections that are so common on the dorsum. In the palm the subcutaneous connective tissue, like that in the plantar region and in the scalp between the skin and aponeurosis, is very dense. This similarity has already been alluded to (page 491) in relation to the absence of hair-follicles in the Uvo former regions and the frequency of baldness in the latter. On the dorsal surface the subcutaneous tissue is loose. As a result, in whitlow, in palmar abscess, in hemorrhagic extravasation, in oedema or cellulitis, the swelling is apt to be much more marked on the dorsum and may be misleading as to the real seat of the trouble. Abscesses immediately beneath the palmar fascia will sometimes point in a metacarpal space on the dorsum. The thickness and close adhesion of the skin to the dense fascia beneath, while admirably protecting the vessels and nerves of the palm and enabling it to withstand pressure and friction, greatly increase the pain in cutaneous or subcutaneous infections. On account of this same adhesion, superficial wounds of the palm do not gape, and heal readily if non-infected and kept at rest. 614 HUMAN ANATOMY. Ext. carp, ulnarls Posterior annular ligamen Ext. min. digiti Ext. communis et indicis Extens. carp. rad. long, et brev. r Ext. brevis pollicis Ext. ossis etacarpi pollicis Ext. Ipngus pollicis " It must be noted that the front of the hand, and especially the palm, is singu- larly free from surface veins. Indeed, the great bulk of the blood from the hand is returned by the superficial veins on the dorsum of the fingers and hand" (Treves). The annular ligaments at the wrist are of importance in their relation to the tendons and their sheaths. The tendon-sheaths (Fig. 591) which pass through the six compartments in or under the posterior ligament behave as follows. . i. That for the short extensors and the extensor of the metacarpal bone of the thumb runs from the joint between the first metacarpal and the trapezium to a point almost an inch above the styloid process of the radius. 2. That for the long and short radial extensors of the carpus runs FIG. 591. from the insertions of those muscles to a point a half inch above the ligament. 3. That for the extensor longus pol- licis runs from the insertion to the upper border of the ligament. 4. That for the extensor indicis extends from the upper border of the met- acarpus, and that for the ex- tensor communis from the middle of the metacarpus, both to the upper border of the ligament. 5. That for the extensor minimi digiti runs from the middle of the metacarpus ; and 6, that for the ulnar extensor of the car- pus from the insertion, both to the upper border of the ligament. Infective disease of the dorsum of the wrist and hand is rare as compared with the palmar surface. The dense connective-tissue fibres of the palm run vertically down- ward to the palmar fascia and tendon-sheaths, and thus convey infection directly to the deeper parts. This layer is often described as the su- perficial palmar fascia. The subcutaneous connective-tis- sue fibres on the dorsum run horizontally, and infective in- flammation is therefore more likely to remain superficial (Warren). If, however, it does penetrate and gains access to the tendon-sheaths, the natural anatomical limitations are those indicated above. Teno-synovitis from strain, from gout, or from rheumatism is especially frequent in these sheaths, on account of their exposure to wet and cold, and also because the muscles connected with them are relatively weak and are less often used than those on the palmar surface of the forearm. They are thus more liable to strain from unaccustomed exertion. (ianglion of the simple- (non-tuberculous) variety is also frequent here, pronably lor the same reasons. \ Dissection ot dorsum of hand, showing artifi extensor tendons. ially distended sheaths of PRACTICAL CONSIDERATIONS : WRIST AND HAND. Bursa surrounding ten-, don of flexor longus pollicis One of the most common and most serious of the sequelae of fracture of the lower end of the radius is stiffness of the wrist and fingers from adhesions of these extensor tendons and their sheaths to the bone, to each other, and to the surrounding structures. It is important to remember, as Treves has pointed out, that ' ' the tendons do not lie free within the sac, but are bound to it by folds of synovial membrane in much the same way as the bowel is bound to the abdominal parietes by its mesen- tery (Fig. 492). These folds may be ruptured in severe sprains, when the nutrient vessels for the tendon, which are contained in them, may be torn. Rupture is fol- lowed by effusion into the sac. These folds are almost absent within the digital sheaths, the slight ligamenta longa and brevia, near FIG. 592. the insertion of the tendons, being the sole representatives. Sy- novial sacs are lined by endothelium, and have extremely free com- munication with the lymphatic vessels of the part. Hence the free absorption of in- fective matter from such cavities. ' ' The arrangement of the synovial sheaths beneath the anterior annular ligament is of great practical im- portance (Fig. 592). There are two sacs, one for the tendons of the superficial and the deep flexors ; one for the long flexor of the thumb. They extend upward to about two finger-breadths above the annular ligament. Downward, that for the thumb extends to the insertion of the tendon in the terminal phalanx ; the divertic- ula for the index, mid- dle, and ring fingers end about the mid- die of the metacarpal 4-U 4- 4.U 1'j. Dissection of palmar surface bones ; that for the lit- tie finger accompanies the tendon of the deep flexor to its insertion in the last phalanx. The synovial sheaths for the digital portions of the flexors for the index, middle, and ring fingers extend upward only to about the necks of the corresponding metacarpal bones. They are thus separated by an interval of from half an inch to an inch from the synovial sac, extending up under the annular ligament to the forearm (Fig. 592). It results from this that infections (felons, wounds, etc. ) of the thumb or little finger are especially apt to extend upward above the wrist and involve the forearm. Compound ganglion (tuberculous teno-synovitis) frequently affects the common svnovial sac of the flexor tendons and not infrequently that of the longus pollicis. Digital sheath: of long flexor tendons Anterior annu- lar ligament (cut) -Palmar bursa sur- rounding long flexor tendons Prolongation into tendon sheath of lit- tle finger right hand, showing artificially distended sheaths of flexor tendons. 616 HUMAN ANATOMY. The two sacs occasionally communicate with each other. On account of the density of the annular ligament, the distention has a central constriction and expansions in the palm and above the wrist, " hour-glass shape." These tendons also are often involved in fractures of the lower end of the radius, although, on account of the fact that the extensors are in closer relation to that bone than is the deep flexor, and that the other flexors excepting the longus pollicis are still farther separated from it, limitation of their motion is neither so frequent nor so marked. In the palm of the hand the thenar and hypothenar eminences are covered in by their fasciae, which separate them from the central space of the palm through which the flexor tendons run, and over which is spread the fan-shaped, deep palmar fascia, beginning at the tendon of the palmaris longus above, and spreading out to be divided below into the slips for the fingers (Fig. 587). Transverse fibres unite and strengthen these slips, which send fibres also to the sheaths of the flexor tendons and to the skin. It may be noted here that progressive muscular atrophy usually begins in the hand muscles, affecting first those of the thenar, then those of the hypothenar emi- nence, and next the interossei. When the latter are greatly wasted the hand assumes the appearance of a bird's claw, the main en griff e (Duchenne). Dupuytreri s contraction affects chiefly the digital prolongations of the palmar fascia, although it extends secondarily to the bundles of fibres uniting the skin and the aponeurosis. It begins usually as a dense thickening of the fascia near the line of the metajcarpo-phalangeal articulation. It extends in both directions, the concomitant shortening slowly drawing down first the disfal and then the intermediate phalanx. The skin becomes closely adherent to the contracted fascia. The condition is seen oftenest in hands subjected to frequent slight tcaumatism, as in laborers, or in those of gouty or rheumatic persons past middle age. Beneath the flexor tendons, and above the interossei, the metacarpal bones, and the radial arch, lies another layer of fascia (interosseous) which resists but feebly the passage of pus towards the dorsum of the hand. It is connected with the thenar and hypothenar fasciae. Several varieties of palmar abscess have been described (Tillaux)- in accord- ance with the original site of the infection, the spread of which will be determined by the above-mentioned anatomical considerations, (a) Infection just beneath the thick- epidermis causes a superficial pustule or abscess (subepidermic) which, if promptly and freely opened, gives rise to no difficulty. () Infection beneath the skin (subdermic) is attended by more pain, and, if neglected, may penetrate the aponeurosis ; but it is separated by that structure from the synovial sheaths and cavities ; it may be widely opened with no reference to the latter or to vessels ; it is accompanied by little or no swelling on the dorsum ; it has. no tendency to extend up to the wrist ; movements of the fingers are not very painful, (r) Subdermic infec- tion beginning in the spaces just above the interdigital clefts (i.e., between the digital slips of the palmar fascia) may extend by continuity of connective tissue very rapidly to the dorsum of the hand, which may then appear to be the x chief seat of the infection ; the symptoms are relatively mild, as the toxic exudate is not under great pressure. (d) Subaponeurotic infection true palmar abscess is excessively painful, extends rapidly to the dorsum by perforating the interosseous fascia, and often to the front of the wrist and forearm by following up the flexor tendons ; move- ments of the fingers are painful ; the dorso-palmar diameter of the hand is vastly increased ; the constitutional symptoms are often marked. Such abscess may also point just above the interdigital webs or near the ulnar or radial borders of the hand. Early incision is imperative and, if made over the line of a metacarpal bone and limited in an upward direction by a transverse line correspond- ing to that of the web of the fully extended thumb (to avoid the digital vessels and palmar arches), may be made freely. Above the wrist the region of safety is just to the ulnar side of the palmaris longus. i On the fingers the skin resembles in its characteristics that of the hand. On the palmar surface of the first and second phalanges the -skin and the subcutaneous fat are connected with the dense fibrous sheath of the flexor tendons by vertical connective- tissue fibres, and at the level of the joints where the sheaths are lax and thinner PRACTICAL CONSIDERATIONS : WRIST AND HAND. 617 Head of metacarpal bone Abductor poll Flexor. brevis poll. Tendon of flex, longus poll. Adductor poll., obi. portion Dissection of metacarpo-phalangeal dislocation of thumb. by vessels which penetrate the sheath to supply the tendons. Over the last phalanx the fibro-fatty subcutaneous layer the ' ' pulp' ' of the finger lies directly upon the periosteum. Infection of the dorsum of a finger often originates near or about the root of a nail (onychia) and may involve the matrix of the latter. It is not under much pressure, and is therefore not usually serious, although through the FIG. 593. veins and lymphatics it may exceptionally extend rapidly up the arm. Infection of the palmar surface of a finger (panaritium, paronychia, whitlow, felon) is of two chief varieties : (a) subcutaneous, in which the symptoms are at first limited to the seat of infection and are superficial, although, as it is a true cellulitis, they may ex- tend to the dorsum or towards the palm ; and (b) thecal, with more severe pairi, greater lim- itation of flexion, and more rapid extension upward. If the felon involves the distal portion of the finger, the close relation of the "pulp" and the periosteum of the last phalanx makes necrosis of that bone frequent, although its upper part usually escapes because (a') it is an epiphysis ; (<) the insertion of the tendon of the deep flexor probably keeps up its blood-supply (Treves). The absence of the tendon-sheath over the body and tip of the last phalanx pre- vents the conversion of the subcutaneous into the thecal variety, unless the infection, extends upward as far as the base of the phalanx. Elsewhere the thecal variety often results from extension from a subcutaneous focvis by the vertical connective-tissue fibres and the vessels already mentioned. The interphalangeal joints are often affected because it is opposite them that (a) the tendon-sheaths are thinnest and FIG. 594. (() the vessels enter. In infection of the tendon-sheaths of the index, middle, and ring fingers the upward extension is arrested, at .least for a time, about opposite the necks of the metacarpal bones. If the thumb or little finger is involved, the infection is likely to spread to a higher level (page 615). The so-called ' ' subcuticular' ' felon is a superficial pustule, while the " subperiosteal" felon may either result from extension of the foregoing varieties or may be origi- nally an infective osteo-periostitis or osteo-myelitis. In relation to amputation of the finger it may be noted that the insertion of the flexor sublimis tendon into the sides of the second phalanx renders amputation at the metacarpo-phalangeal joint often more satisfactory in its results than one done through the first phalanx or first interphalangeal joint. Dislocation of the first phalanx of the thumb upon the dorsum of its metacarpal bone requires special mention on account of the difficulty of reduction. It has been Dissection showing position of bones in dislocation of thumb 618 HUMAN ANATOMY. attributed (a) to the gripping of the neck of the metacarpal bone between the flexor brevis pollicis and the oblique portion of the adductor pollicis (these often being considered as the two heads of the flexor brevis pollicis) ; (b) to a similar entanglement of the head and neck in the slit in the capsule ; (c) to the winding of the tendon of the flexor longus pollicis around the neck of the bone ; and (d) to the interposition of the gleno-sesamoid plate. Of these theories the last two seem to offer the most satisfactory explanation of the difficulties met with in attempts at replacement. The Surface Landmarks of the Upper Extremity. The axilla (page 574) is very distinctly bounded anteriorly by the lower border of the pectoralis major, which runs in the line of the fifth rib from the sixth costal cartilage to the external bicipital ridge ; posteriorly by the lower edge of the latissiums dorsi and teres major, extend- ing to the bicipital groove. The shape of the axillary fossa varies with the position of the arm, becoming deeper when the arm is raised at a right angle to the trunk or when the great pectoral and latissimus are contracted. With the arm still farther elevated, the depth of the space decreases as traction on those muscles approximates the axillary borders and the humeral head enters and partly obliterates the cavity. With the arm close to the thorax, the third rib may be reached by the exploring finger. The concavity of the space is lessened or effaced by glandular tumors, effu- sions of blood, or collections of pus (page '582). In opening an axillary abscess it should be remembered that the inner or thoracic wall is the direction of safety so far as the great vessels are concerned. In the region of the shoulder the rounded surface is produced by the thick deltoid muscle spread over the greater tuberosity of the humerus. It is fuller anteri- orly than posteriorly, partly on account of the presence of the lesser tuberosity in the former position, but chiefly because the hinder portion of the muscle is thinner than the fore part and because of its close attachment to the infraspinatus fascia and muscle. The greatest width of the shoulders does not correspond to the points at which the deltoid muscles overlap the head of the humerus, but is at the level of the lower border of the anterior axillary fold, i.e. , on the level of the point at which the various bundles of deltoid fibres are gathered together to pass to their insertion (Thomson). The bony points in this region have been described (pages 270, 279, 280). The anterior border of the deltoid presents a rounded eminence bounded internally above by the infraclavicular fossa (vide infra} and below by the closely applied outer margin of the pectoralis major. In the shallow groove between these two muscles the cephalic vein and a branch of the acromio-thoracic artery are to be found. Just external to the groove under the inner fibres of the deltoid is the cora- coid process (page 255). The infraclavicular fossa is the triangular interval'bounded by the outer fibres of the pectoralis major internally, the inner fibres of the deltoid externally, and the clavicle above. The surface depression known by this name may be much larger than this intermuscular interval, and may almost correspond in extent to the roof of the superficial infraclavicular triangle (page 581). It is not very marked in muscular subjects. It is effaced owing to tension of fascia and muscles in sub- coracoid luxation of the humerus, or in fracture of the clavicle with marked displace- ment of the fragments. It may be converted into a rounded elevation by glandular growths extending upward from the axilla, or by the head of the humenis in intra- coracoid (infraclavicular) luxation. At the bottom of this fossa, just within the cora- coid process, i.e., not far from the middle of the clavicle, the first portion of the axillary artery may be compressed against the second rib by pressure directed back- ward and a little inward, the patient being supine. The posterior border of the deltoid above is tendinous, is closely attached tc the infraspinatus muscle beneath it, and is scarcely discernible. Below it is thick* and presents a well-marked rounded eminence which inclines from behind forward t< meet the anterior border at the middle of the outer side of the arm, where a distinct depression indicates the insertion of the deltoid (Fig. 595). This depression is a valu- able practical landmark for the reasons that : ( i ) It corresponds to the middle of the shaft of the hunicnis, where tin- two curves of the bone unite and where the cylin- drical joins the prismatic part of the shaft, which is there smallest, hardest, and least elastic (page 272), and hence is most frequently broken. ( 2) It indicates the region PRACTICAL CONSIDERATIONS : SURFACE LANDMARKS. 619 of insertion of the deltoid and coraco-brachialis, and embraces part of the origin of the brachialis anticus and internal head of the triceps, and is therefore, and on account of the intimate attachment of the periosteum (page 272), a not uncommon seat-of exostoses. (3) The region is by reason of the close relation of these mus- cles to the bone a frequent seat of ununited fracture (page 273). (4) The nutrient artery enters the bone and the superior profunda artery and musculo-spiral nerve wind around its posterior surface at that level, at which also the lesser internal cuta- neous nerve and the basilic vein penetrate the deep fascia, the median nerve crosses the brachial artery, and the ulnar nerve leaves it. On the outer surface of the arm below the insertion of the deltoid can be seen the shallow furrow (Fig. 596) between the outer head of the triceps and the brachio- radialis which indicates the position of the external intermuscular septum and of the external supracondyloid ridge (page 273) . On the posterior surface of the arm the three heads of the triceps can be seen when the forearm is strongly extended (Fig. 596). The outer head makes a distinct prominence just beneath the posterior border of the deltoid ; the inner head is less distinct ; the long head conies into view where it descends from between the two teres muscles, and lower in the arm where it has become tendinous is indi- cated by a broad, shallow depression ending at the olecranon. The long and outer heads cover the musculo-spiral nerve and superior profunda artery from just beneath the posterior axillary fold to the point where they perforate the external septum. On the anterior and inner surfaces of the arm the rounded swell of the biceps and the external and internal bicipital furrows are the most important landmarks. FIG. 595. Deltoid U Tendon of palmaris longus Transverse furrows Brachial Triceps, long artery and inner heads Pectoralis major Antero-median surface of right arm, showing modelling on living subject. The elevation of the biceps shades off superiorly into the narrower and less distinct prominence of the coraco-brachialis where it comes into view below and beneath the anterior axillary fold. Inferiorly it narrows externally and merges into the biceps tendon, easily seen passing into the forearm in the deep interval between the rounded supinator and extensor mass on the radial side and the pronator and flexor mass on the ulnar side (Fig. 595). Internally the broader flat slip of bicipital fascia the inner tendon may be seen with its sharp upper edge when the forearm is semi- flexed and the biceps is in strong action. The outer bicipital furrow indicates the posi- tion of the subcutaneous cephalic vein. The inner and deeper furrow marks the line of the basilic vein (subcutaneous in its lower half, then subfascial), of the median nerve and the brachial vessels, and in its upper half of the ulnar nerve. To the outer side of the outer furrow from above downward lie the deltoid, the outer head of the triceps, the outer portion of the brachialis anticus and the brachio-radialis, and the common extensor mass (Fig. 596). To the inner side of the inner furrow are seen the coraco-brachialis, the long head and then the inner head of the triceps, the brachialis anticus, and the pronato-flexor mass. At the bend of the elbow anteriorly the subcutaneous veins are often visible. Their arrangement is sufficiently described and figured elsewhere (page 892, Fig. 764). The bicipital fascia passes between the median basilic vein and brachial artery, and, by springing from the inner edge of the biceps tendon, makes that edge 620 HUMAN ANATOMY. less distinct to both sight and touch than the outer edge. Just within the inner edge is the brachial artery and farther in the median nerve. The fold of the elbow is a transverse crease in the skin, seen in flexion, convex downward, and running from the tip of one condyle to the tip of the other. lulies above the line of the elbow-joint. In dislocation of the radius and ulna backward the lower end of the humerus is below this crease ; in fracture of the humerus above the condyles the lower end of the upper fragment is either on a line with or above the crease. This relation will not be demonstrable in the presence of much swelling, as this fold is then obliterated. On the front of the forearm, below the apex of the triangular space resulting from the convergence of the two muscular masses descending from the condylar regions, there are no salient surface landmarks, and none of great practical importance until the wrist is reached. Many of those of that region and of the hand have been de- scribed (pages 228, 229, 230, 320). It should, however, be noted that, instead of being flattened from before backward and widest from side to side as when in the supine position, the forearm when the hand is pronated becomes rounded and its antero-posterior slightly exceeds its lateral thickness (Thomson). This is due to the fact that the tendons of the supinator and extensor masses are held in grooves in the lower end of the radius by the posterior annular ligament, and are thus car- ried towards the ulna when the radius moves in that direction. Outer head of triceps FIG. 596. Brachialis anticus External bicipital furrow Brachio-raclialis Common extensor Anconeus Extensors of thumb Extensor longus pollicis Olecranon Ulna Internal condyle Posterior surface of arm shown in preceding figure. Ulnar styloid process Of the two transverse furrows on the flexor surface of the wrist the lower is the more marked. It is almost three-quarters of an inch below the summit of the upward curve of the wrist-joint, is on the line of the intercarpal joint and of the upper border of the anterior annular ligament, and is about a half-inch above the carpo-metacarpal joint. 'At the wrist the palmaris tendon when present is made prominent by extending the digits, slightly flexing the wrist, and closely approximating the thenar and hypothenar eminences. To its radial side from within outward lie the. median nerve, the tendon of the flexor carpi radialis, and the radial artery. To its ulnar side lie first the rounded elevation made by the flexor sublimis tendons, then the ulnar artery, and then the flexor carpi ulnaris tendon, made easily palpable, although not very prominent, by strong flexion of the wrist and little linger. On the postero-lateral aspect of the forearm may be seen : 1. The elevation of the anconeus, triangular in shape, to the radial side of tin- posterior subcutaneous surface of the olecranon and separated from tin- common extensor mass by a well-defined depression. This muscle and the expansion of the triceps tendon that covers it are of great value in the movement of extension of the forearm after excision of the elbow. 2. The curved border of the ulna (subcutaneous in stipulation), at the bottom of the- it I iiar ft/ >>(>;>', between the flexor carpi ulnaris and the common extensor group, is easily accessible for examination through its whole length (page 289). 3. The very important depression just below the external condyle and exter- nal to the olecranon has been described (page 296). PRACTICAL CONSIDERATIONS : SURFACE LANDMARKS. 621 4. The oblique elevation beginning at the lower third of the forearm in the interval left by the divergence of the supinator and the common extensor muscles, and running do\vmvard and outward, to be lost on the posterior surface of the thumb, represents the extensors of the thumb crossing over the tendons of the extensores carpi radialis longior and brevior to their points of insertion (Fig. 582). 5. The bony points to be seen and felt at the elbow and wrist have been de- scribed in their practical relations in connection with the bones and joints (pages 287, 296, 308, 320, 330). The tendon most easily identified on the dorsum of the wrist is that of the extensor longus pollicis when the thumb is strongly extended and abducted. It is the posterior or inner boundary of the hollow at the base of the thumb ( vide infra), and its groove in the lower end of the radius is about the middle of the posterior surface and just to the ulnar side of the prominent middle thecal tubercle, a useful landmark (page 296). The tendon, just before it reaches the radius, corresponds approximately to the scapho-semilunar joint. The surface markings of the palm of the hand are often valuable landmarks. The most important are : (i) The triangle called the " hollow of the hand," the " cup of the palm," etc., the base of which corresponds to the three elevations oppo- site the interdigital clefts, formed by protrusion of fat between the flexor tendons and the digital slips of the palmar fascia and by the distal extremities of the lumbri- cales, and seen best when the metacarpo-phalangeal joints are extended and the interphalangeal joints are flexed. The sides of the triangle are formed by the thenar and hypothenar eminences. Over this palmar hollow the intimate connection of the skin and fascia is of practical importance (page 613). (2) The chief cutaneous creases (Fig. 597) are four in number : (a) from just above the apex of the palmar triangle to the radial side of the hand above the base of the index-finger ; (b) from the lower end of a to a point a little above the middle of the ulnar border of the palm, which it does not quite reach ; (_c) from about the junction of the lower fourth with the upper three-fourths of the ulnar border of the palm to a point a little above the cleft between the index and middle fingers; (d) from b tor, often extending upward towards the wrist and downward towards the base of the middle finger. a and d are longitudinal, the former being caused by adduction of the first meta- carpal, the latter by adduction of the fifth metacarpal bone, both movements being towards the mid-line of the hand ; b and c are transverse, and are produced chiefly by flexion (6) of the first and second (r) of the three inner metacarpo-phalangeal joints. a represents the inner border of the thenar eminence and therefore, approxi- mately, of the outer group of the short muscles of the thumb and the inner margin of the fascia intervening between them and the palmar space through which run the flexor tendons. It intersects the deep palmar arch at about the highest point where it crosses the metacarpal bone of the middle finger. b, at the centre of the palm, where it is intersected by d, crosses the same metacarpal bone a line or two below, i.e. , nearer the fingers than the superficial palmar arch, which runs about on a curved line from the lower border of the thumb, when it is at right angles to the hand, to the pisiform bone. The deep palmar arch is from a quarter to a half an inch nearer the wrist. c represents the upper limits of the synovial sheaths of the flexor tendons of the index, middle, and ring fingers, is a little above the division of the palmar fascia into the digital slips and the bifurcation of the digital arteries, crosses the necks of the three inner metacarpal bones, and is as much above the corresponding meta- carpo-phalangeal joints as they are above the webs of the fingers. d, at its upper portion, irregularly outlines the outer border of the hypoth- enar eminence, i.e., of the short muscles of the little finger and of the fascia sepa- rating them from the central space of the palm, but it is the most irregular and unimportant of these creases. The transverse folds on the palmar surfaces of the fingers correspond, the highest to the web of the fingers, i.e. , from one-half to three- quarters of an inch below the metacarpo-phalangeal joint, the middle to the proxi- mal interphalangeal joint, and the lowest to a line a little above the distal interpha- langeal joint. On .the thumb the line of the radial side of the index-finger, if continued upward, almost coincides with the higher of the creases, which crosses the 622 HUMAN ANATOMY. metacarpo-phalangeal joint obliquely. The lower crease corresponds to the inter- phalangeal joint. The papillary ridges of the skin covering the terminal phalanges assume varied curves and form patterns, immutable and characteristic in the indi- vidual, impressions of which have been used of late years for purposes of identifica- tion of criminals. On the dorsum of the hand the hollow at the base of the thumb (the so-called "snuff-box") is bounded externally ( radially ) by the tendon of the extensor of the FIG. 597. VI Surface markings of rijfht palm. metacarpal bone of the thumb and the short extensor, and internally by the tendon of the long extensor (Fig. ,s*-M. The radial artery, a large vein, cephalic vein of the thumb (Treves), and the inner division of the radial nrrvr cross this space. Beneath it are the scaphoid and trapezium and the articulation between the latter and the first metacarpal bone. The abductor indicis muscle makes a distinct fusiform prominence when the thumb is adducted. The tendons of the common extensor and of the extensor of the little finger and the slip connecting them may be seen. It should be remembered that the "knuckles" are at each joint, the distal extremities of the proximal bones entering into the articulation. THE MUSCLES OF THE LOWER LIMB. 623 THE MUSCLES OF THE LOWER LIMB. In describing the muscles of the lower limb a classification similar to that which was employed for the upper limb muscles will be followed. Owing, however, to the firm articulation of the innominate bones to the sacrum, the muscles extending between the axial skeleton and the pelvic girdle are greatly reduced, and those (such as the psoas) which might be included in this group are continued to the femur, and for present purposes are more conveniently grouped with the muscles extending from the girdle to the femur. There is also, in the lower limb, a greater number of muscles passing over two joints ; indeed, many of the muscles which are inserted into the upper portions of the leg bones take their origin from the pelvic girdle. Most of these seem to be, primarily, members of the femoral group of muscles and will be so classified in the succeeding pages, but one (the gracilis), at least, appears to belong to the group extending from the girdle to the femur. THE MUSCLES EXTENDING FROM THE PELVIC GIRDLE TO THE FEMUR. (a) THE PRE-AXIAL MUSCLES. 1. Psoas magnus. 6. Adductor brevis. 2. Iliacus. 7. Adductor magnus. 3. Pectineus. 8. Quadratus femoris. 4. Gracilis. 9. Obturator externus. 5. Adductor longus. 10. Obturator internus. ii. Gemelli. i. PSOAS MAGNUS (Fig. 598). Attachments. This muscle (m. psoas major) arises from the sides of the bodies of the twelfth thoracic and all the lumbar vertebrae and from the transverse processes of the lumbar vertebrae. Its fibres pass directly downward and slightly forward over the superior ramus of the pubis and are inserted by a tendon, in com- mon with the iliacus, into the lesser trochanter of the femur. Nerve-Supply. By branches from the lumbar plexus from the second, third, and fourth lumbar nerves. Action. To bend the spinal column laterally and to flex the body and pelvis upon the femur. Acting from above, it flexes the thigh and rotates it outward. Relations. The psoas magnus lies along the side of the lumbar vertebrae, resting upon their transverse processes and the medial portion of the quadratus lumborum. Extending as high as the last thoracic vertebra, it passes beneath the internal arcuate ligament, or medial lumbo-costal arch, of the diaphragm, and below it passes beneath Poupart's ligament to reach the thigh. In its abdominal portion it is in relation ventrally with the peritoneum, on the right side with the ascending colon and duodenum, and on the left side with the descending colon and pancreas. The inner border of the kidney overlaps the lateral portion of the muscle, and the ureter and spermatic (or ovarian) arteries descend obliquely along it. The inferior vena cava lies in front of the right muscle. The nerves formed by the lumbar plexus perforate the muscle, and the genito-crural nerve passes down on its anterior surface. In the pelvis the external iliac vessels lie along its medial border, and it is crossed, just before it passes beneath Poupart's ligament, by the vas deferens. In the thigh it forms a portion of the floor of the femoral or Scarpa's triangle, and lies between the iliacus and pectineus muscles, behind the femoral vessels. As the ten- don which is common to it and the iliacus passes over the hip-joint it rests upon a rather large bursa Omrsa iliopectinea) ; just above the insertion a second bursa (bursa iliaca subtendinea) intervenes between the tendon and the femur. 624 HFMAN ANATOMY. The psoas magnus appears to be formed by the union of a hyposkeletal trunk muscle with a femoral muscle, the remaining portions of which are represented by the iliacus and pectineus. It is interesting to note in tliis connection that in those mammalia in which the quadratus lum- borum is well developed the psoas magnus is correspondingly weak, and vice versa. The psoas parrns or FIG SQ8 minor ( Fig. .598 ) is a long, flat muscle which lies upon the ventral surface of the psoas magnus, represent- ing a separated portion of it, and is present in sonic- thing over 50 per cent, of cases. It arises from the bodies of the last thoracic and first lumbar vertebrae and is inserted into about the middle of the ilio-pec- tineal line (linea termina- lis) of the pelvis. External arcuate ligament XII rib Internal arcuate ligament Psoas parvus Quadratus lumborum superior spine of ilium Pyriformis Gluteus medius Tensor fasciae - latae Symphysis pubis 2. ILIACUS (Fig. 598). Attachments. The iliacus arises from about the upper half of the anterior surface of the ilium. Its fibres converge downward to form a common tendon with the psoas major, which is inserted into the lesser trochanter of the femur. Nerve-Supply. By the anterior crural nerve from the second, third, and fourth lum- bar nerves. Action. To flex the thigh and rotate it slightly outward ; when the thigh is fixed, to flex the pelvis and trunk upon the femur. Relations. The iliacus covers the pos- terior wall of the false pelvis, and upon the right side has resting upon it the caecum and on the left side the sigmoid colon. It is crossed obliquely by the external cutaneous and the anterior crural nerves ; its inner border is covered by the psoas magntis. It passes beneath Poupart's ligament external to the psoas magnus, its relations in the thigh being identical with those of that muscle. ' Variations. The iliacus and psoas magnus are not infrequently extensively united, and the two muscles, together with tin- psoas parvus, when this is present, are frequently spoken of as the m. i/io-/>soas. The fibres of the iliacus which arise from the posterior superior spine of tlie ilium are often separated from the rest of the muscle to form an /// after it has followed the muscle under and below Poupart's ligament, usually perfo- rates the sheath and the fascia lata and points external to the vessels at the upper part of the thigh ; but after escaping from the sheath it may be unable to penetrate the fascia, and may be guided by it to the lower third of the thigh, the knee, or even as low as the leg or ankle. The fascia has been torn or wounded, and, as it embraces the subjacent muscles so closely, the latter have bulged through the opening, appearing on the surface of the thigh as rounded elevations varying in size and tension with the position of the limb. 644 HUMAN ANATOMY. Rupture of the fascia has, in recorded instances, been associated with rupture of the ilio-psoas, the rectus, and the biceps femoris. The outer and inner intermuscular septa (page 636) are of less surgical importance than the corresponding structures in the arm, and have but little effect in limiting or determining the course of a cellulitis or an abscess. On the outer side of the thigh, running from the forepart of the crest of the ilium above to the outer tuberosity of the tibia and the head of the fibula below, is the thickening of the fascia lata known as the ilio-tibial band, the dense, glistening fibres of which bridge over the supratrochanteric space between the summit of the trochan- ter and the iliac crest. Normally at this point the band offers distinct resistance to pressure with the fingers. In fracture of the neck of the femur, with shortening, it must be relaxed and less resistant (Allis), and this sign is of especial value in obscure cases of impacted fracture of the neck in which crepitus, preternatural mobility, and other of the conventional symptoms of fracture are lacking (pages 364, 367, 390). The relations of the muscles about the hip to dislocation (Figs. 395, 396, pages 377, 378) and to hip disease (page 381) have been described. Suppuration affecting the iliacus or the ilio-psoas has also been dealt with (page 381). Strains of the ilio-psoas muscle are not infrequent, and may, especially in chil- dren, give rise to a mistaken diagnosis of hip-joint disease. In sprains, however, the movements of the joint that do not affect the ilio-psoas will be painless and most of the other anatomical symptoms (page 380) will be absent. The extensive bursa between the capsule of the hip-joint and the ilio-psoas muscle (ilio-psoas bursa} may enlarge and become visible at the front of the thigh below the middle of Poupart's ligament. The thigh will be found flexed from reflex irritation of the ilio-psoas and to lessen pressure on the bursa (page 381). As the latter not infrequently communicates with the hip-joint, infectious disease of one may extend to the other. The adductors are also often strained or overworked, particularly during horse- back exercise, and are sometimes sprained or stretched close to their pelvic origins. The latter injury may result in a sclerosis of one of the adductor tendons, possibly going on to true ossification, and producing a condition seen oftenest in cavalrymen, and known as " rider's bone." Fractures of the femur situated below the neck (page 363) and above the con- dyles (page 366) are much influenced by muscular action, as might be expected from the number and strength of the muscles concerned. Three of these fractures may be considered in this relation : 1. Fracture just below the trochanters (subtrochanteric fracture). This is one of the most difficult of femoral fractures to manage because of the flexion, abduc- tion, and outward rotation of the upper fragment, caused by the action of the ilio- psoas, the gluteus minimus and medius, the obturators, quadratus, pyriformis, and gemelli. The lower fragment is drawn upward by the rectus, gracilis, tensor fascia- latae, and sartorius, upward and inward by the adductors, upward and a little backward by the hamstrings. In the treatment, elevation and abduction of the thigh i.e., of the lower fragment are often resorted to for obvious reasons. 2. Fracture of the middle of the shaft is very frequent (page 365). It usually moderately oblique from behind downward and forward. The upper frag- ment is almost always in advance of the lower fragment because (a) the fracturing force is more apt to be applied from in front and to the lower rather than the upper part of the thigh ; (&} the weight of the limb in the supim- position would favor a posterior position of the lower fragment ; (Y) the ilio-psoas tends to advuna- the upper fragment, and the adductor magnus and gastrocnemius draw the lower frag- ment somewhat backward (Fig. 614). Then- is often a forward angulation or bow- ing in the direction of the normal curve of the femoral shaft (page 365), thought to In- din- to the action of the adductors which subtend the arc of the curve. The shortening is produced, as usual, by the muscles running from the pelvis to the thigh and leg. 3. Fracture just above the eondyles ( supraeondylar fracture). This is usually the result of seven- injury or of direct violence. It is commonly oblique from be- hind forward and downward. The fracture takes place at about the point of junction PRACTICAL CONSIDERATIONS: THE KNEE. 645 of the compact tissue of the shaft with the cancellated tissue of the expanded lower extremity. It is from one to two inches higher than the epiphyseal line. The same backward rotation of the lower fragment occurs as in disjunction of the epiphysis (page 365), and in both cases from the action of the gastrocnemius. In the fracture, however, the sharp lower end of the upper fragment is far more apt to project ante- riorly than is the diaphysis in cases of epiphyseal disjunction. It is not infrequently entangled in fibres of the rectus and may lacerate the suprapatellar synovial pouch. The difference probably results from the character of the fracturing force, which in the epiphyseal accident is, in the majority of cases, hyperextension of the leg on the thigh. The action of the ilio-psoas tends to advance the lower end of the upper fragment, but must be feeble. The pectineus slightly and the adductors quite strongly draw it inward. The shortening is produced by the hamstrings, rectus, sartorius, etc. The most difficult element of the deformity to do away with is the posterior rotation of the lower fragment, which may also result in serious pressure upon or injury to the popliteal vessels and nerves. In setting such a fracture it may be neces- sary to relax the chief muscles concerned by flexing the thigh to a right angle with FIG. 614. FIG. 615. "Iliacus Psoas major Lower fragment -f- Popliteal artery Cast rocnem ins. - outer head Patella Tibia Gastrocnemius, inner head Dissection of fracture of upper third of right femur, showing forward and inward displacement. Dissection of fracture of lower third of left femur, show- ing displacement of popliteal artery by lower fragment. the pelvis to relax the ilio-psoas, drawing the knee inward a little to relax the ad- ductors, and flexing the leg on the thigh to relax the gastrocnemius, and then to make extension by means of the forearm placed in the ham. Not uncommonly the displacement recurs so obstinately that it becomes necessary to treat the case with the leg fully flexed on the thigh, and even to divide the tendo Achillis. 3. The Knee. The skin over the front of the knee is dense, coarse, and loose, qualities that diminish the gravity of the frequent injuries to the integument itself and also serve to protect the underlying joint, " especially in stabs with bluntish instruments" (Treves) and, in fact, in many forms of accident in which the free movement of the skin over the subjacent structures serves to make the application of force to the latter much less direct. In full flexion the skin, in spite of its laxity, is drawn tensely over the patella, and a fall may result in an extensive wound. The relation of the cutaneous nerves and vessels over the knee to those supply- ing the articulation should be studied in connection with the common application of counterirritants or of blisters to the region. 646 HUMAN ANATOMY. FIG. 616. Vastus ititernus The quadriceps tendon is separated from the femur by a large bursa, which, in from 70 to 80 per cent, of cases, communicates with the knee-joint and may be in- volved in its diseases. When separate from the joint and distended by effusion, it may be mistaken for synovitis of the knee, but the patella will not be floated up and the concavities at either side of that bone and those at the sides of the ligamentum patellae will not be effaced. The prepatellar bursa, separating the patella from the skin, is frequently enlarged in persons who spend much time kneeling, " housemaid's knee." The bursa between the ligamentum patellae and the tubercle of the tibia may be enlarged or inflamed, and is then apt to be painful on account of its compression between two non-distensible structures, the bone and the ligament. The little pad of fat (page 400) between the tubercle and the ligament, which protrudes at the sides of the latter when the quadriceps extensor is in action (page 405), should not be mis- taken for enlargement of this bursa. Posteriorly over the ham the skin is thinner and less movable. The deep fascia here the popliteal fascia is dense and exerts marked obstruction to the exten-* sion of abscess, growth, or aneurism towards the surface, in this way causing severe pain from the pressure upon the nerves that run through the space. As the latter is open above and below, abscesses may extend in either direction. Pus or infection may be guided to the subfascial region in the ham from the pelvis or the buttock by the great sciatic nerve, or from the thigh by the femoral vessels, or from the leg by the short saphenous vein, or by the deeper vessels and the lymphatics. The relations of the fascia and muscles of the thigh to the patella and the knee- joint and to their injuries and diseases have been sufficiently described (Figs. 424-430, pages 409-418). The hamstring tendons are not infre- quently divided, as, for reasons already given, ankylosis of the knee-joint is usu- ally in the position of flexion (page 412). They are made very tense when the pelvis is strongly flexed on the thigh, the knee remaining extended. They may be ruptured if excessive force is applied under these circumstances. The biceps tendon is easily felt on the outer side of the ham, with the peroneal nerve, also readily palpable, lying against its inner and posterior border. At the inner side of the ham the semitendinosus tendon is nearer the mid-line, nearer the surface, more easily outlined, thinner, and more cord-like than the semimembranosus tendon, which is the most deeply situated of the three hamstrings. The line for dividing these tendons is preferably a little above the level of the knee-joint and about opposite the most salient parts of the femoral condyles. In the popliteal region there are several bursae : (a) the largest is between the inner head of the gastrocnemius and the semimembranosus and the inner condyle of the femur, extending downward to the inner tibial tuberosity and even as low as the upper margin of the popliteus ; it communicates with the joint in 50 per cent, or more of cases (Foucher, Gruber); () a smaller bursa is found between the st-mi- membranosus and the internal tuberosity of the tibia, communicating usually with the above-described bursa. Externally there are : (r) a bursa brtwoen the lateral ligament and the tendon of the popliteus ; (uen>neus lon- gus, beneath the fibrous bands or retinacula to be inserted into the tuberos- ity of the fifth metatarsal bone. Nerve-Supply. By the musculo - cutaneous THE MUSCLES OF THE FOOT. 659 FIG. 626. alcis, inner tubercle eo-metatarsal Action. To extend and evert the foot. Variations. A slip is very frequently given off from the tendon of the short peroneus which is inserted either into the tendon of the extensor longus digitorum passing to the fifth toe or directly into that digit. In some cases the slip arises from the belly of the muscle, from that of the peroneus longus, or even from the fibula directly, and represents what has been termed the peroneus quiiitus. \peroneusquartiis, where distinctness from the quintus seems doubtful, sometimes occurs as a muscle arising from the lower part of the fibula and inserting into the calcaneum or the tuber- osity of the cuboid. THE MUSCLES OF THE FOOT. The plantar fascia or aponeurosis (Fig. 626) is a dense sheet of connective tissue lying immediately beneath the skin of the plantar surface of the foot and covering the pre-axial mus- cles. It is attached behind to the tuberosity of the cal- caneum, and extends dis- tally in a fan-like manner to be attached by five processes to the skin over the meta- tarso-phalangeal joints of the digits. The aponeuro- sis is much thicker in its middle portion than at the sides, where it is continued dorsally over the sides of the foot to become continu- ous with the fascia of the dor- sum of the foot and with the crural fascia. Between its cutaneous insertions trans- verse bands of fibres stretch across to form the super- ficial transverse metatarsal ligament (fasciculi trans- versi ) ; from its deep sur- face strong sheets are given off which pass to the sheaths of the flexor tendons. Ex- pansions are also given off from its deep surface which invest the flexor brevis digi- torum and, on either side, the abductor hallucis and abductor minimi digiti. Between the aponeu- rosis and the integument over the inferior surface of the tuberosity of the calca- neum a bursa (Imrsa subcu- tanea calcanea ) is constantly present. The dorsal surface of the foot is covered by the fascia dorsalis pedis, a rather thin sheet continuous with the crural fascia above. It covers the long extensor tendons. (a) THE PRE-AXIAL MUSCLES. Like the pre-axial muscles of the hand, those of the foot may be regarded as derived from five primary layers, which have undergone a considerable amount of modification, including some fusion. Plantar fascia, central portion Plantar fascia, inner lateral portion Plantar fascia, slip for great toe Flexor longus hallucis tendon Superficial transverse met- atarsal ligament Plantar fascia, outer lateral portion Plantar fascia, digital slips Superficial dissection of sole of right foot (subject lying on belly), showing plantar fascia. 66o HUMAN ANATOMY. (aa) THE MUSCLES OK THE FIRST LAYER. 1. Flexor brevis digitorum. 3. Abductor hallucis. 2. Flexor brevis hallucis. 4. Abductor minimi digiti. i. FLEXOR BREVIS DIGITORUM (Fig. 627). Attachments. The short flexor of the toes (m. flexor digitorum brevis) arises from the inner process of the calcaneal tuberosity and from the plantar aponeurosis. It extends distally, beneath the aponeurosis, as a thick quadrangular muscle, the fibres of which are collected FIG. 627. over the metatarsal bones into four tendons which pass to the second, third, fourth, and fifth toes. Over the first phalanx of the toe each tendon divides into two ter- Oscaids /JMfc j ~WKI minal slips, between which the corresponding tendon of the flexor longus digitorum passes and which are in- setted into the second pha- lanx. Nerve-Supply. By the internal plantar nerve from the fourth and fifth lumbar and first sacral nerves. Action. To flex the second, third, fourth, and Flexor brevis fifth tOCS. minimi digiti Variations. The most fre- quent variation in this muscle is the absence of the tendon to the fifth toe, an absence which occurs in somewhat over 21 per cent, of cases examined. Some- times the tendon is replaced by a slip or muscle which arises from the tendon of the flexor longus digitorum. The flexor brevis repre- sents the middle portion of the superficial flexor layer, and cor- responds, accordingly, to the terminal portions of the ten- dons of the flexor sublimis of the hand. Its origin is primarily from the plantar aponeurosis, and hence the occasional origin of the portion for the fifth toe becomes intelligible, since the tendon of the ilexor longus is a differentiation of the dccpet layer of the aponeurosis. Ab'ductor hallucis Flexor brevis digitorum Flexor brevis hallucis Flexor longus hallucis tendon Abductor minimi digiti Flexor longus digitorum ten- dons Flexor brevis digitorum ten- dons Flexor tendons in sheath Flex. brcv. digi- tonmi tendon Flexor longus digitorum tendon Superficial muscles of sole of right foot. 2. FLEXOR BREVIS HALLUCIS (Fig. 628). Attachments. The short flexor of the great toe (m. flexor hallucis brevis) from the plantar surface of the internal cuneiform bone and the adjacent liga- mentous structures. Its libn-s pass distally to a tendon which contains a sesamoid bone, and is inserted into the inner surface of the base of the first phalanx of the great toe. Nerve-Supply. By the internal plantar nerve from the fourth lumbar ner Action. To tle\ the !4 real toe. THE MUSCLES OF THE FOOT. 66 1 Variations. The flexor b.revis hallucis is frequently intimately fused with the abductor hallucis. A portion of the deeper fibres of the flexor brevis hallucis is frequently inserted into the whole length of the first metatarsal. Occasionally these fibres are quite distinct from the rest of the muscle, forming what has been termed an opponens hallucis. In the description of the muscle given above, account has been taken only of what is usually described as the inner portion, the flexor brevis pollicis being usually regarded as consisting of two bellies, the second of which is inserted into the lateral side of the base of the first phalanx of the great toe. The relations of this outer belly and its nerve-supply, however, indi- cate that it belongs to an entirely different layer than the medial belly. It will, therefore, be considered later in connection with the interossei (page 663). FIG. 628. Os calcis, inner tubercle -j Abductor hallucis, Itt-J calcaneal origin Internal annular ligament % Flexor brevis digitorum, origin Flexor longus hallucis tendon \2 Tibialis posticus tendon-: ^ Flexor longus digitorum tendon Abductor hallucis, part of origin. Abductor hallucis, cut First plantar interosseu.s Flexor brevis hallucis Lumbricales Flexor longus hallucis tendon Flexor brevis digitorum Flexor longus digitorum Os calcis, outer tubercle Abductor minimi digiti, origin Long plantar ligament Peroneus longus tendon Abductor minimi digiti, occasional insertion (Abductor ossis metatarsi quinti) Flexor accessorius Tubercle of fifth metatarsus Flexor brevis minimi digiti, part of its origin Flexor longus digitorum Flexor brevis minimi digiti Abductor minimi digiti, insertion Flexor longus digitorum tendons Flexor brevis digitorum tendons, cut Long and accessory flexors of right sole, exposed by removal of superficial muscles. 3. ABDUCTOR HALLUCIS (Fig. 627). Attachments. The abductor hallucis extends along the inner border of the foot, arising from the inner tubercle and surface of the calcaneum and from the plantar aponeurosis and being inserted, along with the flexor brevis hallucis, into the inner side of the base of the first phalanx of the great toe. Nerve-Supply. By the internal plantar nerve from the fourth and fifth lumbar and first sacral nerves. Action. To abduct and flex the hallux. 662 HUMAN ANATOMY. ABDUCTOR MINIMI DIGITI (Fig. 627). Attachments. The abductor of the little toe (m. abductor digiti quinti) is situated along the outer border of the foot. It arises from the under surface of the calcaneum and from the plantar aponeurosis, and extends distally and laterally to be inserted partly into the tuberosity of the fifth metatarsal bone and partly into the lateral side of the base of the first phalanx of the little toe. Nerve-Supply. By the external plantar nerve from the first and second sacral nerves. Action. To abduct and flex the little toe. Variations A portion of the abductor digiti quinti frequently separates from the rest of the muscle to form a fusiform belly which has been termed the abductor ossis metatarsi quinti. It arises from the lateral part of the inferior surface of the os calcis and is inserted, either inde- pendently or in common with the abductor, into the tuberosity of the fifth metatarsal. (bb) THE MUSCLES OF THE SECOND LAYER. I. LUMBRICALES (Fig. 628). Attachments. The lumbricales are four spindle-shaped muscles which arise from the adjacent borders of the tendons of the flexor longus digitorum and from the inner border of its first tendon. They pass distally to the inner surfaces of the first phalanges of the second, third, fourth, and fifth digits, where they are inserted into the membranous expansions of the tendons of the extensor longus digitorum. Nerve-Supply. The first or first and second muscles, counting from the tibial side, are supplied by the internal plantar nerve ; the remaining three or two are sup- plied from the external plantar from the fourth and fifth lumbar and first sacral nerves. Action. To flex and draw medially the second, third, fourth, and fifth toes. Variations. Absence of one or other of the lumbricales has been noted, the fourth and third being those most frequently lacking ; these same muscles are frequently bifid at their insertions. Small bursae may intervene between the tendons and the first phalanges. The significance of the lumbricales is similar to that of the corresponding muscles of the hand. They arise primarily from the deeper layers of the plantar aponeurosis, and when these differentiate into the tendons of the flexor longus digitorum they come to arise from those structures. (cc) THE MUSCLES OF THE THIRD LAYER. i. ADDUCTOR HALLUCIS (Fig. 629). Attachments. The adductor hallucis consists of two portions, often described as two distinct muscles, united orlly at their insertions. The oblique portion (caput obliquum), or adductor obliquus, arises from the bases of the second, third, and fourth metatarsals and from the long plantar ligament and passes distally and inward along the interval between the first and second metatarsals, its fibres converging to a strong tendon which unites with that of the transverse portion (caput transversum), or adductor transversus. This extends almost transversely, under cover of the three medial tendons of the long and short flexors and the lumbricales, over the heads of the fourth, third, and second metatarsals. It arises from the capsules of the four lateral metatarso-phalangeal joints and passes medially to join the tendon of the oblique portion. The common tendon so formed unites with the tendon of the first plantar interosseous and is inserted into the sesamoid bone of that tendon and into the lateral surface of the base of the first phalanx of the great toe. Nerve-Supply. By the deep branch of the external plantar nerve from the fifth lumbar and first and second sacral nerves. Action. To flex and adduct the hallux. Variations. Some variation occurs in the extent of the origin of both portions of the adductor hallucis. The oblique portion may be limited to the long plantar ligament, or may receive an accessory slip from the shaft of the second metatarsal, wade the origin of the trans- verse portion from the fifth metatarso-phalangeal joint may be lacking. It is to be noted that in the fa-tus the two portions of the adductor are not separated by a wide interval as in the adult, but lie in contact with each other. THE MUSCLES OF THE FOOT. 663 A small muscular slip has occasionally been observed passing from the long plantar liga- ment to the lateral surface of the base of the first phalanx of the second toe. It appears to represent an adductor secundi digiti. FIG. 629. Os calcis, inner tubercle- Flexor brevis digitorum Flexor longus hallucis tendon Flexor longus digitorum tendon Flexor accessorius, inner head Tibialis posticus tendon Abductor hallucis, cut Flexor brevis hallucis First plantar interosseus Adductor hallucis, oblique portion Tendon of flexor longus digitorum Tendon of flexor brevis _ digitorum Flexor longus hallucis tendon Os calcis, outer tubercle Abductor minimi digiti Flexor accessorius, outer head -Peroneus longus tendon Long plantar ligament k Abductor ossis metatarsi quinti 7W (part of abductor minimi digiti) Tendon of peroneus longus in sheath Flexor brevis minimi digiti Abductor minimi digiti Adductor hallucis, transverse portion Deep dissection of sole of right foot, showing short flexors of great and little toes and adductor muscles. (dd) THE MUSCLES OF THE FOURTH AND FIFTH LAYERS. i. Interossei plan tares. 2. Interossei dorsales. 3. Flexor brevis minimi digiti. As in the hand, the fourth and fifth layers of the pre-axial musculature become united to form the dorsal interossei, portions of the fourth layer remaining distinct to form the plantar interossei. The arrangements in the hand and foot differ, however, in this respect, that in the foot the lateral muscle derived from the fourth layer forms a large, well-developed structure termed the flexor brevis minimi digiti. i. INTEROSSEI PLANTARES (Fig. 630). Attachments. The plantar interossei are four spindle-shaped muscles. The first is very much stronger than the others, and is often described as the outer head of the flexor brevis hallucis (page 661). It arises, in common with the flexor brevis 664 HUMAN ANATOMY. hallucis, from the inner cuneiform bones and the adjacent ligamentous structures. It extends distally along the lateral surface of the first metatarsal bone and passes over into a strong tendon, which contains a sesamoid bone, and is inserted into the outer surface of the base of the first phalanx of the great toe, along with the adductor hallucis. The remaining three muscles are much smaller and arise in succession from the medial surfaces of the third, fourth, and fifth metatarsals, and, passing distally, are inserted by slender ten- FIG. 630. dons into the membranous expansions of the long ex- tensor tendonsof the third, fourth, and fifth toes, on the medial sides of their first phalanges. Nerve -Supply. By the external plantar nerve from the first and second sacral nerves. Action. To flex the first, third, fourth, and fifth toes and to draw the last three medially. Variations. As above stated, the first plantar inter- osseus is usually describee] as a second head of the flexor brevis hallucis. It is some- times more or less insepara- ble from the oblique portion of the adductor hallucis. 2. INTEROSSEI DORSALES (Figs. 623, 630). Attachments. The dorsal interossei are also four in number. They arise from the adjacent sides of each pair of nut- atarsals and pass distally in the interspaces between these bones. The fibres of each muscle converge to a narrow tendon which is inserted into the mem- branous expansions of the extensor tendons over the first phalanges of the sec- ond, third, and fourth toes. The first and second mus- Insertion of peroneus longus Insertion of. tibialis anticus Adductor, obliquus hallucis Long plantar ligament Peroneous brevis tendon Peroneus longus tendon .Superficial fibres of long plantar lig. Tubercle of fifth metatarsus Flexor brevis minimi digiti, stump Tendons of flex- or brevis hallucis and first plantar inter os seus re- flected, with ab- ductor and ad- ductor tendons, showing the two sesamoid bones Deep dissection of >f right foot, showing interosseous muscles. cles insert into the opposite sides of the second toe and the third and fourth into the lateral sides of the third and fourth toes. Nerve-Supply. By the external plantar nerve from the first and second sac nerves. Action. To flex the second, third, and fourth toes; the first also draws the second toe medially and the rest the second, third, and fourth toes laterally. 3. FLEXOR BREVIS MINIMI DIGITI (Fig. 629). Attachments. The short flexor of the little toe (m. flexor digiti quinti brevis), which really represents a fifth plantar interosseus, arises from the base of the fifth PRACTICAL CONSIDERATIONS : THE LEG. 665 metatarsal and passes distally along the outer side of the fourth plantar interosseus to be inserted by a tendon into the outer surface of the base of the rirst phalanx of the fifth toe and also into the distal portion of the fifth metatarsal. Nerve-Supply. From the external plantar nerve from the second sacral nerve. Action. To flex the fifth toe and draw it lateralward. Variations. The portion of the flexor brevis minimi cligiti which passes to the fifth meta- tarsal is frequently more or less distinct from the rest of the muscle, and has then been termed the opponent quinti digiti. (f>) THE POST-AXIAL MUSCLES, i. EXTENSOR BREVIS DIGITORUM (Fig. 624). Attachments. The short extensor of the toes (m. extensor digitorum brevis) (irises from the lateral and superior surfaces of the calcaneum. It passes distally beneath the tendons of the extensor longus digitorum and divides into four portions, the outer three of which soon become tendinous and are inserted by fusing with the tendons of the extensor longus to the second, third, and fourth toes over the first phalanges of those toes; the innermost tendon is inserted into the base of the first phalanx of the great toe. Nerve-Supply. By the anterior tibial nerve from the fourth and fifth lumbar and first sacral nerves. Action. To extend and draw laterally the first, second, third, and fourth toes. Variations. Occasionally one or other of the tendons of the extensor brevis may be doubled, this condition being most frequent in the tendon to the second toe ; sometimes a fifth tendon passes to the little toe. The innermost tendon is nearly always much stronger than the others ; the fibres which insert into it are occasionally separate from the remainder of the muscle, then forming the e.v tensor brei'is liallucis. PRACTICAL CONSIDERATIONS: MUSCLES AND FASCIAE OF THE LEG, ANKLE, AND FOOT. i. The Leg. The skin over the leg is everywhere more adherent to the un- derlying fascia than it is in the thigh. Its inability at certain places, as over the spine and antero-internal surface of the tibia, to glide away when force is applied partly accounts for the frequency with which bruising or laceration, superficial ulceration, or even periostitis or caries follows injuries to the ' ' shin. The deep fascia blends with the periosteum at the head and inner and anterior borders of the tibia, at the head of the fibula, and at the two malleoli. It is thicker and denser above and anteriorly than below and posteriorly. The two septa (Figs. 627, 623) that run inward from it on the outer side of the leg and are attached to the anterior and external borders of the fibula constitute an osseo-aponeurotic space that contains the peroneal muscles and that may, for a time, limit the spread of infection or of suppuration. The peronei, in their compartment, and, farther in, the bones and interosseous membrane, separate the anterior group of muscles the tibialis anticus, extensor communis, etc. from the posterior group. The fascia over the anterior group embraces them so closely, that when it is wounded or' torn the muscle-fibres protrude and approximation of the edges of the fascial wound may be difficult. In the anterior compartment the muscles are intimately adherent to its fibrous walls, as is the case in the forearm, but not in the arm or thigh (Tillaux). In the posterior compartment, on the contrary, a loose layer of connective tissue intervenes between the gastrocnemius and the deep fascia, and permits the greater degree of motion between the muscle and the aponeurosis necessitated by the greater range of motion in plantar, as compared with dorsal, flexion of the foot. The difference will be noted in dealing with wounds involving these regions, or in some operations, as amputation of the leg. The septum, anteriorly, at the upper third of the leg, between the tibialis anticus and extensor longus digitorum, is of variable density, gives no indication of its pres- 666 HUMAN ANATOMY. FIG. 631. ence on either the skin or fascial surface, and although described as a guide to the anterior tibial artery (g.v.), is untrustworthy on account of the difficulty of recog- nizing it (Treves). Posteriorly the deep layer of fascia that holds down the deep muscles to the tibia and fibula and runs transversely beneath the soleus and gastrocnemius, is weaker above, where it is covered and reinforced by the latter muscles, and stronger below, where it loses their sup- port. It is continued downward and separates the tendo Achillis from the deeper structures. In ap- proaching the vessels behind the malleolus, one finds, therefore, two layers of deep fascia. Growths originating in the head of the tibia or occupying the interosseous space are much influenced by the resistance of the deep fascia, which, as is the case with the fascia lata, may for a time determine their shape and direction and alter their surface ap- pearance and their apparent density. Cellulitis and abscess are for a while confined beneath the fascia, but, like the coloring matter of the blood after fracture, may soon find their way to the surface by following the vessels that perforate it. Some fibres of the gastrocnemius or, more fre- quently, the tendo Achillis at its weakest point, on a level with the internal malleolus, may be ruptured during strong effort, as in raising the body on the toes while bearing a weight. Sometimes, however, this accident follows comparatively trifling exertion. 2. The Ankle and Foot. The skin around the ankle and upon the dorsum of the foot is thin and lax. The absence of a fatty or muscular layer between it and the subjacent bones and the distance of the region from the centre of circulation make gangrene from relatively slight contusion, or from the pressure of splints or dressings, more common here than elsewhere. Over the sole, especially at those places which normally bear the weight of the body, the heel, the ball of the great toe, the line of the heads of the metatarsal bones (page 452), and the outer side of the foot, the skin is much denser. It often contains callosities which cause pain by pressure and are usually the result of friction between the sole and an ill-fitting shoe. Its close connection with the underlying plantar fascia is similar to that between the skin of the palm and the palmar fascia, "and between the skin of the scalp and the occipito-frontalis aponeurosis, in all of which regions the integument is exceptionally thick and dense, and in the former two hairless (pa 491). Under the heel the thick skin and the pad of subcutaneous fascia containii fat are especially valuable in lessening the force of falls upon that part of the foot where there is no elastic arch composed of a number of bones and joints to take and distribute the force, as do both the transverse arch and the anterior pillar of the main arch (page 436). This tissue, vertical and scanty in the sole, is loose and abundant on the dorsum and around the tendo Achillis, in which latter region it contains some fat. Its laxity over the dorsum, while it somewhat protects the inst from the effects of direct violence, adds greatly to the ease with which swelling oedema may occur in cellulitis or, on account of the dependent position of the pai and its remoteness from the heart, in anasarca. The deep fascia at the ankle is thickened on the dorsum and sides to form the annular ligaments, the chief function of which is to hold in place the tendons that move the foot and toes. Anteriorly this is done by two bands, beneath the upper of which the tendon of the tibialis anticus runs, while the lower covers in the tendon of the same muscle and those of the extensor proprius pollicis and of the extensor coin- Dissection of fracture of left tibia, showing effect of muscular action on fragments. PRACTICAL CONSIDERATIONS: ANKLE AND FOOT. 667 munis and peroneus tertius, the last two running in one sheath. Internally i.e., between the heel and the internal malleolus the tendons of the flexor longus pol- licis, the flexor longus digitorum, and the tibialis posticus run beneath the internal annular ligament, the last named being the deepest and in the closest proximity to the ankle-joint, disease of which may originate in the tendon. The relation of the flexor longus pollicis tendon to the posterior ligament is intimate, and is believed to be of advantage in resisting posterior luxation of the astragalus (page 450). The peroneus longus tendon is thought to be more frequently displaced than anv other tendon in the body. When this accident happens, the tendon slips from its groove behind the external malleolus and over the thin posterior border of the latter to its anterior face. This dislocation is favored by (a) the length and slender- ness of the tendon ; () the shallowness of the groove in which it runs ; (c~) the relative weakness of the single slip of the external annular ligament that covers the tendon; (d) the fact that it changes its direction twice between the lower third of the leg and its insertion, i.e. , once at the malleolus and once at the margin of the cuboid. Disease of the sheaths of the tendons about the ankle-joint is not rare, is apt to be tuberculous, and is favored by the frequent strains and the exposure to cold and wet to which they are subjected, and by their dependent position and remoteness from the heart. Their relation to disease of the tarsal bones should be remembered (page 437). The approximately vertical direction of the swelling in the early stages is some- times of use in differentiating teno-synovitis from ankle-joint disease (page 451). The involvement of the tendon-sheaths in sprain of the ankle-joint (page 450) adds to the duration of the disability produced by that accident. On the sole of the foot the dense plantar fascia is of importance in relation to infection or suppuration beneath it. Of its three divisions (page 659), the central one is much the strongest. With the intermuscular septa that run from its lateral bor- ders into the sole and separate the flexor brevis digitorum from the abductor minimi digiti externally and from the abductor hallucis internally, it makes a compartment the floor of which is rarely penetrated by inflammatory or purulent effusions. An abscess beginning in the mid-region of the sole beneath the plantar fascia may pass forward between the digital slips or upward through the interosseous spaces, or along the tendon-sheaths to the ankle. More rarely apertures in the plantar fascia permit suppuration to spread through it to the subcutaneous region of the sole. The abscess cavity then consists of two portions connected by a narrow neck, abces en bouton de chemise (Tillaux). The lateral progress of such an abscess through the intermuscular septa above described is easier than penetration of the strong central leaflet of the plantar fascia. It will be noted that the three compartments into which the sole is then divided are analogous to the thenar, hypothenar, and central divisions of the palm. Con- traction of the plantar fascia, which aids in maintaining the curve of the arch of the foot, as a string would that of its bow, increases that arch, is often associated with the different forms of talipes, and is thought to be one of the common causes of a subvariety, pes cavus. Relaxation or elongation of the plan tar fascia favors depres- sion of the normal arch, and hence contributes to the development of the condition known as "flat-foot" (pes planus} (vide infra). Club- Foot. The mechanics of the normal foot have already been sufficiently described (pages 436, 447). Of the deformities, either congenital or acquired, which are grouped under the name club-foot, it is necessary to describe, from the anatomical stand-point, only the chief varieties. i. Talipes equino-varns, when congenital, is believed to result from retention of the foetal position, i.e. , from defective development. The inward rotation of the flexed and crossed limbs in utero, which in the later periods of fcetal life removes the pressure from the fibular side of the legs and the dorsum of the feet and puts the latter in the position of extreme flexion with the soles instead 'of the tops of the feet against the uterine walls (Berg), does not take place. This is the commonest of all the forms of club-foot. When it is acquired, it may be due to paralysis of those muscles that oppose the adduction and extension of the foot, i.e., chiefly of 668 HUMAN ANATOMY. the extensor longus digitorum and the peronei. The muscles that draw up the heel, the gastrocnemius and soleus, the muscles that elevate the inner border of the foot and adduct it, the tibalis anticus and posticus and the flexor longus digitorum, are not resisted ; or, if the case is congenital, are assisted by the position of the foot, which is therefore found with (a) the heel elevated ; (6) the inner edge of the sole drawn upward ; (c) its axis turned inward ; (d) the sole shortened, partly through contraction of the plantar fascia. In marked cases the calcaneum will be almost vertical, as will the astragalus, which will also be rotated forward so that its head may have two articular facets, one of them projecting on the dorsum ; the scaphoid is atrophied and is close to the inner malleolus; the cuneiform bones accompany it, and the cuboid becomes the chief point of support of the weight of the body. Corresponding changes occur in the metatarsal bones and phalanges, which may be at right angles to the line of the inner side of the leg. Pure talipes varus, in which the elevation of the heel is absent, is very rare. The other varieties of club-foot are seldom congenital. 2. Talipes Valgus. The foot is abducted and the outer border elevated by the peronei, the inner side being correspondingly depressed and the arch of the foot flattened out. 3. Talipes Equinus. The heel is drawn up by the gastrocnemius and soleus ; the patient walks on the balls of the toes ; the os calcis and the astragalus are changed in position as in equino-varus. The astragalo-scaphoid and calcaneo- cuboid joints are much flexed, so that the scaphoid may even be in contact with the os calcis. 4. Talipes Calcaneus. The extensor longus digitorum and the extensor pro- prius pollicis raise the toes and with them the foot, so that the anterior portion of the os calcis is elevated and the astragalus is rotated backward until its articular sur- face points in that direction. The patient walks on the heel. Flat-foot results from weakness or relaxation of plantar muscles, fascia?, and ligaments, especially the inferior calcaneo -scaphoid (page 445). When, in persons who stand much of their time, or in those with defective ankles originally, this liga- ment yields, the head of the astragalus is carried downward and inward by the body weight, which, owing to the width of the pelvis, the obliquity of the femur, and the curve of the tibia, is transmitted to the astragalus somewhat from without inward. This is associated with abduction of the foot, resisted by the internal lateral and calcaneo-astragaloid ligaments. This sinking of the astragalus and increased promi- nence of the internal malleolus may be seen in many normal feet when the weight of the body is thrown on one foot (page 449). In well-marked cases of flat-foot the tibialis posticus fails to resist this change effectually, the peronei add to the abduction or shortening, the arch of the sole of the foot entirely disappears or may even become a rounded downward curve, the deltoid ligament stretches, as do the long and short plantar ligaments, and the head of the astragalus, the scaphoid tubercle, and the sustentaculum tali (page 449) become unduly prominent and may be the main poin of support. Two bursae about the foot are of enough importance to demand attention. The retrocalcaneal bursa lies between the os calcis and the tendo Achillis, the depressions at the sides of which are effaced when the bursa is distended. The cor- responding obliteration of the anterior depressions just beneath the malleoli (page 451), which occurs in ankle-joint disease, does not take place. Flexion or extension of the foot or contraction of the calf muscles is painful. /> unions. There may be normally a bursa over the metatarso-phalangeal join of the great toe, or an "adventitious" bursa formed by dilatation of lymph-spaces, condensation of connective tissue, and localized effusion may develop there, as a result of pressure and friction from badly fitting shoes. The great toe is forced out- ward, the internal lateral ligament of the articulation is elongated, the joint is made unduly prominent,' the head of the first metatarsal bone sometimes enlarges, and the cartilage over its inner surface not uncommonly atrophies and disappears, leaving a communication between the bursal sac and the synovial cavity of the joint. Mat- foot and all degrees of valgus tend to produce a similar condition by exposing the ; SURFACE LANDMARKS : THE LOWER EXTREMITY. 669 inner border of the foot and thus the first metatarso-phalangeal joint to excessive pressure. Adventitious burs;e are found over the external inalleolus, " tailor's bursa," over the cuboid in equino-varus, and at other points exposed to pressure in the different forms of club-foot. Crest of ilium SURFACE LANDMARKS OF THE LOWER EXTREMITY. i. The Buttocks and Hip. The iliac furrow (page 349 ) indicating the line of the crest of the ilium, with the external oblique above and the gluteus medius below, passes forward to the anterior superior spine, and is more or less FIG. 632. effaced posteriorly where the crest is covered by the flat tendon of the erec- tor spincE. The posterior superior spine is always indicated by a surface depression. In women the continuous layer of fat passing from the loin to the but- tock blends the surface forms of these regions into one uniform curve (Thom- son i , and there is no such marked defi- nition of them as is seen in the male. The rounded prominence of the buttock (Fig. 632) is clue partly to subcutaneous fat, partly to the thick muscular mass of the gluteus maximus, especially developed in man by reason of his assumption of the upright po- sition. It is more prominent posteri- orly, becomes flattened as it passes outward, and ends in a distinct de- pression ( Fig. 632 ) at the tendinous insertion of that muscle just behind and below the greater trochanter. Al- though the trochanter is on a plane external to that of the iliac crest, the hollow between it and the ilium is so obliterated by the gluteus medius and minimus muscles that it ordinarily does not appear as a surface prominence. Its upper border on a level with the centre of the acetabulum is indistinct on account of the presence of the glu- teus medius tendon which passes over it to be inserted into the outer surface of the trochanter. In front the muscular eminences where the region of the buttock passes into that of the hip are due to the glu- teus medius above and more anteriorly to the tensor facise latre (Fig. 632), which shows as a broad elevation just behind a vertical line drawn through the anterior superior spine and just below the forepart of the iliac crest. It can be best seen if the thigh is in abduction and inward rotation. As the skin of the buttock is made tense when the thigh is flexed on the pelvis, the fold of the nates ( gluteo-femoral crease), due to creasing or drawing in of the skin, is formed when the thigh is extended. It begins just below the level of the Extensor brevis digitorum Extensor longus digitorum Lateral surface of right leg. showing mock-Hint; on living subjrct. 670 HUMAN ANATOMY. tuberosity of the ischium, runs horizontally outward, and crosses the middle of the lower edge of the gluteus maximus, part of which the inner is therefore above it and part the outer below it. In flexion of the hip the gluteus maximus is flattened and the skin stretched over it, and hence this fold is more or less completely effaced. As flexion is an almost constant early symptom of hip-joint disease (page 381), and is usually associated with atrophy of the muscles moving the joint, the obliteration of the gluteo-femoral crease, characteristic of this disease, can readily be understood. In women, on account of the thickness of the supragluteal layer of fat, the gluteo- femoral crease is longer and deeper than in men. The various bony points of this region have been described (pages 345, 349), as have the different lines and measurements employed in the diagnosis of fractures of the neck of the femur and of dislocation (pages 362, 364, 367). 2. The Thigh. (a) Anterior criiral region. The hip passes insensibly in front and below into the region of the thigh. The inguinal furrow, a valuable land- mark, separates the surface of the abdomen from that of the thigh (page 1774). It indicates the line of Poupart's ligament, which may be felt, in the absence of much subcutaneous fat, from the iliac spine to the pubic spine, more easily over its inner half, and still more easily if the thigh is in extension, abduction, and outward rotation. The ligament is relaxed by flexion, adduction, and inward rotation of the thigh, and with it, to some extent, the deep fasciae of the thigh and abdomen ; therefore that position is the one most favorable to reduction of either inguinal or femoral hernia by taxis (pages 1770, 1774). Below this a second furrow " Holden's line" is sometimes seen with the thigh in slight flexion, beginning at the scroto-femoral angle and becoming less distinct until it is lost at or over the supratrochanteric space. It runs across the front of the cap- sule of the hip-joint and is lost in the presence of synovitis of that joint. It is often indistinct, and in some subjects cannot be made out at all (Treves). On the line of this furrow, and just external to a vertical line drawn through the middle of Poupart's ligament, the head of the femur can sometimes be made palpable by extension and rotation of the thigh, but this is rarely possible in fat or muscular persons. The depression or flattening of Scarpa's triangle (page 639) can usually be seen. The tendon of origin of the adductor longus made prominent by abduction and the upper portion of the sartorius, emphasized by flexion and outward rotation of the thigh with the knee bent, mark its inner and outer borders respectively. The sar- torius, continued downward, becomes flattened and is lost in the rounded fulness on the inner side of the knee. Just internal to a line bisecting the triangle the femoral artery may be felt and its pulsations sometimes seen. A very trifling depression is occasionally present near the inner angle at the base of the triangle, and then indi- cates the position of the saphenous opening (page 635), the centre of which is from one to one and a half inches below and the same distance external to the pubic spine, which is on a transverse line drawn through the upper margin of the greater trochan- ter. From the apex of the triangle the shallow groove, extending towards the inner side of the knee, marks the course of the sartorius and the interval between the quad- riceps extensor and the adductors. To the outer side of the triangle the rectus can be seen, showing below the anterior superior spine in the interval between the sartorius and the tensor fasciae latse ; it runs down the front of the thigh, giving it its convex fulness, and narrowing to its ending in the flattened quadriceps tendon, the edges of which stand out when the leg is strongly extended on the thigh. The obliteratior of Scarpa's triangle, in full extension of the thigh, is due to the thrusting forwar of the overlying tissues by the neck and the upper end of the shaft of the femur. To the inner side of Scarpa's triangle, below and posteriorly to the adductc longus, the other adductors and thegrudlis give- the rounded outline to the inner side of the upper thigh. Near the knee, when the leg is flexed, the tendon of insertion of the adductor magnus can be plainly felt between the sartorius and vastus internus. The latter muscle stands out along the lower half of the thigh and is still more promi- nent near the knee, where it becomes superficial between the rectus and the sartorius. On the outer side the vastus externus gives the thigh its broad, slightly convex surface, down the centre of which there is sometimes a slight vertical groove im" FIG. 633. Poupart's ' ligament Sartorius- Rectus - femoris Femoral artery Scarpa's triangle Quadriceps tendon Patella- Tubercle of tibia Subcutaneous- surface of tibia SURFACE LANDMARKS : THE LOWER EXTREMITY. 671 eating the position of the ilio-tibial band of fascia between the insertions of the tensor fasciae latae and gluteus maximus and the external tibial tuberosity. More pos- teriorly a distinct longitudinal depression corresponds to the external intermuscular septum, between the vastus externus and the short head of the biceps. At the lower third of the thigh this groove indicates the line of nearest approach of the shaft of the femur to the surface. Elsewhere it is usually so covered by muscular masses that it is not to be felt, even indistinctly. The corresponding internal septum between the vastus iuternus and the adductors and pecti- neus produces no surface marking. (&) Posterior crural region. The ham- strings, descending from beneath the lower edge of the gluteus maximus, cannot at first be separately identified. Lower, a very slight depression may mark the interval between the semimembranosus and the semitendino- sus, and the biceps tendon becomes a salient rounded cord. When the limbs are straight with the knees together there should be but a slight interval between the thighs, and that only where the sartorius muscles curve back to lie along the inner surface of the limb. In women, owing to the greater quantity of sub- cutaneous fat, the thighs may be in contact all the way down (Thomson). 3. The Knee. On the anterior sur- face the quadriceps tendon and the ligamen- tum patellae are made more prominent by strong extension of the leg, and on each side of the ligament the little eminence made by the protrusion of the soft subpatellar fat becomes visible. The angle made by the axes of the tendon and ligament should be noted (page 418). The outline of the patella is easily felt and can usually be seen. Above it is a slight depression. At its sides are two concavities the inner of which is a little more marked, as the inner border of the patella is the more prominent which in fat persons may disappear, as they do, together with the su- prapatellar depression, in synovitis of the knee-joint (page 413). Both anteriorly and laterally the landmarks have been sufficiently described (pages 367, 390). Posteriorly the popliteal space the ham is slightly convex during extension of the leg and deeply concave when it is flexed. The boundaries, the relations of the ham- string tendons, of the ilio-tibial band externally and of the sartorius tendon internally have been described (pages 409, 646). At the lower portion of the space the con- verging fleshy bellies of the gastrocnemius may be felt. 4. The Leg. The landmarks relating to the tibia (page 390) and fibula (page 396) have been described. Between these bones the belly of the tibialis anticus causes a distinct prominence, to the fibular side of which is the narrower and less-marked elevation due to the extensor longus digitorum. Below the middle third of the leg these muscles are tendinous, but by dorsal flexion of the foot and of the toes (exten- < Muscles of calf .Ankle- joint Abductor and tlcxor breyis hal- lucis Antero-median surface of right leg, showing modelling on living subject. 672 HUMAN ANATOMY. sion) they can be made to stand out with the tendon of the extensor proprius hallucis between them ; to the outer side of the extensor longus digitorum tendon a slight groove indicates the interval between that muscle and the peroneus tertius. The latter as a muscle peculiar to man and probably developing as a result of his assump- tion of the erect posture is not invariably present. Above, between the extensor longus digitorum and the soleus, the peroneus longus makes a longitudinal elevation shading off below where the fleshy fibres become tendinous into the flatter pero- neus brevis. Posteriorly the swell of the calf is formed by the gastrocnemius, and its surface markings are due to the peculiar arrangement of the fleshy and tendinous portions of that muscle. When the calf muscles are in action, as in standing on the toes, it will be seen that the inner head is the larger and descends somewhat lower than the outer head ; and the lateral borders of the soleus will be seen coming to the surface beyond the lower part of the gastrocnemius and the tendo Achillis and showing as curved eminences, of which the outer is the longer. 5. The Ankle and Foot. The bony landmarks have been described (pages 390, 396, 437, 449, 453). At the front of the ankle the extensor tendons are easily recognized. The largest and most internal is that of the tibialis anticus ; then, in order, the extensor proprius hallucis, extensor longus digitorum, and when present the peroneus ter- tius. Beneath the tendons of the long extensor and just below the external mal- leolus, the fleshy belly of the short extensor of the toes, filling the space between the os calcis and astragalus, can easily be felt as a soft swelling over the outer part of the tarsal region, and is distinctly visible when in action. On either side of the tendi- nous elevation, on a level with the line of the ankle-joint and in front of each malleolus, is a little depression. This is effaced when the capsule is distended by effusion (page 451). The two fleshy masses on the inner and outer border of the foot are due respectively to the abductor and flexor brevis hallucis and the ab- ductor and flexor brevis minimi digiti. The dorsal interossei project upward slightly between the metatarsal bones. The lines on the dorsum of the foot corresponding to the various joints have been described (page 453). Behind the ankle and at the sides of the tendo Achillis between it and the pos- terior surfaces of the malleoli are two concavities, of which the outer is the deeper. In it the tendons of the peroneus longus and brevis may be felt, the latter the nearer to the fibula. In the inner concavity lie, in order from the malleolus backward, the tendons of the tibialis posticus, the flexor longus digitorum, and the flexor longus pollicis. On the sole of the foot the abductors of the great and little toes show somewhat on the surface, but the chief outlines are determined by the arch of the foot, the strong plantar fascia, and the thick integument. The digital creases have but little practical value. As the foot, taken as a whole, acts as a lever, and as the calf muscles are attached to the heel, the short end of such a lever, it follows that the develop- ment of these muscles will stand in some relation to the length or projection of the heel. As a short lever will require the application of a greater force to produce the same result than will a long lever, we find the most marked muscular develop- ment of the calf associated with a short foot and a short heel, while- a long foot and a long heel are the usual concomitants of a poorly developed calf (Thomson ). The athletic feats of some runners with poorly developed calves may sometimes be explained by observing the unusual length and projection of the heel. THE VASCULAR SYSTEM. THE vascular system is composed of the organs immediately concerned in the circulation throughout the body of the fluids which convey to the tissues the nutritive substances and oxygen necessary for their metabolism and carry from them to the excretory organs the waste products formed during metabolism. The system is usually regarded as being composed of two portions, the one con- sisting of organs in which circulates the red fluid which we term 'blood, while the organs of the other contain a colorless or white fluid known as lymph or chyle ; the former of these subsystems is the blood-vascidar system, and the latter is the lymphatic system. It must be recognized, however, that the two systems communicate, and that the lymphatic system develops as an outgrowth from the blood-vascular system ; so that while it proves convenient for descriptive purposes to regard the two systems as distinct, nevertheless, they are intimately associated both anatomically and embryo- logically. THE BLOOD-VASCULAR SYSTEM. The blood-vascular system consists of ( i ) a system of canals known as blood- vessels, traversing practically all parts of the body, and (2) of a contractile organ, the heart, by whose pulsations the blood is forced through the vessels. The vessels are again divisible into ( i ) vessels, which carry the blood from the heart to the tissues and are known as arteries, (2) exceedingly fine vessels which form a net-work in the tissues and are termed capillaries, and (3) vessels which return the blood from the tissues to the heart and are known as veins. THE STRUCTURE OF BLOOD-VESSELS. Although passing into one another insensibly and without sharp demarcation, where typically represented the arteries, capillaries, and veins present such character- istic histological pictures that they are readily distinguished from one another. All blood-vessels, including the heart, possess an endothelial lining which may constitute a distinct inner coat, the tunica intima, or, as in the capillaries, even the entire wall of the vessel. Usually, however, the intima consists of the endothelium reinforced by a variable amount of fibre-elastic tissue in which the elastica predomi- nates. Except within the walls of capillaries, external to the intima lies a thick middle coat, the tunica media, which typically is composed of intermingled lamellae of involuntary muscle and elastica and fine fibrillae of fibrous tissue. Outside the media follows the tunica externa or advcntitia, which, although usually thinner than the middle coat, is of exceptional strength and toughness characteristics conferred by its fibre-elastic tissue and upon which the integrity of a ligature often depends. It should be noted that the endothelial tube is the fundamental and primary structure in all cases, the outer coats being secondary and variable according to the size and character that the vessel attains. The customary division into the three coats is more or less artificial and in the larger vessels is often uncertain. The recognition of an inner endothelial and an outer musculo-elastic coat often more closely corresponds to the actual arrangement of the tissues than the conventional subdivision into three tunics. The endothelial lining of the arteries consists of elongated spindle-shaped plates united by narrow sinuous lines of cement substance which, after silver-staining, map out the irregular contours of the cells with diagrammatic clearness (Fig. 634). At the junction of the plates, occasional accumulations of the cement substance mark minute intercellular areas, the stigmata, that indicate points of less accurate apposi- tion. Within the veins, the endothelial plates are shorter and broader than in the arteries, approaching somewhat irregular polygons in outline. The demarcation of 43 673 6 7 4 HUMAN ANATOMY. the endothelium into distinct cells is less evident in the capillaries than in the larger vessels, in some cases a continuous syncytial sheet replacing the definitely outlined plates. The presence of a relatively small oval nucleus is readily demonstrated by suitable stains. The involuntary muscle varies in amount, from the imperfect single layer of muscle-cells found in the arterioles, to the robust muscular coat of many lamellae in the larger arteries. It is relatively best developed in arteries of medium size, where the muscle occurs in distinct broad or sheet-like bundles between the strands of elastic tissue. The component fibre-cells are short and often branched and, for the most part, circularly disposed. The distribution of the muscular tissue is much less regular and constant in the veins than in the arteries, since in many it is scanty, in some entirely .wanting, and in a few veins excessive, occurring in both circular and longitudinal layers. The striated tmiscle found in the large vessels communicating with the heart resembles that of the cardiac wall from which it is derived. Connective-tissue is represented in the arteries and veins by both fibrous and elastic tissue. The former is present as delicate or coarser bundles of fibrillae that extend between the other components of the vascular wall. FIG. 634. B. A. A, endothelium of aiteriole after silver-staining ; X 200. B, endothelial cells more highly magnified. X 500. The elastic tissue is very conspicuous in all arteries save the smallest, and in many veins. It presents all variations in amount and arrangement from loose net- works of delicate fibres in the smaller vessels to robust plates and membranes in the largest arteries. Within the intima of the latter, the elastica often occurs as sheets broken by pits and perforations, which are, therefore, known as fene strated branes. Nutrient blood-vessels are present within the walls of all the larger vessel down to those of i mm. in diameter, and provide nourishment for the tissues com- posing the tubes. These vasa vasorum, as they are called, are usually branches from some neighboring artery, their favorite situation being the external coat within which they ramify, breaking up into capillaries that, in the larger vessels, invade the adja- cent media. The blood from the vascular wall is collected by small veins that accom- pany the nutrient arteries, or, as in the case of the veins, empty directly into the venous trunk in whose walls they course. Lymphatics are represented by spaces both within the muscular tissue and beneath the endothelium. In certain situations, conspicuously in the brain and the retina, the blood-vessels are enclosed within lymph-channels, the pcrivascular lymph- sheaths, that occupy the adventitia. The nerves distributed to the walls of blood-vessels, especially to the arteries, are numerous and include both sympathetic and spinal fibres. The former are des- STRUCTURE OF BLOOD-VESSELS 675 tined particularly for the muscular tissue and, therefore, are directed to the media, although vessels in which muscle is wanting, as in certain veins and the capillaries, are not without nerves. From the plexus that surrounds the vessel, notably rich about the arteries, nerve-fibrillae penetrate the media and end among the muscle- fibres in the manner usual in such tissue (page 1015). Special sensory nerve- endings have been described in both the external and internal tunics. The Arteries. Since the arrangement of the component tissues is most typical in arteries of medium size (from 4-6 mm. in diameter), the radial artery may appropriately serve for description. Seen in cross-section (Fig. 635), after the usual methods of preservation and staining, the intima presents a plicated contour as it follows the foldings of the internal elastic membrane that appears as a conspicuous corrugated light band marking the outer boundary of the inner tunic. The lining endothelial cells are so thin that in profile their presence is indicated chiefly by the slightly projecting nuclei. Between the endothelium and the elastic membrane the FIG. 635. Intima .-,f Media Endothelium Internal elastic membrane ^S^^sgy^"' ' " *^^~.r Involuntary muscle Elastic tissue Ad vent it ia External elastic membrane Elastica Vasa vasorum Transverse section of artery of medium size. X 150. intima includes a thin layer of fibrous and elastic fibrillae. The media, thick and conspicuous, consists of circularly disposed flat bundles of involuntary muscle sepa- rated by membranous plates of elastic tissue, that in the section appear light and unstained. After the action of selective dyes, as orcein, the elastica is very con- spicuous (Fig. 636). Delicate fibrillae of fibrous tissue course among the musculo- elastic strands. Beneath the outer coat, the elastica becomes condensed into a more or less distinct external elastic membrane that marks the outer boundary of the media. The adventitia varies in thickness, in the medium-sized arteries being relatively better developed than in the larger ones. It consists of bundles of fibrous tissue intermingled with elastic fibres of varying thickness. The adventitia contains the vasa vasorum and chief lymph-channels of the vascular wall. Followed towards the capillaries, the coats of the artery gradually diminish in thickness, the endothelium resting directly upon the internal elastic membrane so long as the latter persists, and afterwards upon the rapidly attenuating media. The elastica becomes progressively reduced until it entirely disappears from the middle HUMAN ANATOMY. coat, which then becomes a purely muscular tunic and, before the capillary is reached, is reduced to a single layer of muscle-cells. In the precapillary arterioles the muscle no longer forms a continuous layer, but is represented by groups of fibre-cells that Intima External elastic membrane Adventitia Transverse-section of artery of medium size, stained to show elastic tissue. X too. partially wrap around the vessel, and at last are replaced by isolated elements. After the disappearance of the muscle-cells, the blood-vessel has become a true capillary. The adventitia shares in the general reduction and gradually diminishes in thickness until, in the smallest arteries, it consists of only a few fibre-elastic strands outside the muscle-cells. In the large arteries, on the other hand, the intima and media chiefly undergo augmentation. Although the inner coat greatly thickens and contains a large amount of fibrous tissue and elastica, a conspicuous internal elastic membrane, as seen in the smaller vessels, is lacking, since the elastic plates and membranes are now so abundant that the local accumulation is no longer striking, the boundary between the inner and middle coats being, therefore, less sharply defined. The character of the thickened media also changes, the muscular tissue be- ing relatively reduced and over- shadowed by the excessive de- velopment of the fibro-elastic tissue, which is arranged in reg- ularly disposed lamellae separa- ting the muscle-bundles and conferring a more compact and denser character to the wall of the vessel. The adventitia, while relatively thinner than in arteries of medium size, is also increased and consists of robust fibres and plates of elastica, many of \\hirh are longitudinally disposed and irreg- ular, although strong, bundles of fibrous tissue. Exceptionally, longitudinal strands of muscle appear in the outer coat next the media. In the roots of the aorta and FIG. 637. Small aiteries in which muscular coat is reduced to single layer of cells. X 150. STRUCTURE OF BLOOD-VESSELS. 677 g? Intima Media pulmonary artery, the media consists chiefly of striated muscle which resembles that of the myocardium with which it is continuous, both vessels having been derived from a common trunk, the bulbus arteriosus, the anterior segment of the primary heart-tube. The Veins. The walls of the veins are always thinner than those of corre- sponding arteries and are more flaccid and less contractile in consequence of the smaller amount of elastic and muscular tissue that they contain. In veins of medium size (from 4-8 mm. in diameter), the intima consists of the lining endothelium, the cells of which are relatively broad and short, a thin layer of fibrous connective tissue and net-works of fine elastic fibres. A distinct internal elastic membrane is seldom pres- ent, at most a condensation of FIG. 638. elastic fibrillae marking the outer limit of the inner coat. In some veins, as the cephalic, basilic, femoral, long saphenous, and pop- liteal, bundles of smooth muscle occur within the intima. In ad- dition to the circularly disposed thin sheets of muscular and fibro- elastic tissue, the media contains fibro-elastic plates, sometimes mingled with a few bundles of muscle-cells, that extend longi- tudinally. In certain veins, as in the saphenous, deep femoral, and popliteal, the longitudinal fibres may constitute a zone beneath the intima to the exclusion of the mus- cular tissue. The adventitia is often thicker than the media, and consists of interlacing fibres and net-works of fibro-elastic strands, the general direction of which is lengthwise. In many veins, par- ticularly in those of the lower ex- tremity, the outer coat contains bundles of longitudinally disposed muscle-cells. The valves with which many veins are provided consist of paired crescentic folds (Fig. 641) of the intima, covered on both sides with endothelium, containing a small amount of fibro-elastic tis- sue. The attached border of the leaflets ends in narrow prolonga- tions that extend beyond the free margin of the valve. Between the leaflets of the valve and the wall of the vein lie the pocket-like si- nuses, which the blood distends when the valve is closed. Adventitia Transverse section of abdominal aorta. X 90. In the structure of their walls, the large veins present many deviations from the typical arrangement. While ; intima is only exceptionally increased, as in the hepatic part of the inferior vena cava and the beginning of the portal vein, the media is often markedly thickened. I his increase is chiefly due to augmentation of the elastic and fibrous tissue, the mus- 2 remaining comparatively scanty. The splenic and portal veins, however, are particularly rich in muscular tissue ; on the other hand, the media may be almost wanting, as in the greater part of the inferior vena cava and the larger hepatic veins. 678 HUMAN ANATOMY. ~. Intima Adventitia Lack of muscle within the media is often compensated by an unusual develop- ment of such tissue in the adventitia; in some large veins, as in the hepatic portion of the inferior cava, su- FIG. 639. perior mesenteric, or external iliac, the in- ner half or two-thirds of the outer coat is occupied by robust bundles of longitudi- nally arranged muscle. In some cases, how- ever, as in the renal and portal veins, the longitudinal muscle in- vades the entire thick- ness of the adventitia, or, as in the supra- renal vein, the muscle of the outer tunic may include both circular and longitudinal layers. The walls of the small veins (less than .040 mm. in diameter) consist of only endo- thelium and connective tissue. The latter rep- resents a relatively ro- bust adventitia and a feebly developed me- dia, muscle-fibres being wanting. Traced tow- ards the capillaries, the connective tissue gradually diminishes until the endothelial coat alone remains. In passing into veins of medium size, at first the muscle-cells are short and scattered and only partly encircle the tube. Far- ther along the elastica appears in the form of delicate fibres and net-works that increase in size and density as the muscu- lar tissue becomes more pro- nounced. It is worthy of mention that certain veins, no- tably those of the brain and pia mater, the dural sinuses, and the blood-spaces of cavernous tissue, are usually entirely devoid of muscle, although in the walls of some of the larger cerebral veins, small strands of such tissue occur. The Capillaries. The most favorable arrangement for efficient nutrition is mani- festly one insuring the passage of the blood-Stream at a re- duced rate of speed in inti- mate relations with the tissue-elements. These requirements are met in the capil- laries whose collectively increased calibre and thin walls favor slowing of the blood- Transverse section of pulmonary artery near its root, showing striated muscle. X 15- FIG. 640. Intima Media - , Adventitia Transverse section of vein of medium size. X 250. STRUCTURE OF BLOOD-VESSELS. 679 FIG. 641. Portion of fem- oral vein, opened to show bicuspid valve. stream and the passage of the plasma and oxygen into the surrounding tissues. The walls of the capillaries consist of only the lining plates, the entire vessel being in fact a delicate endothelial tube. The cells composing the latter are elongated lanceolate plates, possessing oval nuclei, united by nar- row lines of cement substance. Although the transition from the arterioles is gradual, the final disappearance of the muscle-cells marks the beginning of the true capillaries ; the passage of the latter into the veins is less certain, since muscular tissue is wanting in those of small size. In the smallest capillaries two endothelial plates may suffice to encircle the entire lumen; in the larger three or four cells may be required to complete the vessel. Preformed openings (sto- mata) in the walls of the capillaries do not exist, the passage of the leucocytes and, under certain conditions, also of the red blood-cells (diapedesis) and of small particles of foreign substances, being effected between the endothelial plates. In some capillaries, as in those of the choroid, liver, or renal glomeruli, the usual demarcation of the wall into distinct cells is wanting, the individual endothelial plates being replaced by a continuous nucleated sheet or syncytial layer. Where the capillaries course within fibrous tissue, not uncommonly the vessel is accompanied by delicate strands of connective tissue (adventitia capillaris) that suggest an external sheath. The capillaries are usually arranged as net-works, of which the channels are of fairly constant size within the tissue to which they are distributed. During life it is prob- able that none are too small to permit the passage of the red blood-cells, while many admit two or even three such elements abreast. Their usual diameter varies between .008 and .020 mm. The capillary net- works in various parts of the body differ in the form and closeness of their meshes, since these details are influenced by the arrange- ment of the component elements and by the function of the structures supplied. Thus, in muscles, tendons, and nerves the meshes are elongated and narrow; in glands, the lungs, and adipose tissue they are irregularly polygonal; in the liver-lobules converg- ingly or radially disposed; while in the subepithelial papillae of the mucous membranes and the skin the capillaries commonly form loops. In general, it may be assumed that FIG. 642. > v^ ( ; / W V -E?^W I ; " .::. 'J '$ \, / ' I & a^ . -^ '-. ^-^^ -/'~. : ,.^-^' c ^<~, m^^^m^^^^^M^ ^^Jj^^^^^^m { > * :-*&^^*?l&~^*^jm^ >v- < \ - rt eHo,e ^&(QI^^ LU ^ ! ^^^^^M^^'^jf \-^ih, * ^ ?%?*':% ' -if U_/ ^KwifeM 1 ^* Capillaries arising from arteriole and ending in small vein in omentum. X 200. the greater the functional activity of an organ, the closer is its capillary net-work. Organs actively engaged in excretion, as the kidneys, or the elimination of substances 68o HUMAN ANATOMY. from the blood, as the lungs or liver, as well as those producing substances directly entering the circulation (organs of internal secretion), as the thyroid gland, are pro- vided with exceptionally rich and close net-works. The mesh-works within the walls of the pulmonary alveoli are of remarkable closeness and are often narrower than the capillaries surrounding them. Under the name, sinusoids, Minot 1 has grouped the circulation occurring in certain organs, as the liver, in which the capillaries are formed by the invasion and subdivision of the large original blood-channel by the tissue-cords. The resulting sinusoids differ from ordinary capillaries, therefore, in connecting afferent and efferent vessels of the same nature, both being either venous or arterial. Capillaries, on the contrary, form communications between arteries and veins. In consequence of the invagination of the original vessel, its endothelium bears an unusually intimate rela- tion to the tissue-trabeculae, little or no connective tissue intervening. F. T. Lewis 2 has shown that the Wolffian body and the developing heart also present examples of sinusoidal formation, and suggests the significance of sinusoids as representing a primitive type of circulation. THE BLOOD. The fluid circulating within all parts of the blood-vascular system consists of a clear, almost colorless plasma or liquor sa^^g^^,^n^s in which are suspended vast numbers of small free corpuscular elements, the blood-cells. The latter are of two chief kinds, the colored cells, or erythrocytes, and the colorless or leucocytes. The characteristic appearance of the blood is due to the presence of hemoglobin con- tained within the erythrocytes which, while individually only faintly tinted, collect- ively impart the familiar hue as well as a certain degree of opacity. That the characteristic pigment is limited to the cells is shown by the lack of color and the transparency of the plasma when examined under the microscope, although to the unaided eye the blood appears uniformly red and somewhat opaque. The most im- portant property of hemoglobin is its great affinity for oxygen which, taken up from the air during respiration and combined as oxyhemoglobin, is carried by the red cells to all parts of the body. When rich in oxygen (containing about twenty vol- umes) the blood possesses the bright scarlet hue characteristic of arterial blood; after losing approximately one-half of its oxygen and acquiring about an equal volume of carbon dioxide during its intimate relations with the tissues, the blood returned by the veins is dark purplish-blue in color. If the hemoglobin escapes from the eryth- rocytes into the plasma, the latter becomes deeply tinged and the blood loses its opacity and becomes transparent or ' ' laked. ' ' The specific gravity of normal blood is about 1060; its reaction is alkaline and due chiefly to the presence of sodium carbonate. Immediately after withdrawal from the body the blood possesses a characteristic odor that probably depends upon cer- tain volatile fatty acids. When fresh it is slippery to the feel, but after exposure to air becomes sticky. Upon standing it undergoes coagulation, whereby the cor- puscles become entangled among the innumerable delicate filaments of fibrin, a pro- teid substance that appears in the plasma after withdrawal of the blood from the body. As the result of this entanglement the corpuscles are collected into a dark- colored, jelly-like mass, the blood-clot or crassamentum, that separates from the sur- rounding clear straw-colored serum. The latter possesses an alkaline reaction and a specific gravity of 1028. The serum closely resembles the liquor sanguinis, con- taining about ten per cent, of solid substances, of which about three-fourths are pro- teids serum-albumin, serum-globulin, and fibrin-ferment, the latter replacing the fibrinogen present in the plasma before coagulation occurs. Blood-Crystals. The chief constituent of the red cells, the hemoglobin, prob- ably exists within the corpuscles as an amorphous mass in combination with other substances (Hoppe-Seyler) from which it must be freed by solution before crystal- lization can occur. After laking, the coloring matter of the blood, in the form of oxyhemoglobin, separates into microscopic crystals that belong to the rhombic sys- tem, usually appearing as elongated rhombic or rectangular plates (Fig. 643). 1 Proceedings Boston Sor. Nat. History, vol. xxix, 1900. * Anatomischer Anzeiger, Bd. xxv., 1904. THE BLOOD. 681 When unusually large or superimposed they exhibit the characteristic crimson hue, but when single and small the hemoglobin crystals are colorless or of a faint greenish- yellow tint. On mixing dried blood with a few grains of sodium chloride and a small quantity of acetic acid and heating until bubbles appear, minute brown crystals are formed in large numbers. These are known as Tcichmanri s or hemin crystals and re- present one of the products derived from the reduction of hemoglobin. Being yielded by FIG. 643. blood from various sources, they are indica- tive only of the presence of blood and are valueless in differentiating the blood of man from that of other animals. In blood-clots of long standing minute hematoidin crystals often appear as yellowish-red plates. This substance is likewise a reduction-product of hemoglobin. The Colored Blood-Cells. The ma- ture colored blood -cells, erythrocytes, or red corpiiscles, of man and other mammals (ex- cept those of the camel family, which are elliptical in outline) are small, biconcave, circular, nonnucleated discs, with smooth contour and rounded edges. When viewed by transmitted light, the individual "red" cells possess a pale greenish-yellow tint, and only when they are collected in masses or superimposed in several layers is the distinc- tive blood-color evident. The peculiar form of the corpuscle biconcave in the centre and biconvex at the periphery renders accurate focussing of all parts of its broader surface in one plane impossible ; hence under the high amplification necessary for their satisfactory examination, the entire cells are never sharply defined and, according to focal adjustment, appear either as light rings enclosing dark centres or vice versa. Viewed in profile, the thicker convex marginal areas are connected by the thinner concave centre, the corpuscle presenting a general figure somewhat resembling a dumb-bell. After fresh blood has been distributed as a thin layer and allowed to remain unshaken for some time, the red cells exhibit a peculiar tendency to become arranged in columns, with their broad surfaces in contact, similar to piles or rouleaus of coin (Fig. 646). Agitation dis- perses the corpuscles, which, however, may resume their former grouping when again undisturbed. The columns may join one another until a net-work of rouleaus is formed. If the stratum of blood be thin, the red cells f usually later separate, but they may retain their columnar grouping. Crystals of oxyhemoglobin from human blood. X 160. FIG. 644. ) ^ Hemin crystals from human blood. X 250. The long-accepted biconcave discoidal form of the mam- malian erythrocytes has been questioned by Dekhuyzen * and, more recently, by Weidenreich 2 and by F. T. Lewis, 3 who be- lieve that the normal form of the red blood-cells is cup-shaped, similar to a sphere more or less deeply indented, thus reviving the conception held by Leeuwenhoek nearly two centuries ago. Although such cupped corpuscles are familiar, they are generally regarded as changed cells resulting from modification of the density of the plasma. The posi- tive testimony of so careful an observer as Lewis as to the occurrence of the cup-shaped red cells within the circulation during life entitle these views to consideration. 4 1 Anatomischer Anzeiger, Bd. xv., 1899. 3 Archiv. f. mikrps. Anatom., Bd. Ixi., 1902. 3 Journal of Medical Research, vol. x., 1904. 4 A critical review concerning the form and structure of the red cells is given by Weiden- reich in Ergebnisse d. Anat. u. Entwick., Bd. xiii., 1904. 682 HUMAN ANATOMY. Dresbach 1 has recorded the presence of elliptical red cells in the blood of an apparently healthy mulatto. The oval corpuscles, which measured .010 mm. by .004 mm., were approxi- mately constant in size, slightly biconcave, and constituted ninety per cent, of all the red cells. They were observed over a period of four months, during which time the number of erythro- cytes and leucocytes and the amount of FIG. 645. hemoglobin were normal. Dresbach con- cludes that the oval form was not an arti- fact, but probably due to developmental variation. The average diameter of the red blood-cells of man is .0x378 mm. (STTHF m -)> some corpuscles meas- uring as little as .0045 mm. and others as much as .0095 mm. Their average thickness is about .0018 mm. It is probable that the average diam- eter is uninfluenced by sex and is constant for all races, although ac- cording to Gram, the size of the cor- puscles is somewhat greater in the inhabitants of northern countries. The number of red cells normally contained in one cubic millimeter of blood is approximately 5,000,000 in the male and something less (4,500,- ooo) in the female. The number of corpuscles is practically the same whether the blood be taken from the arteries, capillaries, or veins, but is lower in the blood from the vessels of the lower extremity than of the upper, probably owing to the greater proportion of plasma in the more dependent parts of the body. Within the first day after birth, the number of erythrocytes is normally very high; in ad- vanced old age it is usually diminished. In general, the red blood-cells of mammals are small and their size, which greatly varies in different orders, bears no relation to that of the animal. The corpuscles of man, which are among the largest and exceeded by only those of the elephant (.0094 mm.) and the two-toed sloth (.0091 mm. ), are approximated by those of the guinea-pig (.0075 mm.), dog (.0073 mm.), rab- FIG. 646. bit (.0069 mm. ), and cat (.0065 mm.). Those of many familiar mammals are distinctly smaller, as the hog (.006 mm.), horse (.0056 mm.), sheep (.005 mm.) and goat (.004 mm. ). , , ^X The smallest mammalian corpuscles are those of the musk-ox, with a diameter of only .0025 mm. It is obvious that a positive differentiation . >, of human blood from that of some of the do- mestic animals, based on the measurement of the red cells, is uncertain and often impossible. ,'&. The application of the "biological" test has placed a much more reliable and even specific means in the hands of the medico-legal expert. This test depends upon the fact, demonstrated by Bordet, Uhlenmuth, and others, that the blood-serum of an animal that has been repeat- edly injected with small quantities of human Red cells from human blood ; near centre of field. leucocyte seen X86 5 . Human blood corpuscles ; two leucocyte seen among the red cells, most of whicl grouped in rouleaus. X 625. blood will produce a distinct cloudy precipitate or turbidity when added to a dilute solution of human blood, but will yield no result when added to similar solutions of blood from other animals. An important advantage of this test is that even when the blood is putrid, contaminated, or derived from old dried dots, the char- acteristic changes occur. Certain exceptional disturbing conditions, such as the presence of 1 Science, March 18, 1904, and March 24, 1905,. THE BLOOD. 683 monkey's blood, human lachrymal or nasal secretion, being eliminated, a positive reaction with the serum-test is strong evidence of the presence of human blood. The nonnucleated condition of the mature erythrocytes is the distinguishing characteristic of mammalian blood as contrasted with the colored corpuscles of other vertebrates, since even in the exceptional oval red cell of the camel family the nucleus is wanting. The mammalian red corpuscles, however, must be regarded as a secondary deviation from the fundamental type represented by the oval nucleated erythrocyte of the other vertebrates, the nucleated embryonic red cell losing its nucleus as maturity is acquired. In general, the oval nucleated red cells are larger than the mammalian nonnucleated discs. The largest erythrocytes are found in the tailed amphibians, those of the amphiuma, the largest known, attain the gigantic length of .080 mm., and are approximately ten times as large as the human red blood-cell. The structure of the red blood-cell has long been and still is a subject of dis- cussion, two opposed views finding ardent supporters. According to the one, held by Schaefer, 1 Weidenreich, and others, the erythrocyte consists of a membranous external envelope inclosing the colored fluid contents. On the other hand, Rollett and many others regard the corpuscle as composed of an insoluble uniform spongy stroma of great delicacy, occupied by the coloring matter or hemoglobin. Although no definite envelope is present, in the sense of a distinct cell-membrane, it is highly probable that a peripheral condensation of the stroma exists. The fact that the FIG. 647. B. Nucleated amphibian red blood-cells; A, from newt ; B, from amphiuma. X 75P. fragments into which the red blood-cells may be broken up after certain treatment, as by heating, retain the appearance and structure identical with the larger original cell, is strong evidence that the hemoglobin has not escaped and, therefore, does not exist in a fluid condition within the cell, notwithstanding the ingenious but scarcely convincing explanations of the phenomena advanced by the supporters of the vesicular structure of these cells. The further evidence afforded by those parts of the corpuscles that remain after abstraction of the hemoglobin by water, ether, and other reagents, points to the existence of a distinct stroma, the thicker edges of which appear in profile as outlines of the ' ' ghosts ' ' that then represent the former colored cells. The erythrocytes are extremely sensitive to a wide range of reagents and conditions and, therefore, require great care in their collection and examination if distortions are to be avoided. Exposure to even a current of air often suffices to produce conspicuous changes in the red blood- cells. Alterations in form may be grouped into those resulting from the action of solutions of lower and of higher density than that of the normal plasma. The latter is conveniently sub- stituted by an .85 per cent, solution of sodium chloride. If the proportion of salt be grad- ually reduced, the corpuscles show evidences of swelling, at first by losing their concavity on one side and later, as the density of the reagent approaches that of water, assuming the spherical form and parting with the hemoglobin and becoming colorless. On the other hand, 1 Anatomischer Anzeiger, Bd. xxvi., 1905. 684 HUMAN ANATOMY. FIG. 648. when subjected to saline solutions stronger than the "normal," the exterior of the corpuscles becomes irregular and beset with knob-like projections or spines. When the concentration of the medium is increased, the "crenation" gives place to marked shrinkage and distortion, until the cells lose all resemblance to their normal form. Upon treatment with water, aqueous dilutions of acetic acid, ether, and other reagents, the erythrocytes are promptly decolorized by the extraction of the hemoglobin. An interesting modification of the phenomenon may be produced by solutions of tannic acid or potassium bichromate of varying strength. When the reaction is vigorous, the decomposed hemoglobin is caught within the cell and appears as a mass somewhat resembling a nucleus. When tin- reaction is feeble, as with very weak solutions, the hemoglobin is less suddenly precipitated, and appears as a minute projection attached to one part of the exterior of the decolorized corpuscle. Alkaline solutions effect the complete destruction of the red cells. Among the reagents employed in histological investigations, osmic acid (i per cent.) deserves especial confidence as preserving the form of the red corpuscles. Fixation by heat, so commonly used in the prepara- tion of blood specimens for clinical examinations, produces alterations and often marked changes in the red cells, and, therefore, is unsuitable for histological study of these elements. Attenua- tion of the central parts of the cells produces appearances that have been mistaken for a nucle- ated condition of the erythrocytes. Upon cautious application of heat, with precautions against evaporation and drying, the corpuscles extrude portions of their substance which, after separation, resemble miniature red cells. The Colorless Blood-cells. It may at once be emphasized that the colorless cells observed within the blood are only incident- ally related to the red cells and, further, that they, in part at least, primarily circulate within the lymph-vascular system, from which they are poured into the blood. When examined in fresh and unstained preparations, the colorless cells or leuco- cytes appear as pale nucleated elements which, by their pearly tint and refracting properties, are readily distinguished from the much more numerous surrounding erythro- cytes. Their shape is very variable, but when first withdrawn from the body is usually irregularly spherical or oval. When placed on a warmed slide and maintained at the temperature of the body, many of these cells soon exhibit amoeboid motion, whereby are produced not only alterations in their form, but often also changes in their actual position. A nucleus is always present, but may be obscured in the contracted spherical condition of the cell by the overlying granular cytoplasm. In the expanded con- dition, as when the cell is undergoing amoeboid change, the nucleus is very evi- dent and the cytoplasm often differentiated into a homogeneous peripheral zone (exoplasm) and a central granular area (endoplasni) surrounding the nucleus. A distinct cell-wall is absent, although it is probable that a slight peripheral condensa- tion serves to outline the corpuscle. That such condensation does not constitute a definite envelope is shown by the readiness with which foreign particles may be taken into the body of the cell. Although the size of the colorless corpuscles varies with the type of the cell, as presently described, in general the diameter of these elements is larger than that of the erythrocytes, and is commonly from .oio-.oi2 mm. Their number is much U-ss than that of the red corpuscles, the usual ratio between the white and red cells being about i : 600. Even within physiological limits this ratio varies considerably, from 5000 to 10,000, with an average of 7500, white cells being normally found in one cubic millimeter of blood. Critical examination of the colorless cells, after fixation and staining, has shown that among the elements collectively designated as the "white cells" or "leucocytes," five varieties are usually present in normal blood. Since the recognition of these forms is sometimes of practical Varieties of colorless blood-cells seen in normal human blood ; a, small lymphocytes ; b, large lymphocyte or mononuclear leucocyte; c, transitional leucocyte ; rf, polymorphonuclear leucocytes ; e, eosinophile ; /, red cells. X 900. THE BLOOD. 685 importance, a brief resum of their characteristics, based on the descriptions of Ehrlich and of Da Costa, 1 may appropriately here find place. It should be noted that the differentiation of these cells is founded upon not only their morphological characters, but also the behavior of the granules embedded within their cyto- plasm when subjected to certain combination stains. A generation ago Ehrlich divided the aniline dyes into three groups acid, basic, and neutral. The first includes such dyes as acid fuchsin, orange G or eosin, in which the coloring principle acts or exists as an acid and exhibits an especial affinity for the cytoplasm. The second group, the basic stains, includes dyes, as hematoxylin, methylene-blue, methyl-violet, methyl-green or thionin, in which the coloring prin- ciple exists chemically as a base in combination with a colorless acid and particularly affects the chromatin ; hence, such are nuclear stains. Neutral dyes, produced by mixture of solutions of an acid and a basic stain, have a selective affinity for certain so-called neutrophilic granules. Assuming that the blood-film has been fixed by heat and tinged with Ehrlich's "triacid stain" (a combination of solutions of acid fuchsin, orange G, and methyl-green) the following varieties of colorless cells are distinguishable in normal blood : 1. Small Lymphocytes. These are non-granular cells, with an average diameter of .0075 mm. or about that of the erythrocytes, distinguished by a large deeply staining nucleus that occupies almost the entire cell. The meagre cytoplasm is reduced to a narrow peripheral zone, so inconspicuous that it may be overlooked. The small lymphocytes, which constitute from 20-30 per cent, of all the white corpuscles, are the most common derivative from the lymphoid tissues. 2. Large Lymphocytes, or Mononuclear Leucocytes. These elements, about .012 mm. in diameter, possess a relatively small round or oval nucleus, which is usually eccentrically placed and so poor in chromatin that it stains faintly. The cytoplasm is non-granular and comparatively large in amount. 3. Transitional Leucocytes. Assuming that the lymphocytes and leucocytes are related and not distinct elements, the transitional forms represent the developmental stage linking the large lymphocytes with the mature leucocytes. Their distinguishing feature is the indented or kidney-shaped nucleus which usually occupies an eccentric position within the non-granular cytoplasm. The latter, as well as the diameter of the transitional forms, corresponds with that of the large mononuclear leucocyte. 4. Polymorphonuclear Leucocytes. These represent by far the most common type of white cells, of which they constitute about 70 per cent. Their diameter is approximately .010 mm., hence they are somewhat smaller than the transitional forms, but larger than the red cells. Their cytoplasm is relatively large in amount and contains fine neutrophilic granules. On account of the great diversity of the forms that they assume, the nuclei are very conspicuous features of this type of leucocyte. At first sight the nuclei appear multiple; closer examination, however, shows the seemingly distinct nuclei to be connected by delicate processes, so that, although exceptionally two or more isolated nuclei exist and the cells are truly polynuclear, their actual condition is appropriately designated as polymorphonuclear. 5. Eosinophiles. Leucocytes of this type are conspicuously distinguished by- the coarse, highly refractive granules within the cytoplasm that display an especial affinity for acid dyes, particularly for eosin. These resemble the polymorphonuclear leucocytes in size (.010 mm.) and in the character of their nuclei, the latter, however, in general being less distorted and commonly eccentrically placed. The eosinophiles are prone to rupture, after which the pale nucleus lies in the midst of a swarm of brightly tinged granules. Although other types of colorless cells, as myelocytes and mast cells, are of clinical interest, they do not occur in normal blood and, hence, need not be here discussed. An occasional addi- tional type of leucocyte, the basophile cells, is rarely present in normal blood. These elements resemble the polymorphonuclear leucocytes, but are distinguished from the latter by the presence within the cytoplasm of closely packed fine granules that possess a strong affinity for basic dyes. In the foregoing grouping the varieties of white cells are regarded as different stages of elements genetically related and derived from the same sources a view supported by the early development of the leucocytes. It should be mentioned, however, that Ehrlich and many other hematologists consider the lymphocytes and the leucocytes as entirely distinct elements, believing the former to be derived from lymphoid tissues and the leucocytes exclusively from bone-marrow. Accordingly, the large lymphocytes and the large mononuclear leucocytes are of different nature, although, as universally admitted, their assumed differentiation is at best uncertain. The presence of all forms of white cells in the circulation of the embryo long before the appearance of bone- marrow ( Ebner) seems conclusive evidence that the origin of the leucocytes is not limited to the marrow tissue. The Blood Plaques. In addition to the erythrocytes and leucocytes, the blood of man and other mammals regularly contains small bodies, the blood plaques 'Clinical Hematology. Phila., 1901. 686 HUMAN ANATOMY. or blood platelets. As they are extraordinarily sensitive to exposure, even to entire disappearance, special precautions are necessary to insure their presence in an unal- tered condition in preparations examined. If blood be drawn directly into and mixed with a drop of .7 per cent, salt solution, or, still better, into one of weak osmic acid solution, the blood plaques appear as round or oval discs, from .002-. 004 mm. in diameter, usually somewhat less than one-third of the size of the red cells. From these they further differ in being colorless and devoid of hemoglobin and in staining readily in very dilute solutions of methyl-violet. The blood plaques are homogeneous or faintly granular, nonnucleated, never exhibit amoeboid movement, and may be directly observed as free bodies circulating within the vessels. On withdrawal from the latter, without precautions for their preservation, they at once collect in irregular masses and undergo disintegration, their remains usually being centres from which radiate the fibrillae of the fibrin net-works. Notwithstanding the attention bestowed upon these bodies, the source and significance of the blood plaques are still unde- termined, although numerous theories have been advanced. Their source has been variously attributed to disintegration of the FIG. 649. leucocytes, to extrusion from the red cells, to precipitation of globulin or to destruction of the endothelial lining of the vessels. None of these assumptions can be regarded as es- tablished, or even probable, in view of their constant presence and large normal quota an average of 300,000 plaques in one cubic millimeter of blood. Granules. In addition to the corpus- cles and the plaques, extremely minute gran- ules occur in varying numbers in normal human blood. The nature of these particles differs. Some are undoubtedly finely divided fat; others, described by H. F. M tiller under the name, hemoconia, are of uncertain compo- sition, but not fatty; while a certain propor- Human Wood p , showing^cells ^ . g probably derived f rom the disintegration of endothelial and blood-cells. The destruc- tion of the latter is accountable for the minute particles of pigment that are constant, if not numerous, constituents of the circulation. DEVELOPMENT OF THE BLOOD-VESSELS AND CORPUSCLES. The earliest blood-vessels appear within the extra embryonic mesoblast covering the vitelline sac and, therefore, beyond the limits of the embryo proper and entirely independent of the heart and axial trunks. In the lower mammals, the formation of the primary vessels takes place towards the periphery of a limited field, known as the vascular area, that encircles only a portion of the vitelline sac; in man the limited proportions of the latter enable the net-work of developing blood-channels to extend completely over the vesicle, so that the vascular area becomes coextensive with the yolk sac. Although the earliest stages in the formation of the primary blood-vessels have never been observed in man, since the vessels were already present over the vitelline sac in the youngest embryo so far examined, it is probable that the development of the human vascular tissues is essentially the same as t 1 " seen in other mammals. In the rabbit, the first indications of the developing blood-vessels are cords or groups of spherical cells that appear within the deeper, later splanchnic, layer of the mesoblast covering the vitelline sac. These tracts become larger in consequence not only of proliferation, but also of separation of the component cells. The meso- blastic elements surrounding the tracts soon become disposed as enclosing walls, within which the separated cells, now suspended in a clear fluid that has meanwhile appeared, represent the earliest blood-cells. The channels thus established unite into a net-work of primary blood-vessels that at first occupies the periphery of the vascular area, but later extends towards the DEVELOPMENT OF BLOOD-VESSELS AND CORPUSCLES. 687 embryo and, after the appearance of the large converging trunks, the vitelline veins and arteries, joins the intra-embryonic trunks that coincidently have been formed. Although the generally accepted current views relating to the independent origin of the primary blood-vessels within the vascular area have not escaped challenge, it may be regarded as established that the development of subsequent blood-vessels proceeds from the cells constituting the walls of pre-existing channels. The walls of the growing capillaries consist of delicate endothelial plates from which pointed sprouts grow into the surrounding tissue (Fig. 651). These outgrowths, direct pro- longations of the cytoplasm of the endothelial cells, are at first solid, but later become hollowed out by the gradual extension of the lumen of the capillary. Vascular loops are often formed by the meeting and fusion of the outgrowths proceeding in opposite directions, the communication being established by the final disappearance of the sep- tum in consequence of the extension of the lumen of the parent vessels. At first rep- resented by only a single layer of endothelial cells, the walls of the FIG. 650. larger blood-vessels become rein- forced by the additional layers derived from the surrounding mesoblast. Development of the Erythrocytes. The first, and for a time the only, blood-cells present within the embryo are the primary nucleated erythro- cytes derived probably directly from the mesoblastic elements within the angioblastic areas in which the earliest vessels appear. These cells, separated by the colorless plasma which appears between them and in which they henceforth float, undergo mitotic division, producing nucleated elements that, in turn, give rise to other corpuscles. The pri- mary erythrocytes are spherical, nucleated, and larger (about .01 2 mm. in diameter) than the adult red cells. At first their cyto- plasm is colorless and slightly granular, but soon becomes ho- mogeneous and tinged with hemoglobin. After the earlier fcetal months, during which prolifera- tion of the blood-cells occurs in all parts of the circulation, the corpuscles engaged in division withdraw to localities in which the blood-current is sluggish and, therefore, favorable for mitosis. Such localities are particularly the liver, spleen, and bone-marrow, the large capil- laries and tissues of which afford temporary resting places during proliferation. After a time the primary erythrocytes lose their nuclei, diminish in size, and assume their definite form. These changes begin during the second fcetal month, more and more nonnucleated discoidal red cells appearing as gestation advances, so that at birth almost all the nucleated erythrocytes have disappeared from the circulation. Since the red cells possess only a limited vitality, their constantly occurring death requires the production of new corpuscles. Preceding the development of the spleen and bone-marrow, the liver is the principal centre of blood-formation. Later the splenic and marrow tissues share this function, while after birth the red bone- marrow is the chief seat in which the continual additions of new erythrocytes necessary . . - Surface view of vascular area of chick embryo with twelve somites (29 hours) ; net-work of developing blood-vessels, most distinct in periphery of area, is connected with vitelline veins from embryo by faint channels ; cephalic segment of neural tube shows brain-vesicles and eye-buds ; caudal segment still widely open. X 16. ,' 688 HUMAN ANATOMY. to maintain the normal quota are made. The production of the new red cells within the marrow proceeds from colorless nucleated elements, the erythroblasts, that by division give rise to the nucleated erythrocytes or normoblasts which, upon the appear- ance of hemoglobin and the FIG. 651. disappearance of their nuclei, are transformed into the usual red cells, and as such enter the circulation. The disappearance of the nucleus of the normoblasts has long been a subject of discus- sion and speculation. Accord- ing to the older view still, however, accepted by many the nucleus is extruded from ^ the erythrocyte and under- _ _^7 ._ goes disintegration, thus, in the opinion of some, supply- ing the source of the blood plaques. According to the more recent views, held by Developing blood-vessels in embryonal subcutaneous tissue; Neumann, Kolliker, Pappen- a, larger capillary; b, young capillaries; c, solid protoplasmic T i -r-i outgrowths forming new vessels, x 300. heim, Israel, Ebner, and others, the disappearance of the nu- cleus is due to its solution and absorption within the erythrocyte. Under normal conditions nucleated red cells or normoblasts do not occur in the circulation. After severe hemorrhage or in other conditions requiring unusual activity of the blood- forming processes, they may be present in large numbers until the normal quota of erythrocytes has been once more established. In view of the constant presence of erythroblasts and nucleated erythrocytes within the splenic pulp, the spleen must be regarded as an additional, although under usual conditions limited, source of the red blood-cells. When, however, the necessity for rapidly augmenting the number of red cells arises, the spleen may assume the r61e of an active blood-producing tissue. Since such cells are found also in the thymus, this body probably must be included among the blood-forming organs of early life. There is no satisfactory evidence that the erythrocytes are derived from the colorless cells or from the blood plaques. Development of the Leucocytes. During the first weeks succeeding the appearance of the primary red cells, the latter are the only elements within the circu- lation. In the second foetal month, however, leuco- cytes appear, and henceforth are companions of the FIG. 652. erythrocytes. As already noted, the white cells are elements that primarily belong to the lymphatic sys- tem, from which they are poured into the blood- _ channels. Genetically the red and white cells are entirely distinct and unrelated. M $ Concerning the origin of the first leucocytes much @ Q ^' uncertainty exists, although it is generally assumed that they arise from mesoblastic cells, and, therefore, to that * extent, share with the erythrocytes a common source. Suggestive as are the views of Beard, 1 Retterer, Nus- baum and Prymak, 2 and others, supporting the origin Of leucocytes within the early thymUS in loco and not, Nucleated embryonal erythro- ,, , i i , . . r i-vtcs; two dividing cells exhibit as generally held, by invasion from the surrounding mttotk figures, x 600. mesoblast, they cannot be regarded as established. The conclusion of Beard, that the first leucocytes to appear within the embryo o\\v tlu-ir production to the metamorphosis. of the entoblastic epithelium of the primary thymus, and that the subsequent migration of the leucocytes so derived establishes foci from 1 Anatom. Anzeiger, Bd. xviii., 1900. 2 Anatom. Anzeijjer, Bd. xix., 1901. THE HEART. 689 Megakaryocyte Leucocytes which are developed the various masses of lymphoid tissue occurring throughout the body, has been challenged by Hammar, ' who found leucocytes in the blood and con- nective tissues of the human foetus before they appear in the thymus. In any event it is probable tha"t the first leucocytes originate as amoeboid cells outside the ves- sels, which they later enter, aided by their migratory powers. Their subsequent multiplication is effected by division, for the most part mitotic, of the pre-existing cells. This proliferation occurs chiefly within the lymphoid tissue throughout the body, the lymph-nodules, spleen and bone-marrow being the most important local- ities. The germ-centres of the lymph-nodules (page 936) are seats of especial activity for the formation of the types of colorless cell known as the mononuclear lymphocyte, although whether the proliferating cells originate within the germ- centres, or only complete their division in these situations after being carried from other points (Stohr), is still unsettled. From the developmental standpoint, the sharp separation of the colorless blood- cells into lymphocytes and leucocytes, as insisted upon by Ehrlich and his supporters, based on the assumption that the leucocytes originate exclusively within bone-marrow, is not well founded in view of the presence of all the typical forms of white cel.s, in- cluding the polymorphonuclear leucocytes, shortly after the first appearance of the white corpuscles and long before the advent of the earliest bone- FIG. 653. marrow (Ebner). For the pres- ent, at least, it seems most reason- able to regard the various forms of the white cells as constituting a genetic sequence in which the lymphocyte, leucocyte, and eosin- ophile represent different stages in the development of elements hav- ing a common origin. In addition to the red blood- cells in various stages of develop- ment and the different types of leucocytes, peculiar huge elements early appear in the embryonic blood-forming organs, and after birth in bone-marrow. These giant cells, or megakaryocytes (Howell), are distinguished by their large, irregularly lobulated but single nucleus from the osteo- clasts, since the nuclei of the latter are usually oval and multiple. The 'megakaryo- cytes are often observed containing within their substance the remains of both white and red cells; they are, therefore, regarded as phagocytes upon which devolves the removal of effete blood-corpuscles. Their origin is uncertain, by some (Howell, van der Stricht, Heidenhain) being referred to the leucocytes, and by others (Kolliker, Kuborn) to the endothelium of the vessels, while Ebner regards those within the bone- marrow as probably derived from fixed connective-tissue cells of the reticulum. Nei- ther form of these giant marrow-cells is normally found within the post-natal circulation. THE HEART. General Description. The heart is a hollow, muscular organ of a somewhat conical shape, situated in the lower part of the thoracic cavity, behind the lower two- thirds of the sternum. It is enclosed within a double-walled serous sac, \hapericar- diuin, and has a somewhat oblique position in the thorax, its base (basis cordis) looking upward, dorsally, and to the right, while its apex (apex cordis) points downward, ven- trally, and to the left. In consequence of this obliquity about two-thirds of the organ lies to the left and one-third to the right of the median plane of the body. 1 Anatom. Anzeiger, Bd. xxvii., 1905. 44 Osteoclast Bone trabecula Osteoblasts Section of embryonal bone-marrow, showing nucleated erythrocytes, leucocytes and mega- karyocyte. X 625. 690 HUMAN ANATOMY. It may be regarded as possessing two surfaces, which are not, however, distinctly separated, but pass into each other with rounded edges, especially upon the left side. One of these surfaces looks forward and somewhat upward, and is separated by the peri- cardium and some loose areolar tissue from contact with the sternum and the lower costal cartilages, the thin anterior edges of the lungs and pleurae also intervening to a considerable extent; this is the antcro-superior surface (facies sternocostalis), and for convenience it may be more briefly termed the anterior surface. The other, the postero-inferior or posterior surface (facies diaphragmatica), rests directly upon the upper surface of the diaphragm. At about one-third of the distance from the base to the apex a deep circular groove, more distinct upon the posterior surface, surrounds the heart, separating an FIG. 654. Superior vena cava Systemic aorta (aorta) Right auricular appendage Right auricle Auriculo-ventricular groove Line of reflection of pericardium Ductus arteriosus Pulmonary aorta (pulmonary artery) Right ventricle Anterior interventricu lar groove Anterior aspect of heart hardened in situ ; probe lies in transverse sinus of pericardium. upper thin-walled auricular portion of the organ from a lower thick-walled ventricular one : this groove is termed the auricuh-ventricular groove (sulcus coronaritts), and contains the proximal portions of the coronary vessels which supply the heart's sub- stance. Extending towards the apex from this groove, two other shallower grooves are to be observed, one situated towards the right side of the anterior surface and the other upon the posterior surface. These grooves, which also lodge portions of the coronary vessels, are the anterior and posterior interventricular grooves (sulci limui- tudinalcs), and mark the line of separation of the ventricular portion of the heart into two chambers known as the right and left ventricles. From the base of tin- right ven- tricle a large blood-vessel, \\\v pn/)HO)iary aorta ^\ pulmonary artery, arises, while from the base of the lett ventricle, and almost immediately posterior to the root of the pul- monary aorta, the systemic aorta takes its origin. The orifices by which each of these THE HEART. 691 vessels communicates with its ventricle are guarded by special valves known as the scniilitnar rak'cs. The auricular portion of the heart rests upon the posterior part of the base of the ventricular portion, and is best viewed from the posterior surface (Fig. 655), since it is almost completely hidden anteriorly by the two aortae. Like the ventricular portion, it is composed of two separate chambers, which are not, however, very apparent on surface view. These chambers are the right and left auricles, and com- municate with the corresponding ventricles by auricula-ventricular orifices guarded by special auricula-ventricular valves. From the lateral part of the anterior sur- face of each auricle a process, the aw icular appendix, arises. These appendices are FIG. 655. Left common carotid artery" Left subclavian artery Innominate artery Left pulmonary artery Vestigial fold Sup. left pulm. vein Left auricular appendix Inf. left pulm. vein Coronary sinus / Left ventricle Azygos vein Superior vena cava Right pulmonary artery Superior Inferior right pulmonary veins Left auricle Right auricle Inferior vena cava Right ventricle Apex x Posterior aspect of heart hardened in situ ; showing lines of reflection of pericardium. slightly flattened prolongations of the auricles, and bend forward around the bases of the aortae, which they slightly overlap in front ; they are the only portions of the auricles visible upon the anterior surface of the heart. Upon its superior surface the right auricle receives the termination of a large venous trunk, the vena cava superior, which returns to the heart blood from the head, neck, upper extremities, and walls of the thorax ; while upon its posterior surface is the opening of another large vessel, the vena cava inferior, which returns blood from the abdominal and pelvic walls and viscera and from the lower limbs. The left auricle receives upon its surface the four pulmonary veins arranged in pairs, one pair situated towards the left portion of the auricle and the other towards the right. 692 HUMAN ANATOMY. FIG. 656. Position. The heart may vary considerably in position without being regarded as abnormal, but what may be considered its typical position with reference to the anterior thoracic wall may be stated about as follows : The apex is situated behind the fifth intercostal space, about 8 cm. (3^ in.) from the median line, this position being median to and slightly below the junction of the fifth costal cartilage with its rib. The level of the base may be approximately indicated by a line drawn from a point slightly above the upper border of the third costal cartilage of the left side, about 4. 5 cm. (i^4 m -) ^ rom t^ 6 median Hire of the sternum, to a point upon the upper border of the third costal cartilage of the right side, about 3 cm. (i^ in.) from the middle line. If now the left end of the base-line be. united to the apex point by a line which is slightly convex towards the left, and a line, markedly convex towards the right, be drawn from the right end of the base-line to the junction of the seventh costal cartilage of the right side with the sternum and thence to the apex point, a heart-area will be en- closed which corresponds to the out- line of the organ as seen from in front. Considerable importance at- taches to the location of the auriculo- ventricular and aortic orifices with reference to the anterior thoracic wall. The right auriculo-ventricular ori- fice in a typical heart lies on a level with the attachment of the fifth costal cartilages to the sternum, almost be- hind the median line of that bone and opposite the fourth intercostal space, while the left auricuh-ventriculaf orifice is opposite the sternal end of the left third intercostal space. In other words these openings lie along a line which corresponds with the auriculo-ventricular groove, and this may be represented by a line drawn from the upper border of the junc- tion of the seventh costal cartilage of the right side with the sternum to the sternal end of the third left costal cartilage. The right orifice is lo- cated upon the line where it is inter sected by a line joining the sternal ends of the fifth costal cartilages. while the left one is situated at its upper end. The systemic and pulmonary aortic orifices are situated at about the level of the attachment of the third costal cartilages to the sternum, the pulmon- ary orifice being behind the sternal end of the third left cartilage-, while the aortic orifice is behind the left half of the sternum, a little below and to the right of the pul- monary one, the two orifices overlapping for about one-quarter of their diameters It is to be noted, however, that the pulmonary aorta is directed upward and to the left, while the systemic aorta inclines decidedly towards the right in the first part of its course; and since the sounds caused by the valves which guard the orifices are carried in the direction of the blood-stream, auscultation of the pulmonary seinilnnar valves may be practised over the sternal end of the second left intercostal space, while that of the systemic valves is best performed over the sternal end of the second right space. Similarly the close proximity of the areas of the left auriculo-ventricular and systemic aortic orifices, as projected upon the thoracic wall, might lead to confusion, Positicn of heart and valves in relation to anterior thoracic wall. A, aortic valve; P, valve of pulmonary aon a; T, tri- cuspid valve ; M, mitral valve. THE CHAMBERS OF THE HEART. 693 were it not that the course of the blood passing through the two orifices is in opposite directions, and the auscultation of the auriculo-ventricular orifice is consequently satisfactorily performed towards the apex of the heart. Considerable variation from the position of the heart indicated above may be found. Thus, the apex may be situated behind the fifth costal cartilage, or more rarely the sixth, and the pul- monary aortic orifice may occur as high up as the second intercostal space, or as low as the level of the fourth costal cartilage. The heart naturally has its position altered somewhat during its contraction and during the respiratory acts, and the position of the body will also have some effect in modifying its location. Resting, as it does, upon the diaphragm, the heart will alter its position somewhat with altera- tions <>f that muscle ; and since in the child the diaphragm is somewhat higher and in the aged somewhat lower than in the middle period of life, corresponding changes according to*age will be found in the position of the heart. It may be noted, furthermore, that the position of the heart as determined in the cadaver will, as a rule, be slightly higher than in the living body, owing to post-mortem tissue changes which allow the diaphragm to assume a more vaulted form than is usual in life. Relations. As regards its relations the heart is completely enclosed within the pericardium, with which alone surrounding organs come into contact. In what fol- lows it is really the relations of the pericardium that will be described, although of necessity these relations are indirectly those of the heart and will be spoken of as such. Anteriorly the greater part of the heart is covered by the anterior borders of the lungs and pleurae, which separate it from contact with the anterior thoracic wall. As a rule, the anterior borders of the pleurae are in contact from the level of the scvond costal cartilage to that of the fourth, but below the latter level they separate, the border of the left pleura diverging from the median line more rapidly than that of the right. In consequence, throughout an irregularly triangular area (Fig. 1580), whose vertical diameter extends from the level of the fourth to that of the sixth costal cartilages, the heart is uncovered by the pleurae and lies directly behind the thoracic wall. This area forms what is termed by clinicians the area of absolute dul- ncss. Laterally the heart is in relation with the lungs, the phrenic nerves passing downward on either side between the pericardium and the pleura. Posteriorly the relations are again with the lungs and with the oesophagus and the thoracic aorta. Infcriorly the heart rests directly upon the diaphragm, beneath which is the stomach. Size and Weight. There is considerable individual variation in the size of the heart, and marked discrepancies exist in the- observations that have been re- corded. It may be said that in the adult the heart, on an average, will possess a length of from 12-15 cm - (4?4~6 in.), a greatest breadth of from 9-11 cm. -4% in.) and a thickness of from 5-8 cm. (2-3^ in.). Its weight has been given at from 266-346 gm. (9^-12^ oz. ) for males and from 230-340 gm. (8^5-12 oz. ) for females, ( the average of a series of observations by different authors giving 312 gm. ( 1 1 oz. ) for the male and 274 gm. (9^ oz. ) for the female. The proportion of heart to the weight of the entire body, according to an average drawn from several observers, is i : 169 in the male and i : 162 in the female. It must be remembered, however, that the weight of the heart increases with age up to about the seventieth year, probably a slight diminution taking place after that period. THE CHAMBERS OF THE HEART. It has already been noted that the heart is composed of four chambers, a right and left auricle and a right and left ventricle. As the heart lies in position, little of the auricles, with the exception of the auricular appendices, can be seen, since they have in front of them the roots of the aortae. In the ventricular portion the greater part of the anterior surface is formed by the right ventricle, a small portion only of the left ventricle showing to the left and at the 'apex, the whole of which is formed by the left ventricle. The four chambers will now be considered in succession, begin- ning with the auricles. The Right Auricle. The right auricle (atrium dcxtrunO is a relatively thin- walled chamber having in cross-section a roughly triangular form, the various sur- 694 HUMAN ANATOMY. faces, however, passing into one another almost insensibly without forming distinct angles. Viewed externally, the roof of the chamber is directed upward, backward, and somewhat to the right, and near its junction with what may be termed the poste- rior wall receives the superior vena cava. The posterior wall, also smooth and rounded, receives, near its junction with the median wall, the inferior vena cava, and below and to the left of this, in the posterior auriculo- ventricular groove, is the ter- minal portion of a vein which winds around the heart from the left and is termed the coronary sinus. The antero-lateral wall is prolonged into a somewhat triangular diverticulum with crenulated edges, which winds anteriorly around the proximal por- tion of the pulmonary aorta and is known as the right auricular appendix (auricula dextra}. The median wall is not visible on surface view, and is formed by a rather thin muscular partition, the auricular septiim (septum atriorum), which is common to both auricles ; and the floor, also invisible from the exterior, corresponds to the base of the right ventricle, and is perforated by an oval aperture, the right auricula-ven- tricular orifice, which places the cavity of the auricle in communication with that of the right ventricle. FIG. 657. Vena azygos Right pulmo- nary artery Systemic aorta Pulmonary aorta or artery Right auricular appendage Right ventricle, conus arteriosus Sup. pulm. vein Right auriculo- Inf. pulm. vein )M Hit HHL ventricular valve ''^fc^^Bfek^ / ii^k\ .v -aa m\"% Fossa oval is, surrounded by annulus Inferior vena cava Orifice of coronary sinus, guarded by Thebesian valve Eustachian valve Depression receiving Thebcsian veins Interior of right auricle exposed after removal of part of heart wall. When the interior of the right auricle is examined (Figs. 657, 661), tin- surface is found to be for the most part smooth, being lined throughout by a delicate shining membrane covered by flattened cells and termed the endocardium. The general smoothness of the surface is, however, interrupted here and there by minute depressions (foramina venarum minimarum) into some of whih open the orifices of Thebesian veins that traverse the walls of the heart. The cavity of tin- auricular appendix is crossed by a net-work of anastomosing fibre-muscular trabeculse, the muscnli pectiuati, which are everywhere lined upon their free surfaces by endocardium and give to the appendix a somewhat spongy texture. In the roof of the auricle is seen the circular orifice of the superior voni /vrrvr, unguarded bv valves and having a diameter of from 18-22 mm., and on the posterior wall is the somewhat oblique opening of the inferior re)ia eara, somewhat larger than that of the superior one, measuring from 27-36 mm. in diameter. The lower and lateral margins of this orifice are guarded 'by a crescentic fold, the I'".itsiachian ;-alre ( valvula venae cavae inferiors ), which tends to direct the blond entering by the vein upward and medially. and is the remains of a structure of considerable importance- during fu-tal life TH-E CHAMBERS OF THE HEART. 695 FIG. 658. onary aorta 708). Between the superior and inferior venae cavse there may sometimes be seen a more or less marked prominence of the posterior wall, the tubercle of Lower (tuberculum intervenosum), the remains of a structure also of importance in the foetal circulation. Below and somewhat median to the opening of the inferior vena cava is the circular orifice of the coronary sinus, measuring about 12 mm. in diameter, and guarded, like the inferior caval orifice, by a crescentic valve which surrounds its lateral margin and is termed the Thebesian valve (valvula sinus coronarii). The median wall, in addition to a number of Thebesian orifices, presents at about its centre an oval depression, the fossa ovalis, whose superior and anterior borders are surrounded by a thickening or slight fold termed the annulus ovalis (limbus fossae ovalis). The fossa ovalis indicates the position of what was in foetal life the foramen ovale, through which the blood entering the right auricle froni the inferior vena cava passed directly into the left auricle and so joined at once the systemic circulation (page 929). This foramen traversed the auricular septum obliquely, the septum really consisting of two folds, one of which projected backward from the anterior wall of the auricular portion of the heart, and the other forward from the posterior wall, the plane of the latter fold lying slightly to the left of that of the former one. After birth these two folds increase in size so that their free margins overlap and event- ually fuse, closing the foramen, and the original free edge of the ante- rior fold becomes the annulus of Vieussens, while the floor of the fossa ovalis is formed by the pos- terior fold. It occasionally happens that the foramen ovale fails to close after birth, remaining sufficiently open to permit of serious disturb- ances of the circulation which are usually, although not always, early fatal. Very frequently, however, the fusion of the overlapping sur- iaces of the two folds is not quite complete, and a small, oblique, slit- like opening persists between the two auricles. In such cases during the contraction of the auricles the pressure of the blood on the over- lapping walls of the slit brings them into close apposition and effectually closes the slit, so that no disturbances of the circula- tion result from its presence. This slit-like opening has been found to be present in somewhat over 30 per cent, of the adult hearts examined. The Left Auricle. The left auricle (atrium sinistrura) has the same general external form as the right one, and, as in the latter, its antero-lateral wall is prolonged into an auricular appendix which curves forward around the left side of the proximal portion of the systemic aorta. Upon its posterior surface the auricle receives the four pulmonary veins arranged in pairs, one of which is situated nearer the medial and the other towards the lateral edge of the surface, and passing obliquely over this surface towards the coronary sinus is a small vein, known as the oblique vein of the left auricle (vena obliqua atrii sinistri [Marshalli] ), which represents the proximal end of the left vena cava superior present during early embryonic life (page 927). Viewed from the interior, the walls of the left auricle, like those of the right one, are everywhere lined by a smooth, shining endocardium ; in the appendix the spongy structure due to the existence of anastomosing muscidi pcctinati also occurs, and occasional depressions of the surface mark the openings of ven/ r.v. so called because their stimulation produces a marked fall in the blood-pressure, not on account of any action upon the heart-beat, since they lead the stimulus away from the heart, but by acting rellexly upon the intestinal vessels so as to produce their dilatation and, by thus lessening the peripheral resistance against which the heart must contend, lessen the work which the organ lias to do. Whether the various efferent fibres pass directly to the muscular tissue of the heart or ter- minate upon cardiac ganglion-cells which transmit the impulse to the muscle-fibres is a point uhich remains to be determined, although, from analogy with what is known as to the relation of the cerebro-spinal fibres to other portions of the involuntary muscular tissue, it would seem prob.ible that the | meumogastric efferent fibres terminate primarily upon the cardiac ganglion- cells. THE PRIMITIVE HEART. 75 DEVELOPMENT OF THE HEART. In the mammals in which the earliest stages in the development of the heart have been observed, this organ arises as two separate tubes that are formed by folding of the visceral mesoblast near the margin of the embryonic area. This folding occurs while the embryo is still spread out upon the surface of the yolk-sac and produces on each side an elevation, a heart-tube, that projects into the primitive body-cavity ( Fig. 668). Each heart-fold differentiates into a thicker outer or myocardial layer, which gives rise to a portion of the cardiac muscle, and a very thin inner endocardial layer, from which the serous lining of the heart is derived. The latter consists of a single stratum of mesoblastic cells surrounded by the muscle-layer, but separated by a distinct space, as a shrunken cast lies within its mould. With the beginning constriction of the gut-tube from the vitelline sac and the associated approximation of the splanchnopleura of the two sides, the heart-tubes, at first widely apart, gradually approach the mid-line until they meet beneath the ventral surface of the primitive pharynx, in advance of the yolk-sac. Upon coming into contact, the cavities of the two heart-tubes for a brief period remain separated by the partition formed by the opposed portions of the myocardial layers. Very soon, how- ever, solution of this septum occurs and the two sacs become a single heart. The endothelial tubes are last to fuse, retaining their independence after the myocardial walls have blended. Upon fusion of the endothelial layers the conversion of the double tubes into a single heart is complete. FIG. 668. The early venous trunks the body-stems (cardinals and jugulars) within the em- bryo and the vitelline and allantoic (later umbilical) veins from the extra embryonic vas- cular net-works converge to- wards a common sac, the sinus venosus, which joins the caudal end of the cylindrical primitive heart. The slightly tapering cephalic extremity of the latter becomes the truncus arteriosus, from which two trunks, the ventral aorta, are prolonged forward beneath the primitive pharynx, giving off the aortic bows that traverse in pairs the series of visceral arches. The primitive heart consists, therefore, of a cylinder, somewhat contracted at its anterior end, that occupies the ventral mid-line in the later cervical region. The blood poured into the sinus venosus by the veins enters its posterior extremity and escapes anteriorly through the truncus arteriosus. Although for a brief period the heart-tube retains its median position and straight cylindrical form, its increasing length soon causes it to become bent upon itself and to assume the S-like contour shown in Fig. 672 A, from an embryo of 2. 15 mm. in length, in which the venous end of the tube lies below and to the left and the arterial trunk above and to the right. The intermediate portion of the tube, extending at first downward and then obliquely upward and towards the left, is the primitive ventricle, the early sigmoid heart-tube already suggesting the recognition of an arterial, ventricular, and venous segment. During the further development of the heart a rearrangement of these three divisions takes place, since the venous segment, orginally below, gradually acquires a position above and behind, while the primitive ventricle comes to lie in front and below (Fig. 672). With the completion of this rotation, a deep external groove appears between the ventricular and venous chamber, now the primitive auricle, that indicates the position of a contracted passage, the auricular canal (Fig. 672, C), as the common auriculo-ventricular opening is termed. Coincidently with the upward migration of the venous segment, a lateral outpouching of the auricular chamber appears on each side of the truncus arteriosus. These expansions, the primary ait- 45 \. ^ i X Myocardial layer Endocardial layer Gut-tube Splanch- nopleura Heart-tube Transvetse section of very young rabbit em- bryo, showing two heart-tubes widely separated by unclosed digestive tube. X 150. 706 HUMAN ANATOMY. ricular appendages, rapidly increase, until they form the most conspicuous part of the young heart (Fig. 673, C), embracing the upper part of the truncus arteriosus and overlying the ventricle. Meanwhile the ventricular segment has assumed the most dependent and ventral position, for a time appearing as a transversely expanding sac (Fig. 672, B ) that in form recalls a greatly dilated stomach, the truncus arteriosus joining the " pylorus," and the contracted auricular canal suggesting the oesophagus. Soon, however, the higher right end of the ventricular segment sinks to the level and gains the ventral plane of the left end, the ventricle in consequence losing in width but gaining in height. A shallow longitudinal crescentic furrow, the later interventricular groove, now appears on the surface of the ventricle and suggests the subdivision of this seg- ment into right and left FIG. 669. chambers, at the same time indicating the posi- tion of the growing inter- nal partition that leads to this separation. Sections of the young heart ( Fig. 670 ) show the venous and ventricular segments as widely com- municating portions of the sigmoid tube, the walls of which are composed of the myocardial and endothe- lial layers. In somewhat older embryos (Fig. 671), the communication between these divisions of the heart- tube exhibits a slight con- traction, marking the posi- tion of the later auricular canal, which becomes a nar- row transverse cleft that connects the primitive ven- tricle with the auricular chamber. The myocar- dial layer of the heart- wall, particularly in the ventricle, also shows the beginning of the trabeculae that invaginate the endo- thelial lining and event- ually lead to the conspicu- ous modelling of the interior of the adult heart. Frontal sections of the young human heart (Fig. 674, A} show the commencing separation of the ventricular and auricular chambers into right and left halves. This division is effected by the formation of a vertical partition consisting of an upper auricular, a middle valvular, and a lower ventricular part, supplemented by the aortic septum that appears in the truncus arteriosus and subdivides the latter into the pulmonary and systemic aortae. The subdivision of the auricle, which anticipates that of the ventricle, begins in the fourth week with the downward extension of a crescentic fold, the auricular sep- tum, or septum primum, that gradually grows from the postero-superior wall of the auricle towards the auricular canal and fuses with the partition that, as tin- septum intermedium, is formed within the canal by local thickening of its anterior and pos- terior lips. In this manner not only the common auricular chamber, but also the transversely elongated auriculo-ventricular opening, is separated into a right and a Right duct of Cuvier Right cardinal Primitive ventricle Pericardial sac. cut Left urnhil- ical vein Left vitel- line vein Right umbilical vein Right vitelline vein Reconstruction of upper part of human embryo of third weelf (3.2 mm.), showing relation of heart and blood-vessels. X 50. (Drawn from His model.) DEVELOPMENT OF THE HEART. 707 FIG. 670. Neural canal Aorta Digestive tube left half. The interauricular partition, however, is not complete, since an opening appears in its upper part even before it has finished its downward growth and union with the valvular septum. This opening enlarges and remains as lh^ foramen ovale that persists until birth as a direct passage for the blood from the right into the left auricle during the continuance of the foetal circulation (page 929). The subdivision of the ventricular chamber, which commences a little later than that of the auricle, is accomplished chiefly by the formation of the ventricular septum. The latter grows from the postero-inferior wall of the ventricle as a cres- centic projection that continues inward, a thickening of the ventricular wall corre- sponding in position with the external interventricular groove. The partition thus formed extends towards the auriculo-ventricular opening, where it meets and fuses with the septum intermedium, in this manner insuring the communication of the right and left auricles with the corresponding ventricles through the intervening respective portions of the valvular opening. The isolation of the two ventricles from each other, however, is not at first com- plete, owing to the ventricular partition being imperfect above and in front. This deficiency is overcome by the down- ward extension of the aortic septum within the bulbus arteriosus (as the somewhat dilated lower end of the trun- cus arteriosus is now appropriately called ) until it meets and fuses with the ventricular partition, thus completing the separation of the cardiac chambers into a right and left heart. The part of the ventricular partition contributed by the aortic septum always remains thin and constitutes the pars membran- acea of the adult organ. Coincidently with the foregoing changes, the auricles undergo impor- tant modifications in their relations with the blood-vessels opening into them. During the development of the auricles, the oval sinus venosus, into which is conveyed the blood returned by the vi- telline, allantoic (umbilical) and body- veins, elongates transversely into a crescentic sac, the convexity of which is in contact with the back of the auricles, its opening into the latter having shifted so that it is in relation with only the right half of the auricular chamber. With the expanded body and right horn of the venous crescent communicate the vessels that later are represented by the superior and inferior venae cavae, while the elongated and smaller left horn receives the left duct of Cuvier that becomes the coronary sinus. For a time the opening of the sinus venosus, or sinus reuniens (His), into the heart occupies the posterior wall of the right half of the auricle. It is guarded by the venous valve, consisting of a right and left leaflet, that is prolonged forward along the roof of the auricle as a crescentic ridge, the septum spurium (Fig. 674, A), With the continued appropriation of the venous sinus by the expanding auricle, the single aperture of the sinus disappears as the sac becomes part of the auricular chamber, thereupon the two venae cavae and the coronary sinus open directly into the right auricle by an independent orifice. That of the superior cava lies in the upper posterior part of the auricle, that of the inferior cava being lower and more lateral, with the smaller orifice of the coronary sinus slightly below. The septum spurium, the greater part of the left, and the upper part of the right segment of the arching fold that originaHy surrounds the opening of the sinus venosus disappear during the appropriation of the venous sac by the auricle. The lower part of the right, leaflet, docardial layer Myocardial layer Primitive ventricle Transverse section of early rabbit em- bryo passing through young heart, showing venous segment behind and arterial in front. X 75- 708 HUMAN ANATOMY. Fig. 671. on the contrary, persists and differentiates into the larger Eustachian retire, that guards the lower margin of the inferior vena cava and directs its blood-stream towards the foramen ovale, and the smaller Thebesian valve, that protects the orifice of the coronary sinus. As above noted, the separation of the two auricles is incomplete on account of the existence of the foramen ovale within the interauricular partition. From the roof and anterior wall of the right auricle an additional and relatively thick crescentic ridge, the septum secundum, arches around the foramen ovale of \vhich it forms the anterior or ventral boundary. It lies close to and parallel with the auricular septum and fuses below with the lower part of the left segment of the venous valve to form the limbus Vieussenii that later limits the fossa ovalis, marking the former position of the foramen ovale. The latter, therefore, is included between two partially overlapping crescentic margins, that contributed by the septum auriculum lying behind and to the left, and that by the septum secundum in front and to the right, a narrow sagittal cleft intervening so that the surfaces of the lunate borders are not in contact. Since the division of the heart into a right and left side is inseparably con- nected with the development of the lungs and the consequent necessity for a distinct pulmonary circulation, provis- ion for the return of the blood from the lungs to the heart is made by the early formation of the pulmonary veins. These arise in pairs, one pair for each lung; close to the heart each pair unites into a single right or left stem that, in turn, joins with its fellow of the oppo- site side to form one short common trunk. For a time none of these ves- sels communicate with the heart, but later the common single pulmonary vein opens into the left auricle close to the septum. With the subsequent growth and expansion of the auricles an appro- priation occurs on the left side similar to that affecting the sinus venosus on the right, in consequence of which the short Aorta Pharynx ,-ocar- i u in Truncus arteriosus Transverse section of somewhat older em- bryo, showing differentiation into auricles, ventricle and truncus arteriosus. X 75- common pulmonary vein is first drawn into the heart, to be followed next by the two secondary and, finally, by the four primary pulmonary veins, all of which then open by separate orifices into the enlarging left auricle. The fre- quent variations in the number of the pulmonary veins and in their relations to the heart are usually to be referred to arrest or modification of this foetal appropriation. The differentiation of a right and left auriculo-ventricular valve proceeds from the subdivision of the auricular canal by the septum intermedium. The latter is fonm-d by the approximation and union of the median cushion-like projections upon the ventral and dorsal walls of the common auriculo-ventricular opening. The unob- literated lateral portions of the latter are triangular in outline and guarded by pro- liferations of the endocardium. Those of the lower margins of the valves elongate and project into the ventricles on the right side, giving rise to two leaflets, and on the left to a single flap. An additional prolongation from the partition contributes a septal leaflet on each side. In this manner the complement of flaps for the tricuspid and bicuspid (mitral) valves is early provided. The close relation between thr lc if- U-ts and the attached restraining bands, the chordae tendineae, results from the secondary union of the immature Maps with the trabeculae of the spongy myocardium of the young heart. The loose muscular walls undergo partial consolidation, so that ' DEVELOPMENT OF THE HEART. 709 the outer strata of the ventricular muscle become compact while the inner layers for a time retain their characteristic trabeculse. Those attached to the valves undergo thickening and consolidation and become the papillary muscles; a few persist as ties FIG. 672. A B C Reconstructions of developing hearts ; A, from human embryo of about 14 days (2.15 mm. long) ; , of 21 days (4.2 mm.); C of 23 days (4.3 mm.); ta, truncus arteriosus : pv, primitive ventricle; sv, sinus venosus; aa,a'a', right and left auricular appendages ; avc, auriculo-ventricular canal. X 20. (Drawn from His models.) FIG. 673. A B Iv h> Iv Reconstructions of developing hearts; A, from human embryo of 25 days (5 mm. greatest length); , endo- thelial heart from same; C, of 35 days (13.7 mm.); ra, la, right and left auricles represented by large auricular appendages; rv, Iv, right and left ventricles; la, truncus arteriosus; e, endothelial tube; ac, auriculo-ventricular canal; ag, interventricular groove. X 20. (Drawn from His models.) or moderator bands ; while the majority retain their freedom to a lesser degree and, as the columnar carneae, produce the conspicuous modelling of the interior of the ven- tricles. The muscular tissue, which at first extended to and even within the valve- 7 io HUMAN ANATOMY. leaflets, subsequently undergoes partial atrophy and disappears from the flaps and adjoining parts of the attached bands, the latter thereby being converted into the fibrous chordae tendineae. Even before the longitudinal subdivision of the bulbus arteriosus occurs, the junction of this tube with the primary ventricle is marked by four cushion-like thick- enings that project from the interior of the bulb. These elevations, which consist of immature connective tissue covered by endothelium, furnish the leaflets of the aortic and pulmonary semilunar valves. The formation of the aortic septum within the bulbus arteriosus begins some distance above the valve and immediately below the origin of the right and left pulmonary arteries. From this point the partition gradu- ally grows downward until it encounters the elongated lateral pair of the original four valve-cushions, of which one lies in front, one behind, and two at the sides of the bulb. With the completion of the division of the bulbus arteriosus into the systemic and pulmonary aortae, the septum cleaves the two lateral cushions, each of the resulting valves "being guarded by three leaflets so disposed that the original and undivided flap of the pulmonary artery lies in front, and that of the aorta behind. The partial rotation that later places the aortic valve behind and to the left of the pulmonary brings about the disposition observed in the adult (page 700), in which the single leaflet of the aortic semilunar valve lies in front and that within the pulmonary artery is behind. At first comparatively thick, the leaflets suffer partial absorption, whereby they are converted into the membranous cusps that bound crescentic pouches, the sinuses of Valsalva, which lie between the leaflets and the wall of the vessels. PRACTICAL CONSIDERATIONS : THE HEART. It is possible here only to indicate with great brevity certain changes in the position of the heart which should be studied in connection with its relations. The apex beat, normally to be found about one inch below and two inches to the sternal side of the left nipple, is due to the recoil of the left ventricle as it empties its contents into the aorta, to the lengthening of that vessel as the blood enters it, to the consequent straightening of the arch (carrying the heart forward), and to the absence of any interposed lung-tissue over the "area of absolute dulness." The apex beat (and usually the heart itself) is (a) raised in cases of ascites, tympanites, large abdominal tumors, and atrophic pulmonary conditions ; (b) de- pressed in aortic aneurism, mediastinal growths, pulmonary emphysema, pleural effusion, and hypertrophy or dilatation of the left ventricle ; (*-) displaced laterally to the right by left pleural effusion, splenic tumors, hypertrophy of the right ventri- cle, to the left by hepatic tumors, right pleural effusion, hypertrophy of the left ven- tricle. The heart may be drawn to either side by contracting pleural adhesions. As the area of absolute dulness "superficial cardiac area" corresponds to that portion of the cardiac substance which is not separated by pulmonary tissue from the thoracic wall, it follows that its extent varies inversely with the size or expansion of the lungs. In emphysema the area of cardiac dulness may quite disappear ; in the later stages of fibroid phthisis it may be much larger than normal. In relation to the anatomy of the valves and cavities of the heart, the sounds produced by the passage of blood through them should be considered in connection with at least a few of the modifications caused by the chief pathological changes that affect that organ. It may be said here, for the sake of clearness, that the/V-y/ sound occurs during the contraction of the ventricles, when the auriculo-ventricular open- ings should be closed by the mitral and tricuspid valves and the aortic and pul- monary orifices should be open, and that it is due to (#) the shutting of the valves, and () the impulse of the apex against the thoracic wall, with possibly some addi- tion from (r) the contraction of the walls of the ventricles, although this latter factor is doubtful. The second sound occurs during the auriculo-ventricular dilatation, and is due to the closure of the pulmonary and aortic semilunar valves caused by the recoil of the blood-current brought about by the elastic coats of tlu- aorta and pulmonary arteries. If a murmur heard over the chest is synchronous with the radial pulse ( systolic i, it occurs during ventricular contraction, and is usually due either ( a ) to regUTgita- PRACTICAL CONSIDERATIONS: THE HEART. 711 tion of blood through an auriculo-ventricular valve that does not accurately close the corresponding opening or (6} to an obstruction to the exit of blood from the ven- tricle at the aortic or at the pulmonary orifice. If a heart murmur is not synchronous with the radial pulse (diastolic or pre- systolic), it may be caused by.() obstruction to the passage of blood from an auricle into a ventricle (mitral or tricuspid stenosis) ; or () regurgitation from the pulmonary artery or aorta into the right or left ventricle (pulmonary or aortic insuf- ficiency). Of these various murmurs those due to mitral and aortic insufficiency are by tar the most frequent. Valvular disease of the left side of the heart (90 per cent, of all cases) is more frequent on account of the greater work required of this side and the associated greater liability to strain, rarely sudden, usually trifling but oft repeated. 1. Mitral insufficiency an imperfect closure of the segments of the left auriculo- ventricular valve causes a systolic murmur, heard best (a) over the apex and super- ficial cardiac area because there the ear can most nearly approach the left ventricle without the interposition of pulmonary tissue or of the right ventricle ; () in the axilla, because it is transmitted in the direction of the arterial blood-current ; and (c) at the angle of the left scapula, or between the fifth and eighth thoracic vertebrae, for the same reason, and because at that point the left ventricle is posterior. In addi- tion, the pulmonary second sound is louder and sharper than natural (accentuated) because of the following series of occurrences which should be studied in connection with the structures and cavities involved : over-filling and distention of the left auricle, imperfect emptying of the pulmonary veins, pulmonary congestion and re- sistance to the systole of the right ventricle, increased fulness of the pulmonary arter- ies, and corresponding increase of the backward pressure upon the pulmonary valves, shutting them more sharply and forcibly (accentuation). Furthermore, as the distention of both ventricles results in hypertrophy, the transverse diameter of the area of cardiac dulness is distinctly increased. 2. In mitral stenosis (often associated with some degree of mitral insufficiency) a murmur is usually heard, preceding the pulse-beat (presystolic), corresponding, that is, to the auricular systole, and, as the left auricle is distended from imperfect emptying and hence the pulmonary veins and arteries and the right heart are in the same condition, there is again a loud accentuation of the second sound. 3. Aortic insufficiency is characterized by a murmur that follows the radial pulse (diastolic), occurs as the blood is being driven back into the ventricle by the elastic aorta, is heard best over the sternal end of the second right intercostal space (vide supra), is often propagated towards the xiphoid cartilage or down the left side of the sternum, and is more rarely heard in the carotid or axillary vessels, i.e., as it is a murmur primarily due to the reflux of blood from the aorta into the ventricle, it is, in accordance with well-known laws of physics, transmitted in the direction of the current causing it. The great distention and subsequent hypertrophy of the left ventricle caused by its inability to empty itself result in a marked increase of percussion dulness. As the aortic valves do not come together normally, the aortic second sound is feeble or absent. 4. Aortic stenosis (much less frequent than insufficiency) is usually accompanied by a systolic murmur heard at the aortic cartilage and transmitted along the great vessels to the axilla, to the neck, and along the spine, but difficult to distinguish from similar murmurs caused by disease of the inner coat of the aorta or by mere roughening of the valves. As the aorta receives a diminished quantity of blood, one factor in the production of the apex beat is lessened in effectiveness and the cardiac impulse is often also lessened. Dilatation and hypertrophy of the left ven- tricle with subsequent secondary changes in the other cavities may follow, but are not nearly so marked as in aortic insufficiency. Valvular disease of the right side of the heart may, on account of its relative infrequency and to avoid repetition, be even more briefly summarized : i. Tricuspid insufficiency often following pulmonary conditions obstructing the circulation is characterized by (a) a low systolic murmur heard well over the 7i2 HUMAN ANATOMY. lower sternum on account of the relation of the right auriculo-ventricular orifice to the middle of that bone ; (6) increase of percussion area to the right of the sternum because of the distention and dilatation of the right auricle that follow ; and, (<:) from the same cause and the resultant backward pressure on the systemic veins, a venous pulse-wave, seen best in the internal and external jugular on the right side, but not infrequently recognizable on both sides, in the subclavian and axillary veins also, or as a systolic expansile impulse in the liver transmitted through the inferior cava and hepatic veins. 2. Tricuspid stenosis, like that of the mitral valve, is apt to cause a presystolic murmur, and for the same physical reasons. 3 and 4. Pulmonary insufficiency and stenosis (disease of the pulmonary valves) are so rare and so uncertain in their physical signs as to require mention merely to complete the survey of the group. The various forms and degrees of hypertrophy or dilatation of the heart which are associated with the foregoing conditions can be readily understood by con- sidering the increased resistance and correspondingly increased exertion which are brought about by the valvular changes. The essential cause of hypertrophy in the heart, as in other muscles, is increased work. The etiological factors which neces- sitate this should be studied in connection with the anatomy of the heart and have been well summarized by Osier. Hypertrophy of the left ventricle alone, or with general enlargement of the heart, is brought about by (a) Conditions affecting the heart itself : (i) Disease of the aortic valve ; (2) mitral insufficiency ; (3) pericardial adhesions ; (4) sclerotic myocarditis ; (5) dis- turbed innervation with overaction, as in exophthalmic goitre, in long-continued nervous palpitation, or as a result of the action of certain articles, such as tea, alcohol, and tobacco. In all of these conditions the work of the heart is increased. In the case of the valve lesions the increase is due to the increased intraventricular pressure ; in the case of the adherent pericardium, or the myocarditis, to direct interference with the symmetrical and orderly contraction of the chambers. (^), Conditions acting upon the blood-vessels: (i) General arterio-sclerosis, with or without renal disease ; (2) all states of increased arterial tension induced by the contraction of the smaller arteries under the influence of certain toxic substances ; (3) prolonged muscular exertion, which enormously increases the blood-pressure in the arteries ; (4) narrowing of the aorta, as in congenital stenosis. Hypertrophy of the right ventricle is met with under the following conditions : ( i ) Lesions of the mitral valve, either incompetence or stenosis, which act by in- creasing the resistance in the pulmonary vessels ; (2) pulmonary lesions with obliter- ation of any considerable number of blood-vessels within the lungs, such as occurs in emphysema or cirrhosis ; (3) valvular lesions on the right side occasionally, and not infrequently in the foetus ; (4) chronic valvular disease of the left heart and pericardial adhesions. In the auricles simple hypertrophy is never seen ; it is always dilatation with hypertrophy. In the left auricle the condition develops in lesions at the mitral orifice, particularly stenosis. The right auricle hypertrophies when there is greatly increased blood-pressure in the lesser circulation, whether due to mitral stenosis or to pulmo- nary lesions. Narrowing of the tricuspid orifice is a less frequent cause. Hypertrophy or dilatation of the cardiac chambers may cause pressure, some- times injurious, on surrounding structures. Great enlargements of the left ventricle, as seen in the bovine heart of valvular disease, may occasion compression of the lower portion of the left lung when a devi- ation of the mediastinum towards the right is prevented. As a rule, such enlarge- ment compresses the lower part of the left lung comparatively little. Enlargement of the right ventricle frequently causes a depression and forward displacement of the left lobe of the liver and the appearance of a pulsating mass in the epigastrium. Dilatation of the auricles is more likely to produce serious compression of sur- rounding structures than is that of the ventricles because of the greater fixation of the heart at its upper portion where the auricles are placed. Enlargement of the left auricle has in some eases produced compression of the left bronchus with consequent PRACTICAL CONSIDERATIONS: THE HEART. 713 collapse of the lung. Enlargement of the right auricle seems to be the basis of the frequently occurring right-sided hydrothorax of valvular heart disease. Compression of the azygos vein and perhaps of the veins and lymphatics at the root of the right lung by the enlarged auricle accounts for the occurrence of one-sided hydrothorax (Stengel). Rupt^lre of the heart is usually secondary to fatty degeneration of the cardiac muscles. It may follow a complete embolic obstruction of one of the branches of the coronary arteries. Arterio-sclerosis with slow obliteration of one or both of these arteries may result in such atrophy of the myocardium as to favor rupture, and this atrophy is hastened by the fact that there is no direct anastomosis between the branches oif these vessels (page 703). With any of these predisposing conditions present, rupture may follow unusual exertion, or a heavy fall, or direct violence to the precordium, or may occur spontaneously. The right side of the heart is the more frequently involved, the right auricle especially ; but the cavities implicated, in order of frequency, are the right auricle, left ventricle, left auricle, right ventricle. This order probably results from the facts that (a) the right auricle is the weakest part of the heart ; (3) the left ventricle, though normally the strongest part, stands second because it is specially liable to the myocardial degenerations that result from coronary arterio-sclerosis ; (c) the left auricle and the right ventricle, though weaker than the left ventricle, are less frequently affected because they are not so liable to such degeneration. Wound of the heart is not necessarily fatal. A stab wound may be followed by little or no hemorrhage owing to the anatomical arrangement of the muscular fibres, some of which, whatever the direction of the wound, escape division. The thicker the cardiac wall at the site of the wound the more numerous the fibres and the more effective their action in preventing hemorrhage ; hence wounds of the auricles are more certainly and more rapidly fatal than wounds of the ventricles, and wounds of the right ventricle are graver than those of the left. Pain and syncopal attacks are almost always present. Hemorrhage into the pericardium will be attended by great precordial oppression, there will be increase of the area of cardiac dulness, and indistinctness or feebleness of all the heart sounds. The anterior surface of the heart is most frequently wounded. The overlapping of the pleura (page 1860) leads to its usual involvement in wounds of the heart or peri- cardium, except those that reach the latter through those areas of the sternum with which they are in direct relation. Accordingly, in most heart wounds a pleural cavity commonly the left is found to contain blood. As the anterior margin of the lung is also apt to be involved, except when the wound is within the bounds of the area of cardiac dulness, the blood in both the pleural and pericardial cavities may be frothy. The right auricle and ventricle and the left coronary vessels running in the anterior interventricular groove are most frequently wounded ; the right auricle if the wound passes through the inner end of the right third, fourth, or fifth intercostal space ; the right ventricle if it passes through a corresponding space to the left of the sternum. As 40 per cent, of the reported cases operated upon for heart- wounds have recovered, it may be well to associate the study of the normal heart with that of the best method of gaining access to it for surgical purposes. The heart should be exposed by a flap, the lower border of which corresponds to the sixth interspace, the inner border to the left border of the sternum, and the upper border to the third or, if the wound is high up, to the second interspace. The cartilages of the corresponding ribs are divided and the flap is raised, separated if possible from the pleura, and turned outward by fracturing the ribs. The pleura is separated from the pericardium, to which it does not adhere very closely, beginning towards the middle line. The pericardium is then incised and the accu- mulated blood evacuated, which is often a great relief to the heart, to which the pulse quickly responds. Two fingers are now inserted below and behind the apex and the heart tilted forward and sutured. If a second wound that of exit is suspected, it may be found by twisting the heart gently to the right or left. The sutures should go down to the endocardium, but should not enter the cavities of the heart. The pericardium is then closed, the pleura replaced, and the flaps sutured in position. HUMAN ANATOMY. The same incision or an extension downward of this one will permit of suffi- cient exposure of the heart for cardiac massage, a method of resuscitation in des- perate cases of syncope during anaesthesia which has been recently employed, but the value of which, if it has any, cannot now be estimated. THE PERICARDIUM. The pericardium is the serous sac which encloses the heart and the proximal por- tions of the great vessels. Like other serous sacs, it consists of two layers, one of which, the visceral layer, closely invests the heart and at its base becomes continuous with the parietal layer, within which it is invaginated. The visceral layer, sometimes termed the epicardium, is an exceedingly thin membrane, and is throughout the greater part of its extent so closely adherent to the outer surface of the heart that any attempt to detach it results in injury to the super- ficial layers of the heart musculature. Over the right side and the anterior surface of the ventricular portion of the heart, however, a certain amount of fat, even in thin persons, occurs between the muscular tissue and the epicardium. FIG. 675. Sternum Right ventricle Pericardia 1 sac Lung Parietal pericardium Visceral pericardium Pleura - - Right auriculo- ventricular valve Eustachian valve Inferior vena cava (Esophagus Vena azygos VIII. thoracic vertebra Thoracic aorta Portion of cross-section of body at level of eighth thoracic vertebra, viewed from above, showing heart enclosed by pericardium. The parietal layer, much stronger than the visceral, forms a somewhat conical sac, the base of which rests upon and is attached to the diaphragm, while its apex surrounds the roots of the aortae. Notwithstanding its greater size, no cavity exists normally between this and the visceral layer, the two being in contact throughout, except below, where, towards the periphery of the base of the parietal cone, a slight space occurs which is normally occupied by a quantity of pericardial fluid (liquor pericardii}. At the sides, and to a considerable extent on its anterior surface, the parietal layer of the pericardium is united to or is in close contact with the adjacent pleurae. At the upper part of its anterior surface where it covers the aorta it is free from such contact, and over a triangular area near the base of the cone the anterior surface rests upon the posterior surface of the lower part of the sternum, to which it is united by sonic loose areolar tissue. Posteriorly it is free to a considerable extent from the pleurae, that portion of it which covers the posterior surface of the left auricle resting upon the oesophagus and the thoracic aorta. The base of the cone is firmly united to the upper surface of the diaphragm throughout its entire extent, the area of attachment corresponding to the anterior and a portion of the left lobe of the central tendon. THE PERICARDIUM. 715' Above, as has been stated, the parietal layer extends upward some distance upon the proximal portions of the systemic and pulmonary aortae before passing over into the visceral layer, but the amount to which the two vessels are invested differs considerably. If the parietal layer be cut away along the line at which it becomes continuous with the visceral layer, two distinct lines will be found indicating its attachments. One of these surrounds the two aortae (Fig. 654), which are united by connective tissue, and extends upward upon the systemic aorta to a point a little below the origin of the innominate artery, a level which corresponds very nearly with the upper border of the second costal cartilage; upon the pulmonary aorta (artery) the line does no* rise quite so high, reaching to a point a little below where the vessel divides into the right and left pulmonary arteries. The other line of attachment is much more extensive and complicated (Fig. 655). Starting from its attachment to the left FIG. 676. Scalentis anticus muscle Clavicle R. com. carotid art., cut Int. mammary arterji I . costal cartilage Sterno-thyroid muscle Sterno-hyoid muscle Sterno-cleido-mastoid muscle Right subclavian artery Trachea I. costal cartilage Left phrenic nerve Mesial surface of right lung *- Diaphragm, central tendo Recti muscles Anterior thoracic wall has been partly removed, leaving left half of sternum and some ' ribs in place ; lungs have been drawn aside to expose pericardia! sac. pulmonary veins, upon which it ascends for a short distance, it passes directly across the posterior surface of the left auricle to the base of the right pulmonary veins, and is thence continued downward to surround the vena cava inferior close to its entrance into the right auricle. Thence it passes upward to regain the right pulmonary veins, and is then continued around the vena cava superior, upon which it rises to a height of about 3 cm. It then passes towards the left over the posterior surface of the auricles to reach the starting-point at the left pulmonary veins. The existence of these two separate lines of attachment is due to a difference in the arrangement of the visceral and parietal layers in the interval between the aortoe and the anterior surface of the auricles. The parietal layer passes directly across from the aortae to the auricles, while the visceral layer forms an investment for the vessels, extending downward to their origin from the ventricles, and is thence 716 HUMAN ANATOMY. reflected upward over the anterior surface of the auricles until it again meets the parietal laytfr. There is thus produced, between the aortae in front and the auricles behind, a cavity or cleft, known as the transverse sinus of the pericardium (Fig. 654), which is continuous at either extremity with the general pericardial cavity, and is roofed in by the parietal layer, while its walls and floor are formed by the visceral layer. In the roof of the sinus transversus a slight fold is to be found towards the left, which passes backward to the line of attachment of the roof to the left auricle and thence obliquely downward in the visceral layer covering the posterior surface of the auricle towards the coro- nary sinus. This duplicature, known as the vestigial fold of the pericardium ( ligamentum v. cavae sinistrae), contains in its upper part a fibrous cord and in its lower part the oblique vein of the left auricle ; these two structures, the vein and fibrous cord, together with the coronary sinus, representing the remains of an original left superior vena cava. It may be noted that the line of attachment of the parietal layer between the left pul- monary veins and the inferior vena cava extends high up on the posterior surface of the auricles, and there is thus formed in this region a pouch-like diverticulum of the pericardium whose mouth looks downward. This is what has been termed the oblique sinus of the pericardium. Its parietal wall rests upon the oesophagus posteriorly, and in case of extensive effusion into the pericardial cavity, compression of the oesophagus sufficient to interfere with the act of swallow- ing may result. The Ligaments of the Pericardium. The parietal layer of the pericardium is united to the surrounding structures by areolar tissue which may condense to definite bands termed pericardial ligaments. Thus the tissue between the pericardium and the sternum may condense to form a superior and an inferior pericardio-stcrnal liga- ment, the former passing to the posterior surface of the manubrium sterni and the latter to the lower part of the gladiolus. Similarly, bundles of fibres are attached to the apex of the pericardial cone and to the great vessels of the heart, taking their origin from the prevertebral layer of the cervical fascia which is prolonged downward into the thorax ; these are the pericardio-vertebral ligaments. And, finally, a band has been described as extending from the posterior surface of the pericardium to the upper surface of the diaphragm on either side of the vena cava inferior : these form what are termed the pericardia-phrenic ligaments. The Vessels. The arteries which supply the posterior surface of the parietal layer of the pericardium arise from the thoracic aorta, and those of the anterior sur- face are given off by the internal mammary artery. The veins of the parietal layer pursue courses parallel with those of the arteries, and open into the vena azygos behind and the superior phrenic or superior vena cava anteriorly. The lymphatics pass to the nodes lying in the bifurcation of the trachea. The vas- cular supply of the visceral layer is the same as that of the muscular tissue of the heart. The nerves distributed to the pericardium include fibres from the phrenic nerve, especially the left one, and also probably from the cardiac plexus. PRACTICAL CONSIDERATIONS : THE PERICARDIUM. The visceral layer of the pericardium is closely attached, to and practically insep- arable from the heart muscle. It is continuous with the parietal layer at the base of the heart where the two layers ensheathe the great vessels, covering in especially the first inch and a half of the aorta and pulmonary artery and leaving, between those vessels in front and the auricles behind, an open space the transverse sinus which may be the seat of an effusion walled off by adhesions from the general peri- cardial cavity. The least resistant important structure in immediate relation to this sinus is the superior vena cava, also intrapericardial at its lowermost portion,- and such effusion might therefore cause fulness of the veins of the neck or even cyanosis without the evidence of a general pericardial dropsy large enough to give the usual concomitant physical >i^ns (videinfnti). In artificial distention of the pericardium the sac tends to assume the shape of two irregular spheres, the upper or smaller one containing the great vessels just mentioned, the lower embracing the heart, the ascending cava, and the pulmonary veins. At the apex of the In-art, where the peri- cardium is reflected from the diaphragm, unimportant sinuses, analogous to the costo-phrenic sinus of the pleura, may exist. PRACTICAL CONSIDERATIONS: PERICARDIUM. 717 The parietal layer of the pericardium is in relation with an external fibrous layer which extends beyond the serous investment of the roots of the great vessels, blends with their outer coats, and is directly continuous with the deep cervical fascia, thus connecting' the pericardium with two respiratory agents, the diaphragm below and the cervical muscles (omo-hyoid) above. When these act conjointly, as in a full inspiration, they render the pericardium tense and resisting, and minimize the pressure upon the heart by the inflated lungs (page 551). Pericarditis probably more often overlooked than any other serious disease (Osier) may arise from wound from without, as in ordinary penetrating wounds of the chest, or from within, as from the passage of a foreign body from the oesoph- agus into the pericardium (page 1614); or it may follow extension of disease from contiguous organs, as in pleuro-pneumonia. The anatomical relations of the peri- cardium explain these occurrences. The more usual causes, as rheumatism, septi- caemia, gout, and nephritis, have no anatomical bearing. Pericarditis is attended by certain symptoms well detailed by Sibson which should be studied in connection with the anatomy of the heart and pericardium. I. Pain (a) spontaneous and directly over the heart, the pleurae often being involved, both these serous membranes like the peritoneum becoming painful when inflamed, although normally insensitive ; (&) elicited by pressure (tenderness), the skin over the precordium sometimes participating on account of the connection between the upper intercostal nerves and the ganglia and nerves of the cardiac plexus ; (c*) over the epigastric region and increased by pressure, because, although normally the pericardium below is in direct relation with the thoracic parietes over only a small area behind the xiphoid cartilage, distention 'of the pericardial sac, as in effusion from pericarditis, carries it downward so that it may be well below the tip of the xiphoid ; (d ) between the scapulae or deep in the chest, increased by swallowing or by eructations, and worse when the patient is supine, due to the relation between the oesophagus and pericardium just below the aortic arch ; (e) in the side, usually pleuritic (from extension), and more common on the left side on account of the greater extent to which the inflamed pericardium occupies the left side of the chest than the right side, to the marked backward displacement of the lower lobe of the left lung by the distended pericardial sac, and possibly (Sibson) to the pressure of the latter on the left bronchus increasing in the left lung the tendency to intercur- rent pneumonia. 2. Feeble or irregular heart action, due to () direct extension of the inflammation from the visceral layer of the pericardium to the heart muscle (myocarditis); () implication of the cardiac nerves ; (<:) pressure by the pericardial effusion on the venae cavae and pulmonary veins, impeding the blood-supply to both auricles ; direct pressure upon the auricles interfering with the ventricular supply ; and pressure upon the whole organ both directly from the effusion and indirectly from the compressed and displaced lungs and the other contiguous structures, embarrass- ing its action, especially in diastole. 3. Dyspnoea, due to the pulmonary congestion produced by the previous causes ; sometimes the result of a pleurisy or pleuro- pneumonia by extension ; or perhaps, as Hilton has suggested, partly from fixation or irregular action of the diaphragm through irritation of the pericardiac filament of the phrenic (ramus pericardiacus), usually given off on the right side. 4. Dys- phagia (page 1614) from compression of the oesophagus between the pericardium and the vertebral column, usually relieved when the patient is put in an approximately vertical position. 5. Aphonia, from involvement of the left recurrent laryngeal nerve by contiguity, or of both nerves through their cardiac branches. 6. Fulness of the cervical veins and flushing or cyanosis of the face, due to pressure upon the thin walls of the right auricle and of the superior vena cava. Compression of the left auricle is better resisted on account of the greater thickness of its walls ; when it occurs, it tends to produce pulmonary congestion or apoplexy. The physical signs of pericarditis are, of course, influenced by the attachment, surroundings, and physical qualities of the pericardium. i . As it is in two layers normally movable upon each other, the roughening caused by inflammation produces a friction-sound which, when typical, is (a) heard best over the middle and the lower half of the sternum, and over the adjoining left costal cartilages or their interspaces, because there a greater extent of the pericardium is yi8 HUMAN ANATOMY. closer to the ear, with fewer intervening structures than elsewhere ; (<) preceded or accompanied by pain (vide supra}', (c)- usually increased by pressure with the stetho- scope, which brings the two roughened pericardial layers into closer apposition ; (d) accompanied by an extension of the area of cardiac dulness (vide infra); (e) is double, that is, corresponding, although not altogether synchronously, to both systole and diastole ; and (/") may disappear when effusion occurs, separating the two layers, or may persist over a small area near either the diaphragmatic attach- ment or the pericardial reflection at the base. 2. As the pericardium is markedly elastic, when effusion takes place the parietal layer may stretch so that the pericardial cavity may hold ten or twelve ounces instead of a few grammes, or in chronic cases may contain several pints. As its cavity is in the shape of that of a hollow cone or pear, the apex corresponding to the fixed portion of the heart held in place by the great vessels and the base enlarged to permit the considerable degree of motion of the heart's apex to the upper surface of the dia- phragm, pericardial effusions also take this general shape, and the area of percussion- dulness will be found to have its base about on a level with the fifth or sixth interspace inferior, and its apex about on a level with the second interspace directed upward towards the first segment of the sternum. It is more marked to the left of the sternum on account of the larger area of heart and pericardium on that side, but may be found to the right of the sternum, especially about the fifth intercostal space (Rotch), because on the right side (owing to the presence of the right lobe of the liver) the lower border of the distended sac is somewhat higher than on the left. 3. As such enlargement must affect the contiguous organs and the overlying parietes, there will be found in full distention : (a) prominence of the intercostal spaces, especially on the left side, or of the left antero-lateral thoracic walls, of the epigastrium (from depression of the diaphragm and left lobe of the liver), of the lower two-thirds of the sternum, or, in children with yielding thoracic walls, of the whole precordia ; () compression of the left lung, sometimes causing a tympanitic percussion-note in the left axillary region ; (c) compression, between the relatively unyielding sternum and the dorsal spine, of the trachea and left bronchus (irritative cough), the oesophagus (dysphagia), and the aorta (affecting the systemic blood- supply); (.-! duct us arteriosus. degenerates as far up as the rigl less rudimentary rax atx'rnins arising from the thoracic aorta. This degeneration may not occur, both the'right and left aortic arches persisting in their entirety (Fig. 683); and, since in THE AORTIC ARCH. 725 such cases the descending aorta usually retains its normal position to the left of the spinal column, a condition is produced in which the aortic arch appears to be split lengthwise into two portions, one of which, the left arch, passes in front of the trachea and oesophagus and gives origin to the left common carotid and the left subclavian arteries, while the other passes FIG- 683. FIG. 684. RAA Right suhcla ft common carotid ft subclavian Ductus arteriosus Developmental variations of Group I, giving rise to anomaly shown in next figure. 1?AA,LAA, right and left aortic arches ; J?S, LS, subclavian arteries; A, aorta; P, pulmonary artery. moiiary artery Double aortic arch through which trachea and ossophagus pass, (ffommel). behind the structures named and gives origin to a right common carotid and a right subclavian (Fig. 684). The relative diameters of the two portions of the aortic arch so formed may vary con- siderably, that passing in front of the trachea (the true left arch) being sometimes larger and at other times smaller than the other one. In the latter case an obliteration of the distal portion of the left arch may occur, and the left common carotid and left subclavian arteries will then appear to arise close to the innominate stem, from a common trunk, the aortic arch passing to the left behind the trachea. Group II. A more frequent anomaly is the complete persistence of the distal portion of the right aortic arch (Fig. 685) associated with the disappearance of a greater or less portion of FIG. 685. FIG. 686. Trachea Left common carotid Right vertebral Right subclavian Aorta Developmental variations of Group II, giving rise to anomaly shown in next figure. A, aorta; P, pulmonary artery ; RS, LS, right and left subclavian arteries; RV, right vertebral artery. :sophagus Left common carotid Left vertebral h-Left subclavian Right subclavian Origin of right subclavian artery from descending aorta. its proximal part, the result being the apparent origin of the right subclavian artery from the descending aorta, whence it passes to the right behind the trachea and cespphagus. Variations of this condition, depending upon the location and extent of the disappearing portion of the right arch, may modify the relations of the right vertebral and subclavian arteries. Thus, in some 726 HUMAN ANATOMY. FIG. 687. KAA DA cases the vertebral may arise as in the normal arrangement from the subclavian, or it may, as it were, exchange positions with the subclavian, arising from the descending aorta, while the sub- clavian arises, in common with the right common carotid, from an innominate stem ; or the vertebral may arise with the right common carotid from the innominate stem, the subclavian alone coming from the descending aorta (Fig. 686). Group III. A third group of anomalies depends upon the complete persistence of the right aortic arch, associated with the disappearance of the distal portion of the left one (Fig. 687). In such cases the result is a complete reversal of the aortic arch and its branches, unaccompanied, however, by a reversal of any of the other organs of the body, and thus differing from a true situs in versus viscerum. The arch is directed from left to right, and gives rise to an innominate stem, from which the left common carotid and left subclavian arteries arise, a right common carotid and a right subclavian, the descend- ing aorta lying upon the right side of the vertebral column. Variations of these anomalies concern principally the rela- tions of the ductus arteriosus or the cord which represents it. It may unite with the descending aorta, in which case it is the persistent right sixth branchial vessel, or it may be formed, as usual, from the left sixth branchial vessel, com- municating distally with the left subclavian, this artery, in cases where the ductus remains patent, appearing to arise by- two roots, one from the innominate stem and one from the pulmonary aorta. Group IV. In the fourth group there is a complete persistence of the right aortic arch associated with a dis- appearance of the proximal portion of the left arch (Fig. 688), the resulting arrangement being the reverse of that seen in cases belonging to the second group. The left sub- clavian artery appears to arise from the descending aorta, which lies upon the right side of the vertebral column, and passes to the; left behind the trachea and oesophagus. Varia- tions in the relations of the ductus arteriosus, similar to those mentioned as occurring in the third group, may be found. Group V. A fifth group includes those cases in which the arch itself is normal, but in which there are variations in the vessels that arise from it. These variations may be either a diminution or an increase of the normal number of vessels or an abnormal arrangement of a normal, number. The diminu- tion and altered arrangement of the vessels depend upon a shifting of more or fewer of them, so that, for example, the left common carotid and left subclavian arteries may arise from a common left innominate stem, all the vessels may arise from a common stem, the two common carotids may have a com- mon origin, while the two subclavians arise independently, or, what is the most frequent of these variations, the left com- mon carotid may arise from the innominate stem and pass upward and to the left obliquely across the front of the trachea. An increase in the number of vessels may be brought about by the independent origin from the arch of both the right common carotid and the right subclavian, the innominate being absent. In other cases, vessels which normally do not come into relation with the arch may take origin from it, this being most frequently the case with the vertebral arteries and less frequently with the internal mammaries ; and, finally, an addit9nal branch to the thyroid gland, the art. thyroidea ima, occasionally takes origin from the arch. Developmental variations of Group III. A, aorta; P, pulmonary artery; RAA, right aortic arch; DA, duc- tus arteriosus ; RS, LS, right and left subclavian arteries. FIG. 688. Developmental variations I> J. aorta; P, of Group lA* Practical Considerations. The Aortic Arch and Thoracic Aorta. Surface Relations. The ascending aorta begins beneath the sternum just to the right of the inner end of the third left costal cartilage. It ascends obliquely and towards the upper border of the second right costal cartilage. The second (trans- verse) part passes backward and to the left, crossing the mid-line about an inch from the suprasternal notch, the lower (concave) border corresponding in level with the ridge between the manubrium and the gladiolus, the upper (convex) border to the level of the third thoracic spinous process, to the middle of the manubrium, and the middle of the first costal cartilage. This border is about one inch below the supra- sternal notch. The surface relations of this portion vary with the development of PRACTICAL CONSIDERATIONS: THE AORTIC ARCH. 727 the thorax. In persons with small chests the upper border may almost reach the level of the top of the manubrium, while in those with large chests it may be no higher than the junction of the first and second pieces of the sternum (angulus Ludovici}. The transverse portion reaches the left side of the vertebral column at a level just above the fourth thoracic spine. The third (descending) portion and the thoracic aorta lie at first a little to the left of the body of the fourth thoracic vertebra and gradually incline to the mid-line, passing through the diaphragm at the level of the twelfth thoracic vertebra. Aneurisms of the aorta are more frequent than are those of any other vessel, on account of the great strains to which the aorta is subject. They may most con- veniently be considered here by following the anatomical subdivisions of the vessel, premising, however, that the symptoms thus described frequently commingle and overlap. A. The ascending, portion is more subject to aneurism than are the remaining portions, because it receives the first and most vigorous impulse of the heart's stroke, and because it is within enclosed by the pericardium, and its walls are not rein- forced by blending with the fibrous pericardial layer, as is the case in the second and third portions. Aneurism most frequently involves the region of the anterior sinus of Valsalva, where regurgitation of blood chiefly takes place ; or, if higher, the anterior wall of the aorta in the vicinity of the normal dilatation, probably due to the impact of the blood-current leaving the heart. The symptoms are : i . Venous con- gestion, causing () lividity of the face from pressure on the descending cava, the left innominate, and the internal jugular veins ; (3) dizziness and headache from the same cause ; (<:) swelling and oedema of the right arm from pressure on the sub- clavian vein ; () the vertebral, by anastomosing respectively with (a) the external carotid branches, (b) the superior thyroid, (c) the princeps cervicis (from the occipital), and (d ) and (f infra-orbital artery Septal artery Superior cor. .nary Buccinator Inferior labial artery Masseteric branch Facial artery Submental artery ^-Muscular branch Submaxillary branch Superior thyroid artery Thyro-hyoid muscle Sterno-mastoid branch Omo-hyoid muscle 'Sterno-hyoid muscle Sterno-thyroid muscle Subclavian artery Subclavian vein Superficial dissection, showing arteries of neck, face and scalp. and the great vessels, where for a short distance it is superficial and run's almost horizontally. The needle should be passed from above downward with the point directed some- what towards the mid-line. The close proximity posteriorly of the superior laryngeal nerve should be remembered. 2. The Lingual Artery. The lingual artery (a. lingualis) (Fig. 692) usually arises from the anterior surface. of the external carotid, between the origins of the superior thyroid and the facial, although it is sometimes given off from a trunk 736 HUMAN ANATOMY. common to it and one or other of these arteries, especially the facial. In the first part of its course it passes forward and slightly upward and inward towards the tip of the lesser cornu of the hyoid bone, and is crossed by the posterior belly of the digastric and the stylo-hyoid muscles and by the hypoglossal nerve. On reaching the p<- terior border of the hyo-glossus, it passes beneath that muscle and is continued almost directly forward beneath the mucous membrane covering the under surface of the tongue and between the genio-hyo-glossus and the inferior lingualis muscles. In this terminal portion it has a sinuous course, and is frequently termed the ranine artery (a. profunda linguae); it gives branches to the adjacent muscular substance and mucous membrane of the tongue, and near its termination anastomoses with its fellow of the opposite side. Branches. (a) The suprahyoid branch (ramus hyoideus), given off from the first portion, passes horizontally forward over the hyoid bone, sending branches to the muscles which are inserted into that bone from below. (A) The dorsal lingual branch (rami dorsales linguae), from the second portion, arises under cover of the posterior border of the hyo-glossus and, passing upward medial to the stylo- glossus, breaks up into branches which are distributed to the mucous membrane of the dorsum of the tongue, as far back as the epiglottis, and also to the tonsil. Occasionally a branch unites with a corresponding one from the artery of the opposite side, immediately in front of the fora- men caecum, and is continued forward in the median line, immediately beneath the mucous membrane of the dorsum of the tongue, as far as the tip. (c) The sublingual branch (a. sublingualis) is given off near the anterior border of the hyo- glossus muscle and runs forward in the same plane as the ranine artery, but on a lower level, resting upon the mylo-hyoid muscle and lying between the genio-hyoid laterally and the genio- hyo-glossus medially. It is accompanied by thesubmaxillary (Wharton's) duct, which lies upon its medial side, and it terminates in the sublingual gland, also sending branches to the neighbor- ing muscles and to the alveolar border of the mandible. Anastomoses. The various branches of the lingual artery anastomose exten- sively with their fellows of the opposite side. The anastomoses of the two aa. dor- sales linguae take place, however, only through exceedingly fine twigs, so that the tongue may be divided longitudinally in the median line without any great loss of blood, except towards the tip, where a larger anastomosis of the ranine arteries occurs. In addition to these contra-lateral anastomoses, the lingual also anastomoses through its suprahyoid branch with the infrahyoid of the superior thyroid artery, through its sublingual branch with the submental branch of the facial, and through the a. dorsalis linguae with the various tonsillar arteries. Variations. The lingual artery sometimes arises from a common trunk with the facial, and it has been observed to terminate at the root of the tongue, being replaced in the rest of its course by branches from the internal maxillary or by the submental branch of the facial. The sublingual branches are not infrequently lacking, being replaced by branches of the submental, and, in addition to its normal branches, the main artery may give rise to a superior laryngeal and an accessory superior thyroid branch. Practical Considerations. The lingual artery is tied most frequently as a preliminary to excision of the whole or part of the tongue, but one or both arteries may be ligated to stop bleeding following wound or malignant ulceration of that organ, or in an effort to arrest growth by cutting off Wood-supply, as in cases of cancer of the tongue or of macroglossia. f.itration. The artery is for convenience divided into three portions, the //Y.v/ between its origin about opposite the greater cornu of the hyoid and the posterior edge of the hyo-glossus muscle, lying upon the middle constrictor of the pharynx ; the st-fond beneath the hyo-glossus muscle, lying upon the genio-glossus : the third, ( ranine } from the anterior border of the hyo-glossus along the under surface of the tongue to its termination. The place of election is in the second part. The skin incision, two inches in length, curved, with the concavity upward, begins a half- inch below and external to the mandibular symphysis and ends a little below and internal to the point where the facial artery crosses the lower edge of the inferior maxilla ; its centre is just above the greater cornu of the hyoid. If the incision is carried too far backward, * THE FACIAL ARTERY. 737 the facial vein may be cut. The remainder of the operation may be described as if it were done in four stages. i. That portion of the deep fascia constituting the anterior layer of the capsule of the submaxillary gland is divided in the line of the incision, the lower edge of the gland exposed, and the gland itself cleared and ele- vated over the lower jaw, with due care to avoid injury to the facial artery which passes through its substance and the facial vein which runs upon its surface. 2. The thin posterior leaf of the capsule of the gland being divided, the white, shining aponeurotic loop attaching the digastric tendon to the greater cornu of the hyoid will be seen. The tendon near the bone or the digastric aponeurosis should be fixed by a blunt hook or tenaculum and drawn downward and towards the surface. 3. After the division of the posterior layer of the capsule of the submaxillary gland, the posterior edge of the mylo-hyoid muscle, the fibres running upward and slightly backward, can be recognized at the anterior angle of the wound and should be clearly defined. 4. The hypoglossal nerve separates from the artery at the poste- rior border of the hyo-glossus muscle, where the vessel disappears to run between that muscle and the middle .constrictor. The nerve, accompanied by the ranine vein, runs almost horizontally across the surface of the hyo-glossus, and in its turn disappears under the edge of the mylo-hyoid muscle. It will have been brought into view when the submaxillary gland has been raised, the posterior layer of its capsule divided, and a little fatty connective tissue picked away. In the irregular triangle formed by the nerve above, the mylo-hyoid anteriorly, and the posterior belly and tendon of the digastric posteriorly, the lingual artery runs beneath the hyo-glossus muscle and near the apex of the triangle i.e., near the hyoid bone. The nerve and vein, which are on a slightly higher level a few millimetres having been raised and the fibres of the hyo-glossus divided parallel with the hyoid and just above it, the artery will be brought into view. In ligation of the lingual for carcinoma of the tongue, the state of the salivary gland, which varies in size, in density, and in the closeness of its attachments, is the main element of uncertainty (Treves). 3. The Facial Artery. The facial artery (a. maxillaris externa) (Fig. 691) arises usually a short distance above the lingual, from the anterior surface of the external carotid. It passes at first forward and slightly upward, lying beneath the posterior belly of the digastric and the stylo-hyoid muscles and the hypoglossal nerve, and is then continued almost horizontally forward in a groove in the submaxillary gland. When it reaches the level of the anterior border of the masseter muscle, it assumes a vertical direction and passes over the ramus of the mandible, and is then continued in a sinuous course obliquely across the face towards the naso-labial angle, resting upon the buccinator and levator anguli oris muscles, and being crossed by the risorius and zygomatic muscles and by some branches of the facial nerve. Arrived at the naso-labial angle, it again takes an almost vertical course, passing upward beneath (or sometimes over) the levator labii superioris and the levator labii'superioris alaeque nasi towards the inner angle of the orbit, where it terminates by anastomosing with the nasal branch of the ophthalmic artery. This terminal vertical portion of the vessel is usually termed the angular artery (a, angularis). Branches. -The branches of the facial artery ( Figs. 691, 693) may be arranged in two groups according to their origin from the cervical or facial portions of the artery. From the cervical portion arise : (a) The ascending palatine branch (a. palatina ascen- dens), a small artery which passes upward between the stylo-glossus and stylo-pharyngeus mus- cles, to which it sends branches, and then comes to lie upon the outer surface of the superior constrictor of the pharynx. It terminates by sending branches to the soft palate, the tonsil, and the Eustachian tube. [b] The tonsillar branch (ramus tonsillaris) is another small branch which passes verti- cally upward. It arises close to the ascending palatine and, passing over the stylo-glossus muscle, pierces the superior constrictor of the pharynx to be distributed to the tonsil. (r) The glandular branches (raini glandulares), two or three in number, are distributed to the submaxillary gland. (of) The submental branch fa. submentalis) arises just before the artery bends upward over the mandible, and continues onward in the horizontal course followed by the facial, 47 738 HUMAN ANATOMY. * through the submaxillary gland. It passes forward upon the mylo-hyoid muscle, close to its origin, until it reaches the insertion of the anterior belly of the digastric, when it passes upward upon the ramus of the mandible to supply the depressor labii mferioris and to anastomose with the mental branches of the inferior dental artery and with the interior labial branches of the facial. It sends branches to the muscles in its vicinity and also to the integument, and branches perforate the mylo-hyoid muscle to anastomose with the sublingual brandies of the lingual. From the facial portion, (e) The masseteric branches arise from the posterior surface of the artery and are directed upward to supply the masseter muscle and to anastomose with branches of the internal maxillary and transverse facial arteries. (f) The inferior labial branch (a. labialis inferior) passes forward along the outer surface of the horizontal ramus of the mandible, supplying the depressor angiili oris, the depressor labii inferioris, and the integument, and anastomosing with the mental branches of the inferior dental and submental arteries. (g) The inferior coronary artery passes forward in the substance of the lower lip between the mucous membrane and orbicularis oris, supplying the latter, and terminates by anastomosing with its fellow of the opposite side. (h) The superior coronary artery (a. labialis superior) has the same course and relations in the upper lip that the inferior coronary has in the lower one. It anastomoses with its fellow of the opposite side, and near its termination usually sends a small branch upward to the septum of the nose, the a. septi narium. (i) The lateral nasal takes its origin just as the artery reaches the naso-labial angle ; it passes forward over the ala of the nose, supplying its muscles and integument. (j) The angular artery (a. angularis) is the terminal portion of the facial artery beyond the naso-labial angle. It passes directly upward in the angle between the nose and the cheek, and gives branches to the adjacent muscles, the lachrymal sac, and the orbicularis palpebrarum, anastomosing with the nasal branch of the ophthalmic artery and with the infra-orbital branch of the internal maxillary. Anastomoses. The facial artery, by means of its facial branches and the sub- mental arteries, makes abundant anastomoses with its fellow of the opposite side. In addition, it is connected with other branches of the external carotid; with the dorsalis linguae and submental branches of the lingual by its tonsillar and inferior labial branches respectively; with the descending palatine, infra-orbital branches, and mental branches of the internal maxillary by its tonsillar, angular, and inferior labial branches; and with the transverse facial branch of the superficial temporal by its masseteric branches. Finally, it is connected with the ophthalmic branch of the internal carotid by the angular artery. Variations. The facial artery may arise by a trunk common to it and the lingual, or it may arise above the level of the angle of the jaw. Quite frequently it does not extend upon the face beyond the angle of the mouth, being replaced in the upper part of its course by branches from the transverse facial or internal maxillary artery. The ascending palatine branch frequently arises directly from the external carotid, or it may take its origin from the ascending pharyngeal or from the occipital, and the tonsillar is frequently a branch of it. The submental branch may be greatly reduced in size or even absent, being replaced in whole or in part by the sublingual, these two arteries being inversely proportionate to each other so fai as their development is concerned. Practical Considerations. The facial artery may require ligation on account of division of one of its branches, as the coronary, but whenever direct ligation of the wounded vessel is possible, it is preferable on account of the very free anastomosis betw r een the branches of opposite sides, leading usually, after ligation of the main trunk, to recurrence of the hemorrhage. In bleeding after tonsillotomy (page 1608), either the tonsillar branch of the facial or the main vessel (where it runs between the posterior belly of the digastric and the stylo-glossus muscles) may be involved ; but as the blood may also be furnished by the ascending pharyngral. ligation of the external carotid itself rather than of the facial would be more likely to be efficient. legation. (#) The cervical portion of the vessel maybe reached through an incision like that for the lingual, placed a little higher, and not extending so far anteriorly. When the submaxillary gland is drawn upward, the artery will be drawn with it and made prominent. This portion may also be reached near its origin by uncovering the external carotid (q.t>. ) and identifying the vessel where it runs THE INTERNAL MAXILLARY ARTERY. between the posterior belly of the digastric above and the hypoglossal nerve below. () The facial portion is easily exposed where it crosses the mandible at the ante- rior border of the masseter, either by a vertical cut parallel with that muscle and the artery or by a horizontal cut crossing the vessel and placed under the inferior margin of the jaw so as to leave the scar in an inconspicuous position. Beneath the skin and the superficial fascia the platysma and deep fascia are the only structures that require division. The vein lies in the groove between the artery and the edge of the masseter. 4. The Internal Maxillary Artery. The internal maxillary (a. maxillaris interna) (Fig. 692) is a large branch which arises from the anterior surface of the FIG. 692. Small meningeal branch Middle meningeal Tympanic ti:anch Superficial tem]>oral Stylo-mastoid Meningeal branch Posterior auricular Trach< O Sterno-m of internal maxillary y to superior maxilla Posterior superior dental Internal maxillary artery Inferior dental arlery Buccal branch Internal pterygoid muscle >Ranine artery .Tonsilar artery .Ascending palatine Facial artery, cut "ublingual artery Dorsalis linguae Scalenus anticus Longus colli Superficial cervical Posterior scapular Scalenus niedius Tendinous origin of Scalenus medius oid artery Thyroid axis Vertebral artery Subclavian artery ammary artery. Sterno-mastoid brancn Suprascapular artery Deeper dissection, showing carotid and subclavian arteries. external carotid, opposite the neck of the mandible. It passes forward with a flexuous course, lying at first between the neck of the mandible and the spleno-mandibular ligament, and then passing either between the two pterygoid muscles, in which case it crosses the inferior dental and lingual nerves, or else over the external surface of the external pterygoid, between that muscle and the temporal. It then passes between the two heads of the external pterygoid, in the one case passing from below upward and in the other from without inward, and enters the spheno-maxillary fossa, in which it is directed upward and inward towards the spheno-palatine foramen, which it traverses under the name of the spheno-palatine artery. Branches. For convenience in description it is customary to regard the internal maxillary artery as consisting of three portions. Its first, or mandibular portion, is that which lies inter- 740 HUMAN ANATOMY. nal to the neck of the mandible ; the second, or pterygoid portion, is that which traverses the pterygoid fossa, and is in relation with the pterygoid muscles ; and the third, or spheno-nia.Yil- lary portion, extends from where it passes between the two heads of the external pterygoid mus- cle to its entrance into the spheno-palatine foramen. Of the sixteen named branches arising from the internal maxillary artery, five arise from the first portion, five from the second, and six from the third. From the first or mandibular portion arise (i) the deep auricular, (2) the tympanic, (3) the middle meningeal, (4) \\\alatine. (&) The alveolar branch (a. alveolaris superior posterior) descends upon the tuberosity of the maxilla, giving off branches which penetrate small foramina in that bone and are distributed to the molar and premolar teeth and the gums of the upper jaw and to the mucous membrane lining the antrum of Highmore. The main stem terminates upon the tuberosity of the maxilla by breaking up into a plexus with which branches from the buccal artery unite. FIG. 693. Anterior temporal Posterior temporal Middle temporal Transverse facial Great meningeal Superficial temporal Small meningeal Tympanic Internal maxillary Inferior dental artery Mylo-hyoid artery Posterior auricular Inferior dental nerve Sterno-mastoid artery Occipital artery Tonsillar artery Ascending palatine Hypoglossal nerve Facial artery Internal carotid External carotid Superior thyroid Common carotid Sterno-mastoid arterv Coronoid process of mandible with insertion of tem- poral muscle - Buccinator -Superior coro- nary artery Inferior coro- nary artery Inferior labial artery Mental branch of facial emerging from mental for- amen Submental artery Genio-hyoid muscle Lingual artery Hyoglossus mus- cle, cut Mylo-hyoid mus- cle of left side Superior laryn- geal artery Thyro-hyoid muscle External carotid, internal maxillary and inferior dental arteries ; condyle and outer table of mandible have been removed. (/) The infraorbital artery (a. infraorbitalis) frequently arises in common with the alveolar. It passes forward and upward through the spheno-maxillary fossa and the spheno-maxillary foramen to traverse the infraorbital groove and canal along with the infraorbital nerve. In this part of its course it gives off (aa) orbital branches, distributed to the adipose tissue of the orbit and to the neighboring muscles of the eye, and (bb) anterior dental branches (aa. alveolares superiores anteriores) which pass down the anterior wall of the antrum of Highmore, along with the anterior and middle superior dental nerves, to supply the mucous membrane lining the antrum and the canine and incisor teeth of the upper jaw. The main stem emerges upon the face at the infraorbital foramen and divides into (cc) palpebral, (dd) nasal, and fee] labial branches, whose distribution is indicated by their names, and which anastomose with the nasal and lachrymal branches of the ophthalmic artery, the transverse facial branch of the superficial temporal, and the superior coronary and angular branches of the facial. (in) The descending palatine artery fa. palatina descendens) accompanies the anterior pala- tine nerve from the spheno-palatine ganglion through the posterior palatine canal, and, on its 742 HUMAN ANATOMY. emergence from the posterior palatine foramen, divides into an anterior and a posterior branch. The former passes forward beneath the mucous membrane of the hard palate, which it supplies, and at the anterior palatine foramen anastomoses with the spheno-palatine artery; the latter passes backward to supply the soft palate and the tonsil, anastomosing with the ascending palatine branch of the facial. I //) The Vidian artery (;i. canalis pterygoidei ) is a small branch which passes backward along tiie Yidian nerve through the Yidian canal, and sends branches to the' roof of the pharynx and to the Eustachian tube. (o) The pterygo-palatine artery (a. palatina major) is also a somewhat slender branch. It passes backward through the pterygo-palatine foramen along with the pharyngeal nerve from the spheno-palatine ganglion, and supplies the roof of the pharynx, the Eustachian tube, and the mucous membrane lining the sphenoidal cells. (/>) The spheno-palatine artery (a. sphenopalatina ) is the terminal branch of the internal maxillary. It passes into the nasal cavity through the spheno-palatine foramen along with the spheno-palatine nerve from the spheno-palatine ganglion. Shortly after traversing the foramen it divides into an internal and an external branch. The internal branch, sometimes termed the naso-palatine, passes transversely across the roof of the nasal cavity to reach the septum, upon which it passes downward and forward, giving off numerous branches which anastomose to form a rich net-work beneath the mucous membrane of the septum. It finally reaches the anterior palatine foramen, where it anastomoses with the anterior branch of the descending palatine. Throughout its course it is accompanied by the naso-palatine nerve. The external branch ramifies downward and forward over the lateral wall of the nasal fossa, forming a rich plexus beneath the mucous membrane lining the meatuses and the turbinate bones. It will be observed that all the branches arising from the first and third portions of the internal maxillary artery traverse bony canals or foramina, while those of the second portion do not, but are distributed directly to muscles. Anastomoses. The communications of the internal maxillary artery are with the branches of the artery of the opposite side, with other branches of the artery of the same side, with other branches of the external carotid, and with branches of the internal carotid. The most abundant anastomoses with the artery of the opposite side are made through the branches of the middle meningeal; the alveolar branch anastomoses with the dental branches of the infraorbital of the same side and with the buccal artery, and the anterior branch of the descending palatine makes a large anastomosis with the naso-palatine branch of the spheno-palatine at the anterior palatine foramen. The other branches of the external carotid with which anastomoses are made are the facial, the temporal, and the posterior auricular; the facial com- municates by means of its submental and inferior labial branches with the mental branch of the inferior dental, by its superior coronary and angular branches with the terminal branches of the infraorbital, by its superior coronary with branches of the naso-palatine, and by its ascending palatine with branches of the descending palatine. The deep temporal arteries anastomose with branches of the superficial temporal and the infraorbital with the transverse facial branch of the same artery; while the posterior auricular communicates by means of its stylo-mastoid branch with the tympanic branch and with the petrosal branch of the middle meningeal. Of the anastomoses with the internal carotid arteries the most important are those between the orbital branch of the middle meningeal and the- lachrymal artery. between the terminal branches of the infraorbital and the terminal branches of the ophthalmic, and between the spheno-palatine branches and the ethmoidal arteries. Variations. In the early stages of development the main portion of the internal maxillary is represented by a Stem which arises from tin- internal carotid (Tandler). This is known as the a. stapedia (Fig. 694, Ast}, since it traverses the middle ear, passing through the foramen of the stapes (st}\ it makes its exit from the middle ear by the ('.laserian fissure and divides into two stems, one of which ( Rs~] passes through the foramen spinosnm (.As/) and is distributed to tin- snpraorbital region, while the other divides into two branches which, from their distribution, are termed the infraorbital ( A'/ ) and the mandibular (inferior dental) (/\in). A branch i_ A' ( /.v . arises later from tin- external carotid which anastomoses with the lower stem \\ here it divides into tin- two brandies just mentioned, and the main stein of the stapedius disappears, except in its distal portion, which persists as the tympanic branch of the internal maxillary, which tre- (liientlv arises in the adult from the middle 'meningeal instead of directlv from the internal max- illary ' By these changes, as mav be seen from the accompanying diagrams, the adult internal maxillary is formed, the snpraorbital branch becoming the middle meningeal ( Mi \ and the mandibular branch the inferior dental, while the infraorbital branch (A 1 /, becomes the main stein of the artery from which the remaining branches gradually develop. THE OCCIPITAL ARTERY. 743 FIG. 694. Ast In correspondence with this history, a persistence of the stapedial artery is occasionally found ; but the majority of the usual variations of the internal maxillary are due to the second- ary anastomoses which its branches make with other vessels. Thus, by an enlargement of the anastomoses between the middle meniirgeal and the branches of the ophthalmic artery, that vessel or some of its branches, notably the lachrymal, may come to arise from the middle meningeal (page 749). And, similarly, by the anastomoses with the facial or transverse facial arteries, the terminal branches of the infraorbital may be transferred to those vessels, the infraorbital itself stopping in the middle of the infraorbital groove. 5. The Ascending Pharyn- geal Artery. The ascending pharyngeal artery (a. pharyngea ascendens) (Fig. 695) differs from all the other branches of the external carotid by its vertical course. It is a comparatively small stem which arises close to or immediately at the origin of the external carotid and passes upward, at first between that vessel and the internal carotid, and later between the internal carotid and the internal jugular vein. Diagrams illustrating development of internal max- illary artery ; A, early stage ; , later stage; C, common carotid; Ce, Ci, external and internal carotid. For ex- planation of other letters, see text. ( Tandler.) Branches. (a) A prevertebral branch which supplies the prevertebral muscles of the neck and anastomoses with the ascending cervical branch of the inferior thyroid artery. (b) Pharyngeal branches (rami pharyngei), two or three in number, which supply the con- strictor muscles and the mucous membrane of the pharynx. (e) Meningeal Branches. A number of small twigs, into which the artery breaks up as it approaches the base of the skull, pass through the jugular and anterior condyloid foramina to supply the dura mater of the posterior fossa of the skull, and through the cartilage of the middle lacerated foramen to simply the dura of the middle fossa. Variations. The ascending pharyngeal frequently gives origin to the ascending palatine and more rarely to the superior laryngeal artery. It is very variable in its origin, not infre- quently being given off from one or other of the neighboring branches of the external carotid. 6. The Sterno-Mastoid Artery. The sterno-mastoid artery (a. sterno- cletdomastoidea) arises from the posterior surface of the external carotid, near its origin, and passes downward and backward to enter the sterno-cleido-mastoid muscle along with the spinal accessory nerve. It is a comparatively small vessel and is not infre- quently absent, being replaced by branches passing to the muscle from other arteries. When it is present, the hypoglossal nerve bends around to it to pass forward to the lingual muscles. 7. The Occipital Artery. The occipital artery (a. occipitalis) (Figs. 691, 692) arises from the posterior surface of the carotid, opposite or a little below the facial. It passes upward and backward, and is at first partly covered by the posterior belly of the digastric and the stylo-hyoid muscles, the parotid gland, and the temporo- maxillary vein. It crosses in succession, from before backward, the hypoglossal nerve, which, when the sterno-mastoid artery is wanting, winds around it to pass for- ward to the tongue, the pneumogastric nerve, the internal jugular vein, and the spinal accessory nerve. It then passes more deeply, lying in a groove on the posterior sur- face of the mastoid process and beneath the origin of the posterior belly of the digastric, the sterno-cleido-mastoid, and the splenius capitis. Emerging from beneath these muscles, it reappears in the upper part of the occipital triangle, and then ascends in a tortuous course over the back of the skull, sometimes perforating the trapezius near its origin, and breaks up into numerous branches which anastomose with branches from the artery of the opposite side and with those of the posterior auricular and superficial temporal. In this last part of its course it is superficial, lying beneath 744 HUMAN ANATOMY. the integument upon the aponeurosis of the occipito-frontalis. The artery pierces the deeper structures, accompanied by the great occipital nerve, a short distance lateral to and a little below the external occipital protuberance. Branches. In addition to its terminal branches, the occipital artery gives off : (a) A superior sterno-mastoid branch which supplies the upper part of the sterno-cleido- mastoid. (o) Posterior meningeal branches, one or more slender vessels which pass upward along the internal jugular vein and, entering the skull by the jugular foramen, are supplied to the dura mater of the posterior fossa. (f ) An auricular branch (ramus auricularis) which passes upward over the mastoid process to supply the pinna of the ear. (d ) A mastoid branch (ramus mastoideus) which enters the skull by the mastoid foramen and supplies the mucous membrane lining the mastoid cells, the diploe, and the dura mater. (e) An arteria princeps cervicis (ramus descendens) which arises from the artery, just as it passes out from beneath the splenius and descends the neck, supplying the adjacent muscles and anastomosing with the superficial cervical branch of the transversalis colli and with the pro- funda cervicis from the superior intercostal. (_/") Muscular branches (rami musculares) which are given off all along the course of the artery to the neighboring muscles. Anastomoses. The occipital artery makes comparatively large and abundant anastomoses in the scalp with the stylo-mastoid and temporal arteries, and also, by means of its art. princeps cervicis, with branches of the transversalis colli and superior profunda arteries, which arise from the subclavian. These latter anastomoses are of considerable importance in the development of a collateral circulation after ligation of either the common carotid or the subclavian arteries. Variations. The occipital artery occasionally passes superficial to the sterno-cleido-mas- toid muscle instead of beneath it, and it not infrequently gives origin to the ascending pharyn- geal artery or to the stylo-mastoid. Practical Considerations. The occipital artery is rarely formally ligated. The cervical portion may be reached through an incision along the anterior border of the sterno-mastoid, beginning midway between the ramus of the mandible and the lobe of the ear and extending downward two and a half inches. The deep fascia at the upper angle of the wound (parotid fascia) is spared on account of the risk of salivary fistula. At the lower angle it is divided, the parotid and sterno-mastoid are separated, and the digastric and stylo-hyoid muscles recognized and drawn upward. The occipital artery, near its origin, will then be seen crossing the internal carotid artery and internal jugular vein and in contact with the curve of the hypo- glossal nerve where it turns to cross the neck. The artery may be ligated close behind the nerve, the needle being passed from without inward to avoid the jugular vein. The occipital portion is approached through an almost horizontal incision two inches in length, beginning at the tip of the mastoid apophysis and extending back- ward and a little upward. The outer fibres of the sterno-mastoid and its aponeu- rotic expansion, the splenius, and often the complexus, must then be divided and the pulsation of the artery sought for in the space between the mastoid and the transverse process of the atlas, whence the vessel may be traced outward. If it is isolated near to the mastoid, great care must be taken not to injure the important mastoid venous tributaries of the occipital vein which in this region connect it with the lateral sinus. S. The Posterior Auricular Artery. The posterior auricular artery < a. aiirkularis posterior) (Fig. 693 ) arises from tin- external carotid after it has passed beneath the posterior belly of the digastric. It passes upward and backward, cov- ered at first by the parotid gland, which it supplies, and divides in the angle between the pinna and the mastoid process into terminal branches, some of which supply the pinna, while others anastomose with branches from the occipital and superficial temporal THE SUPERFICIAL TEMPORAL ARTERY. 745 Branches. In addition to branches to the parotid gland and to neighboring muscles, it gives rise to the stylo-mastoid artery (a. stylomastoidea). This vessel enters the stylo-mastoid foramen and traverses the facial canal (aqueduct of Fallopius) as far as the point at which the hiatus Fallopii passes off from it. During its course through the canal it gives off branches to the mucous membrane lining the mastoid cells, to the stapedius muscle, and to the mucous membrane of the middle ear, those twigs which pass to the inner surface of the tympanic mem- brane anastomosing with the tympanic branch of the internal maxillary. Arrived at the hiatus Fallopii, the artery accompanies the great superficial petrosal nerve through that canal and enters the cranium, supplying the dura mater and anastomosing with branches of the middle meningeal artery. Variations. The stylo-mastoid artery may arise from the occipital or its place may be taken by the petrosal branch of the middle meningeal, with which the stylo-mastoid normally anastomoses. 9. The Superficial Temporal Artery. The superficial temporal artery (a. temporalis superficialis) (Fig. 693) is the continuation of the external carotid after it has given off the internal maxillary. At its origin it is embedded in the substance of the parotid gland, and is directed upward over the root of the zygoma and imme- diately in front of the pinna. After ascending a short distance, usually about 2 cm. , upon the aponeurosis covering the temporal muscle, it divides into an anterior and a posterior branch, which, diverging and branching repeatedly, pass upward over the temporal and occipito-f rental aponeuroses almost to the vertex of the skull, anasto- mosing with the supra-orbital branches of the ophthalmic branch of the internal carotid, with the posterior auricular and occipital branches of the external carotid, and with the artery of the opposite side. Branches. (a) Parotid branches (rami parotidei), small branches to the parotid gland. (b) Articular branches to the temporo-mandibular articulation. (c) Muscular branches to the masseter muscle. (d) The anterior auricular branches (rami auriculares anteriores) supply the outer surface of the pinna and the outer portion of the external auditory meatus. (e) The transverse facial artery (a, transversa faciei) arises just below the main stem of the artery, crosses the zygoma, and is directed forward parallel with the zygoma and between it and the parotid duct. It gives off branches to neighboring muscles and to the integument of the cheek, and anastomoses with the masseteric branches of the facial and with the buccal, alveolar, and infra-orbital branches of the internal maxillary. (_/) The middle deep temporal (a, temporalis media) arises just above the zygoma, and after perforating the temporal aponeurosis and muscle, it ascends upon the surface of the skull to anastomose with the deep temporal branches of the internal maxillary artery. (g) The orbital branch (a. zygomaticoorbitalis) runs forward along the upper border of the zygoma, supplying the orbicularis palpebrarum and also sending branches into the cavity of the orbit. Anastomoses. The superficial temporal artery makes extensive anastomoses in the scalp with its fellow of the opposite side, with the occipital and posterior auricu- lar branches of the external carotid, and with the supra-orbital branch of the oph- thalmic. By means of the transverse facial it makes anastomoses with the facial and internal maxillary arteries. Variations. The principal variations of the superficial temporal are its division into the terminal branches below the level of the zygomatic arch and the absence of its posterior ter- minal branch ; in the latter case the area of distribution of the posterior branch is supplied by the posterior auricular or the occipital artery. Practical Considerations. The superficial temporal artery may require ligation on account of wound of the vessel, or of one of its branches, or in cases of aneurism. It or one of its chief subdivisions used frequently to be selected for the now rare operation of arteriotomy. The vessel never becomes very superficial imme- diately after emerging from beneath the upper part of the parotid. In the first por- tion of its track of ascent its pulsations are difficult to perceive. In the presence of the least swelling of the region they become incapable of serving as a guide for the incision (Farabeuf ). 746 HUMAN ANATOMY. Ligation. The skin, superficial fascia, and some fibres of the attrahens aurem muscle are divided for an inch on a vertical line between the tragus and the condyle of the mandible, a little nearer the latter. The artery will be found closely bound by connective-tissue bands to the temporal aponeurosis. THE INTERNAL CAROTID ARTERY. The internal carotid (Figs. 693, 695) is the second terminal branch of the com- mon carotid, from which it arises on a level with the upper border of the thyroid FIG. 695. Branch of left middle tneningeal artery Posterior cerebral arteries Branch of left middle meningeal Basilar artery Posterior inferior cerebellar artery Left vertebral artery Right vertebral artery Deep cervical artery Vertebral artery Transverse process of I. thoracic vertebra Superior intercostal artery Branch to II. intercostal space 1 1. rib I. aortic intercostal II. aortic intercostal Middle cerebral artery Atlas Arteria princeps cervicis Axis Left complexus Lingual artery Superior thyroid artery Thyro-hyoid muscle Thyroid cartilage Inferior constrictor of pharynx Common carotid artery Anterior cerebral artery Anterior clinoid process Middle fossa of skull Int. carotid, cav. portion Sup. maxilla, malar process Int. carotid, petrous portion Internal maxillary artery Eustachian tube Transverse process of atlas Sup. constictorof pharynx Int. carotid, cervical portion Ascending pharyngeal Stylo-glossus -Stylo-phangeus External carotid artery Stylo-hyoid muscle, cut Suhclavian artery Innominate artery Internal n ammary artery Deep dissection, showing internal carotid, vertebral and superior intercostal arteries. cartilage. In tin- first or cervical portion of its course it lies upon the outer side of tin- external carotid, but. as it passes upward, it comes to lie behind and then internal to that vessel, from which it is separated by the stylo -hyoid, digastric, and stylo- pharyugeus muscles. It passes almost vertically up the neck to the entrance to the carotid canal, ivstin- posteriorly on the prevertebral fascia covering the rectus capitis THE INTERNAL CAROTID ARTERY. 747 anticus major, and having upon its median side the wall of the pharynx and laterally the internal jugular vein, between which and the artery, and on a plane slightly pos- terior to both, is the pneumogastric nerve. It is also in relation in the upper part of this cervical portion of its course with the glosso-pharyngeal nerve, which lies at first behind it, but crosses its external surface lower down as it bends forward towards the tongue, and with the superior sympathetic ganglion, whose cardiac branch descends along its internal surface, while the pharyngeal branches cross it and the carotid branch ascends with the artery to the carotid canal, in which it breaks up to form the carotid plexus. In the second or petrosal portion of its course the internal carotid traverses the carotid canal, to whose direction it conforms, passing at first vertically upward and then bending so as to run forward and inward to enter the cranial cavity at the foramen lacerum medium. It then enters upon the third or intracranial portion of its course, ascending at first towards the posterior clinoid process, but soon bending forward and entering the outer wall of the cavernous sinus. In this it passes forward, accompanied by the sixth nerve (abducens), and at the level of the anterior clinoid process bends upward, pierces the dura mater, and quickly divides into its terminal branches. Branches. Throughout its cervical portion the internal carotid normally gives off no branches, in its petrosal portion, in addition to some small twigs to the peri- osteum lining the carotid canal, it gives origin to (i) a tympanic branch. In its intracranial portion, in addition to small branches to the walls of the cavernous sinus and the related cranial nerves, to the Gasserian ganglion, and to the pituitary body, there arise (2) anterior meningeal branches, (3) the ophthalmic, (4) posterior commu- nicating, (5) anterior choroid arteries. And, finally, its terminal branches, (6) the middle and (7) the anterior cerebral arteries. Variations. In its cervical portion the internal carotid occasionally takes a somewhat sinuous course, and, especially in its upper part, may be thrown into a pronounced horseshoe- shaped curve. It may give rise to branches which normally spring from the external carotid, as, for example, the ascending pharyngeal and the lingual, and accessory branches may arise from its intracranial portion. Practical Considerations. The internal carotid artery, on account of its deeper position, is not so often wounded as the external carotid. It has been punc- tured through the pharynx and has been wounded in tonsillotomy (page 1608). Aneurism of the internal carotid is not common. When it involves the petrosal or intracranial portion of the vessel it causes symptoms referrible to those regions and better dealt with after the venous system has been described (page 873). In its cervical portion it shows a tendency to become tortuous in elderly persons, owing doubtless to its fixity above, where it enters the carotid canal, and to the rela- tive lack of fixation below (Taylor). As the artery is crossed externally by the dense layers of the deep cervical fascia, and by the stylo-hyoid, stylo-glossus, stylo-pharyngeus, and digastric mus- cles, the progress of a swelling in this direction is strongly resisted. Internally the middle constrictor and mucous membrane of the pharynx offer far less obstruction to the extension of the aneurism, and in many of the recorded cases a pulsating pha- ryngeal protrusion has been the chief symptom. The effects of pressure on surround- ing structures, the internal jugular vein, and the pneumogastric and sympathetic nerves, for example, are not unlike those observed in other carotid aneurisms. The direct interference with cerebral circulation is greater in aneurism of the internal carotid, and vertigo, headache, drowsiness, etc. , are apt to be more conspicuous as early symptoms. Ligation. The vessel may be reached close to its origin and tied through the same incision as that used in ligating the external carotid (page 733). The sterno- mastoid muscle is drawn outward, the digastric muscle and hypoglossal nerve (which are usually seen) upward, and the external carotid artery inward. The two vessels should be carefully distinguished. The needle should be passed from with- HUMAN ANATOMY. out inward, avoiding the internal jugular vein, the pneumogastric and sympathetic nerves, and the ascending pharyngeal and external carotid arteries. The collateral circulation is carried on through the vertebrals and the vessels of the circle of Willis and is freely re-established. i. The Tympanic Artery. The tympanic artery (ramus caroticotympani- cus) is a small vessel which arises from the petrosal portion of the internal carotid. It passes through a foramen in the wall of the carotid canal to supply the mucous membrane .of the middle ear, anastomosing with the tympanic branches of the stylo- mastoid and internal maxillary arteries. FIG. 696. Facial artery Frontal arter Internal branch of supraorbital Superior oblique muscle Superior palpebral branch Inferior palpebral branch Frontal artery Nasal artery Anterior ethmoidal branch Supraorbital artery " Posterior ethmoidal branch Superior oblique Superior rectus Optic nerve Ophthalmic arterj Internal carotid artery Posterior clinoid process Internal carotid, cavernous portion Nasal artery Supraorbital artery Iff Superior rectus Levator palpebrae superions Lachrymal artery Lachrymal ^land Temporal branch Arteria centralis retina; Lone |>"-tc-M.>r . iliary arteries ' Short jwsterior ciliary arteries Middle fossa of skull Branches of right ophthalmic artery, sei-n from above after removal of roof of orbit. 2. The Anterior Meningeal Arteries. The anterior meningeal arteries are a number of small branches which arise from the intracranial portion of the inter- nal carotid and are supplied to the neighboring dura mater, anastomosing with the branches of the anterior ramus of the middle meningeal artery. 3. The Ophthalmic Artery. The ophthalmic artery (a. ophthalmica ) i. Fi^s. 696, 697) arises from the internal carotid immediately after it has issued from the- roof of the cavernous sinus. It passes forward beneath the optic nerve and traverses the optic foramen with that structure. v In the orbit it ascends to the outer side of the optic nerve and, crossing over it, passes in a sinuous course towards the inner wall THE OPHTHALMIC ARTERY. 749 of the orbit, along which it runs between the superior oblique and internal rectus muscles to the inner angle, where it terminates by dividing into palpcbral, frontal, and nasal branches. Branches. (a) The arteria centralis retinae arises from the ophthalmic while that vessel is still below the optic nerve. It runs forward along the under surface of the nerve to a point about 15 mm. from the posterior surface of the eye, where it passes into the substance of the nerve and continues its course forward in the centre of that structure. Arrived at the retina, the artery divides into two main branches, one ascending and the other descending, and these, branching repeatedly, form an arterial net-work upon the surface of the retina. The finer branches of the net-work extend deeply into the substance of the retina, although none reach the layer of visual cells. They pass over directly into the corresponding veins without making connections with any of the other arteries supplied to the eyeball. Just after its entrance into the eyeball, however, the main stem of the artery anastomoses with the short ciliary vessels. () The ciliary arteries, \\ hich are distributed to the choroid coat, the ciliary processes, and the iris, are somewhat variable in their number and origin. Two sets are distinguishable, and are named from their relative position the posterior and anterior ciliary arteries. (aa) The posterior ciliary arteries (aa. ciliares posteriores) arise from the ophthalmic artery as it crosses over the optic nerve, either as two trunks which pass forward, the one on the inner and the other on the outer side of the optic nerve, or else as a variable number of small vessels. Eventually the vessels break up into from ten to twenty branches, which surround the distal portion of the optic nerve, and, piercing the sclerotic, are distributed to the choroid coat of the eye. Two of the vessels, lying one on either side of the optic nerve, are usually stronger than the others, pierce the sclerotic some distance nearer the equator of the eyeball, and are termed the long posterior ciliary arteries (aa. ciliares posteriores longae). They pass forward between the sclerotic and choroid coats, send branches to the ciliary muscle, and divide at the peripheral border of the iris into two stems, which, passing around the iris, unite with their fellows of the opposite side and with branches of the anterior ciliary arteries to form the circulus arteriosus iridis, from which branches radiate to the iris and the ciliary processes. (f>6) The anterior ciliary arteries (aa. ciliares anteriores) usually take their origin from the muscular branches of the ophthalmic and accompany the tendons of the recti muscles (two arteries being associated with each muscle, except in the case of the external rectus, where there is only one) to the sclerotic, where they send off perforating branches which, after piercing the sclerotic, unite with the long ciliaries to form the arterial circle of the iris. The main stems are continued onward towards the margin of the cornea, where they divide and anastomose to form a narrow net-work surrounding that portion of the eyeball and also give branches to the conjunctiva. An anterior ciliary vessel is frequently contributed by the lachrymal artery. (c) The lachrymal artery (a lacrimalis) arises from the ophthalmic as it passes upward over the external surface of the optic nerve and passes forward and outward, in company with the lachrymal nerve, along the upper border of the external rectus muscle. It traverses the substance of the lachrymal gland, to which it gives branches, and terminates in small branches to the eye- lids. In its course it gives off a number of small twigs to the external rectus muscle ; a menin- gcal branch, which passes back into the cranium through the sphenoidal fissure and anasto- moses with the middle meningeal ; and a malar branch, which passes to the temporal fossa through a small canal in the malar bone and anastomoses with the anterior deep temporal and the transverse facial arteries. (if) The muscular branches (rami musculares) are somewhat irregular in their number and origin. Usually there are two principal stems and a variable number of small twigs, but occa- sionally the two principal stems arise by a common trunk. When the two are distinct, the in- ferior one arises close to the lachrymal, and is distributed to the inferior and internal recti and the inferior oblique muscles ; while the superior, smaller and less constant, arises after the oph- thalmic has crossed over the optic nerve, and is distributed to the superior and external muscles of tlit- orbit. In addition to branches to the muscles, these arteries also give origin to the anterior ciliary arteries described above. (e) The supraorbital artery (a. supraorbitalis) arises as the ophthalmic passes over the optic nerve. It is at first directed upward, and then passes forward between the periosteum of the roof of the orbit and the levator palpebrae superioris, and, making its exit from the orbit through the supraorbital notch or foramen, terminates in branches which ascend over the frontal bone towards the vertex of the skull, supplying the integument and periosteum and anastomosing with the superficial temporal artery. In its course through the orbit it gives off periosteal, diploic, and muscular twigs, and, after its exit from the supraorbital notch, a palpebral branch to the upper eyelid. (f) The ethmoidal arteries are two in number, and arise from the ophthalmic as it passes along the inner wall of the orbit. The posterior ethmoidal (a. ethmoidalis posterior) , which is the HUMAN ANATOMY. smaller and less constant of the two, passes through the posterior ethmoidal foramen and is distributed to the mucous membrane lining the posterior ethmoidal cells and the upper poste- rior part of the nasal septum, where it anastomoses with the spheno-palatine branch of the internal maxillary. It sometimes arises from the supraorbital artery. The anterior ethmoidal (a. ethmoidalis anterior) passes through the anterior ethmoidal foramen along with the nasal nerve, and, entering the cranium, passes forward over the cribriform plate of the ethmoid to the nasal slit at the side of the crista galli. Through this slit it enters the nasal cavity and passes downward in a groove upon the under surface of the nasal bone, supplying the nasal mucous membrane. While within the cranium it gives off a small meningeal branch to the dura mater of the anterior portion of the cranium, and it also sends branches to the mucous membrane lining the anterior and middle ethmoidal cells and the frontal sinuses. ( g) The palpebral branches (aa. palpebrales mediales) are two in number, and are distrib- uted to the upper and lower eyelids respectively. They arise opposite the pulley of the superior oblique muscle and descend towards the inner canthus of the eye. Each artery then bends out- ward towards the outer canthus along the free border of the lid, between the tarsal cartilage and the orbicularis muscle, forming the palpebral arches (arcus tarseus superior et inferior}, FIG. 697. Lacrimal artery Anterior ethmoidal Posterior ethmoidal Ophthalmic artery Optic nerve Supraorbital artery Frontal artery- Nasal artery Superior and in- ferior palpebral arteries Angular artery Anterior ciliary arteries Internal carotid artery Posterior clinoid process Int. carotid artery, cavernous portion Infraorbital artery Facial artery / ^ I^M '^M Arteria centralis retinae Long posterior ciliary artery Short posterior ciliary arteries Internal maxillary artery Branches of ophthalmic artery, seen from side after removal of lateral orbital wall. from which branches pass upward or downward, as the case may be, to supply the orbicularis, the Meibomian glands, and the integument of the lid. As they approach the outer canthus, the arches anastomose with the palpebral branches of the lachrymal artery. (A) The frontal branch (a. frontalis) is usually small, and is distributed to the integument over the glabella and to the pyramidalis nasi and frontalis muscles. It also sends some twigs to the eyelids. (i) The nasal artery (a. dorsalia nasi) is the true terminal branch of the ophthalmii passes downward in the angle formed by the nose and the lower eyelid and becomes directly continuous with the angular portion of the facial artery. In its course it gives branches to the walls of the lachrymal sac and to the integument of the root of the nose. Anastomoses. The principal communications of the ophthalmic artery are with the- superficial temporal, internal maxillary, and farial branches of tin- external carotid. With the first of these it communicates extensively l>y means of the supra- orbital branch and less importantly through the anastomosis of the malar branch of the lachrymal with the transverse facial artery. It makes a very important anasto- THE POSTERIOR COMMUNICATING ARTERY. 75 1 rnosis with the middle meningeal branch of the internal maxillary through the lachry- mal branch, and communicates also with the spheno-palatine artery by means of the ethmoidal branches. The anastomosis of the nasal branch with the angular ar- tery from the facial is also a large one, the two vessels being practically continuous. FIG Supraorbital Variations. In addition to the varia- tions in the number and origins of its branches, the ophthalmic artery also presents variations in its course, in that, instead of pass- ing to the inner wall of the orbit above the op- tic nerve, it sometimes passes below that structure. The most striking variation which it presents, however, is associated with the development of the branch of the lachrymal artery, which passes back through the sphe- noidal fissure to anastomose with the middle meningeal (Fig. 698). Occasionally this branch becomes exceptionally large and forms the main stem of the lachrymal artery, the connection of that vessel with the ophthalmic vanishing, so that it seems to be a branch of the middle meningeal. A further step in this process which sometimes occurs results in the origin of the entire ophthalmic system of ves- sels from the middle meningeal artery. Degenera- ted portion middle meningeal Variations of ophthalmic artery ; lachrymal coming chiefly from middle meningeal. (Meyer.) 4. The Posterior Communicating Artery. The posterior communicating artery (a. communicans posterior) (Fig. 702) arises from the posterior surface of the FIG. 699. Branch of ascending frontal artery Precentral sulcus Parietal artery / / Ascending frontal artery Branches of anterior cere- bral artery from mesial surface Anterior inferior cerebellar artery Branches of anterior cerebral artery External orbital arterv Inferior frontal artery Middle cerebral artery Temporal branches of middle cerebral artery Parieto-temporal arteries Basilar artery Pons Left vertebral artery Middle cerebellar peduncle Right vertebral artery Lateral surface of brain, showing cortical branches of middle cerebral artery; those of anterior and posterior rebral arteries are seen curving over supero-mesial border of cerebral hemisphere. internal carotid, opposite the sella turcica. It is directed backward beneath the optic tract and the inner border of the crus cerebri, and terminates posteriorly by 752 HUMAN ANATOMY. opening directly into the posterior cerebral artery. In its course it gives off twigs to the tuber cinereum, the corpora albicantia, and the crus cerebri. 5. The Anterior Choroid Artery. The anterior choroid artery ( a. choroi- dea) (Fig. 702) arises from the posterior surface of the internal carotid, slightly distal to the posterior communicating artery. It is directed outward and backward at first, and then, curving upward between the brain-stem and the temporal lobe, it gives branches to the hippocampus major. It is then continued upward and for- ward as the artery of the choroid plexus of the lateral ventricle, and anastomoses at the foramen of Monro with the artery of the choroid plexus of the third ventricle, which comes from the superior cerebellar branch of the basilar artery. 6. The Middle Cerebral Artery. The middle cerebral artery (a. cerebri media) (Figs. 699, 702) is one of the terminal branches of the internal carotid. It passes at first outward to the lower end of the Sylvian fissure, and is then directed backward and upward, lying at first deeply in the fissure close to the surface of the FIG. 700. Middle internal frontal artery Posterior internal frontal artery Internal carotid artery External orbital artery Middle cerebral artery From temporal branch of middle cerebral Posterior communicating artery Ant l brain lies .if erebral Posterio ebral artery Mesial surface of cerebral hemisphere, showing cortical branches of anterior and posterior cerebral arteries. island of Reil, but gradually becoming more superficial until at the posterior ex- tremity of the horizontal limb of the fissure it reaches tlu surface and divides intc branches which ramify over the lateral surface of the cerebral hemisphere. Branches. In its course outward to enter the Sylvian fissure it gives off a number of small central branches which penetrate the substance of the cerebral hemisphere at the anterior per- forated space, and, as the striate arteries, supply the corpus striatum. These antero-lateral anglionic branches, as they are often called, are arranged as two groups : (a) the internal striate arteries, which pass upward through the lenticular nucleus (globus pallidus) and the internal capsule and end in the caudate nucleus, supplying the anterior part of the structures traversed ; (t>) the external striate arteries, which after traversing the putamen and the internal capsule terminate in either the caudate nucleus or the optic thalamus. One of the former (leiiticiilo-striatc} vessels, which passes around the outer border of the lenticular nucleus before traversing its substance, is larger than the others and, since it frequently ruptures, is known as the artery of cerebral hemorrhage. While in the Sylvian fissure the middle cerebral artery gives off numerous branches to the cortex of the island of Reil and continues into the cortical branches, which are distributed to the lateral surface of the hemisphere and are usually four i THE SUBCLAVIAN ARTERY. 753 number, (a) The inferior frontal is distributed to the inferior frontal convolutions, (6) the ascending frontal passes to the lower portion of the ascending frontal convolution, (c) the parietal supplies the whole of the ascending parietal convolution and the neighboring portions of the inferior parietal, and (d) the parieto-temporal passes to all the convolutions around the posterior limb of the fissure of Sylvius. 7. The Anterior Cerebral Artery. The anterior cerebral artery (a. cerebri anterior) (Fig. 700) is the smaller of the terminal branches of the internal carotid. It passes forward above the optic chiasma to the anterior end of the great longitudi- nal fissure, and, bending upward around the rostrum of the corpus callosum, is con- tinued backward along the medial surface of the cerebral hemisphere to the posterior portion of the parietal lobe. At its entrance into the great longitudinal fissure it is connected with its fellow of the opposite side by a short transverse vessel termed the anterior communicating artery (Fig. 702). Branches. Immediately after it has crossed the optic chiasma the anterior cerebral artery gives off a number of small central branches (antero-mesial ganglionic) , which penetrate the base of the brain and are distributed to the lamina cinerea, the rostrum of the corpus callosum, the septum lucidum, and the tip of the caudate nucleus. Throughout its course in the great longitudinal fissure it gives branches to the corpus callosum and also cortical branches to the medial and lateral surfaces of the cerebral hemisphere. These branches are (a) the orbital, which vary in number and are distributed to the orbital surface of the frontal lobe, also sup- plying the olfactory bulb ; (b) the anterior internal frontal, which supplies the anterior and lower part of the marginal convolution and sends branches to the lateral surface of the hemis- phere supplying the superior and middle frontal convolutions ; (c) the middle internal frontal, which is distributed to the middle and posterior parts of the marginal convolution and to the adjacent portions of the superior and ascending frontal and ascending parietal convolutions ; and (d} the posterior internal frontal or quadrate, which, in addition to sending branches to the corpus callosum, supplies the quadrate lobe and the upper part of the superior parietal convo- lution. These branches anastomose upon the inferior and lateral surfaces of the hemisphere with the branches of the middle cerebral artery, the main stem of the artery anastomosing posteriorly with branches of the posterior cerebral. Anastomoses of the Carotid System. Although the majority of the anastomoses of the branches of the carotid arteries are with one another, yet there is a sufficient amount of communication with other vessels to allow of the establishment of a collateral circulation after ligation of the common carotid of one side. . The con- nections which are available for the circulation in such a case are as follows. ( i ) There is abundant communication between the branches of the right and left external carotids across the median line ; (2) the anterior communicating artery forms an important communication between the internal carotids of opposite sides ; (3) anastomoses exist between the ascending cervical branch of the inferior thyroid, the superficial cervical branch of the transversalis colli, and the deep cervical branch of the superior intercostal, on the one hand, all of these being branches of the sub- clavian artery, and the a. princeps cervicis, a branch of the occipital artery ; (4) abundant communications exist between the terminal branches of the inferior thyroid from the subclavian and the superior thyroid from the external carotid ; and, finally, (5) by means of the posterior communicating artery the internal carotid may receive blood from the posterior cerebral artery, which, through the basilar and vertebral arteries, belongs to the subclavian system. THE SUBCLAVIAN ARTERY. In the primary arrangement of the branchial blood-vessels, while there are two aortic arches (Fig. 678), the two subclavian arteries arise symmetrically from these arches as lateral segmental branches corresponding to the seventh cervical segment. With the disappearance of the lower portion of the right arch, however, an apparent lack of symmetry in their origin supervenes, the vessel of the right side arising from the innominate stem, while that of the left side springs directly from the persist- ing aortic arch. As a matter of fact, however, the proximal portion of the right aortic arch is represented by the innominate stem, together with a small portion of the proximal end of the right subclavian artery, so that the original morphological sym- 754 HUMAN ANATOMY. metry is retained ; but, since a portion of the original right aortic arch is included in the adult right subclavian, this vessel is a little more than equivalent to its fellow of the opposite side. Furthermore, since the innominate stem ascends directly upward from its origin, a topographical asymmetry of the two vessels results. The origin of the right subclavian is opposite the right sterno-clavicular articula- tion, and from that point the artery ascends upward and outward in a gentle curve over the dome of the pleura to the inner border of the scalenus anticus. The origin of the left subclavian is from the termination of the transverse portion of the aortic arch, and is consequently much deeper in the thorax (Fig. 690). From its origin it ascends at first almost vertically and then curves outward and slightly forward to reach the inner border of the scalenus anticus. From this point onward the course of the two arteries is the same. Passing behind the anterior scalene muscle, each artery continues its course outward across the root of the neck, curving downward to the outer border of the first rib, at which point it becomes known as the axillary artery. FIG. 701. Traoezius Descending branches of cervical plexus Transverse cervical vessels Omohyoid muscle Brachial plexus Suprascapular vessels Subclavian artery - Subclavian vein Clavicle Clavicular portion of sterno-mastoid External jugular vein Anterior scalene muscle Phrenic nerve Internal jugular vein Sternal portion of sterno-mastoid Common carotid artery Sterno-hyoid muscle irst rib Dissection of neck, showing relations of blood-vessels and nerves ; clavicle disarticulated from sternum and drawn down. In consequence of the difference in origin, the right subclavian artery is usually approximately 7.5 cm. (3 in.) in length, or about one inch shorter than the left. In its course across the root of the neck the height which the subclavian artery may reach varies considerably in different individuals ; in some it never rises above the clavicle, while in others its highest point may be from 2.5-3 cm - O" 1 /^ nl - ^ above that bone. Most frequently it reaches a point about 1.5 cm. (s/g in. ) above the clavicle, this highest point being reached as it passes beneath the scalenus muscle. As it commences its downward Course towards the first rib, the artery undergoes a more or less pronounced diminution in diameter, which persists for a distance of from 0.5-1 cm., and is followed by an enlargement to about its original si/e, what has been termed an arterial isthmus and spindle thus resulting (page 720). Relations. For convenience in description, the subclavian artery is usually regarded as consisting of three portions. The first portion extends from its origin to' the inner edge of the scalenus anticus, the second portion lies behind that muscle, THE SUBCLAVIAN ARTERY. 755 while the third portion extends from the outer border of the scalenus to the con- ventional termination of the artery at the lower border of the first rib. On account of the difference in their origins, the relations of the first portions of the right and left vessels differ somewhat. The first portion of the right subclavian artery lies behind the clavicular portion of the sterno-cleido-mastoid, and is crossed in front by the internal jugular and vertebral veins and by the right pneumogastric, phrenic, and superior sympa- thetic cardiac nerves. Behind, it is in relation with the transverse process of the seventh cervical vertebra, with the inferior cervical sympathetic ganglion, and with the right recurrent laryngeal nerve, which winds around its under surface from in front. Below, it is in contact with the dome of the right pleura. The first portion of the left subclavian artery, at its origin, is deeply seated in the thoracic cavity and ascends almost vertically through the superior mediastinum. Behind, and somewhat medial to it, are the cesophagus, the thoracic duct, and the longus colli muscle, and at its emergence from the thorax the lower cervical sympa- thetic ganglion. Medial, or internal to it, are the trachea and the left recurrent laryn- geal nerve, and lateral to it, on its left side, are the left pleura and lung, which also overlap it in front. Near its origin it is crossed by the left innominate (brachio- ceph- alic) vein, and, shortly before it passes over into the second portion, it is crossed by the internal jugular, vertebral, and 'subclavian veins, as well as by the phrenic nerve and the thoracic duct, the latter arching over it to reach its termination in the subclavian vein. The left pneumogastric and cardiac sympathetic nerves descend into the thorax in front of it, the pneumogastric, before passing over the aortic arch, coming into contact with the anterior surface of the vessel. As it emerges from the thorax the subclavian lies behind the clavicular portion of the sterno-cleido-mastoid. In the neck it rests below upon the dome of the left pleura. The second portion of the subclavian artery, the relations of which and of the succeeding portion of the vessel are the same on both sides, in front is covered by the scalenus anticus muscle, anterior to which and on a slightly lower plane is the subclavian vein. Behind and above it are the trunks of the brachial plexus, which separate it from the scalenus medius, and below it is in contact with the pleura. The third portion of the subclavian artery lies in the supraclavicular fossa, and is covered only by the skin, the platysma, and that part of the deep cervical fascia which contains the external jugular vein and the supraclavicular branches of the cervical plexus, and encloses a quantity of fatty tissue, in which the suprascapular artery passes outward. Behind, it is in contact with the scalenus medius and the brachial plexus, and above it are the brachial plexus and the posterior belly of the omo-hyoid. Below, it rests upon the first rib, at the lower border of which the vessel becomes the axillary artery. Branches. Considerable variation exists in the arrangement of the branches of the subclavian, but in what is probably the most frequent arrangement the branches are as follows : From the first portion arise (i) the vertebral, (2) the internal mammary, (3) the superior intercostal, and (4) the thyroid axis ; from the second portion no branches are given off ; from the third portion. (5) the transverse cervical. Variations. The variations in the origin of the subclavian artery have already been consid- ered in describing the variations of the aortic arch (page 725). Other anomalies occur in its relation to the scalenus anticus, in front of which it sometimes passes, and it may also traverse the substance of the muscle obliquely. More rarely the artery divides at the inner border of the muscle, the two branches so formed continuing onward through the axilla and down the arm to become the radial and ulnar arteries. Numerous supernumerary branches may arise from the subclavian. These may be either (i) accessory to the branches normally arising from the artery, such as an accessory vertebral, an accessory internal mammary, or an accessory inferior thyroid ; (2) they may be branches, such as the long thoracic, dorsal scapular, subscapular, and the anterior and posterior circum- flexes, which normally arise from the axillary artery, but have secondarily shifted to the sub- clavian as the result of the enlargement of anastomoses which they make with branches of that vessel ; or (3) they may be branches to neighboring organs, such as a bronchial or a pericar- dial branch, or occasionally the thyroidea ima (page 729). 756 HUMAN ANATOMY. Practical Considerations. The subclavian artery may require ligation, on account of stab wounds, as a preliminary to the removal of growths axillary or scapular or to an interscapulo-thoracic amputation, or in cases of axillary or sub- clavian aneurism, or, together with the common carotid artery, in aortic or innominate aneurism. On the surface of the neck the subclavian artery is represented by a curve-, convex upward, beginning at the sterno-clavicular articulation and ending beneath the middle of the clavicle, its highest point being on an average about five-eighths of an inch above that bone. The vein is lower, is in front of the artery ( separated from it by the scalenus anticus muscle), and is usually nearly or quite under cover of the clavicle. Aneurism of the subclavian is more frequent on the right side, probably because of the greater use and consequent greater exposure to strain of the right upper extremity. It may affect any portion of the vessel, but the third portion external to the scaleni, where it is least supported by surrounding muscles is most com- monly involved either primarily or by extension of an aneurismal dilatation upward from the axillary or downward from the arch of the subclavian. The thoracic- portion of the left subclavian is never the primary seat of aneurism. The symptoms are: (a) pain or numbness and loss of pou) tumor, usually appearing in the posterior inferior cervical triangle, with its long diameter approximately parallel with the clavicle, and extending upward and outward ; exceptionally it grows down- ward, but this is rare on account of the resistance offered by the clavicle, the first rib, and the structures filling the costo-clavicular space. Digital compression of the first and second portions of the artery is practically impossible. The third portion may be imperfectly occluded by making strong pressure directly backward just above the clavicle, a little external to its middle, so that the artery may be flattened out or narrowed against the scalenus medius muscle and the seventh cervical transverse process. Much more effectual pressure may be made at the same point, especially if the tip of the shoulder can be lowered so as to carry the clavicle downward and make the upper surface of the first rib more accessible, in a direction downward, backward, and inward, i.e. , in a line nearly or quite perpendicular to the plane of that surface. The vessel is thus compressed against it, and is not pushed off of it. It will be useful to recall that the outer border of the scalenus anticus and the posterior border of the sterno-mastoid the latter palpable and often visible are approximately on the same line, immediately outside of which is the third portion of the vessel. The scalene tubercle the elevation or roughening on the upper surface of the first rib between the shallow depression for the subclavian vein and the deeper groove for the subclavian artery gives attach- ment to the scalenus anticus and, when recognized, serves as a valuable guide to tin- vessel. Ligation. The first portion between the origin of the vessel and the inner side of the scalenus anticus has been ligated with uniformly fatal results. On tin- left side it is so situated as to depth, origin of branches the vertebral, internal mammary, thyroid axis, and superior intercostal and contiguity of important structures the heart, the aorta, the pleura, the innominate vein, the thoracic duct, tin pneumogastric, <-an liar, recurrent laryngeal and phrenic nerves that its ligation has only once been accomplished (Rodgers). On the right side the operative procedure is some- \\hat less difficult, but many of the relations are identical (vide .W//VYM, and the procedure is still so formidable that its description is included in some- works on operative surgery only because the ligation "affords good practice on the dead subject " (Jacobson). Tin- steps of the operation are the same as those in ligation of the innominate f pa-e 7^()) until the carotid sheath is reached and opened. The internal jugular vein and pneumOgastric nerve should be drawn aside ( inward, Agnew : outward, Harwell ) and tin- subclavian recoiMii/.ed, springing from the bifurcation of the innom- PRACTICAL CONSIDERATIONS: SUBCLAVIAN ARTERY. 757 inate at an acute angle with the carotid and deeper by the full diameter of the latter. The needle should be passed from below upward, while the pleura is gently depressed with the finger. The second portion behind the scalenus anticus has in a few cases been suc- cessfully ligated for aneurism external to it, but the operation does not require special description. It is identical with that for tying the third portion, with the addition of more extensive division of the clavicular portion of the sterno-mastoid and a partial division of the scalenus anticus, having due regard to the position of the phrenic nerve on the inner part of the anterior surface of that muscle. The third portion from the outer edge of the scalenus anticus to the lower border of the first rib has been frequently and successfully ligated. Three methods may be described : 1. By the first and usual one it is approached by a transverse incision, parallel with the clavicle and extending along the base of the posterior cervical triangle from the middle of the clavicular head of the sterno-mastoid to the anterior border of the trapezius. This is best made by drawing the skin down and incising it directly upon the bone, in this way easily avoiding the external jugular vein. The platysma muscle and the supraclavicular nerves are divided at the same time. On releasing the skin the wound will be placed about a half-inch above the clavicle. The shoulder is then well depressed so as to lower this bone and increase the supraclavicular space. The deep fascia, which, as it is attached to the superior border of the clavicle, is not pulled down with the skin and platysma, is then divided, the external jugular vein drawn aside or tied and cut, the loose cellular tissue, and possibly the omo-hyoid aponeurosis, scratched through or cut, and one or the other of four landmarks iden- tified : (a) the tense outer edge of the anterior scalene muscle or (6) the scalene tubercle at the insertion of that muscle into the first rib, the artery lying just outside these on the rib; (c~) the first rib itself traced inward with the finger from the outer angle of the wound until the artery is reached ; (d} the lowest cord of the brachial plexus, lying immediately above, or sometimes slightly overlapping the artery. The cord has been mistaken for the vessel, but compression between the finger and the rib does not flatten it out, as in the case of the artery, and, of course, does not arrest the radial pulse. The tubercle is often poorly developed, and has a less close relation to the vessel when the latter rises high above the clavicle. The process of cervical fascia reaching from the posterior border of the scalenus to the sheath of the artery may be so tense as to obscure to both sight and touch the line of the outer edge of the muscle The artery is cautiously denuded, care being taken to avoid injury to the pleura or to the subclavian vein. The transverse cervical artery is usually above and the suprascapular artery below the line of incision. The phrenic nerve has been known to pass directly over the third portion of the subclavian (Agnew), and the possibility of the presence of this rare anomaly should be remembered. The needle, the tip kept between the artery and the rib, is passed from above down- ward, and from behind forward and a little inward. In the case of a high arch of the subclavian the third portion is nearly vertical, and it would then be more correct to speak of passing the needle from without inward. 2. The middle of the clavicle for two or more inches, or the whole clavicle, may be resected subperiosteally, as in interscapulo-thoracic amputations, and the ap- proach to the artery greatly facilitated. 3. By strongly elevating instead of depressing the shoulder and clavicle, using the arm as a tractor, the artery may be exposed by an incision just below and parallel with the middle of the clavicle. A portion of the outer edge of the pec- toralis major and some of the inner deltoid fibres will usually have to be divided, although it may be possible to gain sufficient room by drawing the margin of the former muscle inward and that of the latter outward. The cephalic vein dipping in through this intermuscular depression (Mohrenheim's fossa) to join the axillary vein must be avoided. The artery is found lying between the vein internally and the close bundle of the cords of the brachial plexus externally. The point at which the vessel is tied is said to be identical with that at which it is ligated through the usual incision (Dawbarn). 758 HUMAN ANATOMY. The collateral circulation after ligation of the third portion of the subclavian artery is carried on from the proximal or cardiac side of the ligature by (a) the suprascapular and posterior scapular ; (6) the aortic intercostals, the superior inter- costals, and the internal mammary ; and (c) numerous subdivisions of subclavian branches running through the axilla, anastomosing respectively with (a) the sub- scapular, and the acromio-thoracic ; (), the subscapular, long thoracic, infrascap- ular, and dorsalis scapulae ; (c) the axillary trunk or its branches. i. The Vertebral Artery. The vertebral artery (a. vertebralis) (Figs. 695, 704), the first and largest branch of the subclavian artery, is destined chiefly for the supply of the spinal cord and the brain, joining with the internal carotid arteries to form the remarkable intracranial anastomotic circle of Willis. In view of its peculiar course, the vertebral artery may be conveniently divided into four parts. The first portion arises from the upper surface of the first part of the sub- clavian artery, opposite the interval between the longus colli and scalenus anticus, and courses upward and somewhat backward, between these muscles and in front of the transverse process of the seventh cervical vertebra, to the foramen in the transverse process of the sixth cervical vertebra, which it enters. The artery is surrounded by a plexus of sympathetic nerve-fibres, and in front is crossed by the inferior thyroid artery and covered by the vertebral and internal jugular veins. The second portion includes the ascent of the artery through the foramina in the transverse process of the upper six cervical vertebrae, surrounded by plexiform net- works of sympathetic nerve-fibers and of veins, and Lying in front of the trunks of the cervical nerves. As the artery traverses the foramen in the axis it abandons its previous almost vertical course and passes upward and outward to reach the foramen in the atlas. As the artery emerges from this opening, between the suboccipital nerve and the rectus capitis lateralis muscle, the third portion begins, which winds horizontally to the outer side and back of the superior articular surface of the atlas to enter the suboccipital triangle (Fig. 522) where the artery rests in the vertebral groove upon the posterior arch of the atlas, separated from the bone, however, by the suboccipital nerve. The artery then perforates the lower border of the posterior occipito-atlantoid ligament and enters the spinal canal. The fourth portion of the artery pierces the spinal dura mater, passes between the roots of the hypoglossal nerve and the dentate ligament and enters the cranial cavity by traversing the fora- men magnum. Passing forward along the medulla oblongata and gradually inclin- ing towards the mid-ventral line, at the posterior border of the pons the vertebral artery unites with its fellow of the opposite side to form the basilar artery ( a. basi- laris), which extends forward along the median line of the pons to the anterior border of that structure, where it terminates by dividing into the two posterior cerebral arteries. Branches. In its course up the neck the vertebral artery gives off, opposite each inter- vertebral space which it passes, lateral and medial branches which represent the original seg- mental arteries by the anastomoses of whose branches the vertebral \vas formed ( page 721 ). (a) The lateral or muscular branches pass to the muscles of the neck and form anasto- moses with the ascending and deep cervical branches of the subclavian and with the arteria princeps cervicis of the occipital. (b) The medial or spinal branches ( rami spinales) pass through the intervertebral foramina into the spinal canal, accompanying the spinal nerves, and are distributed to the bodies of the vertebrae and to the membranes and substance of the spinal cord. Each branch gives off an rtion Biceps, short head Coraco-brachialis Posterior circumflex Dorsal scapular Subscapular Teres major Latissimus dors! I-onjj thoracic Serratus inagnus VertrlT.il Inferior thyroid _'lhyr"M ,i\i- _ Subclavius mus. ni.-il thor.i. it Buperlcc thoracic _ Alar thoracic Suliscapi laris \ Subclavian and axillary arteries pectoralis minor still in place. the brachial plexus in a downward prolongation of the cervical fascia known as the a.vil/arv sheath, and rests behind upon the upper serration of the serratUS inagnus and up >n the first intercostal space. The internal anterior thoracic and the posterior thoracic nerves cross it obliquely behind, the latter nerve intervening between it and tlu- serratus niagnus. Above, at the outer side, are the ronls of the brachial plexus and the external anterior thoracic nerve, and below and to the inner side is the axillary vein, between which and the artery is the internal anterior thoracic nerve. In its second portion the artery is covered anteriorly by both the pectoralis major and the pectoralis minor. Posteriorly it lies in contact with the posterior cord of the brachial plexus, and is separated by a quantity of aro.lar and fatty tissue from PRACTICAL CONSIDERATIONS: AXILLARY ARTERY. 769 the anterior surface of the subscapularis muscle. External to it is the outer cord of the brachial plexus, and internally the inner cord, which separates it from the axillary vein. In its third portion the artery is covered in its upper half by the lower part of the pectoralis major, but in its lower half only by the integument and the superficial and deep fascue. The inner head of the median nerve passes obliquely across its anterior surface. Posteriorly it is in relation with the subscapularis, latissimus dorsi, and teres major, in that order from above downward, a considerable amount of areolar tissue, in which run the circumflex and musculo-spiral nerves, intervening, however, between the artery and the muscles. To the outer side are the median and musculo- cutaneous nerves and the coraco-brachialis muscle, while internally are the internal cutaneous and ulnar nerves and the axillary vein. Branches. Much variation occurs in the arrangement of the branches of the axillary artery. It is customary to recognize seven branches, but one or more of them is frequently absent as a distinct branch arising directly from the artery. These branches are arranged as follows : from the first part are given off (i) the superior thoracic and (2) the acromial thoracic ; from the second part (3) the long thoracic and (4) the alar thoracic ; and from the third part (5) the subscapular, (6) the anterior circumflex, and (7) the posterior circumflex. Variations. As stated in the description of the variations of the subclavian, the axillary artery may be represented by two parallel vessels which arise from the first portion of the sub- clavian and are continued below into the radial and ulnar arteries. The more frequent varia- tions, however, concern the occurrence of additional branches from the axillary, and of these there may be mentioned the occurrence of the superior profunda, normally a branch of the brachial, but not infrequently arising from the axillary "in common with the subscapular. Practical Considerations. The axillary artery may require to be ligated on account of wounds, of rupture, of high aneurism of the brachial, or, rarely, in distal ligation for subclavian aneurism. Wounds of the axillary are not uncommon when the vulnerating body a knife- blade, a bullet, etc. is directed from within outward, the artery in all positions of the arm maintaining a much closer relation to the outer, or humeral, wall of the axilla than to the inner, or thoracic, wall, which is therefore known as the wall of safety. It is always well in such cases to expose the artery and to tie both ends, as the exact source of the bleeding is often necessarily in doubt and the free anastomosis of its branches is likely to lead to secondary hemorrhage from the wound if the vessel is tied in continuity. Rupture of the axillary artery has occurred in a considerable number of cases as an accident due to the movements employed in attempted reduction of old dislocations of the shoulder. The preponderance of arterial as compared with venous rupture (twenty-six out of twenty-eight cases, Stimson ; or forty out of forty-four, Korte) is striking, the greater thinness of the vein and its attachment to the costo-coracoid membrane circumstances that would seem to favor its rupture being more than counterbalanced by the greater frequency and extent of atheromatous degeneration and consequent loss of elasticity in the artery, and possibly by the greater liability of the latter to undergo tension during the movements of abduction, elevation, and circumduction (which are those chiefly associated with the accident in question), and as the outermost or rather uppermost vessel to contract adhesion to the displaced humeral head. Aneurism of the axillary is comparatively frequent, as might be expected from the number, variety, and range of the movements of the shoulder-joint, during which the vessel is subjected to strains and to a variety of flexures. It is more common on the right side on account of the more general use of the right arm, and affects oftenest the third portion of the vessel, or that least supported by surrounding structures and most subjected to changes in tension and position and to certain injuries, as those which occur during luxation of the shoulder or during efforts at reduction (vide supra}. On account of the looseness of the tissue in which it lies, such an aneurism rapidly attains a large size and, by reason of the minor traumatisms inflicted during the shoulder movements, is especially prone to inflammation. 49 770 HUMAN ANATOMY. The symptoms are (a) swelling showing immediately below the clavicle (in Mohrenheim's fossa) and pushing that bone upward if the first portion is involved, or pushing the pectoral muscles forward if the aneurism is lower, or appearing as a pulsating tumor in the axilla if the third portion is involved ; (b)cedema of the arm and hand from pressure on the axillary vein ; (<:) pain down the arm, in the shoulder and neck, and down the side of the chest, and feebleness and limitation of shoulder and arm movements from, first, spasm, then paresis of the associated muscles, all due to pressure on the brachial plexus and its branches. Digital compression of the axillary artery is only effectively possible in the lower part of the third portion, where, with the fingers beneath the anterior axillary fold, FIG. 706. Cut fibres of pectoral is major Clavicle Subclavius Axillary artery Brachial plexus Pectoralis minor Pectoralis First intercostal space Subclavian vein Pecioraiis major, cut Second rib Dissection showing relations of axillary artery in first part of its course. the vessel, if the effort is made with due care and gentleness, may be flattened against the humerus just within the edge of the coraco-brachialis and biceps. Ligation of the first portion may be effected in two ways : i. With the- arm abducted to a right angle, an incision three inches long, slightly convex downward, and with its centre about an inch below the middle of the clavicle, is made through the skin, superficial fascia, and platysma. The cephalic vein and the descending branch of the acromial thoracic artery will be seen, just beneath the fascia, in the groove between the deltoid and greater pectoral muscles. The outer clavicular fibres of the pectoralis major are then divided close to the clavicle ; the interpectoral and axillary fascia and some loose connective tissue are broken up ; the upper border of the pectoralis minor is identified and traced to the coracoid process ; the costo-rora- roid membrane is cautiously cut through by a vertical incision close to the coracoid ; the artery is then sought for, lying between the brachial plexus of nerves externally and AXILLARY ARTERY: BRANCHES. 771 the vein internally. The internal anterior thoracic nerve is sometimes seen coming out between the vein and the artery. The arm should be brought to the side to relieve tension on the vessels, especially the vein, which in that position will be least prominent. The needle should be passed from within and below outward and upward. 2. With the arm abducted, so as to make evident the fissure between the sternal and clavicular portions of the pectoralis major, an oblique incision is made over this space and will usually begin about a half-inch from the sterno-clavicular joint. The muscular interspace having been exposed, its sides are separated, not directly back- ward, but backward and upward towards the clavicle. The arm is brought to the side to relax the pectoral fibres. The pectoralis minor and the space between it and the clavicle are reached^^ and if the latter is too contracted, the muscle may be divided close to the coracoid process. The artery is then exposed and secured as in the method above given. The second portion is not formally ligated, but may have a ligature applied when- ever, as in the last-mentioned method, the lesser pectoral has been divided. Ligation of the third portion of the subclavian artery is, on account of its ease of performance, almost invariably preferred to any of these operations. The third portion of the axillary is that almost always selected for ligation of that vessel, for a similar reason. The line of the vessel, the arm being at right angles to the trunk, is from the junction of the anterior and middle thirds of the summit of the axilla to the middle of the bend of the arm at the elbow. This line will be found to follow the inner margin of the coraco-brachialis muscle, the prominence of which may be seen just internal to the swell of the biceps where it emerges from beneath the anterior axillary fold. An incision is made on this line through the skin and superficial and deep fasciae, and the fibres of the coraco-brachialis margin are exposed and cleared. Internally to them lies the vessel, the median and musculo-cutaneous nerves external to it, and the inter- nal cutaneous nerve and axillary vein on its inner side. The needle should be passed from within outward. The collateral circulation is established after ligation of the first portion above the origin of the acromial thoracic precisely as after ligation of the third portion of the subclavian (page 757). After ligation of the third portion above the origin of the subscapular the anastomoses take place between (a) the intercostals, long thoracic, posterior scapular, and suprascapular, and (<) the acromial thoracic, on the cardiac side of the ligature ; and (a) the subscapular, and (^) the posterior circumflex on the distal side. When the vessel has been tied between the origins of the subscapular and the two circumflex arteries probably the point of election (Taylor) the anastomoses occur between the branches of the axillary and those of the thyroid axis, i.e. , the suprascapular and acromial thoracic above and the posterior circumflex below. Still lower, i.e., below the circumflex arteries the collateral circulation is established just as after ligation of the brachial above the superior profunda (q.v.}. 1. The Superior Thoracic Artery. The 'superior or short thoracic (a. thoracalis suprema) (Fig. 704) arises just after the axillary has emerged from beneath the subclavius muscle, and is directed downward and forward to the first intercostal space, the muscles of which it supplies. Not infrequently it gives off a branch which supplies the muscles of the second intercostal space also. Its branches anastomose with those of the internal mammary and acromial thoracic, and occasionally its place is caken by a branch from the latter vessel. 2. The Acromial Thoracic Artery. The acromial thoracic (a. thoraco- acromialis) (Fig. 705) is a very constant branch which arises from the front of the axillary artery, a short distance below the superior thoracic. It is directed forward for a short distance, but soon divides into thoracic, clavicular, and acromio-humeral branches. Branches. (a) The thoracic branches (rami pectorales) pass downward and forward to the side of the thorax, supplying the muscles of the second and third, and sometimes of the fourth and fifth intercostal spaces, and also giving branches to the pectoralis major and the pectoralis minor. It anastomoses with the intercostal arteries and the superior and long thoracics. 772 iir.MAN ANATOMY. (t>) The clavicular branch, which is the smallest of the three, passes upward to supply the subclavius muscle, and anastomoses with the suprascapular artery. (c) The acromio-humeral branch passes upward and outward across the costo-coracoid membrane and over the coracoid process of the scapula, and then divides into an acroinial and a liuincral branch. The former (ramus acromialis) passes upward towards the acromial process to supply the deltoid muscle, while the latter (ramus dcltoideus) turns downward in the groove between the deltoid and the clavicular portion of the pectoralis major, accompanying the cephalic vein. It sends branches to the two adjacent muscles and to the integument, and anastomoses with the anterior circumflex artery. 3. The Long Thoracic Artery. The long thoracic (a. thoracica latcralis j (Fig. 704) is a somewhat inconstant branch, whose place is very frequently taken by the thoracic branch of the acromial thoracic or by a branch from the subscapular. It passes downward and forward upon the serratus magnus, sending branches to that muscle, the pectoralis minor, and the muscles of the third, fourth, and fifth intercostal FIG. 707. Transverse cervical artery Superficial Cervical branch Posterior scapular branch Trapeztus, cut Acromion Deltoid, everted Triceps Rhom- boideus niajo _'ost. circumflex art. Infraspinatus Triceps, scapular head Teres minor Spine of scapula Dorsal scapular artery Subscapularis Teres major Latissimus dorsi Arteries of posterior aspect of shoulder. spaces. It also sends branches to the mammary gland (mini maniniarii extern! ), whence it has been termed the external mam man' artery. It anastomoses with t thoracic branch of the acromial thoracic, with the subscapular and the mtercostals. and with the perforating branches of the internal mammary. 4. The Alar Thoracic Artery. The alar thoracic ( Fig. 7"4 > '* :l very " slant small branch which passes to the fascia and lymphatic- glands of the axillary space. Its place may be taken by brandies from the subscapular, the long thoracic, or tin- thoracic branch of the acromial thoracic. 5. The Subscapular Artery. Tin- subscapular (a. suhscapulans 704) 'is the largest branch of tin- axillary and arises just as that artery crosses lower border of the subscapularis muscle. It passes downward and inward, accon named by the long subscapular nerve, along the lower border of tin- subscapiiiar musde as far as the lower angle of the scapula, and distributes branches through out its course to the subscapularis and tens major and to the latissnmis dorsi. also gives off THE BRACHIAL ARTERY. 773 (a) Thoracic branches (rami thoracodorsales) , which supply the serratus magnus and the muscles of some of the intercostal spaces, and not far from its origin it gives off (b) The dorsal scapular (a. circumflex scapulae). This vessel, of large size, winds around the axillary border of the scapula in the triangular space bounded by the teres major, the teres minor, and the long head of the triceps, and is distributed to the infraspinatus and the teres minor. The subscapular artery anastomoses through its thoracic branches with the intercostals and with the long thoracic, and through the dorsal scapular with the suprascapular and posterior scapular arteries. Variations. The subscapular artery varies somewhat in its origin. Occasionally it springs from the second portion of the axillary, and may also arise from the brachial. Quite frequently it arises from a trunk common to it and one or other or both circumflex arteries, and the supe- rior profunda brachii, normally a branch of the brachial artery, may also arise from this common trunk. The subscapular has been observed to give rise to an aberrant artery which passes down the arm and either unites with the brachial or else becomes the ulnar, or may even extend to the neighborhood of the wrist, where it unites with a branch of the anterior interosseous artery to form the radial. 6. The Anterior Circumflex Artery. The anterior circumflex (a. circura- tlexa huraeri anterior) (Fig. 704) is the smallest of the three branches of the third portion of the axillary, and arises either directly from the artery or from a common trunk with the posterior circumflex ; more rarely it arises from the subscapular. It passes outward beneath the coraco-brachialis and the heads of the biceps, and winds around the surgical neck of the humerus, lying close to the bone. Opposite the bicipital groove it gives off a branch which ascends along the groove to be distributed to the capsule of the shoulder-joint, and it also sends branches to the coraco- brachialis and biceps. It terminates by anastomosing with the posterior circumflex and with the humeral branch of the acromial thoracic. 7. The Posterior Circumflex Artery. The posterior circumflex (a. cir- cumtlexa humeri posterior) (Fig. 704) arises from the axillary, almost opposite the anterior circumflex, or from a common trunk with that vessel or with the subscap- ular. More rarely it may arise from the upper part of the brachial artery. It passes backward and outward through the quadrilateral space bounded by the subscapularis above, the teres major below, the long head of the triceps internally, and the humerus externally, and winds around the posterior surface of that bone at the level of its surgical neck. Passing under the deltoid muscle externally, it divides into a number of branches, most of which pass into the muscle to supply it, while some pass to the shoulder-joint. It anastomoses with the acromial branch of the acromial thoracic, with the anterior circumflex, and with the superior profunda branch of the brachial. THE BRACHIAL ARTERY. The brachial artery (a, brachialis) (Figs. 708, 709) is the continuation of the axillary down the arm. It begins at the lower border of the teres major and termi- nates a little below the bend of the elbow by dividing into the radial and ulnar arteries. In the upper part of its course the vessel lies along the inner side of the arm, but as it passes downward it inclines somewhat outward, so that in its lower part it is on the anterior surface of the brachium. Its course may be indicated by a line drawn from the junction of the outer and middle thirds of the folds of the axilla to a point midway between the condyles of the humerus. Relations. Anteriorly the brachial artery is covered throughout the greater part of its course by only the deep and superficial fasciae and the integument. About the middle of its length it is crossed obliquely, from without inward, by the median nerve, and at the bend of the elbow it passes beneath the aponeurotic slip, the so-called bicipital fascia (lacertus fibrosus) from the tendon of the biceps, and is separated by it from the median basilic vein. Posteriorly it rests in succession, from above downward, upon the long head of the triceps, the inner head of the triceps, the insertion of the coraco-brachialis, and the brachialis anticus. The musculo-spiral nerve and the superior profunda artery pass downward and inward between the vessel and the long head of the triceps. Externally to it, above, is the median nerve 774 HUMAN ANATOMY. and the coraco-brachialis muscle, and, lower down, the biceps and its tendon. Internally it is in relation, above, with the ulnar, internal cutaneous, and lesser internal cutaneous nerves, and, in its lower third, with the median nerve. The basilic vein is somewhat superficial to it and to its inner side. Two venae comites accompany the artery, lying respectively upon its inner and outer sides, and cross branches pass between the two. It is also accompanied by two lymphatic vessels which have in their course three or four lymphatic nodes, usually of small size. Branches. The brachial artery gives off muscular branches to the biceps, coraco-brachialis, brachialis anticus, triceps, and pronator radii teres, and a small FIG. 708. Deltoid Cephalic vein Humeral branch of acromial thoracic artery Pectoralis majo: Axillary vein Muscular vein Outer head'of median nerve Inner head of median nerve Axillary artery Musculo-cutaneous ne Brachial artery Superior profunda artery Median nerve I.atissiimis dorsi tendon Teres major Inferior profunda artery Internal intermuscular septum Anastomotic artery Biceps tendon Ant. cutaneous hr.of musculo- cutaneous nrv. Bicipital fascia Musculo-spiral nerve Inner head of triceps Inner condyle ilecranon Brachial artery in relation to nerves of arm. nutrient artery for the humerus (a. nutriciac humeri) arises either directly from the brachial or from one of its muscular branches or from the inferior profunda. It enters the nutrient foramen upon the inner surface of the shaft of the humerus. In addition, there arise from the brachial (i) the superior profunda, (2) the inferior Profunda, and (3) the anastomotica magna. Variations. Tin- variations which the hrachial artery presents are both numerous and important, in that they affect materially the origin of the' two terminal branches, the radial and ulnar. In cases in which there is a well-developed supracondyloid process on the humerus i page 268), the hrarhial artery accompanies the median nerve behind it, and only jtassrs upon the an- terior surface of the arm after it lias passed it. In such cases there generally arises from the upper part of the brachial, or even from the axillary, a vessel which descends upon the anterior surface of the arm, lying superficially and sending branches to the biceps and brachialis anticus THE BRACHIAL ARTERY: BRANCHES. 775 muscles. This has been variously termed the vas aberrans, the a. brachialis superficialis, or the a. radia/is super jicialis, and it appears to be normally present, but much reduced in size and included among the muscular branches. The majority of the modifications of the brachial artery are due to an extraordinary devel- opment of the superficial brachial. Thus it may enlarge and become continuous below with the radial artery, giving rise to a condition usually termed a " high" origin of the radial ; more FIG. 709. Humeral branch of acromial thoracic artery Pectoralis minor, stump. Biceps and coraco-brachialis, stump Axillary artery Anterior circumflex artery Tendon of long head of biceps Insertion of pectoralis major Deltoid Coraco-brachialis Brachialis anticus Tendon of biceps [dorsi Teres major and latissimus lUperior profunda artery Brachial artery Triceps Inferior profunda artery Anastomotic artery Inner condyle Olecranon Origin of superficial flexors Anterior ulnar recurrent artery Posterior ulnar recurrent artery Jlnar artery Radial artery Brachial artery and its branches. rarely it may unite with the ulnar artery, producing a " high" origin for that vessel ; occasion- ally it gives rise to both the radial and ulnar, the true brachial being continuous below with the common interosseous ; or, finally, it may unite with the lower part of the brachial artery proper, the portion of the latter between the origin and anastomosis of the superficial brachial disap- pearing, so that what is termed a brachial artery is formed, which passes behind instead of in front of the median nerve. 77 6 HUMAN ANATOMY. Comparative anatomy and embryology both indicate that the occurrence of a well-devel- oped superficial brachial, continuous below with the radial, is the primary condition, and that the origin of the radial as a terminal branch of the brachial proper is a secondary condition, due to an anastomosis between the lower part of the original superficial stem and the brachial and to the subsequent diminution or partial obliteration of the former above this anastomosis (Fig. 748 E ). Another branch, normally present but usually insignificant, which may reach an extraor- dinary development, is the a. plica: cubiti superficialis. It arises from the lower portion of the brachial and, passing inward and downward beneath the tendon of the biceps, is distributed to the flexor carpi radialis and the palmaris longus. When abnormally developed, it forms what has been termed the accessory ulnar artery, and passes down the forearm, immediately beneath the deep fascia and between the two muscles just mentioned, and terminates by anasto- mosing with the ulnar, or in some cases replaces it and enters into the formation of the palmar arches. Supernumerary branches accessory to the branches usually present may also occur, and, in addition, the brachial may give rise, in its upper part, to the subscapular and the posterior circumflex, normally branches of the axillary ; in its lower part, to the radial recurrent; and, at its bifurcation, to the interosseous artery or to the median, which is usually a branch of the interosseous. Practical Considerations. Spontaneous aneurism of the brachial artery is rare, and is usually associated with marked arterio-sclerosis or with cardiac disease. Wounds and traumatic aneurism are common, though lessened in frequency by the protected position of the upper two-thirds of the artery on the inner side of the arm. Aneurism has, however, followed a stab-wound from the outer side, which, after passing through the biceps, involved the vessel. Arterio-venous aneurism just above the bend of the elbow was formerly often met with as a result of the accidental wounding of the artery during phlebotomy of the median ' basilic vein, parallel with the vessel at that point and separated from it only by the lacertus fibrosus. The line of the artery is from the junction of the anterior and middle thirds of the axilla to the middle of the bend of the elbow when the arm is abducted and the forearm extended and supinated. The artery in the upper two-thirds of its course may be compressed against the inner side of the humerus by pressure directed outward and a very little backward along the internal border of the coraco-brachialis and biceps. This muscular border may be visible, or may be recognized by picking it up between the thumb and finger. The artery may be overlapped by this inner edge of the biceps, especially in mus- cular subjects. At the middle of the arm, over the insertion of the coraco-brachialis into the flat surface above the beginning of the internal supracondyloid ridge, it may most easily be subjected to compression. In the lower third the pressure must be directed backward, as the humerus separated from it by the brachialis anticus muscle then lies behind it. Ligation of the vessel at its upper third is effected through an incision made along the inner border of the muscular ridge of the coraco-brachialis muscle, the fibres of which may with advantage be exposed and identified. Nothing lies between the artery and the muscle except the median nerve. The basilic vein is to the inner side of the vessel and may, before the incision is made, be identified and avoided by compression of the axillary vein above. The ulnar nerve also lies to the inner side. The needle may be passed in either direction. In ligation at the middle of the arm, the limb should be abducted with the elbow slightly flexed, and should be supported by an assistant. If the arm is allowed to rest upon a flat surface, the triceps is pushed upward and may be mistaken for the biceps, and the dissection may bring into view the inferior profunda artery and the ulnar nerve instead of the brachial and the median (Heath |. It is well to see and identify the innermost fibres of the biceps. After they are displaci-d outward, the median nerve (beginning to bear to the inner side) should be separated from the vessel, the sheath opened, the venae comites (the inner of which is usually the larger) drawn aside, and the needle passed from the nerve. jucobson calls attention to the fact that this usually easy ligation may be difficult when the artery is concealed by the median nerve at the point at which it is sought, and when its calibre is small and its beat feeble as the result of hemorrhage. The median nerve (from transmitted pulsation), the inferior profunda artery, ami even the basilic vein have been mistaken for the brachial. THE BRACHIAL ARTERY: BRANCHES. 777 In ligation at the lower third above the bend of the elbow the inner edge of the biceps tendon should be distinctly recognized, and the position of the superficial veins, especially the median basilic, should be made apparent by com- pression above. The incision should lie just within the edge of the tendon and should be parallel with it, running therefore obliquely from within outward. It will usually be just outside of the median basilic vein. Its centre is about on a level with the transverse fold of the bend of the elbow. The fibres of the bicipital fascia are divided in the line of the skin incision, i.e., diagonally, as they run downward and inward. The needle may be passed from within outward so as to avoid the median nerve, which, however, is here some distance to the inner side. In all ligations of the brachial, its frequent variations (vide supra} should be remembered, and the possibility of the presence of a " vas aberrans' ' or an " accessory ulnar' ' should be borne in mind, as should the occasional occurrence of a muscular slip crossing the vessel and derived from the pectoralis major or from one of the humeral muscles. The collateral circulation is carried on after ligation above the superior profunda between the ascending or recurrent branches of that vessel and the circumflex (espe- cially the posterior) and subscapular arteries. After ligation below the origin of the inferior profunda, the circulation is carried on through the anastomosis between the branches of the profunda from above and those of the anastomotic and the recurrents from the radial, ulnar, and posterior interosseous from below. After ligation below the anastomotic, the branches of that vessel, as well as those of the profundae, carry the blood to the recurrents. 1. The Superior Profunda Artery. The superior profunda (a. profunda brachii) (Fig. 709) arises from the upper part of the brachial, on its posterior surface, and is directed downward and outward, between the inner and long heads of the triceps, to reach the posterior surface of the humerus. Accompanied by the musculo- spiral nerve, it curves around to the outer surface of the bone, lying in the musculo- spiral groove, and having arrived at the external supracondylar ridge, it pierces the external intermuscular septum and continues downward between the brachialis anticus and the supinator longus, to terminate by anastomosing in front of the external condyle with the radial recurrent artery. Branches. In its course the superior profunda gives off a number of branches, among which may be mentioned : (a) A deltoid branch (ratnus deltoideus), which passes transversely outward to the inser- tion of the deltoid, and then bends upward in the substance of that muscle. (b) Muscular branches to the triceps. (c) A median collateral branch (a, collateralis media), which passes downward in the sub- stance of the inner head of the triceps to the olecranon process, where it anastomoses with the posterior ulnar recurrent, the posterior interosseous recurrent, and the anastomotica magna. (d) An articular branch, which is given off from the lower portion of the artery, just before it pierces the external intermuscular septum, and is distributed to the elbow-joint. (ami and hand. THE RADIAL ARTERY. 789 the tendons of the extensor carpi radialis longior and the extensor carpi radialis brevior, and anastomoses, either directly or by means of a number of small branches, with the posterior ulnar carpal, forming a posterior carpal a) ch or net-work. Branches. From the posterior carpal arch or net-work a longitudinal stem passes distally in each of the three inner intermetacarpal spaces. These are the dorsal interosseous arteries (aa. metacarpeae dorsales). At the upper extremity of its intermetacarpal space each interosseous artery receives the corresponding perforating branch from the palmar interosseous artery, and when it reaches the interval between the bases of the proximal phalanges, it divides into two branches, which run forward upon the inner and outer surfaces respectively of the proximal phalanges of the adjacent digits and terminate in small branches upon these phalanges. A slender branch, which arises either directly from the dorsal carpal arch or from the in- terosseous artery of the fourth intermetacarpal space, passes along the inner border of the metacar- pal and proximal phalanx of the little finger. It terminates upon the proximal phalanx of its digit. Variations. Considerable variation occurs in the size of the dorsal interosseous arteries. That which traverses the fourth intermetacarpal space is sometimes wanting, while that of the second space is sometimes of considerable size and may arise directly from the radial artery. Occasionally each artery undergoes a sudden increase of calibre at the point where it is joined by the perforating branch from the deep palmar arch, and may appear to be the continuation of the perforating branch. Where it divides into its two terminal branches, each interosseous gives off an inferior perforating branch, which passes forward to communicate with the corresponding palmar digital artery ; but these perforating branches are frequently wanting, with the exception of that given off from the artery of the second intermetacarpal space. 5. The Dorsalis Pollicis Artery. The dorsalis pollicis (Fig. 715) is a slender artery which arises from the radial just before it passes beneath the tendon of the extensor longus pollicis. It passes distally along the dorsal surface of the first metacarpal and terminates upon the dorsum of the first phalanx of the thumb. 6. The Dorsalis Indicis Artery. The dorsalis indicis (Fig. 715) arises from the radial just as it passes between the two heads of the first dorsal interosseous muscle to enter the palm of the hand. It passes distally along the radial border of the second metacarpal, resting upon the first dorsal interosseous muscle, and terminates FIG. 716. Extensor carpi radialis longior Extensor longus pol]icis Lower extremity of radius \ \ Dorsalis indicis Radial artery v Extensor ossis metacarpi pollicis Extensor brevis pollicis Dissection showing relation of radial artery to extensor tendons in "snuff box." upon the first phalanx of the index-finger. It frequently gives off a small branch which passes along the inner border of the metacarpal and first phalanx of the thumb. Variations. The dorsalis indicis, together with the carpal portion of the radial distal to the point at which the posterior radial carpal is given off, represents the dorsal interosseous artery of the first intermetacarpal space The branch to the inner border of the thumb repre- sents one of the terminal branches of that artery, and frequently arises directly from the radial opposite the main stem of the dorsalis indicis. 7. The Princeps Pollicis Artery. The a. princeps pollicis (Fig. 717) arises from the radial just as it emerges from between the two heads of the first dorsal inter- osseous muscle and is bending horizontally inward to form the deep palmar arch. The artery passes directly distally, resting upon the palmar surface of the first dorsal inter- osseous muscle and being covered by the adductor pollicis. While still beneath the 790 HUMAN ANATOMY. caput obliquum of the adductor, the vessel frequently divides into two branches, one of which is continued distally along the radial border of the index-finger, forming what has been termed the a. radialis indicis (a. volaris indicis radialis), while the other extends along the first metacarpal and, passing between the two heads of the adductor, divides beneath the tendon of the flexor longus pollicis into two branches, which pass distally along the palmar surface of the thumb, one along the inner and the other along the outer border, anastomosing with the branches of the dorsalis pollicis. Variations. The a. princeps pollicis is in reality the palmar interosseous artery of the first intermetacarpal space, and, when developed as described, corresponds in the arrangement of its branches with the dorsalis indicis, together with the dorsalis pollicis. Frequently, however, the branch to the radial border of the index-finger is lacking, or, on the other hand, it may be well developed and arise directly from the deep palmar arch, or sometimes both it and the princeps pollicis are derived from the superficial palmar arch (page 784). 8. The Palmar Interosseous Arteries. The palmar interosseous arteries (aa. metacarpeae volares) are three in number, and arise from the deep palmar arch as FIG. 717. Radial artery Anterior carpal branch Superficial volar Posterior carpal branch Metacarpal Dorsales pollicis Radial artery. Princeps pollicis Radialis indicis Dorsalis indicis Branch from radialis in dicis for superficial arcl Ulnar artery Anterior carpal branch 'osterior carpal branch .Posterior carpal branch Posterior carpal arch Deep branch of ulnar A perforating branch of deep palmar arch Superficial palmar arch Dorsal interosseous arteries Palmar interosseous arteries Digital arteries Semidiagrammatic reconstruction of right hand, viewed from palm, showing relations of arteries to surface and to bones; vessels on dorsal surface are represented in outline. it crosses the second, third, and fourth intermetaearpal spaces. Each artery pasdea distally in its intrnm-tararpal spare, resting upon the interosseous muscles, and THE THORACIC AORTA. 791 nates by anastomosing with the corresponding digital artery from the superficial palmar arch just before the digital divides into its two terminal branches. Immediately at its origin each palmar interosseous gives off a perforating branch (ramus perforans) which passes dorsally between the adjacent metacarpals to communicate directly with the corresponding dorsal interosseous artery. Variations. The palmar interosseous arteries vary considerably in size, according as the digital branches from the superficial palmar arch are well or poorly developed (page 784). When the ulnar palmar digital is small, an extra branch may arise from the deep palmar arch, passing along the ulnar border of the little finger. 9. The Radial Recurrent Arteries. The radial recurrent arteries (Fig. 717) are two or three small branches which arise from the concave surface of the deep palmar arch and pass proximally over the carpus to anastomose with the terminal branches of the anterior interosseous and of the anterior radial and ulnar carpal arteries. By the anastomosis of these various arteries there is formed upon the anterior surface of the carpus a net-work, the rete carpale volare, from which branches are distributed to the wrist and to the carpal articulations. The Collateral Circulation in the Forearm. The brachial artery, after being ligated, will convey blood to the forearm arteries by means of its superior and inferior profunda branches and by the anastomotica magna, which form a rich anas- tomosis at the elbow-joint with the radial recurrent, the anterior and posterior ulnar recurrent, and the posterior interosseous recurrent. The collateral circulation in the parts supplied by the ulnar and radial arteries, after ligation of one or other of these vessels, will be carried on by means of the direct anastomoses between the two arteries in the superficial and deep palmar arches and also by way of the anterior and posterior carpal net-works. To the former of these net-works the radial artery sends contributions from its posterior carpal branch and the ulnar from its posterior carpal and anterior and posterior interosseous branches, while to the latter the radial sends its anterior carpal branch and the ulnar its anterior carpal and anterior interosseous branches. THE THORACIC AORTA. The thoracic aorta (aorta thoracalis) (Fig. 718) is the continuation of the descending limb of the aortic arch, and begins upon the left side of the body of the fourth thoracic vertebra. It passes downward through the thorax in the posterior mediastinum and terminates below at the diaphragm, behind which it passes to become continuous with the abdominal aorta. In the upper part of its course it lies a little to the left of the median line, but it tends slightly to the right as it descends, and eventually occupies the median line just before it reaches the diaphragm. Relations. Anteriorly it is in relation with the left bronchus and the root of the left lung in its upper part, and it is crossed very obliquely by the cesophagus, which separates it from the pericardium and the posterior surface of the left auricle of the heart. Posteriorly it rests upon the bodies of the eight lower thoracic ver- tebrae, or rather throughout the greater part of its extent upon the anterior common ligament of the thoracic vertebrae, and at about the level of the fifth vertebra has passing obliquely upward behind it the thoracic duct and, at the level of the eighth vertebra, the vena hemi-azygos. Upon the right side are, above, the cesophagus and lower down the right pleura. The thoracic duct passes upward upon its right side and slightly behind it as far as the fifth thoracic vertebra, and the vena azygos also lies upon its right side, but on a plane slightly posterior to it. On the left side are the left lung and pleura above, and below, the cesophagus, while the vena hemi-azygos also lies upon its left side, but on a somewhat posterior plane. Branches. The branches which arise from the thoracic aorta may be divided into two groups, according as they are distributed to the thoracic viscera or to the parietes. The visceral branches are (i) the bronchial, (2) the cesophageal, and (3) the mediastinal. The parietal branches are (4) the aortic intercostal arteries, and (5) the diaphragmatic branches. 792 HUMAN ANATOMY. Variations. The passage of the thoracic aorta down the right side of the vertebral column in the upper part of its course and the origin from it of the right subclavian artery have already been discussed in connection with the variations of the aortic arch (page 724].' It was there pointed out that both these abnormalities depend upon the more or less perfect persistence of the lower portion of the right primitive aortic arch. Not infrequently a modification of this condi- tion is to be seen in the existence of a small branch arising from the upper part of the thoracic aorta and passing obliquely upward and to the right behind the (esophagus. This is the arteria aberrans, and it is to be regarded as a persistence in a rudimentary condition of the distal por- tion of the right primitive aortic arch. It is regarded by some authors as a normal branch of the thoracic aorta, but it is somewhat inconstant in its occurrence. Occasionally it anastomoses with the first or second intercostal branches of the superior intercostal artery ( page 765). 1. The Bronchial Arteries. The bronchial arteries (aa. hronchialcs) (Fig. 718) are somewhat variable in number; while three are usually described, they may be reduced to two or increased to four. They arise from the upper portion of the thoracic aorta and pass to the right and left bronchi, and are continued along these to supply the tissue of the lungs. The right bronchial artery, which very frequently arises from the first right aortic intercostal, passes to the right in front of the oesophagus and applies itself to the posterior surface of the right bronchus, along which it passes to the lung. In its course it gives off minute branches to the oesophagus, bronchus, and pericardium, and to the lymphatic nodes in its neigh- borhood. The left bronchial arteries, which are usually two in number, apply them- selves at once to the posterior surface of the left bronchus as it passes in front of the aorta and are continued along this to the lung. They give off small branches to the oesophagus and to neighboring lymphatic nodes. The upper of the two vessels fre- quently arises by a common stem with the right bronchial, and may be the only one that is present. 2. The CEsophageal Arteries. The oesophageal branches (aa. asophageae) (Fig. 718) of the thoracic aorta are also variable in number, forming a series of four or sometimes five or six small vessels which arise in succession from above downward from the anterior surface of the aorta. After a short but somewhat tortuous course, they reach the oesophagus, in the wall of which they branch to form a net-work which receives branches from the bronchial arteries, from the inferior thyroid above and the gastric artery below. 3. The Mediastinal Arteries. The mediastinal arteries (rami pericardiaci) are a number of small vessels which arise from the anterior surface of the thoracic aorta and are distributed to the mediastinal lymph-nodes and the posterior surface of the pericardium. 4. The Aortic Intercostal Arteries. The aortic intercostals (aa. inter- costales) (Fig. 718) supplying the tissues of the lower intercostal spaces, are usually nine in number on each side, while a tenth, sometimes termed the subcostal artery, runs along the lower border of the last rib, supplying the upper part of the abdom- inal wall. The arteries arise in pairs from the posterior surface of the thoracic aorta and pass outward over the bodies of the vertebrae to the intercostal spaces, those of the right side being, for the most part, somewhat longer than those of the left, owing to the position of the thoracic aorta to the left of the vertebral column through- out the greater portion of its length. Arrived at the intercostal space, each artery passes obliquely outward and upward across the space towards the angle of the rib next above, resting upon the internal intercostal fascia, and covered by pleura. It then pierces the intercostal fascia and, as far as the angle of the rib, runs between the fascia and the external intercostal muscle. On reaching the angle of the rib the artery passes beneath the internal intercostal muscle and is continued around the thoracic wall in the subcostal groove of the rib, and between the two intercostal muscles, to terminate usually by inosculating in front with the upper of the two Anterior inter* costal arteries given off by the internal mammary or the musculo-phrenic to each intercostal space. The arteries which pass to the tenth and eleventh intercostal spaces continue onward beyond the extremities of their corresponding ribs, and, passing between the oblique muscles of the abdomen, anastomose with the deep epigastric artery. The same arrangement occurs in the case of each of the tenth aortic intercostal (subcostal) arteries. These, however, throughout that portion of THE THORACIC AORTA. 793 their course in which they are in relation to the twelfth ribs, rest upon the quadratus lumborum muscles, beneath the transversalis fascia, and at the outer border of that muscle pass beneath the fibres of the transversalis abdominis, and, more laterally, perforating the internal oblique, come to lie between that muscle and the external oblique. Relations. In the first portion of their course, while passing over the bodies of the vertebrae, the right aortic intercostals are crossed by the thoracic duct and by the vena azygos, and the upper ones are also crossed by the oesophagus. Those of the left side are crossed by the vena hemiazygos, and both sets are covered by the pleura. Opposite the heads of the ribs they are crossed by the ganglionated cord of the sympathetic nervous system, the lower ones also by the splanchnic nerves, and in their course through the intercostal spaces they are in relation to the inter- costal veins and nerves, each artery lying below its corresponding vein and above the nerve, but on a plane slightly posterior to both. The arteries of the upper spaces lie at first below the corresponding nerves, but as they approach the lower borders of their ribs they cross the nerves obliquely, and throughout the greater part of their course possess the relation described. Branches. Each artery gives off small branches to the bodies of the vertebras and to the pleura, and throughout its course through the intercostal space numerous. (a) Muscular branches, which supply the intercostal muscles, the serratus magnus, and the pectorales major and minor, anastomosing with the thoracic branches from the axillary artery. The vessels of the lower spaces and the subcostal also supply the upper portions of the abdominal muscles, the subcostal anastomosing with branches of the uppermost lumbar artery and with the ascending branch of the superficial circumflex iliac ; the lower vessels also give off numerous branches to the diaphragm which anastomose with the phrenic arteries from the abdominal aorta. Some of the muscular branches which arise from the vessels of the third, fourth, and fifth spaces send branches to the mammary gland, assisting the perforating branches of the internal mammary and the long thoracic branch of the axillary in the supply of that structure. These intercostal mammary branches (rami mammarii laterales) may become greatly enlarged during lactation, and may give rise to considerable hemorrhage in the operation for removal of the gland. In addition, each aortic intercostal gives off a dorsal, a lateral cutaneous, and a collateral branch. (b) The dorsal branch (ramus posterior) arises from each artery, just as it enters its inter- costal space, and passes directly backward, in company with the posterior division of the corresponding spinal nerve, between the necks of the adjacent ribs and internal to the superior costo-transverse ligament. Having reached the vertebral groove, it divides into a spinal and a muscular branch. The former (ramus spinalis) passes through the intervertebral foramen in company with the root of the spinal nerve, and, within the spinal canal, gives 'off branches to the body of the vertebra and its neural arches and to the dura mater, and also branches which pass to the spinal cord and anastomose with the anterior and posterior spinal arteries. The muscular branch (ramus muscularis) continues posteriorly in the direction of the main stem of the vessel and divides into an external and an internal branch which pass between the principal masses of the dorsal musculature, supplying these and terminating in branches to the integu- ment of the back. (c) The lateral cutaneous branch ( ramus cutaneus lateralis) arises at about the axillary line and perforates the external intercostal muscle in company with the lateral cutaneous branch of the corresponding intercostal nerve. It is distributed with the nerve to the integument of the lateral portions of the thorax, also supplying the serratus magnus and the pectoral muscles and anastomosing with the perforating branches of the internal mammary and with the thoracic branches of the axillary artery. (d) The collateral branch arises as the intercostal approaches the angle of its rib. It s obliquely outward and downward to the upper border of the rib next below, along which ms to terminate by anastomosing with the lower of the two anterior intercostal branches given off by the internal mammary or the musculo-phrenic to each intercostal space. The collateral branches of the three lower intercostals are small and inconstant and, when present, terminate in the abdominal wall. Variations. The intercostal arteries of the first and second spaces usuallv arise from the .upenor intercostal branch of the subclavian, but occasionally the artery of the second space, ana more rarely that of the first, may arise from the thoracic aorta. Or, conversely, the arteries he third and fourth intercostal spaces, as well as those of the first and second, may arise superior intercostal, the aortic intercostals being correspondingly reduced in number. 794 HUMAN ANATOMY. Occasionally the second intercostal is formed by a branch from the first aortic intercostal which runs upward to the second space over the neck of the third rib, and a similar condition may be met with in the lower arteries, two or more intercostal spaces being supplied from a common stem. Finally, the right and left arteries of one or all of the pairs may arise from a common stem, springing from the posterior median line of the aorta. Practical considerations of the thoracic aorta are discussed with those of the aortic arch on page 726. THE ABDOMINAL AORTA. The abdominal aorta is the continuation below the diaphragm of the thoracic aorta. It may be said to begin, therefore, at the lower border of the twelfth thoracic vertebra, and passes downward upon the bodies of the four upper lumbar vertebra lying almost in the median line. It is usually described as terminating opposite the fourth lumbar vertebra by dividing into the right and left common iliac arteries, although it is really continued onward beyond that point as a relatively feeble \ which is termed the middle sacral artery. It seems advisable, however, to adhere to the classic definitions of the artery, and to regard the middle sacral, for purposes of description, as one of its branches. Relations. Posteriorly, the abdominal aorta rests upon the anterior com- mon ligament of the four upper lumbar vertebrae and crosses the left lumbar veins. Anteriorly, in its uppermost part, it is invested by the sympathetic solar plexus, from which branches pass downward along the vessel, forming the aortic plexus. A little lower it is crossed by the splenic vein, the pancreas, the left renal vein, and the third portion of the duodenum, and still lower it is in relation with the coils of the small intestine, from which, however, it is separated by the peritoneum. Upon a more anterior plane there are, above, the left lobe of the liver, and the stomach and transverse colon. To the right, it is in contact, in its upper part, with the thoracic duct and the receptaculum chyli, which lie partly covered by it, and with the right crus of the diaphragm, which separates it from the inferior vena cava ; lower down it is in direct contact with the vena cava. To the left, is the left crus of the diaphragm and the fourth portion of the duodenum above, while below it is separated by the peritoneum from coils of the small intestine, and has running alongside the left spermatic (ovarian) artery and vein, and still more laterally the left ureter. Branches. The branches of the abdominal aorta, like those of the thoracic, may be divided into two sets, visceral and parietal. The Visceral branches are (i) the cceliac axis, (2) the superior mesenteric, and (3) the inferior 'mesenteric artery. These are median unpaired branches which arise from the anterior surface of the aorta; in addition, there are a number of paired visceral branches: (4) the inferior phrenic, (5) the suprarenal, (6) the renal, and (7 i the spermatic or ovarian arteries. The parietal branches are (8) the lumbar arteries, of which there are four pairs, (9) the middle sacral, and (i) the common iliac arteries. With the excep tion of the middle sacral, the parietal branches are all paired. Considered in the order of their origin from the aorta, the branches are ar- ranged thus: (i) The inferior phrenics, (2) the cceliac axis, (3) the suprarenal s. (4) the superior mesenteric, (5) the first pair of lumbar arteries, (6) the renal s, (7) the spermatics or ovarians, (8) the second pair of lumbars, (9) the inferior mesenteric, ( 10 and 1 1 ) the third and. fourth pairs of lumbars, (12) the middle sacral, and (13) the common iliacs. Variations of the abdominal aorta are not common. In cases in which tin- aortic arch bends to the right, the abdominal aorta may lie somewhat to tin- right of the median line, and i: has been observed to pass downward upon the right of the inferior vena cava. Variations also occur in the level at which the aorta bifurcates Into the common iliacs. In the majority of cases the bifurcation is opposite the middle of the fourth lumbar vertebra, but it is not infrequently lower, taking place opposite the lower half of that vertebra, opposite the succeeding interver- tebral disc, or, in rare cases, opposite the upper portion of the fifth vertebra. Bifurcation at a higher level than usual is less t"iv<|m-nt, but it lias been observed as high as opposite the inter- vertebral disc between the third and fourth vertebra', and, in very rare cases, the artery has been found to divide as high as the second lumbar vertebra. THE ABDOMINAL AORTA 795 FIG. 718. Vertebral artery Common carotid artery Superior intercostal artery Subclavian artery Innominate artery 1 aortic intercostal artery Right bronchus II. and III aortic intercostal arteries Right and left coronary arteries Leaflets of aortic semilunar valve IV. -VII aortic intercostal arteries Vena azygos Thoracic duct Subcostal artery Part of right crus of diaphragm I. lumbar artery Quadratus lumborum Superior mesenteric artery Suprarenal artery Renal artery Inferior mesenteric artery Psoas magnus / i muscle Iliac branch of ilio-lumbar arterv Trachea Left common carotid artery Scalenus anticus muscle Vertebral artery Sectional surface of I. rib Superior intercostal artery I. and II. aortic intercostal Left bronchus arteries Aorta Upper left bronchial artery (Esophagus Lower left bronchial artery III., IV. and V. aortic intercostals A pericardia! branch CEsophageal branches VI. -X. aortic intercostal arteries An cesophageal branch Inferior phrenic arteries Subcostal artery Coeliac axis I. lumbar artery Lumbar fascia middle layer Suprarenal artery Renal artery II. lumbar artery Spermatic arteries III. lumbar artery Origin of quadratus lumborum IV. lumbar arterv Ji Middle sacral artery Left common iliac artery Internal iliac artery -Ilio-lumbar artery Posterior trunk ot int. iliac -Anterior trunk of int. iliac - External iliac artery- Aorta and its branches : ten intercostal arteries are present, first supplying second space ; on right side internal intercostal muscles are in position, on left they have been removed. 796 HUMAN ANATOMY. Although the abdominal aortic stem is very constant in its relations, considerable variation occurs in the origin of its branches. Most of these will be considered in connection with the description of the branches concerned, but it may be noted here that very frequently a number of small branches, terminating in the neighboring organs or connective tissue and lymph-nodes, arise from the abdominal aorta, in addition to the branches which have already been named. These small branches are rather inconstant, and may arise from either the anterior surface of the aorta, in which case they are unpaired vessels, or in pairs from its sides. Their existence seems to indicate the occurrence of a primitively strictly segmental arrange- ment of the branches of the abdominal aorta, and a type-condition has been supposed to occur in which the aorta gives off, opposite each segmental interval that it passes, three pairs of ves- sels, which arrange themselves in three distinct sets FIG 710 (I'lR 7'9)' One set arises from the anterior surface of the aorta, and is usually reduced, either by fusion or by the degeneration of one or other of each pair, to a single unpaired vessel for each segment ; a second set arises from the sides of the aorta and, like the first set, is distributed to the abdominal viscera; and a third set arises from the posterior surface of the aorta and is dis- tributed to the abdominal parietes. Of the unpaired set of vessels, only three persist until adult life, becoming the cceliac axis and the sup- erior and inferior mesenteric arteries, the position oc- cupied by these vessels in the adult being due to a downward migration which they undergo, the cu-liac axis representing the ventral visceral branch of the fourth thoracic or possibly a higher segment, the sup- erior mesenteric that of the seventh thoracic, and the inferior mesenteric that of the twelfth thoracic. The paired visceral branches are developed mainly in con- nection with the embryonic kidney, and on the replace- ment of this by the adult organ the majority of them body-trunk (aorta) ; s, somatic branch to body- disappear, the suprarenal, renal, and spermatic arteries walls, C paired visceral branches; Z>, unpaired an d certain inconstant branches which are lost in the neighboring connective tissue representing them in the adult. Of the parietal paired set, the four pairs of lumbar arteries correspond to the four upper lumbar segments, while the common iliacs are the branches of the fifth lumbar segment. The lumbar arteries are evidently serially homolo- gous with the thoracic intercostals and present many similarities to the lower members of that series, but the common iliacs are peculiar in that they give rise to branches which pass to the pelvic viscera, a condition which may be explained by the fact that the paired visceral branches of the third lumbar segment unite with them and are represented by the hypogastric artery and its branches. Practical Considerations. The abdominal aorta is the subject of aneurism much more rarely than is the thoracic aorta, because of the relatively less powerful cardiac impulse which reaches it. The sac is most often situated in the neighbor- hood of the cceliac axis because (#) in this region the artery has lost the support afforded by the tendinous arch of the diaphragm, which produces a constriction in its walls at each ventricular systole ; () it rather suddenly contracts about one and a half inches below this level (after having given off a number of large branches), so that the intervening portion is somewhat fusiform or pouched (Agnew) ; (Y) the pressure on this aortic segment is increased by the sudden alteration in the direction of the blood-current caused by the presence of these branches (the inferior phn-nics, the cceliac axis, the suprarenals, superior mesenteric, etc.); and (, downward and the impulse lessens or disappears) (Osier). 2. Dyspnoea from interference with the descent of the diaphragm. 3. Dysphagia from pressure on the cesophageal opening. 4. Dys- THE VISCERAL BRANCHES. 797 pepsia and vomiting directly from pressure upon the stomach, and indirectly from involvement of the solar plexus. 5. Jaundice from compression of the common duct and duodenum. 6. Polyuria followed by albuminuria and hcematuria or anuria from pressure on the renal nerves. 7. Oedema of the legs and feet from pressure on the ascending cava. If the tumor enlarges posteriorly there is apt to be also : 8. Pain in the buttocks, thighs, and loins from pressure on the lumbar nerves, and in the back from pressure on the solar plexus and splanchnics, or from erosion of the vertebra ; and rarely there may be : 9. Weakness or paralysis of the lower extremities from involvement of the cord. As a rule, the pain, distress, and disability are not so great in abdominal as in thoracic aneurism, because of the greater mobility of the abdominal contents, which can be much more easily displaced than those of the middle or posterior mediastinum and with consequences not so directly threatening life. Abdominal aneurisms rupture into the retroperitoneal space, the peritoneal cavity, the intestines (most often the duodenum), or after ulcerating through the diaphragm into the pleura. Compression of the abdominal aorta may be effected by special tourniquets, the intestines being first well emptied and then got out of the way, as far as possible, by rolling the patient on the right side before applying the pad, between which and the skin a soft sponge should be interposed. The pad is placed a little to the left of the umbilicus, or, better as the aorta may be median in position directly over the pulsation of the vessel. Macewen has effectively controlled the abdominal aorta by throwing the weight of the body on the aorta through the closed right hand placed a little to the left of the middle line, the knuckle of the index-finger just touching the upper border of the umbilicus. With the left hand the arrest of the blood-cur- rent is ascertained by feeling the femoral at the brim of the pelvis. Only enough weight to arrest the femoral pulse is required. If the patient vomits or coughs, the pressure must be increased, lest the hand be lifted from the aorta by the abdominal muscles. Of course these methods would be applicable only to aneurisms situated near the bifurcation. Compression has cured at least one such case. They have, how- ever, been applied in iliac and common femoral aneurism and to control hemorrhage during inter-ilio-abdominal or hip-joint amputation. Ligation of the abdominal aorta has been done in about a dozen cases with uniformly fatal results. The ligature has been applied between the bifurcation and the origin of the inferior mesenteric artery one and a half to two inches higher. A median incision with its centre at the umbilicus is made, the peritoneal cavity opened, and the intestines displaced. The layer of peritoneum over the artery is carefully divided or scratched through and the vessel isolated, avoiding the sympathetic fibres connecting the aortic plexus (lying above the origin of the inferior mesenteric) with the hypogastric plexus (lying between the common iliacs) (Astley Cooper, Jacobson). The dense areolar tissue surrounding the vessel is penetrated and the aneurism needle is passed through it from right to left to avoid injury to the vena cava. The extraperitoneal operation closely resembles that for ligation of the common iliac (page 808). THE VISCERAL BRANCHES. i. The Coeliac Axis. The cceliac axis (a. coeliaca) (Figs. 720, 721) arises from the anterior surface of the abdominal aorta, a short distance below the aortic opening of the diaphragm, and is a short, stout trunk from 1-1.5 cm. in length, which projects forward above the upper border of the pancreas. It terminates by dividing simultaneously into (i) the gastric, (2) hepatic, and (3) splenic arteries. . Variations. The cceliac axis may be wanting, the three branches to which normally it gives origin arising independently from the aorta. Occasionally it gives rise to but two terminal branches, usually the hepatic and splenic, although more rarely they may be the gastric and splenic ; or, while dividing into three terminal branches, these may be the gastric, hepatic, and a common stem from the two inferior phrenics ; the gastric, splenic, and the right suprarenal ; or the gastric, splenic, and the right gastro-epiploic. It may also give rise to additional branches, such as one or both of the inferior phrenics, a gastro-duodenal, the superior mesenteric, the colica media, or the pancreatica magna, this last being normally a branch of the splenic artery. 798 HUMAN ANATOMY. (a) The Gastric Artery. The gastric artery (a gastrica sinistra) (Fig. 720) is the smallest of the three branches given off from the coeliac axis. In the first portion of its course it passes to the left and slightly upward, across the left crus of the diaphragm, lying behind the posterior layer of the lesser sac of peritoneum. It reaches the lesser curvature of the stomach near the opening of the oesophagus into that viscus, where the upper part of the posterior wall of the lesser sac of peritoneum passes over upon the stomach to become continuous with the posterior layer of the lesser Right lobe of liver Gall bladder Common bile duct Inferior vena cava Castro-duodenal artery Right kidney Pyloric branch of hepatic artery Duodenum Pancreas Ascending colon Crest of ilium Right gastro-epiploic artery Abdominal aorta Spleen Cceliac axis Gastric artery Cut edge of diaphragm Splenic Iiranches of splenic artery Splenic artery Superior mesenteric artery Left gastro- epiploic artery pStomach -if Transverse colon Branches of mi. idle colic artery Coeliac axis and its branches. (gastro-hepatic) omentum. It then curves forward, downward, and to the right along the lesser curvature of the stomach, lying between the two lavrrs of the lesser omentum, frequently dividing into two parallel stems in this portion of its course, and terminates near the pyloric end of the stomach by anastomosing with the pyloric branch of the hepatic artery. Branches. Just at the point where the gastric artery reaches the stomach it gives off (aa) OEsophageal branches (rami resophagci ) which pass upward to supply tin- lower portion of the u-sophagus, anastomosing with the usophageal branches of the thoracic aorta and with branches of the inferior phrenic arteries. Throughout the entire length of its course along the lesser curvature of the stomach the gastric artery gives rise to THE VISCERAL BRANCHES. 799 (bb) Gastric branches which pass downward over both surfaces of the stomach, anasto- mosing with the short gastric branches from the splenic artery and with the gastric branches which pass upward from the gastro-epiploic arch which passes along the greater curvature of the stomach. Some of the branches which arise from the more proximal portion of the artery and ramify over the cardiac portion of the stomach are frequently described as the cardiac branches. (cc) A small hepatic branch passes upward between the two layers of the lesser omentum towards the left end of the transverse fissure of the liver, where it anastomoses with the left branch of the hepatic artery. Variations. The gastric artery occasionally arises directly from the abdominal aorta, in which case it may give rise to one or both of the inferior phrenic arteries. Its hepatic branch is not infrequently enlarged, and then constitutes the main stem of the left branch of the hepatic artery, which thus seems to arise from the gastric (<$) The Hepatic Artery. In the first portion of its course the hepatic artery (a. hepatica) (Figs. 720, 721) passes from left to right and slightly forward, over the right crus of the diaphragm, lying beneath the posterior wall of the lesser sac of perito- neum. Where this passes over into the posterior layer of the lesser (gastro-hepatic) omentum towards the right, the artery bends upward and ascends, in the free edge of the lesser omentum, towards the transverse fissure of the liver, where it divides into two terminal branches. Relations. In the first portion of its course the hepatic artery rests below upon the upper border of the head of the pancreas and is in contact above with the lower surface of the Spigelian lobe of the liver, upon which it frequently makes a distinct impression. It lies at first upon a plane posterior to the portal vein, but later it crosses the left surface of the vein and comes to lie in front of it. In its course upward in the free edge of the lesser omentum the artery lies anteriorly to the portal vein and upon the left side of the common bile-duct. Branches. As the hepatic artery passes between the two layers of the lesser omentum it gives origin to two branches, the pyloric and the gastro-duodenal. (aa) The pyloric branch (a gastrica dextra) is the smaller of the two. It descends to the pyloric end of the stomach and then, bending to the left, runs along the lesser curvature of the stomach, between the two layers of the lesser omentum, and terminates by anastomosing with the gastric artery, It gives branches to either side of the pyloric extremity of the stomach and, like the gastric artery, is frequently represented by two parallel vessels. (bb) The gastro-duodenal (a. gastroduodenalis), the larger branch, descends behind the first portion of the duodenum and terminates at its lower border by dividing into two branches, the superior pancreatico-duodenal and the right gastro-epiploic, (aaa) The superior pancreatico-duodenal branch (a pancreaticoduodenalis superior) descends to the head of the pancreas, upon the surface of which it anastomoses with branches of the inferior pancreatico-duodenal branch of the superior mesenteric artery. It sends branches into the substance of the gland and to the walls of the duodenum. (bbb) The right gastro-epiploic artery (a. gastroepiploica dextra) passes to the left along the greater curvature of the stomach, between the folds of the greater omentum, and inosculates with the left gastro-epiploic branch of the splenic artery. It sends branches upward upon both surfaces of the stomach, which anastomose with branches from the gastric artery and from the pyloric branch of the hepatic, and other branches pass downward into the greater omentum (epiploon). (cc) The terminal branches are two in number and pass the one to the right and the other to the left lobe of the liver The right branch ( ramus dexter) passes towards the right extremity of the transverse fissure of the liver, its course lying either in front of the hepatic and cystic ducts or between these two structures. At the extremity of the fissure it divides into a number of branches which enter the substance of the right lobe of the liver. As it passes across the hepatic duct it gives off a cystic branch (a cystica) which runs downward and forward along the cystic duct to the gall-bladder, whose walls it supplies, also giving some small branches to the liver. The left branch (ramus sinister) is directed towards the left end of the transverse fissure, and. after giving off one or two branches which enter the substance of the Spigelian lobe, terminates by dividing into a number of branches which enter the left lobe of the liver. Variations. Variations of the hepatic artery are exceedingly frequent. The artery itself may arise directly from the aorta instead of from the coeliac axis. or. by the enlargement of its anastomoses and the diminution of the normal main stem, it may appear to be a branch of the 8oo HUMAN ANATOMY. gastric or more frequently of the superior mesenteric artery. It has also been described as arising from the right renal artery. Further, by the enlargement of anastomoses, associated with a persistence of the normal mam stem, accessory hepatic arteries from the gastric or superior mesenteric, or both, may be present, and an accessory stem may arise from the aorta. Great variation occurs in the point at which the artery divides into its two terminal branches. This division may occur as low down as the origin of the gastro-duodenal branch so that in its course up the free edge of the lesser omentum the artery- may be represented by two parallel stems which pass respectively to the right and left lobes of the liver. Indeed, not only may there be a precocious division into the two terminal branches, but each of these may again divide, almost at their origin, into two or more stems, so that a number of parallel vessels". one of which usually represents the cystic branch, ascend to the liver. Occasionally the cystic branch or an accessory cystic branch arises from the gastro-duodenal, and this latter vessel may arise from the cxjeliac axis, while the liver and gall-bladder are supplied by a stem which arises from the superior mesenteric (Brewer). (V) The Splenic Artery. The splenic artery (a. lienalis) (Figs. 720, 721; is the largest branch of the cceliac axis. It passes in a more or less tortuous course over the left crus of the diaphragm and along the upper border of the pancreas, lying behind the posterior wall of the lesser sac of the peritoneum. It crosses the anterior FIG. 721. Under surface of left lobe of liver Gastric artery CEsophajjeal branches Abdominal aorta Coeliac axis Cystic branch of hepatic Common Me duct End of renal vein in vena cava IIe|ntic artery Portal vein Gastro-duodenal artery Duodenum *" Splenic vein " Superior mesenteric vein - Right gastro-epiploic artery Superior pancreatico- ' duodenal artery Inferior pancreatico- duodenal artery Ascending colon Middle colic Superior mesenteric artery Splenic artery Transverse colon, turned up Left kidney- t;astro-epipl.)ic artery lirnncli to jjreatomentu - Descending colon Duodenum Right col Coeliac axis and its branches : stomach has been removed and transverse colon turned up. stirface of the left suprarenal capsule and the upper part of the left kidney, and, passing between the two layers of the lieno-renal ligament, reaches the hilum of the spleen, where it breaks up into a number of branches which pass to the substance <>f that organ. Branches. (aa) Pancreatic branches (rami pancreatic!) are given off from the splenic artery throughout the entire extent of its course along the upper border of the panm-as and supply that organ. One branch, much larger than the others (a. pancrcaiica manna), arises at about the junction of the middle and left thirds of the artery and. entering the substance of the gland obliquely, passes from left to right along with the pancreatic duct. (bk] Short gastric branches (aa gastricac breves V variable in number, are ,i;i\en off either from the terminal portion of the artery or from some of its terminal branches 'They p.is^ between the layers of the gastro-splenic omentum to the left end of the greater curvature of the stomach, and. passing upon the surfaces of that organ, supplv it, and anastomose with the cardiac branches of the gastric- artery and with the branches of the left gastro-epiploic. THE VISCERAL BRANCHES, 80 1 (cc) The left gastro-epiploic artery (a. gastroepiploica sinistra ) arises close to the termination of the splenic and passes between the layers of the gastro-splenic omentum to the greater curvature of the stomach, along which it runs between the layers of the greater omentum, and terminates by inosculating with the right gastro-epiploic branch of the hepatic artery. Throughout its course it gives off numerous branches which pass, on the one hand, upward upon both surfaces of the stomach to anastomose with branches of the gastric artery, and, on the other hand, downward into the greater omentum. Variations. The splenic is remarkably constant in its course and branches. It may arise directly from the aorta, and it has been observed to give off the gastric artery, a large branch to the left lobe of the liver, and the middle colic artery. 2. The Superior Mesenteric Artery. The superior mesenteric artery (a. mesenterica superior) (Figs. 721, 722) arises from the anterior surface of the abdominal aorta, about 1.5 cm. below the cceliac axis. It lies at first behind the pancreas, but, passing downward and forward, it emerges between that organ and the upper border of the third portion of the duodenum and enters the mesentery. FIG. 722. Transverse colon Pancreas Superior mesenteric artery Middle colic artery Duodenum Right colic artery Ascending colon Ileo-colic artery Anterior superior spine of ilium Branches to small intestine Caecum Posterior surface of stomach Left colic artery Duodenum :^ Crest of ilium Branches to small intestine Anterior superior spine of ilium Part of jejunum Parts of ileum Superior mesenteric artery and its branches ; transverse colon and stomach have been drawn upward. It passes downward between the two layers of the mesentery, gradually curving towards the right, and terminates near the junction of the ileum with the caecum by anastomosing with its own ileo-colic branch. Branches. The superior mesenteric artery supplies the whole length of the small intestine, with the exception of the upper part of the duodenum, and also a considerable portion of the large intestine, including the caecum and appendix, the ascending colon, and about half the 802 HUMAN ANATOMY. transverse colon. The lower portions of the duodenum and ileum and the large intestine are supplied by branches given off from the concave surface of the artery, while the rest of the small intestine receives its supply from a somewhat variable number of branches which arise from the convex surface. (a) The inferior pancreatico-duodenal (a. pancreaticoduodenalis inferior) is a small vessel which usually arises from the superior mesenteric just as it emerges from beneath the pancreas, although it occasionally is given off by the uppermost of the intestinal branches. It passes towards the right along the upper border of the third portion of the duodenum, and supplies that portion of the intestine, as well as the neighboring portions of the pancreas, and anastomoses with the superior pancreatico-duodenal branch of the hepatic artery. (b) The intestinal branches (tami iniestinales), also called rasa intestini tennis, are from ten to sixteen in number, and arise from the convex surface of the artery, those branches which arise from the upper portion of the parent stem being, in general, larger than the lower ones. The first two or three branches, as they pass towards the intestine between the two layers of the mesentery, divide into an ascending and a descending branch, and these branches inosculate to form a series of primary arches, which run, in a general way, parallel with the intestine. Lower down, in addition to these primary arches, secondary ones are formed by the inosculation of branches given off proximally to those which form the primary arches ; still later, tertiary arches make their appearance, and finally the arrangement becomes so complicated as to resemble a net-work rather than a definite series of arches. From the convex surfaces of the primary arches a large number of parallel straight branches pass to the intestine and are distributed to its walls. They rarely branch in their course through the mesentery, and are usually distributed to one side of the intestine and then to the other alternately. The rich anastomosis which occurs between the various intestinal branches, and which varies greatly in its complexity, serves to equalize the supply of blood to the entire length of the intestine and to permit of abundant and rapidly collateral circulation to any portion of the tract from which the direct supply may- be cut off by pressure exerted during peristalsis. (r) The ileo-colic artery (a. ileocolica) arises about half-way down the concave surface of the superior mesenteric either independently or in common with the right colic branch. It passes downward and outward, beneath the' peritoneum, towards the ileo-Cecal junction, giving off branches which inosculate with the right colic above, with the terminal portion of the supe- rior mesenteric below, and, in the interval, with one another to form a series of arches from which branches are supplied to the terminal portion of the ileum, to the ccecum and the vermi- form appendix (a. appendicularis) and to the lower third of the ascending colon. (d ) The right colic artery (a. colica dextra) arises from the concave surface of the superior mesenteric either a short distance above or in common with the ileo-colic. It runs towards the right, behind the peritoneum, passing over the right psoas muscle, the ureter, and the spermatic (or ovarian) vessels, and as it approaches the ascending colon it divides into an ascending and a descending branch. These inosculate respectively with the middle colic and the ileo-colic to form arches, from which branches pass to the upper two-thirds of the ascending and to a portion of the transverse colon. (e) The middle colic artery (a. colica media) arises from the concave surface of the superior mesenteric a little below the origin of the inferior pancreatico-duodenal branch. It passes for- ward and downward between the two layers of the transverse mesocolon, and divides into a right and left branch which inosculate respectively with the right colic and with the left colic branch of the inferior mesenteric to form arches, from which branches pass to the transverse colon. Variations. Considerable variation occurs in the number and position of the branches of the superior mesenteric artery and also in the complexity of the anastomoses which occur between these. In addition to those usually present, branches may be sent to any of the neigh- boring organs, such as the liver, stomach, and spleen, and the artery may give rise to the hepatic, as already pointed out, or to the gastro- duodenal, or even the gastric or renal artery. It has been observed to supply the place of the inferior mesenteric artery when that vessel was lacking, giving off left colic, sigmoid, and superior hemorrhoidal branches. From the embryologieal stand-point the superior mesenteric represents the intestinal branch of the omphalo-niesenteric artery, which, during the early months of fatal lite, passes outward through the umbilicus to be distributed upon the surface of the yolk-sac. Usually this artery disappears, except in so far as it is concerned in the formation of the superior mesenteric artery; but it has been observed to persist, appearing as a branch of the superior mesenteric which is continued forward in a strand of connective tissue from the ileum to the umbilicus, where it anastomoses with the epigastric artery -and sends a branch upward along with the round ligament of the liver. 3. The Inferior Mesenteric Artery. The inferior mesenteric artery (a. mesenterica inferior) (Fit;. 723) arises from the anterior surface of the abdominal aorta from 3-40111. above the bifurcation of that vessel into the two common iliacs. THE VISCERAL BRANCHES. 803 It passes downward and to the left, beneath the peritoneum and resting upon the left psoas muscle, and, after having crossed the left common iliac, it terminates upon the upper portion of the rectum, this terminal portion being called the superior hem- orrhoidal artery. Branches. (a) The left colic artery (a. colica sinistra) arises shortly below the origin of the artery and passes upward and to the left. It divides into an ascending and a descending branch, the former of which passes between the two layers of the transverse mesocolon to inos- culate with the middle colic branch of the superior mesenteric, while the descending branch, filtering the sigmoid mesocolon, anastomoses with the sigmoid arteries. From the arches thus formed branches pass to the left portion of the transverse colon and to the whole of the descend- ing colon. (b) The sigmoid branches (aa. sigmoideae ), two or three in number, are given off as the inferior mesenteric crosses the left common iliac. They run downward and to the left over the FIG. 723. Transverse colon, turned upward Part of transverse mesocolon Splenic artery Parcreatica niagna Inferior pancre- atico-duodenal artery Left kidney Inferior mesenteric artery Left colic Descending colon Sigmoid artery Middle hemorrhoidal branches of internal iliac Termination of ileum, cut -Sigmoid flexure Superior hemorrhoidal artery- Ion posterior surface of rectuin) Anterior surface of rect Superior and inferior mesenteric arteries ; small intestine has been removed. left psoas muscle and, passing between the two layers of the sigmoid mesocolon, give off as- cending and descending branches which anastomose with one another and with the left colic and superior hemorrhoidal arteries, forming with them arches from which branches pass to the sigmoid colon. (c) The superior hemorrhoidal artery (a. haemorrhoidalis superior ) is the terminal portion of the superior mesenteric. It descends into the pelvis lying between the folds of the mesentery of the pelvic portion of the colon-, and at the junction of the colon and rectum divides into two branches which continue down the sides of the rectum, supplying that viscus and making anas- tomoses with the middle hemorrhoidal from the internal iliac and with the inferior hemorrhoidal from the internal pudic. 804 HUMAN ANATOMY. Variations. The inferior mesenteric artery may be wanting, its place being supplied by branches from the superior mesenteric. It occasionally gives rise to the middle colic artery or to an accessory renal vessel. 4. The Inferior Phrenic Arteries. The inferior phrenic arteries (aa. phrenicac inferiores) (Fig. 718) most frequently arise from the abdominal aorta, cithcr singly or by a common trunk, immediately beneath the aortic opening of the dia- phragm and above the cceliac axis. They are directed upward and laterally over the crura of the diaphragm, to which they supply branches, and in this portion of their course they also give off superior suprarenal branches ( ranii stiprarenalcs superiores) to the suprarenal bodies. Over the region where the crura pass into the diaphragm proper, each inferior phrenic divides into an internal and an external branch. The former is the smaller of the two, and passes inward towards the ceso- phageal opening of the diaphragm, where it anastomoses with its fellow of the oppo- site side to form an arterial ring from which branches descend upon the oesophagus, supplying the lower portion of that structure and anastomosing with the cesophageal branches of the gastric artery. The external branches are directed laterally upon the under surface of the dia- phragm, supplying it. They pass as far forward as the costal and sternal origins of the diaphragm, anastomosing with the musculo-phrenic, superior epigastric, and superior phrenic branches of the internal mammary arteries, while other branches ramify over the lateral portions of the diaphragm, anastomosing with the lower inter- costals and perforating the central tendon to anastomose with the pericardial arteries and with the diaphragmatic branches of the thoracic aorta. Variations. The inferior phrenic arteries are very variable in their origin. One fre- quently takes its origin from the cceliac axis or from one of its branches, or both may arise from the axis. They have also been observed to arise from the superior mesenteric or the renal, or from the abdominal aorta below the superior mesenteric. They also vary considerably in volume. 5. The Suprarenal Arteries. The suprarenal arteries, sometimes termed the middle suprarenal* (aa suprarenales mediae) (Fig. 718) to distinguish them from the suprarenal branches of the inferior phrenic and renal arteries, are a pair of small but constant branches which arise from the sides of the abdominal aorta, almost oppo- site the origin of the superior mesenteric artery. They pass outward and slightly upward over the crura of the diaphragm to the suprarenal bodies, where they anasto- mose with the other suprarenal branches. 6. The Renal Arteries. The renal arteries (aa. renales) (Figs. 718, 1591) are two large stems which arise from the sides of the abdominal aorta a little below the origin of the superior mesenteric. Usually the two arteries are opposite each other, but frequently that of the right side arises a little lower down than that of the left side. They are directed outward and slightly downward towards the kidneys, each artery, before reaching the hilum, dividing into from three to five branches, which enter the substance of the kidney independently at the hilum. Relations. In their course towards the kidneys the renal arteries rest upon the lower portions of the crura of the diaphragm and more late-rally upon the upper part of the psoas muscles. The right artery is somewhat longer than the left, owing to the position of the abdominal aorta a little to the left of the median line, and it passes behind the inferior vena cava. Both vessels are almost concealed beneath the corresponding renal veins, and at the hilum of the kidney the majority of the terminal branches pass in front of the upper portion of the ureter, only one or two passing behind it. Branches. Near its termination each artery gives off branches which pass to the adipose tissue sum mnding the kidney, and a ureteral branch which supplies the upper part of the ureter. anastomosing with the ureteral branch of the spermatic (or ovarian) artery. More proximally it gives origin to an inferior suprarenal branch (a suprarenalis inferior I which passes upward to the lower part of the suprarenal body and anastomoses with the other brandies which go to that structure. Variations. Not infrequently the division of the renal arteries into their terminal branches takes place <-;irl\, sometimes immediately at their origin, several stems arising directly from the aorta and passing outward to the kidney. Accessory renal branches may arise from theabdomi- THE VISCERAL BRANCHES. 805 nal aorta or from the middle sacral, the common iliac, the internal iliac, or the inferior mesen- tcric, and occasionally the renal artery proper may be lacking and its place taken by a vessel from one or other of these origins. These accessory arteries frequently enter the substance of the kidney elsewhere than at the hilum. The two renal arteries may arise by a common trunk from the anterior surface of the aorta, and they occasionally give off branches which are either accessory to or replace vessels normally arising elsewhere. Thus they have been observed to give rise to the inferior phrenics, the right branch of the hepatic, the spermatics. branches to the pancreas and colon, and one or more of the lumbar arteries. ja. The Spermatic Arteries. The spermatic arteries (aa. sperraaticae internae) (Figs. 718, 1591) are two slender vessels which arise from the anterior surface of the aorta a little below the renals. They are directed downward, and slightly outward and forward, towards the lower part of the anterior abdominal wall, and as they approach this each vessel curves inward towards the median line to reach the internal abdominal ring. Here it comes into relation with the vas deferens and becomes enclosed with it in the spermatic cord. Embedded in this structure, it traverses the inguinal canal and passes into the scrotum, terminating just above the testis by dividing into branches which pass to that organ and to the epididymis. Relations. In its course through the abdomen the left spermatic artery lies behind the peritoneum and rests upon the psoas muscle. About the middle of this portion of its course it crosses obliquely in front of the ureter, and lower down has resting upon it the sigmoid colon. The right artery at first lies in the root of the mesentery ; it descends obliquely upon the anterior surface of the inferior vena cava and then, crossing the ureter obliquely, comes to lie behind the terminal portion of the ileum and frequently behind the vermiform appendix. In the pelvic and inguinal portions of their course the relations of both arteries are the same. The vessels rest upon the psoas muscle to the outer side of the ex- ternal iliac artery, and cross the lower part of that vessel and the accompanying vein to reach the internal abdominal ring. In their course down the spermatic cord the arteries lie behind the anterior group of the spermatic veins and in front of the vas deferens. Branches. In addition to the terminal (a) testicular and (d) epididymal branches, each spermatic artery gives off (c) An ureteral branch which is distributed to the middle portion of that duct, anastomosing with the ureteral branch of the renal artery above and with branches from the inferior vesical artery below. (d) Cremasteric branches are given off in the course through the spermatic cord and sup- ply the cremaster muscle, anastomosing with the cremasteric branch of the deep epigastric artery. Variations. The spermatic arteries occasionally arise by a common trunk, or, on the other hand, they may arise at different levels. They have been observed to arise from the renals, especially the left one, from the suprarenals, or from the superior mesenteric artery. jb. The Ovarian Arteries. The ovarian arteries (aa. ovaricae) (Fig. 726) correspond in the female to the spermatic arteries of the male, and have a similar origin and similar relations in the abdominal portion of their course. Arrived at the pelvis, however, they cross the common iliac arteries and veins and, traversing the suspensory ligament of the ovary, pass inward between the folds of the broad ligament of the uterus, terminating beneath the ovary by inosculating with the uterine artery. Branches. Like the spermatic arteries, the ovarian give off (a) ureteral branches. In ad- dition, they give rise to (b) tubal branches, which pass to the distal portions of the Fallopian tubes ; (r) ligamentous branches, which accompany and supply the round ligament of the uterus ; and (d ) ovarian branches, which enter the hilum of the ovary and are distributed to its substance. 8. The Lumbar Arteries. The lumbar arteries (aa. lumbales) (Fig. 718) are arranged in four pairs, and take origin from the sides of the abdominal aorta, opposite the four upper lumbar vertebrae. They are directed outward upon the bodies of the vertebrae, the lumbar portion of the sympathetic cord descending in front of them, and 8o6 HUMAN ANATOMY. those of the right side also pass beneath the inferior vena cava, while the two upper ones of the same side pass beneath the receptaculum chyli. They then pass beneath the psoas muscle and the branches of the lumbar plexus, the two upper ones H!M> passing beneath the crura of the diaphragm ; and then, farther out, they pass beneath the quadratus lumborum, except in the case of the last pair, which lies upon the ante- rior surface of that muscle. At the outer border of the quadratus they pass between the transversalis and the internal oblique muscles of the abdomen, and are continued onward in the abdominal wall, eventually piercing the' internal oblique and reaching the rectus muscle. Branches. The lumbar arteries are to be regarded as continuations of the scries of inter- costal vessels, and, like the thoracic members of the series, each gives off a dorsal branch ( ramus dorsalis). This arises when the vessel lies behind the psoas muscle and is directed posteriorly, soon dividing into (a) a spinal branch (ramus spinalis). which enters the spinal canal through the intervertebral foramen and anastomoses with the anterior and posterior spinal arteries ; and (b) a muscular branch, which is distributed to the muscles and skin of the back. In addition, each lumbar artery gives off numerous branches to the muscles with which it comes into relation. Variations. One or more of the' lumbar arteries may be wanting and two or more of them may arise by a common stem 9. The Middle Sacral Artery. The middle sacral artery (a. sacralis media ) (Fig. 718), which is to be regarded as the continuation of the abdominal aorta, is a small vessel arising from the posterior surface of the aorta immediately above its bifurcation into the two common iliacs. It passes downward in the median line over the last two lumbar, the sacral and the coccygeal vertebrae, and terminates opposite the tip of the coccyx by sending branches to the coccygeal body or Luschka's gland (glomus coccygeum). Branches. It sometimes gives rise to a fifth pair of lumbar arteries (aa. lumbales imae), and lower down it sends off small lateral branches which send branches inward to the spinal canal through the anterior sacral foramina and anastomose with the lateral sacral branches of the internal iliac artery. These lateral branches appear to represent a continuation of the inter- costal and lumbar series of arteries, the branches which enter the anterior sacral foramina cor- responding to the dorsal branches of those vessels. Variations. The middle sacral occasionally arises from one or other of the common iliac arteries, and it may give origin to an accessory renal artery. Practical Considerations. Some of the branches of the abdominal aorta, including the splenic, hepatic, renal, superior and inferior mesenteric, and the ovarian, have been the subject of aneurism. These aneurisms do not usually attain any great bulk, seldom exceeding the size of a hen's egg. They are apt to be round or oval in shape. Occasionally espe- cially in the aneurisms of the renal artery they may almost fill the abdominal cavity. Except when connected with the hepatic, the renal, or the cceliac axis, they are movable, changing their position in the various movements of the body. They may possess also the characteristics of pulsation and bruit. When the cu-liac artery is affected the disease cannot be distinguished from aneurism of the parent trunk. In cases of implication of the hepatic artery, the pressure-effects of the tumor give rise to pain in the right side and to jaundice from obstruction of the hepatic, cystic, and common bile-ducts (Agnew). The renal artery has been found to be aneurismal in a small number of instances, the majority being of traumatic origin. The chief symptoms have been : ( a ) tumor. varying in size, situated in the region of the kidney, immovable with respiration or with change <>f posture, and almost always without impulse or bruit, on account prob- ably of the usual disproportion, in renal aneurisms, between the large aneurismal cavity and the size of the vessel involved ; (/>) h) the corresponding vessels of the other side (/. e. , the side of the ligature). 1. The Ilio-Lumbar Artery. The ilio-lumbar artery (a. ilio-lumbalis) (Fig. 724) is most frequently given off from the main stem of the internal iliac, shortly above its separation into the anterior and posterior divisions. Not infre- quently, however, it is a branch of the posterior division. It passes upward and outward towards the brim of the pelvis, crossing in front of the lumbo-sacral nerve and behind the external iliac artery, beyond which it passes beneath the psoas muscle. On reaching the crest of the ilium it divides into two Branches. (a) The lumbar branch (ramus luml.alis ') is directed upward and backward be- neath the psoas and supplies that muscle and the quadratus lumborum. It sends a spinal branch (ramus spina/is} through the intervertebral foramen between the last lumbar and (MM s;u T.I! vertebrae, and anastomoses with branches of the last lumbar artery. (t>) The iliac branch (ramus iliacus) passes outward beneath the psoas and ramifies upon t IK- surface of the iliacus muscle, supplying it and usually giving off a nutrient branch to the ilium. 2. The Lateral Sacral Arteries. The lateral sacral arteries (aa. sacrales laterales") (Fig. 724) are usuallv two in number, and arise from the posterior division of the internal iliac. The superior one passes downward and inward to the first anterior sacral foramen, and passes through it to supply the spinal membranes and anastomose THE INTERNAL ILIAC ARTERY. 811 with the other spinal arteries. The inferior artery passes at first inward and then downward upon the surface of the sacrum, parallel to the middle sacral artery, with which it anastomoses at the tip of the coccyx and also, by delicate transverse branches, opposite each sacral vertebra. Opposite each anterior sacral foramen that it passes i.e., opposite the second, third, and fourth it gives off a branch (ramus spinalis) which enters the foramen and behaves like the spinal branch of the superior artery. In its downward course the inferior lateral sacral lies to the outer side of the sacral portion of the sympathetic cord and crosses the slips of origin of the pyriformis muscle. Variations. Very frequently the two lateral sacral arteries arise by a common stem, and occasionally the branch which enters the second anterior sacral foramen arises independently. In all probability the longitudinal stem of the inferior artery is to be regarded as having been formed by the direct anastomosis of ascending and descending twigs from the lateral branches of the middle sacral, each of which is serially homologous with the lumbar and intercostal arte- ries. The process is similar to what has occurred in the formation of the vertebral artery (page 721). 3. The Gluteal Artery. The gluteal artery (a. glutaea superior) (Fig. 727) is the continuation of the posterior division of the internal iliac. It is the largest of all the branches of that vessel, and passes backward between the lumbo-sacral cord and the first sacral nerve to the upper border of the great sacro-sciatic foramen. It passes through the foramen, in company with the superior gluteal nerve, above the pyriformis muscle, and soon after making its exit from the pelvis divides into a superficial and a deep branch. Branches. (a) The superficial branch (ramus superior) soon divides into a number of branches which enter the upper portion of the gluteus maximus, some supplying that muscle, while others traverse it to supply the skin over the upper part of the gluteal region. One branch, larger than the others, passes outward along the upper border of the origin of the glutens medius almost to the anterior superior spine of the ilium, anastomosing with branches of the external circumflex iliac artery. (b) The deep branch (ramus inferior) soon divides into two branches, (aa) The superior branch passes outward along the upper border of the gluteus minimus almost to the anterior inferior spine of the ilium, where, under cover of the tensor vaginae femoris, it anastomoses with tlie descending branch of the external circumflex iliac ; it sends branches to both the glu- tens medius and minimus, (bb) The inferior branch passes outward and downward, over the surface of the gluteus medius, towards the greater trochanter of the femur, and gives branches to both the gluteus medius and minimus and to the hip-joint. 4. The Superior Vesical Artery. The superior vesical artery (a. umbilicalis) (Fig. 724) represents the original main stem of the foetal hypogastric artery, and consequently takes its origin from the hypogastric axis and is continuous anteriorly with the fibrous cord which represents the obliterated hypogastric artery (Fig. 728). It passes forward, beneath the peritoneum, towards the urinary bladder, and as it approaches that structure gives off branches to it (aa. vesicales superiores) which ramify over its surface and sides and supply its upper and middle portions. They anasto- mose below with branches of the prostatic and inferior vesical arteries. Variations. Not infrequently an accessory branch arising from the superior vesical is dis- tributed to the middle and lower portions of the bladder, forming what has been termed the middle vesical artery ( Fig. 724) . 5. The Inferior Vesical Artery. The inferior vesical artery (a. vesicalis inferior) (Fig. 724) may arise from the hypogastric axis, from the anterior division of the internal iliac below the axis, from the middle hemorrhoidal, or quite frequently from the prostatic. It descends towards the lower portion of the bladder, supplying the base and neck of that structure, and also sending branches to the prostate gland and the seminal vesicles in the male. It anastomoses with branches of the prostatic and superior vesical arteries. Variations. The inferior vesical is usually a rather slender branch, and ma)- be replaced by vesical branches from the prostatic or by branches of the superior vesical. 812 HUMAN ANATOMY. 6a. The Prostatic Artery. The prostatic artery arises either from the hypo- gastric axis, or, more usually, from a trunk common to it and the inferior vesical or the middle hemorrhoidal. It passes downward, forward, and inward to the lateral surface of the prostate gland, and sends branches into the interior of that structure and also to the base of the bladder, anastomosing with branches of the inferior vesical artery. 66. The Vaginal Artery. The vaginal artery (a. vaginalis) (Fig. 726), the homologue of the prostatic artery, arises either from the hypogastric axis, more usually from a trunk common to it and the inferior vesical or middle hemorrhoidal, or from the anterior division of the internal iliac, below the hypogastric axis. It passes down- ward and inward towards the lower part of the sides of the vagina, where it divides into numerous branches which ramify over the anterior and posterior surfaces of that organ, anastomosing with the corresponding branches of the artery of the other side. It also anastomoses above with the cervical branches of the uterine artery and below with the perineal branches of the internal pudic. By these anastomoses there is usually formed along the median line of both the anterior and posterior surfaces of the vagina a more or less regular vessel which is known as the azygos artery of the vagina. FIG. 726. Deep circumflex iliac artery Round ligament External iliac artery Ova'ian artery External -liac vein arian veins Deep epigastric artery Obliterated hypogastri Bladder Symphysis puliis ( ibturator nerve Vulva Dorsal artery of clitori Artery to corpi caver Right ureter Common iliac arter\ I-eft common iliac Bowel Obturator artery Superior \ esii al arterv .Middle vesical arter\ ; Oviduct Inferior vesical artery Jterine artery 'Stump of round liga- 'Ovary [ment arian artery Uterine artery Superior vesical artery Vaginal artery Anterior trunk of internal iliac arten Middle hemorrhoidal artery Artery to bulb Vaginal branch Left Vaginal artery of uterine artery ureter Arteries of female pelvis, seen from left side. Variations. The vaginal artery occasionally arises from a common trunk \\ ith the uterine. Frequently, as a result of its precocious division, it is represented by two or more vessels. ja. The Vesiculo-Deferential Artery. The vesiculo-deferential artery (a. deferentialis ) usually arises from the hypogastric axis, but sometimes from the proximal part of the superior vesical or from the anterior division of the internal iliac, below the hypogastric axis. It passes downward, forward, and inward, and, crossing the ureter, gives a branch to the vas deferens and then breaks up into a number of small branches which are distributed to the vesicula seminalis. The deferential branch, on reaching the vas, divides into an ascending and a descending branch. The former passes upward along the vas to the internal abdominal ring and thence through the inguinal canal to the neighborhood of the epididymis, anastomosing with branches of tin- spermatic artery. The descending branch accompanies the vas to the prostate. -,b. The Uterine Artery. The uterine artery (a. utcrina) (Fig. 726) corres- ponds to the vesiculo-deferential antl has a similar origin. It passes at first down\\ aid and inward upon the surface of the levator ani, and then inward in a tortuous course THE INTERNAL ILIAC ARTERY. 813 along the base of the broad ligament towards the neck of the uterus. Just before reaching the uterus, usually about 2 cm. ( ^ in. ) from it, the artery crosses in front of the ureter and then bends upward between the two layers of the broad ligament along the side of the uterus. Arrived at the junction of the Fallopian tube with the uterus, it bends outward along the lower border of the tube, and then, passing beneath the hilum of the ovary, terminates by inosculating with the ovarian artery. In its course between the layers of the broad ligament the artery is accompanied by the large uterine veins, which almost conceal it, and both artery and veins are enclosed in a rather dense sheath of areolar tissue. During pregnancy the artery becomes much enlarged, and its course, as well as that of its branches, becomes exceedingly sinuous and even spiral. Branches. (a) As the uterine artery crosses the renal duct, a ureteral branch is supplied to the ureter. On reaching the sides of the uterus, it gives off (b) One or several cervical branches. These pass to the cervix and divide into numerous branches which supply that portion of the uterus and the upper part of the vagina. They are relatively long and tortuous, and anastomose below with the branches of the vaginal arteries. Throughout the rest of its course along the sides of the uterus it gives off numerous (f) Uterine branches, which, although tortuous, yet differ from the cervical branches in being rather short. They pass to both the anterior and posterior surfaces of the uterus and supply its body and fundus, and it is to be remarked that both these branches and the cervical ones diminish rapidly in calibre as they branch upon the surface of the uterus, so that at the middle line of the organ only exceedingly minute twigs are to be found. From the portion of the artery that runs outward along the lower border of the Fallopian tube (d] Tubal branches (rami tubarii) are given off. One of these, much stronger than the others, arises just before the uterine inosculates with the ovarian artery, and passes outward along the tube to its fimbriated extremity, sending branches to it through its entire course. (e) Ovarian branches (rami ovarii) to the ovary are finally given off from the uterine artery in the vicinity of its anastomosis with the ovarian. 8. The Middle Hemorrhoidal Artery. The middle hemorrhoidal artery (a. haemorrhoidalis media) (Fig. 726) is somewhat variable both in its origin and in its size. It arises either from the anterior division of the internal iliac, below the hypogastric artery, or, as frequently happens, from the inferior vesical or occasionally from the internal pudic. It passes along the lateral surface of the middle portion of the rectum, giving off branches which, in addition to aiding in supplying the vagina and communicating with the vaginal arteries, anastomose above with the superior hemorrhoidal from the inferior mesenteric and below with the inferior hemorrhoidal from the internal pudic. 9. The Obturator Artery. The obturator artery (a. obturatoria) (Fig. 724) arises from the anterior division of the internal iliac, below the hypogastric axis. It passes forward along the lateral wall of the pelvis, resting upon the pelvic fascia which covers the upper portion of the internal obturator muscle, and having the obturator nerve immediately above it and the vein below. Just before reaching the anterior wall of the pelvis it is crossed by the vas deferens in the male, as it passes downward from the internal abdominal ring, and then it pierces the pelvic fascia and makes its exit from the pelvic cavity through the obturator canal, on emerging from which it divides into two terminal branches, an internal and an external. Branches. Within the pelvis the obturator artery gives off several small branches, of which the more important are ( a ) An iliac branch, which is given off near the origin of the obturator and passes up to the iliac fossa, supplying the ilio-psoas muscle, giving nutrient branches to the ilium and anasto- mosing with the iliac branch of the ilio-lumbar artery. (b) Muscular branches, which are distributed to the obturator interims and the levator ani. (c) Vesical branches, which pass to the bladder beneath the false lateral ligament and anastomose with branches from the superior vesical ; and (d) A pubic branch (ramus puhicus) which arises just before the artery enters the obtu- rator canal and ascends upon the posterior surface of the os pubis to anastomose above with the pubic branch of the deep epigastric artery. Outside the peh ~is the obturator artery divides into an external and an internal branch. 8 14 HUMAN ANATOMY. (e) The external branch passes around the external border of the obturator foramen, beneath the external obturator muscle, and terminates by anastomosing with the internal branch and with the internal circumflex from the deep femoral. Near its origin it gives off (aa) An internal branch, which passes downward on the posterior surface of the obturator membrane, under cover of the internal obturator muscle, to the tuberosity of the ischium, and it also gives rise to (bb) An acetabular branch (ramus acetabuli), which passes through the cotyloid notch and supplies the fatty tissue occupying the bottom of the acetabulum. (/) The internal branch runs around the inner border of the obturator foramen, beneath the external obturator muscle, and terminates by anastomosing with the external branch. Variations. The obturator artery varies greatly in its origin, and these variations may In- divided into two groups, according as the origin is from the internal or the external iliac system of arteries. While the origin of the vessel from the anterior division of the internal iliac is the most frequent, yet, when compared with all the variations taken together, it occurs in some- what less than 50 per cent, of cases. Of other origins from the system of the internal iliac there may be mentioned those from the main stem of the iliac before its division, from its posterior division, and from the gluteal artery. Furthermore, its origin may occur from either the sciatic or the internal pudic artery, although such cases are rare. More frequent and of greater importance from the practical stand-point is the origin from the external iliac system, which occurs in about 30 per cent, of cases. In the immense majority of such cases in almost twenty-nine out of every thirty the origin is from the deep epigastric artery, being in the remaining cases from the external iliac distal to the deep epigas- tric or from the upper part of the common femoral artery. Undoubtedly the primary relations of the obturator artery are with the internal iliac system of vessels, and the origin from the ex- ternal iliac system is to be regarded as due to the secondary enlargement of an anastomosis nor- mally present and the diminution or inhibition of the original stem of the obturator. Possibilities for such a process are furnished by the normal anastomosis between the pubic branches of the obturator and the external circumflex, and all gradations may be found between the normal ar- rangement and the complete replacement of the original intrapelvic portion of the obturator by the pubic anastomosis. The origin of the obturator from the deep epigastric artery ( Fig. 728) becomes of importance from the fact that, in order to reach its point of exit from the pelvis, the obturator canal, the vessel must come into intimate relations with the crural ring, and mav thus add an important complication to the operation for the relief of femoral hernia (page *775)- There are three possi- ble courses for the vessel in relation to the ring : ( i ) it may pass inward from its origin over the upper border of the ring and then curve downward and inward along the free border of (iim- bernat's ligament to reach the obturator canal ; (2) it may bend downward abruptly at its origin and pass m an almost direct course to the obturator canal, passing over the inner surface of the external iliac vein, and therefore down the outer border of the crural ring; or (3) it may pass directly across the ring. As regards the relative frequency of each of these courses it is interesting to note that, according to observations made by Jastschinski, the course along the outer border of the ring is much the most frequent, occurring in 60 per cent, of cases, and being more frequent in females than in males. The course across the ring occurs in about 22.5 per cent, of cases, and is again more frequent in females than in males ; while the course along the free edge of Gimbernat's ligament occurs in only 17.5 per cent, of cases, and is more common in males than in females. The differences in the two sexes are associated with the differences in the form of the pelvis and of the obturator foramen. Practical Considerations. The gluteal and sciatic arteries have not uncom- monly been affected by aneurism which has shown itself as a pulsating compressible tumor in the gluteal region, often with a bruit, and usually causing pain over the nates, extending down the posterior aspect of the thigh from pressure on tin- sciatic nerve and causing lameness. The gluteal aneurism is situated somewhat farther back in the buttock than the sciatic, which is apt to be farther forward and downward, near the gluteo-femoral crease (Agnew). Either of these vessels or the internal pudic may require ligature on account of stab-wounds. Serious hemorrhage from a wound in the upper part of the glutens maxinr.is, i.e., a little below a line from the posterior superior iliac spine to the top of the great trochanter, is likely to proceed from the gluteal artery. Lower, nearer to the fold of the buttock, it may come from the sciatic. The gluteal may be tied through an incision made along the line just mentioned, from the posterior superior spine to the trochanter. With the thigh in inward rotation, the junction of the middle with the upper third of that line indicates about the point where the gluteal artery comes out through the sciatic notch. The fibres of the glutens maximus are sepa- rated, the muscle is relaxed by full extension of the thigh, and the upper bony margin THE INTERNAL ILIAC ARTERY. 815 of the sciatic notch is felt for with the finger through the interspace between the pyri- formis and the gluteus medius. The artery may be found as it turns over the bony tip of the sacro-sciatic foramen towards the dorsum ilii. The sciatic artery may be reached through the same incision, the finger then being carried below the pyriformis muscle, when the spine of the ischium and the sharp edge of the sacro-sciatic ligament will serve as landmarks. The point of emergence of both the sciatic and internal pudic arteries is indicated with sufficient accuracy by the junction of the lower and middle thirds of a line drawn from the tuberosity of the ischium to the posterior superior spine of the ilium. The incision employed should follow the direction of the fibres of the greater gluteal muscle. 10. The Sciatic Artery. The sciatic artery (a. glutaea inferior) (Fig. 727) is one of the two terminal branches of the anterior division of the internal iliac. It lies at first internal and posterior to the internal pudic artery, and is directed downward and backward towards the lower part of the great sacro-sciatic foramen, passing usu- ally below the fourth sacral nerve. It makes its exit from the pelvis through the great sacro-sciatic foramen, below the pyriformis muscle, and bends downward beneath the gluteus maximus. It crosses the internal pudic artery at about the level of the spine of the ischium, and in the rest ot its course lies to the inner side of the great sciatic nerve. It descends upon the gemelli, the internal obturator, and the quad- ratus femoris, and, after giving off its principal branches, is continued down the leg as a slender vessel, the comes nervi ischiadici. Branches. Within the pelvis the sciatic artery gives off some small and inconstant branches to the internal obturator and pyriformis muscles and to the trunks of the sacral pelvis. Outside the pelvis it gives rise to several larger branches. (a) The coccygeal branch passes inward and pierces the great sacro-sciatic ligament and the gluteus maximus near its origin, terminating in the tissues over the lower part of the sacrum and coccyx. (f>) Muscular branches, variable in number, pass to the neighboring muscles, some of them being continued beneath the quadratus femoris to reach the capsule of the hip-joint. One branch somewhat larger than the rest can frequently be seen entering the deep surface of the gluteus maximus in company with the inferior gluteal nerve ; it supplies the muscle and forms anastomoses with the gluteal artery. (c) An anastomotic branch passes transversely outward, usually beneath the great sciatic nerve, towards the greater trochanter of the femur. It gives twigs to the gemelli muscles, and in the neighborhood of the trochanter anastomoses with the terminal branch of the internal cir- cumflex, with the transverse branch of the external circumflex, and, below, with the first per- forating artery, completing what is termed the crucial anastomosis, (d) Cutaneous branches, variable in number, wind around the lower border of the gluteus maximus in company with branches of the small sciatic nerve, and supply the integument over the lower part of the gluteal region. (e) The a. comes nervi ischiadici is the continuation of the sciatic artery. It is a long, slender branch which passes downward upon or in the substance of the great sciatic nerve, sup- plying it and anastomosing with the perforating branches of the profunda femoris. Variations. The occasional origin of the sciatic from the gluteal artery or from the hypogastric axis has already been described in connection with the variations of the internal iliac (page 808). Occasionally it has a double origin from both the gluteal and the anterior division of the internal iliac, or it may be double, owing to the existence of stems from each of these vessels which pursue independent courses. In addition to its normal branches, it may give origin to the lateral sacral, the inferior vesical, and the uterine or the middle hemorrhoidal. Especial interest attaches to the comes nervi ischiadici, which occasionally traverses the entire length of the thigh to unite below with the popliteal artery. It represents the original main stem of the sciatic artery, of which the popliteal was primarily the continuation, the connection of that artery with the femoral, and the subsequent diminution of the sciatic being secondary arrangements (page 824). 11. The Internal Pudic Artery. The internal pudic artery (a. pudenda interna) (Fig. 727) is the other terminal branch of the anterior division of the internal iliac. It is directed downward in front of the sciatic artery to the lower portion of the great sacro-sciatic foramen, where it makes its exit from the pelvis, passing between 8i6 HUMAN ANATOMY. FIG. 727. Superior gluteal artery Superficial branch of superior uluteal Gluteus maximus Sciatic arter;- Coccygeal artery - Internal purlic artery Tuber ischii ^ Biceps, stump Transverse branch of internal circumflex Perforating branches of deep femoral artery Semimembranosus Popliteal artery Muscular branches Superior internal articular artery Gluteus medius, cut Upper ramus of deep branch of superior gluteal artery Gluteus minimus Muscular branch of sup. gluteal Lower ramus of deep branch Pyriformis (of sup. gluteal Gluteus medius Greater sciatic nerve Tendon of obturator internus Articular branch from ascending branch of internal circumflex Articular branch of sciatic artery Anastomotic branch Comes nervi ischiadici Gluteus maximus From external circumflex Superior perforating artery From external circumflex Vastus externus Middle perforating artery Inferior perforating artery Biceps short head Biceps long head Muscular branch of femoral artery Popliteal vein Superior external articular artery Hxternal sural artery Inferior external articular artery Gastrocnemius Arteries of gluteal region and posterior surface of right thigh. THE INTERNAL ILIAC ARTERY. 817 the pyriformis and coccygeus muscles. It then bends forward, under cover of the gluteus maximus, and, curving beneath the spine of the ischium, passes through the lesser sacro-sciatic notch to enter the ischio-rectal fossa. Its course is then forward along the lateral wall of the fossa, lying with its accompanying vein and the pudic nerve in a fibrous canal known as AlcocK 1 s canal, formed by a splitting of the obtu- rator fascia near its lower border. At the anterior portion of the ischio-rectal fossa the artery perforates the triangular ligament of the perineum and passes forward between the two layers composing that structure, finally perforating the superficial layer and becoming the dorsal artery of the penis (or clitoris). Branches. In the pelvic and gluteal portions of its course the internal pudic, as a rule, gives off only slender muscular branches to the neighboring muscles. In its ischio-rectal por- tion its branches are more important. (a) The inferior hemorrhoidal arteries (aa. haemorrhoidales inferiores), usually two in num- ber, but frequently only one, which early divides into two or three stems, arise from the internal pudic, just after it has traversed the lesser sacro-sciatic foramen. They perforate the inner wall of Alcock's canal and pass through the fat-tissue which occupies the ischio-rectal fossa towards the lower part of the rectum. They give branches to the ischio-rectal fat-tissue, to the sphincter and levator am, to the gluteus maximus, to the skin over the ischio-rectal and anal regions, and to the lower part of the rectum, anastomosing above with the middle hemorrhoidal branches of the internal iliac. (&} The superficial perineal artery (a. perinei) arises just before the internal pudic enters the space between the layers of the triangular ligament of the perineum. It is at first directed almost vertically downward, but quickly bending around the posterior border of the superficial transverse muscle of the perineum, near its origin from the ischial tuberosity, it is directed for- ward and inward in the interval between the ischio-cavernosus and bulbo-cavernosus muscles. In this portion of its course it is covered only by the superficial perineal fascia and the integu- ment, and passes forward to be distributed to the posterior portion of the scrotum in the male and to the labia majora in the female. In its course it gives off numerous cutaneous branches as well as branches to the neighboring muscles. One of these latter, usually somewhat larger than the rest, passes inward towards the median line, beneath the superficial transverse muscle of the perineum, which it supplies, as also the bulbo-cavernosus and external sphincter ani. This is what has been termed the transverse artery of the perineum. It anastomoses at the central point of the perineum with its fellow of the opposite side, with other branches from the superficial perineal artery anteriorly and with branches of the inferior hemorrhoidals posteriorly. In its perineal portion also the internal pudic gives off important branches. (c) The artery to the bulb (a. bulbi urethrae or a. bulbi vestibuli) arises from the internal pudic a short distance after it has entered the deep perineal interspace. It is a relatively large vessel in the male, and passes almost horizontally inward towards the median line. Before reaching this, however, it perforates the superficial layer of the triangular ligament, enters the substance of the bulbus urethrae about 15 mm. in front of its posterior extremity, and is distributed to that structure and to the posterior third of the corpus spongiosum and urethra. In the female it is of a lesser calibre than in the male, and is distributed to the bulbus vestibuli. (d) The urethral artery (a. urethralis) arises usually some distance anteriorly to the artery of the bulb, and, like it, is directed medially, and penetrates the superficial layer of the tri- angular ligament to enter the substance of the corpus spongiosum. It reaches the corpus spongiosum just behind the symphysis pubis, where the two corpora cavernosa come together to form the penis, and is continued forward in the spongiosum to the glans. It is a somewhat inconstant branch, and is quite small in the female. (e) The artery of the corpus cavernosum (a. profunda penis s. clitoridis) arises from the internal pudic, just posterior to the lower border of the symphysis pubis, and is directed outward towards the bone. It penetrates the superficial layer of the triangular ligament close to its attachment to the pubic ramus, artd enters the corpus cavernosum at about the junction of its middle and posterior thirds. It passes to the centre of the corpus and there divides into a posterior branch which supplies blood to the posterior third of that structure, and an anterior one which distributes to its anterior two-thirds. It is much smaller in the female than in the male. (f) The dorsal artery of the penis or clitoris (a. dorsalis penis s. clitoridis) is the continua- tion of the main stem of the internal pudic beyond the origin of the artery to the corpus cav- ernosum. It penetrates the superficial layer of the triangular ligament near its apex, and passes upward in the suspensory ligament of the penis or clitoris to the dorsal surface of that organ, along which it passes, lying to the side of the median line and separated from its fellow of the opposite side by the single median dorsal vein. Laterally to it is situated the dorsal nerve of 52 8i8 HUMAN ANATOMY. the penis (or clitoris), and still more laterally the deep external pudic branch of the common femoral artery. On reaching the glans, it forms an anastomotic circle around the base of that structure, uniting with its fellow of the opposite side. Throughout its course- it gives branches to the corpus cavernosum and the integument of the penis or the prepuce of the clitoris Variations. The occasional origin from the internal pudic of the inferior vesical, middle hemorrhoidal, and uterine arteries has already been noted. The internal pudic. instead of passing out of the pelvis by the great sacro-sciatic foramen, may be directed forward upon the tloor of the pelvis and pass out beneath the pubic symphysis to become the dorsal artery of the penis. More frequently this course is taken by an accessory internal pudic which arises from the pudic in cases where this vessel appears to arise from the hypogastric axis, a condition which results in the early division of the common stem from which the sciatic and internal pudic arteries normally arise. The artery of the bulb may arise opposite the ischial tuberosity and pass obliquely forward and medially across the ischio-rectal fossa, and in some cases it passes at first directly across towards the anus and then bends forward to reach the bulb. The dorsal artery of the penis or clitoris occasionally unites with its fellow of the opposite side to form a single median artery, or the two arteries of opposite sides may be united by trans- verse anastomoses. Sometimes a third vessel arises either directly from the anterior division of the internal iliac or from the obturator, even when this vessel takes its origin from the deep epigastric. Anastomoses of the Internal Iliac. The internal iliac makes anastomoses with branches of the abdominal aorta, of the external iliac, and with its fellow of the opposite side, and it is through these connections that the collateral circulation may be established. Of branches communicating with the abdominal aortic system there are the hemorrhoidal branches which anastomose with the superior hemorrhoidal from the inferior mesenteric, the uterine which anastomoses with the ovarian, and the lateral sacrals which anastomose with the middle sacral. Communications with the system of the external iliac are through the sciatic with branches of the profunda femoris, through the ilio-lumbar and gluteal with the external and internal circumflex iliacs, and through the obturator with the deep epigastric through the pubic branches. The anastomoses across the middle line occur between the vesical, prostatic (vaginal), obturator, and internal pudic branches. THE EXTERNAL ILIAC ARTERY. The external iliac artery (a. iliaca externa) (Figs. 724, 728) extends from the bifurcation of the common iliac, opposite the sacro-iliac articulation, to a point beneath Poupart's ligament'miclway between the anterior superior spine of the ilium and the symphysis pubis. It there becomes the femoral artery. In the adult the external iliac is usually larger than the internal and is directed more nearly in the line of the common iliac, downward, forward, and outward along the brim of the true pelvis. Relations. Anteriorly, the artery is covered by peritoneum and is enclosed, together with the vein, in a moderately dense sheath derived from the subperitoneal tissue and termed Abernethy 1 s fascia. By the peritoneum it is separated on the right side from the terminal portion of the ileum and sometimes from the vermiform appendix, and on the left from the sigmoid colon. Near its origin it is crossed by the ovarian vessels in the female and sometimes by the ureter ; near its lower end it is crossed obliquely by the genital branch of the genito-crural nerve and by the deep cpi-astric vein. Some lymph-nodes are also found resting upon its anterior surface. Posteriorly, it rests upon the iliac fascia which separates it from the psoas muscle . ni<'dially~\\. is crossed near its lower end^ by the vas deferens in the male and the n .mid ligament of the uterus in the female, and is accompanied throughout its course by the external iliac vein, which lies, however, on a slightly posterior plane. I ., it, nilly, it is in relation to the genito-crural nerve. Branches. In addition to sonic small twigs to the psoas muscle and to th neighboring lymphatic glands, the external iliac gives origin to (l) the .ind ( 2 ) the the deep circumflex iliac: (P~) the internal circumflex: . the perforating \proiu: the external circumflex: ^ ) the external pudic (femoral); and (_/") the deep epigastric from below. 820 HUMAN ANATOMY. i. The Deep Epigastric Artery. The deep epigastric artery (a. epigastrica inferior) (Fig. 728) arises from the anterior surface of the external iliac, a short distance above where it passes beneath Poupart's ligament. Immediately after its origin it bends downward and medially to pass the lower border of the internal abdominal ring, being crossed in this situation by the vas deferens in the male and the round ligament of the uterus in the female. It then curves upward and medially along the medial border of the internal abdominal ring and ascends along the outer border of Hesselbach's triangle (page 526), of which it forms the lateral boundary. Throughout this portion of its course it lies between the peritoneum and the trans- versalis fascia, but at about the level of the fold of Douglas, in the posterior surface of the sheath of the rectus abdominis, it pierces the fascia and ascends between the muscle and the posterior layer of its sheath, eventually entering the substance of the muscle, where it terminates by anastomosing with the superior epigastric branch of the internal mammary artery. Branches. Throughout its course the deep epigastric artery gives off a number of branches. (a) The cremasteric branch (a. spermatica externa in the male, a. ligamenti teretis in the female) is given off a short distance beyond the origin of the deep epigastric and accompanies FIG. 728. Anterior superior spine of ilium Deep circumflex iliac artery Rectus abdominis, turned dowmv.int with part of ab- dominal wall External iliac artery External iliac vein ternal iliac artery as the in "Murator bliterated hypo- mttiM^A"- c^: .* .jur>i the perforating and terminal branches of the profunda ; and (^) the descending branch of the exter- nal circumflex anas- tomosing respectively with (a) the superior articular and muscular branches of the popliteal ; and (b) the anastomotica magna and superior articular from below. 1. The Superficial Epigastric Artery. The superficial epigastric artery (a. epigastrica superticialis) (Fig. 729) arises from the anterior surface of the femoral, about i cm. below Poupart's ligament. It is directed at first forward, but, after per- forating the fascia lata or sometimes the cribriform fascia, it bends upward over Poupart's ligament and ascends between the superficial and deep layers of the super- ficial abdominal fascia to the neighborhood of the umbilicus. It gives branches to adjacent inguinal lymphatic nodes and to the integument, anastomosing with the cutaneous branches of the deep epigastric artery. 2. The Superficial Circumflex Iliac Artery. The superficial circumflex iliac artery (a. circumtlexa ilium superticialis) (Fig. 729) arises from the anterior surface of the femoral, a little below the superficial epigastric, or from a common trunk with that artery. It perforates the fascia lata or the cribriform fascia and is then directed laterally more or less parallel with Poupart's ligament, extending almost as far as the anterior superior spine of the ilium. It gives branches to the adjacent inguinal lym- phatic nodes and to the sartorius muscle, and anastomoses with the cutaneous branches of the deep circumflex iliac. 3. The Superficial External Pudic Artery. The superficial external pudic artery (a. pudenda externa superticialis) (Fig. 729) arises from the inner surface of the femoral artery and is directed inward and slightly upward towards the spine of the pubis. It pierces the cribriform fascia and, crossing over the spermatic cord or round ligament, sends branches to the integument above the pubes.. It is then continued along the dorsal surface of the penis or clitoris, lateral and external to the dorsal artery of that organ, with which it anastomoses at the glans. It supplies branches to the integument of the penis and to the preputium clitoridis, and also gives brain lie- to the scrotum or labium majus. Dissection showing femoral vessels in Scarpa's triangle and disappearing in Hunter's canal. THE FEMORAL ARTERY. 827 FIG. 732. Stump of sartorius Superficial circumflex iliac artery Rectus tendon Femoral artery Ascending branch of external circumflex artery Deep femoral artery Transverse branches of external circumflex artery Descending branch of external circumflex artery Vastus externus Crureus Rectus Tendon of quadriceps extensor, cut Patella, detached and displaced outward Superficial epigastric artery _ Superficial ext. pudic artery- Deep external pudic artery Femoral vein Pectineus Penis sectional surface Buttock Adductor longus .Semitendinosus .Gracilis Adductor tnagnus nastomotica magna nastomotica magna deep portion Anastomotica magna superficial branch Popliteal artery Semimembranosus Inferior internal articular artery Arteries of front of thigh ; deeper dissection. 828 HUMAN ANATOMY. 4. The Deep External Pudic Artery. The deep external puclic artery (a. pudenda cxterna profunda) (Fig. 732) arises from the inner surface of the femoral, either a little below the superficial external pudic or in common with that vessel. It passes medially beneath the fascia lata across the femoral vein and the pectineus and adductor longus muscles. It then pierces the fascia lata close to the ramus of the pubis and is distributed to the sides of the scrotum or labium majus, anastomosing with branches of the superficial external pudic and of the superficial perineal branch of the internal pudic. 5. The Deep Femoral Artery. The deep femoral artery (a. profunda feraoris) (Fig. 733) arises from the outer surface of the femoral, usually about 4 cm. below Poupart's ligament, and at first is directed downward parallel to the femoral and to the outer side of that vessel. It then bends medially and passes obliquely behind the femoral artery and vein, and on arriving at the upper border of the adductor longus, passes behind that vessel and is continued downward between it and the adductor magnus, rapidly diminishing in size. Finally it perforates the adductor magnus and terminates in branches to the lower portions of the hamstring muscles. Relations. At first the profunda lies alongside the femoral and is, like it, su- perficial, having in front of it only the fasciae and integument, together with some- branches of the anterior crural nerve. Later it lies behind the femoral artery and the femoral and profunda veins, and still later the adductor longus and the adductor magnus. Posteriorly it rests at first upon the ilio-psoas and then successively upon the pectineus, the adductor brevis, and the adductor magnus. Branches. The profunda femoris gives origin to the following branches : ( i ) the external circumflex, (2) the internal circumflex, (3) the three perforating arteries. The terminal por- tion of the profunda, after it has pierced the adductor magnus, is sometimes spoken of as the fourth perforating artery. (a) The external circumflex artery (a. circumflexa femoris lateralis) is the largest of the branches of the profunda and arises from it a short distance beyond its origin. It is directed horizontally outward across Scarpa's triangle, resting upon the ilio-psoas muscle and passing between the superficial and deep branches of the anterior crural nerve. It then passes beneath the sartorius and rectus muscles and terminates by dividing into an ascending, a transverse, and a descending branch. The ascending branch passes upward and outward to beneath the tensor vaginae femoris, running along the anterior trochanteric line of the femur, and terminates by anas- tomosing with the gluteal and the deep circumflex iliac arteries. It sends twigs to the neigh- boring muscles and to the hip-joint. The transverse branch is small and runs directly outward to below the greater trochanter, passing between the rectus and the crureus muscles and through the substance of the vastus lateralis. It unites with branches of the sciatic, internal circumflex, and first perforating arteries to form the crucial anastomosis. The descending branch runs downward beneath the rectus muscle, along with the nerve, to the vastus lateralis, and usually extends to the neighborhood of the knee-joint, where it anastomoses with the superior external branch of the popliteus and assists in the formation of the circumpatellar anastomosis. It gives branches to the rectus, crureus, and vastus lateralis. (b) The internal circumflex artery (a. circumflexa femoris medialis) arises from the inner surface of the profunda, very nearly opposite the external circumflex. It passes over the surface of the ilio-psoas and beneath the pectineus to reach the anterior surface of the neck of the femur. It then crosses the upper portion of the adductor brevis and adductor magnus and passes along the lower border of the obturator externus and, finally, upon the anterior surface of the quadratus femoris, where it divides into its terminal branches. (aa) The ascending branch (ramus ascendens) passes upward towards the digital fossa of the femur, sending branches to the capsule of the hip-joint and anastomosing with the sciatic and external circumflex arteries. (bo) The descending branch (ramus descendensl passes downward and curves around the lower border of the quadratus femoris to terminate in the upper portion of the hamstring mus- cles. This branch anastomoses with the sciatic, external circumflex, and first perforating ves- sels to form the crucial anastomosis. In addition, the internal circumflex in its course sends muscular branches to the adjacent muscles and also an articular branch (rnmus acetatuili) to the hip-joint. (r) The three perforating branches arise in succession from the profunda and pass back- ward, curving around the inner surface of the femur. They perforate the adductor muscles close to the bone, and supply the hamstring muscles and the vastus externus, anastomosing with one another and with neighboring vessels. THE FEMORAL ARTERY. 829 (aa) The first or superior perforating artery (a. perforans prima) is generally the largest of the three, and arises just as the profunda passes behind the adductor longus. It either passes through the adductor brevis or between that muscle and the pectineus and pierces the adductor FIG. 733. Superficial circumflex iliac Iliacus muscle Femoral artery Tendon of rectus Tensor vaginae femori Ascending branch of external circumflex Profunda femoris External circumflex Transverse branches of external circumflex Descending branch of external circumflex Vastus externus First perforating artery Adductor brevis Second perforating artery Vastus internus Third perforating artery Adducto Fourth perforating artery. Deep branch of anastomotica magna Adductor niagnus Gracilis Superficial epigastric artery Psoas muscle Pectineus - Spermatic cord Obturator artery Adductor longus Adductor brevis Corpus spongiosum of penis Obturator externus ~ Internal circumflex artery Articular branch of internal circumflex Adductor magnus Femoral artery Semimembranosus Superficial branch of anastomotica magna Deep femoral artery and its branches. magnus, and then divides into an ascending and a descending branch, the latter of which anasto- moses with the ascending branch of the second perforating, while the former assists in the for- mation of the crucial anastomosis. 830 HUMAN ANATOMY. (bb) The second or middle perforating artery (a. perforans secunda) arises a little below the first and, after piercing the adductor brevis and the adductor magnus, divides into an ascending and a descending branch which anastomose respectively with the descending branch of the first and the ascending branch of the third perforating. A nutrient artery to the femur is usually given off from this vessel, although frequently it comes from the third perforating. (cc) The third or inferior perforating artery (a. perforans tertia) arises usually on a level with the lower border of the adductor brevis. It pierces the adductor magnus and terminates, like the other perforating arteries, by dividing into an ascending and a descending branch. The ascending branch anastomoses with the descending branch of the second perforating, while the descending one anastomoses with branches from the terminal portion of the profunda. The nutrient artery to the femur is frequently given off by this branch. Variations. The variations of the profunda and its branches are somewhat numerous, and to a very considerable extent are largely associated with one another. In other words, there may be more or less dissociation of the various vessels of the profunda complex, one or other of them having an independent origin from the femoral, and, indeed, this process may occur to such an extent that a profunda femoris as a definite vessel can hardly be said to exist. The point of origin of the profunda from the femoral is stated to be usually about 4 cm. distant from Poupart's ligament, but the figure must be taken as a general average from which there may be wide departures. Thus, in 430 limbs Quain found that the distance from Poupart's ligament of the origin of the profunda was between 2.5 and 5.1 cm. in 68 per cent., and of this number it was between 2.5 and 3.8 cm. in 42.6 per cent. It was distant less than 2.5 cm. in 24.6 per cent, of the limbs and more than 5.1 cm. in only 7.4 per cent. Quain's figures are as follows : Origin at Poupart's ligament 7 cases. 0-1.3 cm - below Poupart's ligament 13 cases. 1.3-2.5 cm. below Poupart's ligament 86 cases. 2.5-3.8 cm. below Poupart's ligament . 183 cases. 3.8-5. i cm. below Poupart's ligament . . 109 cases. 5.1-6.3 cm. below Poupart's ligament 19 cases. 6.3-7.6 cm. below Poupart's ligament 12 cases. 1 1. 6 cm. below Poupart's ligament i case. Essentially similar results have been obtained by Srb and other observers, and it seems evident from the statistics that the origin of the profunda is more apt to be above than below the point taken as the average. One or other of the circumflex arteries may arise independently from the femoral, this con- dition occurring somewhat more frequently in the case of the internal circumflex than in that of the outer one, and the point of origin of the inde- pendent vessel may be either above or be-low that of the profunda. When it is the internal circum- flex which is the independent vessel, its origin is most frequently above that of the profunda; or per- haps'it would be more correct to say that with an independent internal circumflex the origin of the profunda is apt to be somewhat below the typical point. With a high origin of the profunda, the external circumflex may be represented by two vessels, one of which arises from the profunda, while the accessory one springs from the femoral lower down. Occasionally both circumflexes may arise independently from the femoral, the profunda in such cases having usually a low origin, and one or other of the perforating arteries may arise from the circumflexes. An extreme case of this nature, representing an almost complete dissociation of the profunda, has been described by Ruge, (Fig. 734) in which the superior perforating arises from the internal circumflex and the middle one from the external circumflex, what may be termed the pro funda arising 9.7 cm. below Poupart's ligament and giving off only the inferior perforating. The internal circumflex may be very much reduced in size or even absent, its territory being supplied by branches from the obturator artery. Occasionally, although rarely, one or other of the perforating branches arises directly from the femoral, and a similar origin has also been observed for the descending branch of the external circumflex. 6. The Muscular Branches. The muscular branches (rami musculares) of the femoral artery are rather numerous and are distributed to all the muscles upon tin- front of the thijrh. They are variable in number and position and do not call lor any special description. FIG. 734. iliac Superficial circumflex External circumflex Middle perforating? Inferior perforating (profunda femoris) Diagram showing almost complete dissociation of profunda femoris. (Ruge). Superficial epigastric Internal circumflex Superior perforating THE POPLITEAL ARTERY. 831 7. The Anastomotica Magna. The anastomotica magna (a. genu suprema) (Fig. 733) arises from the femoral, just before it passes through the adductor magnus. It passes downward a short distance in front of the adductor magnus and divides into two branches, a superficial and a deep. Branches. (a) The superficial branch (ramus saphenus) follows the course of the long saphenous nerve and, perforating with it the crural fascia, is supplied to the integument over the inner side of the knee and the upper portion of the leg. It anastomoses with the inferior in- ternal articular branch of the popliteal, then entering into the formation of the circumpatellar anastomosis, (6} The deep branch (ramus musculo-articularis) enters the substance of the vastus interims and passes downward to take part in the formation of the circumpatellar plexus, also sending branches to the capsule of the knee-joint. Variations. The anastomotica magna is occasionally given off from the upper portion of the popliteal artery. Occasionally it is continued some distance down the leg with the long saphe- nous nerve, representing in such cases more perfectly the original saphenous artery (page 849) ; or this vessel may be indicated by a series of anastomoses which accompany the nerve and vein and begin with the superficial branch of the anastomotica. Anastomoses of the Femoral Artery. In the case of obliteration of the external iHac artery, blood may reach the femoral by means of the anastomoses of the iliac arteries already noted (page 821), and, in addition, byway of the anastomoses between the superficial and deep epigastrics and between the superficial circumflex iliac artery and the deep vessel of the same name and the gluteal. The anastomoses between the external and internal pudics would also assist. If the obliteration of the femoral artery be above the origin of the profunda femoris, a collateral circulation may be established by the union of the branches of that vessel with the sciatic in the crucial anastomosis and also by the communication exist- ing between the external circumflex and the gluteal and the deep circumflex iliac. If the obliteration be below the origin of the profunda, circulation will be main- tained through the anastomoses around the knee-joint, in which the descending branch of the external circumflex and the terminal portion of the profunda, on the one hand, and the anastomotica magna, on the other, participate. THE POPLITEAL ARTERY. The popliteal artery (a. poplitea) (Fig, 736) is the continuation of the femoral, and extends from the point where the latter pierces the adductor magnus to the lower border of the popliteus muscle, where it divides into the anterior and posterior tibial arteries. Its course is at first downward and slightly outward, but it soon becomes almost vertical, corresponding practically with the long axis of the popliteal space. Relations. Anteriorly, the popliteal artery is in relation to the posterior sur- face of the lower part of the femur, from which it is separated, however, by a layer of adipose tissue. Lower down it rests upon the posterior ligament of the knee-joint, and still lower upon the fascia covering the posterior surface of the popliteus muscle. Posteriorly, it is somewhat overlapped in the upper part of its course by the border of the semimembranosus, and below by the inner head of the gastrocnemius. In its pas- sage through the popliteal space, however, it is covered only by the integument and fascue, beneath which is a considerable amount of fatty tissue. About the middle of its course it is crossed obliquely from without inward by the internal popliteal nerve, and throughout its entire length it has resting upon and firmly adherent to it the popliteal vein, which lies, however, slightly to its outer side above and to its inner side below. Internally, it is in relation from above downward with the semimembranosus, the internal condyle of the femur, the internal popliteal nerve, and the inner head of the gastrocnemius, and externally with the internal popliteal nerve, the external condyle of the femur, the outer head of the gastrocnemius, and the plantaris. Branches. The branches which arise from the popliteal artery are all small and may be arranged in three groups : (i) muscular, (2) articular, (3) cutaneous. Variations. The popliteal artery occasionally divides into the tibial arteries above the upper border of the popliteus muscle, and more rarely the division is delayed until the artery has reached a point almost half-way down the leg. HUMAN ANATOMY. reater sciatic nerve Popliteal artery Popliteal vein Practical Considerations. The popliteal artery is rarely wounded because of its protected position on the posterior aspect of the limb and in the hollow of the ham. Its upper portion is overlapped by the outer border of the semimembranostis muscle, and its lower portion by the inner head of the gastrocnemius ; the inter- mediate portion, covered only by skin, fascia, and areolo-fatty tissue, is very deeply placed and is not more than an inch in length. It may be torn in luxation of the knee, or wounded in fracture of the lower end of the femur, or during certain opera- tions, as osteotomy of the femur for genu valgum. Laceration or wound of this vessel is more dangerous than a corresponding injury to the brachial at the bend of the elbow, because of the greater proximity in the case of the popliteal of the branches on which the chief anastomotic supply depends ; and because of the unyielding character of the walls of the space in which the effused blood is confined. Aneurism of the popliteal artery comes next in frequency to aneurism of the thoracic aorta. This is due (#) to the frequent minor strains occurring during flexion and extension of the knee. If extreme, the former movement bends th~ artery at such an acute angle that the flow of blood through it is arrested and the pressure abo,ve this F IG - 735- point greatly increased ; and the latter" may so stretch the vessel longi- tudinally that if its elasticity is at all diminished by ather- omatous changes the inner and middle coats are thinned or ruptured. (^) The lack of muscular sup- port which the artery sur- rounded by loose cellular tissue receives also favors the development of aneur- ism. (V) The artery is said to be unusually liable to ath- eromatous degeneration. (d} It divides a short dis- tance below into two vessels, thus increasing the blood-pressure above the bifurcation. (>) Its course is curved (like that of the aortic arch), and hence the pressure is irregularly distributed. (/") The ten- dinous opening in the adductor magnus, through which the vessel runs, con- stricts it slightly at each pulse-beat and tends as in the case of the abdominal aorta below the hiatus aorticus to produce a little dilatation below that level. As both these vessels have been said to be especially weak in these regions, it may be possible that some trifling but oft-repeated interference with the vasa vasorum favors degenerative changes by slightly diminishing the blood-supply to the vessel walls. Aneurism may occur suddenly, with a sensation resembling that produced by a blow with a whip. It may develop slowly, and, if it takes a forward direction, with symptoms simulating rheumatism on account of the pressure upon the posterior ligament oi the knee-joint i.e., dull pain, stiffness, semi-flexion of the knci-, inability to extend the joint freely. If it develops in the opposite direction, the absence of resistance causes the early appearance of a characteristic pulsating tumor with bru : t and the usual signs of aneurism. It should not be confused with an enlarged bursa (page 647), the subject of transmitted pulsation, or with tumor or abscess overlying Semitendin. Semimembrani Inner head of gastrocnemius Communicans peronei nerve External saphenous nerve External saphenous vein Dissection of right popliteal region, showing relation of vessels and nerves. THE POPLITEAL ARTERY. 833 the artery and similarly influenced. Ultimately there is apt to be oedema of the leg from interference with the venous circulation, or erosion of the posterior lower sur- face of the femur, or great pain with weakness of the leg from pressure on the inter- nal popliteal nerve, or even moist gangrene if the aneurism has leaked or burst and the venous current has been cut off by the pressure of the effused blood confined for a time within narrow limits and under great pressure by the fascia of the region (page 646). Compression of the popliteal may be effected directly at its upper end by pres- sure forward, so that it is flattened out against the femur, only a little fatty connective tissue intervening. It is almost impossible, however, to avoid including the thick- walled vein which is nearer the surface and very closely attached to the artery. Compression is therefore almost invariably applied to the common femoral (page 824). On account of the shortness of the popliteal and the consequent proximity of a ligature to the diseased portion, if the vessel itself is tied the superficial femoral at the point of election the apex of Scarpa's triangle is" usually selected for liga- tion when that becomes necessary. Ligation of the popliteal artery is effected at either : (i) its upper, or (2) its lower third, the depth of the middle portion and the density of the lateral fascial border of 1 the space in which it lies rendering it unsuitable for operation. 1. The patient being prone with the leg extended, an incision is made along the external border of the semimembranosus muscle, beginning at the junction of the middle and lower thirds of the thigh. The skin and fascia and some fatty tissue having been divided, the muscle is drawn inward, and the vessel will be found with the internal popliteal nerve external to it and much more superficial, and the vein external and behind it, i.e. , nearer the surface of the popliteal space and closely adherent. The needle is passed from without inward. 2. An incision is made beginning opposite the line of the articulation a little external to the middle of the popliteal space, the inner head of the gastrocnemius being slightly larger than the outer head. The external saphenous vein lying in the superficial fascia is drawn to one side, the fascia is divided, and the two heads of the gastrocnemius are exposed and separated with the finger, the knee being a little flexed so as to relax them. At the bottom of the interval between them will be found the nerve and vein lying to the inner side of the artery and somewhat superficial to it. The needle is passed from within outward. The collateral circulation is carried on from above the ligature by means of (a) the superior articulars ; (b) the anastomotica magna ; (c*) the descending branch of the external circumflex and the terminal portion of the profunda anastomosing respectively with (#) the inferior articulars ; () the tibial recurrent ; and (r) the superior fibular and branches of the popliteal. The rete patellae takes part in this anastomosis. 1. The Muscular Branches. These (Fig. 736) are arranged in two groups, and are supplied to the muscles which bound the popliteal space. The superior group consists of a variable number of small vessels which pass to the biceps, semimembra- nosus, and semitendinosus, while the inferior group is composed of some small branches which pass to the popliteus muscle, and two larger vessels, the largest of all the vessels which arise from the popliteal, which pass respectively to the inner and outer heads of the gastrocnemius, and are termed the sural arteries (aa. surales). They arise just as the popliteal is passing beneath the inner head of the gastrocnemius. 2. The Articular Branches. These (Fig. 736) are five in number, four being arranged in pairs, two above and two below, while the fifth is unpaired or azygos. The paired branches wind around the femur and the capsule of the knee- joint towards the front, where they anastomose with one another and with adjacent vessels to form a rich circumpatellar anastomosis. They give off branches to the capsule of the knee-joint and also to the neighboring muscles. (a and d) The internal and external superior articular branches (aa. genu superior medialis et lateralis) arise opposite each other and pass transversely above the corresponding heads of the gastrocnemius. The external one then passes beneath the biceps and winds around the femur 53 834 HUMAN ANATOMY. above its external condyle, embedded in the substance of the vastus externus, dividing finally into branches which take part in the formation of the circumpatellar anastomoses. The termi- nation of the internal branch is similar, and its course is beneath the semimembranosus and through the tendon of the adductor magnus into the substance of the vastus interims. (c) The internal inferior articular branch (a. gemi inferior medialis) arises about opposite or a little above the line of the tibio-femoral articulation and courses downward and inward over the surface of the popliteal muscle, beneath the inner head of the gastrocnemius. It passes beneath the internal lateral ligament of the knee-joint and winds around the tuberosity of the tibia to join the circumpatellar anastomosis. (d ) The external inferior articular branch ( a. gemi inferior lateralis) arises a little lower down than its fellow and passes almost transversely outward, at first beneath the external head of the gastrocnemius and the plantaris, and winds around the outer tuberosity of the tibia, beneath the long internal lateral ligament of the knee-joint, to join the circumpatellar anastomosis. (e) The azygos articular branch (a. gemi media ) is the smallest of all the articular branches. It arises either from the anterior surface of the popliteal or from the external superior articular branch, and pierces the posterior ligament of the knee-joint to be distributed to the crucial, mucous, and alar ligaments. " The circumpatellar anastomosis (rete patellae) (Fig. 732) is a rich net-work of vessels which occurs in the superficial fascia surrounding the patella, and from which branches are sent to the patella, the capsule of the knee-joint, and the neighboring muscles. The following vessels take part in its formation. From above, the anasto- motica magna from the femoral and the descending branch of the external circumflex ; from the sides, the internal and external superior and the internal and external inferior articular branches of the popliteal and the muscular branches of the same artery ; and from below, the anterior tibial recurrent. 3. The Cutaneous Branches. These are variable in origin and number and are distributed to the integument covering the popliteal space and the upper part of the calf of the leg. One of them occasionally attains a considerable size and is termed the posterior saphenous artery. It accompanies the short saphenous vein down the back of the crus, sending off branches to the adjacent integument. The Collateral Circulation of the Popliteal Artery. The passage of blood to the leg after ligation of the popliteal artery is effected by means of the ricli anastomosis which exists around the knee-joint, and in .which the branches of the popliteal take part. In addition to these, however, it also receives from above the anastomotica magna, the descending branch of the external circumflex, and the terminal portion of the profunda artery, while there pass to it from below the superior fibular and the anterior and posterior tibial recurrent arteries. THE POSTERIOR TIBIAL ARTERY. The posterior tibial artery (a. tibialis posterior) (Fig. 736) is the direct con- tinuation of the popliteal down the posterior surface of the leg. It begins at the bifurcation of the popliteal at the lower border of the popliteus muscle and passes almost vertically downward, under cover of the more superficial muscles of the calf, to the groove between the inner malleolus and the os calcis, where, opposite the tip of the malleolus, it terminates by dividing into the internal and external plantar arteries. Its course may be indicated by a line drawn from the centre of the popli- teal space to a point midway between the inner malleolus and the os calcis. Relations. Anteriorly, the artery rests in succession, from above downward, upon the tibialis posticus, the flexor longus digitorum, the posterior surface of the lower part of the tibia, and the internal lateral ligament of the ankle-joint. It is closely bound down to the muscles upon which it rests by the layer of the deep fascia which covers them, the thickness and density of this fascia increasing towards tin- lower part of the leg. Posteriorly, it is covered by the soleus and gastrocnemiufl throughout the greater part of its course, but in the lower third of the le^ it is super- ficial, being covered only by the skin and fasciae, except just before its termination, where it lies beneath the internal annular ligament and the origin of the abductOf hallucis. A short distance below its commencement it is crossed obliquely, from within outward, by the- posterior tibial nerve. Internally, it is in relation with the posterior tibial nerve for a short distance above, and in the malleolar groove it has THE POSTERIOR TIBIAL ARTERY. FIG. 736. 