^^sr^T/e ^^^^uv/Ci/^>e O^i^zE Ai^G/cjc^A^ Jc f-toO^ UNIVERSITY OF CALIFORNIA MEDICAL CENTER LIBRARY SAN FRANCISCO GIFT OF LESTER J. SAWYER, M.D. Digitized by the Internet Archive in 2007 with funding from IVIicrosoft Corporation http://www.archive.org/details/anatomyofhumanboOOgrayrich ANATOMY OF THE HUMAN BODY BY henry/qbay, f.r.s. FELLOW OF THE KOYAL COLLEGE OF STJHg^NS ; LECTURER ON ANATOMY AT ST. GEORGE's HOSPITAL MEDICAL SCHOOL, LONDON TWENTIETH EDITION THOROUGHLY REVISED AND RE-EDITED BY WARREN H. LEWIS, B.S., M.D. PROFESSOR OF PHYSIOLOGICAL ANATOMY, JOHNS HOPKINS UNIVERSITY, BALTIMORE, MD. lUu0tratc^ witb 1247 jengravinGS LEA & FEBIGER PHILADELPHIA AND NEW YORK Copyright LEA & FEBIGER 1918 PRINTED IN U. S. A. THE FIRST EDITION OF THIS WORK WAS DEDICATED TO SIR BENJAMIN COLLINS BRODIE, Bart., F.R.S., D.C.L. IN ADMIRATION OF HIS GREAT TALENTS AND IN REMEMBRANCE OF MANY ACTS OF KINDNESS SHOWN TO THE ORIGINAL AUTHOR OF THE BOOK FROM AN EARLY PERIOD OF HIS PROFESSIONAL CAREER 672.7 PREFACE TO THE TWENTIETH EDITION. Since the publication of the first English edition of this work in 1858 and the first American edition in 1859 great advances in the subject of Anatomy have been made, especially in microscopic anatomy and the anatomy of the embryo. This knowledge was embodied from time to time in the successive editions until finally considerable portions of the text, sometimes sections, were devoted to these sub- jects. Howe\'er, the main text has always remained primarily a descriptive anatomy of the human body. In the present edition the special sections on embryology and histology have been distributed among the subjects under which they naturally belong. New matter on physiological anatomy, laws of bone architecture, the mechanics and variations of muscles have been added, occupying much of the space formerly devoted to the sections on applied anatomy. The sections on the ductless glands and the nervous system have been largely rewritten. In the latter a more rational presentation of the sympathetic nervous system has been achieved through the use of diagrams and descriptions based on physiological and pharmacological work. The central connections of the spinal and cranial nerves are also emphasized. Illustrations have been added wherever important points could be made more clear, and throughout the work colored pictures have been even more extensively used than heretofore. In this respect special mention might be made of the central nervous system and the section on the muscles. In the section on Syndesmolog}" six illustrations are used from Quain's Anatomy through the courtesy of the publishers, Messrs. Longmans, Green & Company, of London. The use of the B. N. A. nomenclature in English has been retained practically unchanged in this edition and important references to the literature have been added at the end of each section. As a practical work on the subject for the student, Gray's Anatomy has always been recognized and appreciated. The plan originally formulated, which has proved so successful, has been adhered to as much as possible. It is interesting to note that although Henry Gray saw only the first edition, much of the original text persists and many of his illustrations are still in use. Bearing this in mind it has been the endeavor of the Editor to supply only such changes as advances in the science made necessary in order that this work may reflect the latest accessions to anatomical knowledge. W. H. L. Baltimore, 1918. CONTENTS. EMBRYOLOGY. The Animal Cell. Cytoplasm 35 Nucleus 36 Reproduction of Cells 36 Prophase 36 Metaphase • • 36 Anaphase ... 