835 Semimembranosus Semitendinosus Superior internal articular artery Sartorius Gracilis Sural branches Gastrocneinius inner head Inferior internal articular Internal lateral ligament Posterior tibial artery Soleus, cut Flexor longus digitorum External plantar artery Internal plantar artery Flexor longus hallucis tendo Tibialis posticus Popliteal artery Superior external articular artery Azygos articular artery Sural branches Inferior external articular Plantaris Gastrocneinius outer head Tendon of popliteus Anterior tibial artery Peroneal artery Soleus, turned aside Flexor longus hallucis Anterior peroneal artery Communicating branch Tendon of peroneus longus Peroneus brevis Flexor longus hallucis Tendo Achillis External calcanean (posterior peroneal) branches Internal calcanean branch Plantar fascia and flexor brevis digitorum rendon of flexor longus digitorum Arteries of posterior surface of right leg. 836 HUMAN ANATOMY. internally and in front of it the tendon of the flexor longus digitorum, and internal to that the tendon of the tibialis posticus. Externally, the posterior tibial nerve accom- panies it throughout the greater portion of its course, and at the ankle-joint the nerve lies external and posterior to the artery, between it and the tendon of the flexor longus pollicis. The artery is accompanied throughout its course by two venae comites which lie respectively to its outer and inner side. Branches. In addition to numerous muscular branches which are distributed to the neighboring muscles, and cutaneous branches to the inner and posterior sur- faces of the leg, the posterior tibial gives origin to ( i ) a nutrient branch to the tibia, (2) the peroneal artery, (3) a communicating branch, (4) an internal malleolar branch, (5) an internal calcaneal and the two terminal branches, (6) the internal, and (7) the external plantar arteries, Variations. Although apparently the principal artery of the flexor surface of the leg and the direct continuation of the popliteal, developmentally the posterior tibial is a secondary vessel, the original main vessel being the peroneal. The history of the posterior tibial seems to have been somewhat as follows. The saphenous artery, whose origin has been mentioned in connection with the variations of the femoral artery (page 823), in the lower part of the leg winds around to the posterior surface and passes behind the internal malleolus, where it termi- nates by dividing into the plantar arteries. From the upper part of the peroneal artery a branch arises which passes down the tibial side of the leg, beneath the superficial flexor muscles, and at the internal malleolus anastomoses with the saphenous. This vessel is the posterior tibial, and, its calibre enlarging, exceeds that of the peroneal, which thus sinks to the rank of a branch of the artery to which it gave birth. A reason for this increase of calibre in the posterior tibial is to be found in the degeneration of the saphenous artery (page 849), whereby the tibial be- comes the channel of supply for the plantar arteries, which seem to be its continuation. The majority of the principal variations of the posterior tibial are readily explained in the light of such a history. Thus there may be no posterior tibial, or it may be represented by a small vessel whose distribution is confined to the upper part of the leg. In such a case, as the saphenous artery degenerates, anastomoses between it and the terminal portion of the pero- neal may enlarge so that the plantar arteries come to take their origin from that vessel. Or, again, the development of the posterior tibial may proceed normally, but the lower portion of the saphenous may not degenerate completely, but persists, as has been observed, as a branch of the tibial, passing upward upon the leg in company with the long saphenous nerve. Other variations of the posterior tibial which have been observed, however, cannot appar- ently be explained as resulting from modifications of the normal course of development, but are rather to be regarded as progressive variations due to the enlargement of what are usually more or less insignificant anastomoses. Of this nature is the origin from the posterior tibial, at about the middle of the leg, of a branch which pierces the interosseous membrane and divides into an ascending and a descending branch, which together represent the anterior tibial artery. Or, again, the posterior tibial has been observed to perforate the lower part of the interosst-ou-. membrane and to be continued down the dorsum of the foot as the dorsalis pedis artery, the plantar arteries arising from the peroneal. Occasionally, also, the posterior tibial may terminate by inosculating with the peroneal, probably by the enlargement of the communicating branch, the peroneal in this case also giving rise to the plantar arteries. The high and low origins of the posterior tibial have already been mentioned in connection with the variations of the popliteal (page 831). Practical Considerations. The posterior tibial artery on account of its deep position beneath the large superficial calf muscles is rarely wounded and, by reason of the support which it receives in its upper two-thirds from those muscles and the deeper muscular layer on which it lies, and in its lower third 'from the dense fascia covering it, it is seldom the subject of aneurism. Except for a short portion of its course immediately above the ankle, it is separated from the tibia by the deep calf muscles, and is therefore not often involved in fractures of that bone. The bifurcation of the popliteal is not infrequently the region at which an em- bolus carried down from the popliteal is arrested, and such a clot may block both the tibial arteries. Their free anastomosis prevents gangrene if only one of them is occluded ; but if both are involved, and especially if tin- succeeding additions to the clot invade the anterior tibial recurrent interfering with anastomosis from above gangrene almost certainly follows. Compression of the posterior tibial is scarcely possible above its lower third. Above the ankle and behind the inner malleolus it may be flattened against the tibia by pressure directed outward and a little forward. I.igatiou of the posterior tibial may be done at any part of its course, but in its upper third is an operation of some difficulty. THE POSTERIOR TIBIAL ARTERY. 837 FIG. 737. Gastrocnemius, outer head -Venae comites Flexor longus "digitorujn -Post, tibial artery Post, tibial nerve Cut edge of soleus muscle '? / Tendon of plantaris VA i. The artery is best approached from the inner side of the leg. The leg being flexed, the limb is laid on its outer side, and an incision three and a half or four inches in length is made along the inner margin of the tibia, beginning two and a half inches from the upper end of that bone. The skin being divided, care must be exercised in opening the superficial fascia not to injure the internal saphenous vein or nerve, both of which lie directly in the track of the wound. These structures being dis- placed, the deep fascia must be slit up to the full extent of the incision. It should also be cut transversely, so as to allow a freer access to the intermus- cular parts. The next step consists in detaching the origin of the soleus muscle from the tibia. It is at this stage of the operation that one of two errors is often committed, the inter- muscular space between the inner head of the gastrocnemius and the soleus muscle is opened, or all the muscular tissue is separated from the bone, the tibialis posticus muscle be- ing raised along with the soleus. The first mistake leads the operator above the vessel and the second leads him underneath. There is, however, a guide which will afford important assistance. If the soleus has been properly detached and raised, its under surface will present a white, shining sheet of tendinous material, beneath which will be seen a FIG. 738. , . , . ,. , layer of fascia (inter- muscular) covering the tibialis posticus muscle. If search is now made externally and towards the middle of the leg, the artery will be found covered by the inter- muscular fascia, the nerve lying to its outer side. After the vessel has been separated from the investing con- nective tissue and the accompanying veins, the needle must be passed from without inward (Agnew). 2. At the middle third the artery is reached through an incision parallel with the inner edge of the tibia and a half inch from its border. Avoiding the saphenous vein and nerve, the superficial fascia and the deep fascia (with its fibres running transversely) are Dissection of back of right leg, showing relations of pos- terior tibial vessels and nerve ; gastrocnemius and soleus muscles have been cut and drawn aside. 'Post, tibial artery Post, tibial nerve Tendo Achillis Flex. long, halluci: Dissection of inner side of right ankle, showing relation of tendons, vessels and nerves as they pass between calcanium and internal malleolus. 838 HUMAN ANATOMY. divided in the line of the skin wound, the inner margin of the soleus displaced outward, and the vessel, with its venie comites, exposed, the posterior tibial nerve lying to its outer side. A little lower i.e. , in the lower third of the leg the incision should be made midway between the inner edge of the tibia and the inner edge of the tendo Achillis, and the artery will be found lying on the fibres of the flexor longus digitorum, the tendon to the inner side, and the nerve external. 3. To ligate the vessel at the inside of the ankle the incision should be semi- lunar in shape, parallel with the margin of the inner malleolus, and about half-way between it and the margin of the tendo Achillis. After dividing the deep fascia- internal annular ligament the artery will be found, with its accompanying veins, lying between the flexor longus digitorum and tibialis posticus tendons on the inside each in a separate synovial sheath and the latter near the malleolus and the nerve and flexor longus pollicis tendon on the outside. The sheaths of these tendons should not be opened. The collateral circulation is carried on from above the ligature by () the anterior and posterior peroneal arteries and their muscular and communicating branches ; () the external malleolar branch of the anterior tibial ; (c) the internal malleolar (anterior tibial); (a?) the dorsalis pedis. Anastomosing respectively with (a) the muscular branches and the communicating branch of the posterior tibial ; () the external plantar branch of the posterior tibial ; (c) the internal malle- olar (posterior tibial) ; and (a?) the internal and external plantars. 1. The Nutrient Artery. The nutrient artery to the tibia (a. nutritia tibiae > may arise from the posterior tibial, either above or below the origin of the peroneal artery, or sometimes it arises from that vessel. It pierces the tibialis posticus and enters the nutrient foramen on the posterior surface of the tibia, sending off, before it does so, some small muscular branches. 2. The Peroneal Artery. The peroneal artery (a. peronaea) (Fig. 736) is by far the largest of the collateral branches of the posterior tibial. It arises about 2.5 cm. below the lower border of the popliteus muscle and is at first directed outward and downward towards the fibula, and then passes vertically downward along the inner surface of that bone to a point about 2.5 cm. above the ankle-joint, where it termi- nates by dividing into the anterior and posterior peroneal arteries. Relations. In the upper part of its course it is covered posteriorly by the soleus, lying between that muscle and the tibialis posticus. Lower down it passes beneath the flexor longus hallucis or else traverses the substance of that muscle, and just before its termination it emerges from beneath the muscle and becomes super- ficial. It is accompanied by two venae comites. Branches. In addition to numerous muscular branches to the neighboring muscles and cutaneous branches to the integument of the outer border of the cms, the peroneal artery gives off the following vessels : (a) The nutrient artery to the fibula (a. nutritiae fibulae) enters the nutrient foranu-n of that bone. (A) The communicating branch (ramus communicans) passes inward over tin- lower end of the tibia and beneath the tendo Achillis, a short distance above the terminal bifurcation of the peroneal. It inosculates with the communicating branch of the posterior tibial. (c) The anterior peroneal artery ( ramus perfonms) is one of the terminal branches of the peroneal. It passes directly forward and, perforating the interosseous membrane, bends down- ward over the ankle-joint to the dorsum of the foot. It sends branches to the ankle-joint and to the inferior tibio-libular articulation, as well as to the peroneiis tertius muscle, beneath which it ] tasses, and terminates by anastomosing with the tarsal and metatarsal branches of the dorsalis pedis and with the external plantar artery upon the side of the foot. (d) The posterior peroneal artery is the other terminal branch of the peroneal, of which it is the direct continuation. It gives origin to the r.vternal calcancal branch which ramifies over the outer surface of the os calcis and terminates by anastomosing with the internal cal- caneal branch of the posterior tibial artery and with the tarsal and metatarsal branches of the dorsalis pedis. Variations. The peroneal artery is exceedingly subject to variation. It is rarely absent, but not infrei|iiently it terminates over the outer malleolus, its lower portion being given off from a branch which passes across from the posterior tibial and represents the enlarged anastomosis THE POSTERIOR TIBIAL ARTERY. 839 FIG. 739. Internal annular ligament, cut edge Inner malleolus i- Abductor hallucis Internal plantar Flexor longus hallucis tendon From external calcanean Internal calcaneal ot external plantar Plantar fascia, cut Flexor brevis digitorum Abductor minimi digiti External plantar artery of the posterior tibial and peroneal communicating branches. Conversely, when the lower por- tion of the posterior tibial is wanting', it may be replaced by the peroneal, which then gives rise to the plantar arteries. Occasionally the peroneal is larger than usual, and may give origin to the anterior tibial artery, and it may give off the nutrient artery for the tibia. The anterior peroneal artery is sometimes absent, but more frequently it is larger than usual and inosculates with the anterior tibial. Occasionally the lower portion of this latter ves- sel is wanting, and the anterior peroneal may then take its place, being continued downward upon the dorsum of the foot as the dorsalis pedis and giving off the branches which normally arise from that vessel. 3. The Communicating Artery. The communicating artery (r. communicans) (Fig. 736) extends transversely outward across the posterior surface of the tibia, beneath the tendon of the flexor longus hallucis and the tendo Achillis, and an- astomoses with the communicating branch Internal calcanein of of the peroneal. ^ sterior tlbial - 4. The Internal Malleolar Artery. The internal malleolar artery (a. malleolaris posterior medialis) (Fig. 740) passes directly in- ward, beneath the ten- dons of the flexor longus digitorum and tibialis posticus, to ramify over the internal surface of the inner malleolus, anastomos- ing with the internal malleolar branch of the anterior tibial artery. 5. The Internal Calcaneal Artery. The internal calcaneal artery (raraus calcanei medialis) (Fig. 736) arises from the lower part of the posterior tibial, just before it divides into the two plantar vessels. It is frequently represented by several branches which descend along the inner side of the tuberosity of the os calcis, supplying the neighboring parts of the integument and anastomosing with branches of the internal malleolar and posterior peroneal arteries. 6. The Internal Plantar Artery. The internal plantar artery (a. plantaris medialis) (Fig. 740) is the smaller of the two terminal branches of the posterior tibial. It arises in the groove between the internal malleolus and the os calcis and is directed at first downward and forward, under cover of the abductor hallucis, and then forward along the inner border of the foot, between the abductor hallucis and the flexor brevis digitorum, terminating opposite the head of the first metatarsal bone by anastomosing with one or other of the two branches distributed to the plantar surface of the great toe. Branches. In its course it gives off muscular branches to the abductor hallucis and the flexor brevis digitorum, cutaneous branches to the integument over the inner border of the foot, and articular branches to the neighboring tarsal joints. In addition, it usually gives off near its Princeps halluc Interosseous arteries dividing into digital branches Arteries of plantar surface of right foot ; superficial dissection. 8 4 o HUMAN ANATOMY. origin a larger branch, the anastomotic branch, which passes beneath the abductor hallucis to gain the upper border of that muscle, along which it courses forward, giving off numerous branches to the abductor and the adjacent integument and anastomosing with the tarsal and metatarsal branches of the dorsalis pedis. More distally it gives off from its outer surface a varying number of slender superficial digital branches, which pass obliquely forward and out- ward across the sole of the foot to anastomose with one or more of the plantar interosseous branches from the plantar arch. Variations. Occasionally the superficial digital branches of the internal plantar arise from a common stem which anastomoses with a branch from the external plantar to form a superfi- cial plantar arch beneath the superficial fascia. This is the equivalent of the superficial palmar arch of the hand. 7. The External Plantar Artery. The external plantar artery (a. plantaris lateralis) (Fig. 740) is the larger of the terminal branches of the posterior tibial. It passes forward and outward across the sole of the foot, at first between the flexor brevis digitorum and the flexor accessorius, and then in the interval between the flexor brevis digitorum and the abductor minimi digiti. Opposite the base of the fifth meta- tarsal bone it turns somewhat abruptly inward and again crosses the sole of the foot, forming the plantar arch (arcus plantaris), which terminates at the proximal end of the first intermetatarsal space by uniting with the communicating branch from the dorsalis pedis. Relations. In the first part of its course the external plantar lies beneath the abductor hallucis and the flexor brevis digitorum, but as it approaches the fifth meta- tarsal it becomes more superficial, being covered only by the skin and the superficial and plantar fasciae. It rests upon the flexor accessorius and the flexor brevis minimi digiti, and is accompanied by the external plantar nerve. The plantar arch, on the contrary, occupies a much deeper position. It passes beneath the tendons of the flexor longus digitorum, the lumbricales, and the oblique portion of the adductor hallucis, resting upon the proximal ends of the second, third, and fourth metatarsals and upon the interosseous muscles which occur between those bones. Branches. The external plantar artery gives rise to (a) numerous muscular branches which supply the various muscles of the plantar surface of the foot, and in its first part to (b) Cutaneous branches which supply the skin over the sole and outer border of the foot, some of them forming anastomoses with branches of the tarsal and metatarsal branches of the dorsalis pedis. In addition, there are given off from the first portion of the artery (c ) Calcaneal branches, one or more in number, which arise near the commencement of the external plantar and ramify over the inner surface of the os calcis, anastomosing with the internal calcaneal branches of the posterior tibial. From the plantar arch a number of vessels are given off. (d) The articulating branches are given off from the posterior or concave surface of the arch and supply the tarsal articulations. (e) The posterior perforating branches, four in number, arise either from the plantar arch or from the plantar digital branches of the fourth intermetatarsal space. They ascend in the intermetarsal spaces between the heads of the dorsal interosseous muscles and terminate by inos- culating with the first, second, and third dorsal interosseous arteries. The branch which passes through the first intermetatarsal space is much larger than the rest and inosculates with the dor- salis pedis artery ; it is sometimes regarded as the terminal branch of that vessel. (/) The plantar interosseous arteries ( aa. metatarsae jdantares) are five in number, and are usually numbered in succession from the outer side of the foot inward, that is to say, in tin- opposite direction to the intermetatarsal spaces in which they lie. The first arises just where the external plantar artery is bending inward to form the -plantar arch and passes forward along the inner border of the abductor minimi digiti, later crossing over the flexor brevis minimi digiti to reach the outer surface of the little toe, along which it runs. The second, third, and fourth plantar interosseous arteries arise in succession from the plantar arch as it crosses the fourth, third, and second intermetatarsal spaces, and pass forward, resting upon the interosseous muscles and covered by the tendons of the flexor longus digitorum and the lumbricales, and more distally by the transverse adductor of the great toe. Just before reaching the line of the metatarso-phalangeal articulations each artery gives off an anterior per- forating branch, which passes dorsally to communicate with the corresponding dorsal interos- seous artery, and then divides into two plantar digital branches, which pass onward upon the adjacent sides of neighboring digits. THE POSTERIOR TIBIAL ARTERY. The fifth plantar interosseous artery is considerably larger than the others, and arises from the inner end of the plantar arch, opposite the communicating branch which passes between the plantar arch and the dorsalis pedis. It runs forward at first along the first intermetatarsal space and then upon the first metatarsal bone, and gives off a digital branch which passes to the inner surface of the great toe and continues on towards the metatarso-phalangeal joint of that digit. Before reaching this, however, it gives off an anterior perforating branch and then divides into two plantar digital branches, which supply respectively the inner side of the second and the outer side of the great toe. Since the communicating branch which traverses the first intermetatarsal space is some- times regarded as the terminal portion of the dorsalis pedis artery, and the fifth plantar inter- osseous artery seems to be, upon such a view, the branch of the communicating vessel, the fifth plantar has been de- scribed as a branch of FIG. 740. the dorsalis pedis ar- Tendo Achiiiis tery, under the name of the a. princeps hallucu. There can be no doubt, however, that both the communicating and the princeps are equiv- alent to the other pos- terior perforating and plantar interosseous arteries. Posterior tibial Internal malleola Internal lateral ligam Internal plantar Flexor longus hallucis tendon Adductor obliquus, cut Princeps hallucis (V. interosseous) dividing into digital branches Internal calcanean Abductor hallucis Internal calcanean of ext. External [plantar plantar Flexor brevis digitorum Flexor accessorius Superficial fascia Abductor minimi digit! II. and III. plantar interossei and flexor brevis minimi digit! I.-IV. interosseous arteries dividing into digital branches Variations. The external plantar artery may be quite small, in which case the plantar arch seems to be a continuation from the anterior tibial artery through the posterior perforating branch of the first intermetatar- sal space. The arch is occasionally double, owing to its division at its origin into two stems which reunite opposite the first inter- metatarsal space. The first plantar interosse- ous may arise by a common stem with the second, and, con- versely, one or more of the plantar digital branches may have an independent origin from the arch. Anastomoses of the Posterior Tibial Artery. A collateral circulation for the posterior tibial after interruption of that vessel below the origin of the peroneal may readily be established through the anastomoses which its branches form with those of the peroneal and those of the anterior tibial. The anasto- moses with the peroneal are between the communicating branches of the two arteries, between the anterior peroneal and the external plantar, and between the posterior peroneal and the internal calcaneal. With the anterior tibial artery there is communication through the malleolar branches of the two arteries, through the anastomotic branch of the external plantar and the tarsal and metatarsal branches of the dorsalis pedis, and through the union of anterior and posterior perforating branches of the plantar arch and the plantar interosseous arteries with the dorsalis pedis and dorsal interosseae. Arteries of plantar surface of right foot ; deeper dissection. 842 HUMAN ANATOMY. FIG. 741. THE ANTERIOR TIBIAL ARTERY. The anterior tibial artery (a. tibialis anterior) (Figs. 742, 743) is the other terminal branch of the popliteal. It begins at the lower border of the popliteus muscle, and is at first directed forward, passing between the tibia and fibula and the two uppermost slips of origin of the tibialis posticus, above the upper border of the interosseous membrane. It then bends downward and traverses the entire length of the crus to the front of the ankle-joint, where it becomes the dorsalis pedis artery. Its course may be represented by a line drawn from the head of the fibula to a point half-way between the two malleoli. Relations. In its course down the leg the anterior tibial artery rests posteriorly upon the interosseous membrane, to which it is more or less firmly united by fibrous bands ; in the lower quarter of its course it rests upon the front of the tibia. Anteriorly, in the upper two-thirds of its course, it is overlapped by the tibialis anticus, lying along the deep edge of the connective-tissue partition which separates that muscle from the ex- tensor longus digitorum and the extensor proprius hallucis. Lower, however, it is superficial, and just above the ankle-joint it is crossed obliquely, from without inward, by the tendon of the extensor proprius hallucis, and then passes beneath the anterior annular ligament. Internally to it is the tibialis anticus, and at the ankle-joint the ten- don of the extensor proprius hallucis ; externally it has in its upper third the* extensor longus digitorum, in its middle third the extensor proprius hallucis, and at the ankle the inner tendon of the extensor longus digitorum. The anterior tibial nerve lies to tin- outer side of the artery in its upper and lower thirds ; in the middle third of the leg it is usually in front of the vessel. Variations. The anterior tibial artery, as it occurs in man, appears to be the result of a union of two originally distinct vessels, both of which arise from the primitive peroneal artery and pass to the front of the leg. The- up- permost of these forms tin- greater portion of the artery, while the lower one, which is represented by the anterior peroneal artery, forms only the lower part of the anterior tibial and its continuation upon the dorsurn of the foot, the dorsalis pedis. In case of failure in the union of these two vessels, the anterior tibial may appear to terminate in muscular branches a short distance above the ankle- joint, the dorsalis pedis being the continuation of the an- terior peroneal. This ar- rangement is not infrequent ; more rarely the upper portion of the vessel is greatly re- duced, being represented only by a small stem which gives off the posterior and anterior recurrent branches as well as branches to the popliteus muscle, the front of of the leg, in such cases, being Sometimes supplied by an in- dependent perforating branch from the posterior tibial. Practical Consid- erations. The anterior tibial artery is more often Dissection of middle third of right leg, showing relations of anterior tibial - , vessels and nerves; extensor muscles have been drawn aside. WOUImCU tiKll! tin. po tenor tibial because of its in. ire exposed position on the front of tin- limb and its close relation to the tibia. It is not infrequently lacerated by the sharp edge of a fragment in fracture of that bone. It is Peroneus brevis Ext. longus hallucis Ext. longus digitorum Tibialis anticus muscle Tibia Ant. tibial nerve Ant. tibial artery Companion vein THE ANTERIOR TIBIAL ARTERY. 843 Superior external articular External condyle Anterior tibial recurrent Peroneus longus Extensor longus digitoruin Extensor proprius halluci: Branch of superior internal articular Tendo patellce Inferior internal articular artery ^=>Tibialis anticus Interosseous membrane .Anterior tibial artery ribialis anticus rarely the subject of aneurism. Ligation may be done at ( i) the upper; (2) the middle; or ( 3 ) the lower third. The line of the artery is from a point midway between the exter- nal tibial tuberosityand the head of the fibula to the middle of the anteri- or inter malleolar space, i. When through an incision made at this line the deep fascia is reached and divided, the interspace in which the artery lieS Should Inferior external articular be SOUght for. It is Tendon of biceps- that between the tibi- alis anticus and the extensor longus digi- torum, is the only in- termuscular interstice in the upper anterior tibial region, is about an inch or an inch and a quarter external to the tibial crest, and a half to three-quarters of an inch internal to the septum which di- vides the extensor lon- gus from the peroneus longus. This septum is often marked by a white line visible before the deep fascia is di- vided , or it may be recognized by slipping a director outward be- neath the aponeurosis until its point is firmly arrested. The inter- space containing the anterior tibial artery will then be internal to this and can be felt as a line of lessened resist- ance when the fore- finger is pressed length- wise along the muscles (Treves). On the other hand, the apon- eurotic partition be- tween the extensor and the peroneus external to the inter- space sought for resists and vibrates under the point of the director or the fore- finger (Farabeuf). At the bottom of the interspace the artery will be found lying upon the interosseous membrane to the outer side of the tibia and with the nerve external to it.' Peroneus brevis Peroneus longus tendon Aaterior peroneal artery External malleolar artery External calcanean or posterior peroneal arter; External malleolu Tarsal artery Extensor brevis digitoruin Peroneus brevis tendon Metatarsal artery Posterior perforating arteries Dorsal interosseous arteries Internal malleolar artery Inner malleolus Innermost tendon of extensor brevis digitorum Dorsalis pedis Communicating artery Dorsalis hallucis Anterior perforating arteries Tendons of extensor longus digitoruin Arteries of front of leg and dorsum of foot. 844 HUMAN ANATOMY. 2. At the middle of the limb the same interspace is found usually more easily, as there is often some yellowish-white fatty tissue lying between the muscles and seen as a line on the surface of the deep fascia and is opened. The artery which still lies on the interosseous membrane will be found in the deeper space thus disclosed between the extensor proprius pollicis and the tibialis anticus. 3. At the lower third an incision on the same line will expose the vessel lying usually in the innermost of the two interstices found at that part of the limb, viz., that between the tibialis anticus and the extensor proprius pollicis. Occasionally it will be found to the outer side of the tendon of the extensor proprius the second tendon from the tibia in the space between that muscle and the extensor longus digitorum. The vessel lies on .the front of the tibia, with the nerve external. The collateral circulation is carried on from above the ligature by (a) the pero- neals ; and (<5) the posterior tibial, anastomosing respectively with (a) the external malleolar, the branches of the dorsalis pedis and the plantar ; and (fr) the internal malleolar from below, assisted by the many small anastomotic vessels piercing the interosseous membrane and derived from the two tibials. Branches. In addition to numerous muscular branches which supply the adjacent muscles, the anterior tibial artery gives off the following : i. The superior fibular branch (ramus fibularis) is a small vessel which arises from the anterior tibial immediately below its origin ; occasionally it arises by a com- mon trunk with the posterior tibial recurrent or else from the lower part of the popliteal. It passes upward behind the neck of the fibula, traversing the substance of the soleus, and sends branches to that muscle and to the peroneus longus, and anastomoses with the external inferior articular branch of the popliteal. 2. ' The posterior recurrent tibial artery (a. recurrens tibialis posterior) arises while the anterior tibial is still upon the posterior surface of the leg. It passes upward between the popliteal muscle and the posterior ligament of the knee-joint, both of whicn it supplies, and terminates by anastomosing with the external and internal inferior articular branches of the popliteal. 3. The anterior recurrent tibial artery (a. recurrens tibialis anterior) is given off just after the anterior tibial has reached the front of the leg. It runs upward in the substance of the tibialis anticus and oyer the outer tuberosity of the tibia, and terminates by taking part in the formation of the circumpatellar anastomosis. It gives branches to the tibialis anticus, the extensor longus digitorum, the capsule of the knee-joint, and the adjacent integument. This artery is of importance in the establishment of a collateral circulation after ligation of the popliteal artery (page 834), on account of its anastomoses with the descending branch of the external circumflex artery and with the anastomotica magna. 4. The internal malleolar artery (a. malleolaris anterior medialis) arises from the inner surface of the anterior tibial, a little above the ankle. It passes inward beneath the tibialis anticus, over the surface of the inner malleolus, and terminates by anastomosing with the malleolar branch of the posterior tibial, the internal plantar,, and the internal calcaneal arteries. 5. The external malleolar artery (a. malleolaris anterior lateralis) arises from the outer surface of the anterior tibial, usually a little below the internal malleolar. It is directed outward and downward beneath the extensor longus digitorum and the peroneus tertius, over the surface of the external malleolus, and anastomoses with branches from the anterior and posterior peroneal arteries. Anastomoses of the Anterior Tibial Artery. Collateral circulation is readily established, in cases of interruption of the anterior tibial artery, by means of its abundant anastomoses with branches of the posterior tibial. Thus there art- rich anastomoses between the internal malleolar branch of the anterior tibial and the malk-olar branch of the posterior tibial, and between the external malleolar branch of the anterior tibial and the anterior and posterior peroneal branches. Further, since the dorsalis pedis artery is the continuation of the anterior tibial, it will assist mate- rially in the collateral circulation by the anastomoses of its tarsal and metatarsal branches with the plantar and peroneal arteries and by its connections with the plantar arch*. THE DORSAL ARTERY. 845 Tendon of tibialis anticus Branch of musculo- cutaneous nerve Ant. tibial artery Ant tibial nerve Tendon of extensor longus hallucis Musculo- cutaneous nerve Peroneus brevis Peroneus longus Dorsalis pedis artery THE DORSAL ARTERY OF THE FOOT. The dorsal artery of the foot (a. dorsalis pedis) (Fig. 743) is the continuation of the anterior tibial beyond the ankle-joint. It extends to the proximal portion of the first intermetatarsal space, where it receives the large fourth perforating branch of the plantar arch, and is thence continued forward along the intermetatarsal space as the a. dorsalis hallucis. Relations. The dorsalis pedis is covered in the proximal portion of its course by the anterior annular ligament, and is crossed just before it reaches the intermetatarsal space by the tendon of the extensor brevis digitorum which passes to the great toe. It rests successively upon the anterior ligament of the ankle-joint, the head of the astragalus, the astragalo-scaphoid liga- ment, the dorsal surface of the scaphoid bone, the dorsal scapho-cuneiform ligament, and the in- tercuneiform ligaments which extend between the middle and internal cuneiform bones. Ex- ternally it is separated from the innermost ten- don of the extensor lon- gus digitorum and from the extensor brevis digi- torum by the inner termi- nal branch of the anterior tibial nerve, and inter- nally it is in relation with the tendon of the exten- sor hallucis proprius. Branches. In addition to numerous cu- f a 11 cons branches to the skin of the dorsum of the foot and muscular branches to the extensor bn.-vis digitorum, the dorsalis pedis gives rise to the following vessels. 1. The internal tarsal branches (aa. tarseae mediates ) are one or more small vessels which pass over the outer border of the foot, supplying the integument and the tarsal articulations and anastomosing with the internal malleolai and internal plantar arteries. 2. The external tarsal branch (a. tarsea lateralis) arises opposite the head of the astragalus and passes outward and forward over the scaphoid and cuboid bones, under cover of the extensor brevis digitorum. It gives branches to that muscle, to the skin, and to the tarsal articulations, and anastomoses with the external malleolus and anterior peroneal arteries above, with the external plantar laterally, and with the metatarsal below. 3. The metatarsal branch (a. arcuata) arises over the internal cuneiform bone and is directed at first laterally forward and then laterally over the bases of the four outer metatarsal bones and beneath the tendons of the extensor longus and extensoi Dissection showing relations of vessels and nerves in vicinity of left ankle ; portion of anterior annular ligament still in place. 846 HUMAN ANATOMY. brevis digitorum. It thus forms an arch upon the dorsal surface of the foot corres- ponding in position with the plantar arch below. It anastomoses laterally with the external tarsal and with the external plantar, and opposite each of the intermetatarsal spaces which it passes the second, third and fourth gives off a dorsal interosse- ous artery (a. metatarsea dorsalis). Each of these passes forward along its intermetatarsal space, and, immediately beyond its origin, gives off a posterior perforating branch which communicates directly with the corresponding posterior perforating branch of the plantar arch. At the distal end of its intermetatarsal space each artery gives off an anterior perforating branch which unites with the similar branch of the corresponding plantar interosseous, and then divides into two dorsal digital branches (aa. digitales dorsales) which pass along the adjacent surfaces of two neighboring digits and anastomose with one another and with the plantar digital branches. 4. The dorsal interosseous branch of the first intermetatarsal space appears to be the continuation of the dorsalis pedis, and is usually termed the a. dorsalis hallucis. Its course is exactly similar to that of each of the other dorsal interosseous arteries, except that, in addition to the anterior dorsal perforating and terminal dorsal digital branches, it gives off, not far from its origin, a third digital branch which passes forward along the outer surface of the great toe. The posterior communicating artery which should arise from this vessel is represented by the large branch by which the dorsalis pedis communicates with the plantar arch. Variations. The origin of the dorsalis pedis from the peroneal by means of the anterior peroneal branch has already been noted in connection with the variations of the anterior tibia! artery. Another origin which has been observed is from the external plantar artery, \vhich sends upward through the astragalo-calcaneal canal a large branch which is continued distally upon the dorsum of the foot and gives off the tarsal and metatarsal branches. This vessel is represented in the adult by a small branch which arises from the external tarsal artery and pur- sues the course indicated to anastomose with the external plantar ; it appears to be much more highly developed in the embryo than in the adult (Leboucq). Other variations in the dorsalis pedis and its branches depend upon a correlation which exists between the development of the dorsal and plantar system of vessels. If, for example, the plantar interossese are well developed, they will, through the anterior perforating branches, furnish the main blood-supply for the dorsal digital branches, and the dorsal interosseous ves- sels, as well as the metatarsal, may be much reduced. Or the plantar arch, through the pos- terior perforating branches, may be the main supply for the dorsal interosseous vessels, and the dorsalis pedis itself may be diminished in size or may even terminate in a net-work of small vessels over the dorsal surface of the tarsus. DEVELOPMENT OF THE ARTERIES. In the preceding pages some of the more important facts regarding the development of the arteries have been mentioned in connection with the anomalies in whose production they are concerned ; these facts may now be briefly restated in a more connected manner. At an early stage of development, while the heart lies far forward beneath the pharyngeal region and its ventricle is still undivided, the blood leaves it by a single vessel which passes forward along the mid-ventral line of the pharynx and divides to form two ventral longitudinal stems, from each of which six lateral branchial vessels arise, the fifth vessel of each stem, counting from before backward, being quite rudimentary and closely associated with the fourth. These branchial vessels pass dorsally in the branchial arches to the dorsal surface of the pharynx, where those of each side unite to form a longitudinal stem which passes backward, and at about the level of the eighth cervical vertebra unites with its fellow of the opposite side to form a single longitudinal trunk, the dorsal aorta (Fig. 677). This is continued backward to the posterior extremity of the trunk, lying immediately ventral to the vertebral column. From the anterior ends of the ventral and dorsal longitudinal steins brandies pass forward into the cranial region; and from the dorsal longitudinal stems and the dorsal aorta lateral and ventral branches are given off in regular segmental succession. The modifications undergone by the branchial arch vessels in the course of development may first be- traced and then the arrangement and modifica- tions of the segmental branches will be considered. The first modification of the branchial arch vessels consists in the disappearance of the two anterior ones on either side, and then follow a number of changes which may be briefly stated as follows, (i) The portions of the dorsal longitudinal stems intervening between the third and fourth branchial vessels disappear ; (2) the fifth branchial vessels disappear ; (T,) the sixth loses its connection with the dorsal longitudinal stem on the right side 5(4) the proximal portion of DEVELOPMENT OF THE ARTERIES. 847 Fro. 744. Diagrams illustrating primary arrangement (A) and second- ary modifications (S) in branchial arch vessels. TA, truncus arteriosus; I-VI, aortic bows; VA, DA, ventral and dorsal aortae ; A, aorta; AA, aortic arch; 7, innominate artery; CC, C, Cf, common, external and internal carotids; 5, subclavian ; P, pulmonary artery ; da. ductus arteriosus. the ventral longitudinal stem divides in the frontal plane into two portions, one of which is con- nected with the sixth branchial vessels, while the other retains the remaining ones ; and (5) the posterior portion of the right dorsal longitudinal stem disappears, so that the dorsal aorta is formed only by the left stem (Fig. 678). As the result of these changes the anterior portion of the ventral longitudinal stem becomes the external carotid artery ; the anterior portion of the dorsal longitudinal stem the internal carotid ; the third branchial vessel becomes the connection between the two carotids ; the fourth branchial vessel of the left side, together with the left dorsal longi- tudinal stem, becomes the arch of the aorta ; the right fourth branchial vessel and the persisting portion of the right dorsal longitudinal stem become the proximal portion of the right subclav- ian artery ; the sixth branchial vessels become the pulmonary arteries, the persisting connection of the left one with the aortic arch being the ductus arteriosus ; the proximal portion of the ventral longitudinal trunk which re- mains connected with the sixth vessels becomes the pulmonary aorta, while the other portion becomes the prox- imal part of the aortic arch. These changes are shown diagrammatically in Fig. 744, A and B. From the forward prolongations of the carotid arteries the vessels which supply the cranial structures are de- veloped, and lateral branches also pass from the carotids to the structures which are formed from the branchial arches. Of these branches the superior thyroid, lingual, and facial arteries are probably from the beginning connected with the external carotid, but the greater part of the internal maxillary takes its origin from the internal carotid and only secondarily becomes con- nected with the external one (page 743). From the dorsal longitudinal stems, posterior to the point at which the sixth branchial vessels join them, branches pass off laterally to each of the cervical segments, the most anterior pair accompanying the hypoglossal nerve and passing to the occipital segments with which the nerve is associated. Later, as the heart recedes towards its final position in the thorax, carrying with it the dorsal longitudinal stems, the majority of the cervical lateral branches separate from the stems and are represented in the adult by the segmental muscular and spinal branches which arise from the vertebral artery. The seventh branches, however, retain their connection with the longitudinal stems and become the subclavian arteries of the adult. Throughout the entire length of the dorsal aorta segmental branches are distributed not only to the body-wall, but also to the viscera, and in each seg- ment two typical sets of visceral branches may be distinguished, a pair of lateral branches which pass laterally beneath the peritoneum to the paired viscera, and a single median branch which passes ventrally in the mesentery and is supplied to the digestive tract and its derivatives (Fig. 745). The lateral branches to the body-wall persist in the adult as the inter- costal lumbar and lateral sacral branches, the fifth lumbar branches entering into the formation of the iliac arteries. The visceral branches belonging to both sets, however, undergo much modification, some disappearing and others fusing, so that little trace of their primary" segmental arrangement 5 to be recognized in the adult. Representatives of the paired visceral branches are to be found in the bronchial, suprarenal, renal, and spermatic (ovarian)' arteries, and in the fa-tus the umbilical arteries represent the paired branches of the third lumbar segment. At an early stage, however, these vessels make connections with branches of the iliac arteries and FIG. 745. Diagram showing fundamental arrangement of branches from aorta (A) ; , lateral branches to body-wall; C, paired visceral, D, unpaired visceral branch ; E. peritoneum. 848 HUMAN ANATOMY. FIG. 746. then lose their original connections with the aorta, so that they seem in the foetus to arise from the iliac vessels, and these latter, although primarily somatic in their distribution, give off a number of visceral branches. Of the unpaired visceral branches representatives are to be found in the thoracic region in the cesophageal and mediastinal vessels and in the abdomen in the coeliac axis and the superior and inferior mesenteric arteries, the superior mesenteric representing the omphalo-mesenteric or vitelline arteries of the embryo which primarily arise by several roots, only the lowest of which persists to form the adult vessel. According to the general plan of the embryonic arterial system thus outlined, the only ves- sels which have primarily a longitudinal course are the dorsal and ventral longitudinal stems, the dorsal aorta, and its prolongation, the a. sacra media. In the adult however, several other longitudinal vessels exist, such, for instance, as the vertebrals, the internal mammaries, and the superficial and deep epigastrics. All these vessels are secondary formations due to the end-to- end anastomoses of upwardly and downwardly directed branches of the lateral segmental ves- sels. The internal mammaries and the epigas- trics (Fig. 746) are formed in this manner from branches of the intercostal arteries, with which they remain connected to a greater or less ex- tent ; the vertebrals are formed from branches of the lateral cervical vessels, and become inde- pendent stems by the separation of these vessels from the dorsal longitudinal stems, as already described. The arteries of the limbs are formed, as already stated, by the lateral somatic brandies of the seventh cervical and fifth lumbar segments respectively, but in both limbs a series of changes is necessary before the adult arrangement is acquired. In the arm the subclavian artery at first extends as a single main stem as far as the carpus, where it terminates by dividing into digital branches for the fingers (Fig. 747, A\. Throughout its course in the forearm it lies between the two bones, resting on the interos- seous membrane, in the position occupied by the adult anterior interosseous artery ; from the upper part of this portion of its course a branch is given off which takes a more super- ficial course, accompanying the median nerve. This median artery gradually becomes larger. Trunk-arteries of embryo of six weeks, showing wh jj e the anter j O r interosseous undergoes a cor- origin of internal mammary (tm) and epigastric arteries (se, superficial, de, deep); a. aorta ; v, vertebral; ct, responding retrogression, and eventually the median, by fusing with the lower portion of the interosseous, forms the main channel for the digi- tal branches and becomes the principal artery of the forearm (Fig. 747, B\ A further stage is marked by the development of the ulnar artery as a branch from the brachial, and this, extending down the ulnar side of the forearm, unites with the median to form a carpal arch from which the digital branches arise ( C). Later there develops high up upon the brachial a superficial brachial artery, which, after traversing the brachiiim, passes down the radial side of the forearm and near the wrist passes to the posterior surface, dividing over the carpus into branches for the d >rsum of the thumb and index-finger. After tin- appearance of the ulnar artery a retrogression of the median begins, whereby it becomes the a. comes nervi mediani of the adult ; a branch, the superficial volar, arises from the lower part <>f the. superficial brachial and passes downward into the palm to unite with the palmar arch already present (D) ; and, finally, a branch arising from the lower part of the brachial anastomoses with the superficial brachial just below the bend of the elbow and together with the antibrachial part of the superficial brachial, forms the radial artery. The upper part of the superficial brachial then degenerates until it is normally represented in the adult by a small branch of the brachial which passes to the biceps muscle (E). In the leg the changes are equally complicated. Primarily it is the sciatic- artery which forms the main stein, extending the entire length of the posterior surface of the limb into the plantar surface of the foot, where it divides into the digital branches (Fig. 71 s . -"'> Tin- ex- ternal iliac at this stage is a relatively slender vessel which extends but a short distance down the thigh and terminates in what is later the profunda femoris. In a later stage there arises from common iliac, continuing as large hypogastric (ft) ; external iliac, giving off deep epigastric and femoral, is still small. X 5- (Mall.) DEVELOPMENT OF THE ARTERIES. 849 the external iliac a vessel (saph} which accompanies the internal saphenous nerve down the leg aiid, entering the foot, takes from the original main stem its digital branches (B). From this saphenous artery a branch is given off which pierces the substance of the adductor magnus mus- FIG. 747 b b Diagrams illustrating development of arteries of upper limb ; b, brachial ; i, interosseous ; rf, digital ; m, median; , ulnar; sb, superficial brachial ; r, radial. -saph Diagrams illustrating development of arteries of lower limb; s. sciatic ; d, digital ; f, femoral ; saph, saphenous ; pop, popliteal ; per, peroneal ; pt, at, posterior and anterior tibial. cle and anastomoses with the sciatic artery just above the upper end of the popliteal space (C), whereupon the portion of the sciatic artery immediately above the anastomosis degenerates and 54 850 HUMAN ANATOMY. the vessel becomes reduced to the slender a. comes nervi ischiadici of the adult. Its lower por- tions, which become the popliteal and peroneal arteries, now seem to be the continuation of the femoral (i.e., the saphenous). From the lower part of the popliteal a branch arises which anastomoses with the saphenous and, together with the lower part of that artery, forms the posterior tibial, the upper part of the saphenous then disappearing except in so far as it is represented by one of the branches of the anastomotica magna. The anterior tibial is a late formation resulting from the fusion of an upper and lower branch from the peroneal which perforate the interosseous membrane (C), the con- nection of the lower branch with the peroneal degenerating after the anastomosis, except in so far as it persists as the anterior peroneal artery THE VEINS. The veins are those vessels which receive the blood from the capillary net-work and return it to the heart. Compared with the arteries, they present many differences, both of structure (page 677) and arrangement. Their walls are much thinner, so that the color of the blood which they contain shows through, and they are readily compressible to the extent of a complete obliteration of their lumen and are also exceedingly dilatable. Notwithstanding their thinness, they are less easily ruptured by over-distention than are the arteries and are capable of undergoing a remarkable elongation, those of an adult withstanding an extension to at least 50 per cent, more than their original length without losing their elasticity a property which explains the more direct course taken by the veins as compared with the arteries in mobile portions of the body (e.g., the facial vein as compared with the artery). Indeed, it seems that the veins when in place in the body are always stretched to a considerable extent, .the cephalic vein, for example, contracting when removed from the body to 40 per cent, of its length in the extended arm (Bardeleben). The most striking structural peculiarity of the veins, however, is the occurrence in them of semilunar valves, arranged usually in pairs, with their cavities directed towards the heart. These valves resemble in their general form the semilunar valves of the systemic and pulmonary aortae, and, as in those vessels, the veins are somewhat enlarged immediately above the attachment of each pair, so that the blood may readily flow behind the valves, force their free margins together and so occlude the vessel. These valves play an important part in directing the flow of blood in the veins towards the heart, since, in the event of any pressure, such as that exerted by a contracting muscle, acting on the vein, they will prevent a backward flow of blood towards the capillaries. Valves do not occur in veins of less than i mm. in diameter and are also lacking in many of the larger trunks, such as the superior and inferior venae cavae, the pulmonary and the portal veins. In general they are more numerous in the veins of the limbs than in those of the trunk and in the deep than in the superficial vessels. Their number in any vessel in which they normally occur is subject to con- siderable variation in different individuals and even on opposite sides of the body in the same subject. It seems probable that this variation is brought about by a degeneration of a greater or less number of the pairs originally present, since in the majority of the veins the number of valves diminishes with age (Bardeleben), and even in adult bodies evidence of degeneration may be seen in the insufficiency of some of the valves or even in their perforation. It is possible, therefore, that the arrangement of the valves in the adult is a secondary condition, derived from one in which the valves were much more numerous and were situated at regular intervals along the vessels. In favor of this view it has been found (Bardeleben) that in certain veins the valves in the adult are separated by intervals either of a definite length or of a multiple of this, the length of the intervals stand'ng in relation to the length of the part or, in general, to the height of the individua 1 in which the vein occurs. Thus, in a man measuring 160 mm. in height, the valves of the right long saphenous vein were separated by intervals which were all approximately multiples of 6.Ss mm. in length, while the intervals separating the valves of the right cephalic vein were approximately multiples of s-2 mm.; and in a male child 81 cm. in height, the valves of the right long saphenous vein were separated by intervals of 3 mm. or some multiple of this. THE VEINS. 851 A more readily appreciable relation of the valves is that which they bear to the branches which open into the vein, a pair of valves being found immediately distal to the entrance of each collateral vein ; and, furthermore, a pair, or at least a single valve, very generally occurs at the termination of a vein, where it enters either a larger stem or the heart. These terminal valves are present in certain veins which other- wise are quite destitute of valves, as, for instance, in the internal jugular, the internal maxillary, and the vertebral veins. It has already been noted that valves are entirely wanting in certain veins. Among these are the sinuses of the cranium, the cerebral, ophthalmic, periosteal, pulmonary, bronchial, portal, renal, uterine, ovarian, and innominate (brachio-cephalic) veins, and the superior and inferior venae cavae. Furthermore, they are usually absent in the common and internal iliacs and in the facial veins, although occasionally they occur in all three. In their position and arrangement also the veins differ noticeably from the arteries. While veins are usually to be found accompanying the arteries, enclosed with them in a common fibrous sheath, additional veins of considerable size are abundant immediately beneath the skin a condition which is almost entirely foreign to the arteries. Furthermore, although in a general way a vein may pursue the same course as an artery, it may lie at some little distance from the latter and fail to follow its course exactly. This is true, for instance, of the facial and the lingual veins and also of the subclavian vein, which is separated from the corresponding artery by the scalenus anticus muscle ; this likewise applies to the veins at the root of the neck which accompany in a general way the branches of the subclavian artery, but open into the innominate vein instead of the subclavian. In many cases the veins which accom- pany arteries are double, one lying on either side of the artery and forming what are generically known as venae comites (venae comitantes ). The causes which determine this double condition are obscure. The arrangement is not found in the larger venous trunks, occurring, for instance, in the leg only below the knee and in the arm only as far up as the middle of the brachium ; size alone, however, does not seem to be the determining factor, since the internal mammary and epigastric veins are double, while the intercostal and lumbar veins, almost of the same size as the former, are single. Nor does the quality of the tissue in which the veins occur determine their duplication, for those which are embedded within the muscles of the tongue are doubled, while those within the heart musculature are single ; again, while, as a rule, the veins which occur in fibrous tissue as, for instance, the menin- geal veins are double, yet those of the skin are single. Finally, it may be noted that there are exceptions to the rule that the veins which occur in the cavities of the body are single, since a duplication is found in the spermatic veins and also in those of the gall-bladder. Not only doubling of many of the veins occurs, but a prevailing tendency exists towards extensive anastomoses far surpassing that displayed by any of the arteries. Even in the cases of the larger proximal trunks communications exist, those between the pulmonary and bronchial veins and that between the superior and inferior venae cavae by way of the azygos being examples. In the smaller vessels the anastomoses are often so numerous as to result in the formation of plexuses. Venae comites are united by frequent cross-connections, sometimes so numerous as to present the ap- .pearance of a plexus surrounding the artery. Complicated venous plexuses also accompany the various ducts of the body, as, for example, the parotid ducts, the ureters, and the vasa deferentia. In addition, extensive venous plexuses occur in various regions of the body, as in the neighborhood of its orifices, in the terminal phalanges of the fingers and toes, in the diplo of the skull, in the spinal canal, in the pelvis, and in connection with the genito-urinary organs. Since the larger trunks usually arise at several points both from these and from the wider-meshed plexuses occurring elsewhere, opportunity is thus afforded for the return of the blood to the heart by different paths an arrangement explaining the frequent ineffi- ciency of a ligation of even large trunks to prevent venous hemorrhage. Special mention should be made of one set of the venous channels namely, the sinuses of the dura mater which establish communication between the cerebral and ophthalmic veins and the internal jugular. They are channels contained within 852 HUMAN ANATOMY. the dura mater, lined by an endothelium similar to and continuous with that of the cxtracranial veins, but lack any extensive development of elastic fibres in their walls, which are formed by the dura. They possess no valves, although in certain of them, as in the superior longitudinal and cavernous sinuses, the lumen is traversed by irregular trabeculae of fibrous tissue. These are especially well developed and almost tendinous in character in the superior longitudinal sinus, while in the cavernous sinus they are softer, and from them and from the walls of the sinus fringe-like prolongations, .5-2 mm. in length, project freely into the lumen. Connected with certain of these sinuses and developed from certain of the smaller veins which open into them are so-called blood-lakes ( lacunae) cavities or plexuses in the dura mater, lined with endothelium, and connecting either directly or by means of a short canal with an adjacent sinus. They are usually situated more or less sym- metrically with reference to the sinus with which they are connected, and some are very constant in occurrence. Thus, a certain number usually occur on either side of the superior longitudinal sinus (page 1199), others in the tentorium cerebelli con- necting with the lateral sinus, others in the middle fossa of the skull along the course of the meningeal veins, and others in the vicinity of the straight sinus. They occasion- ally reach a considerable size, bulging outward the dura which encloses them and excavating by absorption irregular depressions upon the inner surface of the skull. Occasionally this absorption of the cranial bones proceeds so far that bulging of the outer table of the skull over a lake takes place, and, in the case of those occurring along the course of the superior longitudinal sinus, Pacchionian bodies developed from the subjacent arachnoid tissue may invade them, pushing before them the attenuated floors of the lakes. Classification of the Veins. Theoretically a description of the veins should start with the peripheral vessels and proceed towards the great trunks, following the course of the blood. Such a method would prove, however, somewhat confusing, largely on account of the numerous anastomoses that occur ; it is preferable, therefore, to base a classification primarily upon the great trunks and to consider their afferents topographically, according to the areas which they drain. From the embryological stand-point, there are primarily four great systems of veins : ( r ) the cardinal system, represented by the vena cava superior and its tributa- ries ; (2) the inferior caval system; (3) the portal system ; and (4) the pulmonary system. Owing to subsequent changes, it is necessary to recognize in the cardinal system three sub-systems : (i) that of the cardiac veins ; (2) that of the superior vena cava and its tributaries, except (3) the azygos veins. In all, then, six great systems of veins may be recognized in the adult. They are as follows : 1. The pulmonary system. 2. The cardiac system. ) 3. The superior caval system. V The cardinal system. 4. The azygos system. ) 5. The inferior caval system. 6. The portal system. In the descriptions which follow the veins are considered on the basis of this classification. THE PULMONARY SYSTEM. THE PULMONARY VEINS. The pulmonary veins (venae pulmonales) (Figs. 749, 750) are four in number, two passing from the hilum of each lung to the posterior surface of the left auricle <>f the heart. Each vein is formed at the hilum of its lung by the union of a number of smaller vessels which take origin ultimately from the capillary net-work formed by the branches of the pulmonary artery and to a certain extent from that formed by the bronchial arteries. The arrangement of the afferent branches in the substance of the lungs is described in connection with the anatomy of these organs (page 1854), aml it will be sufficient to note here that they correspond i'i number to the branches of the pulmonary artery and of the bronchi, and pursue a course more or less independent of these, which He side by side. Converging and uniting as they pass towards the hilum. the branches from the superior lobe of each lung unite to form the superior THE PULMONARY VEINS. 853 pulmonary vein of that side, those from the inferior lobe unite to form the in- ferior pulmonary vein, while those from the middle lobe of the right lung unite to form a single trunk which usually opens into the right superior vein, although it occasionally opens independently into the left auricle, forming what is then termed the middle pulmonary vein. Each of the four pulmonary veins has a length of about 15 mm., and for about one-third of its course is partially invested by the visceral layer of the pericardium (page 715). The right superior vein is usually slightly the largest of the four, while the left superior is the smallest, the right and left inferior veins being about the same size. No valves occur either throughout the course or at the orifices of the pulmonary veins. Relations. The superior pulmonary veins have a course which is obliquely downward and inward. In their extraperitoneal portion they lie anterior to and below the pulmonary arteries, and are separated by them from the bronchi ; the FIG. 749. Right innominate vein on carotid artery Left subclavian artery Left pulmonary artery Left auric- ular ap- pendage Conus arteriostis tricular 'branches of left coronary vessels Left ventricle Aorta, systemic Left coronary artery Right coronary vessels Right ventrid Injected heart and great vessels, viewed from before ; parts of superior vena cava and aorta have been removed to show right pulmonary artery. vein of the right side is crossed from above downward by the phrenic nerve and by the vena cava superior. In its intrapericardial portion the right superior vein lies behind the terminal portion of the superior vena cava and the left one behind the pulmonary aorta (pulmonary artery), while posteriorly each is in relation with its corresponding inferior vein. The inferior veins are more horizontal in position, but are directed forward as well as inward. They lie in a plane considerably posterior to that of the corresponding superior veins and are situated internally to and behind an anterior descending branch of each bronchus. Anastomoses. In addition to serving for the return flow of the blood carried to the lungs by the pulmonary arteries, the pulmonary veins also receive a certain amount of the blood carried by the bronchial arteries. Communications between 854 HUMAN ANATOMY. the bronchial and pulmonary veins in the region of the smaller bronchi are abundant, and, in addition, the main stems of the pulmonary veins receive at the hilum of the lung one or more branches from the larger bronchial veins. They also receive com- munications from the venous plexus which surrounds the thoracic aorta in the pos- terior mediastinum, and occasionally also a vein from the pericardium. There is thus a certain commingling of venous blood with the arterialized blood which forms the principal contents of the pulmonary veins. Variations. At one stage in the development of the embryo the veins from each lung converge to a single short trunk before opening into the portion of the atrium which corresponds to the left auricle. As the development of the heart proceeds, this trunk is gradually taken up into the auricle, until the two stems which unite to form it open independently into that structure. An inhibition of this process occasionally obtains, so that but a single vein, repre- senting the original terminal trunk, opens into the auricle from one lung or from both. On the other hand, the taking up of the pulmonary vein into the wall of the auricle may proceed further than usual, or, to state it perhaps more correctly, the union of the various stems emerging from the hilum of the lung may be partly delayed until they have reached the original terminal trunk, so that when this is taken up into the auricle an additional vein will open independently into the latter. This extra vein is most frequently that from the middle lobe of the right lung, but three distinct veins have also been observed upon the left side. THE CARDINAL SYSTEM. The cardinal system of veins is so named because its main trunks are the repre- sentatives of the cardinal veins of the embryo. These veins are four in number, disposed symmetrically in pairs, two returning the blood from the head, neck, and upper extremities, while the other two return that from the thoracic and abdominal walls, from the thoracic viscera, and from the lower extremities. Just before they reach the heart, the superior and inferior or posterior cardinal veins of each side unite (Fig. 776) to form trunks known as the ducts of Cuvier, the two ducts opening independently into the primitive right auricle. By a series of changes, which are described more fully in the section on the development of the veins (page 927), the left superior cardinal becomes connected with the right at the base of the neek, the stem so formed constituting what is termed the superior vena cava. The portion of the left superior cardinal between the connecting .vessel and the heart becomes greatly reduced in size, indeed, almost completely degenerates ; the left duct of Cuvier, however, persisting as the coronary sinus, which receives the coronary veins returning the blood from the heart's walls. On the development of the vena cava inferior the veins of the lower extremity make connection with it, separating from the inferior cardinals; these latter become considerably reduced in size, especially in the abdominal region, a cross-connection develops between the left and right veins, and the former severs its connection with the left ductus Cuvieri, the final result being the formation of the venae azygos and hemi-azygos of the adult. There are, then, developed from the cardinal veins of the embryo three sub- systems of yeins : (i) that of the cardiac veins ; (2) that of the superior vena cava, which includes the jugular and subclavian groups of veins, the original superior cardinals being represented by the internal jugular veins ; and (3) the azygos sub- system. These will be considered in the order in which they have been named. THE CARDIAC VEINS. THE CORONARY SINUS. The coronary sinus (sinus coronarius) (Fig. 750) is a short venous trunk about 3 cm. (a little over an inch) in length, which occupies the right half of that portion of the posterior auriculo-ventricular groove which lies between the left auricle and ventricle. At its right end it opens into the right auricle, its orifice (Fig. 657) being situated upon the posterior surface of the auricle-, below that of the inferior vena cava, and beinu guarded by tin- Tln-bcsian ;vi/;r ( valvula sinus coronarii). At its left end it receives tin great coronary vein, from whose proximal portion it is not always clearly distinguish* able upon superficial examination. A close inspection usually reveals, ho\\ever, either a constriction or a slight dilatation at the union of the two vessels, and on THE CARDIAC VEINS. 855 laying them open a distinct valve, of either one or two cusps, but usually insuffi- cient, will be found at their line of junction. This valve is known as the valve of Vieussens. Furthermore, the walls of the sinus differ from those of the vein in pos- sessing a complete layer of muscular fibres, both oblique and circular, continuous with the musculature of the auricle. In addition to the great coronary vein, the coronary sinus also receives the posterior vein of the left ventricle and the middle cardiac vein, which open into it from below, and the oblique vein of the left auricle, which passes to it from above. Variations. The coronary sinus, as already stated, represents the left ductus Cuvieri of the embryo. It varies somewhat in length, reaching in extreme cases a length of 5.4 cm. It has been observed to be obliterated at its entrance into the right auricle, the great coronary vein then opening into the left innominate ( brachio-cephalic) vein, and, in addition to the veins already noted as emptying into it, it frequently receives the marginal vein of the left ventricle. i. The Left Coronary Vein. The great cardiac or left coronary vein (v. cor- dis magna) (Fig. 749) begins upon the anterior surface of the heart at the apex, where it anastomoses with the veins of the posterior surface, and ascends the anterior FIG. 750. Left pulmonary artery Superior left pulmonary vein Inferior left pulmonary vein Termination of \ eft coronary vein Transverse branch of left coronary artery Left ventricle Superior vena cava Superior right pulmonary vein Right pulmonary artery nferior right pulmonary vein Inferior vena cava Coronary sinus Right coronary vein Transverse branch of right coronary artery Posterior descending branch of right coronary artery Middle cardiac vein Right ventricle Posterior-inferior aspect of injected heart, showing blood-vessels. interventricular groove in company with the left coronary artery, to the anterior auriculo-ventricular groove, in which it passes to the left and, curving around the left border of the heart to the posterior surface, terminates by opening into the left end of the coronary sinus. In the vertical portion of its course it receives veins from the anterior surface of both ventricles, and in its course in the auriculo-ventricular groove, throughout which it is embedded in the fat which usually occupies the groove, it receives a number of small veins from the surfaces of both the left auricle and ventricle. Among those from the ventricle there is especially to be mentioned, as larger and more constant than the rest, the vena marginalis sinistra, which ascends along the left border of the heart and empties into the great coronary vein shortly before its opening into the sinus. 856 HUMAN ANATOMY. 2. The Posterior Cardiac Vein. The posterior cardiac vein (v. posterior ventriculi sinistri) ascends along the posterior surface of the left ventricle, lying about midway between the left border of the heart and the posterior interventricular groove and receiving collateral branches from the walls of the ventricle. It opens above into the coronary sinus near the point of entrance of the great coronary vein and occasionally unites with that vessel. 3. The Middle Cardiac Vein. The middle cardiac vein (v. cordis media; (Fig. 750) occupies the posterior interventricular groove, accompanying the right coronary artery. It arises in the vicinity of the apex of the heart and ascends, receiving collateral branches from the posterior surfaces of both ventricles, to open into the coronary sinus near its termination. This, next to the great coronary vein, is the largest vein of the heart, and occasionally opens independently into the right auricle close to the entrance of the coronary sinus. 4. The Right Coronary Vein. The small cardiac or right coronary vein (v. cordis parva) (Fig. 750) occupies, when present, the right half of the posterior auriculo-ventricular groove and opens into the coronary sinus just before its termi- nation. Occasionally it opens into the middle cardiac vein, or directly into the right auricle, and is not infrequently lacking as a distinct vessel, the tributaries which empty into it from the posterior surface of the right auricle and the upper part of the posterior surface of the right ventricle then opening directly into the auricle. One of the largest and most constant of these tributaries ascends along the right border of the right ventricle and is termed the right marginal vein or vein of Galen. 5. The Oblique Vein of the Left Auricle. The oblique vein of the left auricle (v. obliqua atrii sinistri), also known as Marshall' s vein, is a small vein of variable development which descends obliquely over the posterior surface of the left auricle and opens below into the coronary sinus. Above, it is continuous with a fibrous cord contained within the vestigial fold of the pericardium (page 716), the cord and vein together representing the lower part of an original left superior vena cava. The degree of development of the vein varies greatly, and occasionally the fibrous cord retains its original lumen, so that a more or less developed left superior vena cava is really present. This anomaly may, however, be more conveniently considered in connection with those of the superior caval system of veins (page 859). In addition to these principal veins of the heart there is a varying number of others which open directly into the right auricle and are situated upon the anterior surface of the right ventricle, whence they have been termed the anterior cardiac veins (vv. cordis anteriores). They are all comparatively short vessels and usually accompany descending branches of the right coronary artery. Owing to the fre- quency with which it opens directly into the auricle, the vein of Galen is usually regarded as one of this group of veins. Finally, the Thebesian veins ( vv. cordis minimae) form part of the cardiac venous system. These are minute veins, imbedded in the substance of the In art walls, and communicating with the heart cavities by means of the Thebesian foramina (page 716), -which occur most abundantly upon the walls of the right auricle, though also upon those of the left auricle, and, less abundantly, upon those of the ventricles. At their other ends these veins communicate in the heart's substance with the radicles of the other cardiac veins, and, in cases of stenosis of the coronary arteries, may consequently contribute to some extent to the nutrition of the heart musculature, carrying blood to it directly from the heart cavities. Valves of the Cardiac Veins. The Thebesian vafae, which guards the right auricle, may be considered as the ostial valve of that vessel, which throughout course is destitute of valves. So, too, throughout the extent of the cardiac veil valves are entirely lacking, but certain of those which open into the coronary si are provided with ostial valves. That of the threat coronary vein is the- ra/rc o VieitsscHs, and others are usually present at the mouths of the middle vein and tin posterior vein of the left ventricle, and less constantly at the mouths of the marginal and the small coronary veins. These valves may be either single or paired and are frequently insufficient. No valves are present either throughout the course or at the orifice of the oblique vein of the left auricle. THE SUPERIOR CAVAL SYSTEM. 857 Variations. The principal variations which occur in connection with the cardiac veins have been noted in the description of the vessels, and it need only be added that the oblique vein of the left auricle is not infrequently entirely lacking, except in so far as it is represented by a fibrous cord, that absence of the great coronary vein has been observed, and that the middle vein occasionally opens directly into the right auricle. THE SUPERIOR CAVAL SYSTEM. THE VENA CAVA SUPERIOR. The superior or descending vena cava (Figs. 749, 751) is the main venous trunk which delivers to the heart the blood returning from the head, neck, upper limbs, and thorax. It measures 7-8 cm. (3 in. ) in length, and has a diameter at its termination of about 2. 2 cm. (a little less than i in. ). It is situated throughout its entire course in the thoracic cavity, lying in the superior mediastinum, and is formed immediately FIG. 751. Anterior jugular \e Transverse cervical vein Clavicl. Suprascapular v Right inferior thyroid vein 1. right posterior intercostal mammary vein Left internal jugular vein Scalenus anticus muscle External jugular vein Left subclav Clavicle Right auricular append Right coronary or small cardiac vein Right lung, mesial surface Left inferior thyroid vein I. rib Left innominate vein Superior intercostal vein I. left posterior intercostal ^Internal mammary vein Aorta Line of pericardia! reflection R. and L. pulmonary arteries A division of left bronchus Pulmonary artery 'Left pulmonary vein Bronchus Left auricular appendix I .eft coronary or great cardiac vein Left lung, mesial surface Diaphragm, thoracic surface Dissection showing innominate veins and superior vena cava in position ; lungs have been pulled aside. below the lower border of the first costal cartilage of the right side by the union of the right and left innominate (brachio-cephalic) veins. Its course is downward and slightly backward, with a curvature corresponding to the first portion of the arch of the aorta, with which it is in relation. Below, it opens into the upper posterior portion of the right auricle on a level with the third costal cartilage of the right side. Relations. The lower portion of the superior vena cava is invested by the peri- cardium to an extent varying from a few to 40 mm. , on an average, perhaps to about one-third its length. The upper extrapericardial portion is in relation anteriorly 8 5 8 HUMAN ANATOMY. with the thymus gland or the fatty tissue which replaces it, and is overlapped by the right pleura and lung. Behind, it crosses the origin of the right bronchus and the structures at the root of the right lung, from which it is separated by numerous lymphatic nodes ; to the right it is in contact with the pleura covering the inner surface of the right lung and with the right phrenic nerve ; and to the left it lies alongside the ascending portion of the aortic arch. In its lower intrapericardial portion it has to the left the systemic aorta: anteriorly, the right auricle; posteriorly, the right pulmonary artery, the right superior pul- monary vein, and the right bronchus, while upon the right it is free. The vena cava superior contains no valves. Tributaries. In addition to the right and left innominate veins, by the union of which it is formed, the vena cava superior receives the vena azygos major and small veins from the mediastinum and pericardium. Variations. Cases have been recorded in which the vena cava superior received the right internal mammary or the right superior intercostal vein which normally open into the right innominate vein. It may also receive the vena thyreoidea ima, a vein only occasionally present and draining the territory supplied by the art. thyreoidea ima. A more remarkable and rarer variation is the union with the superior vena cava of a com- paratively large vein which issues from the right lung. A similar condition has been observed in connection with the innominate veins, and its probable significance will be considered in connection with the variations of those vessels. Practical Considerations. The superior vena cava would be involved in a stab-wound passing through either the first or the second intercostal space on the right side, close to the sternum. The vessel is subject to compression in aneurism of the ascending aorta ( in.) and an almost vertical course, opening directly downward into the vena cava superior. It lies behind the inner end of the right clavicle, from which it is separated by the lower portions of the sterno-hyoid and sterno-thyroid muscles, and a little lower it is behinc the first right costal cartilage. ...To the right it is in relation with the inner surfac of the right pleura and with the right phrenic nerve, to the left with the brachic cephalic artery and right pneumogastric nerve, and behind with the pleura. The left innominate vein has a length almost double that of the right, meas- uring 5-9 cm. (2-3^-2 in.) from its origin behind the sternal end of the left clavicle to its union with the right vein to form the vena cava. Its course is transverse from left to right and at the same time slightly downward, and it extends completely across the uppermost part of the thoracic cavity, resting below upon the aortic arch, and passing in front of the left subclavian and common carotid arteries, the trachea, the brachio-cephalic artery, and the pneumogastric nerve. It is separated from the manubrium sterni by the insertion of the sterno-hyoid and sterno-thyroid muscles and by the fatty tissue representing the thymus gland, and, being on a level with or slightly above the upper border of the manubrium, it can usually be felt in the supra- sternal fossa. Neither of the innominate veins possesses valves. The left is of somewhat greater diameter than the right, owing to the greater number of tributaries which it receives. THE SUPERIOR CAVAL SYSTEM. 859 Variations. As pointed out in the account of the development of the great veins (page 926), there is at one stage a symmetrical arrangement of the vessels which open into the right auricle from above ; in other words, the left internal jugular is continued directly downward from the point where the left subclavian vein opens into it to the auricle, this downward continuation bein" usually termed the left superior vena cava. Later a cross-connection, the left innominate veinrforms between the right and left jugulars at the root of the neck, and the left superior vena cava then normally undergoes degeneration, traces of it only persisting as the oblique vein of the left auricle and the coronary sinus. Occasionally this normal progress of events fails to occur, the result being the complete absence or imperfect development of the left innominate vein together with a persistence of the Irft superior vena cava ; or else, even with the perfect development of the.left innominate, there may be a failure of the left superior vena cava to degen- p IG 7^2. erate. Various gradations between the embryonic and adult conditions may occur, and the annexed diagram (Fig. 752) shows the nature of the anomaly. It may be noted that with the persist- ence of the left superior vena cava there is frequently a retention of the communica- tion with it of the left cardinal vein, which normally be- comes the v. hemi-azygos, a condition which will be more especially considered in con- nection with the anomalies of the azygos veins ( page 893 ) . Left internal jugular L. subclavian L. innominate L. sup. vena cava L. azygos L. pulmonary arter Coronary sinus Right int. jugular R. subclavian R. innominate R.sup. vena cava R. azygos julmonary artery ulmonary veins Practical Consid- erations. The left in- nominate vein, running horizontally just below the upper border of the ma- nubrium, lies immediately above the aortic arch. When the latter is unusually high, and occasionally in children, the vein especially if engorged may project above the level of the suprasternal notch and may be endangered during a thyroidectomy, the removal of a tumor, or a low tracheotomy. Inf. vena cava Posterior aspect of heart and great vessels, showing persistence of left superior vena cava ; (semidiagrammatic). Tributaries. In addition to the subclavian and internal jugular veins, by whose union they are formed, each innominate vein receives (i) the deep cervical, (2) the vertebral, (3) the internal mammary, and (4) the inferior thyroid veins of its side. The left innominate vein receives in addition (5) the superior phrenic, (6) the thymic, (7) the pericardial, (8) the anterior mediastinal, and (9) the left superior intercostal vein. Of these' the left superior intercostal vein will be described with the other intercostals. i. The Deep Cervical Vein. The deep cervical vein (v. cervicalis profunda) takes its origin in a plexus situated in the occipital triangle and having also con- nected with it the vertebral and occipital veins. It passes down the neck, lying be- tween the semispinalis cervicis and the splenius cervicis, and in the upper part of its course accompanies the deep branch of the art. princeps cervicis. Lower down it accompanies the deep cervical branch of the superior intercostal artery and bends slightly outward and forward, passes between the transverse process of the seventh cervical vertebra and the first rib, and opens into the innominate vein either behind the vertebral vein or by a common trunk with that vessel. Tributaries. In its course down the neck it receives numerous tributaries from the deeper cervical muscles, and opposite each intervertebral foramen which it passes it makes connections with the vertebral vein and the veins of the spinal canal. The most important of its tributaries is, however, the occipital vein, which arises in a plexus covering the occipital portion of the skull and communicating with branches of the pos- terior auricular and temporal veins. It passes downward with the occipital artery, pierces the 86o HUMAN ANATOMY. trapezius muscle near its origin from the superior nuchal line, and enters the suboccipital tri- angle where it opens into the deep cervical vein. Occasionally, however, it either unites with the posterior auricular vein or opens directly into the external jugular below the posterior auricular. The mastoid emissary vein (page 876) usually opens into one of its branches. 2. The Vertebral Vein. The vertebral vein (v. vertebralis) accompanies the artery of the same name through all but the cranial portion of its course, and is usually a single trunk, although frequently it is double or occasionally even plexiform throughout more or less of its course. It arises in the suboccipital triangle from a plexus of small veins with which the occipital and deep cervical veins also communi- cate, and passes downward through the foramina in the transverse processes of the six (occasionally seven or five or even only four) upper cervical vertebne. At its exit from the foramen of the sixth vertebra it is continued obliquely forward and down- ward behind the inferior thyroid artery and the internal jugular vein, and, passing usually in front of, but occasionally behind, the subclavian artery, opens into the innominate vein near its origin. The opening into the innominate is guarded by a pair of valves. Throughout its course the vein is connected to the periosteum, lining each of the vertebra-arterial canals it traverses, by fibrous bands, and in its terminal portion it is adherent to the deep cervical fascia, so that its walls do not collapse even when it is emptied of blood. Tributaries. Like the vertebral artery, the vein receives tributaries from the deep mus- cles of the neck and, at each intervertebral foramen which it passes, communicating branches from the plexuses in the spinal canal on the one hand, and from the posterior spinal plexus and the deep cervical vein on the other. In its terminal portion, after it has issued from the fora- men in the transverse process of the sixth cervical vertebra, it receives the ascending cervical vein, which arises in the plexus upon the anterior surfaces of the bodies of the upper cervical vertebrae, and accompanies the ascending cervical artery down the neck. Very frequently it also receives, shortly before its termination, the deep cervical vein. 3. The Internal Mammary Vein. The internal mammary vein (v. niamma- ria interna) is formed by the union of the venae comites of the musculo-phrenic and superior epigastric arteries, and throughout the greater part of its course is double, one stem lying along the outer and the other along the inner side of the artery in its course along the inner surface of the anterior thoracic wall. Opposite the second or third intercostal space the two stems unite, the single vein so formed lying to tin- inner side of the artery and opening above into the innominate vein of the same side. Numerous valves occur in the course of the vein. Tributaries. The tributaries of the internal mammary veins correspond in general with the branches of the internal mammary artery, with the exception of the superior phrenic, medi- astinal, pericardia!, and thymic branches, which usually open independently into the left innom- irtate vein. Its sternal branches form plexuses upon both surfaces of the sternum, and so form communication with the vein of the opposite side, and the anterior intercostal branches unite with the posterior intercostals ( page 896) . The perforating branches assist in returning the blood from the pectoral muscles, those of the first and second intercostal spaces being larger than the rest in the female, and serving to return a considerable portion of the blood from the mammary gland. By means of the superior epigastric branches the internal mammary makes connection with the subcutaneous veins of the abdomen, and, since these are also connected with the epigastric and circumflex iliac branches of the iliac veins, an anastomosis is formed between the superior and inferior caval systems of veins. 4. The Inferior Thyroid Veins. The inferior thyroid veins (vv. thyreoideae inferiores) have their origin in a venous plexus (plexus thyrcoidcus impar ) which covers the anterior surface and sides of the trachea immediately below the isthmus of the thyroid gland, the vessels which form the plexus issuing from the substance of the thy- roid gland, or in some cases being downward prolongations of the branches of origin of the superior thyroid veins. From the plexus two or sometimes three veins descend the neck, following paths quite distinct from those of the inferior thyroid arteries, and open below into the innominate veins, their orifices being guarded by valves. When three veins are present, the odd one occupies a median position and is known THE SUPERIOR CAVAL SYSTEM. 86 1 as the vena thyreoidea ima, corresponding to the artery of the same name, which, however, need not be present with it. It opens usually into the" left innominate vein, but occasionally is prolonged inward to terminate in the superior vena cava. Tributaries. The plexus thyreoideus impar receives communications from the superior thyroid veins and also has opening into it the inferior laryngeal veins (vv. laryngeae inferiores) which descend from the larynx. The inferior thyroid veins receive directly branches from the trachea (vv. tracheales) and from the oesophagus (vv. cesophageae). Practical Considerations. An incision across the inferior thyroid vein, whose walls, being imbedded in inflamed tissue, could not collapse, has caused sudden death by the entrance of air. Parise, in attempting to seize the divided inferior thyroid vein during tracheotomy, lifted the superficial wall only, thus per- mitting air to enter the vein with a fatal result (Allen). 5. The Superior Phrenic Vein. The superior phrenic vein (v. phrenica superior) has its origin upon the upper surface of the diaphragm and ascends through the thorax, lying between the pericardium and pleura and accompanying the phrenic nerve and the superior phrenic artery, of which it is a companion vein. Usually the veins of both sides are double. They open above into the left innominate vein, fre- quently uniting with the thymic, pericardial, and mediastinal veins before their termi- nation. They are provided with valves both at their orifice and along their course. 6. The Thymic Veins. The thymic veins (vv. thymicae) are rather insig- nificant in the adult and are usually two or three in number. They arise in the adipose tissue which replaces the thymus gland and empty above into the left innomi- nate vein, frequently uniting with the superior phrenic veins. In the child they are of considerable size in correlation with the development of the thymus gland. 7. The Pericardial Veins. The pericardial veins (vv. pericardiacae) vary considerably in number. They are all small, and empty in part into the left innomi- nate vein and in part into the azygos and internal mammary veins. 8. The Anterior Mediastinal Veins. The anterior mediastinal veins (vv. mediastinales anteriores ) ,' like the preceding, are variable in number and small. They arise in the anterior mediastinum and open above into the left innominate vein. THE INTERNAL JUGULAR VEIN. The internal jugular vein (v. jugularis interna) (Figs. 753, 760) is the principal venous trunk of the neck. It is the continuation of the lateral sinus at the jugular foramen, and descends the neck in company with the internal and common carotid arteries to a point a little external to the sterno-clavicular articulation, where it unites with the subclavian to form the innominate vein. At its origin it rests upon the anterior sloping surface of the jugular process of the occipital bone, .and usually presents at this point a distinct bulbous enlargement (bulbus venae jugularis superior) measuring about 1.5 cm. in diameter. Below the bulbus superior, at its exit from the jugular foramen, the diameter of the vein averages about 9 mm., although subject to consider- able variation, and usually differing on the two sides, since the lateral sinuses, of which the veins are the continuations, differ on the two sides, that of the right being in the majority of cases the larger. As it descends the neck the vein gradually increases in size as it receives its various tributaries, and just before its union with the subclavian vein it presents a more or less pronounced spindle-shaped enlargement (bulbus venae jugularis inferior). This dilatation is usually much more distinct in the right vein than in the left, and at its upper end is provided with a pair of valves or else with a single one, the cavities of the valves being directed downward as if to prevent an upward flow of blood. Even when a pair is present they are insufficient, but they may nevertheless play an important part in preventing the blood from flowing into the innominate through the subclavian vein and from producing, during the systole of the auricle, a back pressure in the cerebral veins which are in connection with the internal jugular. Since the right innominate is much more nearly in a line with the vena cava superior than is the left, the greater development of the inferior bulb in the right internal jugular can be readily understood. 862 HUMAN ANATOMY. Relations. In the upper part of its course the internal jugular rests upon the rectus capitis lat'eralis and the transverse processes of the upper cervical vertebrae. To its inner side and somewhat in front of it is the internal carotid artery, the glosso- pharyngeal, pneumogastric, spinal accessory, and hypoglossal nerves separating the two vessels above. The external branch of the spinal accessory crosses it obliquely either in front or behind, and somewhat lower it is crossed anteriorly by the stylo- hyoid muscle and the posterior belly of the digastric and also by the occipital and posterior auricular arteries. To its inner side is the wall of the pharynx, with which it is not, however, directly in contact. Throughout the neck it lies beneath the sterno-cleido-mastoid muscle, imme- diately to the outer side of the common carotid artery, being enclosed in a common Superficial temporal veta\ FIG. 753- Posterior auricular vein- External auditory meatu Mastoid vein Occipital vein Internal maxillary vein Temporo-maxillary vein Posterior trunk of temporo- maxillary vein Anterior trunk of temporo- maxillaryvem External jugular vein Lingual vein Internal carotid artery Internal jugular vein Posterior external jugular vein Superior thyroid vein Common carotid artery \ Temporal muscle, cut Internal maxillary vein Facial vein Communication bel lin- gual and anterior jugulai Middle thyroid vein Left innominate veil Subclavian vein Innominat Left snierior intercostal vein e artery Right innominate vein Dissection showing; deep veins of neck and hea'd. sheath with it, as is also the pneumogastric nerve, which lies behind and between the two vessels. Below the omohyoid muscle the vein tends to separate from the artery, passing somewhat more anteriorly. In this part of its course it, or, to be more pre- cise, tin- inferior bulb, is situated immediately behind the space which separates the two heads of the sterno-cleido-mastoid. Behind, it rests upon the inner border of the scalenus anticus, crosses the subclavian artery, and has the pneumogastric and phrenic nerves passing downward on either side. Variations. Variations of the internal jus^'hir vein are not numerous. It may be noted, however, that in its course down the neck it occasionally overlaps tin- carotid artery to a con- siderable extent, a condition which is especially marked in the region of the inferior bulb when this is well developed. THE SUPERIOR CAVAL SYSTEM. 863 The left internal jugular has been observed much reduced in size, there being a compen- satory enlargement of the corresponding external jugular, and it may be doubled throughout a greater or less portion of its course, although always single at either extremity. In addition to the normal tributaries described below, it may receive the temporo-maxillary vein, the verte- bral superior laryngeal, or left superior intercostal, a bronchial vein, the suprascapular, or the transverse cervical vein. Practical Considerations. The internal jugular vein the largest of the superficially placed veins of the body may be involved in cut-throat or other wounds of the neck. Like the carotid, it usually escapes in attempts at suicide on account of the usual position assumed with the chin elevated and the head thrown back so that the muscles are rendered tense and prominent and the vessels are protected. If the wound is above the thyroid cartilage they are still safer on account of their inclination backward, and such a wound may reach the spinal column without injuring them. In wounds below the thyroid if the air passages are opened in attempted suicide, the sudden exit of air from the lungs, accompanied by collapse of the chest, may, it has been suggested, result in the dropping of the arm carrying the weapon before the wound has reached the level of the vessels, although they are here more vulnerable than they are above. The internal jugular, the other veins of the neck, and the subclavian and axillary veins, are greatly influenced by respiration, emptying during inspiration, distending during expiration the ' ' respiratory wave, ' ' or " venous pulse." Their attachments to the fascia keep them from entirely collapsing. This is especially noticeable in the internal jugular. After the carotid sheath has been opened the vein will vary in appearance from a distended thin-walled tube perhaps half an inch in diameter, (expiration), to a flaccid, ribbon-like structure with walls apparently in contact (inspiration). During inspiration air may thus be readily drawn into one of these veins if it has been wounded, and if the wound is dry, or if pressure is not immediately applied to the vein on the cardiac side of the wound. If the air is in large quantity it may cause instant death when it reaches the right auricle by over- distension and paralysis of the right side of the heart ; or sometimes less rapidly by asphyxia following air embolism of the pulmonary veins. The internal jugular vein may be infected secondarily to infective intracranial sinus thrombosis, especially of the sigmoid. Phlebitis or thrombosis of the internal jugular is attended by pain and tenderness along the course of the vein; and later by the development of a cord-like- mass to the inner side of the sterno-mastoid muscle and the outer side of the carotid artery. This may involve the whole length of the vein but is apt to be confined to the upper third. When an infected thrombus in the sigmoid sinus has undergone such extensive disintegration that it is unlikely to be entirely removed by operative obliteration of the upper two-thirds of the sinus, or when in a thrombosed internal jugular, giving the sensation of a hard cord-like struc- ture, its upper part becomes soft from disintegration of the thrombus and this disin- tegration descends, ligation of the vessel below this point usually becomes necessary (Macewen). The ligation shuts off the main channel between the sigmoid sinus and the lungs, although the latter may still be infected by way of the occipital sinus and condylar veins and the subclavian vein. The vessel is approached by the same incision as that made for ligation of a caro- tid. The vascular sheath is opened well to the outer side so that the carotid com- partment may, if possible, be left intact. The vein should be tied in two places and divided between the ligatures. After occlusion of the vein either by ligature or by pressure from a growth, the blood from the corresponding side of the head passes by a transverse vein to the internal jugular of the opposite side. Tributaries. In addition to the lateral and the inferior petrosal sinuses, which will be described with the other cranial sinuses, the internal jugular receives the following tributaries : (i) the pharyngeal, (2) the facial, (3) the lingual, (4) the superior thyroid, and (5) the middle thyroid veins. i. The Pharyngeal Veins. The pharyngeal veins (vv. pharyngeae) are small vessels, varying in number, which open, either independently or after having united to a single stem, either directly into the internal jugular or indirectly by way of the 864 HUMAN ANATOMY. lingual or superior thyroid vein. They take their origin from a venous plexus (plexus pbaryngetts) which covers the outer surface of the pharynx, lying between the constrictor muscles and the pharyngeal portion of the bucco-pharyngeal fascia. In addition to branches from the pharyngeal wall, this plexus also receives tributaries from the anterior recti and longus colli muscles, and from the soft palate, the tonsillar plexus and the Eustachian tube, and has opening into it branches from a plexus which surrounds the internal carotid artery in its course through the carotid canal, communi- cating above with the cavernous sinus. It also receives the veins ( vv. canal is pterygoidei) which accompany the Vidian artery through its canal, and communicates with the pterygoid, cesophageal, and vertebral plexuses. 2. The Facial Vein. The facial vein (v. facialis anterior) (Fig. 754) is formed at about the inner extremity of the eyebrow by the union of the frontal and supraorbital veins. From its point of origin it skirts around the inner border of the orbit and is then directed obliquely downward and backward across the face, crosses over the anterior inferior angle of the masseter muscle and the ramus of the mandible a short distance in front of the angle, and is thence continued onward across the posterior part of the submaxillary and the upper part of the superior carotid triangles to open into the internal jugular at about the level of the hyoid bone. It follows in a general way the course of the corresponding artery, lying posterior to it, but the path across the face is much more direct than that followed by the artery. That portion of the vein which extends from the junction of the frontal and supra- orbital arteries to the lower border of the orbit is usually termed the angular vein, and branches arise from this which pass backward into the orbit to communicate with the ophthalmic vein. Just below the ramus of the mandible it usually receives a large communicating branch from the external jugular, and the portion which in- tervenes between this communication and the internal jugular is termed the common facial vein (v. facialis communis). Both the facial and the angular veins are usually described as being destitute of valves ; these structures do occur, however, but they are always insufficient and form no bar to the passage of blood in an inverse direc- tion i.e., from the facial and angular backward into the ophthalmic veins. Relations. The angular vein rests upon the nasal process of the maxillary vein internal to the lachrymal sac. In its upper portion the facial vein lies under cover of the orbicularis palpebrarum, and it also passes beneath the zygomatic muscles, but is superficial to the other muscles of the face. In its inframandibular or cervical portion it lies beneath the platysma in a groove in the submaxillary gland. Variations. --The upper portion of the facial vein may be greatly reduced in size. Below, it frequently unites with the lingual vein to form a linguo-facial trunk, which may also be joined by the superior thyroid. Instead of opening into the internal jugular, it occasionally passes across the sterno-cleido-mastoid muscle to unite with the external or anterior jugular. Practical Considerations. Allen has called attention to the fact that the venous supply of the face differs in some important particulars from that of the trunk and limbs. In the last-named localities, both deep and superficial currents flow in the same direction towards the heart. The facial trunk, however, is not formed by primal venules, as is commonly the case, but by branches communicating with the frontal and supraorbital veins, and by a transverse branch found at the bridge of the nose. The two most important communications with the cavernous sinus are through the ophthalmic vein, which receives tributaries from the angular vein, and the deep facial vein, which empties into the pterygoid plexus, which in its turn communicates with the cavernous sinus by veins passing through the foramen ovale. The veins corresponding to the deep parts of the face, other than those mentioned, also seek an outlet in the same direction, so that much of the superficial blood of the upper part and side of the face passes inward to the brain-case and to the interior of the facial region, while the remaining portion flows downward to join the jugular veins. The facial vein at its lower end receives a large communicating branch from the external jugular, and therefore at or below that point carries a considerable volume of blood, making wounds of the vein dangerous. THE SUPERIOR CAVAL SYSTEM. 865 The facial vein is said to be less flaccid than most superficial veins, and there- fore to remain more patent after section ; it possesses either imperfectly developed or rudimentary valves, or none at all. As a consequence of these facts, septic dis- ease malignant pustule, furuncle, carbuncle, cancrum oris involving the face or forehead, is exceptionally dangerous, as the infection may spread by way of the ophthalmic vein or the pterygoid plexus to the cavernous sinus and result in a fatal thrombosis or meningitis. The relations existing between the venous blood of the face and that of the brain-case are rendered evident by the fact that the state of the circulation of the external nose is sometimes an index of the condition of the vessels of the brain. Moreover, in cases of orbital or intracranial tumors, the ophthalmic, angular, and facial veins become congested, dilated, and tortuous from pressure-interference with the venous current. The line of the facial vein is from the canthus of the eye to a point on the mandible at the anterior border of the masseter muscle and just behind the facial artery. This line is straight instead of tortuous, as is the case with that of the latter vessel. Tributaries. The tributaries of the facial vein are (a) thefronta/and (b] the supraorbitai ', by the union of which it is formed. In addition it receives in its course across the face (c) the palpebral, (d ) the lateral nasals, (e) the superior labial, (f) the inferior labial, ( g) the deep facial, (A) the masseteric, and (i ) the anterior parotid veins. In its cervical portion it has open- ing into it (j) the inferior or descending palatine, and (k) the submental veins. (a) The frontal veins (vv. frontales) descend over the forehead on either side of the median line, lying immediately beneath the skin upon the frontalis muscle. The branches from which they take origin communicate at the sides and vertex of the skull with tributaries of the occip- ital and temporal veins, and also through small foramina in the frontal bone with the superior longitudinal sinus. The two veins are connected by numerous cross-branches, and not infre- quently unite more or less completely to form a single median stem which bifurcates below. Kach vein terminates at the inner angle of the orbit by uniting with the corresponding supraor- bitai vein to form the angular. At the root of the nose the two veins are usually united by a distinct cross-branch, the nasal arch, which receives from below the dorsal nasal veins. (b) The supraorbitai vein (v. supraorbitalis) is a relatively large trunk which runs trans- versely above the superior margin of the orbit and consequently is quite distinct from the artery of the same name. It arises at the external angle of the orbit, where it communicates with affluents of the temporal veins, and passes inward beneath the orbicularis palpebrarum, and, piercing that muscle just above the inner angle of the orbit, unites with the frontal vein to form the angular. It receives numerous small branches from neighboring regions and from the diploic vein of the frontal bone, and at the supraorbitai notch it communicates with the ophthalmic system of veins. (c) The palpebral veins (vv. palpebrales superiores et inferiores) are small vessels which take their origin from the venous plexus of the eyelids and open into the angular vein: The palpe- bral plexus also communicates laterally with the affluents of the temporal veins. (d ') The lateral nasal veins ( vv. nasales externae) arise in a rich plexus which occupies the alae and tip of the nose and with which the dorsal nasal vein communicates and also branches from the extensive pituitary plexus, these latter branches emerging along the line of junction of the nasal bones and cartilage. The veins extend upward and backward and open into the lower part of the angular vein. (e) The superior labial or coronary vein (v. labialis superior) takes its origin in a plexus in the substance of the upper lip with which branches from the septum and ala; of the nose com- municate. The course of the vein is independent of that of the artery of the same name, passing backward and somewhat upward to the naso-labial groove, and opening into the facial vein about opposite the ala of the nose. (f) The inferior labial vein (v. labialis inferior) arises from a venous plexus in the lower lip and passes downward and outward to open into the facial just after it has crossed the ramus of the mandible. Usually a second vein, the inferior coronary, also arises from the inferior labial plexus and passes almost horizontally outward to open into the facial a little below the angle of the mouth. (g) The deep facial vein, also termed the anterior internal maxillary, takes its origin from the pterygoid plexus (page 882) over the tuberosity of the maxilla, through which it receives branches from a net-work lying beneath the mucous membrane lining the antrum of Highmore. It passes forward and downward between the buccinator and masseter muscles, and opens into the outer surface of the facial where that vein passes beneath the zygomatic muscle. 55 866 HUMAN ANATOMY. (h) The masseteric veins (vv. massetericae ) are several small veins which return the blood from the masseteric and buccinator muscles, opening into the outer surface of the facial vein. (i ) The anterior parotid veins (\\. parotiikne jinu-riorcs i consist of several small veins which issue from the anterior border of the parotid gland and from the socia parotidis. They follow the parotid duct, around which they form a net-work, and open into the outer surface of the .facial vein. (j ) The inferior or descending palatine vein (v. palatina) accompanies the ascending palatine or tonsillar branch of the facial artery. It takes its origin in the tonsillar plexus and descends upon the side of the pharynx to open into the facial after it has crossed the ramus of the mandible. FJG. 754. Temporal fascia Superficial tem|x>ral vein Middle temporal vein Occipital vein Internal maxillary vein Temporo- maxillary vein Posterior auricular vein Sterno-cleido- mastoid Communication between facial and external jugular vein External jugular vein Tril nitary of trans- Terse cervical vein Posterior external jugular vein Trapezius Frontal veins Suprai.rtiital vein Branch of cation with ophthal- mic vein Angular vein Deep facial vein Subinental vein Common facial vein Anterior jugular vein Platysma Superficial veins of head and neck; external jujjular lies beneath platysma muscle, winch has been partly iumov<.- in.) behind the centre of the external auditory meatus to a point 12 mm. ()4 in.) above the inion ; the other from a point 3. 8 cm. ( i */ in. ) behind the meatus and on the same level to a point 12 mm. (^ in.) below the inion. The sinus almost never overpasses these limits in either a downward or an upward direction, and hence the trephine or chisel may be safely applied either below or above these lines. Fracture of the base of the skull may extend into the lateral sinus, in which case the blood may pass outward into the tympanum and thence by way of the Eusta- chian tube to the pharynx, or if the tympanic membrane is torn may find exit, mingled with cerebro-spinal fluid, at the external auditory meatus (page 1505). For further remarks on the practical relations of this important sinus, see page 1508. 2. The Superior Longitudinal Sinus. The superior longitudinal sinus (sinus sagittalis superior) (Fig. 756) is an unpaired sinus which lies along the line of attachment of the falx cerebri to the cranial vault. It begins blindly anteriorly by a small vein-like portion which lies in the foramen caecum between the frontal and ethmoidal bones, but soon becomes a true sinus which passes upward and backward in the median line of the frontal bone, beneath the sagittal suture of the parietals, and down the median line of the squamous portion of the occipital to terminate at the internal occipital protuberance by opening into the torcular Herophili, or, usually, more or less directly into the right lateral sinus. The sinus is triangular in section and increases gradually in size from before back- ward, measuring about 1.5 mm. in diameter at the level of the apex of the crista galli and 1 1 mm. at its termination. Its lumen is usually traversed by numerous irregular bands of connective tissue known as chorda Willisii, and frequently, espe- cially in aged persons, Pacchionian bodies, which are numerous along its course, project into it (Fig. 1039). Tributaries. In the fcetus and in early childhood the superior longitudinal sinus communi- cates with the veins of the nasal cavity through the foramen caecum, but this connection is diss. >1 ved in the adult. In addition, it communicates with the neighboring blood-lakes and through these with the meningeal veins, and receives (a) branches from the adjacent portions of the dura mater ; (t>) the superior cerebral veins, from ten to fifteen in number (page 877) ; and (c) diploic veins, some of which traverse the parietal bone and constitute emissary veins, the most noticeable of these being one which traverses the parietal foramen (page 876). Variations. The superior longitudinal sinus varies considerably in size and is occasionally exceedingly small, the tributaries which normally open into it passing downward in the talx to open into the inferior longitudinal sinus. It lias been observed to divide into two trunk throughout a portion of its course, and also to divide at the apex of the occipital bone into tv trunks which followed the lines of tin- lambdoid suture to open into the lateral sinuses, as stated, the sinus communicates more or less directly with the right lateral sinus, but pCCfil ally it may bend to the left of the internal occipital protuberance and open into the left lateral. Practical Considerations. The superior longitudinal sinus may become infected (a from the scalp through the diploic veins : ( h ) from foci of cerebral or meningeal disease through the contiguous blood-lakes or through the cerebral veins : (r the cranial sinuses. Some larger, although rather inconstant, stems also arise from the plexus and fonn what are termed the diploic veins. Of these, four are usually recognized (Fig. 758). THE SUPERIOR CAVAL SYSTEM. 875 1. The anterior diploic vein (v. diploica frontalis) descends in the diploe of the frontal bone and at the level of the supra-orbital notch opens either into the supra-orbital or ophthalmic vein. It communicates with the anterior temporal diploic vein and also with the frontal veins and the superior longitudinal sinus. 2. The anterior temporal diploic vein (v. diploica temporalis anterior) passes downward and forward in the diploe of the anterior portion of the parietal bone and opens either into a deep temporal vein or into the spheno-parietal sinus. 3. The posterior temporal diploic vein (v. diploica temporalis posterior) passes downward in the diploe of the posterior part of the parietal bone and usually opens into the mastoid emissary vein, thus communicating with the lateral sinus. It also communicates with the posterior auric- ular vein and may open into it. 4. The occipital diploic vein ( v diploica occipitalis ) passes downward in the squamous portion of the occipital bone, not far from the median line, and opens either into the occipital vein or into the occipital emissary vein, by which it communicates with the torcular Herophili or the lateral sinus. FIG. 758. Occipital diploic vein Posterior temporal diploic vein Anterior or frontal diploic vein 'rental vein Supra-orbital vein Frontal diploic vein Angular vein Anterior temporal diploic vein Deep temporal vein Outer table of skull has been removed to expose venous spaces of diploe. Practical Considerations. The diploic veins being incapable of effective contraction, bleed very freely and persistently, and -are sometimes a source of embarrassment during operations on the skull. Through their communications with the veins of the scalp on the one hand, and with the endo-cranial sinuses and meningeal veins on the other, they may, as in some cases of compound fracture, convey infection from the surface to the diploe, causing osteomyelitis and necrosis, or within the cranium, causing septic meningitis or sinus thrombosis. Pyaemia has followed an infective phlebitis of the diploic veins themselves. Diploic infection introduced from without pyogenic or through the blood tuberculous is apt to spread rapidly within the diploic tissue itself, as well as to the underlying structures. THE EMISSARY VEINS. The term emissary vein is applied to those branches which place the sinuses of the dura mater in communication with veins external to the cranial cavity. Using the term in its broadest sense, the emissary veins are very numerous, since both the diploic and the meningeal veins might be regarded as such, as well as the carotid 876 HUMAN ANATOMY. plexus (page 873) and the ophthalmic vein (page 879), all these making connections with the sinuses, on the one hand, and with extracranial veins, on the other. It is customary, however, to limit the term to certain veins which, for the most part, traverse special foramina in the cranial walls, a few, however, passing through foramina whose principal content is one of the cranial nerves. 1. The parietal emissary vein (emissarium parietale ), rather variable in size, traverses the cor- respondingly variable parietal foramen, placing the superior longitudinal sinus in communication with the veins of the scalp. 2. The occipital emissary vein (emissarium occipkale) traverses the occipital protuberance and places the torcular Herophili or one or the other of the lateral sinuses in communication with the occipital veins. Its size is variable ; it usually receives the occipital cliploic vein, and may perforate only the external or the internal table of the occipital bone, representing in such cases the terminal portion of the diploic vein rather than a true emissary. 3. The mastoid emissary vein (emissarium mastoideum ) passes through the mastoid foramen and places the lateral sinus in communication with either the occipital or the posterior auricular veins. It is occasionally wanting, and, on the other hand, may be so large as to appear to be the continuation of the lateral sinus, the terminal portion of that vessel between the mastoid and jugular foramina being greatly reduced in size. 4. The posterior condyloid emissary vein (emissarium condyloideum ) is very inconstant, and when present traverses the posterior condyloid foramen, extending between the lateral sinus near its termination and the vertebral veins. 5. The anterior condyloid emissary vein (rete canalis hypoglossi) is a net-work which sur- rounds the hypoglossal nerve in its course through the anterior condyloid foramen. From the plexus two veins arise, one of which passes to the inferior petrosal sinus and the other to the vertebral veins. 6. The emissaries of the foramen ovale ( rete foraminis ovalis) are formed by two veins which communicate above with the cavernous sinus and pass to the foramen ovale, where they form a plexus surrounding the mandibular division of the trigeminal nerve and communicate with the pterygoid plexus of veins. Occasionally, also, a similar plexus accompanies the maxillary division of the trigeminus through the foramen rotundum. 7. The emissary vein of the foramen of Vesalius is, like the foramen, inconstant, occurring only about once in three cases. It extends between the cavernous sinus and the pterygoid plexus of veins. 8. Finally, a variable number of small veins pass through the connective tissue which closes the foramen lacerum medium and place the cavernous sinus in communication with the pterygoid plexus. Practical Considerations. The relations of the emissary veins explain many cases of spread of extra-cranial infection to the meninges and the sinuses. If there were no emissary veins, injuries and diseases of the scalp and skull would lose half their seriousness (Treves). Infected wounds of the scalp, cellulitis or erysipelas involving that structure, osteomyelitis, or necrosis of the cranial bones may through the emissary veins result in serious intra- cranial disease. The largest of these veins is usually the mastoid, the communication between the lateral sinus and the occipital or posterior auricular vein {vide supra}. This relation and the considerable quan- tity of blood carried by the mastoid vein are thought to explain the supposed effect of leeches or blisters applied behind the ear in cerebral hyperaemia or inflammation, especially as nearly all the blood of the brain leaves it through the lateral sinuses. They also explain the extensive oedema behind the ear and around the mastoid region often seen in lateral sinus thrombosis. Pus has formed in the cerebellar fossa outside of the sigmoid sinus, made its exit through the mastoid foramen and appeared as an occipito-cervical abscess (Erichsen). The escape of pus by the mastoid foramen indicates extradural pus in the cerebellar fossa about the sigmoid groove, with the probability that sigmoid sinus thrombosis exists, especially if the mastoid vein is itself thrombosed (Macewen). In suppurative sigmoid sinus disease the posterior condyloid vein may convey infection to the cellular tissue in the upper part of the posterior cervical triangle, causing abscess beneath the deep fascia ; or, as a result of cerebellar pachymen- ingitis, there may be phlebitis of this vein, with marked tenderness in the saint- region. The emissary veins are important agents in the equalization of intra-cranial pressure. THE SUPERIOR CAVAL SYSTEM. 877 THE CEREBRAL VEINS. The cerebral veins (vv. cerebri) convey the blood carried to the brain by the cerebral arteries to the sinuses of the dura mater. They differ from most of the other veins in that they contain no valves, their walls are very thin and destitute of. muscle-tissue, and their arrangement does not usually follow that of the arteries. 1. The Superior Cerebral Veins. The superior cerebral veins (vv. cerebri superiores) are from eight to twelve in number, draining the upper, lateral and medial surfaces of the cerebral hemispheres. They follow, for the most part, the sulci of the hemispheres, although connected across the gyri by numerous anastomoses, and they open above into the superior longitudinal sinus. The various veins show a tendency to increase in size from before backward, and while the anterior ones have a course almost at right angles to the superior longitudinal sinus, the more posterior ones are directed forward as well as upward and open obliquely into the sinus and in a direc- tion contrary to the flow of the blood contained within it. 2. The Middle Cerebral Vein. The middle cerebral vein (v. cerebri media), also termed the superficial Sylvian vein, lies superficially along the line of the Sylvian fissure and opens below into either the cavernous or the spheno-parietal sinus. It receives affluents from the surface of the brain on either side of the fissure and through these anastomoses with both the superior and inferior cerebral veins. One of these affluents which lies approximately along the line of the fissure of Rolando is usually of large size and communicates directly with one of the superior cerebral veins, the two forming what is known as the great anastomotic vein of Trolard, uniting the superior longitudinal sinus with the median cerebral vein. 3. The Inferior Cerebral Veins. The inferior cerebral veins (vv. cerebri inferiores) are a number of small veins which occupy the inferior surfaces of the hemi- spheres. They are somewhat irregular in their arrangement, those of the frontal lobes anastomosing with the superior cerebrals and opening into the anterior portion of the superior longitudinal sinus, while those of the temporo-sphenoidal region anastomose with the middle cerebral and open into the spheno-parietal, cavernous and superior petrosal sinuses and into the basilar vein. 4. The Great Cerebral Vein. The great cerebral vein (v. cerebri magna), also known as the great vein of Galen, is a short stem about i cm. in length which is formed beneath the splenium of the corpus callosum in the neighborhood of the pineal body, by the union of the two internal cerebral veins. It passes backward and upward, curving around the posterior extremity of the corpus callosum, and terminates (Fig. 756) by opening into the anterior end of the straight sinus. Tributaries. The great cerebral vein is formed by the union of the two (a) internal cerebral veins (vv. cerebri interns), also known as the small veins of Galen. These are situated, one on either side of the median line, in the velum interpositum, which forms the roof of the third ventricle. Each is formed at the foramen of Monro by the union of three veins, the choroid vein, the vein of the septum lucidum, and the vein of the corpus striatum. The choroid vein ( v. chori- oidea ) seems to be the direct continuation of the internal cerebral vein. It begins at the junc- tion of the body and descending horn of the lateral ventricle, passes forward along the floor of the ventricle in the outer edge of the choroid plexus, and opens at the foramen of Monro into the internal cerebral vein of its side. The vein of the septum lucidum (v. septi pellucidi) passes backward along the outer (ventricular) surface of the septum lucidum, returning the blood from the head of the caudate nucleus and neighboring parts, and the vein of the corpus striatum (v. terminalis), which drains the lenticular nucleus and to a certain extent the caudate nucleus also, passes backward in the groove between the corpus striatum and the optic thalamus (stria termi- nalis). (b] The posterior vein of the corpus callosum passes backward from about the middle of the superior surface of the corpus callosum and, bending around the splenium, empties into the great cerebral vein or into the internal cerebral vein near its termination. It receives blood from the corpus callosum and from the median surface of the hemisphere. (c) The basilar vein (v. basalis) is a large paired vein which arises at the anterior per- forated space by the junction of the deep Sylvian vein with the anterior vein of the corpus cal- losum. It passes backward over the optic tract of its side and then curves upward around the crus cerebri to reach the dorsal surface of the brain-stem, where it opens into either the great or the internal cerebral vein. Occasionally the terminal portion which bends upward around the 878 HUMAN ANATOMY. crus is lacking, the vein then emptying into the cavernous sinus. The deep Sylvian vein, which is its main stem of origin, begins in a number of vessels which ramify over the surface of the insula (island of Reil) and passes downward and forward at the bottom of the Sylvian fissure to become continuous with the basilar at the anterior perforated space. Occasionally it unites with the lower portion of the middle cerebral vein or opens with it into the spheno-parietal sinus. The anterior vein of the corpus callosum corresponds to the anterior cerebellar artery, sometimes termed the anterior central vein ; it arises on the anterior part of the upper surface of the corpus callosum and bends downward around the genu to unite with the deep Sylvian vein at the anterior perforated space. The basilar vein drains all the central part of the base of the brain, and, in addition to the two veins which are regarded as its stems of origin, it receives branches from the optic tract, the olfactory bulb, the anterior perforated space, the tuber cinereum, the corpora mammillaria, and the posterior perforated space, and it furthermore receives a vein from the superior vt-rmis of the cerebellum. The veins of the anterior perforated space are from ten to fifteen in number and have their origin in the nuclei of the corpus striatum and in the internal capsule, while those of the* posterior perforated space drain the optic thalami. Practical Considerations. The free communication of the thin-walled valveless cerebral veins with one another is one of the agents for the equalization of intracranial venous pressure. An anastomotic trunk unites the middle cerebral vein with the posterior cerebral, thus permitting the passage of venous blood by means of the anterior basilar vein into the sinuses about the foramen magnum. Relief from excessive intracranial blood-pressure may, in addition, be effected by the escape of blood from within the cranium (a} in the occipital region through the internal jugular and mastoid vein ; (^) in the frontal region through the ophthalmic vein and the vein traversing the foramen ovale ; (c) in the basal region through the petrosal sinuses and the posterior condyloid vein ; and {d} at the vertex through the diploic veins and the venules penetrating the outer table of the cranium to join those of the scalp (Allen). The avoidance of sudden depletion of the intracranial venous channels through the inspiratory emptying of the large extracranial veins is admirably provided for and the mechanism should be understood, as it has practical relation to many phe- nomena of cerebral anaemia and hyperaemia, to shock and syncope and concussion, to sinus thrombosis, and to many other intracranial conditions. The chief factors in equalizing the flow in the sinuses and thus practically throughout the brain may be briefly summarized as follows : (a) The oblique entrance into the longitudinal sinus of its tributaries the larger middle and posterior cerebral veins pouring their blood into it against the stream ; (b) the division of the sinus at the Torcular Herophili into two trunks diverging at right angles ; (r) the course of the blood-current in the lateral sinus first horizontal, with a convexity outward ; then in the first part of the sigmoid vertical ; then horizontal, with a convexity downward, and then a quick upward and outward turn, with narrowing of its calibre before entering the jugular fossa ; (,irt of pterygoid plexu: Internal maxillary vein Temporal vein Pterygoid plexus' Internal pterygoid muscle Temporo-maxillary vein Posterior auricular vein Posterior trunk of teinporo-maxillary vein Anterior trunk of temporo-maxillary vein Sterno-cleido-mastoid muscl External jugular vein Internal carotid artery Internal jugular vei Frontal veins Angnlar vein Communicating branch to ophthalmic vein One of deep temporal veins External pterygoid muscle Buccal vein Deep facial vein Inferior dental vein Facial vein Submental vein iubmaxillary gland Common facial vein ommunicating branch to anterior jugular vein oimiiuu carotid anery Veins of head ; part of mandible and associated muscles have been removed to expose pterygoid plexus. . resemble the sinuses of the dura in their structure, and they communicate with the blood-lakes of the dura, with the superior longitudinal, spheno-parietal and petro-squamosal sinuses, and with the superficial Sylvian vein. They open below into the deeper portion of the pterygoid plexus. (f) The inferior dental vein follows the course of the inferior dental artery, opening above into the more superficial portion of the plexus. 2. The Posterior Auricular Vein. The posterior auricular vein (v. auricularis posterior) arises from a plexus situated over the mastoid portion of the temporal bone and communicating with branches of the occipital and temporal veins. It descends 884 HUMAN ANATOMY. behind the pinna, occasionally receiving the mastoid emissary vein, and terminates near the angle of the jaw by uniting with the temporo-maxillary to form the external jugular. 3. The Posterior External Jugular Vein. The posterior external jugular vein arises from the integument and muscles of the upper and back part of the neck, just below the occipital region, and descends obliquely behind the sterno-cleido- mastoid muscle to open into the external jugular just after it has crossed the muscle. 4. The Suprascapular Vein. The suprascapular vein (v. transversa scapulae) is really a double vein, being represented by two vessels provided with valves which accompany the suprascapular artery as its venae comites. They arise upon the upper part of the dorsal surface of the scapula, pass over the transverse ligament of that bone, and are continued inward, parallel with the clavicle and behind it, to open into the external jugular near its termination or else directly into the subclavian. Just before their termination the two venae comites unite to a single stem. The suprascapular vein is usually joined either at or near its termination by the transverse cervical veins which form the venae comites of the transversalis colli artery. These veins may also open, however, directly into the subclavian. 5. The Anterior Jugular Vein. The anterior jugular vein (v. jugularis anterior) (Fig. 753) arises beneath the chin, upon the mylo-hyoid muscle, by branches which come from the integument and superficial muscles of that region, communicating with the submental branches of the facial. The vein passes almost vertically down the neck, resting upon the sterno-hyoid muscle a short distance lateral from the median line, until it meets the anterior (inner) border of the sterno-cleido-mastoid near its sternal attachment. There it makes an abrupt bend, passing almost horizontally outward beneath the muscle to open into the external jugular immediately above its termination. The anterior jugular receives a communicating branch, occasionally of con- siderable size, from the facial subcutaneous veins, and tributaries from the median region of the neck also open into it ; it may also receive small branches from the larynx and thyroid gland. It contains no valves. At its origin it is superficial to the deep cervical fascia. Inn below the hyoid bone it is embedded in the superficial layer of that fascia, and below lies in the spatium suprasternale (space of Burns) formed by the splitting of the fascia into two lamellae. In this space there occurs a transverse anastomosis between tin- two veins, forming what is termed the arcus venosus juguli, and into this a number of small branches from neighboring structures open. The horizontal portion of the vein eventually pierces the posterior layer of the space to reach the external jugular. Variations. The anterior jugular varies considerably in size, inversely to the external jugular. Occasionally the two veins of opposite sides unite throughout the vertical portion o; their course to form a single stem, which passes down the median line of the neck and has con- sequently been termed the v, mediana colli. The communicating branch from the facial vein, which passes downward along the anterior border of the sterno-cleido-mastoid, is sometimes quite large, functioning as the direct continua- tion of the facial, which may thus pour its blood mainly, if not entirely, into the anterior jugular. Below, while the anterior jugular usually opens into the external jugular, yet it sometimes opens directly into the subclavian, and occasionally it receives near its termination an e.rft'rna/ thoracic TV/;/, which ascends from the region of the mammary ghmd over the clavicle, posterior to the attachment of the sterno-cleido-mastoid. THE SUBCLAVIAN VEIN. The subclavian vein (v. subclavia) (Fig. 753) is the terminal portion of the venous system of the upper extremity. It begins at the anterior border of the first rib, where it is directly continuous with the axillary vein, and passes almost horizontally inward, anterior to the scalenus anticus muscle and behind the clavicle, to the junction of that bone with the sternum, where it unites with the internal jugular to form the innominate vein. Its course is very similar to that of the subclavian artery, but it is more horizontal and somewhat anterior to the artery, from which it is separated by the scalenus anticus. It is provided with a pair of valves at its junction with the internal jugular and with another pair at its junction with the axillary vein. In the first portion of its course it is in relation anteriorly with the suhcluvins muscle, and its anterior wall is united to THE SUPERIOR CAVAL SYSTEM. 885 the fascia which encloses that muscle ; near its termination it is united to the middle layer of the deep cervical fascia, behind which it lies. As a result of these connections the vein does not collapse when empty, and, furthermore, its lumen is enlarged by movements, such as those of inspiration or the raising of the arm, which affect the fascia. With the exception of the external jugular and occasionally the anterior ingular, the subclavian vein receives, as a rule, no tributaries, the veins which <-om-spond to the branches of the subclavian artery opening either into the innominate or the external jugular. Occasionally, however, it receives the supra- -rapular and the superior intercostal vein (page 896), and the acromial thoracic vrin may open into it near its beginning. Trapez */* Clavicular portion of ^^^.iding ~~~~~~-Jrs j^J^^Bi ~\ sterno-mastoid, cut and 'branches of , ' . ', . turned forward i t-rvical plexus ~""' a =jgg- ''' ; "> I 1 "^N^r \ :X. "4^^ ' ^~- External jugular vein Transverse ^***\ ~ ~jf % ' ^K\- ^ cervical vessels -X,,^.. '',-,, ',-; \ -., , '. -, v _____Anterior scalene muscle Omo-hyoid '^V' "Hft^S' 3 muscle - \ -J&tor , 'Phrenic nerve Krachial plexus - z5fe=t'*r ' - 4Pf ' r-^v lllternal Jugular vein Vsternal portion c sterno-mastoid 4-Common carotid I^^^^H^r^^L^^'"'" N * Subclavian artery Suprascapular ^^^==- ' ,J^V ~H -Vsternal portion of . :- 1 K \ sterno-mastoid artery Sterno-hyoid muscle L First rib Subclavian vein" Clavicle Dissection of neck, showing relations of subclavian vein ; clavicle has been disarticulated from sternum and drawn down. Variations. Occasionally the course of the subclavian vein has the form of a curve which rises above the level of the clavicle and may even bring the vein to lie above the artery. It may pass with the artery behind the scalenus anticus, the artery and vein may exchange places with reference to that muscle, or the vein may divide to form a ring encircling the muscle. Rarely it passes between the subclavius muscle and the clavicle. Practical Considerations. The subclavian vein occupies the acute inner angle between the clavicle and the first rib, and therefore and on account of its slight resistance in periosteal or osseous growths from those bones is especially likely to suffer compression. The interposed subclavius muscle usually protects it, as it does the artery and the brachial plexus, from injury in case of fracture (page 259). The vein barely rises above the clavicle, and therefore usually escapes in stab- wounds involving the supraclavicular fossa, while the artery which arches an inch to an inch and a half above that line suffers much oftener. The connection of the anterior wall of the vein with the fascia of the subclavius muscle, causing an increase in its calibre during forced inspiration or an elevation of the arm (vide supra), should be remembered in case of wound of this vessel during 886 HUMAN ANATOMY. operation, as elevation of the clavicle may then be followed by the entrance of air into the vein (Henle). Obstruction of the subclavian at the point of junction with the internal jugular results in compression of the orifice of the thoracic duct. THE VEINS OF THE UPPER EXTREMITY. Instead of following distally the various branches which return the blood from the upper limb it will be more convenient to begin with the peripheral branches and trace the vessels proximally towards the subclavian. The veins of the upper extremity may be divided into a superficial and a deep set. The latter follow in general the course of the arteries, of which they are, as a rule, the venae comites. They anastomose frequently with the superficial veins and are more richly supplied with valves than are the latter. THE DEEP VEINS. THE DEEP VEINS OF THE HAND. The deep veins of the hand are all relatively small and are of less importance than the superficial ones in returning the blood. Each of the palmar arterial arches is accompanied by venae comites, and into those of the superficial arch (arcus volaris venosus superficialis) the superficial digital veins (vv. digitales volares com- munes) open, while those of the deep arch (arcus volaris venosus profundus) receive the veins (vv. metacarpeae volares) which accompany the aa. princeps pollicis, radialis indicis, and interossei palmares. Upon the dorsum of the hand even more than on its volar surface the chief part is played by the superficial veins. Three or four pairs of dorsal interosseous veins occur, however, accompanying the corresponding arteries and opening event- ually partly into the radial veins and partly, through the veins corresponding to the posterior carpal net-work, into the superficial veins of the dorsum of the wrist (rete venosura dorsale manus). As in the case of the arteries, the deep veins of the dorsal and volar surfaces of the hand are connected by perforating veins, and both make numerous connections with the superficial veins. THE DEEP VEINS OF THE FOREARM. The deep veins of the forearm are the venae comites which accompany the radial and ulnar arteries and their branches. The radial veins (vv. radiales) are the upward continuation of the veins of the deep palmar arch and are relatively slender. The ulnar veins (vv. ulnares) are larger and are formed by the union of the ulnar ends of the venae comites of both the superficial and deep palmar arches. Usually they have a large communication from the superficial veins of the dorsum of the hand, and receive near the elbow the veins which accompany the interosseous artery and its branches, and also a strong communicating branch, the deep median vein, from the superficial median (page 890). Both the ulnar and radial veins are well supplied with valves, and they unite at the elbow to form the brachial veins. THE BRACHIAL VEINS. The brachial veins (vv. brachiales) (Fig. 762) are the companion veins of the brachial artery and receive tributaries corresponding to the branches of the artery. They are formed at about the elbow-joint by the union of the radial and ulnar veins, and extend upward, one on either side of the brachial artery, to the lower border of the pectoralis major muscle, at about which level they unite to form a single trunk, termed the axillary vein. As is usual with venae comites, the two brachial veins are united by numerous anastomoses and occasionally unite through portions of their course, especially above, to form a single trunk. At the elbow one of the veins frequently lies in front of the artery and sometimes the two veins pursue a spiral course around it. In addition to the tributaries which accompany the branches of the brachial artery, the brachial veins, <>i rather the inner one of the two, receive near their termination the basilic vein (page 890). VEINS OF THE UPPER EXTREMITY. 887 THE AXILLARY VEIN. The axillary vein (v. axillaris) (Fig. 762) is formed by the union of the two brachial veins, usually at about the lower border of the pectoralis major. It lies along the inner side of the axillary artery, and at the lower border of the first rib passes directly into the subclavian vein. In the lower part of its course it is separated from the artery by the ulnar nerve and the inner head of the median ; above, it is more nearly in contact with it. The axillary vein possesses a pair of valves, usually situated at the level of the lower border of the subscapularis muscle. Its walls are intimately connected with the fascia of the axillary space, so that, as in the case of the subclavian, its lumen remains patent even when empty of blood, and con- sequently air may possibly enter in cases where the vein is wounded. Tributaries . These correspond in general with the branches of the artery, except that the axillary vein receives the cephalic, which is un- represented by an artery, and, furthermore, the acromial thoracic, which corresponds to the artery of the same name, instead of opening into the axil- lary, connects with the cephalic. Of especial importance among the tributaries is the long thoracic vein (v. thorac- alis lateralis) which brings to the axillary the blood from the lateral walls of the thorax. Its branches of origin are the FIG. 762. Costo-coracoid ligament Pectoralis minor Subscapular veil 'eres major Posterior circumflex vein .Venae comites of brachial artery- Median cephalic vein Superficial radial vei: Inner vena comes or radial artery. Superficial veins of anterior surface of rig;ht forearm and axillary vein and its tributaries. comites of the branches of the thoracic arteries, and they return the blood from the 888 HUMAN ANATOMY. pectoral and serratus magnus muscles and in part from the intercostals. They are abundantly supplied with valves, and unite to a single stem which presents variations in its connections with the axillary vein similar to those described for the corresponding artery. By means of the costo-axillary veins ( vv. costo-axillares), which pass from the middle portions of the upper six or seven intercostal spaces, it forms anastomoses with the intercostal veins which open into the azygos system. These costo-axillary veins open either directly into the long thoracic or into the thoraco-epigastric vein (v. thoraco-epigastrica), a more or less definite stem which extends upward along the lateral walls of the thorax, subcutaneously, to open into the long thoracic near its termination. It receives numerous tributaries from the rich subcutaneous venous net-work which occurs upon the anterior and lateral walls of the thorax (vv. cutaneae pectoris), and communicates directly below with epi- gastric branches from the femoral vein, thus forming an important communication between the superior and inferior caval systems. It also receives the veins coming from the region of the mammary gland, where the pectoral cutaneous veins form a net-work surrounding the nipple, the plexus venosus mammillae. The deeper veins of the gland open in part directly into the long thoracic, whence this lias been termed the external mammary vein, and partly into the internal mammary by branches which accompany the perforating branches of the internal mammary artery (page 860). Practical Considerations. When the axillary vein is formed by the junc- tion of the two brachial veins with the basilic vein, the union occurs usually at the inferior border of the subscapularis muscle. The vein is then somewhat shorter than the artery. Occasionally the coalescence of these tributaries does not take place until a level just beneath the lower border of the clavicle has been reached. When this is the case, operations in the axilla will involve the ligation of many com- municating transverse veins crossing the artery to join the venae comites lying upon either side of it. Phlebitis of the veins of the upper extremity is' but seldom transmitted to the axillary vein, rarely to the subclavian, and never to the internal jugular or innomi- nate (Allen). This immunity is supposed to be due to disproportionately greater size of a main venous trunk as compared with its tributaries ; any of the radicles of the veins of the hand, forearm, and arm whose calibres are nearly equal readily transmitting infection. Phlebitis of the axillary vein may, through the costo-axillary branches of the long thoracic vein, extend to within the thorax and result in a septic pleurisy. Accidental wounds of the axillary vein especially of its upper portion are dangerous on account of its size, its nearness to the thorax so that it markedly shows the respiratory wave and its' attachment to the costo-coracoid membrane, preventing its collapse, favoring hemorrhage, or, when it is empty, permitting the entrance of air. It lies within and a little below the artery, which it overlaps, particularly towards its upper and lower portions, and when it is distended during expiration. As it is straighter than the artery, the curve of the latter carries it a little away from the vein at the middle portion. Abduction of the arm brings the vein to a higher level and often almost in front of the artery so as partly to hide it. It will therefore be found with this relationship in many operations upon the axilla, and it is on account of it i.e. , its more superficial position and of its larger size that the vein is more frequently wounded than is the artery. On the other hand, the axillary artery is oftener ruptured, as in the manipulations for the reduction of old luxations of the shoulder, probably, as such luxations are more frequent in old persons, on account of the greater loss of elasticity of its thicker walls, and possibly on account of greater traction upon it by reason of its deeper and more external position (page 769). The close relation of the vein to the deep chain of axillary glands makes it the chief source of danger in operations for the removal of the breast and cleaning out the axilla in cases of mammary cancer, especially if the axillary nodes are already notably involved. It is well, therefore, to expose the vein at an early stage of the operation. If the walls have been invaded by the disease, or if extirpation of the cancerous mass is impossible without resection of the vein, the latter operation may VEINS OF THE UPPER EXTREMITY. FIG. 763. Olecranon External condyle Radial vein be performed. The resulting swelling and oedema of the upper limb are minimized by the consecutive enlargement of the cephalic vein. Such swelling and cedema are common symptoms of pressure upon the axillary vein by cancerous lymph-nodes in the later stages of mammary cancer (page 770). Suture of the wall of the vein in cases of accidental and of operative wound has been successfully performed. THE SUPERFICIAL VEINS. THE SUPERFICIAL VEINS OF THE HAND. The veins upon the dorsal surface (Fig. 763) form the principal superficial channels for the return of blood from the hand. They begin in a plexus upon the dorsum of the first phalanges, surrounding the nail, and are continued over the suc- ceeding phalanges as a coarser plexus in which longitudinal trunks (vv. digitales dorsales propriae) can be more or less distinctly perceived. At about the middle of the dorsum of the proximal phalanges transverse arches (arcus venosi digitales), one for each digit, connect the various dorsal digital veins ; each arch is concave proximally, and at either end unites with the extremities of the neighboring arches to form four dorsal metacarpal veins ; vv metacarpeae dorsales) which pass upward along the lines of the intermeta- carpal spaces. Just before joining with its neighbors each digital arch receives intercapitular veins (vv. intercapitu- lares) which ascend in the web of the fingers from the volar surface and assist in the passage of the blood of the superficial volar veins into those of the dorsal surface. The four dorsal metacarpal veins are abundantly connected by anastomosing branches which pass obliquely from one vein to the other, a net- work (rete venosum dorsale raanus) with elongated meshes being thus formed. The veins of the first and fourth intermetacarpal spaces, as a rule, however, retain a greater amount of individuality than the other two, and have consequently received special names, that of the first interspace being sometimes termed the vena cephalica pollicis, while that of the fourth interspace is the vena salvatella. The dorsal net-work is drained by two veins which pass up the fore'arm, the cephalic and basilic veins. The superficial veins of the volar surface of the hand are small and for the most part open into the dorsal veins. They arise as a plexus in the balls of the fingers and pass along the volar surfaces i- .. | i 11 . j- Superficial veins of right hand and Of the digits as a pleXUS in which longltlldl- forearm ; posterior surface. nal trunks (vv. digitales volares propriae) can be distinguished. From the plexus of each finger branches wind around the sides of the digits to open into the dorsal digital veins, and at the roots of the fingers important connections in a similar direction are made by the intercapitular veins (see above). 890 HUMAN ANATOMY. The superficial veins of the palm of the hand are situated superficially to the palmar aponeurosis. They are for the most part small, and form a net-work which is open over the central part of the palm, but much closer over the thenar and hypothenar eminences. These lateral portions communicate with the dorsal net-work as well as the net-work of the anterior surface of the forearm, into which the central portion opens. THE BASILIC VEIN. The basilic vein (v. basilica) (Fig. 762) takes its origin from the ulnar side of the dorsal net- work of the hand, and is sometimes described as the direct continuation of the dorsal metacarpal vein of the fourth interspace. It passes obliquely upward and inward, winding around the border of the hand towards the anterior surface of the fore- arm, up which it ascends. Beyond the bend of the elbow it continues its way upward along the inner border of the biceps muscle as far as the upper third of the brachium, at which level it pierces the fascia of the arm, and after a usually short subfascial course terminates by opening into the internal brachial vein. The basilic is the largest of all the superficial veins of the arm, and is provided with from ten to fifteen pairs of valves. It receives tributaries from the superficial plexus of the thenar eminence and from the anterior and posterior surfaces of the forearm. Near the elbow it receives from the cephalic vein the median vein, and also communicates with the cephalic higher up by branches which pass across the biceps muscle, and with the brachial veins by small branches which pierce the brachial fascia. Variations. The basilic is little subject to variation except in regard to its termination, which is frequently in the axillary and sometimes in the subclavian ; in both these cases the sub- fascial portion of its course is considerably longer than usual. Occasionally it is accompanied throughout its course by an accessory basilic. The portion of the vein extending from its origin to the bend of the elbow is frequently spoken of as the superficial ulnar vein, the term basilic being limited to the brachial portion of the vein as described above. THE CEPHALIC VEIN. The cephalic vein (v. cephalica) (Fig. 762) takes its origin from the radial portion of the dorsal net- work of the hand, and especially from the dorsal metacarpal vein of the first interspace. It passes upward, inclining forward over the surface of the brachio-radialis muscle, and so reaches the anterior surface of the forearm. Arrived at the bend of the elbow, it ascends along the groove which marks the outer border of the biceps muscle and then in the groove between the deltoid and the pectoralis major, and at the upper border of the latter muscle it passes between it and the clavicle, per- forates the costo-coracoid membrane, and, crossing in front of the axillary artery, empties into the axillary vein. It is provided with from twelve to fifteen pairs of valves, of which from four to seven occur in its antibrachial portion, seven in its brachial portion, and one at its union with the axillary. Tributaries. The cephalic vein receives numerous branches from the super- ficial net-work of the posterior surface of the forearm and, indeed, plays a much more important part in the drainage of this region than does the antibrachial portion of the basilic. Quite frequently it is accompanied in its course up the forearm by an accessory cephalic vein (v. cephalica accessoria), which arises in the posterior super- ficial net- work and opens into the main cephalic vein at the bend of the elbow. It also receives branches from the superficial net-work of the anterior surface of the forearm and, a short distance below the bend of the elbow, gives off a strong branch, the median vein (v. mediana cuhiti), which passes obliquely upward and inward to open into the basilic, giving off in its course a communicating branch to one or other of the deep veins of the forearm. In its brachial portion it is connected with the basilic by branches which pass across the biceps muscle, and just before opening into the axillary it receives the acromial thoracic vein (v. thoracoacromialis), which corresponds to the artery of the same name. VEINS 'OF THE UPPER EXTREMITY. 891 Variations. Unlike the basilic, the cephalic vein frequently presents variations which affect principally its brachial portion. One of the most important of these is the complete absence of this portion of the vein, the antibrachial portion emptying its blood into the basilic by means of the median vein. In other cases it is only the uppermost part of the brachial portion that is lacking, the lower part in such cases either making connection with the brachial veins or else conveying its blood downward to the median vein, by which it passes to the basilic. Another interesting anomaly consists in the occurrence of a branch which is given off just as the vein dips downward to pierce the costo-coracoid membrane. It is termed the jugulo- cephalic vein, and passes up over the clavicle to open above into the external jugular near its communication with the subclavian. These variations find an explanation in the changes undergone by the superficial veins of the arm during their development, both the absence of the brachial portion of the vein and the occurrence of a jugulo-cephalic being the persistence of conditions normally passed through in development. It would seem that three, or perhaps better four, stages are to be recognized in the development of the superficial veins of the arm. In the first stage the basilic vein forms the only great superficial trunk, extending up the inner side of the arm from the wrist to the axilla and opening into the axillary vein above. Later, however, this condition is modified by the de- velopment of the antibrachial portion of the cephalic, which increases in size at the expense of the antibrachial portion of the basilic until it becomes the most important vein of the forearm. At the bend of the elbow this vein receives a short transverse branch formed by the union of an ascending and descending limb, and then bends obliquely inward to join the brachial portion of the basilic. Higher up in the groove between the pectoralis major and deltoid muscles is a small deltoid vein, which is unconnected with the veins already described. Such a stage as this gives a clue to the variations in which the brachial portion of the cephalic is either absent or only partially developed. The ascending limb of the transverse branch of the elbow, and this branch itself, together represent what will later be the lower part of the brachial portion of the cephalic, while the deltoid vein represents its upper part ; the descending limb of the trans- verse branch represents the accessory cephalic vein, and the oblique portion of the antibrachial cephalic, between the transverse branch and the basilic, represents the median vein. Indeed, relics of this condition are to be seen even in the normal arrangement, for while the antibrachial portion of the cephalic usually exceeds in size the corresponding portion of the basilic, the con- ditions are reversed in the brachial portions of the two veins, the antibrachial portion of the cephalic and the brachial portion of the basilic (connected by the median) forming the main channel for the return of blood from the superficial portions of the arm. A third stage is brought about by the completion of the cephalic vein by the union of the ascending limb of the transverse branch with the deltoid, the vein so formed being continued up over the clavicle to open into the external jugular ; and, finally, the fourth or adult stage is pro- duced from this by the degeneration of that portion of the cephalic which corresponds to what is termed the jugulo-cephalic. The antibrachial portion of the cephalic is frequently termed the superficial radial vein, the accessory cephalic being then the accessory superficial radial. Furthermore, it is to be noted that quite frequently one or more strong longitudinal stems are developed in the superficial net- work of the anterior surface of the forearm, and to one of these the term median vein has been applied. This condition has generally been accepted by the English and French anatomists as typical, and their description of the origin of the basilic and cephalic veins is as follows. The median vein when it reaches the bend of the elbow divides into two divergent stems (Fig. 764) which are termed the median basilic and median cephalic veins. The median basilic, which corresponds with what has been termed above the median vein, unites with the superficial ulnar to form the basilic vein, while the median cephalic, which represents the foetal transverse branch of the elbow, similarly unites with the superficial radial to form the cephalic. Such an arrange- ment is undoubtedly of frequent occurrence ; but since the median vein, as understood in such a description, is so variable and so manifestly a secondary formation, and since the arrangement taken above as typical is not only also of frequent occurrence, but furthermore follows more closely the embryonic relations of the various vessels, it has been given the preference. PRACTICAL CONSIDERATIONS. THE VEINS OF THE UPPER EXTREMITY. The Deep Veins. The venae comites of the radial artery have been said, when distended, to alter, by pressure, the character of the pulse. The numerous short anastomotic branches which unite the venae comites of the brachial artery cross in front of that vessel and may have to be tied as a preliminary to ligation of the artery. The Superficial Veins. The Hand. The veins of the dorsal surface are subcutaneous, prominent, and, in order that the circulation may not be inter- rupted during prehension, are much larger than those of the palmar surface. Like the other superficial veins of the upper extremity, they are scantily supplied with valves and are therefore easily distended by the effects of gravity or by any constric- tion of the limb above. The Forearm. The large size of the superficial veins in the forearm^ their sub- cutaneous position, the small number of valves they contain, and the fact that most 892 HUMAN ANATOMY. FIG. 764. Cephalic vein Musculo- cutaneous ner Tendon of biceps Median cephalic vein Superficial r.nii.xl vein Basilic vein Part of |>osterior Brachial artery Median nerve Brachial vein ilnar vein Internal cutaneous nerve Posterior ulnar Median basilic il it.il fascia of the venous blood of the limb is returned by them, make circular constriction of the arm or forearm as in cases of poorly applied splints especially dangerous. Swelling and oedema distal to the constriction are sure to result speedily and, if the pressure is continued, to be followed by ulceration or gangrene. On the extensor surface of the forearm the superficial veins are less conspicuous than on the flexor, and between the olecranon and the level of the pronator teres insertion are almost completely lacking. This is the surface most exposed to trau- matism, and along it main arteries and nerve-trunks are also absent. The Elbow. The vein given off by the median vein when it reaches the bend of the elbow, and known by the English and French anatomists (vide supra) as the median basilic, is of the greatest practical importance among the veins at the bend of the elbow. The M-like figure made by the superficial ulnar and superficial radial in uniting respectively with the median basilic and median cephalic to form the basilic and cephalic veins is by no means constant, but is present in only from one-half to two-thirds of all cases (Treves). Even, however, if the basilic and cephalic veins do not originate in this way, the median vein (if from the cephalic), the median basilic (if from the median), will be found begin- ning a short distance below the elbow, to the outer side of the biceps tendons, and crossing the tendon, the brachial artery, the brachial veins, and the median nerve, from all of which it is separated by the bicipitul aponeurosis, the inner of the two lower biceps tendons of the old anatomists. The vein may, however, run either more transversely or more vertically and so have different relations to the artery and nerve ; it is usually the largest of the anticubital veins, but may be smaller than the median cephalic, which is commonly the second in size, followed by the median, ulnar, and radial, in the order mentioned. For reasons explained above, abnormalities and even absence of the cephalic and radial veins are more frequent than those of the basilic. For this reason, and on account of its large size, the greater quantity of blood it carries as it is above the entrance of the deep median vein, and thus receives blood from the deep veins of the forearm its superficial position, its prominence, and its relative fixation to the bicipital fascia by cellular tissue, the median basilic is the vein selected for either intravenous transfusion or phlebotomy. In opening the vein, certain dangers are to be avoided : ( i ) Wound of the brachial artery, if it results in a direct communication between the vein and artery, will cause an aneu- rismal varix ; if it results in the formation of an intervening sac in the perivaseular connective tissue, through which the blood from the artery flows before entering the vein, it will cause a varicose aneurism. (2) A septic wound may cause a lymphan- gitis from jnfection of the lymph-vessels accompanying the vein, and may result in axilary abscess. (3) I'nnecessary damage to the filaments of the internal cuta- Superficial dissection of region of elbow, showing relation of veins and nerves. THE AZYGOS SYSTEM. 893 neous nerve (lying in front of the vein) may give rise to chronic traumatic neuritis (Tillaux), while injury of the cutaneous branches of the musculo-cutaneous nerve (in closer relation to the median cephalic vein), or entanglement of those branches in the cicatrix, may, by reflex irritation acting through the motor fibres, cause tonic spasm of the biceps and brachialis anticus, " bent arm" (Hilton). The Arm. The cephalic vein and its anomalies should be studied in relation to ligation of the axillary artery (q.v.\ the first portion of which it crosses (sepa- rated from it by the clavi-pectoral fascia), on its way to reach the axillary vein. It may be remembered that the basilic vein pierces the brachial aponeurosis a little below the middle of the arm and ceases to be superficial. THE AZYGOS SYSTEM. The principal trunks of the azygos system of veins are persistent portions of the embryonic cardinal veins which drained the thoracic and abdominal walls, as well as the paired viscera of the abdomen, and united above with the jugular trunks to form the Cuvierian ducts (page 926). On the development of the inferior vena cava their importance diminished greatly, and in the adult they serve principally to collect the blood from the intercostal spaces. The reduction of the lower part of the left jugular vein (page 927) brought about further modifications of the left cardinal, its original connection with the left jugular being dissolved and a new one formed with the right cardinal. This latter vein forms what is termed the azygos vein of the adult, while what persists of the left one is known as the hemiazygos and accessory hemiazygos. THE AZYGOS VEIN. The azygos vein (v. azygos) (Fig. 765), sometimes called the azygos major, begins immediately below the diaphragm, where it is directly continuous with the right ascending lumbar vein, formed by the anastomosis of branches of the lumbar veins and connecting below with the ilio-lumbar or common iliac. The azygos vein passes up- ward into the thoracic cavity, traversing the diaphragm either by the cleft between the medial and intermediate portions of the right crus or else by the aortic opening. It then continues its way upward in the posterior mediastinum, resting upon the ante- rior surfaces of the bodies of the thoracic vertebrae a little to the right of the middle line, passing over the right intercostal arteries and having the thoracic aorta and the thoracic duct immediately to the left of it. When it reaches the level of the fourth vertebra it bends forward and somewhat to the right, and, curving over the right bronchus and the right pulmonary artery, it descends slightly to open into the pos- terior surface of the superior vena cava, just above the level at which that vessel becomes invested by the pericardium, The terminal portion of the vein from the fourth vertebra onward is sometimes termed the azygos arch. The azygos vein in a considerable proportion (22 per cent., Gruber) of cases is entirely destitute of valves, and when present they rarely exceed four in number, are, apparently, never exactly paired, and are usually insufficient. They occur more fre- quently in the arch than in the vertical portion of the vein. Tributaries. The azygos vein at its origin has usually some small connections with the vena cava inferior, but its principal tributaries are the right intercostal veins. In addition it receives branches from the oesophagus (vv. oesophageae), from the are- olar tissue and lymph-nodes of the posterior mediastinum and from a plexus which surrounds the thoracic aorta, from the posterior surface of the pericardium, and from the substance of the right lung, these last bronchial veins (vv. bronchiales posted- ores ) issuing from the hilum of the lung and opening into the azygos at the beginning of its arch. They anastomose with the pulmonary veins both along the course of the smaller bronchi and also outside the lung, and they receive some smaller bronchial veins (vv. bronchiales anteriores) situated upon the anterior surface of the bronchi. The azygos vein furthermore receives the hemiazygos vein ; this and the intercostal veins will be described below. Variations. Since the cardinal veins, from which the azygos and hemiazygos are formed, are primarily symmetrical, it may happen, just as was the case with the aortic arches, that it is the left one that is more fully retained and therefore becomes the azygos vein, the right becoming 8 9 4 HUMAN ANATOMY. FIG. 765. Internal jugular vein Right vertebral vein Right subclavian vein Right innominate vein Right inferior thyroid vein Right internal mammary vein Superior vena cava Right bronchial vein Right superior intercostal vein Vena azygos Hepatic veins Inferior vena cava Suprarenal vein Renal vein Vena azygos Right spermatic vein Quadratus lumborum Branch of communi- cation to vena azygos Ascending lumbar vein Right common Iliac vein Ilio-Iumbar vein Thoracic duct Left vertebral vein Left inferior thyroid vein Left innominate vein Left internal mammary veil Left superior intercostal veil fena hemiazygos accessoria Left common iliac vein Ilio-Iumbar vein Internal iliac vein External iliac vein Portion of posterior body-wall, showing azyjjos veins, superior and inferior vena cava, and their tributaries. THE AZYGOS SYSTEM. 895 the hemiazygos. Occasionally, instead of opening into the superior vena cava, the azygos terminates in the right subclavian, the right innominate vein, or even opens directly into the right auricle. A further anomaly is sometimes presented by the azygos, in its upper part, being situated at the bottom of a deep groove upon the surface of the right lung, which thus comes to have an accessory lobe known as the azygos lobe or lobule. Practical Considerations. The azygos veins are the connecting links be- tween the cardinal and the inferior caval systems. In cases of obstruction of the inferior cava they are able to carry on the collateral circulation very effectively, through their communication with the common iliac, renal, lumbar, and ilio-lumbar veins. Growths in the posterior mediastinum, enlarged bronchial glands, or aortic aneurisms may so compress these veins as to cause oedema of the chest wall by interference with the intercostal veins which empty into them. THE HEMIAZYGOS VEIN. The hemiazygos vein (v. hemiazygos) (Fig. 765), also called the azygos minor inferior, is the counterpart, on the left side of the body, of the lower part of the azygos. It arises just below the diaphragm as the continuation upward of the left ascending lumbar vein (page 901), also receiving usually a communicating branch from the left renal vein. It passes upward into the thorax between the medial and intermediate portions of the left crus of the diaphragm, and then ascends upon the left side of the bodies of the lower thoracic vertebrae, passing in front of the lower left intercostal arteries and having the thoracic aorta to its right. At about the level of the eighth or ninth vertebra it bends towards the right and, passing behind the aorta and the cesophagus, opens into the azygos vein. In its course it receives the lower five or four left intercostal veins, which con- stitute its principal tributaries, and in some cases it also receives the accessory hemi- azygos vein. It also receives some branches from the cesophagus and from the posterior mediastinum. THE ACCESSORY HEMIAZYGOS VEIN. The accessory hemiazygos vein (v. hemiazygos accessoria) (Fig. 765), also called the azygos minor superior, is a descending stem which lies upon the left side of the bodies of the upper thoracic vertebrae and receives the upper left intercostal veins. It begins above at about the second intercostal space by the union of a small vein, which connects it with the left innominate, with the left superior intercostal. When it has reached the level of the seventh or eighth thoracic vertebra it bends to the right and, passing beneath the aorta and the cesophagus, opens into the azygos vein. Quite frequently it opens below into the hemiazygos just as that vein bends towards the right, and even when it has an independent connection with the azygos it may be connected with the hemiazygos by an anastomotic branch. It receives the upper seven or eight left intercostal veins and in addition the left posterior bronchial vein. Variations. The hemiazygos and accessory hemiazygos veins together represent the left cardinal vein of the embryo which primarily opened into the left Cuvierian duct. With the dis- appearance of the lower part of the left jugular vein the relations of the left cardinal change, the vein making a connection across the middle line with the right cardinal (the azygos). Indi- cations of the original condition are occasionally seen in a fibrous cord which connects the left superior intercostal vein, which is strictly a portion of the accessory hemiazygos, with the oblique vein of the left auricle (page 856). As already pointed out in speaking of variations of the azygos, cases have been observed in which the hemiazygos and accessory hemiazygos occur upon the right side of the body, being formed from the right cardinal, while the left cardinal gives rise to the azygos. And more rarely the two veins have been observed fused to form a single trunk lying upon the anterior surface of the thoracic vertebrae and receiving all the intercostal arteries. A considerable amount of variation exists in the number of intercostal veins received by the hemiazygos and the accessory hemiazygos respectively. Usually they divide between them the intercostals, since they either unite or cross the median line to the azygos over successive vertebrae. The hemiazygos has been observed to cross the vertebral column anywhere from the sixth to the eleventh vertebra, and the accessory may descend as far as the tenth or may cross at the third. In cases where it makes its crossing high up a number of intercostal spaces may inter- 896 HUMAN ANATOMY. vene between it and the hemiazygos, and the veins of these then open directly into the azygos passing, each independently, across the vertebral column beneath the aorta and oesophagus! Absence of the accessory hemiazygos has been observed, the upper six or eight iiiVr- costal veins uniting to form a common ascending trunk which opens into the left innominate In all probability, however, this common ascending stem is properly to be regarded as the accessory hemiazygos, whose normal connection with the innominate has increased in size while its connection with the azygos or hemiazygos has either degenerated or failed to form. THE INTERCOSTAL VEINS. The intercostal veins (vv. intercostales) (Fig. 765), sometimes designated as posterior intercostal as distinguished from the anterior intercostal tributaries of the internal mammary vein, accompany the intercostal arteries and are twelve in number on each side, one occurring in each intercostal space and one, sometimes termed the subcostal vein, running along the lower border of each twelfth rib. They lie along the upper border of the spaces to which they belong, in a groove on the lower border of the rib, and are above the corresponding arteries. The upper nine or ten veins open anteriorly into the internal mammary or musculo-phrenic veins, but the lower three or two, which are somewhat larger than the rest, have no anterior communica- tion and receive tributaries from the abdominal muscles and the diaphragm. In the middle portion of their course the upper six or seven veins give off branches, the costo-axillary veins, which ascend towards the axilla and open into either the long thoracic or the thoraco-epigastric vein and so into the axillary, and, as it approaches the vertebral column behind, each vein receives a dorsal branch (ramus dorsalis) which accompanies the spinal branch of the intercostal artery and returns the blood from the skin and muscles of the back and also from the spinal column and its contents, this latter drainage being by means of a spinal branch (ramus spinalis) which connects with the intervertebral veins (page 898). Their posterior termination varies considerably in different individuals, especially as regards the upper members of the series. It may be supposed that primarily ail the intercostal veins of the right side opened into the azygos vein and all of those of the left side into the hemiazygos or accessory hemiazygos, and this condition holds in the adult with all but the upper two or three veins. On the right side the vein of the first space that of the second space sometimes uniting with it frequently accompanies the superior intercostal artery as a right superior intercostal vein, and opens above into either the right innominate or one of its branches, usually the vertebral; on the left side the vein of the first space opens into the left innominate vein, being sometimes termed the accessory left superior intercostal vein, while the veins of the second, third, and sometimes the fourth spaces unite to a common trunk which crosses the arch of the aorta and opens into the left innominate vein, forming the left superior intercostal vein. It is to be noted that this last is connected with the accessory hemiazygos vein and really represents, in part at least, its upper portion, a fact which is all the more evident from its frequent connection by means of a fibrous cord with the oblique vein of the left auricle ; and, furthermore, it may also be pointed out that the veins of the second, third, and sometimes the fourth spaces of the right side usually unite to a common trunk which opens into the azvi;< vein. The principal tributaries and connections of the intercostal veins have already been mentioned, but there remain to be described the interesting arrangement shown by the valves in those veins which connect anteriorly with the internal mammary or musculo-phrenic veins. So far as this arrangement is concerned, each vein may he- regarded as consisting of three portions : ( i ) an anterior portion, in which the con- cavities of the valves look towards the internal mammary or musculo-phrenic veins ; (2) a posterior portion, in which the valves look towards the azygos or hemiaxy^os veins ; and (3) an intermediate portion, which is destitute of valves. As a result of this arrangement the blood of the anterior portion of each vein must pass to the internal mammary veins (page 860), that of the posterior portion to the azygos or hemiax\ L;< s, while in the intermediate portion it may puss in either direction. Hut it is with this intermediate portion that the costo-axillary veins are connected, so that in the upper six or seven veins, in addition to passing partly anteriorly and partly posteriorly, some of the blood takes an ascending direction ;'iul empties into the axillary vein. THE AZYGOS SYSTEM. 897 In the two or three lower veins there is no such double flow, the valves all looking towards the azygos veins. Valves occur at the opening of practically all the intercostals into the azygos veins, the last intercostal forming an exception to this rule, and, furthermore, the valves of the lower veins are apt to be insufficient. THE SPINAL VEINS. The spinal veins, which return the blood from the vertebral column and the adjacent muscles and also from the membranes enclosing the spinal cord, present in a high degree the plexiform arrangement which is characteristic of the veins as com- pared with the arteries. They form a series of longitudinal plexuses which extend practically the entire length of the spinal column, communicating extensively with one another, and may be divided primarily into those which lie external to the spinal canal and those which lie within the canal. The external spinal plexuses (plexus venosi vertebrales externi) are two in number, anterior and posterior. The anterior external plexus (plexus venosus vertebralis anterior) rests upon the anterior surfaces of the bodies of the vertebrae, and presents considerable differences in the amount of its complexity in different portions of the spinal column. In the thoracic and lumbar regions it forms a net- work with large meshes, in the sacral region it is represented by transverse anasto- moses between the lateral and middle sacral veins, and in the cervical region it reaches its greatest degree of complexity, forming a close net-work, especially dense above and resting partly upon the bodies of the vertebrae and partly upon the longus colli muscles. At each intervertebral foramen the plexus communicates with the veins issuing from the internal spinal plexuses and also with the posterior external plexus, and in addition sends branches to the vertebral veins in the cervical region and to the rami spinales of the intercostal and lumbar veins in the corresponding regions. The posterior external plexuses (plexus venosi vertebrales posteriores) lie partly upon the posterior surfaces of the laminae of the vertebrae and the ligamenta subflava and partly between the deeper dorsal muscles. As in the case of the anterior plexus, they are more complicated in the cervical than in the thoracic and lumbar regions. In the latter their meshes are somewhat elongated longitudinally, and they communi- cate with the internal plexuses at the intervertebral foramina and also by branches which traverse the ligamenta subflava, and they have further communications with the anterior external plexus and with the spinal rami of the intercostal and lumbar veins. In the cervical region, in correspondence with the greater differentiation of the dorsal musculature, the plexuses become divided into several layers, and in the region between the occiput and the axis vertebra their deep layers form an especially dense net-work, the suboccipital plexus, with which the occipital, vertebral, deep cervical, and posterior external jugular veins communicate. Throughout its course the cervical portion of the plexus communicates with the internal and anterior ex- ternal plexuses and also with the vertebral vein. The internal spinal plexuses (plexus venosi vertebrales interni) are situated in the dura mater lining the spinal canal and are much closer than the external plexuses. The veins which form them have a general longitudinal direction and anastomose abundantly, but nevertheless four subordinate longitudinal lines of vessels can be recognized, two of which are upon the anterior wall of the spinal canal and two upon the posterior wall. The anterior internal plexuses lie one on each side of the median line on the posterior surfaces of the bodies of the vertebrae and the intervertebral disks, from the foramen magnum to the sacral region. They are composed of rather large veins, between which are frequent anastomoses, and transverse connecting vessels run across the body of each vertebra between the two plexuses, passing beneath the posterior common vertebral ligament. Into these transverse connections open the basivertebral reins (vv. basi vertebrales) which return the blood from the bodies of the vertebrae, traversing these to a certain extent to communicate with the anterior external plexus. The anterior internal plexuses also communicate opposite each vertebra with the pos- terior internal plexuses, rings of anastomosing veins thus surrounding the spinal canal opposite each vertebra and constituting what are termed the retia venosa vertebrarum. 57 898 HUMAN ANATOMY. The posterior internal plexuses are situated one on either side of the median line on the anterior surfaces of the laminae and on the ligamenta subflava, through which they send branches to communicate with the posterior external plexus. They are connected by transverse plexuses which complete the retia venosa vertebrarum, and are composed of smaller vessels than the anterior plexuses, and the net-work which they form is more open. Laterally, at each intervertebral foramen the internal plexuses send branches out from the spinal canal along the nerve-trunks, and by means of these intervertebral veins ( vv. intervertebrales), which have the form of plexuses at their origin and receive communicating branches from the external vertebral plexuses and from the veins of the spinal cord, the internal plexuses pour their blood into the vertebral, intercostal, lum- bar, and lateral sacral veins, the connection with the intercostals being through their rami spinales. Above, the internal plexuses form an especially rich rete or plexus around the foramen magnum and communicate with the occipital, marginal, and basilar sinuses. Practical Considerations. The posterior external spinal plexuses, by means of their communication through the intervertebral foramina and the ligamenta sub- flava with the internal plexuses, may convey infection from without septic wounds of the back, severe bed-sores, osteitis of the vertebral laminae to the interior of the spinal canal. External pachy meningitis has thus originated. In operations upon the spine, these veins bleed so freely that it is often well after severing them upon one side to control them by packing and proceed to the exposure of the spine on the opposite side, repeating the packing there. The internal plexuses, interposed between the theca of the cord and the interior walls of the vertebral column, may, as a result of trauma, furnish blood enough to cause compression of the cord. The symptoms are usually relatively slow in developing as compared with those due to injury to the cord itself or to its vessels and are referable mainly to the lower spinal segments, the blood gravitating to that portion of the canal. Hemorrhage may occur within the membranes (haematorrhacis), when the blood will likewise tend to gravitate toward the lower end of the cord, and, unless in large amount, may cause no definitely localizing symptoms. Bleeding from the venae medulli spinales may take place into the substance of the cord (haemato- myelia), and is most likely to occur in the segments from the fourth cervical to tin first dorsal (Thorburn), because of the degree of motion of that portion of the spine, the union toward its base of a fixed and a movable segment, and the frequency with which forces causing excessive flexion or over-extension are applied to the head. If the lesion causes compression only, the paralysis, anaesthesia, etc., will be only temporary. If it is associated with disorganization of the cord, they will be permanent. THE VEINS OF THE SPINAL CORD. The veins of the spinal cord (vv. medulli spinales) occur as six longitudinal stems situated upon the surface of the cord and connected by a fine net-work very much as are the arteries. One of these stems traverses the entire length of the cord along tin- line of the anterior median fissure, and has on either side of it another stem which lies immediately posterior to the line of exit of the anterior nerve-roots. These three stems together form the anterior medulli-spinal veins ( vv. shinnies externae anteriores). The posterior veins (vv. spinales extcrnae posteriores ) have a similar arrangement, one lying along the line of the posterior longitudinal fissure and one posterior to each of the lines of entrance of the posterior nerve-roots. All these stems, together with the plexus which connects them, lie in the pia mater and receive branches (vv. spinales internae) from the substance of the cord. From them branches pass out along the nerve-roots to join the intervertebral veins, and at the upper extremity of the cord they join the veins of the medulla oblongata. THE INFERIOR CAVAL SYSTEM. The inferior caval system includes all the veins from the body- wall below the level of the diaphragm ; those from the abdominal and pelvic cavities, with the exception of those from the stomach, intestines (except the lower part of the rectum), THE INFERIOR CAVAL SYSTEM. pancreas, and spleen ; and those from the lower limb. It receives its name from its principal vessel, the inferior vena cava, which conveys its blood to the right auricle. THE INFERIOR VENA CAVA. The inferior or ascending vena cava (vena cava inferior) (Figs. 765, 766) is formed by the union of the two common iliac veins either on the right side of the intervertebral disk separating the fourth and fifth lumbar vertebras or on the right side of the fifth lumbar vertebra. From this point it ascends directly upward to the level of the first Hepatic veins FIG. 766. Right suprarenal '.,.-. body 17 j Vena cava-i Right renal vein Right kidney \ Right ureter Right spermatic vein Right spermati artery Vas deferens J Spermatic cord i- S^ Cceliac axis CEsophagus / ^Superior mesenteric artery Left suprarenal body [ Left renal vein /-Left kidney I Left renal artery Inferior mesen- teric artery Left ureter Quadratus lumborum Left spermatic artery Common iliac artery Common iliac vein Psoas magnus _Left ureter, pelvic portion i_ Rectum (cut) 4 Vas deferens Bladder Inferior vena cava and iliac veins. lumbar vertebra and there begins to bend slightly to the right to reach the fissure the liver which separates the Spigelian and right lobes. Passing upward in this issure, it reaches the diaphragm and perforates the left lobe of the centrum tendineum that structure, so entering the cavity of the thorax, then bends slightly forward and the left, and opens into the lower and back part of the right auricle of the heart. It is the largest vein of the body, measuring at its entrance into the auricle about 33 mm. in diameter. It increases in size from below upward with the accession of its various tributaries, somewhat sudden increases succeeding the entrance into it of its largest tributaries, the renal and hepatic veins. It contains no valves, unless the Eustachian valve guarding its entrance into the auricle be regarded as belonging to it. 900 HUMAN ANATOMY. Relations. For convenience in description the vena cava inferior may be regarded as consisting of an abdominal and a thoracic portion. The former, which constitutes by far the greater part of its length, has the following relations. Poste- riorly it rests upon the right side of the lumbar vertebrae, upon the origins of the psoas major and minor muscles, and above upon the right crus of the diaphragm ; it crosses in its course the right lumbar and right renal arteries. Medially it is in close relation with the abdominal aorta throughout the greater portion of its course, but separates from it slightly above, the right crus of the diaphragm intervening. Laterally it is in contact with the psoas major muscle below, and at about the middle of its course it is in close relation with the inner border of the right kidney. Ante- riorly it is covered at its origin by the right common iliac artery and in the lower part of its course by peritoneum. At the level of the third lumbar vertebra it lies beneath the third portion of the duodenum, and immediately above that beneath the head of the pancreas and the main stem of the portal vein, which crosses it obliquely. Finally, it lies in the vena caval fissure of the liver, having to the right the right lobe and to the left the Spigelian lobe, and being sometimes completely surrounded by liver-tissue, owing to a thin portion of it bridging over the fissure. Throughout this part of its course it is firmly united to the walls of the fissure by fibrous bands. In its thoracic portion, which, is quite short, measuring not more than 3 cm. in length, it is in relation at first with the right lung and pleura, and in the upper part is enclosed for about 1.2 cm. in the pericardium. Variations. The development of the inferior vena cava (page 927) shows it to be formed by the union of three primarily distinct structures. Its upper part, between the entrance of tin- hepatic veins and the right auricle, is the upper part of the embryonic ductus venosus, then fol- lows a considerable portion derived from the right subcardinal vein, and, finally, its lower part is formed from the right cardinal vein. Of these embryonic veins the ductus venosus is unpaired, the other two are the right members of paired veins, whose fellows undergo almost complete degeneration. Anomalies of the vena cava, which are not uncommon, are for the most part explicable as a persistence or modification of the embryonic conditions. Thus, that portion of the vessel which is formed from the right subcardinal and right cardinal may fail to develop, in which case what is termed a persistence of the cardinals occurs. Up to a point above the level of the ren.1l veins the vena cava is represented by two parallel trunks lying one on either side of the aorta, the one receiving the right common iliac vein and the other the left. These represent the abdominal portions of the cardinal veins or, in the majority of cases, more probably the subcardinals, and unite above with the unpaired ductus venosus, which carries their blood to the heart. In other w< >rds, such cases are, as a rule, to be regarded as a similar development of both subcardinal veins. Occasionally, however, the development of the right subcardinal to form the vena cava may proceed as usual, but it fails to make a connection with the ductus venosus, one of its con nections with the right cardinal enlarging so that this vein receives the caval blood, carries it through the aortic opening of the diaphragm, and. as the a/ygos vein, empties it int. > the superior vena cava. The hepatic veins open as usual into the ductus venosus, which passes to the righl auricle in the normal manner, and the vena cava inferior is thus represented by two distinct veins. the upper part of the ductus venosus. which in such cases is termed the common hepatic vein ( r. hepatica communis), and the subcardinal and cardinal portion. Another variation may be produced by a reversal of the roles of the two subcardinals in forming the vena cava, the left being the one which develops, while the right degenerates. Such a condition is found in all cases of situs inversus viscerum, but it has also been observed in cases in which there was otherwise a normal arrangement of the organs. In such cases the vena cava in the lower part of its course lies to the left of the aorta instead of to the right, and at the level of the renal arteries it crosses to the right side in front of the aorta, its further course being normal. But just as the lower part of the inferior vena cava, when normally formed from the right subcardinal, may fail to unite with the ductus venosus but retain its primary connection with the azygos, so, too, when formed from the left subcardinal, it may retain its connection with the hemiazygos and drain through that vessel into the a/ygos and so into the superior vena cava. These various cases include the principal variations which occur in connection with the vena cava inferior. It may be pointed out that normally connections exist between tin- ;I/\LM>S vein and the vena cava below the diaphragm ; by means of the ascending lumbar veins, and also by the thoraco-epigastric veins, connection is established between tributaries of the interior cava and the external iliac veins and the axillary vein. My means of these normally subordinate channels opportunity is afforded for the maintenance of the circulation in case of obliteration of the vena cava. Practical Considerations. The inferior cava may be ruptured in severe abdominal injuries, as in the case of a weight falling upon, or a wagon passing over, the belly. The site of rupture is most often in' the portion lying in the hepatic THE INFERIOR CAVAL SYSTEM. 901 fissure. Its relation to the right psoas major muscle has resulted, in cases of psoas abscess, in ulceration and opening of the vein, with fatal hemorrhage. Its relation to the inner border of the right kidney has resulted in its compression by a movable kidney, or by a cancerous growth of the kidney, causing caval thrombosis, a condition which has also been noted in connection with chronic nephritis and with infarction of the renal parenchyma. Its relation to the liver results, in some cases of hepatic enlargement, in compression of the vena cava with oedema of the lower limbs, and other symptoms of obstruction. Its close proximity to the lower end of the bile-duct necessitates caution in cutting operations for the removal of impacted stones from the duct (choledochotomy) (page 1732). Enlarge- ment or growth involving the head of the pancreas may compress the cava sufficiently to cause obstructive symptoms, and the nearness of the vein constitutes one of the very serious obstacles to removal of pancreatic tumors. In ureterotomy or other operation on the right ureter, the close relationship of the vena cava at the point of crossing should be remembered. Thrombosis of the cava, from whatever cause, though it may extend the entire length of the vessel, is apt to be limited to a portion of the vessel, as that between the renal veins and the auricle, or that extending from the iliac veins to the renal veins. The collateral circulation after occlusion may be carried on through the saphenous, superficial abdominal, spermatic, pudic, and deep epigastric veins, and the obturator, inferior mesenteric, external mammary, and azygos veins. Tributaries. In addition to the common iliac veins by whose union it is formed, the vena cava inferior receives a number of tributaries from the abdominal walls and organs. These may be arranged into two groups according as they drain t\\& parietes of the abdomen (radices parietales) or its viscera (radices viscerales). Of the former there are : (i) the inferior phrenic and (2) the lumbar veins, and of the latter (3) the hepatic, (4) the renal, (5) the suprarenal, and (6) the spermatic or ovarian veins. 1. The Inferior Phrenic Vein. The inferior phrenic (v. phrenica inferior) is a paired vein which corresponds to the similarly named artery. It is formed by the union of a number of tributaries which ramify upon the under surface of the diaphragm, and ope'ns into the vena cava just before it passes through the diaphragm. It receives tributaries from the upper portion of the suprarenal capsule, and the left vein, by the enlargement of an anastomosis of its suprarenal tributaries with the suprarenal vein, may open through the latter into the left renal vein. The right vein occasionally opens into the right hepatic vein. 2. The Lumbar Veins. The lumbar veins (vv. lumbales) are usually four in number on each side, and accompany the corresponding arteries, lying above them. They resemble closely in their relations and tributaries the intercostal veins, of which they are serial homologues. Each vein arises in the muscles of the abdominal wall and passes backward and inward towards the vertebral column, passing beneath the psoas muscle. Shortly before reaching the vena cava it receives a ram us dorsal is. This has its origin in the dorsal integument and muscles, communicating with the posterior external spinal plexus, and receives a ramus spinalis which communicates with one of the lumbar intervertebral veins and so with the internal spinal plexuses. The veins then continue their course towards the vena cava, those of the left side passing beneath the abdominal aorta, and they open into the posterior surface of the vena cava. As it passes upon the lateral surface of its corresponding lumbar vertebra, each of the three lower veins is connected with the one above by an ascending stem, which also places the lowest vein in communication with the ilio-lumbar or the common iliac vein, while from the uppermost vein it is continued on upward to join with the azygos or hemiazygos as the case may be. This ascending stem is the ascending lumbar vein (v. lumbalis ascendens), and is of especial interest as forming an important collateral channel between the inferior and superior venae cavae. Each lumbar vein possesses one or two valves in its course, and sometimes also valves at its entrance into the vena cava. The concavities of these valves are directed towards the vena cava, but the valves are nearly always insufficient and 902 HUMAN ANATOMY. consequently will not prevent a flow of blood from the vena cava outward to the ascending lumbar veins in cases of occlusion of the upper part of the vena cava. 3. The Hepatic Veins. The hepatic veins (vv. hcpaticae) (Fig. 765) return the blood which has been carried to the liver both by the hepatic artery and by the portal vein. They are two or three in number, and are formed by the union of the intralobular veins of the liver (page 920). They emerge from the substance of the liver at the upper part of the groove* in which the vena cava lies, and, passing obliquely upward, enter that vessel at an angle shortly before it passes through the diaphragm. One of the hepatic veins drains the substance of the right lobe of the liver, the other, when there are but two, the remaining lobes. Quite frequently this second or left vein is replaced by two vessels, one of which drains the left lobe alone, while the other drains the Spigelian and quadrate lobes. Usually, in addition to these principal veins, a varying number of small hepatic veins occur, which make their exit from the liver-substance on the walls of the groove for the vena cava and open directly into that vessel without joining the principal hepatic veins. The hepatic veins possess no valves in the adult, and are characterized by the thickness of their walls, which are provided with both circular and longitudinal muscles. Variations. Occasionally, the right vein, more rarely the left, perforates the diaphragm and opens either into the thoracic portion of the inferior vena cava or else directly into the right auricle. The two (or three) veins sometimes unite to a single trunk before joining the vena cava, and this trunk has been observed to penetrate the diaphragm and open direct!) into the right auricle without communicating with the vena cava. 4. The Renal Veins. The renal veins (vv. renales) (Fig. 766) are two in number, one returning the blood from each kidney. Each vein is formed at the hilum, or some little distance from it, by the union of from three to five branches which come from the kidney substance, and is directed medially and slightly upward, lying in front of the corresponding artery. On account of the position of the vena cava to the right of the median line, the left vein is somewhat longer than the right, and passes in front of the abdominal aorta, just below the origin of the superior mesenteric artery, to reach its point of entrance into the vena cava, this point being usually a little higher than that of the right vein. Tributaries. In addition to the vessels by whose union it is formed, each renal vein receives (a) an inferior suprarenal vein from the lower part of the suprarenal capsule, accompanying tin corresponding artery ; (b] adipose veins, which pass transversely across both surfaces of the kidney, taking their origin in its adipose capsule ; (c) a ureteric vein, frequently more or less plexiform in structure, which returns the blood from the upper part of the ureter, anastomosing below with the ureteric tributaries of the spermatic vein. In addition, the left renal vein receives the left spermatic (ovarian) and the left middle suprarenal veins, both of which will be considered with their fellows of the opposite side. The adipose veins ramifying in the kidney fat penetrate the renal fascia and so come into connection with the tributaries of the lumbar veins, and 'they also send branches to the spermatic or ovarian veins. A more important communication is, however, made through a vein which arises from the lower surface of each renal and empties on the right side into the first lumbar vein, while on the left side it bifurcates, sending one branch downward to the first lumbar and the other upward to open into the hemia/ygos. Since valves occur hut rarely in the renal vein, and its tributaries are likewise either without valves or with insufficient ones, the circulation of the kidney may be maintained by means of these communications of the renal veins, even in cases of obliteration of the vena cava inferior in its upper portion. Variations. The renal veins are occasional I v replaced by from two to seven \essels which open independently into the vena cava, a condition which probably depends upon the failure of tin- vessels from the different portions of the kidneys to unite to a" common stem. _ Accessory veins, which communicate with the vena cava below the level of the renals or even with the com- mon iliac, sometimes occur, but more rarely than the similar arteries. The left renal vein has been observed i n several cases to pass almost vertically downward parallel to the vertebral column, opening into the vena cava at the level of the fourth lumbar vertebra THE INFERIOR CAVAL SYSTEM. 903 5. The Middle Suprarenal Veins. The middle suprarenal veins (vv. stiprarenales ) are the principal veins of the suprarenal bodies, from which, however, the superior suprarenals, emptying into the phrenics, and the inferior, opening into the renals, also arise. Each vein occupies a groove on the anterior surface of the suprarenal body, and descends obliquely inward to open on the right side into the inferior vena cava above the right renal, and on the left side into the left renal. 6a. The Spermatic Veins. The spermatic veins (vv. spermaticae) begin at the internal abdominal ring, whence they pass upward and inward along with the spermatic arteries and are the continuation upward of the venous plexuses which surround the spermatic cords. Each of these plexuses has its origin in the testicular veins (vv. testiculares) which return the blood from the tunica albuginea testis and from the seminiferous tubules, these latter branches passing towards the hilum of the organ in the trabeculae. They make their exit from the testis at about the middle of its superior border, and are joined very shortly by the veins of the epididymis. They are then continued up the spermatic cord in the form of from ten to twenty flexuous stems, which anastomose abundantly to form what is termed the pampiniform plexus (plexus pampiniformis), surrounding the spermatic artery. As the cord enters the inguinal canal the plexus is reduced to some three or four stems, which, at the internal abdominal ring, become the spermatic veins. These are two or three stems which anastomose abundantly with one another and consequently present a plexiform arrangement. They surround the abdominal portion of the spermatic artery and, shortly before reaching their termination, unite to a single stem, which on the right side opens at an acute angle into the vena cava inferior below the right renal vein, while on the left side it opens almost at a right angle into the lower border of the left renal vein. The spermatic veins proper possess no valves, except that there is usually a pair at the entrance of the right vein into the vena cava. In the stems of the pampiniform plexus, however, valves are usually to be found, but they are very frequently insufficient. Tributaries. The spermatic veins receive a ureteric branch from the lower part of the ureter and also peritoneal branches and renal branches from the adipose capsule of that organ. In the scrotum the pampiniform plexus makes connections with the branches of the external pudic veins, and at their entrance into the external abdominal ring the two plexuses of opposite sides are connected by transverse anastomoses which pass in front of the symphysis pubis. A deeper transverse anastomosis also occurs between the two spermatics as they emerge from the internal abdominal rings, and they communicate by means of their peritoneal branches with the branches of the right and left colic veins. Variations. Occasionally the left vein as well as the right opens directly into the vena cava, and in cases in which that vessel is situated upon the left side it is the left vein which opens directly into it, the right one opening into the right renal vein. They communicate sometimes on one side or the other with a lumbar vein or with the middle suprarenal, and the left vein has been observed to open into the hemiazygos. The spermatic veins are very apt to become varicose, and it is well known that this con- dition is more apt to occur in the left vein than.in the right. Various reasons have been assigned for this difference in the two veins, the chief of these being ( i ) that the left vein opens at prac- tically a right angle into the renal, while the right opens at an acute angle into the vena cava ; (2) the left vein is destitute of valves at its opening into the renal, while the right one usually possesses a pair at its orifice ; and (3) that the left vein in its course up the abdominal wall lies beneath the sigmoid colon, while the right has only coils of the small intestine with their more fluid contents in front of it. 66. The Ovarian Veins. The ovarian veins (vv. ovaricae) correspond to the spermatic veins of the male. They take their origin from the veins which issue at the hilum of the ovary and are also connected by wide anastomoses with the veins of the fundus of the uterus. They form a close plexus, the pam- piniform plexus (plexus pampiniformis), which accompanies the ovarian artery between the two layers of the broad ligament parallel with the Fallopian tube, receiving branches from the latter structure and from the round ligament of the 904 HUMAN ANATOMY. uterus. Leaving the broad ligament with the ovarian artery, they ascend along that vessel, the number of trunks becoming reduced to two and eventually to one, and they open above in the same manner as the spermatic veins, the right one into the inferior vena cava and the left one into the left renal vein. They possess no valves. Their variations are essentially similar to those presented by the spermatic veins. Practical Considerations. The Tributaries of the Inferior Cava. In a case of occlusion of the inferior cava by thrombus extending from the renal vein to the right auricle, the phrenic and renal veins opened into the lumbar and azygos veins, the blood of the abdomen thus gaining the superior cava (Allen). The intralobular branches of the hepatic veins may be the source of profuse hemorrhage in cases of wound or rupture of the liver, because (a) they are thin- walled ; (b} they are not encircled by cellular tissue, but are closely attached to the liver substance and thus cannot collapse or retract, a condition which also predisposes to the entrance of air into the divided veins ; (/) they are valveless, and the main trunks open direct into the vena cava, any obstruction of which would therefore result in the escape of great quantities of blood ; (d ) the flow in the main trunks from the vein to the cava is influenced by the movements of the diaphragm, the descent of this muscle tending to constrict the opening through which the veins pass, and thus to obstruct the current and favor bleeding. Hemorrhage from the liver after a wound or during an operation is very difficult to arrest by ligature on account of the thinness of the walls of the intralobular veins and the friability of the liver tissue itself. It is usually controlled by gauze-pressure or by the galvano-cautery. The branches of the portal vein may also bleed freely, but are surrounded by a quantity of lax cellular tissue, as they run in the ' ' portal canals' ' with the branches of the biliary ducts and of the hepatic artery, and can thus retract or collapse when torn or divided. More- over, the blood -pressure within the portal vein is low, favoring the spontaneous arrest of hemorrhage. In obstruction of the common duct, preventing the escape of bile into the intestine, the radicles of the hepatic veins take up the bile-stained exudate that results from the increased intra-hepatic tension. Its entrance into the general circulation through the vena cava gives rise to jaundice. The relative shortness of the right renal vein occasionally adds to the difficulties of a right-sided nephrectomy, the pedicle the vein, artery, ureter, etc. being shorter and less easily controlled by ligature. As the veins are subject to variation as well as the arteries though less frequently supernumerary or misplaced vessels should be carefully looked for. They may be found emerging from the kidney at either pole, or from the hilum behind the pelvis. Fatal results have followed the failure, during a nephrectomy, to find and secure such aberrant vessels. At times the left renal vein passes behind the aorta, to which occurrence may be attributed the greater frequency of hyperaemia of the left kidney (Allen). The renal veins may be obstructed by pressure from retroperitoneal growths, or in the supine position from movable abdominal tumors or the gravid uterus, or from traction caused by displacements of the kidney itself, or as a result of congestion in the cardio-pulmonary system, as in pneumonia or valvular heart disease. By whatever cause produced, the congestion, if sufficiently long-continued, may give rise to a form of chronic interstitial nephritis. The communication (ride supra) between the renal veins and the first lumbar vein and on the left side the hemiazygos vein, accounts for the undoubted good effect often produced in renal congestions by counter- irritation, blisters, cupping, or leeching in the loin. The spermatic veins are of chief practical interest in their relation to varicocele. The anatomical reasons for the frequency of this condition, and for its occurrence by preference on the left side, are given on page 1961. The veins of the pampiniform plexus proper are usually distinct from those which accompany the vas deferens and its. artery. In excision of the former set for varicocele, the vas deferens is always pushed to the rear and held out of harm's way. It carries with it its artery and veins, and the anastomotic communications of the former with the spermatic artery almost always cut or tied with its venous plexus and with the scrotal arteries suffice to maintain the nutrition of the testis, while the THE INFERIOR CAVAL SYSTEM. 905 veins of this smaller and posterior group enlarge to carry on the return circulation. Elevation is of especial value in testicular inflammation, as the dependent position of the spermatic veins and their lack of adequate support greatly intensify the engorge- ment and venous obstruction of inflammatory processes. THE COMMON ILIAC VEINS. The common iliac veins (vv. iliacae communes) (Fig. 765) are two in number, and are formed opposite the sacro-iliac articulations by the union of the internal and external iliac veins. They pass upward, converging as they go, and unite at about the level of the intervertebral disk between the fourth and fifth lumbar vertebrae to form the vena cava inferior. Since their point of union lies somewhat to the right of the median line, the right vein is shorter than the left and its course is more directly upward. Neither vein possesses valves. Relations. The union of the two veins takes place beneath the right common iliac artery, and the right vein, at its origin, lies behind that vessel, although, since its course is more vertical than that of the artery, it gradually comes to lie somewhat lateral to it above. The left vein near its termination is crossed from without inward by the right common iliac artery, and throughout its course lies medially to the left common iliac artery and on a plane somewhat posterior to it. Variations. Occasionally the external and internal iliac veins do not unite to form a common stem, but open directly into the inferior vena cava. This may occur on one or both sides. Tributaries. In addition to the external and internal iliacs, by whose union they are formed, the common iliacs receive but a single tributary, the middle sacral vein (v. sacralis media), and this opens into the left vein. It accompanies the middle sacral artery, and in the lower part of its course it is frequently double, one vessel lying on each side of the artery. Opposite each sacral vertebra it receives a transverse connecting branch from the lateral sacral veins and so forms with these what is termed the anterior sacral plexus. At its origin it communicates with the hemorrhoidal veins. THE INTERNAL ILIAC VEIN. The internal iliac vein (v. hypogastrica) (Fig. 767) of each side is a short but rather large vessel, which accompanies the internal iliac artery, lying to its medial side and in a plane somewhat posterior to it. It extends from the neighborhood of the great sacro-sciatic foramen to the level of the sacro-iliac synchondrosis, where it unites with the external iliac to form the common iliac vein. Tributaries. Its tributaries correspond in general with the branches of the internal iliac artery, but those which arise in the pelvic viscera present the peculiarity that they take their origin from more or less extensive plexuses which communicate with one another. The stems which pass from these plexuses to the internal iliac also anastomose to a considerable extent, the result being that it is not possible in all cases to recognize definite veins corresponding to the visceral arteries. The following are the tributaries that are, as a rule, to be recognized : ( i ) the gluteal, (2) the lateral sacral, (3) the ilio-lumbar, (4) the sciatic, _(s) the internal pudic, (6) the obturator, (7) the middle hemorrhoidal, (8) the uterine, and (9) the vesical veins. i. The Gluteal Vein. The gluteal vein (v. glutaea superior) accompanies the artery of the same name. Throughout its extrapelvic course its tributaries accom- pany the branches of the artery as valved venae comites, and at the upper part of the greater sacro-sciatic foramen the veins accompanying the two main branches of the artery unite to form a double trunk, united by numerous anastomoses. This trunk, which is occasionally single, passes through the greater sacro-sciatic foramen above the pyriformis muscle and, after a short intrapelvic course, opens int the internal iliac vein. Where they pass through the greater sacro-sciatic foramen both artery and vein are surrounded by a dense connective tissue which renders their separation difficult and brings it about that the lumen of the vein remains patent when emptied of blood. 906 HUMAN ANATOMY. 2. The Lateral Sacral Veins. The lateral sacral veins (vv. sacrales laterales) are usually double, and pass upward with their arteries upon the anterior surface of the sacrum just medial to the anterior sacral foramina, and open above either directly into the internal iliacs or into the gluteal veins. As they pass each sacral foramen they receive tributaries from the internal spinal plexuses, and opposite each sacral vertebra are connected by transverse branches with the middle sacral veins, these anastomoses forming the anterior sacral plexus. 3. The Ilio-Lumbar Vein. The ilio-lumbar vein (v. iliolumbalis) follows the course of the corresponding artery and its branches and is richly supplied with FIG. 767. Aorta Vena cava inferior Genito-crural nerve Internal iliac vein Anterior superior spine of ilium Obturator nerve External iliac- artery and vein Superior gluteal vein Dorsal vein of penis Sup. and deep layers of triangular ligament Ischio-cavemosus muscle, cut edge Cowper's gland Bulbo-cavernosus muscle, cut edge .Right and left common iliac arteries Left common iliac vein Internal iliac vein Lateral sacral vein Superior hemorrhoidal Lateral sacral vein Sciatic vein Internal pudL vein Vesical veins i ing to a single trilmt : of internal iliac vein TriUitaries of intern i iliac from vesical plexus Middle hemorrhoidal \ein Vesico-prostatic | : Prostate Superficial anal sphincter. venous plexus trilmt ir; t<> inferior hemorrhoidal veins Anus Transverse perinea! muscle Bulb of corpus spongiosum wt-(l from left side. valves. Its lumbar tributary receives some of the lower intervertebral veins ami occasionally the last lumbar, and anastomoses with the lower portion of the ascending lumbar vein. The iliac tributary, which begins over the crest of the ilium and in the substance of the iliacus muscle, makes anastomoses with tributaries of the drrp circumflex iliac vein and thus establishes an important collateral venous path between the external and internal iliars. The main stem of the vein is a single trunk which opens into the internal iliac or occasionally into the common iliac. 4. The Sciatic Vein. The sciatic vein < v. ulutaea interior) of either side of the body has essentially the same course as the corresponding artrry. Its extrapelvic THE INFERIOR CAVAL SYSTEM. 907 tributaries are venae comites of the branches of the artery, and its usually single main stem passes through the greater sacro-sciatic foramen below the pyriformis to empty into the internal iliac. Anastomoses of comparatively large calibre occur between the extrapelvic portions of the sciatic vein and the internal circumflex and first perforating tribu- taries of the deep femoral vein, thus establishing a collateral venous path between the tributaries of the internal and external iliacs. 5. The Internal Pudic Vein. The internal pudic vein (v. pudenda interim) is associated throughout the greater part of its course with the artery of the same name. It differs, however, somewhat in its origin, since it is not the direct continuation of the dorsal vein of the penis (or clitoris), although it communicates with that vessel by a small branch immediately below the symphysis pubis, but is rather the continuation of the veins of the corpus cavernosum which accompany the artery to that structure. It is throughout the most of its length double, anastomoses between the two stems surrounding the internal pudic artery. It has its origin between the two layers of the triangular ligament of the perineum and passes backward into the ischio-rectal fossa, lying with the artery at the side of that cavity in a canal (Alcock 1 s canal) formed by a splitting of the lower edge of the obturator fascia. It leaves the ischio-rectal fossa by the lesser sacro-sciatic foramen and, curving around the spine of the ischium, enters the pelvis through the lower part of the greater sacro-sciatic foramen and empties into the internal iliac. In addition to the communication with the dorsal vein of the penis (or clitoris) already mentioned, the internal pudic vein makes near its origin a connection with the pudendal plexus and, as it curves over the spine of the ischium, with the sciatic vein. It possesses several valves arranged in a rather characteristic manner. Through- out its course through the perineum it is valveless, but both its terminal portion and its communication with the pudendal plexus possess valves whose concavities look in the one case towards the internal iliac and in the other towards the plexus. Blood contained in the perineal portion of the vein may flow, therefore, either towards the internal iliac directly or to the pudendal plexus (Fenwick), and the communication with the latter cannot well be regarded as the origin of the vein, as is sometimes done. Tributaries. In addition to (a) the vein of the corpus cavernosum (v. profunda penis vel clitoridis) already mentioned, the internal pudic vein receives numerous tributaries which cor- respond with the branches of the artery. Among these may be mentioned : (b) the veins of the bulb ( vv. bulbi urethrae), which are quite numerous and issue from the bulb of the urethra or from the bulbus vestibuli in the female, these latter vessels being quite large ; (c ) the superficial peri- neal veins (vv. scrotales posteriores), which return the blood from the integument and superficial muscles of the perineum and from the posterior surface of the scrotum and the posterior portion of the labia majora, anastomosing in these structures with the tributaries of the external pudic veins; (d) the inferior hemorrhoidal veins (vv. haemorrhoidales inferiores), which traverse the ischio-rectal space from the neighborhood of the anus, where they make communications with the hemorrhoidal plexus of the rectum. 6. The Obturator Vein. The obturator vein (v. obturatoria) accompanies the obturator artery and shares in the variations which that vessel presents (page 814). It takes its origin in the adductor muscles of the thigh, its tributaries uniting to form an internal and an external branch, which curve around the margins of the obturator foramen. The vein formed by the union of these two branches passes through the opening in the upper part of the obturator membrane and passes across the lateral pelvic wall, lying immediately below the artery. It opens, as a rule, into the internal iliac vein. Its communications are somewhat extensive and important. Its external tribu- tary branch receives branches from the scrotum or labia majora and through these communicates with the external pudic veins. At its passage through the opening in the obturator membrane it receives branches from the obturator plexus, which cover both surfaces of the membrane and drain the obturator muscles, and also a branch which passes downward and inward upon the inner surface of the os pubis, frequently communicating above with the pubic tributary of the deep epigastric vein. 908 HUMAN ANATOMY. Additional communications are made with the vesico-prostatic (vesico- vaginal) plexus and the internal pudic vein, and also with the internal circumflex branch of the deep femoral and with the sciatic. 7. The Middle Hemorrhoidal Vein. The middle hemorrhoidal vein (v. haemorrhoidalis media) has its origin in the hemorrhoidal plexus of the rectum, and after receiving tributaries from the seminal vesicles, the prostate gland, and the urinary bladder in the male and from the vagina in the female, opens into the internal iliac or one of its tributaries. It is a comparatively large vein, and of importance in that it forms through its connection with the hemorrhoidal plexus a communication between the portal and inferior caval systems of veins. The hemorrhoidal plexus (plexus haemorrhoidalis) which surrounds the rectum is composed of two venous net-works, one of which, the internal hemorrhoidal plexus, lies in the submucosa of the rectum, while the other, \heexternal hemorrhoidal plexus, rests upon its outer surface. The internal plexus is characterized in the adult, in that portion of it which lies just above the anal opening, by the occurrence of round or elongated bunches (glomera haemorrhoidalia) formed by a number of small veins coiled together into a mass resembling somewhat a Malpighian glomerulus. Upon the veins which form the glomera, or upon those extending between adjacent glomera, ampullar dilatations occur which have been regarded both as the cause and as the result of the glomera formation. Be that as it may, the internal hemorrhoidal plexus presents in the adult, slightly above the anus, a distinct band characterized by the occurrence of glomera and dilatations, and forming what is termed the annulus haemorrhoidalis. The internal plexus opens partly at the anal orifice into the branches of the inferior hemorrhoidal veins and partly, by branches which traverse the muscular coats of the rectum, into the external plexus. This has three sets of efferent veins : (i) the inferior hemorrhoidals, which open into the internal pudic ; (2) the middle hemorrhoidals, which pass to the internal iliac or one of its branches ; and (3) the superior hemorrhoidal, which leads to the inferior mesenteric and so to the portal vein. The external plexus also communicates with "the vesico-prostatic plexus in the male and the vaginal plexus in the female. 8. The Uterine Vein. The uterine vein (v. uterina) arises opposite the external os uteri from the plexus utero-vaginalis. It is at first a double vein, its two trunks accompanying the uterine artery, and where that vessel crosses the ureter one of the trunks passes with the artery in front of the duct and the other behind it. The two trunks then usually unite to a single vein, which passes into the internal iliac, frequently receiving the vesical veins or the obturator. The utero-vaginal plexus is formed by the veins which return the blood from the uterus and vagina. The veins in the substance of the uterus are exceedingly thin-walled, appearing as clefts in sections, and form a more or less distinct layer (stratum vasculare) in the muscular wall of the organ. From this vessels pass to both the anterior and posterior surfaces of the organ and follow a course which is outward and more or less downward towards the lateral borders, where, between the two layers of the broad ligament, they form a rich plexus, the uterine plexus, the vessels of which converge towards the origin of the uterine vein, opposite the external os uteri. The vaginal veins form a rich plexus in the walls of the vagina, the emissaries from which are directed laterally and more or less upward, forming along the lateral walls of the organ a rich vaginal plexus whose stems also convener to the uterine vein at the level of the external os uteri. These two plexuses, the uterine and vaginal, are continuous at the level of the external os uteri and form together the extensive plexus utero-vaginalis. At the fundus of the uterus this plexus makes abundant connections with the pampiniform plexus of the ovarian veins and with the funicular veins which accompany the ligamentum teres. Lower down, throughout its uterine portion, it receives affluents from the plexus of veins which occurs between the layers of the broad ligament, and the lower part of its vaginal portion makes connections anteriorly with the vesico- vagina] plexus and posteriorly with the external hemorrhoidal plexus. 9- The Vesical Veins. The vesical veins (vv. vesicales ) vary somewhat in number, but together represent a vessel of considerable size. They arise at the sides of the bladder from a well-marked plexus which occupies in the male the groove THE INFERIOR CAVAL SYSTEM. 909 between the prostate gland and the bladder and is termed the vesico -pro static plexzts. In the female the plexus lies at the sides and base of the bladder, and from its relations posteriorly is known as the vesico-vaginal plexus. From their origin the vesical veins pass upward, outward, and backward to open into the internal iliac. The vesico-prostatic or vesico-vaginal plexus (plexus vesicalis), occupying the position indicated above, is formed principally by the veins which drain the urinary bladder and, in the male, the prostate gland. Posteriorly, in the male, the plexus communicates with the external hemorrhoidal plexus, and in the female with the vaginal plexus, and anteriorly, in both sexes, it communicates extensively with the pudendal plexus. In addition to the drainage which it possesses through the vesical veins, it also drains by way of the obturator veins, branches from it joining those vessels just after they have passed through the obturator foramina. The pudendal plexus (plexus pudendalis), also known as the plexus of Santo - riui, occupies the space between the lower part of the pelvic surface of the symphysis pubis and the anterior surface of the neck of the bladder, becoming continuous posteriorly at the sides with the vesico-prostatic (vesico-vaginal) plexus. Its chief tributary is the deep dorsal vein of the penis (clitoris) (v. dorsalis penis vel clitoridis), which is a single large vein (sometimes partly double in the female) which passes along the dorsal mid-line of the penis or clitoris, beneath the deep fascia (Fig. 767), in the groove between the two corpora cavernosa, and hasten either side of it one of the two dorsal arteries. It receives branches from the corpora cavernosa and has its origin in two veins which curve from below upward around the base of the glans penis (clitoridis). At the root of the penis (clitoris) it leaves the dorsal surface and perforates the triangular ligament of the perineum, .usually just below the border of the subpubic ligament, so entering the pelvis. It then bifurcates, each of the branches passing into the pudendal plexus. Before entering the pelvis it gives off on either side a small branch which unites with the internal pudic vein, thus representing the course of the artery. In addition to the dorsal vein of the penis (clitoris), the pudendal plexus also receives branches from the internal pudic vein and from the anterior surfaces of the bladder and, in the male, the prostate. It communicates posteriorly and at the sides with the vesico-prostatic (vesico-vaginal) plexus, and through it finds its chief efferents in the vesical veins, although it is also drained by the obturator veins, with each of which it communicates by one or two branches. THE EXTERNAL ILIAC VEIN. The external iliac vein (v. iliaca externa) (Figs. 766, 767) begins at Poupart's ligament, where the femoral vein becomes continuous with it, and passes upward, backward, and inward to the level of the sacro-iliac articulation, where it unites with the internal iliac to form the common iliac. Its course is along the line of junction of the false and the true pelvis, and it lies upon the inner border of the psoas muscle and internal, or in its upper part internal and posterior, to the external iliac artery. Near its termination it is crossed by the internal iliac artery, on the left side almost at a right angle, on the right more obliquely. Valves are present in about 35 veins out of 100, but in a third of such cases they are insufficient. Tributaries. The tributaries of the external iliac vein are : (i) the deep epi- gastric and (2) the deep circumflex iliac veins. i. The Deep Epigastric Vein. The deep epigastric vein (v. epigastrica inferior) has its origin above the umbilicus in the substance of the rectus abdominis muscle, where it anastomoses with the superior epigastric vein. It accompanies the deep epigastric artery as two venae comites which unite below to form a single trunk opening into the external iliac a short distance above Poupart's ligament. Below the level of the umbilicus the vein is provided with valves whose concav- ities are directed downward, but above the umbilicus it is said to be destitute of valves. It receives tributaries from the rectus muscle and, as it passes beneath the 910 HUMAN ANATOMY. internal abdominal ring, from the spermatic cord or round ligament of the uterus. The connections which it makes with other veins are numerous and important. Its connections with the superior epigastric vein have already been noted ; by this communication is established between the superior and inferior venae cavae. In addition, by means of branches which traverse the sheath of the rectus muscle, it communicates with the subcutaneous and subperitoneal veins of the abdominal wall and with the parumbilical veins, forming through these latter a connection with the portal system of veins. Finally, by means of a pubic branch, which is frequently a tributary of the external iliac rather than of the deep epigastric, it communicates with the obturator vein, and by the enlargement of this communication the obturator vein, just as is the case with the artery, may become a tributary of the deep epigastric. 2. The Deep Circumflex Iliac Vein. The deep circumflex iliac vein (v. circumflexa ilium profunda) has the same course as the corresponding artery, which it surrounds in a plexiform manner. It possesses valves and communicates with the iliolumbar veins. Near its termination it becomes a single trunk and opens into the external iliac a little above the deep epigastric ; occasionally it opens into the latter vessel. THE VEINS OF THE LOWER LIMB. The external iliac vein is the channel by which the blood returning from the lower limb is conveyed to the inferior vena cava and is the direct upward continuation of the femoral vein. Instead, however, of proceeding to a description of this latter vessel and so down the leg, it will be more convenient to begin the account of the veins of the lower limb with those of the foot and proceed upward to the femoral. As in the upper limb, two practically distinct sets of veins can be recognized in the leg ; one set is more or less deeply seated and accompanies the arteries, while the other is superficial and, in the adult, has a course quite independent of the arterial distribution. The deep veins will first be considered.. THE DEEP VEINS. THE DEEP VEINS OF THE FOOT. The deep veins of the sole of the foot have their origin in a net-work with more or less distinctly elongated meshes, which occurs upon the plantar surfaces of the digits. These are the plantar digital veins (vv. dictates plantares), and in the webs of the toes the vessels of each digit unite with those of the neighboring ones to form a series of plantar interosseous veins (vv. metatarseae plantares) occupying the metatarsal interspaces and forming venae comites for the plantar interosseous (metacarpal) arteries. Just as the digital veins unite to form the interosseous, they send dorsal branches (vv. intercapitulares), which unite with the dorsal interosseous veins, and, in addition, make connections with the superficial plantar veins, and might, indeed, be classed with these quite as appropriately as with the deep set. The plantar interosseous veins pass backward, receiving branches from the neighboring muscles, and open into a venous plantar arch (arcus vcnosus plantaris), formed by the venae comites of the arterial plantar arch. These are continued pos- teriorly into the external plantar veins, which pass obliquely across the loot along with the corresponding artery and unite behind the inner malleolus with the internal plantar veins to form the companion veins of the posterior tibia! artery. Both plantar veins give off branches which perforate the plantar aponeurosis and communi- cate with the superficial plantar veins, and connecting vessels also pass across the sole of the foot between the two veins. Upon the dorsum of the foot there exist the dorsal digital veins ( vv. dinitales dorsalesi, which, like the corresponding plantar veins, may be equally classified with superficial or deep veins, since they make connections with both sets. In the wd>s of the toes the vessels of adjoining digits unite to form the four dorsal interosseous veins ( vv. metatarseae dorsalcs ). which occupy the metatarsal interspaces and com- municate with the corresponding plantar veins by the intercapitular and perforating THE VEINS OF THE LOWER LIMB. 911 veins. They form the venae comites of the dorsal interosseous (metatarsal) arteries and open into the companion veins of the metatarsal artery. These, together with the veins accompanying the tarsal arteries, open into the venae comites of the art. dorsalis pedis, and these in turn are continuous with the venae comites of the anterior tibial artery. THE DEEP VEINS OF THE LEG. The deep veins of the leg are the venae comites of the posterior and anterior tibial arteries and their branches. The posterior tibial vein (v. tibialis posterior) is formed behind the internal malleolus by the union of the internal and external plantar veins, and consists of two, or in many cases three, veins accompanying the posterior tibial artery. It terminates at the lower border of the popliteus muscle by uniting with the anterior tibial veins to form the popliteal, and possesses in its course from eight to twenty valves. A short distance below the popliteus muscle it receives the peroneal veins (vv, peroneae) which accompany the peroneal artery. They are usually of larger calibre than the posterior tibial veins, receiving a larger share of the vessels which come from the posterior crural muscles, and they anastomose with the posterior tibials by frequent transverse branches, and also with the anterior tibials. They possess from eight to ten valves. The anterior tibial veins (vv. tibiales anteriores) are the upward continuation of the venae comites of the art. dorsalis pedis. They accompany the anterior tibial artery, and are united across the artery by numerous transverse anastomoses. They pass with the artery to the posterior surface of the crus above the interosseous mem- brane and unite with the posterior tibials to form the popliteal vein. They make communications with both the peroneal and posterior tibial veins by branches which perforate the interosseous membrane, and are furnished, on the average, with about eleven valves. THE POPLITEAL VEIN. The popliteal vein (v. poplitea) (Fig. 768) is a single trunk formed by the union of the anterior and posterior tibial veins at the lower border of the popliteus muscle, and it extends from that point to the opening in the adductor magnus which transmits the femoral artery. It is throughout closely bound down by dense connective tissue to the popliteal artery, and lies between that vessel and the internal popliteal nerve. Its course, however, is not quite parallel to that of the artery, but in its lower part it is slightly internal to the artery and in its upper part somewhat external to it. The popliteal vein possesses from one to four valves and is directly continuous above with the femoral vein. In addition to the popliteal vein, the popliteal artery has two other smaller veins accompanying it. The external one (v. comitans lateralis) has its origin from the veins issuing from the outer head of the gastrocnemius and the soleus, and passes upward along the outer surface of the artery to open into the popliteal vein at about the middle of its course. The inner vena comitans (v. comitans medialis) is formed by the veins issuing from the inner head of the gastrocnemius and ascends along the inner side of the artery, making connections with the inferior and superior internal articular veins, to open into the popliteal vein just below the opening in the adductor magnus. Tributaries. The majority of the tributaries of the popliteal vein correspond to the branches of the popliteal artery, that is to say, they are articular and muscular. In addition it receives the short saphenous vein at about the middle of its course. Variations. The popliteal vein may be considerably shorter -than usual owing to the fail- ure of the tibial veins to unite at the customary level. Not infrequently the vein is double throughout a portion of its course, more rarely throughout its entire length, and it occasionally lies beneath (i.e., anterior to) the artery. It normally communicates by means of its tributaries with branches of the deep femoral vein, and occasionally this communication becomes so large that the popliteal seems to bifurcate above, one branch becoming continuous with the femoral and the other with the deep femoral. More interesting from the historical stand-point are the rare cases in which the vein 912 HUMAN ANATOMY. ascends the back of the thigh along with the sciatic nerve, either uniting above with c the branches of the deep femoral or continuing into the pelvis with the nerve to become a FIG. 768. Tibial nerve Semitendinosus muscle Popliteal artery Semimembranosus muscle Azygos articular vein Communication with internal saphenous vein Popliteal vein External saphenous vein Sural veins Gastrocnemius muscle, inner head Popliteus muscle Posterior tibial artery Communication between anterior and posterior tibtel veins Posterior tibial veins Communication with deep femoral vein Biceps muscle Superior external articular veins Plantaris muscle Gastrocnemius, outer head Anterior tibial vein Anterior tibial artery Soleus, cut surface Gastrocnemius, cut surface Deep fascia, cut edge Veins of right popliteal space. tributary of the internal iliac vein. This last arrangement recalls ;m anomaly occasionally pre- sented by the sciatic artery (page 815), and is probably clue to the same embryological conditions. THE VEINS OF THE LOWER LIMB. THE FEMORAL VEIN. The femoral vein (v. femoralis) (Fig. 769) accompanies the femoral artery from the opening in the adductor muscle through Hunter's canal and Scarpa's triangle to its beginning at the lower border of Poupart's ligament. It is a single FIG. 769. Anterior superior spine of ilium Superficial circumflex iliac vein Sartorius, cut Femoral artery Rectus femoris, cut Femoral vein External circumflex vein Deeo femoral vein Vastus externus Rectus femoris, cut Anastomotica magna vein Quadriceps extensor tendot Patella, displaced outwardly Superficial epigastric vein Poupart's ligament External pudic vein Pectineus muscle Dorsal vein of penis Internal saphenous vein Superior perforating vein Deep femoral vein Middle perforating vein Inferior perforating vein Muscular vein Femoral artery Tendon of adductor magnus Internal saphenous vein Popliteal vein Right femoral vein and its tributaries. 58 914 HUMAN ANATOMY. trunk and is the direct continuation of the popliteal vein below, and it terminates by becoming continuous with the external iliac vein above. In its lower part it lies slightly external to the artery, but throughout the greater part of its course it rests upon the posterior surface of the artery and is enclosed in a common sheath with it. Above it inclines somewhat inwardly and comes to lie upon the inner surface of the artery, between it and the femoral canal. It possesses from one to five pairs of valves, the most constant pair, present in 81 per cent, of cases, being situated in the upper 5 cm. of the vein and consequently controlling the flow from all the veins of the lower limb. Tributaries. The tributaries of the femoral vein correspond with the branches of the femoral artery, although some of them communicate with the vein only indirectly, opening primarily into the long saphenous vein, which is itself a tributary of the femoral. Thus, the long saphenous usually receives the external pudic, superficial circumflex iliac, and superficial epigastric veins, and these will be described later with the saphenous veins. Of the remaining tributaries, ( i ) the deep femoral, ( 2 > the vents comites, and (3) the anastomotica magna, the first two deserve special mention. 1. The Deep Femoral Vein. The deep femoral vein (v. profunda fcnioi is t accompanies the deep femoral artery, and, like it, receives as tributaries perforating veins (vv. perforantes) which take their origin upon the posterior surface of the adductor muscles and anastomose with one another, with tributaries of the popliteal below and with the sciatic above. The lowest perforating vein, which represents the actual beginning of the deep femoral, has communicating with it one of the terminal branches of the short saphenous vein. The deep femoral vein also receives the internal and external circumflex veins (vv. circumllexa femoris medialis et lateralis) which accompany the corresponding arteries as their venae comites, the internal circumflex anastomosing with the sciatic and obturator veins and so providing for a possible collateral circulation between the internal and external iliac veins. The deep femoral opens into the femoral usually about 4-5 cm. In-low Poupart's ligament, but not infrequently at a somewhat higher level, and the circumflex veins may open directly into the femoral instead of into the deepe'r vein. 2. The Vense Comites. The venae comites of the femoral artery are two or three small stems which run parallel with the artery and vein through Hunter's canal. One lies to the inner side of the artery (v. comitans medialis) and the other to the outer side (v. comitans lateralis), and when a third is present it accompanies the long saphenous nerve. They communicate with, or in some cases receive, the veins issuing from the adjacent muscles and open into the femoral vein, usually a little below the point where it receives the deep femoral vein. Variations. The portion of the femoral vein above the entrance of the deep femoral is sometimes termed the common femoral vein and the rest of it the superficial femoral, the common femoral being formed by the union of the superficial and deep veins. Occasionally the vein lies anterior to the artery throughout a considerable portion <>f its course, and it may be double to a greater or less extent, the two veins in such cases either lying posterior to the artery or one on either side of it. It occasionally passes up the leg behind the adductor niagmis. passing through the muscle where it is normally perforated by one of the perforating veins, this arrangement being apparently due to the enlargement of a connection with the deep femoral and of the anastomosis between the perforating veins. In such cases the femoral artery- is accompanied by one or two small stems, perhaps representing the venae comites, and in those cases in which the popliteal vein passes up the back of the thigh (page 911) the femoral is also greatly reduced in size. THE SUPERFICIAL VK1NS. THE SUPERFICIAL VEINS OF THE FOOT. It has already been pointed out (page 910) that the dorsal and plantar digital veins may be grouped either with the superficial or deep veins of the foot, since they communicate extensively with both sets. The superficial connections of the plantar digitals are with an arcus vcnosus plantaris cutaneus which runs across the foot at the bases of the toes and, bending upward over the edges of the foot, communicates with the dorsal veins. Posteriorly to this arch is a subcutaneous net-work (rete venosum THE VEINS OF THE LOWER LIMB. 9*5 Biceps Popliteal vein plantare cutaneum) which is especially close in the fatty pad beneath the-heel, but more open towards the bases of the toes. This net-work makes numerous connections with the deep plantar veins, and to a great extent is drained by superhcial emissaries which pass upward over the borders of the foot and open into the superficial dorsal veins. These emissaries are larger on the inner than on the outer side of the foot, and they all have a somewhat backward as well as an upward direction, those from the most posterior portions of the plexus passing directly backward and upward over the tuberosity of the heel. Anteriorly the more central portions of the net-work drain into the superficial plantar arch and communicate through this with the dorsal veins. The dorsal digital veins form by their union in pairs the common digital veins \ v. digitales communes pcdis), which correspond in position to the dorsal interosseous veins, except that they are subcutaneous. Posteriorly these veins anastomose to from a more or less regular dorsal subcu- taneous arch (arcus venosus dorsalis FIG. 770. pedis), which extends across the dorsal portions of the metatarsal bones, being convex distally and increasing in size from the outer to the inner border of the foot. Proximally to this arch there is an irregular net- work of veins (rete venosum dorsale pcdis) which makes numerous connections with the deep veins and passes proximally into the net-work of the anterior surface of the crus. Towards the borders of the foot, M~~ short u ... ,. ' f> n\ saphenous vein and forming the lateral and medial boundaries of the net-work, a more or less distinct longitudinal marginal vein can be seen on each side (vv. margijialcs lateralis et mcdialis), and it is into these that the superficial emissaries from the plantar net-work open from below. The internal marginal vein is somewhat larger than the external and joins the dorsal arch to form the long saphenous vein, while the external is the principal origin of the short saphenous. THE SHORT SAPHENOUS VEIN. The short or external saphenous vein (v. saphena parva) (Fig. 770) is the superficial vein of the back of the crus. It begins behind the external malleolus at the Upward continuation of the ex- ternal marginal vein of the foot. It lies at first upon the outer border of the tendo Achillis, but later takes a more median position and ascends the pos- terior surface of the leg almost in the median line. At about the middle of the leg it perforates the crural fascia and continues its upward course in the groove between the two heads of the gastrocnemius, and, entering the pop- liteal space, terminates by dividing into two branches, one of which opens into the posterior surface of the popliteal vein about on a level with the origins of the gastrocnemius, while the other passes farther upward to communicate with the beginning of the deep femoral vein. Superficial veins on dorsum of right toot and posterior surface of leg. 916 HUMAN ANATOMY. The short saphenous vein possesses from nine to ten valves in its course up the leg. In its lower part it accompanies the external or short saphenous nerve, which lies beneath (i.e., anterior to) it, and above it accompanies a branch of the small sciatic nerve. Tributaries. The short saphenous vein drains the outer border of the foot and the whole of the posterior superficial portion of the crus. Near its origin it receives the posterior emissaries from the superficial plantar net-work, and throughout its course up the crus it receives numerous branches from the superficial net-work of the posterior surface of that portion of the leg, and through this net-work makes communications with the long saphenous vein. The terminal branch which com- municates with the deep femoral vein receives a stem known as the v femoropoplitea, which runs downward upon the back of the thigh, superficially, receiving branches from the posterior superficial net-work of the thigh and communicating above with the sciatic and gluteal veins. Variations. The short saphenous vein occasionally opens into the long saphenous by the enlargement of one of the anastomoses between the two veins, only a small vessel representing its communication with the popliteal. It has been observed to continue up the thigh without or with but a small communication with the popliteal and deep femoral veins, and, entering the pelvis with the great sciatic nerve, to open into the internal iliac vein. In such cases its femoral portion probably represents the original femoral portion of the sciatic vein, and has the same significance as the prolongation of the popliteal up the thigh, of which mention has already been made (page 911). THE LONG SAPHENOUS VEIN. The long or internal saphenous vein (v. saphena magna) (Fig. 771) has its origin in the junction of the inner end of the dorsal arch of the foot with the inner marginal vein. It passes upward in front of the inner malleolus and then in the groove between the medial border of the tibia and the inner border of the gastrocne- mius muscle. As it approaches the knee-joint it bends slightly backward to pass behind the internal condyle of the femur, and then continues up the thigh in an almost direct course to the fossa ovalis, where it pierces the cribriform fascia and opens into the femoral vein. It is subcutaneous throughout its entire course and possesses from twelve to eighteen valves, some of which, especially in old individuals, are apt to be insufficient. Throughout its course up the crus it accompanies the long saphenous nerve, and in the thigh it lies at first along the line of the outer (anterior) edge of the sartorius, but later crosses that muscle obliquely so as to lie internal to it above. Tributaries. At its origin the long saphenous vein receives some of the more posterior internal emissaries of the plantar net-work, and in its course up the crus it receives the blood from all those portions of the superficial crural net-work which do not communicate with the short saphenous. In the thigh it is the collecting stem for all the superficial veins, those from the posterior surface frequently uniting to form an accessory saphenous vein (v. saphena accessoria), while those from the anterior surface may form an external superficial femoral vein (Fig. 771). Throughout its entire course it makes numerous connections with the deep veins. with the anterior tibial by some five or six branches (TT. sapheno-tibiales a uteri ores), with the posterior tibial by usually three (rr. sdfihoio-tibia/cs postcn'tvrs ), and with the femoral or one of its tributaries by usually a single one. Various communications with the small saphenous also occur. In addition to these various connections, the long saphenous receives, just before its entrance into the femoral, a number of vessels which accompany some of the superficial branches of the femoral artery. They are by no means constant tributaries of the saphenous, but frequently pass through the cribriform fascia to open directly into the femoral vein. i. The External Pudic Veins. The external pudic veins (vv. pudcndac externae) are, like the corresponding arteries, two in number, one superficial and one deep. They have their origin in the external genitals, receiving nunierou> veins from the anterior surface of the scrotum (vv. scrotalcs antcriorcs) or tin- anterior portions of the labia majora (vv. labialcs antcriorcs ). They also receive a THE VEINS OF THE LOWER LIMB. 917 Anterior superior spine of ilium Superficial epigastric vein Femoral vein External superficial femoral vein Patella ;; single or paired vein which runs along the dorsal surface of the penis or clitoris immediately beneath the integment (v. dorsalis penis ( clitoridis) subcutanea j, and at the symphysis pubis bends later- ally to join the external pudics. i'ic;. 2. The Superficial Cir- cumflex Iliac Vein. The superficial circumflex iliac vein (v. circumilexa ilium superficialis) accompanies the artery of the same name, receiving subcuta- neous branches from the lower lateral portions of the abdomen and from the anterior hip region. It frequently unites with the superficial epigastric vein before opening into the saphenous. 3. The Superficial Epi- gastric Vein. The superficial epigastric vein (v. epigastrica superficialis ) takes its origin from the subcutaneous veins of the lower part of the anterior abdom- inal wall as high as a little above the umbilicus. It is joined at a varying level by the thoraco- epigastric vein (Fig. 775), which opens above into the axillary vein, and is occasionally pro- longed downwaid to open independently into the long saphenous. Variations. The long saphe- nous vein may perforate the fascia lata some distance below the fossa ovalis. It is not infrequently replaced in the crural portion of its course by a net-work of veins in which no special main stem can be recognized, and in the thigh it is occasionally double. PRACTICAL CONSIDERATIONS. THE ILIAC VEINS AND THE VEINS OF THE LOWER EXTREMITY. The common iliac veins illustrate the rule (Owen) that below the diaphragm the veins of the trunk are on a plane posterior to the arteries (except the renal) and incline generally to the venous the right side. Thus the left common iliac is always on the inner fright) side of the corresponding artery and ulti- mately crosses the right artery, on a posterior plane. The right vein begins slightly to the inner side of the right artery, which it crosses on a posterior plane to reach the right side of the fifth lumbar vertebra. These relations are important in operations on the common iliac arteries (page 808). Dorsal venous arch Inner malleolus Superficial veins of right lower limb; internal aspect . 9i8 HUMAN ANATOMY. The internal iliac veins may become involved in infections of any of the numerous plexuses from which their tributaries arise. Thus, puerperal metritis may not only lead to pelvic cellulitis (page 2014), but may set up a thrombophlebitis in the intra-uterine veins which, spreading to the internal and common iliac veins, will obstruct the venous current from the whole lower extremity, bringing about a wide-spread oedema, with aching and tenderness (phlegmasia alba dolens, milk leg). Similar conditions sometimes follow septic infection of the prostatic vesical and hemorrhoidal plexuses. The practical relations of these venous channels have been described in connection with the prostate, bladder, and rectum. The branches of the internal iliac vein aid indirectly in supporting the pelvic viscera. They are apt to be varicose in the aged, especially in females. They supply the blood in cases of pelvic haematocele. The external iliac vein is frequently involved in femoral phlebitis, the continuity of direction and calibre between it and the femoral being practically unbroken. The femoral vein is not infrequently the subject of thrombo-phlebitis, descend- ing, as a result of some form of pelvic infection (vide supra}, or ascending, following septic infection of the soft parts or bones of the lower extremity ; or occasionally directly caused by contusion of the vessel just below the groin, or by its bruising during forced flexion of the thigh. Femoral phlebitis is not uncommonly a sequel of enteric fever and of other exhausting diseases, and is a familiar post-operative complication of operations for the removal of the appendix, the uterus, the tubes and ovaries, and other abdomino-pelvic procedures, even when apparently unattended by infection. The predisposing causes are thought to be the relative immobility of the patient and the consequent sluggishness of the circulation, especially in the lower extremities, the dependent position of the limb in bed, and the altered constitution of the blood (in the case of fever) ; the exciting cause is probably a very slight degree of infection. Pain and oedema follow, but such cases almost always do well. On account of its nearness to the artery, both vessels are often wounded at the same time, with the resulting formation if the communication between them is direct of an aneurismal varix ; or if it is indirect an aneurismal sac intervening of a varicose aneurism. Wounds requiring ligation and sudden occlusion of the vein from any cause are dangerous from the risk of development of moist gangrene. Lateral suture of wounds in this vein has been successfully employed in a number of instances. The femoral vein is not infrequently involved in ulcerative malignant or phagedenic processes implicating the skin of the groin and upper thigh, or the inguinal lymphatic nodes. After ligation, the collateral circulation is established between the veins of the buttocks and the internal circumflex veins, and between the veins of the pdvis and the external pudic veins. The practical relations of the femoral vein to femoral hernia have been described (page 1773). The popliteal vein, together with the artery (which is closer to the bone, and therefore more easily compressed or torn), has been lacerated in supracondyloid fracture of the femur. It has been so compressed by a popliteal aneurism as to cause thrombosis and enormous distention of the veins and of the leg. Owing to tin- unyielding character of the boundaries of the ham, it may also be sufficiently com pressed by inflammatory exudates, by abscess, or by enlarged bursae, to cause swelling and oedema of the foot and leg. The vein is so exceptionally thick -walled that in spite of its more superficial position it is never ruptured alone, but only when the force is sufficient to tear the artery also. The involvement of both may be favt >red by the fact that the two vessels are so closely united that it is difficult to separate them, and this also favors the occasional production of aneurismal varix or varicose aneurism after stab- wounds. This close connection makes the denudation of the artery difficult in the operation for its ligation. The veins of the leg are, with the possible exception of the veins of the pampiniform and hemorrhoidal plexuses, more often the subject of varicosity than any other veins of the body. This is due to (i) the high blood-pressure in these veins, resulting from -(a) the erect posture of the human species and the consequent THE PORTAL SYSTEM. 919 vertical position of these veins ; (6) the length of the column of blood they carry, extending, in the case of the long saphenous vein, from its beginning at the ankle to the upper orifice of the inferior vena cava ; (V) in many cases to compression above, as from abdominal or pelvic growths, or the gravid uterus, or from garters. (2) In the superficial veins the frequency of varicosity is also due to the lack of adequate external support to their thin and distensible walls, the saphenous veins, for example, lying outside of the deep fascia in loose connective tissue. (3) To the increased resistance that must be overcome at the points where the deep and superficial vessels communicate, and where in many cases the varicosity seems to begin. At such points the upward current of blood has to overcome and the walls of the veins to support not only the downward pressure of the vertical column of blood in the vessels above it, but also the resistance of the blood-stream driven out of the deep vein by the contracting muscles between which it lies, and entering the superficial vein at a right angle. The valve next below this point of entrance prevents the relief that might be obtained from temporary distention of a long lower section of the vein and limits these forces to a circumscribed area, which yields and becomes varicose. The venous plexus between the two layers of the muscles of the calf is often the seat of varices of great size. The six chief veins which pass from the soleus muscle alone to enter into the posterior tibial and peroneal trunks have a united diameter of not less than one inch (Treves). The fact that each of the saphenous veins is accompanied by a sensory nerve accounts for the aches and pains associated with varicosity. THE PORTAL SYSTEM. The portal system is composed of all the veins which have their origin in the walls of the digestive tract below the diaphragm (with the exception of those of the lower part of the rectum) and includes also the veins which return the blood from the pancreas, spleen, and gall-bladder. It presents a marked peculiarity in that the system begins and ends in capillaries, the blood which it contains having entered its constituent veins from the capillaries of the intestine, stomach, and the other organs mentioned above, and passing thence to the liver, where it traverses another set of capillaries, by which it reaches the hepatic veins and so the heart. Coming as it does principally from the intestine, the portal blood is more or less laden with nutritive material, which has been digested and absorbed through the intestinal walls, but is not yet in a condition, so far as some of its constituents are concerned, suitable for assimilation by the tissues. To undergo the changes necessary for its conversion into assimilable material it is carried by the portal vein to the liver, and as it passes through the capillaries of that organ it undergoes the necessary modifications. In other words, the portal vein stands in a somewhat similar relation to the liver that the pulmonary vein does to the lungs. Its purpose is not to convey material to the organ for its nutrition, that being accomplished by the hepatic arteries for the liver just as it is accomplished by the bronchial arteries for the lungs, but to carry to the liver crude material upon which the organ may act, elaborating it and returning it, as required, to the circulation in a purified and assimilable condition. The inclusion of the veins of the spleen, gall-bladder, and pancreas, or even of those of the rectum, in the portal system is to be explained on the ground of topo- graphic relationship rather than on the basis indicated above. The main stem of the portal system will first be described and then its tributaries in succession. THE PORTAL VEIN. The portal vein (v. portae) (Figs. 772, 774) is formed behind the head of the pancreas by the union of the superior mesenteric and splenic veins, the latter receiving the inferior mesenteric vein shortly before its union with the superior mesenteric. The two veins unite almost at a right angle, and from their point of union the portal vein passes obliquely upward and to the right, along the free edge of the lesser omentum, towards the transverse fissure of the liver. There it divides into two trunks, of which the right is the larger and shorter and quickly bifurcates into an anterior and a posterior branch. It is distributed to the whole of the right 920 HUMAN ANATOMY. lobe of the liver and to the greater part of the Spigelian and quadrate lobes, the remainder of these lobes and the left lobe receiving branches from the left trunk. The trunks of the vein or their branches enter the substance of the liver and divide in a more or less distinctly dichotomous manner to form interlobidar veins, which, as their name indicates, occupy a position between the lobules of the organ, and give of? capillaries which traverse the lobule and empty into the intralobular veins, the origins of the hepatic veins. The portal vein measures about 8 cm. (3^ in. ) in length and has a diameter of from 1.5 to 2 cm. Its walls, especially in its upper portion, contain a considerable quantity of muscle-tissue and it is destitute of valves. Relations. At its origin the portal vein lies behind the head of the pancreas and to the left of the vena cava inferior. As it ascends it comes to lie at first behind FIG. 772. Round ligament of liver Hepatic duct Cystic duct Spigelian lobe of liver Kiyht crus of diaphragm Hepatic artery '^Spleen Cystic Portal Common bile-duct Pyloric vein Superior mesenteric vein Right gastro-epiploic vei Tributaries of middle colic vein Gastric artery Coeliac axis Stomach Splenic artery Gastric vein Splenic vein Inferior mesentery \ciii Left jjastro-epiploic vein Pancreas Portal vein and its tributaries; liver has been pulled upward. the first portion of the duodenum and then between the two layers of the lesser omentum. In this latter portion of its course it is associated with the hepatic artery and the common bile-duct, both of which lie anterior to it, the artery to the left and the duct to the right. It enters the transverse fissure towards its right extremity, hence the shortness of the right trunk compared with the left, and its trunks have in front of them the branches of the hepatic artery, the hepatic ducts lyini; anterior to these. Tributaries. The tributaries of the portal vein are : (i) the superior mescn- teric, (2) tin- splenic, (3) the inferior nicscntcric, (4) the gastric, (5) the pyloric, and (6) the cystic reins. In addition to these principal tributaries, the portal vein, or IN 1 Handles within the liver, also receives a number of small veins which have their origin in the- falciform ligament of the liver and in the lesser omentum, and, further- more, it receives at the transverse fissure (7) some panitnbilical reins which ascend the anterior abdominal wall along with the round ligament. THE PORTAL SYSTEM. 921 i. The Superior Mesenteric Vein. The superior mesenteric vein (v. mesen- terica superior) (Fig. 773) accompanies the artery of the same name, lying upon its right side. It has its beginning somewhere in the neighborhood of the terminal portion of, the ileum and ascends in the line of attachment of the mesentery. Above, it passes over the third portion of the duodenum and then between that portion of the intestine and the lower border of the pancreas, uniting behind the head of the pancreas with the splenic vein to form the portal vein. It possesses no valves. Tributaries. The tributaries of the superior mesenteric vein correspond with the branches of the corresponding artery, except that it receives in addition the pancreatico-duodenal and right gastro-epiploic veins which accompany the similarly named branches of the hepatic artery. (a) The veins of the small intestine (vv. intestinales) have their origin in the walls of the small intestine from the last portion of the duodenum to within a short distance of the ileo-csecal valve. Their arrangement is essentially similar to that of the arteries of the small intestine, the numerous small branches which emerge from the intestine being united "by transverse anasto- moses, as a rule more numerous than those of the arteries, and forming one or more series of venous arcades lying between the two layers of the mesentery. From these arcades branches arise which pass towards the superior mesenteric vein, gradually uniting to form about twenty stems which open independently into the superior mesenteric. The branches of origin of the intestinal veins, just after they emerge from the intestine are provided with valves in the child, but they usually degenerate more or less completely before adult life. (6) The ileo-colic vein (v. ileocolica) arises at the junction of the ileum and caecum by the union of a caecal and an ileal branch, the latter of which anastomoses with the origin of the superior mesenteric. The caecal branch receives an appendicular vein from the appendix vermi- formis, and the main stem passes upward between the two layers of the mesentery to open into the superior mesenteric just before it passes over the duodenum. (c) The right colic veins (vv. colicae dextrae) originate in the walls of the ascending colon and are two or three in number. They anastomose by transverse branches with the ileo-colic and middle colic veins and pass almost horizontally medially to open into the superior mesenteric. (d) The middle colic vein (v. colica media) emerges from the transverse colon by a number of small branches which anastomose to the right and left with the right and left colic veins, and unite to a single stem which opens into the superior mesenteric just before it passes beneath the pancreas. (e) The right gastro-epiploic vein (v. gastroepiploica dextra) runs from left to right along the greater curvature of the stomach, communicating directly with the left gastro-epiploic at about the middle of the curvature. It receives tributaries from the lower portions of the anterior and posterior surfaces of the stomach and from the greater omentum, and opens into the superior mesenteric shortly before its union with the splenic. It occasionally receives a pancreatico-duodenal vein, and may unite with the middle colic vein to form a gastro-colic vein instead of opening directly into the superior mesenteric. (_/) The pancreatico-duodenal veins (vv. pancreaticoduodenales), like the arteries, may be two in number, one of which opens directly into the superior mesenteric and the other into the right gastro-epiploic. Frequently, however, they are broken up into a number of separate vessels arising independently from each of the two viscera concerned, the duodenum (vv. duodenales) and the head of the pancreas (vv. pancreaticae). 2. The Splenic Vein. The splenic vein (v. lienalis) (Fig. 774) is formed by the union of five or six branches which emerge from the hilum of the spleen. It passes almost horizontally to the right below the splenic artery, resting at first upon the upper border of the pancreas, but later coming to lie behind that organ. Behind the head of the pancreas it unites with the superior mesenteric to form the portal vein. Tributaries. These correspond with the branches of the artery, and in addition it receives near its termination the inferior mesenteric vein, which for purposes of description will, however, be regarded as independent. (a) The short gastric veins (vv. gastricae breves) arise from the fundus of the stomach and pass between the layers of the gastro-splenic omentum to open partly into the splenic vein and partly into its branches of origin as they emerge from the hilum. (b) The left gastro-epiploic vein (v. gastroepiploica sinistra) passes from right to left along the greater curvature of the stomach, communicating directly with the right gastro-epiploic about half-way along the curvature. It receives branches from the lower portions of both surfaces of the stomach and from the greater omentum, and opens into the splenic vein near its formation. (c) The pancreatic veins (vv. pancreaticae), which may be five or more in number, open into the splenic vein at various points in its passage behind the pancreas. 922 HUMAN ANATOMY. 3. The Inferior Mesenteric Vein. The inferior mesenteric vein (v. mesen- terica inferior) (Fig. 774) is formed by the junction of the superior hemorrhoidal and sigmoid veins opposite the sigmoid flexure of the colon, and passes upward in company with the corresponding artery. It is continued on, however, beyond the point where the artery arises from the abdominal aorta, lying behind the peritoneum slightly medial to the ascending colon, and, finally, it passes beneath the pancreas IMC;. 773. Ascending colon Middle colic veil Right colic vein Superior mesenteric vein lleo-colic vein - Transverse colon Descending colon -Left colic vein Pancreas Inferior mesenteric vein Superior mesenteric arterj Duodenum, transverse par Jejunum Veins of the small intestim Cofls'of lleum Superior mesenteric vein and its tributaries; transverse colon has been pulled upward. to open usually into the splenic vein not far from its union with the superior mesenteric. Occasionally it opens into the latter vein (Fig. 774) or else equally into both, thus taking a direct part in the formation of the portal vein. Tributaries. Its tributaries correspond to tin- branches of the- artery. (a) The superior hemorrhoidal vein i v. haemorrhoidalis superior) has its origin from the upper part of the hemorrhoida! plexus by several branches, and, passing upward, unites with the si-moid veins to form the inferior mesenteric. Through the hemorrhoidal plexus it communi- cates with the middle and inferior hemorrhoidal veins, thus placing the portal and inferior caval systems in communication. (t>) The sigmoid veins (vv. sinmoideae) are variable in number and pass from the sigmoid flexure and the lower portion of the descending colon to the inferior mesenteric, the lowest one uniting with the superior hemorrhoidal to form that vein. THE PORTAL SYSTEM. 923 (c) The left colic vein (v. coiica sinistra) has its origin in the walls of the descending colon, anastomosing above with the middle colic and below with the sigmoid veins. It passes medially to open into the upper part of the inferior mesenteric. 4. The Gastric Vein. The gastric vein (v. coronaria ventriculi) (Fig. 772) accompanies the gastric artery along the lesser curvature of the stomach. It has its origin at the pyloric end of the stomach, where it anastomoses with the pyloric vein, and passes at first from right to left along the lesser curvature, receiving tributaries from the upper part of both surfaces of the stomach. At the opening of the oesophagus into the stomach it makes connections with the cesophageal veins, and then bends upon itself and passes from left to right behind the posterior wall of the lesser sac of the peritoneum, and terminates either in the portal vein or in the splenic shortly before its union with the superior mesenteric. The peculiar reflected course of the gastric vein is readily understood if it be remembered that the adult position of the stomach is a secondary one. When first formed the long axis of the stomach is practically vertical, the pyloric end being directed downward, and a vein starting at the pylorus will have a direct ascending course to the portal vein. When the stomach as- sumes its adult position the course of the vein with reference to the viscus does not alter, and consequently it passes from pylorus to cardia, and must then bend back upon itself to reach the portal vein. 5. The Pyloric Vein. The pyloric vein (v. pylorica) (Fig. 772) accompanies the pyloric branch of the hepatic artery. It takes its origin at the pyloric end of the stomach, where it anastomoses with the gastric vein, and passes downward to open into the portal. 6. The Cystic Vein. The cystic vein (v. cystica) (Fig. 772) returns the blood from the walls of the gall-bladder and opens usually into the right trunk of the portal vein. It is frequently represented by two separate stems. 7. The Parumbilical Veins. The parumbilical veins (vv. parumbilicales) are a number of small veins which have their origin in the anterior abdominal wall in the neighbourhood of the umbilicus and pass upward in the fold of peritoneum which contains the round ligament of the liver. They anastomose below with both the superficial and deep epigastric arteries and also with small vessels which pass down- ward alongside of the urachus to empty into the vesical plexus. Above, the majority of them enter the quadrate and left lobes of the liver, but one of them, the vena supraumbilicalis, enters the substance of the round ligament at a varying level and opens into the more or less extensive lumen of that structure, which represents the umbilical vein of foetal life. This lumen appears to persist in the majority of cases, although greatly reduced in size from that of the umbilical vein, and may extend throughout almost the entire length of the round ligament, although perhaps, more usually, it is limited to its upper part, and opens into the right trunk of the portal vein. When the lumen is entirely obliterated it is possible that the supraumbilical vein, which has also been termed the accessory portal vein, may open directly into the portal vein. Collateral Circulation of the Portal Vein. Considering the fact that the portal vein terminates in capillaries in the substance of the liver, it is evident that certain pathological conditions, such as cirrhotic changes, which may occur in that organ, will more or less completely interfere with the return of the blood to the heart from the intestine, spleen, and pancreas, by producing an obliteration of the capillaries. The possibilities of a collateral circulation are therefore important, and a number of routes occur by which, under stress, the blood of the portal venous system may pass around the liver and reach the heart through one of the other systems. The functional capabilities of these various routes are furthered by the fact that none of the tributaries of the portal vein possess valves except in their finer branches, and the blood can therefore flow in them in a reverse direction if necessary. The principal collateral routes are as follows : 1. Through the gastric vein the blood may pass to the cesophageal veins and thence to the azygos and hemiazygos veins. When this route is functional the oesophageal veins become enlarged and frequently varicose, forming contorted elevations upon the surface of the oesophagus. 2. Through the superior hemorrhoidal veins connections are made by way of the hemor- rhoidal plexus with the hemorrhoidal branches of the internal iliac. These connections seem, however, to be less frequently functional than either the cardiac or parumbilical routes. HUMAN ANATOMY. 3. Through the umbilical and suprauuibilical veins to the superficial or deep epigastrics and so to the external iliac veins. It is interesting to note that in cases where this route is functional the enlargement of the superficial epigastric veins is usually accompanied by a development of varicosities upon them, while this is not the case with the deep epigastrics. An explanation of this difference has been found in the fact that the deep veins, before opening into the external iliac, bend slightly backward, so that their orifices are directed in the same way as the flow of blood in the larger stem, whereas the superficial epigastrics open from above into the long saphenous veins, their orifices being opposed, therefore, to the flow of blood in the saphenous, a condition which naturally predisposes towards stasis of the blood in the epigastrics and, it may be remarked, also of that in the saphenous. These are the principal routes, but it must be noted that anastomoses also exist between the portal system and the phrenic veins by means of the small veins which descend towards the Liver, uiuler surface Spigelian lobe uf Iher Crura of diapliragr Round ligament Vena cava inferior 1'ortal vein Pyloric vein Cystic -duct Cueliac axis Gall-bladder Castro-duodenal vein Common bile-duct Renal vein Superi mesenteric vein Superior mesenteric artery Ascending colon Aorta Inferior mesenteric artery Superior hemorrlioidal \ein Sigmoid colon Termination of ileuiii Cut edge of Cavity ot mesentery Inferior mesenteric and splcni. \rins and tributaries of portal vein; stomarli and transverse colon have been removed and liver pulled upward. liver in the falciform ligament, and communications with the interior caval system also occur by means of anastomoses between the peritoneal and mesenteric veins, both of which are (|uite small. Finally, it may be mentioned that anomalous and therefore inconstant communications of the portal branches with those of other systems have been observed. Thus the gastric, tin- short gastrics. or the pyloric vein may anastomose with the phivnics ; the splenic or the lelt -astro-epiploic with the n-nals ; the right or left colic with the branches from the fatty capsule of the corresponding kidney; and the duodenal branches may open into the inferior vena cava. THE PORTAL SYSTEM. 925 Practical Considerations. The portal system may be obstructed by (a) tumors or swellings involving the liver itself, as carcinoma, hydatids, or abscess ; (6) enlargement of the gall-bladder from new growth or from concretions ; (c) tumors of contiguous structures, as disease of lymph-nodes in the portal fissure or between the layers of the lesser omentum, or carcinoma of the head of the pancreas ; (d) disease of the liver tissue, especially cirrhosis (chronic interstitial hepatitis) in which the interlobular veins are compressed by the contraction of the connective FIG. 775. External jugular vein Subscapula III., IV.. and V anterior irforatin<; veins and tribut; Tributaries of superior epigastric vein Tributary of deep epigastric veia Thoraco-epigastric vein Superficial circumflex iliac vein Saphenous opening Internal saphenous vein External jugular vein Cephalic vein Axillary artery Axillary veil Brachial veins V'., VI., and VII. intercostal vein Tributary of musculo-plirenic vein Thoraco-epigastric vein Tributary of deep epigastric vein Superficial epigastric ven Femoral vein Deep dorsal vein of penis Superficial dorsal vein of penis Internal saphenous vein Superficial veins of anterior body-wall ; pectoralis and external intercostal muscles (of fifth to seventh intercostal spaces) on left side have been removed. tissue in the spaces between the lobules ; (-/-iriiftrs, indicating Mucous glands Germ-centre of nodule Submucous layer Simple lymph-nodule from large intestine. X 120. THE LYMPHATIC SYSTEM. 937 FIG. 788. the birthplaces of new lymphocytes. Although the limits of the lymph-nodules are commonly imperfectly defined by a condensation of the surrounding connective tissue, a distinct capsule is usually wanting. Definite lymph-channels are found neither upon the surface nor within the simple nodules ; the latter are provided, however, with a generous net-work of capillary blood-vessels (Fig. 792): Intermediate in their complexity of arrangement, between the simple nodules on the one hand and the typical lymph- nodes on the other, stand such structures as Peyer's patches and the faucial and pharyngeal tonsils, in which groups of simple nodules are blended into a single organ, the component follicles only partly retaining their individuality. The lymph-nodes interposed along the lymphatic vessels, usually embedded within fatty tissue, represent still higher differentiation as distinct organs. In form and size they vary from minute bodies resembling millet-seeds to flattened oval or bean-shaped organs, that may measure almost an inch in their longest diameter. They are invested by a distinct fibrous capsule, in which elastic fibres constantly and unstriped muscle occasionally are present. From the deeper surface of this envelope numerous radially directed trabeculae penetrate the outer zone, or cortex, which is thus subdivided into a series of pyramidal compartments. On reaching the inner limits of the cortical zone, the trabeculae are less regularly disposed and more freely united, thereby breaking up the deeper parts, or medulla, of the node into uncertain cylindrical compartments. The spaces thus imperfectly defined by the trabeculae are Portion ot lymph-nodule, showing details of germ-centre. X 350. Germ-centre Lymph-sinus Fat FIG. 789. Lymph-sinus Capsule Trabecula Cortical follicles Lymph-sinus Hilum Vasa efferentia Medullary cords Section of small lymph-node through hilum. X 25. incompletely filled by masses of compact lymphoid tissue, the general form and arrangement of which correspond to the compartments in which they lie. The masses contained within the peripheral spaces are spherical or pyriform and constitute HUMAN ANATOMY. the cortical nodules ; those within the communicating central compartments form a net-work of irregular cylinders, the medullary cords, which are continuous with one another and with the deeper i at; '^..j.c-Tjqs*^. * 1U - 79 Capsule Lymph-sinus Cortical follicle Lymph-sinus Lymph-sinus Medullary cord Portion of periphery of lymph-node, showing relation between trabecula, sinus, and lymphoid tissue. X 50. part of the cortical nodules (Fig. 789). The intervals between the tracts of lymphoid tissue and the trabecular frame-work constitute a system of freely intercom- municating channels, the lymph - sinuses, through which passes the lymph brought to the node by the afferent lymphatic vessels. The latter pierce the capsule on the convex surface of the node and empty into the sinuses that surround the outer and lateral surfaces of the cortical nodules. After traversing the periph- eral sinuses, the lymph passes into the irregular channels of the medulla and towards the point at which the efferent lymph- vessels leave the nodule. The position of this exit is usually indicated by a more FIG. 791. *> Trabecula or less pronounced indentation, known as the hilum, on the surface of the node opposite the entrance of the afferent lymph-vessels. The lymph-sinuses, there- fore, are bounded on one side ' *.L*i!i?3^' H. by the capsule or the trabeculae and on the other by the masses of dense lymphoid tissue. The lumen of these channels, however, is not free, but occupied by a delicate wide-meshed reticulum consisting of fine strands of connective tissue where most marked, or of the processes of stellate cells where very delicate (Ebner). The sinuses are lined by an imperfect layer of flattened plate-like cells, that represent the endothelium of the adjoining lymphatic vessels and also cover the more robust trabeculae cross- ing the channels. The reticulum occupying the sinuses is continu- ous with the closer and more delicate net-work within the adja- cent dense lymphoid tissue. Although both the afferent and efferent lymphatics are provided ^ ^ details of lym , )h ., inus with valves, the lymph-channels and medullary cords, x 250. Lymph-sinus THE LYMPHATIC SYSTEM. 939 FIG. 792. Cross-section of small lymph-node, injected to show rich vascular supply. X 10. within the node are destitute of such folds. The passage of the lymph through the nodes is retarded by the reticulum within the sinuses, thus favoring the entrance of the young lymphocytes from the surrounding lymphoid tissue into the sluggishly circulating fluid. Germ-centres, the particular foci for the production of the lympho- cytes, usually are present within the cortical nodules, but are not found within medullary cords. The blood-vessels for the nutrition of the lymph-nodes are numerous. Entering at the hilum, they divide into arterioles which follow the trabeculae, giving off smaller branches that pene- trate the medullary cords and the cortical nodules and break up into rich capillary net- works for the supply of the denser lym- phoid tissue. Both medullated and non-medullated nerves enter the node at the hilum in company with the blood-vessels. They are chiefly sympa- thetic fibres destined for the involuntary muscle of the vessels and of the capsule. The distribution of the medullated fibres is uncertain. According to Tonkoff, fibrillae are traceable into the lymphatic tissue of the medulla. Development. The origin of the first lymph-cells, the lymphocytes, is uncer- tain, these elements appearing outside the vessels as derivatives from the mesoblast (page 688). After the establishment of the lymphoid tissue new cells are continually being formed within the various lymph-nodes and nodules. The development of the lymphatic vessels has generally been believed to proceed from the veins by a process of budding (Ranvier), similar to that followed in the extension of the blood-vessels ; and certain recent investigators, Sabin, 1 who studied the development of the lymphatics in pig embryos, and F. T. Lewis, 2 who worked with rabbit embryos, while differing as to details of the development of the definitive lymphatic stems, agree as regards their origin in this manner. Sabin, by employing a method of injection, found that the first traces of a lymphatic system appear in pig embryos, 14.5 mm. in length, as two small out- growths, which develop, one on each side, at the junction of the subclavian and jugular veins ; from these, by a process of endothelial budding, vessels gradually grow towards the skin, radiating and anastomosing in all directions to form a subcutaneous net-work, which gradually extends throughout the anterior half of the body. Later two additional outgrowths develop at the junction of the femoral and post-cardinal veins, and give rise to a subcutaneous net-work throughout the posterior half of the body, the two sets of net-works thus formed eventually uniting. Lewis's studies of serial sections of rabbit embryos gave somewhat different results and indicated that Sabin' s method of study did not suffice to reveal the actual origin of the lymphatics. He found the first of these vessels along the course of the internal jugular vein as a series of spaces, each of which he supposed to represent an independent outgrowth from the vein. These spaces eventually fused to form a single lymph-channel accompanying each vein, and other channels were found to arise in a similar manner in connection with the subcardinal, mesenteric, and azygos 1 Amer. Jour, of Anatomy, vol. i., 1902. 2 Amer. Jour, of Anatomy, vol. v., 1905. 940 HUMAN ANATOMY. FIG. 793- veins. The various channels finally unite to form a continuous system which acquires new openings with the venous system near the termination of the subclavian veins, the condition found in the adult being thus established. More recently Huntington and McClure, 1 working with cat embryos, have also found the earliest traces of the lymphatic system in a series of spaces which appear in the tissue surrounding the intima of the anterior cardinal veins, but they found that these spaces have at first no connection with the veins, nor are they outgrowths from them. The anterior cardinal vein of each side is early divided longitudinally into two portions by the passage through it of the cervical nerves, and the dorso- lateral portion of the vein later undergoes retrogression, the ventro-medial portion persisting as the internal jugular. As the dorso-lateral portion shrinks, the lymphatic spaces along its course rapidly enlarge, fuse together, and form a large lymphatic stem, which subsequently makes con- nection with the subclavian vein, and thus forms the primary lymphatic trunk of the body (Fig- 793)- Later, spaces develop along the course of the anterior cardinal veins below the point where the subclavians open into them, but it is noticeable that those occur- ring in association with the left vein, which undergoes retrogres- sion, develop more rapidly than those accompanying the same portion of the right vein and form the thoracic duct (Fig. 794), this structure thus belonging essen- tially to the left half of the body, since the principal persistent veins occur on the right side. Similar spaces appear in the peri-intimal tissue of other veins, and in all cases those associated with retro- gressive veins are the most rapidly developed. While most of the principal lymphatic trunks unite with the thoracic duct, yet they may also form temporary or even permanent communications with other veins than the subclavian, certain of the adult anomalies being results of these connections. From these observations it seems that the lymphatics arise from spaces which are primarily independent of, although associated with, the veins, and that, while this mode of origin of the lymphatics applies to those following the primitive systemic veins, yet the more peripheral portions of the system are developed by a process of budding from the main stems, just as is the case with the smaller branches of the blood-vessels. By this budding process the system gradually extends throughout the body, invading the various tissues, the invasion, however, failing to affect certain of the tissues, such as cartilage and the central nervous system. The development of the lymph-nodes has been recently studied by Kling' and by Sabin. :i According to the latter investigator, the lymph-nodes may be regarded as formed by two fundamental parts the Iytnf>hoid element^ consisting of lympho- cytes in a reticulum surrounding the terminal artery and its capillaries within the 1 Anu-r. Jour, of Anatomy, vol. vi., 1907. * Archiv f. mikros. Anat., Bd. 63, 1904. :l Amer. Jour, of Anatomy, vol. v., 1905. * Amer. Jour, of Anatomy, vol. v., 1905. Developing lymphatics in rabbit embryo of 11 mm. (14 days); X 9. Lymphatic vessels are heavily shaded ; veins are light. In.J., Ex.J.. internal and external jugular veins; Pr.U,, primitive ulnar; Ex.M., external mammary; Az., azygos; KC/., inferior vena cava ; G., gastric; S.Af., superior mesenteric ; V., vitelline ; Sc., subcar- dinal; K.A., renal anastomosis of subcardinals ; JPr.Fi., primitive fibular; c.6., connecting branch ; An. T., anterior tibial ; c., caudal; j. 4>5^ 6, position of corresponding cervical nerves, (f. T. Lewis.*) THE THORACIC DUCT. 941 cords and germ-centres respectively, and the sinus-element, represented by channels resulting from the multiplication of the lymph-vessels. The former, or vascular factor, is constant and present in the simplest nodule ; the sinus-element, on the contrary, varies, sometimes (as in the usual type of node) being developed from numbers of closely packed lymph-ducts and, therefore, of lymphatic FIG. 794. origin, and at other times (as in the hemolymph nodes) being venous channels occu- pied by blood. By the sub- sequent intergrowth of the lymphoid element and the greatly multiplied lymph- capillaries, the intervening bridges of connective tissue are reduced in thickness until finally only the reticulum remains and the lymphoid tissue is ultimately brought into intimate relation with the surrounding sinus. In certain nodes the sinus retains its character as a direct out- growth from the veins and becomes filled with erythro- cytes. Such nodes assume the peculiarities of hemolymph nodes, in which the blood- sinuses replace those that convey lymph. As Sabine has emphasized, the follicle is the anatomical as well as the vascular unit, the simplest nodule consisting of a single follicle. The latter may be without a sinus, or surrounded by one which is either a lym- phatic or a venous channel. Developing lymphatics in rabbit embryo of 21 mm. (ry days); X 6. Lymphatic vessels are heavily shaded ; veins are light; for significance of lettering see preceding figure; in addition, Ce., cephalic; Br., bra- chial; /?., radial ; Ss., subscapular; Set., sciatic ; iliolumbar. (f. T. Lewis.*) In describing the various lymphatic vessels and nodes it will be convenient to consider first the great terminal trunks of the system, the thoracic and right lymphatic ducts, and then discuss the remaining portions of the system from the topographical standpoint. Attention will be directed primarily to the nodes of each region, the course of the lymph-paths from each organ and their relations to the nodes being subsequently considered. THE THORACIC DUCT. The thoracic duct (ductus thoracicus) (Fig. 795) extends from the lower border of the second lumbar vertebra, through the entire length of the thorax, to open into the left subclavian vein close to the point where it is joined by the left internal jugular. Its entire length is from 4346 cm. (1718 in.). The duct lies at first in * Amer. Jour, of Anatomy, vol. v., 1905. 942 HUMAN ANATOMY. front of the first and second lumbar vertebrae, and passes upward through the aortic opening of the diaphragm. In the thorax its course, although slightly sinuous, in FIG. 795. Internal jugular vein Trachea Vertebral vein Right lymphatic duct Subclavian vein I. rib Right innominate veil (Esophagus Vena azygos Right lumbar lymph trunk Crest of ilium Left common carotid artery Left innominate vein Thoracic duct Left subclavian vein Scalenus anticus Left subclavian artery Thyroid axis I. rib Vertebral artery Thoracic duct Aorta Intercostal arteries Receptaculum chyli Intestinal lymph trunk Left lumbar lymph trunk Crest of ilium Dissection of posterior body-wall, seen from in front, showing thoracic duct and right lymphatic duct ; veins have been laterally displaced to expose terminations of thoracic duct. general is at first almost directly upward, a little to the right of the median line of the bodies of the thoracic vertebrae ; at the level of from the sixth to the fourth THE THORACIC DUCT. 943 vertebrae, however, it begins to incline slightly towards the left, and, finally, at about the lower border of the seventh cervical vertebra it changes its direction somewhat abruptly, passing upward, forward and to the left, and then downward and forward, thus forming an arch whose convexity is directed upward and whose extremity opens into the subclavian vein. The thoracic duct is formed by the union of the right and left lumbar trunks (trunci lumbales) which drain the lumbar nodes. The left trunk, shortly before its union with the right, is usually joined by an unpaired intestinal trunk (truncus intes* tinalis) that drains the cceliac and mesenteric nodes. Just above its commencement the thoracic duct usually, although not always, presents a pyriform enlargement, the receptaculum chyli (cisterna chyli), which extends upward as far as the level of the eleventh thoracic vertebra, and measures from 5-7.5 cm. (2-3 in.) in length and from 6-8 mm. in diameter. Above the eleventh thoracic vertebra the duct gradually diminishes in calibre until about the middle of its course, where it again enlarges. The thoracic duct possesses few valves in comparison with other lymphatic vessels, those which do occur being frequently insufficient. Its entrance into the subclavian vein, however, is guarded by two well-developed leaflets, which prevent the passage of blood into the duct. Relations. In its abdominal portion the thoracic duct lies almost in the median line in front of the bodies of the first two lumbar and twelfth thoracic vertebrae, and between the crura of the diaphragm, or under cover of the right crus. Anteriorly, it is in relation with the right side of the abdominal aorta, with the greater azygos vein to the right. In its thoracic portion it lies at first within the posterior mediastinum, but above, it enters the superior mediastinum. In the former it lies anterior to the bodies of the eleventh to the fifth thoracic vertebrae, and has in front of it, from below upward, the pericardium, the oesophagus, and the arch of the aorta. The thoracic aorta lies to the left of it, and to the right are the right pleura and the greater azygos vein. The lower right intercostal arteries pass between it and the bodies of the vertebrae, as does also the terminal portion of the hemiazygos vein. In the superior mediastinum it rests upon the lower part of the left longus colli muscle, being separated by it from the bodies of the upper three thoracic vertebrae. Anteriorly, it is in relation with the origin of the left subclavian artery and with the vertebral vein ; to the left is the left pleura and to the right are the oesophagus and the left recurrent laryngeal nerve. Its arch is in relation below with the apex of the left lung and with the left sub- clavian artery ; to the left and posterior to it is the vertebral vein and to the right and anteriorly are the left common carotid artery, the left internal jugular vein, and the left pneumogas.tric nerve. Tributaries. In addition to the right and left lumbar and the intestinal trunks by whose union it is formed, the thoracic duct receives on either side ( i ) near its origin, a descending trunk which drains the posterior nodes of the lower six or seven intercostal spaces ; (2) an ascending stem from the upper lumbar nodes which trav- erses the crus of the diaphragm and joins the duct at about the level of the ninth or tenth thoracic vertebrae ; (3) the efferent vessels from the upper posterior intercostal nodes, which sometimes unite to form a single ascending stem opening into the upper part of the duct ; (4) the efferent vessels of the posterior mediastinal nodes ; (5) the left jugular trunk ; and, occasionally, (6) the left subclavian and (7) the leftbroncho- mediastinal trunks, these last three uniting with the duct just before it opens into the subclavian vein. Variations. The thoracic duct is subject to numerous variations, so much so that certain authors have regarded as typical arrangements which others have considered to be abnormal. Its origin is frequently opposite the body of the first lumbar vertebra or even opposite the last thoracic ; and rarely it is below the lower border of the second lumbar. Instead of being formed by the union of only two trunks, three are frequently found participating in its origin, the odd one being the intestinal trunk which usually opens into the left lumbar trunk. Occasionally all three trunks are represented by a number of smaller stems which anastomose with one another as well as with the descending stems from the posterior intercostal nodes, the plexus so formed communicating by a number of efferents 944 HUMAN ANATOMY. with the receptaculum chyli. It must be remembered that embryologically what are usually termed the origins of the thoracic duct are in reality its prolongations, that is to say, outgrowths from it, so that possibilities for variation in these stems are abundant. In another respect the embryological history of the duct probably throws light upon its anomalies. In the rabbit the spaces formed along the course of the left posterior cardinal vein frequently unite to form two more or less distinct, parallel stems, which together represent the thoracic duct (Fig. 794). Whether this condition also exists in man is unknown, but if it does then an explanation is afforded for one of the most frequent anomalies of the duct, namely, its division in its lower part into two parallel stems which unite again after a longer or shorter inde- pendent course. This condition is so frequent that it has been regarded as typical by some authors ; usually the union of the two stems occurs at about the level of the seventh thoracic vertebra, but occasionally they remain separate throughout the entire length of the thorax and may be connected by transverse anastomoses. Another group of anomalies, probably having a quite different embryological basis, includes cases in which there are either two distinct thoracic ducts, or else a single one which branches in its upper part, one of the two stems in either case passing to the left subclavian vein and the other to the right. This condition is due to the fact that the lymphatic system is symmetrical in its embryological origin, a trunk arising in connection with the right azygos vein as well as with the left. Ordinarily the left trunk, developing more rapidly than the right, becomes the thoracic- duct, while the right outgrowth remains short and forms the right lymphatic duct. Conditions might occur, however, in which the right trunk would undergo a more extensive development and either unite with the left trunk or grow downward to form a second thoracic duct, thus producing the conditions under discussion. A further modification along the same line would lead to the development of the thoracic duct from the right trunk, the left giving rise only to a short lymphatic duct, an exact reversal of the normal arrangement being thus produced. Several such cases have been recorded, and it is interesting to note that they frequently accompany abnormalities of the aortic arch, such as the origin of the right subclavian from the descending portion ; the anomaly also occurs, however, independently of any variation in the blood-vessels. Considerable variation exists in the level to which the arch of the thoracic duct rises in the neck, and it is stated that it may lie anywhere between the levels of the fifth cervical and first thoracic vertebrae. Likewise, variations in the mode of termination of the thoracic duct are often observed. It may open into the subclavian vein at some distance from the junction of the internal jugular. or, occasionally, into its posterior surface, and not infrequently it divides near its termination into two or more stems (Fig. 795), which may open into the internal or the external jugular or into the azygos or vertebral veins as well as into the subclavian. The connection with the azygos vein is probably of frequent occurrence. Practical Considerations. The thoracic duct may be obstructed by () aneurism of the arch of the aorta; (b) enlarged mediastinal nodes (tuberculous, lymphadenomatous, or carcinomatous) ; (c} mediastinal neoplasms especially if in the anterior mediastinum ; ( rupture of the duct or its tributaries. The stomata of the thin-walled THE LYMPHATICS OF THE HEAD. 945 lymphatic vessels offer little obstacle to free transudation, which, when it follows obstruction, may be compared to the hematemesis seen in hepatic cirrhosis (Rolleston). The symptoms of obstruction are neither so constant nor so marked as they would be if it were not that (a) the lymphatic system is not, like the veins, a series of closed vessels, but is practically continuous with the interstices of the tissues; and that (6) it communicates with the venous system, the duct itsdf with the azygos vein in the posterior mediastinum, and the smaller lymphatics with venules elsewhere certainly, for example, in the inguinal region, and probably in other parts of the body (Leaf). The effects of obstruction are most often noticeable when the interference with the flow of lymph takes place near the termination of the duct on the outer side of the internal jugular vein, near its junction with the subclavian. This is probably due to (a) the frequency of tumor or of injury in this situation ; (b~) the consolida- tion of the lymph-vessels here into a single trunk ; (V) the greater difficulty in estab- lishing a compensatory collateral circulation between the parts of the duct above and below the obstruction than if the latter were lower down (Rolleston). Chylous ascites may be due either to obstruction with transudation of chyle from distended lacteals into the peritoneal cavity, or to wound or rupture of the thoracic duct, or of the larger lymph-vessels, or of varicose lymph-vessels, or of lymphangiomata. Chylous pleural effusions may similarly result, or an effusion fol- lowing wound or rupture may be partly thoracic and partly abdominal, as in a case in which, after extreme compression of the chest, death followed in three weeks,' and the thoracic duct was found ruptured where it traversed the hiatus aorticus (Bellamy). When the receptaculum chyli is involved, the thoracic duct above may be quite healthy, and lymph may pass into it by anastomotic channels and no chylous ascites be produced. Carcinoma of the aortic or mesenteric nodes may cause enough dilatation of the lymphatics to bring about chylous ascites. THE RIGHT LYMPHATIC DUCT. The right lymphatic duct (ductus lymphaticus dexter) (Fig. 795) opens into the right subclavian vein and is a very short stem, rarely having a length of more than from IO-I2 mm. It is formed by the union of the right jugular and subclavian lymphatic trunks, the right broncho-mediastinal trunk rarely contributing to its formation, but having usually an independent opening into the subclavian vein. Very frequently no right lymphatic duct exists, the jugular and subclavian trunks, as well as the broncho-mediastinal, opening independently into the vein. THE LYMPHATICS OF THE HEAD. THE LYMPH-NODES. The lymphatic nodes of the head are arranged in groups, which, for the most part, are situated along the line of junction of the head and neck regions, that is to say, along a line extending from the external occipital protuberance to the temporo- mandibular articulation and thence along the rami of the mandible. A few small nodes also occur upon the cheeks, and others which lie upon the surfaces of the hyo-glossus and genio-hyo-glossus muscles and upon the upper part of the posterior surface of the pharynx may be regarded as belonging to the head region. Including these, the various groups recognizable in the region are (i) the occipital, (2) the posterior auricular, (3) the anterior auricular, (4) the parotid, (5) the submaxillary , (6) the submcntal, (7) the facial, (8) the lingual, and (9) the retropharyngeal groups. The occipital nodes (1) mphoglandulae occipitales) are from one to three in num- ber and are situated at the base of the occipital triangle, immediately lateral to the border of the trapezius muscle and resting upon the upper part of the semispinalis capitis (Fig. 796). Their afferents come from the occipital portion of the scalp and their efferents pass to the upper, nodes of the superior deep cervical group. The posterior auricular or mastoid nodes (lymphoglandulae auriculares posteriores) are usually two in number and are of small size ; they rest upon the mastoid portion of the insertion of the sterno-cleido-mastoid muscle (Fig. 796). 60 946 HUMAN ANATOMY. Their afferents are from the temporal region of the scalp, from the posterior surface of the pinna and of the external auditory meatus. Their cffcrents pass to the upper nodes of the superior deep cervical group. Tin- anterior auricular nodes (lymphoglandulae auricularcs antcriores) vary from one to three in number and are situated immediately in front of the tragus, beneath the parotid fascia. Their afferents come from the anterior surface of the pinna and of the external auditory meatus, from the integument of the temporal region, and from the outer portions of the eyelids. Their efferents pass to the superior deep cervical nodes. The parotid nodes (lymphoglandulae parotideae) are situated in the substance of the parotid gland (Figs. 796, 801). They are quite numerous and vary greatly in size. They FIG. 796. receive afferents from the same regions as the anterior auricular nodes, and the lower nodes of the group also receive stems from the soft palate. Their efferents pass to the superior deep cervical nodes. The submaxillary nodes (lymphoglandulae subniaxillares) are from three to eight or more in number, forming a chain along the lower border of the horizontal ramus of the mandible, as far forward as the attachment of the ante- rior belly of the digastric muscle (Fig. 796). One node which rests upon the facial artery just before it passes over the ramus of the mandible is larger than the rest, and this, together with two others, which are some- what smaller and lie one either side of the Posterior auricular node on Superficial lymphatic vessels and nodes of head and neck ; semidiagrammatic. larger node, are the most constant represen- tatives of the group, the remaining nodes being usually still smaller and varying both in number and position. Occasionally a small node occurs imbedded in the substance of the submaxillary gland. These nodes receive, as afferents, vessels from the submental and facial nodes and also directly from the territory drained by the latter, namely, the upper lip, the outer surface of the nose and the cheek, from the inner portions of the eyelids, from the lower lip, the gums of both jaws, and from the anterior part of the tongue. Their efferents descend upon the surface of the submaxillary gland to open into the superior deep cervical nodes, especially into those situated in the neighborhood of the bifurcation of the common carotid artery. The submental nodes are two or sometimes three in number, and are situated in tin- triangular space included between the anterior bellies of the two digastric muscles, each of the two principal nodes resting upon the inner border of one of the THE LYMPHATICS OF THE HEAD. 947 FIG. Submental node Superior deep cervical node Sterno- niastoid muscle Submaxillary and submental lymph-nodes, new-born child. (Stahr.*) muscles (Figs. 796, 797). They receive afferents from the integument of the chin, from the lower lip, and from the floor of the mouth ; their efferents pass partly to the submaxillary nodes and partly to a node of the superior deep cervical group situated on the internal jugular vein a little above the level at which it is crossed by the omo-hyoid muscle. The facial nodes (lymphoglandulae faciales profundae) consist of sev- eral small groups (Fig. 798). One of these is composed of two or three nodes situated upon the outer surface of the horizontal ramus of the mandible, in front of the anterior border of the masseter muscle ; these may be termed the mandibular nodes. A second group is to be found resting upon the surface of the buccinator muscle, and its nodes are therefore termed the buccinator nodes. They are three or four in number and are situated in the interval between the facial vein and artery, or posterior to the vein, almost opposite the angle of the mouth and either beneath or slightly below the FIG. 798. zygomaticus major. A third group is formed by the maxillary nodes, which are somewhat scattered, one or two occurring in the groove formed by the junction of the nose and cheek, while another rests upon the malar bone near the lower border of the orbit. These maxillary nodes are nor- mally quite small and may readily be overlooked. The afferents for the various groups of facial nodes take their origin in the upper lip, in the integument and mucous membrane of the nose and cheek, and probably also in the eyelids, the conjunctiva, and the lachrymal gland. Their efferents pass to the submaxillary nodes. The lingual nodes (lymphoglandulae linguales) are a number of small enlarge- ments situated upon the vessels which drain the lymphatic capillaries of the tongue. They do not possess any very definite grouping and are to be found upon both *Archivf. Anat. u. Physiol., 1898. t Beitrage zur klin. Chirurgie, Bd. 39. I Facial lymph-nodes. ( Trendel.\) 948 HUMAN ANATOMY. surfaces of the hyo-glossus muscle and in the interval between the two genio-hyo- glossi. From the surgical standpoint they are of comparatively little importance, and have been termed. " intercalated nodes," to distinguish them from the true terminal nodes of the lingual lymphatics (page 954), in which enlargement occurs in cases of cancerous or FIG. 799. Longus colli muscle, stump the Internal otid artery Retropharyngeal lymph-nodes. ( Most.*) other infection of tongue. The retro-phar- yngeal nodes are for the most part small, appearing as slight en- largements of the lym- phatics which drain the posterior surface of the pharynx. In addition to these ' ' intercalated nodes," however, one or two much larger nodes occur at the junc- tion of the lateral and posterior surfaces of the pharynx, about on a level with the anterior arch of the atlas. They are imbedded in the bucco-pharyngeal fas- cia and rest upon the lateral portions of the rectus capitis anticus major. Afferents come to them from the upper part of the pharynx and from the mucous membrane of the nose, and their efferents pass to the upper deep cervical nodes (Fig. 799). THE LYMPHATIC VESSELS. The Scalp. The lymphatics of the scalp form a rich net-work, which is espe- cially dense in the neighborhood of the vertex, the meshes becoming more elongated as the vessels pass away from the median line. From the frontal region some ten to twelve vessels pass downward and backward to terminate in the parotid nodes ; from the parietal and temporal regions from six to ten vessels pass downward, some in front of the external auditory meatus to terminate in the anterior auricular and paro- tid nodes, and some behind the meatus to reach the posterior auricular nodes ; and from the occipital region the more posterior vessels pass downward, partly to the occipital and partly to the superior deep cervical nodes, while the more anterior five or six converge to form a single large trunk which descends along the posterior border of the sterno-cleido-mastoid muscle and terminates in the inferior deep cervical nodes. The Brain and the Meninges. No lymphatic vessels have as yet been cer- tainly demonstrated either in the central nervous system or in the meninges, although they have been described as accompanying the middle meningeal artery in the dura mater and the middle cerebral artery in the pia (Poirier). Lymph-spaces, how- ever, some of them of considerable size, are abundantly present. Of these there may be mentioned, first, \\\a periccllular s/xiccs which surround the individual cells of the brain and spinal cord, both the actual nerve-cells and the neuroglia-cells, those accompanying the latter extending along their processes to communicate with an epicerebral space believed to exist between the surface of the brain and the pia (His), and also with spaces which occur along the course of the cerebral blood-vessels. Of this second group of spaces, the pcrivascitlar spaa-s, two sets have been described, one occurring in the adventitia surrounding tin- vessels and the other between the adventitia and the brain substance, and, accompanying the blood-vessels into the pia, * Archiv f. klin. Chirurjjie, Bd. 41, 1900. THE LYMPHATICS OF THE HEAD. 949 they communicate with the subarachnoid spaces. The third group of spaces is formed by the subdural and subarachnoid spaces, but no special description need here be given of these, since they are more properly described (-page 1197) as portions of the meninges than as parts of the lymphatic system. By some authors an epidural space, situated between the dura and the skull, is also recognized. Lymph-spaces have been described as occurring in the substance of both the dura and the pia, forming in the latter a rather close net-work with which the perivascular spaces communicate. The spaces of both membranes communicate with the subdural space, and those of the dura are said also to communicate with the epidural space. Practically nothing is yet known concerning the lymphatics of the spinal cord. The Eye and Orbit. No lymphatic vessels have as yet been described as occurring in the orbital tissues, nor do they occur in the eyeball. But, on the other hand, numerous lymph-spaces occur in connection with the latter structure, one of the most important of these being the space of Tenon (spatium interfasciale), with which the remaining spaces communicate more or less directly (Fig. 800). A description of this space has already been given (page 504), but it may be recalled that, in the first place, the space is continued, by means of the supravaginal lymph- FIG. 800. Conjunctiva! sac Space of Tenon Diagram showing relation of space of Tenon to intracranial lymph-spaces. path surrounding the optic nerve, along the latter to the apex of the orbit, where it communicates with the subdural space of the cranium, injection of that space resulting in the injection of the space of Tenon (Schwalbe), and, secondly, that the sheaths of the anterior portions of the orbital muscles are formed by reflections of the capsule of Tenon, so that no obstacles exist in the way of the passage of lymph from the muscles into the space. The cavities occupied by the vitreous and aqueous humors have also been re- garded as lymph-spaces, and pericellular spaces in the cornea, which come into rela- tion with the lymphatic vessels of the conjunctiva at the corneal margin, are readily demonstrable. In the tissue of the sclerotic spaces also occur, communicating on the one hand with the space of Tenon and on the other with suprachoroid spaces which are abundantly present in the lamina fusca of the choroid coat and, by means of spaces accompanying the venae vorticosae, communicate with the space of Tenon. In the eyelids, conjunctiva, and lachrymal apparatus true lymphatic vessels occur. In the eyelids three net-works have been distinguished, one of which is subcutaneous, the second lies immediately external to the tarsal plate, and the third is subconjunctival. Communicating branches pass between adjacent plexuses, especially between the 950 HUMAN ANATOMY. subcutaneous and praetarsal ones, and all three are united at the palpebral margins in a rather finely meshed plexus. Efferents pass both toward the inner and the outer angle of the orbit, and the former pass downward, obliquely across the cheek, in company with the facial vein, to terminate in the submaxillary nodes, possibly making connections with some of the facial nodes on their way (Fig. 798). The outer ones pass partly to the anterior auricular and partly to the upper parotid nodes. In the conjunctiva two net-works occur, one situated in the superficial and the other in the deeper layers of the conjunctival dermis. Communicating stems pass between the net-works, which are much finer in the neighborhood of the corneal margin than more peripherally. They come into relation with the pericellular lymph-spaces of the cornea, and their efferents pass toward the outer and inner angles of the orbit, to accompany the palpebral efferents to the submaxillary, posterior auricular, and parotid nodes. Of the lymphatic vessels of the lachrymal gland but little is known, but in ma- lignant diseases of the gland enlargement of some of the facial and anterior auricular nodes has been observed, and it is probable that vessels from the gland accompany the palpebral and conjunctival efferents. The vessels from the nasal duct probably partly accompany branches of the facial vein to the facial nodes, while those from its lower portion pass with the efferents from the nasal mucous membrane to the retro- pharyngeal and superior deep cervical nodes. The Ear. No true lymphatics have yet been observed in the tissues of the internal ear, but the space which intervenes between the osseous wall of the ear cavity and the membranous ear has been regarded as a lymph-space, and on that account has been termed the FIG. 801. perilymphatic space. It com- municates with the subdural space of the cranium by the aqueductus cochleae and by the prolongations of it which accom- pany the ductus endolymphaticus and the auditory nerve. In the middle ear spaces have been observed in the con- nective tissue lining the bony walls, as well as in that of the tympanic membrane. In addi- tion a feebly developed net- work has been described as occurring beneath the epithelium lining the inner (tympanic) surface of the tympanic membrane, efferents from it accompanying the tym- panic artery and terminating in the parotid nodes. Much more extensively developed are the lymphatic vessels of the external car. Beneath the epithelium covering the outer (meatal) surface of the tympanic membrane there is a very fine net- work, whose effer- ents accompany the blood-vessels, radiating toward the periphery of the membrane, and eventually open partly into the posterior and partly into the anterior auricular nodes. A net-work also occurs throughout the entire extent of the external auditory meatus, its efferents having the same destination as those of the pinna. The vessels of the last named portion of the ear form a rich net-work extending throughout the whole extent of the organ, and from it stems pass in three principal *An;itom. An/ri^rr, I'd. \v., 1899. Great auricular nerve SupraclavicuUr node Lymphatics of posterior surface of auricle of new-born child. (Stahr.*) THE LYMPHATICS OF THE HEAD. directions ; it must be recognized, however, that this classification of the stems into three groups does not imply a corresponding division of the net-work into distinct areas, since there is a considerable overlapping of the areas drained by the various stems) and, indeed, stems from the same region may pass in some cases with one of the group, and in others with another. From the outer (anterior) surface the stems pass mainly to the anterior auricular nodes, a few bending backward over the helix and terminating in the posterior auricular nodes. Froiii the upper part of the posterior surface (Fig. 80 1) the stems pass mainly to the posterior auricular nodes, some, however, continuing past them to terminate in the external jugular nodes. From the lower part of the pinna, including the lobule, a number of stems pass to the parotid nodes. The Nasal Region. The lymphatic vessels of the integument of the nose (Fig. 802) form numerous anastomoses with those of the mucous membrane, especially with those of the middle and inferior meatuses, and those of the one side of the nose are also continuous with those of the other side. Some of the vessels which drain the upper portion of the nasal integument FIG. 802. pass almost directly backward to the parotid nodes, but the principal path, followed by vessels from all parts of the nasal integument, is downwards and backwards across the cheek, in com- pany with the facial blood - vessels. In their course some of them traverse some of the facial nodes, which appear as if intercalated in their course, but the ma- jority pass directly to the submaxillary nodes. . A rich 1 y m- phatic net-work lies beneath the mucous membrane of the nasal cavities, and from it vessels pass in two directions. Those of the anterior and lower portions of the fossae pass forward and, partly at the external nares and partly by passing between the nasal bones and the cartilages, communicate with the superficial nasal lymphatics. The majority of the vessels, however, take a backward course, terminating in different node groups. Some join the vessels draining the palate and tonsils to pass to the superior deep cervical nodes and especially to that one which is situated in the angle formed by the union of the facial and internal jugular veins, while the rest unite to form from two to four stems which pass over the lateral surface of the pharynx and terminate in the retropharyngeal nodes. The lymphatics of the sinuses which open into the nasal cavities follow, in part at least, the same courses as those of the nasal mucous membrane, their principal termination being in the larger retropharyngeal nodes. The Cheeks, Lips, Gums, and Teeth. The lymphatics from the more posterior portions of the cheeks empty into the parotid nodes ; those from the more anterior portions pass to the submaxillary nodes, and the deeper ones communicate with the facial nodes. * Beitrage f. klin. Chirurgie, Bd. xxv., 1899. llary Lymphatics of nose and cheek. (Kiittner.*) 952 HUMAN ANATOMY. The vessels from the submucous tissues of the lips pass mainly to the submaxil- lary nodes, two or three stems passing from the lower lip and one or two from the upper. Those of the lower lip pass downward and outward toward the facial artery and follow its course into the submaxillary region, while those from the upper lip are directed at first almost horizontally outward toward the facial vein, whose course they follow toward their termination. No anastomoses occur between the submucous vessels of the two sides in either lip. The subcutaneous vessels of the upper lip (Fig. 803) have a course similar to that of the corresponding submucous stems, with which they may unite, and they terminate principally in the submaxillary nodes, although communication may also be made with one of the lower parotid nodes. The subcutaneous vessels of the lower lip are from two to four in number, and pass principally to the submental nodes, from which efferents pass to the sub- FIG. 803. maxillary and superior deep cervical nodes. A noteworthy peculiarity of these lower lip vessels, which is in marked con- trast with what obtains in the submucous stems, is that those of the right and left halves of the lip anastomose, so that an injection may pass from the vessels of the right half into the left sub- mental and submaxillary nodes. The lymphatics of the lower gums form a very rich net-work from which from fourteen to seventeen stems arise. These empty into a single large collecting stem on either side, which passes outward over the outer surface of the mandible and, opposite the last molar tooth, dips down- ward to terminate in the submaxillary nodes. Whether or not the pulp of the teeth contains lymphatic capillaries is a disputed question. All attempts to inject them have failed, but it has been maintained that their existence has been demonstrated by histological methods. Enlargement of the submaxillary nodes lias been observed to follow dental lesions, but this may be due to the involvement of the tissues of the gums rather than to that of the tooth pulp. The Tongue. The lymphatics of the tongue (Fig. 804) are divisible into two groups according as they arise in the submucous tissue or in the musculature. The submucous vessels take their origin from an exceedingly rich net-work which extends throughout the entire surface of the tongue. It is especially close toward the tip, the meshes becoming larger posteriorly, and that portion of it which lies posterior to the circumvallate papillae is independent of that of the more anterior portions of the tongue. The vessels of the muscular portion of the organ are much less extensively developed and the efferent stems which pass from them early unite with those of the submucous net-work. These latter are quite numerous and for purposes of description may be arranged in four groups. * Ink-mat. Monatssclirift f. Anal. u. 1'hysiol., 1900. Deep cervical nodes Subcutaneous lymphatics of lips and superior deep cervical nodes, new-born child. (Dorrendorjf.*) THE LYMPHATICS OF THE HEAD. 953 Faucial tonsil The first or apical group (Fig. 805) consists of from two to four stems which arise from the net-work at the tip of the tongue and pass downward and backward, half of them lying on one side of the frenum and half on the other side. They follow at first the anterior border of the genio-hyo-glossus muscle and then pass upon the outer surface of that muscle and are continued downward and backward, either external or internal to the hyo-glossus, until they reach the greater cornu of the hyoid bone, just below the attachment of the stylo-hyoid. They then cross obliquely over the outer surface of the greater cornu, and are continued down the neck along the outer border of the omo-hyoid muscle to open into one of the inferior deep cervical nodes situated upon the jugular vein just above the point where it is crossed by the omo-hyoid muscle. Sometimes an additional apical stem passes down the frenum in company with those just described, but continues on downward to perforate the mylo-hyoid muscle and terminate in one of the submental nodes. A second or lateral group consists of a number of vessels which emerge from the net- work along the borders of the tongue (Fig. 804). There are from eight to twelve stems in this group on either side, and all are at first directed almost verti- cally downwards, a few, three or four, passing later- ally to the sublingual gland and the rest medial to it. The former continue their downward course, perforate the mylo-hyoid muscle, and terminate in the submaxil- lary nodes, while the others take a course obliquely downward and backward, and, passing some upon the median and others upon the lajteral surface of the hyo-glossus muscle, terminate in the superior deep cervical nodes and especially in one situated a little above the level of the bifurcation of the common carotid artery. This node, on account of its relations to these lingual stems, has been termed the principal node of the tongue (Fig. 805). A third or basal group takes its origin from the dense portion of the submucous net-work which surrounds the circumvallate papillae and the foramen caecum. Four stems issue from the net-work in the neighborhood of the median line, and two on each side more laterally. The median stems pass at first directly backward and then bend outward in the glosso-epiglottidean folds, two on either side, and join the lateral stems beneath the tonsils. The lateral stems, which drain the regions of the lateral circum- vallate papillae, the foliate papillae, and the glandular region of the tongue, are directed backward towards the lower border of the tonsil, and, after being joined in that situation by the median stems, they pass deeply to terminate in the superior deep cervical nodes. Finally, a fourth or median group arises from the net-work of the median portion of the tongue, anterior to the circumvallate papillae. These stems are five or six in number, and pass at first directly downward through the substance of the tongue and through the interval which separates the two genio-hyo-glossal muscles. One or two of them then continue in their downward course and pass, in some cases Apical net-work of lymphatics Lymphatics of dorsum ar of tongue. (Kiittner.*) * Beitrage f. klin. Chirurgie, Bd. xxi., 1895. 954 HUMAN ANATOMY. Basal vessel FIG. 805 , Apical vessels Lateral vessels Apical vessels to the right and in some to the left, between the genio-hyo-glossus and the genio- hyoid muscles, perforate the mylo-hyoid, and terminate in the submaxillary nodes. The remaining three or four stems pass backward along the mylo-hyoid muscle and, emerging at its posterior border, pass to the superior deep cervical nodes. From this account it will be seen that four different groups of nodes stand in relation to the lymphatics of the tongue. ( i ) The submental nodes receive a stem from the tip ; (2) the submaxillary nodes receive stems from the marginal and cen- tral regions ; (3) the superior deep cervical nodes receive stems from the marginal, central, and basal regions ; and (4) the inferior deep cervical nodes receive a stem from the apical region. In addition it may be mentioned that many of the stems have upon their course one or more of the small ' ' inter- calated ' ' lingual nodes ( page 948 ). Special importance, however, attaches to that supe- rior deep cervical node already mentioned as occurring at about the level of the bifurcation of the common carotid artery, on account of the numerous afferents it receives from the tongue. The lymphatics of the floor of the mouth have essentially the same terminations as those of the tongue. The stems which arise from its anterior half pass with the stems from the tip of the tongue to the inferior deep cervical nodes, while from its entire surface stems pass to the submaxillary and superior deep cervical nodes. The Palate, Pharynx, and Tonsils. The lymphatics of the hard palate form a fine net- work in the superficial portions of the mucous membrane and are continuous laterally with those of the upper gum. They empty into several stems which pass backward in the median line of the palate and at about the level of the last molar teeth bend outward to the right and left, and, passing in front of the anterior pillars of the fauces, pierce the superior constrictor of the pharynx to terminate in those superior deep cervical nodes which are situated on the internal jugular vein above the level at which it is crossed by the posterior belly of the digastric muscle. The net-work of the soft 'palate is exceedingly close and especially so in the uvula, which in a successful injection of the lymphatics may treble its volume, be- coming exceedingly turgid (Sappey). Stems emerging from the net-work pass toward both surfaces of the palate, those lying below the upper surface passing l>ack- ward and outward to join the stems from the nasal mucous membrane just below the orifice of the Eustachian tube, whence their course is similar to that of the nasal stems. Some of them pnss upward and backward to perforate the superior con- strictor of the pharynx and terminate in the lateral PetTOpharyngeal nodes, while others descend beneath the mucous membrane covering the posterior pillars of the fauces and, after perforating the superior constrictor, terminate in the upper nodes of the superior deep cervical group. * Gazette hebdomadaire, 1902. Lymphatics of tongue. (Puttier* , THE LYMPHATICS OF THE HEAD. 955 The lymphatics of the tonsil, which resemble those of the soft palate in their abundance, pass with the stems from the basal region of the tongue to the superior deep cervical nodes. Those of the pharynx are also abundant, especially above (Fig. 799). The stems which arise from the roof and upper part pass principally to the retro- pharyngeal nodes, although some reach the superior deep cervical nodes directly by following the course of the ganglionated cord. The stems which have their origin in the lower part of the pharyngeal net-work pass downward toward the larynx and unite with its vessels to be distributed to the superior deep cervical nodes as far down as opposite the level of the second or third tracheal ring. Practical Considerations. The Lymph-Nodes of the Head. The lymphatics of the scalp pass from the plexus of fine radicles on the vertex into the suboccipital (occipital), mastoid (postauricular), parotid (preauricular), and superficial cervical nodes, and a few from the frontal region into the submaxillary node, into one or the other of which infection may be carried from any portion of the scalp. The suboccipital nodes one to three on each side lie on a line drawn from the junction of the upper and middle thirds of the ear to the inion and about two inches external to that point. They are often enlarged as a result of wounds or irritation of the occipital and postauricular portion of the scalp and especially in neglected children as a consequence of eczema affecting the skin back of the ear. The close relation of the node to the great occipital nerve, on which it usually lies, gives rise to marked tenderness on pressure, the nerve being compressed between the node and the bone. The source of infection of these nodes may be intracranial e.g. , suppurative meningitis of the cerebellar fossa (Macewen). The mastoid node, found directly over the mastoid insertion of the sterno-cleido- mastoid, is likewise usually infected from the same scalp region. It may also be involved alone or together with the suboccipital and deep cervical nodes in localized tuberculous mastoiditis or even in tuberculous otitis media. The parotid nodes, lying both in and upon the gland, receive lymph from and consequently may be infected by lesions of the scalp, the outer portion of the lids, the orbit, the cheeks, the nasal fossae, the naso-pharynx, the external auditory meatus, the tympanum, or the temporo-mandibular joint. Chronic enlargement of these nodes, especially of the deeper ones in the substance of the gland and beneath the parotid capsule, may lead to a mistaken diagnosis of parotid tumor. Suppura- tive inflammation of these deeper nodes gives rise to a true parotid abscess, which, on account of the resistance of the strong parotid fascia, will be under great tension. Sloughing of the parotid tissue may occur. There will be shooting pains in the head, neck, and ear, from pressure on the branches of the trigeminus accompanying the facial, or on the auriculo-temporal and great auricular nerves. The contiguity of the temporo-mandibular joint into which the abscess may open makes movement of the lower jaw painful. The relative weakness of the capsule anteriorly and on its inner aspect causes the pus to travel forward towards the cheek, or inward towards the pharynx, following sometimes the pharyngeal process of the parotid and giving rise to a retropharyngeal abscess. Gravity and the cervical process of the parotid may conduct the pus into the neck. The lymphatics of the face empty, the superficial set accompanying the facial vein into the parotid and submaxillary nodes ; the deep set, with some of those of the orbit, palate, nasal fossse, and upper jaw, are said to end in the internal maxil- lary nodes situated at the sides of the pharynx anteriorly. According to Leaf, these are only exceptionally present. Their involvement in infections spreading from the above regions may give rise to " latero-pharyngeal abscess," causing a swelling externally behind the angle of the mandible, and an inward projection of the pharyn- geal wall posterior to the tonsil. The proximity of the internal carotid should be remembered, and the fact that an aneurism of that vessel has been opened under the impression that it was an abscess of this variety (page 747). Some lymphatics from the chin and the mid-portion of the lower lip empty into the suprahyoid (submental) nodes lying on the mylo-hyoid between the two anterior bellies of the digastrics. Enlargement of these nodes may be distinguished 956 HUMAN ANATOMY. from a bursal tumor (thyro-hyoid) by the fact that the former is above, the latter below, the hyoid bone. Enlargement of a submaxillary node, as of a parotid node, may, particularly if it lies within the sheath of the gland, be mistaken for a growth of the gland itself. The latter as compared with the parotid is, however, much less closely and firmly enveloped by its capsule, is more superficial, and is not in near relation to such important structures. On the other hand, the wide area which drains into the sub- maxillary nodes the middle of the forehead and of the face, the inner portions of the lids, the mouth, pharynx, anterior portion of the tongue, gums and teeth of the lower jaw renders them especially liable to pyogenic or tuberculous or syphilitic infection, or to secondary involvement in carcinoma of any of these regions espe- cially of the tongue or lower lip. In examining for enlargement of these nodes, the chin should be lowered so as to relax the depressors of the lower jaw and the deep cervical fascia and permit of more accurate palpation of the region. When these submaxillary nodes require removal for infectious or malignant disease, the salivary gland is often involved and must be removed with them. On account of its accessi- bility and the laxity of its capsular connections, enucleation of this gland is easily accomplished. The relation of the facial artery lying close to the upper part of its deep aspect which it grooves before crossing the jaw in front of the masseter muscle should be remembered. The efferent vessels from all these nodes suboccipital, mastoid, parotid, and submaxillary enter into the superficial cervical nodes, the efferent vessels from which, in their turn, enter the deep cervical nodes (page 957). Extracranial lesions of an irritative kind will thus first show themselves in enlargement of the first mentioned groups ; if the irritation is continued, the superficial cervical nodes will enlarge ; and if it persists and is sufficiently severe, the deep cervical will also participate in the enlargement (Macewen). As the intracranial lymph-paths, having their origin in the cerebral pia mater and the choroid plexuses of the ventricles, pass out of the skull in company with the internal carotid and vertebral arteries and, lower, the internal jugular vein and empty into the deep cervical nodes, these latter are, theoretically, first affected by intracranial irritation. As they lie beneath the cervical fascia, their enlargement may not be early noticed. These variations in the seat of glandular swelling cannot, however, be relied upon as a basis for a positive differential diagnosis between intracranial and more superficial (extracranial) sources of irritation or infection. THE LYMPHATICS OF THE NECK. THE LYMPH-NODES. The principal group of nodes in the neck region is that which is situated along the course of the internal jugular vein, forming the jugular plexus ( plexus jugularis). It consists of a variable, but usually large, number of nodes and is interposed in the pathway followed by the entire lymphatic system of the head and neck. It is prac- tically a continuous chain of nodes, extending the entire length of the neck, but for convenience in description it is convenient to regard the nodes as forming two sub- groups which are named the superior and inferior deep cervical nodes. In addition to these some smaller groups occur more superficially, forming what are termed the superficial cervical nodes, so that altogether there are three main groups of nodes in the cervical region. The superficial cervical nodes (lymphoiilandulae cervicalcs stipcrficinlcs ) may conveniently be divided into two subgroups, both of which are composed of rather small and somewhat inconstant nodes. The external jugular nodes, as their name indicates, are situated along the course of the external jugular vein, and consequently rest upon the outer surface of the sterno-cleido-mastoid muscle. They occur a little below the lower extremity of the parotid gland (Fig. 796), and are usually two or three in number, one or two additional nodes sometimes being present at a somewhat lower level. They receive afferent s from the pinna of the ear and from the parotid region, and their efferent* pass over the anterior border of the sterno-cleido-mastoid to open into the superior deep cervical nodes. THE LYMPHATICS OF THE NECK. 957 FIG. Digastric muscle Anterior cervical node Recurrential node Anterior cervical and recurrential nodes and lymphatics of larynx. (Most.*) The second subgroup is that of the anterior cervical nodes, which are both variable and inconstant and are situated beneath the depressor muscles of the hyoid bone, resting upon the anterior surface of the larynx and on the anterior and lateral surfaces of the trachea. Those which rest upon the trachea are some- what more constant than the others, but like them they are usually small and are therefore likely to be overlooked in normal conditions. The more lateral members of the series, from three to six in number, are arranged in a chain which follows the course of the recurrent (inferior) laryngeal nerve and are some- times spoken of as the recurrential nodes. The anterior cervical nodes receive afferents from the larynx and trachea, and their efferents pass to the lower superior deep cervical nodes. The superior deep cervical nodes (lymphoglandulae cervicales pro- fundae superiores) vary from ten to sixteen in number, and extend along the course of the internal jugular vein from the tip of the mastoid process to the level at which the vein is crossed by the omo-hyoid muscle. They lie either directly upon the vein or slightly posterior to it, beneath the sterno-cleido- mastoid muscle, and are FIG. 807. all united by numerous connecting stems so that they form a veritable plexus. Some of the nodes are exceedingly constant in position, one, especially, which receives numerous afferents from the lingual region and has therefore been termed the principal node of the tongue, occurring at about the level of the bifurcation of the common carotid artery, and a second is situated just above the ofno-hyoid muscle. The afferents of the group are very numerous, and may be divided into two classes according as they take their origin in nodes belonging to other groups or come directly from the lymphatic net-works. Belonging to the first class and terminating in the more posterior nodes are the efferent stems for the posterior auricular and *Anatom. Anzeiger, Bd. xv., 1899. \ Sterno-mastoid muscle, cut Deep cervical lymph-nodes. 958 HUMAN ANATOMY. occipital nodes, while in the more anterior nodes efferents from the retropharyn- geal, parotid, submaxillary, submental, and superficial cervical nodes terminate. Belonging to the second class and terminating in the more posterior nodes are (i) a vessel which descends directly from the occipital region of the scalp ; (2) some stems from the posterior surface of the pinna ; and (3) stems from the upper part of the back of the neck. To the more anterior nodes pass ( I ) the majority of the stems descending from the tongue ; (2) stems from the nasal mucous membrane, the palate, and the upper portions of the pharynx ; (3) stems from the cervical portion of the oesophagus ; (4) the majority of the stems from the larynx and those which come from the cervical portion of the trachea, and (5) the stems from the thyroid gland. The efferents from the lower nodes of the plexus pass partly to the inferior deep cervical nodes, and partly unite with the efferents of these to form the jugular trunk, which is described below. The inferior deep cervical nodes (lymphoglandulae cervicales profundae inferiores), also termed the supraclavicular nodes, occupy the supraclavicular triangle of the neck, resting upon the scalene muscles and upon the trunks of the brachial plexus. They are fewer in number and, as a rule, smaller than the superior deep cervical nodes. In addition to the afferents from the superior nodes they receive ( i ) a stem which passes directly downward from the occipital region of the scalp along the posterior border of the sterno-cleido-mastoid muscle ; (2) vessels from the integument and muscles of the lower portion of the neck ; (3) vessels from the integument of the upper portion of the pectoral region ; (4) occasionally some vessels from the arm which follow the course of the cephalic vein ; (5) some efferents from the brachial groups of the axillary nodes ; and (6) vessels which pass to the lower nodes of the left, rarely the right, side from the liver, ascending in the suspensory ligament of that organ, piercing the diaphragm, and following the course of the internal mammary vessels upward through the thorax. Their efferents unite with some of those from the superior deep cervical nodes to form a single stem, the jugular trunk (truncus jugularis), which on the left side opens into the arch of the thoracic duct and on the right unites with the subclavian trunk to form the right lymphatic duct. Both the right and the left trunks, how- ever, frequently open directly into the subclavian vein. THE LYMPHATIC VESSELS. The Integument and Muscles of the Neck. The lymphatic stems arising from the subcutaneous and muscular net-works of the neck open into the posterior nodes of the superior deep cervical chain. The Larynx and Trachea. The lymphatic net-work of the larynx is very well developed over the greater portion of the mucous membrane and is especially rich in the regions of the false vocal cords and the ventricles. Over the true vocal cords, however, it is very feebly developed, and the entire net-work may therefore be regarded as consisting of two portions, one of which is situated above the level of the true cords and the other below them. The two portions are not, it is true, perfectly distinct, since they are connected by the feeble net-work of the true cords ; but it has not been found possible to force an injection from one portion into the other and, furthermore, each portion gives rise to a special set of efferent stems. The stems which arise from the upper net-work are from three to six in number on each side, and make their exit from the larynx through the lateral portions of the thyro-hyoid membrane, in close proximity to the superior laryngeal artery (Fig. 806). They then pass outward to the anterior nodes of the superior deep cervical chain, some opening into the nodes situated in the neighborhood of the bifurcation of the common carotid artery, while others, bending downward, terminate in lower nodes. The stems from the lower net- work pass in two directions ; a few small ones perforate the crico-thyroid membrane near the median line, while the rest are directed posteriorly and make their exit below the lower border of the cricoid -cartilage. The anterior stems pass partly to an anterior cervical node situated usually in the median THE LYMPHATICS OF THE NECK. 959 line between the two crico-thyroid muscles, another descends over the isthmus of the thyroid gland to terminate in one of the nodes which rest upon the anterior surface of the trachea, while one or two pass outward -along the upper border of the lobes of the thyroid gland and then descend to terminate in one of the superior deep cervical nodes situated about opposite the middle of the sterno-cleido- mastoid muscle. The posterior stems, which are from three to six in number, after making their exit from the larynx, follow the course of the recurrent laryngeal nerves and terminate in the recurrential nodes situated in the course of those nerves, some of the stems frequently anastomosing to form a plexus which descends along the vagus nerve and may be followed, in some cases, to the inferior deep cervical nodes. The net-work of the trachea is formed of delicate and slender vessels arranged so as to form elongated meshes, and the stems which arise from it emerge from the lateral surfaces of the trachea, passing between the tracheal cartilages. Those from the upper part of the trachea pass to the recurrential nodes, while the lower ones pass to the bronchial nodes situated in the neighborhood of the bifurcation of the trachea. The Thyroid Gland. The lymphatic stems from the thyroid gland pass for the most part to the superior deep cervical nodes, following the course of the superior thyroid artery, some of them, however, passing at first directly upward and coming into relation with an anterior cervical node situated upon the crico-thyroid membrane. Those which arise from the lower border of the isthmus and from the neighboring portions of the lobes are directed downward, and terminate in the anterior cervical nodes which are situated upon the anterior surface of the trachea and in the recurrential nodes. The CEsophagus. The cervical portion of the oesophagus will be considered together with its thoracic portion (page 971). Practical Considerations. The Lymph- Nodes of the Neck. i. The super- ficial cervical nodes not invariably present are found over the sterno-mastoid, along the external jugular vein, between the deep fascia and the platysma, and may be enlarged in various affections of the external ear and of the skin of the face and neck, or consecutively to infections of the suboccipital (occipital), mastoid (post- auricular), parotid (preauricular), or submaxillary nodes. Those found posteriorly near the anterior border of the trapezius muscle enlarge early in the secondary stage of syphilis and, on account of their accessibility for palpation, are then of diagnostic value. 2. The deep cervical nodes are divisible, for convenience, into two groups : (ut accessory paths are also furnished by stems which arise from the sack-like enlargements and pass toward the periphery of the gland, avoiding the subareolar net-work. The stems which arise from the subarrolar net-work pass at first almost directly outwards until they reach the lower border of the pectoralis major. They then ascend along the lower edge of this muscle for a short distance, and eventually bend THE LYMPHATICS OF THE THORAX. 969 around it, perforate the axillary fascia, and terminate in the anterior pectoral nodes of the axillary plexus. Occasionally one finds along the course of one or other of the stems a small intercalated node, and one or two small nodes, the paramammillary nodes, may occur a short distance below the lower border of the gland on one of the efferents which passes to the lower principal stem. The accessory paths of the mammary lymph are principally two in number, (i) In about ten per cent, of cases examined a stem issued from the deep surface of the gland, perforated the pectoralis major, and passed upward between that muscle and the pectoralis minor to terminate in the subclavicular nodes. (2) A varying number of small stems leave the medial portion of the periphery of the gland and perforate the sternal border of the pectoralis major and the intercostal muscles, to terminate in the sternal nodes. It may be noted that the obstacle to the flow of lymph presented by enlarged axillary nodes in severe affections of the mammary gland may lead to the development of accessory or collateral paths other than those mentioned above. Thus, since the subareolar net-work is Delto-pectoral node FIG. 814. Brachial node Subscapular node Anterior pectoral node Vessel passing to anterior pectoral node Inferior pectoral node Subclavian node Vessel passing to subclavian node Intermediate node -Subareolar plexus over mammary gland Lymphatics of mammary gland and axillary nodes. (Poirier and Cuneo.*) continuous with the general anterior thoracic subcutaneous net-work, and the latter is continuous across the median line, affection of the gland of one side may cause enlargement of the axillary nodes of the opposite side, and, furthermore, since the thoracic subcutaneous net-work is continuous with that of the abdomen, there is a possibility for the establishment of a collateral path leading to the inguinal nodes. Furthermore, it is to be remembered that, although the anterior pectoral nodes are the termination of the principal mammary stems, yet the connection between these and other axillary nodes, especially those of the intermediate and subclavicular subgroups, is so intimate that practically all the axillary nodes may be involved, or are at least open to suspicion, in cases of mammary carcinoma. The intercostal lymphatics are arranged in two sets corresponding to the two intercostal muscles (Sappey). The vessels from each internal intercostal unite to form a single stem which passes forward along the lower border of the rib forming the upper boundary of its space. The stems of the upper spaces open independently into the sternal nodes, while those from the lower spaces unite to form a common ascending stem which terminates in the lowest node of the sternal chain. Poirier et Charpy : Traite" d'anatomie humaine, Tome ii., 1902. 970 HUMAN ANATOMY. The vessels from the external intercostals are somewhat larger than those from the internal muscles and have a backward direction, terminating in the intercostal nodes. It is upon these stems that the lateral intercostal nodes are situated when present. Anastomoses occur between the two sets of vessels, and the internal set also receives communicating stems from the parietal layer of the pleura, while the external one receives branches from the muscles which cover the thoracic wall, although the principal path for these leads to the axillary nodes. The Diaphragm. The lymphatics of the diaphragm form rich net-works upon both its surfaces, that upon the peritoneal surface being especially well developed, and numerous vessels traverse the substance of both the muscular tissue and the centrum tendineum, uniting the net-work of the abdominal with that of the thoracic surface. Upon the thoracic surface the net-work is exceedingly fine and close-meshed in the region of the centrum tendineum, being most distinct in the regions of the lateral leaflets. From this net-work branches pass outward parallel to the muscular fibres to unite with a series of anastomosing stems whose general direction is forward. Branches coming from the more peripheral portions of the diaphragm also empty into these stems, which carry the lymph forward to the diaphragmatic nodes, whence it passes to the anterior mediastinal nodes. From the net-works of the lateral leaflets of the central tendon collecting stems are also directed backward and medially towards the aortic opening, which they traverse to terminate in the upper coeliac nodes. It is to be observed that the nodes of the thoracic surface are for the most part situated anteriorly, while the coeliac nodes, which may be regarded as the principal nodes of the inferior surface, are located posteriorly. Both sets of nodes, however, receive lymph from both surfaces of the diaphragm by means of the perforating branches which connect the upper and the lower net-works. The lower net-work is, furthermore, connected with the lymphatics of the more lateral portions of the peritoneum and also with those of the liver (page 980), while the upper net-work makes connections with the lymphatic vessels of the pleurae. These communications, when considered in connection with the existence of the perforating branches, explain the occurrence of pleuritis as a sequence of subphrenic abscess or of the latter as a sequence of thoracic empyema. The Heart. The lymphatics of the heart are arranged in two principal net- works, one of which lies immediately beneath the endocardium, while the other is upon the outer surface of the organ immediately beneath the visceral layer of the pericardium. The endocardial net-work communicates with the superficial one by branches which traverse the heart musculature, and the flow of lymph from the endocardial net-work takes place only through these communicating branches. The superficial net-work extends over the whole surface of the heart, the vessels of which it is formed being well supplied with valves and arranged so as to form characteristic quadrate or rhomboidal meshes. From the net-work longitudinal stems pass up- ward towards the base of the heart, corresponding in a general way to the cardiac veins. Upon the anterior surface three stems are to be found passing upward along the anterior interventricular groove, parallel to the anterior cardiac vein, and, on arriving at the auriculo-ventricular groove, they unite to form a single trunk. With this another stem unites which has its origin in the net-work of the posterior surface of the heart and ascends along the posterior interventricular groove, parallel with the posterior cardiac vein. On reaching the auriculo-ventricular gn>o\ e it bends round to the left and, encircling the base of the left ventricle, unites with the anterior vessels. The conjoined trunk so formed passes upward along the pos- terior surface of the pulmonary aorta, perforates the parietal layer of the pericardium, and terminates in one of the bronchial nodes. From the net-work over the right side of the right ventricle another longitudinal stem arises and passes upward parallel to the right marginal vein, and, on reaching the auriculo-ventricular groove, winds around to the right and so reaches the anterior surface of the heart. It then ascends parallel with the anterior trunk, along the pos- terior surface of the pulmonary aorta, and also terminates in one of the bronchial nodes. The Lungs. The lymphatics of the lungs may be regarded as consisting of two sets, deep and superficial. The deep set is composed of a number of stems which accompany the branches of the pulmonary arteries and veins and of others THE LYMPHATICS OF THE THORAX. 971 which are associated more especially with the bronchi. The bronchial vessels take their origin from a net-work contained in the walls of the bronchi, and are traceable along the entire length of each bronchus and its branches until the terminal bronchi are reached ; here the net-work disappears and no indications of it are to be found in the walls of the atria or alveoli. In the larger bronchi the net-work is double, one portion of it occurring immediately beneath the mucous membrane and the other external to the cartilaginous rings, but in the finer bronchi only one layer is present and from this branches pass to the stems which accompany the arteries and veins. All the stems belonging to this deep set of lymphatics pass to the hilus of the lung and there open into the pulmonary nodes. The superficial set consists of a net-work situated upon the surface of the lung, immediately beneath the visceral layer of the pleura. The vessels composing it are well supplied with valves and have communicating with them branches from the visceral layer of the pleura and valved branches which have their origin in the interlobular and intralobular connective tissue. No communication has been observed between the superficial and deep pulmonary net-works, the stems from the superficial net-work alone passing toward the hilus of the lung and terminating in the pulmonary nodes. Lymphatic vessels have been demonstrated in the parietal layer of the pleura. Those upon its costal surface communicate with the intercostal vessels ; those upon the diaphragmatic surface with the diaphragmatic net-work ; and those upon the mediastinal surface with the posterior mediastinal nodes. The CEsophagus. The lymphatics of the oesophagus are arranged in two net- works, one of which is submucous, while the other is situated in the muscular coat. The stems which drain the net-works of the cervical portion of the oesophagus pass to the superior deep cervical and the recurrential nodes, while those draining the thoracic portions of the net-works pass to the posterior mediastinal nodes. Finally, the stems originating in the net-works of the terminal portion pass to the upper nodes of the cceliac group. Practical Considerations. The Lymph- Nodes of the Thorax and Medias- tinum. Anterior Mediastinum. The nodes in close relation to the internal mammary artery are of practical importance on account of their relations (a) to the diaphragm ; (b) to the anterior extremities of the intercostal spaces ; (c) to the inner segment of the mammary gland. They may therefore be involved in cases of subpleural (supradiaphragmatic) abscess, of tuberculous or syphilitic or typhoidal caries of the ribs or sternum, or of carcinoma of the breast (page 2035). Middle Mediastinum. The nodes just below the bifurcation of the trachea (bronchial, peribronchial), in close relation to the trachea, the bronchi, and the r6ots of the lungs, are frequently involved in tuberculous infection of the lungs. The pulmonary lymphatics, both perivascular and peribronchial, communicate on the one hand indirectly with the lymph-spaces in the walls of the alveoli beneath the epithelial cells, and on the other with these nodes. Solid particles and this includes the bacillus tuberculosis and other organisms are thus enabled to pass from within the alveoli into the lymphatic spaces, and from these they are forced on by the respiratory movements of the lungs to the bronchial nodes, to which all the lymphatics converge. These nodes often contain, especially in coal miners, or in the inhabitants of large cities, a large amount of black pigment, consisting of minute particles of dust, smoke (carbon), etc., that have been inhaled (Taylor). Caseation and ulceration of these nodes have involved the trachea (page 1840), the bronchi (especially the right one, with which the larger number are in close relation), and the oesophagus (page 1614), directly in front of which some of them lie. Their enlargement has also produced various pressure symptoms, dyspnoea, dys- phagia, stridulous respiration, etc., which their relations easily explain. Posterior Mediastinum. A group of nodes cesophago-pericardiac (Leaf) lying between the posterior surface of the pericardium and the oesophagus, are in close relation to the trunk of the pneumogastric nerve and its oesophageal branches. Their infection through their direct connection with the not infrequently infected nodes in the neck and thorax lying between the trachea and oesophagus may produce symptoms of vagus irritation. It has been thought (Guiteras) that these nodes and 972 HUMAN ANATOMY. the bronchial nodes are especially enlarged in influenza and that some of the anomalous pulmonary symptoms of that disease simulating congestion, pneumonia, etc., are thus accounted for. Marked enlargement of the bronchial nodes may be indicated by an area of percussion dulness below the level of the fourth dorsal vertebra (Yeoj. In cancer of the oesophagus either the mediastinal nodes or those at the root of the neck may be involved, as both sets receive lymphatics from that tube. Medias- tinal growth (sarcoma) or abscess may originate in these nodes. Either condition but especially the neoplasm will occasion marked symptoms of pressure on the trachea, bronchi, oesophagus, and superior cava and innominate veins, e.g. , dyspnoea, dysphagia, oedema of the face, neck, and upper limbs, dilatation of the superficial veins of the abdomen and thorax. THE LYMPHATICS OF THE ABDOMEN. THE LYMPH-NODES. The principal nodes of the abdominal region are those associated with the viscera and those situated upon the posterior wall in the vicinity of the aorta. A few small and inconstant nodes also occur upon the anterior wall, and of these the most important are the epigastric, the circumflex iliac, and the umbilical nodes. The epigastric nodes (lymphoglandulae epigastricae) are three or four in number and are interposed in the course of the lymphatic stems which accompany FIG. 815, Umbilical node Deep epigastric artery Epigastric node Iliac node Umbilical node Lymphatic vessels accompanying deep epigastric artery Iliac node Epigastric and umbilical lymph-nodes, seen from behind. (Cuneo and MarciUe.*} the deep epigastric vessels (Fig. 815) ; they occur toward the lower part of the vessels and their efferent* pass to the lower iliac -nodes. The circumflex iliac nodes are from two to four in number when present, but are not unfrequently wanting. They are situated along the course of the deep circumflex iliac vessels ; they receive afferent s from the lower lateral portions of the abdominal wall, and send cffcroits to the lower iliac nodes. The umbilical nodes an- situated in the subserous areolar tissue in the neighborhood of the umbilicus. They are three in number, one being situated a little below and to one side of the umbilicus, and the other two above the umbilicus Hull, et Mm. Socit anatom., 1901. THE LYMPHATICS OF THE ABDOMEN. 973 in the median line (Fig. 815). They occur in the net-work which covers the posterior surface of the sheath of the rectus muscles, and are apparently of inconstant occurrence. The remaining abdominal nodes may be regarded as arranged in two principal divisions, one of which includes the groups associated with the various viscera, while the other is formed by the groups occurring in the posterior wall. This latter division may be separated into the cce/iac and lumbar nodes. The coeliac nodes vary in number from sixteen to twenty, and are situated in front of the abdominal aorta, around the origins of the cceliac axis and the superior mesenteric artery. They are extensively connected with one another so as to form a distinct cceliac plexus (plexus coeliacus). They receive affercnts from the lower portions of the oesophagus, from the diaphragm, and from the gastric, hepatic, pan- creatico-splenic, and mesenteric nodes ; the efferent s of the lower nodes pass to the higher members of the group and the efferents of these either open independently FIG. 816. Right suprarenal body Right kidney Right lateral lumbar nodes Median lumbar node Right ureter Iliac node Left suprarenal body Left kidney Left lateral lumbar nodes Lymphatic vessels from testis Lumbar nodes, new-born child. (Cuneo.*) into the receptaculum chyli, or, more usually, unite to form a common trunk, the truncus intestinalis, which joins the left lumbar trunk to form one of the origins of the thoracic duct (page 943). The lumbar nodes (lymphoglandulae lumbales) are twenty to thirty in number, and form three irregular longitudinal rows along the course of the abdominal aorta (Fig. 816), extending from the level of the second lumbar vertebra to the bifurcation of the aorta, and forming with the aid of connecting vessels a well-marked plexus, the plexus lumbalis. The median row is composed of some five or six large nodes situated upon the anterior surface of the aorta, and of four or five retro-aortic nodes which rest upon the bodies of the third and fourth lumbar vertebrae, immediately below the lower extremity of the receptaculum chyli. Of the lateral rows that of the left side is formed by a number of nodes arranged in an almost vertical series upon the successive heads of the psoas muscle. The right lateral nodes occupy a * Bull, et Mem. Societe anatom., 1901. 974 HUMAN ANATOMY. corresponding position with relation to the right psoas, lying posterior to the vena cava inferior, but a varying number of nodes which may be referred to this group also occur upon the anterior surface of that vessel. Since all the nodes are united by communicating vessels, they form a plexus and will receive afferents from and give efferents to one' another. In addition, the median row receives afferents from the descending colon and the mesocolic nodes, while the lateral rows receive them from the muscles of the posterior abdominal walls, from the iliac nodes, from the testes in the male and the ovaries, Fallopian tubes, and uterus in the female, and from the kidneys and suprarenal capsules. The efferents of the upper nodes of the median row pass upward to terminate in the lower cceliac nodes, while those of the lateral rows either pass to the nodes of the median row, or unite together to form on either side a common trunk, the truncus lumbalis, which unites with its fellow to form the receptaculum chyli (page 943), or else they perforate the crus of the diaphragm and open independently into the thoracic duct. The visceral abdominal nodes are arranged in groups or chains which follow in general the principal visceral branches of the aorta, those following the branches of the cceliac axis and the superior mesenteric artery communicating by their efferents FIG. 817. Superior gastric nodes Inferior gastric nodes Lymphatic nodes and vessels of stomach. (Polya and JVavratil.*) mainly with the coeliac nodes, while those accompanying the inferior mesenteric branches communicate with the median lumbar nodes. Corresponding with the branches of the coeliac axis are the gastric, hepatic, and pancreatico-splenic nodes. The gastric nodes consist of two chains (hmpho- glandulae gastricac superiores et inferiores) situated respectively along the lesser and greater curvatures of the stomach. The superior nodes, three to fifteen in number, are situated along the course of the gastric artery, principally along the lesser curvature of the stomach between the two layers of the gastro-hepatic omentum (Fig. 817), although a few also occur along" the course of the artery before it reaches the stomach and others upon the left side of the cardiac orifice of the viscus. The inferior nodes are situated in the vicinity of the pyloric end of the stomach, partly along the right half of the greater curvature, accompanying tin- right gastro-cpiploic vessels, and partly on the posterior surface of the pylorus along the course of the gastro-duodcnal vessels. The gastric nodes receive afferents from the stomach and in tin- case of the retro-pyloric nodes also from the first portion of the duodenum, and their eft', -rents pass to tin- coeliac nodes, those of the superior group following the course of the gastric vessels, while those from the inferior group accompany the Castro-duodenal and hepatic arteries. * Deutsche Zt- itschrift f. Chirurgie, Bd. Ixix. THE LYMPHATICS OF THE ABDOMEN. 975 The hepatic nodes (lymphoglandulac hepaticae) are more or less clearly arranged in two series. One series accompanies the main stem of the hepatic artery along the upper border of the head of the pancreas and throughout the vertical portion of its course in the free margin of the gastro-hepatic omentum, and the other accompanies the superior pancreatico-duodenal branch and ascends along the bile-duct to the portal fissure. The afferents of the nodes come from the liver, the head of the pancreas, and the first and second portions of the duodenum, and their efferents pass to the cceliac nodes. The pancreatico-splenic nodes (lymphoglandulae pancreaticolienales) accom- pany the splenic artery throughout the greater portion of its course, and are consequently situated along and partly behind the upper border of the pancreas (Fig. 8 1 8). They vary in number from four to ten, and their afferents come from the organs supplied by the splenic artery, namely, the stomach, pancreas, and spleen, while their efferents pass to the cceliac nodes. The mesenteric nodes (lymphoglandulae raesentericae) are from one hundred to two hundred in number, and are arranged along the superior mesenteric artery and its branches to the small intestine. They form three more or less distinct series, especially towards the upper portion of the mesentery. One series, in which the FIG. 818. Hepatic node Retropyloric node Mesocolic nodes Pancreatico-splenic nodes Transverse mesocolon "?~ Transverse colon Pancreatico-splenic, retropyloric, and mesocolic nodes, new-horn child ; liver drawn upward, stomach and duodenum laterally. (Cuneo and Delamare.*) nodes are more numerous and smaller than the others, lies close to the intestine, among the terminal branches of the artery ; a second consists of larger scattered nodes situated along the primary branches of the artery ; while the third series includes the closely aggregated nodes which surround its main stem. Towards the lower portion of the ileum the distinction of the first and second series becomes less and less apparent, and at the junction of the ileum and caecum the nodes form a single group, situated a short distance from the intestine between the two layers of the mesentery. These nodes are sometimes termed the ileo-caecal nodes, and associated with them by means of its efferents is a variable group of small nodes, the appendicular nodes, situated partly in the base of the mesenteriole of the appendix and partly in the immediate vicinity of the junction of the ileum and caecum (Fig. 820). The various series of nodes are connected with one another by vessels, which in this region are known as lacteals, and the nodes of the first series receive their afferents from the walls of the small intestine, and, in the case of the ileo-caecal nodes, from the caecum and vermiform appendix. The efferents of the nodes of the third series pass to those nodes of the cceliac group which are situated around the origin of the superior mesenteric artery. * Jour, de 1'anat. et de la physiol., Tome xxxvi., 1900. 976 HUMAN ANATOMY. The nodes which are associated with the abdominal portions of the large intestine are known as the mesocolic nodes ( lymphoglandnlae mesocolicae) and they consist of from twenty to fifty small nodes which are situated close to the intestine (Fig. 818). Their afferents are received from the entire length of the large intestine, with the exception of the caecum and appendix and the rectum, and the efferents of the nodes associated with the ascending colon and the right half of the transverse colon pass to the lower cceliac nodes, while those of the nodes associated with the left half of the transverse colon and with the descending and sigmoid colons pass to the median row of lumbar nodes. In addition to the nodes which are properly included in the mesocolic group there are a number of small nodes situated upon the lateral walls of the upper part of the rectum, along the lines of the superior hemorrhoidal vessels (Fig. 821). These ano-rectal nodes are from two to eight in number on each side, and are situated beneath the fibrous investment of the rectum, resting directly upon the outer surface of the muscular coat. They receive their afferents from the neighboring portions of the wall of the rectum and, in the female, from the posterior surface of the vagina, and their efferents pass to the mesocolic nodes situated in the lower part of the mesentery of the sigmoid colon. THE LYMPHATIC VESSELS. The Abdominal \Afalls. The anterior abdominal wall, as regards its lymphatic vessels, may be divided into a supra- and an infra-umbilical region. The lymphatics of the former area belong in reality to the thoracic cutaneous set, passing upward to join the thoracic stems which terminate in the anterior pectoral nodes of the axillary plexus. The vessels of the infra-umbilical region, on the contrary, descend to terminate in the inguinal nodes. Along the line of junction of the two regions anastomoses occur and the vessels of the right half of the abdominal wall also communicate with those of the left half. The subcutaneous vessels of the posterior abdominal and lumbar regions anastomose with the corresponding vessels of the posterior thoracic region above, and below with those of the gluteal region. They form an extensive net-work, from which stems pass downward and forward, parallel with the crest of the ilium, to terminate in the inguinal nodes. The lymphatic net-work of the deeper structures of the abdominal walls is drained by a number of stems which follow in general the courses of the blood- vessels. Thus, the stems which lead away from the upper portion of the abdominal wall pass upward along the course of the superior epigastric vessels to terminate in the lower sternal nodes ; another set follows the course of the deep epigastric vessels to terminate in the lower iliac nodes, after traversing the epigastric nodes ; another accompanies the deep circumflex iliac vessels, draining the lower portions of the lateral walls of the abdomen, traversing the circumflex iliac nodes, and also terminating in the iliac nodes ; while other sets accompany the lumbar vessels and terminate in the lateral rows of lumbar nodes. Abundant communications exist between the vessels of adjacent drainage areas and from the region of the umbilicus the lymph flow may follow any one of the paths mentioned above. Attention may be called to the occasional presence of nodes in the course of the vessels arising in the umbilical region (page 972). The Stomach. The lymphatics of the stomach have their origin in two net-works, one of which is situated in the mucosa and the other in the muscular coat. The net-work of the mucosa occurs uninterruptedly throughout the entire extent of the gastric surface and is continuous with the corresponding net-works of both the oesophagus and duodenum. From its deeper surface branches pass to a more open net-work situated upon the outer surface of the submucosa, and from this stems traverse the muscular coat obliquely to terminate in a subsenms net-work which also receives branches from the net-work of the muscular coat. Connections between the muscular and mucous net-works occur, but they are so indirect that an extensive cancerous infection of the mucosa may reach the outer layers of the stomach only at limited areas at some distance from one another. The subserous net-work with which both primary net-works communicate gives origin to a number of stems which pass to the gastric nodes, and the course which they follow is such that the entire surface of the stomach may be regarded as presenting THE LYMPHATICS OF THE ABDOMEN. 977 three more or less distinct lymphatic areas (Fig. 817). Not that the areas are perfectly separated from one another ; on the contrary, the subserous net-work is continuous k over the entire surface. But the collecting stems from each area follow a definite route toward different node groups. The largest of these areas occupies roughly the whole of the upper border of the stomach from the fundus to the pylorus, and extends downward on either surface to about two-thirds of the distance to the greater curvature. Its collecting stems all pass to the superior cardiac nodes. The second area occupies about the pyloric two-thirds of the greater curvature, and its efferents pass to the inferior gastric nodes, while the third and smallest area occupies the lower part of the fundus and the cardiac one-third of the greater curvature, and sends its efferents to the splenic nodes. It may be remarked that these areas correspond in a general way with the areas drained by the principal veins arising in the stomach walls. Thus, the large upper area corresponds in general with the drainage area of the gastric vein, the; lower pyloric area to that of the right gastro-epiploic vein, and the lower cardiac area to that of the left gastro-epiploic. It may further be noted that while the subserous net-work communicates with the superficial net-work of the oesophagus, it seems to be completely cut off from connec- tion with the corresponding duodenal net-work, an arrangement which is in striking contrast to the continuity which exists between the gastric and duodenal mucosa net-works and explains the rare extension of a carcinomatous infection of the pylorus to the duodenum by the subserous route. The Small Intestine. Throughout the entire length of the intestine, both small and large, the lymphatic net - works are arranged in two sets, one of which is situated in the mucosa and the other in the muscular coat. The two net-works are more or less independent, though communicat- ing branches occur, and both open into a subserous net-work from which collecting stems arise. The stems which pass from the duodenum are divisible into two groups according as they arise from the anterior or posterior surface. Those coming from the anterior surface pass to the chain of nodes situated along the course of the inferior pancreatico-duodenal artery, and so to the cceliac nodes, which surround the origin of the superior mesenteric artery, while the posterior stems pass to the hepatic nodes situated along the course of the superior pancreatico- duodenal vessels and so to the cceliac nodes which surround the coeliac axis. Some of the stems which take their origin from the first part of the duodenum pass to those nodes of the inferior gastric group which are situated upon the posterior surface of the pyloric region of the stomach, and, since these nodes also receive afferents from the pylorus, they afford opportunity for the transference of a superficial infection from the pylorus to the duodenum, a direct route for infection in this direction being wanting (see above). The collecting stems of the jejunum and ileum pass to the first series of mesenteric nodes, situated along the line of attachment of the mesentery to the intestine, and, after traversing these, are continued onward to the second and third series of nodes, whose efferents pass to the coeliac nodes surrounding the origin of the superior mesenteric artery. The vessels issuing from the jejuno-ileum are usually spoken of as the lacteals, on account of their contents, especially at times when absorption of food constituents is proceeding rapidly in the intestine, having a milky appearance, owing to the presence of numerous fat globules in the lymphocytes. 62 Mesenteric lymphatic nodes and vessels ; peritoneal covering of mesentery has been removed. 97 HUMAN ANATOMY. The Large Intestine. The two sets of lymphatic net-works characteristic of mucous membranes occur in the walls of the large intestine, and they communicate with one another and finally open into a subserous net-work from which collecting stems take origin. In the vermiform appendix (Fig. 820) these collecting stems are from three to five in number and pass upward in the mesenteriole to terminate in the appendicular nodes or, in the absence of these, directly in the ileo-caecal nodes. The subserous net-work of the base of the appendix communicates freely with that of the caecum, whose collecting stems have essentially the same course as those of the appendix, passing primarily to the appendicular nodes situated in the neighborhood of the ileo-caecal junction and thence to the ileo-caecal nodes. The ultimate nodes of the appendicular and caecal systems are situated in the root of the mesentery along the course of the superior mesenteric vessels ; they belong to the group of mesenteric nodes and receive their afferents in part from the ileo-caecal nodes. Communications have been described as existing between the appendicular lymphatics and those of the broad ligament of the uterus as well as the iliac nodes. The more recent observations have failed, however, to confirm the existence of any direct connection with these structures, and patholog- FIG. 820. ical conditions of the broad ligament and iliac nodes asso- ciated with acute appendicitis may perhaps be due to a dissemination of the infection through the subperitoneal net- work by way of the so-called appendiculo-ovarian ligament. lleo-c.necal _LS*^ fi^ The collecting stems from the subserous net- work of the ascending colon pass primarily to some in- constant mesocolic nodes, situated along the line of attachment of the colon to the abdominal wall, and thence are continued along the lines followed by the right colic vessels to the superior mesenteric nodes. The stems from the trans- verse colon have a more varied course in accordance with the arrangement of the blood-vessels. They pass primarily to a series of mesocolic nodes situated between the layers of the transverse mesocolon close to the intestine ; these are of larger size and more numerous than the nodes associated with either the ascending or descending colon and are especially well developed toward either angle of the colon. Their efferents pass principally to some four or five nodes situated along the course of the middle colic vessels and thence to the third group of mesenteric nodes, but those from the vicinity of the splenic flexure follow the course of the branches of the left colic vessels and so pass to the nodes of the median lumbar group situated in the neighborhood of the inferior mesenteric artery. The lymphatics of the transverse colon communicate somewhat extensively with those of the great omentum, as the result of the attachment of the latter to the colon, and they are thus placed in connection with the inferior gastric and splenic nodes. The collecting stems from the descending colon and sigmoid flexure pass primarily to mesocolic nodes situated close to the attached surface of the intestine, and thence follow the courses of the left colic and sigmoid vessels to the median lumbar nodes situated in the vicinity of the origin of the inferior mesenteric artery. Vermiform appendix Ileo-caecal and appendicular lymphatic nodes and vessels. (Potya and Navratil.*) * Deutsche Zeitschrift f. Chirurgie, Bd. Ixix. THE LYMPHATICS OF THE ABDOMEN. 979 The mesocolic nodes associated with the descending colon are less numerous and smaller than those of the sigmoid flexure and resemble in appearance and arrangement those of the ascending colon. The lymphatics of the rectum (Fig. 821), although belonging in large part to the pelvic region, may, for the sake of completeness of the account of the intestinal lymphatics, be considered here in their entirety. Of the two primary net-works that of the muscular coat is injected only with difficulty, but it communicates with the mucosa net-work and its collecting stems follow the same course as those of the deeper net-work. In the mucosa net-work two zones may be distinguished, one of which includes the greater portion of the net-work and extends down to the lower ends of the columns of Morgagni, while the other includes that portion of the mucosa intervening between that level and the anal integument. The upper zone may be termed the net-work of the rectal mucosa, while the lower one may be designated as the net-work of the anal mucosa, since the region in FIG. 821. which it occurs forms the transition between the mu- cosa and the anal integument. The collecting stems from the net-work of the rectal mucosa traverse the muscular coat and enter into relation with the ano-rectal nodes ( page 976 ). After traversing these they are continued onward along the course of the superior hemor- rhoidal vessels and open into the lower mesocolic nodes, from which efferents pass to the median lumbar nodes situated in the neighborhood of the origin of the inferior mesenteric artery. The net- work of the anal mucosa sends numerous branches upward to communicate with the lower part of the rectal mucosa net- work. These branches trav- erse for the most part the columns of Morgagni in which they are so numerous as to earn for themselves the appellation of glomi lymphatici, while, on the other hand, the mucosa of the depressions between the columns is comparatively poor in lymphatics. Some collecting stems from the anal mucosa perforate the muscular coat and pass to the ano-rectal nodes, and thence along with the stems from the rectal mucosa to the lower mesocolic nodes, while others follow the course of the middle hemorrhoidal vessels and terminate in nodes belonging to the hypogastric group (page 984) situated at the point where the internal iliac artery divides into its leash of branches, or else at the level of the great sacro-sciatic notch, a little below the point where the obturator vein joins the internal iliac. The lymphatics of the anal integument will be considered together with those of the perineal region (page 987). The Pancreas. The lymphatics of the pancreas take their origin from a perilobular net-work from which collecting stems pass to the neighboring nodes, following the course of the blood-vessels which supply the gland. The great majority of them pass to the chain of splenic nodes which extends along the upper border of the pancreas, but those of the head of the gland pass in part to nodes of the hepatic *Archivf. Anat. u. Physiol., 1895. Net-work in anal integument Lymphatics of rectum. (Gerota.*} 980 HUMAN ANATOMY. group, following the course of the superior pancreatico-duodenal vessels, while others again accompany the inferior pancreatico-duodenal vessels to terminate in nodes belonging to the mesenteric group. The Liver. The lymphatics of the liver are arranged in perilobular net-works from which stems pass in two principal directions ; those which come from the deeper portions of the net-work follow the course of either the portal or hepatic venous branches, while those arising from the net-works surrounding the more superficial lobules pass to the surface of the liver, upon which they anastomose extensively to form a subserous net-work from which efferent stems arise. The deep efferents which accompany the branches of the portal vein take their course in the substance of the capsule of Glisson, two or three stems accompanying each of the larger branches of the vein and anastomosing with one another to form a plexus around the vessel and the accompanying branches of the hepatic artery and bile-duct. As the branches of the vein are followed to their union to form larger trunks, the accompanying lymphatics unite to a considerable extent, so that from fifteen to twenty stems emerge at the transverse fissure and terminate in the hepatic FIG. 822. Lymphatics of postero-infertor surface of liver, a, a, trunks arising from vicinity of right border of liver and going to one of the nodes surrounding inferior cava (C) as it enters thorax; 6, trunk arising from inferior sur- face of right lobe and emptying at hilum into nodes resting on neck of gall-bladder ; c, trunks arising near gall- bladder and going to lower hilum-nodes ; rf, trunks running on attached surface of gall-bladder; f,e,e, trunks that take origin from superficial net-works and disappear in liver to follow branches of portal vein to hilum- nodes ; f)f,f* caval nodes receiving vessels from Spigelian lobe {g)\ A, A, principal trunks of left lobe; ', i, i, trunks that arise from superficial net-works and dip into liver to join vessels in capsule of Glisson ; j. trunks from superior surface of liver which follow round ligament to hilum-nodes; k, trunks from superior surface that end in nodes in posterior part of longitudinal fissure (/) ; ;, trunks connecting these nodes with those in hilum; n (14), nodes connected with terminal part of oesophagus; o, o, o (15), hilum nodes which receive all trunks accompanying vena porta and large part of those from inferior surface; p,p, vessels from quadrate lobe (q). nodes situated in the fissure. The stems which accompany the branches of the hepatic vein also form more or less distinct plexuses, and, when they emerge from the liver substance, are from five to six in number. They continue upward along the inferior vena cava, pass with it through the diaphragm, and terminate in the nodes situated on the convex surface of the diaphragm around the orifice for the vena cava. The superficial vessels have more diversified courses, and it will be coim-im-nt to consider them as belonging to two groups according as they arise from tin- superior or inferior surface of the liver. And first those arising from the net-wot k of the superior surface may be described. Those which arise toward the posterior portion of the surface of both the right and left lobes pass mainly toward the vena rava inferior and ascend with it through the diaphragm to terminate in the nodes situated * Description et Irono.^niphie des Yaisseaux lymphatiques, 1874. THE LYMPHATICS OF THE ABDOMEN. 981 around the opening for the vena cava. From the more lateral portions of each lobe, however, the collecting stems take a different course, those from the right lobe uniting to form a single stem which passes backward between the layers of the right lateral (triangular) ligament, and then passes medially over the surface of the right crus of the diaphragm to terminate in the nodes surrounding the cceliac axis. Those from the lateral portions of the left lobe pass backward between the layers of the left lateral (triangular) ligament and terminate in the nodes of the superior gastric group which are situated in the neighborhood of the cardiac orifice of the stomach. The collecting stems of the anterior portion of the siiperior surface are relatively small and are more conspicuous on the right lobe than on the left. They pass forward and downward to curve around the anterior border of the liver, and join with the stems arising from the quadrate lobe and gall-bladder to pass with these to the hepatic nodes situated in the transverse fissure. Finally, much more important than these, is a group of vessels which arise from a rich subserous net-work situated along the line of attachment of the suspensory (falciform) ligament. Some of these vessels take a backward course toward the vena cava and accompany the other vessels of the superior surface which terminate in the caval diaphragmatic nodes, and others pass forward until they meet the upper portion of the round ligament, which they follow to reach the nodes situated in the transverse fissure. The remaining stems of the group, from three to ten in number, pass forward and upward, between the layers of the suspensory ligament, toward the under surface of the diaphragm, traverse that structure near its anterior attachment, and come into connection with a number of small nodes situated behind the xiphoid process of the sternum. From these they are continued upward along the course of the internal mammary vessels to terminate in the lower nodes of the inferior deep cervical group, usually upon the left side, rarely upon the right. This path is of importance as furnishing a direct route by which the metastasis of the left supraclavicular nodes, frequently induced by abdominal carcinomata, may be produced. It must, furthermore, be noted that both these vessels and others which arise from the superior surface of the liver com- municate somewhat extensively with the net-work occurring on the under surface of the diaphragm, and since this net-work communicates abundantly with that of the thoracic surface of the diaphragm, and this again with the vessels of the pleurae, opportunity is afforded for the development of pleuritis, especially upon the right side, as a result of a subdiaphragmatic infection. Turning now to the stems arising from the superficial net-work of the inferior surface of the liver, it will be found that they pass principally to the hepatic nodes situated in the transverse fissure, at least these nodes form the termination for the vessels passing from the left and quadrate lobes, the left half of the Spigelian and the anterior and middle portions of the right lobe. Those, however, which take their origin toward the posterior part of the right lobe and from the right half of the Spigelian pass to the vena cava and, ascending along it, terminate in the dia- phragmatic nodes surrounding its opening into the thorax. The lymphatics of the gall-bladder and common bile-duct have their origin in two net-works, one of which is situated in the mucosa and the other in the muscular coat. Efferents from both net-works pass to the surface to form a superficial net-work, from which collecting stems pass, in the case of the gall-bladder to the nodes situated in the transverse fissure, and in the case of the duct for the most part to a chain of nodes belonging to the hepatic group, which occurs along the line of the duct in the edge of the gastro-hepatic omentum ; those from the lower portion of the duct, however, associate themselves with stems from the duodenum and head of the pancreas which open into the uppermost nodes situated along the course of the superior pancreatico-duodenal vessels. Stated in brief, the destinations of the hepatic lymphatics are principally the hepatic nodes situated in the transverse fissure and the diaphragmatic nodes which surround the opening of the inferior vena cava. A vessel from the right lobe also passes to the cceliac nodes, some from the left lobe to the superior gastric nodes, and an important group passes up in the suspensory ligament to communicate with some of the anterior diaphragmatic nodes and terminate in the lower inferior deep 982 HUMAN ANATOMY. cervical nodes. Finally, it is to be remembered that numerous communications exist between the superficial hepatic lymphatics and those which form the net-work on the abdominal surface of the diaphragm. The Spleen. The lymphatics of the spleen are arranged in a superficial and a deep set, numerous communications occurring between the two. The vessels of the superficial set are subserous in position and converge toward the hilus to terminate in the adjacent pancreatico-splenic nodes, to which the deep lymphatics, which accompany the blood-vessels of the spleen, also pass. The Kidneys and Ureters. The lymphatics of the kidney form three net- works, one of which is situated in the cortical tissue of the kidney, the second, whose meshes are very fine, is situated immediately beneath the fibrous capsule, while the third occurs beneath the peritoneum in the superficial portions of the adipose capsule. The efferents of the cortical net-work follow the branches of the renal vessels through the medullary substance and emerge at the hilus in the form of from four to seven vessels, which pass FIG. 823. j^ J^ toward the median line of the posterior abdominal wall along the course of the renal veins, and termi- nate in the upper nodes of the lateral lumbar groups (Fig. 823). Those which come from the right kid- ney terminate partly in nodes which lie in front of the inferior vena cava, and partly in two or three large nodes which are situated behind that vessel upon the right crus of the diaphragm. The efferents from these nodes pierce the crus and terminate directly in the thoracic duct. The uppermost nodes to which the vessels of the left kidney pass are situated upon the left crus of the diaphragm and their efferents also pierce the crus to open into the thoracic duct ; the efferents from the remaining nodes concerned unite with those of the other lateral lumbar nodes to form the lumbar trunks which open into the receptaculum chyli. The net-work which lies beneath the fibrous capsule communicates with both the cortical and subserous net-works, and its drainage is probably mainly through these : a few stems, however, pass toward the hilus, beneath the capsule, and unite with the terminal efferents from the cortical net- work, there being no direct connection between the net-work and the lumbar nodes. The case is different with the subserous net-work, its efferents passing to the upper lateral lumbar nodes quite independently of the cortical efferents. As already noted, it has abundant communication with the net-work beneath the fibrous capsule, and through this with the cortical net-work, so that infections of the kidney tissue are readily communicated to the adipose capsule. The lymphatic net-works of the ureters appear to be limited to the muscular coat and the surface of the ducts (Sakata). The efferents which arise from the upper portions of the net-works, that is to say from the portions above the level at Ovary Lymphatics of kidneys and of ovary, new-born child. (Stahr.*) *Archivf. Anal. u. Physiol., 1900. THE LYMPHATICS OF THE PELVIS. 983 FIG. 824. which the ureter is crossed by the spermatic (ovarian) artery, pass upward to unite with the renal efferents or occasionally to terminate directly in the upper lateral lumbar nodes (Fig. 824). The majority of the efferents arise from those portions of the ducts intervening between the crossing of the spermatic (ovarian) arteries and the level at which the ureters cross the common iliac vessels to enter the pelvis, and these vessels pass either to the lower lateral lumbar nodes, or else, in the case of the lower ones, to the upper iliac nodes. Finally, the efferents from the pelvic portions of the ureters either unite with the vessels passing from the bladder, or else communicate directly with certain of the hypogastric nodes. In and beneath the fibrous capsule of the suprarenal bodies a lymphatic net-work occurs, whose efferents on the one hand join the renal lymphatics, and on the other pass into the substance of the organs to communicate with a net- work situated in the glomerular portion of the cortex. From this latter net-work stems pass centrally in the partitions between the cell columns of the cortex to unite with a rich plexus which traverses all portions of the medullary substance. The main stems of this plexus follow the course of the suprarenal blood-vessels and emerge at the hilus of the organ as four or five stems, which pass to the upper lateral lumbar nodes. Some of the stems are also said to pierce the crura of the diaphragm and terminate in the lower nodes of the posterior mediastinal group. THE LYMPHATICS OF THE PELVIS. THE LYMPH-NODES. The pelvic lymphatic nodes are arranged along the courses of the principal vessels, and may conveniently be divided into three groups, the iliac, the hypogastric, and the sacral nodes. In addition some small inconstant nodes occur in association with the bladder and these will be described in connection with the vessels arising from that organ (page 985). The epigastric and circumflex iliac nodes, already described in connection with the abdominal region (page 972), are really outliers of the iliac group. The iliac nodes (Fig. 825) are from fifteen to twenty in number and form a plexus (plexus iliacus externus) along the course of the common and external iliac vessels, the uppermost nodes lying at the level of the bifurcation of the aorta and the lowermost around the point of exit of the external iliac vessels beneath Poupart's ligament. Three more or less distinct linear series of nodes can be recognized in the plexus, one of which, along the course of the common iliac artery, is situated close to the outer surface of the artery and along the medial border of the psoas muscle. The second lies behind the artery, resting upon the anterior surface of the vein, while the third unites with its fellow of the opposite side to form a group of three or four nodes resting upon the left common iliac vein and the promontory of the sacrum in the angle formed by the bifurcation of the aorta. Of the series along the line of the external iliac vessels one lies to the outer side of the artery along the medial Lymphatics of ureters. (Based on several figures by SaAala.*) *Archivf. Anatotn. u. Physiol., 1903. 9 8 4 HUMAN ANATOMY. border of the psoas, the second in the angle between the vein and the artery, and the third along the lower border of the vein, between it and the obturator nerve. The various nodes of the iliac set communicate with one another so that the efferent* of one node are afferents for the higher ones. In addition they receive ajferents from the inguinal nodes as well as from the epigastric and circumflex iliac nodes as already stated, and the group situated over the promontory of the sacrum also receives afferents from both the hypogastric and sacral nodes. Furthermore, afferents pass to the iliac nodes from the pelvic portions of the ureters, from the bladder and prostate gland, from the lower portion of the uterus and the upper portion of the vagina, from the glans penis and clitoris, from the adductor muscles of the thigh through vessels accompanying the obturator artery, and, in the case of the lateral series of nodes, from the psoas muscle and the adjacent subserous tissue. The efferents pass to the lower lateral lumbar nodes. The internal iliac or hypogastric nodes (lymphoglandulae hypogastricae) are from nine to twelve in number on each side, and are situated on the lateral walls of the pelvic cavity, along the course of the internal iliac vessel and its branches FIG. 825. Lower lumbar node Iliac nodes Iliac node of promontory group Superficial inguinal nodes Iliac nodes. (Cun'eo and Marcille.*) (Fig. 825). They are connected together to form a plexus (plexus hypogastricus), and receive afferents from most of the regions to which the branches of the internal iliac artery are distributed. Thus branches come to them from all the pelvic organs, from the deeper portions of the perineum, including the penial portion of the urethra, from the deep portions of the posterior and internal femoral and the gluteal regions. Their efferents pass mainly to the iliac nodes situated on the promontory of the sacrum, those which arise from the obturator node, situated upon the obturator artery as it passes through the obturator foramen, passing, however, to nodes belonging to the inner series of the group accompanying the external iliac vessels. The sacral nodes are situated on the ventral surface of the sacrum, partly along the course of the middle sacral vessels, and partly internal to the second and third anterior sacral foramina, along the course of the lateral sacral arteries (Fig. 829). All the nodes are small and they are united together by lymphatic vessels to form a sacral plexus (plexus sacralis medius). They receive ajferents from the neighboring muscles and from the sacrum, and their efferents pass to the iliac nodes situated upon the promontory of the sacrum. THE LYMPHATIC VESSELS. Under this heading will be considered the vessels of the various pelvic organs, with the exception of those of the rectum, which have already been described (page 979). In addition there will be included the vessels of the external genitalia, *Bull. et Mm. Societe* anatom., 1901. THE LYMPHATICS OF THE PELVIS. 985 FIG. 826. Obliterated hypogastric and, on account of their intimate relation with these, the superficial lymphatics of the perineal and circumanal regions. The Bladder. It was for a long time a matter for discussion whether or not the mucosa of the bladder was provided with a lymphatic net-work, but the general consensus of recent observers is that it is not. Only the muscular coat possesses a net-work, and from this stems pass to the surface of the viscus to form a superficial net-work beneath the peritoneal or fascial investment. This net-work is continuous at the neck of the bladder with those of the urethra and prostate gland, and, at its base, with the net-works of the ureters and seminal vesicles, and, in the female, of the vagina. The efferent stems which take origin from it may be divided into two groups according as they arise upon the anterior or posterior surface. Those passing from the lower part of the anterior surface are directed laterally and those from the upper part pursue a flexuous course downward and laterally to terminate in the nodes of the iliac group situated along the external iliac vessels (Fig. 826). In their course they usually traverse some small nodes .situated in close proximity to the bladder and divisible according to their position into two groups. One of these is situated upon the anterior surface of the bladder, and consists of two or three nodes, the anterior vesical nodes, two of which are usually situated near the apex of the vis- cus in the course of the superior vesical artery, while the third occurs lower down in the retro- pubic tissue. The other group consists of from two to four nodes, the lateral vesical nodes, situated on either side of the bladder along the course of the obliterated hypogastric arteries. Both groups are some- what inconstant, but occur in a large percentage of cases. The vessels from the upper part of the posterior surface of the bladder pass downward and laterally, often traversing some of the lateral vesical nodes, and terminate in the external iliac nodes which receive the stems from the anterior surface. Others pass to the hypogastric nodes, while others again, arising from the base of the bladder, pass at first directly backward past the lateral surfaces of the rectum and then ascend on the sacrum to terminate in the iliac nodes situated upon the promontory. The Prostate Gland. The lymphatics of the prostate have their origin in net-works surrounding the various acini of the gland. From these net-works stems pass to the surface, where they form a second net-work, and from this the efferent stems pass symmetrically on either side of the median line to somewhat diverse terminations. One or two of the efferents on either side ascend in a tortuous course upon the posterior surface of the bladder, and then bend laterally over the obliterated hypogastric arteries to terminate in one of the middle series of the iliac nodes which accompany the external iliac vessels. Another stem passes backward along the prostatic vessels to terminate in one of the hypogastric nodes ; others pass at first backward on either side of the rectum, and then ascend upon the anterior surface of the sacrum to terminate in the lateral sacral nodes or in the iliac nodes situated on the promontory of the sacrum ; and from the anterior surface of the gland a stem Anterior vesical node Subhypogastric node Anterior vesical node Lymph-nodes of bladder. (Based on figures of Gerota.*) *Archiv f. Anatom. u. Physiol., 1897. 986 HUMAN ANATOMY. passes downward on either side of the membranous portion of the urethra, and, accompanying the urethral lymphatics along the course of the internal pudic vessels, terminates in one of the hypogastric nodes situated upon these vessels. The Urethra. The mucous membrane of the male urethra is furnished throughout its entire extent with a lymphatic net-work, which is especially rich in the region of the glans and diminishes in complexity in the membranous and prostatic portions of the duct. In the last region it communicates with the net-work in the muscular coat of the neck of the bladder. The efferents from the membranous portion of the duct associate themselves with some of the prostatic efferents and pass to a hypogastric node situated on the course of the internal pudic vessels, and those from the penial portion accompany the vessels which arise from the glans and will be described in the account of the lymphatics of the penis. The net-work of the female urethra corresponds with those of the membranous and prostatic portions of the male duct. The External Reproductive Organs in the Male. The lymphatics of the scrotum form an exceedingly rich net-work, especially well developed in the vicinity of the raphe and thence extending laterally over the entire surface. From six to eight stems arise from FlG - 82 7- this net-work, and the uppermost accompany and eventually anasto- mose with the superhcial efferents from the penis and terminate in the in- ner inguinal nodes. The remaining stems pass upward and outward to terminate in the inner superficial subinguinal nodes. The lymphatics of the penis are divisible into a superficial and a deep set which correspond respectively to the super- ficial and deep blood- vessels of the organ. The superficial set forms a net-work in the integu- ment of the penis which radiates in all directions from the frenulum, some stems passing forward and upward into the prepuce and some especially strong stems passing dorsally in the furrow behind the corona of the glans. As they approach the dorsal mid-line these latter give off one or two longitudinally directed efferents, or else they unite to form a single stem which runs along the dorsal mid-line. Other stems arising from the more proximal portions of the net-work curve upward from below over the lateral surfaces of the penis, and either unite with the dorsal stems or form independent lateral stems parallel with the dorsal ones. Numerous anastomoses occur between all the longitudinal stems throughout their courses, and, as they approach the symphysis, they bend laterally, some indeed dividing to send branches to either side, and, after the upper stems from the scrotum have united with them, tiny terminate in the inner inguinal nodes. The deep set forms a net-work especially well developed in tin- glans, in which a superficial and a deep layer may be distinguished. Both these layers communicate at the meatus with the urethral net-work, and from the deeper layer a special plexus Superficial lymphatic vessels of penis and scrotum and inguinal nodes. (Bruhns.*) * Archiv f. Anat. u. Physiol., 1900. THE LYMPHATICS OF THE PELVIS. 987 is developed on either side of the frenulum (Panizzd 1 s plexus}, from which stems ascend in the groove back of the corona glandis. Into these stems the superficial layer of the net-work opens, and they also receive communications from the super- ficial vessels of the penis. From them one or two stems arise which pass proximally in company with the dorsal vein of the penis toward the suspensory ligament. Here they usually divide to form a more or less distinct plexus, lying immediately over the symphysis pubis and provided with some small lymphatic nodes, and from it two or three stems pass off laterally on either side. These pass across the surface of the pectineus muscle and beneath the spermatic cord, and some then pass either to the inner inguinal or deep subinguinal glands, while others extend along Poupart's ligament to the external abdominal ring and, traversing the inguinal canal, terminate in one of the lower iliac nodes. It is to be noted that owing to the anastomoses and bifurcations of both the superficial and deep longitudinal stems it is possible that a unilateral infection may cause enlargment of the nodes of both sides. The External Reproductive Organs in the Female. The lymphatics of the external female genitalia have essentially the same distribution as those of the corresponding organs in the male. In both the labia majora and minora rich subcutaneous net-works occur, from which numerous stems arise and pass to the inner- most inguinal and occasionally the inner superficial subinguinal nodes. The stems from the upper parts of the labia ascend at first directly upward toward the mons veneris and then bend suddenly outward to reach their terminal nodes ; those from the lower parts pass either directly upward and outward or else at first directly upward parallel to the outer edges of the labia and then bend suddenly outward. Some of the stems coming from one or other of the labia may pass to the nodes of the opposite side, and, furthermore, communications exist through the anterior and posterior commissures between the net- works of the opposite labia, so that a unilateral infection may produce enlargement of the inguinal nodes on both sides. The lymphatics of the clitoris present essentially the same arrangement as the deep lymphatics of the penis. They form a rich net- work in the glans and from this longitudinal stems arise and pass toward the symphysis pubis, in front of which they form a plexus which usually contains some small nodes. From the plexus stems arise which pass laterally, and terminate either in one of the deep subinguinal nodes or else in the lower iliac nodes, which they reach by traversing the inguinal canal. The Perineum and Circumanal Regions. The deeper lymphatics of these regions have been considered in connection with the organs to which they belong and there remain for consideration only the subcutaneous vessels. These in the perineal region form an abundant net- work from which stems pass forward, for the most part in the furrow between the perineum and the inner surface of the thigh, and, associating themselves with the stems from the scrotum or labia majora, terminate in the inner inguinal or superficial subinguinal nodes. The subcutaneous lymphatics which surround the anal opening also form a rich net-work, which communicates extensively with that of the anal mucosa (page 979). From it some two or three stems pass forward along the inner side of the thigh to terminate with the perineal and scrotal (labial) stems in the inner inguinal nodes. The Internal Reproductive Organs in the Male. Thetestis possesses an abundant supply of lymphatics, which may be divided into a deep and a superficial set. The former takes its origin in a rich net-work which surrounds the seminal ducts, and the stems which compose it pass toward the hilum in the septa, and, issuing, associate themselves with the stems arising from the superficial net-work. This is double, one layer of it lying beneath the tunica albuginea and the other between that investment and the visceral layer of the tunica vaginalis. Both layers are abundantly connected by vessels which traverse the tunica albuginea, and the deeper layer also receives numer- ous communicating stems from the deep lymphatics and from the lymphatics of the epididymis. Collecting stems from both layers converge toward the hilum, where they become associated with the stems from the deep net-work, from six to eight or rarely more trunks which ascend along the spermatic cord to the internal abdominal ring. They then follow the course of the spermatic veins upward, and terminate in from two to four of the lateral lumbar nodes (Fig. 816). The nodes to which the vessels from 988 HUMAN ANATOMY. the left testis pass lie immediately beneath the level of the renal veins, while those in which the stems from the right testis terminate are lower, being situated about midway between the level of the renal vein and the junction of the common iliac veins. The lymphatics of the vas deferens are probably arranged in two net-works, one belonging to the mucosa and the other to the muscular coat, although so far only the latter net-work has been demonstrated. At the testicular end of the duct the net-work communicates with that of the epididymis, and the stems which arise from it accompany those of the testis to the lateral lumbar nodes. At the vesical end the net-work communicates with that of the seminal vesicles and its efferents pass to one of the hypogastric nodes. The lymphatics of the seminal vesicles are much more readily demonstrable than those of the vasa deferentia. They arise from two net-works, one of which is situated in the mucosa and the other in the muscularis. Stems from the latter form a third net-work over the surfaces of the vesicles and from this efferents, two or three in number, pass to some of the hypogastric nodes. The Internal Reproductive Organs in the Female. The lymphatics of the ovary are very abundant throughout the substance of the organ, a fine net- work Lateral lumbar node Lymphatic vessels from fundus of uterus Iliac node Lymphatic vessels from body and cervix of uterus Ureter Lymphatic vessels from ovary and upper part of uterus Ovary Fallopian tube Bladder Lymphatics of internal reproductive organs of female. (Poirier.*) surrounding each of the Graafian follicles. The stems which arise from these net- works converge toward the hilus, where they form a rich plexus and from this from six to eight efferents arise and follow the ovarian blood-vessels to terminate in the lateral lumbar nodes (Fig. 828). Owing to thinness of the walls it is difficult to distinguish a definitely layered arrangement of the lymphatic net-work of the Fallopian tubes. It is, however, rich, and communicates with that of the fundus of the uterus. It gives rise- to two or three efferents which accompany the ovarian efferents to the lateral lumbar nodes. *Progrds Medical, 1890. THE LYMPHATICS OF THE PELVIS. 989 In the uterus (Figs. 828, 829) the conditions are much more favorable for determining the existence of separate net-works in the mucosa and muscularis than in the Fallopian tubes, but, nevertheless, much difference of opinion exists as to the occurrence of a mucosa net-work. That of the muscularis can be injected without difficulty, but no conclusive injections have yet been made of the mucosa, and while some authors (Bruhns, Sappey, Poirier) are inclined to admit the existence of a net-work in it, others (Leopold) deny it. However that may be, a well-developed net-work occurs in the muscular coat, in the deeper portions of which it becomes especially rich, and, furthermore, it is more abundant in the cervix than in the body or fundus. From it stems pass to the surface of the organ to form a subserous net-work, from which a number of efferents arise. These may be divided into three principal groups according to their termina- tions. ( I ) The efferents from the fundus, usually two in number, pass outward on either side in the upper portion of the broad ligament, and, associating themselves with the efferents from the ovary, terminate in the lateral lumbar nodes. (2) Small stems pass from the fundus along the round ligament of the uterus to terminate in the FIG. 829. 1Hyi>ogastric nodes inguinal nodes. (3) The efferents from the body and cervix pass laterally to terminate in the median iliac nodes situated in the angle between the external and internal iliac arteries. In the course of these last vessels, at the point where they cross the ureter, a small titero-vaginal node is occasionally placed. Other efferents have been described as passing from the cervix to a hypo- gastric node situated at the origin of the uterine or vaginal artery, and two or three stems have been found arising from the posterior surface of the cervix and passing back- ward on either side of the rectum to the anterior surface of the sacrum, up which they pass to terminate in the iliac nodes situated upon the sacral promontory (Fig. 829). In the vagina there is no question as to the existence of definite net-works in both the mucosa and muscularis. That of the mucosa (Fig. 830) is exceptionally fine and communicates abundantly with the coarser net-work of the muscularis, as well as with the net- work of the vaginal portion of the cervix above and with that of the labia minora below. From the muscularis net-work stems pass to the surface of the organ to form a third net-work, from which the main efferent stems arise, and these may be arranged in three groups according to their destinations: (i) those which arise from the upper portion of the vagina join the stems which pass from .the cervix of the uterus (Fig. 830) and terminate with these in the median iliac nodes situated in the angle formed by the external and internal iliac arteries ; (2) those arising from the middle portion accompany the vaginal vessels, passing obliquely upward, outward, and backward, to terminate in one or two hypogastric nodes situated at the origin of the uterine arteries ; and (3) those from the lower portion associate themselves with those from the labia minora and terminate with these Lymphatics of uterus. (Cuneo and Marcille.*) *Bull. et Mem. Societ^ anatom., 1902. 990 HUMAN ANATOMY. Efferent! from infe- rior group Lymphatic net-work of vaginal mucous membrane. (Poirier.*) in the inner inguinal nodes. Certain of the stems from the middle portion also pass to the same middle iliac nodes which receive the efferents from the upper portion, and stems have been observed FIG. 830. (Bruhns) passing from the posterior surface of the vagi- na to the lateral lumbar nodes and even to the iliac nodes situated on the promontory of the sacrum, while others have been traced to the anorectal nodes (page 976). Finally, it may be noted that the superficial net-work of the anterior surface of the vagina communicates with that of the posterior surface of the bladder. Practical Considera- tions. The Lymph-Nodes of the Abdomen and PC Iris. The superficial lymphatics of the wall of the abdomen convey infection, if the pri- mary focus is above the level of the umbilicus, to the axil- lary nodes ; if it is below that level, to the inguinal nodes. Hence, in cases of furuncle or carbuncle, or of chancre, or of epithelioma, the site of the lesion would determine the region in which adenopathy should be sought. The cceliac groitp of nodes may be involved in diseases of the greater portion of the digestive tract, or of the stomach, spleen, or part of the liver ; or their enlarge- ment may follow that of the lumbar or of the mesenteric nodes. The nodes in and about the portal fissure, or between the layers of the gastro-hepatic omentum may so enlarge in cases of carcinoma of the stomach or of the liver as to compress the portal vein (causing ascites) or the common bile duct (causing jaundice). The lymphatic relations of the stomach, liver, spleen, and pancreas have been sufficiently considered from the practical stand-point in connection with these viscera. The mesenteric nodes are frequently and gravely involved in various intestinal diseases. They are often infected and enlarged during typhoid fever. They are especially implicated in peritoneal or intestinal tuberculosis. The lymphoid nodules in the neighborhood of Peyer's patches are surrounded by lymphatic plexuses and are a common site of tuberculous ulceration. The bacilli tuberculosis are carried directly thence to the mesenteric glands (tabes mesenterica), and sometimes by way of the lymphatic vessels and thoracic duct, may reach the general circulation in large numbers (generalized tuberculosis, acute miliary tuberculosis). In some cases of tuberculous peritonitis associated with mesenteric gland disease, the mesentery undergoes marked and extreme contraction, so that the altered coils of intestine are held closely to the spine, and their lumen may be greatly narrowed (peritonitis deformans) (Taylor). Mesenteric cysts (serous or chylous cysts) are usually of lymphatic origin, and may be due to lymphatic obstruction or to a degeneration and dilatation of the mes- enteric nodes analogous to the varicosity of inguinal nodes in filarial disease. The clinical signs of such cysts are : i, a prominent, fluctuating, usually spherical swell- ing near the umbilicus ; 2, marked mobility of the tumor especially in a transverse direction and around the central avis ; 3, the presence of a zone of resonance around the cyst and a belt of resonance across it (Moynihan). The symptoms may be *Progrs medical, 1890. i THE LYMPHATICS OF THE LOWER EXTREMITY. 991 either (a) chronic, of the nature of colicky pain due to interference with the intes- tine and to gastro-intestinal disturbance, the presence of a tumor distinguishing the case from one of simple gastro-enteritis ; or (6) those of acute intestinal obstruction (Rolleston). The lumbar nodes may be enlarged from septic or malignant disease of the lower extremities, the testes, the fundus of the uterus, the ovary, the kidneys and adrenals, the sigmoid or rectum. The wide area thus drained by them exposes them frequently to transmitted infection or disease. Their condition in the presence of carcinoma affecting any of these regions or viscera has an important practical bearing upon the question of operative interference, as, practically without excep- tion, if they are involved only palliation can be hoped for. With an empty intes- tinal tract and a thoroughly relaxed abdomen, even moderate enlargement of these nodes may, in thin persons, be detected by palpation. In persons with very mus- cular or very fat abdominal walls, they cannot be felt until they have formed a con- siderable mass. Their great enlargement especially in carcinoma often results in swelling and oedema of the lower extremities on account of the obstruction to the current in the inferior cava produced by the pressure of the dense indurated glands which may quite encircle both that vessel and the aorta and may even interfere with the circulation in the latter. The lumbar nodes often enlarge consecutively to enlargement of the pelvic nodes (obturator, gluteal, sciatic, internal pudic, external and internal iliacs), some of which are also palpable in thin persons when the subject of carcinomatous infiltration. The external iliac nodes, for example, lying along the anterior and inner aspect of the external iliac vessels, may, when cancerous, be recognizable in this way, and may be found by their tenderness though less distinctly felt in some septic cases. As they receive the lymphatic vessels from the nodes of the groin, and the vessels accompanying the deep circumflex iliac arteries, their enlargement may follow that of the inguinal nodes, or may result from septic or syphilitic or cancerous foci in the supra-inguinal portion of the abdominal wall. In cancer of the testis the iliac and lumbar nodes are in the closest relation to the ascending current of lymph, the inguinal nodes, as a rule, being involved later, after the skin of the scrotum has become infiltrated or ulcerated. In advanced cases of carcinoma of the rectum or uterus, the obturator, epigastric and external iliac groups become considerably affected. QEdema of the legs often results because (a) the enlarged nodes press directly upon the external iliac vessels ; and (<5) the lymphatics pass both over and under these vessels to communicate with the obturator node and thus compress the vein in a ring-like carcinomatous mass (Leaf). The pain felt in these cases is due to the pressure of the affected glands upon the nerve-trunks arising from the lumbo- sacral plexus. Similar pains may be felt when any of the pelvic glands are involved as there is a similarly close relation between the obturator node and the obturator nerve ; the gluteal, sciatic, and internal pudic nodes and the first and second sacral and great sciatic nerves ; and the external iliac nodes and the anterior crural nerve. The obturator group of nodes lying between the external iliac vein and the obturator nerve assume surgical importance because sometimes the lowest node of this group is found projecting through the crural canal. The relation of this node to Gimbernat's ligament shows that when enlarged it would appear as a swelling occu- pying a position similar to that of a femoral hernia (Leaf). Cases are on record (White) in which an inflammation of this node has simulated a strangulated femoral hernia. THE LYMPHATICS OF THE LOWER EXTREMITY. THE LYMPHATIC NODES. The Inguinal Nodes. The principal group of nodes of the lower extremity is situated in the inguinal region over Scarpa's triangle, where they form a consider- able mass, placed for the most part between the layers of the fascia lata, and consist of from twelve to twenty nodes united by connecting branches to form a plexus, the plexus inguinalis. Though in reality forming a single group, they have been divided for purposes of description into a number of subordinate groups which must be recognized to have merely a conventional value. The first of these divisions is a 992 HUMAN ANATOMY. FIG. 831. separation of the nodes which lie respectively above and below a horizontal line drawn through the point at which the long saphenous vein pierces the cribriform fascia, and to those lying above this line the term inguinal nodes (lymphoglandulae inguinales) is applied, while those below it are termed the subinguinal nodes (lymphoglandulae subinguinales). This latter subgroup is again divided into a super- ficial (lymphoglandulae subinguinales superticiales) and a deep (lymphoglandulae sub- inguinales profundae) set, according as they are situated in or beneath the fascia lata. Finally, by means of a vertical line passing through the orifice in the cribriform fascia through which the long saphenous vein passes, the inguinal and superficial subinguinal groups are each subdivided into an inner and an outer set, a small central group of nodes, surrounding the saphenous orifice, being also sometimes recognizable. It may, however, again be emphasized that these subdivisions are purely conventional and cannot always be clearly distinguished, nor do they represent, except in a very general way, the terminations of definite drainage areas. Indeed, the numerous connections which exist between the nodes of the various subgroups cause their distinction to be of comparatively little importance from the surgical stand-point. The inguinal nodes are arranged in a more or less distinct chain over the base of Scarpa's triangle, immediately below Poupart's ligament. They receive as afferents the superficial lymphatics of the abdominal walls and the gluteal region, the superficial vessels of the scrotum and penis in the male and of the labia majora and minora in the female, as well as those from the perineum and the circumanal region. Their efferents perforate the cribriform fascia, enter the abdomen by the femoral ring, and terminate in the lower iliac nodes. The superficial subinguinal nodes receive some afferents from the gluteal regions and also some from the perineum and circumanal regions, but the principal set is formed by the superficial vessels of the leg. Their efferents have essentially the same course as those of the inguinal nodes, piercing the cribriform fascia to accompany the femora] vessels to the abdomen, where they terminate in the lower iliac nodes. In their course through the femoral sheath some of them lie on the anterior surface of the vessels, but the majority lie on their inner side in the crural canal and some of them terminate in the deep subinguinal nodes. The deep subinguinal nodes vary in number from one to three. They are placed along the course of the femoral vein, one occurring immediately beneath the point of junction of the long saphenous vein with the femoral, a second a little higher up in the crural canal, and the third, termed by French authors the node of Cloquet and by the Germans the node of Rosenmuller, is situated at the entrance into the crural canal from the abdomen. Their principal afferents are the deep lymphatics of the thigh which accompany the femoral vessels and their branches, but in addition they receive stems from the superficial subinguinal nodes and the deep vessels of the penis and clitoris. Their efferents pass, like those of the superficial nodes, to the lower iliac nodes. The popliteal nodes (lymphoglandulae popliteae) are some four or more in number and are embedded in the adipose tissue of the popliteal space (Fig. 832). One or two occur in the neighborhood of the short saphenous vein immediately after it has entered the popliteal space, while the rest are situated more deeply upon the popliteal vessels. The more superficial nodes receive as affcrenfs the superficial lymphatics of the leg which accompany the short saphenous vein, while the deeper Superficial horizontal line subdivides nodes into upper and lower groups; vertical line into median and lateral groups inguinal lymph-nodes; subdivi THE LYMPHATICS OF THE LOWER EXTREMITY. 993 Popliteal lymph-nodes. (Poirier and Cuneo.*) ones receive the vessels which accompany the branches of the popliteal vessels and also those accompanying the anterior and posterior tibial vessels. Their efferents for the most part accompany the femoral vessels to terminate in FIG. 832. the deep subinguinal nodes. The anterior tibial node (lymphoglandula tibialis anterior) is a small and probably inconstant node situated in the upper part of the course of the lymphatic vessels which accompany the anterior tibial artery. Its effer- ent pass upward along with the anterior tibial and popliteal blood-vessels to terminate in the deeper popliteal nodes. THE LYMPHATIC VESSELS. The lymphatic vessels of the lower extremity may be divided into two groups, one of which consists of the subcutaneous net- work and its efferent stems and the other of those vessels which accompany the principal blood- vessels. The superficial lymphat- ics take their origin from a net-work distributed throughout all portions of the subcutaneous tissue of the extremity, but increasing in richness and complexity toward the distal part of the limb, until in the foot, and especially in the plantar region, it forms a very close and abundant net-work. This plantar net-work extends not only throughout the entire plantar region, but curves dorsally upon both the outer and inner borders of the foot, and also over the posterior surface of the heel, and from these lateral and posterior portions of the net-work as well as from the subcutaneous net-work of the digits numerous collecting steins arise. These anastomose abundantly, and those from the digits, the whole of the inner border of the foot and the distal half of its outer border form an open plexus upon the dorsum of the foot. The stems, several in number, which arise from this plexus pass upward along the inner surface of the leg (Fig. 833), following in general the course of the long saphenous vein and receiving as they go communications from the superficial net-works of the regions they traverse. In the neighborhood of the knee stems arising from the net-work over the anterior tibial region become associated with them, and above the knee branches which drain the net-work of the outer, inner, and posterior surfaces of the thigh also curve upward and inward or forward, as the case may be, to accompany them. The numerous stems so formed are all situated superficially to the fascia lata, and terminate above in the superficial subinguinal nodes, the more anterior stems passing to the outer and the more posterior to the inner members of the group. The stems which arise from the calcaneal portion of the plantar net-work and from that portion of it which curves upward over the posterior half of the outer border of the foot, pass upward upon the posterior surface of the crus in company with the short saphenous vein. They receive communications from the superficial net-work of the calf and, as they approach the bend of the knee, they perforate the crural fascia and terminate in the more superficial popliteal nodes. Finally, from the net-work over the gluteal region a number of collecting stems arise, the majority of which curve forward and converge to terminate in the outer inguinal nodes, some from the more posterior portions of the net-work, however, * Poirier et Charpy : Trait d'anatomie humaine, Tome ii., 1902 63 994 HUMAN ANATOMY. FIG. 833. passing forward along with the stems from the circumanal region to the inner inguinal or superficial subinguinal nodes. The deep lymphatics of the lower extremity take their origin mainly in the muscles and form stems which accompany the blood-vessels. From the net-work of the plantar muscles one or two stems take origin which follow the course of the plantar arch, ascending to the dorsum of the foot between the first and second metatarsal bones. They then follow the course of the dorsal pedal vessels, receiving the stems which accompany their branches, and then accompany the anterior tibial vessels up the leg. After traversing the anterior tibial nodes they pass with the vessels through the foramen in the interosseous membrane, and, continuing their upward course through the popliteal space, terminate in the deeper popliteal nodes. Other branches arising in the plantar musculature follow the plantar vessels backward, and, ascending behind the internal malleolus, accompany the posterior V aFA tibial vessels. Toward the upper part of the crus they receive the stems which accompany the peroneal vessels and their branches, and terminate, like the anterior stems, in the deeper popliteal nodes. From these nodes four large stems issue, and, passing through the hiatus tendineus of the adductor magnus, continue their course up the thigh in company with the femoral vessels. They receive the stems which accompany the various branches of the femoral vessels and terminate above in the deep subinguinal nodes. In addition to these deep femoral lymphatics others occur in the thigh in company with the obturator and sciatic vessels, and the muscles of the gluteal region are drained by stems which accompany the gluteal vessels. All these stems terminate in nodes belonging to the hypogastric group, those accompanying the sciatic ves- sels traversing some small and inconstant nodes situated beneath the pyriformis muscle, while some ten or twelve similar nodes occur along the course of the gluteal stems. Practical Considerations. The Nodes of the Lower Extremity. The majority of the lymphatics of the sole of the foot unite with those of the inner side of the dorsum and run with the long saphenous vein to enter the inguinal nodes. A smaller number run up the fibular side of the leg, but most of these cross over the leg or at the ham to join the inner lymphatic vessels. A still smaller number run with the short saphenous vein and empty into the popliteal nodes. The far more frequent occurrence of glandular swellings and abscess in the groin than in the ham is thus easily understood. The popliteal nodes (iuicrcondylar, lying on either side of the popliteal artery between the two heads of the gastrocnemius, and supra&mdylar, lying deeper and against the back of the femur) are extremely difficult to feel unless they are enlarged, and even then the only one which can be detected is that which lies over the internal popliteal nerve. This node, probably from the constant movement of the knee-joint, is very apt to suppurate as a result of superficial sores about the heel. The intercondylar nodes cannot be felt ; in the first place, because of their deep position, and secondly, because when pressed they become still further forced clown between the condyles. The suprarondylar nodes lie altogether too deep to be felt by the fingers (Leaf). A small node beneath the fascia close to the point of entry of the short saphenous receives some of the lymphatics that accompany that vein. Superficial lymphatic vessels of lower limb ; semiaiagrammatic. (Based on figures of Sappey.) THE LYMPHATICS OF THE LOWER EXTREMITY. 995 Popliteal abscess will follow pyogenic infection of tlie popliteal nodes. The pressure effects due to the density and rigidity of the popliteal fascia and the conse- quent necessity for early and free incision and drainage have already been described (pages 646). Enlargement of the popliteal nodes has been mistaken for enlarged bursae though the nodes are deeper and nearer the median line for popliteal aneur- ism, and for neoplasms. The inguinal nodes are numerous and, on account of their frequent involvement in diseases of the lower extremity and of the genitals, are important. The arrange- ment into a superficial and deep set, and the division of the former into two groups, the horizontal, parallel with and close to Poupart' s ligament, and the vertical, parallel with and close to the long saphenous vein, is of convenience. The deep set is found to the inner side of the femoral vein and may be said to include one group which is embedded in the fatty layer at the saphenous opening and bears the same relation to the fascia lata that the central group of axillary glands bears to the axillary fascia (Leaf) (page 581). The inguinal nodes receive lymph through the superficial lym- phatics as follows : Lower limb vertical set of superficial nodes ; lower half of abdomen middle nodes of horizontal set ; outer surface of buttock external nodes of horizontal set ; inner surface of buttock internal nodes of horizontal set, (a few of these vessels go to the vertical nodes ; external genitals horizontal nodes, a few going to the vertical set ; perineum-vertical set. The deep lymphatics of the lower limb enter the deep set of nodes (Treves). The deep lymphatics of the penis and those that are found with the obturator, gluteal, and sciatic vessels enter the pelvic nodes. The inguinal nodes communicate with the external and common iliac nodes, the pelvic lymphatics with the internal iliac nodes, and both the iliac groups with the lumbar nodes. The deep node lying in the crural canal and upon the septum crurale is variously described as one of the obturator (pelvic) group (Leaf) and as one of the deep set of inguinal nodes (Treves). It should be remembered that when it is inflamed it may not only simulate strangulated hernia, but, on account of the density of the structures by which it is surrounded and their participation in the movements of the thigh, may give rise to pain suggesting coxalgia. The relations of branches of the anterior crural nerve to the inguinal nodes may, in cases of inflammation or enlargement, give rise to pain or spasm in the region supplied by that nerve. Filariasis (elephantiasis arabum) of the femoral lymphatics, which are obstructed by the worms, gives rise to very great swelling of the lower extremity (Cochin leg, Barbadoes leg). In addition to what has been stated above the practical application of a knowl- edge of the lymphatics of the lower extremity embraces the following considerations : () The lymphatic vessels may be inflamed without involvement of the veins, when the course of some of the main vessels can be distinctly traced under the skin. When chronically inflamed, and obstruction exists at the nearest lymphatic gland, the vessels may become thickened, dilated, and tortuous. The lymphatic vessels of the sheath of the penis are, perhaps, more frequently involved in diseased action than those of any other portion of the skin surface. Inflamed lymphatic vessels often co-exist with a chancre. In cases of neglected chancre, associated with an indurated condition of the lymphatic nodes of the groin, they may even form bulla-like swell- ings which sometimes rupture and permit the lymph to escape externally. Rarely dilatation of the lymphatic vessels occurs without apparent cause. () The lymphatic vessels may, from causes imperfectly understood, become filled with chylous fluid. In one (Petters), remarkable dilatation of the lymphatics existed in the right groin and in the abdomen, in a patient the subject of valvular heart disease. The glands were converted into cyst-like cavities filled with a yellow fluid. Rosary-like dilatations, similar to those seen at the elbow, occur infrequently below the groin. The inguinal lymphatic glands are the common seat of diseased action dependent upon the transmission of the virus of syphilis, or of any other irritant whose point of entrance is through the external genitals. In the nonsyphilitic infections they frequently suppurate or excite suppurative cellulitis in the parts about them. Acute inflammatory engorgement of one of them has been known to induce fatal peritonitis by direct continuity through the lymphatic vessels of the abdominal wall (Allen). THE NERVOUS SYSTEM. THE nervous system the complex apparatus by which the organism is brought into relation with its surroundings and by which its various parts are united into one coordinated whole consists essentially of structural units, the neurones, held together by a special sustentacular tissue, the neuroglia, assisted by ingrowths of connective tissue from the investing membrane, the pia mater. The neurone, the morphological unit of the nervous system, includes a nucleated protoplasmic accumulation, the cell-body, and the processes. The former, usually spoken of as the nerve-cell, presides over the nutrition of the neurone and is the seat of the subtle changes giving rise to nervous impulse. The processes arise as outgrowths from the cell-body and provide the paths along which impulses are conveyed. They are very variable in length, some extending only a fraction of a millimeter beyond the cell-body, while others continue for many centimeters to distant parts of the body. The longer processes, which usually acquire protecting sheaths, are known as the nerve-fibres, and these, associated in bundles, constitute the nerve-trunks that pass to the muscles and various other organs. Reduced to its simplest terms, the nervous system consists of the two parts rep- resented in the accompanying diagram (Fig. 834). The one, the sensory neurone, (A) takes up the stimulus received upon the FIG. 834. integument or other sensory surface and, by means of its process (nerve-fibre), conveys such impulse from the periphery towards the central aggregations of nerve-cells that commonly lie in the vicinity of the body-axis. Functionally, such a path constitutes a centripetal or off ere nt fibre (a). The impressions thus carried are transferred to the second element, the motor neurone {JB}, which in response sends out the impulse originating within the cell -body (nerve-cell) along the process known as tin- ct iitri- fugal or efferent fibre (e~), to the muscle-cell and causes contraction. The simple relations of Diagram showing fundamental units the foregoing apparatus are, in fact, superceded of nervous system. A, sensory neurone, Dy much greater complexity in consequence of the conducting afferent impulses by its pro- . , . . . ,. .* . J . 1-1 i cess (a) from periphery (s) ; 'ft, motor introduction of additional neurones by which the proces 1 s e (')'tomusc!l ere " t impulses by '"* afferent impressions are distributed to nerve-cells situated not only in the immediate vicinity of the first neurone, but at different and often distant levels. Although very exceptionally the relation between the neurones may perhaps be that of actual continuity in consequence of a secondary union of their processes (Held), the view concerning the constitution of the nervous system most worthy of confidence, notwithstanding the bitter attacks by certain histologists, regards tin- neurones as separate and distinct units. While chained together to form the various paths of conduction, they are probably seldom, if ever, actually united to one another but only intimately related, since their processes, although in close contact, are not directly continuous, contiguity but not continuity being the- ordinary relation. During the evolution of the nervous system from the simpler type, the cell- bodies of the neurones forsake their primary superficial position and recede from the periphery. In vertebrates this recession is expressed in the axial accumulation of cell-bodies either within the wall or in the immediate vicinity of the neural tube (brain and spinal cord), from or to which the processes pass. The nervous system is often divided, therefore, into a <-vv//;w/and a peripheral portion. The former, also known as the ccrcbro-sf>inal a\is< includes the brain and spinal cord and contains the chief axial collections of nerve-cells ; the peripheral portion, on the contrary, 996 THE NERVOUS TISSUES. 997 contains the nerve-cells of the sensory ganglia and is principally composed of the nerve-fibres that pass to and from the end-organs. Intimately associated with and in fact a part of the peripheral nervous system, but at the same time possessing a certain degree of independence, stands the sympathetic system, which provides for the innervation of the involuntary muscle and glandular tissue throughout the body and the muscle of the heart. When sectioned, the fresh brain and spinal cord do not present a uniform appear- ance, but are seen to be made up of a darker and a lighter substance. The former, the gray matter, owes its reddish brown color not only to the numerous nerve-cells that it contains, but also to its greater vascularity ; the hue of the lighter substance, the white matter, is due to its chief constituents, the medullated nerve-fibres, in conjunction with its relatively meagre vascular supply. THE NERVOUS TISSUES. The Neurones. The neurones, the essential morphological units of the nervous system, consist of the cell-body and the processes. The latter, as seen in the case of a typical motor neurone (Fig. 835), are of two kinds : (a) the branched protoplasmic extensions, the dendrites, which may be multiple and form elaborate arborescent ramifications that establish relations with other neurones, and (<) the single unbranched axone (neuraxis, neurite) that ordinarily is prolonged to form the axis-cylinder of a nerve-fibre, and, hence, is often termed the axis-cylinder process. The dendrites are usually uneven in contour and relatively robust as they leave the cell-body, but rapidly become thinner, due to their repeated branching, until they are reduced to delicate threads that con- stitute the terminal arborizations, the telodendria, formed by the .end-branches. The latter are beset with minute varicosities and finally end in terminal bead-like thickenings. The axones, slender and smooth and of uniform thickness, are much less conspicuous than the dendrites. They may be short and only extend to nearby cells ; or they may be of great length and con- nect distant parts that lie either wholly within the FIG. 836. Dendrites FIG. 835. Dendrites Arborization of axone Telodendrion Diagram of typical neurone. Diagram of nerve-cell of type II, in which axone is not prolonged as nerve-fibre. cerebro-spinal axis (as from the brain-cortex to the lower part of the spinal cord) or extend beyond (as from the lower part of the cord to the plantar muscles of the foot). 998 HUMAN ANATOMY. FIG. 837. On reaching their destination the axones terminate in end-arborizations (telodendria) of various forms, in a manner similar to the dendrites. According to the distribution of their axones, the neurones are divided into two classes. In those of the first, known as cells of type /, the axone is continued as a nerve-fibre and is, therefore, relatively long. Soon after leaving the cell-body such axones give off delicate lateral processes, the collaterals, which, after a longer or shorter course, break up into arborizations ending in relation with other and often remote neurones. Neurones of the second and much less frequent class, cells of type //, possess short axones that are not continued as nerve-fibres, but almost immediately break up into complex end-arborizations or neuropodia (Kolliker), limited to the gray matter. The processes of the sensory neurones, as in the case of those constituting the spinal and, other ganglia connected with afferent nerves, are so modified during development (Fig. 839) that later both dendrites and axones arise in common from the single robust stalk of an apparently unipolar cell. Branching T-like, one process (the dendrite) passes towards the periphery and the other (the axone) extends to and into the cerebro-spinal axis. The nerve-cells, as the bodies of the neurones Semichagrammatic representation of ,, . . , , < structure of neurone; a, axone. are called, possess certain structural details in common, although in some instances they present characteristics that suffice to identify them as belonging to particular localities. Nerve-cells are relatively large elements, those in the anterior horns of the spinal cord measuring from .070-. 150 mm. in diameter, and contain a large spherical nucleus, poor in chromatin but usually pro- vided with a conspicuous FIG. 838. nucleolus. Their cytoplasm varies in appearance with the method of fixation and staining to such an extent that considerable uncertain- ty exists as to the relation of many described details to the actual structure of the cells. It may be accepted as established, however, that the cell-body of the neurone consists of aground substance, homogeneous or finely granular, in which delicate fibrHla and masses of chromatophilic grannies are embedded ; in addition, a variable amount of brown or blackish pigment is com- monly present in the vicin- ity of the nucleus. The presence of the fibrilke within the nerve-cell, long aim maintained by Max Schultze but later disiv- Nerve-cells of human spinal cord stained to show Nissl bodies ; D, dendrites ; .1. .ixoncs; ( ', Implantation. COM; A', nucleus; A/, nucleolus. X 4. garded, has been placed beyond question by the researches of Apathy. Bethe, Cajal and others. The signifi- cance and relations of the fibrillae to the nerve-cell, however, have given rise to warm THE NERVOUS TISSUES. 999 discussion. The observations based upon the improved methods of silver-staining introduced by Cajal have contributed much towards the solution of these questions, and, at present, the most experienced histologists incline towards the view that the fibrillae demonstrable within the nerve-cell are limited to the body and processes of that particular neurone and do not unite with the 'fibrillae of other neurones. When adequately differentiated by successful staining, the fibrillae form .an intracellular net-work within the cell-body, from which they are continued into the dendrites and axone and in all cases end free in the terminal arborizations (Retzius). After special staining with methylene blue, or other basic anilines, the chrom- atophilic granules appear deeply colored and arranged in groups or masses of vary- ing form and size. Such aggregations, known as Nissl bodies, after the German histologist whose elaborate studies and theories concerning the structure of the nerve- cell have given prominence to these masses of ' ' stainable substance, ' ' are usually most conspicuous in the vicinity of the nucleus. Collectively, they constitute the tigroid substance of Lenhossek and are least marked at the periphery of the nerve- cell. They are continued into the dendrites as elongated flakes or pointed rod-like tracts that finally are resolved into scattered granules along the processes. The axone, on the contrary, is not invaded by the Nissl bodies, and usually joins the nerve-cell at an area free from the stainable substance, the axis-cylinder process com- monly arising from a slight elevation known as the implantation cone. Exception- ally, the axone may arise from one of the dendrites, either at its base or at a point some distance from the cell-body. Notwithstanding the elaborate classification of nerve-cells and the theories based upon the Nissl bodies, their significance is still debatable, although in the light of the more recent studies by Carrier, Holmes and others it seems probable that they are normal constituents of the cell and are directly related to functional activity, undergoing increase under unusual stimulus. The intracellular canals described by Holmgren as existing in nerve-cells, in connection with a reticulum (trophospongium) that appears after certain treatment, have been variously interpreted. By not a few they are regarded as artefacts, or at least dependent upon the intra- cellular fibrillae for their exhibition. Pewsner-Neufeld, however, believes them to be lymph- clefts within the cytoplasm that directly communicate with lymph-spaces which surround the nerve-cell and thus provide a means for the rapid removal of waste products from the neurone. FIG. 839. Every neurone possesses at least one process, which is then an axone, although usually provided with both dendrites and axone. Very rarely more than a single axone is present. Depend- ing upon the number of their processes, nerve-cells are described as unipolar, bipolar, or multipolar. The unipolar condition is often secondary, since two processes may be so blended for part of their course that they form a single process. Conspicuous examples of such relation are seen in the spherical nerve-cells composing the spinal and other ganglia connected with the sensory nerves. Primarily such neurones possess an axone and a dendrite that arise from opposite ends of what is for a time a spindle-shaped bipolar cell. During development, however, the unilateral growth of the cell-body towards the surface of the ganglion brings about the gradual approximation of the two processes until they fuse in the single extension into which the spherical or flask-like cell is prolonged. This process sooner or later undergoes a Y- or T- like division, one process, usually identified as the dendrite, passing to the periphery to end in the free terminal arborization, whilst the other, the axone, passes centrally to end in an arborization around the neurones lying within the cerebro-spinal axis. Examples of bipolar neurones, in which the dendrite and axone pass from opposite sides of the spherical cell-body, are found in the retina and the ganglia Diagram showing transformation of young bipolar sensory neurone into one of unipolar type. IOOO HUMAN ANATOMY. FIG. connected with the acoustic nerve. An interesting modification of bipolar neurones is presented by the olfactory cells, whose dendrites are represented by the extremely short processes embedded within the nasal mucous membrane, whilst the axones are prolonged as the fibres of the olfactory nerves into the cranial cavity to end in telodendria within the glomeruli of the olfactory bulb. The cell-bodies of the multipolar neurones, which possess one axone and several dendrites, vary in form (Fig. 841). Some, as those within the sym- pathetic ganglia, are approximately spherical and o moderate size, with short delicate dendrites ; many are of large size and irregularly stellate form, the dendrites passing out in all directions, as seen in the conspicuous motor neurones within the gray matter of the spinal cord ; others possess a regular and characteristic form, as the flask-shaped cells of Purkinje within the cerebellum, or the pyramidal cells of the cerebral cortex. ' Certain multipolar neurones within the cerebral cortex, and especially those constituting the chief components of the granule layer, of the cerebellum, are distinguished by the small size of their cell-bodies and the peculiar ramifications and claw-like telodendria of their dendrites (Fig. 945^. Within the cerebellar cortex are likewise found examples of FIG. 841. Bipolar neurones; a, from olfactory mucous membrane dendrite is above; b, from retina. (Modified from Cajal.) Multipolar nerve-cells of various forms; A, from spinal cord; B, from cerebral cortex; C, from cerebellar cortex (Purkinje cell) ; a, axone ; c, implantation cone. the multipolar neurones of Golgi's type II, whose axones almost immediately undergo elaborate branching within the gray matter to which they are confined. The Nerve-Fibres. From the foregoing considerations it is evident that tin: nerve-fibres are not independent elements, but that all are the processes of neurones either the axones of those that are prolonged into fibres (type I), or the dendrites of those situated within the spinal and other sensory peripheral ganglia. Although neurones exist which are not continued as nerve-fibres, the latter are always connected THE NERVOUS TISSUES. 1001 FIG. Axis-cylinders Axolemma Medullary sheath - Node of Ranvier Xeurilemma Medullated nerve-fibres, as seen in longi- tudinal sections of spinal nerve. X 500. with neurones. Recognizing, therefore, that the nerve-fibres are only processes of neurones, their separate description is justified only as a matter of convenience. The fundamental part of every nerve-fibre is the central cord, commonly known as the axis-cylinder, which is composed of threads of great delicacy, the axis- fibrilhc, prolonged from the nerve-cell and embedded within a semifluid interfibrillar substance, the neuroplasm, the entire cord so con- stituted being enclosed by a delicate structureless sheath, the axolemma. The existence of the axolemma as a distinct sheath, however, is ques- tionable, the appearance of such investment not improbably being due to a local condensation of the framework of the medullary coat immediately around the axis-cylinder. In the case of the typical fibres, such as form the chief constituents of the peripheral nerves distributed to various parts of the body, the axis- cylinder is surrounded by a relatively thick coat, known as the medullary sheath, outside of which lies a thin structureless envelope, the neurilemma or sheath of Schwann, that invests the entire nerve-fibre. In the case of fibres proceeding from neurones composing the sensory ganglia, the neurilemma is continuous with the nucleated sheath enclosing the individual ganglion-cells. The medullary sheath consists of two parts, a delicate reticular framework and a fatty substance, the myelin, that fills the meshes of the supporting reticulum. The latter, arranged for the most part as anastomosing membranous lamellae, that in transverse sections of the nerve-fibre appear as faint concentric lines, resists pancreatic digestion and fat-dissolving reagents, and was regarded by Ewald and Kiihne as possessing properties similar to the keratin of horny substances and, hence, was named by them ncnrokcratin. The blackening after treatment with osmic acid and other reactions exhibited by myelin indicate its fatty nature, and it is probable that this substance exists during life in the form of a fine emulsion supported by the framework. When fresh, myelin appears highly refracting and homogeneous, and confers upon the medullated nerve-fibres their characteristic whitish color. It is, however, prone to post-mortem changes, so that after death it loses its former uniformity and presents irregular contractions and collections, or at the broken end of the fibre extrudes in irregular globules, due probably to fusion of the normal individual minute droplets into larger masses. The medullary sheath is not uniformly continuous, but almost completely inter- rupted at regular, although in different fibres variable, intervals marked by annular constrictions. These constrictions, the nodes of Ranvier, correspond to narrow zones at which the medullary sheath is practically wanting and the neurilemma dips in and, some- what thickened, lies in close relation with the axis-cylinder. According to Hardesty * the medullary sheath does not suffer complete suppression at the nodes, but is represented by part of its reduced framework which trans- verses the constriction, a conclusion which we can confirm. The nodes occur at regular intervals along the fibre, which they thus divide In general, the latter are longer in large fibres, where they have a length of about i mm., and shorter in those of small diameter, in which they may measure . i mm. or less in length. The axis-cylinder passes uninter- ruptedly across the nodes, although it often presents a slight fusiform enlargement FIG. Axis-cylinder Neurilemma Medullary sheath Medullated nerve-fibres in transverse section. X 550. into a series of interned a I segments. . Journal of Anatomy, vol. iv., 1905. 1002 HUMAN ANATOMY. opposite each constriction (Ranvier). The neurilemma also suffers no break at the nodes, but is continuous from one segment to the other. In addition to the partial interruptions at the nodes, the medullary sheath after treatment with osmic acid frequently appears broken by clear narrow clefts that extend obliquely from the neuri- lemma to the axolemma and thus subdivide each internodal segment into a number of smaller tracts, known as the Schmidt- Lantermann segments (Fig. 844). The oblique clefts do not all extend in the same direction, even within the same inter- nodal segment, since they are usually directed from without inward and towards the nodal constrictions and, therefore, have an opposed disposition at the ends of the same as well as of the adjoining seg- ments. The significance of this subdivision is un- certain ; many regarding the details as artefacts. According to Capparelli l , however, the apparent clefts are in reality unstained membraneous septa that pass obliquely from the axolemma to the inner surface of the neurilemma and serve to hold the axis-cylinder in place and to enclose the myelin. The studies of Hatai 2 on the arrangement of the neurokeratin seem to support these conclusions. Within each internodal segment, beneath the sheath of Schwann, lies a single (sometimes more than one) small neiirilemma-cell which consists of an elongated oval nucleus surrounded by a meagre amount of cytoplasm. These cells represent the remains of the mesoblastic elements (sheath-cells} that during the growth of the jierve-fibre were active in providing its envelope (page ion). Schmidt- Lantermann segment Axis-cylinder Cleft Node of Ranvier Medullated nerve-fibres after treatment with osmic acid; A, fibre showing reticu- lum within medullary coat ; B, one showing same coat divided into segments. X 5- FIG. 845. > Medullated nerve-fibres becoming nonmedullated on approaching their termination. X 235. Depending upon the presence or absence of the medullary sheath throughout the greater part of their course, nerve-fibres a re distinguished as medullated or non- 1 Archiv f. mikros. Anat. u. Entwick., Bd. 66, 1905. * Journal of Comparative Neurology, vol. xiii., 1903. THE NERVOUS TISSUES. 1003 medullated. The medullated fibres constitute the great majority of those making up the peripheral nerves and the tracts of the cerebro-spinal axis ; the component fibres of the latter, however, while medullated are without the neurilemma. The nonmedullated fibres, on the other hand, are chiefly prolongations (axones) from the ganglion cells of the sympathetic system, although in the case of the olfactory nerves the fibres are also without a myelin-coat. The dis- tinction between these two classes of fibres is relative rather than absolute, since every medullated nerve-fibre becomes nonmed- ullated before reaching its termination, central or peripheral. Medullary nerve-fibres vary greatly in thickness, the smallest hav- ing a diameter of only .001 mm., whilst the largest may measure as much as .020 mm. According to their diameter, as determined by Kolliker, the medullated fibres may be grouped as fine (.oo2-.oo4 mm.), medium (.oo^-.oog mm.), and coarse (.oio-.o2o mm.). In general, the thicker fibres are the longer and are the processes of large nerve-cells ; conversely, the finer have shorter courses and belong to small cells. Although subject to many exceptions, the motor fibres are usually the thicker and the sensory the smaller. .Since there are many more nerve-fibres than nerve-cells, it is evi- dent that the former must undergo division along their course. Such doubling always occurs at a point corresponding to a node of Ranvier, never within the internodal segment, the sheaths being continued over the two resulting fibres. On approaching their peripheral termination the branching becomes more frequent and the medullary sheath thinner until it ends, after which the axis-cylinder continues invested with only the attenuated neurilemma. The latter, now reduced to an extremely delicate covering beset with occasional nuclei, sooner or later disappears, the naked axis-cylinder alone being prolonged to end finally in the varicose threads of the telodendrion. The nonmedullated nerve-fibres proper, also termed pale fibres or fibres of Remak, include those that are without the myelin sheath throughout their course. They are chiefly the axones of sympathetic neurones. Devoid of medullary sheath, these fibres, often .002 mm. or less in diameter, consist of only the axis-cylinder and the neurilemma, the latter being thinner and more delicate than on the medullated fibres. Like the latter, the pale fibres end in telodendria composed of naked axis-cylinders, bearing irregular varicosities. Nonmedullated nerve- fibres in longitudinal section of splenic nerve. X 310. FIG. 847. Neuroglia. The neurones (nerve-cells and fibres) within the cerebro-spinal axis are everywhere held together by a special supporting tissue known as neuroglia. The latter is primarily derived from the invagi- nated ectoblast lining the neural tube, certain elements, the sporigioblasts, being devoted to the production of the neuroglia, while others, the neuroblasts, give rise to the neurones. At first the supporting tissue is represented by greatly elongated, radially disposed fibre-cells that often extend the entire thickness of the wall of the neural canal. Later, the neurogliar elements become differentiated into (#) those bordering the lumen of the canal, which are partly retained as the ependymal cells, and (<) those which have early migrated to more peripheral locations and given rise to stellate cells that are converted into spider-like elements, the astrocytes. Seen in chrome-silver preparations (Fig. 847) these appear as irregular triangular or quadrilateral cells from whose angles numerous delicate fibrillae extend between the surrounding nervous elements. According to Rubaschkin, 1 the astro- cytes are transformations from larger branched gliogenetic cells, by the conversion of whose robust protoplasmic processes the delicate fibrillcz that later form the chief 1 Archiv f. mikros. Anat. u. Entwick., Bd. 64, 1904. Young neuroglia cells ; astrocytes, from brain of child. X 300. IOO4 HUMAN ANATOMY. constituents of the neuroglia arise. So long as neuroglia is being produced, as in the nervous axis of young animals, the large gliogenetic cells are present and directly concerned in the production of additional fibrillae, their cytoplasm becoming pro- gressively less granular and reduced through the various transition phases until in the final condition, as the small glia cells, little more than the nucleus remains. During these changes very many fibrillae lose their connection with the cells and, in conjunction with the glia threads still attached to the astrocytes, form an elaborate interlacement in which the neuroglia cells, now reduced and for the most part devoid of processes, lie scattered at uncertain intervals. In all parts of the central nervous system the mature neuroglia consists of essentially the same tissue, the differences presented in certain localities depending largely upon variations in its compactness. Everywhere the chief part of the sup- porting tissue consists of the intricate felt-work of fibrillae, glia-fibrcs, as they are called, w r hich are usually free but to some extent connected with the spider-cells or astrocytes. Where, however, the neuroglia borders the neural tube (the ventricles of the brain and the central canal of the spinal cord) as the ependymal layer, its arrangement exhibits peculiarities that call for later special mention. In the immediate vicinity of the neurones the felt-work of the fibrillse is unusually close, so that the cell-bodies and the roots of the processes are surrounded by a protecting sheath, the glia-capsulc. This diminishes along the dendrites, and after these begin to branch the neuroglia no longer forms a complete special investment. The medullated nerve-fibres within the brain and spinal cord are also provided with delicate neurogliar sheaths which replace the neurilemma which on these fibres is wanting. These sheaths are prolonged for some distance on the fibres of the roots of the spinal nerves. The fibres of the optic nerve and of the olfactory tract are accompanied through- out their length by neurogliar sheaths, those of the remaining cranial nerves losing these envelopes shortly after leaving the brain (Rubaschkin). Beneath the pia mater the neuroglia is especially dense and forms the external subpial layer that every- where invests the nervous mass, following all the inequali- ties of its surface. In this manner the pia mater is excluded and, except where its connective-tissue strands accompany the blood-vessels that enter the nervous mass, takes no part in the make-up of the supporting stroma. The subpial layer consists of a dense felt-work of glia-fibres, disposed in various planes, which are partly free and partly the processes of spider cells. Internally the layer fades into the adjoining diffuse neuroglia without demarcation. At the periphery the fibres often exhibit a radial disposi- tion, their outer ends usually being somewhat expanded. \Yithin the white matter the neuroglia, both in its distri- bution and density, is fairly uniform, although special tracts often separate the larger bundles of nerve-til >n-s. Its arrangement within the gray matter presents less uniformity, since more or less marked condensations occur where the nerve-cells are collected into nuclei, as conspicuously seen in the inferior olive. FIG. 848. Ependymal cells and adjacent neuro- glia surrounding central canal of spinal cord of cat. X 75. (Rubaschkin.) Where the neuroglia borders the neural tube (especially the central canal of the spinal cord) it constitutes the ependymal layer, the peculiari- ties of which call for special mention. The imme- diate lining of the tube consists of a single layer of pyramidal epithelial elements, the ^nidynial celts, whose free surfaces or bases look towards the lumen, and the apices towards the surrounding nervous tissue. At least during the earlier years in man, and throughout life in many lower mammals, the free surface of each cell is beset with a number of hair-like processes that in their relations with the cytoplasm correspond to ordinary cilia. The pointed distal end of the epemlvmal cell is prolonged into a conical process that is directly continued into usually a single neurogliar fibre which, after a course of uncertain length becomes THE NERVOUS TISSUES. 1005 lost in the surrounding complex of glia-fibres. In young tissue the apical processes often exhibit evidences of breaking up into a number of fine fibrillae. Where the processes enter robust tracts of neuroglia, as in the posterior longitudinal septum of the spinal cord, they are of unusual length. In addition to the radially directed fibres connected with the ependymal cells, the fibre-complex of the ependymal zone includes many fibrillae that are circularly and longitudinally disposed. Scattered glia cells, some stellate but mostly small, are also present and represent the elements from which the neuroglia-fibrillae have been derived. In the preceding account of the elements composing the nervous tissues the neurones have been regarded as the morphological units, each retaining its individual anatomical indepen- dence, although functionally closely related with other similar units. This conception, com- monly referred to as the Neurone Doctrine and strikingly formulated by Waldeyer in 1891, stands in contrast to the prior views by which actual continuity was attributed to the nerve-cells by means of the union assumed to exist within the terminal net-works of their processes. The independence and true relation of the neurone was established largely through the convincing embryological investigations of His and the renewed study of the nerve-cells as demonstrated by the improved applications of the Golgi silver-impregnations, supplemented by the method of vital staining by methylene blue introduced by Ehrlich. The Neurone Doctrine has gained wide acceptance and the support of the most distinguished anatomists, among those who have materially strengthened its position being Kolliker, Ramon y Cajal, Retzius, Lenhosse'k, Waldeyer, van Gehuchten, and Edinger. The neurone conception, securely founded as it is upon a vast mass of evidence collected from a wide field by the most painstaking and accurate observation, has not escaped challenge, and at present is assailed by a group of histologists headed by Apathy and Bethe, who not only bitterly oppose the integrity of the neurone as an independent unit, but also strive to depose the nerve-cell from its dignity as the fundamental physiological factor. In 1897 Apathy 1 published his observations on the structure of the ganglia of certain invertebrates, as revealed by a new mercuric gold-chloride method, and thereby established the important fact that the cell-body and processes of the neurone are pervaded by fine neurofibrillae, thus confirming the fibrillar structure of the nerve-cell advanced by Max Schultze more than a quarter of a century before. Following Apathy, Bethe 2 investigated the tissues of the higher animals and succeeded in dem- onstrating the existence of the neurofibrilke within the neurones of man. According to these observers, the neurofibrillae, although interlaced without junction within the cell-bodies, are independent threads, that are not confined to the neurones but pass beyond and unite with fibres from other sources. The neurofibrillae, therefore, and not the nerve-cells, are the essen- tial elements of the nervous system, the cells being only interposed along the path of conduc- tion. Indeed, according to these views, the neurofibrillae are independent of and, in a sense, foreign to the nerve-cells, leaving or entering the latter at pleasure and constituting by their union a continuous path of conduction from the receptive element to the muscle-fibre. Apdthy, moreover, assumes the existence throughout the central nervous system of a fibrillar net-work formed outside and between the nerve-cells by the neurofibrillae from which the axones may arise independently of the nerve-cells. It is evident that if such be the case the conception of the neurone as an individual unit falls. The criticism made by the newer school, that the supporters of the neurone theory relied upon methods which inadequately demonstrated the ultimate terminal relations (the assumed union in net-works) has been met by the introduction of the still newer methods of Beilschow- sky and especially of Cajal, which have yielded preparations that demonstrate that the neuro- fibrillae everywhere form net- works within the' cell-bodies of the neurones, are confined to their processes, and even in their ultimate endings form ununited terminal arborizations. It seems, indeed, that, at present at least, the defenders of the neurone theory may with justice charge their opponents in turn with depending upon methods that only partially show the relations of the neurofibrillae within the neurones. Retzius, than whom no more experienced and competent authority in this difficult field of research can be consulted, has recently reviewed the entire question and presented 3 most convincingly the facts that enable him, as well as the most distinguished anatomists of to-day, still vigorously to champion the Neurone Doctrine. After a critical and scientific discussion of the arguments advanced by Apathy, Bethe and Nissl, 4 Retzius rests his case with little concern as to the verdict of those to whom facts and not speculation most appeal. 1 Mitteilungen aus d. Zoolog. Station zu Neapel, Bd. xii., 1897. 2 Allgemeine Anat. u. Physiol. des Nervensystems, 1903. 3 Biologische Vntersuchungen, N. F., Bd. xii., 1905. 4 Die Neuronenlehre und ihre Anhjinger, 1903. ioo6 HUMAN ANATOMY. The Nerve-Trunks. The fibres composing the peripheral nervous system are grouped into the larger and smaller nerve-trunks which extend to various parts of the body. In the make-up of those that supply both muscles and sensory surfaces (integument or mucous membranes), as, for example, the median or the third division of the trigeminal nerve, three sets of fibres are included : ( i ) the efferent axones of motor neurones whose cell-bodies are situated within the spinal cord or brain ; (2) the afferent dendrites of sensory neurones within the spinal and other sensory ganglia ; and (3) the efferent axones of neurones within the sympathetic ganglia that accompany the spinal fibres to the periphery and serve for the innervation of the involuntary muscle of the blood-vessels and of the skin and the glands. The nerve-fibres, the various kinds usually more or less intermingled, are grouped into bundles, the funiculi, which differ in number and diameter according to the size of the entire trunk that they form. Each funiculus is surrounded by a definite sheath of dense connective tissue, the perineurium, which is directly con- tinuous with the delicate fibre-elastic tissue prolonged between the individual nerve- fibres as the endoneurium. When well represented, the sheath of the funiculus consists of concentric lamellae of fibrous tissue which enclose perineurial lymph-spaces. FIG. 849. Epineurium _^ Blood-vessels ''iV-p. ' ^~ Perineurium - .Funiculus of nerve-fibres SBBfi ' Transverse section of small nerve-trunk composed of loosely united funiculi. X 20. The latter, lined by flattened connective-tissue plates, are in relation with the clefts between the nerve-fibres, on the one hand, and with the lymphatics within the inter- funicular tissue on the other. Where, as usual, the nerve is composed of several funiculi, these are loosely bound together and the entire trunk so formed is invested by a general fibre-elastic envelope, the cpinci(riuin< in which course the blood-vessels and lymphatics. These envelopes of the nerve-trunk are continued over its branches, even onto its smallest subdivisions. The last representative of these coverings is seen on the individual fibres as the sheath of Hcnlc, that surrounds the fibre and consists of flattened cells and delicate strands of connective tissue outside the neurilemma. In cross-sections of the nerve-trunk (Fig. 850), the 'transversely cut individual medullated nerve-fibres appear as small circles, sharply defined by a tine outline (the neurilemma), each enclosing a deeply stained dot (the axis-cylinder in section). The interval between the latter and the neurilemma, corresponding to the space occupied by the myelin, usually appears clear and unstained with the exception of delicate and uncertain suggestions of membranous septa. In contrast with its unstained appearance in sections tinged with carmine, after the action of osmic acid or special hematoxylin staining ( Wcigert ) the medullary substance exhibits a dark color and the axis-cylinder appears surrounded by a deeply tinted ring. The neuri- THE NERVOUS TISSUES. 1007 lemma nuclei are occasionally seen as deeply stained crescentic figures that partially embrace the nerve-fibre, lying beneath the neurilemma within depressions in the medullary substance. FIG. 850. Perineurium ';.j,," '- ~~~^ Nerve-fibres Section o! s)iin;il ganglion, showing nerve-cells surrounded by inn k-ati .1 capsules. X DEVELOPMENT OF THE NERVOUS TISSUES. 1009 Diagram of constituents of spinal ganglion ; blue lines repre- sent efferent fibres ; black, afferent ; red, sympathetic; a, sensory ganglion cells; c, cells of type II, whose axones end (6) around sensory cells; 3, sympathetic neurone; AR, P/f, anterior and posterior roots; AD, PD, anterior and posterior primary divi- sions of spinal nerve; RC, ramus communicans. sympathetic fibres (Dogiel). Finally (<:) a few multipolar nerve-cells are usually found within the spinal ganglia that in shape and structure resemble the cell-bodies of the sympathetic neurones. The sympathetic ganglia are represented by those of the great gangliated cords, certain cranial ganglia (ciliary, spheno-palatine, otic, and submaxillary), the ganglia within the three prevertebral plexuses, and the innumerable small and often micro- scopic ganglia associated with the muscular tissue of the digestive, respiratory and uro-genital tracts, in the heart and in the various glands. In their general structure the sympathetic ganglia are similar to those connected with the spinal nerves, forming definite masses enclosed by a fibrous capsule, from which connective-tissue processes pass into the interior of the ganglion for the support and separation of the nervous elements. The individual gangli- FIG. 854. on-cells unipolar, bipolar or multi- polar are ensheathed by nucleated capsules continuous with the neuri- lemma of the nerve-fibres. The sympathetic ganglion-cells are vari- ously related to the terminal ramifi- cations of (a) other sympathetic neurones and of (^) the neurones of the central nervous system (by way of the white rami fibres or their equivalents). In both cases, the ramification of the nonmedullated and fine fibre in the one and of the medullated fibre in the other, a pericellular plexus, commonly en- closes the cell-body. In the lower vertebrates (amphibians and reptiles), the spinal fibre frequently winds spirally around the single process of the ganglion-cell before breaking up into the pericellular plexus (Huber 1 ). The broader relations of the component nervous elements of the spinal ganglia are considered in connection with the Sympathetic System (page 1354). DEVELOPMENT OF THE NERVOUS TISSUES. Reference to the account of the early development of the nervous system (page 26) will recall the fact that the neural groove, later the neural tube, is lined by invaginated and thickened ectoblast from which the essential nervous tissues are derived. For the fundamental facts concerning the histo- genesis of these tissues we are in large measure indebted to the labors of His, whose account, supplemented by the important contributions of Kolliker, Cajal, Lenhosse'k, Schaper and others, forms the basis of our knowledge concerning these processes. Although in its principal features the histogenesis is similar in all parts of the neural tube, in that portion which becomes the spinal cord the changes are most typical and will, therefore, be here described. During the approximation and closure of the neural tube the cells composing its wall undergo active prolife- ration, whereby the wall, at first composed of only one or two rows of definitely outlined cells, is converted into a multinucleated tract in which the cell boundaries dis- appear and the nuclei lie embedded within a general protoplasmic sheet or syncytium (Hardesty 2 ). The large dividing elements within the latter, the germinal cells of His, are conspicuous on account of their mitotic figures and are situated close to the lumen of the neural tube. His regarded them as special cells directly concerned in the production of the neurones, a conclusion, however, that has not 1 Journal of Morphology, 1899. "Arner. Journal of Anatomy, vol. iii., 1904. 64 FIG Segment from lateral wall of neural tube of pig embryo of 5 mm. ; syncytium replacing distinctly outlined cells, a, inner zone; g, ferminal cells; ilm, internal limiting mem- rane ; m, peripheral zone ; r, radial strands of cytoplasm. X 690. (Hardesty.) IOIO HUMAN ANATOMY. been sustained (Kolliker, Schaper and others) since the primary germinal cells probably only represent proliferating elements engaged in forming what for a time is an undifferentiated tissue. The cells composing the neural wall are at first in close contact, their blended cytoplasm (syncytium) forming an almost unbroken sheet. Soon, however, this continuity is interrupted in consequence of the longitudinal expansion of the tissue and the appearance of spaces, and the cell-substance is resolved into a delicate reticulum, the myelospongium of His, which becomes condensed at the inner and outer margins of the wall of the neural tube into the internal and external limiting membrane. The meshes of the reticulum enlarge, the intervening nucleated tracts of cytoplasm elongate and the increasing nuclei become radially disposed. By reason of these changes the elements next the lumen of the tube assume a columnar form and radial arrangement and become the primary ependymal cells. The remaining elements, appropriately named the indifferent cells (Schaper), increase in number in consequence of the continued division of the germinal cells and gradually become collected as the nuclear layer at some distance beyond the ependymal zone. Meanwhile and very early, the peripheral portion of the supporting framework adjoining the outer border of the neural wall becomes denser and free from nuclei and is converted into the marginal zone ( Randschleier of FIG. 856. His), that is continuous with the delicate reticulum pervading the other parts of the wall. The in- different cells later differentiate into (a) the spongioblasts from which the characteristic constitu- ents of the definite supporting tissue, the neuroglia, are derived, and () the neuroblasts that are directly converted into the neu- rones. Within the resulting cell- complex that for a time occupies the greater part of the wall of the neural tube, it is difficult to distinguish with certainty between the neuroglia and neuron-producing elements, since both are often elongated in shape and prolonged into processes. Histogenesis of the Neuroglia. In addition to the extension, condensation and moulding (by the developing nerve-cells and fibres) that the primary syncytial meshwork undergoes FIG. 857. elm Segment of wall of neural tube of pig embryo of 10 mm.; radial strands (r) of syncytium and differentiation of ependymal (a), nuclear (6) and marginal (m) layers; tint, elm, internal and external limiting membrane ; g, dividing cell ; /, pia mater. X 690. (Hardesty.) Transverse section of ventro-lateral segment of developing spinal cord from pig embrvo of .;<> nun., uppei ; figure from chrome-silver preparation, lower part trom oiu- stained with toltiiclin hi no ; r, central canal ; ff>. ependymai lavi-r H. nuclear layer; m, marginal layer; /, radial fibres ; i'. ventral plate uniting halves of cord. X 240. (Hardesty.} (Hardesty), the gradual transformation of the spongioblasts and their descendants into fibrillae establishes a more definite framework that replaces the primary net-work (myelospongium), and eventually, in conjunction with the fibtilhe derived from the processes of the ependymal cells, DEVELOPMENT OF THE NERVOUS TISSUES. ion FIG. gives rise to the definite supporting tissue, the neuroglia. According to Hardesty, the glia-fibres arise within the syncytial tissue independently of the neuroglia cells, a view in direct opposition to the observations of Rubaschkin, who attributes to the descendants of the spongioblasts, the gliagenetic cells, a positive role in the production of the fibres. Accepting the conclusions of the last-named investigator, the successive stages of the cells concerned in the production of the general neurogliar tissue are represented by the spongioblasts, the gliogenetic cells, the astrocytes, and, finally, the glia cells. The primary ependymal elements are succeeded by the epithelium which lines the ventricles and the central canal of the spinal cord. Their periph- erally directed processes are in large part transformed into glia-fibres and thus, along with the processes of the spider cells, contribute to the formation of the neurogliar felt-work. The accompanying illustration (Fig. 857), taken from Hardesty's paper, affords an instructive comparison of the appearance of the young supporting tissue after true staining with approved reagents (Benda) and after silver precipitation methods (Golgi) upon which so much reliance has been placed. The silver picture shows the classic long neurogliar fibres extending the entire thickness, but fails to reveal the wealth of supporting tissue and nuclei. To what extent the mesoblastic ingrowths that follow the penetrating young blood-vessels into the neural wall take part in the production of the distinctive neurogliar framework is admittedly difficult to determine (Hardesty) ; that such tissue, however, contributes to the support of the nervous elements is certain. Histogenesis of the Neurones. The neuroblasts are distinguishable with certainty from the spongioblasts as soon as they are provided with nerve-processes. The latter appear as out- growths from the pointed and peripherally directed ends of the developing nerve-cells, invade the marginal zone, and later emerge from the wall of the immature cord as the ventral or anterior root-fibres of the spinal nerves (Fig. 858). The deeper tint of their distal ends after staining, their tendency to collect in con- verging groups, and the uniform width of the outgrowing nerve- processes are disinctive character- istics of the neuroblasts (His 1 ). The first, and for a considerable time the only processes with which the neurones are provided cor- respond to the axones that be- come the axis-cylinders of the efferent (motor) nerves. Subse- quently other processes, the den- drites, grow out in various direc- tions from the cell-bodies of the young neurones. Development of the Peripheral Nerves. According to the teaching of His, accepted by most anatomists, the axis-cylinder of the entire future nerve-fibre is formed by the peripheral growth of the original nerve-process of the neuroblast. The assumed development of the nerve- fibre by the union of a number of segments ( Balfour, Dohrn, and others, and, more recently, Bethe and O. Schultze) is not in accord with renewed investigations, and the findings upon which the composite theory of the fibre is based are open to different interpretation (Kolliker, Retzius). According to Bardeen, 2 the development of the peripheral spinal nerves is briefly as follows: The motor neuroblasts and the sensory spinal ganglion-cells send out processes of considerable thickness, all of which soon begin to give rise at their extremities to groups of fibril/a:, which increase in thickness and length and, in turn, at their extremities give rise to new groups of fibrils. At first these proceed as naked bundles, but soon become surrounded with sheath-cells of mesoblastic origin which thus enclose the early embryonic nerve, that may contain hundreds of fibrillas. After a nerve has become distended by ingrowth of new fibrils from behind, the proliferating sheath cells begin to wander from the periphery in among the fibrillae and give rise by anastomosis of their processes to a net-work that divides the original fasciculus into a number of secondary bundles. The intrafascicular cells increase rapidly, the process of subdivision Neuroblasts Efferent axones Portion of spinal cord of human enibiyo, showing development of ventral root-axones as outgrowths from ventral neuroblasts. X 300. (After His.} 1 Die Entwickelung des menschlichen Gehirns, 1904. 2 Amer. Journal of Anatomy, vol. ii., 1903. IOI2 HUMAN ANATOMY. FIG. Developing intercostal nerve of pig embryo of 10 mm. ; tip of nerve is composed of fibrils surrounded by sheath-cells. X 360. (Bardeen.) FlG. 860. fe . ' continues and the bundles of fibrilke become progressively smaller and more compact until, surrounded by membranous septa, they correspond to the axis-cylinders of the individual nerve- fibres, enclosed by the neurilemma and its cells. The endoneurium appears comparatively late and, like the neurilemma, is a product of the mesoblast. Later, condensations of the mesoblast around the definite bundles of nerve-fibres and about the entire nerve-trunk provide the perineiirium and the epineurium respectively. During its course to the periphery the young nerve gives rise to numerous branches, the points of outgrowth being indicated by a preparatory increase of the peripheral cells which often form a tubular projection into which the nerve- fibrillae grow. The proximal plexuses (such as the brachial or lumbar) are formed during the outgrowth of the nerves from the region of the central nervous system ; the coarser distal plexuses arise during the extension of the branches to the various parts for which they are destined ; whilst the finer terminal plexuses are established during the development of functional unity between the nerve-fibres and the structures to which they are distributed. The medullary sheath is a comparatively late acquisition, since it does not appear until about the fourth month of foetal life. Within the central nervous system the tracts of nerve- fibres obtain their medullary coat at different times (some not until after birth), a variation that is of much service in enabling the anatomist to trace the course of the individual paths of con- duction. The origin and method of formation of the medullary substance has been, and in fact still is, a subject of discussion. It is, however, certain that its production is not dependent upon the neurilemma, since the medullated fibres within the cerebro-spinal axis are devoid of this sheath, and, further, that the myelin sometimes appears before the neurilemma ( Roister, Bardeen). While it is doubtful whether the myelin is directly formed from the outer part of the axis-cylinder, as suggested by Kolliker, it is probable that this structure exerts some influence resulting in the deposit of the myelin- droplets either from the blood (Wlassak), or from the apparently fluid substance that after a time surrounds the axis-cylinder (Bardeen). Regarding the formation of \hzframework supporting the droplets of myelin, Hardesty 1 inclines to the view that certain sheath cells, which appear during medullation, are probably concerned. From the foregoing account it is evident that the axis-cylinder is derived from the ectoblast and the neurilemma from the mesoblast ; the origin of the medullary sheath is still undetermined, but most probably is mesoblastic. Development of the Ganglia. The origin of the afferent (sensory) neurones, whose cell-bodies are situated within the spinal and -other ganglia, is entirely different from that of the efferent (motor) ones above described. In the case of the spinal nerves, the development of the ganglia pro- ceeds from a group of ectoblastic cells that form a ridge, the ganglion-crest^ on the margin of either lip of the still open neural tube (Fig. 860), just where the general ectoblast passes into that lining the groove. On approximation of the lips of the latter, the cells of the ganglion-crests fuse into a wedge-shaped mass that completes the closure of the neural tube and constitutes a centre of proliferation from which the cells migrate outward over the dorso-lateral wall of the tube. The proliferation is not uniform but most marked at points that correspond to the mesoblastir somites, in consequence of which a series of segmentally arranged cell-aggregations appears on each side of the neural tube. These collections are the anlages of the spinal ganglia. Within them certain cells soon become fusiform and, assuming the role of neuroblasts, send out a process from either end. One process the axom- grows centrally, while the other the dendrite extends peripherally and becomes the chief part of a sensory nerve-fibre. The subsequent growth of the neurone is not symmetrical, but to one side, and so Transverse sections of dorsal region of human embryos, showini; curly differ- entiation of spinal ganglion ; A, K, neural tube still open; C, f>, tube rl<>M.-e in s> varicose and club-like in form, occur within the connective tissue layers of the skin and the tunica propria of mucous membranes. Within the integument, conspicuous end- ramifications of sensory neurones surround the hair follicles, lying upon the outer surface of the glassy membrane. ioi6 HUMAN ANATOMY. FIG. 867. Tactile cells of Merkel lying 'within inter- papillary epithelium; broken line (e) indicates junction of epithelium and connective tissue layer; () nerve passing into epithelium. X 160. ( Worthmann. ) FlG. 868. The tactile cells of Merkel, found in the deeper layers of the epidermis, represent a somewhat more differentiated form of intraepithelial terminations and suggest transitions to the more specialized end- organs. In these endings the nerve-fibrils terminate in cup-shaped expansions or menisci, against which rest the modified epithelial cells. The latter may be regarded as an imperfectly differentiated newrofpithtlium^ examples of which are seen in the gustatory cells in the taste buds and in the highly specialized visual and auditory cells in the retina and in the organ of Corti respectively. Encapsulated Sensory Endings. In their most highly developed forms these end- ings (corpuscula nervorum terminalia) are represented by relatively large special end- organs in which the terminations of the axis- cylinder are enclosed within an elaborate laminated capsule. The latter, however, is more often present as a much simpler and thinner envelope consisting of strands of fibrous tissue. Transition forms between the intraepithelial tactile cells above noted and the more specialized encapsulated end-organs, always within the connective tissue, are seen in the corpuscles of Grandry (not found in man but conspicuous in the skin covering the bill and in the tongue of many water-fowl), in which the nerve ends in a disc-like expansion enclosed between large modified epithelial cells and the neuromuscular and neurotendinous end-organs, presently to be described (page 1020). The group of simpler encapsulated endings includes three well-known examples : the end-bulbs and the genital corpuscles of Krause and the cor- puscles of Meissner, all of which possess a common structural plan interwoven telodendria embedded within a semifluid interfibrillar substance and surrounded by a thin fibrous envelope. The End-Bulbs of Krause. These endings include a variety of irregularly spherical or ellipsoidal bodies found in the edge of the eyelid, the conjunctiva and corneal margin, the lips and the oral mucous membrane, the glans penis and clitoridis and probably other parts of the integument highly endowed with sensibility. Within the conjunctiva, as described by Dogiel 1 , they lie superficially placed within the con- nective tissue near the summit of the papillae and folds, when such elevations exist, but always close beneath the epithelium. They vary considerably in size, often being small (.002-. 004 mm.), but some- times measuring from .05-. 10 mm. in diameter. Usually a single nerve-fibre, exceptionally two or even more, enters each bulb, losing its medullary sheath as it pierces the thin fibrous capsule. Within the latter the nerve, now represented by the naked axis-cylinder, divides into from two to four branches, which, after describing several annular or spiral turns, give off varicose fibrils that undergo further division, the terminal threads forming a more or less intricate maze within the semifluid substance enclosed by the fibrous capsule. 'Archivf. mik. Anat., Bd. xliv., 1895. i ('.ruiulry from Two corpiiM k- bill of duck ; nerve is seen entering corpuscle on right. X 265. Two end-bulbs of Krause from human conjunctiva. (Dogitl.) NERVE-TERMINATIONS. 1017 FIG. 871. Genital corpuscle from integument of penis; nerve divides before piercing capsule and terminates in intricate end- windings. (Dogicl.) Genital corpuscle from integ- ument of human clitoris. X 350. ( Worthmann. ) FIG. 872. The Genital Corpuscles. These endings, most numerous (from one to four to the square millimeter) in the deeper strata of the corium covering the glans penis and clitoridis, but occurring also in the neighboring parts of the genitalia, are of irregular oval or lobulated outline and from .02 to .35 mm. in diameter. They present the same general architecture as the end- bulbs, but are of larger size, possess a somewhat thicker capsule, and contain a more intricate interlacement of the terminal nerve-fibrillae. The latter are derived from the subdivision of two or three medullated fibres that enter near the base of the corpuscle and are beset with varicosities and club-shaped terminal enlargements. The fibrous capsule, consisting of several connective tissue lamellae possessing flat- tened fusiform nuclei, encloses the semifluid or granular interfibrillar substance in which the end-arborizations are embedded. The Corpuscles of Meissner. In man these are most numerous in the corium of the skin covering the flexor surface of the fingers and toes. They are also found in other regions possessing sensibility in a high degree, such as the lips, margin of the eyelid, nipple, penis and clitoris, as well as on the dorsum of the hand and foot and the radial surface of the forearm. On the volar surface of the distal phalanx of the fingers, where they occur in greatest numbers, some twenty are found to the square millimeter (Meissner). The corpuscles occupy the summit of the papillae and ridges of the connective tissue stratum of the skin, and lie close beneath the cuticle, with their long axes perpendicular to the latter. In shape they are elongated irregular ellipsoids, often somewhat sinuous in outline, and in the larger papillae may be joined at the deeper end with others to form a compound corpuscle. They are relatively large, being from .12-. 1 8 mm. long and about one-third as wide. Depending upon the size, each corpuscle is sup- plied by one or more nerve-fibres which enter in the vicinity of the base, as the deeper end is called, and, on piercing the capsule and losing the medullary sheath, divide into a number of naked axis-cylinders. These pass across the corpuscle in parallel or spiral windings and are beset with fusiform and pyriform varicosities, similar enlargements marking the ends of the terminal threads. The entire fibrillar interlace- ment is embedded within a semifluid substance and enclosed by a thin nucleated fibrous capsule. The Corpuscles of Ruffini. These end- ings are also found within the skin, but at deeper levels, near and sometimes within the subcorium. They are of large size, sometimes measuring as much as 1.35 mm. in length, and of an elongated fusiform contour. The nerve-fibres, often two or more, which usually join the capsule on the side, less frequently near one end, retain the medullary sheath for some distance after penetrating the capsule and throughout Corpuscle of Meissner lying within papilla of corium of skin from finger; only deeper layers of overlying epidermis are shown; , entering nerve-fibre. X 270. ioi8 HUMAN ANATOMY. FIG. 873. Cylindrical end-bulb from con- nective tissue layer of skin. X 180. (Szymonowicz.) a number of bold curves and twistings. After the disappearance of their sheaths, the naked axis-cylinders undergo repeated divisions, the resulting fibrillae becoming varicose and intertwined and ending in free terminal knob-Jike enlargements. In contrast to the foregoing end-organs, in which the axis-cylinder subdivides into numerous terminal threads disposed as more or less elaborate intertwinings, a second group is distinguished by the possession of a thick laminated capsule that encloses a cylindrical core or inner bulb containing the slightly branched axis-cylinder. These endings, of which the Pacinian corpuscle is repre- sentative, are relatively large and ellipsoidal. A transitional form, connecting them with the spherical end-bulbs, is presented by the cylindrical end-bulbs of Krause. These are found in various parts of the corium, the oral mucous membrane and between the bundles of striped muscle and of tendon. They are irregularly cylindrical in form, often more or less bent, and consist of a thin laminated capsule that encloses a core of semifluid substance in which lies the centrally placed axis-cylinder. The latter, after losing the medullary sheath on entering at .the proximal end of the capsule, traverses the core without branching until near the distal pole, where it ends in a single or slightly subdivided terminal enlargement. The Vater-Pacinian Corpuscles. These structures, the most highly special- ized sensory end-organs, are relatively large ellipsoidal bodies, from .05-. 15 mm. in length and about one-third as much in breadth, situated within the connective tissue in many parts of the body. In man they are found in F IG - 8 74- the deeper layers of the connective tissue layer of the skin, especially on the palmar and plantar aspects of the fingers and toes, in the connective tissue in the vicinity of the joints, in tendons, in the sheath of muscles, in the periosteum and in the tunica propria of the serous membranes, the peritoneum, pleura and pericardium. They are particularly large in the mesentery of the cat, where they may be readily de- tected with the unaided eye as oval pearly bodies some- times two millimeters or more in length. The most conspicuous part of the Pacinian body is the robust capsule that constitutes almost the en- tire bulk of the corpuscle and consists of from one tO three dozen thin COn- Vater-Pacinian corpuscles from skin of ohikt s fin.m-i ; ,1. lonKit..,lmal ; Centric lamelke of fibrOUS A', transverse section ; , nerve entci ini; capsule t.. n-:i. h timer bulb. tissue. The surfaces of the lamella are covered with emlothdial plates whose nuclei appear as fusiform thicken- ings, alting the concentric striae of the corpuscle. The axis of the' Pacinian body , NERVE-TERMINATIONS. 1019 Corpuscles of Herbst from bill of duck ; a, longitudinal, b, transverse section ; n, nerve traversing lamellae of capsule ; axis-cylinder within core is surrounded by cells. X 360. is occupied by a core or inner bulb of semifluid substance in which the naked axis-cylinder is embedded. On joining the proximal pole of the corpuscle, the fibrous (Henle's) sheath of the nerve-fibre blends with the outer lamellae of the capsule, while the medullary coat is retained during the somewhat tortuous path of the fibre through the capsule as far as the core. Here the remaining envelope of the nerve-fibre disappears, the terminal part of its course, through the core, being as FIG. 875. the naked axis-cylinder. At a variable distance but often just before gaining the distal pole of the core, the axis- cylinder divides into from two to four branches, each of which terminates in a slightly expanded end-knot. Some- times shortly after penetrat- ing the capsule, the nerve- fibre splits into two or more axis-cylinders which then share the common envelope of semifluid axial substance. Similar end-organs, the corpuscles of Herbst, occur in the velvety skin covering the bill and in the tongue of water-fowl. They closely resemble the Pacinian bodies of mammals, but differ in being generally smaller, relatively broader, and in exhibiting a row of cubical cells within the core and around the axis-cylinder. These cells are regarded as corres- ponding to the large cells enclosing the tactile discs in the Grandry's corpuscles. The Golgi-Mazzoni corpuscles, found in the subcutaneous tissue of the pulp of the fingers, are modifications of the ordinary Pacinian end-organs. They differ from the latter in possessing fewer lamellae, a relatively larger core and a more branched axis-cylinder. Neuromuscular Endings. First described by Kolliker and by Kiihne, although previously seen by Weissmann, these end-organs, often termed muscle- spindles, are now regarded as sensory endings that are probably concerned in afford- ing impressions as to tension or ' ' muscle-sense ' ' . They lie within the connective tissue separating the bundles of voluntary muscle-fibres and are long spindle-shaped structures, varying in length from 1-5 mm. or more and in width from . I-.3 mm. where broadest. They are widely distributed, being probably present in all the skeletal muscles, and are especially numerous in the small muscles of the hand and foot. They have not been found, however, in the intrinsic muscles of the tongue and in the eye muscles, although within the tendons of the latter very similar (neuro- tendinous") end-organs have been demonstrated. Each spindle consists of a capsule, composed of a half-dozen concentric layers of fibrous tissue, which encloses a group of usually from three to ten, but sometimes as many as twenty, striped muscle-fibres, medullated nerves, blood-vessels and inter- spersed connective tissue. These intrafusal fibres, as they are called, differ from those of the surrounding muscle in being much smaller in diameter and length, markedly tapering towards either end, more coarsely but less distinctly striated, and in possessing nuclei within the sarcous substance. The striations are not equally distinct in all parts of the fibres, being much less evident in the middle zone than towards the ends. The fibres are more numerous and of greater diameter in the equatorial region than near the poles of the spindle. The intrafusal fibres collectively are surrounded by a thin special connective tissue envelope, the axial sheath, between which and the capsule lies the periaxial IO2O HUMAN ANATOMY. Nerve-fibre- Sheath- Capsule lymph-space. Each spindle receives usually several medullated nerve-fibres, which, after incorporation of their sheaths of Henle with the capsule, pierce the latter at various points and proceed to the individual muscle-fibres. The terminal relations of the nerves to the intrafusal fibres have been studied by means of the newer methods especially by Ruffini, FIG. 876. Huber and DeWitt and Dogiel. After repeated division during *^ eir course tnrou gh the cap- sule and periaxial space, the nerve-fibres pierce the axial sheath, lose their medullary coat and terminate either as one or more ribbon-like branches that encircle the mus- cle-fibres in annular or spiral windings, or, after further subdivision, as branched telo- dendria in which the ultimate fibrils end in irregular spherical or pyriform enlargements. Neurotendinous End- ings. These end-organs, described by Golgi and sub- sequently more fully investi- gated by Kolliker, Ciaccio, and Huber and DeWitt, in their general architecture resemble closely the sensory endings in muscle. They lie embedded within the intrafascicular con- nective tissue and are usually found in the vicinity of the junction of muscle and tendon. Like the neuromuscular end- ings, the tendon- spindles are long fusiform structures, from i. -i. 5 mm. in length, sur- rounded by a fibrous capsule. The latter encloses a group of from eight to twenty intrafusal tendon fasciculi, which are smaller and apparently less mature than those, of the sur- rounding tendon -tissue. The intrafusal fasciculi are invested by a fibrous axial sheath be- tween which and the capsul( lies a periaxial Lymph-space. On reaching the spindle, after repeated branching, the medullated nerve-fibres pene- trate the capsule, with whicl their fibrous (Henle's) sheaths blend, and undergo furtht division. The medullary coat is lost after they pierce the axial sheath, the naked axis- cylinders breaking up into smaller fibrils that extend along tin- intrafusal fasciculi, terminal ramifications, applied to the surface of the fasciculi, vary in details (Huber). Some arise as short lateral branches that partly encircle the fasciculi and end im -ular plate-like expansions, while others terminate between the smaller fasciculi. J m Axial sheath' ,. Nerve-fibre A, neuromuscular ending; />', neurotendinous ending in longitudi- nal section, imahyli-nc-blue staining. 260. ( Drawn from preparation made by Professor Huber.) THE CENTRAL NERVOUS SYSTEM. THE central nervous system includes the spinal cord and the brain. In principle these parts are to be regarded as the walls of the primary neural tube, modified by unequal growth and expansion, which even after acquiring their definite relations enclose the remains of the canal, as represented by the system of ventricular spaces. In contrast to the spinal segment of the neural tube, which always remains a rela- tively simple cylinder, the spinal cord, the cephalic segment early differentiates into three primary cerebral vesicles, the anterior and posterior of which subdivide, so that five secondary brain-vesicles are present. Coincidently marked flexure of the cephalic segment occurs at certain points and in consequence this part of the neural tube becomes bent upon itself to such a degree that the axis of the anterior vesicle lies almost parallel with that of the spinal segment (Fig. 912). From the five secondary divisions of the flexed and sinuously bent cephalic segment of the neural tube are developed the fundamental parts of the brain in the manner presently to be described (page 1060), whilst from the relatively straight spinal segment proceeds the development of the spinal cord, in which process growth and differentiation convert the originally thin-walled tube into an almost solid cylinder, the minute central canal alone remaining as the representative of the once conspicuous lumen. THE SPINAL CORD. The spinal cord (medulla spinalis) is that part of the central nervous system, or cerebro-spinal axis, which lies within the vertebral canal. Its upper limit, where it becomes continuous with the medulla oblongata, is in a measure conventional, since there is no demarcation on the cord itself to indicate exactly its junction with the brain. Accurately considered, the superior limit of the cord may be assumed to correspond with the emergence of the uppermost root-fibres of the first spinal nerve which pass out between the atlas and the skull ; this level also corresponds to the lowest strands of the pyramidal decussation of the medulla oblongata and to the upper border of the posterior arch of the atlas. For practical purposes, however, the lower margin of the foramen magnum defines with sufficient accuracy the upper limit of the spinal cord. Below, the spinal cord terminates somewhat abruptly in a pointed end, the conus medullaris, that usually ends opposite the disc between the first and second lumbar vertebrae. The level to which the cord extends inferiorly, however, is subject to considerable variation, very rarely being as high as the middle of the body of the last thoracic vertebra (Moorhead), or as low as the upper border of the body of the third lumbar vertebra (Waring). In the female subject the spinal cord, although absolutely shorter than in the male, extends to a relatively lower level hi the vertebral canal. Marked bending of the spine produces slight alterations in the position of the cord, during strong flexion an appreciable ascent of the lower end taking place. The relation of the cord to the vertebral canal varies at different periods. Until the third month of foetal life the cord occupies the entire length of the canal, but subsequently, owing to the more rapid lengthening of the spine than of the spinal cord, the latter no longer reaches to the lower limit of the canal and, therefore, apparently rises, so that by the sixth fcetal month the lower end of the cord lies opposite the first sacral vertebra, and at birth terminates usually on a level with the body of the third lumbar vertebra. Measured from its upper conventional limit to the lower end of the conus medullaris, the spinal cord in the adult male has an average length of 45 cm. (17%" in.), and in the female of 43.7 cm. (i7>( in.), in both sexes the proportion of the length of the cord to that of the pre- sacral spine being approximately as 64 : 100 (Ziehen). The cord-length bears no constant rela- tion to stature, although in a general way tall individuals may possess long cords. The weight of the spinal cord, stripped of its membranes and nerves, is something less than 30 grammes (i oz.), or about 1-2000 of the body-weight. Its proportion to the weight of the brain is i 143. When fresh the spinal cord possesses a soft cheesy consistence and a specific gravity of 1.035. 102 1 IO22 HUMAN ANATOMY. FIG. 877. Skull Pedicles, cut Medulla Laminae, cut Transverse processes Pedicles. Dural sheath XII T- i in rJn .1 In Pedicles, . End of dural sheath Posterior divisions of sacral nerves< Sin-nth of filiini End of Ilium . Coccyx S|nn:il i-i.nl i-nrlosi-d in iiu(,|,,-,ir,| dural slu-atli lying within vertebral canal ; m-ma: an tiei > i>ni|iU-u-lv n-nuived on right side, partially On left, to expose doml aspivt <>l duia: first and last hiinharand lacral groupa are indicated by Italic BgOrcaj corresponding v.-iU-hn- l,\ Roman mnm-iaK. The Membranes of the Cord. The spinal cord, together with the roots of the thirty-one pairs of spinal nerves, lies within the vertebral canal enclosed by three protecting membranes, ormeninges, which, from without inward, arc i the dura mater, (2) the arachnoidca, and (3) the/>/a mater, all of which are directly continuous through the foramen magnum with the corres- ponding coverings of the brain. The external sheath, or thcca, formed by the dura, is a robust fibro-elastic tubular envelope, much longer and considerably wider than the cord, that does not lie against the wall of the vertebral canal, -but is separated by an interval containing thin-walled plexiform veins and loose fatty con- nective tissues (Fig. 879). The dural sheath, about .5 mm. in thickness, extends to the level of the second sacral vertebra and is, therefore, considerably longer than the spinal cord. The part of the sac not occupied by the cord encloses the longitudinal bundles of root-fibres, that pass obliquely to the levels at which the correspond- ing nerves leave the vertebral canal, and a fibrous strand, they?////;/ tcr- minale, prolonged from the cord to the lower end of the spine. The pia constitutes the imme- diate investment of the cord and supports the blood-vessels destined for the nutrition of the enclosed nervous cylinder. The- pial sheath is composed of an outer fibrous and an inner vascular layer, the connective tissue of the latter ac- companying the blood-vessels into the substance of the cord. The arachnoid, a delicate veil- like structure made- up of interlacing bundles of fibro-elastic tissue, lies between the other two membranes and invests loosely the inner surface' of the dura and closely the outer surface of the pia. It effectually Subdivides the considerable space between the external and internal sheaths into two compartments, the one beneath the dura, the subdnral space, being little more than a capil- lary cleft filled with modified lymph, and the other, the siibaniclnwid s/Hrcc, between the arachnoid and THE CENTRAL NERVOUS SYSTEM. 1023 The spinal cord, therefore, hangs FIG. 878. - Pons Arachnoid Medulla Ligamenta denticulata the pia, containing the cerebro- spinal fluid. suspended within the tube of dura, surrounded by a cushion of fluid an arrangement well adapted to insure the nervous cylinder against the inju- rious effects of shocks and of undue pressure during changes in the position of the spine. Both spaces, but par- ticularly the subarachnoid, are crossed by fibrous trabeculae and thus imper- fectly subdivided into secondary com- partments, all of which are lined with endothelium. The spinal cord is fixed within the loose dural sheath not only by the root- fibres of the spinal nerves that pass between the cord and the outer envelope, but also by two lateral fibrous bands, the ligamenta denticulata, that are continu- ous with the pia along the cord, one on each side. Mesially they are attached between the anterior and posterior root- fibres and externally to the inner surface of the dura by the tips of pointed pro- cesses, about twenty-one in all, that stretch across the subarachnoid space, which they imperfectly divide into a general anterior and a posterior com- partment. The ligaments, covered by prolongations of the arachnoid, extend the entire length of the cord, the first pro- cess being attached to the margin of the foramen magnum, immediately above the vertebral artery as it pierces the dura. The succeeding ones meet the dura between the pairs of spinal nerves, the lowest process lying between the last thoracic and the first lumbar nerve. In the cervical and thoracic region, a median fibrous band, the septum posticum, connects the posterior surface of the cord Spinal cord, covered with I arachnoid I and pia Upper part of spinal cord within dural sheath, which has been opened and turned aside ; ligamenta denticulata and nerve-roots are shown as they pass outward to dura. Dural sheath Periosteum \ Spinal cord Posterior root Ligamentutn denticulatum Anterior root Spinal ganglion Spinal nerve Extradural areolar tissue Vertebral artery Body of fourth cerv Transverse section of vertebral canal at level of fourth cervical vertebra, spinal cord in position. with the dura and partially subdivides the subarachnoid space. Lower, this partition, IO24 HUMAN ANATOMY. FIG. 880. Skull Vertebral artery / en Spinal accessory nerve" Pedicles, cut Sen- Pedicles < 12 tn- Medulla -/ en -Spinal accessory , nerve Edge of cut dural sheath -Spinal cord -Edge of cut dural sheath . Spinal cord Pediclesr 5 /. Posterior divisions of sacral nerves ' -End of conus medulla ris -Filum terminale -Descending nerves End of dural sheath , 2 sn . I'iluiii rxternum .Cn Posterior wall of vertebral canal has been removi-.l and dural sheath opened to expose spinal cord mid dorsal roots of attached nerves ; / en, I C, first cervical nerve and vertebra iivrlv ; Cn, eoccygeal nerves. which may transmit blood-vessels, is imperfect or altogether absent. As they cross the subarachnoid space the bundles of root-fibres of the spinal nerves are enclosed by prolongations of the pia and arachnoid. These sheaths are retained by the nerves for only a short distance after the latter receive an additional investment from the dura as they leave the vertebral canal. The dural sheath becomes continuous with the epineurium of the spinal nerves. The Cord - Segments. Although no suggestion of such sub- division is to be seen as constrictions on its surface, in principle tine spinal cord consists of a series of segments, each of which gives origin to the anterior (motor) and receives the pos- terior (sensory) root-fibres of one pair of spinal nerves. These nerves, usually thirty-one pairs in number, are classified as eight cervical, twelve thoracic, five lumbar, five sacral, and one coccygeal. Corresponding to the attachment of the nerves the cord is conventionally divided into cervical, thoracic, lumbar, and sacral regions. Of the entire length of a cord measur- ing 43 cm., approximately 10 cm., or about 23.5 per cent., belonged to the cervical region; 24 cm., or 55.5 per cent., to the thoracic; 6 cm., or 14 per cent, to the lumbar; and 3 cm., or 7 per cent., to the sacral region. The spinal nerves are attached to the lateral surfaces of the cord by fan-shaped groups of anterior and pos- terior root-fibres that are gathered into compact strands as they converge to form a common trunk (Fig. 884). The portion of the spinal cord with which the root-fibres of a spinal nerve are connected constitutes its cord- segment, the limits of which lie in the interval separating the extreme fibres of the nerve and those of the adjacent nerves. In the thoracic cord these intervals are very evident, since the segments are relatively long ; in the cervical and lumbar regions, on the contrary, the groups of root-fibres are so crowded that they form almost unbroken rows. . The length o f the individual cord- segments varies ; thus, according to the measurements of Liideritz, those of the cervical region, are from 11-13.5 mm. ; THE CENTRAL NERVOUS SYSTEM. 1025 those of the thoracic re- gion from 12-26 mm., the longest belonging to the V-VII thoracic nerves; those of the lumbar region rapidly decrease from 15.5 -5.5 cm., followed by a more gradual diminution to less than 4 cm. in the sacral region. In consequence of the disproportion between the length of the spinal cord and that of the vertebral canal, the discrepancy be- tween the level at which the nerves are attached to the cord and that of the intervertebral foramina through which they leave the canal becomes more marked towards the lower end of the series. The growth of the cord, how- FIG. 881. Ye Transverse section of vertebral canal, at level of middle of first lumbar vertebra; spinal cord (conus medullaris), surrounded by nerve-bundles, is seen within dural sheath. 'Conus i In medullaris ever, is not uniform since, as shown by Pfitzner, during the later years of childhood elongation FIG. 882. of the thoracic region occurs to such an extent that this part of the cord once more equals, if indeed not exceeds, the corresponding portion of the spine. While the cervical cord keeps fairly abreast the cervical portion of the vertebral column, the lumbar and sacral segments are left far behind. The results of these changes are seen in the course of the root-fibres, which in the neck, below the third nerve, run somewhat downward to their points of emergence, and in the thoracic region pass more horizontally, while those of the lumbar and sacral nerves descend almost vertically for a considerable distance in the case of the last sacral nerve 28 cm. (Testut) before reaching their appropriate levels. The large and conspicuous leash of descending root-fibres, seen upon open- ing the dural sheath, constitutes the cauda equina, in the midst of which the glistening silvery filum terminale is distinguishable. It is evident, there- fore, that in most cases the level of the cord-segment and that of the vertebra bearing the same designation do not correspond. Likewise, it must be re- membered that, although in general the spinal nerves are named in accordance with the vertebrae immediately below which they escape, in the neck there are eight cervical spinal nerves and only seven vertebrae, the first or sub- occipital nerve emerging between the atlas and the skull, and the eighth between the last cervical and first thoracic End of spinal cord with roots of lower nerves descend- vertebra hence evrpnr rhp lasr nnp rhpv ing in cauda equina to gain their respective foramina ; . ' exCe P t ne < tnev 7 ~J In, f-s sn, en, lumbar, sacral and coccygeal nerves. Correspond With the Vertebra below. 65 Filum externum, in sheath Coccvx IO26 HUMAN ANATOMY. FIG. 883. Medulla Cervical Thoracic Lumbar Sacral Coccygeal Form of the Cord. After removal of its membranes and the root-fibres, the spinal cord is seen to differ from a simple cylinder in the following respects. It is somewhat flattened in the antero-posterior direction, so that the sagittal diameter is always less than the transverse diameter, and its outline in cross-sections, therefore, is not circular but more or less oval ; its width is not uniform on account of two conspicuous swellings that are associated with the origin and reception of the large nerves supplying the limbs. The upper or cervical enlargement (intumescentia cervicalis) begins just below the upper end of the cord and ends opposite the second thoracic vertebra, having its greatest expansion at the level of the fifth and sixth cervical vertebrae, where the sagittal diameter is about 9 mm. and the transverse from 13-14 mm. The lower or lumbar enlargement (intumescentia lumbalis) begins opposite the tenth thoracic vertebra, slightly above the origin of the first lumbar nerve, and fades away in the conus medullaris below. It appears very gradually and reaches its maximum opposite the twelfth thoracic vertebra, where the cord has a sagittal diameter of 8. 5 mm. and a transverse diameter of from 11-13 mm. (Ravenel). The lumbar enlargement is associated with the great nerve-trunks supplying the lower limbs. The inter- vening part of the thoracic region is the smallest and most uniform portion of the cord and is almost circular in out- line. Where least expanded, opposite the middle of the thoracic spine, the cord measures 8 mm. in its sagittal and 10 mm. in its transverse diameter. These enlarge- ments appear coincidently with the formation of the limbs, are relatively small during foetal life, and acquire their full dimensions only after the limbs have attained their definite growth. In a general way, a similar relation between the size of the enlargements and the degree of development of the limbs is observed in the lower animals. At the tip of the conus medullaris the spinal cord is prolonged into a delicate tapering strand, the filum terminale, that consists chiefly of fibrous tissue con- tinued from the pia mater and invested by arachnoid. It extends to the bottom of the pointed and closed end of the dural sac, which it pierces at the level of the second sacral vertebra and, ensheathed by a prolongation of dura (vagina terminalis), as the fihan terminate c.\/cr)ii/ni, proceeds downward through the lower end of the sacral canal for a distance of about 8 cm. (3^ in.), finally t<> be attached to the periosteum covering the posterior surface of the coccyx. The part within the dural sac, the filum terni/na/c intcrnum, is about 16 cm. (6% in.) in length and surrounded by the nerve-bundles of the cauda equina*(Fig. 882), from which it is readily dis- tinguished by its glistening silvery appearance. The upper half or less of the internal filum contains the Spinal >,,ni >Mmdrd ,,i mom- terminal part of the central canal of the spinal cord walled by l)t:m,-s and nerves, slKiwini; pro- ( | ] variable layer of nervous substance in which small portions oi its length contributed . . , .. , by diiTri.-nt n-uions and position nerve-cells are usually present. The minute bundles of ncrve- and relative si/. >i rniaiKi-ni.-nts.as fibres often found adhering to the filum. which sometimes mav be viewed from before : Bemidlagram- , . , . . . , ', , matic, based on im-asmvin.-nts ; followed to and even through the dnral sheath, are regarded by mi, -third actual si/.. Rauberas representing one or two additional (second and third) coccygeal nerves, homologous with the caudal nerves of the lower animals. THE CENTRAL NERVOUS SYSTEM. 1027 The Columns of the Cord. Inspection of the surface and particularly of cross-sections of the spinal cord (Fig. 885) shows the latter to be partially divided into a symmetrical right and left half by a median cleft in front and a partition in the mid-line behind. The cleft, the anterior median fissure ( tissura mediana anterior) extends the entire length of the cord, and is continued on the upper part of the filum terminate. It is narrow, from 2-3.5 mm - m depth, penetrating for less than one-third of the ventro-dorsal djameter of the cord, and occupied by a process of pia mater. Along its floor, which lies immediately in front of the white commissure, it is frequently deflected to one side of the mid-line and presents a slight expansion. The separation into halves is completed by the posterior median septum (septum medianiim posteritis), the so-called posterior median fissure. With the ex- ception of a shallow groove in the upper cervical cord, the lumbar enlargement and the conus medullaris, no fissure exists, but in its place a dense partition extends from the posterior surface to the middle of the interior of the cord, ending in close relation to the gray commissure. The character of the septum is a subject of dispute, according to some anatomists con- sisting exclusively of condensed neuroglia, while others regard it as composed of pial tissue blended with the neuroglia and, therefore, of both mesoblastic and ectoblastic origin. The latter view is substantiated by the mode of development of the posterior septum, the immature pial covering of the developing blood-vessels being imprisoned within and fused with the neu- rogliar partition derived from the expanding dorsal halves of the developing cord (page 1050). The application of differential stains also demonstrates the composite nature of the septum. Each half of the spinal cord is further subdivided by the lines along which the root-fibres of the spinal nerves are attached. The root-line of the dorsal (sensory) fibres is relatively straight and narrow, and marked by a slight furrow, the postero- lateral sulcus (sulcus lateralis posterior) that lies from 2.5-3.5 mm - lateral to the posterior septum and is evident even on the intersegmental intervals where the root- fibres are practically absent. The ventral root-line, marking the emergence of the anterior (motor) fibres, is much less certain, since the bundles of fibres of the indi- vidual nerves do not emerge in the same vertical plane, but overlie one another to some extent, so that each group occupies a crescentic area, whose greatest width cor- responds in a general way with that of the subjacent ventral horn of gray matter. The anterior root-line, which lies from 2-4 mm. lateral to the median fissure, is neither indicated by a distinct furrow nor con- FIG. 884. tinuous. In this manner two longitudinal tracts, the posterior columns (funiculi posteriores) are marked off between the posterior median septum and the sulci of the posterior root- lines. These columns include something less than one-third of the circumference of the cord, and are about 6 mm. in width in the thoracic cord and 8mm. and 7 mm. in the cervi- cal and lumbar enlarge- ments respectively. The tracts included between the dorsal and ventral root-lines constitute the lateral columns (funiculi laterales) and those between the ventral root-lines and anterior median fissure are the anterior columns (funiculi anteriores). Such subdivision into anterior and lateral Skull Vertebra artery i cerv. nerve Medulla Ganglion on 4 nerve Dorsal roots of 5 cerv. nerve Upper end of spinal cord, viewed from behind after partial removal of dnral sheath ; cord-segments are indicated by groups of converging bundles of posterior root-fibres; spinal ganglia are seen lying within the intervertebral foramina; spinal accessory nerve is seen ascending on each side. 1028 HUMAN ANATOMY. columns is, however, largely artificial, since neither superficially nor internally is there a definite demarcation between these tracts. They may be, therefore, conveniently regarded as forming a common antero- lateral column, that on each side embraces something more than two-thirds of the semicircumference of the cord. In the lower cervical and upper thoracic cord, each posterior column is subdivided by a shallow furrow that lies from 1.5-2 mm. lateral to the posterior medium septum. This, the paramedian sulcus (sulcus intermedius posterior), corresponds in position with the peripheral attachment of a radial septum of neuroglia that penetrates the white matter for a variable distance, sometimes almost as far as the gray matter, and subdivides the posterior column into two unequal tracts, of which the inner and smaller is the pos- tero-median column (funiculus gracilis), or column of Goll, and the outer and larger is the postero-lateral column (funiculus cuneatus), or column of Burdach. The Gray Matter. Inspection of the transversely sectioned spinal cord, even with the unaided eye, shows it to be composed of an irregular core of gray substance enclosed by a mantle of white matter. Within each half of the cord the gray FIG. 885. Caput cornu Cervix cornu Lateral cornu Basis cornu Caput cornu Posterior median septum rior column Posterior root-furrow ^%i^ Posterior 3L root-fibres -ateral column Central canal in gray commissure Anterior median fissure Anterior Anterior white commissure Transverse section of thoracic cord, showing disposition of gray and white matter and division of latter into anterior, lateral and posterior columns. X 13. matter forms a comma-shaped area, the broader end of which lies in front and the narrower behind, with the concavity directed laterally. The convex surfaces of the tracts of the two sides, which look towards each other and the mid-line, are connected by a transverse band of gray matter, the gray commissure (cominissiira risea) that extends across the mid-line, usually sonu-what in advance of the middle of the sagittal diameter, and encloses the minute central canal of the cord. By this canal the connecting band, or central gray matter, is divided into a dorsal and a ventral part, the posterior and the anterior gray commissure, which lie behind and in front of the tube respectively. While the posterior median septum reaches the dorsal surface of the gray com- missure, the ventral margin of the latter is separated from the anterior median fissure by an intervening bridge of white matter, the anterior white commissure (com- inissnni anterior alba) which connects the anterior columns of the cord and provides an important pathway for fibres passing from one side to the other. A zone of mod- ified neuroglia immediately surrounding the central canal is known as the substantia gelatinosa centralis (substantia urisea ccntralis). THE CENTRAL NERVOUS SYSTEM. 1029 FIG. 886. I C Each crescent of gray matter is divisible into three parts the ventral and the dorsal extremity, that project beyond the transverse gray commissure and constitute the anterior and posterior -horns or cornua of the gray matter (columnae griseae), and the intermediate portion (pars intermedia) that connects the cornua and receives the commissure. The two horns differ markedly from each other and, although varying in details in different levels, retain their distinctive features throughout the cord. The anterior cornu (columna grisea anterior) is short, thick and rounded, and separated by a considerable layer of white matter from the surface of the cord, through which the ventral root-fibres proceed to their points of emergence in the root-areas. The blunt tip of the anterior horn is known as the caput cornu, and the dorsal por- tion by which it joins the commissure and the pars intermedia as the basis cornu. The posterior cornu (columna grisea posterior) presents a marked contrast in being usually relatively long, narrow and pointed, and in extending peripherally almost to the postero-lateral sulcus. The tip or apex of the dorsal horn is formed of a A-shaped stratum of peculiar character, the sub- stantia gelatinosa Rolandi, that appears lighter in tint (Fig. 885) and somewhat less opaque than the subjacent and broader portion of the horn, caput cornu, which it covers as a cap. More ventrally the posterior horn is usually somewhat contracted, to which portion the term, cervix cornu (cervix columnae posterioris) is applied. In the lower thoracic cord, however, this constriction is replaced by a slight bulging located on the mesial side of the junction of the posterior cornu with the gray commissure. This enlargement corres- ponds to the location of a longitudinal group of nerve- cells constituting the column of Clarke. The fairly sharp demarcation between the gray and white matter is interrupted along the lateral border of the crescent by delicate prolongations of gray matter into the surrounding lateral column (Fig. 888). The subdivisions of these processes unite to form a reticulum of gray matter, the meshes of which are occupied by longitudinally coursing nerve-fibres, the whole giving rise to an interlacement known as fae, processus or for- matio reticularis. Although to some extent present in the greater part of the cord, this structure is most marked in the upper cervical region, where it exists as a conspicuous net-work filling the recess that indents the lateral border of the pars intermedia and the neck of the posterior horn of the gray crescent. In the thoracic and upper parts of the cervical cord, therefore in regions in which the enlargements are wanting, the formatio reticularis is condensed into a compact process of gray matter that is directed outward (Fig. 885) and known as the lateral cornu (columna lateralis). i T Taken as a whole, the gray matter, which in cross-sections appears as the H -shaped area formed by the two crescents and the commissure, constitutes a continuous column, whose irregular contour depends not only upon the peculiar disposi- tion of the gray matter, but also upon the variations in its amount at different levels of the cord. Thus, at the level of the third cervical nerve the gray matter constitutes somewhat more than one-fourth of the entire area of the cord ; at that of the seventh nerve about one-third, while in the thoracic region, between the second and eleventh nerves, it is reduced to about one-sixth. At the last thoracic nerve it again forms one-fourth, and at the third and fifth lumbar two-fifths and three-fifths respectively. In the sacral cord the relative amount of gray matter increases until, at the level Diagram showing amount of gray and white matter in relation to entire area of cord, and relative lengths of cord-segments; the latter are indicated by divisions on left margin of figure I C, I T, I L, I S, first segment of cervi- respectively ; dark zone next left bor- der represents the gray matter, light zone the white matter, outer dark zone the entire area of cord. (Donaldson.) 1030 HUMAN ANATOMY. of the last sacral nerve, it reaches three-fourths. The absolute amount of gray matter is greatest within the cervical and lumbar enlargements of the cord, where it is directly related to the large nerves supplying the lirhbs. On comparing the tracts of white matter and the gray column it follows that while in the lower third ot the lumbar cord these are of approximately equal area, below this level the gray matter exceeds the white. In the remaining regions, on the other hand, the white matter predominates, in the greater part of the thoracic cord exceeding the gray from four to five fold and in the cervical cord being from two to three times greater. The Central Canal. Where well represented, the central canal (canalis cen- tralis), the remains of the once conspicuous neural tube, appears as a minute opening in the gray commissure, about .2 mm. in diameter and barely visible with the unaided eye. In the child it extends the entire length of the cord and, below, ends blindly in the upper half of the filum terminale. Above, it opens into the lower end of the fourth ventricle, from which it is prolonged downward through the lower half of the medulla oblongata into the spinal cord. In not over one-fifth of adult subjects, however, is the canal retained as a pervious tube throughout the cord, its lumen usually being partially or completely obliterated for longer or shorter stretches, the lumen last disappearing in the lower part of the cord. Within the conus medullaris, the central canal regularly exhibits an expansion, the sinus terminalis, that begins below the origin of the coccygeal nerve and extends caudally for from 8-10 mm., with a maximum frontal diameter of i mm. or over. The obliteration of the central canal, complete in about 50 per cent, of subjects beyond middle life (Schulz), is to be regarded as a physiological accompaniment of advancing age. It is effected by displacement and proliferation of the ependyma-cells lining the canal, in conjunc- tion with ingrowth of the surrounding neurogliar fibres (Weigert). The form of the canal, as seen in cross-sections, is very variable and uncertain owing to the changes incident to the use of hardening fluids. In a general way when well preserved the lumen is round or oval and smallest in the thoracic region ; in some places, as in the upper cervical cord and in the lumbar enlargement, it is larger and often appears pentagonal in outline, whilst in others the calibre may be reduced to a sagittal slit. The position of the central canal varies at different levels in relation to the ventral and dorsal surfaces of the cord. In the middle of the lumbar region it occupies approximately the centre of the cord, but above, in the thoracic and cervical segments, it lies much nearer the ventral than the dorsal surface, while below it gradually approaches the dorsal surface, but always remains closed. Mention may be made of a remarkable structure named Reissner* s fibre, after its discov- erer, that as a longitudinal thread of great delicacy lies free within the central canal of the cord and the lower ventricle of the brain, extending from the cavity of the mesencephalon above to the lowest part of the cordrcanal below. The interpretation of this structure as an artefact, which considering its extraordinary position is most natural, seems untenable in view of the positive testimony, confirming its existence as a preformed and true structure in many vertebrates, given by several subsequent observers and especially by Sargent. 1 Its nature and significance are problematic. Although the existence of this fibre has been established in many vertebrates, even in birds, it has not yet been discovered in man. MICROSCOPICAL STRUCTURE OF THE SPINAL CORD. The three chief components of the spinal cord the nerve-cells, the nerve-fibres and the neuroglia vary in proportion and disposition in the white and gray matter. It is, therefore, desirable to consider the general structure of the cord before describ- ing its detailed characteristics at different levels. The Gray Matter. The most distinctive elements of the gray matter are the ni ult if>olar nerve-cells which lie embedded within a complex sponge-like matrix formed by the various processes dendrites, axones and collaterals from other neurones, the supporting neuroglia and the blood-vessels. In two localities immediately around the central canal and capping the dorsal cornu the gray matter varies in its appearance and constitution and exhibits the modifications peculiar to the central and Rolandic substantia gelatinosa, the details of which call for later description (page 1034). Tin nerve-cells of the anterior horn are multipolar, in cross-sections the cell-bodies appearing irregularly polygonal and in longitudinal sections fusiform in out- 1 Bulletin of Harvard Museum of Comp. Zoology, vol. xlv., 1904. MICROSCOPICAL STRUCTURE OF SPINAL CORD. 1031 line. They may vary from .065-. 135 in diameter, unless unusually small, when they measure from .030-. 080 mm. (Kolliker). In a typical example, as represented by one of the ventral radicular cells giving origin to anterior root-fibres, from three to ten dendritic processes radiate in various planes, divide dichotomously with decreasing width and finally end in terminal arborizations. In contrast to the robust dendrites beset with spines, the axone is smooth, slender and directly continuous with the axis-cylinder of a root-fibre of a spinal nerve and unbranched, with the exceptions of delicate lateral processes that are given off almost at right angles. These processes, the collaterals, arise at a variable distance from the cell-body, but usually close to the latter and always before leaving the gray matter. They repeatedly divide and follow a recurrent course within the anterior horn. After appropriate staining the cytoplasm of the nerve-cells exhibits conspicuous accumulations of the deeply staining tigroid substance that lie within the meshes of the reticulum formed by delicate neurofibrillae, which not only occupy FIG. 887. the cell-body but also extend into the various jy^ -\ processes. The fibrillse, however, do not pass beyond the limits of the neurone to which they belong (Retzius). Each nerve-cell possesses a spherical or ellipsoidal nucleus, from .010 to .020 mm. in its greatest diameter, which is en- closed by a distinct nuclear membrane and usually contains a single nucleolus, exceptionally two or three. Within the cytoplasm an accu- mulation of brownish- yellow pigment granules is usually present near one pole, often in the vicinity of the implanta- tion cone from which the axone springs. In addition to the con- spicuous ventral radicular cells above described, the anterior horn contains Nerve-fibres of white matter Anterior root-fibres Other nervous elements, Portion of anterior cornu of gray matter, showing multipolar Some Of which, the Com- nerve-cells. X 120. missural cells, send their axones through the anterior commissure to the opposite half of the cord, while the axones of others, the strand-cells, pass into the columns of white matter of the same, less frequently opposite, side. The commissural cells, which with few exceptions occupy the median portion of the anterior horn, resemble in size and contour the radicular cells, but differ from the latter in pos- sessing smaller nuclei. The majority of the dendrites are directed towards the inner part of the ventral cornu, but some pass into the gray commissure and a few end within the adjacent white matter. The axones traverse the anterior white commissure to gain the ventral column of the opposite side, in which they either divide "f-like into ascending and descending fibres, or undivided turn brainward. The strand cells, variable in form and generally smaller than the root-cells, are only sparingly represented in the anterior horn. They are distinguished by the course of their axones, which usually pass to the anterior column of the same side. In some cases, however, 1032 HUMAN ANATOMY. the axone divides into two, rarely three, fibres, one of which crosses by way of the anterior white commissure to the opposite ventral column, while the other passes to the ventral column of the same side. As well seen in cross-sections, although the nerve-cells of the anterior horn are widely scattered they are not uniformly distributed through the gray matter, but are collected into more or less definite groups that recur in consecutive sections. It is evident, therefore, that the cell-groups are not limited to a single plane, but are continuous as longitudinal tracts or columns for longer or shorter stretches within the core of gray matter of the cord. The grouping of the nerve-cells of the anterior horn includes two general collections, a mesial group, containing many commissural cells, and a lateral group composed chiefly of ventral radicular cells. These collections, however, vary in extent and definition in different parts of the cord and, where well marked, are often FIG. Cells of substantia gelatinosa Rolandi Posterior horn cells Accessory dorso- lateral groups Dorso-latcral group " Ventro-lateral group Mesial group' Transverse section of lower cervical cord, showing grouping of nerve-cells ; Nissl staining. X 20. made up of more than a single aggregation of cells. This feature is particularly rvi- dent in the lateral collection, in which an anterior and a posterior subdivision are recognized as the ventro-lateral and the dorso-lateral group that occupy the corre- sponding angles of the anterior horn. The mesial collection, situated within the ventral angle, is likewise, but much less clearly, divisible into a centre-mesial and a dorso-nn-sial group, of which the latter is variable and at many levels wanting. In a general way the pronounced presence of these cell-groups influences the outline of the anterior horn, so that corresponding projections of the gray matter mark their position. This relation is conspicuously exemplified in the cervical and lumbo-sacral enlargements, in which the presence of large lateral cell-groups is directly associated with a marked increase in the transverse diameter of the anterior horn. Conversely, when these cell-columns become smaller or disappear, the corresponding rlrvations on the surface of the anterior horn diminish or are absent. Owing to such variations the contours of the gray core are subject to constant and sometimes abrupt change. MICROSCOPICAL STRUCTURE OF SPINAL CORD. 1033 The ventro-median cell-column is the most constant, since, as emphasized by the pains- taking studies of Bruce, 1 it is interrupted only between the levels of the fifth lumbar and first sacral nerve in its otherwise unbroken course through the length of the cord, as far as the level of the fifth sacral nerve. An augmentation of this tract in the fourth and fifth cervical segments is probably associated with the spinal origin of the phrenic nerve (Bruce). The dorso-mesial cell-column is much less constant, being represented only in the thoracic region, in a few cervical segments and at the level of the first lumbar nerve. In agreement with van Gehuchten and others, Bruce regards the continuity of the mesial group as presump- tive evidence of its close relation to the dorsal extensor muscles of the trunk. The ventro-lateral cell-column appears first at the level of the fourth cervical nerve, increases rapidly in the succeeding segments and fades away at the lower part of the eighth cervical segment. It reappears in the lumbar enlargement, reaching its maximum at the level of the first sacral nerve and, diminishing rapidly through the upper part of the second, disappears before the third sacral segment is reached. The dorso-lateral cell-column, in places the most conspicuous collection of the anterior horn, begins above at the lower part of the fourth cervical segment and, increasing rapidly, attains its greatest development in the neck in the fifth and sixth segments. It suffers a marked reduction at the level of the seventh cervical nerve, which is followed by a sudden increase in the next segment in which the column presents an additional collection of nerve-cells known as the accessory dorso-lateral or post-postero- lateral group. Below the level of the second thoracic nerve the dorso-lateral cell-column is unrepresented as far as the second sacral segment where it reappears, somewhat abruptly, and attains its maximum size in the fourth and fifth lumbar segments. The column then diminishes and ceases at the lower part of the third sacral seg- ment. Within the sacral cord, between the levels of the first and third nerve inclusive, the dorso-lateral cell- group is augmented by an accessory group. From the third lumbar to the sacral nerve-levels, an additional compact collection of nerve-cells occupies a more median position in the anterior horn and constitutes the central group. From the position of the greatest expansions of the lateral cell-columns within the cervical and lumbo-sacral enlargements it is evident that they are associated with the large nerves sup- plying the muscles of the limbs. Further, according to Bruce, in a general way the size of the radicular cells bears a relation to that of the muscles supplied, the smaller dimensions of the cervical cells, as compared with those of the lumbo-sacral region, corresponding with the smaller size of the upper limb in comparison with that of the lower one. In addition to the nerve-cells assembled within the foregoing more or less well defined groups, some scattered cells are irregularly distributed through the anterior horn and do not strictly belong to any of the groups. Below the level of the first coccygeal nerve, the cells of the anterior horn become so diminished in number, that they are no longer grouped with regularity, but, reduced in size, lie uncertainly distributed within the gray matter as far as the lower limits of the conus medullaris. . The nerve-cells of the posterior horn are neither as large nor as regularly disposed as the anterior horn cells. Only in one locality, along the median border of the base of the posterior horn, are they collected into a distinct tract, the column of Clarke ; otherwise they are scattered without order throughout the gray matter of the posterior cornu. Since, however, the latter comprises certain areas, the cells of the posterior horn may be divided into (i) the cells of Clarke' s column, (2) the cells of the substantia gelatinosa Rolandi, and (3) the inner cells of the caput cornu. The cells of Clarke's column form a very conspicuous collection which extends from the level of the seventh cervical nerve to that of the second lumbar nerve and is best developed in the lower thoracic region of'the cord. Although confined chiefly to the dorsal portion of the cord, and hence sometimes designated as the "dorsal nucleus," Clarke's column is represented to a slight degree in the sacral and upper cervical regions (sacral and cervical nuclei of Stilling) . In cross-sections the cell-column appears as a group of multipolar cells that occupy the mesial border of the base of the posterior horn and, where the column is best developed (opposite the origin of the twelfth thoracic nerve), correspond to an elevation on the surface of the gray matter. The cells usually are about .050 mm. in diameter, polygonal in outline and possess a relatively large number of richly branched dendrites that radiate chiefly within the limits of the group (Cajal). The axones commonly spring from the anterior or lateral margin of the cells and course ventrally for a considerable distance before bending outward toward the lateral column of white matter within which, as constituent fibres of the direct cerebellar tract (page 1044) > they turn brainward. 'Topographical Atlas of the Spinal Cord, 1901. 1034 HUMAN ANATOMY. The nerve-cells of the substantia gelatinosa Rolandi, also known as Gierke ' s cells, include innumerable small stellate, less frequently fusiform or pear-shaped elements that measure only from .oo6-.o2o mm., although exceptionally of larger size. Their numerous short dendrites are irregularly disposed and branched. The axones, which always arise from the dorsal pole of the cell, are continued partly to the white matter of the posterior column, within which they divide into ascending and descending limbs, and partly to the gray matter itself, within which they run as longitudinal fibres. Under the name of the marginal cells are described the much larger (.035-.055 mm. ) nerve-cells which occupy the border of the substantia gelatinosa. They are spindle-shaped or pyramidal in form, their long axes lying parallel or the apices directed towards the Rolandic substance respectively, and constitute a one-celled layer enclosing the substantia gelatinosa, into which many of their tangentially coursing dendrites penetrate. Their axones pass through the substantia gelatinosa and probably continue for the most part within the lateral column, although some enter the posterior column (Cajal, Kolliker). The inner cells of the posterior horn are intermingled with numerous nervous elements of small size irregularly distributed within the head of the dorsal cornu. The inner cells proper are triangular or spindle-shaped in form and, on an average, measure about .050 mm.; they are, therefore, larger than the ordinary cells of the Rolandic substance. The dendrites arise FIG. 889. White matter of posterior column Cells of Clarke's column Substantia gelatinosa centraiis Central canal Part of cross-section of cord, showing cells of Clarke's column in base of posterior horn. X'no. from the angles or ends of the cells and diverge in all directions. The axones pass, either directly or in curves, mostly into the lateral column of the same side ; some, however, have been followed into the posterior or anterior columns of the same side (Kolliker), and, rarely, into the opposite anterior column (Cajal). Exceptionally type II cells those in which the axone is not prolonged as the axis-cylinder of a nerve-fibre, but soon breaks up into an elaborate end arborization confined to the gray matter are found within the gray matter of the posterior horn. Their number is, however, much less than often assumed (Ziehen). The nervous character of most of the cells seen within the substantia gelatinosa Rolandi has been established only since the introduction of the Golgi methods of silver-impregnation. Previously, these elements were regarded as glia cells, an exceptionally large amount of neuroglia in general being attributed to the Rolandic substance. It is now admitted that instr.-ul <>f such being the case, this region of the gray matter is relatively poor in neurogliar elements and numerically rich in nerve-cells. The nerve-cells of the pars intermediate of the gray matter, which connects the dorsal and ventral horns and lies opposite the gray commissure, may be broadly divided into two classes, the lateral and the middle cells, that occupy respectively the outer border and the more central area of this part of the gray matter of the cord. MICROSCOPICAL STRUCTURE OF SPINAL CORD. Those of the first class, or intermedio-lateral cells, are associated with the formatio reticu- laris and its condensation, the lateral horn, and hence are often spoken of as the group or column of the lateral horn. These cells form a slender tract of small closely packed elements that is represented through almost the entire length of the cord, although best marked in the upper third of the thoracic region and partially interrupted in the cervical and lumbo-sacral segments. Where the formatio reticularis is condensed with a distinct lateral horn, as in the thoracic region, the cells occupy the projection, but elsewhere lie within the base of the gray net- work. As a continuous cell-column the tract extends from the lower part of the eighth cervical segment to the upper part of the third lumbar, being most conspicuous at the level of the third and fourth thoracic nerves (Bruce). Practically suppressed in the cervical region between the eighth and third segments, above the latter the column reappears along with the formatio reticularis. Below, it is again seen within the third and fourth sacral segments. The nerve-cells are multi- polar or fusiform in outline, from .oi5~.o45 mm. in their longest diameter, contain little pigment, and are provided with a variable number of dendrites, of which two are usually larger than the others. These arise from opposite poles of the cell and send branches, for the most part, into the adjacent white matter. The axones pass directly into the lateral columns and become ascending or descending fibres ; a few axones, however, enter the anterior column of the same side (Ziehen). The cells of the second class, or intermediate cells, are irregularly disposed and only in the upper part of the cord present a fairly distinct middle group (Waldeyer). They are polygonal or fusiform in outline, small in size (seldom exceeding .025 mm.) and provided with irregular dendrites. The axones are continued chiefly within the lateral column of the same side, although some pass to the anterior column and a few probably cross to the opposite side. A small number of isolated nerve-cells are usually to be found within the white matter, out- side but in the neighborhood of the gray core. These, the outlying cells of Sherrington, 1 by whom they have been studied, occur most frequently in the vicinity of the more superficially placed cell-columns. Within the anterior columns they lie in the paths of the fibres proceeding to the anterior white commissure ; in the lateral columns they are in proximity to the intermedio- lateral group of the lateral horn and formatio reticularis and to the cells of the substantia Rolandi ; and in the posterior columns, where they are relatively numerous, they are associated with the fibre-tracts leading to the column of Clarke. The outlying cells are regarded as elements displaced from their usual position during the course of the differentiation and growth of the white and gray matter. Similar displacement sometimes affects the cells of the spinal ganglia, which then may be encountered within the cord. The Neuroglia of the Gray Matter. As in other parts of the cord, so in the gray matter the neuroglia is everywhere present as the supporting framework of the nervous elements, the FIG. 890. Posterior median septum Paraniedian septum subdividing posterior column cells and fibres. The gen- eral structureof neuroglia having been described (page 1004), it only re- mains to note here the special features of its arrangement within the gray matter. In general, the felt-work of the neu- rogliar fibrils is more compact than that per- meating the white matter, being somewhat denser at the periphery than in the deeper parts of the gray matter. There is, however, no hard boun- dary between the sup- porting tissue of the two, since numerousglia fibrils extend outward from the frame-work of the gra)' matter to be lost between the nerve fibres of the adjoining columns. This feature is marked in the anterior horn, where the glia fibrils form septa of considerable thickness that diverge into the surrounding columns ; further 1 Proceedings Royal Society, vol. 30, 1890. Anterior median fissure Anterior column Transverse section of cord slightly magnified, showing general arrangement of neuroglia. X 10. 1036 HUMAN ANATOMY. the conspicuous processes of the formatio reticularis and the projecting lateral horn consist largely of neuroglia. The larger nerve-cells and their robust processes are ensheathed by interlacements of neuroglia hbrilhe. In the several parts of the posterior horn the amount of neuroglia varies. Thus, the apex consists almost exclusively of glia tissue, while within the Rolandic substance the number of glia fibres and cells is unusually small. Within the caput and remaining parts of the posterior horn the neurogliar elements are similar in quantity and disposition to those in the anterior horn. The ependyma cells lining the central canal of the cord are the direct descendants of the radially arranged embryonal supporting elements (page 1004) ; they may, therefore, be regarded as specialized neuroglia cells. Although most advantageously studied in the foetus and the child, in favorable preparations from adult cords they are seen as a single row of pyramidal cells, from .030-.050 mm. long and from one-fourth to one-third as broad, whose bases are directed towards the lumen of the canal and beset with cilia. Their pointed distal ends, or apices, are prolonged into a long delicate ependymal fibre, that in the adult is soon lost in the surrounding neuroglia, but in the foetus extends through the entire thickness of the cord. The ependyma cells are not all of equal size, those occupying the ventral mid-line, especially in the cervical region, being about twice as long as those on the opposite wall of the canal. The epen- dymal fibres proceeding from these cells are of special length and thickness, the ventral ones con- verging to form a wedge-shaped mass that in the young subject continues as far forward as the bottom of the anterior median fissure. The dorsal ependymal fibres are prolonged through the gray commissure into the posterior median septum, some diverging into the columns of Goll. FIG. 891. Substantia gelatinosa centralis is the name given to a zone of peculiar trans- lucency that immediately surrounds the central canal. This annular area consists of modified neuroglia in which radial ependymal fibers are interwoven with circularly disposed neurogliar fibrillae, the whole giving rise to a compact stratum, interspersed with an unusual number of glia cells, upon which arrange- ment, in conjunction with the absence of nerve-fibres, the characteristic appearance of the gelatinous substance depends. In addition to the branched glia elements, a number of radially directed spindle cells are present in this zone ; they send delicate processes between the ependyma cells, of which they are probably outwardly displaced members. In marked contrast with the Ro- landic substance, which caps the posterior horn, the substantia gelatinosa centralis contains no nerve-cells but only glia elements, in recognition of which the term, sub- stantia gliosa centralis, has been proposed by Ziehen. The Nerve-Fibres of the Gray Matter. Within all portions of the gray core a considerable part of the intricate ground-work in which the nerve-cells lie embedded is contributed by the processes of neurones situated at the same, different or even remote levels. These processes, which constitute the nerve-fibres, medullated and nonmedullated, that are seen traversing the gray matter in all directions, include:(i) the collate- rals and the terminal branches of the dorsal root-fibres that enter the gray matter ; (2) nerve-fibres of the descending tracts that terminate in relation with the ventral (motor) horn cells ; (3) the axones and collaterals given off by the numerous pos- terior horn cells, that traverse the gray matter to and from the respective columns into which they pass. The dendritic processes, as well as the axones of the type II cells, also contribute to the sum of nervous fibrilke encountered within the gray matter of the cord. WHITE MATTER OF THE SPINAL CORD. The predominating components of the white substance being the longitudinal nerve-fibres which pass for a longer or shorter distance up and down in the columns of the cord, in cross-sections the outer field, between the gray core and the periphery Central canal and surrounding substantia jrelatinosa centralis, from child's cord ; canal is lined with ependyma cells, outside of which lies neuroglia with glia cells. X 135. WHITE MATTER OF THE SPINAL CORU. 1037 of the cord, appears to be composed of innumerable, closely set, small cells, held together by delicate supporting tissue. These apparent cells are the medullated nerve-fibres cut transversely, in which the sectioned axis-cylinders show as deeply stained dots, that commonly lie somewhat eccentrically and are surrounded by deli- cate irregularly annular striations representing the framework of the medullary coat. The nerve-fibres of the cerebro-spinal axis are without neurilemma, the lack of this sheath being compensated by a slight condensation of the neuroglia around the fibres. Seen in transverse sections this investment appears as the ring that gives a definite outline to the fibre. The individual nerve-fibres vary greatly in size, even within the same tract large and small fibres often lying side by side. The smallest may be less than .005 mm. and the largest over .025 mm. In a general way, the diameter of the fibre bears a direct relation to its length, those Fig. 892. Trabecula of neuroglia Blood-vessel in pia Subpial layer of neuroglia Peripheral part of transverse section of spinal cord, showing nerve-fibres subdivided into groups by ingrowth of subpial layer of neuroglia. X 230. , having an extended course being larger than shorter ones ; it follows that the fibres occupying the peripheral parts of the white matter, particularly in the lateral columns, are more frequently of large diameter than those near the gray matter. The immediate surface of the white substance beneath the pia mater is formed by a con- densed tract of neuroglia, the subpial layer, from .O20-.O40 mm. in thickness, that is devoid of nervous elements and forms the definite outer boundary of the cord. This zone consists of a dense interlacement of circular, longitudinal and radial neuroglia fibrils among which numer- ous glia cells are embedded. From the deeper surface of this ensheathing layer numerous bundles of fibrillse penetrate between the subjacent nerve-fibres to become lost in the general supporting ground-work. At certain places the bundles are replaced by robust septa by which the nerve-fibres are imperfectly divided into groups or tracts, as conspicuously seen in the pos- terior column where the paramedian septum effects an imperfect subdivision into the tract of Goll and of Burdach. The blood-vessels that enter the nervous substance from the pia, accom- panied by connective tissue, are surrounded by tubular sheaths of neuroglia, and the same is 1038 HUMAN ANATOMY. true of the bundles of root-fibres of the spinal nerves, lint apart from the connective tissue that enters with the blood-vessels, the amount of mesoblastic tissue concerned in the supporting framework of the cord is inconsiderable, according to some histologists, indeed, being practically nothing. Fibre-Tracts of the White Matter. Although microscopical examination of ordinary sections of the cord affords slight indication of a subdivision of the columns of white matter into areas corresponding with definite fibre-tracts, yet the combined evidence of anatomical, pathological, embryological and experimental investigation establishes the existence of a number of such paths of conduction. With few exceptions, they are, however, without sharp boundaries and illy defined, adjoining tracts often overlapping, and depend for their presence upon the fact that nerve-fibres having the same function and destination proceed in company from the same group of nerve-cells (nucleus) along a similar course. In addition to being pro- vided with paths of conduction necessary for the performance of its function as a centre for independent (reflex) impulses in response to external stimuli, the cord contains tracts that connect it with the brain, as well as those that bring the various levels of the cord itself into association. The white matter, therefore, contains three classes of fibres : ( i ) those entering the cord from the periphery and other parts of the body ; (2) those entering it from the brain ; and (3) those arising from the nerve-cells situated within the cord itself. The first two constitute the exogenous, the last the endogenous tracts. It is evident that some of these fibres constitute pathways for the transmission of impulses from lower to higher levels and hence form ascending tracts, while others, which conduct impulses in the opposite direction, form, descending tracts. Since it is impossible to distinguish between these fibres by mere inspection of sections of the adult normal cord, and, moreover, extremely difficult and practically impossible to follow in such preparations the longer fibres throughout their course, advantage is taken of other means by which differentiation of individual tracts is feasible. Such means include chiefly the experimental and embryological methods. The experimental method depends upon the law discovered by Waller, more than half a century ago, that when the continuity of a nerve-fibre is destroyed, either by a pathological lesion or by the experimenter's knife, the portion of the nerve-fibre (the axone of a neurone) beyond the break, and therefore isolated from the presiding nerve-cell, undergoes secondary degeneration, while the portion remaining connected with the cell usually undergoes little or no change. It should be pointed out, however, that occasionally the connected portion of the fibre, and even the nerve-cell itself, undoubtedly exhibits changes known as retrograde degen- eration, which, although uncertain as to occurrence and cause, may at times prove a source of error in deducing conclusions. If a lateral section of one-half of the cord of a living animal be made, and, after the expiration of from three to four weeks, transverse sections be cut and appropriately prepared (by the methods of Marschi or of Weigert), certain groups of nerve- fibres will present degenerative changes. It will be seen, however, that the degenerated tracts in sections taken from above the lesion are not the same as those in sections from below the division, showing that certain fibres have been involved in opposite directions, those arising from nerve-cells lying below the lesion being affected with ascending degeneration, and those from cells situated above with descending degeneration. In this manner, by rare-fill study of consecutive sections, much valuable information has been gained as to the origin, course, ter- mination and function of many fibre-tracts within the central nervous system. The embryological method, also productive of important advances in our knowledge of the nervous pathways, is based on the fact, first demonstrated by Meckel, that the nerve-fibres of the central nervous system do not all acquire their medullary sheath at the same time Taking advantage of such variation, as suggested by Meynert and later extensively carried out by Flechsig and other?, upon staining sections of embryonal tissue with reagents that color especially the medullary substance, it is possible to differentiate and follow certain fibre-tracts in the fcetal cord with great clearness, since only those tracts are stained in which the myelin is already formed. It is of interest to note that, in a general way, the order in which the different strands of the cord acquire their medullary coat accords with the sequence in which nervous function is assumed by the fcetus and child Thus, the paths required for spinal reflexes (the posterior and anterior root-fibres) are first to become medullated (fourth and fifth total months); those bringing into association the different segments of the cord next (from tin- fifth to the seventh month) acquire myelin; those connecting the cord with the cerebellum follow somewhat later, while those establishing relations with the cerebral cortex are last do not begin to medullate until shortly before birth. WHITE MATTER OF THE SPINAL CORD. 1039 Based on the collective evidence contributed by these methods anatomical, physiological, and developmental it is possible to locate and trace with fair accuracy a number of fibre-tracts in the cerebro-spinal axis. Since they are undergoing continual augmentation or decrease, their actual area and position are subject to variation, so that the detailed relations in one region of the cord differ from those at other levels. The accompanying schematic figure, therefore, must be regarded as showing only the general relations of the most important paths of the cord, and not as accurately representing the actual form and size of the fibre-tracts. It must also be appreciated that the definite limits of these tracts in such diagrammatic FIG. 893. Association tracts Cerebro-spinal tract \ \ V Vestibulo-spinal tract Tecto-spinal tract Rubro-spinal tract - Vestibulo-spinal tract jfj~ Spino-thalamic tract Spino-olivary tract (Helweg) representations seldom exist in reality, since the fibres of the adjacent paths in most cases overlap, or, indeed, extensively intermingle, so that the fields seen in cross-sections may be shared by strands belonging to different fibre-systems. The Fibre-Tracts of the Posterior Column. The subdivision of the posterior column of white matter by the paramedian septum into two general parts has been noted (page 1028). Of these the inner one is the postero-median fasciculus, or tract of Goll (fasciculus gracilis), and the outer one is the postero- lateral fasciculus or tract of Burdach (fasciculus cuncatus). These tracts are so intimately associated with the fibres entering by the posterior roots of the spinal nerves, that the general relations and behavior of these fibres must be considered in order to understand the composition of the posterior columns, as well as that of certain secondary paths. All sensory impulses that enter the spinal cord do so by way of the posterior root-fibres. The latter are the centrally directed processes (axpnes) of the neurones whose cell-bodies lie within the spinal ganglia situated on the dorsal roots of the spinal nerves. They convey to the cord the various impulses collected by the peripherally directed processes (the sensory nerves) from the integument, mucous membranes, muscles, tendons and joints from all parts of the body, with the exception of those served by the cranial nerves. The impulses thus conducted are transformed into the impressions of touch, muscle-sense, heat, cold and pain. The last being probably the result of excessive stimulation that by its intensity causes discomfort in various degrees, the existence of special paths for the conduc- tion of painful impressions is unlikely. It is evident that the larger part of the HUMAN ANATOMY. sensory neurones lies outside the spinal cord ; it is, however, with the intramedullary portion of these neurones, as constituents of paths within the cord, that we are here concerned. On entering the spinal cord along the postero-lateral groove, the dorsal root- fibres for the most part penetrate the tract of Burdach, close to the inner side of the posterior horn. Some of the more external root-fibres, however, do not enter Bur- dach' s tract, but form a small adjoining field, the tract of Lissauer, that lies im- mediately dorsal to the apex of the posterior horn. Soon after gaining the posterior column, with few exceptions, each dorsal root-fibre undergoes a >- or | like divi- sion into an ascending and a descending limb, which assume a longitudinal course and pass upward and downward in the cord for a variable distance, the descending limb being usually the shorter. During their course from both, but particularly from the descending limb and from the proximal part of the ascending fibre, collateral branches are given off which bend sharply FIG. 894. inward and pass horizontally into the gray matter to end chiefly in relation with the neurones of the posterior horn, from which cells secondary paths arise. Not only the collaterals, but also the main stem-fibres of the descending and shorter ascending limbs end in the manner just described. In addi- tion to the short collaterals destined for the cells of the dorsal horn, others, the ventral reflex collaterals, pursue a sigmoid course, traversing the substantia gelatinosa Rolandi and the remaining parts of the posterior horn and the intermediate gray matter, to end in arborizations around the radicular cells of the anterior horn, and thus complete important reflex arcs, by which impulses transmitted through the dorsal roots directly impress the motor neurones. The latter are usually of the same side, but some collaterals cross by way of the anterior commissure to terminate in relation with the anterior horn cells of the opposite side. It is probable that a considerable number of such anterior horn reflex collaterals are given off from the fibres that ascend in the long tracts of the posterior column to the medulla oblongata. With possibly the exception of certain fibres which pass directly to the cerebellum (Hoche), all the sensory root-fibres (axones of neurones of the I order) end around the neurones situated either within the gray matter of the spinal cord or within the nuclei of the medulla ; thence the impressions are conveyed by the axones of these neurones of the II order to higher centers, to be taken up, in turn, by neurones of the III or even higher order, in the sequence of the chain required to complete the path for the conduction and distribution of the impulse. The most important groups of the collaterals and stem-fibres of the posterior roots are: 1. The long ascending tracts passing chiefly to the nuclei of the medulla. 2. The fibres passing to the cells of the column of Clarke. 3. The collaterals passing to the anterior horn cells. 4. The fibres entering the posterior horn from the tract of Burdach and of Lissauer to end about the neurones of the II order situated within the gray inattcr of the posterior horn and the intermediate gray matter. The direct ascending posterior tract includes the dorsal root-fibres that pass uninterruptedly upward within the posterior column as far as the nuclei of the medulla. On entering the cord they lie at first within the tract of Burdach, but in their ascent are gradually displaced medianly and dorsally by the continued addition of other root-fibres from the succeeding higher nerves. In consequence, in cross Diagram showing division of posterior root-fibres into ascending and descending branches; long fibre sends collaterals to anterior root cells ; other fibres end at different levels around cells in gray matter of posterior horn ; S. G., spinal ganglion. WHITE MATTER OF THE SPINAL CORD. 1041 sections of the cord in the cervical region the long fibres entering by the lower nerve-roots occupy the inner part of Coil's column, but are excluded from the median septum, except behind, by a narrow hemielliptical area, which with its mate of the opposite side forms the oval field of Flechsig. The fibres entering by the lower thoracic nerves lie more laterally, while those entering by the upper thoracic and cervical nerves appropriate the adjoining part of Burdach's tract, the lateral area of which, next the posterior horn, is occupied chiefly by the posterior root-fibres. It must be understood that while in a general way the fibres of the long ascending tracts have the disposition just indicated, they are so intertwined and mingled with the strands passing to and from the gray matter that the definite outlines of their conventional area, as represented in diagrams, are wanting. Collectively the fibres composing this tract are of medium or FIG. 895. small size, but acquire their medullary coat .-^r---,-'^~ very early, myelination beginning about the s^f^?^ l^R^fe* fourth foetal month, although not completed - %r S.\ until the ninth (Bechterew). . '''- % ^\ The termination of the long ascend- ing fibres is chiefly in relation with the neurones within the lower part of the medulla the fibres of Coil's tract end- ing about the cells of the nucleus gracilis and those of Burdach's tract about the cells of the nucleus cuneatus. From these stations paths of the II order convey the impulses to the cerebel- lum, by way of the inferior cerebellar peduncle, and to the higher sensory centres by way of the mesial fillet, as later described (page 1115). Whether certain of the component fibres of these ascending tracts are directly continued to the cerebellum, and perhaps to the mesial fillet, without undergoing inter- ruption in the nuclei of the medulla is still uncertain, although supported by the statements of Hoche, Kolliker, Solder and others. The root-fibres passing to Clarke's column occupy the middle and median part of Burdach's tract, mingled with those of the long ascending paths. After cours- ing longitudinally, usually for some distance, within the posterior column, they bend outward, and, sweeping in graceful curves, enter the gray matter to end about Clarke's cells. It is noteworthy that the level at which they end is often considerably higher than that at which the root-fibres enter the cord, an arrangement which explains the fact that lesions of the lowermost of these strands may be followed as ascending degenerations into the thoracic region (Mayer). On entering the gray matter the terminal arborization of a single root-fibre usually ends in relation with several neurones of Clarke's column (Lenhossek). The important sensory path of the II order, known as the direct cerebellar tract (page 1044), arises as the axones of these neurones. The anterior reflex fibres to the ventral horn are all collaterals, not continu- ations of the stem-fibres, far the greater part of which come from the fibres of the Hong ascending posterior tract. These collaterals penetrate the gray matter princi- pally at the median border of the head of the posterior horn, behind Clarke's column, but partly also through the substantia Rolandi, and thence pass ventrally or ventro-laterally, with a slightly curved or sigmoid course, towards the anterior horn. As they enter the latter, the collaterals diverge more and more and are distributed to the various groups of the anterior horn cells, chiefly in relation with the lateral groups of radicular cells from which the ventral root-fibres arise ; they thus establish direct reflex paths by which sensory impulses conveyed by the posterior root-fibres impress the motor neurones, while, at the same time, these impulses are transmitted 66 Section of spinal cord at level of second cervical seg- ment; formatio reticularis fills bay between posterior and anterior cornua; substantia gelatmosa caps apex of pos- terior cornu. Drawn from Weigert-Pal preparation made by Professor Spiller. X 6. 1042 HUMAN ANATOMY. FIG. 896. Section of spinal cord at level of sixth cervical segment; anterior cornua are very broad ; obliquely cut bundles of posterior root-fibres lie in postero-lateral sulcus. Preparation by Professor Spiller. X 6. to higher levels by the ascending stem-fibres. Although the anterior reflex collat- erals are, for the most part, in relation with the cells of the same side, it is probable that some cross by way of the posterior commissure, and possibly also by the anterior bridge, to the opposite ventral horn cells. It is doubtful, on the other hand, whether either stem-fibres or collaterals of the posterior roots pass directly to the anterior column either of the. same or opposite sides (Ziehen). The root-fibres passing to the posterior horn include those which pene- trate the substantia Rolandi, either as collaterals or stem-fibres of Burdach's or of Lissauer's tracts, to end about the neurones within the Rolandic substance or within the head of the pos- terior horn. Their longitudi- nal course within Burdach's tract is ordinarily short ; they then bend horizontally and enter the gray matter of the posterior horn, within which they soon terminate in end-arborizations around the neurones of the II order. Some fibres, however, do not undergo T-division until after entering the posterior horn, where, within the Ro- landic substance or caput cornu, they then bifurcate, in some cases the ascending limbs pursuing a vertical course within the gray matter, particularly of the caput cornu, for some distance before ending about the head-cells of the posterior horn. The tract of Lissauer, or marginal zone, situated immediately behind the apex of the dorsal horn, receives the lateral group of the posterior root-fibres. These are all of unusually small size and, after a short longitudinal course in which the descending limbs predominate, they turn horizontally and, both as collaterals and stem-fibres, penetrate the substantia Rolandi, about whose cells and those of the caput cornu they end. From the foregoing description, it is evident that the dorsal root-fibres destined for the posterior horn terminate in relation with neurones of the II order represented chiefly by the cells of the substantia gelatinosa Rolandi, including the marginal cells, and the inner cells of the caput cornu. The secondary or endogenous tracts of the posterior column arise as axones from the neurones of the II order (the marginal cells, the cells of the substantia Rolandi and the head- cells) situated within the posterior horn and include ascending and descending paths. The ascending secondary tract is composed of the axones derived from the posterior horn cells of the same and, by way of the posterior commissure, opposite side, which pass into tin- posterior column. In a general way, they occupy the ventral field, although sharing it with scattered strands of root-fibres and of descending endogenous fibres. The destination of tin- fibres of this ascending tract is uncertain, sonic fibres pursuing a short and others a longer course, within the posterior column before entering the gray matter at higher levels to end in relation with the posterior horn cells, or, perhaps, in some cases, with the neurones within the nuclei of the medulla (Rothmann). The descending secondary tracts, as shown by degenerations following lesions involving the posterior column, occupy varying but fairly well differentiated areas. In the cervical and upper thoracic cord they are collected into the comma bundle of Scluilt/e, which extends from near the neck of the posterior horn dorsal ly along the median margin of Hurdach's tract. In the lower thoracic and lumbar cord they form an elongated half-ellipse along the posterior median septum which, with the corresponding bundle of the Opposite side, produces the oval field of Flechsig. Still lower, in the sacral cord, they lie at the junction of the median septum and the posterior surface of the cord as the medio-dorsal triangular bundle of C.ombault and Philippe. Additional descending endogenous fibres are scattered in the ventral field. It is WHITE MATTER OF THE SPINAL CORD. 1043 likely that these areas represent the principal aggregations of the downward coursing limbs of the axones, after their T-like branching, derived from the posterior horn cells of the same and opposite sides. In the cervical region these axones are col- FIG. 897. lected into bundles which ap- pear as the comma tract ; in the lower thoracic cord these are replaced by, without being directly continuous with, those forming the oval field, and these in turn by the axones of the triangular bundle. No one of these fields is exclusively devoted to the descending limbs of endogenous fibres, since in all the presence of exogenous posterior root- fibres has been demonstrated. The Fibre - Tracts of the Lateral Column. These include : ( i ) the lateral pyramidal, (2) the direct cerebellar, (3) the ascending" antero-lateral Section of spinal cord at level of seventh cervical segment; anterior .v , cornua are less robust ; root-zone is seen just behind Lissauer's tract. X 6. and (4) the lateral ground- Preparation by Professor Spiller. bundle. The lateral or crossed pyramidal tract (fasciculus cerebrospinalis lateralis) forms the chief path by which motor impulses originating in the cerebral cortex are conveyed to the spinal cord. It stands in close relation with the direct pyramidal tract of the anterior column. Both are continuations of the conspicuous pyramidal paths of the medulla oblongata and may be followed upward through the ventral part of the medulla, the pons and the cerebral peduncles into the white matter of the cerebral hemispheres and on to the cortical gray matter where, in the motor areas bordering chiefly the Rolandic fissure, lie the nerve-cells from which the pyramidal fibres arise. These fibres, therefore, are the axones of cortical motor neurones and extend without interruption from the superficial gray matter of the cerebral hemi- spheres to various levels in the cord, constituting long descending (corticifugal) motor tracts. On reaching the lower part of the medulla, from 80-90 per cent, of the component fibres of each pyramid cross to the opposite side by way of the decussation of the pyramids (page 1065) and, entering the cord, descend as the lateral pyramidal tract; the remaining fibres (on an average, about 15 per cent.) pass downward into the ventral column of the cord as the direct pyramidal tract. After decussating, the crossed pyramidal tract passes outward to enter the lateral column of the cord, thereby exchanging its former median and superficial position for a deeper and more lateral one. Since its fibres are continually entering the gray matter to end about the radicular cells from which the anterior root-fibres of the spinal nerves arise, the tract progressively loses in size as it descends, until, at about the level of the fourth sacral nerve, it ceases to exist as a distinct strand, although continued by small scattered bundles of fibres as far as the origin of the coccygeal nerve. This diminution is not regular, since in the sacral and lumbar enlargements the loss is more marked than elsewhere, on account of the relations of the tract-fibres to the large motor limb- nerves. The relatioas, as well as size, of the lateral pyramidal tract vary at different levels. As seen in cross-sections of the upper thoracic region of the cord, the tract occupies an area of considerable size, that mesially lies against the posterior horn and laterally is in contact with the direct cerebellar tract, by which it is excluded from the periphery. In front, where its limits are less definite, the tract extends ventrally for a variable distance into the lateral column, but seldom overreaches the plane of the gray commissure. With the diminution and disappear- ance of the direct cerebellar tract within the lower portions of the cord, the pyramidal field approaches and finally reaches the surface, which relation it retains as it grows smaller, the 1044 HUMAN ANATOMY. FIG. 898. reduction affecting the more deeply placed fibres. In consequence of these variations, the form of the pyramidal tract in cross-section changes from wedge-shape to triangular, with the base lying at the periphery and the apex directed inward. During their descent the fibres of the pyramidal tract give off at different levels col- laterals, which bend horizontally inward and forward, enter the gray matter, and end in rela- tion with the anterior horn cells. A similar course is followed by the parent fibres on reach- ing the segment for which they are destined, the terminal part of the individual fibres sweeping in short curves through the intervening ground- bundle of the lateral column to gain the radicular cells around which they end. By means of its collaterals, each pyramidal fibre establishes rela- tion with several cord-segments. The fibres of this tract are relatively tardy in acquiring their medullary coat, which process does not begin until the last month of fcetal life and is not com- pleted until after the second year. Section of spinal cord at level of sixth thoracic segment ; slender posterior cornua covered with sub- stantia gelatinosa ; postero-lateral angle marks greatest Preparation b width of anterior cornu. fessor Spiller. X 6. jy Pro- The direct cerebellar tract (fas- ciculus cerebellospinalis), is an important ascending path of the second order that establishes communication between the reception sensory cord-nucleus formed by Clarke's cells and the cerebellum. In cross-sections of the thoracic region, the tract forms a superficial flattened comet-shaped field that occupies the dorsal half of the lateral column, extending from the apex of the posterior horn forward along the periphery of the cord, to the outer side of the lateral pyramidal tract, to about the anterior plane of the gray commissure. Its ventral end, particularly in the lower cervical region, is broadest and projects somewhat into the lateral column in advance of the lateral pyramidal field. Although as a compact strand the direct cerebellar tract begins at the tenth thoracic segment, it is represented by isolated fibres in the luinbo- sacral region. The fibres collectively are large and become medullated about the sixth foetal month (Bechterew). In a general way the fibres having the longest course occupy the dorsal part of the tract and those having the shortest the ventral (Flatau). Arising as the axones of the cells of Clarke's column, the components of the tract pass in curves almost horizontally outward through the gray matter and lateral column to the peripheral field, on gaining which they bend sharply brainward and ascend without interruption to the medulla. Their further course includes the pas- sage through the dorso-lateral field of the medulla as far as the inferior cerebellar peduncle, by which the fibres reach the cerebellum to end in relation with the superior worm, on, probably, both the same and the opposite sides. The tract of Gowers (fasciculus antcrolateralis superficialis) constitutes another pathway of the II order, which connects the cord with the cerebellum and probably also establishes relations with the cerebrum. In cross-sections the tract appears somewhat uncertainly defined owing to the intermingling of its fibres with those of adjoining strands, but in the main it includes a superficial crescentic field that touches the direct cerebellar and lateral pyramidal tracts behind, extends along the margin of the cord for a variable distance, and usually ends in front in the vicinity of the ventral nerve-roots. The inner boundary, separating the tract in question from the lateral ground-bundle, lacks in sharpness and is overlaid by the Adjoining strands. Below, the tract appears about the middle of the lumbar region and continues throughout the remainder of the cord. As Gowers' tract ascends, it fails to show the considerable increase in size that might be expected in view of the continual additions that it receives. In explanation of this, the probable mingling of some of its fibres with those of the direct cerebellar tract, rather than their ending in the cord, seems the most plausible (/it-hen). The exact origin of the constituents of Gowers' tract is still uncertain, but it is very likely that its libres are chiefly the axones of the neurones (marginal and inner cells) situated within the posterior horn, partly .from the same and partly from the : WHITE MATTER OF THE SPINAL CORD. 1045 opposite sides, with contributions, possibly, from the cells of the intermediate gray matter. After traversing the cord, the lateral field of the medulla, and the tegmental portion of the pons, the tract ascends the T-, i ... 1-1 r r IG. oQQ. ^ brain stem to the vicinity of the inferior cor- pora quadrigemina. Here the major part of ;- ^Mlii. the fibres turn backward and, by way of the superior cerebellar peduncle and the superior medullary velum, reach the cerebellum to .'. \ V end mostly, in the superior" worm, partly on the same side and partly crossed (Hoche). Possibly a part of the cerebellar contingent may share the path of the direct cerebellar tract and in this way reach the cerebellum by its inferior peduncle (Ziehen). It is probable that all fibres from Gowers' tract do not pass to the cerebellum, but that some continue upward to terminate in relation with the neurones of the superior corpora quadri- .. , s ? cti ? n of s P' nal cord at level of lower part of ... . f ~, nun lumbar segment ; gray matter relatively large gemma and OI the OptlC thalamUS. 1 he in amount ; anterior cornua bulky. Preparation by fibres of the tract acquire the medullary coat about the beginning of the eighth month of foetal life (Bechterew). The lateral ground-bundle (fasciculus lateralis proprius) of Flechsig includes the remainder of the lateral column. Much uncertainty prevails as to its detailed paths, but beyond question the composition of the ground-bundle is very complex and comprises a number of long exogenous paths that descend from the brain, as well as one long ascending and many shorter endogenous strands, both ascending and descending. These short tracts occupy chiefly the central parts of the lateral column and, in a general way, lie close to the gray matter, within an area between the ante- rior and posterior horns, known as the boundary zone. They are, however, not limited to this field, as not a few of their fibres lie scattered among the longer exogenous tracts occupying the more lateral portions of the ground-bundle. One long endogenous path, the spino-thalamic tract, is of unusual importance since it estab- lishes a direct sensory link between the cord and higher centres. This tract arises from the cells of the posterior horn of the opposite side, the axones crossing in the anterior commissure to pursue a course brainward within the antero-lateral ground-bundle. Although the fibres of this tract are scattered and not collected into a compact strand, their chief location is just medial to Gowers' tract. Associated with the fibres destined for the optic thalamus are others (tractus spino-tectalis) that end in the region of the corpora quadrigemina. The short endogenous tracts include both ascending and descending fibres which arise as the axones chiefly of the marginal and inner cells of the posterior horn, some coming from the opposite side by way of the posterior intracentral commissure. FIG. 900. Entering the lateral column the axones undergo T-like division with ascending and descending limbs. The former pass upward for a distance that usually includes only from one to three segments, then bend inward and enter the gray matter to end probably in relation with other posterior horn cells. The down- wardly directed limbs form the descending endogenous fibres, which, in addition to occupying the boundary zone are also scattered among the longer tracts of the ground-bundle. After a relatively long course, they enter the gray matter to end probably in relation with the anterior horn cells. They are, therefore, regarded as establishing reflex-paths. Since these endogenous strands link together various levels of the cord, they Seciton of spinal cord at level are often collectively termed intersegmental association fibres. c^n h ua d ^th ra S ubSi a S'inosn The ^S^ous tracts of the lateral ground-bundle are closely are relatively bulky. Preparation related with those found in the ground-bundle of the anterior by Professor Spiller. ) column and what may be said of the former largely applies to the latter. Notwithstanding the study that these tracts have received, much uncertainty exists as to their exact origin and termination ; it may be stated in a general way, however, that they bring the higher sensory and coordinating centres into relation with the spinal cord and constitute, therefore, descending paths other than the HUMAN ANATOMY. FIG. 901. pyramidal tracts. Among those whose existence within the antero-lateral ground-bundle may be considered as established, or at least probable, are the following: 1. Rubro-spinal fibres from the cells of the red nucleus within the cerebral peduncles. 2. Tecto-spinal fibres from the cells of the anterior corpora quadrigemina. 3. Vestibulo-spinal fibres from the cells of the lateral vestibular (Deiters') nucleus. 4. Medullo-spinal fibres from the cells of the formatio reticularis, arcuate and lateral nuclei. 5. Olivo-spinal fibres from the cells of the inferior olivary nucleus. Of these strands, those from the red nucleus, corpora quadrigemina, and vestibular nucleus, descend chiefly within the lateral ground-bundle, whilst those from the medulla are particularly within the anterior ground-bundle. Although the latter includes t ne greater part of the descending cerebello-rubro-spinal fibres in the narrow peripheral sulco-marginal zone of Marie, other fibres are probably distributed within the lateral column in front of the direct pyramidal tract. These descending indirect cerebellar fibres are often collectively known as the tract of Marchi-Lowenthal. For the most part the exogenous strands are so intermingled and scattered that they are without definite outlines; an exception to this is presented by the olivary fibres, which are sometimes seen as a fairly distinct triangular bundle, J ust behind the anterior root-fibres at the periphery of the cord, known as Helweg's tract. Concerning the exact ending of these descending paths little is known, but it is reasonable to assume that they terminate at various levels in relation with the ventral horn cells which are thus brought under the coordinating influence of the higher centres. Section of spinal cord at level of fifth sacral segment ; anterior cornua small and inconspicuous. Prepara- tion by Professor Spiller. X 8. FIG. 902. - n The Fibre-Tracts of the Anterior Column. According to the simplest classification the anterior column includes two subdivisions : ( i ) the anterior pyra- midal tract and (2) the anterior ground-bundle. The anterior pyramidal tract (fasciculus cerebrospinalis anterior), also called the uncrossed or direct pyramidal tract, stands in complemental relation with the lat- eral pyramidal fasciculus, being composed of the pyramidal fibres that do not undergo decussation in the medulla oblongata. It usually contains about 15 per cent, of the pyramidal fibres, but may include a much larger proportion ; on the other hand, it may be entirely suppressed when, as rarely happens, total crossing occurs. The direct pyramidal tract occupies the inner part of the anterior column, forming a narrow area along the median fissure that extends from the white commis- sure behind to near the ventral margin of the cord. Ordinarily the tract ends below about the middle of the thoracic cord, but in exceptional cases, when a larger pro- portion of the pyramidal fibres than usual is included in the tract, it may extend as far as the middle of the lumbar enlargement, with corres- ponding increase in its cross area. If, on the other hand, the number of uncrossed fibres is unusually small, the tract may reach only as far as the cervical enlargement, with a reduction of its sagittal dimension. Although often spoken of as the ' ' uncrossed ' ' pyramidal tract, this characteristic applies only to the relation of the fibres at the decussation in the medulla, since in their downward journey in the cord the great majority of the fibres traverse the anterior white commissure at appropriate levels to end in arborizations about the ventral root-cells of the anterior horn of the opposite side. It is highly probable, however, that some fibres do not undergo decussation, but terminate about the radicular cells of the same side. The anterior ground-bundle (fasciculus anterior proprius), following the divi- sion of Flechsig, includes the remainder of the ventral column. In front, when- its lateral limits are uncertain, it is continuous with the ground-bundle of the lateral col- umn, the two together being often with advantage regarded as constituting a single antero-lati nil tract. What has been said concerning the constitution of the lateral ground-bundle applies in the main to that of the anterior column, since, here as there, the region bordering the gray matter contains chiefly the short endogenous strands, while the more peripheral parts of the ground-bundle are occupied by the long exogenous paths, intermingled, however, with the longer intrinsic fibres. segment; differentiation of cor- WHITE MATTER OF THE SPINAL CORD. 1047 The endogenous fibres arise as the axones, chiefly of the inner cells of the posterior horn, as well as from the cells of the intermediate gray matter (Ziehen), and in great measure cross by way of the anterior white commissure to the opposite anterior column. After undergoing T-division, their upwardly directed limbs constitute the ascending paths and those coursing downward the descending ones. While both sets of fibres for the most part pursue only a short path, that of the descending limbs is usually the longer, the fibres entering the gray matter to end in relation with the anterior horn cells of lower levels. They are, therefore, regarded as secondary reflex paths. The termination of the ascending limbs is uncertain, but probably is within the gray matter of the posterior horn. The exogenous tracts of the anterior ground-bundle, have been mentioned in connection with those of the lateral column. The investigations of Lowenthal, Marchi, Bechterew, Thomas and others, support the presence within the anterior ground-bundle, also within the lateral column, of long efferent (cortifugal) paths that arise, at least indirectly, from neurones within the cerebellum, and end in relation to the anterior horn cells. These paths, collectively known as the descending cerebello-spinal tract, or tract of Marchi- Lowenthal, are of uncertain extent and outline, and more or less mingled with the constituents of other strands. In a general way the descending cerebello-spinal fibres occupy a narrow crescentic field that appropriates the periphery of the cord for a variable distance both mesially and laterally. In the anterior column the tract includes the anterior marginal bundle, probably from the nucleus fastigii of the cerebellum of the same and opposite side, and mesially mingles with fibres from the corpora quadrigemina as constituents of the visual reflex paths. The termination of these descending paths is assumed to be in relation with the anterior horn cells, which in this manner are brought under the influence of the higher coordinating and reflex centres. In recapitulation the chief fibre-tracts of the spinal cord may be grouped as follows^ I. Within the Posterior Column Ascending Paths : Direct ascending posterior root-fibres. Ascending endogenous fibres. Descending Paths : Descending posterior root-fibres. Descending endogenous fibres. II. Within the Lateral Column Ascending Paths : Direct cerebellar tract. Gowers' tract. Spino-thalamic tract. Short endogenous fibres. Descending Paths : Lateral pyramidal tract. Indefinite exogenous tracts (including the rubro-spinal, quadri- gemino-spinal, vestibulo-spinal, cerebello-spinal and olivo- spinal). Descending endogenous fibres. III. Within the Anterior Column Ascending Paths : Ascending endogenous fibres from posterior horn cells. Ascending endogenous fibres from anterior horn cells. Descending Paths : Direct pyramidal tract. Descending cerebello-spinal fibres. Tegmento-spinal fibres. Blood-Vessels of the Spinal Cord. The arteries supplying the cord are from many sources the vertebral, deep cervical, intercostal, lumbar, ilio-lumbar and lateral sacral of the two sides since the vascular net-work within the pia accompanies the nervous cylinder throughout its length. Above and within the skull, the verte- bral arteries give off the two anterior and the two posterior spinal arteries, of which the latter retain their independence and descend upon the dorso-lateral surface of the cord, one on each side, in front of the posterior nerve-roots. The two anterior spinal arteries, on the other hand, soon unite (somewhere above the level of the third cervical nerve) into a single trunk, which descends along the ventral surface of the cord, just in front of the anterior median fissure. 1048 II I'M AN ANATOMY. FIG. 903. Posterior sulcal Parasulcal f As these stems pass downward, they are joined and reinforced by the segmcntal spinal branches given off by the vertebral, intercostal, lumbar and lateral sacral arteries, which enter the spinal canal through the intervertebral foramina and, after piercing the dura and giving off small radicular brandies to the nerve-roots them- selves, divide into ventral and dorsal branches that follow the respective nerve-roots to the cord, where they join with the longitudinal trunks which they thus assist in maintaining. By the junction of horizontal branches arising from these arteries, a series of complete annular anastomoses is formed around the cord, which is still further enclosed by additional vertical stems resulting from the union of upward and downward coursing twigs. In this manner, in addition to the large single anterior spinal trunk (tractus arteriosus spinalis anterior) in the mid-line in front and the paired postero-lateral trunk (tractus arteriosus postero-lateralis spinalis") just in advance of the dorsal nerve-roots, smaller longitudinal arteries are formed at the side and in the vicinity of the nerve-roots. From the arterial net- work within the pia, the nervous tissue is supplied by pene- trating twigs that enter the surface of the cord at various points. The gray matter receives its principal blood-supply from the series of anterior Jissural arteries, over two hundred in number, which pass from the anterior spinal trunk backward within the median fissure to its bottom and there divide into right and left branches, which traverse the anterior white commissure to gain the gray matter on either side of the central canal. These vessels, the sulco-mar- y Y /Postero-lateral ginal arteries, divide into ascending o ^ VV.U ; H X Penetrating and descending branches that provide for the entire gray matter with the exception of the most peripheral zone. The latter, together with the white matter, receives its supply from the penetrating branches that come from the surrounding intrapial trunks and enter the surface of the cord. Unpaired horizontal twigs, the pos- terior sulcal arteries, follow the posterior median septum at different levels for some distance, but before reaching the posterior commissure usually break up into terminal ramifi- cations, some of which pass to the gray matter of the posterior horns. Communications exist between the penetrating twigs of the radicular arteries and the lateral branches of tin- anterior fissural. After entering the nervous tissue, however, each artery provides the sole supply for some definite part of the cord ; they are therefore ' ' end-arteries, a fact which explains the extensive and elaborate system of vessels necessary to maintain the nutrition of the cord. The plexiform veins within the spinal pia are formed by the union of the small radicles that collect the blood from the intraspinal capillaries and, after an independ- ent course similar to that of the arteries but not accompanying them, emerge at the surface of the cord. From the venous net-work within the pia six main longitudinal trunks are differentiated. These are : the unpaired anterior median rein, in front of the corresponding fissure ; the paired antero-latcral reins, just In-hind the ventral nerve-roots these two sets receiving the tributaries emerging from the median fissure and in the vicinity of the anterior root-fibres ; the unpaired posterior median vein, behind in the mid-line ; and the paired postero-lateral reins, just behind the dorsal roots. The blood is conveyed from these intrapial channels chiefly by the radicular veins, following the nerve-roots, which communicate with or terminate in the anterior and posterior longitudinal spinal veins within the vertebral canal, from which the Penetrating artery- Anterior fissural Anterior Ascending branch spinal artery Part of transverse section of injected spinal cord showing vascular supply of white and gray matter. X 10. WHITE MATTER OF THE SPINAL CORD. 1049 intervertebral efferents carry the blood into the vertebral, intercostal, lumbar and lateral sacral veins. A part of the blood from the intrapial plexus is conducted upward by the anterior and posterior median veins into the venous net-work covering the pons and thence into the lower dural sinuses. Definite lymphatic vessels within the spinal cord are unknown. Development of the Spinal Cord. A sketch of the general histogenetic processes leading to the differentiation of the neurones and the neuroglia has been given (page 1009) ; it remains, therefore, to consider here the changes in the neural tube by which the definite spinal cord is evolved. From the time of its closure, probably about the end of the second week of foetal life, the neural tube presents three regions : the relatively thick lateral walls and the thin ven- tral and dorsal intervening bridges, the floor- and roof -plates, that in front and behind complete the boundaries of the canal in the mid-line. By the fifth week the lateral walls exhibit a distinct differentiation into three zones the inner ependymal layer, the middle nuclear layer and the outer marginal layer, surrounded by the external limiting membrane. In contrast to the other two, the marginal zone is almost devoid of nuclei and, beyond affording support and perhaps assisting in providing a medullary coat, plays a passive role in the production of the nervous elements. By this time the former general oval contour of the developing cord, as seen in cross-sec- tions, has become modified by the conspicuous thickening of the antero-lateral area of the nuclear layer into a prominent mass on each side, whereby the reticular marginal layer is pushed out- FIG. 904. Roof-plate FIG. 905. Roof-plate Dorsal zone Ventral root-fibres Neuroblasts * Floor-plate Developing; spinal cord of about four weeks. X 100. (f/is.) Floor-plate Ventral root-fibres Developing spinal cord of about five weeks. X 60. (His.) ward with corresponding increase in the width of the entire ventral part of the cord, which is now broadest in front. Within this thickened ventro-lateral part of the nuclear layer, later the anterior horn of gray matter, as early as the fourth week young neurones are seen from which axones grow outward through the marginal zone and pierce the external limiting membrane as the representatives of the anterior root-fibres of the spinal nerves. Postero-laterally the thin nuclear layer is covered by a somewhat projecting thickened area within the marginal layer, known as the oval bundle, whose presence is due to the ingrowth of the developing dorsal root- fibres from the sensory neurones of the spinal ganglion, which process begins as early as the end of the fourth week (His). Associated with these changes, the lumen of the cord becomes heart-shaped in consequence of a conspicuous local increase in its transverse diameter, with corresponding bulging of the lateral wall. In this manner a longitudinal furrow appears by which the side walls of the tube are differentiated into two tracts, the dorsal and the ventral zones (the alar and basal lamina? of His). This subdivision is of much importance, since in the cord-segment, and also with less certainty in the brain-segment of the neural tube, these tracts are definitely connected with the root-fibres of the spinal nerves, the dorsal zone with the sensory and the ventral zone with the motor roots. In advance of the floor-plate the ventrally protruding halves of the cord include a broad and shallow furrow which marks the position of the anterior median fissure. During the sixth week the form of the tube-lumen becomes further modified by the elongation and narrow- 1050 HUMAN ANATOMY. ing of the dorsal part of the canal in consequence of the approximation of its walls, which in the course of the seventh week is closer and, by the end of the second month is completed by the meeting and fusion of the adjacent inner layers, with obliteration of the intervening cleft and the production of the posterior median septum in its place. Since the partition is formed by the union of the inner (ependymal) layers, it is probable that the septum is to be regarded as essentially neurogliar in origin and character. It must be remembered, however, that a certain amount of mesoblastic tissue may be later introduced in company with the blood-vessels which subsequently invade the septum. The remaining and unclosed part of the lumen for a time resembles in outline the conventional spade of the playing card, with the stem directed ventrally ; but later gradually diminishes in size and acquires the contour of the definite central canal. During these alterations in the extent and form of its lumen, the gray matter of the develop- ing cord markedly increases, especially behind where the posterior horn appears as a projection beneath the broadening mass of the ingrowing dorsal root-fibres. As the posterior horn becomes better defined, the root-bundle becomes meso-laterally displaced, lying behind the horn, and then constitutes the tract of Burdach. Coil's tract is formed somewhat later and at about the third month appears as a narrow wedge-shaped area that is introduced between the mid-line and Burdach' s tract. Towards the end of the second month, the anterior white commissure is indicated by the oblique transverse ingrowth of axones into the most ventral part of the floor- plate as they make their way to the opposite side. Meanwhile the anterior median fissure has FIG. 906. FIG. 907. Coil's tract Burdach's tract Lateral column Anterior column Developing spinal cord of about seven and one-half weeks. X 44- (His.) Anterior median fissure Anterior Root-fibres with pial process column Developing spinal cord of about three months. X 30. ( His. ) become deeper and narrower in consequence of the increased bulk of medio-ventral parts of the cord. As the fissure is thus differentiated the process of mesoblastic tissue, which from the earliest suggestion of the groove occupies the depression, is correspondingly elongated and affords a passage for the blood-vessels destined for the nutrition of the interior of the cord. Until the third month the gray matter, derived from the nuclear layer, is much more voluminous than the surrounding marginal layer, which, so far as the contribution of nervous elements is concerned, is passive, since its conversion into the white matter depends upon the ingrowth of axones from the neurones situated either within or outside the cord. The development of the individual fibre-tracts includes two stages, between the comple- tion of which a considerable, and sometimes a long, period intervenes. The first marks the invasion of the supporting tissue of the marginal zone by the ingrowing axones as naked axis- cylinders ; the second witnesses the clothing of these fibres with myelin. The period between the appearance of the tract and the development of the medullary coat is variable. In some cases, as in the great cerebro-spinal motor paths, although tin- fibres grow into the cord during the fifth month of fcrtal life, myelination does not begin until shortly before birth and is not completed until after the second year. In other cases, as in the direct cerebellar, a period of three months, from the third to the sixth, elapses. It is probable that the acquisition of the medullary coat commences before the functional activity of the fibres begins, although such stimulation undoubtedly assists; further myelination proceeds gradually along the course of the fibres and in the direction of conduction. PRACTICAL CONSIDERATIONS : SPINAL CORD. 1051 Based on the observations of Flechsig, His, Bechterew, and others, the time of the appearance and of the development of the medullary coat of some of the fibres within the spinal cord may be given. Fibres of Appear Myelinate Anterior root about 4th week during 5th month Burdach's tract during 4th week end of 6th month Coil's tract about gth week beginning of yth month Pyramidal tracts end of 5th month gth month to 2nd year Direct cerebellar tract beginning of 3rd month about 6th month Gowers' tract during 4th month during 6th month The presence of the sinus terminalis (page 1030) in the cord at birth depends partly upon the persistence of the lumen of the central canal at the lower end of the conus medullaris and partly upon a proliferation of the wall-cells of the subjacent segment, followed by secondary dilatation shortly before birth. During the early weeks of development, the neural tube extends to the lowermost limits of the series of somites ; but after differentiation of the root-fibres begins, the segment of the cord below the level of origin of the first coccygeal nerves is marked by feeble proliferation, the effects of which are soon manifest in the rudimentary condition of the caudal end of the cord. With the subsequent development of the other regions, this histological contrast becomes more evident, to which is soon added the conspicuous attenuation caused by the attachment of the lower end of the cord to the caudal pole of the spine, which elongates with greater rapidity than the contained nervous cylinder. In this manner the lowest segment of the cord, with its mesoblastic envelope, is converted into the delicate thread-like filum terminate, within whose upper half are found the remains of the rudimentary nervous tissue. PRACTICAL CONSIDERATIONS : SPINAL CORD. Congenital Errors in Development. The spinal cord may be absent (amyelia), or it may be defective in a certain portion (ateomyelia). In such conditions, however, the patient cannot live. The cord maybe double from bifurcation {diplomyelia). A spina bifida is a congenital condition due to a deficiency in the vertebrae, almost always of the laminae and spinous processes. There is usually a protrusion of the contents of the spinal canal, although in some cases there is no protrusion, and in others the vertebral canal, or even the central canal of the cord may be open to the surface. Three varieties of tumors are described according to their contents. If the meninges ' only protrude from the canal in the form of a sac containing cerebro- spinal fluid, it is called a meningocele ; if the sac contains a portion of the cord also it is called a meningo-myelocele. In the third variety, syringo-myelocele, the cavity of the tumor is found to consist either of the dilated canal of the cord, so that the thinned-out substance of the cord is in the wall of the sac, or of a cavity in the cord tissue itself. This is the least common of the three forms. In the meningo-myelocele, which is the most common form, the cord becomes flattened out and attached to the posterior wall of the sac, but still has its central canal intact. The spinal nerves cross the sac to their corresponding intervertebral foramina. In this and in the syringo-myelocele there is frequently some degree of paralysis in the parts below from disturbance of the cord at the seat of the tumor. The most common seat of the defect is in the lumbo-sacral region. It is rare in other parts of the spine. Therefore, the bowels, bladder, and lower extremities are the parts most frequently affected. If the lesion is confined to the lower part of the sacral region, the extremities usually escape. Paralytic talipes is comparatively common. There is no sharp line of demarcation between the medulla oblongata and the cord. The beginning of the latter is variously given as at the origin of the first cervical nerve, the lower margin of the foramen magnum, or the decussation of the pyramids, the last being the more generally accepted. Since in the adult, the spinal cord ends below usually at the level of the disc between the first and second lumbar vertebrae, injuries of the spine below the second lumbar vertebra do not involve the cord. The membranes of the cord, however, containing cerebro-spinal fluid extend as far as the second or third s.acral vertebra, so that at this level injuries with infection may cause fatal meningitis. 1052 II I'M AN ANATOMY. The bony canal is lined with periosteum, unlike the cranium, in which the external layer of the dura mater serves that purpose. The spinal dura is separated from the posterior common ligament, the ligamenta subflava, and the periosteum by a fatty areolar tissue containing a plexus of veins. Extensive extradural hemorrhage may, therefore, occur without serious pressure on the cord. The blood tends to sink by gravity, and later may produce symptoms of compression. The dura is thick and strong and offers considerable resistance to the invasion of disease from with- out, even to tuberculosis with caries of the vertebrae, or to malignant tumors arising within the vertebrae. Infections outside the spinal column, as in abscess of the back, or bed sores, may extend along the communicating veins, giving rise to extradural abscess and perhaps to extensive meningitis. The spinal cord, surrounded by cerebro-spinal fluid, hangs loosely within the dura, being attached to it only by the roots of the spinal nerves which receive invest- ments from the dura as they pass outward, by the ligamenta denticulata, and by the delicate fibres of arachnoid tissue extending from the pia to the dura. The cord is, therefore, not frequently injured from external violence. The numerous articulations of the vertebrae and the elasticity of the ligaments and of the intervertebral discs permit the distribution of much of the force applied to the spine before it reaches the cord. The greater part of the cerebro-spinal fluid is contained in the subarachnoid space, which communicates freely with the same space in the cranium, and is con- tinuous with the ventricular fluid through the foramen of Majendie. The cord is exposed to the danger of penetration by sharp instruments only from behind, but even here the overlapping of the laminae and spinous processes offers an excellent protection. This protection is largely lacking above and below the atlas, and the risk there from such wounds is correspondingly greater. At lower levels in order that the canal may be reached, the vulnerating instrument must be directed in the line of the obliquity of the laminae, which will vary in the different portions of the spine, being greatest in the dorsal region. Conciission shaking with molecular disturbance and without obvious gross lesion of the cord, although more frequent than has been supposed, is rare because of (a) the arrangement of the different constituents of the vertebral column, which by means of its curves, the elastic intervertebral discs, its numerous joints, and the large amount of cancellous tissue in the vertebral bodies, is able to take up and distribute harmlessly forces of some degree of violence ; (<) the situation of the cord in the centre of the column, where, as the most frequent serious injuries to the spine are caused by extreme forward flexion, it is somewhat removed from danger in accordance with a law of mechanics that " when a beam, as of timber, is exposed to breakage and the force does not exceed the limits of the strength of the material, one division resists compression, another laceration of the particles, while the third, between the two, is in a negative condition" (Jacobson) ; (c) the suspension of the cord in the surrounding cerebro-spinal fluid ( ' ' like a caterpillar hung by a thread in a phial of water" Treves) by its thecal attachments and nerve-roots; (d} its connection above with the cerebellum, itself resting on an elastic "water-bed" which minimizes the transmission downward of violence applied to the cranium. Many of the cases reported as concussion are undoubtedly due to hemorrhage' or other gross lesions of the cord. Contusion of the cord may occur from sprains, as in forced flexion of the spine. The most frequent and most serious cases are those due to fracture-dislocations of the spine, the cord being more or less crushed between the upper and lower fragments. It is so delicate a structure that it may be thoroughly disorganized without evident injury to the membranes or alteration of its internal form. The paralysis of the parts below will be complete or partial according to whether the whole or only a part of the transverse section of the cord at the seat of injury is destroyed. Since when the lesion is complete everything supplied by the cord below tin- scat of the lesion i> paraly/.ed, the higher the injury to the cord the greater the gravity of the case. When the atlas or axis is fractured and displaced the vital centres in the medulla are in danger and death may result immediately. The phrenic nerves which arise chiefly from the four.th cervical segment, but partly from the third and fifth segments, are also paralyzed and respiration ceases. PRACTICAL CONSIDERATIONS : SPINAL CORD. 1053 In fracture-dislocations of the spine it is the body of the vertebra which is most frequently fractured, the ligaments yielding posteriorly and permitting the dislocation. The fractured edges of bone are, therefore, in front of the cord ; and, as the upper fragment passes forward, the anterior or motor portion of the cord is pressed and crushed against the sharp upper edge of the lower fragment. In partial transverse lesions of the cord the paralysis below the lesions affects, therefore, the motor columns of the cord more than the sensory columns which are in part posterior. The most frequent seat of fracture-dislocation of the spine is in the thoraco- lumbar region (page 145). Fortunately, it is this variety which offers the best prognosis, since the cord ends usually just below the lower border of the first lumbar vertebra, and the cauda equina being more movable and tougher than the cord itself, it can better evade the encroachment on the canal, although in spite of these facts, it is not infrequently injured in such lesions. The bodies of the lumbar vertebrae are the largest and most cancellous, the intervertebral discs the thickest and most elastic, so that crushing of them occurs with less tendency to invade the canal and injure the cord than in any other portion of the spine. In caries of the spine (Pott's disease) the lesion is situated in the bodies of the vertebrae, and therefore, in front of the cord. As the inflammatory exudate extends it will invade the spinal canal anteriorly, often producing an external pachymeningitis. The irritation and pressure resulting will again affect the motor portion of the cord, first producing a paralysis of motion in the parts below, varying in degree according to the amount of pressure on the cord. If sensation is impaired it is a later phenomenon and is due to greater pressure upon the cord, and in some cases to myelitis. The loss of motion is often the only effect produced. If the lower cervical region is involved by the lesion the phrenic nerves will escape paralysis, but the arms, trunk, bladder, rectum, and lower extremities will be affected. Since the intercostal and abdominal muscles are involved in the paralysis, breathing will be difficult and will depend upon the action of the diaphragm only. Thus as the lesion occurs at successively lower levels, the highest limits of the paralyzed area descend, and the expectation of life increases. In the cervical and thoraco-lumbar regions where the injuries to the spine and the cord are most frequent, are situated the two enlargements of the cord. The cervical begins at the fourth cervical vertebra, gradually reaches its largest diameter opposite the fifth and sixth vertebrae, and then gradually decreases to the first thoracic, where it merges into the thoracic portion of the cord. Only in the thoracic region does the circumference of the cord remain the same throughout. The lumbar enlargement is shorter than the cervical and begins opposite the tenth thoracic vertebra, gradually increases to the twelfth thoracic, after which it gradually decreases to the conus medullaris. The localization of lesions of the cord, producing symptoms of paralysis, will depend upon the height and extent of the paralyzed areas. It must be borne in mind that the nerve-roots arise from the cord usually at a level higher than the foramina through which they escape from the spinal canal. The first and second cervical nerve-roots pass out of the canal almost horizontally. The intraspinal course of the succeeding nerve-roots increases gradually in obliquity so that the spinous processes of the second, third and fourth vertebrae correspond approximately to the level of the third, fourth and fifth cervical nerve-roots. The seventh cervical spine corresponds to the first thoracic nerve-root. The spinous process of the fifth thoracic vertebra is on a level with the seventh thoracic nerve, and the spine of the tenth thoracic vertebra with the origin of the second lumbar nerve. The first lumbar nerve arises just below the ninth thoracic spine, the second lumbar nerve opposite the tenth thoracic spine, the third and fourth lumbar nerves opposite the eleventh spine, and the fifth lumbar and the first sacral nerves between the eleventh and twelfth thoracic spines. Only the spinous processes can be our surface guides, and it must be borne in mind that they are not always on the level of their corresponding vertebrae. Briefly, it may be said that the eight cervical nerves arise from the cord between the lower margin of the foramen magnum and the sixth cervical spine, the first six thoracic HUMAN ANATOMY. First cervical />/ vertebra Skull First thoracic vertebra First tlioracic spine nerves between the latter spine and the fourth thoracic, the lower six thoracic nerves between the fourth and ninth dorsal spines, the five lumbar nerves opposite the ninth, tenth and eleventh spines, and the five sacral nerves opposite the twelfth thoracic and the first lumbar spine. A convenient rule to locate the levels of origin of the nerve-roots, applicable to the prelumbar nerves, is given by Ziehen as follows : For the cervical nerves, subtract one from the number of the nerve, the remainder indicating the correspond- ing spinous process ; for the upper ( I-V) thoracic nerves subtract two ; for the lower (VI-XII) thoracic nerves subtract three. All the cer- vical nerves pass out through the intervertebral foramina above the vertebrae after which they are named, except the eighth cervical, which emerges between the seventh cer- vical and the first dorsal vertebrae. All the other spinal nerves escape below the vertebrae from which they are named. Since the nerve-roots pass a considerable distance down- ward within the spinal canal before leaving it, it follows that a lesion of the cord at a given level, as from a fracture-dislocation of the spine, may be associated with a paralysis of the nerve-roots passing out at or below that level, and arising from the cord at a higher point. This must be taken into account in determining the seat of the lesion, since when the nerve-roots are not involved the lesion will be as much higher than its corresponding inter- vertebral foramina (as indicated by the upper limits of the paralyzed area) as the length of the intraspinal course of the corresponding nerve- roots. Each root-cell in the anterior horn of gray matter is connected with a motor fibre, which passes out in the anterior root of a spinal nerve to its muscle. Motor impulses originating in the cortex of the brain, pass downward along the antero- lateral columns of the cord, chiefly in the lateral pyramidal tract. They first traverse the ganglion cells of the anterior horns before passing out in the anterior or motor roots to their destination. These ganglion cells constitute, at least functionally, the trophic centres for the muscles. Lesions of the anterior horns, therefore, besides causing First lumbar spine Sacrum First sacral vertebra Coccyx. Diagram, based on frozen section, showing relations of .uil spines <.t vertebrae to levels at which spinal IK-IMS li. .111 \ riti-lnal i anal. THE BRAIN. 1055 paralysis (polio-myelitis), will lead to atrophy of the corresponding muscles. The vasomotor centres are also in the anterior horns, probably in the intermedio-lateral tract. Sensory impulses pass to the posterior horns through the posterior roots, and some of them soon cross to the opposite side of the cord, others ascending in the posterior column. The lemniscus is probably the chief sensory tract in the medulla oblongata, pons, and cerebral peduncles. Every segment of the spinal cord contains centres for certain groups of muscles, and for reflex movements associated with them. A reflex begins in the stimulation of a sensory nerve. The impulse thus created passes to a centre in the cord and thence is transmitted to a motor nerve, thus producing a contraction of the muscle supplied by that nerve. The complete path of this impulse is called a reflex arc. The sensory impulse may be transmitted to different segments of the cord and thence out through the corresponding motor roots. Thus a complicated reflex arc is produced. It is to be assumed, however, that the impulse will take the shortest route, so that simple reflexes will have their reflex arc chiefly in those segments of the cord in which the posterior root enters. Each segment of the cord is connected with fibres from the brain to which must be ascribed the function of reflex inhibition. If the inhibitory fibres are irritated, the reflexes are impaired from stimulation of inhibition. If the conductivity of these fibres is destroyed, the reflexes are increased ; but if the reflex arc is broken at any point, the reflexes are lost. Among the most important of these are the skin and tendon reflexes. The centres for the bladder, rectum, and sexual apparatus, are located in the sacral segment of the spinal cord at and below the third sacral segment. They regulate the functions of these organs and are associated in some unknown way with the brain. (See mechanics of urination, page 1914). H&mato-rachis, or hemorrhage into the membranes of the cord (extramedullary hemorrhage), may result from an injury to the spinal column, as a fracture or a severe sprain. The bleeding may be from the plexus of veins between the dura and bony wall of the canal (most frequent), or from the vessels between the dura and the cord. In either case the symptoms will be much the same. There will be a sudden and severe pain in the region of the spine, diffused some distance from the seat of the in- jury, due to irritation of the meninges, and pain transferred along the distribution of the sensory nerves coming from the affected segments of the cord, accompanied by abnormal sensations, as tingling and hyperaesthesia. In the motor distribution there will be muscular spasm, or sometimes a persistent contraction of the muscles. Gen- eral convulsive movements, retention of urine, and, later, symptoms of paralysis may appear, but as a rule the latter is not complete. Hczrnato-myelia, or hemorrhage into the substance of the cord (intramedullary hemorrhage) from traumatism, usually occurs between the fourth cervical segment of the cord and the first dorsal (Thorburn), and is commonly due to forced flexion of the spine, which is most marked in this region, as in falls on the head and neck. The cord has been crushed in such accidents without fracture of the spine and with only temporary dislocation. The hemorrhage is usually chiefly in the gray matter and may be only punctate in size, or may be large enough to extend far into the white matter, or even outside the cord into the subarachnoid space. The symptoms usually appear immediately after the injury and are bilateral, suggesting a total transverse lesion. There will be much pain in the back, occasionally extending along the arms or around the thorax. Spasms, rigidity, and paralysis rapidly ensue, with loss of the reflexes in the segment of the cord involved. There may be the same dissociation of sensation as in syringomyelia when the hemorrhage is confined to the centre of the cord. THE BRAIN. The brain, or the encephalon, is the part of the cerebro-spinal axis that lies within the skull. It is produced by the differentiation of the cephalic segment of the neural tube. Although the brain is often of great relative bulk and high complexity, as in man and some other mammals, it must not be forgotten that the spinal cord is the 1056 HUMAN ANATOMY. fundamental and essential part of the nervous axis and that the degree to which the brain is developed is, in a sense, accidental and dependent upon the necessities of the animal in relation to the exercise of the higher nervous functions. In the lowest vertebrates, the fishes, in which association of the impressions received from the outer world is only feebly exercised, those parts of the brain rendering such functions possible, as the cerebral hemispheres, are very imperfectly represented. On the other hand, in man, in whom the capacity for the exercise of the higher nervous functions involving association is conspicuous, the antero-superior parts of the brain, the pallium, as the regions particularly concerned are called, are so enormously developed that the human brain is thereby distinguished from all others. Whether of low or high development, all brains are evolved from certain fundamental parts, the brain-vesicles, differentiated in the head-end of the embryonic neural canal ; the underlying conception of the brain, therefore, is that of a tube, bent and modified to a variable degree by the thickening, unequal growth and expansion of its walls. Even when most complex, as in man, the adult organ exhibits unmistakable evidences of subdivision corresponding more or less closely with the primary brain-vesicles, and contains spaces, the ventricles, that represent the modified lumen of these segments. FIG. 909. Orbital surface of frontal lobe Optic commissure Optic tract Cerebral peduncle Interpeduncular space Medulla Cerebellum Olfactory tract Stalk of pituitary body- Tuber cinereum Mammillary bodies Cerebral peduncle Temporal lobe Pons Cerebellum Occipital lobe Spinal cord Simplified drawing of brain as seen from below, showing relations of brain-stem to spinal cord and cerebrum. Preparatory to entering upon a description of the fully formed brain, it is desirable to consider briefly the broad plan according to which the organ is laid down and the general lines along which its evolution proceeds. Before doing so, however, it will l^e necessary to take a general survey of the relations of the several divisions composing the brain. Denuded of its investing membranes and the attached cranial nerves, and viewed from below (Fig. 909), the eneephalon is seen to consist of a median brain-stem, that interiorly is directly continuous with the spinal cord through tin- foramen magnum and above divides into two diverging arms that disappear within the lar^e overhang- ing mass of the cerebrum. The brain-stem includes three divisions, the inferior of which, the medulla obhngala, is the uninterrupted upward prolongation of the spinal cord and above is limited by the projecting lower border of the quadrilateral mass THE BRAIN. 1057 of the next division, the pons Varolii. Beyond the upper margin of the pons the brain-stem is represented by a third division that ventrally is separated by a deep recess into two diverging limbs, the cerebral peduncles^ or crura cerebri, to corre- spond with the halves or hemispheres of the cerebrum, each of which receives one of the crura and in this manner is connected with the lower levels of the cerebro- spinal axis. The greater part of the medulla and pons is covered dorsally by the cerebellum, whose large lateral expansions, or hemispheres, project on either side as conspicuous masses, distinguished by the closely set plications and intervening fissures that mark their surface. Of the five component parts of the brain medulla, pons, cerebral peduncles, cerebrum, and cerebellum the last two are coated with the cortical gray matter, in which, broadly speaking, are situated the neurones that constitute the end-stations for the sensory impulses conveyed by the various corticipetal paths and the centres controlling the lower-lying nuclei of the motor nerves. The brain-stem, on the other hand, whilst containing numerous stations for the reception and distribution of sensory impulses, is primarily the great pathway by which the cerebrum and the cerebellum are connected with each other and with the spinal cord. Viewed in a mesial sagittal section (Fig. 910), each of these divisions is seen to be related to some part of the system of communicating spaces that, as the lateral and third ventricles, the aqueduct of Sylvius and the fourth ventricle, extend from the cerebral hemispheres above, through the brain-stem and beneath the cerebellum, to the central canal of the spinal cord below. Since the lateral ventricles are two in number, in correspondence with the cerebral hemispheres in which they lie, their position is lateral to the mid-plane and hence only one of the openings, the foramina of Monroe, by which they communicate with the unpaired and mesially placed third ventricle, is seen in sagittal sections. Both the roof and the floor of the irregular third ventricle are thin, whilst its lateral walls are formed by two robust masses, the optic thalami, the mesial surface Corpus callosum FlG ' 9>. Septum lucidun Frontal lobe, mesial surface^ / >\ ^^ " j ~^ ^ "\ / Optic thalamus . <* orsa l surface Lateral wall of third ventricle (optic thalamus) __ _ __ _ -Cerebral peduncle Anterior commissur Foramen of Monroe- Lamina cinerea- \^^HZZ^ZZr == ^t^-v ^X^Sl \ ^^" ^_^&^_- Roof of Sylvian aqueduct Optic commissure- - Occipital lobe -Superior medullary velum // jwr . \ ?>K : ".: ^ \ v L . x r Floor of third ventricle Mammillary body , - . _, , . ,.,., . White core of cerebellum Aqueduct of Sylvius' Pons Inferior medullary velun Fourth ventricle Simplified drawing of brain as seen in mesial section, showing relation of brain-stem, cerebrum and cerebellum, and ventricular spaces. of one of which forms the background of the space when viewed in sagittal section. The roof of the ventricle is very thin and consists of the delicate layer of ependyma, as the immediate lining of the ventricular spaces is designated, supported by the closely adherent fold of pia mater which in this situation pushes before it the neural wall and contains within its lateral border a thickened fringe of blood-vessels, the 67 1058 HUMAN ANATOMY. choroid plexus. The two structures, the ependyma and the pia mater together, constitute the membranous velum interposition that forms the roof of the ventricle and lies beneath the triangular fornix, whose vaulted form is suggested by the arching ridge that descends in front of the thalamus and marks the position of the anterior pillar of the fornix. Behind, just over the upper end of the Sylvian aqueduct, lies the cone-shaped pineal body that belongs to the third ventricle, from which it is an outgrowth. The floor of the ventricle is also, for the most part, relatively thin and irregular in contour. It corresponds to the median part of the lozenge-shaped area, the interpeduncular space, which, seen on the inferior surface of the brain, is bounded behind by the anteriorly diverging cerebral peduncles and in front by the optic chiasm and the posteriorly diverging optic tracts. The posterior half of this area includes the deep triangular recess at the bottom of which is seen the numerous minute open- ings of the posterior perforated space through which small branches of the posterior cerebral arteries pass to the optic thalamus and the crura. Passing forward, the paired corpora mammillaria, the tuber cinereum, the stalk of the pituitary body occupy successively the interpeduncular space. Anteriorly, between the trans- versely cut optic chiasm below and the recurved portion of the great arching com- missure, the corpus callosum, above, the third ventricle is closed by a thin sheet of nervous substance known as the lamina cinerea. Through the foramina of Monroe the lateral ventricles open into the third, and the latter communicates with the fourth ventricle by way of the Sylvian aqueduct. This narrow canal is surrounded below and laterally by the dorsal part or tegmentum of the cerebral peduncles ; above it lies a plate of some thickness the dorsal surface of which is modelled into two pairs of rounded elevations, the superior and inferior corpora q^ladrigemina. In sagittal section, the fourth ventricle appears as a triangular space, the anterior or basal wall being formed by the dorsal surface of the pons and medulla and the posteriorly directed apex lying beneath the cerebellum. The upper half of the thin tent-like roof of the ventricle is formed by the superior medullary velum, a thin layer of white matter that stretches from beneath the inferior corpora quadrigemina to the cerebellum. A similar lamina, the inferior medullary velum extends from the cerebellum downward, but before reaching the dorsal surface of the medulla becomes so attenuated that this part of the ventricular roof, known as the tela chorioidea, consists practically of the pia mater, although the ependyma excludes the vascular membrane from actual entrance into the ventricle. The pia, however, pushes in the ependymal layer and in this manner produces the vascular fringes known as the choroid plexus of the fourth ventricle. When viewed from behind, the ventricle exhibits a rhomboidal outline, the lateral boundaries above being formed by two arms, the superior cerebellar peduncles, that divergingly descend from the sides of the corpora quadrigemina to the cerebellum. Similar bands, the inferior cerebellar peduncles, convergingly descend from the cerebellar hemispheres to the posterior columns of the medulla and form the lower lateral boundaries of the fourth ventricle. Seen from directly above (Fig. 984), the cerebrum, divided into its hemi- spheres by the deep sagittal fissure, is the only part of the brain visible, the other four divisions being masked by the enormously developed overhanging cerebral mantle. The effects of this expansion in displacing base- ward parts which, temporarily in man and permanently in the lower vertebrates, occupy a superior position, are conspicuous when the sagittal section of the developing (Fig. 913) and that of the fully formed human brain (Fig. 910) are compared. It should be noted, that although in the latter the brain-stem and the cerebellum are completely overhung by the cerebral hemispheres, they still are in relation with the free surface of the brain, and by passing beneath the posterior part of the cerebrum the dorsal surface of the cerebellum and of the brain-stem may be reached without mutilation of the nervous tissue. THE GENERAL DEVELOPMENT OF THE BRAIN. Even before complete closure of the anterior end of the neural tube, which takes place probably shortly after the end of the second week of foetal life, the cephalic region of this tube, slightly flattened from side to side, exhibits tin- results GENERAL DEVELOPMENT OF THE BRAIN. 1059 of unequal growth in two slight constrictions separating three dilatations known as the primary brain-vesicles. The posterior of these, the hind-brain, 1 is much the longer, exceeding the combined length of the other two (Fig. 911); after a short time when viewed from behind it presents an elongated lozenge-shaped form and, hence, is also called the rhombencephalon. The middle vesicle, the mid-brain, or mesencephalon, is conspicuous on account of its rounded form and prominent position, lying, as it does, over the marked primary flexure which the head-end of the neural tube very early exhibits. The anterior vesicle, known as the fore-brain, or prosencephalon, at first is small and rounded, but soon becomes modified by the appearance, on either side, of a hollow protuberance, the optic vesicle, that pushes out from the lower lateral wall. For a time the optic vesicle communicates with the main cavity of the fore- brain by a wide opening. This gradually becomes reduced and constricted until the FIG. 911. Fore-brain Pallium Mid-brain Optic vesicle Fore-brain (thalamic region) f Pallium Mid-brain Reconstruction of brain of human embryo of about two weeks (3.2 mm.); A, outer surface; , inner surface; up, neural pore, where fore-brain is still open; cs, anlage of corpus striatum ; or, optic recess leading into optic vesicle; A/, hypothalamic region, (ffis.) evagination is attached by a hollow stem, the optic stalk, which later takes part in the formation of the optic nerve that connects the eye with the brain, the vesicle itself giving rise (page 1482) to the nervous coat of the eye, the retina. By the time the optic evagination is formed, the front part of the fore-brain shows a slight bulging, narrow below and broader and rounded above, and separated from the optic outgrowth by a slight furrow. This is the first suggestion of the anlage of the hemisphere or pallium (His). The latter soon gives rise to two rounded hollow protrusions, one on either side of the fore-brain, that rapidly expand into the conspicuous primary cerebral hemispheres. The lower part of the fore-brain includes the region that later, after differentiation and outgrowth from the hemisphere, receives the nerves of smell and is known as the rhinencephalon. A slight ridge (Fig. 911, B), projecting inward from the roof of the fore-brain, suggests a subdivision of the general space into a posterior and an anterior region. 1 This use of the term hind-brain is at variance with its older significance, still retained by sonie German writers, as indicating the upper division (metencephalon) of the posterior primary vesicle. In view, however, of the now general application of fore-brain and mid-brain to the other primary vesicles, it seems more consistent to include hind-brain in the series, as has been done by Cunningham, with a distinct gain not only in convenience, but in avoiding terms which in their Anglicised form are at best awkward and unnecessary. io6o HUMAN ANATOMY. The latter, the outwardly bulging pallium or hemisphere-anlage, is limited below by the optic recess, the entrance into the optic vesicle, and, farther front, by a flattened triangular elevation that marks the earliest rudiment of the corpus striatum. The posterior or thalamic region extends backward to the mid-brain, from which it is separated by the slight external constriction and corresponding internal ridge. During the fourth week the demarcations just noted become more definite, so that the primary anterior vesicle is imperfectly subdivided into two secondary compart- ments, the telencephalon, conveniently called the end-brain, and the dienceph- alon. Considered with regard to the details presented by the interior of the fore- brain, the four areas recognized by His are evident. These are (Fig. 912) the region of the pallium and of the corpus striatum, respectively above and below in the telencephalon, and the region of the thalamus and of the hypothaiamus respec- tively above and below in the diencephalon. Between the protruding hemispheres, the telencephalon is closed in front and below by a thin and narrow wall, the lamina terminalis, which defines the anterior limit of the brain-tube. While the more detailed account of the further development of these regions will be given in connection with the description of the several divisions of the brain, FIG. 912. Mid-brain Mid-brain Diencephalon Thalamencephalon Telencephalon bf Pallium Spinal cord Reconstruction of brain of human embryo of about four weeks (6.9 mm.); A, outer surface; B, inner surface; /, isthmus ; os, aperture of optic stalk ; c/>, cerebral peduncle ; cj, cervical flexure ; bf, cephalic flexure. Drawn from His model. . it may be pointed out here, in a general way, that the pallium gives rise to the con- spicuous cerebral hemispheres, which, joined below by a common lamina, expand out- ward, upward and backward and rapidly dwarf the other parts of the brain-tube which are thus gradually covered over. The striate area thickens into the corpus striatum, which appears as a striking prominence on the outer and lower wall of each lateral ventricle. The latter represents a secondary extension of the original cavity of the fore-brain enclosed by the developing cerebral hemisphere, and at first is large and thin-walled and communicates by a wide opening with the remainder of the brain- vesicle. The unequal growth and thickening, which subsequently modify the surrounding walls, reduce this large aperture until it persists as the small foramen of Monroe, by which the lateral ventricle communicates with the third ventricle. The latter represents what is left of the cavity of the fore-brain and, therefore, the com- GENERAL DEVELOPMENT OF THE BRAIN. 1061 bined contribution of the telencephalon and diencephaion. During the fifth week the diencephaion expands into a relatively large irregular space (Fig. 913), whose roof and floor are thin and whose lateral walls are thickened by the masses of the developing thalami. The hypothalamic region becomes the most dependent part of the fore-brain and gives rise to the structures that later occupy the inter- peduncular space on the base of the brain. The roof of the diencephaion remains thin, does not produce nervous tissue and, in conjunction with the ingrowth of the vascular pia mater, forms the velum interpositum and its choroid plexuses. The pineal body and the posterior lobe of the pituitary body arise as outgrowths from the roof and floor of the diencephaion. respectively. The mid-brain, or mesencephalon, at first large and conspicuous on account of its elongation and prominent position at the summit of the brain-tube, does not keep pace with the adjoining vesicles,, and in the fully formed brain is represented by the parts surrounding the aqueduct of Sylvius. Neither does it subdivide, but, while its entire wall is converted into nervous tissue, retains its primary simplicity to a greater degree than any of the other brain-segments. The lateral and ventral walls of the mid-brain contribute the cerebral peduncles ; its roof gives rise to the corpora quadrigemina ; and its cavity persists as the narrow canal, the aqueduct of Sylvius, that connects the third and fourth ventricles. The posterior vesicle, the hind-brain, or rhombencephalon, the largest of the primary brain-segments, is the seat of striking changes. These include thicken- ing and sharp forward flexion of the ventro-lateral walls, in consequence of which the floor of the space becomes broadened out opposite the bend and assumes a lozenge- shaped outline. The hind-brain is conventionally subdivided (Fig. 913) into a superior part, the metencephalon, and an inferior part, the myelencephalon. Its cavity, common to both subdivisions, persists as the fourth ventricle. The extreme upper part of the metencephalon, where it joins the mid-brain, early exhibits a constriction, which by His has been termed the isthmus rhom- bencephali and regarded as a distinct division of the brain-tube. In the fully formed brain, the isthmus corresponds to the uppermost part of the fourth ventricle, just below the Sylvian aqueduct, roofed in by the superior medullary velum that stretches between the superior cerebellar peduncles. The thickened and markedly bent ventro- lateral wall of the metencephalon gives rise to the pons Varolii, whilst in the roof of the ventricle appears a new mass of nervous tissue, the cerebellum. The myelencephalon, soon limited below by the cervical flexure, shares in the ventral thickening seen in the preceding division. Its floor and particularly its sides, the latter at the same time spreading apart, form the medulla oblongata, which below gradually tapers into the spinal cord. Its roof, in which thinness is always a prominent feature, becomes more attenuated as development proceeds and is converted into the inferior medullary velum and the tela chorioidea that close in this part of the fourth ventricle. The subsequent invagination of this membranous portion of the ventricular roof by the pia mater brings about the production of a choroid plexus similar to that seen in the roof of the third ventricle. From the foregoing sketch of the changes affecting the embryonic brain-tube, it is evident that the anterior and posterior primary vesicles undergo subdivision, while the mid-brain remains undivided, five secondary brain-vesicles the telencepha- lon, the diencephaion, the mesencephalon, the metencephalon and the myelencepha- lon replacing the three primary ones. In consequence of the unequal growth of various parts of the cephalic segment of the neural tube, the latter becomes bent in the sagittal plane at certain points, so that, when viewed from the side, the axis of the developing human brain describes an S-like curve (Fig. 912). These flexures, to which incidental reference has been made, bring about a disturbance, for the most part temporary, in the relations of the brain-segments, which in the lower vertebrates follow in regular order along an axis practically straight. In the developing human brain,' in which they are most conspicuous, there are three flexures >the cephalic, cervical, and pontine. The first of these, the cephalic flexure which appears towards the end of the second week and before the neural tube has completely closed, is primary and involves the entire head. It takes place in the region of the mid-brain and lies 1062 HUMAN ANATOMY. Telencephalon Corpus striatum Optic recess Mesencephalon Isthmus Metencephalon M yelencephaloi i above the anterior end of the primary gut-tube and of the notochord. At first the axis of the fore-brain lies about at right angles with that of the rhombencephalon, (Fig. 911) but, with the in- FIG. 913. creasing size of the middle Diencephalon i i i and anterior vesicles, t he- angle of the flexure becomes more acute until the long axis of the fore-brain and of the rhombencephalon are almost parallel (Fig. 912). During the fourth week a second ventral bend, the cervical flexure, appears at the lower end of the hind- brain and marks the separa- tion of the encephalic from the spinal portion of the neural tube. The cervical flexure, which also involves the head, is most evident at the close of the fourth week, when it is almost a right angle ( Fig. 912); after this it becomes less pronounced in consequence of the elevation of the head which succeeds the period when the embryonic axis is most bent. The third flexure appears about the fifth week in the part of the metencephalon in which the pons is later developed and, hence, is termed the pontine flexure. It concerns chiefly the ventral wall, which is in consequence for a time ventrally doubled on itself ; subsequently this flexure almost entirely disappears. In contrast to the preceding bends, this flexure is only partial and involves chiefly the ventral and only slightly the dorsal wall of the neural tube ; on the exterior of the embryo its presence is not detectable. The developmental relations of the chief parts of the fully formed brain to the embryonic brain-vesicles are shown in the accompanying table. TABLE SHOWING RELATIONS OF BRAIN-VESICLES AND THEIR DERIVATIVES. Ventral Dorsal zone of brain-wall Diagram showing five cerebral vesicles and dorsal and ventral zones of their wall ; based on brain of embryo of four and one-half weeks. ( His. ) PRIMARY SEGMENT SECONDARY SEGMENT DERIVATIVES CAVITY Anterior vesicle Telencephalon Cerebral hemispheres Olfactory lobes Corpora striata Lateral ventricles \ se i ..... Foramina of Monroe i se Anterior part of third ventricle Prosencephalon or Fore-brain Diencephalon Optic thalami Optic nerves and tracts Subthalamic tegmenta Interpeduncular structures Pineal and pituitary bodies Posterior part of third ventricle Middle vesicle Mesencephalon or Mesencephalon Cerebral peduncles Corpora quadrigemina Aqueduct of Sylvius Mid-brain Posterior vesicle Rhombencephalon or Hind-brain Isthmus Superior cerebellar peduncles Superior medullary velum Fourth ventricle Metencephalon Pons Cerebellum M y elencephalon Medulla Inferior medullary velum Notwithstanding the great changes in position and relation which many parts of the human brain suffer during development, chiefly in consequence of the enormous expansion of the pallium and the correspondingly large size of its commissure, the GENERAL DEVELOPMENT OF THE BRAIN: 1063 corpus callosum, the fundamental relationships' indicated by embryology are of such value that, even in the description of the adult organ, grouping of the various parts of the brain upon a develop- mental basis is found advan- FIG. 914. tageous. Although strict adherence to such a plan would be at times inconven- ient, and, therefore, will not be followed, constant refer- ence to primary relations is imperative. It will be con- venient, therefore, at this place, to call attention to the accompanying outline diagrams which illustrate the principles established by His in his epoch-making studies of the human brain. In addition to showing the five cerebral vesicles, Fig. 913 indicates the relative position and extent of the two fundamental subdivisions of the lateral walls of the neural tube, the dorsal or alar and the ventral or basal laminae, which play such important roles in the differentiation of the various parts of the brain-stem. Fig. 914 shows a later stage, in which the genetic relations of all the more important parts of the brain may be recognized. The greatest complexity is presented in the development of the derivations of the fore-brain, particularly of those which are differentiated from the diencephalon and later are found connected with the third ventricle. In order to set forth the developmental relations of the fore-brain, the following table from His, slightly modified, will be of service : Epithalamus Thalamus / Metathalamus ars mammillaris hypothalami Mesencephalon Pedunculi cerebri Isthmus Cerebellum Pons Medulla Dorsal zone Ventral zone Rhinencephalon Pars optica hypothalami Diagram showing chief derivatives from cerebral visicles brain of embryo of third month. (His.) based on Fore-Brain or Prosencephalon (Pallium ' Hetnisphaerium < Corpus striatum ' TELENCEPHALON-^ (Rhinencephalon ^Pars optica hypothalami [DlEN CEPHALON Pars mammillaris hypothalami "Thalamus Epithalamus Habenula Thalamencephalon Corpus pineale Commissura post. Metathalamus Corpora geniculata PARTS OF THE BRAIN DERIVED FROM THE RHOMBENCEPHALON. THE MEDULLA OBLONGATA. The medulla oblongata, sometimes called the bulb and usually designated by the 'convenient but indefinite name " medulla," is the direct upward prolongation of the spinal cord. It begins at the decussation of the pyramids below, about on a level with the lower border of the foramen magnum, and ends at the lower margin of the pons above and is approximately 2.5 cm. (i in) in. length. Its general form is tapering, increasing in breadth from the transverse diameter of the cord (10 mm.) below, to almost twice as much (18 mm.) above, and in the antero-posterior dimen- sion from 8-15 mm. Its long axis corresponds very closely with that of the cord and is, therefore, approximately vertical. The medulla, surrounded by the pia and arach- noid, lies behind the concave surface of the basilar portion of the occipital bone, with its dorsal surface within the vallecula between the hemispheres of the cerebellum. Superficially, in many respects the medulla appears to be the direct continuation -of the spinal cord. Thus, it is divided into lateral halves by the prolongation of the anterior and posterior median fissures ; each half is subdivided by a ventro-lateral and a dorso-lateral line of nerve-roots into tracts that seemingly are continuations of 1064 HUMAN ANATOMY. the anterior, lateral and posterior columns of the cord. This correspondence, how- ever, is incomplete and only superficial, since, as will be evident after studying the internal structure of the medulla, the components of the cord, both gray and white matter, are rearranged or modified to such an extent that few occupy the same posi- tion in the medulla as they do in the cord. The anterior median fissure is interrupted at the lower limit of the medulla, for a distance of from 6-7 mm. , by from five to seven robust strands of nerve-fibres that pass obliquely across the furrow, interlacing as they proceed from the two sides. These strands constitute the decussation of the pyramids (decussatio pyramidum), whereby the greater number of the fibres of the important motor paths pass to the opposite sides to gain the lateral columns of the cord, in which they descend as the lateral pyramidal tracts. The fibres that remain uncrossed occupy the lateral por- tions of the pyramids and, converging towards the median fissure, descend on either side of the latter within the anterior columns as the direct pyramidal tracts. The Infundibulum \ * ' / **r- Optic tract - _ ^ -Cerebral peduncle ^^ ^T T*. \ ^- Mammillary body /THKiMtX "Interpeduncular space ' "^ Pons (basilar groove) ^,^Tiigeminal nerve Middle cerebellar peduncle ^_ y"' cerebellar peduncle jjjjF** 1 -.., /'' Anterior median fissure- --^ i^__ T^__. -^_- "Inferior cerebellar peduncle _ (Restiform body) Cerebellum' ~~ ^^^^^^~ ~^^~^^~ '\ ' \ .'VMftt ^4 L* "t ~V< *^BMh - 1 '-mJ^^V ^~ ^Olivary eminence Root-bundles of ninth s^ ^-^C^ 'S S^ Ef~~~--^ Arcuate fibres and tenth nerves ^i2c^__2i" 1 ^ -~^_ Pyramidal decussation Root-bundles of twelfth nerve ^ ' Anterior roots of first spinal nerve Brain-stem viewed from in front, showing ventral aspect of medulla, pons and mid-brain. decussation varies in distinctness, sometimes the component strands being so buried within the fissure that they are scarcely evident, or even not at all apparent, on the surface and can be satisfactorily seen only when the lips of the groove are separated. Above the decussation the anterior median fissure increases in depth in conse- quence of the greater projection of the bounding pyramidal tracts. Its upper end, just below the inferior border of the pons, is marked by a slightly expanded triangular depression, the foramen c(ecnm. The posterior median fissure, the direct continuation of the corresponding groove on the cord, extends along only the lower half of the medulla, since above that limit it disappears in consequence of (a) the separation and divergence of the dorsal tracts of the bulb, which below enclose the fissure, to form the lower lateral boundaries of the lozenge-shaped fourth ventricle (fossa rhomboidalis), and (t>) the gradual backward displacement of the central canal within the closed part of the medulla until, at the lower angle of the ventricle, it opens out into that space. l-'.ach half of the medulla is superficially subdivided into three longitudinal tracts or areas by two grooves situated at some distance to the side of the ventral and dorsal median fissures respectively. One of these, the antero-lateral furrow, marks tin- line of emergence of the root-fibres of the hypoglossal nerve, which, being entirely THE MEDULLA OBLONGATA. 1065 FIG. 916. Cerebral cortex motor, correspond to the ventral roots of the spinal nerves with which they are in series. The other groove, the postero-lateral furrow, continues upward in a general way the line of the dorsal spinal root-fibres and marks the attachment of the fibres of the ninth, tenth and bulbar part of the eleventh cranial nerves. Unlike the posterior root-fibres of the cord, which are exclusively sensory, those attached along this groove of the medulla are partly efferent and partly afferent, the fibres belong- ing to the spinal accessory being entirely motor, while those of the glosso-pharyngeal and the pneumogastric include both and, therefore, are mixed. The Anterior Area. This subdivision of the medulla, also known as the pyra- mid, includes the region lying between the anterior median fissure and the antero- lateral furrow. Superficially it appears as a slightly convex longitudinal tract, from 6-7 mm. in width, that continues upward the anterior column of the cord. Each pyramid constitutes a robust strand, which belowbeginsat thedecussationand, increas- ing slightly as it ascends, above disappears within the substance of the pons. Just before its disappearance, or, strictly speak- ing, after its emergence, the pyramid is slightly contracted on account of the increased width of the bounding furrows. Its chief components being the descending motor paths formed by the cortico-spinal fibres, of which approximately four-fifths pass to the opposite side by way of the decussation to gain the lateral pyramidal tract, it is evident that only to the extent of the direct pyramidal fasciculus and, for a short distance, the anterior ground-bundle, are its constituents represented in the anterior column of the spinal cord. The fibres destined for the direct pyramidal tract, which above the decussa- tion occupy the lateral part of the pyramid, gradually converge toward the mid-line as the decussating fibres disappear, until, at the lower limit of the crossing, they lie next the median fissure, which position they retain in their further descent within the cord. The space thus afforded at the lower end of the medulla, to the outer side of the uncrossed fibres, is occupied by the prolongation of the anterior ground- bundle, which, however, soon suffers Pyramidal decussation Lateral pyramidal tract Direct pyramidal tract Spinal nerve Diagram showing course and decussation of cortico- spinal (pyramidal) tract ; M, medulla; P, pons; CP, cerebral peduncle; T, thalamus ; C, L, caudate and lenticular nuclei ; CC, corpus callosum. displacement as it encounters the pyramid. The ground-bundle lies at first to the outer side of the strands of decussating fibres and then behind the pyramid; higher, it is pushed backward towards the mid-line by the appearance of the inferior olive and the mesial fillet until, finally, it is continued as the posterior longitudinal fasciculus at the side of the median raphe beneath the gray matter covering the floor of the fourth ventricle. The proportion of the pyramidal fibres taking part in the motor decussation is not always the same, from 80-90 per cent, being the usual number. Vary rarely all the fibres cross, with suppression of the direct pyramidal tracts an arrangement found normally in many lower animals. On the other hand, the direct pyramidal tracts may appropriate an unusually large number of the fibres, even to 90 per cent, of the entire pyramid, the crossed tract, however, never being entirely unrepresented. Ordinarily the tracts of the two sides are approximately of equal extent, but occasion- ally they may be asymmetrical, in which case the excess of the one is offset by a corresponding diminution in the fasciculus of the opposite side (Flechsig). 1066 HUMAN ANATOMY. The Lateral Area. This region is defined on the surface by the antero-lateral and postero-lateral furrows in front and behind respectively, and includes a narrow strip on the lateral aspect of the medulla. Below, the tract is continuous with the lateral column of the cord, a resemblance which is, however, only superficial since within the medulla the large crossed pyramidal tract no longer lies laterally but within the anterior area of the opposite side. The upper part of the lateral area is conspicuously modified by the presence of an elongated oval prominence, the olivary eminence (oliva), produced by the underlying corrugated lamina of gray matter composing the inferior olivary nucleus. The olive measures about 13 mm. in length and about half as much in its greatest width. Its upper end, more prominent and slightly broader than the lower, is separated from the inferior border of the pons by a deep groove, which' medially joins the furrow occupied by the hypoglossal root- fibres and laterally is continuous with a broad depressed area, the fiarao/h'ary fossa, that separates the olive from the restiform body and lodges the fibres of the glosso- pharyngeal and pneumogastric nerves. The demarcation of the lower tapering end of the olive is somewhat masked by the anterior superficial arcuate fibres, which cover for a variable distance the inferior part of the olive in their course backward to gain Thalamus Pulvinar Median geniculate body Inferior brachium Superior colliculus Cerebral peduncle Inferior colliculus Superior cerebellar peduncle Superior medullary velum Middle cerebellar peduncle Line of attachment of roof of IV ventricle Inferior cerebellar peduncle (restiform body) Clava Tuberculum cuneatum Tuberculum Rolandi FIG. 917. Lateral geniculate body- Superior brachium Mesial root of optic tract Anterior perforated space Optic tract Lateral olfactory root Optic nerve Optic commissure Tuber cinereum Mammillary body -Olivary eminence -Arcuate fibres Lateral area of medulla Brain-stem viewed from the side, showing lateral aspect of medulla, pons, and mid-brain. the restiform body. The components of the lateral column of the cord traceable into the medulla the direct cerebellar and Cowers' tract and the long paths of the lateral ground-bundle for the most part, with the exception of the direct cerebellar tract, pass beneath or to the outer side of the olive. The superficially placed direct cere- bellar tract gradually leaves the lateral area and passes outward and backward to join the inferior cerebellar peduncle by which it reaches the cerebellum. The Posterior Area. The posterior region of the medulla is bounded laterally by the fibres of the ninth and tenth nerves ; and mesially, in the lower half of the bulb, by the posterior median fissure and, in the upper half, by the diverging sides of the fourth ventricle. Below, the posterior area receives the prolongations of the tracts of Goll and of Burdach, which within the medulla are known as the funic- ulus gracilis and funiculus cuneatus respectively, and are Separated from each other by the paramedian sulcus. Beginning with a width of about 2 mm., the gra- cile funirulus increases in breadth as 'it ascends until, just before reaching the lower end of the fourth ventricle, it expands into a well-marked swelling, the clava, about 4mm. wide, which is caused by a subjacent accumulation of gray matter. 'Ihrn. diverging from its fellow of the opposite side to bound the ventricle, after a short course it loses its identity as a distinct strand and becomes continuous with the THE MEDULLA OBLONGATA. 1067 inferior cerebellar peduncle or restiform body. The expansion within the upper part of the funiculus gracilis, the clava, contains the nucleus gracilis (nucleus funiculi gracilis), the reception station in which the long sensory fibres of Coil's tract are interrupted. The triangular interval included between the gracile funiculi, where these begin to diverge, corresponds to the level at which the central canal of the cord ends by opening out into the fourth ventricle. A thin lamina, the obex, closes this interval and is continuous with the ventricular roof. Along the outer side of the gracile fasciculus and separated from it by the para- median furrow, extends a second longitudinal tract, the funiculus cuneatus, which at the lower end of the medulla receives the column of Burdach. Slightly above the lower level of the clava, the cuneate strand also exhibits an expansion, the cuneate tubercle (tuberculum cinereum), that is less circumscribed, but extends farther upward than the median elevation. Beneath this prominence lies an elongated mass of gray matter, the nucleus cuneatus (nucleus funiculi cuneati), around whose cells the long sensory fibres of Burdach' s tract end. Still more laterally, between the roots of the ninth and tenth nerves and the cuneate strand, the posterior area of the medulla presents a third longitudinal eleva- tion, the funiculus of Rolando. The latter is caused by the increased bulk of the FIG. 918. Inferior colliculus Cerebral peduncle Median fossa Median sulcus Middle cerebellar peduncle Acoustic strise Acoustic trivone Restiform body Attachment of ventricular roof Obex Funiculus cuneatus Frenulum Superior trochlear nerve Cerebellar peduncle Floor of fourth ventricle Fovea superior Eminentia teres Trigonum hypoglossi Trigonum ragi (fovea inferior) Funiculus separens Area postrema Funiculus gracilis Lateral area Medulla and floor of fourth ventricle seen from behind, after removal of cerebellum and ventricular roof. X iH- underlying substantia gelatinosa that caps the remains of the posterior horn of gray matter, and is overlaid by a superficial sheet of white matter composed of the longi- tudinal fibres of the descending root of the trigeminal nerve. While, therefore, the tubercle of Rolando is produced by the exaggeration of gray matter represented within the spinal cord, the gracile and cuneate nuclei are new stations in which the posterior root-fibres not interrupted at lower levels end, and from which the sensory impulses collected by the cord are distributed to the cerebellum and the higher centres by neurones of the second order. The upper half of the posterior area of the medulla is modified by the presence of the fourth ventricle, the lower lateral boundary of which it largely forms, into a robust rope-like strand that diverges as it ascends. Above, it abuts against and fuses with the lateral continuation of the pons and then, bending backward, enters the overhanging cerebellum as the inferior cerebellar peduncle. This strand, also known as the restiform body (corpus restiforme), is seemingly the direct prolongation of the gracile and cuneate funiculi. Such, however, is not the case, since the fibres passing from these tracts to the cerebellum by way of the restiform body are the axones of the gracile and cuneate nuclei and, therefore, new links in the chain of conduction. io68 HUMAN ANATOMY. The inferior cerebellar peduncle is the most direct path by which the cerebellum is connected with the medulla and the spinal cord. In addition to the tracts originating in the cord and destined for the cerebellum (the direct cerebellar and possibly part of Gowers' tract), it comprises probably fibres passing in both direc- tions; that is, from the cells within the medulla to the cerebellum, and from the cerebellar cells to the medulla. A more detailed account of these components will be given in connection with the structure of the medulla (page 1072). Upon close inspection of the surface of the medulla, the direct cerebellar tract is seen as an obliquely coursing band that at the lower level of the olive leaves the lateral area and gradually passes backward, over the upper and outer end of the Rolandic tubercle, to join the restiform body, within which it continues its journey to the cerebellum. The anterior superficial arcuate fibres also enter the restiform body, after sweeping around the inferior pole of the olive, or crossing its surface, and the upper part of the funiculus of Rolando. Additional contributions, the posterior superficial arcuate fibres, proceed to the restiform body from the gracile and cuneate nuclei of the same side. Just before bending backward to enter the cerebellum, the restiform body is crossed by a variable number of superficial strands, the striae acusticae, that may be traced from the floor of the fourth ventricle and around the inferior peduncle to the cochlear nucleus. INTERNAL STRUCTURE OF THE MEDULLA OBLONGATA. As already pointed out, the correspondence between the spinal cord and the medulla is only superficial, sections across the medulla revealing the presence of con- siderable masses of gray matter and important tracts of nerve-fibres not represented FIG. 919. Ventral (A) and dorsal (B) aspects of brain stem, showing levels of sections which follow. in the cord, as well as the rearrangement, modification or disappearance of spinal tracts which are prolonged into the bulb. In consequence, tin- medulla, even at its lower end, presents new features, and towards its upper limit varies so greatly trom the eord that but slight resemblance to the latter is retained. The character- istic features displayed by transverse sections of the medulla at different levels depend upon the changes induced by four chief factors: (i) the decussation of the pyramids, (2) the appearance of the dorsal nuclei, (3) the production of the formatio reticularis, and (4) the opening out of the fourth ventricle. THE MEDULLA OBLONGATA. 1069 Funiculus 'cuneatus Decussating fibres Anterior cornu Transverse section of medulla at level A, Fig. 919; beginning of pyramidal de decussation. Spiller. Weigert-Pal staining. X Preparation made by Professor The effects of the decussation of the pyramidal tracts, assuming for convenience that the latter pass from below upward, are conspicuous when followed in consecutive transverse sections from the spino-bulbar junction ^ IG - 9 20 - , r , ~J ,-. _^. x Funiculus gracilis cerebralward. Ihe first _/*3iliiSS?53vc suggestion of the decussa- tion appears (Fig. 920) as strands of nerve-fibres, that pass from the field of the lateral pyramidal tract in thelateral column obliquely through the adjacent ante- rior horn of gray matter and across the bottom of the an- terior median fissure to gain the opposite anterior col- umn. At a slightly higher level, where the decussation is fully established (Fig. 921), the large strands of obliquely sectional fibres are seen cutting through the gray matter, partly filling the median fissure, and collecting on either side of the latter as the large ventral bundles which thence upward constitute the prominent pyramidal fields. In consequence of the greater space required by the pyramids, the isolated anterior horns of the gray matter, cut off by the crossing strands, and the adjacent anterior ground-bundle are displaced laterally and at first lie to the outer side of the decussated fibres. Later, the ground-bundle assumes a position behind the pyramid and eventually becomes continuous with the posterior longitudinal fasciculus (page 1116). The detached anterior cornu of the gray matter is pushed outward and backward and gradually becomes broken up by and interspersed among the fibres of the formatio reticularis. The Posterior Nuclei and the Arcuate Fibres. The robust tracts of white matter (nerve-fibres) prolonged into the gracile and cuneate funiculi from the tracts of Goll and of Burdach become invaded by new masses of gray matter, the nucleus gracilis and cuneatus. The gracile nucleus, the first encountered, begins as a narrow area of gray FIG. 921. matter within the correspond- ing strand, on a level with the pyramidal decussation (Fig. 921). It rapidly in- creases in bulk, until it not only invades the entire funiculus gracilis, but also joins the gray matter sur- rounding the central canal. The superficial stratum of spinal fibres gradually dimin- ishes as more and more of its components end around the cells of the gracile nucleus, until, finally, all are inter- rupted. Meanwhile the cuneate nucleus appears within the funiculus cuneatus as a dorsally directed club- shaped mass of gray mat- ter (Fig. 922) which soon becomes a prominent mottled area, sharply defined by the overlying stratum of Burdach fibres. The cuneate nucleus extends to a higher level than the nucleus Nucleus gra Isolated anterior cornu Pyramidal decussation Transverse section of medulla at level B, Fig. 919 ; pyramidal decus- sation well established ; posterior cornua are displaced laterally by posterior columns. X 5%. Preparation by Professor Spiller. IOJO HUMAN ANATOMY. gracilis and, even after the disappearance of the latter, continues as a striking collec- tion of gray matter beneath the dorsal surface of the medulla, from which it is separated by the posterior superficial arcuate fibres. Within the upper part of the fasciculus cuneatus the gray matter becomes subdivided into two masses (Fig. 924), the more superficial and continuous of which is called the nucleus cuneatus extennts, and the deeper and more broken one, the nucleus cuneatus intcrnus. Owing to the increased bulk of the fasciculi of the posterior area occasioned by the appearance and expansion of the contained nuclei, the dorsal horns of the gray matter are displaced laterally and forward, so that they come to lie on a level with the central canal. Meanwhile the posterior cornua themselves, especially the capping substantia gelatinosa, materially gain in bulk and now appear as two club-shaped masses of gray matter that cause the dorso-lateral projections of the Rolandic tubercles seen on the FIG. 922. Nucleus gracilis Funiculus gracilis Funiculus cuneatus Spinal root of V nei Substantia gelatinosa Accessory olivary nucleu Antero-lateral ground-bundle Anterior superficial arcuate fibres' Nucleus cuneatus ffig\ Central gray matter Deep arcuate fibres Fibres of XII nerve Sensory decussation Pyramidal tracts Transverse section of medulla at level C, Fig. 919, showing sensory decussation, posterior nuclei and pyramidal tracts. X 5K- Preparation by Professor Spiller. surface. Beneath the latter and closely overlying the outer border of the extensive area of the substantia gelatinosa, a crescentic tract of the longitudinally coursing nerve- fibres marks the position of the descending root of the trigeminal nerve ( Fig. 922). The chief purpose of the gracile and cuneate nuclei being the reception of the long sensory tracts continued from the 'cord and the distribution of impulses so received to the cerebellum and to the higher centres, it is evident that new paths of the second order must arise within these nuclei. About on a level with the upper limit of the pyramidal or motor decussation, fibres emerge from the gracile and cuneate nuclei, sweep forward and inward in bold curves and cross the median raphe to the opposite side of the medulla, immediately behind the pvramids ( Fig. 922). They then turn sharply upward and form the beginning of the important sensory pathway known as the median fillet (lemniscus medial is) that eonneets the medullary nuclei with the higher centres, as the superior corpora quadrigemina and the optic thalanms. The first fibres that emerge in this manner from the gracile and cuneate nuclei constitute a fairly well defined strand to which the name sensory decussation or decussation of the fillet is given. It must not be supposed, however, that with this deeussation the crossing ceases, for, quite the contrary, it is only the beginning of an extended series of sensory fibres that pass across the raphe at various levels throughout the brain-stem. ' As many longitudinally coursing fibres are encountered by those sweeping from side to side, an interweaving of vertical and hori/ontal fibres occurs, which results in the production of the characteristic formatio reticularis that constitutes a large part of the medulla, as well as of the dorsal or tegmental portions THE MEDULLA OBLONGATA. 1071 Nucleus cuneatus gracilis Coil's tract Fibres from Burdach's tract Post, superficial arcuate of the pons and cerebral crura. A feeble expression of a somewhat similar structure is seen in the reticular formation within the lateral column of the spinal cord. The Arcuate Fibres. These originate as the axones of the cells of thegracile and cuneate nuclei and include three sets. The first, the deep arcuate fibres, turn sharply brainward after crossing the raphe and FlG - 9 2 3- Constitute the Chief COn- Nucleus Fibres from stituents of the mesial fillet. The second set, the anterior superficial arcuate fibres, also cross the mid-line, but these, instead of turning upward, pass forward, enter through the pyra- mid or along its median aspect, and, gaining the surface, sweep over the pyramid and olivary emi- nenceand thenceproceed backward to the restiform body and on to the cere- bellum. An oval collection of small fusiform nerve-cells, the arcuate nucleus (nucleus arcuatus) lies in the path of these fibres, at first on the ventral surface of the pyramid and then along te median fissure. Whilst some additional arcuate fibres arise from the cells of the nucleus, the majority sweep by without interruption. The third set, the posterior superficial arcuate fibres, proceed from the cells of the gracile and cuneate nuclei of the same side and pass beneath the ventricular floor to the adjacent restiform body and thence to the cerebellum. Deep arcuate Anterior superficial arcuate Arcuate nucleus Diagram illustrating source and path of arcuate fibres; RB, restiform body;, P, pyramidal tract ; O, inferior olivary nucleus. FIG. 924. Nucleus gracilis Funiculus cuneatus -. Fasciculus solitarius M- Nucleus latera Nucleus ambiguus Decussation of fillet fibres Median fillet Pyramidal tract Nucleus cuneatus interims Nuc. cuneatus extern us Substantia gelatinosa Spinal root of V nerve Deep arcuate fibres and formatio reticularis Dorsal access, olivary nucleus .Inferior olivary nucleus Mesial access, olivary nucleus Anterior superficial arcuate fibres' Arcuate nucleus Transverse section of medulla at level D, Fig. 919, showing posterior nuclei, inferior olivary nuclei, formatio -eticulans and dorsal displacement of central canal. X 5%. Preparation by Professor Spiller. The Olivary Nuclei. These include, in each half of the medulla, three masses of gray matter the inferior olivary nucleus and the two accessory olivary nuclei. Beneath the prominent olivary eminence lies a corrugated sack-like lamina of gray 1072 HUMAN ANATOMY. FIG. 925. Dorsal Ventral Dorso-lateral aspect of inferior olivary nucleus as reconstructed by Dr. Florence R. Sabin. X 5. matter, the inferior olivary nucleus (nucleus olivaris inferior), which in favorable transverse sections appears as a conspicuous sinuous C-like figure. The nucleus resembles a greatly crumpled bag, of which the closed end lies beneath the corresponding superficial protuberance and the mouth, or hilum, looks mesially and somewhat dorsally. When reconstructed and viewed from the side (Fig. 925), the plications of the lateral and dorso-lateral surfaces display a general antero-lateral disposition. On the ventral surface the grooves radiate from the ventral border of the hilum (Sabin). The greatest length of the inferior olivary nucleus is from 12-15 mm., its transverse diameter is about 6 mm. , and its vertical one about one millimeter less. The somewhat compressed hilum measures sagittally from 8-9 mm. The plicated lamina of gray matter composing the wall of the sac is from .2-. 3 mm. in thickness and contains numerous small irregularly spherical nerve-cells, each provided with a variable number of dendrites and an axone, embedded within a compact feltwork of neuroglia fibres. The interior of the gray sac is filled with white matter consisting of nerve-fibres that, for the most part, stream through the hilum and thus constitute the olivary peduncle. These strands, known as the cerebello-olivary fibres, connect the cerebellar cortex with the inferior olivary nucleus and probably pass in both directions. Many fibres, the axones of the olivary neurones, issue from the hilum on the one side, cross tjie mid-line and, sweeping through the opposite olivary nucleus either by way of the hilum or directly traversing the gray lamina, continue their course to the restiform body and thence to the cerebellum. Other fibres originate in the cells of the cerebellar cortex and proceed in the opposite direction along the same pathway to end in relation with the cells of the inferior olivary nucleus. The further links in the chain of conduction are uncertain ; according FIG. 926. Cerebello-olivary strands to Kolliker it is prob- able that from some of the olivary cells, fibres pass downward into the antero-lateral ground- bundle of the cord. The accessory olivary nuclei are two irregular plate-like masses of gray matter that lie respectively mesially and dorsally to the chief olive. The first of these, the mesial accessory olivary nu- cleus (nucleus olivaris accessorius mesial is) is a sagittally placed lamina, from 10-1 1 mm. in length, which lies between the tract of the fillet and the root-fibres of the tii-rvf Tr pYtft-irJc t-F> Section of inferior olivarv nucleus, showing plicated sheet of ray substance traversed by strands of cerebello-olivary fibres. X too. low the inferior olive and, therefore, is encountered in transverse sections at a lower level immediately above the pyramidal 5. Preparation by Professor Spiller. descending root of the vagus and glosso-pharyngeal nerves, shows as a conspicuous transversely cut bundle which lies ventro-mesially to the vestibular root. (4) The descending root of the trigeminal nerve is easily identified as a superficial crescentic field that on its mesial aspect encloses the remains of the substantia gelatinosa Rolandi. The lateral area, between the diverging vagus and hypoglossal root-fibres, is chiefly occupied, in addition to (i) the inferior olivary and (2) dorsal accessory olivary nucleus, by the feltwork of fibres producing the reticular formation. In con- trast to that within the FIG. 929. anterior area, the retic- ulum within the lateral area contains a con- siderable amount of diffuse gray matter be- tween its fibres, and, hence, is known as (3) \h& formatio reticular is grisea. Accessions to the irregularly distrib- uted nerve-cells occur as two moredefinitecol- lections ; one of these, (4) the nucleus am- bi^iius. consists of an inconspicuous group of large cells lying about the middle of the i^ray reticular substance and is of importance as the nucleus of origin of at least part of the motor fibres of the vagus nerve. The other (5), the nucleus laterally includes an uncertain aggregation of medium si/ed cells, situated near the periphery and ventral o- Nerve-cell Transverse fibr Longitudinal _i fibres / Portion of formatio retimhuis K'ist-a, showing nerve-cells and interlacing transverse and longitudinal fibres. X 13- THE MEDULLA OBLONGATA. 1075 from the trigeminal root. A separate group of somewhat larger cells, nearer the ventral border of the trifacial root, has been designated the nucleus lateralis dorsalis, and by Kolliker regarded as belonging to the origin of the spinal accessory nerve. Cochlear fibres crossing restiform body Kestiform body Descending root of vestibular nerve FIG. 930. Striae acusticae Nucleus of IX Median btibular mcleus Deiters' nucleus ti- Post. long. f.\ fasciculus body Substantia gelatinosa l ; ormatio reticularis alba " Tract of mesial fillet - Inferior olivary body V i Fibres of IX nerve . Spinal root of V neive Substantia gelatinosa Formatio reticularis grisea X* 5 "'*' :'-'; ''' * / ' Pyramidal tracts Transverse section of medulla at level G, Fig. 919; ventral part is narrower, whilst dorsal part is expanded owing to increased size of restitorm oodies. X 4- Preparation by Professor Spiller. In a general way the cells of these nuclei (ambiguus and lateralis) of the Substantia grisea may be regarded as the analogues of the lateral horn-cells of the cord, just as those of the hypoglossal nucleus resemble the anterior root-cells of the spinal nerves. The anterior area, between the mid-line and the hypoglossal root-fibres, is occupied ventrally by ( r ) the pyramidal tract, which appropriates the entire width of the field with the exception of a very narrow peripheral zone that intervenes Nerve- Longitudinal Transverse / cell fibres fibres Median raphe Portion of transverse section of medulla, showing median raphe and adjacent formatio reticularis alba. X 130. between the pyramidal fibres and the surface along the median fissure and the ventral aspect of the medulla. This zone is traversed by (2) the anterior superficial arcuate fibres, among which is lodged an irregular column of nerve-cells that constitute (3) 1076 HUMAN ANATOMY. the arcuate nucleus. The latter lies at first chiefly on the ventral and, higher, on the mesial aspect of the pyramidal tract. The cells of this nucleus, small and fusiform, are the origin of not a few of the superficial arcuate fibres, although those from the dorsal nuclei continue their course over the nucleus without interruption. At the upper end of the medulla, the cells of the arcuate nucleus increase in number and mingle with those of the nucleus of the raphe and the pontine nucleus. Dorsal to the pyramid and immediately next the mid-line lies (4) the compact tract of the median fillet, composed of longitudinal fibres that are the upward continu- ation of the deep arcuate fibres, which, from the sensory decussation to the upper limit of the cuneate nucleus, bend sharply brainward after crossing the mid-line. The fillet-tracts are also known as the interolivary stratum, as they constitute a compact and laterally compressed field between the inferior olivary nuclei. Lateral to the fillet, between the latter and the hypoglossal fibres, lies (5) the mesial accessory olivary nucleus. (6) The posterior longitudinal fasciculus appears in cross-section as a compact oval or laterally flattened strand, which lies next the raphe and immediately beneath the gray matter covering the floor of the fourth ventricle. This important path will be later described (page 1116). The remaining space of the anterior compartment, between the pyramid and the ventricular gray matter, is occupied by the formatio reticularis alba, so designated in distinction to the formatio grisea on account of its meagre number of nerve-cells, since, with the excep- tion of those scattered in the immediate vicinity of the mid-line (nucleus raphe), few cells are present. The Formatio Reticularis. Repeated mention has been made of the reticu- lar formation produced by the interweaving of the horizontal and vertical fibres. Whilst particularly conspicuous within the medulla at the levels occupied by the gracile, cuneate and inferior olivary nuclei, on account of the prominence of the arcuate and cerebello-olivary fibres, the formatio reticularis does not end with the disappearance of these nuclei and fibres, but is prolonged upward, although less marked, by transversely coursing fibres derived from the reception-nuclei of various cranial nerves the vagus, glosso-pharyngeal, auditory, facial, and trigeminal from whose neurones axones of the second order arise that sweep across the mid-line to join chiefly the fillet tract or to end, perhaps, about nerve-cells of other nuclei. In this manner the formatio reticularis finds representation within the dorsal or tegmental areas of the pons and the cerebral crura. The longitudinal fibres within the formatio reticularis grisea are derived from many sources. Some are the continuation of Gowers' tract ; some belong to the long strands concerned in establishing reflex paths connecting the corpora quadrigemina, nucleus rubrum, vestibular and olivary nuclei with the spinal cord ; some are the axones of tegmental neurones and pursue shorter courses, both descending and ascending, as association fibres linking together different levels of the brain-stem ; while still others an- the prolongations of the spino-thalamic and other long tracts of the antero-lateral ground- bundle of the cord. The longitudinal fibres of the formatio alba are chiefly the components of the mesial fillet and of the posterior longitudinal fasciculus with, possibly, the addition of short association fibres proceeding from the nerve-cells that are found within the anterior area. The details of a transverse section passing just beneath the lower border of the pons ( I -"ig. 932) vary considerably from those of the level shown in Fig. 930. The ventral half of the medulla has lost in width in consequence of the disappearance of the superficial olivary emi- nence, the inferior olive being at this level represented by only a few irregular plications. The pyramids, likewise, are narrower, and separated by the broadened anterior median fissure. The mesial fillet and the posterior longitudinal fasciculus are now widely separated by the inter- vening nucleus centralis inferior that appears between them along the raphe. The nuclei of the hypoglossal and glosso-pharyngeal nerves are no longer seen, but instead, along the floor of the ventricle underlying the area acustica, appears a large triangular mass of gray matter, the mesial vestibular nucleus. External to the latter the lateral or l^'Hcrs 1 nucleus and the descending or spinal acoustic root lie close to the restiform body, which in transverse section presents a bean-shaped outline. Between the restiform body and the descending trigeminal root. the fibres of the mesial or rcslibular part of the auditory nerve pass backward to gain the vestib- ular nuclei. The outer surface of the restiform body is closely related to a considerable THE PONS VAROLII. 1077 tract of gray matter that collectively constitutes the reception-nucleus of the cochlear division of the auditory nerve. This ganglion is subdivided into a superior and an inferior portion, these being the dorsal cochlear nucleus and the ventral cochlear nucleus respectively. They both receive the fibres of the cochlear or lateral division of the auditory nerve. The ventral cochlear nucleus is the starting point of a tract of transverse fibres, that pass horizontally inward, many traversing the fillet and crossing the raphe, and intermingle with those from the opposite side. They thus form a broad strand, the corpus trapezoides, that within the pons occupies the lower limit of the tegmental region, which it separates from the ventral. In Fig. 932 FIG. 932. Descend- Gray substance Substantia ing root of floor gelatinosa ofVIII ofventricle Nucleus of facial Mesial vestibular nucleus Post. long. / > fasciculus /^-^ Deiters ' nucleus Restiform body Cochlear nerve Dorso-lateral - cochlear nucleus Cochlear nerve and ventral cochlear nucleus , SpimlrootofV . Trapezoidal fibres' / Inferior olivary nucleus , Median fillet Superior Ventral cochlear nucleus olive Tra Pyramidal tract nsverse section of medulla at level H, Fig. 919; pyramids are small and inferior olivary nuclei are disappearing; roots of auditory nerve are entering in relation to restiform bodies. X 4- Preparation by Professor Spiller. only the beginning of this tract is visible, but slightly higher, in the pons (Fig. 933), the trapezoidal fibres are shown in force. Strands of fibres from the cochlear nuclei arch over the restiform body and proceed beneath the ventricular floor to the mid-groove ; these mark the course of the strice acusticce seen crossing the ventricle. Ventro-mesial to the spinal root of the trigeminus and the associated Rolandic substance the nucleus of the facial nerve appears as an irregularly oval and somewhat broken group of large stellate cells, from which the strands of root-fibres pass dorso-medially. THE PONS VAROLII. Viewed from in front, the pons appears as a quadrilateral prominence on the ventral aspect of the brain, interposed between the medulla oblongata below, the cerebral peduncles above, and the cerebellar hemispheres at the sides. Its lower and upper limits are well defined by grooves that separate the corresponding borders from the adjacent divisions of the brain -stem, and between these boundaries the pons measures from 25-28 mm. in the mid-line. Laterally, however, its limits are unmarked, as here the mass of the pons narrows and is directly continued on each side as a robust arm which sweeps downward and backward into the cerebellum as the middle cerebellar peduncle. The fibres of the trigeminal nerves, which are attached near its upper and lateral margins, are taken as the conventional lateral limits of the pons, the transverse diameter measured between these points being about 30 mm. The ventral surface of the pons, strongly convex transversely and less so in the opposite direction, lies behind the basilar process of the occipital bone and the dorsum sellae. It is marked by a shallow median groove (sulcus basilaris), which broadens as it ascends and lodges the basilar artery and is bounded on each side by a slight longitudinal elevation. Where the latter meets the medulla, the pyramid is seen to plunge into the pons beneath its transversely striated surface. The longitudinal ioy8 HUMAN ANATOMY. ridges are produced by the underlying pyramidal tracts in their journey through the pons from the cerebral peduncles to the medulla. The transverse striation indicates the general course of the superficial fibres towards the cerebellum. The lateral surface, continued from the ventral without interruption, above is rounded and sloping and separated from the cerebral peduncles by a distinct furrow. Below, it passes insensibly into the middle cerebellar peduncle, into which the lower and lateral part of the pons is prolonged. Whilst the superficial striation in a general way follows the contour of the pons, a broad band .( fasciculus obliquus pontis) from the upper part of the ventral surface sweeps-obliquely backward and downward and overlies the more horizontally directed middle and lower fibres. The free portion of the dorsal surface of the pons contributes the upper half of the floor of the fourth ventricle and is, therefore, not visible until the roof of that cavity is removed. Above the middle peduncle, the sides of the pons are blended with the overlying superior cerebellar peduncles, which, in conjunction with the intervening superior medullary velum, complete dorsally the ring of tissue sur- rounding the narrowed superior end of the fourth ventricle. INTERNAL STRUCTURE OF THE PONS VAROLII. Viewed in transverse sections the pons is seen to include two clearly defined areas, the ventral and the dorsal (Fig. 933). The ventral part (pars basilaris) presents a characteristic picture in which the large pyramidal tracts are covered in FIG- 933- Abducent fibres Superior cerebellar peduncle Facial fibres Superior cerebellar peduncle Nucleus Post, long Nucleus \ of VI fasciculus of VI Pyramidal tracts [{merging facia] fibn V'estibular fibres Spinal root of V Olivary peduncle Superior olive 1-ormatio reticnlaris uftegmentum Transverse fibres Transverse section of pons at level I, Fig. 910 ; showing general subdivision into ventral and dorsal (tegmental) areas and nuclei of sixth and seventh nerves. X 3. and excluded from the surface by a conspicuous layer of superficial transverse fibres ( stratum suprrticiale pontis), that laterally sweep backward into the cerebellar peduncle and are traversed by the root-fibres of the seventh and eighth nerves. The pyra- mids no longer appear as compact fields, but are broken up into smaller bundles by the transverse strands of ponto-cerebellar fibres. This subdivision becomes more marked at higher levels of the pons (Fig. 936), in which the interweaving of the longitudinal and transverse bundles produces a coarse feltwork ( stratum complexum At the upper border of the pons, the scattered pyramidal bundles become once more collected into two compact strands, which are continued into the central part of the crusta of the cerebral peduncle. The dorsal limit of the ventral field is occupied by a well marked deeper layer of transverse fibres stratum profiimlum pontis K A considerable amount of gray matter, collectively known as the pontine nucleus THE PONS VAROLII. 1079 Portion of cross-section of pons, showing cells of pontine nucleus. X 300. (nucleus pontis) is distributed within the interstices between the bundles of nerve- fibres. The cells of this nucleus, small in size and stellate in form, are closely related to *the ponto-cerebellar fibres of the same and of the opposite side, many constituting stations of interruption in the cortico-cerebellar paths. The dorsal or tegmental part of the pons (pars dorsalis pontis) resembles to a considerable extent in its general structure the formatio reticularis grisea of the medulla, consisting for the most part of a reticulum of transverse and longitudinal fibres, interspersed with nerve-cells, on each side of the median raphe. The appear- ance of certain new masses of gray matter and of nerve- cm. at the side. The cerebellum weighs about 140 gm. (5 oz. ) and constitutes approximately one-tenth of the entire brain-weight. The conventional division into a narrow median part, the worm, and the two lateral expansions, the hemispheres, while convenient for the description of the cerebellum of man, is not warranted by recent comparative and developmental THE CEREBELLUM. 1083 studies (Stroud, Elliott Smith, Bradley, Bolk and others), since some details given prominence in human anatomy are of secondary importance, and others of greater morphological significance are only slightly emphasized. The surface of the cerebellum is divided by the deeper fissures into more or less well defined areas, the lobiiles, each of which is subdivided by shallower clefts into narrow tracts, the folia, from 2-4 mm. in width, that usually pursue a curved course within a given lobule and, in a general way, run parallel to one another and to the sulci bounding the tract. On separating the plate-like folia, or on making a section across the plications (Fig. 943), it will be seen that the pattern of the folia is greatly extended by the presence of numerous additional furrows on the deeper and hidden aspects of the leaflets, which are, therefore, ordinarily invisible from the surface. Whether free or sunken, the exterior of the cerebellum is everywhere formed by a cortical layer of gray matter, from 1-1.5 mm - thick, that encloses a medullary layer of white matter of variable thickness. Owing to this arrangement, sagittal sections of the cerebellum expose an elaborate system of branching tracts of white and gray matter, designated as the arbor vita (Fig. 938). The general ellipsoidal mass of the cerebellum, comprising the narrow central vermis and the expanded lateral hemispheres, presents a superior and an inferior sur- face and rounded anterior and posterior borders. Of these the anterior border is indented by a wide groove, the anterior notch (incisura cerebelli anterior), which is much larger than the posterior and bounded laterally by the cerebellar hemispheres and behind by the anterior part of the worm. It is occupied by the inferior corpora quadrigemina and the superior cerebellar peduncles and FIG. 938. intervening superior medul- / s y hian aqueduct lary velum. The posterior border is interrupted by a smaller median indentation, the posterior notch (incisura cerebelli posterior), which is bounded on each side by the hemispheres and at the bottom by the hind part of the worm, and contains the crescentic fold of dura known as the falx Tela chorioidea- The upper surface of the cerebellum is modelled by the overlying tentorium and presents a slight median trans- versely furrowed ridge that COr- Mesial sag ittal section of brain-stem and cerebellum, showing fourth responds to the Upper surface ventricle, Sylvian aqueduct, and cerebellar worm. of the middle division, or worm, and is known as the vermis superior. The most elevated part of this surface lies a short distance behind the anterior notch. From this point, designated the mon- ticulus, the upper surface slopes gradually downward on each side to the lateral margins of the hemispheres, whilst it falls off more rapidly towards the posterior notch. The lower surface of the cerebellum is much less regular, owing to the pres- ence of a wide median groove, the vallecula, that is bordered laterally by the rounded hemispheres and is continuous in front and behind with the anterior and posterior notches. The bottom of the vallecula is occupied by the irregular ridge-like surface of the middle lobe which is here known as the vermis inferior. The front of the valley receives the dorsal surface of the medulla. The cerebellum is incompletely divided into an upper and a lower part by a deep cleft, the great horizontal fissure (sulcus horizontalis cerebelli). The sulcus begins in front, at the side of the middle cerebellar peduncle, by the junction of two diverging limbs that embrace the three cerebellar peduncles. It passes usually con- tinuously around the circumference of the cerebellum, but sometimes is interrupted 1084 HUMAN ANATOMY. on the worm, and cuts deeply into the lateral and posterior portions of the hemispheres and the worm behind. It is, however, visible on the upper aspect of the cerebellum only for a short distance as it approaches the posterior notch, the remainder of its course being masked by the overhanging border of the hemisphere. Although of cardinal importance in the usual description of the human cerebellum, the great horizontal sulcus is of secondary morphological significance, being a secondary fissure that is developed relatively late in man and feebly or not at all in many other animals. Both the vermis and the hemispheres are subdivided into tracts, or lobules, by the deeper fissures ; these are grouped into lobes, in the conventional division of the human cerebellum, by regarding each median division of the worm as associated with a pair of lateral lobules, one for each hemisphere. LOBES AND FISSURES OF THE UPPER SURFACE. The subdivisions of the superior worm are, from before backward : (i) the lingula, (2) the lobnlns centralis, (3) the culmen, (4) the clivus, and (5) the folium cacuminis. With the exception of the lingula, which usually is unprovided with lateral expansions, these median tracts are connected respectively with (i) the al& lobuli centralis, (2) the anterior crescentic lobule, (3) the posterior crescentic lobule, (4) the postero-siiperior lobule. Lobus Lingulae. The lingula, the extreme anterior end of the superior worm, is not free, but lies attached to the upper surface of the superior medullary velum, covered by the over- hanging adjacent part, lobulus centralis, of the worm, which must be displaced to expose the FIG. 939. Ala lobuli centralis Anterior notch Lobulus centralis Anterior crescentic lobule Posterior crescentic lobule Postero-superior lobule Postcentral fissure Culmen Preclival fissure Postclival fissure Clivus Great horizontal fissure Postero-inferior lobule Folium cacuminis Tuber Cerebellum viewed from above. structure in question. The lingula consists of a tongue of gray matter, composed of five or six rudimentary transverse folia,. that overlies the median and lower part of the superior medullary velum and, therefore, is behind the upper part of the fourth ventricle (Fig. 938). Occasionally the lingula is prolonged laterally by rudimentary folia onto the superior cerebellar peduncles, in which case these extensions, known as the alae lingula; (vincula lingulae) are reckoned as tin- lateral divisions of the lobus lingulae. Lobus Centralis. The median part of the subdivision includes the second segment of the upper worm, the central lobule (lobulus centralis), that lies chiefly at the bottom of the anterior notch and is visible to only a very limited extent on the upper surface of the cerebellum. The central lobule consists of from 15-18 folia, but not infrequently is divided into two sets of leaflets, which then are collectively somewhat more numerous. It is separated from tin- lingula by the precentral fissure and from the culmen by the postcentral fissure. On each side the central folia are prolonged into a triangular tract that curves along the side of the anterior notch, form- ing a lateral wing-like lobule, the ala (ala lobuli centralis). The two alae, in conjunction with the median worm-segment, constitute the lobus centralis. Lobus Culminis. The third division of the upper worm includes the most prominent part of the upper surface of the hemisphere and, being the crest or summit of the general elevation. THE CEREBELLUM. 1085 the monticulus, is called the culmen (oilmen monticuli). It is formed by a half dozen or more longer and shorter folia that laterally are continuous with a lunate area of the hemisphere known as the anterior crescentic lobule (pars anterior lobuli quadrangularis). The latter is the most anterior division of the upper surface of the hemisphere and is a broad crescentic tract limited behind by the preclival fissure(sulcus superior anterior). The two anterior crescentic lobules and the culmen constitute the lobus culminis. Lobus Clivi. The fourth segment of the superior worm slopes rapidly downward from the culmen and receives the name clivus (declive monticuli). It is separated from the preceding part of the worm by a deep cleft, the central part of the preclival sulcus, which on account of its mor- phological importance has been called the fissura prima (Elliot Smith). Laterally the clivus is connected on each side with the posterior crescentic lobule (pars posterior lobuli quadrangularis) which resembles the lobule in front and is separated from the one behind by the postclival fissure (sulcus superior posterior). The clivus and the two posterior crescentic lobules constitute the lobus clivi. The two crescentic lobules, the anterior and posterior, are regarded by German anatomists as constituting one tract, the lobulus quadrangularis, of which the crescentic lobes then become the pars anterior and pars posterior respectively. Lobus Cacuminis. The fifth and last segment of the superior worm, the folium cacuminis (folium vermis), varies greatly in its details. It consists of a narrow plate that lies between the clivus above and the tuber below and includes usually only one or two, exceptionally as many as five or six, small folia. Sometimes it reaches the level of the adjoining parts of the worm, of which it forms the posterior end ; at other times it is so sunken and buried that its presence can be demonstrated only after separating the clivus and tuber, with either of which it is occasionally joined. At best it is insignificant in comparison with the large crescentic tracts, the postero-superior lobules, that it connects. The postero-superior lobule (lobulus semilunaris posterior) includes -the remainder of the upper cerebellar hemisphere of which it forms the most expanded and lateral tract. In front it is separated from the posterior crescentic lobule by the postclival fissure and behind is limited by the great horizontal sulcus, which it overhangs at the side. The folium cacuminis and the two postero-superior lobules constitute the lobus cacuminis. LOBES AND FISSURES OF THE LOWER SURFACE. The inferior surface of the cerebellum is modified by a wide depression, the vallecula, in the broader upper half of which the posterior surface of the tapering medulla oblongata is received. The bottom of the valley is occupied by the irregular projection of the inferior worm, which, when the brain-stem is in place, is covered and not seen, except at its posterior third (Fig. 940). After removal of the pons and medulla by cutting through the cerebellar peduncles and the medullary vela, not only the entire inferior worm is exposed, but also the lobulus centralis and its alse are seen to good advantage. The inferior worm is separated on each side from the adjacent surfaces of the cerebellar hemispheres by a groove, the sulcus valleculae, that is deepened in its anterior third by the close apposition of its lateral boundary (the tonsil) with the worm. The connections between the divisions of the inferior worm from before back- ward (i) the nodule, (2) the iivula, (3) the pyramid and (4) the tuber and the related parts of the hemisphere are less evident and direct than on the upper surface of the cerebellum. The inferior surface includes four lobules which, from before backward, are: (i) the flocculus, (2) the tonsil, (3) the biventral lobule and (4) the postero-inferior lobule. Lobus Noduli. The nodule (nodulus), the most anterior segment of the inferior worm, varies much in size and form, but frequently appears as a rounded triangular prominence, made up of about a dozen folia, that are limited at the sides by the sulcus valleculae and behind by the postnodular fissure. The relation of the nodule to the inferior medullary velum is somewhat analogous, but less intimate, to that of the lingula to the superior velum. The two structures are more or less extensively united, and the nodule thus excluded from the fourth ventricle by the inferior velum that passes beneath the inferior worm to the apex of the posterior recess of the ventricle (Fig. 938). The division of the hemisphere associated with the nodule, the flocculus, lies at some distance from the worm and appears, on either side of the cerebellum, as a wedge-shaped group of short irregular folia that project between the .middle cerebellar peduncle and the anterior border of the hemisphere. When well developed it may touch the adjacent margin of the anterior crescentic lobule of the upper surface. In addition to the chief floccules, io86 HUMAN ANATOMY. composed of from ten to twelve leaflets, a second and smaller set, known as the paraflocculus or accessory flocculus, lies behind and lateral to the main group, often completely buried beneath the overhanging margin of the bi ventral lobule. In the embryo and in many mammals, the paraflocculus is of considerable size and then shares the relatively much greater development of the flocculus than seen in the adult human brain. The connection between the flocculus and the nodule is established by the lateral part of the inferior medullary velum, which constitutes the peduncle of white matter for the floccular folia. In this manner the nodule and the two flocculi, with the intermediate part of the medullary velum, constitute the lobus noduli. Lobus Uvulae. The uvula, the next part of the inferior worm, is laterally compressed between the deeper parts of .the two tonsils. It" varies in form and often appears as a narrow ridge-like structure, triangular on section, of which the median crest alone is seen when the tonsils are in place. The uvula is limited in front by the postnodular fissure, and behind by the prepyramidal, which laterally, as the post-tonsillar fissure, curves outward along the postero- lateral border of the tonsil. The free median surface of the uvula is usually cleft into two or three major subdivisions, which in turn are scored by shallower incisions, so that from six to ten leaflets are present. Some two dozen additional folia mark the hidden lateral surfaces, the entire number being thus usually raised to thirty or more. The tonsil or amygdala (tonsilla), the segment of the hemisphere associated with the uvula, is a pyramidal mass lying between the worm and the biventral lobule and forming the central zone of the general quadrant embracing the lower surface of the entire hemisphere. The free convex inferior surface of the tonsil is irregularly triangular in outline and bounded by a rela- tively straight median margin (along the sulcus valleculae), an outwardly arched postero-lateral FIG. 940. Lobulus centralis Ala lobuli centralis Superior cerebellar peduncle ^^^..^ f'^%m2i^^^^ < ^^' -Superior medullary velum Middle cerebellar peduncle Inferior. ,,--U^ ^. Fourth ventricle medullary velum Great horizontal fissure ^ ^SJfl^' - ^^t Ife'Z "-r^^TIUBs^^k- Nodule Accessory flocculus Postero-inferior ' - " ' '^ '"^ ^* ^ It 1 ^ I "lTT l( v- Superior cerebellar peduncles Acoustic striae^ XY>^ " 111 \ /"*" ' -1?\ <~^ Eminentia teres Trigonum hypoglossi White core of cerebellum Trigonum acustici ^ ___^ Clava Trigonum vagi- Funiculus gracilis Floor of fourth ventricle exposed after removal of its roof by frontal section. named area is a somewhat depressed triangular field of darker color, the apex of which is placed above, near the acoustic striae, and the base below ; this field is known as the ala cinerea, from the dark tint imparted to it by the pigmented cells lying beneath, and as the trigonum vagi, in recognition of the subjacent glosso-pharyngeo-vagus nucleus. The remainder of the inferior division of the ventricular floor includes an elevated triangular field, the trigonum acustici, that is part of the larger tract, the area acustica, which occupies not only the lateral angle of the rhomboidal fossa, where it is crossed by the acoustic striae, but also the adjacent portion of the superior division of the ventricular floor. Laterally, the acoustic area presents a distinct elevation, the tuberculum acusticum, which, together with the adjacent part of the trigonum acustici, is related to the nuclei of the cochlear nerve ; the more median portion of the acoustic area, on the other hand, belongs to the vestibular division. The superior division of the ventricular floor, above the acoustic striae, is marked on each side of the median groove by a prominent elevation, the eminentia teres, which below is continuous with the trigonum hypoglossi and above narrows and fades away towards the floor of the Sylvian aqueduct. Laterally the eminence is bounded by a depressed area, the fovea superior, which is the expanded upper part of a second longitudinal furrow, the sulcus lateralis, that defines the outer limit of the eminentia teres and below is continued into the depressed trigonum vagi, to which the name, fovea inferior, is sometimes applied. Above and to the outer side of the 1098 HUMAN ANATOMY. superior fovea, the ventricular floor presents a slightly sunken field, the locus coeruleus, which extends upward to the Sylvian aqueduct and in fresh preparations possesses a bluish gray tint in consequence of the deeply pigmented cells of the underlying substantia ferruginea (page 1081) showing through the ependymal layer. The accurate description of the surface markings of the ventricular floor given by Retzius, 1 has been supplemented by Streeter's 2 careful study of the relation of these details to the under- lying structures. The most important results of these observations, which have materially advance'd our understanding of this important part of the brain-stem, may here find mention. The trigonum hypoglossi is seen, especially when examined under fluid with a hand-lens, to include two subdivisions, a narrow median and a broader lateral. The first of these is con- vex, about 5 mm. long by i mm. wide, and corresponds to the rounded upper end of the nucleus of the twelfth nerve ; it is, therefore, appropriately called the eminentia hypoglossi (Streeter). The entire hypoglossal nucleus, however, is of much larger size (about 12 mm. long by 2 mm. wide) and extends some 5 mm. below the tip of the calamus scriptorius, ventral (anterior) to the FIG. 949. Colliculus inferior IV. nerve Superior cerebellar peduncle Stria pontis Median fovea V. nerve Superior fovea Eminentia teres Acoustic striae VIII. nerve IX. and X. nerves Trigonum acustici Trigonum hypoglossi Trigonum or fovea vagi Funiculus separens Area post re ma Nucleus cuneatus Nucleus gracilis Floor of the fourth ventricle ; areas corresponding to nuclei of nerves are shown on right half of figure. X j. (Streeter.) vagus nucleus and nucleus gracilis. Lying immediately above the hypoglossal eminence is a second and somewhat less pronounced elevation, formed by the nucleus funiculi teres and meas- uring nearly 6 mm. in length by i mm. in breadth. Lateral to these two median elevations and limited externally by the ala cinerea, lies a wedge-shaped field that is insinuated between the hypoglossal eminence and the vagal trigone. It stretches from the acoustic striae above to the nib of the calamus scriptorius below. This field, named the area plumifonnis by Retzius on account of its feather-like markings, is regarded by Streeter as corresponding to a group of cells, the nucleus intercalatus, that occupies a superficial position in the ventricular floor and partly overlies the hypoglossal nucleus. The fovea vagi (ala cinerea), which lies lateral to the nucleus intercalatus, corresponds to the middle and superficial third of the vago-glosso-pharyngeal nucleus, the entire extent of tin- latter including a tract measuring about 13 mm. in length by 2 mm. in breadth, that stretches from beneath the vestibular nucleus above to over 2 mm. beyond the inferior angle ot tin- ventricle. The lower third of the area of the vagus nucleus is partly within the ventricle ; immediately above the obex this intraventricular portion is covered by a layer of loose vascular tissue and appears as an upwardly diverging pointed field, area postrema of Retzius. This i separated from the ala cinerea by a translucent ridge, the funiculus separens, composed of thickened ependymal neuroglia (Streeter). 1 Pas Menchenhirn, 1896. *Amer. Journal of Anat. Vol II, 1903. Area n. trigemini N. facialis Area n. abducentis Area n. vestihularis Area n. cochlearis Area nuc. funic. teretis Funiculus solitarius Area n. vagi Area n. hypoglossi THE FOURTH VENTRICLE. 1099 The prominence of the eminentia teres is due to the underlying nucleus of the sixth nerve, enclosed by the knee of the facial ; for it, therefore, Streeter proposes the name eminentia abdu- centis. The longitudinal ridge that continues upward and bounds the median fovea, the last cited author interprets as due to a field of gray matter, thin in the vicinity of the abducent eminence and thicker above, to which the name nucleus incertus is applied. Lateral to the nucleus incertus and the facio-abducent eminence, lies the fovea anterior, which elongated and depressed area (nearly 6 mm. long by i mm. wide) is due to the exit of the root of the fifth nerve ; it may, therefore, be called the fovea trigemini. The median portion of the elevated acoustic area includes the elongated and irregularly lozenge-shaped vestibular area, that measures about 16 mm. in length by 4 mm. in breadth and extends from the fovea anterior (trigemini) to the nucleus gracilis. The lateral part of the area acustica is occupied by the cochlear area, which stretches into the recessus lateralis and overlies the nucleus cochlearis. The Roof of the Fourth Ventricle. Viewed in median sagittal section (Fig. 938), the roof of the fourth ventricle appears as a tent-like structure, whose wings, where they come together, bound a space, the recessus tecti, that penetrates the cerebellar medulla between thesuperior FIG. 950. and inferior worm. The upper wing of the tent is formed by the superior med- ullary velum, the triangular sheet of white matter stretch- ing from beneath the quadrigeminal bodies above to the medullary substance of the cerebellum below, and is over- laid by the rudimen- tary cerebellar folia of the lingula. It must be understood that the ventricular surface of the velum Corpora quadrigemina Superior cerebellar peduncle Roof of fourth ventricle Tela chorioide and choroid pie White core o[ cerebellum Dorsal portion of preparation shown in Fig. 948 ; roof of fourth ventricle is seen from below. is clothed by the ependyma as are all other parts not only of the fourth ventricle but of all the ventricular cavities. Laterally the superior medullary velum is attached to the superior cerebellar peduncles, which to a limited extent share in closing in this part of the ventricle (Fig. 936). The lower half of the roof comprises two parts, an upper and thicker crescentic plate of white matter, the inferior medullary velum, and a lower and extremely thin membrane, the tela chorioidea. Medially the inferior medullary velum is attached for some distance to the front and lower surface of the nodules, which it excludes, strictly regarded, from the ventricle, whilst laterally the velum is prolonged to the flocculus, its fibres becoming continuous with the white core of this subdivision of the cerebellum. The nervous constituents of the velum extend only as far as its crescentic lower border, beyond which the roof of the ventricle, in a morphological sense, is formed by the ependymal layer alone. This, however, is supported by a backing of pial tissue, which, in conjunction with the ependyma, forms the tela chorioidea. On nearing the lower angle of the ventricle, the roof presents a trian- gular thickening, the obex, that closes the cleft between the clavae and lies behind (above) the nib of the calamus scriptorius. On each side the obex, which consists of a layer of white matter fused with the underlying ependyma, is continuous with the slightly thickened margin of the roof, the taenia ventriculi, whose line of attachment passes from the clava upward and outward over the cuneate tubercle of the medulla and the restiform body and, farther upward, runs obliquely across the dorsal surface of this peduncle to close in the lateral i ioo HUMAN ANATOMY. recess one of the pair of diverticula that overlie the inferior cerebellar peduncles and add materially to the transverse dimension of the ventricle. After enclosing the lateral recess the taenia leads to the stalk of the flocculus and the inferior velum. Within the triangular field of the teia chorioidea, the pia mater takes advantage of the attenuation of the ventricular wall to effect invaginations by which its blood- vessels apparently gain entrance into the ventricle. Such invaginations, known as the choroid plexus of the fourth ventricle, occur in the ventricular roof on each side and in the immediate vicinity of the mid-line, where they appear as parallel villous or fringe-like stripes, the median plexus, which extends upward from near the obex to the inferior medullary velum. Opposite the nodules they FIG. 951. Roof-nuclei Nucleus globosus Nucleus emboliformis Nucleus dentat Choroid plex j^Medalta Fibres of IX. ne Spinal root_ of V. nerve" ^__ __ __ ' *-- Cerebellum ) (flocculus) Lateral recess of ventricle' sS^&$S$$&$ Inferior olivary nucleus '' 1 . ." > ' > Posterior longitudinal fasciculus Pyramidal tracts Mesial fillet Section across lower third of fourth ventricle, showing internal cerebellar nuclei, choroid plexus, lateral recesses and medulla ; new-born child. X 3%. Preparation by Professor Spiller. diverge and, as the lateral plexuses, invaginate the wall of the lateral recesses. The vascular complex lies within the fold of pial tissue, the space between the pial layers being occupied by prolongations of the arachnoid. Notwithstanding its conspicuous thinness during the first half of foetal life, the tela chorioidea suffices to completely close the ventricle. From about the fifth month, however, the delicate membrane is perforated by an aperture that remains throughout life. This opening, the foramen of Majendie (apertura medialis ventriculi quart! ') lies immediately above the obex and between the strands of the choroid plexus. Two additional clefts, the foramina of Luschka (aperturae laterales), usually exist, one on each side, in the wall of the lateral recesses in the neighborhood of the vago- glosso-pharyngeal nerves. By means of these three openings, and probably by these alone, the system of ventricular cavities and the central canal of the spinal cord are brought into communication with the subarachnoid lymph-space. A path is thus provided by which the cerebro-spinal fluid, secreted within the lateral, third and fourth ventricles by the various choroid plexuses, constantly escapes and thereby prevents undue accumulation and distension within the cavities of the brain and spinal cord. THE DEVELOPMENT OF THE HIND-BRAIN DERIVATIVES. In the general sketch of the development of the brain previously given (page 1061), it was pointed out that the hind-brain, or rhombcnccphalon, includes two subdivisions, the myclcncef>h- ahnt and the >n<-ti'>ncf>hii/on, the extreme upper part of the latter being designated the isthmus. It has been further noticed that the junction of the cord and brain-segments of the neural tube corresponds with the conspicuous cervical flexure, whose early appearance is followed by an DEVELOPMENT OF HIND-BRAIN DERIVATIVES. I 101 FIG. 952. outward bending of the lateral walls of the brain-vesicle and the stretching and flattening of the roof-plate. In consequence of these changes the roof of the rhombencephalon becomes reduced to an attenuated sheet which, when viewed from above, appears as a lozenge-shaped membrane that closes in the subjacent cavity, the subse- quent fourth ventricle. It has also been pointed out (page 1049) tnat t' ie relatively thick lateral walls of the neural tube exhibit, even within the cord-segment, a differentiation into a dorsal and a ventral zone (the alar and basal lamime of His), which subdivisions are associated with the sensory and motor root-fibres of the nerves respectively. Similar relations, in a more pro- nounced degree, are evident within the brain- stem and are of much interest as indicating the morphological correspondence of the purely motor nerves (the third, fourth, sixth and twelfth) on the one hand, and of the mixed nerves (the fifth, seventh, ninth and tenth) on the other. The Medulla. The great preponderance of the nervous matter along the floor of the fourth ventricle, as represented by the medulla, is due primarily to the outward bending of the lateral walls of the myelencephalon, supple- mented by the accession of large tracts of nerve-fibres that later grow in from other parts of the cerebro-spinal axis. In consequence of the former change, the dorsal zones of the side-walls are gradually displaced laterally ; at the same time they become partly folded on themselves to produce along their outer margin the rhombic lip (His), which is directly continuous with the expanded and thin roof-plate. Later, the dorsal zones come to lie almost horizontally, their ventricular surface corresponding with that of the ventral laminae, in conjunction with which the floor of the definitive fourth Mid-brain Right hemisphere Inferior colliculus Roof-plate Cerebellum Cavity of hind-brain Lateral recess Rhombic lip Attachment of roof Medulla Reconstruction of brain of human embryo of 22.8 mm., showing hind-brain and part of mid-brain viewed from behind. X 12. Drawn from model made by Dr. Ewing Taylor. FIG. 953. Superior colliculus. y of mid-brain Superior medullary velum Hemisphere of cerebellum ventricle is later formed. Coin- cidently with the outward mi- gration of the dorsal laminae, the ventral zones also thicken and assume a much more hori- zontal position, with their inner ends separated superficially by a median furrow and, deeper, by the compressed remains of the floor-plate. Very early and before the flattening out of the myelencephalon has advanced to any marked extent, the de- marcation between the dorsal and ventral zones is evident as a lateral longitudinal groove on the ventricular surface of the myelencephalon. Indica- tions of this division persist and in the adult medulla are represented by the fovea pos- terior and the sulcus lateralis seen on the floor of the fourth ventricle. As in the cord-seg- ment, so in the myelencepha- lon the lateral walls are the only regions of the neural tube in which neuroblasts are devel- oped, the roof-plate and the floor-plate containing spongioblasts alone. Very early and before the flattening out of the myelencephalon has advanced to any marked extent, within the ventral zones and close to the mid-line, appear groups of neuroblast, from which axones grow ventrally to form the root-fibres of the motor (hypoglossal) nerves. Sensory Cavity of hind-brain (IV ventricle) Roof of hind-brain, lo \ Reconstruction of hind-brain of human embryo ot about three months (50 mm.), viewed from side and behind. Drawn from His model. 1102 HUMAN ANATOMY. fibres are also early represented by bundles which grow centrally from the ganglion of the vagus towards the developing medulla, upon whose surface, opposite the junction of the dorsal and ventral zones, they appear as a flattened oval bundle (fasciculus solitarius). For a time super- ficial and loosely applied, this bundle gradually becomes more deeply placed in consequence of the extension, ventral folding, and final fusion of the rhombic lip with the remainder of the dorsal zone. Subsequently the fasciculus solitarius becomes still farther removed from the surface by the ingrowth of tracts of nerve-fibres from the neuroblasts of the rhombic lip and from other sources until, finally, the bundle comes to lie FIG. 954. beneath the ventricular floor where its position permanently indicates the junction between the original dorsal and ventral zones of the medul- lary wall. In a similar manner the sensory fibres of the trigeminal nerve are applied to the sur- face of the developing pons ; since, however, the bundle is attached after consolidation of the dorsal zone of the medulla has begun, the descending trifacial fibres retain the relatively superficial position characterizing the spinal root, while the descending root (fasciculus solitarius) of the glosso-pharyngeo-vagus lies more deeply placed. Subsequent to the invasion of the medulla by the sensory parts of this nerve, the outgrowth of the axones from the neuroblasts constitut- ing the nucleus of origin provide its motor root- fibres. The rhombic lip is a region of much impor- tance, since from the neuroblasts which appear within it are derived the cells of the reception nuclei (substantia gelatinosa) of the sensory cranial nerves, of the nuclei of the posterior col- umns, of the inferior and accessory olivary nuclei and of the arcuate nucleus. From the neuro- blasts many axones grow medio-ventrally, pierce the median spongioblastic septum derived from the primary floor-plate, which later becomes the median raphe, and gain the opposite side and thus establish the systems of arcuate fibres. Other axones grow dorsally and take part in even- tually producing the fibre-tracts connecting the olivary, dorsal and arcuate nuclei with the cere- bellum. It is evident that the development of the myelencephalon primarily contributes the nerv- ous substance that becomes the dorsal part of the medulla and underlies the fourth ventricle. Later the closed part of the medulla, which at first is wanting, as well as the conspicuous pyramidal tracts, are added as the strands of ascending and descending fibres grow into the medulla from the spinal cord and from other parts of the brain. In this manner the important tracts of the posterior columns and the spinal constitu- ents of the restiform body and of the brain-stem are added and, still later, the bulky pyramids take form when the cerebro-spinal paths are established. In accord with the falling apart and thick- ening that affect the lateral walls of the myi- lencephalon and lead to the production of the medulla, the roof-plate of the brain-vesicle becomes flattened and laterally expanded to keep pace with the increasing width of the ventricular floor. In consequence, the roof-plate is converted into a rhomboidal sheet of great delicacy, tin- primary velum, which histologically consists of littK- more than the layer of ependymal rt-lls. These, however, soon come into close relation with the overlying mesoblastir tissue- from which tlu- pia is differentiated. During the third month a transverse fold, tin- f>lica chorioidca, appears in the roof-sheet, near the posterior limit of the developing cerebellum (Fig. 955, B}. Into this Transverse sections of hind-brain of human embryos, showing three stages in development of medulla ; A, about four and a half weeks; H, about six weeks; C, about eight weeks ; rp, roof-plate ; r, raphe ; ti. v, dorsal (alar) and ventral (basal) laminze ; rl, rhombic lip ;./-, lateral recess; fs, fasciculus solitarius; cr. restiform body ; xii, hynoglossal nerve ; sv, spinal root of trigeminus ; to, inferior olivary nucleus, (ffis.) DEVELOPMENT OF HIND-BRAIN DERIVATIVES. 1103 duplicature, directed towards the brain cavity, the mesoblast grows and later develops blood- vessels, and is converted into a vascular complex that eventually forms the choroid plexus of the fourth ventricle. From the manner of its development, it is evident that the plexus is excluded by the ependymal layer from the ventricular space, outside of which the pial blood-vessels, therefore, really lie. The conversion of the upper part of the primary velum into the thicker definite inferior medullary velum follows the addition of nervous substance during the develop- ment of the cerebellum. Similar thickening of the roof-sheet at the lower angle of the ventricle results in the production of the obex and the tasniae. The Pons. The pons arises as a thickening of that part of the metencephalon which forms the anterior wall of the pontine flexure. In its essential phases the development of the pons probably closely resembles that of the medulla, since the early metencephalon presents the same general features as does the myelencephalon. Thus, the ventral zones of its lateral walls play an active role in the production of the tegmental portion of the pons and the nuclei of origin of the motor root-fibres of the fifth, sixth and seventh nerves, whilst the floor-plate becomes the raphe. In addition to providing the reception-nuclei of the sensory cranial nerves, and, per- haps, the pontine nuclei, the dorsal zones contribute the neuroblasts which FIG. 955. become the nervous elements of the cerebellum. As in the medulla, so in the pons the great ventral tracts are secondary and relatively late additions to the tegmentum, which must be re- garded as the primary and oldest part of this segment of the brain-stem, the bulky ventral nervous masses taking form only after the appearance of the cerebro-spinal and cerebro-cerebellar paths. In a manner analagous to that by which the sensory part of the vagus is at first loosely applied and later in- corporated with the medulla, the sen- sory fibres of the trigeminus are for a time attached to the surface of the dorsal zone of the pons, subsequently becoming covered in and more deeply placed by the addition of peripheral tracts. Likewise the fibres of the audi- tory nerve come into relation with the superficially situated reception-nuclei of the cochlear and vestibular nerves. The Cerebellum. The develop- ment of the human cerebellum pro- ceeds from the roof-plate and adjacent parts of the dorsal zones of the lateral walls of the metencephalon. In an embryo 22.8 mm. long, the cerebellar anlage consists of two lateral plates connected by a narrow thin intervening lamina representing the roof-plate (Fig. 952). After the apposition of the lateral plates, which soon occurs, this bridge disappears, the developing cerebellum for a time appearing as an arched lamina enclosing the upper part of the cavity of the hind-brain (Kuithan 1 ). The subsequent development of the human cerebellum has been recently carefully studied by Bolk 2 in a series of about forty foetuses, hardened in formalin and ranging from 5 to 30 cm. in their entire (crown-sole) length. The following account is based largely on these investigations. In a foetus of 5 cm. , about nine weeks old, the cerebellar anlage is represented by a horseshoe- shaped thickening of the metencephalic roof, the cerebellar lamina, whose upper margin is con- nected by the encephalic fold with the mid-brain and whose lower border has attached to it the primary velum the thin rhomboidal roof-plate of the myelencephalon. Median sagittal section of the cerebellar lamina at this stage (Fig. 955, A] shows its form to be asymmetrically biconvex, the more convex surface encroaching upon the brain-cavity. In a slightly older foetus ( Fig. 955. B) the cerebellar lamina has become triangular, in section presenting a superior, an anterior, and an inferior surface. From its attachment along the superior margin of the lamina the inferior velum dips forward toward the pontine flexure and, forming a transversely cresentic 1 Miinchner med. Abhand., 1895. 2 Petrus Camper, 36 Deel, 1905. Median sagittal sections showing four early stages of develop- ment of human cerebellum, from foetuses from 5 to 9 cm. long; nib, mid-brain ; c, cerebellum ; sv, iv, superior and inferior medul- lary velum ; vc, ventricular cavity ; d, cavity of diencephalon ; p, pons ; m. medulla ; .r, spinal cord ; if, incisura fastigii ; /, sulcus primarius ; j, sulcus postnodularis. (Drawn from figures of Bolk.) HUMAN ANATOMY. fold, the plica chorioidea, bounds a narrow recess that extends along the inferior surface of the cerebellar lamina. This recess is only temporary and is soon obliterated by the subsequent at- tachment of the roof-membrane to the inferior surface of the cerebellar lamina. The succeeding stage (Fig. 955, C) emphasizes the alteration in the planes of the cerebellar surfaces, the former superior now becoming the anterior, the anterior the inferior, and the inferior the posterior. From the posterior margin of the dorsal surface the choroid fold dips into the brain-cavity. Between the mid-brain and the cerebellum now stretches the first definite indication of the later superior medullary velum. In agreement with His, Bolk recognizes that the former intraven- tricular (inferior) surface has now become an extraventricular one and that the permanent attach- ment of the plica chorioidea corresponds to a secondary and not to the primary line of union. The stage represented in Fig. 955, D is important, since it marks the beginning of the first fissures. One of these, the sulcus primarius (the fissura prima of Elliot Smith), appears as a transverse groove on the upper part of the anterior surface and thus early establishes the funda- mental division of the cerebellum into an anterior and a posterior lobe. The other fissure appears in the median area near the posterior margin of the cerebellum and is the sulcus post- nodularis. On each side (Fig. 956, A ) an additional fissure cuts off a narrow tract that embraces the postero-lateral area of the cerebellum. This fissure, the sulcns flocc ularis, for a time remains ununited with the postnodular sulcus ; but later, with its fellow, it becomes continuous with the postnodular sulcus and thus defines a narrow band-like tract, the median part of which FIG. 956. 4 2 2 4 Six stages in development of human cerebellum, from foetuses of 9 (A), 13 (B), i (C), 22 (D), 25 (), and 32 cm. (F) length; /, sulcus primarius (preclival) ; 2, s. floccularis ; j, s. postnodulans ; 4, s. mfrapyramidalis ; 5, s. superior posterior (postclival) ; h, great horizontal fissure; mb, mid-brain; r, roof-membrane; Ir, lateral recess; , nodulus ; , uvula ; /, pyramis ; t, tuber ;/, folum. (Drawn from figures of Bolk.) eventually becomes the nodule, the lateral portions the flocculi, whilst the intervening strips become the floccular peduncles and part of the inferior medullary velum. The diverticulum bounded on each side by the floccular area is the beginning of the lateral recess of the fourth ventricle and is early filled by the rapidly growing choroid plexus. A shallow transverse groove, the incisura fastigii, just suggested in Fig. 955, C but distinct in the succeeding sketch, marks the beginning of the tent-like recess that later conspicuously models the roof of the fourth ventricle. Coincidently with and about midway between the fissures just described, a third furrow appears on the posterior cerebellar lobe. This is ihefasura secunda (Elliot Smith) or the infra/>yniini(ln/ sn/cits. Very shortly a fourth groove appears behind the sulcus primarius and marks the beginning of the prepyramidal fissure. In this manner the median trad of the postrior lobe is early subdivided by three fissures into four areas, which, from behind touan! the sulcus priniai !us, give rise to the nodule, the uvula, the pyramid and a still undifferentiated zone. By the subsequent appearance of additional furrows, this narrow /one gives origin to the nil), r, the folium caaiminis and tin- clivus. Meanwhile on the anterior lobe of the cerebellum three short transverse fissures appear, by which the anterior end of the worm-tract is broken up into areas that, while establishing subdivisions of morphological value (Bolk), are later lost in the uncertain foliation of the lingnla and lobulus rentralis of the mature cerebellum. After the fundamental subdivision of the median area (worm) has been accomplished, the lateral masses (hemispheres) of the cerebellum become subdivided into definite tracts (lobules) by fissures that appear during the fourth and filth months of foetal life. The lateral extensions THE MESENCEPHALON. 1105 of the sulcus primarius itself the later preclival fissure separate the anterior and posterior crescentic lobules. During the fourth month the postlunate fissure appears, in each hemisphere, on the upper surface of the posterior lobe. By the extension and medial union of these sulci, for a time separate, are established the posterior limit of the clivus (postclival fissure) and the demarcation between the posterior crescentic and the postero-superior lobule. The post-tonsillar fissure bounds the conspicuous elevation of the tonsil behind and medially joins the infrapyram- idal (later prepyramidal) sulcus. The parapyramidal fissure defines the upper (posterior) limit of the biventral lobule and unites with the suprapyramidal (later postpyramidal) fissure. The great horizontal fissure, so conspicuous in the mature cerebellum, appears relatively late, about the end of the fifth month, and is at first represented by a shallow transverse median fur- row that lies immediately in front of the suprapyramidal fissure (Bolk) , an origin at variance with the generally accepted formation of the horizontal fissure by the union of two lateral sulci, that grow medially from the hemispheres and meet in the worm. The early fissure having such history, Bolk identifies as the postlunate (sulcus superior posterior) and not as the horizontal. This author also emphasizes the fact that at the sixth foetal month the folium cacuminis is, as a rule, not only defined, but forms a well-marked superficial tract that connects the adjoining lateral tracts (postero-superior lobules). This part of the worm, however, does not keep pace with the cortical expansion of the surrounding parts and, hence, becomes overgrown by these and sinks into the relative insignificance that distinguishes this part of the worm in the fully matured cerebellum. In consequence of the rapid growth and expansion of the peripheral portions of the human- cerebellum, some fissures of secondary morphological importance, as the horizontal, become excessively deepened and more conspicuous in man than those of fundamental significance, as the sulcus primarius (preclival) and the postnodular fissures. This cortical expansion, especially within the superior region, likewise brings about prominent changes in the position of the segments of the worm, so that eventually those which primarily lay behind later come to lie below, the divisions of the conventional upper and lower worm of the mature cerebellum following along the C-like curve seen in sagittal sections. The histogenesis of the cerebellar cortex probably primarily proceeds from the invasion of the cellular lamina by the cells of the dorsal zones of the lateral walls of the metencephalon, as well as directly from these zones themselves. The earliest differentiation results in the production of three strata : (a) the inner ependymal layer, and (d) the middle mantle layer, and (c) the outer marginal layer. Of these the mantle layer is the thickest and richest in cells, from which both neuroblasts and spongioblasts arise, although their differentiation occurs relatively late. The Purkinje cells, early distinguishable by their large clear nuclei, appear during the sixth foetal month, but for some time lack their characteristic processes. Likewise from the mantle layer are derived the earliest constituents of the granule layer. Meanwhile within the marginal layer, immediately beneath the external surface of the cerebellum, an additional and temporarily con- spicuous cell-stratum, the external granule layer, becomes a prominent feature of the develop- ing cerebellar cortex. This layer soon exhibits a subdivision into two zones of which the outer contains many dividing cells, while the inner is almost free from karyokinetic figures. During the later months of foetal life the inner sublayer disappears and at birth the outer one is greatly reduced ; finally, this also disappears, so that after the earliest years of childhood the external granule layer is no longer seen. The chief factor in this reduction and eventual obliteration of this stratum is, according to Cajal, the gradual transformation of its neuroblasts into nerve- cells that recede from their peripheral position to assist in the completion of the granule layer, as whose small and characteristically branched elements they persist. Other neurones of the external granule layer are transformed into the basket cells and the large stellate cells. The neuroglia of the cerebellar cortex is derived chiefly from the spongioblastic elements of the inner or ependymal layer, the conversion of the cells of the outer grannie layer into the supporting tissue, as sometimes assumed, being unlikely (Ziehen). Since the molecular layer is composed to a considerable extent of the dendritic processes of the Purkinje cells, the development of the outer division of the cerebellar cortex is complete only after the growth of such processes, as well as of the climbing fibres from the white core, has taken place. The production of the superior cerebellar peduncles and of the definite superior medullary velum is dependent upon the development of the fibres that pass from and to the dentate nucleus and the cerebellar cortex an invasion that occurs during late foetal and early post- natal life. THE MESENCEPHALON. Notwithstanding its considerable size and prominent position in the embryo, in its mature condition the mesencephalon, or mid-brain, forms the smallest and least con- spicuous division not only of the brain-stem but also of the entire brain. Neverthe- less, the many fundamental tracts which it contains, as well as the new paths and combinations which arise within its substance, confer on the mid-brain an importance 70 uo6 HUMAN ANATOMY. not suggested by its size. Its upper limit corresponds with an oblique plane passing through the base of the pineal body and the posterior border of the corpora niam- millaria ; its lower one is indicated on the ventral surface by the upper border of the pons and on the dorsal aspect by the upper margin of the superior medullary velum. As seen in sagittal sections (Fig. 938,) the mid-brain is about n mm. in length, although when measured on the ventral surface it is slightly shorter (9 mm.) and on the dorsal aspect a little longer (13 mm.). Its greatest breadth is approximately 23 mm. The mid-brain is traversed longitudinally by a canal, the Syh'ian aqueduct, which, however, lies much nearer the dorsal than the ventral surface of the brain-stem. When the several parts of the brain are undisturbed, only a portion of the ventral aspect of the mid-brain can be seen. Its dorsal and lateral surfaces are hidden by the overhanging cerebral hemispheres, the splenium of the corpus callosum and the pulvinar of the thalamus being in close relation with these surfaces respectively. Notwithstanding its ventral position and apparent removal from the exterior of the brain behind, the dorsal surface of the mid-brain is, in fact, directly continuous with FIG. 957. Thalamus Trigonum habenulse Pulvinar Colliculus superior Cerebral peduncle Fourth nerve Pons Superior cerebellar peduncle T;eiiia thalami Commissura habenulse "Pineal body Median geniculate body Brachium inferior Colliculus inferior Frenulum veli Lingula Cerebellum, cut surface Mid-brain viewed from behind ; upper part of cerebellum has been removed to expose superior medullary velum with lingula. and a part of the free posterior surface of the brain. It is, therefore, covered with the pia mater, as may be demonstrated by drawing aside the overhanging cerebral hemispheres. In situ the mid-brain occupies the opening bounded by the tento- rium and thus connects the divisions of the brain which lie within the posterior cra- nial fossa (cerebellum, pons and medulla) with those (cerebral hemispheres) that lie above. Its cavity, the Sylvian aqueduct, establishes direct communication between the third and fourth ventricles. The mid-brain includes two main subdivisions, a smaller dorsal part, the quadrigeminal plate, which roofs in the Sylvian aqueduct and bears the corpora quadrigemina, and a much larger ventral part, made up by the cerebral pedimdes. The quadrigeminal plate lies behind the plane of the roof of the Sylvian aqueduct and extends from the base of the pineal body above to the upper margin of the anterior medullary velum below. Its dorsal surface is subdivided into four \\hitc rounded elevations, the corpora quadrigemina, by two grooves, one of which is a median longitudinal furrow and the other a transverse furrow that crosses the first one at right angles and slightly below its middle point. The upper part of the longi- tudinal groove, between the upper pair of elevations, broadens into a shallow trian- gular depression, the pineal fossa (trii{onum subpincnlc) in which rests the pineal body. Below, the mid-furrow ends at the base of the frenum of the superior medul- lary velum. THE MESENCEPHALON. 1107 Pulvinar Superior colliculu; Inferior colliculus Superior medullary velum Superior cerebellar peduncle Lingula Middle cerebellar peduncle, cut FIG. 958. Superior brachium i Median geniculate body / / Lateral geniculate body Tractus transversus Cerebral peduncle Optic tract The elevations forming the upper pair of quadrigeminal bodies, the colliculi superiores, are the larger and more conspicuous, and measure from 7-8 mm. in length, about 10 mm. in breadth, and 6 mm. in height. Laterally each superior col- liculus is continued into an arm, the superior brachium (brachium quadrigeminum superius) which is denned by a groove above and below, and passes upward and outward, between the optic thalamus and the median geniculate body, to be lost within an indistinctly circumscribed oval eminence, the lateral geniculate body (corpus geniculatum laterale), which lies beneath the pulvinar. In like manner, each of the smaller lower pair of quadrigeminal bodies, the colliculi inferiores, (about 6 mm. in length by 8 mm. in breadth and 5 mm. in height) is prolonged laterally into the inferior brachium (brachiura quadrigerainum inferius), which in turn ends in the sharply denned median geniculate body (corpus geniculatum mediale), an oval elevation about 10 mm. in length. Ventrally the quadrigeminal plate becomes directly continuous with the adjacent part of the cerebral peduncles. The cerebral peduncles (pedunculi cerebri), also called the cerebral crura, constitute the bulky ventral part of the mid-brain. Dorsally, the two peduncles are fused into a continuous tract, the tegmentum, which contributes the side-walls and floor of the Sylvian aqueduct and blends on each side with the overlying quadri- geminal plate. Ventrally the peduncles are unfused and appear on the inferior sur- face of the brain as two robust stalks (Fig. 993). These emerge from the upper border of the pons and pass, diverging at an angle of from 70-85, upward and out- ward to enter, one on each side, the cerebral hemi- spheres just where the peduncles are crossed by the outwardly winding optic tracts. At the pons each peduncle possesses a breadth of from 12-15 mm., which increases to from 18-20 mm. at the upper end of the stalk ; the borders of each peduncle are, therefore, not quite parallel, but slightly di- verging. Neither are the mesial margins of the pe- duncles in contact as they issue from the pons, but separated by an interval of about 3 mm. This distance increases until at their upper ends the peduncles are about 13 mm. apart. Superficially each peduncle is formed by strands of fibres which do not pursue a strictly longitudinal course, but wind spirally from within outward ; in consequence of this arrangement the surface of the peduncle presents a characteristic twisted or rope-like striation. The regularity of this marking is sometimes disturbed by a faintly defined strand of fibres (tractus peduncularis transversus), that winds over the median border and ventral surface of the peduncle, passes upward and outward across the lateral surface of the mid-brain, to be lost in the vicinity of the medial geniculate body. The depressed triangular area included between the diverging peduncles is the interpeduncular fossa, the floor of which is pierced by numerous minute openings that transmit small blood-vessels, and hence is known as the posterior perforated substance. The blunted inferior angle of the fossa, immediately above the pons, corresponds with a depression, the recessus posterior; another, but less marked depression, the recessus anterior, is bounded by the postero-median surfaces of the mammillary bodies. A shallow lateral groove (sulcus mcsencephali lateralis) extends along the outer surface of the peduncle, whilst along its inner aspect, and therefore looking into the interpeduncular fossa, runs the median or oculomotor groove (sulcus nervi oculomotorius), that is more distinct than the lateral furrow and Dorso-lateral aspect of mid-brain. iio8 HUMAN ANATOMY. marks the line along which the root-fibres of the third cranial nerve emerge. On transverse section (Fig. 963) these furrows are seen to correspond with the edges of a crescentic field of deeply pigmented gray matter, the substantia nigra, by which each peduncle is subdivided into a dorsal portion, the tegmentum, and a ventral part, the crusta (basis pedunculi). The latter lies ventral to the superficial lateral and median furrows, and contributes largely to the bulk of the free part of the peduncle. When traced upward it is found to enter the cerebral hemisphere and become continuous with the internal capsule. It contains the great motor tracts and is the chief pathway by which efferent cortical impulses are transmitted to the lower lying centres. The tegmentum, on the contrary, in a general way is associated with the sensory tracts, and, above, enters the subthalamic region (page 1127). The dorso-lateral surface of the mid-brain, just where it passes into that of the superior cerebellar peduncle, shares with the latter a triangular area, the trigo- Emerging fibres of fourth nerve Fourth nerve, cut Lateral fillet Posterior longitudinal fasciculus Tegmental field Mesial fillet FlG. 959. Decussation of fourth nerve ,Sylvian aqueduct gray substance Mesencephalic root of trigeminus Substantia ferruginen Superior cerebellar peduncle I)ecussation of cerebellar peduncle Pyramidal tracts Transverse fibres Transverse section of brain-stem at level L (Fig. 919), junction of pens and mid-brain ; superior cerebellar pt-dun- cles are beginning to decussate ; trochlear decussation seen above Sylvian aqueduct. Weigert-1'al staining Preparation by Professor Spiller. num lemnisci, which, as implied by its name, is related to the underlying and here superficially placed tract of the fillet (lemniscus). Above, this area extends as far as the inferior brachium and is limited in front by the sulcus mesencephali lateralis, whilst behind it is defined from the superior cerebellar peduncle by a_ slight furrow (sulcus limitans posterior). When closely examined the triangular field is seen to be subdivided by a faint groove into an upper and a lower area, which correspond with the underlying fibres of the lateral and of the mesial fillet respectively. A superficial strand of fibres, the tractus peduncularis transversus, is sometimes seen crossing the lateral surface of the mid-brain. It appears on the dorsal aspect of the latter, between the inferior brachium and the median genirulate body, winds around the latero-ventral surface of the peduncle and disappears in the vicinity of the mammillary body. According to Marburg, the strand establishes a connection between the optic tract and a nucleus in the floor of the third ventricle and represents, in a rudimentary condition, the basal optic root found in many animals. The Sylvian aqueduct Caqu.-icductus ccrc-bri ) represents the cavity of the middle brain-vesicle and, there-fore, is lined with an ependymal layer continuous above ami below with that clothing the interior of the third and fourth ventricles. As seen in THE MESENCEPHALON. 1109 cross-sections, (Fig. 960) its outline in a general way is triangular, with the base above and the apex directly below ; but the contour of the canal varies at different levels, being triangular near its extremities and irregularly cordiform or elliptical in the intervening part of its course. INTERNAL STRUCTURE OF THE MESENCEPHALON. Disregarding the several small nuclei, the nuclei of the corpora quadrigemina and the red nuclei, the gray matter within the mesencephalon is disposed as three tracts that extend the entire length of the mid-brain. These are the tubular mass of the central gray matter, which surrounds the aqueduct, and the two crescentic columns of the substantia nigra, which subdivide the peduncles into the tegmental and basal portions. The central gray matter (stratum griseum centrale) completely encloses the cavity of the mid-brain and hence is often called the Sylvian gray -matter. It contains numerous irregularly scattered nerve-cells of uncertain form and size, and, along its ventral border, the nuclei of origin of the oculomotor and trochlear nerves ; within its lateral parts lie the nuclei from which proceed the fibres of the mesencephalic roots of the trigeminal nerves. FIG. 960. Inferior colliculus Mesencephalic root of trigeminus Lateral fillet Fibres of fourth nerve Nucleus of fourth nerve Mesial fillet Sylvian aqueduct Central gray substance Posterior longitudinal fasciculus Fountain decussation Mesial fillet Cerebellar peduncle Decussation of cerebellar peduncle Transverse section of dorsal part of mid-brain through lower end of inferior colliculi, at level M (Fig. 919) showing nucleus of trochlear nerve, and decussation of cerebellar peduncle. Weigert-Pal staining. X 3^. Preparation by Professor Spiller. The substantia nigra is disposed as two irregular crescentic columns of dark gray matter that separate the tegmentum from the crustae of the peduncles. The substance begins below at the upper border of the pons and continues uninterruptedly through the length of the mid-brain into the subthalamic region of the diencephalon, where it gradually disappears. The deep color of this tract is due to the conspicuous pigmentation of its numerous nerve-cells. These cells are of medium size and of various form, spindle-shaped elements, interspersed with some of stellate and a few of pyramidal form, predominating. They enclose considerable accumulations of dark brown pigment that render the cells unusually conspicuous. During the earliest years of childhood the pigmentation is absent or very slight, but after the sixth year it is marked, and by the seventeenth has acquired its full intensity. Seen in cross-sections (Fig. 961), the convexity of each column, directed forward and out- ward, is not uniform, but broken into irregular scallops by processes of gray matter that penetrate the subjacent crusta. The concave dorsal margin, on the contrary, is unbroken and even. The horns of the crescentic areas, of which the median is somewhat the thicker, approach the free surface along the bottom of the superficial 1 1 io HUMAN ANATOMY. lateral and median grooves of the mid-brain. Concerning the functions and connec- tions of the neurones within the substantia nigra very little is known. The Quadrigeminal and Geniculate Bodies. The inferior colliculus consists chiefly of a biconvex (in section oval) mass of gray matter, the nucleus colliculi inferioris, in which many nerve-cells of varying form and mostly of small size lie embedded within a complex of nerve- fibres. The lower end of the nucleus stands in intimate relation with the acoustic fibres composing the lateral fillet, many of which enter the ventral aspect of the nucleus colliculi to end around its cells, whilst a considerable number pass superficial to the nucleus and thus form an external fibre- layer that intervenes between the gray nucleus and the surface. Although many of these external fillet-fibres enter the colliculus at higher levels, not a few continue, by way of the inferior brachium, to the median geniculate body, around whose neu- rones they end. A much smaller and less well defined tract of fillet-fibres passes to the mesial side of the nucleus, the ventral margin of which is thus embraced (Fig. 960) by the diverging but unequally robust fillet-strands that in this manner partially encapsulate the collicular nucleus. From the supero-lateral parts of the nucleus fibres proceed which, in conjunction with those continued from the lateral fillet, form the chief constituents of the inferior brachium. A part of this arm, how- ever, is composed of strands of fibres that pass from the cerebral cortex (especially the temporal) to the inferior colliculus. Towards the upper pole of the nucleus some loose strands of fillet-fibres, probably along with commissural fibres uniting the inferior colliculi, cross the mid-line and establish a decussation. The internal or median geniculate body (corpus geniculatum mediate), although genetically belonging to the diencephalon, is so closely related to the inferior colliculus as to require description in this place. It consists of a superficial layer of white matter composed of fibres from the inferior brachium, which pass outward as continuations of the lateral fillet, as axones of the cells of the inferior colliculus, or as fibres forming the lateral root of the optic tract, also known as the inferior commissure of Gudden. Within this fibre-capsule lies an oval mass of gray matter, the nucleus corporis geniculati medialis, from whose cells axones proceed chiefly towards the cerebral cortex in continuation of the auditory paths of which the inferior colliculus and the median geniculate body are important stations. Connections of the Inferior Colliculus and Median Geniculate Body. Mention has been made, when describing the reception-nuclei of the cochlear portion of the auditory nerve (page 1076) , that the tract of the lateral fillet takes origin to an important extent from the cells of these nuclei, and, further, (page 1082), that the fillet-fibres end around either the cells of the inferior colliculus, or those of the median geniculate body. It is evident, therefore, that these parts of the mid-brain stand in intimate relation with the parts concerned in conveying auditory impulses. The more detailed account of the chaining together of the neurones forming such paths is deferred until the auditory nerve is considered (page 1257). The connection of the fibres com- posing the median root of the optic tract with the median geniculate body and the inferior collic- ulus has been established beyond doubt ; further, that this part of the optic tract is not concerned in conducting visual impulses, is shown by the fact that these fibres remain unaffected under conditions (after removal of the eyes) that lead to degeneration of the fibres of retinal ori-in. The destination and significance of the fibre-systems included within the median root of the optic tract are only imperfectly understood, but it may be accepted as certain that they can no longer be regarded as merely establishing a bond between the median geniculate and indiivctly the inferior quadrigeminal bodies of the two sides, as implied by the name commissure, since many of these fibres are probably directed after decussation to the lenticular nucleus (globus pallidus), while others possibly may end on the same side in the subthalamic nucleus (page 1128). The gray matter of the inferior colliculus, like that of the superior, gives rise to fibres of the tecto-bulbar and tecto-spinal tracts, presently to be described (page mi). The superior colliculus is composed of a number of alternating layers of white and gray matter. The latter, however, is not aggregated into a definite nucleus, as in the case of the inferior colliculus, but is broken up into uncertain zones by the tracts of nerve-fibres. Although as many as seven layers have been described, SOUK- of these are so blended that only four well-defined strata can be readily distinguished. From the surface inward these are : THE MESENCEPHALON. mi 1. The stratum zonale, a thin peripheral fibre-layer that occupies the surface of the collic- ulus, whose components are fibres derived, in great part at least, from the optic tract. 2. The stratum cinereum, which is not uniform, but thickest and most marked over the convexity of the colliculus, and appears, therefore, crescentic in transverse sections. The nerve- cells contained in this cap-like sheet are small and relatively few, their axones passing for the most part towards the deeper layers, whilst their dendrites are directed peripherally. The stratum is by no means composed entirely of gray matter, but is invaded by many medullated nerve-fibres. 3. The stratum opticum, which consists of a complex of gray matter and nerve-fibres, the latter including strands derived from the optic tract, which gain the side of the colliculus by way of the superior brachium either as direct continuations of the optic fibres, or after interruption in the lateral geniculate body. That this stratum includes other fibres, is shown by the incomplete involvement of the layer in conditions producing degeneration of the FIG. 961. Inferior colliculus Sylvian aqueduct \ Central gray substance Inferior brachium Posterior | longitudinal -J fasciculus / Tegmental field i. Lateral sulcus -/ Fountain decussation Mesial fillet Decussation .^. of cerebellar s> the mid-line (decussation of Forel) and bend downward as the- rubro-spmal tract. The latter descends within the tegmentum of the mid-brain and pons, traverses the medulla and finally enters the lateral column of the cord as one of the important but uncertainly defined descending tracts. Other fibres enter the red nucleus on H lateral aspect and establish connections between the cerebral cortex (Dejerine), and probably also the corpus striatuni (Fdin^er). and the nucleus. From the cells of the latter the path is continued by fibres which join the rubro-spinal tract, and this manner establish an indirect' motor path that supplements the cortico-spmal tracts identified with the pyramidal. THE MESENCEPHALON. 1115 The Crusta. The crusta, or pes pedunculi, appears in transverse sections (Fig. 963) as a bold sickle-shaped field that occupies the most ventral portion of the mid-brain. It consists chiefly of longitudinally coursing fibres which, having traversed the internal capsule, are passing from various parts of the cerebral cortex to lower levels in the brain-stem and the spinal cord. The longitudinal fibres are separated into bundles by the invasion of numerous strands from the fibre-complex, known as the stratum intermedium, which lies along the ventral border of the substantia nigra. The fibres of the crusta comprise three general sets: the cortico-pontine, the cortico-biilbar, and the cortico-spinal. The cortico-pontine fibres include those passing from the cells of the cerebral cortex to the cells of the pontine nucleus as links in the cortico-cerebellar paths, They are represented by the fronto-pontine and the tempero-occipito-pontine tracts, which occupy approximately the median and lateral fifths of the crusta respectively. The cortico-bulbar-fibres include the efferent strands which pass from the motor areas of the frontal lobe to the nuclei of the motor fibres originating in the bulbar portion of the brain-stem (trigeminal, abducent, facial, glosso-pharyngeal, vagus and hypo- glossal nerves). These tracts occupy something less than the fifth of the crusta lying next the fronto-pontine tract. The cortico-spinal fibres include the great motor strands which, as the pyramidal tracts, are so conspicuous at lower levels. These tracts share with the fronto-bulbar paths the middle three-fifths of the crusta, appropriating approximately the lateral three-quarters of this area (Fig. 1012 ). The Median Fillet. Repeated reference has been made to the median fillet (leraniscus medialis) in the preceding descriptions of the brain-stem ; a general con- sideration of this important sensory tract may here be given. It begins at the lower part of the medulla, about on a level corresponding with the upper limit of the pyramidal decussation, as axones of the cells within the nucleus gracilis. These sweep ventro-medially as the deep arcuate fibres, for the most part cross the raphe, and bend sharply brainward. Succeeding the condensation of the fillet-fibres into the sensory decussation (Fig. 922) which marks the lowest limit of the tract, the fillet receives continuous additions of arcuate fibres from the gracile and cuneate nuclei so long as these collections are present. On reaching the inferior olivary nuclei in its journey brainward, the fillet forms a laterally compressed tract, the interolivary stratum, lying immediately dorsal to the pyramids (Fig. 928). Towards the upper end of the pons, the fillet gradually exchanges its sagittal plane and median position for an obliquely horizontal disposition, with an increasing tendency to migrate laterally. The fibres arising from the nucleus cuneatus, which below occupied the ventral part of the fillet, now constitute the lateral part of the tract, whilst those from the nucleus gracilis form its medial portion. Within the mid-brain the median and the lateral fillets form a continuous crescentic tract which, within the upper part of the tegmentum and after the disappearance of the acoustic paths, is represented chiefly by the superficial and laterally placed tract which the median fillet has now become. A considerable part of its fibres end around the cells of the deeper gray stratum of the superior colliculus, some passing over the aque- duct to the colliculus of the opposite side. The remaining fibres continue upward through the tegmentum, lateral and dorsal to the red nucleus, and the subthalamic region, to terminate chiefly in relation with the cells within the ventral part of the optic thalamus. After such interruption the impulses are carried by fibres arising within the thalamus to various parts of. the cerebral cortex. Whether fillet-fibres gain the cortical gray matter without interruption within the thalamus is uncertain. Other fibres, said to be derived from the cuneate nucleus, end in the corpus subtha- lamicum, and the lenticular nucleus (globus pallidus), from whose cells a certain num- ber of fibres proceed by way of a strand placed above the optic chiasm, the com- missure of Meynert, to the globus pallidus of the opposite side. Still other fibres are traceable into the posterior commissure of the brain and into the mammillary body. The constituents of the median fillet, however, are by no means restricted to the fibres arising from the gracile and cuneate nuclei of the posterior columns, but include numerous important accessions from the reception-nuclei of all the sensory cranial nerves connected with the brain-stem. From the cells within the more 1 1 16 HUMAN ANATOMY. FIG. 964. extensive of such nuclei, as those within the column of substantia gelatinosa accom- panying the spinal root of the trigeminus, numerous arcuate fibres sweep towards the raphe and, with few exceptions, cross to join the median fillet of the opposite side. In this manner provision is made for the transmission to the higher receptive centres of sensory impulses collected not only by the strands of the posterior column of the cord, but also by the sensory fibres of the cranial nerves attached to the brain-stem. Although the principal components of the fillet-tract are the bulbo-tecto- thalamic strands, some fibres running in the opposite direction are also present. Some of these probably arise from cells within the optic thalamus and the corpora quadrigemina. Others are efferent strands which establish connections between the cortical gray matter and the nuclei of the motor cranial nerves, especially the facial and hypoglossal. These cortico- bulbar tracts descend within the crusta to the lower end of the cerebral peduncle ; then, leaving the latter, they traverse the stratum intermedium and in the upper part of the pons join the median fillet and descend within its ventro - median part as far as the superior end of the hypoglossal nucleus. During their course, the fibres of this crustal fillet, as it is called, for the most part undergo decussation on reaching the levels of the motor nucleus for which they are destined ; some fibres, however, possibly end around the cells of the nucleus of the same side. The Posterior Longi- tudinal Fasciculus. This bundle (fasciculus longitudinalis dorsalis) is an association path of fundamental importance, be- Sen Superior collicul y part) eusory Diagram showing chief afferent constituents of median fillet. Posterior tract Spino-thalamii Spinal ganglion -.f 7T?V I *XT\ ing present in all vertebrates. As a distinct strand it begins in the superior part of the mid-brain and thence is traceable as a con- tinuous tract through the teg- mental region of the pons, the dorsal and lateral ventral field of the medulla into the anterior ground-bundle of the spinal cord. Throughout the greater part of its course through the brain-stem, its position is constant, the fasciculi of the two sides lying close to the median raphe and immediately beneath the gray matter flooring the Sylvian aqueduct and the fourth ventricle (Figs. 959, 961). In the lower part of the medulla, the bundle gradually leaves the ventricular floor and rests upon the dorsal border of the median fillet, and, at the level of the pyramidal decussation, where the fillet no longer intervenes, lies behind the pyramid and at some distance from the mid-line. Lower, it assumes a more ventral position, to the medial side of the isolated anterior cornu, and, finally, enters the anterior column of the cord to be lost within the- upper part of the ground bundle. The fasciculus includes association fibres of varying lengths, some of which are ascending and others descending paths. The constitution of the bundle is, there- fore, continually changing, the loss of certain fibres being replaced by the addition of others. Its fibres are among the very first in the brain to become medullated, and begin to acquire this coat during the fourth foetal month (Hosel ). THE MESENCEPHALON. 1117 FIG. 965. CN Notwithstanding the admitted importance of the tract and the prolonged study that it has received, much remains to be determined concerning the source and connections of the many constituents which undoubtedly go to form the bundle. Among the more certain of these com- ponents the following may be mentioned : 1. At the upper end of the fasciculus a considerable number of fibres arise from the cells of the nucleus of the posterior commissure, or Darkschewitscti ' s nucleus, which lies in advance of the oculomotor nucleus, within the gray matter surrounding the superior end of the Sylvian aqueduct. According to Edinger an additional contingent takes origin from a nucleus (n. fas- ciculi longitudinalis dorsalis) within the gray matter of the floor of the third ventricle in the vicinity of the corpus mam- millare. The contributions from both these sources join the fasciculus as crossed fibres from the nuclei of the opposite side. 2. The fibres arising from the vestibular (Deiters') nucleus constitute an important element of the posterior longitudinal bundle, since they establish reflex paths for equilibration impulses. These fibres, both crossed and uncrossed, join the fasciculus and pass in both directions. Those passing brainward have as their chief objective point the oculomotor nucleus, although the nuclei of the sixth and fourth nerves receive fibres or collaterals. In this manner the filaments supplying the various ocular muscles are brought under the influence of the vestibular impulses. It is probable that the facial nucleus likewise receives collaterals, if not main stems, of the vestibulo-nuclear fibres. 3. Upon clinical and experimental evidence, it may be assumed that fibres pass by way of the longitudinal bundle from the abducent nucleus to that part of the oculomotor nucleus sending fibres to the internal rectus muscle of the opposite side (perhaps also from the nucleus of the third nerve to that of the abducens of the same side), by which arrangement the harmonious action of the internal and external recti muscles is insured. Basing their conclusions upon similar evidence, many anatomists accept the existence of fibres which pass by way of the posterior longitudinal bundle from the oculomotor nucleus to the cells of the facial nucleus (page 1251) from which proceed the fibres supplying the orbicularis palpebrarum and the corrugator supercilii. In this manner the coordinated action of these muscles and the levator palpebrae superioris is explained. A similar connection is probably established by the posterior longitudinal bundle between the nucleus of the hypoglossal and that of the facial nerve, whereby the closely associated movements of the lips and tongue are assured. That the function of the posterior fasciculus is by no means limited to association of the nuclei of the ocular nerves is evident from the fact that in animals or individuals in which such centres are wanting (due to absence or imperfect development of the visual organs) the bundle is nevertheless well represented. 4. Fibres arise from the reception-nuclei of the remaining sensory nerves of the brain-stem and pass to the posterior longitudinal fasciculus of the same and the opposite side. On enter- ing the bundle, they course in both directions and by means of their collaterals and stem-fibres send end-brushes to the nuclei of the motor nerves, in this manner establishing direct reflex areas between the afferent and efferent paths. In addition to linking together by longer and shorter association fibres the various levels of the brain-stem and the latter with the upper segments of the spinal cord, it is probable that the relations of the posterior longitudinal bundle are far reaching and may include connections with the thalamus and subthalamic region, the corpora quadrigemina, the red nucleus and the cerebellum. DEVELOPMENT OF THE MESENCEPHALON. Of the three primary cerebral vesicles, the mid-brain undergoes least change. Although much smaller than either of the other segments of the brain-tube, its prominent position, lying as it does at the summit of the cephalic flexure, makes it conspicuous in the early developing brain. During the enormous expansion upward and backward incident to the development of the cerebral hemispheres in man, the mid-brain becomes covered in and deposed to a dependent position and a relatively small size. For a time possessing a spacious cavity, it fails to keep pace with the growth of the adjoining parts ; its walls thicken and its lumen becomes eventually reduced to the narrow Sylvian aqueduct. Diagram showing chief constituents of posterior longitudinal fasciculus. Ill, IV, VI, VII, XII, nuclei of respective nerves; DN, vestibular (Deiters 1 ) nu- cleus ; CN, common nucleus of posterior commissure and posterior longitudinal fasciculus. in8 HUMAN ANATOMY. The dorsal zones of the lateral wall of the mid-brain give rise to the quadrigeminal plate, whose external surface is at first smooth but later marked by a temporary- median longitudinal ridge. About the third fcetal month, with the exception of its lower end, which persists as the frenulum veli, this ridge is succeeded by a longitudinal groove bounded on either side by an elevation. The elevations of the two sides mark the appearance of the corpora bigemina, cor- responding to the optic lobes of the lower vertebrates. During the fifth month, an obliquely transverse furrow forms on each side, by which the paired elevations are subdivided into four eminences, the corpora quadrigemina. About this time the corpora geniculata, which however belong developmentally to the diencephalon, are also differentiated and for awhile are rela- tively very large and prominent. The ventral zones greatly thicken and give origin to the tegmentum, including the nuclei of the oculomotor and of the trochlear nerves and, perhaps, the red nuclei, and the mantle layer of the cerebral peduncles with the interpeduncular substance. The floor-plate becomes com- pressed between the expanding ventral zones of the lateral walls and probably is represented by the raphe. Since the fibre-systems of the crustae are, for the most part, derived from sources outside the brain-stem, their appearance within the peduncles follows a secondary ingrowth, and only after such invasion do the cerebral crura present their characteristic ventral prom- inence. The cortico-pontine tracts share with the pyramidial fibres the characteristic of tardy myelination, since they do not acquire their medullary coat until some time after birth. Among the earliest of the cortico-bulbar fibres to become medullated -(a few weeks after birth i are those destined for the motor cranial nerves by way of the crustal or pyramidal fillet of Flechsig. According to Kolliker, the stratum intermedium, which is closely related to the substantia nigra, not only in position but also by the destination of many of its fibres, contains a consider- able number of medullated fibres by the ninth fcetal month. THE FORE-BRAIN. It will be recalled that the fore-brain, the anterior primary cerebral vesicle, gives rise to two subdivisions, the telencephalon and the diencephalon (page 1060). Since the latter lies immediately in front of the mid-brain, in following the order in which the brain-segments have been described, the diencephalon next claims attention. THE DIENCEPHALON. Strictly considered upon the basis of the classic subdivision suggested by His, the diencephalon, or inter-brain, includes (i) a large dorsal portion, the thalamen- cephalon and (2) a small ventral portion, the pars mammillaris hypothami, together with (3) the enclosed remains of the posterior part of the cavity of the fore-brain, as represented by the greater part of the third ventricle. The thalamen- cephalon, in turn, includes : (a) the thalamus, () the epithalamus, comprising the pineal body, the habenular region and the posterior commissure, and (c) the meta- thalamus, including the corpora geniculata. Since, however, the description of the third ventricle and its surrounding structures the essential features of this segment of the adult brain requires the inclusion of parts belonging to the telencephalon (pars optica hypothalami), it will be more convenient to disregard their strict developmental relations and include the representatives of the pars optica in the consideration of the diencephalon. The Thalamus. After removal of the overlying structures the corpus callo- sum, the fornix and the velum interpositum the thalami (thalami), also called the optic thalami, are seen as two conspicuous masses of gray matter separated by a narrow cleft, the third ventricle. Each thalamus is an ovoid ganglionic mass, blunt wedge-shaped, as seen in cross-sections (Fig. 967), whose long axis extends from the narrow anterior pole backward and outward. Of its four surfaces, the lateral and ventral are blended with the surrounding nervous tissue, and the mesial and dorsal are to a large extent free. The large superior surface is irregularly triangular in outline, slightly convex in the frontal plane and markedly so in the sagittal, and covered with a thin layer of nerve-fibres, the stratum zonale, which imparts a whitish color. This stratum is composed of fibres which are traceable on the one hand to the optic tract, and on the other to the optic radiation in the hind part of the internal capsule. Laterally, the superior surface is separated from the- caudate nucleus by a groove which obliquely crosses the floor of the lateral ventricle and lodges a narrow hand of fibres, the taenia semicircularis (stria tci minalis i and, in its anterior part, the vein of the corpus striatum. In its front half, where it hounds the THE DIENCEPHALON. 1119 ventricle, the inner border is sharply defined from the mesial surface by a delicate but well defined ridge, tsenia thalami, produced by the thickening of the ependyma of the third ventricle, along its line of reflection onto the membranous roof, and the underlying strand of nerve-fibres, the stria medullaris. Traced backward, the tsenia thalami becomes continuous with the stalk of the pineal body. Between this ridge and the diverging mesial border of the upper surface of the thalamus, is included a narrow depressed triangular area, known as the trigonum habenulae. It lies on a distinctly lower level than the adjoining convex upper surface of the thalamus. Since it contains a special nucleus and belongs to the epithalamus, its. description will be deferred until that region is considered (page 1123). The upper surface is not quite even, but subdivided by a shallow oblique furrow, which runs from before backward and outward and marks the position of the overlying lateral border of the fornix. External to this furrow lies a free marginal zone that forms a part of the floor of the lateral ventricle ; internal to it is an attached inner zone over which the velum interpositum is united to the thalamus. By the attachment of this FIG. 966. Septum lucidum Tsenia semicircularis and vena terminalis Tsenia chorioidea Furrow for fornix Tasnia thalami Trigonum habenulse Pulvinar Corpora quadrigemina Corpus callosum Caudate nucleus Anterior pillars of fornix Foramen of Monroe Anterior commissure Middle commissure in III ventricle Thalamus Posterior commissure Pineal body Lingula Thalami, caudate nuclei and ventricles viewed from above after removal of corpus callosum, fornix and velum interpositum ; third ventricle shows as narrow cleft between mesial surfaces of thalami. sheet to the fornix above and to the thalamus below, direct communication between the third and lateral ventricles is shut off save through the foramen of Monroe. In front, the superior surface ends on the rounded elevation (tuberculum anterius thalami) which marks the anterior pole of the ganglion, while behind it goes over onto the prominent posterior projection, the pulvinar, which overhangs the superior brachium and the corpora geniculata. The mesial surface forms the greater part of the lateral wall of the third ventricle. It is covered by a layer of gray matter prolonged from the central gray of the Sylvian aqueduct, over which stretches the immediate lining of the ventricle, the ependyma. The upper boundary of the mesial surface is sharply defined by the taenia thalami, which behind is continuous with the stalk of the pineal body (Fig. 966). Its lower limit is indicated by an oblique furrow, the sulcus hypothalamicus, which separates the thalamic from the hypothalamic regions. Somewhat in advance of their middle, the mesial surfaces of the two thalami are connected by a bridge of gray matter, known as the middle commissure (massa intermedia), usually about 78 mm. in diameter and oval in section, but very variable in thickness and form. From the meagre number of medullated nerve-fibres that it contains, its importance, at least in man, seems to be small. The lateral surface of the thalamus is inseparably blended with the adjacent thick and conspicuous stratum of white matter, the internal capsule, which intervenes between the thalamus and the more laterally placed lenticular JI2O HUMAN ANATOMY. nucleus, and establishes the important pathway transmitting the fibre-tracts con- necting the cerebral cortex with the thalamus and with the lower levels by way of the crusta of the cerebral peduncle. Since the innumerable fibres which pass to and from the thalamus along its ventro-lateral surface interlace, this surface is covered by a distinct reticulated stratum, to which the name external medullary lamina is applied. The ventral surface is also attached, but instead of being united with the internal capsule, as is the lateral, it rests upon and is intimately blended with the upward prolongation of the tegmental portion of the cerebral peduncle, here known as the subthalamic tegmental region, presently to be described (page 1127). FIG. 967. Corpus callosum Choroid plexus Fornix Tsenia thalami Middle commissure Third ventricle Manimillo-thalatnic tract Maininillary body Amygdaloid nucleus Caudate nucleus Thalamus, mesial nucleus Thalamus. lateral nucleus Lenticular nucleus Subthalamic nucleus Optic tract Tail of caudate nucleus Inferior horn of lateral ventricle Hippocampus, cut obliquely Crusta of cerebral peduncle Frontal section of brain passing through thalami, middle commissure and mammilla! y bodies. Structure of the Thalamus. Although composed chiefly of gray matter, the thalamus is partially surrounded and penetrated by tracts of white matter. In addition to being invested on its superior and ventro-lateral surfaces by the stratum zonale and the external medullary lamina respectively, the general ganglionic mass is subdivided by a vertical internal sheet of fibres, continuous with the stratum xonale and known as the internal medullary lamina, into three fairly marked nuclei, the anterior, the mesial and the lateral ( Fig. 967). Of these the lateral nucleus is much the largest and is included between the external and internal medullary lamina-. Whilst the lateral nucleus does not reach as far forward as the anterior pole of the thalamus, its caudal extremity includes the entire pulvinar. Tin- lateral nucleus consists histologically of an intricate complex of nerve-fibres and cells. The latter are in general of the multipolar type, although very variable as to details of t<>rm and sixe. Two principal types are recognixed by Kolliker, the one being elongated or fusiform and possessed of relatively few branches, and the other being stellate and provided with richly branched dendrites. Many of the fibres represent paths ending within the thalamus and therefore terminate in arborixatioiis around the thalamic cells ; others are the a \ones of such cells and pass to various parts of the cortex or other parts of the brain. The historical characteristics of the lateral nucleus, in the THE DIENCEPHALON. II2I main hold good for the other nuclei, although the lateral nucleus is particularly rich in fibres, and therefore of a paler tint, on account of its close relations to the internal capsule and the tegmentum of the cerebral peduncle. The mesial nucleus lies between the central gray matter of the ventricular wall and the internal medullary lamina, and is separated by the latter from the lateral nucleus. Its caudal end is bordered internally by the ganglion habenulae, and, behind, by the pulvinar. The anterior nucleus, the smallest of the three, is a wedge-shaped mass, whose rounded base looks forward and corresponds to the anterior tubercle, and whose apex is directed backward and lies between the front ends of the mesial and lateral nuclei, separated from these by the internal medullary lamina, which divides into two diverging levels that embrace the anterior nucleus. In addition to its contribution of radiating fibres which take part in the production of the thalamic radiation, the anterior nucleus contains a compact bundle of fibres traceable into the mammillary body on the base of the brain. These are the constituents of the mam- millo-thalamic tract, or bundle of Vicq d 1 Azyr, by which a large part of the fibres FIG. 968. Corpus callosmn Choroid plexus Lateral ventricle Stratum zonale Caudate nucleus Genu of internal capsule Thalamus, mesial nucleus Thalamus, lateral nucleus Internal capsule Putamen Globus pallidus Anterior pillars of foriiix/ Lamina cinerea Gyrus callosus Cingulum Corpus callosum .Striate vein Anterior commissure Caudate nucleus Taenia semicircularis Internal medullary lamina External medul- lary lamina Mammillo- thalamic tract Putamen Globus pallidus Thalamo-tegmental tract Olfactory fibres Oblique frontal section through thalamus and anterior commissure; Weigert-Pal staining. X f- Preparation by Professor Spiller. coursing within the anterior pillar of the fornix are carried to the thalamus (page 1159). The entire ventral part of the thalamus is occupied by an illy-defined mass of gray matter, known as the ventral nucleus, which lacks sharp definition from the overlying nuclei and in fact is continuous with the lateral nucleus. The ventral nucleus presents a differentiation into the nucleus centralis of Luys, which occupies a mesial position and appears round in section (Fig. 970), and receives fibres from the red nucleus and the posterior commissure, and the nucleus arciformis, which lies ventro-lateral to the preceding nucleus and is crescentic in outline. The ventral nucleus is of importance, not only because it receives the great sensory paths, but also on account of its phylogenetic rank, since, according to Edinger, it, together with the ganglion habenulas, represents the oldest of the thalamic nuclei and is found through- out the vertebrate series. Connections of the Thalamus. Broadly considered, the thalamus may be regarded as a great ganglionic internode interposed in the corticipetal paths around whose cells most of the constituents of the important secondary paths conveying afferent impulses from the spinal cord, the brain-stem and the cerebellum end, 7' 1122 HIM AN ANATOMY. and from whose cells corticipetal fibres pass to all parts of the cerebral cortex and to the corpus striatum. Further, it must be understood that the thalamus receives fibres from all parts of the cerebral cortex, and, lastly, that from it proceed efferent fibres to the lower centres within the brain-stem and the cord. It is evident, therefore, that the connections of the thalamus are very intricate and far reaching. FIG. 969. i. The lower thalamocipetal tracts include : (a) those passing directly from the spinal cord, as the spino-thalanric and probably a part of Cowers' tract ; ({>) those passing from the various nuclei by way of the median fillet ; (c) those passing from the cerebellum, either directly, as the cerebello-thalaniic tract, or, after interruption in the red nucleus, as the nibro-thala- mic; (d) probably other tracts which arise within the tegmen- tal area of the brain-stem. The fibres from the various sources enter the under surface of the thalamus to end within the ven- tral nucleus, or by means of the internal medullary lamina to be distributed to the other nuclei. 2. The thalamic radiation comprises the fibres which stream from the latero-ventral surface of the thalamus to all parts of the hemisphere ( thalamo-cortical ) , some crossing by way of the corpus callosum to the oppo- site side, as well as those which pass in the opposite direction ( cortico-thalamic ) towards the ganglion. Although as they traverse the external medullary lamina the fibres are not particu- larly grouped, their various rela- tions to the cortex or other parts are established by different and more or less definite paths. These are designated as the stalks of the thalamus, of which a frontal, a parietal, an occipital and a ventral are conventionally distinguished. The anterior or frontal stalk emerges from the fore-part of the lateral surface of the thalamus, traverses the an- terior part of the internal capsule between the caudate and lentic- ular nuclei, to which it distributes fibres, and finally gains the cortex of the frontal lobe. From the cells of this region, cortico- thalamic fibres follow in reversed order the paths just mentioned, thus establishing a double relation between the cortex and the basal ganglion. In addition to the preceding cortico-thalamic fibres, the antero-ventral part of the thalamus receives a strand from the cortex of the olfactory bulb. The parietal stalk leaves the lateral surface of the thalamus and enters the internal capsule and often the lenticular nucleus, in its course to the parietal cortex. Other corticipetal fibres, destined for the parietal and adjacent parts of the frontal lobe, are the continuations of the path of the mesial fillet. To a large extent these fibres pass from the ventral thalamic nucleus outward to the under surface of the lenticular nuck-us, then bend upward and traverse the lenticular nucleus by way of the medullary stria' or the globus pallidus to gain the cortex. Other fibres continue the fillet- path by entering the internal capsule and thus, perhaps, directly proceed to the cortex. The occipital stalk includes the fibres that connect the thalamus with tin- visual cortical areas of the occipital and parietal lobes. They issue from the lateral surface of the pulvinar, and as the Rubro-thalamic Cerebello-thalamic Median fillet Spino-thalamic Diagram showing chief connections of thalamus; black fibres rep- resent afferent tracts ending in thalamus and thalamo-cortical paths : red fibres are the cortico-thalamic and strio-thalatnic paths ; T, thal- amus; C. L, caudate and lenticular nuclei; C, C, corpus callosum; f, P, T, O, frontal, parietal, temporal and occipital lobes; fjr, fornix; M, mammillary body; Pd, cerebral peduncle; SC, /C, superior and in- ferior colliculi ; K, red nucleus ; Ps, pons ; /, frontal stalk ; 2, parietal stalk ; 3, 4, lenticular and temporal parts of ventral stalk ; ,5, occipital stalk. THE DIENCEPHALON. 1123 optic radiations sweep outward and backward around the posterior horn of the lateral ventricle to end in the cortex. The ventral stalk is complex in its relations, since its fibres include two systems. Emerging from the fore-part of the ventral surface of the thalamus, from the lateral and mesial nuclei, the stalk passes downward and outward beneath the lenticular nucleus. Its lower part, known as the ansa peduncularis, continues laterally into the cortex of the temporal and of the central lobe ; its upper part, the ansa lenticularis, closely skirts the adjacent border of the lenticular nucleus which it enters to gain the putamen, or, continuing through the lenticular nucleus by way of the medullary laminae, to reach the caudate nucleus. Under the name tractus strio-fhalamicus, are included the fibres which pass from the caudate nucleus and the putamen to the thalamus, subthalamic body and red nucleus, a small number of fibres probably entering the thalamus from the caudate nucleus by the more direct route of the internal capsule. 3. The stratum zonale, the thin layer of white matter which covers the superior aspect of the thalamus, consists in large part of thalamocipetal fibres derived from the optic tract or the optic radiation. Those from the lateral root of the tract superficially cross the external genic- ulate body and spread over the thalamus, while those from the occipital cortex by way of the optic radiation invest the pulvinar. Other contributions to the stratum zonale include fibres from the temporal cortex by way of the ventral stalk. The Epithalamus. Under this subdivision of the thalamencephalon are included: (i) the trigonum habenulee, (2) the pineal body, and (3) the posterior commissure all structures closely associated with the superior and posterior boun- daries of the third ventricle. FIG. 970. Veins of Galen in Corpus velum interpositum Stria Fornix callosum medullaris Ganglion habenulae Lateral ventricle Caudate nucleus Thalamus, ventral nucleus Thalamus, /f^ mesial nucleus 1 Subthalamic region Crusta of cerebral peduncles _ . External medullary lamina Thalamus Red nucleus enticular ilK^ nucleus >S Internal capsule Subthalamic nucleus Oblique frontal section through thalamus and subthalamic region ; Weigert-Pal staining. X \. Preparation by Professor Spiller. The trigonum habenulae is the narrow triangular area lying between the sharply denned edge (taenia thalami) of the ventricular wall internally and the diverging mesial border of the upper surface of the thalamus externally (Fig. 966). Its surface is depressed and at a lower level than that of the thalamus and behind is continuous with a mesially curving strand, the pineal peduncle. Beneath the ridge of thickened ependyma marking the taenia thalami, lies a distinct strand of nerve-fibres, the stria medullaris, while at a still deeper level and covered by the superficial fibres is situated an aggregation of small nerve-cells, known as the ganglion habenulae. The source of the fibres composing the stria medullaris and the connections of the ganglion habenulae are still uncertain. It is probable, how- ever, that many components of the stria are associated with the olfactory centres and include : ( i ) olfado-habenular fibres, which arise from cells within the septum I I 24 HUMAN ANATOMY. lucidum and the olfactory area, and (2) cortico-habenular fibres, which spring from the cortical cells within the hippocampus or the adjacent region, and by way of the fornix and its anterior pillar are carried to the fore-end of the thalamus, whence they pass backward within the medullary stria. (3) Other thalamo-habenular fibres also probably join the stria medullaris from the interior of the thalamus. Whilst many of the fibres composing the stria end around the cells of the ganglion habenulae, some continue backward, without interruption, within the strand known as the peduncle of the pineal body, cross to the other side in the bundle bearing the name, commissura habenulae, and end in relation with the cells of the opposite habenular nucleus. The ganglion habenulae (Fig. 970), in turn, gives origin to an important bundle, the fasciculus retroflexus of Meynert, which arches down- ward and backward, passing at first between the central gray matter of the third ventricle and the thalamus proper, and later to the medial side of the red nucleus, to reach the base of the brain, and for the most part to end around the cells of the interpeduncular ganglion. This nucleus, which in many animals is a well-defined collection of cells, in man is represented by a more scattered median cell-group within the posterior perforated substance close to the anterior border of the pons. The fasciculus, also termed the habenulo- peduncular tract, receives contribu- tions from the ganglion habenulae of both sides, some fibres having crossed in the habenular commissure ; although the majority -of its fibres end, mostly crossed, in the interpeduncular ganglion, not a few may be traced farther caudally within the tegmentum of the brain-stem (Obersteiner), as may also the fibres from the cells of the ganglion interpedunculare. The Pineal Body. The pineal body (corpus pincale), also often called the cpiphysis, is a cone-shaped organ, from 8-10 mm. in length, attached to the posterior extremity of the roof of the third ventricle. It is slightly compressed from above downward and FIG. 971. Section of pineal body showing calcareous concretions or brain-sand. X 130. rests, with its apex pointing backward, on the dorsal aspect of the mid-brain in the trian- gular pineal depression between the superior corpora quadrigemina (Fig. 966). Its base, as its anterior end is called, is attached above to the commis- sura habenulae, from which on each side a narrow but distinct ridge, the pineal stalk, curves forward to be- come continuous with the stria medullaris. Below, its base is united with the posterior com- missure of the brain overlying the entrance into the Sylvian aque- duct. Between the habenular and posterior commissures a small pointed diverticulum, the pineal recess, extends from the third ventricle for a very short distance into the pineal body, and thus recalls the early condition in which the organ is. developed as a tubular outgrowth in the roof-plate of the diencephalon. This relation to the thin ventricular roof tin body retains, its apex later becoming closely surrounded by and embedded within the loose vascular tissue of the pia mater. The structure of the pineal body, as seen in cross-section ( Fig. 971), includes a reticular framework of connective tissue trabeculce, whose meshes are filled with THE DIENCEPHALON. 1125 Lenticular area Retinal area rounded or sometimes elongated epithelial cells, which often contain brownish pig- ment. With the exception of a few nerve-filaments in the anterior part, probably sympathetic in origin and destined for the blood-vessels, and a dense net- work of neuroglia fibres in the under part, the pineal body contains no ele- FlG - 972. ments of a nervous character, nerve- cells being absent. Quite com- monly the adult organ encloses a variable number of concretions, often called brain- sand (acervulus) , which consist of laminated particles composed of calcium carbonate and phosphate mingled with or- ganic material. They may be of microscopic dimensions, or reach the size of a millet seed, and by aggregation assume a mammillated form. Blood-vessel Diverticulum dividing into tubules Sagittal section of pineal organ of lizard (Lacerta agilis) embryo. X 175. The significance of the pineal body long remained an unsolved riddle and served as the theme for unrestrained speculation. The em- bryological and comparative studies of Graaf, Spencer and others have shown that in many of the lower animals, especially in the reptiles (lizards), the pineal body reaches a high degree of development and is a flattened cup-shaped organ connected with the brain by a stalk containing nerve-fibres. The structural resemblances to the invertebrate visual organ suggested a possible similarity of purpose in the higher types, an assumption that was strengthened by the fact that in certain lizards the pineal body not only is borne by a stalk but reaches an interparietal subcutaneous position on the head by passing through or lying within a special foramen in the skull. The organ was, therefore, designated the pineal eye, although probably in no existing animal a functionating structure. While such a superficial position in the adult is very exceptional, the embryonic relations in many reptiles (Fig. 972) are very suggestive of the probable significance ot the pineal body, at least in such form as a rudimentary sense organ, although not necessarily an eye. These conclusions are likewise suggestive in forming our conceptions concerning the pineal body in man, which is now by many regarded as representing a very imperfectly developed and greatly modified sensory structure. Although strictly belonging to the telencephalon, men- tion may here be made of a second evagination, know as the paraphysis, which arises from the roof-plate of the fore-brain. The pouch appears in advance of the pineal outgrowth and is a temporary structure, seemingly being in nature comparable to an outwardly directed choroid plexus. The paraphysis has been described in the lower vertebrates, including reptiles and birds, in some mammals and, indeed, according to the observations of Francotte and of Ewing Taylor, it is not improbable that a corresponding evagination is recognizable in the early human embryo. FIG. 973. Small portion of pineal body, showing constituent cells more highly magnified. X 600. The posterior commissure (commissura poste- rior cerebri) is a narrow but distinct cord-like band of white matter which overlies the superior entrance into the Sylvian aqueduct (Fig. 976) and is partially masked by the habenular commissure and pineal peduncle above. Behind and laterally it is continuous with the superior colliculi. The commissure provides the paths by which fibres from various sources undergo median decussation, but the details and connections of its component fibres are only imperfectly understood. Among its probable constituents are: (i) fibres originating in the nucleus of the posterior commissure and also from the nucleus of the posterior longitudinal fasiculus (nucleus fasciculi longitudinalis posterior), which occupies the gray matter of the floor of the third ventricle near the mammillary bodies (page 1117); ( 2 ) fibres from the posterior part of the thalamus of the 1 1 26 HUMAN ANATOMY. opposite side which descend within the tegmentum, lateral and ventral to the posterior longitudinal fasciculus ; (3) fibres which cross to join the fasciculus retro- flexus ; (4) fibres from the median fillet and (5) from the superior cerebellar peduncle which traverse the commissure to reach the opposite thalamus ; (6) per- haps fibres from the deeper gray stratum of the corpora quadrigemina to the cerebral cortex of the other side. Its presence in all vertebrates and the very early acquisition of a medullary coat by its fibres indicate, as pointed out by Edinger, the fundamental character of the commissure. The Metathalamus. This subdivision of the thalamencephalon includes em- bryologically both the median and lateral geniculate bodies. Since in the fully formed FIG. 974. Corpus callosum Fornix Choroid plexus Velum inter- positum Nucleus habetiuke Subthalamic nucleus Red nucleus Substantia nigra Oculomotor nerve Crusta of cerebral peduncle Caudate nucleus Thalamus Subthalamic region Crwroid plexus in inferior horn of lateral ventricle Caudate nucleus, tail Hippocam:>u>, obliquely cut Gyms detitatus Ciyrus hippocampi, bounding inferior fissure leading into choroidal pk-\n- Frontal section of brain passing through thalami, subthalamic region and cerebral peduncles; inferior horn of lateral ventricle with hippocampus in section also seen. brain the former are closely associated with the inferior colliculi and their arms, the inferior brachia, they may be conveniently described in connection with the mid- brain, as has been done (page nio). The lateral geniculate bodies, (corpora geniculata laterales), one on each side, are two fusiform elevations, about 16 mm. in length and half as much in width, which project from the outer and under surface of the posterior part of the thalamus ( Fig. 958). They are so buried within the thalamus that they are much less distinct than the median geniculate bodies. In front they receive the outer division of the optic tracts, while behind they are connected by the superior brachia with the superior corpora quadrigemina. In structure the lateral geniculate body consists of alternating layers of white and gray matter. The former, somewhat thinner than the gray substance, are, to a large measure the optic fibres, many of which end around the cells within the gray lamina-. Other fibres of the optic tract continue without interruption into the superior brachium and so to the upper colliculus, while a certain number end within the thalamus, and in their course over the surface of the latter take part in the production of the stratum zonale (page 1118). From many of the cells within the geniculate body, fibres proceed by way of the optic radiations to the cerebral cortex. * e THE DIENCEPHALON. 1127 Then, too, many corticifugal fibres course in the opposite direction as the axones of the cortical cells, and end in relation to the geniculate neurones, thus establishing a double relation between the lateral geniculate body and the occipital cortex. The Hypothalamus. Although, strictly regarded according to its develop- mental relations, the diencephalon claims only the posterior or mammillary part of the hypothalamus, it is desirable to consider at this time the derivations of the entire hypothalamic subdivision of the fore-brain. Under the above heading will be de- scribed, therefore, the structures lying within or forming the floor and the anterior wall of the third ventricle, including the subthalamic region. The subthalamic region in its developmental relations stands, as it were, as a link connecting the diencephalon and the mid-brain. The subthalamic region is the upward prolongation of the tegmentum of the cerebral peduncles and occupies, on each side of the mid-line, the triangular area between the thalamus above and the internal capsule and its continuation, the crusta of the peduncle, below (Fig. 974). It is insepa- FIG. 975. Red nucleus Substantia nigra Choroid plexus Fornix Pulvinar Lateral geniculate body ( leader crosses cut tail of caudate nucleus) Median geniculate body Hippocampus Superior cerebellar peduncle Pons Frontal section of brain passing through posterior poles of thalami, pineal body and brain-stem. rably blended with the ventral surface of the thalamus, which thus obliquely overlies the termination of the tegmental or sensory portion of the cerebral stalk. Through this area the important thalamocipetal paths of the fillet and of the superior cerebellar peduncles reach the thalamus, and within it are seen the upper extremities of the chief ganglia of the mid-brain, the substantia nigra and the red nucleus, and a new mass of gray matter, the corpus subthalamicum. The substantia nigra presents the same characteristics here as in the peduncle, being conspicuously dark and overlying the crustal fibres. As it ascends, it decreases in bulk from within outward until, at the level of the mammillary body, the substantia nigra is no longer recognizable. The connections of the cells within the substantia nigra are imperfectly understood, but it is probable that they receive many fibres from the caudate nucleus and the putamen and, perhaps, also from the frontal cortical areas. From the cells, on the other hand, fibres pass into the tegmentum and into the crusta and thence to lower levels. According to Bechterew, some fibres join the fillet-tract and thus reach the superior quadrigeminal bodies. At first the red nucleus is a very prominent feature in frontal sections of the subthalamic region (Fig. 970), appearing 1128 HUMAN ANATOMY. as a circular area of gray matter enclosed by a zone of cerebello-thalamic fibres ; farther forward it, too, gradually diminishes and disappears at a level somewhat behind that of the corpora mammillaria. The connections of the red nucleus have been considered in connection with the superior cerebellar peduncle (page 1095) ; suffice it here to recall its twofold significance as an interruption station for many of the cerebello-rubro-spinal and for the cerebro-rubro-spinal tracts. The corpus subthalamicum (nucleus hvpothalamicus), or nucleus of Litys, is a mass of deeply tinted gray matter peculiar to the subthalamic region and unrepresented, in the mid-brain. It appears in cross-section (Fig. 970) as a small biconvex area, immediately dorsal to the tract of crustal fibres and lateral to the red nucleus and the substantia nigra. As the latter diminishes, the subthalamic nucleus expands to take its place and, where fully represented, measures from 3-4 mm. in thickness and from 10-12 mm. in its longest diameter,- and extends superiorly considerably beyond the .level of the red nucleus. Histologically the subthalamic body is distinguished by a dense net-work of fine medullated nerve-fibres, enclosing pigmented multipolar nerve- cells of medium size, and by an unusually close mesh-work of capillary blood-vessels. The dorsal surface of the nucleus is defined by the overlying lateral part of the field FIG. 976. Septum hicidum Choroid plexus Foramen of Monroe Genii of corpus callosum Rostrum of corpus callosum Anterior commissure Lamina cinerea 1 Optic recess Optic commissure Anterior lobe of pituitary body Posterior lobe of pituitary y body Infundibulum Body of fornix Velum interpositum covering: Thalamus, [thalamus mesial surface T;cnia thalami plenium Commissura habenuUe Pineal recess Pineal body Posterior commissure -Quadrigeminal plate Sylvian aqueduct Cerebral peduncle Middle commissure Sulcus hypothalamicus Mam mil la ry body Tuber cinereum" Anterior pillar of fornix Right lateral wall of third ventricle : velum interpositum covers superior surface of thalamus. of Forel, as the stream of fibres passing between the red nucleus and the thalamus and the internal capsule is called. From the ventral surface of the nucleus, fibres pierce the adjacent crusta and join the ansa lenticularis to gain, probably, the globus pallidus ; other perforating fibres perhaps connect the subthalamic body with Meynert's and Gudden's commissures (Obersteiner). The ventro-medial ends of the bodies of the two sides are connected by a bridge, the commissura hypothalamica, which traverses the floor of the* third ventricle above the mammillary bodies. In addition to connecting the two subthalamic nuclei, the commissure contains decussating fibres from the anterior pillars of the fornix and, according to Edinger, probably fibres from the fore-end of the posterior longitudinal fasciculus. The corpora mammillaria (corpora mamillaria), also called the corpora albi- cantia, are two hemispherical elevations, about 5 mm. in diameter, which lit- close to the mid-line- within the inter] >eduncular space on the basal surface of the brain (Fig. 993). They are almost but not quite in contact, being separated by a narrow interval which immediately behind the little bodies deepens into the anterior recess marking the front end of the shallow median furrow that grooves the posterior perforated sub- stance. The posterior surfaces of the mammiilary bodies indicate the anterior limit of the ventral surface of the mid-brain. When examined in section (Fig. 970), = THE DIENCEPHALON. 1129 each body is seen to be composed of an outer layer of white matter enclosing a core of gray substance, known collectively as the nucleus mammillaris. The latter is subdivided into a medial and lateral part by fibres from the downward arching ante- rior pillar of the fornix, which penetrate the gray matter as well as invest to a large extent its exterior. Only a part of ( i ) the fornix fibres, however, end directly in the mammillary nuclei, since some pass above and behind the ganglion to gain the hypothalamic commissure (page 1128) and, after decussation, to end in the mam- milliary body of the opposite side. From the dorsal part of the medial nucleus, distinguished from the lateral one by its larger nerve-cells, emerges a distinct and compact bundle of fibers (Fig. 967), which on clearing the nucleus, separates into two strands. One of these, known as (2) the mammillo-thalamic tract, or the bundle of Vicq d' Azyr, courses upward and forward, and ends within the anterior nucleus of the thalamus ; in this manner it completes the paths by which the cortical olfactory centres within the hippocampus major are connected (by way of the fimbria, body and anterior pillar of the fornix and the mammillo-thalamic strand) with the thalamus (Fig. 1049). That fibres pass between the latter and the mammillary nucleus in both directions, is shown by the fact that destruction of either of these centres is fol- lowed in turn by ascending or descending degeneration of the fibres. (3) The other part of the bundle issuing from the mammillary nucleus arches backward and downward and, as the mammillo-teg mental tract, is traceable into the tegmentum of the mid-brain to the vicinity of the inferior colliculus. (4) Under the name, pednn- culus corporis mammillaris, another mammillo-tegmental tract is described. This strand springs from the lateral mammillary nucleus, and, coursing backward and downward along the medial margin of the crusta, enters the tegmentum. Its des- tination is uncertain, but according to Kolliker the tract probably ends in the central gray matter surrounding the Sylvian aqueduct in proximity with the trochlear nucleus. Other, but much less well established, strands have been described by Lenhossek as proceeding forward from the peripheral layer of the mammillary body over the tuber cinereum. Concerning their further course little is known with certainty. The tuber cinereum is the first of a series of median outpouchings which model the thin sheet of gray matter constituting the floor and the anterior wall of the third ventricle and belong to the pars optica of the hypothalamus. As seen from the exterior (Fig. 993), the tuber cinereum is a median elevation placed between the mammillary bodies behind and the optic chiasm in front, and the cerebral peduncles and the optic tracts at the sides. Together with the infundibulum, it forms the most dependent part of the third ventricle and consists of a thin layer of gray matter, less than 1.5 mm. thick, that is continued forward as the attenuated extension of the im- portant sheet found within the mid-brain and fourth ventricle. In addition to the fibre- strands coming from the mammillary bodies noted by Lenhossek, this investigator and Kolliker credit the tuber cinereum with possessing small paired composite gang- lia, the nuclei tuberis and the nuclei supraoptici of Kolliker. Concerning their con- nections nothing is definitely known. The anterior part of the tuber, immediately behind the optic chiasm, descends abruptly and somewhat forward to form a funnel- shaped stalk, the infundibulum, to whose lower end or apex is attached the pos- terior lobe of the pituitary body (Fig. 976). Although in the very young child the infundibulum retains to some extent its original character as a hollow outgrowth from the ventricle, in the mature subject this cavity, the recessus infundibuli, has mostly disappeared and the stalk is solid, save for a slight diverticulum within its upper and widest part. The posterior part of the tuber cinereum, between the root of the infundibulum and the mammillary bodies, exhibits occasionally in the adult brain, and almost con- stantly in that of the foetus, a small rounded median projection, flanked on each side by a slight elevation. To this modelling Retzius has applied the name, emincnlia saccularis in recognition of its similarity to the evagination (saccus vasculosus ) found in fishes. The eminence encloses a shallow pouch, recessus saccularis, which opens into the third ventricle. The pituitary body (hypophysis cerebri) is attached to the dependent tip of the infundibulum, and, closely invested by a loose sheath of connective tissue, hangs 1 130 HUMAN ANATOMY. within the pituitary fossa on the base of the skull, just in advance of the dorsum sellae (Fig. 996). Above, the fossa is closed by a special partition of dura, the diaphragma settee, through an opening in which the intundibulum passes to the mushroom -shaped organ. The pituitary body consists of two distinct parts, of which the so-called anterior lobe is much the larger and of a darker grayish red color. Its posterior surface is concave and receives the small posterior lobe, which is partially embraced at the sides by the expanded lateral margins of the anterior division. Although the two lobes are closely bound together by connective tissue, they are not only distinct as to structure and probably function, but are developed from entirely different regions. The anterior lobe is formed as an outgrowth from the oral diverticulum, while the posterior lobe first appears as a ventral evagination from the diencephalon (Fig. 1530). The anterior lobe, glandular in character, has been described in con- nection with the Accessory Organs of Nutrition (page 1806) and, therefore, calls for no further consideration in this place. FIG. 977. Interlobar septum Posterior or cerebral lobe Blood-vessel Connective-tissue trabecula Capsule Transverse section of pituitary body, showing relation of anterior (oral) and posterior (cerebral) lobes. X 7. The posterior lobe of the pituitary body is lighter in color and softer in con- sistence and directly attached to the floor of the third ventricle by means of its stalk, the infundibulum. During the early stages of its development, this lobe is repre- sented by a tubular outgrowth whose walls partake of the general character of the adjacent brain-visicle. Later the lumen within the lower end of the diverticulum dis- appears in consequence of thickening and approximation of its walls, a funnel-shaped recess of variable depth within the infundibulum alone remaining. In the adult con- dition, the posterior or cerebral lobe retains few histological features suggesting its nervous origin. Of the demonstrable interlacing fibres, with fusiform enlargements and elongated nuclei, none can be identified as nerve-fibres, while of the numerous cells which the lobule contains, only a few of large size and pigmented cytoplasm uncertainly resemble nervous elements. Wijh the exception of possibly neurogliar cells, the existence of definite nervous tissue within the cerebral lobe of the mature human hypophysis is doubtful. The optic tracts and commissure are elsewhere described (page 1223), suffice it at this place to mention their relation to the interpeduncular structures. The optic tracts diverge backward and wind around the ventral surface of the cere- bral peduncles (Fig. 993). Their medial ends are fused into a transversely flattened white band, the optic commissure or chiasm. The latter is connected with the front surface of the tuber cinereum, whilst above the chiasm the anterior wall of the ventricle consists of a delicate sheet of gray matter, the lamina cinerea (lamina terminalis This structure lies in the mid-line, passes almost vertically upward, with a slight forwardly directed curve, and becomes continuous with the rostrum of the corpus THE DIENCEPHALON. 1131 callosum. Just before meeting the latter, the lamina passes in front of the anterior commissure of the brain (Fig. 976). The Third Ventricle. The third ventricle (ventriculus tertius cerebri) is the narrow cleft-like space that separates the medial surfaces of the thalami (Fig. 966). It is somewhat broader behind and much deeper in front, where it comes into close relation with the exterior of the brain, the interpeduncular lamina alone intervening. Seen from the side, as in mesial sagittal sections (Fig. 996), the outline of the ventricle is irregularly comet-shaped, with^the broader end above and behind and the blunted point directed downward and forward (Fig. 978). Behind, it communicates with the Sylvian aqueduct, and through this canal indirectly with the fourth ventricle; anteriorly it connects with the two lateral ventricles by means of the foramina of Monroe. Its sagittal diameter, measured between the anterior commissure and the base of the pineal body, is approximately 2.5 cm. The lateral wall of the ventricle (Fig. 976) is formed chiefly by that part of the thalamus which lies below the level of the taenia thalami. On this surface, slightly in advance of the middle, is seen the small oval field of the middle commissure, and in front of this the downward curving elevation produced by the anterior pillar of the fornix. Between the latter and the prominent anterior tubercle of the thalamus lies the foramen of Monroe (foramen interventriculare), which establishes communication between the third and the cor- FIG. 978. Middle commissure Pineal recess / v / -Foramen of Monroe \ ^^l^fc ^ Suprapineal recess- .Anterior commissure -^ " ^^ i_ Posterior commissure Sylvian aqueduct Mammillary body ^J ^^~~~"~- Optic recess Infundibulum Optic chiasm Cast of third ventricle, viewed from the side. X \. (Retzius.) responding lateral ventricle, and transmits the trunk formed by the union of the vein of the corpus striatum and the choroid vein. A shallow furrow on the ventric- ular wall, the sulcus hypothalamicus leads from the foramen backward and some- what downward (Fig. 976). It is of importance as indicating, even in the adult brain, the demarcation between the thalamencephalon and the hypothalamus parts derived respectively from the dorsal and ventral zones of the embryonic brain-vesicle. The roof of the ventricle extends from the foramina of Monroe, bounded above and in front by the arching pillars of the fornix, to the pineal body behind, over which it pouches out into the suprapincal recess, as the little diverticulum overlying the body is termed. The immediate and morphological roof consists of the delicate ependymal layer, which is attached to the taenia thalami on each side and, stretching across the interthalamic cleft, closes in the ventricle. The ependymal layer, how- ever, is backed by a vascular fold of pia mater, which, in conjunction with the epithelial layer, constitutes the velum interposition. This structure is more fully described in connection with the lateral ventricles (page 1162); but its relation to the third ventricle finds appropriate mention at this place. As in the roof of the fourth ventricle and in the lateral ventricles, so in the third does the vascular tissue of the pia mater invaginate the ependymal layer to form vascular fringes which project into the ventricle (Fig. 974). A double line of such invaginations hangs from the roof of the third ventricle and constitutes the choroid plexus of that space. Since the ependyma everywhere covers these pial processes, it is evident that the fringes are, strictly regarded, outside the ventricle and excluded by the continuous layer of the epithelium. 1 1 32 HUMAN ANATOMY. The posterior wall of the third ventricle is very short and includes the base of the pineal body, with the opening into the minute pineal recess, the posterior com- missure and the orifice leading into the Sylvian aqueduct. The floor slopes rapidly downward and forward (Fig. 976) and comprises a small part of the tegmentum of the cerebral peduncles, the posterior perforated substance, the mammillary bodies, and the tuber cinereum with the infundibulum structures already described and included within the interpeduncular area on the base of the brain. Corresponding with the position of the superficial elevation, the ventricle exhibits the diverticulum of the infundibulum. The optic chiasm marks the anterior limit of the floor and the beginning of the anterior wall. Immediately above the chiasm the anterior wall exhibits a diverticulum, the optic recess, from which the lamina cinerea ascends to join the rostrum of the corpus callosum, in its course passing close to and in front of the anterior commissure. The latter structure shows on the front wall of the FIG. 979. Cavity in septum lucidum Corpus callosum, cut Caudate nucleus N^ X. V , Lateral ventricle W. ^-^L ^ Internal capsule Putamen of lenticular nucleus Cut anterior end of fornix Anterior pillars of fornix Anterior commissure Thalamus, anterior tubercle Optic recess ~~~ " "^X- '" \ \ Foramen of Monroe Optic chiasm Lamina cinerea Portion of frontal section of brain passing through foramina of Monroe, showing anterior wall of third ventricle modelled by anterior commissure and pillars of fornix. ventricle as a transverse ridge between the descending and slightly diverging anterior pillars of the fornix (Fig. 979). Although distinctly modelling the ventricular walls, all of these bands are excluded from the ventricle by its ependymal lining. THE TELENCEPHALON. The telencephalon, or end-brain, consists of two fundamental parts, the hemi- sphaerium and the pars optica hypothalami. The latter includes: (i) the lamina cinerea (terminal is}, (2) the optic commissure, (3) the tiibcr cinereum and (4) the pituitary body, all of which have been already considered, as a matter of con- venience, in connection with the diencephalon and the third ventricle. The hemi- sphere comprises: (i) the pallium, (2) the rhinencephalon, and (3) the corpus striafum. The first of these subdivisions undergoes such enormous development in the anthropoid apes and in man, that the pallium becomes the dominating factor and, expanding upward, laterally and backward as the great cerebral mantle, not only forms the chief bulk of the cerebrum, but overlies the derivatives of the other brain- segments to such an extent that these parts are to a large measure covered and deposed from their primary position on the free dorsal surface of the brain. In conse- quence in man, in whom the pallium reaches its highest development, the thalami, corpora quadrigemina and the cerebellum are masked by the hemispheres and occupy topographically a dependent position. The rhinencephaion. on the contrary, is in man only feebly developed and rudimentary in comparison with the conspicuous and bulky corresponding structures possessed by animals in which the sense of smell is highly developed. The corpus striatton. consisting of two large masses of gray THE TELENCEPHALON. 1133 matter, the caudate and the lenticular nucleus, represents the internal nucleus of the end-brain. Certain commissural structures, as the corpus callosum, the anterior com- missure and t\\e fornix are to be regarded as secondary and as serving to connect the halves of the great brain. The immediate free or outer surface of the pallium is everywhere formed by a thin peripheral layer of cortical gray matter, which, as an unbroken sheet, clothes the various ridges and intervening furrows the convolutions and fissures which model the exterior of the cerebrum and provide the necessary extent of surface. Beneath the cortical gray substance lies the white matter, which constitutes the bulk of the hemisphere and consists of the tracts of nerve-fibres pass- ing to and from the cortex, as well as of those connecting the various regions of the cortex with one another. Embedded within the core of white matter and lying much nearer the basal than the superior surface of the hemisphere (Fig. 1009), the corpus striatum is closely related to the ventricular cavity by means of the caudate nucleus on the one hand, and to the cortical gray matter by the lenticular nucleus on the other. In view of the rudimentary condition of the rhinencephalon and the over-shadowing development of the pallium in man, it is usual and convenient to regard most of the parts derived from the telencephalon as belonging to the hemispheres, the latter term being used in a less restricted sense than warranted by a precise interpretation of its developmental significance. THE CEREBRAL HEMISPHERES. Viewed from above, the human brain presents an ovoid form, the narrower end being directed forward and the broader backward, the greatest width corresponding with the parietal eminences (Fig. 984). The convex surface formed by the hemispheres is divided by a deep median sagittal cleft, the longitudinal fissure (fissura longitudinalis cerebri), that, for a distance less than one-third of its length anteriorly and more than one-third posteriorly, completely separates the hemi- spheres. In its middle third or more, the fissure is interrupted at a depth of about 3.5 cm. by the arched upper surface of the corpus callosum, the chief connection between the hemispheres. The upper and back part of the longitudinal fissure, throughout its length, is occupied by the sickle-shaped mesial fold of dura mater, the falx cerebri, which incompletely subdivides the space occupied by the cerebrum into two compartments. Under the name, transverse fissure (fissura transversa cerebri), is sometimes described the deep cleft which separates the postero-inferior surface of the hemisphere from the cerebellum, the corpora quad- rigemina and the pineal body. This cleft, so evident after the brain has been removed from the skull, when the parts are in situ is filled behind by the tentorium cerebelli and in front by a fold of pia. The hemispheres are advantageously studied after being separated from each other by sagittal section, and from the brain-stem by cutting across the mid-brain. When examined after such isolation, especially when hardened before removal from the skull, each hemisphere presents a dorso-lateral, a mesial and an inferior surface. The dorso-lateral surface (Fig. 980) is convex both from before backward and from above downward and closely conforms to the opposed inner surface of the cranial vault. The mesial surface (Fig. 987) is flat and vertical and bounds the longitudinal fissure. It is in contact with the sagittal fold of dura, the falx cerebri, except in front and below where the partition is narrow; here the mesial surfaces of the hemispheres, covered of course by the pia and arachnoid, lie in apposition. The inferior surface (Fig. 989) is irregular, its approximate anterior third resting in the anterior cerebral fossa of the cranial floor, the middle third in the lateral part of the middle fossa, whilst the posterior third is supported by the upper aspect of the tentorium, which separates it from the subjacent cerebellum. At the juncture of its anterior and middle thirds, the inferior surface of the hemisphere is crossed transversely, from within outward, by the stem of the Sylvian fissure and thus subdivided into an anterior and a posterior tract. The former and smaller, known as the orbital area, rests upon the orbital plate of the frontal bone and is modelled by this convex bony shelf into a corresponding slight con- cavity from side to side. The tract behind the deep Sylvian cleft is at first convex 134 HUMAN ANATOMY. and rounded, as it lies within the middle fossa, but traced backward it passes insensibly into the tcntorial area, supported by the tentorium cerebelli. This area is concave from before backward and directed inward as well as downward, in correspondence with the characteristic curvature of the tent-like dural septum. The borders separating the surfaces of the hemisphere are the dorso-mesial, the infero-lateral and the infero-mesial. The dorso-mesial border intervenes between the mesial and lateral surfaces and, therefore, follows the arched contour of the hemisphere beneath the vaulted calvaria. The infero-lateral border, between the lateral and inferior surfaces, is better dehned in front, where it separates the orbi- tal area from the external surface as the arched superciliary border (Cunningham), than behind, where it is so rounded off as to scarcely be recognizable as a distinct margin. The infero-mesial border intervenes between the mesial and the inferior surface of the hemisphere. It is well marked in front, where it limits the orbital area mesially, and again behind, where it corresponds to the line of juncture between FIG. 980. Lateral aspect of left cerebral hemisphere; dorso-median surface is somewhat foreshortened ; red lines indicate boundaries separating parietal, temporal and occipital lobes ; r, Rolandic fissure ; .$. g .. i. g., its superior and inferior genu; S 1 , S' 2 , S*, S* asc., vertical, horizontal, posterior and ascending limbs of Sylvian fissure; /. p. c., s. p. c., inferior and superior precentral; sf., if., superior and inferior frontal; p.m.. paramedian ; /./., mid-frontal ; d., diagonal, here continuous with inferior precentral; /', p~, p*, /*, inferior, superior, horizontal and occipital limhs of inter-parietal; p. o., parieto-occipital ; 't 1 , t 1 asc., superior temporal and its upturned limb; f-,f- asc., middle temporal and its upturned limb; t. o., transverse occipital; /. o., lateral occipital; A., arm centre;/?. T. O., pars basalis, triangularis and orbitalis ; Arc. p.-o., arcus parieto-occipitalis. the falx cerebri and the tentorium and marks the division between the mesial surface and the tentorial area. This margin has been designated the internal occipital border by Cunningham. The extreme anterior end of the cerebral hemisphere is known as the frontal pole (polus frontalis), and the most projecting part of the posterior end as the occipital pole (polus occipitalis), while the tip of the subdivision of the hemisphere which projects below the Sylvian fissure constitutes the temporal pole (polus tcm- poralis). A short distance behind the latter, the inferior surface exhibits a well defined petrosal depression (impressio petrosa); this is caused by the elevation cross- ing the petrous portion of the temporal bone which corresponds to the position of the superior semicircular canal. Under favorable conditions of hardening, the infero- mesial aspect of the occipital pole sometimes displays a broad shallow groove which marks the commencement of the lateral sinus. The groove is usually better marked on the right side than on the left, in accordance with the larger size of the right sinus as commonly found ; occasionally these relations are reversed, and frequently no groove is recognizable on the side of the smaller sinus. In brains hardened in sil/i, the gently arching curve of the hind-half of the infero-lateral border of the hemi- sphere is interrupted by a more or less evident indentation, the preoccipital notch ( incisura prai-occipitalis ), at a point about 3.75 cm. ( 1 1 A in.) in front of the occipital pole (Fig. 980). This notch, prominent in the child but later variable in THE TELENCEPHALON. 1135 its distinctness, is produced by a fold of dura over the parieto-mastoid suture and above the highest part of the lateral sinus (Cunningham). It is of importance in the topography of the brain, since it is often taken as the lower limit of the paricto-occipital line, establishing the conventional division on the lateral surface of the hemisphere between the parietal and occipital lobes (page 1143). The complex modelling of the surface of the cerebral hemispheres, the charac- teristic feature of the human brain, is produced by the presence of irregular eleva- tions, the convolutions or gyri, separated by the intervening furrows, the fissures or sulci. Although presenting many variations in the details of their arrangement, not only in different individuals but even in the hemispheres of the same brain, the convolutions and fissures of every normal human brain are grouped according to a general and definite plan to which the brain-patterns, whether elaborate or simple, in the main conform. The fissures differ greatly not only as to their depth as observed in the fully formed brain, but also as to their relation with the developing hemi- sphere, a very few, known as the complete fissures, involving the entire thickness of the wall of the cerebral vesicle and in consequence producing corresponding eleva- tions on the internal surface of the ventricular cavities. Of such total sulci the most important permanent ones are : ( i ) the hippocampal fissure, which produces the pro- jection known as the hipptfcampus major within the lateral ventricle ; (2) the ante- rior part of the calcarine fissure, which gives rise to the calcar avis ; and (3) the fore-part of the collateral fissure, which is responsible for the variable collateral emi- nence. The choroidal and the parieto-occipital fissure are also complete fissures of foetal life, but give rise to imaginations which do not permanently model the ventric- ular walls. The remaining furrows merely impress the surface of the hemispheres and are termed incomplete fissures. Their depth varies, in some cases being only a few millimetres and in others as much as 2.5 cm., with an average of about i cm. The height of the convolutions usually exceeds their width, the latter, in turn, being commonly somewhat greater at the surface than at the bases of the gyri. It is evi- dent, therefore that the convoluted condition of the hemispheres provides a greatly increased area of cortical gray matter without unduely adding to the bulk of the brain, the extent of the sunken surface being estimated as twice that of the exposed. The larger and longer adjacent convolutions are frequently connected by short ridges, the annectant gyri, which have no place in the typical arrangement. They may cross the bottom of the intervening fissure and ordinarily be entirely hidden from view (gyri profundi); or they may be superficially placed (gyri transitivi) and materially add to the complexity of the surface configuration. The cause and origin of the cerebral convolutions are still subjects for discussion. The fact, that at the time the fissures begin to appear, towards the end of the fifth fcetal month, the surface of the young brain is not in close contact with the cranial wall, disproves the assumption that the latter is directly responsible for the production of the fissures and convolutions. It is probable that the immediate cause of the surface modelling must be sought in the unequal growth and consequent localized tension which affect the hemispheres, excessive growth in the longitudinal axis resulting in transverse furrows, and that in the opposite axis producing fissures extending lengthwise. Whether the excessive expansion is caused by increase in the gray or white matter is uncertain, although local augmentation of the cortical gray substance is prob- ably the more important factor. After the beginning of the eighth month, when the growing brain comes into contact with the cranial wall, the convolutions, which before were to a large extent unrestrained and therefore relatively broad and rounded, suffer compression, the results of which are seen in the flattening and closer packing of the gyri and the narrowing and deepen- ing of the intervening fissures. By the end of fcetal life the salient features of the plan of arrangement have been established, although the final details of the brain-pattern are not acquired until sometime after birth. The Cerebral Lobes and Interlobar Fissures. For the purposes of description and topography, the cerebral hemispheres are subdivided into more or less definite tracts, the lobes, by certain sulci, appropriately known as the inter- lobar fissures. With few exceptions, however, the lobes so defined have little fundamental importance, since their recognition is warranted by convenience and not by morphological significance, in most cases the conspicuous limiting sulci being of 1 136 HUMAN ANATOMY. secondary importance, while those of primary value are comparatively obscure in the fully formed human brain. The interlobar fissures, six in number, are : ( i ) the fissure of Sylvius, (2) the central fissure, (3) the parieto-occipital fissure, (4) the collateral fissure, (5) the calloso-marginal fissure and (6) the limiting snlcus of Reil. The lobes marked off by these fissures with varying degrees of certainty are : ( i ) the frontal, (2) the parietal, (3) the temporal, (4) the occipital, (5) the limbic, and (6) the insula. An additional division, (7) the olfactory lobe, although of impor- tance as representing the peripheral part of the rhinencephalon of osmatic animals (as those possessing the sense of smell in a high degree are called), is not related to the foregoing sulci and comprises the rudimentary olfactory bulb and tract and associated parts (page 1151). It will be of advantage to describe the interlobar fissures as pre- paratory to a detailed consideration of the lobes. The fissure of Sylvius (fissura cerebri lateralis) is the most conspicuous fissure of the hemisphere. It begins on the inferior surface of the brain in a depression, the vallecula Sylvii, which opens out on the anterior perforated space. The first part of the fissure, its stem, passes horizontally outward to the lateral surface of the hemi- sphere, forming a deep cleft which separates the orbital area from the underlying tem- Rolandic fissure FIG. 981. Inferior precentral sulcus . ^^ Inferior frontal sulci Ascending limb Posterior limb Orbital surface Horizontal limb Portion of lateral surface of right hemisphere, showing ascending, horizontal and posterior limbs of Sylvum fissure radiating from Sylvian point. B, T, O, pars basalis, triangularis and orbitalis of inferior frontal gyms ; .V/', superior temporal gyrus. poral pole. On reaching the surface at the Sylvian point, the fissure divides (Fig. 981) into (a) a short anterior horizontal branch, (^) a somewhat longer anterior ascending branch, and (c) a long posterior branch. The anterior horizontal branch (ramus anterior horizontalis), about, 2 cm. in length, extends forward into the inferior frontal gyrus parallel to and just above the infero-lateral border, and forms the lower limit of the pars triangularis (page 1141 ). The anterior ascending branch (ramus anterior ascendens) passes upward and slightly forward into the hind-part of the inferior frontal convolution for a distance of about 3 cm. The frequently observed variations in the relation and arrangement of the anterior branches of the Sylvian fissure the ascending and horizontal limbs in many cases arising from a common arm, sometimes being fused into a single sulcus, or again being absent are due to atypical growth of the opercula. particularly of the frontal. The posterior branch (ramus posterior), the main continuation of the fissure and about 8 cm. in length, is directed horizontally backward, with a slight inclination upward. It forms a very evident boundary between the anterior parts of the parietal and temporal lobes which it separates by a deep cleft that usually ends behind in an ascending limb surrounded by the angular gyrus (Fig. 980). Not infrequently the fissure ends by dividing into two short anus, one of which penetrates the parietal lobe while the other arches downward into the temporal lobe. THE TELENCEPHALON. FIG. 982. The form and relations of the fissure of Sylvius are so dependent upon the growth of the surrounding parts, that a sketch of the development of this region of the hemisphere is necessary for an understanding of the significance of this conspicuous sulcus. During the third foetal month the lateral surface of the cerebral hemisphere presents a crescentic depressed area, the fossa Sylvii, whose floor corresponds to the insitla or island of J\eil. The latter is seen in the adult brain, on separating the margins of the Sylvian fissure, as a sunken area which is completely hidden by the overhanging parts, the opercula insulae, of the surrounding lobes (Fig. 990). During the fifth month the former shallow crescentic Sylvian fossa gives place to a more definitely walled triangular depres- sion, which, during the succeeding month, begins to be enclosed by the formation of the opercula. The details of this process have been carefully studied by Cunningham 1 and more recently by Retzius. 2 The opercula which bound the triangular fossa, named from the regions which contribute them and at first three in number, are the upper or parieto-frontal, the lower or temporal, and the anterior or orbital. The upper and lower walls first c jme in contact and thereby form the posterior limb of the Sylvian fissure. Later the angle between the upper and front walls of the fossa becomes modified and is finally obliterated by the appearance of a wedge-shaped projection, later the frontal operculum, which insinuates itself between the adjacent end FIG. 983. Inferior precentral Rolandic fissure Left hemisphere of brain of five months fiL-tus ; three-fourths natural size. Inferior frontal Parieto- frontal opercultnn Interparietal Olfactory bulb / Insula Vivian fissure Superior temporal sulcus Lateral surface of left hemisphere of eight months fostus ; insula is partly covered by opercula; three-fourths natural size. (Retzius.) i of the parieto-frontal and the orbital opercula. The orbital and particularly the frontal operculum are late in their differentiation and growth, and not until towards the second year after birth do they come into apposition with each other and the remaining opercula to complete the curtain that overhangs the insula. Along with the closure of the front part of the Sylvian fossa, the dif- ferentiation of the anterior limbs of the fissure pro- gresses, since upon the adequate growth of the frontal operculum depends the production of a distinct pars triangularis and of two separate anterior branches. Faulty development of this intermediate part of the opercular wall accounts for the V or I form, as well as the occasional absence, of the anterior limbs. The central fissure (sulcus centralis), or fissure of Rolando, extends transversely across the upper half of the convex dorsal surface of the hemisphere and therefore, with the bordering precentral and postcentral convolutions, interrupts the general longitudinal course of the gyri and sulci. Bearing this peculiarity in mind, the fissure is readily identified even in brains exhibiting an elaborate and complex modelling. It begins above on the supero-mesial margin of the hemisphere, a short distance behind the middle of the border, and descends with a slight general forward obliquity to the vicinity of the posterior limit of the fissure of Sylvius, above whose mid-point it usually ends. Its upper extremity usually extends over the supero- mesial border of the hemisphere and, passing obliquely backward, cuts for a short distance into the marginal gyrus of the mesial surface (Fig. 987). Its lower ex- tremity usually ends short of the Sylvian fissure, but occasionally (rarely) opens into this cleft. It constitutes a very definite boundary on the external surface of the hemisphere between the frontal and parietal lobes. Although passing obliquely downward and forward, the course of the central fissure is by no means straight 1 Contribution to the Surface Anatomy of the Cerebral Hemispheres, Irish Academy, 1892. 2 Das Menschenhirn, 1896. 72 U 3 8 HUMAN ANATOMY. owing to a marked angular backward projection of the substance of the precentral convolution, situated about the junction of the upper and middle thirds of the fissure. In consequence, the fissure presents in this part of its course a distinct curve, with the concavity directed forward, the upper and lower limits of this bend consti- tuting the superior and the inferior genu respectively (Fig. 980). The cortical tissue filling this recess is of importance, since it represents the part of the precentral gyrus devoted to the motor centre for the arm. Below the inferior genu the fissure descends almost vertically, its lower end often bending slightly backward. The angle which the general direction of the central fissure makes with the mesial plane in the adult brain is on an average 71.7 (Cunningham), the Rolandic angle, as it is called, of the two sides subtending therefore about 143 (Fig. 984). FIG. 984. Superior aspect of cerebral hemispheres; LF, longitudinal fissure; ., r. Rolandic fissuie; s#, /ir. its . and inferior genu ; .s. pc., superior precentral; s.f, i.f, superior ant) inferior frontal ; f>m, paramedian ; />, />-, />', />'. inferior, superior, horizontal and occipital limbs of inlerparietal ; p-o, parieto-occipital; /... /."., transverse and lateral occipital; Sasc, ascending limb of Sylvian ; t*asc., t-asc., ascending limbs of superior and middle temporal. Since the central fissure is usually developed from two separate parts, a longer lower and a short upper (Cunningham, Retzius) which later become continuous, a deep annectant gyrus is generally found crossing the bottom of the sulcus at the junction of its upper and middle thirds. In exceptional cases the original separation is continued by the deep annectant gyrus maintaining its superficial relations, the adult fissure then being interrupted by the bridge which ordinarily is limited to the bottom of the cleft. As a variation of very great variety, completed doubling of tin central fissure has been observed. The parieto-occipital fissure (fissura parieto-occipitalis ) is seen chiefly on the mesial surface of the hemisphere (Fig. 987), where it appears as a deep cleft which extends from a point on the supero-niesial border of the hemisphere, about 4 cm. in front of the occipital pole, downward and forward. This inner part of the fissure, THE TELENCEPHALON. 1139 the so-called internal paricto-occipital fissure, separates the mesial surfaces of the parietal and occipital lobes and ends below by joining the calcarine fissure, the two sulci together forming a > whose posteriorly directed diverging limbs in- clude a wedged-shaped portion of the occipital lobe known as the cuneus. The parieto-occipital fissure is continued without interruption across the upper margin of the hemisphere and onto the external surface for a short distance. This outer exten- sion, usually only from 12-15 mm. in length, constitutes the external parieto-occipital fissure and terminates after its limited transverse course in a bowed convolution, the arcns parieto-occipitalis, which surrounds and separates its end from the occipital part of the interparietal fissure. Although sometimes ending in two short and somewhat open branches, the external limit of the parieto-occipital fissure is usually relatively inconspicuous; notwithstanding, the sulcus is of much importance as affording a readily recognized upper limit of the conventional boundary line between the occipi- tal and the parietal and temporal lobes. In the foetal brain the parieto-occipital sul- cus- produces a distinct invagination of the wall of the cerebrum and corresponds, therefore, to a complete fissure. In the adult brain, however, all trace of this infold- ing has disappeared in consequence of the growth and thickening of the ventricular wall which subsequently takes place (Cunningham). The collateral fissure (fissura collateralis) is a well marked sulcus on the inferior surface of the hemisphere. It begins behind a little to the outer side of the occipital pole and extends forward, crossing the tentorial area parallel with, below and lateral to, the calcarine fissure, until opposite the posterior end of the corpus callo- sum, where it meets the hippocampal gyrus. It is then directed slightly outward, forming the lateral boundary of the last-named convolution, over the temporal area well toward the temporal pole, near which it either embraces or joins with a short curved furrow, the incisura temporalis, which, in conjunction with the collateral fissure, separates the lower or hippocampal part of the limbic lobe from the temporal lobe. According to Cunningham, the collateral fissure is at first represented by three distinct parts a posterior or occipital, an intermediate and a temporal -"which later become one continuous furrow. Of these three primary divisions, the interme- diate, and usually also the temporal, are complete fissures, producing respectively the collateral protuberance and the collateral eminence seen in the lateral ventricle (page 1164). The occipital portion of the fissure is never complete and, therefore, does not give rise to any elevation. The calloso-marginal fissure (sulcus cinguli) is the most conspicuous sul- cus on the mesial surface of the hemisphere, where it appears as a curved furrow running above and concentric with the arched upper surface of the corpus callosum. It begins in front below the fore-end of this bridge, just above the anterior perforated space, sweeps around the genu of the corpus callosum and arches backward above the latter structure almost as far as the splenium, where it turns upward (ramus mar- ginalis) and reaches the supero-mesial border of the hemisphere a short distance be- hind the overturned end of the Rolandic fissure. By its course the calloso-marginal sulcus marks off on the anterior two-thirds of the mesial surface of the hemisphere the marginal convolution of the frontal lobe from the callosal gyrus of the limbic lobe, the somewhat uncertain posterior boundary of the latter beyond the sulcus being indicated by the inconspicuous postlimbic fissure, which arches downward concen- trically with the splenium. The frequent variations in the details of the calloso- marginal fissure depend upon irregularities in the arrangement and fusion of the three separate furrows by the union of which a continuous sulcus is formed. The limiting sulcus of Reil (sulcus circulates Reili) is a shallow furrow that incompletely surrounds the insula and imperfectly separates this buried portion of the central cortex from the deeper parts of the enclosing opercula. The sulcus consists of three parts a superior, separating the island from the parietal and fron- tal lobes, an anterior, intervening in front between the insula and the frontal lobe, and a posterior, imperfectly separating the hind part of the island from the limbic lobe. THE LOBES OF THE HEMISPHERES. The Frontal Lobe. The frontal lobe (lobus frontalis) is the largest of the subdivisions of the hemisphere and includes approximately one-third of the hemi- 1140 HTM AX ANATOMY. FIG. 985. cerebrum. It appears on each of the three aspects of the hemisphere and has, therefore, a dorso-lateral, a mesial and an inferior surface. On the external surface of the hemisphere it is bounded behind by the central fissure, which separates it from the parietal lobe, and below by the fore-part of the Sylvian fissure, which intervenes between it and the temporal lobe. On the mesial surface the frontal lobe includes an irregular > , marked off by the calloso-marginal sulcus, the longer upper limb ending behind the central fissure. On the inferior surface of the hemisphere, the frontal lobe includes the concave orbital area, bounded behind by the transversely directed stem of the Sylvian fissure, which sulcus thus separates it from the temporal lobe. The principal fissures on the dorso-lateral surface of the frontal lobe are : ( i ) the inferior precentral, (2) the superior precentral, (3) the superior frontal and (4) the inferior frontal. The inferior precental sulcus which consists of a longer vertical and a short transverse limb and has a general ~| or T form. The vertical limb begins above the fissure of Sylvius and in front of the central fissure and extends upward parallel to the latter and separated from the lower part of the precentral convolution. The horizontal limb passes obliquely forward and upward and cuts for a variable distance into the middle frontal convolution. Fre- quently the inferior precentral sulcus is directly continuous with the inferior frontal furrow; sometimes it opens below into the Sylvian fissure and above may join the superior. The superior precental sulcus prolongs upward the anterior boun- dary of the precentral convolution. It lies parallel with the upper half of the Rolandic fissure, but does not usually, although sometimes reach the upper margin of the hemisphere. Almost constantly it receives the posterior end of the superior frontal sulcus with which it forms a \ shaped furrow. The superior frontal sulcus extends forward from the preceding fissure with a course which corresponds in general with the supero-mesial border of the hemisphere and thus marks off a longitudinal marginal tract, the superior frontal convolution. Anteriorly the superior frontal may join the median frontal sulcus, while its posterior end may incise the precentral convolution. Often tin- course of the fissure is interrupted by superficial anncctant gyri which connect the adjacent borders of the upper and middle frontal convolutions. The inferior frontal sulcus begins behind in the interval between the hori- zontal and vertical limbs of the inferior precentral furrow, <>r in confluence with one of these. In its general course it arches forward and downward towards the anterior or superciliary margin of the hemisphere and terminates a short distance behind this border by bifurcating into a transverse limb. The line of the fissure is often obscured by superficial annectant gyri and complicated by small secondary furrows which pass from it into the bordering middle and inferior frontal convolutions, The convolutions on the dorso-lateral surface of the frontal lobe are the pre- central, the superior frontal, tin- middle frontal and the inferior frontal. The precentral gyrus ( nyrus centrnlis anterior), also known as tin- ascending frontal, is bounded behind by the central fissure and in front by the superior and inferior precentral snlci. Below it is limited by the Sylvian fissure, whilst its upper end is continuous with the paracentral lobule of the mesial surface. Anteriorly it is connected with all three frontal convolutions. A short distance abo\e its middle, it s<-nds backward a conspicuous projection, triangular or rounded in outline, which encroaches upon the postcentral gyrns and correspondingly modifies the line of the Anterior aspect of cerebral hemisplK-rcs, liar 1cm. 1 ii skull; s/',if, superior and inferior Ironta! fissures; />/. paramedian; tn.f, mid-frontal; /-/., fronto-inarginal. THE TELENCEPHALC )X. 1 141 Rolandic fissure. The observations of Mills and of Grunbaum and Sherrington emphasize the predominating importance of the precentral convolution as containing the important cortical motor areas (page 1211), the backward projection just noted containing the centres controlling the muscles of the upper extremity. The superior frontal gyrus lies between the supero-mesial border of the hemi- sphere and the superior frontal sulcus. Since its course corresponds with the upper margin of the hemisphere, it is much longer than the other frontal convolutions on the external surface and reaches the frontal pole. It is continuous with the marginal gyrus, which, in fact, is only its mesial part. Behind, it joins the precentral convolu- tion by a narrow bridge between the upper end of the precentral sulcus and that of a branch from the calloso-marginal fissure. The superior frontal convolution, notwith- standing its meagre width, is frequently imperfectly divided into an upper and a lower part by a series of shallow longitudinal furrows collectively termed \.\\e para- median sulcus. The latter is regarded as a distinctive feature of the human brain, and is found relatively deep and well marked only in the brains of the higher races. The middle frontal gyrus, the broadest of the three, extends forward parallel with the upper frontal convolution well towards the frontal pole. It is bounded IMC;. 986. Inferior frontal sulcus Inferior precentral sulcus Rolandic fissure Ascending limb Orbital surface Horizontal limb Posterior limb Portion of lateral surface of left hemisphere, showing pars basalis (B), triangularis ( T) and orbitalis (0) of inferior frontal gyrus, known as Broca's convolution : ST., superior temporal gyrus. above and below by the superior and the frontal sulcus respectively and, in man and the anthropoid apes, is almost constantly subdivided into an upper and a lower sub- division by the mid frontal sulcus (sulcus frontalis medius). The latter is often broken by annectant gyri into two or more pieces and in front usually bifurcates to form the fronto-marginal sulcus (sulcus transversus anterior), which runs across the hemi- sphere a short distance above the superciliary margin. The inferior frontal gyrus, the shortest of the three, lies below the inferior frontal sulcus and arches forward and downward around the anterior limbs of the Sylvian fissure. Below and behind it is connected with the lower end of the pre- central convolution by a narrow bridge enclosing the lower end of the inferior pre- central sulcus. By the ascending and horizontal limbs of the Sylvian fissure the inferior frontal gyrus is incompletely divided into three portions the pars basalis, the pars triangularis and the pars orbitalis (Fig. 986). The pars basalis (pars opcrcularis) occupies the posterior part of the convolution and lies between the inferior precentral sulcus and the ascending Sylvian limb. It forms the fore-part of the fronto-parietal operculum and is indented by an inconspicuous although constant furrow, the sulcus diagonalis, which extends obliquely downward and forward across the gyrus for a variable distance. Although usually distinct, the diagonal sulcus may join the inferior precentral (Fig. 986), the inferior frontal or the Sylvian fissure. The pars triangularis is the wedge-shaped tract included between the two limbs of the Sylvian fissure. Its base is directed upward and forward and its n 4 2 HUMAN ANATOMY. apex towards the Sylvian point. The pars orbitalis lies below the horizontal limb and is continued around the margin of the hemisphere onto the orbital surface of the frontal lobe. It is evident, from the description of the boundaries of the Sylvian fissure already given (page 1137), that the preceding subdivisions of the inferior frontal gyrus correspond with certain of the opercula the pars basalis with the anterior part of the fronto-parietal, the pars triangularis with the frontal and the pars orbitalis with the orbital operculum. The posterior extremity of the inferior frontal gyrus on the left side is known as Broca s convolution and has long been regarded as the centre for the movements for articulate speech, although the accuracy of this view has been questioned. According to Marie, Broca' s convolution has no relation with speech, a conclusion, however, so far not convincingly supported. The convolution is sometimes better developed on the left than the right side of the brain, the pars triangularis particularly being increased. As previously noted, the development of this wedge the frontal operculum bears a direct relation to the degree of independence of the two anterior limbs of the Sylvian fissure. The mesial surface of the frontal lobe (Fig. 987), includes only one convolution, the marginal gyrus, which lies between the dorso-mesial margin of the hemisphere and the calloso-marginal sulcus (page 1139), and by the latter is separated from the limbic lobe. It is 3-shaped and directly continuous with the superior frontal gyrus above and with the gyrus rectus on the orbital surface below. Its posterior end is almost completely cut off from the rest of the gyrus by an ascending limb (sulcus para- centralis) from the calloso-marginal sulcus, the portion so isolated forming the front part of the paracentral lobule, which is bounded behind by the upturned end (ramus marginalis) of the calloso-marginal sulcus and contains, near its hind border, the termination of the fissure of Rolando. By means of an annectant convolution passing below the last-named furrow, the frontal part of the paracentral lobule is con- tinuous with the part contributed by the parietal lobe. The middle of the mar- ginal gyrus is often incompletely subdivided by a shallow longitudinal groove, the mesial frontal sulcus, into an upper and a lower tract, whilst its anterior and lower end is uncertainly cleft by two or three short downward curving furrows, the sulci rostrales. The orbital surface of the frontal lobe is marked by two fissures, the olfactory and the orbital and by three chief convolutions, the inner, the middle and the outer orbital. Although such division is convenient for the purposes of description, it must be remembered that these orbital gyri are not separate convolutions, but lankly the inferior portions of the upper, middle and lower frontal convolutions of the outer surface of the lobe. The olfactory sulcus lodges the olfactory bulb, tract and tubercle, and ex- tends parallel with, or inclined somewhat towards the great longitudinal fissure. Its course being straight, the sulcus marks off a narrow strip, about i cm. in width, along the mesial border of the lobe. This area, although specially designated as the gyrus rectus, is only a part of the broader longitudinal tract which corresponds to the orbital surface of the superior frontal convolution. The orbital sulcus includes a number of furrows whose arrangement is very variable, not only in different brains but often on the two sides of the same brain. In the disposition assumed as the typical one, which, however, is far from constant, the orbital sulcus consists of two longitudinal limbs, connected by a shorter trans- verse arm, the three furrows forming a common fissure which corresponds more or less closely with the letter H. In many cases, however, the sulcus more nearly re- sembles an X or K, or it may be still further modified by the presence of additional secondary grooves of variable number and length. Assuming the conventional H- form to exist, the orbital surface is divided into three longitudinal trails, the inner, middle and outer orbital gyri, by the long limbs (sulcus orbitalis interims et cxter- nus). The inner tract is subdivided by the olfactory sulcus into the gyrus rectus, above mentioned, and an outer part, the gyrus orbitalis internns in the more restricted sense. The middle orbital gyrus is subdivided by the curved transverse limb i sulcus orbitalis transversus ) into the anterior and the posterior orbital gyrus, which lie; respectively in front and behind the transverse furrow. In many cases the latter curves out\vanl and backward until it almost re-aches the Svlvian fissure-. THE TELENCEPHALON. The Parietal Lobe. This division includes a considerable part of the hemi- sphere and presents two surfaces, an external and a mesial. The external surface, much the more extensive and irregularly quadrilateral in outline, is bounded above, in front and partially below by well marked fissures, but behind and postero-infe- riorly its limits from the occipital and temporal lobes are defined for the most part by imaginary lines. Its upper boundary corresponds with the supero-mesial border of the hemisphere ; its anterior boundary is the central fissure, by which the pari- etal lobe is completely separated from the frontal except below, where the postcen- tral gyrus is continuous with the precentral by the bridge closing the lower end of the Rolandic fissure. Its posterior boundary, which separates the parietal from the occipital lobe, is largely conventional and indicated by a line drawn from the point where the parieto-occipital fissure cuts the upper margin of the hemisphere to an in- dentation, the preoccipital notch (page 1134), which grooves the infero-lateral border of the hemisphere at a point from 3.5-4 cm. in front of the occipital pole. Its inferior border, between the parietal and the temporal lobes, is definite where formed by the posterior limb of the Sylvian fissure. Beyond the upturned end of the latter, FIG. 987. Infero-mesial aspect of left cerebral hemisphere; cm., calloso-marginal fissure; ros., rostral; r., overturned end of Rolandic ; />. /., post-limbic ; i. p-o., internal parieto-occipital ; p. cal., a. cal., posterior and anterior calcarine ; p. col., a. col., posterior and anterior collateral ; i. t., incisura temporalis or rhinial ; o-t., occipito-temporal. the parietal and the temporal lobes are continuous and their separation is conven- tionally assumed to be made by an arbitrary line prolonged backward in the direc- tion of the posterior limb of the Sylvian fissure until it meets the parieto-occipital line previously described. The external surface of the parietal lobe is subdivided by a composite fissure, the interparietal sulcus, into three general tracts, the postcentral, the superior pari- etal and the inferior parietal gyrus. The interparietal sulcus, especially described by Turner, starts in the antero- inferior angle of the lobe a short distance above the Sylvian fissure, with which it is rarely continuous, ascends for about an inch parallel with the central fissure, and then sweeps backward and slightly upward across the parietal into the occipital lobe. The interparietal sulcus is developed as four originally distinct parts, which in the fully formed brain, notwithstanding their usual fusion, are recognized as the inferior and the superior postcentral sulcus and the horizontal and occipital limbs (Cun- ningham). The inferior postcentral sulcus lies behind and parallel with the lower part of the central fissure. Although in most cases continuous with either the superior postcentral sulcus (in 72 percent, according to Retzius 1 ), or with the horizontal limb 1 Biologische Untersuchungen, VIII., 1898. 1 144 HTM AN ANATOMY. (66 per cent.), or with both (55 per cent.), the inferior limb may remain ununited ( 17 per cent.). When joined, the two limbs together form a continuous postccntral sulcus which parallels the fissure of Rolando and bounds the postcentral convolution behind. In rare instances the inferior postcentral sulcus opens below into the Sylvian fissure. The superior postcentral sulcus lies behind and parallel with the upper part of the fissure of Rolando, gaining the superior margin of the hemisphere between the incisions of the Rolandic fissure and the upturned end of the calloso-marginal sulcus. Although in 59 per cent, of the brains studied by Retzius the fissure was confluent with the horizontal limb, in 24 per cent, it remained isolated. The horizontal limb passes backward and slightly upward and separates the superior and inferior parietal convolutions from each other. It is usually continuous in front with one or the other or with both postcentral sulci and behind with the FIG. 988. Lateral aspect of left side of brain. LF, longitudinal fissure; /., r., r., Rolandic fissure; i. / ., A. /'<'., inferior and superior precentral; sf., if., superior and inferior frontal ; S/>, S. asc.. posterior and ascending limbs of Sylvian fissure; P,p", /> ;t , / 4 , inferior, superior, horizontal and occipital limbs of interparictal ; />-o, parit-to-occipital ; /. o., 1. o., transverse and lateral occipital ; /', t l asc., superior temporal and its upturned limb; (-, t-asc., middle temporal and its upturned limb. posterior or occipital limb. As a rule it joins a continuous postcentral sulcus, in which case the three furrows form a \ shaped fissure, which subdivides the parietal lobe into its three main convolutions. The occipital limb is usually attached to the horizontal one and then directly prolongs the interparietal sulcus into the occipital lobe. Sometimes, however, it retains its original independence and is separated from the ramus horizontalis by a deep annectant gyrus. It is irregularly curved and marks the lower boundary of the gyrus, the arcus parieto-occipitalis, which receives the outer end of the parieto- occipital fissure. Beyond the line of this furrow, the sulcus lies in the occipital lobe and behind the arcus parieto-occipitalis ends by bifurcating into two widely divergent arms, which constitute the transverse occipital sulcus. The chief convolutions on the external surface of tlic parietal lobe are three the postcentral, the superior parietal and the inferior parietal. The postcentral gyrus, also called tin- ascending parietal^ forms the posterior wall of the fissure of Rolando, and itself is bounded behind by the postrentral sulcus, either by the continuous fissure or by its two divisions. The lower end of the gyrus is connected with the precentral convolution in front and with the inferior parietal one behind by the annectant i^yri (-losing the lower ends of the central and postcen- THE TELENCEPHALON. 1145 tral sulci respectively. Above, the convolution is continuous with the preccntral lobule of the mesial surface between the terminations of the calloso-marginal and the Rolandic fissures. In its width and general oblique course across the hemisphere, the postcentral convolution strongly resembles the precentral gyrus and with the latter and the three associated sulci the precentral, central and postcentral forms a conspicuous feature in the modelling of the external surface of the hemisphere and affords a ready means of locating the Rolandic fissure. The superior parietal gyrus is the triangular tract lying between superior postcentral sulcus, the horizontal limb of the interparietal sulcus and the supero- mesial border of the hemisphere. Behind, it is limited by the overturned outer end of the parieto-occipital fissure, around which, however, it is continuous with the occipital lobe by means of the curved convolution, the arcus parieto-occipitalis. Farther forward it is frequently deeply incised by an ascending branch from the inter- parietal sulcus. It is connected with the postcentral gyrus around the upper end of the superior postcentral sulcus and, in those cases in which the last-named sulcus fails to unite with outer segments of the interparietal fissure, additionally joins the post- central gyrus about the inferior postcentral sulcus. The inferior parietal gyrus is included between the curved interparietal sulcus and the conventional lower boundary of the lobe. Since only the front end of this boundary is defined by a groove, its greater part being the arbitrary line above described, it follows that behind the Sylvian fissure the inferior parietal convolution is continuous with the subjacent temporal gyri. The convolution is cut into from below by the upturned end of the Sylvian fissure and the terminations of the first and second temporal sulci and by these incisions is somewhat uncertainly subdivided into three parts, the supramarginal, the angular and the postparietal gyri (Fig. 988). The supramarginal gyrus arches around the upturned extremity of the Sylvian fissure. It lies behind and below the front part of the interparietal sulcus, around whose lower end it joins the postcentral gyrus, whilst below it is continuous with the superior temporal and behind with the angular gyrus. The angular gyrus surmounts the upwardly directed end of the superior temporal sulcus and below is prolonged into the superior and middle temporal convolutions. It is commonly imperfectly sepa- rated from the postparietal gyrus by a shallow furrow. The postparietal gyrus bends over the obliquely vertical extremity of the middle temporal sulcus and below joins the middle and inferior temporal convolutions. It lies approximately opposite the arcus parieto-occipitalis from which it is separated by the occipital branch of the interparietal sulcus. The mesial surface of the parietal lobe includes an irregularly quadrate area ex- tending from the internal limb of the parieto-occipital sulcus behind to the line of the Rolandic fissure in front; below it is imperfectly defined from the limbic lobe by the calloso-marginal sulcus, to a very slight extent, and its continuation, the post-limbic furrow. By far the greater part of this surface is embraced by the quadrate lobule or precuneus, an irregularly quadrilateral area (Fig. 987) limited in front by the upturned terminal limb of the calloso-marginal and behind by the parieto-occipital sulcus. The lobule, the mesial aspect of the superior parietal convolution, is usually marked by one or more furrows, the precuneate sulci, which incise the upper margin of the hemisphere and extend for a short distance onto the outer surface. The Occipital Lobe. The occipital lobe is pyramidal in form and includes the occipital pole and the adjacent parts of the hemisphere. It is represented on all of the aspects of the hemisphere and possesses, therefore, a lateral, a mesial and an inferior or tentorial surface. A well-marked occipital lobe is found only in the brain of man and of the anthropoid apes and is developed as a backward prolongation of the parietal and temporal lobes, from which, therefore, it is but imperfectly sepa- rated. On the mesial surface its extent is definitely limited by the internal parieto- occipital sulcus, by which it is cut off from the quadrate lobule or precuneus of the parietal lobe. On the lateral surface, on the contrary, it is continuous with the pari- etal and temporal lobes, its anterior boundary being arbitrary and indicated by the parieto-occipital line drawn from the overturned limit of the parieto-occipital sulcus above to the preoccipital notch below. On the inferior or tentorial aspect its demar- cation is even more uncertain, the occipital, limbic and temporal lobes being here 1146 HUMAN ANATOMY. directly continuous, and depends upon the recognition of an arbitrary line which may be drawn, as suggested by Cunningham, from the preoccipital notch on the infero-lateral border to the isthmus of the limbic lobe, just below the splenium of the corpus callosum. The external surface of the occipital lobe is modelled by two well-defined fissures, the transverse occipital and the lateral occipital, and by two somewhat uncertain convolutions, the superior and the inferior occipital (Fig. 988). The transverse occipital sulcus is, as above pointed out, the widely diver- gent terminal bifurcation of the interparietal fissure, whose last segment beyond the outer end of the parieto-occipital sulcus enters the occipital lobe to end in the manner just indicated. FIG. 989. Inferior aspect of cerebral hemispheres, t.o., t.o., e.o., internal, transverse and external orbital i.e., incisura temporalis ; cat., calcarine , col., collateral ; o-t., occipito-temporal fissures. fissu The lateral occipital sulcus arches horizontally forward below the lower end of the preceding furrow, not infrequently dividing into an ascending and a descending limb. The superior and inferior occipital gyri are the upper and lower areas into which the outer aspect of the occipital lobe is somewhat uncertainly subdivided by the lateral occipital sulcus. Secondary furrows and ridges often obscure the charae- teristic modelling of this surface, whilst annectant convolutions connect its gyri with the parietal and temporal lobes. The mesial snrface of the occipital lobe presents one sulcus, the calcarine fissure, a triangular tract, the cuneus, and part of the gyms lingualis. The calcarine fissure begins by a forked extremity, the longer lower limb of which incises the occipital pole in the impression made on the hemisphere by the lateral sinus. It then continues forward, slightly arched, a short distance above tin- border of the lobe formed by the junction of the falx cerebri and the teiitorium, and THE TELENCEPHALON. 1147 ends, after a short bend outward, by cutting into the limbic lobe just below the splenium of the corpus callosum (Fig. 987). This incision divides the posterior extremity of the hippocampal gyrus into a narrow upper tract, the isthmus, which links the gyrus with the callosal convolution, and a broader lower arm, which establishes continuity between the hippocampal and fusiform gyri. A short distance in front of its middle, the calcarine fissure is joined by the lower end of the parieto- occipital sulcus, the two furrows forming a > shaped sulcus, between whose diverging limbs lies the triangular cuneus. Although usually appearing as one continuous fissure, the parieto-occipital and calcarine sulci are incompletely separated by a deep annectant gyrus, which connects the cuneus with the limbic lobe. The calcarine fissure itself is subdivided by a second sunken gyrus into an anterior and a posterior part. The latter, the posterior calcarine fissure, is shorter and shallower than the front part and is not a total fissure. The other portion, the anterior calca- rine fissure, is not only the deeper but completely invaginates the brain-wall, thereby giving rise to the elevation known as the calcar avis, seen on the inner boundary of the posterior horn of the lateral ventricle. The cuneus forms the chief part of the mesial aspect of the occipital lobe. It is triangular in outline and lies between the parieto-occipital sulcus in front and the posterior limb of the calcarine fissure below, whilst above and behind it reaches the superior border of the hemisphere (Fig. 987). Its surface is frequently impressed by one or more shallow vertical furrows. The lingual gyrus, also called the infra-calcarine ', is the irregular elongated tract bounded mesially and above by the calcarine fissure, and laterally and below by the collateral (Fig. 989). Its rounded hind-end lies in the occipital lobe, whilst its tapering and greatly narrowed front-end is continuous with the hippocampal convo- lution. The gyrus fits into the angle between the falx cerebri and the tentorium and therefore bears the internal occipital border of the hemisphere and appears on both the mesial and the tentorial surfaces. It is usually modelled by irregular shallow furrows which break up the larger tentorial aspect into uncertain secondary gyri. The inferior or tentorial surface of the occipital lobe is continuous with the more extensive similar surface of the temporal lobe resting upon the tentorium. In addi- tion to the tentorial part of the lingual gyrus, this aspect of the lobe is occupied by the posterior part of the occipito-temporal gyrus. The latter includes an irreg- ular fusiform tract, bounded by the collateral fissure internally and by the inferior temporal sulcus laterally (Fig. 989). As expressed by its name, the occipito- temporal convolution belongs partly to the occipital and partly to the temporal lobe and extends from the occipital to the temporal pole. Its surface is broken by a number of irregularly disposed furrows which add to the uncertainty of its outer boundary. The Temporal Lobe. The temporal lobe includes the irregularly pyramidal division of the cerebral hemisphere, whose apex is lodged within the middle fossa of the skull and whose succeeding part forms the conspicuous dependent mass seen on the infero-lateral surface of the hemicerebrum. In front it is separated from the frontal lobe by the stem of the Sylvian fissure; above it is marked off from the pari- etal lobe by the posterior limb of the Sylvian fissure and the arbitrary line prolonged backward in the direction of this sulcus; externally and below it is defined by the infero-lateral border of the hemisphere; and mesially it is separated from the limbic lobe by the collateral fissure. Its posterior border, however, on both the lateral and the inferior (tentorial) surface is arbitrary and indicated by the lines already men- tioned (page 1143) which afford the conventional demarcation between the occipital and temporal lobes. The temporal lobe presents three surfaces, the convex lateral, the inferior (largely tentorial ), and the buried superior or opercular. Of these the lateral and inferior are separated by a border so broad and rounded that the surfaces pass insen- sibly into each other. Its tip corresponds with the temporal pole of the hemisphere and underlies the posterior part of the orbital surface of the frontal lobe, which it partially masks. The lateral surface of the temporal lobe is modelled by two fissures, the superior and the middle temporal, and three convolutions, the superior, the middle and the H4 S Hl'MAX AXATOMV. inferior temporal (Fig. 988), all of which correspond in the general direction of their course with the posterior limb of the Sylvian fissure and extend backward and slightly upward. Tlu^superior temporal sulcus, also called the parallel sulcus in recognition of the similarity of its course with that of the posterior limb of the Sylvian fissure, is the first in the series of longitudinal furrows, the third of which appears not on the outer, but on the inferior aspect of the lobe. It begins near the temporal pole, runs parallel with the posterior limb of the Sylvian fissure and ends by cutting upward into the inferior parietal convolution, whose angular gyrus surrounds the upturned extremity of the sulcus. The middle temporal sulcus, the second in the series, lies below the pre- ceding fissure, whose direction in a general way it follows. It is, however, much less certainly marked and in most cases is not a continuous furrow, as is the superior sulcus, but broken by superficial annectant convolutions into a number of separate pieces, the exact sequence of which is often difficult to follow. The upturned end of the middle temporal sulcus cuts into the lower parietal convolution towards the pos- terior limb of the interparietal sulcus (Fig. 988) from which, however, it is separated by the arching postparietal gyrus. FIG. 990. Rolandic fissure Right cerebral hemisphere, with opercula displaced to expose island of Reil. The superior temporal gyrus intervenes between the posterior limb of the Sylvian fissure and the superior temporal sulcus. Its lower end lies at the temporal pole, whilst above the tract is continuous with the supramarginal and angular gyri of the parietal lobe. The middle temporal gyrus, between the upper and middle temporal sulci, is connected with the subjacent convolution by the bridges which interrupt the sec- ond temporal furrow. Above and behind it is continuous with the angular and I x istparietal convolutions. The inferior temporal gyrus occupies the rounded infero-lateral margin of the hemisphere, and appears on both the lateral and the inferior surface of the lobe, being continuous with the occipital lobe behind (Fig. 988). Its upper boundary, formed by the middle temporal sulcus, is indistinct ; its lower and mesial limit is defined by the inferior temporal sulcus, which separates it from the occipito- temporal gyrus. The 'inferior surface of the temporal lobe is rounded in front, where it rests in the anterior cerebral fossa, but behind is modelled by the upper surface of the ten- tnrium cerebelli and is, therefore, concave from before backward and slightly convex from side to side. It presents one fissure, the inferior temporal, and one convolu- tion, the anterior part of the occipito-temporal. The inferior temporal sulcus, also called the oeeipito-temporal, courses LmiM tudinallv a short distance internal to the infero-lateral border of the hemisphere and THE TELENCEPHALON. 1149 separates the inferior temporal from the occipito-temporal gyrus. Although for the greater part of its extent on the temporal lobe, it is not confined to this, but continues backward into the occipital lobe which, therefore, claims it as one of its furrows. The sulcus is rarely continuous, usually being broken by annectant gyri into a posterior, a middle and an anterior segment. The occipito-temporal gyrus (gyrus fusiformis) is, as its names imply, a fusiform tract belonging partly to the occipital and partly to the temporal lobe (Fig. 989). Its two ends, in front and behind, are pointed and connected by a broader intervening tract, which is commonly broken up by secondary furrows. The temporal division of the gyrus, including approximately its anterior two-thirds, is embraced between the converging collateral fissure mesially and the inferior temporal sulcus laterally ; its conventional posterior limit is the line drawn from the preoccipital notch to the isthmus of the limbic lobe, immediately beneath the hind-end of the corpus callosum. The superior surface of the temporal lobe is directed towards the insula and is therefore an opercular aspect. On separating the walls of the Sylvian fissure to expose it, this buried surface of the temporal lobe often exhibits several shallow transverse furrows and indistinct gyri ; the deep aspect of the temporal pole being similarly indented. FIG. 991. Rolandic fissure^ Sulcus subdividing precentral lobule / Cut surface of frontal lobe "\ ^*. J ^M .-- ^ jf -St* i ' \, >/ ' / Sulcus centralis^ X^^aaaay^.^ , j| . Sulcus circulans Gyri breves . Sulcus centralis insulse Gyrus longus Temporal Apex Limen lobe, cut Island of Reil exposed after cutting away surrounding parts of right cerebral hemisphere. The Insula. The insula, or island of Reil, sometimes also called the central lobe, is, in the human brain, entirely concealed within the Sylvian fissure by the approximation of the overhanging opercula. The manner in which the latter are developed from the wall surrounding the early Sylvian fossa has been described (page 1137) ; it remains here to note the chief features of this region in the adult brain. On examining the relations of the insula, as seen in frontal sections of the brain (Fig. 967), it will be noted (a~) that the shell of cortical gray matter cover- ing the sunken convolutions is directly continuous along the Sylvian fissure with that covering the convolutions on the freely exposed parts of the hemisphere ; (b) that the insular cortex lies close to the underlying mass of gray matter, the lenticular division of the corpus striatum, a narrow tract of white matter, the external capsule, alone intervening. Since the corpus striatum is one of the earliest of the funda- mental parts of the telencephalon to be developed, it is probable that its close pri- mary relation to the surface of the hemisphere is largely responsible for the failure of the overlying cortex to keep pace with the general expansion of the adjoining parts. When exposed, by separation or removal of the surrounding opercula (Fig. 991), the insula appears as a triangular convex field composed of a group of radi- ating convolutions, whose broader ends lie above and pointed ones below. The 1 150 HUMAN ANATOMY. dependent apex of the insula lies close to the anterior perforated space, with the gray matter of which the cortical sheet of the island is continuous by way of a transitional area, known as the limcn insulic, where the limiting sulcus of the island is incomplete. In addition to being imperfectly separated from the surround- ing opercula by the curved limiting sulcus {sulcus circularis insultc}, the island is divided into an anterior and a posterior part by the sulcus centra/is insithc. This furrow continues in a general way the downward and forward direction of the fissure of Rolando, the deeper part of which is seen above the island (Fig. 991). The anterior part, or precentral lobule, is subdivided by two, sometimes by three, shallow grooves into three or four short downwardly converging ridges, the gvri breves, of which the front one is connected with the deeper part of the inferior frontal convolution by a small arched annectant gyrus transversus. The hind-part of the island, the postcentral lobule, includes a longer wedge-shaped tract, the gyrus longus, which below is continuous with the limbic lobe. The gyrus longus is frequently subdivided by one or more shallow furrows into secondary ridges. The Limbic Lobe. The limbic lobe (gyrus fornicatus) appears on the mesial and inferior surfaces of the hemisphere (Fig. 987) as an elongated o-shapecl tract, Splenium of corpus callosum Collosal fissure FIG. 992. Fornix, body Tlialmus, partly cut away Septum luciduni Fasciola cinerea Calcarine fissure Isthmus' Khinal fissure Uncus Collateral fissure Gyrus dentatus Gyrus Fiinbria hippocampi Portion of infero-mesial surface of left hemisphere, showing lower part of limbic lobe and adjacent structures. whose ends lie closely approximated with each other and with the anterior JKT- forated space. These extremities are further intimately associated with the two limbs of the olfactory tract, in this manner the limbic and olfactory lobes becoming, at least topographically, continuous. The limbic lobe comprises two parts, an antero- superior and an inferior, of which the former, the callosal gynts, lies concentric with the upper surface of the corpus callosum, and the inferior part, the liippo- catnpal gvnts, forms the mesial tract of the tentorial surface of the hemisphere, The limbic lobe is separated from the adjacent convolutions by the calloso-marginal sulcus in front and above, by the postlimbic sulcus behind, and by the anterior part of the collateral fissure below. Its demarcation from the anterior part of the temporal lobe is effected by the inconspicuous rhinal sulcus ( tissura rhinica >. or incisura temporalis, which feeble furrow in man represents the important and fundamental ectorhinal fissure of the lower animals. The callosal gyrus ( <-\nis ciniili >, also called the gyrus foniicatns (not to be mi-taken, however, with the" same name as applied to the entire limbic lobe', begins at the anterior perforated space, below the recurved rostrum of the corpus callosum. Thence it winds around the gi-nu of the latter and follows the convex dorsal surface' of the corpus callosum, separated however from it by the narrow callosal sulcus (sulcus corporis cnllosi). On reaching a point just below the splenium, around which 'c*s , THE TELENCEPHALON. 1151 it bends, the callosal gyrus is markedly reduced in width by the encroachment of the calcarine fissure, the narrowed tapering tract thus formed being the upper part of the isthmus (isthmus gyri fornicati), which below joins the similarly reduced upper end of the hippocampal convolution and so establishes the continuity between the two parts of the lobe. The hippocampal gyrus (gyrus hippocampi) curves forward from the isthmus along the mesial border of the tentorial surface of the hemisphere towards the apex of the temporal lobe, which, however, it fails to reach (Fig. 922). Its anterior extremity is distinctly thickened and forms a rounded hook-like projection, the uncus, which is recurved and directed backward and inward. The uncus is separated from the apex of the temporal lobe by the incisura temporalis (fissura rhinica), whilst the hippocampal convolution is marked off laterally by the anterior part of the collateral fissure. Although blended with the gyrus hippocampi and seemingly a part of the limbic lobe, the uncus, strictly considered, belongs to the rhinencephalon and not to the limbic lobe (Turner, Elliot Smith). The posterior end of the hippocampal convolution is incised by the anterior extremity of the calcarine fissure and so divided into two parts ; of these the upper aids in forming the isthmus and is continuous with the callosal gyrus, whilst the lower one blends with the front part of the gyrus lingualis of the occipital lobe. The Rhinencephalon. Although a division of fundamental importance and differentiated at a very early period in the development of the human telencephalon, in the brain of man it is represented by structures, which to a great extent are rudi- mentary and feeble expressions of the bulky corresponding parts in the brains of many of the lower animals. Its small size in man, as compared with the voluminous structures seen in some mammals in which the rhinencephalon constitutes a large part of the entire hemisphere, is no doubt associated with the relatively feeble olfac- tory sense possessed by man. It is probable, however, that other and unknown factors are responsible for the development of this part of the hemisphere to a degree disproportionate to the olfactory capacity of the animal, as strikingly observed among the lower vertebrates. The conclusions deduced from comparative studies empha- size the fundamental character of the rhinencephalon as phylogenetically being the oldest part of the hemisphere. Indeed of such primary morphological significance is the rhinencephalon that it is termed the archipallium, as distinguished from the neopallium, which comprises almost the entire remainder of the hemisphere with the exception of its nucleus, the corpus striatum. As seen in the human brain, the rhinencephalon includes the rudimentary olfac- tory lobe represented by the olfactory bulb, the olfactory tract with its roots, the olfactory trigone, and the parolfactory area and the uncus and a number of acces- sory parts, including the anterior perforated space, the gyrus subcallosus, the sep- tum lucidum, the fornix, the hippocampus and the gyrus dentatus. Some of these accessory structures can be understood only after their relations to outer parts of the brain have been considered. Deferring the details of certain of these struc- tures, as the septum lucidum, the fornix, and the hippocampus major, until the lateral ventricles are described (page 1160), it will suffice for the present to point out their general features as related to the rhinencephalon. The Olfactory Lobe. This division of the adult human brain is small and rudimentary and comprises the olfactory bulb, the olfactory tract, the olfactory trigone and the parolfactory area (Fig. 993). Of these all but the last lie on the inferior surface of the brain, whilst the parolfactory area occupies a small space on the mesial aspect of the hemisphere. The olfactory bulb (bulbus olfactorius) is an elongated irregularly oval swell- ing, about 10 mm. long, from 3-4 mm. wide and about 2.5 mm. thick, which behind is continuous with the olfactory tract and below receives the olfactory filaments. Its upper surface underlies the olfactory sulcus of the orbital aspect of the frontal lobe, and its under one rests upon the cribriform plate of the ethmoid bone, through the apertures of which the bundles of the olfactory nerve-fibres ascend from the nasal mucous membrane to the bulb. The structure of the olfactory bulb shares the general rudimentary condition which charac- terizes the lobe in man, the bulb having lost the central cavity ( ventriculus bulbi o/factorii) , 1152 I UMAX ANATOMY. which in many animals is continuous with the fore-part of the lateral ventricle, as well as some of the six layers that may be typically represented, as in the dog's bulb. The ventral aspect of the bulb, receiving the olfactory nerves, retains most completely its nervous character and pre- sents three chief strata (Fig. 995). (i) The stratum of olfactory fibres appears as a narrow zone made up of the irregularly intermingled bundles of axones of the olfactory cells situated within the olfactory area of the nasal mucous membrane. This layer is succeeded by a broader tract, (2) the stratum of the mitral cells, so named on account of the numerous nerve-cells of peculiar bishop' s-hat form which occupy its upper border. Along its lower margin extends a narrow zone of large spherical masses, the olfactory glomeruli. These bodies, from .o65-.o9o mm. in diameter, consist of an intricate complex formed by the intertwining of the richly branching axones ascending from the olfactory cells and of the dendrites descending from the mitral cells. The interval between the upper and lower margins of the second stratum is occupied by the molecular layer, composed of small nerve-cells whose dendrites also enter the glomeruli. (3) The stratum of central fibres includes the centrally directed axones of the mitral and other nerve-cells which constitute the second link in the complicated paths by which the olfactory stimuli are carried to the cortical areas. The outer zone of this stratum is known FIG. 993. Olfactory bulb Olfactory tra Mesial olfactory ..tria Lateral olfactory stna Island of Reil Anterior perforated space Cut surface of temporal lobe Cerebral peduncle crossed by optic tract Lateral geniculate body Olfactory sulcus I'arolfactory area Tnberculiiin olfactoriurn Trigomun olfactoriutn Optic chiastn, ~ I artly out away Manimillary body iu interpeauncular space - Oculomotor nerve Cerebral peduncle I'ulvinar Median geniculate body Sylvian aqueduct Anterior part of inferior surface of brain, showing parts of olfactory lobe and Mnictmvs within interpedun- cular space ; tip of right temporal lobe has been removed. as the granular layer and consists of many small nerve-cells intermingled with the fibres. The deeper part of the stratum of nerve-fibres encloses some larger nerve-cells of stellate or enlongated form. The central part of the bulb, which represents the obliterated ventricular space, is filled by a gelatinous substance resembling modified neuroglia. The olfactory tract (tractus olfactorius) is a narrow band of light color, which extends from the olfactory bulb in front to the olfactory trig<>ne behind (Fig. 993). It measures about 2 cm. in length and 2.5 mm. in width, but is broader at its pos- terior extremity, from which the olfactory stria, as its roots are called, diverge. Its ventral surface is flat and its narrow dorsal one ridged, the tract appearing in transverse section more or less triangular in outline. The structure of the olfactory tract further emphasi/es the rudimentary condition of the part in man. The ventral aspect and the rounded adjoining borders consist of: (i) a stratum of >KT;'< -fi/>n-s, longitudinally coursing and therefore transversely rut in cross-sections, which OOVera the sides and dorsal surface of the tract and is reduced to an extremely thin and rudimen- tarv sheet. Next follows (2) a gt'/titimms stratum, which represents the obliterated ventricular cavity seen in main lower animals. Succeeding this and forming the thickest layer of the tract ; the dorsal stratum <>/' mv matter, which still retains its importance as a tract of cortical gray substance from which fibres pass to oilier parts of the hemisphere (page 1222). THE TELENCEPHALON. 1153 The olfactory striae, the so-called roots of the olfactory tract (Fig. 993), are usually two, the mesial and the lateral, an additional intermediate root being some- times represented by faint strands. The mesial stria bends sharply inward, passes along the inner margin of the olfactory trigone and disappears on the mesial surface of the hemisphere by joining probably partly the callosal and partly the subcallosal gyri (Fig. 994). The diverging lateral stria obliquely courses along the antero- lateral margin of the perforated space, but usually disappears as a distinct tract before it can be traced to the uncus, its probable destination (page 1222). Occasionally the lateral root is represented by two strands, an outer and an inner, the last one fading away in the substance of the anterior perforated space. An additional intermediate stria is sometimes recognizable for a short time before it too sinks into the anterior perforated space. The olfactory trigone (trigonum olfactorium ) is the three-sided slightly convex area embraced by the two roots of the olfactory tract at the sides, and behind sepa- rated from the anterior perforated space by a groove (sulcus parolfactorius posterior). The triangular area seen on the inferior surface of the hemisphere (Fig. 993) is really the under aspect of a more extensive pyramidal elevation, the tuberculum olfactorium, which, however, lies in large part within the olfactory sulcus and is therefore superficially not visible except at its base, the trigone. Retzius regards this part of the hemisphere as a constant deep convo- ' FIG. 994. lution, gyrus tuberis olfac- torius, from which proceed two ridges, gyrus olfacto- rius medialis and lateralis. These bend respectively inward and outward and support the white strands of nerve-fibres, the striae olfac- torii, which are usually de- scribed as the roots of the olfactory tract. The tuber- Rostrum of ^ -,^ ir rorrms callosnm ^^T^m _L .<*i >^^ ^Lamina cmerea culum olfactorium contains 111 Septum lucidum / / Sulcus parolfactorius posterior a considerable amount or Sulcus paroitactonus / . , . anterior Gyrus subcallosus gray matter, which is a part of the peripheral olfactory COrtex ana,^V\ltn Other por- Portion ot mesial surface of right hemisphere, showing gyrus subcallosus tioilS of this sheet, shares and parolfactory area. in the reception of axones from the mitral cells and in the origin of fibres passing to other parts of the rhinencephalon. The parolfactory area, Q? field of Broca, lies as a small curved tract upon the mesial surface of the hemisphere, just in front of and below the gyrus subcallosus which extends from the rostrum to the corpus callosum (Fig. 994). The area parolfactoria is bounded in front by the sidcus parolfactorius anterior and behind by the sulcus parolfactorius posterior, and is connected in front with the superior frontal gyrus, above with the callosal gyrus and below with the inner part of the trigonum olfactorium, the mesial olfactory gyrus above mentioned. The anterior perforated space (substantia perforata anterior) is an irregularly triangular area (Fig. 993) lying behind the trigonum olfactorium, from which it is separated by the obliquely coursing sulcus parolfactorius posterior, and in front of the optic commissure. Its inner part is narrow and extends as a point between the mesial root of the olfactory tract and the lower end of the subcallosal gyrus. Its broader outer part extends into the floor of the stem of the Sylvian fissure and behind reaches the deeper part of the uncus and, more medially, the optic tract. Its designation as perforated is justified by the large number of small oval apertures for the transmission of perforating branches from the antero-mesial and antero- lateral groups of the basal arteries. These openings, most numerous along the front margin of the space, are disposed with some regularity in parallel rows and "54 HUMAN ANATOMY. FIG. 995. Atrophic ventricu- lar area Nerve-fibre layer Granular layer Layer of mitral cells Molecular layer Olfactory glomeruli Blood-vessel Olfactory fibre layer decrease in size as they approach the inner border (Foville). The substance of the space proper consists of a thin sheet of gray matter containing groups of nerve-cells, some of which constitute the nuclei of primary centres interposed in the paths connecting the olfactory lobe with the secondary (cortical) olfactory centres (page 1222). In addition to the white strands of nerve-fibres composing the olfactory striae which after a longer or shorter superficial course sink into the substance of the perforated space, an obliquely directed narrow ribbon-like tract, the diagonal band of Broca, may be sometimes made out along the inner margin of the area perforata. In front it is continuous with the subcallosal gyrus and behind passes along the optic tract towards the anterior end of the hippocampal convolution. The band is of interest as being probably the beginning, on the basal surface of the brain, of at least a part of the fibre-tracts contained within the rudimentary supracallosal gyrus (page 1157) that, in turn, is prolonged into the gyrus dentatus. The uncus is the thickened anterior extremity of the gyrus hippocampi, recurved around the front end of the hippocampal fissure (Fig. 992). Antero-inferiorly it is separated from the adjacent part of the temporal lobe by the inconspicu- ous incisura temporalis or rhinal sulcus, which in animals possessing a well developed rhinencephalon constitutes a definite boundary be- tween this part of the hemisphere and the pallium. With its deeper surface the uncus is in close relation with the anterior perforated space, whilst postero-mesially it is connected with the fimbria (page 1165) and the gyrus dentatus (page 1166). Although seemingly a part of the limbic lobe, the comparative studies of Turner and of Elliot Smith have established its morphological inde- pendence from the last-named lobe and emphasized its relation with the rhinencephalon. With the lateral olfactory stria, the uncus constitutes Transverse section of olfactory bulb ; drawing includes part ', m fh e feeble renresentation of of bulb lying ventral to atrophic ventricular area. the large and conspicuous pyramidal lobe, which in many animals forms the most massive part of the olfactory brain. The accessory parts of the rhinencephalon include structures which, for the most part, constitute collectively an elaborate path by which the olfactory cortical centres are connected with each other, on the one hand, and with the optic thalaimis and lower levels on the other. Since these structures are by position closely asso- ciated with parts of the brain still to be described, with the exception of the anterior perforated space already noted (page 1153), they will be merely mentioned here, as components of the rhinencephalon, their details being deferred until the related parts are considered. The fornix (page 1158), the fimbria (page 1165) and the- hippocampus (page 1165), all seen within the lateral ventricle (page 1164), constitute important paths by which fibres pass to and from the olfactory cortical centre. The gyrus subcallosus (page 1153"). the gyrus supracallosus (page 1157) and the gyrus dentatus (page 1 166) together form an additional arched tract, which, beginning at the base of the brain, follows closely the convex surface of the corpus callosum as far THE TELENCEPHALON. 1155 as its hind-end and then, as the dentate gyms, extends forward along the inner sur- face of the hippocampus to the uncus. The septum lucidum (page 1 159), a sickle- shaped partition which lies between the lateral ventricles, the corpus callosum and the fornix, is also a constituent of the olfactory path, as are also, perhaps, the taenia semicircularis (page 1162) and the nucleus amygdalae (page 1172). In the foregoing description of the rhiiiencephalon only such parts have been included as seem warranted on morphological grounds (Turner, Elliot Smith and Cunningham). It should be pointed out, however, that the German and French anatomists include also the limbic lobe, the division and constitution of the rhinencephalon accordingly being as follows : RHINENCEPHALON. I. Peripheral Portion Anterior part : 1. Bulbus olfactorius 2. Tractus olfactorius 3. Tuberculum olfactorium OLFACTORY LOBE II. Central Portion 4. Area parolfactoria JB. Posterior part : 5. Substantia perforata anterior 6. Gyrus subcallosus Gyrus callosus Gyrus hippocampi 3. Gyrus uncinatus 4. Hippocampus 5. Gyrus dentatus 6. Gyrus supracallosus ARCHITECTURE OF THE CEREBRAL HEMISPHERES. On drawing apart the walls of the great longitudinal fissure, it will be seen that, while in front and behind this cleft completely separates the hemispheres, the latter are connected in the intervening part of their length by a robust commissure, the corpus callosum, which floors the fissure along the middle part of its course. On making sections of the hemisphere above the level of this bridge, either in the frontal or transverse plane, the hemibrain is found to be composed of the thin reddish brown sheet of cortical gray matter (substantia corticalis), which everywhere constitutes an unbroken stratum, and the enclosed large tract of white matter, the centrum ovale. Beneath the corpus callosum lies the lateral ventricle, the cavity enclosed within the hemisphere, in whose lateral wall and floor appears the mesial division of the corpus striature, the caudate nucleus, whilst further outward is lodged the lateral division of the nuclear mass of the end-brain, the lenticular nucleus. Attached to the under surface of the posterior half of the corpus callosum is the arched layer of fibres known as faefornix, and below the latter, covering to a large extent the upper surface of the thalamus which forms a part of the floor of the lateral ventricle, lies the thin highly vascular sheet, the velum interpositum. These and the other structures more or less closely related to the lateral ventricle claim fuller description, which may now be undertaken. The Corpus Callosum. This structure is the great commissure which con- nects the hemispheres and, in addition, affords passage to fibres that arise from the thalamus and, probably, other nuclei outside the hemisphere and proceed to the cerebral cortex. It lies considerably nearer the anterior than the posterior end of the hemisphere and occupies approximately one half of the latter' s length. Seen in mesial sagittal section (Fig. 996), the corpus callosum appears as a robust arched structure, white in color and composed of nerve-fibres transversely cut, whose ends are considerably thicker than the intermediate portion, the body (trunctis corporis callosi). Its upper surface is convex, partly free and partly covered by the overlying hemisphere, and its lower one is concave and, where not attached to. the fornix and the septum lucidum, clothed by the ependyma lining the ventricle. Its length is about 7 cm. (2^ in.) and its greatest thickness, at its posterior extremity, is about 8 mm. It is widest behind, where it measures about 20 mm., and somewhat narrower in front. The thickened front end, the genu, bends backward and is 1156 HUMAN ANATOMY. prolonged into the sharply recurved and tapering rostrum, whose thin edge is continued backward and downward into the lamina cinerea, the attenuated anterior wall of the third ventricle (page 1132). The rounded and massive posterior end of the corpus callosum, known as the splenium, overlies the pineal body and the superior colliculi, and above bounds the cleft through which the pia mater gains the velum interpositum (page 1162). The convex upper surface of the corpus callosum, where it forms the bottom of the longitudinal fissure, is free, except behind where in contact with the posterior part of the falx cerebri ; laterally it is partially overlaid by the callosal gyrus, which, FIG. 996. Mesial surface of cere-. bral hemisphere < >pening of cere- S bcU vein Splenium vein of Galen y-' >^Lobulus centralis .^Culmen |vVx LiDguU Superior longitudi- nal sinus Falx cerebri. cut Lamina cinerea Optic chiasm, cut Infundibulum Pituitary body Tuber cinereum Interpeduncular space Mammillary body. Oculomotor nerve Sphenoiclal sinus Cerebral peduncle Pineal body Basilai Corpora quadrigi Pons Aqueduct of Sylviu< Superior medullary velu Fourth ventricle Choroidal plexus Right vertebral artery Mesial section of brain in JI/M, showing relations to skull and dura; cerebral falx has been pactly remove'!, but arachnoid and pia are still in place. however, is separated from it by the intervening co/fara/JM&Kf (sulcus corporis callosi ). Although consisting practically exclusively of transversely coursing nerve-fibres, which produce a corresponding cross striatum, the upper surface of the corpus callosum (Fig. 997) is covered by a thin atrophic layer of _yray matter (induscum gristmill > which laterally is continuous with the cortical substance of the callosal gyrus and contains rudimentary strands of longitudinal nerve-fibres. These are arranged on each side of the slight groove marking the mid-line in two strands ; the nne, the stria medialis, is placed close to. the strand of the opposite side and with it constitutes the so-called w/~v'.f of /^w/.v/. The other strand, the stria lateralis, or teenia tccfa, lies farther outward and is covered by the overhanging callosal gyms. These rudimentary structures, including the thin sheet of gray matter and the two THE TELENCEPHALON. "57 stria, represent an atrophic convolution, the gyrus supracallosus. Traced forward and around the recurved genu and rostrum, the mesial stria is prolonged into the gyrus subcallosus, a small crescentic cortical tract on the mesial surface of the hemisphere immediately below the rostrum (Fig. 994); while the lateral stria is continued into the area parolfactoria (page 1153) and into the anterior perforated space. When followed backward and around the splenium, the striae and gray matter of the corpus callosum become continuous with the gyrus dentatus and, by way of the latter, with the uncus. The under surface of the corpus callosum (Fig. 998) exhibits a very evident transverse striation and forms the roof of the anterior cornu and body of both lateral ventricles. With the exception of a strip of varying width along the mesial plane, where attached to the septum lucidum in front and to the triangular FIG. 997. Frontal pole Genu Mesial longitudinal striae Upper surface of corpus callosum Lateral longitudinal stria Forceps anterior Transverse fibres Tapetura Forceps posterior Splenium Occipital pole Cerebral hemispheres from which upper and median parts have been removed to expose corpus callosum ; on left side longitudinal striae and thin layer of gray matter cover upper surface of corpus callosum; on right side these have been scraped away to expose transverse fibres and anterior and posterior forceps. body of the fornix behind, the corpus callosum is free and covered with the ependyma which lines the ventricular spaces. In consequence of the bridge being shorter than the length of the hemispheres, from most parts of which it receives fibres, the latter are consolidated at the ends of the corpus callosum and give rise to the genu and the splenium. On gaining the lateral margins of the corpus callosum, its fibres are no longer restrained but radiate in all directions (radiatio corporis cal- losi) towards the cortex and intersect the fibres of the corona radiata (page 1186). Those traversing the thinner body and upper part of the splenium of the com- missure pass laterally and in each hemisphere from a thin but definite fibre-sheet, known as the tapetum, which extends over the lateral ventricle, especially its posterior horn, and constitutes the lateral wall of its posterior cornu and of the adjacent part of the descending horn. The fibres composing the fore-part of the genu turn forward as a distinct band, the forceps anterior, towards the frontal HUMAN ANATOMY. pole of the hemisphere, whilst those constituting the greater part of the splenium are consolidated into a robust strand, the forceps posterior, which sweeps abruptly backward into the occipital lobe and in its course produces a curved ridge on the fore-part of the inner wall of the posterior horn of the lateral ventricle. The Fornix. The fornix is an arched structure, white in color, and composed, for the most part, of two crescentic tracts of longitudinally coursing nerve-fibres. The two ends of these narrow crescents are free for some distance, but along their medial borders the intervening parts are connected with the under surface of the cor- pus callosum and with each other (Fig. 998), thus producing a triangular field, the body (corpus fornicis), whose apex is directed forward and is prolonged into two slender diverging stalks, the anterior pillars, and whose lateral angles are con- tinued into the downwardly arching posterior pillars. . The upper surface of the body is subdivided into an attached and an unattached area. The former is a small FIG. 998. Body of fornix Mammillary bodies Splenium of corpus callosum Lyra Free margin of fornix Under surface of corpus callosum Cut surfaces of hemisphere Septum lucidum Anterior pillar T'nder surface of genu of corpus callosum Dissection of brain, showing under surface of fornix and corpus callosum. narrow triangle, the posterior and broader part of which corresponds with the attach- ment of the fornix to the under surface of the corpus callosum ; whilst the anterior part is a mere mesial strip denoting the line along which the arching fornix is bit-mini with the septum lucidum, the sickle-shaped partition that fills the interval betwrrn the corpus callosum and the fornix and separates the anterior horns of the lateral ven- tricles. On either side of the attached field, the fornix presents a smooth and some- what thicker marginal zone, which forms part of the floor of the lateral ventricle and, depending upon the size and distention of the ventricular space, either extends later- ally as a horizontally directed wing that overlies a part of the thalamus, or descends obliquely towards the thalamus upon whose upper surface the margin of the fornix indirectly rests. The triangular central sheet of the fornix, bounded by its unattached margins laterally and the splenium behind, exhibits transverse striation due to the presence of bundles of commissural fibres connecting the hippocampi of the two sides. This part of the fornix constitutes the commissura hippocampi, also known as the psalterium or lyra. A narrow horizontal cleft, the so-called ventricle of } \-rga ( cavnm THE TELENCEPHALON. 1159 psalterii), sometimes intervenes as the result of imperfect union, between the under surface of the corpus callosum and the middle part of the body of the fornix. It should be understood, however, that this cleft is not a part of the series of true ven- tricular spaces. The under surface of the fornix rests upon the velum interpositum, which thus separates it from the third ventricle and the upper surfaces of the two thalami which it overlies. 'The anterior pillars of the fornix (columnae fornicis) are two slender cylin- drical strands, which, slightly diverging- as they leave the anterior angle of the body, arch downward and forward, then somewhat backward, and descend to the basal surface of the brain, where they end in the mammillary bodies. In their descent they lie in the extreme front part of the lateral walls of the third ventricle, where they show as ridges (Fig. 976), and form on each side, the upper and anterior boundary of the foramen of Monroe. A short distance below the latter opening, the pillar disappears from the ventricular wall in consequence of the increasing divergence from the mesial plane. On reaching the mammillary body on the basal surface of the brain, the fibres composing the anterior pillar are interrupted to a large extent in the mammillary nuclei (Fig. 967). The connections of these stations are described elsewhere (page 1129), suffice it here to recall that while a part of their fibres are continued to lower levels, a very considerable strand, known as the bundle of Vicq d' Azyr, arches upward and completes the connection between the fornix and the thalamus, in the anterior part of which these mammillo-thalamic fibres end. The relations of the anterior pillars to the olfactory paths are noted in connection with the olfactory nerve (page 1222). The posterior pillars of the fornix (crura fornicis), the widely diverging backward prolongations from the lateral angles of its body, are at first attached to the under surface of the corpus callosum. They then turn outward, and, sweeping around the posterior ends of the optic thalami, enter the descending horns of the lateral ventricles and arch downward along the dorso- mesial border of the conspicu- ous hippocampi, the elevations which mark the inferior horns of the lateral ventricles. On reaching this situation, however, the posterior pillar no longer retains its previous form, but now appears much reduced in size, as a white flattened band, known as the fimbria, which, broadest in the middle of its course, narrows as it descends, and ends by joining the uncus at the lower extremity of the ventricle. The progressive diminution of the fimbria during its descent is due to the contribution of many of its fibres to the sheet of white matter, the alveus, which covers the hippocampus. It is evident that the fornix constitutes, by means of its several parts, a continuous tract of longitudinally coursing fibres, which convey impulses from the chief cortical olfac- tory centre, the uncus and the hippocampus, to the mammillary nuclei and thence, in great part, by the bundle of Vicq d' Azyr to the thalamus. The fornix may be considered, in a sense, as a tract of white matter representing the lower edge of the hemisphere ; in front and behind these edges remain ununited and more or less widely apart. Beneath the corpus callosum they become attached not only to the under surface of this bridge, but also to each other by the commissural fibres of the psalterium. The peculiar course of the fornix is referable to the backward and downward expansion of the developing hemispheres, as the result of which the posterior end of the fornix follows the hippocampus in its migration into the descending horn of the lateral ventricle as the temporal lobe is devel- oped. Further consideration of these changes, however, may be deferred (page 1167) until the associated structures have been described in connection with the lateral ventricle. The Septum Lucidum. The septum lucidum (septum pellucidum) is the thin median vertical partition which fills the interval between the corpus callosum above and in front and the fornix behind (Fig. 996), with which structures its margins are firmly attached. It separates the anterior horns and adjoining parts of the lateral ventricles and is, in a modified form, triangular in shape when viewed laterally. The sides of the triangle are all curved and its anterior angle, received within the bend of the genu, is blunt and rounded. Its posterior angle is narrow and extends for a variable distance between the under surface of the body of the corpus callosum and the upper arched surface of the body of the fornix. The lower angle occupies the interval between the thin edge of the rostrum and the anterior pillars n6o HUMAN ANATOMY. of the fornix. The septum consists of two thin layers (laminae septi pellucidi), between which lies a narrow cleft (cavum septi pellucidi) to which the misleading name, fifth ventricle, has long been applied. This space, very variable in extent and width, is usually so narrow and contains such a small quantity of modified lymph, that the laminae forming its walls are in apposition. It is entirely closed and, therefore, cut off from the true ventricular system ; neither is it lined with ependyma. The septum lucidum in man is the rudimentary representation of what in many of the lower (macrosmatic) animals is a much more important tract of cortical substance. In some animals, as for example, the rabbit, cat and dog, the septum is solid, a cleft never appearing within it. Notwithstanding the reduction which it has suffered in man, the septum exhibits in its structure its relation to the cortex, comprising, from its cleft outward : (i) a thin layer of nerve-fibres, (2) an uncertain layer of gray matter containing numerous nerve-cells of pyramidal form, and, next to the lateral ventricle, (3) a layer of nerve-fibres, the ventricular surface of which is clothed with FIG. 999. Body of fornix It Corpus callosum. upper surface Anterior Eillar of Drnix Mammil- lary body Fimbria I Hippocampus Uncus. partially cut away the usual ependyma. is probable that axones proceeding from the cells within the septum lucidum are constituents of the olfactory strands within the fornix, which pass to the hippocampus and the uncus, and of the t.enia semicircularis (page 1162), terminating in the amygdaloid nucleus (page 11/2). The Lateral Ven- tricles. The lateral ventricles (ventricula late- rales) are a pair of irreg- ular cavities contained within the cerebral hemi- spheres. They are devel- oped as outpouchings from the original cavity of the end-brain and for a time communicate with this space by wide openings. The latter, however, fail to keep pace in their growth with the expansion of the hemispheres, and in the fully developed brain are represented by the small apertures, the foramina of Monroe, which maintain communication between the lateral and third ventricles, the last- named space representing the primary cavity of the fore-brain. When viewed from above, after removal of its roof, the corpus callosum and its lateral extensions, each lateral ventricle appears as an elongated, irregularly curved cavity (Fig. 1000), which extends for about two-thirds of the entire length of the hemisphere and, in addition, penetrates the temporal lobe almost to its pole. It is lined, as are all the other true ventricles, with a delicate epithelial layer, the ependyma, which likewise clothes the structures which encroach upon its lumen, as the caudate nucleus and the thalamus, as well as those which seemingly hang free within it, as the choroid plexus and the fornix. It is usual to describe the ventricle as consisting of four parts, the body, and the- anterior, posterior and inferior horns. Tin- anterior horn and the body are practically one and separated by only an arbi- trary division ; the posterior and the inferior horn extend into the occipital and the temporal lobe respectively, whilst the anterior horn enters the frontal lobe. The anterior horn (cormi anterius ) includes from the tip of the ventricle to the foramen of Monroe, the latter corresponding with the anterior limit of the con- spicuous choroid plexus, curves forward and outward around the head of the caudate nucleus into the white substance of the frontal lobe and in frontal sections (Fig. Dissection showing fornix in front and above ; drawn from preparation and Steger model. THE TELENCEPHALON. 1161 1007) appears triangular in outline. The upper side or base of the triangle, slightly curved towards the ventricle, is the lower surface of the arched corpus callosum and its antero-lateral radiations ; the mesial side is approximately vertical and formed by the septum lucidum ; the lateral side bulges strongly towards the ventricle in correspondence with the convexity of the massive head of the caudate nucleus. The floor of this part of the ventricle is narrow, often a mere groove along the junction of the sloping lateral and vertical mesial wall, and in front passes insensibly into the concave anterior wall, formed by the lateral part of the hind surface of the genu of the corpus callosum. The body (pars centralis) of the lateral ventricle includes that part of the space which extends from the foramen of Monroe to the bifurcation of the ventricle into its FIG. 1000. pus callosum Anterior ho lateral ven' Caudate nucleus, head Foramen of Monroe l^enticula nucleus, sectioned T;enia semicircularis Thalamus, up] >er surface Hippocampus Collateral eminence Fin. Collateral protruber- ance in trii;onuiii ventriculi Bulb of forceps posterior Calcar avis Posterior horn of lateral ventricle Septum lucidum Cavity within septum Fornix , anterior pillar Posterior horn of lateral ventricle Lateral ventricles seen from above after partial removal of corpus callosum and cerebral hemispheres. posterior and inferior horns, opposite the splenium of the corpus callosum. When viewed in frontal sections (Fig. 1010), it appears as a narrow, obliquely horizontal cleft, directed somewhat upward, roofed in by the corpus callosum. Its mesial wall is formed in front by the hind part of the septum lucidum and behind the latter by the fornix where it is attached to the under surface of the corpus callosum. A distinct lateral wall is wanting, the ventricle being here closed by the meeting of the floor and roof. Its floor is constituted by several structures of importance which, named from without inward, are: (i) the caudate nucleus ; (2) an oblique groove (sulcus intermedius), which extends from before backward and outward, between the caudate nucleus and the thalamus, and lodges, in addition to the vein of the corpus striatum, a white band of nerve-fibres known as the Icenia semicircularis ; (3) a narrow portion of the upper surface of the thalamus, which is Il62 HUMAN ANATOMY. Anterior horn almost completely masked by the overlying choroid plexus ; (4) the choroid plexus of the lateral ventricle ; and (5) the lateral edge of \hefornix. The caudate nucleus will be subsequently described (page 1169), suffice it to note its rapid diminution in size, as it curves backward and downward on the roof of the inferior horn. The taenia semicircularis is more or less hidden by the superficially placed men of the corpus striatum (vena terminalis), which lies immediately beneath the epen- dyma and shows as a distinct sinuous ridge. Receiving tributaries from the adjacent parts of the thalamus, the caudate nucleus and the walls of the anterior horn, includ- ing the septum lucidum, the vein passes to the foramen of Monroe, where, meeting with the choroid vein at the apex of the velum interpositum, it forms with the last- named vessel the vein of Galen. The taenia semicircularis, the band-like tract of nerve-fibres which occupies the sulcus intermedius, is probably a part of the complex pathway by which the pri- mary and secondary olfactory centres are united. Its component fibres arise partly in the anterior perforated space and partly in the septum lucidum from which centres, reinforced by fibres from the anterior commissure, they converge towards the sulcus intermedius which they FIG. 1001. then follow. After leaving the body of the lateral ventricle they descend with- in the roof of the inferior horn, in close relation to the recurved tail of the caudate nucleus, to end within the amygdaloid nucleus (page 1172). The choroid plexus ( plexus chorioideus ventriculi lateralis) is a convoluted vascular complex which occupies the lateral margin of the pial sheet, the velum interpositum, within the body of the lateral ventricle, and, in addition, descends along the inferior horn of the lateral ventricle to its tip. In order to understand the relations of the choroid plexus, those of the larger sheet, of which it is part, must be described. The velum interpositum (tela chorioidea ventriculi tertii) is a delicate sheet of pia mater whose upper surface is exposed after removal of the corpus callosum and the body of the fornix. When viewed from above (Fig. 1102) it is triangular in outline, its apex lying at the foramina of Monroe and its lateral basal angles extending into the descending horns of the lateral ventricles. Its inferior surface forms the roof of the third ventricle, beyond which on each side it covers the greater part of the upper surface of the thalamus and, in turn, is overlaid by the fornix. Behind, the velum interpositum is continuous beneath the splenium of the corpus callosum with the pia mater investing the external surface of the hemisphere. This relation readily gives rise to the impression that the pial tissue has gained entrance to the ventricles by growing forward through the cleft beneath the splenium and the fornix. That such, however, is not the case will be pointed out later, when the development of this sheet is considered (page 1194). The relation of the velum interpositum to the ventricular cavities should be carefully noted by tracing the ependyma from the caudate nucleus inward. Leaving the convex surface of this structure, the ventricular lining covers the sulcus terminalis with its vein, and passes for a short distance over the adjoining outer part of the upper surface of the thalamus. This zone (lamina aftixa) narrows in front and behind, and where broadest measures from 5-7 mm. Along the Lateral recess Posterior horn Cast of ventricles, viewed from above. X % (Relzius.) THE TELENCEPHALON. 1163 inner margin of this zone the ependyma leaves the surface of the thalamus and passes onto the villous projections (Fig. 1003) of pia mater containing the convolu- tions of blood-vessels of which the choroid plexus is composed. Each projection, (glomus chorioideum) consists of: (i) a capillary complex formed by the terminal twigs of the anterior and posterior choroidal arteries, which gain the interior of the hemisphere through the choroidal fissure in the inferior horn of the lateral ventricle ; (2) the connective tissue of the pia ; and (3) the ependymal layer (lamina chorioidea epithelialis), which everywhere invests the pial plications and, therefore, excludes the vascular tissue from actual entrance into the ventricular cavity. While inconspicuous and often overlooked, this ependymal layer is of much morphological significance, since it represents all that persists in certain localities of the true wall of the hemi- sphere. After leaving the surface of the thalamus and investing the vascular pro- FIG. 1002. Septum lucidum Anterior end of fornix, cut Hippocampus Velum interpositum Choroid plexus in inferior horn of lateral ventricle Splenium, under surface Posterior horn of lateral ventricl Lateral parts of fornix, under surface Corpus callosum Caudate nucleus Choroid plexus, overlying foramen of Monroe Vein of corpus striatum f. Choroid vein in plexus .Veins of Galen Crus of fornix and posterior .forceps of corpus callosum, cut Under surface of fornix, Lyra ^ Cut anterior end of fornix Dissection of brain, showing velum interpositum and choroid plexuses of lateral ventricles ; seen from above after removal of corpus callosum and fornix; latter has been cut through in front and behind and turned back, exposing its under surface. jections constituting the choroidal plexus, the ependyma becomes attached along the taenia fornicis to the thin lateral margin of the fornix, beneath which the velum interpositum protrudes to expand into the choroid plexus within the body of the ventricle. The plexus is not confined to this part of the space, but follows the hippocampus to the lower end of the inferior horn. The relation of the vascular pial tissue to this extension of the ventricle is, however, the same as within the body, since the glomeruli here, as there, are completely invested by the ependyma, which they invaginate along a groove, the choroidal fissure, above the hippocampus, in the same manner as they do higher in the ventricle. The line of attachment of the ependyma to the wall of the horn, taenia fimbriae, follows the recurved tail of the caudate nucleus, just beneath which it lies, on the one hand, and the thin mesial edge of the fimbria (the continuation of the fornix) on the other. On pulling out 1164 HUMAN ANATOMY. the entire choroid plexus of the lateral ventricle, the ependyma is torn away and an artificial opening is produced, which may be followed, as a curved narrow cleft, from the lower end of the inferior horn upward above the hippocampus and over the dorsal surface of the thalamus, beneath the fornix and the splenium, to the exterior of the hemisphere. When traced forward from its attachment along the upper surface of the thalamus, the line of the reflection of the ependyma, taenia chorioidea, leads to just above the foramen of Monroe (Fig. 1031), where it is joined by the similar line of the opposite ventricle. From this point the choroidal line of ependymal reflection is continuous with the taenia thalami, the sharp ridge which marks the junction of the superior and mesial surface of the thalamus (page 1119). Leaving the surface of the latter along this ridge, the ependymal layer covers the under side of the velum interpositum, as well as the double row of vascular villous projections, which, one on each side of the mid-line of the roof, constitute the choroid plexus of the third ventricle (Fig. 974). Although similar in its general structure, this vascular fringe is much smaller and less conspicuous than that within the lateral ventricle. It is evident from the foregoing description, that communication between the third and lateral ventricles is completely interrupted by the attachment of the ependymal layer and that at only one place, the foramen of Monroe (page 1161), does such communication exist. It is of interest to note that these several lines of ependymal reflection the taenia chorioidea, the taenia thalami and the taenia fornicis and its prolongation, the taenia fimbriae form a contin- uous line which morphologically marks the transition of the thicker nervous part of the wall of the hemisphere into the thin and atrophic area, which early undergoes an invagination leading to the production of voluminous vascular structures later seen in the definite choroid plexuses of the lateral and third ventricles. Along the margin of the choroidal fissure, at which such invagination primarily occurs, the white matter of the hemisphere becomes condensed into the tract of the fornix and its downward prolongation, the fimbria. These structures, together with the reflected ependyma and the septum lucidum, are regarded, therefore, as modified parts of the mesial surface of the hemisphere. The inferior horn (cornu inferius), also called the descending horn, begins above at the hind-end of the body of the -ventricle, thence curves backward and outward around the thalamus, and sweeps downward and forward and a little inward (Fig. 1000) into the temporal lobe well towards its tip, which, however, it fails to reach by about 2 cm. Its descent is not FIG. 1003. on ^y verv abrupt, but limited for the most part to almost a vertical plane ; hence this part of the ventricle does not diverge to any considerable extent be- yond the plane of the gyrus hip- pocampi, just to the outer side ' of which the lower end of the inferior horn lies. The roof of this cornu is formed chiefly by the tapetum of the corpus cal- losum, and within it descend the recurved attenuated tail of the caudate nucleus and the fcenia semicircularis to join a rounded mass of gray matter, the amyg- daloid nucleus I page 1172), which lies embedded within the temporal lobe, slightly above and in front of the lower end of the inferior horn (Fig. 967). The floor of the inferior horn begins above in the triangular area, the trigonum ventriculi, between the diverging inferior and posterior horns. The greater part of this field is occupied by a low convexity, the collateral protuberance ( triuoiium collateralc >, which is continued into a rounded ridge, the collateral eminence (cmim-mia Taenia chorioidea Taenia thalam Tsenia fornicis Choroid plexus of III ventricle Diagram showing relation of pial tissue in velum interpositum to ependyma in lateral and third ventricle; epenchma is represented by red line; c, c, corpus callosum; /", fornix; TV. so-called ventricle of Verga ; C, T, caudate nucleus and thalamus. THE TELENCEPHALON. 