36 Telophase ... . . 38 The Ovum. The Primitive Segment . 52 Separation of the Embryo . 53 The Yolk-sac .... 54 Development of the Fetal Membranes and Placenta. Yolk . 39 Germinal Vesicle 40 ] The Decidua Coverings of the Ovum 40 The Chorion Maturation of the Ovum 40 The Placenta Fetal Portion The Spermatozoon The AUantois The Amnion The Umbilical Cord and Body-stalk . Implantation or Imbedding of the Ovum Fertilization of the Ovum Segmentation of the Fertilized Ovum. The Primitive Streak; Formation of the Mesoderm Maternal Portion .... Separation of the Placenta The Branchial Region. The Branchial or Visceral Arches and Pharyn- 54 56 57 58 59 60 62 62 63 64 _ _ 47 I geal Pouches 65 Ectoderm" 47 | The Nose and Face 67 Entoderm 49 The Limbs 71 Mesoderm 49 ^ , , , r. 7 ^ •. • to I Development of the Body Cavities . . 7J The Neural Groove and Tube . . 50 ^.„ c. I The Form of the Embryo at Different Stages The Notochord .... 52 i of its Growth .... 74 OSTEOLOGY. Long Bones 79 Short Bones 79 Flat Bones 79 Irregular Bones 80 Surfaces of Bones 80 Development of the Skeleton. The Skeleton 80 The Vertebral Column 80 The Ribs 82 The Sternum 83 The Skull 83 Bone. "Structure and Physical Properties ... 86 Periosteum 87 Marrow 87 Vessels and Nerves of Bone 88 Minute Anatomy 89 Chemical Composition 91 Ossification .......... 91 Intramembranous Ossification ... 91 Intercartilaginous Ossification ... 93 The Vertebral Column. General Characteristics of a Vertebra. The Cervical Vertebrae The First Cervical Vertebra . The Second Cervical Vertebra The Seventh Cervical Vertebra 97 99 100 101 The Thoracic Vertebra The First Thoracic Vertebra The Ninth Thoracic Vertebra The Tenth Thoracic Vertebra The Eleventh Thoracic Vertebra The Twelfth Thoracic Vertebra The Lumbar Vertebrae The Fifth Lumbar Vertebra . The Sacral and Coccygeal Vertebrae The Sacrum The Coccyx Ossification of the Vertebral Column The Vertebral Column as a Whole. Curves Surfaces . Vertebral Canal 102 104 104 104 104 104 104 106 106 106 111 111 114 114 116 The Thorax. Boundaries 117 The Sternuni 119 Manubrium 120 Body 120 Xiphoid Process 121 The Ribs . . 123 Common Characteristics of the Ribs . 123 Peculiar Ribs 125 First Rib 125 Second Rib 125 Tenth Rib 126 Eleventh and Twelfth Ribs . . 126 The Costal Cartilages 127 (9) 10 CONTENTS The Skull. The Cranial Bones. The Occipital Bone 129 The Squama 129 Lateral Parts 131 Basilar Parts 132 Angles 132 The Parietal Bone 133 The Frontal Bone 135 Squama 135 Orbital or Horizontal Part .... 137 The Temporal Bone 138 The Squama 139 Mastoid Portion 141 Petrous Portion 142 Tympanic Part 145 Styloid Process 145 The Sphenoid Bone 147 Body 147 The Great Wings 149 The Small AVings 151 Pterygoid Processes 151 The Sphenoidal Conchae . . . . . 152 Ethmoid bone 153 Cribriform plate 153 Perpendicular Plate 154 Labyrinth or Lateral Mass .... 154 Sutural or Wormian Bones 156 The Facial Bones. The Nasal Bones 156 The Maxillae (Upper Jaw) 157 The Maxillary Sinus or Antrum of High- more 160 The Zygomatic Process 161 The Frontal Process 161 The Alveolar Process 161 The Palatine Process 162 Changes Produced in the Maxilla by Age 163 The Lacrimal Bone 163 The Zygomatic Bone 164 The Palatine Bone 166 The Horizontal Part 167 The Vertical Part 167 The Pyramidal Process or Tuberosity . 168 The Orbital Process 168 The Sphenoidal Process 169 The Inferior Nasal Concha 169 The Vomer 170 The Mandible (Lower Jaw) . . . ' . . 