1165 collateralis), that extends for a variable distance along the outer part of the floor of the inferior horn. This elevation is uncertain as to prominence and length, but even when well developed does not reach the lower extremity of the ventricle. It results from the invagination of the wall of the early hemisphere by the anterior part of the collateral fissure. A second longitudinal elevation, constant and much more conspicuous than the collateral eminence and separated from the latter by a groove, forms the inner part of the floor and the adjoining mesial wall of the inferior horn of the lateral ventricle. This elevation, known as the hippocampus, is the most prominent feature of the horn and curves downward and inward to the extreme lower limit of this part of the ventricle. It is due to the early invagination of the hemisphere by the hippocampal fissure. The lower end of the hippocampus is distinctly broader and somewhat flattened and marked by a number of oblique shallow furrows and intervening low radiating ridges (digitationes hippocampi). These confer on the upper surface and especially on the outer rounded border of the elevation, a corrugated and notched appearance, (Fig. 1004) which suggests a fancied resemblance to a paw, the lower end of the projection being- known as the pes hippo- FIG. 1004. campi. The upper surface and the anterior and lateral border of the pes are free and well defined, but its deeper surface and inner border, to a large extent, are blended with the surround- ing parts of the hemisphere. The intimate structure of the hippocampus is described with that of the cerebral cortex (page 1181). The dorso-mesial aspect of the hippocampus is over- laid by a white flattened band, the fimbria (timbria hippocampi), which, although bearing a special name, is the direct prolongation of the posterior crus of the fimbria, continued from the lateral angle of the corpus fornicis into the inferior horn. Its concave mesial margin is smooth, rounded and free, whilst its sinuous lateral border is thin and sharp and gives attachment through- out its entire length to the delicate ependymal layer which completes the mesial wall and thus closes in the descending horn (Fig. 1005). Above narrow and then broader, on reaching the pes the fimbria becomes abruptly reduced to a narrow strand, which may be followed along the inner margin of the pes to the uncus where it ends. Traced upward the fimbria passes without interruption into the posterior limb of the fornix, of which, as already noted, it is the direct downward prolongation. Beginning in the uncus, the fimbria continually receives accessions of fibres from the underlying hippocampus, with which it is closely united along its deep surface, and therefore increases in bulk as it ascends towards the body of the fornix. When the structures within the inferior horn of the lateral ventricle are viewed in their undisturbed relations (Fig. 1004), little of the hippocampus and nothing of the fimbria are seen, as these parts are hidden by the overlying mass of vascular tissue constituting the choroid plexus, which is not confined to the body of the ventricle, where its connections have been already described, but follows the descending Cyrus hippocampi Fimbria Inferior horn of left lateral ventricle, viewed from above. u66 HUMAN ANATOMY. horn to its lower end. On turning aside the vascular fringe, its relations to this part of the ventricle will be found to be identical with those exhibited in the body of the ventricle, since here, as there, the vascular complex is everywhere covered by the thin layer of reflected ependyma and, therefore, excluded from actual entrance into the ventricular space. Tracing the line of attachment of the reflected ependyma, which alone represents the true ventricular wall closing the crescentic choroidal fissure along the dorso-mesial aspect of the inferior horn, it will be found to be continuous with the thin lateral edge of the fimbria throughout the entire length of this attenuated margin, just as it is connected with the fimbria within the body of the ventricle. Passing from this line of attachment (taenia fimbriae) over all the villous projections of the choroid plexus, the reflected ependyma returns to the thicker ventricular wall, which it joins along the mesial border of the roof. Thence the ependyma remains in close contact with the remaining parts of the walls of the inferior horn, all the surfaces of which, including those formed by the hippocampus and the collateral eminence, it covers. From these relations (Fig. 1005) it follows that the fimbria in large part is excluded, as are some other parts of the fornix, from the ventricle, only that portion of its surface which extends from its sharp lateral border to the underlying hippocampus forming, strictly regarded, a part of the ventricular wall. The rounded mesial border and the dorsal surface of the fimbria belong to the free mesial surface of the hemisphere. The dentate gyrus (fascia dentata) is part of an atrophic convolution belong- ing to the rhinencephalon (page 1151), and as such belongs systematically to that division of the hemisphere. FIG. 1005. Choroid plexus Caudate nucleus, tail / Tienia semicircularis Ependyma Cavity of inferior horn of lateral ventricle Since, however, it is closely associated with the struc- tures found within the inferior horn of the lateral ventricle, its description has been de- ferred until this place. The dentate gyrus lies on the mesial surface of the hemi- sphere, but is so hidden be- hind the hippocampal gyrus that it is satisfactorily dis- played only after the over- hanging parts of the thala- mus and cerebral crura are removed. On cutting away these structures and drawing downward the hippocampal gyrus, a narrow band of gray matter, notched and corru- gated by numerous minute transverse furrows, is seen protruding between the free rounded mesial border of the fimbria above and the hippocampal fissure below ( ML;. 992). This band is the gyrus dentatus. On examining frontal sections passing through the inferior horn of the lateral ventricle (Fig. 1005), the relations of the dentate gyrus will be appreciated. In such preparations the gyrus appears as the free, somewhat thinned off edge of cortical gray matter, which is pushed to the surface just below the choroidal fissure through which the pial tissue invaginates the ventricular wall to gain a seeming entrance to the inferior horn. Between the fimbria, which lies immediately above and parallel with it, and the gyrus a shallow groove, the sulcus fimbrio-dentatus, intervenes, whilst below it is bounded by the remains of the hippocampal or dentate fissure. The latter is no longer an evident furrow, as it was when producing the hippocampus, since it has become closed and almost com- pletely obliterated by the apposition of the bordering cortex. Traced forward, the gyrus dentatus gradually leaves the fimbria and passes deeply along the inner side of the uncus in connection with which it ends. The terminal part of the gyrus, somewhat reduced in size, at first bends sharply medially along Entrance to choroidal fissure Fimbria Fimbrio-dentate fissure Gyrus dentatus \ Hippocampal fissure Alveus \ Hippocampus Gyrus hippocampi Collateral fissure Frontal section of part of left hemisphere passing through lower end of inferior horn of lateral ventricle. X 2. THE TELENCEPHALON. 1167 the under surface of the uncus and then winds over the inner aspect of the latter, from within outwards, as a narrow grayish band, the frenulum of Giacomini, which, continuing upon the upper surface of the uncus, for a short distance passes slightly backward and disappears (Fig. 1006), Followed backward, the gyrus dentatus accompanies the fimbria towards the splenium, at the lower border of which the two structures part company, the fimbria passing to the under side of the corpus callosum, whilst the gyrus dentatus, losing its corrugations and becoming a smooth band, known as the fasciola cinerea, bends backward and curves around the splenium (Fig. 992) to spread out over the upper surface of the corpus callosum as the thin atrophic sheet of gray matter, the induseum griseum in which are embedded the fibre-strands of the longitudinal striae (page 1156). The structure of the gyrus dentatus is described with that of other parts of the cerebral cortex (page 1182). FIG. 1006. Splenium of corpus callosum Frenulum of Giacomini \ 3 , Fasciola cinerea Gyrus hippocampi \ Collateral fissure Gyrus dentatus Part of left gyrus hippocampi has been cut away to expose gyrus dentatus, which is seen continuing as frenulum of Giacomini over uncus. The fornix is to be regarded as the chief fibre-tract connecting the olfactory cortex, situated within the uncus and the hippocampus, with the thalamus. An explanation of its remarkable course as seen in the adult brain, is found in the changes which affect the position of the hippo- campus during development. Reference to Figs. 1030, 1032, will recall the origin of the hemi- sphere (pallium) as an outgrowth from the end-brain, and, further, that the hemisphere in man early covers in the thalamus and other parts of the diencephalon and the mid-brain. For a time the thalamus is connected with the hemisphere by means of only the thin recurved under and inner wall of the pallium, the bulky tracts of white matter in which it is later embedded being for a time wanting. This same independence is retained by the thalamus, even in the adult condition, on its upper and posterior aspects, where the excessively thinned out ventricular wall alone forms the partition between the ventricle and the exterior, and where the thalamus is over- laid by, but not in contact with, the hemisphere. On breaking through this partition, as after removal of the velum interpositum, the thalamus may be directly reached by passing beneath the splenium. When a definite mesial surface of the hemisphere becomes developed, an area along the inferior margin of this aspect becomes marked off by two primary grooves, which are the early choroidal fissure below and the hippocampal fissure above. The area so defined is the primary gyrus dentatus. This tract of gray matter is connected with the thalamus by the fornix, which reaches the thalamus around the front end of the choroidal fissure. In many animals, as in the rabbit, a similar relation is permanently retained, the dentate gyrus, or its equivalent, the hippocampus, being united with the thalamus by a fornix-tract which sweeps from the lower and posterior part of the pallium (hippocampus) over the roof of the third ventricle forward and downward to the basal surface of the brain (mammillary body) and thence by the bundle of Vicq d' Azyr to the thalamus. These primary relations are changed by the future expansion of the hemisphere, which grows not only upward and backward, but also downward to form the temporal lobe, in consequence of which the dentate gyrus and the fornix, and likewise the choroid plexus and its fissure, are carried backward, downward and forward around the thalamus into the temporal lobe, where they lie on the mesial wall of the descending horn of the lateral ventricle which has coincidently been formed. Whilst in this manner the chief mass of the primary gyrus dentatus is carried into the temporal lobe, where it becomes the hippocampus and n68 HUMAN ANATOMY. the definite dentate gyrus, a part of it, greatly attenuated and reduced, retains its connection with the anterior basal surface of the brain (later the anterior perforated substance) and follows the upper surface of the corpus callosum, which likewise has extended backward, into the descend- ing horn of the lateral ventricle. These parts the gyrus subcallosus, the longitudinal stria-, the fasciola cinerea and the gyrus clentatus of the adult brain constitute the supracallosal gyrus, whose gray matter is an atrophic outlying part of the primary gyrus dentatus and whose con- nections with the basal olfactory centres are retained by the fibres of the longitudinal stria;. The fornix shares the displacement of its cortical area, the hippocampus, and is consequently carried with the latter into the descending horn of the lateral ventricle. In this manner parts which at first lay in proximity and were connected by short paths, become widely separated, with corresponding lengthening of the fibre-tracts uniting them, as illustrated in the long course of the fornix in the adult brain. Further, since the path of migration of the fornix and associated structures of the inferior horn of the lateral ventricle describes a curve, it follows that the relations of these parts become reversed, those originally King above, in regard to adjacent structures, within the descending horn being below and vice versa. The posterior horn of the lateral ventricle (cornu posterius), much smaller than either of the others, is an elongated diverticulum which curves backward from Superior frontal gyni> Middle frontal gyrus Longitudinal 6ssure- Genii of corpus callosura- Lateral ventricle, anterior horn- Inferior frontal gyrus Caudate nucleus, head ""Orbital gyri Frontal section of brain passing through genu of corpus callosum. the body of the ventricle into the occipital lobe. In frontal sections (Fig. 1034) its form is irregularly crescentic, the convexity of its outline including the roof and the lateral wall and the concavity corresponding with the mesial wall and narrow floor. Above and to the outer side, the horn is bounded by the arching fibres of the tape- turn of the corpus callosum, lateral to which lies the important thalamo-occipital or optic radiation (page 1123). The lower part of the mesial wall is modelled ( Fig. 1000) by a narrow but well marked crescentic elevation, the calcar avis, also called the hippocampus minor, which is produced by the early imagination of the wall of the hemisphere by the anterior part of the calcarine fissure. On the same wall and just above the calcar avis, a second and broader, but less sharply defined, elevation ( bulbus cornu postcrioris >, marks the course of the fibres of the forceps posterior as they encircle the parieto-occipital fissure in their journey to the occipital lobe. THE TELENCEPHALON. 1169 THE INTERNAL NUCLEI OF THE HEMISPHERE. Embedded within the white matter of each hemisphere and, for the most part, completely separated from the cerebral cortex, lie certain masses of gray matter to which the name basal ganglia is often applied. These include: (i) the caudate nucleus, (2) the lenticular nucleus, (3 ) the claustrum and (4) the amygdaloid nucleus. The first two, the caudate and lenticular nuclei, are parts of the corpus striatum, one of the three fundamental divisions of the end-brain or telencephalon. Although almost completely separated by the intervening tract of white matter, the internal capsule, the caudate and lenticular nuclei are continuous for a limited distance below and in front (Fig. 1008), and together constitute a large mass composed chiefly of gray matter, that extends from the lateral ventricle almost to the cortex of the insula. Between the latter and the lenticular nucleus lies a thin tract of gray matter, the claustrum, whilst within the temporal lobe, above and in front of the anterior extremity of the inferior horn of the lateral ventricle, is situated the amygdaloid nucleus. The Caudate Nucleus. This mass (nucleus caudatus), the inner division of the corpus striatum, is well seen from the lateral ventricle, where it appears as the large and conspicuous elevation which contributes the infero-lateral wall of the anterior horn, and the outer part of the floor of the body of the ventricle. The caudate nucleus is an elongated pyriform or comet-shaped mass of gray matter, whose bulky rounded anterior end or head (caput nuclei caudati) rapidly diminishes into the attenuated and recurved tail (cauda nuclei caudati), which sweeps backward and then downward and forward within the roof of the inferior horn to the tip of the temporal lobe, where it ends in relation with the lower part of the amygdaloid nucleus. The relations of its two chief surfaces, the mesial and lateral, are best seen in frontal sections. When sectioned through its head near the anterior pole (Fig. 1007), the caudate nucleus appears as an ovoid area of gray matter which mesially bulges strongly into the lateral ventricle, but from which it is separated by the ependyma, and laterally is embedded within the white matter of the hemisphere. In sections passing a few millimeters farther back (Fig. 1009), the form of the nucleus has become somewhat changed, its inner convex surface being more extensive and its outer one, now somewhat concave, being serrated by the invasion of obliquely hori- zontal stripes of white matter due to the appearance of the anterior strands of the internal capsule. In the plane, under consideration, these strands are not continuous but interspersed with stripes of gray matter, which below still connect the caudate with the laterally situated lenticular nucleus and produce the coarse striation from which the entire mass, the corpus striatum, derives its name. In sections passing through the body of the ventricle (Figs. 1010, 1025), from the plane of the foramina of Monroe backward, the caudate nucleus is much reduced in size, whilst, on the contrary, the lenticular nucleus, as well as the thalamus, become more conspicuous. The internal capsule, being now well established, appears as a large oblique tract of white matter, which completely separates the two parts of the corpus striatum and lies to the outer side of the thalamus (Fig. 1008). By reason of the recurved course of its attenuated tail, in horizontal sections, as well as in frontal ones passing in front of the splenium, the caudate nucleus is twice cut, one cross- section of the nucleus appearing above in the lateral wall of the body of the ventricle and the other in the roof of the inferior horn (Fig. 967). The Lenticular Nucleus. This division of the corpus striatum (nucleus len- tiformis) is a wedge-shaped mass of gray matter, broken by laminae of white, that lies bordered by the internal capsule mesially, and laterally is separated from the cortex of the insula by a narrow tract of white matter containing a thin stratum of gray sub- stance, the claustrum. The lenticular nucleus reaches neither as far forward nor as high as the caudate nucleus, and lies lateral to both the latter and the thalamus, separated from them respectively by the anterior and posterior limbs of the internal capsule. Its dorso-mesial surface, when seen in frontal sections, is directed from above downward and inward ; in transverse sections (Fig. ion) this surface is replaced by an antero-mesial and a postero-mesial face in correspondence with the limbs of the internal capsule. Its slightly convex lateral surface is approximally 74 I I/O HIM AX ANATOMY. FIG. 1008. Caudate nuclei vertical and in immediate contact with a thin sheet of white matter, the external capsule, which separates the nucleus from the claustrum. Its ventral surface- is hori- zontal and only feebly curved and is continuous in front with the caudate nucleus and farther backward, about its middle, with the anterior perforated substance on the basal surface of the brain. The lenticular nucleus is unequally subdivided by two thin concentric sheets of white matter, the ex- ternal and internal medullary laminae, into three segments. The outer of these, the putamen, is much the largest and occupies the base of the nucleus, being bounded by the external capsule laterally and by the external medullary laminae mesially. Of its two somewhat rounded ends, the anterior is the broader and extends farther forward and alone joins the caudate nucleus of which it morphologically is a part (page 1169). The putamen is the most conspicuous part of the lenticular nucleus, not only on account of its size but also by reason of its darker color, in which respect it corresponds with the caudate nucleus. This contrast depends less upon the actual pigmentation of the cells of the putamen than upon the lighter color of the other zones of the nucleus. In consequence of the small number of fibres entering the external capsule from the putamen, the attachment between the latter and the capsule is relatively loose and the two structures may be Tail of caudate nucleus Lenticular nucleus Reconstruction of corpus striatum and thala- mus ; lateral aspect ; probe lies in space occupied by internal capsule. Drawn from Steger model. FIG. 1009. Superior frontal gyrus Corpus Septum lucidum Right lateral ventricle, anterior horn \ Internal orbital gyrus Middle frontal gyms [-Inferior frontal gyni.< i 'audate niH-li'iis Internal capsule Lenticular nucleus Temporal 1<>K Continuity of caudate and lenticular nuclei Frontal section of brain passing through anterior end of corpus striatum whore caudate and lenticular nuclei are continuous below. readily separated. This condition influences the course taken by extravasations of blood, \\hich are frequent in this locality and may occupy a lari^e part of the lateral surface of the putamen. The remaining divisions of the lenticular nucleus are much lighter in tint and together constitute the globus pallidus. They are subdivided THE TELENCEPHALON. 1171 by the internal medullary laminae and from the edge of the wedge, lying in contact with the internal capsule. Although composed chiefly of gray matter, all these segments of the nucleus, but particulary the inner two, are traversed by numerous strands of nerve-fibres which break the continuity of the gray substance and produce an appearance of radial striation. The structure of the corpus striatum varies in its several parts, that of the caudate nucleus and the putamen being almost identical, whilst that of the globus pallidus, although similar in both zones, differs from the histological make up of the other parts. The close resemblance of the caudate nucleus and the putamen corre- sponds to their early common origin, since at first they constitute a single mass and become partially separated by the ingrowth of the fibres forming the anterior part of the internal capsule. The caudate nucleus is invested throughout the greater part of its periphery by a dense layer of fibres, the stratum zonale, which includes fibres passing both to FIG. ioio. Corpus callosum Choroid plexus Fortiix Thalamus, mesial nucleus Thalamus, lateral nucleus Mammillo- thalamic tract Third ventricle Anterior pillar of fornix Optic tract Caudate nucleus Internal capsule Lenticular nucleus, putamen Insula Globus pallidus Claustrum Amygdaloid nucleus Pituitary body Optic nerve Frontal section of brain passing through caudate and lenticular nuclei and thalamus, showing relation of internal capsule to internal nuclei. and from the nucleus. The nerve-cells are, for the most part, rather small in size and stellate or fusiform in shape and provided with numerous dendrites beset with minute irregularities. They are chiefly cells of type I, although many of the second type are encountered, whose axones are limited to the gray matter and are not prolonged as nerve-fibres (Kolliker). The putamen is invested on its two sides, particularly on the mesial one, with a fibre-layer derived from the external medullary lamina and the external capsule, the fibres being chiefly such as enter the nucleus from other centres by way of the med- ullary layer. In addition to nerve-cells of round or stellate form, Kolliker describes those of distinctive appearance possessing a slender fusiform body and dendrites few in number but of unusual length. The globus pallidus owes its characteristic color to the light yellowish tint of the pigment within its cells and to the large number of medullated nerve-fibres which traverse its substance, especially its inner zone. The nerve-cells are mostly small and stellate, possessing numerous short but richly branched dendrites. 1 1 72 HUMAN ANATOMY. The Connections of the Corpus Gtriatum. Much uncertainty prevails as to the details of the connections of the several parts of the corpus striatum and little is known regarding the function of these nuclei, notwithstanding their size ; certain general principles, however, may be accepted.as established. The comparative studies of Gehuchten, Sala and others, and especially of Edinger, emphasize that the corpus striatum is to be considered as supplemental to the cortical substance, in the lower vertebrates in which the cortex of the cerebral mantle is feebly developed constituting the chief mass of cortical gray matter, and in the mammals and man being subservient to the overshadowing cortex of the hemisphere. Such being the warranted presumption, it is to be anticipated that the striate body both receives fibres conveying sensory impulses and gives off fibres (perhaps motor in function) originating from its cells, these latter tracts constituting the strio-thalamic radiation. The centripetal or afferent paths probably include : (i) the tegmcnto-striate fibres, which are continued chiefly from the mesial fillet, and perhaps also from the red nucleus and subthal- amic region, by way of the internal capsule, to end around the cells of the putamen and head of the caudate nucleus ; (2) the thalatno- striate fibres, already mentioned in connection with the thalamus (page 1 123), which pass from the thalamus either by way of the internal capsule directly to the caudate nucleus, or by way of the ansa lenticularis to the putamen or, traversing the medullary laminae, to the caudate nucleus. No doubt many of the fibres which enter the lenticular nucleus do not end within the latter, but traverse its substance as part of their path to the cerebral cortex. The centrifugal, or efferent fibres, which arise from the cells of the corpus striatum include : (i) the strio-thalamic fibres, passing from the major divisions of the striate body, which comprise (a) those from the caudate nucleus to the thalamus direct ; (6) those which traverse the internal capsule and the medullary laminae and, joining fibres from the putamen, pass by- way of the ansa lenticularis to the thalamus ; (c ) those from the putamen which reach the thalamus by passing partly by way of the globus pallidus and partly, in greater numbers, by means of the ansa lenticularis. (2) Strio-peduncnlar fibres, well represented in the brains of the lower animals as the continuation of the basal tract of the fore-brain (Edinger), which pass from the caudate nucleus, and probably from the lenticular nucleus also, into the sub-thalamic region and the cerebral peduncle, within the latter forming the stratum inter- medium closely related to the substantia nigra. Whether cortico-striate fibres, extending from the cerebral cortex to the corpus striatum, exist in man is uncertain, Dejerine denying their presence, whilst Edinger regards the presence of a meagre number of such bundles as established. The Claustrum. The claustrum is a thin lamina of gray substance embedded within the white matter intervening between the lateral surface of the putamen and the cortex of the island of Reil. Its mesial surface is smooth and parallel with the outer aspect of the putamen, from which it is separated by the thin tract of white matter constituting the external capsule. Its lateral surface presents a series of elevations and depressions which in a general way repeat the contour of the gray cortical lamina of the insula, the intervening layer of white matter being sometimes called the capsula extrema. Seen in horizontal sections (Fig. ion), the claustrum fades away both in front and behind ; in frontal sections (Fig. 1010), however, whilst it gradually disappears above, below the claustrum materially thickens and mesially becomes continuous with the anterior perforated substance. Upon comparative and developmental grounds, the claustrum must be regarded as a separated portion of the corpus striatum. Its nerve-cells are, for the most part, small and either stellate or fusiform in outline. Nothing is known with certainty as to the course or connection of its fibres. The Amygdaloid Nucleus. This structure (nucleus amygdalae) comprises a considerable rounded mass of gray substance (Fig. 1010) which occupies the fore-part of the temporal lobe and lies in close proximity with the uncus, overlying the extremity of the inferior horn of the lateral ventricle. Anteriorly it is continuous with the cortical gray matter of the temporal lobe as a thickened portion of which it may be regarded. Its lower part receives the tail of the caudate nucleus and close to this, the taenia semicircularis (page 116), which accompanies the recurved nuclear tail in its descent within the roof of the inferior horn. The nucleus approaches, if indeed it does not touch, the anterior perforated substance, and above corner into intimate relations with the lenticular nucleus. It is highly probable that the nucleus amygdala.- forms, along with the uncus and the hippocampus, a part of the olfactory cortex (Dejerine). THE TELENCEPHALON. "73 The Internal Capsule. Repeated mention has been made of the important tract of white matter bearing the name of internal capsule (capsula interim); its description, therefore, may be appropriately undertaken at this place. It is a broad, compact band of nerve-fibres which passes between the three large basal ganglia, namely, the caudate and the lenticular nuclei and the thalamus. Although the details of the internal capsule vary with differences both of direction and of position of the FIG. ion. Spleniun of corpu: callosum Calcarine fissure horn of lateral ventricle Horizontal sections of brain, A at higher level than B. which passes through lower part of corpus striatum where caudate and lenticular nuclei are continuous; relations of limbs of internal capsule to internal nuclei seen on right side. planes of section, its general relation to these three masses of gray matter is con- stant, the caudate nucleus and the thalamus always lying to its inner side and the lenticular nucleus to its outer aspect. When exposed by frontal sections passing through the anterior part of the lateral ventricles (Fig. 1010), the internal capsule appears as a broad, oblique stripe, extending from above downward and inward, bounded by the large caudate nucleus mesially, the lenticular nucleus laterally, and below by the gray substance establishing continuity between the two nuclei. H74 III MAN ANATOMY. FIG. 1012. Seen in frontal sections passing some distance behind the preceding section, whilst the capsule is limited laterally by the lenticular nucleus, its mesial boundary now includes the caudate nucleus, the taenia semicircularis and the thalamus. Still farther back (Fig. 968), the internal capsule is bounded internally in addition by the subthalamic structures and becomes continuous below with the crusta of the cere- bral peduncle. An upper and a lower part of the capsule are therefore recognized, the former between the lenticular nucleus on the one side, and the caudate nucleus on the other is known as the thalamic region (rcgio thalamica capsulac internae), whilst that between the lenticular nucleus and the subthalamic structures is termed the subthalamic region (regio subthalamica). Viewed in horizontal sections (Fig. ion, A), the capsule appears not only much more extensive, but is seen to consist of two mesially converging parts, a shorter anterior limb (pars frontalis) and a longer posterior limb (pars occipitalis). The two limbs form an angle which opens outward and encloses on two sides the gray triangle of the lenticular nucleus. The junction of the two mesially converging limbs forms the knee, or genu, of the internal capsule which points inward and lies opposite the taenia semicircularis, between the caudate nucleus and the thalamus. At deeper planes (Fig. ion, j9), passing through the level of the continuity between the two parts of the corpus striatum, the anterior limb is greatly reduced in length or entirely disappears, the posterior one being prolonged into the cerebral peduncle. The importance of the internal capsule will be appreciated when its function as the great pathway connecting the cerebral cortex with the lower lying centres is recalled. Its fibres, both corticipetal and corticifugal, after passing beyond, or before coming under the restraint of the boundaries of the capsule, as the case may be, radiate to and from all parts of the hemisphere, and in this manner form the striking fan-shaped fibre-mass known as the corona radiata, which continues the internal capsule upward to the cerebral cortex. The radiating strands of this great tract interlace with the radiation of the corpus callosum and thereby contribute a large part of the fibres composing the oval centre of white matter within the hemisphere. The anterior limb of the internal capsule (pars lenticulocau- data) includes the front third of the tract and extends from the genu forward and outward. It contains fibres passing both toward and away from the cortex. Its corticipetal fibres are : (1) the thalamo-frontal, which pass from the thalamus by way of its frontal stalk through the anterior limb of the internal cap- sule and the .corona radiata to the cortex of the frontal lobe ; (2) the thalamo-sfriatc, which also pass from the thalamus into the internal capsule and proceed to the caudate and lenticular nuclei. The corticifugal fibres include : (i ) \hefronto-ponf i>tt\ which arise in the cortex of the frontal lobe and descend by way of the corona radiata, the anterior limb of the internal capsule, the crusta of the cerebral peduncle and the ventral tracts of the ponsto end around the cells of the pontine nucleus as links in the connection between the cerebral and the cere- bellar cortex (page 1094) ; (2) the frotito-ffiti/ainic, which extend from the cortex of the frontal lobe to the thalamus ; and (3) the strio-thalamii , which proceed from the caudate and lenticular nuclei to the thalamus. The posterior limb of the internal capsule (pars lenticulo- thalamica) extends backward, outward and downward from the genu, and includes the remaining two-thirds of tin- tiact. Its hind part extends beyond the posterior limit of the lenticular nucleus, hence the posterior limb is subdivided into a Icntii nlar and a retrolcnticular portion. As does the anterior limb, so also does the posterior limb of the capsule contain both corticipetal and corticifugal fibres. The lenticular portion includes corticipetal fibres: ( i ) the thalawo-cortical, which issue from the lateral and lower aspect oi" the thalamus, traverse- the internal capsule and to a considerable Diagram showing relative posi- tions of chief tracts in internal cap- sule (A) and in crusta of cerebral peduncle (H)\ F-T, fronto-tlmlu- mic; F-P, f ronto-pontine ; T-O-P, temporo-occipito- pon tine; C-Ji,cor- tico-bulbar; C-S, cortioo-spmal ; .V, teg[tnental sensory ; OK, optic rad- iation. THE TELENCEPHALON. 1175 number, the lenticular nucleus and the external capsule and proceed to the cortex of the 'hind part of the frontal and of the parietal lobe; and (2) probably some thalamo-lenticular fibres which pass from the thalamus to the lenticular and,' perhaps, the caudate nucleus. The corticifugal fibres include : ( i ) the important motor cortico-bulbar and cortico- spinal tracts, collectively often called the pyramidal tracts, which descend from the precentral (Rolandic) cortical region through the corona radiata and the fore-part of the posterior limb of the internal capsule into the crusta of the cerebral peduncle and thence to the appro- priate levels of the brain-stem or of the spinal cord. A tract supplementary to the pyramidal motor paths, the cortico-rnbral fibres, must be mentioned. These arise from the cortex (perhaps of the parietal lobe) and descend through the lenticular portion of the posterior limb to the mid-brain where they end in relation with the red nucleus. (2) The cortico- thalatnic fibres, which converge from the cerebral cortex to the thalamus. The retro- lenticular portion of the posterior limb is traversed by important corticipetal fibres con- cerned in conveying impressions of special sense, as ( i ) those of the optic radiation, which, issuing as the occipital stalk, connect the thalamus and the lateral geniculate and the superior quadrigeminal body with the occipital cortex ; and (2) those of the auditory radiation, which link together the mesial geniculate and the inferior quadrigeminal body with the auditory cortical area in the temporal lobe. The corticifugal fibres are represented by (i) the temporo-occipito-pontine tracts, which pass from the cerebral cortex through the retrolenticular portion of the capsule into the crusta of the cerebral peduncle and thence to the pontine nucleus within the ventral part of the pons ; and (2) cortico-thalamic fibres, which course in reverse order through the optic radiation to end within the thalamus and lateral geniculate body. The relative positions of the longer tracts composing the internal capsule, as seen in hori- zontal sections, are, in a general way, indicated schematically in Fig. 1012. The anterior limb is shared, from before backward, by the fronto-thalamic and the fronto-pontine tracts in the order named. The genu is appropriated by the cortico-bulbar tracts, the facial fibres lying immediately in advance of the hypoglossal. The succeeding part of the posterior limb, approximately one-third, affords passage to the cortico-spinal or pyramidal tracts. Next follows a narrow segment devoted to the tegmental sensory tracts, behind which the occipito-temporo- pontine tract occupies a small area, the last part of the retrolenticular field being taken up by the optic radiation. STRUCTURE OF THE CEREBRAL CORTEX. The surface of the hemispheres is everywhere clothed with a thin continuous stratum of cortical gray matter; which encloses the white medullary substance com- posed of the interlacing tracts of nerve-fibres. This cortical sheet varies in thick- ness not only in the same area, being thicker over the summit than at the sides IG- IOI 3- of the convolutions or at the bottom of stratum zonaie- the bounding fissures, but in different Externaigray stratum- r M.I. t. i T.U Outer stripe of regions of the hemisphere. Its average thickness is about 3 mm. , but where it borders the upper end of the Rolandic fissure, particularly in the paracentral lobule, this increases to over 5 mm. , whilst over the frontal and occipital poles the thickness of the cortex is reduced to almost 2 mm. The entire superficial extent of the cortex of the two hemi- spheres has been estimated to be about 2000 sq. cm., of which scarcely one- third is exposed surface, the remainder Caicarine fissure Frontal section of hemisphere including- cortex sur- On examining sections of the fresh rounding calcarine fissure; stripe of Gennari (outer stripe ... of Baillarger) is here unusually distinct. X 3- brain, the cortex does not appear uniformly tinted, but exhibits, even to the unaided eye, an indistinct division into alternate light and dark layers. From without in these are : (i) a thin peripheral layer of whitish color, the stratum zonale ; (2) a thicker layer of grayish hue, the external gray stratum ; (3) a thin lighter band, the outer stripe of Baillarger ; and (4) a somewhat broader, yellowish-red zone, the internal gray 1176 HI MAN ANATOMY. stratum four layers being more or less clearly recognizable. In certain localities, as in the precentral convolution, the inner gray lamina is subdivided by an additional white line, the inner stripe of Baillargcr. In the vicinity of the calcarine fissure, particularly in the adjacent part of the cuneus, the outer stripe of Baillarger, whilst narrow, is unusually distinct and confers, therefore, a character- istic appearance upon the cortex of this region (Fig. 1013). The band in this location receives the name of the stripe of Gennari, or the stripe of Vicq cT A'.yr. In recognition of the priority of description, Gennari's name is sometimes applied to the external stripe of Baillarger wherever found. The significance of these light colored strata will be pointed out in connection with the intimate structure of the cortex, suffice it here to note that the stripes of Baillarger correspond to zones in which the felt-work of horizontal cell-processes is unusually dense, the stratum zonale corresponding to a compact layer of fibres running parallel with the surface. Occasionally a condensation of tangential fibres immediately beneath the stratum zonale produces the appearance of an additional light line, which in honor of its discoverer, is known as the stripe of Bechterew. The essential histological elements of the cerebral cortex are the nerve-cells and the nerve-fibres. The importance of the former is evident when their three-fold activity is recalled (i) as receptors of FIG. 1014. corticipetal impulses, (2) as distributors of the impressions so received to other parts of the brain, and (3) as originators of corticifugal impulses which control the nuclei from which immediately arise the motor nerves. No single method of preparation suffices to display satis- factorily both groups of structural elements, for when stains are employed which best bring out the cells, the fibres are inadequately shown ; and, conversely, when methods adapted for the demonstration of the fibres are followed, the cells are but imperfectly displayed. It is advantageous, there- fore, to study the histological details of the brain by more than a single method, combining the results ob- tained by the use of cellular stains with those yielded by procedures ex- hibiting the fibres. Among the latter, the well known method of Weigert, or its modifications, has been of great service in extending our knowledge concerning the various fibre-tracts. The methods of silver impregnation introduced by Golgi, although not producing true staining but only in- crustations on the cell and its pro- cesses, have materially advanced our knowledge concerning the- form of the cell-bodies and the- number and c-xtent of the processes of the neurones. \Yhilst varying as to details in different regions, the cerebral cortex presents a -en. -ral plan of Mnuture which may be considered: (0) in relation to the nerve-cells and ( /> ) in relation to the nerve-fibres. The Nerve-Cells of the Cortex. When sections cut perpendicular t surface of the convolution arc staint-d with basic stains (Fig- y\S) <"' prj-pan-t after silver impregnation (Fig. 1016), the cerebral cortex exhibits tour layers. Subpial layer Tangential fibres Stratum zonale Layer of small pyramidal cells Outer stripe of Baillarger Layer of large pyramidal cells Layer of poly- morphic cells Medullary fibres Diagram showing constituents of cerebral cortex ; cells in tin- right halt, 1'ihrcs in left half of figure; A, /?, large and small pyramidal cells; C. polymorphic cells; D, cell of Martinotti; K. cell of type II; F ; association d-ll; /, /, corticipetal fibres; 2, 2, corticifugal fibres a \Min-s of pyramidal cells) ; JV, N, neuroglia cells. THE TELENCEPHALON. FIG. 1015. BBSiPia Stratum zonale I Small pyra- "midal cells which, from without inward, are: (i) the stratum zonale, (2) the layer of small pyramidal cells, (3) the layer of large pyramidal cells, and (4) the layer of poly- morphic cells. Although each presents characteristics which are distinctive, with the exception of the junction between the first and second layers where the change is well defined, no sharp demarcation separates the strata, each passing insensibly into the adjoining layer. Neither are the modifications which distinguish the cortex of certain regions abruptly assumed, one type of cortical structure being gradually replaced by another without sudden transition. The stratum zonale, also known as the molecular stratum, underlies the pia and measures about .25 mm. in thickness. The layer contains few nerve-cells and appears subdivided into (a) a narrow peripheral zone, from .010 .030 mm. in width, composed of a subpial condensation of neuroglia and ($) a deeper zone characterized by numer- ous fibres or processes, which course parallel to the surface, and a meagre number of nerve-cells whose most distinctive representatives are small fusiform elements (Co/at's cells^) provided with long tangentially directed processes. The latter give off short collaterals, which ascend towards the surface, and intermingle with the number- less terminal filaments derived from the periph- erally coursing processes of the pyramidal and outer cells lying at deeper levels and from the corticipetal fibres which continue from the white core of the gyrus into the outermost layer of the cortex. The layer of small pyramidal cells is marked off from the stratum zonale, which it about equals in thickness, with some distinctness since, in contrast to the last-mentioned zone, it contains very many cells. These, as indicated by the name of the stratum, are of small size (.007 .010 mm.) and pyramidal form, at least in the deepest part of the layer. In the superficial part the cells are rounded or irregu- larly triangular, but they assume the distinctive pyramidal outline as they approach the sub- jacent layer, whose elements they resemble in possessing apical and lateral processes. The layer of large pyramidal cells con- tains the most distinctive neurones of the cere- bral cortex. It measures usually about 1.25 mm. in thickness, but in some localities much more, and blends with the adjoining layers without sharp boundaries. The cells in- crease in size but diminish in numbers as they are traced from the second layer inward, the largest (from .020 .040 mm. in width) and most characteristic lying in the deepest part of the stratum. The typical pyramidal cell possesses a conical body, triangular in section, the apex of which is continued into a long tapering dendrite, the apical process, which extends toward the periphery for a variable but usually considerable distance, depending upon the position of the cell. Upon gaining the stratum zonale, towards which the apical dendrite is always directed, the process breaks up into a number of end-branches that run parallel with the surface and contribute to the fibre-complex of the outer layer. During its journey to the surface, the apical dendrite gives off an uncertain number of branches that continue horizontally and, m y Large pyra- '' midal cells rc Polymorphic cells Section of cerebral cortex. X 90. 1178 HUMAN ANATOMY. Small pyra- ~1 tnidal cells with the collaterals and similarly directed processes from other cells, take part in producing the felt-work giving rise to the outer stripe of Baillarger. From the deeper or basal surface of the cell arises the delicate centrally directed a.votic, which, penetrating the intervening fourth layer, acquires a medullary coat and enters the white core of the convolution as one of the component nerve-fibres. The axone gives off one or more collaterals which, after a shorter or longer course, establish relations with other and often remote cells. In addition to the two chief processes, the peripherally directed apical dendrite and the centrally coursing axones, a variable number from four to twelve of secondary lateral ~ dendrites spring from the basal FIG. 1016. , . F . angles 01 the cell. 1 hese processes usually divided ichotomously, each succeeding pair of branches in turn splitting into twigs, until the den- drite is resolved into an end-brush of fibrillae which aid in producing an intricate felt-work of finest threads. Each pyramidal cell con- tains a conspicuous spherical or ellipsoidal nucleus, within which a distinct nucleus is usually distin- guishable. The cytoplasm exhibits a striation and, in addition to the masses of tigroid substance, the Nissl bodies, a mass of brownish pigment granules. The larger pyramidal cells are surrounded by an evident pericellular lymph- space. The layer of polymorphic cells includes a large number of small nerve-cells, from .008 .010 mm. in diameter, whose forms vary greatly, irregular, spherical, triangular, stellate and fusiform elements being present. Small pyramidal cells are also often seen within this layer. In contrast to dendrites of the typical pyramidal cells, those of the polymorphic elements, although peripherally directed, do not reach the stratum zonale but end before gaining the outermost layer. Their axones pass into the subjacent fibre- layer. The radial disposition of the groups of fibres within the deepest stratum of the cortical substance, limit the polymorphic cells chiefly to the consequently appear arranged in a Nerve- cells of pregnation. X 90. T. G. Lee. cerebral Drawn --t . A~> THE TELENCEPHALON. 1179 FIG. 1017. :"- ' Tangential fibre-layer Supraradial felt-work Outer stripe of Baillarger in other parts of the central nervous system, so too in the cerebral cortex there is found a sprinkling of Golgi' s cells of type II. Although both dendrites and axones of these cells undergo elaborate arborization, the axone is confined to a limited territory in the vicinity of the cell and, therefore, never reaches the stratum zonale. Neuroglia cells are present in all parts of the cerebral cortex and, whilst in a general way they send fibrils in all directions between the nervous elements, which they then support, the arrangement of the fibrillae is fairly definite in certain strata. Thus within the subpial condensation of the neuroglia, the glia cells send most of their processes as inwardly directed brushes. The cells within the deeper part of the cortex give off their processes in two chief groups, one extending towards the periphery and the other towards the white core. The Nerve-Fibres of the Cortex. When viewed in suitably stained sections cut parallel with their general course, the cortical nerve-fibres do not appear as a uni- form layer, but as radially disposed bundles which gradually become less distinct as they traverse the cortex and finally disappear at about the level of the outer border of the layer of large pyramidal cells. The radial fibres are partly afferent and partly efferent. The corticifugal components, which predomi- nate, are largely the centrally directed axones of the pyramidal and the polymorphic cells which are continued as the axis-cylinders ol the fibres composing the subcortical white matter. The peripherally coursing axones of the cells of Martinotti also contribute to the production of the fibre-radii. The coiticipetal constituents of these tracts include the nerve- fibres which are derived from cells situated more or less remote from the convolution in which the fibres (their axones) end. Such, for example, are the thalamo-cortical and the tegmento-cortical fibres, as well as the many commissural fibres that arise in the opposite hemisphere and cross by way of the corpus callosum. Although for the most part the corticipetal fibres end at various levels in arborizations around the pyramidal cells, some are continued into the stratum zonale where, breaking up into horizontal fibrillae, they assist in producing the tangential zone. The spaces between these radial bundles are occupied by a delicate interlacement, the interradial felt- work, which is composed in large part of the lateral and collateral processes of the cells. Within the third layer, the horizontally coursing collaterals and processes of the large pyramidal cells form a complex of unusual intricacy, which condensation gives rise to the outer stripe of Baillarger. Beyond the outer ends of the radial fibre-bundles, the intercel- lular ground-work is occupied by a second delicate interlacement of processes and collaterals, the supraradial felt-work of Edinger ; whilst immediately beneath the narrow subpial neurogliar zone innumerable delicate terminal fibrillae course horizontally and parallel with the surface and constitute the tangential fibre-layer. The components of this layer are the terminal branches of the dendrites of the pyramidal and polymorphic cells and the axones of the cells of Martinotti, as well as the main and secondary processes of the fusiform elements of the stratum zonale. Interradial felt-work Radial fibres Section of cerebral cortex stained to show fibres. X 21. n8o HUMAN ANATOMY. FIG. 1018. Choroid plexus __ Lateral ventricle Alveus covering hippocampus Fimbria The evident purpose of the horizontally directed processes and collaterals being to bring into relation different cortical cells, such association tracts become evident only after the neces- sity for the exercise of the corresponding psychic functions has arisen. Hence in the cortex of young children the strata of horizontal fibres are very feebly developed. With the progressive advance of intellectual capacity, the association paths become correspondingly more marked, according to the suggestive observations of Kaes, the increase continuing beyond even middle life. Whether this augmentation is due to actual increase in the number of association fibres, or, as suggested by Edinger, is dependent upon the further growth and myelination of collaterals already present in an immature condition, is uncertain. Local Variations in the Cerebral Cortex. It has been pointed out, in prefacing the foregoing description of the structure of the cerebral cortex, that, whilst in the main certain features are common to the cortex wherever well devel- oped, more or less evident variations occur in different localities. Such variations are, for the most part, slight and depend upon the size and number of the nerve-cells and the richness and direction of the nerve-fibres changes which produce alterations in the relative proportions of the strata. The width of the stratum zonale is almost constant and subject to little modification, being usually well defined from the layer of small pyramidal cells. The layer of the large pyramidal cells, on the contrary, exhibits considerable variation, either in increased thickness, as in the precentral gyrus, or in diminished breadth, as in the occipital lobe. The layer of poly- morphic cells is fairly uniform, but within the precentral convolutions is reduced almost to disappearance, although Gyrus dentatus the pyramidal cells of the superimposed (third) layer are here of unusual size. Such variations in the histological features ^^^^^^^^ of the cortex are prob- "^-W.,' ably correlated with dif- Frontal section across left hippocampus and gyrus dentatus. X 2%. of its various regions, although the exact relations between such differences are in many cases still obscure. Disregarding the cortical regions which are profoundly modified by their rudi- mentary character, such as the olfactory lobe (page 1152), apart from minor varia- tions in details, the cortex of the greater part of the frontal, parietal, occipital, temporal and limbic lobes and of the insula closely corresponds in its structure. That of the motor (Rolandic) region, of the calcarine (visual) area of the occipital lobe, and of the hippocampus, dentate gyrus and adjacent part of the hippocampal gyrus, however, presents modifications which call for brief description. The Rolandic cortex of the precentral gyrus, particularly towards the upper margin of the hemisphere, of the paracentral lobule and of the adjoining part of the postcentral gyrus the great cortical motor area of the hemisphere is distinguished by the great breadth of the layer of large pyramidal cells, the unusual size of the last-named elements and the feeble development of the layer of polymorphic cells. The pyramidal cells collectively tend to larger size as the upper end of the precentral convolution is approached and, in addition, cells of extraordinary dimensions appear. These elements, known as the giant pyramidal cells of Betz, reach their maximum size within the paracentral lobule, where some attain a breadth of .065 mm. or almost double that of the pyramidal elements in other regions. The giant cells are further distinguished by their robust and rounded form, their distribution in small groups of from three to five in the deeper layers of the cortex, and the exceptional thickness of their axones. The occipital cortex in the vicinity of the calcarine lissure i Fig. 1013) is distinguished even macroscopically by the clearness of the outer stripe of Baillarger, here called the .s/;v/V of (,'finntri or of }'icq d } Azyr. The stratum /onale is somewhat smaller than usual, but is exceptionally rich in tangential fibres and fusiform eel's. The more superficially placed elements of the second stratum are spindle form rather than pyramidal and give off two THE TELENCEPHALON. 1181 dendritic processes, one passing outward and the other toward the subjacent third layer, on entering which it divides and gives off the axone. At about the junction between the layer of small and large pyramidal cells, the stripe of Gennari is produced by a close felt-work of medullated fibres, beneath which the pyramidal cells very gradually increase in size. In the deepest part of the third and adjacent part of the fourth layer, pyramidal cells of unusually large dimensions occur singly or in small groups. The layer of polymorphic cells is well represented. The cortex of the hippocampus and of the gyrus dentatus is a prolongation of that of the gyrus hippocampi, modified by the peculiar folding which here occurs. Reference to Fig. 992 will recall the relations of these gyri as seen on the mesial surface, namely, that at the bottom of the deep groove (the hippocampal fissure) above the hippocampal convolution lies the corru- gated free surface of the dentate gyrus and above this the rounded mesial border of the hippo- campus. Viewed in cross-section (Fig. 1018), the cortex of the hippocampal convolution is seen to bend laterally and pass into that of the hippocampus, which arches upward, mesially and FIG. 1019. ^f ' --V-V .!.-.<.-', ->,- "-" VV ~-:->'- Fimbria glj} Hil > -:-./' - ' ; Part of frontal section across left hippocampus and gyrus dentatus, showing arrangement of cell-layers. then, turning sharply laterally, blends with the dentate gyrus, which recurves mesially to reach the free surface of the hemisphere and fill the recess between the hippocampal gyrus and the under surface of the hippocampus. The cortex of the hippocampus, therefore, is folded upon itself somewhat like the curve of an interrogation mark. On approaching its upper convexity, the cortex of the hippocampal convolution, here called the subiculum, becomes modified by the excessive but unequal thickening of the tangential fibre-layer of its stratum zonale and the irregularity of its layer of small pyramidal cells, the large pyramidal cells at the same time becoming the sole representatives of the third stratum. The layer of tangential fibres, some- what thinned, passes onto the hippocampus which it follows throughout and comes, therefore, into apposition with the corresponding tangential zone of the dentate gyms. The two fibre- layers are so blended that a differentiation between the two is impracticable. Beneath (i) the layer of tangential fibres lies a second stratum of medullated fibres, (2) the lamina medullaris circumvoluta, which is probably an intracortical association tract limited to the hippocampus. The zone succeeding the medullary lamina is penetrated by innumerable long dendritic pro- cesses of the large pyramidal cells and in consequence presents a radial striation, the layer 1182 HUMAN ANATOMY. being appropriately termed (3) the stratum radiatum. Following this comes (4) the layer of pyramidal cells. These are uniformly of large size and closely packed within a clear ground-work which confers a light appearance upon the winding lamella, which is therefore sometimes known as the stratum liicidiim. Beneath the pyramidal cells lies a layer of fibres, (5) the stratum oriens, which pass to and from the hippocampus ; among these fibres are embedded spindle cells, as well as peculiar association cells (Cajalj possessing richly branched axones which ramify among the pyramidal cells which they probably serve to link together. The axones of the pyramidal cells are directed chiefly towards the centre of the gyrus where, next the descending horn of the lateral ventricle, they form a conspicuous layer of fibres called (6) the alveus. It is -this sheet, covered by (7) the ventricular cficndyma, in connection with the stratum oriens, which confers the white color to the hippocampus, as seen within the ventricle. On reaching the recurved end of the hippocampus, the layer of pyramidal cells of the latter is not continuous with that of the dentate gyrus, but ends irregularly and is enclosed by the arched dentate cell-layer. The cortex of the gyrus dentatus is highly modified and Jess in accord with the typical structure of the cortical substance than that of the hippocampus. The outer surface where buried in the concavity of the hippocampal arch lies in contact with the similar surface of the hip- pocampus, hence the peripheral layers of the two gyri are opposed. Within the gyrus dentatus may be recognized ( i ) the stratum zonale, relatively narrow and meagre in fibres. The surface of the gyrus is paralleled by a narrow layer of small and densely packed cells, (2) the stratum granulosum. These almost, but not quite completely, surround the gyrus and, therefore, leave an interval, the hilum, through which the fibres gain and leave the deeper parts of the convolu- tion. Within the area so circumscribed, known as (3) the nucleus of the gyrus, are found, irregularly disposed elements, the representatives of the layer of large pyramidal cells. They are for the most part small in size and atypical in form. Their axones, together with the continuation of the stratum oriens, pass through the hilum, the dentate gyrus thereby forming connections with other parts, either of the hippocampus or of the fimbria. THE WHITE CENTRE OF THE HEMISPHERE. The extensive medullary substance enclosed by the cerebral cortex appears, above the level of the corpus callosum, as a grayish white tract (centrum semiovale} of seemingly homogeneous structure, FIG. 1020. its uniform character being broken ^^^^^ ^^^^^ at most by minute blood-vessels. At lower levels, where the intercor- tical area is encroached upon by the large collections of gray sub- stance composing the corpus stria- turn and the thalamus, the white matter is most conspicuous immedi- ately subjacent to the cortex. When examined with the microscope after suitable preparation, the apparently homogeneous subcortical tissue is resolved into an intricate maze of medullated nerve-fibres, supported by neuroglia, which run in various directions and are, therefore, cut in different planes. When analyzed as to their relations with the cortex, the components of the medullary sub- stance of the hemisphere fall into three general groups: ( i ) the associ- ation fibres, (2) tin- conunissural fibres, and i 3) the projection fibres. The Association Fibres. The association fibres link together different por- tions of the same hemisphere, many uniting adjacent areas whilst others connect parts widely separated. They are grouped, therefore, as long and short association bundles. With the exception of a narrow zone in the immediate vicinity of the upper end of the Rolandic fissure, the cerebral cortex at birth is unprovided with association fibres which have acquired their medullary coat and, therefore, are capable of functioning. Frontal section of brain passing through hemispheres in front of corpus callosum; core of white matter is everywhere enclosed by cortical gray matter. THE TELENCEPHALON. .183 FIG. 1021. Diagram showing; association fibres, lateral surface ; part of left hemisphere removed to expose short fibres ; long fibres are supposed to show through transparent hemisphere ; SLF, superior longitudinal fasciculus ; UF, uncinate fasciculus. Within the early months after birth, however, the myelination of these, as well as of other tracts, progresses rapidly, although this process is not even moderately com- pleted until after the lapse of several years. Indeed, there is sufficient evidence to believe that myelination of additional fibres continues so long as intellectual effort is progressive, the demands made by education and special mental exercise being met by a corresponding completion of additional association fibres. The short association fibres pass in great numbers from one convo- lution to the next, bending in U-like strands around the intervening fissure. Some of these loops are confined to the deeper layers of the gray matter and constitute the intracortical association fibres, whilst others occupy the adjacent white matter. These latter are known as the subcortical association fibres. In addition to the innumerable fibres which unite the adjoining convolutions {fibres proprice) and occupy the white matter immediately below the cortex, many connect gyri somewhat more widely separated, those limited to the convolutions of the same lobe constituting the intralobar fibres and lying at somewhat deeper levels within the medullary substance. The long association fibres connect more or less remote portions of the cortex of the hemisphere, and, therefore, vary in length, but are sometimes of con- siderable extent. Numerous as such intcrlobar bundles undoubtedly are, only a few can be demonstrated with certainty. Among the most definite of these are : (i) the uncinate fasciculus, (2) \htcingulum, (3) the superior longitudinal fasciculus, and (4) the inferior longitudinal fasciculus. The uncinate fasciculus arises from the convolutions of the orbital surface of the frontal lobe, arches over the stem of the Sylvian fissure, close to the ventral border of the insula, and ends in the cortex of the anterior part of the temporal lobe. The cingulum is a long arched tract lying within the limbic lobe. It begins in front in the vicinity of the anterior perforated space, arches around the anterior end of the corpus callosum, follows the up- FIG. 1022. per surface of this structure, lodged within the callosal gyrus, and, curving around the splenium, descends within the hippocampal gyrus to end in the fore-part of the temporal lobe and per- haps also in the uncus. The cingulum is not composed of fibres which extend its entire length, but is made up of a number of shorter tracts, as shown by its incomplete degeneration after section of the fasciculus. The superior longitudinal fas- ciculus, also called the fasciculus arcuatus, passes from the frontal and parietal opercula, over the region of the insula, to the inferior parietal con- volution, the occipital lobe and the superior and middle temporal convolutions. It is composed of a number of short bundles which proceed from the frontal lobe partly in the sagittal direction towards the occipital lobe, and partly in curves into the temporal lobe. The inferior longitudinal fasciculus is a well-marked bundle which extends from the tip of the occipital lobe and the cuneus, along the outer side of the optic Diagram showing association fibres, mesial surface; fibres are supposed to show through transparent hemisphere. 1184 HUMAN ANATOMY. FIG. 1023. radiation and the posterior and inferior horns of the lateral ventricle to the fore-part of the temporal lobe. It is probably an important path by which visual impressions are transmitted to other parts of the cortex (Dejerine). Among the additional association tracts which have been described may be mentioned : The fasciculus occipitalis perpcndicularis, which extends from the upper part of the occipital lobe and the upper part of the inferior parietal convolution to the occipito-temporal convolution. The fasciculus fronto-occipitalis, which courses sagittally and lies in intimate relation with the lateral ventricle and the caudate nucleus, and to the mesial side of the corona radiata. The fasciculus temporo-parietalis, which unites the temporal convolutions with the cortex of the parietal region. The fasciculus fronto-parietalis, which runs between the base of the lenticular nucleus and the claustrum and connects the frontal and parietal cortex. The fasciculus lobi lingualis, which is a bundle passing from the ventral boundary of the calcarine fissure to the occipital cortex of the lateral surface of the hemisphere. The Commissural Fibres. Under this heading are included the fibres which cross the mid-line and connect the cortex of one hemisphere with that of the other, the regions so united being by no means necessarily identical on the two sides. Such discrepancy is accounted for, at least in part, by the frequent introduction of an association neurone in the com- missural circuit, the impulse carried from one hemisphere to the other being thus transferred to another region of the cor- tex, from which there arises the return commissural fibre. Preparatory to cross- ing the median plane, the fibres are col- lected into compact masses which form three definite bridges or commissures : ( i ) the corpus callosum, (2) the anterior commissure and (3) the hippocampal commissure. The fibre-system of the corpus callosum, the chief commissure of the pallium, is so extensive that it includes connecting strands from all parts of the cortex of the hemispheres with the ex- ception of the front and under part of the temporal lobes and the two rhinencephala, which, on account of their isolated position, are provided with special bonds of union. The callosal fibres . stream out in all directions, constituting the radiation of the corpus callosum (radiatio corporis callosi), of which an anterior, a middle and a pos- terior portion are recognized. The anterior division, the pars frontalis, comprises the fibres which cross in the genu and, as the forceps minor, pass to the frontal pole. The fibres constituting the middle portion, the pars parietalis, traverse the body of the corpus callosum and continue outward to the hind-part of the frontal and the parietal and temporal lobes. The posterior portion includes the fibres which form the splenium and the adjoining segment of the body of the corpus callosum. These course outward, downward and backward and as the pars tcwporalis and the pars occipitalis reach respectively the hind-part of the temporal and the occipital lobes. The fibres destined for the latter region lie within the splenium, from which, as a condensed bundle, the forceps major, they arch backward along the inner wall of the posterior horn of the lateral ventricle (page 1158) into the occipital cortex. The fibres composing the corpus callosum probably all terminate in arborizations within tin- cortex of one or the other of the hemispheres. Their source in tin- opposite hemisphere, how- ever, is bv no means always the same, since they may arise: ( i } as the- axones of the pyramidal or of the polymorphic cells ;'( 2) as the collaterals of association fibres; or (3) as collaterals of projec- tion fibres, in the last two cases being, therefore, of the nature of association-fibres rather than of Diagram showing- commissural fibres passing between cerebral hemispheres by way of corpus callosum (CC) an- terior commissure (AC), and hippocampal commissure (HC). THE TELENCEPHALON. 1185 strictly commissural ones. Indeed, with the more exact and extended study of the corpus callosum, it becomes more and more evident that the composition and relations of this great bridge are very intricate and complex, and that it receives contributions from a much larger number of and more diverse sources than was formerly recognized. The observations of E. A. Spitzka upon the size and sagittal area of the corpus callosum have conferred additional interest upon this struc- ture as a possible index as to intellectual develop- ment. The examination of a series of brains which included some from men of acknowledged intellectual superiority, demonstrated a corpus callosum of unusual area as a constant feature in the brains of the more highly endowed individuals. And, further, that the size of the corpus callo- sum bore a direct rela- tion to the character of intellectual superiority which the individual was known to possess, the largest commissure being found in the brain of a man whose intel- lectual greatness implied the exercise of associa- tion paths to an unusual degree. The later con- clusions of Bean, however, Tapetum Choroid plexus Hippocampus, cut obliquely Fasc. long, inferior Frontal section of right hemisphere, passing just behind splenium of corpus cal- losum ; inferior horn of lateral ventricle is cut obliquely. seriously question (consult page 1197) the constancy of the relations above suggested. The anterior commissure consists of a compact cord-like strand, slightly compressed from before backward and- therefore oval in section (Fig. 996), which connects the anterior ends of the temporal lobes, as well as the olfactory bulbs. As it crosses the mid-line, the commissure is placed immediately in front of the downward arching anterior pillars of the fornix, in the interval between which it appears as a white transverse ridge on the narrow anterior wall of the third ventricle (Fig. 979). Its posterior surface is covered with the ventricular ependyma, whilst in front it is in intimate relation with the lamina cinerea (page 1130). Laterally it arches backward and downward, the entire commissure forming a Il-shaped tract, with the convexity presenting forward, whose ends broaden as they sweep backward into the temporal lobes (Fig. 968). In addition to uniting the fore-parts of the last-named lobes, the anterior commis- sure connects the olfactory bulbs and consists, therefore, of a temporal and an olfactory part. The olfactory part is much the smaller and appears as a delicate fasciculus which curves downward and forward to enter the olfactory tract. Its fibres include : ( i ) those which arise in one olfactory lobe and pass to that of the opposite side ; (2) those which connect the olfactory lobe of one side with the cortex of the hippocampal convolution ; (3) those which extend from the olfactory lobe through the commis- sure and, joining the tsenia semicircularis, proceed with this strand along the roof of the inferior horn of the lateral ventricle to end in the amygdaloid nucleus (page 1172). The temporal part includes the greater portion of the commissure. After pass- ing almost horizontally outward beneath the lenticular nucleus (Fig. 1025) as far as the mesial borders of the putamen, it turns backward and continues its course beneath the lenticular nucleus, where it appears in frontal sections as a transversely 75 ii86 HUMAN ANATOMY. cut oval bundle until, farther backward, it bends abruptly downward to disappear in the white matter of the temporal lobe, to the outer side of the inferior horn of the lateral ventricle, preparatory to ending in the cortex. The fundamental and archaic character of the rhinencephalon, this division of the hemi- sphere appearing in animals in which the pallium is only feebly developed, early led to the establishment of a special connection between the olfactory lobes of the two sides. When to this necessity was added that of linking together the fore-parts of the temporal lobes, which are to a considerable degree isolated, the establishment of a commissure supplementary to the corpus callosum was effected. FJG. 1025. Corpus callosum Lateral ventricle Septum lucidum Anterior end of fomix, cut Foramen of Monroe Anterior pillars of fornix Caudate nucleus Striate or terminal vein Internal capsule Thalamus, anterior nucleus Lenticular nucleus, putaman Claustrum Globus pallidus Anterior commissure Olfactory strands Frontal section of brain passing through anterior commissure. The hippocampal commissure connects the two hippocampi by means of fibres which cross in the psalterium (page 1158), in addition, some fibres thus under- going decussation join the longitudinal strands of the fornix and proceed towards the thalamus. The Projection Fibres. These fibres connect the cortex of the cerebral hemisphere with the lower lying parts of the brain the thalamus, the corpus striatum, the tegmental region, the pons and the medulla and the spinal cord. Proceeding, as they do, from all parts of the extended cortical area towards nuclei grouped within the compass of a relatively small space, the fibres, for the most part, at first curve toward their objective points and collectively form the extensive con- verging tract known as the corona radiata. The greater number of the components of the latter pursue a direct path to the lower levels and take part, therefore, in the formation of the compact internal capsule. The projection fibres are by no means uniformly numerous in all parts of the cortex, relatively few issuing from the frontal, parietal and latero-inferior part of the temporal regions areas which, according to Flechsig, are particularly significant as association centres. Furthermore, the olfac- tory cortex does not contribute to the corona radiata, its own special projection fibres being represented by the cortico-mammillary tract within the fornix (page 1158). The projection fibres are not cxelusively corticifu^al tracts, since the connections of the thalamus are of a double nature, numerous corticipetal paths passing from this great sensory nucleus to the cortex of the hemisphere. The projection fibres may THE TELENCEPHALON. 1187 FIG. 1026. be conveniently considered under two groups, the short and the long tracts, accord- ing to the position of the nuclei with which they are associated. The short projection tracts include the following : i. The cortico-thalamic tracts, the fibres of which pass from all parts of the cortex of the hemisphere to the thalamus. The components of these tracts are : (a) fibres passing from the cortex of the frontal lobe to the anterior extremity of the thalamus ; (<5) fibres passing from the cortex of the Rolandic region and the adjoining part of the parietal lobe to the lateral and mesial nuclei of the thalamus ; (V) fibres passing from the occipito-tem- poral lobe to the medio- ventral part of the thalamus ; and (a?) fibres passing from the posterior part of the parietal and from the occipital lobe to the pulvinar. Associated with the foregoing corticifugal paths are the thalamo- cortical tracts which, coursing in the opposite direction (corticipetally), proceed by way of the stalks or peduncles of the thalamus (page 1 1 22) to all parts of the cortical sheet of gray matter investing the cerebral hemisphere. The thalamo- cortical tracts (Fig. 966), are the continuations (by means of the thala- mic neurones) of the sensory paths conveying impulses from the spinal cord and the brain-stem and from the cerebellum to the great sensory internode, the thalamus. These include, on the one hand, chiefly the median fillet, the spino-tha- lamic tract and, probably, a part of Goiuers 1 tract, by which paths the sensory impulses collected by the spinal and the cranial nerves are transmitted to the thalamus ; and, on the other hand, the cerebello- rubro-thalamic tracts, by which the cerebellum is linked with the thal- amus by way of the superior cerebel- lar peduncle. The visual impulses carried by the fibres of the optic tract to the pulvinar are, in a similar manner, conveyed to the occipital cortex, along with those interrupted in the lateral geniculate and the superior quadrigeminal body, by the optic radiation of which the occipital stalk of the thalmus is a part. 2. The cortico-genicidate and the cortico-qnadrigeminal tracts are important constituents of the optic radiation. Their fibres extend from the occipital cortex to the primary optic centres and, as in the case of those going to the pulvinar, are accompanied within the radiation by corticipetal fibres passing from the quadrigeminal and geniculate bodies and the pulvinar. 3. The auditory radiation comprises both corticipetal and corticifugal fibres which, in proceeding outward, pass from the inferior quadrigeminal and the median geniculate body through the retrolenticular portion of the posterior limit of the internal corpuscle and beneath the lenticular nucleus to the auditory centre within the temporal lobe. This cortical centre includes the middle portion of the superior temporal convolution and, probably, the adjoining part of the temporal operculum. Lateral pyramidal Direct pyramidal Diagram of long projective fibres ; nuclei of cranial nerves are indicated by Roman numerals; J?, red nucleus. u88 HUMAN ANATOMY. 4. The cortico-rubral trad constitutes a supplemental motor path. The exact location of its cortical origin is uncertain, but may be assumed, at least provisionally, to lie within the parietal lobe. The long projection tracts embrace two important groups, the cortico-pontine and the motor tracts, the former contributing the first link in the chain connecting the cerebral and the cerebellar cortex, and the latter constituting the bond between the cortical gray matter of the hemisphere and the motor nuclei of the cranial and of the spinal nerves. The long projection fibres are important constituents of the internal capsule which they all traverse. 1. The cortico-pontine tracts include two chief subgroups, the fronto- pontine and the temporo-occipito-pontine, which below end around the cells of the pontine nucleus, whence the impulses are transmitted to the cerebellum by the ponto-cerebellar strands of the same and opposite sides. a. The fronto-pontine tract arises from the cortex of the frontal lobe and, passing by way of the corona radiata, enters the hind-part of the anterior limb of the internal capsule. Descending into the crusta of the cerebral peduncle, in which it occupies the mesial fifth, the tract ends within the ventral part of the pons around the nerve-cells constituting the pontine nucleus. b. The temporo-occipito-pontine tract proceeds from the cortex of the temporal and the occipital lobes through the hindermost segment of the posterior limb of the internal capsule. On reaching the cerebral peduncle, its position corre- sponds approximately with the lateral fifth of the crusta. It ends within the pons around the cells of the pontine nucleus in the same manner as does the last- described tract. 2. The motor tracts are composed of fibres which connect the cells within the cortical areas of the Rolandic region with the nuclei from which arise the root-fibres of the motor nerves. Since the latter take origin within the brain-stem as well as within the spinal cord, the motor tracts comprise two groups the cortico-bulbar and the cortico- spinal tracts. The exact locations of the cortical areas controlling the vari- ous cell-groups giving origin to motor nerves are still far from being accurately known. Clinical and experimental studies have indicated \vith considerable certainty, however, that the cerebral cortex in the immediate vicinity of the Rolandic fissure, chiefly in the precentral convolution and paracentral lobule, and probably also in the adjacent parts of the superior and middle frontal gyri, is the most important seat of such motor centres. In a general way, the areas controlling the muscles of the lower limb lie highest and are situated in advance of and around the upper part of the Rolandic fissure. The conspicuous backward projection of the precentral gyrus (Fig. 984) corresponds to the arm-area, whilst the lower part of the same convolution contains the centres for the neck and face. (Consult also page 1212.) a. The cortico-bulbar tract includes the fibres ending around the nuclei from which proceed the motor fibres of the cranial nerves. The fibres, therefore, arise from the pyramidal cells of the cortex of the lower part of the precentral gyrus and, for the eye muscles, of the adjoining portion of the middle frontal convolution (Mills). Proceeding by way of the corona radiata, the cortico-bulbar path occupies the segment of the internal capsule which forms the genu, being bounded in front by the fibres of the fronto-pontine tract and behind by those of the cortico-spinal tract. The exact location of the strands destined for the several nerves is known only for the facial and the hypoglossal, those for the last-named nerve occupying the most posterior part of the genu, whilst those for the facial lie just in advance of the fibres for the twelfth. Within the cerebral peduncle (Fig. 1012), the cortico-bulbar strand occupies the lateral part of the inner third of the crusta, the fibres destined for the third and fourth nerves soon turning dorsally and crossing the- raphe to end, for the most part, in relation with the nuclei of the opposite side. The fibres for the lower lying nuclei continue through the crusta and enter the ventral part of the pons ; they then assume a medium position and at appropriate levels bend dorsally and cross the mid-line to end in relation with the cells of their objective motor nuclei, some feu fibres probably ending in the nuclei of the same side. b. The cortico-s'piual or the pyramidal tracts include the longest of all the projection fibres, which, as in the case of those passing to the nuclei oi the sacral THE TELENCEPHALON. 1189 1027. Diencephalon Thalaniencephalon Tegmentuni Mid-brain III nerve Mammillary ^ body nerves, may traverse the entire thickness of the brain and the length of the spinal cord. They arise from the pyramidal cells of the Rolandic cortex, follow the corona radiata into the internal capsule, within which they occupy approximately the front half of the posterior limb, those destined for the cervical nerves lying in advance of those for the trunk and leg nerves. Within the peduncle, the cortico-spinal tract appropriates approximately the middle third of the crusta, having the sensory paths to its outer side. The further course of these fibres leads through the ventral part of the pons and of the medulla, until near the lower limit of the last-named division of the brain-stem, the greater part of the pyramidal strands take part in the motor decussation and thence descend within the lateral pyramidal tract to their appropriate levels where they end in relation with the radicular cells of the anterior horn (page 1043). The fibres which do not cross in the pyramidal decussation exchange their lateral position for a median one and continue within the cord as the direct pyramidal tract at the side of the median longitudinal fissure. Before gaining their final levels within the cord, these fibres also cross, by way of the anterior white commissure, to end around the root-cells of the opposite side. DEVELOPMENT OF THE PARTS DERIVED FROM THE FORE-BRAIN. It has been pointed out in the general sketch of the development of the brain (page 1060), that the fore-brain very early undergoes subdivision into two secondary cerebral vesicles, the anterior of which is the ielencephalon, or end-brain, and the posterior the diencephalon. Each of these secondary vesicles gives rise on each side to FIG. two general regions, an upper and a lower, which in the telencephalon are the hemisphcerium and the pars optica hypothalami and in the diencephalon are respectively the thala- mencephalon and the pars tnamillaris hypothalami. These two parts of the hypothalatnic region to- gether constitute the hypo- thalamus, which includes the portion of the lateral wall of the fore-brain lying below the level of the fo- ramen of Monroe and cor- responds to the ventral or basal lamina of the neural- tube (Fig. 914). This tract gives rise to the structures situated along the floor of the third ventricle the mammillary bodies, the tuber cinereum, the in- fundibulum and the posterior lobe of the pituitary body, the optic chiasm and the optic tracts. The anterior wall and the roof of the fore-brain always remain thin. This is especially true of the roof, which, with the exception of its hindmost part where the posterior commissure is formed, does not lead to the development of nervous tissue but remains thin, being later represented by the attenuated epithelial layer which constitutes the morphological roof of. the third ventricle. The anterior wall of the fore-brain is the thin median partition known as the lamina terminalis, which, whilst giving rise to the rudimentary sheets of gray matter found within the lamina cinerea and the septum lucidum, is to a large extent concerned in the production of the great commissure, the corpus callosum. The hemisphccrium, one on each side, comprises by far the greater portion of the end-brain and represents an enormous expansion of the dorsal or alar lamina of the neural tube. Very early it exhibits a differentiation into : (a) \hv pallium, (b] the rhincnccphalon and (c) the corpus striatmn. The Pallium. Of the three parts of the hemisphaerium, in man the pallium soon becomes the most conspicuous, since from the walls of this rapidly expanding hemispherical pouch is derived the great sheet of cortical gray substance which invests the cerebral hemisphere. For a time enclosing a large caviiy with thin walls, the pallium later becomes consolidated by the Hypothalamus Future lateral 1 ventricle Pallium Posterior limit of telenceph- alon Rhinenceph- alon Corpus striaturri Optic recess Infundibular recess' Tuber cinereutil Geniculate ganglion of facial" Vestibular gangli.ni- Membranous labyrinth Reconstruction of brain of human embryo of four and one-half weeks (10.2 mm.), inner surface of the fore-brain and mid-brain exposed by mesial section. (Exterior of same brain shown in Fig. 1141). X 12. Drawn from His model. 1 1 go HUMAN ANATOMY. intergrowth of the fibre-tracts (later the white matter), which arise partly from the young nerve-cells within its walls and partly from neuroblasts situated in other segments. An ad- ditional factor of moment in the production of the bulky cerebral hemisphere is the special mass of gray matter, the corpus striatum, which, with the increasing fibre-tracts, leads to the reduction and conversion of the cavity of the pallium to the irregular lateral ventricle. Its once wide communication (Fig. 1030) with the cavity of the fore-brain is retained as the proportionately narrow foramen of Monroe. The pallium expands in all directions save directly downward, where increase concerns chiefly the rhinencephalon, but the lines of its growth are particularly backward and downward, in consequence of which, in addition to the production of a temporal and the distinctive occipital lobe, the other brain-segments become gradually covered over and deposed from their original superior position toward the basal surface of the brain. This process is already marked during the third month (Fig. 1031), by the end of which period the pallium covers the diencephalon. By the beginning of the fifth month the mid-brain is completely overlaid, and by the eighth month the entire upper surface of the cerebellum is covered. Development of the Sulci and Gyri. The modelling of the surface of the cerebral hemi- sphere begins towards the end of the fifth month of foetal life, by which time the occipital lobe is well formed and the brain-case is separated from the cerebral surface by an intervening layer FIG. 1028. Pallium Lateral ventricle Roof-plate of III ventricle, with' choroid plexus Corpus striatum Thalamu Choroid plexus Hippocampus Choroidal fissures Frontal section of brain of rabbit embryo showing imagination of mesial wall of hemisphere along hippocampal and choroidal fissures ; thin roof-plate of third ventricle stretches between thalann. X 13. of yielding arachnoid tissue, which offers little opposition to the production of the convolutions which now follows. Preceding this period, the outer surface of the young hemisphere is quite smooth, with the exception of the crescentic Sylvian fossa (Fig. 982) which marks the position of the later insula. This depression has been described (page 1137) in connection with the pro- duction of the Sylvian fissure. The uncertain creases, the so-called " transitory fissures," some- times seen on brains of a much earlier period are without morphological significance and are now usually regarded as artefacts ( Ziehen, Hochstetter) . Long antedating the appearance of the fissures on the outer aspect of the pallium, the mesial surface of the latter is early marked by two grooves, tin- choroidal and tin.- kifpocamfftl fissures. The first of these (Fig. 1031) appears by the end of the fifth week as an invagination of the mesial wall of the pallium just above the position of the foramen of Monroe. At first small, the groove is carried backward and downward by the expansion of the pallium until, finally, it is traceable along tin- inner wall of the inferior horn of the lateral ventricle as far as its lower limit. Knterini; by means of this invagination, the mesoblastic tissue forces before it the attenuated cerebral wall and expands into a voluminous mass, the choroid o6. THE MEMBRANES OF THE BRAIN. 1197 of Letters and of Art have possessed a weight little above, or sometimes even below, the aver- age. In this connection it must be remembered that it is not improbable that the cortical cells of different brains vary in their capacity for activity and in their power of retaining impressions; that, in short, differences of quality exist. Further, that notwithstanding the possible low gen- eral weight of a brain, the amount of the cortical gray matter, especially of certain regions con- cerned in some particular phase of mental activity, may exist in unusual abundance. Moreover, it is probable, from the investigations of Kaes ', that actual increase of the functioning associa- tion fibres takes place in response to the stimulus induced by excessive exercise of certain parts of the cortex. It is evident, therefore, that as applied to the individual, brain-weight alone affords little dependable information as to intellectual power, and that brains which, judged from their weight, apparently have been ordinary, may have been exceptional in the amount of cortical gray matter and, perhaps, in the unusual capacity of their neurones. Considered, however, in relation to great groups, as to peoples or to races, brain-weight has been found to correspond to the general plane of intelligence and culture. In this connection the observations of Bean 2 are suggestive. He found the average brain-weight of the male negro to be 1292 gm., with extremes of 1010 gm. and 1560 gm. ; that of the male Caucasian 1341 gm., with extremes of 1040 gm. and 1555 gm. Notwithstanding the relatively low class of the white subjects examined, the average weight of their brains was greater than that of the high-class negroes. Bean concludes that the smaller size of the negro brain is primarily in the frontal lobe, and, therefore, that the anterior association centre is relatively and absolutely smaller. The observations of E. A. Spitzka 3 concerning the area of the corpus callosum in median sagittal section, call attention to the unusual size of this commissure in the brains of men of con- spicuous intellectual power. Moreover, in the particular group of brains thus examined varia- tions in the details of the callosa strikingly suggested well-known differences in the mental traits of the persons during life. The validity of the area of the callosum as a trustworthy index as to intellectual capacity has been seriously affected by the fact, illustrated by Retzius and by Bean, that callosa of uncommon size usually belong to brains of high weight, and that not infrequently such brains are from individuals of ordinary or even of low intelligence, as exemplified by the cases of Bean, among which a number of callosa of very large area were from low-class whites and even from negroes. THE MEMBRANES OF THE BRAIN. Like the spinal cord, the brain is enveloped by three membranes, or meninges, which, from without inward, are: (i) the dtira mater, (2) the arachnoid and (3) the pia mater. The first of these is closely applied to the inner surface of the cra- nium, of which it constitutes the periosteum, and, in addition, by means of its processes serves to support and guard from undue pressure the enclosed mass of nervous tissue. The pia mater is the vascular tunic carrying the blood-vessels for the nutrition of the brain and, therefore, lies in contact with all parts of the external surface of the organ ; whilst the arachnoid, the thinnest and most delicate of the three coats, is free frpm blood-vessels but is intimately related with the intracranial lymph-paths. Although the dura and the pia are closely attached to the skull and the brain respectively, they are separated by an interval which, in turn, is subdivided into two compartments by the arachnoid. The outer of these clefts lies between the dura and the arachnoid and is called the subdural space ; the other, between the arachnoid and the pia, is the subarachnoid space. The first of these spaces is usually a mere capillary cleft, the arachnoid lying against the dura, and contains a small amount of a clear light straw- colored fluid of the nature of lymph. The second one, although much more capa- cious than the subdural, is crossed by so many trabeculae of arachnoid tissue that in many places it acquires the character of a sponge-like tissue, rather than of an unbroken channel. Whilst anatomically the subdural and the subarachnoid spaces are distinct and nowhere communicate, as demonstrated by careful artificial injections into the subdural cleft, it is probable that during life the cerebro-spinal fluid finds its way through the thin partition of arachnoid tissue and enters the subdural space. The interstices of the arachnoid are filled with the cerebro-spinal fluid, a modified lymph, which is produced by the choroid plexuses within the ventricles. After dis- tending these cavities, the fluid gains the subarachnoid space .by way of the foramen of Majendie and trie foramina of Luschka situated in the attenuated roof of the fourth 1 Die Grosshirnrinde des Menschen, 1907 2 Amer. Journal of Anat., vol. v., 1906. 3 Amer. Journal of Anat., vol. iv., 1905. 1 198 HUMAN ANATOMY. ventricle (page uoo). The paths by which the fluids collected within the brain- membrane are carried off, thereby insuring under normal conditions the prevention of excessive intracranial tension, will be considered with the description of the dura and arachnoid, suffice it here to mention the sheaths contributed by these envelopes along the nerve-trunks as they leave the cranium and the Pacchionian bodies as the most important. The Dura Mater. This structure (dura mater encephali) is a dense and inelas- tic fibrous membrane, which lines the inner surface of the cranial cavity and sends partitions between the divisions of the brain. In contrast to its relation within the vertebral canal, where it is separated from the bony wall by a considerable space (page 1022), within the brain-case the dura everywhere lies closely applied to the b one a relation essential in fulfilling its function as a blood-carrying organ for the nutrition of the cranium. Around the margins of the larger foramina, over the pro- jecting inequalities of the fossae and along the lines of the more important sutures, the attachment of the dura to the skull is particularly close, and at some of these points FIG. 1033. Falx cerebri Junction of fal: and tentorium Tentorium cerebelli Opening for brain-stem / Diaphragrna sellae Free margins of tentorium Portion of skull removed, showing? partitions of dura in place. the foramina and the ununited sutures the dura is continuous with the periosteum covering the exterior of the skull. On separating the dura from the bom-, as may be readily done beneath the calvaria, except along the line of the sagittal suture, its outer surface is marked with the conspicuous ridges produced by the meningeal blood-vessels, which lie much nearer the outer than the inner surface of the mem- brane and hence give rise to the corresponding furrows seen on the inner aspect of the skull. In addition, the roughened surface of separation is beset with fine fibrous processes, the larger of which contain minute blood-vessels, that have been drawn out of the canals affording passage for the nutrient twigs. The inner aspect of the dura, on the contrary, is smooth and shinny and clothed with a layer of endothelium which lines the outer wall of the subdural space. As the nerves enter the foramina in their exit from the cranium, they receive a tubular prolongation of the dura which accompanies the nerve-trunk for a short distance as the dural sheath, separated from the nerve by the underlying snbdural cleft, and finally becomes con- tinuous with the epineurinm, whilst the snbdural space communicates with the lymph-clefts within the connective tissue envelopes of the nerves. The dural sheath THE MEMBRANES OF THE BRAIN. 1199 surrounding the optic nerve through its entire length is noteworthy on account of its unusual thickness and completeness (page 1223). The two layers of which the dura is composed are, for the most part, so closely united that only a single membrane is demonstrable. The division into two layers, however, is evident in certain localities, particularly in the middle fossa at the base of the skull. Here, on each side of the body of the sphenoid bone, the layers separate to form the cavernous sinus and, within the sella turcica, enclose the pituitary body. Over the apex of the petrous portion of the temporal bone they include between them a space, the cavum Meckelii, which lodges the Gasserian ganglion, whilst over the aqueductus vestibuli the dilated end of the endolymphatic duct, the saccus endolymphaticus, continued from the membranous labyrinth, lies between the two layers of the dura. Further, along the lines of its attachment to the skull beneath the sagittal suture, to the crucial ridges on the occipital bone and to the ridges of the petrous bones, the inner layer of the dura separates from the outer and forms partitions, which project inward and imperfectly subdivide the cranial cavity into compartments occupied by the larger divisions of the brain, as well as enclose the blood-spaces, known as the dural sinuses. These spaces have been described with the veins (page 867) and will be here only incidentally mentioned in connection with the partitions in which they lie. On either side of the superior longitudinal sinus, the layers of the dura exhibit local areas of separation, which prolong laterally the lumen of the venous channel. These parasinoidal spaces, the lacuna venostz laterales, are of consequence as receiving many of the cerebral veins and as affording additional localities in which the Pacchionian bodies may come into relation with the blood- stream. The septa thus formed by duplicatures of the inner dural layer are : ( i ) the falx cerebri, (2) the tcntorium cerebelli, (3) the falx cerebelli, and (4) the dia- phragma sellce. The falx cerebri is a sickle-shaped partition which occupies the greater part of the longitudinal fissure separating the cerebral hemispheres. Its upper and longer border is attached in the mid-line and extends from the cristi galli of the ethmoid bone in front to the internal occipital protuberance behind and encloses the superior longitudinal sinus. The latter channel appears triangular in cross-section (Fig. 1034), the upward placed base being the outer or parietal layer of the dura and the sides the separated lamellae of the falx. The lower and shorter border of the falx is free and more sharply arched than is the upper, and extends from the hind part of the cristi galli to the highest point of the tentorium. Within its posterior half it encloses the inferior longitudinal sinus. The base of the falx is oblique, approxi- mately at 45 with the horizontal plane, and attached to the upper surface of the tentorium in the sagittal plane. Along this junction lies the straight sinus. The narrow forepart of the falx is the thinnest portion of the partition and is often, more especially during the latter half of life, the seat of perforations, which may be so numerous as to reduce this part of the septum to a fenestrated membrane. Occasional deposits of true bone are found within the falx, which may be without pathological significance and represent the constant ossification of this partition seen in some aquatic mammals. The tentorium cerebelli is the large tent-like partition that roofs in the pos- terior fossa of the skull and separates the cerebellum from the overlying posterior parts of the cerebral hemispheres. In its general form it is crescentic, the longer convex border lying behind and attached to the posterior and lateral margins of the posterior cranial fossa, and the shorter concave anterior border curving backward and upward from the anterior clinoid processes. The upper surface of the tentorium is attached by its entire width to the falx cerebri along the mesial plane, and in this manner the partition is maintained in a tensed condition. The sides of the tent-like fold are, however, not simply flat, but present a slight downwardly directed convexity in both the sagittal and frontal planes. The peculiar curvature of the under surface of the tentorium is reproduced, in reversed relief, by the upper aspect of the cerebellum which is accurately applied to the partition. The posterior border of the tentorium is attached to the horizontal ridge crossing the occipital bone ; farther outward, on each side, it is fixed to the postero-inferior angle of the parietal bone and, continuing forward and inward, to the upper border I2OO HUMAN ANATOMY. of the- petrous portion of the temporal bone, and thence to thev- posterior clinoid pro- cess. From the internal occipital protuberance as far as the parietal bone, this line of attachment corresponds with the course of the enclosed lateral sinus (page 867) ; but beyond, the venous channel leaves the tentorium in its descent to the jugular fora- men, the farther attachment of the tentorium enclosing the superior petrosal sinus. Since the anterior border of the tentorium springs, on each side, from the anterior clinoid process, it follows that the two margins of the crescentic septum intersect in advance of the apex of the petrous bone, the posterior border turning inward to the posterior clinoid process, whilst the anterior margin is connected with the anterior process. The free tentorial border, in conjunction with the dorsum sellae, defines an arched opening, the incisura tcntorii, through which the mesencephalic portion of the brain-stem is continued into the cerebral hemispheres, the highest point of this aperture lying just behind the splenium of the corpus callosum. FIG. 1034. -Skin Superior longitudinal sinus Falx cerebri Cerebral hemisphere Posterior horn of lateral ventricle Tentorium Left lateral sinus Superior worm Fibro-aponeurotic layers of scalp Parietal layer of du'ra Bone Inferior longitudi- nal sinus, cut obliquely Posterior horn of lateral ventricle Tentorium Right lateral sinus erebellum Inferior worm Occipital sinus Frontal section of head, viewed from behind, showing relations of dura mater to cerebral hemispheres and cerebellum and position of sinuses. The falx cerebelli is a small sickel-shaped dural fold which descends in the mid-line from the under surface of the tentorium, with which its broader upper end is attached, towards the foramen magnum. In the vicinity of this opening its apex bifurcates into smaller folds that fade away on either side of the foramen. Its poste- rior border, attached to the vertical internal occipital crest, contains the small occipital sinuses, or sinus when these channels are fused. The narrow crescent projects into the posterior cerebellar notch and thus intervenes between the hemispheres of the cerebellum. The diaphragma sellae is an oval septum of dura, which roofs in the pituitary fossa and is continuous on cither side with the visceral or inner layer of the wall of the cavernous sinus. The diaphragm contains a small aperture, the foramen dia- phragmatis, through which the infumlibulum connects the enclosed pituitary body with the brain. The structure of the duni presents the histological features of dense hbro- elastic tissue, in which the elastic constituents, however, are greatly overshadowed by the white fibrous bundles. The inner surface of the dura is covered with endo- THE MEMBRANES OF THE BRAIN. I2OI thelial plates which constitute the immediate outer wall of the subdural lymph-space. Patches of endothelium sometimes seen on the external aspect of the membrane are regarded as indications of uncertain epidural lymph-spaces. The outer or periosteal lamella is less compact and richer in cells than the inner layer and contains a wide- meshed net-work of capillary blood-vessels. The larger bundles of fibrous tissue are disposed with some order so that a definite radiation from the two ends of the falx cerebri may often be recognized. Within the last-named fold, from the point where the free border of the falx and that of the tentorium meet, the fibres radiate towards the convex attached margin, some, therefore, arching far forward. From the same point the fibres within the tentorium pass laterally. Minute calcareous concretions, also known as brain-sand or acervulus, are not infrequently found in the otherwise normal dura, especially in subjects of advanced years. They consist of aggregations of particles of calcium carbonate and phosphate arranged in concentric layers and surrounded by a capsule of fibrous tissue. They seldom exceed a diameter of .070 .080 mm., but may be so numer- ous that a distinctly gritty feel is imparted to the inner surface of the dura. The blood-vessels within the dura are the branches of the meningeal arteries, and their accompanying veins, derived from various sources from the ophthalmic, FIG. 1035. Medullary branch Larger pial artery White matter Pia within fissure- Portion of injected cerebral cortex, showing capillary supply of gray and white matter. X 18. internal maxillary, vertebral, ascending pharyngeal and occipital arteries. They are destined, for the most part, for the nutrition of the skull, which they enter as minute twigs through innumerable openings in the bone. Some few perforating arteries traverse the bone and communicate with the pericranial vessels, whilst others are distributed to the tissue of the dura itself. Definite lymphatics have not been demonstrated within the dura, the system of absorbent vessels being represented within this membrane by numerous lymph- spaces within the connective tissue stroma. These communicate indirectly with the subdural lymph-space, the contained fluid escaping at the foramina chiefly into the lymph-paths surrounding the cranial nerves, but to some extent also directly into the venous sinuses around the Pacchionian bodies. The nerves of the dura include principally sympathetic filaments, distributed to the blood-vessels and to the bone, and sensory fibres. The immediate sources are the meningeal twigs contributed by the trigeminus, the vagus and the hypo- glossal nerves. Those from the last source, apparently from the twelfth, are really sensory fibres from the upper cervical spinal nerves and sympathetic filaments from the cervical sympathetic cord ; in the other cases, the sensory fibres are probably accompanied by sympathetic filaments, which secure this companionship by means of 76 1202 III MAN ANATOMY. Gray matter White matter the communications which these cranial nerves have with the plexuses surrounding the arteries or with the superior cervical ganglion. The sensory nerves of the dura form a rich net-work of delicate twigs from which filaments have been traced to the inner surface in relation to which some end in bulbous expansions. The Pia Mater. This membrane (pia mater encephali) lies next the nervous substance and, being the vascular tunic supporting the blood-vessels for the nutrition of the brain, follows accurately all the inequalities of its exterior. It not only closely invests the exposed surface of the cerebrum and cerebellum, but penetrates along the sides and to the bottom of all the fissures as well, although within the small shallow fissures of the cerebellum a distinct process of pia mater can not be demonstrated. Additionally, in certain places where the wall of the brain-tube is very thin, the pia pushes before it the attenuated layer and seemingly gains entrance into the ventricles. Examples of such invagination are afforded in the relations of the velum interpositum and the choroid plexuses to the lateral and third ventricles (page 1162) and of the similar plexuses in the roof of the FIG. 1036. fourth ventricle (page 1 100). The pia also contributes a sheath to each nerve, or to its larger component bundles, as the nerve leaves the brain at its super- ficial origin, which sheath surrounds the nerve during its intracranial course and for a variable distance beyond its emergence from the dural sac. The pia is so thin that the larger vessels, especially at the base of the brain, lie within the subarachnoid space, although in most cases they are enclosed within a delicate investment of pial tissue. The smaller vessels, however, ramify within the pia and in this situation divide into the twigs which directly enter the subjacent nervous tissue. As they penetrate the latter they are accompanied by a sheath of pia, which thus gains the nervous substance within which it fol- lows the subdivisions of the arteriole, even their smallest ramifications. Whilst within the pia the larger arteries form frequent anastomoses, the smaller twigs remain isolated and, being ' ' end-arteries, ' ' on entering the subjacent gray matter break up into terminal ramifications which furnish the only supply for a particular district. The capillary net-work within the cortical gray matter is much closer than that within the subjacent white matter (Fig. 1035), in which the vessels are comparatively meagre. Here and there larger medullary branches are seen traversing the cortex, to which they contribute but few twigs, to gain the white matter within which they find their distribution. The contrast in richness between the supply of the gray substance and that of the adjoining white matter is not limited to the cerebral cortex, but is also well shown when the internal nuclei are examined (Fig. 1036). The veins emerge from the surface of the brain, but do not retain a definite relation to the arteries, since, instead of following the latter to their points of entrance, they for the most part seek the dural sinuses into which they empty. The special invaginating layers of pia mater, the velum interpositum (page 1 162) and the choroid plexuses of the lateral and third ventricles, and the choroid plexus of the fourth ventricle (page noo) have been described in connection with the appro- priate parts of the brain. Attention may be again called to the manner in which the velum interpositum and the associated plexuses are formed (page 1194), and to the Portion of injected dentate nucleus of cerebellum, show- ing capillary supply of internal nucleus. X 20. THE MEMBRANES OF THE BRAIN. 1203 Vascular tuft fact that the apparent ingrowth of the pia beneath the spleniurn and the fornix to reach its final position over the third and within the lateral ventricles never occurs, the growth actually taking place in the opposite direction, that is, from before backward (page 1194). The structure of the pia mater presents little for special mention. The membrane consists essentially of a delicate connective tissue envelope in which inter- lacing bundles of white fibrous tissue, intermingled with elastic fibres and containing numerous nuclei, are the chief features. As the arteries leave the pia to enter the brain, they receive sheaths of pial tissue within which are prolonged the lymph- spaces enclosed between the trabeculae of the pial membrane. Along the basal surface of the brain, especially on the ventral aspect of the medulla, the pia frequently contains deeply pigmented branched connective tissue cells. These may be so numerous, particularly in aged subjects, that the membrane appears of a distinct brownish hue. The numerous nerves encountered within the pia mater are chiefly sympathetic filaments destined for the walls of the blood-vessels and derived from the plexuses surrounding the internal carotid and the vertebral arteries. Additional nerve- fibres, probably sensory in function, occur in small numbers. The mode of their FIG. 1037. ending is uncertain, although terminal bul- r^ bus expansions and tactile corpuscles have ^ fij . been observed. The Arachnoid. This covering (arachnoidea encephali), the intermediate membrane of the brain, is a delicate con- nective tissue envelope that intervenes between the dura externally and the pia internally. In contrast to the last-named membrane, which follows closely all the irregularities of the sunken as well as of the free surface of the cerebrum, the arachnoid is intimately related to the convolutions only along their convexities, and on arriving at the margins of the intervening fissures stretches across these furrows to the con- volutions beyond. From this arrangement it follows that intervals, more or less tri- angular on section, are left over the lines of the fissures between the arachnoid and the fold of pia which dips into the sulcus. These clefts form a system of intercom- municating channels which are parts of the general subarachnoid space. Over the summits of the convolutions, the arachnoid and pia are so intimately united that they constitute practically a single membrane, whilst, where parted by the subarachnoid space, they are connected only by the trabeculae of arachnoid tissue. In many places, however, where the intervening cleft is not wide, these trabeculae are so numerous that the space is occupied by a delicate reticulum and becomes converted into a layer of loose subarachnoid tissue. Where, on the other hand, the arachnoid encloses spaces of considerable size, as it does on the basal surface of the brain, the trabeculae are reduced in number to relatively few long, cobweb-like threads that extend from the arachnoid to the pia mater. Over the upper and outer aspects of the cerebrum and cerebellum the arachnoid follows, in a general way, the contour of the brain. On the ventral surface, however, it bridges from the median elevation presented by the brain-stem to the adjacent promi- nences offered by the cerebellum and the cerebral hemispheres. The irregular spaces thus enclosed contain considerable quantities of cerebro-spinal fluid and are known as the cisternae subarachnoidales, of which several subdivisions are recognized according to locality. The cisterna magna (cisterna cerebellomedullaris), the largest of these spaces, overlies the dorsal surface of the brain-stem and is continuous through the foramen Velum inter- positum Small portion of injected choroid plexus of lateral ventricle ; surface view. 1204 HUMAN ANATOMY. magnum with the posterior part of the subarachnoid space of the cord. The arach- noid passes from the back part of the under aspect of the cerebellum to the posterior surface of the medulla and thus encloses a considerable space which at the sides of the medulla is continuous with the upward prolongation of the anterior subdural space of the cord. The lower part of the brain-stem is thus completely surrounded by the subarachnoid cavity. The ventral surface of the pons is enveloped by the upward extension of the anterior part of the spinal arachnoid, the cleft so enclosed constituting the cisterna pontis, of which a median and two lateral subdivisions may be recognized. From the upper ventral border of the pons the arachnoid passes forward to the orbital surface of the frontal lobes, covering the corpora mam- millaria, the infundibulum and the optic chiasm, and laterally to the adjacent project- ing temporal lobes and thence, covering in the transverse stem of the Sylvian fissures, FIG. 1038. Olfactory tract .Optic chiasm Internal carotid artery Basilar artery Extension along 'longitudinal fissure _Extension along Sylvian fissure -Cisterna basalis -Cisterna pontis Vertebral arteries Cisterna magna Inferior aspect of brain covered with pia and arachnoid, showing large subarachnoid spaces. to the frontal lobes. This large space, which includes the deep depression on the basal surface of the brain, is the cisterna basalis. It is imperfectly subdivided by incomplete septa of arachnoid tissue into secondary compartments, one of which lies between the peduncles (cisterna interpeduncularis), another behind the optic commis- sure (cisterna chinsmatis) and a third above and in front of the chiasm (cisterna laminae terminalis). Anteriorly the cisterna basalis is continued over the convex dorsal surface of the corpus callosum (cisterna corporis callosi), and on cither side along the stem of the Sylvian fissure (cisterna tissurae lateralis ). Within the median region of the cisterna basalis lie the large arterial trunks forming the circle- of XYillis. These vessels are invested with delicate sheaths of arachnoid, which accompany the smaller branches until they enter the vascular membrane to become pial vessels. The arachnoid also contributes sheaths to the cranial nerves as they pass from their superficial origins to the points where they pierce the dura, these sheaths over- lie those derived from the pia and, as do the latter, accompany the nerve-trunks for a 1205 variable but usually short distance beyond their emergence from the dural sac. The arachnoid sheath is especially well marked along the optic nerve, which it follows as far as the eyeball, and completely subdivides the space between the pial and dural FIG. 1039. Pacchionian body Dura, reflected medially Cerebral vein Cerebral vein Pacchionian body Portion of superior surface of right hemisphere covered by pia and arachnoid ; dura has been partly separated and reflected towards mid-line to expose Pacchionian bodies and cerebral veins, which are seen entering superior longitudinal sinus. sheaths into a subdural and a subarachnoid perineural compartment, directly contin- uous with the corresponding intracranial spaces. As previously noted, the cerebro-spinal fluid secreted within the ventricles escapes through the openings in the roof of the fourth ventricle foramen of Majendie and the foramina of Luschka (page uoo) into the subarachnoid space. After filling the cisterna magna and the other large spaces on the basal surface of the brain and surrounding the spinal cord, the fluid finds its way into the smaller spaces on the exterior of the cerebrum. In this manner the entire mass of nervous tissue is enveloped by a more or less extensive cushion of fluid which, particularly at the base of the brain, is well adapted to protect the enclosed delicate structures from undue concussion. Since the cerebro-spinal fluid is being continuously secreted, it is evi- dent that some adequate means of escape must be provided to insure, under normal conditions, the maintenance of intra- cranial and intracerebral pressure within due limits. The paths by which this is accomplished include : ( i ) the extension of the subarachnoid space along the nerve-trunks, and (2) the villous projections of arachnoid tissue, the Pacchionian bodies, along the course of the dural blood-sinuses. The Pacchionian bodies (gran- ulationes arachnoidales) are numerous cauliflower-like excrescences of the arachnoid, for the most part small but occasionally reaching a diameter of 5 mm. or over, which lie on the outer surface of the membrane along the course of the dural venous sinuses. Their favorite site is on either side of FIG. 1040. Diagram showing relations of Pacchionian bodies to blood-spaces and dura; B, bone, S, longitudinal sinus; /., lacunas ; P, Pacchionian bodies ; V, cerebral vein emptying into lacuna; S>, subdural space; dura is blue and pia is red, intervening tissue is arachnoid ; A. the superior longitudinal sinus, where they occur in groups, although they occur in smaller number and size in connec- tion with other sinuses, as the lateral, cavernous and straight. They consist entirely of arachnoid tissue and contain no blood-vessels. Although lying mostly at the side of the longitudinal sinus with which they are then indirectly related through the lateral diverticula, the lacuna laterales or blood-lakes, in some instances 1206 HUMAN ANATOMY. they encroach upon the lumen of the main channel itself, within which they appear as irregularly rounded projections on its lateral walls. Whatever their relation, whether with the sinus or the lateral diverticula, the Pacchionian bodies never lie free within the blood-space, but are always separated from the latter by the dural wall. Over the summit of the elevation the dura becomes greatly attenuated, but never entirely disappears, so that only a thin membrane and the subdural cleft, theoretically present but practically more or less obliterated, intervene between the subarachnoid spaces and the blood-stream. This partition offers little obstruction to the passage of the cerebro-spinal fluid, which, unless the pressure within the venous channel is higher than that within the subarachnoid space, passes from the latter into the sinus and thus relieves the intracranial tension. When well developed, as they often are after adolescence but never during childhood when they are small and rudimentary, the Pacchionian bodies are frequently lodged in depressions within the calvaria, whose inner surface is sometimes so deeply pitted that the bom- in places is translucent. THE BLOOD-VESSELS OF THE BRAIN. The course and distribution of the individual blood-vessels supplying and drain- ing the nervous tissue of the brain have been described in the sections on the Arteries (page 746) and the Veins (page 861). It remains, therefore, only to consider at this place the more general relations concerning these vessels. The arteries supplying the brain are derived from two chief sources the inter- nal carotid and the vertebral arteries. After entering the cranium these vessels and their branches form the remarkable anastomotic circuit known as the circle of Willis (page 760). The latter gives off, in a general way, two sets of branches, the gang- lionic for the most part short vessels which soon plunge into the nervous mass to supply eventually the overlying internal nuclei, the corpora striata and the optic thalami and the cortical, which pursue a superficial course and are carried by the pia mater to all parts of the extensive sheet of cortical gray substance, as well as to the subjacent tracts of medullary white matter. The medulla oblongata and the pons are supplied by branches from the anterior spinal, the vertebral, the basilar and the posterior cerebral arteries. These branches gain the nervous substance as two sets, the radicular and the median. The radicular branches follow the nerve- roots and, just before reaching the superficial origins of the nerves, divide into peripheral and central twigs, the former being distributed superficially and the latter following the root-fibres to their nuclei. The median branches are numerous minute vessels which ascend within tin- median raphe towards the floor of the fourth ventricle and assist the centrally directed twigs of the radicular branches in supplying the nuclei of the nerves situated within that region. Those supplying the nuclei of the hypoglossal and the bulbar portion of the spinal accessory nerves are derivations from the anterior spinal arteries ; those to the nuclei of the vagus, the glosso- pharyngeal and the auditory are from the vertebral as they join to form the basilar ; whilst those to the nuclei of the facial, the abducent and the trigeminal are from the basilar. The choroid plexus of the fourth ventricle is provided with branches from the posterior cerelnll.it arteries. The cerebellum receives its supply from three arteries, the anterior and posterior in- ferior and the superior, cerebellar. The general course of these vessels is approximately at right angles to the direction of the fissures and folia of the hemispheres. In the mid-brain the interpcduncular spaced provided with branches from the basilar and the posterior cerebral arter- ies ; the cerebral peduncles with those from the posterior communicating and the terminal part of the basilar; and the corpora qnadrigcmina with those from the posterior cerebral, additional twigs passing from the superior cerebellar to the inferior colliculi. The thalamus is supplied by branches, all end-arteries, from different sources, those for its antero-median portion being from the posterior communicating, those for its antero-lateral por- tion from the middle cerebral, whilst those for its remaining parts, as well as for the pineal and the geniculate bodies, are from the posterior cerebral. The last vessel also supplies the velum interpositnm and the choroid plexus of the third ventricle. The structures on the base of the brain, such as the corpora mammillaria, the tuber cine- reum, the infundibulum and the pituitary body, receive twigs from the posterior communicating arteries. The optic chiasm and tract are supplied with branches from the anterior cerebral, tin- anterior communicating, the internal carotid, the posterior communicating and the anterior choroidal .arteries. PRACTICAL CONSIDERATIONS: THE BRAIN. 1207 The corpus striatum, both the caudate and lenticular nuclei, are supplied chiefly by branches from the middle cerebral artery, which pierce the anterior perforated space and, as the lenticular, lenticulo-striate and lenticulo-thalamic vessels, all end-arteries, traverse the lenticular nucleus and the internal capsule and terminate in the caudate nucleus and the thalamus. One of the lenticulo-striate arteries, which pierces the outer part of the putamen, was named by Charcot the "artery of cerebral hemorrhage" since it is frequently ruptured. The choroid plexus of the lateral ventricle receives its blood-supply from the anterior and posterior choroidal arteries. The first of these, given off by the internal carotid artery, enters the anterior and lower part of the choroidal fissure and takes part in forming the most depend- ent portion of the vascular complex which overlies the hippocampus. The posterior choroidal artery, usually represented by a number of small twigs, is derived from the posterior cerebral and enters the upper part of the fissure. After supplying the velum interpositum, it completes the choroid plexus in the descending horn and in the body of the lateral ventricle. The cerebral hemispheres are supplied by the cortical branches of the anterior, middle and posterior cerebral arteries. Of these the middle one is the largest and is distributed to the most extensive area, which embraces the greater part but not all of the external surface of the hemisphere. This vessel also supplies the outer half or more of the orbital surface and the anterior part of the temporal lobe. The anterior cerebral is essentially the artery of the mesial surface, the anterior two-thirds of which, in conjunction with an adjoining zone on the external and on the orbital surface, it supplies. The distribution of the posterior cerebral is chiefly on the mesial and tentorial surface of the occipito-temporal region, and in addition an adjoining strip along the postero-inferior margin of the hemisphere. It follows, therefore, that, with the exception of the occipital lobe, which is entirely supplied by the posterior cerebral artery, all of the conventional divisions of the hemisphere receive their arterial supply from more than a single source. The frontal lobe is supplied by the anterior cerebral artery : over its entire mesial surface ; over the superior and the anterior two-thirds of the middle frontal convolutions and the upper end of the precentral convolution ; and over the orbital surface internal to the orbital sulcus. Over all the remaining parts, the frontal lobe receives the branches of the middle cerebral artery. The parietal lobe is supplied by the middle cerebral artery on the external surface, with the exception of a narrow strip along the upper border ; this zone, together with the mesial surface of the lobe, is supplied by the anterior cerebral artery. The occipital lobe is supplied exclusively by the posterior cerebral artery. The temporal lobe is supplied by the middle cerebral artery over its superior and the upper half of the middle temporal convolution with the tip of the lobe ; the remainder of the lobe receives the branches of the posterior cerebral. The limbic lobe shares in the distribution of the anterior and posterior cerebral arteries, the district of the former including the gyrus callosum to the vicinity of the isthmus, whilst that of the posterior cerebral includes the remainder of the lobe. The veins returning the blood from the brain are all tributaries of the dural sinuses, and they therefore only to a limited degree follow the course of the cerebral arteries. They are further distinguished by the absence of valves. The superior cerebral veins, after emerging from the surface of the brain, course within the pia over the convex aspect of the hemisphere and proceed, for the most part, towards the superior longitudinal sinus into which they open, either directly or through the lacume laterales, by from 12-15 trunks. The veins draining the structures situated around the lateral and third ventricles are tributary to the paired lesser veins of Galen, which run backward within the velum interpositum and, emerging below the splenium, unite to form the great vein of Galen. This vessel joins with the inferior longitudinal sinus to form the straight sinus, which is lodged in the line of juncture between the falx cerebri and the tentorium cerebelli. PRACTICAL CONSIDERATIONS : THE BRAIN AND ITS MEMBRANES. Congenital Errors of Development. Various defects of development of the brain and its membranes are not uncommon. The brain may be absent (anen- cephalus), it may escape from the skull (exencephalus) , the brain, membranes and vessels may be only rudimentary (pseudencephalus}, or there may be arrest of development in any limited portion ( porencephalus a name more suitably applied when there is a marked depression in the surface of the brain). The brain as a whole may be defective (microcephalus} , or it may be abnormally large (macroccphahis}. I2o8 HUMAN ANATOMY. The most common enlargement of the head, hydroccphalus, is due to a retention of cerebro-spinal fluid within the cranium, ordinarily within the ventricles, but some- times in the subarachnoid space. It is usually a congenital condition ; its cause is not clearly known. It is believed by many that it is due to a prenatal inflam- mation of the ventricular ependyma, and by others to a disarrangement of the orifices of communication between the ventricles (Luschka, Monroe, and Neurath). The aqueduct of Sylvius has been found obliterated, and inflammatory processes have been seen about the foramen of Monroe. Congenital defective ossification of the skull may result in a gap through which may protrude a portion of the meninges with or without brain substance. If such a protrusion consists of a meningeal sac containing only fluid, it is called a meningocele. If it contains a portion of the brain also, it is an cnccphalocclc, and if the protruded portion of the brain encloses a portion of a ventricle, a hydrenccphalocelc. Such tumors may be concealed from view at the base of the skull, or in the pharynx, or may protrude into the nose or orbit. They are usually in the median line and most frequently in the occipital region. Next in frequency they occur at the fronto-nasal suture, and more rarely in other parts of the skull. Pressure on the tumor will often reduce it partly or completely within the cranium, but in the latter case symptoms of pressure on the brain will arise. Violent expiratory efforts, as in crying or coughing, which increase the cerebral congestion, render the tumor more tense. The Meninges. Diseases of the meninges are relatively more common than those of the brain proper, and many conditions often spoken of as brain diseases are affections of the meninges, the pia being closely adherent to the brain and extending into the fissures. Inflammation of the dura is called pachymeningitis , of the pia and arachnoid together lepto-meningitis. External pachymeningitis is usually secondary to disease of the cranial bones, traumatism, infection, or tumors. It is most frequently the result of ear disease, and is therefore generally of surgical interest. Internal pachymeningilis is apt to be associated with effusions of blood into the subdural space ; they may cover a considerable area without producing marked symp- toms, or they may be encapsulated (hsematomata of the dura mater), and may reach the size of a man's fist, causing compression of the brain. Occasionally they become purulent. The blood or pus may gravitate to the base of the brain in the region of the cerebellum, pons, and medulla, when the pressure symptoms will be more serious ; or it may find its way into the spinal canal. The dura is especially adherent at the base of the skull and, to some degree, at the sutures of the vault. In the rest of the vault it is loosely attached, and accord- ing to Tillaux, particularly so in the temporal region. Collections of blood may accumulate between the dura and the bone (extradural hemorrhage}. This variety of intracranial hemorrhage is commonly the result of rupture of one of the branches of the middle meningeal artery in the temporal region, the effused blood separating the loosely attached dura. If the blood is poured out rapidly, compression symptoms will soon appear, but if the hemorrhage is slow, the escape of cerebro-spinal fluid into the spinal canal permits of more delay in the appearance of those symptoms. The patient has often time to recover, at least partially, from the unconsciousness of concussion before that of compression appears ; and it is this recovery of intelligence which is most characteristic of the condition. There will often be localizing symptoms indicating the part of the brain cortex which is irritated or compressed. Subdural hemorrhage may follow the rupture of a number of small vessels, either of the pia or dura under a depressed fracture ; or it may come from a large vessel, particularly the middle cerebral. The symptoms and treatment are very much the same as in the extradural variety. In children extradural hemorrhage is very rare, because of the relatively firmer attachment of the dura during the period of growth. The blood may escape under the scalp through a line- of fracture in the skull ; or, what is more likely, it may pass through a tear in the dura into the subdural space. In fractures of" the base of the skull, at any age, owing to the adhesion of the dura, the latter is likely to be torn ; cerebro-spinal fluid mav escape into the adjacent air cavities, as into the nose, pharynx or middle ear. A close adhesion of the dura to the bone, as sometimes found at PRACTICAL CONSIDERATIONS : THE BRAIN. 1209 operation, indicates a previous inflammation, as does any tendency of the arachnoid to adhere to the dura, since these two are normally not adherent. The arachnoid, however, is normally closely attached to the pia, and for practical purposes they are usually considered as one layer, the lepto-meninx. Inflammation of this layer lepto-meningitis may attack the convexity or the base of the brain, and may be primary or may be secondary to other diseases, usually purulent infections. It is asserted that the primary disease attacks, as a rule, the base, the secondary, the convexity of the brain ; but this is not beyond dispute. Tuberculous meningitis is frequently found at the base, but miliary tubercles are not uncommon on the convexity of the brain. The exudate which is deposited at the base frequently leads to irritation or paralysis from pressure on the cranial nerves in close relation to the under surface of the brain. Tumors growing at the base of the brain produce localizing symptoms early by pressing on the adjacent cranial nerves. A single nerve may be involved, but more commonly a combined paralysis from involvement of several nerves results. The cerebro-spinal flidd is found in the subdural and subarachnoid spaces, and in the ventricles. Over the vault it is comparatively scanty in both spaces. At the base, however, in the subarachnoid space of the middle and posterior fossae, it is abundant, forming an excellent support and protection to the most delicate part of the brain, that containing the vital centres. The frontal lobes, of much less impor- tance as to vital function, rest directly on the bone in the anterior fossa ; and are there- fore more subject to direct traumatic influences. The fact that the subarachnoid space is continuous with the ventricles through the foramina of Magendie and of Luschka, and communicates freely at the foramen magnum with the subarachnoid space of the cord, explains how excess of pressure within the cranium at one part may be relieved by escape of fluid to other parts. It explains also why pressure on a spina bifida will sometimes produce symptoms of cerebral compression ; and vice versa, why the increased congestion of the cerebral vessels from expiratory efforts, as in coughing, will increase the tension in the spinal tumor. Occlusion of the foramen of Magendie, by the products of inflammation, may cause increase of fluid from retention in the ventricles, with the development of hydrocephalus, and it is in this way that internal hydrocephalus occasionally follows meningitis. For the purpose of determining the cause of this condition, subarach- noid fluid is sometimes withdrawn through a hollow needle. The lateral ventricles can be tapped through a trephine opening 3 cm. (i^ in.) behind the external auditory meatus, and the same distance above Reid's base line drawn from the lower margin of the orbit through the middle of the external auditory meatus. The needle is passed towards a point on the opposite side of the skull, 6.5-7.5 cm - ( 2 /^-3 m -) vertically above the external auditory meatus. Under normal circumstances the ventricle is from 5-5.6 cm. (22*^ in.) from the surface, but if the ventricle is distended the distance is shorter. By a trephine opening in the occipital bone in the subcerebellar region, the subarachnoid fluid has been reached at the base of the brain where it is most abundant. Lumbar puncture for withdrawing cerebro-spinal fluid for diagnostic and thera- peutic purposes is sometimes employed. The needle should be introduced between the third and fourth, or between the fourth and fifth lumbar vertebrae, at the level of the lower border of the spinous process, or opposite its lower third, and about I cm. from the median line. It should be passed somewhat upward between the sloping laminae, and should be continued inward toward the canal until, by the diminished resistance, it is recognized that the point of the needle has entered the subarachnoid space. The Brain. Of all the affections of the brain, hemorrhage is the most frequent and most important, whilst in the spinal cord it is comparatively rare unless as a result of trauma. Hemorrhage from the meningeal vessels is most commonly due to trauma, but within the brain substance the usual cause is atheroma, sometimes with the production of miliary aneurisms. A sudden strain increases the intravascular tension and ruptures one of these diseased vessels, giving rise to pressure symptoms, depending on the seat and extent of the hemorrhage. i2io HUMAN ANATOMY. The cortex is supplied by pial vessels distinct from those supplying the basal ganglia and adjoining regions. The latter come directly from the branches of the circle of Willis at the base. The cortical vessels anastomose ; those in the region of the basal ganglia do not. The latter are ' ' end arteries, ' ' so that when one is plugged by an embolus the part supplied is deprived of blood and undergoes necrosis (softening of the brain). In such a case the cortical supply would not be permanently interfered with. When a cortical arteriole is blocked, the anastomosis may furnish a sufficient collateral circulation to prevent necrosis in the affected part, but cortical softening is exceedingly common. When one of the arteries forming the circle of Willis is occluded, as an internal carotid by ligation of the common carotid, the anastomosis in the circle is so free that, in most cases, no marked effect is apparent. Cerebral disturbances, as delirium or convulsions, do occur in some cases, and in some are fatal. Even when both carotids are ligated, with an in- terval of some days or weeks, the operation is not more frequently followed by cere- bral disturbances than when only one is tied (Pilz). A case in which the patient lived after one carotid and one vertebral had been obliterated by disease, and the other carotid ligatured, has been reported (Rossi). In another case, although both carotids and both vertebrals had been occluded, the patient lived a considerable time afterward, the cerebral circulation being maintained through the medium of anas- tomosis of the inferior with the superior thyroids, and the deep cervical with the occipital artery (Davy). Occasionally ligation of the carotid has been followed by hemiplegia. The most common seat of intracerebral hemorrhage is near the basal ganglia in the region of the internal capsule. The artery most frequently at fault is a branch of the middle cerebral, the lenticulo-striate, or artery of Charcot (page 1207). Hemor- rhages occur with less frequency in other portions of the cerebrum, and much more rarely in the pons, medulla oblongata, and cerebellum. The symptoms produced by the hemorrhage are the result of destruction of tissue and of pressure upon adjacent parts, and will vary according to the seat of the lesion. Tumors or inflammatory products will produce essentially the same symptoms. Cerebral Localization. In order to understand the nature of the symptoms produced by brain lesions it will be necessary to study at least some of the functional areas of the cortex and their paths of conduction through the brain substance. Taylor has summarized as follows the researches of His and of Flechsig, which are of comparatively recent date and have thrown new and valuable light upon the functions possessed by the cortical regions of the brain, by the study' of their mode of development. Flechsig succeeded in following the various tracts through their myelination. The tracts which are functional earliest receive their myelin before the others. He has shown that the fibres in the spinal cord, medulla, pons and corpora quadrigemina are almost entirely medullated when the higher parts show little or no myelin. In the new-born child the cerebrum is almost entirely immature, and proportionately few of its fibres are medullated. According to Flechsig, the sensory paths in the brain first become medullau d, and may be observed developing one after another, beginning with that of smell and ending with that for auditory impulses from the periphery to the cortex. In this way it has been ascertained that the individual sensory paths terminate in tolerably sharply circumscribed cortical regions, for the most part widely removed from one another, being separated by masses of cortical substance which remain for a consid- erable period immature or undeveloped. The cortical sense areas thus mapped out correspond entirely to those regions of the surface of the brain which pathological observation has shown to stand in relation to the different qualities of sensation. Olfactory fibres are found to end mainly in the uncinate gyrus. Visual fibres have been traced to the occipital lobe in the neighborhood of the calcarine fissure, and auditory fibre* to the temporal lobe. Flechsig has further observed that new paths begin to develop from the points where certain of the sense fibres terminate and pur- sue a downward course. They can be followed from the cortex to the medulla and to the motor nuclei of the cord. These drsrcnding paths are mainly those known as the pyramidal or motor tracts, and the area from which they proceed, commonly called the Rolandic region, is, according to Flechsig, concerned also in the si -nsation PRACTICAL CONSIDERATIONS : THE BRAIN. I2II of touch ; he calls it the someesthetic area. It includes the precentral and postcentral convolutions, the paracentral lobule. The sensory fibres passing from the periph- ery to this area would appear to excite sensations of touch, pain, temperature, muscle- and tendon-sense, equilibrium, etc. This cortical region probably repre- sents a complex mass of sense centres rather than a single sensory area, and in addition to being a sensory field, the somaesthetic area is the great motor region of the brain. When this sensory-motor area and the various sensory areas are fully taken into account, there still remain about two-thirds of the cortex which appear to have noth- ing to do with the periphery. Flechsig calls these regions of the cortex ' ' associa- tion centres,'" as he believes they furnish arrangements for uniting the various central sense areas. The best known cortical areas are the motor, speech, visual, and auditory, al- though new contributions to our knowledge are being made from time to time. Re- cently Griinbaum and Sherrington have demonstrated in the cortex of the higher apes, including the orang and several species of the chimpanzee and gorilla, that the motor area was found in the whole length of the precentral convolution and the en- FIG. 1041. Left cerebral cortex illustrating diagrammatically motor zone and its subdivisions. (Mills.) tire length of the central fissure. It did not at any point extend behind the central fissure. They demonstrated other important facts in connection with this and, other areas. These results have been in part at least confirmed by recent histological re- searches, and by faradization of the human brain during operation for the purpose of more accurately identifying the relations of the opening to the area to be exposed. The most important, because the best known, area of the cortex, is that asso- ciated with the fissure of Rolando and the fissure of Sylvius. Before the publication of the experiments and observations just alluded to, the motor zone was regarded as extending over both central convolutions which lie one anterior and the other posterior to the central fissure or fissure of Rolando, also over the paracentral lobule on the median aspect of the hemisphere, and to some extent into the posterior extremities of the first and second convolutions. The trend of opinion is now in favor of the view that the motor region is entirely or almost en- tirely in front of the central fissure (Monakow, Mills). This is, of course, a matter of considerable importance in trephining for a tumor or hemorrhage supposed to be situated in this area, as instead of making the opening directly astride of the fissure of Rolando it would be better, if these views are correct, to operate with the idea of exposing a region two-thirds or three-fourths in front and one-third or one-fourth behind the central fissure. 1212 HUMAN ANATOMY. In the lower one-third or fourth of the motor zone are found the motor centres for \h&face and tongue, that is, for the facial and hypoglossal nerves. In the middle third or half are the arm centres. In the upper part of the region and paracentral lobe, are the centres for the lower extremity. Localized lesions of the motor zone may therefore produce a paralysis limited to one part controlled by the affected por- tion of the cortex, as of the face, arm or leg (monoplegia). The lesion is much more likely to involve two adjacent areas, as of the face and arm, or of the arm and leg, giving rise to a combined paralysis ; but no single lesion, unless it were crescentic in form, could involve at the same time the leg and face areas without including the intervening arm area. Within each of the larger areas a more specialized differentiation is possible, although none of them can be sharply defined, not even the larger. That the facial centre lies in the lower part of the anterior central convolution is certain, and it is believed that the upper and lower muscles of the face are each represented by a sepa- rate centre. In the upper and forward part of the face-area are represented the movements of the cheek and eye-lids ; in the posterior part the movements of the pharynx, platysma and jaws. FIG. 1042. Diagram illustrating probable relations of physiological areas and centres of lateral aspect of left cerebral hemisphere. ( Mills.) In the arm-area it is considered as certain that the centre for the movements of the thumb and index finger is below; above is that for the finger and hands; and in th highest part is that for the shoulder. In the posterior parts of the second frontal convolution and in a portion of the third frontal convolution are the centres for the associated lateral movements of the eyes and lateral movement of the head (Beevor and Horsley). Our knowledge of the more special localization within the leg centre is not at all exact, and the many views held are very contradictory. It is believed that the centres for the movements of the thigh, knee, foot, and toes, are arranged in the order named, from before backward on the lateral border of the hemisphere and in the paracentral lobe. A narrow zone for the movements of the trunk, as shown by Griinbaum and Sherrington, is located between the upper border of the arm-area and the lower border of the leg-area. It is now considered probable, however, that the cutaneous sensory centres are posterior to and in close contact with the motor centres in the postcentral convolution, while other centres for stereognostic perception and the muscular sense are located in the superior and inferior parietal convolutions. The speech centres are in the posterior part of the third left frontal convolution (Broca's convolution), in right-handed people in the first left temporal convolution, and perhaps in the left angular gyrus. PRACTICAL CONSIDERATIONS : THE BRAIN. 1213 In Broca's convolution is probably the centre for motor speech, and a lesion here gives motor aphasia, an inability to transform concepts into words, although the patient is conscious and the tongue can be moved. A minor part in speech is played by the posterior part of the right third frontal convolution, but in the left- handed it is probably the chief centre. In the first left temporal convolution is the auditory centre for speech, a lesion of which leads to a loss of memory for word-sounds, though the hearing may be undisturbed. The centre for memory of printed words is probably in the left angular gyrus ; and a lesion there probably causes a loss of the ability to read or to understand written language, though ordinary sight is undisturbed. The existence of a motor writing centre is doubtful (Oppenheim). If it exists, it is probably located in the posterior portion of the left second frontal convolution. We have no definite knowledge of the location of centres for smell and taste. That for smell is thought to lie in the uncinate gyrus. The centre for taste has been supposed to be in the anterior portion of the gyrus fornicatus, but it is not decided, although it is probably near the centre for smell. FIG. 1043. Diagram illustrating probable relations of physiological areas and centres of mesial aspect of left cerebral hemisphere. (Mills.} The auditory centre, as indicated,, is in the upper temporal convolution. It is very likely that the centre of each side is connected with both auditory nerves, so that a paralysis of one side by a unilateral lesion of one side may be compensated for by the centre of the opposite side. It is probable that no part of the cerebral cortex is absolutely without function, although the functions of some areas are very little known. Unilateral disease of the anterior portion of the frontal lobe may be extensive without notable symptoms of" any kind. The atrophy is often most marked here in general paralysis of the insane, and in other forms of dementia. It is generally agreed that the seat of " the higher psychical functions ' ' is located in the prefrontal lobes, the left side being perhaps more active than in the right. Reference has already been made to the relation of the occipital cortex to sight, and of the temporal to hearing. The cuneus and calcarine fissure together constitute a primary or lower cortical or visuo-sensory centre, while the lateral aspect of the occipital lobe is a visuo-psychic area, containing sub-areas or centres concerned with higher visual processes. Mind blindness, for instance, results from destructive lesion of the lateral occipital lobe, particularly if the lesion is a large one, in the left hemi- sphere, or if lesions of both occipital lobes are present. A lesion of the cuneo- calcarine cortex causes lateral homonymous hemianopsia. This may be produced I2i4 HUMAN ANATOMY. also by a lesion in the lateral portion of the occipital lobe, if it extends inwards sufficiently to interrupt the optic radiations. In spite of extensive researches the functions of the central ganglia are very little known. Lesions of the cerebellar hemispheres may not produce distinct phenomena until the median lobe or vermiform process is involved, when two especially charac- teristic symptoms .will almost certainly develop. These are a peculiar disturbance of equilibrium with a staggering gait (cerebellar ataxia), and a troublesome vertigo. Although the patient can scarcely stand alone he may possibly be able to perform the most delicate movements with his upper extremities. The vertigo occurs only in standing or walking, and is then almost always present. Nystagmus is also a frequent symptom. Vomiting is very often present, but is not characteristic, since it is equally frequent in other brain diseases. Extending along the floor of the aqueduct of Sylvius and of the fourth ventricle, that is, along the cerebral peduncles, pons and medulla, we find the nuclei of origin of the motor fibres of the cranial nerves. It should be borne in mind that the con- trolling centres of these nerves are in the cerebral cortex. Many automatic centres, as of circulation, respiration, sweating, and regulation of heat, as well as the motor and sensory tracts are found in the medulla. Cranio-Cerebral Topography. In order that the surgeon may expose and recognize certain areas of the cortex, it becomes very important that the relations between these areas and the corresponding external surface be well understood. For this purpose advantage is taken of the landmarks of the skull (page 241). From these bony points, ridges and depressions, by means of lines and measurements, the known cortical areas may be accurately mapped out. The upper limit of each cerebral hemisphere is indicated, approximately, by the median line at the top of the skull from the glabella to the external occipital protu- berance, due allowance being made for the superior longitudinal sinus, which lies under the skull, in the longitudinal fissure, between the two hemispheres. The lower limit is represented by a transverse line, in front, just above the upper margin of the orbit. At the side of the skull the line passes from about a half inch above the external angular process of the frontal bone to just above the external auditory meatus. From here it passes to the external occipital protuberance ; this part of the line corresponding, approximately, to the lateral sinus. The cerebellum lies immediately below this line. Of the brain fissures, those of greatest importance in cerebral localization are the Rolandic and Sylvian, since by means of these all the best known cortical centres can be located. Of the two, the fissure of Rolando is much the more important, because the motor, the most definitely known cortical area, is associated with it. Its upper limit is at a point about 12 mm. (one-half inch) behind the mid-point between the glabella and the inion, and about one-half inch from the median line. It passes outward, downward, and forward, approximately, at an angle of 71 with the median sagittal line of the skull. It is 8.5 cm. (3^ in.) long (Thane), and ends below just above the fissure of Sylvius. Near its fower end it turns rather suddenly downward, so that, in this part, it is not in the line of the angle of 71. Many methods have been devised for the purpose of making the line of the fissure on the scalp. Chiene 1 s method consists of folding an ordinary square sheet of paper on the diagonal line, thus dividing an angle of 90 in half, making two of 45. One of these angles of 45 is again halved in a similar manner, making two new angles each of 22^. The paper is then so unfolded that one of the angles of 22^ is added to that of 45, making a new angle of 67^ ; this will be sufficiently near that of the fissure of Rolando for all practical purposes. Hors/fv s crrtoiiiticr consists of two strips, either of thin, flexible metai or of parchment paper, each graduated in inches. The lateral arm is placed at an angle of 67 with tin- long arm, the apex of the angle being at a point 12 mm. or one-half inch behind the mid-point of the long arm. Le Fort simply drew a line from the beginning of the fissure, above, to the mid- dle of the zygoma, below, and marked off on this line the proper length of the fissure. PRACTICAL CONSIDERATIONS : THE BRAIN. 1215 Anderson and Mackins suggest : ( i ) a median sagittal line from the glabella 1,0 the inion ; (2) a frontal line from the mid-sagittal point to the depression just in front of the ear at the level of the upper border of the meatus ; (3) a squamosal line from the most external point of the external angular process, at the level of the superior border of the orbit to the junction of the middle and lower thirds of the frontal line, and prolonged for about 3. 7 cm. ( i y z in. ) behind the frontal line. The upper ex- tremity of the central fissure was found by them to lie between the mid-sagittal point and a point 18 mm. (3/ in.) behind it, and the lower extremity of this fissure they located near the squamosal line, about 18 mm. (^ in.) in front of its junction with the frontal line. The commencement of the lateral portion of the Sylvian fissure is not at a definite fixed point, but will usually be hit at a point from 3.7-5 cm. (1^-2 in. ) behind the angular process, the course of the horizontal portion of this fissure corresponding closely to the squamosal line (Mills). Fissure of Rolando FIG. 1044. Bregma Line for Rolandic fissure Pos Interparietal fissure- External parieto- occipital fissure Parietal eminence Inion Lateral sinus isteripr limb of Sylvian fissure ne for Sylvian fissure Vertical limb of Sylvian fissure Horizontal limb of Sylvian fissure Glabella Nasion Semidiagrammatic view of head, showing relation of Rolandic and Sylvian fissures and lines. The fissure of Sylvius begins anteriorly, approximately, at a point 3 cm. (i/^ in. ) behind the external angular process of the frontal bone ; and ends posteriorly at a point 18 mm. (^ in.) below the parietal eminence. A straight line between these two points will represent the fissure, which is about 10 cm. (4 in.) long. The an- terior 1 8 mm. (24 in-) of this line will correspond to the main portion of the fissure and the remainder to the horizontal limb. The vertical limb ascends for about 2.5 cm. (i in.) from the posterior end of the main fissure. Around the posterior end of the horizontal limb, and approximately under the parietal eminence lies the supramarginal convolution. It is continuous in front with the ascending parietal convolution, and behind with the angular gyrus. The parieto-occipital fissure is most marked on the mesial surface of the brain. The external limb passes outwards, almost at right angles to the longitudinal fissure on the external surface for about 2.5 cm. and lies from 2-3 mm. in front of the lambda. The frontal lobe is divided into three main convolutions by the superior and in- ferior frontal sulci. The line for the superior frontal sulcus passes directly backward I2l6 HUMAN ANATOMY. from the supraorbital notch, and parallel to the longitudinal fissure to within 18 mm. (^ in.) of the fissure of Rolando. The inferior frontal sulcus is represented, approximately, by the anterior end of the temporal ridge. In the parietal lode the most important sulcus is the intraparietal. It begins near the horizontal limb of the fissure of Sylvius, and passes upward and backward about midway between the fissure of Rolando and the parietal eminence. It then turns backward, running about midway to the longitudinal fissure and the centre of the parietal eminence. Above the sulcus, in front, lies the ascending parietal convolution, just posterior to the fissure of Rolando and behind the superior pari- etal lobule. Below the sulcus, anteriorly, is the supramarginal convolution, and posteriorly, the angular gyrus. FIG. 1045. Eregma Lateral ventricle Middle meningeal rtery, anterior branch Posterior horn "f lateral ventricle (I) Iniou Lateral sinus Middle meningeal artery, posterior branch ; inferior horn of lateral, ventricle seen beneath / Semidiagrammatic view of head, showing position of ventricles, lateral sinus and middle meuiugeal arteries as projected on skull. The temporal lobe lies below the fissure of Sylvius and extends forward as far as the edge of the malar bone. The first temporal sulcus lies about one inch below and parallel with the fissure of Sylvius, and the second about 18 mm. (3/ in.) lower. The occipital lobe lies posterior to the parieto-occipital fissure and the tem- poral lobe. The motor tracts are made up of the fibres passing from the motor portion of the cortex in the Rolandic region to the motor nuclei from which arise the nerves supplying the muscles which the cortical areas control. After leaving the cortex the fibres pass downward in the corona radiata, and converge to the posterior limb of the internal capsule. The motor fibres of the cortico-bulbur and cortico-spinal tracts, occupy the genu and adjacent third of the internal capsule (page 1188), although Dejerinc holds that the whole posterior limb is motor. They continue their course downward through the crura cerebri, pons, and medulla ; in the lower part of the latter the givatrr number cross to the opposite side and pass down in the cord as the lateral or crossed pyramidal tract. A small number, sometimes absent, pass down PRACTICAL CONSIDERATIONS: THE BRAIN. 1217 on the same side. We have already seen that lesions of the cortex produce mono- plegia, unless large enough to involve the whole motor zone, but cortical hemiplegia is much more common than cortical monoplegia. In the internal capsule the motor fibres are gathered together so compactly that a small lesion, as an apoplectic hemor- rhage, will frequently interrupt the whole tract and give a hemiplegia of the opposite side of the body. In the medulla and cord the tracts of both sides are so close together that a lesion may easily paralyze both sides (paraplegia) ; indeed, diseases of the cord fre- quently involve the whole transverse section, paralyzing sensation as well as motion. Hemiplegia is, therefore, the common form of cerebral paralysis ; paraplegia the common form of spinal paralysis ; while monoplegia occasionally results from lesions of the brain cortex, but more commonly from lesions of peripheral nerves. The sides and convexity of the brain can be exposed for operation, so that lesions of the cortex can be attacked and often removed ; but the region of the internal capsule, which is near the basal ganglia, cannot be reached. The soft brain may be injured by contact with its bony walls when the head is violently shaken, the spaces surrounding the brain and filled with fluid permitting considerable movement of the brain. The injury in cerebral contusion occurs more frequently on the under surface, both as regards the cerebrum and cerebellum, than on any other part (Prescott Hewett). That portion, however, which includes the medulla, pons, and interpeduncular space, rests on a large collection of cerebro- spinal fluid, and is least frequently injured. 77 THE PERIPHERAL NERVOUS SYSTEM. IN a broad sense and as contrasted with the cerebro-spinal axis, the peripheral nervous system includes all the nerve-paths by which the various parts of the body are brought into relation with the brain and spinal cord. These paths embrace, in a general way, two groups. One group, the somatic nerves, includes the nerves FIG. 1046. Olfactory bulb Orbital surface of frontal lobe Temporal lobe Anterior perforated space Mammillary bodies Cerebral peduncle Pon Cerebellum Ante rior roots of spinal nerves Olfactory tract Optic nerve, cut _ Optic commissure "Optic tract Oculomotor nerve Trochlear nerve _Trigeminal '"nerve Abducent nerve -Facial nerve Auditory nerve ' Glosso-pharyn- feal nerve neumogastric nerve Spinal accessory nerve, spinal portion Pyramidal decussation Spinal part of XI. nerve Occipital lobe Spinal cord Inferior aspect of brain, denuded of its membranes, showing superficial origins of cranial nerves ; origin of trochlear nerve is on dorsal surface and therefore not seen. supplying the voluntary muscles, integument and organs of special sense ; the sec- ond group, the visceral nerves, includes those supplying the involuntary muscle throughout the body and the thoracic and abdominal viscera. The somatic nerves are subdivided into (a) the cranial nerves, which are attached to the brain and pass through foramina in the skull, and (b) the spinal ttrrz'cs, which are attached to the spinal cord and traverse the intervertebral foramina. The visceral, or splanchnic I2lS THE CRANIAL NERVES. 1219 nerves, although directly or indirectly connected with the cerebro-spinal axis, pre- sent peculiarities and, as the system of sympathetic nerves, are accorded, at least for convenience of description, a certain degree of independence. While by no means all of the spinal nerves contribute splanchnic branches such branches being given off especially by the thoracic and upper lumbar nerves they all receive sympathetic filaments, which form, therefore, integral parts of the somatic nerves. From the sympathetic neurones of the gangliated cords axones pass, by way of the gray rami communicantes (page 1357), to the trunks of the spinal nerves and thence by these are carried to all parts of the body for the supply of the involuntary muscle occur- ring within the blood-vessels and the integument and for the cutaneous glands. Fur- thermore, it must be remembered, that although the predominating constituents of a spinal nerve may be axones derived from anterior horn root-cells and destined for voluntary muscle, such trunk also contains a number of afferent fibres which convey impulses received from the neuromuscular and neurotendinous sensory endings, the nerve-trunks reckoned as ' ' motor ' ' in all cases, when analyzed, being found to con- tain sensory and sympathetic fibres as well as efferent ones. THE CRANIAL NERVES. The cranial nerves (nervi cerebrates) include twelve pairs of symmetrically arranged nerve-trunks, which are attached to the brain and, traced peripherally, escape from the skull by passing through various foramina at its base to be distrib- uted for the most part to the structures of the head. The point at which a cranial nerve is attached to the surface of the brain is designated its superficial origin ; the group of more or less deeply situated nerve- cells with which its fibres are directly related is often spoken of as its deep origin. From what has been said (page 1278) concerning the position of the cell-bodies of motor and sensory neurones, it is evident that only the motor fibres of the cranial nerves spring from nerve-cells within the cerebro-spinal axis, while the fibres con- ducting sensory impulses arise from nerve-cells situated within ganglia lying outside the central nervous axis and somewhere along the course of the nerve-trunks. It follows, therefore, that the term "deep origin," as applied to the cell-groups within the brain, can properly relate only to the origin of motor fibres ; the cell-groups with which the sensory fibres come into relation after entering the brain-substance are in reality nuclei of reception, or of termination, and not of origin. The sensory impulses so received are transmitted to various parts of the brain by the more or less complex paths afforded by the neurones of the second, third, or even higher order. In addition to their relation to the deep nuclei, whether of origin or of reception, the fibres of every cerebro-spinal nerve are directly or indirectly influenced by neurones situated within the shell of gray matter that covers the cerebrum. The position of these higher cortical centers, as they are termed, is known with considerable accuracy for many groups of nerves, but regarding others more definite data con- cerning cerebral localization must be awaited. Bearing in mind the foregoing distinctions, for convenience we may follow the conventional description in which all the nerves are regarded as passing away from the brain, the direction in which they convey impulses, centripetally or centrifugally, being for the time disregarded. On leaving the surface of the brain at its superficial origin, each cranial nerve, invested by a sheath of pia mater, traverses for a longer or shorter distance the sub- arachnoid space, pierces the arachnoid and from the latter acquires an additional, but usually not extensive, sheath. It then enters a canal in the dura mater that leads to the foramen in the skull, through which the nerve escapes from the cranium, invested by a sheath prolonged from the dura which is continuous with the epi- neurium covering the nerve-trunk. The position of the dural aperture and that of the foramen by no means always correspond, some of the nerves, notably the fourth and sixth, pursuing an intradural course of some length before gaining their osseous exit. According to the order in which they pass through the dura lining the cranium, ihe pairs of cranial nerves are designated numerically from the first to the twelfth. They are further distinguished by names based upon their distribution or functions. I22O HUMAN ANATOMY. Certain of the cranial nerves are entirely motor ; some convey the impulses of special sense ; while others transmit impulses of both common sensation and motion. A general comparison of these relations, as now usually accepted, is afforded by the following summary : THE CRANIAL NERVES. Number. I. II. III. IV. V. VI. VII. VIII. IX. X. XI. XII. Name. OLFACTORY : OPTIC : OCULOMOTOR : TROCHLEAR : TRIGEMINAL : ABDUCENT : FACIAL : AUDITORY, (a) Cochlear division : (d) Vestibular division GLOSSO-PHARYNGEAL : PNKUMOGASTRIC OR v.\<;rs SPINAL ACCESSORY : HYPOGLOSSAL : Function. Special sense of smell. Special sense of sight. Motor to eye-muscles and levator pal- pebrse superioris. Motor to superior oblique muscle. Common sensation to structures of head. Motor to muscles of mastication. Motor to external rectus muscle. Motor to muscles of head (scalp and face) and neck (platysma). Probably secretory to submaxillary and sublingual "lands. Sensory (taste) to anterior two-thirds of tongue. Hearing. Equilibration. Special sense of taste. Common sensation to part of tongue and to pharynx and middle ear. Motor to some muscles of pharynx. Common sensation to part of tongue, pharynx, oesophagus, stomach and respiratory organs. Motor (in conjunction with bulhar part of spinal accessory) to muscles of pharynx, oesophagus, stomach and intestine, and respiratory organs ; inhibitory impulses to heart. Spinal Part: Motor to sterno-mastoid and trapezius muscles. Motor to muscles of tongue-. Practical Considerations. Lesions may affect a cranial nerve within the brain or .in its peripheral portion. A central lesion clinically is one above the nucleus of the nerve, and may be cortical or may encroach upon its intracerebral connections. It may merely irritate the nerve or may paralyze it. By a peripheral lesion is meant one involving the nucleus or the fibres of the nerve below the nucleus. THE OLFACTORY NERVE. The olfactory nerve (n. olfactorius), the first in the series of cranial nerves, presents some confusion in consequence of the name, as formerly employed, being applied to the olfactory bulb and tract as well as to the olfactory filaments struc- tures of widely diverse morphological values. As already pointed out (page 1151), the olfactory bulb and tract (Fig. 993), with its roots, represent, as rudimentary structures, the olfactory lobe possessed by animals in which the sense of smell is highly developed. It is evident that these structures, formerly regarded as parts of the first cranial nerve, are not morphological equivalents of simple paths of rondiu-- tion. On the other hand such paths are represented by a series of minute filaments, the true olfactory nerves, that connect the perceptive elements within the nasal mucous membrane with the rudimentary olfactory lobe. The olfactory nerves proper, some twenty in number, are the axones of tile- peripherally situated neurones, the olfactory cells (page 1414), which lie within the limited olfactory area. The latter embraees in extent on the outer nasal wall less THE OLFACTORY NERVE. 1221 than the mesial surface of the superior turbinate bone and a somewhat larger field on the adjacent upper part of the nasal septum. The olfactory nerves (Fig. 1048), FIG. 1047. Exit ext. br. nasal nerve y Olfactory bulb ^Olfactory nerve-fibres An upper ant. nasal br. 'Meckel's ganglion I'pper post, nasal brs. Meckel's ganglion Naso-palatine nerve Sup. ant. nasal br. of Meckel's gangl. and inf. ant. nasal br. of ant. descending t palatine nerve A posterior nasal br. Meckel's ganglion Ant. descending palatine nerve, the middle palatine appearing posteriorly Right nasal fossa showing distribution of olfactory and nasal nerves on lateral wall; mucous membrane has been partly removed to expose nerves. whose fibres are nonmedullated, exhibit a plexiform arrangement within the deeper part of the nasal mucous membrane, pass upward through the cribriform plate of FIG. 1048. Crista galli Int. (septal) br. of nasal nerve , Olfactory bulb Ext. br. nasal n Naso-palatine nerve Olfactory nerve-fibres ,-Sphenoidal sinus n upper ant. nasal br. of eckel's ganglion Naso-palatine nerve An upper ant. nasal br. of Meckel's ganglion fiustachian orifice Vomer, posterior border Soft palate, cut mesially Right nasal fossa showing distribution of olfactory and nasal nerves on septal wall ; mucous membrane has been partly removed to expose nerves. the ethmoid bone and enter the under surface of the olfactory bulb. Within the latter the nerve-fibres end in terminal arborizations in relation with the dendritic processes of the mitral cells (Fig. 995), sharing in the production of the peculiar o/ factory glomcrnli. 1222 HUMAN ANATOMY. Central and Cortical Connections. The impulses conveyed by the olfactory nerves and received by the mitral cells of the olfactory bulb, which cells may be regarded as constituting the end-station or reception-nucleus of the peripheral path, are carried to neurones situated either within the gray matter of the olfactory tract, the anterior perforated space or the adjacent part of the septum lucidum (Fig. 1049). Fibres connecting the olfactory centres of the two sides pro- ceed from the cortex of the tract by way of the anterior commissure, forming the pars olfactoria of the latter, to end in relation with the cells within the opposite tract or bulb. From these primary centres the impulses are transmitted by different paths to the secondary or cortical centres situated in the anterior part of the hippocampal convolution in the vicinity of its uncus, including the hippocampus major and the nucleus amygdalae. i. The most direct path is by way of the lateral root of the olfactory tract (page 1046), by which fibres from cells within the trigonum olfactorium pass, skirting the Sylvian fissure, to the anterior part of the gyrus hippocampi to terminate in relation with the cortical cells of that convolution. FIG. 1049. Diagram showing most important connections of olfactory tracts ; LC lamina cribrosa ; B, olfactory bulbs : TV, olfactory tract ; Tjf, olfactory trigone ; Ls, Ms, lateral and .mesial striae ; A, anterior commissure ; CC, corpus callo- sum ; SL, septum lucidum; /!*, anterior pillar of fornix; M, mammillary body; m-t, mammillo-thalamic tract ; AP, anterior perforated space; Tsemj.\.xn\& semicircularis ; T, thalamus; Fm, fimbria descending on hippocampus; U, uncus; AN, amygdaloid nucleus; TL, temporal lobe. 2. Fibres from the cells within the olfactory trigone (page 1153) and the anterior perfo- rated space (page 1 153) pass into the septum lucidum and, reinforced by others from cells of the septum, enter the fornix ; thence continuing backward and downward by way of the fimbria they reach the hippocampus major. 3. Fibres from cells within the olfactory trigone turn inward and by way of the medial root of the olfactory tract gain the gyrus subcallosus ; thence they pass along the upper surface of the corpus callosum within its longitudinal striae and descend by way of the dentate gyrus to reach the anterior end of the hippocampus major. 4. Fibres from cells within the anterior perforated space and septum lucidum, joined by accessions from the opposite olfactory tract by way of the anterior commissure, converge to the tacnia semicircularis (page 1162) and, passing along the floor of the lateral ventricle, descnul within the roof of the descending horn to end in the amygdaloid nucleus (Dejerine). During their ascent from the anterior perforated space, some fibres diverge almost at right anglrs and pass backward directly to the optic thalamus. The connections between the cortical centres of olfartion and the optic thalamus, as well as those between the olfactory centres of the two sides, by way of the fornix, are described on page 1 167. Practical Considerations. Lesions of the uncinate gyrus may cause loss of the sense of swell on one or both sides. Paralysis of the olfactory nerve with loss of smell may also occur in fractures of the base of the skull in the anterior fossa, involving the cribriform plate. THE OPTIC NERVE. 1223 THE OPTIC NERVE. The optic nerve (n. opticus) is, as conventionally described, part of the pathway which includes additionally the optic commissure and the optic tract and transmits the visual impulses received by the retina to the primary centres within the pulvinar of the optic thalamus and the external geniculate and superior quadrigeminal bodies. The retina, the nervous tunic of the eye (page 1462), comprises three fundamental layers (a) the percipient visual cells, (b~) the receptive ganglion retina and (c) the cerebral layer. The latter contains the neurones, the axones of which constitute the nerve-fibres that converge towards the optic disc and, piercing the vascular and fibrous coats, form the greater part of the optic nerve, commissure and tract. In addition to the fibres of retinal origin, which alone carry visual impulses, the optic nerve contains a considerable number of supplementary fibres, which are only indirectly con- cerned in sight. Some of these fibres, distinguished by their small diameter, pass towards the retina, originating within the brain from the cells of the primary visual centres or from sympa- thetic neurones, and probably transmit vasomotor impulses controlling the retinal blood- vessels. Other supplementary fibres, perhaps by way of a centre situated within the medulla, pass from the retina and are regarded as conveying indirectly to the oculomotor nucleus the impulses resulting in reflex pupillary movements. The optic nerve (Fig. 1198) extends from the eyeball, which it leaves about 3 mm. to the medial side of the posterior pole, to the optic commissure. Leaving the eyeball, the nerve pursues a slightly sinuous course backward, inward and up- ward towards the apex of the orbit, where, surrounded by the origins of the recti muscles, it traverses the optic foramen in the sphenoid bone in company with the ophthalmic artery, which lies to its outer and lower side. On gaining the interior of the cranium, it converges towards the nerve of the opposite side with which it joins to form the major part of the optic commissure in the vicinity of the olivary eminence, medial to the internal carotid artery. The entire length of the optic nerve is from 30-40 mm., of which the intraorbital part includes from 20-30 mm., thus allowing for changes in ihe position of the eyeball without undue stretching of the nerve. Its diameter is from 3-4 mm. Within the orbit the nerve is embedded in the orbital fat and surrounded by the ocular muscles and, near the eyeball, by the ciliary vessels and nerves. It is crossed above and from without inward by the ophthalmic artery and the nasal nerve, and, about 10 mm. from the eyeball, is penetrated by the central artery of the retina, which, with its companion vein, continues its intra- neural course as far as the optic disc. In addition to a sheath from the pia mater and a delicate one from the arachnoid, the optic nerve receives a robust tubular pro- longation from the dura at the optic foramen. These sheaths, with the intervening subarachnoidal and subdural lymph-spaces, are continued on the nerve as far as the eyeball, where they blend with the sclerotic coat. The optic commissure (Fig. 1046), formed by the meeting of the converging optic nerves in front and the diverging optic tracts behind, is somewhat flattened and transversely oblong and measures about 12 mm. where broadest. It rests upon the olivary eminence, is embraced at the sides by the internal carotid arteries, and lies beneath the floor of the third ventricle in advance of the tuber cinereum in close rela- tion with the inferior surface of the brain. It divides posteriorly into the two optic tracts. On reaching the commissure, or chiasm, as it is sometimes called, the optic fibres, estimated at upwards of half a million (Salzer), undergo partial decussation, those from the nasal or inner half of each retina crossing to the mesial part of the opposite optic tract, while those from the temporal or outer half continue into the lateral part of the tract of the same side. The existence of a commissural loop con- necting the two optic nerves has not been established, although formerly accepted. Occasional instances have been encountered in which the decussation of the optic fibres was complete, thus repeating in man the condition that normally obtains in all nonmammalian vertebrates, as well as in a few rodents (mouse, guinea-pig). Rarely the optic commissure has been absent, the optic fibres passing directly into the tract of the same side. 1224 HUMAN ANATOMY. The entire commissure, however, is not composed of optic fibres, ^ince its posterior part is formed by a bundle, known as Gudden's commissure (commissura inferior) (page mo), which passes forward along the mesial side of the optic tract, 1< >ops around the posterior angle of the commissure and enters the opposite tract. These fibres have no connection with the path of sight-impulses, but are probably chiefly related with the median or internal geniculate bodies and the inferior corpora quadrigemina (page mo). The optic commissure also contains fibre-strands that arch around its posterior angle, par- allel with, but separated by, a thin layer of gray matter from Gudden's tract. Concerning the origin and destination of these fibres, termed Meynert's commissure (commissura superior), little is known. By some they are regarded as continuations of the mesial fillet that, after decussa- FIG. ioso. RayqffLight Diagram showing course of retinal fibres fn optic pathway and their connection with basal ganglia and primary cortical centres ; smaller figure illustrates path of light-ray and resulting impulse through retina : R, retina : ON, OC, OT, OR, optic nerve, chiasm, tract and radiation , /*, pulvinar ; Eg, SQ, lateral geiiiculate and superior quadrigem- inal bodies; Oc Or, occipital cortex; ///, IV, VI, nuclei of eye-muscle nerves. tion, pass to the globus pallidus of the lenticular nucleus of the opposite side. Others deny such relations, while Kolliker describes them as bending upward, traversing the ventral part of the cerebral peduncle, to end within the corpus subthalamicum (page iias i. Additional commissural fibres (commissura ansata) descend from the floor of the third ventricle and from the peduncle of the septum lucidum, by way of the lamina terminalis, to the front and upper part of the optic chiasm ; other fibres pass from the ventricular floor to the back of the chiasm. For the most part these fibres cross to the opposite sick- to be lost in the sub- stance of the optic commissure. Although regarded as in a way constituting a ventral <>f>tit roof, their connections and significance are not understood. The optic tract (Fig. 993) is the continuation of the optic nerve, its chief constituents being the crossed and uncrossed retinal and the supplementary fibres. On leaving the commissure, the tract diverges in front of the interpeduncular space, mesial to the anterior perforated space and tin- termination of the- internal carotid artery, and sweeps outward and backward from the base of the brain around and close to the cerebral peduncle, becoming flatter and broader as it proceeds. Near THE OCULOMOTOR NERVE. 1225 its posterior end the tract exhibits a furrow that indicates a subdivision into a mesial and a lateral root (Fig. 915). The latter, the visual portion of the optic tract, is traceable into the prominent overhanging pulvinar of the optic thalamus, the ill- defined lateral geniculate body and, by means of the superior brachium, into the supe- rior quadrigeminal body. The mesial root, on the other hand, contains the fibres forming Gudden's commissure (page mo) and is related to the distinct median geniculate body and, by the inferior brachium, to the inferior quadrigeminal body. Central and Cortical Connections. Arising as axones of the retinal neurones, the optic nerve-fibres are continued backward through the commissure and tract and end in relation with the neurones of the primary centres situated in the pulvinar, the lateral geniculate and the superior quadrigeminal body. . It is, however, within the lateral geniculate body that the greater number (80 per cent, according to Monakow) of the visual fibres terminate, relatively few pass- ing to the pulvinar and the superior quadrigeminal body (Spiller). The cortical connections are established by fibres which pass from the cells of these primary centres and, as the optic radia- tion (page 1123), sweep outward and backward into the occipital lobe to end in the cortex of the cuneus in the vicinity of the calcarine fissure. It is probable that a limited number of retinal fibres pass directly to the cerebral cortex without interruption in the primary centres. In addi- tion to the centripetal paths just mentioned, fibres arise from the cortical cells of the cuneus and, sharing the optic radiation, pass as efferent tracts which not only terminate in the lateral geniculate and quadrigeminal bodies, but also establish indirect relations with the nucleus of the oculomotor nerve. The ultimate distribution and influence of the impressions of sight are very complex and far reaching, such impressions being capable of affecting numerous motor and sensory centres. The exact path by which pupillary impulses reach the oculomotor nucleus is uncertain and perhaps two-fold. It may be assumed, however, that if they proceed by way of the superior quadrigeminal body, the optic fibres are not directly continued to the nucleus of the third nerve, but end within the superior colliculus, from whose neurones the immediate connecting links pro- ceed to the oculomotor nucleus. Accumulating evidence points to the existence of a more remote special centre for pupillary reflexes within the lower part of the medulla ; in such case the oculomotor nucleus is, perhaps, influenced by impulses which pass from the medullary centre upward by way of the posterior longitudinal fasciculus (Bach). Practical Considerations. The cranial nerves of the eye will be discussed in connection with that organ. THE OCULOMOTOR NERVE. The third or oculomotor nerve (n. oculomotorius), the chief motor nerve of the intrinsic and extrinsic muscles of the eyeball, supplies branches to all the extraocular muscles, with the exception of the external rectus and superior oblique, as well as fibres to the sphincter pupillae and the ciliary muscle within the eyeball. Its deep origin is from the oculomotor nucleus situated medially and deeply within the gray matter of the floor of the Sylvian aqueduct, in close relation with the dorsal surface of the posterior longitudinal fasciculus (Fig. 963). The nucleus is from 6-8 mm. in length and extends from opposite the upper end to the caudal pole of the superior quadrigeminal bodies. Below, its posterior end comes almost into contact with the nucleus of the fourth nerve, but is separated from it by a narrow interval. In its entirety the oculomotor nucleus includes a number of more or less distinct cell-groups, which vary in importance as well as in their individual prominence. Of these the most impor- tant and constant are two long columns of cells, the chief nuclei, that extend, one on each side, along the dorsal surface of the posterior longitudinal fasciculi. Each nucleus tapers slightly towards either end and consists of two fairly distinct subdivisions which, from their relative positions, are termed the dorsal and the ventral cell-group. The component nerve-cells include those of large, medium and small size, the large multipolar ones (from .040-. 045 mm. in diam- eter) probably being the elements from which the root-fibres of the third nerve arise. Dislo- cated portions of the chief nucleus are seen as small groups of nerve-cells that lie scattered among or even beneath the fibres of the posterior longitudinal bundle. Dorsal to the chief nucleus and partially overlying its postero-median surface is the taper- ing column of small nerve-cells known as the Edinger-Westphal nucleus. This tract, much more bulky above than below (Tsuchida), exhibits a subdivision into a dorso-lateral and a ventro-median portion, which, however, are fused in the superior pole of the nucleus. The 1226 HUMAN ANATOMY. exact relations of the Edinger-Westphal nucleus to the fibres of the third nerve are still unde- termined, and, indeed, even its close association with these has been questioned. The assumed importance of the nucleus as a centre for pupillary reflexes (Bernheimer) has been seriously shaken by the recent observations of Tsuchida. 1 This investigator also denies the existence of a well marked and constant unpaired median nucleus as described by Perlia, but admits the presence of broken groups of medially placed cells, especially in the upper and lower thirds of the nucleus. The lateral group of cells, beginning in the floor of the third ventricle and extend- ing caudally as far as the upper third of the chief nucleus, constitutes the nucleus of Darksche- witsch. Notwithstanding its proximity to the origin of the third nerve, this nucleus is now regarded as having no direct relation with that of the oculomotor, but as standing in intimate asso- ciation with the posterior longitudinal bundle, among whose fibres the cells to a large extent lie ; it is, therefore, now often referred to as the nucleus fasciculi longitudinalis posterioris. FIG. 1051. 3. a o ^ \ ~\ 5 K 11 u, t; 3 b s li _ *S B 2 O Lachrymal gland Xevator palpe- brae superioris Superior rectus muscle External rectus, insertion Inferior oblique -muscle Cut surface of malar bone Dissection of right orbit, showing oculomotor and abducent nerves. Although it may be assumed with much probability that the fibres destined for the different eye-muscles originate from definite groups of nerve-cells, all attempts to locate with accuracy the position of such centres within the oculomotor nucleus have met with only partial sue \ vss. Tsuchida's conclusions, based upon histological, embryological, comparative and clinical data, point to an unexpected diffuseness in the origin of the oculomotor fibres with only a limited relation to distinct groups. Concerning the mooted question as to the extent of decussation of the oculomotor librt-s it seems probable that such crossing occurs principally within the caudal portion of the chief nuclei, although, according to Tsuchida and others, some decussating fibres are found throughout the greater part of the nuclei. The fibres of the third nerve originate principally as the axones of the cells on the same side, although a small number are derived from the neurones lying on the opposite side of the mid-line. Some of these decussating fibres supply the internal rectus and are related with the nucleus of the sixth nerve, which sends fibres by way of the posterior longitudinal bundle into the oculomotor nucleus. Whether these 1 Arbeiten a. d. Hirnanatom. Institut in Zurich, Heft ii., 1906. THE OCULOMOTOR NERVE. 1227 fibres end within the latter nucleus around the cells from which the decussating fibres proceed, or are actually prolonged as certain of the decussating fibres is uncertain ; their purpose is to bring into coordinated action the internal rectus of one side with the opposite external rectus when the two eyes are directed laterally, as in conjugate deviation. Cortical and Central Connections. As in the case of all other motor cranial nerves, the nucleus of the third nerve stands in direct relation to the cerebral cortex. Fibres from the cells of the cortical centre axones from the neurones within the posterior part FIG. 1052. Branch of supraorbital nerve Supratrochlear branch of frontal Supraorbital branch of frontal Lachrymal gland Olfactory bulbs Olfactory tract Optic nerve Optic chiasm Optic tracf"^ III. nerve VII. nerve VIII. nerve- IX. nerve X. nerve XI. nerve XI. nerve spinal portion Part o XII. nerve Superior medullary velum Lachrymal nerve Ophthalmic division of V. nerve its division into frontal, lachrymal III. nerve [and nasal Maxillary division of V. nerve IV. nerve, to inner side of which is VI. nerve Mandibular division of V. nerve Gasserian ganglion Sensory root of V. VII. nerve [nerve VIII. nerve Middle cerebellar peduncle IX. nerve X. nerve, XII. nerve IV. ventricle Medulla, closed part Base of skull, viewed from above, showing cranial nerves passing through dura; roof of right orbit has been removed to expose the ophthalmic nerve. of the inferior frontal convolution, slightly in front of the precentral fissure (Mills) proceed by way of the corona radiata, the internal capsule and the cerebral peduncle to the oculo- motor nucleus, around whose cells, chiefly but not exclusively ,on the opposite side, they end. Other connections of the nucleus of the third nerve include : (i) indirectly with the cor- tical visual area by fibres that pass from the occipital cortex through the optic radiation and superior brachium to the superior corpora quadrigemina ; (2) indirectly with the visual centres by fibres that descend from the cells within the superior corpora quadrigemina ; (3) by means of the posterior longitudinal bundle with the nuclei of the other ocular nerves (the fourth and the sixth) and also with the vestibular (Deiters') nucleus of the eighth; (4) with the facial nucleus by fibres that descend from the oculomotor nucleus along the posterior longitudinal bundle to the cells from which proceed .the fibres supplying the orbicularis palpebrarum and the corrugator supercilii muscles, which are thus brought into coordinated action with the levator palpebrarum. 1228 HUMAN ANATOMY. Intracranial Course. Leaving their deep origin as the axones of the nuclear cells, the oculomotor fibres sweep in ventrally directed curves (Fig. 963) through the posterior longitudinal bundle, tegmentum, red nucleus and inner margin of the substantia nigra and, collected into about a dozen root-bundles, have their super- ficial origin along a shallow groove, the oculomotor siilcus (Fig. 974), on the medial surface of the cerebral peduncle, just in front of the pons and at the side of the interpeduncular space. Beyond this superficial origin, the linear group of root-fibres soon becomes consolidated into the large and conspicuous trunk of the third nerve, although not infrequently one root-bundle emerges more laterally from the ventral surface of the cerebral peduncle and for a short distance remains separated from the other constit- uents. The nerve courses forward and outward from the posterior perforated space, between the posterior cerebral and superior cerebellar arteries, to the outer side of the posterior clinoicl process, where, in the triangular interval between the free and attached borders of the tentorium, it enters the dura (Fig. 1033). Embedded within this membrane, the nerve follows the upper portion of the outer wall of the cavernous sinus and leaves the cranium by entering the orbit through the sphenoidal fissure. On gaining the median end of the fissure the nerve divides into a superior and an inferior branch, which enter the orbit by passing between the two heads of the external rectus muscle, in company with, but separated by, the nasal branch of the trigeminal nerve, the sixth nerve lying below. Branches and Distribution. The superior branch framus superior) (Fig. 1051), the smaller of the two, passes upward, over the optic nerve, to the superior rectus muscle, which, together with the levator palpebrae superioris, it supplies. In both cases the nerve enters the ocular surface of the muscle. The inferior branch (ramus inferior) (Fig. 1051) is directed forward and, after giving off twigs to the ocular surface of the internal and inferior recti, is continued below the eyeball, between the inferior and external straight muscles, to supply the inferior oblique, whose posterior border it enters. This, the longest branch of the oculomotor nerve, in addition to sending one or two fine twigs to the inferior rectus, contributes a short thick ganglionic branch (Fig. 1051), which joins the postero-inferior part of the ciliary ganglion (page 1236) as its short or motor root and conveys fibres destined for the sphincter pupillae and ciliary muscles. Sensory fibres from the ophthalmic division of the fifth nerve are distributed to the muscles along with the fibres of the third, having joined the latter before it entered the orbit. Similarly in the wall of the cavernous sinus, the nerve is joined by sympathetic fibres from the cavernous plexus on the internal carotid artery. Variations. These consist, for the most part, of unusual branches which at times seemingly replace one of the other motor orbital nerves. Thus, the third nerve may give a branch to the external rectus, either in addition to, or to the exclusion of the sixth, which may be absent ; or it may give a filament to the superior oblique. Minor deviations in the course of its branches, such as piercing the inferior rectus or the ciliary ganglion, have also been recorded. THE TROCHLEAR NERVE. The fourth or trochlear nerve (n. trochlearis), also called the pathetic, is the smallest of the cranial series and supplies the superior oblique muscle of the eyeball. The deep origin of the nerve is from the trochlear nucleus, a small oval collection of cells situated in the ventral part of the gray matter surrounding the Sylvian aque- duct, that extends from opposite the upper part of the inferior quadrigeminal body to the lower pole of the superior colliculus. This nucleus, about 2 mm. in length, lies near the mid-line and immediately below (caudal to) that of the third nerve, from which, however, it is distinct, being separated by a narrow interval from the ventral part of the oculomotor nucleus. It lies in intimate relation with the pos- terior longitudinal fasciculus in a distinct depression on the dorsal surface of that bundle (Fig. 960). In structure the trochlear nucleus resembles that of the oculo- motor, its nerve-cells including those of large, medium and small size. Arising from the nucleus, the root-fibres of the fourth nerve pursue a course of considerable length within the mid-brain before gaining their superficial origin. THE TROCHLEAR NERVE. 1229 Leaving the upper and lateral part of the nucleus as axones of the trochlear neurones, the strands of fibres pass outward and backward within the gray matter of the floor of the aqueduct until they near the inner concave surface of the mesencephalic root of the fifth nerve, which, after being condensed into one or two bundles, they follow downward as far as the superior extremity of the fourth ventricle. Then bending sharply medially, the fourth nerve, so far as the great majority of its fibres are concerned, enters the superior medullary velum, in which it decussates with its fellow of the opposite side and crosses the mid-line to emerge at its superficial origin on the dorsal surface of the brain-stem (Fig. 957) just below, the inferior corpora quad- rigemina, between the frenum of the velum and the mesial border of the superior cerebellar peduncle. Cortical and Central Connections. The trochlear nucleus is directly connected with the cerebral cortex by fibres which descend from the inferior frontal convolution through the corona radiata, the internal capsule and the cerebral peduncle and cross to the nucleus of the opposite FIG. 1053. Olfactory tracts Optic chiasm Gasserian ganglion Int. carotid artery II I. nerve Mid. lie peduncle of cerebellum Medulla oblongata XI. nerve \ \ , X. nerve \ \ \ IX. nerve \ \ Frontal nerve Supratrochlear Supraorbital Levator pal- pebrae superioris Rectus superior Lachrymal nerve Rectus extern us lir. of communi- cation bet. lachry- mal and temporo- n.alar br. maxil- lary nerve - Malar br. tempo- ro-malar nerve Temporal br. temporo-malar nerve ^ Ophthalmic div. V. nerve Maxillary div. V. nerve . v Mandibular div. V. nerve \ Geniculate ganglion of VII. nerve fa part of great 4 4 VII. nerve superficial petrosal nerve is seen passing beneath VIII. nerve Temporal bone, cut Gasserian ganglion) Dissection showing right trochlear nerve throughout its length, also oculomotor and frontal and lachrymal branches of trigemiual nerve ; roof and outer wall of orbit have been removed. side. By means of the posterior longitudinal bundle it is brought into relation with the nucleus of the third and of the sixth nerve, thus insuring harmonious action of the eye muscles; further, by means of the same path, it is probably connected with the cochlear nucleus by way of the superior olive and its peduncle. Course and Distribution. Emerging at its superficial origin, the nerve is directed outward over the superior cerebellar peduncle, then winds forward around the outer surface of the cerebral peduncle, parallel to and between the posterior cerebral and superior cerebellar arteries, and appears at the base of the brain (Fig. 1053). Proceeding forward to the floor of the cranium, the nerve enters the dura immediately beneath the free border of the tentorium, slightly behind and external to the posterior clinoid process and the third nerve, and continues in the outer wall of the cavernous sinus, at first having the third nerve above it and the ophthalmic division of the fifth below, and then crossing above the third from below inward, to gain the medial end of the sphenoidal fissure. It enters the orbit above the heads, of 1230 HUMAN ANATOMY. the external rectus muscle and, directed medially, crosses above the levator palpebrse superioris and superior rectus and reaches the superior oblique, which it enters on the upper surface close to the external border (Fig. 1056). The communications of the trochlear nerve, as it courses in the wall of the cavernous sinus are: (i) filaments from the carotid sympathetic plexus; (2) fibres of common sensation from the ophthalmic division of the fifth. Variations. The course of the trochlear nerve is sometimes through instead of over the levator palpebrse superioris. Unusual branches to sensory nerves, as the frontal, supratroch- lear, the infratrochlear and the nasal, are probably due to the aberrant course of sensory fibres from the trifacial. The fourth nerve occasionally sends a branch to the orbicularis palpebrarum. THE TRIGEMINAL NERVE. The fifth, trigeminal or trifacial nerve (n. trigeminus), the largest of the cranial series, is a mixed nerve and consists of a large sensory part (portio major) and a much smaller motor portion (portio minor). The former supplies fibres of common sensation to the front part of the head, the face, a portion of the external ear, the eye, the nose, the palate, the naso-pharynx in part, the tonsil, the mouth and the tongue. The motor portion is distributed to the muscles of mastication, the mylo- hyoid and the anterior belly of the digastric. The relation of the fibres composing these two parts to the cells within the brain-stem is, therefore, very different, in the case of the motor fibres the cells being a nucleus of origin and in that of the sensory fibres one of reception. The Sensory Part. The fibres comprising the sensory part of the trigeminal nerve, which convey sensory impulses from the various head-structures, are the pro- cesses of cells lying outside the central axis in the Gasserian ganglion on the sensory root. The portions of the fibres between the periphery and the ganglion correspond to elongated dendrites, while the much shorter centrally directed constituents of the sensory root, connecting the ganglion with the brain-stem, are the axones of the Gasserian neurones. The general resemblance between the fifth cranial nerve and a typical spinal nerve is striking, in each case the sensory root bearing a ganglion and the motor root proceeding from cells within the central nervous axis. Proceeding brainward as axones of the Gasserian cells, the sensory fibres of the trigeminal nerve become consolidated into the large sensory root, which passes through an opening in the dura mater (Fig. 1033) situated beneath the attachment of the tentorium cerebelli to the posterior clinoid process. Coursing backward through the posterior fossa of the cranium it enters the brain-stem on the lateral sur- face of the pons, slightly behind the superior border, as the conspicuous group of robust bundles that mark the superficial origin of the nerve (Fig. 1046). Just above it is the superficial origin of the motor root, from which it is separated by a small bundle of pontine fibres which belong to the middle cerebellar peduncle. Below and in line with it are the superficial origins of the facial and auditory nerves. Entering the tegmental portion of the pons, close to the overlying superior cerebellar peduncle, the sensory fibres soon come into relation with the extensive trigeminal reception- nucleus, a columnar mass of gray matter within the lateral part of the tegmentum (Fig. 935). This nucleus extends from the middle of the pons through the entire length of the medulla and into the spinal cord as far down as the level of the second cervical segment, where it becomes continuous with the substantia gelatinosa of the cord. The rounded and enlarged upper end of this tapering column is described as the sensory nucleus of the fifth nerve, although it com- prises only a small part of the reception-nucleus. The latter, in turn, is the upward prolongation of the substantia gelatinosa Rolandi, conspicuous in all cross-sections of the lower pons and medulla as an oval field of gray matter (Fig. 930). On nearing this column the sensory fibres divide into ascending and descending brandies, much in the same way as the posterior root-fibres bifurcate within the posterior columns of the cord. The ascending fibres, distinctly finer than the descending, soon penetrate the sensory nucleus and the substantia gelatinosa and end in arbori/ations around the neurones of the reception nucleus. The coarser descending fibres become collected into a compact bundle, the descending or spinal root (tractus spinalis n. irim-mini), whose medially directed concavity closely embraces the lateral surface of the column of gray substance. Beginning with its descent, the THE TRIGEMINAL NERVE. 1231 spinal root gives off collaterals and fibres that bend medially, enter the adjacent substantia gel- atinosa and end in arborizations around the reception cells of that nucleus. Since the number of fibres is thus progressively reduced during the descent of the spinal root, the tract is tapering, becoming smaller and smaller as it approaches the spinal cord until within the upper part of the latter, at about the level of the second cervical nerve, it finally disappears. In its descent through the brain-stem the spinal tract becomes more and more superficially placed, in the lower part of the pons lying to the inner side of the restiform body, separated from it by the vestibular division of the auditory nerve, and lower, in the lateral area of the medulla, occupying a position close to the surface as it rests upon the expanded gelatinous substance of the tuberculum Rolandi. The central connections of the sensory part of the trigeminus (Fig. 1054), by way either of the collaterals of the fibres of the spinal root or of the axones and collaterals of the axones of the reception neurones, are undoubtedly very extensive, since the impulses collected by this important nerve are widely dispersed. The most important paths for such distributions are : 1. By axones that pass, as arcuate fibres, from the cells of the reception-nucleus across the raphe to join the opposite mesial fillet and ascend to the optic thalamus and FIG. 1054. thence, after interruption in the cells of the latter, by axones of thalamic neu- rones to the cerebral cortex. It is prob- able that some of the arcuate fibres do not cross the mid-line, but ascend within the mesial fillet of the same side. It is also probable that collaterals of the arcuate fibres pass to the trigeminal, facial and glosso-pharyngeo-vagal motor nuclei. 2. By axones from the cells of the reception nucleus that enter the infe- rior cerebellar peduncle of the same side and pass to the cerebellar cortex as con- stituents of the nucleo-cerebellar tract. 3. By collaterals that are distrib- uted to the nuclei of origin of the hypo- glossal and of the motor part of the tri- geminus and facial nerves, whereby these important motor nerves are brought directly under the influence of the sensory part of the fifth. The Motor Part. In con- trast to the median position of the nuclei of origin of the oculomotor, trochlear, abducent and hypoglos- sal nerves, the deep origin of the f . . . . Diaeram showing relations of tngeininal root-fibres to nuclei motor part OI the tngemmUS in- within brain-stem ; GC, Gasserian ganglion with divisions (/, rlnHpc o-rminc r>f rv>11c rhaf lip at II, HI) of sensory part of nerve ; SR, MR, sensory and motor 6 al roots : S, sensory nucleus ; SG, substantia gelatinosa : Sp.K, spi- some distance from the raphe and nal or descending root ; /s mesial fillet ; Cb nucleo-cerebellar f ,. . -ill 11 fibre: M, motor nucleus; Ms/t, mesencepnalic root; S/, sub- fall mtO Series With the laterally stantia ferruginea ; CB, cortico-bulbar fibres. placed nuclei of the motor parts of the other mixed cranial nerves the facial, the glosso-pharyngeal and the vagus. 1. The largest contingent of the motor fibres of the trifacial nerve arise as axones from the neurones within the chief motor nucleus (nucleus masticatorius) (Fig. 935). This nucleus con- sists of a short columnar collection of gray matter, oval on cross-section, which lies in the upper part of the pons, close to the median side of the sensory nucleus. It is composed of large stel- late cells from which, as their axones, the motor fibres proceed outward through the tegmentum to their superficial origin on the pons. A small number of fibres, from the more medially situ- ated cells of the nucleus, pursue a dorsally convex course toward the raphe, which they cross close beneath the floor of the fourth ventricle to join the motor nucleus of the opposite side and become incorporated in the opposite trigeminal motor root. 2. A second and smaller constituent of the motor root, the descending mesencephalic root (radix descendens n. trigemini) includes fibres that arise from cells lying within the lateral part of the gray matter surrounding the Sylvian aqueduct. In cross-sections (Fig. 936) this root appears as a delicate crescentic bundle that descends from the mid-brain to join the larger tract 1232 III MAN ANATOMY. of fibres from the chief motor nucleus. In its downward course the mesencephalic root is joined by numerous fibres which have their origin in the pigmented cells of the substantia ferru- ginea (page 1081) of the same and, possibly, of the opposite side. The fibres from these various sources the mesencephalic nucleus, the substan- tia ferruginea and the motor nucleus become consolidated into the motor root of the trigeminal nerve, whose superficial origin (Fig. 1046) is just above that of the sensory root, from which it is separated by some of the superficial transverse fibres of the pons. Leaving the side of the pons, the motor root follows the same course to and through the dura mater as does the sensory, to the inner side of which it lies. It eventually passes beneath the Gasserian ganglion to become exclusively an integral portion of the mandibular division of the trigeminal. The cortical connections of the motor root are established by fibres that arise from cells within the cortical gray matter of the lower third of the precentral convolution. Thence, as constituents of the pyramidal tracts, they descend through the corona radiata, the internal cap- sule and the cerebral peduncle into the pons, where, for the most part after decussation, they terminate in end-arborizations around the radicular cells of the motor trigeminal nuclei. The Gasserian Ganglion. The Gasserian ganglion (ganglion semilunare [Gasseri]) (Fig. 1055) is an important complex of nerve-fibres and cells, which lies in a slight depression on the FIG. 1055. apex of the petrous portion of the temporal bone. In shape it is a flattened crescent with its convexity forward, measuring from 1.5-2 cm. in width and about i cm. in length. The sur- face of the ganglion presents an irregular longitudinal or reticu- lar striation. From the anterior expanded convex border of the ganglion arise the ophthalmic and maxillary nerves and the sensory portion of the mandib- ular nerve, while its narrow concave posterior margin is con- tinued into the sensory root of the fifth nerve. The ganglion lies in McckcC s space (cavuni Meckclii), a cleft produced by a delamination of the dura mater, and comes in relation internally with the cavernous sinus and the internal carotid artery. Be- neath, but unconnected with it, are the motor root of the trifacial and the great superficial petrosal nerve. In struc- ture it resembles a spinal ganglion, being composed of the characteristically modified neurones, from whose single processes proceed the peripherally directed dendrite> and the centrally coursing axones. In addition to the three large trunks given off from the anterior margin, the branches of the Gasserian ganglion include some fine meningeal filaments which arise from the posterior end of the ganglion and are distributed to the adja- cent dura mater. Optic nerve Internal carotid artery ( '.asset-fan ganglion Gasserian ganglion of left side viewed from above; sensory and motor roots and three divisions of trigeminal nerve are seen. Communications. At its inner side the < '.asserian ganglion receives filaments from tin- adjacent carotid plexus of the sympathetic, which end in relation with the cells of the ganglion. Divisions of the Trigeminal Nerve. These are three in number, the o/>/i- f/itifinic, the: nta. \illarv and the iinuulihidar nerves. They arise- from the anterior THE TRIGEMINAL NERVE. I2 33 margin of the Gasserian ganglion, the formation of the mandibular nerve being com- pleted by the accession of the motor root of the trigeminal. I. The Ophthalmic Nerve. The ophthalmic nerve (n. ophthalmicus) (Fig. 1056), the smallest of the three divisions, is purely sensory and supplies the upper eyelid, the conjunctiva, the eyeball, the lachrymal gland, caruncle and sac, the fore- head and anterior part of the scalp, the frontal sinus and the root and anterior por- tion of the nose. It arises from the anterior margin of the Gasserian ganglion and passes upward and forward for about 25 mm. in the external wall of the cavernous sinus, lying below the fourth nerve. Reaching the sphenoidal fissure it breaks up intb its terminal branches, which pass through the fissure into the orbit. Branches and Distribution. The branches of the ophthalmic nerve are: (i) the recurrent, (2) the communicating, (3) the lachrymal, (4) the fro ntal, and (5) the nasal, of which the last three are terminal branches. FIG. 1056. Supratochlear nerve Nasal nerve Olfactory bulbs Superior oblique muscle IV. nerve Cut edge of bone Optic nerve Optic chiasm Internal carotid artery Optic tract VI. nerve III. nerves Cerebral peduncles Supraorbital nerve Lachrymal gland Levator palpebrse superioris Superior rectus Frontal nerve External rectus Lachrymal nerve Ophthalmic division of V. nerve Maxillary division of V. nerve Mandibular division of V. nerve Gasserian ganglion Meatus auditorius internus VII. nerve, motor part Pars intermedia VIII. nerve Roof of right orbit has been removed to expose branches of ophthalmic division of trigeminal nerve; Gasserian ganglion, and third, fourth, sixth, seventh and eighth nerves also seen. 1. The recurrent branch (n. tentorii) arises shortly after the nerve leaves the ganglion. It passes across and is adherent to the trochlear nerve and is distributed between the layers of the tentorium cerebelli. 2. The communicating branches are three slender filaments which are given off before the nerve breaks up into its terminal branches ; they join the trunks of the third, fourth and sixth nerves, to whose muscles they supply sensory fibres. During its passage through the cavernous sinus, the ophthalmic nerve receives some tiny filaments from the cavernous sympathetic plexus. 3. The lachrymal nerve (n. lacrimalis) (Fig. 1053) is the smallest of the terminal branches. It lies to the outer side of the frontal nerve and traverses the outer angle of the sphenoidal fissure in its own sheath of dura mater. It passes above the origin of the orbital muscles and courses along the lateral wall of the orbit, above the external rectus, to the upper outer angle of trie orbit, where it pierces the palpebral fascia near the external canthus to terminate in the upper eyelid. It sup- plies the lachrymal gland, the upper eyelid and the skin around the external canthus. 78 1234 HUMAN ANATOMY. Within the orbit the lachrymal nerve communicates with the temporal branch of the temporo-malar nerve and on the face with the temporal branch of the facial. The latter is one of the numerous sensory-motor communications between the terminal fibres of the fifth and seventh nerves. Variations. Occasionally the lachrymal nerve seems to be partly derived from the troch- lear ; the true source of such fibres, however, is probably the ophthalmic nerve, by way of its communicating branch to the fourth. Considerable variation is found in connection with the temporal branch of the temporo-malar nerve. The lachrymal nerve or the temporal branch of the temporo-malar may be absent, the place of either being taken by the other, or the lachrymal may be small at its origin and later increased to normal size by accessions from the temporal branch of the tem'poro-malar. 4. The frontal nerve (n. frontalis) (Fig. 1053) is the largest branch of the ophthalmic. It enters the orbit, invested by its own dural sheath, through the sphenoidal fissure and above the orbital muscles and passes directly forward between the periosteum and the levator palpebrae superioris. At a variable point, usually about the middle of the orbit, it divides into its terminal branches, the (a) supra- trochlear and (6) the supraorbital. a. The supratrochlear nerve (n. supratrochlearis) is the smaller of the two terminal branches. It passes inward and forward over the pulley of the superior oblique and thence between the orbicularis palpebrarum and the frontal bone, leaving the orbit at its upper inner angle. Near the pulley it gives off a branch which joins the infratrochlear (Fig. 1057) and at the edge of the orbit supplies filaments (nn. palpebrales superiores) to the skin and conjunctiva of the upper eyelid. It then turns upward and subdivides into a number of small branches which pierce the substance of the frontalis and orbicularis palpebrarum muscles to supply the inner and lower part of the forehead. b. The supraorbital nerve (n. supraorbitalis) (Fig. 1056) continues directly the course of the frontal nerve. It lies close to the periosteum throughout its entire orbital course and leaves the orbit through the supraorbital notch or foramen. In this situation it sends a small filament to the frontal sinus to supply its diploe and mucous membrane. As it leaves the orbit it sup- plies some fine twigs to the upper eyelid and then divides into a larger outer and smaller inner branch. These pass upward on the forehead beneath the frontalis muscle, occasionally occupy- ing quite deep grooves in the frontal bone, and terminate by being distributed to the scalp and pericranium. The outer branch extends back nearly to the occipital bone, while the inner passes only a short distance posterior to the coronal suture. Both branches of the frontal, the supratrochlear and the supraorbital, communicate with branches of the facial nerve and thereby supply sensory filaments to muscles supplied by the seventh. Variations. The nerve may divide before leaving the orbit and in that event only the outer branch passes through the normal osseous channel. The inner sometimes has a special groove, named by Henle ^n& frontal notch. 5. The nasal nerve (n. nasociliaris) (Fig. 1057) is intermediate in size between the lachrymal and the frontal. It enters the orbit, clothed in dura mater, through the sphenoidal fissure, between the heads of the external rectus and between the superior and inferior divisions of the oculomotor nerve. Turning obliquely in- ward, it crosses the optic nerve and passes beneath the superior oblique and superior rectus muscles and above the internal rectus. Thence it traverses the anterior eth- moidal foramen to enter the cranial cavity, where it passes forward in a groove in the lateral part of the cribriform plate of the ethmoid bone. Leaving the cranium through the nasal fissure, the nerve enters the nasal fossa, where it breaks up into its three terminal branches. Branches. These are : (a) tib&gangliomc, (6) the long ciliary, (c) tin- infra- trochlear, (d) the internal nasal, (c) the external nasal and (/) the anterior nasal, of which the last three are terminal branches. a. The gang/ionic branch (radix longa) (Fig. 1057) usually leaves the nerve between the heads of the external rectus and passes forward along the outer side of the optic nerve to enter the upper posterior portion of the ciliary ganglion, of which it forms the sensory or long root. b. The long ciliary branches (nn. dliares lonyi) (Fig. 1058) are two in number. They pass forward along the inner side of the optic in-rve and, after joining one or motv of the short ciliary nerves, pierce the sclerotic coat of the eye to be distributed to the iris, ciliary muscle and form -A. THE TRIGEMINAL NERVE. 1235 c. The infratrochlear nerve (n. infratrochlearis) (Fig. 1058) runs forward along the inner orbital wall and beneath the superior oblique muscle and its pulley to the inner end of the pal- pebral fissure, where it terminates. Near the pulley it receives a filament (the supratrochlear) from the nasal nerve. It supplies the skin of the upper eyelid and root of the nose, as well as the conjunctiva and the lachrymal caruncle and sac. d. The internal nasal or septal branch (rr. mediates) (Fig. 1048) supplies the mucous mem- brane of the anterior portion of the septum. e . The external nasal branch (rr. laterales) (Fig. 1047) supplies the front part of the middle and inferior turbinate bones and outer wall of the nasal fossa. f. The anterior nasal branch (r. nasalis extremus) passes downward in a groove in the under side of the nasal bone and then between the lower end of the nasal bone and the FIG. 1057. Superior oblique musclex. \ Internal rectus muscle > x N j1 Infratrochlear br. of nasal Nasal nerve Olfactory bulb' Levator palpebrse superi- oris, inverted III. nerve, superior, division Frontal nerv Optic nerve Internal carotid artery III. nerv FOILS, displaced backward Levator palpebrre superioris Superior rectus Lachrymal gland Nerve to inferior oblique External rectus muscle iliary ganglion Nasal nerve Lachrymal nerve Maxillary division of V. Ophthalmic division of V. Mandibular division of V Gasserian ganglion VI. nerve IV. nerve Cerebral peduncl Deeper dissection of right orbit, viewed from above ; branches of nasal nerve shown. upper lateral cartilage of the nose, finally emerging from under cover of the compressor naris muscle. It supplies the skin of the fore-part and tip of the nose. Variations. The nasal nerve may send branches to the superior and internal recti and levator palpebrse superioris muscles. In one case a small ganglion connected with the nasal nerve sent fibres to the third and sixth nerves. Instances are recorded of absence of the infratrochlear branch, the deficiency being supplied by the supratrochlear. Branches to the frontal and ethmoidal sinuses are described as being given off in the anterior ethmoidal fora- men, and a branch has been found which passes through the posterior ethmoidal foramen to supply the sphenoidal and posterior ethmoidal sinuses. The latter has been called by Luschka the spheno-ethmoidal and by Krause the posterior ethmoidal branch. The Ganglia associated with the Trigeminal Nerve. Four small ganglia are connected with the extracranial portion of the fifth nerve. They are the ciliary, the spheno-palatine, the otic and the submaxillary. The ciliary ganglion is associated 1236 HUMAN ANATOMY. with the ophthalmic nerve, the spheno-palatme with the maxillary and the otic and submaxillary with the mandibular. Each is the recipient of three roots a motor, a sensory and a sympathetic and from each ganglion branches are given off to more or less contiguous structures. The significance of these bodies whether of the nature of spinal or sympathetic ganglia has long been a subject of discussion. The close resemblance of their nerve-cells to the stellate neurones of undoubted sympathetic ganglia, as shown by the investigations of Retzius, Kolliker and others, as well as the results of experimental studies (Apolant), justifies the conclusion that these ganglia are properly regarded as belonging to the sympathetic group. They are, therefore, probably stations in which certain motor and secretory fibres contributed by various nerves end in arborizations around sympathetic neurones, from which axones pass for the immedi- ate supply of involuntary muscle and glandular tissue. The fact that these small ganglia are derivations of the early Gasserian ganglion is in accord with the mode of origin of the sympathetic ganglia elsewhere (page 1013). FIG. 1058. Internal carotid artery IV. nerve Cerebral peduncle s " * > .fc'C>-E " X'o 8 i S.2 1, | Ifl 5:2 2S.5 Rs 5 ! II > jlll^ ^ |l i Middle cerebella. peduncle Levator palpebrae superioris Superior oblique muscle Lachrymal gland uperior rectus muscle Long ciliary branches of nasal nerve Ext. rectus, insertion Inferior oblique muscle Gasserian ganglion ^Ext. rectus muscle VI. nerve Ganglionic branch of nasal Ciliary ganglion Branch to Inf. oblique Inferior rectus muscle Short ciliary nerves ..... .. ...^.^ Dissection of right orbit after removal of its lateral wall ; external and superior eye-muscles have been cut and displaced to expose ciliary ganglion and nerves. The Ciliary Ganglion. The ciliary, ophthalmic or Icnticulat ganglion (g. ciliare) (Fig. 1058), as it is varyingly called, is a small reddish mass, about 2 mm. long in the antero-posterior direction, and approximately quadrilateral in out- line. It is compressed laterally and to each angle is attached one or more bundles of nerve-fibres. It lies near the apex of the orbit on the outer side of the optic nerve, between the latter and the external rectus muscle and anterior to the ophthalmic artery. The nerve-cells within the ganglion are chiefly multipolar elements, which closely resemble sympathetic neurones (Retzius) and send their axones towards the eye by way of the short ciliary nerves. Roots. All of these enter the posterior margin of the ganglion. The motor or short root (radix brcvis), the thickest of the roots and sometimes double, is an off- shoot from the branch of the oculomotor nerve which supplies the inferior oblique muscle. It is short and comparatively robust and joins the postero-inferior portion of the ganglion. The sensory or long root (radix lonsja) arises from the nasal branch of the ophthalmic, leaving the latter between the heads of the external reetns. It is long and slender and passes forward to enter the- upper posterior angle of the gang- lion, occasionally being fused with the sympathetic root. The sympathetic root (radix THE TRIGEMINAL NERVE 1237 media) is a tiny filament which arises from the cavernous plexus and runs forward to enter, either alone or with the sensory root, the upper posterior angle of the ganglion. Branches. These are the short ciliary nerves (nn. ciliares breves). They number from four to six and by division are increased to twelve or twenty before reaching the eyeball (Fig. 1058). They arise as two fasciculi from the upper and lower anterior angles of the ganglion and pass forward above and below the optic nerve. The lower set is the more numerous and on its way forward is joined by the long ciliary nerves from the nasal, with which one or more of its constituent branches usually fuse. After piercing the sclerotic coat in two groups, one below and the other above the entrance of the optic nerve, they pass forward in grooves on the inner surface of the sclerotic to supply the choroid, iris, ciliary muscle and cornea. The short ciliary nerves include three sets of fibres : ( i ) Sympathetic fibres destined for the walls of the blood-vessels and the radial (dilator) muscle of the iris ; these are links in the chain made up of (a) white rami communicantes from the upper thoracic spinal nerves to the cervical gangliated cord, and (b) the axones of neurones within the sympathetic ganglia. (2) Fibres supplying the ciliary muscle and the circular (sphincter) muscle of the iris, which, while in a sense the continuations of the oculomotor nerves, are immediately the axones of the stellate sympathetic neurones within the ciliary ganglion. (3) Trigeminal fibres which transmit sensory impulses from the interior of the eyeball, in conjunction with the long ciliary nerves. Variations. The motor root occasionally bifurcates before it reaches the ganglion. As noted above, the sensory and sympathetic roots frequently form a common trunk of entrance into the ganglion. Occasionally the ganglion is very small, due possibly to the scattering of its constituent neurones among the nerves connected with it (Quain). Additional roots have been described as coming from the superior division of the oculomotor, from the trochlear, from the lachrymal, from the abducent and from the spheno-palatine ganglion. Absence of the sensory root has been noted, the deficiency possibly being corrected by the long ciliary nerves convey- ing sensory fibres directly from the nasal to their destination, instead of these fibres passing through the ganglion. The sympathetic root may be multiple, a condition held by some to be normal, some of the fibres accompanying the oculomotor nerve. II. The Maxillary Nerve or superior maxillary nerve (n. maxillaris) is purely sensory and is intermediate in size between the ophthalmic and mandibular divisions of the trigeminus. It supplies the cheek, the anterior portion of the temporal region, the lower eyelid, the side of the nose, the upper lip, the upper teeth, and the mucous membra'ne of the nose, naso-pharynx, maxillary antrum, posterior ethmoidal cells, soft palate, tonsil and roof of the mouth. Arising from the middle of the anterior convex border of the Gasserian ganglion, it passes forward beneath the dura mater in the middle cranial fossa, lying below the cavernous sinus (Fig. 1053). The nerve leaves the cranium through the foramen rotundum, traverses the spneno-maxillary fossa and enters the orbital cavity by means of the spheno-maxillary fissure. It occupies and then parallels the floor of the orbit in the infraorbital groove and canal, finally emerging on the face by passing through the infraorbital foramen. Here it breaks up fanlike into three terminal groups of branches (Fig. 1060). Branches and Distribution. Branches are given off from the maxillary nerve in the cranium, in the spheno-maxillary fossa, in the infraorbital canal and on the face. These are : within the cranium, ( i ) the recurrent ; within the spheno-maxillary fossa, (2) the spheno-palatine, (3) the posterior superior dental and (4) the temporo- malar ; in the infraorbital canal, (5) the middle superior dental and ( 6 ) the anterior superior denial ; on the face ( 7 ) the inferior palpcbral, ( 8 ) the lateral nasal and ( 9 ) the superior labial. The last three are terminal branches. 1. The recurrent branch (n. meningeus) is given off before the maxillary nerve passes through the foramen rotundum. It supplies the dura mater in the middle cranial fossa. 2. The two or three spheno-palatine branches (nn. sphenopalatini) (Fig. 1061) arise in the spheno-maxillary fossa. They are short and thick and pass directly downward to the upper margin of the spheno-palatine ganglion, whose sensory root they supply. Only a small part of their fibres actually traverse the ganglion, the much larger part passing lateral to or in front of the ganglion, to be continued 1238 HUMAN ANATOMY. into the orbital, posterior nasal and palatine branches. While in neither case are the trigeminal fibres interrupted in the ganglion, in both instances they receive sympa- thetic fibres from the ganglion, which accompany the trigeminal ones. 3. The posterior superior dental nerve (r. alveolaris superior posterior) (Fig. 1060) is frequently double. It passes downward and forward with the posterior dental artery through the pterygo-maxillary fissure to reach the zygomatic surface of the maxilla. It supplies tiny filaments to the gum and adjacent mucous membrane of the cheek and enters the posterior dental canals to supply the molar teeth. It forms a fine plexus (plexus dentalis superior) (Fig. 1059) with the middle and anterior superior dental nerves. Variation. In the absence of the buccal branch of the fifth, the posterior superior dental has been observed to be of large size and to assume the distribution of the buccal. 4. The temporo-malar or orbital nerve (n. zygomaticus) (Fig. 1053) after arising from the maxillary passes from the spheno-maxillary fossa into the orbit FIG. 1059. Diagram showing plan and connections of second and third divisions of trigeminus and their ganglia. through the spheno-maxillary fissure. It courses along the external orbital wall and divides into a temporal and a malar branch. The temporal branch (n. zygomaticotem- poralis) after inosculating with the lachrymal nerve passes through the spheno-malar foramen to enter the temporal fossa. It then runs between the bone and the temporal muscle and pierces the temporal fascia to be distributed to the skin of the anterior temporal region. It communicates with the tc'inporal branch of the facial nerve. The malar branch (n. zygomaticofacialis) traverses the malar foramen to supply the skin of the malar region. It joins with filaments from the malar branch of the seventh. Variations. The nerve may pass through the malar bone before it divides, both branches may pass separately through canals confined to the malar bone, or the temporal branch may pass THE TRIGEMINAL NERVE. 1239 through the spheno-maxillary fissure. Either branch may be absent or smaller than normal, the other branch supplying the deficiency. The malar may be replaced in its distribution by the infraorbital and the temporal may be substituted or augmented by the lachrymal. 5. The middle superior dental nerve (r. alveolaris superior medius) leaves the maxillary in the posterior part of the infraorbital canal. It occasionally arises from the anterior superior dental. It passes down in a canal in the outer wall of the maxillary antrum and after forming a plexus with the other two dental nerves supplies the premolar teeth. 6. The anterior superior dental nerve (r. alveolaris superior anterior) is the largest of the three superior dental nerves. It arises from the maxillary just before the exit of the latter at the infraorbital foramen and descends in a canal in the anterior wall of the antrum. It gives off a nasal branch, which enters the nose FIG. 1060. Middle superior dental nerve Maxillary Posterior superior dental Buccal Sensory division of mandibular Middle meningeal ar Auriculo-temporal ne Ext. pterygoid muscle Lingual n< Inferior dental nerve Superficial temporal artery Internal maxillary artery Int. pterygoid muscle Part of mandible I Ext. carotid artery __ Parotid gland Mylo-hyoid branch of inferior dental Submaxillary ganglion Submaxillary gland Inferior palpebral Lateral nasal and superior labial branches of infraorbital nerve Anterior superior dental nerve Nasal branch of anterior superior dental Sectional surface of mandible ,Digastric muscle, anterior belly Myo-hyloid muscle, cut to shov lingual nerve Dissection showing maxillary and mandibular nerves and their branches; outer wall of orbit, part of facial wall of maxillary sinus and part of mandible have been removed. through a tiny canal in the outer wall of the inferior meatus of the nose and supplies the mucous membrane of the anterior part of the inferior nasal meatus and floor of the nose. After helping to form the superior dental plexus, the anterior superior dental supplies the canine and incisor teeth. Two thickenings are sometimes found in the superior dental plexus. One of these, known as the ganglion of Valentin, lies above the tip of the root of the second premolar tooth, at the junction of the middle and posterior superior dental nerves; and the other, sometimes called the ganglion of Bochdalek, is situated more anteriorly, at the junction of the middle and anterior dental nerves. Neither of these enlargements is a true ganglion, being without nerve- cells and consisting of interlacing bundles of nerve-fibres. 1240 HUMAN ANATOMY. 7. The inferior palpebral branches (rr. palpebrales inferiores) (Fig. 1060) usually two in number, are the smallest of the terminal branches. They pass upward from the infraorbital foramen, pierce the origin of the levator labii superioris, pass around the lower margin of the orbicularis palpebrarum and supply the conjunctiva and skin of the lower eyelid. 8. The lateral nasal branches (rr. nasales externi) (Fig. 1060), from two to four in number, pass inward under the levator labii superioris alaeque nasi and supply the skin of the side of the nose. 9. The superior labial branches (rr. labiales superiores) (Fig. 1060), two to four in number, are the largest of the terminal branches. They pass downward under the levator labii superioris and, after supplying the anterior portion of the skin of the cheek, terminate in the mucous membrane and skin of the upper lip. The last three branches inosculate freely under the levator labii superioris with the infraorbital branch of the facial, forming the infraorbital plexus (Fig. 1068). The Spheno-Palatine Ganglion. The spheno-palatine ganglion (g. spheno- palatinum), also known as Meeker 's, the spheno-maxillary or the nasal ganglion, is a small triangular reddish-gray body, with the apex directed posteriorly, situated in the upper portion of the spheno-maxillary fossa. It is flat on its mesial surface, and convex on its lateral, and measures about 5 mm. in length. It lies in close proximity to the spheno-palatine foramen and just beneath the maxillary branch of the trigeminal nerve (Fig. 1061). The ganglion is regarded as belonging to the series of sympathetic nodes, and consists of an interlacement of nerve-fibres in which are embedded numerous stellate sympathetic neurones. Roots. The sensory root consists of two, sometimes three, short stout filaments, the spheno-palatine nerves (nn. sphenopalatini), which pass directly downward from the lower margin of the maxillary nerve to the upper border of the ganglion. While some few of the fibres of this root are axones of the sympathetic ganglion-cells, the great majority are dendrites of the- cells of the Gasserian ganglion which pass to a limited extent through, but mostly around, the spheno-palatine ganglion independently of its cellular elements. They are continued entirely into the various trunks that are usually described as branches of distribution of the ganglion (see below). The motor root is the great superficial petrosal nerve (n. petrosus superficialis major) which, in all probability, carries sensory as well as motor fibres. It arises from the facial nerve in the facial canal, passes through the hiatus Fallopii and a groove in the petrous portion of the temporal bone and then under the Gasserian ganglion to- reach the cartilage occupying the middle lacerated foramen. Here the great super- ficial petrosal nerve is joined by the sympathetic root, the great deep petrosal, (n. petrosus profundus), which is a branch from the carotid plexus. The two givut petrosal nerves fuse over the cartilage at the middle lacerated foramen to form the Vidian nerve (n. canalis pterygoidei [Vidii] ) (Fig. 1061), which traverses the canal of the same name and enters the spheno-maxillary fossa to join the spheno-palatine ganglion. In its course through the canal the Vidian nerve gives off a few tiny nasal branches, which, composed of trigeminal and sympathetic fibres, supply the pharyngeal ostium of the Eustachian tube and the posterior part of the roof of the nose and the nasal septum. While in the canal, the Vidian nerve receives a filament from the otic ganglion. In addition to supplying (according to many anatomists) motor fibres to the levator palati and azygos uvulae muscles, some of the facial fibres are especially destined for glandular struc- tures. Such fibres are probably interrupted around UK- stellate cells of the spheno-palatine ganglion, the axones of which then complete the paths for the secretory impulses. The sensory constituents of the great superficial petrosal nerve are, perhaps, of two kinds: (a) fibres from the cells of the geniculate "ganglion of the facial to the palatine taste-buds, and (b} recurrent trigeminal fibres, that, byway of tin.- maxillary, spheno-patetfatt and great superficial petrosal nerves, are distributed with the peripheral branches of the Vidian or of tin- facial m-rvr. The great deep petrosal nerve represents tin- association cord between the superior cervical sympathetic and the spheno-palatine ganglion. Many of its fibres end in arbori/ations around the stellate spheno-palatine cells, from which, in turn, axones pass to blood-vessels and glands by way of the ganglionic branches of distribution. THE TRIGEMINAL NERVE. 1241 Branches. The branches of distribution of the spheno-palatine ganglion are conveniently grouped into four sets : (i) the ascending, (2) the descending, (3) the internal and (4) ^\^ posterior. 1. The ascending or orbital branches (IT. orbitales) (Fig. 1059) are two or three tiny filaments, which pass into the orbit through the spheno-maxillary fissure and, after traversing the posterior ethmoidal canal or a small special aperture, are distrib- uted to the sphenoidal and posterior ethmoidal air-cells and the periosteum of the orbit. 2. The descending branches (nn. palatial) (Fig. 1059) are three : (a) the large posterior palatine, {b) the small posterior palatine, and (<:) the accessory pos- terior palatine nerves. a- The large posterior palatine nerve (n. palatinus anterior) leaves the spheno-maxillary fossa by means of the large posterior palatine canal, through which it descends to the inferior surface of the hard palate. While in the canal it gives off one or two posterior inferior nasal branches. FIG. 1061. Cavernous plexus and t. carotid artery , Great superficial ^'petrosal nerve Great deep petrosat nerve from carotid plexus Post. inf. nasal brs. of large posterior palatine Large, small am accessory poste rior palatine nerves Naso-palatine nerve, termination Otic ganglion, cut Cartilage of Eustachian tube, cut Int. br. of ascending ram us sup. cerv. gangL Ext. br. of ascending ramus of sup. cerv. ganglion Sup. cerv. ganglion of sympathetic Int. carotid artery Uvula :onstrictor tor palati Tensor palati, cut above Dissection showing spheno-palatine and otic ganglia viewed from within. (rr. nasales posteriores inferiores) , which, escaping through small apertures in the perpendicular plate of the palate bone, enter the nasal fossa and supply the mucous membrane of all but the anterior portion of the inferior turbinate bone and the adjoining portions of the middle and infe- rior nasal meatuses. Emerging from its canal the main nerve passes forward in a groove on the inferior aspect of the hard palate and inosculates with the terminal filaments of the naso-palatine nerve. It supplies the hard palate and its mucous membrane, as well as the inner side of the gum. b. The small posterior palatine nerve (n. palatinus posterior) descends in the small pos- terior palatine canal. It supplies sensory filaments to the mucous membrane of the soft palate and the tonsil and motor ones to the levator palati and azygos uvulae muscles. c. The accessory posterior palatine nerves (nn. palatinus medius) are one or more small filaments which pass through the accessory posterior palatine canals and supply the mucous membrane of the soft palate and tonsil. 3. The internal branches (rr. nasales posteriores superiores) (Fig. 1059) pass from the spheno-maxillary into the nasal fossa through the spheno-palatine foramen. They are : (a) the posterior superior nasal and (b) the naso-palatine nerve. i2 4 2 HUMAN ANATOMY. a. The posterior superior nasal nerve (rr. laterales) supplies the mucous membrane of the posterior superior portion of the outer wall of the nasal fossa. b. The naso-palatine nerve (n. nasopalatinus) (Fig. 1059) crosses the roof of the nasal chamber and passes downward and forward in a groove in the vomer and septal cartilage to reach the anterior palatine canal. It then passes through the foramen of Scarpa, the left nerve through the anterior and the right one through the posterior canal, the two nerves forming in this situation a fine plexus. Having reached the inferior surface of the hard palate, the naso- palatine inosculates with the large posterior palatine nerve. It supplies the roof and septum of the nose and that portion of the hard palate which lies posterior to the incisor teeth. 4. The posterior branch (Fig. 1059) also known as the pharyngeal or pterygo-palatine, leaves the spheno-maxillary fossa through the pterygo-palatine canal and supplies the mucous membrane of the naso-pharynx in the region of the fossa of Rosenmiiller. Variations. Branches of the ganglion have been described as passing to the abducent nerve, to the ciliary ganglion and to the optic nerve or its sheath. The accessory posterior palatine nerve is sometimes absent. Quite frequently the left naso-palatine nerve passes through the posterior foramen of Scarpa and the right nerve through the anterior. III. The Mandibular Nerve. The mandibular or inferior maxillary branch (n. mandibularis) of the trigeminal nerve is the largest of its three divisions and, being a mixed nerve, consists of two portions, one sensory and the other motor. The sensory part is the larger and arises from the lower anterior portion of the Gasserian ganglion. The smaller motor part is the motor root of the trigeminal nerve, which contributes exclusively to this division of the fifth nerve. Although these two portions are inti- mately associated in their passage through the foramen ovale, the motor bundle lying to the median side of the sensory, it is not until they emerge from the skull that they unite, immediately below the lower margin of the foramen ovale, to form the mandibular nerve. The sensory portion supplies the skin of the side of the head, the auricle of the ear, the external auditory meatus, the lower portion of the face and the lower lip, the mucous membrane of the mouth, tongue and mastoid cells, and the lower teeth and gums, the salivary glands, the temporo-mandibular articulation, the dura mater and the skull. The motor portion supplies the muscles of mastication (the temporal, the masseter and the external and internal pterygoids), the anterior belly of the digastric, the mylo-hyoid, the tensor palati and the tensor tympani muscles. By union of the two constituents, a thick common trunk is formed, which, after a course of from 2-3 mm. , separates under cover of the external ptery- goid muscle into an anterior and a posterior division (Fig. 1063). Branches and Distribution. The branches from the main trunk of the mandibular nerve are : (i) the recurrent branch and (2) the internal pterygoid nerve. 1. The recurrent branch (n. spinosus) arises just beneath the foramen ovale and accompanies the middle meningeal artery into the cranium through the foramen spinosum. It then divides into two branches, the anterior of which supplies the greater wing of the sphenoid and the adjacent dura mater, while the posterior passes through the petro-squamous suture and supplies the mucous membrane of the mastoid air-cells. 2. The internal pterygoid nerve (n. pterygoideus interims) (Fig. 1059) passes downward on the mesial side of its muscle and, in addition to supplying the pterygoid muscle, gives off the motor root of the otic ganglion and filaments to the tensor tympani and tensor palati muscles. The Anterior Division of the mandibular nerve (n. masticatorius) is motor, with the exception of its buccal branch, and receives almost the entire motor constit- uent of the trigeminal. It passes downward and forward for a short distance under the external pterygoid muscle and then breaks up into its branches. Branches. These are: (i) the masscleric , (2) the external pterygoid , (3) the deep temporal and (4) the buccal nerve. i. The masseteric nerve (n. massctericus) (Fig. 1063) passes over the upper border of the external pterygoid and behind the posterior margin of the temporal muscle. It takes a course horizontally outward and traverses the sigmoiil THE TRIGEMINAL NERVE. 1243 notch of the mandible to enter the posterior portion of the mesial surface of the masseter. It supplies one or two filaments to the temporo-mandibular articulation. 2. The external pterygoid nerve (n. pterygoideus externus) (Fig. 1063), usually takes its origin as a common trunk with the buccal nerve. It enters the deep surface of the external pterygoid. 3. The deep temporal nerves (nn. temporales profundi anterior et posterior) (Fig. 1063), are usually three or two in number. The anterior accompanies the buccal nerve between the heads of the external pterygoid, after which it passes upward to supply the anterior portion of the temporal muscle. The middle passes outward across the upper margin of the external pterygoid and then upward close to the bone to enter the deep surface of the temporal muscle. It often fuses with either the anterior or posterior deep temporal, thus reducing the number of temporal FIG. 1062. Gasserian ganglion V. nerve, sensory root Maxillary division V. nerve 'Spheno-palatine nerves division V. nerve Auriculo- temporal ner Mandib. div. V. nerve, partly cut Chorda tympan Otic ganglion ; it! br. to tensor tym pani is seen above the leader Mlddli neningeal artery Part ol parotid gland Br. from otic ganglion to auriculo-temp. nerve' / Br. from otic gang, to chorda tympani Int. pterygoid nerv Int. pterygoid muscl Inferior dental nerve Lingual br. V Buccinator muscle Dissection showing lateral view of spheno-palatine and otic ganglia. nerves to two. The posterior frequently accompanies the nerve to the masseter for a variable distance, after which it turns upward along the bone to enter the deep surface of the posterior portion of the muscle. 4. The buccal nerve (n. buccinatorius) (Fig. 1063) is purely sensory. It arises in common with the external pterygoid and anterior deep temporal nerves and is accompanied by the latter between the heads of the external pterygoid. Passing downward on the inner side of the temporal muscle it reaches the outer surface of the buccinator, where it breaks up into several branches which form a plexus around the facial vein, with the buccal branch of the facial nerve. Some of its branches pierce the buccinator muscle to supply the mucous membrane of the cheek as far forward as the angle of the mouth, while the others supply the skin of the cheek. Variations. Instead of lying to the inner side, the nerve may pierce the temporal muscle. It may be derived from the posterior superior dental nerve or from the inferior dental, in the latter instance emerging from the inferior dental canal by a small foramen in the alveolar border 1244 HUMAN ANATOMY. of the mandible, just anterior to the ramus. It has been seen in one case to arise directly from the Gasserian ganglion and emerge from the cranium through a special foramen situated bt-tu een the foramina rotundum and ovale. % The Posterior Division of the niandibular nerve is sensory, with the exception of the mylo-hyoid nerve. It passes downward beneath the external pterygoid and, after giving off the two roots of the auriculo-temporal nerve, terminates by dividing into the lingual and the inferior dental nerve. Branches. These are : (i) the auriculo- temporal, (2) the lingual and (3) the inferior dental. 1. The auriculo-temporal nerve (n. aunculotemporalis) (Fig. 1063) arises just below the foramen ovale by two roots which enclose between them the middle meningeal artery. It passes backward beneath the external pterygoid muscle and between the spheno-mandibular ligament and the neck of the mandible, and then turns upward through the parotid gland between the temporo-mandibular articulation and the external ear. Emerging from the upper margin of the gland, the nerve passes over the root of the zygoma and ascends to the temporal region behind and in company with the superficial temporal artery. Branches. These are : (a) the articular, (b) the parotid, (c~) the mealal, (d*) the anterior auricular and (e) the superficial temporal. The last three are terminal branches. a. The articular branches (rr. articulates) are one or two delicate filaments which enter the posterior portion of the tempor-mandibular articulation. b. The parotid branches (rr. parotidei) pass to the gland; they arise either from the auriculo-temporal or from its communicating filaments with the facial nerve. c. The meatal branches (nn. meatus auditorii externi) are two in number, an upper and a lower. They enter the external auditory canal between the bone and the cartilage and supply the skin covering the corresponding parts of the meatus, the upper branch in addition sending a twig (r. membranae tympani) to the tympanic membrane. d. The anterior auricular nerves (nn. auriculares anteriores) , usually two in number, supply skin of the tragus and of the upper anterior portion of the auricle. e. The superficial temporal nerve (rr. temporales superficiales) (Fig. 1068) breaks up into a number of fine twigs which supply the skin of the temporal region and of the scalp almost to the sagittal suture. The auriculo-temporal communicates by its roots, close to their origin, with branches from the otic ganglion, and by its parotid and superficial temporal branches with the facial nerve. By the first of these communications secretory fibres of the glosso-pharyngeal and sympathetic fibres are carried to the parotid gland ; by means of the second junction sensory trigeminal fibres accompany the peripheral motor filaments of the facial. Variations. In a specimen found in the anatomical laboratory of the University of Pennsyl- vania, the middle meningeal artery, instead of passing between the two roots of the nerve, pierced the anterior one. 2. The lingual nerve (n. lingualis) (Fig. 1079) is the smaller of the terminal branches of the mandibular nerve. Lying internal and anterior to the inferior dental nerve, it passes downward beneath the external pterygoid as far as the lower border of that muscle. It is usually connected with the inferior dental nerve by an oblique strand of fibres, which occasionally crosses the internal maxillary artery and, close to its origin, it is additionally joined at an acute angle by the chorda tympani nerve. After emerging from undercover of the external pterygoid, it passes between the internal pterygoid and the ramus of the mandible. It then turns inward, forward and downward under the mucous membrane of the floor of the mouth, cross- in- over the superior border of the superior constrictor of the pharynx and the deep portion of the submaxillary gland, and passes under the submaxillary duct between tlie mylo-hyoid and hyo-glossus muscles. Reaching the side of the tongue tin- nerve continues forward to the apex, lying just beneath the mucous membrane. Branches. The lingual nerve supplies small filaments to the sublingual gland, the floor and side of the month, the side- of the tongue and the lower gum. It gives off the sensory root of the submaxillary ganglion and its terminal filaments (rr. linnuak's) pass upward through the muscles of the tongue to supply the mucous THE TRIGEMINAL NERVE. 1245 membrane of the anterior two-thirds of the dorsum. Its fibres have their main termination in the filiform and fungiform papillae. The lingual nerve communicates with the chorda tympani and the inferior dental and in its anterior portion forms loops with the hypoglossal. 3. The inferior dental nerve (n. alveolaris inferior) (Fig. 1063) is the larger of the terminal branches of the mandibular. Lying posterior and external to the lingual, to which it is connected by a small nerve strand, it passes downward and forward under cover of the external pterygoid. Leaving the lower margin of that muscle, it runs between the ramus of the mandible and the spheno-mandibular ligament and enters the inferior dental canal, along which it courses in company FIG. 1063. Motor division of mandibular nervi Deep temporal branches Sensory division of Internal pi Chorda tym Middle meningea Auriculo- temporal nerve Superficial temporal artery Mylo-hyoid nerve Inte maxillary artery auriculo-temporal and facial nerves Facial nerve Inferior dental nerve Part of mandible Parotid gland External carotid artery Mylo-hyoid nerve Zygomatic process ot malar bone Hxt. pterygoid muscle, cut, and its nerve Masseteric branch giving off a temporal branch Cut edge ot buccinator Int. pterygoid muscle Lingual nerve Mylo-hyoid muscle, cut to show lingual nerve ibmaxillary ganglion Digastric muscle, anterior belly Submaxillary gland Dissection showing mandibular nerve and its branches; mandible has been partially removed, exposing inferior dental nerve in its canal. with the inferior dental artery, and supplies filaments to the teeth, as far as the mental foramen. Here the nerve breaks up into its terminal branches, one of which, the incisor, continues within the mandible to the mid-line, while the other and larger, the mental, emerges at the mental foramen. Branches. These are : (a) the mylo-hyoid, (t>) the dental, (c) the incisor and (d) the mental, of which the last two are terminal branches. a. The mylo-hyoid nerve (n. mylohyoideus) (Fig. 1063) is the only motor strand in the posterior division of the mandibular nerve. It arises from the inferior dental nerve, just before the latter enters its bony canal, and passes downward and forward in the mylo-hyoid groove, sometimes a canal for part of the way, in the mandible. The nerve descends into the digastric triangle and reaches the inferior surface of the mylo-hyoid muscle, in this situation being overlain by the submaxillary gland and the facial artery and vein. It here breaks up into filaments which supply the mylo-hyoid muscle and the anterior belly of the digastric. b. The dental branches (rr. dentales inferiores) are given off as the nerve traverses the inferior dental canal. They combine and unite to form the inferior dental plextis (plexus 1246 HUMAN ANATOMY. dentalis inferior) which supplies filaments to the molar and premolar teeth, one filament to each fang, and the adjacent portion of the gum. c. The incisor branch (n. alveolaris inferior anterior) is the smaller of the terminal divisions and continues forward within the mandible the course of the inferior dental nerve from the mental foramen to the mid-line. It supplies the canine and incisor teeth. d. The mental nerve (n. mentalis) (Fig. 1063) is much the larger terminal branch of the inferior dental. Emerging from the mental foramen, it breaks up under cover of the depressor anguli oris muscle into a number of filaments which supply the skin of the chin and the integument and mucous membrane of the lower lip. It forms a free communication with the supramandibular branch of the facial nerve. The Otic Ganglion. The otic or Arnold' s ganglion (g. oticum) (Fig. 1064) is one of the two ganglia associated with the mandibular nerve. It is a small flattened FIG. 1064. Ophthalmic division.V. nerve Maxillary division, V. nerve Gasserian ganglion, inf. surface V. nerve, sensory root :rve, motor root Mandibular division, V. nerve Tensor tympani, cut (tensor tympani Br. from otic ganglion to Cartilaginous portion of 'Eustach. tube, cut Petrosa of temporal bone Small superf. petrosal nerve Br. from ganglion to chorda tympani Middle meningeal artery and plexus Carotid canal outer, Auriculo-tem- [wall poral nerve Lingual nerve Inf. dental nerve Int. maxillary artery Temporal artery Otic ganglion ~^^fc Br. to auriculo-temp. nerve-^ Int. pterygoid nerve Br. to tensor palati Tensor palati, cut Hamulus of int pterygoid plate Ext. carotid artery 'Styloid process Otic ganglion and branches seen from mesial aspect, section of skull being not sagittal, but approaching plane of long axis of petrosa. body, of irregularly oval or stellate outline and reddish-gray color, and measures about 4 mm. in its longest or antero-posterior dimension. It lies just below the foramen ovale on the mesial side of the mandibular nerve and covers or even encloses the origin of the internal pterygoid nerve. Internally the ganglion is in relation with the tensor palati muscle and the cartilaginous portion of the Eustachian tube and posteriorly with the middle meningeal artery. It is a sympathetic ganglion and con- tains numerous stellate neurones which are characteristic of such structures. Roots. Of the communications that the otic ganglion receives from several sources, some are regarded as its roots, of which the sensory root is contributed by small superficial petrosal nerves (n. petrosus superficialis minor). The latter establish connection between the otic ganglion and the petrous ganglion of the glosso- pharyngeal nerve by way of its tympanic branch (page 1075) on the one hand and, by means of communicating filaments, between the otic and the- geniculute ganglion of the facial nerve on the other. As the continuation of the tympanic nervr, afu-r union with the filaments from the geniculate ganglion, the small superficial petrosal leaves the upper and fore part of the tympanic cavity, traverses a small canal in the temporal bone, and emerges on the upper surface of the latter, to the outer side of the hiatus Fallopii. It then turns downward, passes through the petro-sphenoidal fissure or through a special canal in the sphenoid bone, and joins the otic ganglion. THE TRIGEMINAL NERVE. 1247 By means of these connections and the branches of distribution from the otic gang- lion, secretory fibres are carried along with those of the auriculo-temporal (page 1244) to the parotid gland. The small superficial petrosal nerve also contains taste- fibres, which pass either to the petrous ganglion of the ninth or to the geniculate ganglion of the seventh, and thence centralward to the reception-nuclei in the medulla. The motor root is a branch from the internal pterygoid nerve. The sympathetic root is represented by one or two nerve-filaments from the plexus on the middle meningeal artery. The ganglion also receives the sphenoidal branch from the Vidian nerve. Branches. A number of delicate strands pass from the otic ganglion to adja- cent nerves. These so-called branches of distribution include : (#) two or more fila- ments which join the roots of the auriculo-temporal nerve and so convey secretory fibres from the glosso-pharyngeal to the parotid gland, () a communicating branch FIG. 1065. Ophthalmic Ophthalmic Maxillary Diagrams showing distribution of cutaneous branches of trigeminal and cervical spinal nerves. to the chorda tympani and (c~) another to the buccal nerve, () and (/") branches to the nerves supplying the tensor palati and tensor tympani muscles. The Submaxillary Ganglion. The submaxillary ganglion (g. submaxillare) (Fig. 1063) is a reddish triangular or fusiform body, measuring from 2-3 mm. in its greatest length, and is the smallest of the sympathetic ganglia connected with the fifth nerve. It is situated above the deep portion of the submaxillary gland and upon the hyo-glossus muscle and lies between the submaxillary duct and the lingual nerve, apparently suspended from the latter by two short slender- filaments. The anterior of these transmits chiefly sympathetic fibres that pass from the ganglion to the lingual nerve, the posterior fibres going from the lingual to the ganglion as its sensory and motor roots. Roots. The sensory root is contributed by the lingual nerve ; the motor root proceeds from the facial by way of the chorda tympani and contains secretory fibres ; and the sympathetic root is derived from the adjoining plexus on the facial artery. Branches. The branches of distribution include: (a) a number of fibres which pass to the submaxillary gland, (<) others which are distributed to the submaxillary duct and the mucous membrane of the floor of the mouth and (^) filaments which join 1248 HUMAN ANATOMY. the lingual nerve and, after accompanying it for a short distance, are distributed to the sublingual gland. The sensory fibres, processes of the Gasserian neurones, tra- verse the submaxillary ganglion without interruption ; the secretory fibres from the facial end, at least in part, around the stellate sympathetic neurones of the ganglion, from which cells axones pass to the alveoli of the submaxillary and sublingual glands ; while other sympathetic filaments proceed, as the axones of stellate cells either within the submaxillary or a more remote sympathetic ganglion, to supply the glandular tissue and ducts, as well as to accompany the peripheral branches of the lingual nerve. Practical Considerations. The fifth cranial nerve is the sensory nerve of the face and the motor nerve to the muscles of mastication. It is more frequently the seat of excessively painful neuralgia than any other nerve in the body. Extra- cranial lesions are much more commonly the cause of such neuralgia than intracra- nial. The neuralgia is rarely bilateral, and usually does not involve all three divisions of the nerve. It rather attacks one or two divisions, or only a branch of one, the first and second divisions being most frequently involved. Certain tender regions can almost always be found, as over the points of emergence of the nerve on the face, at the supraorbital, infraorbital and mental foramina, where in an interval from pain pressure may produce a paroxysm. The supraorbital notch or foramen can usually be felt at the junction of the inner and middle thirds of. the supraorbital margin. The mental foramen is in the lower jaw, below and between the two bicuspid teeth, while the infraorbital foramen lies just below the lower margin of the orbit in a straight line between the supraorbital and mental foramina. When the first division is the seat of neuralgia, the disease is almost always con- fined to the supraorbital branch. Excision of this branch will usually give relief for about two years, sometimes permanently. The same may be said of the infraorbital nerve when the disease is confined to the second division. The infraorbital may be excised at the foramen, through the mucous membrane of the mouth or by an in- cision in the skin along the lower margin of the orbit. Through the latter the orbital tissues may be raised and the nerve reached farther back in its canal, which in its anterior part has a thin bony covering. By going through the antrum of Highmore from the cheek, just below the infraorbital foramen, the second division, with Meckel's ganglion attached to it may be excised at its emergence from the skull. The anterior wall of the antrum is opened by a trephine or chisel and the floor of the infraorbital canal in the roof of the antrum is gouged away so that the nerve is ex- posed and followed to the posterior wall of the antrum. This wall is then opened, the spheno-maxillary fossa exposed and the nerve is divided at the foramen rotundum and removed with the ganglion. The bleeding will be severe, since large and numerous branches of the internal maxillary artery surround the ganglion and are divided. When the neuralgia is confined to the inferior dental nerve the mental branch may be excised at its foramen through the mucous membrane of the mouth. The inferior dental itself is more frequently attacked through a trephine opening in the ascending ramus of the lower jaw. It may with greater difficulty be reached through the mouth, the incision being made along the anterior margin of the descending ramus, and the soft tissues separated from the inner surface of the ramus until the xiental spine marking the dental foramen is exposed; the inferior dental nerve and artery will be found entering the canal. The nerve may then be exposed and ex- cised with due regard for the accompanying vessels and the* internal maxillary artrry, from which the inferior dental branch has just been given off. The buccal nerve is sometimes the seat of neuralgia, and may be reached by an incision through the cheek in front of the coronoid process and the insertion of the tendon of the temporal muscle. The nerve can be reached from the mouth in the same situation. When the peripheral operations for trigeminal neuralgia (tic douloureux) have failed to effect a curt-, or when the neuralgia piimarily shifts from one branch to an- other, indicating an extensive central involvement, tin- (rasst'r/'tut ga>ig/i) without interruption through the inferior brachium to the cells within the median geuiculate body. THE AUDITORY NERVE. 1259 FIG. 1072. Floor of IV. ventricle Superior cerebellar peduncle Inferior cerebellar peduncle Lateral vestibular (Deiters') nucleus Median vestibular nucleus Cochlear fibres Dorsal cochlear nucleus Descending vestibular root 4. Neurones of the inferior colliculus and of the median geniculate body, whose axones pass, as the auditorv radiation, to the auditory cortical area within the temporal lobe of the cerebrum. Although the exact extent of the auditory area is still uncertain, the most important part of this centre includes the superior temporal and the subjacent part of the middle temporal convolution. The cochlear fibres that do not undergo decussation ascend through the lateral fillet of the same side and eventually establish cortical relations with the corresponding hemisphere ; from the preceding account, however, it is manifest that the auditory area is connected chiefly with the cochlea of the opposite side. Peripheral, Central and Cortical Connections of the Vestibular Nerve. The fibres of the vestibular portion of the auditory nerve are the axones of the bipolar nerve-cells situated within the small vestibular ganglion (g. vestibulare) or ScarpcC s ganglion, which lies at the bottom of the internal auditory canal. The dendrites of these cells constitute the five branches of dis- tribution of the vestibular nerve and pass through the various openings in the inner wall of the bony labyrinth, in the manner above described (page 1256), to reach the specialized areas, the maculcf acustica', within the saccule, the utricle and the ampullae of the semicircular canals, where the nerve-filaments end, really begin, in intimate relation with the neuro- epithelium. While the centrally directed axones of the neurones supplying the utricle and the superior and external semicircular canals become consolidated to form the vestibular nerve of descriptive anatomy, those from the saccule and the posterior semicircular canal join the coch- lear fibres and with these course within the cochlear nerve until the latter and the vestibular nerve unite to form the common auditoiy trunk. Where the common trunk separates into the two roots, the vestibular fibres leave the cochlear and permanently assume their natural companionship with the remain- ing fibres of the vestibular root. The vestibular fibres enter the brain-stem at a slightly higher level than does the cochlear root, lying mesial to the latter and the ventral cochlear nucleus, and pass dorsally within the pons between the inferior cerebellar peduncle and the spinal trigeminal root. On reaching a level dorsal to the latter, the vestibular fibres divide into short upward and longer downward coursing branches, which, after condensing into an ascending and a descending root respectively, end in arborizations around the cells of the vestibular nucleus of reception. The exact extent and constitution of this nucleus, which under- lies the area acustica in the floor of the fourth ventricle (page 1097), are uncertain, since the neurones directly related to the vestibular fibres contribute only a part of those contained within a large diffuse complex of cells and fibres, many of whose constituents probably have only an indirect connection with the vestibular nerve. When reconstructed, as has been successfully done by Sabin, this complex has the form shown in Fig. 1072 and comprises two general parts, (a) an extended irregularly triangular mass of cells lying for the most part mesial to the tract formed by the ascending and descending branches of the vestibular fibres, and (b) a smaller mass of cells which lies above the larger one and partly to the inner and partly to the outer side of the tract of the vestibular fibres. The apex of the large triangular mass approaches the mid-line and its superior and inferior basal angles are prolonged upward and downward along the vestibular tract. When examined microscopically the large mass is found to include three subdivisions : (a) a tapering caudally directed nucleus which continues the inferior angle along the descending vestibular root, (b) an extended triangular nucleus that includes the greater part of the large mass and (c) an irregular pyramidal nucleus that prolongs upward the superior angle. The first of these subdivisions (a] is known as the spinal vestibular nucleus (nuc. spinalis n. vestibularis), the second (b') as the median vestibular nucleus (nuc. mediali.s n. vestibularis), also as the chief nucleus or the triangular nucleus and the third (r) as the superior vestibular nucleus or the Nucleus cuneatus Closed part of medulla Vestibular nuclei as shown in reconstruction by Dr. Florence R. Sabin. i26o HUM AX ANATOMY. nucleus of Bechterew. The small mass corresponds with the lateral vestibular nucleus (nuc. lateralis n. vestibularis) or nucleus of Deiters. The fibres of the descending root end around the neurones within the spinal nucleus in a manner similar to that in which the constituents of the spinal root of the trigeminus terminate in relation with the neurones within the substantia gelatinosa, whilst those of the ascending vestibular root end around the cells within the remain- ing vestibular nuclei. Although much uncertainty and conflict of opinion exist as to the details of the secondary paths by which the impulses carried by the vestibular fibres are distributed, it may be accepted as established that fibres pass from the nuclei of reception : (a) to the cerebellum (chiefly to the roof nucleus of the opposite side and, possibly, also to the nuclei globosus and emboliformis ) as constituents of the nucleo-cerebellar tract, by which the impulses of equilibration are carried to the great coordinating centres, (b) as arcuate fibres ventro-medially into the tegmentum of the pons, cross the mid-line and bend upward or downward to pass to other levels, some fibres, however, remaining on the same side. From the character of the impulses it is probable that only relatively few vestibular fibres join the median fillet to ascend to the optic thalamus. Other connections of the nuclei include : (c) commissural fibres between Bechterew's nucleus of the two sides, (d ) fibres to the abducent nucleus, (e) crossed and uncrossed fibres from Deiters' nucleus to the posterior longitudinal fasciculus and (f) fibres from the same nucleus to the spinal cord. It must be understood that by no means all of the neurones of Deiters' nucleus are con- cerned in transmitting afferent impulses to the cerebellum, for, as a matter of fact, many are links in the path by which the cerebellar cells exercise coordinating influences over the root- cells of the spinal nerves. Starting in the cerebellum, such efferent impulses are carried by efferent fibres which descend through the median part of the inferior cerebellar peduncle and probably end around certain of the cells within Deiters' nucleus. From these cells, in turn, originate the fibres of the vestibulo-spinal tract, which, after traversing the medulla, enter the antero-lateral column of the cord and end in relation with the motor root-cells. A shorter and more direct path for vestibular reflexes is probably formed by the collaterals of the vestibular fibres that end around the spinal neurones of Deiters' nucleus. It must not be forgotten that Deiters' nucleus is the origin for important contributions to the posterior longitudinal fasciculus (page 1117), by which the vestibular impulses impress the nuclei of the motor and, perhaps to a limited degree, also those of the sensory nerves. Practical Considerations. The auditory nerve is rarely the seat of primary disease. It is most frequently affected consecutively to disease of the middle and in- ternal ears. It is sometimes, though seldom, paralyzed in fractures of the base of the skull. Operations on this nerve have been performed for relief from persistent and annoying tinnitus. THE GLOSSO-PHARYNGEAL NERVE. The ninth or glosso-pharyngeal nerve (n. glossopharyngeus) is a mixed nerve, containing motor and sensory fibres, the latter including those transmitting the impulses of the special sense of taste. The motor element is quite small and sup- plies only the stylo-pharyngeus muscle and secretory fibres to the parotid gland, while the sensory fibres are distributed to the mucous membrane of the middle ear, fauces, tongue and pharynx. The Nuclei of the Glosso-Pharyngeal, Vagus and Accessory Nerves. In the description of the medulla (page 1073) attention was called to the presence of nuclei common to a greater or less extent to the series of lower lateral nerves including the seventh, ninth, tenth and vagal part of the eleventh, which, with tin- exception of the last named, are mixed nerves. The motor fibres of these nerves differ from those of the series of median motor nerves the third, fourth, sixth and twelfth ( a ) in the more lateral situation and less compact grouping of their cells of origin and (/?) in the less direct course they follow to reach the surface of the brain. To avoid repeti- tion, the general arrangement and characteristics of the nuclei related to the glosso- pharyngeal, vagus, and accessory part of the eleventh nerve will be here described. The Motor Nuclei. These include the root-cells within the dorsal HHC/CI/S and those constituting the nuc/ciis ignns. The dorsal nucleus (nucleus ) to the auricular branch of the vagus and sometimes (c) to the ganglion of the root of the vagus. Branches. The branches of the giosso-pharyngeal nerve are: (i) the tym- panic, (2) the pharyngeal, (3) the muscular, (4) the tonsillar and (5) the lingual. 1. The tympanic nerve (n. tympanicus) or Jacobsoris )icrrc, arises from the petrous ganglion as its most important branch and traverses a tiny canal in the osseous bridge between the jugular fossa and the carotid canal. Entering the tym- panic cavity and receiving fibres from the carotid plexus of the sympathetic by way of the small deep petrosal (n. caroticotympanicus), the tympanic nerve passes upward and forward in a groove on the promontory and breaks up in this situation to form the tympanic plexus (plexus tympanicus [Jacobsoni] ). After distributing filaments to the mucous membrane lining the tympanic cavity and the associated air-spaces (mastoid cells and Eustachian tube), its fibres reassemble and join with a filament from the geniculate ganglion to continue as the small superficial petrosal nerve to the otic ganglion (Fig. 1075). Branches. These are : (a) the small superficial petrosal ncrrc, (6) the branch to the fenestra ovalis, {c} the branch to the fcncstra rotunda, (d) the branch to the Eustachian tube, (<*) the branch to the mastoid cells and (/") the branch to the great superficial petrosal nerve. a. The small superficial pelrosal nerve (n. petrosus superficial is minor) (Fig. 1075) is the continuation of the tympanic nerve, formed by a reassembling of the fibres of the plexus, sup- plemented by a filament from the geniculate ganglion of the facial. It traverses a canal which begins at the anterior superior portion of the tympanic cavity, passes beneath the upper end of the canal for the tensor tympani and appears on the superior surface of the petrous portion of the temporal bone, to the outer side of the cranial opening of the hiatus Fallopii. While in the canal it sometimes receives a communicating branch from the great superficial petrosal nerve. It leaves the cranium through a canal in the greater wing of the sphenoid, or through the fissure between the greater wing and the petrous portion of the temporal bone, and on reaching the base of the skull, joins the otic ganglion as its sensory root ( Fig. 1075). b. The branch to the fenestra ovalis supplies the mucous membrane in the neighborhood of the oval window. c. The branch to the fenestra rotunda is distributed to the mucous membrane over and around the fenestra. d. The branch to the Eustachian tube supplies the mucous membrane lining the osseous portion of that canal. e. The branch to the mastoid cells supplies the mucous lining of these cells. f. The branch to the great superficial petrosal nerve joins the latter in the hiatus Fallopii. 2. The pharyngeal branches (rr. pharyngei) number two or more, of which the largest descends along the course of the internal carotid artery and joins the pharyngeal branches of the vagus and sympathetic to form the pharyngeal plexiis, which supplies the mucous membrane and muscles of the pharynx. The smaller pharyngeal branches pierce the superior constrictor and are distributed to the mucous membrane lining the upper portion of the pharynx. 3. The muscular branch (r. stylopharyngetis) enters the stylo-pharynegus, and, after giving off fibres for the supply of that muscle, passes through it to be distributed to the mucous membrane of the pharynx. 4. The tonsillar branches (IT. tonsillarcs) are given off near the base of the tongue. They are slender filaments which form a pk-.xiform ramification, the circulus tonsillaris, around tin- tonsil. From this plexus filaments are distributed to the tonsil, the soft palate and the faudal pillars. 5. The lingual branches (rr. linguales ) are the two terminal filaments of the nerve. The larger posterior branch passes upward and separates into a number of filaments which supply the rircumvallate papilla- and the mucous membrane covering THE VAGUS NERVE. 1265 the posterior part of the dorsum of the tongue, the glosso-epiglottic and pharyngo- epiglottic folds and the lingual surface of the epiglottis. The smaller anterior branch supplies the mucous membrane of the side of the tongue half way to the tip. FIG. 1076. Thyro-hyoid br. XII. nerve 'Superior laryngeal nerve I. cervical n Spinal accessory n Occipitalis minor nerve 1 1. cervical m Hypoglossal (XII.) n. Sup. cerv. gangl. of sympathetic Br. from II. cerv. nerve to sp. access. III. cervical ne Communicans hypoglossi Great auric, and superf. cerv.ne IV. cervical n Descendens hypoglossi Pneumogastric nerve V. cervical nerve Br. to rhomboidei Omo-hyoid, part of ant. belly Communicating br. to sp. accessory A cutaneous br. External pterygoid Ling. br. V. nerve ) Chorda j tympani nerve Int. pterygoid Edge of oral mu- cous membrane Glosso-pharyngeal nerve Mental nerve Jnf. dental nerve, distal portion "ublingual gland llary gangl. Stylo-pharyngeus Middle cervical ganglion of sympathetic (the cord connecting it with superior gangl. Is also seenj ubclavian artery Deep dissection of neck showing ninth, tenth, eleventh and twelfth cranial nerves and their branches. Variation. Instances are recorded in which the mylo-hyoid nerve was absent and a branch of the glosso-pharyngeal supplied the mylo-hyoid muscle and the anterior belly of the digastric, the innervating fibres being, probably, aberrant filaments of the trigeminus. THE VAGUS NERVE. The tenth, vagus or pneumogastric nerve (n. vagus) is the longest and most widely distributed of the cranial series. Starting in the cranium, it passes through the neck, thorax and upper part of the abdomen before breaking up into its terminal branches. In addition to certain filaments concerned with special functions, distrib- uted to the heart and abdominal viscera, it contains both motor and sensory fibres. Some of the motor constituents of the nerve arise from its own origin, but the major- ity perhaps are contributions of the accessorius vagi, the so-called accessory part of the spinal accessory nerve. The vagus supplies motor fibres to the muscles of the . soft palate (with the exception of the tensor palati and, probably, partly the levator palati and azygos uvulae), pharynx, oesophagus, stomach, and intestine (with the exception of the rectum), and to those of the larynx, trachea, and bronchi and their subdivisions. It distributes sensory fibres to the dura mater, external ear, pharynx, oesophagus, stomach, larynx, trachea, bronchi and subdivisions and pericardium. 80 1266 HUMAN ANATOMY. Special fibres are furnished to the heart, liver, spleen, pancreas, kidneys, suprarenal bodies and intestinal blood-vessels. It is generally admitted that the bulbar or accessory portion of the eleventh nerve forms air integral part of the motor division of the vagus, and, hence, should he included with the efferent fibres of the tenth. As to the ultimate distribution of these accessory fibres, and conversely of the vagus motor fibres proper, much discussion and many conflicting views have existed and, even at present, a consensus of opinion can scarcely be said to have been reached. After reviewing the evidence, both anatomical and experimental, Van Gehuchten ' concludes that the accessory fibres are distributed chiefly, if not indeed exclusively, to the larynx through the infe- rior laryngeal branch of the vagus, and are continued neither to the heart nor to the stomach. The efferent vagus fibres proceeding to the heart are inhibitory in function ; whether they directly reach the cardiac muscle is doubtful, since, reasoning from analogy, it is probable that the vagus fibres end around sympathetic neurones whose axones are the filaments coming into immediate relations with the muscle-fibres. Of the efferent -fibres of the vagus distributed to the stomach and other parts of the digestive tract, some are secretory, while others, possibly, influence the caliber of the blood-vessels, in both cases being interrupted in sympathetic ganglia before gain- ing their destination. Deep Origin of the Motor Portion. As stated above, the efferent fibres of the vagus consist of two sets, vagus fibres proper and those derived from the acces- sory portion of the spinal accessory. The former have their deep origin in the nu- cleus ambiguus and the dorsal motor nucleus, in series with the motor fibres of the ninth nerve ; the accessory fibres arise from the nucleus ambiguus only. The detailed description of these nuclei has been given (page 1260). The fibres arising from the nucleus ambiguus at first pass backward toward the floor of the fourth ventricle, then bend sharply outward and, condensed into compact strands that receive the fibres originating from the motor cells of the dorsal nucleus, proceed, ventro-laterally in company with the sensory fibres, to their superficial origin alont^ the postero-lateral groove behind the olivary eminence. Central Connections of the Sensory Portion. The afferent root-fibres of the vagus are the axones of the neurones lying within the ganglia of the root and of the trunk situated on the upper part of the nerve. The centrally directed processes pass into the medulla, in company with the motor strands, and divide into two sets. Those forming the larger of these end in arborizations around the cells within the lower portion of the dorsal sensory nucleus ; those of the smaller set bend downward and enter the fasciculus solitarius to terminate in arborizations around the cells of the spinal nucleus of reception. (For details of these nuclei see page 1260). As in the case of the other mixed nerves the fifth, seventh and ninth the secondary- paths distributing the sensory impulses include (#) fibres that pass from the recep- tion-nuclei to the tract of the mesial fillet, and so on to the great brain, and (b) those that pass to the cerebellum. Course and Distribution. The vagus, disregarding its accessory fibres which at first are incorporated in a common trunk with the eleventh nerve, arises from its superficial origin by a row of twelve or fifteen filaments which emerge from the surface of the medulla along the postero-lateral sulcus between the olivary eminence and the inferior cerebellar peduncle. These fasciculi lie in series with those of the ninth nerve above and of the eleventh below (Fig. 1046). After leaving the surface of the brain-stem, the converging rootlets of the vagus fuse to form a single flattened trunk, which passes outward beneath the flocculus of the cerebellum to the jugular foramen (Fig. 1074). The trunk leaves the cranium through the rear division of the middle compartment of this foramen, invested by a dural sheath shared by the spinal accessory nerve. In this situation it presents a ganglionic enlargement called the gang/ion of the root. Emerging from the jugular foramen, the vagus bears a second thickening, \hzgangK0n of the trnnk\ and enters the carotid sheath, through which it passes downward tin- entire length of the neck. Within the carotid sheath the nerve lies at first between the internal carotid artery and the internal jugular vein, and then between the common carotid artery and the vein, occupying the posterior ^mnve between these vessels. At the root of the 1 Anatomii- dn System*- Nervrux, 1906. THE VAGUS NERVE. 1267 neck it leaves the carotid sheath and becomes an occupant of the thorax. Entering the thoracic cavity the nerve traverses first the superior and then the posterior mediastinum, its course differing widely on the two sides. The right vagus (Fig. 1090), after passing in front of the first portion of the subclavian artery and behind the right innominate vein and the superior vena cava, descends along the right side of the trachea to reach the posterior aspect of the root of the lung. Here the entire nerve breaks up to form the posterior pulmonary plexus, which assembles at its lower border to form two cords. These pass inward across the vena azygos to the oesophagus and again break up to unite with a similar contribution from the left side to form the cesophageal plexus (Fig. 1081). On approaching the cesophageal opening in the diaphragm, the fibres of the plexus become reunited to form the continuation of the trunks of the two vagus nerves. The right vagus, somewhat larger than the left, follows the posterior aspect of the oesophagus and, after entering the abdomen through the cesophageal opening, is FIG. 1077. 2C Diagram showing connections between the superior cervical sympathetic ganglion and the glosso-pharyngeal, vagus and hypoglossal nerves. distributed to the posterior surface of the stomach and to the solar plexus, and indirectly to the spleen, pancreas, intestine, kidney and suprarenal body. The left vagus, after passing between the left common carotid and subclavian arteries and behind the left innominate vein, crosses the anterior surface of the aorta and then bends backward to reach the posterior surface of the root of the lung. In a manner similar to the right, it forms the posterior pulmonary plexus and reassem- bles into two cords. These pass inward anteriorly to the thoracic aorta and enter the icsophageal plexus, at the lower end of which the fibres of the left nerve gather on the anterior surface of the oesophagus, traverse as a single solid trunk the cesophageal opening and are distributed to the anterior surface of the stomach and to the liver. Ganglia of the Vagus Nerve. Two ganglia are found in the course of the nerve, the ganglion of the root and the ganglion of the trunk. They are collections of neurones whose axones form the sensory root-fibres of the vagus, the greater number, however, being connected with the cells of the ganglion of the root. The ganglion of the root (g. jugularc) or upper ganglion (Fig. 1077) is a grayish spherical mass of nerve-cells, about 4 mm. in length, situated in the upper part of the jugular foramen. 1268 HUMAN ANATOMY. The communications of this ganglion include filaments which pass between the ganglion and (a) the facial and (o) spinal accessory nerves, (c ) the superior cervical ganglion of the sympathetic nerve and (d) the petrous ganglion of the glosso-pharyngeal. The ganglion of the trunk (g. nodosum) or lower ganglion (Fig. 1077) is a reddish, flattened, fusiform group of nerve-cells. It lies beneath the jugular foramen, about i cm. below the ganglion of the root, and measures from 1.5-2 cm. in length and about 4 mm. in diameter. The accessory part of the spinal accessory nerve passes over the ganglion on its way to fuse with the vagus, which it does usually immediately beyond the ganglion. The communications of this ganglion include filaments which pass between the ganglion and (a) the hypoglossal and (d) spinal accessory nerves, (c) the loop between the first and second cervical nerves and (d) the superior cervical ganglion of the sympathetic. Branches. The vagus nerve gives off the following branches: from the ganglion of the root, (i) the meningeal and (2) the auricular ; from the ganglion FIG. 1078. ICERVN HCERV. Diagram of upper part of right vagus nerve, showing its pharyngeal and laryngeal branches with connections. of the trunk, (3) \hapharyngeal and (4) the superior laryngeal ; in the neck, (5) the superior cervical cardiac, and (6) the inferior cervical cardiac ; in the thorax, (7) the inferior laryngeal, (8) the thoracic cardiac, (9) the anterior pulmonary, (10) the posterior pulmonary, (n) the cesophageal and (12) the pericardia/ ; and in the abdomen, (13) the abdominal. 1. The meningeal branch (r. tncniiigcus) arises from the ganglion of the root and follows a recurrent course upward through tin- jugular foramen to supply the dura mater of the posterior fossa of the cranium, especially in the vicinity >f tin- lateral and occipital sinuses. 2. The auricular branch (r. atiriculaiis i is ^ivm off from tlu> ganglion of the root. It receives a filament of communication from tin- petrous ganglion of the ninth nerve and follows tin- outer margin of the jugular foramen to an opening between the stylo-mastoid and jugular foramina. Kim-ring this foramen it traverses a canal in tin- temporal bone which crosses the inner side of the facial canal and terminates between the mastoid process and the external auditory im-atus. THE VAGUS NERVE. 1269 Leaving the canal the nerve supplies the skin of the posterior part of the auricle and of the posterior inferior portion of the external auditory meatus. While traversing the temporal bone the auricular nerve communicates with the facial and, after reaching its area of distribution, with the posterior auricular nerve. Variations. The auricular nerve may be absent or may fuse with the main trunk of the facial, its fibres under these circumstances probably reaching their destination through the pos- terior auricular nerve. Its branch of communication with the facial may be absent. 3. The pharyngeal branches (rr. pharyngei), usually an upper and a lower but sometimes more or only one, are given off from the upper portion of the gang- FIG. 1079. Pneumogastric ner Inferior dental ner Spinal accessory ner Part of facial nerv< Hypoglossal nerv< Stylo-pharyngeus muscle Glosso-pharyngeal nerve I. cervical nerve Pneumogastric nerve Superior cervical ganglion of sympathetic Superior laryngeal nerve Descendens hypoglossi 1 1 . cervical nerve III. IV. cer- Association cord of sympathetic Middle cervical gangl Inferior cervical gangl Phrenic nerve Branches from inf. cervical ganglion Lingual nerve External laryngeal branch iuperior cervical cardiac of sympathetic Middle cervical cardiac of sympathetic -Recurrent laryngeal nerve Middle cervical cardiac of Common [pneumogastric carotid artery Inferior cervical cardiac of pneumogastric Inferior cervical cardir of sympathetic Recurrent laryngeal nerve Internal mammary artery Cartilage of I. rib Clavicular facet of st Deep dissection of right side of head and neck, showing lingual, glosso-pharyngeal, pneumogastic, hypoglossal and sympathetic nerves. lion of the trunk and include to a considerable extent fibres brought to the vagus by its accessory portion. They pass downward and inward, between the external and internal carotid arteries, and join the pharyngeal branches from the glosso-pharyn- geal nerve and from the superior cervical ganglion of the sympathetic to form the pharyngeal plexus (plexus pharyngeus) (Fig. 1078). This plexus contains one or 1270 HUMAN ANATOMY. more minute sympathetic ganglia and ramifies over the middle constrictor of the pharynx. It supplies motor fibres to the muscles of the pharynx and of the soft palate, with the exception of the stylo-pharyngeus and the tensor palati. From the plexus proceed sensory filaments to the mucous membrane of the pharynx. A filament from this plexus, the lingual branch of the vagus (r. lingualis vagi), com- posed of fibres from both the ninth and tenth nerves, joins the hypoglossal as it hooks around the occipital artery. Variation. A slender branch, the middle laryngeal nerve, is described as arising from the pharyngeal plexus and supplying the crico-thyroid muscle, after which it pierces the crico- thyroid membrane and supplies the mucous membrane of the lower part of the larynx. 4. The superior laryngeal nerve (n. laryngeus superior) (Fig. 1079) arises from the middle of the ganglion of the trunk and takes a downward and inward course beneath the external and internal carotid arteries toward the superior cornu of the thyroid cartilage. It divides terminally into (a) the external and () internal laryngeal branches. Communications. Before dividing, the superior laryngeal nerve receives filaments from the superior cervical sympathetic cardiac and from the pharyngeal plexus. The cardiac twig given off by the external laryngeal nerve joins with the superior cervical cardiac branch of the sympathetic. In the lower part of the larynx the external laryngeal nerve inosculates with the terminal fibres of the internal laryngeal. At the inferior portion of the larynx, the internal laryngeal nerve communicates with the terminal filaments of the external laryngeal, and in this way supplies sensory fibres to the mucous membrane lining the lower part of the larynx and to the muscles. Variation. Instead of passing to the inner side of the internal carotid artery the nerve may lie external to it. a. The external laryngeal branch (r. externus), much smaller than the in- ternal, passes downward upon the inferior constrictor of the pharynx and beneath the infrahyoid muscles to the crico-thyroid muscle, which it supplies. It sends filaments also to the inferior pharyngeal constrictor and gives off a cardiac twig which joins the superior cervical cardiac branch of the sympathetic. Variations. The external laryngeal has been seen to send filaments to the thyroid gland, the pharyngeal plexus, the sterno-hyoid, sterno-thyroid. thyro-hyoid and crico-arytenoideus lat- erahs muscles and to the mucous membrane of the vocal cord and lower portion of the larynx. b. The internal laryngeal branch (r. interims), larger than the external, passes downward and inward between the middle and inferior constrictors of the pharynx and enters the larynx by piercing the thyro-hyoid membrane. By means of its epiglottic, pharyngeal, descending and communicating branches, it supplies the mucous membrane covering the internal and pharyngeal surfaces of the larynx and the mucous membrane of the base of the tongue. Variation. Instead of piercing the thyro-hyoid membrane the nerve may obtain entrance to the larynx through a small foramen in the thyroid cartilage. 5. The superior cervical cardiac branch (IT. canliaci superiorcs both cervi- cal cardiacs) arises from the vagus in the upper part of the neck. It either joins a cardiac branch of the vagus or passes independently down the neck and along (In- side of the trachea to end in the deep cardiac plexus (Fig. 1132). 6. The inferior cervical cardiac branch leaves the vagus at the root of the neck. On the right side it courses along the side of the innominate artery and either independently, <>r after joining one of the other cardiac nerves, enters the deep car- diac plexus. The left passes in front of the arch of the aorta and joins the superior cervical cardiac branch of the left sympathetic to form the superficial cardiac plexu-. (Fig. 1132). 7. The inferior or recurrent laryngeal nerve (n. recurrens) (Fig. mSo) differs on the two sides in the early part of its course. The right n<-rrr is given otf at : THE VAGUS NERVE. 1271 the root of the neck as the vagus crosses the anterior surface of the subclavian artery, from which point it passes under and behind the artery and ascends. The left nerve takes its origin as the vagus crosses the anterior aspect of the aortic arch, and after passing below and behind the arch, lateral to the obliterated ductus arteriosus, ascends in the superior mediastinum to enter the neck. After entering the neck the further course of the nerve is the same on both sides. It passes upward posterior to the carotid sheath, either anterior or posterior to the inferior thyroid artery, occupies the FIG. 1080. Superior cervical cardiac branch of sympathetic Middle cervical ganglion Inferior cervical ganglion Superior cervical cardiac of vagus Middle and inf. cervical cardiac branches of sympathetic Recurrent laryngeal nerve Pulmonary branch of vagi Vena azygos major Phrenic nerve Right pulmonary artery Pulmonary Aorta Right auricular appendix Pericardium Superior cervical cardiac branch of sympathetic Superior cervical cardiac branch of vagus Middle cervical ganglion Middle cervical cardiac branch of sympathetic [of sympathetic I nf. cervical cardiac branch inf. cervical ganglion Middle cervical cardi; branch of vagus Inf. cervical cardiac branch of vagus Phrenic nerve Left vagus nerve Recurrent laryngeal net Left pulmonary artery 'Pulmonary veins Pulmonary orifice Mesial surface of lung Pericardium Dissection showing cardiac branches of pneumogastric nerves and of sympathetic cords ; aortic arch and branches and pulmonary artery partially removed ; pericardium laid open. groove, between the cesophagus and the trachea, and, dipping beneath the lower edge of the inferior constrictor of the pharynx, enters the larynx at the inferior margin of the cricoid cartilage. The asymmetry observed in the first part of the course of the nerves of the two sides is secondary and referable to the changes incident to the development of the large arterial trunks. In the fcetus both nerves hook around the fourth aortic arch of the corresponding sides and are, therefore, for a time symmetrically disposed. Since, however, on the left side this arch becomes the arch of the aorta, and on the right the innominate and subclavian arteries (page 726), it is evident that the vagi, although retaining their primary associations, later alter their actual position and relations in consequence of the unequal growth and downward displacement which these blood-vessels undergo. Branches. During its course the inferior laryngeal nerve gives off : (a) the cardiac, (<) the trachcal, (c) the cesophageal, (d} the rmiscular and (V) the terminal branches. I2J2 HUMAN ANATOMY. a. The cardiac branches (rr. cardiac! inferiores) are given off in the superior mediastinum and enter the deep cardiac plexus. b and c. Tracheal and oesophageal branches ( rr. tracheales et oesophagei) are given off as the nerve ascends in the neck between the trachea and cesophagus. d. Muscular branches enter the inferior constrictor of the pharynx. e. The terminal branches (n. laryngeus inferior) are formed at the point where the nerve breaks up on the inner side of the thyroid cartilage. They supply the intrinsic muscles of the larynx, with the exception of the crico-thyroid. As it turns to ascend, the inferior laryngeal nerve communicates with the inferior cervical ganglion of the sympathetic, its terminal filaments joining with those of the internal laryngeal. Variations. The inferior laryngeal nerve has been seen to supply twigs to the crico-thyroid muscle. In cases in which the subclavian artery arises dorsally, the right recurrent laryngeal passes directly downward and inward from the vagus to the larynx. 8. The thoracic cardiac nerves (rr. cardiaci inferiores) of the right side are derived both from the vagus as it lies beside the trachea and from the inferior laryn- geal. Those of the left side arise exclusively from the inferior laryngeal. They help to form the deep cardiac plexus. 9. The anterior pulmonary branches (rr. bronchiales anteriores) are two or three small filaments which, on the right side, receive communicating fibres from the deep cardiac plexus and, on the left side, are joined by filaments from both car- diac plexuses. These unite to form the anterior pulmonary plexuses (plexus pulmonales anteriores) (Fig. 1080), which communicate with each other and with the posterior plexuses, and ramify over and supply the anterior aspect of the bronchus and root of the lung. 10. The posterior pulmonary branches (rr. bronchiales posteriores) are several large twigs which join with filaments from the second, third and fourth tho- racic ganglia of the sympathetic to form the posterior pulmonary plexus (plexus pulmonalis posterior). Fibres from this plexus communicate with the corresponding structure of the opposite side and with the anterior pulmonary plexuses, in this way each vagus sending fibres to both lungs. Branches from the plexus, bearing tiny ganglia, follow the subdivisions of the bronchi to supply the ultimate units of the lung. 11. The cesophageal branches (rr. oesophagei) are given off in two situa- tions : in the superior mediastinum, where the right vagus and the left inferior laryngeal distribute cesophageal branches, and in the posterior mediastinum, where the cesophagus is surrounded by branches from the cesophageal plexus or pic. \ us gula (Fig. 1081). This plexus is composed of the two vagus nerves, after they leave the posterior aspect of the bronchi, in conjunction with filaments from the great splanchnic nerves and from some of the lower thoracic ganglia. Both the muscular and mucous coats of the cesophagus are innervated from this source. 12. The pericardial branches (rr. pericardiaci) are given off to the upper anterior portion of that membrane by either vagus and to the posterior portion by the oesophageal and frequently the posterior pulmonary plexuses. 13. The abdominal branches come from both nerves. On gaining the pos- terior surface of the stomach after following the corresponding aspect of the cesopha- gus, the right vagus forms the posterior gastric ple.vus along the lesser curvature, from which gastric branches supply the posterior surface of the stomach ; the remaining and larger part of the plexus is continued as the ccrliac branches to the plexus of the same name and, thence, in company with the sympathetic strands, to the subsidiary plexuses supplying the spleen, the pancreas, the intestine, the suprarenal bodies and the kidneys. In a similar manner, along the lesser curvature the left vagus forms the anterior gastric plexus, from which numerous gastric- branches are distributed to the anterior surface of the stomach, the continuation of the plexus being hepatic branches, which join the sympathetic filaments accompany- ing the hepatic artery to supply the liver. Practical Considerations. The pneumogastric nerve may be compressed or displaced by tumors in the neck, or it may be injured in accidental or operative wounds, >r by fracture of the base of the skull. Its division is not always fatal ; in THE VAGUS NERVE. 1273 fact, a portion of it has been deliberately removed with success. In those cases in which the nerve was divided, difficulty in breathing and swallowing, slowing of the respiration, laryngismus, changes in the voice, diminished inspiratory murmur, asthma and pneumonia were noticed (Park). In cases of pressure by tumors on the pneumogastrics of both sides, lung disturbances, dyspnoea, weakening of the pulse, and a ravenous appetite were observed. FIG. 1081. Superior cervical cardiac branch of sympathetic Vagus nerve Middle cervical ganglion of sympathetic Clavicle Recurrent laryngeal nerve, displaced outward Inferior cervical cardiac of sympa- thetic, joining superior branch Recurrent laryngeal nerve 1 Inferior cervical cardiac branch of vagus Innominate artery Aorta Combined sympathetic and vagal inferior cervical cardiac nerves Right bronchus Pulmonary artery" Right vagus' Thoracic duct Vena azygos Vena cava inferior, s_ sectional surface Liver, under surface Branches to liver and gall bladder' Vagus nerve Superior cervical cardiac branch Subclavian artery I f vagus Inferior cervical cardiac branch Clavicle [of vagus I. rib Inferior cervical cardiac branch of sympathetic Recurrent laryn- geal nerve Inferior cervical cardiac branch of sympathetic Left bronchus Pulmonary artery Lung, mesial surface CEsophagus Part of left vagus about to aid in formation of plexus guise Part of right vagus about to pass through diaphragm Left vagus Dissection showing lower part of pneumogastric nerves and their branches. Lesions of the recurrent laryngeal branch of the pneumogastric, from tumors, abscesses, etc., are comparatively common. Injury to this nerve is the chief danger to be feared in the removal of the thyroid gland, passing as it does so close to the gland and to the inferior thyroid artery where the latter is usually ligated preliminary to or during the excision of the gland. As it is the main motor nerve of the larynx, HUMAN ANATOMY. its irritation causes spasm of the laryngeal muscles, with brassy cough and stridulous breathing. The tendency to closure of the glottis is sometimes so threatening as to demand immediate tracheotomy or intubation. Paralysis causes hoarseness or loss of voice (aphonia). In a bilateral paralysis both cords fall into the cadaveric position. Loss of voice results and marked inspiratory dyspnoea, which may demand tracheotomy or intubation. THE SPINAL ACCESSORY NERVE. The eleventh or spinal accessory nerve (n. accessorius) is purely motor. It con- sists of two portions, a spinal and an accessory, which differ widely in origin, course and distribution. The spinal portion or accessorius spinalis (r. externus) is so termed because it arises from the spinal cord and the accessory portion or accessorius vagi (r. interims) receives its name in recognition of the fact that it is accessory to the vagus. As emphasized in connection with the last-named nerve (page 1266), the so-called accessory portion of the eleventh is, in reality, an integral part of the vagus and the description of its deep origin and distribution has been included with those of the vagus. There remains, therefore, only the spinal portion of the nerve to be considered. The spinal part the eleventh nerve proper supplies the sterno- mastoid and trapezius muscles. Deep Origin. The fibres constituting the spinal part of the nerve arise as the axones of a column of large multipolar neurones which is situated in the anterior horn of the spinal gray matter and extends from the lower end of the medulla to the fifth or sixth cervical segment of the spinal cord. The cells of this column, known as the accessory nucleus, occupy a dorso-lateral position in the horn, lying posterior to the cells from which arise the fibres of the anterior roots of the cervical nerves. Leaving these cells, the fibres pass dorsally within the gray matter to the vicinity of the bay between the anterior and posterior horns, where, while some at once curve outward and traverse the white matter to gain the lateral surface of the cord, the majority bend abruptly brainward and pursue a short ascending path before turning outward. Course and Distribution. The superficial origin of the accessory nerve is marked by the emergence of a series of fasciculi along the lateral surface of the spinal cord between the anterior and posterior roots of the cervical spinal nerves, the fasciculi progressively nearing the posterior roots as they issue at higher levels. Consecutively joining shortly after they escape from the cord, the fasciculi unite to form a common trunk, which gradually increases in size by accessions of fibres at each succeeding segment. The nerve-trunk thus formed passes upward in the sub- dural space, between the ligamentum denticulatum and the posterior nerve-roots (Fig. 879), to the foramen magnum, through which it enters the cranium. Upon reaching the side of the medulla, the spinal accessory nerve turns outward to enter the middle compartment of the jugular foramen and to unite temporarily with the accessory vagus. It occupies the posterior part of the middle compartment of the jugular foramen, lying within a dural sheath which contains also the vagus. On reaching the lower margin of the foramen, the fibres accessory to the vagus perma- nently leave the eleventh nerve. The latter, often described as the spinal part, courses downward for a short distance in the interval between the internal carotid artery and the internal jugular vein and then passes backward, either anterior or pos- terior to the vein, until it reaches the deep surface of the sterno-mastoid muscle, which it usually enters. While within the substance of the muscle, the spinal accessory gives off filaments which unite with a branch from the second cervical nerve to form the stcrno-wattoid plf\ns (Fig. 1082) for the supply of that muscle. Emerging from beneath the posterior edge of the sterno-mastoid, the eleventh nerve crosses the occipital triangle and dips under the anterior margin of the trape/ius along the deep surface of which it descends almost to the lower margin of the muscle. Under the trapezius the nerve forms a plexus of varying degrees of intricacy with the third and fourth cervical nerves. This is called the siihtmfH'-icil plt-.vus (Fig. 1082 ), its fibres of distribution supplying solely the Ti]>e/ins muscle. THE HYPOGLOSSAL NERVE. 1275 Variations. Considerable deviation from the normal has been described with regard to the spinal portion. The lower limit of its origin has been observed as high as the third cervical nerve and from that level as far down as the first thoracic. In one instance the nerve left the subdural space below the first cervical nerve and re-entered at a higher level. Quite fre- quently it fails to pierce the sterno-mastoid muscle. In one reported case the nerve ended in the sterno-mastoid, the trapezius being supplied only by the third and fourth cervical nerves. Two similar cases have been observed in the dissecting room of the University of Pennsylvania. Rarely it gives off a filament which joins the n. descendens cervicalis. Practical Considerations. The spinal accessory nerve supplies the sterno- cleido-mastoid and trapezius muscles. A few fibres of the second and third cervical nerves enter into the supply of the sterno-mastoid, but the muscle is almost com- pletely under the control of the spinal accessory. The cervical nerves take a greater part in the supply of the trapezius, so that paralysis of the spinal accessory does not always paralyze this muscle. Spasm of the trapezius will draw the head backward and toward the affected side and will pull the scapula toward the spine. In spasm of the sterno-mastoid, as in "wry neck," the chin will be turned to the opposite side and elevated, while the ear will look forward. If both sterno-mastoids are in contraction the chin will be in the median line and will be drawn toward the sternum. Paralysis of one muscle will produce a condition somewhat similar to that produced by a spasm of the opposite one. The spinal accessory nerve enters the under surface of the sterno-mastoid muscle near the junction of its upper and middle thirds, where it may be reached by an incision along the anterior border of the muscle. The nerve emerges from the muscle near the middle of its posterior border. THE HYPOGLOSSAL NERVE. The twelfth or hypoglossal nerve (n. hypoglossus) is a purely motor nerve and supplies the musculature of the tongue, intrinsic as well as extrinsic, with the excep- tion of the palato-glossus. Central and Cortical Connections. The hypoglossal nerve takes its deep origin from several associated groups of neurones called the hypoglossal nucleus (nucleus n. hypoglossi) (Fig. 949), which underlies the floor of the fourth ventricle. This nucleus is a narrow elongated collection of large multipolar cells, measuring about 18 mm. in length by 2 mm. in width, that partly corresponds in position to the trigonum hypoglossi in the floor of the fourth ventricle. The entire nucleus, however, is more extensive than the trigonum and extends from the level of the striae acusticae above into the closed part of the medulla as far down as the decussation of the pyramids (Fig. 927). It lies ventral and very slightly lateral to the central canal of the medulla and the median groove in the floor of the fourth ventricle, close to the mid-line and its fellow of the opposite side. The large size and branched form of the nerve-cells composing the nucleus, as well as their ventral position in relation to the central canal, emphasize the close correspondence of these elements with the cells of the motor roots of the spinal nerves. Indeed, as has been noted (page 1380), the gray matter enclosing the hypoglossal nucleus is the morphological equivalent of the bases of the anterior cornua. Immediately after arising and before leaving the nucleus, the axones converge into a number of fasciculi which, emerging from the ventral aspect of the nucleus, take a ventro-lateral course and traverse the interval between the gray and white reticular formations. From this situation the hypoglossal fibres continue their course to the anterior surface of the medulla by passing, for the most part, between the nucleus of the inferior olive and the mesial accessory olivary nucleus, although quite a number of the strands penetrate the ventral portion of the olivary nucleus (Fig. 927). The central connections of the hypoglossal nucleus include: (a] crossed fibres from the nucleus of the opposite side ; (b) fibres from, and probably also to, the posterior longitudinal fasciculus, by means of which the nucleus of the twelfth is brought into relation with the nuclei of other cranial nerves; and (<*} fibres which join the dorsal bundle of Schiitz, a system of longitudinal fibres underlying the floor of the fourth ventricle and traceable upward beneath the Sylvian aqueduct, but concerning whose destination and connections little is known. The cortical centre of the hypoglossal nerve probably lies within the lower or opercular extremity of the precentral convolution. The fibres arising as the axones of the cells within this area pass over the upper border of the lenticular nucleus and through the internal capsule and descend in the brain-stem within the median part of the pyramidal tract as far as the 1276 HUMAN ANATOMY. medulla. The cortico-nuclear fibres then bend dorso-medially and, for the most part but not entirely, cross the raphe to enter the ventro-lateral surface of the hypoglossal nucleus of the opposite side and end in arborizations around the root-cells. Course and Distribution. The hypoglossal takes its superficial origin from the surface of the brain-stem in the form of from ten to fifteen slender fasciculi, which emerge from the ventral surface of the medulla in the groove between the olivary eminence and the pyramid (Fig. 1046). FIG. 1082. I >igastric muscle, cut I. cervical nerve Spinal accessory nerve Small occipital nerve 1 1. cervical Hypoglossal ner Superior cervical ganglion anch of 1 1 . cervical to spinal accessory III. cervical nerve Communicans hypoglossi nps of great auricular and superficial ical nerves] Iv cervical nerve V. cervical nerve Branch to rhomboidei scle xternal pterygoifl ingual branch of V. ner , _ ^Chorda tympani nerve E - Internal pterygoid muscle E - Edge of oral mucous membrane ^___ Glosso-pharyngeal nerve - Mental nerve I - Inferior dental nerve, cut I Sublingual gland 1 -- Submaxillary ganglion --- Stylo-hyoid muscle Thyro-hyoid branch of XII. nerve Superior laryngeal nerve Descendens hypoglossi ; sympathetic cord is to its outer side Vagus nerve External laryngeal nerve VI. cervical ner ranch of communication to spinal accessory Cutaneous branch VII. cervical nerve Nerve to subclavius VIII. cervical nerve Posterior thoracic nerve Suprascapular I. thoracic nerve ' Omo-hyoid muscle, cut Phrenic nerve Middle cervical ganglion of sympathetic Scalenusantlcus muscle Subclavian artery Deep dissection of neck showing branches of vagus, spinal accessory and hypoglossal nerves. These root-bundles pass outward, dorsal to the vertebral artery, and assemble into two groups, which pierce the dura mater separately at a point opposite the anterior condyloid foramen. Either within this canal or as they leave the cranium through its external opening they unite into a single trunk. Arriving at the inferior aspect of the base of the skull, the deeply placed hypoglossal nerve descends and hooks around the ganglion of the trunk of the vagus, to which it is closely attached by connective tissue. It then takes a downward and forward course between the internal carotid artery and the internal jugular vein. Arriving at the inferior margin of the posterior belly of the digastric, the nerve winds around the occipital artery and courses downward and forward to the outer side of the external and internal carotid arteries. It then continues forward above the hyoid bone to the under surface of the tongue, passing beneath the tendon of the digastric, THE HYPOGLOSSAL NERVE. 1277 under the stylo-hyoid and mylo-hyoid muscles and over the hyo-glossus (Fig. 1082). It terminates by piercing the genio-hyo-glossus and breaking up into a number of fibres for the supply of the lingual muscles. Communications. Immediately after emerging from the anterior condyloid foramen, (a) a tiny branch connects with the superior cervical ganglion of the sympathetic, ( b ) one or two filaments pass to the loop between the first and second cervical nerves and (c) several fibres associate the nerve with the ganglion of the trunk of the vagus. At the point where the hypo- glossal nerve and the occipital artery cross, (d) the lingual branch of the vagus joins the twelfth ; and as the nerve lies beneath the mylo-hyoid and upon the hyo-glossus muscle, it communi- cates with (e) the lingual branch of the mandibular nerve. Branches. The branches of the hypoglossal nerve are : (i) the meningeal, (2) the descending, (3) the thyro-hyoid and (4) the lingual. 1. The meningeal branch (r. meningeus) consists of one or two minute filaments which supply the dura mater of the posterior cranial fossa and the-diploe of the occipital bone. As the hypoglossal is motor in function, it is likely that these twigs are contributed to the nerve by the loop between the first and second cervical nerves. 2. The descending branch (r. descendens), or r. descendens hypoglossi, is in reality only to a limited extent a branch of the twelfth, since the greater number of its fibres are accessions to the hypoglossal from the first and second cervical nerves. There is reason, however, to believe that these cervical nerves are not the exclusive source of the fibres of the descendens hypoglossi, but that some arise from the cells of the hypoglossal nucleus. The descending branch arises near the point where the hypoglossal nerve hooks around the occipital artery and runs downward and inward in front of or within the carotid sheath. It gives off a branch to the an- terior belly of the omo-hyoid and, about the middle of the neck, joins the descend- ing cervical nerve, or n. communicans hypoglossi, from the second and third cervical nerves. A loop or plexus, termed the ansa hypoglossi, is thus formed and from it filaments are supplied to the sterno-hyoid and sterno-thyroid muscles and to the posterior belly of the omo-hyoid (Fig. 1082). 3. The thyro-hyoid nerve (r. thyreohyoideus) is also only an apparent branch of the hypoglossal, as its fibres can be traced back to the cervical plexus. It is given off before the nerve dips beneath the stylo-hyoid muscle and passes down behind the greater cornu of the hyoid bone to reach its distribution to the thyro-hyoid muscle. 4. The lingual branches (rr. linguales) with one exception, comprise the real distribution of the hypoglossal. As the nerve lies beneath the mylo-hyoid muscle filaments are given off to the hyo-glossus, the stylo-glossus and the genio-hyoideus. The fibres going to the genio-hyoid are in all probability de- rived from the cervical plexus and are not of true hypoglossal origin. After giving off the above-named branches, the hypoglossal nerve breaks up into the terminal filaments which pierce the genio-hyo-glossus to supply it and the lingualis muscle. Variations. Occasionally the hypoglossal has been found to possess a posterior root bear- ing a ganglion. This condition is to be regarded as a persistence of the temporary embryonal stage during which the nerve is provided with a posterior root and a ganglion of Froriep (page 1380). In one case the superficial origin was located at the posterior aspect of the me- dulla. Quite frequently the vertebral artery passes between the rootlets of origin and in rare instances behind them. Sometimes a cross filament, situated either between the genio-hyo- glossus and genio-hyoid muscles or in the substance of the latter connects the two hypoglossal nerves. Rarely the hypoglossal has been seen to send a filament to the mylo-hyoid, the digas- tric or the stylo-hyoid muscle. Occasionally the r. descendens hypoglossi seems to be derived, either entirely or in part, from the vagus, but in these instances the fibres can be traced back to their true origin from the cervical nerves. A filament from the descending nerve sometimes passes into the thorax, where it joins the vagus or the sympathetic ; in such cases the aberrant branch is probably derived originally from either the sympathetic or the vagus. The r. descen- dens hypoglossi may send a branch to the sterno-mastoid muscle. Practical Considerations. Involvement of the hypoglossal nerve, usually together with other cranial nerves is frequent in bulbar disease. The most character- istic symptom is a deviation of the tongue, when protruded to the affected side, caused 1278 HUMAN ANATOMY. by the unopposed action of the muscles of the opposite side. The nerve may be injured by operative or other wounds in the submaxillary region or in the mouth, as in gun-shot wounds. It can be easily reached in the submaxillary region by the same incision as that used for ligating the lingual artery (page 736). It passes for- ward to the tongue, just above the hyoid bone, and forms the upper boundary of the small "lingual triangle," which is exposed when the submaxillary gland is elevated. THE SPINAL NERVES. The cranial division of the somatic nerves having been considered, the spinal group next claims attention, the visceral or splanchnic (sympathetic) nerves being reserved for a final and separate description. The spinal nerves (nn. spinales) include a series of usually thirty-one pairs of symmetrically disposed trunks which pass laterally from the spinal cord and emerge from the vertebral canal through the intervertebral foramina ( Fig. 880). Each nerve arises from the cord by a dorsal sensory and a ventral motor root, which sepa- rately traverse the subarachnoid and subdural spaces and evaginate or pierce the pia mater, arachnoid and dura mater. Within the intervertebral foramina the roots unite to form a common trunk, which carries with it a sheath composed of the three membranes, the contribution of the arachnoid and pia, however, soon ending, whilst the dural covering is prolonged to become continuous with the epineural sheath of the nerve. Nomenclature. The spinal nerves are designated not relative to the position at which they arise from the cord, but according to' their point of emergence from the vertebral canal. They are divided, therefore, into the cervical, thoracic, lumbar, sacral and coccygcal groups. With the exception of those in the cervical region, the individual nerves are named according to the vertebra below which they emerge from the vertebral canal. On account of the disproportion between the eight cervi- cal nerves and the seven cervical vertebrae, this arrangement necessarily can not prevail in the neck. The first cervical nerve, often called the suboccipital nerve, emerges between the occipital bone and the atlas ; the second emerges below the first vertebra, the third below the second and so on down to the eighth, which traverses the foramen between the seventh cervical and first thoracic vertebral segments. Constitution. Every spinal nerve arises by two roots, a posterior sensory and an anterior motor, the latter being composed of the axones proceeding from the motor neurones situated within the gray matter of the anterior cornu of the spinal cord, whilst the fibres composing the posterior or sensory root are the axones of the neurones within the ganglia which are invariably present on these roots. The formation of the common trunk, by the union of the two roots, affords opportunity for the two varie- ties of fibres to intermingle, so that the anterior and posterior primary divisions into which the common trunk divides contain both sensory and motor fibres. In addition to these fibres, which are destined for the somatic muscles and the integument, others are added from the sympathetic neurones for the supply of the outlying involuntary muscle and glandular tissue occurring in the regions to which the spinal nerves are distributed. It is evident, therefore, that the terms "motor" and "sensory," as applied to the somatic branches of the spinal nerves, are relative and not absolute, since in all cases the nerves passing to the muscles contain sensory and sympathetic fibres in addition to those ending as motor filaments in relation with the striated muscle fibres. Likewise, in the case of the sensory branches distributed to the integ- ument, sympathetic filaments (motor to the involuntary muscle of the blood-vessels and secretory to the glands) accompany those concerned in collecting sensory impulses. On the other hand, where they retain their typical plan, as in the case of the thoracic nerves, the spinal nerves contribute motor fibres which end around the sympathetic neurones to supply motor impulses either to the involuntary muscle of the organs, by way of the splanchnic efferents, or to the outlying involuntary muscle along the somatic nerves in the manner above described. The sensory, posterior or dorsal roots (radices posteriores) of the spinal nerves are usually larger than the motor, a condition due to the increased number of their filaments and the greater size of those filaments ( fila ladicularia ). The fas- ciculi which form the sensory root are attached to the cord along the postero-lateral POSTERIOR PRIMARY DIVISIONS OF SPINAL NERVES. 1279 groove as a continuous series, called the posterior root zone (Fig. 884). These rootlets are sometimes so numerous and so crowded, that those of adjacent nerves overlap and adhere to one another. Where more typically disposed, as in the thoracic region, the cord-segments (page 1024) are distinct. The fasciculi for any one nerve usually collect into two bundles which pass to the proximal aspect of the spinal ganglion. The spinal ganglia (e nearly to the mid-line, where it pierces the muscle and becomes superficial as the anterior terminal cutaneous branch ( r. cutanens anterior). THE CERVICAL PLEXUS. 1285 FIG. 1086. 1C. The integument is therefore supplied, from dorsal to ventral mid- line, by the posterior primary division, the posterior and anterior divisions of the lateral cutaneous branch and the anterior cutaneous branch of the anterior primary division. The muscles derive their nerve-supply from both the anterior and the posterior primary divisions. THE CERVICAL NERVES. The anterior primary divisions (IT. anteriores) of the eight cervical nerves (nn. ccrvicales), assisted by the first and second thoracic, supply the head, neck, upper extremity, thoracic integument and diaphragm. The first, second, third and fourth communicate freely and form the cervical plexus for the supply of the head and neck and the skin of the upper pectoral and shoulder regions, whilst the fifth, sixth, seventh, and eighth, aided by the first and sometimes by the second thoracic, form the brachial plexus, which supplies the upper extremity and the lateral thoracic wall. THE CERVICAL PLEXUS. The cervical plexus (plexus cervicalis ) is formed by the union of the anterior primary divisions (rr. anteriores) of the upper four cervical nerves (Fig. 1086). After traversing the intervertebral foramina, they pass behind the vertebral artery and emerge, the first be- tween the rectus capitis lateralis and the rectus capitis anticus minor muscles, and the others first between the inter- transversales muscles and then between the rectus capitis anticus major and scalenus me- dius muscles. Each is joined by a gray ram us communicans, derived either from the superior cervical ganglion of the sympathetic or from the association cord be- tween the superior and middle cervical ganglia. Under cover of the sterno-mastoid the four nerves are connected to form the cervical plexus. The second, third and fourth each divide into an ascending and a descending branch ; the first does not divide. These branches are connected in an irregular series of loops that constitute the cervical plexus, which lies opposite the first four cervical vertebrae and upon the sca- lenus medius and levator anguli scapula; muscles, and is covered by the sterno-mastoid. Branches. The branches of the plexus may be divided into a superficial and a deep set. The former reach the under surface of the deep fascia at about the middle of the posterior margin of the sterno-mastoid and are distributed to the integument of the head, neck, shoulder and upper pectoral region. The latter are divided into an internal and an external group, some of which supply the muscles of the neck Diagram illustrating plan of cervical plexus. 1286 HUMAN ANATOMY. and the diaphragm, whilst others communicate with the ninth, eleventh and twelfth cranial and the sympathetic nerves. THE CERVICAL PLEXUS. I. Superficial Branches. II. Deep Branches. A. Ascending- branches : D. External branches : 1. Small occipital 7. Muscular 2. Great auricular 8. Communicating B. Transverse branch : E. Internal branches : 3. Superficial cervical 9. Muscular C. Descending branches : 10. Phrenic 4. Suprasternal n. Communicating 5. Supraclavicular 6. Supraacromial i. The superficial branches are purely sensory. They become superficial at the posterior border of the sterno-mastoid, slightly above its middle, and from that point radiate in all directions to reach their cutaneous destinations (Fig. 1087). 1. The small occipital nerve (n. occipitalis minor) (Fig. 1087) may be either single or double. It originates from the second and third cervical nerves, or from the second only, and passes backward and upward beneath the deep fascia along or overlapping the posterior border of the sterno-mastoid muscle, where it gives off (a) the cervical branches. It pierces the deep fascia at the upper angle of the occipital triangle and breaks up into its terminal branches : (^) the auricular, (c) the mastoid and (d) the occipital. a^ The cervical branches are tiny twigs which supply the skin over the upper part of the occipital triangle. b. The auricular branch supplies the integument over the cranial aspect of the posterior part of the pinna. c. The mastoid branch supplies the scalp overlying and above the mastoid process. d. The occipital branch is distributed to the area of scalp of the occiput lying between the mastoid process and the distribution of the great occipital nerve. The small occipital communicates with the posterior and great auricular nerves and with the great occipital. Variations. The small occipital varies in size and may be so small as to be distributed only to the integument in the neck. In such an event, and usually in case of any deficiency, the unsupplied area receives fibres from the great occipital. It sometimes passes backward instead of upward and pierces the trapezius near the upper border before reaching the scalp. 2. The great auricular nerve (n. auricularis magnus) (Fig. 1087) is the larg- est of the superficial set and arises, usually with the superficial cervical nerve, from the second and third, from the third alone, or from the third and fourth cervical nerves. Turning over the posterior margin of the sterno-mastoid it ascends toward the ear between the platysma and the deep fascia. Below the ear it gives off a few (a} facial twigs and then terminates by dividing into () auricular and {c} mastoid branches. a. The facial twigs pass through the parotid gland and over the angle of the mandible, supplying the integument over the parotid gland and masseter muscle and communicating with the cervico-facial division of the seventh cranial nerve. b. The auricular branches (r. interior) supply mainly the cranial surface of the posterior part of the pinna. One filament passes through the cartilage by means of a cleft between the concha and the antihelix and supplies the outer surface, while a few twigs are distributed to the outer surface of the lobule. The auricular branches inosculate with the small occipital and pos- terior auricular nerves. c. The mastoid branch ( r. posterior) is distributed to the skin overlying the mastoid process and the upper part of the sterno-mastoid muscle. It inosculates as does the auricular branch. Variation. The mastoid branch may arise independently from the plexus and pass upward to its destination between the small occipital and great auricular nerves. THE CERVICAL PLEXUS. 1287 <* The superficial cervical nerve (n. cutancus colli) usually arises m com- mon with the great auricular from the second and third, the third only, or from the third and fourth cervical nerves (Fig. 1087). From the posterior margin of the sterno- mastoid it passes almost directly forward over the middle of that muscle and FIG. 1087. Temporal branch of facial Occipital branch of great auricular Great occipital nerv Posterior auricular nerve Small occipital nerve Branch of communication with facial Cutaneous branch of III. cervical Great auricular nerve Communication between spinal accessory Supraacromial branch Supraclavicular branch Spinal accessory nerve Supraorbital nerve Supratrochlear nerve Malar branch of facial nerve Infraorbital nerve Infraorbital branch of facial Buccal branch of facial Communication with buccal branch of mandibular Supramandibular branch of facial Inframandibular branch of facial perficial cervical nerve Superficial descending branch Suprasternal branch Dissection showing superficial branches of cervical plexus, as well as parts of trigeminal, facial, spinal accessory and great occipital nerves ; ear has been drawn lorwara. the platysma myoides and the external jugular vein. It perforates the deep cervical fascia near the anterior border of the sterno-mastoid and divides into O) an upper and () a lower set of branches. a. The upper branches (rr. superiores) form an extensive inosculation with the inframandib- ular branch of the facial nerve, after which they pierce the platysma and supply the integument of the neck as far forward as the median line and as far up as the inferior margin of the mandit b. The lower branches ( rr. inferiores ) after piercing the platysma are distributed to the skm of the lower part of the neck to the mid-line as far down as the sternum. 1288 HUMAN ANATOMY. Variation. The superficial cervical, instead of a single nerve, may arise as two or more filaments from the cervical plexus. The descending branches ( nn. stipraclavicularcs) (Fig. 1089) arise from the third and fourth cervical nerves and pass downward in the anterior margin of the occipital triangle along the posterior edge of the sterno-mastoid. On nearing the clavicle they break up into three distinct sets : (4) the suprasternal, (5) the supra- clavicular and (6) the snpraacromial. FK;. 1088. Third occipital nerve Great occipital nerve i Branch from III. cervical, dorsal division Branches trom IV vical, dorsal divi Inosculation between facial nerve and small occipital and great auricular ni-rvcs Sterno-cleido-mastoid muscle Great auricular nerve Small occipital nerve Superficial cervical nerve perficial descending branch of cervical plexus; " leader crosses the suprasternal branch nal accessory nerve scular branch to trapezius araclavicular branches Supraacroinial branches Dissection showing superficial branches of cervical plexus and posterior cutaneous branches. 4. The suprasternal branches (rr. supraclaviculares anteriores) are the smallest. They pass over the lower end of the sterno-mastoid and the inner end of the clavicle and supply the skin of the chest as far down as the angulus Ludovici. One or two filaments terminate in the sterno-clavicular articulation. 5. The supraclavicular branches (rr. supraclaviculares mcdii) pass across the middle of the clavicle and supply the integument of the chest as far down as the third or fourth rib, inosculating with twigs from the anterior cutaneous branches of the upper thoracic nerves. Variation. A twig may perforate the clavicle. THE CERVICAL PLEXUS. 1289 6. The supraacromial branches ( rr. supraclaviculares posterities) cross the clavicular insertion of the trapezius and are distributed to the skin over the anterior, external and posterior aspects of the shoulder as far down as the lower portion of the deltoid. II. The deep branches are divided into two sets, an external and an internal. Both arising beneath the sterno-mastoid, the former pass away from and the latter toward the median line of the neck. 7. The external muscular branches are distributed as follows: a. The sterno-mastoid receives a branch from the second cervical which enters the deep surface of the muscle and interlaces with a branch of the spinal accessory nerve to form the sterno-mastoid plexus. FIG. 1089. V. cervical nerve, dorsal division Ext. brs. dorsal division VI. cervical n VI. cervical nerve, dorsal division Small occipit Complexi Muscular brs. to complexus and biventer from occip. major Third occipital nerve Fascial septum from ligamentum nucha; Great occipital nerve Rectus capitis posticus majc. Branch toobliquusinferinr Spine of II. cervical vertebra Cutaneous br. from III. cervical- Part of complexus and biventer Third occipital ner -~ Branch to complexus from II. cervi Branch to complexus from III. cervical Part of splenius Cutaneous brs. from IV. cerv "Internal br. dorsal division of VI. cervical ne VII. cervical, dorsal division VIII. cervical, dorsal division- Internal branch of post. div. of V. cervical ner Spinous process of VII. cervical vertebra Obliquus superior Transverse process of atlas Ant. division I. cervical, cutaneous "br. of dorsal div. passing backward "Obliquus inferior 'II. cervical nerve, dorsal division Levator anguli scapulae ~ : : - ... . . Branch to tr.:c!ielo-mastoid III. cervical nerve, dorsal division Communication between II. and I II. dorsal divisions External brs. oflll. cervical, dorsal division 'IV. cervical nerve, dorsal division Ext. branch of dorsal division V. cervical nerve Transverse process I . thoracic vetebra Transverse process II. thoracic vertebra Levator anguli scapula; Trapezius Dissection of right side of neck, showing deeper relations of cervical nerves. f>. The trapezius receives fibres from the third and fourth cervical nerves which arise with and accompany the descending branches of the superficial set through the occipital triangle. They dip under the anterior margin of the trapezius, before and after which they form a more or less complex inosculation with the spinal accessory, called the subtrapezial plexus, from which filaments are distributed to the trapezius muscle (Fig. 1088). c. The levator anguli scapulae receives two branches which take their origin from the third and fourth nerves. d. The scalenus medius and (e) scalenus posticus also receive fibres from the third and fourth. 8. The communicating branches form points of contact and union with the spinal accessory nerve (#) under the sterno-mastoid and () in the occipital triangle and under the trapezius. By means of these inosculations are formed the sterno-mastoid and subtrapezial plexuses. 1290 HUMAN ANATOMY. 9. The muscular branches are distributed to (a) certain prevertebral muscles and to (<5) the genio-hyoid and the infrahyoid muscles. a. The rectus capitis anticus major and minor and the rectus capitis lateralis are supplied by a filament arising from the loop between the first and second cervical nerves. The intertrans- versales, the longus colli and a portion of the rectus capitis anticus major receive their supply from the second, third and fourth, and the upper part of the scalenus anticus receives a twig from the fourth cervical nerve. b. The genio-hyoid and the four muscles of the infrahyoid group are innervated by the cervical plexus in a rather roundabout manner. From the first and second cervical nerves are given off one or more branches which join the hypoglossal nerve shortly after its appearance in the neck. These fibres for a time form an integral portion of the hypoglossal and eventually escape from it as the nerve to the genio-hyoid, the nerve to the thyro-hyoid and the n. descen- dens hypoglossi (Fig. 1082). The last-mentioned nerve leaves the hypoglossal at the point where the latter crosses the internal carotid artery and then descends in the anterior cervical triangle. In front of, or sometimes within, the carotid sheath it forms a loop of communication, called the hypoglossal loop or ansa cervicalis (ansa hypoglossi) by inosculation with the descending cervical nerve (n. descendens cervicalis) (Fig. 1082). This descending cervical nerve is derived from the second and third cervical nerves and at first consists of two twigs which later unite in front of the internal jugular vein. From this point it passes downward and inward as a single trunk to reach its point of entrance into the ansa hypoglossi. The ansa may be either a simple loop or a plexus and is situated anterior to the carotid sheath at a variable point in the neck. From it branches are given off to the sterno-hyoid, the sterno-thyroid and the posterior belly of the omo-hyoid (Fig. 1076). 10. The phrenic nerve (n. phrenicus), although an internal muscular branch of the cervical plexus, is of such importance as to merit a separate description. Whilst mainly the motor nerve to the diaphragm, it contains some sensory fibres ; in this connection it may be pointed out that the phrenic is not the only motor nerve to the diaphragm, the lower thoracic nerves aiding in its innervation. The phrenic arises mainly from the fourth cervical nerve but receives additional fibres from the third and fifth (Fig. 1090). It passes down the neck on the scalenus anticus, which it crosses from without inward, and at the base of the neck accompanies that muscle between the subclavian artery and vein. At the entrance to the thorax it passes over the root of the internal mammary artery from without inward and backward^ occupying a position behind the sterno-clavicular articulation and the point of junc- tion of the subclavian and internal jugular veins. It then follows a course almost vertically downward, over the apex of the pleura and through the superior and middle mediastina, to the upper surface of the diaphragm. The right phrenic (Fig. 1090) is shorter than the left on account of its more direct downward course and the greater elevation of the diaphragm on that side. It crosses the second part of the subclavian artery and accompanies the right innominate vein and the superior vena cava on their lateral aspect. It then passes in front of the root of the lung and finishes its course by de- scending between the lateral aspect of the pericardium and the mrdiastinal pleura. Nearing the diaphragm it breaks up at the antero-lateral aspect of the quadrate foramen into its terminal branches, a few of which enter the abdomen through this opening. The left phrenic (Fig. 1090), having to wind around the left side of the heart and reach the more inferior half of the diaphragm, is longer than its fellow, about one-seventh longer (Luschka). Entering the thorax between the subclavian artery and the left innominate vein it crosses the anterior face of the left vagus nerve and continues its downward course by passing over the left side of the aortic arch. Reaching the middle mediastinum it courses in front of the root of the lung, behind the lower left angle of the pericardium, and descends to the diaphragm between the pericardium and the mcdiastinal pleura. It breaks up into its terminal branches before arriving at the thoracic surface of the diaphragm, which it enters at a point further from the median line and more anterior than dors the right. Branches of the phrenic nerve are : (a) the pleural,(b} the pcricardiac and (f) the terminal. H THE CERVICAL PLEXUS. 1291 a. The pleural branches, two in number, are almost microscopic in size, and are given off as the nerve crosses the apex of the pleura. One supplies the costal pleura and the other, which sometimes accompanies the internal mammary artery, is distributed to the medias- tinal pleura. b. The pericardiac branch (r. pericardiacus) is a tiny filament which is usually given off opposite the lower margin of the third costal cartilage. It is sometimes absent on the left side. c. The terminal branches arise under cover of the pleura and differ to some extent on the two sides. The right phrenic divides antero-lateral to the opening for the inferior vena cava into (aa) an anterior and (bb) a posterior branch. aa. The anterior branch breaks up under the pleura into five or six fine twigs, which spread out antero-laterally in the sternal portion and the anterior part of the right costal portion of the FIG. 1090. Scaletius medius muscle Vagus nerve V. cervical nerve Scaletius atiticus muscle Upper trunk of brachial plexus VII. cervical nerve Superior intercostal arte VIII. cervical nerve I. thoracic nerve Clavicle Phrenic nerve Internal mam- mary artery Innominate veins Vena cava superior I.ung, mesial surface Pericardium Sterno-cleido-mastoid Vagus nerve Internal jugular vein Subclavian artery Omo-hyoid muscle Subclavian vein Clavicle Subclavius r Lung, mesial surface. Showing hiluin IV. rib Diaphragm, up- per surface VII. rib Dissection showing phrenic nerves ; parts of sternum and ribs have been removed ; lungs are pulled aside ; pericardium is undisturbed. diaphragmatic musculature. Tiny filaments traverse the interval between the sternal and costal portions and enter the abdomen, where they are distributed to the peritoneal covering of the diaphragm and to the falciform ligament of the liver in the direction of the umbilicus. bb. The posterior branch pierces the central tendon at the outer margin of the quadrate opening and divides into a muscular branch and the right/// rt 'iiico-abdoin inal branch (r. phrenico- abdominalis dexter). The former supplies the lumbar portion of the musculature of the diaphragm. The latter traverses the quadrate foramen and first gives off a recurrent branch which accompanies the inferior vena cava back to the right auricle. After giving off this branch, under cover of the peritoneum some of its fibres enter the diaphragmatic ganglion and others unite with filaments from the cceliac plexus to form at the inferior surface of the diaghragm the diaphragmatic plexus, which is joined by twigs from the diaphragmatic ganglion. From this plexus fibres are distributed to the coronary ligament and peritoneum of the liver and to the right supra- renal body. The left phrenic pursues a general antero-lateral course and pierces the diaphragm at the junction between the musculature and the central tendon. Under cover of the peritoneum it splits up into an anterior, a lateral and a posterior branch. The anterior branch supplies the muscle of the left sternal portion and the antero-lateral part of the left costal portion. The i2 9 2 HUMAN ANATOMY. lateral branch supplies the corresponding part of the left costal portion. The posterior branch (r. phrenicoabdominalis sinister) is distributed to the left lumbar portion of the muscle of the diaphragm and usually either a filament passes to the left semilunar ganglion or several small threads to the ca-liac plexus, one of which can be traced to the left suprarenal budy. The phrenic nerve communicates in the lower part of the neck with the middle or inferior cervical ganglion of the sympathetic. At the inferior aspect of the diaphragm it communicates, on the right side, with the diaphragmatic plexus of the sympathetic and, on the left side, with the semilunar ganglion or the cceliac plexus. Variations. The phrenic may receive additional roots from the nerve to the subclavius, the nerve to the sterno-hyoid, the second or the sixth cervical nerve, the n. descendens cervi- calis or the ansa hypoglossi. It may arise exclusively from the nerve to the subclavius or, aris- ing normally, may give a branch to that muscle. It sometimes passes along the lateral border of or pierces the scalenus anticus muscle. Instead of descending behind the subclavian vein it may pass anterior to it or even through a foramen in it. The accessory phrenic nerve arises either from the fifth alone or from the fifth and sixth cervical nerves and, entering the thorax either anterior or posterior to the subclavian vein, joins the phrenic at the base of the neck or in the thorax. II. The communicating branches of the internal set effect unions with (a) the sympathetic, (6) the vagus and (c ) the hypoglossal. a. The superior cervical ganglion of the sympathetic or the association cord connecting the superior and middle ganglia sends gray rami communicates to the first, second, third and fourth cervical nerves. b. The ganglion of the trunk of the vagus is sometimes connected by means of a tiny nerve with the loop between the first and second cervical nerves c. The hypoglossal nerve receives, just below the anterior condyloid foramen, a good sized branch from the loop between the first and second cervical nerves. This communication furnishes sensory fibres to the hypoglossal nerve which subsequently leaves the latter as its men- ingeal branch ; other spinal fibres leave the twelfth as the n. descendens hypoglossi and as the nerves to the genio-hyoid and thyro-hyoid muscles. Practical Considerations. Of the motor ncrrcs of the cervical plexus the phrenic is most commonly the seat of trouble and this may result in or be associated with spasm or paralysis of the diaphragm. The involvement of the diaphragm may be part of a progressive muscular paralysis, as from lead poisoning, or from injuries or diseases of the spine. The nerve may be compressed by tumors or abscesses of the neck, or be injured in wounds of the neck. It passes downward under the sterno- mastoid muscle and on the scalenus anticus, from about the level of the hyoid bone. It is covered and somewhat fixed by the layer of deep fascia covering the scalenus anticus muscle. The clonic variety of spasm, singultus or hiccough, is very common, and is occasionally though rarely dangerous by preventing rest and sleep ; it may complicate apoplexy, peritonitis or chronic gastric catarrh. If only one phrenic is paralyzed the disturbance of function is slight and not easily recognized. In a bilateral paralysis, as from alcoholic neuritis, respiration depends almost entirely on the intercostal muscles, since the diaphragm is completely paralyzed. Dyspnoea, therefore, occurs on slight exertion. The epigastrium is depressed rather than prominent and the lower border of the liver is drawn upward. The superficial branches of the cervical plexus emerge together through the deep fascia near the middle of the posterior border of the sterno-mastoid muscle, and from this point pass in various directions. The auricularis magnus passes upward and forward over the sterno-mastoid to the ear and parotid gland, the occipitalis minor along the posterior margin of the same muscle to the scalp, and the superficial cervical branch obliquely forward and upward to the submaxillary region. The descending branches are three in number and puss respectively in the direction of the sternum, clavicle and acromion. They give rise to little or no disturbance when wounded. THE BRACHIAL PLEXUS. The brachial plexus (plexus brachialis) is a somewhat intricate interlacement of the anterior primary divisions of usually the lower four cervical and first thoracic- nerves. To these are sometimes added a branch from the fourth cervical, a branch from the second thoracic, or branches from both of these nerves. The fasciculi form- THE BRACHIAL PLEXUS. 1293 ing tliis plexus emerge in the interval between the scalenus anticus and medius and from the side of the neck pass beneath the clavicle and into the axilla through its apex. The plexus is divided, therefore, into two portions, a cervical or supraclavicular part (pars supraclavicularis) and an axillary or infraclai'icular\)Wi\. (pars infraclavicularis). In the posterior cervical triangle the plexus lies first above and then to the outer side of the subclavian artery and vein, is crossed by the posterior belly of the omo-hyoid muscle and is frequently threaded by the transverse cervical or the posterior scapu- lar artery. After entering the axilla its component parts, while lying mainly to the outer side, form a close fasces around the axillary artery, whose sheath they occupy. In the upper part of the axilla the plexus is overlain by the subclavius and pectoralis major muscles and before dividing into its terminal branches it lies enclosed between the pectoralis minor and subscapularis muscles. Constitution and Plan. In the various weavings of the component elements of the plexus five stages can be recognized : () anterior primary divisions of the spinal nerves, (/>) trunks, (r) divisions, (a) cords and (>) terminal branches (Fig. 1091). !'!(.;. 1091. Diagram illustrating plan of brachial plexus. Emerging from the interval between the anterior and middle scalene muscles, the fifth and sixth cervical nerves unite to form the outer or upper trunk, the seventh alone is continued into the middle trunk, whilst the eighth cervical and first thoracic fuse to form the inner or lower trunk. These trunks continue undivided until slightly beyond the lateral margin of the scalenus anticus, each one then sepa- rating into an anterior and a posterior division. These are of about equal size, with the exception of the posterior division of the inner trunk, which is much smaller than the others because the first thoracic nerve sends few if any fibres to the posterior division. The six divisions, three anterior and three posterior, unite differently to form three cords. The outer cord (fasciculus lateralis) is the bundle formed by the union of the anterior divisions of the outer and middle trunks. The posterior cord (fasciculus posterior) is the result of the fusion of the posterior divisions of all of the trunks and the inner cord (fasciculus medialis) is the continuation of only the anterior division of the inner trunk. The trunks are named in correspondence with 1294 their position as regards one another, while the cords are denominated according to their relation to the axillary artery, the outer lying lateral to, the inner mesial to, and the posterior behind, the artery. Variations. Considerable variety exists as regards the length of the component nerve- bundles in their several portions, division and union caking place at different levels in different individuals. The fifth cervical nerve may pass in front of or through the scalenus anticus. The sixth, though not so frequently as the fifth, may traverse the scalenus anticus. The seventh cervical nerve, as the middle trunk, may break up into three branches, one going to each of the three cords. The fibres of the posterior cord may arise from only the seventh and eighth, or the sixth, seventh and eighth cervical nerves. Plexuses have been seen in which only two cords, a smaller and a larger, were present, the latter taking the place of either the inner and outer or the inner and posterior cords. Communications. The five nerves comprising the source of the plexus are connected to the sympathetic system by gray rami communicantes and there is possibly a white ramus communicans passing from the first thoracic nerve to the first thoracic ganglion of the sympathetic. FIG. 1092. I. cervical nerv-- II. cervical nerve III. cervical nerve IV. cervical nerve Scalenus inedius m iscle Median nerve Ulna External anterior thoracic j Su|>raca|>ularnerve Upper subscapular nerve Outer cord of plexus Posterior cord of plexus Circumflex n Deltoid muscle Musculo-cutaneoiis nerve Musculo-spiral nerve Internal cutaneous nerve , Lesser internal cutaneous nerve Internal anterior thoracic nerve Insertion of soak-mis anticus Posterior thoracic nerve I. rib Serratus magnus, first serration II. rib Inner cord of plexus 'Middle subscapular nerve I.owi-r Mibsoupular nerve Deep dissection of neck, showing constitution of right brachial plexus. Practical Considerations. Sensory disturbances are rather rare in the distribution of the brachial plexus of nerves, but motor troubles are comparatively common, and are sometimes associated with disturbances of sensation, plexus, or only an individual branch, may be involved. The most common cause is injury, such as dislocation of tin- head of the humerus, a fracture of the clavicle, or a forced apposition of the clavicle to the first rib. Other causes are the pressure of tumors or the constitutional effects of poisons and infections, plexus is so superficial above the clavicle that it can be felt or even seen in thin people. Branches. These fall naturally into two groups, those -iven off from the sH/>nicf^ Musculo-cutaneous nerve \^Xy Median nerve -^ jX'jip Acromial thoracic artery Deltoid Cephalic vein f)t, ' Sterno-cleido-mastoid !~ r.xt. anterior thoracic nerve ^" Clavicle Axillary vein lOsA ~~~" > - Internal anterior thoracic nerve Less cuta Long thoracic artery Intercosto-humeral nvs: Subscapular artery Latissimus dorsi Long Subscapular nerve Teres Posterior thoracic nerve Serratus magnus Dissection of right axilla, showing relations of brachial plexus to blood-\ become prominent. When the arm is in front of the chest the deformity is most marked and the lower angle approaches the mid-line of the back. The patient can- not lift anything heavy with the affected arm. Since the incision to open an axillary abscess is made vertically in the middle of the thoracic wall of the axillary space, to avoid the vessels at its borders, this nerve is in some danger as it passes to the serratus magnus muscle. 4. The muscular branches supply the l<>ngus colli, the sraleni anticus, medius and posticus and the subclavius. a. The longus colli and scalenus anticus are supplied by small twigs which arise from the anterior surface of the lower four cervical nerves as they leave the vertebral column. b. The scaleni medius and posticus receive fibres given off from the posterior aspect of the lower four cervical nerves as they pass through the intervertebral foramina. r. The nerve to the subclavius (n. snhckiviiis) takes its origin from the outer trunk of the plexus, its fibres coming mainly from the fifth cervical nerve. It passes through the subclavian triangle, over the third portion of the subclavian artery and behind the clavicle, to enter the deep surface of the subclavius muscle. \r\ct- THE BRACHIAL PLEXUS. 1297 Variations. The phrenic nerve may give off a branch to the subclavius or may receive a fila- ment from the nerve to the subclavius. A branch of communication with the external anterior thoracic and a branch to the clavicular head of the sterno-cleido-mastoid have been noted. 5. The communicating branch to the phrenic nerve (Fig. 1090) arises usually from the fifth cervical nerve, sometimes from the fifth and sixth. Originating at the outer margin of the scalenus anticus it passes inward and joins the phrenic. If .this nerve is not present the nerve to the subclavius usually supplies the deficiency. II. The Infraclavicular Branches. These branches comprise those given off by the three cords of the plexus after the latter has passed beneath the clavicle into the axilla. 6. THE EXTERNAL ANTERIOR THORACIC NERVE. The external anterior thoracic nerve (n. thoracalis anterior lateralis) (Fig. 1093) receives its fibres from the fifth, sixth and seventh cervical nerves. Leaving the outer cord beneath the clavicle, it passes mesially over the axillary artery and, after giving FIG. 1094. a ^ I 1 Common carotid artery Phrenic nerve Scalenus 'anticus muscle Lesser internal cutaneous nerve Internal cutaneous nerve Duociavian artery Subclavian vein Dissection of right axilla, showing relation of brachial plexus to subclavian and axillary vessels with arm abducted. off a filament which unites with a similar structure from the internal anterior thoracic nerve, divides into two branches which pierce the costo-coracoid membrane and enter the deep surface of the pectoralis major. The upper branch supplies the clavicular portion of the muscle and the lower branch the upper part of the sternal portion. The loop between the anterior thoracic nerves gives off a filament which pierces the pectoralis minor and ends in the sternal part of the pectoralis major, to both of which muscles it is distributed. Variations. This nerve may supply fibres to the clavicular portion of the deltoid and to the acromio-clavicular articulation. 82 1298 HUMAN ANATOMY. 7. THE MUSCULO-CUTANEOUS NERVE. The musculo-cutaneous nerve (n. musculocutaneus) (Fig. 1098) derives its fibres from the fifth and sixth, and sometimes the seventh, cervical nerves and is a branch of the outer cord. The nerve to the coraco-brachialis muscle, derived from the seventh or sixth and seventh nerves, is usually found as an integral part of it. Leaving the outer cord under cover of the pectoralis minor it pierces the coraco-brachialis and passes obliquely downward and outward between the biceps and brachialis anticus muscles. Reaching the outer margin of the biceps a short distance above the elbow, the nerve pierces the deep fascia and passes under the median-cephalic vein. It then becomes superficial (n. cutaneus antebrachii lateralis) and divides into its terminal cutaneous branches. Branches. These are : (a) the muscular, (b) the humeral, (c) the articular and (d) the terminal. a. The muscular branches supply the coraco-brachialis, the biceps and the brachialis anticus. The nerve to the coraco-brachialis, which commonly has an independent origin, is usually double, one filament going to each portion of the muscle. The nerves to the biceps and brachialis anticus are given off while the musculo-cutaneous is in transit between those muscles. b. The humeral branch accompanies the nutrient branch of the brachial artery into the humerus. c. The articular branch aids in the supply of the elbow joint. d. The terminal part (n. cutaneus antebrachii lateralis) (Fig. 1103) of the musculo-cutaneous divides into two branches, (aa) an anterior and (66) a posterior. aa. The anterior branch descends in the antero-lateral portion of the superficial fascia of the forearm (Fig. 1104). It inosculates above the wrist with the radial nerve and supplies the in- tegument of the antero-lateral part of the forearm. It also distributes fibres to the skin over the thenar eminence, to the wrist joint and to the radial artery. bb. The posterior branch passes downward and backward and supplies the skin of the postero-lateral portion of the forearm down to or slightly beyond the wrist joint (Fig. 1102 ). It inosculates with the radial nerve and with the inferior external cutaneous branch of the musculo- spiral. Variations. Instead of piercing the coraco-brachialis the nerve may adhere to the median or its outer head for some distance down the arm, and then either as a single trunk or as several branches pass between the biceps and brachialis anticus muscles. Sometimes only a part of the nerve follows this course, joining the main trunk after the latter' s transit through the muscle. The muscular part only or the cutaneous part only may pierce the muscle. The nerve may be accompanied through the muscle by fibres of the median which rejoin the latter below the coraco-brachialis. The nerve may remain independent and fail to pierce the coraco-brachialis, either passing behind it or between it and the associated head of the biceps. It may perforate not only the coraco-brachialis but also the brachialis anticus or the short head of the biceps. Rarely the entire outer cord, after giving off the external anterior thoracic, may traverse the coraco-brachialis. Anomalies in distribution include a branch to the pronator radii teres, the supply of the skin of the dorsum of the hand over and adjacent to the first metacarpal bone, a branch to the dorsum of the thumb in the absence of the radial nerve and the giving off of dorsal digital nerves to both sides of the ring finger and the adjacent side of the little finger. 8. THE MEDIAN NERVE. The median nerve (n. mcdianus) (Fig. 1098) consists of fibres which can be traced to the sixth, seventh and eighth cervical and first thoracic nerves. It arises by two heads, an outer and an inner, which are derived respectively from the outer and inner cords of the plexus, the former containing fibres from the sixth and seventh cervical and the latter fibres from the eighth cervical and first thoracic nerves. The two heads, the inner of which usually crosses the main artery of the upper extremity at about the point where the axillary becomes brachial, unite either in front of or to the outer side of the artery. From the point of fusion of the two heads the nerve passes down the arm in close relation with the brachial artery, usually lying lateral or antero-lateral to the artery in the upper part of the arm, and as the elbow is neared, gradually attaining the inner side by crossing obliquely the anterior surface of the artery (Fig. 1098). It passes through the cubital fossa beneath the median-basilic vein and the bicipital fascia, and enters the forearm between the heads of the pronator radii teres muscle, the deep head of THE BRACHIAL PLEXUS. 1299 which separates the nerve from the ulnar artery. It follows a straight course down the forearm, accompanied by the median artery, lying upon the flexor profundus FIG. 1095. Deltoid Sup. ext. cutaneous br. musculo-spiral Inf. ext. cutaneous br. musculo-spiral Musculo-cutaneous nerve, ant. and post. brs. Musculo-spiral nerve - Posterior interosseous nerve . Radial nerve . Supinator brevis Pronator radii teres. Extensor carpi rad. longior Extensor carpi rad. brevior - Radial artery . Brachio- radialis _ Flexor subl. digitorum radial head " Flexor carpi radialis Median nerve Palmar cutaneous br. of median Abductor pollicis Digital brs. of median nerve Median nerve " Brachial artery -Edge of triceps Ulnar nerve "Inferior profunda artery Brachialis anticus Biceps tendon Pronator radii teres, humeral head Articular branches of median nerve Flexor caroi radialis Flexor sublimis digitorum Ulnar nerve Ulnar artery -Flexor profundus digitorum Flexor carpi ulnaris Palmar cutaneous br. of ulnar -Dorsal br. of ulnar nerve -Flexor sublimis digitorum -Pisiform bone -Deep br. of ulnar nerve -Palmaris brevis, reflected -Abductor minimi digiti -Flexor brevis minimi digiti .Digital brs. of ulnar nerve Dissection of right upp} the cutaneous and (r) the muscular. a. The articular branches are usually two in number. The upper arises near the origin of the circumflex and the lower during the passage of the nerve through the quadrilateral space. They supply the anterior inferior portion of the capsular ligament of the shoulder. A third articular branch is described as passing up the bicipital groove, supplying a twig to the upper end of the humerus and one to the neighboring portion of the capsular ligament of the shoulder. b. The cutaneous branch (a. cutaneus brachii lateralis) arises as a common trunk with the nerve to the teres minor. It becomes superficial between the long head of the triceps and the posterior border of the lower third of the deltoid and is distributed to the integument over the posterior half of the deltoid and the posterior surface of the upper half of the arm. One or two cutaneous filaments are derived from the muscular branches to the deltoid. They pierce the deltoid and are distributed to the skin over the lower portion of that muscle. c. The muscular branches (rr. musculares) innervate (aa) the teres minor and (bb} the deltoid. aa. The nerve to the teres minor arises from the circumflex at the posterior margin of the quadrilateral space and enters the middle of the posterior inferior border of the muscle which it supplies. bb. The deltoid branches comprise the largest portion of the nerve and consist of its termi- nal fibres. The terminal portion of the circumflex forms a bow, with its convexity in contact with the deep surface of the deltoid, extending around the upper part of the humerus almost as far forward as the anterior margin of the deltoid muscle. It gradually diminishes in size as the result of the departure of a series of twigs which enter and supply the fasciculi of the deltoid. Variations. The circumflex may receive very few or no fibres from the sixth cervical nerve. It may pierce the subscapularis and may supply that muscle. It may give origin to the nerve to the teres major and has been observed to furnish filaments to the long head of the triceps and to the infraspinatus. Practical Considerations. The circumflex nerve is frequently paralyzed from injuries to the shoulder, as in birth palsies when pressure is made in the axilla. It undergoes special strain in dislocations of the shoulder, the nerve being stretched over the head of the humerus and often lacerated. Other branches of the brachial plexus may be injured in this dislocation. Since the circumflex passes around the humerus at about the level of the surgical neck it is sometimes damaged in fractures in that situation. The most prominent symptom in paralysis of this nerve is loss of the rotundity of the shoulder from atrophy of the deltoid muscle. As the circumflex winds around the posterior surface of the humerus and reaches the anterior part of the deltoid muscle from behind, incisions for reaching the shoulder joint, as in excisions, should be made anteriorly, since only the terminal branches of the circumflex will then be divided ; paralysis of the deltoid is thus prevented. 1 6. THE MUSCULO-SPIRAL NERVE. The musculo-spiral nerve (n. radialis) (Fig. noo), the larger terminal branch of the posterior cord, is in fact the continuation of the latter. Its component fibres are derivatives of the sixth, seventh and eighth, and sometimes of the fifth, cervical nerves and it is distributed to the muscles and integument of the extensor surface of the arm, forearm and hand. After separating from the circumflex, it passes down- ward behind the axillary artery and over the surface of the latissimus dorsi and teres major muscles. Accompanied by the superior profunda artery, it turns backward on the inner aspect of the arm and, entering the musculo-spiral groove and traversing the interval between the internal and long and the external head of the triceps, reaches the lateral aspect of the arm. It then takes a forward course through the external intermuscular septum and becomes an occupant of the cleft between the brachioradialia and the bntchialis anticus. Continuing in this space as far as the level of the external condyle of the humerus the nerve divides into its terminal branches, i&bit posterior intcrosseous and the radial (Fig. 1095). THE BRACHIAL PLEXUS. 1309 Branches. These are : (b) after leaving the groove. aa. Before entering the groove branches arise for the supply of the three heads of the triceps and the anconeus. THE BRACHIAL PLEXUS. 1311 Int. cutaneous branch of nius- culospiral nerve Lesser int. cu- taneous nerve Inf. ext. cutaneous branch of musculo spiral nerve Int. cutaneous nerve, post branch Post, cutaneous br. of niusculo- cutaneous nerve The branch for the long head of the triceps, before its entrance into the muscle, breaks up into four or five filaments. The nerve supply of the inner head of the triceps is usually effected by two branches, an upper and a lower. The upper is short and enters the muscle soon after leaving the musculo- spiral. The lower, called the collateral ulnar branch, is longer and extends for a considerable distance along the inner surface of the triceps in close association with the ulnar nerve. Posterior to the internal intermuscular septum it enters its muscle. Tiny FIG. 1102. filaments accompany the collateral ulnar artery to the capsular ligament of the elbow. The nerves to the outer head of the triceps and to the anconeus take their origin as a single trunk. The former passes directly to the inner surface of the outer head, while the latter leaves the musculo-spiral groove and tra- verses the outer portion of the internal head of the triceps until the anconeus is reached. bb. After leaving the groove and while lying in the cleft between the brachialis anticus and the brachio- radialis, twigs are given off for the supply of the brachio-radialis, the extensor carpi radialis longior and the brachialis anticus. The nerve to the brachio-radialis enters the mesial surface of that muscle and usually supplies a filament to the capsule of the elbow. The nerve to the extensor carpi radialis longior may arise either from the posterior interosseous or directly from the musculo-spiral. The nerve to the brachialis anti- cus, while usually present, is not con- stant. It enters and supplies the lateral portion of that muscle. c. The humeral branches com- prise one which is supplied to the periosteum of the extensor surface of the humerus and one which enters the shaft of the humerus with the nutrient artery, when the latter arises as a branch of the superior profunda. d. The articular branches are des- tined for the elbow. They arise from the musculo-spiral as it lies between the brachialis anticus and the brachio- radialis, from the ulnar collateral nerve and from the nerve to the anconeus. e. The terminal branches of the musculo-spiral arises at about the level of the external condyle and in the fis- sure between the brachialis anticus and the brachio-radialis. They com- prise (aa) the posterior interosseous and (bb) the radial. Radial nerve Inf. txt. cutaneous branch musculo-spiral" Dorsal branch of ulnar nerve From ulnar nerve Superficial dissection of right forearm, showing cutaneous nerves of posterior surface. aa. The posterior interosseous nerve (r. profundus n. radialis) ( Fig. noo) is the larger of the terminal branches and is mainly motor in function. Its fibres can be traced back to the sixth, seventh and sometimes the eighth cervical nerve. Shortly after its origin it approaches the supinator brevis, through a fissure in whose substance it makes its way to the lateral side of the radius, in this way reach- 1312 HUMAN ANATOMY. Supraacromial brs. cervical plexus ing the posterior aspect of the forearm. Here it takes a position between the two layers of the extensor muscles and rapidly decreases in size by giving off in quick succession branches to the neighboring muscles. As a much attenuated nerve it reaches the posterior surface of the interosseous membrane at the junction of the middle and lower thirds of the forearm. From the interval between the extensores longus and brevis pol- FIG. 1103. licis it courses along the membrane, cov- ered in turn by the ex- tensor longus pollicis, the extensor indicis and the tendons of the extensor longus digitorum, finally reaching the dorsum of the wrist, where it presents a small gangliform swelling. In the lower fourth of its course it is some- times called the e.v- t e r n a I interosseous nerve. B ranches of Lesser internal the posterior interos- cutaiieous nerve SCOUS nerve Comprise two sets: those given off before and after traversing the supina- tor brevis. Cutaneous brs. . circumflex nerve Sup. ext. cutaneous br. of musculo- spiral nerve Inf. ext. cutaneous br. of rnusculo-i spiral nerve M uscu lo-cuta neous nerve, post, cutaneo branch Muscuio-cutaneous nerve, ant. cutaneous brancb Muscuio-cutaneous, post, cutaneous br. Internal cutaneous nerve Those arising be- fore the nerve enters the muscle comprise the nerves for the extensor carpi radialis brerior and the supinator brevis. The latter receives two filaments, which supply the two strata of muscle consequent upon the de- lamination of the supin- ator brevis by the pos- terior interosseous nerve. Quite frequently the nerve to the exten- sor carpi radialis long- ior arises from this por- tion of the posterior interosseous. The branches giv- en off after leaving the muscle include the sup- ply of the extensor car- pi H/itaris, the extensor communis dig if or urn , the extensor minimi digiti, the three extensors of the thumb and the extensor indicis. The first three of these muscles are supplied by a branch which leaves the posterior inter- osseous soon after its emergence from the supinator brevis. This nerve divides into two branches, one of which is distributed to the extensor carpi iilnaris and the other to the remain- ing two muscles. The extensor communis digitorum receives additional innervation from a tu is; which arises from the posterior interosseous further down the forearm. Superficial dissection of right arm, showing cutaneous nerves of anterior surface; cephalic vein is seen passing up to di-lto-pectoral interval; basilic vein pierces deep fascia at lower inner aspect of arm. THE BRACHIAL PLEXUS. 1313 Inf. ext. cutaneous br. of niusculo-' spiral nerves Musculo-cuta- neous nerve, ant- cutaneous br. Musculo-cuta- neous nerve, post. cutaneous br. Lesser internal cutaneous nerve Internal cutaneous nerve The extensor ossis metacarf>i pollicis and the extensor brevis pollicis are innervated by a branch arising below the preceding, which breaks up into two decurrent twigs, one of which goes to each muscle. The extensor longus pollicis is the recipient of a small filament, which arises from the posterior interosseous a short distance below the preceding nerve. The extensor indicis is sup- plied b y the lowermost motor FIG. 1 104. filament arising from the poste- rior interosseous. Terminal twigs are distrib- uted to the dorsal portion of the wrist joint, the intercarpal and carpo-metacarpal joints, the peri- osteum of the radius and ulna and the interosseous membrane. One of the filaments supplying the last-mentioned structure fre- quently inosculates with a branch from the anterior interosseous. The filaments to the carpus are continued through the meta- carpal spaces and are joined by twigs from the deep branch of the ulnar (page 1305). The joint nerves thus formed break up into two branches which accompany adjoining metacarpal bones to the metacarpo-phalangeal articu- lations. The branch to the first metacarpal space breaks up into seven branches (Rauber). Ant. br. internal cutaneous nerve Brs. of ant . br. of musculo-cutaneous Palmar cuta- neous br. of ul- nar nerve Palmar cutane- ous br. of me- dian nerve Digital brs. of ulnar nerve Digital brs. of median nerve bb. The radial nerve (r. superficialis n. radialis) (Fig. 1095) is smaller than the posterior interosseous and is purely sensory in its function. Its fibres originate from the sixth cervical nerve and sometimes from the fifth or seventh. From the end of the musculo-spiral it passes down the radial side of the forearm under cover of the brachio-radialis and anterior to the supinator brevis, the pronator radii teres and the radial head of the flexor sublimis digitorum. It accompanies, for the greater part of its course, the radial artery, to the radial side of which the nerve lies. At the junction of the middle and lower thirds of the forearm it begins to turn gradually backward over the radius and under the tendon of the brachio-radialis (Fig. 1095). Reaching the extensor surface of the forearm just above the wrist it divides into two diverging branches, which supply the back of the hand and the three outer digits (Fig. 1102). Branches. The radial nerve divides into two terminal branches, an external and an internal. S3 Superficial dissection of rierht forearm and hand, showing cutaneous nerves of anterior and palmar surface. 1 3 i4 HUMAN ANATOMY. The external or radial branch inosculates with the musculo-cutaneous nerve and dis- tributes filaments to the integument of the thenar eminence and the radial side of the thumb as far out as the base of the nail. The internal or ulnar branch splits into two parts. The inner of these likewise under- goes dichotomous division and supplies the dorsal aspect of the adjacent surfaces of the thumb and the index finger. The outer divides similarly to the inner and is distributed to the adjoining sides of the index and middle fingers. It gives off a branch which inosculates with the adjacent filament from the dorsal branch of the ulnar nerve, so that the contiguous surfaces of the middle and ring fingers are the recipients of fibres from both the radial and ulnar nerves. As the ulnar side of the hand is approximated the digital area of distribution of the radial nerve gradually recedes toward the wrist. On the thumb the radial extends as far out as the base of the nail, on the index finger as far as the middle of the second phalanx and on the middle finger only over the proximal portion of the first phalanx. The deficiency in these instances is supplied by twigs from the digital branches of the median nerve. Variations. The musculo-spiral may accompany the circumflex nerve through the quad- rilateral space. It may communicate with the ulnar nerve in the upper arm. Cases are recorded in which the dorsal digital nerves to the little and the ulnar side of the ring finger were furnished by the musculo-spiral instead of by the ulnar and in which the inferior external cutaneous branch extended to the first phalanx of the ring finger and the second phalanx of the little finger. The radial nerve may supply the entire dorsum of the hand and the dorsal aspect of all the fingers, or it may be absent, the musculo-cutaneous going to the thumb and the ulnar to the remainder of the digits. The external division may send a branch to the palm. The posterior interosseous may pass over the surface of the supinator brevis and may furnish a branch to the anconeus muscle. Two instances are reported in which the posterior interosseous supplied the opposed surfaces of the middle and index fingers. Practical Considerations. The musculo-spiral is more frequently paralyzed than any of the other branches of the brachial plexus. Its axillary portion often suffers from crutch pressure ; and the nerve is also particularly exposed to com- pression where it passes between the triceps muscle and the humerus, as when the arm, during sleep, is used for a pillow. It has been injured by violent contraction of the triceps muscle, as in the act of throwing. It is frequently lacerated by the fragments in fractures of the middle of the shaft of the humerus When the lesion is in the axilla the triceps will be included in the paralysis. If the portion in the arm is affected the tri- ceps and anconeus will escape, but the following muscles will be paralyzed : the supina- tors, the extensors of the hand, the extensor communis digitorum, together with the extensor indicis, the extensor minimi digiti and the extensors of the thumb. The characteristic symptom is the inability to extend the hand at the wrist (wrist drop), and this is the most common form of musculo-spiral paralysis. THE THORACIC NERVES. The thoracic nerves (nn. thoracales) (Fig. 1105) consist of twelve pairs of sym- metrical nerve-cords, the upper eleven of which, because of their position in the intercostal spaces, are called intercostal nerves, and the twelfth, which lies below the twelfth rib and is an occupant of the abdominal wall, the subcostal. Since only seven ribs reach the sternum, the upper six thoracic nerves alone are continued throughout their entire course in intercostal spaces. The lower six, with the exception of the twelfth, after traversing their respective intercostal spaces proceed within the abdom- inal wall, through which they course to within a short distance of the median line. In accordance with the direction of the ribs, the upper nerves lie more horizontally than the lower, the latter becoming more and more oblique as the lower part of the abdominal wall is reached. As they advance from the spine, they distribute motor filaments to the external and internal intercostals, the subcostals, the levatores costarum, the serrati postici superior et inferior, the triangularis sterni, the external oblique, the internal oblique, the transversalis, the rectus, the pyramidalis and a por- tion of the diaphragm. Their cutaneous distribution comprises the integument of the chest and abdomen anterior to the area supplied by the posterior primary divisions of the thoracic nerves. On account of the presence of the shoulder girdle, the usual nerve distribution is modified in the upper thoracic region and the supra- clavicular branches of the cervical plexus assume a function belonging to the thoracic nerves. At the lower portion of the trunk the usual arrangement is likewise altered, THE THORACIC NERVES. 1315 the area immediately above Poupart's ligament and the pubes being innervated, not by the thoracic, but by the lumbar nerves (Fig. 1105). The supply of the cutane- ous area is provided by two rows of sensory twigs, which become superficial by piercing the musculature and deep fascia of the trunk. Each of the thoracic nerves, with the exception of the first, sends out a lateral cutaneous branch and, with no exceptions, an anterior cutaneous branch. The upper thoracic nerves deviate variously from this typical arrangement, the first having no lateral and sometimes no anterior cutaneous branch, and a portion of the lateral cutaneous branch of the second, called the intercosto-humeral nerve, leaving the thorax to be distributed in the upper extremity. The third nerve of the series is the first to present a typical arrangement, although it, indeed, sometimes forms a loop with the lesser internal cutaneous nerve of the arm. The anterior cutaneous branches are the terminal portions of the thoracic nerves and are constant in their arrangement and distribution, with the exception of the first, which is either very small or absent and a filament from the last, which passes over the crest of the ilium to the gluteal integument. After separating from the posterior primary divisions, the anterior primary divisions of the thoracic nerves, with the exception of the twelfth, enter the inter- costal spaces by passing between the anterior costo-transverse ligaments and the external intercostal muscles. From this situation to the angles of the ribs they lie between the posterior intercostal membrane and the external intercostal muscles. Anterior to this point, they are situated between the two sets of intercostal muscles, as far forward as the termination of the external set of muscles at the costo-chondral articulations, from which point forward their superficial covering is the anterior inter- costal membrane and the deep the internal intercostal muscles. At first they lie within the upper part of the intercostal space, but as they advance they show a tendency to occupy the middle of the space. While accompanying the intercostal vessels, they lie below the latter and at a greater distance from the rib next above. The upper two nerves extend for a portion of their course along the inner surface of the corre- sponding ribs; the twelfth passes in front of the quadratus lumborum. The upper thoracic nerves, as they approach the margin of the sternum, tra- verse the substance of the internal intercostal muscles and hold a position anterior to the internal mammary artery and the lateral portion of the triangularis sterni muscle. They terminate by piercing the anterior intercostal membrane and the pec- toralis major, and ramify in the pectoral integument as the anterior cutaneoiis nerves of the thorax (Fig. 1105). The lower thoracic nerves pass forward and at the anterior ends of the ribs take up a deeper position in the trunk wall by piercing the substance of the internal intercostal muscles. They then traverse the intervals between the digitations of the diaphragm and enter the abdominal wall, the seventh, eighth and ninth nerves lying behind the cartilages of the eighth, ninth and tenth ribs respectively. From this point their course is ventral, between the internal oblique and the transversalis, as far as the lateral edge of the rectus sheath, which they enter by piercing its pos- terior lamella. They ultimately turn forward and become superficial by traversing the rectus and its anterior aponeurotic covering, terminating as the anterior cutaneous nerves of the abdomen (Fig. 1105). Communications. Each thoracic nerve is connected with the sympathetic gangliated cord by one or two rami communicantes (Fig. 1130). Ordinarily there is no intercommunication between the upper intercostal nerves, but in rare instances a twig passes from one nerve over the inner surface of the rib .next below to the sub- jacent nerve. The lower three or four thoracic nerves, while lying between the broad abdominal muscles are occasionally united to one another, sometimes to the extent of forming a small plexus. Peculiar thoracic nerves. The first, second, twelfth, and sometimes the third, thoracic nerves present peculiarities which differentiate them from the others. The first thoracic nerve sends a large portion of its fibres to the brach- ial plexus, thus suffering great reduction in its size. Although occasionally a very small branch to the axilla is found, a lateral cutaneous branch is rare, it being generally held that the contribution of this nerve to the brachial plexus is the 1310 HUMAN ANATOMY. Supraacromial branches of cer- Pectoralis minor muscle vical plexus Pectoralis major muscle Lesser internal cutaneous nerve FIG. 1105. Descending branch of superficiahs colli Suprasternal and supra- clavicular branches of cervical plexus \ Lateral cutaneous branches of III., IV., V. and VI. thoracic nerves VII., VIII., IX. and X. thoracic nerves Lateral cutaneous branch of XI. thoracic nerve XI. thoracic nerve Lateral cutaneous branch of XII. thoracic nerve External oblique muscle, cut and everted Internal oblique muscle, cut Transversalis muscle Ilio-hypogastric nerve Ilio-hypo-j hyP h ^ stricnerve I iliac bran Internal oblique muscle /'.) I li' > in-uin.il nerve Poupart's ligament Anterior cutaneous brs. of II., III., IV., V. and VI. tho- racic nerve-. Anterior brs. of IX. thoracic nerve, the lowest one be- longing to the X. Umbilicus Rectusabdom- ^ inis, cut jfl Anterior V branch of X. thoracic nerve Anterior j^B branch of XI. thoracic Anterior # branch nfXTI thoracic nerve Hypogastric portion of ilio- nerve of external oblii|ue mus- cle, cut edge Ilio-inguinal nerve Dissection showing thoracic, ilio-hypogastric and ilio-inguinai nerves. equivalent of a lateral cutaneous branch. In addition to the lateral cutaneous, the anterior cutaneous branch may also be wanting, the- area typically supplied by the absent branch beiii^ served by the descending branches of the cervical plexus. THE THORACIC NERVES. 1317 The second thoracic nerve sometimes contributes fibres to the brachial plexus. The posterior ramus of its lateral cutaneous branch is called the inter costo- humeral nerve. The intercosto-humeral nerve (n. intercostobrachialis) (Fig. 1105) is quite large and pierces the inner axillary wall between the second and third ribs. Enter- ing the axilla, it crosses that space toward the arm and communicates with the lesser internal cutaneous nerve from the brachial plexus. After piercing the deep fascia, the intercosto-humeral nerve supplies the internal and posterior portion of the integ- ument of the upper half of the arm, a few of its fibres extending slightly beyond the margin of the scapula. The third thoracic nerve may form an inosculation with the lesser internal cutaneous nerve. The twelfth thoracic or the subcostal nerve lies below the last rib and therefore does not occupy an intercostal space, but passes outward below the external arcuate ligament and anterior to the quadratus lumborum muscle. It contributes a twig to the lumbar plexus which passes down to join the first lumbar nerve. Its lateral cutaneous branch is not confined in its distribution to the abdominal wall, since, after piercing the internal oblique and sending a filament to the lower digitation of the external oblique, it penetrates the substance of the latter muscle at a point from 2-10 cm. above the crest of the ilium and supplies the integument of the gluteal region as far down as the upper margin of the great trochanter (Fig. 1083). Branches of the thoracic nerves are : (i) the muscular and (2) the cutaneous. I. The muscular branches (rr. musculares) may be divided into two groups: (a) the thoracic and (b) the abdominal. a. The thoracic muscular branches arise from the first to the seventh inclusive and supply the external and internal intercostals, the subcostals, the levatores costarum, the serratus posticus superior, the triangularis sterni and the rectus abdominis. The branches to the intercostal and subcostal muscles are distributed throughout the course ~>f each nerve. The first to be given off is the largest and courses forward for some distance along the lower part of the intercostal space. The others vary greatly in number and size. The branches to the levatores costarum consist of fine threads, one arising from each nerve beyond the anterior costo-transverse ligament. They pierce the external intercostal muscles and enter the deep surface of the muscles which they supply. THe branches to the serratus posticus superior arise from the upper four nerves. After piercing the external intercostal muscles they pass along the outer margin of the ilio-costalis and supply the four digitations of their muscle. The branches to the triangularis sterni are terminal continuations of the third to the seventh intercostal nerves. After piercing the internal intercostal muscles they pass forward between the triangularis sterni and the internal intercostals or, in the case of the seventh, anterior to the transversalis muscle. In addition to supplying the triangularis sterni the seventh sends fibres to the first digitation of the transversalis. The branches to the rectus arise from the fifth, sixth and seventh and enter the deep surface of the muscle. b. The abdominal muscular branches arise from the eighth to the twelfth inclusive and are distributed to the intercostals, the subcostals, the levatores costarum, the serratus posticus inferior, the external obique, the internal oblique, the transversalis, the rectus, the pyramidalis and the diaphragm. The branches to the intercostal, subcostal and levatores costarum muscles, with the excep- tion of arising from the lower thoracic nerves, resemble in origin, course and distribution those arising from the upper nerves. The branches to the serratus posticus inferior are larger than those to the serratus posticus superior. They arise from the ninth, tenth and eleventh nerves and pass around the lateral margin of the ilio-costalis to reach their destination. The branches to the external oblique, the internal oblique and the transversalis comprise numerous fine twigs which supply those muscles and arise from the lower five thoracic nerves as they course forward between the transversalis and the internal oblique. The branches to the rectus arise from the eighth to the twelfth nerves inclusive after they have entered the sheath and as they pierce the rectus on their way to the surface. The branches to the pyramidalis are derived from the twelfth thoracic and first lumbar nerves. The branches to the diaphragm are supplied to its costal portion and consist of fine filaments which are given off by the lower six thoracic nerves (Luschka). I 3 i8 HUMAN ANATOMY. 2. The cutaneous branches are larger than the muscular and consist of two sets : (a) the lateral cutaneous and (6) the anterior cutaneous. a. The lateral cutaneous branches (rr. cutanei laterales) consist of two series, an upper and a lower, the former originating from the first to the sixth and the latter from the sixth to the twelfth thoracic nerves. Those of the upper series pierce the external intercostal muscles and those of the lower the external oblique in a line situated midway between the mammary and mid-axillary lines. The upper seven pass between the dictations of the serratus magnus and the lower between the digitations of the latissimus dorsi and the external oblique. The one arising from the twelfth pierces the musculature of the external oblique. Each lateral cutaneous nerve divides into (aa) an anterior and (bb} a posterior branch (Fig. 1083). aa. The posterior branches (rr. posteriores) are smaller than the anterior. They wind around the edge of the latissimus dorsi and supply the integument of the lateral area of the trunk as far back as the anterior margin of the region supplied by the posterior primary divi- sions of the thoracic nerves. The branches from the third to the sixth inclusive have fibres which are distributed over the lateral portion of the scapula. bb. The anterior branches ( rr. anteriores [pectorales et abdominales] ) are of considerably greater size than the posterior. Those from the second to the seventh pass toward the lateral margin of the pectoralis major and supply the integument of this region as far forward as the nipple. Branches (rr. mammarii laterales) from the fourth, fifth, and sixth send filaments to the skin and substance of the mammary gland. Those from the seventh to the eleventh supply the integument of the abdomen as far anterior as the lateral margin of the rectus. The anterior branch from the twelfth has a filament which passes over the iliac crest to the integument of the gluteal region, usually sending a branch as far as the great trochanter. It maintains a more or less even balance with the corresponding branch of the first lumbar nerve, each supplying any deficiency in the other. b. The anterior cutaneous branches (rr. cutanei anteriores) are the terminal fibres of the thoracic nerves. Those from the upper six (rr. cutanei pectorales anteriores) pierce the pectoralis major near the lateral margin of the sternum and supply the adjacent integument of the thorax. Filaments (rr. mammarii mediales) are distributed to the skin of the mesial portion of the mam- mary gland. The anterior cutaneous branches from the lower six (rr. cutanei al>dominales ante- riores) vary in position. They consist of the terminal filaments which perforate the anterior portion of the rectus sheath at a situation anywhere between the lineae alba and semilunaris. Those from the seventh become superficial near the ensiform cartilage, those from the tenth supply the region of the umbilicus and those from the twelfth are distributed to the area located midway between the umbilicus and the pubic crest (Fig. 1105). # Practical Considerations. Of the branches of the thoracic spinal nerves, the anterior or intercostals suffer most frequently from sensory disturbances, and the posterior from motor disturbances. Intercostal neuralgia may result from pressure, as from aneurism or spinal disease, or it may be due to injury. The lower intercostals enter into the supply of both the thoracic and the anterior abdominal walls, the pleura also being supplied by them. Pain referred to the abdominal wall and rigidity of the abdominal muscles may therefore be due to diseases within the chest, as pleurisy. Such diseases in the upper part of the chest may cause pain to extend down the arm along the intercosto-humeral nerve, which is the lateral cuta- neous branch of the second intercostal nerve, or sometimes of the second and third intercostals. The pain of intercostal neuralgias often becomes intense, especially after violent expiratory efforts, as in coughing and sneezing ; not infrequently after the pain ceases, herpes zoster appears in the line of the nerve affected. This may be a trophic disturbance or an extension of the inflammation along the nerve endings to the skin. Mastodynia, or the so-called "irritable breast of Cooper," is due to intercostal neuralgia, and occurs in the female during the child-bearing period. The lower intercostal nerves, with the ilio-hypogastric and ilio-inguinal, supply the muscles of the abdominal wall, and are frequently injured by the incisions mack' in abdominal operations, thus leading to more or less impairment of the muscles sup- plied and favoring the later development of hernia. The incision should therefore, so far as possible, be made in the line of the fibres of the muscles (page 535)- The intercostal nerves continue their oblique line through the abdominal mus- cles. The pain from Pott's disease' is often transferred along the nerves coining from the affected segment of the cord. In this way pain in the abdominal region may THE LUMBAR PLEXUS. 13*9 result from this disease, and an abdominal lesion may be suspected ; this has occurred more particularly in children. A feeling of tightness is sometimes observed about the abdomen, corresponding to the course of one or more pairs of these nerves, and may be due to impaired sensation in them. Since the abdominal muscles are supplied chiefly by the seven lower intercostal nerves, they are concerned in respiration. When they are contracted as in general peritonitis, the lower ribs become immobile, and breathing takes place chiefly in the upper portion of the chest. FIG. 1106. THE LUMBAR PLEXUS. The lumbar plexus (plexus lumbalis) lies in the substance of the psoas magnus muscle, anterior to the transverse processes of the lumbar vertebrae, and consists of a series of loops formed by the anterior primary divisions of the first, second and third lumbar nerves, the smaller subdivision of the fourth lumbar and sometimes a branch from the twelfth thoracic nerve. The remainder and major portion of the fourth lumbar nerve unites with the entire anterior primary division of the fifth to form a conjoint trunk, the lumbo-sacral cord (truncus lumbosacralis), which passes into the pelvis to become a constituent of the sacral plexus (Fig. 1106). The lumbar nerves increase in thickness from above downward, the first being only 2.5 mm., while the fifth attains a diameter of 7 mm. The length of the nerves from their exit at the intervertebral foramina to their point of division varies considerably, in the case of the first being i mm. or less, of the second 10 mm. 'and of the third from 20-25 mm - Constitution and Plan. In forming the plexus (Fig. 1106), the first lumbar nerve divides almost immediately after its exit from the vertebral column into an upper and a lower branch. The upper, which may receive a contribution from the twelfth thoracic nerve, becomes the ilio-hypogastrica.nd ilio-inguinal nerves. The lower branch, near the body of the second lumbar vertebra joins the upper part of the second lumbar nerve, which, like the first, divides into an upper and a lower branch. The union of the lower branch of the first and the upper branch of the second results in the formation of the genito-crural nerve. Sometimes fibres from the first aid in the formation of the anterior crural and obturator nerves. The lower branch of the second, all of the third and that part of the fourth which enters the lumbar plexus divide into smaller anterior and larger posterior trunks. From the union of the anterior branches of these three the .obturator nerve is formed, and from the union of the posterior results the an- terior crural nerve. The posterior por- tions of the second and third nerves give off from their dorsal aspect small branches which unite into the external cutaneous nerve. The accessory obturator nerve, when it exists, arises from the third and fourth lumbar between the roots of the anterior crural and obturator nerves. Communications. All of the lumbar nerves receive gray rami communicantes from the gangliated cord of the sympathetic ; and from the first and second, and possibly the third and fourth, white rami communicantes pass to the lumbar portion of the gangliated cord. Diagram illustrating plan of lumbar plexus. 1320 HUMAN ANATOMY. Variations. That portion of the fourth lumbar nerve, or n. f urea/is, which joins the lumbo- sacral cord, is usually less than half of the parent trunk, but varies from one-twentieth to nine-tenths. When large, it may be joined by a branch from the third lumbar, and when small the fifth lumbar may contribute to the lumbar plexus, the fibres going to the ante- rior crural alone or to the anterior crural and obturator nerves. The branch to the lumbo- sacral cord from the fourth lumbar may be absent and in such an event the fifth is the only furcal nerve sending fibres to both the lumbar and the sacral plexus. It is thus possible to have as furcal nerves the third and fourth, the fourth alone, the fourth and fifth or the fifth alone, and according to the high or low position of these there is found a corresponding origin of the branches of the lumbar plexus. In this manner are accounted for the high and low, or prefixed and postfixed types of plexus. Branches of the lumbar plexus are : 1. The Muscular 5. The External Cutaneous 2. The Ilio-Hypogastric 6. The Obturator 3. The Ilio-Inguinal 7. The Accessory Obturator 4. The Genito-Crural 8. The Anterior Crural i. THE MUSCULAR BRANCHES. The muscular branches (rr. musculares) supply the quadratus lumborum, the psoas magnus and the psoas parvus. The branches to the quadratus lumborum arise from the upper three or four lumbar nerves, and sometimes from the last thoracic, and pass directly into the quadratus. The branches to thefisoas mag-mts arise mainly from the second and third lumbar nerves, there sometimes being additional ones from the first and fourth. They pass directly into the muscle. The branches to the psoas parvus consist of filaments from the first or second lumbar nerve which reach the muscle by piercing the underlying psoas magnus. 2. THE ILIO-HYPOGASTRIC NERVE. The ilio-hypogastric nerve (n. iliohypogastricus) (Fig. 1107) is the uppermost branch of the plexus and is somewhat larger than its associate, the ilio-inguinal. Whilst it derives the major portion and sometimes all of its fibres from the first lumbar nerve, it usually receives others from the twelfth and occasionally the eleventh thoracic. It emerges from the lateral margin of the upper portion of the psoas magnus and runs, below and parallel with the twelfth thoracic nerve, outward and downward, posterior to the kidney and anterior to the quadratus lumborum. Reaching the crest of the ilium, it pierces the transversalis muscle and occupies the intermuscular space between the internal oblique and the transversalis. After coursing along this interval as far as the middle of the iliac crest, it divides into its terminal branches, (a} the iliac and () the hypogastric, which correspond morphologically with the lateral and anterior cutaneous branches of the thoracic nerves. There are also some (c~) muscular branches. a. The iliac branch (r. cutaneus lateralis) pierces the internal and external obliques about the middle of the iliac crest and is distributed to the integument of the anterior gluteal region which covers the gluteus medius and the tensor fasciae femoris (Fig. 1083). It forms an inosculation with the lateral cutaneous branch of the twelfth thoracic nerve and maintains an even balance 1 with it, deficiency in the development of either being recompensed for by a com- pensating increase in size of the other. b. The hypogastric branch (r. cutaneus anterior) continues the direction and course of the main trunk between the transversalis and the internal oblique almost to the linea alba. Near the anterior superior spine of the ilium it forms an inosculation with the ilio-inguinal nerve. As it approaches the region of the internal abdominal ring it begins to push its way gradually through the internal oblique and gain the interval between the internal and the exter- nal oblique (Fig. 1105). A short distance superior and internal to the external abdominal ring it traverses a tiny foramen in the aponeurosis of the external oblique and breaks up into fibres of termination which supply the integument of the suprapubic region. c. Muscular branches (rr. musculares) arise from the hypogastric branch in its course through the abdominal wall and supply the transversalis, the internal oblique and the external oblique. THE LUMBAR PLEXUS. 1321 Variations. The iliac branch may be absent, its place being taken by the lateral cutaneous branch of the twelfth thoracic nerve. The hypogastric branch may inosculate with the twelfth thoracic and may supply the pyramidalis muscle. 3. THE ILIO-INGUINAL NERVE. The ilio-inguinal nerve (n. ilioinguinalis) (Fig. 1107) is the second branch of the lumbar plexus and is somewhat smaller than the ilio-hypogastric. Its fibres usually arise from the first lumbar nerve, with accessions from the twelfth thoracic. FIG. 1107. XII. rib XII. thoracic nerve Quadratus lumborum Psoas magnus External oblique Lateral cutaneous branch of XII. dorsal nerve Internal oblique Transversalis Ilio-hypogastric nerve Ilio-inguinal nerve Iliac branch of ilio-hypogastric Lateral cutaneous branch of XII. dorsal nerve External cutaneous nerve Anterior crural nerve Genital branch of genito-crural nerve Crural branch of genito-crural nerve Branches of middle cutaneous nerve I. lumbar ganglion Rami communicantes Aorta IV. lumbar nerve lumbar ganglion lumbar nerve rt of V. lumbar ganglion nito-crural nerve sacral ganglion sacral nerve II. sacral nerve sacral ganglion urator nerve :essory obturator nerve ) Hypogastric branches j of ilio-hypogastric nerve Ilio-inguinal nerve Branch of internal cutaneous nerve Deep dissection, showing nerves arising from lumbar plexus and lower part of sympathetic gangliated cord. Sometimes it arises entirely from the twelfth thoracic or from the second lumbar or from the loop between the first and second lumbar nerves. It occasionally forms a common trunk of considerable length with the ilio-hypogastric. In the early part 1322 HUMAN ANATOMY. of its course it parallels the ilio-hypogastric, appearing at the edge of the psoas magnus, crossing the quadratus lumborum behind the kidney and piercing the trans- versalis to reach the intermuscular cleft between the transversalis and the internal oblique (Fig. 1105). While in the last situation it inosculates with the ilio-hypo- gastric and continues forward to enter the inguinal canal, from which it emerges either through the external abdominal ring or through the external pillar of the ring, infero-lateral to the spermatic cord. Some of the branches of the ilio-inguinal supply the integument of the upper inner portion of the thigh. Others (nn. scrotales anteriores) are distributed to the pubic region and the base of the penis and scrotum or, in the female ( nn. labiates anteriores ), the mons Veneris and labia majora. Tiny motor filaments (rr. musculares) are given off in the course of the nerve to the transversalis, the internal oblique and the external oblique. Variations. The ilio-inguinal may be small and terminate near the iliac crest by joining the ilio-hypogastric, which then sends off an inguinal branch with the course and distribution of the absent portion of the ilio-inguinal. The nerve may be absent entirely and replaced by either branch, usually the genital, of the genito-crural. It may give off a lateral cutaneous or iliac branch for the supply of the integument in the region of the anterior superior spine of the ilium. The ilio-inguinal may partially replace the genital branch of the genito-crural or, in rare in- stances, the external cutaneous. 4. THE GENITO-CRURAL NERVE. The genito-crural nerve (n. genitofemoralis) is formed by two roots, one of which arises from the loop between the first and second lumbar nerves and the other directly from the second lumbar nerve, its fibres being derivatives of the first and second lumbar. The nerve passes obliquely forward through the musculature of the psoas magnus, near the inner border of whose anterior surface it emerges opposite the body of the third lumbar vertebra, where division into the two terminal branches, (a) the genital and (t>~) the crural, takes place (Fig. 1107). Occa- sionally division occurs earlier in the course of the nerve, in the substance of the psoas, and under these circumstances the two branches emerge separately from the muscle. In addition to the terminal branches there are some (r) muscular twigs. a. The genital branch (n. spermaticus externus) obtains its fibres from the first lumbar nerve. Passing downward on the inner margin of the psoas magnus, it crosses the external iliac artery and bends forward toward the posterior wall of the inguinal canal. It then enters the canal either by piercing the infundibuliform or the transversalis fascia and, lying internal to and below the spermatic cord, traverses the canal and enters the scrotum (Fig. 1108). It sends a filament to the external iliac artery and supplies the cremaster muscle, the skin of the scrotum and the integument of the thigh immediately adjacent to the scrotum. In the female it is smaller and accompanies the round ligament of the uterus to the labium majus, to whose in- tegument it is distributed. It communicates with the ilio-inguinal nerve and with the spermatic plexus of the sympathetic. b. The crural branch (n. lumboinguinalis) consists of fibres from the second lumbar nerve. It courses down on the anterior surface of the psoas magnus, lateral to the genital branch and to the external iliac vessels, and enters the thigh by passing beneath Poupart's ligament. One of its filaments traverses the saphenous opening, while the remainder of the nerve pierces the fascia lata to the outer side of the opening (Fig. 1107). Its branches vary considerably in size and length and are distributed to the cutaneous area of the upper anterior part of the thigh between the regions supplied by the external cutaneous and ilio-inguinal nerves, sometimes extending downward as far as the middle of the thigh. It furnishes a minute branch to the femoral artery and inosculates with the middle cutaneous nerve. c. Muscular branches to the internal oblique and transversalis are frequently given off by the genital branch. Variations. The genital and crural branches may arise as separate offshoots of the lumbar plexus and either of them may be derived entirely from the- first or the second lumbar nerve. The genital branch sometimes contains fibres from the twelfth thoracic. Absence of the genito- crural or of either branch may occur, the fibres of the genital branch being contained in the ilio- inguinal and those of the crural in the external cutaneous or the anterior crural. The genital branch may replace or reinforce the ilio-inguinal nerve; the crural branch may act similarly toward the 'external or the middle cutaneous nerve. A specimen found in the anatomical labo- ratory of the I niv. rsity of Pennsylvania showed unusually extensive distribution of the crural THE LUMBAR PLEXUS. 1323 branch. It was larger than normal, its size being that of the normal external cutaneous, and it emerged from the deep fascia below Poupart's ligament directly anterior to the femoral vein. It FIG. 1108. Psoas parvus Genito-crural nerv.e Psoas magnus Anterior crural nerve External cutaneous nerve Genital branch of genito-crural Sartorius, stump Branch to pectineus Branch to rectus femoris Branch to vastus externus Rectus femoris Middle cutaneous nerve Rectus femoris -Accessory obturator Crural branch of genito-crural Ilio-inguinal nerve Pectineus Adductor longus Internal saphenous nerve Internal cutaneous nerve Muscular branch of superficial division of obturator nerve Branch from internal saptienous to subsartorial plexus Branch to vastus interims Anterior branch of internal cutaneous Cutaneous branch of superficial division of obturator nerve Posterior branch of internal cutaneous From posterior branch of internal cutaneous- Articular branch from nerve to vastus internus Cutaneous patellar branch of internal saphenous nerve -Internal saphenous nerve Dissection of right thigh, showing branches of anterior crural nerve. divided into a smaller mesial and larger lateral branch and was distributed to the integument of the thigh as far down as the junction of the middle and lower thirds. i 3 2 4 HUMAN ANATOMY. 5. THE EXTERNAL CUTANEOUS NERVE. The external cutaneous nerve (n. cutaneus femoris lateralis) (Fig. 1109) arises at the posterior aspect of the lumbar plexus from the second and, to a less extent, the third lumbar nerve. It may arise from the first and second, from the second alone or may derive a majority of its constituent fibres from the third. It passes obliquely downward and outward beneath the lateral margin of the psoas magnus and over the iliacus muscle, through the iliac fossa, covered by the iliac fascia. After crossing the deep circumflex iliac artery it enters the thigh beneath Poupart's ligament, mesial to the anterior superior spine of the ilium, and passes over, sometimes through or under, the pointed tendinous origin of the sartorius. The nerve then descends in the thigh beneath the fascia lata and soon divides into (a) an anterior and () a posterior terminal branch (Fig. moj. a. The anterior branch (r. anterior) follows a downward course in the thigh in a tubular canal in the fascia lata, from which it emerges at a point 10-15 cm. below the anterior superior iliac spine. It continues downward anterior to the vastus externus muscle and is distributed to the integument of the antero-lateral aspect of the thigh as far as the knee. Numerous collateral branches are given off, the majority of which arise from its lateral edge and supply the skin over the ilio-tibial band. The main trunk may extend quite to the knee and become a participant in the formation of the patellar plexus. b. The posterior branch (r. posterior) passes obliquely backward through the fascia lata and breaks up into several branches which are distributed to the integument over the tensor fasciae femoris and the lower portion of the gluteal region. The uppermost filaments are crossed by twigs from the lateral cutaneous branch of the twelfth thoracic nerve. Variations. The external cutaneous may be associated with the anterior crural until after Poupart's ligament has been passed. A branch of the genito-crural may replace the posterior branch. In one case a branch of the ilio-inguinal took the place of the external cutaneous. Three specimens found in the anatomical rooms of the University of Pennsylvania showed decided anomalies. In one the nerve passed beneath Poupart's ligament at a point midway between the anterior superior spine of the ilium and the femoral artery. In another the nerve of the right side resembled in position the one just mentioned, while the left was apparently absent, its place being taken by a branch of the anterior crural. In the third the posterior branch emerged from beneath Poupart's ligament 5 cm. to the inner side of the anterior superior iliac spine. The anterior branch formed a common trunk with the external branch of the mid- dle cutaneous nerve. From the joint trunk a small branch passed to join the internal branch of the middle cutaneous after the latter had pierced the sartorius muscle. 6. THE OBTURATOR NERVE. The obturator nerve (n. obturatorius) (Fig. 1109) is composed of fibres which arise from the second, third and fourth lumbar nerves, the fourth supplying the largest and the second the smallest contribution, the latter sometimes being absent entirely. Occasionally additional roots are derived from the first and fifth lumbar nerves, and sometimes the nerve arises, in the high form of plexus, from the first, second and third lumbar nerves. The three roots having united in the substance of the psoas magnus, the nerve passes vertically downward and emerges, the only constant branch of the plexus to do so, from the mesial margin of the psoas muscle opposite the brim of the true pelvis. Lying posterior to. the common and lateral to the internal iliac vessels, the obturator nerve courses along the antero-lateral wall of the pelvis below the ilio- pectineal line, above the obturator vessels and upon the inner surface of the pelvic fascia. It escapes from the pelvis through the obturator canal in the obturator mem- brane and divides into its terminal branches, either while still within the foramen or shortly after emerging from it. These branches are separated from each other first by the anterior fibres of the obturator externus muscle and later by the adductor brevis muscle. They supply the adductor muscles, the hip and knee joints and the integument of the mesial aspect of the thigh. Branches. The obturator gives off: (a) a branch to the obturator c.\-fcnms muscle and then divides into its terminal branches, (b) the anterior and (c) the posterior. THE LUMBAR PLEXUS. 1325 a. The branch to the obturator externus arises within the pelvis from the inner surface of the obturator nerve. It accompanies the parent trunk through the foramen, immediately after FIG. i 109. Ext. cutaneous nerve Ant. sup. spine of ilium Ant. crural nerve Br. to rectus Sartorius Artie, br. of accessory obturator Iliacus Br. to vastus ext. and crureus Rectus Middle cutaneous nerve Int. cutaneous, ant. branch Femoral artery Int. cutaneous, post, branch Int. saphenous nerve Nerve to vastus interims Rectus Artie, br. from nerve . to vastus int. Ext. iliac artery Int. iliac artery Accessory obturator nerve Obturator nerve Pectineus Obturator nerve, ant. division Adductor longus, cut Obturator nerve, post division Articular br. to hip-joint Adductor brevis Pectineus Adductor magnus ictor brevis ilis ictor longus nal br. ant. division obturator nerve neous branch an int. cutaneous to subsartorial plexus :. br. to knee-joint from obturator o subsartorial plexus and femoral Cutaneous br. to inner surface of thigh and knee Internal saphenous nerve Cutaneous patellar br. int. saphenous Sartorius, insertion Post. br. int. cutaneous Internal saphenous Dissection of right thigh, showing branches of anterior crural and obturator nerves. escaping from which it dips down in the interval between the obturator membrane and the obtur- ator externus muscle. From this situation its fibres pass through the deep surface into the substance of the muscle. 1326 HUMAN ANATOMY. b. The anterior branch (r. anterior), the more superficial, descends in front of the obturator externus and adductor brevis muscles and between the pectineus and the adductor longus. Having reached the interval between the adductores brevis and longus it separates into its terminal branches. Branches of the anterior division are : (aa) the articular, (bb) the muscular, (cc) the cutaneous, (dd) the communicating and (ee) the vascular. aa. The articular branch leaves the obturator at the inferior margin of the obturator foramen and passes through the cotyloid notch to supply the hip joint. bb. TJie muscular branches supply the adductores brevis and longus and the gracilis. The branch to the adductor brevis enters the muscle near the upper margin of the anterior surface. The branch to the adductor longus enters the posterior surface of the muscle and some- times gives off the cutaneous branch of the obturator (see below). The branch to the gracilis passes inward behind the adductor longus and enters the deep surface of its muscle. cc. The cutaneous branch (r. cutaneus) (Fig. mo) is variable in size and maintains an approximately even balance with the internal cutaneous branch of the anterior crural. Some- times arising from the nerve to the adductor longus, it becomes superficial in the middle of the thigh by passing between the adductor longus and the gracilis. It supplies the integument of the lower inner portion of the thigh and beneath the sartorius forms an inosculation with branches of the internal cutaneous and internal saphenous nerves, called the subsartorial or obturator plexus. dd. The communicating branches consist of twigs which unite in the pelvis with the accessory obturator nerve and in the thigh anterior to the capsular ligament of the hip joint with the anterior crural. ee. The vascular branch enters Hunter's canal along the mesial edge of the adductor longus and spreads out over the lower portion of the superficial femoral artery. c. The posterior branch (r. posterior), the deeper, pierces the anterior fibres of the obturator externus muscle and descends in the cleft between the adductores brevis and magnus, and in the latter situation splits into its terminal twigs. Branches of the posterior division are : (aa) the muscular and (bb) the articular. aa. The muscular branches supply the obturator externus, the adductor magnus and the adductor brevis. The branch to the obturator externus is additional to the twig from the main trunk of the obturator which supplies that muscle. It arises from the posterior surface of the posterior division and enters the superficial surface of the muscle. The branch to the adductor magnus is associated with the branch to the knee and leaves the latter as the conjoint nerve passes through the substance of the adductor magnus. The branch to the adductor brevis enters the posterior surface of the muscle and is present only when the usual branch from the anterior division is absent. bb. The articular branches are destined for the supply of the hip and knee joints. The branch to the hip joint consists of one or two fine twigs which pass beneath the pectineus to be distributed to the antero-median portion of the capsular ligament. The branch to the knee joint or the geniculate branch continues the course of the posterior division. Associated with the nerve to the adductor magnus, it courses down the anterior sur- face to the adductor magnus, which it pierces at the lower portion of the thigh. Here its muscu- lar fibres terminate in the adductor magnus while the articular portion enters the popliteal space. The nerve continues downward on the popliteal artery, to which it distributes filaments, and finally terminates by entering the knee joint through the posterior ligament. Variations. In rare instances the root from the second lumbar nerve is absent. Branches are sometimes given off to the obturator internus and to the pectineus. Tiny branches have been found going to the obturator artery and to the periosteum of the pelvic surface of the os pubis. In a cadaver dissected in the anatomical laboratory of the University of Pennsyl- vania the obturator of the right side divided into the usual anterior and posterior branches, but both of them passed posterior to the adductor brevis. On the left side the normal arrangement was present. In another specimen in the same laboratory the branch from the- main trunk to the obturator externus muscle lay to the outer instead of the inner side of the obturator nerve. 7. THE ACCESSORY OBTURATOR NERVK. The accessory obturator nerve is an inconstant branch of the lumbar plexus, being found in 29 per cent, of the cadavers examined (Eisler). Its fibres arise from the third and fourth lumbar nerves, with an occasional root from the fifth ; it may be derived from the third alone. The roots of origin are sittiated between those of the anterior crural and the obturator, and the nerve may be intimately associated with either of these two, usually the former. THE LUMBAR PLEXUS. 1327 The accessory obturator courses downward mesial to the psoas magnus and beneath the iliac fascia, and leaves the pelvis by passing over the horizontal ramus of the pubes and under the pectineus. In the latter situation it breaks up into its branches, one of which () supplies the pectineus, another (<5) the hip joint, while the third (V) inosculates with the anterior division of the obturator nerve. Some- times it is very small and its fibres pass only to the hip joint. By means of its in- osculation with the obturator some of its fibres may reach the adductores longus and brevis and gracilis muscles, as well as the integument of the inner region of the thigh. 8. THE ANTERIOR CRURAL NERVE. The anterior crural or femoral nerve (n. femoralis) (Fig. noS), the largest branch of the lumbar plexus, arises from the first, second, third and fourth lumbar nerves. It passes obliquely downward and outward, posterior to the psoas magnus, and emerges from beneath the middle of the lateral margin of that muscle. Thence it continues its course between the outer edge of the psoas and the mesial edge of the iliacus, covered by the iliac fascia, as far as Poupart's ligament, under which it passes to become an occupant of the anterior portion of the thigh. The nerve lies to the outer side of the external iliac and femoral vessels, in the abdomen being separated from them by the psoas magnus, but, as the thigh is reached, gradually nearing them until in Scarpa's triangle the nerve lies in apposition to the femoral sheath. ' In the immediate neighborhood of Poupart's ligament, the anterior crural nerve rapidly splits up into a number of Branches, which may be grouped into (/>) a superficial division, principally sensory, and (c) a deep division, mainly motor. In addition there are (a) branches arising from the main trunk. a. The branches from the main trunk consist of (aa) the muscular branches and (bb) the nerve to the femoral artery. aa. The muscular branches supply the iliacus, the psoas magnus and the pectineus. The branches to the iliacus consist of two to four filaments which arise in the abdomen, pass outward and enter the inner margin of the iliacus muscle. The branch to the fisoas magmis arises in the lower part of the iliac fossa and supplies the inferior portion of that muscle. It may originate in common with the nerve to the femoral artery. The branch to the pectineus leaves the anterior crural beneath Poupart's ligament, passes inward posterior to the femoral vessels and enters the anterior surface of its muscle. bb. The nerve to the femoral artery usually takes origin in the iliac fossa, but frequently arises higher, sometimes as a distinct branch from the third lumbar nerve. It accompanies the anterior crural as far as Poupart's ligament, leaving the parent trunk at the lateral margin of the femoral sheath. At the ligament it gives off fine twigs which ramify over the posterior part of the femoral vessels, and from them tiny filaments pass to the middle of the thigh. Other twigs are distributed to the deep femoral artery and from this group a fine terminal thread traverses the nutrient foramen of the femur, after supplying branches to the periosteum. b. The anterior or superficial division is mainly cutaneous in distribution. It supplies sensory twigs to the anterior and mesial surfaces of the thigh and motor twigs to the sartorius. Branches of this division are : (aa} the middle cutaneous and (bb) the internal cutaneous. aa. The middle cutaneous nerve (rr. cutaneianteriores) (Fig. mo) consists of two branches, an external and an internal, both of which contain motor as well as sensory fibres. The external branch passes downward under the sartorius, to whose posterior surface are given off a row of fine twigs which enter the upper portion of the muscle. The continuation of the nerve pierces the sartorius at the junction of the upper and middle thirds, then pushes its way through the fascia lata and splits into fine filaments which supply the integument over the rectus femoris as far as the knee. The internal branch is sometimes united in the upper part of its course with the external. It supplies twigs to the sartorius but seldom pierces that muscle, usually passing internal and anterior. This branch, like the external, is distributed to the anterior integument of the thigh as far down as the knee and frequently inosculates with the crural branch of the genito-crural. Variations. Sometimes the middle cutaneous arises from the beginning of the anterior crural or from the lumbar plexus and replaces in toto or in part the crural branch of the genito-crural. 1328 HUMAN ANATOMY. FIG. 1 1 10. From ext. cutaneous nerve Communication be- tween ext. cutaneous and middle cutaneous Crural br. of genito-c rural From ext neous Middle cuta- neous nerve Ilio-inguinal nerve (emerging through ext. abd. ring). bb. The internal cutaneous nerve (rr. cutanei mediates) leaves the anterior crural in the neighborhood of Poupart's ligament and descends in Scarpa's triangle, at the apex of which it crosses obliquely the femoral vessels to attain their mesial side. It passes superficial to or through the sartorius muscle and divides, either anterior or internal to the superficial femoral artery, into its terminal branches, the anterior and the posterior ( Fig. mo). Two or three branches are given off by the main trunk. One of these pierces the fascia lata immediately below the saphenous opening and accompanies the internal saphenous vein down to the middle of the thigh, supplying the integument in its immediate vicinity. Another branch pierces the fascia lata at about the middle of the thigh and supplies the skin of the antero-median aspect as far down as the knee. These branches sometimes arise di- rectly from the anterior crural, and not infrequently the nerve to the pectineus gives off a branch which forms a loop at the linner side of the femoral artery with a nerve which passes anterior to that vessel. The anterior branch pierces the fascia lata in the lower third of the thigh, de- scends in the neighborhood of the tendon of the adductor magnus and eventually passes across the patella to reach the lateral region of the knee. It supplies the skin in the vicinity of the adductor magnus tendon and inosculates at the knee with a branch of the internal saphenous nerve. "The posterior branch con- tinues down beneath the pos- terior edge of the sartorius and becomes superficial by perforating the fascia lata at the mesial aspect of the knee. Its ultimate filaments supply the integument of the lower part of the inner side of the thigh and the upper portion of the leg. Before becoming su- perficial it inosculates below the middle of the thigh with the obturator and internal saphenous nerves to form the subsartorial or obturator plexus (Fig. 1109). At the knee anil in the upper part of the leg it again forms connections with the internal saphenous nerve. c. The posterior or deep division of the anterior crural nerve consists of a fasces of nerve-bundles which furnishes br. of int. cutaneous (or twigs from ior branch) Cutaneous br. of obturator nerve Internal saphenous vein Anterior br. of int. cutaneous nerve | From lower (posterior) j br. int. cutaneous nerve Lower (posterior) br. int. cutaneous nerve Cutaneous patellar br. int. saphenous nerve nt. saphenous nerve Int. saphenous vein Superficial dissection of right thigh, showing ciit:itii-ous IUTVCS of inner anterior aspect ; long saphenous vein is seen disappearing through saphe- nous opening. innervation to those muscles which comprise the quadriceps extensor femoris and terminates as the internal saphenous nerve. Branches of this division are: (aa) the niuscu/ar, (bb} the articular and (cc} the internal saphenous. aa. The muscular branches ( rr. iniiscularcs ) supply the rectus femoris, the vastus externus, the crureus, the subcrureus and the vastus interims. THE LUMBAR PLEXUS. 1329 The branch to the rectus femoris usually splits into three twigs, which separately enter the posterior surface of their muscle. It furnishes fine twigs to the antero-lateral portion of the capsule of the hip joint. The branch to the vastus externus passes over the rectus and, in company with the descending branch of the external circumflex artery, reaches the vastus externus, whose anterior margin it enters in a series of twigs. It sends a branch down to the knee joint. The nerves to the crureus number usually either two or three. The upper branch is usually the shortest and passes directly to the anterior surface of the crureus, where it penetrates the sub- stance and supplies the upper portion of the muscle. A sec- p IG ^ lll and branch pierces the vastus internus and passes down- ward under the anterior bor- der of that muscle. It sup- plies the lower portion of the crureus, the subcrureus, the periosteum of the lower an- terior part of the femur and the capsular ligament of the knee joint. A third branch is distributed to the lateral por- tion of the crureus and by means of its terminal filaments aids in the innervation of the knee joint. The branch to the vastus internus accompanies the in- ternal saphenous nerve along the inner side of the vastus internus, under cover of the strong aponeurosis which forms the roof of Hunter's canal. It sends filaments to the upper part of the vastus internus and then enters that muscle about the middle of the thigh. Its continuation accompanies the deep branch of the anastomotica magna artery and supplies the cap- sule of the knee joint. b b . The articular branches (rr. articulares) supply the hip and knee joints. Those filaments which are destined for the hip are derivatives of the branch to the rectus femoris. Those which aid in the innervation of the knee arise from the in- ternal saphenous and from the nerves to the vasti exter- nus and internus and the crureus. cc. The internal or long saphenous nerve ( n. saphenus ) (Fig. 1109) is the continuation of the posterior division of the anterior crural nerve. It courses down the thigh first lateral to and then an- terior to the superficial femoral artery under cover of the sartorius muscle. At the apex of Scarpa's triangle it enters Hunter's canal and accompanies the vessels therein contained as far as the opening in the adductor magnus. Departing from the vessels at this point, the nerve piercing the anterior wall of Hunter's canal, continues a downward course between the vastus iliactti Anterior crural nerve, Rectus femoris. Femoral \ Nerve to pectineus' Femoral artery Articular branch Nerve to rectu Ext. circumflex artery. Middle cutaneous, nerve Rectus femoris, cut A descending branch of ext. circumflex art. Nerve to vastus interim: Nerve to crureus Crureu Pubic bone Pectineus Adductor longus Adductor magnus Int. saphenous nerve Tost. div. int. cutaneous nerve Aponeurotic roof of Hunt- er's canal A br. of int. sa- phenous nerve A muscular hr. of femoral artery Vastus internus Internal saphenous nerve Superficial br. anasto- motica magna art. Tendon of adductor magnus Dissection of right thigh, showinj to blood-vessels an< ; relation of anterior crural nerve to Hunter's canal. 8 4 1330 HUMAN ANATOMY. interims and the adductor magnus. At the inner side of the knee it becomes superficial by passing between the tendons of the sartorius and gracilis and by piercing the deep fascia in this situation. Thence it descends in the leg in association with the internal saphenous vein, at the ankle passing anterior to the internal malleolus and reaching the inner aspect of the foot, on which it extends only as far as the metacarpo-phalangeal articulation of the great toe (Fig. 1118). Branches of the internal saphenous are : the communicating, the infrapatcllar, the articu- lar and the terminal. The communicating branch arises beneath the sartorius at about the middle of the thigh and inosculates with filaments from the obturator and internal cutaneous nerves to form the subsartorial or obturator plexus. The infrapatellar branch (r. infrapatellaris) (Fig. 1117) arises at the lower part of the thigh. It perforates the sartorius and the fascia lata and spreads out beneath the integument of the knee, where it inosculates with terminal filaments of the internal, the middle and some- times the external cutaneous nerve to form \\\o. patellar plexus (Fig. m?). The articular branch (r. articularis) is an inconstant twig which supplies the inner portion of the capsule of the knee joint. The terminal branches are distributed to the integument of the anterior internal portion of the leg and the posterior half of the dorsum and mesial side of the foot. Practical Considerations. All the branches of the lumbar plexus have motor and sensory fibres, both of which are affected in paralysis. The lesion is usually central, involving the spinal cord, as in tabes dorsalis, fracture of the spine or Pott's disease, and involves several nerves, or all of them below the seat of the lesion ; the individual branches are not often affected. The ilio-hypogastric may be divided by the incision in kidney operations or may be included in the sutures. This nerve and the ilio-inguinal are sometimes involved in operations in the inguinal region. The genito-crural sends one branch through the inguinal canal to the cremaster muscle, and another under Poupart's ligament to the skin of the inner side of the thigh, just below the ligament. Gentle irritation of the skin here will cause retraction of the testicle (cremaster reflex), especially in children. The anterior crural has been paralyzed by the pressure of tumors in the pelvis, has been involved in a psoas abscess, and has been injured in fracture of the pubic ramus and rarely in fractures of the femur. If the lesion involving the nerve is within the pelvis the paralysis would affect the ilio-psoas, quadriceps extensor femoris, sartorius and pectineus. If the lesion is outside the abdomen the ilio-psoas will escape. A complete paralysis would prevent flexion of the hip, or extension of the knee. The patient is then compelled to avoid flexion of the knee in walking. There will be anesthesia in the parts supplied by the middle and internal cutaneous, and long saphenous nerves, that is, in the thigh along the anterior and inner surface (middle and internal cutaneous), except in the upper third (crural branch of the genito-crural), and along the inner surface of the leg and inner border of the foot to the ball of the big toe (long saphenous). The long saphenous vein and nerve lie close together, about a finger's breadth behind the inner border of the tibia. In the thigh, while they have the same general direction, the vein lies in the superficial fascia, the nerve under the deep fascia. The nerve in the thigh is, therefore, not so liable to injury as is the vein. Since the anterior crural breaks up into numerous branches just below Poupart's ligament, its trunk in the thigh is very short. It lies slightly external to the femoral artery and can be exposed by an incision extending downward from the middle of Poupart's ligament. Paralysis of the obturator nerve would interfere with adduction of the thigh as well as with internal and external rotation. It may be caused by pressure within the pelvis, as by the child's head in difficult labor, by a tumor or by an obturator hernia. Paralysis of the obturator is usually found in conjunction with paralysis of the anterior crural. The nerve may be irritated in coxalgia. in sacro-iliac disease, and on the left side in carcinoma or fa cal impaction in tin- sigmoid flexure. On account of its ter- minal distribution pain in the knee is usually complained of whenever this nerve or one of its brandies is involved. THE SACRAL PLEXUS. FIG. ii 12. THE SACRAL PLEXUS. The sacral or sciatic plexus (plexus sacralis) (Fig. 1112) is formed by a portion of the fourth lumbar nerve, all of the fifth lumbar, the entire first sacral and parts of the second and third sacral nerves. As previously stated (page 1320) the fourth lumbar nerve or n. furcalis splits into two portions, a larger upper and a smaller lower, the former contributing to the lumbar plexus and the latter uniting with the fifth lumbar nerve. The lower portion of the fourth lumbar having passed downward behind the internal iliac vessels, divides into anterior and posterior branches, which fuse respectively with similar branches of the fifth lumbar, the two trunks thus formed compris- ing the lumbo-sacral cord (truncus lumbosacralis). This double structure emerges from the mesial margin of the psoas magnus, passes down over the brim of the pelvis and constitutes the lumbar contribution to the sacral plexus. The first and second sacral nerves leave their foramina, pass laterally, anterior to the pyriformis, and split into anterior and posterior branches. The third sacral nerve or n. bi- geminus divides, not into ante- rior and posterior branches, but into upper and lower, the upper becoming a constituent of the sacral and the lower a portion of the pudendal plexus. Con- verging toward the lower por- tion of the great sacro-sciatic foramen, the posterior portion of the lumbo-sacral cord and the posterior branches of the first and second sacral nerves fuse and form the external popliteal or pcroneal and some minor pos- terior nerves. The anterior por- tion of the lumbo-sacral cord. 3S GREAT SCIATIC Diagram illustrating plan of sacral plexus. the anterior branches of first and second sacral the nerves and the upper part of the third sacral unite in the internal popliteal or tibial nerve and some small anterior branches (Fig. 1112). The resulting composite structure, the sacral plexus, is a broad triangular felt-work of nerve-strands, whose base points toward the sacrum and whose apex presents at the great sacro-sciatic foramen. The plexus is an occupant of the pelvis, on whose posterior wall it is situated, lying upon the pyriformis muscle and under cover of the parietal portion of the pelvic fascia. In relation with it anteriorly are the ureter, the pelvic colon and the internal iliac artery and vein. The ilio-lumbar vessels pass above the lumbo-sacral cord and between the cord and the first sacral nerve are found the superior gluteal vessels. The interval between the second and third sacral nerves is occupied by the sciatic artery and vein. In size the roots of the sacral plexus vary considerably, the largest, the fifth lumbar nerve, measuring about 7 mm. in diameter and the smallest, the third sacral, 3.5 mm. As regards length, the contribution from the fourth lumbar has the long- est course and that from the third sacral the shortest. Branches. The branches of the sacral plexus and their classification centre around the great sciatic nerve and its distribution. This nerve comprises two 1332 HUMAN ANATOMY. essential and frequently independent elements, the internal popliteal or tibial and the external popliteal or peroneal. Typically the sciatic divides into these two nerves in the lower part of the thigh ; very often, however, they are distinct from the outset, arising independently from the plexus, being separated in the great sacro-sciatic fora- men by the inferior fibres of the pyriformis muscle and passing through the thigh as contiguous but ununited structures. Moreover, even when the sciatic appears to be a single cord, dissection will reveal its duality in origin and course. The branches of the sacral plexus may be grouped as follows : I. Collateral Branches. A. Anterior branches : 1. Muscular 2. Articular B. Posterior branches : 3. Muscular 4. Articular II. Terminal Branches. A. Anterior branch: 5. External popliteal B. Posterior branch: 6. Internal popliteal COLLATERAL BRANCHES. The collateral branches comprise two sets, designated according to the portion of the plexus from which they arise as the anterior and the posterior. The anterior collateral branches include: (i) the muscular branches and (2) the articular branches. FIG. 1113. Superior gluteal nerve, giving abr. to pyriformis Psoas magnus, cut Ext. iliac artery Obturator nerve Pubic bone. mesial surface Obturator interims " White line" of pelvic fascia Left corpus cavernosum, cut Hr. to quadratus fern., ^emellus inf. and hip Joint Inf. gluteal nerve Urethra - Levator ani ' Coccygeus' Br. to levator ani Nerve to obturator internus andgemellus superior Anterior crural nerve . lumbar vertebra ""V. lumbar nerve I. sacral ganglion I. sacral nerve Dissection of right half of pelvis, Brs. to pyriformis If. sacnil ganglion II. sacral nerve Visceral br. of II. sacral nerve III. sacral ganglion IV. sacral ganglion (V. ganglion is seen l>elow) isceral brs. of III. and IV. sacral nerves . sacral nerve (ventral division) 'Coccygeal nerve (ventral division) Pudic nerve ; the small sciatic nerve is just in front Br. to sphincter ani, piercing levator am showing sacral and pudenda! plexuses; section is not mesial, but to left ot mill-line. i. The muscular branches supply (a) the quadratus femoris, () the obtura- tor internus, the ^emelli and i c } the hamstring muscles and the adductor magnus. a. The nerve to the quadratus femoris arises from tlu- anti-riot surface of tin- upper portion of the plexus, its fibres coming from the fourth and fifth lumbar and first sacral nerves. It is ire(|uently united in the first part of its course with the nerve to tin- obturator interims. Ha\ in- traversed the great sacro-sciatic foramen it courses downward anterior to the s^teat sciatic nerve, COLLATERAL BRANCHES. 1333 the obturator internus and the gemelli and posterior to the capsular ligament of the hip. Reaching the upper margin of the quadratus femoris it passes anterior to that muscle and terminates in fibres which enter the anterior surface of the muscle for which it is destined. In addition to supplying the quadratus femoris it sends twigs to the gemellus inferior and to the hip joint. Variations. The nerve to the quadratus femoris may supply the upper portion of the adductor magnus and may send filaments to the superior gemellus, either as an additional or as a sole supply. b. The nerve to the obturator internus has an origin one step lower than that of the preceding nerve, with which it is frequently associated for a short distance. It arises from the anterior aspect of the fifth lumbar and first and second sacral nerves and leaves the pelvis through the great sacro-sciatic foramen, below the pyriformis and the great sciatic nerve and lateral to the pudic nerve and vessels (Fig. 1114). Crossing the spine of the ischium it courses anteriorly through the lesser sacro-sciatic foramen and enters the ischio-rectal fossa, where it terminates by splitting into filaments which enter the posterior surface of the obturator internus. A small branch of this nerve supplies the gemellus superior. c. The nerve to the hamstring muscles consists of a bundle of fibres which forms the mesial edge of the gluteal portion of the sciatic nerve. Arising from the anterior aspect of the plexus and deriving its fibres from the fourth and fifth lumbar and first, second and third sacral nerves, it descends in close connection with the sciatic, lying first anterior to the latter and then to the inner side (Fig. 1115). In the thigh the nerve breaks up into two sets of fibres, an upper and a lower. The upper set leaves the sciatic below the tuber ischii and sends fibres to the upper portion of the semitendinosus and the long head of the biceps femoris. The lower set arises further down in the thigh and funishes twigs to the semimembranosus, the adductor magnus and the lower part of the semitendinosus. 2. The articular branches are derived from the nerve to the quadratus femoris and sometimes from the anterior aspect of the sciatic. After descending between the capsule of the hip and the gemelli they supply the posterior portion of the capsular ligament of the hip joint. The posterior collateral branches comprise, like the anterior, (3) the musctilar and (4) the articular branches. 3. The muscular branches include (a) the nerve to the pyriformis, (b*) the superior and (c) the inferior gluteal nerves and (rf) the nerve to the short head of the biceps. a. The nerve to the pyriformis may be. either single or double. It arises from the dorsal aspect of the second or first and second sacral nerves and enters the anterior surface of its muscle. There may be an additional filament from the root to the superior gluteal nerve con- tributed by the first sacral nerve. b. The superior gluteal nerve (n. glutaeus superior) (Fig. 1114) arises by three roots from the dorsal surface of the posterior portion of the lumbo-sacral cord and the first sacral nerve, its fibres being derivatives of the fourth and fifth lumbar and first sacral nerves. After passing above the pyriformis muscle in company with the superior gluteal artery and vein, it leaves the pelvis through the great sacro-sciatic foramen and divides into (aa) a superior and (bb) an inferior branch. aa. The superior branch (Fig. 1114) is the smaller of the two, and after passing beneath the gluteus medius and along the upper margin of the gluteus minimus reaches and enters the middle of the inner surface of the former muscle, of which it is only the partial nerve supply. bb. The inferior branch, larger than the superior, is the continuation of the main trunk. After a forward course between the glutei medius and minimus in company with the lower branch of the deep portion of the superior gluteal artery, it reaches the under surface of the tensor fasciae femoris (Fig. 1114). It supplies the glutei medius and minimus and its terminal fibres constitute the supply of the tensor fasciae femoris. c. The inferior gluteal nerve (n. glutaeus inferior) (Fig. 1114) is formed by twigs which arise from the dorsal surface of the posterior part of the lumbo-sacral cord and the first, and some- times the second, sacral nerve. It is frequently fused in the early part of its course with the small sciatic nerve and not infrequently with the nerve to the short head of the biceps. It usually sends a small branch down to join the small sciatic nerve. Passing beneath the pyriformis it emerges from the pelvis into the gluteal region through the great sacro-sciatic foramen, super- ficial to the great sciatic nerve. Immediately upon entering the buttock it breaks up fan-wise into a number of twigs which enter the deep surface of the gluteus maximus about midway between the origin and insertion. 1334 HUMAN ANATOMY. d. The nerve to the short head of the biceps (Fig. 1115) apparently arises from the lateral margin of the upper part of the great sciatic nerve. The fibres comprising it can be traced back to the fifth lumbar and first and second sacral nerves, sometimes in combination with the roots of the inferior gluteal nerve. Leaving the great sciatic in the middle of the thigh, often as a common trunk with the articular branch, it enters the substance of the short head of the biceps. Gluteus maximus Br. from V. lumbar nerve I. sacral nerve, posterior division Cutaneous br. from loop of posterior sacrals II. sacral nerve, posterior division III. sacral nerve. Interior division IV. sacral nerve posterior division Cutaneous br. from loop ol pos- Great sacro- sciatic ligament Nerve to obtu- rator internus Cutaneous and muscular branch of IV. ant. sacral Small sciatic tierve Tuberosity of ischium Inferior pu- dendal nerve Gluteus medius Tensor fascia; lata; Superior gluteal nerve .Gluteus minimus Pyriformis Trochanter major Nerve to quadratus femoris Tendon of obturator ii ith gemellussuperic .Gemellus intt-rior Branch to hipjoint Inferior gluteal nerve Quadratus femoris Great sciatic nerve Deep dissection of right buttock, showing emergence of great sciatic nerve below pyriformis muscle; also muscular branches and posterior divisions of sacral nerves. 4. Thf: articular branches supply the knee and are usually two in number. The upper arises either in common with the nerve to the short head of the biceps or independently from the lateral portion of the great sciatic. Descending on the pos- terior surface of the femoral head of the biceps it passes between the external condyle of the femur and the tendon of the biceps and supplies the lateral portion of the capsular ligament of the knee. The lower arises from the external popliteal nerve in the upper portion of the popliteal space and divides into two portions which supply the lateral and posterior portions of the capsular ligament of the knee. From the branch to the posterior part of the capsule is given off a tiny thread to the superior tibio-fibular articulation. TERMINAL BRANCHES. The terminal branches of the sacral plexus are the c.\t,ial and the internal popliteal, and these are usually fused in the upper part of their course into the great sciatic nerve. TERMINAL BRANCHES. 1335 THE GREAT SCIATIC NERVE. The great sciatic nerve (n. ischiadicus) , the largest nerve of the entire human body, is a thick bundle of nerve-fibres derived from both the anterior and posterior portions of FIG. 1115. Glutens maximus Great sciatic nerve Great sacro-sciatic ligament Small sciatic nerve Tuber ischii Great sciatic nerve Brs. to semitendinosus Adductor magnus Biceps, long head Semitendinosus Semimembranosus Br. to adductor magnus Br. to semimembranosus Semimembranosus . Popliteal artery Articular branch Popliteal vein Communicans tibialis Gluteus medius Pyriformis Gemellus superior '- Obturator internus Gemellus inferior Obturator externus Trochanter major Quadratus femoris Gluteus maximus Br. to .biceps Biceps, short head Int. popliteal nerve External popliteal nerve Articular branch Azygos articular branch Femur, popliteal surface > Muscu lar branches Gastrocnemius Communicans fibularis Deep dissection of posterior surface of right thigh, showing great sciatic nerve dividing into external popliteal (peroneal) and internal popliteal (tibial) nerves. the sacral plexus (Fig. 1112). Properly it consists of two elements only, the ex- ternal and internal popliteal nerves, the former from the posterior and the latter 1336 HUMAN ANATOMY. from the anterior portion of the plexus, its constituent fibres being derivatives of all of the spinal nerves contributing to the sacral plexus. Bound up with it and apparently integral portions of it, are the nerve to the hamstring muscles and the nerve to the short head of the biceps. From within outward, the four components are arranged in the following order: the nerve to the hamstrings, the internal popli- teal nerve, the external popliteal nerve and the nerve to the short head of the biceps. Arising from the apex of the sacral plexus and proceeding as its direct continua- tion, the great sciatic leaves the pelvis through the greater sacro-sciatic foramen below the pyriformis muscle and above the gemellus superior. In the form of a thick flat trunk, about 1.5 cm. wide, it turns downward and lies anterior to the gluteus maximus and posterior to successively the gemellus superior, the tendon of the obturator internus, the gemellus inferior, the quadratus femoris and the upper portion of the adductor magnus, being accompanied in the upper part of its course by the sciatic artery and the arteria comes nervi ischiadici. Lying external to the nerve is the great trochanter and internal to it is the tuberosity of the ischium (Fig. 1115). Entering the thigh by emerging from beneath the gluteus maximus, the nerve lies under cover of the hamstrings and at a varying position in the thigh it splits into its terminal divisions: (5) the external popliteal and (6) the internal popliteal. As previously stated (page 1332), these nerves may be separate from their origin. 5. THE EXTERNAL POPLITEAL NERVE. The external popliteal or peroneal nerve (n. peronaeus communis) (Fig. 1115) is homologous with the musculo-spiral of the upper extremity. It comprises fibres derived from the posterior portions of the fourth and fifth sacral and first and second lumbar nerves. As a part of the great sciatic, it follows the course in the thigh just described and after the bifurcation of the sciatic enters the popliteal space as an inde- pendent nerve. In the upper part of the popliteal space it lies beneath the biceps and later inclines gradually outward between the tendon of the biceps and the outer head of the gastrocnemius. Passing over the latter, it reaches the under surface of the deep fascia posterior to the head of the fibula, 2-3 cm. below which it divides into its terminal branches. Branches of the external popliteal nerve are : the cutaneous and the terminal. The cutaneous branches are: (a) the sural and () the peroneal communi- cating. a. The sural branch (n. cutaneus surae lateralis) (Fig. 1119) consists of one or more, usually two, filaments which arise in the popliteal space, frequently in common with the peroneal communicating nerve. Becoming superficial by piercing the deep fascia overlying the outer head of the gastrocnemius, it is distributed to the integument of the upper two thirds of the lateral aspect of the leg. Its degree of development is in inverse ratio to that of the small sciatic and short saphenous nerves. b. The peroneal communicating nerve (r. anastomoticus peronaeus) (Fig. 1119), also called the n. communicant fibularis, is larger than the preceding. Leaving the peroneal in the popliteal space, often in combination with the sural nerve or nerves, it descends beneath the deep fascia and over the lateral head of the gastrocnemius to the middle of the leg. Here it is usually joined by the tibial communicating branch from the internal popliteal and the joint trunk so formed (Fig. 1125) is called the external or short saphenous nerve (page 1342). The terminal branches comprise: (a) the recurrent articular, () the anterior tibial and (r) the musculo-cidancous. a. The recurrent articular or recurrent tibial branch ( Fig. 1 1 1 6 ) is the smallest of the three. Given off a short distance below the head of the fibula it passes forward under the peroneus longus and the extensor longus digitorum, courses upward in the musculature of the tibialis anticus and divides into filaments which supply the upper fibres of the tibialis anticus, the anterior portion of the knee joint, the superior tibio-fibular articulation and the periosteum of the external tuberosity of the tibia. b. THE ANTERIOR TIBIAL NERVE. The anterior tibial nerve (n. peronaeus profundus) originates below the head of the fibula in the interval bi-t uvm the peroneus longus and the fibula. After winding TERMINAL BRANCHES. 1337 externally around the head of the fibula beneath the peroneus longus, the extensor proprius hallucis and the extensor longus digitorum it reaches the anterior aspect of FIG. 1116. Extensor longus digitorum Anterior tibial artery' Anterior tibial nerve- Musculo-cutaneous nerve Peroneus longus, laid open Tibialis anticus- Extensor longus digitorum . Anterior tibial nerve Articular branch External branch Head of fibula Peroneal nerve Recurrent tibial branch Branch to extensor longus digitorum Muscular branch to peronei Peroneus brevis Internal branch of musculo-cutaneous External branch of musculo-cutaneous Peroneus longus tendon Peroneus brevis tendon Origin of extensor brevis digitorum External saphenous nerve Dissection of antero-lateral surface of left leg and of dorsum of foot, showing anterior tibial and musculo-cutaneous nerves. the leg. Lying on the anterior surface of the interosseous membrane it joins the anterior tibial vessels 812 "cm. below its origin and accompanies these vessels 1338 HUMAN ANATOMY. down the front of the leg as far as the ankle, lying first to their outer side, then anterior to them and at the ankle to the outer side again (Fig. 1116). Branches of the anterior tibial nerve are : (aa) the muscular, (66) the articular, () the external and (dd) internal terminal. aa. The muscular branches are distributed to the tibialis anticus, the extensor longus digitorum, the extensor proprius hallucis and the peroneus tertius. The nerves to the tibialis anticus consist of two twigs, an upper and a lower. The upper arises at the origin of the anterior tibial, passes beneath the peroneus longus and the extensor longus digitorum and enters the upper portion of the muscle. The lower arises in the interval between the tibialis anticus and the extensor longus digitorum and passes obliquely downward into the substance of the tibialis anticus. The nerve to the extensor longus digitorum arises immediately below the preceding and enters the inner surface of the muscle which it supplies. The nerves to the extensor proprius hallucis, usually two in number, arise in the middle of the leg and enter the substance of their muscle. The nerve to the peroneus tertius is usually derived from the nerve to the extensor longus digitorum. bb. The articular branch leaves the anterior tibial above the anterior annular ligament and is distributed to the forepart of the ankle-joint. cc. The internal terminal branch (Fig. 1117) courses forward in the foot under the inner tendon of the extensor brevis digitorum and lateral to the dorsalis pedis artery, and reaches the base of the first digital cleft. Here it splits into two branches (nn. digitales dorsales hallucis lateralis et digiti secundi medialis), which supply the contiguous sides of the great and second toes and ino'sculate with branches of the musculo-cutaneous nerve. In the region of the tarsus it sends off the first dorsal interosseous nerve, which supplies the first dorsal interosseous muscle, the mesial metacarpal articulations and the first and second metacarpo-phalangeal joints. Like the other interosseous nerves, it sends a filament between the heads of its dorsal interosseous muscle for the supply of the adjacent articulations (Ruge). dd. The external terminal branch (Fig. 1118) passes laterally over the tarsus undercover of the extensor brevis digitorum, to which muscle it sends branches. From it are given off two to four, usually three, dorsal interosseous branches, which decrease in size from within outward, the fourth often being lacking and the third quite rudimentary. These interosseous nerves are distributed to the adjacent articulations and sometimes to the second and third dorsal inter- osseous muscles. The fibres from the anterior tibial to the dorsal interosseous muscles are usually not their sole supply, the external plantar supplying constant branches for their innerva- tion. From the latter are probably derived the motor innervation and from the occasional ante- rior tibial branches some extra sensory filaments. This branch usually ends in a gangliform enlargement, from which its branches are distributed. Variations. The anterior tibial sometimes supplies the mesial side of the great toe or the adjacent sides of the second and third toes. In one case the anterior tibial supplied the outer three and one-half toes, the inner toe and one-half being innervated by the musculo-cutaneous nerve. Rarely the anterior tibial has no digital distribution whatsoever. c. THE MUSCULO-CUTANEOUS NERVE. The musculo-cutaneous nerve (n. peronaeus superflcialis) (Fig. 1116) continues the course and direction of the external popliteal. Descending through the leg in a fascial tube in the septum between the peroneal muscles and the extensor longus digitorum it becomes superficial by piercing the deep fascia anterior to the fibula in the lower third of the leg. It may make its superficial appearance as a single nerve or as two branches. Branches of the musculo-cutaneous are: (aa) the muscular, (bb} the internal and (cc} the external terminal. aa. The muscular branches (rr. musculares) are destined for the peronei longus and brevis. The nerves to the peroneus longus are two in number, an upper and a lower. They are given off at the upper and lower portions respectively of the fascial canal occupied by the parent nerve and enter the mesial surface of their muscle. The nerve to the peroneus brevis arises with the lower branch to the peroneus longus and enters the musculature of the peroneus brevis. TERMINAL BRANCHES. 1339 bb. The internal terminal branch (n. cutaneus dorsalis medialis) (Fig. 1117), larger than the external, passes obliquely inward in front of the ankle and then forward over the dorsum of the foot. Cutaneous twigs are distributed FIG. 1117. From internal . cutaneous nerve to the anterior aspect of the lower third of the leg and the dorsum of the foot. Just below the anterior annular ligament the nerve breaks up into an inner, a middle and an outer branch. The inner branch inosculates with the internal saphenous nerve, from which it receives an accession of fibres, and passes forward to supply the integument of the mesial aspect of the foot and great toe. The middle branch follows the first metatarsal space and inosculates with the inner branch of the anterior tibial nerve. The outer branch courses down the second metatarsal space and divides into the two dorsal digital nerves (nn. digitales dorsales pedis) which supply the contig- uous sides of the second and third toes. This branch is sometimes derived from the external terminal part of the musculo- cutaneous. ct. The external terminal branch (n. cutaneus dorsalis intermedius) (Fig. 1117) courses down the leg anterior to the ankle and lateral to the inner branch, giving off twigs to the antero-lateral por- tion of the integument of the lower part of the leg and dorsum of the foot. Having reached the foot it breaks up into inner and outer branches. The inner branch divides into dorsal digital branches for the supply of the adjacent sides of the third and fourth toes, and the outer branch, after receiving an accession of fibres through inoscula- tion with the external saphenous, divides similarly into twigs for the contiguous sides of the fourth and fifth toes. The dorso-lateral aspects of the terminal phalanges and the nails receive addi- tional filaments from the plantar nerves. Variations. Deficiencies in the in- ternal branch are usually supplied by the anterior tibial nerve and in the ex- ternal by the short saphenous. In case the external branch ends at the dorsum of the foot, the external saphenous, which would fill the vacancy at the digits, has its root from the external popliteal more strongly developed than usual, and thus the toes are supplied in an unusual manner but still by fibres from the ex- ternal popliteal nerve. 6. From middle cutaneous nerve From peroneal nerve Sural brs., peroneal nerve Musculo-cuta- ueous nerve Ext. saphenous ( nerve ] Kxt. terminal br. musculo- cutaneous nerve From internal cutaneous nerve Cutaneous patellar br. int. saphenous nerve Int. saphenous nerve Crest of tibia Int. saphenous nerve Int. saphenous vein Int. terminal br. musculo- cutaiieous nerve Int. terminal br. ant. tibial nerve THE INTERNAL POPLITEAL NERVE. The internal popliteal or tib- ial nerve (n. tibialis) (Fig. 1115) is of greater size than the external and corresponds in its distribution to the combined median and ulnar nerves of the arm. Arising from the anterior portion of the sacral plexus, it includes fibres derived from the fourth and fifth lumbar Superficial dissection of right leg and foot, showing cutaneous nerves of anterior surface. 1340 HUMAN ANATOMY. and first, second and third sacral nerves. Leaving the pelvis through the greater sacro-sciatic foramen below the pyriformis, and passing through the gluteal region and upper part of the thigh as the inner portion of the great sciatic nerve, it becomes an independent trunk at the point of bifurcation of the sciatic. Emerging from beneath the hamstring muscles and descending vertically through the middle of the FIG. 1118. Musculo-cutaneous nerve Fibula Extensor longus digitorum tendon Peroneus tertius tendon Anterior tibial nerve Articular branches to ankle joint Peroneus longus tendon External saphenous nerve Musculo cutaneous nerve external division External division of anterior tibial nerve Extensor brevis digitorum Metatarsal branches of external division of anterior tibial nerve External saphenous nerve Digital branches of external division of musculo- cutaneous nerve Extensor proprius hallucis tendon Internal saphenous nerve Tibialis anticus tendon Extensor brevis digitorum Internal division of musculo- cutaneous nerve Anterior tibial nerve internal branch Dissection of dorsum of right foot, showing distribution of anterior tibial, musculo-cutaneous, and internal and external saphenous nerves. popliteal space, it gradually attains the inner side of the popliteal vessels, crossing them superficially from without inward. In the lower part of the space the nerve lies posterior to the popliteus muscle and anterior to the plantaris and the gastroc- nemius. At the lower border of the popliteus muscle the internal popliteal becomes the posterior tibial nerve (Fig. 1119). TERMINAL BRANCHES. Branches of the internal popliteal are : (#) the articular, (<) the cutaneous and (//) the posterior tibia/. FIG. 1119. Gracilis Semitendinosus Semimembranosus Superior internal articular nerve Inner head of gastrocnemius Inferior internal articular nerve Tihial (internal popliteal) nerve Peroneal (external popliteal) nerve Superior external articular nerve Biceps tendon Ext. head of gastrocnemius Tibial communicating Inferior external articular branch Muscular branch \fl'Af\

f the -astrocneinins be-fore joining then. communicans fibularis. Variations in distribution may occur, the nerve sometimes supplying the dorsal aspect of two and one-half digits, under such circumstances the n. communicans fibularis usually being of increased si/e. The in r\e may terminate in the foot and not have any digital distribution. d. Tin-: POSTERIOR TIBIAL NEKYI. The posterior tibial nerve (n. tihialis ) ( Fi^. 1 1 10. ) is the direct continuation of the- internal popliteal and begins at the lower Imrder < >t tin- popliteus muscle. It extends downward, in a sheath shared by the posterior tibial vessels, between the superficial and deep muscles of the posterior portion <>f the lei;. Anterior to it are TERMINAL BRANCHES. 1343 the tibia and the deep leg muscles and posteriorly lie the soleus and gastrocnemius in the tipper part of the leg. Above the ankle ihe nerve becomes superficial, and is covered only by integument and the fasciae. Owing to the inward inclination of the posterior tibial vessels the nerve, while pursuing a straight course, changes its rela- tive position to the vessels, in the upper part of the leg lying to the inner side, lower down behind and above the ankle attaining the outer aspect of the vessels (Fig. 1121). Passing posterior to and then below the internal malleolus, the posterior tibial nerve divides, under cover of the internal annular ligament, into its terminal branches, the internal and the external plantar. FIG i i 20. Internal calcanean branch of posterior tibial nerve Digital branches of internal plantar nerve External saphenous nerve jf\ External saphenous nerve Digital branches of external plantar nerve Superficial dissection of right foot, showing cutaneous nerves on plantar surface. Branches of the posterior tibial nerve are : (aa} the muscular, (bb} the infernal calcanean, (cc) the articular, (dd) tint internal plantar and (cc) the external plantar. aa. The muscular branches (rr. musculares) supply the tibialis posticus, the soleus, the flexor longus hallucis and the flexor longus digitorum. The nerve to the tibialis posticus supplies that muscle and sends a branch to the flexor longus digitorum and one to the lower part of the soleus. At the posterior aspect of the tibialis posticus it gives off a long slender branch which accompanies the peroneal artery nearly to the ankle, supplying tu-igs to the artery, to the periosteum of the fibula and a branch which enters the nutrient canal of the fibula. The nerves to \\\e fle.rores longus hallucis and longus digitorum leave the posterior tibial about the middle of the leg and pass directly to their muscles. 1344 HUMAN ANATOMY. bb. The internal calcanean nerve (rr. calcanei mediates) arises from the posterior tibial at the lower part of the leg and becomes superficial by traversing an opening in the internal annular ligament. Dividing into two sets of twigs, internal calcanean and calcaneo-plantar, it is distributed to the integument of the internal aspect of the heel and posterior portion of the sole. cc. The articular branches are two tiny twigs, given off beneath the internal annular ligament, which supply the ankle joint. dd. The internal plantar nerve (n. plantaris medial is) (Fig. 1121), larger than the external, resembles in its distribution the median nerve in the hand. From the point of division of the posterior tibial nerve it courses forward in the foot in company with the internal plantar artery, lying first above the internal annular ligament and the calcanean head of the abductor hallucis and then between the abductor hallucis and the flexor brevis digitorum. Passing thence for- ward between the flexor brevis hallucis and the flexor brevis digitorum it divides into two ter- FlG. TT2I. Calcaneo-plantar cutaneous br. of tibial nerve Articular br. (usually a br. of tibial nerve) Br. to abductor hallucis Int. plantar nerve Brs. to flex, brevis digitorum I. and Il.lumbricales Digital brs. of int. plantar nerve Flexor brevis digitorum Ext. plantar nerve Br. to abductor minimi digit! Abductor minimi digiti Flexor accessorius Br. to flex, accessorius Superficial br. ext. plantar nerve Brs. to flex. brev. minimi digiti Deep br. ext. plantar nerve Digital branch Brs. to interossei of fourth space Digital branch III. and IV. lumbricales Dissection of right foot, showing internal aud external plantar nerves and their branches. minal branches, an inner and an outer. In addition to the terminal branches it gives off certain collateral twigs. The collateral branches are muscular, cutaneous and articular in distribution. The muscular supply the abductor hallucis and the flexor brevis digitorum. The cutaneous pass between the muscles just mentioned to be distributed to the integument of the inner portion of the sole. The articular furnish innervation to the inner tarsal and tarso-metatarsal joints. The terminal branches are an inner or mesial and an outer or lateral. The inner or mesial terminal branch (Fig. 1121) courses forward upon the under surface of the abductor hallucis, pit-revs tin: plantar fascia posterior to tin- tarsi )-nu-tatarsal articulation of the great toe and terminates by extruding along tin- im-sial side of that toe as its inner plantar digital nerve. In its course it furnishes filaments to the inner surface of the foot and a twig to the mesial head of the flexor brevis hallucis. THE PUDENDAL PLEXUS. 1345 The outer or lateral terminal branch (Fig. 1121) is larger than the inner and is situated below the distal portion of the flexor brevis digitorum and above the deep plantar fascia. After a short forward course it splits into two branches, the lateral of which soon divides into two. There are thus formed three plantar digital nerves (nn. digitales plantares communes), each of which at the distal end of its metatarsal space divides into two digital nerves (nn. digitales plantares proprii), the inner supplying the contiguous sides of the great and second toes, and the middle and outer being distributed similarly to respectively the second and third and third and fourth toes. The inner of the three sends a filament to the first lumbricalis, the middle some- times to the second lumbricalis, while the outer forms an inosculation with the external plantar nerve. In addition to innervating the muscles enumerated and the integument of the plantar sur- face of the mesial three and one-half toes, each of the digital nerves sends tiny filaments toward the dorsum for the supply of the nails and the tips of the toes. ee. The external plantar nerve (n. plantaris lateralis) ( Fig. 1121 ) is a smaller nerve than the internal and corresponds in its arrangement and distribution with the palmar branch of the ulnar nerve. After separating from the internal plantar beneath the internal annular ligament, it follows a course in company with the external plantar artery obliquely forward and outward above the flexor brevis digitorum and below the flexor accessorius. Reaching the interval between the abductor minimi digiti and the flexor brevis digitorum it divides near the head of the fifth metatarsal bone into superficial and deep terminal branches. Branches of the external plantar, like those of the internal, include : collateral and terminal branches. The collateral branches comprise muscular and cutaneous twigs. The muscular branches are given off soon after the origin of the parent nerve and supply the flexor accessorius and the abductor minimi digiti. The cutaneous branches are a series of small twigs which follow the septum between the flexor brevis digitorum and the abductor minimi digiti and become super- ficial by piercing the deep plantar fascia. They supply the integument of the lateral portion of the sole. The terminal branches are : the superficial and the deep. The superficial or cutaneous branch (r. superficialis) inosculates with a branch of the internal plantar and continues forward in the interval between the flexor brevis digitorum and the abductor minimi digiti, eventually splitting into an external and an internal branch. The external branch (Fig. 1121) sends filaments to the flexor minimi digiti and the inter- ossei muscles of the fourth metatarsal space, after which it becomes cutaneous near the fifth metatarso-phalangeal articulation and continues forward as the plantar digital nerve for the lateral aspect of the fifth toe. The internal branch (Fig. 1121) courses forward in the fourth metatarsal space, at whose distal end it separates into two filaments which supply the opposed surfaces of the fourth and fifth toes. The digital branches send filaments dorsally for the nails and the tips of the toes. The deep or muscular branch (r. profundus) accompanies the external plantar artery in an obliquely forward and outward course above the adductor obliquus hallucis and the flexor accessorius and below the interossei muscles. It forms an arch (Fig. 1121) whose convexity is directed forward and outward, and terminates in the region of the base of the great toe. From the convex aspect of the arch are given off the filaments which innervate the interossei muscles of the first, second, third and sometimes the fourth interosseous space. Other muscular twigs supply the adductores obliquus and transversus hallucis and the outer three lumbricales, the branch to the second lumbricalis first passing beneath the adductor transversus hallucis. The branches to all of these muscles enter their deep surface. In addition to the muscular distribu- tion, articular twigs are furnished to the tarsal and tarso-metatarsal articulations. THE PUDENDAL PLEXUS. The pudendal plexus (plexus pudendus) is the downward continuation of the sacral plexus, and, whilst each retains more or less its individuality as a distinct structure, there is no sharp line of demarcation between the two. Considerable interlacing and overlapping is the rule, so that often some of the important branches of the pudendal plexus are derivatives to a large extent from the elements giving rise to the sacral plexus. The pudendal plexus (Fig. 1122) is situated on the posterior wall of the pelvis and is formed by contributions from the anterior primary divisions of the first, second and third sacral nerves, from the entire anterior primary divisions of the fourth and fifth sacral and from the coccygeal nerve. Communications. The nerves helping to form the plexus receive gray rami communicantes from the gangliated cord of the sympathetic, which join them shortly after the nerves emerge from their intervertebral foramina. 85 1346 HUMAN ANATOMY. FIG. i 122. Branches. The branches of the pudendal plexus are : (i) the visceral, (2) the muscular, (3) the perforating cu- taneous, (4) the small sciatic, (5) the pudic and (6) the sacro-coccygeal. 1. The visceral branches are really white rami communicantes. They are derived from the second and third or third and fourth sacral nerves and are distributed to the pelvic viscera by way of the pelvic plexus of the sympathetic. The details of these nerves are des- cribed with the pelvic plexus of the sympathetic (page 1374). 2. The muscular branches furnish innervation to the levator ani, the coccygeus and the external sphinc- ter ani. They arise from a loop-like interlacement of nerve-fibres, formed by the third and fourth sacral nerves, with sometimes the addition of fibres from the second. The nerve to the external sphincter pierces the great sacro-sciatic ligament and the coccygeus muscle, sending filaments to the latter, and enters the ischio-rectal fossa, lying between the edge of the gluteus maximus and the sphincter ani externus. It supplies the Diagram illustrating plan of pudendal and coccygeal plexuses. FIG. 1123. From II. lumbar nerve From I. lumbar nerve From III. lumbar nerve Cutaneous brs. post . divisions of sacral nerves Coccygeal nerves, posterior divisions Coccygeal nerve, anterior division From ant. V. sacral From ant. IV. sacral Inferior hemor- _ rhoidal nerves \ 1 Iliac brs. of ilio- ( hypogastric Glutcal brs. of small sciatic nerve Inferior pudenda! nerve Superficial dissection of right buttock and adjacent regions, showing cutaneous IK i \ H. THE PUDENDAL PLEXUS. 1347 posterior portion of the external sphincter and distributes sensory fibres to the integument over the base of the ischio- FIG. 1124. rectal fossa and the tip of the coccyx. Variation. This nerve, instead of pierc- ing the coccygeus, may pass between that mus- cle and the levator ani. The nerve to the levator ani is derived usually from the third and fourth, sometimes the second and third, sacral nerves and en- ters the muscle by piercing its mesial surface. 3. The perfo- rating cutaneous nerve (Fig. 1126) is an inconstant branch, being found in about two thirds of the bodies examined. It springs from the dor- sal aspect of the second and third sac- ral nerves and at its point of origin may be associated with the pudic or the small sciatic. Passing downward and back- ward it pierces the great sacro-s ci at i c ligament in company with the coccygeal branch of the sciatic artery and winds around the lower bor- der of, or in rare in- stances pierces, the gluteus m a x i m u s . Perforating the deep fascia slightly lateral to the coccyx, it be- comes superficial and is distributed to the integument over the inner and lower por- tion of the gluteus maximus. Variations. I n - Inf. piidendal nerve, and a glu- teal cutaneous br. of small sciatic Small sciatic nerve From lateral cutane- ous br. of XI I. thoracic From I. lumbar nerve A gluteal cuta- neous br. of small sciatic nerve From lateral cuta- neous br. of XII. . thoracic jr~From ext. cutaneous nerve An ext. femoral br. of small sciatic From ext. cuta- neous nerve Superficial dissection of right buttock and thigh, showing cutaneous nerves of posterior surface. stead of piercing the ligament it may accompany the pudic nerve or pass between the ligament and the gluteus maximus. It may be replaced by a branch of the small sciatic or by a nerve, called by Eisler 1348 HUMAN ANATOMY. the n. per/orans coccygens major, \\-hich arises from the third and fourth or fourth and fifth sacral and pierces the coccygeus muscle. FIG. 1125. From small sciatic nerve From obturator nerve ^m> From internal cutaneous Internal saphenous nerve Inner malleolus External calcanean branches Small sciatic nerve Sural from peroneal nerve Peroneal communicating Part of sural branch Tibial communicating External saphenous nerve branch of musculo-cutaneous -Anterior branch of ext. saphenous Cutaneous nerves of posterior surface of right leg. 4. THE SMALL SCIATIC NERVE. The small sciatic nerve (n. cutanciis fcinoris posterior) (Fig. 1114) is a purely sensory structure. It originates from the back of the first, second and third, or THE PUDENDAL PLEXUS. 1349 from only the second and third, sacral nerves, the upper root usually being associ- ated with one of the roots of the inferior gluteal nerve, and the lower root with the perforating cutaneous or the pudic nerve. Leaving the pelvis through the great sacro-sciatic foramen below the pyriformis, it descends in the gluteal region between the tuber ischii and the great trochanter, posterior to the great sciatic nerve and anterior to the gluteus maximus, accompanied by the inferior gluteal nerve and the sciatic artery. Emerging into the thigh at the lower border of the gluteus maximus it continues downward beneath the deep fascia and superficial to the hamstring muscles to a short distance above the knee, where it pierces the deep, and becomes an occupant of the superficial, fascia. Thence it passes downward through the roof of the popliteal space and through the upper part of the calf, in the latter situation accompanying the external saphenous vein and inosculating with the external saphenous nerve. It rarely extends beyond the middle of the calf, tapering off into tiny threads which are distributed to the skin of the posterior surface of the upper half or two thirds of the leg (Fig. 1125.) Branches of the small sciatic nerve are : (a} the inferior pudendal, (b) the ghiteal, (r) \.\\Q femoral and (d) the sural. a. The inferior pudendal or perineal branch (rr. perineales) (Fig. 1126) leaves the parent nerve at the lower margin of the gluteus maximus, curves mesially below the tuberosity of the ischium and over the origin of the hamstrings and courses through the groove between the thigh and the perineum. Piercing the deep fascia lateral to the pubic ramus, it enters the perineum and supplies the integument of the scrotum and base of the penis, or of the labium majus and clitoris. Branches are distributed to the skin of the upper mesial portion of the thigh and to the perineal body and anus. This nerve communicates with the ilio-inguinal nerve and with the perineal and inferior hemorrhoidal branches of the pudic nerve. It may pierce the great sacro-sciatic ligament. b. The gluteal cutaneous branches (rr. clunium inferiores) (Fig. 1124) consist of two, three or more stout filaments which arise from the small sciatic a short distance above the inferior margin of the gluteus maximus, around which they wind. Piercing the fascia lata individually they turn upward over the lower portion of the gluteus maximus and are dis- tributed to the skin of the inferior gluteal region, as far externally as the great trochanter and internally almost to the coccyx. The outer branches overlap the terminal twigs of the posterior branch of the external cutaneous nerve and the posterior primary divisions of the first, second and third lumbar nerves. The inner branches sometimes pierce the great sacro-sciatic liga- ment ; they reinforce or may replace the perforating cutaneous nerve. c. The femoral branches (Fig. 1124) consist of two series of twigs, an internal and an external, which pierce the fascia lata of the posterior aspect of the thigh and supply the integu- ment of that region. d. The sural branches (Fig. 1125) are usually two terminal twigs which innervate to a varying extent the integument of the back of the leg, sometimes not extending beyond the confines of the popliteal space and sometimes continuing all the way to the ankle. They inosculate with the external saphenous nerve, and when they are lacking their place is taken by the external saphenous. Variations. In those cases in which the internal and external popliteal nerves are separate from their incipiency, the small sciatic also is double. The ventral portion accompanies the internal popliteal and gives off the inferior pudendal and internal femoral branches, while the dorsal portion accompanies the external popliteal and gives off the gluteal and external femoral branches. Sometimes the small sciatic is joined in the thigh by a branch from the great sciatic. 5. THE PUDIC NERVE. The pudic nerve (n. pudendus) arises from the front of the second, third and fourth sacral nerves, its main root coming from the third and there being a doubtful root from the first. Leaving the pelvis by way of the great sacro-sciatic foramen between the pyriformis and the coccygeus and below the great sciatic nerve, it passes forward, with the internal pudic artery and the nerve to the obturator internus, over the base of the lesser sacro-sciatic ligament to the spine of the ischium (Fig. 1126). Reaching the small sacro-sciatic foramen internal to the internal pudic artery, the nerve traverses this opening and enters the ischio-rectal fossa, where it gives off the inferior hemorrhoidal nerve. The main trunk courses forward in a canal (Alcock's) in the obturator fascia on the outer wall of the ischio-rectal fossa 135 HUMAN ANATOMY. (Fig. 1126), at whose anterior portion the nerve approaches the base of the tri- angular ligament and divides into its terminal branches, the perineal and the dorsal nerve of the penis or clitoris. Branches of the pudic nerve are : (a) the inferior hemorrhoidal nerve, (b) the perineal nerve and (c) the dorsal nerve of the penis or clitoris. a. The inferior hemorrhoidal nerve (nn. hemorrhoidales inferiores) (Fig. 1127) is usually given off by the pudic upon entering the ischio-rectal fossa, hut it may be derived directly from the plexus, its fibres being offshoots of the third and fourth sacral nerves. In company with the inferior hemorrhoidal vessels it passes mesially across the base of the ischio-rectal fossa toward FIG. 1126. Coccygeal nerves, posterior divisions Coccyx anterior division .Cutaneous branches from loops of V. luniUir and I. II. and III. sacral nerves, posterior divisions Branch of IV. sacral nerve, (perforating cutaneous) Levator ani and anal fascia Pudic nerve Cut edge of obturator fascia Inferior hemor- rhoidal nerve Internal pudic artery Perineal division of pudic nerve Dorsal nerve ot clitoris Inferior pudenda! Vulva Superficial dissection of right side of female perineum and adjacent region, showing cutaneous nerves ; obturator fascia has been partly removed to expose pudic nerve and accompanying blood-vessels in canal on outer wall of ischio-rectal fossa. the anus, on approximating which it splits into a number of filaments, which supply the external sphincter and the integument of the anal region, and inosculate with the small sciatic, pudic and fourth sacral nerves. b. The perineal nerve (n. perinei) (Fig. 1126) is one of the terminal branches of the pudic and arises at the bifurcation of that nerve near the posterior margin of the triangular ligament. Soon after its origin it splits into : (aa i a superficial and (bb) a deep branch. aa. The superficial branch is entirely sensory and consists of two parts, a lateral or posterior and a mesial or anterior. These pass forward toward the base of the scrotum in company with the superficial perineal vessels. The lateral, c vt,-ial or posterior branch courses along the lateral margin of the perineum, distributing twigs in this region and sometimes sending branches to the inner aspect of the thigh and a filament to the origin of the ischio-cavernosns muscle ( Scluvalbe). The mesial, internal or anterior branch is larger than the lateral and is more deeply- placed. It pierces the posterior margin of the triangular ligament and runs forward either beneath or through the transversus perinei muscle. It splits into two or more branches (nn. scrotales vet lal.iales posteriores ) which inosculate freely with each other and supply the integument of th- scrotum or labinm majus. They communicate with the pudendal branch of the small sciatic nerve and with the inferior hemorrhoidal. THE PUDENDAL PLEXUS. 56. The deep branch of the perineal nerve is mainly muscular and consists of a single trunk which breaks up into several branches, whose main destination is the muscles of the perineum. Passing forward from the ischio-rectal fossa it enters the deep perineal interspace and sends filaments to the external sphincter ani, the levator ani, the transversus perinei, the ischio-cavernosus, the bulbo-cavernosus or sphincter vaginae and the compressor urethras. One branch, the nerve to the bulb, accompanied by the artery of the same name, enters the bulb, supplying its tissue and that of the corpus spongiosum, and innervating the urethra as far forward as the glans penis. c. The dorsal nerve of the penis (n. dorsalis penis) (Fig. 1127) a terminal branch and the most deeply situated of all the branches of the pudic, accompanies the dorsal artery of the penis through the deep perineal interspace. It lies beneath the crus penis, the ischio-cavernosus muscle and the inferior layer of the triangular ligament and over the compressor urethra: FIG. 1127. Dorsal nerve of penis Crus penis, detached Ischio-cavernosus. detached Nerve to ischio- cavernosus Nerve to bulbo- cavernosus Nerve to bulb Nerve to trans- versus perinei Muscular br. of perineal division of pudic nerve Dorsal nerve of penis Cutaneous br. of perineal division of pudic nerve Pudic nerve Inferior hemor- rhoidal nerve Sphincter anij exterrius Colics' fascia, reflected Crus penis and ischio-cavernosus Anterior (internal) superficial perineal nerve Inferior pudendal nerve Transyersus perinei Posterior superfi- cial perineal nerve Dorsal nerve of penis Perineal division of pudic nerve, muscular portion Pudic nerve Inferior hetnor- rhoidal nerve Gluteus maximus From IV. sacral nerve Perforating cutaneous nerve and a branch of IV. sacral nerve Dissection of male perineum, showing; distribution of pudic nerve; on left side of body Colics' fascia has been reflected to expose superficial perineal interspace ; dorsal nerve of penis is seen in deep interspace on right side. muscle. Piercing the inferior layer of the triangular ligament and the suspensory ligament of the penis it reaches the dorsum of the penis, along which it courses as far as the glans. It gives off the nerve to the corpus cavernosuin, which pierces the triangular ligament and supplies the erectile tissue of the crus penis and corpus cavernosum. The main nerve innervates the anterior two thirds of the penis, including the glans, and sends off ventral branches which pass around to the under surface of the organ. The dorsal nerve of the clitoris (n. dorsalis clitoridis)(Fig. 1128), while much smaller than the dorsal nerve of the penis, has a corresponding course and distribution. The dorsal nerve of the penis or clitoris communicates with the inferior pudendal branch of the small sciatic. Variations. The pudic may receive a root from the fifth lumbar, in the high form of plexus. A root from the fifth sacral is described by Henle. The inferior hemorrhoiclal may pierce either the greater the small sacro-sciatic ligament, and the former of these ligaments maybe perforated by the lateral superficial perineal nerve. 1352 HUMAN ANATOMY. THE COCCYGEAL PLEXUS. 6. The sacro-coccygeal nerves (nn. anococcygei) are derived from a small nerve inosculation called the coccygeal plexus (plexus coccygeus), a structure formed by the fifth sacral and the coccygeal nerve, with a contribution from the fourth sacral which descends over or through the great sacro-sciatic ligament. The fifth sacral, having been joined by this twig from the fourth, descends along the margin of the coccyx and is joined by the coccygeal nerve, the resulting nerve-bundle constituting the coccygeal plexus. From it arise minute filaments which pierce the great sacro- sciatic ligament and are distributed to the integument in the immediate neighbor- hood of the coccyx (Fig. 1084). Practical Considerations. Of the branches of the sacral plexus, the great sciatic nerve is the most important, owing to its size, its extensive distribution and its exposed position. The greater part of the sacral plexus is continued into the FIG. 1128. Bulbo-cavernosus Ischio-cavernosus Inferior pudenda! nerve Posterior superficial perineal nerve Anterior superficial perineal nerve Transversus perinei superficialis 1'erineal division of pudic nerve Inferior hemorrhoidal nerve Sphincter ani Anal fascia I >eep fascia of buttock Glansclitoridis Deep layer of triangular ligament Superficial perineal nerves Dorsal i ofclitor Perineal dhision of pudic nerve Levatorani (",reat scacro-siatic ligament Inferior hemorrhoidal nerve Perforating Uluteustnavimus From IV. sacral nerve Coco Dissection of female perineum, showing nerves; anal fascia in position on right side of body, removed on left ; Colics' fascia removed on right side, exposing superficial perineal interspace; superior layer of triangular ligament, denuded of muscular tissue, seen on left side. nerve. Except in complete lesions of the spinal cord this nerve is rarely paralyzed in all its branches. The paralysis may result from fractures of the lumbar vertebra, of the sacrum or of the innominate bone, from pressure of tumors in the pelvis or of the child's head in labor or from the use of forceps. It is the structure in greatest danger in dislocation of the hip, since the head of the femur in the most frequent varieties sweeps backward against this nerve. In the reduction of these posterior dislocations the nerve lias been hooked up by the head and made to pass across the front of the neck of the bone. From its close relation to the head and neck, it may be injured in violent movements of the hip joint without dislocation. It passes out of the pelvis through the greater sacro-sciatic foramen, below the pyriformis muscle, and after curving outward and downward under the glutens maxi- nius muscle it continues its course, approximately, in a line from a point midway THE SYMPATHETIC SYSTEM OF NERVES. 1353 between the greater trochanter and the tuberosity of the ischium above to the middle of the popliteal space below. At about the junction of the middle and lower thirds of the thigh it divides into the internal and external popliteal nerves. Below the gluteus maximus muscle it is comparatively superficial, so that tenderness of the nerve, as from sciatica, is easily elicited by pressure. At the point where it emerges from under the gluteus maximus it is readily reached for operation. After a vertical in- cision through the skin and fascia at this level, the biceps muscle is exposed. The lower margin of the gluteus maximus is raised and the biceps drawn inward, when the nerve can be easily hooked up with the finger. Because of the great importance of this nerve to the lower extremity it is not advisable to excise or divide it as this would paralyze its whole area below. Stretching is the only justifiable operation, although the results obtained are often disappointing, and the operation may cause acute neuritis. According to Trombetta, it will require a tension equal to the weight of 183 Ibs. to break it, and it is more likely to yield at its attachment to the spinal cord than elsewhere. It should, therefore, tolerate a stretching force of from 100 to 1 60 Ibs. (Treves). A safe working rule is to use a force sufficient to raise the affected limb from the table, the patient lying in the prone position. It has been observed that when the paralysis is due to some pressure upon the nerves of the sacral plexus within the pelvis it is 'often confined to the peroneal or ex- ternal popliteal nerve, or is most marked in it. This has been explained by the fact that the fibres for the peroneal nerve lie close together directly on the pelvic bones, and are, therefore, particularly exposed to pressure. They arise for the most part from the lumbo-sacral cord, formed by the fourth and fifth lumbar and first sacral nerves, which lie directly on the innominate crest, the rest of the plexus lying on the pyriformis muscle. In paralysis of the external popliteal or peroneal nerve the extensors of the foot and toes, the tibialis anticus and the peronei muscles are involved. The foot hangs down from its own weight (foot drop), and turns in from paralysis of the peronei. In some cases the anterior tibial muscle escapes. In walking the knee must be un- duly flexed to prevent the toes from dragging on the ground and the arch of the foot is flattened from the loss of the support given to the arch by the peroneus longus. If sensation is disturbed it will be only to a slight extent over the anterior part of the leg about the shin, and outward from this on the dorsum of the foot and toes, but not at the sides of the foot. The percmeal nerve may be divided accidentally in a sub- cutaneous tenotomy of the biceps tendon for contraction at the knee, the nerve lying close to the inner border of the tendon. It may be injured by external violence, as it passes around the head and neck of the fibula, where if necessary, an incision will easily expose it ; or it may be injured by pressure, as in prolonged kneeling. In paralysis of the internal popliteal nerve all the other muscles of the leg, in- cluding the superficial and deep flexors, the tibialis posticus, the plantar muscles and interossei are affected. The patient cannot extend the ankle and therefore cannot stand on his toes. The toes cannot be flexed or moved sideways. Sensation is dis- turbed on the inner and posterior surface of the leg, the outer border of the foot, the sole and the plantar surface of the toes. In paralysis of the entire sciatic nerve the flexors of the knee also are involved, so that the patient cannot bring the heel toward the buttock. If only one sciatic is involved he can still walk by fixing the knee in extension, the whole limb being brought forward by the quadriceps extensor, which is supplied by the anterior crural nerve. THE SYMPATHETIC SYSTEM OF NERVES. The sympathetic portion (systema nervorum sympatheticum) of the peripheral nervous system differs from that already described the spinal and the cranial nerves in being particularly concerned in carrying efferent and afferent impulses to and from the thoracic and abdominal organs (collectively termed the splanchnic area), in contrast to the great somatic ("skeletal) masses of voluntary muscle. Whilst the paths for the afferent or sensory impulses conducted from the splanchnic area differ in no important respect from those formed by the cerebro-spinal nerves, the efferent or motor paths are peculiar () in supplying the involuntary and cardiac muscle and 1354 HUMAN ANATOMY. FIG. 1129. SoE the glandular tissue and (6~) in consisting of at least two, often of several, links between the source of the impulse (the spinal cord) and the structure upon which it is expended. It is these interposed links that constitute the sympathetic elements proper the sympathetic neurones. The cell-bodies of these neurones exhibit a marked disposition to become aggregated into larger or smaller collections, which constitute the innumerable ganglia that form a conspicuous feature of the sympathetic system, whilst their axones serve to connect the ganglia with the terminal structures (muscles or glands) or with other neurones. It is evident, therefore, that the sympathetic system consists of a complex of spinal and sym- pathetic fibres intermingled with groups of ganglion-cells. The latter are, for the most part, stellate in form and pro- vided with axones which, while often pursuing a long course as splanchnic efferenis, acquire only partially or not at all a medullary coat and hence may be classified usually as non- medullated fibres. Since the spinal fibres are provided with this covering, the bundles of such fibres present the whitish color distinguishing medullated strands, in contrast to the gray- ish tint of the strands of the nonmedullated sympathetic fila- ments. It is upon this histolog- ical variation of their predomi- nating fibres that the difference recognized in the white and gray rami communicantes, pres- ently to be described, depends. Although the supply of the thoracic, abdominal and pelvic organs constitutes an important part of the duty of the sympa- thetic nerves, it is by no means their entire concern, the inner- vation of the involuntary muscle of the vessels and of the skin and the glands throughout the body being likewise their task. In order to meet their obliga- tions to the structures within the body cavities, the sympa- thetic nerves naturally follow the course of the blood-vessels, with the result that every artery of consequence within these re- gions is surrounded by a more or less elaborate net-work, these plexuses in most cases bearing the names of the arteries which they accompany. In order to pn>\i'C, gangliated cord; SyG, sympathetic ganglia; CG, cervical sympathetic ganglion ; PvG, 'SubG, TrG, prevertebral, subsidiary and terminal ganglia; SpKf, splanchnic efferents; SoEf, somatic efferents; V, vessels of the spinal meninges; /, intestine. THE SYMPATHETIC SYSTEM OF NERVES. 1355 Constitution and General Arrangement. The sympathetic system serves to receive, rearrange and distribute the visceral filaments of the cerebro-spinal nerves, FIG. 1130. Common carotid artery Vagus nerve Superior cervical cardiac branch of vagus Middle cardiac br. of vagus Scalenus anticus Cray ramus cominunicans to VIII. cervical nerve VIII. cervical nerve I. thoracic nerve I. rib 1 1 1. thoracic nerve IV. thoracic ganglion Raini communicantes XII. thoracic ganglion Branch to I. lumbar ganglion Hyoid bone Interganglionic cord of sympathetic Thyroid cartilage [sympathetic Superior cervical cardiac branch of Middle cervical ganglion >-thyroid muscle Inferior cervical ganglion I. thoracic ganglion Right recurrent laryngeal nerve Combined cervical cardiac branches Right vagus [of sympathetic 1 nferior cervical cardiac branch of vagus Left middle and inferior cervical cardiacs of sympathetic Trachea Right bronchus (Esophagus Vena azygos Great splanchnic nerve Aorta *A Left vagus nerve Small splanchnic nerve - Least splanchnic nerve ** Diaphragm Dissection showing right gangliated cord of sympathetic and its branches. and to complete, by the interposition of one or more of its especial neurones, the path for the impulses brought by such fibres to the objective organs. It comprises 1356 HUMAN ANATOMY. two principal parts, the gangliated cords and the plexuses, with their associated ganglia. The gangliated cord (truncus sympatheticus), one of a symmetrically placed pair of gangliated trunks situated anterior or lateral to the bodies of the vertebra (Fig. 1133), begins in the head and extends through the neck, thorax and abdo- men to the lower portion of the pelvis. In the head it consists of a plexus of fibres continued up from the neck in an intricate interlacement which follows the internal carotid artery ; and in the pelvis it terminates by the two cords forming a loop or fine inosculation, situated anterior to the coccyx and containing the coccygcal ganglion or ganglion impar. The plexuses (plexus sympathetic!) are a series of more or less distinct col- lections of groups of nerve-cells (ganglia) and fibres, situated mainly in the axial line and giving off and receiving fibres connected with the various viscera of the trunk. The component elements of the plexuses and, indeed, of the entire sympathetic system, are the ganglia and the nerve-fibres. The ganglia, whilst following a general plan of arrangement as to number, size and position, are subject to wide individual variations and, moreover, where they approach a segmental type, as in the gangliated cord, there is considerable deviation from the arrangement presented by the cerebro-spinal system. A ganglion may or may not be connected with a spinal nerve, but it is always linked by association cords with other ganglia. According to their position, three varieties of ganglia are recognized. One group includes the prevertebral ganglia (g. trunci sym- pathetici), those found as nodes in the gangliated cord ; a second variety comprises the collateral or intermediate ganglia (g. plexuum sympatheticorum), which lie either on the peripheral branches of the gangliated cord or in a prevertebral plexus ; whilst to the third set belong the innumerable minute terminal ganglia, composed of nerve-cells which lie at or near the visceral distributions of the sympa- thetic fibres. Each ganglion consists of an indefinite number of multipolar neurones, which possess one axone and a number of dendrites, the whole cluster of cells being enclosed in an envelope of fibrous tissue. The axone is often medullated in the immediate vicinity of its cell, but usually loses this sheath as it gets farther and farther away from its origin. The course taken by the axone of a prevertebral gang- lion-cell may be one of three : (i) it may pass by means of an association cord into an adjoining prevertebral ganglion, (2) it may proceed as a constituent of a gray ramus communicans to join a spinal nerve or (3) it may follow a splanchnic efferent toward a viscus. The nerve-fibres encountered within the sympathetic system include two sets : (a) those derived from the cerebro-spinal system, which are usually medullated, and () the sympathetic fibres proper, for the most part nonmedullated, although as stated above, many of the axones possess a medullary sheath for a short distance beyond their origin from the nerve-cell. This distinction between medullated and nonmedullated fibres is, however, somewhat indefinite, since the medullated spinal fibres often become nonmedullated before terminating, whilst the sympathetic fibres occasionally are medullated throughout their course. Rami Communicantes. Where the typical segmental arrangement prevails, as in the thoracic region, each spinal nerve is connected with the adjacent gangliated cord by a pair of short nerve-trunks, known as the raini comnntnicantfs (Fig. 1 129). These are divided into two groups, the white rami and \\\G. gray rami, a distinction depending primarily upon the difference in the appearance of the strands when seen in the fresh condition ; this distinction, moreover, corresponds with the histological difference above noted white rami appearing so in consequence of the prepon- derance of opaque medullated fibres, and the gray rami possessing the darker tint on account of the absence of the refracting myelin coat. The rami communicantes pass directly between the spinal nerves and the gangliated cord, in relation to the latter joining either a ganglion or an association cord between nodes. The white rami communicantes are composed almost exclusively of the visceral branches of certain of the spinal nerves which use tin- sympathetic systrm as the pathway by which they arrive at their destination. They consist of fasciculi of THE SYMPATHETIC SYSTEM OF NERVES. 1357 medullated nerve-fibres derived from both the anterior and the posterior roots of the spinal nerves. The fibres arising from the anterior root are called the splanch- nic efferent fibres and those from the posterior root the splanchnic afferent. Not all of the spinal nerves, however, give off white rami, these strands of communication forming a thoraco-lumbar group, from the first or second thoracic to the second or third lumbar nerve inclusive, and a sacral group, derived from the second and third, or third and fourth sacral nerves. The cervical nerves do not give off white rami. The splanchnic efferent fibres are the axones of cells located within the lateral horn of the gray matter of the spinal cord. They furnish motor impulses to the unstriped muscle of the vessels and viscera, and secretory ones to the glands of the splanchnic area ; they also convey motor impulses to the heart. Leaving the spinal cord by way of the anterior root, they pass peripherally, enter a white ramus communicans and reach the gangliated cord. One of three courses is then pursued by these fibres : ( I ) they may end at once by forming arborizations around cells in the ganglion which they first enter, (2) they may pass through this ganglion, thence up or down through an association cord to end around the cells of a node of the gangliated cord above or below the level of entrance or (3) they may course through the gangliated cord and one of its visceral branches, and terminate in arborizations around the cells of a prevertebral or of a collateral ganglion. It is possible that in some cases the spinal efferents may continue without interruption through the several divisions of its path as far as the terminal ganglia. In any event, whether ending in the gangliated cord, the prevertebral, the collateral or the terminal ganglia, the cerebro-spinal fibre as such probably never actually gains the tissue of the organ, the last link in the path of conduction being supplied by a sympathetic neurone. The splanchnic afferent fibres are the sensory fibres of the splanchnic area and consist of the dendrites of cells situated within the intervertebral ganglia on the pos- terior roots of the spinal nerves. Whilst the greater number of these fibres are found in the white rami, a few are thought to be constituents of the gray rami. Beginning in the viscera, they run centrally, without interruption, through the terminal and collateral ganglia, through the gangliated cord and the white (or gray) rami to the spinal nerve, and thence after coming into relation with the cells of the ganglion of the posterior root, they pass by way of the posterior roots into the spinal cord. The gray rami communicantes are bundles of axones of sympathetic neu- rones which pass from the gangliated cord to each one of the entire series of spinal nerves. The reason of this generous provision will be evident when the purpose of the communications effected by the gray rami is recalled, namely, to provide sympa- thetic filaments to the outlying muscles and glands by way of the convenient path afforded by the distribution of the somatic nerves. Mingled with the gray fibres, a few of the medullated variety are often encountered ; these are probably partly splanchnic afferent fibres and partly medullated sympathetic fibres. Variation in the origin of the gray rami from the gangliated cord is not uncommon ; they may arise either from a ganglion or from the association cord between two ganglia ; after leaving the gangliated cord, a single ramus may divide and supply two spinal nerves ; or the reverse may happen, two or more rami arising independent!)' and either separately or after fusing, joining a single spinal nerve. The further course of the sympathetic fibres, after having joined the spinal nerves by way of the gray rami, is as follows : ( i ) they may course peripherally along with the anterior or posterior primary divisions of the spinal nerve and convey vasomotor, pilomotor or secretory impulses to the involuntary muscle and glands of the somatic area; or (2) they may enter the spinal canal byway of the anterior or posterior nerve-roots and be distributed to the spinal meninges, but not to the nervous column. According to Dogiel, it is probable that a small number of axones of sympathetic neurones enter the root-ganglia of the spinal nerves to end in arborizations around cells of type II (page 1008). The association cords (Fig. 1130) are the longitudinally disposed bundles of fibres comprising the interganglionic portion of the gangliated cord ; they contain both white and gray fibres. The gray ones are the axones of sympathetic neurones which are either passing between adjacent or more remote ganglia, or taking an upward or 1358 HUMAN ANATOMY. downward course before passing distally to their ultimate splanchnic distribution. The white fibres are either spinal splanchnic efferent or afferent fibres. The branches of distribution from the gangliated cord include the somatic and the visceral. The somatic branches are the rami communicantes ; the vis- ceral branches comprise the splanchnic efferents, which consist of both white and gray efferent fibres, as well as the white splanchnic afferents. THE CERVICO-CEPHALIC PORTION OF THE GANGLIATED CORD. The cervico-cephalic portion of the gangliated cord (pars cephalica et cervicalis systematis sympathetici) consists of a series of ganglia, usually three, but often only two, connected by composite association cords (Fig. 1131). It lies posterior to the FIG. 1131. Lower head of external pterygoid muscle Internal pterygoid muscle \ \ Auriculo-temporal nervi Internal carotid arterr Pneumogastric nerve- Inferior dental nerve- Spinal accessory nerve- Part of facial m Hypoglossal nerv Stylo-pharyngeus muscl Glosso-pharyngeal ner I. cervical ner Pneumogastric nerv Superior cervical ganglion of sympathetic Superior laryngeal nerve Descendens hypoglossi 1 1 . cervical nerve III. cervical nerv IV. cervical nerve Interganglionic association cord of sympathetic Middle cervical ganglion A Inferior cervical ganglio Branch to, I . thoracic ganglion Inferior cervical cardiac of sympathetic Recurrent laryngeal nerve Internal mammary artery Cartilage of I. rib Clavicular facet of sternum ' Lingual nerve External laryngeal branch uperior cervical cardiac of sympathetic Middle cervical cardiac of sympathetic Recurrent laryngeal nerve Middle cervical cardiac of C,.iiMi.,,n [pneumogastric carotid artery Inferior cervical cardiac of pneumogastric Deep dissection of neck, showing cervical portion of sympathetic gangliated cord and its connections. carotid sheath and anterior to the prevertebral fascia and the rectus capitis anticus major and scalenus anticus muscles. Inferiorly it is continued into the thoracic portion of the gangliated cord, and superiorly, at the base of the skull, it forms an intricate plexus around the internal carotid artery, in whose company it enters the THE SYMPATHETIC SYSTEM OF NERVES. 1359 cranium. The small ganglia connected with the trigeminal nerve the ciliary, the spheno-palatine, the otic and the submaxillary are regarded as outlying nodes be- longing to the cephalic continuation of the gangliated cord. The dominant characteristic of this portion is the absence of white rami, the spinal fibres present reaching the cervical region from the upper thoracic nerves by way of the association cord between the highest thoracic and lowest cervical gang- lion, around whose cells, as well as those of the higher cervical ganglia, the processes of the spinal neurones end. The distribution of the cervical portion of the cord includes pupillo-dilator fibres, cardio-accelerator fibres, vasomotor fibres to the arteries of the head, neck and upper extremities, pilomotor fibres to the integument of the head and neck, motor fibres to the involuntary muscles of the orbit and eyelids and secretory fibres to the glands. The branches consist, as elsewhere, of two groups, somatic and visceral, the former reaching their area of distribution by way of certain cranial and spinal nerves, and the latter, either alone or in conjunction with other nerves, forming plexuses which accompany blood-vessels and supply various viscera and vessels of the head, neck and thorax. The ganglia of the cervical portion include a superior, a middle and an inferior. The Superior Cervical Ganglion. The superior cervical ganglion (g. cervi' calc superius) (Fig. 1077) is the largest of the entire sympathetic series, measuring 2-3 cm. in length and 46 mm. in width. It rests posteriorly on the rectus capitis anticus major muscle opposite the second and third cervical vertebrae, with the internal carotid artery anterior to it and the vagus nerve to its lateral aspect. With the typical reddish-gray hue of the sympathetic ganglia, it is fusiform in outline, although it may present constrictions, usually three, which indicate its composition of four fused ganglia. The somatic branches consist of (i) rami communicantes and (2) communi- cating branches to the cranial nerves. 1. The rami communicantes consist of four gray rami which join the anterior primary divisions of the first four cervical nerves. 2. The communicating branches to the cranial nerves are given off from the upper portion of the ganglion, (i) one joining the petrous ganglion of the glosso- pharyngeal, (2) others entering the ganglia of the root and trunk of the vagus and (3) another joining the hypoglossal nerve. In addition to these there is frequently given off from the lower portion of the ganglion (4) a branch which joins the exter- nal laryngeal nerve. The visceral branches comprise : (i) the pharyngeal , (2) the superior cervi- cal cardiac , (3) the vascular and (4) the vertebral. 1. The pharyngeal branch or branches (rr. laryngopharyngei) arises from the antero-mesial aspect of the ganglion and courses obliquely inward and downward posterior to the carotid sheath to reach the surface of the middle constrictor of the pharynx. Here it unites with the pharyngeal branches of the glosso-pharyngeal and vagus nerves to form the pharyngeal plexus (page 1269), from which fibres are distributed to the muscles and mucous membrane of the pharynx, a few filaments joining the superior and external laryngeal nerves. 2. The superior cervical cardiac nerve (n. cardiacus superior) (Fig. 1131) arises as two or three twigs from the ganglion, with sometimes an additional filament from the association cord between the superior and middle ganglia. It courses down- ward anterior to the longus colli muscle in the posterior part of the carotid sheath, crosses the anterior or the posterior surface of the inferior thyroid artery, and then descends in front of the inferior laryngeal nerve. At the base of the neck the course of the nerve begins to differ on the two sides. The right nerve enters the thorax either anterior or posterior to the subclavian artery and accompanies the innominate artery to the aorta, where it enters the deep cardiac plexus, a few fibres passing to the anterior surface of the aorta. On the way down a few twigs join the inferior thyroid artery and with it enter and supply the substance of the thyroid body. The left nerve upon entering the thorax joins the common carotid artery, along whose lateral and anterior surfaces it courses to the aorta, upon reaching which it 1360 HUMAN ANATOMY. joins the superficial cardiac plexus. In some instances the nerve remains behind the carotid artery and joins the deep cardiac plexus. A pretracheal branch, derived from the loop between the superior cervical cardiac nerve and the inferior laryngeal, descends anterior to the trachea and is dis- tributed to the pericardium and the anterior pulmonary plexus (Drobnik. ) The superior cervical cardiac nerve communicates freely in the neck with the middle cardiac and other branches of the sympathetic, and with the external laryngeal and superior cervical cardiac branches of the vagus. In the thorax it inosculates with the inferior laryngeal nerve. Variations. The superior, as well as the other cardiac nerves, presents a considerable degree of variation, sometimes to so grea: an extent as to show no resemblance to the accepted typical plan of arrangement. It is sometimes absent, especially on the right side, and in such event appears to be replaced by a branch from the vagus or from the external laryngeal nerve. It may have no independent course, but join one of the other sympathetic cardiac nerves and reach its destination as a part of the latter. 3. The vascular branches comprise plexiform nerve-structures which accom- pany the terminal divisions of the common carotid artery. They consist of : (a) the external carotid branch and () the internal carotid branch. a. The external carotid branch (n. caroticus externus) (Fig. 1061) joins the external carotid artery and furnishes subsidiary plexuses which accompany the branches of that vessel. In addition to supplying vasomotor fibres to the external carotid tree, sympathetic filaments are furnished to two of the ganglia of the trigem- inal nerve. A branch (radix g. submaxillaris) from the plexus on the facial artery (plexus maxillaris externus) joins the submaxillary ganglion as its sympathetic root, and one or more, the smallest deep petrosal nerve, from the plexus on the middle meningeal artery (plexus meningeus), forms the sympathetic root of the otic ganglion. Ganglia of microscopic size have been described on these vascular plexuses. The most important of these, the temporal ganglion, is situated on the external carotid at the point of origin of the posterior auricular artery and is said to receive a filament of communication from the stylo-hyoid branch of the facial nerve. b. The internal carotid branch (n. caroticus internus) is apparently an upward, cranial extension of the superior ganglion (Fig. 1061). Ascending beneath the internal carotid artery, it accompanies that vessel into the carotid canal, where it divides into two plexuses, the carotid and the cavernous, the former ramifying on the lateral and the latter on the mesial aspect of the artery. While the individuality of these two is distinct, there are numerous fine fibres connecting them as they pass upward into the cranium. The carotid plexus (plexus caroticus internus) is located on the lateral or outer surface of the internal carotid artery at its second bend. In addition to supplying fine plexuses which accompany the branches of the artery to their ultimate ramifica- tions, the following arise from the carotid plexus : (aa) the carotid branches, (bb) the communicating branch to the abducent nerve, (cc} the communicating branches to the Gasserian ganglion, (dd ) the great deep petrosal nerve and (ee ) the small deep petrosal nerve, aa. The carotid branches consist of numerous fine twigs which are supplied to the internal carotid artery. bb. The communicating branch to the abducent nerve consists of one or two twigs which join the nerve as it lies in the wall of the cavernous sinus in close proximity to the internal carotid artery. cc. The communicating branches to the Gasserian ganglion comprise several small fila- ments which pass to the ganglion ; they usually arise from the carotid but sometimes are derived from the cavernous plexus. dd. The great deep petrosal nerve courses forward to the posterior end of the Vidian canal, where it joins the great superficial petrosal to form the I'idian nerve (page 1059), finally en- tering Meckel's ganglion as its sympathetic root. ee. The small deep petrosal nerve or ;/. carolicn-tymt>amcns joins the- tympanic plexus (page 1075), a structure formed by the tympanic branch of the glosso-pharyngeal, a filament from the geniculate ganglion of the facial nerve and the small deep petrosal nerve. In addition THE SYMPATHETIC SYSTEM OF NERVES. 1361 to furnishing twigs to the mucous membrane of the middle ear and vicinity, this plexus con- tributes a large part of the small superficial petrosal nerve, which joins the otic ganglion as its sensory root (page 1246). The cavernous plexus (plexus cavernosus) lies inferior and internal to the internal carotid artery and in intimate relation with the cavernous sinus. Its branches are: (aa) the carotid branches, (bb} the communicating branch to the oculo- motor nerve, (cc) the communicating branch to the trochlear nerve, (dd} the com- municating branch to the ophthalmic division of the trigeminus nerve, (ee~) a branch to the ciliary ganglion and Q/) branches to the pituitary body. FIG. 1132. Superior cervical cardiac branch ot sympathetic Sympathetic association cord Right vagus ne: Middle cervical ganglion Middle and inf. cervical card branches of sympathetic Recurrent laryngeal n Pulmonary branch of vagus Vena azygos major Phrenic nerve Right pulmonary artery Right auricular appendix Pericardium Superior cervical cardiac branch of sympathetic Superior cervical cardiac branch of vagus Middle cervical ganglion Middle cervical cardiac branch of sympathetic [of sympathetic cal cardiac branch cal ganglion Middle cervical cardia branch of vagus Inf. cervical cardiac branch of vagus Phrenic nerve Left vagus nerve Recurrent laryngeal nerve Left pulmonary artery Pulmonary veins Pulmonary orifice Mesial surface of lung Pericardium Dissection showing cardiac branches of pneumogastric nerves and of sympathetic cords ; aortic arch and branches and pulmonary artery partially removed ; pericardium laid open. aa. The carotid branches are distributed to the internal carotid artery. bb. The communicating branch to the oculomotor nerve joins the latter about at the point where it breaks up into its superior and inferior divisions. cc. The communicating branch to the trochlear nerve, sometimes derived from the carotid plexus, joins the trochlear in the wall of the cavernous sinus. dd. The communicating branch to the ophthalmic division of the trigeminus nerve joins the mesial surface of that nerve. ee. The branch to the ciliary ganglion (radices sj mpatheticae g. ciliaris) arises in the cranium and enters the orbit through the sphenoidal fissure, either as an independent structure or jointly with the nasal or with the oculomotor nerve. As the sympathetic root (radix media), it enters the upper posterior angle of the ciliary ganglion (Fig. 1058), either alone or as a common trunk with the sensory root. 86 1362 HUMAN ANATOMY. ff. The branches to the pituitary body consist of several tiny filaments which enter the substance of that body. 4. T4ie vertebral branches consist of two or three filaments which pass backward, pierce the prevertebral muscles and are distributed to the bony and liga- mentous structures of the upper portion of the vertebral column. The Middle Cervical Ganglion. The middle cervical ganglion (g. cervicale medium), a structure not infrequently absent, consists of one or two collections of nerve-cells situated posterior to the carotid sheath in the neighborhood of the inferior thyroid artery (Fig. 1131). It lies about the level of the sixth cervical vertebra and represents the fusion of two primitive cervical ganglia. The somatic branches are : (i) the gray rami communicantes and (2) the subclavian loop. 1. The gray rami communicantes arise either from the ganglion or from its upper or lower association cord. They consist of two trunks which pass backward and join the anterior primary divisions of the fifth and sixth cervical nerves. 2. The subclavian loop (ansa subclavia [Vieussenii] ) is a nerve, frequently double, which passes over the subclavian artery and joins the inferior cervical gang- lion sending twigs (plexus subclavius) to the subclavian artery and its branches and to the phrenic nerve. The visceral branches are: (i) the thyroid plexus and (2) the middle cervical cardiac nerve. In case of absence of the middle cervical ganglion, these branches arise from the interganglionic association cord between the superior and inferior ganglia. 1. The thyroid plexus (plexus thyreoideus inferior) consists of several fine inosculating twigs which accompany the inferior thyroid artery into the substance of the thyroid body. 2. The middle cervical cardiac nerve (n. cardiacus medius) (Fig. 1131) differs in its course on the two sides of the body. Descending in the neck, where it inosculates with the superior cervical cardiac and inferior laryngeal nerves, it passes, on the right side, either anterior or posterior to the subclavian artery, to the front of the trachea where it receives filaments of inosculation from the inferior laryngeal nerve. On the left side it enters the thorax between the common carotid and subclavian arteries. On both right and left sides it terminates posterior to the arch of the aorta by entering corresponding sides of the deep cardiac plexus. Variations. The gangliated cord, in the region of the middle ganglion, may lie posterior to the inferior thyroid artery or may be bifurcated, the artery lying between the two portions. The Inferior Cervical Ganglion. The inferior cervical ganglion (g. cervicale infenus) (Fig. 1079) is situated at the root of the neck, over the first costo-central articulation, between the neck of the first rib and the transverse process of the seventh cervical vertebra. In shape it is irregular, being flat, round or cres- centic, and it is often fused with or only partially separated from the first thoracic ganglion. Situated in the external angle between the subclavian and vertebral arteries it is usually connected above with the middle ganglion by an association cord and by the subclavian loop, the former, passing posterior to the vertebral artery, but sometimes, especially on the left side, forming a nervous ring around that vessel. The somatic branches consist of: (i) the grav rami communicantes^ (2) the subclavian loop and (3) a communicating branch to the inferior laryngeal ncrrc. 1. The gray rami communicantes consist of two nonmedullated trunks which join the anterior primary divisions of the seventh and eighth cervical nerves. 2. The subclavian loop (ansa subclavia [Vieussenii] ) has already been dt - scribed, as a branch of the middle cervical ganglion. 3. The communicating branch to the inferior laryngeal nerve frequently accompanies the inferior cervical cardiac nerve ; it joins the inferior laryngeal pos- terior to the subclavian artery. The visceral branches comprise : (i) the vertebral plexus 9sv& ( 2 ) tin- inferior cervical cardiac THE SYMPATHETIC SYSTEM OF NERVES. 1363 i. The vertebral plexus ( plexus vertebralis) is a closely woven net-work of fibres which follows the course and distribution of the vertebral artery in the neck and 'cranium. FIG. 1133. I. rib II. thoracic nerve Intercostal artery III. thoracic nerve Intercostal artery V. thoracic nerve XI. thoracic ganglion ; immedi- ately below it is the XII. XII. rib Diaphragm I. lumbar ganglion Ilio-hypogastric^ nerve II. and III. lumbar ganglia, fused Ilio-inguinal nerve IV. lumbar ganglion IV. lumbar nerve V. lumbar ganglion Interganglionic association cord I. sacral ganglion 1 Anterior crural nerve II. sacral ganglion III. sacral nerve IV. sacral ganglion I. thoracic ganglion partially blended with inferior cervical ganglion II. thoracic ganglion Aorta Great splanchnic nerve Small splanchnic nerve Least splanchnic nerve Semilunar ganglion and solar plexus Dissection showing thoracic, lumbar and sacral portions of right gangliated cord and their branches. 2. The inferior cervical cardiac nerve (n. cardiacus inferior) (Fig. 1132), sometimes arising from the first thoracic ganglion, descends in the thorax posterior to 1364 HUMAN ANATOMY. the subclavain artery, inosculates with the middle cervical cardiac and inferior laryngeal nerves and terminates in the deep cardiac plexus. THE THORACIC PORTION OF THE GANGLIATED CORD. The thoracic portion of the gangliated cord (pars thoracalis systematis sympa- thetic!) consists of a series of eleven, twelve, ten or even fewer irregularly triangular, fusiform or oval ganglia (gg. thoracalia), situated lateral to the bodies of the thoracic vertebrae, covered by parietal pleura and interconnected by association cords which lie anterior to the intercostal blood-vessels (Fig. 1133). The largest of the ganglia is the first, which is situated at the mesial end of the first intercostal space and is not infrequently fused with the inferior cervical ganglion. The location of the thoracic ganglia corresponds usually to the heads of the ribs, the lowest being placed anterior to the head of the twelfth rib and at the upper margin of the twelfth thoracic vertebra. A characteristic of the thoracic ganglia is the almost unvarying presence of white rami communicantes, all of the series, with the possible exception of the first, receiving these rami from the thoracic spinal nerves. They consist of an upper and a loti 'cr series, the former coming from the upper five nerves and coursing head-ward to enter and be distributed mainly by way of the cervico-cephalic portion of the gangliated cord ; and the lower arising from the lower seven and being distributed to certain thoracic and abdominal structures. As elsewhere, so here from each of the ganglia is given off a gray ramus communicans to a thoracic spinal nerve. The somatic branches of the thoracic portion of the gangliated cord are chiefly the gray rami communicantes. These arise from each of the thoracic ganglia and, in close proximity to the white rami, pass backward and join the anterior pri- mary divisions of all the thoracic spinal nerves. The visceral branches arise from the ganglia and their association cords and consist of gray splanchnic efferent and white splanchnic efferent and afferent fibres. The splanchnic afferent fibres have no sympathetic connections, and consist merely of tracts which carry impulses from the splanchnic area through the thoracic and spinal ganglia to the posterior roots of the spinal thoracic nerves. The splanchnic efferent fibres, after passing through the gangliated cord or its peripheral branches, form links with the cells of the collateral or terminal ganglia, from which nonmedullated axones are derived for the supply of various visceral or vascular structures. Those of the upper series are distributed mainly as branches of the cervical ganglia; while those of the lower series, from the sixth to the twelfth thoracic nerves inclusive, in the thorax supply the aorta and lungs with vasomotor fibres. Below the thorax their distribution is quite extensive, including, in conjunction with the vagus, viscero-inhibitory fibres for the stomach and intestine, motor fibres for a portion of the circular muscle of the rectum, vasomotor fibres for the abdominal aorta and its branches and secretory and sensory fibres for the abdominal viscera. The thoracic gangliated cord is peculiar in containing, along with the visceral fibres dis- tributed by its splanchnic efferents, many efferents proceeding from the spinal cord destined for regions supplied by way of the limb nerves arising from the cervical and lumbo-sacral segments of the spinal cord. In order to provide gray rami at appro- priate levels to join the spinal nerves the spinal efferents course both up and down in the gangliated cord beyond the thoracic region. In this manner the thoracic nerves, in addition to giving off the splanchnic efferents, provide vasomotor, pilo- motor and secretory filaments for the greater part of the lower half of the body. The visceral branches comprise : (i) the pulmonary branches, (2) the aortic branches and (3) the splanchnic nerves. 1. The pulmonary branches (IT. pulmonales) are derived from the second, third and fourth ganglia and proceed forward to join the posterior pulmonary plexus. 2. The aortic branches arise from the upper four or five ganglia and, after furnishing a few fine twigs to the vertebrae and their ligaments, inosculate around the thoracic aorta in the form of a fine plexus (plexus aorticus thoracalis). 3. The splanchnic nerves inn. splanchnic! > (Fig. 1133^ are three trunks which arise from the lower part of the thoraeir cord and are distributed to structures situated in the abdominal cavity. THE SYMPATHETIC SYSTEM OF NERVES. 1365 The great splanchnic nerve (n. splanchnicus major) arises by a series of roots from the gang-Hated cord from the fifth to the ninth ganglia inclusive. Descending along the antero-lateral aspect of the vertebral column, this nerve pierces the crus of - the diaphragm and enters the upper end of the semilunar ganglion, some of its fibres being traceable to the suprarenal body and the renal plexus. In the thoracic portion of its course is developed the great splanchnic ganglion (g. splanchnicum) from 1366 HUMAN ANATOMY. which, as well as from the nerve itself, are given off filaments for the supply of the oesophagus, the thoracic aorta and the vertebrae. Sometimes in the thorax it is divided and forms a plexus with the small splanchnic and in this event several small ganglia are present. This nerve consists mainly (four-fifths, according to Riidinger) of medullated fibres, which are direct continuations of white rami from as far up as the third thoracic aerve or even higher. The small splanchnic nerve (n. splanchnicus minor) arises from the ninth and tenth, or tenth and eleventh ganglia or from adjacent portions of interganglionic cords. Entering the abdomen by piercing the crus of the diaphragm either in association with or in close proximity to the great splanchnic, it terminates in that portion of the semi- lunar ganglion called the aortico-rcnal ganglion. The least splanchnic nerve (n. splanchnicus imus) arises from the lowest of the thoracic ganglia and may receive a filament from the small splanchnic, from which it occasionally takes origin. Piercing the diaphragm in company with the gangli- ated cord it terminates in the renal plexus. A fourth splanchnic nerve is rarely present. It is described by Wrisberg as having been found in eight cadavers out of a large number examined. It is formed by filaments from the cardiac nerves, aided by twigs from the lower cervical and upper thoracic ganglia. THE LUMBAR PORTION OF THE GANGLIATED CORD. The lumbar portion of the gangliated cord (pars abdominalis systeniatis sympa- thetici) (Fig. 1 134) consists usually of four small oval ganglia connected by association cords. There may be a decided increase in the number of the ganglia, as many as eight having been found, and, on the other hand, occasionally there are fewer than four, there being under these circumstances a compensatory increase in the size of the ganglia present. The lumbar portion of the sympathetic lies nearer the median line than does the thoracic, the cords being placed anterior to the bodies of the lumbar vertebrae and the lumbar vessels, along the mesial border of the psoas magnus, on the left side being partially concealed by the aorta and on the right by the inferior vena cava. It is connected with the thoracic portion by a small association cord, which passes either through or posterior to the diaphragm, and with the sacral portion by a cord which descends behind the common iliac artery. White rami communi- cantes are received from the first, the second and sometimes the third lumbar nerve, additional white fibres being derived from the lower thoracic nerves by way of the gangliated cord. The somatic branches comprise: (i) the white and (2) the gray rami communicantes. These are the longest to be found in the body, on account of the distance between the ganglia and the inttirvertebral foramina. They accompany the lumbar vessels and pass beneath the fibrous arches from which the psoas magnus takes origin. 1. The white rami communicantes are derived from the upper two or three lumbar nerves and join the upper ganglia or the adjacent portion of the inter- ganglionic cord. They contain splanchnic efferent and afferent fibres, which continue downward the distribution of the thoracic portion of the gangliated cord, including vasomotor and secretory fibres for the lower extremities, pilomotor fibres, vaso- motor fibres for the abdominal vessels, motor fibres for the circular musculature of the rectum and inhibitory fibres for the longitudinal muscle of the rectum. Fibres peculiar to the lumbar region include vasomotor nerves of the penis and motor fibres for the bladder and uterus, those to the bladder supplying the sphincter as well as the circular and longitudinal muscle-fibres, those to the last-mentioned group being inhibitory. 2. The gray rami communicantes are irregular in number and arrange- ment, sometimes a single one dividing and joining two lumbar nerves and sometimes two to five- passing to a single spinal nerve. The visceral branches vary considerably in their distribution, some joining the hypogastric plexus (plexus hypouastricus ), others the aortic plexus ( plexus aorticus abdominalis) and still others supplying the vertebrae and their ligaments. THE SYMPATHETIC SYSTEM OF NERVES. 1367 THE SACRAL PORTION OF THE GANGLIATED CORD. The sacral portion of the gangliated cord (pars pelvina systematis sympathetic!) consists of four ganglia interconnected by association cords, there being a consider- able degree of variation in both the number and the size of the ganglia (Fig. 1133). Lying anterior to the sacrum and internal to the anterior sacral foramina, it is con- nected above with the lumbar portion by a single or double association cord which lies posterior to the common iliac artery, and below it gradually approaches the median line and is united in front of the coccyx with its fellow of the opposite side by a loop or fine plexus in which is situated the single coccygeal ganglion or gang- lion impar. While this portion of the gangliated cord receives no white rami communicantes, in the sense of trunks passing from the sacral spinal nerves to the sacral ganglia, the visceral branches of the pudendal plexus pass directly to the pelvic plexus without traversing ganglia, and are considered as being homologous with white rami. In addition to these, white fibres reach the sacral from the lumbar portion of the gangliated cord. The somatic branches are the gray rami communicantes. They arise from the sacral ganglia and pass dorsally to join the anterior primary divisions of the sacral and coccygeal spinal nerves. The visceral branches are distributed through the medium of the pelvic plexus (page 1374) and furnish motor fibres to the longitudinal and inhibitory fibres to the circular musculature of the rectum, the chief motor fibres to the bladder (probably to the longitudinal muscular fibres), motor fibres to the uterus, the nervi erigentes or vaso-dilators of the penis and secretory fibres to the prostate gland. Additional strands, the parietal branches unite and ramify, anterior to the sacrum, with similar twigs from the opposite side and furnish filaments to the sacrum and coccyx and their ligaments, and to the coccygeal body. THE PLEXUSES OF THE SYMPATHETIC NERVES. The tendency of the sympathetic nerves to form intricate and elaborate plexuses (plexus sympathetici) is a marked feature of this portion of the nervous system. They lie, in the main, anterior to the plane of the gangliated cord and consist of fibres alone or of fibres and ganglia, from which smaller plexuses or branches pass to the viscera. Some of them are of sufficient importance, size and individuality to merit separate descriptions ; such are the cardiac, the pulmonary, the cesophageal, the solar and the pelvic. The pulmonary and cesophageal plexuses have been described in connection with the vagus nerve (page 1272). THE CARDIAC PLEXUS. The cardiac plexus (plexus cardiacus) consists of an interlacement of nerve-fibres, containing one well-marked ganglion, to which accessions are brought by the vagus and sympathetic nerves and from which fibres are furnished to the heart and, to a slight degree, the lungs. It comprises two portions: (i) the superficial cardiac plexus and (2) the deep cardiac plexus. 1. The superficial cardiac plexus (Fig. 1135) is much the smaller of the two and consists of a fine inosculation of nerve-fibres in the meshes of which is con- tained a small ganglion, the ganglion of Wrisberg (g. cardiacum [Wrisbergi] ). It is situated in the concavity of the arch of the aorta, between the obliterated ductus arteriosus and the right pulmonary artery. Tributary to it are the superior cervical cardiac branch of the left gangliated cord and the inferior cervical cardiac branch of the left vagus, whilst its fibres of distribution contribute to (a) the right coronary plexus, () the left half of the deep cardiac plexus and, along the left pulmonary artery, (r) the left anterior pulmonary plexus. 2. The deep cardiac plexus (Fig. 1135), considerably larger than the su- perficial, is located above the bifurcation of the pulmonary artery, posterior to the arch of the aorta and anterior to the lower end of the trachea. It comprises two 1 3 68 HUMAN ANATOMY. distinct portions, a right and a left, united by numerous fibres around the lower end of the trachea. The right portion receives as tributaries all of the cardiac branches of the sympathetic, vagus and inferior laryngeal nerves of the right side. The left portion receives all of the cardiac branches of the left vagus and sympathetic nerves, except the two which enter the superficial plexus (the superior cervical cardiac branch of the left gangliated cord and the inferior cervical branch of the left vagus), with the addition of filaments from the left inferior laryngeal nerve and from the superficial cardiac plexus. FIG. 1135. Thyroid body Superior cervical cardiac branch of sympathetic Clavicle Combined cervical cardiac brs. of right sympathetic I. rib Phrenic nerve- Pericardium, cut edge Right coronary artery Superior cervical cardiac branch of sympathetic Sympathetic nerve Vagus nerve Superior cervical cardiac branch of vagus Middle cervical ganglion Scalenns anticus Middle cervical cardiac of sympathetic Brachial plexus Inferior cervical ganglion Inf. cervical cardiac l>r. of sympathetic, cross- Phrenic nerve I ing vertebral artery Subclavian artery to join middle br. Inf. cervical cardiac branch of vagus Recurrent laryngeal nerve Phrenic nerve Recurrent laryngeal nerve 1 i ardiac plexus, showing ganglion of Wrisberg Pulmonary artery Left coronary artery Dissection showing constituents of superficial cardiac plexus, other cardiac nerves and right coronary plexus. From the right portion of the plexus arises the right or anterior corona plexus (plexus coronarius cordis anterior), to which fibres are sent from the supert'u-ial plexus. This plexus reaches the heart by coursing along the ascending aorta and then follows the right coronary artery, in whose course it distributes fibres to adjacent portions of the heart. Other branches from the right portion join the superficial cardiac plexus and the right anterior pulmonary plexus. From the left portion originates the left or posterior coronary plexus (plexus coronarius cordis posterior) which, reinforced by fibres from the superficial plexus, follows the course and distribution of the corresponding artery. The left portion contributes filaments to the superficial cardiac and left anterior pulmonary plexuses. THE SOLAR PLEXUS. The abdominal and pelvic cavities are innervated by the solar, hypogastric and pelvic plexuses, composed of the visceral branches of the lower thoracic, lumbar and upper sacral portions of the gangliated cord, in conjunction with the central nervous THE SYMPATHETIC SYSTEM OF NERVES. 1369 axis by means of the rami communicantes of the lower thoracic and upper lumbar nerves and the visceral branches of the pudendal plexus. The solar or epigastric plexus (Fig. 1136), the largest of the series, is situated in the upper abdominal region, posterior to the stomach, anterior to the aorta and the crura of the diaphragm, superior to the pancreas, between the suprarenal bodies and around the origins of the cceliac axis and the superior mesenteric artery. It is continuous above with the diaphragmatic plexus, laterally with the suprarenal and FIG. 1136. Phrenic nerve Diaphragmatic gangli- Great splanchnic nerve Right semilunar ganglion Spermatic artery III. lumbar ganglion Aortic plexus ~ Hypogastric plexus Disc between V. lumbar vertebra and sacrum I. sacral ganglio: Left common iliac vein Left pelvic plexus Dissection of abdominal sympathetic nerves, showing solar, hypogastric and secondary plexuses. renal plexuses, below with the superior mesenteric and aortic plexuses and, by means of the aortic and hypogastric plexuses, with the two pelvic plexuses. Con- tributory to it are the right vagus and the great and small splanchnic nerves. The fully formed plexus consists of two portions: (i) the semilunar ganglia and (2) the cceliac plexus. i. The semilunar ganglia (gg. coeliaca) (Fig. 1136), the largest of the ganglionic elements in the solar plexus, are situated upon the crura of the diaphragm at the superior and lateral portions of the plexus, partly overlapped by the suprarenal bodies and separated from each other by the cceliac axis and the superior mesenteric artery ; the right one is partially covered by the superior vena cava and the two are HUMAN ANATOMY. connected by cords which pass transversely above and below the root of the cceliac axis. The upper end of each is expanded and receives the termination of the great splanchnic nerve, while the lower portion, the aortico-renal ganglion, is partially detached and receives the small splanchnic nerve. A third portion, located below and to the right of the root of the superior mesenteric artery, is called the superior mesenteric ganglion (g. mcsentericum superius). From each semilunar ganglion branches emerge in all directions to join those plexuses which are continuous with the solar. 2. The cceliac plexus (plexus coeliacus) embraces the cceliac axis and consists of a dense felt-work of nerve-fibres, in which are embedded numerous small ganglia, and which is joined by branches from both semilunar ganglia and from the right FIG. 1137. Kiisiform cartilage -Liver, Spigelian lobe "CEsophagus - Left vagus nerve -Right vagus nerve -Aorta - Gastric artery and plexus" Splenic artery and plexus -Hepatic artery and plexus "Left gastro-epi- ploic artery -Branches of left vagus Gall-bladde Hepatic artery. and plexus Right gastro-epi- ploic artery and plexus Dissection showing gastric and hepatic plexuses. vagus. Inferiorly it is continued into the superior mesenteric and aortic plexuses and from it arise the coronary, hepatic and splenic plexuses. The gastric plexus (plexus gastricus superior) accompanies the gastric artery along the lesser curvature of the stomach, inosculates with both vagus nerves and distributes branches which run for a short distance beneath the peritoneum and then enter and supply the deeper coats of the stomach. The hepatic plexus (plexus hepaticus ) traverses the lesser omentum in company with the bile duct, the hepatic artery and the portal vein and, after inosculating with fibres of the left vagus, enters the liver, in which it ramifies. In addition to its terminal distribution it contributes filaments to the right suprarenal plexus and furnishes offshoots which follow the collateral branches of the hepatic artery, sup- plying the areas to which these arteries are distributed. The splenic plexus (plexus licnalis), which surrounds the splenic artery, receives accessions from the left semilunar ganglion and the right vagus and enters the spleen. Branches of the plexus accompany the branches of the splenic artery and are distributed similarly. THE SYMPATHETIC SYSTEM OF NERVES. 1371 The diaphragmatic or phrenic plexus (plexus phrenicus) is derived from the upper portion of the semilunar ganglion and accompanies the phrenic branch of the abdominal aorta to the diaphragm, the right being larger than the left. After supplying some filaments to the suprarenal body, it enters the musculature of the diaphragm and there unites with the phrenic nerve from the cervical spinal plexus. At the point of inosculation, on the right side only, near the suprarenal body and on the under surface of the diaphragm, is a small ganglion called the phrenic ganglion (g. phrenicum). From it are given off branches to the suprarenal body, the inferior vena cava and the hepatic plexus. The suprarenal plexus (plexus suprarenalis) arises from the lateral aspect of the semilunar ganglion and is joined by filaments from the diaphragmatic and renal FIG. 1138. Liver, inferior surface Gastrq-epiploica dextra with plexus Pylqric artery with plexus Castro-duodenal artery with plexus Hepatic artery with plexus Inf. pancreatico-duodenal artery Sup. pancreatico-duodenal artery Pancreas, cut Superior mesenteric artery with plexus Duodenum Stomach, turned up Gastro-epiploica sinistra with plexus Right vagus nerve Gastric artery with plexus .Splenic artery with plexus Spleen \ Dissection showing gastric, hepatic and splenic plexuses; stomach has been turned up and part of pancreas removed. plexuses. It consists mainly of medullated fibres and, while very short, is made up of a number of filaments and is of considerable size. Numerous tiny ganglia are scattered throughout the meshes of this plexus. The renal plexus (plexus renalis) is derived mainly from the aortico-renal ganglion, additional fibres being contributed by the smallest splanchnic nerve, some- times by the small splanchnic, and by the aortic and suprarenal plexuses ; there is occasionally present a twig from the first lumbar ganglion. Entering the hilum of the kidney with the renal artery, the plexus splits up and ramifies in the renal sub- stance. In its course along the artery a number of ganglia of varying size, called the renal ganglia, are found. In addition to supplying the kidney, filaments are furnished to the spermatic plexus and to the ureter, and on the right side to the inferior vena cava. 1372 HUMAN ANATOMY. The spermatic plexus (plexus spermaticus) follows the course of the spermatic artery through the abdomen, inguinal canal and scrotum, inosculating with filaments which arise in the pelvis and accompany the vas deferens and its artery to the scrotum. It is derived from the renal and aortic plexuses, a small spermatic gang- lion being situated at the point of origin of the fibres contributed by the aortic plexus. The ovarian plexus (plexus ovaricus), arising similarly to the spermatic, accompanies the ovarian artery and is distributed to the ovary, the oviduct, the broad ligament and the uterus. In the broad ligament it inosculates with those pelvic fibres which constitute the uterine plexus. FIG. 1139. Hepatic artery and plexus Transverse colon Splenic artery Jejunum Duodenum Superior mesen- teric artery and plexus Superior mesenteric artery Termination of ileum Caecum Dissection showing hepatic and superior mesenteric plexuses ; transverse colon has hi-en turned up. The superior mesenteric plexus (plexus meseiitcricus superior) (Fig. 1139"), firm in texture and containing a large admixture of mcdullated fibres, is continuous with the coeliac plexus above and with the aortic below. Its fibres are derived from the semilunar ganglia, the cceliac plexus and the right vagus. Situated in the root of the plexus and lying below and to the right of the origin of the superior mesen- teric artery is the superior mesenteric ganglion (j. mcsciitericum supcrius), from which a number of the fibres of the plexus arise. Accompanying the superior mesenteric artery, the plexus gives off subdivisions which correspond to and follow the course of the branches of that artery, supplying filaments to the small intestine, the ccecum, the vermiform appendix and the ascending and transverse colons. As THE SYMPATHETIC SYSTEM OF NERVES. 1373 the fibres approach the distal edge of the mesentery some of them leave the vessels and form minute independent plexuses from which filaments pass to the gut. The aortic plexus (plexus aorticus abdominalis) (Fig. 1136) is the direct downward extension of the solar. Embracing the aorta, it extends from the origin of the superior mesenteric artery above to that of the inferior mesenteric below, and is connected with the semilunar ganglia and with the renal and superior mesenteric plexuses superiorly and with the hypogastric inferiorly. It consists of a pair of FIG. 1140. Aorta Renal ganglion / / Ureter ^Ovarian artery Nerve from aortic plexus Ovarian vein Ovarian artery Ureter Branches from renal plexus Vena cava inferior Ovarian vein Part of inferior mesenteric plexus Inferior mesenteric artery . . ... Left common iliac vein Ilium, sec- tional surface - Pelvic plexus Branches of right pelvic plexus to. rectum Right ovary Fallopian tube Ligament of ovary Dissection showing hypogastric and pelvic plexuses. symmetrically placed nerve trunks situated at the sides of the aorta and connected with each other by several branches which lie anterior to that vessel ; filaments from the lumbar ganglia join the main cords of the plexus. It gives off the inferior mes- enteric plexus, sends contributions to the suprarenal, renal and spermatic or ovarian, supplies filaments to the aorta and inferior vena cava and terminates in the hypo- gastric plexus. The inferior mesenteric plexus (plexus mesentericus inferior) is derived from the left portion of the aortic plexus and follows the course and distribution of the artery for which it is named. Situated a short distance beyond its origin is the small inferior mesenteric ganglion. From this plexus branches are 1374 HUMAN ANATOMY. distributed to the descending and sigmoid colons and to the upper portion of the rectum. The hypogastric plexus (plexus hypogastricus) (Fig. 1140), the continuation of the aortic, lies on the posterior wall of the pelvis in the angle between the common iliac arteries, and enclosed in a firm investment of fibrous tissue. In addition to the fibres derived from the aortic plexus, others are contributed by the lumbar ganglia, and the resulting, intricate interlacement, in which there are no ganglia, constitutes the hypogastric plexus. It supplies the pelvic contents and at its lower end divides into the two pelvic plexuses. The pelvic plexuses (plexus hypogastrici inferiores), (Fig. 1140) the terminal divisions of the hypogastric, are situated lateral to the rectum and to the vagina in the female. They comprise fibres derived from the hypogastric plexus and from the upper part of the sacral portion of the gangliated cord, aided by the visceral branches of the pudendal. plexus, all of these forming an elaborate net-work, in which are dotted numerous small ganglia. The completed structure follows the course of the internal iliac artery, around whose branches it sends derivatives for the supply of the pelvic contents. The hemorrhoidal plexus (plexus hemorrhoidalis medius) arises from the upper portion of the pelvic plexus and after inosculating with the superior hemorrhoidal branches (nn. hemorrhoidales superiores) of the inferior mesenteric plexus, are distributed to the rectum. The vesical plexus (plexus vesicalis) consists of branches of the pelvic which accompany the vesical arteries to the lateral and inferior portions of the bladder, after reaching which they leave the vessels and split into small twigs for the supply of the bladder, some filaments going to the ureter, the vas deferens and the seminal vesicle. The prostatic plexus (plexus prostaticus) comprises a number of nerves of con- siderable size and is situated between the lateral aspect of the prostate gland and the mesial surface of the levator ani muscle. After furnishing twigs to the prostatic urethra, the neck of the bladder and the seminal vesicle, it continues forward as the cavernous plexus. The cavernous plexus (plexus cavernosus penis) extends forward through the triangular ligament and the compressor urethrae muscle to the dorsum of the base of the penis, where it receives some communicating filaments from the pudic nerve. After supplying branches to the apex of the prostate gland and the membranous urethra, the plexus terminates by breaking up into (i) the small and (2) large cavernous nerves of the penis. 1. The small cavernous nerves (nn. cavernosi penis minores) pierce the fibrous envelope of the crus penis and end in filaments which supply the erectile tissue of the corpus cavernosum. 2. The large cavernous nerve (n. cavernosus penis major), consisting mainly of medullated fibres, passes directly along the dorsum of the penis, giving off fila- ments which enter the substance of the corpus cavernosum. At about the middle of the body of the penis it inosculates with the dorsal nerve of the penis, both of these nerves sending twigs to the corpus spongiosum. The utero-vaginal plexus (plexus uterovaginalis) corresponds to the prostatic plexus of the male and consists of two portions : (i) the uterine plexus and (2) the vaginal plexus. 1. The uterine plexus (plexus uterinus) is derived from the pelvic plexus and is supplemented in its distribution by the visceral branches from the pudendal pk-xus. These fibres accompany the uterine vessels along the side of the uterus, most of them entering the cervix and the lower portion of the body of the uterus. They inoscu- late with fibres from the ovarian plexus and in their meshes arc found many small ganglia, a collection of which is located near the cervix uteri and is called the gang- lion cervicale. 2. The vaginal plexus (plexus va^iualis) arises from tin- lower part of the pelvic and comprises mainly fibres derived from the viseeral branches of the puden- da! plexus. It supplies the- vagina and the urethra and continues forward as the cavernous plexus of the clitoris (plexus cavernosus clitoridis ). DEVELOPMENT OF PERIPHERAL NERVES. 1375 Practical Considerations. The cervical sympathetic may be injured by deep wounds of the neck, or may be compressed by tumors, abscesses or aneurisms. It supplies motor fibres to the involuntary muscles of the orbit and eyelids, vasomotor fibres to the face, neck and head, dilator fibres to the pupil, accelerator fibres to the heart and secretory fibres to the salivary glands. If it is irritated, some or all of the following symptoms will be present : the palpebral fissure will open wider, the eyes will be protruded, the skin of the face and neck will be pale and cold, the pupils dilated, and the sweat, nasal secretion and saliva diminished. Section or destruction of the cervical sympathetic will give the opposite symptoms. The cervical sympathetic has been removed for epilepsy, glaucoma and exoph- thalmic goitre. The greatest success has been obtained in the last condition, espe- cially by Jonnesco, who advises this procedure in hysteria, chorea, and tumors of the brain, as well as in the above-mentioned conditions. It may be excised through an incision anterior to the sterno-mastoid, as it lies posterior to the carotid sheath on the prevertebral fascia. The superior cervical ganglion is the largest and lies opposite the transverse processes of the second and third vertebrae. Branches of it go upward along the external and internal carotid arteries, the ascending branch passing along the internal carotid artery through its bony canal in the base of the skull to form the carotid and cavernous plexuses, both of which are really parts of one plexus arranged around this artery. Other branches communicate with the cranial nerves, the pharyngeal nerves and the superficial cervical cardiac nerve. The middle cervical ganglion is the smallest, lies on the inferior thyroid artery oppo- site the sixth cervical vertebra and is in danger in the ligation of that artery. The inferior ganglion, intermediate in size between the other two, lies in a depression between the neck of the first rib and the transverse process of the seventh cervical vertebra. The branches of the upper four or five thoracic ganglia of the sympathetic enter into the supply of the thoracic viscera, but the branches of the lower seven or eight form the splanchnic nerves and go to the supply of the abdominal viscera through the solar plexus and its extensions into other sympathetic plexuses of the abdomen. It is of interest and importance to observe that those intercostal nerves corresponding in their origin from the spinal cord with the ganglia giving off the splanchnics, together with the first two lumbar nerves, the ilio-hypogastric and ilio-inguinal, supply the abdominal wall with motor and sensory branches. In this way the same segments of the spinal cord supply the abdominal viscera as well as the skin and muscles over them. A similar arrangement of the nerves is seen in the joints, where the same nerves supply the skin covering the joint, the muscles which move it, and the joint structures. As a result of this, when necessary, all parts of the joint act in sympa- thy. In an inflammation of the joint the skin becomes sensitive, tending to ward off interference, and the muscles become rigid, preventing motion and favoring rest. In a similar manner the abdominal muscles become rigid to protect inflamed viscera underneath, the muscles of one side only if the inflammation is localized to one side, but the muscles of both sides if a general peritonitis is present. DEVELOPMENT OF THE PERIPHERAL NERVES. The manner in which the nerve-fibres composing the peripheral nervous system develop from the primary cells, the neuroblasts, has been indicated in the previous sketch of their histogencsis given on page ion. It remains, therefore, to describe briefly at this place the more important features of their morphogenesis. The fundamental fact has been repeatedly empha- sized, that efferent or motor fibres are outgrowths from neurones situated within the cerebro- spinal axis, whilst all afferent or sensory fibres arise from cells placed outside this axis and within the ganglia located along the course of the nerves. It is evident, furthermore, that the efferent constituents of the peripheral nerves have their nuclei of origin within the spinal cord or brain and grow outward, as axones, to their destinations. The afferent fibres, on the other hand, proceed in both directions, the axones early growing centrally to join the nervous axis, hence, having usually a short course, being represented by the entering sensory roots. The dendrites grow in the opposite direction and contribute the sensory fibres that extend often to remote parts of the body. Whilst in the lowest vertebrates, the amphioxus and the cyclos- tomes, the ventral and dorsal roots of the spinal nerves remain distinct, in the higher types they join to form the mixed nerve, which typically divides into the anterior, posterior and 1376 HUMAN ANATOMY. visceral divisions. Such typical division, however, is displayed only by those spinal nerves dis- tributed to that part of the trunk in which the primary segmentation is retained, namely, the thoracic region, where the skeletal muscular, and vascular segments, as well as the nerves, retain their identity. In the other parts of the spinal series, the cervical and the lumbo-sacral, where provision is made for the supply of the highly differentiated musculature of the ex- tremities from a number of cord-segments, the nerves early unite to form plexuses from \vhich the limb-trunks grow out, an arrangement well adapted for the distribution of fibres from different sources without undue multiplication of nervous paths. Concerning the factors which guide the young nerve to its destination with such remarkable constancy, nothing is known, but it may be assumed that these are probably influences of a physical character, the developing nerve taking the path offering least resistance. The visceral division of the spinal nerve, to which reference has been made, corresponds to the white ramus communicans given off by certain of the thoracic and lumbo-sacral nerves. These splanchnic fibres differ from the somatic efferent ones in taking their origin from cells which occupy a more lateral position within the gray matter of the spinal cord than do the root-cells giving rise to the motor fibres destined for the skeletal muscles. Whilst the great majority of the splanchnic fibres reach the ramus of communication by way of the anterior root, some few probably traverse the posterior or sensory root and its ganglion before continuing their course to the sympathetic. The sensory fibres described within the anterior roots of the spinal nerves are not actual constituents of these roots, which are exclusively motor, but recurrent meningeal twigs destined for the membranes of the cord. The Cranial Nerves. From the preceding account of these nerves, it is evident that the optic nerve differs morphologically widely from an ordinary nerve, since it may be regarded as a modified outlying portion of the brain. Its development may be omitted, therefore, from this series and appropriately considered in connection with the development of the eye (page 1482). There is sufficient reason, as will appear later, for regarding the hypoglossal nerve as a cranially displaced member of the spinal series. Of the remaining nerves, only the olfactory and auditory are purely sensory ; the third, fourth, sixth and eleventh are exclusively motor ; and the fifth, seventh, ninth and tenth are mixed, the motor strands taking origin from the neu- rones within the brain-stem, while the sensory ones are derivations from the neurones lying within the ganglia connected with the afferent fibres. Although at first sight the trigeminus closely corresponds to a spinal nerve in the possession of a gangliated sensory and a motor root, critical examination of the origin of its motor fibres discloses an important differ- ence, namely that they arise from the lateral nuclei and not from the mesial, which correspond to collections of ventral root-cells. A similar difference also appears between the efferent trigeminal fibres and those of the eye-muscle nerves, the latter arising from groups of root-cells occupying a position close to the mid-line. In order to appreciate the significance of this differ- ence, reference must be made to the primary division of the musculature of the head already referred to in connection with the grouping of the muscles (page 472 ). It was there pointed out that it may be assumed that the segmented condition of the trunk musculature, as expressed by the metameres, is continued into the cephalic region but with subsequent suppression of the middle members of the possible nine or ten segments which constituted the original quota of head-metameres. Of those persisting two groups are recognized one including the first three metameres, giving rise to the ocular muscles and being supplied by the third, fourth and sixth nerves ; the other including the last three or four, producing the tongue-muscles, and being sup- plied by the twelfth nerve. To these groups of cephalic metameres is added a third, the branchiomeres, which are regarded as representing a supplementary series connected with the branchial arches and not present in the trunk. The branchiomeres receive the mixed cranial nerves, whose motor filaments supply muscular masses surrounding the visceral tubes ( digestive and respiratory), and arise from the lateral motor nuclei. It follows that none of the cranial nerves contain fibres from all these sources, in the case of the fifth, seventh, ninth and tenth, the fibres being derived from the lateral motor and the sensory nuclei, and in the case of the third, fourth and sixth, from the mesial (ventral) nuclei alone. From the primary conditions, as revealed by studies on the lower vertebrates, it is probable that the dorsal fibres also are by no means of similar morphological value, since some represent a somatic sensory system, as those distributed to the integument, and others belong to a visceral sensory one, as those distributed to the walls of the mouth, pharynx and larynx. Following the principle already emphasized, the motor fibres of the cranial nerves grow from the brain outward, while the sensory ones extend centrally from the ganglia of the nerves associated with the brain. The cranial and spinal nerves appear on the surface of the neural tube at a very early period, their presence being conspicuous by the end of the fourth week (Fig. 901 ). The olfactory nerve is developed in connection with the epithelial lining of the primary olfactory pit (page 1429). As early as the end of the first fiL-tal month, in the human embryo, cells corresponding to neuroblasts appear in the anlage of the olfactory organ. From these elements processes soon grow brainwanl, nucleated tracts indicating the formation of the later olfactory fibres. The cell-bodies of the young neurone mi-rate so that for a time their position DEVELOPMENT OF PERIPHERAL NERVES. 1377 is no longer within the primary epithelium, but deeper and within a cell aggregation known as the olfactory ganglion. The neurones, however, retain connection with the olfactory epithe- lium by means of their peripherally directed processes, which correspond to dendrites, and with the brain by means of their axones. With the thickening of the olfactory epithelium which sub- sequently occurs, the peripheral fibres and their nuclei comes to lie entirely within the epithelial stratum and persist as the olfactory cells, whose centrally directed processes form the olfactory filaments that end as arborizations within the characteristic olfactory glomeruli. The first cranial nerve is peculiar in the superficial position of its cell-bodies and in the extreme shortness of its dendrites, which are represented by the rod-like fibres of microscopic length extending from the cell-bodies toward the free surface of the olfactory mucous membrane. This superficial position of the olfactory neurones is regarded as an unusual persistence of the primary condition of all sensory elements and as evidence of the archaic nature of the olfactory nerves. FIG. 1141. Superior colliculus Mid-brain ineal body Diencephalon Median geniculate body Pallium Inferior colliculus Oculomotor nerve Trochlear nerve Cerebellum Trigeminal nerve Auditory nerve Glosso-pharyngeal nerve Vagus nerve Spinal accessory nerve Rhinencephalon Optic stalk nferior part of III. ventricle Facial nerve Abducent nerve Hypoglossal nerve Reconstruction of brain of human embryo of four and one half weeks (10.2 mm.); outer surface, showing developing nerves. X 12. Drawn from His model. The optic nerve is so inherently a derivative of the cerebral and optic vesicle, that its develop- ment is appropriately considered with that of the eye (page 1482) ; moreover, its morphological significance being so at variance with that of the other nerves, it may be omitted from further discussion in the series now being described. The oculomotor nerve being strictly a motor nerve has much in common in its mode of formation with the ventral root of a spinal nerve, with which it is homologous. The nerve originates as an outgrowth from a group of neuroblasts, which occupies the ventral zone about the middle of the mesencephalon. From these neurones, visible in the fourth week in the human embryo, the axones proceed as a converging group of fibres which, piercing the wall of the brain-tube close to the mid-line, appear on the ventral surface of the brain-stem as the fibres of the third nerve. Although by some regarded as possessing a transient rudimentary dorsal root that early entirely disappears, thus bringing the nerve of a cranial myomere into close correspondence with those of the spinal series, it is doubtful whether such structure is usually present, the suppression of the dorsal portion of the nerve being complete. Soon after its for- mation, the main trunk undergoes division into a smaller upper and a larger posterior limb, which foreshadow the superior and inferior divisions of the mature nerve. The trochlear nerve, although springing from a central group of neuroblasts in close proximity with those giving rise to the third, is peculiar in the course of its axones. Instead of maintaining a ventral course, these proceed dorsally and become superficial on the upper (dorsal) aspect of the hind-brain, piercing the plate which later becomes the superior medul- 8? 1378 HUMAN ANATOMY. lary velum. As in the case of the third, so for the trochlear an abortive transient dorsal ganglion and root have been described (Martin). If present these must be regarded as ex- ceptional and not constant features. The trigeminal nerve is a mixed nerve and therefore takes its origin differently for its two roots. The motor one is developed from a series of neuroblasts, which lie at some distance from the mid-line within the wall of the neural tube, at a position corresponding to the junction of the dorsal and ventral zones of the mid-brain and metencephalon. The axones of these neuroblasts grow forward and converge to the surface of the later pons at a position close to where the ingrowing sensory fibres join the neural tube. The sensory fibres are the axones of neurones located within the Gasserian ganglion. The latter is derived as a ventrally directed outgrowth from the ectoblast of the roof of the hind-brain, with which it remains attached for a short time, but later becomes entirely separated. The neuroblasts acquire a bipolar form, one set of processes, the axones, growing centrally to establish secondary connections with the hind-brain as the large sensory root, while the others, the dendrites, extend peripherally into the substance of the fronto-nasal and maxillary processes to form the ophthalmic and maxillary nerves and into the mandibular process to form, in conjunction with the smaller motor root, FIG. 1142. Reconstruction of brain and cranial nerves of pig embryo; cranial nerves indicated by figures ; ci-C3, cervical spinal nerves; in connection with seventh nerve., l.s.p, large superficial petrosal ; ch.ty., chorda tympani ; fa., facial ; j., ., vagus ganglia of root and trunk ; com., comtnissuraF extension of ganglion of root ; f, Froriep's hypoglossal ganglion, (f. T.Lewis.) the mandibular division of the trigeminus from the ganglion ridge. Provision for the ciliary ganglion is made early by the migration of cells from the major ganglion along the de- veloping ophthalmic division. Similar migrations along the other divisions give rise to the spheno-palatine, the otic and the submaxillary ganglia. The later histological characteristics of these cells, as well as their mode of origin, warrant the view that the ciliary ganglion, as well as the others connected with the trigeminus, belong to the sympathetic system. On entering the wall of the brain-tube, the bulk of the sensory trigeminal fibres assume a longitudinal course and early establish the tract of the spinal cord. The abducent nerve developes, in a manner identical with the third and fourth, from a median group of cells occupying the ventral zone of the upper part of the hind-brain. In the human embryo of about four and a half weeks (Fig. 1141), the nerve appears at its super- ficial origin mesial to the Gasserian ganglion. The root-fibres early consolidate into a compart strand. The facial nerve being a mixed one also arises from a double source, its motor fibres taking origin from efferent neuroblasts situated in the ventro-lateral wall of the metencephalon. In contrast to the direct ventral course of the axones of the mesial motor nerves, those of t lie- facial pursue a path to the surface of the brain-stem even more indirect than that taken by the lateral motor fibres of the other mixed nerves. Proceeding as the axones of neuroblasts lying within the lateral part of the ventral zone of the wall of the hind-brain, they are directed dor- sally, then grow forward, turn outward and, finally, ventrally to gain emergence from the brain. The sensory portion of the facial is topographically closely connected during its development with the auditory, the nuclei of the two nerves often being designated the facial-acoustic com- plex. The three components of this aggregation the geniculatc, the cochlear and the vestibu- lar ganglia are primarily derived from an ectoblastic cell-mass in tin- vicinity of the otic vesicle. DEVELOPMENT OF PERIPHERAL NERVES. 1379 FIG. 1143. Vagus root gang. Accessory root gang. The neuroblasts of the facial constituent, the geniculate ganglion, send their centrally directed processes to the brain-stem as the pars intermedia, whilst their peripherally growing dendrites contribute the sensory fibres, passing by way of the chorda tympani and the greater and lesser superficial petrosal nerves. The geniculate ganglion and the pars intermedia correspond, therefore, to a dorsal root. The auditory nerve, although for a time closely related in position (Fig. 1103) with the facial (geniculate) ganglion, developes entirely independently and at no time has more than an incidental relation. The primary auditory nucleus is defined in human embryos by the begin- ning of the fourth week as an elongated ellipsoidal mass in contact with the anterior wall of the otic vesicle. According to Streeter 1 , the nucleus very shortly exhibits a differentiation into a superior and an inferior part, from the latter of which soon appears a third portion. This third portion, the later ganglion spirale, early manifests a tendency to coil in consequence of its close relations with the d u c t u s cochlearis. The major part of the primary acoustic complex, including the superior and most of the inferior part, becomes the vestibular ganglion, from the neuroblasts of which centrally directed a x o n e s pass to the young brain- stem as the vestibular nerve, while the dendrites become connected at certain places with the semicircular canals, the utricle and the saccule. The grouping of the vestibular rami seen in the adult is early foreshadowed in the develop- ing nerve, since from the upper part of the vestibular ganglion grows out the su- perior division of the vestib- ular nerve which, supplies the utricle and the ampullae of the superior and external semicircular canals (Fig. 1070) . The lower part of the ganglion, in addition to fur- nishing the anlage for the cochlear nerve, gives off the inferior division of the vestib- ular nerve, by which the IX. root gang. N. tymp. Gang, petros. IX. Gang, nodos. N. iaryg. sup. XI I. with r. descend. Froriep Sympathetic Vagus Reconstruction of peripheral nerves of human embryo of five weeks (14 mm.) X 13- (Streeter.) saccule and the posterior canal are supplied. During the subsequent growth of the structures, the neurones of the spiral ganglion send ax- ones towards the brain which become the cochlear nerve, whilst their dendrites-grow peripherally into the ductus cochlearis and are represented by the minute filaments extending from the cells of the spiral ganglion to the auditory cells of Corti's organ. The glosso-pharyngeal nerve is a mixed nerve and has, therefore, a double origin. Its motor fibres arise from neuroblasts situated in the dorsal part of the ventral zone of the wall of the hind-brain just posterior to the otic vesicle. The sensory part of the nerve, along with that of the vagus, offers greater complexity, since it is developed, as shown by Streeter 2 , from two sources. The ganglion of the root (g. stiperius or jugular ganglion) arises very early as a small mass of cells derived from the ganglion-crest of the hind-brain. It varies in size and soon ceases to grow, which behavior, in connection with the preponderating ingrowth of the motor fibres, accounts for the well-known inconstancy of the structure. The ganglion of the trunk (g. petrosum) arises, according to Streeter, not from the neural crest, but in relation with the ectoblast of the second visceral furrow. At first ununited with the smaller ganglion superius, the ganglion of the root subsequently becomes joined to it, the two nodes 1 Amer. Jour, of Anatomy, vol. yi., 1907. 2 Amer. Jour, of Anatomy, vol. iv., 1904. 1380 HUMAN ANATOMY. being later closely related, both as to position and fibres. An outgrowth of distally directed fibres establishes the main trunk of the nerve, while a forwardly growing strand represents the later tympanic branch. The vagus and spinal accessory nerves are so inseparably related in their development that their origin must be regarded as proceeding from a common vagus complex. The latter comprises three elements : (a] a series of motor roots, which arise from the ventral zone of the hind-brain and extend from near the glosso-pharyngeal anlage in front as far as the third or fourth spinal segment below ; () a partially subdivided, but at first continuous, ganglionic mass, which arises from the ganglion-crest of the hind-brain and represents the root-ganglia ; (c) a secondary ventral cell-mass, the primitive ganglion of the trunk, which, as in the case of the glosso-pharyngeal nerve, is developed in close relation with the ectoblast of the posterior branchial furrows. Whilst the motor rootlets persist and become the efferent root-fibres of the later vagus and accessory nerves, the dorsal or crest-ganglia soon exhibit differences in their growth, the one situated farthest forward outstripping the others and becoming the vagal gang- lion of the root, and the remaining ones becoming the accessory root-ganglia. These latter constitute a chain which below meets with the spinal dorsal ganglia. Primarily, therefore, the entire length of the vagus complex is occupied by a series of mixed nerve strands possessing both motor and sensory elements. The head-end of the series later becomes predominatingly sensory, while in the tail-end of the same the motor character prevails. The ventral vagus nucleus is attached secondarily to the dorsal nucleus by centrally growing fibres, while from its distal end extend the dendritic processes which constitute the trunk of the vagus and its branches. In consequence of the intergrowth of these afferent and efferent fibres, the definite tenth nerve in the usual sense, with its two ganglia, becomes established. Although for a short period the accessory part of the complex is provided with both motor and sensory parts, the latter are subsequently overpowered by the efferent fibres, so that the presence of the rudimen- tary ganglionic elements within the accessorius can be demonstrated only by microscopic exam- ination (Streeter) . From the preceding facts it is evident that the estimate of the eleventh nerve as an integral part of the vagus is well founded. The hypoglossal nerve appears in the human embryo, towards the close of the third week, as several strands which grow from the ventral zone of the wall of the hind-brain and are in series with the ventral root-fibres of the upper cervical spinal nerves. Soon the separate root- lets converge and consolidate into a common trunk, from which, by the end of the fifth week, the chief branches of distribution arise. The production of the wide-meshed net-work which distinguishes the communications between the upper cervical and hypoglossal nerves results from the separation of fibres which are at first closely adjacent, the subsequent migration of the growing tongue-muscles drawing the hypoglossal fibres away from the spinal nerves, except at such points where they have become enclosed in a common sheath. There is good reason for regarding the hypoglossal nerve as representing the ventral roots of trunk-nerves, which have been cephalicly displaced and drawn within the cranium. Moreover, the observations of Froriep and others upon adult mammals and of His upon the human embryo have shown the presence of a rudimentary dorsal ganglion and abortive dorsal root-fibres. The occasional presence of a rudimentary ganglionic mass, known as Froriep's ganglion, attached to the fibres of the adult hypoglossal nerve in man is to be interpreted as the persistent dorsal element which ordinarily disappears. From the preceding sketch it is evident that in no instance, as observed in the usual adult condition in man, is there complete correspondence between the members of the cephalic series and those of the trunk. The group of purely sensory nerves the olfactory, optic and auditory includes one, the optic, which is so exceptional in its fundamental relations as to lie without the pale of peripheral nerves in their strict sense. The remaining two sensory nerves are held to be primarily the equivalents of constituents of a peculiar system of sensory organs, best developed in fibres, known as the organs of the lateral line. The third, fourth, sixth and twelfth, the ventral motor nerves, are undoubtedly associated with head-somites, although the exact number and nerve relations of such mesoblastic segments are uncertain ; in fundamental significance, therefore, these nerves agree with those of the trunk-series, although modified by the suppression of their dorsal or sensory constituents. The mixed nerves the fifth, seventh, ninth and tenth (the eleventh being reckoned as part of the vagus) are unrepresented in the spinal series and belong to the branchiomere represented by the visceral arches. Of these nerves, the trigeminus most nearly accords in constitution with a typical spinal nerve, since, with the exception of ventral motor constituents which are wanting, it pos- sesses as does the typical spinal nerve, both somatic (general cutaneous) sensory and visceral sensory fibres. A further rest -mblance is found in the character of the gray matter constituting the reception-nucleus for the sensory fibres of the trigeminus, since this column is composed of substantia gelatinosa continuous with the Rolandic substance capping the posterior cornu of Un- cord. A similar, although less intimate, arrangement is seen in the column of gray matter accom- panying the descending root (funiculus solitarius)of the facial, glosso-pharyngeal and vagus nerves. THE ORGANS OF SENSE. THE cells directly receiving the stimuli producing the sensory impressions of touch, smell, taste, sight and hearing are all derivations of the ectoblast the great primary sensory layer from which the essential parts of the organs of special sense are differentiations. The olfactory cells nervous elements that correspond to ganglion cells retain their primary relation, since they remain embedded within the invaginated peripheral epithelium lining the nasal fossae, sending their dendrites towards the free surface and their axones into the brain. Usually, however, the nerve cells connected with the special sense organs abandon their superficial position and lie at some distance from the periphery, receiving the stimuli not directly, but from the epithelial receptors by way of their dendrites. In the case of the most highly specialized sense organs, the eye and the ear, the percipient cells lie enclosed within capsules of mesoblastic origin, the stimuli reaching them by way of an elaborate path of conduction. THE SKIN. Since the extensive integumentary sheet that clothes the exterior of the entire body not only serves as a protective investment, an efficient regulator of body temperature and an important excretory structure, but also contains the special end- organs and the peripheral terminations of the sensory nerves that receive and convey the stimuli producing tactile impressions, the skin may be appropriately considered along with the other sense-organs of which it may be regarded as the primary and least specialized. On the other hand, the correspondence of its structure with that of the mucous membranes, with which it is directly continuous at the orifices on the exterior of the body, emphasizes the close relation of the skin to the alimentary and other mucous tracts. This general investment, the tegmentum commune, includes the skin proper > with the specialized tactile corpuscles, and its appendages the hairs, the nails and the cutaneous glands. Its average superficial area is approximately one and a half square meters. The skin (cutis), using the term in a more restricted sense as applied to the covering proper without its appendages, everywhere consists of two distinct portions a superficial epithelial and a deeper connective tissue stratum. The former, the epi- dermis, is devoid of blood-vessels, the capillary loops of which never reach farther than the subjacent corium, as the outermost layer of the connective tissue stratum is called. The thickness of the skin, from .5-4 mm., varies greatly in different parts of the body, being least on the eyelids, penis and nymphae, and greatest on the palms of the hands and soles of the feet and on the shoulders and back of the neck. In general, with the exception of the hands and feet, the skin is thicker on the extensor and dorsal surfaces than on the opposite aspects of the body. Of the entire thick- ness, the proportion contributed by the epidermis is variable, but in most localities it is about . i mm. Where exposed to unusual pressure, as on the palms of laborers or on habitually unshod soles, the epidermis may attain a thickness of 4 mm. As seen during life, the color of the skin results from the blending of the in- herent tint of the tissues with that of the blood within the superficial vessels. When the latter are empty, as after death, the skin assumes the characteristic pallor and ashen hue. Where the capillaries are numerous and the overlying strata thin, the skin exhibits the pronounced rosy color of the lips, cheeks, ears and hands. Where, on the contrary, the contents of fewer vessels shimmer through the epidermis, the paler tint of the limbs and trunk is produced. In certain localities especially over the mammary areolae after pregnancy, the axillae, the external genital organs and around the anus the skin presents a more or less pronounced brownish color owing to the unusual quantity of pigment within the 1381 I 3 82 HUMAN ANATOMY. epidermis. The amount of skin-pigment not only differs permanently among races (white, yellow and black) and indi- FIG. 1144. Imprint of dorsal surface of left hand near ulnar border; radiating lines are produced by creases connecting points at which hairs emerge. viduals (blond and brunette), but also varies in the same person with age and exposure, as contrasted by the rosy tint of the infant and the bronzed tan of the weather beaten mariner. Unless bound down to the underlying tissues, as it is over the scalp, external ear, palms and soles, the skin is freely movable. Its physical properties include con- siderable extensibility and marked elasticity. By virtue of the latter the temporary displacement and stretch- ing produced by movements of the joints and muscles is overcome and the smoothness of the skin, so con- spicuous in early life, is maintained. With advancing age the elasticity becomes impaired and folds are' no longer effaced, resulting in the perma- nent wrinkles seen in the skin of old FIG. 1145. people. Certain folds and furrows, however, are not only permanent and ineffaceable, appearing in the foetus, but are fairly constant in position and form. One group, produced by flexion of the joints, includes the conspicu- ous creases on the flexor surface of the wrist, palm and fingers, and the similar markings on the soles of the feet. The other group, more extensive but less striking, includes the fine grooves that connect the points of ^emergence of the hairs and cover the trunk and extensor surface of the limbs with a delicate tracery (Fig. 1144)- The surface modelling of the skin covering the palms, soles and flexor aspects of the digits is due to the disposition of numerous minute ridges (cristae cutis) and furrows (sulci cutis). The cutaneous ridges, about . 2 mm. in width, correspond to double rows of papillae which they cover, the sweat glands opening along the summit of the crests. The patterns formed by the cutaneous ridges (Fig. 1145) remain throughout life unchanged and are so distinctive for each individual that they afford a reliable and practical means of identi- fication. In addition to the various longitudinal, trans- verse and oblique ranges of ridges that cover the greater part of the hand, groups of concentrically arranged ridges occupy the volar surface over the distal phalanges, the pads between the metacarpo-phalangeal joints and the middle of the hypothenar eminence. These highly characteristic areas, the so-called tactile pads (toruli tactiles) are most strikingly developed over the bulbs of the fingers, where the ridges are often disposed in whorls rather than in regular ovals. The markings of corresponding areas of the two hands are symmetrical and sometimes identical. Structure. The two parts of which the skin is everywhere composed the epidermis and the connec- tivr tissue stratum are derivatives of the ectoblast and of the mesoblast respectively. The connective tissde portion includes two layers, Imprint of palmar MM laic of left middle finger, showing arrangement of cutaneous ridges ; transverse in- ti-rniptions arc produced by flexion creases over joints. THE SKIN. 1383 the corium and the tela subcutanea, which, however, are so blended with each other as to be without sharp demarcation. The corium or derma, the more superficial and compact of the connective tissue strata, lies immediately beneath the epidermis from which it is always well defined. With the exception of within a few localities, as over the forehead, external ear and perineal raphe, the outer surface of the corium is not even but beset with elevations, ridges, or papillae, which produce corresponding modelling of the opposed under surface of the overlying epidermis. The pattern resulting from these eleva- tions varies in different regions, being a net-work with elongated meshes over the back and front of the trunk, with more regularly polygonal fields over the extremi- FIG. 1147. Portion of corium from palmar surface of hand after removal of epi- dermis ; each range includes a double row of papillae, which underlie the superficial cutaneous ridges and en- close openings of sweat glands ; latter appear as dark points along ranges of papillae. X 5- Small portion of preceding specimen, showing papillae under higher magnifica- tion ; orifices of torn sweat glands are seen between papillae. X 24. ties and with small irregular meshes on the face (Blaschko). The best developed papillae are on the flexor surfaces of the hands and feet, where they attain a height of .2 mm. or more and are disposed in the closely set double rows that underlie the cutaneous ridges on the palms and soles above noted. The papillae afford favorable positions for the lodgement of the terminal capillary loops and the special organs of touch and are accordingly grouped as vascular and tactile. In recognition of the elevations, which in vertical sections of the skin appear as isolated projections, the corium is subdivided into an outer papillary stratum (corpus papillare), containing the papillae, and a deeper reticular stratum (tunica propria), composed of the closely interlacing bundles of fibrous and elastic tissue that are continued into the more robust and loosely arranged trabeculae of the tela subcutanea. These two strata of the corium, however, are so blended that they pass insensibly and without definite boundary into each other. Although composed of the same histological factors bundles of fibrous tissue, elastic fibres and con- nective tissue cells the disposition of these constituents is much more compact in the dense reticular stratum than in the papillary layer, in which the connective tissue bundles are less closely interwoven. While the general course of the fibrous bundles within the corium is parallel or oblique to the surface, some strands, continued upward from the underlying subcutaneous sheet, are vertical and traverse the stratum reticulare either to bend over and join the horizontal bundles or to break up and disappear within the papillary stratum. The elastic tissue, HUMAN ANATOMY. which constitutes a considerable part of the corium, occurs as fibres and net-works, which within the reticular stratum form robust tracts corresponding in their disposition with the general arrangement of the fibrous bundles. Towards the surface of the corium, the elastic fibres become finer and more branched and beneath the epidermis anastomose to form the delicate but close subcpithelial elastic net-work that is present over the entire surface of the body with the exception, possibly, of the eyelids (Behrens). The tela subcutanea, the deeper layer of the connective tissue portion of the skin, varies in its thickness, and in the density and arrangement of its component bundles of fibro-elastic tissue, with the amount of fat and the number of hair-follicles and glands lodged within its meshes. The latter are irregularly round and enclosed by tracts of fibrous tissue, some of which, known as the retinacula cutis, are prolonged from the corium to the deepest parts of the subcutaneous stratum. Here they often blend into a thin but definite sheet, the fascia subcutanea, which forms the innermost boundary of the skin and is FIG. 1148. Epidermis Papillary stratum Reticular stratum Hair follicle Retinaculum Fat Section of skin, showing its chief layers epidermis, corium and tela subcutanea. X 17. connected with the subjacent structures by strands of areolar tissue. Where such loose connection is wanting, as on the scalp, face, abdomen (linea alba), palms and soles, the skin is intimately bound to the underlying muscles or fasciae and lacks the independent mobility that it elsewhere enjoys. The integument covering the eye- lids and penis is peculiar in retaining to a conspicuous degree its mobility although devoid of fat. Where the latter is present in large quantity, the term panniculiis adiposus is often applied to the tela subcutanea. In places in which the skin glides over unyielding structures, the interfascicular lymph-spaces of the tela subcutanea may undergo enlargement and fusion, resulting in the production of the subcutaneous mucous bursce. These are found in many localities, among the most constant bursae being those over the olecranon. the patella and the metatarso-phalangeal joints of the little and the great toe. The bursae in the latter situation, when abnormally enlarged, are familiar as bunions. In addition to the strands of inroluntayy II/HSC/C associated with the hairs as the arrectores pilorum, unstriped muscular tissue is incorporated with the skin in the mammary areolae and over the scrotum and penis (tunica dartos). The facial muscles having largely cutaneous insertions, the skin covering the face is invaded by tracts of striated muscular tissue that penetrate as far as the corium. THE SKIN. 1385 The epidermis or cuticle, the outer portion of the skin, consists entirely of epithelium and, being partly horny, affords protection to the underlying corium with its vessels and nerves. The thickness of this layer varies in different parts of the body. Usually from .08 .10 mm., it is greatest on the flexor surfaces of the hands and feet, where it reaches from .5-. 9 mm. and from 1.1-1.3 mm. respectively (Drosdoff). The cuticle consists of two chief layers, the deeper stratum germinativum, con- taining the more active elements, and the stratum corneum, the cells of which undergo cornification. Between these layers lies a third, the stratum intermedium, that is FIG. 1149. Stratum corneum .... , Portion of section of skin from sole of foot, showing layers of epidermis. X 70. ordinarily represented by only a single row of cells to which the name, stratum granulosum, is usually applied. This layer marks the level at which the conversion of the epithelial elements into horny plates begins and also that at which the separation effected by blistering usually occurs. On the palms and soles, where the epidermis attains not only great thickness but also higher differentiation, four distinct layers may be recognized in vertical sec- tions of the cuticle. From the corium outward, these are: (i) the stratum germina- tivum, (2) the stratum granulosum, (3) the stratum lucidum and (4) the stratum corneum. The first two represent the portion of the epidermis endowed with the greatest vitality and powers of repair and the last two the horny and harder part. The stratum germinativum, or stratum Malpighi, rests upon the outer sur- face of the corium, by the papillae of which it is impressed and, hence, when viewed from beneath after being separated, commonly presents a more or less evident net-work of ridges and enclosed pits, the elevations corresponding to the 3 86 HUMAN ANATOMY. Stratum corneum Stratum lucidum _ Stratum granulosum Stratum germinativum Deepest cells of epidermis Corium Portion of preceding preparation, showing in more detail layers of epidermis only deeper part of stratum corneum is represented. X 200. interpapillary furrows and the depressions to the papillae. In recognition of this reticulation the name, rete Malpighi, is sometimes applied to the deepest layer of the epidermis. As in other epithelia of the stratified squamous type, the deepest cells are columnar and lie with FIG. 1150. their long axes perpen- dicular to the supporting connective tissue. The basal ends of the colum- nar cells are often slight- ly serrated and fit into corresponding indenta- tions on the corium. Their outer ends are rounded and received between the super- imposed cells. Succeed- ing the single row of columnar elements, the cells of the stratum germinativum assume a pronounced polygonal form, but become some- what flatter as they approach the stratum granulosum. The num- ber of layers included in the germinal stratum is not only uncertain, but varies with the rela- tion to the papillae, being greater between than over these projections. The finely granular cytoplasm of the cells of the stratum germinativum contains delicate but distinct fibrilla:, which, longitudinally disposed in the deep columnar cells, in the polygonal elements (Fig. 1151), radiate from the nucleus towards the periphery (Kromayer). The fibrillae are not confined to the cells, but extend beyond and pass across the intercellular lymph-clefts as delicate protoplasmic bridges that connect the units of the various layers of the stratum and confer upon them the character- istics of the so-called ' ' prickle cells. The stratum granulosum is exceptionally well marked on the palms and soles and in these localities includes from two to four rows of polygonal cells, FIG- "Si- somewhat horizontally compressed, that stand out conspicuously in stained sections by reason of the intensely colored particleswithin theircytoplasm. The nature of the peculiar substance, deposited within the body of the cells as particles of irregular form and size, is still uncertain. To it Ranvier gave the name of eleidin and Waldeyer that of keratohyalin. Since the nuclei of the cells in which the deposits occur always exhibit evidences of degenera- tion, it is probable that keratohyalin is in some way derived from disintegra- tion of the nucleus (Mertsching) and represents a transition stage in the process ending in cornification of the succeeding layers of the cuticle (Brunn). The stratum lucidum, usually wanting in other localities, in the palm and sole appears as a thin, almost homogeneous layer, separating the corneous from the Fibrillae Portion of horizontal section of skin, showing intracellular fibrillie within cells of stratum germinativum. X 800. THE SKIN. 1387 Pigmental epidermis Duct of sweat gland granular layer. With the latter it constitutes the stratum intermedium. As indicated by its name, the stratum lucidum appears clear and without distinct cell boundaries, although suggestions of these, as well as of the nuclei of the component elements, are usually distinguishable. The cells of the stratum lucidum are uniformly cornified and differ, therefore, from those of the overlying layers in which the process is often confined to a mantle zone. The stratum corneum includes the remainder of the epidermis and consists of many layers of horny epithelial cells that form the exterior of the skin. Where no stratum lucidum exists, as is usually the case, the corneous layer rests upon the stratum granulosum, from which its horny elements are being continually recruited. During their migration towards the free surface, the cells lose their vitality and become more flattened until the most superficial ones are converted into the dead horny scales that are being constantly displaced by abrasion. The pigmentation of the skin, which even in white races is conspicuous in certain regions (page 1381), depends upon the presence of colored particles chiefly within the epidermis, although, when the dark hue is pronounced, a few small branched pigmental connective . . T? tissue cells may appear within 1G - i: 5 2 - the subjacent corium. The dis- tribution of the pigment particles varies with the intensity of color, in skins of lighter tints being principally, and sometimes en- tirely, limited to the columnar cells next the corium. With increasing color the pigment particles invade the neighboring layers of epithelium until, in the dark skin of the negro, they are found within the cells of the stratum corneum but always in diminishing numbers towards the free surface. Even when the cells are dark and densely packed, the colored particles never encroach upon the nuclei, which, therefore, appear as con- spicuous pigment free areas. The source of the pigment within the epidermis is uncertain, by some being found in an assumed transference of the colored particles from the corium, by means of wandering cells or of the processes of pigmented connective tissue cells that penetrate the cuticle, and by others ascribed to an independent origin in situ within the epithelial elements. While it may be accepted as established that at times the connective tissue cells are capable of modifying pigmentation (Karg), it is equally certain that the earliest, and probably also later, intracellular pigmenta- tion of the epidermis appears without the assistance of the connective tissue or migratory cells. The blood-vessels of the skin are confined to the connective tissue portion and never enter the cuticle. The arteries are derived either from the trunks of the subjacent layer as special cutaneous branches destined for the integument, or indi- rectly from muscular vessels. When the blood supply is generous, as in the palms and soles and other regions subjected to unusual pressure or exposure, the arteries ascend through the subdermal layer to the deeper surface of the corium where, having subdivided, they anastomose to form the siibcutaneoiis plexus (rete arteriosum cutaneura). From the latter some twigs sink into the subdermal layer and contribute the capillary net-works that supply the adipose tissue and the sebaceous glands. Other twigs, more or less numerous, pass outward through the deeper part of the corium and within the more superficial stratum unite into a second, subpapillary plexus (rete arteriosum subpapillare), that extends parallel to the free surface and Section of skin, surrounding; anus, showing pigmentation of deeper layer of epidermis. X 50. I 3 88 HUMAN ANATOMY. Papillary loops beneath the bases of the papillae. The latter are supplied by the terminal twigs which ascend vertically from the subpapillary net-work and break up into capillary loops that occupy the papillse and lie close beneath the epidermis (Fig. 1153). With the exception of the loops entering the hair-papillae, the capillaries enclosing the hair- follicles arise from the subpapillary plexus. The arrangement of the cutaneous veins, more complex than that of the arteries, includes four plexuses (retes venosum) lying at different levels within the corium and extending parallel to the FIG. 1153. surfaces. The first and most superficial one is " '^-.. formed by the union of ^-^ ^^ the radicles returning the blood from the papilla?. w The component veins lie below and parallel to the rows of papillae and im- mediately beneath the bases of the latter. At a slightly lower level, in the deeper part of the stratum papillare, the ve- nous channels proceeding from the subpapillary net- work join to form a second plexus with polygonal meshes. A third occurs about the middle of the corium, while the fourth shares the position of the subcutaneous arterial plexus at the junction of the corium and subdermal strata. The deepest plexus receives many of the radicles returning the blood from the fat and the sweat glands, the re- mainder being tributary to the veins accompany- ing the larger arteries as they traverse the tela subcutanea. The lymphatics of the skin are well repre- sented by a close super- ficial plexus within the papillary stratum of the corium into which the terminal lymph-radicles of the papillae empty. The relation of these channels to the interfascicular connective tissue spaces is one only of indirect communication, since the lymphatics are provided with fairly complete endothelial walls. It is probable that the lymph-paths within the papillae are closely related to the intercellular clefts of the epidermis, according to Unna, indeed, direct communications existing. Migratory leucocytes often find their way into the cuticle where they then appear as the irregularly stellate cells of I.ungerhans seen between the epithelial elements. A wide-meshed deep plexus of lymphatics is formed within the subdermal layer, from which the larger lymph -trunks pass along with the subcutaneous blood-vessels. Section of injected skin, showing general arrangement of blood-vessels. X 4<>- THE HAIRS. 1389 The numerous nerves within the highly sensitive integument are chiefly the peripheral processess of sensory neurones which terminate in free arborizations between the ephithelial elements of the cuticle, or in relation with special endings located, for the most part, within the corium or subdermal connective tissue. Some sympathetic fibres, however, are present to supply the tracts of involuntary muscle that occur within the walls of the blood-vessels or in association with the hairs and the sweat glands. On entering the skin the medullated nerves traverse the subdermal layer, to which they give off twigs in their ascent, and, passing into the corium, within the papillary stratum divide into a number of branches. Those destined for the epidermis beneath the latter break up into many fibres which, losing their medullary substance, enter the cuticle and end in arborizations that ramify between the epithelial cells as far as the outer limits of the stratum germinativum. The ultimate endings of the fibrillee, whether tapering or slightly knobbed, always occupy the intercellular channels and are never directly connected with the substance of the epithelial elements. According to Merkel, special tactile cells, (Fig. 1016) occur in the human epidermis, particularly over the abdomen and the thighs. These cells, spherical or pyriform in shape and composed of clear cytoplasm, occupy the deeper layers of the cuticle and, on the side directed towards the corium, are in contact with the end-plate or meniscus of the nerve. The nerve-fibres particularly concerned with the sense of touch terminate within the connective tissue portion of the skin, either within the corium in special end-organs the tactile bodies of Meissner, the end-bulbs of Krause, the genital corpuscles and the end-organs of Ruffini, or within the subdermal layer in the Vater-Pacinian cor- puscles, or their modifications, the Golgi-Mazzoni corpuscles. The structure of these special end-organs is elsewhere described (pages 1018, 1019), their chief locations being here noted. Meissner's corpuscles (Fig. 1017) are especially numerous in the tactile cushions on the flexor surface of the hands and feet. While much more plentiful in all the tactile pads than in the intervening areas, the touch corpuscles are most abundant in those on the volar surface of the distal phalanges, where they approxi- mate twenty to the square millimeter (Meissner). Their favorite situation is the apex of the papillae, where they appear as elongated elliptical bodies, sometimes in pairs, whose outer pole lies immediately below the epidermis. These corpuscles are additionally, although sparingly, distributed on the dorsum of the hand, the flexor surface of the forearm, the lips, the eyelids, the nipple and the external genital organs. The Vater-Pacinian corpuscles (Fig. 1018) are well represented in the hands and feet and usually occupy the subdermal tissue, although sometimes found within the corium. Their distribution corresponds closely to that of Meissner's corpuscles, they being most numerous beneath the tactile cushions in the order above described. The Golgi-Mazzoni corpuscles are modifications of the Pacinian bodies and, like the latter, are found within the subdermal tissue. The end-bulbs of Krause (Fig. 1016) occur within the corium, either slightly below or within the papillae, on the lips and external genital organs, as well as probably in other regions. The genital corpuscles (Fig. 1017) lie within the corium of the modified skin covering the glans penis and the prepuce and the clitoris and surrounding parts of the nymphae. The end-organs of Ruffini resemble the sensory terminations in tendons (page 1017) and lie within the deeper parts of the corium, often associated with the Pacinian bodies. The mode of ending of the nerves supplying the hairs and sweat glands will be described in connection with those structures (pages 1394, 1400). THE HAIRS. The appendages of the skin the hairs, nails and cutaneous glands are all specializations of the epidermis and are. therefore, exclusively of ectoblastic origin. The hairs (pili) are present over almost the entire body, the few localities in which they are absent being the flexor surface of the hands and feet, the extensor aspect of the terminal segment of the fingers and toes, the inner surface of the 1390 HUMAN ANATOMY. prepuce and of the nymphae and the glans penis and clitoridis. With the exception of those regions in which the growth is sufficiently long to constitute a complete cover- ing the scalp, Bearded parts of the face in the male, axillae and mons pubis the hairs are for the most part short and scattered, although subject to great individual variation and sometimes to remarkable redundance. The hairs in various locations are known by special names ; those of the scalp being capilli ; of the eyebrows, superdlia ; of the eyelashes, cilia; of the nostrils, vibrissa ; of the external ear, tragi ; of the beard, barba ; of the axillae, hi ret ; of the pubes, pubes ; while the fine downy hairs that cover other parts of the body are designated lanugo. The closest set hairs are on the scalp, where according to Brunn, in the vertex they number from 30x3-320, and in the occipital and frontal regions from 200-240 per square centimeter. On the chin 44 were counted, on the mons pubis 30-35, Epidermis Erector muscle Sweat gland Hair-papilla Inner root-sheath Outer root-sheath Bulb Papilla Paniculus adiposus Section of scalp, showing longitudinally cut hair-follicles. X 14- on the extensor surface of the forearm 24 and on the back of the hand 1 8 for like areas. Even where their distribution is seemingly uniform, close inspection shows the hairs to be arranged in groups of from two to five. The length of the hairs includes the extremes presented by the lanugo, only a few millimeters long, on the one hand, and by the scalp-growth, sometimes measur- ing 150 cm. (108 in.) or more, on the other. Their thickness, likewise, shows much variation, not only in different races, individuals and regions, but also in the same person and part of the body, as on the scalp where fine and coarse hairs may lie side by side. The thickest scalp-hairs have a diameter of .162 mm. and the finest one of .on mm., with all intermediate sizes. The hairs of the beard vary from .101-. 203 mm. and those on the pubes from .054-. 135111111. (Falck). In a general way hairs of light color are finer than dark ones, the respective diameters of blond, brown and black hairs being .047, .054 and .067 mm. (Wilson). On attaining their full growth without mutilation, hairs do not possess a uniform thick- ness throughout their length, since they diminish not only towards the tip, when the >haft ends in a point, but also towards the root. This feature is most evident in short hairs, as in those of the eyebrows. The color of the hair, which varies from the lightest straw to raven black, is closely associated with racial and individual characteristics, being usually, but by no THE HAIRS. 1391 means always, in harmony with the degree of general pigmentation. The latter is commonly uniform throughout the length of the hair, but in rare cases it may be so variable that the shaft presents a succession of alternating light and dark zones (Brunn). The straight and curly varieties of hair depend chiefly upon differences in the curvature of the follicle 1 and the form of the hair. In the case of straight hairs the follicle is unbent and the shaft is cylindrical, and therefore circular in cross- section ; hairs that are wavy or curly spring from follicles more or less bent and are flattened or grooved, with corresponding oval, reniform, irregularly triangular or indented outlines when transversely cut. Arrangement of the Hairs. Since the buried part of the hair, the root, is never vertical but always oblique to the surface of the skin, it follows that the free part, the shaft, is also inclined. The direction in which the hairs point, however, is by no means the same all over the body, but varies in different regions although constant for any given area. This disposition depends upon the peculiar placing of the hair-roots which in certain localities incline towards one another along definite lines, an arrangement that results in setting the shafts in opposite directions. As these root-lines are not straight but spiral, on emerging from the skin the hairs diverge in whorls (vortices pilorum), the position and number of which are fairly definite. Such centres include : (i ) the conspicuous vertex whorl on the head, usually single but sometimes double; (2) the facial whorls surrounding the openings of the eyelids; (3) the auricular whorls at the external auditory meatus ; (4) the axillary whorls in the armpits ; and (5) the inguinal whorls, just below the groin ; additional (6) but less constant lateral whorls may be located, one on each side, about midway between the axilla and the iliac crest and somewhat beyond the outer border of the rectus muscle. These whorls, all paired except the first, apportion the entire surface of the body into certain districts, each covered by the hairs proceeding , from the corresponding vortex. The whorl-districts, moreover, are irregularly subdivided into secondary areas by lines, the hair- ranges (flumina pilorum), along which the hairs diverge in opposite directions. Additional lines, the converging hair-ranges, mark the meeting of tracts pointing in different directions and in places also assume a spiral course. In consequence of these peculiarities the body is covered with an elaborate and intricate hair-pattern, that is most evident on the foetus towards the close of gestation ; later in life the details of the pattern are uncertain owing to its partial effacement by the constant rubbing of clothing. Structure. Each hair consists of two parts, the shaft, which projects beyond the surface, and the root, which lies embedded obliquely within the skin, the deepest part of the root expanding into a club-shaped thickening known as the bulb. The root is covered with a double investment of epithelial cells, the inner and outer root- sheaths, which, in turn, are surrounded by a connective tissue envelope, the theca. The entire sac-like structure, consisting of the hair-root and its coverings, constitutes the hair-follicle (folliculus pili). At the bottom of the latter, immediately beneath the bulb, the wall of the follicle is pushed upward to give place to a projection of connective tissue, the hair-papilla, which carries the capillary loops into close relation with the cells most active in the production of the hair. Save in the case of the finest hairs (lanugo), which are limited to the corium, the hair-follicles traverse the latter and end at varying levels within the fat-laden subdermal layer (panniculus adiposus ). In a general way the follicle may be regarded as a narrow tubular invagi- nation of the epidermis, at the bottom of which the hair is implanted and from the entrance of which the shaft projects. The most contracted part of the follicle, the neck, lies at the deeper end of the relatively wide funnel-shaped entrance to the sac. Closely associated with the hair-follicle, which they often surround, are the sebaceous glands that pour their oily secretion at the upper third of the follicle into the space between the shaft and the wall of the sac. The Hair-Shaft. In many thick hairs, but by no means in all, three parts can be distinguished the cuticle, the cortex and the mediilla. The latter, however, is usually wanting in hairs of ordinary diameter, being often also absent in those of large size. 1 Frederic : Zeitschr. f. Morph. u. Anthropol., Bd. ix., 1906. 1392 HI MAN ANATOMY. FIG. 1155. Portion of shaft of hair; //, shaft covered with cuticle ; s, cuticle re- moved to expose cortical substance; *, medulla X 125. a, b, isolated cells of cuticle and of co respectively. X 240. jrtical substance The cuticle of the hair appears as a transparent outermost layer marked by a net-work of fine sinuous lines, the irregular meshes of which have their longest diameter placed obliquely transverse. These lines correspond to the free borders of extremely thin glassy cuticle-plates that overlie the hair as tiles on a roof, the imbrication involv- ing from four to six layers. Seen in profile (Fig. 1155), the contour of the hair-shaft, therefore, is not smooth but serrated, the minute teeth formed by the free margins of the scales being directed towards the tip of the hair. After isolation by suitable reagents, the cuticular elements appear as transparent structureless cells, quadrilateral in outline and curved to con- form to the hair-shaft which they cover. The cortical substance, often indeed constituting practi- cally the entire shaft, consists of elongated fusiform cells so compactly arranged that the individual elements are only dis- tinguishable after the action of disassociating reagents. In addition to the remains of the shrunken nuclei the hair- spindles, as these modified epithelial cells are called, possess fibrillse that pass between adjacent cells similar to the inter- cellular bridges in the epidermis. A variable amount of pigment, present either as a diffuse tint of the spindles, or as granules within or between the same, is a constant constituent of the cortical substance. In blond hair the color is chiefly diffuse, the pigment granules being often entirely wanting ; in hair of darker shades, the granules predominate and increase in intensity of color as well as in quantity. As the hair grows outward from the bulb, it loses much of its moisture, and in consequence later contains minute air-vesicles that replace the fluid previously occupying the clefts between the hair-spindles. Even when conspicuous, the medulla does not extend the entire length of the hair, often being interrupted and always disappearing before reaching the tip. The medulla, when well represented, is seen as an axial stripe, somewhat uneven in outline, that varies with illumination, with transmitted light appearing as a dark band and with reflected light as a light one. This peculiarity depends upon the presence of air imprisoned between the shrunken and irregular medullary cells -dried and cornified epithelial elements which are con- nected by branching processes into a net-work incompletely filling the medulla. The air within the shaft is a factor modifying the color of the hair, since the resulting reflex tends to lessen the intensity of the tint directly referable to the pigment ; FIG. 1156. this diminution affects par- ticulary the lighter shades, * er root-sheath Hair surrounded by as in dark hairs the large /f/^Tb ,/ l^ in " er root " sheath amount of pigment masks the reflex. f<'.'**^- ,<9t0q^.; .'/- The Hair-Folli- cle. This structure consists essentially of ( i ) a connective tissue sheath, the theca, con- tributed by the corium ; (2) an epithelial lining, the outer root- sheath, continued from the deepest layer of the epidermis; and (3) the inner root-sheath, an epithelial investment probably differentiated within the follicle, and not a direct prolonga- tion from the cuticle. The theca folliculi includes three strata : an outer, composed of loosely dis- posed longitudinal bundles of fibrous tissue with few cells and elastic fibres ; a middle one, madi- up of closely placed circular bundles; and a very thin, homogeneous inner coat, the glassy membrane, which represents an unusually well developed s Adipose Fibrous tissue Horizontal section of scalp, showing group of transversely cut hair-follicles. X 65. THE HAIRS. 1393 basement membrane separating corium from cuticle. Greatly attenuated, it is prolonged over the hair-papilla, which, as a special vascularized thickening of the connective tissue of the follicle, carries nutrition to the bulb of the growing hair. The outer root-sheath is the continuation of the stratum germinativum alone, the other layers of the epidermis thinning out and disappearing before reaching the neck of the follicle. Its cells present the characteristics of those of the germinating layer, with exceptionally well marked fibrillae. On approaching the level of the papilla, the outer root-sheath, which farther above consists of numerous layers, rapidly diminishes in thickness until, on the sides of the papilla, it is reduced to a single row of low columnar cells. The inner root-sheath, which is best developed over the middle third of the hair-root and fades away on reaching the upper third, includes three layers. The outer, known as Henle 1 s layer, consists of a single row of flat polygonal cells, often partially separated by oval spaces. Their nuclei are very indistinct or invisible FIG. 1157. Theca folliculi Middle layer Henle's layer of inner root-sheath Hf* Outer root-sheath gkr~. Transverse section of hair-follicle, showing hair surrounded by internal and external root-sheaths. X 285. within the cornified cytoplasm. The middle or Huxley' s layer, also horny in nature, often comprises only one stratum of nucleated cuboidal cells, but in the thicker hairs two or even three rows of irregularly interlocked cells may be present. The third layer, known as the sheath cuticle, resembles the external coat of the hair, against which it lies, in being extremely thin and composed of flat horny plates. The latter, however, are always nucleated and so disposed that they are opposed to the serrations of the thicker hair-cuticle. Traced towards the bottom of the follicle, the root-sheaths and the hair, which above are sharply defined from one another, become more and more alike until, in the immediate vicinity of the hair-papilla, they blend into a still imperfectly differentiated mass of cells. The deepest elements of this complex, however, are cuboidal or low columnar and form an uninterrupted tract over the papilla, continuous with the outermost cells of the outer root-sheath. It is from the proliferation of these deepest cells that the formative material, or matrix, is provided to meet the requirements of growth and replacement of the hairs. Without anticipating the account of the detailed changes described in connection with the development of the hair (page 1401), it may be here noted that of the three parts of the hair, the medulla is produced by 88 1394 HUMAN ANATOMY. FIG. 1158, the cells overlying the summit of the papilla, while those converted into the cortical substance, cuticle and inner root-sheath occupy the sides of the papilla and deepest part of the follicle. With few exceptions, the hair follicles are associated with two or more sebaceous glands, rarely with only one, the ducts of which open into the sac in the vicinity of the neck. The glands usually lie on the side towards which the hair inclines, but sometimes, especially in the case of the smaller hairs, they may completely surround the follicle. Since these glands are outgrowths from the same tissue that lines the follicles, their ducts pierce the outer root-sheath, bringing their oily secretion into direct relation with the hairs. The structure of the sebaceous glands is described with the cutaneous glands (page 1397). Most of the larger hair-follicles, particularly those of the scalp, are provided with ribbon-like bundles of involuntary muscle, called the arrectores pilorum in recog- nition of their effect on the hairs. They arise from the superficial part of the corium, passobliquely downward to be inserted into the sheath of the hair-follicle near the junction of corium and subdermal tissue and on the side corresponding with the inclination of the hair and the situation of the sebaceous glands. Since the latter are closely embraced by the muscular bands, contraction of the muscles exerts pressure upon the glands and facilitates the discharge of their secretion {sebum} hence these muscles are sometimes also designated expressores sebi. The effect of con- traction of the arrectores pilorum is oftenconspicuouslyseen on the surface in the condition known as "goose- flesh" (Vw/'/.ytfw.f^TzVm), where the hairs and surrounding tissue appear to be unusually elevated owing to the upward pull on the hair-follicles and the consequent erection of the hairs in the opposite direction. The blood-vessels supplying the hair-follicle, which in a sense con- stitute a special system for each sac, include the capillary loops ascending within the hair-papilla and the net-work of capillaries surrounding the follicle immediately outside the glassy membrane. The first are derived from a small special twig that ascends to the follicle, and the second from the subpapillary net-work of the corium. With the exception of those draining the papilla, which are tributary to the deeper stc-ms, the veins join the subpapillary plexus. The nerves distributed to the follicles follow a fairly definite arrangement. As shown by Retzius, usually each hair-sac is supplied by a single fibre, sometimes by two or more, which approaches the follicle immediately below the level of the mouth of the sebaceous glands. After penetrating the fibrous sheath as far as the glassy membrane, the nerve-fibre separates into two divisions that encircle more or less completely the follicle and on the opposite side break up into numerous fibrillre constituting a terminal arborization. The nerve-endings usually lie on the outer surface of the glassy membrane within the middle third of the follicle and only exceptionally are found within the outer root-sheath or the hair-papilla. THE NAILS. The- nails (unties), the horny plates overlying the ends of the dorsal surfaces of the fingers and toes, correspond to the (-laws and hoofs of other animals and, like them, are composed exclusively of epithelial tissue. They are specializations of the Papillary Portion of section of injected scalp, showing capillary net-works surrounding hair-follicles and twigs entering papillae. X 20. THE NAILS. 1395 epidermis and, therefore, may be removed without mutilation when the cuticle is taken off after maceration. The entire nail-plate is divided into the body (corpus unguis), which includes the exposed portion, and the root (radix unguis), which is embedded beneath the skin in a pocket-like recess, the nail-groove (sulcus unguis). The modified skin supporting the nail-plate, both the body and the root, constitutes the nail-bed (solum unguis), the cutaneous fold overlying the root being the nail-wall (vallum unguis). The sides of the quadrilateral nail-plate are straight and parallel and at their distal ends connected by the convex free margin (margo liber) that projects for a variable distance beyond the skin. The proximal buried border (margo occultus) is straight or slightly concave, more rarely somewhat convex, and often beset with minute serrations (Brunn). Both surfaces of the transversely arched nail are smooth and even, with the exception of the longitudinal parallel ridges that often mark the upper aspect. Inspection of the latter during life shows color-zones, the translu- cent whitish crescent formed by the projecting portion of the nail being immediately followed by a very narrow yellow band that corresponds to the line along which the stratum corneum of the underlying skin meets the under surface of the plate. The FIG. 1159. ABC Distal portions of fingers, showing relations of nail ; A was drawn from living subject ; B atid C are lateral and under veiws respectively of inner surface of cuticle with nail ; nothing but the epidermal structures are present, the cuticle and nail having been removed together, a, i>, distal and proximal borders of nail ; c, under surface of nail ; d, nail in section ; e, line of deflection of cuticle to under surface of nail ; f, lunula ; g, nail-wall ; A, cuticle in section. succeeding and larger part of the nail is occupied by the broad pink zone which owes its rosy tint to the blending of the color of the blood in the underlying capillaries with that of the horny substance. On the thumb constantly, but on the fingers often only after retraction of the cuticle, is seen a transversely oval white area, the so-called lunula, which marks the position of the underlying matrix. Additional white spots, irregular in position, form and size, are sometimes seen as temporary markings. The thickness of the nail-plate greatest on the thumb and large toe and least on the last digits diminishes towards the sides, but in the longitudinal direction, between the lunula and the free margin of the nail, is fairly uniform ; beneath the white area, however, the under surface of the nail shelves off towards the buried border, where it ends in a sharp edge. Structure. The substance of the nail-plate (stratum corneum unguis) consists entirely of flattened horny epithelial cells, very firmly united and containing the remains of their shrunken nuclei. These cornified scales are disposed in lamellae, which, in transverse section, pursue a course in general parallel with the dorsal sur- face. In nails which possess the longitudinal ridges, however, the latter coincide with an upward arching of the lamellae dependent upon the conformation of the nail matrix (Brunn). In longitudinal section the lamellation is oblique, extending 1396 HUMAN ANATOMY. from above downward and forward, parallel to the shelving under surface beneath the white area that rests upon the matrix. Minute air-vesicles, imprisoned between the horny scales, are constant constituents of the nail-substance. When these occur in unusual quantities, they give rise to the white spots in the nail above mentioned. Corresponding respectively to the colored zones the white, rosy and yellow seen on the dorsal surface of the nail, the nail-bed is divided into a proximal, FIG. 1160. Subcutaneous Stratum ger Stratu Corium ^^VY'; ; of nail-bed /' ..--^ './'.-''; V>*s Transformation -''., zone Matrix *.'/* : Longitudinal section of proximal part of nail lying within the nail groove. X 30. a middle and a distal region, each of which exhibits structural differences. The most important of these regions is the proximal, known as the matrix, which lies beneath the white area and alone is concerned in the production of the nail. The corium of the nail-bed varies in the different regions in the arrangement and size Of its elevations. Within the proximal third of the matrix, these elevations occur in the form of low papillae, which decrease in height and number until they disappear, a smooth field occupying the middle of the matrix. This even field is succeeded by one possessing closely set, low, narrow longitudinal ridges,. that at the distal margin of the lunula suddenly give place to more pronounced, but less numerous broader, linear elevations. These continue as far as the distal end of the nail-bed and are then replaced by papillae. Owing to the strong fibrous bands and the absence of the usual layer of fatty subdermal tissue, the corium of the nail-bed is closely attached to the bone. The fibrous reticulum formed by the interlacing of the longitudinal with the vertical bundles contains few elastic fibres, since these are entirely wanting beneath the body of the nail and only present in meagre numbers within the matrix. In view of its genetic activity, the relations of the epidermis underlying the nail are of especial interest. While the stratum germinativum of the skin covering the finger tip passes directly and insensibly onto the nail-bed, the entire extent of which it invests (stratum Kermina- tivum im^uis), the stratum corneum ends on reaching the under surface of the nail-plate, the line of apposition corresponding to the narrow yellow zone which defines the distal boundary ot the rosy area. Beneath the latter, therefore, the epidermis of the nail-bed consists of the stratum germinativum alone, which, without cornification of any of its cells, rests against the under sur- face of the nail. Beneath the white zone, that is, within the matrix, the epidermis includes a half dozen or more layers of the usual elements of the stratum germinativum, surmounted by a like number of strata of cells distinguished by a peculiar brownish color. On reaching tin- nail these modified epithelial elements, which appear white by rellected light, are not circumscribed, but pass over into the substance of the nail, into the constituent cells of which they are directly con- verted. Their cytoplasm presents a marked fibrillation to which, according to Brunn, the light appearance of the cells is referable as an interference phenomenon and not as a true pigmenta- tion. This peculiarity of the cells, coupled with the relatively small si/e of subjacent capillaries, THE CUTANEOUS GLANDS. 1397 probably accounts for the tint distinguishing the white area. Since the transformation of the cells of the stratum germinativum into those of the nail-plate is confined to the matrix, it is evi- dent that the continuous FIG. 1161. Nail-plate Nail-bed growth of the nail takes place along the floor and bottom of the nail-groove, the last formed increment of nail-substance pushing forward the previously dif- ferentiated material and thus forcing the nail to- wards the end of the digit. The relation of the epi- dermis of the nail-wall to the substance of the plate is one of apposition only, production of the nail oc- curring in no part of the fold. Over the greater extent of the latter all the typical constituents of the cuticle are represented, but within the most proximal portion the stratum germi- nativum alone is present, the stratum corneum fad- ing away. Where the horny layer exists, it rests directly upon the nail, but is differentiated from the latter by being less dense and by its response to stains. As the nail leaves the groove, a part of the stratum germinativum of the nail-wall is prolonged distally for a variable distance over the dorsal surface of the nail-plate as a delicate membranous sheet, the eponychium, which usually ends in a ragged abraded border. Stratum corneum and Stratum germinativum of nail-wall Eponychium Margin of nail Corium Transverse section of nail- wall and adjacent part of nail-plate and nail-bed. X 90. THE CUTANEOUS GLANDS. These structures include two chief varieties, the sebaceous and the sweat glands, together with certain modifications, as the ceruminous glands within the external auditory canal, the circumanal glands, the tarsal and ciliary glands within the eyelid and the mammary glands. In all the epithelial tissues the secreting elements and the lining of the ducts are derivatives of the ectoblast and, therefore, genetically related to the epidermis. THE SEBACEOUS GLANDS. Although these structures (glandulae sebacae) are chiefly associated with the hair-follicles, in which relation they have been considered (page 1394), sebaceous glands also occur, if less frequently, independently and in those parts of the skin in which the hairs are wanting, as on the lips, angles of the mouth, prepuce and labia minora. The size of these glands bears no relation to that of the hairs, since among the smallest (.2-.4 mm.) are those on the scalp. The largest, from .5-2.0 mm., are found on the mons pubis, scrotum, external ear and nose. Conspicuous aggre- gations, modified in form, occur in the eyelid as the Meibomian glands. Depending upon the size of the glands their form varies. The smallest ones are each little more than a tubular diverticulum, dilated at its closed end. In those of larger size the relatively short duct subdivides into several expanded compartments, which, in the largest glands, may be replaced by groups of irregular alveoli, with uncertain ducts that converge into a short but wide common excretory passage. Structure. The structural components of these glands include a fibrous envelope, a membrana propria and the epithelium, the first two being continuous with the corresponding coverings of the hair-follicle. The epithelium continued 1398 HUMAN ANATOMY. . Mouth of gland Alveoli Corium Sebaceous glands from skin covering nose. into the ducts and alveoli of the sebaceous glands is directly prolonged from the outer root-sheath of the epidermis, where associated with the hair-follicles, or from the epidermis where the hairs FIG. 1162. are wanting. The periphery of the alveolus is occupied by a single, or incompletely double, layer of flattened and imper- fectly defined basal cells, that rest immediately upon the mem- brana propria and are distin- Duct guished by their dark cytoplasm ?**e^a ,- an d outwardly displaced oval nuclei. Passing towards the centre of the alveolus, the next .... . ./. , I ce jj s contain a number of small " r~ '.'\ > ^' oil drops which, with each suc- cessive row of cells, become larger and appropriate more and more space at the expense of the protoplasmic reticulum in which they are lodged. In consequence, the cells occupy- ing the axis of the alveoli, which are completely filled and with- out a lumen, contain little more than fat. As the cells are escaping from the glands they x 60. lose their nuclei and individual outlines and, finally, are merged as debris into the secretion, or sebum, with which the hairs and skin are anointed. The necessity for new cells, created by the continual destruction of the glandular elements that attends the activity of the sebaceous glands, is met by the elements recruited from the FIG. 1163. proliferating basal cells, which in turn pass towards the centre of the alveolus and so displace the accumulating secretion. THE SWEAT GLANDS. These structures (glandulae stidoriferae), also called the sudoriparous glands, are the most important representatives of the coiled glands (glandulae glomi- formes) often regarded as constituting one of the two groups (the sebaceous glands being the other) into which the cutaneous glands are divided. They occur within the integument of all parts of the body, with the exception of that covering the red margins of the lips, the inner surface of the prepuce and the glans penis. They are especially numerous in the palms and soles, in the former locality numbering more than noo to the square centimetre (Horschelmann), and fewest on the back and buttocks, where their number is reduced to about 60 to the square centimetre ; their usual quota for the same area is between two and three hundred. Modified simple tubular in type, each gland consists of two chief divisions, the body (corpus) or gland-coil, the tortuously wound tube in which secretion takes place, and the c.vcrrtorv duct (ductus sudoriferus') which opens on the surface of the skin, exceptionally into a hair-follicle, by a minute orifice, the sweat pore (porus sudoriferus), often distinguishable with the unaided eye. The body of the gland, irregularly spherical or flattened in form and yellowish red in color, consists of the windings of a single, or rarely branched, tube and com- monly occupies the deeper part of the corium, but sometimes, as in the palm and I'mm ahvoli of sebaceous glan showing irtiou'aU'il protoplasm due to presence of oil droplets, x 700. THE CUTANEOUS GLANDS. 1399 Stratum "corneum S. lucidum S. granulosum -S.germinativum Duct of sweat-gland Corium scrotum, lies within the subdermal connective tissue. The coiled portion of the gland is not entirely formed by the secretory segment, since, as shown by the recon- structions of Huber, about one fourth is contributed by the convolutions of the first part of the duct. On leaving the gland-coil, in close proximity to the blind end of the gland, the duct ascends through the corium with a fairly straight or slightly wavy course as far as the epidermis. On entering the latter its further path is marked by conspicu- ous cork-screw-like windings, which, where the cuticle is thick as on the palm, are close and number a dozen or more and terminate on the surface by a trumpet-shaped orifice, the sweat-pore. In its course through FlG - Il6 4- the corium the duct never traverses a papilla or ridge, but always enters the cuti- cle between these ele- vations. On the palms and soles, where the pores occupy the sum- mit of the cutaneous ridges, the ducts enter the cuticle between the double rows of papillae. Structure. The secreting portion of the gland-coil, called the ampulla on account of its greater diameter, possesses a wall of remarkable structure. The thin external sheath, composed of a layer of dense fibrous tissue and elastic fibres, supports a well defined membrana propria. Immediately within the latter lies a thin but compact layer of invol- iintary muscle whose longitudinally disposed spindle - shaped ele- ments in cross-section appear as a zone of irregularly nucleated cells that encircle the secreting epithelium and displace it from its customary position against the basement membrane. This muscular tissue enjoys the distinction, sharing .it with the muscle of the iris, of being developed from the ectoblast. The secreting cells constitute a single row of low columnar epithelial elements, that lie internal to the muscle and surround the relatively large lumen. Their finely granular cytoplasm contains a spherical nucleus, situated near the base of the cell, and in certain of the larger glands, as the axillary, includes fat droplets and pigment granules. These are liberated with the secretion of the gland and when present in unusual quantity account for the discoloration produced by the perspiration of certain individuals. In the case of the ceruminous glands, the amount of oil and pigment is constantly great and confers the distinguishing characteristics on the ear-wax. The sudden and conspicuous reduction in the size of the tube which marks the termination of the secreting segment and the beginning of the duct, is accompanied by changes in the structure of its wall. In addition to a reduction of its diameter to f-S?''' .,- Fat-cells Coiled part of sweat-gland Section of skin from palm, showing different parts of sweat-glands extending from surface into tela subcutanea. X 65. 1400 HUMAN ANATOMY. Muscle-cell Secreting-cells Parts of duct one-half or less of that of the ampulla, the duct loses the layer of muscle and becomes flattened, with corresponding changes in the form of its lumen. The single row of secreting elements is replaced by an irregular double or triple layer of cuboidal cells, which exhibit an homogeneous zone, sometimes described as a cuticle, next the lumen. On entering the epidermis, the duct not only loses its fibrous sheath and membrana propria, but the epithelial constituents of its wall are soon lost among the cells of the stratum gerfninativum, so that its lumen is continued to the surface as a spiral cleft bounded only by the cornified cells of the cuticle. Apart from mere variations in size, certain glands the circumanal, the ciliarv and the ceruminous depart sufficiently from the typical form of the coiled glands to entitle them to brief notice. The circumanal glands, lodged chiefly within a zone from 12-15 mm - wide and about the same distance from the anus, are not all the same, but include, according to Huber, four varieties. In addition to ( i ) the usual sweat glands and (2) some (Gay's) of excep- tional size, (3) others have relatively straight ducts that end in expanded saccules, from which' secondary alveoli arise ; finally (4) branched glands of the tubo-alveolar type are present. The cili- ary glands (Moll's ) of the eyelid are not typical coiled structures, but belong to the branched tubo-alveolar groups. The ceruminous glands, distinguished by the large amount of oil and pigment mingled with their secretion, are likewise refer- able to the branched tubo- alveolar type. The blood-vessels of the sweat glands include arterial twigs given off from the cutaneous rete, a capillary net-work outside the mem- brana propria, best developed within the coiled portion of the tube, and the veins that join the deeper plexus within the corium. The nerves are especially numerous and consist of nonmedullated sympathetic fibres that traverse the fibrous sheath and form a close plexus on the outer surface of the membrana propria. From this net-work fibrillae penetrate the basement membrane and end in close apposition with the gland-cells and muscle-elements. Their termination on the secreting cells is, according to Arnstein, in the form of peculiar endings consisting of groups and clusters of minute terminal knobs with which the nerve fibrillae, without or after division, are beset. THE DEVELOPMENT OF THE SKIN AND ITS APPENDAGES. The Skin. The integument consists of two genetically distinct parts the t-fiillu'/inni (epidermis) developed from the ectoblast, and the connective tissue (corium and tela subcutanea) from the mesoblast. During the earliest stages of development the ectoblast is represented by a single layer of cells, which, by the end of the first month, is in places reinforced by an external second layer, that by the seventh week has appeared over the entire surface. This double layer now consists Parts of coiled secreting segment Muscle-cells T Section of deeper coiled portion of sweat-gland. X 325. DEVELOPMENT OF SKIN AND APPENDAGES. 1401 FJG. 1166. Sections of developing skin, showing earliest stages in formation of hair-follicles; in D epithelial cylinder is invading mesoblast. X 90. of a deeper row of cuboid or low columnar cells, covered by a superficial sheet, known as the epitrichium, composed of flattened elements often lacking in definition, and nuclei. During the succeeding weeks the epitrichial cells become swollen and vesicular and differentiated from the underlying elements, which meanwhile are engaged in producing the epidermis. The epitrichium persists until the sixth month, when it becomes loosened and is cast off. During the third and fourth months the ectoblastic cells have so multiplied, that from four to five layers are present, those next the mesoblast being columnar and rich in protoplasm, while the more superficial are irregular and clearer. By the middle of the fifth month, by which time the layers have increased to almost a dozen, the outer cells become horny and assume the characteristics of a stratum corneum, while the deepest ones represent the stratum germi- nativum, with an intervening transitional zone. About the sixth month desquamation of the surface cells begins, the discarded epitrichial and other scales mingling with the secre- tion from the sebaceous glands, which meanwhile have been developed, as constituents of the white unctuous coating, the vernix caseosa (smegraa embryonum), that covers the surface of the fcetus, especially in the folds and creases. During the last weeks of gestation the epidermis acquires considerable thickness and a sharper differentiation of its component strata. The connective tissue part of the skin is developed as a superficial condensation of the mesoblast, that during the first month consists of closely placed spindle cells. Coinci- dently with the appearance of the fibrous fibrillae, in the third month, differentiation takes place within the condensed mesoblastic tissue, which so far exists as a uniform zone, into a superficial and more compact layer and a deeper and looser one ; the former becomes the corium and the latter the tela subcutanea. Within the last layer soon appear larger or smaller groups of round cells in which oil drops, at first minute and then of increasing diameter, indicate the beginning of their conversion into adipose tissue. By the sixth month the panniculus adiposus is established. About the fifth month the line marking the junction of cuticle and corium becomes uneven in consequence of the development of the papillae and ridges of the corium and the attendant invasion of the epidermis. Certain of the mesoblastic cells are transformed into the component elements of the involuntary muscle that occurs either associated with the hair follicles as the arrectores pilorum, or as the more extended tracts of the dartos. The Hairs. The primary development of the hair begins about the end of the third month of fcetal life as localized proliferations of the epidermis. In section these appear as lenticular thickenings and on the surface as slight projections. Very soon solid epithelial cylinders sprout from the deeper surface of these areas and invade the subjacent corium to form the anlages of the hair-follicles. The original uniform outline of these processes is early replaced by a flask-shaped contour in consequence of the enlargement of their ends which in their growth surround connective tissue processes to form the hair-papilla. The embryonal connective tissue immediately surrounding the epidermal ingrowth differentiates into the fibrous sheath and the glassy membrane. Meanwhile and even before the formation of the papilla the epithelial contents of the young follicles differentiate into an axial strand of spindle cells that later undergo keratinization and become the hair-shaft that grows by subsequent additions FIG. 1167. -follicle Papilla Developing skin, showing later stages of forma- tion of hair-follicles; surrounding mesoblast is forming hair-papilla and fibrous sheath of follicle. X 90. 1402 HUMAN ANATOMY. FIG. 1168. from the matrix surmounting the papilla. In addition to forming the outer root- sheath the peripheral elements contribute the matrix-cells that occupy the fundus of the follicle and surround the papilla. The cells covering the summit and adjacent sides of the papilla are converted into elongated spindles that later gradually become horny and assume the characteristics of the cortical substance of the hair. When present, the medulla is developed by the transformation of the cells occupying the summit of the papilla, which enlarge, become less granular and grow upward as an axial strand that invades the chief substance of the hair and accumulates kerato- hyalin within its cells. At first present as minute drops, this substance increases in quantity until it occupies the cells in the form of large vesicles. The subsequent disappearance of these, followed by shrinkage of the cells and the introduction of air, completes the differentiation of the medulla. The pigment particles, which appear later, are first evident in the hair-bulb and probably arise within the epithelial tissue. The elements of the hair-cuticle and of the inner root-sheath are differentiated from the matrix-cells at the sides of the papilla. The tall columnar elements become elongated and converted into the cornified plates of the cuticle both of the hair and of the inner root-sheath. The layers of Huxley and of Henle are derived from cells that soon exhibit granules of keratohyalin, so that on reaching the level of the summit of the papilla the process of cornification has been estab- lished. This is especially marked in the elements of Henle' s layer, in which the deposit takes the form of a longi- tudinal fibrillation. The growth of the hair takes place exclusively at the lower end of its bulb, where, so long as the hair grows, the conversion of the matrix- cells into the substance of the hair is continuously progressing. By this pro- cess the substance already differentiated is pushed upward by the cells under- going transformation and these in turn are displaced by the succeeding elements. In this way, by the addition of new increments in its bulb, the hair is forced onward and, in the case of those first formed, through the epidermis that still blocks the mouth of the follicle. This eruption begins on the scalp and regions of the eyebrows about the fifth foetal month and on the extremities about a month later. Sebaceous gland Root-sheath Bulb Papilla- Developing skin, showin is now ing later stage of hair-follicle; hair differentiated. X 80- The hairs covering the foetus are soon shed, during the last weeks of gestation and immedi- ately following birth, and are replaced by the stronger hairs of childhood. These latter, too, are continually falling out and being renewed until puberty, when in many localities, as on the scalp, face, axilla and external genital organs, they are gradually replaced by the- much longer ami thicker hairs that mark the advent of sexual maturity. Even after attaining tlu-ir mature growth, the individual life of the hairs is limited, those on the scalp probably retaining their vitality for from two to four years and the eyelashes for only a few months (Pincus). During the years of greatest vitality not only are the discarded hairs replaced by new ones, but the actual number of hairs may increase in consequence of the development of additional follicles from the epidermis after the manner of the primary formation. When from age or other cans, the hair-follicles loose their productive activity and, therefore, are no longer capable of replacing the atrophic hairs, more or less conspicuous loss of hair results, whether only tem- porary or permanent evidently depending upon the recuperative powers of the follicles. The change of hair that is continually and insensibly occurring in man, in contrast to the conspicuous periodic shedding of the coat seen in other animals, includes the atrophy of the old hair on the one hand, and the development of the new on the other. The earliest manifestations of this atrophy, as seen in longitudinal sections of the hair- follicle, are reduction in the sixe and differentiation of the mass of matrix-cells at the bottom of the follicle and the diminution of the hair-papilla. The progressive reduction of the matrix is DEVELOPMENT OF SKIN AND APPENDAGES. 1403 FIG. 1169. accompanied by the production of a club-shaped enlargement of the hair, between which and the shrunken matrix a strand of atrophic epithelial cells for a time remains. With the continued progress of these changes, the root of the club-hair, as the degenerating hair is termed, shortens so that the bulbus enlargement recedes from the bottom of the hair-sac, until it lies just below the narrow neck of the follicle, where it remains for a longer or shorter period until the hair is dislodged and finally discarded. A hair that has fallen out in consequence of these atrophic changes presents well-marked differences in the appearance and structure of its root from a growing hair removed by force. In the discarded hair the root possesses the characteristic club shape, with contours broken by irregular processes composed of the splintered cortical substance, which alone forms the terminal bulb that is always solid and has neither cuticle nor medulla. While the old hair is still lodged in the upper part of the follicle, the first steps towards its replacement are initiated by the stratum germinativum of the old hair-sac. Whether surrounding a new papilla, as held by many, or capping the revived original one (Brunn), the deepest follicle-cells contribute by proliferation the material from which the new hair is developed in a manner agreeing essentially with that in which its predecessor was evolved. pilla Section of foetal skin, show- ing sebaceous gland developing from hair-follicle. X 90. FIG. 1170. The Nails. The first appearance of a definite nail- area on the dorsum of the distal phalanx is seen towards the end of the third foetal month (Kolliker), although Zander has described a local thickening of the epidermis covering the tip of the digit at the ninth week. By the fourth month the nail-area shows as a slightly depressed field that is defined proximally and laterally by a curved swelling, the earliest suggestion of the nail-wall. Distally the field is limited by a transverse elevation. Shortly after the nail-area has been thus defined, the outer cells of its stratum germinativum exhibit deposits of keratohyalin which, by the end of the fourth month, lead to the formation of a thin overlying layer of nail-substance. For a time this gains in thickness by additions to its under surface alone, the primary nail being produced by the progressive conversion of the cells of the stratum granu- losum, which is present throughout the nail-area. At this stage the young nail lies completely buried within the epidermis, lying between the most superficial elements of the epidermis and the epitrichial cells above, and the deeper layers of the cuticle below. The overlying epithelial mass, composed of the epidermal and epitrichial elements, constitutes the eponychium, the remains of which, after the disappearance of its middle and distal parts, are subsequently seen as a thin mem- brane covering the proximal part of the nail-plate. As yet the young nail-plate has not come into relation with the epidermis of the nail-groove, since it is still confined to the primitive area. But during the fifth month the proximally growing root invades more and more the sulcus until it attains its definite relations with the nail-wall. Meanwhile the nail-bed beneath the developing root undergoes thickening and becomes the matrix, while the cells containing keratohyalin gradually disappear from, the distal region of the nail-area in consequence of their com- pleted conversion into the nail-substance. Subse- quently these cells are limited to the proximal nail-producing zone of the matrix from which, after the initial formation of the primary nail-substance, the nail alone receives the additions necessary for its continued growth. In consequence of the resulting forward growth the nail pushes its way through the elevated distal boundary of the nail-field, the epithelium lying above the nail-plate being lost, while that below remains as the representative of the sole-plates that are well marked in many other animals. Section of foetal skin, showing develop- ing sweat-glands ; a, is less advanced than b and c. X 100. 1404 HUMAN ANATOMY. The Sweat Glands. The development of these, the most important members of the group of coiled glands, begins during the fifth foetal month as solid epithelial sprouts from the under surface of the epidermis. At first cylindrical in form, these processes soon acquire a club-shaped lower end and for a time resemble developing hair-follicles. The terminal segment of the gland-anlage enlarges in diameter and thus early differentiates the later ampulla. With subsequent increase in length, the characteristic coils soon appear, after which a lumen makes its appearance in the ampullary segment and gradually extends to the surface. Practical considerations of the skin find mention in connection with the various regions, to which the reader is referred. THE NOSE. Although only a small part of the nasal chambers is occupied by the peripheral olfactory organ in man, the greater part forming the beginning of the respiratory tract, comparative anatomy and embryology establish the primary significance of the nasal groove and its derivations as the organ of smell, the relation of the nose to respiration being entirely secondary. The nose, therefore, is appropriately grooped with the organs of special sense, notwithstanding its relation to the proper production of voice and to taste and the role that it plays in varying facial expression. The nose consists of two portions, the outer nose (nasus externus) and the inner chamber (cavum nasi), which is divided by the median partition into the right and left nasal fossa? The outer nose forms the prominent triangular pyramid that projects from the glabella forward and downward, supported by a bony and cartilaginous framework and covered by muscles and integument. Its upper end or root (radix nasi) springs from below the glabella from the frontal bone, with which it usually forms an angle and from which, in consequence, it is separated by a groove. When the latter is wanting and the rounded median ridge, or dorsum, of the nose continues the plane of the forehead, the nose is said to be of the Grecian type. The dorsum ends below in a free angle or point (apex nasi), the upper or bony part of the dorsum, often termed the bridge, in the aquiline type of nose forming a more or less conspicuous angle with the cartilaginous part. The sides of the nose (partes laterales nasi) descend from the root with increas- ing'Obliquity until they reach the broadest part of the nasal pyramid, or base, which is pierced by the openings of the nostrils or anterior nares (nares). Just before meeting the base, each lateral surface expands -into the mobile and rounded wing (ala nasi) that forms the outer wall of the nostril and is limited above by a shallow- groove, the alar sulcus. Under the influence of the attached muscles, the alae are subject to dilitation, compression, elevation and depression and thereby participate in modifying facial expression. In addition to the endless minor variations of form that the outer nose presents, which, apart from individual distinction, have little significance, the relation of its greatest breadth across the ala; to its total length, from root to tip, is of sufficient anthropological importance to receive attention in the classification of the races of /greatest breadth X ioo\ mankind. This relation, the cephalometnc nasal index I = -r \ greatest length / varies with different races, according to Topinard the index of the white races being below 70 (leptorhines} , that of the yellow and red races between 70 and 85 (mesorhines), and that of the black races above 85 (platyrkmes). THE CARTILAGES OF THE NOSE. The cordiform nasal opening (.-iportura pyrifonnis) of the facial skeleton, bounded by the free margins of the nasal and superior maxillary bones, is enclosed and continued to the anterior nares by the nasal cartilages and contiguous fibrous tissue. These cartilages arc- usually considered as including five chief plates, the unpaired sef>a/-am\ the paired nf>f>er and lower lateral, and a variable number of smaller THE CARTILAGES OF THE NOSE. 1405 supplemental pieces (cartilagines minores). The conventional division of the first three, however, is unwarranted, since embryologically and morphologically they constitute one piece (cartilage mediana nasi), which even in the adult is represented by the connected septal and upper lateral plates. The cartilage of the septum (cartilage septi nasi) (Fig. 1171) completes the median partition that divides the right and left nasal fossae from each other and represents the anterior extremity of the primordial cartilaginous cranum. It is irregularly rhomboidal in form and so placed that its superior angle lies above, received between the nasal bones and the median plate of the ethmoid, and its inferior angle below, resting upon the incisor crest of the maxillae. The anterior angle is directed forward and the posterior, much the more pointed, is prolonged as the sphenoidal process (processus sphenoidalis septi cartilaginei) for a variable distance between the mesethmoid and the vomer towards the body of the sphenoid, which exceptionally it may reach. The antero-superior margin of the septal carti- lage, thickest above, is attached to the under surface of the internasal suture for a FIG. 1171. Perpendicular plate of ethmoid Frontal sinus Septal cartilage ^. ' I Sphenoidal sinus Mesial crus of left lower lateral cartilage Sphenoidal process Vomer Nasal septum viewed from left side ; mucous membrane has been partially removed. distance of from 12-15 mm - Below the nasal bones, the margin of the septal cartilage is continuous with the upper lateral cartilages which form ring-like expan- sions (alae) of the median plate. Still lower, the free-margin of the latter extends between the lower lateral cartilages to within about a half inch from the tip of the nose which, however, it does not reach, the medial crura of the lower lateral plates intervening. The postero-superior margin, the thickest part of the cartilage, is attached to the free margin of the perpendicular plate of the ethmoid bone. The postero-inferior margin rests upon the anterior part of the upper margin of the vomer and the incisive crest as far as the anterior nasal spine, where the border passes into the rounded antero- inferior margin that joins the nasal spine with the anterior angle. This border is always convex and does not reach the lowest part of the partition between the nostrils, which being devoid of septal cartilage, is freely movable and constitutes the septum -mobile. The upper lateral cartilages (cartilagines nasi laterales) (Fig. 1172) are two triangular plates, one on either side, that by their median and longest border are attached to the septal cartilage, with which in their upper part they are directly continuous. The upper margin of each is joined to the free border of the nasal bone, which it slightly underlies, and, exceptionally, the adjacent edge of the maxilla. The lower margin is embedded in fibrous tissue which connects it with the adjoining plates. The median parts of the cartilages are markedly convex and separated by a slight groove that is, for the most part, obliterated by fibrous tissue. 1406 HUMAN ANATOMY. Upper lateral cartilage Nasal bone Septal cartilage Cartilage at tip Bony and cartilaginous framework of nose, front aspect. The lower lateral cartilages (cartilagines alares majores) (Fig. 1172) area pair of thin curved plates that encircle the apertures of the nostrils anteriorly and constitute the framework of the tip of the nose. Each cartilage consists of an inner P/ate(crus mediate), from 67 mm. FIG. 1172. broad, which, with its fellow of the opposite side, embraces the lower and anterior part of the septal cartilage and aids in com- pleting the partition separating the nares. In front it narrows, bends sharply outward, and passes more or less abruptly into a broader outer plate ( crus laterale), which is of very uncertain form and size, although of a general elongated oval shape and some 12 mm. broad. The triangular space between the varyingly prolonged posterior end of the lateral plate, the maxilla and the upper lateral cartilage is filled out by fibrous tissue in which are embedded two, three or more small cartilaginous pieces (cartilagines alares minores). These vary greatly in size and form, but in a general way tend to complete the ring of cartilage surrounding the lateral wall of the nares. They do not, however, reach the lower border of the nasal ring, which, as well as the remaining part of the lower boundary of the aperture of the nostril, is devoid of cartilage and composed of integument and fatty connective tissue. The rounded anterior angles of the lower lateral cartilages occupy the tip of the nose, close together when this is pointed, but separated by a space that shows externally as a more or less evident groove when the tip of the nose is blunt and broad. The median plates approach the septal cartilage closer in front than behind, where they curve outward to end in a rounded and upward curving hook. The fibrous tissue uniting the median borders of the lower lateral plates with the anterior edge of the septal cartilage usually contains two small sesamoid cartilages (cartilagines sesamoideae nasi) that partly fill the triangular intervals on either side of the median line. The vomerine cartilages (cartilagines vomeronasales) are two narrow strips, from 1-2 mm. wide and from 10-15 mm. long, that lie, one on either side, along the lower border of the septal cartilage in the vicinity of the nasal crest. They are attached to the carti- lage and bone by fibrous tissue and situated beneath the mucous membrane lining the nasal fossae. Their chief interest is their rela- tion to the rudimentary organ of Jacobson (page 1417) below which they lie. In animals in which the organs are well devel- oped these cartilages form protect- ing and supporting scrolls ; in man, however, both organ and cartilage are so feebly developed that they loose their close relation. The integument covering the outer nose is in general thin and closely bounc down to the underlying fibrous tissue, being particularly unyielding over the Up ami al;c. With the exception of within the al;i- and lateral borders of the nostrils, the FIG. 1173 Lower lateral cartilage Upper lateral cartilage Small alar cartilage Cartilage of tip Lateral crus Mesial crus canilage Nasal aperture Septal cartilage Cartilages of nos>-. \ if\\ PRACTICAL CONSIDERATIONS: THE EXTERNAL NOSE. 1407 fatty tissue is very meagre. The sebaceous glands, on the other hand, are well developed and open in many instances in conjunction with the follicles of the delicate hairs that cover all parts of the surface. On the alae the closely placed glands are of exceptional size and open by ducts readily seen as minute depressions. Vessels. In order to compensate for the exposed position, the external nose is generously supplied with arteries, derived chiefly from the facial and ophthalmic, which are united by numerous anastomoses with each other as well as with branches from the infraorbital. The veins are all tributary to the angular vein, which begins at the inner canthus and descends along the side of the nose to the facial trunk, receiving in its course the dorsal, lateral, and alar branches. The angular vein communicates with the ophthalmic and the veins of the nasal fossa. The lymphatics are arranged in three sets (Kiittner). The first, beginning at the root of the nose, passes above the upper eye-lid and along the supraorbital ridge to the parotid nodes. The second group, formed by the superficial and deep lym- phatics at the nasal root, skirts the lower margin of the orbit and ends in the lower parotid nodes. The third and most important set includes from 6 to 10 trunks that follow the blood-vessels and end in the submaxillary nodes. The nerves supplying the outer nose include the motor branches of the facial . to the muscles and the sensory twigs from the trifacial to the skin, distributed by the infratrochlear and nasal branches of the ophthalmic and by the infraorbital of the superior maxillary. PRACTICAL CONSIDERATIONS : THE EXTERNAL NOSE. The Nose may be congenitally absent, or bifid, or imperfect, as from absence of the septum or of one nostril, or very rarely of both nostrils. As to its external aspect it may be of various types, e.g.: Grecian, when the dorsum is on a practi- cally continuous straight line with the forehead, with no marked naso-frontal groove ; aquiline, with the dorsum slightly arched ; rounded, with the arch much more pronounced; foetal "pug" with the bridge depressed and the nostrils directed somewhat forward. The foetal type is simulated in the new born by the subjects of inherited syphilis in whom the bridge of the nose is often much depressed as a result either of (a) imperfect development following the severe specific coryza that affects the nasal mucosa and, through the close apposition of the latter to the periosteum of the fragile nasal bones, interferes with their nutrition ; or () by actual caries or necrosis of those bones or of the septum favored by the same conditions. In acquired syphilis the similar nasal deformity is practically always the result of the destruction of the septum, or, less frequently, of the nasal bones, by late (tertiary) lesions. As a consequence of faulty development in the anterior mid-portion of the frontal bone the membranes of the brain may protrude, forming a meningocele, which is more common at the naso-frontal junction than elsewhere. Occasionally the defect permitting the protrusion exists in the cribriform plate of the ethmoid, and the meningocele occupies the nasal fossa, having under these circumstances been mistaken for a nasal polyp and removed, death resulting from subsequent septic meningitis. The cosmetic importance of the nose is so great, the diseases producing deformity so frequent, and the susceptibility of the organ to injury so marked, that much ingenuity has been expended upon devices to restore it when lost, or to improve its appearance. In the Tagliacotian operation a cutaneous flap is taken from the arm which is held close to the nose by a complicated dressing until the flap is firmly united in its new position, when its pedicle is detached from the arm. The Indian method is more particularly anatomical, since the flap taken from the fore- head is so fashioned that it receives intact the blood from the frontal branch of the ophthalmic artery from the internal carotid, "the ophthalmic receiving at the origin of the frontal an important anastomosis from the angular branch of the facial artery, which is given off from the external carotid artery. For partial deformities flaps may be taken from the sides according to the size and situation of the deficiency. I 4 o8 HUMAN ANATOMY. As upon other parts of the face, plastic operations are very successful owing to the free blood supply. Acne rosacea is common on account of the ready response in vascularity of the nose to external irritating influences, and to internal disturbances of the circulation, as from heart and lung disease, chronic gastritis, and alcoholism. Furuncles and superficial infections are frequent because of the number of sebaceous and sweat glands present. Lupus and in the alar sulcus rodent ulcers are com- mon because of the constant exposure of the nose to external irritation and to lowering of temperature, depressing its vital resistance. Frost-bite of the nose is also common, especially about the tip, because of its exposed position and the lack of protection to the delicate vessels from overlying tissues. The nerve supply to the nose is likewise very free, as is shown in a practical manner by the pain which accompanies inflammatory conditions, especially those involving the lower cartilaginous portion where the skin and subcutaneous tissues are very adherent. The resulting exudate is therefore much confined, pressing upon the nerves ; this accounts also for the frequency with which gangrene occurs under these circumstances. Watering of the eyes from irritation of the skin or mucous membrane of the nose is due to the free nerve supply, and to the fact that the same nerve, the tri- geminal, supplies the nose and the lachrymal apparatus ; as a portion of the nasal chamber is supplied by a branch of the ophthalmic nerve, raising the eyes to the sun will often give the added irritation necessary to precipitate a sneeze when the nasal stimulus suggests one, but is not quite strong enough unaided. Cough and bronchial asthma have resulted from nasal affections due to the indirect relations between the fifth cranial nerve and the pneumogastric. As the olfactory portion of the nasal fossa is in the upper portion of the cavity, an earnest effort to recognize an odor or to enjoy one to the utmost, is accompanied by a deep inspiration through the nose with dilatation of the nostril. In paralysis of the facial nerve, the involvement of the dilatores naris has been thought to explain the lessening of the olfactory sense sometimes seen in this condition. Paralysis of the levatores alae nasi muscles has permitted the nostrils to close during inspiration, causing stridor and mouth-breathing. The loss of the sense of smell is a not uncommon result of severe blows, especially on the forehead, and may be due to (a) concussion of the olfactory bulbs ; () fracture of the cribriform plate of the ethmoid ; (c) injury to the olfactory roots where they cross the lesser wing of the sphenoid ; or (d) lesion of the olfactory nerves where they traverse the cribriform foramina. Sneezing from irritation of the nose is probably due to the indirect relationship between the fifth pair and the vagus and may be so violent that serious injury may result, as in cases in which a subcoracoid luxation of the shoulder, a fracture of the ninth rib, and the rupture of all the coverings of a large femoral hernia were produced by this act (Treves). The abundant sweat and sebaceous glands in the skin of the nose account for the frequency with which acne vulgaris attacks it. The alse, the only movable por- tions, take part in the movements of expression, as in contempt and scorn. Fractures of the nose are common because of its exposed position, and of the frequency of blows and other forms of violence applied to the face. Their chief importance depends upon the prominence of the nose as a feature of the face, any change in its shape attracting general attention. The fracture occurs most com- monly in the lower part, because of the greater weakness of the bones and their greater prominence at that level. In its upper part, the relative depression of the dorsum, the greater thickness of the bones, and their more firm support, make fracture less common. On the other hand, the higher fractures arc mere dangerous because of their possible relation with the cribriform plate and sinuses of the ethmoid bone, the frontal sinuses and the nasal duct. Involvement of the cribriform plate is in effect a compound fracture of the base of the skull, exposing the meninges to the danger of infection. Fractures of the nose are almost always compound, because of the intimate adhesion of the mucous membrane to the bone, with little intervening tissue, so th:it when the hone breaks the overlying adherent tissue is torn through. This accounts for the practically uniform occurrence of epistaxis, on account of which it is often difficult to detect the presence of escaping cerebro-spinal fluid when the THE NASAL FOSS.E. 1409 cribriform plate is also fractured. On the other hand, the rich glandular supply of the mucous membrane, which makes the usual mucous secretion exceptionally free, may, in a post-traumatic coryza, result in a watery discharge of such quantity as to suggest the escape of the cerebro-spinal fluid. Emphysema within the orbit and under the skin may result from the communication of the nose with the ethmoidal or frontal sinuses. In the effort to keep the nose clear of blood by blowing, the air is forced into the subcutaneous tissues. In fractures at the lower part, the deformity is frequently lateral, because of the greater exposure to side blows, and the tendency of the cartilaginous alae and septum to avoid crushing. In the upper part depression is more likely, because of the tendency to escape any but forces from in front, the greater force necessary to produce the fracture, and the presence of a bony septum underneath, which crushes rather than bends. When the deformity has been replaced there are no strong muscles to repro- duce it, so that little or no effort is necessary to maintain the fragments in position. The deformity must be reduced early and the reduction maintained, because owing to the free blood supply, union is usually rapid, sometimes occurring in a week. One must bear in mind in reducing the deformity that the roof of each nasal fossa is not more than 2-3 mm. wide, and that, therefore, a narrow rigid instrument is necessary to press the fragments upward into their normal positions. THE NASAL FOSSAE. The cavity of the nose is divided by the median septum into two nasal fossae which extend from the anterior to the posterior nares, or choance, through which they open into the naso-pharynx. They communicate more or less freely with the accessory air-spaces within the frontal, ethmoid, sphenoid and maxillary bones, into which, as a lining, the mucous membrane of the nasal fossae is directly continued. Seen in frontal section (Fig. 1176), each fossa is triangular in its general outline, the apex being above at the narrow roof and the base below on the floor. The smooth median wall is approximately vertical and meets the floor at almost a right angle, while the sloping lateral wall is modelled by the projecting scrolls of the three turbinates, which overhang the corresponding meatuses. In sagittal sections (Fig. 1 174) the contour of the fossa resembles an irregular parallelogram from which the upper front corner has been cut off, so that in front the upper border slopes downward to correspond with the profile of the outer nose. The greatest length of the fossa, measured along the floor, is from 7-7.5 cm. (2^-3 in.) and its greatest height from 4-4.5 cm. The width is least at the roof, where it is less than 3 mm., and greatest in the inferior meatus a short distance above the floor, where it expands to from 15-18 mm. The Vestibule. The anterior part of the fossa, immediately above the open- ing of the nostril and embraced by the outer and inner plates of the lower lateral cartilage and adjoining portion of the septum, is somewhat expanded and constitutes ] the vestibule (vestibulutn nasi), a pocket-like recess prolonged towards the tip being ; the ventricle (recessus apicis). These spaces are lined by delicate skin, directly con- tinuous with the external integument and tightly adherent to the underlying cartilage, and, in the lower half of the vestibule, containing numerous sebaceous glands and hairs. In the vicinity of the nostril the hairs, known as vibrissce, are coarse and long and curved downward to afford protection to the nasal entrance. Over the upper part of the vestibule, the skin is smooth and closely attached to the lower lateral cartilage, the upper margin of the outer plate projecting as a slightly arching ridge, the limen vestibuli, which forms the superior and lateral boundary of the vesti- bule and marks the line of transition of the skin into the mucous membrane that lines the remaining parts of the nasal fossa. Above and beyond the vestibule, the nasal fossa rapidly expands into a triangular space, the atrium nasi, that lies in advance of the entrance into the middle nasal meatus. Above and in front the atrium is bounded by a low and variable ridge, the agger nasi, that represents a rudimentary naso-turbinate, which in many mammals attains a large size. The space lying in front of the agger, extending 89 1410 HUMAN ANATOMY. from the limen to the cribriform plate of the ethmoid and roofed in by the forepart of the arched upper boundary of the fossa, is long and narrow in consequence of the approximation of the median and lateral walls. It leads from the nasal aperture to the summit of the nasal fossa and to it Merkel applied the name carina nasi. The Nasal Septum. The median wall consists of the partition formed chiefly by the perpendicular plate of the ethmoid, the vomer and the septal cartilage, cov- ered on both sides by mucous membrane. The extreme lower and anterior part of the septum, consisting of the alar cartilage and the integument, is flexible, and there- fore called the membranous portion, or septum mobile ; the terms bony and cartilagi- nous portions are applied to the remaining parts of the septum supported by bone and cartilage respectively. While during early childhood its position is median, in the great majority of adults the septum presents more or less asymmetry and lateral deflection, most often FIG. 1174. Frontal sinus Nasal bone Superior turbinate Spheno-ethmoidal recess Opening of sphenoidal sinus Superior meatus Agger nasi Opening of Eustachian tube rm\ltl* \ \ \ \ Posterior limit of nasal fossa Middle meatus Middle turbinate Inferior meatus Right nasal fossa, lateral wall ; and naso-pharynx. to the right. This deviation may affect the septal cartilage alone, may be limited to the bones (in 53 per cent, according to Zuckerkandl), or may be shared by both. The most common seat of the deflection is the junction of the ethmoid and vomer, in the vicinity of the spheno-ethmoidal process, or along the union of the vomer and the septal cartilage. The asymmetry may involve the entire septum, which then is oblique ; or it may take the form of a simple bulging towards one side, a double or sigmoid projection ; or be an angular deflection resembling a fold, crest or spur that projects into one, sometimes both, of the fossae (Heymann). Although the mucous membrane covering the nasal septum is generally smooth and of fairly constant thickness, its surface is marked by inequalities caused chiefly by variations in the amount and development of the glandular and vascular tissue. One such accumulation, the tubcrcidnm scpti, is relatively constant and on the septum about opposite the anterior end of the middle turbinate. During early life a series of from four to six or more oblique ridges, plica scpti, often model the lower and posterior part of the septum, extending from below upward and forward. Slightly above the anterior nasal spine, the septal mucosa presents the minute openings lead- ing into the rudimentary organ of Jacobson. Behind, the margin of the bony septum is covered by mucous membrane of unusual thickness which, therefore, forms the immediate free edge of the partition separating the posterior nares. The Lateral Wall. The lateral wall of the nasal fossae is characteristically modelled by the projecting scrolls (conchac nasi) of the three turbinates. The latter partly subdivide each fossa into three lateral recesses, the superior, middle, and THE NASAL 1411 inferior meatuses. These are overhung by the corresponding bony concha, the superior meatus being roofed in by the upper turbinate and the inferior lying between the lower turbinate and the floor of the fossa. That part of the nasal fossa between the conchae and the septum, into which the recesses open medially, is sometimes called the meatus nasi communis. The details of the nasal fossa as seen within the macerated skull have been described in connection with the skeleton (page 223). In the recent condition, when the soft parts are in place, while their general contour is preserved, the compartments of the fossae are materially reduced in size by the thickness of the mucous membrane and the erectile tissue that cover the bony framework. The Superior Meatus. Corresponding to the small size of the upper turbinate, the superior meatus (meatus nasi superior), or ethmoidal fissure, is narrow and groove-like and little more than half the length of the middle one. It is directed downward and backward and is floored by the convex upper surface of the middle concha. When the upper turbinate is replaced by two scrolls (conchae superior et suprema) a condition that Zuckerkandl regards as very frequent, if indeed, not the more usual the meatus is accordingly doubled. Into the upper and front part of the superior meatus the posterior ethmoidal air-cells open by one or more orifices FIG. 1175. Frontal sinus Probe in infundibulum Middle turbinate, partly removed Hiatus semilunaris Ethmoidal bulla Openings Agger nas: of maxillary sinus into infundibulum Ventricle Li men nasi Vestibul Probe in naso-lachrymai duct Opening of middle ethmoidal cells Superior turbinate, partly removed ening into spheno-ethmoidal recess Ope Sphenoidal sinus Opening of posterior ethmoid cells into superior meatus Naso-pharynx Opening of Eustach- ian tube Inferior meatus Inferior turbinate, partly removed Middle meatus Lateral wall of nasal fossa ; portions of turbinate bones have been removed to expose openings into air spaces. of variable size. Above and behind the upper turbinate and in front of the body of the sphenoid bone lies a diverticulum, the spheno-ethmoidal recess, into the posterior part of which opens the sphenoidal sinus. The Middle Meatus. The recess beneath the middle turbinate (meatus nasi medius) is spacious and arched to conform with the contour of the middle and inferior conchae which constitute its roof and floor respectively. On elevating, or still better removing close to its attachment, the lower turbinate bone/ a deep crescentic groove, the infundibulum, is seen on the outer wall of the fossa overhung by the anterior half of the concha. The crescentic cleft leading from the middle meatus into the infundibulum is the hiatus semilunaris? which extends from above downward and backward, with its convexity directed forward. Its anterior boundary is a sharp crescentic ridge due to the uncinate process of the ethmoid covered with thin mucous membrane, while behind it is limited by a conspicuous elevation produced by the corresponding underlying bony projection of the ethmoidal bulla. 1 Some confusion exists in the use of this term, since it is often applied to the entire groove and not merely to the cleft which leads from the meatus into the groove. The name is here employed as indicating the lunate cleft and not the groove (which is the infundibulum), as originally used by Zuckerkandl, who introduced it. See Antomie der Nasenhohle, Wien, 1882, page 39. 1412 HUMAN ANATOMY. When the infundibulum does not end blindly above, which it often does (page 194), its upper extremity, usually somewhat expanded, receives the opening of the frontal sinus, ostium frontale. The sinus is, however, not dependent upon the infundibulum for its communication with the middle meatus, since, as pointed out by Zuckerkandl, between the front of the attachment of the middle turbinate bone and the uncinate process of the ethmoid there exists a passage which leads to the ostium frontale. Into the upper part of the infundibulum usually open some of the anterior ethmoidal air-cells ; lower in the groove lies the oval or slit-like ostium tnaxillare, the chief communication of the antrum of Highmore. When the latter is provided with an additional orifice, as it is in 10 per cent. (Kallius), the smaller accessory communication opens into the infundibulum a few millimeters behind the principal aperture. Above the hiatus semilunaris, either on or above the bulla, is usually seen the slit-like opening through which the middle ethmoidal cells communicate with the meatus. The Inferior Mealus. This passage (meatus nasi inferior), the largest of the three, measures from 4. 5-5. 5 cm. in length, its anterior end lying from 2.5-3.5 cm - behind the tip of the nose. At first relatively contracted, it abruptly expands, not FIG. 1176. Scalp Cerebral hemisphe Superior longitudinal sinus Bone Falx cerebri Ethmoidal cells Lower end of probe lying in hiatus semilunaris Middle turbinate_ Probe passing from antrum into infundibulum Inferior turbinate Nasal septum/ Right eyeball Hiatus semilunaris Middle meatus -Maxillary sinus 'Inferior meatus Floor of nasal fossa mucous membrane Tongue Frontal section of head, viewed from behind, showing nasal fossic and communications with frontal and maxillary sinuses. only in height, in correspondence with the arched attached border of the lower turbinate, but also in width. Farther backward, it gradually diminishes and is again reduced at its choanal end. On the lateral wall of the inferior meatus, usually from 3-3.5 cm. behind the posterior margin of the nostril, after removal of the lower turbinate, may be seen the opening of the naso-lurhrymal duct. The position and form of the orifice are subject to much variation. When close to the arching attached border of the concha, the aperture is usually oval or even round ; when its position is lower, it is narrow and slit-like, obliquely vertical, and often guarded by a fold of mucous membrane, the so-called rakr of rfasner. The arched roof of the nasal fossa is divisible into a naso-frontal, an ethmoidal and a sphenoidal part in accordance with the bones over which the THE NASAL MUCOUS MEMBRANE. 1413 mucous membrane stretches. The lower part of the naso-frontal division, below the nasal bone, is cutaneous and cartilaginous. Anteriorly the roof is reduced to little more than a groove on account of the approximation of the lateral and median walls, but posteriorly broadens towards the choana. The median part of the roof, formed by the cribriform plate of the ethmoid, is very thin and makes a sharp angle with the steeply descending sphenoidal division. Between the latter and the superior turbinate bone lies the spheno-ethmoidal recess. The floor of the nasal fossa, much broader than the roof and supported by the palatal process of the maxilla and the horizontal plate of the palate bone, from before backward is approximately horizontal, but from side to side is distinctly con- cave. Anteriorly this wall is robust, but rapidly diminishes in thickness as it passes backward. About 2 cm. behind the posterior margin of the nostril and close to the septum, the floor of each nasal fossa presents a slight depression, sometimes narrow and funnel-shaped, that leads into a small canal lined with a prolongation of mucous membrane. This canal converges towards the septum with its fellow of the opposite fossa, descends almost vertically, and passes through the incisive foramen in the hard palate to end on the roof of the mouth as a minute slit at the side of the incisive pad or papilla palatina. Although the two tubes of mucous membrane may join to form a single incisive canal, they usually retain their independence (Leboucq, Merkel). They are often closed and impervious ; sometimes, however, even in the adult communication is retained between the nasal and oral cavities. The posterior nares or choanae, the apertures through which the nasal fossae communicate with the naso-pharynx, one on either side of the septum, resemble in form somewhat a Gothic arch (Fig. 1354). They are relatively much lower in the new- born child than in the adult, in which they measure about 3 cm. in height and 1.5 cm. in breadth (Zuckerkandl), although individual variation is considerable. Each opening is bounded below by the horizontal plate of the palate bone ; laterally by the inner surface of the internal pterygoid plate of the sphenoid ; above by the vaginal process of the sphenoid and the ala of the vomer ; and mesially by the vertical posterior borders of the vomer. Over this bony arch the nasal mucous membrane is continuous with that lining the pharynx. Laterally the posterior limit of the nasal fossa in the recent condition is indicated by a furrow (sulcus nasalis posterior) that extends from the under surface of the sphenoid downward to about the junction of the hard and soft palates. Behind this furrow, about on a level with the lower border of the inferior turbinate, lies the opening of the Eustachian tube (Fig. 1174). Since the turbinates end approximately 12 mm. in advance of the choanae, the outlines of these openings are unbroken by the scrolls that model the lateral wall of the nasal fossae, all three conchae, however, being visible through the posterior nares. THE NASAL MUCOUS MEMBRANE. Beyond the limen that marks the limit of the integument clothing the vestibule (page 1409), the nasal fossa is lined by mucous membrane continuous with that of the naso-pharynx through the choanae. Since in addition to lining the tract over which the respired air passes the nasal mucous membrane contains the cells receiving the impressions giving rise to the sense of smell, it is appropriately divided into a respir- atory and an olfactory part. The Olfactory Region. The highly specialized regio olfactoria is quite limited in extent and embraces an area situated over the middle of the upper tur- binate and the corresponding part of the septum. According to Brunn, x whose conclusions are here presented, the olfactory area of each fossa includes only about 250 sq. mm. , the septum contributing something more than one-half of the entire surface. Accordingly the specialized field is by no means coextensive with the upper turbinate bone, as it reaches neither its lower nor posterior border (Fig. 1177). The anterior margin of the area, which lies about i cm. behind the front wall of the nasal fossa, is irregular in outline owing to the invasion of the specialized region by the adjacent 1 Archiv f. mikros. Anat, Bd. 39, 1892. * HUMAN ANATOMY. FIG. 1177. respiratory mucous membrane, tongues or even islands of the latter projecting into or being surrounded by the former. Upon the evidence derived from careful dissection of the olfactory mucous membrane, however, it is difficult to avoid the conclusion that Brunn's areas are too limited, as nerve-fila- ments clearly attached to the olfactory bulb are usually traceable onto the upper part of the middle turbinate bone. In fresh preparations the olfactory area usually, but not always, can be approximately mapped out by the yellowish hue, lighter or darker, that distinguishes it from the respiratory region in which the mucous membrane exhibits a rosy tint. The epithelium contains two chief con- stituents the supporting and the olfactory cells. The supporting cells are tall cylindrical elements, about .06 mm. in height, that extend the entire thickness of the epithelium. Their outer and broader ends are of uniform width and contain the oval nuclei which, lying approximately at the same line and staining readily, form a deeply colored and conspicuous nuclear stra- tum at some distance beneath the free margin. Between the latter and the row of nuclei, the Right nasal fossa, septum (s) has been . . ' partially separated and turned upward ; dark epithelium presents a Clear ZOttC devoid OI field shows olfactory area on lateral and mesial nllr |: Trip innpr rvjrt rf rhp ciinnnrrino- rf>11c walls of fossa, as mapped out by Brutin.. 1C*. is thinner and irregular in contour and often terminates by splitting into two or more basal processes that rest upon the tunica propria. Between these ends lie smaller pyramidal elements, the basal cells, that FIG. 1178. Outer zone Nuclear layer of supporting cells Olfactory cells Blood-vessel Glands Bundle of olfactory nerves ^fetl^ffe -^<^^is^^^^v - V> *"*.?& A*& -^fiSL^X'v ^ v M *"*5Ss*^**^--^ > < ;1 *"-^' - " - : " v -\\ Section of olfactory mucous membrane; epithelium displays outer nuclei-free and nuclear layers formed by supporting cells and broad stratum containing nuclei of olfactory ci-lls. < 300. probably represent younger and supplementary forms of the sustentacular cells. The granular protoplasm of the basal processes often contains pigment particles. The olfactory cells, the perceptive elements receiving the- smell-stimuli, con- sist of a fusiform body, lodging a spherical nucleus enclosed by a thin envelope of cytoplasm, and two attenuated processes, a peripheral and a central. The olfactory cells are in fact sensory neurones that have retained their primitive position within the surface epitheliinfl, as in many invertebrates, instead of receding, as is usual ii THE NASAL MUCOUS MEMBRANE. the higher animals, to situations more remote from the exterior. The slender peripheral process of the olfactory cell, which corresponds to the dendrite of the neurone, is of uniform thickness and ends at the surface in a small hemispherical knob that projects slightly beyond the general level of the epithelium and bears from 6-8 minute stiff cilia, the olfactory hairs. The length of the peripheral processes, being dependent upon the position of the nuclei, varies, since the latter occupy different levels within the epithelium in order to accommodate their greater number about 60 per cent, in excess of those of the supporting cells (Brunn). The central FIG. 1180. FIG. 1179. Olfactory cell Supporting cell Nerve-fibre Section of numan olfactory mucous membrane, silver preparation ; two olfactory cells are seen, one of which sends nerve-fibre towards brain. X 335. (Brunn.) Isolated elements of epithelium of olfactory mucous membrane ; a, olfactory cells ; &, sup- porting cells. X 1000. (Brunn.) processes of the olfactory cells, much more delicate than the peripheral, are directly continued, as the axis-cylinders, into the subjacent nonmedullated nerve-fibres within the tunica propria, from which they pass through the cribriform plate to enter the brain and end in the arborizations within the olfactory glomeruli of the bulbus olfactorius (page 1152). The tunica propria is differentiated into a superficial and a deep layer by the adenoid character of the stratum immediately beneath the epithelium. The superficial layer, from .01 5 -.020 mm. thick, consists of closely packed irregularly round cells, resembling lymphocytes, and meagre bundles of delicate connective tissue. The deep layer, on the other hand, contains robust bundles of fibro-elastic tissue and relatively few cells. A distinct membrana propria is wanting within the olfactory region. The glands of Bowman (glandulae olfactoriae) are characteristic of the olfactory region and probably elaborate a specific secretion (Brunn). They open onto the free surface by very narrow ducts that lead into saccular fusiform dilatations, into which the tubular alveoli open. The ducts possess an independent lining of flattened cells that extend as far as the surface and lie between the surrounding epithelial ele- ments. The dilatations are clothed with flattened or low cuboidal cells, which are replaced by those of irregular columnar or pyramidal form within the tubular alveolar. From the character of their secretion the glands of Bowman are probably to be reckoned as serous and not mucous (Brunn, Dogiel). The Respiratory Region. The mucous membrane lining of the respiratory region differs greatly in thickness in various parts of the nasal fossa. In situations where the contained cavernous tissue is well represented, as over the inferior turbinate, it may reach a thickness of several millimeters, while when such tissue is wanting, as on the lateral wall, it is reduced to less than a millimeter. 1416 HUMAN ANANOMY. The epithelium is stratified ciliated columnar in type, from .050-. 070 mm. thick, and includes the tall surface cells, bearing the cilia, between the inner ends of which lie the irregularly columnar basal cells. Numerous elements exhibit various stages of conversion into mucous containing goblet cells. The current produced by the cilia is toward the posterior nares. Beneath the epithelium stretches the membrana propria or basement membrane, that varies greatly in thickness ; although in certain localities feebly developed, it is usually well marked and measures from .010-. 020 mm. in thickness (Brunn) Duct of glands Blood-vessel /^^^^^ap^jv^v^gi I "'fcilSf^li^^^S Glands '[:-' ' Section of respiratory mucous membrane covering nasal septum. X 75- Under pathological conditions its thickness may increase fourfold or more. In many places the membrana propria is pierced by minute vertical channels, the basal canals, in which connective-tissue cells and leucocyctes are found, but never blood-capillaries (Schiefferdecker). The tunica propria consists of interlacing bundles of fibro-elastic tissue which are most compactly disposed towards the subjacent periosteum. The looser super- ficial stratum is rich in cells and here and there contains aggregations of lymphocytes that may be regarded as masses of adenoid tissue (Zuckerkandl). In certain parts of the nasal fossa the stroma of the mucous membrane contains vascular areas com- posed of numerous intercommunicating blood-spaces that confer the character of a true cavernous tissue. These specialized areas, the corpora cavernosa, as they are called, are especially well developed over the inferior and the lower margin and posterior extremity of the middle conchae, and less so over the posterior end of the upper turbinate and the tuberculum septi. When typical, they occupy practically the entire thickness of the mucous membrane from periosteum to epithelium, tin- interlacunar trabeculae containing the glands and blood-vessels destined for the sub- epithelial stroma. The blood-sinuses, tin general disposition of which is vertical to the bone (Zuckerkandl), include a superficial reticular zone of smaller spaces and a deeper one of larger lacuna?. The engorgement and emptying of the cavernous tissue is controlled by nervous reflexes and probably has warming of the inspired air as its chief purpose (Kallius ). The glands of the respiratory region are very numerous, although varying in size, tubo-alveolar in form and, for the most part, mixed mucous in type. The chief ducts open on the free surface by minute orifices barely distinguishable with the unaided eye. Their deeper ends branch irregularly into tubes that bear the ovoid terminal alveoli. The latter are lined with mucous-secreting cells, between which lie PRACTICAL CONSIDERATIONS: THE NASAL CAVITIES. 1417 FIG. 1182. the crescentic groups of serous cells that stamp the glands as mixed (Stohr). Exceptionally exclusively serous glands are also encountered (Kallius). Jacobson's Organ. Mention has been made of the rudimentary structure (organon vomeronasale) found in man, almost constantly in the new-born child and frequently in the adult, as a representative of the organ of Jacobson that is present> in varying degrees of perfection, in all amniotic vertebrates (Peter). In many animals possessing in high degree the sense of smell (macros- matic), the organ is well developed and functions, serving possibly as an accessory and outlying surface by which the first olfactory impressions are received (Seydel). In man the organ is represented by a laterally compressed tubular diverticulum, from 1.5-6 mm. in length, that passes backward and slightly upward to end blindly be- neath the mucous membrane on each side of the septum. The entrance to the tube is a minute aperture situated near the lower border of the septum, above the anterior nasal spine and the rudimentary vomerine cartilage. The median wall of the diverticulum is clothed with epithe- lium composed of tall columnar cells resembling those of the olfactory region, but the characteristic olfac- HIHUWIHW orv rgUs are wanting?" The eoithe- Portion of frontal section through nasal fossae of kitten, showing p" . organ of Jacobson. X 20. hum covering of the lateral wall corresponds to that of the respiratory region. In macrosmatic animals branches of the olfactory nerve are traceable to Jacobson's organ in which are found olfactory cells. PRACTICAL CONSIDERATIONS : THE NASAL CAVITIES. The nasal cavities have certain important clinical relationships which may be classified as (i) physiological (a) respiratory, phonatory and olfactory ; ($) sexual ; (2) topographical (a) the nasal chamber and the vestibule ; () the premaxillary, maxillary, and palatal portions ; (c) the septum, and the turbinate bones. i. (a) The air passing out from the pharynx, being confined to the plane of the posterior nares, is not carried up to the olfactory region, so that the odors on the expired breath are not appreciated. When the communication between the respira- tory and olfactory portions is cut off, as by swell of the mucous membrane at the region of union of these portions, loss of smelling supervenes. Discharge which may accumulate about the middle turbinate bone or in the upper portion of the vestibule cannot be removed by the act of blowing the nose, for the reason above assigned that the air of expiration cannot pass within the olfactory portion. The act of blowing the nose, or the process of washing out the nose by a current thrown in from the naso-pharynx, will wash out the inferior meatus with ease, provided the discharge is not inspissated, and the parts of the floor of the nose are normal (Allen). An abnormal width or patency of the respiratory portion of the fossa especially of the inferior meatus due to imperfect development of the inferior turbinates, has been thought (Lack), by diminishing the vis a tcrgo in blowing the nose and thus favoring the retention and decomposition of the nasal mucus, to contribute to the occurrence of atrophic rhinitis (ozaena). The value of the nose as an accessory organ of phonation consists in its action as a resonating cavity which adds quality, color and individuality to the voice. This function of the nose becomes strikingly I 4 i8 HUMAN ANATOMY. apparent when, as during an acute coryza, the fossae are more or less completely obstructed and the voice becomes flat and entirely without resonance. () The relations between the nasal chambers and the sexual apparatus are of practical importance and have as an anatomical basis the analogy between the mucosa covering much of the turbinates and part of the septum, and the erectile tissue of the penis, and the sympathy between the erectile portions of the generative tract and erectile structures e. g. , the nipple in other parts of the body. 2. (a) The distinction between the nasal chamber and the vestibule is, in the main, based upon the difference in their lining membrane, that of the vestibule being simply a continuation inward of the external integument to the line (timen nasi} at which the nasal fossa proper begins. The vestibular cavity is provided with rigid hairs (to aid in arresting foreign particles carried in with the air current), and sebaceous glands, and is especially susceptible to eczematous or furuncular affections. Diseases of the vestibule may, therefore, be dealt with as though they were affections of the skin ; while diseases of the mucosa of the nasal chambers are to be treated on the same principles as those of the mucous membranes generally, with special refer- ence to its erectile character and to its close relation to the underlying periosteum .and bone. (<) The sutural lines of the premaxilla, of the maxilla, and of the palatal bones aid in determining the boundaries of the subdivisions of the nasal chamber, which are indicated to some degree by the production of the planes of the sutures of the roof of th^ mouth, vertically upward through the nasal chambers. (c') The morphological significance of the septum, placed as it is in the median line of the face of the embryo, with the turbinate bones lodged to its right and left sides, remains the same in the skull of the adult, notwithstanding the fact that, with cultivated races at least, the septum is usually deflected through the greater part of its course from the median line. This deflection has been said to be due to the persistent growth of the septal bones in a vertical plane after their edges have united the apex of the deflection being often found at the junction of the ethmoid and vomer ; any preponderance in strength of one of these bones will cause bending of the weaker usually the perpendicular plate of the ethmoid. The usual direction of the deflection is to the left, and this has been thought to be due to the habit of using the right hand in blowing the nose. Asymmetry of the nasal chambers is a result of the deflection. One of these chambers, commonly the left, is much smaller than its fellow of the opposite side, and may be occluded, when the right chamber will be larger than normal and possess both osseous and erectile structures which have undergone physiological hypertrophy. Care should be taken to distinguish between such hypertrophy and the effects of diseased action (Allen). The anterior nares are directed downward and are on a lower plane than the floor of the nose. To examine the interior of the nose the movable nostril must therefore be elevated and the head thrown backward. The speculum shaped for the purpose should not be passed beyond the dilatable cartilaginous portion. With good . r . 1 "ill. !.!-_ 1 _ *.. _f light one may see the anter the inferior turbinate, the b inferior meatus, the septum duct cannot be seen, although it is only about an inch from the orifice of the nostril, and three-fourths of an inch above the floor of the nose. This is due to the fac' that it is concealed behind the attached and depressed anterior end of the inferio turbinate. To expose better the structures in the external wall of the narrow and rigi nasal fossa, various procedures have been adopted. Rouge made an opening into the anterior nares from the mouth, by incising in the angle between the upper lip and the gum. By separating the alar cartilages from the bones and dividing the cartilag- inous septum the movable anterior portion of the nose can be turned upward, giving a full exposure of the nasal fossae, without leaving an unsightly scar. To permit a freer exploration with the linger, Kocher divided the septum as far back as possible with scissors. He also divided the roof of the nose near the septum, turning the divided parts aside. An osteoplastir flap may be made by extending this incision upward, dividing the bone in this line and making a second incision around PRACTICAL CONSIDERATIONS: THE NASAL CAVITIES. 1419 the alae and along the side of the nose, again dividing the bone. The flap thus formed can be turned upward, after breaking the bridge of bone between the upper ends of the two incisions, exposing the nasal fossa. The finger can be passed backward through the nostril far enough to meet the finger of the other hand passed to the posterior nares through the mouth. The posterior nares can be examined by the rhinoscopic mirror or by the finger introduced through the mouth. Posterior rhinoscopy, like laryngoscopy, is carried out with difficulty, because the region of the naso-pharynx is sensitive and is intol- erant of intrusion. In the act of swallowing, the epiglottis protects the larynx by closing the laryngeal opening, and the soft palate rises against the posterior wall of the pharynx, preventing regurgitation into the nose. When the rhinoscopic mirror is used the same thing occurs, so that the view of the larynx and naso-pharynx is shut off. Considerable difficulty is sometimes experienced in training the patient to overcome this tendency. The employment of the nasal douche is based upon the same mechanism. When the stream of fluid passed through one nostril reaches the posterior part of the nose, its progress toward the mouth is obstructed by the elevated soft palate, and it therefore passes around the posterior edge of the septum and back through the opposite nasal fossa. With the rhinoscopic mirror in good position, and the soft palate quiet, one may see the posterior nares divided by the septum, the turbinated bones, and the meati (especially the middle turbinate and the middle meatus), the roof of the naso- pharynx and "the orifices of the Eustachian tubes. The finger introduced through the mouth can feel the same structures, and can recognize naso-pharyngeal adenoids, tumors, or abscesses. The mucous membrane over the turbinates, owing to the presence of a rich venous plexus, is one of the most vascular in the body, and resembles erectile tissue (page 1968). This and the general vascularity of the nose partly explain the great frequency of epistaxis. The excessive supply of blood to the mucosa may be (a) for the purpose of enabling it to raise the temperature and add to the moisture of the inspired air ; ($) to favor the activity of the numerous mucous glands, the free secre- tion of which together with the action of the cilia of the epithelial cells is required to remove the dust and the micro-organisms that are filtered from the air during inspi- ration by the vibrissse and the cilia themselves ; (c) to endow it with sufficient vitality to resist the pathogenic action of such micro-organisms. In spite of this defensive quality, the constant exposure to atmospheric irritants often leads to congestions and coryzas, which if long continued and frequently repeated result in hypertrophy of the mucous membrane. This may require removal by cauterization or excision to relieve the consequent obstruction. The mucous membrane is somewhat less closely attached to the septum than to the neighboring parts, and hence haematomata of the septal submucosa are not infrequent after an injury to the nose. Such haematomata are almost invariably infected and proceed to suppuration forming septal abscesses, the constitutional symptoms (toxaemia) of which may give rise to anxiety if their local cause is overlooked. Epistaxis is common not only because of (a) this vascularity of the mucosa, but also by reason of () the frequency of trauma to the nose ; the relation of its veins (c~) to the general venous current so that they may be congested in cardiac or in pul- monary disease, or in straining, or in paroxysms of coughing, as in whooping cough ; and (d) to the intracranial sinuses, so that nose-bleed may be a symptom of cerebral congestion or tumor ; () downward, pushing down the arch of the hard palate so that the roof of the mouth on the affected side becomes convex, and, by pressure on the superior dental nerves, causing severe odontalgia in the upper teeth, which later become loosened. Benign growths ma be removed through an opening made by cutting away the anterior wall. Malignan growths necessitate excision of the superior maxilla. In diseases of the sphenoidal sinuses their intimate relation with the brain above, the optic nerve and ophthalmic artery above and to the oirter side, and, along the outer wall, with the internal carotid artery, the cavernous sinus and the nerv passing through the sphenoidal fissure, should be borne in mind. Such diseas< may lead to (0) optic neuritis and blindness, if the optic nerve is involved ; (I) tc. general Ophthalmoplegia if the third, fourth, the ophthalmic division of the fifth, the sixth, and the sympathetic filaments from the cavernous plexus (all transmitted through the sphenoidal fissure) are implicated ; (r) to cavernous sinus thrombosis if the ophthalmic vein passing through the same fissure is infected. Tumors of the pituitary body resting in the pituitary fossa in the sella turcica and just above the roof of the sinus may penetrate its cavity. The opening of each sinus is in the upper part of the anterior wall, a very unsuitable position for drainage, in the presence of infection. Encroachment on any of the surrounding structures might lead to serious results. The anterior wall may be exposed and attacked by the surgeon, but only with considerable difficulty, because of its deep situation and its 1 DEVELOPMENT OF THE NOSE. 1429 restricted avenue of approach through the nasal fossa. The chief obstacle is the middle turbinate bone, which must be removed before the orifice can be seen or the anterior wall removed. Any efforts at cleaning pathological tissue from the sinus must be made with due regard for the important structures just outside and the thin intervening bone. Inflammation of the ethmoidal cells is most frequently associated with the presence of myxomatous polypi within the nose. Infection may extend (#) upward to the cranial cavity, either directly or by way of the ethmoidal veins, or into the cavernous sinus via the ophthalmic vein, or to the longitudinal sinus especially in children by the small vein traversing the foramen caecum ; () outward to the orbit, causing an orbital cellulitis ; (c) to the lachrymal sac (on account of the contiguity of the lachrymal bone) causing dacryo-cystitis. A valuable, but not always reliable, sign of involvement of the ethmoidal cells, is localized pain at the inner canthus of the eye (Kiimmel), and swelling of the mucous membrane around the middle turbinate may in this as in infection of the other sinuses be considered an important symptom. In order to evacuate the diseased cells, the middle turbinate (as in the case of the sphenoidal sinus) must be removed before the ethmoidal cells can be exposed. As, in the large majority of cases at least, the condition is coincident with similar infection of the frontal sinus, the anterior cells may be easily reached from the floor of the latter after it has been opened. The optic nerve, the trochlear nerve, the superior oblique ocular muscle and the anterior and posterior ethmoidal arteries, are the most important structures endangered during this operation. DEVELOPMENT OF THE NOSE. The earliest trace of the nasal anlage appears about the beginning of the third week of foetal life as a thickening of the ectoblast to form the nasal area at each side of the anterior portion of the head. About one week later the convexly cres- centic outline of this area gives place to a slight depression that deepens into the olfactory pit or fossa in consequence of the increased thickness of the surrounding mesoblast. The encircling ridge thus produced is best marked on the mesial and lateral boundaries of the fossa (Kallius), where the resulting elevations foreshadow the development of the inner and outer nasal processes. With the forward growth and union of the maxillary process of the first visceral arch with the median nasal process, or processus globularis, to complete the upper boundary of the primitive oral cleft (page 62), the margin of the entrance of the nasal pit becomes closed in below. Subsequently, however, the lateral nasal process extends medially above the maxillary process until it meets the median nasal process and thus becomes the immediate lower and lateral boundary of the opening of the fossa. The latter grows and deepens chiefly upward, towards the brain, and backward and in consequence the olfactory organ for a time consists of two blind pouches, separated by the frontal process, lying above the primitive oral cavity. These pouches invade the mesoblast until their blind posterior ends reach the primitive oral cavity between which and the olfactory diverticula a thin partition, composed of the two abutting layers of epithe- lium, alone intervenes. This septum, bucco-nasal membrane of Hochstetter, becomes attenuated and finally ruptures, the resulting openings, the primitive choancs, estab- lishing communication between the nasal fossae and the primitive oral cavity. That part of the roof of the latter which extends from the choanae to the nasal apertures constitutes the primitive palate, and contributes not only the anterior portion of the definite palate, but also the tissue forming the lips (Hochstetter). The primitive palate includes contributions from different sources, its middle portion being from the median nasal process and its lateral portions being derived from the lateral nasal process in front and from the maxillary process behind (Peter). Subsequent to the formation of the primitive palate, about the fifth week, the primitive nasal fossae increase in size, sink deeper into the head between the median plane and the eye, and come into closer relation with the brain. The nasal fossae, however, in acquiring their definite expansion additionally appropriate a considerable portion of the primitive oral cavity which becomes separated from the remainder of that space by the formation of the dejinite palate. 1430 HUMAN ANATOMY. Nasal area Fore-brain Nasal area The first step in the production of the latter is the appearance, about the ninth week, of the palatal ridges, wedge-shaped elevations that grow downward and in- ward from the maxillary processes. In front these ridges begin at the primitive choanae, where they are continuous with the primitive palate, and extend backward as far as the tympanic pouches. At first almost sagittal in their plane, the palatal ridges become gradually converted into horizontal plates that come into contact and finally unite along their FIG. 1188. opposed median edges to com- Fore-brain plete the roof of the mouth and the floor of the nasal fossae and the definite or secondary choantc, this fusion being accomplished by the end of the third month. Coincidently with these changes the primitive choanae elongate and come to lie on either side of the posterior por- tion of the nasal septum to which the frontal process has now become reduced. The union of a pair of outgrowths from the palatal plates, beyond their point of fusion beneath the choanae, produces the uvula, while the remaining ununitecl portions of the ridges give rise to the palato-pharyngeal arches. For a time the nasal sep- tum is still incomplete, since it has not yet reached the palate, and the nasal fossae communi- cate by means of a cleft between the septum and the palate. With the downward growth of the partition this communica- tion is obliterated, the septum joining the palate along the line of the median suture. The formation of the ante- rior part of the floor of the nasal fossae is more complex since, according to Peter, 1 in this region the palatal processes do not come in contact with each other owing to the interposi- tion of a portion of the partition that separates the primitive choanae. The palatal plates, however, fuse with this wedge of tissue along the line of appo- sition except at one point on each side, where the epithelium persists as a solid strand leading downward and inward from the fore part of the floor of the nasal fossa to the roof of the oral cavity. These strands acquire a lumen and become the incisive canals (page 1413 ) that may persist throughout life and establish communication between the nasal and oral chambers. The further differentiation of the nasal fossae of man follows the same funda- mental plan that applies to other mammals, but is modified by the reduction that Fore-brain Lateral nasal process mil Nasal fossa Fore-brain Nasal fossa Naso-frontal process Processus globularis Frontal sections of fore-brain of rabbit embryos, illustrating early stages in development of nose ; in A. nasal area shows as thickening of ectoblast ; in B, nasal area is slightly depressed ; in C and I), nasal fossae are forming. X 30. Anatom. r, I'.il. xx., 1902. DEVELOPMENT OF THE NOSE. occurs in the production of the relatively feebly developed human olfactory apparatus. With this differentiation is associated the formation of the turbinates and the intervening clefts (the meatuses) and of the acces- an i Cartilaginous capsule sory air-spaces. 1 he stud- Ethmo-turbinai iesof Zuckerkandl, Killian, Schoenemann, Peter 1 and others have shown that the typical development of the conchae proceeds from three primary outgrowths from the lateral nasal wall in regions later correspond- ing to the maxilla, ethmoid and nasal bones. These elevations, appropriately known as the maxillo-tur- binal, the ethmo-turbinal and the naso-tur&inal, un- dergo differentiation that leads to the simple or com- plex definite arrangement of the conchae found in various animals. Maxillo-turbinal Nasal fossa Jacobson's organ Palatal process Oral cavity Tongue Frontal section through developing nasal fossae and oral cavity which communicate ; palatal processes are forming. X 15. In man the maxillo-turbinal, later the inferior turbinate, first appears and pre- cedes the ethmo-turbinal plate that later is supplemented by a second scroll, thus producing the middle and superior turbinates respectively. The naso-turbinal, always rudimentary in man, is represented by a small ridge that appears in front of the ethmo-turbinal and above the maxillo-turbinal plates and persists as the agger nasi. The ethmo-turbinal is most intimately related to the true olfactory area and undergoes, even in man, conspicuous subdivision. Although finally reduced to two (the upper and middle turbinates), in the human fcetus, just before birth, five ethmo- turbinal plates defined by six grooves are present (Killian). Persistence in excess of the usual complement accounts for the presence of the supernumerary ethmoidal turbinates so often observed. As interpreted by Killian, the subsequent modifications of the ethmo-turbinals and the intervening furrows, either by further expansion or by fusion, are not only intimately concerned in producing details modelling the lateral wall of the nasal fossa, as the uncinate process, ethmoidal bulla, hiatus semilunaris and infundibulum, but also associated with the first appearance of the accessory air-spaces. The earliest establishment of these spaces pre- FIG. 1190. cedes the appearance of the carti- lage that later encloses them, their relations to the skeleton being, therefore, secondary (Kallius). The ethmoidal air-cells and the sphenoidal sinus are primarily con- Maxiiiary process strictions from thenasal fossae, while the maxillary and frontal sinuses are more or less direct extensions from the same cavities. The maxillary sinus ap- pears about the middle of the third fcetal month as a minute epithe- lium-lined sac within the mesoblast at the side of the nasal fossa, from which it has been evaginated ; by the sixth month it measures some 5 mm. , and at birth has acquired the size of a pea. Until the eruption of the milk teeth provides the Fore-brain Nasal aperture Lateral nasal process Primitive choana Palatal process Part of head of fcctus 15 mm. in length, showing primitive choanas and palate. X 8. (Peter.) 1 In Hertwig's Handbuch d. Entwikelungslehre, Lief. 4 and 5, 1902. 1432 HUMAN ANATOMY. FIG. 1191. Fore-brain Infranasal area Nasal fossa Lateral nasal process Median nasal process Processus globularis Maxillary process Mandibular process Anterior end of head of foetus 10.5 mm. in length, showing early development of external nose. X 8. (Peter.) necessary room for expansion, its growth is retarded. After the sixth year, when the eruption of the permanent teeth begins, the antrum loses its general spherical outline and gradually acquires the definite pyramidal form. The frontal sinus formed as an extension of the nasal fossa during the third foetal month, is for a time so small that it is usually regarded as absent at birth. Although indistinctly seen during the third year, not until about the seventh is the sinus a definite space ; it remains small, how- ever, until puberty, after which its adult proportions are gained. The sphenoidal sinus, primarily arises by the constriction and partial isolation of a part of the primitive nasal fossa. Although its development begins during the third fcetal month, the space remains so rudimen- tary that not until the seventh year has absorption of the cancellous bone progressed sufficiently to make the sinus apparent. Notwithstanding its rudimentary condi- tion in man, the organ of Jacobson devel- ops at a very early period, beginning as a groove-like depression on the median wall of the nasal pit. This groove is converted into a tubular pouch that soon becomes laterally compressed and, by the middle of the third month, measures about .5 mm. in length and receives twigs from the olfac- tory nerve (Kallius). After the fifth fcetal month the organ suffers regression and becomes rudimentary and variable in comparison with the perfection it attains in animals possessing olfactory sense in a high degree. The development of the outer nose is closely associated with the changes affecting the median and lateral nasal processes prominences considered in connection with the formation of the upper boundary of the primitive oral cleft (page 62). Reference to Fig. 1 192 shows the median nasal processus, separated by a distinct furrow that soon becomes filled and partially obliterated by ingrowth of young connective tissue, as does likewise the groove between the globular and maxillary processes. At first sepa- rated by a relatively wide interval, the infranasal nasal area of His, the nasal apertures are brought nearer together by the rapid narrowing of the interposed portion of the frontal process. Eventually the tissue be- tween the globular processes becomes the philtrum of the upper lip and that between the nasal openings persists as the partition between the nostrils. By the end of the second month the external nose is defined, but is very broad and flat and lim- ited above by an arched furrow that separates the convex nasal margin (His) from the forehead. The nos- trils, originally placed high and for a long time directed forward, grad- ually descend and assume a hori- zontal plane as the middle of the arched nasal margin grows downward and forward to become the point of the nose. These changes, however, are not accomplished until near the end of gestation and at birth the bridge of the nose is still small and flat which, in connection with the general breadth of the organ, imparts to the infantile nose its peculiar stumpy appearance. Not until long after birth, and, indeed, not until after puberty, does the outer nose acquire its definite individual form in FIG. 1192. Fore-brain Infranasal area Nasal aperture Lateral nasal process Medial nasal process Processus globularis Mandibular process Head of foetus of about 20 days, showing developing nose. X 13- (Rabl.) THE ORGAN OF TASTE. H33 which family and racial characteristics are often so strikingly reproduced. From the second until the sixth month the nostrils are occluded by epithelial plugs which subsequently undergo gradual resolution, so that before birth the nasal apertures are unobstructed. The cartilages of the outer nose are derived from the common carti- laginous capsule that constitutes the primary nasal skeleton. Subdivision into the individual plates is probably effected by ingrowth of the surrounding connective tissue (Mihalkovics, Kallius). THE ORGAN OF TASTE. In the description of the tongue and its papillae (page 1575), reference is made to the presence of specialized epithelial structures, the taste-buds, that serve for the reception of gustatory stimuli. These bodies collectively constitute the peripheral sense-organ of taste and as such will be here considered. As implied by their name, the taste-buds (calyculi gustatorii) are irregular ellip- soidal or conical bodies, sometimes broadly oval but more often slender in outline, and in the adult measure from .070-. 080 mm. in length and about half as much or FIG. 1193. Lymphoid nodules Foramen caecum Circumvallate papillae Anterior palatine arch Folia linguae Fungiform papilla Part of dorsum of tongue, showing papillae. less in breadth. Since they lie entirely within the epithelium clothing the mucous membrane, the necessary access to the interior of the buds is afforded by minute pore-canals, each of which, beginning on the free surface at the outer taste-pore, leads through the intervening layer of epithelium to the inner pore that caps the subjacent pole of the bud. By means of these canals the sapid substances dissolved in the fluids of the mouth reach and impress the gustatory cells within the taste-buds. Pore-canals are not, however, invariably present, since, as pointed out by Graberg, certain taste-buds remain immature and retain their embryonal form and relations, being broad and conical and in contact with the free surface. In such buds the gustatory cells are few, only two or three, and so superficially placed that a dis- tinct canal is absent. Occasionally double buds are encountered in which two gustatory bodies are implanted by a common base, but partly retain their inde- pendence in having separate distal poles, each provided with its separate taste-pore and canal. The chief position of the taste-buds is within the epithelium lining the sides of the annular groove on the circumvallate papillae, the buds being more numerous and closely placed on the median than on the lateral wall of the furrow. Their number H34 HUMAN ANATOMY. has been variously estimated, but it is probable that from 100 to 150 represents the maximum for a single papilla, in many cases the quota being less than one half FIG. 1194. Epithelium Section of circumvallate papilla from tongue of child. X 70. FIG. 1195. of these figures (Graberg). The locality of next importance numerically is the papillae foliatae on the sides of the tongue in the furrows of which, even in man, the taste-buds are plentiful. Additional situations, in which, however, the taste-buds are very sparingly and uncertainly distributed, include the fungiform papillae, the soft palate, the posterior surface of the epiglottis and the mesial surface of the arytenoid cartilages. Within the fungiform papillae a few buds may be found on the free surface, where the epithelium is thinnest. Over the soft palate their distribution is irregular and uncertain, while in the larynx the buds are lim- ited to the areas covered by squamous epithelium. According to Davis, between fifty and sixty taste- buds of varying size may be counted on the epiglottis within an area 3 mm. in diameter. Structure. Wherever found, the taste-buds consist exclusively of epithelial tissue and, in cor- respondence with other sense organs, include two chief varieties of elements the supporting cells and the more highly specialized neuro-epithelium, the gustatory cells, among which lie the terminal fibrillae of the nerve of taste. The supporting cells are represented prin- cipally by elongated epithelial elements that occupy both the superficial and deeper parts of the taste- buds of which they contribute the chief bulk. They vary in their individual contour, being lanceolate, wedge-shaped or columnar, according to the model- lint; to which they are subjected by the neighboring cells. They possess large, clear, vesicular nuclei that contain little cliroinatin and, therefore, stain faintly. The position of the nucleus is inconstant, in some cells being near the base and in others in the middle or nearer the apex. The peripheral ends of the Taste-hud Taste-pore Epithelium Taste-bud Taste-buds in section ; upper one shows gustatory hairs projecting into pore-canal. X440. THE ORGAN OF TASTE. H35 FIG. 1196. Outer taste-pore supporting cells, somewhat blunted and flattened and beset with a narrow cuticular zone, are closely grouped to bound the annular opening of the inner taste-pore, through which project the stiff hair-processes of the gustatory cells. Their deeper or central ends are prolonged into one or more protoplasmic processes which unite with similar extensions of the basal cells, as the peculiar supporting cells at the base of the bud are called. The basal cells are modified sustentacular elements, probably epithelial in nature, which occupy the lower fourth of the buds, resting upon the subjacent epithelium and, in turn, affording support for the elongated cells. Although differing in size and details of form, the basal cells are provided with oval nuclei and are generally more or less branched. By means of their protoplasmic processes they are united with the central ends of the longitudinally disposed supporting and gustatory cells, with one another and with the surrounding epithelial cells. The number of basal cells in each bud is small, often only two or three and seldom more than half a dozen being present (Graberg 1 , Kallius 2 ). The percipient elements, the gustatory cells, are irregularly arranged between the more deeply placed supporting cells and enclosed within a shell formed by the more superficial ones. They are long and fusiform, reaching from the base of the bud to the inner taste-pore, through which the stiff hair-like processes that cap their outer ends project. Their slender nuclei, rich in chromatin and deeply staining, occupy the thickest parts of the cells, which beyond the nucleus are continued in either direction as thin processes. The peripheral ones, as noted, extend not only as far as the inner taste-pore, but through the latter and into the canal by means of the gustatory hairs into which the taste cells are prolonged. The centrally directed ends are usually much the shorter and join the processes of the basal cells. The number of gustatory cells within a single taste-bud varies, in exceptional cases only two or three being present, but more often they are almost as numerous as the supporting cells (Graberg). The capillary clefts observed within and around the taste-buds the intra- sub- and peri-bulbar juice-spaces described by Graberg are regarded by some as existing during life and, therefore, not as artefacts. To these intercellular clefts the last-named authority attributes the func- tion of insuring and facilitating an active lymph-circulation within and around the taste-buds, whereby is effected the prompt removal of foreign substances that might prove deleterious if too long retained in close relation with the delicate sensory elements. Hermann has shown that the taste-buds are the seat of continual degeneration and repair, sometimes, indeed, entire buds undergoing regression. Whether such destructive processes are to be ascribed directly to the invasion of leucocytes, al- though the latter are normally found in insignificant numbers within the buds, is still a subject of discussion. The nerves distributed to the gustatory bodies are the fibres of the glosso- pharyngeal, the nerve of taste. From the rich subepithelial plexus numerous twigs ascend into the epithelium, one set going directly into the taste-buds and the other ending within the surrounding tracts of epithelium. Since the last set the inter- bulbar fibres probably have no concern with the impressions of taste and serve to convey sensory stimuli of other value, it suffices to note that after repeated division Peripheral supporting cell Gustatory cell Central supporting cell Lymph-space Basal cell Diagrammatic sectioti illustrating architecture of taste-bud. (Graberg.} 1 Anatomische Hefte, Bd. xii., Hf. 2, 1899. 2 Bardeleben's Handbuch d. Anatomic des Menschen, Lief. 13, 1905. 1436 HUMAN ANATOMY. the ultimate fibrillae terminate in minute bead-like endings that lie free between the epithelial cells, either near the free surface or at a deeper level. The nerves distributed to the taste-buds the intrabulbar fibres enter at the basal pole. Usually numbering from two to five for each bud, on gaining the interior of the latter they undergo rapid division and become numerous. A majority of the resulting fibrillae ascend in tortuous windings FIG. 1197. towards the apex of the bud in the vicinity of which some end, while others recurve and end at lower levels. The fibrillae terminate in free, usually minute knob-like endings, that lie between and often in close contact with the supporting and gustatory cells. It is probable that in no instance do the nerve-fibrillae actually unite with the gustatory cells, the relation being one of apposition and not of continuity. Partially separated ceils of taste- Development. The earliest evidences of the ^^^"x^^M^ taste-buds ' appear, about the third foetal month, within the deepest stratum of the immature epithelium as groups of ectoblastic cells that are distinguished by their large size and elongated form from the surrounding epithelial elements. The anlage tends to become conical, the apex gradually reaching the free surface and the base resting or slightly encroaching upon the subjacent connective tissue, from which it is only indistinctly defined. The primary slender form of the developing bud is later replaced by one of broad conical proportions in which the wide base is supported directly by the connective tissue without the interposition of epithelium. For a time the height of the young taste-bud equals the entire thickness of the epithelium, the position of its apex being marked by a slight depression on the free surface. In consequence of the rapid increase of the surrounding epithelium, this depression gradually deepens until the bud, which meanwhile has grown but slightly, lies at the bottom of a narrow funnel-shaped passage, the pore-canal (Graberg). Previous to the fifth month, the constituents of the taste-bud are apparently of the same character and not until towards the end of gestation is the differentiation between the supporting and gustatory cells clearly established. The definition of the taste-buds from the surrounding tissue is sharpened by the appearance of the so-called extrabtdbar cells, flattened protecting epithelial elements in which partial cornification probably takes place (Kallius). Coincidently many of the conical embryonal buds gradually assume their more slender and ovoid mature form. Before birth the taste-buds are present not only on the sides but also over the summit of the circumvallate papillae. While exceptionally some of those in the latter situation may remain, as a rule they disappear and, hence, in the adult the gustatory bodies are usually confined to the sides of the papillae. Likewise the complement of taste- buds on the fungiform papillae is much larger at birth than later (Stahr 2 ), giving to these papillae an importance during early childhood that subsequently is lost. THE EYE. Although the organ of sight (organon visus), strictly regarded, consists only of the eyeball or globe of the eye, it is closely associated with other structures, as the eyelids, the lachrymal apparatus, the orbital fascia and fat and the ocular muscles, which serve for its protection, support and change of axis. The description of some, at least, of these accessory structures therefore appropriately here finds place. THE ORBIT AND ITS FASCIAE. The walls of the orbit have been described in connection with the skull (page 222) ; suffice it here to point out that in its general form the orbital cavity resembles a pyramid, so modified by the rounding of its angles that it approximates an irregu- lar cone. The base corresponds with the orbital opening on the face and the apex 'Graberg : Srhwalbe's Morpholog. Arheiten, Bd. viii., 1898. -A'itsihr. f. Morphol. u. Anthropol., Bd. 4, 1901. THE ORBIT AND ITS FASCIA. H37 with the optic foramen. The median walls of the two orbits are slightly divergent behind, but almost parallel with the sagittal plane and with each other ; the lateral walls are obliquely placed and with the sagittal plane form an angle of about 48 and, therefore, with each other one of something more than a right angle. The axis of the orbit is directed inward and upward, forming an angle of from i5-2o with the horizontal plane, and one of about 45 with the orbital axis of the opposite side, which it intersects in the vicinity of the sella turcica. The width of the orbital en- trance is about 4 cm. and the height about 5 mm. less, while the depth of the orbit is approximately 4 cm. The space, therefore, is much more capacious than necessary to accomodate the eyeball and the associated muscles, blood-vessels and nerves. The interspaces thus left are occupied by the orbital fat (corpus adiposum orbitae), sup- ported by a framework of connective tissue lamellae prolonged from the orbital fascia which, in turn, is continuous with the periosteum lining the orbit. The latter, also known as the periorbita, is thin but resistent and at the various openings in the walls of the orbit continuous with the periosteum covering the adjacent surfaces of the skull. FIG. 1198. Eyelid Nasal fossa Anterior ethmoidal cells Mesial orbital wall Internal rectus muscle Posterior ethmoidal cells Conjunctival sac Anterior chamber Cornea Lens Vitreous chamber Check ligament Orbital wall External rectus muscle Solera Orbital fat , Optic nerve Horizontal section of right orbit showing eye in position. The eyeball does not rest directly in contact with the fatty cushion forming the walls of the cup-shaped recess in which it lies, but is separated from the surrounding adipose tissue by a fascial investment, the capsule of Tenon (page 504). This sheet covers the posterior three-fourths of the eyeball and encloses, between it and the eye, the space of Tenon. The latter in front begins beneath the conjuctival sac, close to the corneal margin, and behind ends in the vicinity of the optic nerve. It does not, however, quite reach the latter, but terminates where the eyeball is pierced by the posterior ciliary vessels and nerves, thus leaving an irregular oval area uncovered (Merkel). Farther backward the space of Tenon communicates with the subdural lymph-channel prolonged along the optic nerve and thus establishes relations with the intercranial lymph-paths (page 949). The eye muscles, which together with the elevator of the upper lid have been described (page 502), are inserted by fascial sheaths prolonged from the orbital periosteum. These sheaths increase in thickness as they approach the eyeball until, at the points where the tendons of the ocular muscles meet the fascial sheet investing the posterior part of the eye the capsule of Tenon the muscle sheaths blend with this capsule on the one hand, and, on the other, are attached at certain points to the orbital wall as robust pointed processes of considerable strength. One such process, 1438 HUMAN ANATOMY. attached to the upper lateral wall, is formed by the fusion of the fascial lamellae con- tributed by the sheaths of the levator palpebrae superioris and of the superior and external straight muscles. Another and broader process, inserted along the median wall, includes the blended extensions from the investments of the internal rectus and superior oblique ; whilst a third process, formed by the union of prolongations from the fasciae covering the inferior and internal recti and the inferior oblique, is attached to the lower and median orbital wall. These fascial extensions, passing as they do from the tendons of the eye-muscles to the orbital wall, restrain excessive muscular action and hence the name, check ligaments, has been applied, especially to those limiting the action of the internal and external recti. The processes also materially assist in maintaining the position of the eyeball within the orbit. This function is particularly exercised by the robust fascial expansion which stretches across the orbit below the eyeball and as the suspensory ligament of Lockwood serves to support the bulbus oculi. The orbital fat is prevented from projecting forward beyond a certain limit and, therefore, from encroaching unduly upon the eyelid, by a sheet of fibrous tissue, the FIG. 1199. Upper tarsal plate Palpebral fascia ^. Lachrymal sac Lachrymal gland. Palpebral fascia, cut Lateral palpebral ligament ft ^~ ^fSftf^^" ^ ~T^^f Median palpebral ligament Lachrymal punctum and canaliculus Nasal duct Lower tarsal plate __ Opening of nasal duct in inferior nasal meatus Maxillary sinus Dissection of orbit and adjacent structures, showing palpebral fascia, lachrymal sac and nasal duct. palpebral fascia or septum orbitale (Henle), which stretches across the orbital entrance and materially strengthens- and aids the eyelid in closing this aperture. Above, the septum is attached to the border of the orbit, just behind the margin, from which it extends downward to become firmly united with the common fascial investment of the levator palpebrae superioris and superior rectus and, still lower, with the upper convex border of the superior tarsal plate. On each side the septum blends with the corresponding palpebral ligament, while below it passes from the orbital margin to the inferior tarsal plate, after becoming united with the sheath of the inferior rectus. The septum orbital is not of uniform thickness, but is strongest above, especially towards the sides, and weakest beneath the lower eyelid ; further, in a general way, the sheet is more robust near its peripheral bony attach- ment than where it joins the tarsal plates. In conjunction with the palpebral liga- ments, it is so strong behind the angles of the eye that in these localities, particularly medially, it is very unyielding and capable of resisting forward displacement. The internal union of the levator palpebrae superioris with the septum orbitale enables this muscle when it contracts to tense the fascial diaphragm. Practical Considerations. The orbital cavity is somewhat pyramidal in shape and its anterior or basal portion is occupied chiefly by the eyeball, which lies slightly nearer the roof and the outer walls than the lower and inner walls. Its diameter PRACTICAL CONSIDERATIONS: ORBIT AND FASCIA. 1439 is greatest just back of its anterior margin, which is thickened and offers the best protection to the eye from injury. The upper margin is most marked and with the eyebrow offers a good protection to the eye in that direction. The inner margin is not prominent, but is well reinforced by the bridge of the nose. The outer edge is least prominent, and on that side palpation is possible as far back as the equator of the globe. For this reason, and because the outer walls converge backward while the inner walls are parallel, incisions for reaching the interior of the orbit are best made on the outer side. The walls are thin and easily fractured by direct violence, as from canes and similar objects, which sometimes enter the adjacent cavities, as the ethmoidal. Tumors may encroach upon the orbital space either by causing the absorption of the thin intervening bone, or by growing through one or more of the openings in its wall, as through the optic foramen and sphenoidal fissure from the cranial cavity, the nasal duct from the nose, or the temporo-maxillary fissure from the temporal or zygomatic fossae. The eyeball occupies about one-fifth of the orbital cavity, the remaining space being filled by nerves, vessels, muscles, the lachrymal gland, fat, and a system of fasciae. In the ordinary case a straight edge placed against the upper and lower margins of the orbit will just touch the closed lids covering the apex of the cornea, but will not compress the eye. A straight line between the two lateral margins would pass back of the cornea, on the outer side posterior to the ora serrata and on the inner side at the junction of the ciliary body and iris. An exophthalmos is a protrusion forward of the ball, and is usually due to- pressure from behind, more rarely to paralysis of the recti muscles. Some of the more common causes of retrobulbar pressure are orbital cellulitis or abscess, tumors, distension of the orbital vessels, and excess of fat. Enophthalmos, due to exhausting disease, is more apparent than real, but a true sinking of the globe may be due to paralysis of Miiller's muscle due to lesion of the sympathetic, to atrophy of the retro-bulbar cellular tissue caused by trophic dis- turbance, to fracture and depression of the orbital bones with cicatricial adhesion and contraction, and to injury of Tenon's capsule and the check ligaments. Inflammation of the capsule, or Tenonitis, may be due to constitutional poison or to infection following operations involving it, as in tenotomy of the ocular muscles. It may be an extension from an inflammation of the eyeball. The inflam- matory exudate in the capsule and adjacent tissues will sometimes cause a slight exophthalmos, and the eye will be immobile. All the extrinsic muscles of the eye pierce the capsule about the equator of the globe to reach their insertions in it. Each muscle receives a tubular investment from the capsule, which fuses with the proper sheath of the muscle and leaves a small bursa on the anterior surface of each. To open the capsule for a tenotomy, the incision is made just back of the cornea, and goes through only the conjunctiva and outer layer of the capsule. The desired tendon is easily found and brought out with a hook when it is divided. The capsular prolongation about the tendon prevents retraction of the stump after the division, and so preserves the function of the muscle. This is aided by expansions of the capsule passing to the margins of the orbit and continuous with the perios- teum. Those passing from the internal and external recti are stronger than the others and are called the internal and external check ligaments. They are united by a layer of fascia (suspensory ligament of the eyeball) passing under the eyeball so that the eye is supported after the bony floor of the orbit has been removed, as after excision of the superior maxillary bone. If the outer layer of the globe is left after enucleation of the eye, the muscles will still have an attachment and be capable of moving an artificial eye fitted to the stump. While the movements of the eyeball are free in all directions, as in a ball and socket joint, no change in position of the eyeball, as a whole, takes place, as the centre of rotation is about in the centre of the globe. By these movements the image of the object to be especially seen is fixed upon the most sensitive part of the retina. The internal rectus draws the ball directly inward and the external rectus directly outward. The other four muscles, the superior and inferior recti and the two oblique, have a complicated action. The upward and downward movements 1440 HUMAN ANATOMY. are controlled chiefly by the superior and inferior recti respectively, but each has a slight adducting and a slight rotating movement i.e., the superior rectus will move the upper extremity of the vertical meridian slightly inward (intorsion), and the inferior rectus will move the same part slightly outward (extorsion). The superior oblique is attached to the globe behind the equator, and lower than its pulley, so that in addition to its chief or internal rotating action upon the upper limit of the ball it has also an elevating effect upon the posterior portion, the cornea moving down- ward. Since its pull is inward, the cornea also moves outward. The chief move- ment of the inferior oblique is rotary in the opposite direction (extorsion of the upper part). It is likewise inserted into the posterior half of the globe, which is depressed by it, and the cornea is raised and moved outward. In elevation of the cornea by the superior rectus the internal rotation of this muscle is counteracted by the inferior oblique, and in a similar manner when the cornea is moved downward by the inferior rectus, its external rotation is opposed by the superior oblique. The upward and outward movement is produced chiefly by the superior and external recti, the infe- rior oblique opposing the intorsion of the superior rectus. Motion downward and outward is due to the external and inferior recti, the superior oblique opposing the outward wheel action of the inferior rectus. The downward and inward motion is due to the internal and inferior recti, the superior oblique opposing the inferior rectus. When one muscle is weaker or larger than its opposing muscle, the eye is turned to the side of the stronger, producing strabismus or squint. It is usually turned laterally, most frequently to the inner side producing internal or convergent strabis- mus. All the recti except the external are supplied by the oculomotor nerve. If that nerve is paralyzed only the external rectus can act, and an external squint will result. If the sixth cranial nerve (abducens) which supplies the external rectus is paralyzed, the eye will turn inward, the superior and inferior recti opposing each other. Paralyses of one or more muscles may occur. If a single muscle is involved it is usually the superior oblique or external rectus, as each of these is supplied by a separate cranial nerve, the fourth and sixth respectively. Although the third or oculomotor has a much wider distribution than these, sup- plying all the other extrinsic muscles, as well as the ciliary muscle and sphincter of the iris, when it is completely paralyzed the clinical picture is definite. Ptosis is present and is due to paralysis of the levator palpebrae. External strabismus and slight depression of the eye are produced by the unopposed action of the external rectus and superior oblique, while the eye is otherwise motionless. The pupil is dilated from paralysis of the sphincter of the iris, and accommodation for near objects is lost from paralysis of the ciliary muscle. Slight exophthalmos appears from paral- ysis of all but one of the recti muscles. The fourth nerve alone is rarely paralyzed. There will be little disturbance of function, since the motion of the superior oblique is performed partly by the other muscles. The eye will turn inward when the object looked at is lowered, and upward only when the object is turned far toward the healthy side. One eye must be closed to prevent double vision or diplopia. Of the single paralyses, that of the sixth nerve is most frequent on account of its extended course from its origin in the brain to its peripheral termination in the external rectus, rendering it liable to involvement by adjacent pathological processes, as meningitis, tumors, or hemorrhages. Such lesions may involve it alone, or together with a series of cerebral nerves, paralyzed one after another from a progress- ing pathological condition, which would then probably be at their central origin, or in the wall of the cavernous sinus, where they are close together. The sixth nerve may be paralyzed by a fracture of the base of the cranium in the middle fossa. When the ophthalmic division of the fifth ncrrc is paraly/ed. there follows anesthesia of the conjunctiva of the globe and upper lid, and of the other parts supplied by this nerve. The lids do not respond reflexly, as usual, for protection of the cornea, which is liable then to troublesome ulceration. The cen lids are adherent. It is called ankylo-blcpharon. Lagophthahnus is an incomplete closure of the lids, and is sometimes congenital, sometimes the result of paralysis of the facial nerve which supplies the orbicularis muscle. Voluntary contraction of this muscle will usually close the lids in the lesser degrees of the congenital variety, but in sleep they are not closed. Since the eye turns up as the lids are brought together, the cornea is concealed. Ptosis is a drooping of the upper lid, and when congenital is usually associated with epicanthus, and is bilateral. The forehead is often wrinkled from the effort of the occipito-frontalis muscle to aid the orbicularis in lifting the lid. The head is usually thrown back and the eyes depressed to bring the sensitive part of the retina and pupil in line with the object to be seen. Blfpharospasm is an irritable spasm of the orbicularis closing the lids, and is usually due to disease of other parts of the eye. The skin of the lids is the thinnest in the body and is very loosely applied, through the loose areolar subcutaneous tissue. It therefore wrinkles easily, is readily deformed by scars, and is a favorable field for plastic operations. If cicatricial con- traction everts the lower lid, as it often does, the condition is known as cctropiou. More rarely contraction of the conjunctiva after ulceration or injury inverts a lid, THE EYEBALL. 1447 producing cntropion. The eyelids become cedematous or ecchymotic from slight causes, and in erysipelas are markedly swollen, closing the lids, or in severe cases may become gangrenous, the exudate interfering with the blood-supply. Herpes zoster is sometimes seen along the cutaneous distribution of the frontal and nasal branches of the trigeminal nerve. It is found on the forehead, lids, nose, and even the cornea. The iris, ciliary body, or choroid may be involved, since- through the lenticular ganglion, the nasal nerve supplies these structures. The cause is an inflammation of the trunk of the trigeminal nerve, the Gasserian ganglion, or the lenticular ganglion. Hordeolum or stye is a suppuration of one of the sebaceous glands (Zeiss's glands) associated with the follicles of the eyelashes. A chalazion is an affection of one of the Meibomian glands, with occlusion of the duct and retention of the secre- tion. There is often no inflammation present. For this reason, and because of its situation on the under surface of the tarsal cartilage, it is often not noticed until it reaches considerable size and shows through the lid. Normally the cilia or eyelashes curve away from the surface of the eyeball. Sometimes from inflammation, most commonly in trachoma or granular lids, they take the opposite direction and irritate the cornea (trichiasis or wild hairs). The Conjunctiva. Congenital fatty growths occur rarely in the outer part of the upper conjunctival sac. Dermoids and nsevi have also been seen in the con- junctiva. This membrane covers the anterior third of the eyeball, and where it passes to the lids forms the fornices. Because the upper fornix is deeper than the lower, being therefore turned less easily, foreign bodies are removed from the upper sac with greater difficulty. These particles strike first on the surface of the globe, and are usually brushed down into the lower sac by the upper lid. They frequently, however, catch in the conjunctiva of the ball or of the upper lid, and are held in the conjunctival sac only when they get above the upper retro-tarsal fold, where, if not removed, they may set up a chronic inflammation, or remain unnoticed. They have been found there months or even years afterward, entirely embedded in the outgrowths of the inflamed conjunctiva (Fuchs). A pterygium is an elevated layer of conjunctiva and subconjunctival tissue, triangular in shape with its apex near the edge of the cornea, and its base usually towards the inner canthus. It tends to progress towards the pupil, but may stop anywhere short of it. A pinguccula is a yellowish elevation of conjunctiva, to the inner side of the cornea, sometimes to the outer side. It corresponds to the part of the conjunctiva constantly exposed in the interpalpebral fissure, which therefore undergoes a change in structure. That at the inner side is most marked and may become a pterygium later. The scleral portion of the conjunctiva is loosely applied to permit of free motion of the ball. Near the margin of the cornea it becomes more fixed, and should be caught there by the forceps in the effort to fix the eye when operating upon it. The palpebral portion is more firmly attached, especially at the back of the tarsal plates where it is more vascular, and where paleness is taken to indicate a general anaemia. In fractures of the base of the skull involving the roof of the orbit the hemor- rhage into the orbital tissues shows first under the conjunctiva of the globe (subcon- junctival ecchymosis). It finds its way under the conjunctiva of the lids later because that is more firmly attached, and unless the lid is lifted, it will first be noticed at the margin of the lid, after which it may grow upward under the skin. This is due to the fact that the orbito-tarsal or palpebral ligament passes between the margin of the orbit and the upper edge of the tarsal plate like a curtain and prevents the progress of the blood forward to the skin until it has first passed down behind the tarsal plate and under its lower margin. Owing to the thinness of the conjunctiva, oxygen per- meates it more readily than it does the skin, so that blood under it retains its redness instead of becoming dark, as under the skin of the lid in ordinary " black eye." THE EYEBALL. The eyeball is situated in the anterior part of the orbit, about 2 mm. nearer the lateral than the nasal wall, and slightly nearer the superior than the inferior wall. A line drawn from the superior margin of the orbit to the inferior is tangent to HUMAN ANATOMY. the surface of the cornea. The axes of the eyeballs are practically parallel, when fixed on a distant object, but the optic nerves converge considerably, so that they enter the eyeball from 2-3 mm. to the nasal side of the posterior pole of the eye. The general form of the eyeball is that of a sphere, but in sagittal section it is found to be composed of the segments of two spheres, an anterior smaller segment, corre- sponding to the transparent cornea, which has a radius of from 7-8 mm. and a pos- terior opaque segment, corresponding to the sclera, with a radium of 12 mm. The junction between the two segments is marked externally by a broad, shallow groove. the snlcns sclera:,. which is filled by the scleral conjunctiva. The diameters of the eyeball measure approximately as follows : the antero-pos- terior, 24.2 mm. ; the vertical, 23.2 mm. ; and the transverse, 23.6 mm. Its shape is, therefore, that of a spheroid somewhat flattened from above downward, and from FIG. 1202. Lens Suspensory ligament of lens Canal of Schlemm Ciliary process Conjunctiva Cornea Anterior chamber Iris Posterior chamber Sclerocorneal juncture Tendon of in- ternal rectus muscle Vena vorticosa Tendon of external rectus muscle Sclera Ciliary nerve-' Posterior ciliary vessel Hyaloid canal Optic nerve Central retinal vessels roid Retina Fovea centra lis Optic papilla Diagrammatic horizontal section of right eye. X 3%. side to side. The diameters are slightly greater in the male than in the female, am vary according to the refractive power, being longer in nearsighted or myopic, am shorter in oversighted or hyperopic eyes. The eyeball consists of three concentric coats or tunics : ( i ) the external fibrous tunic, composed of the sclerotic and the cornea ; (2) the middle or rasculat tunic, which is pigmented and partly muscular, and is composed, from behind for ward, of the choroid, the eiliarv body, and the iris ; and (3) the inno -or nerroi tunic, the retina, an expansion of the brain, which contains beside the nerve-cell and the nerve-fibres the specialized neuroepithelium for the reception of visual stimuli Within these tunics are enclosed the refracting media, the crystalline lens, tl at/neons /minor and the rifrcons body. Practical Considerations. Congenital anomalies may affect the whole eyt the appendages, or the individual structures of the eye. The eye may be congcnitafly absent, on one or both sides ( anophthalmos ). Ii cases of apparent absence the eyeball has been found to be exceedingly sin; THE FIBROUS TUNIC. 1449 ( microphthalmos) and situated deep in the orbit near the optic foramen. The patient may otherwise be entirely normal ; or other developmental errors, as hare-lip or cleft-palate may be present. In some instances where no eyeball was found, the optic nerve had not entered the orbit, and in others the chiasm had not formed, the primary optic vesicle having failed to develop. Multiple eyes occur in some monsters. As digits sometimes bifurcate to form supernumerary digits, so the cephalic end of the embryo may divide, giving rise to two heads. These may fuse, when, according to the extent of fusion, there will be four, three, or two eyes ; or if both the orbits and the eyes fuse there may be only one eye (cyclopia). The actual size of the eye in man varies little, the apparent size depending chiefly upon the projection from the orbit and the part exposed between the lids. The variation in different animals depends rather upon the necessity for acuteness of vision than upon the size of the animal. The larger the globe the farther the cornea and lens from the retina, and FIG. 1203. -Fibre layer . .:.*' . I ,an orlirn r-<^ Ganglion cells Bipolar cells Visual cells Pigment layer Stroma Large vein Lamina fusca Fibrous tissue of sclera therefore the larger and more distinct the image on the retina of the object seen. The more active the animal the greater is the necessity for acuteness of vision, and therefore the larger the eye. The eyes of birds are pro- portionally larger than those of other animals. Nocturnal animals, such as the owl, have large eyes. The large retinal image probably com- pensates for the scarcity of light, to which they are accustomed. THE FIBROUS TUNIC. The Sclera. The sclera, or sclerotic coat, is a firm, dense fibrous coat which forms the posterior four-fifths of the outer coat of the eye, being closely con- nected with the sheaths of the optic nerve posteriorly, and joining in front with the cornea. In the neigh- borhood of the optic nerve it measures i mm. in thickness, and gradually becomes thinner toward the equator, until, just posterior to the attachment of the tendons of the ocular muscles, it measures only .4 mm. After receiving the expansions of these tendons it again becomes thicker and reaches a thickness of .6 mm. In children and in individuals who have thin sclerae and deeply pigmented eyes, the sclera possesses a bluish white color, while in old age it assumes a yellowish tinge. The optic nerve passes through this tunic at a position i mm. below and from 3-4 mm. to the inner side of the posterior pole of the eye ; the canal is partially bridged over by interlacing fibrous bundles, the lamina cribrosa, which are intimately associated with the supporting tissue of the nerve. Grouped around the nerve entrance are small openings for the ciliary nerves and posterior ciliary arteries, and toward the equator four or five for the vencz vorticose which emerge from the choroid. Structure of the Sclera. The sclera is composed of interlacing bundles of white fibrous tissue, which on the outer and inner surface have chiefly a meridional direction, while the central bundles form a fairly regular alternation of circular and Episcleral endothelium Space of Tenon between sclera and capsule of Tenon Section of three coats of eyeball, about five millimeters from optic papilla capsule of Tenon seen below sclera. X 40. HUMAN ANATOMY. Epithelium - Anterior limiting membrane ?r- Cortical cell meridional lamellae. The tissue yields gelatine on boiling. With the fibrous bundles is associated a rich net-work of fine elastic fibers. The clefts between the lamella- contain irregularly stellate connective tissue cells the scleral corpuscles. On the inner surface of the sclera many of these cells are pigmented and give it a brownish color. This layer the lamina fusca- forms with the underlying choroid a narrow lymph-space, the suprachoroidal lymph-space, both walls of which, together with the fine connective tissue trabeculae which cross it, are lined with endothelial cells. The outer surface of the sclera, from the optic nerve entrance to the attachment of the ocular muscles, is similarly covered with endothelial plates, and forms part of the lining of Tenon's lymph-space. Anterior to the muscle-insertions it is covered with a loosely meshed connective tissue, the episderal tissue, which is richly supplied with blood-vessels, nerves and lymph- vessels, and is continuous with the subconjunctival tissue of the conjunctiva scler&. The blood-vessels of the sclera arise from the arteries which per- forate it to supply the vascular coat of the eye, viz : the anterior and posterior ciliary arteries. They form a wide meshed net-work on S ro S rfa tia t ^ ie sur ^ ace f tne sclera, which sends anastomosing vessels to a deeper lying set in the substance of the membrane. In the neighbor- hood of the optic nerve entrance the branches of the short posterior ciliary arteries form an arterial circle, the circulus Zinni, which sends branches to the optic nerve and choroid, and is therefore of great importance in establishing an anastomosis between the cho- roidal circulation and the artcria centra/is retina; which supplies tin retina. The veins of the sclera empty into the anterior and posterior ciliary veins, and into the vemr vorticosce. At the junction of the cornea and sclera is an important circular venous channel, the canal of Schlcnun, which will be described later. The lymphatics of the sclera are represented by the intercommunicating cell-spaces, which communicate with the suprachoroidal and suprascleral lymph-spaces, and anteriorly with the spaces of Fontana, at the corneo-scleral angle. The nerves of the sclera are derived from the ciliary nerves during their course between the sclera and the choroid, their terminal filaments being distributed to the vessels, and also as a fine tortuous net-work between the bundles of the scleral tissue The relations of the sclera to the optic nerve sheaths will be considered in tl description of the optic nerve entrance (page 1470). The Cornea. The cornea forms the anterior one-fifth of the fibrous tunic the eyeball, and, although composed, like the sclera, of bundles of connective tissue, is transparent and allows rays of light to enter the eyeball. Its anterior surface is nearly but not quite circular, measuring ii.<) nun. in its greatest transverse diameter, and n mm. in its vertical diameter. The posterior surface is circular and measures 13 nun. in diameter. The sclera therefore encroaches more upon the cornea anteriorly than posteriorly, so that the cornea fits into a groove in tin- sclera. The radius of curvature of the anterior corneal surface is about 7.7 mm., that of the hori- zontal meridian being slightly greater (7. S nun.) than that of the vertical. The Section of human cornea. X 85. THE FIBROUS TUNIC. H5I radius of curvature of the posterior surface is only 6 mm. ; the cornea is consequently thicker in the periphery than at the center, in the proportion of. i.i mm. to .8 mm. The degree of curvature varies in different individuals and at different periods of life, being greater in youth than in old age. As the radius of curva- FIG. 1205. ture of the sclera, with which its bundles are continuous, is 12 mm. , the cornea rests upon the sclera as a watch-glass upon a watch. At the junction of the two membranes, on the outer surface, is the shallow groove, the snh'i/s sclcra'. Structure of the Cor- nea. The cornea is composed of five distinct layers, which from without in are: (i) the anterior epithelium, (2) the an- terior limiting membrane, (3) the substantia propria, (4) the posterior limiting mem- brane, and (5) the posterior endothelium. The anterior epithelium of the Cornea is Continuous Corneal corpuscles (connective tissue cells), surface view. X 350. with that covering the surface of the adjacent conjunctiva sclerae. It is of the stratified squamous variety, usually five cells deep in man, and measures .045 mm. in thickness at the center, and .080 mm. at the periphery. The deepest cells are columnar in form, with broad basal plates resting upon the anterior limiting membrane, to which they are firmly attached by means of minute projections which roughen the anterior surface of the latter. The outer parts of the basal cells contain the nucleus and fit into corre- sponding depressions in the cells of the superimposed layers. The middle layers are composed of irregular polyhedral cells, which usually present fine protoplasmic denticulations, and resemble prickle cells. The superficial layers consist of flattened cells which lie parallel to the free surface and contain well-staining nuclei. The anterior limiting membrane, <>r Bowmari s membrane, is situated immedi- ately below the epithelium, and appears as a homogeneous band, about .02 mm. in thick- ness at the center and thinner at the periph- ery, where it terminates without extending into the conjunctiva of the sclera. The mem- brane may be split into fine fibrillae by the use of suitable reagents, is connected firmly with the cornea proper by delicate filaments, and is to be considered a special condensation of the latter. It contains no elastic tissue. The substantia propria constitutes the main portion of the cornea, and is made up of interlacing bundles of connective tissue, which are directly continuous with those of the adjacent sclera. The bundles are composed of fine fibrillae, have a flattened form, and are so disposed as to produce regular lamellae, about sixty in number, running parallel with the surface. The alternating lamellae have a direction approximately at right angles to each other and are frequently joined together by FIG. 1206. Corneal spaces, after action of argentic nitrate ; surface view. < 350. 1452 HIM AX ANATOMY. FIG. 1207. Canal of Schlemm hands, which are especially numerous in the anterior lamelke, to which the name fibres arcuatcc has been given. The fibril ke and bundles are held together by an amorphous cement substance, and embedded in it are the cellular elements, the corneal corpuscles. These are flattened connective tissue cells, with faintly granular protoplasm, the nuclei of which in the adult are irregular and show nucleoli. The cells are provided with branching processes which anastomose with those of other cells both on the same level and with those between adjacent lamellae, and so con- stitute a continuous net-work of protoplasm, upon which the nutrition of the cornea largely depends. They have been described as occupying part of a regular system of cell-spaces and canaliculi, but most recent investigations seem to indicate that during life they fill out the spaces completely, and leave no gaps through which fluid can pass. Occasionally leucocytes or wandering cells are found between the fibrous elements. The posterior limiting membrane, also known as Deseemet \v membrane, the Membrane of Demours, or the posterior elastic membrane, is a practically homo- geneous band, which varies in thickness from .006 .012 mm. at the center and at the periphery respectively. It is less firmly united to the substantia propria than is the anterior limiting membrane, and is less easily affected by acids, alkalies, boiling water and other regents. It resembles elastic tissue and is very firm and resist- ant to injury or perforation from inflam- mation. At the periphery, Descemct'> membrane splits up into bundles of fine fibres, which are gradually strengthened and form a series of firm connective tissue trabecuke, some of which form the point of attachment of the ciliary muscle ; others run into the iris, and still others constitute the outer wall of a circularly disposed venous channel, tin- sinus circulars iridis, or canal of Schlemm. These fibres are known as the ligamentum pectinatum iridis and form the outer boundary of the angle of the anterior chamber. They are incompletely covered with endothelial cells and enclose between their loose meshes the spaces of Fontana. These, better developed in lower animals than in man, directly communicate with the aqueous chamber, and thus form an important point for filtration of fluid from the interior of the eye, by way of the canal of Schlemm, into the anterior ciliary veins. The posterior endothelium covers the inner surface of Descemet's membrane. It is composed of a single layer of flattened polygonal cells, the nuclei of which often extend above the level of the cell body. The cells are connected together by deli- cate protoplasmic processes and are continuous with the cells lining the spaces of Fontana and the anterior surface of the iris. With Descemet's membrane they con- stitute a barrier to the filtration of fluid from the anterior chamber into the cornea. although its passage by diffusion is possible; The blood-vessels of the normal cornea are limited to a peripheral /one, from 1-2 mm. in width, where the terminal twigs of the episcleral brandies of the anterior ciliary arteries end in loops (F"ig. 1215), from which the blood is carried to the anterior ciliary veins. The remainder of the cornea is free from blood-channels. The ncri'i's of the cornea are exceedingly numerous. They are branches ot the long and short ciliary nerve-, from 40 to 45 in number, and form a plexus which surrounds the margin of the cornea (plexus annularis). Those which supply the anterior part of the cornea anastomose first with the conjum Ural nerves. Entering the cornea, they are accompanied for a distance of I mm. by a perineiiral lymph- sheath, and then losing this and their medullary sheath, they form within the corneal stroma a number of plexuses at various depths. A few of the fibres pass backward Trabeculae of pectinate ligament Bundles of ciliary muscle Meridional section through angle of anterior chamber showing spaces of Fontana between relaxed fibres of pectinate ligament and canal of Schlemm. X 65. PRACTICAL CONSIDERATIONS: THE FIBROUS TUNIC. 1453 and supply the posterior layers. Fully two-thirds, however, after forming a funda- mental plexus, push forward and send perforating branches through Bowman's mem- brane and form on its surface a subepithclial plexus, the minute fibres of which pass in a radial manner toward the center of the cornea. From this plexus fine fibrils ascend between the epithelial cells, and end either as varicose fibrils, or in connection with special end-bulbs (the intracpithelial plexus). In the substantia propria the branches from the fundamental plexus, after forming complex secondary plexuses, end as naked fibrilke between the lamellae, probably in close connection with the corneal corpuscles. Practical Considerations. The external or fibrous covering of the eyeball consists of the sclera and cornea, and is the protective covering. The posterior five- sixths is made up of sclera, which in some animals becomes cartilaginous or even bony. In the human eye the average normal tension within the globe is equivalent to a column of mercury 26 mm. high. Excessive intraocular tension occurs under pathological conditions (glaucoma) and may reach 70 mm. or more. The more delicate structures then suffer severely and unless the pressure is relieved they are functionally destroyed. The sclera is thickest and strongest posteriorly and grad- ually grows thinner as it passes forward. Immediately behind the insertions of the recti muscles it is thinnest (.4 mm.). Here bulging is most likely to occur from internal pressure (anterior scleral or ciliary staphyloma), or pus within to burrow through. In front of this zone it is reinforced by expansions from the insertions of the muscles, and would seem therefore to be stronger, although it is in this region, just back of the margin of the cornea, that ruptures are most likely to occur from external violence. Ruptures of the sclera occur close to within 3 mm. of the corneal margin and concentric with it, because in most cases, as Fuchs points out, the application of the force does not lie in the centre of the cornea, but in the sclera below and to the outer side of the cornea. The greatest expansion of the sclera takes place in its upper half near the margin of the cornea, at which place, therefore, the sclera ruptures. This region is the so-called dangerous zone of the eyeball, because the iris and ciliary body correspond to it, and in wounds involving these structures, sympathetic ophthalmia frequently results, often leading to destruction of both eyes. Besides the anterior staphyhmata of the sclera, \ve may have the eqiiatorial and the posterior. The equatorial develops at the spots where the venae vorticosae penetrate and thus weaken the sclera about the equator of the globe. The posterior is assumed to be the result of a congenital weakness of the sclera. The anterior or equatorial can be seen or palpated, while the posterior is recognized only by demonstrating the existence of a high degree of short-sightedness, which is due to an increase of the sagittal axis of the eyeball. Rupture of the sclera is usually the result of a blow on the eye. The ciliary body and anterior portion of the choroid are frequently forced into the wound, the vitreous and aqueous chambers contain blood, while the lens may find its way through the rent and lie under the conjunctiva, which may or may not be torn. Rarely the rup- ture will be in the posterior portion of the globe. Congenital opacities of the cornea may occur and may be complete or partial. In some of the cases reported of the complete variety the anterior elastic lamina was absent, and the anterior layers of the stroma were not laminated as usual, but crossed each other, and among them were found blood-vessels. The partial varieties may consist of a dense white opaque ring at the margin of the cornea, as though the sclera had extended into the cornea, or they may resemble an arcus senilis in which a perfectly clear strip of cornea divides the opaque line from the margin of the sclera. The cornea in health is transparent, and almost all pathological lesions render it opaque. It is the most exposed and therefore the most frequently injured part of the eye. Wounds of the cornea heal readily under favorable circumstances, showing that its nutrition is good, although there are no vessels in it, except within 1-2 mm. of its margin. When the cornea is inflamed, however, new vessels may form from those at the margin and extend a variable distance inward. Under the influence of 1454 HUMAN ANATOMY. irritating conditions a superficial inflammation may develop, covering the cornea with a new vascular tissue (pannus), the deeper layers still being bloodless. Owing to a very free nerve-supply the cornea is very sensitive. As in the sclera, weakness of the cornea leads to bulging, from internal pressure. The causes of weakness may be congenital and acquired. Congenital conical cornea or kerataconus may occur, and it is believed that some congenital defect predisposes to the same condition that occurs in the adult. It is not due to weakening from pre- vious ulceration or injury of the cornea, and the exact cause is not known. A staphyloma of the cornea is a similar condition in which the protuberance is due to the distention of a cicatrix, to the posterior surface of which the iris may be attached (anterior synechiae of the iris). The cicatrix involves all the layers of the cornea, and is the result of a perforating ulcer. If the ulcer had been a non-per- forating one, and the iris did not adhere to its posterior surface, the protrusion of the cornea would then be called a keratedasia. If all the layers of the cornea to the posterior elastic lamina had been destroyed by the ulcer, and this layer had bulged through the weakened spot like a hernial pouch it would be called a keratocele. Arcus sent/is is usually a sign of old age. Modern investigation indicates that it is due to a fatty degeneration of the substantia propria, the exact nature of the fatty material being unknown. It first appears as a crescent above, then below, and finally a complete circle is formed. It never interferes with sight. It is occasionally seen in children. THE VASCULAR TUNIC. The middle or vascular coat of the eye (tunica vasculosa oculi), or uveal tract, consists of a vascular connective tissue sheath, which lies internal to the outer fibrous FIG. 1208. Anterior chamber Pupil Circulus arteriosus minor Artery joining ring ._ Vena vorticosa Short post, ciliary artery Cornea Iris Circulus arteriosus major Anterior ciliary artery Ciliary nerves Venous whorl Ciliary nerve ']] }}f posterior ciliary artery' \ Sclera ptic nerve Injected eyeball, showing arrangement of ciliarv aiu-ne> ami \ choroidal veins, v 3. Drawn from ptrparation made l>v 1'iotessoi Kciller. tunic. It cMrnds from tin- entrance of the optic nerve to the pupil and include three portions, which from behind forward arc- the choroid, the ciliary body and the iris. The choroid and ciliary body arc in contact with tin- sclcra, but the iris bends THE VASCULAR TUNIC. H55 sharply inward and floats in the aqueous humor, incompletely dividing the space anterior to the crystalline lens into a posterior and an anterior chamber. The Choroid. The choroid (tunica chorioidea) forms the posterior two-thirds of the vascular coat. It lies between the sclera and the retina and extends from the FIG. 1209. -,-*" ~ optic nerve entrance to the anterior limit of the visual part of the retina at the ora serrata, its main function being to supply nutrition to the nervous tunic. It is a delicate coat, which has a thickness of . i mm. near the nerve and gradually diminishes in thickness towards the ora serrata, where it measures only .06 mm. The outer surface is roughened by the tra- beculae of connective tissue which cross the suprachoroidal lymph- space and connect the choroid with the overlying sclera. The connection is main- tained partly also by the larger vessels and nerves, which lie within this space during their course forward and send branches to supply the choroid. The inner Membrana vitrea Chorio- capillaris Large vein Choroiclal stroina Lamina su- prachorioidea Suprachoroi- dal space Lamina fusca of sclera^ Section of choroid. 275- Large vein Artery Surface view of injected human choroid, showing venous radicles converging to form larger veins. is. surface of the choroid is smooth and covered by the pigmented cells of the retina, which are so closely attached that they frequently adhere to the choroid when the membranes are separated. Posteriorly, the choroid helps to form the lamina crib- rosa, the fenestrated membrane through which the optic nerve-fibres pass ; anteriorly it is continuous with the ciliary body. HTM AN ANATOMY. FIG. 121 i. Portion of injected choriocapillaris layer human choroicl. X 130. Structure of the Choroid. The choroid consists of four layers, which from without inward, are : (i) the lamina sitprachorioidea, (2) the choroid proper, which contains the larger vessels, (3) the choriocapillaris, or layer of fine capillaries, and (4) the membrana vitcra. The lamina suprachorioidea forms the outer boundary of the choroid and connects it with the sclera. It is composed of interlacing bundles of fibrous connec- tive tissue, which are strengthened by a rich net- work of elastic fibres. The cellular elements consist of (a) flattened endothelial plates, which line the lymph-clefts and cover the connective tissue trabeculae connecting the choroid and the sclera by traversing the suprachoroidal lymph- space ; and () large, irregularly branched con- nective tissue cells, the chromatophorcs, which are conspicuous on account of their deeply pigmented protoplasm. The lamellae of the suprachoroid continue, without definite boun- dary, into the subjacent choroidal stroma. The choroid proper, as the choroidal stroma is called, has the same general structure as the suprachoroidal layer, but the connective tissue elements are denser and support a large number of blood-vessels, between which are placed the stellate chromatophores. The largest vessels occupy the outer part of the coat, and are chiefly venous. They are surrounded with perivascular lymph-sheaths, and converge in peculiar whorls to form four or five large trunks, the vence vorticosa, which pierce the sclera in the equatorial region and, running obliquely backward, drain not only the choroid, but partly also the ciliary body and iris. The arteries are derived from the short ciliary vessels, which pass through the sclera near the optic nerve. They lie internal to the veins and their walls contain longitudinally disposed muscu- lar fibres in addition to the customary cir- cular ones. The choriocapillaris, or membrane of Ruysch, is composed of the fine capillaries of the choroidal vessels, which form an extremely fine mesh-work embedded within a homogeneous, nonpigmented matrix. Between the choriocapillaris and the layer of larger vessels is a narrow boundary zone of closely woven fibro-elastic strands, which is nearly free from pigment. In some animals this layer possesses a peculiar metallic reflex and is known as the tapetum fibrosum ; in carnivora its iridescent appearance is due to the presence of cells containing minute crys- tals (tapetion cellnlosnm'}. The membrana vitrea, or membrane of Bruch, the innermost layer of the choroid, measures only .002 mm. in thickness. It separates the choriocapillaris from the retina and is composed of two strata, an inner homogeneous one, probably an exu- dation product of the retinal pigment cells, and an outer highly elastic portion. The lymphatics of the choroid are represented (i) by vessels which begin in the lymph-spaces between large blood-vessels, and are in communication with the space> between the suprachoroidal lamellae, and (2) by the perivascular lymph-spaces of FIG. 1 212. Sclera Cornea Anterior part showing nis, cili serrata. X 3. of sectioned eye-ball, processes and ring and ora THE VASCULAR TUNIC. H57 the veins, which begin between the meshes of the choriocapillaris, the two systems being separate. The nerves of the choroid arise from the long and short ciliary nerves during their course on the inner surface of the sclera. They form a plexus within the lamina suprachorioidea, which contains groups of ganglion cells, and sends numerous nonmedullated fibres chiefly to the muscular coats of the arteries. A few ganglion cells are found along the blood-vessels. The choroid contains no sensory nerve-fibres. FIG. 1213. Choroidal strom Pigmented cells- Clear cells Blood-vessels Clear cells Sections of ciliary processes; A,trom anterior; B, from posterior part ; two epithelial layers, pigmented and clear, of pars ciliaris retinae cover choroidal stroma. X 80. The Ciliary Body. The ciliary body (corpus ciliare), the middle portion of the vascular tunic, extends from the ora serrata to the sclero-corneal junction. Sections through the eyeball in a meridional direction (Fig. 1214) show that it has a triangular form. The outer side is in apposition to the sclera, the inner is covered by the pigmented extension of the retina, and the short anterior side, at right angles to the outer, extends inward from the pectinate ligament toward the lens. The ciliary body presents three subdivisions ; the ciliary ring, the ciliary pro- cesses and the ciliary muscle. Cornea FIG. 1214. Canal of Schlemm . Pectinate ligament - Ciliary muscle (radial fibres) :vJv* !=> _^'Sclera K^ ^ Meridional fibres Ciliary processes Circular fibres Choroid Pars ciliaris retinae Meridional section of ciliary region, showing ciliary body with its muscle and processes. X 40. The ciliary ring, or orbictihis ciliaris, consists of a smooth band of tissue, 4 mm. in width, in advance of the ora serrata. It differs in structure from the choroid in the absence of the choriocapillaris, its vessels running in a longitudinal direction and returning the blood from the iris and ciliary body to the venae vorticosae. On its inner surface, delicate meridionally placed folds make their appearance, by the union of which the ciliary processes are formed. The ciliary processes constitute the remainder of the inner portion of the ciliary body. They form an annular series of folds, about seventy in number, which surround the lens and act as points of attachment to its suspensory ligament. 92 H58 HUMAN ANATOMY. Commencing by the union of several plications of the orbiculus ciliaris, they rapidly increase in height and breadth, until they reach an elevation of from .8-1 mm., and then fall suddenly to the iris level. They consist of a rich net-work of vessels em- bedded in a pigmented connective tissue stroma, like that of the choroid. The inner surface is covered with a homogeneous membrane, which is continuous with the membrana vitrea of the choroid, on the inner surface of which is placed the double layer of cells representing the ciliary portion of the retina (pars ciliaris retina^. Each ciliary process is composed of a number of irregularly projecting folds which increase in height as the iris is approached. Cornea Greater arterial ring Iris Lesser arterial ring Ciliary process FIG. 1215. Canal of Schlemm jrneal loop Perforating branch 'onjunctival vessels Recurrent cho- roidal artery Long posterior ciliary artery Choroidal vein Anterior ciliary vessels Sclera Episcleral vessels Communication between Retinal vessels choroidal and optic vessels Central retinal vessels Vena vorticosa Supplying choroid Short posterior ciliary artery Long posterior ciliary artery Communicating twig Inner sheath vessels Outer sheath vessels Communication between optic and sheath vessels Diagram illustrating circulation of eyeball. (Leber.) The ciliary muscle occupies the outer portion of the ciliary body, lying between the sclera and the ciliary processes. It forms an annular prismatic band of involuntary muscle, which in meridional sections has the form of a right-angled triangle, the hypothenusc being the outer side, next to the sclera, and the right angle facing the lens. Its main fibres arise from the sclera and pectinate ligament, at the corneo-sclera junction internal to the canal of Schlemm, and run in a nn > hiioual direction backward along the sclera to be inserted into the choroidal stroma (hence their name, tensor chorioidc Pigmented layer 2. Layer of rods and cones ") Neuro- 3. Layer of bodies of visual cells or outer nuclear j- epithelial layer 4. Outer plexiform layer 5. Layer of bipolar cells, or inner nuclear layer 6. Inner plexiform layer 7. Layer of ganglion cells 8. Layer of nerve-fibres J layer Cerebral layer FIG. 1219. To these nervous layers must be added two delicate membranes, ( i ) the membrana limitans interna, which bounds the inner surface of the retina, and (2) the membrana limitans externa, which lies between the outer nuclear layer and the layer of rods and cones. These membranes represent the terminal portions of the supporting neu- rogliar fibres, or fibres of Miiller. The pigmented layer, formed of deeply pigmented cells, constitutes the most external layer of the retina and represents the outer wall of the fcetal optic vesicle. It is composed of hexagonal cells, from .oi2-.oi8 mm. in diameter, the protoplasm of which is loaded with fine, needle-shaped crystals of pigment (fuscin). The outer portion of the cells is almost free from pigment and con- tains the nucleus. From the inner border fine proto- plasmic processes extend inward between the rods and cones of the neuroepithelial layer. Under the influence of light, the pigment particles wander into these processes and, under such conditions, the pigmented cells may remain attached to the retina when the latter is separated from the choroid. Ordinarily, the pigmented layer ad- heres to the choroid and, hence, was formerly considered to be a part of that membrane. The pigmented cells are separated by a distinct intercellular cement substance and in some of the lower animals contain colored oil droplets and particles of a highly refracting myelin-like substance (myefoid granules of Kiihne). The layer of rods and cones, although usually described as a distinct stratum, is only the highly specialized outer zone of the layer of visual cells and, therefore, constitutes the outer portion of the neuroepithelial division of the retina. It is com- posed, as its name indicates, of two elements, the rods and the cones, which are the outer ends of the rod and cone visual cells. They are closely set, with their long axes perpendicular to the surface of the retina. The rods far outnumber the cones, except in the fovea centralis, in which location cones alone are found. In the macula each cone is surrounded by a layer of rods ; elsewhere the cones are separated by intervals occupied by three or four cones. The rods of the human retina (Fig. 1221) have an elongated, cylindrical form, and measure approximately .060 mm. in length and .020 mm. in diameter. Each rod Pigmented cells from outer layer of retina ; surface view. X 250. 1464 HUMAN ANATOMY. is composed of an outer and an inner segment, of about equal length. The outer segment possesses a uniform diameter, is doubly refracting, and readily breaks up into minute disks. It is invested with a delicate covering of neurokeratin, contains myeloid (Kuhne) and is the situation of the visual purple or rhodopsin. The inner rod segment is somewhat thicker and has an ellipsoidal form. It is singly refracting, homogeneous in structure (rapidly becoming granular after death) and from its inner extremity sends the delicate rod-fibre through the external limiting membrane into the outer nuclear layer where the nucleus of the rod visual cell is found. The cone visual cell is composed of the same general divisions as the rod-cell, including the specialized outer part, the cone, and the body within the external nu- clear layer. The cones are shorter than the rods, and, except in the fovea, have a length of .035 mm. Each one (Fig. 1221) is composed of an outer narrow cone- shaped segment, and an inner broader segment, which is distinctly ellipsoidal in form, with a diameter of .060 mm. The inner segment is double the length of the outer, and is continue'd inward as FIG. 1220. the cone-fibre with its nucleus in the outer nuclear layer. In the fovea, where the cones alone are found, they are of approximately the same length as the rods, and possess about one half the usual diameter. The outer nuclear layer, the inner portion of the neuroepi- theleal layer, is composed of the bodies of the rod and cone visual cells, which show chiefly as the nuclei, the so-called rod- and cone- granules. The rod-granules oc- cupy an elliptical enlargement of the attenuated rod-fibres. They exhibit a transverse striation and are placed at varying levels within the layer. The rod-fibres are con- tinued as a thin protoplasmic pro- cess into the outer reticular layer, where they form small end-knobs which are associated with the outer terminals of the small nerve-cells, the rod-bipolars. The cone-gran- nies are less numerous than those of the rods, display no transverse Internal limiting membrane Ganglion cell Fibre of Miiller Bipolar nerve- cells Blood-vessel H Layer of visual cells Nucleus of cone- cell" Cone - Rod- Pigment layer Section of human retina from near posterior pole. X 230. markings, and are found only in the outer portion of the nuclear layer, near the external limiting mem- brane. The cone-fibres, the attenuated bodies of the cone visual cells, are broader than the corresponding parts of the rods and are continued through the outer nuclear layer as far as the outer portion of the external plexiform layer, where they end with a broad base, from which delicate processes extend inward to interlace with the terminal arborizations of the cone-bipolars. The outer nuclear layer is about .05 nun. in thickness. The outer plexiform layer is a narrow granular looking stratum, between the outer and the inner nuclear layer, and constitutes the first of the cerebral layers of the retina. It is composed of the dendritic arborizations of the bipolar nerve-cells of the- succeeding layer, which lie in close relation with the centrally directed proces- ses from the foot-plates of the cone-cells and with the end-knobs of the rod-fibre's. In addition to these constituents of the plexiform layer, numerous fibres arising from the protoplasmic processes of the horizontal cells of the inner nuclear layer also take part in its formation. THE NERVOUS TUNIC. 1465 FIG. 1221. The inner nuclear layer, the most complicated of the retinal strata, measures .035 mm. in thickness near the optic disc. It contains nervous elements of three main types the horizontal cells, the bipolar cells, and the amacrine cells and, associated with these, the nuclei of the sustentacular cells. The horizontal cells form the external layer, and were formerly included in the outer plexiform layer. They have flattened cell-bodies and send out from five to seven dendrites, which divide into innumerable branches- and, passing into the outer plexiform layer, terminate in close association with the bases of the rod and cone visual cells. Each horizontal cell possesses also an axone, which is directed outward through the outer plexiform layer, and ends in a richly branched arborization about the visual cells. A second type of large horizontal cells is also described, some of which send axis-cylinder pro- cesses through the inner nuclear layer to form terminal arborizations in the inner plexiform layer. The function of the horizontal cells is not well understood, but they prob- ably serve as association fibres between the visual cells. The bipolar cells, the ganglion cells of this layer, are of two chief varieties, the rod-bipolars and the cone- bipolars. They are oval cells, each sending an axone inward toward the inner plexiform layer, which ends in communication with the large nerve-cells of the ganglion cell layer, and a dendrite outward which is associated with the end terminals of the visual cells and with the arboriza- tions of the horizontal cells. The dendrites of the rod- bipolars form an arborescence of vertical fibrils, which enclose from three to twenty end knobs of the rod-fibres, whilst their axis-cylinders pass entirely through the inner plexiform layer and usually embrace the cell-body of one of the large ganglion cells. The dendrites of the cone- bipolars, on the other hand, bear horizontal arborizations which interlace with the fibrils from the foot-plates of the cone-cells. Their axones penetrate less deeply into the inner plexiform layer than do those of the rod-bipolars, coming in contact at various levels with the peripherally directed dendrites of the ganglion cells. The amacrine cells are placed in the inner portion of the nuclear layer. Formerly considered as sustentacu- lar elements, they are now recognized as nerve-cells, although, as their name indicates, no distinct axone can be demonstrated. They possess, however, richly branched dendritic processes, which ramify in the inner plexiform layer and end either as the brush-like arborizations of the diffuse amacrines, or as the horizontally branching arborizations of the stratiform amacrines. A third type, known as association amacrines, is also described. They connect widely separated amacrine cells of the same layer (Cajal). The nuclei of the sustentacular cells, the fibres of Miiller, will be described later (page 1466). The inner plexiform layer, .04 mm. in thickness, appears granular, similar to the corresponding outer zone, and is composed of the interlacing axones of the bipolar, amacrine and horizontal cells from the inner nuclear layer and the dendrites of the large ganglion cells in the subjacent retinal layer. Intermingled with them are also the fibres of Miiller, which form conspicuous vertical striae, with lateral offshoots within the stratum. The layer of ganglion cells, consists, throughout the greater part of the retina, of a single row of large multipolar neurones, each with a cell-body containing a vesicular nucleus and nucleolus and showing, like many other ganglion cells of The central nervous system, typical Nissl bodies and a fibrillar structure. Near the macular region, the ganglion cells are smaller but more numerous and arranged as several superimposed layers; toward the ora serrata, on the contrary, the individual Visual cells from human ret- ina, A, cone-cell; B, rod-cell; a, b, outer and inner segments; c, attenuated bodies (fibres), with nucleus (d) and central ends (< - directly to the nerve-disc. The sustentacular tissue, the neuroglia of the retina, exists in two forms as faz fibres of Mutter and as the spider cells. The fibres of Miiller are modified neuroglia fibres which pass vertically from the inner surface of the retina through the succeeding layers as far as tin- bases of the rods and cones (Fig. -1222). The inner extremities of the fibres possess conical expansions, which are in apposition and form an incomplete sheet. known as the membrana limitans interna. As the fibres traverse the retinal layers, they give off delicate lateral offshoots, which break up into a fine supporting retieu- lum. Within the inner nuclear layer each fibre presents a broad expansion, in which is situated the oval nucleus of the sustentacular cell, the fibre of Miiller. After traversing the outer nuclear layer their broadened peripheral ends come into contact and form a continuous sheet, the membrana limitans externa. From the latter deli- cate offshoots continue outward and embrace the bases of the individual rods and cones. In addition to the robust fibres of Miiller, neuroglia cells, in the form of spider cells, are found in the nerve-fibre and ganglion cell layers. These cells send out long delicate processes which extend between the processes and cells and thus help to support them. The Macula Lutea. The structure of the retina undergoes important modifi- cations in two areas, at the macula lutea and at the ora serrata. In the former the ganglion cells increase rapidly in number as the macula is reached, so that instead of forming a single layer they are distributed in from eight to ten strata. The inner nuclear layer is also increased in thickness. Within the fovea centralis, however, in order to reduce to a minimum the layers traversed by the light-rays, the cerebral layers are almost entirely displaced, only the absolutely essential retinal strata the pigment cells and the visual cells with their necessary connections being retained within the area of sharpest vision (Fig. 1223). On approaching the fovea, the ganglion cells rapidly de-crease in number, until at the centre of the depression, they are entirely absent and the nerve-fibre layer, therefore, disappears. The bipolar Supporting fibres of Miiller from retina of ox; Golgi preparation. (Cajal.) THE NERVOUS TUNIC. 1467 cells are present as an irregular layer within the fused remains of the two plexiform layers. The most conspicuous elements are the visual cells, which in this position are represented solely by the cones, which have about twice their usual length and thickness, the increase in length being contributed by the outer segments. The cone-cell nuclei become removed from the external limiting membrane; the cone- fibres are therefore lengthened, pursue a radial direction, and constitute the so-called FIG. 1223. Internal limiting membrane Inner plexiform layer Ganglion cells Fovea centralis ^&& Bipolar cells Outer Pigmented Cone Cones plexiform layer layer visual cells Section of human retina through fovea centralis. X 80. fibre-layer of Henle. Opposite the centre of the fovea, the choroid is thickened by an increase in the choriocapillaris. The yellow color of the macula is due to a diffuse coloration of the inner retinal layers. The Ora Serrata. The visual part of the retina ends anteriorly in an irregu- lar line, the ora serrata. Within a zone of about i mm. in width, the retina dimin- ishes in thickness from .50 to .15 mm., in consequence of the abrupt disappearance of its nervous elements. The rods disappear first ; then the cones become rudimen- tary, and finally cease ; the ganglion cells, nerve-fibre layer and inner plexiform layer fuse, and the two nuclear layers unite and lose their characteristics, most of the nuclei present being those of the supporting fibres of Muller, which are here highly developed. These elements continue beyond the ora serrata (Fig. 1224) as the transparent cylindrical cells composing the inner layer of the pars ciliaris retince, the densely pigmented cells of the outer layer being a direct FIG. 1224. .Pi K m layer Inner cells Pigmented cells ^PlffipPj - Bipolar cells 9 Ganglion =~ cells Section of human retina through ora serrata, showing transition of pars optica into pars ciliaris. X 165 continuation of the retinal pigmented cells. These two strata of cells are prolonged over the ciliary body and the iris as far as the pupillary margin, over the iris constituting the pars iridica retina. As the columnar cells pass forward, they gradually decrease in height, and at the junction of the ciliary body and the iris the cells of both layers become deeply pig- mented, with consequent masking of the boundaries of the individual elements. The cells of the anterior layer are of additional interest as giving rise to the dilatator muscle of the iris. The aggregation incident to the convergence of the nerve-fibres from all parts of the retina produces a marked thickening of the fibre-layer around the optic disc, and as the fibres turn outward to form the optic nerve the other layers of the retina, together with those of the choroid, suddenly cease. On the temporal side a narrow meshwork of intermediate tissue separates the nerve-fibres from the other retinal strata, but at the nasal side this tissue is absent. The ganglion cells dis- appear first, whilst the pigmented cells, with the lamina vitrea of the choroid, extend furthest inward. The blood-vessels of the retina are derived from a single artery, the arteria centralis retinas, which enters the optic nerve at a point from 15-20 mm. behind the eyeball, and, with its accompanying vein, runs in the axis of the nerve and 1468 HUMAN ANATOMY. emerges slightly to the nasal side of the centre of the optic disc. Here the artery divides into two main stems (Fig. 1225), the superior -and inferior papillary branches, each of which subdivides at or near the disc-margin into superior and inferior nasal and temporal branches which run respectively mesially and laterally, dividing dichotomously as end arteries, no anastomosis existing. The macular region is supplied by special macular branches, the center of the fovea, however, being free from blood-vessels. The larger branches from the central artery course within the nerve-fibre layer, and send fine twigs peripherally inward to form an inner and an outer plexus, the former on the outer surface of the inner plexiform layer, and the latter within the inner nuclear layer. Beyond the outer plexiform layer the vessels do not penetrate, the visual cells being dependent for their nourishment upon the choriocapillaris of the choroid. At the nerve entrance an indirect communication exists between the arteria centralis and the posterior ciliary arteries, through the medium of the small branches which constitute the circulus arteriosus Zinni. FIG. 1225. Temporal Nasal Normal fundus of right eye as seen with ophthalmoscope ; central retinal vessels seen emerging from optic nerve; arteries are lighter, veins darker vessels; fovea centralis shows as light point in macular region, which lies in temporal field and is devoid of large vessels. The lymphatics of the retina are represented chiefly by the perivascular lym- phatic spaces which surround all the veins and capillary blood-vessels. These spares may be injected from the subpial lymph-space of the optic nerve, and by the same method communications may be demonstrated between (i) this space and the interstices between the nerve bundles which converge toward the optic papilla, (2) a space between the membrana limitans interna and the hyaloid membrane of the vitreous, and (3) a narrow cleft between the pigmented cells and the layer of rods and cones. Practical Considerations. All pathological conditions of the retina ap- pear as opacities, and thus interfere with sight. The medullary sheaths of tin- optic nerve-fibres end at the lamina cribrosa. Rarely the sheaths around these may extend some distance into the retina, showing as a white striated margin around the optic disc and continuous with it. Sometimes the blood-vessels of the retina may enter at the margins of the optic disc, instead of at its centre, as usual, which is then free of vessels and very pale. At the entrance of the optic nerve, the transparency of the retina is lessened by the thickening of its fibre-layer PRACTICAL CONSIDERATIONS : THE RETINA. 1469 The integrity of the central artery of the retina is necessary to the preservation of sight. The branches of this vessel are distributed to the retina only, and have no communication with those of the other coats, nor do they anastomose with one another. If the main artery or one of its branches is plugged with an embolus, the area supplied by the blocked vessel is then deprived of sight. The retina may undergo inflammatory change in nephritis, syphilis, diabetes, and other constitutional diseases. Of all these inflammations of the retina, that due to kidney disease (albuminuric retinitis) is the most characteristic. Besides the signs of general inflammation, as haziness of the retina, choked disc, distended retinal arteries, or hemorrhages into the retina, pure white or even silvery patches often occur ; they are due to fatty degeneration. Retinitis without these charac- teristic changes may occur from albuminuria, so that the urine should be examined in all cases of retinitis. The retina between the optic nerve and the ora serrata is held in apposition to the choroid only by the support afforded by the vitreous body. It may be readily detached from the choroid by such causes as injury, extravasation of blood or serum between the two layers, or by tumors of the choroid. In contusions of the eye the retina is sometimes torn alone, although this is rare. The retina does not tear as easily as the choroid, as is shown by the fact that in ruptures of the choroid the retina is generally not lacerated. Glioma is the only tumor found in the retina, and occurs exclusively in children, usually under three years of age. A rare tumor arising from the pars ciliaris retinae has been described, to which the name terato-neuroma has been applied by Verhoeff. The Optic Nerve. The extraocular portion of the optic nerve has been de- scribed elsewhere (page 1 223). Likewise, the three sheaths the dural, the arachnoid FIG. 1226. Physiological excavation Lamina cribrosa Fibre-layer Visual cells tjg Choroid--^ Sclera JL Subarachnoid space rr V5 \ L__ '31 Subdural space Pial sheath / Central retinal vessels within optic nerve Section of eyeball through entrance of optic nerve. X 20. and the pial which, with the subdural and the subarachnoid lymph-spaces, are con- tinued over the nerve as prolongations of the corresponding brain-membranes ( page 949). On reaching the eyeball, the dural sheath bends directly outward, its fibres commingling with those of the outer third of the sclera (Fig. 1226) ; the arachnoid ends abruptly on the inner wall of the intervaginal space ; whilst the pia arches outward to form part of the inner third of the sclera, but sends longitudinal fibres as far as the choroid. As the nerve-fibres enter the eyeball, for convenience assuming that they are passing from the brain toward the retina, they traverse a fenestrated 1470 HUMAN ANATOMY. Blood-vessel Bundles of . nerve-fibres Interfascicular connective tissue membrane, the lamina cribrosa, which is formed by interlacing bundles from the inner third of the sclera and from the pial sheath. As they penetrate the lamina cribrosa they lose their medullary sheaths ; in consequence the optic nerve is reduced one third in diameter. The intervaginal lymph-space ends abruptly, being separated from the choroid FlG - I22 7- by the fibres of the pia which arch outward to join the sclera. The nerve projects slightly into the eyeball on account of the thickness of the layer of arching nerve- fibres and forms, therefore, a circular elevation, known as the optic papilla or optic disc, about 1.5 mm. in diameter, the center of which is occupied by a fun- nel-shaped depression, the so-called physiological exca- vation. The axis of the nerve is occupied by the central artery of the retina, which gives off minute branches for Transverse section of part of optic nerve, showing several fasciculi of the nutrition of the nerve nerve-fibres. X 125. . . , ' that anastomose with the pial vessels, and, through the circulus arteriosus Zinni, with branches of the posterior ciliary arteries. When seen in transverse sections (Fig. 1227), the optic nerve appears as a mosaic of irregular polygonal areas, composed of bundles of medullated nerve-fibres surrounded by connective tissue envelopes. Although provided with medullary sheaths, the optic fibres are devoid of a neurilemma, in this respect agreeing with the nerve-fibres composing the central nervous system. The entire nerve corresponds to a huge funiculus, the perineurium being represented by the pial sheath, and the endoneurium by the interfascicular septa of connective tissue prolonged from the pia between the bundles of fibres. Numerous connective tissue cells occur along the strands of fibrous tissue. Practical Considerations. Any disturbance of the optic nerve-fibres passing from the retina to the cortex of the brain (page 1225) will cause disturbance of vision, and within certain limits the lesion may be localized by the character of the symptoms produced. The most characteristic symptom from a lesion on one side behind the chiasm is a homonymous lateral hemianopsia, that is, the right or the left half of each eye will be blind. This is explained by the fact that the optic tracts are made up of tibn-s coming from the corresponding lateral halves of both retinae, i.e., the fibres from the right half of each retina pass to and make up the right optic tract, and puss therefore to the right half of the brain. It will thus be seen that anything com- pressing the optic fibres of the right side behind the chiasm, for instance a hemorrhage, would produce a blindness more or less complete according to the extent of tin- fibres involved of the right half of each eye. Since most of the optic fibres enter the lateral geniculate bodies, a lesion there always causes hemianopsia, or half-eye blindness. Lesions of the optic thalamus, or of the superior quadrigeminal body, may also by compression of the adjacent optic tract produce hemianopsia. In the optic radiation are other than optic fibres, so that hemianopsia may or may not follow lesions in that tract, according to whether optic fibres arc- involved or not. The exact course of the visual fibres in the optic radiation is uncertain. If the visual area of the brain cortex is involved by the lesions, no other symptoms will be present, but the hemianopsia will be complete and homonymous that is, tin- corresponding halves of the two eyes will be blind. THE CRYSTALLINE LENS. 1471 FIG. 1228. If the lesion affect the chiasm, as from tumors of the pituitary body, periostitis of the body of the sphenoid bone, tuberculous or syphilitic exudate, causing pressure on the mesial portion of the chiasm involving the decussating fibres, the nasal half of each eye supplied by these fibres will be blind (heteronymous hemianopsia). Since the nasal half of each eye perceives the temporal half of the visual field, this variety of half-blindness is called bitemporal hemianopsia. If the optic fibres of one side in front of the chiasm are involved, the disturbance of vision will affect one eye only, so that the occurrence of absolute blindness of one eye, without other known cause, with good sight in the other, would suggest a lesion in front of the chiasm. Inflammation of the intraocular end of the optic nerve that is, of the optic disc, or papilla gives rise to the condition to which the name optic neuritis, or papillitis, is applied, which is then recognizable with the ophthalmoscope. If in addition to or independently of the signs of inflammation there are marked engorgement, oedema, and the evidence of mechanical compression, so that the swollen nerve-head protrudes into the vitreous beyond ^ to ^ mm., the phenomena of "choked disc" are pre- sent. This variety of papillitis, as well as more moderate grades of optic neuritis, constitutes one of the important symptoms of brain tumor, occurring in fully 80 per cent, of the cases. The development of the papillitis does not necessarily depend upon the size of the growth, nor upon its situation, except that tumors of the medulla are less apt to originate optic neuritis than those in other parts of the brain. Usually a bilateral condition, it is sometimes unilateral, and under such circum- stances it suggests that the cerebrum is the seat of the growth, and is, on the whole, in favor of the tumor being on the same side as the neuritis. With this exception, however, optic neuritis, although an important symptom of brain tumor, has no localizing significance. Other intracranial causes of optic neuritis are the various types of meningitis (when the ophthalmoscopic picture often appears in the form of the so-called "descending neuritis"), abscess and soft- ening of the brain, cerebritis, hydrocephalus and aneu- rism. In addition to the intracranial causes of papillitis, this phenomenon may arise from a general infection- for example, influenza, syphilis, rheumatism, small-pox, etc. and is then known as infectious optic neuritis. It is also caused by various toxic agents, by anaemia, by menstrual disturbances, nephritis, and other constitu- tional disorders (de Schweinitz). Injuries of the optic nerve are most frequently the result of fractures of the base of the skull at the optic foramen, the nerve being injured by the fragments. It may be wounded by foreign bodies entering the orbit, with or without injury of the eyeball. THE CRYSTALLINE LENS. The lens, the most important part of the refractive apparatus of the eye, is a biconvex body situated on a level with the anterior plane of the ciliary body, from which it is suspended by the suspensory ligament, or zonulc of Zinn. Its anterior surface supports the pu- pillary margin of the iris, and its posterior surface rests in a depression, the patellar fossa, on the anterior sur- face of the vitreous body. It is completely transparent and enclosed in a transparent elastic membrane, the lens capsule. Together with the capsule, the lens measures from 9-10 mm. in its transverse diameter, and about 4 mm. in thickness from pole to pole. The convexity of its two surfaces is not the same, that of the posterior being greater than that of the anterior. Neither are these convexities constant, since they are continually changing with the variations in lens-power incident to viewing distant or near objects. The radius of curvature of the anterior surface is approxi- mately 9 mm. and that of the posterior surface 6 mm. when the eye is accommodated Meridional section of human lens and its capsule ; anterior epithelium and transitional zone are seen. X 7- (Babuchin.) 1472 HI. MAN ANATOMY. FIG. 1229. P 6(1 Fragments of isolated lens-fibres; A, from superficial layers; B, from deeper layers; C, young fibres with nuclei. X 275. for distant objects ; these radii are reduced to about 6 and 5 mm. respectively in accommodation for near objects. The anterior surface is therefore more affected in the act of accommodation, the lens becomes more convex and its antero-posterior diameter increases from 4 to 4.4 mm. The superficial portion of the lens beneath the capsule is composed of soft compressible material, the substantia corticalis ; the consistency gradually increases toward the centre, especially in later life, so that the central portion, the nucleus lentis, is much firmer and dryer. The structure of the lens includes the capsule and its epithelium and the lens substance. The capsule, which entirely surrounds the lens, is a transparent, struc- tureless, highly elastic membrane, which, while resistent to chemical reagents, cuts easily and then rolls outward. It is thickest on the anterior surface, where it measures from .oio-.oi5 mm., and thinnest at the posterior pole (.005-. 007 mm.). In the adult the lens is devoid of blood- vessels, but during a part of foetal life it is surrounded by a vascular net-work, the tunica vasculosa lentis, which is supplied chiefly by the hyaloid artery. This temporary vessel is the terminal branch of the central artery of the retina and passes from the optic disc forward through the hyaloid canal or canal of Cloquct in the vit- reous to the posterior surface of the lens. The vascular lens tunic and the hyaloid artery are temporary structures and usually disappear be- fore birth. Exceptionally they may persist, the tunic being represented by the pupillary membrane and the artery by a fibrous strand within the vitreous, stretching from the optic disc towards the lens. The capsule probably represents an exudation product of the cuticular elements from which the lens- substance is developed. The anterior portion of the capsule is lined by a sin- gle layer of flat polygonal cells, the epithelium of the lens capsule, which represents morphologically the anterior wall of the original lens-vesicle (page 1480). On ap- proaching the equator of the lens, these cells become elongated, and gradually converted into the young lens- fibres, the nuclei of which form a curved line, with its convexity forward, in the superficial part of the lens. The lens-substance is composed of long flattened fibres, the cross-sections of which have a compressed hexagonal outline, from .005 .01 1 mm. broad and from .002 .004 mm. thick, held FIG. 1231. together by an interfibrillar cement substance. These fibres are modified epithelial elements, which develop by the elongation of the original ectoblastic cells of the poste- rior layer of the lens-vesicle. The subsequent growth of the lens depends upon a similar modification of the anterior capsule-cells, the re- gion where this transforma- tion occurs being known as the transitional rifttf. The individual lens-libres vary greatly in length, those form- ing the outer layers being longer and thicker than those which constitute the nucleus of the lens. The edges of the fibres are finely serrated, and, as the points of the Serrations >f adjacent fibres are in contact, tine intercellular channels are left for tl FIG. 1230. Lens-fibres seen in transverse section. X 280. Adult crystalline lens, showing lens-stars; A, anterior; />'. sun. n . ; r.uliating lines of juncture meet at central area. X 4- (Arnold.) THE VITREOUS BODY. 1473 passage of nutritive fluid. The fibres are so arranged that their ends terminate along definite radiating striae, or lens-stars, which in the young lens are three in number on each surface. In the adult lens additional rays increase the number to from six to nine, the striae being less distinct but distinguishable with the ophthalmoscope. The lens-fibres which come from the pole of one surface of the lens terminate at the end of one of the radial striae in the other, and conversely ; the intervening fibres take up intermediate positions. In adult life the lens-fibres become more coridensed, the lens loses its clear appearance, and assumes a yellowish tint. This change affects the nucleus first and the periphery later, coincidently the lens becoming less elastic as the result of its loss of water. Practical Considerations. The lens may be congenitally absent (aphakiaj, or it may be abnormal in size, shape, position, or transparency. Its anterior or posterior surface may be abnormally convex (lenticonus). Congenital anomalies of position (ectopia lentis) occur rarely. The lens may remain in its fcetal position in the vitreous chamber, or it may be displaced in an equatorial direction from faulty development and weakness of some part of the suspensory ligament. This weakness usually occurs below so that the lens moves upward. The ligament may be absent in its whole circumference, when the lens may be protruded into the anterior chamber. Coloboma or partial deficiency of the lens is very rare. It is with comparative frequency associated with a similar defect in the iris, ciliary body and choroid, and, like it, is usually in the lower portion. A defect of the corresponding part of the suspensory ligament is occasionally present. Traumatic luxation of the lens may take place into the vitreous or aqueous chamber. It may occur laterally through the coats of the eyeball into the capsule of Tenon or under the conjunctiva. That into the vitreous is most frequent. The capsule of the lens is strong and elastic. It is at the same time brittle, breaking like thin glass when torn as by a sharp instrument. For this reason it is sometimes called the vitreous membrane. The anterior layer of the capsule is con- siderably thicker than the posterior, and is more liable to pathological changes, pro- ducing opacities. Wounds of the capsule permit the aqueous fluid to reach the lens fibres, which then become swollen, opaque, and finally disappear from the dissolving action of the aqueous. Advantage of this is taken in the needling operation (dis- cission ) for the removal of a cataract. In children the lens substance is of nearly equal consistency throughout, but as age advances the central portion becomes gradually more condensed, and is called the nucleus. A well-marked nucleus, however, does not exist until adult life. In old age the lens loses its elasticity so that the changes necessary for accommodation are interfered with, and sight is disturbed. The hardened nucleus permits a greater reflection of light than the outer portion, so that the lens is more readily seen in older people, and the pupil loses more or less its blackness. A cataract is an opacity of the lens, or its capsule, but that of the lens is so much more common than that of the capsule, that by the word cataract the lenticular is usually meant, unless the word is otherwise qualified. All cataracts are at sometime partial, and they are called according to their location, anterior polar or capsular, posterior polar or capsular, central or nuclear, lamellar, perinuclear and cortical. Cataract occurs sometimes in the young, and is then soft ; that is, the lens has no nucleus. THE VITREOUS BODY. The vitreous body (corpus vitreum) fills the space between the lens and the retina, being in close contact with the retina and acting as a support to it as far forward as the ora serrata. Here it becomes separated from the retina and passes to the posterior surface of the lens, presenting a shallow depression, the fossa hya- loidea or patellar fossa, on its anterior surface for the reception of the lens. The fresh vitreous is a semifluid, perfectly transparent mass which consists of about 98.5 per cent, of water. The structure of the vitreous has been a subject of protracted dispute, but recent investigations have established beyond question that it possesses a framework, 93 M74 HUMAN ANATOMY. FIG. 1232. Portion of adult vitreous body, showing; felt-work of fibres and atrophic traces of cells. X 450. (Retzius.) composed of delicate, apparently unbranched fibrils, which pass in all directions through the vitreous space and form the meshes in which the fluid constituents of the mass are held. The surface of the vitreous is enclosed by a delicate boundary layer, called the hyaloid membrane, formed by condensations of the fibrils, which are here arranged parallel to the surface, and closely felted. It is, however, not a true membrane, but only a con- densation of the vitreous fibres. The vitreous is attached firmly to the retina at the nerve entrance and at the ora serrata, between these points the hya- loid being indistinct. As the vitreous leaves the retina, the boundary layer becomes thicker, in some cases to be- come thin again or absent in the region of the patellar fossa. The central part of the vitreous is occupied by a channel, the hyaloid canal, also known as the canal of Stil- ling or the canal of Cloqud, which is about one millimeter wide and extends from the optic entrance toward the pos- terior pole of the lens. During total life this canal lodges the arteria hya- loidea, the continuation of the central artery of the retina, which passes to the lens and assists in forming the embryonal vascular envelope surrounding the lens. Usually the embryonal connective tissue, together with the blood-vessel, disappears ; occasionally, however, delicate remnants of this tissue can be detected. The normal adult vitreous ordinarily contains no cells, but some are occasionally seen near the surface, beneath or on the hyaloid membrane. They are amoeboid, often contain vacuoles and are to be considered as modified leucocytes. In addition a few branched connective-tissue cells may be present. Practical Considerations. Congential abnormalities of the vitreous are due either to a persistence of some part of its foetal vascular apparatus or to an atypical development of the tissue from which it is formed. The remains of these structures may occasionally be seen as a filamentous band, free at one end, which floats in the vitreous, the other end being attached to the optic disc behind, or the posterior sur- face of the lens in front. The strand may be attached at both ends, with or without a patent artery. Small rounded gray bodies, apparently cystic and attached to the disc, are occasionally seen. They are in some way the remains of the fcetal vascular apparatus. The congenital opacities sometimes seen at the posterior pole of the lens are probably derived from the posterior fibre-vascular sheath of the lens. Materials from the blood are readily absorbed by the vitreous, as the bile in jaundice. Muses volitantes are the flocculi, seen by the patient as black spots be- fore the eyes, and are sometimes made up of inflammatory exudate from inflam- mation of the internal or middle coat of the eye. They may be due to blood from traumatic or spontaneous hemorrhage into the vitreous. Muscae volitanU s arc often seen independently of any vitreous disease and are due to the shadows thrown upon the retina by naturally formed elements in the vitreous body, perhaps the remains of embryonic tissue. Some of the vitreous may be lost and rapidly replaced with- out seriously disturbing sight. In the removal of cataract, the suspensory ligament may be divided and an embarrassing loss of vitreous may result. A foreign body in the vitreous chamber generally gives rise to a serious inflam- mation, which may destroy the eye. If loose, it tends by gravity to settle in the lower portion, and usually rests on the posterior part of the ciliary body ( T. Collins). Rarely, in the absence of infection, it has remained for years without setting up inflammation. The rule is, however, to remove them, when recent, as early as possible, as inflammation may set in at any time. In most cases the foreign body SUSPENSORY APPARATUS OF THE LENS. H75 can be exactly localized by the X-ray, and if of iron or steel, may often be removed by a magnet. The accident is always serious and may be followed by a virulent inflammation, demanding an excision of the globe to prevent a sympathetic involve- ment of the other eye. Because of the risk of infection and loss of fluid, operative interference in the vitreous chamber is usually to be avoided. Svipathctic ophthahnitis, or more accurately, infective irido-cyclitis, or uveitis, is an inflammation of one eye, usually called the "sympathizer,'" owing to injury or disease of the fellow eye, usually called the ' ' exciter. ' ' Traumatisms of the ciliary region (danger zone) which have set up an irido-cyclitis or uveitis are responsible for fully 80 per cent, of the cases of so-called sympathetic inflammation. This disease was formerly supposed to be due to reflex action through the ciliary nerves, and this theory in a modified form is still maintained by a few clinicians. The " mi- gration theory" propounded by Leber and Deutschmann that the inflammation is a progressive process in the continuity of the tissue of one eye to the other by way of the optic nerve apparatus and is of bacterial origin, has not been proved. It is believed by some investigators that the bacteria which enter the primarily affected eye produce a toxin which causes the disease, and by others that it represents an endogenous infection produced by invisible bacteria, that is, that it is a metastasis (de Schweinitz). THE SUSPENSORY APPARATUS OF THE LENS. The lens is held in position by a series of delicate bands, which pass from the vicinity of the ora serrata over the ciliary processes to be attached to the periphery of the lens. These fibres collectively con- FIG. 1233. stitute the suspen- sory ligament, or zonula of Zinn, a structure of impor- tance not only for the support of the lens but also in assisting the ciliary muscle in effecting the changes in the curvature of the lens incident to accommodation. The zonula is not, as for- merly believed, a con- tinuous membrane, but is composed of a complicated system of fibres. The latter, varying in thickness from .005-. 022 mm., arise chiefly from the Cornea Canal of Schlemm Sclera Meridional section of ciliary region, showing ciliary processes and suspensory ligament of lens. X 20. cuticular membrane covering the pars ciliaris retinse in the vicinity of the ora serrata. The investigations of Retzius, Salzmann and others indicate that some fibres arise also from the mein- brana limitans interna of the pars optica retina-, whilst others pass into and end within the vitreous body. The greater number of the fibres pass forward chiefly in the depressions between the ciliary processes, and along the sides of the latter, closely applied to the surface ; they then proceed outward across the circumlental space to be attached to the capsule of the lens. Some of the fibres are inserted anterior to the equator, others posterior to the equator, and some directly into the lens margin. Those inserted anteriorly arise behind and chiefly from the valleys between the ciliary processes, whilst those inserted back of the equator come from the ciliary processes in front. As they diverge to gain their insertion in the lens-capsule, the crossing- fibres enclose an annular space, triangular in section, whose base is directed toward 1476 HUMAN ANATOMY. the lens equator. The fibres are so closely interlaced that it is possible to inject air between them and so produce a beaded ring surrounding the lens. This appearance was long interpreted as demonstrating the presence of a delicate channel, the canal of Petit, encircling the lens. The existence of a definite channel, however, is no longer accepted, the space capable of inflation being part of the larger circumlental space, which is filled with fluid and communicates, by means of fine clefts, with the posterior chamber. In addition to the chief zonular fibres, accessory bands occur, some of which pass from the ciliary processes to the long zonular fibres, whilst others extend from point to point on the ciliary processes. The origin of the vitreous body and of the suspensory ligament has long been and still is a matter of dispute. The fact that these structures are very closely connected, that fibres from the suspensory ligament pass through the vitreous, and, in some cases at least, end in that body, renders it probable that the two structures have a common genesis. Anatomists are divided, however, in their views, some believing the structures in question to be derived from the mesoblast which enters the choroidal cleft with the blood-vessels, whilst others assign to them an ectoblastic origin, either from the lens-vesicle, or from the retina ( inner wall of the second- ary optic vesicle). In many of the lower animals the vitreous contains no blood-vessels, and, further, since the vitreous is formed without the presence of embryonal connective tissue, the presumption is strong that the vitreous arises from the retina. That the ectoblast in mam- mals, however, is the sole source of the vitreous has not been proven ; moreover, the close histological resemblance of the vitreous to embryonal connective tissue suggests with much force the probability that the mesoblast has at least some share in the formation of the vitreous body. THE AQUEOUS HUMOR AND ITS CHAMBER. The aqueous humor is the transparent fluid which fills the space between the anterior surface of the vitreous body and the posterior surface of the cornea. In chemical composition it closely resembles water, containing only traces of albumin and extractives, and differing from lymph in its low percentage of albumin. It is produced chiefly by the blood-vessels of the ciliary processes, the iris taking probably little or no part in the process. The albumin of the blood is separated by the action of the double layer of cells covering the pars ciliaris retinae, which act either as a filter- ing medium (Leber), or as a secreting epithelium (Treacher Collins). The aque- ous humor is constantly being produced and is carried off through the spaces of Fontana into the canal of Schlemm, and also through the lymph-spaces in the iris, its quantity being an important factor in determining intraocular tension. With the exception of a few migratory leucocytes, the aqueous humor is devoid of morpho- logical elements. The space occupied by the aqueous humor is incompletely subdivided by the iris into two compartments, the anterior and posterior chambers. The anterior chamber (camera oculi anterior) is bounded in front by the cornea, and behind by the ids and lens, and has a depth at its centre of from 7.5-8.5 mm. The posterior chamber (camera oculi posterior) is the small annular space, triangular in cross-st <- tion, which has for its anterior boundary the iris, and is limited laterally by the ciliary processes, and medially and posteriorly by the lens and the vitreous body. Tin- spaces between the fibres of the suspensory ligament communicate with the poste- rior chamber, are filled with aqueous humor, and are, therefore, only a part of the posterior chamber. Practical Considerations. When the cornea is perforated as by a wound or by ulceration, the aqueous is forced through the opening so rapidly that the iris is swept along by it, and unless great rare is observed it will become adherent to tin- margin of the corneal opening (anterior synechia). The aqueous humor is of importance in the removal of foreign matter. Blood will often be removed in a few days. Suppuration of the adjacent tissue may lead to the collection of pus in the anterior chamber (hypopion). Hyphaemia is a collec- tion of blood in this chamber, and of itself is not a grave condition, although it may be a sign of a more serious disease. LACHRYMAL APPARATUS. H77 Glaucoma is a disease due to excessive intraocular tension which, unless re- lieved, progressively increases until the eye is destroyed, and which almost always involves the other eye. The abnormal tension is the result of disturbance in the outflow of the intraocular fluid. This fluid is an exudation from the blood-vessels of the ciliary body. From the posterior chamber the fluid passes through the pupil to the anterior chamber. It then escapes' in the angle formed by the iris and cornea by passing through the lymph-spaces in the ligamentum pectinatum and by diffusion reaches the canal of Schlemm. Thence it passes out by the anterior ciliary veins. Obstruction in the path of this current occurs usually either in the lymph- channels of this region, or at the pupil from adhesion of the whole pupillary margin to the lens, or from occlusion of the pupil by inflammatory exudate, in iritis. Iridectomy frequently gives relief in both varieties ; in the former by opening up the lymph-spaces near the corneal angle of the anterior chamber, the incisions being carried well into this angle ; in the latter by making a new opening for the current between the posterior and anterior chambers. The symptoms, like the cause, may be explained largely upon an anatomical basis. The venae vorticosae pass obliquely through the sclerotic and are therefore compressed and obstructed by the distension. Their blood is then compelled to escape through the anterior ciliary veins, which penetrate the sclerotic more at a right angle, and are consequently distended. CEdema of the cornea results causing a superficial haziness. The cornea is insensitive from paralysis of the anterior ciliary nerves. Usually the anterior chamber is shallow because the lens and iris are pushed forward by the obstructed fluid behind, and the ciliary nerves being paralyzed the pupil is dilated and immobile, giving a staring expression. The optic disc is at first hyperaemic, and is consequently markedly depressed from the intraocular tension, giving rise to one of the most important symptoms, pathological cupping of the disc, or the glaucomatous cup. The great pain in glaucoma is due to compression of the sensory nerves of the ciliary body and iris against the unyielding sclera. The distended retinal veins can be seen through the ophthalmoscope. A condition analogous to glaucoma, hydrophthalmos, occurs in children, and is either congenital or acquired very early in life. Unless relieved it almost always produces blindness. THE LACHRYMAL APPARATUS. The lachrymal apparatus consists of the gland secreting the tears, situated in the anterior and outer portion of the orbital cavity, and the system of canals by which the tears are conveyed from the mesial portion of the conjunctival sac to the inferior nasal meatus. The lachrymal gland (glandule lacrimalis), resembling in shape and si/e a small almond, consists of two fairly distinct parts the superior orbital portion and the inferior palpcbral or accessory portion. The former occupies the fossa lacrimalis in the frontal bone and is the larger portion. It measures 20 mm. in length, 12 mm. in breadth and reaches from the edge of the superior palpebral muscle, along the upper margin of the orbit to the suture between the frontal and malar bones. The upper convex border is attached to the periosteum of the fossa by means of a number of bundles of connective tissue, which are inserted into its capsule. Below, it rests upon a fascial arch, which runs from the trochlea to the fronto-malar suture. The lower or palpcbral portion of the gland, glandula lacrimalis inferior, is somewhat smaller than the upper and separated from the latter by the fascial expansion already mentioned. Its lower concave surface rests upon the lornix of the conjunctiva, extending laterally almost to the outer canthus. The ducts from both portions of the gland are exceedingly fine, those from the upper portion, from three to six in number, passing downward through the inferior portion. Some of the ducts from the lower gland join those coming from above ; others run independently, in all about a dozen ducts opening into the conjunctival sac along a line just in front of the fornix. In structure the glands correspond to the tubo-alveolar type, and resemble the serous glands in their general character. The acini of the lower portion are separated by robust septa of connective tissue, which contain considerable lymphoid tissue. 1478 HUMAN ANATOMY. The arteries of the gland are derived from the lachrymal, and the veins empty into the ophthalmic vein. The nerves include sensory fibres from the lachrymal branch of the ophthalmic, as well as secretory fibres from the sympathetic. Accessory lachrymal glands ott found in both the upper and lower fornices, from eight to thirty being present in the upper lid and from two to four in the lower. They are very small and situated chiefly near the outer angle of the palpebral fissure. FIG. 1234. Alveoli ?& Ducts FIG. 1235. Beginning of dm t 'Fat-cells Section of lachrymal gland, under low magnification, showing general arrangement of alveoli. X 20. The lachrymal passages (Fig. 1236) begin by minute openings, the lachrymal puncta, which are usually placed at the summit of the conical lachrymal papillae. The latter occupy the margins of the eyelids, near the mesial extremity, at a point where the arched palpebral borders passes over into the approximately horizontal boundaries of the lachrymal lake. The upper punctum is situated 6 mm. from tin- inner canthus ; the lower one is slightly larger and a trifle farther removed from the canthus. The puncta open into the lachrymal canaliculi, which at first are vertically directed, then bend abruptly mesially and, taking a nearly horizontal course parallel with the borders of the lachrymal lake, run as far as the inner canthus, where they empty usually by a common canal into the lateral and slightly posterior wall of the lachrymal sac. Occasionally the two canaliculi do not unite but open separately into a diverticulum of the sac, known as the sinus of Maier. Each canaliculus is from 8-10 mm. in length. The- I ton en of the canal measures only .1 mm. in diameter at the punctum, presents a diverticulum i mm. in diameter at the bend, and continues with an approximately uniform calibre of .5 mm. in its horizontal portion. The structure of the canaliculi includes a lining of stratified squamous epithelium, which rests upon a delicate tunica propria rich in elastic fibres, muscular fibres from the orbicularis palpebrarum affording additional support. The muscle bundles run parallel to the horizontal portion of the canaliculi, but are arranged as a circular sphincter about the vertical portion. The lachrymal sac (saccus lacrimalis) may be regarded as the upper dilated portion of the naso-lachrymal duct, the lower part of which passes through a bony canal and opens into the inferior nasal meatus beneath the lower turbinate bone, Alveoli of lachrymal gland more highly magnified. X 235. PRACTICAL CONSIDERATIONS : LACHRYMAL APPARATUS. 1479 The sac is about 15 mm. long, and 5-6 mm. in diameter when distended. It is situated near the inner canthus and lies within the deep lachrymal groove between the superior maxillary and the lachrymal bone. Its closed upper end, or fundns, extends beneath the internal tarsal ligament and some of the fibres of the orbicularis palpebrarum, whilst its orbital surface is covered by the fibres of the latter muscle, which spring from the lachrymal bone and are known as the tensor tarsi or Horncr \v iwiscle. The lower end of the sac narrows where it passes into the nasal duct. The wall is lined with a double layer of columnar epithelial cells, which in part are provided with cilia. It is composed of fibro-elastic tissue and is loosely connected with the periosteum. The nasal or naso-lachrymal duct, the lower portion of the tear-passage, is situated within the bony canal formed by the superior maxillary, lachrymal and infe- rior turbinate bones. It varies in length from 1224 mm -. according to the position of the lower opening, and is from 34 mm. in diameter. Its direction is also subject to individual variation, but is slightly FIG. 1236. backward, as well as downward, and is usually indicated by a line drawn from the inner canthus to the anterior edge of the first upper molar tooth. The duct opens into the lower nasal meatus, at a point from 30-35 mm. behind the poste- rior margin of the anterior nares. The aperture may be imperfectly closed by a fold of mucous membrane, the so- called valve of Hasner (plica lacrimalis). The structure of the duct includes a lining of mucous membrane which is clothed with columnar epithelium and may contain glandular tissue in the lower portion. The mucous membrane is sep- arated from the periosteum by areolar tissue and a venous- plexus ; it may present additional folds, resembling valves, i 1 i i r i 1 i i ' c 1 icdr-passages , c, the best marked of which is situated at the junction or the canaiiculi; s, lachrymal sac; I.,, D, naso-lachrvmal duct ; nat- SaC and the dtlCt. uralsize. (Divight.} The arteries supplying the lachrymal duct are from the nasal and the inferior palpebral. The large and numerous veins mostly join the nasal plexus and empty into the ophthalmic and facial. The nerves are derived from the infratrochlear division of the nasal branch of the ophthalmic. Practical Considerations. The most frequent congenital error of develop- ment in the lachrymal apparatus is found in connection with the canaliculus. It may be entirely absent, or, what is more common, may appear only as a groove, the edges having failed to unite. This union of the edges may occur only in part, so that the canaliculus may have two or more openings. The lachrymal gland is rarely the seat of inflammation. Hypertrophy or enlargement may be congenital or syphilitic. Prolapse or dislocation forward may occur so that the gland can be seen or felt below the upper outer margin of the orbit ; it has been excised in extreme cases. Cysts are due to occlusion of one or more ducts. The ducts of the gland open into the outer third of the upper conjunctival fornix, and the tears sweep over the front of the eye towards the puncta under the influence of gravity and the contractions of the orbicularis muscle. The lower punctum is frequently everted so that it no longer dips into the lacus lacrimalis, arjd the tears, instead of finding their way into the normal passage, flow over the lower lid on to the cheek (epiphora). This is usually the first step in the development of ectropion or turning out of the lid (vide supra). When the eversion cannot be cor- rected, the canaliculus is usually slit up on its posterior side so as to form a groove dipping into the lacus, from which the tears may again be taken up by the natural passages. The most common cause of epiphora is obstruction of the lachrymal passages. This occurs most frequently at the junction of the lachrymal sac and nasal duct, which is the narrowest part of the duct. The method of correcting such an obstruction is by the use of sounds, which are passed from the punctum with or without first slitting the canaliculus. The rule is to slit the canaliculus when the sound- ing is to be kept up for any length of time, but if it is performed for diagnosis only, the slitting is not done. The upper canaliculus is shorter but narrower than the lower, 1480 HUMAN ANATOMY. which is usually selected, as there is less danger of laceration of the lining mucous membrane leading to narrowing or occlusion of the canaliculus by scar tissue. Congenital fistula sometimes result from non-closure of the groove from which the sac and nasal duct are formed. The lachrymal sac is situated at the inner side of the inner canthus, behind the inner palpebral ligament, which is the best guide to it, and crosses about the junction of the upper and middle thirds of the sac. A collection of mucus or pus in the lachrymal passage is usually in the sac, and when not otherwise relieved, it tends to discharge itself through the skin below the tendo-oculi, and frequently lower than the level of the sac. The abscess is therefore opened below the tendon and external to the inner edge of the lachrymal groove. The line of the sac and duct, taken together, is approximately from the inner canthus to the space between the second premolar and first molar teeth. It opens below into the inferior meatus of the nose, just below and behind the anterior end of the inferior turbinate bone, which conceals it from view at the anterior naris. The sac and duct form a slightly curved line with its convexity backward, and its course downward, backward and slightly outward. To pass a probe along the lachrymal passage, the lower lid is everted by the thumb so that the punctum may be seen. The probe should be entered into the punctum vertically. It should then be turned horizontally and passed through the canaliculus to the inner wall of the lachrymal sac. It is then made vertical and passed along the duct i.e. , downward, slightly backward, and outward to the nose. DEVELOPMENT OF THE EYE. The development of the eye begins as a lateral diverticulum which very early appears on either side of the fore-brain (Fig. 911). These outgrowths, the primary optic vesicles, are hollow and directly communicate with the general cavity of the primitive brain by means of the optic stalks, which are at first broad, but later become narrowed. As the development proceeds, the transversely placed optic stalks gradually assume a more oblique axis, and, after the differentiation of the fore-brain into its two subdivisions, open into the diencephalon or inter-brain. The primary optic vesicle expands until it comes into contact with the surface ectoblast. The next important step is a thickening of the wall of the vesicle where it is in con- tact with the ectoblast (Fig. 1238). In consequence of the rapid multiplication of its cells, this portion of the wall becomes invaginated and, as a result, the cavity of the primary optic vesicle is gradually obliterated, the application of FIG. 1237. the invaginated portion of the wall to the inner sur- face of the uninvaginated part of the vesicle bringing about the formation of a cup-shaped structure pro- vided with a double wall. This cup is called the secondary optic vesicle and from it the retina is developed, which must be considered, therefore, as modified portion of the brain itself. Coincidentally with the invagination of the optic vesicle, the overlying ectoblast undergoes active proliferation and pushes into the space vacated the receding invaginated wall, thus producing depression known as the lens-pit. The lens-pit (Fig. 1238) deepens and becomes cup-shaped ; the edges of its anterior walls approach each other and then fuse, and in this manner form a closed sac, the lens- vesicle. This remains for a time connected with the surface ectoblast, but later becomes separated from it and forms an isolated sac of epidermal tissue, which, by the proliferation of its cells, becomes converted into a solid structure and constitutes the crystalline lens. At first the lens-vesicle fills the cavity of the optic cup completely, but with the deepening of the latter, a space appears between its anterior wall and the lens-vesicle, which gradually widens and forms the vitreous cavity. The space between the lens-vesicle and the ectoblast is invaded by a process from the surrounding mesoblast, which pushes in from the side. From this ingrowth is developed the cornea, with the exception of the surface epithelium, and the stroma of the iris. Almost from the first appearance of the invagination of the primary optic vesicle, the invaginated portion of the wall exhibits a marked tendency to proliferation of its cells. The Part of frontal section of head of early rabbit embryo, showing optic vesicles evaginated from brain-vesicle. X 30. DEVELOPMENT OF THE EYE. 1481 FIG. i2; r s. Brain-vesicle Uninvaginated wall Invaginated wall Optic stalk Optic vesicle -Lens-pit Lens-pit shows as depressed area of thickened ectoblast ; anterior wall of optic vesicle beginning to be invaginated ; optic stalk narrowing. X 30. uninvaginated portion of the wall, on the contrary, gradually becomes thinner, until it is repre- sented by a single layer of cubical cells. These soon assume a dark color in consequence of the appearance within their protoplasm of fine pigment particles. From this wall, there- fore, the layer of pigmented cells composing the outermost stratum of the retina is developed, whilst from the rapidly augmenting layers of the inner wall, the essential nervous elements of the retina, together with the supporting neurogliar tissue, are formed. The invagination of the optic vesicle is not confined to its outer wall, but also affects its lower wall, in consequence of which a groove, the fcttal ocular cleft, appears in this position (Fig. 1240). This is continued backward to and along the under surface of the optic stalk, in the form of a furrow. By means of this slit a com- munication is established between the cavity of the secondary optic vesicle and the centre of the optic stalk, and through it blood-vessels from the sur- rounding mesoblast gain entrance to the interior of the nerve and the eyeball. The walls of this fcetal cleft gradually approximate and become fused. The imprisoned vessel, the hyaloid artery, later gives rise to the arteria centralis retinae. The vitreous body has been usually considered as a derivative exclusively of mesoblastic tissue which entered the eye in company with the blood-vessels. According to the recent investigations of Schon, Kolliker and others, however, this view is inadequate, since at least the anterior or ciliary portion of the vitreous is a product of the cells of the inner wall of the secondary optic vesicle. The choroid and the sclera are differentiated from the mesoblast, which surrounds the eyeball. Development of the Lens. Soon after the iso- lation of the primitive lens-vesicle from the surface ectoblast, the cells in the posterior wall begin to proliferate actively, while those on the anterior wall are reduced to a single layer. The latter persists as the lining epithelium of the adult lens-capsule. By the growth of the cells of the posterior wall and their elongation into lens-fibres, the hollow vesicle is gradually converted into a solid mass of lens-substance, the fibres extending forward until they come in contact with the anterior wall. Subsequently the growth of the lens proceeds by the application of additional layers of fibres to the surface of the primary nucleus, the new fibres developing from the cells lining the anterior capsule. Their con- version takes place at the equator of the lens, where the nuclei of the elongating lens-fibre are arranged in a convex line known as the nuclear zone (Fig. 1228). The capsule of the lens appears very early, even before the closure of the lens-vesicle, and long before the appearance of blood-vessels around the lens. It forms a sharp boundary line, at first along the posterior border, which gradually thickens and finally surrounds the entire lens. The capsule is to be considered as a secretion product of ihe lens-cells. The rapid early growth of the young lens requires an adequate blood supply. This is insured by the development of a vascular net-work, the tunica vasculosa lentis, which completely surrounds the lens from the second month until the close of foetal life, when this temporary membrane is ab- sorbed. The chief supply of this vascular net-work is derived from the vessels of the vitreous, which, as already noted, enter the eye through the cleft in the optic nerve. Passing forward through the canal of Cloquet in the centre of the vitreous cavity, the chief vessel, the hyaloid artery, reaches the posterior pole of the lens, when it divides into numerous branches. These branches pass around the equator of the lens onto the anterior surface, where, joined by vessels from the mesoblastic tissue which is to constitute the future iris and ciliary body, they proceed to the centre of the pupil and break up into their terminal loops. The portion of the net-work covering the pupillary area is called the membrana pupil- laris, whilst the remainder is known as the membrana capsularis. This vascular sheet is usually entirely absorbed before birth, but occasionally portions of it may be seen persisting in the form of fine threads in the pupillary space, or on the posterior pole of the lens. The retention of such strands is sometimes associated with the persistence of portions of the hyaloid artery. FIG. 1239- Ectoblast Outer layer Lip of optic cup _ Inner layer Anterior wall - Optic stalk Posterior wall of lens-sac Lens-sac closed ; outer and inner layers of sec- ondary optic vesicle now almost in contact. HUMAN ANATOMY. FIG. 1240. Outer layer Inner layer I'osh Tior wall of lens-sac Mesohlast Lip of optic cup Foetal cleft Sagittal section of developing eye at same stage as preceding specimen, showing invagi- nation of optic vesicle along foetal cleft. X 30. Development of the Retina. As already pointed out, the retina develops from the walls of the optic vesicle, the pigmented layer being derived from the uninvaginated outer wall, the pig- ment appearing early and first near the anterior margin of the optic cup; the remainder of the retina comes from the rapidly growing cells of the inner wall. The first cells to be differentiated in the nervous portion of the retina are the spongioblasts which develop into the supporting neurogliar fibres, the fibres of Wilier. These are strengthened by the addition of mesoblastic elements, which enter the inner layers along with the blood- vessels. The neuroblasts develop from cells which correspond in position to those of the external nu- clear layer. As they divide, the cells are displaced inward, so that the ganglion-cells represent the oldest descendents. When seven or eight layers have been differentiated, the ganglion-cells send out axones, which form the fibre-layer and converge toward the optic nerve. The visual cells are the last to appear, the layer of rods and cones developing as cuticular outgrowths from the cells of the external nuclear layer. Anteriorly the walls of the secondary optic vesicle are reduced to a double layer of cells. For a certain distance, corresponding to the position of the future ciliary body (pars ciliaris retinae), the outer cells are pigmented, whilst the inner ones are trans- parent. Still farther forward, the rudimentary portion of the nervous tunic is continued over the posterior surface of the iris (pars iridica retinae) as a double layer of deeply pigmented cells which extends as far as the pupillary margin which thus corresponds to the anterior lip of the secondary optic vesicle. The optic nerve is developed secondarily and in close association with the early optic stalk, which is at first hollow, and later becomes grooved along its inferior surface. The walls of this foetal cleft become approximated and, after the entrance of the blood-vessels, the lips of the cleft fuse, the vessels being thus enclosed. Since the fibres of the optic nerve are for the most part axones of the ganglion-cells of the retina, it is evident that they are not developed within the nerve, but invade the latter as outgrowths of fibres from the retina, pushing along the optic nerve and tract to reach their cerebral connections. In addition to these centripetal fibres, a certain number of centrifugal ones appear later as outgrowths from cells within the brain. The supporting tissue is developed by proliferation of the cells of the optic stalks and their differentiation into neurogliar ele- ments, assisted by the mesoblastic elements from the surrounding pia and the portion which enters the cleft with the blood-vessels. The nerve-fibres are at first naked axis-cylin- ders, which later acquire medullary sheaths. Development of the Fibrous and Vascular Tunics. With the separation of the lens- vesicle from the overlying ectoblast, the meso- blast insinuates itself between these structures, in addition to surrounding the entire ecto- blastic optic vesicle. The portion surrounding the optic vesicle posteriorly thickens rapidly and becomes differentiated into the vascular tunic, or choroid, whilst the outer layer be- comes the fibrous tunic, or sclera. The choroid appears first, the pigmentation of its cells being FIG. 1241. Upper eyelid outer pigmented retinal layer Inner retinal layer Mesoblast Lens, now solid Optic nerve Vascular vitreous tissue Ectoblast Lip of retinal coa Mesoblast Lower eyelid Much later stage, showing lens now solid; layti-. i optic vesicle converted into retinal coat ; vascular vi'treous tissue; condensation and invasion of mesoblast. -'<>. evident by the seventh month. The meso- blastic process between the lens and the ecto- blast is very thin at first, but subsequently splits into two layers. The anterior of these becomes the substantia propria of the cornea and its lining endothelium. The latter produces the membrane of Descemet. The posterior mesoblastic layi-r carries blood-vessels which help to form the capillary net-work surrounding the lens. The space between the two mesoblastic layers represents the future anterior chamber of the eye. About the fourth fu-tal month the an- terior lip of the optic vesicle pushes forward in advance of the lens and carries with it additional mesoblastic tissue. From this the iris is developed, the stroma being formed by the mesoblast, whilst the posterior pigmented portion represents the anterior part of the optic vesicle, from which the dilatator muscle (and, according to some authorities, also the sphincter pupillae) is derived. The ciliary processes are produced by the rapid lateral expansion of the walls of the THE EAR. 1483 optic vesicle, about the fourth or fifth month, in consequence of which folds in the membrane arise, into which blood-vessels and other mesodermic elements extend. The corneal stroma becomes blended with the sclera, thenceforth the two forming a continuous tunic. Development of the Vitreous Body. As already stated, the vitreous body is at present re- garded as developing chiefly by proliferation of the cells of the inner wall of the optic vesicle, especially from its anterior or ciliary portion. The suspensory ligament of the lens is derived from the same source. The cells develop into the fibres which form the fine net-work of the vitreous body; at the periphery these become condensed and form the boundary layer or hyaloid membrane. The vitreous is supplied with blood by branches of the hyaloid artery, which springs from the head of the optic nerve. An especially complete net-work is found at the periphery of the vitreous and these vessels pass forward to the equator of the lens and assist in forming the tunica vasculosa lentis. The retinal vessels are formed later as branches of the central artery, the vitreous vessels usually undergoing complete absorption before birth. The development of the eyelids begins with the production of folds of integument, which appear above and below the cornea during the second foetal month. The folds approach each other and the epidermal cells fuse about the third month, the eyelids remaining united until shortly before birth. The Meibomian and other glands of the lids are produced by ingrowths of the surface ectoblast. The lachrymal gland arises during the third month as a solid ingrowth from the conjunctiva! epithelium close to the upper lid. The lachrymal canal begins as a solid process of epithelial cells from the lid, which dips inward along the lachrymal furrow, between the superior maxillary and nasal processes. This cord of cells becomes isolated from the sur- face, and later acquires a lumen, connecting by means of the canaliculi with the conjunctival sac .above. The duct establishes communication with the nasal fossa just before birth. THE EAR. The ear (organon audittis) may be conveniently studied under its three natural subdivisions, which are conventionally described as the external, middle and the internal ear structures lodged entirely or in part within the temporal bone. The FIG. 1242. Bone Malleus Incus Stapes Inner ear Semicircular canal Internal auditory canal Auditory nerve Endolymphatic sac Cartilage Diagram showing relations of three subdivisions of ear. (Modified from Schwalbe.) external ear includes the auricle and the external auditory canal ; the middle ear the tympanum, the Eustachian tube and the mastoid cells ; and the internal ear the labyrinth, with the peripheral ramifications of the auditory nerve. Such division, moreover, is justified by the developmental history of the organ, since the internal ear is developed essentially from the highly differentiated otic vesicle which gives rise to the complicated membranous labyrinth ; the middle ear largely from the first pharyngeal pouch ; whilst the external ear represents the deepened and modified boundaries of the first external visceral furrow. 1484 HUMAN ANATOMY. Fossa helici THE EXTERNAL EAR. The external ear, the outermost subdivision of the auditor)- organ, includes ( i ) the auricle, the funnel-shaped appendage attached to the side of the head for the collection of the sound-waves, and (2) the external auditory catial, which conveys these stimuli to the tympanic membrane, the flexible partition closing the canal and separating it from the middle portion of the ear. THE AURICLE. The auricle (auricula), also called the pinna, is attached to the side of the head around the opening of the external auditory canal, midway between the forehead and the occiput. It presents two surfaces, an external and an internal. The angle which its internal surface forms with the head, the cephalo-auriailar angle, is usually about 30, but varies from 20-45. The circumference of the auricle is somewhat pyriform in outline, with the broadest part of the figure above. The external surface of the auricle is irregularly concave and presents for examination several well-marked depressions and elevations, which depend, for the most part, upon the corresponding modelling of the underlying cartilage. The concha, the largest and deepest of the concavities, surrounds the entrance or meatus to the external auditory canal. This funnel-like fossa is subdivided by an obliquely transverse ridge, the crus helicis, continuous with the helix, into the upper and smaller part, the cymba con- chae, and a lower and larger part, the concha proper or cavum conchae. The tragus is an irregular FIG. 1243. eminence in front of, and slightly overlapping, the meatus. At the upper extremity of the tragus, just below a notch, the incisura anterior, that separates the tragus from the upper part of the auricle, is sometimes seen a small elevation, the Tra s us tuberculum supratrag- icum. The antitragus is an eminence behind the tragus and separated from it by a deep notch, the incisura intertragica. The lobule contributes the rounded lower ex- tremity of the auricle. In contrast to other parts of the pinna, it possesses no framework of cartilage and, hence, is soft and inelastic. The helix forms the scroll-like margin of the ear, sweeping from the upper part of the tragus in front to the lobule behind. It is more or less rolled upon itself so that its margin looks forward. On the anterior edge of the helix, near the junction of its upper and middle thirds, is sometimes found a small triangular ele- vation, the car-point or tubercle of ' fhvicin, which is of interest as representing, ac- cording to the last-named authority, the erect pointed extremity in the expanded ears of certain quadrupeds. It is said to be constant in the fcetus of about the sixth month and to be more common in the- male than in the female. In front of and parallel to the helix, is a curved ridge, tin- antihelix which begins at the antitragus below, forms the concave posterior boundary of the concha, and divides above it into a superior and an inferior crus between which lies the fossa of the antihelix or the fossa triangularis. A narrow groove between the helix and the antihelix marks the fossa of the helix or the scaphoid fossa. The elevations on the external surface of the auricle are represented by depressions on the cranial surface, and conversely tin- depressions on the external Cavum concha: Fossa triangularis Crura antihelicis Cymba conchse Crus helicis Incisura anterior Incisura intc-rtragica Lohulii> Right auricle, outer aspect. THE EXTERNAL EAR. surface are represented by eminences. Thus, the concavity of the concha is represented on the cranial surface by the eminentia conchae ; the antihelix by the fossa antihelicis ; the fossa triangularis by the eminentia fossae triangu- laris ; the scaphoid fossa, by the eminentia scaphae. The other elevations and depressions corresponding- to those of the outer surface are not seen on the cranial surface, except in the dissected cartilage denuded of the integument. Structure of the Auricle. The auricle consists of integument and an enclosed plate of yellow elastic cartilage continuous with that of the meatus. It is also provided with several unimportant ligaments and muscles. The lobule, however, contains no cartilage, but only fibrous tissue and fat enclosed within the integumentary fold. The skin of the auricle is thin and closely adherent to the cartilage, especially on the outer surface. In certain parts it contains fine hairs and sebaceous and sweat glands. The hair follicles are especially abundant over the tragus, antitragus and the notch lying between them, the hairs guarding the entrance into the external auditory canal, known as tragi, being exceptionally long. The sebaceous glands are especially well developed in the cavity of the concha. Cartilage of the Auricle. The cartilage of the auricle may be divided into two parts : (a~) the scroll-like plate forming the tragus and external auditory canal, and () the large irregular plate forming the main cartilage. These two divisions FIG. 1244. Insertion of auricularis superior Ohliquus Helicis major Tragicus Plate of tragus and external auditory canal Cartilaginous framework of right auricle, with intrinsic auricular muscles; A, outer, B, inner surface. are connected by a cartilaginous isthmus lying between the incisura intertragica on its outer side and the deep fissure, (incisura terminalis auris), which in the isolated cartilage is seen between the posterior wall of the outer meatus and the anterior border of the lower part of the concha, on its inner side. Two smaller clefts, the fissures of Santorini, are found between the three plates which form the carti- laginous scroll supporting the tragus and outer end of the external auditory canal. The cartilage of the tragus is an irregular plate and subject to considerable variation. The depressions and elevations of the cartilage proper correspond in general to the surface modelling of the auricle, but are sharply marked, especially on the cranial aspect. A deep notch, the fissura antitragohelicina, separates the lower part of the helix from the antitragus, thus defining the caudal process (cauda helicis), as the lower extremity of the cartilage forming the helix is called. The spin a helicis is a small conical projection, directed forward and down- ward, opposite the first bend of the helix. This serves for the attachment of the anterior ligament. The upper end of the tragus-plate fits into an angle formed by the junction of the beginning of the helix and the upper end of the anterior border of the concha. In addition to the elevations and depressions already referred to, on the mesial surface is found a ridge, the ponticulus, which extends downward and forward over the eminence of the concha and serves for the attachment of the posterior auricular muscle (Fig. 1244, B}. 1486 HUMAN ANATOMY. Ligaments of the Auricle. The extrinsic ligaments of the auricle, those which attach the auricle to the temporal bone, form a more or less continuous mass of fibres. These are separated somewhat arbitrarily and described as the anterior and posterior ligaments. The anterior ligament extends from the helix and the tragus to the root of the zygoma. The posterior ligament extends from the emi- nence of the concha and ponticulus to the anterior part of the mastoid process. A number of bands of fibrous tissue, the instrinsic ligaments, bind the parts of the cartilage together. The Muscles of the Auricle. These include the extrinsic and the intrinsic muscles. The extrinsic muscles of the auricle, those which extend from the head to the auricle and move it as a whole, have been described under the muscular system (page 483). They are the anterior, superior and posterior auricular muscles. The intrinsic muscles, six in number, consist of small strands of muscle-fibres attached to the skin, which extend from one part of the auricle to another and are confined to the auricle itself. Of these, FIG. 1245. four are on the external surface of the auricle and two on the cranial. Plate of trains Cartilaginous canal 1. The smaller muscle of the helix (m. lie/ids minor} lies upon the crus helicis and the beginning of the helix, its fibres running obliquely upward and forward. 2. The greater muscle of the helix (in. helicis major') arises from the spine of the helix and extends upward along the anterior border of the helix and is inserted into the eminence of the triangular fossa. 3. The muscle of the tragus (in. tragi- cus) is a flat muscle on the outer surface of the tragus ; usually only its vertical fibres are distinguishable. Occasionally a separate bundle of muscular fibres (///. pyrainidalis] extends from the tragus to the spine of the helix. Likewise another band, the in. in- cisurce Sanforhii, sometimes called the dilatator concha?, bridges the incisura terminalis. Both of these, however, belong to the system of the tragus muscle. 4. The muscle of the antitragus i in. antitragicus)'\s attached to the outer surface of the antitragus. Its fibres run obliquely from the antitragus upward and backward and are inserted into the caudate process of the helix. On the cranial surface of the auricle are the transverse and the oblique muscles. 5. The transverse muscle (///. traiisi'crsus) bridges over the fossa antihelicis and extends from the eminence of the scaphoid fossa to the eminence of the concha. 6. The oblique muscle (/;/. ob/iquits), considered by Gegenbauer as a part of the trans- verse muscle, extends from the back of the concha to the eminence of the triangular fossa. Actions. Duchenne and Ziemssen found that by stimulating the muscles of tin- tragus and antitragus the external auditory canal was narrowed. Duchenne further demonstrated that the greater and lesser muscles of the heli,\ were antagonistic to those of the tragus. The transverse muscle and the oblique muscle by their contraction are said to cause a slight flattening of the auricle. Bony canal Dissection showing bony and cartilaginous rx>rtions of right external auditory canal ; seen from in front. Vessels of the Auricle. Arteries. The auricle receives its blood supply from branches of the superficial temporal artery and the posterior auricular artery, and thus indirectly from the external carotid. The superficial temporal sends three brandies to the- outer surface of the auricle: (a) the artery of the hc/i.v to the ascending part of the helix, fossa triangularis and the superior crus of the anti- helix; ) the artery of the cms helicis to the region of the crus helicis; (<) the artery of Hie trains to the region of the tragus and lobule, the lobule receiving THE EXTERNAL EAR. 1487 a branch, the anterior artery of the lobule, from the artery of the tragus. The pos- terior auricular artery supplies a variable number of branches to the auricle. Usually two of these are given off below and one above the posterior auricular muscle. These branches are larger and longer than those from the superficial temporal. After rami- fying over the cranial surface of the auricle, they reach its outer surface by piercing the auricle or by passing over its free margin. They supply the posterior part of the outer surface and anastomose with the branches of the superficial temporal. The veins of the auricle accompany the arteries and include : (a) the anterior auricular, which empties into the superficial temporal ; (b) the posterior auricular, three or four in number, which join a plexus behind the ear which empties principally into the external jugular vein, but also unites with the posterior facial vein. Com- munications with the mastoid emissary vein of the lateral sinus also frequently exist. The Lymphatics. The lymphatics of the auricle form a close net- work within the deeper layers of the integument, from which lymphatic stems pass in three general groups. Those from the outer surface are afferents chiefly of the anterior auricular nodes, which are placed immediately in front of the tragus and beneath the parotid fascia ; a few, however, bend backward over the helix to end in the posterior auricu- FIG. 1246. A. perforans fossae triangularis A. helicis A. auricularis post. sup. A. temporalis , Posterior auricular muscle A. cruris helicis A. perforans cymba: A. caudae helicis A, tragi A. auricular^ post. inf. A. auricularis posterior Parotid branch Arteries of right auricle, A, lateral surface; B, postero-mesial surface. (Schivalbe.) lar nodes that overlie the insertion of the sterno-mastoid muscle. Those from the upper part of the cranial surface pass mainly to the posterior auricular nodes, some being tributary to the external jugular nodes. A number of stems from the lower part of the auricle and from the lobule terminate in the parotid nodes. Nerves of the Auricle. The motor nerves supplying the intrinsic muscles of the auricle are from the temporal and posterior auricular branches of the facial nerve, the former being distributed to the muscles of the helix, tragus and antitragus, whilst the posterior auricular supplies the tranverse and "oblique muscles. The sen- sory nerves include branches from : (a) the great auricular nerve, which supplies the integument of the lower three-quarters of the inner surface of the auricle, with the exception of a small portion near the meatus, and sends filaments to the outer surface of the lobule and adjacent area ; ($) the small occipital nerve, which supplies the upper one-quarter of the inner surface ; (c~) the auricular branch of the vagus, which supplies the small muscles on the back of the concha and a limited cutaneous area near the meatus ; and ('rk from which trunks pass in three general groups, as do those of the auricle, (i) The trunks of the posterior group arise in the posterior wall of the external meatus and empty, for the most part, into FIG. 1250- the posterior auricular (mastoid) nodes. Some, however, avoid this first station and join the efferent vessels of the upper nodes of the superior deep cervical chain. (2) The inferior group includes a vari- able number of trunks coming from the lower wall of the external audi- tory meatus, some of which pass to the nodes placed along the course of the external jugular vein at its exit from the parotid, whilst others end in the mastoid' nodes. (3) The anterior group is from the concha and the anterior wall of the meatus. These vessels are tribu- tary to the parotid nodes, more particularly to the anterior auricular nodes situated immediately in front of the tragus. Nerves. The sensory nerves supplied to the external auditory canal are derived from the auriculo-temporal branch of the trigeminus and from the auricular branch of the pneumogastric. The latter, also known as Arnold's nerve, perforates the wall of the meatus and supplies its lining membrane. Practical Considerations : The Auricle. The auditory mechanism may be said to consist of two portions that which conducts the sound and that which receives it. The former is represented by the external and the middle ear ; the latter, by the internal ear. The function of the auricle is to collect and intensify the sound-waves and to direct them into the external auditory canal. That it does not play a very important part in hearing is shown by the fact that its removal has been followed by comparatively little loss in the acuteness of hearing (Treves). Complete .absence of the auricle is exceedingly rare ; partial defect (microtia} is more frequent ; while congenital fisluhe are comparatively common. These fistulce are considered to be due to a defective closure of the first branchial cleft. According to His, however, they are due to deficient union of the crus helicis and the crus supratragicus. If a fistula closes at its orifices, a retention cyst, sometimes dermoid, may result. The ear may be abnormally laryr ( )nacrotid), or, as a result of defective union of the rudimentary tubercles from which the auricle is developed, auricular appendages (polyotia) may be met with. A supernumerary auricle may very rarely be found on the side of the neck at the orifice of one of the lower branchial clefts. Owing to the rich blood-supply of the auricle, wounds heal rapidly. When, however, they occur near the external auditory meatus and are large, cicatricial closure of the canal must be guarded against. I' n>st-bite is frequent because of the exposure to cold and the lack of protec- tion to the blood-vessels from overlying tissues, since little more than skin covers tin -m. An intense reactive congestion follows, and frequently leads to gangrene. Cast of right external auditory canal, seen from be- hind ; natural size. Drawn from cast made by Professor Randall. PRACTICAL CONSIDERATIONS : THE EXTERNAL EAR. 1491 The skin is closely adherent to the underlying tissues, especially on the anterior surface, so that the exudate is under much tension, interfering with the blood- supply. The nerves are also compressed, accounting for the great pain. Hesmatomata of the auricle are due to effusions of blood between the cartilage and its perichondrium. They occur usually on the concavity of the auricle from a blow, as in boxers, or foot-ball players. They may occur rarely, without traumatism, as in the insane, although some believe that injury is the exciting cause in these cases ; or even, in very exceptional instances, may appear without precedent trauma or mental disease. In those cases in which there is great tension, it may be neces- sary to incise and drain to prevent necrosis. Of the tumors, keloid, following punctures for ear-rings, is common in the negro ; capillary naevi are frequent, whilst cirsoid aneurism may occur. Cysts in connection with the first branchial cleft have already been mentioned. The External Auditory Canal. Congenital atresia is rare and is often associated with malformations of the auricle, the middle and the internal ear, so that correction of the external condition will usually fail to restore the hearing. The length of the external meatus is about i^ inches, about ^ inch of which is bony and about ^ inch cartilaginous. In the new-born it consists of skin and cartilage only, and its lumen is very small. Owing to the obliquity of the tympanic membrane, that structure, in the new-born, is in close contact with the floor of the canal, so that the latter must be drawn away from the membrane to expose it. For this purpose the auricle should be drawn downward and backward. The skin of the cartilaginous portion is supplied with hair, sebaceous and ceruminous glands. Furuncles are frequent, the infection passing along the hair-follicles to the asso- ciated sebaceous glands. In some persons, one boil follows another from successive glandular infection. The skin of the bony portion is thinner than that of the car- tilaginous, except in the posterior part of the roof, where a thicker wedge-shaped piece containing glands extends as far as the drum-head. Ceruminous masses often collect, and frequently contain pathogenic bacteria. They may press upon the tympanic membrane, and through intralabyrinthine pres- sure may produce vertigo, or may lead to vomiting or convulsions. Interference by the mass, with air conduction, may result in loss of hearing. A diffuse infection of the meatus may be primary, but it is more apt to be a secondary result of otitis media. In severe cases the pus may extend to the bone separating the periosteum. It may then pass to the parotid region through the anterior bony wall, but it is more likely to do so through the fissures in the cartilag- inous portion. Abscesses in the parotid region more frequently extend by the same route in the reverse direction. The general direction of the canal is from without inward, downward, and slightly forward. The auricle and cartilaginous meatus are suspended from the margin of the bony portion so that an angle is formed opening downward. For a short distance from the external orifice the meatus inclines forward. In the remain- ing cartilaginous portion it turns backward, while in the bony portion it is again deflected forward. Therefore, to examine the tympanic membrane the cartilaginous meatus must be drawn upward to correct the vertical curve, and backward to straighten the antero-posterior curve. The diameter of the canal is greater at the two extremities than in the centre. The smallest diameter in the bony portion is at the inner third, where foreign bodies most frequently lodge, which have been known to remain in the canal for years without much discomfiture, or even, in some cases, without their presence being known. Care is necessary in their removal lest the tympanic membrane be injured. The anterior wall of the meatus is in relation with the temporo-maxillary articu- lation, and its bony portion has been fractured from blows upon the lower jaw. The parotid gland is in relation with this wall as well as with the floor, so that tumors of the gland may narrow or occlude the canal by pressure. Parotid abscesses opening into the canal are likely to pass through the deficiencies in the cartilage (fissures of Santorini). Since the lower jaw is in relation with the cartilaginous as well as with the bony portion of the meatus, the former is drawn forward when the mouth is opened. Hence the mouth is usually opened when one listens intently. 1492 HUMAN ANATOMY. The posterior wall is separated from the mastoid process by the tympano-mas- toid fissure. The auricular branch of the pneumogastric (Arnold's nerve) passes through this fissure to the posterior wall of the canal. The coughing, sneezing, or vomiting that sometimes follows irritation of the canal, as from cleaning the ear, or ex- amining it with instruments, is said to be due to a reflex effect upon the pneumogastric through this branch. The auriculo-temporal branch of the trigeminal nerve enters into its supply, and may explain the earache in cancer of the tongue or disease of the lower teeth. Between the posterior wall of the meatus and the mastoid cells is a thin plate of bone one or two millimeters in thickness. The sigmoid portion of the lateral sinus is usually about 12 mm. back of this wall, and the mastoid antrum about 5 mm. posterior to its deeper portion. The superior wall, which is from 4-5 mm. in thickness, often contains air- cells between two plates of compact bone. Pus may burrow through it from the canal to the interior of the cranium. At the posterior superior angle .of the canal are a number of small openings for blood-vessels and some connective tissue fibres, through or along which pus may find its way from the mastoid antrum to the under surface of the periosteum in the meatus. THE MIDDLE EAR. The middle ear includes three subdivisions : the tympanic cavity , the Eustachian tube, and the mastoid cells. It is an irregular air-chamber, beginning on the lateral wall of the naso-pharynx with the Eustachian tube, which leads upward, backward and outward, for about one inch and a half into the temporal bone. Opposite the external auditory canal, it widens into the tympanic cavity and continues backward into the mastoid cells. THE TYMPANIC CAVITY. The tympanic cavity (cavum tympani), also called the tympanum, is an irregu- lar space within the temporal bone, lying between the internal ear and the external FIG. 1251. Superior ligament Articular surface for incus Head of malleus \ __Z Tendon of tensor tympani \ V/"/ZI^ - _ -/" EP 11 - 1 !*" 110 s P ace Posterior semicircular canal' Facial nerve. ^X~^-^f/^ V -?* ^"Lateral ligament Handle of malleus External auditory canal ** Tympanic membrane, cut Vestibule Internal auditory canal Cochlea Promontory Probe in Eustachian tube Tympanic cavity Frontal section through right ear, viewed from behind. X 2^. auditory canal. It is lined with mucous membrane and contains, in addition to the air which enters by way of the Eustachian tube, the chain of ear ossicles. Its short- est diameter, that between the middle of the tympanic membrane and the wall of the labyrinth, is alxmt 2 mm. The antero-posterior diameter is about 12 mm., whilst the distance from the roof (tegmen tympani) to the floor, the supero-inferior diam- eter, is about 15 mm. THE MIDDLE EAR. H93 The cavity of the tympanum is subdivided into three parts : ( i ) the atrium or tympanic cavity proper; (2) the cavnm epitympanicum, the upper part of the space which overlies the atrium ; and (3) the antrum, which leads into the mastoid cells. The atrium (Fig. 1251) resembles in shape a short cylinder with concave ends, the outer end being formed by the tympanic membrane and its bony margin, whilst the inner end is formed by the outer wall of the labyrinth. The cavurn epitympanicum or attic occupies the space between the atrium and the roof and constitutes approximately one-third (about 5 mm. ) of the supero- inferior diameter. It contains the head of the malleus and the body of the incus (Fig. 1252). It extends considerably over the external auditory canal and is bounded laterally by a wedge-shaped portion of the temporal bone, called the scutum. The antrum tympanicum is an irregularly pyramidal space communicating with the upper back part of the tympanicum by a triangular orifice. Its dimensions vary, but its average length is about 12 mm., its height 8.5 mm., and its width 6.7 mm. It is larger in the infant than in the adult, and its lumen is frequently lessened by bands of mucous membrane which stretch across it and thus encroach upon the space. Its roof is formed by the tegmen tympani sometimes called the tegmen antri in this location. Its external wall is formed by the squamous portion of the FIG. 1252. Superior ligament Superior ligament Head of malleus Chorda tympani nerve Tensor tympani Processus cochleariformis Eustachian tube Epitympanic space Process for stapes Handle of malleus Tympanic membrane Inner aspect of outer wall of right tympanic cavity, showing incus and malleus and tympanic membrane in position. X 2%. temporal bone, and on its internal one is seen the outer wall of the horizontal semicir- cular canal. The thin mucous membrane of the antrum is closely united with the periosteum and possesses a layer of low nonciliated squamous epithelium. The walls of the tympanic cavity present many irregularities and depres- sions and the boundaries are not sharply defined. As the direction of the supero- inferior axis of the cavity is not perpendicular but oblique, it follows that the outer wall, composed of the tymparric membrane and its bony margin, is, accurately speaking, the infero-lateral wall, whilst that formed by the labyrinth is the dorso- mesial wall. For convenience of description, however, there may be recognized with advantage an external and an internal, a superior and an inferior, and an anterior and a posterior wall. The outer wall (paries membranacea) of the tympanic cavity proper (the atrium) is formed by the drum-head and the margin of bone into which it is inserted, whilst the outer wall of the epitympanic space is formed by the scutum. In the infant the bony external auditory canal consists of a ring of bone, the annulus tympani- cus. This ring, incomplete at its upper anterior part at the notch of Rivinus, possesses a well-marked groove, the sulcus tympanicus, for the reception of the tympanic membrane. At the notch of Rivinus, the tympanic membrane is attached to the bony margo tympanicus and the external lateral ligament of the malleus, and is continuous with the skin lining the bony auditory canal. 1494 HUMAN ANATOMY. The Membrana Tympani. The tympanic membrane or drum-head is a delicate transparent disc, irregularly oval or ellipsoidal in outline and concave on its outer surface. It is placed obliquely with the horizontal plane, forming an angle of about 55, opening outward. As the middle portion of the membrane is drawn inward, the inclination of its different parts varies. The obliquity of the membrane is about the same in the infant as in the adult. With the upper back wall of the external auditory canal the drum-head forms a very obtuse angle, whilst with the antero-inferior wall it encloses an angle of about 27. The longest diameter of the membrane is directed from above and behind, forward and downward, and measures from 9.5-10 mm. ; the shortest is from 8.5-9 mm - The membrane is about . 10 mm. thick, except at the periphery, where it is thickened. Like the rest of the tympanum and the labyrinth, it is practically as large in the infant as in the adult. Embedded in the tympanic membrane is the handle of the malleus (Fig. 1252), which extends from a point near its middle, upward and forward toward its periphery, and ends at the short process. At its lower end, the handle of the malleus is flattened laterally and broadened at the umbo, which corresponds to the deepest part of the concavity of the membrane. The short process of the malleus forms a conspicuous rounded projection at the antero-superior part of the drum- head. Extending from the short process of the malleus to the anterior and posterior ends of the tympanic ring are two straight striae. The part of the drum-head included between these striae and the Riviniah notch is known as the membrana flaccida (pars flaccida) or Shrapnell's membrane. It is thinner and less tense than the remaining larger part of the drum-head which is called the membrana tensa (pars tensa). The inner aspect of the drum-head presents two folds of mucous membrane which stretch horizontally backward and forward to the annulus and form an anterior and a posterior inverted pocket. The anterior pocket contains in its wall, in addition to the mucous membrane, the long process of the malleus, the chorda tympani nerve and the inferior tympanic artery, the nerve also running along the lower border of the posterior fold. The structure of the tympanic membrane includes three main layers : ( i ) the middle fibrous stratum, or membrana propria ; ( 2 ) the external cutaneous layer, the prolongation of the skin lining the external auditory canal ; and ( 3 ) the internal mucous membrane, a continua- tion of the mucous membrane clothing other parts of the tympanic cavity. The fibrous layer or membrana propria represents the mesoblastic portion of the drum-head and consists of an outer stratum of radially disposed fibres which diverge from the malleus towards the periphery of the membrane, and an inner stratum of circular fibres, concentrically arranged and best developed near the periphery of the membrane but absent at the umbo. The radiating fibres, on the contrary, become more dense at the umbo, partly through accumulation and partly through splitting (Gerlach). Between the fibres of the two layers are seen connect- ive tissue corpuscles which are spindle-shaped in longitudinal and stellate in cross-section. The membrana propria is absent within the pars flaccida or Shrapnell's membrane. At the periphery of the membrana propria, the fibres, especially those of the radial stratum, are con- nected with those of a ring of thick connective tissue, the annulus fibrosus which occupies the sulcus tympanicus. The fibres of the annulus fibrosus run in various directions, but for the most part radially, that is, toward the tympanic membrane proper (Fig. 1253) . Round cells are found between these fibres. The cutaneous layer consists of a thin epidermal stratum, composed of two or three rows of cells and a delicate sheet of connective tissue, but neither a definite corium nor papillae are present. A thickened band of subepithelial connective tissue extends across Shrapnell's mem- brane and along the handle of the malleus and contains the large vessels and nerves which pass from the meatus to the membrana tympani. The mucous membrane cove-ring the inner surface of the drum-head consists of a scanty layer of connective tissue, invested with a sheet of large low nonciliated epithelial cells. The vessels of the tympanic membrane include arteries which are arranged as an outer and inner set, separated by the membrana propria. The former set is derived from the deep auricu- lar branch of the internal maxillary artery ; the latter from the tympanic branch of the internal maxillary and from the stylo-mustoid branch of the posterior auricular. Each of these sets forms a plexus of vessels with a large branch extending downward along the malleus handle, and another around the periphery of the membrane, these two branches being connected by numerous radiating twigs. Perforating vessels connect the two sets of arteries, especially along THE MIDDLE EAR. H95 the malleus handle and at the periphery of the membrane. The veins are most numerous at the handle of the malleus and periphery of the membrane and communicate with those of the exter- nal meatus and tympanic cavity. The lymphatics are arranged similarly to the blood-vessels in two sets, one under the skin and the other under the mucous membrane. They communicate freely with each other and probably empty partly into the lymph-nodes situated over the mastoid process and in the region of the tragus, and partly into the lymph-tracts of the Eustachian tube and thence event- ually into the retropharyngeal and deep cervical nodes. FIG. 1253. Epithelium of tympanic surface Circular fibres Radial fibres Mucous membrane Blood-vessels Epidermis of drum-head Subepidermal layer External auditory canal Epidermis of canal Corium of skin lining canal '_ Epidermis passing onto drum-head Bone Radial fibres of annulus fibrosus Section through attached margin of tympanic membrane, showing continuation of skin and mucous membrane over its outer and inner surfaces respectively. X 75- Drawn from preparation made by Dr. Ralph Butler. The nerves supplying the tympanic membrane are derived chiefly from the auriculo-tem- poral branch of the trigemlnus, supplemented by twigs from the tympanic plexus and by the auricular branch of the vagus. They accompany, for the most part, the blood-vessels and, in addition to supplying the latter, form both a subcutaneous and a submucous plexus. The inner wall (paries labyrinthica) of the tympanic cavity separates it from the internal ear. It presents for examination a number of conspicuous features. The promontory appears as a well-marked bulging of the inner wall near its middle (Fig. 1254) and corresponds to the first turn of the cochlea. The branches of the tympanic plexus are found in the mucous membrane covering it. At the bottom of a niche, whose anterior border is formed by the lower posterior margin of the promontory, lies the round window (fenestra cochlea). It is closed by the secondary tympanic membrane (membrana tympani secundaria), which separates the tympanic cavity from the scala tympani of the cochlea (Fig. 1259). The membrane is attached in an obliquely placed groove, is slightly concave toward the tympanum, and measures from 1.53 mm - m diameter. The oval window (fenestra vestibuli) lies at the bottom of a depression, the fossula vestibuli, in the upper back part of the inner wall, above the round window, and leads into the vestibule. It is somewhat kidney-shaped, its upper border being concave, its lower slightly convex. In the recent state the oval window is closed by the foot-plate of the stapes and the ligament which connects the ossicle with the sides of the window (Fig. 1260). The longest diameter of the latter is about 3 mm. and its shortest 1.5 mm. Abov~ the oval window a well-marked 1496 HUMAN ANATOMY. ridge indicates the position of the facial canal or aqueductus Fallopii. This ridge is bordered posteriorly and superiorly by the elevation which corresponds to the wall of the horizontal semicircular canal ( prominentia canalis semicircularis later- alis). The sinus tympani, a well-marked depression, is behind the promontory, between the niche of the round window and the pyramid, below and behind the oval window. It is separated from the fossulae of the two windows by bony ridges. It varies in depth from 2-5 mm. , with a vertical diameter of from 2-6 mm. The superior wall (paries tegmentalis) is formed by a plate of bone, the teg- men tympani, which is a part of the upper and anterior surface of the petrous portion of the temporal bone. Posteriorly it forms the roof of the antrum tympani- cum, and anteriorly contributes the roof of the canal for the tensor tympani muscle and of the adjoining part of the Eustachian tube. It varies in thickness and may be defective to a large extent from atrophy or arrested development. The inferior wall (paries jugularis), narrower than the superior, separates the typanum from the jugular fossa. Its bony plate may be incomplete and may lie considerably below the level of the membrana tympani. The anterior wall (paries carotica) separates the tympanum from the carotid artery and at times presents a fissure. At its upper part is the irregular trian- gular opening of the Eustachian tube and above this opening lies the small canal for the Outer end of horizontal part of facial canal Stapes lying in oval window Stapedius muscle Round window Facial canal FIG. 1254. Promontory Tensor tympani Eustachian tube Outer aspect of inner wall of right tympanic cavity ; stapes lies within oval window. X zj^. tensor tympani muscle. The canaliculus caroticus tympanicus perforates the anterior wall just below the mouth of the Eustachian tube, and transmits the tympanic branch of the internal carotid artery and carotico-tympanic nerves. The posterior wall (paries mastoidea) of the tympanum at its upper part is occupied by the antrum tympanicum, which leads into numerous irregular cavities, the mastoid cells. At the lower border of the antrum is a saddle-shaped notch, the fossa incudis, which lodges the short process of the incus. Extending forward from the posterior wall, on a level with the lower border of the oval window, projects the small bony elevation, the pyramid (eminentia pyramidalis), which encloses the stapedius muscle (Fig. 1254). Its apex is pierced by a small round opening for the exit of the stapedius tendon. The canal within this eminence communicates posteriorly with the facial canal. On a level with the eminentia pyramidalis, close to the posterior margin of the drum-membrane, lies the apcrtura tympanica canaliculi chordae tympani, the opening through which the chorda tympani nerve enters the middle ear. THE CONTENTS OF THE TYMPANUM. The Auditory Ossicles. Three small bones (ossicula auditus) form a chain extending across the upper part of the tympanum from the tympanic membrane to the labyrinth. The outermost of these, the malleus (hammer), is attached to the tympanic membrane ; the innermost, the- .v/W/V.v (stirrup), is fixed in the oval window, and between these two bones and connected with both of them, lies the third link in the chain, the incus (anvil). THE MIDDLE EAR. 1497 The malleus (hammer) is about 8 mm. long and consists of a head, a neck and three processes. The head is the upper club-shaped portion, lying in the epitympanic space ; the constricted portion just below the head is the neck, and below this is a prominence to which the three processes are attached The posterior surface of the head bears, for the articulation with the incus, an oblong depressed surface with prominent margins extending in a spiral manner downward and inward to the neck. This articular surface consists of two principal facets separated by an oblique ridge, the upper facet looking backward, the lower, inward. The axis of the head forms with that of the handle an angle of about 140, opening upward and inward. FIG. 1255. Read / Articular Head Point of insertion of lateral ligament Manubrium "Processus gracilis Manubrium Right malleus \A, seen from behind; B, seen from in front. X The manubritiin (handle), a tapering process extending downward backward and inward, is embedded in the substance of the tympanic membrane (Fig. 1255). Near the upper part of the inner anterior surface of the handle is sometimes found a slight projection for the insertion of the tensor tympani muscle. The lower end of the manubrium is spatula shaped, flattened transversely. The long process is directed toward the Glaserian fissure, whilst the short process looks toward the external meatus. The processus brevis (short process) is a small conical elevation situated at the upper end of the handle, below the neck of the malleus. Like the handle it is attached to the tympanic membrane and covered by a layer of cartilage, notably on its external surface. The processus gracilis (long process) arises from the anterior angle of the internal surface of the neck, close to the base of the short process, and extends downward and forward to the Glaserian fissure. It is well developed in the foetus and in young children, but is often rudi- mentary in the adult. FIG. 1256. Body Upper facet Lower facet I'rocessus longiis Right incus; A, lateral; />, anterior aspect. "X 4 1 A. _Processus brevis Processus orbicularis The incus (anvil) resembles a molar tooth with two widely separated fangs, rather than an anvil. It consists of a body, a long process and a short process. The body of the incus has two main facets on its anterior and antero-external surfaces, which correspond to those on the head of the malleus and articulate with them. The processus brevis (short process) is conical in shape, flattened laterally and projects nearly horizontally backward to a depression in the posterior wall of the tympanum at the entrance of the antrum, where its apex is attached. The processus longus (long process) runs downward and backward, behind and nearly parallel with the handle of the malleus, and forms nearly a right angle with the short process. At its lower end it is bent inward and narrowed, or constricted, into a neck, which terminates in a rounded tubercle, the processus orbicularis, that articulates with the head of the stapes. In the fu-tus this process is separated from the rest of the long process. 1498 HUMAN ANATOMY. The stapes (stirrup), as its name implies, is stirrup-shaped and consists of a head, neck, two crura and a base or foot-plate. The external surface of the small rounded head is hollowed out for articulation with the orbicular process of the incus. Just below this is the constricted neck, from which the two crura diverge to become attached to the foot-plate near its lower FIG. 1257. Upper edge Posterior Lower edge Foot-plate Right stapes, A, seen from above; B, mesial surface of foot-plate. X 4^. margin. The anterior crus is shorter and straighter than the posterior, both being slightly curved. The fool-plate consists of a lamina of bone and corresponds to the bean-shape of the oval window, into which it neatly fits. The upper edge of the foot-plate is convex ; its lower edge is almost straight, being si ightly. hollowed out near its middle. Articulations of the Ossicles. In the malleo-incudal joint, both articular surfaces are covered with a thin layer of hyaline cartilage. The fairly well-developed capsular ligament, reinforced mesially, is fastened to the depressed margins of the articular surfaces. A wedge- shaped meniscus of fibre-cartilage projects from the superior wall of the capsule between the FIG. 1258. layers of hyaline cartilage. "When the manubrium handle moves inward, its lower cog catches the corresponding cog of the incus and the long process of the latter must follow. If the handle moves outward, the lower cog moves away from the incus and the latter moves but little" (Politzer). The articulation of the incus and stapes is a very delicate but true joint. Both the slightly convex surface of the lenticular process of the incus and the slightly concave surface of the head of the stapes are covered with hyaline car- tilage and united by a capsular ligament made up largely of elastic fibres and thickened on the posterior surface. Sometimes a meniscus of fibro-cartilage separates the two articular surfaces. The articulation of the stapes and oval window is effected by the margins of the window and the foot-plate of the stapes. These surfaces, as well as the vestibular aspect of the stapes, are cov- ered with a layer of hyaline cartilage. The cartilage of the foot-plate and that of the window are connected by a liga- ment of elastic fibres, forming a syn- chondrosis. In addition to the ligaments con- cerned in the foregoing articulations, four bands attach ossicles to the tym- panic walls and prevent their excessive Frontal section passing through malleus and tympanic membrane, movement; of these, three Connect the 60. Drawn from preparation made by Dr. Ralph Butler. m;l n eus and one the incus. 1. The superior ligament of the malleus extends from the legmen tympani to the head of the malleus. 2. The anterior ligament of the malleus is a strong, broad, fibrous band arising from the anterior part of tin.- head and neck of the malleus. Some of its fibres are attached to the ante- rior end of the annulus tympanicus (spina tympana -a major } and other fibres pass through the < ilaserian fissure to become attached to the spine of the sphenoid. These fibres correspond to the remains of the embryonic process of Meckel of the malleus and envelop the processus gnu ills. Sup. ligament Head External ligament Mem. flaccida or Schrapnell's membrane Prussak's space Neck Short process Chorda tympanum Tendon of tensor tympani Handle Cartilage Epithelium of epidermis Mcmhrana propria -Mucous membrane Membrana tensa Annulus tendinosus THE MIDDLE EAR. 1499 3. The lateral ligament of the malleus is somewhat fan-shaped and extends between the roughened neck of the malleus and the external wall of the tympanum above the Rivinian notch. The posterior fibres of this ligament are called the posterior ligament of the malleus ( Helmholtz) , and, together with the fibres of the anterior ligament lying in the same plane, form the " axis- ligameiit of the malleus," since the axis on which the malleus turns passes through the attach- ment of these two fibrous structures. 4. The posterior ligament of the incus extends from the apex of the short process of the incus to the tympanic wall at the lower part of the mouth of the antrum. It is fan-shaped, the incudal attachment being less extensive than that of the tympanic. The end of the short process is covered with hyaline cartilage. The Intratympanic Muscles. The muscles within the tympanum connected with the ossicles (musculi ossiculorum auditus) are : (i ) the tensor tympani and (2) the stapedins. The tensor tympani is a diminutive spindle-shaped muscle, about 1.25 cm. long, lying in the bony canal directly above the osseous part of the Eustachian tube, from which it is partly FIG. 1259. Facial nerve Ramus utriculus ampulla ris Utricle Foot of stapes Cisternaperi- >/ lymphatica Lowest part of spiral lamina Beginning of posterior ampulla Secondary tym- panic membrane Stapedius muscle External ii auditory canal 3*1 \< Handle of malleus jj Promontory Drum-head or tympanic membrane Tympanic cavity Vertical section through human middle and internal ear. Drawn from preparation made by Dr. Ralph Butler. separated by the bony scroll, the processiis cochleariformis. The posterior fibres arise from the top of the cartilage of the Eustachian tube and the adjoining part of the great wing of the sphenoid. Some of the fibres are connected with the tensor palati muscle and others arise from the wall of the canal which the muscle occupies. The fibres converge in a feather-like manner to the tendon, which begins within the muscle about the middle of the canal, and, pass- ing through the tympanic opening of the canal, turns at nearly a right angle over the end or rostrum of the processus cochleariformis to be inserted into the anterior part of the inner margin of the malleus-handle just below the short process. The tendon is almost per- pendicular to the plane of the tympanic membrane, is oblique to the long axis of the manu- brium and is enveloped, along with the muscle-belly, in a fibrous sheath. The tensor tympani and tensor palati muscles receive their nerve supply from the same source, namely, the trigem- inus, through the otic ganglion. The stapedius muscle lies within the triangular canal of the eminentia pyramidalis, arising from its floor and sides. Its fibres converge to the tendon, which, passing through the opening at the apex of the canal, extends forward, slightly upward, and outward, to be inserted into the lower posterior part of the head of the stapes. Some of the fibres of the tendon also pass to the 1500 HUMAN ANATOMY. lenticular process and the capsular ligament. The tendon is frequently enveloped in a fold of mucous membrane. A branch of the facial nerve passes through a small orifice between the Fallopian canal and the canal for the stapedius to supply this muscle. Movements of the Ossicles. When the tympanic membrane and malleus-handle are moved inward, the long process of the incus is also moved inward and pushes the head of the stapes inward, and slightly upward. This causes pressure upon the liquid within the labyrinth, and, since the bony walls of the labyrinth are inelastic, the membrane of the round window is bulged outward. As the tympanic membrane regains its normal position, these movements are re- versed. When on the other hand the tympanic membrane is moved outward, the movement of the long process of the incus is very slight because of the unlocking of the malleo-incudal articu- lation. Contraction of the tensor tympani muscle draws the centre of the tympanic membrane inward and in this way increases the tension of the membrane and of the posterior part of the axial ligaments of the malleus, especially of its external ligament. Contraction of the stapedius muscle pulls the head of the stapes backward, thus tilting the anterior end of the foot-plate outward, the posterior end acting as a fulcrum. The Mucous Membrane of the Tympanum. The tympanic cavity is lined by a thin transparent mucous membrane, closely adherent to the periosteum and continuous with that of the Eustachian tube and naso-pharynx anteriorly, and, FIG. 1260. Posterior crus of '? stapes Lower end of incus Malleus handle Cochlear nerve Basal turn of cochlea Tympanic cavity Horizontal section through human middle and internal ear; stapes occludes oval window. X 5 1 A. Drawn from preparation made by Dr. Ralph Butler. with that of the mastoid cells posteriorly. It covers the ossicles and their ligaments, the muscles, the tendons and the chorda tympani nerve, and forms a number of folds extending across the cavity. These folds vary in location, direction and number, and form pouches within the tympanum. The attic is divided into an external and an internal compartment by the incus, the head of the malleus, the superior ligament of the malleus and the superior mallco- tncudal fold of mucous membrane. The external compartment is bounded on the outer side by the external tympanic wall, and is itself subdivided into a superior and an inferior space by the external ligament of the malleus. The inferior division is called Prussak's space and is hounded externally by Shrapnell's membrane, inter- nally by the neck of the malleus, interiorly by the short process of the hammer, and superiorly by the external ligament of the malleus (Fig. 1258). A number of THE MIDDLE EAR. 1501 inconstant folds of mucous membrane, extend from the wall of the tympanum to the malleus and the incus. The most constant of these is the outer malleo-incudal plica, which stretches backward to the posterior ligament of the incus. Additional folds frequently extend between the cura of the stapes and from them to the wall of the tympanum. The epithelium of the tympanic mucosa varies in different parts of the cavity. Over the promontory, the ossicles and the tympanic membrane, it consists of a single layer of low cuboidal nonciliated cells, whilst over the other parts the cells are ciliated columnar in type. Small tubular glands occur within the lining of the anterior part of the cavity. The subepithelial connective tissue, which supports the vessels and nerves, comprises two layers, the outer forming the periosteum of the bony wall. The secondary tympanic membrane closing the fenestra cochleae, bulges somewhat toward the cochlea and is attached to the bony crest or ridge of the win- dow by its widened rim. It consists of three layers, of which the middle one is a middle fibrous lamina propria, which is covered on the tympanic surface by mucous membrane, and on the other side by an extension of the lining of the perilymphatic space. The lamina propria is composed of radially disposed bundles of fibrous tissue. The outer mucous stratum is formed of a thin fibrous tunica propria, invested by a single layer of flattened nonciliated epithelial cells, similar to those covering the neighboring promontory. The innermost stratum of the membrane includes a thin layer of subendothelial fibrous tissue, over which stretches a layer of endothelial plates. Vessels and Nerves of the Tympanum. The arteries supplying the tympanic cavity are from five sources. 1. The stylo-mastoid branch of the posterior auricular artery passes through the stylo-mastoid foramen and the Fallopian aqueduct, and sends a branch to the sta- pedius muscle and three branches to the posterior part of the tympanic cavity. One of these passes to the floor, one through the canal for the chorda tympani nerve, and one to the posterior part of the oval window. 2. The tympanic branch of the internal maxillary artery enters the tympanic cavity through the Glaserian fissure and supplies the anterior part of the cavity, including the anterior ligament of the malleus, the processus gracilis and the tympanic membrane. 3. The middle meningeal branch of the internal maxillary artery sends a branch through the hiatus Fallopii to anastomose with the stylo-mastoid artery, a branch through the canaliculus tympanicus to the promontory, and a branch to the tensor tympani muscle. 4. The ascending pharyngeal sends branches to the floor and the promontory, one of them accompanying Jacobson's nerve. 5. The internal carotid artery in its passage through the carotid canal gives off branches to the anterior wall of the tympanic cavity. The veins follow, in a general way, the course of the arteries. They are tribu- tary to the middle meningeal, the pharyngeal plexus and the jugulars. The lymphatics arise from a net- work within the mucous membrane and end chiefly in the retropharyngeal and the parotid nodes. The nerves supplying the mucous membrane of the tympanum are branches from the tympanic plexus formed by the tympanic branch of the glosso-pharyngeal nerve, in conjunction with sympathetic filaments from the net-work accompanying the carotid artery. The tensor tympani muscle receives its supply from the trigeminus; the stapedius muscle from the facial. Although the chorda tympani nerve has an intimate topographical relation to the space, which it traverses close to the outer wall, it gives no filaments to the structures within the tympanum. THE EUSTACHIAN TUBE. The Eustachian tube (tuba auditivaj is a canal, partly bony and partly cartilagi- nous, extending from the lateral wall of the naso-pharynx backward, upward and out- ward to the anterior part of the tympanum. In the adult it measures about 37 mm. (i l /2 in.y in length, of which approximately the upper third (tympanic portion^ 1502 HUMAN ANATOMY. belongs to the bony division, whilst the remainder is contributed by the cartilaginous division of the tube. With the sagittal plane it forms an angle of 45, and with the horizontal plane one of about 33. With the long axis of the external auditory canal it forms an angle of from i35-i45, opening outward. The cartilaginous and bony divisions of the tube do not lie exactly in the same plane, but join at a very obtuse angle opening outward. The tube has somewhat the shape of an hour glass, being wider at the ends and narrowed at the junction of the cartilaginous and bony portions into the isthmus, where its height is about 3 mm. and its breadth about half as much. The osseous or tympanic portion (pars ossea) about 12 mm. long, is bounded above by the tegmen tympani and the canal for the tensor tympani muscle, from which it is incompletely separated by the processus cochleariformis. Below and internal to it lies the canal for the carotid artery. Its lumen is irregularly triangular in cross-section. FIG. 1261. Tympanic membrane Tympanic cavity Ant ram Condyle of jaw Basilar process External audi- tory canal Parotid gland Fossa of Kosen- muller Cartilage of. EuStachian tube 1 list. i< hi, in tube Levator palati Tensor palati Hamular process Palatal raphe Palatal rugae Internal auditory canal Right internal carotid artery Incisor canal Incisi%'e pad -Tympanic membrane External auditory meatus Parotid gland External pterj'goid muscle Ramus of jaw Internal pterygoid muscle Soft palate Masseter muscle .Vestibule Buccinator muscle Anterior part of section through hend at plane shown in small outline figure, viewed from below ; left Eustachian tube exposed throughout its length. Drawn from preparation made by Professor Dwight. The cartilaginous or pharyngeal portion (pars cartilaginea) is about 25 mm. (i In.) in length and attached to the rough oblique margin of the anterior end of the osseous, portion of the tube. Its posterior wall is formed by a plate of cartilage Ccartilago tubac auditivae), the upper margin of which is curled outward upon itself to form a guttrr, which appears as a hook on transverse section, whose inner and outer plates are known as the mesial and lateral lamina respectively. The interval between the margins of this cartilagjnous groove presents outward and forward and is rilled up with a strong fibrous membrane, thus completing tin- canal. Therefore part of the anterior wall and the posterior superior wall of the tube are formed by this cartilage and the rest of the anterior wall and all of the inferior by fibrous tissue. The cartilage is attached to the base of the skull and frequently is deficient in places, sometimes being divided into several pieces. At birth the cartilage is entirely of the hyaline variety, but later, particularly in the pharyngeal division, this is more or less extensively replaced by fibrocartilage, except in the upper part where the hyaline cartilage THE MIDDLE EAR. 1503 persists. It is this cartilage, covered by the cushion of mucous membrane, that confers the characteristic Gothic arch contour to the lower opening, the osteum pharyngeum, of the tube. The Mucous Membrane of the Eustachian Tube. The Eustachian tube is lined throughout its length with mucous membrane, which differs some- what in the cartilaginous and osseous portions. That in the former resembles the mucous membrane of the naso-pharynx, with which it is directly continuous, whilst that of the osseous division resembles, to some extent, the mucous membrane of the tympanic cavity. The epithelium of both divisions consists of the ciliated stratified columnar type, with some goblet cells, but the cells in the pharyngeal division, especially in the lower part, are taller than those of the tympanic portion, which are low cuboidal. In the tympanic portion the mucous membrane is closely united with the perios- teum and contains very few mucous glands and little or no adenoid tissue. In the cartilaginous division, on the contrary, the epithelium overlies a layer of adenoid FIG. 1262. Lateral lamina ^4* Oblique musclc-fibres- _Mesial lamina of cartilage of tube Lumen of iube- fc J l*< >'. i -.--Glands Tensor palati dilator tuba: i^SsSji^ Levator palati " Transverse section of cartilaginous Eustachian tube. X 7. tissue, often called the tubal tonsil. This tissue is especially abundant in children, and beneath it are found numerous mucous glands which open on the free surface of the tube. These glands extend nearly to the perichondrium and sometimes can be traced even through the fissures in the cartilage into the surrounding connective tissue. A considerable amount of adipose tissue often occupies the submucosa of the lower and lateral walls. The submucous layer is well developed in the cartilaginous division of the tube, particularly in the outer membranous wall. It consists of loosely arranged fibro-elastic tissue, which supports the mucous glands and the larger vessels and nerves. The muscles of the Eustachian tube are the levator and the tensor palati, which when they contract not only affect the palate, but also produce changes in the position of the floor and in the lumen of the tube. These muscles are described in connection with the palate fpage 1593), suffice it here to note their close relations to the Eustachian tube, beneath and to the inner side of which the levator lies, and to the outer side of which the tensor extends. By reason of the intimate attachment which both muscles have to the cartilage of the tube, since both take partial origin from this structure, contraction of their fibres tend to draw apart the walls of the canal and they thus serve as dilators. Such action is particularly true of the tensor palati, many of 1504 HUMAN ANATOMY. whose fibres are inserted into fibrous tissue completing the lateral wall of the tube (Fig. 1262), this part of the muscle being designated the dilator tnbfc. In addition to opening the tube, the levator palati causes elevation of its floor. The blood-vessels of the Eustachian tube include the arteries, which arise from the ascending pharyngeal and from the middle meningeal and the Vidian branches of the internal maxillary; and the veins, which communicate with those of the tym- panum and of the pharynx and also form a plexus connecting with the cavernous sinus. The nerves are supplied from the tympanic plexus and from the pharyngeal branches from the spheno-palatine ganglion. THE MASTOID CELLS. The antrum tympanicum communicates posteriorly with a variable number of irregular pneumatic cavities, the mastoid cells (cellulae mastoideae), so called because the majority of these spaces occupy the mastoid process. Unlike the antrum, these cells are not developed at birth. As the mastoid process develops, the original diploetic structure is usually more or less replaced by larger cavities forming the pneumatic type. In a study of one thousand bones, Randall found that scarcely two per cent, of mastoids could be classed as diploetic, and only some ten per cent, as combining a notable amount of diploe with pneumatic spaces ; further, that no mastoid is absolutely pneumatic, although some senile bones show a single thin-walled cell occupying the greater part of the process. The pneumatic cells of this region may extend to the sigmoid portion of the lateral sinus ; into the occipital bone ; into the squamous portion of the temporal bone and above the external auditory canal ; into the root of the zygomatic process ; into the floor of the Eustachian tube close to the carotid canal, and occasionally as far as the apex of the petrous portion of temporal bone. These spaces are lined by a very thin mucous membrane, which is continu- ous with that of the antrum and of the tympanic cavity. It is closely united with the periosteum and possesses a layer of low nonciliated squamous epithelium. The blood-vessels supplying the mastoid cells are the arteries derived from the stylo-mastoid and the middle meningeal, and the veins, which communicate with those of the tympanum and the external wall of the mastoid process. Some of the veins are tributary to the mastoid emissary and the lateral sinus, whilst others pass beneath the superior simicircular canal through the cranial wall to join the dural veins. The nerves are the mastoid ramifications of the tympanic plexus. Practical Considerations : The Tympanum. This cavity is continuous anteriorly with the nasopharynx by way of the Eustachian tube, and posteriorly with the mastoid antrum and air cells by way of the attic, so that infection, which is very common in the pharynx, may extend throughout this whole tract. The tympanic cavity extends above the limits of the membrane about 5-6 mm. as th attic, and about 2-3 mm. below as the ' ' cellar ' ' or hypotympanic recess. Secre tions on the floor, therefore, may not be seen through the membrane. The defective drainage which results from the lower level of the floor of the tympanum, as com- pared with that of the external meatus, is one of the causes of the frequency o chronic otitis media with purulent discharge, even after the early evacuation o the products of inflammation in the acute stage. On the internal wall the facial nerve passes in a curve over the vestibule in the angle between the roof and inner wall of the tympanum, then downward in the slightly projecting Fallopian canal with a concave turn above and behind the oval window, continuing its course downward at the junction of the posterior and inner wall to emerge below from the skull at the stylo-mastoid foramen. This canal offers considerable resistance to caries in its immediate neighborhood, although the disease not infrequently communicates itself to the nerve. Such involvement of the nerve is often the prodromal symptom of a fatal cerebral affection (Politzer). At birth this portion of the Fallopian canal is very thin and translucent, and is deficient as it arches over the oval window, so that involvement of the nerve is much more common in children than in adults. PRACTICAL CONSIDERATIONS : THE MIDDLE EAR. 1505 Roofing in the antrum and the passage leading into it from the attic is a thin layer of bone (tegmen antri), which is particularly thin over the antrum and separates these spaces from the middle fossa of the skull. Not infrequently there are membranous defects in the tegmen, upon which the dura rests (Macewen). Pus frequently passes through this bony plate, or its deficiencies, to the temporo- sphenoidal region of the brain, which is the most frequent seat of brain abscess. Fractures of the base of the skull in the middle fossa may pass through the tegmen, rupturing the adherent dura, and permitting cerebro-spinal fluid to pass into the tympanum. If there is coincident rupture of the tympanic membrane, the fluid will likely appear at the external auditory meatus, or if the membrane remains intact, the fluid may pass to the pharynx through the Eustachian tube. Often the hearing in chronic plastic otitis media is better during a great noise than when the surroundings are more quiet, because the stiffened ossicles transmit additional ordinary sounds more readily after they have been loosened by the more violent vibrations; or it may be because the auditory nerve, owing to the greater irritation, becomes more sensitive (Urbantschitsch). The various relationships of the tympanum as involved in infectious disease should be understood from the standpoint of etiology and from that of sequelae or complications. Infection may reach the tympanum from () the naso-pharynx through the Eustachian tube (scarlatina, diphtheria, pharyngitis, tonsillitis, rhinitis); or (<) the mastoid antrum and cells posteriorly. It may extend from the tympanum (#) upward, by perforation of the tegmen, often deficient at places, leading to external pachymeningitis, or to subdural abscess ; the dura, arachnoid, and pia mater at this level are fused, so that when the dura is ulcerated through, a diffuse meningeal infection does not ensue, but the process tends rather to spread into the brain along the perivascular lymphatic sheaths of the pial vessels, resulting in an abscess in the temporal lobe (Taylor); () to the internal jugular vein through venules that penetrate the fundus tympani to empty into the jugular bulb, and thence to the lateral sinus ; (^r) to the superior petrosal sinus and the dura mater of the middle fossa of the skull by the structures (veins and areolar tissue) passing through the petro-squamous suture ; ( ) encroaching upon the Fallopian canal and destroying the facial nerve ; (r) invading the middle cerebral fossa ; (< >\ e the ear. A cerebellar abscess might be reached by an opening one and one-half inches behind the centre of the bony meatus and one inch below Reid's base line. Till: INTERNAL EAR. The internal ear consists essentially of a highly complex membranous sac, con- nected with the peripheral ramifications of the auditory nerve, and a bony capsule, which encloses all parts of the membranous structure and is embedded within the substance of the petrous portion of the temporal bone. These two parts, known respectively as the' membranous and the bony labvrhitli, are not everywhere in close apposition, but in most places are separated by an intervening space filled with a tluid, the f)-ri/yin/>/i, the inner sac lying within the osseous capsule like a shrunken cast within a mould. The membranous labyrinth is hollow and everywhere filled with a fluid, called the ciidolyinfih, which nowhere gains access to the cavity occupied by tin- perilymph. The internal ear is closely related with the bottom of the internal auditory canal, which its inner wall contributes, on the one side, and with the inner wall of the tympanic cavity on the other. Its entire length is about 20 mm., and its long axis corresponds closely with that of the pyramidal or petrous THE INTERNAL EAR. portion of the temporal bone. The position of approximately its posterior third is indicated by the transverse ridge that crosses the upper surface of the temporal bone a short distance behind the internal auditory meatus. The irregular cavity of the bony labyrinth, hollowed out in the temporal bone, comprises three subdivis- FIG. 1264. '"T Tympanic cavity Facial canal Cochlea Semicircular canals Internal auditory canal Right temporal bone, upper part of petrous portion has been removed to show bony labyrinth lying in position. ions : a middle one, the vestibule, an anterior one, the cochlea, and a posterior one, the semicircular canals. Both the front and hind divisions communicate freely with the vestibule, but neither communicates with the membranous labyrinth nor, in the recent condition, with the tympanic cavity. Although corresponding in its general form with the bony compartments of the cochlea and semicircular canals, the membranous labyrinth less accurately agrees in its contour with the bony vestibule, since, instead of presenting a single cavity, it is subdivided into two unequal compartments, known as the saccule and the utricle, which are lodged within the bony vestibule. The divisions of the membranous labyrinth are, therefore, four, which from before backward are : the membranous cochlea, the saccule, the utricle and the membranous semicircular canals. THE OSSEOUS LABYRINTH. The Vestibule. The vestibule (vestibulum), the middle division of the bony labyrinth lies between the cochlea in front and the semicircular canals behind and communicates freely with both. It is an irregularly elliptical cavity, measuring about 5 mm. from before back- ward, the same from above F IG - 1265. downward, and from 3-4 mm. from without inward. The lateral (outer) wall separates it from the tympanic cavity, and contains the oval window with the foot-plate of the stapes. The medial (inner) wall, directed toward the bottom of the internal audi- tory canal, presents two depressions separated by a ridge, the crista vestibuli, the upper pointed end of which forms the pyramidalis vestibuli. The anterior and smaller of these depressions is the spherical recess (rcccssus sphaericus) and lodges the saccule. In the lower part of this fossa, about a dozen minute perforations mark the position of the macula cribrosa media for the passage of branches of the vestibu- lar nerve from the bottom of the internal auditory canal to the saccule. The posterior and larger depression is the elliptical recess (recessus ellipticus). Behind the lower Superior ampulla Common cms Lodges utricle Lodges saccule Cochlea Superior canal External canal Posterior canal Posterior ampulla Cast of right bony labyrinth, mesial aspect. X 2. 1512 HI MAN ANATOMY. part of the spherical recess, the crista vestibuli divides into two limbs between which is the recessus cochlearis, which lodges the beginning of the ductus cochlearis and is pierced by a number of small openings for the passage of nerve filaments to this duct. The numerous minute holes piercing the crista (pyramid) and the elliptical recess collectively form FIG 1266. the macula cribrosa superior (Fig. 1266) and transmit branches of the vestibular nerve to the utricle and to the ampullae of the superior and hori- zontal semicircular canals. Below and behind the re- cessus ellipticus lies a groove, the fossula sul- ciformis, which deepens posteriorly into a very small canal, the aqueduct of the vestibule (aquae- ductus vestibuli) which runs in a slightly curved course to the posterior surface of the petrous portion of the temporal bone, where it ends in a slit-like opening, the apertura externa aquaeductus vestibuli, situated between the internal opening of the internal auditory canal and the groove for the lateral sinus. The canal transmits the ductus endolymphaticus and a small vein. The anterior wall of the vestibule is pierced by the large opening leading into the scala vestibuli of the cochlea. Near this aperture is seen the beginning of the lamina spiralis ossea which lies on the floor of the vestibule below the oval window. Posteriorly the vestibule directly communicates with the semicircular canals by five round openings. The Semicircular Canals. The three bony semicircular canals the superior, the posterior and the horizontal lie behind the vestibule and are perpendicular to one another (Fig. 1265). Their disposition is such that the planes of the three canals Crus commune Aquaeductus vestibuli Recessus ellipticus Macula inferior Crista vestibuli Recessuss pfcaeri- cus with macula media Lamina spiralis Section of right bony labyrinth passing through plane of superior semi- circular canal ; anterior wall of vestibule is seen from behind. X 4- FIG. 1267. Small end of posterior canal Crus commune correspond with the sides of the corner of a cube, suggestively re- calling the relations of the three cardinal planes of the body the sagittal, frontal and transverse. Each canal possesses at one end a dilatation, called the osseus ampulla. The superior canal (ca- nalis superior) lies farth- est front and in a nearly vertical plane at right angles to the long axis of the petrous portion of the temporal bone, whilst the plane of the longest canal, the pos- terior (canalis posterior) is approximately parallel to it. The external portion of the horizontal semicircular canal forms a prominence on the inner wall of the middle ear behind the facial canal, while the upper part of the superior semicircular canal produces the conspicuous elevation, the eminentia arouata, si-en on the superior Ampulla of superior canal Ampulla of external canal Facial canal oval ( vestibulnr) wi in low Lamina spiralis Round (cochlear) windo\\ Section of right bony labyrinth passing through plain- of superior semicircular canal; posterior wall of vestibule is seen from before. X 4. Small end of external canal Ampulla of posterior canal THE INTERNAL EAR. 1513 surface of the petrous bone. The semicircular canals open into the posterior part of the vestibule by five apertures (Fig. 1267), the unciilated ends of the superior and posterior canals joining to form a common limb (crus commune). The horizontal canal (canalis lateralis) alone communicates with the vestibule by two distinct open- ings. Its ampulla is at its outer end and lies at the upper part of the vestibule above the oval window, from which it is separated by a groove corresponding to the facial canal. Lying above and close to this opening is placed the ampullary end of the superior canal. The ampullary end of the posterior canal lies on the floor of the vestibule, near the opening of the non-dilated end of the horizontal canal and of the canalis communis. In the wall of the ampulla of the posterior canal, a number of small openings (macula cribrosa inferior) provide for the entrance of the special branch of the vestibular nerve destined for this tube. The Cochlea. The bony cochlea constitutes the anterior part of the labyrinth and appears as a short blunt cone, about 5 mm. in height, whose base forms the an- terior wall of the inner end of the internal auditory meatus. Its apex is directed hori- FlG. T268. Scala vestibuli Sea la tynipani Modiolus Area cochlearis Area vestibularis inferior. Internal auditory can Foramen singulare Hamulus, overlying helicotrema Lamina spiralis ossea Canalis spiralis iiiodioli Facial canal Crista falciformis Area vestibularis superior Cochlea and bottom of internal auditory canal exposed by vertical section passing parallel with zygoma ; prepara- tion has been turned so that cochlea rests with its base downward and apex pointing upward. X 5. zontally outward, somewhat forward and downward, and reaches almost to the Eusta- chian tube. Its large lower turn bulges into the tympanic cavity and produces the conspicuous elevation of the promontory seen on the inner wall of the middle ear (Fig. 1269). The bony cochlea consists essentially of a tapering central column, the modiolus, around which the bony canal, about 30 mm. long, makes something more than two and a half spiral turns, the basal, middle and apical. The conical modiolus has a broad concave base which forms part of the base of the cochlea (basis cochlea), and a small apex which extends nearly to the apex of the cochlea, or cupola (cupula). It is much thicker within the lowest turn of the canal than above, and is pierced by many small canals for the nerves and vessels to the spiral lamina (Fig. 1268). The axis of the modiolus, from base to apex, is traversed by the central canal, whilst a more peripherally situated channel, the canalis spiralis, encircles the modiolus and contains the spiral ganglion and a spiral vein. Project- ing at a right angle from the modiolus into the canal of the bony cochlea is a thin shelf of bone, the lamina spiralis ossea, which is made up of two delicate bony plates between which are fine canals containing the branches of the cochlear nerve. The spiral lamina begins between the round window and the lower wall of the 1514 HUMAN ANATOMY. vestibule (Fig. 1269), and after winding spirally around the modiolus to the apex of the cochlea, ends in a hook-like process, the hamulus, which forms part of the the boundary of the helicotrema (Fig. 1269). The partial division of the canal of the bony cochlea effected by the osseous spiral lamina is completed by the membranous spiral lamina, which stretches from the free edge of the osseous lamina, to which it is attached, to the outer wall of the canal (Fig. 1271). The upper division of the canal is called the scala vestibuli and communicates with the vestibule, whilst the lower division, the scala tympani, would open into the tympanic cavity, were it not separated from that space by the secondary tympanic membrane. These scalae communicate with each other through an opening, the helicotrema, at the apex of the cochlea. Close to the beginning of the scala tym- pani at the round window is the inner orifice of the aquaeductus cochleae (ductus peril} mphaticus), its outer opening being in a depression on the lower surface of the pyramid near its posterior edge. It transmits a small vein and establishes a communication between the subarachnoid space and the scala tympani. The internal auditory canal communicates with the cranial cavity by an oval opening on the posterior surface of the pyramidal portion of the temporal bone, from which it extends outward to the internal ear. Its outer or lateral end, the fundus. is divided into a smaller superior and a larger inferior fossa by a transverse ridge, the crista falciformis. In the anterior part of the superior fossa (area fascialis ) is the opening of the facial canal (aquaeductus Fallopii) for the transmission of the facial nerve. In its posterior part are the openings (area vestihularis superior) for the branches of the vestibular nerves which supply the utricle and the ampullae of the superior and horizontal semicircular canals. These openings appear in the macula cribrosa superior on the inner surface of the bony labyrinth (page 1512 ). The ante- rior part of the inferior fossa is called the area cochlearis and is perforated about its middle by the opening of the central canal of the modiolus. Surrounding this are the numerous small apertures of the tractus spiralis foraminosus for the trans- mission of branches of the cochlear nerve to the two lower turns of the cochlea. Behind the area cochleae and separated from it by a ridge, lies the inferior area of the vestibule (area vestihularis inferior) with its small openings for the passage of nerves to the saccule. The macula cribrosa media, described above, is formed by these openings. Behind the fossula inferior is a large opening, the foramen singu- lare, which leads into a canal at the other end of which are the small openings of the macula cribrosa inferior. It transmits the branch of the vestibular nerve di->- tined for the ampulla of the posterior semicircular canal. THK MEMBRANOUS LABYRINTH. The membranous labyrinth (labyrinthus membranaceus ) lies within the bony labyrinth, which it resembles in general form. This agreement is least marked within the vestibule, since here the single division of the bony capsule is occupied by two compartments of the membranous sac, the utricle and the saccule. The membranous labyrinth comprises: (i) the utricle and the saccule, which, with the ductus endolympkaticuS) lie within the vestibule; (2) the three membranous semi- circular canals lodged within the bony semicircular canals; and (3) the mem- branous cochlea enclosed within the bony cochlea. The membranous labyrinth is attached, especially in certain places, by connective tissue to the inner wall of the bony capsule. The interval between the membranous and bony labyrinths, larg- est in the scahe tympani and vestibuli of the cochlea and in the vestibule, constitutes the perilymphatic space (spatium peiilymphaticnm) and contains a modified lym- phatic fluid, the perilymph. The fluid within tin- membranous labyrinth, appro- priately (ailed the endolymph, can puss from one part of the labyrinth to another, although the saccule and utricule are only indirectly connected through a narrow channel, the ductus endolymphaticus. The Utricle. The utricle (utricafae) occupies the recessus ellipticus in the upper back part of the vestibule. It is larger than the saccule and communicates with the three membranous semicircular canals. Attached to the upper and inner walls of the vestibule by connective tissue, it extends from the roof of the vestibule THE INTERNAL EAR. 1515 backward and downward to the opening of the posterior ampulla, a distance of from 5.5-6 mm. The utricle is made up of three subdivisions, the uppermost of which is respresented by a blind sac, from 3-3.5 mm. in length and breadth, called the recessus utriculi, whilst the two lower divisions together form the utriculus pro- prius, which measures 3 mm. by from 1.5-2 mm. The lower part of the utricle proper is prolonged into the tube-shaped sinus posterior, which connects the am- pulla of the posterior semicircular canal with the utricle. The openings of the semicircular canals into the utricle are disposed as follows: into the recessus utriculi open (i) the ampulla of the superior semicircular canal and (2) that of the horizontal canal. Into the utriculns propriris open (3) the sinus superior, which lies within the crus commune and receives in turn the nonampullated ends of the superior and posterior semicircular canals; (4) the non- ampullated end of the horizontal semicircular canal ; and (5) the ampulla of the posterior semicircular canal through the sinus posterior. On the antero-lateral wall of the recessus utriculi is placed the macula acustica of the utricle, whilst from its FIG. 1269. Hamulus Helicotrema Facial canal Vest i bii la r i oval) window Pyramxl Tympanic cavity/ \ IliliMF ^Scala tympani \ " \ \- ' \ / \ ~V "\ Scala vestibuli Promontory \ \ \Lamina spiralis ossea Probe passes through cochlear (round) window Lamina spiralis secundaria Right bony cochlea partially exposed by section passing through outer wall of apex and of first turn. antero-mesial wall springs the canalis utriculo-saccularis, the small canal from the utricle that joins even a smaller passage from the saccule to form the ductus endolymphaticus. The Saccule. The saccule (sacculus) is an irregularly oval compartment, about 3 by 2 mm. in size, which occupies the recessus sphericus in the lower and anterior part of the vestibule, to which it is attached by connective tissue. It is somewhat flattened laterally and at its lower end gradually narrows into a passage, the canalis reuniens, which connects the saccule with the ductus cochlearis. Its upper end bulges backward forming the sinus utricularis, whose wall comes in contact with that of the utricle. The small canal, already mentioned as helping to form the ductus endolymphaticus, arises from the posterior wall of the saccule. The ductus endolymphaticus passes through the aquaeductus vestibuli to end in a blind dilated extremity, the saccus endolymphaticus, lying between the layers of the dura mater below the opening of the aqueduct. Through the openings in the recessus sphericus branches of the vestibular nerve enter and pass to the macula acustica sacculi on the anterior wall of the saccule. The canalis reuniens is the very small tube passing from the lower part of the saccule into the upper wall of the cochlear duct near the caecum vestibulare, as its blind vestibular end is called. The Membranous Semicircular Canals. These tubes (ductus semicircu- lares) occupy about one third of the diameter of the osseous canals and correspond 1516 HUMAN ANATOMY. FIG. 1270. Trabeculae Membranous canal to them in number, name and form. They are closely united along- their convex margins with the bony tube (Fig. 1270), whilst their opposite wall lies free in the perilymphatic space, being attached only by irregular vascular con- nective tissue bundles, ligamenta labyrin- thi canaliculorum, which stretch across this space. Like the bony canals, each of the membranous tubes possesses an ampulla, which in the latter is relatively much larger than in the former, being about three times the size of the rest of the tube. The part of the ampulla corre- sponding to the con- vexity of the semicir- Bony waii cular canal is grooved on the outer surface at the entrance of the ampullary nerves. On the corresponding in- ternal surface is a pro- jection, the septum transversum, which partially divides this space into two parts and is surmounted by the crista acustica, which contains the endings of the vestibular nerves. The crescent-shaped thickening beyond each end of the crista is called the planum semilunatum. Trabecnhe Perilymphatic. space Transverse section of superior semicircular canal, showing relations of membranes to bony tube. X 35. Structure of the Utricle, Saccule and Semicircular Canals. The vestibule and the bony semicircular canals are lined by a very thin periosteum composed of a felt-work of resistant fibrous tissue, containing pigmented connective tissue cells. Endothelium everywhere lines the perilymphatic space between the membranous and osseous canals, covering the free inner sur- face of the periosteum, the fibrous trabeculae, and the outer or perilymphatic surface of this part of the membranous labyrinth. The walls of the utricle, saccule and membranous semicircular canals are made up of (a) an outer fibrous connective tissue lamella and (b} an inner epithelial lining, the latter consisting throughout the greater part of its extent of a single layer of thin flattened polyhedral cells. Be- neath the epithelium, especially in the region of the maculae, is (r) a thin, almost homogeneous hyaline membrane, with few cells. This middle layer presents in places on its inner surface small papillary elevations covered by epithelium. On the concave side of each of the semicircular canals is a strip, the raphe, of thickened epithelium in which the cells become low cylindrical in type. In the plana semilunata they are cylindrical in type. Over the regions receiving the nerve-fibres, the maculae acusticae and the crista; acusticae, the epithelium undergoes a marked alteration, changing from the indifferent covering cells into the highly specialized neuroepithelium. The maculae acusticae are about 3 mm. long by 2 nun. broad, the macula of the saccul' being a little narrower (1.5-1.6 mm. ) than that of the utricle (2 mm. ). At the margin of these areas the cells are at first cuboidal, next low columnar, and thru abruptly increase in length, until they measure from .030-. 