172 Changes Produced in the Mandible by Age 175 The Hyoid Bone !!!!!!!! 177 The Exterior of the Skull. Norma Verticalis 178 Norma Basalis 179 Norma Lateralis 182 The Temporal Fossa 183 The Infratemporal Fossa . . .184 The Pterygopalatine Fossa . . . .185 Norma Occipitalis 185 Norma Frontalis 185 The Orbitf 188 The Interior of the Skull. Inner Surface of the Skull-cap . . .189 Under Surface of the Base of the Skull . 190 The Anterior Fossa 190 The Middle Fossa ...... 190 The Posterior Fossa 192 The Nasal Cavity 194 Anterior Nasal Aperture 196 Differences in the Skull Due to Age . 196 Sexual Differences in the Skull .... 197 Craniology 197 Thk Extremities. The Bones of the Upper Extremity. The The The The The Clavicle Lateral Third .... Medial Two-thirds The Sternal Extremity The Acromial Extremity . Scapula .... The Spine The Acromion .... The Coracoid Process Humerus Upper Extremity . The Head ... The Anatomical Neck The Greater Tubercle The Lesser Tubercle The Body or Shaft . The Lower Extremity Ulna The Upper Extremity The Olecranon The Coronoid Process The Semilunar Notch The Radial Notch . The Body or Shaft . . The Lower Extremity Radius The Upper Extremity The Body or Shaft . . The Lower Extremity 20011 200 201 202 202 202 203 203 207 209 209 209 209 209 209 209 212 214 214 214 214 215 215 215 218 219 219 219 220 The Hand. The Carpus 221 Common Characteristics of the Carpal Bones . 221 Bones of the Proximal Row .... 221 The Navicular Bone .... 221 The Lunate Bone 224 The Triangular Bone .... 224 The Pisiform Bone 225 Bones of the Distal Row .... 225 The Greater Multangular Bone 225 The Lesser Multangular Bone . . 225 The Capitate Bone 226 The Hamate Bone 227 The Metacarpus . . 227 Common Characteristics of the Meta- carpal Bones 227 Characteristics of the Individual Meta- carpal Bones 228 The First Metacarpal Bone . . 228 The Second Metacarpal Bone . . 228 The Third Metacarpal Bone . . 228 The Fourth Metacarpal Bone . 228 The Fifth Metacarpal Bone . . 228 The Phalanges of the Hand 230 Ossification of the Bones of the Hand . 230 The Bones of the Lower Extremity. The Hip Bone 231 The Ilium 231 The Body ....... 231 The Ala 232 The Ischium 234 The Body 234 The Superior Ramus .... 235 The Inferior Ramus 235 The Pubis 236 The Body 236 The Superior Ramus .... 236 The Inferior Ramus 237 The Acetabulum 237 The Obturator Foramen . . 237 The Pelvis 238 The Greater or False Pelvis .... 238 The Lesser or True Pelvis .... 239 Axes ... 240 Position of the Pelvis 241 Differences between Male and Female Pelves 241 Abnormalities 242 CONTENTS The Femur The Upper Extremity The Head The Neck The Trochanters The Body or Shaft The Lower Extremity The Architecture of the Femur . The Patella The Tibia The Upper Extremity The Body or Shaft The Lower Extremity The Fibula The Upper Extremity or Head . The Body or Shaft The Lower Extremity or Lateral Malleolus The Foot. The Tarsus . The Calcaneus 242 243 243 243 244 246 247 248 255 256 256 257 259 260 260 260 262 263 263 The Tarsus— ^^^^_ The Talus .... J^^^^ . 266 The Cuboid Bone . . . ^^^^. . 269 The Navicular Bone 270 The First Cuneiform Bone .... 270 The Second Cuneiform Bone . . . 271 The Third Cuneiform Bone . . . .271 The Metatarsus 272 Common Characteristics of the Meta- tarsal Bones . . . . . . . 272 Characteristics of the Individual Meta- tarsal Bones 272 The First Metatarsal Bone . . . 272 The Second Metatarsal Bone . . 273 The Third Metatarsal Bone . . 274 The Fourth Metatarsal Bone . . 274 The Fifth Metatarsal Bone . . 274 The Phalanges of the Foot 275 Ossification of the Bones of the Foot . ■ 275 Comparison of the Bones of the Hand and Foot 276 The Sesamoid Bones 277 SYNDESMOLOGY. Bone 279 Hyahne Cartilage 279 Articular Cartilage 280 Costal Cartilage . 281 White Fibrocartilage 281 Ihterarticular Fibrocartilages . . . 281 Connecting Fibrocartilages .... 282 Circumferential Fibrocartilages . . . 282 Stratiform Fibrocartilages .... 282 Ligaments 282 The Articular Capsules 282 Mucous Sheaths 283 Bursse Mucosae 283 Development of the Joints . . 283 Classification of Joints Synarthrosis 284 Sutura 284 Schindylesis 284 Gomphosis 284 Synchondrosis 284 Amphiarthrosis 285 Diathrosis 285 Ginglimus 285 Trochoid 285 Condyloid . . . _ . . . . _ . .286 Articulation by Reciprocal Reception . 286 Enarthrosis 286 Arthrodia 286 The Kind of Movement Admitted in Joints. Gliding Movement 286 Angular Movement 286 Circumduction 286 Rotation 287 Ligamentous Action of Muscles .... 287 I^V Articulations of the Thunk. I H Articulations of the Vertebral Column 287 I^L Articulations of Vertebral Bodies 287 I^H The Anterior Longitudinal Liga- l^t^ ment . ..287 I^^^^K The Posterior Longitudinal Liga- |^^H| ment 288 l^^^^r The Intervertebral Fibrocartilages 289 I^V Structure 289 1^^ Articulations of Vertebral Arches 289 I^^^K The Articular Capsules .... 290 I^^^B. The Ligamenta Flava .... 290 1^^^^^^^^ The Supraspinal Ligament . 290 Articulations of the Vertebral Column — Articulations of Vertebral Arches — The Ligamentum Nuchse . . . 290 The Interspinal Ligaments . . . 291 The Intertransverse Ligaments . 291 Articulation of the Atlas with the Epistro- pheus or Axis 292 The Articular Capsules 292 The Anterior Atlantoaxial Ligament . 293 The Posterior Atlantoaxial Ligament . 293 The Transverse Ligament of the Atlas . 293 Articulations of the Vertebral Column with the Cranium ....... 295 Articulation of the Atlas with the Occipital Bone 295 The Articular Capsules .... 295 The Anterior Atlantooccipital Mem- brane 295 The Posterior Atlantooccipital Mem- brane 296 The Lateral Ligaments .... 296 Ligaments Connecting the Axis with the Occipital Bone 296 The Membrana Tectoria . . . 296 The Alar Ligaments 296 Articulation of the Mandible 297 The Articular Capsule 297 The Temporomandibular Ligament . 297 The Sphenomandibular Ligament . . 297 The Articular Disk 298 The Stylomandibular Ligament . . 298 Costovertebral Articulations 299 Articulations of the Heads of the Ribs . 299 The Articular Capsule .... 299 The Radiate Ligament .... 299 The Interarticular Ligament . . 300 Costotransverse Articulations . . 300 The Articular Capsule .... 301 The Anterior Costotransverse Liga- ment 301 The Posterior Costotransverse Liga- ment 301 The Ligament of the Neck of the Rib 302 The Ligament of the Tubercle of the Rib 302 Sternocostal Articulations 302 The Articular Capsules . _ . . . . 302 The Radiate Sternocostal Ligaments . 302 The Interarticular Sternocostal Liga- ment 303 The Costoxiphoid Ligaments . . . 304' Interchondral Articulations .... 304 Costochondral Articulations .... 304 Articulation of the Manubrium and Body of the Sternum 304 Mechanism of the Thorax .... 304 12 CONTENTS Articulation of the Vertebral Column with the Pelvis 306 The Iliolumbar Ligament .... 306 Articulations of the Pelvis 306 Sacroiliac Articulation 306 The Anterior Sacroiliac Ligament . 307 The Posterior Sacroiliac Ligament. 307 The Interosseous Sacroiliac Liga- ment . 308 Ligaments Connecting the Sacrum and Ischium 309 The Sacrotuberous Ligament . 309 The Sacrospinous Ligament . . 309 Sacrococcygeal Symphysis .... 