035 mm., in contrast with their usual height of from .oo3-.cx>4 mm. The acoustic area includes two kinds of elements, the sustentacular or fibre-cells and the hair-cells. The sustenfacufar ce//s are long, rather narrow, irregularly cylindrical dements and extend the entire thickness of the epithelial layer, resting upon a well-developed basement-membrane by their expanded or divided basal processes. At a variable distance from the base, they present a swelling enclosing an oval nucleus and terminate at the surface in a cuticular zone. The cylin- drical hair-cell a are broader but shorter than the sustentacular cells, and reach from the free surface only as far as the middle of the epithelial layer, where each cell terminates usually in a THE INTERNAL EAR. 1517 rounded or somewhat swollen end containing a spherical nucleus. The central end, next to the free surface, exhibits a differentiation into a cuticular zone, similar to that covering the inner ends of the sustentacular elements. From the free border of each hair-cell, a stiff robust hair (.O2O-.O25 mm. long) projects into the endolymph. This conical process, however, is resolv- able into a number of agglutinated finer hairs or rods. The free surface of the neuroepithelium within the saccule and the utricle is covered by a remarkable structure, the so-called otolith membrane. This consists of a gelatinous membrane in which are embedded numberless small crystalline bodies, the otoliths or ear-stones. Between it and the cuticular zone is a space, about .020 mm. in width and filled with endolymph, through which the hair-cells pass to the otolith membrane. The otoliths (otoconia) are minute crystals, usually hexagonal in form, with slightly rounded angles, and from .oog-.on mm. in length. They are composed of calcium carbonate with an organic basis. On reaching the macula the nerve-fibres form a subepithelial plexus, from which fine bundles of fibres pass toward the free surface. The fibres usually lose their medullary substance in passing through the basement membrane and enter the epithelium as naked axis-cylinders. Passing between the sustentacular cells to about the middle of the epithelium, they break up into fine fibrillae, which embrace the deeper ends of the hair-cells and give off fine threads that pass as free axis-cylinders between the cells to higher levels. The crista acustica and the planum semilunatum are covered with neuroepithelium similar to that of the maculae. The hairs of the hair-cells, however, are longer and converge to and are embedded within a peculiar dome-like structure, known as the cupola, which probably does not exist during life, but is an artefact formed by coagulation of the fluid in which the ends of the hairs are bathed. Otoliths probably do not exist in the cristae acusticae. The Cochlear Duct. The membranous cochlea (ductus cochlearis) lies within the bony cochlea, and like it includes from two and one-half to two and three- quarter turns, named respectively the basal, middle and apical, the latter being FIG. 1271. Organ of Corti Corti's membrane Ganglion spirale Ligamen- tum spirale f ^~-.*,**- , - . "- : - Basilar membrane Ganglion spirale Scala vestibuli Ductus 'cochlearis _ Scala "tympani / \ \ Cochlear nerve in inters Modiolus auditory canal Section of human cochlea passing through axis of modiolus. X 12. three-fourths of a turn at the apex of the cochlea. The tapering tube of the bony cochlea, winding spirally around the modiolus, is subdivided into three compart- ments by the osseous spiral lamina and two membranes, namely, the membranous spiral lamina and Reissner's membrane. The membranous spiral lamina (lamina basilaris) or basilar membrane extends from the free border of the lamina spiralis ossea to the outer wall of the cochlea, where it is connected to an inward bulging of the periosteum and subperiosteal tissue, called the spiral ligament. The lower of the two tubes thus formed is the scala tympani and communicates, in the macerated skull, with the tympanum through the round window. The upper tube is subdivided into two compartments by an exceedingly delicate, partition, known as Reissner's membrane (membrana vestibularis) which extends from the upper surface of the osseous lamina near its outer end, obliquely upward and outward, to the external wall of the cochlea. The compartment above this membrane is the 1 5i 8 HUMAN ANATOMY. scala vestibuli and communicates with the perilymphatic space of the vestibule. The scalae tympani and vestibuli communicate only at the apex of the cochlea through the helicotrema. They contain perilymph and are brought into relation with the subarachnoid space through the aquaeductus cochleae. They are lined by a delicate fibrous periosteum, usually covered on the surface which is in co'ntact with the enclosed perilymph, by a single layer of endothelial plates. In some localities, however, as on the tympanic surface of the basilar membrane, the lining cells retain their primitive mesoblastic character and never become fully differentiated into endothelium. The third compartment, the ductus cochlearis, is triangular on cross-section (Fig. 1271), except at its ends, and bounded by Reissner's membrane above, by the basilar membrane and a part of the osseous spiral lamina below, and by the outer wall of the bony cochlea externally. Save for the narrow channel, the canalis reuniens, by which it communicates with the saccule, the cochlear cluct is a closed tube and contains endolymph. It begins below as a blind extremity, the caecum vestibulare, lodged within the recessus cochlearis of the vestibule and, after making two and three-quarter turns through the cochlea, ends above at the cupola of the cochlea in a second blind extremity, the caecum cupulare, or lagena, which is attached to the cupola and forms a part of the boundary of the helicotrema. Architecture and Structure of the Cochlear Duct. Reissner's membrane (membrana vestib- ularis), the delicate partition separating the cochlear duct from the scala vestibuli, begins on the upper surface of the lamina spiralis, about .2mm. medial to the free edge of the bony shelf, and extends at an angle of from 40-45 with the lamina spiralis ossea to the outer wall of the cochlea, where it is attached to the periosteum. Notwithstanding its excessive thinness (.003 mm.), it consists of three layers : (a) a very delicate middle stratum of connective tissue, (b) the endothelium covering the vestibular side, and (c ) the epithelium derived from the coch- lear duct, and contains sparingly distributed capillary blood-vessels. The outer wall of the cochlear duct (Fig. 1272) is bounded by a part of a thickened cres- centic cushion of connective tissue, whose convex surface is closely united with the bony wall and whose generally concave surface looks toward the cochlear duct. This structure, the liga- mentum spirale, extends slightly above the attachment of Reissner's membrane and to a greater distance below the attachment of the basilar membrane, thus forming part of the outer walls of the scalae vestibuli and tympani. At its junction with the basilar membrane it presents a marked projection, the crista basilaris, whilst a very slight elevation marks the point of attach- ment of the membrane of Reissner. The part of this ligament lying between these projections corresponds to the outer wall of the cochlear duct. Its concave free inner surface is broken In a third elevation, the prominentia spiralis, or accessory spiral ligament, distinguished usually by the presence of one large (vas prominent] or several small blood-vessels. The lower and smaller of these two divisions of the outer wall is called the sulcus spiralis externus and is lined by cuboidal epithelium, whilst the larger upper division is occupied by a peculiar vascular structure, the striae vascularis, which contains capillary blood-vessels within an epithelial struc- ture. Its surface is covered with pigmented irregular polygonal epithelial cells, and its deeper strata consist of cells which, especially in the superficial layers, resemble the surface epithelium, but in the deeper layers assume more and more the character of connective tissue. Over the prominentia spiralis the cells become flat and polyhedral. The ligamentum spirale is composed of a peculiar connective tissue, rich in cells and blood- vessels. Its thin outer layer forms the periosteum and is denser than the adjacent loose con- nective tissue. The latter is broadest opposite the scala tympani, where its fibres converge towards the crista basilaris. Opposite the outer wall of the cochlear duct it again becomes more compact and is rich in cells and blood-vessels. An internal layer extending from near UK- prominentia spiralis to the basilar membrane consists of a hyaline, noncellular tissue. Some authors claim to have found smooth muscle-fibres in the ligamentum spirale. The tympanic wall or floor of the cochlear duct (Fig. 1272) comprises the fmsi/ar mcm- hnuii\ extending from the basilar crest to the outer end of the bony spiral lamina, and the- limbus lamiiKt- spini/is, which includes this wall from the attachment of Reissner's membrane to the end of the bony lamina. The limbus (criM.i spir.-ilis'i is a thick mass of connective tissue upon the upper surface of the outer end of the osseous lamina spiralis. Its outer extremity is deeply grooved to form a gutter, the sulcus spiralis internus, the projections of the limbus above and below the sulcus forming lespi-ctively its superior (vestibular) and inferior (tympanic) labia. The upper surface of the limlnis is marked by clefts and furrows which are most conspicuous near the outer margin of the upper lip ( l.iliium vestiluilare), where the irregular projections between THK INTERNAL EAR. 1519 the furrows form the so-called auditory teeth, because of their fancied resemblance to incisor teeth. The lower lip (labium tympanicum ) is continuous externally with the basilar membrane and is perforated near its outer end by some 4000 apertures (foramina nervosa) transmitting minute branches of the cochlear nerve. The epithelium covering the elevated portions of the limbus, including the auditory teeth, is of the flat polyhedral variety, the intervening furrows and clefts being lined by columnar cells. The epithelium of the sulcus spiralis consists of a single- layer of low cuboidal or flattened cells, continuous with the epithelium of the auditory teeth above and with the highly specialized elements of Corti's organ below. The basilar membrane consists of a median (inner) and a lateral (outer) part. The former, known as the zona arcuata, is thin and supports the modified neuroepithelium constituting the organ of Corti; the outer part, named the zona pectinata, is the thicker division and lies external to the foot-plates of the outer rods of Corti. The basilar membrane is made up of three distinct layers, the epithelium, the substanlia propria and the tympanic lamella. The snbstantia propria is formed of an almost homogeneous connective tissue with a few nuclei and fine fibres, which radiate toward the outer edge of the spiral lamina. The fibres of the zona arcuata are very fine and interwoven, appearing to be an extension of those of the lower lip of the limbus, whilst straight and more distinct fibres stretch from the outer rods of Corti to the spiral ligament and constitute the so-called auditory strings. According to the estimate of Retzius, there are 24,000 FIG. 1272. Stria vascularis issuer's membrane otninentia spiralis Membrana tectoria V Spiral ligament \ Nerve-fibres Crista basilaris Basilar,- ' Vas spiralis Bone membrane Cross-section of ductus cochlearis from human cochlea. X W- Drawn from preparation made by Dr. Ralph Butler. of these special fibres. Their length increases from the base toward the apex of the cochlea, in agreement with the corresponding increase in breadth of the basilar membrane. The tympanic lamella contains numbers of fusiform cells of immature character interspersed with fibres. In this location the differentiation of the mesoblastic cells lining the tympanic canal has never advanced to the production of typical endothelial plates, the free surface of the lamella being invested by the short fusiform cells alone. The inner zone of this layer contains capillaries which empty into one, or sometimes two, veins, frequently seen under the tunnel of Corti and known as the vas spimle. The epithelium covering the inner zone of the basilar membrane forms the organ of Corti, the highest example of specialization of neuro-epithelium. The Organ of Corti. The organ of Corti (organon spiralej consists in a general way of a series of epithelial arches formed by the interlocking of the upper ends of converging and greatly modified epithelial cells, the pillars or rods of Corti, upon the inner and outer sides of which rest groups of neuroepithelial elements the auditory and the sustentacular cells. The triangular- space included between the converging pillars of Corti above and the basilar membrane below constitutes the tunnel of Corti, which is, therefore, only an intercellular space of unusual size. It contains probably a soft semifluid intercellular substance serving to support the nerve-fibrils traversing the space (Fig. 1273). The pillars or rods of Corti, examinee! in detail, prove to be composed of two parts, the denser substance of the pillar proper, and a thin, imperfect proto- plasmic envelope, which presents a triangular thickening at the base directed toward the cavity of the tunnel. Each pillar possesses a slender slightly sigmoid, longitudinally striated body, whose 1520 HUMAN ANATOMY. upper end terminates in a triangular head, and whose lower extremity expands into the fool resting upon the basilar membrane. The inner pillar is shorter, more perpendicular and less curved than the outer ; its head exhibits a single or double concave articular facet for the recep- tion of the corresponding convex surface of the head of the outer rod. The cuticular substance of both pillars adjoining the articular surfaces is distinguished by a circumscribed, seemingly homogeneous oval area of different nature. The upper straight border of the head of both pil- lars is prolonged outwardly into a thin process or head-plate, that of the inner lying uppermost and covering over the head and inner part of the plate of the outer pillar. The head-plate of the latter is longer and projects beyond the termination of the plate of the inner rod as the phalan- geal process, which unites with the adjacent phalanges of the cells of Deiters to form the mcm- brana reticularis. The inner pillars of Corti are more numerous, but narrower than the outer elements, from which arrangement it follows that the broader outer rods articulate with two and sometimes three of the inner pillars, the number of the latter in man being estimated by Retzius at 5600, as against 3850 of the outer rods. Immediately medial to the arch of Corti, resting upon the inner rods, a single row of spe- cialized epithelial elements extends as the inner auditory or hair-cells. These elements, little more than half the thickness of the epithelial layer in length, possess a columnar body contain- ing an oval nucleus. The outer somewhat constricted end of each hair-cell is limited by a FIG. 1273. Nnel's space Inner hair-cells Inner hair cells Hensen's cells . Cells of Deiters Membrane tectoria Sulcus spiralis Section showing details of Corti's organ from human cochlea ; owing to slight obliquity of section, width some- what exaggerated. X 375. Drawn from preparation made by Dr. Ralph Butler. sharply denned cuticular zone, from the free surface of which project, in man, some twenty-five rods or hairs. The inner hair-cells are less numerous (according to Retzius about 3500), as well as shorter and broader, than the corresponding outer elements. Their relation to the inner rods of Corti is such, that to every three rods two hair-cells are applied. The inner sustentacular cells extend throughout the thickness of the epithelial layer and exhibit a slightly imbricated arrangement as they pass over the sides of Corti's organ to become continuous with the lower cells of the sulcus spiralis. The cells covering the basilar membrane from the outer pillar to the basilar crest comprise three groups: (a) those composing the outer part of Corti's organ, including the outer hair- cells and cells of Deiters ; {b} the outer supporting cells, or cells of llcnscn ; (r) and the "low cuboidal elements, the cells of Claudius, investing the outermost part of the basilar membrane. The outer auditory or hair-cells are about five times more numerous (approximately 18,000 according to Waldeyer) than the corresponding inner elements, and in man and apes are dis- posed in three or four rows. They alternate with the peculiar end-plates or "phalanges"' of Deiters' cells, which separate the ends of the hair-cells and join to form a cuticnlar mesh-work, the nicinhnuni rt-liculuris, through the openings of which the Iviir-cells reach the free surface. The inner row of these cells lies directly upon the outer rods of ("orti, so placed that each cell, as a rule, rests upon two rods. The cells of the second row, however, are so disposed that each cell lies opposite a single rod, whilst the third layer repeats the arrangement of the first. In conse- quence of this grouping, these elements, in conjunction with the" phalanges," appear in surface views like a checker-board mosaic, in which the oval free ends of the auditory cells are included between the peculiar compressed and indented octagonal areas of the end-plates of I )eiters' cells THE INTERNAL EAR. 1521 FIG. 1274. Cells of Hensen !- Deiters' cells Outer hair-cells Plate-like processes of hair-cell |j Outer pillar cells Inner hair-cells (Fig. 1274). The outer hair-cells are cylindrical in their general form, terminating about the mid- dle of the epithelial layer in slightly expanded rounded ends, near which the spherical nuclei are situated. The outer sharply defined ends of the cells are distinguished by a cuticular border sup- porting about twenty-five rigid auditory rods or hairs which project beyond the level of the mem- brana reticularis. The deeper end of each outer hair-cell contains a dense yellowish enclosure, known as the body of Retzius, which is triangular when seen in profile. The bodies are absent in the inner hair-cells. The cells of Deiters have much in common with the rods of Corti, like these being special- ized sustentacular epithelial cells which extend the entire thickness of the epithelial stratum to terminate in the peculiar end-plates or phalanges. It follows, that whilst the free surface of Corti's organ is composed of both auditory and sustentacular cells, the elements resting upon the basi- lar membrane are of one kind alone the cells of Deiters. The bodies of the latter consist of two parts, the elongated cylindri- cal chief portion of the cell, con- taining the spherical nucleus and resting upon the basilar mem- brane, and the greatly attenuated pyramidal phalangeal process. A system of communicating in- tercellular clefts, the spaces of Nuel, lie between the auditory and supporting cells ; like the tunnel of Corti, these spaces are occupied by a semifluid intercel- lular substance. The cells of Deiters are arranged, as a rule, in three rows, although in places within the upper turns four or even five alternating rows are sometimes found. Each cell contains a fine filament, \h& fibre of Retzius, which begins near the 12: middle of the base with a conical expansion, and extends through the cell-body to the apex of the phalangeal process, where, according to Spee, it splits into seven or more fine end-fibrils, that extend into the cuticular superficial layer under and about the phalanges. The membrana tectoria or Corti's membrane stretches laterally from the upper lip of the limbus, above the sulcus spiralis and Corti's organ, as far as the last row of outer hair-cells. The membrane is a cuticular production, formed originally by the cells covering the region of the auditory teeth and the spiral sulcus. Medially it rests upon the epithelial cells, but farther outward it becomes separated from the free edge of the auditory teeth and assumes its conspic- uous position over the organ of Corti. The membrane seems to be composed of fine resistant fibres, held together by an interfibrillar substance. During life the membrane is probably soft and gelatinous, and much less rigid than its appearance indicates after the effect of reagents. The lower surface of the free portion of the membrane, opposite the inner hair-cells, is mod- elled by a shallow furrow, which indicates the position of a spirally arranged band known as the stripe of Hensen. Like the basilar membrane, the membrana tectoria increases in width from the base towards the apex of the cochlea. The outer sustentacular cells or cells of Hensen form an outer zone immediately external to the last Deiters' cells. These elements resemble the inner sustentacular cells, but differ somewhat in form and arrangement. In consequence of their oblique position, the bodies are not only greatly elongated, but also imbricated. They do not contain the fibres of Retzius. The cells of Claudius are the direct continuations of Hensen's cells, and laterally pass uninterruptedly into the low columnar elements covering the remaining part of the basilar membrane. They consist of a simple row of cuboidal cells possessing clear, faintly granular protoplasm and spherical nuclei. The Nerves of the Cochlea. The branches of the cochlear division of the auditory nerve enter the base of the cochlea through the tractus spiralis foraminosus (page 1514), those destined for the apical turn traversing the central canal of the modiolus. From the modiolus a series of stout lateral branches diverge at quite regular intervals through canals which communicate with the peripheral spiral canal within the base of the bony spiral lamina. Within the peripheral canal the nerve- fibres join numerous aggregations of bipolar nerve-cells, which continue along the 96 Corti's organ viewed from above, showing mosaic formed by pillars and Deiters' cells ; outer ends of auditory cells occupy meshes of cuticular net-work. (Retzius). 1522 HUMAN ANATOMY. spiral canal and collectively constitute the ganglion spirale. From these cells numerous dendrites are given off, which pass along the canals within the spiral lamina towards its margin, the twigs meanwhile subdividing to form an extensive plexus contained within corresponding channels in the bone. At the edge of the spiral lamina bundles of fine fibres are given off, which escape at the foramina nervina of the labium tympanicum and enter the epithelial layer close to the inner rod of Corti. During or before their passage through the foramina, the nerve-fibres lose their med- ullary substance and proceed to their destination as fine naked axis-cylinders. The radiating bundles pass within the epithelium to the mesial side of the base of the inner pillar ; here they divide into two sets of fibrillae, one, the mesial spiral fasciculus, going to the inner hair-cells and the other, the lateral spiral fasciculus, passing between the inner pillars to reach the tunnel of Corti. Within this space fibrillae are given off which, after crossing the tunnel, escape between the outer rods into the epithelium lying on the lateral side of the arch. The further course of the fibrilke seems to be such that some extend between the outer pillar of Corti and the first n >ws of hair-cells, whilst succeeding groups of fibrillae course between the rows of Deiters' FIG. 1275. iperior canal Ductus endolymphaticus External canal Ligamentum spirale Branches of cochlear nervr to Corti's organ Membranous cochlea Canalis reuniehs opening into cochlear duct Posterior canal Blind sac of ductus coclilcaris Branch of vestibular nerve to posterior canals Membranous labyrinth of five months foetus, postero-mesial aspect ; u, utricle; ss, sp, superior and posterior utric- ular sinus; s, saccule ; us, utriculo-saccular canal ; cr, canalis reuniens; pa, posterior ampulla. X 6. (Rftzius). cells to reach the remaining hair-cells. The relation between the nerve-fibrils and the auditory cells is in all cases probably close contact and not actual junction with the percipient elements. The paths by which the impulses collected from the audi- tory cells are conveyed to the cochlear nucleus, and thence to the higher centres, are described in connection with the Auditory Nerve (page 1258). Blood-Vessels of the Membranous Labyrinth. The arteries supplying the internal ear arise from the internal auditory artery, supplemented to a limited extent by branches from the stylo-mastoid. The auditory artery, a branch of the basilar, after entering the internal auditory meatus divides, according to Siebenmann, into three branches : (i) the anterior vestibular, (2) the cochlear proper, and (3) the vestibulo-cochlcar arterv. 1. The vestibular artery accompanies the utriculo-ampullary nerve and sup- plies the upper part of the vestibule, including the posterior part of the utricle with its macula, the saccule and the cristae of the upper and outer ampullae of the corre- sponding semicircular canals. 2. The cochlear artery pursues a spiral course. It gives off three branch* s, two of which are distributed to the lower turn of the cochlea, whilst the third sup- plies the middle and apical turns. 3. The vestibulo-cochlear artery arises either from the cochlear artery or independently and divides, within the; spiral lamina, into a cochlear and a vestibular DEVELOPMENT OF THE EAR. 1523 branch. The cochlcar branch is distributed to the lower turn of the cochlea and anastomoses with the cochlear artery proper. The vestibular branch is distributed to the lower part of the vestibule, including the lower part of the saccule and utricle, to the cms commune and part of the semicircular canals, and to the lower end of the cochlea. According to Siebenmann, the macula of the saccule receives its arterial supply from a blood-vessel which usually arises from the common stem of the vestib- ulo-cochlear artery, or, more rarely, runs independently through the whole internal meatus. A similar origin applies to the artery supplying the nerve of the posterior ampulla. In the base of tl^e spiral lamina the arteries are connected by capillary loops especially in the lower turn of the cochlea. As mentioned above, one or more spiral vessels are often seen under the tunnel of Corti within the tympanic covering of the basilar membrane. The region of the stria vascularis and prominentia spiralis are especially well supplied with blood-vessels. Those seen in the scala tympani are principally veins, while a larger number of arteries are found in the scala vestibuli. The blood-supply of the lower turn of the cochlea is much more generous than that of the others. The veins by which the blood escapes from the cochlea include : ( i ) the vein of the vestibular aqueduct, which empties into the superior petrosal sinus ; (2) the vein of the cochlear aqueduct, which empties into the internal jugular and (3) the venous plexus of the inner auditory canal, which empties either into the transverse or inferior petrosal sinus. The first of these channels collects the blood from the semi- circular canals; the second from the whole cochlear canal through the anterior, pos- terior and middle spiral veins and from most of the vestibule through the anterior and posterior vestibular veins. The veins of the internal auditory canal form collat- erals to the other veins of the labyrinth and receive the large central cochlear vein (Siebenmann), which leaves the cochlea near the border of the central foramen of the modiolus, as well as tributaries corresponding to the branches of the acoustic nerve. FIG. 1276. Hind-brain Otic pit THE DEVELOPMENT OF THE" EAR. The development of the ear includes the formation of two morphologically distinct divis- ions, the membranous labyrinth, the essential auditory structure, and the accessory parts, com- prising the middle ear, with its ossicles and associated cavities, and the external auditory canal and the auricle. The developmental history of the organ of hearing proper in its early stages is largely an account of the growth and differentiation of the ectoblastic otic vesicle, since from this is produced the important membranous tube, the enveloping fibrous and osseous structures being comparatively late contributions from the mesoblast. Development of the Labyrinth. The internal ear appears as a thickening and soon after depression of the ectoblast within a small area on either side of the cephalic end of the neural tube, at a level correspond- ing to about the middle of the hind-brain (Fig. 1276). This depression, the auditory pit, is widely open for a considerable time and distinguished by the greater thickness of its depressed wall, which contrasts strongly with the adjacent ectoblast. After a time the lips of the pit approximate until, by their final union, the cup-like depression is converted into a closed sac, the otic vesicle. This sac, after severing all connection with the ectoblast, gradually recedes from the sur- face in consequence of the growth of the intervening mesoblastic layer ; it next loses its sphe- roidal form and becomes somewhat pear-shaped, with the smaller end directed dorsally. The smaller end rapidly elongates into a club-shaped diverticulum, the recessus endolymphaticus, which later becomes the ductus and the saccus endolymphaticus. The remainder of the otic sac soon exhibits a subdivision into a larger dilatation, the vestibular pouch, and a smaller ventral one, the cochlcar pouch (Fig. 1297). 77\ Dorsal aorta Oropharynx r visceral furrow I visceral arch Frontal section of early rabbit embryo, showing otic pits. X 40. 1524 HUMAN ANATOMY. FIG. 1277. Hind-brain Otic sac The semicircular canals differentiate from three folds which grow from the vestibulat pouch opposite the attachment of the ductus endolymphaticus. The central parts of the two walls of each fold unite and undergo absorption, while the peripheral part of each fold remains open, thus forming a semicircular tube, one end of which becomes enlarged to form the ampulla. The superior vertical canal appears first, and the horizontal or external last. The growth of the epithelial diverticula is later accompanied by a condensation of the surrounding mesoblast, which differentiates into an external layer, the future cartilaginous and later bony capsule ; a layer internal to this becomes the perichondrium and later periosteum. A second mesoblastic layer is formed from the cells immediately surrounding the otic vesicle, whilst the space between these fibrous layers is filled by a semi-gelatinous substance which later gives place to the perilymph occupying the perilymphatic space. Within the ampullae, which early develop, the epithelial lining undergoes specialization, accompanied by thickening of the meso- blastic wall within circumscribed areas, to form the cristae acusticae. Coincidently with the development of the semicircular canals, a diverticulum, the cochlear canal, appears at the lower anterior end of the membranous sac. This tube, oval in section, grows forward, downward, and inward, and represents the future cochlear duct. After attaining considerable length, further elongation is accompanied by coiling and the assumption of the permanent disposition of the tube. The epithelium of the cochlear tube early exhibits a distinction, the cells of the upper surface of the somewhat flattened canal becoming attenuated, whilst those on the lower wall undergo thickening and further differentiation. The flattened cells form the epithelial covering of Reissner's membrane and of the outer wall, and the taller elements are converted into the complicated structures of the tympanic wall of the ductus cochlearis, including the crista, the sulcus, and the organ of Corti. The development of these structures includes the differentiation of two epithelial ridges ; from the inner and larger of these is derived the lining of the sulcus spiralis and the overhanging membrana tectoria. The outer ridge is made up of six rows of cells, the inner row becoming the inner hair-cells, the outer three rows becoming the outer hair-cells, whilst the two rows between these two groups form the rods of Corti. The crista appears between the sulcal cells and the cochlear axis as a thickening of the spiral lamina. The cochlear outgrowth of the primary otic vesicle forms the membranous cochlea, or scala media, alone, the walls of the adjacent divisions, the scala vestibuli and scala tympani, resulting from the changes within the surrounding mesoblast. The latter differentiates into two zones, an outer, which becomes the cartilaginous, and finally osseous, capsule, and an inner, lying immediately around the membranous canal, which for a time constitutes a stratum of deli- cate connective tissue between the denser capsule and the ectoblastic canal. Within this layer clefts appear, which gradually extend until two large spaces bound the membranous cochlea above and below. These spaces, the scala vestibuli and the scala tympani, are separated for a time from the scala media by a robust septum consisting of a mesoblastic layer of considerable thickness and the wall of the ectoblastic tube. With the further increase in the dimensions of the lymph- spaces, the partitions separating them from the cochlear duct are correspondingly reduced, until, finally, the once broad layers are represented by frail and attenuated structures, the membrane of Reissner and the basilar membrane, which consequently include an ectoblastic stratum, the epithelial layer, strengthened by a mesoblastic lamina, represented by the sub- stantia propria and its endothelioid covering. The main sac of the otic vesicle from which the foregoing diverticula arise constitutes the primitive membranous vestibule, and later subdivides into the sarcule and utricle. This separa- tion begins as an annular constriction of the primitive vestibule, incompletely dividing the vesicle into two compartments. The still relatively large ductus endolymphaticus, the direct successor of the recessus endolymphaticus, unites with tlu- narrow canal connecting these vesicles in such a manner that each space receives one of a pair of converging limbs, an arrangement foreshad- owing the permanent relations of the parts. Even before tin- subdivision of the primitive vestibule is established, the vestibular end of the cochlear canal becomes constricted, so that communication between this tube and the future saccule is maintained by only a narrow passage, later the canalis reunions. The devel- opment of the macula; acusticae of the saccule and utricle depends upon the specialization ot Part of frontal section of head of rabbit embryo ; otic sac is separated from ectoblast and beginning to elongate. X 40. ! DEVELOPMENT OF THE EAR. 1525 Wall of braiii-vesicle- Endolymphatic recess Vestibular pouch -Cochlear pouch Otic vesicle shows differentiation into three subdivisions, endo- , lymphatic, vestibular and cochlear. X 40. the epithelium within certain areas associated with the distribution of the auditory nerves. The nerve-fibres form their ultimate relations with the sensory areas by secondary growth into the epithelial structures. Development of the Auditory Nerves. The vestibular and cochlear nerves, according to Streeter 1 , develop from a ganglion-mass first seen at the anterior edge of the otic vesicle. This consists of an upper and lower part from the dorsal and ventral portion p IG 1278. of which peripheral nerve branches are developed, whilst a single stem connects it with the brain. The nerves destined for the utricle and the superior and external ampullae develop from the upper part of the ganglionic mass, while the nerves which supply the saccule and posterior ampulla develop from the lower part of this mass. The stem extending centrally from the ganglion toward the brain becomes the vestibular nerve. The spiral ganglion begins its development at the ventral border of the lower part of this mass, the cochlear nerve growing toward the brain while the peripheral division containing the ganglion extends into the membranous cochlea. From the foregoing sketch, it is evident that the membranous labyrinth is genetically the oldest part of the internal ear, and that it is, in fact, only the greatly modified and specialized closed otic vesicle surrounded by secondary mesoblastic tissues and spaces. Development of the FIG. 1279. Middle Ear. The tympanic cavity and the Eustachian tube are formed essentially by the backward prolonga- tion and secondary expansion of the inner entoblastic por- tion of the first branchial fur- row, the pharyngeal pouch. The dorsal part of the latter, in conjunction with the adja- cent part of the primitive pharynx, gives rise to the sec- ondary htbo-tympanic space (Fuchs); the posterior end of this becomes dilated to form the tympanic cavity, while the segment interven- ing between the tympanic diverticulum and the pharynx is converted into the Eusta- chian tube. The first and second branchial arches con- tribute the roof of the tym- panic cavity. The ear ossicles are de- veloped in connection with the primitive skeleton of the visceral arches. The malleus Endolymphatic duct Wall of brain- vesicle Canalicular recess Utriculo- saccular pouch t Surface Cochlear duct Further differentiation of otic vesicle into endolymphatic duct, utriculo- saccular pouch and cochlear duct. and incus represent specialized parts of the cartilaginous rod of the first arch, the tensor tym- pani being developed from the muscular tissue of the same arch. The stapes is developed from the second arch. The mesoblast which surrounds the structures of the tympanic cavity during their development becomes spongy and finally degenerates toward the end of fcetal life. 1 Amer. Jour, of Anatomy, Vol. VI., 1907. 1526 HUMAN ANATOMY. The air-cells of the temporal bone, including those of the mastoid process, are formed later by a process of absorption. The tympanic membrane results principally from changes which take place in the first branchial arch ; it is originally thick and consists of a mesoblastic middle stratum, covered on its outer surface by the ectoblast and on its inner surface by the entoblast. Development of the External Ear. The median portion of the ectoblastic groove of the first branchial furrow becomes deepened to form the outer part of the external auditory canal, Fie. 1280. sac.rnaolyfriph. ^ 10 vwEEKS f . Diagram illustrating development of human membranous cochlea ; primary otic vesicle subdivides into vestibular and cochlear pouches and endolymphatic appendage; cochlear pouch becomes duct us cochlearis ; from vestibular pouch are derived utricle, saccule and semicircular canals ; whilst endolymphatic appendage gives rise to endo- lymphatic sac and duct. (Streeter. ) while the surrounding parts of the first and second arches develop into the auricle. About the fourth week of foetal life, the thickened posterior margin of the first arch is broken up into three tubercles "by two transverse furrows. Similarly on the adjoining margin of the second arch, a second vertical row of three tubercles is formed and, in addition, behind these a longitudinal groove appears marking off a posterior ridge. From these six tubercles and the ridge are differ- entiated the various parts of the auricle, the lowest nodule of the first arch becoming the tragns, the remaining ones with the ridge giving rise to the helix, whilst from the three ventricles of the second arch are developed, from above downward, the antihelix, the antilragiis and the lobule. THE GASTRO-PULMONARY SYSTEM. GENERAL CONSIDERATIONS. THE food-stuffs required to compensate the continual loss occasioned by the tissue-changes within the body are temporarily stored within the digestive tube. During this sojourn the food is subjected to the digestive processes whereby the sub- stances suitable for the nutritive needs of the animal are separated by absorption from the superfluous materials which, sooner or later, are cast out as excreta. Closely associated with digestion, and in a sense complementary to it, is the respiratory func- tion by which the supply of oxygen is assured. In the lowest vertebrates these two life-needs, food and oxygen, are obtained from the water in which the animal lives, this medium containing both nutritive materials and the air required for the perform- ance of the respiratory interchange of gases (oxygen and carbon dioxide). FIG. 1281. Wolffian body Spleen / Notochord Neural canal ^ J ^ Oral cavity Pharyngeal / I * ^ Cloacal orifice pouches Heart Luilgs c U Stomach Pancreas Hind-gut Sagittal section of schematic vertebrate (Modified from Fleischntann.) Since, therefore, in these animals both food and oxygen are secured from the same source, the water, the digestive and respiratory organs form parts of a single gastro-pulmonary apparatus. This close relation is seen in the lower vertebrates (fishes), in which the anterior segment of the digestive tube is connected on either side with a series of pouches and apertures, the branchial clefts, bordered by the vascular gill-fringes by means of which the blood-stream is brought into intimate relation with the air-containing water. When the latter element is forsaken as a permanent habitat and the animal becomes terrestrial, a more highly specialized apparatus, suited for aerial respiration, becomes necessary. This need results in the development of the lungs. The latter, however, retain the intimate primary relation to the digestive tract, and are formed as direct ventral outgrowths from the gut-tube. The vertebrate digestive tract early becomes differentiated into three divisions : fore-gut, mid-grit, and hind-gut. The first includes the mouth, pharynx, cesopha- gus, and stomach, and serves for the mechanical and chemical preparation of the food materials. The second comprises the longer or shorter, more or less convoluted small intestine, and forms the segment in which absorption of the nutritive materials chiefly takes place. The third embraces the large intestine, and contains the super- fluous remains of the ingested materials which are discarded from the body at the 1527 I 5 28 HUMAN ANATOMY. anal opening. Associated with the mid-gut are two important glands, the liver and the pancreas. Greater complexity in the character of the food and in the manner of securing it necessitates increased specialization in the first segment of the digestive tube ; hence the addition of accessory organs, as the lips, oral glands, tongue, and teeth, the latter often serving as prehensile as well as masticatory organs. Reference to the early relations of the embryo to the vitelline sac (page 32) recalls the important fact that the greater part of the gut-tract is formed by the con- striction and separation of a portion of the yolk-sac by the approximation and closure of two ventral folds, the splanchnopleura. Since the latter consists of two layers, the entoblast and the visceral lamina of the mesoblast, the tube resulting from the union of the splanchnopleuric folds possesses a lining directly derived from the inner germ- layer, supplemented externally by mesoblast. The latter contributes the connective tissue, muscular and vascular constituents of the digestive tube, while the epithelium and the associated glandular elements are the products of the entoblast. MUCOUS MEMBRANES. The apertures of the digestive, respiratory, and genito-urinary tracts mark loca- tions at which the integument becomes continuous with the walls of cavities and passages communicating with the exterior. The linings of such spaces constitute FIG. 1282. S_Epithelium ^_Papilla of tunica propria occu- pied by blood- vessels p Connective- t issue stroma Section of oral mucous membrane. X 350. mucous membranes. The latter, however, not only form the free surface of th chief tracts, but also that of the ducts and tubes continued into the glands which ar developed as outgrowths from the mucous membranes. Temporarily in the higher types and permanently in such of the lower animals as possess a common cloacal space, all the mucous membranes of the body are con- tinuous. After acquiring the definitive arrangement whereby the uro-genital tract becomes separated from the digestive tube, these membranes in man and mammals (except monotremata) form two great tracts, the gastro-pulmonary and the genito- urinary. The free surfaces of the mucous membranes are kept continually moist by a viscid, somewhat tenacious secretion, the mucus, derived from the glands ; they are thus protected from the drying and irritating influences of the air, foreign substances, and secreted or excreted matters with which they are brought into contact. Structure. Every mucous membrane comprises two distinct parts : the epi- thelium, which forms the immediate free surface and furnishes protection for the more delicate tissues beneath ; and the tunica propria, a connective-tissue layer which constitutes the stroma and gives place and support to the terminal branches of the MUCOUS MEMBRANES. 1529 FIG. 1283. -Epithelium nerves and the blood-vessels and the beginnings of the lymph-radicles. Thus it will be seen that the general structure of a mucous membrane corresponds closely with that of the integument, the protecting epidermis of the latter being represented by the epithelium of the former, while both the corium and the tunica propria include the connective-tissue basis over which the epithelial layer stretches. A stratum of sub mucous tissue, corresponding with the subcutaneous layer in the skin, connects the mucous membrane with the surrounding structures. The epithelium may be squamous or columnar, simple or stratified. Its char- acter is usually determined by the conditions to which it is subjected ; thus, where covering surfaces exposed to mechanical influences of foreign bodies, it is commonly stratified squamous, as in the upper part of the digestive tract. Where, on the other hand, the mucous membrane is concerned in facilitating absorption, as in the intestinal tube, the epithelium is simple columnar in type. In localities in which the existence of a current favors the function of an organ, either as a means of freeing the surface from secretion or particles of foreign matter, as in the respiratory tract, or of propul- sion through a tube, as in the epididymis or the oviduct, the epithelium is of the ciliated columnar variety. Modifications of the epithelial cells, due to the presence of pigment or of secretion, distinguish certain mucous membranes, as those clothing the olfactory region and the large intestine respectively. The tunica propria or stroma consists of interlacing bundles of fibre-elastic tissue which support spindle or stellate connective-tissue cells. The latter usually lie within the uncertain clefts between the stroma bundles, which may be re- garded as lymph-spaces. In many localities the surface of the tunica propria is beset with numerous ele- vations or papilla:, over which the epithelium extends. Such irregu- larities, when slight, may not modify the free surface of the mucous mem- brane, since the epithelial layer com- pletely fills the depressions between the elevations ; when more pro- nounced, the papillae or folds of the connective tissue produce the con- spicuous modelling of the surface seen in the papillae of the tongue or the rugae of the vagina. The papillae contain the terminal loops of the blood-vessels and the nerves supplying the mucous membrane. Where especially concerned in ab- sorption, the mucous membranes often gain increase of surface by cylindrical eleva- tions, or villi, as conspicuously seen in the small intestine. These projections, consisting of the stroma covered by epithelium, contain the absorbent vessels, or lacteals, in addition to the blood-capillaries. A more or less well-defined line separates the epithelium from the subjacent tunica propria. This demarcation is the basement membrane, or membrana propria, a detail which has been variously interpreted. Usually the basement membrane appears as a mere line beneath the epithelium, and is then, probably, formed by the apposition of the basal processes of the epithelial cells. When surrounding glandular tissue it is better developed, presenting a distinct and much more robust structure. In these positions the basement membrane is probably a product of the tunica propria and occurs in two types, sometimes being homogeneous, at other times reticular (Flint 1 ). In many localities the deepest part of the mucous membrane, next the submu- cous tissue, is occupied by a narrow layer of involuntary muscle, the muscularis mucosce. While not everywhere present, it is especially well developed in the intes- tinal tract from the gullet to the anus, and in places consists of two distinct layers, 1 American Journal of Anatomy, vol. ii., No. i, 1902. Section of mucous membrane of oesophagus. X 55. 1530 HUMAN ANATOMY. a circular and a longitudinal. The inner surface of the stratum is often broken by processes of muscular tissue which penetrate the tunica propria well towards the epithelium. The muscularis mucosae belongs to the mucous membrane, and there- fore must be distinguished from the muscular coat proper, which is frequently a conspicuous additional layer in the digestive tract. Mucous membranes are attached to the surrounding structures by a submucous layer of areolar tissue. The latter varies in thickness and density, consequently the firmness of the union between the mucous and submucous strata differs greatly in various localities. Usually the attachment is loose, and readily permits changes in position and tension of the mucosa, which, in the relaxed condition, is often thrown into temporary folds or rug&, as in the oesophagus and stomach. In other places the folds are permanent and not effaced by distention of the organ ; a conspicuous example of such arrangement is seen in the valvulae conniventes of the small intestine, in which the submucous tissue forms the basis of the elevation. The blood-vessels supplying mucous membranes reach the latter by way of the submucous tissue, in which the larger branches divide into the twigs which pass into FIG. 1284. gmHMK''' ' ' r r >s : ' "T"', *? ' ' *"--'- -\on-vascularepithelium :&* Terminal capillary loops _Tunica propria Larger branches within suhmucosa Section of injected oral mucous membrane. X 60. the mucosa. Within the deeper parts of the tunica propria the, smaller arterial branches break up into the capillaries forming the subepithelial and papillary net- works, the vascular loops being limited to the connective tissue stroma and never entering the epithelium. The venous stems usually follow the arteries in their gen- eral course. When glands are present, the capillaries surround the tubules or alveoli with rich net- works in close relation to the basement membrane. The lymphatics within mucous membranes are seldom present as definite chan- nels, since they begin as the uncertain interfascicular clefts between the bundles of stroma-tissue. Towards the deeper parts of the mucosa the lymph -paths become more definite, and exist as delicately walled varicose passages which converge towards the submucous tissue. Within the latter the lymph-vessels form net-works richly provided with valves and the accompanying dilatations. The nerves distributed to mucous membranes include cerebral or spinal and sympathetic branches, the latter supplying especially the involuntary muscle of the GLANDS. stroma and of the blood-vessels. Surfaces highly endowed with general and tactile sensibility are provided with a generous supply of twigs containing medullated fibres. As the latter pass towards their ultimate destination (for convenience assuming that all are peripherally directed) they lose their medullated character and, as naked axis- cylinders, form the siibepithelial plexuses, from which delicate filaments pass into the papillae, where they terminate either as free club-shaped or special sensory endings. It is probable that in places the nerves penetrate between the epithelial cells forming the layers next the basement epithelium and terminate in varicose free endings. GLANDS. Certain of the epithelial cells lining the mucous membranes of the body become modified to assume the role of secretion-forming organs or glands, the products of which are poured out upon the free surface and keep the latter moist. The latter purpose is secondary in the case of many important glands, as the parotid, pancreas/ FIG. 1285. Diagram showing types of glands, a-e, tubular; f-i, alveolar or saccular. a, simple; 6, coiled; c-d, increasingly complex compound tubular; e, tubo-alveolar ; f, simple ; g-h-i, progressively complex compound alveolar. or liver, since these organs supply special secretions for particular ends. Aggrega- tions of the secreting elements vary greatly in size, form, and arrangement, as well as in the character of their products. The simplest type is the unicellular gland found in the lower forms; in principle this is represented in man and the higher animals by the goblet-cells seen in pro- fusion in mucous membranes covered with columnar epithelium. The secretion poured out by these goblet-cells serves to protect and lubricate the surface of the mucous membranes in which they occur. The term "gland," however, usually implies a more highly developed organ composed of a collection of secreting epithe- lial elements. Glands are classified according to their form into two chief groups, the tubular and the alveolar, each of which occurs as simple or compound. It should be empha- sized that in many instances no sharp distinction between these conventional groups 1532 HUMAN ANATOMY. FIG. 1286. Opening on mucous membrane Excretory duct exists, some important glands, as the salivary, being in 'fact a blending of the two types ; such glands are, therefore, appropriately termed tubo-alveolar. In the least complex type, the simple tubular, the gland consists of a cylindrical depression lined by epithelium directly continuous with that covering the adjacent sur- face of the mucous membrane, as an outgrowth of which the gland originally devel- oped. In such simple gland the two fundamental parts, \hafundus and the duct, are seen in their primary type. The fundus includes the deeper portion of the gland in which the epithelium has assumed the secretory function, the cells becoming larger and more spherical in form, while in structure the distinction between the spongioplasm and hyaloplasm is usually marked in consequence of the particles of secretion stored up within the meshes of the spongioplastic net-work, which is often sharply displayed. The duct connects the fundus with the free surface and carries off the products elabo- rated within the gland. It is lined with cells which take no part in secretion and hence retain for some distance the character of the adjacent surface epithelium. Dilatation of the fundus of the primitive type produces the simple alveolar or saccular gland ; division of the fundus and part of the duct gives rise to the compound tubu- lar variety ; repeated cleavage and subdivi- sion of the duct, with moderate expansion of the associated terminal tracts, lead to the production of the tubo-alveolar type. Simple tubular glands may be minute cylindrical depressions of practi- cally uniform diameter, as the crypts of Lieberkuhn in the intestine, or they may be somewhat wavy and slightly expanded at the fundus, as often seen in the gastric glands towards the cardiac end of the stomach. When the torsion becomes very pronounced, as in the sweat-glands, the coiled variety results. Compound tubular glands pre- sent all degrees of complexity, from a simple bifurcation of the fundus and ad- jacent part of the duct, as in the pyloric or uterine glands, to the elaborate duct- system ending in terminal divisions either of a tubular form, as in the kidney and tes- ticle, or of a modified, somewhat dilated, alveolar form, the tubo-alveolar type, as in the salivary glands. Tubo-alveolar glands, modified compound tubular, constitute a verv im- Diagram showing relations of various portions of duct- ,_, system in glands of tubo-alveolar type. portant group, since they embrace many of the chief secretory organs of the body. They are made up by repetition of similar structural units, differences in the size of the organ depending upon the number of those associated to compose the gland. These units correspond to the groups of terminal compartments, or alveoli, con- nected with a single ultimate division of the duct-system. The alveoli or acini contain the secreting cells, and are limited externally by a basement membrane, often well developed, which supports the glandular epithelium and separates the latter from the blood- and lymph-vessels that surround the acinus. The alveoli belonging to the same excretory duct, held together by delicate connective tissue, constitute a pyramidal mass of glandular tissue, \ht primary lobules. The latter are assembled into larger groups, or secondary lobules, which in turn are united by interlobular connective tissue into the lobes composing the entire gland. The lobes are held together more or less firmly by the interlobar areolar tissue continuous with the general fibrous envelope, which forms a capsule for the entire organ and separates it from the surrounding structures. Beginning of uct in alveoli 'erminal alveolus GLANDS. 1533 The interlobar tissue and its interlobular continuations contain the blood-vessels, lymphatics, and nerves supplying the gland and, in addition, the major portion of the excretory ducts. In the larger glands the latter form an elaborate system of pas- sages arranged after the general plan shown in -the accompanying diagram (Fig. 1285). Traced from the terminal compartments, or alveoli, of the gland, the duct- system begins as a narrow canal, the intermediate dud, lined by low cuboidal or flat- tened cells directly continuous with the glandular epithelium of the alveoli. After a short course the tube increases in diameter and becomes the intralobular duct, which is often conspicuous on account of its tall and sometimes striated or rod-epithelium. The further path of the excretory tubules lies within the connective tissue separating the divisions of the glandular substance, and embraces the interlobular and the inter- lobar ducts, the latter joining to form a single main excretory duct which opens upon the free surface of the mucous membrane. The last-named passage is lined for some distance by cells resembling those covering the adjacent mucous membrane ; where these are stratified squamous in type, this character is maintained for only a limited FIG. 1287. i & - ;i i % v '' : ' " / '. - Wl,,;r :-'-,. ^w/- J^i'i^ ; / "^ '^si'' >i I / : ,- \ ;'" ' .-V 1 ^.^'':':" " '. \ _: --:/ . v .. -.' \ v lfit$'' ; '^''~ '' J ^'' Serous alveoli Section of posterior part of tongue, showing alveoli of serous and mucous types of glands. X 60. extent, before the interlobar ducts are reached gradually giving place to a simple, sometimes at first double, layer of columnar epithelium which extends as far as the intralobular tubules. The walls of the larger ducts consist of a fibro-elastic coat, lined by epithelium, and sometimes, in the case of the large glands, as the parotid, liver, pancreas, or testicle, are strengthened externally by a layer of involuntary muscle. In the case of the large ducts the latter is usually disposed as a transverse and longi-' tudinal layer, to which, as in the hepatic duct (Hendrickson), a third oblique one may be added. Differential stains show the presence of a large amount of elastica. The glandular epithelium lining the alveoli rests upon the limiting basement membrane as a single layer of irregularly spherical or polygonal secreting cells ; these do not completely fill the alveolus, but leave an intercellular cleft into which the product of the cells is poured and in which the system of excretory ducts begins. Depending upon the peculiarities of the cells and the character of their secretion, glands are divided into serous and mucous. 1534 HUMAN ANATOMY. FIG. 1288. The serous glands are distinguished by cells which are distinctly granular, generally pyramidal in form, with nuclei situated in the vicinity of the centre. The secretion elaborated by such glands is thin and watery. The general appearance- < >f the cells depends upon the number and size of the granules stored within their cyto- plasm, and changes markedly with the variations of functional activity of the gland. When a serous gland is in a condition of rest, the cells are loaded with secretion, and appear, therefore, larger and coarsely granular. After active secretion, on the contrary, the cells are exhausted and smaller and contain little of their product, often exhibiting differentiation into a clear outer zone, free from granules, and a darker inner zone, next the lumen, in which the granules still remain. The mucous glands elaborate a clear, viscid, homogeneous secretion, which, when present in considerable quantity, as during rest, distends the cells, crowding the nuclei to the periphery against the basement membrane, and gives to the glandu- lar epithelium a clear and transparent appearance in marked contrast to the granular character of the elements of a serous gland. During rest, when loaded and distended with mucoid secretion, the transparent cells possess well-defined outlines, and present a nar- row peripheral zone con- taining the displaced nuclei and granular protoplasm. After prolonged activity the exhausted cells contain rela- tively little mucoid secre- tion, and hence the threads of spongioplasm are no longer widely separated, but lie closely ; in consequence of these changes the cells lose their former transpar- ency and resemble the elements of serous glands, becoming smaller, darker, and more granular than the cells of the quiescent mucous gland The alveoli of mucous glands often contain small crescentic groups of small granular cells lying between the usual larger clear ele- ments and the basement membrane ; these are the crescents of Gianurjzi, or demilunes of fJcidenhain, the interpretation of which has caused much discussion. The older view regarded the crescents as groups of cells differing from the surrounding ones only in their stage of activity and not in their essential characters, all the cells within the alveolus being of the same nature. Tin- opposite view, advanced by Ebner over a quarter of a century ago, has received sup- port from more recent critical studies by Kuchenmeister, Solger, Oppel, R. Krause, and others, who have shown that the cells composing the crescents differ from the mucus-containing elements, elaborate a special secretion, and are similar to, if not identical with, those tilling the alveoli of serous glands. According to these observers, the crescents are groups of serous cells compressed and displaced by the predomi- nating mucous elements, but not excluded from the lumen of the alveolus, as was Demilune of serous cells Duct Mucous cells V Demilune Section of human sublingual gland, showing serous cells arranged as demi- lunes. X 300. GLANDS. 1535 formerly thought to be the case, since extensions of the lumen pass between the mucous cells to reach the demilunes. In addition to the main alveolar lumina, always narrow in serous and wider in mucous acini, the existence of intercellular passages, or secretion-capillaries, has been established for many glands, especially by the employment of the Golgi and other special methods. These clefts penetrate laterally be- tween the glandular epithelium from the axial lumen 1289. towards the basement membrane, partially enclosing the secreting cells with a branching system of minute canals. Alveoli containing exclusively mucous cells do not possess these intercellular canaliculi, the axial lumen alone being present. In acini of the serous type the accessory channels are represented by minute branching passages which penetrate between the cells, but seldom reach the basement membrane. The most conspicuous of the secretion-capillaries occur in alve- oli containing the demilunes, the product of the serous cells escaping into the main lumen by means of the lateral intercellular canals which pass between the mucous elements to reach the peripheral group of Section of several alveoli of submax- serous cells composing the crescent. The view that |jg f^mi^Zriipsbfg the secretion -capillaries normally extend into the cyto- t crescentic (stippled) groups of serous , , 111 -11- i r cells - x 5o- (Retzms.) plasm of the glandular epithelium, and are, therefore, also intracellular, must be regarded as doubtful and still undecided, although sup- ported by many able histologists. Depending upon the distribution of the two varieties of alveoli, the tubo- alveolar glands may be divided into four groups (Ebner): 1. Pure serous glands, in which only serous alveoli occur, as the parotid. 2. Mixed serous glands, in which a few mucous alveoli are intermingled with the serous, as the submaxillary. 3. Mixed mucous glands, in which the serous cells occur as crescentic groups or demilunes, as the sublingual and buccal. 4. Pure mztcous glands, without serous alveoli or demilunes, as the palatal. Simple alveolar or saccular glands in their typical flask-like form, as seen in the skin of amphibians, are not found in man. The dilated spherical fundus is lined with clear and distended secreting cells, in which the nuclei are displaced towards the periphery by the mucus elaborated within the epithelial elements. In the higher animals this type of gland is represented, somewhat modified, by the simple sebaceous follicles. Compound alveolar or saccular glands constitute a group much less exten- sive than formerly supposed, since careful study of the form and arrangement of many organs, as the salivary glands, pancreas, etc. , has shown that these are more appro- priately regarded as tubo-alveolar than as branched saccular glands. The latter, however, still have representatives in the larger sebaceous and Meibomian glands. The most conspicuous example of the compound saccular or racemose type is the lung, which in its development and the arrangement of the air-tubes and the sac-like terminal compartments corresponds to this variety. The blood-vessels distributed to glands are always numerous, since secretory activity implies a generous blood-supply. In the case of the smaller and simpler glands, the capillaries within the mucosa form a mesh-work outside the basement membrane enclosing the glandular epithelium. The large compound glands are pro- vided with a vascular system which usually corresponds in its general arrangement to that of the excretory ducts, following the tracts of the interlobar and interlobular areolar tissue and its extensions between the groups of the alveoli. On reaching the individual acini, the capillaries form net-works which surround the basement mem- brane enclosing the alveoli, thus bringing the blood-current into close, but not direct, relation with the secreting cells, an arrangement favoring the selection by the proto- plasm of the particular substances required for the function of the gland. When the relation between the glandular epithelium and the capillaries is unusually intimate, 1536 HUMAN ANATOMY. as in the case of the liver, a distinct basement membrane is sometimes wanting, a delicate supporting reticulum alone intervening between the blood-stream and the protoplasm of the cells. Although subject to local deviations, conspicuously excep- tional in the liver, the veins follow in general the course of the arterial branches, the larger blood-vessels, together with the main excretory ducts, the lymphatics, and the nerves, occupying the principal extension of the connective tissue into the glandular mass. The lymphatics are represented by the larger trunks which follow the excretory ducts and freely anastomose within the interlobular areolar tissue. After the intra- lobular portion of the vessel is reached, its definite character is gradually lost until the lymphatic channels are to be recognized only as the clefts between the bundles of connective tissue separating the alveoli. FIG. 1290. FIG. 1291. Injected gastric mucous mem- brane, showing capillary net-work surrounding tubular glands. X 55- Section of submaxillary gland of rabbit ; upper half of figure shows distribution of nerve-fibres to alveoli ; lower half shows terminal ducts and secretion-capillaries. X 290. (Jfftsinx.t The nerves supplying the larger glands include fibres from two sources, the cranial or spinal nerves and the sympathetic. They follow the interlobular excretory ducts, around which plexuges are formed, ganglion-cells being frequent at the points of junction. The stronger twigs contain a preponderating proportion of thick medullated fibres, which become progressively less in size and number in their course towards the alveoli. Upon reaching the latter the nerves consist almost entirely of nonmedullated fibres, and in the end-plexuses around the alveoli such fibres alone are present. The terminal distribution, as demonstrated by the Golgi and methylene- blue methods, includes cfiilctnniar and hypolcmmar fibriUa:, the former lying upon and the latter beneath the basement membrane. The hypolemmar fibrillae pass into the acini from the extra alveolar plexus formed by the filaments surrounding the base- ment membrane. The ultimate relation between the terminal fibrillce and the glandu- lar epithelium is still uncertain, but it may be regarded as established that the nerves extend between and around the cells ; an intracellular termination, on the contrary, is doubtful. Retxius, Ebner, and others agree in picturing the delicate perialveolar plexus as consisting of tortuous and convoluted filaments which end in occasional GLANDS. 1537 FIG. 1292. delicate varicosities. Arnstein l has described a special minute plate-like end-organ as a widely occurring mode of nerve-ending in glands. W. Krause 2 has noted in certain glands a form of end-capsule resembling a simplified Pacinian corpuscle. The sympathetic fibres are distributed especially to the involuntary muscle of the blood- vessels and the ducts, the peristaltic wave within the muscular coat of the latter facili- tating emptying of the secretion. Development. Since glands are only extensions of the mucous membrane or integument upon which they open, their development begins as an outgrowth or budding from the epithelium covering such surfaces. In the simple tubular glands the minute cylinders are closely placed and composed of densely packed cells. In the case of the larger compound glands, as the salivary or pancreas, the first anlage consists of a solid cylindrical plug which, penetrating into the mesoblast, soon begins to branch. The ends of the terminal divisions enlarge and eventually become the alveoli. Meanwhile the sur- rounding mesoblast undergoes condensation and forms the interlobular and other septa, as well as the general envelope, or capsule, thereby giving definite form to the general glandular aggregation. The vascular and other structures usually found within the interparenchymatous tissue are secondary and later formations. The develop- ment of the gland involves a double process of active growth, not only the extension of the epithelial pro- cesses, but also a coincident invasion and subdivision of the latter by the mesoblast to form the constituent units of the organ. The lumen of the gland appears first in the main excretory duct, from which it extends into the secondary tubes and, finally, into the alveoli. Growth, separation, and more regular arrangement of the cells composing the epithelial cylinders are the chief factors in producing the lumen. In the early condition of the glands, before the assumption of functional activity, the cells later constituting alveoli of the serous or mucous type are similar and without histological distinction. Upon the establishment of their different roles, however, the characteristics distinguishing the varieties of glands appear, the differences de- pending upon physiological rather than upon inherent anatomical variation. 1 Anatom. Anzeiger, Bd. x., 1895. 2 Zeitschrift f. rational. Med., Bd. xxiii., 1865. Section of foetal oral mucous membrane, showing developing tubo-alveolar gland. X 50. 97 THE ALIMENTARY CANAL THIS is a long and complicated tube extending from the mouth to the anus. Excepting the two ends, each of which is at first a pouch from the ectoblast, it is developed from the entoblast with a mesoblastic envelope. It consists of the month, pharynx, and oesophagus above the diaphragm, and of the stomach and small and large intestines below it. There are many accessory organs connected with it whose primary function is to assist in the process of nutrition. The chief ones above the diaphragm are the teeth, the tongue, and the salivary glands ; those below it are glands of various kinds, mostly so small as to be contained in the mucous membrane. But two distinct organs, the liver and the pancreas, belong to this class, both being originally outgrowths from the gut. The trachea and lungs have a similar origin, but their physiological function is so different that they are treated of under a separate heading. The general structural plan of the digestive tube, presenting in places great mod- ifications, is : (i) a lining of mucous membrane ; (2) a submucous layer of areolar tissue, into which glands may penetrate from the former ; (3) a double layer of non- striped muscular fibres, of which, as a rule, the inner is circular and the outer longi- tudinal ; (4) below the diaphragm, a serous covering from the peritoneum, which, although originally complete, is in the adult wanting in certain parts. The length of the alimentary canal is, on the average, not far from 9 m. (ap- proximately 30 ft.), of which not more than 45 cm. (about 18 in.) is above the diaphragm. A preliminary sketch of the divisions above the diaphragm may be con- venient. The vestibule of the mouth is the space between the lips and cheeks exter- nally and the jaws and teeth internally. The (potential) cavity of the mouth is within the arches of the gums and teeth. It is bounded above by the hard palate and its backward continuation the soft palate. The greater part of the floor is occupied by the tongue. There is a free horseshoe-shaped space beneath the tongue within the lower jaw, called the alveolar-lingual groove or, better, the sublingual space. The pharynx joins the mouth at the anterior pillar of the fauces, a fold passing outward and downward to the tongue from the soft palate. The pharynx extends from the base of the skull to the lower border of the larynx. The upper part, the naso- pharynx, is behind the nasal chambers which open into it, the oro-pharynx is behind the mouth, and the laryngo- pharynx behind the larynx. At the lower border of the larynx it is followed by the oesophagus, a long tube which, piercing the diaphragm, opens into the stomach. THE MOUTH. The framework of the mouth is made by the hard palate and the alveolar processes of the upper jaw, by the greater part of the body (including the alveolar processes) of the lower jaw and part of the ramus, and by the hyoid bone, to which may be added the mylo-hyoid muscle forming the floor. When the lips are opened and the lower jaw dropped, the mouth is a true cavity extending to the pharynx ; when these parts are closed, the tongue fills practically the whole space. It is convenient, however, to speak of the cavity of the mouth. This space is subdivided into the vestibule or preoral cavity and that of the oral cavity or mouth proper. The former is the region between the closed lips and cheeks in front and the closed jaws and teeth behind. When the lips are closed, it communicates with the mouth proper only by a small passage behind the wisdom-teeth, in front of the ramus of the jaw. THE LIPS, CHEEKS, AND VESTIBULE. The orifice of the mouth (rima oris) is a transverse slit of variable length, bounded by projecting folds, the lips. These, like the checks, with which they arc continuous, are composed of complicated layers of muscle, covered externally by skin ami internally by mucous membrane. 1538 THE LIPS, CHEEKS, AND VESTIBULE. 1539 Fat is found irregularly disposed among the muscles of the cheeks in varying quantity, but in the depression in front of the masseter and superficial to the buccinator there is a distinct ball of fat enclosed by a capsule, which is the remnant of the so- FIG. 1293. Frontal sinu Orbicularis oris Sphenoidal sinus Sphenoid Pharyngeal tonsil .Orifice of Eustachian tube Soft palate Atlas Genio-glossus Genio-hyoid Epiglottis Mylo-hyoi Hyoid bone Sagittal section of head of young adult, three-fourths natural size. called " button" of infancy, a collection which gives resistance to the cheek and pre- vents it from being flattened by atmospheric pressure during nursing. The mucous membrane is reflected from the cheeks onto the jaws, where it covers the gums. This line of reflection at the middle of the lower jaw is 7 or 8 mm. from the alveolar 154 HUMAN ANATOMY. border and about twice as far from it in the upper. In both jaws, but especially in the lower, the line approaches the teeth as it passes backward. There is a distinct fold or frenum of mucous membrane passing from the anterior nasal spine to the middle of the upper lip. The free edge is often irregular, and may have a nodular enlargement. A much smaller fold is often found on each side in the region of the bicuspids. A median fold to the lower lip is small and inconstant. Externally the lips present a red region of modified mucous membrane, intermediate between the skin of the face and the mucous membrane of the mouth. A sagittal section through either lip shows these three parts. In the new-born the intermediate ' part is subdivided into two, of which the inner rather the broader more closely resem- bles true mucous membrane than the latter. After death in the young child it assumes a brownish color, which has been mistaken for the effect of acid. In the adult these two subdivisions lose their distinctness. The lower lip is the larger and FIG. 1294. ^^f Ul.lf, UMl " . / / Sublingual glan Facial artery _i_ Mandible V Mylo-hyoid Platysma Anterior belly of digastric Genio-hyoid Genio-glossus Frontal section, showing oral cavity and lower part of nasal fossae ; plane of section passes through anterior end of zygoma. Three-fourths natural size. 1 fuller, showing more red except towards the angles of the mouth, where it disap- pears. Its lower border is slightly indented in the middle. The upper lip shows a more marked indentation below a little gutter, the philtrum, running down from the nasal septum. A slight median prominence of the lower edge of the upper lip is the tubercle, which interrupts the straightness of the cleft when the lips are closed, making the line resemble a Cupid's bow. The muscles of the lips are a complicated interlacement from many sources. The orbicularis oris, formerly supposed to form a sphincter, has no separate exist- ence. The general plan is as follows. The upper fibres of the buccinator enter the lower lip and pass out at the opposite angle to ascend into the upper part of the other buccinator. Those of the lower part traverse the upper lip in a similar manner. The layer formed by the buccinator lies under the mucous membrane near the border of the lips, and bends forward so that its edge is nearest the skin at about its junction 1 Otto Neustatter : Ueber den Lippensaum, etc., Inaug. Dissert., Munich, 1894. THE LIPS, CHEEKS, AND VESTIBULE. FIG. 1295. with the free red surface. In the lower lip the quadratics (depressor labii inferioris) runs upward under the skin to. break up into fibres ending in the lips. The tri- angularis (depressor anguli oris) passes at the angle of the mouth into the upper lip and ends as a series of separate fibres inserted into the mucous membrane, many of them crossing the middle line. This muscle, before it breaks up, is in the same plane as the buccinator, but farther from the edge of the lips. Some German au- thors, by grouping together the various muscles of the upper lip, have made a siiperior quadratics and triangularis which are disposed in a similar manner .to the lower ones. Besides these there are two muscles, the zygomaticus, de- scending, and the risorius, ascending, which meet at the oral angles and end -there in the skin or mucous membrane, or in both. There are also numerous fibres, seen only with the microscope in sagittal sections, passing from the skin to the mucous membrane ; these consti- tute the rectus. 1 Philtrum Tubercle Labial region, from life, reduced one-fifth. FlG. 1296. - , |w ( Hi Labial glands Fibres of orbicularis-iiiti V^ Transition into true mucous membrane Modified mucous membrane Integument Sebaceous gland Transition into modified skin Sagittal section of lip of young child. X 20. The mucous membrane, which is smooth, is so closely attached to the muscles that it follows the movements of the latter. Mucous glands are lodged in its 1 Aeby : Archiv f. mikro. Anat. , Bd. xvi., 1879. 1542 HUMAN ANATOMY. deeper parts and in the scanty submucous tissue. They are named labial, buccal, and molar, according to their situation. The labial glands are gathered into a series of groups near the inner border of the lips, the buccal glands are smaller and scattered, and the molar glands are well-defined groups opposite the molar teeth. The duct of the parotid gland (y.v.) opens into the vestibule, the space between the lips and cheeks externally, and the teeth and alveolar processes internally. Separating the vestibular space from that of the mouth proper behind the alveolar processes is a prominent fold of mucous membrane over the pterygo-maxillary ligament. This fold appears at the inner side of the last upper molar and runs downward and outward to that of the lower. The space behind the teeth when the mouth is closed is small, but a tube some 5 mm. in diameter can be passed through it. Vessels. The arteries supplying the lips, which are very vascular, are chiefly the coronary branches of the facial arteries, each of which forms an arch meeting its fellow in each lip. The vessel lies between the muscles and the glands of the mucous membrane, nearly opposite the line of junction of the latter and the intermediate por- tion. The pulsation is easily felt through the mucous membrane. The veins, less regular, lie on the outer side of the muscles. The lymphatics empty into the glands at the angle of the jaw, excepting those near the median line of the lower lip, which run into the suprahyoid glands. Nerves. The mucous membrane of the cheek is supplied by the buccal branch of the inferior maxillary division of the fifth cranial nerve, the lips by the terminal branches of its second and third divisions. THE TEETH. In form the teeth present three parts, the body or crown, coated with enamel ; a somewhat constricted part, the neck, covered by the gums ; and the root or fang, which, covered by the cementum, is fixed in the socket. The greater part of the tooth is composed of the dentine and surrounds the pulp-cavity, to which minute openings in the root or roots transmit vessels and nerves. The shape of the crowns is the basis of classification. Thus, in the front teeth the crown is flattened so as to have a chisel-like shape, adapted to cutting, hence these are termed incisors ; the canine teeth have the crown forming a single point or cusp ; the bicuspids have two, and the multicuspids, or molars, several cusps. The crowns of all the teeth may be considered as modifications of a simple cone, or as combinations of several cones. 1 In man the teeth come in two sets, the temporary or milk and the permanent teeth ; the total number of the former is twenty, that of the latter thirty-two. The number and arrangement of the teeth of any animal is expressed in its dental formula ; this for man, for the left half of the mouth, may 'be written as follows : Temporary Teeth : i 2 c z i 2 (= 5 X 2 = 2oY a i 2 V 5 ) Permanent Teeth : / 2 c I tn ~ m 3 ( - X 2 = 32^. 2 i 2 3 \ 8 / It will thus be seen that in the milk-teeth there are no bicuspids and one molar less. Since the typical mammalian dental formula is i- C- bi- w v , it may be assum 3^43 that in man three pairs have been suppressed. These suppressed teeth are occasion ally represented by supernumerary ones ; from the position of the latter it is probable that the missing teeth are the second incisors and the first and fourth bicuspids. To avoid confusion in the nomenclature of the teeth from the curve of the jaws, it is customary to speak of the Ar/>/V?/ and //;/;> ual surfaces of the incisors and canines, ami of the facial, or bnccal, and lingual surfaces of the bicuspids and molars. The sides against the other teeth are often called tin- median and distal, supposing the teeth to be implanted in a straight transverse line. This is not satisfactory in all 'See Homologies, page 1566. THE TEETH. 1543 cases. We shall speak instead of the inner and outer sides of the incisors and canines and of the anterior and posterior sides of the bicuspids and molars. If the position of the tooth in the jaw be remembered, no confusion is possible. The Incisors. The crowns are characterized by slightly convex quadrilateral labial surfaces, rather broader than the lingual ones, and ending in straight cutting edges, slightly concave lingual surfaces slanting forward and bevelled at the edge, triangular lateral surfaces, and single roots. The labial and lingual surfaces of the crowns are bounded at the root by curved lines, the convexity being towards the gums. At the sides these borders are continued as straight lines towards the free FIG. 1297. Partly developed fangs of last molar, Crown of last molar Permanent teeth, showing their forms and relations; outer surface of jaws partly removed. Last molars are only partially formed. edge, and meet at an acute angle. The enamel is continued farther on the lingual surface, especially in the lateral incisors of both jaws. The cutting edge shows three small scallops on its first appearance, but they speedily wear away (Fig. 1298). The superior median incisors are much the largest. The labial surface of the crown is nearly square. The inner half of this surface is more strongly convex than the lateral. Traces of three swellings are often found on the labial side of the lower half of the crown extending to the three primitive scallops on the edge. The free edge meets the internal border at nearly a right angle, but the outer angle is rounded. The lingual surface, narrower than the labial, is a little concave. Some- times the edges are raised so as to leave a distinct V-shaped depression, in the middle of which runs a vertical ridge, the cingulum, which ends below in a tubercle. 1544 HUMAN ANATOMY. Often the cingulum of the incisors is represented merely by the tubercle. There are all kinds of intermediate stages between this and a nearly plane surface. Sometimes the tubercle is triple. The fang is nearly conical, and usually has an outward slant. The superior lateral incisors are more cusp-shaped, the angles, especially the outer, tending to be rounded. The lingual surface is less plane than in the median incisors and the cingulum larger. Sometimes it is almost a distinct cusp. The fang is also conical, with an outward inclination. The inferior incisors are smaller than the superior, and the median ones the smallest of all. The croivns broaden from the neck to the edge. This feature is more marked in the lower races, and still more in apes. The labial surface is more nearly plane than in the upper ones ; the lingual surface is more even. The cingulum is small, often not very evident. The angles of the free edge are sharper than those of the upper jaw, excepting the outer one of the lateral tooth, which is generally rounded. The fangs are compressed from side to side and their tips turn a little away from the median line. This is particularly true of the lateral one, but FIG. 1298. Unworn surfaces of upper and lower permanent incisor teeth, lingual aspect. X 2. Median incisor teeth of left side, labial (A) and lateral (B) aspects. (Letdy.) Temporary incisor teeth of left side. A, median ; B, lateral in- cisors. (Leidy.) The is a constant feature of neither. The sides of the fangs are often grooved, external groove is the deeper, and when only one is present it is on that side. The pulp-cavity is relatively large in the superior median incisors, in which it presents three expansions towards the free edge. It is smaller in the others, and has usually but two distinct diverticula. The canal of the lower teeth, especially when the roots are deeply grooved, often divides below the pulp-cavity into an anterior and a posterior branch, which usually reunite before reaching the tip of the fang. ' The upper incisors occupy in all more space than the lower, which is due chirfly to the great size of the upper median ones. In the lower jaw the median incisors are the smaller, but there is no great difference between them and the laterals. The superior laterals are but slightly larger than those below them. The temporary incisors differ only slightly, save in size, from the permanent ones. The edges, however, are originally straight, except those of the inferior median ones, which show the irregularities. 1 ' The Canines. These, called by the Germans the "corner teeth" as marking the point where the alveolar arch changes direction most suddenly, are characterized by a crown with a single cusp, a long conical root somewhat compressed laterally and marked by a groove on each side. The crown, convex on the labial side, expands 1 Miihlreiter : Anatomic des Menschlichen drbisses, I.Hp/ig, 1891. 1 Zuckerkandl : Anatomic der Mundhohle, mit besondere Beriicksichtigung der Zaline Wien, 1891. THE TEETH. 1545 FIG. Canine teeth of left side, labial (A) and lateral (ft) as- fects. C, temporary canines. Leidy.) from the root and suggests that of an incisor with the angles taken off. The lingual side of the crown of the upper tooth tends to be convex, often having a ridge running down to the small tubercle at the base. In the lower tooth this side is plane or con- cave, with a distinct tubercle, which exceptionally is enlarged so as to hint at a secondary cusp. The sides of the crown are triangular. The borders of the enamel are convex to the gum on the labial side, less so on the lingual, and slightly concave laterally. The _/# of the upper tooth is the longer and the less compressed ; it very rarely ends in a bifurcation, but this is less uncommon in the lower. The direction of the end of the fang is uncertain. The whole tooth is broader on the labial than on the lingual side. The pulp-cavity is most marked in antero-posterior sections, which show an en- largement of its continuation at the beginning of the root, just beyond the neck. The milk canines are much like the second ones, only smaller. The labial surface of the upper tends to divide into an outer and an inner facet. The root is approximately triangular on section, with rounded edges. The Bicuspids or Premolars. These teeth, of which the second is the larger in both jaws, are characterized by crowns with two cusps, one on the buccal and one on the lingual side. The upper ones, being very much the more typical, will be used for the general description. Both the labial and the lingual aspects of the crowns are convex ; they expand laterally from the neck, and each ends in a pointed cusp of which the anterior border is the shorter. This is used in determining the side, but we agree with Testut that the guide is often useless. The buccal cusp is the larger. The cusps are separated by a furrow from which small ramifications often run onto the buccal one. The lin- gual cusp has an unbroken surface. The buccal cusp of the first bicuspid is more prominent than the lingual, but in the second they reach the same plane. The bor- der of the enamel is convex towards the root on both the buccal and lingual aspects, the ends of these curves meeting on the other sides. The fang is compressed with a groove on the sides next its neighbors. That of the second is often bifid just at the tip, but that of the first is very often, per- haps usually, divided into two throughout, having a buccal and a lingual root. Sometimes the former is subdivided, so that it has three like a molar. The root has in general a backward slant. The lower bicuspids have smaller grinding surfaces on the crowns than the upper, but the roots are longer, and the crowns, seen from the side, are at least as large. The first has a well-developed buccal cusp, curving in from the buccal surface, and a very small lingual one connected to the former by a ridge interrupting the fissure between them, which gives the tooth something of the effect of a small canine. The second, like that of the upper jaw, has the two cusps in one plane ; the lingual one is sometimes double, and the plane is often obscure. The flattened fang is but faintly grooved, if at all, and is rarely bifid. The pulp-cavity of the bicuspids ends in an expansion below each cusp, that under the buccal being the larger. In the upper teeth the cavity is much compressed from side to side in the root. In the first upper bicuspid there are usually two pro- longations to the point of the fang, even when the root is not split. In the second the cavity generally agrees with the conformation of the root. In the lower teeth the cavity is less compressed and is tolerably roomy as it enters the root. It. is usually single, but may split. FIG. First premolar teeth of left side, labial (A) and lateral () aspects. (Leidy.) 1546 HUMAN ANATOMY. The Molars. These teeth three on each side are distinguished by the large crown, into which the neck expands, the number of cusps on the surface, and the greater subdivision of the root. Those of the lower jaw are the larger ; and in both jaws the first is the largest and the last (called from its late appearance the tcisdom- tooth} the smallest. The croivns are convex on both the buccal and lingual sides, but nearly plane on the others. The enamel ends in a nearly straight line all the way round. The grinding surfaces are four-sided ; those of the upper are somewhat dia- mond-shaped, the buccal anterior angle being rather in front ; those of the lower are nearly parallelograms, the long diameter being antero-posterior. Typical upper molars have four cusps at the angles ; typical lower ones have an additional cusp at the posterior border ; but in the upper jaw the first is the only one that can be called typical. In the upper molars the largest cusp is the anterior lingual, which is connected by a ridge (the cingulum) to the posterior buccal. The posterior lingual cusp is the smallest. A minute rudimentary cusp is found on the lingual surface of the anterior lingual cusp, usually too small to reach the grinding surface, and often hard to recog- nize. Not counting this, the first upper molar has four cusps in more than 90 per cent. Owing to the cingulum, the grooves on the grinding surface are best described as two oblique ones, the first from the anterior border to the middle of the FIG. 1303. A B FIG. 1304. Upper molars First Another first Lower molars Second First Another first Second Second molar teeth of left side, labial (A) and lateral (/?) aspects. (Leiity.) Triturating surfaces of molar teeth of right side. The upper margin of the figures corresponds to the labial surface. ( Leidy. ) buccal, the second from the lingual border to the middle of the buccal. They are deepest at the middle. They appear on the buccal and lingual sides, deeper on the former, but rarely reach the gum. They may end in a pit, a favorite seat of caries (Tomes). The crown of the second upper molar presents three chief forms (Miihl- reiter). It may have four cusps and differ but slightly from the first molar. The lingual surface is relatively narrower and the posterior lingual cusp smaller. In the second form the last-mentioned cusp is wanting. The cingulum persists and the grinding surface is approximately triangular. The third form is compressed from side to side into a very narrow diamond, with the anterior buccal cusp in front and the posterior lingual behind. Three and four cusps are about equally common in this tooth in Caucasians, but the lower races have more often four. The crown of the upper wisdom-tooth presents many remarkable variations. The posterior lingual cusp is wanting in about two-thirds of the cases. The crown may be strongly com- pressed, as has been described for the second molar, but with greater variation. In size the wisdom-tooth may be very large or very small. The crowns of the lower molars are divided oy a crucial fissure, the main line running antero posteriorly. The hind part of this splits so as to enclose the fifth cusp, which is near or actually at the buccal side. The effect of this is to form a cavity at the crossing of the lines in the middle of the crown. The lines on the sides THE TEETH. 1547 of the crowns are less deep than in the. upper jaw. Sometimes the fifth cusp is wanting, in which case the posterior part of the furrow does not divide and the arrangement is remarkably symmetrical. Very rarely the first molar has a sixth cusp on the lingual side. The first molar has five cusps in more than 90 per cent. ; the second four only in more than 80 per cent. ; the third four rather more often than five. The buccal cusps of the lower molars are worn down earlier than the lingual ones. The following tables from the independent researches of Rose l and of Zuckerkandl show the percentage of frequency of different groupings of cusps. Although there is some discrepancy in the percentages, both agree as to the most and least common arrangement in both jaws. These statistics, like those of the separate teeth, apply to Europeans. (It is to be remembered that a certain percentage of teeth cannot be included.) Cusps . . Cusps . . Cusps . . UPPER JAW. Molars. 444 443 433 Per Cent. Rose. Zuck. LOWER JAW. Molars. 123 Per Cent. Rose. Zuck. 19.9 28.9 37-9 9.6 28.7 60. 1 Cusps Cusps Cusps 555 I9- 8 u-5 545 30-4 30-5 .544 40.4 50.0 FIG. 1305. The fangs of the first and second upper molars are two buccal and one lingual, which latter is much the largest. It is often, especially in the first molar, grooved on the lingual side. It is conical and strongly divergent. It often shows a tendency to subdivision, which may actually occur, although rarely. The two buccal ones are compressed antero-posteriorly and nearly vertical. The front one is the broader, and is grooved before and behind. This is often the case with the other. The roots of the upper wisdom-tooth are smaller ; the lingual is less divergent, and may be connected by a plate with one of the buccal ones. All may be fused more or less completely into one. The roots of the inferior molars are two : an anterior and a posterior, of which the former is rather the larger, both compressed from before backward and, especially the first, deeply grooved, suggesting the fusion of two. Sometimes, again especially in the first, each root is bifid. Those of the wisdom-tooth are usually nearer together, and are frequently fused into a common coni- cal root. Apart from their position in the jaws, the roots of the molars, excepting the upper wisdom-tooth, have a back- ward slant of varying degree. Their twists and curves are remarkably uncertain. Sometimes they converge and some- times diverge unduly, hooking in either case under bone, so as to make extraction difficult or impossible. The pulp- cavity of the molars is large, especially at the level of the neck. In the upper teeth it is distinctly wider transversely than from before backward. It has as many prolongations towards the surface as there are cusps. There is a canal in each root of the upper teeth. Those in the buccal fangs are compressed, that- in the lingual cylindrical. The anterior fang of the lower molars has two canals which develop from a single one. The posterior fang has but one. The milk molars are two in number. Like the perma- nent ones, the lower are the larger ; but, unlike them, the second tooth is larger than the first in both jaws. The crown of both first molars presents a prominence on the buccal sur- face near the root. The crown of the first upper molar is rather suggestive of a bicuspid, although there are two buccal cusps and one lingual. The first inferior molar is relatively narrow and long from before backward. The length of the buccal side is greater than that of the second permanent one. The second molars resemble very closly the first permanent ones. The upper has four cusps and a cingulum, the lower five cusps. The hollow in the crown of the tem- porary molars is relatively deeper than that of the permanent ones, but smaller and more divergent. . They straddle the crowns of the developing bicuspids. 1 Anatom. Anzeiger, Bd. vii., 1892. Temporary molar teeth (A, first; B, second) of left side. Triturating surfaces of crowns also shown. (Leidy.) 1548 HUMAN ANATOMY. TOOTH-STRUCTURE. In principle, and among the lower vertebrates, in fact, as well, teeth may be regarded as hardened papillae of the oral mucous membrane ; they consist, therefore, of two chief parts, the connective-tissue core and the epithelial capping. Of the three constituents present in typical mammalian teeth, the enamel is the derivative of the ectoblastic epithelium, the dentine, with the pulp, and the cementum being con- tributions of the embryonal connective tissue. The Enamel. This, the hardest tissue of the body, covers the crown, being thickest on the cutting edge or grinding surface of the tooth. It gradually thins away FIG. 1306. Contour lines Schreger's lines Neck Stripes of Retzius (longitudinal) Prism-stripes of Schreger (light and dark) Gum Pulp-tissue IJfJL- Dentine . Cementum Alveolar periosteum Osseous tissue of jaw Root-canal Sagittal section of canine tooth in situ. Semi-diagrammatic. towards the neck, around which its terminal border appears as a more or less distinct and often serrated edge. The external surface of the enamel, especially in young teeth, often exhibits a tine striation composed of horizontally disposed lines. Under a hand-glass these lines are seen to be minute elevations, the enamel-ridges, which encircle the crown. The remarkable hardness of this tissue is due to the large- amount (97 per cent.) of earthy material and the small proportion of organic matter, which latter in adult enamel averages only about 3 per cent. ; in infantile enamel the amount of animal material is from five to six times greater (Hoppe-Seyler). STRUCTURE OF THE TEETH. 1549 The enamel the product of epithelial cells, the ameloblasts consists of an aggre- gation of five- or six-sided columnar elements, the enamel-prisms, which measure from .0035-. 0045 mm. in diameter and from 3-5 mm. in length. Their general disposition is at right angles to the surface of the dentine upon which they rest, on the one hand, and to the exterior of the crown on the other. They usually extend the entire thickness of the FIG. 1307. enamel, and are of slightly larger diameter at the surface of the tooth than next the dentine, in this manner com- pensating for the increase in the external circumference of the crown. The assumption that additional prisms are intercalated at the periphery is not supported by the manner of the production of the enamel-columns. The latter run for a short distance almost at right angles to the surface of the dentine, then bend laterally for a considerable part of their course, but assume a vertical disposition on approaching the external surface. In addition to these general curves, the ranges of enamel- columns possess a spiral arrangement, in consequence of which the parallelism of the prisms, as seen in ground- sections, is disturbed and their bundles are apparently interwoven. T , . , . , Ground-section of enamel, showing In thin accurately transverse sections enamel pre- ranges of enamel-prisms, x 500. sents a mosaic in which the hexagonal areas represent the ends of the individual prisms. Critically examined, the areas consist of a darker central portion surrounded by a narrow lighter peripheral zone. The interpreta- tion of the latter has been various, many observers regarding such lines as cement- substance holding together the prisms. According to Walkhoff, 1 however, what is usually regarded as cement-substance is a cortical, apparently homogeneous layer of less thoroughly calcified material which encloses the denser central portion of the prism and acts as a cushion, thereby reducing the effect of pressure. After the decalcifying action of acids, the prisms may be outlined by stains which color the very meagre amount of true cement-substance which exists between the enamel- columns and appears as delicate lines defining the prisms. Under favorable conditions, especially, but not only, after the action of acids, the enamel-prisms exhibit alternate light and dark transverse markings. The true rela- tions of these bands are to be appreciated only by accurate focusing in thin sections passing exactly parallel to the axes of the prisms ; otherwise the obliquity of section produces the optical distortions often represented in the assumed wavy contour of the enamel-rods. The varicose appearances commonly seen depend upon the beaded form and consequently scalloped border of the denser central portion of the prisms, which give a corresponding arrangement to the lighter cortical substance whreh fills the minute inequalities of that portion ; the true outline of the enamel-prism, how- ever, is smooth and straight, and not varicose, as the optical impressions lead one to believe and as usually pictured. According to Williams, the apparent varicosities depend upon the spherical form of the enamel -globules of which the prisms are built up. When an axial longitudinal section of a tooth is examined by reflected light, the enamel displays a series of alternate dark and light bands, the prism-stripes of Schreger. These markings extend generally vertical to the surface of the enamel, and depend upon the relation of the ranges of the enamel-prisms to the axes of the light-rays. Rotation of the illuminating pencil through 180 effects the change of the dark stripes to light ones and vice versa. Each stripe includes from ten to twenty enamel-prisms, and is invisible by transmitted light. In addition to the foregoing markings, the enamel often presents, in radial longi- tudinal sections, brownish parallel lines, the stripes of Retzius, which run in the general direction of the contour of the tooth, but at an angle of from 15 to 30 with the free surface. Seen in sections cut at right angles to the tooth-axis, these stripes appear as a series of concentric lines encircling the crown parallel to and near the surface ; in the middle and deeper parts of the enamel they are less evident or entirely 1 Normale Histologie mensch. Zahne, 1901. 1550 HUMAN ANATOMY. FIG. 1308. Longitudinal ground-section of enamel, treated with acid, showing disposition of ranges of enamel-prisms (p,p') in stripes of Schreger. Left third of figure shows alternate light 's as seen " X 200. (Ebner.) (s) and dark (s') bands as seen by re- flected light absent. The interpretation of the stripes of Retzius is still a subject of dispute. The brown appearance of the stripes by transmitted light only, by reflected light appear- ing bluish white, disproves the assumption that they depend upon the presence of pigment within the enamel. The widely accepted view of -Ebner, that the stripes are due to air contained in the interfascicular clefts, has been modified by Walkhoft, who regards the markings as due to local diminution in the calcification of the enamel-prisms during certain periods in the growth of the tissue when the central as well as the cortical substance of a great number of columns fails to take up sufficient lime salts. The enamel- cuticle, or membrane of Nasmyth, forms a continuous investment of the crown of the newly erupted tooth. In the course of time it dis- appears from the areas exposed to wear, but over the protected surfaces it may persist during life. The membrane (.oog-.oiS mm. in thickness) is transparent and remarkably resistant to the action of acids, less so to alkalies, affording admirable protection to the underlying enamel. After separation from the latter by acids it appears structureless, or at most granular. The inner surface of the membrane presents markings and slight irregularities which correspond to the free ends of the subjacent enamel-prisms. The origin of the enamel-cuticle has been much discussed, and even now is not without some uncer- tainty. It may be regarded as established that it rep- resents the remains of part of the tissue once concerned in the production of the enamel. The latter is formed, as more fully described on page 1561, through the agency of the epithelial cells constituting the inner layer of the enamel-organ. With the completion of their task as enamel builders, these cells produce a continuous cuticular envelope which persists as Nasmyth' s membrane, the epithelial elements of the enamel-organ, so far as they are concerned in forming enamel, subsequently degenerating. The enamel-cuticle is continuous with the cortical substance of the prisms, with which it agrees in optical and chemical properties, a relation which confirms the identity of origin of Nasmyth' s membrane and the enamel-columns. The Dentine. The dentine or ivory resembles bone both in its genesis and chemical composition, being a connective tissue modified by the impregnation of lime salts. Dentine exceeds bone in hardness, containing a larger proportion (72 per cent.) of earthy matter and a smaller amount (28 per cent.) of organic substance. When decalcified by acids, the remaining animal material retains the previous form of the dentine and yields gelatin on prolonged boiling. Dentine, like bone, is formed through the agency of specialized connective-tissue cells, the odontoblasts , but differs from osseous tissue in the small number of these cells which become imprisoned in the intercellular matrix. When this occurs, as it exceptionally does in normal human dentine and more frequently in pathological conditions or in the lower animals, the dentine-cells correspond to the bone-corpuscles, both being connective-tissue elements lying within lymph-spaces in the calcified intercellular substance. Examined in dried sections under low magnification, the dentine presents a radial striation composed of fine dark lines which extend from the pulp-cavity internally to the enamel or the cementum externally. These dark lines are the dentinal tubules, filled with air, which are homologous with the lacunae and canaliculi of bone, and contain the processes of the odontoblasts. In the crown, as seen in longitudinal sections, the course of the dentinal tubules is radial to the pulp-cavity ; in the root their disposition is horizontal and almost parallel. The canals, however, are not straight, but sigmoid, the first convexity being directed towards the root, the second towards the crown. In addition to these primary curves, which are especially marked in the crown, the dentinal tubules present numerous shorter secondary curves which STRUCTURE OF THE TEETH. impart to the individual canaliculi a spiral course. The cause of the latter Kollmann refers to the more rapid growth of the dentinal fibres than of the slowly forming dentinal matrix. In consequence of the correspondence of the curvature of the den- tinal tubules, the tooth-ivor-y exhibits a series of linear markings, Schreger' s lines, which run parallel to the inner surface of the dentine. These markings must not be confounded with the contour lines of Owen (page 1552), also within the dentine, or with Schreger' s prism-stripes within the enamel (Fig. 1306). The dentinal tubules are minute canals, from .001 3-. 002 mm. in diameter, which begin at the pulp-cavity with the largest lumen and extend to the outer surface of the dentine, to end beneath the enamel or cementum. Each spirally coursing canal undergoes branching of two kinds, a dichotomous division at an acute angle in the vicinity of the pulp-cavity, resulting in two canaliculi of equal diameter, and a lateral branching during the outer third of their course whereby numerous twigs are given off with a corresponding dimi- nution in the size of the cana- FIG. 1309. liculi ; the terminal tubes, often reduced in diameter to mere lines, frequently anas- tomose with one another or form loops. The dentinal tubules are occupied by the delicate dentinal fibres, the processes of the odonto- blasts, which in the young tooth constitute a net-work of protoplastic threads through- out the dentine of importance for the nutrition of the tis- sue. The relation of the den- tinal tubules on the external surface of the dentine varies on the crown and root. In the former situation the free surface of the dentine pre- sents crescentic depressions, filled by the enamel, in which the tubules appear as ab- ruptly terminating or cut off ; on the root, on the contrary, where the dentinal surface is smooth, the tubules stop in curved ends or loops beneath the cementum, only in very exceptional cases communi- cating with the canaliculi of the latter. The immediate wall of the dentinal tubules is formed by a delicate membrane, the sheath of Neumann, which in appropriate transverse sections appears as a con- centric ring. On softening the decalcified dentine by acids or alkalies, the sheaths may be isolated, since they resist the action of the reagents which attack the sur- rounding intertubular substance. The sheaths of Neumann are formed through the agency and at the expense of the dentinal fibres, the latter being smaller in old than in young dentine. The sheaths, therefore, may be regarded as specialized parts of the intertubular matrix, distinguished by less complete calcification and greater density. The intertubular ground- sub stance of dentine resembles that of bone in being composed of bundles of extremely delicate fibrillae of fibrous connective tissue. The latter, best seen in decalcified tissue, swell on treatment with water containing acids or alkalies, and yield gelatin after prolonged boiling. The disposition of the bundles Ground-section of dried tooth including adjacent enamel and dentine. X 300. 1552 HUMAN ANATOMY. of fibrillae more regular in dentine than in bone is longitudinal and parallel to the primary surfaces of the dentine. In addition to the fibres which extend lengthwise, others run obliquely crosswise in the layers of dentine. The bundles of fibrillae measure from .002-. 003 mm. in diameter, and appear in transverse sections as small punctated fields. The fibrillae are knit together by the calcified organic matrix, in which the lime salts are deposited in the form of spherules, the interstices between which are later filled and calcification thus completed. When, as often happens, the latter process is imperfect, irregular clefts, the interglobular spaces, remain, the con- tours of which are formed by the spheres or dcntinal globules of calcareous material. The interglobular spaces are of irregular form and uncertain extent, being usually largest in the crown. At the border between the dentine and the cementum there exists normally a distinct zone, the granular layer of Tomes (Fig. 131 1), composed of FIG. 1310. Alveolar periosteum -^w|^B Transverse section of root of lower canine tooth. X 30. closely placed interglobular spaces of small size ; under low magnification in ground- sections the spaces appear as dark granules, hence the designation of the zone. Since the existence of these spaces depends upon imperfect calcification of the intertubular ground-substance, the dentinal tubules are unaffected and pass through the spaces on their course to the surface of the dentine, several of the canals traversing the larger spaces. The contour lines of Owen, or the incremental lines of Salter, appear as linear markings, which usually run obliquely to the surface of the dentine (Fig. 1306). They probably depend upon variations in calcification incident to the growth of the dentine, and resemble the interglobular spaces in their origin. The contour lines are best marked in the crown and are only exceptionally seen in the fang. As pointed out by Walkhoff, the lines of Owen and those of Retxius in the enamel are usually present at the same time, since both are expressions of imperfect calcification. The Cementum. The cement, or crusta fr-trosa of the older writers, forms an investment of slightly modified osseous tissue from the neck of the tooth to its STRUCTURE OF THE TEETH. 1553 FIG. 1311. apex. Beginning where the enamel ceases, or overlapping the latter to a small extent, as a layer only .02 .03 mm. thick, the cement gradually increases in thick- ness until over the root, especially between the fangs of the molars, its depth reaches several millimetres. When well developed the cement usually presents two layers, an inner, almost homogeneous stratum next the dentine, in which the cement-cells are absent, and an outer supplemental layer which exhibits the appearance of true bone- tissue. The ground-substance of cemen- tum differs from that of ordinary bone in containing, according to Bibra, slightly less organic matter and a great number of fibre-bundles that extend vertically to the lamellae, corresponding to Sharpey's fibres. The lacunae are larger than those of bone and vary greatly in their number and form ; their processes, the canaliculi, are unusually long and elaborate. As in bone, so these lymph-spaces contain con- nective-tissue cells, the cement- corpuscles. The lamellae are so disposed that the lacunae lie generally parallel with the long axis of the tooth, their processes extend- ing vertically to the free surface. While connecting with one another by means of the canaliculi, the lacunae very rarely communicate with the dentinal tubules, the latter terminating in blind endings. The union between the outer surface of the cement and the pericementum is in- timate, since the latter is in fact the alve- olar periosteum from which the cement was derived ; this close relation is indi- cated by the roughness which the outer surface of the cement presents when macerated. Although at times feebly developed under normal conditions, typical Haversian canals are found only in con- ditions of hypertrophy. The Alveolar Periosteum. The periosteum investing the jaws likewise lines the sockets receiving the roots of the teeth, which are by this means securely held in place. The name pericementum is often applied to this special part of the peri- osteum, which clothes the alveoli on the one hand and covers the cement on the other, thereby fulfilling the double role of periosteum and root-membrane. The latter consists of tough bundles of fibrous tissue, elastic tissue being almost want- ing, which are prolonged into the penetrating fibres characterizing the cementum on one side and into the fibres of Sharpey of the alveolar wall on the other. The fibrous bundles run almost horizontally in the upper part of the root, but become more oblique towards the apex of the fang. In the latter situation the pericemen- tum loses its dense character and becomes a loose connective tissue through which the blood-vessels and nerves pass to reach the tooth. The less dense portions of the root-membrane between the penetrating bundles of fibrous tissue contain, in addition to the vessels and nerves, irregular groups of epithelial cells which appear as cords or net-works within the connective-tissue stroma. These groups are the remains of the epithelial sheath which surrounded the young tooth during its early development. They have sometimes been described as glands, lymphatics, and other structures, their true nature being unrecognized. At the alveolar mar- gin the pericementum is directly continuous with the tissue composing the gum, the fibrous bundles being so disposed immediately beneath the enamel-border that they form an encircling band of dense fibrous tissue, the ligamenttim circulare dentis of Kolliker, which aids in maintaining firmer union between the tooth and the alveolar wall. 9 8 Granular layer of Tomes Cementum -Lacuna Ground-section of root of dried tooth including adjacent dentine and cementum. X 300. 1554 Fir MAN ANATOMY. FIG Dentine The Pulp. The contents of the pulp-cavity is the modified tissue of the mesoblastic dental papilla remaining after the completed formation of the dentine. The major part of the adult pulp consists of a soft, very vascular connective tissue containing few or no elastic elements, but numerous irregularly distributed cells of uncertain form. The general type of the tissue resembles the embryonal, both in the character of the fibrous tissue and of the cells, which are round, oval, or stellate with long processes. The fibrous bundles and the more elongated cells are most regu- larly disposed around the blood-vessels and nerves, which they invest in delicate fibrous sheaths. The peripheral zone of the pulp, next the dentine, presents the greatest special- ization, since in this situation lie the direct descendants of the dentine-producing cells, the odontoblasts. In this locality the pulp, especially in older teeth, presents three layers. The outer (.04 .08 mm. thick) consists of several rows of large cylindrical elements, of which the most superficial are arranged vertically to the free surface of the pulp, after the manner of an epithelium. These are the odontoblasts, now no longer active, about .025 mm. in length and .005 mm. broad, which send out long, delicate processes (the dentinal fibres) into the den- tal tubules externally, and shorter ones towards the pulp-tissue. When very young they probably possess also lateral processes. The deeper cells of the odontoblastic layer are less regularly disposed and less cylindri- cal in form. The second, or H'eit's layer, best seen in older teeth, is characterized by absence of cells, the fibrous tissue and the cell-processes forming a clear, cell-free i. fW6 IfcT^nsif ^W "SSV^ zone wmch separates the striking layer of ll $^|^4O 4 v -%r Blood - odontoblasts from the subjacent third or in- * -$ a> A WMffifflk Tft termediate layer. The latter consists of nu- merous small round or spindle-cells, closely placed, but irregularly disposed, which grad- ually blend with the ordinary pulp-tissue. The blood-vessels supplying the pulp are from three to ten small arteries which soon after entering the pulp-cavity break up into very numerous branches from which a rich capillary net- work is derived. In human teeth the capillaries usually do not invade the layer of odontoblasts, although at times the vascular loops may extend between these cells. The venous radicles form larger veins which follow the course of the arteries. Distinct lymphatics have not been demonstrated within the pulp. The nerves are numerous, each fang receiving a main stem and several additional smaller twigs, which in a general way accompany the blood-vc-ssrls in their coarser distribution. On reaching the crown-pulp the larger twigs are replaced by tiiu-r branches, which divide into innumerable interwoven fibres. The latter, on reaching the margin of the pulp, form a peripheral plexus beneath the layer of odontoblasts, from which terminal non-medullated fibrillae are given off. Some of these rnd beneath the odontoblasts in minute knot-like swellings ; others penetrate the odonto- blastic layer to terminate in pointed free endings. There is no trustworthy evidence supporting the view that the nerves directly communicate with the odontoblasts or enter the dentine. Pulp- tissue Section of periphery of pulp-tissue of young tooth. X 175- IMPLANTATION AND RELATIONS OF THE TEETH. The Permanent Teeth. Each fang is implanted in a socket corresponding to it in shape, so that the pressure is transmitted from the surface of the conical fang throughout, except at the very tip, which has a hole for the vessels and nerves. A corresponding hole in the socket communicates with the dental canals. The human IMPLANTATION AND RELATIONS OF THE TEETH. 1555 teeth are all in contact with their neighbors, there being no break or diastcma in the upper jaw between the incisors and canines for the points of the canines of the lower jaw. The canines project very little beyond the line of the free edges. The crowns increase in size from the incisors to the first molars and then decrease. The ver- tical distance from the gum to the free edge regularly diminishes from the median incisors backward, with the exception of the canines. The lines of the teeth above and below are practically of the same length. When the mouth is closed the superior canines lie to the outer side of the FIG. 1313. inferior ones, opposite the ends of the lips ; thus the median upper incisors impinge on both the lower ones of the same side, and the upper lateral incisors strike both the lower lateral and the canine. In the same way the point of the cusp of the upper first bicuspid rests between the points of both the inferior ones, and that of the second on both the second lower and the first molar. The first upper molar has, perhaps, a quar- ter of its grinding surface on that of the inferior second molar, but a smaller part of the second upper molar rests on the lower wisdom- tooth. The smaller size of the upper wisdom-tooth brings its posterior border into line with that of the lower. This arrangement causes the opposed crowns to interlock to a certain extent, but not so closely that grinding movements cannot occur between them. The advantage of each tooth coming in contact with two is evident after the loss of a tooth, as the one cor- responding to it is not rendered useless. In the upper jaw the incisors have a marked FIG. Dental arches seen from before. Letters in this and subsequent cuts indicate the groups of teeth: i, incisors; c, canines; b, bicus- pids ; m, molars. Dental arches seen from behind. forward inclination, and overlap the lower, concealing nearly a third of their crowns, the mouth being closed. The crowns of the upper bicuspids look pretty nearly downward and those of the molars slant outward. This is very marked in the wisdom-tooth and may be very slight in the first molars. The lower incisors have the front surfaces nearly vertical ; the molars have an inward slant, so as to bring their axes into the same line 1556 HUMAN ANATOMY. FIG. 1315. Dental arches seen from the side, showing relations of upper and lower teeth. as those of the upper ones ; hence it follows that the alveolar arches of the upper and lower teeth are in different curves, the latter having a great transverse distance between the necks of the wisdom-teeth. The right half of the jaw is usually the stronger and the teeth form a smaller curve. It has been pointed out in the section on the motions of the lower jaw that the line between the molars, and probably the bicuspids, is a part of the circumference of a circle the centre of which is near the top of the lachrymal bone ; it may now be added that the line of the cutting edges of the lower incisors is a part of a transverse curve with the convexity upward. There is no corresponding concavity in the line of the edges of the upper incisors, for the lower do not naturally meet them ; but the convexity plays along the lingual surfaces of the upper ones. The position and shape of the superior incisors make their inner surface a part of a vault. A transverse section of this is necessarily a curve with an upward convexity. The wearing of the outer corners of the lateral incisors is evidence of this action. The fact that there is no purely lateral motion, but an oblique one, modifies, without invalidating, this con- ception. The relations of the roots of the su- perior teeth to the antrum are very impor- tant. The incisors have no relation with it whatever. The long fang of the canine is opposite the wall between the antrum and nose, and separated by diploe from the former. The first bicuspid is usually sepa- rated in the same manner. The second is very close to its front wall and may indent the floor. The first and second molars always do this. The wisdom-tooth also in- dents it at the junction of the floor with the posterior wall. Its relation, owing in part to its varying development, is less certain. Exceptionally the first bicuspid and even the canine may be in contact with the antrum. Thus caries of the roots of any of the molars, but especially of the first and second, sometimes of the second bicuspid and exceptionally of the first, or even of the canine, may lead to inflamma- tion of the antrum. In certain cases pus may pass directly into it from the root. The Temporary Teeth. In the first dentition the dental arches differ from the permanent ones in showing a broader curve, more nearly approaching half a circle, symmetrical on both sides, in having the upper incisors less slanting, and the molars of each row more nearly vertical. This implies less difference in curve between the jaws. The line of meeting of the teeth is more horizontal. The crowns increase in size from the incisors backward. In the young child the antrum is but a small pouch, and the roots of the first teeth and the sacs of the second lie in diploetic tissue. The first permanent molar, as its fangs grow, is nearest the antrum, having extended above it by the end of the second year. In its early stages the first bicuspid is too far forward to have any relation to the antrum, and the second reaches only its extreme anterior border. The second permanent molar is at first behind rather than below it, and the third is still higher. As these descend they swing around the antrum. Thus the roots of only the first permanent molar are in approximately the same relation to the antru throughout. DEVELOPMENT OF THE TEETH. About the beginning of the seventh week of foetal life the ectoblastic epithelium presents a thickening along the margins of the oral cavity. The ridge-like epithelial proliferation, or labio-dcnUU strand, so formed grows into the surrounding mrsoblast and divides into two plates which, while still continuous at the surface, diverge almost at right angles at the deeper plane. The lateral or outer plate is vertical, and cor- responds to the plane of separation which soon occurs in the differentiation of the borders of the lips and jaw. The median or inner plate grows more hori/ontally into the mesoblast, and is the one intimately concerned in the tooth development ; for this DEVELOPMENT OF THE TEETH. 1557 reason it is termed the dental ledge. It will be seen that the formerly described pri- mary stage of the dental groove is unfounded, since the furrow that does exist is secondary and not directly related to the formation of the teeth, but to the differ- entiation of the lips. During the third foetal month the anlages for the entire set of milk-teeth become evident along the dental bar, coincidently, by the eleventh week, the completion of the labial furrow separating the lip from the original epithelial strand with which the dental ledge alone for a time remains attached. The anlages of the milk-teeth are indicated by club-shaped epithelial outgrowths which grow down from the deeper surface of the dental ledge to form the enamel- FIG. 1316. Id Reconstructions of oral ectoblast of human embryos; only epithelium of lips, mouth, and enamel-organs shown. A, embryo of 2.5 cm. length; m, oral opening; e, labial epithelium; Id, reverse of labio-dental groove; ds, dental ledge. B, embryo of 4 cm. ; /, projection caused by labio-dental groove ; ds, dental' ledge. C, embryo of 11.5 cm., or of about fourteen weeks; m l , enamel-organ of first molar tooth. ), embryo of 18 cm., or of about seventeen weeks ; /'- i >, enamel-organs of second incisor and of first molar teeth. (Drawnfrom Rosens models.) organs and to meet, and later cap, the mesoblastic elevations or denial papilla. With the rapid growth and expansion of the extremity of the epithelial plug, a differentia- tion of the latter into the typical three-layered enamel-organ takes place, the pro- jecting dental papilla apparently invaginating the overlying epithelial structure. At first connected by a broad band of cells, the attachment of the enamel-organ with the HUMAN ANATOMY. dental ledge becomes more and more attenuated until finally it is broken ; its remains appear for some time as nests or islands of epithelial cells embedded within the young connective tissue of the alveolar border. The Dental Papilla. This structure first appears shortly after the beginning expansion of the club-shaped developing enamel-organ as a condensation of the meso- FIG. 1317. Dental ledge Thickened oral epithelium Labiodental strand \ Dental ledge] '^imrnm^m" ,r J../'. '.'.'' . ','S;'i ':'::.. ' .'" ' .' .' J& Inner layer of enamel- organ Dental papilla Frontal sections, showing four early stages of tooth-development blast beneath the epithelial ingrowth. The papilla consists for a time of a close aggregation of small, round, proliferating cells ; with the differentiation of the lavcrs of the enamel-organ, the elements occupying the periphery of the dental papilla become elongated and arranged as a continuous row of cylindrical cells over the api- cal portion of the papilla beneath the capping enamel-organ. These cylindrical nieso- blastic cells are the odontoblasts, the active agents in the formation of the dentine. DEVELOPMENT OF THE TEETH. 1559 FIG. 1318. When engaged in the latter process the cells measure from .035-. 050 mm. in length and from .005 .010 mm. in breadth, but over the sides of the papilla they gradually become lower until towards the base they blend with and become indistinguishable from the deeper cells of the mesoblastic elevation. So long as the tooth grows, division proceeds and odontoblasts are differentiated in the vicinity of the last-formed parts of the root ; after, however, the odontoblasts are engaged in forming dentine, mitosis is no longer to be observed in these elements. The formation of the dentine is accomplished through the agency of the odontoblasts much in the same manner that the osteoblasts produce the matrix of bone. The earliest trace of the dentine appears as a thin homogeneous stratum, the membrana prceformaliva, overlying the coincidently forming layer of odontoblasts. Although separable by certain reagents as a cuticular structure, the membrane is only a part of the general dentinal ground-substance with which it blends ; later it is prob- ably absorbed when brought into contact with the enamel. The dentinal matrix, deposited through the influence of the odontoblasts, is for a time without fibrous structure and uncalcified, the deposition of the lime salts occurring first near the apex of the papilla and next the enamel, a zone of uncalcified matrix around the pulp- cavity marking the youngest dentine. The calcareous material is first deposited in the form of globules, the dentinal spheres, the calcification being completed by the subsequent invasion of the interstices between the spherical masses. When for any reason calcification is incomplete these clefts remain lime free, a condition seen in the interglobular spaces already described. The spherical form of the calca- reous deposits is indicated by the uneven condition of the inner surface of the dentine in macerated teeth, the wall of the pulp-cavity presenting numerous minute hemispherical projections which correspond to the globular masses of lime salts. The scalloped border and pitted outer surface of the dentine, together with the extension of the dentinal tubules as far as or into the enamel, point to the absorption of the primary dentine constituting the preformed membrane, proba- bly through the influence of the enamel. As empha- sized by Ebner, 1 the formation of the fibrillae of the ground-substance takes place independently of the direct influence of the dentine-cells, since the general disposition of the earliest fibrillae is at right angles to that of the odontoblasts and their processes. The dentinal matrix differs from that of bone in being the production of a single set of cells, while the osseous tissue is the collective work of different elements, many of which, after contributing their increment, be- come surrounded by the ground-substance to form the bone-corpuscles within the. lacunae. In human dentine, on the contrary, the odontoblasts are only rarely, under normal conditions, imprisoned within the ground-substance which they have formed. The de- mands made upon the odontoblasts during their active r61e as dentine producers are met by the nutrition supplied by the rich vascular supply of the dentinal papilla, so that for a time the cells are enabled not only to increase the dentinal matrix, but also to extend their processes, which they send into the tubules of the dentine as the den- tinal fibres, without diminution in size. With the completion of dentine production, and the consequent decrease in the area upon which they rest, the odontoblasts become narrower and smaller (Walkhoff) ; later they exhibit evidences of impaired vitality and degeneration, their dentinal processes likewise growing thinner and less flexible and assuming the characteristics of the fibres of Tomes of the adult tissue. According to Walkhoff, the dentinal fibres suffer in size as the result of their activity in the production of the sheath of the tubules. 1 In Kolliker's Gewebelehre des Menschen, 6te Auf., 1899. Isolated odontoblasts from incisor tooth of new-born child, a, b, from upper part of crown ; c, d, e, from lat- eral region. X 400. (Ebner.) 1560 HUMAN ANATOMY. After the entire dentine has been formed, the odontoblasts remain as the periph- erally situated pulp-cells, retaining their connection with the dentine by means of the dentinal fibres. The other portions of the dental papilla become converted into the pulp-tissue, which retains the embryonal type throughout life and later receives the larger vascular and nervous trunks. The Enamel-Organ. The extremity of the cylinder of ectoblastic epithelium which early marks the position of the future tooth by its ingrowth from the dental ledge soon broadens out and becomes invaginated to form the young enamel-organ overlying the apex of the mesodermic dental papilla. In contrast to the latter, which as the pulp-tissue remains as a permanent structure, the enamel-organ is but embry- onal and transient, and later entirely disappears. When fully developed, the enamel- organ consists of three principal parts, the outer, middle, and inner layers. Since the organ, originally pyriform, is converted into a cap by the invagination of its broader and deeper surface, it follows that the external and internal layers are directly continuous at the margin of the inverted area. FIG. 1319. Sublingual space Fibres of genio-glossus d.' Oral epithelium Developing gland Dental papilla Muscular fibres Skin Sagittal section through mandible and surrounding structures of eighteen-weeks foetus. X 30. The outer layer consists of larger and smaller epithelial cells of flattened form and about .010 mm. average diameter ; these cells send numerous processes into the surrounding vascular connective tissue forming the tooth-sac which invests the dental germ, whereby, in conjunction with the vascular tufts, the sac and the enamel-organ are intimately united. The middle layer of the enamel-organ consists apparently of mucoid tissue, since it presents a net-work of stellate cells separated by large clear spares. Critical examination, however, shows that this tissue consists of epithelial elements which have become modified in consequence of an enormous distention <>f tin- intercellular spaces by fluid and a corresponding elongation of the intercellular bridges, the ep- thelial plates in this manner being reduced to stellate cells connected by long, delicate processes. The inner border of tin- highly characteristic middle layer forms a transi- tion zone, known as the intt-rnifdiatc layer, .in which gradations from the modified to the ordinary type of stratified epithelium are seen. The intermediate layer is best marked over the upper part of the crown, at the sides thinning out and entirely dis- DEVELOPMENT OF THE TEETH. 1561 appearing at the margin of the enamel-organ, where the outer and inner layers of the latter are continuous. The modified epithelial tissue of the middle layer, sometimes called the enamel-pulp, is greatest in amount just prior to, or during the beginning of, active tooth-formation, about the fifth or sixth foetal month. The inner layer of the enamel-organ comprises a single row of closely set, tall, cylindrical elements, the enamel-cells, adamantoblasts, or ameloblasts, through the active agency of which the enamel is produced. The ameloblasts are best developed where they cover the apex of the dental papilla, the location of the earliest formed den- tine ; in this situation the cells measure from .025-. 040 mm. in length and from .004 .007 mm. in breadth. They possess an oval nucleus about .010 mm. long, which usually lies close to the outer end of the cell, embedded in cytoplasm exhibit- ing a reticulum and often minute granules. The ameloblasts are united with one another by a small amount of cement-substance, and are denned from the interme- diate layer by a fairly distinct border. Opposite the sides of the dental papilla, cor- responding to the limits of the future crown, the ameloblasts gradually diminish in height until they are replaced by low cubical cells which, at the margin of the enamel- organ, are continuous with the epithelium of the outer layer. Preparatory to the for- mation of the dentine of the tooth-root, this margin grows downward towards the base of the elongating dental papilla, which is thus embraced by the extension of the Dental groove Oral epithelium v Atrophic epithelial net-work __i^^{fj Enamel^ Dentine Epithelial sheath Position of mesoblastic dental papilla Reconstruction of developing lower incisor tooth from embryo of 30 cm. length, about twenty-four weeks. (Drawn from Rose' s model.) enamel-organ. The investment thus formed constitutes the epithelial sheath (Fig. 1320), a structure of importance in determining the form of the tooth, since it serves as a mould in which the young dentine is subsequently deposited ; there is, however, insufficient evidence to regard the epithelial sheath as an active or necessary factor in the production of the dentine. The formation of the enamel, in contrast to that of the dentine, results from the activity of ectoblastic epithelium, and may be regarded as a cuticular development carried on by the ameloblasts. The earliest stage in the production of enamel is the appearance of a delicate cuticular zone at the inner end of the ameloblast ; this fuses with similar structures tipping the adjoining cells to form a continuous homo- geneous mass. The latter soon exhibits differentiation into rod-like segments, the enamel-processes, or processes of Tomes, which are extensions from the ameloblasts and are the anlages of the enamel-prisms, and the interprismatic substance. The latter becomes greatly reduced in amount as the development of the enamel-columns progresses ; the major part, becoming incorporated with the processes of Tomes, forms the cortical portion of the enamel-prisms, while the remainder persists as the cement-substance which exists in meagre quantity between the mature prisms. The enamel -processes are for a time uncalcified, but with the more advanced formation of the enamel-prisms the calcareous material, which is deposited as granules and spherules, appears first in the axis of the prism, later invading the periphery (Ebner). The 1562 HUMAN ANATOMY. enamel increases in thickness by the addition of the last-formed increments at the inner ends of the ameloblasts, the same cells sufficing for the deposit of the entire Owing to the expansion of the external surface of the crown, the diameter of mass. FIG. 1321. Section of developing tooth throu Intermediate layer of enamel-organ Ameloblasts Young enamel with Tomes 's processes Dentine Last-formed dentine Odontoblasts Embryonal pulp-tissue nction of enamel and dentine. X 400. FIG. 1322. the enamel-prisms augments towards their outer ends to compensate for the increased area which they must fill, since no additional prisms are formed. The complex curvature of the enamel-prisms and the oppositely directed ranges of the latter, producing the appearance of Schreger's stripes, result from changes in the position of the enamel-cells incident to the growth of the crown, since the axes of the newly formed prisms correspond with those of the ameloblasts, variations in the direction of which affect the disposition of the enamel-columns. The earliest formed enamel lies in close apposition with the oldest dentine con- stituting the membrana praeformativa ; the last devel- oped immediately beneath the ameloblasts. The enamel, therefore, is deposited from within outward, or in the reversed direction followed by the growth of the dentine. The oldest strata of both substances lie in contact ; the youngest on the extreme outer and inner surfaces of the tooth. After the requisite amount of enamel has been pro- duced, differentiation into prisms ceases, in consequence of which the last-formed enamel remains as a continu- ous homogeneous layer investing the free surface of the crown, known as the membrane of Nasmyth. The Tooth-Sac. Coincidently with the develop- ment of the enamel-organ and the growth of the dental papilla, the surrounding mesoblast undergoes differen- tiation into a connective-tissue envelope known as the dental or tooth-sac. The latter not only closely invests the enamel-organ, but is intimately related to the base of the dental papilla, with which it is continuous. In contrast to the epithelial enamel-organ, which is entirely without blood-vessels, the Isolated ameloblasts from in- cisor of new-born child, a, basal plate; />, cuticular border; c, pro- of Tomes; :) DEVELOPMENT OF THE TEETH. 1563 inner part of the tooth-sac is richly provided with capillaries, and therefore is an important source of nutrition to the developing dental germ. The part of the sac opposite the root of the young tooth is at first prevented from coming into direct contact with the dentine by the double layer interposed by the epithelial sheath. This relation is maintained until the development of the cement begins, when the vascular tissue of the dental sac breaks through the epithelial sheath to reach the surface of the dentine, upon which the cementum is deposited by the mesoblast. In consequence of this invasion, the epithelial sheath is disrupted into small groups or nests of cells which persist for a long time as epithelial islands within the fibrous tissue of the alveolar periosteum into which the dental sac is later converted. The formation of the cementum takes place through the agency of the mesoblastic tissue in a manner almost identical with the development of subperiosteal FIG. 1323. Jaws of child of six years, showing all temporary teeth in place with permanent teeth in various stages of development. bone, the active cement-producing cells, or cementoblasts, corresponding to the osteo- blasts which deposit the osseous matrix upon the osteogenetic fibres of the periosteum. A conspicuous feature of cementum is the unusual number of transversely disposed bundles of fibrillae, or Sharpey's fibres, among which many are imperfectly calcified. The cementum appears first in the vicinity of the neck of the tooth, and progresses towards the apex of the root as the dentine of the fang is deposited. After the tooth is fully formed, the layer of cement continues to grow until thickest at the apex, which it completely invests, with the exception of the canal leading to the entrance of the pulp-cavity. The cement being deposited directly upon the homogeneous layer con- stituting the external surface of the dentine, the firm connection between the two portions of the teeth is one of adhesion rather than of union. Later secondary changes may exceptionally bring the canaliculi of the cement into communication with the terminations of the dentinal tubules. During the changes incident to the 1564 HUMAN ANATOMY. completed tooth-development the tissue of the dental sac becomes denser, the part opposite the root persisting as the pericementum which intimately connects the cementum with the alveolar wall, while the more superficial part blends with the tissue forming the gum. The development of the permanent teeth is early provided for by the dif- ferentiation of the anlages of the secondary dental germs during the growth of the first. This provision includes the thickening and outgrowth of the dental bar to form the enamel-organ of second dentition, and later the appearance of a new dental pa- pilla beneath the epithelial cap. The enamel-organ for the first permanent molar appears about the seventeenth week of foetal life, followed soon by the corresponding dental papilla. The germs of the permanent incisors and canines, including the papillae, are formed about the twenty-fourth week ; those for the first bicuspids are seen at about the twenty-ninth week, and those for the second bicuspids about one month later. The interval between the formation of the enamel-organ and the asso- ciated dental papilla increases in the case of the last two permanent molars. While the enamel-germ of the second molar appears about four months after birth and the corresponding papilla two months later, the enamel-organ for the third molar, or wisdom-tooth, which is visible about the third year, precedes its papilla by almost two years. The First and Second Dentition and Subsequent Changes. At birth the jaws contain the twenty crowns of the milk-teeth, the still separate cusps of the first permanent molars, one of which has begun to calcify, and the uncalcified rudi- ments of the permanent incisors and canines behind and above the corresponding milk-teeth of the upper jaw, behind and below those of the lower. At birth the bony plate above the alveoli of the upper jaw is separated by a little diploe from the floor of the orbit. The milk-teeth come through the gum in five groups at what are called dental periods, separated by intervals of rest. The grouping is more regular than the time of eruption. The teeth of the lower jaw have a tendency to precede their fellows of the upper. TABLE OF ERUPTION OF MILK-TEETH. 1 Dental Periods. Groups of Teeth. I. Six to eight months. Two middle lower incisors. II. Eight to ten months. Four upper incisors. III. Twelve to fourteen months. Two lateral lower incisors and four first molars. IV. Eighteen to twenty months. Four canines. V. Twenty-eight to thirty-two months. Four second molars. The interval between the first and second periods is practically nothing. It is very common to have the first two groups appear together. After this every interval is longer than the preceding one. In the matter of time no part of development is more irregular than that of the teeth. The first incisors occasionally appear early in the fifth month and sometimes not till the tenth, or even later. The first dentition is sometimes complete at or shortly after the close of the second year. The roots arc- not fully formed when the crowns pierce the gums. The first set of teeth is in its most perfect condition between four and six years. Calcification of the second set begins in the first molar before birth, in the incisors and canines at about six months, the bicuspids and the second upper molar in the third year, the second lower molar at about six, and the wisdom-tooth at about twelve. The first permanent molars come into line with the- milk-teeth, piercing the gums before any of the latter are lost. Before eruption the upper first molars lie nearer tin- median line and farther forward than the lower. The roots of the incisors arc- absorbed and the crowns fall out to make way for their successors. The molars do the same for the bicuspids which grow between their roots. The permanent superior canines are developed above the interval between the lateral permanent incisors and the first bicuspid, which are almost in contact. An expansion of the jaw is necessary for them to come into place. The inferior ones have more room. Both are somewhat external to their predecessors. The second upper molar comes down from above and behind, 1 From Hotch's JVdiatrirs. DEVELOPMENT OF THE TEETH. 1565 and so does the wisdom-tooth much later. The inferior second molar is formed almost in the angle between the body and ramus. The inferior wisdom-tooth, before it cuts the gum, faces forward, inward, and slightly upward. To the table from FIG. 1324. Permanent molars Permanent molar Permanent canine Bicuspids Permanent incisors Temporary canine Temporary molars Permanent incisors Temporary canine Permanent canine Bicuspids Jaws of child of ten years, showing partially erupted permanent teeth with temporary canines and molars still in place. Rotch we add one from Livy, 1 who made observations on several thousand children of English and Irish operatives. TABLE OF ERUPTION OF PERMANENT TEETH. 2 Years. Groups. 6 Four first molars. 7 Four middle incisors. 8 Four lateral incisors. 9 Four first bicuspids. Years. Groups. 10 Four second bicuspids. 11 Four canines. 12 Four second molars. 17 to 25 Four wisdom-teeth. TABLES SHOWING TIME OF ERUPTION OF PERMANENT TEETH. 3 BOYS. Ages. 9 Lateral incisors .... 2 42 First bicuspids .... i Second bicuspids Canines Second molars 76 12 4 I 59 36 5 18 28 25 5 16 Total. 59 90 . . loi 79 British Medical Journal, 1885. 42 67 275 184 78 12 663 2 From Rotch. 3 From Livy. 1566 HUMAN ANATOMY. GIRLS. Ages. 9 10 ii 12 13 14 15 16 Total. Lateral incisors 24 8 4 . . . . . . . . 36 First bicuspids 56 13 2 i i . . . . 73 Second bicuspids 51 16 2 2 71 Canines 30 34 12 5 . . i . . 82 Second molars 5 44 80 288 249 66 14 746 ( It seems possible from the method employed that, especially in the case of the second molars, the tables may err on the side of overstating the age.) Livy's researches sho\v that in the first dentition the first molars, incisors, and canines conn- through first in the lower jaw. In most cases the bicuspids come first in the upper. The second molars come first in the lower jaw, unless their appearance is delayed, in which case the order is uncertain. The date of the appear- ance, of the second molar can be only an approximate guide to the age. When it is present the child is unlikely to be under twelve. The change in the shape of the jaw namely, the lengthening necessary for a longer row of larger teeth, as well as the widening required to make room for the canines begins in the course of the second dentition and continues after its close, as the second molar does not at once assume its permanent position in regular line with the rest. It was pointed out in the section on the growth of the face that the greatest activity of growth takes place at the pauses of dentition. The roots of the permanent teeth are by no means fully developed at their eruption. With their perfection the sockets are formed around them by the harmonious moulding of the parts involved. Homologies. There are two chief evolutionary theories of the origin of the mammalian teeth : one, the concrescence theory, is that they are formed by the growing together of originally separate cones, the primitive reptilian teeth. This view is supported by Rose l and Kiikenthal, 2 at least for the bicuspids and molars. Cope,* whom Osborn* has followed, advanced the differentiation theory, according to which the many cusps of the molars have arisen as outgrowths from a primitive cone. This is based on comparative anatomy and paleontology. According to this, there was first the cone, in the upper jaw called the protocone and in the lower the/ro/o- conid. Two secondary cusps next appeared respectively before and behind it : the paracone and metacone of the upper teeth and the paraconid and mctaconid of the lower. The next change is for these to move to the labial side in the upper jaw and to the lingual in the lower. Thus the primitive cone and these two secondary ones form the points of a triangle with the base outward in the upper jaw and inward in the lower. A prolongation, the talon or heel, is next developed on the posterior end of the tooth, and rises into a single cusp, the hvpocone in the upper jaw and the hypoconid in the lower. The last, however, has two secondary cusps spring from it, the entoconid and the hypoconid. According to this theory, the paraconid of the lower teeth has disappeared in the human molars owing to want of room consequent on the develop- ment of the talon of the upper teeth. The following table shows the homologies of the cusps of the human molars according to Osborn. UPPER MOLARS. Anterior lingual Protocone. ") Anterior buccal "... Paracone. \ Forming the triangle. Posterior buccal Metacone. ) Posterior lingual Hypocone. The talon. LOWER MOLARS. Anterior buccal Protoconid. ) D Anterior lingual Metaconid. ( R Posterior buccal Hypoconid. Posterior lingual .* Entoconid. J- The talon. Posterior Hypoconulid. Rose has advanced, in support of his theory of concrescence, that calcification begins sepa- rately for each cusp. Osborn points out that Rose has shown that they ossify very nearly in the order of their alleged evolution. Schwalbe 5 professes himself unable to decide on "the relative merits of the two theories. Variations. -Variations of the cusps and of the fangs have been described with the teeth. Those of number affect chiefly the incisors and molars. An additional incisor may occur on one or both sides in either dentition, not very rarely in the upper jaw, but extremely so in the lower, the condition in the latter being more stable. Extra upper incisors are often more or less displaced to the rear and implanted obliquely. They are particularly common in rases of cleft palate ; not impossibly the presence of additional teeth predisposes to the non-union of the 1 Anatom. Anzeiger. Hd. \ii., 1892. 2 Jenaiselie Xeitschrift, Hd. xxviii., 1893. s Journal of Morphology, iSSS, iss () . 4 American Naturalist, iSSS, and International Dental Journal, 1895. 5 Anatom. An/ei^er, Hd. ix., iS<4. THE GUMS. 1567 premaxillary and the maxillary bones, or to the non-union of two parts of the former, supposing that two such parts really exist. The extra incisor may apparently appear on the median side of the first, between the first and second, or between the latter and the canine. To account for this Rosenberg 1 asserts that the typical number is five, as in the opossum, of which the second and fourth are the two persistent ones, and that either the first, third, or fifth may occasionally present itself. Th. Kolliker 2 records a case of right cleft palate in which, besides the four regular incisors, three were found between the cleft and the right canine. As cases of excess of incisors are much more common than of deficiency, the disappearance of the upper lateral one does not seem imminent ; still, there are signs of degeneratiqn. The crown is less square than that of the central, it is occasionally pointed, often unusually small, sometimes not reaching the line of the other crowns. It may be absent, and then a series of cases can be made ranging from those in which the remaining incisor is separated both from its fellow of the other side and from the canine beside it by large gaps to those in which the teeth are regular and continuous. Very rarely one of the lower incisors is wanting, and, according to Rosenberg, either may fail. A fourth molar is very uncommon ; but not at all rarely the wisdom-tooth is late in coming through the gum, and occasionally it never does. It seems sometimes to be wanting and often is rudimentary. It has been seen represented by three detached cusps, an apparent confirmation of Rose's views of the homology of the teeth. The entire dental series may be unusually large or small. In the former case the face is prognathous, probably as a result of the increase of space required for the teeth. The upper central incisors are occasionally very large without increase in size of the other teeth. The same is true of the molars ; in which case the number of cusps is generally greater, but the converse does not occur when the molars are unusually small. 3 The points of the canines may project beyond the line of the other teeth and the molars may increase in size from the first to the third. Teeth are sometimes remarkably displaced. The superior canines, owing to their high origin in the second dentition, are particularly subject to it. They may appear on the front of the jaw, in the antrum, the nose, or the back of the mouth. The molars, and especially the wisdom-teeth, are also erratic. THE GUMS. This term is used rather vaguely to indicate the mucous membrane and sub- mucous tissue covering the alveolar processes and closely attached to the necks of the teeth. Whether the neck is entirely surrounded by it varies in different indi- viduals as the teeth are not in all equally close ; as a rule, owing to the ordinary expansion of the crown from the neck, at least a little of the gum is found between the teeth. It is some 3 mm. thick, dense, firmly fastened to the bone, and is neither very vascular nor very sensitive. In structure the gums resemble other parts of the oral mucous membrane, con- sisting of the epithelium and the connective-tissue layer. The latter, directly con- tinuous with the periosteum of the alveolar border and the pericementum, is composed of closely fitted bundles of fibrous tissue and beset with numerous papillae. On young teeth the epithelium is prolonged for from .5-1 mm. over the enamel and often for a short additional distance over the cement, ending in an abrupt margin. In the immediate vicinity of the tooth the papillae sometimes exhibit infiltrations of lym- phoid cells. The gums are without glands. The structures sometimes described as such, as the "glands of Serres," consist of nests of epithelial cells derived from the remains of the atrophic embryonal epithelial sheath (page 1563). THE PALATE. The Hard Palate. The shape and proportions of the hard palate have been discussed with the bones (page 228), so we have here to do only with its mucous covering. This is very firmly fastened to the rough surface of the bones by dense connective tissue which is particularly thick at the sides, doing much to fill up the angle between the roof and the alveolar process. On either side near the front, extending onto the inner surface of the alveolar processes, is a series of raised ridges (Fig. 1325), in the main transverse, although slightly convex anteriorly, the analogues of the palatal riigce of most mammals. They never extend behind the first molar tooth, are numerous and prominent in childhood, but much reduced in middle age, and occasionally wholly lost. 1 Morphol. Jahrbuch, Bd. xxii., 1895. 2 Nova Acte des Leopold. Carol. Akad. der Naturforscher, Bd. xliii., 1882. 3 Magitot : Traite" des Anomalies du Systeme Dentaire, 1887. i 5 68 HUMAN ANATOMY. Just behind the incisors, at or before the iiicisor canal, there is a small raised pad or fold of mucous membrane, on either side of which the orifice of the incisor canal is often found. When pervious, it is very minute, admitting merely a bristle. Behind this the palate presents a median raphc of paler color than the rest, which may FIG. 1325. Orifices of palatine glands Incisor pad with orifice of incisor canal Raphe Mucous membrane removed to show layer of glands Soft palate Superior dental arch and palate ; palatal rugae occupy anterior part. Soft palate partially cut away. run to the root of the uvula or may stop short of it, being often deflected to the left. A little behind the pad this line may be interrupted by a pale oval elevation or more often a depression. The membrane of the roof of the mouth is nowhere bright red ; that of the hard palate, however, is paler than the rest. There are no glands in the oval white space, but there is a continuous layer on either side of it. The orifices of the glands are easily seen with a lens, sometimes with the naked eye. A little in FIG. 1326. Muscular fibres of tongue Dorsal surface of tongue Anterior pillar of fauces Plica triangularii Tonsil Soft palate upratonsillar fossa Uvula Posterior pillar of fauces Epiglottis Sagittal section through palate, uvula, and tongue, showing il^ht l.iu-nil wallot i.uuvs; tongue has bri-n pulled downward by hook. front of the origin of the soft palate the mucous membrane becomes deeper colored. These differences in color are more striking in children. The Soft Palate. This structure consists of a fold of mucous membrane, con- tinuous with the hard palate, enveloping several layers of interlacing muscular fibres, at least i cm. in thickness at its origin. Its lower border is the edge of the fold. THE PALATE. 1569 This is concave on each side, and presents a median elongation, the uvula, which varies from a short prominence to a cord 2 cm. in length. Thus the palate has' a lower surface looking downward and forward and an upper one looking upward and backward. When the mouth is closed the palate and uvula rest against the tongue ; when open they hang free, but the muscles inside can modify their shape and position. Median sections show the tip of the uvula often reaching within half FIG. 1327. Pharvngeal mucous membrane Azygos lu A ul f Tendon f ^*. Pajati v Artery / Levator palati Palato-pharyngeus Masses of glands Oral mucous membrane Transverse section of soft palate near its anterior attachment. X 4. an inch of the tip of the epiglottis. Possibly muscular relaxation allows it to descend somewhat farther than in life, but it is certain that no very great elongation is neces- sary for it to touch that organ and give rise to great discomfort. The soft palate can be raised so as to touch the back of the pharynx and close all communication between the nose and the mouth. Two folds, the pillars of the fauces, each the reflection of the mucous membrane over a muscular bundle, start from the palate on either side. The anterior pillar, enclosing the palato-glossus muscle, arises from the front of the palate near the uvula, some distance anterior to the edge, and, curving downward, runs to the tongue at the junction of the middle and posterior thirds, separating the mouth from the pharynx and forming the posterior border of the sublingual space. The posterior pillar starts from the lower border of the palate on either side of the uvula, covering \hzpalato-pharyngeus, and runs down the throat to the superior cornu of the thyroid cartilage, the lower part being indistinct. Some of the muscular fibres within it go to the upper border of the thyroid cartilage in front of the horn, but the fold is not often found so low, except in frozen sections, in which it appears at the sides of the back of the pharynx. A deep triangular recess on either side, between the anterior and posterior pillars, contains the tonsil. This region is often vaguely described as the isthmus of the fauces, one being left in doubt whether it belongs to the pharynx or to the mouth. In the preceding pages the pharynx is described as beginning at the anterior pillar. The reasons for this divi- FIG. 1328. sion are developmental, Fibres of azygos uvulae Pharyngeal mucous membrane morphological, and phys- \rvvrv~'* "':'. '.x-.,^ iological. The part of the tongue anterior to pa.ato^yn.cus fi/^^ th j s io ^ * . Thicker short papillae are also found near the beginning of tin- pharyngeal surface. Small adenoid collections occur on the upper surface, as well as small glands situated in the depth of the mucous membrane. The orifices of the chief glandular layer pierce the inferior palatal surface. The Muscles of the Soft Palate. Some of the muscles arise in the soft palate ; others run into it. Isolation of the individual sets of fibres is not always possible. The tensor palati (dilatator tube) (Fig. 1330) arises from the scaphoid fossa at the root of the internal pterygoid plate, from the spine of the sphenoid, and from the outer membranous part of the Eustachian tube. It descends, vertically along the internal pterygoid plate as a round, red, and distinct muscle, which become s tendinous as it turns inward under the hamular process at right angles to its previous course, after which it broadens into the fibrous expansion in the soft palate already described, above the other muscles. A bursa lies between the tendon and the hamular process. THE PALATE. The levator palati (Fig. 1330) arises from the base of the skull at the apex of the petrous portion of the temporal bone and from the cartilaginous part of the Eustachian tube beside it. At first thick, it passes downward, forward, and inward with the tube, and, leaving it, expands into a layer which spreads out through the soft palate. Some of the anterior fibres from the tube go to the back of the hard pajate, constituting the salpingo-palatinus, while others, descending in the lateral wall of the pharynx, form the salpingo-pharyngcus, beneath the fold of corresponding name. The great body of the fibres crosses the middle line in the front part of the soft palate. Most of them descend in the opposite side. Some seem to form loops with an upward concavity with fibres from the fellow-muscle. Near the hard palate this decussation completely divides the glandular layer (Fig. 1327). The azygos uvulae (Fig. 1331), although probably a double muscle originally, soon (even at birth) becomes practically a single one. Arising from the tendinous fibres of the tensor palati just behind the posterior nasal spine, it soon becomes mus- cular and increases in size. Its course is downward into the uvula, but on reaching *he base it is already broken up into separate bundles which pass about and through FIG. 1330. Hard palate Hamular process Tensor palati Levator palati Soft palate (cut) External pterygoid plate Posterior nares Opening oi Eustachian tube Cut edge of pharynx Mass of adenoid tissue Fossa of Rosenmuller (opened) Styloid process Occipital condyle Inferior surface of skull with upper part of opened pharynx and palatal muscles attached ; viewed from behind. the glandular core of the uvula. The belly of the muscle lies near the dorsal surface, between the fibrous expansion of the tensor palati and the levator palati, which decus- sates on its oral surface. The palato-pharyngeus (Fig. 1331) has a complicated origin in more than one layer from the border of the hard palate, from the lower surface of the apo- neurosis, and perhaps from fibres of the levator palati. Certain fibres, either arising in the middle line or coming from the other side, pass downward and outward over the azygos uvulae ; others lie beneath the glandular layer. Some of the fibres seem to continue the course of the salpingo-pharyngeus of the opposite side, with- out being directly continuous. The muscle passes down near the edge of the soft palate and then in the posterior pillar into the side of the pharynx, where it min- gles with the stylo-pharyngeus. A part is inserted into the upper border of the thyroid cartilage, and sometimes into the superior horn. It also expands, together with the stylo-pharyngeus, into a thin layer just beneath the mucous membrane of the back of the pharynx, which meets its fellow in the median line where it is inserted into the pharyngeal aponeurosis. Its lower limit is a curved line with the concavity looking upward and outward, behind the larynx (Fig. 1361). (This part 1572 HUMAN ANATOMY. of the muscle must be dissected from behind, after removing the constrictors of the pharynx. ) The palato-glossus (Fig. 1339) is a small bundle arising from near the middle line of the oral side of the lower part of the soft palate, forming by its projection the anterior pillar of the fauces, in which it runs to the tongue, where it joins the trans- verse fibres. The pair of muscles act as a sphincter tending to close the passage from the mouth to the pharynx. A thin expansion from this muscle passes over the tonsil. Vessels. The arteries of the palate (both hard and soft) come chiefly from the descending palatine, which, emerging from the posterior palatine canal, runs for- ward along the inner side of the base of the alveolar process. It sends a few branches FIG. 1331. Salpingo- pharyngeus Levator palati Palato-pharyngeus Nasal septum Eustachian tube ^ External \ pterygoid Levator palati I Tensor palati Internal pterygoid f- Hamular process Tensor palati ygos uvula- Palato-pharyngeus Stylo-pharyngeus Posterior surface of tongue .Superior orifice of larynx Posterior crico-arytenoid (Esophagus Muscles of palate and pharynx, seen from behind ; pharynx laid open. inward and backward to the front of the soft palate, which is supplied on the side by a branch either from the facial or from the ascending pharyngeal. It is to be noted that no vessel is likely to interfere with the division of the tensor palati at the inner side of the hamular process. The veins of the hard palate follow in the main the arteries. Those of the upper side of the soft palate join the plexus of the zygomatic fossa. The larger ones of the under side connect with the veins of the tonsil and tin- root of the tongue. The lymphatics of the hard palate and of the under side of the soft palate form a rich plexus. Those on the upper side of the latter are small. The chief current is to the deep glands of the neck. THE TONGUE. 1573 Nerves. The tensor palati is supplied by the mandibular division of the fifth pair, the other muscles by the pharyngeal plexus. The mucous membrane of the hard palate is supplied by the anterior palatine nerve and terminal branches of the naso-palatine. That of the soft palate is supplied by the other palatine nerves and by branches from the glosso-pharyngeal. THE TONGUE. The tongue is a median muscular organ attached to the floor of the mouth, the symphysis of the jaw, and the body and both horns of the hyoid, covered with mucous membrane, which when the mouth is closed it practically fills (Fig. 1339). The root is the attached portion, extending from the hyoid to the symphysis, com- posed of the genio-glossi and the hyo-glossi muscles. The tip is the free anterior end, flat both above and below when extended, and surrounded by mucous mem- brane. Behind this the tongue is a solid mass. The dorsum in its anterior two- thirds is convex from side to side, and rests against the hard and soft palates ; the posterior third, nearly vertical, looks backward, forming the front wall of the pharynx when the mouth is closed. There is a median groove in the upper part of this pos- terior third, continued for a little distance onto the top, in which the uvula rests. This hind portion is so broad that the edges of the tongue reach quite to the sides FIG. 1332. Anterior tongue anlage II arch III arch Larynx Reconstruction of floor of primitive oro-pharynx of embryo 12.5 mm. in length. X 16. (His.) Under surface of tongue of new-born child. (Gegenbaur,) of the pharynx. In the anterior two-thirds the edges of the tongue are prominent, overhanging the sides. Development shows that the tongue has a double origin, the posterior third arising from the sides of the pharynx and overlapping on each side the anterior two- thirds, which comes from a median mass, the tuberculum impar, of buccal origin ( Fig. 1332). The thyro-glossal duct comes to the surface at the junction of these parts, which in the infant are separated by the snlcus terminalis. As will later be evident, the manner of development is of much significance. The mucous membrane of the lateral and inferior surface is thin and smooth with small papillae at the tip. In the middle it forms a fold, \\\nx ; tongue drawn forward and downward. papilla. The mucous membrane covering the dorsum of the tongue is closely beset with elevations, or pafiillte, of which there are three varieties, the filiform, fungifonn, and circumvallate. In general they consist of a core of connective-tissue stroma cov- ered with stratified squamous epithelium ; the projection formed by the connective tissue bears minute secondary papilla-, which, however, do not model the free sur- Arbeilcn, Mil. vi., 1896. THE TONGUE. 1575 face of the mucous membrane. The anterior two-thirds of this surface are rough with fungiform and filiform papilla; ; the former, less numerous, appear as red points chiefly near the edges, while the filiform are everywhere, but arranged in par- allel rows continuing forward the lines of the circumvallate papillae. At the edges of the tongue, just in front of the end of the anterior pillar of the fauces, close inspec- tion, especially with a lens, will generally show a small series of minute transverse parallel ridges, corresponding to the papilla foliata of rodents in a rudimentary con- dition. The papilla circumvallata: are fungoid papillae surrounded by a depression bounded externally by a low annular wall. The usual number of these papillae is from nine to ten, ranging from six to sixteen (Miinch). The sides of the V in which they are disposed are not very symmetrical. Usually there is at least one median papilla behind the apex, and very rarely one or two before it. The circumvallate papillae are of especial interest as being the most important seat of the gustatory end- 1335 Filiform papilla Surface epithelium covering fungiform papilla Projections of tunica pro- pria constituting basis of Muscular tissue of tongue Section of lingual mucous membrane, showing filiform and fungiform papillae. X 75- organs, or taste-buds, which lie embedded within the epithelium lining the groove encircling the central elevation. A detailed description of the taste-buds is given with the organs of special sense (page 1433). The surface of the vertical posterior third of the tongue is smooth, in the sense that there are no papillae nor roughnesses, but it is studded with masses of lymphoid tissue, sometimes called the lingual tonsil ( Fig. 1334), which make numerous eleva- tions on its surface. The mucous membrane of the back of the tongue is continued in a thinner layer onto the front of the epiglottis. It presents the median glosso- epiglottic fold, containing fibro-elastic tissue and muscular fibres of the genio-glossi, which separate two little depressions, the glosso-epiglottic fossa. These may be with- out any definite lateral boundary, or may be embraced by the small lateral glosso- epiglottic folds, the internal borders of which are concave. The mucous membrane is firmly attached to the subjacent muscles in the anterior two-thirds of the tongue, but less firmly behind. Glands of the Tongue. The lingual glands include both serous and mucous varieties, which are distributed as three groups : (i) serous glands, (2) posterior mucous glands and (3) anterior mucous glands. '576 HIM AN ANATOMY. The tubo-alveolar glands surrounding the circumvallate and the foliate papillae are the only ones of a purely serous type ; their thin, watery secretion is no doubt an important medium in conveying sapid substances to the taste-buds situated in this FIG. 1336. / Epithelium covering filiform papillae Capillary loops within connective-tissue basis of papillae Mucous membrane Muscular tissue I Injected mucous membrane and subjacent areolar and muscular tissue from upper surface of tongue. X 60. FIG. 1337 E fc\ -.' ,"v :lx \m- ': ':*? Taste-bud Annu]ar wal , Central/ ^\"vv' portion (it | >a- - *- ' pilla con- ., nective tissue .,".') ;sue * .* * * I'allate papilla from child's tongue, showing central portion ami cnnirlin.i; lold. X 75- s >~$yi \&^\ *' Miisi-ular tissue * * * * Si-, tidii at ran fin-umvallatf papilla from child's tongue, showing central porti vicinity. The glands encircling the circumvallate papillae constitute an annular group some 4 nun. wide.- and alxuit t \\icc as deep. Those alxnit the pajtilhr foliata foKin an elongated group, about 3.5 mm. in width, which extends from, 815 mm. in front of THE TONGUE. 1577 the base of the palato-glossal fold. Anteriorly towards the dorsum the serous glands remain isolated ; posteriorly they come into contact with the mucous glands, so that alveoli of both varieties may be included within a single microscopical field ( Fig. 1 287 ). The posterior third of the dorsum, from the circumvallate papillae backward, possesses a rich, almost continuous layer of mucous glands, 5 mm. or more in thick- ness, which lie beneath the mucous membrane and mingle with the lymphoid tissue. Since the alveoli lie among the muscles at some depth, the excretory ducts often attain a length of from 10-15 nim. , and open on the free surface in close association with the lymph-follicles. The anterior mucous glands (Fig. 1287) are disposed principally as two elon- gated groups, glandules linguales anteriores, or glands of Nuhn, or of Blandin (from 15-20 mm. in length, 7-9 mm. in width, and somewhat less in thickness), which lie on either side of the mid-line, near the tip of the tongue, among the mus- cular bundles. They meet in front, but diverge behind, where they may be con- FIG. 1338. Glands Interlacing fibrous and muscular bundles Glands Section from posterior third of child's tongue, showing lymph-nodes constituting a part of lingual tonsil. X 30. tinned backward by additional collections of mucous glands akmg the edges of the tongue. The ducts five or six in number open on the folds occupying the under surface of the tongue near the frenulum. Muscles of the Tongue. These include two groups, the extrinsic and the intrinsic muscles. The former pass from the skull or hyoid bone to the tongue ; the latter comprise the particular muscles forming the principal mass of the organ. Their general arrangement is as follows. Under the mucous membrane is a dense sheath of longitudinal fibres, surrounding the others completely near the apex, and farther back wanting at the middle of the under surface where the fibres of the genio-glossi and hyo-glossi enter the organ. This outer layer is the cortex. The inner part is divided into two by a vertical median septum of areolar tissue, which is quite dense in its upper part. It is sickle-shaped, with the point in front and not reaching the apex. The inner portion, or medulla, is composed of transverse muscle-fibres inter- posed between layers of those called vertical, which in fact present many degrees of obliquity. The extrinsic muscles are the genio-^ glossus, the hyo-glossus, the stylo-glossus, and the palato-glossus, to which may be added, from its position, the genio-hyoid. All of these are in pairs and symmetrical. 1578 HUMAN ANATOMY. The genio-hyoid (Fig. 1339) is a collection of fleshy fibres extending close to the median line, from the inferior genial tubercle to the anterior surface of the body of the hyoid bone. It is a thick band, four-sided on transverse section, with rounded angles, and expands laterally on approaching its insertion. A layer of areolar tissue separates it from its fellow. Nerve. The nerve-supply is from the hypoglossal, but probably consists of fibres derived from the cervical nerves. Action. To draw the hyoid forward and upward ; or, when fixed below, to depress the mandible. The genio-glossus (Fig. 1339) arises just above the preceding by short ten- dinous fibres from the superior genial tubercle. Its inferior fibres run horizontally backward to the base of the tongue, passing over the hyoid bone to the base of the epiglottis ; the fibres above these, inserted successively into the mucous membrane of FIG. 1339. Stump of masseter Tensor . palati _ palati ^B/ Hamula process styd process Superior constrictor Pterygo-mandibular ligament Stylo-glossus Stylo-pharyngeus Stylo-hyoid (cut) Middle constrictor Genio-hyoid Hyo-glossus Inferior constrictor Pharyngeal and extrinsic lingual muscles the dorsum of the tongue near the middle line, are at first oblique, then vertical, and finally concave anteriorly as they approach the apex, so that the muscle is fan-shaped when seen from the side. Each muscle is separated from its fellow by the median septum. Nerve. The hypoglossal. Action. The complex action of this muscle includes retraction of the tongue by the anterior fibres, drawing forward and protrusion by the posterior fibres, and depres- sion, with increased concavity, of the dorsum by its middle part. The hyo-glossus (Fig. 1339), external to the preceding, from which it is sepa- rated by areolar tissue, arises from the side of the body of the hyoid, the whole of the greater horn, and the lesser horn. The last portion, rather distinct from the rest, is deseribed sometimes separately as the chondro-glossus. The whole muscle, applied to the side of the tongue, forms a layer of fibres directed upward and for- THE TONGUE. 1579 ward ; towards the front its fibres are almost longitudinal. The fibres from the lesser horn run on the dorsum beneath the mucous membrane, forming a part of the super- ficial longitudinal system. Nerve. The hypoglossal. Action. To depress the sides of the tongue, thereby increasing the transverse convexity of the dorsum ; the muscle also retracts the protruded tongue. The stylo-glossus (Fig. 1339) arises from the tip of the styloid process and from the beginning of the styio-maxillary ligament. It is a small ribbon-like muscle with an anterior and a posterior surface, but as it descends it twists so as to lie along the outer side of the tongue, which it reaches in the region of the circumvallate papillae. On joining the tongue the fibres divide into an upper and a lower bundle, both of which are chiefly longitudinal, although some fibres blend with the transverse series. It is soon lost in the sheath of longitudinal fibres. Nerve. The hypoglossal. Action. To retract the tongue and to elevate the sides, thus aiding in pro- ducing transverse concavity of the dorsum. The palato-glossus (Fig. 1339) arises from the anterior or buccal aspect of the palate, and descends within the fold forming the anterior pillar of the fauces to the tongue, where it joins the transverse fibres, passing between the two parts of the stylo-glossus. Nerve. From the pharyngeal plexus, the motor fibres coming probably from the spinal accessory nerve. Action. To elevate the tongue, to depress the soft palate, and, with its fellow by approximating the anterior pillars, to close the fauces. FIG. 1340. Longitudinal fibres Longitudinal , .>^: <..*.i*MtitftattClft}MafeMnaM. / fibres .Transverse fibres \ \ Plica fimbriata Glands Vertical fibres Transverse section of tongue of child, near tip. X 3. The intrinsic muscles are the lingualis, the transversus, and the perpendicu- laris (Fig. 1340). The lingualis, sometimes divided into a superior and an inferior, comprises the greater number of the longitudinal fibres, all, in fact, that do not come from the extrinsic muscles. The thickness of this layer is some 5 mm. The transversus furnishes nearly all the transverse fibres, the most important extrinsic contribution being from the palato-glossus. It arises from the septum and runs outward to the mucous membrane ; as it approaches the cortex the fibres break up into bundles, among which pass groups of the fibres of the lingualis. The trans- versus is arranged in a series of vertical layers, between which pass layers of the vertical set. Thus a horizontal section has the effect of a series of transverse fibres like the bars of a gridiron with the cut ends of the vertical fibres between them and the longitudinal fibres of the lingualis at either side. Near the apex fibres of this system run directly from the mucous membrane of one side to that of the other. The perpendicularis is the name given to the few vertical fibres that do not come from the extrinsic muscles. They occur chiefly at the tip and sides, passing from the lower to the upper mucous membrane. Nerve. All the intrinsic muscles are supplied by the hypoglossal. Action. The tongue is protruded chiefly by the action of the posterior fibres of the genio-glossus, drawing the posterior part of the tongue forward, assisted, perhaps, by the contraction of the transversus. It is withdrawn by its own weight. The HUMAN ANATOMY. longitudinal system, the various parts of which can act separately, turns the tip in any direction. The stylo-glossus and palato-glossus raise the posterior portion, particularly at the edges, but the latter probably acts more on the palate than on the tongue. Vessels. The principal arteries supplying the tongue are branches of the lingual, elsewhere described (page 735). Although there may be a trifling anasto- mosis at the tip between the vessels of the opposite sides, there is no communication sufficient to re-establish the circulation at once, so that ligation of either artery will render that half of the tongue bloodless for an operation. The -veins consist of four sets on each side, communicating freely with one another. They are ( i ) the dorsal veins forming a submucous plexus on the back of the tongue above the larynx and joining those of the tonsil and pharynx, (2) two veins accompanying the artery and sometimes forming a plexus about it, (3) two with the lingual nerve, (4) two with the hypoglossal nerve. Of these latter, the one below the nerve is the larger and is the ranine vein, running on the under surface of the tongue on either side of the frenum. The lymphatics present a rich net-work on the anterior two-thirds of the dorsum. The multitude of spaces throughout the organ communicate with lym- FIG. 1341. Longitudinal fibres Glands Portion of sublingual gland Vertical fibres Transverse fibres Septum Genio-glossus Hyo-glossus Transverse section of tongue of child, through middle third. X 3. phatics. Some from the median part empty into the suprahyoid glands, but most go to the submaxillary and to the deep cervical glands. Nerves. The motor fibres are supplied by the hypoglossal, aided probably by the facial through the chorda tympani. Those of common sensation are from the lingual branch of the fifth for the anterior two-thirds and from the gkeso-pharvngeal for the remainder, excepting the region just in front of the epiglottis, which is supplied by the superior laryngeal from the vagus. The glosso-pharyngeal a-rca somewhat overlaps the posterior third, as it supplies the circumvallate and foliate papillae. The chief fibres of special sense are derived from the glosso-pharyngeal, their principal distribution being to the taste-buds on the circumvallate papillae. Re- garding the source of the taste-fibres to the anterior parts of the tongue opinions still differ. According to many anatomists, these fibres reach their destination through the chorda tympani, since the latter nerve is supposed to receive taste- til >res from the ninth by way of the pars intermedia of \VrisU-rg, which accompanies the facial. According to Zander, 1 Dixon, 2 Spiller, 8 and others, however, the view attributing fibres of special sense for the anterior part of the tongue partly to the fifth nerve is eorrect. Growth and Changes. At birth the tongue is remarkable chiefly for its want of depth, as shown in a median section, which depends on th'e undeveloped condition of the jaws. This is gradually corrected coincidently with the growth of the face. 1 Anatomischer Anzeigef , Hd. \i\., 1897. - Kdinbur the font h -^a r<^ Trip cently erupted ; central notch marked out but not yet cleared out by breaking away of unpro- may be deficient, Opaque Or Chalky, the tected dentine; four lower incisors present pe>j- , ef r 11 .1 -u i 'ike excrescences due to loss of enamel and dentine soft or friable, the teeth irregular in size exposure of dentine. (Hutchison.) and uneven in position. The permanent teeth may show the same general aberrations as to growth and nutrition that are produced by stomatitis from digestive derangements or from local irritation. After mercurial stomatitis, for example, the teeth are irregularly outlined, horizontaHy seamed, scraggy, malformed, deficient in enamel, separated too widely, and dirty yellow in color. 1592 HUMAN ANATOMY. The typical (and pathognomonic) syphilitic teeth " Hutchinson's teeth" are the upper permanent central incisors. The type is observed in its perfection soon after the extrusion of these teeth. The essential characteristic is a crescentic notch (Fig- iSS. 1 !-^) in tne free edge of the tooth, the anterior border of the notch being bevelled from above downward and from before backward, i.e. , at the expense of the anterior surface and border of the tooth. Typical Hutchinson's teeth are, fur- thermore, reduced in length and narrowed, "stunted ;" their angles are rounded off, the lateral and inferior borders merging in a curved line ; they deviate from nor- mality in direction, their axes being obliquely convergent, or more rarely divergent, instead of parallel. The other surgical relations of the teeth and of the dental tissues which are of chief importance are concerned with the new growths originating in dental elements. The odontomata are divided by Sutton as follows, and the classification should be remembered in studying the anatomical development of the teeth : (i) Persistent portions of the epithelial sheath (page 1561), taking on over- growth, may give rise to an epithelial odontome (multilocular cystic tumor). (2 ) Expansion of the tooth-follicle with retention of the crown or root of an imperfectly developed tooth results in a follicular odontome (dentigerous cyst). (3) Hyper- trophy of the fibrous tooth-sac causes a fibrous odontome, especially frequent in rickets, which usually affects the osteogenetic fibrous membranes. (4) If the fore- going hypertrophy occurs and the thickened capsule ossifies, a ceviciitome results. ( 5 ) If this takes place irregularly, small malformed teeth "denticles" may form in large numbers and occupy the centre of the tumor (compound follicular odontome}. (6) Tumors of the root, after the full formation of the crown, are of necessity com- posed of dentine and cementum only, enamel not entering into them (radicu/ar odontomata}. (7) Tumors composed of irregular conglomerations of enamel, den- tine, and cementum, and often made up of two or more tooth-germs fused together, constitute composite odontomata. All these growths can be understood only by careful study of the normal development of the teeth. They are rarely diagnosed before operation, which is therefore in some cases needlessly severe. Sutton says very truly, " In the case of a tumor of the jaw the nature of which is doubtful, par- ticularly in a young adult, it is incumbent on the surgeon to satisfy himself, before proceeding to excise a portion of the mandible or maxilla, that the tumor is not an odontome, for this kind of tumor only requires enucleation. In the case of a follicular odontome it is usually sufficient to excise a portion of its wall, scrape out the cavity, remove the tooth if one be present, stuff the sac, and allow it to close by the process of granulation. ' ' The Roof of the Mouth and the Palate. The mucous membrane cov- ering the hard palate is so fused with the periosteum as practically to be inseparable from it. It is dense, resistant, and comparatively insensitive. A vertical trans- verse section of the roof of the mouth (Fig. 1294) shows the mucous membrane to be thickest laterally and thinner in the median line. Cleft palate (page 1590) results from imperfect fusion between the horizontal palatal plates of the maxillary processes of the first visceral arch. It is always in the middle line. It may involve the soft palate and uvula. If it extends forward as far as the alveolus, it follows the line between the maxilla and the premaxillary bone, usually terminating in a harelip (page 1589) opposite the interval between the lateral incisor and canine teeth. If it separates the maxillae on both sides from the pre- maxillary bone, it is almost always associated with double harelip. The toughness of the muco-periosteum of the hard palate facilitates the forma- tion of flaps in operations for the closure of such a cleft. In dissecting up the flaps it is well to keep close to the bone and to avoid the descending or posterior pala- tine branches of the internal maxillary artery. These vessels, on which the nutri- tion of the flaps as well as of the bone depends, emerge from the posterior palatine canal at a point on the line of junction of the hard and soft palates 8 mm. (y$ in.) anterior to the hamular process and a little to the inner side of the last molar tooth. They run forward in a shallow groove just internal to the outer border of the hard palate. They are nearer to the bone than to the mucous surface, but their pulsa- tions can often be felt by the finger. For these reasons incisions in uranoplasty PRACTICAL CONSIDERATIONS: THE MOUTH. 1593 FIG. 1352. Anterior lingual gland should be made close to the alveolus and the bone should be hugged as the flaps are raised. In troublesome bleeding from these arteries the posterior palatine canal may be plugged by a sharpened stick, which should previously be sterilized. When the clelt involves only the soft palate, staphylorrhaphy is required. The muscles that tend to pull the edges apart are the tensor palati and levator palati. The former turns around the hamular process and passes almost horizon- tally towards the median line, the latter lies close to the posterior surface of the soft palate and runs obliquely from above downward and inward. These muscles may be divided by various incisions, the simplest being a section of the velum near its lateral border and parallel with the cleft. The hamular process may be felt behind and a little internal to the last molar tooth. The pterygo-mandibular ligament may be felt passing from the hamular process to the posterior end of the mylo-hyoid ridge of the lower jaw just behind the last molar tooth. The fold of mucous membrane covering it may be seen when the jaws are separated widely. The lingual branch of the fifth nerve may be felt between the mucous membrane and the bone anterior to the base of the pterygo-mandibular ligament and below the last molar. With a finger passed behind the last molar, the swell of the alveolar ridge can be recognized as it nar- rows to pass into the ramus. The nerve is below and parallel with that ridge. It is sometimes divided for the relief of the unbearable pain of carcinoma of the tongue. This may be done by entering the point of a curved bistoury a little less than three-quarters of an inch be- hind and below the last molar and cutting on the bone towards the tooth. The Floor of the Mouth. The mylo-hyoid muscle, extend- ing from the symphysis to the last molar tooth, separates the buccal cavity from the neck. Infections or neoplasms beginning above this muscle are first recognized through the mouth ; those below it in the neck. The SublingfUal Sfland for Dissection of under sunace of tongue and sublingual space; , ,. . mucous membrane removed and tongue drawn upward and for- example, lies altogether above it ward from mouth. and directly beneath the mucous membrane of the floor of the mouth ; the duct of the submaxillary gland occupies a similar position. Affections of these structures, therefore, manifest themselves in the mouth. The submaxillary gland, however, lies partly beneath the poste- rior border of the mylo-hyoid. Accordingly, disease of this gland is apt to show most markedly beneath the jaw (Fig. 267, page 247). " Ludwig's angina" (page 553) may spread to the loose connective tissue between the mylo-hyoid muscle and the mucous membrane of the floor of the mouth. That membrane is reflected from the under surface of the tongue to the alveoli and is divided anteriorly by the frenum linguae. On either side of this may be seen the ridges indicating the situation of the sublingual glands, and close to the frenum at the inner end. of the ridge the papillae at the opening of Wharton's ducts, into which a fine probe may be passed (Fig. 1352). The inelastic character of the walls of the latter should be remembered as explaining in part the intense pain caused by an impacted submax- illary calculus. This is also in part due to the close relation of the duct to the - Cut surface of mucous membrane jjr Lingual vein \ il Lingual artery Submaxillary duct Sublingual gland 1594 HUMAN ANATOMY. lingual nerve. The relation of that nerve to the floor of the mouth posteriorly has already been described (page 1249). The fold of mucous membrane constituting the frenum may be abnormally short and prevent the free movements of the tongue, interfering with sucking during infancy and with articulation later. When its division is necessary, it should be cut through close to the jaw, and with blunt-pointed scissors directed away from the tongue so as to avoid the ranine veins which may be seen close to it on the under surface of the tongue. The ranine arteries lie farther out and are more deeply situated, being placed beneath two converging raised fringed lines of mucous membrane, the plica fimbriattz. A sublingual bursa is described by Tillaux as a triangular space situated between the genio-hyo-glossus and the mucous membrane, its tip being at the frenum, its base at the sublingual gland. Its existence, by no means constant, is said by Tillaux to explain the occurrence of the acute cystic tumor (grenmtillette) , "acute ranula,'' which is occasionally met with in this region. Ranulae ordinary retention cysts are common in the floor of the mouth, and .branchiogenic cysts, due to the incomplete closure of the first branchial cleft, are sometimes found there. The Cheeks. The buccal limits of the cheeks are accurately indicated by the reflections of mucous membrane lining them. By making outward traction on the angle of the mouth that membrane can be seen and palpated, and ulceration, as from a jagged tooth or beginning epithelioma, or mucous patches, or abscess, or new growths, can easily be detected. The papilla indicating the opening of the parotid duct may be seen or felt opposite the upper second molar tooth. A fine probe may be made to enter the duct for a short distance, the normal curves then interfering with its passage (Fig. 1343). Lipoma originating in the " boule de Bichat" (page 493) can be recognized. As the jaws are separated and closed the anterior border of the masseter may be seen and felt. The important structures of the cheek the facial vein and artery and the parotid duct are all anterior to this line (Fig. 691). The Tongue. Congenital deformity of the tongue is rare. Forked tongue normal in some birds and reptiles and in seals is rare ; it is usually in asso- ciation with other developmental defects, as cleft palate. Congenital absence has been noted (de Jussieu). Macroglossia {lymphangioma cavernosum, Virchow) is a congenital affection in which the lymph-channels and lymph-spaces are dilated and the lymphoid tissue throughout the tongue, but especially at the base, greatly increased. The tongue may attain an enormous size, and has even, by pressure, caused deformities of the teeth and alveolar arches and luxation of the mandible. The foramen caecum, indi- cating the junction of the pharyngeal and buccal parts of the tongue, is the superior termination of the foetal thyro-glossal duct. " Ducts lined with epithelium have been found leading from the foramen caecum to accessory glands about the hyoid bone. It is probably from these glandular and epithelial collections about the hyoid bone that certain deep-seated forms of cancer of the neck are developed. Some of these take the form of malignant cysts" (Treves). The upper surface of the tongue has for centuries been the object of especial observation in disease. The practical value of these observations is not univer- sally conceded, and too much weight has been placed upon them ; but there can be no doubt that some help in prognosis and even in diagnosis in digestive - *f* Li men-/ vestibuli I Pterygo-mandibular fold 1 Anterior pillar of fauces j Ventricle of larynx V \ Thyroid cartilage ', Sella turcica ffc V Naso-pharyngeal fold Fossa of Rosenmiiller Eustachian tube _L-J>haryngeal tonsil ; X-Salpingo-palatine fold _ ,lpingo- ' pharyngeal fold Faucial tonsil c Posterior wall of pharynx Palato-pharyngeal fold Pharyngo-epiglottic fold Epiglottis Cuneiform tubercle Tubercle of Santorini 1 Cricoid cartilage t (Esophagus Tracheal cartilag Sagittal section of head, slightly to right of median plane ; tongue has been pulled down. posterior pharyngeal wall. The greatest depth in this direction (3-4 cm.) is at the side, from the anterior pillar to the posterior wall. Behind the cricoid cartilage the 1598 HUMAN ANATOMY. front and back walls are probably in contact. In the female several of these distances are smaller. Thus the pharynx is in horizontal sections at most levels a transverse cleft. The naso-pharynx, broad from side to side and short from before backward, passes insensibly into the oro-pharynx when the soft palate is not raised so as to cut off communication. Anteriorly are the nasal openings, described with the nose. The separation of the two regions on the lateral waH is determined by the naso- pharyngcal fold which runs from the base of the skull to the beginning of the soft palate. This fold is very irregular in course and development. It occasionally is grooved so as to present a furrow. Sometimes the furrow takes the place of the fold and at other times the fold joins that in front of the opening of the Eustachian tube. This orifice is on a level with the end of the inferior turbinate bone and less than I cm. behind it. It is usually a triangular opening without a distinct border below, although it may be oval or even round. The longest diameter is about i cm. The end of the cartilage of the tube curves over the top of the opening from the front and descends along its posterior border, producing a strong fold of the mucous mem- brane, the salpingo-pharyngeal, which descends to be lost in the lateral wall of the oro-pharynx, or even sooner. The salpingo-palatine fold in front of the opening of the Eustachian tube is, as a rule, less prominent and very variable. It is formed above by the bent end of the cartilage, and below by a small band of fibrous tissue, the salpingo-palatine ligament, running from the cartilage into the soft palate. The fossa of Rosenmuller is a deep pocket at the angle of the pharynx between the posterior wall and the back of the projection of the cartilage of the tube. Its anterior and posterior walls are almost in contact and are often connected by accidental adhesions. This is the broadest part of the naso-pharynx. Adenoid collections the tubal tonsils are found in varying degree about the orifice of the tube, especially over the fold behind it. The belly of the levator palati muscle makes a prominence in the lateral wall below the tubal orifice. The oro-pharynx opens into the mouth at the anterior pillar of the fauces. The posterior pillar, covering the palato-pharyngeus muscle, runs down the side of the pharynx as the palato-pharyngeal fold. It may be traced to the base of the superior horn of the thyroid cartilage, or, as is most common, it is lost on the lateral wall a little higher. The pharyngo-epiglottic fold above mentioned arises from the front of the epiglottis near the lateral edge and runs upward and backward across the pharynx. It may end soon, or it may reach the palato-pharyngeal fold, or, crossing this, may extend even as far as the salpingo-pharyngeal one. It contains muscular or tendinous fibres from the stylo-pharyngeus. If well marked, it may bound below the niche containing the tonsil. The anterior wall of the oro-pharynx is formed, the mouth being closed, by the posterior vertical part of the tongue. The respiratory tract, passing through the nose, and the digestive, passing through the mouth, cross each other in the oro-pharynx, so that the former is the anterior below this point. The laryngo-pharynx, the lowest part of the pharynx, is, roughly speaking, the part below the level of the hyoid bone. It is separated from the oro-pharynx by the pharyngo-epiglottic fold. In the middle of it is the opening of the larynx behind the epiglottis and enclosed by the aryteno-epiglottic and interarytenoid folds. The sinus pyriformis is a depression on either side of the entrance of the larynx between the aryteno-epiglottic fold and the arytenoid cartilage internally and a part of the great wing, of the- thyroid cartilage and the thyro-hyoid membrane externally. It is open behind. The thin mucous membrane lining the sinus has a transverse fold, formed by the superior laryngeal nerve, in front between the hyoid bone and the thyroid cartilage. The lower part of the palato-pharyngeal fold is seen in frozen sections near the superior horn of the thyroid cartilage at the lateral aspect of the cleft, which is all that appears of the pharynx. The anterior wall behind the aryte- noid cartilages and the structures between them slants backward as it descends. Behind the cricoid cartilage it is vertical. Here the pharynx narrows to join the oesophagus. The mucous membrane of the pharynx is smooth, except for the elevations caused by collections of lymphoid follicles. It is more loosely attached and more THE PHARYNX. 1599 disposed to be thrown into folds in the lower part. Mucous glands, on the other hand, are numerous in the upper part, scarce below ; they lie partly within the mucosa and partly in the submucous tissue and between the muscular bundles. The character of the pharyngeal epithelium varies in different localities. In the nasal pharynx the stratified ciliated columnar cells of the nasal fossa are continued as the covering of the pharyngeal mucous membrane, while the oro-pharynx is clothed with stratified squamous epithelium continued from the mouth. The last-named type of epithelium likewise covers the greater part of the laryngeal portion. The exact distribution of the two varieties of cells is subject to considerable individual variation. The ciliated columnar type extends laterally to include the openings of the Eustachian tubes, but lower down gives place to the squamous. By no Base of skull I FIG. 1354. Nasal septum N'aso-pharyngeal fold Lymphoid tissue Posterior pillar of fauces.. Faucial tonsil - Pharyngo-epiglottic fold- ' - ' jSl-Uvula Dorsum of tongue ' "N, /ytiStyf*'. 1 Glosso-epiglottic fossa djjrjjjp-ff Median glosso-epiglottic fold ^Epiglottis. turned back Cut edge of pharynx Posterior surface of larynx Pharynx opened from behind ; epiglottis turned back. means the entire posterior surface of the soft palate is clothed with ciliated colum- nar cells, since the entire uvula and the edges of the palato-pharyngeal folds are invested with stratified squamous epithelium. The latter also covers the posterior wall of the pharynx and extends above as far as the vault. When covered with ciliated epithelium, the mucous membrane is redder, thicker, and contains more glands, but fewer papillae, than in those parts in which the squamous cells prevail. While containing much lymphoid tissue, fat is limited to a few deeply seated lobules of adipose tissue. Lymphoid Structures. The upper .part of the pharynx contains many lymphoid collections which make the surface uneven. They are much less frequent below. The larger and more constant masses are called ' ' tonsils. ' ' These include tin&faucial tonsi/s in the oro-pharynx, between the pillars of the fauces, the pharyn- i6oo HUMAN ANATOMY. FIG. X 355- geal tonsil in the upper part of the pharynx, the tubal tonsils at the openings of the Eustachian tubes, especially on the posterior fold, and the lingual tonsil, con- sisting of the scattered adenoid collections over the posterior third of the tongue. Many- additional lymph-nodules are scattered over the sides and roof, so connected as to form a lymphoid ring at the upper part of the pharynx. The faucial tonsils (Figs. 1326, 1353) are theoretically two almond-shaped masses of adenoid tissue, placed one on each side of the oro-pharynx, between the pillars of the fauces. The long diameter is vertical, and they have an outer and an inner surface and an anterior and a posterior border. The length is conventionally put at from 20-25 mm., the breadth at 15 mm., and the thick- ness at 10 mm. Practically, however, there is no definite shape nor size. In childhood the tonsil generally projects as a globular mass. If it extends more than slightly be- yond the level of the faucial pillars, it is said to be enlarged. After middle life it rises usu- ally but little from the floor of the niche. The shape of the free surface gives no clue to the size of the deep surface. In structure the tonsil is a mass of adenoid tissue en- closed in a fibrous capsule which is crossed on both the deep and free surfaces by a thin layer of muscular fibres. The superficial layer belongs to the palato-glossus ; the deep or external layer arises from the superior con- strictor and passes to the tongue. Beyond this externally are fat and areolar tissue. The closely adherent mucous membrane covers the free surface, which is full of pits from i or 2 mm. to i cm. in depth. Section through faucial tonsil, showing general dis- position of lymphoid tissue. X 20. FIG. 1356. Lymphocytes, invading Epithelium Blood-vessel The larger ones often expand be- low the orifice, so that they may collect and retain secretions. A small free space, the supratonsillar fossa, lies above the tonsil at the apex of the niche containing it ; at the front of this there is very often a series of crypts with detached adenoid tissue about them, bur- rowing under the anterior pillar from behind and making a pouch beneath a fold, the plica trian- gularis. The adenoid tissue is continuous below with that of the tongue. The mucous membrane of the oro-pharynx shows many scattered lymphoid follicles in its walls, especially on the sides at and above the level of the tonsils. Vessels. The arteries sup- plying the faucial tonsil are de- rived from several sources, and the arrangement of the vessels is extremely irregular ; the branch from the ascending pharyngral and that from the facial artery one or both enter its base, while twigs from the lingual and descending palatine arteries, Portion of faucial tonsil, showing epithelial lining of crypt invaded by escaping lymphocytes. X 325. THE PHARYNX. 1601 and perhaps others, reach it beneath the mucous membrane. Under ordinary cir- cumstances the tonsil is not very vascular, but receives a large quantity of blood when inflamed. There is a -venous plexus communicating with the veins of the pharynx. The lymphatics probably communicate both with those of the dorsum of the tongue and with the glands near the angle of the jaw. Nerves. The nervous supply is from the fifth and the glosso-pharyngeal. (The relations of the tonsils are given with those of the pharynx, page 1602.) The pharyngeal tonsil (Fig. 1353), sometimes called the third tonsil, is a median mass of adenoid tissue in the postero-superior wall of the pharynx, which reaches its greatest development in early childhood, generally dwindling after the twelfth year. When well developed, it lies below the occipital and the basi-sphenoid, nearly filling the space from the nasal septum to the back of the pharynx and almost touching on either side the folds made by the tubal cartilages. Its thickness in the median line is nearly i cm. Thus without being hypertrophied it nearly fills the naso- pharynx. The pharyngeal tonsil is a lobulated organ, the swellings being often regu- Foramen caecum FIG. 1357. Crista galli Cartilage of septum Vomer Permanent incisor Tongue Frenum of tongue Pituitary body Cranio-pharyngeal canal Pharyngeal tonsil Occipital bone Pharyngeal tonsil V Anterior arch of atlas Genio-hyoid Mylo-hyoid Hyoid bone Thyroid cartilage Third cervical vertebra Ventricle of larynx Cricoid cartilage Reduced one-fourth. " LUWIS& (j.. ijjj- *-/ r 't-: i .v.i Anterior portion of mesial sagittal section of child's head, probably of about three years. larly arranged around a central depression ; consequently it presents many pockets. The central one, which varies widely, is often improperly called the bursa pharyngea. It has absolutely nothing to do with the canal from the mouth to the sella turcica, through which a process of the oral tissue passes in early foetal life to the pituitary body (Fig. 1357), being decidedly behind that passage. Neither is it the true bursa pharyngea, since this term is more properly applied to a structure of uncommon occurrence, namely, a still more posterior pocket in the mucous membrane leading from the roof of the pharynx, just behind its tonsil, into a small recess not over 1.5 cm. in length, on the under side of the basilar process. Relations of the Pharynx. The structures behind the posterior wall have been mentioned (page 1596). The tip of the normal uvula hangs on a level near the lower part of the axis or the top of the third cervical vertebra. The tip of the epi- glottis is usually opposite the lower part of the third. The second and third cervical vertebrae are those behind that part of the pharynx seen through the open mouth. The pharynx ends at about the top of the seventh cervical vertebra. The lateral wall of the pharynx is very narrow, except in the region of the tonsils, where it reaches for- ward to the anterior pillar of the fauces. From the top of the thyroid downward it TOT 1602 HUMAN ANATOMY. Pharyni isil of child one year (Schwabach. ) Lymph-nodule is nothing more than the fold around the end of a transverse linear cleft. The whole lateral aspect is covered by a thick layer of areolar tissue, continuous with that of the carotid sheath. It 'is most convenient to give the relations of the lateral wall from below upward, excepting the nerves. The upper part of the lobes of the thyroid gland comes very close FIG. 1358. to the lower part of the pharynx, and may even touch it without undue enlargement. They separate the common carotid from the pharynx. A little higher this vessel is on the outer side of the great wing of the thyroid cartilage, but if the head be turned to one side the vessel of the other side will rest on the pharynx. The common carotid artery is very close to the pharynx just before its division. The inter- " " old. nal carotid lies against it until it reaches the skull. The beginning of the external carotid with its lingual and facial branches is also against it. The ascending pharyngeal artery runs along it, the middle meningeal lying against its upper part. The internal jugular vein is, probably, nowhere in direct contact with the pharynx unless just below the skull. The submaxillary gland touches it at the angle of the jaw. The sympathetic nerve comes in contact with the back or side of the pharynx. The vagus lies against the pharynx behind the internal carotid ; on reaching the common carotid, however, FIG. 1359. it is in less direct contact. Its superior laryngeal branch crosses the pharynx to reach the thyro-hyoid membrane. The spinal accessory and the glosso-pharyngeal nerves lie against the upper part of the pharynx. The faucial tonsil lies about 2. 5 cm. above 'the angle and opposite a vertical line di- viding the ramus of the jaw into a front and a back half. It lies between the pillars of the fauces, and is separated from the mucous membrane by a thin layer of muscular fibres. The lower end reaches the tongue, the adenoid tissue being at times continuous between them. The tonsil covered by the superior co stricter. External to this is yielding mass of areolar t sue, continuous with that o the carotid sheath, into which the tonsil may force its way if enlarged. This areolar tis- sue is bounded in front by the internal pterygoid muscle, and is pierced by the stylo- t ylossus and the stylo-pha- ryngeus, which subdivide it, leaving a small part of it be- tween them and the tonsil. At this level both carotids are at a considerable dis- tance from the tonsil. The internal is posterior and external, about 2 cm. distant. According to Zuckerkandl, a transverse line through the posterior pillar will pass tSar* Bundles of muscular tis- _siu ul constric- tors -Pharynjjeal apom-uroMs ffl Surface epithelium Sagittal section of posterior wall of pharynx ol child, showing part of pharytiKcal tonsil. THE PHARYNX. 1603 2 cm. in front of the vessel. The external carotid is placed more directly outward and is rather the nearer of the two. The parotid inland, according to Tillaux, sends a process in front of the styloid process, which reaches the lateral wall. This extension, however, does not seem to be by any means constant. Development and Growth of the Pharynx. An account of the formation of the primitive pharynx is included in the Development of the Alimentary Tract (page 1694), the later changes being here noted. In the section on the bones it was shown that the chief peculiarities of the infant skeleton in this region are due to the small size of the face and the more horizontal base of the skull. The naso-pharynx has very little height, while, owing to the peculiar disposition of the parts, it has nearly the same antero-posterior diameter as in the adult. It is relatively broad and long, but very shallow. The tongue, in proportion, is much less thick at the base than later. The larynx is small, and, moreover, is placed higher in relation to the vertebral column, so that the termination of the pharynx is also higher. The position of the larynx at different ages is considered with that organ (page 1571 ). The soft palate is in the main horizontal at birth and about on a level with the top of the atlas. The uvula is rudimentary. In a child of probably not over three years we have found the tip of the uvula rather below the middle of the body of the axis. In Symington's section of a girl of thirteen it is pretty nearly in the adult position. In infancy the soft palate probably closes the passage into the naso-pharynx from below less perfectly than later. The opening of the Eustachian tube, although necessarily in the naso-pharynx, is in the foetus below the level of the hard palate. At birth it is at about that level, but rather below than above it. According to Disse, there is but little change for nine months, after which the opening is on the level of the inferior meatus. Proba- bly the adult position is generally reached after puberty. The opening is small in the infant and young child, and, owing to want of development of the cartilage, there is but a slight elevation about it and consequently but a small fossa of Rosen- miiller. The entire adenoid system of this region l has made but little progress before birth. At birth the pharyngeal tonsil is a very small collection of adenoid tissue at the back of the roof, covered by more or less converging folds of the mucous membrane. It is not necessarily present. During the first year it grows rapidly, and particularly forward, so that by the end of that time it extends to the back of the upper margin of the choanae. Under normal conditions the pharyngeal tonsil retains its relative size to the cavity of the pharynx up to twelve years ; but during this time the total amount of adenoid tissue has decidedly increased, owing to the development of the tubal tonsils. The faucial tonsils are developed in a recess of the primitive pharynx between the second and third visceral arches. By the fourth fcetal month the tonsillar anlage presents a number of slit-like depressions, lined with entoblastic epithelium, from which secondary epithelial sprouts invade the neighboring mesoblast. This process continues after birth during the first year. The young connective tissue surrounding the epithelial sprouts the latter being at first solid, but later possessing a lumen becomes infiltrated by accumulating leucocytes and gradually assumes the character of adenoid tissue, the differentiation into distinct lymph-nodes, however, being delayed until after birth. The source of the lymphoid cells is a matter of dispute. Accord- ing to some, these elements, are leucocytes from the circulation caught within the young connective tissue ; others maintain that they are derived from the transforma- tion of the epithelium, the lymphoid tissue resulting from the mutual invasion and in- tergrowth between the ento- and mesoblastic elements. According to Hammar,* who has carefully studied the development of the tonsils, the lymphoid cells are derived chiefly from the fixed connective-tissue elements. At birth the tonsils are insignifi- cant, but grow rapidly during the first year. At from the twelfth year to puberty the entire adenoid system of the pharynx enters .upon a stage of retrogression. In the adult the pharyngeal and tubal tonsils are much smaller ; after middle age they undergo atrophy. 1 Escat : Evolution de la Cavit6 Naso-Pharyngienne, 1894. 2 Archiv f. mikro. Anat., Bd. xli., 1902. 1604 HUMAN ANATOMY. THE MUSCLES OF THE PHARYNX. The arrangement of the muscular tissue differs from the ordinary one of the digestive tract, inasmuch as the outer layer is approximately circular and the longi- tudinal fibres are largely internal. The chief elements are the three constrictors, which overlap one another from below upward, the stylo-pharyngeiis, the palato- pharyngeus, and certain accessory and rather irregular bundles of muscular fibres. Internal carotid artery Internal jugular vein Central attachment of pharynx , Pharvn- / seal ' aponeu- rosis Styloid process Digastric, posterior belly Stylo- pharyngeus Stylo-glossus Stylo-hyoid Stylo-hyoid< ligament Tip of great cornu of hyoid bone Thyro-hyoid ligament Superior cornu of thyroid cartilage Middle constrictor Mandible Raphe Inferior constrictor Longitudinal muscle of oesophagus Muscles of pharynx from In-hind ; portion of interior constrictor has been removed. The superior constrictor ( Figs. 1339, 1360) arises from the lower part of the internal pterygoid plate, from the Kamular process, the pterygo-mamlibular ligament which is stretched from it to the lingula of the lower jaw, from the neighboring end of the mylo-hyoid ridge, and from the side of the tongue. From this origin the fibres pass backward to meet their fellows in a median raphe, which extends almost the THE PHARYNX. 1605 entire length of the posterior wall of the pharynx, being attached above to the pharyngeal tubercle on the under side of the basilar process. The upper edge of the muscle is concave on either side, not reaching the base of the skull and passing under the Eustachian tube, the vacant space being filled by the pharyngeal aponeu- rosis. The lower fibres pass somewhat downward as well as backward. The pterygo- mandibular ligament separates the superior constrictor from the buccinator, with which it would otherwise be continuous, forming a circle around the alimentary canal. FIG. 1361. Anterior margin of foramen magnum Styloid process Pharyngeal aponeurosis Stylo-hyoid ligament r'lo-glossus Stylo-hyoid Deep fibres of superior constrictor Palato-pharyngeus Great cornu of hyoid bone * Stylo-pharyngeus _J._Thyroid cartilage Pharyngeal aponeurosis i (Esophagus Pharyngeal aponeurosis and longitudinal musculature, seen from behind. The middle constrictor (Figs. 1339, 1360) arises from the lower end of the stylo-hyoid ligament, from the lesser horn of the hyoid bone, and from the upper border of the greater horn. The fibres diverge from this narrow origin, the upper reaching the pharyngeal tubercle, the lower going to nearly the lower end of the pharynx, and all meeting their fellows in the median raphe. It conceals a consider- able part of the preceding muscle. 1606 HUMAN ANATOMY. The inferior constrictor (Figs. 1339, 1360), the thickest of the three, arises from the posterior part of the outer aspect of the cricoid cartilage, from the oblique line and the triangular surface below and behind it on the thyroid cartilage, including the inferior horn. It overlaps the preceding muscle, its upper fibres reaching to some 3 cm. below the base of the skull and the lower ones being nearly horizontal. The median raphe, which receives almost all the fibres, is wanting below. The lowest fibres are circular and continuous with the circular fibres of the gullet. The stylo-pharyngeus (Fig. 1361) arises from the inner side of the styloid process near its root and descends to the interval between the superior and middle constrictors near the hyoid bone, where it passes under the latter and ends by expand- ing in the side of the pharynx, some of its fibres going to the posterior border of the thyroid cartilage and others joining the expansion of the palato-pharyngeus. A bundle from the thyroid division passes to the side of the epiglottis, forming on the wall of the pharynx the fold known as the plica pharyngo-epiglottica. The fibres of the superior constrictor may be inseparable from the upper part of this layer. The salpingo-pharyngeus has been described in connection with the levator palati (page 1571). Variations. Additional muscles are very common, being chiefly longitudinal bundles due to splitting of one of the normal muscles, especially the stylo-pharyngeus, or to new bundles of fibres arising from the base of the skull in the vicinity of the upper insertion of the pharyngeal fascia. There may be a pair of occipito-pharyngeal muscles, arising from the occipital bone on either side of the median line and descending to be lost in the posterior pharyngeal wall ; or there may be an azygos muscle instead . Bands may arise at the side from the petrous portion of the temporal bone or the spine of the sphenoid. Actions. The general action of the pharyngeal muscles is sufficiently evident ; the constrictors decrease the size of the pharynx, probably drawing the larynx upward and backward at the same time. The longitudinal muscles raise the larynx and pharynx, acting chiefly on the latter. Vessels. The arteries of the pharynx are from many sources and are irregu- lar. The chief is the ascending pharyngeal, which runs up near the posterior lateral angle. Occasionally, when enlarged, it is seen pulsating on the posterior wall. Branches from the facial play an uncertain part. The veins form the pharyngeal plexus situated outside of the constrictors and communicating in all directions. The chief outlets are by a pair of veins on each side, one going up to the internal jugular near the base of the skull and the other down to the external jugular or some of its tributaries (Luschka). A submucous plexus is particularly developed in the lower posterior wall, which opens into the pharyngeal plexus by several branches piercing the inferior constrictor. The following are nearly constant : a superior and posterior one near the middle line, one running outward on each side near the back of the thyroid cartilage, forming a part of the origin of the pharyngeal vein, and one passing forward to the superior thyroid vein. 1 The lymphatics, which are numerous, run in the upper part to the prevertebral nodes and to the deep cervical system, as do the lower ones at another level. The presence of lymphatic nodes behind the naso-pharynx is of practical importance, as they are sometimes inflamed and may suppurate. They lie near the fossae of Rosenmiiller. Nerves. The constrictors are supplied by the pharyngeal plexus, the lower receiving fibres also from the recurrent laryngral. The stylo-pharyngeus is supplied by the glosso-pharyngeal. The nerves of the mucous membrane are from the glosso- pharyngeal, the pneumogastric, and the sympathetic, to a great extent in a plexiform arrangement. PRACTICAL CONSIDERATIONS : THE PHARYNX. The pharynx may be said to present only three sides for consideration, but its continuity above with the nares, anteriorly with the mouth, and below with the ori- fices of the larynx and oesophagus associates it intimately with the diseases of those iv- ions. The naso-pharynx and the laryngeal relations will be considered with the Respiratory Passages (page 1829). 1 Bimar et I.apeyre : Comptes rendus de 1'Acacl. drs Srirmvs, Tan's, tome cv., 1887. PRACTICAL CONSIDERATIONS: THE PHARYNX. 1607 The posterior -wall of the pharynx is separated from the anterior surfaces of the bodies of the first five cervical vertebrae only by some loose connective tissue and by the prevertebral fascia and muscles. Through it, by pushing the finger up above the soft palate, the basilar process of the occipital bone may be felt, and below the bodies of the upper four cervical vertebrae in children the upper six may be pal- pated. The hard palate, or the lower margin of the posterior nares, and the anterior arch of the atlas are on the same level. In disease of the body of the sphenoid, in fracture of the base of the skull involving the basilar process, or in fracture or dislocation of the cervical vertebrae the information gained by this examination will often be of great value. The retropharyngeal alveolar tissue which is necessarily loose to permit of the movements of the pharynx during deglutition and of its distensibility is some- times the seat of infection which may have gained access through the pharynx itself, or through the lymphatics which spring from the posterior nares, the summit of the pharynx and the prevertebral muscles, and which empty into a lymph-gland situ- ated between the prevertebral fascia and the pharyngeal wall. Abscess in this situation may by gravity descend by the side of the oesophagus into the mediasti- num and has been known to reach the base of the thorax (page 553, Fig. 546). During its descent it may cause much dyspnoea by setting up oedema in the region of the glottis. Usually it first pushes forward the posterior wall of the pharynx, and can be recognized as a fluctuating swelling and opened by direct incision. Collections of fluid resulting from tuberculous disease of the cervical vertebrae may occupy the same space after perforating the thin prevertebral fascia and may take the same course, or they may be guided by the lateral expansions of that fascia to the posterior and lateral portions of the root of the neck or to the axilla (page 552, Fig. 545). As in these cases the avoidance of mixed infection is very important, such tuberculous collections, when they require opening, should be approached through the neck by an incision along the posterior border of the sterno-mastoid. Retropharyngeal abscess of any type should never be allowed to open spon- taneously on account of the danger of immediate suffocation from flooding of the larynx with pus. In cases of fracture of the posterior fossa of the base of the skull, with hemor- rhage into the pharynx (fracture of the basilar process), or of the middle fossa, with hemorrhage reaching the pharynx through the Eustachian tube (fracture of the petrous portion of the temporal), the need for frequent and persistent attempts to make and keep the pharynx as nearly aseptic as possible should never be forgotten. The adenoid tissue of the posterior wall the pharyngeal tonsil may undergo hypertrophy, cause deafness or respiratory obstruction, and require removal. The lateral walls of the pharynx are in such close relation with the internal carotid artery that in aneurism of that vessel the pulsations may most easily be felt and seen through the pharynx. In many instances the vessel has been opened in penetrating wounds of the pharyngeal wall by foreign bodies. The internal jugular vein is not so exposed to injury and is more rarely wounded. In one instance of pulsating tumor of the pharynx, pressure on the external carotid arrested the pulsa- tions (Barnes). The styloid process and a rigid or ossified stylo-hyoid ligament can be felt through the lateral wall. Attempts have been made (in cases of hysterical persist- ence of pharyngeal symptoms after the supposed swallowing of a foreign body) to remove these structures or a cornu of the hyoid bone, under the impression that they were the offending substances. The pharynx is very distensible, and foreign bodies, if not of great size, are apt to pass through it as far as the level of the cricoid cartilage, where its diameter is only 18 mm. (^ in.). In an adult this point is beyond the reach of an average finger, as it is about the entrance of the oesophagus, which is about six inches from the incisor teeth. For the removal of impacted foreign bodies, or for operation on malignant dis- ease, the pharynx may be reached, after a preliminary tracheotomy, by an incision i6o8 HUMAN ANATOMY. through the neck from a point midway between the symphysis and the angle of the jaw to the cricoid cartilage, dividing the platysma and the omo-hyoid and sepa- rating the posterior belly of the digastric and the stylo-hyoid from the hyoid bone ; or a subhyoid pharyngotomy will give access to the lower walls of the pharynx by division of the superficial fascia, the sterno-hyoid and thyroid muscles, the thyro- hyoid ligament and membrane, and the mucous membrane of the pharynx at the level of the lower margin of the hyoid bone. These operations are more interest- ing anatomically than surgically. The tonsils, as seen from the mouth, are situated between the arches of the palate and the base of the tongue. They may be almost concealed in these re- cesses or may project into the pharynx, and when hypertrophied may actually meet in the middle line. They rest on the superior constrictor muscles and move with those muscles during the act of deglutition. They are somewhat elevated and with- drawn from the pharynx by the coincident contraction of the stylo-pharyngei. Swallowing is therefore apt to be painful in all forms of tonsillitis. If not enlarged, they are often almost hidden in persons who have large palato-glossi muscles, and therefore prominent anterior palatal arches. Externally they are separated by the pharyngeal aponeurosis and the superior constrictor muscle from . the pharyngo- maxillary space. This space is bounded by these fibro-muscular structures internally, the internal pterygoid muscle externally, and the antero-lateral aspects of the bodies of the second and third cervical vertebrae. It is occupied by some con- nective tissue and fat. According to Zuckerkandl, the stylo-pharyngeus and stylo- glossus muscles divide the space into an anterior portion in relation to the tonsil and a posterior in relation to the internal carotid artery and internal jugular vein. Tonsillitis in the lacunar or follicular form does not usually involve the stroma of the gland, the infection and the exudate being limited to the tonsillar crypts and to the surface. In the suppurative form the infection is deeper, the stroma is affected, and the resulting abscess may in rare cases become peritonsillar, extend to the cellular tissue of the pharyngo-maxillary space, and open the internal carotid artery. Usually, as the infection progresses, even if this space is invaded, the out- ward extension is limited by the internal pterygoid muscle, and the swelling and the ulceration or necrosis take the line of least resistance, i.e. , towards the pharynx, where tonsillar abscesses often open spontaneously. During an acute tonsillitis the palato-glossus and its covering of mucous mem- brane, with the soft palate on the affected side, are tense, thinned, and spread out over the surface of the tonsil. Abscesses may be evacuated by incision directly through these structures and from above downward in a direction parallel with the anterior pillar, that is, with the fibres of the palato-glossus. The vascular relations of the tonsil should be remembered in this operation or in tonsillotomy for hypertrophy. The internal carotid is nearly 2.5 cm. (i in.) behind and to the outer side of the tonsil. The external carotid is still farther re- moved, as it lies outside of the stylo-glossus and stylo-pharyngeus muscles. Its ascending pharyngeal branch is nearer the tonsil than either of the main trunks, and in a case of accidental wounding by a foreign body has been the source of fatal hemorrhage. Wounding of the tonsillar branch of the facial artery has likewise proved fatal after tonsillotomy, and either this vessel or the facial itself, especially if it is tortuous where it passes between the stylo-glossus and digastric muscles, is prob- ably involved in cases of grave hemorrhage after this operation. The plexus of lymphatics surrounding the follicles of the tonsils communicates directly with the deep cervical lymph-glands behind and beneath the angle of the jaw. These glands are therefore commonly enlarged in affections of the tonsils, and when tender and palpable are sometimes mistaken for the tonsils themselves. The latter cannot, however, be palpated externally, except in cases of new growth, as the resistance offered by the constrictor, the internal pterygoid, and other structures intervening between the tonsils and the skin causes them to project towards the pharynx. This projection may be a cause of various forms of ill health associated with deficient oxygenation, of chronic pharyngitis from mouth-breathing, of thickened articula- tion, and even of alterations in the facies or in the skeleton, e.g. , "pigeon- breast" (page 167). THE (ESOPHAGUS. 1609 The deafness often associated with hypertrophied tonsils is the result of adenoid growth in and about the Eustachian tube. The intervention of the soft palate pre- vents direct pressure by the enlarged tonsil upon that canal. Reflex spasmodic cough may follow irritation of the glosso-pharyngeal filaments by inspissated secre- tion within the follicles' ; fetid breath often results from the decomposition of such secretion ; epithelial necrosis and denudation render such tonsils a common seat of entrance of various infections, as the tuberculous emphasized by the frequency with which the cervical glands just mentioned are the first to enlarge in tuberculous adenitis of the neck or those streptococcic or staphylococcic varieties in which acute arthritis (including many cases of so-called "inflammatory rheumatism") or endocarditis may follow a trifling "sore throat." THE (ESOPHAGUS. The oesophagus or gullet is a musculo-membranous tube, about 25 cm. (10 in.) in length, connecting the pharynx and the stomach. It begins at the lower border of the cricoid cartilage near the disk between the sixth and seventh cervical vertebrae, about 15 cm. from the incisor teeth, and ends below the diaphragm, opposite the tenth (sometimes the eleventh) thoracic vertebra. The entrance into the stomach is marked by a groove on the left of the gullet, best seen when the organs are inflated. There is no line of separation on the right when the parts are unopened. The form and calibre of the oesophagus are very variable and uncertain. Longitudinal folds are sometimes found, especially in the upper part, which give the cavity a star-shaped appearance on transverse section. Often the front wall lies in contact with the back one ; at the lower part, however, there may be a permanent cavity. Constrictions have been described very variously. Probably the most marked occurs at the very beginning, with a diameter of perhaps only 14 mm. There is usually one at the passage through the diaphragm, often one at the point where the arch of the aorta crosses the gullet, and another where the latter goes behind the origin of the left bronchus. Mehnert l has described thirteen places, at any one of which there may be a constriction. They correspond to the points of entrance of the arteries, and, accord- ing to him, have a metameric significance. Occasionally the oesophagus is much dilated, the diameter exceeding 3 cm. It is probably constricted in life. After passing through the diaphragm it presents a funnel-like expansion. Course and Relations. Throughout its course the gullet is surrounded by much areolar tissue and frequently sends fibres from its muscular coat to neighbor- ing parts. While following the general direction of the vertebral column, although not closely, below the bifurcation of the trachea the gullet lies i or 2 cm. in front of the spine. Directly after its beginning it inclines to the left, so that soon it pro- jects by one-half beyond the left border of- the trachea. We have seen, in a child, the two tubes lie side by side. Just above the bifurcation of the trachea the oesophagus meets the arch of the aorta, which, so to speak, pushes it to the right ; it lies, how- ever, always behind the beginning of the left bronchus, while to a less degree, or even not at all, it is in relation to the right one. Owing to the influence of the aorta, the gullet passes farther to the right; but, leaving the spine, it lies behind the pericardium in a plane somewhat anterior to that of the aorta, and near the diaphragm sweeps in front of the aorta to the left of the median line, passes into the abdomen near the lower border of the tenth thoracic vertebra, and, running very obliquely, presently ends in the stomach. Hardly more than i cm. , which lies behind the left lobe of the liver and in front of the left pillar of the diaphragm, can be said to be subdiaphrag- matic, when examined from without. The line of separation between the oesophagus and the stomach, however, is very clear on the inner surface, owing to the sudden change in the nature of the epithelial lining. There is often a fold on the left of the end of the gullet, usually at the upper and back part, from 2-5 mm. broad, 2 which, perhaps, acts as a valve against regurgitation. The subdiaphragmatic part is about 3 cm. long. Sometimes the longitudinal folds of the gullet seem to project into the stomach, but usually it ends in a gradual expansion. 1 Verhandlung. der Anat. Gesellschaft, 1898. J Berry and Crawford : Journal of Anatomy and Physiology, vol. xxxiv., 1900. i6io HUMAN ANATOMY. At first the oesophagus lies behind the trachea on the prevertebral fascia, the lobes of the thyroid gland touching it on either side. As it descends to the left, the trachea is partly on the right. The left recurrent laryngeal nerve runs on the front. The right one is in relation with only the very beginning of the gullet. The right inferior thyroid artery is against it. On the right also a chain of lymphatics in the areolar tissue lies very close to it. The left carotid and subclavian arteries are very near it, if not in actual contact. As may be inferred, the gullet and the aorta are FIG. 1362. Superior cornu of thyroid cartilage Thyroid body Left common carotid Left subclavian artery- Arch of aorta, Left pulmonary artery Left bronchus Thyroid body Right common carotid Right subclavian artery Innominate artery Trachea Superior vena cava Right bronchus Left pulmonary vein CEsophagus Diaphragm Cardiac end of stomach Abdominal aorta Spleei Right pulmonary veins Azygos major vein Diaphragm Inferior vena cava Posterior surface of liver Right suprarenal body .Right kidney CEsophagus and related structures, seen from behind. Lungs have been pulled aside and posterior part of diaphragm removed. spirally entwined. The thoracic duct and the vena a/ygos major are in contact with ii from the diaphragm to above the roots of the lungs, the former lying between it and the aorta as far as the level of the aortic arch, the latter, at first more posterior than the duct, passing as it rises behind the oesophagus and finally arching forward close to its right side. The left vena azygos, such left intercostal veins as open into the azygos major, and the right intercostal arteries pass behind the gullet. The pneu- mogastrics reach it in thr thorax : the right after crossing the subclavian artery and THE (ESOPHAGUS. 1611 the left after crossing the aorta. The nerves then break up into plexuses, from which they emerge near the diaphragm, the left in front, the right behind the food-tube. On entering the thorax, the oesophagus is in contact with the left pleura, and con- tinues to be until separated from it by the aorta. Behind the pericardium it is in contact with the right pleura, and just before passing through the diaphragm it is in contact with both. Muscular fibres bind the oesophagus to various neighboring structures. A toler- ably constant band attaches it to the left bronchus, and others may go obliquely to the right bronchus. Several irregular bands, mostly muscular, pass from it to various parts of the pleurae and pericardium. Structure. The wall of the oesophagus (3.5-4 mm. thick) consists of four FIG. 1363. Epithelium Tunica propria of mucous membrane :|V ^^mi} ^>,%l V 4 ' >*%^;?SP tf t Gland-ducts. >/&>' - -.%^t?kK ^ ^A;^V - ,-. v;>^, :^; ; ^ ,:.-, ^S %; .Glands '^' ' .-* '*-*>., s^Submucous coat ^.Circular bundles of non-striated muscle Striated fibres Longitudinal bundles of non- striated muscle Bundles of striated fibres Transverse section of oesophagus, junction of middle with upper third. X 25. layers, which, from within outward, are the mucous, the submucous, the muscular, and the fibrous coats. The mticous coat, usually thrown into longitudinal folds, is composed of a tunica propria formed of fibrous connective tissue and delicate elastica and covered with stratified squamous epithelium. Beneath the latter the surface of the stroma-layer presents longitudinal ridges and papillae, between which pass the ducts of the glands in their course to the free surface. The deeper part of this layer is occupied by a mus- cularis mucostz, the involuntary muscle of which begins at the cricoid cartilage, first l6l2 HUMAN ANATOMY. FIG. 1364. Lymph ide in no mucosa appearing in the continuation of the elastic lamina of the pharynx. At the upper end only slightly developed, the muscularis mucosae becomes more robust until in the lower portion of the oesophagus it is conspicuous. The submucous coat, between the mucous and muscular layers, although consid- erable, is not dense, and therefore allows free motion of the former upon the latter, as well as the formation and effacement of folds. It is continuous with the pharyn- geal fascia above. The cesophageal glands are of two kinds, the ordinary mucous, situated within the submucous coat and scattered throughout the length of the tube, and special glands within the tunica propria limited to the two ends of the oesophagus. The last mentioned correspond in structure to those found at the cardiac orifice of the stomach ; they are therefore known as the upper and lower cardiac acsophageal glands (J. Schaffer). The usual secretory structures are small tubo-alveolar mucous glands in which mucus-producing cells are alone present, crescents of serous elements being absent. The ducts are commonly somewhat tortuous, and often present dilatations or ampullae; the smaller tubes are clothed with simple columnar epithelium. In the larger the epithelium may be stratified, and near the free surface assume a squamous character. The cardiac glands at the lower end of the oesophagus are continuations of those situated about the entrance of the gullet into the stomach, in connection with which organ they are more fully described (page 1624). They form oval or pyrami- dal groups of branched tubular glands, the bases of which lie against the muscularis mucosae, the narrow parts being directed towards the free surface onto which their wavy or tortuous ducts open. The upper cardiac glands form, according to Schaf- fer, 1 a constant, though variable, group around the superior end of the oesophagus. Lymphatic tissue occurs within the mucosa of the oesophagus as more or less distinct aggregations. Sometimes these are in the form of small diffuse areas of infiltration around the ducts of the mucous glands ; in other places, especially towards the lower end, distinct lymph-nodules are present (Fig. 1364). The muscular coat consists of an inner circular and an outer longitudinal layer, although the disposition of the individual bundles is often irregular and oblique, and above somewhat intermingled. In the upper third of the tube the muscular tissue consists entirely of striped fibres, the circular ones being continuous with the simi- larly disposed fibres of the inferior constrictor of the pharynx. The longitudinal fibres arise from a tendon attached to the median ridge of the cricoid cartilage and to the fascia covering the posterior crico-arytenoid muscles, whence they descend to embrace the gullet. They are few at the top behind, but lower down the circular and longitudinal layers are distinct and symmetrically disposed. Towards the middle of the oesophagus the muscular coat includes both the striated and non-striated form of tissue, the involuntary variety gradually predominating until in the lower third it alone is present. The fibrous coat is poorly developed above the diaphragm, consisting of the areolar tissue which connects the gullet to the surrounding structures. After piercing the diaphragm, the peritoneal investment contributes a limited serous tunic which from this point on is well represented. Vessels. The arfcn'cs are links in the chain running the whole length of the alimentary canal. The highest are from the inferior thyroids, succeeded by those 1 Beitrage zur Histologie mensch. Organe, Bd. vi. Musculai tissue Section of mucous membrane of oesophagus, showing lymph-node. X 55. PRACTICAL CONSIDERATIONS: THE CESOPHAGUS. 1613 from the thoracic aorta and the gastric. The veins are interesting only inasmuch as the upper ones open into the azygos system and that of the inferior thyroid above and the gastric system below ; they thus form a communication between the general and the portal venous systems. The lymphatics not numerous go to the nodes of the deeper part of the neck and of the posterior mediastinum. Nerves are from the oesophageal plexus. The mechanism of the closure of the cardiac end of the stomach is most properly considered with the oesophagus, depending as it does partly on the direction of that tube, partly on the relation of the diaphragm to it, and partly on the folds of mucous membrane at its orifice. Frozen sections (Fig. 1372), both horizontal and frontal (Giibaroff 1 ), show that the termination is almost horizontal. Dissections of the dia- phragm from above demonstrate that the arrangement of the muscular fibres is that of a sphincter, although a weak one. The projection of the folds into the stomach is a further protection. It has been shown that the cardia will resist moderate pressure from below upward, but will yield to considerable force. The action of the longi- tudinal fibres from both the cricoid cartilage and the diaphragm is to dilate the tube. PRACTICAL CONSIDERATIONS : THE CESOPHAGUS. Congenital malformations are rare, as yet unexplained embryologically, and usu- ally fatal. The oesophagus may be double, deficient, or absent. Most commonly there are an upper cul-de-sac and a lower segment opening into the stomach, some- times communicating with the respiratory passage. Cases in which there has been an cesophago-pleuro-cutaneous fistula are possibly associated with this malformation (MacLachlan, Osier). Congenital diverticula are found, and Francis suggests three theories for their occurrence : first, that they might be analogous to the diverticula which were found in some of the Sauropsida and in ruminant animals, forming the first two compartments of the stomach ; secondly, that they were fcetal varieties analogous to the oesophageal diverticulum from which the larynx, trachea, and lungs are formed ; and thirdly, that they resulted from a failure in the internal closure of a branchial cleft (May lard). The curves, distensibility, and constrictions of the normal oesophagus and its relations to surrounding structures are of importance with reference to foreign bodies, to stricture, to disease of the gullet with possible extension to neighboring organs, or to extrinsic disease involving the oesophagus either by mechanical pressure or traction or by extension to its walls. Foreign bodies, if moderately smooth or regular in shape, are apt to be arrested at one of the three relatively constricted portions, i.e. (i), and most commonly, at the commencement, 15 cm. (6 in.) from the incisor teeth, which (with the head midway between flexion and extension) is opposite the lower edge of the cricoid cartilage and the sixth cervical vertebra. At this point its average diameter is 14 mm. (approximately ^ in. ) ; foreign bodies arrested here are really in the lower pharynx. (2) At the point, about 10 cm. (4 in.) lower, where the left bronchus crosses the oesophagus and where the lumen is again lessened by pressure (the dis- tance occupied by the left bronchus in crossing the oesophagus is about 2.5 cm.). (3) At the diaphragmatic opening, where the diameter is once more reduced to 14 mm. by the constriction of the muscular and tendinous fibres surrounding the opening. This point is about 12.5 cm. (5 in.) below the level of the left bronchus, and therefore, approximately, 38 cm. (15 in.) from the incisor teeth. The majority of foreign bodies that pass completely from the pharynx and are arrested in the oesophagus are stopped at' or about the level of the left bronchus. Many of them can be extracted through the mouth by suitable instruments ; others require an cesophagotomy, which may be done through an incision along the anterior border of the left sterno-mastoid muscle from the cricoid cartilage to the sternum. The longitudinal fibres of the oesophagus will be recognized a little to the left of the trachea, at the bottom of the space between the sterno-thyroid muscle and the common carotid artery. An oesophageal bougie passed through the mouth will aid in the recognition of the tube. 1 Arch, fur Anat. und Phys., Anat. Abtheil., 1885. i6i4 HUMAN ANATOMY. The recurrent laryngeal nerve lying in the groove between the trachea and oesophagus should be avoided, as should the superior and inferior thyroid arteries which run across the deeper part of the wound. With the additional help of a gastrotomy, digital exploration (with perhaps the disengagement of impacted foreign bodies) is possible throughout at least the lower two-thirds of the gullet. If the impaction is near the cardiac end, gastrotomy alone may suffice. Mediastinal or posterior cesophagotomy has been done on both the left and right sides by resection of three or four ribs (third to eighth), pushing the parietal pleura to One side. The pleura on the left side is more easily displaced than that on the right, which extends across the median line as far as to the right of the thoracic aorta. Strictures from escharotics or from trauma of foreign bodies may occur at any point, but are, for obvious reasons, most often found at the upper end. Compression of the oesophagus, giving rise to the clinical phenomena of stricture, may be sec- ondary 'to enlargement of the thyroid body or of the bronchial lymph-glands, to tumors of the mediastinum, to disease of the lower cervical or upper dorsal verte- brae, or to aortic aneurism. The measurement from the incisor teeth to the seat of the narrowing, and comparison with the cesophageal relations at that point, may be of great service in diagnosis. Carcinoma is the chief disease by which the gullet is attacked. It is found most often at either the upper or lower end of the tube in accordance with its predi- lection for sites where epithelium changes in character, as at the various muco- cutaneous outlets of the body. It is also not infrequent at the region where the left bronchus crosses. It may extend by continuity to the pharynx or stomach or to any of the structures with which the oesophagus is in close contact, or it may spread to the bronchial or mediastinal lymph-glands. Extrinsic disease may not only (as in the case of tumors or of aneurism) affect the oesophagus by causing compression of its walls (vide supra}, but may open it by pressure-necrosis or ulceration, or may involve it in the extension of the disease, as in cases of tracheal, bronchial, or pulmonary suppuration or gangrene, or of verte- bral caries. Disease extending from the left lung or pleura to the oesophagus, or in the reverse direction, is more apt to affect the upper portion of the gullet on account of its closer relation to the pleural sac on the left side. Below it is in more intimate relation to the right pleura. Diverticula of the oesophagus, when acquired, may be due to (a) pressure from within, as in the region just above a stricture, or oftener on the posterior wall at the pharyngo-oesophageal junction. At this point the inferior constrictor and the circular fibres of the oesophagus both horizontal in direction fuse ; it is a point of marked constriction ; the cricoid cartilage in front is movable and non-resistant. In whatever situation found they are apt to be in effect a hernia of the mucous and submucous tissues through the thinned and weakened muscular fibres of the oesoph- agus or of the inferior constrictor ; or they may be due to (b') traction from without. as in cases of bronchial lymphadenitis, in which adhesions and subsequent ricatridal contraction have dragged the wall out into a pouch. It is apparent that tin- aim rior wall in the neighborhood of the bifurcation of the trachea and of the left bronchus is most likely to be thus affected. The recorded cases in which hemorrhage into the oesophagus has taken place from the ascending portion of the aorta, the innominate artery, and the superior vena cava will readily be understood. The relation of the oesophagus just below the aortic arch to the pericardium and left auricle explains the dysphagia soim tinu-s seen in pcricardial dropsy or in cardiac enlargement when the patient is supine, as well as the cases in which foreign bodies impacted in the oesophagus have wounded the heart. In a general way it may be said that the upper or tracheal curve 'or segment of the oesophagus is most liable to invasion by diseased conditions from without and to obstruction from within, and the lower or aortic curve is relatively free from liability to external pressure or intrinsic occlusion (Allen). THE ABDOMINAL CAVITY. 1615 In the use of cesophageal instruments the normal curves, measurements, and constrictions should be remembered, as should the possible relation of abnormal narrowing to abscess, aneurism, or thoracic disease. The curve made by the roof of the mouth, the pharynx, and the beginning of the oesophagus should be some- what straightened out by throwing the patient's head slightly back ; the tongue and anterior pharyngeal wall should be pulled forward or pushed in that direction by a ringer in the pharynx. The point of the instrument should be guided past the epiglottis and brought in contact with the posterior wall of the pharynx before it is pushed downward. This wall like the upper wall of the urethra is the more fixed and should guide the instrument safely into the gullet, except in cases of pressure of diverticula. The beginning of the procedure may be facilitated by voluntary deglutition on the part of a non-anaesthetized patient. In some cases, especially in children, it is preferable to pass the instrument through the nose to avoid the struggle to keep the mouth open. THE ABDOMINAL CAVITY. The general shape of the abdominal cavity is best understood by dividing it into three imaginary zones, one above the lumbar region of the spine, one opposite to it, and one below it. The anterior wall is but slightly convex. The upper zone, excepting a small part in front, is within the cage of the thorax, from which it is separated by the dome of the diaphragm, the lower part of which is nearly vertical and posterior to the abdominal viscera. This zone is very capacious. The second zone, bounded behind by the convexity of the lumbar spine, which is broadened on each side by the psoas muscle, is very shallow in the middle, the antero-posterior diameter not being more than 5 cm. (2 in.). At the sides it is deep, extending into the hollow of the lower ribs. Thus it presents two deep lateral recesses connected by a shallow median portion. The lowest zone, below the promontory of the sacrum, consists in the middle of both abdominal cavity proper and of the cavity of the true pelvis ; for, owing to the inclination of the pelvis, the promontory is near the level of the anterior superior spines of the ilia. On each side of this deep median portion the lower zone is bounded behind by the shallow iliac fossae, rendered yet more so by the ilio-psoas muscles. The deep lateral divisions of the middle zone pass with- out interruption into these shallow ones. It has been so long the custom to divide the abdomen into nine regions by drawing two vertical and two transverse lines on the anterior wall, that the names applied to these conventional regions must be retained for general and vague use, although the method is' worthless for accurate description. 1 Hardly two authorities agree as to the location of the lines, but for general purposes the following suffices. Draw a vertical line upward from the middle of Poupart's ligament on each side. Let the upper transverse line cross these at their points of contact with the lower borders of the costal cartilages ; let the lower line connect the anterior superior spines of the ilia. The three middle regions thus mapped out are named, from above down- ward, epigastric, umbilical, and hypogastric ; the lateral ones, the right and left hypochondriac, lumbar, and iliac. The advantage of this method is that the vertical lines approximately represent the borders of the median divisions of the two lower zones, and the lower cross-line is near the level of the sacral promontory. The abdominal cavity is lined by a serous membrane, the peritoneum, which, in addition to covering the walls of the space, forms a more or less extensive investment for the abdominal organs. The latter, however, all lie really without the cavity of the peritoneal sac, the serous membrane being pushed in by the viscera. When the latter remain attached to the body-wall, as the kidneys, the peritoneal reflection is limited ; if, on the contrary, the organ becomes otherwise free, as the small intestine, the serous covering forms practically a complete investment. The latter is, however, never absolutely complete, since there is always an uncovered area through which the blood-vessels, lymphatics, and nerves reach the organs. The detailed description of the complex relations of the peritoneum will be given later (page 1740) ; suffice it 1 The information conveyed by this method is of the same nature as that given by saying that Boston is north of Washington and Chicago west of it. i6i6 HUMAN ANATOMY. now, in anticipation of the references to peritoneal relations which necessarily follow in the consideration of the organs, to point out that the parietal and visceral portions of the serous membrane are continuous, the former investing the abdominal walls, the latter the organs. The peritoneal folds passing from a viscus to the body-wall have received in many cases the name ligaments, although often such bands con- tribute little support. The intestinal canal was originally attached to the abdominal wall by a fold covering vessels and nerves named the mesentery, parts of which per- FIG. 1365. Infraclavicular fossa Coracoid process Groove between deltoid -j and pectoralis major X-rib cartilage Duodenum Linea semilunaris Ascending colon Anterior superior iliac spine Line of Poupart's ligament Suprasternal notch ^Clavicle Sternum Aeromion Deltoid Left lung Ensifortn cartilage Infrasternal depression Spleen Stomach Vermiform Spermatic cord emerging at external abdomi ring Anterior surface of body, drawn from photograph. General relations of thoracic and abdominal organs to body-wall are shown by colored outline. sist as free folds, while others fuse with the abdominal walls. The term incscntcn' is vaguely applied to that portion going to the jejuno-ileum, while other parts are distin- guished by tin- name of the part of the intestine to which they are attached, as HICSD- colon. The term onicntuin is applied to folds attached to the stomach, as the gastro- hepatic cnio/fiiin. The peritoneal sac is entirely closed, except in the female at the upper end of the oviduct, where the mucous membrane of the tube and the serous lining are directly continuous. The opposed smooth walls of the peritoneal sac are THE STOMACH. 1617 in contact and lubricated with a thin layer of serous fluid, secreted by the membrane, by which friction between the organs and movable surfaces is reduced to a minimum. The serous membrane, consisting of the endothelium and the fibro-elastic tunica propria, is attached to the subjacent fasciae of the abdominal wall and the organs by a layer of subperitoneal tissue, an areolar stratum forming a more or less intimate connection between the serous coat and the structures which it covers. The relations and attachments of the peritoneum observed in the adult are in some places entirely different from those existing in early life ; hence the history of the changes occurring during development is essential for understanding the complex relations found at later periods. PLAN OF THE DIGESTIVE TRACT BELOW THE DIAPHRAGM. The subcliaphragmatic digestive tube is divided into the stomach, the small intes- tine, and the large intestine. The small intestine is subdivided into the duodemim and the jejuno-ileum. The former of these is an imperfect ring or horseshoe-shaped portion from 2530 cm. (10-12 in.) long, all of which, except the first inch or two, lies on the posterior abdominal wall behind the peritoneum in the adult ; then comes something over 6 m. (usually about 21.5 ft. ) of intestine thrown into folds by its attachment to the free edge of the mesentery. The upper two-fifths of this is called the jejunum and the rest the ileum ; but, as the division is absurd, it is better to speak of this portion of the small intestine as the jejuno-ileum, sometimes alluding to the upper part as jejunum and to the lower as ileum. It ends at the right iliac fossa by joining the large intestine, a little over 1.5 m. (usually about 5.5 ft.) long, which is subdivided into the c&cum, a blind pouch, and the colon, which is ascend- ing in the right flank, transverse across the middle of the abdomen, and descending on the left. This is followed at the crest of the ileum by the sigmoid flexure, a free fold attached to the left of the pelvis, usually reckoned as a part of the colon, which, after crossing the left sacro-iliac joint, descends in the hollow of the sacrum, to become the rectum at the third sacral vertebra. The termination of the gut, passing through the thickness of the floor of the pelvis, is the anal canal. Two large glands the liver and the pancreas pour their secretions into the second part of the duo- denum, from which they originally sprouted. The liver, the stomach, and the spleen occupy nearly all the space in the dome- like upper zone of the abdomen ; the right kidney, caecum, and ascending colon on the right, the left kidney and the descending colon on the left, occupy the lower lateral recesses, leaving the middle space shallow in the umbilical region and deep below it for all the rest of the intestines, except such parts as can be squeezed into the preceding regions, and for the greater part of the pancreas. THE STOMACH. The stomach, the most dilated part of the digestive tube, follows the oesopha- gus, lying in the upper part of the abdomen below the diaphragm on the left, and passing downward and inward across the median line. In the early embryo it is a tubular dilatation, but it becomes flattened from side to side and the posterior border develops excessively, so that it rises above the upper opening and descends below the lower one. The stomach also swings -on its long axis, so that its posterior border is carried to the left and the original left side to the front. The lesser curva- ture is that part of the right border of the stomach between the two orifices. It is straight or nearly so, and runs downward and forward to near its end, when it rises and passes to the right. The lesser omentum, originally the anterior mesentery, is attached . to it. The greater curvature is more difficult to define. It is usually erroneously described as identical with the line of attachment of the greater omentum. It is more accurate to define it as the line from one orifice to the other which passes along the left side of the stomach and separates the anterior from the posterior aspect. The greater omentum the original posterior mesentery is attached to the greater curvature all along except at the upper part, where it passes onto the pos- terior surface. i6i8 HT.MAX ANATOMY. FIG. 1366. Gastro-phrcnic ligament Oesophagus Gastro-hepatic omentuni Fundus Pylorus The shape of the stomach may be compared to that of a pear, somewhat flat- tened, with the large end up and the point bent to the right. The fundus is the highest part of the stomach which projects upward above the level of the end of the oesophagus. The greatest breadth of the stomach is at about the level of the oeso- phageal or cardiac orifice, and exceeds the antcro-posterior diameter. The fundus generally contains air, if nothing else, and is somewhat distended, although thrown into uncertain contours by the partial contraction of its walls. Towards the lower or pyloric end the stomach gradu- ally becomes more tubular, but the termination is often dilated into a cavity known as the antrum Pylori. The constriction on its left may be very slight, so that the antrum is hardly to be seen, or it may be so deep as to be mistaken for the pylorus. The antrum may be double or even triple. Sometimes, on the other hand, the terminal part of the Anterior aspect of stomach, moderately distended. stomach is tubular and to be dis- tinguished from the intestine only by its thick walls. Fig. 1368 shows such a case which seems to extend beyond the usual limits of the stomach. The superior or cardiac orifice faces upward and to the right, being much nearer the front than the back of the stomach. Its diameter is at least 2 cm. and may be much more. When the stomach is distended a well-defined grpove appears between the fundus and the left of the oesophagus. Further details have been given with the gullet (page 1609). The position of the lower orifice or pylorus may not be recognizable on the outer surface, or it may be marked by a groove. Internally, it presents a distinct ring caused by the thickening of the layer of circular muscular fibres, improperly called the valve of the pylorus, which raises the mucous membrane. This can always be felt through the walls. It is only by touch that the position of the pylorus can be certainly recognized when the FIG. 1367. Greater omentum (cut) Antrum Gastro-splenic omentum Fundus parts are unopened. The gastric cavity gradually narrows towards the pylorus on the stomach side, but from the duo- denum there seems to be a perforated partition across the tube like an optical diaphragm. The opening, although nearly always elliptical, is sometimes almost circular. Some of the larger openings in a series of thirty casts ' show a long diameter of from 17-18 mm. and a short one of from 13-15 mm. Some of the smaller openings measure 6x7 mm. and 8x8 mm. We have observed more extreme figures at both ends of the series than those quoted. It is difficult to say whether some of the smaller ones would admit of greater dilatation. Probably 13x15 mm. is not far from the average size. The position of the longer axis of the orifice is uncertain, although it usually runs down- ward and backward. 2 Owing to the difference in size of the two ends of the organ, the axis of the 1 I hviirht : Journal of Anatomy and Physiology, vol. xxxi., 1897. Berry ana Crawford : Ibid., vol. xxxvi., 1902. Gastro-phrenic ligament > f Uncovered - area CEsophagus Posterior surface Gastro-ln-]i:itif omentum Pylorus Superior aspect Antrum rh, moderately distended. THE STOMACH. 1619 FIG. 1368. Pyloru; Outline of stomach with constricted and greatly elon- gated pylorus. stomach is necessarily oblique, although the lesser curvature is vertical until near its end. The axis slants downward and to the right as well as forward, the pyloric portion being disregarded. The stomach is sometimes comparatively tubular, the fundus being but little developed, although the cardiac opening is always on the right side. This is a continuation of the fcetal form, and is more often seen in women. There is often (possibly normally) a hint of a con- striction about the middle. The above description, which is essentially the conven- tional one, is that of a distended stomach. The constrictions marking off a single, double, or even triple antrum pyloris are due to the contraction which generally persists for some hours after death of bundles of the circular fibres. Such constrictions sometimes become fixed. The true shape of the stomach in life when non-distended is very different, but not yet thoroughly known. It is rather tubular, owing to the contraction of the muscles in its walls. The fundus is puckered and more or less constricted off from the rest, as is 'shown by the study of hardened bodies (Fig. 1369). Weight and Dimensions. Not only is the normal development of the stomach very variable, but it is impossible to define the limits between the normal and the pathological ; naturally, therefore, statements differ widely and are of little value. According to Glendinning, the weight is 127 gm. (4^ oz. ) for man and a little less for woman. The greatest length, directed nearly vertically, is some 25 cm. (10 in. ), the greatest breadth from 10-12 cm. (4-5 in. ), and its diameter from before backward from 7.5-10 cm. (3-4 in.). The average adult capacity is said to range from 600-2000 cc. (1.25-4.25 pints), with an average of 1200 cc. (2.50 pints). Peritoneal Relations. The greater omentum, the original posterior mesen- tery, passes to the back of the stomach just to the left of the oesophagus, where its layers diverge so as to leave a small triangular part behind it attached to the dia- phragm without peritoneal covering. The lower of the diverging lines runs to the lesser omentum. The line of attachment then passes across the posterior surface of the fundus near the top, but posterior to the greater curvature. At the left of the stomach the line of insertion is at the greater curvature, and continues FIG. so till it reaches the pylorus. The fold passing to the diaphragm at the beginning is the gastro-phrenic ligament. This is joined by the gastro-pancreatic fold on the pos- terior abdominal wall which con- veys the coronary artery to the right of the cardiac opening. This last fold is important in relation to the topography of the peritoneum, but not to the stomach. The lesser omentum is attached along the whole of the lesser curvature, ex- cept that its posterior layer may leave it below the cardia to join on the back of the stomach the layer of the greater omentum which forms the inferior border of the non-serous triangle. With the exception of this triangle, and of the trifling interval between the lines of attachment of the omenta, the whole organ is invested by peritoneum. Position and Relations. The cardiac opening is opposite the tenth thoracic vertebra and not far from the level of, but from 8-10 cm. (3-4 in.) behind, the sixth left costal cartilage, about 12 mm. (*/> in.) to the left of the median line. The lesser curvature descends vertically in an antero-posterior plane, parallel to the left border of the ensiform, but slanting strongly forward, until it suddenly turns to the Fundus Pylorus Stomach with puckered fundus, seen from behind and somewhat from left ; hardened by formalin. i6 2 o HUMAN ANATOMY. right, rises, and ends opposite the space between the ensiform and the end of the eighth or ninth right costal cartilage, on a level with the first lumbar vertebra or the disk below it, about 1.2 cm. (^ in.) from the median line. The pyloric orifice is affected to such an extent by changes incident to variations in distention that it is manifestly impossible definitely to fix the position of the lower end of the stomach. The pylorus is usually separated from the anterior abdominal wall by the over- lapping liver, when the stomach is empty lying near the mid-line. According to Addison, a point 12 mm. (^ inch) to the right of the median plane midway between the top of the sternum and the pubic crest will ordinarily correspond to the position of the pylorus. The fundus is at the top of the left side of the abdomen un'der the diaphragm, reaching the level of the sternal end of the fifth costal cartilage. The anterior surface, looking upward as well as forward, is covered by the left and quad- rate lobes of the liver. A varying part of it touches the diaphragm in front of the former. The extent of this must depend on the size of both organs. The liver may separate it entirely from that part of the diaphragm below the pericardium, or the stomach may be against the diaphragm in the anterior part of this region. A small triangular part of the stomach, normally in contact with the front wall of the abdo- men, bounded below by the greater curvature, is seen, on opening the abdomen, between the liver and the line of the left costal cartilages. This appearance gave rise to the old error that the stomach is placed transversely. According to Tillaux, the stomach in its most con- FIG. 1370. tracted state always descends to a line between the ends of the ninth costal cartilages. The pos- Non-peritoneal area terior surface, forming a part of the anterior wall of the lesser peritoneal cavity, rests against the transverse mesocolon, which lies on the organs at the back of -Lesser omentum that space, so- as to make a part of the concavity for it which Bir- mingham 1 has well called the -pylorus stomach-bed (Fig. 1371). This hollow is made by the diaphragm on the left of the aorta, by the left Suprarenal capsule, the gas- Posterior aspect of stomach at birth, showing peritoneal relations, trie surface of the spleen, t antero-superior surface of the pancreas, and usually by the upper part of the left kidney, although exceptionally this may be shut off from the stomach by the spleen and pancreas. The left crus of the diaphragm makes a deep indentation in the stomach to the left of the car- dia. The cceliac axis and the semilunar ganglia are rather to the right of the lesser curvature. The transverse mesocolon continues the lower part of the stomach-bed forward to the transverse colon, which lies below the stomach, following its curve when the stomach is distended. The splenic flexure of the colon is close against it. When free from solid contents, the stomach is usually found in dissecting-room subjects hanging more or less vertically in longitudinal folds containing more or less air and fluid ; but during life, as already stated, it is in a contracted and puckered condition, the long axis running strongly forward as well as downward. With dis- tention the stomach enlarges at first upward, backward, and to the left, then forward against the abdominal walls. The upper part enlarges chiefly backward, the lower forward. This does not imply a forward swing of the greater curvature such as has been described. The pyloric end is moved to the right, it may be as far as the gall-bladder. The antrum may thus, according to Birmingham, be carried to the right of the pylorus. The latter rarely moves more than 5 cm. to the right of the median line. Except in its last part, the lesser curvature continues essentially vertical, as seen from before. The transverse colon is driven downward unless it be so much distended as to offer effectual resistance. 1 Journal of Anatomy and Physiology, vols. xxxi., xxxv., 1897, 1901. THE STOMACH. 1621 Structure. The walls of the stomach, thickest and most resistant near the pylorus, consist of four coats, the mucous, the submucous or areolar, the muscu- lar, and the serous. The mucous coat or mucosa is soft and velvety, easily movable on the lax subjacent areolar tissue, thickest near the pylorus, and presents many folds or ruga, which during distention are more or less completely effaced. The folds are in the FIG. 1371. Falciform ligament Ascending colon - Ca?cum Ileui Left lobe of liver Transverse mesocolon Transverse colon Descending colon Ileum Sigmoid Abdominal organs of formalin subject ; stomach has been removed to show that part of its "bed " formed by trans- verse mesocolon and colon. main longitudinal, especially at the pyloric end, but many smaller ones run in all directions. The epithelium covering the free surface of the mucous membrane consists of a simple layer of tall columnar elements, from .020-. 030 mm. in height, many of which are goblet-cells engaged in producing the mucus lubricating the gastric surface. At the passage of the oesophagus into the stomach, some 2-3 cm. below the diaphragm, the opaque stratified squamous epithelium of the gullet abruptly changes into the 1622 III MAN ANATOMY. transparent columnar cells clothing the stomach. The line of transition is zigzag and well defined, the cesophageal surface being paler than the highly vascular red gastric mucosa. At the pylorus the mucous membrane -is raised into a ring, chiefly FIG. 1372. Ensiform cartilage VI rib-cartilage VIII rib-cartilage VII rib-cartilage ] VII rib-cartilage / Falciform ligament Transverse mesocolon ^_ ^ r ,,-^--^, VI rib-cartilage Pyloric antrum of stomach Diaphragm Hepatic artery A ^Gall-bladder Pyloric sphincter Cystic duct Pleura! cavity Duodenum Hepatic duct Right supra- renal body Pancreatic duct Splenic vein Xrib Left supra- 1 renal body XI rib XII rib XII vertebra XII rib Frozen section across body at level of twelfth thoracic vertebra. in consequence of the local thickening of the circular fibres of the muscular coat, but also in part on account of the increased thickness of the mucosa itself, which in this part of the stomach may measure over 2 mm. At the cardia it is thinnest, .5 mm. or less, while in the intermediate region it is about i mm. The increased thick- ness at the pyloric end is due to the considerable depth of the depressions, or FIG. 1374- FIG. 1373. Surface view of mucous membrane from pyloric end of stomach. Natural size. Surface view of gastric mucous membrane, show- ing reticular appearance due to orifices of group-- ol gastric glands. X 30. gastric crypts, into which open the gastric glands. Beyond the summit of the pyloric ring the mucous membrane assumes the characteristics of the intestine. In addition to the larger rugae, the gastric surface exhibits a mammillated condition THE STOMACH. 1623 consisting- of small polygonal areas pitted by the crypts which receive the orifices of the glands. The gastric glands constitute two principal groups, the /undies and \\\z pyloric glands ; the former occupy the major part of the stomach, including the fundus, the anterior and posterior walls, and the curvatures ; the latter occur in the pyloric fifth of the organ. An additional fundus variety the cardiac glands is represented by a narrow zonular group in the immediate vicinity of the cesophageal opening. The fundus or peptic glands the gastric glands proper consist of numerous closely set tubules, usually somewhat wavy and from .42 mm. long, which extend the entire thickness of the mucosa and abut against the muscularis mucosae. Each gastric crypt, corresponding to the excretory duct, usually receives a group of sev- eral of the smaller tubules, which include the body and fundus of the gland, the constricted commencement of the tubule constituting the neck. At the latter position FIG. 1375. r,astric glands ML ; *- *-" -* ^-^*V - * -r - "~* '.--"-i'V'-* -."". i-v_-, < --'.; t^.,/^ .- -. . -'.:*,, .*w' -. --''^Tv- Blood-vessel Submucosa Muscularis Serosa ->%. -r*^ ^ , f-^- '.x -T - V - -- *"-. * - re ^1^ ^-i^*^- ^ " ' '** ^ - >''''<^. ' Obliquely cut bundles of circular muscle >;> . Transverse section of stomach (left end), showing general arrangement of coats. X 20. the columnar epithelium prolonged into the crypts from the free surface becomes lower and modified into the secreting elements. The cells lining the gastric tubules are of two kinds, the chief and the parietal. The chief, central or adelomorphous cells correspond to ordinary glandular epi- thelium, being low columnar or pyramidal, and surrounding a circular lumen from .002 to .007 mm. in diameter. During certain stages of digestion they contain numerous granules, which are probably concerned in producing pepsin. The parietal cells, known also as acid, oxyntic, or delomorphous, although rela- tively few, are conspicuous elements which occupy the periphery of the gland-tubes. Their position is indicated by protrusions of the profile of the gastric tubules caused by the cells lying immediately beneath the basement membrane. The parietal cells, although arranged with little regularity, are most numerous in the vicinity of the neck, where they may equal or even outnumber the central cells ; in the body of the 1624 1 1 T. MAX ANATOMY. FIG. 1376. gland they decrease in number towards the fundus, in which locality they may be almost absent. Their protoplasm is finely granular and lighter than that of the chief cells. The parietal cells, although apparently excluded by the central ones, are con- nected with the gland-lumen by means of lateral intercellular secretion-capillaries ; the latter extend from the axial space to the peripherally situated elements, over which they form characteristic basket-like net-works. The pyloric glands, branched tubular in type, differ from the fundus glands in the excessive width and depth of their excretory ducts, into which a group of relatively short but very tortuous gland-tubules opens, and in the simple character of their lining. The latter consists of a single layer of low columnar or pyramidal elements, which corre- spond to and resemble the chief cells of the fundus glands. Their secretion often reacts as mucus (Bensley). Owing to the tortuous course of the pyloric tubules, the deeper parts of the glands are cut in all planes, portions of the same tubule often appearing as isolated transverse, oblique, or longitudinal sections. The transitional or in- termediate zone connecting the py- loric and adjoining portions of the stomach contains both forms of glands, those of the fundus variety with parietal cells being intermin- gled with the pyloric type. Towards the intestine the change of the py- loric glands into those of the duo- denum is gradual, the gastric tubules sinking deeper until, as the glands of Brunner, they occupy the sub- mucous coat of the intestine. The cardiac glands form a narrow annular group, some 5 mm. broad, surrounding the orifice of the gullet, into which they are con- tinued for a short distance (page 1612). These glands, which in some animals constitute a much wider zone (in the hog almost a third of the entire stomach), are to be re- garded as modified fundus glands Chief cell Parietal cell (Oppel), since they possess similar epithelium, including usually a few :ts Deeper portion of gastric glands from fundus, showing two varieties of lining cells and secretion-capillaries connecting pari- etal cells with lumen. X 423. parietal cells. Their excretory due or crypts, lined with the gastric epithelium, often exhibit ampulla- like dilatations. Among the typi- cal tubules area few shorter ones which recall the glands of Lieber- kiihn of the intestine, since they contain goblet-cells and exhibit a cuticular bord' (J. Schaffer). The stroma or tunica propria of the gastric mucous membrane consists of a loose fibro-elastic connective tissue containing numerous cells and resembling lym- phoid tissue, which fills the interstices between the glands and, in conjunction with the extensions of the muscularis mucosa?, forms envelopes and partitions for the groups of tubules constituting the deeper parts of the gastric glands. In THE STOMACH. 1625 the vicinity of the pylorus, and sometimes also at the cardia, a number of small lymphatic nodes the so-called lenticular glands normally occupy the deeper parts of the mucosa ; occasionally they are of sufficient size to almost reach the free surface. The muscularis mucosce, as in other parts of the intestinal tube, consists of a well-marked collection of involuntary muscle, deeply situated next the submucous coat. Two layers are usually distinguishable, an inner circular and an outer longi- FIG. 1377. Mucous coat Wide orifice of glands Pyloric glands Submucous coat ^ Circular muscle Longitudinal muscle Serous coat Transverse section of stomach, pyloric end ; ruga is cut across, showing mucosa supported by core of submucous tissue. X 20. tudinal. Towards the mucosa numerous bundles of muscle-cells extend between the glands and in places penetrate almost as far as the epithelium. The submucous coat consists of lax connective tissue, allowing the mucous membrane to move freely on the muscular layer. It contains blood-vessels of con- siderable size, a mesh-work of lymphatics, and the nerve-plexus of Meissner. The muscular coat comprises three layers, an outer longitudinal, a middle circular, and an imperfect inner oblique, of which the middle one is the most 1626 HUMAN ANATOMY. important. This layer is composed of circular fibres, which are thickest and most simply arranged near the pylorus. Owing to the enlargement of the upper end of the stomach, and the fact that the cardiac opening is not at the end but at the side, the arrangement becomes complicated. The fibres surround the cardia, but become oblique at a short distance from it. At the top of the fundus they are arranged in a whorl mingling with those of the internal layer. Still lower, although in the main circular, their course is uncertain. Towards the pylorus they thicken considerably, being particularly well developed in stomachs of which the pyloric part is tubular. At the opening they are collected into a ring \\\z pyloric sphincter capable of closing the orifice. The longitudinal layer is outside of the circular one and continuous FIG. 1378. Mouth of gla Pyloric gla ' liteiiil IP^I^^^ x" ." V V -V ;.' , aSIJ.VWS^ Lymph-node vS3*i_ 'y't^Vf'^r^'R'^'- Fundus of gland. Muscularis mucosae- :tion of pyloric end of stomach, showing glands and part of lymph-node. too. Section < with the longitudinal fibres of the oesophagus. Along the lesser curvature, and to less extent along the greater, these fibres are collected into bands ; over the front and the back of the stomach they are oblique. At the antrum pylori, although the layer is continuous all around, it presents an anterior and a posterior band, the Pyloric ligaments, that pass over folds of all the layers internal to them, thus forming the duplicature at the beginning of the antrum. At the pylorus itself the longitudinal layer, which has become thicker, sends a series of fibres through the circular fibres, subdividing them into n, any groups, (Fig. 1392). The innermost muscular layer consists of oblique fibre* spreading out from tin- cardia over the front and back of the stomach. They are continuations of the circular fibres of THE STOMACH. 1627 the gullet and diverge to either side, showing a well-marked border near the lesser curvature. Their posterior expansion is the stronger. The diverging fibres are lost near the pylorus, while in the vicinity of the fundus they mingle with the circular ones that form the whorl. The latter, according to Birmingham, is formed by this layer alone. The serous coat corresponds in structure with other portions of the perito- neum, consisting of the endothelium of the free surface, beneath which lies the fibre-elastic stroma attached to the muscular tunic. Blood-Vessels. The arteries of the stomach, de- rived from the coeliac axis, are arranged in two arches along the lines of attachment of the omenta ; hence that which is attached to the greater cur- vature below passes behind it on the fundus. The arch along the lesser curvature is formed by the coronary ar- tery, which sends an cesopha- geal branch upward to meet the lowest of the cesophageal arteries, and joins the py- loric branch of the hepatic artery below. The arteries of the greater omentum are the right and left gastro-epi- ploic, reinforced behind the fundus by the vasa brevia of the splenic artery. The gastro-epiploicadextra passes down on the right of the first part of the duodenum close to the pylorus ; branches arising on the front at that region may nearly or quite make an arterial ring around the organ. The coronary artery supplies the longer branches to the walls, there being a richer arterial distri- bution on the back than on the front and at the cardiac than at the pyloric end. The general plan is as follows : on the anterior surface several arteries, of which some four are large ones, run from the lesser curvature across the stomach, sending out successive lateral branches to inosculate with those from their fellows ; finally, the main vessel breaks up into branches that meet those from the greater curvature. On the posterior surface the chief trunks divide with less regu- larity. At first the arteries are just beneath the peritoneum, between the folds of which they gain the stomach ; presently they enter and pierce the muscular coat, the outer parts of which are supplied during their passage. On reaching the submucous coat the arteries, now reduced, but still of considerable size, divide into smaller branches, some of which pass to the muscular tunic, while the majority enter the mucous coat. The latter soon break up into capillaries which surround the gland- Oblique section of mucous membrane from pyloric end of stomach, show- ing glands cut at various levels. X 100. 1 628 Iir.MAX ANATOMY. Pyloric ring Stomach turned ir of oblique and tubules with a close mesh-work. Somewhat larger capillaries constitute a superficial plexus beneath the epithelium encircling the orifices of the gastric crypts. The veins, relatively wide, begin in the subepithelial capillary net-work and traverse the gland-layer, between which and the muscularis mucosae they form FIG. 1380. a plexus ; from the latter radicles pass into the submucous coat, in which the venous trunks run paral- lel with the arteries, but lie nearer the mucosa (Mall). The emerging tributaries are often provided with valves at their junction with the larger gastric veins. The lymphatics originate within the mucous membrane, be- neath the epithelium, as wide, ir- regular capillary channels which freely communicate with one an- other and pass between the glands as far as the muscularis mucosae ; at this level they form a plexus from which vessels descend into the areolar coat to join the wide-meshed submucous plexus. Larger lymphatics pierce the muscular tunic and unite to form the chief channels which escape from the walls of the stomach along both curvatures to empty into the lymph- nodes which occur in these situations. The nerves supplying the stomach are from the pneumogastric and the sympathetic, and contain both medullated and nonmedullated fibres, the latter predominating. On FIG. 1381. reaching the organ, the stems pierce the exter- nal longitudinal muscu- lar layer, between which and the circular layer they form the plexus of Aiterbach. The points of juncture in this net- work are marked by mi- croscopic sympathetic ganglia, from which non-medullated fibres supply the involuntary muscle. Leaving the intramuscular plexus, twigs pass obliquely through the circular muscular tunic, and on gaining the subnuicous coat form a second net- work, the f>le.\ns of Me issuer. Numerous non-medullated fibres leave the latter to enter the mucous coat, in which some end in deli- cate plexuses supply- ing the gastric glands ( Kytmanow >, as well as in special endings in the muscularis mucosae (Berkley). Large medullated fibres, the dendrits of sensory neurones, are also present within the mucosa, where' they form a subepithelial plexus after losing their medullary substance. The ultimate termi- MUCO! Submucos:; =s? Muscular Seros;< - _ _. Transverse section of injected stomach. X 50. PRACTICAL CONSIDERATIONS: THE STOMACH. 1629 nations of the nerve-fibres within the mucosa, especially their relations with the gland-cells, are still uncertain. Growth. At birth the capacity of the stomach is 25 cc. The organ, although sometimes rather tubular, does not differ very much in shape from that of the adult. The oesophagus enters it less obliquely than later, so that regurgitation occurs more readily. The sphincter of the pylorus is already developed. We do not remem- ber ever to have seen at birth a well-marked antrum pylori. An important pecu- liarity of the growth of the stomach is the unequal development of the two sides at the fundus. At an early period the top of the original left side, which becomes the anterior one, grows upward, so that the FIG. 1382. line of attachment of the greater omentum 3v-i is along the posterior surface. This unequal growth is quite analo- gous to that of the caecum. According to Keith and Jones, this asymmetry is most marked in the third and fourth months of fcetal life. We have examined no younger foetuses than these, and cannot state how earlv the process be- i t7> u J Surface view of fragment of muscular coat of stomach, showing groups of gau- glllS. r rom the end ^lion-cells and nerve-fibres of plexus of Auerbach. > 70. of the first week after birth the growth of the stomach is very rapid during the first three months. It is slow in the fourth month, and in the two months following it is almost quiescent. 2 We have seen it at a few weeks relatively broader than in the adult. While it is probable that individual variations show themselves early, the shape and size of the stomach depend, beyond question, to a great extent on the nature and quantity of the food. With advancing years the stomach often becomes dilated, and, apart from dilatation, is likely to descend lower in the abdomen. The female stomach, except for its greater tendency to subdivision, differs less than the male from the fcetal form. Variations. Apart from those of size and shape, already alluded to, the important ones are those of subdivision. There may be a constriction at the middle dividing the organ into two chambers connected by a narrow passage : the " hour-glass stomach." There may also be a reduplication of the antrum, or, indeed, there may be three, or, on the other hand, the place of the antrum may be taken by a tube with thick walls. It is probable that these changes are sometimes caused by a local contraction becoming fixed. PRACTICAL CONSIDERATIONS : THE STOMACH. Congenital malformations are rare. Perhaps the most common is a constriction dividing it into two unequal compartments, " hour-glass constriction," a condi- tion somewhat similar to that found normally in the kangaroo. The position of the stomach varies with its degree of distention. When it is empty the pyloric end descends and the long axis of the stomach is oblique from left to right, approximating the vertical (i.e., the fcetal) position or that which pre- ceded functional use. This falling of the pyloric end is due to gravity, the nearest firmly fixed point of the alimentary canal below being the lower portion of the duo- 1 Priority of publication of this peculiarity of development belongs to Mr. Arthur Keith and to Mr. F. Wood Jones : Proceedings of the Anatomical Society of Great Britain and Ireland. Journal of Anatomy and Physiology, vol. xxxvi., 1902. 2 Rotch's Pediatrics. !6 3 o HUMAN ANATOMY. denum (the fixation being due to the relation of the superior mesenteric artery and to the root of the mesocolon in front), while above the cardiac end is suspended from the oesophagus and held in place by the gastro-phrenic and gastro-splenic liga- ments. The transverse colon may then lie in front of the stomach and may, if dis- tended, be taken for it. The empty stomach lies upon the posterior abdominal wall. If the emptiness is habitual, the pylorus will resemble the first portion of the duodenum and regurgitation of duodenal contents is exceptionally easy. The "gnawing pains" of hunger or starvation (distinct from the sensation of hunger itself) are at least partly due to the traction on the nerve-plexuses and filaments resulting from this altered position, and can, therefore, in many cases be relieved temporarily and partially by tightening the clothing about the waist and abdomen, giving support to the viscera. When the stomach is distended the enlargement, which occurs at first upward and backward and towards the left side, raises the arch of the diaphragm in that region and with it the heart and pericardium. The gastric plexuses derived from the two pneumogastrics and the associated sympathetic fibres, together with the coronary plexus from the sympathetic, are all in close relation with the lesser curvature, especially its cardiac end. It is not, therefore, difficult to understand how this change in the position of the stomach aids in producing the flushed face, embarrassed respiration, and irregular heart action often seen in various forms of dyspepsia or after overeating. If distention continues, the right lobe of the liver is also pushed upward, the pylorus moves to the right, and the transverse colon downward ; the stomach comes in close contact with the anterior wall of the abdomen, the " scrobiculus cordis" (page 171) is obliterated, and a tympanitic note replaces the normal resonance. Conversely, cardiac disease may cause vascular congestion of the stomach, catarrh, dyspepsia, or even hsematemesis. The " black vomit" of moribund per- sons is due to a similarly produced distention and rupture of the stomach capillaries. The position of the stomach varies with the respiratory movements. In forced inspiration the cardiac opening descends about one inch with the crura of the dia- phragm ; the pylorus reaches about the level of the umbilicus. Eructation of stomach contents in its typical form is accomplished by con- traction of the muscular walls of the stomach ; vomiting by compression of the stomach against the under surfaces of the liver and diaphragm through contrac- tion of the abdominal muscles. This is associated with contraction of the circular pyloric fibres and relaxation of the oblique fibres at the cardia, and is probably aided by contraction of the stomach walls themselves. It is obvious that a full stomach is more easily and directly compressed in this way, and therefore the ingestion of large quantities of fluids favors emesis. Vomiting is a clinical symptom often of the greatest significance, and should be studied in relation to the pneumogastric and sympathetic distribution to the stomach, lungs, and abdominal viscera ; and its various causes central, reflex, and direct should be worked out systematically. Injuries of the Stomach. The changes in position and the degree of distention are of the utmost importance in trauma expended upon the stomach, which, if quite empty, almost certainly escapes contusion and rupture. It is, at any rate, much less frequently ruptured than the intestines on account of its thicker walls and of the protection afforded it by the overhanging ribs and the interposed liver. The "stomach-bed " (page 1620) supplies an elastic and movable base of support, which also favors its escape from injury. In penetrating or gunshot wounds its condition as to emptiness or the reverse is even more important. When either wall is opened by rupture or wound, eversion of the mucous membrane, which is favored by its thickness and by the laxity of the submucous connective tissue, may temporarily plug the opening, and through the formation of adhesions permit of spontaneous cure. The different directions of the muscular fibres in the three layers of that coat ordinarily prevent wide separa- tion of the margins of the wound, and thus also favor its closure by natural processes. In escape of storuach contents through tilccration, wound, or rupture, if the poste- rior wall is involved, the lesser onu-ntal cavity is infected, and a localized sub- PRACTICAL CONSIDERATIONS: THE STOMACH. 1631 phrenic abscess may follow ; if the anterior wall is opened, infection of the general peritoneal cavity and septic peritonitis are more likely to result. On account of the course of the blood-vessels (page 1627), wounds parallel with the axes of the curva- tures are attended by free bleeding, especially if near those borders of the stomach. Wounds running more or less at right angles to the curvatures and removed from them are much less likely to open large vessels. The vessels just beneath the sur- face of the mucous membrane are numerous but smaller. Bleeding from them may be controlled by separate suture of the mucosa, which is facilitated by its thickness and by the looseness of the submucous cellular tissue. Ulcers of the stomach are found most often on the posterior wall at the pyloric end and along the lesser curvature. It has been suggested that they originate in a bacterial necrosis of the epithelium, which is favored by the absence of the fundus or peptic glands (page 1623) at this region, and is followed by "digestion" of the subjacent tissues. Allen thinks that the immense preponderance of pyloric ulcers is an illustration of the "law of localization of diseased action," viz., that parts enjoying the most rest are least liable to involvement by structural disease. When they cause hemorrhage, it is apt to be from the branches of the coronary artery. Per- foration occurs with much greater frequency in ulcers situated on the anterior wall, which is the one with the greatest range of motion in varying stages of digestion and degrees of distention, and also during the movements of respiration. Perfora- tion from such ulcers with spontaneous cure may result in adhesions between the stomach and pancreas, colon, duodenum, or gall-bladder, and may be followed by fistulas communicating with those viscera. They may perforate the diaphragm and cause empyema. They have opened into the pericardium and into a ventricle of the heart. An ulcer may be so surrounded by adhesions that, even when on the anterior wall, perforation does not cause a general peritonitis, but a localized abscess. If this is, for example, in the splenic region, it will be observed that there is immo- bility of the upper left quadrant of the abdomen with restriction of the respiratory movements of the left thorax, both occasioned by the connection between the splanchnic and the intercostal nerves through the sympathetic ganglia. The local- ization of such collections of pus after perforation of the anterior wall near the cardia is favored by the " costo-colic" fold of peritoneum extending from the dia- phragm opposite the tenth and eleventh ribs to the splenic flexure of the colon and forming part of the left portion of the "stomach-bed." This fold, especially with the patient supine, forms a ' ' natural well, ' ' containing the spleen and a part of the stomach, into which any fluid exudate or stomach contents may gravitate (Box). Cancer of the stomach occupies by preference the pyloric region. When the growth becomes palpable, but before it is tied down by adhesions to neighboring organs, it often illustrates the mobility of the pyloric end of the stomach ( vide snpra), as it can be pushed even across the mid-line of the body into the splenic region. Carcinoma, according to its situation, may extend in the course of the lym- phatic vessels running along the lesser curvature in the gastro-hepatic omentum and emptying into the lymph- nodes near the cceliac axis and hepatic blood-vessels, or along the greater curvature and the cardia to the retro-cesophageal glands. The retro-pyloric lymph-nodes may be invaded in cancer of the pylorus. Its early recog- nition as a tumor obviously depends upon its anatomical site. If it occupies the fundus, the cardia, the lesser curvature, or the upper and outlying portions of the anterior wall, the ribs and the liver intervene and prevent palpation of the growth ; and if on the posteridr wall, the depth at which the tumor lies renders its palpation difficult and unsatisfactory. Dilatation of the stomach (gastrectasis} may be due to simple hypertrophy of the pyloric muscle, may follow stricture of the pylorus or duodenum from cicatriza- tion of an ulcer, or may result .from pyloric occlusion, as from carcinomatous growth invading the pylorus itself, or from pressure of an extrinsic tumor, or a displaced liver or right kidney. The distention is often extreme, and in some instances the outline of the distended stomach can plainly be seen, the lesser curvature a couple of inches below the ensiform cartilage and the greater curvature passing obliquely, 1632 HUMAN ANATOMY. from the tip of the tenth rib on the left side, towards the pubes, and then curving upward to the right costal margin (Osier). The dilatation may be of any degree, the lower border of the stomach sometimes reaching to the level of the pubes. Displacement of the stomach {gastroptosis) is attended by great stretching of the gastro-hepatic, gastro-splenic, and gastro-phrenic folds. It is sometimes a dila- tation with the stomach vertical instead of oblique rather than a true descent of the whole organ. Three forms are described : ( i ) a slight descent of the pylorus, and with it of the lesser curvature, so that the latter comes from beneath the liver ; (2) " vertical stomach," already alluded to ; (3) a descent of the lesser curvature, the pylorus remaining fixed, making a U-shaped stomach (Riegel). The last is very rare. All forms are favored by the use of corsets or clothing constricting the lower thorax, especially in women with flaccid abdominal walls. The displacement may be con- genital, or may be due to primary elongation or relaxation of the peritoneal folds which act as ligaments, or to malposition or displacement of other abdominal viscera. Hernia of the stomach is usually diaphragmatic and often congenital. The viscus may enter the thorax through a stab wound or rupture, or through weakened or enlarged spaces at ( Descending colon Sigmoid flexure Abdominal organs of formalin subject. Stomach was unusually large, giving an exaggerated impression of it transverse jxjsition. Structure. The small intestine, as other parts of the alimentary tube below the diaphragm, consists of four coats, the witcon.f, tin- submit cons, the muscular, and the serous. The mucous coat, in addition to the glandular structures, possesses folds and villi that not only greatly increase its surface, hut also contribute peculiarities which aid in differentiating between typical portions taken from various regions. The THE SMALL INTESTINE. 1635 epithelium covering the free surface consists of a single layer of cylindrical cells which exhibit a striated cuticular border next the intestinal lumen. This border lacks stability, and is resolvable into minute prismatic rods, placed vertically and probably continuous with the spongioplastic threads within the body of the cell. In many places, especially over the villi, mucus-producing goblet-cells share the free surface with the ordinary epithelial elements. Between the latter migratory leucocytes are always to be seen. The stroma or tunica propria of the mucous coat resembles lymphoicl tissue, being composed of a connective-tissue reticulum containing numerous small round cells similar to lymphocytes. This stroma fills the spaces between the glands and forms the core of the villi over which the epithelium stretches. The deep- FIG. 1384. Villus Duct of Brunner's glands V^ij Muscularis mucosae Brunner's gla Orifice of gland of Lieberkiihn Brunner's glands ". -^-5- ^v-i^sagwsifcwss:' 1 **^ ..' , Serous coat ire/ 1 - H-S--V Circular muscle Longitudinal muscle Transverse section of small intestine (lower part of duodenum), showing general arrangement of coats. X 90. est part of the mucous coat is occupied by a well-marked muscularis mucosce, in which an inner circular and an outer longitudinal layer are distinguishable. The villi are minute projections of the mucous surface, barely visible to the un- aided eye, the presence of which imparts the characteristic velvety appearance to the inner surface of the small intestine. Although found throughout the latter, from the pylorus to the ileo-colic valve, they are most numerous (from 20-40 to the sq. mm. ) in the duodenum and jejunum and less frequent (from 15-30 to the sq. mm.) in the ileum. In the duodenum they appear immediately beyond the pylorus, but reach their best development in the second part, where they measure from . 2-. 5 mm. in height and from .3-1 mm. in breadth ; they are, therefore, here low and broad. In the jejunum the villi are conical and somewhat laterally compressed, while in the ileum their shape is cylindrical, filiform, or wedge-like, their length and breadth being from .5-1 mm. and from .2-. 4 mm. respectively. The villi are projections of i6 3 6 HI. MAN ANATOMY. FIG 1385. v / t V./, the mucous coat alone, and consist of a framework of the lymphoid stroma-tissue, covered by columnar epithelium, which supports the absorbent vessel and the blood- vessels, together with involuntary muscle. The reticular tissue constituting the villus is condensed at the periphery, the existence of a definite limiting membrane being assumed by some (J. Schaffer, Spalteholz, Ebner). Each villus is supplied by from one to three small arteries, derived from the vessels of the submucosa, which break up into a capillary net-work lying beneath the peripheral layer of the stroma. The blood is returned usually by a single vein which, beginning at the summit by the confluence of capillaries, traverses the central parts of the villus and becomes trib- utary to the larger venous stems within the submucous coat. The absorbent, chyle-vessel, or lacteal, as the lymph-vessel occupying the villus is variously termed, lies near the centre of the projection, surrounded by the mus- cular tissue and the blood-capillaries. While the slender cylindrical villi contain only a single lymphatic, from .025-. 035 mm. in diameter, those of broader form often contain two, three, or even more such vessels, which may communicate by cross- channels. Their walls consist of a single layer of endothelial plates. The muscular tissue within the villus, prolonged from the muscularis mucosse, forms a delicate layer of slender fibre-cells, longitudinally disposed, which surround the central chyle- vessel. Contractions of this tissue shorten the villus and aid in propel- ling the emulsified contents of the lymphatic. The presence of numerous oil- droplets of considerable size within the epithelial cells, as well as stroma, of the villi during certain stages of digestion has caused much specula- tion as to their mode of entrance. On histological grounds there is good reason for assuming that a large part of the fat particles seen within the tissues gains access in a condition either of solubility, saponification, or exceedingly fine molecular sub- division, the accumulations observed within the tissues being due to sec- ondary change (Ebner). The valvulae conniventes (plicae circulates), within the duo- denum and jejunum, additionally model the mucous coat and greatly increase its secreting and absorbent surface ; they also retard the passage of the intestinal contents, thereby facilitating the digestive processes. These transverse folds begin in the second part of the duo- denum and consist of duplicatures which involve not only the entire thickness of the mucosa, but contain a central supporting projection of the submucous coat ; hence, while they may fall on their sides, they cannot, as a rule, be effaced by dis- tention. The height of the folds, where well developed, rarely much exceeds i cm., and towards the lower part of the jejunum is much less. The majority of the valves do not extend more than two-thirds or three-fourths of the circumference of the gut ; exceptionally, however, circular and spiral ones describe two or three com- plete turns. Their ends, usually simple, may be bifurcated. Smaller folds, more or less effaceable, run obliquely as offshoots from the larger ones. The valves are much larger on the attached side of the gut than on the free one ; in the latter position they may be entirely absent in localities in which the folds are feebly developed. Succeeding the first part of the duodenum, the yalvuhe conniventes are very numer- ous and large, and so near together that in falling over any fold would come in con- tact with the next one. Descending the small intestine, they gradually become smaller and farther apart, so that the 'distance between them considerably exceeds their height. They also become more effaceable, and finally very much so. In Gland Villus Surface view of mucous membrane of jejunum, showing villi and orifices of glands. X 35. THE SMALL INTESTINE. 1637 this respect much variation exists, which partially accounts for the differences found at the lower part of the small intestine, where often the valves are absent, while at other times they are well marked. Sernoff ' found in subjects treated with chromic acid injections that the valves were as frequent in one part of the small intestine as another, but less regularly transverse in the lower. He observed places without valves, usually at the convexity of folds, in all parts of the gut, and regards them as largely dependent upon the condition of the muscular coat. It is certain, however, that the valves of the upper part of the intestine are independent of this influence ; those in the lower portion, perhaps, may be produced in such manner. Glands. The structures within the alimentary tube to which the term " glands" has been applied include two entirely different groups, the true and \hefalse glands. FIG. 1386. Stroma of tunica p Circular m Tra 'irrnln- mi:m-lp _ "2^- ;" -^ ^V* -, - " - "_^.~i*- Transverse section of small intestine (jejunum), showing villi cut lengthwise X 150. The former are really secreting organs, the glands of Lieberkiihn and of Brunner ; the latter are more or less extensive accumulations of adenoid tissue, and are appro- priately spoken of as lymphatic nodules or follicles. The glands of Lieberkiihn are simple tubular depressions which are found not only throughout the entire small intestine, but in the large as well. They are very closely set, narrow, and extend the thickness of the mucous coat as far as its mus- cular layer. In length they vary from .3-. 4 mm. and in diameter from .060-. 080 mm. The fundus of the glands is slightly expanded and in exceptional cases divided. The lining of the crypts rests upon a delicate basement membrane, and consists of a single 1 Internal. Monatsschrift f. Anat. u. Physiol., Bd. xi., 1894. i6 3 8 HUMAN ANATOMY. layer of columnar cells directly continuous with those covering the villi. They differ from the latter in being only about half so high (.018 mm. ) and in not presenting the characteristic cuticular border. This last gradually disappears as the cells dip into FIG. 1387. -Goblet-cell Capillary Cuticular border r~~of epithelium Lacteal Transverse section of single intestinal villus, showing relation of epithelium, stroma, and vessels. X 350. Surface view of mucous membrane from end of jejunum showing valvulae conni- ventes. Stippled appearance is clue to villi covering folds. Natural size. the follicles to become the lining of the glands. Under low magnification the sur- face of the small intestine presents numerous pits, the orifices of the glands, which almost entirely fill the spaces between the bases of the villi ; with the exception of FIG. 1389. Subtnucous coat Villi Mucosa Submucosa Longitudinal section of duodenum ; valvuhr i-onnivontes cut across, showing relation of these folds to villi. X 15. the areas immediately over the lymph-nodules, where they are partially pushed aside, ihcsc glands are present in all parts of the intestine. They, however, take no part in .absorption, never containing fatty particles during periods in which such substances THE SMALL INTESTINE. 1639 arc seen within the epithelium of the villi. It is worthy of note that even in the adult mitotic figures are frequently observed within the cells lining Lieberkuhn's glands, although such evidences of cell-division are rare among the elements covering the Lymph- node Circular '.'.;'_' ''.';: .- muscle "' ' - ; /.'TT Gland of Lieberkiihn Longitudinal, muscle Serous coat . Longitudinal section of duodenum, showing Brunner's and Lieberkuhn's glands, villi, and lymph-node. X too. villi. Bizzozero therefore regards the lining of these glands as an active source for the regeneration of the intestinal epithelium by the production of new cells. As on the villi, so also in these glands goblet-cells lie among the usual epithelial elements ; likewise migratory leucocytes are present between the gland-cells. FIG. 1391. Pyloric glands sss! ' .:'-;---;- - - - Longi- tudinal muscle Stomach Duodenum Longitudinal section through junction of stomach and duodenum, showing transition of pyloric into duodenal glands ; also thickening of circular muscle to form sphincter pylori. X 23. The glands of Brunner, also often appropriately termed the dtwdenal glands, are limited to the first division of the small intestine. Beginning at the pylorus, where they are most numerous and extensive, they gradually decrease in number and 1640 HUMAN ANATOMY. size, being sparingly present beyond the opening of the bile-duct and entirely want- ing at the lower end of the duodenum. These glands are direct continuations of the pyloric glands of the stomach, with which they agree in all essential details. While, however, their gastric representatives are confined to the mucous coat, FIG. 1392. Solitary Fold nodules jff *>". /'," r 393- Surface views of mucous membrane from upper (A) and lower (B) part of ileum, showing folds and solitary lymph- nodules. The velvety appearance is due to the villi. Natural size. Brunner's glands chiefly occupy the submucosa, the migration taking place at the pyloric ring (Fig. 1392). The duodenum, therefore, possesses a double layer of true glands, those of Lieberkiihn within the mucous coat, beneath which, in the submu- cosa, lie those of Brunner. The individual glands, tubo-alveolar in type, form some- what flattened spherical or polygonal masses, measuring from .5-1 mm., which con- sist of richly branched tubules, ending in dilatations. Their excretory ducts pierce the mucous coat and open either directly on the free surface or into the crypts of Lieberkiihn. While narrower than the flask-shaped alveoli, the epithelium of the ducts is the same as that found in the deeper parts of the tubules. FIG. The clear, low columnar cells lining the duodenal glands are proba- n'-^ffgiP'^M bly identical in nature with those of the pyloric glands, the varia- tions in size and granularity some- times observed depending upon differences in .functional condition. Brunner's glands correspond to the pure mucous type (Bensley). Lymph - Nodules. - - The lymphatic tissue within the intesti- nal tube occurs in the form of cir- cumscribed nodules, which may remain isolated, as the solilarv nod- ules, or be collected into consider- able masses, as Pcycr s patches. The solitary nodules vary greatly in number and size, some- times being present in profusion in all parts of the small intestine, at other times almost wanting ; they are usually scanty in the upper anil more numerous in the middle and lower parts. They appear as small whitish elevations, spherical or pyri- form in shape, and In. in .2-2 or even 3 mm. in diameter, at the bottom of small pits. Surface view of mncout membrane of ik-um. x 30. THE SMALL INTESTINE. 1641 The walls of the latter, however, are so closely applied to the nodules that the exist- ence of the pit is not at first evident. Villi are wanting over the prominence of the nodules ; likewise the glands of Lieberkiihn, the orifices of which are arranged as a wreath around the nodules. The latter are found as much on one side of the intestinal tube as on the other. In structure the solitary nod- ules correspond to similar lymph- nodes in other localities, con- sisting of a capsule of denser tissue enclosing the delicate ade- noid reticulum which supports the characteristic lymphocytes within its meshes. Within the larger nodules germ-centres, spherical or ellipsoidal in form, occupy the middle of the nodules; the germ-centres are, however, not constant, being present, as a rule, in young subjects, but often absent in old individuals. A Surface view of portion of mucous membrane of ileum, showing rrr>nam,ic K1<~./~v/-l cnr.i-.Kr i' c nm Peyer's patch and solitary lymph-nodules. Natural size. vided by the rich net-work of small vessels which surrounds the nodules ; fine capillaries penetrate into their interior, but usually do not reach the centre of the nodes. Definite lymph-paths have not been demonstrated within the nodules, although a plexus of lymphatics surrounds their exterior (Teichmann). Peyer's patches (noduli lymphatic! aggregati) are collections of solitary lymph-nodules, the individual follicles being blended by intervening adenoid tissue. They are seen in the lower half of the small intestine, especially near the lower end (ileum) ; exceptionally they are found in the upper part of the jejunum in the vicinity of the duodenum. The patches appear as slightly raised, elongated ovals, FIG. 1395. Submucous fold supporting mucosa with villi Transverse section of ileum, showing Peyer's patch cut across. X 10. always on the side of the intestine opposite to the attachment of the mesentery. Their usual number is about thirty, although as few as eighteen and as many as eighty-one have been counted (Sappey). In length they ordinarily measure from 1642 HUMAN ANATOMY. Mucous coat 1-4 cm. and in breadth from 6-16 mm. ; exceptionally their length may reach 10 cm. or more. In general the size of the patches increases as the termination of the ileum is approached. Each patch contains usually from twenty to thirty lymph-nodules, although as many as sixty or less than ten may be present. The individual nodules are commonly somewhat pear-shaped, and when well developed occupy both the mucous and submucous coats, their smaller end almost reaching the epithelium and their base the muscular tunic. The free surface of the patches is modelled by minute pits, from .4-2 mm. in diameter, and low intervening ridges ; the former mark the positions of the component nodules, the latter that of the blending internodular tissue. The villi and the crypts of Lieberkiihn are present over the areas between the pits, although less developed than beyond the patch. In their minute structure the lymph-nodes composing the patch closely correspond to the solitary nodules, the aggregated nodules be- FIG. 1396. ing blended into a con- tinuous mass by the less dense adenoid tissue which fills the spaces between the individual follicles. The entire patch is defined from the surrounding struc- tures by an imperfect capsule. The submucous coat is lax, but not enough so to allow the displacement of the val- vuhr conniventes, ex- cept at the lower part. As in other segments of the intestinal tube, the submucosa contains blood- and lymph-ves- sels of considerable size and the nerve-plexus of Meissner. The muscular coat, about .4 mm. thick, consists of an outer longitudinal and an inner circular layer. The latter is some two or three times as thick as the former and is pretty regularly arranged. Th< thin longitudinal laye: thickest at the free bor- der, is often imperfect, especially at the attachment of the mesentery. The entire muscular coat diminishes in thickness from above downward. The serous coat, with the exception of that of the duodenum, completely su rounds the gut except at the line of attachment of the mesentery, where the two layers of peritoneum diverge, leaving an uncovered space between them just large enough for the passage of the vessels and nerves. Its structure resembles that of the serous coat of the stomach (page 1627), and includes the fibro-elastic stroma covered with the endothelinm. The blood-vessels supplying the small intestine are distributed to the walls of the tube in a manner closely agreeing with the arrangement found in the stomach (page 1627); the same general plan applies also to the large intestine. The tutfn't*, which pass to the intestine between the peritoneal folds constituting the mesentery, Muscular coat Transverse section of injected small intestine, showing general distribution. X 55- THE SMALL INTESTINE. after supplying the serous coat, penetrate the muscular tunic to reach the submucosa. Within the latter branches arise which, in conjunction with those directly given off during the passage through the muscular coat, supply the muscular tissue. The more important and larger arterial twigs from the vessels of the submucosa enter the mucous coat, in which some break up into capillaries forming net-works surrounding the gland-tubules and supplying the muscular and stroma tissue ; others pass directly towards the villi, which they enter and supply by capillary net-works occupying the periphery of the projections. The veins of the intestinal walls commence within the mucosa beneath the epithelium and, gradually enlarging as they descend, become tributary to the larger veins within the submucosa. The latter follow the arteries ,in their passage through the muscular tunic, uniting to form the larger emergent venous channels which accompany the arterial trunks between the peritoneal folds. The lymphatics of the small intestine, long known as the lacteals from their conspicuous milky appearance when filled with emulsified fat during certain stages of digestion, begin as the absorbent or chyle-vessels within the villi. In addition to these, radicles commence within the stroma-tissue of the mucosa, in which the lym- Branch of mesenteric artery Mesenteric vein Lymph-node Lymphatics Cut edge of removed peritoneum Nerves Portion of small intestine and mesentery, showing arteries, nerves, and lymphatics; latter have been injected with quicksilver. Anterior layer of mesentery has been removed. phatics form a plexus in the plane of the muscularis mucosae. From the latter tribu- taries descend to the larger plexus within the submucosa, which is characterized by channels of irregular form and calibre containing numerous valves. The emergent lymphatics form larger vessels within the serous coat, which pass to the lymph- nodes situated between the peritoneal layers ; from these smaller lymphatic masses efferent vessels converge to the larger mesenteric lymph-glands at the root of the mesentery. The nerves supplying the small intestine, derived from the solar plexus and consisting of both medullated and non-medullated fibres from the cerebro-spinal and sympathetic systems, closely follow the disposition observed in the stomach (page 1 628). After piercing the other longitudinal layer they form the intramuscular plexus of Auerbach, consisting of both varieties of fibres and microscopic sympathetic gan- glia. The nerves continue obliquely through the circular muscular layer and form within the submucous coat the plexu s of Meissncr. From this plexus non-medullated fibres enter the mucous coat and are distributed as periglandular and subepithelial net-works, as well as supplying the muscular tissue, in which, according to Berkley, additional special end-organs exist. Within the villi a rich plexus of non-medullated 1 644 HUMAN ANATOMY. fibres has been demonstrated from which terminal fibrillae are distributed to the mus- cular tissue and vessels, as well as beneath the epithelium. THE DUODENIM. The duodenum at an early stage is a loop with a forward convexity passing from the pylorus back to the spine. It enlarges into nearly a circle and turns onto its right side, its termination remaining attached below the cceliac axis to the top of the second lumbar vertebra. The part immediately following the stomach remains free, but a little farther back it is suspended from the liver by the duodeno- hepatic ligament, which is the free border of the lesser FIG. 1398. omentum, containing the portal vein, the hepatic artery, and the bile-duct with the connective tissue about them. This structure is strong enough to de- serve to be called a ligament. The duodenum is therefore nearly a ring sus- pended at two points, one near the beginning and the other (to be de- scribed later) at the end. In the adult f , ,- the shape is more or less a modification of this imperfect ring. When relaxed Casts of duodenum, showing u- and v-forms. and empty it often nearly retains this shape. When distended by inflation or injection it usually shows four parts. The first, some 5 cm. (2 in.) long, runs backward from the pylorus, slightly upward and to the right. The beginning of this portion is movable ; later the part is fixed by the structures just mentioned. The other divisions of the duodenum are disposed so as to form a U. The second part descends along the right of the spine to the fourth lumbar vertebra. The third runs forward and to the left, with a slight rise. The fourth ascends on the spine to the upper part of the second lumbar vertebra, where, after a sharp bend, the duodeno-jejunal flexure, it becomes the jejunum. The next most common form is the V-shaped, of which there are two varieties. In the more usual one the second part descends, as in the preceding form, and the third and fourth are represented by one which ascends obliquely to the termination. The less frequent variety has the second part inclining forward and to the left as it descends, so that the V is more sym- metrical. A modification of the U-form, which we have called the C-shaped, is characterized by a very short second part, so that the first and third parts are almost in contact. From seventy observations 1 on adults (including one girl of fourteen), mostly by means of casts, we find the following forms : Male. Female. Sex not noted. U-shaped 10 3 9 V-shaped ....9. 9 3 Ring-shaped 2 2 Indeterminate 7 3 * C-shaped .... 5 Not to be classified 5 _^ 3 '7 '5 By "indeterminate" is understood those that might be placed in any two of the U, V, or C types, according to the classifier. Those marked " not to be classified" are absolutely irregular. The V-shape is particularly common in women and the irregular forms in men. It slit mid be noted that a very large part of the duodenum lies in an essentially antero-posterior plane, namely, the first, second, and a considerable portion of the third part, the organ being moulded on the spinal column. The length of the whole duodenum and of its parts is so variable that a statement can be only general. The first part is, according to Testnt, 5 cm., the second S cm., the third 6 cm., and the fourth 7 cm., the total length of the duodenum being 2h cm., or about 10 in. The circumference varies greatly in different bodies. The fourth part is the smallest. The second increases in si/e as it descends, and the largest point is in either the second or third. The two largest circumferences that we have measured \vere in the second part. _ \Ye are sat- isfied that the si/.- of some immense duodena is in no way due to artificial distention ; to what extent it is pathological is uncertain. 1 Journal of Anatomy and Physiology, vol. xxxi., 1X97. THE DUODENUM. 1645 The first part is often egg-shaped, narrowing at the ends. Its main direction is backward, slightly upward and to the right, to reach the first lumbar vertebra ; but, as it is movable, its direction is somewhat variable. The gut rests above against the quadrate lobe of the liver and the neck of the gall-bladder, behind which it is free, forming the lower border of the foramen of Winslow. The left side looks into the lesser peritoneal cavity, and is crossed near the back by the common bile-duct. The right side is chiefly against the liver and gall-bladder ; otherwise it is in contact, as is the lower side, with coils of the small intestine. The lower side, moreover, rests on the head of the pancreas. The second part descends vertically, forming an acute angle with the first. It is bent so sharply that a fold of the entire thickness often projects into the gut. It lies on the right side of the vertebral bodies beside the vena cava, and behind rests on the right suprarenal capsule and kidney, being in contact also with the pelvis of the latter, the renal vein, and the beginning of the ureter. The precise relations with the right kidney are uncertain, owing to the variations both of that organ and of the duodenum. It lies on the right against the ascending colon and on the left against the head of the pancreas, which may overlap it in front. The bile-duct runs along the left side and passes obliquely through the intestinal wall, to empty, in conjunction with the pancreatic duct, some 10 cm. from the pylorus. From observations on fifty-four adult duodena (thirty-eight male, sixteen female) we have found that in the great majority of duodena of both sexes the lowest point is opposite the fourth lumbar vertebra or the disk above or below it. In about one-quarter of the cases it is opposite the third, and only some half dozen times opposite the fifth, of which cases some were probably pathological. The mean of the female duodenum, in which sex the V-shape is most frequent, is a little lower than that of the male, but not strikingly so. The angle between the second and the third parts in the U-form is rather less sharp than that between the first and the second. The third part curls around the spinal column, passing forward to its front and then to the left with a slight ascent till it reaches the aorta. It crosses the vena cava and has the pancreas above it, which, with the first and second parts, it tends to enclose. The head of the pancreas may, however, more or less overlap the third part as it does the second, and also insinuate itself behind it. In less than one-quarter of the cases the third part crosses the aorta, its course being more transverse than the one just described. It may be connected to the aorta by areolar tissue or, especially if it run only just beyond the aorta, a fold of peritoneum may intervene. The fourth part usually begins at an obtuse angle with the third, and ascends on the front of the spine to the top of the second lumbar vertebra. In this course it overlaps the aorta and usually ends either directly over it or just at its left. In fifty-four observations the duodenum was on the right of the aorta until just before its final flexure twenty-six times. It was wholly on the right of the aorta six times. The fourth part lay in front of the aorta eleven times and the third part actually crossed it eleven times. It is clear from the above that it is exceptional for the duo- denum to reach the left kidney and ureter, but it may do so when it really crosses the aorta. The tail of the pancreas is behind it, as is usually a part of the left supra- renal capsule. The head of the pancreas may be so developed as to overlap it, but this is rare. The mesentery of the small intestine usually rises above on its front sur- face and gradually crosses it to the right. It may be very nearly surrounded by peritoneum, or the posterior surface may be without it. Sometimes, although rarely, the last part stops short of the second lumbar. In the V-shaped duodenum the third and fourth parts are in one. This form evidently is wholly to the right of the aorta, except, perhaps, the very end. It sometimes ascends along the right side of the right iliac artery, and then on the right or front of the aorta. The duodenum ends in a sharp turn, the duodeno-jejunal flexure. The very top of the gut at the bend is suspended from the left cms of the diaphragm and from the areolar tissue about the cceliac axis by the duodenal suspensory muscle of Treitz, a small triangular band of muscular and fibrous tissue, which reaches the gut where it is uncovered by perito- neum, and is said to join the layer of longitudinal muscular fibres. This band and the duodcno- hepatic ligament hold all the duodenum after the very beginning sus- pended and fixed so that only the beginning is movable. It is further secured by 1646 Hl'MAN ANATOMY. the retro-peritoneal connective tissue and by the peritoneal reflections. The shape allows the food from the stomach as well as the fluid poured into it from the liver and pancreas to accumulate and thus to act as an S-trap to prevent the passage of gases from the intestine into the stomach. At the same time the great development of the valves tends to retard the passage of the food. Peritoneal Relations. The peritoneum of the front and back of the stomach is continued along the right and left sides of the first part of the duodenum respec- FIG. 1399. Right lunj. Cut diaphragm Hepatic veins- Vena cava_B Right suprarenal body Castro-hepatic omerttum Probe in foramen ot Winslow Right kidney Beginning of duodenum Beginning of transverse colon JL Head of pancreas Duodenum Right mesocolon Ascending colon nd of ileum V \ Appendix Rectum Bladder Left lung -Pericardium Cayal opening in diaphragm _CEsophagus _Spleen Left suprarenal body Left kidney Splenic flexure Tail of pancreas Left end of cut transverse colon Jejunum Superior mesen- teric artery- Left mesocolon Cut root of mesentery igmoid flexure Abdomen of formalin subject ; peritoneum partially dissected off, exposing organs in situ on posterior wall ; transverse colon, mesocolon, mesentery, and jejuno-ileum removed. lively. These layers meet above along the greater portion of the first part to form the lesser omen turn, which ends posteriorly, as already stated, by forming the hepatico- duodenal ligament, consisting of the vessels entering the portal fissure of the liver with their enveloping connective tissue. The free edge where the peritoneum passes behind the ligament is on the inner side rather than above the gut. Just back of this THE DUODENUM. 1647 fold the upper surface of the first part of the duodenum is covered by peritoneum and forms the floor of the foramen of Winslow. The attachment of the greater omentum, which is continued from the greater curvature of the stomach onto the under side of the duodenum, passes along its inferior surface to the second part, where in the adult it has fused with the mesentery of the transverse colon. The peri- toneum of the right side of the first part of the duodenum looks into the general peritoneal cavity and that of the left side into the lesser cavity. The relations of the remainder of the duodeuum necessarily vary with the dis- tention of the intestine ; but it is correct to say that it lies behind the peritoneum, owing to the change into connective tissue subsequent to the fusion of the serous membrane of the right side of the duodenum and that of the posterior abdominal wall. Very often when the fourth part lies in front of the aorta a fold of peritoneum passes some distance in between them from the left ; but this pocket disappears when the gut is distended. The pancreas, when it overlaps the second, third, or even the fourth part, more or less displaces the peritoneum. The duodenum is crossed by the attachment of the mesentery of the jejuno-ileum and by that of the transverse mesocolon. The series of changes by which this has occurred is dealt with under FIG. 1400. Transverse mesocolon Jejunum Duodenum Superior duodenal fossa Branch of left colic artery Inferior duodenal 'M f ssa Descending colon .' '.-&- ~-!$L Mesentery of small / .'? '"'' intestine v f Duodeno-jejunal junction, showing duodenal fossae ; jejunum turned to the right. Peritoneum (page 1742), the adult condition alone being here considered. The line of attachment of the. transverse mesocolon crosses the second part of the duodenum a little below the deep flexure which on the front separates it from the first. The position of the line of attachment of the mesentery of the jejuno-ileum varies with the shape and position of the duodenum. Should the latter have its third part crossing the aorta, the attachment of the mesentery will cross the third part only, passing somewhat obliquely downward to the right. In the more usual arrangement, in which the fourth part of the duodenum either ends on the front of the aorta or crosses it only just before its termination, the line of attachment starts on the front of the fourth part or somewhat on the right of it and descends on more or less, sometimes on the whole length of this portion, or else lies just to the right of it and then crosses the third part. In the case of the V-shaped duodenum the mesentery runs down on or along the right of the oblique portion. Duodeno-jejunal Fossae. Several pockets formed by folds of peritoneum are found near the end of the duodenum in the greater cavity of the peritoneum. Some are vascular, that is, containing a vessel at or near the edge of the.fold, while others are not. We have adopted the classification of Jonnesco, who describes five forms. HUMAN ANATOMY. The inferior duodenal fossa (Fig. 1400) is the most common form, occurring, according to Jonnesco, in 75 per cent., and to Treves in 40 per cent. It is non- vascular, formed by a fold of peritoneum passing from the left of the fourth part of the duodenum to the posterior wall, with a free concave edge looking upward. The pocket extends down behind this fold for a variable distance. It may reach the fourth lumbar vertebra. The superior duodenal fossa occurs in 50 per cent. This corresponds to the preceding, only it runs upward behind a fold, with a concave free edge looking downward, passing from the duodeno-jejunal flexure to the posterior wall on the left. The pocket is less deep than the preceding. It is usually vascular, the in- ferior mesenteric vein running in the fold, sometimes near its edge. These two fossae frequently coexist, and the left ends of the folds may be continuous, so as to form a large C-shaped fold, open to the right, with a pocket under both the upper and the lower limbs. In this case the vein may be in the vertical part of the fold. An arterial arch, formed either by the ascending branch of the left colic artery or by the left branch of the middle colic, is often very close to the vein. Such a pouch may extend deeply under the fourth part of the duodenum. The mesocolic fossa, 1 found in 20 per cent., and always alone, is a little pocket on the top of the duodeno-jejunal flexure under a fold from the posterior layer of the transverse mesocolon. When th s membrane is reflected so as to show it, the fossa appears to run upward. The in- ferior mesenteric vein may be in the fold. The paraduodenal fossa is in the peritoneum of the posterior abdominal wall, less intimately connected with the gut than the others. It is a pocket formed by ' the superior branch of the left colic artery raising a fold of the perito- neum. The mouth of the pouch is to the right. It is not uncom- mon in the infant, rare in the adult. The retrodnodcnal fossa is an uncommon pouch under the third and fourth parts of the duodenum, extending upward with the mouth below. Interiorof the Duodenum. FIG. 1401. Surface view of mucous membrane of duodenum ; entrance of The I11UCOUS COat is smooth ill bile and pancreatic ducts shown by probe, which lies in bile-duct. Papilla is surrounded by hood-like fold. Natural size. the first part and OVerllCS the glands of Brunner (page 1639), which lie chiefly within the submucosa and form a continuous layer for some 4 or 5 cm. ; beyond they are scattered for some distance farther. The villi are small at the beginning, but soon attain their complete size. The valvulae conniventes are at first absent for about 4.5 cm., appearing at the end of the first part, and are almost at once large, near together, and non-effaceable. A very large one is formed by the folding in of the wall at the junction of the first and second parts ; beyond this tin- valves at once reach their greatest development. In the second part tin- bile-papilla is seen in the back part of the left or inner wall, from 8. 5-10 cm. (about 3^-4 in.) beyond the pylorus, or rather below the middle, through which the common bile-duct and the duct of the pancreas pass to open by a common orifice. The papilla is almost always overhung by a valvular fold (Fig. 1401 ), and when non-distended is only some 5 mm. long. The accessory duct of the pancreas often opens 2 or 3 cm. above the main one through a much smaller and inconstant papilla. The submucous coat holds the mucous membrane pretty firmly in place, so that the folds are permanent. 'Jonnesco calls this also the fossette duodcno-jcjnnale ; but. although following him other- wise we !..iv. retained duodeno-jejunal as the generic name. We have applied the named fossa duodenO'jejunalis in Fig. 1418 to what is probably an accidental and quite irregular fossa. THE JEJUNO-ILEUM. 1649 Blood-Vessels. Arteries. The duodenum, like the stomach, is attached to that part of the original mesentery through which the branches of the cceliac axis run. The stomach is supplied chiefly by the coronary and the splenic arteries, the duodenum by the hepatic with the help of a recurrent branch from the superior mesenteric. The hepatic artery gives off the pyloric, which sends some insignificant twigs to the beginning of the duodenum, and the gastro-duodenal, which runs on the left of the first part and sends off the superior FIG. 1402. pancreatico-duodenal, which passes downward and to the left in the concavity of the duodenum between it and the pancreas, lying rather on the front of the duodenum, of which it is the chief artery. The superior is met by the inferior pancreatico-duodenal artery, which arises from the right side of the superior mesenteric and descends along the right of the fourth part of the duodenum. The superior mesenteric distributes one or two small twigs to the very end of the duodenum. Veins. The pyloric vein, larger than the artery of the same Abnormal form name, in conjunction with the superior pancreatico-duodenal, and course of duo- , . . , . , , ^L clenum. (Schicffet- drams the greater part of the duodenum. Ihey may open in com- decker.) mon or separately into the portal vein, and are in direct connection with the inferior pancreatico-duodenal, which opens into the superior mesenteric vein. The lymphatics pass to the pre-aortic lymph-nodes. The nerves of the duodenum, as are those supplying other parts of the small intestine, are from the solar plexus. Variations. As already shown (page 1644), much variation exists in the shape of the duodenum ; moreover, very extraordinary duodena sometimes occur. It is probable that these are generally due to an over-long duodenum, which, after having completed the usual course, describes one or more additional curves before reaching the duodeno-jejunal flexure. We have seen a case in which the end of the V almost touched the pylorus and then, mounting still higher, described a ioop to the left behind the peritoneum. This occurred in a man with the sigmoid flexure and rectum on the right. These cases usually are associated with other errors of intestinal or peritoneal development. In the remarkable case of Schiefferdecker 1 (Fig. 1402) there was a mesenterium commune. THE JEJUNO-ILEUM. The jejuno-ileum includes the remainder of the small intestine, which, disposed in folds attached on one side to the mesentery, extends from the duodeno-jejunal fold to the caecum, its length being, therefore, approximately 6.75 m. (nearly 22 ft.), of which the first two-fifths are conventionally credited to the jejunum and the remain- ing three-fifths to the ileum. It is a cylindrical tube continually decreasing in size. The diameters are variously stated, Testut giving the mean diameter of the upper part as from 25-30 mm. and that of the lower as from 2025 mm. These latter figures our own measurements confirm, since on thirty-seven inflated specimens of the lower end the average diameter was 24 mm., the extremes being 17 and 37 mm. Chaput and Lenoble 2 assert that the inferior circumference is reduced internally to 32 mm. (on inflated specimens to 50 mm.) by a valve near the caecum. This valve, which we have found in about one-third of the cases, is remarkable in being always situ- ated on the posterior aspect of the gut, generally at a sharp bend ; it often contains a small artery, and is probably formed by the folding in of the muscular coat. Its position is frequently near the point at which the ileum begins to lie against the wall of the caecum, but it may be 2.5 cm. or more higher. The valve is sometimes double, and varies in height from 2 mm. to i cm. We have not found, however, that this fold is necessarily the narrowest point of this part of the gut. A piece of the intestine from the upper part of the jejunum weighs more than one of equal area from the lower part of the ileum, owing to the greater thickness of the walls of the former and to the greater development of the valves in that part. The structure of this part of the small intestine has already been described (page 1634). 1 Arch, fiir Anat. und Entwicklng., 1887. 2 Bull. Soc. Anat. de Paris, 1894. 104 1650 HUMAN ANATOMY. The Mesentery and Topography of the Jejuno-Ileum. Since consid- eration of the mesentery is indispensable for the study of the disposition of the folds and relations of the small intestine, this structure next claims attention. The serous covering of the gut itself requires no further description than to note that it com- pletely surrounds the bowel, except at the double line of its attachment, where there is left space just large enough for the passage of the vessels and nerves. The attached border of the mesentery (Fig. 1399) extends from the left of the front of the first FIG. 1 103. . - ,-. v; Right lung Diaphragm (cut) Hepatic vein Behind Spigelian lobe Right suprarenal body. Probe in foramen of Winslow Right kidney. Beginning of duodenum Left end of, transverse colon Duodenum Jejunum- Ascending colon L& Ileun Left lung H CEsophagus Spleen Left suprarenal body Left kidney Left end of colon Duodeno-jejunal Formalin subject; liver, stomach, transverse mesocolon, and colon have been removed, leaving other abdominal organs in situ ; attachment of cut peritoneum Indicated by white line. or second lumbar vertebra, immediately below the end of the duodenum, where the superior mesenteric artery enters it, to the right sacro- iliac joint, a distance of about 15 cm. (6 in.). The relations of the upper part of the fold are'determined by the shape and position of the duodenum. Probably the usual course of the mesenteric attachment is from the front of the aorta downward on the fourth part of the duo- denum, across the vena cava to the right sacro-iliac joint. With a V-shaped duo- THE JEJUNO-ILEUM. 1651 denum the line of the mesentery is usually on the right of the gut ; with a duodenum that crosses the aorta the line is across the third part. The lower end of the mesen- tery is determined by the degree of adhesion of the right mesocolon to the abdomi- nal wall. It rarely stops short of the sacro-iliac joint, but it may be continued farther into the right iliac fossa. The free or intestinal border of the mesentery is some 6 m. or about 20 ft. long. In the middle the distance between the borders is from 20-22.5 cm - (8-9 in.). Near its origin, in the first six inches of the intestine, the mesentery has reached a breadth of from 12-15 cm - (5~6 in.). At the lower end its breadth is more uncer- tain, being usually slight, only from 2.5-5 cm - f r tne l ast s i x inches. It increases with age, presumably concurrently with the increase of girth. The mesentery con- tains vessels and nerves as well as lymphatic glands between its folds ; these struc- tures may lie in a considerable mass of fat, adding to the thickness, which is much greater, on account of the size and number of the vessels, in the upper part than in the lower. The larger lymph-nodes and the fat accumulate chiefly near the FIG. 1404. spinal border, where the mesentery may be very thick and heavy, while the part near the intestine, except in the case of excessive fatty accumula- __... tion, is always thin and yielding. It -.^Si amr***' *-*'* ' ; is evident that the mesentery with an attached border of only 15 cm. (6 in.) and a free one of 6 m. (20 ft. ) must be very much folded ; and further, that while the intestinal border must pre- sent a vast number of totally irregular and transitory folds, changing with the movements of the gut, the heavier and more fixed part of the mesentery near the root must present certain chief folds the position of which is tolerably stable. Henke l has shown that if the hand be introduced among the coils of intes- tines in the line of the left psoas muscle and carried upward, it enters the con- cavity of a horseshoe-shaped fold of the mesentery, and that the intestines easily fall apart to either side. The coils on the left are in the main transverse and those to the right chiefly vertical. This plan, although sometimes obscure, is often beautifully clear, especially in infants. Weinberg, 2 from studies on the new-born infant, has carried the plan into further details. He finds that the upper two-fifths of the intestine are arranged in trans- verse folds in the upper left part of the abdomen ; the middle fifth lies in the left iliac region without definite arrangement ; the last two-fifths are in the median part and in the right iliac region, disposed in the main vertically. Still, cases occur at all ages in which the plan is obscure. Mall s has traced the plan of the intestines throughout development, and incidentally confirms Weinberg' s state- ments. The following account of the normal arrangement in the adult is essentially according to his researches. The gut is to be conceived as arranged in spiral coils travelling from the left hypochondriac region to the right iliac fossa, successive coils being in the main parallel. Starting from the duodenum, there are two transverse folds in the left hypochondrium, followed by a long fold that goes across the body and back. Some less distinctly transverse folds occupy the left iliac fossa. The 1 Arch, fur Anat. und Entwicklng., 1891. 3 Internal. Monatsschrift fur Anat. und Phys., Bd. xiii., 1896. 3 Arch, fiir Anat. und Entwicklng., 1897. Supplement Bd. Typical disposition of folds of mesentery shown after removal of jejuno-ileum. i, end of duodenum ; 2, 3, 4, jeju- num ; =;, ileum ; 6, termination of ileum into large intestine. (Mall.) 1652 HUMAN ANATOMY. remainder is disposed vertically, occupying the lower part of the umbilical region and the pelvis, and extending on the right as far as the large intestine will allow. The vertical arrangement of this portion is generally less striking than the trans- verse disposition of the preceding. The end of the ileum rises from the pelvis into the right iliac fossa. There are, of course, frequent deviations from the above plan of arrangement of the folds. It is easy to see that the appearance at the surface of some that are usually deep would obscure the plan. It is worth noting that adjacent folds should never be assumed to be continuous. Blood-Vessels. The arteries of the jejuno-ileum are branches of the superior mesenteric, which enters the mesentery below the pancreas. The vessels for the gut are straight ones arising from the arterial arches. In the upper part they are from 4-5 cm. long, 3 cm. in the middle, and very small at the end of the ileum. They run without anastomoses to the edge of the gut, where they break up into bunches of slightly diverging branches. All of these usually go to one side of the gut, each alternate vessel taking a different side, although sometimes a vessel may send branches to both sides. Anastomoses in the walls of the gut between the branches of neighboring arteries are not numerous, and occur only between very fine vessels, except opposite the mesentery, where vessels of the different sides meet. The distribution of the veins is essentially the same. The lymphatics, large and numerous, empty into the mesenteric nodes, which they connect. These lymph-nodes vary in number from one to two hundred, the largest lying near the root of the mesentery, from which position they grow smaller as they approach the free edge. There are no nodes, however, between the gut and the last vascular arch, unless, perhaps, near the very end of the small intestine. The nerves of the entire small intestine are from the solar plexus. They receive many cerebro-spinal fibres through the splanchnics. Meckel's Diverticulum. This is an outgrowth from the ileum, shaped like the finger of a glove, and found in some 2 per cent. It is the remnant of the vitel- line duct, which at an early stage connects the gut with the yolk-sac. It springs most frequently from the free border of the bowel, sometimes, however, from the side, and, as a rule, but not invariably, is composed of all the intestinal coats. Its usual position is within i m. (on an average, 82 cm. ) of the caecum. Diverticula said to have been found in the upper part of the small intestine are regarded with suspicion. The diameter of the diverticulum is usually that of the gut, but it may be less and associated with a conical form. The length varies from 2.5 cm. or less to 17.5 cm. (7 in.), although ordinarily between 2.5 and 7.5 cm. (i and 3 in.). As a rule, its end is free, but often a delicate band extends from its apex to the umbilicus or to some of the contents of the abdomen, generally the mesentery. ' PRACTICAL CONSIDERATIONS : THE SMALL INTESTINE. i. The Peritoneal Coat. This is complete below the duodenum except at the mesenteric aspect, where the two layers of peritoneum diverge for about 8 mm. ( */3 in. ). The jejuno-ileum is therefore practically an intraperitoneal, and not merely an intra-ab- dominal, viscus, although, of course, really outside the peritoneal sac. Inflammation of this portion of the general peritoneum is more apt to be acute, to spread rapidly, and to be attended by serious or fatal results than is that of any other portion. Such infection is frequent on account of the great length of the small intestine, its exposure to trauma, the thinness of its muscular walls, the variety and number of the lesions of its mucosa, its close relation to all the intra-abdominal viscera, and its consequent participation in their injuries and diseases. Direct transmission of infection from within outward is favored by the relatively intimate relation between the peritoneal and muscular coats, the subserous areolar tissue being much scantier and containing much less fat than that intervening between the parietal peritoneum and the fascia' and muscles of the abdominal wall. The extent and fatality of peritoneal inflam- mation result from the facility with which it spreads by both continuity and contiguity, and from the fact that, ctrtcrh f>aribus, its toxic products are proportionate in amount to the area involved. The association of the spinal and sympathetic nerves in the 1 Lamb : American Journal of the Medical Sciences, 1893. PRACTICAL CONSIDERATIONS : THE SMALL INTESTINE. 1653 intramuscular plexus of Auerbach and the submucous plexus of Meissner, and their connection with the lower seven intercostal nerves distributed to the skin and muscles of the abdomen, explain (a) the abdominal rigidity and tenderness which often pre- cede an extension of disease from the visceral to the parietal peritoneum ; (^) the paresis or paralysis of the intestines which is so common as a symptom of peritonitis, and which favors stasis of intestinal contents, putrefaction, and distention ; (c) the vasomotor disturbance which is an important, if not the chief, factor in the production of meteorism ; (d) the vomiting, first reflex and then from irregular muscular con- traction (reversed peristalsis) ; and (e) the reference of the early pains, no matter what the seat of the peritonitis, to the epigastrium or umbilicus, i.e. , to the solar and superior mesenteric plexuses. The usual cause of peritonitis of the small intestine, by infection from within, is penetration of its walls by the colon bacillus, following epithelial necrosis or ulceration due to catarrh or to various forms of infection, or secondary to diseases which pro- duce engorgement of the terminal vessels of the portal system. It is sometimes, in a less acute form, a final phenomenon in fatal cases of renal or cardiac disease. It may follow tuberculosis or typhoid ulceration of the solitary or agminated lymph- nodules. In all cases of enterorrhaphy as after resection or anastomosis especial atten- tion should be paid to the non-peritoneal area included between the two mesenteric layers. The success of these operations depends primarily upon the rapid union of apposed peritoneal surfaces ; hence the serous coat, including the two layers of the mesentery, should be brought together through the complete circumference of the bowel and ''accurately sutured. 2. The Muscular Coat. Irregular or spasmodic contraction of the muscular wall of the small intestine produces typical ' ' colic, ' ' the pain being analogous to that felt in a "cramp" of one of the voluntary muscles. Intestinal colic is not associated with tenderness of the surface of the abdomen, or with rigidity of the abdominal muscles, and is usually relieved by firm pressure, supporting and controlling the affected segment of gut. The abdominal wall may be moved freely over the under- lying viscera. It may thus be distinguished from the early pain of peritonitis. The greater thickness of the inner circular coat causes longitudinal wounds to gape more than transverse ones. The latter are more apt to gape if they are at the free border of the gut, where the longitudinal fibres are most numerous. As the muscular coat in its entirety lessens in thickness from above downward, wounds of the jejunum gape more than those of the ileum. Intestinal punctures usually, and very small wounds not infrequently, are closed by muscular action, so that healing takes place without extravasation of intestinal contents. Slightly larger wounds may be stopped by a plug of mucous membrane. This is favored in the upper portion of the tube by the presence of the valvulae conniventes and in the lower part by the laxity of the submucosa. This eversion of the mucous membrane, caused by muscular contraction, must always be overcome in the suture of intestinal wounds, since the mucous surfaces will not unite with each other. 3. The mucous and submucous coats and their contained glandular and vascu- lar structures are subject to many varieties of disease. If catarrhal inflammation affects the mucosa of the small intestine, it is apt, if localized in the duodenum, to be associated with gastritis and to extend into the bile-ducts, causing jaundice. If in the jejuno-ileum, it may be mistaken for colitis ; usually, if in the small intestine, the diarrhoea is less marked, the colicky pains are greater, borborygmi are fewer, less mucus is found in the stools, and tenesmus is absent. Neither duodenitis, jeju- nitis, nor ileitis can, however, positively be diagnosticated from one another or from general intestinal catarrh (Osier). Ulcers of the duodenum are in the vast majority of cases (242 out of 262, Col- lin, quoted by Weir) situated within 5 cm. (2 in.) of the pylorus (the most movable portion of the duodenum) and are most often on the anterior wall, especially its right side. The peritoneum of the right side of the first part of the duodenum looks into the general peritoneal cavity, and of the left side into the lesser cavity (page 1645). When perforation follows, the general peritoneal cavity is therefore likely to be infected, and the death of one-half of the subjects of perforating duodenal ulcer from general peritonitis is thus accounted for. The second part of the duodenum is 1654 HUMAN ANATOMY. in close relation on the lower part of the right aspect with the liver and gall-bladder, on the upper part of the left aspect with the head of the pancreas and foramen of Winslow, and posteriorly is partly uncovered by peritoneum and rests on areolar tissue and the common bile-duct. The general relations of the duodenum (page 1645) explain the remaining lesions following duodenal ulcer, e-g-, perforations into the gall-bladder, liver, or colon ; opening of the hepatic artery or the aorta, or of the superior mesenteric or portal vein ; or the development of subphrenic abscess. As compared with the symptoms of gastric ulcer, pain is apt to be less on account of the relative immobility of the duodenum ; vomiting after feeding is later ; hemorrhage is often greater on account of the larger vessels that may be involved ; bloody stools are more common, as is jaundice from the involvement of the bile-duct. In exposure of this part of the duodenum it is well to remember the suggestions of Pagenstecher (quoted by Weir), viz., that the fundus of the gall-bladder when distended lies in front of the duodenum ; that by raising and drawing forward the transverse colon, which lies in front of and below the horizontal portion of the duo- denum, the first portion is revealed ; and that by pushing the stomach and pylorus to the left and elevating the liver, access to the region of perforation may be gained. In emaciated patients with contracted stomachs the duodenum may be found lying above the level of the transverse colon. Infection through the mucous coat has already been spoken of. If of the tuber- culous variety, it affects chiefly the lower part of the ileum, and tends, as is charac- teristic of that disease, to follow the course of the vessels which run from their entrance at the mesenteric attachment transversely around the gut. If such ulcers cicatrize, they are therefore especially prone to lead to stricture of the intestine, a very rare sequel of typhoid ulceration, which, affecting the same portion of the small intestine, extends in the line of the agminated lymph-nodules, i.e., longitudinally. The tuberculous ulcer sometimes produces a slow general peritonitis, rarely a local- ized abscess, much more rarely an acute perforation with general septic peritonitis, as the process is so slow that protective adhesions to neighboring coils of gut or to the parietal peritoneum have time to form. Typhoid ulcers cause perforation in 6.58 per cent. (Fitz) of all cases. The large majority of perforations occur in the ileum, most of them within 60 cm. (2 ft.) of the ileo-caecal junction. In operation this should therefore be sought for and the ileum followed upward from that point. The ulceration may so thin the intestinal wall as to permit of leakage and the production of general peritonitis without actual perforation ; or it may be accompanied by such an extensive exudate as to make the ileum palpable, a condition which, in conjunction with localized tenderness and abdominal rigidity (vide supra), has led to many mistaken diagnoses of appendicitis in cases of typhoid fever. Syphilitic ulceration of the small intestine is rare, but is said to be most frequent in the upper portions (Rieder). The lymphatics of the mucous and submucous coats empty into the mesenteric lymph-nodules (page 1643) and convey to them various forms of infection or disease, typhoid, carcinomatous, tuberculous, etc. The veins emptying into the vena porta through the superior mesenteric are likewise channels of infection, ulceration of the bowel sometimes resulting in abscess of the liver. Contusion and rupture of the small intestine are favored by its exposure to trauma through its close apposition to the abdominal wall, which, if relaxed, offers but little protection. The interposition of the greater omentum with its con- tained fat is a slight safeguard, but the movement of the coils of gut upon one another and their elasticity are of much more value. Contusion here, as elsewhere, may be followed later by infection and ulceration. Traumatic rupture is much more frequent in the jejunum and ileum than in any other portions of the alimentary canal (of 219 cases, 79 per cent, were in the small intestine, 11.5 per cent, in the colon, and 9.5 per cent, in the stomach, Petry). The duodenum suffers very infrequently on account of its sheltered position ; other- PRACTICAL CONSIDERATIONS : THE SMALL INTESTINE. 1655 FIG. 1405. Intussusceptum -Entering layer .Returning layer wise its lower portion the most fixed part of the intestine would probably be more often injured. The upper portion of the jejunum, which partakes somewhat of this fixity, is more commonly ruptured than any other part. So, too, the most fixed part of the ileum that nearest the ileo-caecal junction is most often the site of rup- ture. An incarcerated or irreducible hernia may constitute a fixed point of the gut and favor its rupture elsewhere from trauma to the surface of the abdomen. Ruptures of the intestine, like wounds or obstruction, are more serious the higher they are situated. The nervous disturbance and shock are greater, possibly on account of the more immediate relation of the lesion and of the resulting patho- logical changes to the great nerve-plexuses or to the pericardial portion of the dia- phragm (Crile) ; vomiting begins earlier and is more severe for the same reason ; peristalsis is more vigorous (as the muscular coat of the gut is better developed) and therefore rapid extravasation of intestinal contents is more likely and spontane- ous closure of a wound less likely to occur ; and, if the condition is at all chronic, nutrition is interfered with to a greater extent. Clinical experience shows that in such injuries the anatomical are more potent than the purely bacteriological factors, which would tend to make jejunal wounds less dangerous than those lower in the tract. Investigation has shown (Cush- ing and Livingood, and later Lorrain Smith and Tennant) that the bacterial flora in the upper portion of the intestinal tract is more scanty than in the lower portion ; and it is true that peritonitis following intestinal wounds, operative or accidental, is dependent for its charac- teristics upon the bacteria at the site of lesion, and that the prognosis should be favorable in proportion to the scarcity and innocuousness of the micro-organ- isms present. But the anatomical con- ditions, by adding to shock, favoring intestinal extravasation, and minimizing the chance of a reparative peritonitis, are more than sufficient to counterbalance the relative dearth of bacteria. It should be remembered that the position of the wound or contusion on the surface of the abdomen is of but slight value in determining the area of gut in- volved. Thus, a jejunal fistula following a wound was situated midway between the umbilicus and pubes, but measurements made by attaching ligature silk to portions of food swallowed and extruded at the fistula showed that the latter was but 119 cm. (3 ft. ii in. ) from the incisor teeth, and was therefore high in the jejunum ( Gushing. ) It may be noted that fistulae so situated are apt to be complicated by excessive dermatitis, supposed to be due to the presence of pancreatic juice in the discharge, as gastric, biliary, and colonic fistulae do not give rise to this trouble in any such degree of severity. Obstruction of the small intestine may be due to (^_ Surface views of mucous membrane of ascending colon. A, natural size ; B, magnified 30 diameters, showing orifices of Lieberkiihn's glands. often exist in such profusion that the ordinary cells are almost entirely replaced ; towards the deepest part, or fundus, of the glands they are comparatively infrequent. The presence of goblet-cells in such numbers accounts for the considerable amount of mucus normally poured into the large intestine. FIG. 1407. Lieberkiihn's glands Solitary lymph-nodule Mucous coat jri&^ Longitudinal muscle Serous coat Longitudinal section of ascending colon, showing general arrangement of coats and solitary lymph-nodule. X 30. The lymphatic tissue in definite collections occurs as solitary nodules only, Peyer's patches being absent within the large intestine. The lymph-nodules, which occupy a portion of the submucous coat as well as the mucosa, are largest and most THE LARGE INTESTINE. 1659 numerous in the caecum, and especially in the vermiform appendix, in which the nodules are so plentiful that they form in places almost a continuous mass of lymphoid tissue. The solitary follicles are less fre- FIG. 1408. quent in the colon, but are again numer- ous in the rectum. They are generally of larger size than in the small intestine, measuring from 1.5-3 mm. in diameter, and are situated at the bottom of pit-like depressions on the mucous surface into which the nodules project. The submucous coat closely cor- responds with the similar areolar tunic of the small intestine, allowing of fairly free : Peritoneal coat ij Adipose tissue _Vein Artery Portion of descending colon, somewhat distended, show- ing sacculations, taenia, and epiploic appendages. Longitudinal section of epiploic appendage. X 23. play of the mucosa. In addition to the blood-vessels, lymphatics, and nerve-plexus of Meissner, it contains the deeper and more expanded parts of the solitary nodules. i66o HUMAN ANATOMY. The muscular coat consists of a thicker layer of internal circular fibres and of an external longitudinal one, the fibres of which are in most places collected into three bands. Although longitudinal fibres exist between these, they are fe\v and apparently not quite universal. Beginning in the caecum, at the base of the vermi- form appendix, the three bands, or tcenia; coli, continue along the large intestine as far as the sigmoid flexure, over which 1412. FIG. Mucous coat =' Serous coat Transverse section of injected large intestine, showing distribution of arteries to coats. X 30. and the rectum the bands only two, and no longer sharply defined. In the rectum one is on the front and the other the stronger behind. The circular fibres increase very much towards the end of the rectum, the muscu- lar apparatus of which will receive special description (page 1675). The serous coat which once surrounded the gut, in certain places disappears during develop- ment, and in others its arrange- ment becomes modified by new relations with other peritoneal layers. These features will be described with the parts con- cerned. In structure it corre- sponds with the serous coat of other parts of the intestinal tube. The appendices epiploicae are little fringes or bags of perito- neum containing fat hanging from the large intestine. They may be as much as 2.5 cm. (i in.) in length, and are very prominent in fat subjects, but in thin ones may be overlooked. They are found particularly on the inner aspects of the ascending and descending colon and on the lower one of the transverse colon. It is often stated that they occur along one of the bands, but this relation is at least not constant, although they are generally arranged in a single line. They are found also on the sigmoid flexure. It is usu- ally stated that they are not pres- ent during childhood. Oddono, 1 however, has shown that they ap- first on the descending colon and sigmoid pear in the fifth month of foetal life, flexure. We have seen them before birth. The blood-vessels, lymphatics, and nerves of the large gut in general follow the arrangement already described in connection with the small intestine (luge- 1642). THE CAECUM. The caecum, or blind gut, the first part of the large intestine, is a pouch hanging downward at the junction of the ileum and colon, from which the vermiform appendix arises. The ileum opens into the large intestine by a transverse orifice placed in- 1 Dal Bollettino della Societa Medico-Chirurgica di Pavia, 1889. THE C^CUM. 1661 FIG. 1413. Anterior band Ascending colon ternally and somewhat posteriorly. From the top of the ileum a deep furrow passes posteriorly partly around the gut, and a less marked one is found in front. Although starting as just stated, the furrows at once descend a little, so as to repre- sent truly the middle of the orifice. These serve as an external boundary between the caecum and the colon, which are much alike in general characters. The average length of the caecum in the adult is between 6 and 7 cm. (about 2^ in.), and its breadth about 8 cm. (3^5 in.). 1 The bands of the colon are continued onto the caecum of the adult, and terminate at the origin of the appendix. One band is in front and the other two externally and internally at the back. The parts between the bands are generally expanded pouches, which may be subdivided by horizontal constrictions. There are two chief forms of caecum with several minor modifica- tions : the first is a persistence of the fcetal type, in which the caecum has the shape of a cornucopia bent towards the left, with the tapering end continued as the vermiform appendix ; the other, which is the usual, and occurs in from 91-94 per cent, of adults, is due to the part between the external and the anterior band growing out of all proportion, so that the pouch be- tween them becomes the lowest part, apparently the apex, the ap- pendix arising from the internal posterior side near the ileum. In extreme cases the two may be very close together. Very rarely the caecum is symmetrically sacculated, with the appendix at the lower end. To understand the interior of the caecum it must be remem- bered that the end of the ileum is thrust in at the angle between the colon and caecum in such a way that originally in fcetal life all the coats were involved. The serous coat is replaced by areolar tissue where two layers come together and new longitudinal muscular fibres are subsequently developed which do not enter the folds ; how- ever, the original longitudinal mus- 11 11 .1 i Beginning of large intestine, somewhat inflated ; part of an- CUiar layer, as Weil as me Circular terior wall removed to show ileo-cascal valve and orifice of vermi- one, does so. The latter is thick- form appendix. ened inside the fold. The ileum, as it approaches its end, lies between "the surface of the caecum below and the lower swelling of the colon above ; thus the upper of the two lips of the elliptical opening is composed of colon and ileum, the lower of ileum and caecum. They form promi- nent shelf-like projections into the large gut, opposite the external furrows, and constitute the ileo-caecal valve (valvula coli). The folds meet at the ends of the opening, forming single continuations or retinacula, of which the posterior is much the larger. It often extends across the posterior to the lateral aspect of the gut. The two segments converge, but at different angles. The upper, slanting somewhat downward, is approximately horizontal, while the lower is more nearly vertical. The orifice of the ileum between these folds is elongated when the gut is distended, the posterior end being sharper than the anterior. The diameter of the segments, measured from the origin to the free edge on 35 inflated and dried 1 Berry : The Anatomy of the Caecum, Anat. Anzeiger, Bd. x., 1895. - Upper fold Retinaculum .Ileo-caecal valve ' j> Lower Ileum Caecum Opening of appendix 1662 HUMAN ANATOMY. specimens, is as follows: average of upper segment 25 mm., of lower 33 mm. The largest pair was an upper of 37 mm. and a lower of 44 mm. ; the smallest of 12 mm. and 3 mm. respectively. The last, perhaps, was pathological ; the next smallest was 14 mm. and 19 mm. We have seen a caecum with the upper seg- ment entirely wanting. The absence of both has been observed. The average length of the ileo-caecal opening on 30 similar specimens was 31 mm., the extremes being 46 mm. and 21 mm. It is probable that, owing to the shrinking of the tissues, these dimensions of the opening are excessive. Although the lower fold is the larger, the upper overlaps it almost invariably, so that when the valve is closed the two edges do not come in contact, the orifice being closed by the application of the lower fold to the under surface of the upper one. Inflated specimens show that the upper fold is tense, while the lower remains flaccid. Much difference of opinion exists as to the completeness of the closure of the ileo-caecal valve, and experiments do not agree. If the experiment of injecting water or air from the colon be performed in situ, the closure is more likely to be perfect than if the parts have been removed. These experiments, however, do not represent the true con- FIG. 1414. Ascending color Anterior band Caecum Ileo-caecal artery Superior ileo-caecal fossa Mesentery Ileum Meso-appendix Vermiform appendix/ Caecum and related structures seen from' the left. Artery ditions during life, since the tonicity of the muscular fibres of the gut is lost, in the opened abdomen, the pressure of the viscera on the end of the ileum is less than normal. In life the valve probably is efficient. The orifice of the vermiform appendix is very variable. In sonic cases the caecum narrows to it so gradually that it is hard to say where it begins ; in others it begins suddenly with an oval or round opening measuring from 5 mm. or less to i cm. or more. The valve which often is found at the orifice is not usually a true valve, but the projection made by the wall at the union of caecum and appen- dix in the entering angle when it arises obliquely. According to Struthers, there is no valve when it arises at right angles. Owing to its usual upward course, the fold is most often on that side when present. We have seen a true valve as a small independent fold ; usually, however, there is no effective guard to the entrance of the appendix. Position. The caecum is situated in the right iliac fossa, resting ^ on the iliac fascia covering the ilio-psoas muscle, above the outer part of Poupart's ligament, THE C^CUM. 1663 about half below and half above the level of the anterior superior iliac spine. Some- times, owing to the shortness of the ascending colon, the caecum remains in the foetal position under the liver, or it may be arrested at any part of its descent. It not rarely hangs down into the pelvis, and when the lower part of the mesentery is long, particularly if the lower part of the ascending colon be not attached to the posterior wall, it may be very freely movable. In cases of mesenterium commune there seems to be no anatomical reason why it should not be anywhere. The caecum is sometimes turned up over the lower part of the ascending colon, but we cannot agree with Curschmann's 1 statement that this is not rare. In these cases the appendix rises from near the highest point of the caecum. We have seen the caecum in the umbilical region with two vertical coils of small intestine occupying the right flank. Structure. The description of the structure of the large intestine already given (page 1657) applies in general to the caecum. Its mucous membrane, like Lymph-nodules ..Lieberkiihn's glands Mucous coat Longitudinal section through junction of appendix with caecum. X 12. that of the rest of the large intestine, has no villi. This change occurs near the margin of each segment of the ileo-caecal valve, the villi gradually diminishing and finally disappearing before the free edge of the folds is reached (Langer). The bands of longitudinal muscular fibres always end at the base of the appendix, but the precise manner of their termination is uncertain. According to Struthers, 2 each band bifurcates as it approaches the appendix, and the divisions, meeting those of the others, form a ring around a weak spot close about it. According to Toldt, 3 the ring is formed by the circular layer. The arrangement is not always clear, but we incline to think the latter the more common. The coats of the caecum are all found in the appendix. The lumen of the latter is small, except near the entrance, and the walls may be in contact. The lymph-nodules of the appendix are exceedingly numerous and large, in places fusing into masses of considerable size, which en- 1 Deutsches Archiv fur Klin. Med., Bd. liii., 1894. 2 Edinburgh Medical Journal, 1893. 3 Sitzungsber. Acad. Wissen., Wien, Bd. ciii., 1894. 1664 HUMAN ANATOMY. croach upon the mucosa and its glands to reach almost the free surface. The layer of circular muscular fibres is i mm. thick, or about twice the thickness of the lon- gitudinal one. Both layers have interruptions, so that the submucous and subperi- toneal layers are in places continuous. This occurs particularly along the insertion of the fold of peritoneum called the mesentery of the appendix. The vermiform appendix (processus vcrraiformis) is a long, slender, worm- like outgrowth from the caecum, formed of all the coats of the intestine. Its length varies from I cm. (^3 in.) to 24 cm. (9^ in.), the average being probably about 8.4 cm. 1 (3^ in.). Monks and Blake," from the records of 641 autopsies at the Boston City Hospital, give the average length as 7.9 cm. (3 in..), with the extremes as above. Berry finds that the appendix is on the average about i cm. longer in FIG. 1416. Longitudinal muscle .Circular muscle Transverse section of vermiform appendix. X the male ; others find no particular difference. The diameter at the base is 6 mm. and at the apex 5 mm. Its usual origin is from the postero-median aspect of the caecum. According to Berry, this occurs in more than 90 per cent., the point of origin being 1.7 cm. distant from the end of the ileum. This is very important as showing a relatively fixed point of origin, as the general direction of the appendix is very uncertain. That of the distal half especially is largely a matter of chance. Moreover, the position after death is, except in certain cases, no guide to that during life. The appendix is attached to the caecum and to neighboring structures by a peritoneal fold to be described later. If this fold be long and narrow, the movements of the appendix are much restricted ; if the base of the fold be short and its attachment to the appendix a long one, the appendix is thrown into coils. 1 Fawcett and Blatchford (for the average length) : Proceedings of the Anatomical Society of Great Hritain and Ireland, Journal of Anatomy and Physiology, vol. xxxiv., 1900. 2 Boston Medical and Surgical Journal, November 27, 1902. THE CAECUM. 1665 This, to a greater or less extent, is the normal condition. There is no doubt that in the great majority of cases the appendix is wholly behind the caecum, mesial to it, or below it. Monks and Blake found a reference to this point in the records of 572 autopsies. It was "down and in" 179 times, "behind" with no statement of the direction 104 times, "down" 79 times, and "in" 62 times. Thus in almost three-quarters of the cases it was in one of these positions. It ran " up" 52 times, "up and in" 39 times, and "up and out" 29 times. In 9 cases it was "out," "down and out" in 5, and "in pelvis" in 14. It sometimes is attached to the as- cending colon by its peritoneal fold, and runs upward with probably accidental incli- nations to one side or the other. It may also be found in some of the peritoneal fossae of the region. In many of the cases marked "down and in" it hung over the pelvic brim. Of 123 cases in which the appendix was covered by peritoneum, and therefore presumably normal, Ferguson 1 found it hanging downward in n, placed mesially in 18, on the right of the caecum in 19, and behind it in 75. Total absence of the appendix is extremely rare, but has been observed by ourselves and others. Obliteration of the Cavity of the Appendix. The adenoid tissue of the vermiform ap- pendix is, as elsewhere, most developed in childhood and tends to atrophy in middle life. Coincident with this atrophy is a tendency (the cause of which is not clear) in the walls to adhere, more or less obliterating the cavity. Ribbert a found in 400 specimens more or less obliteration in 25 per cent., and, putting aside those under twenty years, in 32 per cent. After fifty it occurred in more than 50 per cent. He found, however, the obliteration complete in only 3^ per cent. In approximately one-half of the cases it involved only about one-half of the tube. The process usually begins at the closed end of the tube, and is much more fre- quent in short than in long appendices. Zuckerkandl 3 observed more or less obliteration in 23.7 per cent, of 232 specimens, the process being nearly or quite complete in 13.8 per cent. Ribbert saw the process beginning in childhood, but never under five years. Fawcett and Blatchford* found the appendix pervious 196 times in 221 cases, and 91 of the pervious ones were from those over fifty years. We agree with them that much more conclusive evidence is needed to establish the existence of a special atrophy of the appendix in old age or after middle life. Peritoneal Relations. The caecum, being originally an outgrowth from the convex side of the primitive intestinal loop, is completely covered by peritoneum and has no mesentery, since the mesentery of the ileum passes directly to the colon. The appendix, being the original end of the caecal pouch, is consequently also com- pletely invested with peritoneum. When the ascending colon has come to lie in the right flank, the posterior layer of its mesentery degenerates into areolar tissue, fusing with that resulting from the degeneration of the parietal peritoneum behind it, and by the same process the back of the colon is attached by areolar tissue to the abdominal wall behind. This condition almost always ends a short distance above the caecum. It is far more common to find the lower third of the ascending colon with peritoneum on its posterior surface than to find none on the upper posterior part of the caecum. This condition, indeed, does occur, we having seen it at birth ; but it is very exceptional. From the preceding facts it follows that the caecum and the appendix can have no mesentery in the strict sense ; nevertheless, the term mesentery of the appendix, or meso-appendix ( mesenteriolum processus vermi- formis), is applied to an almost constant fold of peritoneum, presumably caused by the artery of the appendix, which usually is attached to nearly the entire length of that organ. Authorities differ widely as to how far the line of attachment ex- tends along the appendix. Beyond question it is very variable. According to Monks and Blake, it extends nearly or quite to the end in fully one-half of the cases, and in most of the other half it reaches or passes the middle of the appendix. Its general appearance is triangular, but, according to both Jonnesco 5 and Berry, 6 with whom we agree, it is more properly described as quadrilateral. One side runs 1 American Journal of the Medical Sciences, 1891. 2 Virchow's Archiv, Bd. cxxxii., 1893. 5 Anat. Hefte, Bd. iv., 1894. * Proceedings of the Anatomical Society of Great Britain and Ireland, Journal of Anat- omy and Physiology, vol. xxxiv., 1900. 5 Hernies internes re'tro-pe'ritone'ales, Paris, 1890. 6 The Csecal Folds and Fossae and the Topographical Anatomy of the Vermiform Appendix, Edinburgh, 1897. 105 1 666 HUMAN ANATOMY. Ileum, turned up Inferior ileo-caecal fold along the proximal half or even the whole length of the appendix, one is free, and the other two are attached to the left side of the mesentery and to the caecum respectively. These latter are not readily distinguished from each other; hence the triangular effect. The artery of the appendix enters the fold on the back of the caecum, and runs at first from 5 mm. to i cm. distant from its free edge, which gradually approaches it. Although the fold may terminate before reaching the end of the appendix, it does not follow that the whole of the latter is not enclosed in peri- toneum, since under normal circumstances it always must be. The course, shape, and size of the meso-appendix are very irregular. It is almost invariably so short that the proximal half of the appendix is thrown into coils. We have seen this fold attached to the right side of the mesentery, as well as not attached to it at all. Sometimes it runs upward along the posterior part of the left side of the colon, so that the appendix is vertical ; at other times it is attached to the floor of the iliac fossa ; and very rarely it is wanting. In the female adult a secondary fold can very often, but by no means always, be traced from the meso-appe'ndix to the broad ligament. This fold is probably due to the persistence of one which in the fcetus often connects the appendix or caecum with the early ovary and the oviduct. The lymph-node which the meso-appendix is said to contain we have seldom found. It happens frequently that, from FIG. 1417. pathological causes by which ad- hesions have changed the perito- neal relations, the appendix lies behind the peritoneum. Fergu- son found it so 77 times in 200. Pericaecal Fossae. An indefinite number of fossae or pouches, all more or less variable, are to be found about the caecum. The two following are usually demonstrable, although not so constant as held by some authors. The superior ileo-caecal fossa 1 (Fig. 1414) is roofed in by a peritoneal duplicature, the superior ileo-ccecal fold, which, starting from the right surface of the mesentery, curves over the end of the ileum from behind forward. The attached border, in which the ileo-coljp artery lies, runs along the colon just where it joins the ileum, and is usually con- tinued forward down onto the front of the caecum for a short distance. The pouch between this fold above and the end of the ileum below opens to the left, but if the ileum be distended, the free edge of the fold is so closely applied to it that the fossa is easily overlooked. The depth of the fossa may reach 3 cm. It is most distinct in infants and frequently obliterated in middle life, although careful examination often reveals a small fold and recess that may be overlooked. Berry found this fossa absent in 12 of 100 cases, all of the 12 being over forty years. The inferior ileo-caecal fossa 2 (Fig. 1417) is less constant and much more complicated than the preceding. Its practical importance is greater, since it may contain the appendix. To display it the ileum must be drawn upward and the appendix downward and to the right ; the caecum may or may not require to be displaced to the right or inverted. This fossa is situated in the entering angle formed by the end of. the ileum joining the caecum, and is bounded on the right by the first part of the appendix. The meso-appendix shuts it in behind, and in front it is covered by the inferior ileo-ca'cal fold? The latter, which usually joins the 1 There is much to he said in favor of the term ilco-colii\ since the pocket lies at the angle of the ileum and colon. It, however, so frequently extends downward to tin- front of the caecum that the more usual nomenclature is here adopted. 2 Known also as the ilro-folic fossa, the ilco-appendicular fossa, etc. 8 This is the " bloodless" fold of Treves or the ileo-appendicular fold of Jonnesco. Meso-appendix Caecum from inner side and below. THE CAECUM. 1667 meso-appendix, is in its conventional form described as having four sides : a superior on the ileum, a right one on the caecum, an inferior joining the appendix or the meso-appendix, and a free concave one looking towards the left and overhanging the entrance to the fossa, which may be nearly 4 cm. ( i ^ in. ) in depth. The fold usually contains only small vessels, and has been described as "bloodless." It sometimes contains muscle-fibres passing between the ileum and caecum. The size as well as the formation of this pocket is very variable. When we consider the extreme variability of the meso-appendix which is concerned in its typical forma- tion, it is manifest that such must be the case. Sometimes the meso-appendix is in no way connected with it, only a small fold of peritoneum passing from the ileum to the caecum at the side most removed from the mesentery. Berry found this fossa in 74 per cent. The Retro-Colic Fossa. In the great majority of cases the posterior sur- face of the caecum lies free in the abdominal cavity, covered by its original peri- toneum. At a variable distance from it the back of the colon becomes adherent to the posterior abdominal wall and to the front of the right kidney ; hence there is, or may be, especially if the colon be drawn away from the wall, a fold on either side stretching from the gut to the wall. These are the ligaments of the colon, the exter- nal and the internal. The former runs outward and downward from the side of the colon along the abdominal wall, or perhaps across the lower end of the kidney, and presents a free concave border overhanging a pouch running upward and outward. The internal or mesian fold is the more often distinct, and is formed chiefly by the insertion of the mesentery. According to its degree of development, the free falci- form edge overhangs a pouch, looking downward and more or less to the right. The fold may be continued downward either to the right or to the left. In the former case it may form a pocket, of which the lower end opens upward. It is clear, therefore, that with both these folds well developed a retro-colic fossa exists, which is shown when the caecum is turned up. Its greatest depth is in the middle behind the colon, and it is continued downward on either side under the folds caused by these ligaments. Should either ligament be wanting, there can be no fold on that side. Some authors have thought it best to describe an external and an internal fossa under each of the ligaments, of which the internal is the more fre- quent ; it is more simple, however, to describe only one. The fossa may be sub- divided by a median fold. Very often there is no definite fossa at all. The internal part is more commonly well developed than the external. The subcaecal fossa is an uncommon pouch, sometimes small and sometimes large, situated above the middle of the iliac fossa. It seems to be due to an irregu- lar development of the iliac fascia, which forms a pocket in itself, with the mouth above, guarded in front by a semilunar fold. The fossa is lined by the parietal peri- toneum. It may unite with the inner fold of the retro-colic fossa, or the two may exist at the same time. It may contain the appendix, even a part of the caecum, or, according to Jonnesco, coils of the small intestine. Blood-Vessels. The artery supplying the caecum is the ileo-colic, a branch of the superior mesenteric artery, which sends to it both an anterior and a larger posterior branch, which ramify downward over the front and back of the caecum. A large branch from the posterior division runs between the folds of the posterior retinaculum ; less constantly a smaller vessel courses in the anterior one. The segments of the ileo-caecal valve are very vascular. The artery of the vermiform appendix arises from the posterior division of the ileo-colic, crosses the back of the ileum, and runs in the fold of peritoneum to the end of the appendix. The veins of the caecum are arranged on much the same plan as the arteries. That of the appendix is relatively more important, receiving tributaries from the front and the back of the caecum. It passes behind the end of the ileum to the ileo-colic vein. The lymphatics are divided into a posterior and an anterior set. The former empty into small nodes on the back of the caecum beneath its peritoneal covering. The anterior ones are in or near the fold between the caecum and colon. The appendix contains a large lymph-sinus at the base of the follicles. Lymphatics pass through the interruptions of the muscular layer. They may enter a node in the peritoneal fold in the angle between the caecum and ileum. There are several possible communi- 1 668 HUMAN ANATOMY. cations : one with nodes in the mesentery ; one with nodes on the left of the as- cending colon behind the peritoneum ; one with nodes of the iliac fossa ; and, in the female, one with the system of the ovary. There is a constant lymph-node at the angle between the ileum and colon. 1 The nerves supplying the caecum and appendix are derived from the superior mesenteric plexus. Their mode of distribution within the gut has already been given (page 1643). Development and Growth. At birth and for some years after the caecum is very small and the fcetal or cornucopia shape is more frequent than later. The appendix is relatively rather long. In eleven cases below ten years Berry ~ found the average length of the caecum 28 mm. and the breadth 37 mm. In eighteen cases he found the average length of the appendix 74 mm. (2^5 in.). Ribbert gives the following lengths of the appendix : at birth, 34 mm. ; up to five years, 76 mm. (3 in.); from five to ten years, 90 mm. (3^ in.). At birth the caecum is usually higher than in the adult, since it has not de- scended to its permanent position and the adhesion of the mesentery of the ascend- ing colon has not occurred in the lower part of the flank. It is often rather above the anterior superior spine of the ilium. In five of about thirty-five observations on young children, mostly newly-born, it was so free from fixed attachment that it could hardly be said to have any definite position. THE COLON. The ascending colon extends from the caecum to the under side of the liver, where it makes a sudden bend the hepatic flexure (flexura coli dextra) and be- comes the transverse colon, which crosses the abdomen to the splenic flexure (flexura coli sinistra) at the spleen, whence, as the descending colon, it passes to the crest of the ilium. From that point to the middle of the third sacral vertebra it is known as the sigmoid flexure. The three bands of the colon, or t&nicz coli, formed by accu- mulations of longitudinal fibres, are each about i cm. broad. Their disposition in the walls of the gut is difficult to follow and is not constant. The following arrange- ment is probably the most usual. In the ascending colon one is in front and two behind, one of the latter being near the outer and the other near the inner aspect. On reaching the transverse colon, the anterior becomes the inferior, while the external becomes the superior, receiving the attachment of the transverse meso- colon. The internal also lies on the upper surface, but behind the preceding. On the descending colon they resume their original positions, but tend to grow indis- tinct. They are still more so in the sigmoid flexure, and before the rectum is reached there are but two bands, an anterior and a posterior, of which the latter is the stronger. The interior of the colon shows the sacculated condition, but there are no folds or valvulae conniventes like those of the small intestine. The solitary lymph-nodules continue, much like those of the jejuno-ileum. Relations. The ascending colon is in the right flank against the psoas and quadratus lumborum, but does not overlap the latter unless greatly distended. It lies in front of the lower end of the right kidney, projecting but little beyond its outer border, with the second part of the duodenum on its inner side. It ends with the hepatic flexure, which makes a large impression on the under side of the right lobe of the liver directly anterior to the kidney. It is often completely covered in front by the small intestine. The transverse colon is suspended between its beginning, the hepatic flexure, and its end, the splenic flexure, like a festoon, forward and downward ; for the ends are near the back of the abdominal cavity. The splenic flexure, in front of the lower part of the spleen, is both higher and more posterior than the hepatic one. The transverse colon is covered above and in front by the greater omentum. It runs along the liver, touching the gall-bladder and the greater curvature of the stomach, around which it ascends to the spleen. The splenic flexure may or may 1 Lockwood : Proceedings of tin- Anatomical Society of Great Britain and Ireland, Journal of Anatomy and Physiology, vol. xxxiv., 1900. * Anat. Anzeiger, Bd. x., 1895. THE COLON. 1669 not rest against the under side of the diaphragm, according to its distention and that of the stomach. It rests behind and below on the small intestine. It may or may not be in immediate relation to the tail of the pancreas. The descending colon descends partly in front, but still more external to the kidney, and after passing the kidney rests wholly on the quadratus lumborum. Although more externally placed than the ascending colon, it does not usually project beyond that muscle. The sigmoid flexure (colon sigmoideum), the continuation of the large intestine, begins at the crest of the ilium as a loop of very varying length, which is attached by FIG. 1418. Left side of abdomen; small intestine turned to right, exposing- mesentery, mesocolon of descending colon, and mesosigmokl. a mesentery, and ends at the middle of the third sacral vertebra. Its usual length is from 25-56 cm. ( 10-18 in. ), but is occasionally much longer. While it is true that the gut does not always become free at the crest of the ilium, but may descend, bound down closely, to the iliac fossa for some distance, it is best to regard the sigmoid flexure as beginning at a definite although arbitrary point rather than at the less certain one at which the gut really has a mesentery. Moreover, there is no great inaccuracy in the statement that this generally occurs at the crest of the ilium or just below it. The simplest form of the sigmoid flexure is a loop. If it be a small one, it usually is made of the last part of this section of the gut ; very often the first part is but slightly free while the last part is very much so. Short sigmoid flexures, i6yo HUMAN ANATOMY. especially with short mesenteries, can hardly vary much from a simple loop ; under opposite conditions, however, they may present the most diverse forms, so that a definite shape can hardly be assumed. The M-form is common. We have seen the sigmoid disposed in three parallel vertical folds occupying all of the left iliac fossa and overhanging the true pelvis. As the sigmoid flexure descends along the sacrum it usually curves to the right and crosses the median line. Peritoneal Relations. The lower part of the ascending colon is very often, for one or two inches, completely surrounded by serous membrane. The ligaments of the colon (described with the retro-colic fossa, page 1667) occur more or less well marked at the line where the peritoneum leaves the posterior wall. Above this the colon is connected by areolar tissue to the kidney. Occasionally the colon is adherent as far as the csecum. The non-peritoneal portion of the upper part of the ascending colon equals about one-third of its circumference. The transverse colon is attached to the transverse mesocolon and otherwise completely surrounded by peritoneum. The transverse mesocolon, after attaining its permanent condition, arises along the back of the abdomen from one kidney to FIG. 1419. Sigmoid flexure pulled up Anterior band Rectum Bladde Anterior abdominal wall turned^ forward Mesentery of sigmoid Anterior superior spine of ilium Recto-vesical fold Sigmoid flexure and rectum ; sigmoid has been displaced upward to show its mesentery. the other. It crosses the front of the right kidney, the second part of the duo- denum, and passes along the lower border of the pancreas above the duodeno-jejunal flexure, to end on the left kidney. Sometimes in the left part of its course its origin rises onto the superior anterior surface of the pancreas. Its greatest breadth i.e., the distance from its origin to insertion is at the middle, and varies from 10-15 cm - The posterior layer of the greater omentum fuses with it. The phn-no- colic ligament, which runs inward, shelf-like, from the left abdominal wall under the spleen, although in acquired relation with the mesentery of the transverse colon, is really a part of the greater omentum. The latter hangs down from the transverse colon over the small intestine, but its relation to the colon is not the same through- out. On the right it is fused with the peritoneum of the anterior surface of the gut and lea'ves it at the lower border. On the left it leaves the upper surface of the colon, or even the transverse mesocolon, before the latter reaches the gut. Thus the line at which it leaves the intestine rises gradually from right to left. The descending colon is usually uncovered posteriorly by peritoneum. According to Lesshaft, 1 whose results have been generally accepted, it has mon- or less of a mesentery once in six times. According to Symington, 1 the mesenteries 1 Reichert and Du Bois-Reymond's Archiv, 1870. 2 Journal of Anatomy and Physiology, vol. xxvi., 1892. THE COLON. 1671 thus found are due to a displacement of the peritoneum, which is but loosely attached. True mesenteries are probably less frequent. At the sigmoid flexure the peritoneum usually begins to surround the gut, although the point at which this commences maybe much lower. In the former case the line of origin of the mesentery descends tolerably straight to the middle of the third sacral vertebra, where it ends. The gut may, however, be pretty closely bound down to the iliac fossa as far as the true pelvis over the posterior border of the obturator foramen, in which case the line of attachment runs thence backward along the border of the true pelvis until it crosses the sacro- iliac joint, after which it descends across the sacrum. There may, of course, be an indefinite number of variations between these extremes. The attachment to the sacrum is usually near the median line over the second and third vertebrae, but it may diverge to either side of it. Variation also exists as to the point at which the mesentery ends. The greatest breadth i.e., from origin to insertion of the latter is usually found in the part which springs from the first sacral vertebra. It is, on the average, about 9 cm. , rarely less than 5, not more than 16 ; exceptionally it may be as much as 25 cm. With a long loop it is, of course, relatively narrow at its origin. The intersigmoid fossa is an inconstant small peritoneal pouch, present about three times out of four, on the under side of the mesentery of the sigmoid flexure, which is shown by throwing the loop upward and to the right. It is ob- viously due to the failure of the sigmoid mesentery to unite completely with the peritoneum of the posterior wall, and consequently is under the edge of the part that fails to unite, lying usually just above the true pelvis near the common iliac artery. The orifice of the pocket is very likely to be circular, with a diameter of from 13 cm. , in most cases nearer the lower figure. The pouch may be quite rudimentary, or may extend up like a tunnel between the layers of peritoneum for an inch or two, or exceptionally for a greater distance. Development and Growth. The length of the intestines, and especially of the colon, is, according to Treves, singularly constant at birth. He found the average length of the small intestine about 287 cm. (9 ft. 5 in.) and that of the large about 56 cm. ( i ft. 10 in. ). It is remarkable that while during the first two months the small intestine grows at the rate of about two feet a month, the large intestine remains of the same length for three or even four months. This is due to the fact that during this period the large intestine grows at the expense of the sigmoid flexure, which at birth forms nearly one-half of the whole, while at four months it has assumed approximately its permanent proportions (Treves). After this the growth of both small and large intestine is extremely irregular, as shown by the following table : Observer. Age. Small Intestine. Large Intestine. Dwight. 10 months. 670 cm. 78 cm. Dwight. 10 months. 435 cm. 90 cm. Treves. i year. ... 76 cm. Dwight. 3 years. 490 cm. 84 cm. Treves. 6 years. ... 91.5 cm. Treves. 13 years. . . . 107 cm. As the sigmoid flexure is relatively large in the infant and the pelvis very small, the convexity of the loop lies in the right side of the abdomen. Variations. The mesentery of the small intestine and of the ascending and the transverse colon may remain attached only at the origin of the superior mesenteric artery, giving the con- dition known as mesenterium commune. The ascending colon may, on the other hand, be so long as to make secondary folds. Curschmann ' has seen its mesentery long enough to be twisted. The transverse colon may be short, wanting one or both flexures. In the latter case the ascending and the descending colon are almost like the sides of an inverted V. Probably much more often the transverse portion may be too long and descend in the middle like an M, with the middle point at the pelvis. A fold is more common at the left than the right. A double fold of the transverse colon has been seen. This part of the gut, when over large, may decidedly diminish the area of the liver dulness. The descending colon may also present folds, but an immense sigmoid flexure, which usually is accompanied by great length of the large intestine, is more common. The convexity of this fold may reach to the transverse colon or to the caecum. Sometimes the sigmoid flexure consists of two successive folds. 1 Deutsches Archiv fur Klin. Med., Bd. liii., 1894. 1672 HUMAN ANATOMY. Blood-Vessels. The arteries of the colon are derived from the superior and the inferior mesenteric. The former supplies the caecum, the ascending and the transverse colon, and a varying amount of the descending colon. The supply of the latter is completed by the inferior mesenteric, which is also distributed to the sigmoid flexure. The general plan includes a series of anastomoses between neighboring branches, by which long arterial arches run near the border of the gut, to which they give off irregular twigs. There is no system of straight vessels as in the greater part of the small intestine. In the sigmoid flexure there is a recurrence of the superimposed arches, which may be three in number. The superior hemorrhoidal branch of the inferior mesenteric artery runs in the last part of the mesentery of the sigmoid, and often divides in it into two branches, which run side by side on the back of the gut towards the rectum. The veins are disposed much the same as the arteries, but with a system of straight vessels from the intestine. The lymphatics, which are many, empty into lymph-nodes on the posterior wall of the abdomen, which are a part of the same system as those of the small intestine. The nerves are from the superior and inferior mesenteric plexuses, which are derived chiefly from the solar and the aortic plexus respectively. THE RECTUM, ANAL CANAL, AND ANUS. The Rectum. The rectum begins at the middle of the third sacral vertebra, the point at which usually the mesentery that restrains the sigmoid flexure termi- nates. It was formerly described as beginning at the left sacro-iliac joint, but this division, which is unwarranted, is falling into disuse. The rectum descends FIG. 1420. Rectal folds I .^-Bladder \mi&^^. \\S&Es^i^''fc- :-'- ----- Seminal vesicle jJQfe -*\S$ : sf ' -^-. :.',.,. Symphysis pubis EAK^'- -" /:( v x / Sacro-coccygeal articulation Hemorrhoidal vein Veins of mucosa of anal canal ( Fold of mucous membrane l sphincter Sagittal section of pelvis passing through rectum, anal canal, bladder, and urethra. along the hollow of the sacrum and coccyx, passes the point of the latter, and con- tinues until it reaches the lower and back part of the prostate gland in the male or the vagina in the female. Its length is about 12.5 cm. (approximately 5 in.). The gut is then continued by the anal canal, sometimes called the sphincteric portion of THE RECTUM, ANAL CANAL, AND ANUS. 1673 the rectum, situated in the thickness of the pelvic floor, and directed downward and backward, making a sharp angle with the rectum proper. The rectum proper, having passed the tip of the coccyx, rests on the levator ani muscle, although separated from it, as well -as from the sacrum and coccyx, by the dense rectal fascia. The rectum, although not exhibiting the pouching seen in the colon, is sacculated, presenting, when distended, usually three dilatations, of which the lowest and largest, called the ampulla, may measure 25 cm. (9^3 in.), or even more, in circumference. The saccules are separated by deep creases, passing about two-thirds around the gut, caused by a folding in of all the coats internal to the two bands of longitudinal muscular fibres. The folds form the valves of the rectum, to be described with its interior. In the male the ampulla extends against the back of the prostate and the lower part of the seminal vesicles and the terminal parts of the vasa efferentia, to all of which it is connected by areolar tissue. A pocket of peritoneum intervenes higher up, the walls of which, however, come in contact when the hollow organs are distended. In the female the end of the ampulla lies against the posterior wall of the vagina from about opposite the level of the os uteri to the junction of the middle and lower thirds. There is above this a fold of peritoneum corresponding to that of the male. FIG. 1421. Glands of mucosa Levator ani External sphincter Levator ani Internal sphincter. Longitudinal muscle External sphincter Skin Anal glands Anal glands Frontal section through anal canal. The Anal Canal. This part of the large intestine (pars analis recti) is situ- ated in the thickness of the pelvic floor and extends downward and backward. It differs from the rest of the intestinal canal in having no lumen under ordinary cir- cumstances, when the sphincters surrounding it are contracted. The anus is the very vaguely used name of the termination of the anal canal. It is deeply situated between the nates, especially in the female ; its distance from the tip of the coccyx, variously stated by different observers, may be said to be about 5 cm. (2 in.). Much confusion has arisen from the difficulty of defining the lower end of the anal canal, since the skin, which is puckered up by the external sphincter and the cor- rugator cutis ani, somewhat resembles mucous membrane, so that the canal appears longer than it really is. The anatomical boundary, the ano-rectal groove, the so- called white line of Hilton, is a slight zigzag furrow, usually to be seen on the living and not on the dead. It lies a little above the lower limit of the internal sphincter, which, covered by dilated veins, projects towards the potential lumen above the external sphincter, and is i cm. or more within what, on a superficial examination, would be called the anus. When the dissected rectum is laid open, much is evidently a part of the skin which during life is drawn into the canal by the contraction of the muscles ; hence the length of the canal is very variously stated. Seldom does it 1 674 HUMAN ANATOMY. FIG. 1422. measure as much as 15 mm. from its upper end to the ano-rectal groove ; probably this distance is usually about i cm., while what may practically be called the canal is twice as much, or even more. It is longer in men than in women. In the male the beginning of the anal canal is near the lower part of the prostate and the mem- branous urethra, at a point from 3.5-4 cm. in front of and somewhat lower than the tip of the coccyx. Lower still, the bulb of the urethra is separated from the anal canal by the pyramidal mass of connective tissue constituting the perineal body, The latter is of greater importance in the female, and separates the anal canal from the lower part of the vagina and from the vulva. The moist and dark skin which is puckered up to form the continuation of the anal canal is at first very thin, but gradually assumes the appearance of ordinary integument. The so-called anal glands surrounding the anus are of two kinds, both of which have their orifices in this skin. Those nearest to the boundary line are sebaceous follicles, and external to them is a zone of large sweat-glands. Just at the termination of the skin apparently forming the end of the canal there is, especially in the male, a considerable development of hair. Structure of the Rectum. The mucous coat is thick and vascular, and corresponds in its general histological details with the mucosa of other parts of the large intestine. The glands of Lieberkiihn, however, are exceptionally large, at- taining a length of . 7 mm. The muscularis mucosae is better developed than in the colon. The rectal valves (plicae transversales recti) are two or three folds, exceptionally four or five, projecting like transverse shelves into the cavity when it is distended, and hanging loose when it is not. They are semilunar in shape, with the greatest breadth from the attached border to the free edge, ranging from i cm. to more than 3 cm. They cor- respond to, or rather are the causes of, the constrictions between the saccules. They contain all the coats of the gut, except that, chiefly on the posterior wall, some of the longitudinal muscle-fibres pass outside of them, thus securing the fold. In large folds there is an accumulation of the circular fibres. These folds tend to be effaced in the isolated and opened rectum, but they are unquestionable, being shown by casts and frozen sections, and in both the living and the dead body when placed in the knee-chest position with the rectum cleared of faeces and distended with air. They are placed laterally, and have in common that their points cross the middle line, although not symmetrically, extending more onto the front than the back. According to the usual arrangement, the lowest, which is also the smallest, projects from the left ; the second, the largest, from the right ; and the third from the left. The first is about 2.5 cm. (i in.) above the anal canal and the second about as much higher. If the first as often happens be wanting, the second is not necessarily any lower. The third is usually at about the same distance above the second, but is subject to greater variations, since the two may be very near together. 1 The columns of Morgagni are a series of per- manent vertical folds of mucous membrane passing from the anal canal upward into the rectum. The number of these folds varies from five to considerably more than ten, which latter number is perhaps about the average. The length of the folds is in most cases from 1-2 cm., but some are considerably longer. They are broad and highest at their anal end, or base, from which they diminish to the upper t-nd, a transverse cut near the lower end showing them to be triangular on section. The rn/rt's of Morgagni arc semilunar folds of the mucous membrane connecting the bases of the columns of the same name, and forming with them a number of 1 Otis : Anatomische Untersuchungen am menschlichen Rectum, Leipzig, Folds of rectum seen after dilatation. (Otis.) THE MUSCLES AND FASCIAE OF THE RECTUM AND ANUS. 1675 pouches opening upward. They are situated in the anal canal at the upper part of the internal sphincter. The mucous membrane of the rectum is thrown into a series of longitudinal folds. These are easily effaceable, although some are continu- ous with the columns of Morgagni. The submucous coat is lax, allowing the mucous membrane to be readily dis- placed, but at the lower end of the anal canal the latter is firmly attached to the muscles. The muscular coat of the rectum is thicker than that of the colon, reaching to 2 mm. The thickening is greatest in the layer of the circular fibres. The longitu- dinal ones, although forming a continuous layer, are for the most part collected front and back into the two bands already mentioned, of which the posterior is the larger and the more concerned in bridging over the folds. The internal sphincter is but an hypertrophy of the circular muscles, while the external sphincter is a muscle of the perineum. It has been thought advisable to here describe together the muscles and some of the fasciae of the. rectum and anus, including some that are largely extrinsic. THE MUSCLES AND FASCIA OF THE RECTUM AND ANUS. The levator ani (Figs. 1423, 1424) arises from the back of the body of the pubes, about midway between the upper and lower border, very close to the middle line, and thence, from the ' ' white line' ' formed by the splitting of the pelvic fascia, as far as the spine of the ischium. The anterior fibres from the pubic bone pass below the prostate, some going to its capsule, as a strong muscular bundle to the central Fro. 1423. Bulbo-cavernosus Ischio-cavernosus Trans, perinei superf. Obturator interims White line Levator ani . Coccygeus Triangular lig- ament, inf. layer Perineal centre Tuberosity of ischium Anus Obturator fascia Gluteus maximus (cut) Greater sacro- sciatic ligament Coccvx Muscles of pelvic floor and perineum from below. point of the perineum and the front and sides of the rectum, in which some of them end. The remainder of this set passes with the fibres from the white line to the side of the coccyx and to a fibrous band (ligamentum anococcygeum) running from it to the anus. This latter part of the muscle is thinner and more transversely placed than the former. In the female the pubic portion sends some fibres to the vagina and some around it to the central point of the perineum. The fibres, for the most i6 7 6 HUMAN ANATOMY. part in both sexes, pass by the rectum so as to compress it, although some enter its walls and mingle with those of the sphincters. Nerve. A branch from the sacral plexus (sometimes there are more than one) runs to the levator ani on its upper surface. The fibres come from the third and fourth sacral nerves. According to some, the muscle also receives fibres from the inferior hemorrhoidal branch of the pudic nerve. The coccygeus (Fig. 1424), a triangular muscle arising from the spine of the ischium and inserted into the border of the coccyx, is in the same plane and practi- cally continuous with the levator ani. The two muscles of both sides have been well called the diaphragm of the pelvis. They form a funnel-like structure with the walls converging downward to the anal canal, and an anterior opening for the prostate in the male and the vagina and urethra in the female. FIG. 1424. Sacrum (cut) Pyriformis - -Coccygeus Levator ani Recto-coccygeal fibres evator ani (cut) Obturator internus Ischial spine Obturator canal Cut edge of pelvic I fascia, white line Pubic bone Triangular ligament, superior layer / Triangular ligament, inferior layer Urethra Bulb of penis, covered by muscle Muscles of pelvic floor from within ; sivtion passed to left of mid-line. Nerve. The muscle receives branches from the fourth and fifth sacral nerves and perhaps from the first coccygeal. The external sphincter ani (Fig. 1423), situated beneath the skin and car- ried up into the puckering at the anus, is a flat oval muscle composed of striated fibres surrounding the end of the rectum. It arises from the tip of the coccyx, from the skin over it, and from a raphe extending from it to the anus. The fibres diverge on either side to enclose the anus, meeting in front of it at the central point of the perineum (page 1917), where they mingle with other muscles which meet at that point. Some of the inner fibres completely encircle the anus. In the female some fibres decussate with those of the sphincter vaginae. This sphinc- ter is "external " in two senses : it is nearer the outer surface' than the inner, and also surrounds it. Nerve. It is supplied by branches of the fourth sacral and of the inferior hemorrhoidal nerve'. THE MUSCLES AND FASCIAE OF THE RECTUM AND ANUS. 1677 The internal sphincter ani (Fig. 1421), composed of involuntary muscular fibres, is a thickening of the circular layer of the rectum, which becomes marked at the beginning of the anal canal. It surrounds the latter for a distance of from 2.5-3 cm -> an d is about 4 mm. thick. Nerves reach the internal sphincter through the sympathetic system. Very probably some of them come directly from spinal nerves. Accessory Muscular Bundles. As they reach the anal canal, the longi- tudinal fibres of the rectum send bundles to the skin, which gain their destination by coursing through those of the external sphincter ; the longitudinal muscle-fibres of the mucous coat, becoming enlarged, pass in the same way between the bundles of the internal sphincter. No important accessions are received from the levator ani. The longitudinal muscular fibres of the rectum, moreover, enter into connection with the areolar tissue of the pelvic fascia between the peritoneum and the levator ani, and perhaps with the latter also. Various bundles of muscle-fibres, apparently arising FIG. 1425. External, iliac vessels Pelvic fascia White line. Recto-vesi- - cal fascia Obturator fascia Obturator membrane Cowper's_ gland Iliacus Iliac fascia .Peritoneum Ilio-pecti- neal line Obturator internus Ampulla Seminal vesicle _ Anterior wall of rectum Levator ani _.Prostate gland Obturator externus Pubic ramus Corpus cavernosum Ischio-cavernosus Triangular ligament, inferior layer Bulbo-cavernosus Colles's fascia Triangular ligament, superior layer Trans, perinei superf. Bulb of penis Frontal section or pelvis passing just behind the bladder, posterior surface. from the pelvis, mingle with those of the rectum. The recto-coccygeus of Treitz arises from the anterior surface of the coccyx above the pelvic floor and mingles with both the longitudinal and circular fibres at the back of the rectum. It is said to con- sist of striated fibres at its origin. Bundles of fibres are described as arising from the fascia on the deep surface of the transversus perinei profundus muscle and pass- ing to the front of the gut. The corrugator cutis ani is a small system of muscular fibres radiating from the submucous tissue at the anus to the deep side of the skin, which it tends to pucker. Actions. The function of the sphincters is to keep the anal canal closed. They differ, inasmuch as the external, although mostly acting automatically, is under the control of the will and the internal is not. The levator ani has a more complicated and in part an apparently inconsistent action, since it may pull the anus upward and probably dilate it, as it pulls its borders apart under the resistance of 1678 HUMAN ANATOMY. the descending faeces, while at other times, by its antero-posterior fibres, it may compress the sides of the gut. To the action of the levator is probably due the control of the heces which sometimes persists after division of the sphincter, unless, indeed, the upper part of the latter has escaped. The Ischio-Rectal Fossa. This space is a deep, roughly pyramidal hollow, filled chiefly with fat, on either side of the rectum. The base is at the skin between the tuberosity of the ischium and the anus, bounded in front by the line of reflection of the deep perineal fascia and behind by the great sacro-sciatic ligament and the edge of the glutens maximus. The base measures some 5 cm. (2 in.) from before backward and half as much crosswise. The fossa is bounded externally by the tuber- osity of the ischium and above the latter by the obturator fascia, internally by the external sphincter and the under surface of the levator am'. The space narrows above to a line at the splitting of the pelvic fascia ; hence it can only vaguely be called pyramidal. The depth of the fossa is about 5 cm. (2 in.). FIG. 1426. Venous plexus Anterior wall of bladder Pelvic fascia j Prostate gland | Superior pubic ramus Obturator internus Diaphragmatic or recto-vesical fascia Obturator fascia Levator ani Gluteus maximus Ischio-rectal fossa External sphincter Internal sphincter Oblique transverse section through pelvis in plane shown in small outline figure. The diaphragmatic fascia, the inward continuation of the pelvic fascia which covers the upper surface of the levator ani, reaches the side of the rectum as a bed of areolar tissue beneath the peritoneum, and is more or less closely attached to the gut, sometimes by muscular bands, as already stated. The systematic deseriptio of this fascia is given elsewhere (page 559). The rectal fascia is a dense layer of areolar tissue surrounding the rectui below the reflection of the peritoneum, being continuous below with the preceding fascia. It is particularly dense behind the rectum, which it separates from the sacrum and coccyx. The anal fascia is a web-like areolar sheet covering the under side of the levator ani. A superficial fascia between the skin and the base of the ischio-rectal fossa can be artificially dissected, but is of little importance. THE MUSCLES AND FASCIA OF THE RECTUM AND ANUS. 1679 Peritoneal Relations of the Rectum. The posterior surface of the highest part of the rectum is usually coated like the rest with peritoneum, except near the median line ; but this narrow retroperitoneal surface enlarges rapidly, so that soon the entire posterior surface in the hollow of the sacrum and coccyx is without serous covering. The gut rests on the dense rectal fascia. The sides and front of the rectum are covered with peritoneum, which is reflected laterally, first onto the sides of the posterior wall of the pelvis, then onto the floor. The peritoneum forms a deep pouch in front of the rectum, the pouch of Douglas, known from its anterior wall as the recto-vesical in the male and the recto-vaginal in the female. In man this pouch separates the rectum from the bladder and the upper part of the seminal vesicles and in woman from the upper part of the vagina. The distance of the line of reflection of peritoneum that is to say, the bottom of the pouch from the ano- rectal groove may be as little as 5 cm. (2 in.), as usually given ; if, however, by the word ' ' anus' ' be understood what is practically the orifice of the gut, the distance is nearly 7 cm. (2^ in.) in both sexes. If both bladder and rectum be distended, the pouch is considerably raised; when the rectum is collapsed, it contains loops of the small in- testine or the sigmoid flexure. The recto-vesical folds in the male, although described with the bladder (page 1 905) , should be mentioned here. They are reckoned among the false ligaments of the bladder, and bound laterally the pouch just described ; extending backward from the bladder around the rectum to the sides of the sacrum, they tend to divide the cavity of the pelvis into an upper and a lower com- partment. Their free edges are semi- lunar and sharp, and curve around the rectum above the ampulla, which they partially roof in. These liga- FIG. 1427. Internal hemorrhoidal vein Levato Middle hemorrhoida vein Groove lernal emorrhoidal ein Skin Frontal section of wall of anal canal, showing relations of hemorrhoidal veins. (Otis.) ments contain more or less fibrous tissue. In the female they are less developed, although important, and, arising from the uterus instead of the bladder, are known as the sacro-uterine folds. Blood-Vessels. The arteries supplying the rectum are derived chiefly from the three hemorrhoidals. The superior hemorrhoidal, the ter- mination of the inferior mesenteric artery, divides opposite the sacrum, sometimes near the beginning of the rectum, sometimes higher, and even above the pelvis, into two branches, of which the right is the larger, that descend on either side of the rectum and give off smaller branches. A median posterior branch usually arises from the right one. The mucous membrane is supplied by these above the boundary line. Vessels may be received also from the sacra media. The middle hemorrhoidal arteries, of uncertain origin and distribution, rarely give any consider- able supply to the gut. The inferior hemorrhoidals two or three small branches from the internal pudic supply chiefly the external sphincter, but also form a num- ber of fine anastomoses with the superior hemorrhoidal artery. The general dis- tribution of the veins is not very different from that of the arteries. The superior hemorrhoidal veins, tributaries of the inferior mesenteric, drain into the portal system. They form a very rich plexus throughout the rectum, particularly in the upper and middle parts of the anal canal. In this situation they present a series of dilatations encircling the gut on the bases of the columns of Morgagni, just above the boundary line between the mucous and cutaneous areas ; this line also marks the parting of the ways between the superior and external hemorrhoidal veins. The latter form i68o HUMAN ANATOMY a circle of smaller dilatations just below the line of demarcation, in the region that is reckoned as skin, but is practically puckered into the anus. There are communi- cations between the two systems, some of which pierce the muscular coat. Lymphatics. The principal lymphatics of the rectum, after joining the lymph-nodes situated along the superior hemorrhoidal veins, pass to the sacral glands on the front of the sacrum. In the lower part of the bowel a very rich plexus is found under the skin around the anus, which drains into the superior internal inguinal glands, and a still richer one inside, which at the lower part is concentrated on the columns of the rectum, but few vessels lying in the pouches. A considerable system of lymphatics exists also in the muscular layer. Most of those of the inside of the anus run to a few small lymph-nodules discovered by Gerota I on the back of the muscular coat of the rectum, distributed with the branches of the superior hemorrhoidal artery. Nerves. The nerve-supply of the rectum includes both sympathetic and cerebro-spinal fibres. The former are derived chiefly from the inferior mesenteric and the pelvic plexuses, accompanying the superior and middle hemorrhoidal arteries respectively. The cerebro-spinal fibres are contributed by the second, third, and fourth sacral nerves. The skin around the anal orifice is supplied by the inferior hemorrhoidal branch from the pudic nerve. Growth. At birth the rectum is tubular and generally relatively small. We do not remember to have seen a well-marked ampulla at that period. At least frequently the anal canal is very long, about i cm. The transverse folds of the rectum are apparent in the latter months of pregnancy. We have found an ampulla with a circumfejence of 13 cm. (5 in. ) at three years. In the same specimen the valves were well developed, and, except in size, it resembled the rectum of the adult. The peculiarities of the infantile sacrum have their effect on the course of the rec- tum, which is necessarily straighter than in the adult and does not run so far forward in front of the coccyx. PRACTICAL CONSIDERATIONS : THE LARGE INTESTINE. The Caecum. This part of the large intestine may remain undescended in its foetal position in the left hypochondrium, at a point above and to the left of the umbilicus, the ileum opening directly into it in this locality ; or it may be found in the right hypochondrium just below the liver, or at any level between that and its normal situation. The caecum is rudimentary in man and other meat-eating animals, being much more capacious and of greater functional importance in the herbivora. The caecum is larger, more distensible, and more superficial than any other portion of the large intestine, and more mobile than any other portion except the sig- moid. On account of its mobility it is selected for the operation of iliac colostomy when that operation is done on the right side. As a result of the inspissation of the intestinal contents, which first occurs here, it is a common seat of fecal impaction, or of distention by gases arising from fermen- tation. The increase in numbers of the intra-intestinal pathogenic bacteria due to impaired inhibiting power, which, as we descend the gut, first becomes marked in the lower ileum, continues in the caecum. As in the former situation, where it prob- ably aids in determining the localization of typhoid and tuberculous lesions, so in the caecum, in conjunction with fecal accumulation, or with disturbance of circulation from distention, such augmentation adds to the frequency and severity of catarrhal inflammations and of stercoral ulcers, which are found oftener here than elsewhere. Fecal concretions (the formation of which is favored by intestinal catarrh just as is that of renal calculi by catarrhal pyelitis) are often found in the co-aim, and undoubtedly by mechanical irritation favor here, as they do in the appendix, epi- thelial necrosis and subsequent infection. In the erect position gravity aids in bringing about these pathological condi- tions, since the caecum, having no mesentery of its own, and yet completely covered by peritoneum (so that it is never anchored to the posterior parietes or to the iliac- fossa by areolar tissue), depends upon its attachments to the colon and ileum to hold 1 Arch, fiir Anat. und Entwicklng., 1895. PRACTICAL CONSIDERATIONS : THE LARGE INTESTINE. 1681 it in position. It has often been part of the contents of right inguinal or femoral hernia, and has even been found in such herniae on the left side. The influence of gravity in retaining fecal masses and favoring concretion is illustrated by the fact that foreign bodies small enough to pass through the ileo-caecai valve are prone to remain in the caecum, where they have in many cases given rise to ulceration and perforation, followed by perityphlitis. With varying degrees of displacement or of distention of the caecum come changes in the tension of the ileo-colic vessels, and congestion so often the first stage of serious pathological processes is thereby favored. The close relation of the caecum, if distended even slightly, to the anterior abdominal wall and to the ilio- psoas muscle exposes it to frequent trauma. These relations explain why flexion of the thigh on the abdomen will empty a moderately distended caecum. Enormous distention sometimes occurs, so that the caecum may fill the larger part of the abdomen, and in nearly all cases of intestinal obstruction between the anus and the ascending colon the caecum shows the most marked evidence of the backward pressure, the ileo-caecal valve, although not absolutely complete, resisting, for a time at least, the participation of the ileum even in distention from gases. Manifestly, in uncomplicated cases of obstruction of the small intestine the caecum will be found flaccid or collapsed. The ileo-ccecal valve is usually competent to prevent the return of fecal matter from the caecum into the ileum. Gas injected per rectum under pressure of from .7-1.02 kilos (1^2-2^ Ibs. ) (Senn) may be made to enter the ileum, and has been used in detecting and localizing wounds of the small intestine and in the treatment of intussusception. Less force is necessary when the patient is anaesthetized, proba- bly because of the relaxation of both the abdominal muscles and the circular fibres of the valve itself. Fluids are arrested at the valve, although they may be made to pass it either by immediate force sufficient to lacerate the peritoneal attachments and covering or by slow increase of pressure until the distention of the caecum gradually overcomes the weak resistance of the circular muscular fibres in the segments of the valve and separates their margins. Organic or spasmodic narrowing of the ileo-caecal valve has been suggested as a possible cause of chronic constipation, and two cases have been operated upon by making a longitudinal incision through the valve and uniting its edges transversely, as in pyloroplasty (page 1633) (Mayo). Invagination of the ileum and the caecum into the colon is the most common form of intussusception (44 per cent, of all cases, Leichtenstern ; 89 cases out of 103, Wiggin), and occurs most commonly (70 per cent, of all cases) in children. The ileo-caecal valve forms the summit or apex of the intussusceptum, and may pass through the entire colon (the intussuscipiens), reaching the rectum or anus. Ileo- colic intussusception in which the ileum passes through the valve, the caecum re- maining in place is much rarer (8 per cent, of all cases). In acute cases, here as elsewhere in the intestinal tract, pressure on the mesen- tery produces consecutively venous congestion, oedema, swelling, obstruction or strangulation of the mesenteric vessels, and either leakage through the damaged in- testinal walls and septic peritonitis or actual perforation, rupture, or gangrene of the bowel. In chronic cases dense adhesions form between the peritoneal coats of the entering and returning layers of gut (Fig. 1405). The traction upon the mesentery narrows the lumen of the intussusceptum so as to prevent the passage through it of the contents of the intestine. In adults the situation of the ileo-caecal valve corresponds to a point on the wall of the abdomen from 3-5 cm. (1-2 in.) internal to and above the anterior superior spine of the ilium. The Vermiform Appendix. On account of the frequency with which it is the seat of catarrhal or infectious disease, the appendix is of the greatest surgical interest. In addition to the description of its structure, position, and peritoneal relations already given (pages 1664, 1665), various important anatomical data relating to the causes, symptoms, results or complications, and treatment of appendiceal inflammations should be here considered, even at the risk of repetition. Etiology of Appendicitis. i. The appendix is an apparently functionless organ, found only in man, in certain of the anthropoid apes, and in the wombat. An analo- 106 1682 HUMAN ANATOMY. gous organ exists in some of the rodents and marsupials, but it is a long, tapering- caecum rather than an appendix strictly comparable to that of man. The appendix is a vestige of the capacious caecum of some of the lower animals, or may be regarded as a rudimentary caecum just as the human caecum is a rudiment of that found in the herbivora or the rodents. Like other vestigial structures, or those which in the his- tory of either the race or the individual have outlived their usefulness, it appears to be of low resistant power. This doubtless explains in part the special susceptibility of the appendix to disease, as it does that of the uterus and the female breast during the post-sexual period of life. 2. Its mesentery a fold made by the passage of the appendicular artery from the ileo-colic at the back of the ileum to the appendix (page 1665) is scanty; its free border is shorter than the border applied to the appendix, and sometimes does not extend much beyond its middle. The appendix, like the small intestine, is therefore thrown into irregular curves or coils. Another peritoneal duplicature the ileo-caecal fold runs from that part of the ileum most remote from its mesenteric attachment and is united with the mesentery of the appendix. It carries no blood- vessels of consequence, and is regarded by Treves as the remains of the true mesen- tery of the appendix. It is interesting to note the fact that in the different types of the human caecum those which involve a disproportionate growth of the caecum show that it derives its peritoneal covering partly at the expense of the mesentery of the appendix, which becomes more scanty and more vertical in direction the larger the relative size of the caecum. The appendix moves directly with the caecum, but, through the attachments of the meso-appendix to the caecum and to the mesentery of the ileum, distention or displacement of those portions of the intestine makes trac- tion upon it and causes increased curving or angulation. For these reasons, and on account of the lessened interference with the blood-supply (vide infra), appendices with exceptionally ample mesenteries extending to the tip of the organ are less fre- quently the seat of disease and, when diseased, are less often found in a condition of complete gangrene. 3. The single artery supplying the appendix and running in the folds of the meso- appendix, and its accompanying veins, are subjected to pressure by such traction, or by the angulation of the organ itself, and various degrees of vascular obstruction and congestion may result. The consequent oedema and swelling of the mucous mem- brane aid the distortion of the appendix in causing interference with the escape of the contents of the appendix into the caecum. After infection has started the vessels are not infrequently occluded by septic thrombi. The peritoneal fold, which in the female is often found running from the appendix to the broad ligament (page 1666), may contain a second artery the presence of which has been offered as an explana- tion of the relative infrequency of appendicitis in women. 4. The disproportion between the length and the lumen of the appendix (16 to i, Finkelstein), the similar disproportion between the lumen and the area of th secreting surface, its removal from the direct intestinal current, the feebleness of i muscular walls, its dependent position, the absence or inefficiency of any valvula: arrangement at the appendiculo-caecal orifice, and the ease with which that orince may be diminished in size by oedema of the mucous membrane in its vicinity readily explain the fact that under most circumstances in which drainage from the appendix into the intestine would be desirable, it is apt to be lacking. Even a hyperaemic catarrh from twists, kinks, or traction may in this way become the starting-point of serious trouble, the successive steps of which might subsequently be retention of mucus, epithelium, and fecal contents (possibly in the form of a concretion), ulceration, parietal infection, or perforation or gangrene, and peritonitis, localized or general. 5. The abundance of lymphoid tissue in the appendix, as in the tonsils, favors rapid swelling and infectious inflammations and aids in obstructing drainage. It may to some extent account for these pathological conditions showing themselves during the periods of growth and activity of the system much more frequently than in old aiM-, when the lymph-nodules in the walls of the intestinal canal become atrophied (Stnithers ). In this connection it may be noted that other causes contributing to the relative frequency of appendicitis in early life are (a) the susceptibility of children PRACTICAL CONSIDERATIONS : THE LARGE INTESTINE. 1683 to catarrhal enteritis, favoring the formation of concretions, or at least impairing the protective power of the intestinal epithelium ; (6) the relatively 'greater length of the appendix in young persons (in infants one-tenth and in adults one-twentieth the length of the large intestine, according to Ribbert) increasing the difficulty of drainage ; and possibly (c) the tendency to shrinkage or obliteration after middle life, a process to be expected in a rudimentary organ. 6. It must not be forgotten, in interpreting the foregoing anatomical facts as to (a) the rudimentary character of the appendix, (b) the scantiness of its mesentery, (c) its dependence for its blood-supply upon one vessel, (af') its imperfect drainage, and (//nei- brane (Fig. 1644), consisting of the apposed entoblast and ectoblast. A slight de- pression, the primitive anal groove, indicates the position at which the membrane breaks through to establish the cloacal orifice in those forms, as birds and mono- FIG. 1430. Optic vesicl Fore-brain Hind-brain I pharyng. pouch Ventral aorta._ i aortic bow Primitive pi- ventricle SjU Sinus -^ reuniens ^^ Liver mm Liver- diverticulum. Vitelline-1 duct \ II pharyng. pouch III pharyng. pouch Gut-tube Duct of Cuvier Aorta Liver Vitelline duct Vitelline- Neural tube artery Gut-tube, lower part Allantoic duct Belly-stalk_ Reconstruction of sagittally sectioned human embryo of third week, showing relations of digestive tube. X 26. (After His model.) 1 pharyng. pouch 2 aortic bow II pharyng. pouch 3 aortic bow III pharyng. pouch 4 aortic bow IV pharyng. pouch Lung-anlage Allantoic duct. Umbilical artery- Reconstruction of digestive tube of preceding bryo ; aortic bows and trunk also shown. X 26. (Aft> His model.) tremes, in which the cloaca persists. In the higher mammals the cloacal stage is only temporary, the cloaca becoming subdivided into two compartments by the for- mation of a septum, which grows downward to meet the cloacal membrane. The anterior compartment becomes the uro-genital sinus, the posterior the rectum. Later the remains of the cloacal membrane disappear, and these spaces are provided with the uro-genital cleft and the definitive anus respectively. Differentiation of the simple gut-tube into distinctive segments begins with the stomach, which appears as a small spindle-form enlargement at some little distance below the primitive pharynx, the portion of the tube between the two correspond- ing to the early oesophagus. The gut-tube lies close to the posterior wall of the body-cavity, and at this stage ( corresponding to about the fourth week in the human embryo) presents five divisions, the primitive oral cavity, the primitive pharynx, the oesophagus, the stomach, and the intestinal tube, which latter freely communi- cates with the yolk-sac through the vitelline duct. DEVELOPMENT OF THE ALIMENTARY TRACT. 1697 The digestive tube is at first closely bound to the posterior body-wall by a short, broad mesoblastic band. This attachment, or primitive mesentery, from the lower end of the oesophagus downward, gradually increases in its sagittal dimensions, at the expense of its breadth, in consequence of the gut-tube leaving the dorsal wall and assuming a more ventral position, the entire gastro-intestinal tube being thus attached by a mesentery. That portion of the latter connected with the stomach is known as the mesogastrium t that with the intestinal tube as the mesenterium commune (Fig. 1478). The elongation of the stomach soon results in loss of the primary sagittal direc- tion of its axis, which becomes oblique, the lower end of the organ passing to the right, while its upper end is displaced towards the left in consequence of the increasing volume of the liver. Embryos of the sixth week exhibit marked change in the form of the stomach, since the dorsal wall, later the greater curvature, has become bulged spineward, while the ventral surface presents a slight concavity foreshadowing the later smaller curvature. Somewhat later the stomach also undergoes rotation about its longitudinal axis, its primary left surface becoming the ventral or anterior, and its primary ventral border the lesser or upper curvature. The primary wall of the Allantoic duct- External surfa Intestine Cloaca I Cloacal membrane Tail-bud Part of caudal end of sagittal section of rabbit embryo of twelve days, showing cloacal space in communication with lower end of gut-tube and allantoic duct. X 35- stomach consists of the entoblastic lining surrounded by the splanchnopleuric meso- blast. The differentiation of the gastric glands begins towards the close of the third month as minute epithelial outgrowths from the entoblastic layer. A few weeks later the glands become branched, and the parietal cells appear as differentiations from single epithelial elements lining the peptic follicles. In the fifth month the length of the glands has increased to about .20 mm., and during the succeeding month to from .40. 70 mm. (Kolliker). Differentiation of the mesoblastic tissue into the inner circular and outer muscular layers occurs during the fourth month. The lower funnel-shaped pyloric end of the stomach at first passes insensibly into the relatively wide beginning of the characteristic U-shaped intestinal loop which extends from the stomach ventrally, its closed end or arch being attached to the vitelline duct, and then returns to the posterior body-wall to be continuous with the terminal segment, which maintains its sagittal relations in close attachment with the dorsal boundary of the body-cavity. The inferior limb of the loop early shows beginning differentiation into large intestine, the junction of the latter with the small intestine being indicated by the slight ca?cal expansion. Even at this period a defi- nite vascular relation has been established by the three main segments of the gastro- 107 1698 1 1 1. MAN ANATOMY. intestinal tube and its mesentery. Within the mesogastrium course the three branches of the cceliac axis ; the superior mesenteric artery passes within the mesen- tery between the limbs of the intestinal loop, while the inferior mesenteric artery is distributed to the last part of the intestinal tube. The subsequent changes which the intestinal tube exhibits during its growth have been carefully studied in reconstructions by Mall, 1 whose conclusions differ materially from the prevailing views. According to this investigator, the rapidly augmenting liver-mass occupies so large a portion of the still small abdominal cavity that there is no space left for the expansion of the intestinal tube. In consequence of this con- dition the greater part of the gut is early displaced from the abdominal cavity into the ccelom within the umbilical cord, the upper limb of the U-loop then lying to the right and the lower to the left. The growth of the small intestine more rapid than that of the large soon results in the production of six primary coils, the identity of which is retained not only throughout development, but can be established even in the adult (Mall). The first part of the gut- tube, continuous with the stomach and receiving the ducts of the liver and the pancreas, increases relatively little in its FIG. 1432. Future diaphragm Anterior mesentery (falciform ligament) Liver- Anterior mesentery (gastro-hepatic omentum) Connectioi vitelline stalk Umbilical veit Body-cavity___^pS Mt . j ion of__^ Stomach Spleen Mesogastrium CoL-liac axis Pancreas Duodenum .Superior mesen- teric artery Mesenterium commune Inferior mesenteric artery Allantoic duct Clocca Beginning of large intestine Diagram showing early relations of anterior and posterior mesentery. (Based on figures of Mall and Toldl.) length, and therefore does not become secondarily convoluted, as do the remaining coils of the small intestine. This part is later represented by the duodenum. The outer primary coils undergo great elongation, and consequently present secondary convolutions of increasing complexity, all of which for a considerable time (until the embryo has attained a length of about 30 mm.) are retained within the umbilical ccelom. About this period the lower part of the body grows rapidly, resulting in increased space within the peritoneal cavity, which now affords room for the tempo- rarily displaced gut-coils. In consequence of these changes the intestine returns to the abdominal cavity, and in embryos of 40 mm. length the coils no longer lie within the umbilical cord. Mall has shown that their return to the abdominal cavity occurs in a definite order, the upper part of the small intestine being first withdrawn, the l.ii-r intestine with its ca-cal dilatation last. On re-entering the abdomen the upper |..ut of the small iMit passes to the left hypochondriac region, while the lower segment of the small intestine with the ca rum takes up a position towards the right hypo- chondriac region. Coincident with this migration the large intestine is differentiated 1 Arch, fiir Anat. n. Physiol., Supplement Bd., 1897. DEVELOPMENT OF THE ALIMENTARY TRACT. 1699 FIG. M33- into a descending and a transverse colon, the former being the upper part of the vertical limb of the original dorsal flexure lying below the stomach. This flexure indicates the division between the descending and transverse colon, since the latter corresponds to the segment in front of the bend. Once back in the peritoneal cavity, the loops, which collectively lay in the sagittal plane of the cord, are arranged gen- erally at right angles to the long axis of the body, and the antero-posterior colon becomes transverse ( Mall ' ). In consequence of these changes the por- tion of the large gut that lay within the cord now lies obliquely across the ab- domen in front of the duodenum, the remaining coils of the small intestine being placed below. The caecum, therefore, occupies a position beneath the liver, on the right side, as a slight dilatation at the beginning of the transverse colon. The caecum, while gradually increasing, retains this gen- eral position until adjustment in the length of the segments of the large intestine takes place shortly after birth. The lower part of the large gut is thrown into a loop extending across the abdominal cavity, which becomes the sigmoid flexure, the latter at birth including nearly one-half of the entire length of the colon. After the fourth month after birth, the sigmoid flexure becomes shorter and the other parts of the colon proportion- ately longer, in consequence of which the caecum is pushed downward towards the right iliac fossa, with corresponding lengthening of the ascending colon. These por- tions of the large intestine, however, continue to grow for some time after birth, and it is not until the third year that they acquire their definitive relations. The anomalous arrangement and position of the transverse and ascending colon and the caecum, not infrequently observed in the adult, are usually dependent upon arrested development, the large intestine failing to take up a transverse and superior location, and hence altering its relations with the small intestine. Reconstruction of intestinal tube and part of liver of human embryo of 17 mm. vertex-breech length. (Same em- bryo as represented in Fig. 1436.) 77K, hepatic vein; UV, umbilical vein; PV, portal vein; GB, gall-bladder; FW, foramen of Winslow. The figures in this and in the two following reconstructions refer to corresponding parts of the gut-tube, i being gastro-duodenal junction. X 12. (Mall.) FIG. 1434. FIG. 1435- Reconstruction of intestinal coils of human embryo of 28 mm. vertex-breech length. Arrow indicates po- sition of foramen of Winslow. X 8. (Mall.) Reconstruction of intestinal coils of human embryo of 80 mm. vertex-breech length. X 2. (Mall.) The caecum, which first appears as a slight lateral diverticulum from the larger inferior limb of the primary U-loop of the gut-tube (Fig. 1432), increases in size until it forms a conical pouch, joining the colon where the latter receives the small in- testine. The growth of all parts of the caecum, however, is not uniform, since its ^natom. Anzeiger, Bd. xvi., 1899. T7oo HUMAN ANATOMY. dependent terminal portion does not keep pace with that nearest the intestine. The apical segment of the caecum remains proportionately small, and persists as the ver- miform appendix. The latter, therefore, corresponds to the unexpanded morpho- logical termination of the caecum. This relation is evident at birth, when the appendix forms the direct continuation of the funnel-shaped caecum ; it is exceptionally re- tained in the adult as the foetal type of caecum occasionally observed. Usually the caecum continues to expand with the colon, the demarcation of the appendix be- coming progressively more emphasized, until the relative size of the two tubes com- monly seen is established. The usual displacement of the appendix, so that it arises from the left and posterior wall of the caecum, results from the later unequal expansion of the right side of the latter, whereby the origin of the appendix is pushed to the left. Differentiation of the walls of the intestinal tube begins early in the third month by the formation of longitudinal folds, at first in the upper part, later the entire length of the small intestine. These folds increase in number and size, and subse- quently break up transversely into areas from which the villi are formed. The latter first appear in the upper part of the small intestine in embryos of about 30 mm. in length (Berry 1 ), and gradually extend to the lower segments, the villi being- present throughout the small intestine in embryos of about 10 cm. in length. Yilli also exist temporarily in the large intestine, but later undergo absorption, so that shortly after birth they have completely disappeared, while those within the small intestine have greatly increased in numbers and size. Early in the fourth month the intestinal glands appear in the upper part of the tube as minute diverticula clothed with extensions of the entoblastic lining of the gut. The glands of Brunner develop somewhat later during the same month as outgrowths of the entoblast. During the fourth month the mesoblastic stratum, from which arise all parts of the intestinal wall except the epithelial elements of the mucosa and the glands, undergoes differentia- tion into the muscular and areolar layers ; by the close of the fifth month all coats of the intestine are well defined. Differentiation of the Body-Cavity. Owing to the precocious develop- ment of the mammalian heart, the latter organ is formed by the approximation and fusion of two lateral anlages, at first widely separated, in consequence of which union the upper part of the ventral body-wall is closed, while the more caudally situated is still incomplete, the gut-tube being but imperfectly separated from the yolk-sac. With the more advanced closure of the ventral body-wall the abdominal cavity is de- fined. The primary ccelom, according to His, may be divided, therefore, into an upper and a lower portion, the parietal and the trunk-cavity respectively. These spares communicate on either side by an extension of the parietal cavity, \\\e parietal recess of His. The ventral portion of the parietal cavity, which from its earliest appear- ance contains the heart, becomes the pericardial cavity, and is, therefore, appropri- ately named the pericardial ccelom (Mall 2 ). The upper part of the parietal recess, since it later contains the lung and forms the greater portion of the surrounding lung-sac, may. similarly be designated the pleural ccelom. For a time the separation between the pericardial and pleural cceloms is imperfect, owing to the incompleteness of the postero-lateral walls of the heart-sac. This deficiency is corrected by tin- growth and differentiation of fat. pulmonary ridge (Mall), a structure that extends from the liver along the dorsal wall of the duct of Cuvier to the dorsal attachment of the early fold suspending the he-art, or mesocardium. Mall has shown that the pul- monary ridge grows headward as the plenro pericardia! membrane, which complet the separation between the heart- and lung-sacs, and later tailward to form \\\c pleitro- peritoneal membrane, which subsequently aids in closing the communication U-t \\een the pleural and peritoneal cavities. At first, immediately below the young heart lies the wall, of the wide yolk-stalk. embedded within the mesoblastic tissue of which the two large vitelline veins pass in their course towards the lower end of the heart. With the formation of the body- wall and the narrowing of the yolk-stalk, the enlarged vitelline veins, in their journey towards the heart, produce a broad fold which projects horizontally into the body- 1 Anatom. An/dger, Hd. xvii., 1900. 1 Johns Hopkins Hospital Bulletin, vol. xii., 1901 ; Journal of Morphology, vol. xii., 1897. DEVELOPMENT OF THE ALIMENTARY TRACT. 1701 cavity, and extends from the ventral wall to the sinus venosus, its median part be- neath the heart being attached dorsally to the gut-tube, while its lateral expansions form the floor of the pleural ccelom. This imperfect partition, the septum trans- versum of His, also affords passage for the two ducts of Cuvier, formed on each side by the union of the primitive jugular and cardinal veins, to gain the sinus venosus ; the septum transversum receives the hepatic outgrowth from the primitive duodenum, which soon develops a conspicuous liver-mass within the substance of the septum. The rapid increase in the mass of the developing liver is attended by great thicken- ing of the septum transversum, particularly towards its dorsal edge. Coincidently with this augmentation, the septum differentiates into a thinner upper and a thicker lower stratum, the former constituting the floor of the pericardial cavity and sur- rounding the ducts of Cuvier, the latter enclosing the liver. FIG. 1436. Trachea Per Septum transv Loop of small Intestine extend- ing into cord Vitelline vessels"" Caecum (Esophagus Lung Communication between pleural __ and peritoneal sacs _1. Suprarenal body _i Aorta Wolffian body Mesogastrium Duodenum Kidney Wolffian duct Ureter Allantoic duct Reconstruction of human embryo of 17 mm. vertex-breech length. X 14- (Mall.) The subsequent development of the liver is attended by progressive, although only partial, separation of the inferior layer from the superior stratum of the septum transversum, the latter layer remaining as the primitive, but still imperfect, dia- phragm between the pleuro-pericardial and peritoneal divisions of the body-cavity. The dorsal attachment of the septum transversum, at first high in the cervical region, gradually recedes tailward. On reaching the level of the fourth cervical segment the fourth myotome is prolonged into the upper layer of the septum to supply muscular tissue to what now becomes the diaphragm. The latter, however, is still incomplete dorsally, owing to the existence on each side of the communication between the pul- monary and peritoneal sacs. This opening is gradually closed by the backward growth of the diaphragm and the forward and downward extension of the pleuro- peritoneal membrane until the aperture between the thoracic and abdominal cavities is effaced and the diaphragm is complete. IJO2 IIT.MAN ANATOMY. Development of the Peritoneum. The attachment of the primitive ali- mentary tube, from the oesophagus downward, to the posterior wall of the body- cavity by means of a sagittal fold, the primary mesentery, has already been noted (page 1697). Likewise the conventional division of this duplicature into a lower part attached to the intestines, the mcsenterium commune, and an upper portion passing to the dorsal surface of the stomach, the mesogastrium. The latter differs from the common mesentery in not ending at the ventral border of the digestive tube, but, after enclosing the stomach and the upper part of the duodenum, in continuing for- ward, embracing the liver, to be attached to the ventral body-wall. The portion of the duplicature between the stomach and duodenum and parietes is known as the ventral mesogastrium, or anterior mesentery, as distinguished from the dorsal meso- gastrium behind the stomach. The ventral mesentery is at first attached above to the septum transversum and in front to the body-wall as far as the entrance of the umbilical vein, which occupies its lower free border as far as the liver. As already FIG. 1437. Vertebral column Spinal cord Truncus arteriosus Ventricle Diaphragm Liver Stomach Omental sac Greater omentuni .Communication between pleu- ; f'.iJ3| ral and perito- neal cavities Spleen Sexual gland _Lj Kidney -1 \ Atrophic Wolffian body Part of sagittal section of pig embryo of 23 mm., showing thoracic and abdominal organs. X 15. noted incidentally, the latter organ during its development is almost entirely fre from the diaphragm by the appearance of grooves on each side and before which cleave the septum transversum and almost completely separate the lower layer con- taining the liver, the lateral expansion of which organ materially aids in this process of delamination. The separation, however, is not complete, since the recesses over the sides and top of the liver do not quite meet in the mid-line, but leave a sagittal fold attached above to the diaphragm and below to the supero-ventral surface of the liver, beyond which it extends along the body-wall as far as the umbilicus. It is evident that this primitive, sickle-shaped fold foreshadows the persistent falciform or s/ts/y, ns, pancreas; du, duodenum; Ips, lesser peritoneal sac; os, omental sac; lo, lesser omentum; go, greater omentum ; ago and pgo, its anterior and posterior layers ; f, fusion between posterior wall of lesser peri- toneal sac and transverse mesocolon. {After Kollmann and Hertwig.} unattached over the caecum and appendix, but forms secondary connections where the ascending colon comes into contact w r ith the abdominal wall ; hence this part of the colon usually possesses a serous coat only anteriorly and laterally. Sometimes, however, obliteration of the serous covering does not take place, the ascending colon being attached by a mesocolon. The vermiform appendix being primarily an outgrowth from the large gut, since it represents the morphological apex of the caecum, is completely invested with peritoneum and is without a mesentery. Later the appendicular artery, in its course from the ileo-colic to the appendix, produces a serous fold which stretches from the left layer of the mesentery of the ileum to the caecum and appendix. This fold, the meso-appendix, is, therefore, functionally, but not morphologically, a true mesentery. THE LIVER. The liver (hepar), the largest gland in the body, is formed of very delicate tissue disposed around the ramifications of the portal vein. It is developed in the anterior mesentery, its mesoblastic elements having a common origin with the diaphragm, 1706 Hl'.MAX ANATOMY. while its duct and glandular elements are derived from a sprout from the duodenum ; hence the liver, as are other glands connected with the digestive tract, is an out- growth and appendage of the alimentary tube. Its peculiar shape is chiefly due to the pressure of surrounding organs, as its tissue is so plastic that it is moulded by them. In the adult it becomes firmer from the increase of connective tissue, but under normal circumstances it is always very soft, and, unless hardening agents are used before its removal, collapses into a flattened cake-like mass affording little information as to its true form. Indeed, it is only in the present generation, since the introduction of adequate methods of hardening in situ, that this has been learned. The liver in general may be described as an ovoid mass which in the young foetus nearly fills the abdomen, but in the adult has the appearance of having had at least a third of its substance scooped out from below, the back of the right end alone having been left intact. The organ is therefore a thick mass in the right hypochon- drium, growing thinner to the left. The greatest diameter is transverse and the next vertical. The liver is usually described as composed of five lobes, namely, the right, the left, the lobe of Spigetius, the quadrate, and the caudate. More properly it consists of a right and a left lobe, separated on the superior surface by the falciform ligament. The other lobes are subdivisions of the right lobe, the lobe FIG. 1440. Left layer of falciform ligament continuous ...with lateral ligament Union of right^ and left layers of falciform ligament Right lobe- irdiac impression -Left lobe Obliterated umbilical vein in free margin of falciform- ligament ^Gall-blarfder Antero-superior surface of liver hardened in situ. of Spigelius being at the back and the other two below. They are described wit the respective surfaces. The size varies greatly with the size of the body and from many other causes. The transverse diameter usually nearly equals that of the cavity of the abdomen, although it often falls an inch or so short of it. It may be given at from 22-24 cm - (8^-9^ in.). The greatest vertical dimension or depth is about i6cm. (6J< in.); the antero-posterior diameter 1218.5 cm. (4^4-7 Y\ in.). On peculiar form of liver occasionally met with shows great increase of the right lob particularly in the vertical direction, with a want of development of the left lob which is thin and short (Fig. 1456). The weight is, with considerable variations, generally from 1450-1750 gm., or approximately from 3-3^ Ibs. , and in the adult is about one-fortieth of the body weight. The specific gravity is given at from 1.05-1.06. The color is a reddish brown. The naked eye can recognize that the surface is covered with the outlines of polygons from 1-2 mm. in diameter. These are the lobules, each of which is surrounded by vessels and ducts in connective tissue, and contains in the middle a vessel, the beginning of the system of the hepatic vein. Sometimes the centre of the lobule is lighter that! the periphery, sometimes the reverse, depending upon whether the blood has stagnated in the portal or hepatic system respectively. THE LIVER. 1707 Surfaces. In its natural form, as shown in specimens hardened before removal from the body, the liver presents five surfaces. The superior surface is in the main convex, looking upward beneath the diaphragm. The anterior surface, directed forward, is continuous with the former, on the hardened liver a fairly distinct line marking the change of direction that separates them. The right surface faces towards the right and is separated in a similar way from the superior. It passes insensibly into the anterior surface. In a flaccid liver, in which the normal form has been lost, these three surfaces are indistinguishable, constituting the old superior surface. In the hardened organ the three represent a dome, of which the flattened upper surface is slightly separated from the others. The posterior surface is on the back of the right lobe. The inferior surface is moulded over the organs beneath it. The borders are best described from the posterior surface as a starting-point. The upper border of the latter separates it from the superior and right surfaces ; the lower border from the inferior. On the right these meet at a mor: or less acute angle. On the left the posterior surface narrows to a border, first thick and then sharp, which runs around the liver, separating first the upper and lower surfaces of the left lobe and later the lower from the anterior and right ones, until finally it reaches the right end of the lower border of the posterior surface. Along the front of the liver the border is sharp and directed downward, overhanging the concave lower surface. A conspicuous incision, the umbilical notch (incisura umbilicalis), in the anterior border marks the place at which a sickle-like fold of peritoneum, the falci- form ligament, conveying the obliterated umbilical vein, now the round ligament (ligamentum teres hepatis), to the lower surface, reaches the liver. The falciform ligament is continued back between the top of the liver and the diaphragm, and marks off on the anterior and superior surfaces a large right lobe and a small left one. The superior surface (Fig. 1440) includes the upper part of both lobes and is moulded to the opposed surface of the diaphragm. The top of the right lobe fills in the whole of the space below the corresponding half of the diaphragm, but the left lobe does not usually reach the walls of the abdomen, unless in front. It may, however, touch the left wall. Well-hardened livers show a slight cardiac depression on the left lobe beneath the heart. The posterior border of the superior surface is marked on the right lobe by the reflection of the peritoneum onto the diaphragm above the triangular posterior surface, and on the left by the rounded posterior border of the liver. The right and anterior surfaces lie against the diaphragm, except where the anterior rests against the abdominal wall between the costal arches, and offer little for description. The posterior surface (Figs. 1441, 1456), on the back of the right lobe, con- sists of a triangular non-peritoneal area and of the lobe of Spigelius. The former, adherent to the diaphragm, extends from the inferior vena cava to the right, where it ends in the point formed by the meeting of the upper and lower borders. The greatest vertical dimension of the non-peritoneal area is not over 7.5 cm. (3 in. ), and the transverse not over 12.5 cm. (5 in. ). A triangular hollow at the lower border of this space, just to the right of the vena cava, receives the right suprarenal capsiile, which rests also on the lower surface. To the left of this depression is a deep furrow for the inferior vena cava, which sometimes at the top is converted into a canal. Still farther to the left is the lobe of Spigelius (lobus caudatus), a four-sided prism placed vertically on the back of the liver, bounding a part of the lesser cavity of the perito- neum. The lower end, which hangs free, is continuous on the right with the caudate lobe (processus caudatus). It often presents on the left of the lower end a distinct tubercle, the tuber papillare (His), which is by no means constant. The Spigelian lobe lies between the fossa of the vena cava on the right and the fissure of the duct us venosus on the left. The latter joins the former in front of this lobe, just below the diaphragm, so that the lobe ends in a point above. It more or less encircles the vena cava, sometimes meeting the right lobe behind it. The vena cava is frequently over- lapped by a projection from the right lobe, and sometimes the overlapping is done both by this and by the lobe of Spigelius. The prismatic shape of the latter is well shown by transverse sections. The amount of attachment to the rest of the liver varies, and the shape of the lobe with it. Sometimes the fissure of the ductus 1708 HUMAN ANATOMY. venosus makes but a small angle with the portal fissure, so that it is a three- instead of a four-sided prism. It is also influenced by the depth of the fossa for the vena cava, at times being attached merely by a line of tissue. To the left of the fissure of the ductus venosus the posterior surface of the liver is continued as the posterior border. This at first is thick, and presents a rounded cesophagcal impression for the end of the gullet to the left of which it becomes sharp. The inferior surface (Fig. 1442) of the liver is subdivided by a system of fissures formerly described as resembling an H. This description must be modified by recognizing that the posterior limbs of the H are not horizontal, but run vertically on the hind surface of the liver, and that the cross-piece the portal fissure is not in the middle, but very near the posterior border of the inferior surface. The old error came from studying distorted livers in which the posterior surface had flattened out so as to be reckoned a part of the inferior. The portal or transverse fissure (porta hepatis) is of an entirely different nature from the others. It is the hilum of the organ for the passage of the vessels and ducts ; while the other fissures more properly deserve the name, being due to the pressure of the gall-bladder and of vessels. The portal fissure is from 4-5 cm. (1^2-2 in.) long. It transmits the por- tal vein, the hepatic artery, the subdivisions of the gall-duct, the lymphatics, and Spigelian FlG. 1441. Falciform ligament Fissure for. ductus venosus Vena cava N'on-peritoneal surface Suprarenal vein Tuber omentale Obliterated umbilical vein Quadrate lobe Renal impression Right lateral ligament Caudate lobe Gall-bladder Posterior surface of same liver ; peritoneal reflection indicated by white line. the nerves, all enveloped in a mass of areolar tissue known as Glissori 's capsule. The large portal vein is posterior. The hepatic artery lies before it on the left and the hepatic duct, formed by two chief tributaries, lies before it on the right. The lesser omentum is attached to the lips of the fissure outside of these structures. At its left end the portal fissure receives the umbilical fissure, which runs backward from the notch in the anterior border and contains the obliterated umbilical vein, in the adult known as the round ligament. This fissure is very often bridged over. Continuous with the umbilical fissure, the fissure of the ductus venosus ascends the posterior surface, only a small part of it being on the inferior aspect. In foetal life it contained the blood channel (ductus rcnosus) which established a short cut between the umbilical vein and the inferior vena cava ; after birth it is redm-ed to a cord of fibrous tissue ( ligamcntum venosmn). At the left end of the portal fissure the falciform liga- ment joins the lesser omentum, the latter being continued backward in the fissure of tin ductus venosus. The fossa for the gall-bladder ( fossa vcsica> fellcae) is a depres- sion on the under surface of the right lobe, in which that organ rests. It may or mav not indent the anterior border. Broad in front, the fossa narrows to a fissure behind that joins the right end of the portal fissure. The quadrilateral region on the under surface of the ri^ht lobe, bounded by the portal fissure behind, the border of the liver in front, the gall-bladder on the right, and the umbilical fissure on the left, THE LIVER. 