309 The Anterior Sacrococcygeal Liga- ment • . . 309 The Posterior Sacrococcygeal Liga- ment 309 The Lateral Sacrococcygeal Liga- ment 310 The Interarticular Ligaments . . 310 The Pubic Symphysis 310 The Anterior Pubic Ligament . . 310 The Posterior Pubic Ligament . . 310 The Superior Pubic Ligament . . 310 The Arcuate Pubic Ligament . 310 The Interpubic Fribrocartilaginous Lamina 311 Mechanism of the Pelvis 311 Articulations of the Upper Extremity. Sternoclavicular Articulation 313 The Articular Capsule 313 The Anterior Sternoclavicular Ligament 313 The Posterior Sternoclavicular Liga- ment 313 The Interclavicular Ligament . . . 314 The Costoclavicular Ligament . . .314 The Articular Disk 314 Acromioclavicular Articulation . . 315 The Articular Capsule 315 The Superior Acromioclavicular Liga- ment 315 The Inferior Acromioclavicular Liga- ment 315 The Articular Disk 315 The Coracoclavicular Ligament . . . 315 The Trapezoid Ligament . . . .315 The Conoid Ligament 315 The Ligaments of the Scapula . . 316 The Coracoacromial Ligament . . . 316 The Superior Transverse Ligament . . 317 The Inferior Transverse Ligament . . 317 Humeral Articulation or Shoulder-joint . . 317 The Articular Capsule 317 The Coracohumeral Ligament . . . 318 Glenohumeral Ligaments . . . . 318 The Transverse Humeral Ligament . 319 The Glenoidal Labrum 319 Bursae 319 Elbow-joint 321 The Anterior Ligament 321 The Posterior Ligament 322 The Ulnar Collateral Ligament . . . 322 The Radial Collateral Ligament . . 322 Radioulnar Articulation 324 Proximal Radioulnar Artifculation . . 324 The Annular Ligament .... 324 Middle Radioulnar Union .... 325 The Oblique Cord 325 The Interosseous Membrane . . 325 Distal Radioulnar Articulation . . . 325 The Volar Radioulnar Ligament . 325 The Dorsal Radioulnar Ligament . 325 The Articular Disk 325 Radiocarpal Articulation or Wrist-joint . . 327 The Volar Radiocarpal Ligament . . 327 The Dorsal Radiocarpal Ligament . . 328 The Ulnar Collateral Ligament . . 328 The Radial Collateral Ligament . 328 Intercarpal Articulations 328 Articulations of the Proximal Row of Carpal Bones 328 Intercarpal Articulations — Articulations of the Proximal Row of Carpa Bones — The Dorsal Ligaments . The Volar Ligaments The Interosseous Ligaments Articulations of the Distal Row of Carpal Bones The Dorsal Ligaments . The Volar Ligaments The Interosseous Ligaments Articulations of the Two Rows of Carpal Bones with Each Other The Volar Ligaments The Dorsal Ligaments . The Collateral Ligaments . Carpometacarpal Articulations Carpometacarpal Articulation of the Thumb Articulations of the Other Four Meta carpal Bones with the Carpus The Dorsal Ligaments . The Volar Ligaments The Interosseous Ligaments Intermetacarpal Articulations The Transverse Metacarpal Ligament Metacarpophalangeal Articulations . The Volar Ligaments The Collateral Ligaments Articulations of the Digits .... 328 328 328 329 329 329 329 329 329 329 329 330 330 331 331 331 331 331 331 332 332 332 333 Articulations of the Lower Extremity. Coxal Articulation or Hip-joint . The Articular Capsule .... The Iliofemoral Ligament The Pubocapsular Ligament The Ischiocapsular Ligament The Ligamentum Teres Femoris The Glenoidal Labrum .... The Transverse Acetabular Ligament The Knee-joint The Articular Capsule .... The Ligamentum Patellae The Oblique Popliteal Ligament 'The Tibial Collateral Ligament . The Fibular Collateral Ligament The Cruciate Ligaments .... The Anterior Cruciate Ligament The Posterior Cruciate Ligament The Menisci The Medial Meniscus The Lateral Meniscus The Transverse Ligament The Coronarj' Ligaments Bursae Articulations between the Tibia and Tibiofibular Articulation The Articular Capsule . The Anterior Ligament . The Posterior Ligament Interosseous Membrane . Tibiofibular Syndesmosis The Anterior Ligament . The Posterior Ligament The Inferior Transverse Ligament The Interosseous Ligament Talocrural Articulation or Ankle-joint . The Articular Capsule .... The Deltoid Ligament .... The Anterior Talofibular Ligament The Posterior Talofibular Ligament The Calcaneofibular Ligament . Intertarsal Articulations Talocalcaneal Articulation The Articular Capsule . The Anterior Talocalcaneal Liga ment The Posterior Talocalcaneal Liga ment The Lateral Talocalcaneal Liga ment The Medial Talocalcaneal Liga ment 333 334 335 335 335 336 336 336 339 340 340 340 341 341 342 342 342 342 343 343 343 343 345 347 348 348 348 348 348 348 348 348 349 349 349 350 350 351 351 351 352 352 352 352 352 352 353 CONTENTS 13 Intertarsal Articulations — Talocalcaneal Articulation — The Interosseous Talocalcaneal Ligament Talocalcaneonavicular Articulation . The Articular Capsule . The Dorsal Talonavicular Ligamen Calcaneocuboid Articulation The Articular Capsule . TheDorsalCalcaneocuboidLigament The Bifurcated Ligament The Long Plantar Ligament The Plantar Calcaneocuboid Liga ment The Ligaments Connecting the Calca neus and Navicular The Plantar Calcaneonavicular Ligament Cuneonavicular Articulation The Dorsal Ligaments . The Plantar Ligaments . Cuboideonavicular Articulation . The Dorsal Ligament 353 353 354 354 354 354 354 354 354 354 355 355 356 356 356 356 357 Intertarsal Articulations — Cuboideonavicular Articulation — The Plantar Ligament .... 357 The Interosseous Ligament . . 357 Intercuneiform and Cuneocuboid Articu- lation 357 The Dorsal Ligaments .... 357 The Plantar Ligaments .... 357 The Interosseous Ligaments . . 357 Tarsometatarsal Articulations .... 358 The Dorsal Ligaments 358 The Plantar Ligaments 358 The Interosseous Ligaments .... 358 Intermetatarsal Articulations 358 The Dorsal Ligaments 358 The Plantar Ligaments 358 The Interosseous Ligaments .... 358 The Transverse Metatarsal Ligament . 359 Metatarsophalangeal Articulations . . . 359 The Plantar Ligaments 359 The Collateral Ligaments .... 359 Articulations of the Digits 359 Arches of the Foot 360 MYOLOGY. Mechanics of Muscle. The Direction of Muscle Pull . . The Action of Muscle Pull on Tendon The Strength of Muscles .... The Work Accomplished by Muscles The Action of Muscles on Joints 363 364 364 365 368 Development of the Muscles. The Ventro-lateral Muscles of the Neck . . 371 Muscles of the Shoulder Girdle and Arm . 371 The Muscles of the Leg 372 The Muscles of the Head 372 Striped or Voluntary Muscle 373 _ ^ Vessels and Nerves of Striped Muscle . . 376 ■ H Tendons, Aponeuroses, and Fascia. ■ H Tendons 376 ■ H Aponeuroses 376 ■ ■ Fasciaj 376 I ^^^^ The Fascia and Muscles of the Head. ■ ^^HB The Muscles of the Scalp. The Skin of the Scalp 378 The Superficial Fascia 378 Epicranius 378 Occipitalis 379 Frontalis 379 Galea Aponeurotica 380 The Muscles of the Eyelid. Orbicularis Oculi 380 Corrugator 381 The Muscles of the Nose. Procerus ... 382 Nasalis 382 Depressor Septi . . 382 Dilator Naris Posterior 382 Dilator Naris Anterior 382 The Muscles of the Mouth. Quadratus Labii SuperioriD 383 Caninus 383 Zygomaticus 383 t: Quadratus Labii Inferioris 383 Triangularis 383 Buccinator 384 Pterygomandibular Raph6 .... 