1709 is the quadrate lobe ( lobus quadratus). Behind the portal fissure the lower end of the lobe of Spigelius appears on the inferior surface, with the groove for the vena cava on its right and the fissure of the ductus venosus on its left. The caudate lobe ( processus caudatus) is a rounded ridge, particularly developed in early life, running from the under side of the right lobe, just behind the right part of the portal fissure and in front of the vena cava, obliquely backward and to the left into the lower end of the lobe of Spigelius. A groove caused by the hepatic artery separates it from the tuber papillare. The caudate lobe overhangs the foramen of Winslow. In the adult it is sometimes rounded, sometimes sharp, and not always to be distinguished. The under side of the liver, being moulded over the neighboring organs, presents many irregularities dependent on their pressure. The posterior part of the under side of the right lobe is hollowed into the renal impression, a concavity fitting closely over the right kidney. The suprarenal capsule rests against the liver to the left of this, at the beginning of the caudate lobe on the under surface and also on the posterior surface. The first part of the duodenum rests against and moulds the under side of the right lobe between the renal impression and the gall-bladder. This area of con- FIG. 1442. Vena cava Spigelian lobe / CKsophageal impression Fissure for duct us venosus lateral ligament Hepatic arter |^P-x- / -pi , _C,,lic impression Common bile-duct' / II Obliterated umbilical vein / j yuadrate lobe / ^^^^ Cystic duct Gall-bladder Inferior and posterior surfaces of same liver. It must be clearly understood that the Spigelian lobe and vena cava are on the posterior surface, the limit of the inferior surface behind being the transverse fissure. tact can hardly be called an impression, for the surface here is slightly convex. In front of the renal impression is a hollow for the colon of very varying size. It may be almost wanting, or it may be very deep. It may be confined to the right part of the under surface, or it may compress the front of the gall-bladder and indent the quadrate lobe, and even the left one. The under side of the right lobe presents also one or more occasional fissures which seem in the main to diverge from the right end of the portal fissure and from the fossa for the gall-bladder. They are more common in the foetus, and some of them occur more or less frequently in anthropoid apes. 1 The under side of the left lobe is in general concave, resting against the fundus and anterior wall of the stomach. Near the posterior part of the umbilical fissure on the left lobe is a rounded prominence, tuber omeniale, due to the growth of the liver against the non-resisting lesser omentum. The Blood-Vessels. The portal vein, some 15 mm. or more in diameter, divides into a right and a left branch, 10 mm. or over in diameter, of which the right is a little the larger and shorter. From the right end of the transverse fissure it runs 1 Thomson : Journal of Anatomy and Physiology, vol. xxxiii., 1899. ryio HUMAN ANATOMY. backward in a curve to the right of the vena cava, keeping in the lower part of the liver and giving off successively a series of large branches to the front and right of the organ. Smaller branches arise from the sides of these. The right primary division soon gives off a large superior branch almost equal to itself, which describes a similar but smaller curve at a higher level. The general course of the left subdi- vision is towards the posterior angle of the organ, giving branches chiefly from its anterior side, and also one that supplies the greater part of the quadrate lobe. The lobe of Spigelius generally receives a chief branch near its lower end, which runs upward within it. This branch is most often from the left subdivision, but it may be from the right, or from the vessel directly behind the end of the portal vein. There are several systems of so-called accessory portal veins around the liver in the lesser omentum near the gall-bladder, about the diaphragm, and, most important, in the falciform ligament, where the par-umbilical veins communicate with veins of the integument of the abdominal walls. These accessory vessels, small and incon- spicuous under normal conditions, may become enlarged and important channels FIG. 1443- ;\ Portions of inferior and posterior surfaces of liver have been removed to show injected blood-vessels and bile- ducts. Vena cava is somewhat displaced forward, its course being more venical when supported on posterior sur- face. Large upper branch of right division of portal vein is hidden by liver-substance. Portal vein ami branches are purple ; hepatic artery, red ; hepatic veins and vena cava, blue ; bile-ducts, yellow, uv, obliterated umbilical vein ; vc, inferior vena cava. for the return of the blood conveyed by the portal vein when the hepatic circula- tion is obstructed. Under such conditions the blood finds its way from the portal vein into the accessory veins and by the anastomoses of the latter into the general circulation. The hepatic veins carrying off the blood from the liver arise as the intra- lobular veins, which empty into the siiblobular, which join larger vessels conver^in^ towards the vena cava. At first the general direction of the small branches is paral- lel to that of those of the portal system of the same size ; but the hepatic branches always travel alone. The direction of the large branches as they near the vena cava is at right angles to that of the portal. The arrangement of the hepatic branches is in the main like that of the portal, but near the edge of the liver we find more instances of the union of two rather small trunks meeting symmetrically like the arms of a Y. The main trunks of the right lobe run between the upper and lower branches of the portal. The upper end of the vena cava is considerably enlarged, and immediately below the diaphragm receives two large hepatic veins, a right and a left one, from 15 to 20 mm. in diameter. The latter is formed by two large branches that unite just before its end. Many small veins open into the vena cava at different THE LIVER. 1711 points along its course in the groove on the posterior surface of the liver, several coming from the Spigelian lobe. Sometimes quite a large branch from the right lobe opens at a low level. There is no such thing as an hepatic vein in the adult considered as an isolated structure. The ramifications of the portal and hepatic veins are inextricably mingled throughout, but in the main the branches of the latter lie above those of the former (Fig. 1443). The hepatic artery, the nutritive vessel of the liver, divides into two branches which, together with the bile-duct, accompany the portal vein, the two arte- ries generally being on the same side of the vein. The hepatic artery gives off so many branches in its course as to be almost or quite of capillary size when it reaches the twigs of the portal vein that break up into the intralobular net-work. The blood conveyed by the hepatic artery is distributed by three sets of branches, the capsular, the vascular, and the lobular. The first ramify within the connective-tissue envelope of the organ and anastomose with branches from the internal mammary, phrenic, cystic, suprarenal, and sometimes right renal. The second supply the structures between the lobules, especially the walls of the ramifications of the portal vein and the bile- ducts. The third are small in size, and accompany the intralobular branches of the portal vein for a short distance within the lobule. There is no special system of veins to return the blood carried by the hepatic artery to the venous trunks outside the organ, the minute veins collecting the blood from the capsular and vascular sets being tributaries usually of the smaller branches of the portal vein. The blood passing through the lobular arterioles is emptied into the intralobular capillary net- work. The lymphatics of the liver constitute a superficial and a deep set, the former lying beneath the peritoneum, the latter within the deeper interlobular connective tissue. The superficial lymphatics of the superior surface are arranged as three groups, posterior, anterior, and superior. The posterior group forms a right trunk which passes from the right triangular ligament across the right crus of the dia- phragm to the cceliac lymph-nodes. Middle trunks from five to seven in number accompany the inferior vena cava to end in diaphragmatic nodes around the vein. Left trunks traverse the left triangular ligament and terminate in the cesophageal nodes surrounding the lower end of the gullet. The anterior group passes in the op- posite direction to those just described and, crossing the anterior border of the liver, empties into the hepatic lymph-nodes within the lesser omentum. The superior group, the most important of those of the upper surface, ascends within the falciform ligament. A number of anastomosing vessels form a posterior trunk which crosses the inferior vena cava and enters the thorax with the latter, to end in the lymph-nodes around the vena cava. An anterior trunk accompanies the round ligament to the infe- rior surface and ends in the hepatic nodes at the hilum. Numerous middle trunks form vessels which pierce the diaphragm, to end in the anterior mediastinal nodes, becoming tributaries to the right lymphatic duct. The superficial lymphatics of the inferior surface include, on the right lobe, a posterior group, accompanying the vena cava into the thoracic cavity, to end in nodes around that vein, a middle group passing to the hepatic nodes around the cystic duct, and an anterior group terminating in the same nodes as the preceding. On the left lobe the vessels pass to the nodes of the hilum and about the hepatic artery. The lymphatics of the Spigelian lobe pass partly to the hilum nodes and partly to those surrounding the thoracic segment of the infe- rior vena cava. Communications exist between the superficial and deep lymphatics. The deep lymphatics include two distinct groups, the one following the branches of the portal vein, the other accompanying the hepatic veins. The first descends within the capsule of Glisson in company with the portal vein and other interlobular vessels. On emerging at the hilum, the fifteen to eighteen trunks, arranged as two groups at the ends of the transverse fissure, join the hepatic nodes. The lymphatics which accompany the hepatic veins form a plexus surrounding the blood-vessels and proceed towards the vena cava, with which they pass through the diaphragm to enter the nodes lying immediately above the caval opening. The nerves are chiefly derived from the solar plexus of the sympathetic with some fibres from the left pneumogastric which reach the liver by passing from the anterior surface of the stomach between the layers of the lesser omentum. The 1712 HUMAN ANATOMY. sympathetic fibres accompany the hepatic artery, forming the hepatic plexus, to the transverse fissure, where, together with the fibres from the vagus, they pass into the liver along with the interlobular vessels, to the walls of which they are chiefly distributed. According to Berkley, the interlobular plexuses give off fine intralob- ular twigs which terminate between the liver-cells. STRUCTURE OF THE LIVER. In its fundamental arrangement the liver corresponds to a modified tubular gland, the system of excretory ducts of which is an outgrowth from the primary gut-tube. Early in foetal life, however, the terminal divisions of the tubules unite to form net-works, after which the tubular character of the liver becomes progressively FIG. 1444. Portal vein Blood-capillaries Central vein Blood-capillaries Portal vein Hepatic artery Bile-vessel Bile-vessel Blood-capillary Hepatic cords Bile-vessel Portal vein Bile-capillaries Blood-capillaries Portal vein Suhlobular branch of hepatic vein Diagram of hepMtic lobule ; portion-; of figure represent median longitudinal section of lobule ; parts of transv sections also shown. Branches of portal vein :ue purple ; of hepatic artery, red ; of bile-ducts, yellow. Intralobular bile-capillaries are black. more masked by the intergrowth of the cell-cords and the large veins. Among some of the lower vertebrates, as in certain vermiform fishes or cyclostomes (Afvxtne), the primary tubular arrangement is retained. The glandular tissue composing the liver is subdivided into small cylindrical masses, the lobules, by the connective tissue which, in continuation of the fibrous STRUCTURE OF THE LIVER. 1713 envelope, or capsule, investing the exterior, at the transverse fissure enters the organ and accompanies the interlobular vessels in their ramifications as the capsule of Glisson (capsula tibrosa). The distinctness with which the lobules are defined depends upon the amount of this interlobular tissue. In certain animals, notably in the hog, this is great, the lobules being completely surrounded and plainly dis- tinguishable as sharply marked polygonal areas. In the human liver, on the con- trary, the interlobular connective tissue is present in small amount, the lobules, in consequence, being poorly defined and uncertain in outline. The Lobular Blood-Vessels. Since the arrangement of the blood-vessels is the salient feature in the architecture of the fully formed lobule, it is desirable to study the vascular distribution before considering the disposition of the hepatic cells. As already described, the branches of the portal vein, the functional blood-vessel of the organ, ramify within the capsule of Glisson and encircle the periphery of the lobule ; inasmuch as these vessels supply the divisions of glandular tissue with blood for the performance of their secretory role, they correspond with the inter- lobular arterioles of ordinary glands. Numerous minute branches are given off from the interlobular ramifications of the portal vein which enter the periphery of the adjacent lobules and break up into Central vein "Hi Section of liver injected from hepatic vein, showing intralobular capillary net-work. X 100. the intralobular capillary net-work. The disposition of the latter is in general radial, the capillaries converging towards the middle of the lobule, where they join to form the central or intralobular vein, the beginning of the system of the hepatic veins by which the blood passing into the lobules is eventually carried into the inferior vena cava. The general course of the central vein corresponds to the long axis of the lobule (Fig. 1444), and hence in cross-sections of the latter the vein appears as a transversely cut canal towards which the capillary vessels converge (Fig. 1445). The capillary net-work within the lobule is composed of channels with a diameter usually of about .010 mm. ; the widest capillaries some .020 mm. in diameter are found in the immediate vicinity of the afferent and efferent veins, the narrowest occupying the intermediate area. The meshes of the vascular net- work vary from .OI5-.O4O mm. in their greatest dimension, those at the periph- ery being broader and more rounded, while those near the centre are narrower and more elongated. The central vein occupies the long axis of the lobule and increases in size as it proceeds towards the base of the lobule, as the side of the latter through which the vein escapes is termed. It begins usually about midway 108 I7H HUMAN ANATOMY. between the base and the opposite side of the lobule, by the confluence of the capil- laries, which, after the central vein is formed, open directly into the latter at lower planes. In those lobules which form part of the exterior of the liver the central vein ascends almost to the free surface ; otherwise its commencement is separated from the periphery by about one-half the thickness of the lobule. Im- mediately on emerging from the lobule the central vessel opens into the sublobular vein, which runs generally at right angles to its intralobular tubularies and along and beneath the bases of the lobules, the outlines of which are often seen through the walls of the vein. The channels for the sublobular veins are thus surrounded by the bases of the lobules, a single central vein returning the blood from each. The Hepatic artery Portal vein Bile-duct Centra] (intra- lobular) vein Interlobular connective tissue Section of uninjected liver, showing Ki-iu-ral arrangement of lobules, interlolmlui and intralobular vessels. X 120. sublobular veins join to form larger vessels, which in turn unite and constitute the branches of the hepatic veins. The Liver-Cells. The meshes of the interlobular capillary net-work are oc- cupied by the hepatic cells, the bile-capillaries, and a meagre amount of connective tissue. The cells are arranged as cords or trabecuke which conform in their general disposition to the intercapillary spaces, which they completely fill. In a sense, the entire lobule consists of a solid mass of hepatic cells elaborately tunnelled by the radially coursing capillaries and their short anastomosing branches, the proportion of the space occupied l>v the' vascular channels to that filled by the cells being ap- proximately as one to three. When isolated, the liver-cells present a polygonal STRUCTURE OF THE LIVER. 1715 outline and measure usually from .01 5-. 025 mm. in their longest dimension. Each cell comes into contact with from six to nine other elements, the surfaces of contact being- plane from mutual pressure. Always one side, often more than one, exhibits a shallow depression which indicates the surface of former contact with a capillary and emphasizes the intimate relation existing between the blood-vessels and the cells. The latter lie against at least one capillary and sometimes several, this relation being dependent upon the size of the blood-channels. The larger the latter, as at the periphery and near the centre of the lobule, the greater the number of cells with only one or two capillary facets ; conversely, where the capillaries are of small diameter, the cells come into contact with three or four. The liver-cell consists of finely granular protoplasm which sometimes exhibits a differentiation into an outer and an inner zone. It is without a cell-membrane, although the peripheral zone of its cytoplasm is condensed, especially when it forms part of the wall of the bile- canaliculi. The nucleus, of vesicular form and from .006-. 008 mm. in diameter, contains a small amount of chromatin and usually a nucleolus. Occasional cells are conspicuous on account of their large size, as well as the unusual diameter of FIG. 1447- - . IS, Section of uninjected liver, showing cords of hepatic cells between capillary blood-vesseis. v 450. their nucleus. Such cells, according to Reinke, 1 undergo direct division and pro- duce the double nucleated elements constantly encountered in sections of normal liver. Centrosomes have also been observed in resting hepatic cells. Particles of glycogen, minute oil droplets, and granules of bile-pigment are more or less constant constituents of these elements. The fat-containing cells are most numerous at the periphery of the lobule, those enclosing pigment particles near the centre. The Bile-Capillaries. These minute canals, representing the lumena of ordinary tubular glands, form a net-work of intercommunicating channels throughout the lobule closely related to the liver-cells. Whereas in the usual arrangement a single surface of several gland-cells borders the lumen, in the exceptional case of the liver the excretory channels are bounded by the opposed surfaces of only two cells, the bile-capillary occupying but a small part of the surfaces, on each of which it models a narrow, centrally situated groove. Moreover, not only a single surface of the hepatic cell takes part in bounding the canaliculi, but the latter are found between all surfaces where two liver-cells are directly in contact, so that each hepatic element comes into direct relation with a number of bile-capillaries. The latter, 1 Verhandlung d. Anatom. Gesellschaft, 1898. HUMAN ANATOMY. however, never lie on the narrow sides of the liver-cells opposed to the blood- vessels, the bile-canal never separating the blood-capillary from the cell. While the predominating direction of the bile-capillaries is radial and corresponds to the Blood-capillary Bile-capillary Liver-cell FIG. 1449. Section of liver in which both blood- and bile-capillaries have been injected ; the latter surround the individual liver- cells. X 3- similar general disposition of the cylinders or leaflets of hepatic tissue, the radial arrangement is converted into a net-work by the numerous cross- branches. The resulting meshes correspond in size with the individual liver-cells, which, in appro- priate sections, often appear almost com- pletely surrounded by the bile-capillaries. The latter possess no walls other than the substance of the liver-cells between which they lie. The diameter of the bile-capil- laries, from .OOI-.OO2 mm., remains prac- tically the same throughout the lobule until the canaliculi reach the extreme periphery. At this point the liver-cells abruptly dimin- ish in height and are transformed into the low cuboidal cells lining the excretory tubes that pass from the lobule into the surround- ing connective tissue to become tributaries to the larger interlobular bile-ducts. The ultimate relations between the bile-capillaries and the liver-cells is still a subject of discussion. Based upon the evi- dence supplied by injections and silver impregnations, it is believed by some (Kupffer, R. Krause, and others) that ex- tensionsof the bile- capillaries normally exist within the substance of the cells, thus form- ing intracellular secretion catialiculi. The latter are sometimes pictured as ending in connection with minute dilatations or accretion vacuolcs. It is by no means certain that such appearances are not artifacts, or at least due to changes after death of Section of liver treated by Goljji silver meth< showing part of intralobular m-t \voik of bili-capil- l:u U-s. X 200. STRUCTURE OF THE LIVER. 1717 FIG. 1450. the cells. The secretion vacuoles, probably due to the coalescence of minute drops of bile, exist only as transient details, and cannot be regarded as constant features of the hepatic cells. Holmgren 1 asserts the existence of " juice-canaliculi" within the liver-cells in addition to and independent of the intracellular secretion channels. Schiifer 2 has described nutritive channels within the liver-cells which communicate with the blood-capillaries. The intralobular connec- tive tissue, or reticulum, consists of delicate prolongations of the fibrous tissue of Glisson's capsule which unite the blood-capillaries and cords of liver-cells. This tissue, in general meagre in amount, forms a delicate reticulum extending be- tween the blood-channels and the glandular elements throughout the lobule, and connects the peripheral fibrous tissue with the perivascular tissue that exists around the central vein in considerable quantity. In addition to the delicate fibres of the intralobular reticulum, the perivas- cular tissue contains lymph-spaces and connective-tissue elements, the Artificially digested section of liver, showing supporting inter- Cells Of Knpjjer. I he latter are lobuiar fibrous tissue and intralobular reticulum. x 230. small spindle or stellate and lie in close relation with the blood-vessels, their processes penetrating for a limited distance between the adjacent liver-cells. The interlobular bile-ducts, which receive the biliary canals that pierce the periphery of the lobule as the outlets of the intralobular net-work, accompany the FIG. 1451. Fibrous tissue Reticulum Portal vein Bile-duct Hepatic artery Interlobular connective tissue Hepatic ceils Section of liver, showing interlobular tissue and vessels. X 160. branches of the portal vein and the hepatic artery within the capsule of Glisson. These ducts, from .030-. 050 mm. in diameter, constitute a net-work over the exterior 1 Anatomischer Anzeiger, Bd. xxii., No. i, 1902. 2 Ibid., Bd. xxi., No. i, 1901. iyi8 HUMAN ANATOMY. surface of the lobule. They consist of a dense fibre-elastic coat lined with cylindri- cal epithelium, some .020 mm. thick, which latter is continued into the low cuboidal or flattened cells that form the lining of the excretory channels connecting the intra- lobular net-work of bile-capillaries with the bile-ducts. Beginning as the small vessels that surround the lobules, they become tributary to the larger bile-ducts, which increase in diameter as they approach the transverse fissure. In the vicinity of the latter these trunks join into the two main lobular ducts forming the hepatic duct. The largest bile-vessels possess bundles of unstriped muscle which in the hepatic duct are arranged principally as a longitudinal layer, supplemented by cir- cular and oblique bundles (Hendrickson). Gall-bladder Hepatic duct Cystic duct THE BILIARY APPARATUS. In addition to the small interlobular bile-vessels already described, the system of canals receiving and conveying the secretion of the liver to the intestinal tract consists of the hepatic duct, the excretory tube of the organ ; the gall-bladder, a res- ervoir in which the bile ac- FIG. 1452. cumulates during intervals of digestion ; the cystic duct, the continuation of the bile- sac opening into the side of the hepatic duct ; and the common bile-duct, which, al- though formed by the union of the other two, is in struc- ture and direction really the continuation of the hepatic duct. The hepatic duct (due- tus hepaticus) is formed be- low the hilum by the union of its two a right and a left chief tributaries. The latter issue from the portal fissure, one on each side, and generally unite with the hepatic duct nearly in the shape of a T, the last-named canal forming almost a right angle with each of its tribu- taries. Tracing the chief ducts into the liver, the left branch runs at first in front of the left division of the portal vein, while the right one usually crosses it. We have seen the hepatic duct issue from the right lobe and, forming a loop in the fissure, leave it with the K ft division of the portal vein, receiving branches along its convexity from the various parts of the liver. Sometimes the chief ducts are longer than usual, and meet to form the hepatic duct at an acute angle farther from' tlu liver. The length of the hepatic duct, therefore, varies with these details, proba- bly being usually from 20-40 mm. (^-i^ in.), with a diameter of from 4-6 mm. It lies in the gastro-hepatic omentum, in front of the portal vein and to the right of the hepatic artery, and inclines downward to the inner side of the second part of the duodenum, resting previously on the top of the first part. The hepatic duct Vena cava Probe in foramen of Winslow Portions of liver, duodenum, and pancreas, showing biliary and pancreatic ducts; head of pain n-as turned back. THE BILIARY APPARATUS. 1719 ends at the point at which the cystic duct opens into it. The duct is lined with mucous membrane, covered with simple columnar epithelium, and presents many minute pits, into which open the orifices of numerous small tubular glands. Its walls consist of fibro-elastic connective tissue and unstriped muscular fibres. The latter, neither numerous nor separated into a distinct layer, are grouped for the most part into longitudinal bundles, but there are also circular and oblique ones. 1 The gall-bladder (vesica fellea) is a pear-shaped receptacle for the bile, rest- ing in its fossa on the under side of the liver, with the large end forward. The long axis runs also somewhat inward. The length is from 8 10 cm. (3^4 in.) and the capacity some 50 c.c. (about i% fl. oz. ). It narrows to a point where it usually bends to the left and ends in the cystic duct without definite external demarcation. The bent terminal portion, or neck, about i cm. long, is more or less closely bound beneath the peritoneum to the side of the gall-bladder, so that before this is separated it sometimes looks as if the duct arose from the side of the latter. The fundus of the gall-bladder lies near the end of the ninth right costal carti- lage. The neck is at the right end of the portal fissure. Anteriorly the bladder rests on the transverse colon, behind which it lies first to the right of and then above the first part of the duodenum. FIG. 1453- ll-bladder Surface view of portion of mucous membrane of gall- bladder. X 12. Portion of gall-bladder and biliary passages laid open, showing surface of mucous membrane. Natural size. The wall of the gall-bladder is very resistant, being composed of a mixture of fibrous tissue and of unstriped muscular fibres. Most of the latter are disposed circu- larly, but oblique and longitudinal ones are interwoven. The fibro-muscular tunic is lined by a layer of mucous membrane which is very adherent to it. The mucous membrane, covered with simple columnar epithelium, presents slightly raised ridges marking off a net-work of small irregular spaces some 5 mm. in diameter. The small bifurcated tubular glands are few and may be wanting. The bent portion, or neck, is separated from the bladder by a strongly raised fold. There are, or may be, one or two smaller folds within the neck, the separation of which from the duct is usually arbitrary. Vessels of the Gall- Bladder. Arteries. The chief distribution of the cystic artery, a branch of the hepatic, is on the free under surface, which it ap- proaches from the left, running on the cystic duct. There is a smaller branch which lies deeply on the right between the gall-bladder and the liver-substance. Veins. The superficial veins join the cystic artery and empty into the right division of the portal vein. According to Sappey, a number of small veins run directly into the liver-tissue joining the portal system. The lymphatics, for the most 1 For the musculature of the biliary apparatus, see Hendrickson : Johns Hopkins Hospital Bulletin, Nos. 90, 91, 1898. 1720 HUMAN ANATOMY. FIG. 1455. part, empty into the nodes in the portal fissure. Some open into a node said to lie in the angle at the bend of the neck. The nerves are from the solar plexus through the hepatic plexus. The peritoneal relations of the bladder and ducts are considered with those of the liver (page 1721). The cystic duct (ductus cysticus), 3 or 4 cm. in length, with a diameter of from 23 mm., passes in a fold of peritoneum from the neck of the gall-bladder to the gastro-hepatic omentum, where it joins the hepatic duct at an acute angle or, rather, opens into its side. It is said sometimes to present an enlargement at its end. In its natural condition it looks externally like the other ducts, but if distended and dried it presents a series of irregular folds giving the impression of a spiral fold which, in the adult at least, a closer inspection does not confirm. Structure. In structure the cystic duct presents much more of a muscular layer than the others. This is thickest at the upper part, and consists chiefly of circular fibres. These enter, especially near the beginning, the valvular folds of the mucous membrane, which is clothed with simple columnar epithelium. In the foetus there is a fairly distinct spiral valve, most developed in the upper part, and, in fact, starting in the neck of the gall-bladder. Later the continuous spiral ridge (valvula spiralis Heisteri) usually atro- phies and is broken up at many places, leaving detached folds with a semilunar outline and no longer distinctly spirally ar- ranged. Little pockets also de- velop between them. Small tubular glands are few in the upper part, but plentiful in the lower. The common bile-duct (ductus choledochus) is about 7 cm. (2^4 in. ) long. Its diam- eter is from 67 mm. at the commencement and rather less at the end. Beginning imme- diately below the transverse fissure, although conventionally regarded as formed by the union of the cystic and the hepatic ducts, being, in fact, the direct continuation of the latter, the common bile-duct passes down- ward between the layers of the gastro-hepatic omentum, in front of the foramen of Winslow, with the hepatic artery to its left and the portal vein behind. It descends along the postero-inner aspect of the bend joining the first and second parts of the duodenum, then along the inner side of the second part, where it is more or less surrounded by the head of the pancreas. Near its termina- tion it meets the pancreatic duct and, in company with the latter, pierces the duo- denal wall, which it traverses obliquely for the distance of some 15 mm., to empty into the duodenum at a papilla marking the common orifice of the two ducts. This papilla is situated near the posterior border of the internal aspect of the descending part of the duodenum, from 9-10 cm. (about 3^-4 in.) from the pylorus. In the natural condition it is not easy to find, being situated beneath a transverse fold and not being prominent in the shaggy mucous membrane. Its length umlistended is only about 5 mm. When inflated or injected it is a prominent object more than twice as large. Moreover, it does not project freely, but lies on its side pointing downward, the surface next to the wall becoming free only very near its end. The orifice looks downward. It may be oval or circular, with a diameter of from 1-2 mm. A slight vertical fold, the frenum, often runs downward from the opening for the Bile-du Ampulla Pancreatic duct A, portion of duodenum, with anterior wall removed, showing entrance of bile and pancreatic ducts; B, papilla laid open, showing floor of ampulla. One-half natural size. THE BILIARY APPARATUS. 1721 distance of I cm. The structure of the common duct is much the same as that of the hepatic, containing but little muscular tissue and that not well denned. The papilla contains a fusiform dilatation, the ampulla (of Vater), which may be i cm. broad when distended. Into this the bile-duct and the duct of the pancreas usually open by a common orifice. Be these orifices common or distinct, each is sur- rounded by an accumulation of the circular muscular fibres which amounts to a sphincter. The glands, which are found throughout the common duct, are particu- larly large and numerous in the ampulla. Ligaments and Peritoneal Relations. The term "ligament," applied to the folds of serous membrane, is entirely inappropriate. It is in part retained, but the enumeration of five ligaments as separate entities is antiquated. The round ligament (ligamentum teres hepatis) is a cord of fibrous tissue, the remains of the obliterated umbilical vein, running from the umbilicus to the left end of the portal fissure. Its continuation, the ductus venosus, is represented by fibrous tissue (liga- mentum venosum ) in the fissure of that name. The round ligament lies against the abdominal wall for an inch or more above the navel and then passes backward in the free edge of the falciform ligament, a fold of peritoneum presumably detached from the anterior wall and from the diaphragm by the development of this vein. The FIG. 1456. CEsophageal impression Vena cava Left coronary ligament Fissure of ductus venosus Spigelian lobe Portal vein Caudate lobe, left end Right coronary ligament Posterior non-peritoneal surface Right triangular ^/"-ligament Suprarenal impression Renal impression Vena cava I Colic impression Posterior surface of liver, showing peritoneal reflections. front part of the falciform ligament is appropriately described as sickle-shaped. The point is in front, and it grows broader as it passes backward until it reaches the liver, where, growing narrower, it extends above the liver to the spine at about the median line. It contains very little tissue between its folds, which are reflected on either side over the superior surface of the liver. At the notch in the anterior border the round ligament passes onto the inferior surface of the liver in the umbilical fissure. The coronary ligaments are differently arranged on the two sides. The right one is made by the two reflections onto the diaphragm from the. upper and lower borders of the part of the posterior surface adherent to it. These come together at the right of that surface and are continued as a fold, the right triangular ligament, on the right surface, connecting it to the diaphragm in the flank by a line of attach- ment some 5 cm. long. On the top of the left lobe, but not on the posterior bor- der, there is a small area without peritoneal covering, enclosed by the two folds of the left coronary ligament, of which the anterior is analogous to the right one, but the posterior begins at the left of the upper end of the fissure of the ductus venosus. They soon unite to form the left triangular ligament, which lies between the dia- phragm and the top of the left lobe, being considerably longer than the right one. 1722 HUMAN ANATOMY. On the under side of the liver the end of the round ligament lies in its fissure cov- ered by a slight fold of peritoneum. The same is true of the gall-bladder. Some- times the latter is more or less surrounded, and it may be almost completely so, hanging from the fossa by a fold. The lesser or gastro-hcpatic amentum is a fold enclosing the vessels in the portal fissure and passing to the lesser curvature of the stomach and the first part of the duodenum. A secondary fold containing the cystic duct, the duodena-cystic fold, joins it on the right. Near this it presents a free border forming the edge of the foramen of Winslow. On the left it runs along the fissure of the ductus venosus to the notch in the liver made by the passage of the oesophagus. There its left layer is reflected as the under one of the left coro- nary ligament, while the right layer descends along the left of the vena cava to join the right inferior coronary ligament. The posterior surface of the Spigelian lobe is covered with peritoneum which is almost surrounded by these lines of attachment, but is continuous, by means of the caudate lobe, with the serous coat of the under surface of the right lobe. Thus a pocket is roofed in behind the lobe of Spigelius. FIG. 1457. Pericardial fat IV rib Cavity of__ pericardium V rib- Inferior vena cava VI rib VIII rib Aorta IX rib Major azygos vein X thoracic vertebra Transverse section at level of tenth thoracic vertebra, upper surface of diaphragm exposed, showing relation viscera ; outline of liver, ; of stomach, ; of colon, o o o o o ; of spleen, x x x x x. The hepatic duct lies within the lesser omentum to the right and in front of th( portal vein. It is joined by the cystic duct in its fold, already mentioned. As it leaves the gall-bladder, the duodeno-cystic fold is a distinct duplicature which joins the lesser omentum at an angle ; but at the lower part, where the cystic duct opens into the hepatic, the folds become one. The common bile-duct may be in the very lowest part of the lesser omentum, where it is attached to the postero-inner surface of the duodenum where the first part bends down to become the second ; but the relations are variable, and the common duct may have no peritoneal relation. Position of the Liver. The relations to other organs have been treated in the account of the surfaces. The relations to the walls of the abdomen can be given only in general, owing to the variations of both the organ and the thorax in size and shape. The liver lies under the dome of the diaphragm, which separates it from the ribs. Occasionally it extends across the whole breadth of the abdomen, but the left lobe may end at the left mammary line. The highest point is on the THE BILIARY APPARATUS. 1723 right, where, after death, it reaches to the level of the sternal end of the fifth costal cartilage. It is doubtful whether in life the liver is ever quite so high. On the left it is about i cm. lower, and in the middle it is not more than 2 cm. lower still. The relation of the left lobe to the floor of the thorax varies considerably. If large, the organ may extend to the left wall, but this is rather uncommon. The liver may reach the front wall as far to the left as the mammary line, in which case it will be below nearly the whole of the floor of the pericardium, although it may not lie below the anterior part. It always passes just in front of the cesophageal opening. The inferior border rests against the posterior wall on the right, the diaphragm of course intervening, at the right border of the right kidney near the end of the last rib, on about the level of the second lumbar spine, and descends to the right along the line of the eleventh rib. At the mid-axillary line it begins to rise, following pretty closely the border of the thorax, to the ninth and tenth costal cartilages, VI FIG. 1458 VII rib-cartilage Transverse fissure i-cartilage \ Left lobe ' sc iibbuie Falciform ligament Quadrate lobe VII rib VIII rib IX ri Left supra renal body X rib .Spigelian lobe .Right supra- renal body XI rib Diaphragm XII rib, head 1 Diaphragm XII thoracic vertebra Frozen section across body at level of twelfth thoracic vertebra. after which it crosses the epigastrium to strike the left costal arch at the eighth car- tilage. The notch for the round ligament is a little to the right of the median line and the fundus of the gall-bladder at or near the end of the ninth right cartilage. It is usually crossed by a vertical line from the middle of the clavicle. 1 In the re- cumbent position the liver gravitates to the top of the abdomen, so that normally in the male no portion is left below the costal arch except near the middle. The inferior vena cava runs in a groove on the back of the organ, but the aorta, passing the diaphragm at a lower point, has the latter muscle between them. The vena cava pierces the diaphragm at the level of the body of the ninth thoracic vertebra. The lungs, especially the right, overlap the liver very considerably. Development and Growth. Very early, in the human embryo of 3.5 mm. in length, a groove-like evagination appears on the ventral wall of the gut-tube, immediately above the widely open vitelline duct. This evagination, the first indi- cation of the hepatic anlage, extends into the primitive ventral or anterior mesentery 1 Carmichael : Journal of Anatomy and Physiology, vol. xxxvii., 1902. 1724 HUMAN ANATOMY. which connects the stomach and the duodenum with the anterior body-wall. The hepatic diverticulum grows forward and upward into the anterior mesentery until it comes into relation with the imperfect partition which partially separates the thoracic and abdominal divisions of the body-cavity. This partition, the septum transversum, primarily consists of lateral folds, projecting at right angles from the anterior mesen- tery, caused by the large vitelline veins traversing the anterior mesentery on their way to the sinus venosus of the early heart. The relation of these structures is more fully considered in connection with the development of the diaphragm ( page 1701); for the present purpose it is sufficient to note that the liver-anlage early comes into relation with the septum transversum. The ventral portion of the pri- mary liver-evagination, clothed with the entoblastic lining of the gut-tube, very soon differentiates into two diverticula : the one nearer the head, or hepatic division, pro- duces the liver proper ; the other, or cystic division, later becomes the gall-bladder and its duct. These divisions are gradually removed from the primitive duodenum by the growth of the primary diverticulum, which at one end becomes converted into a tube connected with the digestive canal and at the other bifurcates into the hepatic and cystic channels. This tube, evidently later the common bile-duct, is at first short and wide, but later rapidly lengthens. FIG. 1459. Septum transversum Hepatic diverticulum Liver-anlage Cystic diverticulum Cut-tube V N V vr '< f */'"'*' .* . f <| Portion of sagittal section of early rabbit embryo, showing liver-anlage and ducts. X 95. The cells lining the longer hepatic diverticulum undergo marked proliferation and produce the liver-mass which invades the septum transversum almost as far as the sinus venosus and surrounds the vitelline veins. The formation of the liver-mass follows at first the type of development seen in tubular glands, outgrowths of the hepatic tube branching and subdividing to form solid sprouts and buds composed of epithelial cells. In some of the lower animals, as the amphibians, the tubular type is retained in the adult organ; but in the higher forms, including man, the tubular character of the young liver is soon lost and replaced by the reticular arrangement produced in consequence of the growing together and union of the terminal divis- ions of the gland. Coincidently with the formation of the net-work of glandular tissue by the junction of the cylinders of hepatic cells, the meshes of the reticulum become occu- pied by blood-vessels derived from vitelline veins. These are now represented at the hepatic anlage by venous stumps from which numerous afferent branches (vfn- hepaticce advchentes} penetrate the liver-mass to become the portal system. The division, subdivision, and union of these blood-vessels keep pace with the increasing complexity of the net-work of hepatic cords, the intergrowth of these constituents eventually leading to the intimate relations between the hepatic secreting tissue and the intralobular capillaries seen in the fully developed organ. The cell-trabeculae composing the primary hepatic net-work are partly solid and partly hollow ; the THE BILIARY APPARATUS. 1725 bile-duct latter, with a portion of those without a lumen, are converted into the system of bile-canals, while the remaining cylinders give off additional sprouts which reduce the intervening meshes and increase the solidity of the organ. The solid cylinders of secreting tissue at first contain no bile-capillaries. The latter are hollowed out between two adjacent cells as extensions of the meanwhile differentiating biliary ducts. Differentiation of the developing liver into lobules does not occur until the beginning of the fourth foetal month, by which time the larger blood-vessels and bile-ducts become surrounded by condensations of the mesoderm which form the capsule of Glisson. The details of the formation of the hepatic blood-vessels are considered in con- nection with the development of the veins (page 928). It may be here men- tioned, however, that the primary circulation of the liver, including the portal vein, the intralobular capillary net-work, and the hepatic veins, is derived from the modi- fication of the vitelline veins, in conjunction with their tubularies from the digestive organs. The relations of the placental circulation to the liver are secondary. The left umbilical vein for a time pours practically all the blood returned from the placenta into the portal vessel ; when the latter is no longer capable of receiving the entire amount of the placental blood, the development FIG. 1460. of the ductus venosus brings relief by establish- ing a short cut by which the excess of placental blood passes directly into the ascending vena cava. The development of the gall-bladder and its duct proceeds, as already indicated, from the more caudally placed cystic di- vision of the primary he- patic diverticulum. The subsequent changes in- clude the growth and ex- pansion of the terminal portion of the primitive cystic canal to form the bile-sac, its elongated stalk becoming the cystic duct, while differentiation of the entoblastic lining and the surrounding mesoblast produces the distinguishing details of the fully formed organs. With the conversion of the primary liver-mass into the more definite organ, the relations of the ventral mesentery, into which the early liver-anlage grows, become changed. For a time the developing liver lies within the septum transversum, but later, with the formation of the diaphragm, it separates from the latter and projects into the body-cavity. This projection results in a differentiation of the ventral mesentery into three parts : (a) the middle portion, the layers of which become separated by the growing liver to form its serous investment ; () the anterior portion, which extends from the front surface of the liver to the umbilicus and becomes the falciform ligament enclosing the umbilical vein, later the ligamentum teres ; (c) the posterior portion, which stretches between the digestive tube and the liver and, as the gastro-hepatic, or lesser omentum, maintains similar relations and encloses the biliary ducts. In the foetus the liver is relatively immense, especially at an early period. At the fourth fcetal month it practically fills the whole of the top of the abdomen. Although it increases absolutely after this, it relatively diminishes, but at birth is still considerably above the relative size of the adult organ, forming approximately one- Portion of sagittal section of rabbit embryo, showing developing liver and ducts. X 95- 1726 HUMAN ANATOMY. eighteenth of the entire body weight. The left lobe reaches across the stomach so as to be in contact with the spleen. The tubercle at the lower extremity of the Spigelian lobe and the caudate lobe are relatively large. In the infant there is little connective tissue in the organ, which is very friable and also easily moulded on the surrounding structures. At birth the weight of the liver is about 150 gm. (3 oz. ). PRACTICAL CONSIDERATIONS: THE LIVER, GALL-BLADDER, AND BILIARY PASSAGES. The Liver. Anomalies in the position of the liver occasionally occur, as in " transposition," when the whole organ may be on the left side ; in such cases the spleen and other asymmetrical abdominal viscera (and frequently, but not neces- sarily, the thoracic organs) will also be found to be transposed. " Accessory" lobes are not uncommon and have been mistaken for new growths. The shape of the liver may obviously be affected by compression exerted through the parietes. The chief type of the so-called "lacing" or "corset" liver is marked by a transverse groove separating the main body of the organ from a pro- longation downward of the anterior portion, especially of the right lobe, which may reach to below the umbilical level. This portion has been mistaken for a movable right kidney. Knuckles of intestine may lie between it and the anterior abdominal parietes and prevent the recognition of its continuity with the liver by either palpa- tion or percussion. Movable liver (hepatoptosis} is a condition in which, through stretching of the tissues and structures which normally retain it in place beneath the arch of the dia- phragm, it sinks by gravity to a lower level. It has then been mistaken for various forms of abdominal or renal tumor and for movable kidney. Hepatoptosis is often associated with displacements or abnormal mobility of other abdominal viscera. Traction of the liver on the suspensory ligament is said to produce a fold of skin which hides the lower part of the umbilicus (Glenard). The structures most potent in holding it in its proper position are, in the order of their importance : (a) the attachment of the hepatic veins to the inferior vena cava, (&y the coronary ligaments and the cellulo-vascular bands in and between its layers, (c} the fibrous tissue near the vena cava and on the non-peritoneal posterior surface of the right lobe, (a?) the muscular wall of the abdomen (keeping the in- testinal mass pressed upward beneath the liver), and (e) the lateral and "suspen- sory" ligaments. Coincidently with the descent of the viscus it undergoes a rotation or tilting forward so that its diaphragmatic surface is in contact with the abdominal wall. Hepatopexy consists in suturing such a movable liver in its normal position by stitches which may be variously placed, but the most useful of which seem to be those which unite the round ligament and liver-substance with the anterior abdominal wall near the xiphoid cartilage (Francke, Treves). The normal relations of the liver to the diaphragm and the abdominal parietes cause it to be much influenced especially as to its circulation by the respiratory and other movements associated with energetic exercise ; hence the congestion of the organ resulting in "biliousness," or even in jaundice, seen in cases in which, from accident or disease, persons who have led active lives are confined to bed. In walking, and more markedly in horseback riding, the compression of the organ be- tween the diaphragm and the upper or respiratory segment of the abdominal wall which takes place during deep inspiration is aided by its downward movement from gravity. It has been suggested ( Jacobson) that such movement must slightly open the inferior vena cava, which is then immediately compressed by the following up- ward movement, during expiration, thus directly influencing the systemic venous current and with almost equal directness that in the hepatic veins. In deep inspiration the anterior edge of the liver descends from under cover of the lower ril>s, and in very thin persons may be palpated. A similar descent occurs when a reclining is exchanged for an erect position. The direct connection between the gastrointestinal and the portal circulation causes the latter to be markedly affected by the use of alcoholic or other irritants and PRACTICAL CONSIDERATIONS : THE LIVER. 1727 by the amount and character of food taken. Drinking and overeating thus exaggerate the periodic physiological congestions of the liver and often result ultimately in organic changes. Of course, passive congestion is likely to follow valvular disease of the heart, emphysema, pulmonary cirrhosis, or any condition in which the right heart is engorged, the backward pressure through the vena cava reaching the hepatic veins and their sublobular tributaries. The thin interlobular and perihepatic connective tissue, known as Glisson's capsule, which closely invests the ducts and vessels, is commonly affected in chronic irritation of the liver, especially that form due to al- coholic excess, and in some infectious diseases, notably the specific fevers and syphilis. Its anatomical relations explain the usual sequence of phenomena. Pro- liferation of the portions surrounding the terminal branches of the portal vein causes obstruction which, either alone or aided by the concurrent toxaemia, results in con- gestion and catarrh of the stomach and intestines, in enlargement of the spleen and pancreas, and later in ascites. As the obstruction increases, a collateral circulation is often established to re- lieve the portal congestion by means of communication between (#) the accessory portal veins (particularly those in the falciform ligament) and the diaphragmatic, para-umbilical, and epigastric veins ; (b} the veins of Retzius and the retroperitoneal veins ; (c^ the hemorrhoidal and the inferior mesenteric veins ; (d ) the gastric and the cesophageal veins. An operation has been employed to establish a better and more satisfactory compensatory circulation in cases of cirrhosis by effecting adhesions between the surfaces of the liver and the spleen and the diaphragmatic peritoneum, on the one hand, and the parietal peritoneum and omentum, on the other. When compression of the liver is carried beyond physiological limits, as from contusion or from forced flexion, rupture results. This is more frequent in the liver than in the other abdominal viscera on account of its size, its friability, its fixity, its close diaphragmatic and parietal relations, and its great vascularity. A similar disjunction of liver-substance may occur from a fall on the feet from a height. It is grave in proportion to the extent of the rupture and to its involvement or non- involvement of the peritoneal covering. Ruptures confined to the liver-substance, i.e. , not reaching the surface, and moderate in extent, are not infrequently recovered from. The commonest seat of rupture of the liver is near the falciform and coro- nary ligaments, with which the rupture is apt to be parallel. If they are extensive enough to reach the surface of the organ, death often results from hemorrhage, the intimate association of the hepatic substance with the thin-walled vessels preventing their retraction or collapse. Hemorrhage is also favored by the direct connection of the valveless hepatic veins with the vena cava and by the absence of valves in the portal veins. According to the situation of the rupture, the blood may be poured into the general peritoneal cavity ; into that portion of it known as the subhepatic space, and bounded below by the transverse mesocolon ; or into the retroperitoneal space behind the liver and ascending colon. The local symptoms will vary with the situation of the collected blood. Wounds of the liver should be considered with reference to its relations to the parietes, especially on the right side, where, on account of its greater bulk, it is more often injured. Except at the subcostal angle, where a small part of the anterior surface lies against the abdominal wall (the lower edge being on a line between the eighth left and the ninth right costal cartilages), the lower ribs and costal cartilages surround the liver. Thus stab wounds must pass between them, while fracture of the ribs with depression may penetrate the interposed diaphragm and then the liver- substance. Anteriorly, a little internal to the mammary line, the liver may reach to the fourth intercostal space or even quite to the level of the nipple, and may be directly wounded throughout that area. Laterally it is not usually found above the sixth interspace. Posteriorly a stab wound through the sixth, seventh, or eighth intercostal space, or even down to the level of the tenth dorsal spine, would pene- trate four layers of pleura, the thin concave base of the right lung, and the dia- phragm before reaching the liver. Still lower, the base of the lung may escape, but a wound of the liver may involve the two layers of pleura of the costo-phrenic sinus and the diaphragm. Of course, the alterations in position of the liver during inspiration and expiration, and according to the position of the body, must be i 7 28 HUMAN ANATOMY. remembered in obscure cases before basing a diagnosis upon the situation of the external wound. In bleeding from the liver after either rupture or stab wound, or during opera- tions, temporary occlusion of the portal vein and hepatic artery may be secured by pressing them between the finger and thumb, the former being placed just within the foramen of Winslow and the latter externally on the gastro-hepatic omentum. Enlargement of the liver, if uniform (congestion, multiple abscess, perihepatitis, fatty degeneration, hypertrophic cirrhosis), causes a bulging of the- right lower ribs and their cartilages and an increase of the area of absolute percussion dulness. The upper limits of the latter should normally be found at the sterno-xiphoid junction in the median line, the sixth intercostal space in the right mammary line, the seventh rib in the axillary line, and the lower border of the ninth rib in the scapular line. A modified dulness is obtained posteriorly over the area where the lung overlaps the liver, down to the level of the ninth rib. The lower level of the dulness and thus of the liver itself is in the mid-line, half-way between the sterno-xiphoid junction and the umbilicus, at or a little below the costal margin in the mammary line, on a level with the tenth and eleventh ribs laterally and opposite the eleventh dorsal ver- tebra posteriorly. At this point it is continuous with the lumbar dulness due to the thickness of the spinal muscles, the quadratus lumborum, the kidneys, and the perirenal fat. In localized enlargements, as from tumor, abscess, or hydatids occupying the upper surface of the right lobe, the diaphragm is pushed upward and the upper limit of the percussion dulness raised, the lower limit remaining temporarily unaf- fected, the area of dulness being thus increased. In emphysema or pneumothorax both limits are lowered (as they are also in empyema, although in that condition the liver-dulness merges into that of the pleural abscess), and in phthisis, collapse or retraction of the lung, or abdominal meteor- ism both limits are raised, the total area of dulness remaining unchanged in these cases. Of course, in atrophic disease the area is diminished and, as in cases in which the whole liver is drawn or pushed up, or there is free gas in the abdominal cavity, there may be tympany over the right lower ribs. Abscess of the liver may be due to infection through the portal system, as from dysentery or hemorrhoids, or from typhoid fever, colitis, or appendicitis ; or through the general blood -supply, as from osteomyelitis or cranial trauma. In addition to the usual symptoms of suppuration, it, like many other liver troubles, is sometimes characterized by pain in or above the right shoulder. This is thought to be explained by the facts that (a} the right lobe is far more commonly affected, (6) the phrenic contributes to the nerve-supply to the liver and is derived partly from the fourth cervical, and (c) the supra-acromial nerve is a branch of the latter. Other evidence showing relations between the supra-acromial and phrenic nerves, e.g. , hiccough in shoulder arthritis, makes this explanation seem reasonable. Hepatic abscess may open (a) inferiorly into the stomach, colon, duodenum, or right kidney, or into some portion of the peritoneal cavity, either the subhepatic space, the general cavity, or the lesser cavity via the foramen of Winslow ; () superiorly into the pleura, lung, or bronchi, or into the pericardium ; (c) posteri- orly into the retroperitoneal space and the loin ; (d} anteriorly on the surface of the body, sometimes following the remains of the umbilical vein to the umbilicus. The resistance of the ribs, intercostal muscles, and diaphragm makes pointing in other directions of rare occurrence. Pus may invade the suprahepatic (subdia- phragmatic) space or the liver itself from above the diaphragm. Many empyemas have taken this course. Nephric or perinephric abscess on the right side may extend to the liver. Hydatid cysts are more common in the liver than elsewhere, as the embryo of the egg of the trenia echinococcus, freed from its shell by digestion, readily pene- trates the gastric and intestinal vessels, and is very likely to enter a tributary of the portal system and thus be carried direct to the liver, where it multiplies and develops into the mature hydatid. Spontaneous evacuation of the cysts may occur in any of the directions already mentioned. In opening an hepatic abscess or hydatid cyst the liver must be reached, as in PRACTICAL CONSIDERATIONS : THE GALL-BLADDER. 1729 other operations, by traversing either the peritoneal or the pleural cavity. In doubtful cases, or when there is an anterior swelling, a vertical incision in the mid- line through the right rectus or at its outer edge, beginning at the costal margin and prolonged downward, will permit of exposure of the liver and evacuation of the abscess or cyst, the peritoneal cavity being walled off by gauze packing. If the liver is approached above the lower ribs or posteriorly, it will be necessary to resect a portion of one or more ribs, suture the diaphragmatic and parietal pleurae together or to the thoracic wound, and then incise the diaphragm. If the liver is to be reached laterally, i.e., in the right axillary line, resection of the tenth rib will disclose the diaphragm with no intermediate layer of pleura. Penetration of the diaphragm opens the peritoneal cavity and permits access to the lower and outer portion of the right lobe. Cancer of the liver is usually secondary (to metastasis through the portal system), multiple, and diffuse. When primary and consisting* of a single nodule, excision may be attempted. In controlling hemorrhage, the friability of the liver- substance makes ligation of separate vessels difficult, and it may be necessary to employ an elastic tourniquet, the cautery, gauze pressure, or all three. Lymphatic involvement secondary to hepatic cancer may be found in the cesophageal, mediastinal, lumbar, or omental glands. The relation to the cesophageal lymphatics is also shown by a case in which hepatic abscess followed a mediastinal cesophagotomy. The Gall-Bladder. This sac may be absent, as is normally the case in some of the lower animals ; it may be congenitally of hour-glass shape ; it may be bifid ; it may communicate directly with the liver by a " hepato-cystic' ' duct ; it may be transposed (in conjunction with other viscera), and in one such case cholecystostomy for gall-stones was performed on a gall-bladder lying on the left side. Wounds of the gall-bladder are rare. Rupture of the gall-bladder may occur from traumatism to the abdominal pari- etes ; it is favored by distention of the viscus and by enlargement of the liver, both of which carry the gall-bladder downward to a less protected position and favor the direct transmission of the force. Extravasation of bile into the general peritoneal cavity follows. It may be sterile, and may then act merely as an irritant, causing an extensive plastic exudate, but is apt to be fatal by setting up septic peritonitis. If operation discloses such a rupture, it may be remembered (i) that the extravasated bile first flows into the large peritoneal pouch bounded above by the right lobe of the liver, below by the ascending layer of the transverse mesocolon covering the duodenum internally, externally by the peritoneum lining the parietes down to the crest of the ilium, posteriorly by the ascending mesocolon covering the kidney, and internally by the peritoneum covering the spine ; (2) that this pouch can be easily and thoroughly drained through a lumbar incision ; and (3) that it is capable of holding nearly a pint of fluid before it overflows into the general peritoneal cavity through the foramen of Winslow or over the pelvic brim (Morison). Distention of the gall-bladder is ordinarily due to ( i ) inflammatory obstruction of the cystic duct (cholangitis) ; (2) mechanical obstruction of the cystic duct, usu- ally from the impaction of gall-stones ; (3) acute cholecystitis, (a) catarrhal, (b} suppurative ; or (4) obstruction of the common duct from tumor or, much more rarely, from impaction of a calculus in that duct before the gall-bladder has become inflamed, contracted, and formed adhesions. The gall-bladder itself may be the primary seat of a malignant growth. It is impossible to feel the normal gall-bladder through the abdominal wall. Enlargement of the gall-bladder from any cause usually takes place in a down- ward and forward direction on a line which, beginning a little below the ninth costal cartilage, crosses the linea alba just below the umbilicus. If the liver is of normal size, the neck of the gall-bladder is about opposite the ninth costal cartilage. If the liver is enlarged, the gall-bladder will be so much depressed that its neck may be on a level with, or even lower than, the umbilicus. The rounded, pear-shaped, or gourd-like fundus can usually be felt, movable laterally, and sometimes with a pal- pable groove between it and the lower edge of the liver. The swelling descends 109 1730 Hl'MAN ANATOMY. during inspiration. If the cause of the enlargement is inflammatory and adhesive peritonitis has resulted, the tumor may be fixed so that it does not move with res- piration ; but there is then, especially in acute cases, apt to be pain and tender- ness over the swelling or at a point between the ninth costal cartilage and the umbilicus. It may be mentioned here that the diagnosis between the chronic form of gall- bladder disease and movable kidney is not always easy ; that the two conditions not infrequently coexist in the same person ; and that the possibility of error is increased by the fact that they are each met with much oftener in women than in men, and that the right kidney is far more frequently movable than the left. The anatomical explanation is that in women with flabby abdominal walls either tight lacing or a relatively slight jar or strain tends to produce displacement of both the kidney and the liver, the latter resulting in tension or angulation and con- sequent obstruction' of the bile-ducts. The two conditions also act reciprocally, descent of the liver causing displacement of the kidney, which, through its traction upon the duodenum, tends to obstruct the bile-ducts. A movable kidney, as compared with an enlarged gall-bladder, is less influenced by respiration ; has a wider range of motion, especially in the long axis of the body ; is more influenced by position ; slips backward towards the loin instead of upward beneath the liver ; is less often visible and less frequently tender on pressure, which is apt to cause a sickening sensation analogous to testicular nausea (page 1951). Acute cholecystitis (phlegmonous) is due to infection. The colon or typhoid bacillus, or the pneumococcus, streptococcus, or staphylococcus, may reach the gall- bladder either through the blood, as during a pneumonia, by lymphatic and vascular channels, as after an appendicitis, or through the intestine and bile-ducts, as in some of the post-typhoidal cases. The symptoms are (#) generalized abdominal pain, due to the association of the cystic plexus, through the coeliac, with the superior mesenteric ; (b) pain below the right costal margin passing towards the epigastrium, i.e. , referred to the coeliac and solar plexuses, and towards the right scapular region, from the association of the phrenic and the supra-acromial nerves through the fourth cervical (page 1758) ; (c) rigidity over the right hypochondrium, due to the connection between the splanch- nics and the intercostals ; (.-.' Section of injected pancreas, showing intralobular capillary net-works; also convolutions of islands of Langerhans. 50. Development. The human pancreas develops from two separate anlages, a dorsal and a ventral one. The former, which appears by the fourth fcetal week, is a direct outgrowth from the primitive duodenum. The ventral anlage, slightly later in its formation, develops as two outgrowths, one from each side of the early bile- duct, and is therefore not strictly a direct derivative from the gut. The left ventral outgrowth soon disappears, leaving the right one connected with the bile-canal. This close association is retained throughout life, as evidenced by the intimate rela- tions between the common bile and pancreatic ducts. The dorsal pancreas rapidly grows, elongates, and soon becomes the chief part of the organ, opening by an in- dependent canal the duct of Santorini into the duodenum. The repeated division of the duct and the proliferation and extension of the terminal compartments pro- duce the system of excretory passages and glandular tissue of the organ. The ven- tral pancreas, which has meanwhile increased more slowly, and in consequence of the changes in the gut has suffered displacement to the left and behind, grows towards the dorsal gland, with which it soon inseparably fuses. The head of the fully formed 1738 HUMAN ANATOMY. organ represents the primitive ventral pancreas, the body and tail the dorsal seg- ment. The duct of the ventral portion, which remains as the duct of Wirsung, forms a communication with that of Santorini, and for a time the pancreas possesses t\vo outlets into the duodenum. Usually the duct of Santorini loses its intestinal con- nection and becomes tributary to the duct of Wirsung. Variations from this ar- rangement are often encountered, the different combinations being due to deviations FIG. 1466. h d Diagrammatic reconstructions, showing development of pancreas and relations to liver-ducts, a, common bile- duct ; *, hepatic and c cystic ducts; d, right and e left ventral pancreatic anlages ; /, dorsal pancreas and its duct (g) ; h, junctipn of common bile (a) and ventral pancreatic (d ) ducts. After fusion of ventral and dorsal pan- creas, d becomes duct of Wirsung,^- duct of Santorini, and /' head of pancreas. from the ordinary progress of development as to the fusion of the two parts and per- sistence of their canals. The areas of Langerhans are developed from the same entoblastic outgrowths as give rise to the ordinary glandular tissue (Laguesse, Pearce 1 ). The connective-tissue septa are derived from the ingrowing mesoblast. Variations. The pancreas has been seen to surround the descending part of the duodenum. Small accessory pancreases have been found in the walls of the intestine. Although usually in the duodenum, they may be in the stomach or at the beginning of the jejunum, and occasionally some distance from it. Presumably they are parts of the gland which became separated at an early stage and were drawn by the growth of the intestine away from their original position. 2 PRACTICAL CONSIDERATIONS: THE PANCREAS. Certain abnormalities that may affect surgical procedures or may of themselves produce symptoms of disease should be mentioned. Accessory pancreases are found in various localities and may be mistaken for new growths. The anterior wall and the two curvatures of the stomach and the walls of the small intestine, especially the duodenum, are the situations in which such glands are most frequently foun They have ducts opening into the intestine. An accessory gland has been found to the right of the duodenum entirely dis- tinct from the main gland. Perhaps the most important anomaly is one in which the gland completely surrounds the second part of the duodenum, constricting it and causing dilatation of the first portion and of the stomach. Several cases have been reported. The common bile-duct may also be contained within the head of the pan creas, as may the superior mesenteric vessels within its body. The accessory pan- creatic duct may be absent, or there may be three ducts, all opening into the duodenum. Movable Pancreas. The gland may fall forward or downward (when it may sometimes be felt below the stomach), or it may be a part of the contents of a dia- phragmatic hernia, or may even but with great rarity be contained within the sac of an umbilical hernia. Injuries. The situation of the pancreas behind the lesser peritoneal cavity and the stomach and between the spleen and the duodenum, the partial protection it receives from the costal arch, and the depth at which it lies render its uncompli- 1 American journal of Anatomy, \ol. ii., 1903. 2 Zenkrr : Yirdiow's Archiv, Bd. xxi., 1861. PRACTICAL CONSIDERATIONS : THE PANCREAS. 1739 cated injury of very rare occurrence. In only three fatal cases in which all other abdominal viscera escaped has it been found to be ruptured. In less severe cases it has been bruised or torn, hemorrhage has occurred, a rapidly enlarging, fluctuating epigastric tumor has formed, and the patient has recov- ered after a laparotomy, evacuation of the blood-cyst, and drainage. In such cases it is probable that the traumatism has caused a laceration of the posterior layer of the lesser sac of the peritoneum (with which the pancreas is intimately adherent) and of the pancreas itself. Blood, or blood with pancreatic secretion, is poured into the lesser sac, causing adhesive peritonitis and sealing the foramen of Winslow. The lesser cavity, now converted into a closed sac, is distended with serous exudate, blood, and pancreatic fluid. After evacuation and drainage, the pancreas may con- tinue to pour its secretion into the cyst-cavity through the original peritoneal tear (Robson and Moynihan). Pancreatitis. The close relation of its duct to the common bile-duct, which it often joins at the ampulla and before reaching the duodenum, explains the frequent association of gall-stones with chronic inflammation of the pancreas. A small ball- valve calculus in the ampulla has been thought, by occluding the duodenal orifice, to convert the two ducts into a continuous channel, permitting, if the gall-bladder is functionally active, the entrance of bile into the pancreatic duct (duct of Wirsung) and causing pancreatitis. A larger stone might occlude also the orifices of both the pancreatic duct and the bile-duct and produce in both glands the troubles associated with retained secretions. In the pancreas these troubles are lessened by the fact that occlusion of the main pancreatic duct does not of necessity completely obstruct the egress of the pancreatic fluid (Opie). In about 50 per cent, of bodies the acces- sory duct (duct of Santorini) communicates within the gland with the main duct and opens into the duodenum by a separate orifice about 2.5-3.5 cm. (1-1^6 in.) nearer the stomach than the papilla at which the ampulla of Vater opens (Schirmer). Nevertheless, just as jaundice follows occlusion of the common bile-duct by forcing the secretion of the liver back upon that gland, whence it finds its way into the inter- stitial tissue, the lymphatics, the thoracic duct, the blood, and the tissues at large, so the fat-splitting ferment of the pancreatic juice, in cases of occlusion of the pan- creatic duct, finds its way beyond the parenchyma of the gland and causes fat- necrosis, first in the vicinity of the pancreas, later over widespread areas (Opie). There can, at any rate, be no question of the etiological association of gall- stones with many cases of pancreatitis ; but it is probable that in a large proportion, in addition to mechanical pressure or independently erf it, bacterial invasion follow- ing inflammation of the ducts or of the duodenum is an important factor. The anatomical symptoms of acute pancreatitis depend upon the close associa- tion of the gland (#) with the solar plexus through the cceliac, superior mesenteric, and splenic plexuses ; (<) with the duodenum ; (c ) with the bile-ducts ; (d ) with the great blood-vessels behind it ; and (, spleen ; P, pancreas ; K, kidney. 1746 HUMAN ANATOMY. tinuous with them. The two layers join at the bundle of vessels just mentioned. thus forming a fold which is the termination of the lesser omentum on the right, known as the duodena- hepatic omentum (ligamentum hepatoduodenale). The lesser omentum is sometimes described as prolonged across the first part, of the duodenum to the transverse colon, fusing with the greater omentum. This is only an acci- dental modification, although a very common one. An accessory fold, the duodeno- \cystic ligament, is prolonged to the right from the front of the lesser omentum, around the cystic duct from the gall-bladder. The hepatic attachment of the lesser omentum is to the transverse fissure of the liver and from its left end to the fissure of the ductus venosus. From the point at which the latter reaches the diaphragm the two layers diverge, the FIG. 147 1 . j Diagram showing changed relation of visceral peritoneum in consequence of twisting, so that original right and left sides of mesentery of small intes- tine and of part of colon have exchanged places. The detached portion which is twisted is supposed to be attached at a higher level. D, duode- num ; C, C, ascending and descending colon ; /, smallintestine ; K, kidney ; /?, C, Care being displaced towards posterior wall. to t h e j ou - er side of the left lobe and the right one to the lobe of Spigelius. The structure of the lesser omentum is dense and fibrous at the right. It is very delicate in the middle, but somewhat thicker at the left end. The fold around the vessels at the free edge (Fig. 1473) forms the anterior border of the foramen of Winslow (foramen epiploicum), a nar- row part of the peritoneal cavity by which the general cavity communicates with that behind the stomach which has been formed by the rotation of that organ and the inordinate growth of the mesogastrium. The foramen is circular, with a diameter of from 2-3 cm. Of the three vessels in the fold forming its anterior border, the portal vein is the posterior at the point of entrance into the liver, with the hepatic artery in front on the left and the hepatic duct in front on the right. The cystic duct is really in an accessory fold. The hepatic artery, which passes along the left side of the duodenum and turns upward, is the vessel that most definitely bounds the foramen in front. The duo- denum lies below the foramen, but its lower border is often formed, not by the gut, but by a fold of serous membrane arising from it. The foramen is bounded behind by the vena cava and above by the caudate lobe of the liver, which is covered by peritoneum. The Posterior Mesentery : Part I. The posterior mesentery arises from the spine, with the aorta between its folds. The first part is the mesogastrium, in which run the branches of the cceliac axis. It will be remembered that, except at the fundus, this is attached to the greater curvature of the stomach, which was originally the posterior border, but which has turned to the left. The spleen and most of the pancreas are developed in this fold, which grows inordinately. We must trace it both in a horizontal and in a sagittal plane. To understand the horizontal arrangement, it is sufficient to remember that the original mesentery, which ran straight forward from the spine to the stomach, in its subsequent excessive growth describes a loop to the left (Fig. 1470), so that the original left side of the mesentery near its root faces backward, and later, after the bend of the loop, forward, ultimately covering the an- terior wall of the stomach. This fold forms a givat pouch behind and below the stomach called the lesser cavity of the peritoneum ( Imrsa onic-ntalis), which, of course, is continuous with the general cavity. The mesothelium of the left side of the mes- entery nearly to the spleen fuses with that of the posterior wall of the abdomen, so that the splenic vessels and the pancreas which are in it come to lie behind the per- THE PERITONEUM. 1747 Diagram showing later stage where secondary mesentery is formed and duodenum (D) and colons (C, C) lie against posterior body-wall. The ad- ditional colors indicate the fusion of the original parietal and visceral perito- neum, purple from the blue with the red, green from the blue with the yellow. manent serous covering of the posterior abdominal wall, which here is that of the original right side of the mesogastrium. The spleen, and perhaps the tail of the pancreas, lie free, surrounded by peritoneum. If the hand be introduced into the left hypochondrium, it slides along the wall behind the spleen to the point at which the splenic vessels leave the FIG. 1472. posterior wall and pass in a fold, the lieno-renal liga- ment, to the hilum of the spleen. From this position the hand can be carried around the spleen to the front of the vessels at the hilum and thence to the right along the continua- tion of the mesogastrium to the greater curvature of the stomach, where its layers separate to coat the front and back of that organ. T,he part of the mesogas- trium between the stomach and the spleen is \hegastro- splenic omentum. The right layer of peritoneum of the mesogastrium, lining first the hind wall of the abdo- men and then the back of the stomach, bounds the lesser cavity of the peritoneum. The gastro-phrenic ligament is a small vertical fold, usually found extending from the left of the end of the oesophagus to the top of the stomach. Near it is often another, the suspensory ligament of the spleen, extending from the diaphragm to the top of that organ, of which it may enclose a small part. It marks the upper part of the line of reflection of the mesogastrium from the posterior abdominal wall. The phreno-colic fold, also derived from the mesogastrium, is a horizontal shelf with a free anterior semi- lunar edge forming the floor of a niche for the spleen. It extends from about the eleventh rib inward onto the upper surface of the trans- verse colon. That this liga- ment is really a part of the mesogastrium, and not a lig- ament of the colon, is shown by development, as well by its existence (as in the mon- key) when the descending colon is unattached to the wall. The Greater Omentum. We are now to trace the mesogastrium in a sagittal plane downward from the greater curvature of the stomach. On opening the abdomen the first thing that appears below the stomach is the greater omentum (omentum majus), which is spread like an apron over the intestines. It is that part of the mesogastrium which is situated in front. The terms gastro-colic and g astro -splenic omenta are but names for different parts of this structure. It extends from the greater FIG. 1473. Diagrammatic section passing through level of foramen of Winslow, showing relations of parietal and visceral peritoneum within lesser sac (LS) ; GH, cut gastro-hepatic omentum, containing portal vein (/"), he- patic artery (//),and bile-duct (B}\ Si, stomach ; CrS, gastro-splenic omen- tum ; LR, lieno-renal omentum ; VC, A, vena cava and aorta. 1748 HUMAN ANATOMY. curvature of the stomach, where it is continuous on the left with the double layer coming from the spleen and on the right with that coming from the inferior sur- face of the first part of the duodenum ; from this broad origin the greater omentum hangs down over the intestines to near the pubes, where it turns upon itself and ascends posteriorly. Often it does not descend so far, but may be folded upon itself to almost any degree and in almost any position. For purposes of description it is supposed to lie spread out smoothly, and to consist of an anterior and a pos- FIG. 1474. Ensiform cartilage Liver Gall-bladder Ascending colon Caecum Undisturbed abdominal viscera of formalin subject; liver and stomach abnormally large, hence the exaggerated apparent transverse position of stomach. terior fold (Fig. 1467). The former passes down over the transverse colon, but with- out adhering to it. The peritoneum on its anterior surface faces forward into the greater peritoneal cavity, while that on its posterior surface looks into the lesser one. On turning backward upon itself, it runs up to the transverse colon. If this were literally true-, it is evident that the lesser cavity would extend from behind the stomach over the colon down into this fold ( reccssus inferior omcntalis) of the greater omen- tum, and in fact this is actually the case in the foetus (Fig. 1439) and exceptionally THE PERITONEUM. 1749 in the adult ; but generally, except just below the colon, the two layers fuse into one. In the adult, when the returning fold reaches the transverse colon, the two layers composing it seem to diverge to enclose the intestine, and, reuniting above it, to be continued upward as the transverse mesocolon to a line running across the back of the abdomen, to be described later. This is an extraordinary and apparently con- tradictory arrangement by which a part of the mesogastrium, or mesentery of the stomach, has become also the mesentery of a part of the colon. The explanation is furnished by embryology, since the original arrangement is very different. In the fcetus (Fig. 1439) the returning fold of the greater omentum passes up in front of the colon to the posterior wall along the lower border of the pancreas. The pos- terior layer of the greater omentum is in fact the left layer of the original mesogas- trium, which we should be able to follow to the aorta, had it not, with the pancreas, become adherent to the posterior wall. It has no connection whatever with the transverse mesocolon ; it simply lies upon it. At about birth, however, the two opposed layers begin to fuse. The acquired line of attachment to the transverse colon is low on the right and high on the left. Sometimes near the spleen it joins, not the colon, but the mesocolon above it. The Structure of the Greater Omentum. There is hardly any framework apart from the vessels that course through it, save a most delicate layer of nbro-elastic tissue which supports the mesothelium. In the adult more or less fat is found about the vessels, and in some cases the omentum is loaded with it. The two layers of serous membrane are sometimes beautifully distinct ; in other cases no trace of a double origin can be recognized. Sometimes parts of the omentum atrophy and disappear, leaving windows, or fenestw, between the meshes of the vessels. The arteries are long and very slender. They arise from the gastro-epiploic arteries at the greater curvature of the stomach and run straight downward to the folded border of the omentum, and then up again in the posterior fold, to anastomose with the arteries of the colon. In their course they send off small side branches which meet those from the next branch. The arrangement of the veins is essen- tially the same. The Lesser Cavity of the Peritoneum. The mesogastrium, starting at the aorta, takes a great turn to the left, and its first part, containing the pancreas, fuses with the posterior abdominal wall. This fold is only a part of a great pouch that runs downward also. If examined before it has become adherent to the transverse meso- colon, its continuation from below the pancreas is to be followed down over the colon as the posterior layer of the greater omentum. In the description of the folds of the adult in a sagittal plane it was necessary, on account of this adhesion, to reverse the normal course and to follow it from its insertion into the stomach back to its origin. If a cut be made through the greater omentum between the stomach and the transverse colon, the lesser sac ( bursa omentalis) is opened so that its pos- terior wall can be examined (Fig. 1475). This is seen covering the pancreas, the splenic vessels and the posterior abdominal wall, part of the spleen, part of the left kidney, and the left suprarenal capsule. At the right is the foramen of Winslow, which is generally, but inaccurately, considered the communication between the greater and lesser cavities. It cannot be the true entrance into the lesser cavity, because, owing to the median arrangement of the original mesentery, this opening cannot be on the right of the median line. The real communication between the two cavities is somewhat contracted (isthmus bursa' omentalis) and indicated by the median vertical fold plica gastro-pancreatica made by the mesogastrium over the gastric artery of the stomach as it arises from the cceliac axis to the cardia. On the left of this fold is the lesser cavity proper ; on the right of it, extending to the foramen of Winslow, is a small cavity, the vestibule ( vestibulmn bursa 1 omentalis), bounded behind by the original parietal peritoneum of the right abdominal wall and extending upward behind the lobe of Spigelius (Fig. 1476). The sides of the pocket behind the liver (recessus superior) are the reflections of the peritoneum over the left of the inferior vena cava and the right of the ductus venosus, which meet above, roofing it in. The first part of the duodenum, which forms the lower boundary of the foramen of Winslow, passes backward and upward, so that the loop of intes- tine, which the duodenum originally formed, must be considered as having fallen 1750 HUMAN ANATOMY. over onto the right side against the right of the spinal column, to the peritoneal covering of which it has grown with the transformation into connective tissue of the right serous covering of its mesentery. The second or descending portion of the duodenum lies against the right of the column under the permanent parietal peri- toneum, derived from the mesocolon, as is shown later. The great difficulty of un- derstanding the lesser cavity is that in man the duodenum rises to so near the liver that the entrance to the vestibule at the foramen of Winslow is very small. If, as in many animals, these parts were more distant, it would be evident that this is a pouch- FIG. 1475. Hepatic artery Gastro-hepatic omentutn Accidental peritoneal fold Pylorus First part of duodenum Foramen of Winslow Gastro-pancreatic fold Stomach Peritoneum lining posterior wall of lesser sac Transverse colon Greater omentum, cut Spleen Pancreas Folds of greater omcntum Gastro-splenic omentum The subject, lying on its back, is seen from the left side ; the stomach, except fundus, is turned ovi-r. Tin- greater omentum has been cut below the greater curvature of the stomach so as to open the lesser sac to show the- toiaineti of Winslow from the left side. like formation, the mouth of which is behind the edge of the lesser omentum. The relations to the mesogastrium of three branches of its artery, the cceliac axis, are as follows. The splenic artery, in the adult condition, lies entirely behind the perma- nent peritoneum to near the hilum of the spleen, where the mesogastrium is no longer attached to the wall. It then sends its terminal branches to the spleen, the gastro-epiploica sinistra to the greater curvature of the stomach, and the vasa brevia to the fundus. The gastric artery, originally in the mesentery of the duodenum, reaches the cardiac end of the stomach through the /V/Vv gastro-pctncreaticct^ and then runs between the layers of the lesser omentum along the lesser curvature. THE PERITONEUM. The hepatic artery reaches the duodenum through its mesentery, and crosses the left side of the gut, to which it gives branches. Thence it runs in or near the edge of the lesser omentum at the foramen of Winslow to the portal fissure. FIG. 1476. Gastro-pancreatic fold ieno-renal fold Vestibule of lesser sac Lesser or gastro-hepatic omentum. Gastro-splenic omentum Greater omentum Schematic reconstruction, showing relations of peritone.il layers in vicinity of lesser sac. Upper surface of duo- denum ()) at floor of foramen of Winslow lies at deeper level than plane of section. It is to be noted that only that part of peritoneum covering posterior wall of lesser sac is derived from greater omentum which lies to left of aorta, beginning at gastro-pancreatic fold. L, liver; .S*, stomach ; Sp, spleen ; P, pancreas ; A', kidney. The Posterior Mesentery : Part II. This is that part of the peritoneum derived from the original mesentery of the jejuno-ileum, the caecum, and the ascend- ing and transverse colon. Its artery is the superior mesenteric. If the transverse colon with the greater omentum be turned upward and the small intestine to the right, the left side of the mesentery of the jejuno-ileum is seen running from the left of the top of the body of the second lumbar vertebra to the right sacro-iliac joint. At the beginning this is attached to the lower side of the gut, where it makes a sharp flexure at the origin of the jejunum from the end of the duodenum. This flexure lies directly in front of the aorta, which usually lies covered with peritoneum at the back of the abdomen, with the fourth part of the duodenum to the right of it. (This relation is more fully described with the duodenum (page 1647). The line of attach- ment of the mesentery (Fig. 1477) descends over the fourth part of the duodenum, crossing the third part and the inferior vena cava. The greatest breadth of the mes- entery to the free border is from 20-23 cm - (8-9 in.). It reaches its full breadth almost at once after its origin. Usually it becomes very narrow perhaps only 1 2 mm. at its termination ; but this varies much, as does also the point of that termina- tion. The connective tissue between the layers is thickest and the lymph-nodes most numerous near the attached part. Except in very fat subjects, there is little between the layers of peritoneum besides the vessels, within an inch or so of the gut. The superior mesenteric artery can be felt at the top, entering it from under the lower border of the pancreas. The peritoneum can be followed at any point across from the left to the right side of the mesentery. From the latter it is followed along the posterior wall to the kidney and the ascending colon, lying on the front of the latter, where they are in contact. The membrane crosses the ascending colon, leaving its posterior surface without covering attached to the parts behind it, and completely envelops the caecum, passing on the left into the mesentery. Very often the peritoneum is carried for an inch or two behind the lower part of the ascending colon. It then passes into the left flank and the pelvis without incident. Development shows that this is a departure from the original condition, in which the 1752 HUMAN ANATOMY. attachment of this mesentery was exceedingly short, merely broad enough to contain the superior mesenteric artery. The so-called permanent mesentery is caused by the falling over to the right of the fold of mesentery for the ascending colon, twisting the membrane, and the downward growth of that part of the gut which brings the caecum down from under the liver to the right iliac fossa. The twist having occurred, and the ascending colon having fallen against the abdominal wall, the fold bearing the ascending and transverse colon becomes fused with the peritoneum of the pos- terior right abdominal wall on the right of a line from the beginning of the jejunum FIG. 1477. Right supra- renal body Vena cava Portal vein I Duodenum Right kidney Transverse mesocolon (cut) Beginning of transverse colon Mesentery of. jejuno-ileum (cut) Ascending _ colon 1 leu in, lower end Pancreas Splenic flexure of colon Jejunum Mesentery of descending colon ami si.ij- moid flexure Sigmoid flexure, lower end Bladder Caecum Showing relations and attachments of mesentery of small and large intestines; greater part of transverse colon, of sigmoid flexure and of jejuno-ileum has been removed, the latter by cutting through the mesentery near its posterior attachment. to the end of the ileum, the part bearing the small intestine remaining free. This oblique line of attachment becomes the permanent mesentery. The peritoneum to the right of it, as far as the ascending colon, forms the permanent parietal perito- neum, having fused with the original parietal layer behind it. When the colon under the liver becomes the transverse, the part nearest to the latter continues free and lianas down as a transverse fold, on which the greater omcntum lies, and sub- sequently fuses, as already described. The transverse colon is attached by the transverse mesocolon (also a secondary adhesion) to the front of the right kidney and to the posterior wall across the second part of the duodenum and the head of THE PERITONEUM. 1753 the pancreas along the lower border of that gland to the left kidney (Fig. 1477). Its greatest breadth is some five or six inches. (For a fuller description, see peritoneal relations of the colon, page 1670.) The breadth of the transverse mesocolon is from 12-15 cm - (5~6 in.). In the adult it is fused with the greater omentum, as already described. The superior mesenteric artery enters this mesentery under the pancreas, and gives from its left or convex side the branches for the small intestine. From its right, just after its origin, it gives off the inferior pancreatico-duodenal and the branches for the caecum and the ascending and transverse colon. In the adult the right colic artery runs behind the permanent posterior parietal peritoneum. The Posterior Mesentery : Part III. The region of the inferior mesen- teric artery is very simple. Starting at the left of the permanent mesentery of the small intestine, the peritoneum is traced over the posterior abdominal wall, over Caecum FIG. 1478. Small intestine Transverse colon Ascending colon Lower end of ileum Mesentery Duodenum Descending colon Mesentery Posterior wall of abdom Bladder Mesenterium commune in child of three years ; the usual relations would be restored by bringing upper dotted line in contact with lower. the lower part of the left kidney, and over the descending colon, which, although touching that organ, lies chiefly external to it. The posterior surface of the gut is retroperitoneal. The descending colon has fallen over to the left, so that the peri- toneum of the left side of its mesentery has fused with that of the abdominal wall, and the permanent serous covering of the posterior wall is derived from that of the right side of the original mesentery. This fusion ceases at the crest of the ilium, and the sigmoid flexure retains at least a part of the original mesentery (Fig. 1478). The line of its attachment runs in more than one direction, according to the amount of freedom of the fold, from that point to the middle of the third sacral vertebra. (The chief forms are described on page 1671.) Beyond the latter level the rectum is partly uncovered behind, where the mesentery ceases, and its gradually diverging 1754 HUMAN ANATOMY. lines pass onto its sides, leaving the termination of the gut without any peritoneal covering. The branches of the inferior mesenteric artery in this region are the left colica sinistra, which runs behind the permanent parietal peritoneum ; the sigmoid, which does the same until it reaches the part of the mesentery which is free ; and the superior hemorrhoidals, which descend in the lower part of the original mesentery until they reach the retroperitoneal area behind the rectum. PRACTICAL CONSIDERATIONS : THE PERITONEUM. The development, topography, and relations of the peritoneum have already been sufficiently described. It remains to consider its diseased conditions and those in which it is an important or controlling factor in the production of disease in so far as they are influenced by anatomical circumstances. Peritonitis is the most common and the most serious of peritoneal diseases. The separate consideration of wounds of the peritoneum is not necessary, as traumatism, unassociated with infection, produces merely hyperaemia and exudation. The pro- cess is for convenience known as plastic or reparative peritonitis, a term also applied to those forms of true (infective) peritonitis in which the bactericidal and absorptive powers of the membrane itself and of its serum have resulted in the destruction or the isolation of the invading bacteria. The anatomical routes by which bacteria may reach the peritoneum are : 1. From without, as through an accidental or operative wound. 2. From within, as from an escape of the micro-organisms through intestinal walls leaky as a result of strangulation (as in intestinal hernias or volvulus or intussuscep- tion) or of inflammation (as in appendicitis) ; or through an actual perforation, as in gastric ulcer, typhoid fever, or intestinal cancer. 3. Through the blood- or lymph-channels, as in many cases of tuberculous peritonitis and possibly in so-called rheumatic, nephritic, and other clinical forms of peritonitis, in some of which the infecting organism is still unknown. 4. Through the Fallopian tubes. The peritoneum is not equally susceptible to traumatism or to infection on both its surfaces or in all its parts. The external, areolar, or "wrong" side (page 1740) may be extensively separated from the subjacent structures (as in the extraperi- toneal approach to the ureter or to the common iliac artery), or may be in contact for a long time with an inflamed or a suppurating surface (as in perirenal or other retroperitoneal abscess) without damage to the mesothelial or free surface of the membrane, and with but little risk of the supervention of peritonitis. On the other hand, a small penetrating wound made with a dirty instrument will probably set up a diffuse and perhaps a fatal inflammation. The difference in results is due to the delicacy and vulnerability of the mesothe- lial as compared with the fibrous surface ; to the great absorbent power of the former (vide infra), the area of which is about equal to that of the cutaneous surface of the body, favoring toxaemia if the bacteria and their toxins are not destroyed or encap- sulated ; to the excellent culture material supplied by blood-clot or by the injured or necrotic epithelial surface ; and to the involvement in diffuse or spreading cases of th peritoneal covering of the neighboring viscera, particularly the intestines. These facts determine the surgical rule that in doubtful cases of bullet and stab wounds of the abdominal wall it is well under aseptic conditions to enlarge the wound, ascertain the presence or absence of penetration, and cleanse or drain i necessary. Not only are the two sides of the peritoneum thus unlike in susceptibility to in- fection, but a similar difference exists between the parietal peritoneum and that cover- ing the viscera. The former, applied by a layer of fat-containing connective tissue t the relatively immobile muscular 'layer of the abdominal wall, is less easily inflamed, or if inflamed develops a less diffused and less quickly spreading form of peritonitis than docs the thinner, more sensitive, and more vulnerable visceral peritoneum, especially that covering the most mobile of the abdominal viscera, the small intestine. So, too, peritonitis originating in certain regions is, l>y reason of the facility with which they may be shut off by adhesions, less threatening in its course and PRACTICAL CONSIDERATIONS : THE PERITONEUM. 1755 more amenable to surgical treatment than that beginning elsewhere. Pelvic perito- nitis, para-appendical and paracolic peritonitis, subdiaphragmatic and subhepatic peritonitis, and peritonitis limited to the lesser peritoneal sac (vide infra) are all va- rieties that are less dangerous than is peritonitis beginning among the shifting coils of small intestine. The anatomical sources of peritoneal infection may therefore be arranged ap- proximately in the order of their gravity, as follows : (a) perforations or wounds of the small intestine ; () perforations or wounds of the stomach or large intestine ; (c) perforations or wounds of other viscera, including kidneys, ureters, bladder, pan- creas, and bile-passages ; (d) entrance of bacteria by continuous growth through inflamed gastro- intestinal walls ; ( Internal oblique, cut edge i^ \^- Transversalis muscle Triangular fascia Spermatic blood-vessels Cremasteric fascia, reflected from spermatic cord -'2 Cremaster muscle Internal oblique muscle has been partially removed, showing fibres of transversalis arch- ing over spermatic cord to reach conjoined tendon ; fascia lata has been opened to expose femoral vessels lying within sheath ; temoral canal has been artificially distended. FlG. 1482. Aponeurosis of transversalis Internal oblique, cut edge Transversalis muscle Transversalis, cut edge Internal oblique, iliac origin External oblieme, iliac insertion Transversal Branch of deep circumflex iliac artery Deep epigastric artery Internal abdominal rin Poupart's ligament Infundibuliform fascia, artificially distended] Anterior crural nerve Femoral sheath^ Sartorius Fascia lata Fascial septum betw irtery and vein Femoral vein - 1 t Septum between vein arid femoral canal Femoral canal External pillar of external ring, turned down Cremasteric fascia, cut edge Deep epigastric artery Posterior wall of sheath of rectus Rectus abdominis Anterior wall of sheath of rectus Aponeurosis of external oblique, cut edge Transversalis fascia - Conjoined tendon -Triangular fascia Spermatic cord .Cremasteric fascia reflected from spermatic cord Transversalis muscle has been partially cut away to expose transversalis fascia ; sper- matic cord is seen issuing from internal abdominal ring, covered by infundibuliform fascia, which has been artificially distended ; anterior layer of femoral sheath has been removed; showing femoral vessels and canal ; anterior wall of sheath of rectus has been opened above upper part of muscle removed atid posterior wall of sheath exposed. Ill 1 762 HUMAN ANATOMY. developmental defects ; (b) the presence in the abdomen of portions of the pelvic organs increasing intra-abdominal pressure ; (c) the habitual flexion of the thighs on the abdomen in infants, relaxing the tissues about the hernial orifices ; (d ) the ex- treme shortness of the inguinal canal, the internal ring then lying almost directly behind the external ring, so that the canal is about equal in length merely to the thickness of the abdominal wall. The diminution in frequency during childhood is due to the improvement in posture, to the lessening in size of the abdominal rings and to the shortening of the tissues about them, and to the lengthening of the interval between the rings as the ilia grow and incline outward and the internal ring follows them, i.e., to the formation of the inguinal canal with its valve-like resistance to the protrusion of viscera. The increase in frequency as puberty approaches and is passed is due to the more active' habits of life and the assumption of occupations often laborious. It may also be due to a slight extent to the fact that until the pel- vis has fully developed the femoral ring and canal scarcely exist, and that therefore the femoral variety of hernia is rarely found before that time of life. Later in life hernia is still more frequent, although it, like aneurism, lessens in numbers as old age draws on. This is due to the fact that although in both instances the pre- disposing cause the weakness of vessels or of the abdominal wall may be said usually to increase when the active period of life is passed, the exciting causes due to occupation and muscular effort diminish with relatively greater rapidity. Sex. Hernia is more frequent in males because (a) the structures connected with the male genitalia are more often the subject of developmental defects (ride infra), and (b) the inguinal canal in the female is narrower (containing only the round ligament) and longer (the distance between the anterior superior iliac and the pubic spines being greater), and for both these reasons offers less opportunity for the descent of viscera. The descent of the testicle and the associated changes, which are often imperfect, sufficiently account for the great frequency of inguinal (92-95 per cent. ) as compared with all other forms of hernia in males. In females femoral hernia is less common than inguinal hernia. It, is however, relatively more common than in males because (a) in females Gimbernat's ligament (q.v.) is narrower, thus increasing the area of the femoral ring ; and (t>) it is weaker and less firmly attached, and accordingly offers less resistance to visceral protrusion. In loo ruptured persons the percentages as to inguinal and femoral hernia in the two sexes are as follows : male inguinal, 83.5 ; female inguinal, 8.5 ; female femoral, 5.9; male femoral, 2.1 (Macready). The extent of the influence of a certain shape of the abdomen with lateral bulgings parallel with and just above Poupart's ligament and extending above the level of the crest of the ilium is doubtful, but it certainly indicates a laxity of the abdominal wall, and just as certainly is often, as a precedent condition, associated with hernia. The almost invariable preponderance of right-sided hernia in all varieties, at all ages, and in both sexes has been variously attributed to (a) the greater bulk and weight of the liver ; (6) to right-sidedness in walking and lying, and to the greater strain on the muscles of the right side caused by "right-handedness ;" (c) to the inclination from left to right of the mesentery of the small intestine as it descends ; (d) to the greater frequency of incomplete descent of the testis and of a patulnus funicular process on the right side ; and (e) to the larger capacity and circumference of the right side of the pelvis (Knox, Macready) as compared with the left, causing a corresponding increase in the size of the right femoral ring. External hernia; are influenced as to the site of their protrusion by anatomical conditions causing a diminution over certain localized areas in the resistance of the abdominal wall to intra-abdominal pressure. These conditions depend usually upon the necessity for the passage from within out of (a) normal structures such as the spermatic cord ( oblique M external inguinal hernia) or the round ligament (the labial variety of oblique hernia} ; or (6) such as tin larger vessels Of nerves {umbilical, femoral, obturator, seiatie hernia) ; or (e) upon the weakness or absence at givrn points of some of the components of the abdominal wall, as at the internal inguinal fossa or the supravesical fossa {direct or internal inguinal hernia), along the linea Mouth Peritoneum nsversalis fasci Superficial fascia and skin PRACTICAL CONSIDERATIONS: ABDOMINAL HERNIA. 1763 alba or the linea semilunaris (ventral hernia) , through the pelvic diaphragm, the coc- cygeus and levator ani {perineal hernia) ; or through Petit's triangle (page 530) or the superior lumbar triangle of Grynfelt and Lesshaft (page 1777), or ' ' Braun's space" (page 1777) {lumbar hernia}. Other varieties depend upon (d~) congenital defects, as in some forms of inguinal, umbilical, ventral, and diaphragmatic hernia ; or in the varieties of properitoneal or interstitial hernia FIG. 1483. that accompany misplaced or undeveloped testes ; or (e) pathological changes, as in those ventral hernia that follow abscesses or wounds. This classification, although not exhaustive, will serve as a basis for the later and more de- tailed consideration of the anatomical factors concerned in the production of special external herniae and of their symptoms. The component parts of an external ab- dominal hernia (Fig. 1483) are (i) the sac, consisting of distended and protruding parietal peritoneum, and subdivided into (a) the mouth, the aperture corresponding to the internal her- nial orifice ; (b) the body, the expanded pro- truding portion, the lowest portion of which is called the fundus ; and (c ) the neck, the constricted portion connecting the body and mouth ; and (2) the contents, which in the order of frequency are ileum, omen- turn, jejunum, sigmoid, caecum, and transverse colon. More rarely the ascending and descending colon, the bladder, the ovary, and the various abdominal viscera, with the exception of the liver, have been found among the contents of herniae. Inguinal hernia, by far the most frequent of all the varieties of hernia, (9597 per cent, in males, 5560 per cent, in females), may best be studied anatom- FIG. 1484. Body Fundus Diagram showing- general components of external abdominal hernia. Anterior superior iliac spine Aponeurosis of external oblique Poupart's ligament Falciform process Iliac portion of fascia lata. Femoral ring. Femoral artery. Femoral vein Internal saphenous vein -Intercolumnar fibres External abdominal ring External pillar Internal pillar .Gimbernat's ligament Pubic portion of fascia lata permatic cord Scrotum Dissection of right inguinal region, showing external abdominal ring and saphenous opening in fascia lata. ically by considering its mode of production when, (a) as a direct result of some developmental defect, it is present at or soon after birth ; () the hernial sac being present congenitally, the hernia follows some increase of intra-abdominal pressure ; or, (c) as a consequence of a less marked or less complete original defect or of 1764 HUMAN ANATOMY. an acquired defect (vide supra), the hernia develops in the presence of causative factors (page 1759). Acquaintance with the changes in the abdominal wall and peritoneum involved in the descent of the testis is necessary to an understanding of the anatomy of inguinal hernia. Although these changes are described with the development of the testicle (page 2040), the chief features of the process may be noted here with advantage. By the end of the second foetal month the developing testicle lies behind the peritoneum at the side of the upper lumbar vertebrae, the epididymis and later the testicle being attached to a fibro-muscular band, the genito-inguinal ligament, which stretches from the sexual gland to the lower part of the anterior abdominal wall. During the third month, guided by this attachment, the testicle migrates from its primary location to a position which later corresponds to the internal abdominal ring. About this time the muscular, fascial, and peritoneal layers of the abdominal wall show a protrusion in the inguinal region which results in the production of a sac, the inguinal bursa ; this deepens and extends into the scrotal fold, which meanwhile is formed independently as an integumentary fold. The genito-inguinal ligament, FIG. 1485. Internal oblique- Cremaster muscle Aponeurosis of external oblique, turned outward Saphenous opening Cut edge of aponeurosis of external oblique Sheath of rectus Transversalis fascia Conjoined tendon Triangular fascia ^Spermatic cord Dissection of right inguinal canal ; aponeurosis of external oblique has been cut and turned outward. being attached to the structures undergoing evagination, extends into the inguinal bursa. The muscular tissue within the wall of the latter is derived from the internal oblique and transversalis and constitutes the en-master. The lining of the inguinal bursa is obviously the direct continuation of the general serous membrane of the abdominal cavity and later constitutes the processes vaginulis pcritonei. Thicken- ing of the lower end of the genito-inguinal ligament produces an elevation of tin- floor of the bursa known as the inguinal conns, a structure, however, that in man is very feebly developed as compared with that found in some lower animals. Subse- quently, during the seventh and eighth months, the inguinal conns and the attached testicle are drawn downward into and through the inguinal canal until, shortly before birth, the sexual gland gains its permanent position in the scrotum. The rudimentary conns and the genito-inguinal ligament, which together correspond to the structure usually described as the guba-nacnlunt /fs//'s, become progressively shorter and smaller as the testicle descends, their remains constituting the scrotal ligament, the subserous band which permanently attaches the tunica vaginalis and the testicle to the surrounding tissue of the walls of the scrotum. The original retroperitoncal position of the testicle is always retained, this organ .ind the accompanying constituents of tin- spermatic cord descending outside the PRACTICAL CONSIDERATIONS : ABDOMINAL HERNIA. 1765 peritoneal pouch which extends into the scrotum. For a time free communication with the abdominal cavity is maintained by the now tubular processus vaginalis ; usually, however, by the time of birth, or shortly after, this canal is obliterated, the isolated lower end of the peritoneal pouch persisting as the sac of the tunica vaginalis which almost surrounds the testicle. The peritoneal evagination occurs in both sexes, in the female extending into the labium majus as the diverticulum of Nuck ; this usually early disappears, but, as a great rarity, may remain as an open peritoneal process at the time of puberty (Merkel). If obliteration of the processus vaginalis does not occur, a congenital hernial sac results (Fig. 1488 ), and this may become a hernia, either at birth or in later life, by the descent of some of the abdominal viscera. During their descent the testicle and spermatic cord obtain more or less extensive investments of such parts of the abdomi- nal walls as have taken part in the formation of the original bursa ingualis. From within outward these would be, therefore, ( i ) peritoneum, after obliteration of the stalk of the peritoneal pouch, however, coextensive with only the tunica vaginalis ; (2) infundibuliform fascia (tunica vaginalis communis), continued from the trans- FIG. 1486. Internal oblique, cut and- turned outward Transversalis muscle- Aponeurosis of external - oblique External abdominal ring Saphenous openin, Aponeurosis of external oblique, cut edge Aponeurosis of internal oblique, cut edge Internal abdominal ring; cord covered by infundib- uliform fascia Transversalis fascia (weak spot) -Conjoined tendon Triangular fascia Dissection of right inguinal canal; external and internal oblique cut and reflected, exposing transversalis muscle. versalis fascia ; (3) cremaster fibres, from the transversalis and internal oblique mus- cles, blended by areolar tissue into the cremasteric fascia ; (4) inter columnar fascia, from the aponeurosis of the external oblique. In addition to these coverings from the abdominal wall, the envelopes forming the scrotum proper contribute (5) the modified superficial fascia or tunica dartos and (6) the skin. Unusual attachments of the gubernaculum below to the tuber ischii and sphincter ani account for some of the forms of testicular ectopia (q.v.). Attachments above to the peritoneum of the caecum or ileum, or of the sigmoid, or to the loosely attached peritoneum lining the iliac fossa, account in part for the formation of the sac in infantile hernia (vide infra}. The strength of the attachments of the gubernacula to the testes and to the dartos is shown by the fact that in cases of elephantiasis scroti, although the enormously thickened skin and dartos may form a tumor reaching to the knee, the testicles will usually be found near its lower extremity. The next step in the anatomical study of inguinal hernia should consist in a survey of the inner surface of the abdominal cavity in the inguinal, iliac, and hypo- gastric regions (Fig. 1487 ). This will show that the space between the lateral wall of the abdomen and the mid-line marked by the peritoneal fold over the urachus 1766 HUMAN ANATOMY. (plica urachi) is divided on each side into two shallow depressions by a slight eleva- tion of the peritoneum over the deep epigastric artery (plica epigastrica} running from a little internal to the middle of Poupart's ligament to a point on the outer edge of the rectus muscle about one-third the distance between the level of the symphysis pubis and that of the umbilicus. The outer of these depressions is called the external inguinal fossa (hernial fossa). The inner contains a triangular space known as Hesselbach's triangle, bounded by the plica epigastrica, the outer edge of the rectus, and Poupart's ligament. The whole inner region extended to the mid-line is further subdivided by a line corresponding to the peritoneal fold over the obliterated hypogastric artery (plica hypogastrica) into two other fossae, the internal inguinal and the supravesical, which are of use as aids to the description of hernia, but, viewed as mechanical factors, have little bearing on its production. The external inguinal fossa is deepened just to the outer side of the epigastric artery into a slight pouch (Fig. 1487), which marks the point of exit of the sper- matic cord from the abdomen, and therefore the site of the internal abdominal ring and of the mouth of one form of inguinal hernia, the external, oblique, or indirect. On the external surface of the abdomen this pouch corresponds to an area about three- quarters of an inch in circumference, situated a finger' s-breadth above the middle of Poupart's ligament. To the inner side of the epigastric artery are two other and FIG. 1487. Peritoneal surface - Plica epigastrica Hesselbach's triangle Vas deferens External iliac artery External iliac vein Plica hypogastrica Median umbilical ligament Posterior surface of anterior abdominal wall of formalin subject. Outer edge of rectus muscle -Supravesical fossa Outer inguinal fossa Inner inguinal fossa Bladder, somewhat distended still slighter depressions corresponding approximately in position to the outer part of the posterior wall of the canal and to the external abdominal ring (page 1771) and the lower fifth of the inguinal canal. When viscera make their way outward from either of these depressions as the point of departure, the resulting hernia is known as direct because it does not pass through the entire length of the inguinal canal, but takes a shorter route, or internal because it lies to the inner side of the epigastric artery. A further examination of the structures (already described on pages 523, 524) which are related to the production of inguinal hernia will serve to ex- plain its occurrence in certain localities and in certain forms that may now be considered separately in their simpler varieties, the rarer and more complicated being merely mentioned or altogether omitted as unessential to the anatomical study of hernia. Obliqiie, external, or indirect inguinal henna, which makes its exit from the abdo- men at the internal ring, is incomplete if it remains in the inguinal canal, complete if it emerges at the external ring, and scrota/ if it descends into the scrotum. In frequency it bears about the same relation to the other form of inguinal hernia the direct as inguinal hernire do to all other forms of hernia in males, viz., from 95-97 per cent. This frequency depends upon the following anatomical conditions. (a) The descent of the testicle from behind the peritoneum (page 2040), carrying with it a process i vaginal > of peritoneum, a portion of the transversalis fascia (infundibuliform fascia), PRACTICAL CONSIDERATIONS : ABDOMINAL HERNIA. 1767 and of the transversalis and internal oblique muscles (cremaster muscle), makes its region of exit from the abdomen i.e., of its entrance into the inguinal canal the area in the abdominal wall best adapted by reason of its weakness and its shape to favor the exit of viscera. (6) This spot is situated near the lowest level of the inferior zone of that cavity, i.e., at a level at which, when the size of the cavity is either temporarily decreased (as during coughing or straining), or relatively decreased (as when the upper zone is compressed by tight lacing),* or actually decreased (as by intra-abdominal fat, or by a tumor or ascites), the outward thrust of the abdominal viscera is added to by their superincumbent weight, (c} The peri- toneum over the lower part of the anterior abdominal wall is thin and loosely attached, so that it .is unable to offer much effective resistance to distention by pressure from within. Such distention is favored by the funnel-shaped depression at this point, and, having once begun, its influence in localizing a hernia is obvious, (d) The union of the iliac fascia with the transversalis fascia, which is strongest in the imme- diate vicinity of Poupart's ligament, presents an insuperable obstacle to the descent of hernia external to the internal ring, (e) The conjoined tendon of the trans- versalis and internal oblique muscles inserted into the crest of the pubes and the ilio- pectineal line is strong internally, but has an ill-defined outer edge ; while that por- tion of the tendon which is derived from the internal oblique has generally a less extensive attachment than that from the transversalis muscle, so that the space between the border of the rectus and the internal ring is closed by the two tendons conjoined at the innermost part, farther outward by the transversalis tendon alone, while near the entry of the cord there may be a space unprotected by tendon or muscle (Macready). The thinnest and least protected portion of the inner posterior wall of the canal is therefore that adjacent to the inner edge of the internal abdominal ring (Ibid.). It should be noted that Treves is inclined to consider the resistant power of the normal abdominal wall as less over Hesselbach's triangle than over the external inguinal fossa ; but even if this is true, the existence of the internal ring and of the canal more than compensates for it in favoring hernia. These facts sufficiently explain the frequency of oblique inguinal hernia of the acquired form (vide infra), i.e. , the form in which the congenital deficiencies or definite pathological changes next to be mentioned are not demonstrable, although it is not unlikely that some original or acquired defect of the abdominal wall in the neighborhood of the hernial orifices is present in the great majority of cases of hernia of this as of all varieties. (/) The not infrequent total or partial patency of the vaginal process gives rise to a number of subvarieties of inguinal hernia {congenital, infantile, funicular}, all of which are oblique, i.e., enter the inguinal canal at the internal ring and to the outer side of the epigastric artery. These herniae, depend- ing on anomalies in the closure of the processus vaginalis, have been variously sub- divided and defined, often with unnecessary complexity. It will suffice here to say that congenital hernia (Fig. 1488) is due to complete patency of the vaginal process, the cavity of which is directly continuous with the cavity of the abdomen, the sac of the hernia enclosing both its visceral contents and the testicle, which lie in con- tact. Although the condition leading to the formation of this hernia is truly con- genital, the hernia itself is very rarely in existence at the time of birth, but is apt to occur in early life when intra-abdominal pressure is either habitually or suddenly increased. It should be remembered that, although a true congenital hernia neces- sarily depends upon a patent processus vaginalis, patency of the process may exist without hernia. A fold of peritoneum at the edge of the infundibuliform fascia partly screening the abdominal opening of such a process has been described and has been thought to aid in preventing hernia (Macready). In women patency of the canal of Nuck acts similarly as a predisposing cause of congenital hernia, which is, however, of great rarity, on account of the narrowness of the canal itself, the fact that its internal orifice is still smaller, and supposedly by reason of the relatively larger size and greater distinctness in the female than in the male of the peritoneal and fascial fold covering the entrance to the canal. Infantile hernia (Fig. 1489) results from occlusion of the processus vaginalis at the internal ring only, the visceral pressure, aided by the attachments of the guber- naculum testis above described, carrying this septum and the neighboring perito- 1768 HUMAN ANATOMY. neum downward to constitute a sac that descends behind the tunica vaginalis, especially if the latter is capacious, as it is apt to be when its upper limit is at the in- ternal ring. A hernia of this variety has, therefore, between the skin and the con- tents three layers of serous membrane, two of the tunica vaginalis and one of peri- toneum (its own sac) connected with one another at the neck. Not uncommonly, however, as might be expected from the tendency of serous membranes to adhesive FIG. 1488. FIG. 1489. Peritoneum Spermatic cord in and fascia Peritoneum Spermatic cord Skin and fascia Diagram of congenital hernia, showing relation of hernial sac to peritoneum. Hernial sac Tunica vagina Diagram of infantile hernia, showing relation of hernial sac to tunica vaginalis. inflammation, the posterior layer of the tunica vaginalis is intimately blended with the front wall of the sac. Infantile hernia, while due, like the congenital variety, to anomaly in development, is even less apt to exist at birth and, in fact, is rarely seen in infancy. A variety of infantile hernia known as the encysted (Fig. 1490) is de- scribed, in which the intestine depresses the septum at the internal ring, making a sac which passes into instead of behind the processus vaginalis, so that the hernia has in front of it a layer of tunica vaginajis and a layer of septum (sac). This hernia is very properly described (Lockwood, Macready) as "a figment of the imagination." When, after occlusion of the process at the internal ring only, the septum gives way suddenly during some unusual intra-abdominal pressure, the intes- tine may descend at once into instead of behind the tunica vaginalis and lie in con- tact with the testicle, a form of " congenital" hernia that appears in adult life. FIG. 1491. Peritoneum Spermatic cord '. Skin and fascia Peritoneum ^_ Spermatic cord Skin and fascia Hernial sac Tunica vagina Diagram of so-called encysted hernia, showing sup- posed relation of hernial sac tn pel itoneimi. Diagram of funicular lu-inia. showing relation of hernial sac- to tunica \;tgin:ilis. Funicular hernia ( Fig. 1491") is a sequence of the closure of tin- vaginal process at the upper end of the epididymis only, the short pouch of peritoneum remaining in communication with the peritoneal cavity. Tin- contents of such a hernia are separated from the testicle by the septum formed at the- point of closure. Inlcrf>arictal ( intraparietal, interstitial i hernia is so usually a variety of oblique inguinal hernia, and is so commonly associated in the male with anomalies of the PRACTICAL CONSIDERATIONS : ABDOMINAL HERNIA. 1769 testis, that it may be described here. It derives its name from the protrusion from the sac of an inguinal hernia (usually of the incomplete variety) of a pouch or diverticulum which insinuates itself into or between the separate layers of the ab- dominal wall, as (a) between the peritoneum and transversalis fascia ( properitoneal hernia) ; (6) between that fascia and the transversalis muscle, or among the fibres of the internal oblique, or between the internal and external oblique muscles, or sometimes the transversalis and internal oblique having been pushed aside, a's in the descent of an ordinary acquired inguinal hernia (vide infra) between the transver- salis fascia and the external oblique muscle or aponeurosis (interstitial hernia) ; (c) between the external oblique aponeurosis and the skin {superficial inguinal hernia) (Sultan). While the exact mechanism of the formation of these herniae is still unknown, and the various conflicting theories although of great anatomical interest cannot here be set forth, it is perhaps safe to say that the following facts have a direct bear- ing upon the question : (a) a hernia, like other swellings, enlarges in the direction of least resistance ; (b) the preponderance of the association of these interparietal herniae with incomplete inguinal herniae and with retained testis, in neither of which cases have the external ring and the scrotum undergone dilatation, may be due to a lesser resistance in the course of the diverticulum than at the external ring ; (c) they are also often associated with imperfections of the abdominal wall, correlated with the anomalies of the testicle, because, as Macready says, when that organ is defective it is very probable that the parts through which it passes and with which it is so in- timately associated will likewise be deficient. The mechanism of formation of the so-called acqtiired oblique inguinal hernia the most frequent and therefore the most important of all forms of hernia will now readily be understood. Because of the anatomical conditions above enumerated (page 1763), and in the presence of one or more of the etiological factors, the peri- toneum covering the internal ring yields to the pressure of the viscera (usually a portion of the small intestine) and, together with the latter, passes through the in- ternal ring above the cord, the component structures of which, with the artery to the vas deferens, the cremasteric artery, the genital branch of the genito-crural nerve, and the inguinal branch of the ilio-inguinal nerve, are close to the lower margin of the ring. After entering the canal it meets with less resistance, and, aided by gravity and sometimes by prolapse of the mesentery, a loosening or slipping down of its vertebral attachment, which slightly increases the weight of the intestines that must be borne by the abdominal wall, descends until it reaches a point at which the resistance is greater than the forces that are carrying it downward. Its descent has been thought to be aided by the weight of masses of fat (subserous lipomata) sometimes found in the extraperitoneal connective tissue that precedes the sac and forms one of the coverings of nearly all abdominal herniae, but this is more than doubtful. The most frequent point of arrest is at the lower part of the canal, where the rigid, non-elastic pillars of the external ring, strengthened by the intercolumnar fibres, often closely embrace the cord, and where the course of the hernia changes slightly in direction. Until it emerges from the external ring it is known as an in- complete hernia (bubonocele). It is obvious that, with the exception of a few con- genital herniae, every inguinal hernia must at some time have been incomplete. After emerging from the external ring it is known as a complete hernia and usually enters the scrotum. It then meets with but little resistance until it reaches the level of the upper end of the testicle, where it may be again arrested often permanently by the close connection of the coverings of the cord to the tunica vaginalis, or it may descend quite to the bottom of the scrotum (scrotal hernia). It lies throughout its course in front of the spermatic cord. In females the corresponding hernia follows the round ligament through the inguinal canal and appears in the labium majus (labial hernia). As the peritoneal sac and its contents follow this course from the abdominal cavity downward, they are covered by various structures that represent portions of the different layers of the abdominal wall, modified in character, however, at the time of the descent of the testis and designated by new names. The clinical importance of this list of "coverings" has been greatly exaggerated, but they have a certain 1770 HUMAN ANATOMY. Peritoneum and suhserous t issue Infundibuliform (transversalis fascia) Internal oblique External oblique (intercolumnar fascia) Superficial fascia and skin Deep epigastric, artery usefulness as denoting the route of the hernia, and are occasionally of value as land- marks during herniotomies or operations for the radical cure of hernia. The sac of a complete oblique inguinal hernia (Fig. 1492) would carry with it (i) a layer of extraperitoneal connective tissue ; (2) that portion of the transversalis fascia known as the inf undibul if orm fascia ; (3) the muscular fibres derived from the transversalis and internal oblique muscles, and called the cremaster -muscle ; (4) the fibres from the external oblique aponeurosis that aid in strengthening the external "ring," especially the upper angle, the intercolumnar fascia ; (5) the siiperficial fascia, in the scrotum the dartos layer ; (6) the skin. The coverings of an incomplete oblique inguinal hernia will obviously depend upon the point of its arrest, but such a hernia cannot be covered by either inter- columnar fascia or dartos. The sac of a complete oblique inguinal hernia, if followed from within outward, would show first a puckered or pleated appearance at the mouth, due to the folds of peritoneum produced by FIG. 1492. constriction ; next a portion narrow and elongated by the pressure of the walls of the canal, the neck, which in such a hernia would extend from the in- ternal to the external ring ; and finally a portion the fundus or body which, re- lieved from pressure, is usu- ally irregularly ovoidal in shape. The anatomical points at which strangulation is likely to occur are, in the order of frequency, ( i ) the edge of the internal ring, (2) the edge of the exter- nal ring, and (3) in the canal (from fibres of the transversalis or internal oblique), but the constriction of the contents is not infre- quently due to pathological changes in the neck of the sac itself. In operating to relieve constriction at the internal ring, the relation of the epigastric artery should be remembered. The incision should be directly upward. Taxis. In reducing i.e. , returning to the abdominal cavity an oblique in- guinal hernia, the shoulders and thorax should be raised to relax the abdominal muscles ; the thigh flexed and adducted to relax the fascia lata and external oblique aponeurosis, and thus the margins of the external ring and the anterior wall the most unyielding of the inguinal canal ; and the pelvis elevated so as to secure by the aid of gravity a backward or upward pull on the contents of the hernia. After gentle downward traction in the line of the canal so as to remove folds and lessen lateral bulging of the sac and contents over the pillars of the external ring, and while making pressure with the thurhb and fingers of one hand at that point to prevent its recurrence, the other hand encircles the fundus of the sac and with as evenly dis- tributed force as possible makes pressure at first upward, then upward and outward, in the line of the canal, and finally backward. Direct or internal inguinal hernia occurs in only 35 per cent, of cases. The reasons for its relative infrequency have been given. To understand it, the region internal to the deep epigastric artery should 1>< examined ( Fig. 1487). It has been mentioned that this region has been subdivided by a fold corresponding to the plica hypogastrica into a supravesical and an internal inguinal fossa ( Fig. 1487). At the inner angle of the former we find the abdominal wall strengthened ( a) by the presence of the rectus muscle, which extends outward as far as the pubic crest ; (6) by Colics' s ligament {triangiv> ^ ( *l?"*'* ; ^^^ *?^?*?c' M^'^r ; - - v ^: ^ : S X ^ W -Jhr. & T* &,; ?',- , - ty 'mm ^ W:^':. *V^V^* r T :i P - - an d is said to be relatively rather large. In the foetus accessory spleens are found very frequently along the course of the splenic vessels. On the other hand, Parsons seems to find the surface of the spleen more regular than in later life. The fissures on the convex surface are less frequent and less deep. The great size of the liver in the foetus brings the left lobe into contact with the spleen. The relatively large suprarenal capsule nearly or quite separates it from the left kidney. Accessory spleens 2 are common, but they are not all of the same signifi- cance. Some are constricted parts of the spleen which have become separated, mostly from the anterior border, and are connected with the organ only by fibrous tissue. Others, found chiefly in the greater omentum near the hilum, are apparently distinct masses of splenic tissue. Many of them, however, have no Malpighian corpuscles, are intermediate between the spleen and the lymph-nodes, and, proba- bly, are to be classed as haemolymph-glands. They are said to be found some- times within the pancreas. It is not impossible that certain irregular nodules occa- sionally found on the spleen near the hilum are due to the fusion of such accessory spleens. Otto has seen twenty-three accessory spleens in one body. They are usually of the size of a pea. Surface Anatomy. The relations of the spleen to other organs have been described, but it should be stated that the phrenic surface lies beneath the ninth, tenth, and eleventh ribs (sometimes the eighth also), and that its long axis is that of the shafts of these ribs. It is important to note that the spleen is situated behind the stomach rather than to the left of it, so that in general language the organ is more in the back than in the flank. The highest level of the spleen is opposite the body of the ninth thoracic vertebra, and its lowest opposite that of the first or second lumbar. A line from the top of the sternum to the tip of the eleventh rib should be entirely anterior to the spleen. PRACTICAL CONSIDERATIONS : THE SPLEEN. The spleen may be congenitally absent, or it may be of extremely small size, no larger than a walnut ; or there may be supernumerary spleens connected with the main gland ; or there may be nmltiple spleens entirely separate and lying in the folds of the greater omentum, the gastro-splenic omentum, or the transverse meso- colon. It is conceivable but unlikely that these anomalies may lead to mistaken diagnoses. The outline of the normal spleen is difficult of accurate determination by either palpation or percussion because (a) it is covered in front by the stomach, the cardiac end of which if the stomach is distended completely overlaps it ; (b~) posteriorly it is covered at its lower portion by the diaphragm and by the tenth and eleventh ribs and the thick muscles overlying them, and at its upper portion by the same muscles, the diaphragm, the ninth rib, the pleura, and the lung ; (r) inferiorly it is in contact internally with the upper end and part of the outer edge of the left kidney, and externally with the splenic flexure of the colon ; (a?) the upper part of the phrenic surface is occasionally in contact with the left lobe of the liver (Quain) ; (>) it is the most variable in both shape and size of all the abdominal viscera ; (_/") it 1 Archiv f. mikro. Anat., Bd. Ivi., 1900. 2 Consult articles by Parsons and by Haberer, just noted. 1788 HUMAN ANATOMY. changes in position with the movements of the stomach, having its longest diameter vertical when the latter is contracted and horizontal when it is distended. These relations sufficiently explain the difficulty not only in determining the size of the normal spleen, but also in distinguishing by percussion its abnormal enlargement from cases of colonic fecal impaction, of tumors of the left kidney, of large plastic exudate at the base of the left pleura or lung, of hypertrophic cirrhosis involving the left lobe of the liver, and of certain growths of the stomach or omentum. In cases of hypertrophy or of swelling of the spleen, as in malaria ( " ague-cake" ), palpation is often of more value than percussion, the sharp crenated anterior border being recognizable below the tenth costal cartilage. Physiological increase in size occurs during digestion, but pathological enlargement may follow portal congestion, leukaemia, malaria, typhoid, or other infectious disease, including most forms of general sepsis, or may result from infection of the splenic substance. It may as in some malarial and leuksemic cases so enlarge as to occupy most of the abdominal cavity. It is then closely applied to the parietes, and is not, like renal tumors, covered ante- riorly by the intestines. Enlargement of the spleen in infants is often due to inherited syphilis, and if it occurs at the age of two or three months is usually of that character. It is of more diagnostic value than enlargement of the liver, because that organ is normally dispro- portionately large in infancy, and because other causes than congenital syphilis lead to its enlargement. In all forms of enlargement of the spleen in children there is said to be more relative encroachment upon the thoracic cavity than in adults, owing to the firmer support of the phreno-colic ligament in young persons (Treves). Whenever it is greatly enlarged, at any age, it is apt to push upward the diaphragm and compress injuriously the base of the left lung and the heart. In splenic tumors, therefore, irregular cardiac action and dyspnoea are often present for mechanical reasons as well as on account of the associated anaemia. The normal movements of the spleen are not so much affected by respiration as are those of the liver, which is more closely and extensively connected with the dia- phragm. It rises slightly in expiration and descends during inspiration. It is pushed down in emphysema and in left-sided empyema, haemothorax, or pneumo- thorax. It is pushed up by ascites or by intra-abdominal new growths. Its relations explain why abscesses of the spleen (usually due to septic emboli, as in pyaemia or septicaemia, typhoid fever, or ulcerative endocarditis) open spontaneously in the following directions: (i) Into the general peritoneal cavity (the most fre- quent). (2) On the cutaneous surface below the costal margin anteriorly or poste- riorly. (3) Into the large intestine. (4) Into the left pleural cavity. (5) Into the left kidney. Movable spleen {dislocated, floating, wandering spleen} occurs only in adults, and is especially found associated with some degree of splenic enlargement in- creasing its weight in persons with relaxed or flabby abdominal walls. It is, there- fore, often found in anaemic multiparae, as it is held in position normally not only by the phreno-splenic and phreno-colic ligaments, but also by the pressure of the other abdominal viscera due to the general tonicity of the abdominal muscles. In such cases, after elongation of the phreno-splenic ligament, the spleen falls forward, lies horizontally with the hilum directed upward, and is sustained only by the gastro-splenic attachments and the vessels, thus drawing the stomach downward and causing serious gastro-intestinal disturbance, or possibly, if the vessels are twisted and obliterated, a fatal peritonitis (Shattuck >. In exceptional cases a movable spleen may reach the pelvis. I'Yoin a movable kidney a wandering spleen may be distinguished l>y the super- ficial position of the latter, its shape, the disappearance of the spleen from its normal position, and the absence of urinary symptoms. H'oHHctx of the spleen, if posterior, usually involve the diaphragm and the base of the left pleiiral cavity, or, if higher, the lung itself : if anterior, the stomach may In penetrated. Ill gunshot wounds the kidney, colon, or pancreas may likewise be involved. THE THYROID BODY. 1789 In fractures of the ninth, tenth, or eleventh rib the fragments may lacerate the spleen. On account of its great vasctllarity, wounds of the spleen are serious and often necessitate operation, but occasionally, after small stab wounds or gunshot wounds from bullets of small calibre, spontaneous recovery takes place, and has been attributed (Treves) to the contractility of the muscular tissue of the splenic capsule, which narrows the wound-track, enables it to retain the blood-clot, and thus stops the hemorrhage. The blood from a wound of the spleen is usually bright red. In wounds of the liver it is apt to be dark, if the lung is wounded the blood is commonly frothy, and if the stomach has been penetrated the blood is mixed with the acid gastric contents. Rupture of the normal spleen is not very frequent, in spite of its friability, on account of the way in which it is suspended from the diaphragm, supported beneath by the elastic colon and indirectly the small intestine, and partially protected anteriorly by the stomach and posteriorly by the lung. When it is enlarged, on the contrary, it extends beyond the region of safety, becomes more closely and exten- sively applied to the parietes, and may be ruptured by blows, by falls from a height, or even by muscular violence. Spontaneous rupture can occur only in cases of ad- vanced hypertrophy with softening of the parenchyma. The latter may be ruptured, but the elastic capsule escape. In all these cases of splenic injury the symptoms of localized intra-abdominal lesion, pain, often at first general, then referred to the epi- gastrium or umbilicus, then more marked in the splenic area, sometimes accompanied by nausea or vomiting and followed by rigidity of the left upper quadrant of the abdomen, immobility of the lower thorax on that side, meteorism, etc., plus the symptoms of internal hemorrhage, will be present to a greater or less degree. They have been sufficiently explained in the sections on the intestine, the appendix, and the peritoneum. In operations on the spleen it may be approached through incision either at the outer edge of the left rectus muscle or in the median line. In splenectomy great care must be taken to avoid premature tearing or division of the large vessels contained within the gastro-splenic omentum and lieno-renal ligament, particularly the splenic vein. The "pedicle" omentum and vessels may sometimes best be reached by lifting the inner border of the spleen, and some- times (Warren) by pulling the spleen down from beneath the diaphragm and turning it completely over. Next to hemorrhage, the chief risk is that arising from damage to adjoining viscera during the separation of adhesions, and the relations of the stomach, pan- creas, colon, and kidney should therefore be carefully borne in mind. THE THYROID BODY. This organ is situated in the neck in front and at the sides of the trachea. It is symmetrical in plan, but not usually in the details, consisting of two lateral lobes connected by a narrow strip, the isthmus, from 5 mm. to 2 cm. in breadth. The height of the lateral lobes ranges from 3 cm. , or less, to twice as much within normal limits. The transverse diameter of the whole organ is 6 or 7 cm. The weight is from 3040 gm. (i i^j oz. ), with wide variations. It has the appearance of a lobulated glandular body, reddish yellow in color. Shape and Relations. Each lateral lobe is an irregular body, vaguely pyramidal in form, which can be properly studied only in situ. There is an antero- external surface which meets the inner at a sharp border. The, inner surface is con- cave, being moulded over the side of the trachea and larynx. These surfaces are connected by a third, the posterior surface (usually improperly called a border), which faces backward and outward, sometimes nearly backward. The surfaces come to- gether above in an apex over the posterior part of the body, so that the border sepa- rating the antero-external and the internal surfaces rises from the middle of the body obliquely backward. The lower end of the lateral lobe is thick and rounded. The isthmus, connecting the lateral lobes below the middle, usually crosses the second and third rings of the trachea. Its anterior surface passes without interruption into the 1790 HUMAN ANATOMY. Epiglottis Superior cornu of thyroid cartilage antero-external surfaces of the lateral lobes. The isthmus varies much in size, and is often more or less incorporated in one of the lobes. In 10 per cent, it is absent. 1 An upward projection, the pyramidal process, rising from either the isthmus or one of the lateral lobes, and usually regarded as a remnant of the median anlage ot the thyroid, is found more or less developed in probably half the cases. A typical one reaches the hyoid bone, to the body of which the process is generally attached either by muscle or ligament. It is rarely quite median, being more frequently found on the left. Statements as to its frequency vary greatly. Streckeisen * says it is wholly wanting in only about FIG. 1510. 20 per cent. ; but, since goitre is common in Switzerland, his sources of information are not of the best. Ztickerkandl, however, puts the occurrence of the process at 74 per cent. Gruber, in Russia, found it in only 40 per cent., and Mar- shall, in England, in 43 per cent. We incline to believe that these latter figures rep- resent the more common pro- portion. The thyroid lies beneath the group of infrahyoid mus- cles, from which it is separated by the middle layer of the cervical fascia. The sterno- mastoid muscle crosses the lower part of the lateral lobes. The inner surface lies against the trachea, the cricoid carti- lage, and the lower posterior part of the wings of the thy- roid cartilage. It reaches back to the oesophagus, which it touches on the left, and some- times on the right also. It may touch the lower part of the pharynx on both sides. The sheath of the carotid lies against the posterior surface at its outer border and is in part external to the organ. The common carotid is usually be- hind the thyroid and the inter- nal jugular vein beyond it. This explains how an enlarged gland insinuates itself between these vessels. Frozen sections show that often the carotid is external rather than posterior to the organ, but still in close relation to it. Internal to the carotid sheath, it rests behind against the prevertebral fascia. The inferior thyroid arteries enter the lateral lobes from the inner side and the superior thyroid arteries from the antero-external. The middle cervical sympathetic ganglion is behind. The inferior laryngeal nerves lie at its inner surface, the left one being in actual contact with the thyroid and the right one at least very close to it. The sheath connects the thyroid body very closely to neighboring parts. It is so firmly bound to the trachea as to follow its movements. Median bands to the cricoid and thyroid cartilages have been 1 Marshall : Journal ot Anatomy and Physiology, vol. xxix., 1895. * Virchow's Archiv, Bel. dii. Lobule Trachea Thyroid body in xitii ; anterior aspect. THE THYROID BODY. 1791 distinguished as suspensory ligaments. A lateral ligament from the inner side of the lateral lobe is tolerably well defined. It passes backward and upward to the first ring of the trachea, to the cricoid, and perhaps to the inferior horn of the thyroid. The levator glandule thyroidea; is a small muscle often found passing down from the hyoid bone to the capsule. It may or may not be connected with the pyramidal process. Sterno-thyroid muscle FIG. 1511. Sterno-hyoid muscle Left internal jugul Left pneumogastr Left com mon caro Infer Right internal jugular vein Pneumogastric nerve Right common carotid artery Infer Prevertebral fascia Tra Inferior laryngeal nerve chea CEsophagus Anterior part of frozen section across neck, showing relations of thyroid body. Structure. Although in principle corresponding in its development with other compound alveolar glands, the thyroid body possesses no excretory ducts and pre- sents peculiarities in the structure of its terminal compartments. The fibre-elastic capsule investing the gland gives off septa which subdivide the organ into the chief lobules, the latter being composed of smaller compartments separated by thin parti- tions of connective tissue. These subdivisions, or primary lobules, from . 5-1 mm. FIG. 1512. { , '*,!"" <.-3T. w j? >$"' V> Interlobular connective-tis- sue septum " "I*"' - >^-h 'V,? "- ( >O. a/'3 '. #- i&J '$.;'. '/Baf...'.;'.' Acinus dis- : ^ ; " V--,/^-::^ tended with * rtjjti ,'bfjj&'^ colloid '' .Undistended acinus r ''^yy~ Section of thyroid body, showing acini in various degrees of distention. X 100. Interactions connective tissue in diameter, contain a variable and usually large number of terminal vesicles or folli- cles which correspond to the alveoli or acini of ordinary glands. The delicate and highly vascular framework supporting the follicles consists essentially of fibrous con- nective tissue, elastic fibres being few or entirely absent. The acini vary greatly in size (.050 .200 mm.), depending upon the amount I79 2 HUMAN ANATOMY. of secretion and the distention of the acini. Their lining consists of a single layer of fairly regular polygonal cells, about .010 mm. in diameter, the height of the cells varying with the dilatation of the follicle. In young subjects, in whom the acini are generally less completely filled than in older ones, the epithelium of the follicles approaches the columnar type. A similar condition is often to be noted in certain acini, even in thyroids in which the usual distention affects the majority of follicles. A distinct basement membrane is wanting, the cells resting directly upon a somewhat condensed stratum of the surrounding connective tissue. Since the epithelial lining is the source of the peculiar colloid secretion of the gland, the cells ordinarily con- tain a variable number of highly refracting granules, particularly in the zone next the sac. The peculiar substance or colloid commonly found within the follicles of the adult organ is regarded as a proteid, although its exact chemical characteristics are still uncertain. The consistence of this substance varies, being more fluid in young than in old glands. Its varying appearance within the follicles, as vacuo- lated, reticular, or shrunken, is referable to the action of reagents, in its natural condition the secretion being homogeneous and entirely filling the follicle. The differentiation of the epithelial lining of the acini into chief and colloid cells (Lang- endorff), as representing distinct elements, is doubtful, since specific differences probably do not exist. Vessels. The blood-supply is very generous, coming from two pairs of rela- tively large arteries, the superior thyroids from the external carotids, and the in- ferior thyroids from the FIG. isn. subclavians. The superior descend to the top of the lateral lobes and ramify over the front of the organ, sending branches to the interior, and sometimes meeting on the isthmus. The inferior arteries pass upward behind and enter the organ on its inner sur- face. Their relations to the inferior laryngeal nerve are of practical impor- tance. In 437 observa- tions ' the artery was found in front of the nerve on the right in about 41 per cent, and on the left in 63 per cent. In over 10 per cent, of the cases the branches were so inter- laced that the relation was uncertain. It is evident that in enlargement of the thyroid body, with conse- quent enlargement of the arteries, the number of such indefinite- relations would be very much increased, as very minute branches would then spring into importance. An enlarged tortuous artery tends to curl around the nerve. There was no artery on the right in one case and none on the left in five cases of this series. An artcria tkyroidea ima springing from the arch of the aorta and ascending in the median line is occasionally seen. From the rich superficial arterial plexus numerous branches pass along the interl. .bular septa, following the ramifications of the latter to the follicles, where the arterioles break up into capillaries. These surround the follicles with close- meshed net -\vorks, \\hich are often common to the adjacent sacs, resembling the capillary net-works around the pulmonary alveoli. The veins are very numerous. Emerging from the organ, they form a large 1 Dui-lit: Anatom. An/ri-.-r, Md. \., i$95- Acinus con- taining col- loid Section of injected thyroid body. X 46. THE THYROID BODY. 1793 plexus beneath the capsule, from which the blood escapes by three chief courses on each side. The superior thyroid veins are double, and follow the artery to open either into the internal jugular directly or into the facial. They may communicate with the linguals. The middle thyroid vein, less regular, passes from the side of the lobe into the internal jugular, anastomosing, as a rule, with the pharyngeal venous plexus. The interior thyroid veins, generally two in number, some 5 mm. in diameter, come from the deeper part of the organ and form a rich plexus in front of the trachea under the middle layer of the cervical fascia, draining, for the most part, into the left in- nominate ; but a vein may end at the angle of the two innominate veins. The in- ferior thyroid veins can be injected from below. The lymphatics begin within the organ as perifollicular lymph-spaces ; from these plexuses follow the interlobular septa in their course to the exterior, where they constitute a superficial plexus from which the lymph passes in all directions. Some runs upward from the isthmus to small lymph-nodes in front of the larynx, some from the sides to the deep glands about the internal jugular, and some from the isthmus and adjacent parts downward to pretracheal lymph-nodes. The nerves are derived, for the rnpst part, from the cervical sympathetic. It is probable that filaments are contributed by sympathetic fibres running in company with the inferior laryngeal and the hypoglossal nerves. In addition to the fibres destined for the walls of the blood-vessels, the terminal twigs end around the follicles in close relation with the glandular epithelium. Development. The thyroid is developed from three anlages, an unpaired median and two lateral. The median an/age (Fig. 1521) appears in embryos of from 3-4 mm. as an epithelial outgrowth from the anterior wall of the primitive pharynx in the region of the second visceral arch, and therefore in close relation with the posterior part of the tongue. At first possessed of a narrow lumen, the evagination soon loses its cavity and becomes a solid pyriform mass, which for a short time is connected with the pharyngeal wall by a delicate epithelial strand. Usually the latter soon disappears and the isolated median thyroid, which meanwhile rapidly increases as a bilobed mass, passes to the lower level of the lateral anlages. The position of the primary outgrowth is later indicated by the depression on the tongue, the fora- men ctzcum, just behind the apex of the V-row of the circumvallate papilte. Occa- sionally the evagination persists, and then forms the thyro-glossal duct, a narrow tube extending for a variable distance from the tongue towards the thyroid body. The lateral anlage appears on each side as an epithelial outgrowth from the ventral wall of the fourth pharyngeal furrow (Fig. 1521), the minute pocket soon becoming trans- formed into a sac, which early separates from the pharynx. The three primary rudi- ments grow ventrally, and later, in embryos of about 20 mm. , join to form the definitive thyroid surrounding the larynx. Of the three, the median anlage contributes the most important part of the thyroid body. Comparative embryology emphasizes the significance of the median anlage as the thyroid proper ; indeed, all participation of the lateral rudiments in forming the organ in certain animals is denied (Verdun). The histogenesis of the thyroid includes two stages, the first being distinguished by numerous cylindrical epithelial cords from which grow out lateral branches. The second stage witnesses the fusion of these epithelial cords into a net-work the meshes of which are occupied by vascular mesoblastic tissue. During the third fcetal month the epithelial reticulum breaks up into masses corresponding to the follicles of the thyroid. These gradually acquire a lumen around which the cells become arranged to constitute the epithelial lining of the compartments in which later the characteristic colloid substance is secreted. The thyroid agrees with the parathyroids and the thymus in originating from the walls of the primitive pharnyx and, likewise, in devi- ating in its later development from its primary correspondence to a typical gland. Accessory Thyroids. Small detached bodies of the same structure as the thyroid are occasionally found about the hyoid bone in the median line, both before and behind and sometimes below it. They are remnants of the median thyroid diver- ticulum from the primitive pharynx, sometimes represented by the thyro-glossal duct. This passed originally in front of the hyoid bone, thus accounting for suprahyoid and prehyoid accessory thyroids. Those behind and below the hyoid are probably the result of an upward or downward growth from the primary diverticulum. 1794 HUMAN ANATOMY. PRACTICAL CONSIDERATIONS: THE THYROID BODY Congenital absence of the thyroid body, or its atrophy with loss of function, occurring at any time before puberty, is apt to be followed by the interference with nu- trition and with normal mental and physical development that produces the condition known as cretinism. Similar atrophic changes occurring later in life cause wr.iv/-- dema, and the same condition also known as cachexia strumipriva may be brought about by the complete excision of the gland. Calcification of the gland may take place in old age. The isthmus may be congenitally absent and. two separate lobes be present, representing the originally distinct embryonic lateral anlages of the organ. Accessory thyroids may undergo hypertrophy and form large masses occupying the pleural or the mediastinal cavity (Osier- Packard) ; or they may develop at the base of the tongue, lingual goitre ; or, on account of their embryonic relation to the thyro-glossal duct (which passes behind the hyoid bone), they may be found in the median line of the neck below or behind the hyoid, and may be mistaken for growths of a different character (page 554): The thyroid gland may be temporarily enlarged in women during menstruation. Hypertrophy of the thyroid gland (goitre) may be (a) parenchymatous when it results from a general hyperplasia of the gland-tissue ; (3) -vascular, due to a great increase in the size and number of the blood-vessels ; (c ) cystic, characterized by the formation of walled-off cavities within the already enlarged gland ; (d ) fibrinous, the connective-tissue elements being in excess ; (^) exophthalmic ( Graves' s disease), in which the thyroid enlargement is associated with exophthalmos and functional derangement of the vascular system ; (_/") adenomatous, the hypertrophy affecting one or more lobules or the isthmus. This last form appears as a one-sided or asym- metrical swelling, is common, and is often classified with tumors of the thyroid, rarer forms of which are the cancerous and sarcomatous. It may be noted that the gland is relatively larger in females, and that the right lobe is larger than the left. This has been thought to explain the greater frequency of goitre on the right side, and in women. Inflammation of the thyroid is rare, and usually occurs during typhoid or other infections, although it is favored by previous thyroid disease or overgrowth. The tumefaction which it produces may cause acutely many of the symptoms brought on more slowly by the chronic forms of enlargement. These symptoms, so far as they have any anatomical bearing, are : (i) The swelling rises and falls with the larynx during deglutition. This is due to the attachment of the thyroid gland to the cricoid cartilage by the upward prolongations of its capsule known as the suspensory liga- ments and to the subjacent larynx and trachea by connective tissue. (2) Dyspna-a. The gland is covered and its growth anteriorly resisted by the sterno-hyoid and sterno-thyroid muscles (Fig. 545), and, to a less degree, by the omo-hyoid and the anterior border of the sterno-mastoid. Its forward progress is also resisted by the pretracheal layer of the cervical fascia. Its close relation to the trachea, therefore, renders the latter subject to direct pressure, especially in the firmer forms of bilateral enlargement, or in those adenomata which begin in the isthmus or lie between the trachea and the sternum. In the unilateral forms the trachea may be displaced to one side. (3) Headache, vertigo, cyanosis, and cpistaxis. The relation of the outer border of the thyroid to the carotid sheath explains the disturbance of the cir- culation in the carotid and internal jugular (either through direct pressure or by deflection of the vessels outward) and accounts for these phenomena. (4) Hys- phagia is relatively rare, but may occur as the result of pressure upon the upper < MK! of the gullet or the lower portion of the pharynx. It is more common in left- sided goitres, owing to the curvation of the oesophagus towards the left. As a great rarity the isthmus of the gland is found between the trachea and oesophagus ( Burns ). (5) Hysphonia, or aphonia, due to pressure upon the recurrent laryngeal nerves. (6) Pulsation or bruit. These may be apparent, and caused by the close relation of the enlargement to the common carotid artery, or much more rarely real, and due to the relatively enormous bloed-supply of the vascular form of goitre, the thyroid with its four constant arteries and occasional fifth one (the thyroidea inia, 10 per THE PARATHYROID BODIES. 1795 cent, of cases) being' normally one of the most vascular structures of the body. They are most common in the exophthalmic form. (7) The tremor, tachycardia, and protrusion of the eyeballs seen in Graves' s disease in association with thyroid enlargement have no satisfactory anatomical explanation, although the close relation of the sympathetic nerve and middle cervical sympathetic ganglion to the inferior thyroid artery, the distribution of their vasomotor fibres to the thyroid vessels, and of other associated fibres to the ocular apparatus, and their possible central connec- tion " probably in the medulla" (Treves) have been invoked to explain the phe- nomena of this form of goitre. Operations on thyroid enlargements vary with the character of the latter. In the adenomatous and cystic varieties, after division of the capsule of the gland, the tumor or the cyst may generally be shelled out with the finger or by blunt dissection (enucl cation). Under these circumstances only some superficial veins may require ligation, although free bleeding may occur from the intrinsic vessels of the gland. In most of the other varieties of goitre the greater part of the growth should be removed (excision, thyroidectomy). This should always be partial, i.e., a portion of the gland should be left in place with sufficient vascular connection to insure its vitality. In excision the skin platysma and cervical fascia should be freely divided and the sterno-hyoids and thyroids retracted or divided ; after its anterior surface has been well exposed the growth is first loosened externally, as it will be found fixed above by the superior thyroid vessels, below by the inferior thyroids, and internally by the isthmus, the vessels separately ligated, great care being taken to avoid the recurrent laryngeal nerve when the ligature is applied to the inferior thyroid artery, the posterior surface dissected from the larynx, trachea, and other underlying structures, and the growth removed. FIG. 1514. THE PARATHYROID BODIES. These organs, the epithelial bodies of many authors, are small elliptical masses situated near the thyroid, which formerly were mistaken either for accessory thy- roids or for lymphatic nodules. They arise from the posterior wall of the third and fourth pharyngeal pouches, and thus differ from the thyroid body in origin as well as in structure. They are 6 or 7 mm. long, 3 or 4 mm. broad, and 1.5 or 2 mm. thick. The length may be as much as 15 mm. "They are always separated from the thyroid by the capsule. Most frequently the parathyroids exist as two pairs on each side ; their disposition, however, may be asymmetrical, in some cases as many as four, in others none, lying on one side. The position of the siiperior pair is the more constant. According to Welsh, 1 they lie on the pos- terior wall of the oesophagus, about the level of the lower edge of the cricoid cartilage, immediately internal to the posterior border of the lateral lobe of the thyroid and in front of the prevertebral fascia. They are always behind the lateral thyroid ligament, unless, as sometimes happens, they are placed so high or so low as to have no relation with it. The inferior pair is lower and more anterior than the superior, their position being less constant. Sometimes they lie against the side of the trachea near the ends of the rings, under cover of the lower part of the thyroid lobes ; sometimes they are found in a corresponding rela- tion to the windpipe, but much lower, so as to have no relation with the thyroid ; occasionally they lie on the front of the trachea below the thyroid. The lower pair are always below the inferior thyroid arteries. Structure. Each organ is invested by a thin fibrous capsule and subdivided into ill-defined lobules by a few delicate septa which support the blood-vessels. 1 Journal of Anatomy and Physiology, vol. xxxii., 1898. Diagram showing more usual positions of parathyroid bodies, seen from behind, sp, superior pair, lying at level of cricoid cartilage (cc) ; ip, in- ferior pair; th, lateral lobe of thyroid body ; />k, pharynx ; ce, oesophagus ; ita, inferior thy- roid artery. (After li'elsh.) 1796 HUMAN ANATOMY. The gland-tissue consists of closely placed polygonal epithelial cells, about .010 mm. in diameter, varyingly disposed as continuous masses or imperfectly separated cords and alveoli. The cells possess round nuclei which contain chromatin reticula. The cells are surrounded by a honey-comb of delicate membranes, fibrous tissue appear- ing only in the immediate vicinity of the larger blood-vessels and not between the epithelial elements. The latter lie against the endothelial lining of the relatively wide and numerous capillaries, the attenuated membrane of the intercellular honey- comb alone intervening. While admitting the independence of the parathyroids as FIG. 1515. /> c * . * *" ~ ^^v Sections of human parathyroid bodies, showing different types of structure. .!, ptmi-ipal ix-lls an uniform continuous masses; B, broken up into lobules by vascular septa (v) ; C, disposed as acini, some of whic contain colloid (c). X 200. (After Welsh.) distinct organs, as now established by both anatomical and physiological investiga- tions, 1 opinions differ as to their histological relations. Schaper 2 and others incline to the view advanced by Sandstroem, that the parathyroids correspond in structure to the immature and undeveloped thyroid. Welsh, on the contrary, denies this resemblance and points out the close similarity to the anterior lobe of the pituitary body, in both organs colloid-containing alveoli being occasionally present. The arteries distributed to the parathyroids are derived from the branches sup- plying the thyroid body. Regarding the lymphatics and the nerves little is known ; the latter are chiefly sympathetic fibres destined for the walls of the blood-vessels. THE THYMUS BODY. The thymus is apparently an organ of service to the nutrition possibly blood- formation of the foetus and infant, since it usually reaches its greatest size at about the end of the second year, having grown since birth fairly in proportion to the body. It continues for some years to enlarge in certain directions and to dwindle in others ; coincidently deposits of fat appear and it gradually degenerates. When in its prime it is moderately firm and of a pinkish color ; later it becomes very friable and resembles fat and areolar tissue. Shape and Relations. The appearance of the thymus is that of a glandular organ. It is surrounded by a fibrous capsule which sends prolongations among the lobules. It is situated beneath the upper part of the sternum, rising, when largest, perhaps 2 cm. into the neck, descending to about the fourth costal cartilages, excep- tionally as far as the diaphragm. The organ is thickest above, where it rests on the pericardium, and descends in front of the latter in two flattened lobes, more or less distinct, which grow thinner and sometimes diverge below. These are separated by a layer of fibrous tissue which enters obliquely from the front in such a way that above the left lobe overlaps the other. The lobes are generally of unequal si/e, the left one being more often the larger. Sometimes the lobes arc fused, and there may be a third one between them, such variations merely implying irregularities of the fibrous septa. The thymus lies in front of and above the pericardium, and against 1 A critical n-viru <>t tin- relations of the epithelial organs derived from the pharyogeal pouches is given by Kohn in Merkel and Bonnet's Krgebnisse, lid. i\., 1X99. 'Archiv f. mikro. Anat. u. Kntwick., Bd. xlvi., 1X95. THE THYMUS BODY. 1797 the aorta and the pulmonary artery after they have emerged from the heart-sac. It is in contact with a large part of the arch of the aorta, and is grooved on the posterior surface by the innominate veins and the superior vena cava. If strongly developed, its highest P al "t may rest on the trachea and even on the oesophagus where this tube appears on the left of the former. It extends laterally on each side into the interval between the pericardium and the pleura. At the time of its greatest size, a hori- zontal section in this region shows the thymus as a thick crescent (Fig. 1518), which becomes thinner as the organ atrophies. Behind the very top of the sternum its out- FIG. 1516. Common carotid artery. Pneumogastric nerve Internal jugular vein I rib Larynx Thyroid body uspensory ligament Trachea Left lobe of thymus Dissection of new-born child, showing thyroid and thymus bodies in situ. line on section is roughly quadrilateral. One or more fibrous bands from the thyroid body to the capsule of the thymus are known as the suspensory ligaments. The internal mammary vessels run in front of it. Weight and Changes. According to Friedleben, the average weight of the thymus at birth is 13. 75 gm. ; the statements of authors, however, vary widely, Sappey giving 3 gm. and Testut, from twenty observations, an average of 5 gm. When heavi- est, about puberty according to Hammar, its average weight is 37.52 gm. Atrophy and the replacement of thymus tissue by fat set in while growth in length is still pro- 1798 HUMAN ANATOMY. Groove for left innominate vein gressing ; this increase is said to continue even after puberty, the organ, how- ever, becoming thinner and softer. Although later almost completely replaced by adipose and connective tissue, the thymus never entirely disappears, remains of its tissue being present even in extreme FIG. 1517. old age (Waldeyer). Cntil about twenty years the organ is usually readily found. In ordinary dissec- tions it is not easily recognized in mid- dle age, although still clearly shown in frozen sections. Occasionally a well-preserved thymus persists in the adult ; on the other hand, it may suffer atrophy very early in child- hood. Structure . The histological character of the thymus completely changes during its development, since it begins as an epithelial outgrowth from the third pharyngeal pouch, for a time attains the nature of a tubo- alveolar gland, and later permanently assumes the type of a lymphoid organ. Externally the thymus is invested by a loose fibro-elastic capsule, from which septa, rich in blood-vessels, pass towards the interior and subdivide the organ into a number of indefinite lobes. The latter are broken up into small, almost spheri- cal lobules, which correspond to lymph-nodules, and consist, therefore, of a denser cortical and looser medullary zone, although these are not sharply defined from each other. The cortical substance presents histological characteristics resembling those of dense lymphoid tissue, closely packed lymphocytes lying within the narrow meshes of the supporting reticulum. The latter consists' of stellate anastomosing cells. Posterior aspect of thymus body hardened in situ. II rib-cartilage FIG. 1518. Sternum II rib-cartilage Left lung III rib / 1 v \ IV rib Head of IV rib Head of IV rib IV lib Transverse section of body at level of fourth thoracic vertebra ; from child of about one year In addition to the usual elements, eosinophilic cells ;m- t<>un', p", superior and inferior parathyroids; vc, vena cava superior ; a, aorta. ( Tournrux and l-'erdun.) derivation of which is indicated by the connective tissue separating the right and left divisions. The upper ends of the latter are often continued as far as the thyroid as lateral processes. Subsequent to the second year regression sets in, and the THE SUPRARENAL BODIES. 1 80 1 Thymus tissue thymus structure is largely replaced by fibrous and adipose tissue, vestiges of the characteristic tissue, however, persisting (Fig. 1522). In addition to the chief anlage from the third pharyngeal pouch, a rudimentary outgrowth occurs from the ventral wall of the FIG. 1522. fourth one, external to the origin of the lateral thyroid. According to Groschuff, 1 this anlage may persist in man as \\~\eparathvmus, a small body which occurs in close association, or even encloses, the para- thyroid derived from the dorsal wall of the fourth pouch. The lat- ter, -therefore, corre- sponds to the third pharyngeal pouch in giving rise to both a parathyroid and a thy- mus ; in addition it pro- duces the lateral thy- roid anlage. According to Beard, ~ , , Section of thymus body of man of twenty-eight, showing invasion and replace- rreiiaut, and Others, ment of thymus tissue by fat. X 20. the transformation of the thymus into a lymphoid organ occurs as the direct conversion of its original epithelial elements into lymphocytes and not by invasion of pre-existing lymphoid cells. While accepting such origin for the reticulum, Hammar 2 regards the lymph- ocytes as entering from without. Fat V Thymus tissue THE SUPRARENAL BODIES. These are a pair of cocked-hat-shaped bodies situated at the back of the abdo- men, on the inner aspect of the upper ends of the kidneys. Each has a base, or renal surface, corresponding to the bottom of the hat, and an anterior and a posterior surface, the basal borders of which are concave and look outward and downward. There are an upper and a lower angle at either end of the base. The inner convex border tends, especially in the right capsule, to present a third angle rather above the middle. Thus the right one is more triangular and the left more crescentic. They may be 6 or 7 cm. long and about half as broad. The thickness does not probably often exceed 2 cm. The base is concave, adapted to the kidney, of which it overhangs the anterior surface. The lower end is much thicker than the upper. The concavity deepens above into almost a furrow filled by areolar tissue. The an- terior surface bears a deep fissure, the hilum, in the main parallel with the base, sub- dividing it into two approximately equal regions. The posterior surface is con- siderably smaller than the anterior, owing to the projection of the latter over the front of the kidney. It also presents a fissure nearly parallel with the base-line, but neither extending the whole length of the organ nor so deep as the front one. In color the suprarenals are of a dirty yellowish brown and more or less pig- mented. They weigh 6 or 7 gm. The left one is usually the larger. Relations. The basal surfaces are on the kidneys. The posterior surfaces are against the diaphragm. The anterior surface of the right capsule has its lower inner part behind the inferior vena cava. The part of the lower end near this may be behind the duodenum. The remainder is in contact with the liver. The highest 1 Anatom. Anzeiger, Bd. xvii., 1900. 1 Ibid., Bd. xxvii., 1905. 1802 HUMAN ANATOMY. part is between the non-peritoneal posterior surface of the liver and the abdominal wall. This, of course, like the two preceding areas, has no peritoneum. The rest lies in contact with the lower surface of the liver, and is coated by the peritoneum of the posterior abdominal wall. The anterior surface of the left capsule is nearly or quite peritoneal, resting against the stomach, the spleen, and the tail of the pancreas. Structure. The suprarenal body is invested by a thin, but fairly strong, fibrous capsule. Section across the thicker parts of the organ displays an outer zone, or cortex (.25-1.20 mm. in thickness), which surrounds the central medulla. Where thinnest, as towards the borders, the medulla is reduced to a narrow zone and may be entirely wanting ; where best developed, as in the middle of the organ, it may attain a thickness of over 3 mm. The cortex is usually of a dirty yellow color, presenting FIG. 1523. Crura of diaphragm Capsular vein in groove for vena cava Hepatic surface Peritoneal surface Inferior vena cava _ j Right kid Cceliac artery L_ Superior mesenteric artery Capsular vein emerging from hilum Left renal vein .Left kidney Diaphragmatic surfa Anterior aspect of suprarenal bodies hardened in situ. FIG. 1524 Renal surface Diaphragmatic surface Renal surface Left Right Posterior aspect of suprarenal bodies shown in preceding figure. next the medulla a narrow darker zone of varying shades of brown. The medulla is of a grayish tint and generally lighter in color than the cortex. Its exact tint, how- ever, varies with the amount and condition of the contained blood, when engorged with venous blood appearing dark. In consistence the medulla is less resistant and more friable than the cortex. The cortical substance consists of a delicate framework of connective tissue, con- tinuous with and prolonged imvanl from the capsule, in the meshes of which lies the glandular epithelium. The arrangement of the latter, although generally columnar, varies at different levels, three zones being distinguished within the cortex. The zomt x/flnirnt/osti lies next the capsule, and consists of the somewhat tortuous or coiled groups of cells. The -:onn faxciculata forms the chief part of the cortex, and maintains the radial disposition of the cell-columns. The zona rcticularis, next the THE SUPRARENAL BODIES. 1803 w Capsule Cortex medulla, includes the net-works of epithelial elements formed by the union of the cyl- inders. The cells throughout the cortex are very similar, being rounded polygonal elements .01 5-. 020 mm. in diameter, and very often contain fat granules. Those composing the zona fasciculata are largest, while those within the reticular zone are more or less pigmented and responsible for the darker tint of this portion of the cortex. The medullary substance consists chiefly of net-works composed of anastomosing cords of epithelial cells from .020 .036 mm. in diameter; in addition there are numer- ous blood-vessels, particularly veins, and many bundles of nerve-fibres with ganglion- cells. The protoplasm of the medullary cells is finely granular and possesses an especial affinity for chromic acid and its salts, staining yellow or brown. They vary from polyhedral to columnar in form, and often border large blood- and lymph- spaces. The cells of the medulla are more prone to undergo post-mortem F IG - I 5 2 5- change than those of the cortex. Vessels. The chief arteries supplying the organ- are the three suprarenal or capsular arteries, the middle from the aorta and the su- perior and inferior from the phrenic and renal arteries respectively. They break up into a dozen or more fine branches before reaching the organ, which they enter at various points, some penetrating directly into the medulla, others terminating in the cortex. The latter form a superficial capillary net-work within the cap- sule, from which continuations pass between the cortical cell-columns, around which they constitute capil- lary net-works. The medulla is di- rectly supplied by arteries destined for the interior of the organ. These soon break up into capillaries which surround the medullary cords and pass over into an unusually rich plexus of veins. The latter claim as tributaries the venous radicles of the zona reticularis and impart to the medulla in general a spongy charac- ter. The veins form a rich plexus about the organ, communicating freely with those of the kidney. The chief vein of the right suprarenal passes into the inferior vena cava and that of the left one into the renal. The lym- phatics are numerous, the chief trunks accompanying the arteries. In addition to the superficial net-works in the outer part of the cortex, the medulla contains many deeper lymphatics in the vicinity of the larger veins. Nerves. The very rich supply is derived principally from the solar and renal plexuses. The number of medullated fibres would imply that many come through the splanchnic nerves. Branches probably come also from the vagus and the phrenic (Bergmann). Within the capsule lies a superficial plexus from which small bundles of nerve-fibres enter the cortex, between the cell-columns of which they form plexuses, chiefly for the walls of the blood-vessels. The greater number of the nerves, how- ever, pass to the medulla, where they unite into coarse plexuses, from which finer twigs are distributed to the vessels and the cords of medullary cells surrounding the veins. Dogiel has traced the terminal filaments between the epithelial elements. Numerous ganglion-cells lie within the medulla. Sometimes they occur in groups along the larger nerve-bundles ; at other times they are encountered as isolated ele- Capsule Section of suprarenal body including entire thickness of organ, showing general arrangement of cortex and medulla. X 27. 1804 HUMAN ANATOMY. FIG. 1526. sj--"" 1 Capsule gp Papillary Zona isciculata ments ; but in all cases they exhibit the characteristics of sympathetic cells. Indeed, so numerous are the latter that the suprarenal is regarded by some anatomists as an organ accessory to the sympathetic nervous system. Development and Growth. The genesis of the suprarenal body has been the subject of much discussion and uncertainty, especially as to the origin of the medulla. Comparative and embryological studies clearly indicate that the mam- malian suprarenal body consists of two separate and distinct organs, which, although intimately united as cortex and medulla, possess a different origin and function. 1 According to the investigations of Aichel, 2 the suprarenal in the higher mammals first appears in close rela- tion to the Wolffian body, the anlage arising from the proliferation of meso- blastic cells at the ends of imaginations of the mesothelium lining the body- cavity. The individual cell-groups thus arising with the several in vagi na- tions fuse into the general anlage of the suprarenal. The primary close asso- ciation of the latter with the Wolffian body is later lost, the subsequent mi- gration of the organ bringing it into secondary relation with the permanent kidney. Regarding the origin of the me- dulla two views obtain. According to the one now widely accepted, the medullary portions are developed from cells which are derived from the ad- jacent embryonic sympathetic gan- glia, the chief support of this opinion being found in the close correspond- ence of the medullary cells with the chromaffin elements of sympathetic ori- gin occurring in other localities, such cells wherever found exhibiting an especial affinity for chromium salts. When fully developed, the medullary cells may be regarded as highly special- ized cells which elaborate a powerful stimulant that passes into the blood (Vincent). The other view, supported by Janosik, Valenti, and Aichel, attri- butes the origin of the medullary cells to the same mesoblastic anlage that produces the cortical cords of which Medulla those of the medulla are only speciali- zations. The differentiation of the su- prarenal into cortex and medulla Occurs comparatively late and long after the primitive organ has become sharply de- fined from the surrounding tissue. For a time the entire organ consists of cells which are identical in appearance. During the third month this common tissue differenti- al es into cortex and medulla, in consequence of the breaking up of the outer zone into columnar masses by the advent of connective-tissue trabeculae from which delicate tibrill.t arise, forming the inner boundary of the cortex. Within the central part of the organ thus defined numerous venous capillaries appear and break up the tissue 1 Vincent: Journal of Anatomy and Physiology, vol. xxxviii., 1903. a Archiv f. mikro. Anat., Bd. Ivi., 1900. Zqna isciculata K\ Capillary Section of suprarenal body, showing details of superficial and deep portions of cortex. X 225. THE SUPRARENAL BODIES. 1805 into the cords of medullary cells which lie directly in contact with the endothelium of the veins. The subsequent ingrowth of the nervous constituents provides the unusually rich supply of nerve-fibres and ganglion- cells distinguishing the medulla. These F IG - 1528. organs are proportionally very large in the fcetus (Fig. 1529). At birth the antero-posterior diameter is i cm. and the greatest transverse diameter at the base is FIG. 1527. Section of suprarenal body, showing portions of cortex and medulla. X 225. Section of injected suprarenal body ; the vessels in lower third of figure are chiefly tribu- taries to the central vein. X 25. FIG. 1529. Suprarenal Kidney Ureter Fallopian tube Round ligament Bladder _ Suprarenal 1.5 cm. ; the length from the apex to the anterior end of the base is 3.5 cm. and to the posterior end 1.5 cm. At this age the suprarenal covers most of the upper half of the kidney. At an earlier period these organs are markedly lobulated so as closely to resemble the kidneys ; at term, however, the lobulation has nearly disappeared. Accessory Suprarenals. These are mostly very small, rarely surpassing a pea in size. They may be found near the su- prarenal body, in the kidney, in the liver, in the solar and renal plexuses, or beside the testis or the ovary. The accessory su- prarenal situated within the broad ligament in the vicinity of the ovary is regarded by Marchand and others as a normal and .almost constant organ. The latter under- goes compensatory hypertrophy after re- moval of the chief suprarenal. The in- vestigations of Aichel emphasize that the organs included under the designation ' ' accessory suprarenals' ' comprise two groups of structures of different origin and morphological significance. Those asso- ciated in position with the chief organ, as when in the kidney or liver, are derived from separated and isolated portions of the principal anlage of the suprarenal, and, Dissection of three months female foetus, show- ing huge suprarenals, lobed kidneys, and sexual glands. 1806 HUMAN ANATOMY. therefore, are supernumerary. The bodies, on the contrary, situated within the broad ligament, or in intimate relations with the epididymis, are probably developed from the atrophic tubules of the Wolffian body, and hence must be regarded as inde- pendent structures. It is said that the suprarenal bodies are sometimes wanting. PRACTICAL CONSIDERATIONS : THE SUPRARENAL BODY. Hemorrhage into the suprarenal body in new-born infants has been observed (pqst mortem) in a number of cases. Various opinions as to its cause have been expressed. They have been summed up (Hamill) as follows : (i) weakness of the vessel-walls, normal or abnormal ; (2) traumatism, especially during labor, from pressure of the hands in making traction in delivery by the lower pole, and from the frictions and flagellations used to resuscitate the apparently dead-born ; (3) asphyxia from delay in the establishment of respiration at birth ; (4) acute fatty degeneration of the vessel-walls ; (5) fatty degeneration of the tissues of the organ ; (6) firm contraction of the uterine muscles, the resistance of the parts traversed, - and consequent compression of the inferior vena cava between the liver and the vertebral column, thereby producing congestion and hemorrhage into the non- resistant tissues of the suprarenal gland ; (7) convulsions ; (8) syphilis ; (9) cen- tral vasomotor influence from cerebral lesions ; (10) mechanical squeezing of blood into the part during the process of labor ; (n) too early ligation of the cord ; (12) arrest of the circulation through the umbilical artery from compression of the cord or separation of the placenta ; (13) thrombosis of the renal vein or inferior vena cava; (14) infection. Hamill concludes that the first of these seems to be the fundamental anatomical element favoring the occurrence of hemorrhage, that in still-born children prolonged and difficult labor is the exciting cause, and that in those dying later some form of infection is responsible. In cases of tumor of the suprarenal body the following symptoms have been noted (Mayo Robson) : (a) shoulder-tip pain, probably explained by the fact that a small branch of the phrenic nerve passes to the semilunar ganglia ; () pain radi- ating from the tumor across the abdomen and to the back, not along the genito-crural nerve ; (c*) marked loss of flesh ; (>-< - V; ,.-v $& ^i^^sgs ;ff^:^:^ [HEBBIS^r^Ai^^ '' '*' s *" T^s^^isiiii ; ' fe?S$ 'V- &; f ^Y&3&t ?stf '** - -'r ^ $' tC'-.N*^ \ L Capillaries ^ ^1^^ ^* k Section of adult human carotid body ; one entire lobule is shown. X 170. In view of ( i ) the identity of its elements with other chromaffine cells, which are now recognized as closely associated with the sympathetic system in other locali- ties, as in the medulla of the suprarenal body, (2) its extraordinary richness in nerve- fibres, (3) its general resemblance to a sympathetic ganglion, and (4) its direct development from embryonal sympathetic ganglion cells, Kohn' 2 concludes that simv the carotid body is neither a gland nor a typical ganglion it must be regarded as ace sory to the sympathetic system and, in recognition of this relation, proposes t name paraganglion caroticum for the organ. Concerning its function nothing definitely known. The blood-vessels supplying' the carotid body are branches which pass directl from either the common carotid artery or its terminal branches. THE COCCYGEAL BODY. This organ (tjlonius coccyneum), also often called the coccygcal gland, Liischka s gland ( in honor of the anatomist who described it half a century ago :i ), is a small reddish yellow ovoid body which lies embedded in fatty areolar tissue usually immediately in front of the tip of the coccyx, but sometimes just below. According to Walker, 4 the surest guide to the body is the middle sacral artery , to whose ante- 1 Archiv f. mikros. Anatomic, Bd. 40, 1892. 2 Archiv f. mikros. Anatomie, Bd. 56, 1900. ; Die Hirnanhan^ uiul die Stdssdriise cfes Menschen. Berlin, 1860. 4 Archiv f. mikros. Anatomic, Bd. 64, 1904. THE COCCYGEAL BODY. 1811 rior surface the little organ is attached, its long axis lying transverse to that of the blood-vessel. Approached from the posterior surface, the body is found just beneath or within a small opening in the tendinous insertion of the levator ani muscle into the last coccygeal segment, covered by the origin of the external sphincter muscle (Luschka). The dimensions of the organ are small, its transverse and greatest diameter being from 2. 5-3mm. and its thickness less than 2 mm. It sometimes is divided into two or even more tiny lobes. The body thus described is, however, only the largest of a series of nodules which includes a variable number of structures, for the most part of minute size, irregularly grouped around the chief mass (Walker). The additional nodules are in many cases connected with the principal body by means of delicate pedicles, in others entirely free, but in all instances they are grouped around the middle sacral artery or its branches. In opposition to the pre- vailing belief, Walker found neither an unusually rich nerve-supply nor intimate connection between the coccygeal body and the sympathetic. FIG. 1536. Coccygeal gland Capillaries Connective tissue .' **V* ^ stromaV %&j^\^^ i f^hl, ^ '*E? - . , - - yjE . '.- - I irr^B $Urc^*r \VJS9>/ Cells Blood-vessels Section of human adult coccygeal body. X 220. The structure of the body, as seen in transverse sections (Fig. 1536), includes an irregularly oval field of connective tissue, fairly well defined from the surrounding fatty areolar tissue, in which are enclosed numerous aggregations of epithelial cells and, sometimes, a thick-walled artery. The proportion of cell-masses to the connec- tive tissue stroma varies, in some cases the cellular constituents predominating, but commonly the fibrous stroma being the more bulky. The individual cell -groups are uncertainly circumscribed by a slight condensation of the surrounding fibrous stroma. Each aggregation of cells contains a central blood-space, limited by an endothelial wall similar to that of a capillary. Against this wall the epithelial cells lie without the intervention of connective tissue ; likewise the cells themselves are closely packed in direct apposition with one another and in consequence present a polygonal con- tour. They are disposed around the central vessel in from two to five layers, the individual cells being indistinctly outlined and composed of clear protoplasm con- taining a relatively large and deeply staining nucleus. Concerning the mooted ques- tion as to the presence of chromaffine cells within the coccygeal body, the testimony of Walker, Schumacher and especially of Stoerk ' as to their absence seems convin- cing. The last-named investigator concludes that these cells at no period exhibit the chrome-reaction, and, further and in opposition to Jakobsson, that they have no his- togenetic relation to the sympathetic system. On the other hand, the epithelial character of the cells, their intimate relation to the blood-vessels, and the absence of 1 Archiv f. mikros. Anatomic, Bd. 69, 1906. I8l2 HUMAN ANATOMY. Irv LAB RLE " excretory ducts, seem to justify the inclusion of the coccygeal body, at least, pro- visionally, among the organs of internal secretion, as suggested by Walker. THE AORTIC BODIES. These temporary organs were described by Zuckerkandl ' a few years ago and are also known as the bodies of Zuckerkandl. According to their discoverer, as found in the new-born child, they are a pair of small narrow bodies that lie upon the anterior surface of the abdominal aorta, opposite the origin of the inferior mesenteric artery (Fig. 1537), in close relation with the aortic plexus of the sympathetic nerves. Although usually separated, in about 15 percent, of the bodies examined, in which they were invariably present, the bodies were joined by an isthmus into a horseshoe- shaped organ of varying dimensions. FIG. 1537. The right body is usually the larger, ic a with an average vertical length of 1 1 . 6 j mm. the corresponding dimension of the left body being 8. 8 mm. The ex- tremes of length for the right body are from 8-20 mm., and of the left one from 3-15 mm. The width is about one-fifth of the length, and the thickness something less. The sur- face of the little organ is smooth and its color light brown. Whilst its consistency is about the same as that of the neighboring lymph-nodes, the body is softer than the adjacent sym- pathetic ganglia. The aortic bodies are essentially organs of foetal life or at most of early childhood, and in the adult they are represented by mere atrophic remains (Zucker- kandl). The structure of the aortic body includes a fibrous capsule, which is prolonged into the interior as con- nective tissue strands that accompany the numerous blood-vessels entering the organ. The arteries, minute twigs from the aorta, the inferior mesenteric and sometimes the sper- matic, break up into a rich capillary net-work whose wide meshes are filled with closely packed cells of varying size. These are polygonal, spherical or cuboidal in form and distinguished in many cases by exhibiting the peculiar color reaction, after treatment with the chrome-salts, entitling tin in to be classed as chromaffine cells. According to the observations of Zucker- kandl, the genetic relations of the sympathetic ganglia, the medulla of the supra- renals, and the aortic bodies are most intimate, since these various structures are derivatives of a continuous primary cell-mass. In consideration of this association and the constant presence of the distinctive chromafifine cells, it is highly probable that the aortic bodies are to be regarded, along with the medullary portion of tin- suprarenal and the carotid bodies, as appendages or paraganglia of the sympathetic. 1 Verhancllungen der Anatom. Gesellschaft, 1901. Aortic bodies of new-born child ; RAB, LAB, right and left aortic bodies ; a, aorta ; I'M, inferior mesen- teric artery ; let, left common iliac ; ic, inferior cava ; Irv, left renal vein ; ap, aortic sympathetic pk.xu- w, ureter. X 2. {Zuckerkandl.) THE ORGANS OF RESPIRATION. THIS tract includes the organs by which an interchange of gases takes place between the blood and the air. It consists of the larynx, the trachea or windpipe, and its subdivisions the bronchi, the lungs, and the serous membranes, the pleitrce, which surround them. Morphologically this tract is an outgrowth from the fore- gut. The larynx is a specialized apparatus for the production of the voice, situated at the beginning of the windpipe, of sufficient importance to be considered by itself. THE LARYNX. The larynx consists of a number of cartilages which, by their relative changes of position, modify the approximation and tension of two folds of mucous mem- brane over fibrous tissue, known as the vocal cords, on either side of the cleft through which the air enters the \vindpipe. The larynx is in the neck, being suspended from the hyoid bone and leading to the trachea. It is practically subcutaneous in front. Its superior orifice is behind the base of the tongue, and can be seen in life only by a mirror. The cartilages are connected by joints and ligaments, moved by muscles, and covered by mucous membrane, the folds of which form important morphological parts of the larynx. THE CARTILAGES, JOINTS, AND LIGAMENTS. The cartilages which form the framework of the larynx are three single ones : the cricoid, \hethyroid, and the epiglottis; and three pairs: \\\Q arytenoid cartilages , the cor- niculce laryngis or cartilages of Santorini, and the cuneiform cartilages or those of Wrisberg. The last pair, although determining well-defined swellings of the mucous membrane, are very small ; indeed, the cartilage is not always to be found. There are other minute points of cartilage to be mentioned with the structures in which they occur. The epiglottis, the upper part of the cartilages of Santorini, those of Wrisberg, and the ends of the vocal and apical processes of the arytenoids consist of elastic. cartilage, the others being of hyaline cartilage. The cricoid and arytenoid cartilages are derivations from the trachea and represent the more primitive form of larynx. The thyroid and the epiglottis appear in mammals. In monotremes the epiglottis is of hyaline cartilage. The Cricoid Cartilage. This is the foundation of the larynx, being a ring on the top of the trachea. It is nearly circular, the diameter in the male being 19 mm. (Luschka). It is narrow in front, being from 3-8 mm., usually about 5 mm. broad, and some four or five times as much behind. The height at the back is approxi- FIG. 1538. mately 25 mm. in the male and from 16-23 mm. in the female. The cricoid is 3 or 4 mm. Articu ] ar facet . thick in the lower part and in the upper as for arytenoid i .- .-pi cartilage much as 5 or 6 mm. 1 he posterior aspect is somewhat quadrilateral, the upper border de- , i . ,1 -i T . 11 Articular facet scending very steeply at the sides. Internally for thyroid the cricoid is perfectly smooth. The lower cartilage border presents a slight median descent in front Cricoid cartilage, right lateral aspect, and an inconspicuous notch behind. Never- theless, the cricoid is so placed that its posterior margin is a trifle the lower. A small median depression occurs in the superior border behind, and on either side is an articular eminence for the arytenoid cartilage. Being situated on the superior border of the cricoid, this elongated eminence has its long diameter (8-10 mm.) slanting outward, downward, and somewhat forward. Its free edge may be slightly coin-ex or concave in the long axis, but is not far from straight. . It is convex transversely and about 4 mm. thick. The whole elevation is inclined slightly away from the interior of the larynx, so as somewhat to overhang its posterior surface, and is 1813 1814 HUMAN ANATOMY. J 539- Cartilage of Santorini Posterior surface for ,r L ^t arytenoideus Posterior crico- /X arytenoid ligament . Muscular process *>^ Posterior ridge on 4- cricoid cartilage \ Depression for crico-arytenoideus posticus Cricoid and arytenoid cartilages from behind. extremely variable in all its details. A median ridge divides the posterior surface of the cricoid cartilage into two symmetrical depressions for the origin of the posterior crico-arytenoid muscles. Each lateral surface of the cricoid, below the middle, and nearer the back than the front, bears an oval articular facet for the crico-thyroid joint, its long diameter extending upward, backward, and inward. The facet, which is nearly plane, faces chiefly outward, but also somewhat upward and a little backward. The FIG. long diameter is about 5 mm. and the cross one nearly as great. A ridge connecting it with the superior articular facet bounds the posterior sur- face of the cartilage. The anterior surface of the cricoid is somewhat convex vertically, so as to resemble an over-large tracheal ring. The Thyroid Cartilage. This, the shield-shaped cartilage, consists of two quadri- lateral plates, the alee, broader than high, which meet in front and are widely apart behind. The posterior border of each is prolonged upward and downward into two horns, or cornua, some- what flattened from side to side. The lower pair rest on the inferior articular facets of the cricoid and the upper are attached by ligaments to the ends of the greater horns of the hyoid bone. Being thus open behind, the thyroid cartilage is complementary to the cricoid upon which it rests. The thyroid notch (incisura thyroidea) is a deep median depression of the upper border in front, extend- ing nearly or quite^ half-way down. The plates are strongly everted (especially in the male) at the sides of the notch, thus causing most of the prominence known as Adam's apple (protuberantia laryngea). The resulting median ridge ends shortly below the notch, and at the lower border the front of the thyroid is smooth and convex. The upper border is slightly convex on either side, and usually presents a small notch just in front of the root of each superior horn. The superior tubercle is a little prominence on the outer surface, just below and anterior to this notch. The lower border is alternately convex and concave. There is a moderate median con- vexity followed by a hollow, external to which is a marked prominence, the inferior tubercle, between which and the inferior horn is a deep notch. The posterior border is slightly concave in the middle. FIG. 1540. The oblique line is a ridge running downward and forward from the upper tubercle to the lower. It marks the interruption of the mu cular layer out of which the sterno thyroid and the thyro-hyoid mus- cles arise. The inferior constrictor of the pharynx is inserted behind it. The superior horns, usually longer and more flexible than the inferior, run upward, backward, and inward. They become more cylindrical and have blunt rounded ends. The in- ferior horns, broader than thick, run downward and slightly inward, with a turn forward at the ends. In- ternally each presents near the tip a round articular surface of indefi- nite shape for the inferior articular surface of the cricoid. The dimensions of the aloe vary with the sex : in man the height is 30 mm. and the breadth ; V S mm.; in woman, _'.} and 2S mm. respectively. The prominence and sharpness of the angle are male characteristics, in man the average being 00 and in woman 120. It is chiefly through the thyroid cartilage that the male larynx acquires its relatively large si/e. Epiglottis Oblique line, end- ing in tubercles above and 1 \"\\ ':<>]<. I ion. be- low notch, formitit; pi> mum Adami Inferior cornu 'I liM'i.iil OUtibgB, with i-pigluttis. right nntero-lateral aspect. THE LARYNX. 1815 Development and Growth. The thyroid, probably formed from the fourth and fifth branchial arches, is originally rounded in front, the angle becoming- promi- nent at puberty, when the great increase in size in the male and the greater promi- nence occur. A slight strip of cartilage, separate from the rest, is found in the angle in early childhood ; subsequently it becomes less and less distinct. Variations. It is not rare to find a foramen near the upper outer angle, a little below the superior tubercle, which transmits the superior laryngeal artery and exceptionally some fibres of the external branch of the superior laryngeal nerve. Assuming that the thyroid' is developed as above stated, the foramen represents a cleft between the fourth and fifth branchial bars. It is common for one of the superior horns to be shorter than the other, and not very rare for one to be absent. Our experience agrees with that of others in finding the absence more common on the left side. Cartilage triticea r Thyro-hyoid membrane, left half Cartilage of Santorini Posterior crico-arytenoid ligament Joints and Ligaments connecting the Thyroid with the Cricoid Car- tilage and with the Hyoid Bone. The crico-thyroid joints, between the lower articular facets of the cricoid and the inferior horns of the thyroid, are very indefinitely shaped. The facet of the thyroid is on the inner side of the inferior horn, and is nearly plane, but either par- ticipant of the joint may be the FIG. 1541. contained one. The capsule is Epiglottis lax, although somewhat strength- ened by two by no means con- stant ligamentous bands. An an- terior one extends downward and forward from the front of the lower horn ; a posterior one ex- tends upward and backward from the back of the same. The motion is usually described as rotation on a transverse axis passing through both joints, but in fact a great deal of irregular sliding is possible. The crico-thyroid mem- brane, although connecting the cartilages in front, has no direct attachment to the thyroid at the sides, and consists of a central anterior and a lateral part. The anterior part, also known as the conoid ligament, is triangular in shape, with its base attached to the upper edge of the cricoid car- tilage and its truncated apex to the lower border of the thyroid. This is the strongest part of the membrane, con- taining considerable elastic tissue, and closes the middle of the space between the two cartilages. It is pierced by several small holes for blood-vessels, and is crossed superficially by the crico-thyroid artery. The lateral part (Fig. 1544), while directly continuous with the anterior and attached below to the upper border of the anterior arch of the cricoid cartilage, is thin and membranous, and on each side extends upward and inward beneath the lower border of the thyroid alae without being at- tached. The upper border of this part of the membrane becomes directly blended and continuous with the inferior thyro-arytenoid ligament, the latter being practically the thickened and free superior border of the crico-thyoid membrane, which in this sense, becomes the supporting framework for the true vocal cord. The lateral crico- arytenoid and thyro-arytenoid muscles intervene between the thyroid ahe and the lateral parts of the membrane. The inner surface of the latter is covered by the laryngeal mucous membrane. The thyro-hyoid ligament or membrane is one continuous sheet of fibrous tissue, the posterior borders of which are thickened as they extend between the supe- Posterior crico-thyroid ligament . Trachea Cartilages of larynx united by their ligaments ; right half of thyro- hyoid membrane has been removed ; poslero-lateral aspect. i8i6 HUMAN ANATOMY. Crista arcuata Fovea oblongata, for thyro-arytenoideus muscle Muscular process FIG. 1542. 'artilage of Santorini Apex ubercle for false vocal d Fovea triangularis Anterior border Vocal process - Postero- medial surface Articular facet Articular facet A, antero- rior horns of the thyroid and the tips of the greater horns of the hyoid. They may be artificially dissected to resemble cords ( li^amenta thy reohyo idea lateralia), although in fact they are continuous, not only with the rest of the membrane, but with its expansion which mingles with the fasciae of the neck. As a rule, a little nodule {cartilago triticea) is found in the middle of this lateral thickening (Fig. 1541). According to Gegenbaur, it is the remnant of a closer connection between the third and fourth branchial bars. The more membranous part of the ligament extends from the superior border and the inner side of the superior horns of the thyroid to the upper border of the body of the hyoid and its greater horn. A bursa, extending under the body of the hyoid, lies on the anterior surface of this membrane, which is denser beneath it. The Arytenoid Cartilages. These are a pair of very irregular four-sided pyramids (one side being the base) perched on the superior articular facets of the cricoid. The vocal cords extend between them and the entering angle of the thyroid. Besides the base, there is a posterior, an internal, and an antero- external surface, sep- arated by tolerably distinct borders. A section near the base is semilunar, the bound- ary between the posterior and internal surfaces being effaced. The two remaining angles are each prolonged (Fig. 1542). The anterior, extending forward as ihevoca/ process for the attachment of the true vocal cord, is long and slender ; the ex- ternal or muscular process, short and thick, projects out- ward and backward. The base is chiefly occupied by an oval articular cavity rest- ing on that of the cricoid. The long axis of this articu- lar facet, which does not much surpass its transverse one, extends in the main for- ward, crossing that of the opposed facet. The concavity is nearly at right angles to the long axis. The posterior surface is well defined and deeply concave, being filled by the arytenoid muscle. The internal surface is nearly plane, offering nothing for description. The antero-external surface is triangular. A ridge, the crista arcnata, starts from the vocal process and runs backward and upward, ultimately describing nearly a circle around a hollow, the fovea triangularis, which is quite as often oval. This little hollow is filled by a mass of glands, and is overlooked unless the cartilage be cleaned very carefully. The false vocal cord is attached to a little tubercle on this ridge either above or behind the fovea. The borders meet above at a blunt apex. The Crico-Arytenoid Joint. From the foregoing description of the two opposed articular surfaces it is evident that in consequence of the crossing of their long axes the whole of one is not in contact with the whole of the other. The joint is surrounded by a lax capsule, strengthened behind by straight vertical fibres, which have been called the posterior crico-arytenoid ligament ( Fig. 1541). The motions are very difficult to analyze. The arytenoid may tip on the elongated elevation of the cricoid or slide along it ; moreover, it may rotate upon it at any point occupied. This movement, from the nature of the surfaces, is a screw motion rather than a true rotation, but the term is sufficiently accurate. The Epiglottis. This is a leaf-shaped plate of elastic cartilage which, inserted by its stalk into the angle of the thyroid, rises above the hyoid bone and guards the entrance into the larynx. The length is some 3.5 cm. The epiglottis expands trans- versely and curls forward over the root of the tongue. Its posterior surface is entirely free, but less than the upper half of the anterior surface is exposed. Begin- ning at the free border, which is bent forward towards the tongue, the posterior surface is convex, slightly concave, and finally convex again, owing to a prominence, called the tubercle, which its root forms in the larynx. The free edge is rounded traiisvrrsrlv and the posterior surface in the main concave across. The stalk, when well developed, is triangular on section, fitting into the angle of the thyroid. The Right arytenoid cartilage, capped by cartilage of Santorini. lateral aspect ; B, postero-medial aspect. X j}. THE LARYNX. 1817 FIG. 1543- Depressions for glands cartilaginous stroma is full of pits, or even perforations, containing glands. The mucous membrane is attached to it very closely, so that in dissecting the cartilage it is difficult to determine its true outline. The Ligaments of the Epiglottis. The thyro-epiglottic ligament is an elastic band continuing the stalk of the epiglottis into the angle of the thyroid, just below the notch. Owing to the ill-defined structure of the epiglottis, it is often hard to say what is ligament and what is stalk. The glosso-epiglottic ligaments, one median and two lateral, are three folds of mucous membrane with more or less elastic tissue within them, extending from the front of the epiglottis to the tongue, with which they have been more particularly described (page 1575). The hyo-cpiglottic ligament 1 is de- scribed as a bundle of elastic tissue extending between the middle of the anterior surface of the epiglottis and the upper border of the hyoid. Such a structure may be artificially dissected ; but the important point is the presence of a mass of very dense areolar tissue, probably largely elastic, and with fat in its meshes, which forms a firm pad between the front of the epiglottis below the line of reflection of the mucous membrane and the thyro-hyoid membrane which is attached to the upper border of the hyoid. This mass gives support to the epiglottis, and -probably may be made to press it backward when the hyoid is carried in that direction. It is continuous with the septum of the tongue. The Movements of the Epiglottis. The old idea that the epiglottis turns over backward like a lid to close the larynx in swallowing is disproved. That it could ever be so bent is unlikely. In swallowing it is carried bodily backward, probably receiving the bolus on its laterally concave posterior surface and transferring it to the grasp of the pharynx. While there are muscular fibres in the aryepiglottic fold, they are scanty and irregular and hardly capable of exercising any great influence on the shape of the epiglottis. The corniculae laryngis, or cartilages of Santo- rini, are a pair of small horn-like structures of elastic car- tilage on the apices of the arytenoids (Fig. 1542). As their sheath is continuous with the perichondrium of the latter, they are not very easily isolated. They are 4 or 5 mm. long, curve backward and inward, and are attached by their fibres to the arytenoids. The cuneiform cartilages (of Wrisberg} are two very slender rods of elastic cartilage situated a little in front of the corniculae laryngis in the aryepiglottic folds (Fig. 1545). They are some 5 mm. or more long and i mm. thick. While the swellings which they seem to produce in the folds are constant, the same cannot be said of the cartilages. They are often difficult to isolate. Minute nodules of elastic cartilage are occasionally found in certain parts of the larynx. The posterior sesamoid cartilages are on the lateral sides of the joints be- tween the arytenoids and the corniculae. The anterior sesamoid, which may be double, is at the anterior origin of the true vocal cords. An occasional interarytenoid has been described under the mucous membrane of the pharynx between those cartilages. It is regarded as representing a prccricoid cartilage. The elastic sheath of the larynx is a layer of areolar tissue, rich in elastic fibres, which lines the inside of the larynx, and is prolonged from it into the folds of mucous membrane to be presently described. The superior and inferior thyro- arytenoid ligaments in the false and true vocal cords repectively and thicking of this layer. The superior thyro-arytenoid ligaments (ligamcnta ventricularia), one on each side, extend between the angle of the thyroid above its middle (the point of origin will be described accurately with the vocal cords) and the tubercle on the bor- der of the fovea of the arytenoid. They are. in no sense ligaments, but at most slight thickenings of the elastic tissue in the folds of the mucous membrane forming the false vocal cords, and can be demonstrated only by an artificial dissection. 1 Dieulafe : La membrane glosso-hyoidienne, Bibliographic Anatomique, tome xi., 1901. .Stalk Epiglottic cartilage from behind. i8l8 HUMAN ANATOMY. The inferior thyro-arytenoid ligaments ( li^amenta vocalia) are a pair of bands of fibrous tissue, chiefly elastic, supporting the free edges of the true vocal cords, extending from the angle of the thyroid a little below the false ones to the vocal processes of the arytenoids. These ligaments are continuous with the lateral parts of the crico-thyroid membrane, as the thickened and modified upper borders of which they may be regarded (Fig. 1544)- Each band is triangular on section, having the free edge at that of the FIG. 1544- cord. There may be a minute nodule of cartilage in the ligament just in front of its posterior attach- ment. Superior cornu of thyroid car- tilage Cartilage of Santorini Arytenoid cartilage Articular facet for inferior thyroid cornu Right thyroid ala (cut) eral part of crico-thyroid mcm- rane attached to vocal process Median part of crico- thyroid membrane Cricoid cartilage Trachea Ossification of the Larynx. The process, beginning as it does at about twenty, is a normal change. Chievitz ' found some ossification in every male larynx of over twenty and in every fe- male one of over twenty-two. It ap- pears at about the same time in the cricoid and thyroid, namely, at about the beginning of the twentieth year, and in the arytenoid at about the mid- dle of the twenties in man and nearer the thirties in woman. The Cricoid. The first nucleus appears on each side at the back of the facet for the arytenoid, and almost at the same time another appears at its front. These are shortly followed by one at the joint for the thyroid. These three unite, forming a lateral ossification which spreads across the back. One or mpre points appear in front near the upper border of the arch, which is thus ossified and joins with the sides. After these various unions the entire lower border of the cricoid is still cartilaginous. The youngest man observed by Chievitz with complete ossification was forty-four and the youngest woman seventy-six. The Thyroid. The process begins near the posterior inferior angle and invades the in- ferior horn. It appears next near the lower part of the anterior angle, and these tun centres on each side join by spreading along the inferior border. The superior horn then ossifies either by a separate centre or by extension along the hind border, finally a tongue-like process, starting near the inferior tubercle, extends upward and forward across the ala to meet the ossi- fication which has spread along the superior border, leaving before and behind it places which are the last to ossify. This tongue-like process is peculiar to the male ; in the female ossifica- tion advances chiefly from the posterior border. The youngest man with complete ossification of the thyroid was fifty and the youngest woman seventy-six. The Arytenoids. The process begins in the base. In man the starting-point is the mus- cular process, but in woman it is less certain. The youngest man in whom the process was complete was seventy-five and the youngest woman eighty-five. The cartilago triticea, when present, also tends to ossify. Lateral view of larynx after removal of greater part of right thyroid ala, showing attachment of crico-thyroid membrane to arytenoid cartilage. The free border of the membrane constitutes the thyro-arytenoid ligament and the framework of the vocal cord. THE FORM OF THE LARYNX AND ITS MUCOUS MEMBRANE. The shape of the larynx depends not only on the cartilages, but also on folds of mucous membrane stretched over bands of connective tissue and over muscles. The cavity of the larynx is subdivided into three parts : the supraglottic, the glottic, and the infraglottic. The supraglottic region (vestilmlum laryngis) begins with the entrance to tin- larynx, an oval (or rather a heart-shaped) plane, which, owing to the height and the position of the larynx, faces nearly backward. It is bounded by the free border of the epiglottis in front and by the arvcf>iglottic fold which passes from this on either side back over the top of the arytenoid cartilages. It is interrupted in the median line behind by a notch. On either side of this the fold presents a small swelling ( tuhcmilum corniculntuni ), caused by the cartilage of Santorini, anterior to which is a larger one ( tubc-rculuin cimeifoi me) containing that of Wrisberg. Between 1 Archiv f. Anat. und Phys., Anat. Abth., 1882. THE LARYNX. 1819 these and the sides of the epiglottis the fold contains only the general fibrous envel- ope and some stray muscular fibres. Below the entrance in front lies the posterior surface of the epiglottis, concave from side to sick', and presenting in the median line, from above downward, first a convexity, extending so far back as to overhang much of the larynx, then a hollow, and finally a prominence, the tubercle or cushion. A deep crease descends on each side, bounding the lower part of the epiglottis, and meeting its fellow below the tubercle. The mucous membrane is very closely attached to the epiglottis, and so thin that the straw color of the cartilage is seen through it, turning into red at the lower part. The pits for the glands in its substance can also be made out. The lateral wall of this region, which is separated from the front by FIG. 1545- ["ongue Cushion of epiglottis Cuneiform tubercle Tubercle of Santorini Posterior crico-arytenoid muscle Cricoid cartilag Foramen caecum Right faucial tonsil t Median ) . T_ ; Lateral I Gtose< *P i S lotti C fold Superior hyoid cornu Superior thyroid cornu Sinus pyriformis Glottis Pharyngeal wall .(Esophagus Pharynx opened from behind, showing superior laryngeal aperture and mucous pouches embraced by wings of thyroid cartilage ; cricoid cartilage and muscles are covered with mucous membrane. the crease, inclines inward, and becomes the fold of mucous membrane known as the false vocal cord. Farther back a shallow groove, the philtrum, runs from the inter- val between the tubercles of Santorini and of Wrisberg to the ventricle. The sinus pyriformis (Figs. 1545, 1354) is a shallow cavity to the outer side of the aryepiglottic fold, bounded externally by the greater horn of the hyoid, the upper part of the ala of the thyroid, and the thyro-hyoid membrane between them. It is bilateral and properly a part of the pharynx (page 1598). Its mucous membrane, continuous with that of the larynx, is smooth and thin, and but loosely attached to the areolar tissue below it. In the front part there is a transverse fold caused by the internal branch of the superior laryngeal nerve passing from the thyro-hyoid mem- brane, which it perforates, to the larynx proper. 1 820 HUMAN ANATOMY. The glottic region extends from the free edges of the false cords above to those of the true ones below. The narrowest part of the larynx, the rima glottidis or chink of the larynx, is the interval between the true cords in front and the arytenoid FIG. 1546. Cartilage of epiglottis Areolar tissue Mucous membrane covering epiglottis Fissure between cartilages of Santorini Internal jugular vein Cartilage of Santorini tubercle Stern o-hyoid Thyro-hyoid Sinus pyriformis Prevertebral muscles Fourth cervical vertebra Superior cornu of hyoid (cut) Sterno-mastoid Aryteno-epiglottic fold (cut) Posterior wall of pharynx Anterior part of section across neck at level of fourth cervical vertebra, passing through upper part of superior aperture of larynx. cartilages behind. The false vocal cords (plicae ventriculares) are folds of mucous membrane continuous with the sides of the supraglottic space. They are attached in front to the inner side of the angle of the thyroid, above its middle, and behind to the antero- external surface of the arytenoids. They are soft folds of mucous mem- brane containing connective tissue (out of which a skilful dissector can manufacture FIG. 1547. Superior hyoid cornu /lj. Thyro-hyoid ligament Body of hyoid bone Thyro-hyoid membrane Mass of fat. Ventricle Thyroid cartilage Crico-thyroid membrane Cricoid cartilage, anterior arch Trachea Median sagittal section of larynx ; ri^-lit side seen from within. Superior thyroid cornu Cuneiform tubercle Tubercle of Santorini False vocal cord Vocal cord Thyroid cartilage >icoid car- Arytenoid tilage, pos- cartilage terior arch FIG. 1548. Ventricle Larynx has been parlK rut ;u rss at level between false HIM I true \u. Ml COrat; Upper half of figure re]iiesents under surface of upper pieee, which is turned backward. a superior thyro-arytenoid ligament), many glands, and some fibres from the thyro- arytenoid muscle. The true vocal cords (plicae vocnles) arise a little below the false ones, and run to the vocal processes of the arytenoid cartilages. They arise in both THE LARYNX. 1821 sexes^a little above the middle of a line from the bottom of the thyroid notch to the lower border of the thyroid. Taguchi l gives the average distance in men from the notch to the vocal cord as 8.5 mm., and from below as 10.5 mm. In women he finds these distances 6. 5 mm. and 8 mm. respectively. The cords arise either di- rectly from the thyroid, just on each side of the depth of the angle, or from a FIG. 1549. False vocal cord Vocal cord Ventricle of larynx Arytenoid cartilage Stern o-hyoid Ventricle of larynx Bursa Thyroid cartilage Thyro-hyoid Pharynx Omo-hyoid Sterno-mastoid Sterno-mastoid Internal jugular vein Pneumogastric nerve Carotid artery Palato-pharyngeus Prevertebral fascia \ Thyro-arytenoideus Inferior pharyngeal constrictor Arytenoideus Anterior part of section across neck at level of false vocal cords ; on left side ventricle of larynx is exposed. median cartilaginous nodule, or from one for each cord, the distance between them being 1.5 mm. in both sexes. The false cords arise about 3.5 mm. above the true ones, and, on the average, 4 mm. apart from each other. The true cords are tri- angular on section, with a sharp free edge, an upper surface slanting downward and outward from it, a longer internal surface which slants steeply downward and out- ward, and an imaginary attached base placed laterally. The free edge is composed of the whitish ligament which shows through the thin and closely attached mucous membrane. The substance is chiefly muscular tissue from the thyro-arytenoid, which forms a three-sided prism, giving a solidity which the false cord has not. Behind the cords the glottic region is bounded by the arytenoid cartilages, and, as the true FIG. 1550. Base of tongue Epiglottis- Vocal cord Aryteno-epig-lottic fold Sinus pyriformis Vocal proces Cuneiform tubercl Tubercle of Santorini HE-- Lateral glosso- epiglottic fold &L, Median glosso- epiglottic fold B* Epiglottis False vocal cord Ventricle of larynx Vocal cord .Rima glottidis .Cuneiform tubercle Vocal process -Tubercle of Santorini Interior of larynx as seen with laryngoscope. A, rima glottidis widely open ; B, rima glottidis closed. cords end at the vocal processes, a considerable part of the chink of the glottis is bounded by these cartilages. The posterior part between them is called the respira- tory, and the anterior, between the cords, the vocal part. According to Moura, 2 the entire length of the chink in the male is 23 mm., of which the vocal part is 15.5 mm. 1 Archiv f. Anat. u. Phys., Anat. Abth., 1889. 2 Bull, de 1'Acad. de Mdecine, Paris, 1879. 1822 HUMAN ANATOMY. and the respiratory 7.5 mm. In the female the length is 17 mm., and the respective parts measure 11.5 mm. and 5.5 mm. The elasticity of the vocal part, however, allows it to stretch. The shape of the rima glottidis \ aries with the position of the arytenoids, and the theoretically straight lines of its borders may both be approxi- mated and drawn asunder, and, moreover, may be bent at the junction of the two parts. The ventricle or laryngeal sinus (ventriculus laryngis) is a pouch, lined with mucous membrane, opening into the larynx between the true and false cords of each side. The horizontal elliptical opening has a breadth (vertically) of from 3-6 mm. As has been stated, the upper surface of the true cord slants downward and outward ; but the ventricle is partly under cover of the false cord, around which it ascends. The ascent may be due to an appendix of the ventricle (Fig. 1551), which may be an almost separate cavity connected with the front of the ventricle by a slit or an irregular FIG. 1551. Glands Epiglottis ,Lymphoid tissue .Glands . \Vntricle -Point at which squatnous epithe- lium ends ..Lateral crico- arytenoid muscle False vocal cord Lymphoid tissue Vocal cord Thyro-aryten muscle Thyroid cartilage Cricoid cartilage Frontal section of larynx, about middle of vocal cords. X 3. opening. Not rarely, however, it is without separation from the rest of the ventricle. It may ascend to a height of 15 mm. from the bottom of tin- ventricle. These cavi- ties are compressed laterally, and situated in the thickness of the wall of tin- larynx proper, internal to the fossa pyriformis. According to Riidinger, the ventricles are relatively much larger in the male. Occasionally cases of great over-development of the ventricles are met with. They may even perforate the thyro-hyoid membrane. This is analogous to the sacs of the anthropoid apes. Brosike l has seen a median pouch perforating the thyroid in the region of the vocal cords. A similar structure occurs in the horse, ass, and mule. The function of the true cords is to change the size and shape of the glottis both during respiration and phonation, and to cause sound by their vibrations, which depend in part on their tension. When drawn into 1 Virchow's Archiv, Bel. xcviii., 1884. THE LARYNX. 1823 contact, they close the glottis and prevent the entrance of air, but from their shape they seem unfitted to prevent its exit. This, according to the general teaching, is accomplished by the valvular action of the false cords, to which the ventricles con- tribute, but it is not clear that they contain the musculature necessary for such action. The infraglottic region (conus elasticus) expands laterally beneath the true cords so as to become practically circular before reaching the lower border of the cricoid. The little fossa beneath the arytenoid cartilages is the upper part of this region, which is broadest between them. The mucous membrane of the larynx is in parts thin and tightly bound down to the cartilages beneath it, and elsewhere thick, with much subjacent areolar tissue. It is very intimately connected to the free part of the epiglottis and to all of its intralaryngeal surface, but less so to the anterior part near the tongue. It is closely applied to the arytenoids and also to the lower part of the cricoid. It is thin and adheres very tightly to the true vocal cords along the ligament. In the aryepiglottic FIG. 1552. Glands Vocal cords Thyro-arytenoid muscle Ventricle - Fibres of thyro arytenoid perhaps inserted into vocal process Lateral crico- arytenoid muscle Glands False vocal cord i Ventricle Vocal process of arytenoid cartilage Cricoid cartilage Frontal section of larynx through vocal processes of arytenoid cartilages. X 3. folds it is lax and redundant. Beginning at the base of the epiglottis, the epithelium covering the mucous membrane is of the stratified ciliated columnar type throughout the larynx, with the exception of that over the vocal cords, false as well as true, which abruptly changes to stratified squamous. Mucus-secreting goblet-cells occur in varying profusion among the columnar elements. The superficial layers of the fibro-elastic stroma of the mucous membrane contain many lymphocytes, which in places are so numerous that the tunica propria resembles lymphoid tissue. The glands are very general. They occupy pits in the epiglottis, are very numer- ous and large in the false cords, and plentiful in the walls of the ventricles. They do not occur on the upper surface of the true cords within 3 or 4 mm. of the free edges, but in the infraglottic region form nearly a continuous shallow layer to within 2 or 3 mm. of the free edge of the vocal cord. The laryngeal glands are tubulo-alveolar in form and mixed mucous in type, in addition to the mucus-producing cells containing groups of serous elements. Lymphoid tissue, as distinct nodules, is occasionally observed on the posterior HUMAN ANATOMY. surface of the epiglottis and the side and back walls of the larynx, its most usual position being the ventricle (Fig. 1551). Within the laryngeal pouch the lymphoid tissue is so constant and plentiful that laryngeal tonsz/has been suggested (Fraenkel) as an appropriate name for these collections. Cartilage triticea Thyro-hyoid membrane Aryepiglotticus Arytenoideus, oblique portion Arytenoideus, transverse por- tion Crico- arytenoideus posticus Epiglottis, dorsal surface Superior cornu of hyoid bone Superior thyroid cornu THE MUSCLES OF THE LARYNX. The extrinsic muscles of the larynx should include those going to the hyoid bone, which is physiologically a part of this apparatus. These have been described in the systematic consideration of the Muscular System (page 543). The intrinsic muscles are the crico-thyroid, \\\& posterior crico-arytenoid, the lateral crico-arytenoid, the thyro- arytenoid, and the arytenoid. All of these, except the last, are in pairs. From a physiological stand-point these muscles may be divided into three groups : the con- strictors, including both the adductors of the cords and those which draw together the supraglottic portion of the larynx ; the dilators, which abduct the cords ; and those which modify the tension of the cords without necessarily approaching or separating them. The constrictors are the lateral crico-arytenoids, the thyro-arytenoids, and the arytenoid. The dilators are the posterior crico-arytenoids. Those modifying the tension of the cords are the crico-thyroids, which stretch them, and a part of the thyro-arytenoids, which relax FIG. 1553. them. Moreover, many of these muscles, even antagonistic ones, when acting together may be con- sidered as parts of a sphincter. The laryngeal muscles are ex- tremely variable, especially the thyro-arytenoid, detached fibres of which have been described as the thyro-epiglottideus. The crico-thyroid muscle (Fig. 1510) is well defined, pass- ing upward and outward from the anterior ring of the cricoid to the under border and the inferior horns of the thyroid. The origin is from the whole of the anterior surface of the arch, except for a slight interval between the mus- cles. The internal fibres are nearly vertical and the lateral ones nearly horizontal. The insertion is into the lower border of the thyroid cartilage from a point a few milli- metres in front of the inferior tubercle to all the rest of the lower border and the front of the inferior horn. It often extends a little onto the posterior surface of the ala. The muscle is frequently divided into a superficial and a deep part. The distinction may be very striking, and also not to be seen. The superficial is the more internal vertical part, which conceals a little of the origin of the deeper. The crico-thyroid may be continuous by some fibres with the inferior constrictor of the pharynx. It may descend to the first ring of the trachea, and it may give off fibres to the capsule of the thyroid body. Occasionally the muscles of the two sides are connected at the lower border of the cricoid. In extreme cases each may cross the median line. Action. This muscle is a tensor of the vocal cords by separating their points of attachment on the thyroid cartilage from those on the arytenoids. Although the conventional names of origin and insertion have been used, the more movable of tin- two cartilages is the cricoid, and the action of the muscles is to raise its anterior arch, thereby tipping the posterior plate with the arytenoids backward, and so stretching the cords. While the thyroid can be held fixed by many muscles, the only extrinsic one attached to the cricoid is a part of the inferior constrictor of the pharynx, so that Posterior margin of thyroid car- tilage Inferior thyroid cornu Cricoid cartilage Trachea Muscles of larynx from behind. THE LARYNX. 1825 upon the cricoid cartilage devolves the whole, or nearly the whole of the movement. Although the movement is generally described as rotation on a transverse axis pass- ing through the two crico-thyroid joints, the articulation is of so vague a character that a great deal of sliding occurs. The posterior crico-arytenoid muscle (Fig. 1554) is very distinct and occupies the hollow on either side of the median ridge on the back of the cricoid cartilage. It is triangular, with rounded angles at the base, which is at the ridge, and the third sharp angle at the posterior border and upper aspect of the muscular process of the arytenoid. The origin is not from the whole of the fossa on the cri- coid, but chiefly from the region of the ridge whence it springs by tendinous fibres. It arises also from the lower part of the cricoid, but not from the part near the arytenoid. It passes over the capsule of the joint, with which it is intimately fused, and is inserted as above stated, some of its fibres becoming tendinous. Action. It pulls the muscular process downward and inward, thus raising and everting the vocal process and consequently enlarging the cleft of the glottis. Two occasional small muscles in the neighborhood of the inferior horn of the thyroid are- probably aberrant bundles of the posterior crico-arytenoid. One, the posterior crico-thyroid, slightly diverging from the lower external fibres, runs from the back of the cricoid upward and outward to the internal aspect of the inferior horn of the thyroid. The other, ti\e posterior thyro- arytenoid, runs from the lower horn upward to be inserted with the posterior crico-arytenoid into the muscular process. Epiglottis Superior thyroid cornu Aryepiglotticus Arvtenoideus Crico-arytenoideus - lateralis Crico-arytenoideus posticus Cricoid cartilage Hyoid bone Laryngeal pouch Right thyroid ala (cut) The lateral crico-arytenoid muscle (Fig. 1554), of an elongated triangular form, arises from the upper border of the lateral part of the cricoid and from the ascending edge of the plate as far as the arytenoid joint. It also may have fibres springing from the crico-thyroid membrane. It is inserted into the FIG. 1554. front of the muscular process. This muscle is less well defined than the posterior crico-thyroid, and may be more or less fused with the thyro-arytenoid, on the one hand, and the crico-thyroid, on the other. Action. It pulls the muscular process forward, thereby bringing the vocal cord nearer to its fellow. The thyro-arytenoid mus- cle (Fig. 1554) arises from the inner surface of the thyroid, just outside the entering angle, from the level of the true cord to the lower border. At the side it arises from a part of the crico-thyroid membrane, and may there be con- tinuous with the lateral crico-ary- tenoid. It runs backward and is inserted into the upper surface of the vocal process of the arytenoid and into the antero-external sur- face of that cartilage. It is convenient to speak of an internal and an external part, but there is no separation between them. The internal portion (m. thyreoarytae- noideus vocalis) is a prismatic mass, triangular on section (Fig. 1551), forming the bulk of the true cord, with one of its angles against the ligament in the free edge. Ludwig taught that fibres diverged from the body of this muscle to be inserted suc- cessively into the ligamentous band of the vocal cord, which thus resembled the tendon of a muscle receiving oblique fibres along its side. These were supposed to modify its tension indefinitely by pulling upon it at various points. This view has been denied by Luschka, and the point remains undecided. Jacobson l found on 1 Archiv f. mikro. Anat., Bd. xxix., 1887. US Thyro-arytenoideus externus ' Crico-thyroideus (cut) Trachea Muscles of larynx, lateral view after partial removal of right thyroid ala. 1826 HUMAN ANATOMY. FIG. 1555. Body of hyoid bone (cut) microscopic sections that fibres were often inserted obliquely into the cord and into the end of the vocal process. There was, however, much variation, and in some cases no such fibres were found. Our own observations incline us to look upon such fibres as possible, but probably in the ordinary larynx they are few and far between. The external portion (Fig. 1554) is a thin membrane on the outer side of the ven- tricle, with its fibres spreading upward and backward towards the aryepiglottic fold. Some few fibres are, or may be, found in the false cord, and some occasionally arch over the ventricle. The external portion is very irregular and inclined to give off aberrant bundles. The superior thyro-arytenoid is a common one. It arises from the inner side of the ala of the thyroid, near the top, a little outside of the notch, and runs downward and backward to the top and anterior aspect of the vocal process, resting on the outer side of the external part of the thyro-arytenoid and crossing it at right angles. It consists of long parallel fibres and varies much in size. The thyro-epiglottic muscle is simply fibres of the system of the thyro-arytenoid that pass upward to the side of the epiglottis. We incline to consider the aryepiglottic muscle (F"ig. 1554) a little bundle ex- tending from the side of the arytenoid to the epiglottis in the edge of the fold a part of this same system. Action. That of the in- ternal part of the thyro-aryte- noid is to relax the vocal cords by approximating their ends ; if, however, the fibres inserted into the cords be worth consid- ering, this action must be modi- fied by the stretching of parts of the cords while others are relaxed. The irregularity of this arrangement is quite in har- mony with the endless variations of the human voice. The shape of the walls below the true cords must also be modified by the swelling of the contracting mus- cle. The action of the outer portion of this muscle must be in the main that of a constrictor of the supraglottic region. It is possible that when the cords are abducted some of the fibres inserted into the muscular processes may act as adductors. The arytenoid muscle (m. interarytaenoideus) is a mass of fibres running trans- versely between the hollows on the posterior surfaces of the arytenoid cartilages, which it fills (Fig. 1553). There is usually a superficial oblique part of this muscle which, when well developed, is formed by two bands crossing each other like the arms of an X placed on its side. Each arm starts from the muscular process of the arytenoid and crosses to the summit of the arytenoid of the opposite side. Here it may end or be continuous with the fibres of the aryepiglottic muscle, which ascend to the epiglottis. One or both arms may be wanting, and this part may be more or less fused with the deeper transverse fibres. Action. It draws the arytenoid cartilages together, and is, moreover, an im- portant part of the sphincter-like arrangement. Vessels. The arteries are the superior laryngeal and the crico-thyroid from the superior thyroid artery and the inferior laryngeal from the inferior thyroid artery. The superior laryngeal pierces the thyro-hyoid membrane some 5 mm. from the superior horn of the thyroid and about midway between the top and the bottom. After giving off an epiglottic branch, which on its way supplies the areolar tissue anterior to the epiglottis, the vessel runs downward and backward under cover of the ala of the thyroid to its distribution in the upper part of the larynx. The crico- Epiglottis Mass of fat False vocal cord Thyroid cartilage True vocal cord Thyro-arytenoideus, internus Crico-thyroideus Anterior arch of cricoid cartilage Tracheal cartilages Greatei hycid cornu Superior thyroid cornu Ventricle of larynx Arytenoid cartilage Crico-arytenoideus lateralis Posterior arch of cricoid cartilage Line of cut mucosa Trachea Sagittal section of larynx from within ; mucous membrane has been removed from vocal cord to lower level of cricoid cartilage. THE LARYNX. 1827 FIG. 1556. thyroid branch meets its fellow so as to form an arch across the median line and sends perforating branches into the larynx through the crico-thyroid membrane. The inferior laryngeal from the inferior thyroid reaches the region of the back of the larynx from the side. It anastomoses with the superior laryngeal and sometimes sends branches through or into the arytenoid muscle. The vocal cords possess relatively few blood-vessels. The veins correspond in the main to the arteries, but, owing to their greater size and freer anastomoses, they seem in more immediate relation with those of the thyroid body. Moreover, they tend to form a median descending vessel in the front of the neck. There is a plexus on the pharyngeal side of the back of the larynx which communicates through the folds at the sides of the entrance with the veins of the dorsum of the tongue. The inferior laryngeal vein empties into the inferior thyroid through a circular plexus around the entrance of the trachea. The lymphatics of each side empty into two chief vessels, of which the superior pierces the thyro-hyoid membrane, carrying the lymph from the supraglottic region to the nodes under or near the sterno-mastoid. The inferior vessel descends under the mucous membrane outward and backward to the nodes along the posterior sur- face of the trachea. It may, however, open into an inconstant node in front of the crico-thyroid membrane. This node occurs in 44 per cent, of adults and in 57 per cent, of children. It may be double. 1 Nerves. These are the superior and the inferior laryngeal nerves, both from the vagus. The superior, on reaching the thyro-hyoid membrane, divides into an exter- nal and an internal branch. The external continues down- ward and forward to the crico-thyroid muscle, which it supplies. It is in relation with the pharyngeal plexus and the superior sympathetic ganglion. The internal branch pierces the membrane together with the superior laryngeal artery, and supplies the greater part of the mucous mem- brane. Its ramifications are in two groups : ascending ones to the epiglottis, the region just before it, and to the aryepiglottic folds ; others passing to the mucous mem- brane within the larynx and to that of the posterior surface looking towards the pharynx. The inferior laryngeal, as- cending by the side of the back of the trachea, divides into two branches. The branch nearer the median line inner- vates the posterior crico-arytenoid and the arytenoid mus- cles. Its fibres, in part sensory, enter into communication with those of the superior laryngeal. The other branch of the inferior laryngeal goes to the other intrinsic muscles of the pharynx. Thus the superior laryngeal divides into a motor branch that ends in one muscle, and a sensory division which plays the greater part in supplying the mucous membrane. The inferior laryngeal is also a mixed nerve, but chiefly motor. It supplies all the other muscles and helps to sup- ply the mucous membrane. A remarkable peculiarity of the sensory nerves is a tendency to cross the median line, so that certain regions are reached from both sides. The general teaching by English anatomists has been that the superior laryngeal is as above stated and that the inferior is purely motor. Exner * made observations, in part confirmed and in part disputed, to the effect that both nerves are mixed, supplying both muscles and mucous membrane (the superior supplying, in part at least, certain muscles within the larynx), and that both motor and sensory fibres cross the median line, so that some muscles receive the corresponding nerve of both sides. Moreover, he found in some animals a middle laryngeal nerve from the pharyngeal branch of the vagus, of which the analogue exists in man, in whom it goes, together with the superior laryngeal, to the crico-thyroid muscle of both sides. 1 Nicolas in Poirier's Trait d' Anatomic Humaine. 2 Vienna Akad. Sitzungsbericht, 1884. t Vestibule alse vocal cord Ventricle Vocal cord Trachea Cast of cavity of larynx and adjacent part of trachea ; anterior aspect. 1828 HUMAN ANATOMY. In the above description we have followed Onodi, 1 who denies entirely the existence of the middle laryngeal in man. The endings of the numerous sensory nerves in the mucous membrane, as described by Retzius, Fusari, Ploschko, and others, include free terminations between the epithelial cells and subepithelial end-arborizations. According to Ploschko, special end-organs, composed of columnar cells surrounded by delicate nerve-fibrilke, exist within the true vocal cords. Taste-buds occur not only on the posterior sur- face of the epiglottis, but also within the laryngeal mucous membrane in the vicinity of the arytenoid cartilages. Position and Relations of the Larynx. The larynx forms a part of the anterior wall of the pharynx and rests, therefore, against its posterior wall. In the adult male the tip of the epiglottis is opposite the lower border of the third cervical vertebra and the lower end of the cricoid opposite some part of the seventh vertebra. Thus in man it covers about four vertebral bodies, with the intervening disks. It is small in the female and rather higher. Mehnert ' 2 believes that in the living body in the upright position the cricoid is about one vertebra lower than it is after death in the recumbent position. Individual variation is marked, as is shown by the results compiled from the researches of Taguki. 3 Thus in thirty-five men the lower border of the cricoid was opposite or below the seventh vertebra twenty-nine times, but in thirty-three women only twenty-one times. It was above it six times in men and twelve times in women ; in one case (male) it was as high as the fifth vertebra. Anteriorly the larynx lies beneath the middle layer of the cervical fascia. The lobes of the thyroid rest on either side against the cricoid and thyroid. The larynx as a whole can be raised and depressed by muscles, and changes its position with the movements of the spine. Thus, when the neck is bent, it falls i cm. , and rises 3 cm. when the neck is extended. When the head is turned to one side, the hyoid is twisted less than the head, but more than the larynx, although the latter and the trachea may share in the movement. The larynx may be displaced sideways by external pressure. Changes with Age and Sexual Differences. At birth the larynx is very small, but may be said to be relatively larger than later. The sharp angle of the thy- roid cartilage is entirely wanting. The larynx grows gradually up to puberty, when it takes on a sudden expansion, which occurs in both sexes, but is much more marked in the male. According to Luschka, it doubles in man and increases by less than half in woman. The most marked sexual difference is the size and prominence of the thyroid cartilage in the male. The duration of the process by which the larynx of a child changes into that of an adult may, according to F. Merkel, be as much as two years, and, in fact, changes may occur throughout growth. In the foetus the position of the larynx is very high. At birth the lower border of the cricoid is oppo- site the lower border of the fourth vertebra. Symington found it at six years at the lower border of the fifth and at thirteen at the top of the seventh. Probably it reaches what may be called its permanent position at about puberty. Mehnert, however, finds from his observations on the living that the descent continues till about thirty, when there is a great retardation, or even a suspension, of the process till about sixty, when it goes on again with renewed activity. According to him, the cricoid may ultimately reach the second or even the third thoracic vertebra. It is to be noted that, while the earlier descent is a physiological process, that of old age is a degenerative one, depending in part on changes in the spine and on the loss of elasticity of the tissu PRACTICAL CONSIDERATIONS: THE LARYNX. The Air-Passages. The hyoid bone is closely contiguous to the opening of the larynx, and as its injuries derive their chief surgical importance from that rela- tion, they are considered here. Fracture of the hyoid results from compression by the grasp of a hand, by the rope in cases of hanging, or from a direct blow. It usually occurs near the junction of the greater cornu with the body of the bone. Displacement is not apt to be 1 Die Anatomic und Physiologic der Kehlkopfnerven, Berlin, 1902. 1 Ueber topographische Altersveriindertingen des Atmungsapparates, 1901. 1 Archiv f. Anat. u. Phys., Anat. Abth., 1889. PRACTICAL CONSIDERATIONS: THE LARYNX. 1829 marked, because the great horn is held above by the digastric aponeurosis and the hyo-glossus muscle and below by the thyro-hyoid ligament and muscle. Excep- tionally the middle constrictor of the pharynx may draw it somewhat backward and inward. The attachments to the hyoid of the constrictor and of the hyo-glossus and genio-hyo-glossus invariably make deglutition and speech painful after this fracture, while the genio-hyoid and digastric, by their contraction, cause pain on opening the mouth. The associated swelling may involve the epiglottic mucous membrane and, spreading thence, give rise to serious dyspnoea. The thyro-hyoid membrane, springing from the posterior upper margin of the hyoid bone and attached to the upper border of the thyroid cartilage, has interposed between its anterior surface and the posterior face of the body of the hyoid a bursa which descends below the lower border of that bone, and when enlarged forms a cystic swelling situated in the median line of the neck, just beneath the hyoid. Thyro-lingual cysts are sometimes found in the same situation. A similar cystic swelling, lined with columnar epithelium and occupying the same region, is referable to the persistence of the fcetal thyro-lingual duct. At the upper end of that duct such a cyst would lie in the mid-line of the tongue between the two genio-hyo-glossi muscles. At the lower end it would lie over the thyroid or the cricoid cartilage. The sinuses formed by the bursting of such cysts, or originally by the persistence of portions of the thyro-lingual duct, are obstinate, and, on account of their epithelial lining, must be dissected out completely to secure healing. The lower portion of the thyro-hyoid membrane is covered in the mid-line by cervical fascia and skin, laterally by the sterno-hyoid and thyro-hyoid muscles. Cut-throat wounds of the neck, especially if suicidal, are apt to pass through this membrane, which is made tense when the head is thrown backward, and, if they are deep, will divide the inferior constrictor, open the pharynx, and possibly wound or sever the epiglottis near its base, first passing through the cellulo-adipose tissue that intervenes. If the wound is not immediately beneath the lower border of the hyoid, it may divide the internal branches of the superior laryngeal nerve, leading ultimately to a pneumonia from the inspiration of foreign matter. In infrahyoid pharyngotomy such a transverse wound, hugging the lower edge of the hyoid, gives access to the base of the pharynx and the supraglottideal region. Above the hyoid a cut-throat wound would divide the tongue muscles and enter the mouth. Below the thyroid it would pass through the crico-thyroid membrane and open the larynx. Still lower the trachea would be incised or severed. The great vessels often escape in suicidal wounds, as the usual position of the head in extreme extension increases the projection of the laryngeal apparatus and therefore the depth of the vessels from the surface. One reason for their escape when the air-passages below the glottis are opened may be that the sudden rush of air from the lungs and consequent collapse of the chest-walls deprive the muscles running from the thorax to the humerus of their fixed point of support, and that the arm necessarily drops (Hilton). Death may be caused, however, by hemor- rhage from the superior thyroid or the lingual artery, or even from the crico-thyroid if the blood enters the larynx or trachea ; or may result from suffocation produced by the dropping backward of the tongue after division of the genio-hyoid, hyo- glossus, and genio-hyo-glossus muscles, or by the occlusion of the glottis by a partly divided epiglottis or arytenoid. Fracture of the thyroid or cricoid cartilage may occur from the same causes that produce fracture of the hyoid bone. The thyroid, on account of its greater prom- inence, suffers more frequently. Fractures of the thyroid are seen oftener in males than in females, because () in the former it is relatively more prominent ; (3) the process of ossification which, in common with other hyaline cartilages, it undergoes after adult life has been reached is more complete in them ; and (<:) males are oftener exposed to violence. The symptoms depend for their gravity chiefly upon the degree of involvement of the laryngeal mucous membrane. If that is wounded, bloody expectoration, aphonia, and dyspnoea are present, and tracheotomy may be urgently indicated. In any event, deglutition is painful. The voice is usually altered, and there is apt to be some ex- ternal deformity. Crepitus may be present, but should be distinguished from the 1830 HUMAN ANATOMY. sound produced by moving the normal larynx laterally, and caused by the friction be- tween the somewhat irregular anterior surface of the vertebral column and the posterior border of the thyroid, the corresponding surface of the cricoid, and the lower part of the pharynx, which move together. This normal crepitus disappears in retropharyn- geal abscess, but persists in retrolaryngeal abscess (Allen). It should be remembered that the superior cornua of the thyroid are sometimes found separate from the body. The cricoid and, much more rarely, the thyroid and arytenoid cartilages may be the subject of perichondritis secondary to ulceration (typhoidal, cancerous, syphi- litic, or tuberculous) of the interior of the larynx. In the case of the cricoid it is asserted that the condition may result from the pressure of the posterior aspect of the cartilage against the spine in very debilitated subjects, or from the traumatism caused by the frequent passage of an cesophageal bougie (Pearce Gould). The origin of the inferior constrictor from the cricoid accounts for the pharyngeal spasm and dysphagia said to accompany disease of this cartilage (Gibbs). Allen says that the cricoid is relatively more prominent in women than in men, and that it is often the site to which abno.rmal sensations originating in the pharynx are referred, because in such conditions deglutition is painful, and since the cricoid lies at the lower part of the pharynx, its motions determine a greater amount of distress than do the corresponding motions at any other part of the throat. The epiglottis is not infrequently affected by syphilis, and is also, although more rarely, the seat of tuberculous lesions, and may be extensively ulcerated or may become necrotic. The danger of such cases results usually from the accompanying oedema (vide infra), but in rare instances a sloughing and wholly or partially separated epi- glottis may directly occlude the laryngeal aperture. Infection originating m disease of the epiglottis may involve the cellulo-adipose tissue between its base and the thyro-hyoid membrane, giving rise to a thyro-hyoid abscess which may extend towards the mouth and project in the groove between the root of the tongue and the epiglottis. Such an abscess may also follow primary infection of either the tongue or the thyroid. It is very apt to cause oedema of the glottis. The condition known by this name may occur in any form of laryngitis, or by extension of inflammation from the mouth, tongue, or pharynx, or as a result of trauma or of wound, scald, or the application of local irritants. It involves the glottis only secondarily. The thin mucous membrane covering the true vocal cords and the arytenoids is so closely applied to them, and the subcutaneous connective tissue is so scanty, that there is no opportunity for much exudation. But in the supraglottidean region the mucosa is thick and the submucosa plentiful, especially over the aryteno-epiglottidean folds, and almost equally so in the ventricles and over the false cords and the posterior surface of the epiglottis. Effusion of serum and swelling are thus favored and, according to their degree, will produce hoarseness, aphonia, dyspnoea, cyanosis, or positive suffocation. In some cases of oedematous laryngitis the swelling affects chiefly the region below the glottis {subglottic a-dcma ) and causes the same symptoms. This is rarer and is attended by less effusion on account of the relatively closer association of the mucosa and the cricoid cartilage. The mucous glands of the larynx which supply the moisture needed in normal phonation are sometimes inflamed as an indirect result of the over-use of the voice, as in clergymen, costermongers, public speakers, etc. The increased volume of air taken in through the mouth dries up the mucous surface of the larynx, and the effort to compensate for this may result in such irritation of the glands and mucosa as to cause a form of chronic laryngitis, " clergyman's sore throat." The rima glottidis, the aperture of \he glottis, the narrowest portion of the air-passages, measures a little less than one inch antero-posteriorly in the adult male. Its transverse diameter at its widest portion is about one-third of an inch. In the male before puberty, and in the female, these measurements are about one-fourth less. They are important in reference to the introduction of instruments and the arrest of foreign bodies (vide infra). The level of the glottis i.e. , of the true vocal cords is a little above the middle of the anterior margin of the thyroid cartilage. The shape of the aperture varies. It is linear when a high note is produced in speaking or singing, triangular (with the apex forward, equal sides and a narrow PRACTICAL CONSIDERATIONS : THE LARYNX. 1831 base) during quiet respiration, and diamond- shaped (with the posterior angle cut off) in forced breathing. As various forms of ulceration (tuberculous, syphilitic, diphtheritic) may affect the mucous membrane covering the true vocal cords, or the cords themselves, or the structures in their immediate vicinity (especially the aryteno- epiglottidean and interarytenoid folds and the ventricular bands), and as cicatrization with subsequent contraction of scar tissue may follow, diminution of the calibre of the rima glottidis (stricture) is not uncommon. Polyps, warty growths, and other benign tumors are found in the vicinity of the vocal cords, and if they cannot be removed by intralaryngeal operation, may neces- sitate thyrotomy. Subglottic tumors are relatively infrequent. They often spring from the inferior surface of the vocal cords, intraglottic growths from the free border of the anterior part of the vocal cords, and supraglottic growths from the epiglottis and the aryteno-epiglottic folds (Delavan). Spasm of the glottis (laryngismus stridulus) may occur, especially in infancy, from reflex irritation, and may cause great dyspnoea or may even result fatally. The irritation is conveyed chiefly to the inferior laryngeal nerves through the pneumo- gastrics, if the cause is undigested food ; through the trifacial, if the irritation is asso- ciated with dentition ; or through the spinal accessory, if vertebral disease is present. The different forms of laryngeal paralysis should be studied in connection with the physiology of phonation. Some of the chief anatomical considerations may be indicated by the following classification, which is, however, necessarily incomplete, as failing to include the central causes of paralysis as in bulbar palsy and those due to toxaemia, as the post-diphtheritic. 1. Those due to direct or indirect involvement of the superior laryngeal nerves. (a) Sensory and thyro-epiglottic or aryepiglottic paralysis, characterized by a tendency of food or liquids to enter the larynx, by dysphagia, by immobility of the epiglottis, and by diminished sensation in both the pharyngeal and laryngeal mucous membranes, would suggest especial implication of the internal branch. () Crico-thyroid and thyro-arytenoid paralysis, causing loss of tension in the vocal cords, inability to regulate and control the voice, and with evidence of the want of action of the crico-thyroids detected by the finger placed on either side of the crico-thyroid interval externally during phonation (Agnew), may, in some cases, be referred anatomically to the external branch. 2. Those due to involvement of the inferior laryngeal nerves. (#) Lateral crico-arytenoid paralysis, causing separation of the vocal cords, with more or less complete aphonia, may be due to implication of the external branch. In many cases there will be evidence of the existence of innominate or aortic aneurism, thyroid or bronchial glandular enlargement, carcinoma of the cesoph- agus, or some other condition competent to produce pressure on the nerve. The paralysis may be unilateral and attended only by hoarseness and partial loss of voice. (b'} In posterior crico-arytenoid paralysis (abductor paralysis) the loss of power in the abductors permits the lateral crico-arytenoid muscles to narrow the glottis into a mere fissure, so that inspiration becomes stridulous and dyspnoea is marked ; the voice is not materially interfered with. The condition may be due to intra- or extralaryngeal growths, or to inflammatory conditions, possibly causing pressure on the inner branch. It may be unilateral and due to aneurism. It should be understood that the relation of these paralyses to the external and internal branches of the superior and inferior laryngeal nerves cannot be demonstrated clinically with definiteness. Pressure on the main trunk of either nerve, tabes, hysteria, toxaemia, and other central or general causes may produce any of these forms of paralysis. In intubation of the larynx (employed in some forms of acute stenosis, as in diphtheria or oedematous laryngitis) an irregular cylindrical tube with a fusiform enlargement and an expanded upper extremity so that it may rest on the ven- tricular bands is carried into place by an " introducer 1 ' and is guided by the left forefinger of the surgeon, which is passed over the dorsum of the tongue to the epiglottis and made to recognize the laryngeal opening. Thyrotomy is sometimes done for the removal of intralaryngeal tumors. The incision extends from the thyro-hyoid space to the top of the cricoid cartilage, is I8 3 2 HUMAN ANATOMY. directly in the median line, and divides skin, superficial and deep fascia, the junction of the alae of the thyroid, and the mucous membrane of the larynx. Laryngotomy (through the crico-thyroid membrane) may be indicated in adults for impending suffocation from any form of obstruction of the glottis. In children the space is too small. A median incision beginning over the thyroid cartilage is carried to half an inch below the cricoid cartilage. The skin and fasciae having been divided, the crico-thyroid membrane is exposed between the two crico-thyroid muscles, which sometimes require separation. The crico-thyroid arteries may be exception- ally large, and in any event should usually be ligated, although in cases of great emergency that step may be postponed until the membrane has been divided. This may be done by a transverse incision to minimize the risk of hemorrhage. The nearness of the vocal cords to the opening renders this operation unsuitable to cases in which a tracheotomy tube must be worn for some time. Excision of the larynx, occasionally done for malignant disease, necessitates the separation of the larynx from the sterno-thyroid and thyro-hyoid muscles laterally, from the inferior constrictor and the hyoid bone above, from the trachea below, and from the pharynx and oesophagus posteriorly. The superior and inferior thyroid arte- ries, or their branches, and the superior and inferior laryngeal nerves will be divided. For landmarks of the neck, see page 554. THE SUBDIVISIONS OF THE THORAX. As the entire respiratory apparatus, with the exception of the larynx and a part of the trachea, is within the thorax, it is advisable to describe the subdivisions of that FIG. 1557. (Esophagus Innominate art pry Left innominate vein Arch of aorta Trachea 1 IV thoracic vertebra Right pulmonary artery Sternum Ascending aorta Right ventricle Right auricle_J. Diaphragm Inferior vena cava Spigelian lobe Median s:igittal section of formalin subject ; relative position of mediastitial spaces outlined in red. cavity. The lungs, enveloped in their serous coverings, the pleune, fill the greater part of the sides of the chest external to planes passing forward from the sides of the PRACTICAL CONSIDERATIONS : THE MEDIASTINUM. 1833 bodies of the vertebrae to the sides of the sternum. The median space between the pleurae is called the mediastinal space, and is subdivided into four parts called medi- astina. The above statement of the lateral boundaries of the mediastinal space is only a general one, for in the middle the mediastinal space expands beyond them and in front is restricted by the advance of the pleurae beneath the sternum. The superior mediastinum is that part of the space above a plane passing from the disk below the fourth thoracic vertebra to the junction of the first and second pieces of the sternum. This is occupied by the upper part of the thymus, the arch of the aorta and the vessels rising from it, the innominate veins, and the superior vena cava. It is traversed by the trachea and oesophagus, the thoracic duct, the pneumogastric, the phrenic, and the sympathetic nerves. The region below the above-mentioned plane is subdivided by the pericardial sac into an anterior, middle, and posterior compartment. The middle mediastinum is occupied by the heart within the peri- cardium. The roots of the lungs are partly in this and in the superior mediastinum. The shallow anterior mediastinum is between the middle one and the sternum. It contains the lower part of the thymus, a few lymph-nodes, fat, and areolar tissue. The posterior mediastinum, between the spine and the middle mediastinum, contains the oesophagus, the aorta, the thoracic duct, the azygos veins, the pneumogastric and sympathetic nerves. PRACTICAL CONSIDERATIONS: THE MEDIASTINUM. Wounds penetrating the mediastinum, even when they do not involve the air- passages, may, in consequence of air being drawn into the space by respiratory movements, be followed by general emphysema or by mediastinal emphysema. This condition is not infrequent after tracheotomy, the conditions favoring its production being free division of the deep fascia, continued obstruction of the air-passages, and labored inspiration. If there is hemorrhage into the mediastinal space, or if abscess results from infec- tion of a clot, or from extension of tuberculous disease of the bronchial glands, or as a sequel of typhoid fever, the anatomical symptoms will be those of pressure (vide infra). In the presence of a large abscess, pus may perforate the sternum by ero- sion or may find its way out through the little circular openings sometimes found as a result of developmental failure (page 168). It may also be evacuated through an intercostal space or into the trachea or oesophagus. Tumors may be malignant or benign (lymphomata, dermoids, hydatids, fibro- mata), the order of mention being that of their relative frequency. The chief symp- toms are those due to intrathoracic pressure, which is, of course, not uniform, and varies with the origin, extent, and density of the tumor, but in its effects upon the separate structures contained within the mediastinum affords a reasonably accurate basis for an anatomical classification of the clinical phenomena of these growths. 1. Compression of veins, (a) The superior vena cava : cyanosis or lividity of the face ; dilatation of the superficial veins of the neck, face, and head ; oedema of the same region ; epistaxis ; disturbances of vision or amaurosis ; tinnitus aurium or total deafness ; cerebral effusion or hemorrhage ; cedema of one or both arms. (^) The greater azygos vein : dilatation first of the right and later of the left intercostal veins ; oedema of the upper part of the chest-wall ; right-sided hydrothorax with secondary or later effusion into the left pleura (Stengel) ; pericardial effusion ; medi- astinal effusion. (<:) The pulmonary vein : cedema of the lung ; haemoptysis. 2. Compression of arteries (much rarer than of venous channels), (a) The aorta : inequality in the radial pulses ; engorgement of the left side of the heart ; pulsation of the growth, if it is visible or palpable (as the suprasternal notch or over the sternal ends of the clavicles '); pallor; giddiness; anginose pains. (6) The pulmonary artery : distention of the right heart ; dyspnoea ; ultimately as a sec- ondary result of the cardiac condition ascites ; cedema of the lower extremities ; general anasarca. 3. Compression of nerves, (a) The pneumogastric : irregular heart action with marked rapidity or slowness ; syncope ; vomiting ; hiccough ; pharyngeal or laryngeal spasm or paralysis ; dysphagia ; spasmodic cough. () The inferior laryn- HUMAN ANATOMY. Thyroid cartilage geal nerve : posterior crico-arytenoid paralysis with stridor and inspiratory dyspnoea (page 1273). (c) The sympathetic : various disturbances of vision ; irregular pupils. 4. Compression of the thoracic duct. Emaciation ; chylo-thorax ; chylous ascites ; mediastinal effusion of chyle. 5. Compression of the air-passages, (a) The trachea : stridor ; dyspnoea. () The bronchi : feeble breath-sounds ; dyspnoea ; recession of the suprasternal and supraclavicular fossae and base of chest ; cough. (V) The lungs and pleura : dyspnoea ; collapse of the lungs ; pleural effusion. 6. Compression of the heart and pericardium. Displacement of the heart ; peri- cardial effusion ; irregular heart action. 7. Compression of the oesophagus. Dysphagia. 8. Outward pressure upon the walls of the mediastinal space. Widening of inter- costal spaces ; bulging of the sternum ; increase of the circumference of the chest on one side ; weakness or FIG. 1558. absence of vocal fremi- tus ; increased area of transmission of heart- sounds. Of course, all of these symptoms are not present in any given case of mediastinal growth, but some of them are sure to be and can be more readily understood if referred to their ana- tomical causes. The phenomena ref- erable to the separate subdivisions of the me- diastinum can be classi- fied only in a very gen- eral way. It may be said, however, that : ( i ) The anterior mediasti- num is the most fre- quent seat of abscess ; that its growths usually begin in the thymus ; and that the chief symp- toms are apt to be those of pressure upon the su- perior vena cava, inva- sion of the suprasternal fossa, involvement of the Trachea and bronchial tree, anterior aspect. R, L, right and left bronchus; Cervical glands, bulging A, left apical bronchus dividing into ventral (a) and dorsal (a') branches; fi, or erosion of the Ster- continuation of main bronchus; *, *', ventral and dorsal branches; c, cardiac , , , <. bronchus. num, and dyspnoea. (2) Growths of the poste- rior and middle mediastinum are apt to originate in the lymph-nodes, and the chief symptoms are those of pressure upon the pneumogastric, recurrent laryngeal or sym- pathetic nerves, the greater azygos vein, the oesophagus, and the air-passages. The urgent dyspnoea and troublesome cough are out of all proportion to the physical signs (Osier). THE TRACHEA. The trachea or windpipe (Fig. 1558) is a tube, composed of cartilage and mem- brane, extending from the cricoid cartilage to a point opposite the disk below the fourth thoracic vertebra, corresponding to the level of the junction of the first and THE TRACHEA. 1835 Epithelium .Tunica propria _Tracheal glands Pi _Submucous layer ' Cartilage second pieces of the sternum, where it divides into the two bronchi. The point of division is usually on the right of the median line : sometimes so far as to lie behind the right edge of the sternum. The trachea is a cylindrical tube, flattened behind. The convexity is due to the so-called rings, which represent only about three-quarters of a circle. The length is difficult to determine with accuracy on account of the elas- ticity of the organ as well as of its variation. It may be said to be, on the average, from 10.5-12 cm. (44^ in.) in man and from 9-11 cm. (3^-4 /^ in.) in woman. The isolated trachea can be stretched and compressed to a surprising extent, and even in life the changes are considerable. The antero-posterior and the transverse diameters are not very different, except just at the lower end, where the trachea enlarges transversely. It is very plausibly stated by Lejars l that in life the windpipe is more or less constricted by the tonic contraction of its muscles. FlG - 1 559- According to him, it grows con- j?~ tinually smaller from above down- ward. Braune and Stahel 2 be- lieved that after death it is largest in the middle. We have no doubt whatever that, as a rule, the dead trachea is enlarged transversely at the lower end. Abey 8 gives the following measurements for the upper and lower ends : upper transverse diameter 13.1 mm., sagittal 1 6 mm. ; lower transverse diameter 20.7 mm., sagittal 19.1 mm. The framework of the trachea is so light that its shape may be influenced by neighbor- ing organs, such as the thyroid body and the arch of the aorta. . Structure. The frame- work of the anterior and lateral walls of the trachea consists of i the so-called rings of hyaline car- ,-&'' tilage, which form some three- quarters of a circle. In the great 1 _Fibrous tunic majority of cases there are from W^H^ sixteen to nineteen rings. It is '^jjf**^-' not rare to find twenty, but very rare to find more. The rings are from 2-5 mm. broad, usually measuring 3 Or 4 mm. They are Transvers e section of trachea, showing general arrangement plane externally and convex in- of its wail, x 80. ternally, becoming pointed at the ends. They are very irregular in many respects. Sometimes one end bifurcates, the rings above and below ending prematurely. Occasionally bifurcation of the oppo- site ends of alternate rings is observed. Rarely both ends of the same ring may divide. The first ring, which is broader than the others, is occasionally fused with the cricoid cartilage. A highly elastic fibrous sheath, continuous with the peri- chondrium of the rings, envelops them, connects their posterior ends, and completes the tube. The distance between the rings is less than their breadth, at times only half as much. Involuntary muscular fibres of the trachealis muscle lie between the fibrous sheath and the lining mucous membrane. They are in the main disposed transversely, some of them connecting the ends of the rings ; some bundles, however, run longitudinally. 1 Revue de Chirurgie, 1891. 2 Archivf. Anat. u. Phys., Anat. Abth., 1886. 3 Der Bronchialbaum der Menschen, u. s. w., 1880. .Perichondrium i8 3 6 HUMAN ANATOMY. A layer of connective tissue, representing a submucosa, separates the cartilage and muscle from the mucous lining of the trachea. The submucosa contains small aggregations of fat-cells and the trachea! glands. The latter, tubulo-alveolar mucous in type, are most numerous and largest between the rings of cartilage, especially towards the lower end of the trachea. Over the cartilages they are small and often wanting. Their ducts pierce the mucosa to gain the free surface of the latter. The mucous membrane, smooth and attached with considerable firmness to the underlying tissues, is clothed with stratified ciliated columnar epithelium. Many of the surface cells contain mucus and are of the goblet variety. The stroma of the mucosa is rich in fine elastic fibres, which, in the lower part of the trachea, are con- densed into a distinct elastic lamella separating the mucous membrane from the sub- mucosa. Lymphoid cells are constantly found in the mucosa, in places, particularly around the openings of the ducts of the tracheal glands, being aggregated into small collections which suggest lymph-nodules. Vessels. The arteries, which are insignificant, are branches of the inferior laryngeal from the inferior thyroid, and tend to form a series of horizontal arches between the rings. They anastomose below with the bronchial arteries and with the internal mammaries FIG. 1560. through the anterior mediastinal twigs. The veins, arranged like the arteries, belong to the system of the inferior laryngeals. They com- municate with those of the oesophagus, with the thyroid plexus, and, according to Luschka, with the azygos. The lymphatics, which are very numerous, are also disposed in horizontal curves. Leaving the windpipe at the sides of the membranous portion, they open into small tracheal lymph- nodes and communi- cate with the bronchial nodes also. The nerves are from the pneumogas- tric and sympathetic nerves. Their ultimate distribution, in addition to the supply for the muscular tissue and the walls of the blood-vessels, includes sensory endings within the mucous membrane which, accord- ing to Ploschko, are similar to those of the larynx. The Relations of the Trachea. The oesophagus, beginning at the lower border of the cricoid cartilage, lies at first behind the trachea, to which it is con- nected by areolar tissue ; but almost at once it is, relatively to the trachea, displaced to the left, to be pushed over again by the arch of the aorta, where this vessel lies on the left of the trachea. The gullet always lies behind the origin of the left bron- chus. Behind the first piece of the sternum the arch of the aorta passes in front of the trachea, which is placed almost symmetrically in the fork made by the innomi- nate and left carotid arteries. The isthmus of the thyroid crosses usually the second and third rings, its lobes resting on the sides of the trachea. The inferior thyroid veins constitute a vascular layer before the lower part of the cervical portion of the trachea. The recurrent laryngeal nerves run up at the back of either side of the Longitudinal muscle Submucous layer Epithelium of oesophagus Circular muscle Cartilage Transverse section of trachea and oesophagus of child, seen from below. X 15. THE TRACHEA. 1837 trachea, the left one being the first to reach this position. The inferior laryngeal artery and veins are near them. The relations of the artery and nerve are given with the relations of the thyroid. The remains of the thymus lie in front of the trachea within the thorax. Owing to the forward inclination of the sternum, the trachea is more deeply placed as it descends. A lymph-node or, more frequently, a group of them is constantly found under the bifurcation. Tillaux ' found the dis- tance of the cricoid cartilage above the sternum (in a small series) to range in the male from 4.5-8.5 cm., with an average of 6.5 cm.; and in the female from 5-7.5 cm., with an average of 6.4 cm. This distance, however, may be modified by other factors than the length of the trachea. Growth and Subsequent Changes. In the infant the trachea measures from 4-5 cm. in length, begins at a higher point in the neck, as has been shown for the larynx, and divides at a higher point in the thorax. The level of this division varies very much in the foetus, but at birth is generally opposite the third thoracic vertebra. The lowest position is opposite the fourth and the range extends over two vertebrae. There are comparatively few records of the changes during childhood. 2 We have found it opposite the lower part of the fourth thoracic vertebra in a child whose age was estimated at about three. Symington s has found it at the top of the fifth in two children of six and oppo- site the fourth in one of thirteen. In the young adult it is opposite the disk between the fourth and fifth thoracic vertebra;, which is its normal position, although it is not abnormal for it to be opposite the fifth. Late in life it descends to the lower border of the fifth and even to the seventh vertebra. 4 The trachea of the infant appears almost round, the rings forming a relatively larger part, perhaps five-sixths of the periphery. According to several authorities, the transverse diameter much exceeds the sagittal ; but, although we have seen this condition, we are not inclined to agree that it is normal in the infant, unless, perhaps, at the lower end. The size of the transverse section of the trachea is, for many reasons, hard to determine. Merkel 5 thinks we may accept the following statement of the diameter of the upper part of the trachea without fear of being much out of the way in particular instances : from six to eighteen months, 5 mm. ; from two to three years, 6 mm. ; from four to five, 7 mm. ; from five to ten, 8 mm.; from ten to fifteen, 10-11 mm. Ossification of the rings begins decidedly later than in the larynx. The earliest appearances of it observed by Chievitz were at about forty in man and about sixty in woman. His youngest case of complete ossification was at fifty in man and seventy-eight in woman. The deposit is first seen in the upper rings, but not in the first one, the points being irregularly distributed along the borders. They come next in the lower rings, and here at the posterior ends. As the process spreads, there is left a median unossified tract along the trachea, which probably is usually invaded from below. THE BIFURCATION OF THE TRACHEA AND THE ROOTS OF THE LUNGS. The carina trachea? (Fig. 1561) is a prominent semilunar ridge running antero- posteriorly across the bottom of the trachea between the origin of the two bronchi. It usually starts from a larger anterior triangular space and ends at a smaller pos- terior one. Heller and v. Schrotter 6 found the framework of the spur cartilaginous in 56 per cent., membranous in 33 per cent., and mixed in n per cent. The spur, when cartilaginous, is derived in various ways : from a tracheal ring, from the first ring of either bronchus, or from a combination of these sources. The height of this ridge, especially when membranous, is difficult to measure, but these authors believe that it may reach 6 mm. According to Luschka, the free edge of the spur is 15 mm. from the apparent lowest point of the windpipe, seen from without. This great distance should in part be accounted for by the interbronchial ligament, a col- lection of fibres running transversely in the angle between the bronchi. This band is, however, very variable in development and not constant, so that Luschka' s estimate of the distance is probably excessive for most cases. Heller and v. Schrotter found 1 Anatomic Topographique, 3tne e"dit., 1882. 2 Dwight : Frozen Sections of a Child, 1881. 3 Anatomy of the Child, 1887. 4 Mehnert : Ueber topographische Altersveranderungen des Atmungsapparates, 1901. 5 Handbuch der Topograph. Anat., Bd. ii., 1899. 6 Denkschrift der Acad. Vienna, 1897. l8 3 8 HUMAN ANATOMY. FIG. 1561. Anterior surface Carina, anterior triangle Cartilage Left bronchus Carina tracheae / Origin of apical bronchus Continuation of right main bronchus Bifurcation of trachea, seen from above after section of windpipe just above carina. the spur on the left of the middle of the trachea in 57 per cent. , in the middle in 42 per cent., and on the right of it in the remainder. 1 Semon, in 100 examinations of the living, found it on the left in 59, at the middle in 35, and on the right in 6. The roots of the lungs consist of the bronchi (the right one giving off a branch before entering the lung), the pulmonary artery and vein, the bronchial arteries and veins, the lymphatic vessels and nodes, and the nerves. The bronchi (Fig 1562) are the two tubes into which the windpipe divides, one running downward and outward to each lung. Until they enter the lungs, their shape and structure are precisely those of the trachea, the membranous por- tion being still posterior. This applies also to the branch that springs from the right bronchus before it enters the lung. While treating of the root of the lung we shall consider only the extrapulmonary part of the bronchi. According to modern usage, the term ' ' bronchus' ' is applied to the whole of the chief tube that runs through each lung ; formerly it was restricted to the part from the trachea to the first branch. As the left bronchus gives off no branch before entering the lung, it was described as much longer than the right one. The length of the left bronchus to its first branch is about 5 cm. (2 in. ) , that of the right is rarely more, and often less, than 2 cm. (^ in.). There are some eight or ten rings in the left bronchus before the branch, while in the right one there are three, often two, and sometimes four. The right bronchus, which is the more direct con- tinuation of the trachea, is the larger. The diameter of the bronchi at their origin is greater from above downward than from before backward. The dimensions are very differently given. According to Aeby, the transverse diameter of the right bronchus is from 13.5-21 mm. and that of the left from 12.5-17 mm. Braune and Stahel found that the calibre of the right pne is to that of the left as 100:77.9. The extreme ratios of the series were 100 : 7 1. 6 and loo : 83.3. We have deduced from Heller and v. Schrotter's tables that in some 10 per cent, the calibres are equal. It was formerly taught that the larger right bronchus is more nearly horizontal than the'left, but that the contrary is true is easily proved by a glance down the trachea in a frozen section (Fig. 1561). The cause of the error is that, if it be not recognized that after the apparent splitting of the right bronchus the lower division is the main trunk, the eye is apt to follow the upper border of the primitive bron- chus, which carries it along the upper branch. It is very difficult to determine the angles at the origin of the bronchi, for the parts are so flexible that observa- tions on non-hardened subjects are of little value, and it is not easy accurately to measure even good preparations, on account of the irregularity of the outline. One fact which adds to the difficulty of taking satisfac- tory measurements, and which also tends to make the right bronchus the more direct continuation of the trachea, is the inclination of the latter to the right as it descends. 1 They state that this remainder consists of 8 cases, but as their series comprised 125, it would seem that there must be a misprint. FIG. 1562. Membranous Right - apical bronchus Left bronchus Bifurcation of trachea laid open after incision along an- terior wall of trachea and bronchi. THE TRACHEA. 1839 We have made measurements on two casts from frozen sections of the adult, and one from a section of a child thought to be of about three years, and have calculated the angles between the prolongation of the axis of the terminal part of the windpipe and that of each bronchus. An attempt was also made to measure the angles from a skiagraph made by Blake 1 after injecting fusible metal into the trachea of a hardened body. Two observations on adults by Kobler and v. Hovorka 2 are included for comparison. It seems that the subtracheal angle, that of divergence of the bronchi, is about 70. We have found it precisely that in another specimen. Kobler and v. Hovorka measured the lateral angles in the hardened bodies of sixteen new-born infants. The average was right 25.6, left 48.9. The variations ranged on the right from 10 to 35 and on the left from 30 to 65. We found their average angle of divergence 74.5. This shows that, contrary to the general im- pression, the bronchi are not more nearly vertical in the infant than subsequently. Aeby gives the angles of divergence of two new-born children as 33 and 61 ; Mettenheimer * as 50 and 63. Vessels. The pulmonary artery at its bifurcation is anterior to the bronchi and at a lower plane. Each branch of the artery rises over the bronchus and comes to lie more or less external to it. This apparent crossing of the bronchus by the artery occurs on the right just after the origin of the first secondary bronchus. The usual teaching, following Aeby, that the artery actually arches over the extrapul- FIG. 1563. Sternum Pulmonary semilunar valve Left lung Aorta / Superior vena cava Left pulmonary veins Left bronchus .Parietal pleura .Visceral pleura Reflection of visceral onto mediastinal pleura _III rib - N Right bronchus - Right lung Thoracic aorta Body of vertebra (Esophagus Right pulmonary artery Transverse section of thorax at level of fifth thoracic vertebra. Spine of scapula Superior fissure monary bronchus and lies behind it, is incorrect. The artery divides before enter- ing the lung, one branch entering through the upper and the other through the lower part of the hilum. The pulmonary veins are usually two on each side. The superior lie in front of and below the artery. The inferior are the lowest of the large vessels of the lung- root, passing from behind under the bronchus into the heart. The bronchial arteries follow the bronchi along their posterior surfaces. The bronchial veins are both anterior and posterior. On the right side both open into the larger azygos vein. The left posterior ones often receive the anterior and open into the superior hemiazygos. There may be various anastomoses with mediastinal, pericardial, and tracheal veins. The lymphatics run for the most part behind the bronchi. The lymph-nodes are for the most part on the posterior and inferior aspects of .the tubes, the group under the bifurcation joining others at the sides. Some nodes occur on the front. The nerves from the sympathetic and vagus form plexuses both before and behind. 1 American Journal of the Medical Sciences, 1899. 2 Sitzbericht. Acad., Vienna, 1893. 3 Morpholog. Arbeit. Schwalbe, 1894. 1840 HUMAN ANATOMY. The dimensions of the lung-roots are difficult to determine. They are nar- rower below than above and shorter behind than in front. The lower posterior bor- ders, which are formed by the inferior pulmonary veins, are of about the same length (2 cm. ) on each side and very symmetrical. We may put the right root in front and above at from 4-4. 5 cm. and the left at about i cm. longer. They are thickest above, and expand as they approach the hilum of the lung, where the diameter is approximately 3.5 cm., the left one being rather the thicker. The height at the hilum is from 5-6 cm. , probably sometimes rather more. The Relations of the Roots. Below lies the pericardium covering the heart, chiefly the left auricle. The great azygos vein arches over the right root from be- hind, to join the superior vena cava, which is against the root in front. The arch of the aorta crosses the left root from before backward, being less closely applied to it behind than elsewhere. The oesophagus is behind the very beginning of the left root. The pleura is reflected over each root, which it completely envelops as it passes from the parietal into the visceral layer. The broad ligament of the lungs is a fold of pleura extending downward from the end of the root. The phrenic nerve of each side passes in front of the root, between the pericardium and the pleura. PRACTICAL CONSIDERATIONS : THE AIR-PASSAGES. The Trachea and Bronchi. The elasticity and mobility of the trachea, the compressible character of its walls, the loose cellular tissue in which it lies, and the variety of the structures with which it is in close relation should all be remembered in considering its injuries and diseases. Wounds of the cervical portion of the trachea as in cut throat below the cricoid are not rare. The trachea is rendered more superficial by extreme extension of the neck, and is also elongated. A deep wound may therefore sever it completely, in which case the lower end may retract below the level of the superficial wound, making the hurried introduction of a tracheotomy tube difficult. Rupture "fracture" of the cervical trachea has resulted from contusion, and in the presence of pre-existing disease has followed coughing. The depth of the thoracic trachea protects it from all but penetrating wounds, and these, on account of the important structures also implicated, are usually fatal. Disease beginning in or confined to the trachea is rare, but it may be involved in the extension of either bronchial or laryngeal morbid processes. The normal tracheal mucous membrane is said to resist cadaveric disintegration longer than any other mucous membrane of the body (Elsberg). Stenosis of the trachea, if from intrinsic change, is usually due to ulceration, either syphilitic or tuberculous, followed by cicatrization. It is, however, far more commonly due to extrinsic causes, the mechanism of which will be readily under- stood if the relations of the trachea are recalled (page 1836). From above down- ward it is evident that the trachea may be compressed by enlargements of the thyroid gland, by retro-cesophageal tumors or abscesses, by carotid, innominate, or aortic aneurism, or by lymphatic swellings in the neck or near the bifurcation. As the posterior part of the tracheal wall is musculo-membranous (partly in order to avoid undue pressure of the trachea on the oesophagus), the impaction of a foreign body in the latter tube may cause tracheal narrowing. The trachea may be involved in dis- ease originating elsewhere, as in tuberculous infecti6n of the thoracic lymphatic glands, or in carcinoma of the same glands, or of the cervical chain, or of the oesoph- agus. Abscesses or aneurisms may ulcerate through its \valls and empty into its lumen, suffocating the patient. The close relation of the trachea to the aorta makes it possible in some cases of aortic aneurism to hear a systolic bruit either in the trachea or at the patient's mouth when opened. This is either the sound conveyed from the sac or is produced by the air as it is driven out of the trachea during the systole (Osier). The sign known as "tracheal tugging" also depends upon the same close relation. With the patient erect, his mouth closed and his chin elevated, when the cricoid is grasped between the finger and thumb and pressed gently and steadily upward, if aortic aneurism or dilatation exists, the pulsation of the aorta will be distinctly transmitted through the trachea to the hand (Oliver). PRACTICAL CONSIDERATIONS: THE AIR- PASSAGES. 1841 Tracheotomy may be required for obstruction in the larynx or above it, for the removal of foreign bodies, or as a preliminary step in other operations, as excision of the tongue. It may be done at any point between the cricoid cartilage and a short distance above the suprasternal notch. The difficulties of the operation increase with the distance from the cricoid because (a) the depth of the trachea from the surface in- creases as it approaches the thorax ; (6) it is more movable ; (c) it is more com- pletely covered in by the sterno-hyoid and sterno- thyroid muscles ; (d ) it is more apt to be overlapped by the common carotids ; or (e) crossed by the left common carotid when it arises from the innominate artery ; or by (_/) various venous trunks, as the transverse branches between the anterior jugulars, or the inferior thyroids, or even by the left innominate vein, which, lying as it does in front of the trachea, in the presence of venous congestion, may extend above the level of the top of the sternum. Moreover, in children under two years of age the upper edge of the vas- cular thymus gland may lie in front of the trachea at the root of the neck. The in- nominate artery itself or the thyroidea ima may occupy the same position. For these reasons tracheotomy is done with comparative rarity below the level of the isthmus, which lies in front of the second, third, and fourth tracheal cartilages. The incision is made with the head in full extension so as to lengthen the trachea, steady it by increasing its tension, and bring it nearer the surface. The chin, thyroid angle, and suprasternal notch should be in the same line. The incision should be exactly in this line, extend about two inches downward from the cricoid, and divide the skin, platysma, and fascia and expose the interval between the sterno-hyoid and sterno-thyroid muscles, which may be separated by blunt dissection. The pretracheal fascia is then divided, exposing the upper ring of the trachea and the thyroid isthmus. The isthmus may be depressed to give more room for the tracheal opening, or may, after ligation on both sides, be divided in the mid-line, where, as Treves says, it, like other median raphes, has but slight vascularity. A large communicating branch between the superior thyroid veins often runs along the upper border of the isthmus, and over its anterior surface there may be a plexus made up by the branches of the thyroid veins of the two sides. These vessels, if present, may be dealt with sepa- rately or may be picked up with the two sides of the divided isthmus in the grasp of heavy haemostatic forceps, which by dropping over the neck raise the trachea into the wound (Pearce Gould). The trachea is then seen and felt, steadied and made still more superficial by upward traction by a small, sharp hook thrust into the lower edge of the cricoid, and opened exactly in the middle line by a bistoury thrust in at about the level of the third or fourth ring and made to cut upward to about the first. In very fat or very muscular persons the depth of the trachea is increased. In children its small size, its shortness (one and a half inches in the neck in a child of from three to four years of age), its mobility, its depth (on account of the considerable quantity of subcutaneous fat usually present), the compressibility of its thin cartilaginous rings, the height to which the great vessels may rise in front of it, the venous engorgement usually present, and the occasional interposition of the thymus (vide supra}, all increase the difficulties of the operation. Foreign bodies in the air-passages are most likely to be arrested at the upper laryngeal opening, at the ventricle or the glottis, at the bifurcation of the trachea, or in the right bronchus. They are apt to enter that bronchus instead of the left because (a) the right lung is larger (the left being encroached upon by the heart) and there is a greater intake of air and a stronger current ; (3) the right bronchus has the larger transverse diameter ; (r) it is less horizontal and therefore more directly a continuation of the trachea than the left bronchus (page 1838); and (f the rib articulating with the transverse process of the vertebra immediately below ; the tips of the spinous processes of the first, eleventh, and twelfth dorsal veru-bra- are above rather than opposite the transverse processes of the vertebne immediately below ; the space between the ends of the transverse processes and the angles of the ribs varies* from one to two and a half inches, according to the numerical position of the rib ; the incomplete rings of the bronchi render those tubes easily recognizable by touch ; they are found about an inch and a half anterior to the opening in the thoracic wall. THE LUNGS. The lungs are a pair of conical organs, each enveloped in a serous membrane, the pleura, occupying the greater part of the cavity of the thorax, and separated from each other by the contents of the mediastina. Although in general conical, the lung differs in many respects from a true cone. The base is concave, moulded over the con- vexity of the diaphragm, and descending farther at the back and side than at the front and internally. The apex is not over the middle of the base, but much to the inner and posterior side of it, so that the back and inner side of the lung descend much more directly than the rest. The right lung is the larger on account of the greater encroachment of the heart on the left. The surfaces of the lungs are the base, the external surface (which is the mantle of the cone from apex to base, and embraces all the periphery from the front of the mediastinal space around the wall of the thorax to nearly opposite the front of the vertebral column), and the internal or mediastinal surface. The borders are the inferior, which surrounds the base, and the anterior and posterior, which bound respectively the back and front of the internal surface. The external surface (fades costalis), much the largest, is closely applied to the portion of the wall of the pleural cavity formed by the ribs and the intercostal muscles. The region of the apex is a part of this surface. It rises slightly possibly i cm. above the oblique plane of the first rib, which indents it towards the front. The apex itself is in the internal and posterior part of this region. It rests closely against the firm fibrous structures that roof in this region, and is grooved trans- versely by the subclavian artery, more anteriorly on the right lung than on the left. A slight groove made by the subclavian vein may be found in front of the arterial one. The rest of the external surface is smooth, except where it may be slightly depressed beneath the individual ribs. It should be noted that a part of what is termed the external surface faces inward against the vertebral column and the first part of the ribs as they pass backward. The external surface descends lowest at the back and at the side. The internal surface (fades mcdiastinalis) is approximately plane, except for the cardiac fossa, which is much deeper oil the left than on the right, and extends as far as the lower surface. The left lung presents a shelf-like projection from behind under this fossa. The other chief feature of the internal surface is the hilion for the entrance of the structures composing the root of the lung. It is situated nearer the back than the front and below the middle, being behind and above the cardiac fossa. The outline of the hilum in the left lung is approximately oval, with the lower end sharpened and the long diameter vertical. It is more triangular in the left lung, as the root expands forward near the top. The position of the bronchi and the chief vessels as they enter the lungs differs on the two sides. Rio lit IIDIO . the chief bron- chus enters at the middle or lower part and its first branch near the top, both being at the back of the hilum ; the pulmonary artery, generally in two branches, enters one branch in front of the main bronchus and the other in front of the secondary bronchus, but at a higher level ; the superior pulmonary vein is high and in front of the higlu-r arterial branch ; the inferior, often subdivided, is near the lower end of the hilum ; one branch may be in front of the bronchus and one below it. Left //on: : the bronchus enters the back of the hilum rather above the middle ; the pulmonary artery is at the top, sometimes in two divisions ; the superior pulmonary vein is high up in front, HUMAN ANATOMY. FIG. 1564. Apex Groove for subclavian artery Groove for nnominate vein Anterior border Middle lobe Inferior lobe Right lung, hardened in situ antero-lateral aspect. causing the expansion which makes the outline triangular, the inferior vein being in the lower angle. The inner surfaces are also marked by certain adjacent structures which require a separate account for each lung. The right lung presents a vertical groove above and in front for the superior vena cava, and one for the vena azygos major, which is distinct behind the upper part of the hilum and above it where this vein runs forward to the cava. The right subclavian artery, owing to its high origin from the innominate, indents but little of the internal surface. A more or less marked vertical groove for the oesophagus is seen behind the hilum and below that for the azygos. There is also a groove below on the inner surface where the in- ferior vena cava turns forward to enter the heart. A slight impression made by the trachea may also be present near the apex. The inner surface of the left lung is deeply grooved by the aorta arching over the root and descending behind it, the imprint growing faint and disappear- ing at the lower end. The left carotid and subclavian arteries make distinct impressions at the upper part diverging from the aortic groove. The base (facies diaphragmatica) is concave, that of the right one being rather the more so. Both are semilunar in outline, owing to the part cut out of them by the heart ; since this encroachment is greater on the left, the base of that lung is a narrower FIG. 1565. crescent. The inferior border surrounds the base. The latter forms about a right angle with the internal sur- face, but at the periphery, especially at the back and at the side, a sharp edge of lung is prolonged down into the narrow space be- tween the diaphragm and the thoracic walls. The anterior border is sharp and somewhat irregular, often presenting a series of convexities. Starting near the apex, it descends on both lungs with a forward curve, which is most promi- nent in the upper part, so that the lungs nearly or quite meet behind the ma- nubrium. The anterior b< >r- der of the right lung then inclines downward and out- ward so as to meet the inferior border in a gradual curve. On the left this ronvex- ity is changed into a sharp concavity where the border curves outward around the Groove for. innominate artery Groove for right innominate vein Groove for vena cava superior Secondary, bronchus Branches of pulmonary artery Cardiac impression Inferior pul- monary vein Groove for vena a/ygos major Main bronchus ^ _^ ^ Diaphragmatic surface Preceding lung ; median aspect. THE LUNGS. FIG. Groove for subclavian artery Groove for - - innominate vein Superior lobe Inferior lobe Left lung, hardened in situ ; antero-lateral aspect. heart. As this concavity ends in front, the anterior and inferior borders enclose a prolongation of the lung towards the median line, known as the lingula. The pos- terior border is variously described. Often the term is applied to the thick mass of lung that fills the region of the thorax along the sides of the vertebrae and the part of the ribs running back- ward. Properly, it is a ridge starting on the inner side of the apex, growing sharp as it descends, but becoming vague and effaced at the lower end. The position of this line is not the same on both sides, nor is it probably always dependent on the same causes. On the left it is more regular, beginning as the posterior bor- der of the groove for the subclavian ar- tery, and continuing as that of the aortic impression until it is lost near the lower border of the lung. Sometimes the be- ginning has no relation to the subclavian groove, but appears posterior to it, the lung-tissue forming a ridge which enters a little into the space between the front of the spine and the oesophagus, which is here deflected to the left. The line behind the aortic groove lies on the side of the vertebrae, and consequently is the farther back the more the aorta is on the side of the column. On the right the posterior border is farther forward, being about opposite the anterior surface of the spine. It may begin as the posterior bor- der of the subclavian groove, or more posteriorly, and continues as a ridge tending to insinuate itself between the spine and the contents of the posterior mediastinum. From just above the root of the lung it is for a short distance continued as the back of the groove for the major azygos vein, below which F IG - i5 6 7- it tends to pass between the oesophagus and the pericar- dium, and finally disappears a little above the lower border. The Lobes and Fis- sures. The lungs are di- vided into lobes by deep fissures. The chief fissure starts on the inner aspect of the lung, behind the upper part of the hilum, and as- cends to the posterior sur- face, which it may reach at the same level on both sides, or, as is perhaps more frequent, the right fissure may be one intercostal space lower. The fissure then descends obliquely along the outer aspect of the lung, and reaches the inferior border, where it ends somewhat sooner on the right side than on the left. In the right lung this occurs at the front of the lateral aspect, while it is likely to -Groove for left subclavian artery oove for left imon carotid Superior pulmo- nary vein Lingula Diaphragmatic surface Preceding T 8 4 6 HUMAN ANATOMY. encroach somewhat anteriorly in the left, terminating below the lingula. The left lung is thus divided into a superior and an inferior lobe. In the right lung a middle lobe is cut off from the superior by a secondary fissure, which starts from the main fissure far back on the lateral aspect and runs forward, either straight or with an upward or a downward inclination. The foregoing description applies to the course of these fissures as seen on the surface ; but the chief fissure is, moreover, very deep, penetrating to the main bronchus, and completely dividing the lung into a part above it and one below it. The depth from the surface of an inflated lung to the bronchus at the bottom of the fissure (taken at the point of origin of the secondary fissure on the right and at a corresponding point on the left) is from 7-8 cm. on the right and about i cm. less on the left. The secondary fissure is much less deep and may end prematurely, or even be wanting, so that the middle lobe is a very irregular structure. The left superior lobe comprises the apex and the entire front of the lung, while the inferior takes in most of the back and all of the base, unless the lingula be re- garded as constituting its anterior border. In the right lung the middle lobe forms a varying part of the front and one-fourth or one-third of the base. The volume of the upper and lower lobes of the left lung is about equal. In the right lung that of the inferior is about equal to that of the other two. We consider the middle lobe simply as a piece cut off from the upper, so that the right upper and middle lobes correspond to the left upper one. Variations of the Lobes and Fissures. Were it not for the great difficulty in properly examining the lungs, their marked tendency to variation would doubtless be more fully appre- ciated. Schaffner * has shown that an accessory inferior lobe is very frequently found on the under surface, extending up onto the inner surface in front of the broad ligament. This lobe may be merely indicated by shallow fissures or sharply cut off from the rest. It may present a tongue-like projection inward or may comprise the entire inner portion of the base. It usu- ally represents, when present, from one-fifth to one-third of the base. It may occur on either side or on both, but is larger and more frequently well defined on the right. On the other hand, it is present, or at least indicated, rather more often on the left. Schaffner found it in 47. i per cent, of 210 lungs. The lobe of the right lung represents the subcardiac lobe of many mam- mals, that of the left being evidently its fellow. The irregularity and occasional absence of the fissure marking off the middle lobe have been mentioned. An irregular fissure may subdivide the left lung into three lobes, and both lungs may exceptionally be still further subdivided, espe- cially the right one. A little process of the right lung just above the base, behind the termina- tion of the inferior vena cava, may very rarely become more or less isolated as the lobus carer. The azygos major vein may be displaced outward, so that, instead of curving over the root of the lung, it may make a deep fissure in the upper part of the right lung, marking off an extra lobe. External Appearance and Physical Characteristics. The adult lung is bluish gray, more or less mottled with black. At birth the lung-tissue proper is nearly white, but the blood gives it a pinkish or even a red color. It grows darker with age, partly, perhaps chiefly, by the absorption of dirt, but also by the greater quantity of pigment. Before middle age the lungs become decidedly dark by t he- presence of black substance (be it dirt or pigment), arranged so as to bound irregular polygons from 1-2.5 cm - m diameter, which are the lobules. At first, while the black is scanty, the lines seem to enclose considerably larger spaces, but when more of the lobules appear, owing to a greater deposit of the pigment in the areolar tissue and lymphatics marking them off, it is clear that their diameter rarely much exceeds 1.5 cm. Some, however, are relatively long and narrow. It is re- markable that the deposit of pigment is much greater in certain places than in others. Thus the rounded posterior parts of the lungs are darker than the anterior portions. In general the external surface is much darker than the mediastinal or the base, while the surface within the fissures is the lightest of all. Moreover, the pigment on the external surface, before the coloration has become' general, is often in stripes corre- sponding to the intercostal spaces, as if there were more pigment in the places most accessible to li.uht. The lungs being filled with air, after respiration has begun, arc soft and crack- ling on pressure. They are extremely elastic, so as to collapse to perhaps a third of their size when the chest is opened. 1 Yin-how's Arrhiv, Ikl. clii., iSi,s. THE LUNGS. 1847 FIG. 1568. External surface of lung, showing polygonal areas corresponding to lobules mapped out by deposits of pigmented particles within connective tissue. The weight of the lung is difficult to determine, owing to the impossibility of quite excluding fluids. Sappey puts it at 60 or 65 gm. for the foetus at term, and at 94 g m - on the average for the new-born infant that has breathed (thus show- ing convincingly the worthlessness of the method). Krause gives the adult weight as 1300 gm. in the male and 1023 gm. in the female. According to Braune and Stahel, the weight of the right lung is to that of the left as 100 : 85. The specific gravity of the lung be- fore breathing is greater than that of water, so that the lung sinks in it. Wilmart l has recently stated it as 1068, which is the same as Sappey 's statement and greater than that of Krause (1045-1056). After breathing it may be as little as .342, but may go as high as . 746. Probably figures like the latter represent either diseased or congested lungs. The dimensions are necessarily of lit- tle value. According to Krause, the length in man is 27.1 cm. on the right and 29.8 cm. on the left. In woman these dimen- sions are 21.6 cm. and 23 cm. respectively. There is little difference in length between the lungs, but such as there may be is in favor of the left. The other dimensions are probably more variable. According to Sappey, the antero-posterior diameter, which increases from above downward, finally reaches 16 or 17 cm. Krause gives the transverse diameter at the base in man as 13.5 cm. on the right and 12.9 cm. on the left, and in woman as 12.2 cm. and 10. 8 cm. respectively. The average capacity of the lungs of a powerful man, after an ordinary inspiration, is stated at from 34003700 cc. The vital capacity, which is the greatest amount of air that can be expelled in life after a forced inspiration, is from 3200-3700 cc. for men and 2500 cc. for women. The Bronchial Tree. The plan of the bronchi of the human lung (Fig. 1558) is as follows. The two primary bronchi, resulting from the bifurcation of the trachea, run down- ward and outward into the lowest lateral part of the lungs, the right one descending more steeply. Their course has been variously described. That of the right one has been said to resemble a C with the concavity inward, and that of the left an S ; but both comparisons are very forced. On their way they give off secondary bronchi, which are divided into ven- tral and dorsal branches. The ven- tral might more properly be called lateral, since they spring from the outer aspect of the primary bronchus. They are much the larger, and supply all the lung, except the apex and the posterior portion lying along the spine ; the latter is supplied by the 1 La Clinique, 1897. FIG. i 569. Relations of bronchial tree to anterior thoracic wall, as shown by X-rays. (After Blake.) 1848 HUMAN ANATOMY. dorsal branches, which are small and irregular. There are usually four large and well- marked ventral secondary bronchi, besides one or two insignificant ones the nature of which is not easily determined. The ventral bronchi describe a spiral course through the lung, curving forward and inward as they descend, so as to be in the main parallel with the chief fissure. The dorsal branches, running backward, inward, and downward, are not more than four in number, and may be reduced to two. There are two bronchial tubes besides those mentioned above : one, the apical bronchus, supplies the upper part of the lung, on the right springing from the primary bronchus 2 cm. or less from its origin. It is a large branch, about 10 mm. in diameter, running upward and outward, and divides into three branches, orie of which ascends and two of which run downward and outward on the front and back respectively. It is really the first dorsal branch of the right primary bronchus, but we have not included it in the dorsal branches. On the left the apical bronchus, which closely resembles the right one, but is rather smaller, rises from the first ventral bronchus, of which it may be called a dorsal branch. The other secondary bronchus, not included in the foregoing scheme, is the subcardiac bronchus, which on the right arises usually from the main trunk between the first and second ventral bronchi, or from the second ventral bronchus. It FIG. 1570. runs downward and inward to the region in front of the hi- lum and above the lower border of the lung, which may be marked off as a sep- arate lobe, held to represent the cardiac lobe of mammals. On the left the cor- responding bronchus arises always from the second ventral branch. Homologies of the Bronchi. We are in- debted to Aeby * for the idea, now practically universally accepted, that there is a mam or primary bronchus ex- tending through the lung and giving off both ventral and dorsal branches. After the bifurcation of the pulmonary artery, each of its subdivisions reaches the front of the primary bronchus of each lung, and (according to Aeby) crosses over it so as to lie behind it. This alleged crossing occurs on the right just after the origin of the apical bronchus, which is said, therefore, to be above the cross- ing, and is called by Aeby the eparterial bronchus. Thus on the right all but one of the branches, and on the left all, without exception, are given off below the crossing, and are called hyparterial bronchi. Aeby attached so much importance to this relation that he considered the little irregu- lar middle lobe of the right lung, because it is supplied by the first hyparterial bronchus, the representative of the left upper lobe, the right upper lobe being without a mate and the t\vo lower lobes homologous. It is difficult to understand why such a relation should be of so great import. Narath,* in refutation of Aeby, pointed out that during fcetal life the pulmonary artery is a very insignificant, and withal variable structure, and, moreover, that it does not cross fairly over the main bronchus, but runs on its outer side, the crossing occurring, if at all, deep in the lung. Narath showed also that the so-called eparterial apical bronchus of the right lung is present in the left, arising from the first ventral instead of the primary bronchus. It is a ter- tiary bronchus from the 'first ventral which, especially on the right, is (among mammals) given to wandering, so that it may spring from the main bronchus or even from the trachea. arterial relation he considers of no importance. Huntington, 3 after much work on human and mammalian lungs, came to somewhat similar conclusions. He believes that the primary type among mammals is one with a hyparterial bronchus on both sides, and the furthest 1 Der Bronchialbaum der Siiugethiere und des Menschen, 1880. 1 Verhandl. d. Anat. Gesellschaft, 1892. 3 Annals of the New York Academy of Sciences, 1898. Relations of bronchial tree to posterior thoracic wall, as shown by X-rays. (After Slake.) THE LUNGS. 1849 departure from it one with symmetrical eparterial bronchi. The type found in man is the most common among mammals. Huntingdon would do away entirely with the terms "eparterial" and "hyparterial," except for purposes of topography. Certainly there is no need of them in human anatomy as a special study ; whether or not the arterial relations should, as Narath main- tains, be absolutely discarded in comparative anatomy, we must leave undetermined. 1 It must be admitted that were our knowledge derived solely from the human lung it would be impossible to make out this plan. We shall now describe what is actually to be seen. Distribution of the Bronchi. In the right lung the apical bronchus, with a diameter of about 10 mm., arises about 2 cm. from the trachea (often nearer and rarely farther), and, entering the top of the hilum, divides as described above. The diameter of the main trunk, after giving off the apical branch, is 12 mm. The first right ventral branch arises from its outer side, about 5 or 6 cm. from the bifurcation of the trachea, and runs downward, outward, and for- ward. It is about 8 mm. in diameter. The apical branch and the first ventral supply the supe- rior lobe, of which the middle lobe is really a part. Shortly after the origin of the first ventral branch the chief bronchus seems to break up into a bundle of branches running mostly in the same general direction, but diverging. It is usually not possible to determine which is the main trunk, but the subcardiac branch may sometimes be distinguished. In the left lung the first branch is the first ventral, with a diameter of 12 mm., arising some 40 mm. from the bifurca- tion. It gives off the apical, 7 or 8 mm. in diameter, after which the diameter of the main branch is 12 mm. It presently breaks up like the right one. On this side the first ventral sup- plies the upper lobe. A branch from the second ventral goes to the accessory lobe, if there be one. The branches of the left bronchus are very apt to give the appearance of being divided into an upper and a lower set, the former, consisting of the first ventral branch, bearing the apical and supplying the superior lobe, while the lower sheaf of branches supplies the inferior. The secondary bronchi give off branches of 4 or 5 mm. in diameter, which diverge at acute angles from the parent trunk, and in turn give off smaller branches at continually greater angles. The branches to the lobules are probably the fourth or fifth branches. They are about i mm. in diameter and arise by the subdivision of the preceding branch. In the larger tubes the ramification is clearly from the side, but in the smaller ones it is more suggestive of a splitting. His, 2 Minot. 3 and more recently Justesen 4 defend the theory that the origin of the bronchi is throughout by bifurcation, with subsequent unequal growth of the subdivisions until we come to the smallest. Aeby gives the following table of diameters of the main bronchus above the origin of the chief branches, the nomenclature being his. Right. Left. Above the eparterial branch 12.8 mm. . . . Above the first hyparterial branch 9.6mm. 10. i mm. Above the second hyparterial branch 7.2 mm. 7.7 mm. Above the third hyparterial branch 5.8 mm. 6.4 mm. Above the fourth hyparterial branch 4.6 mm. 5.3 mm. The variations of the bronchial tree are very numerous. Very rarely indeed the right apical branch does not spring from the primary bronchus, so that the disposition of the two sides is symmetrical. The origin of the left apical from the primary bronchus has been observed in two or three cases of infants, which also makes the arrangement symmetrical. Chiari 5 has seen several cases in which the right apical bronchus is double, the duplication being apparently due to the springing of one of its branches from the main bronchus. The right apical bronchus may spring from the trachea, as in the sheep and other mammals. \Ye have such an instance in which it is separated from the chief bronchus by the azygos vein. The dorsal secondary bronchi are particularly likely to be reduced in number. The ventral ones may also be reduced by two having a common origin or by one becoming merely the branch of another. The number may be apparently increased by the separate origin from the parent stem of what are normally branches of branches. The Lung Lobule. The surface of the lung is covered with lines of con- nective tissue containing blood-vessels and lymphatics, with pigment either within the latter or free, the lines marking off little polygons (Fig. 1568), which are the bases of pyramidal masses of pulmonary tissue known as the lobules. The shape of the latter within the depths of the lungs is not accurately known ; those at the sharp borders are modifications of the typical ones at the surface. The bases of the pyramids at the surface are bounded by four, five, or six sides, the larger diameter varying from 10-25 mm. and the smaller from 7-12 mm. If the base be assumed to be square, the average breadth would be 12.57 mm. 6 The average height is 13 mm. The lobules are separated from one another by a layer of connective tissue containing 1 The latest and most elaborate work on this subject is Narath's Der Bronchialbaum der Siiugethiere und des Menschen, Stuttgart. 1901. 2 Archiv f. Anat. u. Phys., Anat. Abth., 1887. 3 Human Embryology, 1892. 4 Archiv f. mikro. Anat., Bd. Ivi., 1900. 5 Zeitschrift fiir Heilkunde, Prag., Bd. x., 1890. 6 Bibliographic Anatomique, 1898. i8 5 o HUMAN ANATOMY. FIG. 1571. vessels. Each lobule is entered by an iniralobular bronchus (.5-1 mm. in diam- eter), accompanied by its artery, not quite at the apex of the pyramid, but slightly to one side of it. The bronchus divides into two, at an angle of from 9O-ioo, a little above the middle of the lobule, having previously given off two or three col- lateral branches to its upper part. In the third quarter of the lobule the two subdivisions ( 2-3 mm. in length) again split, with about the same degree of divergence as the parent stems, but in a plane at right angles to that of the previous splitting. This is repeated in three or four suc- cessive bifurcations, a varying number of col- lateral branches being given off. Thus the num- ber of branches in the third quarter is much in- creased ; but it is in the last quarter and towards the periphery of the lobule throughout that the tubes break up into the great number of truly ultimate bronchi. The various collaterals, spread- ing and even reascending, undergo subdivision also. Laguesse and d' Hardiviller 1 estimate the number of terminal bronchi (ductuli alveolares) within a single lobule at from fifty to one hun- dred or even more. The slightly dilated distal ex- tremity of the terminal bronchus communicates with from three to six spherical cavities, the atria of Miller 2 (so named by him from the resemblance to the arrangement of an ancient Roman house). The atria, in turn, communicate with a group of larger and irregular cavities or air-sacs (sacculi alveolares), into which directly open the ultimate air-spaces, the alveoli or air-cells (alveoli pulmonis). The. latter open not only into the air-sacs, but also into the atria, the dilated distal part of the terminal bronchus being likewise beset with scattered alveoli. Miller holds that the terminal bronchus, the air-chambers connected with it, together with the vessels and nerves, is the true lung-unit, and calls it the lobule. We cordially agree that this is the true lung-unit, and pro- pose that name for it, retain- ing the term ' ' lobule' ' for the above-described more or less isolated portion of the lung which is surrounded by connective tissue- and vessels and receives a single intra- lobular bronchus and artery. In some animals the lobules are perfectly distinct ; they may be isolated in the infant, and can be in the main easily- made out in the adult. The lung-unit, on the other hand, is not surrounded by areolar tissue, and its limits can be Diagram showing relations of terminal sub- divisions of air-tubes. , bronchiole ending in terminal bronchi ( 7') ; latter divide into atria (A), each of which communicates with several air-sacs (s) into which open the alveoli ( ending in terminal bronchi (/>,/; r, atria ; ii, air-sac ; /, alveoli. X 8. determined only by recon- struction from microscopical sections ; hence, apart from its minuteness, it is practi- cally too much <>t an abstraction to deserve the name almost universally applied to something tangible. apliie Anntomiqne, 1898. 'Journal of Morphology, 1X93. Archiv f. Anat. u. 1'lus., Anat. Alith., 1900. THE LUNGS. 1851 Bronchiole Mucous membrane Cartilage The intralobular bronchus is accompanied by some areolar tissue, and certain fibrous prolongations extend into the lobule from the connective tissue disposed about its surface. Although superficially these appear to divide the lobule into from four to twelve parts, they FIG. 1573. penetrate but a short dis- Bronchioie tance. They are not real partitions, and the sub- divisions they suggest have no morphological significance. Structure. As far as their entrance into the lungs, the bronchi pos- sess essentially the same structure as the trachea. After the division of the bronchus within the lung, the cartilage-rings are replaced by irregu- lar angular plates, which appear at longer and longer intervals until they finally cease, the last nodules usually marking the points of bifurcation Alveoli/ 7l i .; r of the bronchi. Within Section of lung, showing small air-tubes and branch of pulmonary artery. X 35- the Walls of bronchioles of a diameter of i mm. or less cartilage is seldom present. As the cartilage disappears the unstriped muscle broadens into a continuous layer, which, however, gradually becomes thinner as the air-tube diminishes, and extends only as far as the terminal bronchi. Around the circular openings, by which the latter communicate with the atria, the muscle is arranged as a sphincter-like band (Miller). The walls of bronchi of medium size consist of three coats, which from without in are : ( i ) an exter- nal fibro-elastic tunic which encloses the cartilage and blends with the surrounding lung-tissue ; (2) a usu- ally incomplete layer of involuntary muscle composed of circularly dis- posed elements ; (3) the mucosa, consisting of a stratum of compact elastic fibres next the muscle, the fibro-elastic stroma and the cili- ated columnar epithelium. Mucous glands, similar to those of the trachea, are present, decreasing in number and size until the bronchus approaches i mm. in diameter, when they disappear. Their chief location is outside the muscular layer, which is pierced by the ducts. In addition tO diffused Cells within Portion of wall of small bronchus. X 180. the mucosa, more definite aggre- gations of lymphoid tissue occur as minute lymph-nodules along the bronchi, the points of bifurcation of the latter being their favorite seats. The epithelium lining the air-tubes retains the ciliated columnar type, with many FIG. F.pithelium Goblet-cell Cartilage I8 5 2 HUMAN ANATOMY. goblet-cells, as far as the smaller bronchi. Within these the ciliated cells are replaced by simple columnar elements which, in turn, give place to low cuboidal cells within the proximal part of the terminal bronchi. Towards the termination of the latter, transition into a simple squamous epithelium takes place. The walls of the air-spaces the atria, the air-sacs, and the alveoli have es- sentially the same structure, consisting of a delicate fibre-elastic framework which supports the blood-vessels and the epithelium. Within the adult lung the latter is simple and is represented b'y two varieties of cells, the large, flat, plate-like elements (.020 .045 mm. ) and the small nucleated polygonal cells (.007-. 015 mm.) occurring singly or in limited groups between the plates. Before respiration and the conse- quent expansion of the air-spaces take place, the cells lining these cavities are small and probably of one kind. The groups of the smaller cells are larger, more numer- ous, and more uniformly distributed in young animals than in old ones, in which they are often represented by single cells irregularly disposed. The adjacent alveoli share in common the interposed wall, which consists of the two layers of delicate elastic membrane beneath the epithelium lining the alveoli and Air-sacs Passage from atrium into air-sa Alveolus j Terminal bronchus Pulmonary artery Bronchiole Atrium Alveolus Air-sacs Section of lung, showing general relations of divisions of air-tubes. X 50. the intervening capillary net-work, supported by a delicate framework of elastic fibn The capillary net-work is noteworthy on account of the closeness of its meshes, which are often of less width than the diameter of the component capillaries. The latter are not confined to a single plane, but pursue a sinuous course, projecting first into one alveolus and then into the one on the opposite side of the interalveolar septum. The capillaries are, therefore, excluded from the interior of the air-cells by practically only the attenuated respiratory epithelium, the large plate-like cells lying over the blood-vessels while the small cells cover the intercapillary areas. Distinct intercellu- lar apertures or stomata, formerly described as affording direct entrance from the alveoli into definite lymphatics, probably do not exist. That, however, inspired foreign particles may pass between the epithelial cells into lymph-spaces within the alveolar wall and thence into lymphatics, to be transported to more or less dis- tant points, is shown by the gradual accumulation of carbonaceous and other parti- cles within the interlobular tissue and the lymph-nodules along the course of the lymphatic vessels. Such accumulations may acquire conspicuous proportions, the entire interlobular septum appearing almost black. In view of the very frequent presence of pigment-loaded leucocytes within the alveoli, as well as outside the alve- I THE LUNGS. 13.53 FIG. 1576. Capillary- net-work Branch of pul Portion of injected and inflated lung. X 80. olar walls, it is highly probable that such cells are important agents in transporting the particles of inspired carbon through the walls of the air-cells. Additional par- ticles, however, usually occupy the cement-substance between the alveolar epithelial cells, sometimes lying appar- ently within the cytoplasm of the latter. Blood-Vessels of the Lung. T\\e pulmonary artery, serving not for the nutrition of the lung but for the aeration of the blood, is very large, at first larger than the bronchus, which it follows very closely throughout its ramifications to the terminal bronchi. Situated at first anterior to the bronchus, it passes onto its superior and then onto its outer side, and in most cases twists around the bronchus, so as finally, when deep in the lung, to reach its dorsal aspect. This is very dif- ferent from Aeby's alleged cross- ing of the main bronchus. The arterial branches accompanying the apical bronchus are in the main anterior to the tubes in the right lung and behind them in the left. According to Narath, the general course of the artery along the main bronchus is between the ventral and dorsal branches ; but, as he states, this is not constant. We FIG. have found certain ventral bronchi in the lower part of the lung with the artery before them. An in- tralobular branch en- ters each lobule near the apex with the bronchus, and follows its ramifications until the ultimate bronchi have ended in the air- chambers of the lung- unit. The terminal arterioles are in its interior until they break up into capil- laries in the walls of the alveoli. Side branches, interlobu- lar arteries, run in the connective tissue between the lobules. It is from these, ac- cording to Miller, that the subpleural net- work is filled ; formerly the latter was held to be supplied by the bronchial arteries. The pulmonary veins, which return the aerated blood to the left auricle, are also large w r hen they leave the hilum, two on each side, one near the top and the other Smaller cells Larger cells Epithelium lining al- Section of lung, showing collections of particles of carbon in perivascular connective tissue. X 14. 1 854 HUMAN ANATOMY. FIG. 1578. Portion of injected lung, showing relation of blood- vessels to bronchi ; pulmonary arteries (blue) accompany- ing bronchi (white) ; pulmonary veins (red) at periphery of lobule. X 2 near the bottom. They arise from the capillaries in the walls of the air-chambers, running first on the outside, of the lung-units, unite with others, and ramify in the connective tissue about the lobules, so that, first in the lung-units and then in the lobules, the circulation is from the centre towards the periphery. As they ascend to the hilum they unite with others and form trunks that accompany the bronchi, lying in the main lower and to the inner side of the latter. Corrosion preparations (Fig. 1578) show very clearly that the small arteries travel in close company with the bronchi, while the veins course by themselves. The bronchial arteries carry the blood for the nutrition of the' lungs, es- pecially that of the air-tubes, the lymph- nodes, the walls of the blood-vessels, and the areolar tissue about them ; hence they follow the course of the bronchi. They are in communication with the interlobular system of the pulmonary arteries. The bronchial veins are very irreg- ular. Both anterior and posterior are described. The former carry the blood back from the bronchi and the tissues about them, becoming perceptible at the bronchi of the third order (i.e., the branches of the first branches) and running to the hilum anterior to the bronchi, two with each. The posterior bronchial veins appear at the back of the hilum and, without any close connection with the bronchi, anastomose with other veins at the back of the roots of the lungs. Anastomoses betiveen the FIG. 1579. Pulmonary and the Bron- pieura chtal Systems. Not only do the capillaries at some places drain into either system of veins, but important com- munications occur between both the arteries and the veins. (a) The bronchial arteries as they enter the lungs give off occasional branches which, running tor some distance beneath the pleura, suddenly plunge into the lung to anastomose with an interlobular artery. Such a branch may arise from an cesophageal artery. There are also deep connections between the arteries of the two systems on or ivar the secondary bronchi and their branches. () The com- munications between the two systems of veins are very extensive. Apparently ail the blood from the smallest branches of the bronchial arteries returns by the pul- monary veins ; and, moreover, the bronchial veins about the larger bronchi have free communication with those of the pulmonary system. According to Zucker- Pnliiionarv vein Lymph-vessel Section of injected lung, showing Ivtnphalir arrompanving pi-riphi-ral In. iin h "I pulmonary vein, >. i.i////v.) THE LUNGS. 1855 kandl, 1 the pulmonary veins anastomose freely with those of the organs of the pos- terior mediastinum, and even of the portal system. The lymphatics of the lung- are very numerous. The deeper ones probably begin as lymph-spaces within the interalveolar septa, distal to the terminal bronchi, distinct lymphatics being found only along the arteries and veins. These commu- nicate with the subpleural lymphatic plexus. Surrounding the walls of the terminal bronchi Miller found usually three lymph-vessels. The latter increase in size and number as the calibre of the air-tubes enlarges. On reaching the bronchi the lym- phatics form plexuses along them which ultimately open into the lymphatic nodes, which are numerous in the hilum and in the roots of the lungs. According to Miller, where cartilage-rings are present a double net-work exists, one on each side of the cartilage, the inner lying within the submucosa. The lymph-nodes of the lungs are deeply pigmented, owing to the colored particles of foreign substances inspired. Nerves. The nerves of the lungs, from the pneumogastrics and sympathetics, form the very rich anterior and posterior pulmonary plexuses about the roots, whence they enter the lungs, runni-ng along the branches of the bronchial arteries and the bronchi to their ultimate distribution in the septa between the alveoli (Retzius, Berk- ley). The nerves are destined chiefly for the walls of the blood-vessels and of the air- tubes. Berkley describes interepithelial end.-arborizations within the smaller bronchi. THE RELATIONS OF THE LUNGS TO THE THORACIC WALLS. The relations of the median and diaphragmatic surfaces of the lungs have been given (page 1844). The apex rises vertically about 3 cm. above the level of the upper border of the first costal cartilage and about i cm. above the level of the clavicle. These distances are to be reckoned on a vertical plane, not on the slanting surface of the root of the neck. They vary extremely, depending, as they do, on the formation of the body. Thus a sunken chest, which means a very oblique first rib, would have more lung above the cartilage than a full chest with a more nearly horizontal first rib. In extreme cases the lung may rise as much as 5 cm., or as little as i cm., above the first cartilage. The plane of the inlet of the chest is made by the oblique first ribs. The fibrous parts enclosing it are dome-like, the roof of the cavity, to which the lung is closely applied, swelling upward perhaps i cm. above this oblique plane ; the top of the lung, however, is never above the level of the neck of the first rib. It was formerly taught that the right lung rises higher than the left. As a rule, there is no appreciable difference between the two sides. The most that can be said for the old view is that, if there be some trifling difference, it is probably rather more often in favor of the right. The anterior borders of the lungs descend obliquely behind the sterno-clavicular joints, and curve forward so as to nearly, or quite, meet in the median line on the level of the junction of the manubrium and body of the sternum. Below this the right lung extends a little across the median line and the left recedes slightly from it. The right border leaves the sternum at the sixth right costal carti- lage, to which it has gradually curved, runs along that same cartilage, or a little above it, to its junction with the sixth rib, then crosses the ribs, passing the eighth at about the axillary line, and reaches the spine at the eleventh rib or a little higher, the guide being the spine of the tenth thoracic vertebra. The lowest part of the lung is on the side at the axillary line or behind it, but the line thence along the back, although rising a little, is very nearly horizontal. The course of the border of the left lung is essentially the same, except that, leaving the sternum at the fourth cartilage, or at the space above it, the border describes a curve with an outward convexity, exposing a large piece of the pericardium, and turns forward to end as the lingula opposite the sixth cartilage, 'some distance to the left of the sternum. As this point depends on the development of the lingula, it cannot be stated accurately. It may be said in general to be 3 or 4 cm. to the left of the median line. The greatest depth of this curve is in the fourth intercostal space, about 5 cm. from the median line. The course of the inferior border along the side and back is practically that of the right one, although, perhaps, the left lung may descend a trifle lower at the side. At the back the lower borders are very symmetrical. 1 Sitzungsberichte d. Wiener Akad., Bd. Ixxxiv., 1881. 18^6 HUMAN ANATOMY. Apart from variations in the lungs themselves, the different shapes and sizes of the chest, with the consequent differences in the inclination of the ribs, make these relations very uncertain, especially at the side. In forced respiration there is no change in the relations of the top of the lungs and the dome of the pleura, as they are always in close apposition, and but little change in the first part of the anterior borders. The latter, however, approach one another behind the sternum in forced inspiration, a considerable advance of the left lung taking place at the cardiac notch. We agree with Hasse that during inspiration the anterior parts of the lungs rise just about as much as the thoracic walls. The greatest changes of relations are below and at the side. It is said that in the axillary line the border may descend as much as from 3-4 cm., and at the back as much as 3 cm. According to Hasse, 1 the lower border of the lung in the axillary line never descends nearer to the lower edge of the thoracic wall than 7 cm. on the right and 5 cm. on the left. He finds that in FIG. 1580. Semidiagrammatic reconstruction, showing relations of pleural sacs (blue) and lungs (red) to thoracic wall; anterior asprrt. extreme expiration the lower borders of the lungs rise in the axillary lines to 13 cm. on the right and 14 cm. on the left above the lower border of the chest. He states also that the anterior borders may withdraw to the parasternal lines (vertical lines dropped from the inner third of the clavicles), which to us appears excessive. In our opinion, the great factor in the expansion of the lungs is the increase in the vari- ous diameters of the chest rather than the changes of relation of the borders of the lungs to the walls. The relations of the fissures to the surface are rather variable. The chief ones ascend from the hila and reach the posterior surface at the sides of the vertebral col- umn, generally at different levels, the right being the lower. We must, therefore, 1 Die Formen des menschlichen Korpers und die Kormanderungen bei der Athmung, Jena, 1888 and 1890. THE LUNGS. 1857 trace the course of each fissure separately. The fissure of the right lung leaves the vertebral column either at the fifth rib or at the interspace above or below it. The fissure tends to follow the fifth rib, being in the axillary line still, either beneath it or beneath an adjacent intercostal space. Towards the front the fissure gets relatively lower, ending in most cases either at the fifth space or beneath the sixth rib, near the junction of the bone and cartilage, from 5-10 cm. from the median line. The secondary fissure of the right lung leaves the chief one somewhat behind the axillary line, and, running about horizontally forward, ends at a very uncertain point. Rochard, in his small series of twelve observations, found it at the third intercostal space seven times. Once it was higher and four times lower. The fissure of the left lung leaves the side of the spine at a less definite point, ranging in most cases from beneath the third rib to the upper border of the fifth, and being sometimes even FIG. 1581. Semidiagrammatic reconstruction, she // relations oi pleura! sacs (blue) and lungs (red) to body-wall; posterior aspect. lower. At the axillary line it is at the fifth rib a little more often than at any other particular point, but it is almost as often at the fourth and more often somewhere below the fifth. Its termination is more constant than its course, being beneath the sixth rib, or the space above or below it, usually from 6-1 1 cm. from the median line. 1 The relations of the bronchi to the chest-wall have not been studied on a suffi- cient number of bodies for satisfactory conclusions. Blake 2 has had X-ray photo, graphs taken of an adult body hardened with formalin, the bronchi being injected with an opaque substance. The bifurcation was normally placed. We attach the 1 Gazette des Hopitaux, 1892. Our description is almost wholly a synopsis of Rochard's American Journal of the Medical Sciences, 1899. "7 i8 5 8 HUMAN ANATOMY. most importance to the course of the main bronchus : ' ' On the posterior wall the course of the left bronchus is from a point to the right of the fourth thoracic spine to a point on the eighth rib three inches to the left of the spine. The course of the right bronchus is from the same point above to a point on the eighth rib two inches to the right of the spine. On the anterior wall the course of the left bronchus is from the lower part of the second right sterno-chondral articulation to a point on the fifth rib just internal to the mammillary, and of the right bronchus from the same point above to the intersection of the fifth rib with the parasternal line. ' ' The hilum is opposite the bodies of the sixth and seventh thoracic vertebrae and a part of the adjacent ones. (The changes of the relations of the lungs during growth and in old age are considered with those of the pleurae. ) THE PLEURAE. The pleurae are a pair of serous membranes disposed one over each lung and then reflected so as to line the walls of the cavity containing it, thus forming a distinct closed sac about each lung ; hence the pleura is divided into a viscera/ and a. parietal layer. The latter is subdivided according to its situation into a mediastinal, a costal, a cervical, and a diaphragmatic part. FIG. 1682. The visceral layer closely invests the lung, following the surface into the depth of the fissures. It leaves the lung at the borders of the hilum and invests the root for a short distance (1-2 cm.), when it leaves the latter and spreads out as the mediastinal pleura, which is applied, back to back, to the pericardium, thus form- ing on each side a vertical antero- posterior septum between the lungs and the contents of the mediastina. The prolongation over the root is not quite tubular, since a triangular fron- tal fold extends from beneath the n >< >t to the inner side of the lung, growing narrower as it descends, to end at or near the lower borders. This is the broad ligament of the htng ( liuamen- tum latum pulmonis). Its line of at- tachment to the lung often slants backward. The mediastinal pleura, besides being applied to the side of the pericardium, lies also against s< >me of the structures of the other medi- astina. Above it is in contact with the thymus on both sides, the superior vena cava on the right and the arch of the aorta on the left. The phrenic nerve descends on each side between it and the pericardium in front of the root of the lung. In the posterior mediastinum it lies against the left side of the descending aorta and the right of the upper part of tin- greater a/ygos vein. It is in contact with nearly the whole of the oesophagus on the right, and just before the latter passes through the diaphragm on the left also. It covers the gangliated cord of the sympathetic on both sides as it passes into the costal pleura, and is here stretched so tightly across the terminations of the intercostal veins as to keep their walls distended. Anteriorly it crosses the areolar tissue of the anterior mediastinum below the remnants of the thymus. It SemtdiafiTammatic reconstruction, showm)- relations of null! plfiiral sac (blue) and lunjf (reil) to tliorarii- wall ; lateral Mpect. THE PLEURA. is continued outward, both before and behind, to become the costal pleura, and is continuous above with the cervical pleura which lines the dome in the concavity of the first rib. It passes below into' the diaphragmatic pleura which invests the upper surface of the diaphragm. Laterally, and still more behind, it follows for a certain distance the vertical fibres of the diaphragm, and then is reflected onto the thoracic wall so as to line a potential cavity between the two layers which, except for some little serous fluid, are here in apposition. Villous projections occur along the borders of the lungs, especially at the inferior border, where they form a dense, but very minute fringe, not over i mm. broad. Relations of the Pleurae to the Surface. In some places the lungs and the pleurae are always in the same relation ; in others the pleurae extend a certain distance beyond the lungs, which fill them in complete inspiration so that their out- lines correspond ; in other places the pleurae extend so much beyond the lungs FlG - J 5^3- that even in the most extreme inspira- tion the latter do not reach the limits of the former. At the apices the relations of the lungs and pleurae are constantly the same, both being in contact. All that has been said of the relation of one to the body-walls is true of the other. Behind the first piece of the sternum the relations are nearly the same, but below this level a space exists in the pleurae into which the lungs enter during deep inspiration. This is notably the case at the left half of the body of the sternum. The pleurae present inferiorly at the sides and behind a merely potential cavity between the diaphragm and the chest- walls, to the bottom of which (probably at the sides and certainly behind) the lungs can never descend. The pleurae, however, never approach closely the lower border of the chest at the sides, for the diaphragm arising from the inner surface of the frame of the thorax takes up a certain amount of space, and above it the connective tissue fills the cleft so that the pleurae do not descend to within 3 cm. of the lower border. In the sub- ject used by Hasse the space in the ax- illary line below the reflection of the pleurae to the origin of the diaphragm (the lower border of the chest) was 5.5 cm. on the right and 4 cm. on the left. The outlines of the pleurae are as follows. Beginning at the apex, about 3 cm. vertically above the cartilage of the first ribs, the anterior borders descend behind the sterno-clavicular joints to meet at the median line at the level of the second cartilage. They then descend together, or nearly so, behind the left half of the body of the sternum. Half-way down the body of the sternum the left pleura tends to diverge to the left, passing from behind the sternum usually at about the junction with the sixth cartilage. The right pleura descends more nearly in a straight line and turns suddenly outward at the level of the seventh cartilage. Laterally the pleurae run pretty close to the cartilages of the sixth rib on the left and the seventh on the right, but both cross the eighth rib at or near the junction of bone and cartilage. In the axillary line, or a little behind it, the pleura crosses the tenth rib at about the same place on both sides, and usually ends posteriorly opposite the lower part of the twelfth thoracic vertebra, the right one being often the lower (Tanja). While such is the general outline, there are considerable and important variations both anteriorly and pos- Semidiagrammatic reconstruction, showing relations of left pleural sac (blue) and lung (red) to thoracic wall ; lateral aspect. i860 HUMAN ANATOMY. FIG. 1 584. teriorly. The former teaching, according to which the left pleura describes at the front a curve somewhat similar to that of the left lung, is quite wrong. However, the point at which it leaves the sternum, the extent to which it is in contact with the right pleura, and the distance the latter advances under the sternum are all very uncertain. The most important point is the extent to which the pleura covers the pericardium. According to Side's 1 observations on twenty-three bodies of adults, the reflection of the left pleura at the fifth cartilage was in seventeen either behind the sternum or just at its border ; thus it left the sternum at a higher point only six times. At the sixth cartilage the pleura was ten times behind the sternum and less than i cm. from it in six. At the seventh cartilage it was five times at the border of the sternum or behind it and five times not over i cm. external to it. It left the sternum close to the seventh cartilage five times. Tanja, * however, found the left pleura leaving the sternum at the fourth cartilage in four of fourteen bodies ranging from eight years upward. The left pleura may ex- ceptionally cross the median line, and, it is said, may not extend forward as far as the sternum ; but such a condition must be very exceptional. There is con- siderable variation as to the depth of the descent posteriorly. Tanja never found the lower fold at the back in the adult higher than the middle of the last thoracic vertebra. It may descend to the first lumbar and even to the second. Structure. The pleura, like other serous mem- branes, consists of a stroma-layer composed of bun- dles of fibrous tissue intermingled with numerous elastic fibres. The general disposition of the con- nective-tissue bundles is parallel to the free surface, although the bundles cross one another in various directions. The free surface of the pleura is covered with a single layer of nucleated endothelial cells (from .020 .045 mm. in diameter), which rest upon a delicate elastic limiting membrane differentiated from the stroma-layer. The existence of definite openings, or stomata, between the endothelial plates, leading into the numerous lymphatics of the pleura, is doubtful. The subserous layer is very thin over the lung where it is continuous with the elastic interlobulur tissue. In the mediastinum it has a firm fibrous backing so as to make a strong and dense membrane. The cervical pleura is extremely thick and resistant, being strengthened by fibrous or muscular bands from the system of the scaleni muscles spreading into it from behind, as well as by expansions from the areolar tissue about the trachea, cesopha- gus, and subclavian vessels. The costal pleura has a subserous layer, known as the fascia endothoracica, through which it is attached to the thoracic walls less closely than elsewhere. This fascia is thickest near the top. The ribs show clearly through the pleura of the opened thorax, appearing light in contrast to the congested inter- costal spaces. The subserous layer is hardly existent beneath the diaphragmatic pleura, but at the sides of the thorax there is a considerable space below the reflection of the pleura from the diaphragm, occupied by areolar tissue connecting the dia- phragm and walls. Blood-Vessels. The arteries of the visceral pleura have been shown by Miller to come from the system of the pulmonary arteries instead of from that of the bronchial, as previously believed. They form a fine net-work over the lung. Those of the parietal pleurae come from the aortic and superior intercostals, the in- ternal mammaries, the mediastinal, the cesophageal, the bronchial, and the phrenic arteries. 1 Archiv f. Anal. u. I'hys., Anat. Abth., 1885. s Morphol. Jahrbuch, 1891. I literal veolar wall -Endothelium or free surface Connective-tissue stronia of pleura Section through free ed^e of lung, show- ing visceral pleura. X 150. THE PLEUR/E. 1 86 1 FIG. 1585. Injected lymphatics of pleura, seen frotn surface. X 75- (Miller.) The veins of the visceral pleurae are tributary to the pulmonary system ; those of the parietal pleurae open into the veins corresponding to the arteries. It is important to note that the intercostal spaces have many veins and that the pleura over the ribs has but few, these chiefly communicating with the veins above and below them. Owing to the arrangement by which the intercostal veins are kept open, the venous circulation of the parietal pleurae is under the influence of the suction power both of respiration and of the heart. The lymphatics are numerous over the lungs and also in the intercostal spaces. Those of the parietes open into both inter- costal and substernal lymph-nodes. Nerves. The nerves of the visceral pleurae are from the pulmonary plexuses, con- taining both pneumogastric and sympathetic fibres ; those of the parietal pleurae are from the intercostal, the phrenic, the sympathetic, and the pneumogastric nerves. Development of the Respiratory Tract. The respiratory tract develops as an outgrowth from the primitive digestive tube. Early in the third week, in embryos of little over 3 mm. in length, a longitudinal groove appears on the ventral wall of the fore-gut, extending from the primitive pharynx above well towards the stomach below. This groove becomes deeper, constricted, and finally separated from the fore-gut as a distinct tube, the differen- tiation resulting in the production of two canals, the respiratory tube in front and the oesophagus behind. Separation and completion of the former proceeds from the lower end of the groove upward as far as the pharynx, into which both oesopha- gus and air-tube open. The cephalic end of the latter becomes enlarged and forms the larynx, the adjoining portion correspond- ing to the trachea. The Lungs. The distal extremity of the primary respiratory tube soon enlarges and becomes bilobed, pouching out on each side into a lateral diverticulum which rep- resents the primitive bronchus and lung. These pulmonary diverticula elongate and subdivide, the right one, which is somewhat the larger, breaking up into three secondary divisions and the left into two, thus early foreshadowing the later asymmetry of the lung-lobes. Since the primary air-tube lies medially in the dorsal attachment of the sep- tum transversum, the pulmonary buds extend laterally and backward into the dorsal parie- tal recesses (later the pleural cavities), carry- ing before them a covering of mesoblast. The primary lobes increase in size and complexity as additional outgrowths arise bv the division of the enlarged terminal part of each diverticulum. The resulting divisions, or new bronchi, are at first equal, but soon grow at an unequal rate, the one elongating most rapidly becoming so placed as to continue the main air-tube, while the less rapidly elongating division becomes a lateral branch. The repeated bifurcation in this manner results in the production of a chief bronchus, traversing the entire length of the lung, into which open numerous lateral tubes or secondary bronchi. FIG. 1586. CEsophagu Lung-tub Part of sagittal section of rabbit embryo, ing lung-tube growing downward and forward f n primitive laryngo-pharynx. X 40. 1 862 HUMAN ANATOMY. FIG. 1587. The latter, from their relation to the principal stem of the pulmonary artery which accompanies the chief air-tube, are regarded as dorsal and ventral. They alternate with one another, and usually number four in each series ; not infrequently, how- ever, the third dorsal bronchus fails to develop, thereby leading to a corresponding reduction and asymmetry in the series. In the left lung the first dorsal bronchus springs from the corresponding ventral bronchus instead of the chief tube, as on the right side. This arrangement is probably associated with the fusion of the upper and middle lobes in the left lung. The secondary bronchi elongate and give origin to tertiary bronchi, and these, in turn, to air-tubes of lesser calibre, until the ramifications end as terminal bronchi and the associated divisions atria, air-sacs, and alveoli of the lung-unit. Since the fore-gut is clothed with entoblast, it is evident that the lining of the respiratory tract is derived from the same germ-layer. At first the outpouchings of the respira- tory tube are surrounded by relatively thick masses of mesoblastic tissue. Since the growth of the latter fails to keep pace with the increasing mass and complexity of the bronchial tree, the intervening mesoblast becomes greatly reduced. Coincidently the mesoblast becomes vascular and rich net-works of blood-vessels appear between the terminal divisions of the epithelial tubes, later forming the chief constituents of the alveolar walls. The mesoblastic tissue remains between the lobules as the interlobular septa, as well as contributing all con- stituents of the walls of the air-tubes except the lining epithelial and its glandular derivatives, which are ento- blastic. By the close of the fourth month of foetal life the low columnar cells lining the trachea and bronchi acquire cilia. The peripheral layer of the mesoblast invaded by the lungs eventually becomes the investing serous membrane, or pulmonary pleura, all parts of which are of mesoblastic origin. Before inflation occurs at birth, the lung-tissue is comparatively solid and re- sembles in many ways a racemose gland. With the expansion following the establishment of respiration, the epithelial cells lining the ultimate air-spaces undergo stretching, a majority of the small polygonal elements becoming converted into the flat plate-like cells seen in the functionating lung. The Larynx. The pharyngeal end of the pri- mary respiratory tract is surrounded in front and later- Kc,onstructions of developing all 7 b Y a U-shaped ridge, known as the/r/a, anterior bronchial tree, ^.fourth week; B, to which lies the paired posterior anlage of the tongue. beginning of fifth week ; C, close of r^t r .1 -j r j- i fifth week. (His-Merkei.) The anterior portion of this ridge forms a median ele- vation from which is formed the epiglottis ; the later; portions constitute the arytenoid ridges which bound the laryngeal aperture at the sides. During the fourth month a furrow on the median side of the arytenoid ridges marks the first appearance of the ventricle of the larynx, the margins of the groove later becoming the vocal cords. About the eighth week the cartilaginous framework is indicated by mesoblastic condensations. The thyroid cartilage consists for a time of two separate lateral mesoblastic plates, in each of which cartilage is formed from two centres. These are regarded as representing the cartilages of the fourth and fifth branchial arches. As development proceeds the cartilages formed at these centres fuse and extend ventrally until they unite anteriorly in the mid-line. Chondrification is completed comparatively late, and when incomplete or faulty may result in the production of an aperture, the thyroid foramen. The anlages of the cricoid and arytenoid cartilages are at first continuous, but later become differentiated by the appearance of a centre of choiulrification for each arytenoid and an incomplete ring, for a time open behind, for the cricoid. The latter thus resembles in development a trachea! ring, with which it probably morphologically corresponds. The cartilages e. s ! THE PLEURA. 1863 of Wrisberg (cuneiform) and of Santorini (cornicula laryngis) are formed from small portions separated from the epiglottis and the arytenoids respectively. The Neural canal Spinal cord FIG. 1588. Spinal ganglion X Vertebra Cardinal vein; -Cardinal vein -Aorta -(Esophagus Right lutif *n?. Right bronchus Dia Inferior vena cava 3~Pleural cavity ^r-* "v v? ?f.v^| V Liver Left bronchus Portion of transverse section of rabbit embryo, showing developing lungs. X 30. FIG. 1589. Air-tube epiglottis and the cricoid possibly represent rudiments of the cartilages of the sixth and seventh branchial arches. Changes in the Relations of the Lungs and Pleurae to the Chest-Walls. At birth the thorax is small, relatively very narrow, with the lower part undeveloped and with more horizontal ribs. The costal car- tilages are relatively long to the ribs proper. Nevertheless, at birth and in childhood the borders of the lungs have very nearly the same relations to the chest-walls that they have in the adult, excepting in front. Here they do not extend so far forward, and conse- quently the pericardium is at first less covered by the left lung. The course of the pleurae is much less certain. Tanja found much variation in that of the lower borders of the pleurae, the latter crossing all the costal cartilages -._ ^ _,.^. .,-_,., ,. ,*-. m . fourteen times in twenty-four bodies ("nexpanded alveoli of children under two years and not a single time in the adult. In eleven of the same series the pleurae did not meet behind the sternum, and in nine the left pleura did not reach it. He found neither of these conditions even once in the adult. According to Mehnert, there is a very slight progressive sinking of Branch of r . pulmonary * :' '*> . artery cs f>^>'"' Bronchiole FT -V, '- ^'-' Section of foetal lung, showing compact character of unin- flated pulmonary tissue. X 200. i86 4 HUMAN ANATOMY. the lower border of the lung during the period preceding old age, which is more rapid than the senile increase of the declination of the ribs. PRACTICAL CONSIDERATIONS: THE LUNGS AND PLEURAE. The Lungs and Pleurae. Many of the most important practical questions arising in cases of injury or disease of the lungs and pleurae can be answered only after a physical examination, the value of which will depend primarily upon com- plete knowledge of the normal phenomena associated with respiration. Such knowledge must be based upon acquaintance with the structural conditions that influence the sounds caused by a current of air entering and leaving the normal air passages and with the chief modifications caused by disease. Only a few of even the most elementary facts bearing upon this subject can here be mentioned, but their consideration at a time when the pulmonary system is being studied can scarcely fail to be of practical value, and is necessary to an understanding of those symptoms of pulmonary or pleural injury or disease which have the most obvious anatomical bearing. Anatomical Basis for Varied Character of Breath-Sounds. The normal sounds of respiration vary with the situation of the air-passages examined. Their loudness is in direct proportion to their nearness to the larynx, so that laryngeal, trachea!, bronchial, and vesicular breathing sounds are here mentioned in the order that indi- cates progressively increasing softness. These terms acquire pathological significance when breathing of one type is heard in a portion of the chest where it should not be heard. The nearness of the larynx to the surface and its inclusion of air, as if within a hollow box (West), make laryngeal sounds loud and noisy on both expiration and inspiration. In the trachea, part of which is deeper, and a portion of the walls of which is of soft muscular and fibrous tissue, both these sounds, as heard over the suprasternal notch, or over the lower cervical or upper dorsal vertebrae, while still loud, are softer and are raised in tone. Over the bronchi, heard best between the scapulae (page 1842), they are both audible and are harsh, but have still further diminished in loudness. Over the pulmonary tissue inspiration has become soft and blowing and expiration can scarcely be heard. The reasons for these differences are as follows. The sounds of breathing are produced chiefly at or about the glottis, therefore distance from the larynx accounts for the diminution in loudness. The decrease in the diameter of the air-tubes accounts for the rise in pitch of the respiratory note. The entrance of the air into compartments of various sizes within the pulmonary tissue breaks up the air-column which carries the sound and distributes the vibrations, so that the sounds are muffled and soft (West). If the bronchial tubes or tubules are obstructed, as from hyperaemia of the mucosa, or the presence of viscid secretion, the exit of air will be interfered with, and there will be ' ' prolonged expiration. ' ' , In a broad way, it may be said that in cases in which vesicular breathing is dimin- ished or absent the cause should be sought : (i) In obstruction (pseudo-membrane or fibrinous exudate). (2) In compression (aneurism, glandular swellings, medias- tinal tumors); (3) In immobilization of the chest-wall on the affected side (fracture of rib, intercostal neuralgia, pleurisy or pleuritic adhesions). (4) In distention of the pleura by liquids or air (pneumothorax, empyema). If as a result of disease the vesicular structure is occupied by an exudate (as in pneumonia), the vibrations art conveyed more directly to the ear, expiration becomes audible, and, as consolidation increases, the sounds, first of the smaller bronchioles and then of the larger bronchi, replace the normal blowing sound, and "bronchial breathing" is established. If the cavity of the pleura is distended with air ( ficuniotJioi-a\}, which separates the- lung- tissue from the thoracic wall and conducts sound vibrations much less effectively than do solids, the breath-sounds will be feeble and distant or absent. If the pleural cavity is so filled with either air or fluid (cmpyona ) that the lung is collapsed or compressed against the spine, the breath-sounds may be feeble or distant or entirely wanting over the front and sides of the chest, but bronchial breathing can be heard over the back. In exceptional cases of pleural effusion such breathing is also heard PRACTICAL CONSIDERATIONS : THE LUNGS AND PLEUR/E. 1865 over the sides and front, and it has been suggested that this is due to contact between a bronchus and a rib, the latter conveying the breath-sounds directly to the c-ar. If the larynx or trachea is narrowed, the air has to pass through a constricted aperture, must do so at a greater rate, and will make a louder noise, stridor. Rales are caused by changes in the mucous and epithelial lining and contents of the air-passages. Like the normal breath-sounds, they are louder and noisier the nearer they are to the larynx or the larger the tubes in which they are produced. Mucous rales are moist, are thought to be produced by the bursting of air- bubbles in viscid or watery mucus occupying the larger air-passages, as in bronchitis, and vary in character (i.e., in fineness or coarseness, or in loudness) in accordance with the size of the tube that they occupy. The bubbling of air through the ac- cumulating mucus in the larynx, trachea, and bronchi of a moribund person the " death-rattle" is an example of the larger kind of mucous rales. Crepitant rales are dry rales, due, it is thought, to the gluing together of the opposing surfaces of a number of air- vesicles by an exudate, the entrance .of air on inspiration then causing a fine crackling sound, "like that which is heard when a small bunch of hair near the ear is rolled backward and forward between the tips of the finger and thumb" (Owen). If a similar condition affects the lumen of a tube, i<- may produce larger rales, still dry, known as rhonchi (snoring) or sibili (hissing ). Other factors enter into the production of rales, but the chief underlying anatom- ical conditions have been mentioned. Air entering a cavity ( pulmonary vomic&, bronchiectasis} causes a sound re- sembling that produced by blowing into an empty bottle, amphoric. A peculiar sound heard often in pneumothorax, and caused by the air from the fistulous com- munication with the lung entering the pleural cavity and producing a bubbling sound at the orifice, is described as metallic tinkling. It is also thought to be due to the dropping of liquid into an accumulation of fluid at the base of the pneumo- thorax. Voice-sounds, like breath-sounds, are louder over the laryngeal, tracheal, and bronchial regions. When the voice seems very close and loud to the ear placed over other regions ( pectoriloquy, bronchophony), it indicates increased power of conduction, i.e., consolidation of lung-tissue. If the tremor from the vibration of the vocal cords in speaking (vocal f rein it us ) is transmitted with increased distinctness to the hands placed on the surface of the thorax,, it has the same significance. If it is absent, it usually indicates the interpo- sition of some relatively non-conducting substance, as air ( pneumothorax), or pus ' empvcmd}, or blood (hcemothorax^. Percussion- sounds vary with the region and the condition of the lungs and pleurae. Normally, during quiet breathing, the resonance is increasingly clear from the supraclavicular region downward over the front of the chest to about the fifth rib on the right side where the pulmonary tissue begins to decrease in thickness on account of the presence of the liver and to the sixth rib on the left side. It is less above the clavicle and over it, on account of the comparatively small amount of lung- tissue in the apices ; and over the upper part of the back, on account of the interpo- sition of the scapulae and of thick muscular masses. It becomes diminished in the presence of moderate effusion, as in oedema ; dull if there is consolidation of lung- tissue ; and is absent (flat) if there is either plastic exudate or fluid effusion in the pleural cavity. In pneumothorax, or over a cavity in the pulmonary tissue, especially if it is superficial, the percussion-note is fympanitie. Injuries. Confusions of the lung may occur without fracture of the bones of the thorax or obvious lesion of the parietes. They are thought to be due to suddenly applied elastic compression when the glottis being closed the lung or the lung and pleura are ruptured as one may burst an inflated paper bag between the hands. The consequences are intcrlobnlar emphysema, the air having escaped from the ruptured air-cells into the connective-tissue spaces of the lung ( ride infra ) ; general emphysema, the air reaching the subcutaneous cellular tissue of the neck and trunk through a ruptured pleura, or, the pleura being unbroken, passing from the root of the lung into the mediastinum and thence to the base of the neck ; pneumo- i866 HUMAN ANATOMY. thorax, the air entering the pleural cavity ; in traumatic interlobular emphysema, or pneumothorax, the chest on the affected side will be hyper-resonant, the vesicular murmur will be feeble or absent, and in the latter there may be amphoric breathing and if there is a coincident effusion metallic tinkling ; haemoptysis, not an invaria- ble symptom in either these injuries or lacerations by fractured ribs, probably because they are usually on the external lung surface and remote from the larger bronchi (Bennett) ; hcemothorax, indicated by percussion dulness gradually extending upward, by weakness or absence of respiratory murmur, by bronchial breathing over the compressed lung, and by absence of vocal fremitus. Penetrating wounds of the lung will have many of these signs plus the escape of blood from the external wound. In the absence of haemoptysis, the possibility of a wound of the costal pleura and of an intercostal or internal mammary artery causing haemothorax, dyspnoea (from pressure), and hemorrhage, apparently in- fluenced by respiration, should be borne in mind. Wounds of the pleura without involvement of the lungs are rare, the visceral pleura being closely adherent to the lung surface and the two pleural layers in close contact with each other. At the base of the pleura, where a potential cavity (page 1859) costo-phrcnic sinus exists between the costal and diaphragmatic layers, a wound could penetrate both layers and the diaphragm and open the abdominal cavity and involve the liver or spleen (page 1788) without implicating the lung, which even in forced inspiration does not descend to the bottom of this sinus. Wounds of the pleura are apt to be followed by pneumothorax and by collapse of the lung, which is partly driven back towards its root and the vertebral column by the atmospheric pressure from without, and partly drawn there by its own elasticity even when the pressure within and without is equal. In operations for empyema this collapse of the lung may take place, but is infrequent because the pulmonary tissue has often already undergone considerable compression, and because the atmospheric pressure is resisted by preformed pleural adhesions. General emphysema is often associated with wounds of the lungs and pleura. It may be due to (a) escape of air from a pneumothorax into the subcutaneous tissue during respiratory movements, or (b) escape of air direct from injured lung-tissue when pleural adhesions about the wound prevent the formation of a pneumothorax. Its occasional occurrence in laceration of the lung without external wound and without involvement of the pleura has been explained (vide supra}. It may follow a non-penetrating wound of the chest if the opening happens to be valvular, so that the air drawn in during respiratory movements cannot make its exit by the same channel. Pneumocele hernia of the lung is rare as a result of thoracic wounds because the elasticity of the lung-tissue and atmospheric pressure tend to cause collapse and retraction of the lung rather than protrusion. When it is primary it therefore follows (a) a limited and oblique wound through which air cannot freely enter the pleural cavity, although the egress of the lung under the pressure of muscular effort or the strain of coughing is unopposed ; or () a very large wound when the lung escapes at the moment of injury (Bennett). Treves says that these recent herniae are most common at the anterior part of the chest where the lungs are most movable, and that the injuries that cause them are often associated at the time with violent respiratory efforts. Pneumocele is more apt to follow the rare wounds that divide only the costal pleura, as a wound of the lung itself tends to the production of a pneumothorax which would lead to collapse of the lung and instantly lessens the pressure of air con- tained in the lungs and trachea, one of the forces favoring protrusion. Diseases of the pleurae and lungs ran here be very briefly summarized only with reference to the anatomical factors. /'///irisv is at first attended by a " friction-sound" due to the roughening of the opposed surfaces of the visceral and parietal pleura' by librinmis exudate. Later it may be lost by reason of ( a } the temporary disappearance of the roughness, i /> j tlu formation of adhesions between the surfaces, or (r) their separation by effusion. It is lost momentarily when the patient holds his breath, which will serve to differ- entiate it from a pericardia! friction-sound. As the costal pleura, the intercostal PRACTICAL CONSIDERATIONS : THE LUNGS AND PLEURA. 1867 muscles, and the abdominal muscles are all supplied by the lower intercostal nerves, the respiratory movements on the affected side are painful and are therefore greatly limited. Accordingly there will be hurried, shallow breathing with a weak vesicular murmur on the affected side and exaggerated respiratory sounds on the opposite side. Pain and tenderness in the epigastrium may result from implication of the trunks of the lower intercostal nerves when the pleurisy is near the base of the chest. When it is higher the pain may be felt in the axilla and down the inner side of the arm from involvement of the intercosto-humeral nerve, or in the skin over the seat of disease through the lateral cutaneous branches of the upper intercostals (Hilton). In diaphragmatic pleurisy the pain may be intensified by pressure over the point of insertion of the diaphragm into the tenth rib (Osier). Plcural effusion (hydrothora.v, empyema), in addition to the signs already described (vide supra), causes, when it is of sufficient amount, additional symptoms, as bulging of the side of the chest with obliteration of the intercostal spaces, disten- tion of the net- work of superficial veins (from pressure on the vena cava or greater azygos vein), and displacement of other viscera. If the fluid occupies the left pleura, as its weight depresses the diaphragm, the pericardium, w r hich is attached to the central tendon, descends also, and with it the apex of the heart. At the same time the heart is pushed towards the right so that the apex beat may be felt in the epigastrium (Owen). An empyema may point and discharge itself spontaneously, in which case it often does so at about the fifth interspace just beneath and external to the chondro- costal junction (Marshall ). At this place the chest-wall is exceptionally thin, as the region is internal to the origin of the serratus magnus, external to the insertion of the rectus, and above the origin of the external oblique (McLachlan). Evacuation of the fluid may be effected by paracentesis in pleurisy with serous effusion through the sixth or seventh intercostal space in the mid-axillary line, or through the eighth or ninth space just anterior to the angle of the scapula. The same regions are selected for thoracotomy incision and drainage in empyema. The former site is usually preferred for anatomical reasons already given (page 170). Pneumonia is often limited to one lobe of a lung, usually the lower. The fis- sure between the two lobes of the narrower left lung runs from the third rib behind, or from about the third dorsal spinous process or the inner end of the spine of the scapula, to the base in front. The fissure between the two lobes of the right lung begins at about the same level behind and extends to the base of the lung anteriorly. Where it crosses the posterior axillary line a second fissure springs from it which passes horizontally forward to the fourth chondro-costal junction making the middle lobe. Both lower lobes are posterior to the anterior lobes, and on both sides the fissures run from the level of the inner end of the spine of the scapula behind to the base in front. Therefore the dulness, crepitant rales, bronchial breathing, and increased vocal fremitus of a lobar pneumonia affecting the base would often be below that line posteriorly and would be less marked in front ; while the flatness, prolonged expiration, and other physical signs of a tuberculous infection (which affects by preference the upper lobe) would be above the spine of the scapula posteriorly, and lower would be more marked anteriorly. The relations of the lungs to the thoracic walls have been described in detail (page 1855). The congestion and oedema which precede the so-called ' ' hypostatic pneumonia' ' are very apt to begin in the thick lower and posterior portions of the lower lobes in . weak or aged persons kept long in the supine position. Tuberculous infection of the lungs is found oftenest in the apices, probably because of the relatively defective expansion in that region \vhich exists in all persons, and particularly in those of the so-called phthisical type, with round shoulders, long necks (page 143), and flat chests ; possibly also because of the greater exposure to changes of external temperature ; and perhaps somewhat owing to the short distance intervening between the outside atmosphere and the ultimate bronchioles where tuberculous pulmonary disease usually has its inception. The physical signs are those indicating consolidation followed by softening or the formation of a cavity (vide supra}. 1 868 HUMAN ANATOMY. Surface Landmarks of Thorax. The most important of the bony points have already been described in connection with the spine, thorax, clavicle, and scapula. The relations of the thoracic viscera to the surface have likewise been given (page 1855). Inspection or palpation of the front of the chest will show (a) the oblique eleva- tions of the ribs and the intercostal depressions ; (^) the curved arch of the costal cartilages ; (<:) the sternal groove ; {d} the angulus Ludovici ; (e) the infrasternal depression ; (_/") the lower border of the great pectoral muscle ; () the dictations of the serratus magnus from the fifth to the eighth rib ; (//) the nipple (pages 168, 170, 171). The infraclavicular fossa, the coracoid process, and the pectoral deltoid groove have been described in connection with the muscles and fascia- of the shoulder 579). FIG. 1590. Infraclavicufar fossa Coracoid process Suprasterna) notch ^Clavicle ^Sternum 'Acromion Groove between deltoid and pectoralis major f Ensiform cartilage Infrasternal depression Surface !a Sis ?. thnra.\. On the posterior surface of the thorax the most useful landmarks that may l>e seen or felt are (#) the spine, acromion, vertebral edge and inferior angle of the scapula (pages 255, 256) ; () the spines of the dorsal vertebrae (page 148 ) ; (<} tin median spinal or dorso-lumbar furrow, the groove between the erector spinae masses overlaid by the trapezius above and by the latissimus dorsi below ; (d ) the depres- sion at the inner end of the scapular spine indicating the tendinous insertion of the lower fibres of the trapezius, the level of the third intercostal space, and a portion of the right bronchus ; (e) a slight groove passing upward anil outward over the erector spiiue elevation from one of the lowest dorsal spines to this depression and marking the lower edge of the trapezius (Ouain). The landmarks of the ilio-costal space and lumbo-sacral region are sufficiently described on pages 148, 349. THE URO-GENITAL SYSTEM. THE uro-genital system comprises two groups of organs, the urinary and the generative ; the former serves for the elaboration and removal of the chief excretory fluid, the urine, and the latter provides for the formation and liberation of the prod- ucts of the sexual glands. The primary relations between these sets of organs, as seen in the lowest vertebrates, are so intimate that the excretory duct of the primitive kidney may also transmit the sexual cells, both groups of organs being inseparably united. In the higher vertebrates the primary relations are suggested by only tem- porary conditions in the embryo, since with the development of a definite kidney differentiation and separation take place until the urinary and generative organs con- stitute independent apparatuses except at their terminal segment, where they are more or less blended in the external organs of generation. After serving for a time as the functionating excretory organ of the foetus, parts of the Wolfnan body and its duct become transformed into the ducts of the male sexual gland. In the female analogous canals, represented by the oviducts, uterus, and vagina, are not derived from the Wolfnan duct, but from an additional tube, the Miillerian duct, which, how- ever, is closely related to the primary canal of the fcetal excretory organ. THE URINARY ORGANS. These include the kidneys, the glands which secrete the urine, the ureters, the canals which receive the urine and convey it from the kidneys to the bladder, the receptacle in which the urine is temporarily stored, and the urethra, the passage through which the urine is discharged. THE KIDNEYS. The. kidneys (renes) are two flattened ovoid glands of peculiar form, described as bean-shaped, deeply placed within the abdominal cavity against its posterior wall and the diaphragm, one on either side of the lumbar spine. They are invested in a distinct, although thin, smooth, fibrous capsule (tunica fibrosa) and lie behind the peritoneum, surrounded by loose areolar tissue, which usually contains considerable fat (tunica adiposa). This fat is particularly conspicuous along the convex lateral margin and about the lower pole of the kidney and is least abundant around the upper end and over the anterior surface. The fresh adult organ, of a brownish-red color, weighs about 130 gm. (4^ oz. ) in the male, slightly less in the female, and measures about 11.5 cm. (4^ in. ) in length, 6 cm. (*% in.) in width, and 3.5 cm. (i y z in. ) in thickness. The left kidney is usually somewhat longer, narrower, and thicker, and slightly heavier than the right. Individual variations, especially as to length, are responsible in some cases for organs unusually long (15 cm.), in others for those relatively short. Each kidney presents two surfaces, a convex anterior or visceral, when the organ is in place directed forward and outward, and a posterior or parietal, some- what flattened and looking backward and inward ; two rounded ends, or poles, of which the upper is usually the blunter and bulkier ; and two margins, the external, marking the convex lateral outline of the organ, and the straighter internal. Tin- latter is interrupted by a slit-like opening, the hilum ( hilus rcnalis), bounded by rounded edges, which leads into 'a more extended but narrow space, the sinus (sinus renalis), enclosed by the surrounding renal tissue. The capsule is continued from the exterior of the kidney through the hilum into the sinus, which it partly lines. In addition to the blood-vessels, lymphatics, and nerves passing to and from the kid- ney through the hilum, the sinus contains the expanded upper end of the renal duct 1*69 1870 HUMAN ANATOMY. or ureter, which also emerges at the hilum. The interspaces between these structures are filled with loose areolar tissue, in which lie accumulations of fat continuous with the perirenal tunica adiposa. Position. The kidneys lie behind the peritoneum, embedded within the sub- peritoneal tissue, so placed against the side of the vertebral column and the posterior abdominal wall that they occupy an oblique plane, their anterior surfaces looking forward and outward. The long axes of the organs are not parallel, but oblique to the spine, in consequence of which disposition the upper ends of the two organs are closer (8.5 cm.) than the lower extremities (u cm.), the planes of the inner margins Hepatic veins FIG. 1591. Vas deferens Spermatic cord CuL-liac axis Superior mesenteric artery x -^Left suprarenal body Left renal vein ft kidney Left renal artery Inferior mcsen- teric artery Left ureter [ yuadratus lumborum I Left spermatic artery .Common iliac artery Common iliac vein Psoas niagnus Lett ureter, pelvic portion Rectum i cut ) - Yns (leleieli- . Madder Dissection of abdomen, showing kidneys in position and course and relations ol uuteis. being anterior to those of the external. The greater part of both kidneys lies within the epigastric region, but their outer margins reach within the hypochondriac areas and their lower ends ordinarily encroach to a limited and variable' extent upon the umbilical and lumbar regions. The intersection of the plane of the transverse infra- costal line and that of the vertical Poupart line usually passes through the lower pole of tin- kidnev, falling, as a rule, somewhat higher in the right than in the left organ. Approximately the kidneys maybe said to lie opposite the last thoracic and the upper two lumbar vertebrae, reaching to within from 2.5-3.5 cm. (i-i l /> in. ) of the highest part of the iliac crest. The exact level of the kidneys, however, is subject THE KIDNEYS. 1871 to ponsiderable individual variation, as well as usually differing on the two sides in the same subject. The right organ commonly lies somewhat lower than the left, in consequence chiefly of the greater permanent volume of the right lobe of the livrr. Not infrequently the kidneys occupy the same level, and in exceptional cases the ordinary relations may be reversed, the right lying a trifle higher than the left. Addison l found that in 30 per cent, of the subjects examined by him the right kidney lay as high or higher than the left. According to Helm, 2 in women the kid- neys lie, as a rule, about one-half of a lumbar vertebra lower than in men, this differ- ence depending upon the smaller size of the vertebrae and the greater curvature of the lumbar spine in the female subject. As a rule, the right kidney extends from the upper border of the last thoracic to the middle of the third lumbar vertebra, or somewhat below the lower border of the third lumbar transverse process. While always obliquely crossed by the twelfth rib, the outer margin of the right kidney usually falls short of the eleventh rib. FIG. 1592. Stomach Pancrea (Castro-hepatic omentum Superior mesenteric artery Hepatic artery Portal vein Left kidney Perirenal fat. ^ _ '-'^Ri^^ 1 ' .- ^= _ -= \Ri R ht kidney Cross-section of formalin-hardened body at level of first lumbar vertebra. Since the left kidney usually lies from 1.5-2 cm. higher than the right, its upper pole is opposite the lower half of the eleventh thoracic vertebra, its lower level being opposite the lower border of the second lumbar vertebra and the third transverse process. Its outer margin may reach, or be crossed by, the eleventh rib ; the costal relations are, however, variable and influenced by the obliquity of the ribs, which is greater when the ribs are well developed than when they are rudimentary. The kidneys in young children in general lie somewhat lower than in later life. Fixation. Although possessed of mobility to a limited degree, slight depres- sion and elevation probably normally accompanying respiratory movements, the kidneys have a fairly fixed position. The maintenance of the latter has been variously ascribed to the support afforded by the peritoneum, the perirenal con- nective tissue and fat, the blood-vessels, and the surrounding organs, all of which during life may contribute to this end. Gerota, however, 3 has shown that, apart from the blood-vessels and, especially in children, the suprarenal bodies, the peri- toneum and adjacent organs may be removed without materially lessening the fixation of the kidneys, the latter receiving support particularly from their peculiar and inti- mate relations with the subperitoneal tissue. This, in the vicinity of the kidney, 1 Journal of Anatomy and Physiology, vol. xxxv., 1901. 2 Anatom. Anzeiger, Bd. xi., 1896. 3 Archiv f. Anat. und Entwick., 1895. IS; 2 HUMAN ANATOMY. assumes the character of a distinct fascia (fascia renalis), which at the outer botder of the organ splits into an anterior and a posterior layer. The former passes in front of the kidney, renal vessels, and ureter, and, crossing the great prevertebral vascular trunks, joins the corresponding layer of the opposite side. Traced upward, the anterior layer covers the suprarenal body, above this organ fusing with the pos- terior layer of the renal fascia. The latter passes behind the kidney, over the fascia covering the transversalis, quadratus, and psoas, as far as the inner border of the last muscle, along which it becomes attached to the spine. The posterior layer extends upward behind the suprarenal body, which, in conjunction with the anterior layer, is completely invested on all sides except below, where it lies against the kidney, to Fro. Diaphragm - "Diaphragm .ybt suprarenal body -Liver Right kidney iii!' colon .is muscle Posterior aspect of kidneys in situ in formalin subject; portion of posterior body. wall bus been removed, as bi'i-n also parts of pleural sacs and diaphragm. the support of which organ it materially contributes. Although everywhere sepa- rated from the fibrous tunic of the kidney by the intervening layer of fat (tunica adi/>osa}, the renal fascia is attached to the renal capsule proper by bands of con nective tissue, which are especially strong at the lower pole, thus directly affording support to the organ. Behind, the posterior layer of the renal fascia is likewise attached to the transversalis fascia by means of areolar tissue, between the connecting bands of which a variable amount of fat is usually present. Above, beyond the suprarenal body, the renal fascia fades away over the diaphragm ; below, it passes into and is lost within the fatty subperitoneal tissue of the iliac fossa. The fixation of the left kidney is tinner than that of the right, greater security being gained for the left organ in consequence of its more extensive relations to the THE KIDNEYS. 1873 Diaphragm - Liver XII rib fusion which takes place during the development (page 1704) of the large intestine between the original parietal peritoneum and that covering the applied surface of the primary mesentery of the descending colon ; in consequence, the left kidney is invested anteriorly with a subperitoneal layer of exceptional strength. When, for various reasons, the tonicity of the tissues supporting the kidney becomes impaired and these structures become abnormally lengthened, the organ may acquire undue mobility and suffer displacement. Relations. The position of the kidneys being wholly retroperitoneal, the posterior relations of both organs are chiefly muscular, since they lie closely applied to the diaphragm, psoas magnus, quadratus lumborum, and the posterior aponeurosis of the transversalis, the parietal fascia and perirenal areolar tissue alone intervening. The inequalities in the supporting structures produce corresponding modelling of the opposed renal surfaces, which is clearly distinguishable on organs hardened in situ. In specimens hardened in formalin, the psoas area appears as a nar- row, slightly depressed tract along the inner border ; an adjoining broader band marks the area for the quadratus lumborum, beyond which the outer part of the posterior sur- face rests upon the transversalis apo- neurosis. The crescentic diaphragmatic FIG. 1594. area crosses the upper pole, the inner limb of the crescent marking the con- tact with the crus. In organs hardened in the recumbent posture, conspicuous and probably exaggerated indentations show the former position of the trans- verse processes of the second and third lumbar vertebrae. An oblique, shallow furrow crossing the kidney from the upper pole outward, usually locates the course of the twelfth rib. In connec- tion with the posterior relations of the kidneys, it is important to recall the inferior limits of the pleural sacs (page 1859). which, where they cross the twelfth rib, may descend as low as the level of the first lumbar transverse pro- cess and therefore cover the upper part of the kidneys. The anterior relations of the kidneys differ on the two sides, not only as to the viscera concerned, but also in the manner of their contact and the consequent extent of the renal peri- toneal investment. Primarily the entire visceral surfaces of the kidneys are covered by serous membrane ; later this invest- . ment becomes only partial, in consequence of the permanent attachment which certain organs, as the pancreas, duodenum, and colon, obtain. When these viscera undergo the backward displacement incident to acquiring their final location, they are pressed against the abdominal wall and the kidneys, to which they become attached by areolar tissue, since the intervening opposed peritoneal surfaces lose their serous character. Where the organs touching the kidneys remain covered with peritoneum, the renal areas of contact retain the original serous investment. The right kidney is in relation with the corresponding suprarenal body, the liver, the duodenum, the hepatic flexure of the colon, and, to a limited extent, usually the small intestine. The right suprarenal body covers the upper pole and adjacent part of the inner border of the kidney, the surface of contact being devoid of peritoneum, since the organs are closely connected by areolar tissue. The liver covers the larger part of the anterior surface and outer border of the kidney, which models the hepatic tissue as the conspicuous renal impression seen on the inferior surface of the organ. Both the liver and the kidney are invested by serous membrane, and are, therefore, us Iliac fascia Iliacus muscle Diagrammatic longitudinal section, showing relations of supporting tissue to right kidney. (Gerota.) i8 7 4 HUMAN ANATOMY. separated by an extension of the greater sac of the peritoneum. The second part of the duodenum overlies the hiluni and the inner renal border, the non-peritoneal area being of uncertain extent in consequence of the variations in the position of this part of the intestinal tube. Although covering usually about the middle two-fourths of the median border, the duodenal area may embrace the entire inner third or more of the anterior surface of the kidney, extending from the extreme upper to the lower pole ; or, on the contrary, the duodenum may touch the kidney only near its lower pole. The hepatic flexure occupies a triangular area, external to the adjoining duodenal one and also non-peritoneal, which includes the outer and lower third, more or less, of the anterior surface of the kidney. The extent and form of the surfaces of con- tact between the kidney, colon, and duodenum are very variable ; when large they may cover the entire lower half of the kidney, or when less extensive they may leave uncovered the lower pole. In the latter case coils of the small intestine often occupy this area, which is covered with peritoneum. The left kidney is in relation with the corresponding suprarenal body, the spleen, the stomach, the pancreas, the splenic flexure of the colon, and the small in- testine. The suprarenal body lies upon the median side of the upper pole, attached FIG. 1595. Suprarenal area (non-peritoneal) Hepatic area (peritoneal) Colic area (non-peritoneal) Jejunal area (peritoneal) Duodenal area (non-peritoneal) Right renal duct Suprarenal area (non-peritoneal) Gastric area (peritoneal) Splenic area (peritoneal) Pancreatic area ( non-peritonea 1 ) Colic area (non-peritoneal) Jejunal area i peritoneal) Left renal duct (ureter) Inferior vena cava Anterior surface of kidneys of formalin-hardened subject, showing visceral areas, blood-vessels, and renal ducts. by areolar tissue ; its area is therefore non-serous. The upper two-thirds of the outer border and the adjacent part of the anterior surface of the kidney are covered by the spleen, the peritoneum intervening, except within the narrow attachment of the layers of the lieno-renal ligament. Below the splenic area the kidney is covered to a variable extent by the splenic flexure of the colon, this non-peritoneal area usually including the outer half of the lower pole. The pancreas lies in front of the hilum and approximately the middle third of the kidney, frequently reaching as far as the outer border. Above this non-peritoneal area, between the latter and the suprarenal and splenic surfaces, lies the small triangular serous area which the stomach touches, while below the pancreatic zone, internal to that for the splenic flexure, the kidney presents a triangular peritoneal area over which the coils of the jejunum glide. From the foregoing it is evident that each kidney rests within a depression, the "renal fossa," formed by the structures with which it comes into contact above, behind, at the sides, and below. The fossae are deeper and narrower in the male than in the female, owing chiefly to the greater development of the muscles against which the kidneys lie. The Renal Sinus. The longitudinal, slit-like hilum, occupying somewhat less than the middle third of the inner border of the kidney, opens into a more extensive but shallow C-shaped space, the renal sinus, which, surrounded by the kidney-tissue, THE KIDNEYS. FIG. 1596. Area still covered by fibrous cap- sule, exter- nal surface of which is roughened by strands of connec- tive tissue Renal artery takes in approximately the median half of the interior of the organ. The greatest dimension of the sinus corresponds with the long axis of the kidney, the shortest with the distance between the anterior and posterior walls. The space most extended vertically is compressed from before backward, while its greatest depth (2. 5-3. 5 cm. ) is just above the upper border of the hilum. The sinus is occupied in large measure by the dilated upper end of the ureter, the renal pelvis, and its subdivisions, the calyces; the remaining space accommodates the blood-vessels, lymphatics, and nerves that pass through the hilum and the intervening cushion of areolar and adipose tissue continuous with the perirenal fatty capsule. The fibrous capsule of the kidney covers the rounded lips of the hilum and is continued into the sinus, to which it furnishes a partial lining. In contrast to the even external surface of the kidney, the walls of the sinus are beset with conical elevations, the renal papill/z, which are well seen, however, only after removal of the contents and the fibrous lining of the sinus. The papillae mark the apices of the pyramidal masses of kidney-tissue of which the organ is composed. The individual cones, from 7 to 10 mm. in height, are in many instances somewhat com- pressed, so that their bases are elliptical in section instead of circular. Adjacent ones may undergo more or less complete fusion, the resulting compound papillae being often grooved and irregular in form. Usually from eight to ten papillae are present in each kid- ney, but their number varies greatly, as few as four and as many as eighteen having been observed (Henle). The walls of the sinus between the bases of the papillae are broken up into elevations and depressed areas, the latter marking the localities at which the blood-vessels and nerves enter and leave the renal substance. The apex of each papilla is pierced by a number of minute openings, barely recognizable with the unaided eye, which mark the terminal orifices (foramina papillaria) of the uriniferous tubules from which the urine escapes from the renal tissue into the receptacles formed by the calyces which surround the papillae and are attached to their bases. The number of uriniferous tu- bules opening at the apex of a single papilla the field in which the pores open being the area cribrosa varies with the size of the cone, from eighteen to twenty-four being the usual complement for a simple papilla. When the latter is compound and of large size, more than twice as many orifices may be present. Architecture of the Kidney. The entire organ a conspicuous example of a compound tubular gland is made up of a number of divisions which in the mature condition are so closely blended as to give little evidence of the striking lobulation marking the foetal kidney. The external surface of the latter (Fig. 1597) is broken up by furrows into a number of irregular polygonal areas, each representing the base of a pyramidal mass of renal tissue, the kidney lobe or rcnculus, which, sep- arated from its neighbors by an envelope of connective tissue, includes the entire thickness of the organ between its exterior and the sinus, a renal papilla being the apex. For a short time after birth the lobulation is evident, but later the de- marcations gradually disappear from the surface, which becomes smooth, and the interlobular connective-tissue septa within the organ disappear, the pyramids alone indicating the original lobulation. Anterior surface of right kidney from which fibrous capsule has been partly removed ; blood- vessels and renal duct are seen entering and emerging through hilum. Although evidences of the latter occasionally persist in the adult human organ, the kidneys of many of the lower animals (reptiles, birds, ruminants, cetaceans, and certain carnivora) retain 1876 HUMAN ANATOMY. the divisions in a more or less marked degree, the renal lobules of the aquatic mammals being unusually distinct. In some mammals (rodents, insectivora) the entire kidney corresponds to a single papilla, while in others (elephant, horse) no distinct papilla; exist. Right kidney of new- born child, showing tabula- tion of surface. FIG. 1598. On making a longitudinal section of the fresh kidney, from its convex border through the sinus, the papillae will be seen to form the free apices of conical masses, the renal pyramids, the bases of which lie embedded within the darker surrounding kidney-substance composing the outer third of the organ. This peripheral zone, which appears darker and granular in contrast to the lighter and striated renal pyra- mids, constitutes the cortex; the medulla includes the conical areas formed by the pyramids and partially occupies the inner two-thirds of the thickness of the organ. The cortex contrib- utes the bulk of the kidney, alone forming the entire surface, including the lips of the hilum, and receiving and surrounding the bases of the pyramids. The cortical tissue further pene- trates for a variable distance between the pyramids, separating the latter and in places gaining the sinus. These interpy- ramidal extensions are the renal columns , or columns of Berlin, and consist of typical cortical substance. Since the branches of the renal blood-vessels lie within the interlobular connective tissue separating the primary divisions of the foetal organ, these vessels never enter the kidney by passing into the papillae, but always enter at the side of these. They therefore sink into the renal substance within the areas occupied by the renal columns, the surfaces of which directed towards the sinus are pitted by the vascular foramina. Within the sinus the blood-vessels surround the calyces with coarse net-works, enter- ing and emerging from the renal substance through the orifices encircling the papillae. On close inspection, preferably with the aid of a hand-glass, it will be seen that the cortex, including that within the renal columns, is not uniform, but is subdivided by narrow striated bands, wedge-shaped in outline and lighter in color, into radially disposed darker and lighter areas. The latter, consisting of groups of parallel tubules, are known as the medullary rays (pars radiata), since they are apparently due to prolonga- tions of the medullary tissue. The darker tracts intervening between the medullary rays form the labyrinth (pars convoluta), and appear granular, owing to the tortuous character of the com- ponent tubules. The labyrinth is studded with bright red points mark- ing the position of the vascular tufts or glomeruli, which are never present within the medullary rays or the renal pyramids, although found within the columns of Bertin. On sectioning minutely injected organs, it will be observed that the larger radially coursing interlobular ar- teries, on gaining the boundary zone between the cortex and medulla, break up into smaller branches, some of which pass directly towards the surface, while others change their direction and assume an arched horizontal course, thus producing the impression of "arcades" at the baseot the pyramids. The terminal twigs " end-arteries," since anastomoses are wanting rim generally perpendicular to the exterior of the kidney and occupy the centre of the tracts separating tin- im-dullary rays. The latter, therefore, are the axes of Cortex Interlobar blood- vessel Medulla oiigUudmal section of right kidney, shoi pelvis ami its divisions to renal lUDStanC , showing relations of v and to sinus. THE KIDNEYS. 1877 abvrinth minute conical masses of renal substance, the cortical lobules, the bases of which lie at the surface and the apices within the pyramids of the medulla. From the fore- going it is evident that each renal pyramid corresponds to a group of cortical lobules, the tubules of which, on entering the medulla, become progressively less numerous but larger, in consequence of repeated juncture, until, as the wide excretory ducts, they end at the summit of the papilla. The relations of the pyramids to the papillae are less simple than formerly recognized, since, instead of each of the latter embracing but one of the former, Maresch ' has shown that a single papilla, as a rule, includes from two to four pyramids, which are blended into one conical mass culminating in the papillary apex. Structure of the Kid- ney. The fundamental components of the verte- brate excretory organ, both in the foetal and mature con- dition, include (i) a tuft of arterial vessels derived more or less directly from the aorta, (2) tubules lined with secretory epithelium, and (3) a duct for the convey- ance of the excretory pro- ducts. These constituents are represented in the kid- ney of man and the higher animals by ( i ) the glomeru- lus, (2) the convoluted uri- niferous tubules, and (3) the collecting tubes, pelvis, and ureter. Since, in a general way, to the epithelium lining the tubules may be ascribed the function of taking from the circulation the more solid constituents of the urine, and to the glomerulus the secretion of its watery parts, obviously the most favora- ble arrangement to secure the removal of the excretory products is one insuring flushing of the entire tubule with the fluid secreted by the glomerulus. Such ar- rangement implies the loca- tion of the vascular tuft at the very beginning of the tubule, a disposition which in fact is found in the kidneys of all higher animals. The number of the glomeruli, therefore, corresponds with that of the uriniferous tubules, each of which begins in close relation with the vascular tuft. The kidney-substance consists of an intricate but definitely arranged complex of uriniferous tubules, supported by the interstitial connective-tissue stroma, which have their commencement in the cortex and their termination at the apices of. the papillae, their intervening course being marked by many and conspicuous variations in the character, size, and direction of the tubules. The uriniferous tubule begins as a greatly expanded blind extremity, the capsule (i), which surrounds the vascular tuft or glomcrulus, the two together con- stituting the Malpighian body, which lies within the labyrinth. On leaving the Mal- J Anatom. Anzeiger, Bd. xii., 1896. Proximal con- voluted tubule Intermediate tubule (distal convoluted) Intermediate tubule Efferent vessel Neck Afferent vessel Capsule Interlobular artery Descending limb -Ascending limb Loop of Henle Papillary du Papilla Diagram showing course of uriniferous tubule. 1878 HUMAN ANATOMY. FIG. 1600. Capsule Malpighian body in labyrinth pighian body the tubule becomes very tortuous and arches towards the free surface as the proximal convoluted tubule (2) ; this, after a course of considerable length, usually leaves the labyrinth and enters the medullary ray, which it traverses, somewhat reduced in diameter and slightly winding in course, as the spiral tubule (3) and passes into the medulla. Immedi- ately upon gaining the latter, the tubule suffers marked decrease in size, penetrates the renal pyramid for a variable distance towards the papilla, then bends sharply upon itself and retraces its course to once more enter the labyrinth. Its ex- cursion into the medulla includes the descending limb (4) and as- cending limb (5) of the loop of Henle. The ascending limb the longer and wider of the parallel limbs of the loop rises within the labyrinth to the immediate vicinity of the corresponding Malpighian body, the neck of which it crosses, and then, after arching over the cor- puscle, gives place to the distal convoluted or intermediate tubule (6), a segment which, marked by increased diameter and tortuosity, crosses the general course of the convoluted tubule and is succeeded by the narrower and arching con- necting tubule (7). The latter enters the medullary ray and, join- ing with similar canals, forms the straight collecting tubule (8), which, progressively increasing in size by junction with others, traverses the remaining length of the medullary ray and enters the renal pyramid. Within the deeper part of the latter the collecting tubules fuse into larger and larger canals until, as the relatively wide papillary ducts (9), they terminate on the apex of the papilla at the orifices (fe inina papillaria) which open into the calyces. The relations between the various segments of the uriniferous tubules and subdivisions of the kidney are, therefore, as follows : Blood- vessels Section of cortex, showing relation of labyrinth and medullary rays. X 50. CORTEX Labyrinth Medullary ray MEDI i i \ Malpighian body, capsule and glomerulus Proximal convoluted tubule Ascending limb of Henle' s loop Distal convoluted or intermediate tubule Connecting tubule (beginning > Connecting tubule (termination) Spiral tubule Collecting tubule Descending limb and Ascending limb of Henle' s loop Collecting tubule Papillary ducts THE KIDNEYS. 1879 FIG. 1601. Efferent vessel Injected glomenilus, showing afferent and efferent vessels and continuation into intertubular capillaries. X 250. Although as a matter of convenience the entire canal, from its commencement in the Malpighian body to its termination on the papilla, has been described as the uriniferous tubule, both geneti- cally and functionally two dis- tinct parts must be recognized. These are the unbranched uri- nijerous tubule proper, which includes all divisions from the Malpighian body to the termi- nation of the intermediate tu- bule, and the duct-tube, which, when traced from the papilla towards the cortex, undergoes repeated division until from a single stem the number of con- necting tubules is sufficient to provide each uriniferous tubule proper with its own excretory canal. ^W^-'" - . ^fci -'. 'i&m....*~^KZ : imenuhuiar capillaries I. The Malpighian Body. This structure, spherical in form and from .OI2-.O20 mm. in diameter, consists of two parts, the glomerulus and the capsule. The former is an aggrega- ion of tortuous capillary blood-ves- sels into which break up the lateral terminal twigs given off from the arteries as these pass between the cortical lobules towards the free surface of the kidney. The lateral branches very short, often arched, and only .oo2-.oo4 mm. in diameter spring at vary- ing angles from all sides of the interlobular arteriole and enter the Malpighian body as the vas afferent. On entering the glomerulus, the afferent vessel divides into from four to six twigs, each of which breaks up into capillaries. These may anastomose and form a vascular complex that may be filled from any branch ; not infrequently, however, such communication does not exist, each terminal twig then giving rise to an iso- lated capillary territory, the entire glomerulus con- sisting of vascular lobules, each drained by its own radicle. Sooner or later all the channels of exit unite to form the single vas efferent, through which the blood from the en- tire glomerulus escapes. The efferent vessel as it emerges from the Mal- pighian body is close to t .-A ,"s,j. .- -v.,... the vas afferens, both usu- fs ' ;' arteriole . . . ., ally lying on the side op- posite to that occupied by the neck of the capsule from which the uriniferous tubule is continued. In consequence of the short course and manner of ori- gin of the twigs from the interlobular arteries, the glomeruli are disposed in rows, somewhat like berries attached to a straight common stalk. The capsule of Bowman, the dilated beginning of the uriniferous tubule, almost com- pletely invests the glomerulus with a double layer derived from the wall of the tubule, which seemingly has suffered invagination by the vascular tuft. Such pushing in, however, is only FIG. 1602. Capsule Section of renal cortex, showing details of Malpighian body; glomerulus is surrounded by capsule which passes into obliquely cut neck. X 200. i88o HUMAN ANATOMY. FTG. 1603. Blood-vessel Convoluted tubules, cut transversely and ob- liquely, showing character of epithelial lining. X 400. apparent, since the close relations of glomerulus and capsule result from the growth of the latter around the vascular tuft and not from invagination of the dilated tubule. The capsule consists of a distinct membrana propria and a lining composed of a single layer of flat, plate-like cells, the modified epithelium of the uriniferous tubule. In sections pass- ing through the afferent vessel and the neck the lumen of the capsule appears crescentic in outline, since the space between its outer and inner walls is widest at the neck and reduced to a mere slit where the two layers are continuous around the narrow stalk tra- versed by the afferent and efferent vessels. The inner or "visceral" layer of the capsule, the thicker of the two, is firmly attached to the glomerulus by the deli- cate intervening connective tissue, the entire complex appearing rich in nuclei which belong to the epithe- lium of the capsule, the endothelium of the capillaries, and the connective-tissue cells. 2. The Proximal Convoluted Tubule. After un- dergoing the conspicuous constriction marking the neck of the capsule, the uriniferous tubule abruptly enlarges into the convoluted segment which forms ap- proximately one-fifth of the length of the entire canal and has a diameter of from .O4o-.o6o mm. In com- mon with other parts of the tubule, its wall consists of a membrana propria, apparently structureless, but com- posed of a delicate reticulum and intervening homoge- neous substance and a single layer of epithelial cells. Although the histological details of the latter vary in different, but not constant, parts of the convo- luted segment, the lining cells present certain charac- teristics, chief among which is the differentiation of the cytoplasm of the cells into a broader outer and a narrow inner z.one. The former exhibits coarse radial striations, the so-called "rods," pro- duced by rows of granules within the vertically disposed threads of spongioplasm (Rothstein) which occupy approximately the pe- ripheral half of the cell extending from the membrana propria towards the inner zone. The latter, next the lumen, usually appears as a well- defined narrow border which, when successfully preserved, presents a fine vertical striation ("bristle bor- der") that depends not upon rows of granules, as do the rods of the outer zone, but upon the disposition of the threads of the spongioplasm. In consequence of maceration and other post-mortem changes, the inner zone may undergo partial disintegration and break up into short hair-like rods which have been mistaken for cilia. Although the spherical nuclei (.005- .007 mm.) of the epithelium of the convoluted tubule are sharply de- fined, the demarcations between the individual cells are obscure and often wanting, the tubule being lined by a seemingly continuous nucleated layer or syncytium. The lumen is not uniform throughout the convoluted tubule, in sonic places bring ; wide and in others reduced to mere clefts; these r.; I-VCMC! differences depend chiefly upon the Portion of medullary my, showing spiral and i-olUvtingtuhuli's. X 4<- varying height of the epithelial lining. 3. The Spiral Tubule. Following the tortuous path of the convoluted tubule, the canal is usually continued into the medullary ray by a segment which, while comparatively straight, de- FIG. i 604. ollecting tubule THE KIDNEYS. 1881 scribes a wavy or spiral course in its descent to the pyramid. This, the spiral tubule of Schachowa, liffersfrom the preceding in the gradual reduction of its diameter (.35-. 040 mm.) and in the thickness of the epithelial lining, the cells of which, although ivtuining the general character of those of the convoluted tubule, exhibit a distinct demarcation from one another and a narrow homogeneous inner zone. The spiral tubules are distinguishable from the surrounding collecting tubules by the lighter sharply defined cuboidal lining cells of the latter. Just before passing into the medulla to become the descending limb of Henle's loop, the spiral tubule diminishes in width and in consequence ends as a canal of conical form. 4. The Loop of Henle. The descending /iib of this U-like segment is distinguished not only by the conspicuous reduction in its diameter (.012-015 mm.), being the narrowest part of the entire uriniferous tubule, but also by the altered character of its epithelium. The latter consists of low elements, so thin that the oval nuclei cause distinct elevations in the cells which project beyond the general level of the epithelium. Since the nuclei usually do not lie exactly FIG. 1605. FIG. 1606. Henle's loop Collecting tubule Longitudinal section of medulla passing through Henle's loop. X 400. Ascending limb Longitudinal section of medulla, showing parts of limbs of Henle's loop. X 400. opposite each other, the projections on one wall alternate with those of the other, in consequence of which dispo- sition the lumen appears wavy and irregular, although not much reduced below the diameter of that of the pre- ceding spiral segment and generous in proportion to the entire width of the tubule. The flattened cells consist of clear, slightly granular cytoplasm, in which is embedded a distinct elliptical nucleus of relatively large size. The ascending limb differs from the descending in its increased diameter (.024-. 028 mm.), which depends upon sudden augmented thickness of the walls and not upon the width of the lumen, the darker and striated appearance of its epithelium, and its extension from the medulla into the cortex. The outlines of the individual lining cells are not sharply defined in well-pre- served organs, although the readiness with which these elements undergo post-mortem change often results in their artificial separation. The cells are often irregular in height, the lumen, in consequence, varying and in places, especially within the cortex, being almost obliterated. The nuclei often occupy a clear area, and are separated by striations of unusual length. Although the cells exhibit a differentiation into an outer rodded zone, a finely striated inner border, as seen in the epithelium of the convoluted tubules, is wanting ; where an inner zone is represented, it assumes a variable vesicular rather than a striated character. The length of the loop of Henle is influenced by the level of the corresponding Malpighian body within the cortex the nearer the latter lies to the medulla the greater the descent of the loop towards the papilla, and rice rersa, this relation probably depending upon the intimate association between the termination of the ascending limb and the Malpighian body. According to the reconstructions of Huber, 1 1 Amer. Journ. of Anatomy, vol. iv., Supplement, 1905. 1 88 2 HUMAN ANATOMY. Vein on gaining the Malpighian corpuscle the ascending limb crosses the neck in close proximity to the glomerulus, with which it is connected by twigs from the vas efferens (Hamburger 1 ), and then arches over the corpuscle to end in the succeeding connecting tubule. The position of the sudden transition from the narrow into the wider tube of Henle's loop varies, the change exceptionally occurring after the turn is reached, sometimes within the loop itself, but most fre- quently within the descending limb a short distance above the loop. 5. The Distal Convoluted Tubule. On gaining the level of the corresponding Malpighian body, the ascending limb gradually widens into the distal convoluted or intermediate tubule, a canal approximating the diameter (.o4o-.o45 mm.) of the surrounding convoluted tubules, but differing from the latter in its wider lumen and in the character of its epithelium. This consists of well-defined cuboidal cells, with spherical nuclei, the cytoplasm of which, while granular, is comparatively clear and devoid of stria- FIG. 1607. tions. The moderately tortuous path of the intermediate tubule is marked by a number of abrupt changes in direction, but in general lies for a time enclosed by the arch described by the corresponding convoluted segment (Schweiger-Seidel), which it finally crosses (Huber). 6. The Connecting Tubule. This portion of the tubule (.023-. 025 mm. in diameter) resembles the preceding seg- ment in its clear epithelium, the lining cells, however, being lower, with a cor- responding increased lumen. After a short and usually arched course, the con- necting tubule enters the medullary ray and, uniting with similar canals, joins in forming the collecting tubule. 7. The Collecting Tubule. This first lies within the medullary ray, where it forms the beginning of the system of straight duct-tubes that culminates in the canals opening upon the papilla, and then passes into the renal pyramid. During their course through the medul- lary ray the collecting tubules repeatedly unite to produce stems, which, while in- "-''- ft G^MTOWfrflM .TO / ft) W'l creasing four- or fivefold in diameter, are 'OOP : HlSiWlillWiy,f 1FJ diminishing in number. In consequence of this fusion within the pyramid, the col- lecting tubules are disposed in groups (Fig. 1609), each of which corresponds to the tubules prolonged from a single medullary ray and is surrounded by the limbs of the loops of Henle. On enter- ing the renal pyramid, the groups of col- lecting tubules at first are separated by the intervening bundles of straight blood- vessels (t'tisa recta-} that are given off from the larger twigs within the boun- dary /one for the supply of the medulla. After passing to within about 5 mm. of the apex of the papilla, towards which they converge, the large collecting canals undergo repeated junction, increasing in diameter but rapidly dimin- ishing in number, to form the wide papillary ducts. The epithelium lining the collecting tubules the larger as well as the smaller consists of clear cuboidal or low columnar cells, sharply defined from one another and provided with spherical nuclei. The light-colored cytoplasm and distinct demarcation of these elements render the collecting tubules conspicuous and their recognition easy. s. The Papillary Ducts. These, the final segments of the kidney tubules, number from ten to eighteen for each single papilla, at the apex of which they end. Kach is formed by the junction of from ten to thirty of the larger collecting tubules (.O5Q-.o6o mm.) and attains a diameter of from .2-.3 mm. The lining epithelium is composed of conspicuous, clear columnar cells, about .020 mm. in height and one-third as much in width, which rest upon a distinct 1 Archiv f. Anat. u. Entwick., Suppl. Hd., 1890. Collecting tubule Longitudinal section of renal medulla, showing Henle's loops and collecting tubules. X 45- THE KIDNEYS. 1883 Blood-vessel YV> m ):< S . y\ C. I'ifc Vq,. '',..0 Descending A *(?^ F 1'i'b of loop membrana propria almost as far as the termination of the canal. At this point the membrane fades away and the epithelium of the duct becomes continuous with that clothing the surface of the papilla and lining the pelvis of the kidney. FIG- 1608. It is evident that the num- ber of Malpighian bodies and uri- niferous tubules proper is greatly in excess of the larj; tubes, each papillary senting the termination of orate system of dividing canals far as the connecting tubules, from which point the true uriniferous tu- bules complete their tortuous path without further subdivision. The Supporting Tissue. The interstitial stroma holding in place the tubules and the blood- vessels consists of a net-work of modified connective tissue, or re- ticulum, whigh has been shown by Mall to withstand pancreatic digestion and to form a continu- ous framework throughout the kidney. The stroma is most abun- dant along the paths of the in- terlobular and the larger blood- vessels, from the adventitia of which delicate trabeculae extend in all directions to form the meshes lodging the tubules, smaller ves- sels, and capillaries. Within the cortex the supporting tissue is meagre, being best developed along the interlobular vessels and around the Malpighian bodies. According to Mall, the membrana propria of the tubules is resolvable into delicate net-works of reticulum directly continuous with the surrounding stroma, the general arrangement of which corresponds to the disposition of the tubules. Within the medulla the interstitial tissue is much more abundant than in the cortex, its amount increasing towards the apex of the papilla, in which location considerable tracts of comparatively coarse stroma-fibres separate the papillary ducts. At the surfaces of the divisions of the renal substance Ascending imbof loop 0> Section of medulla across renal pyramid, showing large collecting tubules, limbs of Henle's loops, blood-vessels, and stroma. X 13- FlG. 1609. Section across upper part of renal pyr.-i- mid, showing groups of blood-vessels sur- rounded by uriniferous tubules. X 50. FIG. 1610. Space for blood-vessel Supporting Stroma-tissue of kidney after pancreatic digestion; spaces lodged tubules and blood-vessels. X no. the interstitial tissue is continuous with the investing fibrous capsule, the interlobar septa, or the lining of the pelvis, as the case may be. Not only the blood-vessels, but likewise the nerve- trunks and the lymphatics are provided with sheaths of the renal stroma. 1 884 HUMAN ANATOMY. FIG. 1611. Two calyces Blood-Vessels. Arteries. The renal arteries usually one to each kidney, but not infrequently two, and in exceptional cases three or even four are of unequal length, the right one being the longer in consequence of the parent stem, the aorta, lying to the left of the mid-line. Embedded within the subperitoneal tissue and covered by the renal fascia (page 1594), they pass laterally, accompanied and more or less masked by the renal veins, to the hilum of the kidney, during their course giving off small twigs to the capsula adiposa as well as to the suprarenal bodies. Just before entering the kidney, or within the hilum, the renal artery divides into an anterior (ventral) and a posterior (dorsal) branch, each of which embraces the pel- vis and divides into four or five twigs that hug their respective wall of the sinus. Preparatory to entering the kidney, each twig breaks up into from three to five smaller divisions which enter the renal substance through the vascu- lar foramina surrounding the pa- pillae. On entering, they pass along the sides of the papillae, their course corresponding in position to the original tracts of connective tis- sue that separate the primary di- visions of the foetal kidney (page 1876) ; they are therefore appro- priately designated intcrlobar ar- teries. The general expansion of the branches derived from the an- terior and posterior arteries is par- allel to the corresponding ventral and dorsal surfaces of the kidney : the intervening zone along the convex border of the organ con- tains few, if any, of the larger ves- sels and, in consequence, appears lighter in color, constituting the white line of Brodel. The vessels supplying the kidney do not anas- tomose, each such ' ' end ' ' artery providing for a particular area of renal substance. On reaching the level of the bases of the renal pyramids, each interlobar artery breaks up into a tree-like bundle of twigs, some of which pursue an arched course across the bases of the pyramids, thereby producing the impression of a series of arcades at the junction of the medulla and cortex. From these vessels two series of terminal branches arise, one for the supply of the cortex, the other for that of the medulla. The cortical arterioles pursue a course generally perpendicular to the free- surface, towards which they run between the cortical lobules, giving off short lateral twigs that end as the vasa afferentia in the glomeruli of the Malpighian bodies. The latter are arranged in columns in correspondence with the path of the interlohular cortical arterioles. Some pf these, however, do not give off vasa afferentia, but ascend to the kidney capsule, for the supply of which they provide in conjunction with the direct branches from the renal artery. After traversing the capillary complex, the blood is carried from the glomerulus by the vas efferens, which, smaller than the vas afferens, on its exit immediately breaks up into the Cortical capillaries that form net-works enclosing the tubules within the labyrinth, and, continuing, surround those within the medullary ray, in the latter situation the meshes being relatively longer and more open and containing blood that has already supplied the proper urinilerous tulniles. The int',<=~ Stellate vein Glpmerulus of Malpighian body Interlobular artery Interlobular vein f/^f~ Capillary net-work in \ff > labyrinth Capillary net-work in medullary ray Large blood-vessels at junction of cortex and medulla Longitudinal section of injected kidney of dog, showing general arrangement of blood-vessels of cortex and adjacent medulla. X 40. plexus accompanies the renal artery, which it surrounds with its mesh-work, into the sinus ; within the latter is formed a well-marked perivascular net-work from which a number of twigs are given off to supply the walls of the pelvis and ureter, while the majority accompany the vessels into the kidney. The investigations of Ret/ins, Kolliker, Disse, Berkley, and especially of Smirnow, 1 have shown that all the renal blood-vessels are generously provided with fibres for th'e supply of the muscular 1 Anatom. Anzeiger, Bd. xix., 1901 PRACTICAL CONSIDERATIONS : THE KIDNEYS. 1887 tissue of their walls. In continuation the nerve-fibres pass between the uriniferous tubules and form plexuses surrounding the membrana propria. Smirnow traced the ultimate fibrilke within the tubules, their free endings lying between the epithelial cells. The vessels and tubules of the medulla are provided with similar but less closely disposed nervous filaments which are destined chiefly for the muscular tissue. According to the last-named investigator, the nerves of the kidney include some sensory and both medullated and non-medullated fibres. The fibrous capsule also possesses a rich nervous supply. Variations. More or less conspicuous furrows are frequently seen on the surface of the adult kidney ; these represent a persistence of the lobulation normally present in the foetus and the young child. In addition to variations in size, a marked deficiency on one side being usually compensated by a large organ on the other, the kidneys often present different degrees of union depending upon abnormal approximation or fusion of the primary renal anlages. The connection may consist of a band, chiefly of fibrous tissue, that unites otherwise normal organs ; or it may be formed by an isthmus of renal tissue that extends between the approximated lower poles ; or the two organs may form one continuous U "Shaped mass across the spine, then constituting a "horseshoe" kidney. Extreme displacement and fusion may produce a single irregular organ whose primary double anlage is indicated by the presence of two renal ducts that descend on different sides of the pelvis to terminate normally in the bladder. Absence of one kidney occasionally occurs, the organ present usually being correspondingly enlarged. Complete absence of both kidneys has been observed as a rare congenital malformation. PRACTICAL CONSIDERATIONS : THE KIDNEYS. Congenital abnormalities of the kidneys may affect (#) their shape, size, and number ; (>) their position ; and kidneys that are abnormal in one of these respects are apt to be so in others. The matter is of practical importance in relation to the diagnosis of intra-abdominal swellings and to the many operations now undertaken for the relief of various renal conditions. (a) Anomalies as to Shape, Size, or Number. One kidney may be congenitally absent or greatly atrophied ; may be constricted so as to assume an hour-glass shape ; or lobulated, as in the fcetal condition ; or the two kidneys may be fused so that ( i ) their inferior portions are united by a band of tissue glandular or fibrous that crosses the vertebral column, usually in the lumbar region ("horseshoe kidney") ; or (2) they may form an irregularly bilobed mass, one side of which is much larger than the other, or become one single ' ' disk-like' ' kidney lying in the mid-line on the lumbar spine, on the sacral promontory, or in the hollow of the sacrum (Rokitansky, Morris). Of these conditions the rarest is the true congenital absence, or extreme atrophy of a kidney ( i in 2650) ; horseshoe kidneys are more than twice as common ( i in 1000) ; while one-sided renal atrophy associated with post-natal disease is relatively frequent (i in 138) (Morris). Both kidneys have been absent in many still-born children and acephalous monsters. In a very few cases a supernumerary kidney has been found. Anomalies affecting the blood-supply to the kidney occur in nearly 50 per cent, of cases. The renal arteries are usually increased in number, or divide at once before reaching the hilum into several branches, fcetal conditions in the human species that are permanent in many birds and reptiles. Accessory or supernumerary veins are much more rarely found. (&) Anomalies of Position. Congenital displacement apart from the horseshoe kidney usually affects one kidney, which is apt to be found, in the vicinity of the sacral promontory or the sacro-iliac joint, but may be either higher or lower, and may, by its malposition, give rise to serious or even fatal error in diagnosis or treat- ment. It would seem proper to include here those rare temporary displacements that are due to the congenital presence of a mesonephron, which as the usual support given by the peritoneum is lacking, and as the contained blood-vessels are in such cases of abnormal length permits mobility of the kidney beyond the physiological limits (floating kidney). 1888 HUMAN ANATOMY. Movable Kidney. The extent of the normal kidney movement of ascent during expiration or while lying supine, and of descent during inspiration or while standing erect does not, on an average, much exceed an inch in the vertical direction. There may also be a slight lateral movement. When this limit is distinctly and greatly overpassed the condition known as ' ' movable kidney' ' results. The normal kidney- is usually not palpable below the costal arch. Occasionally the lower end of the right kidney may be felt there just external to the rectus muscle. In emaciation the lower ends of both kidneys may be palpable. Three degrees of abnormal mobility have been arbitrarily but usefully agreed upon for purposes of description : ( i ) The lower half may be felt by bimanual pal- pation the fingers of one hand being pressed into the ilio-costal space posteriorly, and of the other, into the subcostal region anteriorly during deep inspiration. (2) The greater part of the kidney or the whole organ may be felt during deep inspiration, but ascends under cover of the ribs and liver during expiration. (3) The whole kidney descends and can be retained between or below the examiner's fingers during the respiratory movements (Morris). The most important factors in holding the kidney in its normal position in the renal fossa (page 1874) are : (a) the perirenal fascia, which through its attachment to the transversalis fascia and to the perinephric fat, in conjunction with (<) the peri- toneum, where that covering exists, prevents any undue mobility; (c~) the renal vessels, which must correspond in length to the radius of the circle of movement of the kidney and, to an extent, resist elongation ; {d") intra-abdominal pressure, which, through the upward thrust of the more mobile viscera, adds to the support that (e) they and their attachments give to the viscera in the upper zone of the abdomen ; (/") the shape of the renal fossae, which, like the kidneys themselves, are somewhat narrower at their lower extremities. Undue mobility of the kidney is thus favored by (a) congenital absence of the peritoneal support (floating kidney, vide supra) ; (^) diminution of the tension of the peritoneum and perirenal fascia from absorption of perinephric fat ; (<:) repeated jars and jolts, as from jumping or falling, or from coughing or straining, that tend to elongate the renal vessels as well as to stretch the peritoneum and its attachments and thus increase both the retroperitoneal space in which the kidney moves and the radius of the arc of its movement ; (d ) pregnancy, the removal of intra-abdominal tumors or of accumulations of fluid, or other conditions that produce laxity and weakness of the abdominal walls ; (^) ptosis of other viscera, acting either by their push from above (liver, spleen) or their drag from below (colon) ; or (/") general muscular weakness, acting not only by reason of the associated lack of tonicity of the abdominal wall, but also through the modification in shape of the renal fossae, the depth of which depends, c&teris paribus, on the development of the loin muscles, and especially of the psoas and quadratus lumborum. A careful study of the body-form in its relation to movable kidney seemed to show (Harris) that a relative diminution in the capacity of the middle zone or area of the body-cavity (containing the liver, stomach, spleen, pancreas, and larger por- tion of each kidney), either original or acquired (as from tight lacing), acts by forcing the liver and spleen downward upon the kidneys, and at the same time depriving them of the support afforded by the narrowest or most constricted portion of the parietes of this zone, which narrow portion is then above the centre of the kidney instead of below it, as it should be normally. Consideration of the above-mentioned anatomical factors makes clear the greater frequency (80 per cent.) of movable kidney in women than in men. It should be added that in women the renal fossae are normally shallower and less narrowed at the lower ends than in men, the depth and the narrowing depending, as has been said, upon muscular development. It will be understood, too, why among the women who suffer from this condition is found a so considerable proportion who are thin and round-shouldered, with long, curved spines and flattening and adduction of the lower ribs, or who have had several children, or one difficult labor, or an exhausting illness attended by emaciation, or have been addicted to tight lacing. In both sexes the history of a violent fall or of a chronic cough is not infrequent. Movable kidney is thirteen times more frequent on the right side than on the PRACTICAL CONSIDERATIONS : THE KIDNEYS. 1889 left, because of the following conditions, which are of varying relative importance in different cases : (a) the left perirenal fascia is strengthened by some fibrous bands, remnants of the fusion of the descending mesocolon with the primitive parietal peri- toneum (Moullin), the left kidney being thus more firmly bound to the descending colon than is the right to the ascending colon ; (6) the greater size, weight, and density of the liver as compared with the spleen, and its more intimate association with respiratory movements, making the impact of the former on the upper surface of the right kidney both more frequent and more potent than the similar contact of the spleen with the left kidney ; (c) the greater length of the right renal artery, which has to cross the mid-line to reach the kidney ; although the right vein is similarly shorter than the left vein, it offers less resistance to elongation than does the left renal artery ; (X) the right kidney is usually lower than the left kidney (page 1871), and therefore more easily loses the support of the parietes at the region where that support is most effective (vide supra} ; (f)cr and a lower segment (calyces majores), extending towards the respective poles of the kidney. Each of these segments receives a group of from four to six smaller conical passages, the calyces or infun- Depression on calyx re- ceiving re- nal papilla Calyces Casts obtained by corrosion, showing two forms of renal pelvis: A, usual tvpi- ; /.'. \aiiation. THE RENAL DUCTS. 1895 dibula (calyces minores), that 'proceed from the renal substance, where they surround the papillae. The latter are embraced by the expanded bases of the conical calyces, the walls of which are intimately blended with the kidney-substance around the sides of the free part of the papillae, a narrow cleft separating the latter from the enclosing calyx. The epithelium of the papillary ducts is directly continuous with that lining the calyx, while the subepithelial tissue of the latter blends with the intertubular renal stroma. On laying open the calyx, the papilla is seen as a conical elevation project- ing into the funnel-shaped envelope (Eig. 1598); although usually enclosing a single papilla, the calyx may receive two or even more such projections. The two general groups of calyces an upper and a lower open into the two large primary subdivisions {superior and inferior pelvis") that join to produce the main compartment of the pelvis. The lower end of the latter emerges through the hilum and arches downward to pass about midway between the hilum and the inferior pole of the kidney Insensibly into the ureter; exceptionally this junction is marked by a constriction in the lumen of the canal. Although surrounded in its upper part and smaller divisions by the branches of the renal blood-vessels, the general position of the pelvis within the sinus and as it emerges through the hilum is behind the blood-vessels, the intervals between the renal duct and the other occupants of the sinus being filled with adipose tissue. On the right side the lower part of the pelvis is covered in front by the second part of the duodenum ; on the left by the pancreas. The Ureter. Tfiis part of the renal duct is a flattened tube which connects the renal pelvis with the bladder. It lies beneath the parietal peritoneum, embedded within the subserous tissue and surrounded by fat, and descends along the posterior abdominal wall to the pelvic brim ; crossing the latter, it follows the lateral wall of the pelvis, curving downward, forward and finally inward along the pelvic floor, to reach the bladder. The general direction of its course is indicated by a vertical line on the surface of the abdomen drawn from the junction of the inner and middle thirds of Poupart's ligament (Tourneux). The average length of the undisturbed ureter is approximately 27 cm. (10.5 in.), the left duct being usually about one centimetre longer than the right in consequence of the higher position of the corre- sponding kidney. Apart from the uncertainty of determining just where the pelvis ends and the ureter begins, its length is influenced by several factors, such as the level of the kidneys and of the bladder, the descent of the renal pelvis, body height, and sex, so that considerable variation is encountered ; the excessive figures some- times given are probably based upon measurements of the ducts after removal and abnormal relaxation.' The diameter of the ureter from 4-5 mm. is not uniform, since at certain points, corresponding to changes in the direction or relations of the canal (Solger), constrictions regularly occur, above which the tube exhibits fusiform dilatations or spindles (Schwalbe). The most constant narrowings are situated (i) from 4-9 cm. (1^-3^2 in.) below the hilum, at which point the upper isthmus of Schwalbe the diameter of the canal is reduced to almost 3 mm.; (2) near the pelvic brim as the duct crosses the iliac vessels {lower isthmus}, preceded by a fusi- form enlargement {chief spindle") ; and (3) at the lower end of the ureter as the canal penetrates the wall of the bladder. Since its course and relations vary in different parts of its path, the ureter is divided for description into an abdominal and a pelvic portion. The abdominal portion (pars abdominalis) from 13-14 cm. (about 5-5^ in.) in length begins a short distance below the hilum and descends upon the anterior surface of the psoas magnus muscle and its fascia towards the sacro-iliac articulation, with a slight inclination towards the mid-line (Fig. 1591). The distance between the two ureters at their upper ends is about 9 cm. (3^ in.) and at the pelvic brim about 6 cm. (2^/3 in.). Just before reaching the latter level the ureters obliquely cross the common iliac vessels, approximately the point at which the artery divides into its external and internal divisions, or, especially on the right side, they may pass over the external iliac vessels instead. About midway in their course to the pelvis both ducts are crossed in front, at a very acute angle, by the spermatic (or ovarian) ves- sels and behind and obliquely by the genito-crural nerve. The right ureter passes 1896 HUMAN ANATOMY. J2u- Reflection -,- of calyx onto renal papilla behind the descending part of the duodenum, lies to' the right of the inferior vena cava, which it approaches and even touches in its descent, and is covered by the attachment of the mesentery. Above the left ureter may be covered by the pancreas when that organ is unusually broad, and below it is crossed by the attachment of the sigmoid flexure. The pelvic portion (pars pelvina) from 12-13 cm - (5 m -) m length lies against the lateral wall of the pelvis, close beneath the serous membrane embedded within the subperitoneal tissue, and curves downward and forward to about the level of the ischial spine, where it turns inward upon the visceral layer of the pelvic fascia to reach the dorsal wall of the bladder (Fig. 1619). In its descent it lies in front of the internal iliac artery as far as the greater sciatic notch (Merkel), crosses the ob- literated hypogastric artery and the obturator nerve and vessels to their inner side, and, as it traverses the pelvic floor, is surrounded by the tributaries from the vesical plexus to the internal iliac vein and may lie upon the middle and inferior vesical arteries. The ureter is crossed FIG. 1615. on its inner side by the vas defer- ens, and pierces the bladder-wall immediately in front, or under cover of the anterior part, of the seminal vesicle or of the ampulla ( Fraenkel l ) . The space between the ureter and the seminal vesi- cle, which when the bladder is empty may be considerable, is filled by areolar tissue containing veins and fat. The relations of the ureter to the bladder are pe- culiar, since, in addition to pene- trating the latter so obliquely that the last 1 8 mm. (|^ i n - ) of the renal duct are embedded within the vesical wall, the muscular tis- sue of the latter is seemingly pro- longed (page 1897) over the ure- ter outside the bladder for some 5 mm. as a distinct sheath (Wal- deyer). The ureteral orifices on the inner surface of the vesical wall are slit-like and valvular in form and, in the contracted condi- tion of the bladder, about 2. 5 cm. apart, thisdistance being increased twofold or even more when that organ becomes distended. The female ureter (Fig. 1622) calls for special description on account of the relations of its pelvic portion to the generative organs. On gaining the lateral wall of the pelvis, the ureter descends in close proximity to the unattached border of the ovary and constitutes the postero-inferior boundary of the ovarian fossa (page 1986). On the pelvic floor the ureter enters the base of the broad ligament, within which duplicature it crosses the uterine artery, passes between the veins of the vesico- vaginal plexus, and continues downward and forward in the vicinity <>f the uterine cervix to the vagina; its terminal segment lies embedded within the connective tissue between the cervix and bladder, close to the anterior vaginal wall for a distance of from 1-1.5 cm -> where, bending somewhat inward, it reaches the posterior vesical wall, which it pierces obliquely in the manner above described. Structure. The wall of all parts of the renal duct is tin- same in its general construction and includes three layers, (i) the mucous membrane, (2) the mus- cular tunic, and (3) the outer fibrous coat; the mucosa and the muscular layer are 1 Die Samenblasen der Menschen, Berlin, 1901. Renal blood- vessels Ureter Sagittal section through sinus of child's kidney, showing lower part of pelvis and commencement of ureter. X 10. THE RENAL DUCTS. 1897 more or less blended, a distinct submucosa being wanting. The mucous membrane is clothed with "transitional" epithelium consisting of several strata of cells, the su- perficial elements being plate-like and the deepest ones irregularly columnar. The tunica propria constitutes a subepithelial layer of fibre-elastic tissue which blends with the subjacent muscular tunic. Within the ureter the mucous membrane is usually thrown into longitudinal folds, and in consequence in transverse section the lumen of the canal appears stellate. Neither well-marked papillae nor true glands are pres- ent, although in places the subepithelial tissue invades the epithelium and subdivides the latter into nest-like groups of cells. Occasional aggregations of lymphoid cells occur, which in the vicinity of the calyces sometimes form distinct minute lymph- nodules within the mucosa (Toldt). On the papillae the epithelium lining the renal duct passes uninterrupted into that of the papillary canals, while the underlying tunica propria becomes continuous with the intertubular renal stroma. The muscular tunic consists of bundles of the involuntary variety disposed as a thin inner longitudinal and a chief external circular layer. Within the renal pelvis and its larger subdivisions both layers are well represented, but are reduced on the calyces ; at the junction of the latter with the kidney the circular muscle increases and surrounds the papilla with a minute sphincter-like bundle (Henle). Except in the upper part of the renal FIG. 1616. . Epithelium Mucous coat, thrown into longitudinal folds &"~^ * - ;>; ; -\ .'- ; <*^' -'/zra uretericce, or iorus uretericus of Waldeyer, that unites the open- ings of the renal ducts. This ridge, best marked at its outer ends, is less evident and often interrupted near the mid-line, and is subject to much individual variation. Its production depends upon the eleva- tion of the mucosa and muscular tissue in consequence of the oblique path of the ureters through the vesical wall. The margins of the trigonum lateral as well as posterior are raised and its central area is somewhat depressed towards the urethral opening . The lat- ter (orificium urethrae interntim) occu- pies the apex of the trigonum, and is usually not circular, but crescentic, owing to the projection of its posterior border as a small median elevation, the vesical crest (uvula vesicae), that ex- tends from the apical end of the trigone into the urethra to become continuous with the urethral crest in the prostatic part of the canal. The vesical crest consists of a thickening of the mucous membrane enclosing bundles of muscular tissue. When hypertrophied, as it not infrequently is in aged subjects, this fold may form a valvular mass that occludes the urethral orifice. The anterior wall of the latter is commonly marked by low converging folds continuous with the longi- tudinal plications of the urethral mucous membrane. The ureteral orifices are usually slit-like in form (4-5 mm. long), obliquely trans- verse in direction, but may be oval, round, or punctiform (Disse). The lateral bor- der of the opening is guarded by a valve-like projection (valvula ureteris) that forms part of the nodular elevation that is produced by the wall of the ureter. The median margin of the opening is embedded in the interureteral plica. The urethral and the two ureteral openings mark the angles of an approximately equilateral triangle, the sides of which, in the contracted condition of the bladder, measure from 2-2.5 cm.; when the organ is expanded, this distance increases to from 3. 5-5 cm. or even more. The urethral orifice lies from 1.752.2 cm. in front of the base of the trigone when the latter is contracted. Immediately behind the vesical 'triangle the posterior bladder- wall presents a slight depression, the rctrotrigonal fossa or fovea retroureterica (Waldeyer), that corresponds to the "bas-fond" of the French writers. When abnormally enlarged and pouch-like, as it often is in advanced life when associated with an enlarged prostate, this fossa becomes of practical importance (page 1981). Peritoneal Relations. The superior surface of the empty or but slightly filled bladder is completely covered by peritoneum as far as the lateral and posterior Interior of lower segment of partly distended and hardened bladder, viewed from above and behind. THE BLADDER. 1905 borders. On each side the serous covering passes from the organ to line the para- vesical fossa, the sickle-shaped depression that separates the contracted bladder from the adjacent pelvic wall. In front these side folds, the lateral false ligaments, meet at the vesical apex, where they cover the fibrous band of the urachus and are reflected onto the anterior abdominal wall as the anterior false ligament (ligamcntura umbiliculc medium). An uncertain fold, the plica I'esicalis transi'crsa, often crosses the other- wise smooth upper surface of the bladder. This peritoneal ridge, sometimes repre- sented by two or more low wrinkles, extends laterally to be lost either on the pelvic wall or, passing over the pelvic brim, towards the internal abdominal ring. Dixon ' found the fold well represented in the male foetus, and inclines to the view that its production is connected with a drag on the peritoneum incident to the formation of the inguinal pouches. Behind the peritoneum passes from the posterior border of the empty bladder over the upper end of the seminal vesicles and the vasa deferentia, to form a horizontal crescentic shelf-like fold (plica recto vesicalis) from 1-1.5 cm - wide, that extends from the bladder backward, embracing the rectum and ending at the sacrum on either side of the gut (Fig. 1619). Since this duplicature includes parts of the seminal ducts and vesicles, Dixon and Birming- ham 3 have suggested for its lateral and backward extensions, which contain bundles of invol- untary muscle (tn. rectovesicalis) attached to the sacrum and rectum, the appropriate name, sacro-genital folds, and pointed out their correspondence to the utero-sacral folds in the female (page 2007). The median part of the shelf-like plica, conspicuous behind the empty bladder, but more or less obliterated on the distended organ, overhangs the lowest part of the peritoneal recess, the recto-vesical fossa, that intervenes between the rectum and the seminal vesicles and ampullae of the vasa deferentia, and towards which the fundus of the bladder is directed. In recognition of these relations, the anterior wall of this recess being in direct relation with the seminal tracts, the authors last mentioned propose to call this depression the recto-genital fossa, a term alike applicable to both sexes, since the relations of the rectum to the uterus in the pouch of Douglas in the female are similar. All other parts of the bladder, including the postero-inferior (fundus) and the antero-inferior surfaces, are entirely devoid of peritoneal covering. In the female the serous membrane passes from the posterior border of the bladder onto the anterior uterine wall, the shallow utero-vesical fossa intervening. Occasionally a corre- sponding depression exists in the male as a slight indentation between the posterior vesical wall and the seminal vesicles (Dixon). With the changes of form and position which the bladder undergoes when it becomes dis- tended are associated alterations in its peritoneal relations. These include the gradual obliter- ation of the upper part of the recto-vesical fossa, along with the shelf-like fold, and the elevation of the line of peritoneal reflection at the sides, so that the lateral false ligaments no longer reach the pelvic floor, but pass from the lateral wall of the pelvis directly to the superior surface of the bladder, from which the plica transversa has disappeared. Anteriorly the relations of the serous covering are also affected, since with the rise of the bladder above the level of the symphysis the peritoneum is carried upward and a suprapubic non-peritoneal area becomes progressively more extensive until, in extreme distention, a space measuring vertically from 8-9 cm., or about 2, l /i in., may be uncovered. Fixation. The attachments of an organ so subject to considerable alterations in size and form as is the bladder must obviously provide for such changes as well as the maintenance of a more or less definite position. The ' ' ligaments ' ' of the bladder are conventionally described as tnie andjfa&e, under the latter being included the peritoneal folds (above described) that pass from the organ to the adjacent ab- dominal and pelvic walls. The sacro-genital folds were formerly sometimes called the posterior false ligaments. From the manifest instability of the relations and attachments of the peritoneum incident to distention and contraction, it is evident that such peritoneal folds can contribute little to the definite support or fixation of the bladder ; hence those parts of the organ possessing a serous covering are movable. The inferior surface, on the contrary, is comparatively fixed on account of its close relations to the pelvic floor (and in the male to the prostate) and the presence of fascial bands or true ligaments. The latter are derived from the pelvic fascia, which in the vicinity of the bladder presents a stout, glistening, band-like thickening (arcus tendineus) that on each side stretches from the posterior surface of the symphysis, a 1 Journal of Anatomy and Physiology, vol. xxxiv., 1900. 2 Journal of Anatomy and Physiology, vol. xxxvi., 1902. 1906 HUMAN ANATOMY. short distance above its lower border, backward to the ischial spine (page 1899). On either side of the mid-line the anterior ends of these tendinous arches pass as strong fascial bands, the pubo-prostatic ligaments, from the symphysis to the prostate, blending with its capsule, and thence continue to the inferior surface of the bladder, where they are lost in the outer fibrous coat of the vesical wall. In the female these fascial bands pass directly to the bladder as the anterior true ligaments. After leaving the symphysis, the tendinous arches send expansions the lateral true ligaments to the side of the bladder, which materially assist in fixing the organ. The cleft left between the medial borders of the two levator ani muscles is occupied in the male by the rectum and prostate and in the female by the rectum, vagina, and urethra, over some of which organs (rectum, vagina, and prostate) the pelvic fascia covering the upper sur- face of the levator ani muscles (fascia diaphragma pelvis superior) sends more or less extensive investments and thus binds them to the pelvic floor. Additional support is afforded by more or less definite processes of muscular tissue pro- longed from the bladder to adjacent structures ; those passing within the arcus tendineus to be attached on either side to the back of the symphysis constitute the pubo-vvsical musc/es, while others, the recto-vesical muscles, extend backward to blend with the rectal wall. FIG. 1621. Symphysis pubis Pubo-vesical space, cleaned out Arcus tendineus _ _ fasciae pelvis White line, (arcus tendineus in. levatoris ani) Pubo-vesical ligament Arcus tendineus ^Levator ani muscle ^Obturator canal White line Bladder, partly distended Anterior part of pelvis of female, viewed from above and behind, showing relations of bladder to pelvic fascia ; bladder has been partly distended and pulled backward. Hetween the lateral pubo-prostatic ligaments, the symphysis, and the bladder lies a deep recess (fovea pubovesicalis), traversed by the dorsal vein of the penis and filled with fatty areolar tissue, the floor of which is formed by the fusion of the pelvic fascia with the transverse ligament of the perineum. Above the level of the pubo-prostatic ligaments lies the preresical space, or space of Retzius, which is bounded in front by the anterior wall of the pelvis below and the transversalis fascia above, and behind by a thin membranous condensation of areolar tissue, the fascia umbilico-vesicalis (Karabeuf), that passes from the pelvic floor over the prostate and bladder to the abdominal wall, to fuse with the transversalis fascia at a variable distance In-low the umbilicus. Laterally the boundaries of this space, filled with areolar tissue loaded with fat, are uncertain, since when distended, as when the seat of an abscess, it may embrace the sides of the bladder below and extend above as far as the obliterated hypogastric arteries. Under usual conditions, however, the space may be regarded as confined chiefly between the antero-inferior surface of the bladder and the adjacent anterior pelvic wall. Relations. When empty, or containing only a small quantity of fluid, the bladder possesses two general surfaces, a superior and an inferior. The anterior two- thirds of the the latter rests upon the prostate and the pelvic floor, and, according to Dixon, 1 when hardened /// situ presents a rounded median ridge which, together with the ureters, outlines two forward, upward, and outward sloping infero-lateral areas. These rest upon the pelvic floor and the posterior surface of the pubis, separated 1 Journal of Anatomy and Physiology, vol. xxxiv., 1900. THE BLADDER. 1907 from the latter by the retropubic pad of fat from .5-1 cm. thick. The fundus the posterior part of the inferior surface included between the urethral opening and the posterior border is in contact with the median ends of the seminal vesicles and of the ampullae of the seminal ducts, by which structures and their musculo-adipose bed the bladder is separated from the anterior wall of the recto- vesical fossa. The internal orifice of the urethra lies immediately above the prostate, usually from 1.2-2.5 cm. (X~i m - ) above the plane passing through the lower border of the symphysis and the lower end of the sacrum ; the distance from the upper border of the symphysis to the orifice measures from 5-6 cm. (2-2^ in.) ; in the horizontal plane it lies from 2. 5-3 cm. behind the symphysis, its nearest point on the latter being about 2 cm. (Disse). These measurements are influenced by changes in the position of the inferior surface, being shortest when the empty bladder is pushed upward. FIG. 1622. Ureter Suspensory ligament of ovary Fallopian tube ll_ Round ligament Ovary Obliterated hypogastric artery Uterus Symphysis pubis External ureth orifice in vestibi 1 ,' Vi _Utero-sacral fold Rectum . External os uteri Bottom of recto- uterine pouch .Vagina Perinea] body Sagittal section of female pelvis of formalin subject. Laterally the paravesical fossa" intervene between the empty bladder and the sides of the pelvis. In the contracted condition the superior surface usually lies below the plane of the pelvic inlet, the entire bladder being within the anterior third of the pelvis and close to the pelvic floor. This tipper surface, covered with peri- toneum, is in contact with coils of small intestine which, when the rectum is empty, may occupy a part of the recto-vesical fossa. In the distended bladder the relations of the inferior surface suffer little change on account of the intimate attachments of the vesical wall to the prostate and to the fixation to the pubis afforded by the pubo-prostatic (pubo-vesical) ligaments and enclosed muscle. The postero- inferior surface, expanding backward and outward, comes into more extensive and closer rela- igo8 HUMAN ANATOMY. Uterus Uiachus Bladder Symphysis pubis Urethra tions with the seminal vesicles and ducts. The condition of the rectum markedly influences the degree to which the distending bladder rises above the symphysis, since, when the bowel is empty, and hence more intrapelvic space is available, the bladder gains a lower suprapubic level than when its ascent is favored by a distended rectum. With the elevation of the vesical apex above the level of the symphysis, the bladder acquires a temporary relation with the anterior abdominal w : all in front, and its sides, in case of marked distention, may come nearly or actually into con- tact with the vasa deferentia, the obliterated hypogastric arteries, and the obturator vessels and nerves, as these structures lie along the pelvic wall embedded within the fat-laden subperitoneal tissue. The bladder in the female lies lower within the pelvis than in the male, chiefly in conse- quence of the absence of the prostate, and when empty never quite reaches the level of the upper border of the symphysis. When distended, therefore, it less often rises into the abdomen, since the capacity of the normal organ in the female is somewhat less than in the male. The fundus, or postero-inferior surface, is firmly united by connective tissue with the anterior vaginal wall and sometimes the lower part of the uterus. Where reflected from the anterior surface of the uterus onto the bladder, the peritoneum lines the shallow utero-vesical fossa and then con- tinues over the superior vesical surface. Upon the latter rests the body of the uterus, rising or falling with the expansion or contraction of the bladder-wall, but normally remaining in contact, a relation predisposing to the production FIG. 1 623. of the concave or sunken condition of the su- Rectum perior surface not infrequently seen in frozen sections of the female pelvis. The infantile bladder differs both in form and position from the adult organ. Since the greater part of the bladder represents a persistent and dilated portion of the intra- embryonic segment of the allantois, its fcetal form is essentially tubular. In the new-born child (Fig. 1623), in both sexes alike, the bladder is spindle-shaped and extends from about midway between the umbilicus and the symphysis to the level of the pelvic brim, its anterior surface being in contact with the abdominal wall. Only the lower pole of the infantile bladder, corresponding to the ure- thral orifice, lies slightly below the upper border of the symphysis, the body lying entirely within the abdomen, lateral and posterior surfaces being undifferentiated. Leaving the anterior abdominal wall, the peritoneum completely invests the posterior surface of the bladder, as well as the semi- nal vesicles and the ampullae of the seminal ducts, before passing onto the rectum. The bottom of the recto-vesical fossa lies often below the level of the urethral orifice, which does not come into relation with the pelvic floor. In the new-born female child the uterus is situated rela- tively high and comes into contact with the bladder, while the vagina does not, only touching the urethra. The reflection of the peritoneum to form the utero-vesical fossa varies in position, and when high, as it often is, may leave a part of the young bladder unprovided with a serous covering. Coincident with the descent of the bladder, associated with the growth and expansion of the pelvis, its posterior wall increases more rapidly than the anterior, this inequality resulting in the production of a fundus that gradually approaches the pelvic floor. According to Disse, 1 the descent of the young bladder is rapid during the first three years, slower from the fourth to the ninth year, between which and puberty little change occurs. Succeeding this period of rest the bladder renews its descent, and by the twenty-first year has gained its definite position on the pelvic floor. Before the third year the empty bladder always remains above the symphy- sis ; by the ninth year it has sunken below that level, but when distended the apex rises within the abdomen. During descent the non-peritoneal area on the posterior surface progressively increases, the serous investment in general extending farther downward in the male than in the female child. Persistence of infantile relations often ace. units f< >r variations observed in the adult. Structure. The bladder consists essentially of a muscular sac lined with mucous membrane and covered on its upper surface with peritoneum, a layer of connective tis- sue loosely uniting the mucous and muscular coats. From within outward, four coats 1 Anatomische Hefte, Hd. i., 1892. Vagina Sagittal section through pelvis of new-horn female child, hardened in formalin, showing infantile form and suprapubic position of bladder. THE BLADDER. 