384 Orbicularis Oris 384 Risorius 385 The Muscles of Mastication. Parotideomasseteric Fascia 385 Masseter 385 Temporal Fascia 386 Temporalis 386 Pterygoideus Externus 386 Pterygoideus Internus 387 The Fascia and Muscles of the Antero- lateral Region of the Neck. The Superficial Cervical Muscle. Superficial Fascia 387 Platysma 388 Variations 388 The Lateral Cervical Muscles. The Fascia Colli 388 Sternocleidomastoideus 390 Variations 390 Triangles of the Neck 390 The Supra- and Infrahyoid Muscles. Digastricus 391 Variations 391 Stylohyoideus 392 Variations 392 The Stylohyoid Ligament .... 392 Mylohyoideus 393 Variations 393 Geniohyoideus 393 Sternohyoideus 393 Variations 393 Sternothyreoideus 393 Variations 394 Thyreohyoideus 394 Omohyoideus 394 Variations 394 The Anterior Vertebral Muscles. Longus Colli 394 Longus Capitis 395 Rectus Capitis Anterior 395 Rectus Capitis Lateralis 395 14 CONTENTS The Lateral Vertebral Muscles. Scalenus Anterior 396 Scalenus Medius 396 Scalenus Posterior 396 Variations 396 The Fasci.e and Muscles of the Thunk. The Deep Muscles of the Back. The Lumbodorsal Fascia 397 Splenius Capitis 397 Splenius Cervicis 397 Variations 397 Sacrospinalis 397 Iliocostalis Lumborum 399 Iliocostalis Dorsi 399 Iliocostalis Cervicis 399 Longissimus Dorsi 399 Longissimus Cervicis 399 Longissimus Capitis 399 Spinalis Dorsi 399 Spinalis Cervicis 400 Spinalis Capitis 400 Semispinalis Dorsi 400 Semispinalis Cervicis 400 Semispinalis Capitis 400 Multifidus 400 Rotatores 400 Interspinales 400 Extensor Coccygis 401 Intertransversarii 401 The Suboccipital Muscles. Rectus Capitis Posterior Major Rectus Capitis Posterior Minor Obliquus Capitis Inferior . Obliquus Capitis Superior . The Suboccipital Triangle 401 401 402 402 402 The Muscles of the Thorax. Intercostal Fascia 402 Intercostales 403 Intercostales Externi 403 Variations 403 Intercostales Interni 403 Subcostales 403 Transversus Thoracis 403 Levatores Costarum 403 Serratus Posterior Superior 404 Variations 404 Serratus Posterior Inferior 404 Variations 404 Diaphragm 404 Medial Lumbocostal Arch .... 404 Lateral Lumbocostal Arch .... 405 The Crura 405 The Central Tendon 406 Openings in the Diaphragm . . . 406 Variations 406 Mechanism of Respiration 407 The Muscles and Fascice of the Abdomen. The Antero-lateral Muscles of the Abdomen 408 The Superficial Fascia 408 Obliquus Externus Abdominis . . 409 Aponeurosis of the Obliquus Externus Abdominis . . 410 Subcutaneous Inguinal Ring . 410 The Intercrural Fibers . 410 The Inguinal Ligament . 411 The Lacunar Ligament . . 412 The Reflected Inguinal Liga- ment 412 Ligament of Cooper . 412 Variations 412 Obliquus Internus Abdominis 412 Variations 414 Cremaster . . 414 Transversus Abdominis ... 414 The Antero-lateral Muscles of the Abdomen — Transversus Abdominis — Variations 414 Inguinal Aponeurotic Falx . . . 414 Rectus Abdominis 415 Pyramidalis 416 Variations 417 The Linea Alba 417 The Lineae Semilunares 417 The Transversalis Fascia .... 418 The Abdominal Inguinal Ring . 418 The Inguinal Canal 418 Extraperitoneal Connective Tissue . 418 The Deep Crural Arch 419 The Posterior Muscles of the Abdomen . 419 The Fascia Covering the Quadratus Lumborum 419 Quadratus Lumborum 420 Variations 420 The Muscles and Fascice of the Pelvis. Pelvic Fascia 420 Levator Ani 422 Coccygeus 424 The Muscles and Fascice' of the Perineum. Muscles of the Anal Region 424 The Superficial Fascia 424 The Deep Fascia 425 Ischiorectal Fossa 425 The Corrugator Cutis Ani .... 425 Sphincter Ani Externus 425 Sphincter Ani Internus . . 426 The Muscles of the Urogenital Region in the Male 426 Superficial Fascia 426 The Central Tendinous Point of the Perineum 427 Transversus Perinsei Superficialis . . 