1909 FIG. 1624. Epithelium Mucous mem- brane, thrown into folds are distinguishable, the mucous, the submucous, the muscular, and the incomplete serous. The mucous coat varies in thickness with both location and the degree of con- traction. Over the vesical trigone, where always comparatively smooth, it is thin, measuring only about . i mm. ; where strongly wrinkled by contraction, it may attain a thickness of over 2 mm. The mucosa resembles closely that of the renal duct, consisting , of a fibro-elastic tunica propria covered with transitional epithelium. The latter includes several strata of cells, the deepest of which are columnar, the middle irregularly polygonal or club-shaped, and the inner plate-like, their deeper surface fitting over and between the underlying elements. Although glands may be con- sidered as absent, tubular depressions are occasionally found in the vicinity of the trigone which are regarded by some (Kalischer, Brunn) as true glands. Waldeyer has suggested that these structures may be interpreted as representing in a sense urethral glands displaced during the development of the vesical trigone. The submucous coat, loose and elastic, permits free gliding of the mucous over the muscular tunic when readjustment becomes necessary during contraction. Com- posed of bundles of fibrous tissue interwoven with elastic fibres, it supports the blood-vessels and nerve-plexuses, and contains numerous bundles of involuntary muscle. It is not sharply defined from the adjoin- ing coats, but blends with the stroma of the mu- cosa on the one side and extends between the tracts of the mus- cular coat on the other. Beneath the trigonum a distinct submu- cous layer is wanting or re- placed by a sheet of muscular tis- sue. The muscu- lar coat, thicker than the mucosa and compara- tively robust, va- ries according to the condition of the bladder, being thin during distention and very thick in strong contraction, when it may measure as much as 1.5 cm. The bundles of involuntary muscle are arranged in two fairly distinct chief layers, a thin outer longitudinal and a thick inner circular. Inside the latter, and virtually within the submucosa, lies an incomplete additional layer. The longitudinal bundles, best developed on the upper and lower surfaces, do not constitute a continuous sheet, but interlace, leaving inter- fascicular intervals which are occupied by connective tissue. In the vicinity of the prostate extensions of the outer layer are attached to the anterior pelvic wall as the pubo-vesical muscles ; others pass backward to blend with the intestinal wall as the recto-vesical muscles, while from the apex bundles are prolonged into the urachus. The circular layer, although more robust and uniform than the outer, is weak and imperfect over the trigonal region, and in both sexes is well developed only after attaining the level of the internal ureteral orifices (Disse). Towards the apex of the bladder the bundles of the circular layer assume an oblique and less regular dispo- sition. The innermost layer that within the submucosa is represented by isolated and indefinite muscular bundles that are blended with the connective tissue. Over Obliquely cut longitudinal bundles Section of wall of bladder, under very low magnification, showing general disposition of coats. X 12. HUMAN ANATOMY. the vesical trigone, however, this layer becomes condensed and forms a compact transverse muscular sheet that is closely united to the overlying mucous membrane and, in conjunction with the muscular tissue of the urethra, surrounds the beginning of that canal with a constrictor-like tract, the internal vesical sphincter. The outer fibrous coat of the vesical wall is strongest over the inferior surface, where it receives reflections from the pelvic fascia; towards the apex and beneath the peritoneum it is less definite and often intermingled with adipose tissue. Over the postero-inferior surface in the male it is fused with the fibrous tissue surrounding the seminal vesicles and ducts, and in the female is blended with the anterior vaginal wall. Vessels. The arteries supplying the bladder are chiefly the superior and inferior vesical, from the anterior division of the internal iliac ; these are reinforced by branches from the middle hemorrhoidal, as well as by small twigs from the internal pudic and the obturator arteries. The superior vesical supplies the upper segment of the bladder and sends small branches along the urachus. The inferior vesical divides into two or more branches which are distributed to the infero-lateral and postero-inferior surfaces. In addition to twigs to the region of the trigone, others pass to the prostate, seminal vesicles, and ducts. On gaining the bladder, the vesical branches anastomose . and enclose that organ in an arterial net-work from which twigs enter the muscular coat and break up into capillaries for its supply. Others penetrate the muscular tunic and within the submucosa form a net-work from which arterioles pass inward for the supply of the mucous membrane. The veins do not accompany the arteries, but form a submucous plexus that drains the mucous membrane and empties into a muscular plexus which, in turn, is received by an external subperitoneal plexus. From the latter the blood from the entire organ passes into the large prostatico-vesical plexus at the sides of the bladder and thence into the tributaries of the internal iliac veins. With the exception of the smaller ones on the inferior surface, all the vesical veins possess valves (Fenwick). The lymphatics of the bladder begin as a close-meshed net-work within the mus- cular coat, according to Gerota, 1 being absent within the mucous membrane. Out- side the muscular coat they form a wide-meshed subperitoneal plexus, those from the apex and body coursing downward and laterally and those from the fundus upward. Leaving the sides of the bladder, the efferent channels, chiefly in company with the arteries, pass to the internal iliac lymph-nodes and to those situated at the bifurca- tion of the aorta. Along the path of the lymphatics on the antero-inferior surface of the bladder Gerota describes one or two very small nodes as usually present. The nerves of the bladder include both sympathetic and spinal fibres. The former, distributed chiefly to the muscular tissue, are from the vesical plexuses, which, as subordinate divisions of the pelvic plexuses, lie at the sides of the bladder. The sympathetic fibres accompany the arteries and are joined by the vesical branches from the sacral plexus derived from the third and fourth, possibly also the second, sacral spinal nerves. The principal trunks reach the bladder in the vicinity of the ureters, the trigonal region receiving the most generous nerve-supply and the apical segment the fewest fibres. Within the outer fibrous coat the larger nerves divide into smaller branches that are connected with ganglia, especially in the neighborhood of the ureters, from which twigs enter the muscular tunic and break up into smaller ones bearing terminal microscopic ganglia before ending in the muscle. Other branches penetrate the submucosa, where they form plexiform enlargements contain- ing numerous minute ganglia, from which fine twigs proceed to the mucosa to end, according to Retzius, between the epithelial cells. In general the sensibility of the normal bladder is comparatively slight, the trigonal region, especially at the ureteral openings, being its most sensitive area. PRACTICAL CONSIDERATIONS: THE BLADDER. Absence of the bladder is a very rare abnormality, but in more than one case has proved to be consistent with prolonged life, the dilated ureters opening into the urethra having acted as reservoirs for the urine and the muscle-fibres at their con- stricted orifices having taken on sphincteric action and prevented urinary incon- 1 Anatom. Anzeiger, Bd. xii., 1896. PRACTICAL CONSIDERATIONS: THE BLADDER. 1911 tinence. In other less fortunate cases in which the ureteral openings were on the surface of the body, implantation of the ureters into the intestinal tract (page 1901) has been done with varying degrees of success. Extroversion (exstrophy) of the bladder, the most frequent congenital ab- normality of this organ, is associated with failure of the ventral plates forming the abdominal wall to unite in the mid-line. In this condition, which occurs in males in from 80 to 90 per cent, of cases, the symphysis pubis and the anterior wall of the bladder frequently are also lacking, and the posterior vesical wall protruded by intra-abdominal pressure forms a rounded prominence, deep red in color, from chronic congestion. The ureteral orifices are often plainly visible. Cryptorchism, bifid scrotum, inguinal hernia, and epispadias are frequently present. Although the opinions regarding the causes and factors leading to these malformations are various and conflicting, it is certain that these defects depend upon faulty development at a very early period of foetal life, probably in connection with abnormalities of the allantois and of the cloacal region of the embryo, and that the suggested explana- tions on a mechanical basis, as over-distention of the allantois or unusual shortness or location of the umbilical cord, are entirely inadequate to account for malformations which often so profoundly affect the entire lower segment of the anterior body-wall and the associated organs. Occasionally a vesico- abdominal fissure occurs without extroversion, when the posterior wall of the bladder will be concave instead of convex and partially covered by the imperfect abdominal wall. The posterior wall of the bladder and the anterior wall of the rectum or vagina may be defective at birth, resulting in a congenital vesico-rectal or vesico-vaginal fistula. The foetal communication between the extra- and intra-abdominal portions of the allantoic sac may remain pervious, so that the urachus, instead of becoming a fibrous cord extending from the umbilicus to the summit of the bladder, is patent and constitutes a channel by means of which urine is discharged at the navel. Cystocele. A portion of the bladder may be found either alone or together with intestine or omentum in the sac of an inguinal or femoral hernia, or more rarely it may be part of an obturator or perineal or ventral hernia. The ordinary causes of abdominal hernia (page 1759) favor the production of this condition. In their presence, and especially if there is also present an intestinal hernia of long standing, a thinned and dilated bladder may readily be drawn by gravity into one of the hernial orifices by the connection of its extraperitoneal portion with the subperitoneal fat with which it is in close contact. The bladder " diverticulum," thus formed, is a result, not a cause of the hernia, and in 75 per cent, of cases includes only the extraperitoneal bladder-wall. As vesical dilatation and atony are usually the result of obstructive disease, most common in elderly males, and as abdominal hernia is frequent during late middle life (page 1762), it will be understood why 75 per cent, of cases of hernia of the bladder occur in men (irrespective of cases of vaginal cystocele) and more than 50 per cent, in persons over fifty years of age. In old herniae there has, of course, been an opportunity for the stretching and elongation of the bladder-wall essential for the production of the cystocele. The laxity of the attachments of the bladder to surrounding structures necessi- tated by its changes in size or capacity favors the production of hernia. Effects of Distention. The cavity of the normal empty bladder, which is strongly contracted during life, presents little more than a narrow, cleft-like lumen, with a gentle upward curve, continuous with that of the urethra. As it distends the pyriform bladder becomes oval in shape, its summit rises from the pelvis above the symphysis pubis, its anterior wall becomes applied to the inner surface of the ab- dominal wall in the hypogastric region, and the whole organ assumes an ovoid shape or, in extreme distention, one nearly spherical. Its normal capacity in the adult is about one pint, but the looseness of the submucosa over the greater part of its sur- face, the reticular arrangement of its muscle-fibres, and the yielding nature of the structures by which it is surrounded when it has risen from the pelvis permit of its enormous distention, especially as a result of slowly increasing obstructive dis- i9i 2 HUMAN ANATOMY. ease. Its summit may then pass above the level of the umbilicus and it may fill almost the whole abdomen. Retention of urine inability to empty the bladder may be due (a) to obstruc- tion at the neck of the bladder, the prostate, or the urethra, as from clots in bleeding from the kidneys, ureters, or the bladder itself, prostatic hypertrophy, stricture, or rupture of the urethra ; (<5) to affections of the bladder muscles, as paresis or paralysis of the detrusors in cerebral or spinal injury or disease, or reflex spasm of the sphincter after operations on the anus or rectum ; or incoordination, as in hysteria, or neurasthenia, or shock. The distended bladder forms a rounded fluctuating tumor in the hypogastric region, which, as the intestines are pushed up with the fold of peritoneum back of the urachus (plica vesico-umbilicalis), is always dull on percussion. If the disten- tion is acute, the pressure on the sensory nerves of the bladder gives rise to dis- tressing pain. If it takes place slowly, or if it follows cerebral or spinal injury, it may be quite painless. After a time, in cases of great distention, the sphincter vesicae and compressor urethrae yield to the pressure and the urine overflows the bladder more or less con- tinuously, incontinence of retention, a condition which should always be suspected to exist in aged male patients who have either very frequent urination or constant uri- nary dribbling. Great paresis or actual paralysis of the detrusors may result from distention, so that the power to empty the bladder is temporarily or permanently lost even after all obstruction has been removed. During marked distention certain changes take place in its relations that are of much practical importance. The neck of the bladder is so firmly fixed in position by the base of the prostate, with its dense capsule continuous with the deep layer of the triangular ligament (page 1977), by the anterior true ligaments of the bladder itself, and by its close attachment to the rectum or to the uterus and vagina, that it does not participate in the upward movement of the summit and body, but if the rectum is not distended, rather sinks slightly in the pelvis. The looseness of the fatty con- nective tissue occupying the space of Retzius (page 1906) and separating the antero- lateral walls of the bladder below the peritoneal reflection from the pubes and the obturator internus and levator ani muscles permits the elevation, during distention, of all the remainder of the bladder. The anterior peritoneal fold, which, with the bladder undistended, reaches to the symphysis pubis, is so raised that if the summit of the bladder is half-way between the pubes and the umbilicus, there will be from 5-6.5 cm. (2-2^4 in.) of the non- peritoneal portion of the anterior bladder-wall in close apposition with a similar area of the inner surface of the abdominal wall. In a male child five years of age the space between the upper edge of the symphysis pubis and the reflection of the peri- toneum will be one inch when the bladder contains three ounces of liquid. The close attachment of the peritoneum to the summit of the bladder and its very loose attach- ment to the parietes (necessitated by the changes in size and position of the bladder) permit this upward displacement. Coincident distention of the rectum by a rubber bag limits the backward and downward extension of the distended bladder, adds slightly to its elevation in the abdomen, keeps it in close contact with the abdominal parietes, and increases the distance between the recto-vesical fold and the anus from two and a half inches to three and a half inches. The use of the rectal bag has practical disadvantages which have led to its abandonment in most cases. The Trendelenburg position elevates the partly distended bladder and carries upward the peritoneal folds by gravity. Various operations (vide infra} are so planned as to take advantage of this uncover- ing of the bladder-wall, which permits access to that viscus and to its cavity without danger of peritoneal infection. Prevesical inflammation may follow infection through an operation or other wound, involving tin- prevesical space of Retzius, or may be caused by extravasa- tion of urine into that space ; and as the connective tissue occupying it is continuous superiorly with the abdominal and inferiorly with the pelvic extraperitoneal tissue, a cellulitis beginning there may be widespread, or may result fatally. Some of the relations of this space are indicated in the fact that such infection has been known to PRACTICAL CONSIDERATIONS : THE BLADDER. 1913 follow chronic cystitis, uterine or periuterine inflammation, post-partum suppuration of the symphysis pubis, and purulent thrombosis of the umbilical vein in a new-born infant (Thorndike). Collections of pus have opened from here spontaneously through the anterior abdominal wall, into the rectum, the bladder, or the urethra, and into the peritoneal cavity. Rupture of the bladder rarely follows distention alone, but is not uncommon as a result of trauma expended upon the pelvis or lower abdomen when the bladder is dis- tended. The cases in which rupture follows over-distention from obstructive disease, without the intervention of force, are usually prostatic in origin, as in retention from stricture the urethra ordinarily ulcerates behind the constriction and periurethral extravasation of urine relieves the tension. The liability to traumatic rupture is directly proportionate to the degree of dis- tention and consequent elevation of the viscus, and if that condition exists in a blad- der the subject of chronic dilatation and atrophy, or in one rendered unnaturally immobile by pericystitis or pelvic cellulitis, the force required to produce rupture is much lessened. Occasionally in the presence of fracture of the pelvis it is difficult to decide whether a given lesion of the bladder is a rupture or a wound from a fragment of bone. Eighty-five per cent, of ruptures are intraperitoneal, because, (a) in distention the peritoneal becomes the most tense of the coats of the bladder-wall ; () it is the least elastic ; (c) it covers that portion of the bladder which, as it rises into the abdomen, first loses the protection afforded by the pelvis, and is less reinforced by pressure from surrounding tissues ; {d ) the bladder- walls are thinnest over that area ; (f urim- occurring through a solution of continuity in this region of the urethra will first follow the space enclosed by this fascia in front and below and by the inferior layer of the triangular ligament posteriorly, and as it cannot reach the ischio-rectal space on account of the attachment of the fascia to the base of the ligament, and cannot reach the thighs on account of the attachment of tin- fascia to the ischio-pubic line, it is directed into the scrotal tissues, and thence up between the pubic spine and symphysis until it reaches the abdomen. PRACTICAL CONSIDERATIONS : MALE URETHRA. 1933 When it escapes from the membranous urethra, extravasated urine is confined to the region included between the layers of the triangular ligament, and only gains access to the other parts after suppuration and sloughing have given it an outlet, the consecutive symptoms then depending upon the portion of the aponeurotic wall which first gave way. If the opening is situated behind the superior layer of the triangular ligament, i.e., in the prostatic urethra, the urine may either follow the course of the rectum, making its appearance in the anal perineum, or, as it is separated from the pelvis only by the thin pelvic fascia, it may make its way through the latter near the pubo-prostatic ligament, and may spread rapidly through the subperitoneal con- nective tissue. (e) The bladder, ureteral, and kidney changes are similar to those that follow obstruction from any other cause, and cystitis, sacculated bladder, ureteral dilatation, and pyonephritis are not uncommonly terminal conditions in cases of stricture. Catheterism is one of the most important of the minor operations of surgery. For its proper performance, even in the normal urethra, an acquaintance with the differences in direction, mobility, dilatability, and contractility of that canal is essen- tial (vide supra}, as is familiarity with its relations to such structures and organs as the triangular ligament, the prostate, and the rectum (q.v.}. The following points are worthy of mention here in their relation to the anatomy of the urethra, (a) The penis is gently stretched, the dorsum facing the abdominal wall to avoid folds or twists in the mobile anterior urethra, (b) In persons with protuberant bellies the shaft of the catheter is at first kept parallel with the line of the groin ; if this is not done, the point of the instrument may be made to catch in the upper wall, at the tri- angular ligament, owing to the elevation of the handle necessitated by the protrusion of the abdomen ; the handle should, in any event, be kept low until the tip of the instrument is about to enter the membranous urethra, (c) The penis is drawn up with the left hand while the instrument is gradually pushed onward, the handle being finally swept around to the median line, the shaft being kept parallel to the anterior plane of the body and nearly touching the integument. The instrument is now . pressed downward towards the feet, while the left hand still steadies the penis and makes slight upward traction. After four or five inches of the shaft have disappeared within the urethra, it will be found that the downward motion of the instrument is arrested, (d) The fingers of the left hand are then shifted to the perineum and used as a fulcrum, while the handle is lifted from its close relation with the anterior abdomi- nal wall and swept gently over in the median line, describing the arc of a circle, (e) After the shaft has reached and passed the perpendicular, the handle should be taken in the left hand and the index and middle fingers of the right hand should be placed one on either side of the root of the penis, making downward pressure (to straighten the anterior limb of the subpubic curve, vide supra}, while the left hand, depressing the handle, carries the point of the instrument through the membranous and prostatic urethra into the bladder. The entrance into that organ will be recognized by the free motion that can be given the tip of the instrument when the handle is rotated, and by the latter remaining exactly in the median line and pointing away from the pubes when the hold upon it is relaxed. In urethral instrumentation it should never be forgotten that the elasticity or extensibility of the urethra resides for the most part in the spongy portion, as is clearly demonstrated by erection, and this elasticity belongs in the greatest degree to the inferior wall, which permits of easy distention or elongation, and changes its dimen- sions and form with notable facility ; while the superior wall yields with much more reluctance, and offers a certain resistance to all agents tending to depress or elongate it. This difference increases with age, and obtains especially in senile urethra. The extensibility of the inferior wall is brought into play even by a moderate force, and the surgeon cannot count on its resistance. It glides before an instrument, and cannot serve to guide it ; it cannot be incised with any accuracy or precision ; it lacerates or ruptures when surprised by distention ; and it yields rapidly and easily to mechanical pressure testing its extensibility. It should be noted, too, that this elongation of the canal is chiefly at the expense of the anterior urethra. Again, the spongy portion does not yield equally in all its parts, since it has been shown that of the different regions the perineo-bulbar is the most distensible. The inferior wall of 1934 HTM AN ANATOMY. the urethra can then be considered as normally longer than the superior surface. The term "surgical wall," proposed for the upper wall by Guyon, would seem to be merited, because it offers the shortest route to the bladder, is the most regular and constant as to form and direction, presents the smoothest and firmest surface, is the less capable of gliding before an instrument or being modified by mechanical pressure, offers the greatest resistance to rupture and penetration, is less intimately connected with important structures, and is the less vascular of the two walls. As to the calibre and distensibility of the urethra, enough has already been said ; but it should not be forgotten that there are three relatively constricted parts, the internal or vesical mea- tus, the external meatus, and the membranous regions ; and three dilatations, the fossa navicularis, the bulbar cul-de-sac, and the prostatic depression, the last two dila- tations presenting numerous individual variations ; and in this connection it is impor- tant to remark that all three of these dilatations are excavated at the expense of the inferior wall of the canal. The urethral curve only remaining regular in the superior wall, it results that the more pronounced the curve the more accentuated are the bul- bar and prostatic depressions ; and as a certain degree of lengthening of the urethra always corresponds to the greatest curve, since these are both produced by bulbar and prostatic augmentation of volume, one can reasonably conclude that urethrae of the greatest curves present at the same time the greatest length. With a knowledge of these facts, the instrumental exploration of the urethra becomes a matter of much accuracy and precision (Morrow). The anatomy of the various forms of urethrotomy and other operations on the urethra is sufficiently dealt with in the foregoing and in the practical considerations relative to the bladder, male perineum, and prostate (q.v.}. DEVELOPMENT OF THE URINARY ORGANS. The development of the essential parts of the urinary tract the kidney and its duct is so intimately related with the foetal excretory organ, the Wolffian body, that a brief account of the latter and of the principles underlying its genesis is a necessary introduction to the intelligent consideration of the subject here to be presented. The excretory apparatus of amniotic vertebrates, even in the highest mammals and man, includes three structures which, although as functionating organs existing in no single animal, stand in genealogical sequence. These are the pronephros, the meso- nephros or Wolffian body, and the metancphros or definitive kidney. The Pronephros. The first of these, the pronephros, sometimes called the " head-kidney" on account of its anterior position in its primary condition, in all higher forms is at best a rudi- mentary and functionless organ ; nevertheless, it is of extreme interest as indicating the funcla- FIG. 1636. Neural tube Somite FIG. 1637. Neural tube Somite Intermediate mass Ectoblast Parietal mesoblast Body-cavity Visceral mesoblast ntoblast Part of transverse section of c.irlv rabbit em- bryo, showing primary division of mesoblast into somite, internu'diati- mass, and parietal and vis- ceral layers. X 100. Anlage of nephric duct Parietal mesoblast Body-cavity Visceral mesoblast Remains of inU-itm'iliaU- mass Section of slightly older embryo, show- ing differentiation of duct-anlagc and mass in which tubules develop. X 100. mental plan upon which, in a modified form, the later Wolffian body is developed. Although, so far as known existing as a permanent organ alone in the hag fishes ( MyxiiwkeY as a temporary structure the pronephros attains considerable development in many fishes and amphibians; in the higher animals, even as an embryonal organ, it remains very rudimentary and transient. When adequately represented, the pronephros consists of a more or less extensive series of DEVELOPMENT OF THE URINARY ORGANS. 1935 slightly transverse tubules within the postero-lateral body-wall that internally communicate with the body-cavity or ccelom, the openings being known as nephrostomata, and externally join a common canal, the pronephric duct, which extends caudally and empties into the dilated terminal segment of the intestinal tube, the cloaca. In relation with the inner end of each tubule, but projecting freely into the body-cavity, lies a group of convoluted blood-vessels, the glomerulus, supplied by branches of the aorta. These three parts of the primitive excretory FIG. 1638. tegument Semitic ca Malpighian body of m Mesonephr Mesonephric d Pron Parietal peritoneum Body-ca ity of somite continuous with ccelom otochord phric tubule Pronephric duct Mesoblast of body-wall cavity (coelom) omerulus of pronephros Suprarenal body/ Gut-tube Aorta Visceral peritoneum Diagram showing fundamental relations of pronephros (on right side) and of mesonephros or Wolffian body (on left side of figure). (Wiedersheim.) FIG. 1639. organ provide for the essential requirements of the most elaborate urinary apparatus, the pro- duction of the watery constituents, the excretion of the waste products, and the conveyance of the excretion so elaborated. The pronephros is fundamentally a segmental organ, the tubules being so arranged that each corresponds to a single body-segment or metamere, although by no means every such division contains a tubule. It may be assumed that the tubules of the pronephros represent the segmental ducts which in ancestral forms extended from the body-cavity directly onto the external surface of the body and thus carried off the fluids accumulated within the coelom. In consequence of the closure of this direct communication with the exterior, which may be accepted as having occurred during the evolution of a more elaborate excretory system, the necessity for a new path of exit is met by the formation of the common pronephric duct into which the tubules open, and which, by its prolongation to and termination in the end-gut, insures the escape of the excretions. The development of the pronephros is closely associated with the mesoblastic somites. A transverse section of an early mammalian embryo (Fig. 1636) shows theparaxial mesoblast, be- tween the neural canal and the cleavage of the lateral mesoblast into the somatic and visceral plates, to comprise two parts, the mesial forming the somite and the lateral or intermediate cell-mass. It may be assumed that in the higher types the solid somite and the intermediate cell- mass have arisen by fusion of the primarily distinct dorsal and ventral mesoblastic plates (Fig. 1638). The inter- mediate cell-mass soon separates into a small duct-anlage, situated dorsally and in close relation with the ectoblast, and a larger ventral tract comprising the remainder of the intermediate cell-mass. Within this ventral area the tu- bules shortly appear, and later the glomeruli. Although reaching a comparatively high development in certain fishes and amphibians (especially in Ichthyophis described by Se- mon), in mammals the pronephros consists of a few tubules connected with the duct, and even as an organ of embryonic life never attains more than a feeble and transient exist- ence. In the human embryo of 3 mm. length, studied by Janosik, it was represented by two rudimentary tubules that extended from the mesothelial lining of the body-cavity towards the pronephric duct, with which one of the tubules still communicated. The pronephros of the amniotic ver- tebrates, therefore, must be regarded as a rudimentary inherited organ which appears in response to transmitted ancestral tendencies. The Mesonephros or Wolffian Body. This organ may conveniently be regarded as comprising a later generation of excretory tubules opening into a common canal, the Wolffian duct, which is usually looked upon as the continuation and mor- phological persistence of the pronephric duct. In their development these tubules and duct bear a similar relation to the intermediate cell-mass as do those of the pronephros, only the body- segments involved lie farther tail ward and the strict segmental arrangement of the tubules is lost owing to their multiplication and, as in mammals, precocious development. In contrast to the Body-cavity Longitudinal section of young embryo, showing early stage of Wolffian body ; tu- bules are joining duct. X 50. 1936 HUMAN ANATOMY. FIG. 1640. rudimentary character of the pronephros, the Wolffian body not only serves for a time as the chief excretory organ of the embryo, but in many lower vertebrates continues to functionate during life. The anlage of the Wolffian duct first appears as bud- like outgrowths from the dor- sal side of the intermediate cell-mass ; these fuse into a strand which, separating from the cell- mass, lies as a solid cord beneath the ectoblast. The latter takes no part in the formation of the duct, which is entirely of mesoblastic origin, the appearances leading to the assumption by certain authori- ties of its derivation from the outer germ-layer depending upon the temporary apposition or attach- ment that the duct effects in con- sequence, probably, of its inher- ited inclination, since in ancestral forms the tubules opened on the free ectoblastic surface. At first solid, the Wolffian duct later pos- sesses a lumen which gradually follows the tailward growth of the strand until, finally, it opens into Wolffian duct Mesothelium Wolffian tubule Developing capsule "Aortic branch to glomerulus Part of transverse section of embryo, showing commencing develop- ment of Malpighian corpuscle in Wolffian body. X 150. Capsule of Malpighian body the dilated end-gut or cloaca. In mammals the Wolffian tubules are developed within the ventral division of the intermedi- ate cell-mass as solid cords that later acquire a lumen and an at- tachment to the Wolffian duct. Although in the lower vertebrates (fishes, amphibians) retain- ing a communication with the coelom by means of a nephrostome, in mammals this connection is lost and the* expanded inner end of each tubule comes in close relation with the convoluted vascular tuft, the glomerulus, which now, however, no longer projects freely into the body- cavity. As in the kidney, the glomerulus is supplied by an afferent twig from a branch of the aorta, and is drained by an efferent vessel that breaks up into a capillary net-work surrounding the convoluted tubule and eventually becomes tributary to the cardinal vein. FIG. 1641. The first appearance of the Wolffian body in the human embryo occurs very early (2.4 mm. length) and at a time when the remains of the pronephros are still present. The duct precedes the tubules and opens into the cloaca in em- bryos of 4.2 mm. length (Keibel), the tubules, which develop independently, establishing communication with the duct shortly before. The development of the glomeruli is relatively tardy, since these bodies are not found until the human embryo has attained a length of about 7 mm. Their formation and growth continue during the first and second months until the embryo meas- ures 22 mm, in length, when their great- est perfection is reached (Nagel). When fully developed, about the end of the second month, the Wolffian body appears as an elongated organ (Fig. 1720 } which extends along almost the entire length of the posterior wall of the body-cavity, on either side of the mid-line, from behind the lung-anlage to the lower end of the gut-tube. About the eighth week, the Wolffian body en- ters upon its stage of regression which, continuing during the third and fourth months of foetal life, results in the grad- ual atrophy of the organ and its replace- ment as the functionating excretory gland by the kidney which meanwhile lias been formed. This atrophy invokes Wolffian duct Transverse section of fully developed Wolffian body, showing also indifferent sexual gland. X 80. first the glomeruli of the anterior portion of the organ, which, together with many of the tubules, completely degenerate, the retrogressive process extending tailward and gradually involving the middle and posterior segments. Although the glomeruli suffer destruction, some of the tubules and the Wolffian duct for a time remain and contribute in varying degree, according to the sex DEVELOPMENT OF THE URINARY ORGANS. 1937 p IQ Primary collecting tubules opening into subdivisions of pelvis Renal pelvis Stroma Malpighian body Malpighian corpuscle of atrophic Wolffian -body Longitudinal section through developinc tion of atrophic Wolffian body is seen 1 kidney ; por- elow. X 35- of the foetus, to the formation of certain structures and parts of the excretory canals of the sexual glands. In the male the Wolffian duct and tubules persist chiefly as the vas deferens and the epididymis ; in the female, in whom the atrophy is more complete, these remains are represented principally by the epoophoron and Gartner's duct. In both sexes certain ad- ditional rudimentary organs the paradidy- mis in the male and the paroophoron in the female are derived from the tubules of the sexual segment of the Wolffian body. A more detailed account of these transformations is given in connection with the development of the reproductive organs (page 2037 and Fig. 1719). The Metanephrosor Kidney. The development of the definitive kidney in mammals begins as a pouch-like out- growth from the posterior wall of the Wolffian duct, a short distance above its termination into the cloaca. In man the renal diverticulum makes its appearance during the fourth week, at which time the embryo measures from 6-7 mm. in length. At first short and wide, the stalk of the pyriform sac soon becomes tubu- lar, growing upward and backward into the mesoblast of the posterior body-wall. This stalk rapidly elongates, and termi- nates above in a blind club-shaped ex- tremity which after a time lies behind the upper atrophic segment of the Wolffian body. The tubular duct becomes the ureter and its dilated end-segment the renal pelvis. The latter is surrounded by a sharply defined oval area of compact mesoblast that is intimately concerned in the production of the convo- FIG. 1643. luted kidney-tubules (of Ampullary terminations of _**?- __ which as yet no trace is s ^^.^^ri^ss^SSSg^^s&^^SSBSEs^ present), and hence is termed therenal 'blastema. From the ventral and dorsal walls of the primi- tive pelvis, which is com- pressed from before back- ward, a number of hollow sprouts grow into the surrounding mesoblastic stroma. Each is a short cylinder that terminates in a slight dilatation. At first few, these sprouts in- crease rapidly in number as well as in length, and by repeated dichotomous division give rise to a sys- tem of branching canals that later are represented by the straight collecting tubules of the kidney. Concerning the ori- gin of the remaining portions of the uriniferous tubules two opposed views obtain. According to the one, all parts of these canals develop as direct continuations of the Developing v Malpighian bodies . Primary collecting tube Large col- lecting duct Section of developing kidney, showing formation of urinifer- ous tubules and collecting canals. X 100. 1938 HUMAN ANATOMY. Right umbilical artery Gut-tube outgrowths from the primitive renal pelvis ; according to the other, the convoluted tubules (from their beginning in the capsule to their termination in the collecting tubules within the medullary ray) arise independently within the renal blastema, and, secondarily, unite with the duct-system from the pelvis to complete the canals. The careful studies and reconstructions of Huber l leave little doubt as to the cor- rectness of the latter view, which, FIG. 1644. moreover, accords with the prin- ciple observed in the develop- ment of the pronephros and the Wolffian body, in which the tu- bules and the duct join subse- quent to an independent forma- tion. The attenuated proximal end of the convoluted tubule for a short time solid and in close rela- tion with the anlage of the glom- erulus soon becomes a sickle-like process which gradually incom- pletely surrounds the vascular tuft and later expands into the charac- teristic capsule. With the con- tinued growth of the tubules their tortuosity becomes more marked, the loop of Henle early becoming a conspicuous feature of their course. By the third month the formation and group- ing of the tubules have progressed to such extent that the surface of the young kidney exhibits the outlines of the individual lobes composing the organ. This lobu- lation is retained until some months after birth. In addition to the convoluted tubules, the vascular and supporting tissues are derived from the renal blastema, the con- densed peripheral part of which becomes the fibrous capsule of the kidney. As the latter assumes the r61e of active excretory organ, the Wolffian body undergoes atrophy, with the exception of such parts as are concerned in the development of the sexual ducts. The Bladder and the Urethra. The details of the development of the bladder and urethra in mammals and man have been materially advanced by the Notochord End-gut Tail-bud Reconstruction of caudal portion of human embryo of seven- teen days (3 mm. greatest length), showing cloaca connected with gut and allantoic duct. X 48. (Drawnfrom Keibel model.) AHantoic duct Fio. 1645 Gut-tube FIG. 1646. Gut-tube Allantoic duct Cloacal membrane Reconstruction of cloacal region of human embryo of twenty-six days (6.5 mm. length) ; Wolffian duct opens into ventral segment of cloaca. X 75- (Drawn from Keibel model. ) Cloacal membrane Preceding model viewed from li.uht M<|<-. ^l ing beginning division of clo:u\i into vi-ntral (uro- xenitul) and dorsal (intestinal) segment by longi- tudinal septal fold. (Drawn from Keibel model.) investigations of Keibel, Retterer, and Nagel, upon whose conclusions the following account is based. A sagittal section through the caudal pole of an early human embryo of 6.5 mm., about the beginning of the fourth week (Fig. 1645), exhibits 'American Journal of Anatomy, vol. iv., Supplement, 1905. DEVELOPMENT OF THE URINARY ORGANS. 1939 FIG. 1647. Aorta Allantoic duct the end-segment of the gut dilated into an elongated chamber, the cloaca, from the upper end of which the allantois passes forward and on the sides of which open the Wolffian ducts. The ventral wall of this space is thin, and consists of the opposed outer and inner germ-layers alone, no mesoblast intervening. This ecto-entoblastic septum is the cloacal mem- brane. During the fourth week the subdivision of the cloaca into a ventral and a dorsal compartment begins by the for- mation of a frontal fold that Belly-stall^ projects downward from the angle between the gut and the allantois. Subsequently this partition is supplemented by two lateral folds that appear on the side walls of the cloaca and are continuous above with the frontal fold (Fig. 1646). By the union of these three plicae, above and from the sides, a septum is formed that gradu- ally grows caudally and sub- divides the cloaca into a ventral allantoic and a dorsal intestinal chamber. This partition, however, for a time is incom- plete below, communication between the two spaces being thus maintained. During these changes the short canals common to the Wolffian ducts and the primitive ureters are drawn into the ventral chamber, the four tubes thereafter open- ing independently, but in close proximity, on the posterior wall of the ventral cloaco- allantoic space. This undergoes further differentiation into an upper (vesical) and a lower (genital) segment, the latter gradually narrowing into a tubular space, closed below by the fore part of the cloacal membrane, which becomes the uro-genital sinus and, after rupture of the membranous floor, communicates with the exterior. For a time the orifices of the Wolffian ducts and the ureters are closely grouped, those of the former, how- 1648. Tail \ \ Notochord duct Renal pelvis Reconstruction of cloacal region of human embryo of thirty-three days (11.5 mm. length); cloaca now incompletely separated into uro- genital and intestinal segments. X 25. (Drawn from Keibel model.) FIG. Notochord Wolffian duct Reconstruction of cloacal region of human embryo of thirty-seven days (14 mm. length); ureter now opens independently into uro-genital sinus, which above contributes lower segment of bladder and below is now almost separated from gut-tube. X 17. (Drawn from Keibel model.') ever, lying nearer the mid-line and slightly higher than the more widely separated ureteral openings. During the second month an important modification of these relations occurs, associ- ated with elongation and expansion of the upper part of the vesical seg- ment, by which the ure- ters are drawn upward and the Wolffian ducts downward. The inter- vening tract corresponds to the lower segment of a spindle-shaped sac that extends upward and is continued towards the umbilicus by the allantois. The upper part of this sac, which is the dilated allantois, forms the body and summit of the bladder and the urachus ; the lower part, into which the ureters open (Fig. 1649) and which is derived from both allantois and cloaca, differentiates into the vesical trigone and the urethra as far as the openings of 1940 HUMAN ANATOMY. the ejaculatory ducts, the permanent representatives of the Wolffian ducts. In the female the tract produces the entire urethra, since the orifice of the sexual canals opens into the uro-genital sinus. The bladder, therefore, is composite in origin, its Broad ligament FIG. 1649. ,Ovary Bladder Symphysi; Clitoris Glans Epithelial knob. Uro-genital sinus Rectum L Spinal cord Notochord Ureter Miillerian ducts Wolffian duct Reconstruction of human embryo of nine weeks (25 mm. length) ; ureter has migrated to bladder, leaving Wolffian and Miillerian ducts attached to uro-genital sinus, which is com- pletely separated from intestine. X 10. (Drawn from Keibel model.) upper part being from the allantois alone, while in the formation of the trigonal region both allantois and cloaca take part. The remaining portions of the urethra in the male are formed by the extension of the uro-genital sinus along the under surface of the corpora cavernosa of the developing penis (page 2044). THE TESTES. 1941 THE MALE REPRODUCTIVE ORGANS. THIS group comprises the sexual glands (the testes), the ducts (vasa deferentia) and their appendages (the seminal vesicles'), the copulative organ (the penis), and certain accessory glands (the prostate and Cowper 1 s glands). Although at first situated within the abdominal cavity, the testes migrate through the inguinal canal into the scrotum, which sac they usually gain shortly before birth. In their descent they are accompanied by blood-vessels, lymphatics, nerves and their ducts, which structures, with the supporting and investing tissue, constitute the spermatic cord that extends from the internal abdominal ring through the abdominal wall to the scrotum. THE TESTES. As often employed, the term " testicle" includes two essentially different parts, the testis the true sexual gland and the epididymis, the highly convoluted begin- ning of the spermatic duct. The testes, or testicles proper, the glands producing the seminal elements, are two slightly compressed ellipsoidal bodies so suspended within the scrotum the left lower FIG. 1650. Lower end of spermatic cord, with strands of cremaster muscle' Tunica vaginalis communis, cut Tunica vaginalis cut Epididymis. Globus minor Reflection of tunica vaginalis covering scrotal ligament Tunica vaginalis communis Tunica vaginalis Globus major of epididymis Appendix epididymidis Appendix testis Sac of tunica vaginalis Right testis Serous sa Reflection of serous covering A, antero-lateral view of right testicle after enveloping membranes have been cut and turned aside ; , antero-median view of same. than the right that their long axes are not vertical, but directed somewhat forward and outward. Each testis measures from 4-4.5 cm. (i^-i^ in.) in length, about 2.5 cm. in breadth, and 2 cm. in thickness, and presents a lateral and a medial sur- face, separated by an anterior and a posterior border, and an upper and a lower pole. The lateral surface looks outward and backward, and the flatter medial one inward and forward. Both surfaces, as well as the anterior border, are completely covered with serous membrane (the visceral layer of the tunica vaginalis) and are, therefore, smooth. The rounded anterior border is free and most convex, the much less arched posterior border, covered by the epididymis and attached to the spermatic cord, being devoid of serous membrane and corresponding to the hilum. In consequence of the obliquity of the long axis of the organ, the upper pole, capped by the head of the epididymis, lies farther outward and forward than the more pointed lower one, which is related to the tail of the epididymis and attached to the scrotal ligament (page 1942 HUMAN ANATOMY. 2042). The testis is of a whitish color, and, although readily yielding, imparts a characteristic impression of resilience when compressed between the fingers. Architecture of the Testis. The framework of the testicle proper consists of a stout capsule, the tunica albuginea, a dense fibre-elastic envelope from .4-. 6 mm. in thickness, that gives form to the organ and protects the subjacent soft glandular tissue. Along the posterior border of the testis the capsule is greatly thickened and projects forward as the mediastinum testis or corpus Highnwri, a wedge-shaped body (from 2.5-3 cm - m length), from which radiate a number of membranous septa that pass to the inner surface of the tunica albuginea. In this manner the space within the capsule is subdivided into pyramidal compartments, the bases of which lie at the periphery and the apices at the mediastinum. These spaces contain from 150 to 200 pyriform masses of glandular tissue, more or less completely separated from one another, that correspond to lobules (lobuli testis). Each of the latter is made up of from one to three greatly convoluted seminiferous tubules, held together by delicate vascular intertubular connective tissue. The seminiferous tubules from .15-. 25 mm. in diameter and from 25-70 cm. (1028 in.) in length begin as blind canals, which are moderately branched and very tortuous ( tubuli contorti) throughout their course until they converge at the apex of the lobule, where they pass over, either directly or after junction with another canal, into the narrow, straight tubules (tubuli recti} that enter the mediastinum and unite into a close net-work, the rete testis. The latter extends almost the entire length of the mediastinum, and consists of a system of irregular inter- communicating channels, the cuboid epithelial lining of which rests directly upon the en- sheathing fibrous tissue of the mediastinum. With these passages the canals of the testicle proper end, the immediate continuation of the spermatic tract being formed by from fifteen to twenty tubules, the ductuli efferentes, that pierce the tunica albuginea along the posterior border and near the upper pole of the testis and, forming the coni vasculosi, connect the sexual gland with the tube of the epididymis. Structure. In contrast to the dense fibre-elastic tissue that composes the frame- work of the testis, the capsule, mediastinum, and interlobular septa, the con- nective tissue occupying the spaces between the seminiferous tubules is loose in texture and arrangement, consisting of delicate bundles of white fibrous tissue in which elastic fibres are few or absent. In addition to the plate-like cells, leucocytes, and eosinophiles that occur in varying numbers within the meshes of this tissue in conjunction with blood-vessels and nerves, groups or cord-like masses of peculiar polygonal elements, the interstitial cells, also occupy the intertubular stroma, especi- ally in the vicinity of the mediastinum. These cells (Fig. 1654), from .01 5-. 020 mm. in diameter, possess relatively small round or oval eccentrically placed nuclei and a finely granular protoplasm that usually contains numerous brownish droplets, pigment particles, and, sometimes, crystalloid bodies in the form of minute needles or rods. In some animals, notably in the hog, the deeply colored interstitial cells form conspicuous tracts that impart a dark tint to the testicle in section. Their significance is obscure, but they are probably modified connective-tissue elements derived from the mesoblast of the germinal ridge (Allen, Whitehead). The wall of the convoluted seminiferous tubules consists of a delicate tunica propria, composed of an inner elastic lamella strengthened externally by circularly disposed fibres, within which are several layers of epithelial cells. The latter vary not only before and after the attainment of sexual maturity, but subsequently with functional activity or rest ; in man, however, the variations depending upon these FIG. 1651. Globus major of epididymis Vas deferens Coni vasculosi Ductus epididymidis Ductuli efferentes Tubuli recti Rete testis in mediastinum Tubuli contorti Vas aberrans Ductus epididymidis Globus minor Septum Tunica albuginea Diagram showing relations of secretory tubules and system of ducts. THE TESTES. 1943 causes are much less marked than in animals, in which sexual activity is limited to definite periods. Seen in sections of the mature human testicle (Fig. 1656), the epi- thelium lining the seminiferous tubules includes two chief kinds of cells, the support- ing and the spermatogenetic. The former the cells of Sertoli take no active part in the production of the spermatozoa, but serve chiefly as temporary supports for the more essential elements during certain stages of spermatogenesis. They are elongated elements of irregularly pyramidal form that rest by expanded bases upon the mem- brana propria, and project towards the lumen of the tubule between the layers of the FIG. 1652. Epididym Convolutions of duct of epididymis in globus major t%r^*t\ ^S*//**^* - arc two sacculated appendages of the vasa deferentia that lie behind the bladder and in front of the rectum. Flattened from before backward, their gnu-nil shape is pyriform, with the- larger ends, or bases, directed upward and outward, the !<>n- axes converging towards the mid-line as the Cross-section of vas deferens. X 20. THE SEMINAL VESICLES. 1957 Bladder, longi- tudinal muscle exposed Vas deferens Ureter Ampulla Seminal vesicle ' Ejaculatory duct Membranous urethra Cowper's glands Dissection showing seminal ducts and vesicles, prostate and Cowper's glands ; viewed from behind. organs taper, often abruptly, at their lower ends to join the spermatic ducts. Usually from 4-5 cm. in length, sometimes much longer and relatively slender and at others short and broad, the seminal vesicles vary greatly in size and in the detail of arrange- ment of their component parts and not infrequently are markedly asymmetrical, the right one being often, but not in- variably, the larger. FIG. 1665. Divested of the nbro-muscular tissue that invests the organ as its capsule and blends its divisions into a tuberculated common mass, each vesicle may be resolved into a chief duct and diverticula. The former from 10-12 cm. (4-5 in.) in length ends blindly after a more or less tortuous course, its terminal part often describing a sharp hook- like returning curve (Fig. 1667). From the main canal an uncertain number (from four to eight or more *) of blind tubular diverticula branch at varying angles and in different directions and by their tortuosities add to the complexity of outline. The lumen of the chief duct, as seen in section, is irregu- lar, constrictions and dilatations following one another with little regularity. The opening of the duct into the lateral wall of the vas deferens is large in comparison with the terminal lumen of the ejaculatory duct, thus favoring the entrance of the secretions temporarily stored within the ampulla into the sacculated vesicle. The latter contains a fluid of light brownish color in which sper- matozoa are nearly always found during the period of sexual activity. Relations. The seminal vesicles, together with the ampullae, lie embedded within a dense fibro-muscular layer, so that their position remains relatively fixed, especially below, and to a certain degree independent of the changes in volume of the bladder and the rectum, neither FIG. 1666. of which they directly touch. Although when distended these organs are in close relation with the seminal vesicles, when empty the bases of the latter lie laterally and at some distance from both the vesical and rectal wall, sur- rounded by numerous veins that continue the prostatic and vesi- cal plexuses. The lower half of the seminal vesicles and the ampullae lie behind the fundus of the bladder, their axes ap- proximately corresponding with the sides of the vesical trigone and embracing the retroureteric fossa, which part of the bladder- wall, when distended, may pro- ject between and even displace laterally the seminal ducts and vesicles. In passing from the slightly expanded bladder onto the rectum, the peritoneum covers the upper fourth of the seminal vesicles and the adjoining part of the ampullae. The 1 Pallin : Archiv f. Anat. u. Entwick., 1901. Ejaculatory ducts Cast ot ampullae and seminal vesicles, showing wind- ings and sacculations of lumen. (Pallin.) 1958 HUMAN ANATOMY. FIG. 1667. extent of this investment, however, varies with the depth of the recto-vesical pouch, which in turn depends upon the degree of distention of the bounding organs, the bladder and the rectum. Structure. In their general make-up the seminal vesicles closely resemble the ampulke, possessing a robust muscular wall composed of an inner circular and an outer longitudinal layer of involun- tary muscle. The mucous mem- brane is conspicuously modelled by numerous ridges and pits, so that the free surface appears honey-combed (Fig. 1668). The epithelial covering consists of a single or imperfect double layer of low columnar cells, many of which present changes indicating secretory activity. Although true glands are wanting within the seminal vesicles, the minute di- verticula within the epithelium Diagram showing course of main canal in preceding preparation: Containing goblet-Cells may be re- a, ampulla ; c, seminal vesicle; d, ejaculatory duct. (Palhn.) garded as Concerned in producing the peculiar fluid found within these sacs, which is of importance probably not only in diluting the secretion of the testicle and supplying a medium favorable for the motility of the spermatic fila- ments, but also in completing the volume of fluid necessary for efficient ejaculation (Waldeyer). Vessels of the Seminal Ducts and Vesicles. The arteries supplying the spermatic duct are derived chiefly from the deferential, a vessel of small size but long course that arises either directly from the internal iliac or from its vesical branches. On reaching the duct, just above the ampulla, the artery divides into a smaller de- scending and a larger ascending division. The former, in conjunc- tion with accessory twigs from trie middle hemorrhoidal and the in- ferior vesical arteries, generously provides for the ampulla, and the latter accompanies and supplies the vas deferens throughout its long course, finally, in the vicinity of the testicle, anastomosing with branches from the spermatic, a communica- tion of importance for collateral cir- culation. The twigs passing to the spermatic duct enter its wall and break up into capillary net-works within the muscular and mucous layers. The rich arterial supply for the seminal vesicle includes anterior and upper and lower branches, con- tributed by the deferential, the in- *..'. . j Cross-section of seminal vesicle, showing fe'nor vesical, and the superior ana modelling <>t aracouturfece. x 16. middle hemorrhoidal arteries. The minute distribution is effected by capillary net-works to the muscular and mucous coats. The veins that follow the spermatic duct as the deferential plexus, and within the spermatic cord communicate with the pampiniform plexus, increase in size and FIG. 1668. Lumen Pits of mu- cous coat Partition separating adjacent diverticula Epithelium PRACTICAL CONSIDERATIONS : SEMINAL VESICLES. 1959 number as they approach the bladder and seminal vesicle ; in the vicinity of the latter they communicate with the seminal plexus and empty with the trunks of the posterior bladder-wall into the vesico-prostatic plexus. The posterior and lateral surfaces of the seminal vesicle are covered with a net- work of large veins (plexus venosus semi- nalis) that become tributary to the vesico-prostatic plexus. The lymphatics of the seminal ducts and vesicles are numerous and arranged as deeper and superficial sets which form afferent trunks that pass to the internal iliac lymph-nodes. Those from the lower part FIG. 1669. of the seminal vesi- cles join the vesical lymphatics. The nerves sup- plying the spermatic duct are derived from the hypogastric plexus of the sympa- thetic and consist chiefly of pale fibres destined for the in- voluntary muscle, some medullated fibres, however, be- ing present. They accompany the greater part of the duct as the deferen- tial plexus and have been traced into the muscular tissue and the mucosa. Within the former they form the dense plexus myospermaticus described by Sclavunos, 1 and are fairly plentiful within the mucous coat (Timofeew 2 ). The nerves distributed to the seminal vesicles are very numerous and are derived in part directly from the hypogastric plexus (Fraenkel 3 ), or through prolongations of the latter as secondary plexuses that follow the vesical and middle hemorrhoidal arteries. Fibrous Coat Portion of wall of seminal vesicle in longitudinal section, showing pitting of mucous coat. X 45- PRACTICAL CONSIDERATIONS: THE SEMINAL VESICLES. The seminal vesicles are rarely injured. The two forms of infection that are most common are the gonorrhceal and the tuberculous, although vesiculitis may be due to the ordinary staphylococci or to the colon bacillus. The channels of infection are comparable to those which convey disease to the epididymis; the ejaculatory ducts are continuous with the vas deferens and the vesicular duct, and the inferior vesical and middle hemorrhoidal arteries replace the spermatic artery. The tuber- culous disease is, however, usually secondary to similar infection of the prostate or of the epididymis. The anatomical relations of the vesicles to (a) the vesical trigonum, (3) the prostate and prostatic urethra, and (r) the rectum sufficiently explain the usual symptoms of acute vesiculitis : (#) frequent, painful, straining urination, hypogastric pain ; (^) priapism, painful emissions of blood-stained semen, occasionally epididy- mitis as a complication ; (<:) painful defecation, rectal tenesmus, perineal and anal pain. Rectal exploration (page 1692) will usually establish the diagnosis, as it will in tuberculous vesiculitis, in which condition, as in other forms acute and chronic of vesiculitis, there are apt to be pains referred to the loins, the hypogastrium, the 1 Anatom. Anzeiger, Bd. ix., 1894. 2 Anatom. Anzeiger, Bd. ix., 1894. 3 Zeitsch. f. Morph. u. Anthrop., Bd. v., 1903. 1960 HUMAN ANATOMY. anus and perineum, the hip-joint and sacro-iliac articulation of the affected side and the other side of the thigh, due to the association of the vesical, prostate, and pelvic plexuses with the lumbar and sacral nerves and their plexuses. Vesiculitis may be a very serious condition, as it may result in abscess with per- foration into the bladder within the limits of the peritoneal covering, or directly into the peritoneal cavity by way of the recto-vesical cul-de-sac. Cases of both these acci- dents have been reported. Pyaemia has also been known to follow a septic phlebitis of the adjacent venous plexuses; pelvic cellulitis with diffuse suppuration has resulted ; and various troublesome abscesses burrowing between the bladder and rectum, and leaving fistulous tracts very slow to heal, have had their origin in suppurative vesicu- litis. The chronic form may be associated with persistent vesical irritability, with some pain on emission of semen, with sexual excitability accompanied by premature ejacu- lation, and with persistent urethral discharge often mistaken for an ordinary gleet. In chronic cases " massage" through the rectum has been advised and practised with some benefit in comparatively rare cases. The contents of the vesicles can sometimes be pressed through the ejaculatory ducts into the prostatic urethra and so evacuated. A similar expression of the normal secretion of the vesicles by fecal masses at stool is a fertile source of sexual hypochondriasis in young male neuras- thenics, who, in consequence, imagine that they are afflicted with " spermatorrhoea. " THE SPERMATIC CORD. In consequence of its migration from the abdominal cavity into the scrotal sac, the testicle is followed by its duct, vessels, and nerves through the abdominal wall into the scrotum. These structures, held together by connective tissue and invested by certain coverings acquired in their descent, form a cylindrical mass, known as the spermatic cord (funiculus -spermaticus), that extends from the internal abdominal ring obliquely along the inguinal canal, emerging at the external ring, and thence descends vertically, beneath the integument, into the scrotum to end at the posterior border of the testicle. Most constant within the inguinal canal, where its diameter is about 1 5 mm. ( ^i in. ) , the thickness and length of the spermatic cord vary with the con- traction of the cremasteric muscular fibres that FIG. 1670. control the position of the testicle. Posterior veins The constituents of the spermatic cord vas deferens are num erous and fall under four groups. I. The vas deferens with its accompanying deferential artery and plexuses of veins, lym- phatics, and nerves. The vas, surrounded by pampini- jj- s artery and a venous plexus, occupies the plexus , . . . . posterior part of the spermatic cord, and is ic artery readily distinguished as a hard, round cord, inaiis from 2-3 mm. in diameter, by virtue of its L, a unusually firm walls. _ . . . 2. The spermatic artery, zn/is, Ivmphatics, Section across left spermatic cord hardened in 11- i formalin, showing position of vas deferens. and nerves belonging to the testicle proper. In contrast to the artery, the veins are particu- larly large and numerous and form the conspicuous pampiniform plexus which con- tributes in no small measure to the bulk of the cord. 3. The coverings with their blood-vessels and nerves. The coverings proper of the spermatic cord, contributed by the layers of the abdominal wall, correspond to those of the testicle, with the exception of the serous coat, which is wanting after closure of the processus vaginalis. From within outward they are : (a) the infundib- uliform fascia (tunica vaginalis communis), a distinct layer continued from the trans- versalis fascia ; (b) the cremasteric fascia, consisting of the muscular fibres prolonged from the internal oblique and transversalis, blended together by connective tissue. The muscular fibres descend as loops along the spermatic cord, especially on the posterior surface as far as the testicle, over the coverings of which they spread out in festoons and net-works ; and (c~} the intercolitwnar fascia, a delicate sheet derived from the aponeurosis of the external oblique at the margin of the external abdominal WpVeins of ll \ form pi THE SCROTUM. 1961 ring, is most distinct above, becoming thinner as it descends, until over the testicle it loses its identity as a distinct investment. The coverings of the spermatic cord receive their blood-supply from chiefly the cremasteric branch of the deep epigastric artery ; additional cremasteric twigs from the spermatic artery are distributed to the upper part of the cord, anastomosing with those from the first-named source. The nerves include the genital branch of the genito-crural and usually a twig along the front of the cord from the terminal branch of the ilio-inguinal. 4. The rudimentary structures, the remains of the processus vaginalis, the para- didymis, and sometimes the vas aberrans. After closure of the communication between the serous pouch and the peritoneal cavity, the processus vaginalis is represented by a delicate fibrous band (ligamentum vaginale) that maybe traced, under favorable con- ditions, from the internal abdominal ring above through the spermatic cord as far as the upper margin of the tunica vaginalis below. The paradidymis (page 1950) lies within the lower end of the spermatic cord, immediately above the epididymis, or behind its upper pole, and in front of the venous plexus. Occasionally, when unusu- ally developed, the vas aberrans (page 1950) may also extend into the lower end of the spermatic cord. In addition to the foregoing coverings proper, the spermatic cord is enveloped by the skin, the superficial and the deep layer of the superficial fascia. The deep layer of the latter is important, being continuous above with the fascia on the abdomen and below, after investing the testicle, with Colics' s fascia in the perineum. PRACTICAL CONSIDERATIONS : THE SPERMATIC CORD. The most frequent pathological condition associated with the cord (and not else- where described) is varicocele, an enlargement with dilatation and lengthening of the veins of the cord, occurring most frequently in young unmarried adults (fifteenth to twenty-fifth year) and on the left side (90 per cent, of cases). The veins composing the spermatic plexus can be ranged in three groups, the most anterior of which has in its midst the spermatic artery, the middle the vas def- erens, and the posterior is composed of those veins which pass upward from the tail of the epididymis. The anterior group is the one first affected, or, if the dilatation affects all the veins, is most extensively involved. It is thought that varicocele often depends upon a congenital predisposition, but many anatomical reasons have been given to account (a) for its occurrence, and () for its greater frequency on the left side, (a) i. The relative length and the vertical course of the veins. 2. The lax tissue surrounding them, so that (as with the long saphenous vein) they derive little support and their blood-current receives no aid from the presence or contraction of surrounding muscles. 3. Their large size as compared with the corresponding artery, so that the vis a tergo must be reduced to a minimum (Treves). 4. Their tortuosity, frequent anastomosis, and few and imper- fect valves. 5. The pressure exerted upon them as they pass through the inguinal canal, not altogether unlike that experienced by the hemorrhoidal veins in their passage through the walls of the rectum. () i. The veins in the left cord are much larger than those in the right. 2. The left testicle hangs lower than the right, so that the column of blood in the left veins is longer. 3. The left spermatic vein empties into the left renal vein at a right angle, whereas the right spermatic vein empties into the vena cava at an acute angle. 4. The left spermatic vein running behind the sigmoid flexure of the colon is constantly subjected to pressure from accumulation of faeces in the bowel. In the operation for varicocele by excision of the pampiniform plexus the sper- matic artery is often included, but gangrene of the testicle does not follow because of the escape of the deferential artery and of its free anastomosis with the spermatic and scrotal vessels. THE SCROTUM. The scrotum, the more or less pendulous sac of integument that contains the testicles and the associated structures and the lower part of the spermatic cords, is attached to the under surface of the penis in front and to the perineum behind. Flat- 1962 HUMAN ANATOMY. tened in front above, where attached to the penis and receiving the spermatic cords, its general form is pear-shaped and somewhat asymmetrical, since the left of the two oval swellings produced by the enclosed testicles and separated by a shallow longi- tudinal furrow is lower than the right owing to the position of the corresponding sexual gland. The scrotum varies, however, in form and appearance, even in the same individual, with the condition of the subcutaneous muscular tissue. When the latter is contracted, as after the influence of cold, the scrotum is drawn up and com- pact and its surface corrugated by numerous transversely curved folds ; when relaxed, it becomes smooth, flaccid, and pendulous. Indications of its formation from two distinct parts are seen externally in the longitudinal raphe, which marks the line of fusion of the original halves and extends longitudinally from the urethral surface of the penis over the scrotum onto the peri- FIG. 1671. Aponeurpsis of external oblique External abdominal ring Suspensory ligament of penis Stump of penis Skin Septum of scrotum Loops of cremaster muscle Dartos Skin T-Skin Supcrf. fascia, superf. layer Deep layer Aponeurosis of external oblique Internal oblique Infundibuliform fascia Aponeurosis of external oblique, cut and reflected Spermatic cord Intercolumnar fascia, reflected Dissection of spermatic cord and scrotum. rieum. Owing to the greater dependence of the left half of the sac, the raphe does not occupy a strictly median position, but is deflected towards the left. Internally evidence of the union of the scrotal halves is found in the sagittal partition {septum scroll} that is continued inward from the raphe and effectually divides the scrotum into a right and a left pouch. This septum, consisting of fibrous tissue rich in elastic fibres and the prolongations of tlte dartos muscle, is attached above to the root of the penis and the perineum, blending with the sheath of the bulbo-cavernosus muscle. Since the labio-scrotal folds, which produce the scrotum or its homologue, the labia majora, according to sex, are developed (page 2041) independently of the cov- erings of the spermatic cord and the testicle derived from the musculo-fascial walls of the abdomen, the scrotum contributes additional envelopes for the enclosed structures. These envelopes are the skin, which is here thin, delicate, and very elastic, unusually dark, and beset with scattered crisp hairs and numerous sweat and sebaceous glands ; THE SCROTUM. 1963 and the tunica dartos, a layer of modified subcutaneous tissue the superficial fascia distinguished by the presence of numerous longitudinally disposed bundles of invol- untary muscle-fibres and much elastic tissue and by the entire absence of fat. The muscular tissue {dartos muscle}, where best developed, as in the anterior and lateral walls of the scrotum, is sufficient in quantity to be recognized as a dis- tinct layer, but so closely attached to the integument as to form practically a part of it. At the raphe, while some fibres follow the skin and remain superficial, the majority enter the septum, being especially well developed in the lower part, and at the attached upper border pass over into the dartos of the penis and the perineum. The numerous bundles of elastic tissue within the tunica dartos in the upper and anterior part of the scrotum become condensed into robust bands which efficiently aid in supporting the scrotal sac, since they are continued laterally at the sides of the penis and over the spermatic cords into the superficial fascia of the abdomen, and in the mid-line blend with the suspensory ligament of the penis. Those on the posterior surface are attached over the pubic and ischial rami. Enumerated from without inward, the layers interposed between the surface of the scrotum and the serous cavity surrounding the testis are : (i) the skin, (2) the modified superficial fascia or tunica dartos, (3) the intercolumnar fascia, (4) the cre- masteric fascia, (5) the infundibuliform fascia, and (6) the tunica vaginalis. Of these the first two alone, strictly considered, are contributed by the scrotum, the remaining layers being derived from the deeper structures of the abdominal wall and associated with the descent of the testicle. The connection between the tunica dartos and the underlying intercolumnar fascia is by no means firm, being effected by a loose layer of areolar tissue, devoid of fat, that permits a ready separation, particularly in front, between the external scrotal envelope and the coverings proper of the testis. Beneath the posterior surface of the scrotum the connection is firmer (Disse). This separation, however, is arrested at the lower part of the scrotum, owing to the presence of the scrotal ligament (Fig. 1723), a mass of fibrous tissue that anchors the lower end of the tunica vaginalis and the testicle to the external envelopes. With the exception of the serous coat, the tunica vaginalis, these coverings have been considered in connection with the spermatic cord (page 1960) ; it remains, there- fore, to describe more fully the serous coat to which incidental reference has been made (page 1941) in its relations to the testis and the epididymis. The production of an isolated, closed serous sac within each half of the scrotum results from partial obliteration of the serous pouch, the processus vaginalis, that during fcetal life extends from the general peritoneal cavity into the scrotum in an- ticipation of the descent of the sexual gland. The tunica vaginalis (tunica vaginalis propria testis), in correspondence with other serous membranes, consists of a parietal and a visceral portion, the latter pro- viding an extensive but incomplete investment for the testis and the epididymis and the former lining the serous cavity into which these organs, thus covered, project. With the exception of small spaces caused by the elevation of the epididymis, espe- cially of the globus major, these two layers are practically in contact and separated by only a capillary cleft. Whatever space exists is filled by a clear straw-colored serous fluid. In addition to walling the cavity, the parietal layer invests the spermatic cord for about 12 mm. above the testicle and the blood-vessels behind, and then is continued into the visceral layer along the line of reflection that passes over the back of the testis to its lower pole on the one side and along the posterior surface of the epi- didymis on the other, thus leaving an intervening uncovered strip as a passage-way for the duct, vessels, and nerves. From the line of reflection the thin visceral layer completely invests the testis and the epididymis, adhering intimately with the tunica albuginea, and dipping deeply between these organs to form the digital fossa (sinus epididymidis). This pocket (Fig. 1650), the entrance to which is narrowed by two transverse folds (liga- menta epididymidis superior et inferior), may be so deep that the serous membrane at its bottom is in contact with that reflected from the median side of the testicle. Nu- merous bundles of involuntary muscle -the in. cremaster internus of Henle radiate from the scrotal ligament at the lower part of the scrotum to spread out between the 1964 HUMAN ANATOMY. parietal layer of the tunica vaginalis and the infundibuliform fascia, extending upward into the spermatic cord. Vessels. The arteries supplying the scrotum, as distinguished from those des- tined for the spermatic cord and the sexual gland and associated structures, although of small size, are derived from different sources. Those distributed to the front and sides are the anterior scrotal branches from the deep external pudics, supplemented above by twigs from the superficial external pudics. The back of the scrotum and the septum are supplied by the posterior scrotal arteries, superficial branches from the internal pudics. Free communication exists not only between the vessels of the two sides across the mid-line, but also between the anterior and posterior branches at the sides. The scrotal arteries anastomose with twigs from the obturator and internal circumflex, as well as with those from the cremasteric artery. The veins, numerous and plexiform in arrangement, form trunks that follow the general course of the chief arteries, becoming tributary to the external saphenous or the femoral and the internal pudic veins. They anastomose freely with the adjoining venous paths of the penis, perineum, and pubic region. FIG. 1672. Veins ^^^ -Vas deferens ^n>\ <'*' \ _^-js**Spermatic veins ^V'^v - **?> X- Spermatic arteries Saw \ Blood-vessels Sac of tunica vaginalis Tunica vagina Mediastinum teslis Visceral tunica vaginalis Parietal tunica vaginalis Lobules of left testis lis Cremasteric fascia Skin and dartos Septum of scrotum Obliquely cut vas deferens Section across formalin-hardened scrotum, showing lower end of spermatic cords and testes in section. The lymphatics of the scrotum are very, numerous and form a superior and an inferior group of vessels, all of which lead to the median group of superficial inguinal lymph-nodes. Frequent communications occur with those of the penis and perineum, but only sparingly with the deep lymph-tracts within the spermatic cords. The nerves supplying the scrotum are derived from both the lumbar and sacral plexuses. Those from the former source are distributed to the front and sides of the scrotum and include cutaneous twigs from the genital branch of the genito-crural nerve, usually reinforced by twigs from the ilio-inguinal that end in the integument in the vicinity of the root of the scrotum. Those from the sacral plexus supply the posterior surface of the scrotum and are from the perineal or inferior pudenda! branches of the small sciatic nerves and the anterior or external superficial perineal branches of the pudic nerves. Sympathetic fibres accompany the cutaneous nerves for the dartos muscle. PRACTICAL CONSIDERATIONS: THE SCROTUM. The scrotum, from a practical stand-point, may be studied as if composed of two layers, an external, made up of the skin and dartos, and an internal, consisting of the three coverings fascial, muscular, and aponeurotic derived from the abdomi- nal wall, the infundibuliform, cremasteric, and intercolumnar. As the testes are safer from injury in a loose pouch, in which they can readily glide away from threatened trauma, the scrotum is redundant (more so on the left THE PENIS. 1965 side on account of the greater length of the left spermatic cord) and lax. Advantage of these facts is taken in certain operative procedures, as in making the flaps in Roux's operation for vesical exstrophy, or excising a portion of the scrotum (to secure firmer support for the vascular structures of the cord) in varicocele. The redundancy, thinness, and elasticity of the skin and the laxity of the fatless areolar tissue connecting the internal and external layers combine to favor : () marked discoloration and great extravasation of blood in cases of hemorrhage from the vessels between the two layers ; hence in orchitis leeches are applied, not over the scrotum, but in the line of the cord in the groin ; () extreme distention, as in large scrotal herniae, in hydrocele, in bulky testicular tumors; (c) extensive oedema in general anasarca, as a result of pelvic venous thrombosis, or accompanying an infectious cellu- litis or an extravasation of urine, which, when it proceeds from a solution of contin- uity anterior to the triangular ligament, is directed by Colics' s fascia into this cellular space between the two layers. The thinness of the scrotal skin, increased when it is distended, makes it, in spite of its vascularity, very susceptible to gangrene from pressure, as in ; ' strapping' ' an inflamed testicle, or from underlying cellulitis. The longitudinal contractile fibres of the dartos draw the redundant skin into transverse rugse which, by retaining extraneous dirt and the secretions of the sweat- glands and sebaceous follicles, become often the starting-point of eczema, of mucous patches, or even (as in " chimney-sweep's cancer" ) of epithelioma. The contractil- ity of the dartos is marked in young and robust persons, and is increased by cold, by sexual excitement, and by light friction. It is lessened in old age, by debility, or by continued warmth and moisture, the scrotum, in the presence of those conditions, becoming smooth, elongated, and pendulous. It is useful in aiding the scrotum to regain its normal size after distention, as following the tapping of a hydrocele or the removal of a tumor. On the other hand, the dartos tends to invert the edges of a scrotal wound (as the platysma does those of a wound of the neck), and warm appli- cations may therefore be useful before a scrotal incision is sutured. The muscular (cremasteric) element of the inner layer gives it contractility, and the intimate connection between it, the deeper (infundibuliform) plane of fascia, and the parietal layer of the tunica vaginalis enables it to elevate the -testicle with its coverings when it is excited to contraction. This may be done {cremasteric reflex} by drawing the finger-nail over the skin of the thigh a little below Poupart' s liga- ment, the sensory impression being conveyed from the skin through the crural branch, and to the cremaster through the genital branch, of the genito-crural nerve. The infundibuliform (internal spermatic) fascia, by its close relation to the pos- tero-inferior portion of the testicle, on the one hand, and to the external scrotal layer, on the other, assists the scrotal ligament (page 2042) in preventing the testicle from being floated up when the space between the two layers of the tunica vaginalis is filled with fluid (hydrocele, haematocele), and holds it in the lower back part of the scrotum. In exploratory puncture, or in the tapping of hydrocele, the spot selected is therefore on the anterior surface of the upper two-thirds of the scrotum, care being taken to avoid the large superficial veins. THE PENIS. The penis, the organ of copulation of the male, consists of three cylinders of erectile tissue the paired corpora cavernosa and the single corpus spongiosum united with one another and invested by coverings of fascia and skin. Since the upper or proximal portion of the penis (pars perinealis) is buried beneath the integu- ment and fascia of the perineum and the scrotum, only the free pendulous distal portion of the organ is visible in the undissected subject. When exposed throughout its entire extent, the penis presents a cylindrical shaft or body (corpus penis), which begins above in a three-pronged root (radix penis) attached to the pubic arch and the triangular ligament and terminates below in a blunted conical end, the glans penis. The anterior or upper surface (dorsum penis) is somewhat flattened and formed by the corpora cavernosa. The posterior, under, or urethral surface (facies urethralis) corresponds to the corpus spongiosum, traversed 1966 HUMAN ANATOMY. FIG. 1673. Glaus corpus by the urethra, and is marked by a median raphe, which is continuous with that of the scrotum and, as the latter, indicates the line of fusion of the original components of the spongy body. The conical glans, which forms the distal end of the organ, is limited along its oblique base by a prominent rounded border, the corona glandis, that runs downward and forward from the dorsum towards the under surface and marks a groove (sulcus retroglandularis) that separates the glans from the body of the penis. The constricted zone immediately behind the glans constitutes the neck (collum penis). In conse- quence of the obliquity of the corona, the dorsal expansion of the glans measures about twice the length of its under sur- face. The skin covering the pendulous portion of the penis very thin, delicate, and elastic, and possessing only fine hair (lanugo) except in the immediate vicinity of the pubes is loosely attached over the body of the organ by subcu- taneous tissue, devoid of fat, that permits of ready movement of the integument. Along the under surface of the organ bundles of involuntary muscle closely adhere to the integument and constitute a stratum, the tunica darlos penis, that resembles the similar layer of the scro- tum. Just behind the corona the skin forms a free duplicature, the prepuce or foreskin (praeputium penis), that covers the glans to a variable extent ( in children and in some adults completely) and is firmly attached by its inner layer to the neck of the penis along a line about 3 mm. above the corona. From this point the skin is prolonged over the glans, to which it is intimately applied, as far as the meatus, where the integu- ment becomes continuous with the ure- thral mucous membrane. The lines of reflection of the prepuce on the two sides converge and finally meet along the under surface of the glans in a sharp median fold, \\\efrcnum (frenulum prae* putii), that extends as far as the pos- terior border of the slit-like urethral opening. On either side of this fold a shallow recess (fossa frenuli) extends the preputial sac. The skin lining the latter and covering the glans is modified so that it somewhat resembles a mucous membrane, as which it is often inaccurately described. While entirely devoid of hairs, small sebaceous glands are sparingly distributed over the glans, corona, and inner layer of the prepuce. These, formerly supposed to be of large size and named the glands of Tyson ( ^landnlae praeputiaU-s , secrete unctuous material which, mixed with discarded epithelial cells, may collect in the groove behind the corona as a cheesy substance, the snicgnia. The corpora cavernosa (corpora cavernosa penis) are two cylinders of erectile tissue, when relaxed about 15 cm. (6 in.) in length, that form the chief bulk of the body of the penis. Each is enclosed within a dense fibro-elastir envelope, or tunica albuginca, which internally is continuous with the trabecnla- between the blood- spaces. Beginning above at the root of the penis as the diverging pointed and then of triangular >>-** ligament Attachment of bulb, cut Dissection of penis, showing three component cylin- ders of erectile tissue ; distal end of corpus spongiosum, with glans, has been freed and turned aside; attachment of urethral bulb has been cut and bulb drawn aside. THE PENIS. 1967 somewhat expanded crura attached to the inner border of the pubic arch, the cavern- ous bodies are at first separated by an interval occupied by the bulb of the corpus FIG. 1674. D ddv sdv sk da ddv sdv FIG. 1675. Cross-sections of formalin-hardened penis at different levels. A, through glans, near tip; B, about middle of glans ; C, through corona; D, body, distal part; E, body, proximal part, cc, corpus caver- nosum ; cs, corpus spongiosum ; da, dorsal artery ; ddv, deep dorsal vein ; r, fibrous envelope ; eg, erectile tissue of glans ; f, frenum ; ft, fibrous tissue ; s, fibrous septum ; sdv, superficial dorsal vein ; sf, super- ficial fascia; s&, skin; ta, tunica albuginea ; u, urethra. spongiosum. Farther forward, in the vicinity of the penile angle, the corpora caver- nosa press against each other with their median surfaces, the opposed flattened cap- sules blending to form a median partition (septum penis). Lower the latter becomes imperfect and replaced by a series of vertical bands, and hence is often designated the pectiniform septum, the intervening slit-like apertures permitting commu- nication between the blood-spaces of the two cavernous bodies, as well as the passage of anastomotic branches of their arteries. In certain mammals, especially the carnivora and some marsupials, a bone (os penis) is de- veloped within the fibrous septum. On approaching the corona, the cor- pora cavernosa again become discrete and rapidly taper to blunt-pointed ends that are separated externally by a slight furrow and capped by the over- lying glans. The dorsal and under surfaces common to the closely ap- plied cavernous bodies are marked by longitudinal grooves ; that along the former surface lodges the dorsal ves- sels of the penis, while the under fur- row is filled by the spongy body. The corpus spongiosum (cor- pus cavernosum urethrae), the third and much smaller, although longer (about 17 cm. or 6^ in.), cylinder of erectile tissue, occupies the groove along the under surface of the cavernous bodies. The two ends of this cylinder are enlarged, the Dorsal v now doubl Pubic bo Cms Deep artery in corpus cavernosum Urethra Ischio-cavernosus muscle Bulb Bulbo-cavernos muscle Colles's fascia- Frontal section through pubic arch and root of penis. 1968 HUMAN ANATOMY. upper expanding into a pyriform mass of erectile tissue, the urethral bulb (bulbus urethrae), and the lower broadening into a conical cap of erectile tissue that covers the ends of the corpora cavernosa and contributes the bulk of the glans. With the exception of the bulb, the major part of which lies behind the canal, the corpus spon- giosum is traversed by the urethra, the cavernous tissue completely surrounding the urinary tube. The bulb, attached by its upper surface to the inferior layer of the triangular ligament and covered below by the bulbo-cavernosus muscle, presents a slight median furrow (sulcus bulbi) that suggests a division into the so-called hemi- spheres. Internally an imperfect median septum bulbi partially subdivides the erectile tissue below and behind. The glans penis consists almost entirely of erectile tissue (corpus cavernosum glandis) directly continuous with that of the spongy body. Its upper surface is hollowed out to receive the pointed extremities of the corpora cavernosa, so that a section across the upper part of the glans shows the erectile tissue of the cavernous bodies surrounded by an overhanging crescent of the cavernous tissue of the glans (Fig. 1674, C). Along the frenum the fibrous envelope of the glans is prolonged inward towards the urethra as a fibro-elastic band (ligamentum medianum glandis) which, in conjunction with a similar band connecting the ends of the cavernous bodies with the upper urethral wall, forms a median partition, the septum glandis, that in- completely divides the erectile FIG. 1676. Erectile tissue of corpus Tunica albuginea cavernosum broken up / by pectiniforrn septum Prepuce- Erectile tissue of glans Anterior extremity of corpus cav- ernosum External urethral orifice Navicular fossa Frenum Erectile Urethra tissue of corpus spongiosum Mesial longitudinal section of end of penis. tissue of the glans and sur- rounds the terminal part of the urethra. The penile portion of the urethra is described with the other parts of the urinary tract in the male (page 1923). Beneath the skin and sub- cutaneous tissue the cylinders of erectile tissue, enclosed and united by their albuginea, are enveloped by the superficial fascia (Fig. 1674, E}. The latter, directly continuous with that of the perineum (Colles 1 fascia) behind and of the ab- domen (Scarpa's fascia) above, invests the penis as far as the neck, where it becomes blended with the prepuce. This fibro-elastic sheath is often called the fascia penis. In addition to the attachment of the crura of the corpora cavernosa to the peri- osteum of the pubic arch and of the bulb of the spongy body to the triangular liga- ment, the penis is supported by fibrous bands, that extend from the abdominal wall and pubes to the dorsum penis. This triangular sheet, the suspensory ligament, in- cludes a superficial and a deeper portion. The former (ligamentum fundiforme penis) begins at the linea alba, from 4-5 cm. ( I ^-2 in. ) above the symphysis, and consists of elastic bundles prolonged from the deep layer of the superficial fascia downward to the dorsum of the penis (Fig. 1671) at the so-called angle, where it divides into two arms that embrace the penis and, after uniting on the urethral surface, are continued into the septum scroti. The deeper portion (ligamentum suspensorium penis) contains compact fibrous bands that pass from the symphysis to the corpora cavernosa, just in advance of their separation into the diverging crura, to blend with the dense albuginea. Structure. Each of the component cylinders of erectile tissue is enclosed in a. robust sheath, the tunica albuginea, composed of dense white fibrous tissue, inter- mingled with relatively few elastic fibres and no muscle. The sheath surrounding the corpora cavernosa, which in places attains a thickness of 2 mm. and is much stronger than that enclosing the spongy body, is imperfect along the opposed median surfaces of the two cylinders, where it forms the pectiniforrn septum. From the inner surface of the tunica albuginea septa and trabeculae are given off which constitute the framework supporting tin- vessels and nerves and enclosing the characteristic blood-spaces of the erectile tissue. Numerous bundles of involuntary THE PENIS. 1969 muscle, circularly, longitudinally, and obliquely disposed, occupy the connective-tissue trabeculse and plates separating the venous lacunae, around which they form imperfect layers of contractile tissue. The trabecular muscle is most developed within the cav- ernous and spongy bodies and least so within the glans. The arteries conveying blood to the cylinders of erectile tissue are of two kinds, those nourishing the tissues themselves (vasa nutritia) and those carrying blood to the venous lacunae. The latter are connected with the arteries either directly by minute channels or through intervening capillaries. Within the trabeculse of the deeper parts of the erectile masses the deep arteries of the penis give off short, tortuous branches {arteries helicince}, about 2 mm. in length, that project into the blood-spaces with which they directly communicate by minute openings at their ends. Notwith- standing their exceptional development in man, the fact that the helicine arteries are wanting in many mammals shows that they are not essential, although advantageous, for erection. The arteries of the erectile tissue are distinguished by the unusual thick- ness of the circular muscle within their walls. In places the intima likewise exhibits excessive thickness. Since the increase is not uniform but local, it leads to the pro- duction of cushion- like elevations that FlG - I(5 77- encroach upon and even temporarily oc- clude the lumen of the arteries. The blood-spaces or lacuncz that occupy the interstices between the trabeculse are to be regarded as venous net- works which com- municate with the ar- teries, on the Deep dorsal vein Subcutaneous tissue Skin Tunica albuginea Septum one fascia Urethra Corpus spongiosum Transverse section of penis of child. X 10. hand, and with the radicles forming the veins, on the other. Their form and size Superficial ! evidently depend upon the degree of distention, when con- taining little blood the spaces being often mere slits or irregu- larly stellate clefts, while when filled they become more cylin- drical in form. In a general way three districts may be distinguished : () a narrow outer peripheral zone of almost capillary spaces, for the most part narrow and trian- gular in outline ; (^) an inner peripheral zone of larger spaces of uncertain form and from . 15-. 20 mm. in diameter ; and (c} a central zone of still more extensive spaces, which in places attain a diameter of one or more millimetres and are enclosed by rela- tively thin intervening lamellae and trabeculae. Since their expansion is usually greater in one direction, the general form of the larger and deeper lacunae is often ap- proximately cylindrical. Within the corpus spongiosum in the immediate vicinity of the urethra the blood-spaces are somewhat concentrically disposed owing to the feeble development of the radial lamellae (Eberth). The spongy body is further distin- guished by the robustness of its trabeculae and the consequent reduction in the size of the blood-spaces. Beyond the single layer of endothelial plates, the lacunae do not possess a distinct wall other than the fibro-muscular tissue of the surrounding trabeculae. The deep veins draining the cylinders of erectile tissue do not directly open into the blood-spaces, but are formed by tributaries of various size that begin as apertures in the walls of the lacunae, of which they are in fact extensions. The tributaries of the 124 HUMAN ANATOMY. more superficially situated venous trunks, as the dorsal vein, arise chiefly from the venous net-works of the peripheral zone. The veins possess an unusually well- developed muscular coat, and in places exhibit local cushion-like thickenings of their intima similar to but less marked than those seen in the arteries. Vessels. The arteries of the penis constitute a superficial and a deep set, the former supplying the integument and associated envelopes, while the latter convey blood to the masses of erectile tissue. The superficial arteries include twigs from the external pudic branches of the femorals to the lateral and under surface of the penis, from the dorsal arteries to the anterior surface and the prepuce, and from the superficial perineals by small vessels to the posterior part of the urethral surface. The deep arteries all branches from the internal pudics supply the three cylinders of erectile tissue, including the glans. The corpus spongiosum receives the arteries of the bulb, their continuations (sometimes described as the urethral arteries) accom- panying the urinary canal as far as the glans, where they anastomose with the terminal branches of the dorsal arteries. The last-named vessels also send small twigs around the corpora cavernosa to the spongy body. The corpora cavernosa are supplied chiefly by the deep arteries of the penis, supplemented by twigs from the dorsal arteries that pierce the albu- FIG. 1678. ginea. Entering the cavern- Central blood-spaces Inner peripheral spaces Outer peripheral spaces OUS bodies about where the crura unite, the deep arteries of the penis traverse the cyl- inders somewhat eccentri- cally, to. the median side of their axes. Communication between the vessels of the two bodies is established by anastomotic twigs that pass through the apertures in the median septum, as w r ell as by the terminal loop. The dorsal arteries, the longest branches of the internal pudics, pass along the dor- sum between the fascia and the albuginea, in company with the dorsal nerves and vein, and, in addition to the twigs distributed to the cov- erings, the cavernous bodies, and the corpus spongiosum, supply the erectile tissue of the glans. The anastomoses between the various vessels supplying the penis are very free, not only between the corresponding and other branches of the two sides, but also between those of the superficial and deep sets. The veins of the penis, like the arteries, constitute a superficial and a deep group which freely communicate and carry off the blood from the envelopes and from the erectile tissue respectively. The superficial veins for the most part are tributary to a subcutaneous trunk (v. dorsalis penis superficialis) that passes upward along the dorsum beneath the skin to the pubes and terminates either by dividing into branches that empty into the internal saphenous or the femoral veins on either side or by joining the deep dorsal vein ; both modes of ending, however, may exist. A number of vessels from the integument covering the posterior part of the urethral surface are collected by the anterior scrotal veins. The deep veins, which begin by tributaries from the erectile tissue that they drain, to a large extent discharge their contents into the deep dorsal vein ( v. dorsalis penis profunda ) that lies beneath the fascia and occupies the groove on the dorsum as far as the suspensory ligament, between the superficial and deep parts of which it Trabeculae V Bundles of muscle Dense fibrous tissue of tunica albuginea Transverse section through periphery of corpus cavernosum. X 50. THE PENIS. 1971 passes. Continuing between the subpubic and transverse ligaments and piercing the fascia, it gains the pelvis and ends, after dividing into two trunks, in the prostatic plexus. Beginning above the corona by the union of two stems that collect branches from the glans and the prepuce, the deep dorsal vein, as it courses upward, receives tributaries from all three cylinders of erectile tissue. Those from the corpora caver- nosa either pierce the albuginea as short branches that pass directly into the dorsal vein, or emerge from their under surface along the urethral groove and wind around the body of the penis to reach the collecting trunk on the dorsum, the anterior of these circumflex veins taking up tributaries from the under surface of the glans. Within the posterior part of the cavernous bodies are formed the deep veins of the penis, which emerge where the crura diverge and, after establishing communications with the prostatic plexus, become important tributaries of the internal pudic veins that accompany the corresponding arteries. The corpus spongiosum is drained by anterior branches that convey the blood to the dorsal vein by joining the circumflex or other veins from the corpora cavernosa, and by posterior stems (vv. urethrales) that pass upward and backward and empty partly into the prostatic plexus and partly into the internal pudic veins, the veins from the urethral bulb having a similar destination. Numerous anastomoses between the cutaneous veins and those from the erectile tissue establish free communication between the superficial and deep vessels. The lymphatics are numerous and disposed as superficial and deep vessels. The former are tributary chiefly to a superficial dorsal stem that accompanies the cor- responding vein and begins by the confluence of plexiform lymphatics within the integument of the prepuce and frenum. During its course the dorsal trunk receives lymphatics from the adjacent territory as well as others from the under surface that gain the dorsum by following the circumflex veins around the body of the penis. At the pubes the superficial dorsal lymph-trunk passes either to the right or left, or, when double, as it occasionally is, to both or even opposite sides, and joins the median group of superficial inguinal lymph-nodes. Direct comrriunications with the deep subinguinal nodes sometimes exist (Kiittner). The deeper lymphatics are particularly numerous in the periphery of the glans, around the meatus communi- cating with the urethral and preputial plexuses. Trunks are formed which occupy the retroglandular sulcus and unite into a deep dorsal lymph-stem, sometimes double, that accompanies the corresponding vein beneath the fascia and terminates, when single, in the median inguinal nodes of the left side (Marchant). The nerves of the penis include both spinal and sympathetic fibres, the former from the ilio-inguinal and the pudic nerves, and the latter from the hypogastric plexus. The integument around the root of the penis is supplied by the cutaneous branches of the ilio-inguinal and the inferior pudendal nerves, while that of the body and the prepuce is provided with the cutaneous branches of the dorsal nerves. The cylinders of cavernous tissue also receive twigs from the pudic nerves, the bulbar branches of which pass to the bulbus urethrae and in addition supply the mucous membrane of the urethra. Each corpus cavernosum receives a deep branch from the dorsal nerve which is given off as the latter lies between the layers of the triangular ligament. The sympathetic fibres destined for the blood-vessels and muscle of the erectile tissue are continued from the hypogastric plexus through the prostatic plexus to the plexus cavernosus, where, joining the dorsal nerves of the penis, twigs (nervi cavernosi penis minores) are sent to the posterior part and the crura of the corpora cavernosa, while others (nervi cavernosi penis majores) are distributed to the lower portions of the erectile masses, some fibres terminating within the spongy body. Close net-works of non-medullated fibres have been traced within the bundles of invol- untary muscle of the blood-vessels and trabeculae of the erectile tissue. Certain cerebro-spinal fibres (nervi erigentes) supposed to be especially concerned in erection are conveyed, in company with the sympathetic fibres, along the paths of the cavernous plexus. In addition to a generous supply of the more usual nerve-terminations, the skin of the glans and the prepuce is provided with special nerve-endings, the tactile bodies and the genital corpuscles of Krause (page 1017) lying within the papillae and the Pacinian corpuscles within the subcutaneous stratum. The paths of the sensory impressions lie within the dorsal nerves. 1972 HUMAN ANATOMY. Variations. Apart from the unimportant individual differences due to age, growth, and sexual activity, the variations of the penis are for the most part referable to imperfect develop- ment and are recognized as malformations rather than as anatomical deviations. The explana- tion of many of these conditions is supplied by the developmental history of the structures involved (page 2044) . PRACTICAL CONSIDERATIONS : THE PENIS. The size of the penis bears less constant relation to general physical develop- ment than does any other organ of the body. The normal average size of the flaccid penis of the adult is about three inches in circumference and from three and a half to four inches in length, measured from the suspensory ligament. When erect, this length increases to about six and a half inches and the circumference to three and a half or more. Absence of the penis may occur, but is rare unassociated with other anomalies. Apparent absence (concealed penis) may be due to the subcutaneous situation of an atrophic or undeveloped organ which may be palpated through the skin and revealed by an incision. Micropenis (infantile penis) is not uncommon, and varies in degree from a mere failure to attain quite the average size (annoying chiefly to sexual neurasthenics) to a retention throughout life of the dimensions and development normal in early childhood or infancy. Occasionally in such cases, after puberty and following physiological activity of the organ, rapid growth takes place and conditions approximating normal- ity may result. Megalopenis. As has already been observed, the size of the organ bears no constant relation to the size or strength of the individual. In congenital imbeciles it is often of unusual size, and in dwarfs and hunchbacks it is not uncommonly devel- oped, not only out of proportion to the other parts of the organism, but beyond even the average for individuals of normal growth. Hypertrophy of the penis is at times an inconvenience, and may even be a source of danger, since an excessive develop- ment predisposes to abrasions and fissures through which inoculation with venereal diseases may occur. Double penis has been .recorded in a few instances, in at least two of which each organ was functionally perfect. The skin of the penis is thin and delicate (to maintain the sensitiveness of the organ), and is lax and elastic (to permit of its changes in size). On account of these qualities abrasions are not unusual, and through them syphilitic infection frequently takes place. The loose, plentiful layer of subcutaneous connective tissue permits of enormous cedematous swelling as a result of ordinary staphylococcic or streptococcic (pyogenic or erysipelatous) infection; its abundance in conjunction with the elasticity of the skin, accounts for the disappearance of the penis in cases of very large scrotal hernia, in hydroceles of similar size, and in elephantiasis scroti. Anterior to the corona the skin is modified and resembles a mucous mem- brane, at the meatus becoming continuous with the mucosa of the urethra. The line of demarcation between the ordinary and modified cutaneous surfaces is not, however, so distinct as on the lips or the nostrils, the passage of one surface into the other more closely resembling that which takes place at the margin of the anus. On the proxi- mal face of the corona the subcutaneous tissue is still abundant. Over the glans it practically disappears and the modified integument closely embraces the erectile tissue of the expanded anterior extremity of the corpus spongiosum. Chancres anterior to the corona (except at the frenum) are apt to exhibit the variety of induration known as "laminated" or "parchment-like," corresponding to a sclerosis limited to the papillary layer of the derma and to the vascular net-work of the papillae. At the frenum, corona, or cervix, where the cellular tissue is abundant, " nodular" induration a sclerosis of the whole thickness of the derma, of thesubder- moid areolar tissue, and of the associated vascular net-work, which is much larger than the superficial or papillary supply is apt to occur, and is, as the name indicates, deeper, thicker, and harder. On the skin of the penis chancres are apt to be exten : sive in area, but are limited in depth by the firm, resistant fascia penis. PRACTICAL CONSIDERATIONS: THE PENIS. At birth the prepuce is normally adherent to the glans, its moderate retraction barely exposing the meatus. Continued retraction everts the lips of the meatus and then separates the epithelial adhesions between glans and prepuce, ultimately exposing a congested surface and causing punctate hemorrhages. This separation should normally take place during infancy or early childhood,, either spontaneously as a result of erections and of the growth of the organ or because of gradual mechanical retraction by nurse or mother. When it fails to do this, the condition of phimosis inability to retract the prepuce follows, and is due partly to the persistent adhesions and partly to a frequently associated narrowing of the preputial orifice. Both these factors may be the result of disease, and acquired phimosis may occur at any time of life and follow any form of inflammation of the skin covering the glans (Jbalanitis*) , of the inner surface and cellular tissue of the prepuce ( posthitis'} , or of both (balano-posthitis) , the last named being the most common. Following phimosis there may be, (a) as a result of retention of secretion and of urine in the subpreputial space, balanitic or herpetic ulceration, or the development of papillomata (venereal warts) ; () as a result of obstruction to the flow of urine and the consequent strain- ing, vesical irritability, dilatation of the bladder, ureters, and kidneys, hemorrhoids, and hernia (62 per cent, of cases of congenital phimosis) (Kempe, quoted by Jacob- son) ; (c) as a result of nerve irritation (the region having an unusually rich nerve- supply), spastic palsies, reflex joint pains and muscular spasm (simulated coxalgia), or even general convulsions. These complications -are most apt to occur in infants and very young children, and their frequency has been exaggerated. As a result of phimosis, even when the preputial orifice is ample, there may be a contracted or ' ' pin-point' ' meatus, which may give rise to the same train of symp- toms and will require to be divided (meatoiomy) by a linear incision directed towards the frenum, and kept open during the process of healing. Circumcision, whether done for phimosis or to meet other indications, requires for its successful performance attention to the following anatomical points : (a) the laxity of the skin, permitting it easily to be drawn so far in front of the glans that when it is severed at that point so much may be removed that the remainder retracts quite to the root of the organ, which is left denuded ; () the close attachment of the inner or mucous layer of the prepuce to the corona, so that the length of the portion of that layer that is allowed to remain will determine the distance of the operative scar (at the muco-cutaneous junction) from the meatus ; if this stump is not exces- sive, it will thus effectually prevent the mortifying but not infrequent accident of re- formation of a phimosis after a circumcision ; (c) the loose, abundant cellular tissue and rich vascular supply in the frenal region, which, together with the dependent position of the part, may determine an excess of exudate that will result in an objec- tionable fibrous mass in that region if full haemostasis is not secured or if any redun- dant tissue is left there. When a relatively small preputial orifice is drawn behind the corona it causes marked constriction at that point, especially if it is not only small but also inelastic as a result of chronic inflammation. If the constriction remains unrelieved, paraphimo- sis results ; the glans becomes distinctly enlarged, increasing the constriction, purplish in color, and glossy. It is often partially concealed by a thick collar of shiny, cedem- atous skin, behind which there is a deep, excoriated sulcus, and back of this sulcus there is usually a second cedematous band less marked than the one lying immediately behind the coronary sulcus. The penis seems to have a distinct upward kink or bend just behind the glans. This appearance is due to the deep notch caused by the margin of the retroverted orifice of the prepuce and to the oedematous swelling which is particularly marked about the position of the frenum. In some cases, where the tense, inelastic edge of the orifice exerts a more than usual amount of constriction, circulation is markedly interfered with, and ulceration and even sloughing involving both the foreskin and the head of the penis may take place. This complication would undoubtedly be more frequent were it not for the rich blood-supply to the glans and the anastomosis between its vessels and those of the corpora cavernosa. The ulceration usually involves the foreskin only. 1974 HUMAN ANATOMY. When the swelling consequent upon paraphimosis is well developed there is en- countered first a furrow, the coronary sulcus, which is normally found behind the corona ; in these cases it appears deeper because it is intensified by the cedematous swelling. Covering this furrow, and even overlapping the glans somewhat, is the portion of the prepuce which is normally in contact with the posterior face and border of the corona. Behind this swollen fold is found a second deep, often ulcerated fur- row indicating the position of the preputial muco-cutaneous margin ; this is the actual seat of constriction, and behind it is placed yet another ridge of swollen integument. The fascia penis (page 1968) gives the organ some of its most important physical characteristics. The tensile strength of the penis, because of its tough fibrous invest- ments, is sufficient to bear the entire weight of the body. That portion of this fibrous investment which covers the blunt extremities of the two cavernous bodies where they are capped by the glans, delays, and sometimes prevents, the backward extension of inflammatory or infiltrating processes, particularly cancerous infiltration, which pri- marily involve the glans. This fibrous sheath, being a continuation of the deep layer of the superficial fascia, also limits the forward extension of urinary and purulent infiltra- tions beneath this fascia, such infiltrations leaving the glans uninvolved. The free blood-supply to the penis and its rich innervation insure rapid healing in case of wounds, and justify conservative treatment even although the organ has been nearly severed or extensively crushed. Contusion of the penis is often followed owing to the laxity of the skin by such rapid and pronounced ecchymosis and oedema as to simulate gangrene. When the vessels of the cavernous bodies are involved there is free subcutaneous bleeding, giving rise to a circumscribed fluctuating tumor, most prominent during erection. This tumor is somewhat slow in forming, and occasionally suppurates. Under conservative treatment it usually disappears. When injury has not only occa- sioned extensive extravasation of blood, but has lacerated the urethral canal, the inflammatory phenomena observed after rupture of the urethra quickly develop. Moreover, there is immediately bleeding from the meatus, which should lead to prompt diagnosis and appropriate treatment. Wounds, if involving the erectile tissue, bleed freely, and, if transverse and ex- tensive, may be followed by loss of erectile power in the region anterior to the wound. Fracture, in a literal sense, is possible only when the organ has undergone calcifica- tion or ossification (vide infra], but the term is applied to injuries that result when, during vigorous erection, the penis is subjected to a sudden twist or bend. The resulting condition is not unlike that caused by contusion, but the subcutaneous effusion is apt to be lacking. The chief lesion is usually in the corpora cavernosa, or in one of them, and is apt, as a result of obliteration of erectile spaces, to leave a flail-like organ, erection anterior to the break being impossible. Chronic induration (ossification, calcification, chronic inflammation) of the sheath and erectile tissue, especially of the corpora cavernosa, is marked by the formation of fibrous, calcareous, or bony thickenings or plates, which form usually in middle- aged or elderly men of gouty diathesis. They cause but little pain, are easily recog- nized by palpation, and are accompanied by bending of the penis to the affected side during erection, which is incomplete in the region anterior to the induration. The condition is unknown before forty or forty-five, and is probably analogous to the thickening and toughening of the palmar fascia, which goes by the name of Dupuy- tren's contraction, and which we recognize as partly due to gout and partly to some constant irritation. Thus they may be met with in both, the penis and the hands of the same gouty person (Jacobson). It has been suggested (Metchnikoff) that in their osseous form they represent reversions to the condition existing in many mam- mals and even in the anthropoid apes, in whom an os pen is is present. Lymphangitis may follow peripheral inflammation of any type, but is usually of venereal origin. The diagnosis between lymphangitis and phlebitis of the dorsal vein is based upon the much smaller size of the lymphatic vessels as compared with the vein ; upon the fact that the former vessels do not pass upward in the middle line, but are directed .into the groins ; and finally upon the ability to lift the indurated vessel up from the deeper parts, this not being possible in the case of the vein, since it is placed in a THE PROSTATE GLAND. 1975 furrow between the two cavernous bodies. Phlebitis occasions much more marked cedema. Epithelioma of the penis is not uncommon. It usually follows prolonged subpre- putial irritation. It involves ultimately both the inguinal and the deep pelvic nodes. Amputation of the entire penis may be required for the relief of malignant dis- ease. The following description (Treves) should be studied in connection with the anatomy of the penis and of the urethra. The patient is placed in the lithotomy posi- tion, and the skin of the scrotum is incised along the whole length of the raphe. With the finger and the handle of the scalpel the halves of the scrotum are separated down to the corpus spongiosum. A full-sized metal catheter is passed as far as the trian- gular ligament, and a knife is inserted transversely between the corpora cavernosa and the corpus spongiosum. The catheter is withdrawn, the urethra is cut across, and its deep end is detached from the penis back to the triangular ligament. An incision is made around the root of the penis continuous with that in the median line. The suspensory ligament is divided and the penis is separated, except at the attachment to the crus. The knife is then laid aside, and with a stout periosteal elevator or rugine each crus is detached from the pubic arch. The two arteries of the corpora cavernosa and the two dorsal arteries require ligature. The urethra and corpus spongiosum are split up for about half an inch, and the edges of the cut are stitched to the back part of the incision in the scrotum. The scrotal incision is closed by sutures, and if drain- age is used, the tube is so placed in the deep part of the wound that its end can be brought out in front and behind. No catheter is retained in the urethra. THE PROSTATE GLAND. Although developed as an appendage of the urinary tract, and not directly as part of the sexual apparatus, the prostate is functionally so closely related to the gen- erative organs that it may appropriately be regarded as one of the accessory glands, the others being the glands of Cowper. The prostate is complex in both its make-up and relations, being partly glandu- lar and partly muscular and traversed by the urethra and the ejaculatory ducts. In general form it resembles an inverted Spanish chestnut, having the base FIG. 1679. applied to the under surface of the bladder and the small end, or apex, directed downward. Additional an- ^^ -Slight groove produced , i j . r f HBk by symphysis tenor, lateral, and posterior surfaces are recognized. Grayish red in ^-inferior surface color and of firm consistence, the adult prostate varies considerably within physiological limits in size and weight. The former includes a length, from apex to base, of from 2. 5-3. 5 cm. ( i to i y% in. ) , a breadth or transverse diameter of from 3. 5- 4.5 cm. (i-Hi 1^4 m -)> an d a thick- ness of from 2-2.5 cm - (I-" 1 m -)- Its average weight is about 22 gm. (24 oz. ). Marked increase in size ^ surface and weight is Common in elderly Slightly distended bladder, hardened in situ, show- i ing prostate, seminal vesicles, and semitial ducts ; viewed SUDjeCtS. from below and behind. The oblique upper surface or base (basis prostatae, facics vesicalis) is applied to the under surface of the bladder, with which it is inseparably blended by muscular tissue surrounding the urethral ori- fice, and is pierced by the urethra usually slightly in advance of the middle. The base is outlined by free rounded borders, so that its limits are separated from the vesical wall by a groove. The posterior surface (fades posterior), directed backward and towards the rectum, is defined laterally by prominent rounded borders that extend from the base to the apex and enclose a flattened cordiform or triangular area 1976 HUMAN ANATOMY. Seminal vesicle Ampulla Prostate, middle lobe Ejaculatory duct Inferior wall of bladder Internal urethral V orifice \ Urethral crest^ Prostatic urethra Portion of sagittal section showing prostate and related structures. that often presents a shallow concavity. The junction of the upper and posterior surfaces is marked by a transverse, crescentic slit (incisura prostatae) into which sink the ejaculatory ducts in their course to the urethra. The imperfectly denned wedge- shaped mass bounded by FIG. 1 680. the urethra in front, the ejac- ulatory ducts at the sides and behind, constitutes the so-called middle lobe (lobus medius), the base of which lies beneath the vesical tri- gone. The prominent por- tions of the prostate lying external to the ejaculatory ducts are known as the lat- eral lobes, which, however, superficially are not dis- tinctly marked off. The prominent convex lateral surfaces, directed outward, downward, and forward, and behind limited by rounded borders, in front pass insen- sibly into the narrow con- vex anterior surface (fades anterior) that is approximately vertical and faces the symphysis. The urethra traverses the prostate with a vertically placed curve, the concavity looking forward, that above begins slightly in advance of the middle of the base, and below ends on the anterior surface just in front and above the apex. The posterior wall of the prostatic urethra is marked by a longitudinal median ridge, the urethral crest, on the most expanded and elevated part of which (colliculus seminalis) are situ- ated the openings of the/rar- talic utricle (utriculus prostati- FIG. 1681. cus) and of the ejaculatory ducts (page 1955). In the grooves or recesses on either side of the crest, open the mi- nute orifices of the prostatic tu- bules, some twenty in number, that discharge the products of the glandular tissue. Owing to the continuity of the muscular tissue with the surrounding structures in front, above, and below, the outlines of the prostate in places lack definition. Except over its base, apex, and lower anterior surface, the prostate is enclosed by a fibrous envel- ope or capsule, the extension of the visceral layer of the pel- vic fascia in conjunction with the investment of the bladder and the seminal vesicles. The capsule is best developed on the posterior surface, where it separates the prostate from the rectum and constitutes a part of the recto-vesical fascia in its restricted sense. Relations. Lodged between the bladder and the pelvic floor, the prostate is in relation with a number of important structures. Above, its base is intimately Folds of mucous membrane Urethral mucous tory ducts Section across prostatic urethra above entrance of ejacula- tory ducts, showing crescentic form of urethral lumen pro- duced by encroachment of urethral crest. X 10. THE PROSTATE GLAND. 1977 Terminal duct opening into alveol Involuntary muscle, attached to the lower surface of the bladder, lying beneath the vesical trigone. Below, its apex rests upon the superior layer of the triangular ligament, surrounded by fibres of the compressor urethras muscle that constitute the external vesical sphincter (page 1925). In front, the rounded anterior surface is directed towards the pubic symphysis, from which it is separated by an intervening wedge-shaped space occupied by loose areolar tissue containing part of the prostatic plexus of veins and fat. The pubo-prostatic ligaments (the continuations of the arcus tendineus of the two sides) stretch between the symphysis and the prostate and contain muscular tissue prolonged from the latter and the bladder. At the sides, the prostate is embraced by the levator ani muscles, the prostatic venous plexuses, embedded within the reflections of the pelvic fascia that here constitute the capsule of the gland, inter- vening. Behind, the prostate is in relation with the ampullae of the vasa deferentia and the seminal vesicles above and with the lower part of the rectum below, separated from the latter by the dense capsule and the overlying layer of areolar tissue. The position of the prostate is not constant, since it is affected by movements of the vesi- cal wall, with which the prostate is intimately united, incident to marked distention and contraction of the bladder. On the other hand, the at- tachments of the prostate to the trian- gular ligament and pelvic fascia indi- rectly confer upon the lower segment of the bladder its most efficient means of fixation. The pros- tate is further influ- enced by changes in the anterior wall of the rectum, under- going compression and displacement forward when the bowel is distended. Structure. The prostate is a gland of the tubo- alveolar type and is made up of three chief components, the connective-tissue framework, involuntary muscle, and the glan- dular tissue. Of these the latter constitutes usually a little more than one-half of the entire organ, and the connective tissue and muscle each somewhat less than one-quarter. The connective-tissue framework consists of an external investing fibro-elastic en- velope, the capsule proper, and a median septum, which encloses and blends with the walls of the urethra. Between these denser lamellae numerous partitions radiate and subdivide the organ into from thirty to forty pyramidal lobules occupied by the glandu- lar tissue. The involuntary muscle, embedded within the capsule and ramifications of the connective-tissue framework, surrounds the gland-substance as a superficial layer from which a median septum, about 2 mm. in width, extends ventro-dorsally, enclosing the urethra in an annular thickening. In consequence, the interior of the prostate is occupied by a dense fibro-muscular nucleus, in which the glandular tissue is represented by only the narrow prostatic ducts passing towards the urethra. The muscle is not limited, however, to the foregoing positions, but extends also between the ultimate divisions of the gland-tissue, the interalveolar septa in places consisting largely of the variously disposed muscle-bundles. The glandidar tissue consists of twenty or more distinct tube-systems, each drained by an independent duct that opens into the urethra in the groove on either side Alveoli Blood-vessel Portion of cross-section of prostate gland. X 75. 1978 HUMAN ANATOMY. Muscle cell Small concretion of the colliculus. Beginning at their narrow orifices, these excretory tubules (ductuli prostatici ) pass outward into the lobules, and after a course of about I cm. divide into tubules that repeatedly branch and expand into the terminal alveoli. Throughout the greater part of their course the wavy ducts are beset with saccular and tubular diver- ticula, simple or compound, that give the canal an irregular lumen and constitute what have been termed the duct alveoli as distinguished from the terminal alveoli. The latter form a series of irregularly branched tubular and saccular spaces lined with a single or imperfect double layer of columnar epithelial cells, the secreting elements of the gland. In places the alveoli intercommunicate and form net-works of spaces of variable lumen. The epithelium in the ducts and their diverticula corresponds with that lining the more deeply situated alveoli, the change into the transitional variety of the prostatic urethra not taking place until very near the termination of the ducts. Peculiar concretions ( ' ' amyloid bodies' ' or " prostatic calculi' ' ) are almost con- stantly present within some of the tubules of the adult organ, especially in advanced life. These bodies (Fig. 1683), round or oval in outline and very variable in size (from .2-1 mm. and more in diameter), usually exhibit a faint concentric striation and a light brownish color. FIG. 1683. Their nature is uncertain, but they probably consist of a colloid substance giving the reactions of albumen. The secretion of the prostate gland (sticcus prostaticus) is milky in ap- pearance, thin in consist- ence, slightly alkaline in reaction, and possesses a characteristic odor (Fiar- bringer). It is discharged into the urethra and min- gled with the fluid enter- ing by the seminal ducts during ejaculation, and probably serves an impor- tant purpose in facilitating and perhaps stimulating the motility of the sper- matozoa. The "sperm crystals" formed in semen after standing, and attributed to the products of the prostate, are not found in the secretion of the living subject (although frequently present in the gland after death ) until after the addition of ammonium sulphate (Furbringer). Vessels. The arteries supplying the prostate are small branches from the inferior vesical and middle hemorrhoidal. They enter the periphery of the gland at various points, particularly in company with the ejaculatory ducts, and break up into capillary net-works that surround the alveoli. The veins are exceedingly numer- ous, forming close mesh-works within the glandular tissue and around the ducts. They leave the organ on either side and unite into a plexus within the capsule, which, receiving the deep dorsal veins of the penis and communicating with trunks from the bladder, seminal vesicles, and rectum, is. continued as the prostatico-vesical plexus, tributary to the internal iliac veins. The lymphatics are numerous and form a net- work on the lower and posterior surface of the organ from which on either side pass two trunks, a superior and a lateral. The upper and smaller trunks are afferent to the obturator lymph-nodes of the pelvic wall, and the lateral and larger terminate in the internal iliac nodes (Sappey). The nerves of the prostate are chiefly sympathetic fibres derived from the hypogastric plexus, numerous minute ganglia being included along their course. Peripherally situated Pacinian corpuscles are said to be connected with the sensory fibres (Griffiths). Epithelium ing alveoli Intcralveolar tissue vessel 'Portion of section of prostate gland, showing details of alveolf X 270. PRACTICAL CONSIDERATIONS : PROSTATE GLAND. Development. At about the third month of foetal life the wall of the primitive urethra undergoes thickening, leading to the production of an annular mass of meso- blastic tissue that surrounds the lower ends of the Wolffian and Mullerian ducts (later the ejaculatory ducts and the prostatic utricle respectively) and subsequently becomes differentiated largely into unstriped muscle. Into this penetrate solid' epi- thelial outgrowths, from the lining of the urethra, which expand into branched cylinders that give rise to the prostatic glandular tissue. These outgrowths are arranged in three groups (Pallin), a ventral, an upper and a lower dorsal. The ventral group gives rise to the glandular tissue in front of the urethra, which at first is relatively abundant, but soon suffers reduction, and in the adult organ is often almost wanting. The dorsal groups produce the important glands of the median and lateral lobes. For a time the latter are arranged as two separate lobes, but afterward become consolidated by the capsule and broken up by the invasion of the nbro-muscular septa. At birth the prostate measures about 12 mm. in its transverse dimension and remains small until puberty, when it begins to rapidly enlarge, acquiring its full pro- portions with the establishment of sexual activity. With the approach of old age, the prostate usually undergoes increase in size, an augmentation often resulting in pathological conditions. Variations. Apart from abnormalities in size, the prostate is subject to few variations. Among the latter have been persistence of the original independence of the lateral lobes, ab- sence of the middle and the presence of a fourth lobe. Variations in the relations and mode of ending of the ejaculatory ducts (fusion into a single canal or termination in the prostatic utricle or by a special canal below the crest) or in the prostatic utricle (absence, enlarged size, or un- usual opening) are properly referred to deviations in the development of the generative tract. PRACTICAL CONSIDERATIONS : THE PROSTATE GLAND. The prostate gland is a portion of the male generative system. The prostatic utricle, or sinus pocularis, is the homologue of the sinus genitalis in the female, the uterine and vaginal cavities, since it represents the persistent part of the fused Mul- lerian ducts (page 2039). Alhough the prostate and the uterus cannot be regarded as homologous organs, they are similar in structure, and would be strikingly alike if the tubular glands found in the inner walls of the uterus were prolonged into its muscular substance. During infancy and childhood the prostate is still immature ; at puberty it enlarges coincidently with the enlargement of the testicles. In eunuchs and after castration in man and other animals it is atrophied. The seminal vesicles are in close relation to it and the ejaculatory ducts penetrate it (page 1955). Its size and perfection of struc- ture in animals rise and fall with the breeding season (Hunter, Owen, Griffiths). These facts sufficiently demonstrate the essential relation of the prostate to the gen- erative system. It, however, affords passage to the prostatic urethra, its unstriped muscle-fibres are continuous with the vesical muscle at the trigonum and with the circular fibres of the bladder, and both the anatomical and subjective effects of the more common pathological changes in the prostate are observed in relation to the urinary system, with which, therefore, it is most intimately associated. Injuries of the prostate are rare on account of its protected position, and usually involve also the rectum or the bladder. Hemorrhage from the prostato-vesical plexus may be dangerous in amount ; and if a wound extend upward into the neck of the bladder, that organ may become distended with blood and form a tense, globu- lar hypogastric tumor. Infiltration of urine following a prostatic wound may, in accordance with the situation of the latter, reach the hypogastrium from the pre- vesical space, the ischio-rectal region or the perineum from coincident division of the fascia of Colles, or the recto-vesical space and the pelvis from similar division of the recto-vesical fascia. Disease of the prostate, if infectious, is usually gonorrhoeal in origin. It is often due to the use of unclean urethral or vesical instruments. It tends to suppuration on account of the very imperfect drainage of the products of inflammation from the numerous follicles. 1980 HUMAN ANATOMY. Prostatitis is attended by (a) much swelling, owing to the vascularity and spongy structure of the gland. As the forward enlargement of the prostate is pre- vented by the resistance of the dense pubo-prostatic ligaments, the subpubic liga- ment, and the firm superior layer of the triangular ligament, the swelling is greatest in tne posterior two-thirds of the gland. Its downward extension is evidenced by (6) a sense of weight and uneasiness in the perineum and (c) rectal irritation and tenesmus. Its upward and backward spread is shown by (d ) interference with mic- turition, due to compression of the prostatic urethra and elevation of the vesical out- let. The symptoms of (V) painful and frequent micturition and (_/) vesical tenesmus are due in part to the mechanical obstruction, but chiefly to the extension of the inflammation to the trigonal region and to the obstruction by pressure of the pros- tatic venous plexus into which the vesical plexus empties, causing intense conges- tion of the vesical mucosa. The unyielding character of the prostatic sheath produces () the heavy, throbbing pain felt in the infrapubic, perineal, and rectal regions, and results in such tension that (//) referred pains are very common, and, on account of the derivation of the nerve-supply of the prostate from the lower three dorsal and upper three sacral segments, are apt to be widely distributed, as, e.g. , pain over the tip of the last rib (tenth dorsal nerve), over the posterior iliac spine (eleventh dorsal nerve), or even in the soles of the feet (third sacral nerve) (Treves); reflex irrita- tion of the inferior hemorrhoidal nerve may cause intense pruritus ani, sometimes a very annoying symptom. Prostatic abscess usually takes the direction of least resistance and opens into- the urethra. Its progress towards the pelvis is resisted by the dense investment contributed by the pelvic fascia; towards the perineum, by the superior layer of the triangular ligament. It sometimes points towards the rectum, from which it is sepa- rated by a thinner and less resistant layer of the pelvic fascia, and may then open directly into the rectum, or be guided by it to the perineum. Hypertrophy of the prostate to some degree occurs in about one-third of all males who have passed middle life, and in about one-tenth of all males over fifty-five the enlargement becomes of pathological importance. Its cause is unknown. Various theories having a more or less direct bearing upon its anatomical and physio- logical characteristics have been advanced to explain its occurrence, but none has been demonstrated. It has been attributed to (a) the general arterio-sclerosis of old age (Guyon); () a primary change in the bladder necessitating a compensatory hypertrophy of the prostate (Harrison); (<:) a growth analogous to uterine fibro- myoma (Thompson) ; (d) the persistence, in an adjunct sexual organ, of physiological activity intended for the control and determination of the masculine characteristics after the need for such activity had disappeared (White); (e) an attempt to com- pensate quantitatively for a qualitative deterioration in the prostatic secretion, whose function (Fiirbringer) is to facilitate the mobility and vitality of the spermatozoa (Rovsing); and, recently, (/") infection (most often by the gonococcus), aggravating a senile degenerative process (Crandon). The enlargement may affect chiefly any of the separate components of the pros- tate, and may thus be adenomatous, myomatous, or fibrous in its character, although usually the glandular element predominates. It may involve particularly the lateral lobes, or may affect almost exclusively the so-called median portion placed at the lower posterior part of the gland, between the ejaculatory ducts. This portion is directly beneath the vesical neck. The degree of hypertrophy is extremely variable, the prostate being increased from its normal weight of between four and six drachms to a weight of many ounces, and, of course, correspondingly increased in size. It is not possible here to do more than call attention to these varieties of hyper- trophy, but its usual and general effects may be considered with reference to their anatomical causation. i. The direction of greatest resistance to enlargement is forward (ride supra} and next downward (towards the rectum). Hence the growth usually takes place in an upward and backward direction, although the resistance offered by the recto- vesical layer of fascia does not prevent marked extension in that direction in many cases. As a direct result of this enlargement there follow : (a) compression, flatten- PRACTICAL CONSIDERATIONS : PROSTATE GLAND. 1981 ing, and elongation of the prostatic urethra, or lateral deviation of that canal (if one lobe greatly exceeds the other in size); (6) elevation of the vesical neck and outlet, which are carried up by reason of their intimate connection with the prostate, especially with its median lobe, the base of the bladder remaining relatively un- affected ; ( a width of from 1.5-3 cm - (y%- i y% in.), and a thickness of from .6-1.5 cm - (/^-^8 in.), according to German authorities. The right ovary is frequently somewhat larger than the left. The adult organ weighs about 7 grm. (^ oz. ). After the cessation of menstruation, about the forty-fifth year, the ovary decreases in size and weight, in old women being reduced to one-half or less of its normal proportions. The ovary presents two surfaces a. median (fades medialis), directed inward, and a lateral (facics lateralis), looking outward and in more or less close relation with the pelvic wall ; two margins connecting the surfaces an anterior (margo meso- varicus), which is thin, straight, and attached to the posterior surface of the broad ligament by a short peritoneal fold or mesovarium, and a posterior (margo libra), which is thicker, rounded, convex, and unattached ; and two poles an upper (ex- tremitas tubaria), rounded, embraced by the oviduct and attached to the suspensory ligament of the ovary and usually to the fimbriated extremity of the Fallopian tube, and a lower (extremitas uterina), pointed and attached to the uterus by a fibro- muscular band, the utero-ovarian ligament. The portion of the attached anterior border through which the vessels and nerves enter and emerge is known as the hi I um (hilus ovarii). The surfaces of the mature ovary are not even, as in early life, but modelled by rounded elevations of uncertain number and size and by irregu- lar pits and scars. The elevations are produced by the underlying Graafian follicles in different stages of growth, while the irregular scar-like areas indicate the position of corpora lutea of varying age and development. Just behind the attachment of the mesovarium and parallel to the hilum, the surfaces of the fresh ovary are crossed by a narrow stripe of lighter color, straight or curved and often slightly raised. This band, the white line of Farre, marks the transition of the usual peritoneal endothe- lium into the cylindrical germinal epithelium that covers the exterior of the organ and appears dull and lacking in the lustre characteristic of serous surfaces. 125 HUMAN ANATOMY. Position and Fixation. Although subject to deviations due to the influence of other organs, especially the pull of the uterus, and of pregnancy, the long axis of the normally placed ovary, in the erect posture, is approximately vertical (Fig. 1684). The margin attached to the broad ligament of the uterus is directed forward and slightly outward 'and the free convex border backward and inward. The outer sur- face usually lies in contact with the peritoneum covering the lateral pelvic wall within a more or less well-marked depression, the ovarian fossa (fossa ovarica). This recess, triangular in its general outline and variable in depth, is included within the angle formed by the diverging peritoneal folds covering the external and internal iliac vessels. In favorable subjects, in which the amount of subperitoneal fat is small and the em- bedded structures, therefore, not masked, the ureter and the uterine artery will be seen forming the immediate boundary of the ovarian fossa behind, while above and in front extends the remains of the obliterated hypogastric artery. Below, where its FIG. 1684. Internal iliac artery Fimbriated end of Fallopian tube, pulled forward Suspensory ligament of ovary External iliac vessels Round ligament- Deep epigastric artery Mesosalpinx Obliterated hypogastric artery Fallopian tube Bladder Symphysis pubis ^Peritoneum, cut edge L'reter . Right ovary, median surface Ligament of ovary Utero-sacral ligament Rectum Recto-uterine pouch \Uterus, pulled to the left Right lateral wall of pelvis, showing ovary in position ; Fallopian tube has been pulled forward and uterus to the left. boundary is indistinct and uncertain, it fades into the pelvic floor, often without demarcation. The floor of the fossa is obliquely crossed by the obturator vessels and nerve. Within this depression the ovary lies, hidden to a considerable extent beneath the oviduct, which arches over the upper pole and largely covers the median surface with its expanded fimbriated end. The upper or tubal pole reaches almost to the level of the external iliac vein and the pelvic brim, and is overhung by the inner edge of the psoas muscle. The lower pole rests upon the upper (posterior) sur- face of the broad ligament and nearly touches the pelvic floor about 2 cm. above and in front of the upper border of the pyriformis muscle and the trunk of the greater sciatic nerve (Rieffel). The vertical position of the ovary is maintained by the suspensory ligament (ligamcntuin suspensorium), also called infundibulo-pdvic ligament, which is a trian- gular band of fibre-muscular tissue, attached to the upper tubal pole of the ovary and invested by a peritoneal fold continued from the upper and outer corner of the broad THE OVARIES. 1987 Surface -- epithelium ligament. It passes outward across the external iliac vessels in front of the sacro-iliac articulation and is lost in the fascia covering the psoas muscle. Embedded within the enclosed fibro-muscular tissue lie the ovarian vessels and nerves, which thus gain the broad ligament in their passage to the ovary. The anterior margin of the ovary is attached to the posterior surface of the broad ligament by a short but broad band the mesovarium covered on both sides by peritoneum, that conveys the ovarian vessels proper and the nerves to the hilum through which they enter and emerge from the organ. The somewhat pointed lower end of the ovary is connected with the posterior border of the uterus, between the oviduct and the round ligament, by a cord-like band, the utero-ovarian ligament or ligament of the ovary (ligamentuin ovarii proprium). This band, from 3-4 mm. thick, lies within the posterior layer of the broad ligament beneath the peritoneum, through which it is seen as a distinct cord. Since the uterus and its broad ligament are subject to continual changes of posi- tion, the attachment of the ovary to these structures often produces deviations from its typical location. These in- fluences affect particularly the FlG - l68s> lower pole, the upper enjoying greater fixation from the support afforded by the suspensory liga- ment. Asymmetry in the po- sition of the two ovaries is usual, as the fundus of the uterus seldom lies strictly in the mid-line, and hence the lower pole of the ovary of the opposite side is dragged medially. The long axis of the ovary, under such conditions, is oblique on the side opposite to that towards which the uterus is deflected. Conversely, relaxa- tion of the ligaments occurs on the side towards which the uterus tends and thus favors the reten- tion of the vertical position of the ovary. Notwithstanding the lati- tude of movement possible, the position of the normal ovary is fairly constant, the close relation of the oviduct to the median surface, aided by the pressure exerted by other organs within the pelvis, materially assisting in retaining the ovary within its fossa. The stretching and subsequent relaxation of the suspensory ligament incident to pregnancy are predisposing causes of displacement of the ovary due to insufficient fixation. Structure. The ovary consists of two principal parts, the cortex (zona parenchymatosa) a narrow superficial zone, from 2-3 mm. thick, that forms the entire periphery of the organ beyond the white line ; and the medulla (zona vascu- losa,) that embraces the deeper and more central remaining portion of the gland. The cortex alone contains the characteristic Graafian follicles and the ova, while the medulla is distinguished by the number and size of the blood-vessels, especially the veins. The cortex, as seen in vertical sections of the functionally active organ, con- sists chiefly of the compact ovarian stroma that is composed of peculiar spindle- shaped connective tissue-cells, from .01 5-. 030 mm. in length and about one-fifth as much in width, and fibrillar intercellular substance. The stroma-cells, which some- what resemble the elements of involuntary muscle in appearance, are arranged in Ovarian stroma Immature . primary ( follicle Follicle beginning ;,; to grow Stratum granulosum Ovum \ Theca- Section of cortex of ovary of young woman, showing primary and growing follicles within ovarian stroma. X 190. 1988 HUMAN ANATOMY. Blood-vessel Connective- jj tissue stroma bundles that extend in all directions (chiefly, however, obliquely vertical to the surface) and are seen cut in different planes. Immediately beneath the germinal epithelium covering the surface, the stroma-elements are disposed with greater reg- ularity and form a compact superficial stratum, the tunica albuginea. Embedded within the stroma lie the most characteristic components of the cortex, the egg-sacs or Graafian follicles. These are seen in different stages of development, but for the most part are small, inconspicuous, and immature, in the human ovary being much fewer and less prominent than in many other mammals. Corresponding with their stages of development the egg-sacs may be divided into primary, growing, and ma- turing follicles. In general, the youngest lie nearest the surface, the more advanced deeper and towards the FIG. 1686. medulla, while those ap- proaching maturity ap- pear as huge vesicles that occupy not only the entire thickness of the cortex, but often produce marked eleva- tion of the free surface. The medulla, the vascular zone of the ovary, consists of loosely disposed bundles of fibre-elastic tissue sup- porting the blood-ves- sels, lymphatics, and nerves. In the mature organ, with the excep- tion of the encroaching ripening Graafian folli- cles, egg-sacs are not found within the me- dulla. The larger ves- sels are accompanied by bundles of involuntary muscle prolonged from the utero-ovarian ligament through the mesovarium and the hilum into the medulla. The veins are particularly large and appear in sections as huge blood-spaces of irregu- lar outline in consequence of their tortuosity and plexiform arrangement. Follicles and Ova. The immature primary follicles (folliculi oophori primarii) are micro- scopic in size (from .04-. 06 mm. in diameter) and vary greatly in number, in the ovaries of young adults forming an incomplete and scattered single or, at most, double layer. Each follicle consists of the centrally situated young egg (ovulum) surrounded by a single layer of flattened epithelium or mantle cells (Fig. 1685). Immediately outside the latter lies the stroma, in the interstices of which the young egg-sacs are lodged. The primary ova are approximately spherical and measure from .O35-.045 mm. in diameter in ordinary sections, but a third more in the fresh unshnmken condition (Nagel). They possess a finely granular cytoplasm, a centrally placed spherical nucleus, about .016 mm. in diameter, and a nucleolus. The primary ova may remain for years, sometimes from early infancy to advanced age, practically unchanged, until they undergo either atrophy, as do most of them, or further growth leading, under favorable conditions, to the development of the mature sexual cell. Of the thousands of primary eggs contained in the ovaries just before puberty, only comparatively few attain perfection. Sooner or later, but at some uncertain time, the primary follicles enclosing ova destined for complete development enter upon a period of active growth, the earliest indication of which is the con- version of the flat mantle cells of the egg-sac into a single layer of cuboid epithelium. In addition to increasing sixe, the growing follicles are distinguished by rapid prolifera- tion of the cuboid epithelium, which results in the production of a stratified follicular epithe- lium that surrounds the ovum. Outside these polygonal elements the stroma becomes con- densed into a connective-tissue envelope or theca (thcca folliculi). Increasing in thickness, the latter is subsequently differentiated into two layers, an outer (tunica externa), consisting of Section of medulla of ovary, showing numerous blood- vessels and fibro-muscular stroma. X 75- i THE OVARIES. 1989 centrically disposed connective-tissue fibres, and an inner (tunica interna), composed of round and spindle cells, and provided with numerous capillaries. After the follicular epithelium has been formed, the ovum itself begins to grow, the expansion proceeding uniformly and affecting all parts of the cell, including nucleus and nucleolus. It attains its maximum diameter com- paratively early and long before the follicle has reached full growth. Through the agency of the follicular epithelium, the egg becomes invested with a protecting envelope, the zona pellucida, after which little or no further increase in the size of the ovum takes place (Nagel). At first solid, the growing follicle is converted into a vesicle containing fluid by the vacuolation and breaking down of cells within the middle layers of the follicular epithelium, the resulting clefts fusing into a common space. The intra-epithelial cavity so formed contains accumulating fluid, the liquor folliculi,.i\ia.t is supplied by the continued proliferation, vacuolation, and destruction of the follicle cells and by the transudation from the surrounding blood-vessels. This fluid increases in amount to such an extent that it soon occupies the greater part of the expanding egg-sac, now entering upon its final stage of growth. The maturing follicles (folliculi oophori vesiculosi) occupy the deeper parts of the cortex and reach to the medulla. With their expansion and consequent requirement of space, the vesicles seemingly rise, appropriating more and more of the cortex, until the entire thickness of the latter, and sometimes a part of the medulla in addition, is occupied by the ripe follicle, which just before its final rupture attains a diameter of from 1-2 cm. or more, and appears on the FIG. 1687. Surface epitheliunv ^-VX^-FF^^S*- Primary follicles ~^r ,. : ' . Theca of follicle rr-; : .' . , ir" Stratum granulosum ,. N >, <\ , V Zona pellucida . /" " Cavity filled by liquor folliculi Section of ovary, showing partially developed Graafian follicle. X 100. free surface of the ovary as a tense rounded elevation. After liberation of the ovum, the folli- cle is converted into the conspicuous corpus luteum (page 1990). Seen in section, the wall of the ripe follicle, now known as the Graafian follicle, consists of a well-developed capsule or fheca (from .I4-.20 mm. in thickness), of which the outer layer is a lamellated fibrous membrane, and the inner tunic is composed of looser connective tissue containing numerous peculiar large cells which, as maturity approaches, exhibit granularity and a faint yellowish color. Next the inner layer of the capsule lies a delicate membrana propria, against the inner surface of which is applied the stratum granulosum, composed of the outer layers of the follicular epithelium that bound externally the fluid-space of the vesicle. At one point, always opposite the place where the follicle ruptures (stigma), the stratum granulosum is prolonged into a pedunculated spherical mass of epithelial cells that projects into the cavity occupied by the liquor folliculi. This mass (cumulus oophorus) contains the egg and on section appears as a ring ( discus proligerus ) that encircles the zona pellucida and the enclosed ovum and consists of two or three layers of epithelial cells. Those next the zona are elongated, with their ends directed towards the ovum pointed and prolonged into delicate processes that are attached to or penetrate within the zona pellucida. The latter, from .ooy-.on mm. in thickness, is the product of the surrounding follicular cells and does not form a part of the ovum proper. The radial striations which the envelope sometimes exhibits (hence the name, zona radiata, under which it is often described) are probably due to the processes of the epithelial cells and not to the existence of minute canals (micropyfes) seen in the eggs of many lower animals. 1990 HUMAN ANATOMY. FIG. 1688. The human ovum when about to be liberated from the Graafian follicle pos- sesses a diameter of from .16-. 20 mm. Its cytoplasm, or rite/his, exhibits differ- entiation into a peripheral protoplasmic and a central dciitoplasmic zone. According to Nagel, within the former are to be distinguished a narrow slight superficial marginal layer, apparently homogeneous and free from yolk-particles, and a finely granular zone containing mi- nute and scattered deutoplas- mic granules. The dark or central deutoplasmic zone is conspicuous on account of the irregular refraction of the enclosed yolk-particles that represent the important nutri- tive materials for the embryo contained in the eggs of birds and reptiles, but which in the mammalian ovum, especially in that of man, have been for the most part lost during the evolution of the higher types. Beyond a slight condensation of the surface, the presence of a distinct cell-wall, or zv- ttiline membrane, in the mam- malian ovum is doubtful. In the fresh condition the egg- Cytoplasm is usually closely ~~i:~.j + *u^ ' 11 -j applied to the ZOna pellucida (Ebner), the narrow inter- vening cleft that is sometimes seen being the perivitelline space. Embedded within the deutoplasmic zone, and always eccentrically placed, lies the spherical germinal reside, as the egg-nucleus is termed. The vesicle measures from .030-. 045 mm. in diameter, is bounded by a sharply defined double-contoured nuclear membrane, and contains the germinal spot or nucleolus (from .004-. 008 mm.) and the nuclear reticulum. Corpus Luteum. The causes leading to the final rupture of the Graafian follicle are still uncertainly known, although in the light of later researches the older view, attributing the bursting of the ripe vesicle to mechan- ical overdistention induced by accumulation of the liquor folliculi, is inadequate. According to Nagel, when the follicle approaches maturity the inner layer of the theca becomes the seat of great activity. The blood-vessels in- crease in size and number and the cells undergo not only rapid proliferation, but extraordinary growth, the enlarged elements becoming filled with a peculiar yellowish sub- stance and transformed into lutein cells. In consequence of this activity, the formerly smooth theca becomes thickened and wavy and projects into the cavity of the follicle as vascular papillae and ridges. The encroachment thus effected gradually forces the contents of the vesicle towards the surface and that part of the dis- tended follicular wall possessing least vitality and resist- ance, until, finally, rupture takes place. Coincidently with the proliferation of the lutein cells, the follicular epithelium undergoes fatty change which results in the breaking down of the cumulus and the setting free of the ovum, encircled with the cells of the discus proligerus, into the cavity of the ogg-sac. When rupture of the follicle occurs, the expulsion of the egg and the epithelial cells immediately surrounding it is followed by hemorrhage Almost mature human ovum taken from fresh ovary. Ovum, with germinal vesicle and spot, is encircled by clear zona pel'lucida, which is surrounded by cells of the follicular epithelium. X 300. (Waldeyer.) FIG. 1689. Ligament Ovary has boon laid opi'ti by longitudinal incision, exposing follicli-s ami coi;>us luteum. THE OVARIES. 1991 Central connective tissue into the cavity of the former egg-sac, which now becomes converted into a corpus luteum. The latter, long known as the corpus luteum verum when associated with preg- nancy, grows to huge dimensions and forms a conspicuous oval mass that may approach 3 cm. in length and occupy a considerable part of the entire cortex. When impregnation does not take place, the yellow body (now called the corpus luteum spurium) is smaller, seldom exceeding 1.5-2 cm. in diameter. The classic distinction of "true" and "false," apart from difference of size, has no anatomical basis, since both forms possess identical structure. The assumption that the presence of a large corpus luteum is positive proof of the existence of pregnancy, must be accepted with caution, since yellow bodies of unusual size are sometimes observed in ovaries of virgins. Shortly after the rupture of the follicle and the replacement of its contents by blood, the opening in the wall of the egg-sac is closed. The rapid proliferation and growth of the lutein cells pro- duces an irregularly plicated FIG. 1690. wall of increasing thickness that encloses the remains of the degenerating follicular epithe- lium (granulosa) and invades the hemorrhagic mass. The latter is gradually absorbed until, finally, the encroaching projections of lutein cells and connective tissue meet and the cavity of the follicle obliter- ated, its former position being subsequently indicated by a central core of connective tis- sue. The cells of the stratum granulosum, the original epi- thelial lining of the egg-sac, entirely disappear and take no direct part in the formation of the corpus luteum, their function during the develop- ment of the Graafian follicle having been to contribute the liquor folliculi (Schottlaender). Along with the proliferating masses of lutein cells, strands of connective tissue are car- ried inward from the theca, whereby, after a time, the yel- low body becomes broken up by numerous radially disposed vascular septa and their prolongations. With the production of a solid corpus luteum and the absorption of the blood (evidences of which latter for a long time remain as hematoidin crystals), the active role of the lutein cells is finished. These elements now lose their distinc- tive yellow pigment (luteiii), undergo fatty metamorphosis, and finally entirely dis- appear. With the subsequent shrinking and decrease in the vascularity of the corpus luteum, the connective tissue, which now constitutes the entire mass (corpus fibro- sum), undergoes hyaline change, becoming clear and non-fibrillar. In consequence the aging corpus luteum loses its former appearance and is transformed into an irreg- ular body, light in color and sinuous in outline, sometimes known as the corpus albicans (Fig. 1691). This gradually suffers absorption, but remains for a consider- able time, especially when associated with pregnancy, as a conspicuous light corru- gated area within the cortex, the last traces of its scar-like tissue finally disappearing in the ovarian stroma. The greatly increased vascularity, within the wall of the ripe Graafian follicle and later around the corpus luteum, subsides as the yellow body Lutein cells Proliferating * cells of inner layer of theca fcijr- Outer layer *" of theca ^~~ Blood-vessels Section of human corpus luteum. X 7. 1992 HUMAN ANATOMY. undergoes regression, until all the new vessels concerned in its nutrition have disap- peared and the circulation of that particular part of the ovary is permanently reduced. The function usually ascribed to the corpus luteum is that of filling the empty follicles and thus restoring the equilibrium of circulation and tension. Clark l regards the corpus luteum as a preserver of the circulation, since, when performing its functions most perfectly (during the earlier years of menstrual life), it effects the elimination of the effete follicle and the superfluous blood- vessels without leaving dense and disturbing scars. Later in life, however, when the ovarian stroma becomes denser, the corpora lutea are less efficient and are incompletely absorbed, their remains impairing the circulation until, finally, the follicles are no longer matured and ovulation ceases. The origin of the lutein cells has long been a subject of discussion, and even at present two opposed views share the support of eminent anatomists. According to the older theory, advanced by Baer, these cells are modified connective-tissue elements, derived from the pro- FIG. 1691. Blood-vessels Mesosalpinx Corpus luteum Mesovarium Corpora lutea Remains of corpora lutea Sections of Fallopian tube Cross-section through ovary, oviduct, and part ot broad ligament. X 6. liberation of the cells of the inner layer of the theca folliculi. The other view, formulated by Bischoff, regards the lutein cells as modified follicular epithelium. In the foregoing sketch of the corpus luteum, the lutein cells are ascribed to the theca, a conclusion based upon the con- vincing observations of Nagel, Rabl, and Clark, and confirmed by the writer's own studies. Sobotta, on the other hand, is most positive in his support of the follicular origin of the lutein cells, based upon an exhaustive investigation on the ovaries of the mouse and rabbit. The difficulty of obtaining human corpora lutea in the earliest stages places the conclusions as to man not beyond challenge. Vessels. The arteries supplying the ovary are four or five branches that arise from the anastomosis of the ovarian artery with the ovarian branch of the uterine. The trunks (aa. ovaricce proprice} given off from this anastomotic arch pass to the ovary between the layers of the mesovarium and, entering through the hilum as closely grouped tortuous vessels, reach the medulla. According to Clark, 2 whose description is here followed (Fig. 1692), immediately after gaining the medulla each stem divides into two branches, the medullary or parallel arteries, that proceed in a direct course. towards the opposite free margin of the organ, lying just beneath the cortex* to which they distribute cortical branches at regular intervals. In their course to the periphery the cortical branches, losing the characteristic corkscrew-like 1 \\ist- iu^s of the parent stems, supply hundreds of follicidar hcigs to the egg-sacs, each of the latter being provided with a rich vascular net-work anastomosing with two or more follicular branches an arrangement of ^ivat importance in assuring an adequate blood-supply for the growth of the follicle (Clark). At the periphery, the cortical arterioles pass into the veins through an intervening capillary net-work. 1 Archiv f. Anat. u. Physioloi;., Anat. Abth., 1898. 1 Welch Anniversary Contributions, 1900. THE OVARIES. 1993 FIG. 1692. Superficial anastomoses Follicular anastomoses Follicular branches The veins follow the general arrangement of the arteries within the cortex and medulla ; the pairs of parallel veins, however, do not unite into single stems, but emerge from the hilum as independent tortuous trunks. Within the mesovarium they are interwoven with the bundles of involuntary muscle, and when distended present a conspicuous venous complex (bulb us ovarii). The veins proceeding from the ovary (vv. ovaricce proprite) become tributary to both the uterine and the ovarian (pampiniform) plexus. The lymphatics begin in the cortex as net-works within the thecse surrounding the Graafian follicles and as lymphatic clefts within the ovarian stroma. From these radicles the larger and irregular channels enter the medulla, where they form con- verging stems that follow the blood-vessels and leave the hilum of the ovary usu- ally as nine larger trunks (Polano) that pass upward along the free border of the suspensory ligament and empty into the lumbar lymph-nodes surrounding the aorta. Occasionally, but by no means constantly, the ovarian lymphatics communicate with those from the fundus of the uterus and the oviduct. The nerves supplying the ovary are de- rived from the sympathetic plexus surrounding the ovarian artery (plexus arteriae ovaricse), which, in turn, is formed by contributions from the renal and aortic plexuses and corresponds to the spermatic plexus in the male. The small nerve-trunks, composed for the most part of non-medullated fibres, accompany the arteries through the hilum into the ovary, where they are distributed chiefly to the walls of the blood-vessels, around the larger of which terminal plexuses are formed. From the fairly close plexus within the cortex, additional mi- nute twigs pass to the periphery, to end in close relation with the surface (germinal) epi- thelium, and others to the follicles. The ulti- mate relation between the latter and the sur- rounding net-works is uncertain, but it is probable that the nerve-fibrillae end in the walls of the follicular blood-vessels and do not penetrate beyond the inner tunic of the theca, the terminations within the follicular epithelium described by some ob- servers needing confirmation. Sensory fibres are probably contained within the cortical branches. The claimed existence of minute, true, sympathetic ganglia within the medulla, has not been established. Development. The primary development proceeds from the indifferent germinal ridge which is early formed on the median surface of the Wolffian body (page 2038). Whether, as usually accepted, the ova in common with the follicular epithelium are directly derived from the modified mesothelium (germinal epithelium) covering the sexual ridge, or are the descendants of germ-cells early set apart from the somatic cells for the special role of reproduction, remains to be decided, al- though evidence in support of this latter hypothesis the continuity of the germ- cells is accumulating from observations on the lower animals, in which the origin of the primordial sex-cells is less obscured. In human embryos of 12 mm. in length, among the cells of the germinal ridge, certain elements are already distinguished by their exceptional size and large, clear nuclei. These are the primary sexual cells, the primordial ova (Fig. 1717), usually regarded as originating from the transformation of the germinal epithelium. At first the latter and the subjacent stroma of the Wolffian body are well differentiated from each other. This demarcation is soon lost in consequence of the active inter- growth which takes place between the proliferating germinal epithelium and the in- growing vascular connective tissue of the Wolfrian body the two chief factors in the histogenesis of the ovary. As the mass of epithelial elements increases, it becomes broken up by the con- nective-tissue strands into large tracts, composed of the primary ova surrounded by Arteria propria Ovarian artery Diagram illustrating arranj vessels of ovary. Ovarian veins ement of blood- Clark.) 1994 HUMAN ANATOMY. FIG. 1693. Germinal epithelium Primordial ovum Ova multitudes of the smaller and less specialized cells of the germinal epithelium. The larger tracts are subdivided into smaller spherical cell-aggregations (the egg-balls of Waldeyer) by the continued intergrovvth and mutual invasion of the tissues, and the " egg-balls," in turn, are broken up by the same process until the final division results in the isolation of the ultimate groups, the primary follicles, that include the primary ova surrounded by a single layer of flattened germinal epithelium. In places the larger compartments are cylindrical and attached to the germinal epithe- lium, appearing as solid outgrowths connected with the surface ; to them Prliiger gave the name "egg-tubes" and attributed an aggressive invasion. Since the con- nective tissue of the Wolffian stroma first invades the deeper stratum of the germinal epithelium, this region, the fu- ture medulla of the ovary, is subdivided into the ultimate groups of cells, the primary fol- licles, earlier than the more su- perficial and younger layers, this genetic relation being seen in the fully developed ovary, in which the youngest and least mature follicles always occupy the peripheral zone. The most superficial stratum of the ger- minal ridge remains as the ger- minal epithelium that covers the exterior of the ovary and replaces the usual peritoneal mesothelium plates. The details of the trans- formation of the primary folli- cles, consisting of the ovum and the investing single layer of mantel-cells, into the ripening Graafian follicles have been de- scribed (page 1988). Of the thousands of primary follicles within the young ovary (esti- mated by Waldeyer at over 100,000 in the two ovaries of the new-born* child) very few reach maturity,and by advanced life nearly all have disappeared. This reduction begins during intrauterine life and first affects the fol- licles situated within the deeper parts of the ovary destined to become the medulla, from which the ova are later entirely absent. The remains of these earl}- follicles probably account for certain of the minute epithelial bodies occasionally seen in the medulla of young adults. Section of developing ovary from human embryo, wing intergrowth between stroma tissue derived from We showing intergrowth between germinal epithelium a'nd "Yolfnanbody. Numbers of follicles within the cortex also are continually undergoing; destruction. This affects especially the primary follicles while they lie naked wjthin the stroma, and are unpro- vided with a theca, the ovum undergoing hyaline degeneration and, along with the mantel- cells, finally entirely disappearing within the ovarian stroma. Beginning in the young ovary long before puberty, as well as throughout the period of sexual maturity, certain egg-sacs are continually transformed, more or less fully, into (iraafian follicles that develop to a certain stage and an- then arrested, after which they enter upon regression, degenerate, and finally may completely disappear. This process, known as atn-sia of the follicles, is probably closely related to alterations in their blood-supply ((.Mark). With possibly few exceptions, the formation of new follicles ceases during the first few years after birth, the supply developed early in life being in such lavish excess of all possible needs that ample provision is made against dearth of reproductive cells. Infrequently follicles are encountered in which two or more ova an- (in-sent. This condition results from the inclusion of more than a single primary egg when the follicle was formed, and not from division of an ovum already enclosed, since after the mantel-cells surround the ovum it is PRACTICAL CONSIDERATIONS: THE OVARY. 1995 doubtful whether the latter ever undergo division. In certain cases it is also possible that the delicate partition separating two closely applied follicles may disappear, the ova thence occupying the common sac ( Ebner. ) The changes in form and position which the ovary undergoes during life are conspicuous. In the new-born child the organ is relatively long (from 12-18 mm.) and narrow (from 4-5 mm.), triangular on cross section, and lies entirely above the brim of the pelvis, with its long axis transversely placed and its inner pole close to the fundus uteri. During the first two years, owing to the increasing capacity of the pelvis and interabdominal pressure and its attachments to the uterus, it gradually sinks into the pelvic cavity, during this descent the direction of its long axis becoming more vertical. At birth the surface of the ovary is marked with furrows and folds, inequalities that disappear as the organ expands in consequence of the rapid increase in its stroma-tissue during the first year or two. Later the growth of the young ovary is gradual and slow, until the advent of sexual maturity, from the twelfth to the fifteenth year, when the organ undergoes sudden increase and acquires its definite form and size. Further enlargement, however, usually takes place in women who bear children, until towards the fortieth year. The repeated development and rupture of the Graafian follicles and the formation of the corpora lutea produce irregularity of the surface, which becomes knobbed and scarred and contrasts strongly with the smooth organ of childhood. After the cessation of menstruation, about the forty- fifth year, gradual decrease (involution) of the ovary follows, until the organ may be reduced to a dense fibrous body of less than half of the original size. Variations. Abnormalities in the sexual glands of the female are, for the most part, referrible to developmental deviations. Incompleteness or modification of its descent affect the position of the organ, so that it may retain its original suprapelvic position and lie above or upon the psoas magnus muscle ; or it may follow the pull of the round ligament (the homologue of the genito-inguinal ligament of the male, page 2006) and pass partly or entirely through the inguinal canal into the labium majus. Variations of position in the adult are commonly asso- ciated with diseased conditions of the peritoneum and adjacent organs and are therefore patho- logical. The adult ovary may present marked deviations from its typical form, sometimes being unusually long, spheroidal, flattened, triangular, crescentic, or irregular. Supernumerary ovaries, varying in size from a hempseed to a small hazelnut, are not in- frequent, occurring in from over 2 (Beigel) to 4 (Rieffel) per cent. Their usual situation is along the white line marking the transition of the peritoneum into the germinal epithelium. Isolation of a portion of the ovarian anlage, often probably by a peritoneal band (Nagel), is responsible for these bodies, which consist of normal follicle-bearing ovarian tissue. PRACTICAL CONSIDERATIONS : THE OVARY. Since the ovaries project below the Fallopian tubes from the posterior surface of the broad ligaments, in seeking for them in abdominal operations the hand should be passed outward from the posterior surface of the uterus along the broad ligament, on each side. In its usual position the long axis of the ovary is approximately vertical, its external surface lying against the pelvic wall close to the obturator vessels and nerve. The ureter and uterine artery lie behind and below it. Prolapse of the ovary occurs most frequently as the result of subinvolution after labor. If involution is in any way arrested or rendered incomplete, the conditions favorable for prolapse of the ovary will be present, increased weight of the ovary and relaxation and lengthening of its attachments. The left ovary is more frequently prolapsed than the right, because it normally becomes more enlarged during pregnancy, and therefore suffers more from subinvolu- tion, and because the arrangement of the veins on the left side is such that venous congestion is very liable to occur (Penrose). An analogous anatomical condition exists to that which, in the male, favors left-sided varicocele, the left ovarian vein emptying into the renal vein at a right angle, while the right ovarian vein empties into the vena cava at an acute angle (page 1961). In complete prolapse the organ lies in Douglas's pouch between the rectum and the posterior vaginal wall. There is apt to be pain on walking, because the ovary is then compressed between the cervix and the sacrum, and on coitus or defecation, 1996 HUMAN ANATOMY. because of direct trauma. The pain is often nauseating and may be felt in the breast on the same side. In spite of its small size the ovary gives origin to a great variety of tumors and cysts which may grow to enormous proportions, filling and distending the abdomen. As they grow they at first crowd the uterus and other pelvic structures towards the opposite side ; later they ascend into the abdomen, drawing the attached structures upward with them in their pedicles. The pedicle is the base of attachment, and consists of the same anatomical structures as those by which the ovary is normally attached. The relations of the structures making up the pedicle to one another will vary greatly according to the manner in which the tumor grows. This relationship should be studied carefully to establish a correct diagnosis as to the origin of the tumor. The anatomical structures involved in the pedicle are the mesovarium^ mesosalpinx, Fallopian tube, and broad ligament. THE FALLOPIAN TUBES. The Fallopian tube (tuba uterinae) or oviduct is in principle the excretory canal of the sexual gland, the ovary, since it conveys the ova liberated from the Graafian follicles to the uterus, "into which it opens. The relation between the ovary and its duct, however, is exceptional in that these organs are not continuous, but only in ap- position, the ova liberated from the ovary finding their way into the expanded end of FIG. 16)4. Sigmoid artery Internal iliac vessels External iliac vessels Ureter Suspensory ligament of ovary Right ovary Fimbrias of oviduct Ligament - of ovary Oviduct Round -' ligament Bladder Pelvic organs of young woman, viewed from above and in front; hardened hi situ and undisturbed Kimbriated extremity of right oviduct lay in position shown and not in relation with o\xry. the oviduct. This canal, one on each side of the body, lies within the free margin of the upper division of the broad ligament, known as the mesosalpinx, and extends from the uterus medially to the ovary laterally, in relation to the inner surface of which it ends after numerous windings. The entire length of the tube is about 11.5 cm. (4^ in.), although variations from 6-20 cm. (2^-7^ in.) have been observed. Emerging from the lateral angle of the fundus uteri, in the immediate vicinity and just above the uterine attachments of the utero-ovarian and round ligaments, the first part of the 1 tube is narrow and THE FALLOPIAN TUBES. 1997 ^comparatively straight and constitutes the isthmus (isthmus tubae uterinae), about .35 cm. ( 1 2/6 in. ) in length and from 3-4 mm. in diameter. Throughout the succeeding 8 cm. (3^ in.) of the tube, known as the ampulla (ampulla tubae uterinae), the diameter gradually increases (from 6-8 mm.) until the canal suddenly expands into the terminal trumpet-shaped infundibulum. The margins of the latter are prolonged and slit up into long, irregular processes, \hzjimbri(e, from 10-15 mm. in length, the resulting Jimbriatcd extremity of the tube resembling, when examined in fluid, an ex- panded sea-anemone (Nagel). One of the fimbriae (timbria ovarica) is usually longer than the others, attached to the free border of the mesosalpinx and stretches towards the ovary, the tubal pole of which it often, but by no means always, reaches. The lumen of the oviduct varies greatly at different points. Beginning at the lateral angle of the uterine cavity as a minute, inconspicuous opening (ostium uterinum tubae), -commonly obscured by mucus and about i mm. in diameter, the canal traverses the uterine wall (pars uterina) and gains in size and longitudinal folds, so that on cross- section the isthmus presents a stellate lumen. Within the ampulla the plications of the mucous membrane become progressively more marked, appearing in transverse sections as a complex figure of primary and secondary folds (Fig. 1695) that greatly encroach upon the calibre of the tube. The folds are continued into the infundibulum and onto the inner side of the fimbriae. The outer or ovarian end of the oviduct opens directly into the peritoneal cavity by a small aperture (ostium abdominale tubae), 2 mm. or less in diameter, that lies at the bottom of the infundibulum and is produced by local contraction of the muscular tissue of the wall of the tube, a special sphincter, however, not being demonstrable. The mucous lining of the oviduct is continued from the infundibulum onto the fimbriae, the line of transition into the peri- toneum following the bases and outer sides of the fringes. The exceptional relation of the tubal lining to the serous membrane, this being the only place in the body where a mucous tract opening onto the exterior communicates with a closed serous sac, is referrible to the similar original relation of the embryonal Miillerian duct from which the Fallopian tube is directly derived (page 2038). Course and Relations. Since each Fallopian tube occupies the free border of the broad ligament, changes in the position of the uterus affect the course of the oviduct. From the upper angle of the uterus the tube may, therefore, first pass out- ward towards the ovary in a strictly transverse direction, or describe a gentle forward or backward curve, depending upon the position of the fundus uteri, this part of the tube, however, never being tortuous. On gaining the uterine or lower pole of the ovary, it there bends upward and winds obliquely, from below upward and backward, across the median surface of the ovary, close to the anterior border and tubal pole, to the convex posterior margin, where the tube bends sharply downward, its fimbriated end being in relation with the lower and back part of the median surface. When in its usual position, the ovary is, thus, partly covered not only by the tortuous oviduct itself, but also necessarily by the mesosalpinx in which the tube lies, so that when viewed from above the ovary is often entirely hidden by the Fallopian tube and the attached portion of the broad ligament. In consequence of this arrangement, the ovary is partly surrounded by a hood of serous-membrane and lies within a pocket, known as the bursa ovarii, which may facilitate the entrance of the liberated ova into the Fallopian tube. In its course from the uterus to the ovary the oviduct lies in front of and generally parallel with the utero-ovarian ligament and is overlaid by the coils of the small intestine. As the tube ascends and arches over the ovary, the intestinal coils cover its medial surface, the sigmoid colon also occasionally being in relation on the left side. In formalin-hardened subjects, with otherwise normal pel- vic contents, we have so often found the termination of the Fallopian tube lying away from the ovary, that Merkel's suggestion, that the assumed constant close relation between the fimbriated extremity and the ovary may sometimes, at least temporarily, be wanting during life, seems well founded. Structure. The wall proper of the Fallopian tube, consisting of the mucous and muscular coats, lies embedded within the loose connective tissue of the broad ligament (tunica adventitia) surrounded by the peritoneum, which completely invests the tube with the exception of the narrow interval through which the tubal vessels -and nerves pass. The wall is thickest and firmest in the isthmus, less so in the 1998 HUMAN ANATOMY. FIG. 1695. Mucosa- Epithelium r^f^r'T :'M -'- :' .'.- Lumen ampulla, and thinnest and most relaxed in the infundibulum and fimbriae. The mucous membrane is thrown into longitudinal folds, which increase from 515 low ridges in the commencement of the isthmus to double the number in the ampulla, where they attain a much greater height as well as complexity of arrangement, the main folds being supplemented by secondary and tertiary ones, so that in transverse section the lumen appears almost occluded by branching villus-like projections. The surface of the mucosa is covered with a single layer of columnar epithelium (from .015 .020 mm. in height) provided with cilia that produce a current directed from the infundibulum towards the uterus, and thus, while facilitating the progress of the ova along the tube, retard the ascent of the spermatozoa. The elaborate plications and recesses within the outer part of the ampulla favor the temporary retention of the sexual cells and thereby promote the chance of their meeting, fertilization usually taking place within this part of the tube. The vascular connective-tissue stroma of the folds, which in the chief plications may reach a thickness of . 2 mm. , within the acces- sory folds is reduced to a narrow interepi- thelial layer in places measuring less than the height of the covering- cells. The tunica pro- I )r ' a ^ ^ ie mucosa i s directly continuous with the intermuscular connective tissue, and, with the exception of a few bundles prolonged into the deepest part of the mucous mem- brane, does not contain muscular tissue. The muscular coat, most robust towards the uterus and thinnest at the infundibulum (therefore the reverse of the arrangement of the mucosa), includes an inner circular and an outer longitudinal layer of involuntary muscle. At the isthmus, where the firmness of the tubal wall depends chiefly upon the muscular coat, the circular layer is the thicker (from .5-1 mm.) and the longitudinal one repre- sented by an incomplete stratum of muscle-bundles. Towards the infundibulum, on the contrary, the longitudinal layer is better developed, the circular-muscle being- reduced to .2 mm. or less in thickness. The surrounding fibrous tissue, sometimes regarded as a distinct coat of the tube (tunica advent ilia), and the outer serous in- vestment are only the usual connective tissue and peritoneal constituents of the broad ligament, and, therefore, call for no further description in connection with the oviduct. As evidenced in pathological conditions, and especially in tubal pregnancy, the wall of the oviduct is capable of distention to a remarkable degree. Vessels. The arteries supplying the oviduct are derived from the tubal branches of the uterine and ovarian vessels. The branch from the uterine artery (rn>nus tubarius a. nterinai) passes in front of the utero-ovarian ligament to the median end of the oviduct, along the under side of which it courses outward until it meets the tubal branch from the ovarian artery. The latter (rain us tu bar ins a. ovariccz} passes within the mesosalpinx, in front of the ovarian timbria, towards the outer part of the ampulla, distributing branches to the fimbriated extremity, and mesially joins the tubal branch from the uterine. From the anastomotic branch so Fold cut- Circular- muscle Cross-section of oviduct near outer end of ampulla. X 35 PRACTICAL CONSIDERATIONS : FALLOPIAN TUBES. 1999 formed numerous twigs are given off to the wall of the Fallopian tube and to the mesosalpinx. Those distributed to the oviduct gain the canal along its nonperitoneal tract between the peritoneal reflection and, piercing the wall, break up into capillary net-works within the muscular and mucous coats. The veins, which begin within the walls of the tube, especially between the muscular layers, and as a subserous net-work, follow the arteries and become tributary to both the uterine and ovarian trunks. The lymphatics, after emerging from the wall of the tube, form three or four stems that accompany the blood-vessels and pass in front of the attached border of the ovary. For the most part they follow the ovarian lymphatics through the sus- pensory ligament to become finally tributary to the lumbar lymph-nodes surrounding the aorta. It is probable that some of the lymphatics of the tube communicate with those of the fundus uteri (Poirier, Bruhns). The nerves supplying the Fallopian tube, numerous and chiefly sympathetic fibres, follow the arteries and, therefore, reach the oviduct from both the ovarian and the uterine plexus. Within the subserous tissue they form a pcritubal plexus from which twigs penetrate the wall of the canal and are distributed principally to the muscular tissue, some filaments taking part in the production of a subepithelial plexus within the mucous membrane (Jacques). Development and Changes. The early development of the oviducts is directly associated with that of the embryonal Miillerian ducts (page 2038), the unfused portions of which the tubes represent. The margin of the abdominal open- ing (the persistent original evagination from the primary body-cavity or ccelom) is at first cushion-like, but soon exhibits indentations which, by the fifth foetal month, devek>p into distinct fimbriae. At birth, while smaller, the latter possess their charac- teristic appearance and are lined by ciliated columnar epithelium that covers the plications of the tube. The upper (outer) segment of the oviduct participates in the migration incident to the descent of the ovary, lying for a time within the abdomen above the pelvic brim. In contrast to the ovary, the tube early acquires its definite form, in the new-born child presenting its chief characteristics, although it is more twisted than later and the fimbriae are still small ; the plication of the mucosa, how- ever, is almost fully developed. During childhood, beginning at the uterine end, the tube becomes less tortuous and the fimbriated extremity assumes its definite propor- tions. In advanced age, the oviduct suffers atrophy, losing its former tortuosity, the infundibulum becoming flaccid and the fimbriae shrivelled. Owing to the atrophy of the muscle its wall becomes thinner ; the ciliated columnar epithelium is replaced by cuboidal cells, the lumen narrows and in places may disappear in consequence of the adhesion of the mucous folds. Variations. Apart from anomalous situation depending upon malposition of the uterus and ovary, in which the tube of necessity shares, the variations of the oviduct usually depend upon developmental faults traceable to imperfect or aberrant formation of the Miillerian ducts. Retention of the foetal tortuosity, stunted development or entire absence may affect one or both tubes. Complete doubling of the oviducts may occur in association with supernumerary ovaries. Occasionally partial duplication of the tube is observed, consisting of a short canal ending in a diminutive fimbriated extremity in the vicinity of the infundibulum. Such accessory tubes are to be referred probably to a repetition of the invagination that normally produces the infundi- bulum (Nagel). Quite frequently the oviduct is beset with from one to three fringed accessory openings that may lie close to the fimbriated end, or at a distance from the latter along the tube. The explanation of these apertures is uncertain, although it seems most probable that they result from aberrant development of the Miillerian duct, rather than as secondary perforations of the tube and prolapse of its mucosa, as held by Nagel and others. PRACTICAL CONSIDERATIONS : THE FALLOPIAN TUBES. The function of the Fallopian tube is to transmit the ovum from the ovary to the uterus, the ciliated epithelium of the tube favoring movement in that direction. An impregnated ovum may adhere to the wall of the tube, giving rise to an ectopic gestation (tubal pregnancy). Such pregnancy may occur in the ampulla, the most usual place, in the infundibulum (tubo-ovarian pregnancy), or in the intra-mural portion of the tube, i.e., that part traversing the wall of the uterus. 2000 HUMAN ANATOMY. The chief causes of tubal pregnancy are pathological or abnormal conditions of the tube. The more important of these are: (a) congenital, such as exaggerated con- volutions, diverticula, and atresias ; (b) sagging and attachments by adhesions dis- torting the tube ; (c) pressure from surrounding structures ; (d ) thickening of the tubal walls, interfering with peristalsis ; and (e) destruction of the cilia or narrowing of the tube following salpingitis. Complete occlusion of the tubes of both sides would result in sterility. The great danger of ectopic gestation is that of hemorrhage following rupture of the tube by the growing fcetus. This will occur some time prior to the fourth month, and may be intraperitoneal, i.e., directly into the peritoneal cavity; or extraperitoneal, i.e., downward, cleaving the layers of the broad ligament, and finally rupturing the tube within the layers of the ligament ; or, in case the pregnancy is "interstitial," the rupture may be intrauterine. The intraperitoneal rupture usually takes place before the seventh week ; the extraperitoneal usually from the seventh to the twelfth week. If the fcetus should survive the primary rupture in the extraperitoneal variety, secondary rupture into the general peritoneal cavity may occur later, and the ovum may go on to full term within the abdominal cavity. The Fallopian tube offers a passageway in the opposite direction for the entrance of infections, especially gonorrhceal, from the vagina and uterus into the peritoneal cavity. When inflammation involves the tube, it is followed soon by a closure of the fimbriated extremity, the fimbriae adhering to each other, to the ovary, or to some adjacent peritoneal surface. Later the uterine end of the tube also closes, and the pus which results from the infection now accumulates within the tube {Pyo- salpinx^) and may greatly distend it. If the infection is gonorrhceal, such a pus-tube without rupture is frequently unaccompanied by acute symptoms. Slight ruptures with leakage into the peritoneal cavity followed by sharp attacks of localized pelvic peritonitis often occur. A large rupture may give rise to a diffuse septic peritonitis, although the danger of this result in a case of chronic pyosalpinx, even if of enormous size, is far less than after acute gangrene of the appendix with escape of a relatively minute portion of its contents. In the former case a certain degree of immunity has probably been established during the slow formation of the pyosalpinx (Binnie) ; and moreover, in many such cases (61 per cent., Penrose) the contained pus has become sterile. When the inflammation is of a mild grade the accumulation may be of a serous character (hydrosalpinx), and may become so large as to reach half-way to the umbilicus. If hemorrhage occurs into the tube it is called an htzmatosalpinx. The proximity of the right Fallopian tube to the appendix should be recalled, as salpingitis on that side has not infrequently been mistaken for appendicitis, and vice versa. The right ovary is often connected with the meso-appendix by a fold of peri- toneum, the appendiculo-ovarian ligament ; and it is stated that the fact that this fold often contains a small artery which gives an additional blood-supply to the ap- pendix helps to account for the relative infrequency of appendicitis in females. RUDIMENTARY ORGANS REPRESENTING FCETAL REMAINS. The development of the reproductive organs (page 2042) emphasizes the fact that whereas, in the male, the Wolffian body and its duct play a very important r6le in the production of the excretory canals for the sexual gland, and .the Miillerian duct remains rudimentary; in the female, the converse is true, the Miillerian ducts forming the excretory canals the tubes, the uterus, and the vagina while the Wolffian structures are secondary in importance and give rise to only rudimentary and func- tionless organs, situated chiefly in the vicinity of the ovary and Fallopian tube between the layers of the broad ligament. These fcetal remains include the epoophoron, Gartner s duct, the paroophoron, and the vesicular appendages, which may be appro- priately described in this place. The Epoophoron. This rudimentary organ, parovariuni or organ of Rosenmuller, lies between the layers of the broad ligament (mesosalpinx ) in front of the ovarian vessels, in the area bounded by the ampulla of the oviduct, the ovarian fimbria and the tubal pole of the ovary. It is quite flat, triangular, or RUDIMENTARY ORGANS. 2001 trapezoidal in outline, and measures from 2-2.5 cnl - m length and about 1.75 cm. in width. It consists of from 8-20 narrow wavy canals, which, beginning with closed and slightly expanded ends, diverge from the vicinity of the hilum of the ovary and join, almost at right angles, a common chief duct that lies close and parallel to the oviduct and bears to the smaller tubules the relation of the back of. a comb to its teeth. The transverse tubules (ductuli transversi), the remains of the sexual tubules of the Wolffian body, may extend as far as the hilum, or, as in the young child, even penetrate into the medulla of the ovary and be continuous with the rudi- mentary medullary tubes therein found, since the latter, as well as the transverse tubules themselves, are vestiges of the same embryonic structures. The common longitudinal canal (ductus epoophori longitudinalis), closed at both ends, is a persistent portion of the Wolffian duct. From its embryological relations it is evident that the epoophoron is homologous with the epididymis (the transverse tubules corresponding to the ductuli efferentes and the coni vasculosi, and the longitudinal duct to the canal of the epididymis), since both are direct derivations from the Wolffian tubules and duct. In the erect posture, when in its normal position within the mesosalpinx, the longitudinal duct is approximately vertical and lies parallel with the Fallopian FIG. 1696. Ligament Epoophoron Oviduct f ovar y Ostium < I f abtlominale \ I / Cavity of uterus Ligament of ovary Oviduct laid open Hydatid of Morgagni Left ovary | V, --^ Round ligament Broad ligament Epoophoron r I Infundibulum Fimbriae Fimbria ovarica 'Round ligament Right ovary ^Vagina Broad ligaments, viewed from behind, have been stretched out and pinned, the posterior wall of uterus and vagina removed and right oviduct laid open. Ovaries do not occupy their normal position, their long axes here being horizontal instead of approximately vertical. tube, while the transverse tubules are horizontally disposed. The chief duct may be interrupted and connected with the secondary tubules in groups, or, on the other hand, it may be prolonged as Gartner's duct (page 2043) far beyond its usual length. In the child, the transverse tubules, from .3-. 4 mm. in diameter, usually possess a lumen throughout their entire length, but later in life the minute canals may undergo partial or complete occlusion and may be the seat of cystic dilatations. The walls of the tubules and duct consist of a fibrous coat, which sometimes contains bundles of involuptary muscle, lined by a single layer of epithelial cells that vary in form from low cuboid to columnar, and in places, or occasionally in the adult and frequently in the child, bear cilia. The epoophoron is most satisfactorily demonstrated by holding the stretched mesosalpinx against the light ; it is more conspicuous in the broad liga- ment of the young child on account of its development and the greater transparency of the overlying tissues. In common with the sexual organs, the epoophoron increases during the years leading to sexual maturity and atrophies in advanced age. During pregnancy it is said to be unusually vascular (Merkel). Gartner's duct results from the more or less extensive persistence of portions of the Wolffian duct that usually disappear by the end of fcetal life, and is, therefore, a continuation, direct or interrupted, of the longitudinal canal of the epoophoron. Although by no means constant and often represented by only a short atrophic 126 2 oo2 HUMAN ANATOMY. segment, the duct is present in about twenty per cent. (Merkel) of adult subjects, in children being relatively better developed. When complete, as it exceptionally is, the duct continues from the epoophoron along the Fallopian tube to the fundus of the uterus, then descends within the lateral border of the uterus, between the vessels, and sooner or later (usually in the lower part of the body) enters the uterine muscle. As it traverses the cervix, the duct becomes more and more medially placed until, in the supravaginal segment, it approaches the mucosa. The duct then assumes a more lateral course, and in the vagina descends within the muscular coat, at first along the side and lower more on the anterior wall, to end blindly in the vicinity of the hymen (R. Meyer). Such complete persistence is, however, very unusual, Gartner's duct being most frequently represented in the lower part of the body and the upper part of the cervix, less often in the cervical segment alone (Maudach). The canal is lined by a single layer of columnar epithelium and beset with lateral diverticula, uncertain in number and form, which in the lower part of the duct are often short-branched tubules that resemble glands. Accumulations of secretion within the tubules or the duct may lead to the production of cysts. The Paroophoron. Under this name Waldeyer described an inconspicuous rudimentary organ, distinct at birth, but usually disappearing, and only exceptionally retained after the second year, that lies between the layers of the mesosalpinx medially to the epoophoron and, therefore, nearer the uterus. It consists of a small, flat, irregularly round group of blind canals, which represent the remains of Wolffian tubules. The accuracy of Waldeyer' s assumption that this organ is homologous with the paradidymis (page 1950) has been challenged by later investigators (Aschoff, R. Meyer), who have discovered similar groups of rudimentary tubules within the lateral part of the mesosalpinx near the division of the ovarian artery, in a position corresponding to that of the paradidymis. It is to this group, therefore, that the term, paroophoron, may be applied with greater propriety, although there can be little doubt that both sets of tubules are deviations from those of the Wolffian body. The tubules are blind, lined with columnar epithelium, and in places resemble the tortuous canals of the Wolffian body. Apart from their interesting morphological relations, they may become of importance as the seat of cysts. Vesicular Appendages. Under this heading are included the little vesicles or hydatids (appendices vesiculosi) attached to the broad ligament by longer or shorter pedicles. These structures present two general groups, the first including the con- spicuous long-stalked hydatids of Morgagni, and the second the smaller vesicles, vary- ing in form and size, connected by short stems. The hydatid of Morgagni, present on one or both sides in fifty per cent, or over of all female subjects, is a spherical or pyriform thin-walled sac, that contains a clear fluid, and usually measures from 4-8 mm. in diameter, but sometimes much more, and is attached by a slender stalk (from 1.5-4 cm - i n length) to the anterior surface of the broad ligament. Traced towards the latter, the stalk crosses the ovarian or other fimbriae without being attached and sinks into the mesosalpinx about i cm. from its free border, from which point it may be followed through the broad ligament to the upper end of the main or longitudinal duct of the epoophoron, as the continuation of which it may be identified (Watson). In structure the hydatid consists of a fibrous coat, lined by a layer of columnar epithelium and covered externally with a delicate prolongation of the peri- toneum. The smaller vesicles, present in about twenty per cent. (Rossa), often num- ber two or three on each side, and are attached to the anterior surface of the mesosal- pinx, usually over the epoophoron. They are found at birth and even in the foetus, as well as later in life, in advanced age undergoing atrophy The origin and mor- phological significance of the vesicular appendages have occasioned much discussion, but it may be accepted as established that the chief hydatid of Morgagni is derived from the upper end of the Wolffian (pronephric) duct, and is, therefore, the equivalent of the stalked appendage of the epididymis (page 1949). The smaller vesicles prob- ably owe their origin to the distention and elongation of the transverse canals of the epoophoron (Rossa), and, hence, are derivatives of the Wolffian tubules. THE UTERUS. 2003 FIG. 1697. Internal Peritoneum (perimetrium) Cavity of body Posterior fornix External os THE UTERUS. The uterus, or womb, is a hollow muscular organ, receiving the Fallopian tubes above and opening into the upper part of the vagina below, in which the fertilized ovum is retained and undergoes development, and from which the resulting foetus is expelled at the completion of pregnancy. Its lower segment is embedded within the pelvic floor between the bladder and the rectum, while its upper and larger end is free and movable and rests upon the superior surface of the bladder (Fig. 1700). Before undergoing the profound changes incident to pregnancy, the uterus, pear- shaped in its general form, measures about 7 cm. (2^ in.) in length, of which the lower 2.5 cm. (i in.) constitutes the cylindrical neck or cervix (cervix uteri), and the remainder the body (corpus uteri). Its greatest breadth is about 4 cm. (iys in.) and its thickness about 2.5 cm. (i in.). In women who have borne children, the uterus seldom quite returns to its virgin size, but shows a permanent increase of about i cm. in its various dimensions, except in the cervix, which is relatively shorter than before. The convex upper extremity of the organ, above the level of the entrance of the Fallopian tubes, is known as the fundus (fundus uteri), which in front and behind passes into the anterior and posterior surfaces and at the sides into the lat- eral borders (margo late rales). Of the two sur- faces, the anterior (facies vesicalis) is the more flattened and less convex and only partially cov- ered with peritoneum, while the more rounded and projecting posterior surface (facies intesti- nalis) is completely invested with serous mem- brane. The lower end of the cylindrical cervix, flattened somewhat from before backward and slightly tapering downward, is divided by the attachment of the surrounding vaginal wall, which it seemingly pierces, into a free lower seg- ment (portio vaginalis), that projects into the vault of the vagina, and an upper one above the ring of attachment (portio supra vaginalis). Be- low, the vaginal segment of the cervix termi- nates in thick, rounded, and .prominent lips that bound a sunken opening, the external os (ori- ficiura externura uteri) that marks the lower limit of the cervical canal and is directed towards the posterior vaginal wall. Owing to the horizontal position of the cervix, the thicker anterior lip (labium anterius cervicis) is shorter and somewhat lower than the over- hanging posterior lip (labium posterius cervicis). The weight of the virgin uterus varies between forty and fifty grammes (i/^- i^ oz. ), that of the organ after pregnancy being about twenty grammes (.7 oz. ) more. The cavity of the uterus is small in comparison with the size of the organ and the thickness of its walls, and differs in form according to the plane of section. In sagittal section, it is little more than a narrow cleft separating the opposed anterior and posterior walls, and measures about 6 cm. (2^4 in.), of which 2.5 cm. (i in.) belongs to the cervix. In frontal section, the cavity of the body is triangular in out- line (Fig. 1698), the apex being below, where the upper end of the cavity of the cer- vix passes into that of the body, and the base above, between the tubal orifices which mark the lateral angles. The sides of the triangle are not straight but convex, owing to the inward curve of the thick projecting uterine walls. The greatest transverse width of the cavity of the body, just below the tubal openings, is about 2.5 cm. The canal of the cervix (canalis cervicis uteri), as the lower segment of the uterine cavity is called, is fusiform in longitudinal sections, being widest midway between the external os below and the somewhat smaller and more circular internal os (orificium internum uteri) above, where the contracted lumen of the virgin uterus expands into t 'torus laid open by sagittal section, showing cavity and relations of labia to vagina. 2004 HUMAN ANATOMY. FlG. i6g8. Oviduct Internal the cavity of the body. In cross-section the canal appears as a markedly compressed oval. The position of the internal os corresponds with the slight external constriction (isthmus uteri) that uncertainly marks the neck from the body of the uterus. In contrast to the smooth mucous surface of the body, that of the anterior and posterior walls of the cervical canal is marked by conspicuous ridges (plicae palmatae) the arbor vita uteriruz of the older writers consisting of a chief median longitudinal fold from which numerous secondary rugae divert upward and outward on each wall. Attachments and Peritoneal Relations. In addition to the Fallopian tubes that embryologically are direct continuations of the component Miillerian ducts by the fusion of which the uterus is formed, the uterus is connected with the ovaries, the abdominal wall, the lateral and posterior walls and the floor of the pelvis, the vagina, the bladder, and the rectum by fibre-elastic tissue, muscular bands, and peri- toneal folds. Most of these attach- ments, or so-called ligaments, however, have little influence in supporting the uterus, but, owing to the intimate con- nection of the cervix with the vagina, and thus with the pelvic floor, and with the sacrum by fibre-muscular bands, the lower segment enjoys a relatively fixed position ; the body, on the con- trary, being freely movable. The Broad Ligament. With the exception of a narrow strip along the sides between the layers of the broad ligaments, the body of the uterus is completely invested by peritoneum. The cervix, on the contrary, possesses a serous covering only behind and at the sides above the attachment of the vagina. From each lateral border of the uterus this serous investment is reflected to the pelvic wall and floor as a conspicuous transverse duplicature of peritoneum, the broad ligament ( lig- ;i men tu in latum), that passes across the pelvis and encloses between its layers the round and ovarian ligaments, the Fallopian tube, the epoophoron and the paroophoron, together with the associated vessels and nerves. Although enclosed by a peritoneal duplicature continued from its posterior surface, the ovary is attached to, rather than lies within, the broad ligament. When detached from the pelvic wall and floor and spread out (Fig. 1699), the broad ligament is wing-like in form and has four borders, of which the median or uterine is vertical, the upper or tubal is horizontal, longest, and free, the lateral short and approximately vertical to correspond with the plane of the pelvic wall, and the lower sloping downward and inward in agreement with the direction of the pelvic floor. Within the body, the plane of the median portion of the fold depends upon the position of the uterus, in the erect posture usually extend- ing more or less horizontally, so that the posterior surface presents upward and backward, and the anterior downward and forward ; when the uterus assumes an upright position, the fold likewise becomes erect. On nearing its lateral attachment, the upper border of broad ligament becomes not only more vertical, but also parallel with the pelvic wall in consequence of the support afforded by the suspensory liga- ment of the ovary. From their attachment to the pelvic walls and floor the two serous layers of the broad ligament pass in opposite directions and are continuous with the general peritoneal lining of the pelvis. Along the pelvic floor their divergence leaves a non-peritoneal interval through which the vessels and nerves and the ureter gain the side of the uterus. The free border of the broad ligament is occupied by the Fallopian tube, the course of which it follows as far as the outer end of the infundibulum, and thence passes to the pelvic wall to become continuous with the suspensory ligament of the "^External os Vagina Uterus laid open by frontal section, showing form of cavity "of body and cervix. THE UTERUS. 2005 ovary. As the tube crosses the medial surface of the latter organ the broad liga- ment is drawn over it, so that the ovary lies partly within a peritoneal pocket, the bursa ovarii. The anterior border of the ovary is attached to the posterior surface of the broad ligament by a short fold, the mcsovarium, that encloses the hilum and is continued into the modified serous investment that covers the sexual gland. The utero-ovarian ligament and the attached border of the ovary unequally divide the broad ligament into an upper narrow triangular portion, the mesosalpinx, that encloses the tube, and a lower broad part, the mcsometrium, that passes medially to the sides of the uterus and becomes continuous with the perimetrium, as the serous investment of that organ is termed. Within the mesosalpinx the connective tissue filling the interval between the two serous layers of the broad ligament is very scanty, but within the mesometrium this tissue increases to a considerable stratum and con- tains numerous strands of smooth muscle prolonged from the uterus. Surrounding the uterus, it is known as the parametrium, and along the attached borders of the ligament laterally, and below, becomes continuous with the general subserous layer of the pelvis. The Round Ligament. In addition to the Fallopian tube and the ligament of the ovary, already described (page 1987), a third band, the round ligament (liga- FIG. 1699. Fallopian tube, ampulla Ligament of ovary Abdominal opening of Fallopian tube Epoophoron Mesosalpinx | Fallopian tube Hydatid of Morgag Ovarian fimbr Round ligament Mesometriutn Anterior wall of Douglas's pouch/ I" Vagina Uterus and appendages seen from behind ; broad ligament and oviduct have been stretched out to show mesosalpinx. mentum teres), passes on each side from the upper lateral angle of the uterus. This structure, a flattened cord from 12-14 cm. (4^-5^ in.) long and about .5 cm. thick, springs from the side of the uterus, in front and below the entrance of the oviduct, and extends (Fig. 1684) between the layers of the broad ligament horizon- tally outward to the lateral pelvic wall, which it reaches near the floor. Thence it continues its course beneath the peritoneum forward and slightly upward, crosses the obliterated hypogastric artery, the pelvic brim, and the external iliac vessels, and, hooking around the outer side of the deep epigastric artery, gains the internal ab- dominal ring. Passing through the latter and traversing the entire length of the inguinal canal, the round ligament emerges from the external abdominal ring and ends by breaking up into a number of diverging fibrous bands that become mostly lost in the subcutaneous tissue of the labium majus, while a few find attachment to the pubic spine. In its median third the round ligament contains robust bundles of involuntary muscle prolonged from the superficial layers of the uterus, but beyond the muscular tissue disappears, and in its lower part the band consists entirely of fibro- elastic tissue. During its passage through the inguinal canal, the ligamentum teres is accompanied, along its upper border, by small, short bundles of striped muscle 2006 HUMAN ANATOMY. derived from the internal oblique and transversalis, which represent a feebly developed cremaster muscle. After gaining the pelvic wall, the round ligament pursues a course very similar to that of the vas deferens ; morphologically, it corresponds to the genito-inguinal ligament (page 2040). In the foetus the round ligament is preceded by a small peritoneal diverticulum representing the larger processus vaginalis peri- tonaei in the male ; usually this disappears, but may persist as a distinct serous pouch, the canal of Nuck, that accompanies the round ligament for a short distance within the inguinal canal. In exceptional cases it may extend throughout the entire length of the canal into the labium majus. The peritoneal relations of the two surfaces of the uterus (Fig. 1700) are dif- ferent, the anterior surface being covered with serous membrane only as far as the FIG. 1700. Ureter Suspensory ligament of ovary Fallopian tube Round ligament Ovary Obliterated hypogastric artery Uterus Symphysis pubis Urethra External urethral orifice in vestibule s uteri Bottom of recto- uterine pouch .Vagina Perinea! body Sagittal section of pelvis of female. junction of the body and cervix, from which line the peritoneum passes on to the bladder as the utero-vesical fold and lines the shallow utero-vesical pouch (excavatio vesicouterina). Below the reflection of the peritoneum and as far as its attachment to the vagina, the anterior surface of the cervix is connected by areolar tissue with the adjacent posterior wall of the bladder. As far as the attachment of the vaginal wall, the posterior surface of the uterus is covered with peritoneum, which then continues downward for about 2.5 cm. over the upper part of the back wall of the vagina before being reflected onto the rectum as the vagi no-rectal fold. The latter forms the bot- tom of the deep serous pouch of Douglas (excavatio rectouterina) that lies between the uterus in front and the rectum behind. The lateral boundaries of the opening into this pouch are formed by the two crescentic utero-rectal folds (plicae rectouterina ) that curve from the hind surface of the cervix backward to the posterior pelvic wall at the THE UTERUS. 2007 sides of the rectum. Between the layers of these folds robust bundles of fibrous and smooth muscular tissue extend from the uterus to be inserted partly in the rectum, there constituting the utero-rectal muscle, and partly into the front of the sacrum as the utero-sacral ligament. The latter structure contributes efficient aid in supporting the cervical segment of the uterus, which is thus enabled to maintain its position independently, to a certain degree, of that of the body. Position and Relations. The attachment of the cervix to the vaginal walls and utero-sacral ligaments give to the lower uterine segment a more definite position than that enjoyed by the body, which, being little restrained by its lateral attachments, is especially affected by the condition of the bladder and rectum. When these organs are but slightly distended, the uterus normally, in the erect posture, lies tilted for- ward (anteverted), with the body resting upon the upper vesical surface. Since, under these conditions, the cervix is comparatively fixed and directed backward and the body more or less bent forward (antiflexed), the uterine axis exhibits a marked flexure at the beginning of the cervical segment. This angle varies continually with the position of the fundus, which, receiving little support from its peritoneal and other attachments, is influenced by the changing condition of the bladder. When the latter is contracted and the uterus strongly anteflexed, the angle is more pro- nounced than when the upper vesical wall, and consequently the fundus, lies higher. With increasing distention of the bladder the angle gradually disappears and the uterine axis becomes straight ; in excessive vesical expansion, associated with an empty rectum, the entire uterus may be tilted backward (retro verted), its axis then corresponding with that of the vagina. When both bladder and rectum are dis- tended, the entire uterus may be pushed up above the level of the symphysis. Usually the fundus does not lie strictly in the mid-line but to one side, probably more frequently to the left (Waldeyer, Merkel). This deflection may also affect the axis of the ovary of the opposite side, which, in consequence of the pull thus exerted, then lies more obliquely than on the side on which the utero-ovarian liga- ment is relaxed. The anterior surface of the uterus following the changes of the upper vesical wall upon which it lies, the utero-vesical fossa very seldom contains in- testinal coils, which, on the contrary, frequently occupy the pouch of Douglas. The posterior (upper) surface of the uterus is overlaid by coils of the small intestine, and may also be in contact with the pelvic and sigmoid colon. Anteriorly, below the reflection of the utero-vesical fold, the lower segment of the uterus is connected with the posterior bladder-wall by loose connective tissue ; posteriorly, it is sepa- rated from the rectum by the intervening peritoneal pouch of Douglas ; laterally, it is crossed by the ureters, which, opposite the middle of the cervix, lie about 2 cm. from the uterine wall. In the erect position, the level of the external os corresponds ap- proximately with that of the upper margin of the symphysis, and in the antero- posterior axis lies slightly behind a frontal plane passing through the ischial spines {Waldeyer). Structure. The uterine walls, thickest in the fundus and posterior wall of the body, where they measure from 1-1.5 cm -' an d somewhat thinner (from 8-9 mm.) at the entrance of the tubes and in the cervix, comprise three coats, the mucous, muscular, and serous. The mucous coat, or endometrium, of a light reddish color, soft, and friable, and from .5-1 mm. thick, consists of a connective-tissue stroma, loose in texture but rich in cells and resembling the tunica propria of the intestinal mucous, and the surface epithelium. The latter is a single layer of columnar cells, about .028 mm. high, that in their typical condition possess cilia by which a down- ward current is established towards the external os. It is probable, however, that the cilia are neither always present, nor uniformly distributed, since they are lost during the disturbances incident to menstruation, and are often present only in patches (Gage). The uterine glands are simple tubular, or slightly bifurcated, wavy invaginations of the mucosa, said to be lined with a single layer of ciliated col- umnar cells resembling those covering the interior of the uterus. They are dis- tributed at fairly regular intervals and extend the entire thickness of the mucosa, their tortuous, blind extremities in many cases being lodged between the adjacent muscular bundles, since a distinct submucosa is wanting. In the vicinity of the orifices of the Fallopian tubes, the uterine mucosa becomes thinner, the epithelium lower, 2OO8 HUMAN ANATOMY. Gland opening on mucoussur- face. Gland and the glands shorter and fewer, until they finally disappear, glands being absent in the tubal mucous membrane. The cervical mucosa differs from that lining the body in being somewhat denser, owing to the greater amount of fibrous tissue within its stroma, and in possessing a taller epithelium, a single layer of columnar cells from .040-. 060 mm. in height, and larger mucous glands. The latter (glandulae cervicales uteri), from 1-1.5 mm! long and .5 mm. wide, are branched and often reach with their blind ends between the muscle bundles. The mucus secreted by these glands is peculiar, being clear and exceeding tenacious, and sometimes is seen as a plug protruding from the external os. Not infrequently the orifices of the cervical glands become blocked, which condition results in FIG. 1701. the production of retention cysts that appear as minute vesicles between the folds of the plicae palmatae. These bodies were formerly de- scribed as the ovules of Na- both (ovula Nabothi). The transition of the cylindrical epithelium of the cervical canal into the squamous cells covering the vaginal portion of the uterus takes place ab- ruptly at the inner border of the external os. At the inner os, where the cervical mu- cosa passes into that lining the body, the change is so gradual and inconspicuous that no sharp demarcation exists. The muscular coat, or myometrium, although com- posed of bundles of involun- tary muscle arranged with little individual regularity, may be resolved into a robust inner layer, in which the bundles possess a general circular disposition, and a thin, imperfect outer /aver in which their course is for the most part longitudinal. The longitudinal muscle bundles Muscle bun- dles invad- ing mucosa Blood-vessel Section of endometrium, showing uterine glands cut in various planes. X 40. of the feeble outer layer, which is present only over the fundus and body, are con- tinued beyond the uterus onto the tubes and into the broad, round, ovarian and utero-sacral ligaments. The thick inner layer, the chief component of the myome- trium, is distinguished by the number and size of the blood-vessels that traverse the intermuscular connective tissue and, hence, is known as the stratum vascnlarc ( Kreit- zer). The bundles of this layer are confined to the uterus, except below, where they become continuous with the muscle of the vaginal walls. At the three angles of the body, corresponding to the two tubal orifices and the internal os, the dispo- sition of the bundles surrounding these openings suggests the existence of distinct sphincters. In other places the innermost bundles are less regularly disposed and are oblique or even longitudinal. Within the cervix the outer longitudinal layer is unrepresented, the musculature of this segment consisting chiefly of circular and oblique bundles, intermingled with a considerable amount of dense fibrous and elastic- tissue that confer upon the cervix greater resistance and hardness. The component fibre-cells of the uterine muscle vary in form, being in some places short and broad THE UTERUS. 2009 and in others long and spindle form. During pregnancy their usual length (from .04o-.o6o mm.) may increase tenfold. The serous coat, or peri met rium^ continuous laterally with the peritoneal invest- ment of the broad ligament, is so closely adherent to the uterine muscle over the fundus and adjacent parts of the anterior and posterior surfaces that it is removed with difficulty. Lower, the presence of the intervening loose connective tissue ( para- mdrinm} renders the attachment less intimate. Vessels. The arteries supplying the uterus are the two uterine, each a branch of the internal iliac that accompanies the ureter along the pelvic wall, behind and below the ovarian fossa, to the attached border of the broad ligament beneath which it passes in its course to the uterus. On gaining a point about 2 cm. from the cervix and on a level with the internal os (Merkel), the uterine artery bends medially and crosses the ureter obliquely and in front. It then traverses dense connective tissue, and on approaching the lateral wall of the cervix bends sharply upward to course between the layers of the broad ligament along the lateral borders of the uterus, as far as the lateral angle. Immediately below the ovarian ligament the FIG. 1702. Anterior surface Longitudinal muscle Blood-vessels , ., ligament en- * (t. Jim 1 , / /' 5 '/ " " Mucosa (endometrium) / '^' V' : '' jJS > - ft -i gp: m '^ >. Longitudinal muscle - - ^L^,~. ._' - : c^> Peritoneum (perimetrium) Posterior surface Transverse section of uterus through body. X 2. uterine artery divides into its terminal branches distributed to the fundus, Fallo- pian tube, and ovary. In addition to a small branch to the ureter, just before bending upward it gives off the vaginal artery that passes downward and assists in supplying the cervix and the vagina. As it ascends along the sides of the uterus, from 5-10 mm. removed and surrounded by a dense plexus of veins, the very tortuous uterine artery sends numerous but variable branches to the cervix and body, as well as to the broad ligament, those distributed to the posterior surface being somewhat larger than those to the anterior (Robinson). The terminal branch passing to the fundus (ramus fundi) is especially strong and freely anastomoses with the corresponding vessel from the opposite artery, thus insuring exceptional vascu- larity to that part of the uterus in which the placenta is usually attached ( Charpy). Twigs also accompany the ovarian and round ligaments. After the establishment of the junction between the ovarian artery and its ovarian branch, the uterine artery plays am important part in maintaining the nutrition of the ovary. On gaining the muscular coat the larger branches divide into vessels that penetrate the outer layer of the myometrium and within the inner muscular layer break up into numerous minute twigs that confer upon this stratum its highly vascular character. Within 20io HUMAN ANATOMY. the mucosa the capillaries surround the glands and form a superficial net-work beneath the epithelium. The veins, already of considerable size within the inner muscular layer, emerge from the myometrium and form a dense plexus of thin-walled vessels that surround the uterine artery at the sides of the uterus between the layers of the broad ligament. The veins are arranged as an upper, middle, and lower group. The first of these includes the veins from the fundus and upper part of the body, which become tribu- tary to trunks that join the ovarian veins and leave the pelvis by way of the sus- pensory ligament. The middle group comprises the venous radicles from the lower half of the body and upper part of the cervix that unite into one or two main stems that accompany the uterine artery. The lower group is formed by the veins from the most dependent part of the uterus, the anterior vaginal wall, and the posterior surface of the bladder. These unite into robust ascending stems that become tribu- tary to the trunks following the uterine artery. The middle and lower groups freely anastomose with the vesical plexus and also communicate with the hemorrhoidal plexus. The lymphatics, within the mucosa not demonstrable as definite vessels but only as uncertain clefts, constitute an intermuscular net-work of which the larger trunks follow the blood-vessels and establish communication between the cervical lymphatics and those of the body. On emerging from the myometrium a superficial (subserous) plexus is formed, especially over the posterior surface in the vicinity of the lateral angles ; large trunks also accompany the blood-vessels along the sides of the uterus. The lymphatics from the cervix, usually two or three stems, pass to the lymph-nodes occupying the angle between the external and internal iliac arteries. According to Bruhns, 1 those from the remaining parts of the uterus follow different paths : one set, from the body, goes likewise to the iliac nodes ; another, from the fundus, courses towards the ovary, and in company with the trunks from the latter organ follows the ovarian artery to terminate in the lumbar nodes. A third set, also from the fundus, eventually gains the lumbar glands after joining the lymphatics of the Fallopian tube, while a fourth group diverges from the fundus along the round liga- ment to become afferents of the inguinal lymph-nodes. In addition to free anasto- mosis among themselves, the uterine lymphatics communicate with those of the vagina, rectum, ovaries, Fallopian tubes, and broad ligament. The nerves of the uterus, being chiefly destined for the involuntary muscle, are numerous and of large size to correspond with the highly developed myome- trium. They are derived not only from the sympathetic system from the utero- vaginal subdivision of the pelvic plexus (the continuation from the hypogastric), but also directly from the second, third, and fourth sacral spinal nerves. According to the classic description of Frankenhiiuser, the utero- vaginal plexus divides into two parts, the smaller of which is distributed to the posterior and lateral parts of the uterus, while the larger includes a chain of minute ganglia along the cervix and vaginal vault. One of these, the cervical ganglion, is especially large, and lies behind the upper part of the vagina, receiving, in addition to the sympathetic, spinal fibres from the sacral nerves and giving off twigs to the uterus. These latter pass to the uterine walls between the layers of the broad ligament, particularly at the sides in company with the blood-vessels, and penetrate the myometrium, to the fibre-cells of which the nerve-filaments are chiefly distributed ; others pass into the mucosa to end beneath the epithelium. Development and Changes. In consequence of the medial rotation of the ventral border of the Wolffian body, the relations of the Mullerian to the Wolffian duct change. Instead of lying laterally to the Wolffian duct, as it does above, the Mullerian duct gains the inner side of that tube as they pass into the urogenital fold (page 2038) which prolongs the lower end of the Wolffian body into a median strand known as the genital cord. Within the latter, formed by the fusion of the plicae urogenitales, the two Mullerian ducts lie next the mid-line, side by side and in contact with the Wolffian duct on either hand. Beginning about the eighth \v k. the opposed smtares become united, the intervening septum disappears and the two Mullerian ducts are converted into a single tube from which the uterus is derived. 1 Archiv f. Anat. u. 1'hys., 1898. THE UTERUS. 2011 For a time this tube ends blindly and is continued to the urogenital sinus, with which it unites, as a solid cylinder of larger cells ; this lumenless segment of the fused Mullerian ducts represents the anlage of the vagina. The extent to which the Miillerian ducts undergo fusion is early indicated by a sharp inward bend of these tubes just below the lower and medial ends of the Wolffian bodies, the flexure on each side corresponding to the attachment of fibres that pass to the anterior abdom- inal wall and later from the round ligament. The portions of the Mullerian ducts above this point remain separate and ununited and become the oviducts, those below undergo fusion and produce the uterus and vagina. After the vaginal portion of the united Mullerian ducts acquires a lumen (by the end of the fourth month), the uterine and vaginal segments of the tube are dif- ferentiated by the tall cylindrical and the larger cuboidal epithelial cells that line the two portions respectively. The transition zone, which becomes progressively more marked, corresponds to the position where later the cylindrical uterine epithe- lium changes into the squamous vaginal cells at the inner margin of the external os. Soon the distinction between the uterine and vaginal portions of the genital canal is additionally emphasized by the forward curve of the former and the straighter downward course of the latter. The more definite division of the uterus from the vagina is effected by the appearance of crescentic thickenings of the anterior and posterior walls of the canal which mark the beginnings of the corresponding lips of the cervix. Distinction between the body and cervix is early suggested by the uterine epithelium, the cells lining the lower portion being taller, more cylindrical and numerous than those of the body. The connective and muscular tissue of the uterine wall are differentiated from the condensed mesoderm that surrounds the epithelial tube. Distinct muscle is not distinguishable before the fifth month, about which time the cervical glands also make their appearance (Nagel), thus anticipa- ting by some weeks the development of the glands in the corpus uteri. At birth the uterus measures about 3 cm. in length, of which the cervix con- tributes more than half, and is thicker and denser than the thin-walled and flaccid body. The characteristic arched form of the fundus is lacking and the lateral angles are prolonged into the tubes, often recalling a bicornate condition. The portio vaginalis is inconspicuous and projects to only a slight degree, although the plicae palmatae are well developed and not limited, as they later are, to the cervical canal, but extend throughout the uterine cavity. Since at this time the internal os is still immature, the division of the uterine cavity into an upper and a lower segment is only suggested. The general position of the uterus is higher than later, it, together with the bladder, lying above the level of the pelvic brim, with the fundus opposite about the fifth lumbar vertebra (Merkel). With the increasing capacity of the pelvis, the uterus sinks, so that by the end of the sixth year the external os is little higher than in the adult (Symington). Apart from the gradual development of the glands and the disappearance of the folds of the mucosa within the body, during childhood the uterus grows slowly until near puberty, when the body thickens, lengthens, and acquires the arched contours of its mature form. In its relatively long cervix and slightly prominent fundus, the uterus of the virgin retails the characteristics of early childhood. The repeated changes incident to the men- strual cycle, produce gradual thickening of the uterine walls and enlargement of the lumen, so that, even independently of pregnancy, the uterus increases somewhat in size and weight during the years of sexual activity. After the cessation of menstruation, between the forty-fifth and fiftieth years, the uterus suffers gradual atrophy (involution). This first affects the cervix, which becomes smaller and more slender, the entire organ in consequence assuming a more pronounced pyriform outline. The general reduction in the size and prom- inence of the vaginal portion is accompanied by atrophy of the plicae palmatae of the cervical canal. The walls of the body are also involved and become thinner and less resistant with atrophy of the muscular tissue and decreased vascularity, and hence paler color, of the mucosa. For a time the uterine cavity is enlarged, but, later, sharing in the general atrophy and not inconsiderable diminution in size of the organ, the lumen likewise undergoes reduction and, in some cases, suffers obliteration in the vicinity of the internal os. 2012 HUMAN ANATOMY. Changes during Menstruation and Pregnancy. Although liberation of a mature ovum may occur at any time, such independence is exceptional, and in the vast majority of cases o\ ulution and menstruation are synchronous processes, the uterine changes occurring regularly, every twenty-eight days, only when the ovaries are functionally active. In anticipation of the possible reception of a fertilixed ovum, the uterine mucous, membrane becomes swollen, exces- sively vascular and hypertrophied, with conspicuous enlargement of the subepithelial blood- vessels and the glands. The resulting thickened and modified mucosa, now from 3-6 mm. in thickness, offers a soft velvety surface favorable for the implantation of the embryo-sac. Should this purpose be realixed, the hypertrophy proceeds, and the lining of the uterus is con- verted into the deciduu? and takes an important part in the formation of the placenta and at- tached membranes (page 44). If, on the contrary, fertilization does not occur, the proliferative processes are arrested and the hypertrophied mucosa (now called the dccidua nicnstrualis} enters upon regression. Incidental to the latter are subepithelial extravasation and rupture and partial destruction of the epithelium, followed by the characteristic discharge of blood. While usually the destruction of the mucosa is limited to the epithelium, it is probable that at times the superficial layer of the subjacent tissue is involved. During pregnancy the most conspicuous changes are occasioned by the growth necessary to accommodate the rapidly augmenting volume of the uterine contents, by the provision of an adequate source of nutrition and protection for the fcetus, and by the development of an efficient contractile apparatus for the expulsion of the same. From an organ ordinarily weighing about 45 grams (\y 2 oz.), measuring 7 cm. in length and possessing a capacity of from 3-5 cc., by the close of pregnancy the uterus has expanded into a rounded or oval sac about 36 cm. (14 in. ) in its greatest length, from 900-1000 grm. (about 2 Ibs. ) in weight and with a capacity of 5000 cc. (169 fl. oz. ) or more. This enormous increase depends especially upon the hypertrophy of the muscular coat of the organ, which during the first half of pregnancy becomes greatly thickened, but later thinner and membranous owing to stretching. The increase in this coat results from both the growth of the previously existing muscle-cells and, during the first half of pregnancy, the development of new muscle elements. The individual cells may increase tenfold in length and measure between -4-.5 mm. Although the cervix actually almost doubles in size, its growth is overshadowed by that of the body, since it remains relatively passive. During the first five months, the mucous membrane of the body of the uterus also becomes greatly hypertrophied, in places attaining a thickness from 7-10 mm. The glands and blood-vessels, particularly the arteries, enlarge and, within the specialized area, are concerned in the formation of the placenta (page 48). The cervical mucosa takes no direct part in the formation of the deciduae, although it thickens and is the seat of enlarged glands that secrete the plug of mucus that for a time occludes the mouth of the uterus. After the termination of pregnancy, the uterus enters upon a period of involution and repair, the excessive muscular tissue undergoing degeneration and absorption and the lacerated mucosa regeneration, the latter process being completed in from five to six weeks (Minot). In sympathy with the growth of the myometrium, the round ligaments enlarge and also show marked augmentation of their muscular tissue. The peritoneal relations are disturbed by the excessive bulk of the uterus, so that at the sides the layers of the broad ligament become separated. Variations. The chief anomalous conditions of the uterus depend upon defective devel- opment or imperfect fusion of the Mullerian ducts by the union of which the normal organ is formed. Arrested development of the lower part of these fcetal canals accounts for entire ab- sence of the uterus and vagina. Depending upon the extent to which failure of fusion occurs, all degrees of doubling are produced. In the most pronounced cases, in which the Mullerian ducts remain separate throughout their entire length, two completely distinct uteri and vagina' may result, each pair being capable of performing the functions of the normal organs. On the other hand, slight indentation of the fundus may be the only evidence of imperfect union. Be- tween these extremes all gradations occur ; the "body may be completely cleft ( uterus informs), with or without divided cervix ; or the duplicity may be partial and limited to branching of the fundus ; or the faulty fusion may be manifested by only a partition, more or less complete, that divides the uterine cavity into two compartments (it ferns S<-/>/HS), although the external form of the organ is almost or quite normal. When, in conjunction with any of the foregoing variations, one of the component Miillerian ducts fails to keep pace in its growth, all decrees of asymmet- rical development may result, from complete suppression of one of the tubes in a bicornate uterus to merely unilateral diminution of the fundus. Subsequent arrest of what to a certain stage was a normal development may result in permanent retention of the fcetal or infantile type of uterus. PRACTICAL CONSIDERATIONS : UTERUS AND ITS ATTACHMENTS. In the female the pelvis is subdivided into two compartments by a fold of peri- toneum reflected from the floor and sides of the cavity. This fold passes from one side to the other and includes between its layers in the median line the uterus. On each side of the uterus it is known as the broad ligament, and encloses the uterine PRACTICAL CONSIDERATIONS: THE UTERUS. 2013 appendages, their blood-vessels, together with their nerves and their enveloping connective tissue. This transverse fold of peritoneum is analogous to the mesentery of the small intestine, serving the same purpose for the uterus and its appendages i.e., to hold them in position and to transmit their blood-vessels and nerves. The posterior compartment of the pelvis, the recto- uterine, is the larger and deeper of the t\vo. The lower portion of it, included between the two recto-uterine folds of the peritoneum, is the pouch of Douglas, or recto-vaginal pouch, because it lies between the rectum and the upper fourth of the vagina, from which it is separated only by subperitoneal connective tissue. The rectum, bulging forward the posterior wall, and the ovaries, hanging from the anterior wall, tend to fill this compartment, the remaining space being occupied by small intestine and a portion of the sigmoid flexure. Abnormally it may be encroached upon by a retroposed uterus, which tends to drag downward and backward its appendages, the tubes and ovaries, towards Douglas's pouch, where they may be palpated by the finger through the vagina. Because of the greater depth of the posterior compartment and because of the fact that abscess and other pelvic operative conditions are usually situated in it, it must almost always be drained, if drainage is necessary after operation in this region. The anterior or vesico- uterine compartment of the pelvis extends below only to the isthmus of the uterus. The remaining supravaginal portion of the cervix is in close relation to the bladder, but the loose intervening layer of subperitoneal tissue permits a ready separation of the two in the operation for the removal of the uterus (hysterectomy). Since the body of the uterus inclines forward, nor- mally, touching the bladder, the space in this compartment is slight. It excep- tionally contains a few coils of small intestine, and may lodge also a part of the sigmoid flexure. A tumor or pregnant uterus filling the pelvis may press upon the iliac veins, producing cedema and varicose veins of the lower extremities, of the vulva, and of the rectum (hemorrhoids) ; upon the lumbar and sacral nerves, causing cramps, neuralgia, or paralysis ; upon the bladder, with resulting vesical irritability and pain ; upon the rectum, inducing constipation and hemorrhoids ; upon the ureters, giving rise to hydronephrosis ; or upon the renal veins and kidney, producing albuminuria and possibly uraemia. The uterus is held in position between the bladder and the rectum by its liga- ments, and is kept from dropping to a lower level (prolapse) mainly by the support received from atmospheric pressure acting through the floor of the pelvis. The broad or lateral ligaments attach it and its appendages the Fallopian tubes and ovaries to the sides of the pelvis. The round ligaments act chiefly in tending to prevent retro-displacements. The musculo-fibrous utero-sacral ligaments and the anterior and posterior reflections of peritoneum materially steady the cervix, which is also fixed by its attachments to the bladder and vagina. Moreover, the intra-abdominal pressure applied through the intestinal convolutions that are normally in contact with its posterior surface aids in holding it in position. The body of the uterus is more freely movable than the cervix, and in spite of its supports the uterus, as a whole, is one of the most mobile of the viscera. The cervix, for example, may easily be made, through traction by means of a tenaculum, to present at the orifice of the vagina, in such operations as amputation of the cervix, repair of lacerations, or dilatation and curettement. On account of its mobility, its intrapelvic situation, and the elastic support received from the bladder, and indirectly from the levator ani muscles, the uterus is very rarely injured by blows on the abdomen. If upon examination it is found to be fixed, or not easily movable, some abnormal cause should be sought for, such as pelvic inflammations or tumors. The essential conditions in the production of a prolapsed uterus obtain when the uterus is the seat of subinvolution from any cause, especially a puerperal infection, and the pelvic floor is relaxed or torn. The stretching of the pelvic ligaments has then not been fully overcome by later contraction, and the atmospheric support (dependent upon a tightly closed vaginal outlet) is lacking because of the weak- ened perineal floor. As the uterus reaches a lower level its ligaments become truly ' ' suspensory' ' and resist its further downward progress as soon as their uterine attach- 2014 HUMAN ANATOMY. ments are below their pelvic attachments. Normally their insertions and origins lie approximately in the same horizontal plane when the woman is erect (Penrose). The integrity of the levator ani muscle, ensuring a well-closed vaginal outlet, is the most important factor in supporting the uterus within the pelvis. It keeps the outlet forward under the pubic arch out of the line of abdominal pressure, gives it the form of a narrow slit, preventing the protrusion of the pelvic viscera, and directs the axis of the vaginal canal forward instead of directly downward, so that the intra- abdominal pressure strikes the pelvic floor at a right angle ; and by aiding in main- taining the vagina in its normal condition of a closed slit with its walls in contact, it prevents disturbance of the forces which hold the uterus in place. If a laceration of the perineum converts the vagina into an open air-containing tube, the equilibrium of these forces is destroyed and prolapse often follows. In severe cases of prolapse the ureters are so stretched that, at their vesical ends, their lumen is narrowed and ureteral dilatation or hydronephrosis may result. Anterior and posterior flexions of the uterus occur at the isthmus, which is the weakest point and is the junction of the larger and more movable portion the body with the smaller and more fixed portion the cervix. On account of the normal anteflexion of the uterus, it is not always easy to decide in a given case whether the degree of anteflexion is normal or abnormal. When it is abnormal the most important symptom is dysmenorrhcea, from obstruc- tion of the canal by the flexion ; if irritability of the bladder occurs, it is probably reflex in its origin. Anything which weakens the support of the uterus, or increases its weight, tends not only to cause prolapse, but also to the production of retroflexion or retro- version of the uterus, the first degree of prolapse being associated with some retro- displacement. The uterus then loses its normal anteversion, and the intra-abdominal pressure is brought to bear on its anterior surface, especially if the patient is either confined too long in the supine position after labor, with the abdomen too tightly bandaged, or if she leaves her bed too soon or undertakes any physical work. The uterus is larger and heavier than normal, as a result of imperfect involution ; the uterine ligaments are lax ; the vagina and the vaginal orifice are relaxed, and the support of the pelvic floor is consequently deficient ; the abdominal walls are flabby and the retentive power of the abdomen is diminished. These are also the causes that favor prolapse of the uterus ; in fact, a slight degree of uterine prolapse usually accompanies such cases of retrodisplacement. A certain amount of retro- version must always exist before the uterus can pass along the vagina. It must turn backward, so that its axis becomes parallel to the axis of the vagina (Penrose). In the purely retroverted positions the uterus revolves on the isthmus as on a pivot, so that as the fundus goes in one direction the cervix passes in the other. Therefore, as the cervix is turned forward against the base of the bladder, the fundus presses backward on the rectum, often producing reflex symptoms. The uterus may be found inclined to one side more usually the fundus to the left, and the cervix, on account of the presence of the sigmoid and rectum on the left side, to the right. Unless extreme, such inclination is not to be regarded as patho- logical. Between the layers of the broad ligaments is a quantity of loose adipose cellu- lar tissue, the parametrium, separating the contained structures those of the most importance being the tubes and ovaries with their vessels and nerves from one another and from the serous membrane. This cellular connective tissue is continuous with the surrounding subperitoneal areolar tissue of the pelvis, and is especially abundant near the base of the broad ligaments. In f>chic cell id itis there is infection of this loose cellular tissue, usually through the lymphatics and often puerperal in origin. It may follow other septic intrapdvic conditions, especially salpingitis, but a simple cellulitis unaccompanied by tubal inflammation is in the vast majority of cases due to infection through the uterus from a septic endometritis. Because of the laxity of the tissue it may spread rapidly and extensively in virulent cases. It may extend backward along the utero-sacral liga- ments, then upward along the retroperitoneal tissue, as far as the kidneys. It may pass forward and upward to the groin, where, should an abscess form, it may be PRACTICAL CONSIDERATIONS: THE UTERUS. 2015 opened. It may also burrow into the vagina or rectum. Suppuration takes place, however, in only a small percentage of cases. The condition is usually recognized by the rapid swelling and induration at the sides of or behind the uterus, and in closer relation to it than is the swelling of a pyo- salpinx or of an ovarian abscess. Pelvic collections of pus of this nature may be evacuated through the vagina by an incision made close to the cervix, to avoid the ureters and the uterine arteries ; but it should be remembered that this procedure does not remove the focus of primary infection, such as a diseased Fallopian tube. Blood collections (haematoceles) or tumors (intraligamentous) may also occur between the layers of the broad ligaments. The narrow lower border of each ligam ^nt lies on the floor of the pelvis, but is separated from it by a thick layer of subperitoneal tissue, in which the uterine artery with its veins passes nearly transversely inward from the internal iliac artery at the side of the pelvis to the cervix at about the level of the vault of the vagina. The ureter, on its way from behind forward to the bladder, passes through this loose cellular tissue just below the base of the broad ligament. It lies close under the uterine artery from one-half to one inch from the side of the cervix. It is within this short distance that the uterine vessels are tied, either from within the abdomen or from the vagina, according to the method of operation, in the removal of the uterus (hysterectomy). The inclusion of the ureter within the ligature is one of the greatest dangers in this operation. This accident is more likely to occur if the artery is crowded closer to the ureter of one side, by a tumor or other mass, in the opposite side of the pelvis. The ureter is also in danger, as it lies along the side and floor of the posterior compartment of the pelvis. It may there be injured in the removal of adherent masses, such as inflamed tubes and ovaries, or of retroperitoneal tumors or cysts. Calculi in the vesical ends of the ureters may be removed through the vaginal wall (page 2020). The free upper border of the broad ligament between the fimbriated extremity of the tube and ovary and the side of the pelvis the suspensory ligament of the ovary or the infundibulo-pelvic ligament is of practical importance because, in addition to supporting the ovary, it contains the ovarian vessels where they are usu- ally tied in the operations for the removal of the uterus or its appendages. Kelly calls attention to a space immediately below the vessels in this region, where the two layers of the peritoneum, forming the broad ligament, come close together. By pass- ing a ligature through this membranous interval and tying over the top of the broad ligament, all the ovarian veins and the artery are included. If the uterine vessels also are tied by a separate ligature, at the cornu of the uterus, there should be no danger of hemorrhage in a salpingo-oophorectomy ; or, if the uterine vessels are secured at the sides of the cervix, in the floor of the pelvis, and the ovarian vessels are ligated, as above, on both sides of the pelvis, the hemorrhage will be controlled for a hysterectomy. The round ligaments, passing outward and forward from the sides of the uterus through the internal ring and inguinal canals to the labia majora, tend by their direction to maintain the uterus in its normal anteflexed position. When retrodis- placements of the uterus do occur these ligaments become stretched and lengthened. They have frequently been shortened by operation to correct such displacements. This may be done by the extra-abdominal method in the inguinal canal (Alexander's operation), or within the abdomen (Palmer Dudley operation), the latter method per- mitting a more accurate estimate of the special peculiarities or difficulties of a given case. Occasionally in the adult always in the foetus and in 20 per cent, of cases in children (Zuckerkandl, quoted by Woolsey) a patulous process of peritoneum, the canal of Nuck, accompanies the round ligament, lying above and in front of it for a variable distance through the inguinal canal. If is analogous to the vaginal process of peritoneum which descends with the testicle, and, like it, predisposes to congenital inguinal hernia (page 1767) and to hydrocele (page 1953). Should its lumen become constricted at some point, the portion beyond the obstruction may secrete fluid and give rise to the so-called "cyst of the canal of Nuck," which is analogous to an encysted hydrocele of the cord in the male (page 1953). 2Ol6 HUMAN ANATOMY. FIG. 1 703. THE VAGINA. The vagina is a flattened muscular tube, lined with mucous membrane and about 7.5 cm. (3 in. ) long, that extends from the genital cleft enclosed by the labia minora below to the uterus above, to the lower segment of which it is attached a short dis- tance above the external os. From this relation and the direction, downward and backward, of the portio vaginalis, the vagina is seemingly pierced obliquely by the uterus, whose external os looks towards the posterior vaginal wall. In the erect posture the long axis of the vagina is approximately straight, directed from below upward and backward, and corresponds in general with the lower part of the pelvic axis. With the horizontal plane it forms an angle of about 70, and with the axis of the cervix one that is usually somewhat more than a right angle. The arched upper blind end of the vagina, known as the vault (fornix vaginae), is largely occupied by the obliquely placed portio vaginalis and thereby reduced to an annular groove that surrounds the neck of the uterus. This groove is deepest behind, where it constitutes the posterior fornix, a narrow pouch from i . 5-2 cm. in length lying between the cervix and the adjacent vaginal wall. The recess in front of the cervix, the anterior fornix , is shallow and only slightly marked. In consequence, the length of the posterior wall of the vagina, measured from the summit of the posterior fornix to the vaginal orifice, is from 8.5-9 cm. (3^4-3^ in.), that of the anterior wall being about 7 cm. (2^ in.), or from 1.5-2 cm. shorter. The opening at the lower end of the vagina (ori- ticiuin vaginae) is contracted, and in the virgin is still further narrowed by a duplicature of mucous mem- brane, the hymen, of variable form but usually cre- scentic in outline, that stretches from the posterior wall forward and occludes more or less the vaginal entrance. After rupture the hymen is for a time represented by a series of irregular or fimbriated pro- jections that become the carunculcc hymenales. These surround the opening of the vagina and undergo re- duction and partial effacement after childbirth. The anterior and posterior walls of the main and widest part of the canal (corpus vaginae) are modelled by median elevations (columnae rugarum), from which numerous oblique folds diverge laterally. These markings, most pronounced in the lower half of the vagina, are particularly conspicuous on the front wall. Here the anterior column is beset with close V-like ridges and ends below in a crest-like elevation the carina urethralis that lies behind the urethral orifice. Relations. With the exception of the triangular area, from 1.5-2 cm. long, over the uppermost part of the posterior wall, where the bottom of the recto-uterine pouch reaches the canal, the vagina is devoid of peritoneum, being attached to the surrounding organs by areolar tissue. In front its upper fourth is in relation with a small part of the fundus and the trigone of the bladder, being attached to the vesical wall by loose connective tissue. Embedded within the latter and surrounded by veins, course the converging ureters, which reach the anterior vaginal wall at about the level of the lower end of the cervix. Below the bladder, the anterior wall of the vagina and the urethra are intimately connected by the intervening dense fibrous tissue- ( septum urethrovnginalis ), with which the vaginal wall blends without sharp demarcation. In consequence of the forward curve of the urethra this partition broadens below. Behind, the chief relation is with the rectum, which is separated from the upper- most part of the vagina, for a short distance (from 1.5-2 cm.), by the pouch <4 Vagina of virgin, posterior wall has been removed exposing rugous condition of anti-riot wall. THE VAGINA. 2017 Douglas. Below the latter, as far as the levator ani muscles, the vagina and bowel are connected by the dense recto-vaginal septum, strengthened by the intervening prolongation of the pelvic fascia. Further down, where the rectum bends backward, the partition broadens into a wedge-shaped mass, the perineal body, which on sagittal section appears as a triangle with the base below in the perineum (Fig. 1700). At the sides the vagina is embraced by, although unattached to, the median (pubo- rectal) portion of the levator ani muscles, which, in conjunction with the pelvic fascia, afford efficient support. Below the pelvic floor, the vagina gains additional fixation in passing through the triangular ligament with which it is intimately attached. In relation with the lower end of the vagina lie the bulbus vestibuli and Bartholin's glands. The triangular interval, on each side, between the levator ani and the pelvic fascia and the lateral surface of the vagina, is occupied by the veins of the vesico- FIG. i 704. Pubo-vesical ligament^ Pelvic fascia covering levator ani Obturator membrane.^ Visceral exten- sion of pelvic fascia Obturator fascia Fat removed ex posing pelvic floor Visceral reflec- tion of pelvic fascia Obturatoi- internus Levator an'i- - Ischium, cur Anal fascia-" --Symphysis pubis , Pubic bone, cut Prevesical space, cleaned out _ Portion of wall of bladder Urethra Vesico-vaginal venous plexus -Rectum Ischio-rectal fossa Anterior portion of horrzontal section through pelvis, of temale, passing just below bladder ; visceral reflections of pelvic fascia are seen extending to bladder, vagina, and rectum. vaginal plexus that above surrounds the ureter and the vaginal branches of the uterine artery. Structure. The vaginal walls, from 2-3 mm. thick, include a mucous and a muscular coat, supplemented externally by an indefinite fibrous tunic. The mucous coat consists of a tunica propria, exceptionally rich in elastic fibres and veins, the inner surface of which is beset with numerous conical papillae that encroach upon the overlying epithelium, but do not model the free surface. The epithelium, from o. 15-0. 20 mm. thick, is stratified squamous in type and possesses a superficial stratum of plate-like cells (.020-. 030 mm. in diameter) that resemble the epidermal ele- ments of the skin and are constantly undergoing maceration and abrasion. Although normally moistened by a thin mucous secretion of acid reaction, the vagina is devoid of true glands and probably derives its lubricating fluid for the most part from the uterine glands, the alkaline secretion becoming modified. Small nodules of lymphoid tissue are scattered within the mucosa, especially in the upper part of the canal. The duplicature of the mucous membrane forming the hymen corresponds in structure with that lining other parts of the canal. The muscular coat, which directly sup- ports the mucosa without the intervention of a submucous tunic, consists of bundles of involuntary muscle that are arranged, although not with precision, as an inner circular and an outer longitudinal layer. The latter is best developed over the 127 201 8 HUMAN ANATOMY. Tuni propria anterior vaginal wall, from which bundles of muscular tissue are continued into the urethro-vagmal septum; behind, bundles pass into the recto-vaginal partition. Above, the vaginal muscle is directly continuous with that of the uterus and below penetrates the perineal body. Within, the conspicuous columnae rugarum, the muscular coat, as well as the mucous, is thickened, the elevations acquiring the character of erectile FlG J.Q,. tissue owing to the great num- ber of veins intermingled with the irregularly disposed mus- cle bundles. After piercing the superior layer of the tri- angular ligament and in the vicinity of the orifice, the vagi- nal walls receive strands of striated fibres derived from the middle part of the com- pressor urethrae (m. urethro- vaginalis) and the bulbo-cav- ernosus muscles.' Vessels. The arteries supplying the vagina, all de- rived from the internal iliac, reach the organ by various routes. The upper part of the vagina is supplied by twigs continued from the cervical branch of the uterine arteries, that descend along the sides of the canal and communicate with the branches from the middle hemorrhoidal and vagi- nal (vesico-vaginal), that are distributed to the middle and lower portions of the vagina respectively. Those from the vaginal, of the two sides, form encircling anastomoses from which an unpaired vessel (a. azygos vagina) fre- quently is given off on the posterior, and sometimes anterior, wall. Additional branches pass to the lower part of the vagina from the arteries to the bulbus vestibuli from the internal pudics. Free anastomosis exists between the vessels derived from these various sources. The veins, numerous and large, after emerging from the mus- cular tunic unite on each side to form the rich vaginal plexus that extends along the sides of the genital canal and communicates with the vesical and uterine plexuses. It receives tributaries from the external generative organs and is drained by a trunk, the vaginal vein, that passes from its upper part to the internal iliac vein. The lymphatics within the mucous membrane form a close net-work that commu- nicates with the lymph-vessels of the muscular coat. The collecting trunks pass from the upper and middle thirds of the vagina, in company with those from the cervix uteri, chiefly to the lymph-nodes along the internal iliac artery. Additional stems from the posterior vaginal wall encircle the bowel and terminate either in the rectal or the lumbar nodes (Bruhns). The lymphatics from the vicinity of the vagi- nal orifice pass chiefly to the upper median group of inguinal nodes ; some, however, join the lymph-paths from the upper segments. The nerves are derived from the hypogastric sympathetic plexus, through the pelvic, and from the second, third, and fourth sacral nerves. The immediate source of the sympathetic fibres is the cervical ganglion, at the side of the neck of the uterus, from which, in association with the sacral branches, twigs pass to form, on each side, the vaginal plexus that embraces the vagina and provides filaments chiefly for the involuntary muscle of its walls and blood-vessels. The sensory fibres supplying the mucous membrane of the upper part of the vagina are meagre, since, under normal conditions, this part of the canal possesses sensibility in only very moderate degree. Towards the orifice the vagina receives fibres from the pudic nerves which endow Section of wall of vagina. X 80. PRACTICAL CONSIDERATIONS : THE VAGINA. 2019 the mucous membrane of the lower third with greater sensibility and send motor fila- ments to the striated muscle surrounding the entrance. Sensory nerve-endings of different kinds have been described within the mucosa. Development. The vagina is formed by the downward extension and fusion of the Miillerian ducts. After union of the latter with the posterior wall of the uro- genital sinus and the appearance of a lumen, which at first is wanting, the genital canal opens into the sinus by an aperture, later the orificium vaginae, that lies between and closely united with the Wolffian ducts. The latter subsequently atrophy and disappear, but may, in exceptional cases, persist to a greater or less extent as Gart- ner's ducts. The entrance of the immature vagina is early guarded by an annular fold that becomes the hymen and owes its differentiation to a pouching of the vaginal wall behind a zone of thickened epithelium (Nagel). For a time, usually until about the seventh month of fcetal life, the orifice of the vagina is occluded by epithelium. The proliferation and thickening of the vaginal lining, which begin below, gradually extend upward and result in the production of conspicuous rugae, which, during the last months of pregnancy, cover not only the entire surface of the vagina, but also that of the cervix, which even at birth is slightly corrugated. In consequence of the increasing irregularity and thickening of the mucosa, the vaginal walls, which for a time are adherent, become separated and the lumen of the canal is definitely estab- lished, remains of the desquamated epithelium being often visible in the new-born child. Distinct muscular tissue within the vaginal wall is not distinguishable before the fifth month. At birth, the vagina is relatively long (Fig. 1623) and its wall is comparatively thick, with conspicuous rugae extending as far as the vault. During the early years of childhood the vagina remains small and vertical, but after the tenth year grows rapidly, the increased width causing reduction in the rugae, which from now on are feebly marked in the upper part of the canal. After undergoing the stretching inci- dent to labor, the rugae and columns are much less conspicuous, and after repeated distention may suffer almost complete effacement. The vagina shares in the general involution of the sexual organs, and in advanced years loses much of its former elas- ticity and undergoes atrophy. Variations. The most important variations depend upon defective development and im- perfect fusion of the component Miillerian ducts, and are, therefore, often associated with anomalies of the uterus. When these tubes fail to reach the urogenital sinus, the vagina ends blindly above the vestibule ; or when their lower segments are stunted, the vagina (and often uterus) may be entirely wanting. Duplication, more or less complete, follows persistence of separate or imperfectly fused Miillerian ducts. The doubling may not extend throughout the length of the vagina, but may be represented by an imperfect and partial septum, isolated bands, or a twin hymen. Unequal development of the Miillerian ducts accounts for the marked asym- metry occasionally observed, notably in double vaginae, where one canal may be very rudi- mentary or end blindly. The hymen presents great variety in the details of its opening, which may be crescentic, circular, stellate, linear, double, or multiple (hymen cribriformis] . It may be a mere pin-hole or entirely wanting (imperf orate), in which case retention of menstrual dis- charges occurs. PRACTICAL CONSIDERATIONS : THE VAGINA. Congenital malformations of the vagina, such as absence of the vagina, rudi- mentary vagina, or vaginal septa, are usually associated with corresponding errors in development of the uterus. While other malformations due to faulty union of the Miillerian ducts occur, the more common is a uterus bicornis, or a double uterus and vagina. They are not incompatible with pregnancy, labor and the puerperium often passing without unusual incident ; indeed, this condition is usually recognized by accident, since no external evidence is seen. Conception may occur on one or both sides simultaneously. A vaginal septum which interfered with the progress of the head should be divided. From imperfect development of one side of a bicornate uterus, pregnancy may lead to great danger of rupture of the weak uterine wall, or to a failure to expel the child. While varying within normal limits with the distention of the bladder, when the latter is empty the axis of the fundus of the uterus lies at about a right angle with the vagina. The inner or uterine end of the broad ligament is, except at its base, 2020 HUMAN ANATOMY. more nearly horizontal than vertical in direction. As a result of this position of the uterus, it will be seen that the lower surface of the cervix presents against the pos- terior vaginal wall, and that, therefore, this wall of the vagina must be longer than the anterior. The posterior wall is usually about three and a half inches long ; and the anterior about two and a half to three inches. The length of the ordinary ringer is about three inches ; it can, therefore, reach the anterior fornix of the vagina and anterior lip of the cervix. To explore the posterior fornix of the vagina considerable pressure is required. To palpate structures in Douglas's cul-de-sac the bimanual method of examination will be necessary, and a relaxed abdominal wall, to obtain which a general anaesthetic may exceptionally be required. An empty bladder facili- tates a bimanual examination. In the knee-chest posture the vagina becomes dis- tended with air, permitting a more thorough visual examination of its walls. The rectum posteriorly, and the base of the bladder and the urethra anteriorly, are within reach of the finger in the vagina. Calculi, either in the lower ends of the ureters (vide supra) or in the bladder, can be removed through the anterior vaginal wall (page 2015). The intravaginal portion of the cervix uteri can, with little or no pain, be grasped by a tenaculum and drawn down towards the vaginal orifice so that local applications can be made. It is so insensitive that such applications, even when strong and irri- tating, do not necessitate the use of an anaesthetic. Since it is the part of the cervix most exposed to traumatism and infection, it is the most frequent seat of pathological lesions, such as the so-called "erosions." Persistent i.e. , unhealed lacerations are often sources of irritation, of reflex pains, and of some forms of dysmenorrhcea. Much of the pelvic pain, associated with them, is probably due to pelvic lymphangitis or lymphadenitis (Penrose). These lacerations seem to invite the development of cancer. Primary involvement of the body of the uterus is comparatively rare, the great majority of cancers of the uterus beginning in the cervix. As a result of the relations and contiguity of the cervix to surrounding important structures, such as the bladder, ureters, and rectum, the prognosis of cancer of the cervix is less favorable than that of the body of the uterus, where infiltration of neighboring structures does not occur so early. As a rule, dissemination by lymphatic channels from carcinoma of the cervix, affects first the sacral or the iliac glands; carcinoma of the body of the uterus is more likely to involve the lumbar glands surrounding the common iliacs, the aorta, and the vena cava. Pressure on the last-named vessel may result in cedematous swelling of the lower extremities or in ascites. An hypertrophied cervix shows as an increased projection into the vagina and a deepening of the vaginal fornices. This condition may be a cause of sterility. The vagina is most roomy in its upper portion, and is narrowest at its lower end, where it passes through the triangular ligament and is surrounded by the con- strictor vaginae muscle. This favors the retention of blood-clots within the vagina during the menstrual period and after labor. Spasmodic contraction of this muscle (vaginismus) is described as being sometimes strong enough to prevent coitus and to call for surgical treatment, though such cases, if they exist at all, are due to reflex irritation, such as from urethral caruncle. The dilatation of the vagina seems to be limited only by the pelvic wall. In nullipara the rugosity of its mucous membrane- necessitated by its great changes in diameter is marked. The transverse folds favor retention of secretions and of discharges resulting from infection and render sterilization of the vagina difficult. Vaginitis may be followed by endometritis, as the uterine and vaginal mucosae are directly continuous. The hymen rarely may have no opening, when it will require incision to relieve the obstructed first menstrual flow. The exact importance to be attached to the presence or absence of the hymen in medical jurisprudence is still undetermined. While it is usually broken at the first coitus, it may remain intact until the first parturition. Therefore its presence does not prove virginity. Its original perfora- tion may have been large enough to leave little or no evidence of the membrane, so that its absence does not prove that coitus has taken place. Fistula 1 between the bladder and vagina (vesico- vaginal), between the urethra and vagina (urethro- vaginal), between tin- rectum and vagina (recto-vaginal), and between the cervical canal and the bladder (utero-vesical), may occur. THE LABIA AND THE VESTIBULE. 2021 Recto-vcsical fistula in a woman has followed ischio-rectal abscess, after the dis- charge of which the patient passed gas and faecal matter through the urethra (Noble). Vesuo-vaginal fistulae are usually due to sloughing consequent upon the impac- tion of the head in a difficult labor ; they are not due, as erroneously believed, to the use of forceps, but to too long delay in using them (Emmet). Urethro-vaginal fistulae following labor are rare. More frequently the com- munication between the vagina and the upper part of the urethra is part of a larger opening into the bladder. It is in reality a vesico-urethro-vaginal fistula. Vesico-uterine fistulae are usually due to a tear extending forward through the anterior vaginal fornix into the bladder, and upward along the cervical canal. The lower part of the tear heals, leaving an opening between the bladder and cervical canal, the urine dribbling outward from the bladder into the cervical canal and thence into the vagina. If the lower part of the tear does not heal, we then have a vesico- utcro-vaginal fistula. Recto-vaginal fistulae are found usually at the upper or lower end of the vagina. At the upper end they are most frequently due to extension of an epithelioma of the cervix into the rectum, and in the lower end to incomplete closure of a torn perineum extending into the rectum. They are very rarely due to labor itself. THE FEMALE EXTERNAL GENITAL ORGANS. The external generative organs of the female include those parts of the repro- ductive apparatus that lie below the triangular ligament and in front of and below the pubic arch. They are the labia majora, with the mons pubis above and the urogen- ital cleft between them, the labia minora or nymphcz, and the enclosed vestibule, the clitoris and the bulbus vestibuli, together with the glands of Bartholin ; within the vestibule are the orifices of the urethra and of the vagina. Of these structures, col- lectively termed \he pudendum (pudendum muliebre), or vulva, in the upright posture usually little more than the mons pubis and the labia majora are visible, although exceptionally the labia minora and the clitoris may be seen within the genital fissure. THE LABIA AND THE VESTIBULE. The labia major (labia majora pudendi) are two prominent rounded cutaneous folds, the homologue of the scrotum, about 7.5 cm. (3 in.) long and 2.5 cm. thick, that extend backward from the mons pubis and enclose between their medial surfaces the urogenital cleft (rima pudendi). Above, their inner margins are continuous (com- missura labiorum anterior) over the ridge formed by the body of the clitoris ; behind, where their tapering ends blend with the perineum, they are connected by a trans- verse fold (commissura labiorum posterior), often only slightly marked and sometimes wanting, that crosses the mid-line in advance of the anus. Their outer surface is covered with thick, dark-hued integument and beset with hairs, in varying profusion, that encroach for a limited zone on the inner surface of the labia and may extend as far as the anus. The medial surface, on which the hairs are few and minute, is clothed with skin of much more delicate texture, that at the bottom of the nympho- labial furrow passes onto the outer surface of the nymphae. In addition to the skin, each labium consists of a layer of subcutaneous fat, between which and the integu- ment in the posterior half, a thin stratum of involuntary muscle (tunica darto- labialis) is continued forward from the dartos of the perineum and represents the similar but better developed sheet in the scrotum. The centre of the labium is occu- pied by a fairly well defined mass of fat (corpus adiposum) that is connected with the adipose tissue within the inguinal canal continuous with the subperitoneal tissue and is, therefore, of different derivation than that of the subcutaneous fat, from which it is separated by a delicate fascia. Into the latter are inserted some of the fibres of the round ligament of the uterus that ends within the labium majus. Sweat and sebaceous glands are numerous within the integument of the labia. The mons pubis or Veneris, as the triangular rounded eminence above the genital cleft is called, consists of a cushion of fat, enclosed by dense skin and thickly covered with hair. The subcutaneous fatty layer, usually from 23 cm. thick, but 2022 HUMAN ANATOMY. sometimes as much as 8 cm. or more, is supported by connective-tissue septa that pass from the underlying periosteum to the skin, whereby the tension of the latter is maintained. The labia minora, or nymphae (labia minora pudendi), are two thin folds of delicate skin that, for the most part, lie concealed between the larger labia, unless the latter are separated, and enclose the vestibule. Their length is from 2.5-3.5 cm -. their width about half as much, and their thickness from 3-5 mm. Near its anterior end, each labium divides into a lateral and a medial limb ; the lateral divisions of the two sides unite above the free end of the clitoris, which they enclose with a hood, the preputium clitoridis, while the medial limbs join at an acute angle on the under side of the clitoris to form \\sfrenum (frenulum clitoridis). Behind, the nymphae grad- ually fade away by joining the inner surface of the labia majora. In the virgin, and when well developed, the medial border of the posterior ends of the nymphse are usu- ally connected by a slight FIG 1706 transverse crescentic fold, the frenum or fourchette (frenulum labiorum pudendi) that marks the posterior boundary of the shallow navicular fossa (Fig. 1706). Both surfacesof the nymphae are covered with delicate skin, which, on account of the protection afforded by the greater labia and con- stant contact with the vagi- nal secretions, remains moist and soft and assumes the color and appearance of a mucous membrane. The entire absence of mucous glands and the presence of numerous sebaceous folli- cles, on the inner as well as on the outer surface, to- gether with the develop- ment of the nymphae from the margin of the cloacal fossa, establish their cuta- neous character. The skin covering the nymphae ex- ternally is continuous with that of the labia majora at the bottom of theinterlabial furrow ; internally the line of transition into the mucous membrane lining the vesti- bule follows the medial attachment of the folds which overlie the vestibular bulb. In addition to the two cutaneous layers, the nymphae consist of an intermediate stratum of loose connective tissue, rich in blood-vessels, and containing many bundles of in- voluntary muscles that possess the character of erectile tissue. Hairs and fat are entirely wanting in the labia minora, but sebaceous and sweat glands are present, the latter small and scattered but most plentiful in the anterior part and in the prepuce (Webster). The vestibule (vestibuluiii vaginae) is the elliptical space enclosed between the labia minora, extending from the clitoris in front to the crescentic frenum behind. When the nympha- arc separated, the vestibule resembles an almond in outline, being pointed in front and broader behind. In the roof (as usually examined the floor) of this space are seen the; urethral and vaginal orifices and the minute openings of the paraurethral ducts and of the canals of Bartholin's glands. The- urdliral orifice occu- pies a more or less conspicuous corrugated elevation ( papilla urethral is ) that lies about Posterior commissure External genital organs of virgin ; lahia have been separated to expose vestibule and vaginal orifice. THE LABIA AND THE VESTIBULE. 2023 2 cm. behind the clitoris and breaks the smooth mucous surface of the vestibular roof. The opening' of the urethra is very variable in form, being crescentic, stellate, crucial or linear, a sagittal cleft of about 5 mm. being the most usual type. Close to the urethral orifice, at the sides or somewhat behind, lie the minute depressions marking the openings of the paraurethral ducts (page 1706). In young subjects, a pair of fine sagittal folds can often be traced over the roof of the vestibule from the urethral papilla to the frenum of the clitoris. The area between the orifice of the urethra and that of the vagina is subject to considerable individual variation in size and detail owing to differences in the extent to which the lower end of the anterior vaginal column (carina urethralis) encroaches upon the vestibule. After rupture of the hymen has occurred, the vaginal entrance is surrounded by a series of irregular fimbriated projections that form the caruncula hymenales which, after labor, become reduced to inconspicuous nodules. Included between the posterior margin of the hymen and the backwardly directed arching fold of the fourchette is the fossa navicularis, a shallow, crescentic, pocket-like depres- FIG. 1707. Labium majus n-- Central fat-body Labium minus Inner surface Sebaceous glands on external^ cutaneous surfaces Interlabial groove Section across the labia of very young child. X 18. sion. This recess is best marked in the virgin, when the nymphee are well developed, and is usually effaced after child-bearing. Vessels. The arteries supplying the labia majora are chiefly the anterior and posterior labial branches from the external and internal pudics respectively. A small twig from the superficial external pudic is distributed in the vicinity of the anterior commissure ; several others from the deep external pudic end in the anterior half of the labium, while the posterior half is supplied by the posterior labial twigs from the superficial perineal branch from the internal pudic artery. Additional small twigs from the anterior terminal branch of the obturator artery are distributed to the outer surface of the labia. The nymphse also receive their blood from the anterior and posterior labial arteries through small branches that enter the front and hind parts of the folds and assist in nourishing the mucous membrane lining the roof of the vestibule. The arteries from these various sources freely anastomose with one another as well as with adjacent vessels. While the veins of the labia majora in general follow the corresponding arteries, they communicate with neighboring systems, particularly with the inferior hemorrhoidal and the pelvic plexuses. The veins of the nymphae, unusually numerous and large, present a plexiform arrangement, whereby the labia acquire the character of erectile structures. The collecting stems 2024 HUMAN ANATOMY. join those of the labia majora, as well as communicate with the veins of the clitoris and bulb. The lymphatics of the labia are very numerous, notably in the more superficial parts of the folds, a half dozen or more trunks passing to the upper and medial group of inguinal lymph-nodes. The lymphatics from the nymphae, also very numerous, join the afferents from the labia majora and end in the same inguinal nodes. Communications sometimes exist with the nodes of the opposite sides (Bruhns). The nerves supplying the anterior half of the labia majora are derived from the ilio-inguinal and the genital branch of the genito-crural, while the posterior part of the labia receive filaments from the perinea! branches of the pudic and the small sciatic trunks. The nymphae are highly sensitive and receive branches from the superficial perineal nerves upon which special sensory endings are found within the subepithelial tissue. THE CLITORIS. The clitoris, the homologue of the penis, repeats in reduced size and modified form the chief components of the organ of the male. Morphologically considered, it consists of two corpora cavernosa, united in front into the body and separated behind into the crura attached to the pubic arch, and the imperfectly developed and cleft corpus spongiosum known as the bulbus vestibuli and usually described as an inde- pendent organ. The clitoris lies so buried within the subcutaneous tissue and beneath the labia that only its small conical anterior end, called the glans clitoridis, and the low verti- FIG. 1708. Suspensory ligament of clitoris orpus clitoridis lans clitoridis Pars intermedia Urethral orifice Bulbus vestibuli Vaginal orifice Inferior layer of - triangular ligament Crus clitoridis curved by ischio-cavernosus muscle Cut edge Compressor bulbi Transversus perinei Dissection of urogenital triangle of female, showing clitoris and bulbus vestibuli. cal ridge of integument over the body (torus clitoridis) appear when the labia are separated. The glans, about 5 mm. in diameter, is partly concealed by an annular duplicature of skin, the prcputium clitoridis, that is free in front and at the sides, but behind is attached by a median fold, the frcniim, continuous with the nymphae. When exposed after removal of the labia and skin, the clitoris (using the term in the more restricted and conventional sense) is seen to consist of the small unpaired body (corpus clitoridis), from 2 to 2.5 cm. long, composed of the fused corpora earcrnosa, and the diverging and much larger crura, from 3.5-4 cm. in length, that are attached to the sides of the subpubic arch, as are the corresponding parts of the penis. The crura clitoridis are, however, relatively flat and blunt. The dependent body forms a sharp bend with the diverging crura, bring fixed to the lower part of the symphy- sis pubis by a diminutive suspensory ligament. Owing to its attachments to the in- THE CLITORIS. 2025 tegument and nymphae, the position of the body and its angle undergo but slight change even in the turgescent condition of the organ. In their general structure the corpora cavernosa clitoridis, apart from their reduced size and feebler develop- ment, correspond with those of the penis, including cylinders of erectile tissue en- closed by a tunica albuginea and separated where blended by a septum. The glans, however, is composed chiefly of fibrous tissue and contains little true cavernous structure ; it is, of course, not perforated by the urethra. The Bulbus Vestibuli. The vestibular bulb consists of two converging elongated masses of cavernous tissue, completely separated except in front, where they are connected by a narrow isthmus, the pars intermedia. They embrace the lower end of the vagina and the urethra, and anteriorly meet the under surface of the cavernous bodies of the clitoris. The organ, as above noted, represents the bulbar and adjoining parts of the corpus spongiosum, of which the component parts have remained ununited in consequence of the persistence of the urogenital cleft, each half corresponding to a semibulb of the united structure in the male. Each bulb, regarding the organ as paired, is a wedge-shaped body, narrow in front and broad and rounded behind, that measures from 3-4 cm. in length, where broadest from 1-1.5 cm. in width, and less than i cm. in thickness. Above, it rests against the inferior layer of the triangular ligament, its lower margin, somewhat medially di- rected, being covered by the base of the labium majus and the nympha. Behind, the medial surface is closely related to the lateral wall of the vaginal entrance, and when well developed may extend backward as far as the posterior wall of the vagina. In front, the bulb passes at the side of the urethra and joins the under surface of the clitoris. Laterally and below, it is covered by the fibres of the bulbo-cavernosus mus- cle. The rounded hind end meets or covers the gland of Bartholin. The two bodies together form a compressed crescentic or horseshoe-shaped complex of venous spaces, enclosed by a thin tunica albuginea, that resembles the cavernous tissue of the corpus spongiosum, although less definite in structure. Vessels. The arteries supplying the clitoris and vestibular bulb correspond with those distributed to the homologous parts of the penis, but are of smaller size. As in the male, the first branch to the cavernous tissue is the artery of the bulb (a. bulbi vestibuli), which enters that body near its posterior end as a short and comparatively strong vessel and joins with additional twigs to the bulb from the deep artery of the clitoris (a. profunda clitoridis), a branch corresponding to the urethral artery passing to the pars intermedia. Each cavernous body receives the deep branch that enters the crus and, sending a minute twig backward, traverses the cylinder of erectile tissue towards the glans, communicating with its fellow of the opposite side as well as with the dorsal artery (a. dorsalis clitoridis). The latter, the terminal part of the internal pudic and smallest of the vessels supplying the clitoris, pursues a course identical with that of the corresponding vessel of the penis, but is minute in consequence of the reduced dimensions of the parts supplied. The veins follow the general arrangement observed in the penis, the blood being carried off chiefly by the dorsal vein and the venous channels that more closely accompany the arteries. The most important modification is the presence of the plexus intermedius (Kobelt), a venous complex that lies between the under surface of the corpora cavernosa, just as they begin to diverge into the crura, and the united anterior ends of the halves of the bulbus vestibuli. This plexus not only establishes connections between the blood-spaces of the corpora cavernosa and the bulbus vestibuli, but also receives tributaries from the prepuce and frenum of the clitoris, the nymphae, and the adjacent parts of the vestibule. In addition to the stems that join the internal pudic veins, the cavernous spaces of the bulb communicate with the urethral, vaginal, and hemorrhoidal plexuses. In consequence of the connections between the plexus intermedius and the dorsal vein of the clitoris, the latter vessel is relatively of large size. The lymphatics for the most part are afferents of the superficial inguinal lymph- nodes; communications exist, however, with the deeper intrapelvic paths and nodes. The nerves of the clitoris are derived and distributed in correspondence with the plan observed in the penis. They are, therefore, extensively from the sympa- thetic system for the walls of the blood-spaces and from the pudic nerves. The 2026 HUMAN ANATOMY. dorsal nerve is relatively large and supplies the integument of the glans and prepuce with fibres connected with special sensory end-organs. THE GLANDS OF BARTHOLIN. The glands of Bartholin (glandulae vestibulares majores), the homologues of Cowper's glands in the male, are a pair of small organs, situated one on either side of the vaginal orifice, behind the bulbus vestibuli and about the middle of the base of the labium majus. The organ measures from 1-1.5 cm - m length and somewhat less than i cm. in width, and is covered on its anterolateral aspect by the bulbo- cavernosus muscle and, often, also by the end of the bulbus vestibuli. Its superior surface lies against the inferior layer of the triangular ligament, and its medial about 1 cm. external to the vestibule, from which it is separated by dense fibrous tissue. From the anteromedial border of the gland emerges the duct, a narrow tube, about 2 mm. in diameter and from 1.52 cm. long, that passes obliquely inward and for- ward, beneath the base of the nympha, to open in the groove between the latter and the hymen about opposite the posterior third of the lateral boundary of the vagi- nal orifice. The minute FIG. 1709. Dorsalnerve opening of the duct, from Corpus clitoridis Dorsal artery / Artery of bulb . 5-. 6 mm. Wide, IS often Glans ciitoridis X. / /Crusof at the bottom of a small j^tf^^^^^^aMMMtf^^_ / / clitoris < **.!_ >* \ j^^ttg^T'T'l pulled depression in the mu- upward cous mem brane of the / 7\ vestibule. /' \ * n struct ure the gland corresponds to the Crus of - mucous tubo - alveolar Jjr/i 1 ^.Portion of type, the small compo- Right lobe / 1 u 1 u of bulbus M / A *C\ nent lobules, however, being separated by con- -T ube .r siderable tracts of fibro- ischii muscular tissue. Theter- hgament t minal compartments are lined with columnar epi- thelium containing many rf goblet cells. The lobular Glands of Bartholin .\ ducts unite to torm the Dissection of uroeenital triangle of female; left lobe of cincr1i=> ^vrr^rr^rv rani! vestibular bulb has been removed. which is beset with mi- nute mucous follicles. The main duct, which sometimes exhibits ampullary enlarge- ments, is clothed with columnar epithelium until near its termination, where its lining becomes stratified squamous in character, to correspond with that of the vestibule. The secretion of the gland is whitish in color and viscid. Vessels. The arteries supplying the gland are usually twigs given off from the bulbar branch of the internal pudic. The veins are tributary chiefly to the internal pudic, but also communicate with the trunks of the vestibular bulb and of the vagina. The lymphatics join those of the vagina and rectum that are afferents of the internal iliac nodes. Tt is probable that, to'a limited extent, communication also exists with the paths ending in the superficial inguinal nodes. The nerves are very numerous, and include sympathetic fibres and twigs from the pudic. Development. The glands of Bartholin first appear in embryos from 4-5 cm. Ion-, as solid epithelial outgrowths from the lateral walls of the urogenital sinus. At first simple cylinder, they later become branched, acquire a lumen and, in embryos of from 12-15 cm. in length, begin to exhibit alveoli lined with mucus secreting fells i V. Miiller). Although fully developed at birth, the glands remain small until lu-ar puberty, when they enlarge, acquiring their greatest si/e during the years of sexual activity. After the cessation of menstruation they gradually diminish, and are atrophic in the aged subject. THE MAMMARY GLANDS. 2027 Variations. The glands of the two sides often vary in size and may be asymmetrically placed. The ducts may be doubled and the lobules so separated that the usual gland-mass is replaced by isolated divisions. The glands are sometimes seemingly wanting on one or both sides. PRACTICAL CONSIDERATIONS : THE EXTERNAL GENITALS. Owing to the protected position of the vulva it is rarely wounded except from tears in childbirth. When lesions from external violence do occur, they are usually the result of falls astride hard objects, of kicks, of blows, or of wounds inflicted by horned cattle. Because of the laxity of the tissues and the free blood-supply in the labia majora large haematomata may collect, especially if the bulbus vestibuli is opened. Again, because of the free blood-supply and loose tissue in this region, plastic operations are commonly very successful. The hemorrhage is free, but ordi- narily stops spontaneously unless the erectile tissue of the clitoris or its continuations backward, the bulbus vestibuli, is 'wounded. The lymphatics and veins of the vulva pass to the groin, thus explaining the en- largement of the vulva in lymphatic obstructions in the inguinal nodes, such as elephantiasis, and in venous stasis in the same region, as in milk leg. The clitoris is especially involved in elephantiasis, either alone or as part of a general enlarge- ment. The absorbents of the vagina pass to the pelvis. About the orifice of the vagina is a zone in which the two sets intercommunicate. Cysts of the vulva are commonly due to retention of secretion within the glands of Bartholin. They occupy the posterior third on each side of the vaginal orifice, and project more from the mucous than from the cutaneous surface. These glands are often the seat of abscess, almost, if not always, the result of gonorrheal infection. The female urethra, running downward and forward so that it is nearest to the vaginal wall in its upper portion is much shorter, much less curved, relatively much wider, and as it is not surrounded at any point by structures of such density much more dilatable than the male urethra. In consequence of its shortness, its width, the direc- tion of its course, and the limitation of its function to serving as a passage for urine, it is, as compared with the male urethra, infected less frequently, and its inflammation is associated with less severe symptoms, yields more readily to treatment, and gives rise to fewer complications and sequelae, stricture, for example, being very rare. As a result of its dilatability it may be used as a channel for digital exploration of the bladder, or for the extraction of vesical calculi or pedunculated tumors, if small, or of foreign bodies. The dilatation should be accomplished very slowly under an anaesthetic and is then rarely followed by persistent paralysis. The imper- fect development of the triangular (subpubic) ligament in the female and of the muscular wall of the urethra the emptying of the canal being so facilitated by its direction, width, and shortness explains the relative ease and safety of extreme dilatation. A small red vascular tumor, called a urethra! caruncle, is sometimes found pro- truding, usually from the posterior wall of the female urethra. It is extremely sensi- tive, giving rise to much pain on pressure, movement, or urination. The vaginal process of peritoneum accompanying the round ligament, already spoken of, may reach as far as the labium majus, and may give rise to a congenital hernia or hydrocele in that part. Owing commonly to the presence of vaginal dis- charge, the vulvar region is frequently the seat of venereal warts. Because of the warmth, moisture, and friction to which syphilitic papules are exposed in these parts, condylomata and mucous patches are common and well marked. One of the most frequent seats of chancre in women is about the fourchette and anus, because the infected discharges of the vagina tend to run over and lodge on these structures. THE MAMMARY GLANDS. Although morphologically considered they are modified cutaneous glands and developed in both sexes, the functional importance of the mammary glands (mammae) in the female entitle them to be reckoned as organs accessory to the reproductive apparatus. Each mamma, or breast, consists of a group of twenty or more individual 2028 HUMAN ANATOMY. and separate glands, opening by independent ducts, that collectively constitute the true secreting organ (corpus mammae), as distinguished from the enveloping layer of fat and areolar tissue. As seen in the young, well-developed subject, before the occurrence of preg- nancy, the mammae form two hemispherical projections that lie upon the thoracic wall, one on either side of the sternum, extending from the outer margin of the latter to the axillary border and from the level of the second to that of the sixth rib. The outline of the organ is not quite circular but elliptical, the horizontal diameter, from 10-12 cm. (4-4^4 in.), being about one centimetre more than the vertical. The height of the projection measures about 5. 5 cm. The rounded contour of the breast depends chiefly upon the fat that forms a complete envelope for the glandular tissue, FIG. 1710 Areol Lobule of gland-tissue Excretory duct Nipple \ Ampulla Lactiferous duct Lilt mamma drawn from living subject ; ducts and glandular tissue have been drawn from dissection. except beneath the nipple and, in places, on the deep muscular surface. In the young subject, in whom the gland has never enlarged in consequence of pregnancy, the secre- tory tissue is relatively small in amount and masked by the fat that penetrates between the lobules. The approximate summit of each breast, when firm and non-pendulous as in young women, is marked by the conical or wart-like nipple (papilla mammai- which lies opposite -the lower border of the fourth rib and is pierced by the excretory canals, or lactiferous ducts, from the lobes. The nipple, about I cm. high, and marked by numerous shallow furrows, is surrounded by the arcola, a cutaneous /one about 4.5 cm. in diameter that is modelled by minute low elevations produced by the small subcutaneous areolar ^ land .^, Vt glands of Montgomery , which represent isolated accessory portions of secretory tissue. Although varying with the complexion, the THE MAMMARY GLANDS. 2029 Suspensory band Pectoral muscle pigmentation of the integument covering the nipple and areola is very slight, and hence the color of these parts is usually a rosy pink. After the earlier months of pregnancy the color of the nipple and areola changes to brown, in varying shades of intensity, which tint thereafter never entirely disappears, but becomes temporarily augmented with each pregnancy. The mammary gland lies within the superficial fascia of the thorax, which not only forms a general investment for the or- gan, but also sends into it septa that mate- FIG. 1711. rially aid in supporting the fat and glandular tissue. Local peripheral thickenings of the fascia occur above and below and assume the character of suspensory bands, those above being known as the ligaments of Cooper. Although for the most part separated from the underlying muscle by a layer of fascia that permits of shifting of the mamma, its deepest lobules may occupy recesses between the fas- ciculi of the pectoralis major. Structure. The corpus mam nice con- sists of from 15-20 or more flattened pyrami- dal lobes (lobi mammae), each of which is a distinct gland measuring from 1.5-2 cm. The lobes are radially disposed, the groups of al- veoli or lobules lying towards the periphery and the excretory ducts converging towards the nipple, upon which they open. When enlarged, as during lactation, the lobes pro- duce irregularities in the outline and on the surface of the gland-mass that may be felt through the covering of adipose tissue. Each lobe is subdivided by connective tissue into several lobules (lobuli mammae), which in turn are made up of the ultimate divisions of the secreting tissue or alveoli. The latter are sacular compartments, the walls of which con- sist of a well-defined membrana propria, or basement membrane, lined, in the resting con- dition, by a double layer of cells. Those next the membrana propria are probably to be regarded as muscular in nature (Lacroix, Benda), thus emphasizing the resemblance between the mammary and sweat glands. The inner cells, the secretory elements, are cuboid or low columnar, from .005- .007 mm. high, and present the usual appearances of glandular epithelium. Ditring lactation the alveoli become greatly enlarged and distended and the intervening connective tissue correspondingly reduced, so that the alveoli are pressed closely together, the general appearance of the tissue often recalling that of the lung. Under such conditions the secreting cells vary with the distention of the alveoli, being low in large compartments and higher in those less expanded. The protoplasm of the cells actively engaged in the production of milk contain minute oil droplets that occupy chiefly the inner zone. As these increase in size, they press the nucleus towards the basement membrane and project into the alveolus, being separated from the lumen by only a thin protoplasmic stratum. Finally, the latter ruptures, and the oil droplets escape into the albuminous fluid that is additionally secreted by the glands and occupy the alveolus. After liberation of the oil droplets, the epithelial cell is much reduced in height, but after a time again becomes the seat of renewed accumulation of fat and the production of milk-globules. Destruc- tion of the fat-liberating cells, therefore, does not take place. The excretory ducts begin as the minute canals into which the alveoli open. Gland- tissue Fascial envelope Sagittal section of mamma of young woman who had never borne children ; hardened in formalin. 2030 HUMAN ANATOMY. ._- -Excretory duct ' Section of mammary gland before lactation. X 170. At first they are small and much like the terminal compartments of the gland and lined with a thin stratum of longitudinally disposed involuntary muscle, upon which rests a single layer of cuboid epithelial cells. The latter give place to cells of col- umnar type within the lactiferous FIG. 1712. ducts that are formed by the junction of the smaller canals. On approaching the base of the nipple, beneath the areola, each milk-duct presents a spindle-form enlargement or ampulla ( sinus lactifcrus), from 10-12 mm. long and about half as wide, that serves as a temporary reservoir for the secretion of the gland. Beyond the ampulla the duct narrows to a calibre of little over 2 mm. , passes into the nipple, and ends, after traversing the lat- ter parallel with the other ducts, in a minute orifice from . 5-. 7 mm. in diameter, at the summit of the papilla. On gaining the last-named point, the lining epi- thelium of the duct assumes the stratified squamous type of the adjacent epidermis. Embedded within the delicate but more or less pigmented skin that covers their exterior, the areola and nipple contain well- marked bundles of involuntary muscle, by the contraction of which the nipple becomes erect and prominent, as after the application of mechanical stimulus. Within the areola this contractile tissue forms a layer, in places almost 2 mm. thick, that encircles the base of the nipple and is continued into its substance as a net-work of bundles, between which the lactiferous ducts pass. Deeper longitudinal strands of unstriped muscle occupy the axial portions of the nipple. Over both areola and nipple the skin is provided with large sebaceous glands, the secretion of which is increased during lactation and designed FIG. 1713. for protection while nursing. Sweat-glands are absent over the nipple, but large and modi- fied in the vicinity of the periph- ery of the areola. The surface of the latter is modelled, especially towards the close of pregnancy, by low rounded elevations that indicate the positions of the sub- cutaneous areolar or Montgom- ery* s glands. The latter are rudimentary accessory masses of glandular tissue, from 1-4 mm. in diameter, that correspond in their general structure with that of the mammary glands. Their ducts open by minute orifices on tin- surface of tin- areola. Milk. The fully estab- lished secretion of the mammary gland (lac femininuin) is an emulsion, the fatty milk- globules being suspended in a clear, colorless, and watery plasma, the variations in tint from bluish to yellowish-white depending upon the amount of fat. Section of mammary gland during: lactation, showing distended alveoli liiifd with fat-bearing cells. X '7"- The THE MAMMARY GLANDS. - 2031 composition of human milk includes over 86 per cent, of water, about 3 of albuminous substances, 5.3 of fat, 5 of sugar, and less than i per cent, of salts. The chief mor- phological constituents of milk are the milk-globules (fat droplets liberated from the alveolar cells), that vary in size from the most minute spherules to those having a diameter of from .003 .005 mm. and, exceptionally, even twice as much. Their average number per cubic millimetre is something over one million (Bouchut). Whether the milk-globules are enclosed within extremely thin envelopes of casein is still uncertain. Whether the fat is actually produced within the cells, or is to be regarded as only in transit, and, likewise, whether the milk leaves the cells already emulsified, are also questions undecided. During the last weeks of pregnancy and for two or three days after its termina- tion, the breasts contain a clear watery secretion, known as colostrum, that differs from milk in containing relatively little fat and numerous conspicuous bodies the colostrum corpuscles of uncertain form and size. These bodies are usually spherical, but may be irregular in outline, and measure from .oi2-.oi8 mm., although they may attain a diameter of more than .040 mm. Their protoplasm is markedly granu- lar and often of a yellowish or reddish-yellow tint. The colostrum corpuscles are modified alveolar epithelial cells that have been cast off during the initial changes and FIG. 1714. FIG. 1715. "~ ot) Jft L-' c O O r r O o r \ Human milk. X 500. Colostrum, showing corpuscles and oil-drops. X 500. expansion of the alveoli preparatory to the establishment of lactation. They again appear after this function has ended, and may continue to be expressed from the gland for months or, in exceptional cases, for even years. Vessels. The arteries supplying the mamma are principally the second, third, and fourth anterior perforating branches of the internal mammary. These vessels, in addition to their distribution to the skin and more superficial parts of the breast, send deeper twigs to the glandular tissue, which eventually break up into capillary net-works enclosing the alveoli. The lower and lateral portion of the organ receives an addi- tional supply from the external mammary branches from the long thoracic artery from the axillary. During lactation these vessels are markedly increased in size. The veins follow chiefly the arteries, emptying into the internal mammary and the long thoracic. The cutaneous veins, which during lactation are enlarged and show through the delicate skin as a net-work of blue lines, in part join those accompanying the arteries and in part form vessels that take an independent course over the clavicle to become tributary to the external jugular vein. Within the areola the cutaneous veins form a plexus that more or less completely encircles the nipple and receives its blood. The lymphatics of the mamma are exceptionally numerous and important. The deeper ones surround the groups of alveoli as channels that lie within the interlobular connective tissue and pass towards the surface, where they join the rich subareolar plexus. The latter also receives the collecting stems from the close cutaneous net- works that drain the integument covering the nipple and areola. With the exception 2032 HUMAN ANATOMY. of a few trunks that follow the perforating arteries and become afferents of the lymph- nodes lying along the internal mammary artery, all the lymphatics of the breast join to form two or three large trunks that pass from the lower and lateral border of the organ through the subcutaneous tissue towards the axilla to empty, sometimes united into a single stem, into the lymph-node that lies upon the serratus magnus over the third rib. The nerves supplying the glandular tissue are from the fourth, fifth, and sixth intercostals, the accompanying sympathetic fibres passing by way of the rami com- municantes from the thoracic portion of the gangliated cord. Their ultimate distri- bution may be traced to the plexuses upon the basement membrane surrounding the alveoli and, according to Arnstein, even between the secretory cells. The cutaneous nerves are derived from both the supraclavicular branches of the cervical plexus and the anterior and lateral cutaneous branches of the second to the fifth intercostals. Development. The arrangement of the several pairs of mammary glands possessed by a majority of the lower animals in two longitudinal rows is foreshadowed in the earliest stage of the development of these organs, so characteristic of the highest class of vertebrates (mammalia). A linear thickening of the ectoblast, known as the milk-ridge, appears as a low elevation that extends obliquely from the base of the fore to the inguinal region. Along this ridge a series of enlargements, later sepa- rated by absorption of the intervening portions of the ridge, indicates the anlage for a corresponding number of mammae. The occurrence of a definite milk-ridge in the human embryo is uncertain, although its presence has been observed (Kallius), and the position of supernumerary mammae suggests its influence. In man a knob-like thickening of the ectoblast appears during the second month of foetal life. This thickening sinks into the underlying mesoblastic tissue, which undergoes proliferation and condensation and forms an investment for the growing epithelial mass. From this envelope the fibrous and muscular tissue of the areola and nipple are derived, while the subjacent mesoblast produces the connective-tissue stroma. The ectoblastic ingrowth represents a sunken area of integument that in principle corresponds to the marsupial pouch of the lowest mammals (monotrctncs}. Solid epithelial sprouts grow out from the sides of the conical or flask-shaped epidermal plug and are the first anlages of the true mammary gland, later becoming the excretory ducts. Subsequently the central part of the ectoblastic ingrowth undergoes degeneration and destruction, and what at first was an elevation now becomes a depression of the surface. From the middle of this depressed area there appears, shortly before or immediately succeeding (Basch) birth, an elevation that later becomes the nipple. Meanwhile, the epithelial duct-outgrowths penetrate the surrounding condensed mesoblastic stroma, increase in length, subdivide, and acquire a lumen at their expanded distal ends, thus giving rise to the system of ducts and the lobules of immature gland-tissue. With the further development of the latter, the surrounding mesoblastic stroma is broken up into the interlobular septa and fibrous framework of the corpus mammae. At birth the gland is represented by the lactiferous ducts with their ampullae, the smaller ducts, and the immature alveoli. Quite commonly the mammary glands in both sexes are the seat of temporary activity during the first few days after birth, the breasts yielding a secretion resembling colostrum, popularly known as "witch-milk." The mammae remain rudimentary during childhood until the approach of sexual maturity, when they increase in size and rotundity in consequence chiefly of the deposition of fat. The full development of the true gland is deferred until the occur- rence of pregnancy, when active proliferation and increase in the gland-tissue take place in preparation for its functional activity as a milk-producing organ. After lacta- tion has ended, the mammre undergo regression or involution, the glandular tissue being reduced in amount and returning to a condition resembling that existing before pregnancy. With the recurrence of the latter, the gland again enters upon a period of renewed growth and preparation, to be followed in time by return to the resting condition, in which the amount of glandular tissue is inconspicuous. After cessation of menstruation the mammary gland gradually decreases in size, and in advanced years the corpus mammae may be reduced to a fibrous disc in which gland-tissue is almost entirely wanting. PRACTICAL CONSIDERATIONS : MAMMARY GLANDS. 2033 Variations. The mammae are frequently asymmetrically developed, the left being often larger than the right. While very rarely one or both may be wanting, with or without associated absence of the nipple, increase in their number is of relatively common occurrence. The super- numerary mammae vary greatly in the extent to which they are developed, sometimes being represented by well-formed accessory glands (polymastia) that may become functionating organs, but more often, particularly in the male subject, by only rudimentary nipples (polythelia), or even by pigmented areas suggesting areolae. In women polythelia is usually associated with greater or less development of glandular tissue. Although the astonishing frequency (14 per cent. ) of polythelia in men, as announced by Bardeleben, 1 is to be reconciled only by accepting many doubtful pigment spots as of significance, the occurrence of rudimentary supernumerary nipples in males is undoubtedly more common than formerly recognized. Exceptionally above and to the outer side, the usual position of the accessory mammas is below and somewhat medial to the normal glands, and in general corresponds to the mammary line of the lower animals, The number of the accessory glands varies, as many as three pairs in one case, and five milk-secreting organs in another, having been observed. They are often asymmetrically placed and not uniformly developed. Comparative studies of the mammae in the lower animals and the disposition of the supernumerary organs in the human subject, suggest the probability that man's remote ancestors normally possessed a greater number than two, 2 the occasional occurrence of the anomalous mammae indicating a reversion to the primary condition. In addi- tion to the supernumerary mammae in positions anticipated by the milk-ridges, rudimentary organs sometimes occupy very unusual situations, among which have been the back, shoulder, thigh, and labium majus. Erratic mammae are also met with among the lower animals. PRACTICAL CONSIDERATIONS: THE MAMMARY GLANDS. The skin covering the bfeast is thin and movable, with plainly visible cutaneous veins which enlarge during lactation, or in cases of mammary hypertrophy, or when obstruction due to abscess or new growth exists in the breast or in the post-mam- mary region. The frequent occurrence of asymmetry in size, the left breast being larger, is said (Williams) probably to be due to the fact that most mothers, being right-handed, suckle chiefly with the left breast, which is also said to be on an aver- age heavier, more intimately associated with the pelvic sexual organs, more prone to hypertrophy, and more likely to be the seat of carcinoma or other neoplasms. The greater part of the breast lies upon the sheath of the pectoralis major muscle, on which it is freely movable, the intervening cellular tissue being extremely lax. About one-third of the gland, however, extends beyond and below the axillary border of the pectoralis major, and is in relation in the axilla with the serratus mag- nus and, when large, with the origins of the rectus and the external oblique. While the normal breast moves freely over the pectoral muscle, it also moves slightly with it when the muscle is contracted. Hence in inflammation of the breast, or after operation upon it or for its removal, the muscle should be kept at rest by binding the arm to the side. In testing for pathological adhesion of the breast to the pec- toral sheath, it is well to move the breast in the direction of the fibres of the pecto- ralis major. If it is moved transversely to them, it may carry the relaxed muscle with it and no diminution of mobility will be noticeable. In examining for growths of the breast, the normal lobes, especially if at all enlarged, may be felt through the adipose envelope and may be mistaken for tumors. To avoid this, the gland should be palpated with the flat hand, which should gently compress it against the chest wall. In this manner very small cysts or neoplasms may be recognized, as they become more resistant and more prominent than the normal gland tissue. The two breasts should be thus examined at the same time, so that any difference in their size, consistence, or sensitiveness may be detected. The nipple in men and in young virgins is found over the fourth intercostal space, or over the fifth rib, about three-quarters of an inch external to the costo- ch'ondral junction. In older women its position is not constant, and, of course, it varies with the degree of the enlargement, laxness, and pendency that follow preg- nancy and that are common in women of tropical lands and in negresses and women of other of the lower races. The development of the nipple may be arrested at the stage when the central part of the ectoblastic ingrowth has undergone degeneration and when a depression 1 Anatom. Anzeiger, Bd. vii., 1892. 2 An interesting review of the subject is given by Bonnet in Ergebrisse d. Anat. n. Entwick., Bd. ii., 1892. 128 2034 HUMAN ANATOMY. exists towards the bottom of which the ducts of the mamma converge. In such cases the depression persists ; in others the areola is present, but the nipple absent. In both, while lactation may be normal, the suckling of children is impossible. The nipple may be absent or defective as a result of trauma or of disease wounds, burns, ulcers, abscesses during infancy. The normal nipples of virgins or nulliparae may be almost on a level with the areola, while those of multipart are often greatly elongated from the traction upon them. Temporary elongation or erection of the nipple may be caused by reflex stimulation of the unstriped muscular tissue of the skin of the nipple and areola. Infection of the nipple is common, because, on the one hand, of the many folds of its delicate cutaneous covering, containing a number of sebaceous glands and closely connected to the underlying structures ; and, on the other, of its frequent exposure during suckling to irritation from unhealthy discharges from the child's mouth, leading to epidermic maceration and to painful erosions, fissures, and ulcers. Atrophy of the mammary glandular elements is of normal occurrence after the menopause, the fibrous and fatty structure being also affected in many instances of noticeable withering of the breasts. In early life this condition may result from disease, or from removal of the ovaries, and become a true deformity. Hypertrophy of the breast consists in an overgrowth of both the glandular and the fibrous elements, the latter predominating, and occurs usually between 14 and 30 years of age the period of greatest sexual activity. Amenorrhcea and pregnancy are frequently associated with it. Infection of the breast is usually carried through either the lymphatics or the milk ducts, most commonly during the early period of lactation ; more rarely it appears during the other notable periods of mammary physiological excitement i.e. , in the newly born the "witch-milk" period (vide supra) and at puberty. In the nursing woman the presence of fissures or abrasions of the nipple predisposes to lymphatic infection. Lack of cleanliness, with fermentation or decomposition of milk and of cutaneous secretions in the folds or crevices of the nipple, favors infec- tion in the ampullae of the ducts. If the superficial lymphatics are the channels of infection, suppuration in the cellulo-fatty tissue superficial to the breast may result (supramammary abscess) and, owing to the lack of tension, pointing will occur early, the course of the case will be rapid, and the constitutional symptoms relatively slight. If the deeper lym- phatics or milk ducts convey the infection, suppuration occurs within the lobules (intramammary abscess) and spreads slowly from one to another through the inter- lobular connective tissue. As the pus is surrounded by the unyielding breast tissue and confined by the capsule of subcutaneous fascia and its septa, pain, tenderness, fever, and other constitutional symptoms are marked and the progress of the disease is slow. Occasionally, by extension from an intramammary focus, the connective tissue lying between the breast and the pectoral sheath is involved (retro, infra, or submammary abscess), but suppuration in this region is more apt to be consecutive to caries of a rib (usually tuberculous). The constitutional symptoms are less marked. The whole breast is pushed forward and made more prominent. Point- ing by reason of the effect of gravity is apt to occur somewhere at the circum- ference of the breast, usually towards the inframaxillary region. Sometimes these abscesses ulcerate directly through the breast tissue to the subcutaneous area, making two cavities, one infra, the other supramammary, connected by a narrow channel, a form of Velpeau's "abces de bouton en chemise." As the breast is thinnest along a line drawn from the sterno-clavicular joint to the nipple, it is in that region that such perforation of the gland usually occurs. As the breast glandular and other structures, including the skin covering it is supplied chiefly by the lateral cuta- neous branches of the second to sixth intercostal nerves, pain in inflammatory or sup- purative affections, or in the case of new growth, may be felt down the arm ( intercosto- humeral) ; over the shoulder-blade (posterior branches of the thoracic nerves) ; down the side or along the posterior parietes of the thorax (intercostals) ; or up the neck (supraclavicular from the cervical plexus anastomosing with the second inter- costal). Incisions for the evacuation of pus should be made on lines radiating out- PRACTICAL CONSIDERATIONS : MAMMARY GLANDS. 2035 ward from the nipple so that the larger lactiferous ducts converging to that point may not be wounded. Carcinoma of the breast is ,the most important of the diseases affecting that gland, about 85 per cent, of the neoplasms involving the female mamma being can- cerous. About 99 per cent, of all neoplasms of the breast occur in the female, only i per cent, in the male, " illustrating the law of which many other instances might be cited that functionless, obsolete structures have but little tendency to take on the neoplastic process" (Williams). It begins most often in the cuboid (glandular) epithelium of the alveoli acinous cancer ; but not uncommonly in the columnar epithelium of the ducts duct cancer. In either case it is usually at first a dense nodule of small size, growing by infiltration of the neighboring tissues. In tracing the methods of extension and dissemination from the original nodule in the gland substance, the various structural relationships must be borne in mind. The ana- tomical routes along which such a growth may spread, and the chief symptoms thereby produced, are as follows : 1. By way of the lymphatic vessels that empty into the lymph nodes (pectoral or anterior) overlying the digitation of the serratus magnus arising from the third rib. This is the most frequent form of lymphatic dissemination, because (a) these vessels include the great majority of the mammary lymphatics ; () the nodes .first involved in cancer are those into which is emptied the lymph from the part of the gland affected by the primary growth ; and (<:) cancer originates most frequently in the upper and outer quadrant of the breast, possibly because that area is most exposed to minor traumatism ; or possibly because the alveoli are much more numerous in the peripheral than the central part of the gland, the majority of mam- mary neoplasms arising in the seats of the greatest development of postembryonal activity where cells still capable of growth and development most abound (Williams) i.e. , in the vicinity of the alveoli. Williams calls attention to the fact that the ' ' axillary tail' ' of the mamma lies close to the pectoral nodes and might be mistaken for the enlarged gland. By placing the flat of the hand or the palmar surfaces of the fingers against the inner (thoracic) wall of the axilla and moving the superficial structures to and fro, enlargement of the pectoral nodes may easily be detected. 2. From these pectoral nodes situated along the anterior border of the axilla, carcinoma may invade (#) the central nodes, receiving the lymph from the upper extremity, and lying on the inner side of the axillary vein, on either the superfi- cial or deep aspect of the axillary fascia, embedded in a quantity of fat, and half- way between the anterior and posterior folds of the axilla. The inner portion of the axillary tuft of hair overlies this group of glands. The axillary fascia at this place may present an opening very similar to the saphenous opening of the thigh (Poirier, Leaf) and the nodes may occupy this. These nodes may be palpable, but if only slightly enlarged cannot readily be felt in stout persons. If no axillary opening is present and the nodes lie on the superficial aspect of the fascia, they can best be felt by pressing them against the unyielding fascia, with the arm in the abducted posi- tion ; if, on the other hand, an opening is present, the arm should be adducted so as to relax the fascia, when the nodes may be recognized by pressing them against the thoracic wall. For these reasons, in examining for enlarged axillary nodes, the arm should always be placed in both these positions (Leaf). As this set of nodes is traversed by the intercosto-humeral nerve, carcinoma involving them often causes pain down the inner and posterior aspect of the arm. As they receive the lymph vessels of the upper limb, the structures in the deltoid region and down the arm may become infiltrated. Or the disease may invade (<5) the deep axillary nodes, lying along the inner and anterior aspect of the axillary vessels, and communicating with both the pectoral and the lower deep cervical nodes; extensive implication of this group results in oedema and swelling of the upper limb, compression of the axillary vein, and in widely distributed pain in the regions supplied by the brachial plexus; (f) the infra- clavicular (cephalic) nodes, lying just below the clavicle, between the deltoid and pec- toralis major muscles and, like the deep axillary nodes, communicating below with the pectoral nodes, and above with the supraclavicular or inferior cervical nodes, the disease often reaching these latter ; (d") the subscapular nodes, lying along the sub- scapular vessels and receiving lymph from the scapular region, and often, when the 2036 HUMAN ANATOMY. central group of nodes lies on the deep surface of the axillary fascia, forming one large group with it. Involvement of these nodes with their afferent lymph vessels probably accounts for the extensive infiltration o,f the structures over the upper lateral and posterior aspects of the thoracic parietes occasionally seen in advanced cases. 3. The nodes at the summit of the axilla may be involved through lymph vessels passing above the pectoralis minor and through Mohrenheim's fossa without entering the pectoral nodes. 4. The anterior mediastinal glands may be invaded especially if the inner segment of the breast is affected by way of the lymph vessels following the per- forating arteries and emptying into the nodes along the internal mammary artery. In this manner, as well as by direct extension through the inframammary tissue, the pectoral fascia and muscles, and the chest wall, the pleura and lung may become involved. Other symptoms due to mediastinal growth have been described in rela- tion to that region (page 1833). 5. The free communication in the subareolar plexus between the glandular lymphatics, deep and superficial, (paramammary) and the subcutaneous and thoracic lymphatics, together with the connection established between the periglandular tissue below and the skin above by the ligaments of Cooper (suspensory ligaments), explains the frequency with which mammary carcinoma extends to the overlying skin. As a result of its infiltration the latter becomes dense, inelastic, brawny, dusky, and adherent. It cannot be picked up between the thumb and finger in a fold; and often quite early and before it has become adherent, and as a result of con- traction of the growth pulling on the fibrous bands uniting it to the deeper parts, it is drawn into a number of little depressions or dimples like those on the skin of an orange. When such infiltration is diffuse and spreads largely through the subcu- taneous net-work of lymph vessels, the condition known as cancer en cuirasse is pro- duced. In the later stages ulceration, infection, hemorrhage, and foul discharge are frequent results of the cutaneous involvement. 6. If the growth is central it may extend to the lactiferous ducts or to the peri- acinous tissue continuous with that surrounding the ducts, and through its own or their cicatricial contraction it may depress or retract the nipple or pull it so that it deviates from its normal direction. This is not so valuable a symptom as the dim- pling of the skin above described, as it may be caused by injury or by chronic disease, such as abscess, tubercle, or mastitis. Moreover, it may not be present if the growth is peripheral. 7. The carcinoma may extend through the lymph communications between the gland and the underlying connective tissue and pectoral fascia and muscle, so as to become fixed to or incorporated with those structures, the breast losing much of its mobility, especially in a direction parallel with the pectoralis major fibres. It may thence continue through the thoracic wall and invade the pleural or mediastinal cavity directly. 8. Through the intercommunication of the lymph system of the two breasts through the subcutaneous thoracic lymphatics, cancer of one breast may extend to the other (Moore), or to the glands of the opposite axilla (Volkmann, Stiles), or to the glands of both axillae (Scarpa, Cooper ; quoted by Williams). , 9. General dissemination of the cancerous disease may also take place through detached cells or particles (emboli) from the primary growth entering the blood stream. The liver is the organ most frequently affected by metastasis in cases of breast cancer. The bones, the lungs, and the pleurae come next, but almost no organ or structure of the body is exempt. In removal of the breast the following anatomical points should be borne in mind : (a) The intimate connection between the skin and the gland itself by means of lymph- and blood-vessels, by the suspensory ligaments, and by glandular processes accom- panying or contained within these ligaments (Stiles), shows the necessity for free sacrifice of the skin overlying the breast. ( h ) The irregular shape of the breast, which has two extensions that frequently reach into the axilla, and one that reaches to or overlaps the border of the sternum, and not uncommonly similar processes that spring from other parts of the surface of DEVELOPMENT OF THE REPRODUCTIVE ORGANS. 2037 the gland and radiate in the paramammury fatty tissue (Williams) emphasizes the need for incisions that shall permit the removal of all such portions of possibly dis- eased glandular tissue. O) The usual defect in the retroglandular fatty envelope, bringing the glandu- lar lobules into intimate relation with the pectoral fascia and muscle (Heidenhain), facilitates extension of the disease in that direction and indicates the free removal of the pectoralis major in most cases. (d} The lymphatic distribution (vide supra} supplies the same indication as to removal of the greater pectoral and to a lesser degree as to the lesser pectoral also. It, of course, points unmistakably to the need for thorough cleaning out of the axilla. In doing this it is well to remove the chain of lymphatic nodes pectoral, central, deep, subscapular, etc. in one piece, not only because it minimizes the risk of infection of healthy structures during the operation (Cheyne), but because if the clavi-pectoral fascia (suspensory ligament of the axilla) and the axillary fascia, together with the greater part of the pectoralis minor muscle (on account of the continuity of its sheath with the clavi-pectoral fascia), are removed in one piece, the groups of nodes enumerated above and embedded in them will be removed also (Leaf). To this there are three exceptions: ( i ) a node of the subscapular group sometimes projects backward and is found between the teres minor and infraspinatus muscles ; (2) some nodes of the infraclavicular group may lie to the outer side of the axillary vein, and when this is so, as the suspensory ligament is stripped off the inner side these glands would remain behind ; (3) the cephalic node would not be reached during the removal in one piece of the ligament and axillary fascia with their contained groups of nodes. Of course all these nodes should be sought for and removed separately (Leaf). (e) The most important blood-vessel in danger during the operation is the axillary vein (page 888), made somewhat more prominent together with the artery and the brachial plexus when the arm is raised and the head of the humerus is made to project into the axilla. These structures normally lie on the outer wall of the axilla, but may be so embedded in a mass of cancerous tissue as to be difficult of recognition. On the posterior aspect of the axilla the subscapular vessels and (in close proximity to the subscapular nodes) the long subscapular nerve supplying the latissimus dorsi muscle should be avoided. The inner (thoracic) wall of the axilla is the region in which the dissection may be conducted with the greatest freedom, the posterior thoracic nerve running almost vertically downward in close contact with the outer surface of the serratus magnus muscle to which it is distributed. The arteries met with or divided in the course of the operation are ( i ) the pectoral branches of the acromial thoracic ; (2) the alar thoracic ; (3) the long thoracic (external mammary) running along the lower border of the pectoralis minor muscle ; (4) lateral branches from the second, third, and fourth intercostal arteries ; and (5) anterior perforating branches of the internal mammary artery, emerging at the second, third, and fourth intercostal spaces. The vessels in the last two groups are normally small, but by enlarging during the growth of a carcinoma and by retracting after division to beneath the surface of the chest- wall, they are sometimes slightly trouble- some during operation. DEVELOPMENT OF THE REPRODUCTIVE ORGANS. The development of the internal organs of reproduction includes two distinct but closely related processes, the one leading to the formation of the sexual glands, the testes or ovaries, and the other to the provision of the canals for the conveyance and temporary storage of the products of these glands. Provision of the excretory canals is accomplished by the secondary changes and further growth of parts of the Wolffian tubules and ducts in conjunction with two additional canals the Miillerian ducts. References to the preceding account of the Wolffian body (page 1935) will recall the constitution of the latter as including a series of transverse tubules opening into a common longitudinal duct, and, further, that the Wolffian tubules comprise an anterior sexual and a posterior excretory group. 2038 HUMAN ANATOMY. During the development of the Wolffian body, or mesonephros, a second tube, the Miillerian duct, is formed within a linear thickening, the genital ridge, that appears upon the ventro-lateral surface of the Wolffian body. Near the cephalic end of the latter, an evagination of the lining of the body-cavity into the genital ridge occurs, by the contin- FIG. 1716. ued proliferation and 'Aorta downward growth of the cells of which the evagination is con- verted into a tube the Miillerian duct. This tube communi- cates directly with the body-cavity by means of its trumpet-shaped cephalic extremity, extends parallel with and closely related to the Wolffian duct and, later, below reaches the urogeni- tal sinus. The con- Mesothelium Ipighian body 1 Anlage of sexual glands Portion of cross-section of early human embryo, showing first appear- ance of sexual glands within germinal ridges. X 60. verging lower seg- ments of the two Wolffian and the two Miillerian ducts are embedded within a median mesoblastic band, the genital cord, that represents the continuation of the fused geni- tal ridges of the two sides. Within the genital cord the Miillerian ducts lie in the middle, closely applied to each other, with one Wolffian duct on each side (Fig. 1649). The development of 'the sexual glands begins about the time that the Miillerian ducts are forming, as a linear thickening of the mesothelium and underlying meso- blastic stroma, situated, however, on the median surface of the Wolffian body (Fig. 1716). Over this raised area, the germinal ridge, the character of the primary peri- toneum changes, its cells becoming taller and undergoing proliferation. Very early among the increasing elements appear specialized cells distinguished by their large size, clear protoplasm, and conspicuous nucleus. These are \he primary germ-cells, which later become the primordial ova or sperm-cells, according to sex. For a time this cannot be determined, since in this indifferent stage of the sexual gland special- ization has not yet progressed sufficiently to make differentiation possible. The dis- tinctive features of both sexes, there- FIG. 1717. fore, are acquired by farther devel- opment of a neutral sex-type in which the indifferent sex- ual glands, the Wolffian tubules, the Wolffian and the Miillerian ducts are the chief com- ponents. Whether determination of sex is dependent upon nutrition, and, therefore, more or less acci- dental, or is established early and antedates the appearance of indifferent organs, is a question still undecided. Differentiation of the Male Type. The development of the testis from the indifferent sexual gland includes the invasion of the proliferated mesothelial cells of Primary germ-cells Proliferating Wolffian stroma Cross-sue tii in df germinal ridjji- of young human embryo, showing early dinVrrntiution <>t pimi.uv mTin-cells. X 500. DEVELOPMENT OF THE REPRODUCTIVE ORGANS. 2039 Globus major FlG. 1718. the germinal ridge by the underlying mesoblastic stroma, whereby the epithelial muss becomes broken up into cylinders and cords that extend into the subjacent stroma. The cell-cords are composed of two kinds of elements, the numerous chief epithelial cells and the larger sperm-cells, the direct descendants of the indiffer- ent primary germ-cells, which they embrace. About the fifth week a layer of mesoderm insinuates itself between the superficial and deeper portions of the epi- thelial mass, thereby separating a peripheral zone. This ingrowth results in the formation of a robust fibrous envelope, the tunica albuginea, around the entire testis, while the separated mesothelial layer differentiates into the serous covering. The cell-cords become subdivided by the ingrowth of the mesoblastic stroma into smaller spherical masses, which subsequently are converted into the seminiferous tubules, while from the stroma are supplied the interlobular septa and the intralobular support- ing tissue. About the sixth week additional cell-cords grow into the young testis from the adjacent Wolfifian tubules. These ingrowths invade the attached border of the testicle and become the medullary cords, which are so disposed that each comes into relation with one of the spheri- cal epithelial cell-masses. Although both the latter and the medullary cords are solid, the later relation of the secreting tubules of the gland to the excretory channels is thus foreshadowed, since from the ingrowths from the Wolffian tubules are derived the straight tubules and those of the rete testes. The farther differen- tiation of the seminiferous canals, which, as well as the medullary cords, are with- out lumen until near puberty, proceeds from the growth and branching of the cell- masses, the cells of which become the epi- thelium of the tubules. The latter are enclosed by an investment of condensed mesoblastic stroma continuous with the supporting tissue and framework of the gland. At the approach of sexual ma- turity the primary sperm-cells within the tubules proliferate and become the sperma- togonia, while from other epithelial ele- ments are derived the Sertoli cells. The roles played by these elements in the pro- duction of the spermatozoa are described under Spermatogenesis (page 1945). Coincidently with the growth of the testis the Wolfifian body atrophies, with the exception of some of its tubules and duct, which increase and, in conjunction with the medullary cords also derived from the mesonephros, establish the elaborate excretory passages of the sexual gland. From the Wolfifian tubules are developed the coni vasculosi and the cluctuli efferentes, while the Wolfifian duct gives rise to the tube of the epididymis, the vas deferens, and, as a secondary outgrowth, the seminal vesicle. The caudal group of mesonephric tubules are represented in both sexes by rudimentary structures, which in the male are the paradidymis and the vasa aberrantia. The appendix of the epididymis, or stalked hydatid, probably also owes its origin to the Wolfifian duct. Although, as is evident from the foregoing, the Wolffian tubules and duct are largely concerned in the development of the generative tract in the male, the Mul- lerian duct is not without representation, since its two extremities persist. The upper (after migration lower) end remains as the appendix of the testis, and the lower, fused with its fellow, is seen as the prostatic utricle, which, therefore, is the homologue of the vagina and, possibly, the uterus. In exceptional cases, where it Longitudinal section of developing testicle. X 20. 2040 HUMAN ANATOMY. persists, the intervening portion of the Miillerian duct is represented by Rathke's duct. Since the prostate gland arises as an outgrowth from the urogenital sinus (page 1979), it has no genetic relation with the seminal ducts. Descent of the Testes. The development of the sexual glands, in both sexes, is attended with conspicuous migration from their original position on either side of the upper two lumbar vertebrae, opposite the lower pole of the kidney. In the case of the testis, this migration is so extensive that by birth the organ usually has passed through the abdominal wall and entered the scrotum, having completed its so-called descent. Certain peritoneal folds (mesenteries) and fibre-muscular bands (ligaments) merit brief description, since they are more or less concerned in the migration of the sexual glands. The Wolffian body is enclosed and attached to the posterior body-wall by a fold (mesonephridium), of which the upper elongated end is continued to the FIG. 1719. AE AT rVGM WT WT RD Ur CG Pr EC, Diagrams illustrating differentiation of two sexes from indifferent type. A, Indifferent : G, sexual gland; WD, Wolffian duct; WT. WT, groups of Wolffian tubules; MD, Miillerian duct; RD. renal diverticultim ; C, cloaca; G, gut; A, allantois. B, Male: T, testicle; VE, vasa efferentia ; GM. globus major; VD, vas deferens ; Pa, para- didymis ; VA. vas aberrans ; SV, seminal vesicle ; AT, appendix testis AE, appendix epididymidis ; B, bladder ; PU, prostatic utricle; Pr, prostate; Ur, urethra; CG, Cowper's gland; CC, corpus cavernosum ; R. rectum; RD, renal duct ; K, kidney. C, Female : O, ovary ; Ov, oviduct ; F, fimbria ; U, uterus ; V, vagina ; DEp, duct of epoophorpn ; TEp. tubules of epoophpron ; Po, paroophoron ; HM, hydatid of Morgagni ; GD Gartner's duct; BG, Bartholin's gland; C, clitoris; K, kidney; R, rectum. (Modified from Wiedershetni.) diaphragm (plica phrenico-mcsonephricd) and the lower to the abdominal wall in the inguinal region (plica inguino-mesoncphrica). The early sexual gland is also provided with a mesentery (mesorchium or mesovariurri), that above and below is continuous with folds that pass from the upper and lower poles of the gland to the mesentery of the mesonephros. Within the inferior plica, of the two much the better marked, lies a fibro-musciilar strand (the ligament of the testis or orarv}, that below is attached at first to both the Wolffian and Mullerian ducts. Later, owing to the atrophy of the one or the other of these ducts, according to sex, the ligament of the testes remains connected with the Wolffian duct and the ligament of the ovary with the Mullerian duct. A second band of muscular tissue appears within the lower part of the inguino- mesonephric fold, and has its upper attachment also to the Wolffian and Mullerian ducts at a point about where they receive the insertion of the ligament of the testes or ovary. The lower end of the band blends with the subperitoneal tissue of the anterior abdominal wall in the vicinity of the future abdominal ring. This band, the gcnito- 1720. Wolffian duct DEVELOPMENT OF THE REPRODUCTIVE ORGANS. 2041 inguinal ligament, corresponds with the gubernaculum testis in the male and with the round ligament of the uterus in the female. In the former it is not directly attached to the testis, but only through its ligament, the point of attachment later corre- sponding to the origin of the vas deferens FIG. from the epididymis. The testicle begins its descent during the second foetal month, coincidently with com- mencing atrophy of the Wolffian body, and, under the influence and guidance of the genito- inguinal ligament, by the end of the third month reaches the an- terior abdominal wall in the vicinity of the later internal abdomi- nal ring. This position it retains until the close of the sixth month, when it enters upon its final descent. Meanwhile, the musculo-fascia layers of the abdominal wall undergo evagination, resulting in the production of a shallow pouch, the inguinal bursa, into which a sac of peritoneum, the processus vaginalis, extends, together with the closely associated genito-inguinal ligament. The inguinal bursa, in turn, sinks into the shallow scrotal pouch that has independently devel- oped as an integumentary fold. The wall of the bursa contains the constituents that later differentiate into the coverings proper of the spermatic cord and testicle the intercolumnar, cremasteric, and infundibuliform fasciae. Its muscular fibres, pro- longed from the internal oblique and transversalis layer, correspond with the cre- master, and surround the genito-inguinal ligament. Owing to the thickening of the lower end of the latter, a slight elevation appears on the floor of the bursa, which thus seemingly becomes pushed up towards the testis to form the rudiment of what in some animals becomes a well-marked projec- tion, the conns ingualis, but in man always remains insignificant. In consequence of these changes, during the fourth month the testis is displaced upward and its descent temporarily inter- FIG. 1721. . Epididymis Testis Plica phrenic mesonephrica Sexual gland Wolffian bodvk- Mesentery of gland Wolffian duct Genito-inguinal ligament Plica inguino- mesonephrica Ligament of gland Umbilical arterie: Gut Allantoic duct Umbilical vein Wolffian bodies and sexual glands of human embryo of about six weeks (17 mm. long). X 15. (Modified from Kollmann.) fascia s deferens Deep epig-asti Rectus muscle rupted. About the beginning of the seventh month, the final descent of the testicle is in- augurated with deepening of the bursa and downward extension of the peritoneal pouch, accompanied by the now thickened and short- ened genito-inguinal liga- ment. Although shorten- ing of the latter, together with the pull exerted by the cremasteric fibres, plays an active role in drawing the testicle through the abdominal wall and into the scrotum, these factors are undoubtedly supplemented by forces result- ing from the growth and expansion of the pelvis and inguinal regions. The processus vaginalis reaches the bottom of the scrotal sac in advance of the Peritoneal cavity Int. obi. and transver. muse Aponeurosis of external oblique Periton Genito-inguinal ligai Transversal Cremastei Intercolumn? Integumentary scrotal pouch 5cessus vaginalis :) Attachment of ligament to Mr thickened floor of inguinal Diagram showing early stage in descent of testicle. (After Waldeyer.} 2042 HUMAN ANATOMY. Peritoneum ,Vasd rens p epigastric vessels testicle, which, drawn from its mesentery (mesorchium), descends outside and behind the peritoneal pouch that later constitutes its partial serous investment, the tunica vaginalis. After the descent is completed, usually shortly before birth, but some- times not until afterward, the tubular FIG. 1722. upper segment of the peritoneal sac closes normally during the early months of childhood. This closure takes place first in the vicinity of the internal ab- dominal ring and in the middle of the tube, passing upward towards the ring and downward to within a short distance of the sexual gland. The occluded portion of the vaginal process is later represented by a small fibrous band (lig- amentum vaginale) that extends from the internal abdominal ring above, through the inguinal canal and for a variable dis- tance down the spermatic cord, some- times, although not commonly, as far as the tunica vaginalis. When the pro- processus vag Perito Interco fasc Skin and d Diagram showing relations of descended testicle to processus vaginalis, which still freely communicates with peritoneal sac of abdomen. (After Waldeyer.) cessus vaginalis fails to close, as it oc- casionally does in man and always in certain animals, as the rat, in which de- scent and retraction of the testis periodically occur, the serous sac surrounding the tes- ticle communicates throughout life with the peritoneal cavity, a condition favorable to the production of hernia. With the obliteration of the lumen of the processus vaginalis, an inguinal canal, in the sense of a distinct tube, disappears, the spermatic duct and associated vessels and nerves, that necessarily share in the migration of the sexual gland into the scrotum, passing between the muscular and fascial layers of the abdominal wall embedded in connective tissue. The remains of the shrunken genito-inguinal liga- ment, or gubernaculum, are represented by a fibro-muscular band, the scrotal liga- ment, that connects the lower end of the epididymis to the scrotal wall (Fig. 1687). Descent of the testicle may be imperfectly accomplished, so that the gland, failing to reach the bottom of the scrotal sac, may be arrested within the inguinal canal or spermatic cord, or permanently retained within the abdomen, a condition known as cryptorchism, usually leading to atrophy of the gland. Associated with faulty descent may be anomalous situation,, the testis lying beneath the integument near the external abdominal ring, in the thigh, or in the perineum. After descent the axis of the testicle may be abnormally di- rected, the gland assuming a transverse, rotated, or even inverted position. Differentiation of the Female Type. Development of female internal reproductive organs proceeds along the same lines as in the male, the ovary being differentiated from the indifferent sexual gland and the genital canals from the Mullerian and Wolffian ducts. Differentiation of the ovary has been described in connection with that organ (page 1993). That of the Fallopian tubes, uterus, and vagina results from further growth, fusion, and modification of the Mullerian ducts. Lower segments of the latter, below the attachment of the ligament of the ovary (page 2040), undergo fusion and form the uterus and vagina. Their upper segments remain unfused and be- come Fallopian tubes. Details of these changes are given under the respective organs. FIG. 1723- Peritoneum Vas deferens Deep epigastric vesse Closed portion of processus vaginalis Cremaster Infundibuliform f is. i,i Sac of tunica vaginalis Visceral layer Parietal layer Skin and dartos Diagram showing relation brane after upper part of pro (After Waldry,-> ) --tir].- to serous mem- vat>inalis has closed. Suprarenal body DEVELOPMENT OF THE REPRODUCTIVE ORGANS. 2043 In the female the Wolffian tubules and duct play a subordinate role, remaining to form rudimentary organs, the epoophoron (page 2000), the paroophoron (page 2002), and, when the Wolffian duct persists, the duct of Gartner (page 2001). The broad ligament is formed by the enlargement of the primary peritoneal fold containing the Miillerian and Wolffian ducts. Descent of the Ovary. The primary position of the ovary, at the side of the upper two lumbar vertebrae, corresponds with that of the testis, the sexual gland, as in the male, undergoing migration in order to gain its permanent loca- tion. In the case of the ovary, however, this migration is much more limited, notwithstanding the provision of the same equipment for descent as in the male, in- cluding the genito-inguinal ligament, inguinal bursa, peritoneal evagination, and even cremaster muscle. The gland fails to reach the internal FIG. 1724. abdominal ring and remains until birth at the brim of the pelvis in consequence of the large size of the uterus in relation to the small pelvis. When the growth and expan- sion of the latter have pro- vided additional capacity, as the uterus sinks to its definite position, the ovaries, attached by their ligaments and ovi- ducts, follow into the pelvis. The genito-inguinal liga- ment becomes the round ligament of the uterus, the lower end of which is attached to the subcutaneous tissue of the labium majus at the exter- nal abdominal ring. These relations are foreshadowed by the close association of the lower end of the fcetal liga- ment to the bottom of the inguinal bursa and the wall of the processus vaginalis. The lumen of the latter usually disappears, but in exceptional rww mav r,f-ri'Qt a* rh<- ranal Sexual organs of female foetus of third month, showing ovaries Cabeb may perblbl ab trie canal s till undescended and bicornate uterus. X 2. of Nuck (page 2015). Asso- ciated with this condition, occasionally the ovary more closely imitates the descent of the testicle by passing into or even through the inguinal canal. DEVELOPMENT OF THE EXTERNAL ORGANS. The external genital organs develop from an indifferent type and, until the beginning of the third month, do not exhibit the distinguishing characteristics of either sex. While the differentiation of the sexual glands occurs early, in embryos of 22 mm. length, not until about the ninth week, in embryos of 31 mm., is sex determinable by inspection of the internal organs. The earliest trustworthy external indication of sex is the downward curve of the growing genital tubercle, later the clitoris, that takes place at this time in the female (Herzog). About the fifth week, before the rupture of the cloacal membrane, the tissue bordering the external cloacal fossa in front grows forward into a rounded projection, the genital tubercle. The latter rapidly increases in size and differentiates into a distal knob-like end and a bulbous ventral expansion at its base which becomes divided by a groove that extends along the under surface of the genital tubercle. The lips of this groove elongate into the genital folds that lie on either side of the opening into Hypogas- tnc artery 2044 HUMAN ANATOMY. FIG. 1725. Cloacal membrane Surface markings of cloacal region of human embryo of seventeen days (Fig. 1644). X 12. (Keibel.) FIG. 1726. the urogenital sinus that appears when the cloacal membrane ruptures. Somewhat later, about the ninth week, a pair of thick crescentic swellings, the outer genital, or labio-scrotal folds, make their appearance on either side of the genital tubercle. In the female, in which the original relations are largely retained, the genital tubercle grows slowly and is converted into the glans and body of the clitoris, while the inner genital folds become the nymphae and the outer ones the labia majora. The urogenital sinus remains as the vestibule and its opening as the vulvar cleft. The wedge of tissue between the posterior margin of the latter and the anus becomes the perineal body. A description of the development of the glands of Bartholin is given in connec- tion with the consideration of these organs (page 2026). In the male the modifications lead- ing to the fully differentiated external organs are more pronounced in conse- quence of the formation of the urethra. The genital tubercle rapidly increases in size, becomes somewhat conical and differentiated into the glans and shaft of the penis. The parts of the outer genital folds behind the penis soon become en- larged, rounded, approach each other, and, finally, unite along a line afterward indicated by the median raphe, so that in embryos of 45 mm. length the scrotum is already well defined. According to Her- zog, 1 the development of the urethra pro- ceeds from an epithelial ridge that appears on the cloacal membrane and extends for- ward along the under surface of the geni- tal tubercle towards its distal end. This ridge sinks into the mesoblastic tissue of the elongating genital tubercle as a nar- row longitudinal strand (urethral septum), and later becomes partially divided by a superficial furrow, the urethral groove, the lips of which correspond to the inner geni- tal folds. In consequence of the cleavage of the posterior third of the epithelial ridge, the cloacal membrane is ruptured and communication established with the urogenital sinus by means of a small canal that opens into the urethral groove. As the latter grows farther forward towards the glans, approximation and fusion of its edges occur behind, whereby the groove is gradually converted into the urethral canal. In this manner the distal opening of the urethra is carried forward until its definite position on the glans is reached. Arrested development or fusion of the edges of the urethral groove results in defec- tive closure of the canal, a condition known as hypospadias (page 1927). The formation of the prepuce begins as a thickening and ingrowth of the surface epithelium at the bottom of an annular groove that separates the glans from the body of the penis. From this thickening the epithelium grows backward, invading the young connective tissue as a narrow wedge-shaped mass that encircles the glans, except below, where it is incomplete and the frenum later appears. In this manner an annular fold, the prepuce, is defined around the base of the glans that later, just before or shortly after birth, becomes free by the partial solution of the intervening solid epithelial stratum and its conversion into the preputial sac. 1 Archiv f. mikros. Anatom., Bd. Ixiii., 1904. Genital tubercle Cloacal membrane Lower limb Caudal process External genitals of human embryo of about twenty- seven days. (Kollmann.) FIG. 1727. Glans enital folds Labio-scrotal folds Opening of urogenital sinus Anal groove ' Coccygeal eminence Indifferent stage of external genitals of human embryo of thirty-three days (Fig. 1647). X 8. (Keibel.) DEVELOPMENT OF THE REPRODUCTIVE ORGANS. 2045 The developmental relations of the various parts of the urogenital system to the embryonal structures, as well as their morphological relations to one another in the two sexes, are shown in the diagrams (Fig. 1995) and accompanying table : MALE. FIG. 1728. FEMALE. Glans Urethral groove . Scrotal fold Anal groove Coccygeal eminence .Glans clitoridis .abium majus Nympha Urogenital sinus nus Coccygeal eminence Seven and a half weeks. (Herzog.) Glans Urethral groove closing Nine weeks. (Keibel.) Glans clitoridis 'Nymphae Labium majus Vaginal orifice Eleven weeks. (Kollmann.) Epithelial knob Urethral groove closed Glans clitoridis Prepuce Urethra Nympha .Vaginal orifice Anus Fifteen weeks. (Herzog.) Sixteen weeks. (Kollmann.) Development of external generative organs. Male Testis Coni vasculosi and ductulieffer- entes Paradidymis Duct of epididymis Vas aberrans Seminal vesicle Appendix of epididymis Appendix of testis Prostatic utricle Ureter Pelvis and collecting tubules of kidney Bladder Prostatic urethra Prostate gland Cowper's gland Penis Lips of urethral groove Scrotum Indifferent Type Sexual gland Wolffian tubules (sexual groiip) Wolffian duct (upper end] Miillerian duct Renal outgrowth from Wolffian duct Lower segment of allantois and part of cloaca Urogenital sinus (outgrowths from wall] Genital tubercle Genital folds Labio-scrotal folds Female Ovary Short tubules of epoophoron Paroophoron Main tube of epoophoron Gartner's duct, when persisting Hydatid of Morgagni Oviduct Uterus Vagina Ureter Pelvis and collecting tubules of kidney Bladder Urethra and vestibule Paraurethral tubes Bartholin's gland Clitoris Labia minora Labia majora 2046 HUMAN ANATOMY. THE FEMALE PERINEUM. The structures closing the pelvic outlet in the female correspond with those found in the male, modified, however, by the presence of the urogenital cleft and the small size of the clitoris. Owing to the greater divergence of the bony boundaries of the subpubic angle and the increased distance between the ischial tuberosities, the width of the lozenge- shaped perineal space (when the limbs are separated) is somewhat greater in the female. As in the" male (page 1916), the perineal region is divisible into a posterior rectal and an anterior urogenital triangle by an imaginary transverse line drawn between the anterior borders of the ischial tuberosities. Distinction must be made between the term "perineum," as above used, to indicate the entire region, and when applied in a restricted sense to the bridge separating the anal and vulvar orifices. Reference to sagittal sections (Fig. 1700) shows that this superficial bridge forms the FIG. 1729. Cut edge of super- ficial layer of su- perficial fascia Prepuce of clitoris - Glans clitoridis Labia minora{ Labia majora Superficial fascia / Superficial layer of superficial II fascia reflected Colles's fascia Vulvar fissure -Posterior commissure Cut edge of skin Anus Superficial dissection of female perineum ; on right side skin only has been removed ; on left, superficial layer of superficial fascia has been reflected. lower part of a triangular fibre-muscular mass, fat perineal body, that divides the vagina from the rectum and anal canal and contains the perineal centre with the con- verging fibres of the external sphincter, transverse perineal, and bulbo-cavernosus (sphincter vaginae) muscles. Apart from its somewhat greater breadth and more generous layer of fat, the rectal triangle presents no special features and contains the same structures as in the male. The superficial fascia, prolonged from the thighs and buttocks and usually laden with fat, closes in the ischio-rectal fossae and is directly continuous with the fatty areolar tissue filling these spaces. The internal pudic vessels and pudic nerve occupy the fascial (Alcock's) canal on the outer wall of the ischio-rectal fossa and give off the inferior hemorrhoidal branches distributed to the skin and muscles sur- rounding the anal canal. Over the urogenital triangle the superficial fascia is divisible into two distinct layers, a superficial and a deep. The former, loaded with fat, is continuous above and at the sides with the corresponding stratum on the abdomen and the thighs, and behind with the superficial fascia covering the rectal triangle. The deep layer, or Colles's fascia, is devoid of fat and membranous in character. Behind, where it turns he THE FEMALE PERINEUM. 2047 over the transverse perineal muscles, it blends with the posterior border of the tri- angular ligament along the perineal shelf ; laterally, it is attached to the ischial and pubic rami ; and in front it is prolonged over the labia majora to become continuous with the corresponding fascia (Scarpa's) over the abdomen. FIG. 1730. Glaus clitoridis- Superficial- fascia Labia minora- Vulvar fissure- Labia majora- Colles's fascia- Edge of cut skin- Anus -Inferior pudenda] nerve -Fascia lata of thigh Inferior -pudenda! nerve -Tuber ischii Cutaneous In ofinte lUndexte nal perineal nerves -From internal perineal nerve "Inf. hemorrhoidal art. -Inf. hemorrhofdal .From fourth sacral nerve Coccyx Superficial layer of superficial fascia has been removed from urogenital triangle ; Colles's fascia and cutaneous nerves and vessels exposed. Pubic ramus - FIG. 1731. Dorsal artery of clitoris Dorsal nerve of clitoris Dorsal vein of clitoris K / / Dorsal artery of clitoris Glans clitoridis Crus clitoridis Cms clitoridis Triangular ligament, in- ferior layer "Labium majus, denuded Tuber ischii Glands of Bartholin Dissection exposing bulbus vestibuli, Bartholin's glands and inferior layer of triangular ligament after removal of overlying structures ; left crus clitoridis displaced. The fascia of Colles forms the lower boundary of the superficial perineal inter- space, a triangular pocket limited above by the inferior layer of the triangular liga- ment and behind by the fusion of the latter with Colles's fascia. In addition to the superficial perineal vessels and nerves, the long pudendal nerves, the transverse peri- 2048 HUMAN ANATOMY. neal muscles, and the glands of Bartholin, this space contains the crura of the clitoris, the vestibular bulb and their associated muscles (ischio- and bulbo-cavernosus). IG. 1732. Dorsal vein Left dorsal artery of clitoris bnjiaai vein of clitoris Colles's fascia - reflected Pars intermedia - Ischio- cavernosus" Bulbus vestibuli Bulbo- cavernosus Triangular liga-~ ment, inf. layer Transversus~ perinei Superficial fascia- External - sphincter Glans clitoridis Ischio- cavernosus Superficial perineal artery Inf. pudendal nerve Ant. perineal artery Post, perineal nerve -Trans, perineal art. Inf. hemorrhoidal -artery int. hemorrhoidal -Anal fascia -Coccyx Deep layer of superficial fascia (Colles's fascia) removed, exposing structures within superficial interspace. Crus clitoridis- Triangular ligament, deep layer Tuber ischii External sphincter FIG. 1733. Glans clitoridis Dorsal artery of clitoris Dorsal vein of clitoris f Dorsal artery of clitoris Artery of corpus cavernosus Dorsal nerve of clitoris Internal pudic artery ..Triangular ligament Artery of bulb Internal -pudic artery -Perineal division of pudic nerve -Inf. hemorrhoidal art -Pudic nerve -Levator ani From fourth sacral nerve Creator sacro- seiatii- ligament "Glutens maximus, cut Glutens maximus Coccyx Inferior hemorrhoidal nerve Coccygeus Deeper dissection of perineum ; inferior layer of triangular ligament has been removed, exposing deep perineal Interspace; isrhio-tvctal fossa partially > li-ani'cl out. Owing to the diminutive size of the crura clitoridis, the ischio-cavernosus muscles are correspondingly small, but otherwise agree with those in the male. THE FEMALE PERINEUM. 2049 The presence of the urogenital cleft prevents the fusion not only of the vestibular hemibulbs (the homologues of the halves of the corpus spongiosum), but also of the bulbo-cavernosus muscles, which, therefore, are present in the female as separate bands that encircle the vestibule. The bulbo-cavernosus muscle, often called the sphincter vagince, arises from the perineal centre, blending with the fibres of the external sphincter and the transverse perineal muscles, and divides into a median and a lateral portion as it passes forward. The lateral and more superficial strand encircles the vagina, crosses the crus to gain the dorsum clitoridis, and ends, with the tendon of the opposite muscle, by blending with the fibrous sheath of the clitoris. The median and deeper portion of the muscle (the compressor bulbi of Holl ) partly covers the gland of Bartholin and the vestibular bulb, and in front unites with the corresponding strand of the opposite side in a Glans of clitoris " Gluteus maximus Coccygeus Vulvar fissure White line of pel- vic fascia slightly displaced toward midline Tuber ischii -Levator ani Anus - Coccygeus Greater sacro-sciatic ligament Gluteus maximus (cut) Coccyx Deep dissection of perineum, exposing muscles of pelvic floor. delicate tendinous expansion that passes beneath the body of the clitoris and is attached to the crura. Between the inferior and superior layers of the triangular ligament is included the deep perineal interspace. In addition to the continuations of the internal pudic vessels and pudic nerves, this interfascial space is occupied by a thin and imperfect muscular sheet that corresponds with the compressor urethrae. The posterior part of this sheet is differentiated, with variable distinctness, into the deep transverse perineal muscles which, arising from the ischial tuberosities, pass behind the vagina to the perineal centre. The remaining part of the sheet, collectively much less developed than the sphincter-like compressor urethrae in the male, is continued forward from the perineal centre as a thin stratum that closely encircles the vagina, and in front either surrounds the urethra or passes in front of the urethra in the interval between the latter and the transverse ligament (Kalischer). In recognition of its relations to both the vaginal and urethral canals, this muscular sheet has been appropriately called the urogenital sphincter. 129 INDEX. Abdomen, examination of, anatomical rela- tions, 536 fascia, superficial of, 515 landmarks and topography of, 53 1 lymphatics of, 972 lymph-nodes of, 974 muscles of, 515 pract. consid., 526 ventral aponeurosis of, 521 Abdominal cavity, 1615 region, epigastric, 1615 hypochondriac, 1615 hypogastric, 1615 iliac, 1615 lumbar, 1615 umbilical, 1615 hernia, 1759 incisions, anatomy of, 535 ring, external, 524 internal, 524 walls, lymphatics of, 976 posterior surface of, 525 Acervulus, 1125 Acetabulum, of ischium, 336 Acromio-clavicular articulation, 262 pract. consid., 264 Adamantoblasts, 1561 Adipose tissue, 79 chemical composition of, 83 After-birth, 55 Agger nasi, 193 Air-cells, ethmoidal, 1424 pract. consid., 1429 Air-sacs of lung, 1850 Air-spaces, accessory, 1421 pract. consid., 1426 Ala cinerea, 1097 Albinism, 1461 Alcock's canal, 817 Alimentary canal, 1538 tract, development of, 1694 Allantois, 32 arteries of, 33 human, 35 stalk of, 33 veins of, 33 Alveoli of lung, 1850 Ameloblasts, 1561 Amitosis, 14 Amnion, 30 false, 31 folds of, 30 human, 35 cavity of, 35 fluid of, 41 liquor of, 31 suture of, 31 Amniota, 30 Amphiarthrosis, 107 Anal canal, 1673 Analogue, 4 Anamnia, 30 Anaphases of mitosis, 13 Anastomoses, of ophthalmic veins, 880' Anatomy, i Ankle, landmarks of, 672 muscles and fasciae of, pract. consid., 666 Ankle-joint, 438 movements of, 440 pract. consid., 450 Annuli fibrosi, of heart, 698 Annulus ovalis, 695 tympanicus, 1493 of Vieussens, 695 Anorchism, 1950 Anthropology of skull, 228 Anthropotomy, i Antihelix, 1484 Antitragus, 1484 Antrum, 227 of Highmore, 1422 pract. consid., 1428 pylori, 1618 of superior maxilla, 201 Anus, 1673 formation of, 1695 muscles and fascias of, 1675 pract. consid., 1689 Aorta, abdominal, 794 branches of, pract. consid., 806 plan of branches, 796 pract. consid., 796 dorsal, 721 pulmonary, 722 segmental arteries of, 847 systemic, 723 thoracic, 791 valves of, 700 ventral, 721 Aortic arch, 723 pract. consid., 726 variations of, 724 bodies, 1812 bows, 847 septum, 707 Aponeurosis, 468 abdominal, ventral, 521 epicranial, 482 (fascia) plantar, 659 palmar, 606 Appendages,vesicular,of broad ligament, 2 002 Appendices epiploicae, 1660 Appendix epididymidis, 1949 testis, 1949 vermiform, 1664 blood-vessels of, 1667 development and growth of, 1668 lymphatics of, 1667 mesentery of, 1665 nerves of, 1668 orifice of, 1662 peritoneal relations of, 1665 pract. consid., 1681 Aquaeductus cochleae, 1514 Aqueduct of Fallopius, 1496 sylvian, 1108 Aqueous humor, 1476 chamber, anterior of, 1476 2051 2052 INDEX. Aqueous humor, chamber, posterior of, 147 pract. consid., 1476 Arachnoid, of brain, 1203 of spinal cord, 1022 Arantius, nodules of, 700 Archenteron, 25 Arches, visceral, 59 fifth or third branchial, 61 first or mandibular, 60 fourth or second branchial, 61 second or hyoid, 60 third or first branchial, 61 Arcuate nerve-fibres, 1071 Area acustica, 1097 embryonic, 23 parolfactory, 1153 pellucida, 25 Areola, 2028 Arm, lymphatics, deep, of, 965 superficial, of, 963 muscles and fascia of, pract. consid., 589 Arnold's ganglion, 1246 Arrectores pilorum, 1394 Arterial system, general plan of, 720 Artery or arteries, 719 aberrant, of brachial, 775 allantoic, 33 alveolar, 741 of internal maxillary, 741 aorta, systemic, 723 anastomoses around the elbow, 778 anastomotica magna, of brachial, 778 of femoral, 831 angular, 738 of facial, 738 articular, of popliteal, 833 auditory, internal, 759 auricular, anterior, of temporal, 745 deep, 740 of internal maxillary, 740 of occipital, 744 posterior, 744 axillary, 767 pract. consid., 769 azygos, of vaginal, 812 basilar, 758 brachial, 773 pract. consid., 776 brachialis superficjalis, 775 bronchial, 792 buccal, 741* of internal maxillary, 741 to bulb (bulbi urethrae), 817 calcaneal, external, 838 internal, 839 of external plantar, 840 calcarine, 760 carotid, common, 730 pract. consid., 731 external, 733 pract. consid., 733 internal, 746 pract. consid., 747 system, anastomoses of, 753 carpal, of anterior radial, 788 of anterior ulnar, 782 arch, posterior, 789 of posterior radial, 788 of posterior ulnar, 782 reta, anterior, 791 centralis retinae, 749 cerebellar, inferior, anterior, 759 posterior, 759 Artery or arteries, cerebellar, superior, 759 cerebral, anterior, 753 middle, 752 posterior, 760 cervical, ascending, of inferior thyroid, 766 of transverse cervical, 767 deep, 764 superficial, 766 transverse, 767 choroid, anterior, 752 ciliary, 749 anterior, 749 posterior, 749 circle of Willis, 760 circumflex, anterior, 773 external, of deep femoral, 828 internal, of deep femoral, 828 posterior, 773 circumpatellar anastomosis, 834 coccygeal, of sciatic, 815 cceliac axis, 797 colic, left, 803 right, 802 comes nervi ischiadici, 815 communicating, anterior, 753 of peroneal, 838 posterior, 751 of posterior tibial, 839 coronary, inferior, 738 of facial, 738 left, 728 right, 728 superior, 738 of facial, 738 of corpus cavernosum, 817 cremasteric, of deep epigastric, 820 of spermatic, 805 crico-thyroid, 734 of superior thyroid, 734 cystic, of hepatic, 799 dental, anterior, of internal maxillary, 74i inferior, 740 development of, 846 of lower limb, 848 of upper limb, 848 digital, collateral, of ulnar, 784 of ulnar, 784 dorsal, of foot, 845 of penis (clitoris), 817 dorsalis hallucis, 846 indicis, 789 pedis, 845 pollicis, 789 epigastric, deep, 820 superficial, 826 superior, 763 ethmoidal, 749 anterior, 750 posterior, 749 facial, 737 anastomoses of, 738 glandular branches of, 737 pract. consid., 738 transverse, 745 femoral, 821 anastomoses of, 831 deep, 828 development of, 823 pract. consid., 824 fibular, superior, of anterior tibial, 844 frontal, of ascending middle cerebral, 7 53 INDEX. 2053 Artery or arteries, frontal, of inferior middle cerebral, 753 internal, anterior, 753 middle, 753 posterior, 753 of ophthalmic, 750 Gasserian, of middle meningeal, 740 gastric, 798 short, of splenic, 800 gastro-duodenal, 799 gastro-epiploic, left, 80 1 right, 799 glandular, of facial, 737 gluteal, 8n pract. consid., 814 hemorrhoidal, inferior, 817 middle, 813 superior, 803 hepatic, 799 hyaloidea, 1474 hypogastric axis, 808 obliterated, 808 ileo-colic, 802 iliac, circumflex, deep, 821 superficial, 826 common, 807 pract. consid., 807 external, 818 anastomoses of, 821 pract. consid., 819 of ilio-lumbar, 810 internal, 808 anastomoses of, 818 pract. consid., 810 ilio-lumbar, 810 infrahyoid, of superior thyroid, 734 infraorbital, 741 of internal maxillary, 741 innominate, 729 pract. consid., 729 intercostal, of anterior internal mam- mary, 763 aortic, 792 of internal mammary, 765 superior, 764 internal mammary, pract. consid., 764 interosseous, anterior, 781 common, 781 dorsal, 846 posterior, 782 intestinal, of superior mesenteric, 802 labial, inferior, 738 of facial, 738 of internal maxillary, 741 lachrymal, 749 laryngeal, inferior, 766 superior, of superior thyroid, 734 lateral cutaneous, of aortic intercostals, 793 lenticulo-striate, of middle cerebral, 752 lingual, 735 anastomoses of, 736 dorsal, 736 pract. consid., 736 lumbar, 805 of ilio-lumbar, 810 malleolar, external, 844 internal, of anterior tibial, 844 of posterior tibial, 839 mammary, of aortic intercostals, 793 internal, 763 lateral internal, 764 masseteric, 740 Artery or arteries, masseteric, of facial, 738 of internal maxillary, 740 mastoid, of occipital, 744 maxillary, internal, 739 anastomoses of, 742 development of, 742 median, 781 mediastinal, of internal mammary, 763 of thoracic aorta, 792 meningeal, anterior, 748 of ascending pharyngeal, 743 middle, 740 of internal maxillary, 740 posterior, of occipital, 744 of vertebral, 758 small, 740 mesenteric, inferior, 802 superior, 80 1 metacarpal, dorsal, 789 metatarsal, of foot, 845 middle, colic, 802 musculo-phrenic, 763 nasal, lateral, 738 of facial, 738 of ophthalmic, 750 naso-palatine, of internal maxillary, 742 nutrient, of brachial, 774 of peroneal, 838 of posterior tibial, 838 of ulnar, 781 obturator, 813 from deep epigastric, 814 occipital, 743 pract. consid., 744 cesophageal, of gastric, 798 of thoracic aorta, 792 omphalomesenteric, 32 ophthalmic, 748 anastomoses of, 750 orbital, of middle meningeal, 740 of temporal, 745 ovarian, 805 of uterine, 813 palatine, ascending, 737 of facial, 737 descending, 741 of internal maxillary, 741 palmar arch, deep, 785 superficial, 784 deep, 782 interosseous, 790 palpebral, of internal maxillary, 741 of ophthalmic, 750 pancreatic, of splenic, 800 pancreatico-duodenal, inferior, 802 superior, 799 parietal, of middle cerebral, 753 parieto-occipital, 760 temporal, 753 parotid, of temporal, 745 perforating, of anterior internal mam- mary, 763 of deep femoral, 828 posterior, of external plantar, 840 of radial, 791 perineal, superficial, 817 transverse, 817 peroneal, anterior, 838 posterior, 838 of posterior tibial, 838 petrosal, of middle meningeal, 740 pharyngeal, ascending, 743 of ascending pharyngeal, 743 2054 INDEX. Artery or arteries, phrenic, inferior, 804 superior, 763 plantar arch, 840 digital, 840 external, 840 internal, 839 interosseous, 840 popliteal, 831 pract. consid., 832 posterior choroidal, 760 princeps cervicis, 744 hallucis, 841 pollicis, 789 profunda, inferior, 777 superior, 777 prostatic, 812 pterygoid, 740 of internal maxillary, 740 pterygo-palatine, 742 of internal maxillary, 742 pubic, of deep epigastric, 820 of obturator, 813 pudic, external, deep, 828 superficial, 826 internal, 815 accessory, 818 pulmonary, 722 valves of, 700 pyloric, of hepatic, 799 radial, 785 development of, 786 pract. consid., 786 recurrent, 787 radialis indicis, 790 superficialis, 775 ranine, 736 recurrent, of palm, 791 > of posterior interosseous, 782 renal, 804 sacral, lateral, 810 middle, 806 scapular, dorsal, 773 posterior, 767 sciatic, 815 septal, of nose, 738 sigmoid, 803 spermatic, 805 spheno-palatine, 742 of internal maxillary, 742 spinal, anterior, of vertebral, 759 posterior, of vertebral, 758 splenic, 800 sterno-mastoid, of external carotid, 743 of occipital, 744 of superior thyroid, 734 striate, external, of middle cerebral, 752 internal, of middle cerebral, 752 structure of, 675 stylo-mastoid, 745 subclavian, 753 pract. consid., 756 subcostal, 792 sublingual, 736 submental, 737 of facial, 737 subscapular, 772 suprahyoid, 736 supraorbital, 749 suprarenal, 804 inferior, 804 suprascapular, 767 tarsal, external, 845 internal, 845 Artery or arteries, temporal, anterior, of vertebral, 760 deep, 740 of internal maxillary, 740 middle, 745 posterior, of vertebral, 760 superficial, 745 pract. consid., 745 thoracic, acromial, 771 alar, 772 long, 772 superior, 771 thyroid axis, 765 pract. consid., 766 inferior, 766 superior, 734 pract. consid., 735 tibial, anterior, 842 anastomoses of, 844 pract. consid., 842 posterior, 834 anastomoses of, 841 development of, 836 pract. consid., 836 recurrent, anterior, 844 posterior, 844 tonsillar, 737 of facial, 737 tubal, of ovarian, 805 of uterine, 813 tympanic, of internal carotid, 748 of internal maxillary, 740 of middle meningeal, 740 ulnar, 778 accessory, 776 development of, 779 pract. consid., 780 recurrent, anterior, 781 posterior, 781 umbilical, 54 ureteral, of ovarian, 805 of renal, 804 of spermatic, 805 of uterine, 813 urethral, 817 uterine, 812 vaginal, 812 vertebral, 758 pract. consid., 761 vesical, inferior, 811 middle, 81 1 of obturator, 813 superior, 81 1 vesiculo-deferential, 812 Vidian, 742 vitelline 32 volar, superficial, 788 Arthrodia, 113 Articulation or articulations, acromio-clavic- ular, pract. consid., 264 carpo-metacarpal, 325 movements of, 326 costo- vertebral, 160 of ethmoid, 194 of foot, 440 of frontal bone, 197 of inferior turbinate bone, 208 of lachrymal bone, 207 of malar bone, 210 metacarpo-phalangeal, 327 movements of, 328 of nasal bone, 209 of occipital bone, atlas, and axis, 135 INDEX. 2055 Articulation or articulations, of palate bone, 205 of parietal bone, 199 sacro-iliac, 338 scapulo-clavicular, 262 of sphenoid bone, 190 sterno-clavicular, 261 pract. consid., 263 of superior maxilla, 202 of temporal bone, 184 temporo-mandibular, 214 development of, 215 movements of, 215 thoracic anterior, 158 of thorax, 157 of thumb, 326 tibio-fibular, inferior, 396 superior, 396 of vertebral column, 132 of vomer, 206 Arytenoid cartilages, 1816 Asterion, 228 Astragalus, 423 development of, 425 Astrocytes, 1003 Atlas, 1 20 development of, 131 variations of, 120 Atria of lung, 1850 Auditory canal, external, 1487 blood-vessels of, 1489 nerves of, 1490 pract. consid., 1491 internal, 1514 ossicles, 1496 path, 1258 Auerbach, plexus of, 1643 Auricle or auricles, 1484 antihelix of, 1484 antitragus of, 1484 blood-vessels of, 1486 cartilage of, 1485 concha of, 1484 of heart, 693 helix of, 1484 ligaments of, 1486 lobule of, 1484 muscles of, 1486 nerves of, 1487 pract. consid., 1490 structure of, 1485 tragus of, 1484 Auricular canal, 705 Axilla, 574 muscles and fascia of, pract. consid., 579 Axis, 121 development of, 131 Axis-cylinder, 1001 Axones, of neurones, 997 Azygos system of veins, 893 Bartholin, glands of, 2026 Basion, 228 Bell, external respiratory nerVe of, 1295 Bertin, bones of, 191 columns of, 1876 Bicuspid teeth, 1545 Bile-capillaries, 1715 Bile-duct, common, 1720 opening of, 1720 pract. consid., 1731 interlobular, 1717 lymphatics of, 981 Biliary apparatus, 1718 Bladder, lymphatics of, 985 urinary, 1901 capacity of, 1903 development of, 1938 in female, 1908 fixation of, 1905 infantile, 1908 interior of, 1904 nerves of, 1910 peritoneal relations of, 1904 pract. consid., 1910 relations of, 1906 structure of, 1908 trigone of, 1904 vessels of, 1910 Blastoderm, 22 bilaminar, 23 trilaminar, 23 Blastodermic layers, 22 derivatives of, 24 vesicle, stage of, 56 Blastomeres, 21 Blastopore, 25 Blastula, 25 Blood, 680 Blood-cells, colored, 68 1 , colorless, 684 development of, 687 Blood-crystals, 68 1 lakes of dural sinuses, 852 plaques, 685 Blood-vascular system, 673 Blood-vessels of auricle, 1486 of bone, 93 of brain, 1206 capillary, 678 of cartilage, 81 development of, 686 of duodenum, 1649 of Eustachian tube, 1504 of external auditory canal, 1489 of eyelids, 1445 of glands, 1535 of hair-follicles, 1394 of kidney, 1884 of liver, 1709 lobular, of liver, 1713 of lung, 1853 of membranous labyrinth, 1522 of nasal fossa, 1425 of non-striated muscle, 456 of nose, 1407 of pericardium, 716 of pleura, 1860 of small intestine, 1642 of rectum, 1679 of retina, 1467 of skin, 1387 of spinal cord, 1047 of stomach, 1627 of striated muscle, 464 structure of, 673 of sweat glands, 1400 vasa vasorum, 674 Body-cavity, differentiation of, 1700 Body-form, general development of, 56 Body-stalk, 37 Bone or bones, 84 age of, 1 06 astragalus, 423 of Bertin, 191 blood-vessels of, 93 2056 INDEX. Bone or bones, calcaneum, 419 canaliculi of, 86 cancellated, 85 carpus, 309 cells of, 89 chemical composition of, 84 clavicle, 257 compact, 86 development of, 100 cranium, 172 cuboid, 422 cuneiform, 310 external, 428 internal, 426 middle, 427 development of, 94 endochondral, 94 intramembranous, 98 diaphysis of, 104 elasticity of, 105 ethmoid, 191 femur, 352 fibula, 390 frontal, 194 general considerations of, 104 growth of, 1 01 Haversian canals of, 88 system of, 86 humerus, 265 hyoid, 216 ilium, 332 inferior turbinate, 208 innominate, 332 intramembranous, 101 ischium, 336 lachrymal, 207 lacunae of, 86 lamellae of, circumferential, 86 Haversian, 86 interstitial, 86 lymphatics of, 93 malar, 209 maxilla, inferior, 211 superior, 199 mechanics of, 105 metacarpal, 314 metatarsal, 428 nasal, 209 nerves of, 94 number of, 107 occipital, 172 os magnum, 312 palate, 204 parietal, 197 parts of, 1 06 patella, 398 periosteum of, 89 phalanges of foot, 432 of hand, 317 physical properties of, 85 pisiform, 311 pubes, 334 radius, 287 relation of to figure, 107 ribs, 149 scaphoid, 309 of foot, 425 scapula, 248 semilunar, 310 sesamoid, 104 sex of, 1 06 shapes of, 104 Sharpey's fibres of, 87 Bone or bones, of shoulder-girdle, 248 skull, 172 sphenoid, 186 sphenoidal, turbinate, 191 sternum, 155 structure of, 85 subperiosteal, 98 tarsal, 419 temporal, 176 of thorax, 149 tibia, 382 trapezium, 311 trapezoid, 311 ulna, 281 unciform, 312 variations of, 107 Volkmann's canals of, 89 vomer, 205 Bone-marrow, 90 cells of, 92 eosinophiles, 92 giant cells of, 92 nucleated red cells of, 92 erythroblasts, 92 normoblasts, 92 primary, 95 red, 90 yellow, 93 Bowman, glands of, 1415 membrane of, 1451 Brachium, inferior, 1107 internal structure of, uio superior, 1107 Brain, 1055 blood-vessels of, 1206 general development of, 1058 lymphatics of, 948 measurements of, 1195 membranes of, 1197 pract. consid., 1207 pract. consid., 1207 weight of, 1196 Brain-sand (acervulus), 1125 Brain-stem, 1056 Brain-vesicles, primary, 1059 secondary, 1061 Branchial arches, derivatives of, 847 Bregma, 228 Bronchial tree, 1847 variations of, 1849 Bronchus or bronchi, 1838 distribution of, 1849 eparterial, 1848 homologies of, 1848 hyparterial, 1848 pract. consid., 1840 terminal, 1850 Bruch, membrane of, 1456 Brunner, glands of, 1639 Buccal fat-pad, 489 Bulb, 1063 of internal jugular vein, 86r olfactory, 1151 urethral, "1968 Bulbo-tecto-thalamic strands, 1116 Bulbus vestibuli, 2025 Bulla, of ethmoid, 194 Burns, space of, 543 Bursa or bursse, in iliopectineal, 623 ischiatic, of gluteus maximus, 630 of knee-joint, 406 of m. pyriformis, 561 INDEX. 2057 Bursa or bursse, subdeltoid, 578 subscapular, 578 troc-hanteric, of gluteus maximus, 630 Buttocks, landmarks of, 669 muscles and fasciae of, pract. consid., 641 Cascum, 1660 blood-vessels of, 1667 development and growth of, 1668 interior of, 1661 lymphatics of, 1667 nerves of, 1668 peritoneal relations of, 1665 position of, 1662 pract. consid., 1680 structure of, 1663 Calamus scriptorius, 1096 Calcaneum, 419 development of, 422 structure of, 421 variations of, 421 Camper's fascia, 515 Canal or canals, alimentary, 1538 anal, 1673 auditory, external, 1487 auricular of heart, 705 carotid, 184 central, of spinal cord, 1030 of Cloquet, 1474 facial, 184 femoral, 625 Haversian, of bone, 88 Hunter's, 628 hyaloid, 1474 incisive, 1413 inguinal, 523 neural, 26 neurenteric, 25 of Nuck, 2006 palatine, anterior, 201 posterior, 204 reuniens, 1515 of Scarpa, 201 of Schlemm, 1452 semicircular membranous, 1515 osseous, 1512 structure of, 1516 of Stenson, 201 of Stilling, 1474 Vidian, 189 Volkmann's, of bone, 89 Canaliculi, of bone, 86 lachrymal, 1478 Canine teeth, 1544 Canthi of eye, 1442 Capitellum of humerus, 268 Capsule, external, 1172 internal, 1173 of Tenon, 504 Caput medusas, 534 Cardiac muscle, 462 Cardinal system of veins, 854 Carina tracheae, 1837 urethralis, 2016 Carotid body, 1809 chromamne cells of, 1810 sheath, 543 Carpo-metacarpal articulations, 325 Carpus, 309 development of, 313 pract. consid., 319 variations of, 313 Cartilage or cartilages, 80 Cartilage or cartilages, articular, 81 arytenoid, 1816 of auricle, 1485 blood-vessels of, 8 capsule of, 80 chemical composition of, 83 costal, 1 53 cricoid, 1813 cuneiform of Wrisberg, 1817 development of, 82 elastic, 81 fibrous, 82 hyaline, 80 lacunas of, 80 lateral, of nose, 1405 matrix of, 80 of nasal septum, 1405 of nose, 1404 perichondrium of, 81 of Santorini, 1817 thyroid, 1814 triangular, of nasal septum, 224 vomerine, 1406 Cartilage-cells, 80 Carunculas hymenales, 2016 salivares, 1581 Caruncle, lachrymal, 1443 Cauda equina of spinal cord, 1025 Cavity, abdominal, 1615 nasal, 223 pneumatic accessory, 226 segmentation, 22 synovial, of foot, 447 tympanic, 1492 of tympanum, 183 Cell or cells, animal, 6 of bone, 89 of connective tissues, 73 decidual, 47 gustatory, 1435 mastoid, 1 504 of Rauber, 23 spermatogenetic, 1943 tactile, of Merkel, 1016 Cell-division, 10 direct, 14 indirect, 1 1 reduction division, 18 Cell-mass, inner, 23 intermediate, 29 Cementoblasts, 1563 Cementum, 1552 formation of, 1563 Centrosome, 9 Cephalic flexure, 1061 Cerebellar peduncle, fibre-tracts of, 1093 inferior, 1067 inferior, fibre-tracts of, 1093 middle, fibre-tracts of, 1094 superior, fibre-tracts of, 1094 Cerebellum, 1082 architecture of, 1088 cortex of, 1090 histogenesis of, 1105 development of, 1103 flocculus of, 1085 hemispheres of, 1082 lobus cacuminis of, 1085 centralis of, 1084 clivi of, 1085 cultninis of, 1084 lingulas of, 1084 noduli of, 1085 2058 INDEX. Cerebellum, lobus pyramidis of, 1086 tuberis of, 1087 uvulae of, 1086 medullary substance of, 1093 nuclei, internal of, 1088 nucleus, dentate of, 1088 emboliformis (embolus) of, 1089 fastigii of, 1089 globosus of, 1089 Purkinje cells of, 1090 tonsil (amygdala) of, 1086 worm of, 1082 Cerebral commissures, development of, 1194 convolutions (gyri), 1135 fissures (sulci), 1135 hemispheres, 1133 architecture of, 1155 longitudinal fissure of, 1133 lobes, 1135 localization, 1210 peduncles, 1107 Cerebro-spinal fluid, 1023 Cerumen, 1489 Cervical flexure, 1062 Cheeks, 1538 lymphatics of, 951 pract. consid., 1594 Choanae, 1413 (bony), 224 primitive, 1429 Chorda dorsalis, 27 Chordae tendineae, of heart, 697 Choriocapillaris, 1456 Chorion, 32 allantoic, 33 canalized fibrin of, 49 epithelium of, 49 frondosum, 38 human, 41 laeve, 38 primitive, 31 syncytium of, 49 villi of, 49 Choroid, 1455 development of, 1482 plexus of fourth ventricle, noo of third ventricle, 1131 pract. consid., 1459 structure of, 1456 Chromaffine cells of carotid body, 1810 Chromatin, 9 Cilia, 70 Ciliary body, 1457 ganglion, 1236 muscle, 1458 processes, 1457 ring, 1457 Circulation, general plan of, 719 Cisterna magna, 1203 Claustrum, 1172 Clava, 1066 Clavicle, 257 development of, 258 fracture of, 259 landmarks of, 260 pract. consid., 258 sexual differences, 258 surface anatomy of, 258 Clinoid process, anterior, 189 processes, middle, 186 posterior, 186 Clitoris, 2024 glans of, 2024 Clitoris, nerves of, 2025 prepuce of, 2024 vessels of, 2025 Cloaca, 1696 Cloquet, canal of, 1474 lymph-nodes of, 992 Coccygeal body, 1810 Coccyx, 127 development of, 131 Cochlea, membranous, 1517 nerves of, 1521 organ of Corti of, 1519 Reissner's membrane of, 1517 structure of, 1518 osseous, 1513 Cceliac plexus, lymphatic, 973 Ccelom, 28 pericardial, 1700 pleural, 1700 Cohnheim's fields of striated muscle-fibre, 461 Collagen, 83 Colles, fascia of, 562 ligament of, 523 Colliculi inferiores, 1107 superiores, 1107 Colliculus, inferior, internal structure of, mo superior, internal structure of, mo Colon, 1668 ascending, 1668 blood-vessels of, 1672 descending, 1669 flexure, hepatic of, 1668 splenic of, 1668 lymphatics of, 1672 nerves of, 1672 peritoneal relations of, 1670 pract. consid., 1685 relations of, 1668 transverse, 1668 Colostrum, 2031 corpuscles, 2031 Columnae carneae, of heart, 697 Column, spinal, 114 Columns, anterior, of spinal cord, 1027 lateral, of spinal cord, 1027 of Morgagni, 1674 posterior, of spinal cord, 1027 Commissura habenulae, 1124 hippocampi, 1158 hypothalamica, 1128 Commissure, anterior, 1185 of Meynert, 1115 middle, 1 1 19 posterior, 1125 Concha, 1484 Condylarthrosis, 113 Conjunctiva, 1441 bulbar, 1445 palpebral, 1445 pract. consid., 1447 Connective substances, chemical composi- tion of, 83 tissues, 73 cells of, 73 fixed, 74 typical, 74 wandering, 74 chemical composition of, 83 granule-cells of, 74 ground-substance of, 75 intercellular constituents of, 74 pigment -cells of, 74 INDEX. 2059 Construction, general plan of, r Conus medullaris, of spinal cord, 1021 Convolutions (gyri) cerebral, 1135 Cooper, ligaments of, 2029 Cord, spermatic, 1960 Corium, 1383 Cornea, 1450 nerves of, 1452 pract. consid., 1453 structure of, 1451 Corniculae laryngis, 1817 Cornua sphenoidalia, 191 Corona radiata, 1186 Coronoid process, of ulna, 281 Corpora cavernosa of penis, 1966 mammillaria (albicantia), 1128 quadrigemina, 1106 Corpus albicans, 1991 callosum, 1155 fibrosum, 1991 Highmori, 1942 luteum, 1990 spurium, 1991 verum, 1991 spongiosum, of penis, 1967 striatum, 1169 connections of, 1172 development of, 1193 structure of, 1171 subthalamicum, 1128 trapezoides, 1079 Corpuscles, corneal, 1452 genital, 1017 of Grandry, 1016 of Hassall, 1799 of Herbst, 1019 of Meissner, 1017 of Ruffini, 1017 Vater-Pacinian, 1018 Cortex of cerebellum, 1090 cerebral, histogenesis of, 1192 local variations in, 1180 nerve-cells of, 1176 nerve-fibres of, 1179 structure of, 1175 Corti, ganglion of, 1257 membrane, 1521 organ of, 1519 Costal cartilage, 153 Cotyledons of placenta, 50 Cowper, glands of, 1984 Cranial capacity, 230 nerves, 1219 abducent (6th), 1249 auditory (8th), 1256 development of, 1376 facial (7th), 1250 glosso-pharyngeal (gth), 1260 hypoglossal (i2th), 1275 oculomotor (3rd), 1225 olfactory (ist), 1220 optic (2nd), 1223 pract. consid., 1220 spinal-accessory (nth), 1274 trigeminal (sth), 1230 trochlear (4th), 1228 vagus (loth), 1265 Cranio-cerebral topography, 1214 Cranium, 172 architecture of, 220 exterior of, 218 fossa, anterior, 220 middle of, 220 Cranium, fossa, posterior of, 220 fractures of, 238 interior of, 220 muscles and fascia 1 , pract. consid., 489 pract. consid., 235 vault of, 220 Cretinism, 1794 Cricoid cartilage, 1813 Crista galli, of ethmoid, 191 Crura of penis, 1967 Crusta, 1115 Cuboid bone, 422 development of, 423 Cumulus oophorus, 1989 Cuneate tubercle, 1067 Cuneiform bone, 310 external, 428 internal, 426 middle, 427 Cuticle, 1385 Cuvier, ducts of, 854 Cystic duct, 1720 pract. consid., 1731 Cytoplasm, structure of, 7 Dacryon, 228 Darwin, tubercle of, 1484 Decidua, 44 capsularis, 46 cells of, 47 placentalis, 48 reflexa, 45 serotina, 48 vera, 46 Decussation of pyramids, 1064 sensory, 1070 Deiters, cells of, 1521 nucleus, 1076 Demours, membrane of, 1452 Dendrites, of neurones, 997 Dental formula, 1542 papilla, 1558 Dentine, 1550 formation of, 1559 Dentition, first and second, 1564 Derma, 1383 Descemet's membrane, 1452 Deutoplasm, i 5 Development of alimentary tract, 1694 of atlas, 131 of auditory nerves, 1525 of axis, 131 of bone, 94 of carpus, 313 of cartilage, 82 of cerebellum, 1103 of clavicle, 258 of coccyx, 131 of cranial nerves, 1376 of ear, 1523 early, 15 of elastic tissue, 77 of ethmoid bone, 194 of external ear, 1526 of external genital organs, 2043 of eye, 1480 of face, 62 of Fallopian tube, 1999 of femur, 359 of fibrous tissue, 76 of fibula, 393 of frontal bone, 197 of ganglia, 1012 2060 INDEX. Development, general, of brain, 1058 of general body-form, 56 of glands, 1537 of hairs, 1401 of heart, 705 of humerus, 269 of hyoid bone, 216 of inferior turbinate bone, 208 of innominate bone, 337 of internal ear, 1523 of lachrymal bone, 207 of liver, 1723 of lungs, 1 86 1 of lymphatic vessels, 939 of lymph-nodes, 940 of malar bone, 210 of mammary glands, 2032 of maxilla, inferior, 213 of maxilla, superior, 202 of medulla oblongata, 1101 of mesencephalon, 1117 of middle ear, 1525 of muscle, non-striated, 457 of muscle, striated, 465 of nails, 1403 of nasal bone, 209 of nerves, 1375 of nervous tissues, 1009 of nose, 1429 of occipital bone, 175 of oral cavity, 62 glands, 1589 of ovary, 1993 of palate bone, 205 of pancreas, 1737 of parietal bone, 199 of patella, 400 of pelvis, 344 of peripheral nerves, ion of peritoneum, 1702 of pharynx, 1603 of pituitary body, 1808 of pons Varolii, 1103 of prostate gland, 1979 of radius, 293 of reproductive organs, 2037 of respiratory tract, 1861 of ribs, 1 53 of sacrum, 129 of scapula, 253 of skin, 1400 of sphenoid bone, 190 of spinal cord, 1049 of spleen, 1787 of sternum, 157 of suprarenal bodies, 1 804 of sweat glands, 1404 of sympathetic system, 1013 of teeth, 1556 of temporal bone, 184 of thymus body, 1800 of thyroid body, 1793 of tibia, 387 of ulna, 285 of urethra, 1938 of urinary bladder, 1938 organs, 1934 of uterus, 2010 of vagina, 2019 of veins, 926 of vertebrae, 128 of vomer, 206 Diaphragm, 556 Diaphragm, lymphatics of, 970 of pelvis, 1676 Diaphragma sellae, 1200 Diaphysis, of bone, 104 Diarthrosis, 107 Diencephalon , 1 1 1 8 development of, 1193 Diverticulum of Meckel, 44 Dorsum sellag, 186 Douglas, fold of, 522 pouch of, 1743 Duct or ducts, cochlear, 1517 of Cuvier, 854 cystic, 1720 ejaculatory, 1955 Gartner's, 2001 hepatic, 1718 lactiferous, 2028 nasal (naso-lachrymal) 1479 pancreatic, 1736 .papillary, of kidney, 1882 paraurethral, 1924 parotid, 1583 renal, 1894 spermatic, 1953 sublingual, 1585 submaxillary, 1584 thoracic, 941 thyro-glossal, 1793 vitelline, 32 vitello-intestinal, human, 37 Wolffian, 1935 Ductus arteriosus, 723 endolymphaticus, 1514 venosus, fissure of, on liver, 1707 Duodenal glands, 1639 Duodeno-hepatic ligament, 1644 Duodeno-jejunal flexure, 1645 fossae, 1647 Duodenum, 1644 blood-vessels of, 1649 interior of, 1648 lymphatics of, 1649 nerves of, 1649 papilla of, 1720 peritoneal relations of, 1646 variations of, 1649 Dupuytren's contraction, 616 Dura mater of brain, 1198 of spinal cord, 1022 Ear, 1483 development of, 1523 external, 1484 development of, 1526 internal, 1510 development of, 1523 membranous labyrinth of, 1514 osseous labyrinth of , 1 5 1 1 perilymph of, 1514 lymphatics of, 950 middle, 1492 antrum of, 1 508 development of, 1525 Eustachian tube, 1501 mastoid cells, 1 504 sigmoid sinus, 1 509 suprameatal triangle, 1510 suprameatic spine, 1 508 tympanum of, 1492 Ear-point, 1484 liar-wax, 1489 Ectoblast, 23 INDEX. 2061 Egg-nucleus, 16 Elastic tissue, 76 development of, 77 Elastin, 83 Elbow-joint, 301 landmarks of, 308 movements of, 303 pract. consid., 305 Embryo, stage of, 56 Eminentia hypoglossi, 1098 teres, 1097- Enamel, 1548 formation of, 1561 Enamel-cells, 1561 Enamel-cuticle, 1550 Enamel-organ, 1 560 Enarthrosis, 113 Encephalon, 1055 End-bulbs of Krause, 1016 End-knobs of free sensory nerve-endings, 1015 Endocardium, 702 Endolymph of membranous labyrinth, 1514 Endometrium, 2007 Endomysium, 458 Endoneurium, 1006 Endothelium, 71 Enophthalmos, 1439 Ensiform cartilage of sternum, 156 Entoblast, 23 Entoskeleton, 84 Ependymal cells, 1004 Epicardium, 702 Epidermis, 1385 Epididymis, 1947 appendix of, 1949 canal of, 1948 digital fossa of, 1947 globus major of, 1947 minor of, 1947 nerves of, 1948 structure of, 1947 vasa abberrantia of, 1950 vessels of, 1948 Epiglottis, 1816 ligaments of, 1817 movements of, 1817 Epimysium, 458 Epineurium, 1006 Epiphysis,, 1124 ossification of, 98 Epispadias, 1928 Epithalamus, 1123 Epithelium of chorion, 49 columnar, 69 glandular, 70 ' modified, 70 pigmented, 70 specialized, 70 squamous, 68 stratified, 68 transitional, 69 Epitrichium, 1401 Eponychium, 1403 Epoophoron, 2000 Erythroblasts, 92 Erythrocytes, 68 1 development of, 687 Ethmoid bone, 191 articulations of, 194 bulla of, 194 cells of, 192 development of, 194 Ethmoid turbinate bone, middle of, 193 superior of, 193 uncinate process of, 193 Eustachian tube, 1501 blood-vessels of, 1 504 cartilaginous portion, 1502 mucous membrane of, 1 503 muscles of, 1503 osseous portion, 1502 pract. consid., 1507 valve, 694 Exocoelom, 32 Exophthalmos, 1439 Exoskeleton, 84 Extremity, lower, 332 landmarks of, 669 lymphatics of, 991 upper, landmarks of, 618 lymphatics of, 961 Eye, 1436 development of, 1480 lymphatics of, 949 plica semilunaris of, 1443 pupil of, 1459 Eyeball, 1448 aqueous humor of, 1476 chamber anterior of, 1476 posterior of, 1476 choroid of, 1455 ciliary body of, 1457 processes of, 1457 cornea of, 1450 fovea centralis of, 1466 iris of, 1459 lens, crystalline of, 1471 macula lutea of, 1466 movements of, 505 optic nerve of, 1469 ora serrata of, 1467 pract. consid., 1449 retina of, 1462 sclera of, 1449 vascular tunic of, 1454 vitreous body of, 1473 Eye-lashes, 1442 Eyelids, 1441 blood-vessels of, 1445 development of, 1483 lymphatics of, 1445 nerves of, 1446 pract. consid., 1446 structure of, 1443 Face, 222 architecture of, 228 development of, 62 landmarks of, 246 muscles and fasciae, pract. consid., 492 pract. consid., 242 Falciform ligament, 1745 Fallopian tube, 1996 changes in, 1999 course of, 1997 development of, 1999 fimbriae of, 1997 infundibulum of, 1997 isthmus of, 1997 lymphatics of, 988 nerves of, 1999 pract. consid., 1999 relations of, 1997 Fallopian tube, structure of, 1997 vessels of, 1998 2062 INDEX. Fallopius, aqueduct of, 181 Falx cerebelli, 1200 cerebri, 1199 Fascia or fasciae, 470 anal, 1678 of ankle, pract. consid., 666 antibrachial, 592 of anus, 1675 of arm, pract. consid., 589 of axilla and shoulder, pract. consid., 579 axillary, 574 bicipital (semilunar), 586 . brachial, 585 bucco-pharyngeal, 488 of buttocks, pract. consid., 641 of Colles, 562 of cranium, pract. consid., 489 cribriform, 635 crural, 647 deep, 470 of back, 508 cervical, 542 of hand, 606 dentata, 1166 of face, pract. consid., 492 of foot, pract. consid., 666 of hip and thigh, pract. consid., 642 iliac, 624 infundibuliform, 524 intercolumnar (external spermatic), 524 of knee, pract. consid., 645 lata, 633 of leg, pract. consid., 665 obturator, 559 of orbit, 504 palmar, 606 palpebral, 1438 parotido-masseteric, 474 pectoral, 568 pelvic, 558 perineal, superficial, 562 plantar, 659 prevertebral, 543 rectal, 1678 recto- vesical, 1678 of rectum, 1675 of scalp, pract. consid., 489 superficial, 470 of abdomen, 515 temporal, 475 transversalis, 520 Fasciculus, auriculo- ventricular of heart, 701 posterior longitudinal, 1 1 1 6 retroflexus, 1124 solitarius, 1074 Fat, orbital, 1437 Fat-cells, 79 Fauces, isthmus of, 1 569 pillars of, 1569 Femoral canal, 625 ring, 625 Femur, 352 development of, 359 landmarks of, 366 pract. consid., 361 structure of, 357 surface anatomy, 360 variations, sexual and individual, 359 Fertilization, 18 Fibres, intercolumnar, 524 Fi1>rin, canalized, of chorion, 49 Fibro-cartilage, 82 Fibrous tissue, 74 Fibrous tissue, development of, 76 Fibula, 390 development of, 393 landmarks of, 396 pract. consid,, 393 Fillet, decussation of, 1070 median, 1115 Fimbria, 1159 hippocampi, 1165 Fissure, calcarine, 1146 calloso-marginal, 1139 central, of cerebrum, 1137 collateral, 1139 ethmoidal, 1411 of Glaser, 178 palpebral, 1441 parieto-occipital, 1138 portal, of liver, 1708 pterygo-maxillary, 204 of Rolando, 1137 sphenoidal, 188 (sulci) cerebral, 1135 of Sylvius, 1136 Fistula, cervical, 61 Flexure, cephalic, 58 cervical, of embryo, 59 dorsal, of embryo, 59 sacral, of embryo, 59 Flocculus, 1085 Foetus, membranes of, 30 stage of, 63 eighth month, 66 week, 64 fifth month, 66 week, 63 fourth month, 65 ninth month, 66 seventh month, 66 week, 64 sixth month, 66 week, 63 third month, 65 Follicles, Graafian, 1988 Fontana, spaces of, 1452 Fontanelles, 231 Foot, articulations of, 440 as whole, 447 bones of, 419 landmarks of, 437 pract. consid., 436 joints of, landmarks of, 453 landmarks of, 672 muscles of, 659 and fasciae of, pract. consid., 666- surface anatomy, 449 synovial cavities of, 447 Foramen or foramina, caecum, 1574 ethmoidal, anterior, 192 posterior, 192 jugular, 220 of Luschka, 1 100 of Majendie, noo mastoid, 180 of Monroe, 1131 optic, 189 ovale, 1 88 of heart, 695 pterygo-spinosum, 190 rotundum, 187 sacro-sciatic, great, 341 lesser, 341 sphenoidal, 187 spheno-palatine, 204 INDEX. 2063 Foramen or foramina, spinosum, 188 stylo-mastoid, 182 thyroid (obturator), 337 of vena cava, of diaphragm, 557 of Vesalius, 188 of Winslow, 1746 Forceps anterior, of corpus callosum, 1157 posterior, of corpus callosum, 1158 Forearm, 281 as whole, 299 intrinsic movements of, 299 motion of on humerus, 303 pract. consid., 603 Fore-brain, 1059 Formatio reticularis, 1076 reticularis alba, 1076 grisea, 1074 Fornix, 1158 pillars of, anterior, 1 1 59 posterior, 1159 Fossa or fossae, duodeno-jejunal, 1647 glenoid, 178 hyaloidea, 1473 ileo-caecal, 1666 infraspinoue, 250 inguinal, inner, 526 lateral, 1743 median, 1742 outer, 526 interpeduncular, 1107 intersigmoid, 1671 ischio-rectal, 1678 jugular, 182 nasal, 1409 navicular of urethra, 1924 ovalis, 695 ovarian, 1986 pararectal, 1744 paravesical, 1744 pericaecal, 1666 pineal, 1106 pituitary, 186 retro-colic, 1667 of Rosenmiiller, 1 598 spheno-maxillary, 227 subscapular, 249 supraspinous, 250 supratonsillar, 1600 supra vesical, 526 Sylvii, 1137 temporal, 218 zygomatic, 227 Fourchette, 2022 Fourth ventricle, 1096 choroid plexus of, noo floor of, 1096 roof of, 1099 Fovea centralis, 1466 vagi, 1098 Frenulum of Giacomini, 1166 Frenum of prepuce, 1966 of tongue, 1573 Frontal bone, 194 articulations of, 197 development of, 197 lobe, 1139 sinus, 1423, 226 (bony) Fundamental embryological processes, 26 Funiculus cuneatus, 1066 gracilis, 1066 of Rolando, 1067 Furrows, visceral, 59 Furrows, visceral, external, 61 external, first, 61 inner, 61 inner, fourth, 62 inner, second, 62 inner, third, 62 Galen, vein of, 856 Gall-bladder, 1719 cystic duct of, 1720 fossa of, 1708 lymphatics of, 981 nerves of, 1720 pract. consid., 1729 vessels of, 1719 Ganglion or ganglia, 1007 basal, 1 1 69 cervical inferior (sympathetic), 1362 middle (sympathetic), 1362 superior (sympathetic), 1359 ciliary, 1236 coccygeal (impar), sympathetic, 1367 development of, 1012 Gasserian, 1232 geniculate, 1252 habenulae, 1123 interpeduncular, 1124 jugular, of glosso-pharyngeal, 1263 of vagus, 1267 lenticular, 1236 mesenteric, inferior, 1373 superior, 1372 nodose of vagus, 1268 ophthalmic, 1236 otic, 1246 petrous, of glosso-pharyngeal, 1264 semilunar, sympathetic, 1369 spheno-palatine, 1240 spinal, 1279 spiral, 1257 spirale of cochlea, 1522 splanchnic, great, sympathetic, 1365 submaxillary, 1247 sympathetic, 1009 of sympathetic system, 1356 vestibular, 1259 Ganglion-crest, 1012 Gartner's duct, 2001 Gasserian ganglion, 1232 Gastric glands, 1623 Gastro-pulmonary system, 1527 Gastrula, 25 Gelatin, 83 Geniculate bodies, lateral, 1107 median, 1107 (internal) internal structure of, mo ganglion, 1252 Genital cord, 2038 folds, 2043 organs, external, development of, 2043 female, 2021 pract. consid., 2027 ridge, 2038 tubercle, 2043 Genu of corpus callosum, 1155 Germinal spot, 16 Gestation, ectopic, 1999 Giacomini, frenulum of, 1166 Gianuzzi, crescents of, 1 534 Gimbernat, ligament of, 523 Ginglymus, 113 Giraldes, organ of, 1950 Glabella, 228 2064 INDEX. Gladiolus of sternum, 155 Gland or glands, 1531 alveolar (saccular) compound, 1535 (saccular) simple, 1535 anal, 1674 areolar, 2028 of Bartholin, 2026 blood-vessels of, 1535 of Bowman, 1415 of Brunner, 1639 cardiac of stomach, 1624 ceruminous, 1489 ciliary, 1400 circumanal, 1400 of Cowper, 1984 cutaneous, 1397 development of, 1537 gastric, 1623 of Henle, 1445 of intestines, 1637 of Krause, 1445 lachrymal, 1477 ducts of, 1477 of Lieberkuhn, 1637 lymphatics of, 1536 mammary, 2027 Meibomian (tarsal), 1444 of Moll, 1444 of Montgomery, 2028 mucous, 1534 nerves of, 1536 parotid, 1582 prostate, 1975 pyloric, 1624 salivary, 1582 sebaceous, 1397 serous, 1534 sexual, development of, 2038 sublingual, 1585 submaxillary, 1 583 sweat, 1398 blood-vessels of, 1400 development of, 1404 duct of, 1399 nerves of, 1400 structure of, 1399 of tongue, 1575 tubo-alveolar, 1532 tubular, compound, 1532 simple, 1532 of Tyson, 1966 unicellular, 1531 of Zeiss, 1444 Glans of clitoris, 2024- penis, 1968 Glaser, fissure of, 178 Glisson's capsule of liver, 1708 Globus pallidus, 1170 Goblet-cells, 70 Golgi-Mazzoni corpuscles, 1019 Gonion, 228 Graafian follicles, 1988 Grandry, corpuscles of, 1016 Growth, 6 of bone, 101 Gudden, inferior commissure of, mo Gums, 1567 lymphatics of, 951 pract. consid., 1590 Gustatory cells, 1435 Gyrus or gyri, callosal (fornicatus), 1150 (convolutions) cerebral, 1135 dentate, 1166 Gyrus or gyri, development of, "i 190 hippocampal, 1151 Hair-cells (auditory) inner, 1520 outer, 1520 Hair-follicle, 1392 blood-vessels of, 1394 nerves of, 1394 Hairs, 1389 arrangement of, 1391 development of, 1401 growth of, 1402 structure of, 1391 whorls of, 1391 Hair-shaft, 1391 Hamular process of inner pterygoid plate, 189 Hamulus of bony cochlea, 1514 Hand, 309 deep fascia of, 606 landmarks of, 320 lymphatics of, 964 muscles of, 606 pract. consid., 613 surface anatomy of, 328 Harelip, 1589 Haversian canals of bone, 88 system of bone, 86 Hassall, corpuscles of, 1799 Head, movements of, 142 Heart, annuli fibrosi of, 698 annulus ovalis, 695 of Vieussens, 695 architecture of walls, 700 auricles of, 693 blood-vessels of, 703 canal auricular of, 705 chambers of, 693 chordae tendineae of, 697 columns? carnese of, 697 development of, 705 endocardium of, 702 epicardium of, 702 fasciculus auriculo-ventricular, 701 foramen ovale of, 695 fossa ovalis of, 695 general description of, 689 His's bundle, 701 lymphatics, 703 muscle of, 462 muscles, pectinate of, 695 nerve-endings in, 1015 nerves of, 704 position of, 692 practical considerations, 710 relations of, 693 septum, aortic, 707 auricular of, 694 intermedium, 706 interventricular of, 696 primum, 706 secundum, 708 spurium, 707 Thebesian veins of, 694 tubercle of Lower, 695 valves, Eustachian, '>< )( auriculo-ventricular, 699 mitral, 699 position of, 692 structure of, 703 Thebesian, 695 tricuspid, 699 vein, oblique of, 695 ventricles of, 696 INDEX. 206 s Heidenhain, demilunes of, 1534 Helicotrema, 1514 Helix, 1484 Hemispheres, association fibres of, 1182 of cerebellum, 1082 cerebral, 1133 commissural fibres of, 1184 lobes of, 1139 projection fibres of, 1186 white centre of, 1182 Henle, glands of, 1445 loop of, 1 88 1 Hensen, node of, 25 Herbst, corpuscles of, 1019 Hernia, abdominal, 1759 diaphragmatic, 1778 femoral, 1773 funicular, 1768 infantile, 1767 inguinal, 1763 direct, 1770 indirect, 1766 internal (intra-abdominal retroperito- neal), 1779 interparietal, 1768 labial, 1769 lumbar, 1777" obturator, 1777 perineal, 1778 sciatic, 1778 scrotal, 1769 umbilical, 1775 acquired, 1776 congenital, 1775 ventral, 1776 Hesselbach, ligament of, 525 triangle of, 526 Hiatus, aortic, of diaphragm, 557 Fallopii, 181 oesophageal, of diaphragm, 557 semilunaris, of nasal cavity, 194 of nose, 1411 Highmore, antrum of, 1422 Hind-brain, 1061 Hip, landmarks of, 669 muscles and fasciae of, pract. consid., 642 Hip-joint, 367 movements of, 373 pract. consid., 374 synovial membrane of, 372 Hippocampus, 1165 His's bundle, of heart, 701 Histogenesis of neuroglia, 1010 of neurones, ion Homologue, 4 Horner, muscle of, 484 Howship, lacunae of, 97 Humerus, 265 development of, 269 pract. consid., 270 sexual differences, 269 structure of, 269 surface anatomy, 270 Humor, aqueous, 1476 Hunter's canal, 628 Hyaloid canal, 1474 Hyaloplasm, 8 Hydatid of Morgagni, 2002 Hydramnion, 42 Hymen, 2016 Hyoid bone, 216 development of, 216 Hyomandibular cleft, 61 Hypogastric lymphatic plexus, 984 Hypophysis, 1806 Hypospadias, 1927 Hypothalamus, 1127 Hypothenar eminence, 607 Ileo-caecal fossae, 1666 valve, 1 66 1 Ilio-femoral ligament, 369 liio-pectineal line, 334 Ilio-tibial band, 634 Ilium, 332 Implantation, 35 Impregnation, 18 Incisor teeth, 1543 Incus, 1497 Inferior caval system of veins, 898 Infundibulum, 1129 of nasal cavity, 194 of nose, 1411 Inguinal canal, 523 lymphatic plexus, 991 Inion, 228 Innominate bone, 332 development of, 337 structure of, 337 Insula, 1149 Intersigmoid fossa, 1671 Intervertebral disks, 132 Intestine or intestines, development and growth of, 1671 glands of, 1637 large, 1657 appendices epiploicae, 1660 blood-vessels of, 1660 glands of Lieberkuhn of, 1657 lymphatics of, 1660 lymphatic tissue of, 1658 nerves of, 1660 pract. consid., 1680 structure of, 1657 taenia coli of, 1660 lymph-nodules of, 1640 small, 1633 blood-vessels of, 1642 glands of Lieberkuhn of, 1637 lymphatics of, 1643 nerves of, 1643 Peyer's patches of, 1640 pract. consid., 1652 structure of, 1634 valvulae conniventes of, 1636 villi of, 1635 solitary nodules of, 1640 Involuntary muscle, 1015 Iris, 1459 pract. consid., 1461 structure of, 1460 Irritability, 6 Ischio-rectal fossa, 1678 Ischium, 336 Islands of Langerhans, 1735 of Reil, 1 149 Isthmus of fauces, 1569 rhombencephali, 1061 Jacobson's nerve, 1264 organ, 1417 development of, 1432 Jejuno-ileum, 1649 blood-vessels of, 1652 lymphatics of, 1652 mesentery of, 1650 130 2O66 INDEX. Jejuno-ileum, nerves of, 1652 topography of, 1650 Joint or joints, of ankle, 438 calcaneo-astragaloid, posterior, 445 calcaneo-cuboid, 446 calcaneo-scapho-astragaloid, anterior, 445 capsule of, no of carpus, metacarpus and phalanges, pract. consid., 330 costo-central, 160 costo-sternal, 160 motions in, 166 costo-transverse, 160 costo- vertebral, motions in, 165 crico-arytenoid, 1816 crico-thyroid, 1815 elbow, 301 fixed, 107 general considerations, 107 half, 1 08 of hip, 367 interchondral, 160 intersternal, 159 motions in, 165 of knee, 400 limitation of motion, 112 metatarso-phalangeal, 447 modes of fixation, 112 of pelvis, 337 of pelvis, pract. consid, 350 raaio-ulnar, 297 inferior, pract. consid., 308 saddle, 113 scapho-cubo-cuneiform, 446 of shoulder, 274 synovial membrane of, no tarso-metatarsal, 446 of tarsus, metatarsus and phalanges, pract. consid., 45 true, 1 08 motion in, 112 structure of, 109 varieties of, 113 vessels and nerves of, in Jugular ganglion, of glosso-pharyngeal, 1263 of vagus, 1267 plexus, lymphatics, 956 Karyokinesis, 1 1 Karyosomes, 9 Kidney or kidneys, 1869 architecture of, 1875 blood-vessels of, 1884 capsule of, 1869 cortex of, 1876 development of, 1937 ducts of, 1894 fixation of, 1871 glomeruli of, 1876 hilum of, 1869 labyrinth of, 1876 lobule of, 1875 loop of Henle of, 1881 lymphatics of, 1885 Malpighian body of, 1879 medulla of, 1876 medullary rays of, 1876 movable, 1888 nerves of, 1886 papillae of, 1875 papillary ducts of, 1882 pelvis of, 1894 Kidney or kidneys, position of, 1870 pract. consid., 1887 pyramids of, 1876 relations of, 1873 sinus of, 1874 structure of, 1877 supporting tissue of, 1883 surfaces of, 1869 tubule, collecting of, 1882 connecting of, 1882 distal convoluted of, 1882 proximal convoluted of, 1880 spiral of, 1880 uriniferous of, 1877 Knee, landmarks of, 671 muscles and fasciae of, pract. consid., 645 Knee-joint, 400 bursas of, 406 capsule of, 400 landmarks of, 416 movements of, 408 pract. consid., 409 semilunar cartilage of, 402 synovial membrane of, 405 Krause, end-bulbs of, 1016 glands of, 1445 Kupffer, cells of, 1717 Labia major, 2021 minora, 2022 nerves of, 2024 vessels of, 2023 Labyrinth, membranous, 1514 blood-vessels of, 1522 canalis reuniens of, 1515 cochlea of, 1517 ductus endolymphaticus of, 1514 endolymph of, 1514 maculae acustica; of, 1516 saccule of, 1515 semicircular canals of, 1515 utricle of, 1514 osseous, 1511 cochlea of, 1513 semicircular canals of, 1512 vestibule of, 1511 Lachrymal apparatus, 1477 pract. consid., 1479 bone, 207 articulations of, 207 development of, 207 canaliculi, 1478 caruncle, 1443 gland, 1477 lake, 1443 papillae, 1478 puncta, 1478 sac, 1478 Lactation, 2029 Lacteals, 1643 Lacunae, of bone, 86 of cartilage, 80 of Howship, 97 Lambda, 228 Lamina cinerea (terminalis), 1130 fusca, 1450 suprachoroidea, 1456 Landmarks, of abdomen, 531 of ankle and foot, 672 of bones of foot, 437 of buttocks and hip, 669 of clavicle, 260 of elbow-joint, 308 INDEX. 2067 Landmarks, of face, 246 of femur, 366 of fibula, 396 of hand, 320 of joints of foot, 453 of knee, 671 of knee-joint, 416 of leg, 671 of lower extremity, 669 of male perineum, 1918 of neck, 554 of pelvis, 349 of radius, 296 of scapula, 255 of shoulder-joint, 280 of skull, 240 of spine, 146 of surface of thorax, 1868 of thigh, 670 of thorax, 170 of tibia, 390 of ulna, 287 of upper extremity, 618 of wrist-joint, 330 Langerhans, islands of, 1735 Lanugo, 66 Laryngo-pharynx, 1598 Larynx, 1813 age changes of, 1828 arytenoid cartilages of, 1816 corniculag laryngis, 1817 cricoid cartilage of, 1813 cuneiform cartilages of, 1817 development of, 1862 elastic sheath of, 1817 epiglottis, 1816 form of, 1818 lymphatics of, 958 mucous membrane of, 1823 muscles of, 1824 nerves of, 1827 ossification of, 1818 position and relations of, 1828 pract. consid., 1828 region, glottic of, 1820 infraglottic of, 1823 supraglottic of, 1818 sexual differences of, 1828 thyroid cartilage of, 1814 ventricle (sinus) of, 1822 vessels of, 1826 vocal cords, false of, 1820 true of, 1820 ligaments of, 1818 Leg, bones of, as one apparatus, 397 surface anatomy, 397 framework of, 382 landmarks of, 671 lymphatics, deep of, 994 superficial of, 993 muscles and fasciae of, pract. consid., 665 Lens, crystalline, 1471 development of, 1481 pract. consid., 1473 suspensory apparatus of, 1475 Leptorhines, 1404 Leucocytes, 684 development of, 688 varieties of, 685 Lieberkuhn, glands of, 1637 Lieno-phrenic fold, 1785 Ligament or ligaments, 112 alar, of knee-joint, 405 Ligament or ligaments, anterior annular, of ankle, 647 of wrist, 325, 607 posterior, of wrist, 325 annular, of wrist, 607 arcuate, external, 557 internal, 557 atlanto-axial, anterior, 137 atlan to-axial, posterior, 137 of auricle, 1486 broad, of uterus, 2004 broad, vesicular appendages of, 2002 check, of orbit, 1438 of Colles, 523 common anterior and posterior, of spine, J 33 coraco-acromial, 256 coraco-clavicular, 262 conoid part, 262 trapezoid part, 262 coronary, of liver, 1721 costo-clavicular or rhomboid, 262 cotyloid, of hip-joint, 367 crucial, of knee-joint, 404 cruciform, of axis, 136 deltoid (lat. int.) of ankle-joint, 439 denticulate, of spinal cord, 1023 duodeno-hepatic, 1644 dorsal, of foot, 442 of epiglottis, 1817 external check, of eyeball, 505 falciform, 1745 of liver, 1721 gastro-phrenic, 1747 of Gimbernat, 523 of Hesselbach, 525 ilio-femoral, 369 ilio-lumbar, 339 interclavicular, 262 interosseous, of foot, 441 interspinous, 134 intertransverse, 135 ischio-femoral, 370 of laminae and processes of vertebrae, 133 lieno-renal, 1747 of liver, 1721 nuchae, 134 occipito-atlantal, accessory, 137 anterior, 137 posterior, 137 occipito-axial, 137 odontoid, or check, 136 orbicular, of radius, 297 of ovary, 1987 palpebral, 1441 internal, 484 patellae, 400 pectinate of iris, 1452 of pelvis, 337 of pericardium, 716 plantar, 444 of Poupart, 523 pterygo-mandibular, 488 radio-ulnar, 297 round, of hip-joint, 370 of liver, 1721 of uterus, 2005 sacro-iliac, posterior, 338 sacro-sciatic, 339 great or posterior, 339 lesser or anterior, 341 of scapula, 256 of shoulder-joint, 274 2068 INDEX. Ligament or ligaments, spino-glenoid, 257 stylo-mandibular, 475 subflava, 133 suprascapular or transverse, 256 supraspinous, 133 suspensory, of lens, 1475 of orbit, 1438 of ovary, 1986 thyro-arytenoid, inferior, 1818 superior, 1817 thyro-hyoid, 1815 transverse, of atlas, 136 triangular, of liver, 1721 of perineum, 563 of vertebral bodies, 132 of Winslow, of knee-joint, 401 of wrist and metacarpus, 320 Limb, lower, muscles of, 623 Limbic lobe, 1150 Linea alba, 522 semilunaris, of abdomen, 532 transverse, of abdomen, 532 Linin, 9 Lips, 1538 lymphatics of, 951 muscles of, 1 540 nerves of, 1542 pract. consid., 1590 vessels of, 1542 Liquor amnii, 31 pericardii, 714 Littre, glands of, 1925 Liver, 1705 bile-capillaries of, 1715 biliary apparatus, 1718 blood-vessels of, 1709 borders of, 1707 caudate lobe of, 1709 cells of Kupffer, 1717 common bile-duct, 1720 cystic duct of, 1720 development and growth of, 1723 fissure of ductus venosus of, 1707 fossa for gall-bladder of, 1708 gall-bladder of, 1719 Glisson's capsule of, 1708 hepatic artery of, 1711 ducts of, 1718 veins of, 1710 impression, oesophageal of, 1708 renal of, 1 709 intralobular connective tissue of, 1717 bile-ducts of, 1717 veins of, 1710 ligaments of, 1721 coronary, 1721 falciform, 1721 round, 1721 triangular, 1721 lobes of, 1706 lobular blood-vessels of, 1713 lobules of, 1712 lymphatics of, 1711 nerves of, 1711 non-peritoneal area of, 1707 peritoneal relations of, 1721 portal (transverse) fissure of, 1708 vein of, 1709 position of, 1722 pract. consid., 1726 quadrate lobe of, 1 709 size of, 1706 Spigelian lobe of, 1707 Liver, structure of, 1712 sublobular veins of, 1710 surfaces of, 1707 tuber omentale of, 1709 umbilical fissure of, 1708 notch of, 1707 weight of, 1706 Liver-cells, 1714 Lobe or lobes, cerebral, 1135 frontal, 1139 of hemispheres, 1139 limbic, 1150 occipital, 1145 olfactory, 1151 parietal, 1 143 temporal, 1147 Lobule of auricle, 1484 Loin, pract. consid., 530 Lordosis, 144 Lumbar plexus, lymphatic, 973 Lumbo-sacral cord, 1331 Lung or lungs, 1843 air-sacs of, 1850 alveoli of, 1850 atria of, 1850 blood-vessels of, 1853 borders of, 1843 development of, 1861 external appearance of, 1846 fissures of, 1845 ligament broad of, 1858 lobes of, 1845 lobule of, 1849 nerves of, 1855 physical characteristics of, 1846 pract. consid., 1864 relations to chest-walls, changes in, 1863 to thoracic walls, 1855 roots of, 1838 dimensions of, 1840 nerves of, 1839 relations of, 1840 structure of, 1851 surfaces of, 1843 vessels of, 1839 Lunula, of nail, 1395 Luschka, foramina of, 1 1 oo gland of, 1 8 10 Lutein cells, 1990 Luys, nucleus of, 1128 Lymphatic or lymphatics, of abdomen, 972 of abdominal walls, 976 of arm, deep, 965 superficial, 963 of bile-duct, 981 of bladder, 985 of bone, 93 of brain, 948 of brain and meninges, 948 broncho-mediastinal trunk, 968 capillaries, 933 of cervical skin and muscles, 958 of cheeks, 951 of diaphragm, 970 duct, right, 945 of ear, 950 of eye and orbit, 949 of eyelids, 1445 of Fallopian tubes, 988 of gall-bladder, 981 of glands, 1536 of gums, 951 of hand, t INDEX. 2069 Lymphatic or lymphatics, of the head, 945 of heart, 970 hemolymph nodes, 936 intercostal, 969 of intestine, large, 978 small, 977 jugular trunk, 958 of kidney, 982 lacteals, 931 of larynx, 958 of leg, deep, 994 superficial, 993 of lips, 951 of liver, 980 of lower extremity, 991 mammary gland, 968 of meninges, 948 of muscle, non-striated, 456 of nasal fossa, 1426 region, 951 nodes, 935 of nose, 1407 of oesophagus, 971 of palate, 954 of pancreas, 979 of pelvis, 983 of pericardium, 716 of perineum, 987 of pharynx, 954 of prostate gland, 985 of rectum, 1680 of reproductive organs, external, fe- male, 987 external, male, 986 internal, female, 988 internal, male, 987 of retina, 1468 of scalp, 948 of seminal vesicles, 988 of skin, 1388 of small intestine, 1643 of spleen, 982 of stomach, 976 of striated muscle, 464 subclavian trunk, 963 of suprarenal body, 983 system, 931 of teeth, 951 of testis, 987 thoracic duct, 941 pract. consid., 944 of thorax, 966 cutaneous, 968 of thyroid gland, 959 of tongue, 952 of tonsils, 954 of trachea, 958 of upper extremity, 961 of ureter, 982 of urethra, 986 of uterus, 989 of vagina, 989 of vas deferens, 988 vessels, development of, 939 Lymph-corpuscles, 931 Lymph-nodes, of abdomen, pract. consid., 990 abdominal, visceral, 974 ano-rectal, 976 anterior auricular, 946 appendicular, 975 of arm, pract. consid., 965 of axilla, pract. consid., 965 axillary, 961 Lymph-nodes, brachial, deep, 961 superficial, 961 bronchial, 967 buccinator, 947 cervical, deep, inferior, 958 superior, 957 of Cloquet, 992 coeliac, 973 delto-pectoral, 961 development of, 940 epigastric, 972 epitrochlear, 961 facial, 947 gastric, 974 of head, pract. consid., 955 hepatic, 975 hypogastric, 984 iliac, circumflex, 972 internal, 984 inguinal, 991 intercostal, 966 of intestine, 1640 jugular plexus, 956 of leg, pract. consid., 994 lingual, 947 mammary, internal, 966 mandibular, 947 mastoid, 945 maxillary, 947 mediastinal, anterior, 967 posterior, 967 mesenteric, 975 mesocolic, 976 of neck, 956 pract. consid., 959 occipital, 945 pancreatico-splenic, 975 parotid, 946 pectoral, 962 of pelvis, pract. consid., 990 popliteal, 992 posterior auricular, 945 retro-pharyngeal, 948 of Rosenmuller, 992 sternal, 966 structure of, 937 submaxillary, 946 submental, 946 subscapular, 962 superficial cervical, 956 thorax, pract. consid., 971 tibial, anterior, 993 tracheal nodes, 967 umbilical, 972 Lymph-nodules, 936 Lymphocytes, 931 varieties of, 685 Lymphoid structures of pharynx, 1599 tissue, structure of, 936 Lymph-spaces, 931 Lymph -vessels, 934 Lyra, 1158 Macula lutea, 1466 Maculae acusticae, 1516 Majendie, foramen of, noo Maxilla, inferior, 211 development of, 213 structure of, 213 superior, 199 antrum of, 201 articulations of, 202 development of, 202 2070 INDEX. Maxillary sinus, 1422 Malar bone, 209 articulations of, 210 development of, 210, 2032 Malleus, 1497 Malphighian bodies of spleen, 1784 Mammary glands, 2027 development of, 2032 lymphatics, 968 nerves of, 2032 pract. consid., 2033 structure of, 2029 variations of, 2033 vessels of, 2031 Manubrium of sternum, 155 Marrow, of bone, 90 Mast-cells of connective tissue, 74 Mastoid cells, 1 504 pract. consid., 1508 process, pract. consid., 1508 subdivision, of petro-mastoid bone, 179 Maturation of ovum, 16 Meatus, auditory, internal, 181 inferior, of nose, 1412 middle, of nose, 1411 superior, of nose, 1411 Meckel, diverticulum of, 44 Mediastinum, anterior, 1833 middle, 1833 posterior, 1833 pract. consid., 1833 superior, 1833 Medulla oblongata, 1063 central gray matter of, 1073 development of, nor internal structure of, 1068 Medullary folds, 26 groove, 26 sheath, 1001 velum, inferior, 1099 superior, 1099 Medullated fibres, 1003 Megakaryocytes, 689 Meibomian (tarsal) glands, 1444 Meissner, corpuscles of, 1017 Slexus of, 1643 rane or membranes, Bowman's, I45 1 of Bruch, 1456 cloacal, 1939 costo-coracoid, 568 cri co-thyroid, 1815 of Demours, 1452 Descemet's, 1452 fenest rated, 77 fcetal, 30 human, 35 chief peculiarities of, 39 hyaloid, 1474 interosseous, of tibia and fibula, 396 mucous, 1528 obturator, 341 pharyngeal, 1694 pleuro-pericardial, 1700 pleuro-peritoneal, 1700 of Ruysch, 1456 of spinal cord, 1022 synovial, of joint, no tectoria, 1521 thyro-hyoid, 1815 of tympanum, 1494 vitelline, 15 vitrea, 1456 Meninges of brain, pract. consid., 1208 lymphatics of, 948 Menstruation, 2012 Merkel, tactile cells of, 1016 Mesencephalon, 1105 development of, 1117 internal structure of, 1109 Mesenteries, 1741 Mesenterium commune, 1697 Mesentery, anterior, 1744 of appendix, 1665 of jejuno-ileum, 1650 permanent, 1752 posterior, part ist, 1746 part 2nd, 1751 part 3rd, 1753 primitive, 1697 Meso-appendix, 1665 Mesoblast, 23 lateral plates of, 29 paraxial, 29 parietal layer, 29 visceral layer, 29 Mesogastrium, 1697 Mesognathism, 229 Mesometrium, 2005 Mesonephros, 1935 Mesorarium, 2040 Mesorchium, 2040 Mesorhines, 1404 Mesosalpinx, 1996 Mesotendons, 471 Mesothelium, 71 Mesovarium, 1987 Metabolism, 6 Metacarpal bones, 314 development of, 317 peculiarities of, 315 Metacarpo-phalangeal articulations, 327 Metacarpus, pract. consid., 319 Metanephros (kidney), 1937 Metaphase of mitosis, 12 Metaplasm, 8 Metatarsal bones, 428 development of, 432 Metathalamus, 1126 Meynert, commissure of, 1115 Mid-brain, 1061 Milk, 2030 Milk-ridge, 2032 Mitosis, ii anaphases of, 13 metaphase of, 12 prophases of, 12 telophases of, 13 Molar teeth, 1 546 Moll, glands of, 1444 Monorchism, 1950 Monroe, foramen of , 1131 Mons pubis, 2021 veneris, 2021 Montgomery, glands of, 2028 Morgagni, columns of, 1674 hydatid of, 2002 sinus of, 497 valves of, 1674 Morula, 22 Mouth, 1538 floor of, pract. consid., 1593 formation of, 1694 pract. consid., 1589 roof of. 228 pract. consid., 1592 INDEX. 2071 Mouth, vestibule of, 1538 Mucoid, 83 Mucous membranes, 1528 structure of, 1528 Mullerian duct, 2038 Muscle or muscles, abdominal, 515 abductor hallucis, 66 1 minimi digiti, 608 minimi, of foot, 662 pollicis, 608 adductor brevis, 626 hallucis, 662 longus, 626 magnus, 628 pollicis, 610 anconeus, 589 of ankle, pract. consid., 666 antibrachial, 591 post-axial, 598 pre-axial, 592 of anus, 1675 appendicular, 566 of arm, pract. consid., 589 arytenoid, 1826 of auricle, 1486 auricularis anterior, 483 posterior, 483 superior, 483 axial, 502 of axilla and shoulder, pract. consid. 579 azygos uvulae, 496 biceps, 586 femoris, 636 brachial, 585 post-axial, 588 pre-axial, 586 brachialis anticus, 586 brachio-radialis, 598 branchiomeric, 474 buccinator, 488 bulbo-cavernosus, 565 of buttocks, pract. consid., 641 cardiac, 462 cervical, 542 chondro-glossus, 1578 ciliary, 1458 coccygeus, 561, 1676 compound pinnate, 469 compressor urethrae, 565 constrictor inferior of pharynx, 1606 middle of pharynx, 1605 pharyngis inferior, 499 medius, 498 superior, 497 superior of pharynx, 1604 coraco-brachialis, 575 of cranium, pract. consid., 489 cremaster, 519 crico-arytenoid lateral, 1825 posterior, 1825 crico-thyroid, 1824 crural, 647 post-axial, 655 pre-axial, 648 crureus, 640 dartos, 1963 deltoideus, 578 depressor anguli pris, 487 labii inferioris, 485 diaphragma, 5.56 digastricus, 477 dilator pupillae, 1460 Muscle or muscles, dorsal, of trunk, 507 of Eustachian tube, 1503 extensor brevis digitorum, 665 pollicis, 602 carpi radialis brevior, 598 longior, 598 ulnaris, 60 1 communis digitorum, 599 indicis, 603 longus digitorum, 655 longus hallucis, 656 pollicis, 603 minimi digiti, 600 ossis metacarpi pollicis, 602 of face, pract. consid., 492 facial, 479 femoral, 633 post-axial, 638 pre-axial, 636 flexor accessorius, 654 brevis digitorum, of foot, 660 hallucis, 660 minimi digiti, 609 digiti of foot, 664 pollicis, 608 carpi radialis, 593 radialis brevis, 597 ulnaris, 594 longus digitorum, 651 hallucis, 651 pollicis, 596 profundus digitorum, 595 sublimis digitorum, 595 of foot, 659 post-axial, 665 pract. consid., 666 pre-axial, 659 gastrocnemius, 649 gemelli, 630 genio-glossus, 1578 genio-hyoid, 1578 genio-hyoideus, 545 gluteus maximus, 630 medius, 631 minimus, 633 gracilis, 626 of hand, 606 pre-axial, 607 of hip and thigh, pract. consid., 642 hypoglossal, 506 hyo-glossus, 1578 hyoidean, 480 variations of, 480 iliacus, 624 ilio-costalis, 508 infraspinatus, 576 intercostales externi, 538 interni, 539 interossei dorsales of foot, 664 of hand, 613 plantares, 663 volares, 612 interspinales, 513 intertransversales, 513 anteriores, 547 laterales, 521 intratympanic, 1499 involuntary, arrectores pilorum, 1394 nerve-endings of, 1015 ischio-cavernosus, 564 of knee, pract. consid., 645 of larynx, 1824 latissimus dorsi, 574 2072 INDEX. Muscle or muscles, of leg, pract. consid., 665 levator anguli oris, 487 scapulae, 571 ani, 560, 1675 labii superioris, 487 labii superioris alaeque nasi, 485 menti (superbus), 485 palati, 496, 1571 palpebrae superioris, 502 levatores costarum, 540 lingualis, 1579 of lips, 1540 longissimus, 510 longus colli, 548 of lower limb, 623 lumbricales, of hand, 610 of foot, 662 masseter, 474 of mastication, 474 variations of, 477 metameric, 502 multifidus, 512 mylo-hyoideus, 477 nasalis, 486 non-striated, blood-vessels of, 456 development of, 457 (involuntary), 454 lymphatics of, 456 nerves of, 456 structure of, 455 obliquus capitis inferior, 514 superior, 514 externus, 517 inferior, 504 internus, 517 superior, 504 obturator externus, 629 internus, 629 occipito-frontalis, 482 omo-hyoideus, 544 opponens minimi digiti, 608 pollicis, 608 orbicularis oris, 486 palpebrarum, 484 orbital, 502 of palate and pharynx, 495 palato-glossus, 497, 1579 palato-pharyngeus, 497, 1571 palmaris brevis, 607 longus, 593 pectinate, of heart, 695 pectineus, 625 pectoralis major, 569 minor, 570 pelvic, 559 perineal, 562 peroneus brevis, 658 longus, 657 tertius, 656 of pharynx, 1604 pinnate, 469 plantaris, 649 platysma, 481 popliteus, 655 pronator quadratus, 597 radii teres, 592 psoas magnus, 623 parvus (minor), 624 pterygoideus externus, 476 internus, 476 pyloric sphincter, 1626 pyramidalis, 517 Muscle or muscles, pyriformis, 561 quadratus femoris, 629 lumborum, 521 quadriceps femoris, 639 of rectum, 1675 rectus abdominis, 516 capitis anticus major, 549 capitis anticus minor, 550 lateralis, 547 posticus major, 513 posticus minor, 514 externus, 503 femoris, 639 inferior, 503 internus, 503 superior, 503 rhomboideus major, 572 minor, 572 risorius, 487 rotatores, of back, 513 sacro-spinalis, 508 salpingo-pharyngeus, 1606 sartorius, 638 scalene, variations of, 547 scalenus anticus, 546 medius, 546 posticus, 547 of scalp, pract. consid., 489 semimembranosus, 438 semi-pinnate, 469 semispinalis, 511 semitendinosus, 638 serratus magnus, 571 posticus inferior, 541 posticus superior, 541 of soft palate, 1570 soleus, 649 sphincter ani, external, 1676 externus, 563 internal, 1677 pupillae, 1460 vesical, external, 1925 internal, 1925 spinalis, 511 splenius, 510 stapedius, 480, 1499 sternalis, 570 sterno-cleido-mastoideus, 499 sterno-hyoideus, 543 sterno-thyroideus, 545 striated, attachments of, 468 blood-vessels of, 464 bursse of, 471 classification of, 471 development of, 465 form of, 469 general considerations of, 468 lymphatics of, 464 nerves of, 464 nerve-supply, general, 473 structure, general of, 458 variations, 461 (voluntary), 457 stylo-glossus, 1579 stylo-hyoideus, 480 stylo-pharyngeus, 495, 1606 subclavius, 570 subcostal, 539 subcrureus, 640 submental, 477 subscapularis, 578 supinator, 60 1 supraspinatus, 575 INDEX. 2073 Muscle or muscles, temporalis, 475 tensor fasciae latas, 631 palati, 479, I 57 tympani, 479, 1499 teres major, 577 minor, 576 thoracic, 538 thyro-arytenoid, 1825 thyro-hyoideus, 545 tibialis anticus, 655 posticus, 654 of tongue, 1577 trachealis, 1835 transversalis, 519 transverso-costal tract, 508 transverso-spinal tract, 511 transversus perinei profundus, 565 superficialis, 564 of tongue, 1579 trapezius, 500 triangularis sterni, 540 triceps, 588 trigeminal, 474 palatal, 479 tympanic, 479 of trunk, 507 of upper limb, 568 vago-accessory, 495 vastus externus, 640 internus, 640 ventral, of trunk, 515 voluntary, motor nerve-endings of, 1014 zygomaticus major, 485 minor, 485 Muscle-fibre, structure of, 459 Muscular system, 454 tissue, general, 454 Myelin, 1001 Myelocytes, of bone-marrow, 92 Myeloplaxes, of bone-marrow, 92 Myometrium, 2008 Myotome, 30 Myxcedema, 1794 Naboth, ovules of, 2008 Nail, structure of, 1395 Nail-bed, 1396 Nail-plate, 1395 Nails, 1394 development of, 1403 Nares s anterior, 1404 posterior, 1413 Nasal bone, 209 articulations of, 209 development of, 209 cavities, pract. consid., 1417 cavity, 223 hiatus semilunaris of, 194 infundibulum of, 194 meatus inferior of, 225 middle of, 225 superior of, 225 chamber, 224 fossa, blood-vessels of, 1425 floor of, 1413 lymphatics of, 1426 nerves of, 1426 roof of, 1412 fossae, 1409 index, 1404 mucous membrane, 1413 (naso-lachrymal) duct, 1479 septum, 223, 1410 Xasal septum, triangular cartilage of, 224 Nasion, 228 Nasmyth, membrane of, 1550 Naso-pharynx, 1 598 Naso-optic groove, 62 Navel, 37 Neck, landmarks of, 554 pract. consid., 550 triangles of, 547 Nephrotome, 30 Nerve or nerves, abdominal, of vagus, 1272 abducent, 1249 development of, 1379 aortic (sympathetic), 1364 auditory, 1256 development of, 1379 of auricle, 1487 auricular, great, 1286 posterior, of facial, 1254 of vagus, 1268 auriculo-temporal, of mandibular, 1244 of bone, 94 buccal, of mandibular, f 243 calcanean, internal, 1344 cervical, anterior divisions of, 1285 cardiac inferior, of vagus, 1270 superior, of vagus, 1270 first, posterior division of, 1281 posterior divisions of, 1281 second, posterior division of, 1281 superficial, 1287 third, posterior division of, 1281 cervico-facial, of facial, 1254 chorda tympani, of facial, 1253 ciliary, long, of nasal, 1234 circumflex, 1307 pract. consid., 1308 of clitoris, 2025 coccygeal, posterior division of, 1284 of cochlea, membranous, 1521 cochlear, of auditory, 1256 of cornea, 1452 cranial, 1219 crural, anterior (femoral), 1327 cutaneous internal, of anterior crural, 1328 middle, of anterior crural, 1327 perforating, of pudendal plexus, 1347 dental, inferior, of mandibular, 1245 superior anterior, of maxillary, 1239 middle, of maxillary, 1239 posterior, of maxillary, 1238 descendens hypoglossi, 1277 development of, 1375 digastric, of facial, 1254 digital of median, 1301 dorsal of clitoris, 1351 of penis, 1351 of epididymis, 1948 of external auditory canal, 1490 external cutaneous, of lumbar plexus, of eyelids, 1446 facial, 1250, 1251 development of, 1378 genu of, 1251 pract. consid., 1255 of Fallopian tube, 1999 frontal, 1234 INDEX. Nerve or nerves, ganglionic, of nasal, 1234 genito-crural, 1322 of glands, 1536 glosso-pharyngeal, 1260 development of, 1379 gluteal, inferior, 1333 superior, 1333 of hair-follicles, 1394 of heart, 704 hemorrhoidal, inferior, 1350 hypoglossal, 1275 development of, 1380 pract. consid., 1277 ilio-hypogastric, 1320 ilio-inguinal, 1321 infratrochlear, 1235 intercosto-humeral, 1317 intermedius of Wrisberg, of facial, 1250 internal cutaneous, 1303 cutaneous lesser, 1303 interosseous anterior of median, 1300 of kidney, 1886 of labia, 2024 labial, superior, of maxillary, 1240 lachrymal, 1233 laryngeal, external, of superior laryn- geal, 1270 inferior (recurrent) of vagus, 1270 internal, of superior laryngeal, 1270 superior, of vagus, 1270 of larynx, 1827 lingual, of glosso-pharyngeal, 1264 of hypoglossal, 1277 of mandibular, 1244 of lips, 1542 of liver, 1711 lumbar, posterior divisions of, 1282 of lungs, 1855 of mammary glands, 2032 mandibular, (maxillary inferior), 1242 masseteric, of mandibular, 1242 maxillary (superior), 1237 median, 1298 branches of, 1300 pract. consid., 1301 meningeal, of hypoglossal, 1277 of vagus, 1268 mental, of inferior dental, 1246 of muscle, non-striated, 456 muscular of glosso-pharyngeal, 1264 musculo-cutaneous, of arm, 1298 of leg, 1338 musculo-spiral, 1308 branches of, 1309 pract. consid., 1314 mylo-hyoid, of inferior dental, 1245 nasal, 1234, 1235 anterior, 1235 external, 1235 fossa, 1426 internal (septal), 1235 lateral, of maxillary, 1240 septum, 1410 suj>erior posterior, of spheno-pala- tine ganglion, 1241 naso-palatine, of spheno-palatine gan- glion, 1241 of nose, 1407 obturator, 1324 accessory, 1326 occipital, small, 1286 Nerve or nerves, oculomotor, 1225 development of, 1377 cesophageal, of vagus, 1272 of oesophagus, 1613 olfactory, 1220 development of, 1376 pract. consid., 1222 ophthalmic, 1233 optic, 1223 development of, 1482 pract. consid., 1470 orbital, of spheno-palatine ganglion, 1241 of ovary, 1993 of palate, 1573 palatine, of spheno-palatine ganglion, 1241 palmar cutaneous of median, 1301 palpebral, inferior, of maxillary, 1240 of pancreas, 1737 of parotid gland, 1583 of penis, 1971 pericardial of vagus, 1272 of pericardium, 716 perineal, 1350 peripheral, development of, ion peroneal, communicating, of external popliteal, 1335 petrosal, deep, small, 1264 superficial, external, of facial, great, of facial, 1252 small, 1264 pharyngeal of glosso-pharyngeal, 1264 of vagus, 1269 of pharynx, 1606 phrenic, 1290 plantar external, 1345 internal, 1344 of pleurae, 1861 popliteal, external (peroneal), 1335 internal (tibial), 1339 posterior interosseous, 1311 of prostate gland, 1978 pterygoid, external, of mandibular, 1243 internal, of mandibular, 1242 pterygo-palatine (pharyngeal), of spheno-palatine ganglion, 1242 pudic, 1349 pulmonary, anterior, of vagus, 1272 posterior, of vagus, 1272 (sympathetic), 1364 radial, 1313 of rectum, 1680 recurrent, of mandibular, 1242 of maxillary, 1237 respiratory, external of Bell, 1295 sacral, posterior divisions of, 1282 sacro-coccygeal, 1352 posterior, 1283 saphenous, internal (long), of anteriof crural, 1329 short (external), 1342 scapular, posterior, 1295 sciatic, great, 1335 small, 1348 of scrotum, 1964 of skin, 1389 of small intestine, 1643 somatic, 1218 of spermatic ducts, 1959 spheno-palatine, of maxillary, 1237 INDEX. 2075 Nerve or nerves, spinal, 1278 spinal-accessory, 1274 . pract. consid., 1275 splanchnic, (sympathetic), 1364 of spleen, 1787 stapedial, of facial, 1253 of stomach, 1628 of striated muscle, 464 stylo-hyoid, of facial, 1254 of sublingual gland, 1585 of submaxillary gland, 1585 subscapular, 1306 supraorbital, 1234 of suprarenal bodies, 1803 suprascapular, 1295 supratrochlear, 1234 sural, of external popliteal, 1335 of sweat glands, 1400 of taste-buds, 1435 temporal, deep, of mandibular, 1243 superficial, of auriculo-temporal, 1244 temporo-facial, of facial, 1254 temporo-malar (orbital), of maxillary, 1238 of testis, 1948 thoracic, 1314 anterior, external, 1297 internal, 1303 branches of, 1317 cardiac, of vagus, 1272 first, 1315 lower, 1315 posterior divisions of, 1282 posterior (long), 1295 pract. consid., 1296 pract. consid., 1318 second, 1317 third, 1317 twelfth (subcostal) 1317 upper, 1315 of thyroid body, 1793 of thymus body, 1800 thyro-hyoid, of hypoglossal, 1277 tibial, anterior, 1336 communicating, 1342 posterior, 1342 recurrent, 1335 of tongue, i 580 tonsillar of glosso-pharyngeal, 1264 of trachea, 1836 trigeminal, 1230 development of, 1378 divisions of, 1232 pract. consid., 1248 trochlear, 1228 development of, 1377 t tympanic, of glosso-pharyngeal, 1264 to tympanic plexus, of facial, 1252 ulnar, 1303 branches of, 1305 pract. consid., 1306 of ureter, 1898 of urethra, 1927 of urinary bladder, 1910 of uterus, 2010 of vagina, 2018 vagus, 1265 and spinal accessory, development of, 1380 ganglia of, 1267 pract. consid., 1272 vestibular, of auditory, 1256 Xerve or nerves, visceral, 1218 Nerve-cells, 998 bipolar, 999 multipolar, 1000 unipolar, 999 Nerve-endings, motor, 1014 of cardiac muscle, 1015 of involuntary muscle, 1015 of voluntary muscle, 1014 sensory, 1015 encapsulated, 1016 free, 1015 genital corpuscles, 1017 Golgi-Mazzoni corpuscles, 1019 Krause's end-bulbs, 1016 Meissner's corpuscles, 1017 Merkel's tactile cells, 1016 neuromuscular endings, 1019 neurotendinous endings, 1020 Rumni's corpuscles, 1017 Vater-Pacinian corpuscles, 1018 Xerve-fibres, 1000 arcuate, 1071 axis-cylinder of, 1001 cerebello-olivary, 1072 cerebello-thalamic, 1114 cortico-bulbar, 1115 cortico-pontine, 1115 cortico-spinal, 1115 medullary sheath of, 1001 medullated, 1003 neurilemma of, 1001 nonmedullated, 1003 rubro-thalamic, 1114 of sympathetic system, 1356 Nerve-terminations, 1014 Nerve-trunks, 1006 endoneurium of, 1006 epineurium of, 1006 funiculi of, 1006 perineurium of, 1006 Nervous system, 996 central, 1021 peripheral, 1218 sympathetic, 1353 development of, 1013 tissues, 997 development of, 1009 Neurilemma, 1001 Neuroblasts, 1010 Neuro-epithelium, 70 Neuroglia, 1003 ependymal layer of, 1004 glia-fibres of, 1004 of gray matter, of spinal cord, 1035 histogenesis of, 1010 spider cells of, 1004 Neurokeratin, 1001 Neuromuscular endings, 1019 Neurone or neurones, 996 axones of, 997 dendrites of, 997 histogenesis of, ion nerve-cells of, 998 Neurotendinous endings, 1020 Nipple, 2028 Nodose, ganglion of vagus, 1268 Nodules of Arantius, 700 Nonmedullated fibres, 1003 Nor'moblasts, 92 Nose, 1404 blood-vessels of, 1407 cartilages of, 1404 2076 INDEX. Nose, development of, 1429 hiatus semilunaris of, 1411 inferior meatus of, 1412 infundibulum of, 1411 lateral cartilages of, 1405 lymphatics of, 1407 middle meatus of, 1411 nerves of, 1407 olfactory region of, 1413 pract. consid., 1407 respiratory region of, 1415 superior meatus of, 1411 vestibule of, 1409 Nostrils, 1404 Notochord, 27 Nuck, canal of, 2006 Nuclein, 9 Nucleolus, 9 Nucleus or nuclei, abducent, 1249 acoustic, 1257 ambiguus, 1074 amygdaloid, 1172 arcuate, 1076 caudate, 1 169 cuneate, 1069 facial, 1251 dentate, of cerebellum, 1088 emboliformis (embolus) of cerebellum, 1089 facial, 1251 fastigii, of cerebellum, 1089 globosus, of cerebellum, 1089 gracile, 1069 internal, of cerebellum, 1088 of lateral fillet, 1258 lenticular, 1 1 69 mammillaris, 1129 olivary, 1071 olivary, superior, 1257 red, 1114 structure of, 8 trapezoideus, 1257 vago-glosso-pharyngeal, 1073 vestibular, of reception, 1259 Nuhn, glands of, 1577 Nutrition, accessory organs of, 1781 Nymphas, 2022 Obelion, 228 Obex, 1096 Occipital bone, 172 development ot, 175 lobe, 1145 protuberance, external, 174 internal, 175 Odontoblasts, 1558 (Esophagus, 1609 course and relations of, 1609 lymphatics of, 971 nerves of, 1613 pract. consid., 1613 structure of, 1611 vessels of, 1612 Olecranon, of ulna, 281 Olfactory bulb, 1151 cells, 1414 hairs, 1415 lobe, 1151 pits, 62 region of nose, 1413 striae, 1153 tract, 1 152 trigone, 1153 Olivary eminence, 1066 nuclei, 1071 accessory, 1072 nucleus, inferior, 1072 Omental sac, 1703 Omentum, duodeno-hepatic, 1746 gastro-colic, 1747 gastro-hepatic (lesser), 1745 gastro-splenic, 1747 greater, 1747 greater, structure of, 1749 Oocyte, primary, 17 secondary, 17 OSplasm, 15 Opercula insulae, 1137 Ophryon, 228 Opisthion, 228 Optic commissure, 1130 recess, 1132 thalami, 1118 tracts, 1130 Ora serrata, 1467 Oral cavity, development of, 62 glands, development of, 1589 Orbit, 222 axes of, 222 dimensions of, 222 fasciae of, 504 lymphatics of, 949 pract. consid., 1438 Organ or organs, accessory, of nutrition,. 1781 of Corti, 1519 genital, external female, 2021 Jacobson's, 1417 reproductive female, 1985 male, 1941 of respiration, 1813 of sense, 1381 of taste, 1433 urinary, 1869 Oro-pharynx, 1598 Orthognathism, 229 Os intermetatarseum, 432 magnum, 312 Osseous tissue, 84 Ossicles auditory, 1496 articulations of, 1498 incus, 1497 malleus, 1497 movements of, 1500 stapes, 1498 of ear, development of, 1525. Ossification, centres of, 94 of epiphyses, 98 Osteoblasts, 95 Ost;um maxillare, 1422 Otic ganglion, 1246 Ova or ovum, 15 centrolecithal, 22 fertilization of, 18 holoblastic, 22 homolecithal, 21 human, 1990 maturation of, 16 meroblastic, 22 primordial, 1993 segmentation of, 21 stage of, 56 telolecithal, 22 x.ona pellucida of, 1989. Ovary or ovaries, 1985 cortex of, 1987 INDEX. 2077 Ovary or ovaries, descent of, 2043 development of, 1993 fixation of, 1986 Graafian follicles of, 1988 hilum of, 1985 ligament of, 1987 medulla of, 1988 nerves of, 1993 position of, 1986 pract. consid., 1995 surfaces of, 1985 suspensory ligament of, 1986 structure of, 1987 vessels of, 1992 Oviduct, 1996 Pacchionian bodies, 1205 depressions, 198 Palate, 1567 bone, 204 articulations of, 205 development of, 205 hard, 1567 lymphatics of, 954 nerves of, 1573 pract. consid., 1592 soft, 1568 muscles of, 1570 vessels of, 1572 Pallium, development of, 1189 Palmar aponeurosis, 606 fascia, 606 Pancreas, 1732 body of, 1733 development of, 1737 ducts of, 1736 head of, 1732 interalveolar cell-areas of, 1735 islands of Langerhans of, 1735 lymphatics of, 979 nerves of, 1737 pract consid., 1738 relations to peritoneum of, 1736 structure of, 1734 vessels of, 1736 Panniculus adiposus, 1384 Papilla or papilla?, circumvallate, 1575 dental, 1558 of duodenum, 1720 filiform, 1575 fungi form, 1575 lachrymal, 1478 renal, 1875 Paradidymis, 1950 Parametrium, 2005 Parathyroid bodies, 1795 structure of, 1795 Parietal bone, 197 articulations of, 199 development of, 199 impressions, 199 lobe, 1143 Paroophoron, 2002 Parotid duct, 1 583 gland, 1582 nerves of, 1 583 relations of, 1582 structure of, i 586 vessels of, 1 583 Parovarium, 2000 Patella, 398 development of, 400 movements of, 409 Patella, pract. consid., 416 Peduncle, cerebellar, inferior, 1067 cerebral, 1107 Pelvic girdle, 332 Pelvis, 332 development of, 344 diameters of, 342 diaphragm of, 559 index of, 343 joints of, 337 pract. consid., 350 of kidney, 1894 landmarks of, 349 ligaments of, 337 lymphatics of, 983 position of, 342 pract. consid., 345 sexual differences, 343 surface anatomy of, 345 white line of, 559 as a whole, 341 Penis, 1965 corpora cavernosa of, 1966 corpus spongiosum of, 1967 crura of, 1967 glans of, 1968 nerves of, 1971 pract. consid., 1972 prepuce of, 1966 structure of, 1968 vessels of, 1970 Pericaecal fossae, 1666 Pericardium, 714 blood-vessels of, 716 ligaments of, 716 lymphatics of, 716 nerves of, 716 pract. consid., 716 Perichondrium, 81 Pericranium, 489 Perilymph of internal ear, 1514 Perimetrium, 2009 Perimysium, 458 Perineal body, 2046 Perineum, female, 2046 lymphatics of, 987 male, 1915 landmarks of, 1918 triangular ligament of, 563 Perineurium, 1006 Periosteum, 89 alveolar, 1553 Peritoneum, 1740 cavity, lesser of, 1749 development of, 1702 parietal, anterior, 1742 folds of, 1742 fossae of, 1742 pract. consid., 1754 Peri vascular lymph-spaces, 931 Pes anserinus, 1252 hippocampi, 1165 Petit, triangle of, 574 Petro-mastoid portion of temporal bone, 179 Petrous ganglion, of glosso-pharyngeal, 1264 subdivision, of petro-mastoid bone, 181 Peyer's patches, 1641 Phalanges of foot, 432 development of, 432 of hand, 317 2078 INDEX. Phalanges of hand, development of, 318 peculiarities, 318 pract. consid., 320 variations of, 319 Pharyngeal pouches, 1695 Pharynx, 1596 development of, 1603 growth of, 1603 laryngo-, 1598 lymphatics of, 954 lymphoid structures of, 1599 muscles of, 1604 naso-, 1598 nerves of, 1606 oro-, 1598 pract. consid., 1606 primitive, 1694 relations of, 1601 sinus pyriformis of, 1598 vessels of, 1606 Philtrum of lips, 1 540 Pia mater, of brain, 1202 of spinal cord, 1022 Pigment-cells of connective tissue, 74 Pillars of fauces, 1569 Pineal body, 1124 Pinna, 1484 Pisiform bone, 311 Pituitary body, anterior lobe of, 1806 development of, 1808 (hypophysis), 1129 Placenta, 49 basal plate of, 51 cotyledons of, 50 discoidal, 34 foetal portion, 50 giant cells of, 51 intervillous spaces of, 51 marginal sinus of, 53 maternal portion, 51 multiple, 34 septa of, 51 vitelline, 32 zonular, 33 Placentalia, 34 Plane, frontal, 3 sagittal, 3 transverse, 3 Plasma-cells of connective tissue, 74 Plasm osome, 9 Plates, tarsal, 1444 Platyrhines, 1404 Pleura or pleurae, 1858 blood-vessels of, 1860 nerves of, 1861 outlines of, 1859 pract. consid., 1864 relations to chest-walls, changes in, 1863 of to surface, 1859 structure of, 1860 Plexus or plexuses, aortic, 1373 of Auerbach, 1643 brachial, 1292 branches, infraclavicular of, 1297 supraclavicular of, 1295 constitution and plan of, 1293 pract. consid., 1294 cardiac, 1367 carotid (sympathetic), 1360 cavernous, of penis, 1374 (sympathetic), 1361 cervical, 1285 branches of, 1285 Plexus or plexuses, cervical, branches, communicating of, 1289 deep, of, 1289 descending of, 1288 muscular of, 1289 superficial of, 1286 supraacromial of, 1289 supraclavicular of, 1288 suprasternal of, 1288 pract. consid., 1292 coccygeal, 1352 cceliac, 1370 lymphatic, 973 gastric, 1370 hemorrhoidal, 1374 hepatic, 1370 hypogastnc, 1373 lymphatic, 984 iliac, lymphatic, 983 inguinal, lymphatic, 991 lumbar, 1319 constitution and plan of, 1319 lymphatic, 973 muscular branches of, 1320 of Meissner, 1643 mesenteric inferior, 1373 superior, 1372 cesophageal, 1272 ovarian, 1371 pampiniform, 1960 parotid, 1252 pelvic, 1374 phrenic, 1371 pract. consid., 1330 prostatic, 1374 pudendal, 1345 branches, muscular of, 1346 visceral of, 1346 pulmonary, anterior, 1272 posterior, 1272 renal, 1371 sacral, 1331 branches, articular of, 1334 collateral of, 1332 muscular of, 1333 terminal of, 1334 lymphatic, 984 posterior, 1282 pract. consid., 1352 solar, 1368 spermatic, 1371 splenic, 1370 suprarenal, 1371 of sympathetic nerves, 1367 tympanic, 1264 utero-vaginal, 1374 vesical, 1374 Plica fimbriata, 1573 semilunaris, of eye, 1443 sublingualis, 1573 Polar body, first, 16 second, 16 Pons Varolii, 1077 development of, 1103 internal structure of, 1078 Pontine flexure, 1062 nucleus, 1078 Portal system of veins, 919 Postaxial, 4 Pouch of Douglas, 1743 pharyngeal, 61 recto-uterine '1743 recto-vesical, 1743 INDEX. 2079 Poupart, ligament of, 523 Preaxial, 4 Pregnancy, 2012 Prepuce of penis, 1966 Primitive streak, 24 significance of, 25 Process or processes, ciliary, 1457 fronto-nasal, 62 mandibular, 62 maxillary, 62 nasal, mesial, 62 lateral, 62 styloid, of petrous bone, 183 uncinate of ethmoid, 193 Processus cochleariformis, 182 vaginalis, 2041 Proctodaeum, 1695 Prognathism, 229 Pronephros, 1934 Pronucleus, female, 16 male, 20 Prophases of mitosis, 12 Prosencephalon, 1059 Prostate gland, 1975 development of, 1979 lymphatics of, 985 nerves of, 1978 pract. consid., 1979 relations of, 1976 structure of, 1977 vessels of, 1978 Proteins, 8 Protoplasm, 7 Protovertebrae, 29 Psalterium, 1158 Pseudostomata, 72 Pterion, 228 Pterygoid plate, inner, 189 outer, 189 processes of sphenoid bone, 189 Pubes, 334 Pulmonary system of veins, 852 Pulp of teeth, 1554 Pulvinar, 1119 Puncta, lachrymal, 1478 Pupil, 1459 Purkinje cells of cerebellum, 1090 Putamen, 1170 Pyramid, 1065 Pyramidal tract, in medulla, 1075 Pyramids, decussation of, 1064 renal, 1876 Pyrenin, 9 Radius, 287 development of, 293 landmarks of, 296 pract. consid.. 293 structure of, 292 surface anatomy, 300 Kami communicantes of sympathetic system, 1356 Ranvier, nodes of, 1001 Rauber, cells of, 23 Recto-uterine pouch, 1743 Recto-vesical pouch, 1743 Rectum, 1672 blood-vessels of, 1679 growth of, 1680 lymphatics of, 1680 muscles and fascia? of, 1675 nerves of, 1680 peritoneal relations of, 1679 Rectum, pract. consid., 1689 structure of, 1674 valves of, 1674 Reduction division, 18 Reil, island of, 1149 limiting sulcus of, 1139 Reissner's fibre, 1030 membrane, of cochlea, 1517 Remak, fibres of, 1003 Reproduction, 6 Reproductive organs, development of, 2037 external, female, lymphatics of, 987 male, lymphatics of, 986 female, 1985 internal, female, lymphatics of, male, lymphatics of, 987 male, 1941 Respiration, organs of, 1813 Respiratory region of nose, 1415 tract, development of, 1861 Restiform body, 1067 Rete Malpighi, 1386 Reticular tissue, 75 Reticulin, 83 Retina, 1462 blood-vessels of, 1467 development of, 1482 layers of, 1463 lymphatics of, 1468 pars optica of, 1462 pract. consid., 1468 structure of, 1463 Retro-colic fossa, 1667 Retzius, prevesical space of, 525 space of, 1906 Rhinencephalon, 1151 development of, 1193 Rhombencephalon, derivatives of, 1063 Ribs, 149 asternal, 150 development of, 153 exceptional, 152 floating, 150 pract. consid., 169 sternal, 150 variations of, 1 53 Right lymphatic duct, 945 Rima glottidis, 1820 Ring, abdominal, external, 524 internal, 524 femoral, 1773 Riolan, muscle of, 484 Rivini's ducts, 1585 Rivinus, notch of, 1493 Rolando, fissure of, 1137 funiculus of, 1067 Rosenmiiller, fossa of, 1598 lymph-nodes of, 992 organ of, 2000 Rostrum, of corpus callosum, 1156 of sphenoid bone, 187 Ruffini, corpuscles of, 1017 Ruysch, membrane of, 1456 Sac, conjunctival, 1443 lachrymal, 1478 vitelline, 32 Saccule, 1515 structure of, 1516 Sacral lymphatic plexus, 984 Sacro-ihac articulation, 338 2080 INDEX. Sacro-sciatic ligaments, 339 Sacrum, 124 development of, 129 sexual differences of, 127 variations of, 127 Salivary glands, 1582 structure of, 1585 Santorini, cartilages of, 1817 duct of, 1736 Saphenous opening, 635 Sarcolemma, 459 Sarcous (muscular) substance, 459 Scala tympani, 1514 vestibuli, 1514 Scalp, lymphatics of, 948 muscles and fasciae, pract. consid., 489 Scaphoid, 309 bone of foot, 425 development of, 426 Scapula, 248 development of, 253 landmarks of, 255 ligaments of, 256 pract. consid., 253 sexual differences, 252 structure of, 253 Scapulo-clavicular articulation, 262 Scarpa, canals of, 201 fascia of, 515 ganglion of, 1259 triangle of, 639 Schlemm, canal of, 1452 Schwann, sheath of, 1001 Sclera, 1449 development of, 1482 pract. consid., 1453 structure of, 1450 Sclerotome, 30 Scoliosis, 144 Scrotum, 1961 dartos muscle of, 1963 nerves of, 1964 pract. consid., 1964 raphe of, 1962 tunica vaginalis of, 1963 vessels of, 1964 Segmentation, 21 complete, 22 equal, 22 partial, 22 Sella turcica, 186 Semilunar bone, 310 cartilages of knee-joint, 402 valves, 700 Seminal vesicles, 1956 lymphatics of, 988 pract. consid., 1959 relations of, 1957 structure of, 1958 vessels of, 1958 Seminiferous tubules, 1942 Sense, organs of, 1381 Septum or septa, aortic, 707 auricular, 694 crurale (femorale), 625 intermedium, 706 intermuscular, 470 interventricular, 696 lucidum, i i 50 median, posterior, of spinal cord, 1027 nasal, 1410 cartilage of, 1405 plaivntal, 51 Septum or septa, primum, 706 secundum, 708 spurium, 707 transversum, 1701 Serosa, 31 Sertoli, cells of, 1943 Sesamoid bones, 104 of foot, 432 of hand, 318 Sharpey's fibres of bone, 87 Shoulder, muscles and fascia consid., 579 Shoulder-girdle, 248 surface anatomy of, 263 Shoulder-joint, 274 bursae of, 277 dislocation of, 582 landmarks of, 280 ligaments of, 274 movements of, 277 pract. consid., 278 Shrapnell's membrane, 1494 Sigmoid cavity, greater, of ulna, lesser, of ulna, 281 flexure, 1669 peritoneal relations of, pract. consid., 1685 Sinus or sinuses, basilar, 874 pract. consid., 874 cavernous, 872 pract. consid., 873 circular, 872 confluence of, 868 of dura mater, 867 frontal, 1423; 226 (bony) development of, 1432 pract. consid., 1427 intercavernous, 872 lactiferus, 2030 lateral, 867 pract. consid., 869 longitudinal, inferior, 871 superior, 870 pract. consid., 870 marginal, 872 of placenta, 53 maxillary, 1422; 20 (bony) development of, 1431 pract. consid., 1428 of Morgagni, 497 occipital, 872 palatal, 1425 petrosal, inferior, 874 superior, 874 pocularis, 1922 praecervicalis, 61 pyriformis of pharynx, 1 598 renal, 1874 Reunions, 707 sphenoidal, 1425 development of, 1432 pract. consid., 1428 spheno-parietal, 874 straight, 872 uro-genital, 1939 of Valsalva, 700 venosus, 705 Skeleton, 103 appendicular, 104 axial, 103 Skene, tubes of, 1924 Skin, blood-vessels of, 1387 development of, 1400 of, pract 281 1671 INDEX. 2081 Skin, end-bulbs of Krause, 1389 end-organs of Ruffini, 1389 genital corpuscles, 1389 Golgi-mazzoni corpuscles, 1389 lymphatics of, 1388 Meissner's corpuscles, 1389 nerves of, 1389 pigmentation of, 1387 stratum corneum of, 1387 germinativum of, 1385 granulosum of, 1386 lucidum of, 1386 structure of, 1382 Vater-Pacinian corpuscles, 1389 Skull, 172 alveolar point of, 228 anthropology of, 228 asymmetry, 230 auricular point of, 228 capacity of, 230 changes in old age, 233 chordal portion, 28 dimensions of, 229 fontanelles of, 231 glenoid point of, 228 growth and age of, 230 index, cephalic of, 229 facial of, 229 of height of, 229 nasal of, 229 orbital of, 229 palatal of, 229 landmarks of, 240 malar point of, 228 mental point of, 228 occipital point of, 228 pract. consid., 235 prechordal portion, 28 sexual differences, 234 shape of, 229 subnasal point of, 229 surface anatomy, 234 weight of, 233 as whole, 216 Smegma, 1966 Solitary nodules of Intestine, 1640 Somatopleura, 29 Somites, 29 Space or spaces, of Burns, 543 of Fontana, 1452 perforated, anterior, 1153 posterior, 1107 quadrangular, of m. teres major, 578 of Retzius, 1906 subarachnoid, of spinal cord, 1022 subdural, of spinal cord, 1022 sublingual, 1581 of Tenon, 1437 triangular, of m. teres major, 578 Spermatic cord, 1960 constituents of, 1960 pampiniform plexus of, 1960 pract. consid., 1961 ducts, 1953 nerves of, 1959 structure of, 1956 vessels of, 1958 filaments, 1946 Spermatids, 1944 Spermatocytes, primary, 1944 secondary, 1944 Spermatogenesis, 1944 Spermatogones, 1944 Spermatozoa, 1946 Spermatozoon, 16 Sperm-nucleus, 20 Spheno-ethmoidal recess, 1411 Sphenoid bone, 186 articulations of, 190 development of, 190 great wings of, 187 lesser wings of, 188 pterygoid processes of, 189 Sphenoidal sinus, 1425 Spheno-palatine ganglion, 1240 Spigelius, lobe of, 1707 Spinal column, 114 Spinal cord, 1021 anterior horn, nerve-cells of, 1030 arachnoid of, 1022 blood-vessels of, 1047 cauda equina of, 1025 central canal of, 1030 columns of, 1027 anterior, 1027 lateral, 1027 posterior, 1027 commissure, gray of, 1028 white, anterior of, 1028 conus medullaris, 1021 denticulate ligaments of, 1023 development of, 1049 dura mater of, 1022 enlargement, cervical, of, 1026 lumbar of, 1026 fibre-tracts of white matter, 1038 fissure, median anterior of, 1027 form of, 1026 gray matter of, 1028 nerve-fibres of, 1036 neuroglia of, 1035 ground-bundle, anterior, 1046 lateral, 1045 horn, anterior of, 1029 lateral of, 1029 posterior of, 1029 membranes of, 1022 microscopical structure of, 1030 nerve-cells, grouping of, 1032 pia mater of, 1022 posterior horn, nerve-cells of, 1033 pract. consid., 1051 root-line, ventral of, 1027 segments of, 1024 septum, median posterior of, 1027 substantia gelatinosa Rolandi of, 1029 sulcus postero-lateral of, 1027 tract, anterior pyramidal (direct), 1046 of Burdach, 1039 direct cerebellar, 1044 of Goll, 1039 of Gower, 1044 lateral (crossed pyramidal), t T of Lissauer, 1042 white matter of, 1036 ganglia, 1279 nerves, 1278 constitution of, 1278 divisions, primary, anterior, of, 1284 posterior, of, 1279 number of, 1279 size of, 1279 typical, 1284 13* 2082 INDEX. Spinal nerves, ventral (motor) roots of, 1279 Spine, 114 articulations of, 132 aspect, anterior of, 138 lateral of, 138 posterior of, 138 curves of, 138 dimensions and proportions of, 141 landmarks of, 146 lateral curvature of, 144 ligaments of, 132 movements of, 142 practical considerations, 143 sprains of, 144 as whole, 138 Splanchnopleura, 29 Splanchnoskeleton, 84 Spleen, 1781 development and growth of, 1787 lymphatics of, 982 movable, 1788 nerves of, 1787 nodules (Malphighian bodies) of, 1784 peritoneal relations of, 1785 pract. consid., 1787 pulp of, 1783 * structure of, 1783 surface anatomy of, 1787 basal, 1782 gastric, 1782 phrenic, 1781 renal, 1782 suspensory ligament of, 1786 vessels of, 1786 Spleens, accessory, 1787 Splenium, of corpus callosum, 1156 Spongioblasts i o i o Spongioplasm, 8 Sprains, of spine, 144 Squamous portion of temporal bone, 177 Stapes, 1498 Stenson, canals of, 201 duct, 1583 Stephanion, 229 Sterno-clavicular articulation, 261 pract. consid., 263 Sternum, 155 development of, 157 pract. consid., 168 sexual differences of 156 variations of, 1 56 Stigmata, 72 Stilling, canal of, 1474 Stomach, 1617 blood-vessels of, 1627 curvature greater of, 1617 curvature lesser of, 1617 fund us of, 1618 glands of, 1623 growth of, 1629 lymphatics of, 976, 1628 nerves of, 1628 peritoneal relations of, 1619 position and relations of, 1619 pract. consid., 1629 pylorus, 1618 shape of, 1618 structure of, 1621 variations of, 1629 weight and dimensions of, 1619 Stomata, 72 Stomodaeum, 1694 Strabismus, 1440 Stratum zonale, of thalamus, 1123 Stria medullaris, 1119 Striae, acoustic, 1096 Structure, elements of, 5 Styloid process of ulna, 285 Sublingual ducts, 1585 gland, 1585 nerves of, 1585 structure of, 1587 vessels of, 1585 space, 1581 Submaxillary duct, 1584 ganglion, 1247 gland, 1583 nerves of, 1585 structure of, 1587 vessels of, 1585 Subpatellar fat, 405 Subperiosteal bone, 98 Sub-peritoneal tissue, 1742 Substantia nigra, 1109 Sulci, development of, 1190 fissures, cerebral, 1135 Sulcus hypothalamicus, 1119 Suprarenal bodies, 1801 accessory, 1805 development of, 1804 growth of, 1804 nerves of, 1803 pract. consid., 1806 relations of, 1801 structure of, 1802 vessels of, 1803 body, lymphatics of, 983 Suture or sutures, 107 amniotic, 3 1 coronal, 216 cranial, 216 closure of, 233 lambdoidal, 217 sagittal, 216 Sylvian aqueduct, 1108 gray matter, 1109 Sylvius, fissure of, 1136 Sympathetic nerves, plexuses of, 1367 Sympathetic system, 1353 aortic nerves, 1364 association cords of, 1357 constitution of, 1355 ganglia of, 1356 gangliated cord of, 1355 gangliated cord, cervico-cephalic portion, 1358 lumbar portion, 1366 sacral portion, 1367 thoracic portion, 1364 nerve -fibres 0^-1356 plexus, aortic, 1372 cardiac, 1367 carotid, 1360 cavernous, 1361 cavernous, of penis, 1374 coeliac, 1370 gastric, 1370 hemorrhoidal, 1374 hepatic, 1370 hypogastnc, 1374 mesenteric, inferior, 1373 superior, 1372 ovarian, 1372 ivlvic, 1374 phrenic, 1371 prostatic, 1374 INDEX. 2083 Sympathetic system, plexus, renal, 1371 solar, 1368 spermatic, 1372 splenic, 1370 suprarenal, 1371 utero-vaginal, 1374 vesical, 1374 plexuses of, 1356 pract. consid., 1375 pulmonary nerves, 1364 rami communicantes of, 1356 splanchnic afferent fibres of, 1357 efferent fibres of, 1357 nerves, 1364 Symphysis, 108 pubis, 339 Synarthrosis, 107 Synchondrosis, 108 Syncytium of chorion, 49 Syndesmosis, 108 System, gastro-pulmonary, 1527 muscular, 454 nervous, 996 uro-genital, 1869 Tasnia coli, 1660 semicircularis, 1162 thalami, 1119 Tapetum, 1157 Tarsal bones, 419 plates, 1444 Tarsus, 419 Taste, organ of, 1433 Taste-buds, 1433 development of, 1436 nerves of, 1435 structure of, 1434 Teeth, 1542 alveolar periosteum, 1553 bicuspids (premolars), 1545 canines, 1544 milk, 1545 cementum of, 1552 crown of, 1542 dentine of, 1550 development of, 1556 enamel of, 1548 fang of, 1542 homologies of, 1566 implantation and relations of, 1554 incisors, 1543 milk, 1544 lymphatics of, 951 milk, eruption of, 1564 (temporary), 1542 molars, 1546 milk, 1547 neck of, 1542 permanent, 1542 development of, 1564 eruption of, 1565 relations of, 1554 pract. consid., 1591 pulp of, 1554 pulp-cavity of, 1542 temporary, relations of, 1556 variations of, 1566 Tegmen tympani, 1496 Tegmentum, 1112 Tela chorioidea, 1097 subcutanea, 1384 Telencephalon, 1132 Telophases of mitosis, 13 Temporal bone, 176 articulations of, 184 cavities and passages, 183 development of, 184 portion, petro-mastoid, 179 squamous, 177 tympanic, 179 lobe, 1147 Temporo-mandibular articulation, 214 Tendo oculi, 484 Tendon, 77, 468 conjoined, 518 Tendon-cells, 78 Tendon-sheaths, 470 Tenon, capsule of, 504 space of, 1437 Tentorium cerebelli, 1199 Terms, descriptive, 3 Testis or testes, 1941 appendages of, 1949 architecture of, 1942 descent of, 2040 lymphatics of, 987 mediastinum of, 1942 nerves of, 1948 pract. consid., 1950 structure of, 1942 tubules seminiferous of, 1942 tunica albuginea of, 1942 vessels of, 1948 Thalamic radiation, 1122 Thalamus, 1 1 1 8 connections of, 1121 structure of, 1120 Thebesian valve, 695 veins, 694 Theca folliculi, of hair, 1392 Thenar eminence, 607 Thigh, landmarks of, 670 muscles and fasciae of, pract. consid. 642 Third ventricle, 1131 choroid plexus of, 1131 Thorax, 149 articulations of, 157 in infancy and childhood, 164 landmarks of, 170 lymphatics of, 966 movements of, 165 pract. consid., 167 sexual differences, 164 subdivisions of, 1832 surface anatomy, 166 landmarks of, 1868 as whole, 162 Thumb, articulation of, 326 Thymus body, 1796 changes of, 1797 development of, 1800 nerves of, 1800 shape and relations of, 1796 structure of, 1798 vessels of, 1 799 weight of, 1797 Thyroid bodies, accessory, 1793 Thyroid body, 1789 development of, 1793 nerves of, 1793 pract. consid., 1794 shape and relations of, 1789 structure of, 1791 vessels of, 1792 cartilage, 1814 2084 INDEX. Thyroid cartilage, development of, 1815 growth of, 1815 gland, lymphatics of, 959 Tibia, 382 development of, 387 landmarks of, 390 pract. consid., 387 structure of, 387 variations of, 383 Tibio-fibular articulation, inferior, 396 superior, 396 Tissue or tissues, adipose, 79 connective, 73 elastic, 76 elementary, 67 epithelial, 67 fibrous, 74 muscular, general, 454 nervous, 997 osseous, 84 reticular, 75 Tongue, 1573 foramen caecum of, 1574 frenum of, 1573 glands of, 1575 growth and changes of, 1580 lymphatics of, 952 muscles of, 1577 nerves of, 1580 papillae, circumvallate of, 1575 filiform of, 1575 fungiform of, 1575 pract. consid., 1594 vessels of, 1 580 Tonsil or tonsils (amygdala), of cerebellum, 1086 faucial, 1600 faucial, relations of, 1602 lingual, 1575 lymphatics of, 954 pharyngeal, 1601 pract. consid., 1608 tubal, 1503 Tooth-sac, 1562 Tooth-structure, 1 548 Topography, of abdomen, 531 cranio-cerebral, 1214 Trachea, 1834 bifurcation of, 1837 carina of, 1837 growth of, 1837 lymphatics of, 958 nerves of, 1836 pract. consid., 1840 relations of, 1836 structure of, 1835 vessels of, 1836 Tract or tracts, (fibre) rubro-spinal, 1114 habenulo-peduncular, 1124 mammillo-thalamic, 1121 of mesial fillet, 1076 olfactory, 1152 thalamocipetal, lower, 1122 Tragus, 1484 Trapezium, 311 Trapezoid bone, 311 Treitz, muscle of, 558 Triangle of Hesselbach, 526 rectal, 1916 uro-genital, 1916 Triangles of neck, 547 Trigone of bladder, urinary, 1904 Trigonum acustici, 1097 habenulae, 1 1 23 hypoglossi, 1097 lemnisci, 1108 urogenitale, 563 vagi, 1097 Trochanter, greater, of femur, 352 lesser, of femur, 353 Trochlea of humerus, 268 of orbit, 504 Trochoides, 113 Trophoblast, 46 Truncus bronchomediastinalis, lymphatic, 968 subclavius, lymphatic, 963 Tube, Eustachian, 1501 Tuber cinereum, 1129 Tubercle of Lower, 695 Tuberculum acusticum, 1097 olfactorium, 1153 Tubes, Fallopian, 1996 Tunica vaginalis of scrotum, 1963 Turbinate bone, inferior, 208 articulations of, 208 development of, 208 middle, of ethmoid, 193 superior, of ethmoid, 193 Tympanic portion of temporal bone, 179 Tympanum, 1492 attic of, 1 500 cavity of, 183 contents of, 1496 membrane of, 1494 pract. consid., 1505 mucous membrane of, 1 500 oval window of, 1495 pract. consid., 1504 promonotory of, 1405 pyramid of, 1496 round window of, 1495 secondary membrane of, 1495 tegmen of, 1496 Tyson, glands of, 1966 Ulna, 281 development of, 285 landmarks of, 287 pract. consid., 285 structure of, 285 surface anatomy, 300 Umbilical cord, 53 allantoic duct of, 54 amniotic sheath of, 54 blood-vessels of, 54 furcate insertion of, 55 jelly of Wharton of, 54 marginal insertion of, 55 velamentous insertion of, 55, fissure of liver, 1708 hernia, 1775 notch of liver, 1707 vesicle, 42 Umbilicus, 37 Unciform bone, 312 Uncus, 1154 Upper limb, muscles of, 568 Urachus, 525 Ureter or ureters, 1895 female, 1896 lymphatics of, 982 nerves of, 1898 pract. consid., 1898 INDEX. 2085 Ureter or ureters, structure of, 1896 vessels of, 1897 Urethra, 1922 crest of, 1922 development of, 1938 female, 1924 structure of, 1926 fossa, navicular of, 1924 glands of, 1925 lymphatics of, 986 male, pract. consid., 1927 structure of, 1924 meatus of, 1924 nerves of, 1927 orifice of, external, 1924 internal, 1904 portion, membranous of, 1923 prostatic of, 1922 spongy of, 1923 vessels of, 1926 Urethral bulb, 1968 crest, 1922 Urinary organs, 1869 development of, 1934 Uriniferous tubule, 1877 Urogenital cleft, 2021 sphincter, 2049 system, 1869 Utero-sacral folds, 1743 Utero-vesical pouch, 1943 Uterus, 2003 attachments of, 2004 body of, 2003 broad ligament of, 2004 cavity of, 2003 cervical canal of, 2003 cervix of, 2003 changes of menstruation, 2012 of pregnancy, 2012 development of, 2010 fundus of, 2003 glands of, 2007 lymphatics of, 989 nerves of, 2010 os, external of, 2003 peritoneal relations of, 2004 position of, 2007 pract. consid., 2012 relations of, 2007 round ligament of, 2005 structure of, 2007 variations of, 2012 vessels of, 2009 Utricle, 1514 prostatic, 1922 structure of, 1516 Uveal tract, 1454 Uvula, 1569 Vagina, 2016 development of, 2019 fornix, anterior of, 2016 posterior of, 2016 lymphatics of, 989 nerves of, 2018 pract. consid., 2019 relations of, 2016 structure of, 2017 variations of, 2019 Vagina, vessels of, 2018 vestibule of, 2022 Vaginal process of inner pterygoid plate, 189 Vallecula, 1083 Valsalva, sinus of, 700 Valve or valves, aortic, 700 uuriculo-ventricular, of heart, 699 Eustachian, 694 ileo-cascal, 1661 mitral, 699 of Morgagni, 1674 pulmonary, 700 of pulmonary artery, 700 rectal, 1674 semilunar, 700 Thebesian, 695 tricuspid, 699 Valvulae conniventes, 1636 Vasa aberrantia of epididymis, 1950 Vas deferens, 1954 ampulla of, 1955 lymphatics of, 988 Vasa vasorum, 674 Vater, ampulla of, 1721 Vater-Pacinian corpuscles, 1018 Vein or veins, allantoic, 33 circulation, 929 angular, of facial, 864 auditory, internal, 869 auricular, anterior, 882 posterior, 883 axillary, 887 pract. consid., 888 azygos, 893 arch, 893 development of, 928 major, 893 minor, 895 superior, 895 pract. consid., 895 system, 893 basilar, 877 basilic, 890 median, 891 basi vertebral, 897 brachial, 886 brachio-cephalic, 858 bronchial, 893 of bulb, 907 cardiac, 854 anterior, 856 great, 855 middle, 856 posterior, 856 small, 856 valves of, 856 cardinal, 926 posterior, 854 superior, 854 system of, 854 centralis retinas, 879 cephalic, 890 accessory, 890 median, 891 cerebellar, inferior, 879 superior, 878 median, 878 cerebral, 877 great, 877 inferior, 877 posterior, 869 internal, 877 middle, 877 pract. consid., 878 superior, 877 cervical, ascending, of vertebral, 860 2o86 INDEX. Vein or veins, cervical, deep, 859 middle, 884 chordae Willissi, 870 choroid, 877 ciliary, anterior, 879 posterior, 879 circulation, foetal, 929 circumflex, iliac, deep, 910 superficial, 917 of leg, 914 classification of, 852 clitoris, 909 colic, middle, 921 right, 921 condyloid, anterior, 874 confluence of the sinuses, 868 coronary, of facial, 865 inferior, of facial, 865 left, 855 right, 856 of corpus callosum, anterior, 878 posterior, 877 cavernosum, 907 striatum, 877 costo-axillary, 896 crico-thyroid, of superior thyroid, 867 cystic, 923 deep dorsal of penis (clitoris), 909 of forearm, 886 of hand, 886 dental, inferior, 883 superior, 883 development of, 926 diploic, 874 anterior, 875 occipital, 875 pract. consid., 875 temporal, anterior, 875 posterior, 875 dorsal, of foot, 910 interosseous, 886 ductus Arantii, 929 arteriosus, 930 Botalli, 930 venosus, 929 emissaries of foramen lacerum medium, 876 emissary, 875 condyloid, anterior, 876 posterior, 876 of foramen ovale, 876 of Vesalius, 876 mastoid, 876 occipital, 876 parietal, 876 pract. consid., 876 epigastric, deep, 909 superficial, 917 superior, of internal mammary, 860 ethmoidal, 870 facial, 864 common, 864 deep, 865 pract. consid., 864 transverse, 882 femoral, deep, 914 pract. consid., 918 foetal circulation, 929 of foot, deep, 910 stijH-rlicial, 914 foramen lacvrum medium, 876 fnmtal, of facial, 865 of Galen, 856 Vein or veins, gastric, 923 short, 921 gastro-epiploic, left, 921 right, 921 gluteal, 905 hemiazygos, 895 accessory, 895 hemorrhoidal, inferior, 907 middle, 908 plexus, 908 superior, 922 hepatic, 902 pract. consid., 904 hepatica communis, 900 ileo-colic, 921 iliac, common, 905 pract. consid., 917 external, 909 pract. consid., 918 internal, 905 pract. consid., 918 ilio-lumbar, 906 inferior cava, pract. consid., 900 caval system, 898 innominate, 858 development of, 859 pract. consid., 859 intercapitular of hand, 889 intercostal, 896 anterior, of internal mammary, 860 superior, 896 accessory left, 896 intervertebral, 898 jugular, anterior, 884 external, 880 posterior, 884 pract. consid., 88 1 internal, 861 bulbs of, 86 1 prac. consid., 863 labial, inferior, of facial, 865 superior, 865 lacunae of dural sinuses, 852 laryngeal, inferior, 86 1 superior, of superior thyroid, 867 of leg, deep, 911 pract. consid., 918 of limbs, development of, 929 lingual, deep, of facial, 867 of facial, 867 lumbar, 901 ascending, 901 mammary, external, 888 internal, 860 marginal, right, 856 marginalis sinistra, 855 of Marshall, 856 masseteric, of facial, 866 mastoid emissary, 869 maxillary, internal, 882 internal, anterior, of facial, 865 median, 890 deep, 886 mediastinal, anterior, 86 1 medulli-spinal, 898 meningeal, middle, 883 mesenteric, inferior, 922 superior, 921 metacarpal, dorsal, 889 nasal, lateral, of facial, 865 oblique, of heart, 605 of left auricle, 856 obturator, 907 INDEX. 2087 Vein or veins, occipital, 859 ophthalmic, anastomoses of, 880 inferior, 879 pract. consid., 880 superior, 879 ovarian, 903 palatine, ascending, of facial, 866 inferior, of facial, 866 palmar arches, 886 superficial, 890 palpebral, of facial, 865 pampiniform plexus, 903 pancreatic, 921 pancreatico- duodenal, 921 parotid, anterior, of facial, 866 posterior, 882 parumbilical, 923 perforating, of internal mammary, 860 pericardial, 86 1 perineal, superficial, 907 peroneal, 911 pharyngeal, 863 % plexus, 864 phrenic, inferior, 901 superior, 86 1 plantar, 910 external, 910 plexus, alveolar, 882 external, spinal, 897 hemorrhoidal, venous, 908 internal, spinal, 897 pterygoid, 882 sacral, 905 of Santorini, 909 venosus mammillag, 888 popliteal, 911 pract. consid., 918 portal, 919 accessory, 923 collateral circulation of, 923 development of, 928 of liver, 1709 system, 919 pract. consid., 925 pterygoid, plexus, 882 pudendal plexus, 909 pudic, external, 916 internal, 907 pulmonary, 852 anastomoses of, 853 development of, 929 pyloric, 923 radial, 886 superficial, 891 accessory, 891 renal, 902 pract. consid., 904 sacral, anterior, plexus, 905 lateral, 906 middle, 905 saphenous, accessory, 916 long, 916 short, 915 sciatic, 906 of septum lucidum, 877 sigmoid, 922 sinus, basilar, 874 pract. consid., 874 cavernous, 872 pract. consid., 873 circular, 872 coronary, 854 of dura mater, 867 Veins or veins, sinus, dural, blood-lakes of, 852 structure of, 851 intercavernous, 872 lateral, 867 pract. consid., 869 longitudinal, inferior, 871 superior, 870 pract. consid., 870 marginal, 872 occipital, 872 petrosal, inferior, 874 superior, 874 sphe no-parietal, 874 straight, 872 small, of Galen, 877 intestine, 921 spermatic, 903 pract. consid., 904 spheno-palatine, 882 spinal, 897 cord, 898 pract. consid., 898 splenic, 921 sterno-mastoid, of superior thyroid, 867 structure of, 677 subclavian, 884 pract. consid., 885 subcostal, 896 sublingual, 867 submental, of facial, 866 superficial of hand, 889 superior caval system, 857 supraorbital, of facial, 865 suprarenal, middle, 903 inferior, 902 suprascapular, 884 Sylvian, deep, 878 temporal, deep, 883 middle, 882 superficial, 882 temporo-maxillary, 882 testicular, 903 Thebesian, 694 thoracic, acromial, 890 long, 887 thoraco-epigastric, 888 thymic, 86 1 thyroid, inferior, 860 pract. consid., 86 1 middle, 867 plexus, 860 superior, 867 tibial, anterior, 911 posterior, 911 torcular Herophili, 868 tympanic, of temporal, 882 ulnar, 886 superficial, 890 umbilical, 54 of upper extremity, 886 pract. consid., 891 ureteric, of renal, 902 of spermatic, 903 uterine, 908 plexus, 908 utero-vaginal plexus, 908 vaginal, 908 plexus, 908 valves of, 850, 851 vena cava inferior, 899 development of, 927 2088 INDEX. Vein or veins, vena cava superior, 857 development of, 927 pract. consid., 858 cephalica pollicis, 889 salvatella, 889 supraumbilicalis, 923 thyreoidea ima, 861 venae comites, 851 vorticosae, 879 vertebral, 860 vesical, 908 vesico-prostatic plexus, 909 vesico-vaginal plexus, 909 vitelline circulation, 929 Velum interpositum, 1162 Ventricle or ventricles, fifth, 1160 fourth, 1096 of heart, 696 lateral, 1160 anterior horn of, 1 1 60 body of, 1161 choroid plexus of, 1162 inferior (descending) horn of, 1 164 posterior horn of, 1 1 68 (sinus) of larynx, 1822 third, 1131 Vermiform appendix, 1664 Vernix caseosa, 66 Vertebra or vertebras, 114 articular surfaces of, 1 1 6 body of, 115 cervical, 116 development of, 128 dimensions of, 122 gradual regional changes of, 122 laminae of, 115 lumbar, 117 mammillary processes of, 1 1 8 peculiar, 119 pedicles of, 115 presacral, 128 prominens, 121 spinal foramen of, 115 spinous process of, 115 structure of, 128 thoracic, 115 transverse processes of, 115 variations of, 131 Verumontanum, 1922 Vesalius, foramen of, 188 Vesicle, germinal, 15 umbilical, 42 Vesicles, seminal, 1956 Vessels of clitoris, 2025 of epididymis, 1948 <>i" Fallopian tube, 1998 of gall-bladder, 1719 of labia, 2023 of larynx, 1826 of lips, 1542 of mammary glands, 2031 of oesophagus, 1612 of ovary, 1992 of palate, 1572 of pancreas, 1736 of parotid gland, 1 583 of penis, 1970 of pharynx, 1606 of prostate gland, 1978 of roots of lungs, 1839 of scrotum, 1964 Vessels of seminal vesicles, 1958 of spermatic ducts, 1958 of spleen, 1786 of sublingual gland, 1585 of submaxillary gland, 1585 of suprarenal bodies, 1803 of testis, 1948 of thymus body, 1799 of thyroid body, 1792 of tongue, 1 580 of trachea, 1836 of ureter, 1897 of urethra, 1926 of urinary bladder, 1910 of uterus, 2009 of vagina, 2018 Vestibule of mouth,' 1538 of nose, 1409 of osseous labyrinth, 1511 of vagina, 2022 Vicq d'Azyr, bundle of, 1121 Vidian canal, 189 Villi of chorion, 49 of intestine, 1635 lacteals of, 1636 Vincula tendinum, 471 Vital manifestations, 6 Vitelline arteries, 32 duct, 32 membrane, 1 5 sac, 32 Vitello-intestinal duct, 37 Vitellus, 15 Vitreous body, 1473 development of, 1483 pract. consid., 1474 Vocal cords, false, 1820 true, 1820 Volkmann's canals, of bone, 89 Volvulus, 1687 Vomer, 205 articulations of, 206 development of, 206 Wharton duct of, 1 584 jelly of, 54 Winslow, foramen of, 1746 Wirsung, duct of, 1736 Wisdom-tooth, 1546 Wolffian body, 1935 duct, 1935 Womb, 2003 Worm of cerebellum, 1082 Wrist, anterior annular ligament, 607 movements of, 326 pract. consid., 613 surface anatomy of, 328 Wrist-joint, landmarks of, 330 pract. consid., 329 Xiphoid process of sternum, 156 Yolk-stalk, 37 Zeiss, glands of, 1444 Zinn, annulus of, 503 zonula of, 1475 Zona pellucida, 1 5 radiata, 15 Zonula of Zinn, 1475 Zuckerkandl, bodies of, 1812 Zygomatic process of temporal bone, 178 This book is due on last date given below. A fine of 5c will be charged for each day the book is kept overtime. Date Due > 1-4 DAY DEC 17 1963 p . ; Mi 3 s - \ '* JUL 1 2 1994 618477 3 1378 00618 4777 . University