427 Variations 427 Bulbocavernosus 428 Ischiocavernosus 428 The Deep Fascia 428 Transversus Perinsei Profundus . . 429 Sphincter Urethrae Membranacese . . 429 The Muscles of the Urogenital Region in the Female 430 Transversus Perinsei Superficialis . . 43o Bulbocavernosus 43Q Ischiocavernosus 430 Transversus Perincei Profundus . 431 The Fascia and Muscles of the Upper Extremity. The Muscles Connecting the Upper Extremity to the Vertebral Column. Superficial Fascia 432 Deep Fascia . 432 Trapezius 432 Variations 432 Latissimus Dorsi 432 Variations 434 Rhomboideus Major 434 Rhomboideus Minor 434 Variations 435 Levator scapulae 435 Variations 435 The Muscles Connecting the Upper Extremity to the Anterior and Lateral Thoracic Walls. Superficial Fascia 435 Pectoralis Major 436 Variations 437 Coracoclavicular Fascia 437 Pectoralis Minor 438 Variations 438 Subclavius 438 Variations 438 Serratus Anterior 438 Variations 439- CONTENTS 15 The Muscles and Fascice of the Shoulder. Deep Fascia 439 Deltoideus 439 Variations 440 Subscapular Fascia 440 Subscapularis ' . 440 Supraspinatous Fascia 440 Supraspinatus . 440 Infraspinatous Fascia 441 Infraspinatus 441 Teres Minor 441 Variations 442 Teres Major 442 The Muscles and Fasciae of the Arm. Brachial Fascia 442 Coracobrachialis 443 Variations 443 Biceps Brachii . 443 Variations 444 Brachialis 444 Variations^ 444 Triceps Brachii 444 Variations 445 The Muscles and Fascia of the Forearm. Antibrachial Fascia 445 The Volar Antibrachial Muscles .... 445 The Superficial Group . . . . . 446 Pronator Teres 446 Variations 446 Flexor Carpi Radialis .... 446 Variations 446 Palmaris Longus 446 Variations 446 Flexor Carpi Ulnaris .... 447 Variations 447 Flexor Digitorum Sublimis . 448 Variations 448 The Deep Group 448 Flexor Digitorum Profundus . 448 Fibrous Sheaths of the Flexor Tendons 448 Variations 449 Flexor Pollicis Longus .... 449 Variations 449 Pronator Quadratus 449 Variations 450 The Dorsal Antibrachial Muscles. .451 The Superficial Group 451 Brachioradialis 451 Variations 451 Extensor Carpi Radialis Longus 452 Extensor Carpi Radialis Brevis . 452 Variations . . . . . . 452 Extensor Digitorum Communis . 452 Variations 454 Extensor Digiti Quinti Proprius . 454 Variations 454 Extensor Carpi Ulnaris .... 454 Variations 454 Anconseus 454 The Deep Group 454 Supinator 454 Abductor Pollicis Longus 455 Variations 455 Extensor Pollicis Brevis . . . 455 Variations 455 Extensor Pollicis Longus . . . 455 Extensor Indicis Proprius . 456 Variations 456 The Muscles and Fascia; of the Hand. Volar Carpal Ligament 456 Transverse Carpal Ligament 456 The Mucous Sheaths of the Tendons on the Front of the Wrist 457 Dorsal Carpal Ligament 458 The Mucous Sheaths of the Tendons on the Back of the Wrist . 459 Palmar Aponeurosis 460 Superficial Transverse Ligament of the Fingers 461 The Lateral Volar Muscles 461 Abductor Pollicis Brevis 461 Opponens Pollicis 461 Flexor Pollicis Brevis 461 Adductor Pollicis (Obliquus) ... 462 Adductor Pollicis (Transversus) 462 Variations 462 The Medial Volar Muscles 462 Palmaris Brevis 463 Abductor Digiti Quinti 463 Flexor Digiti Quinti Brevis .... 464 Opponens Digiti Quinti 464 Variations 464 The Intermediate Muscles 464 Lumbricales 464 Variations 464 Interossei 464 Interossei Dorsales 464 Interossei Volares 465 The Muscles and Fasci.*; of the Lower Extremity. The Muscles and Fascice of the Iliac Region. The Fascia Covering the Psoas and Iliacus 466 Psoas Major 467 Psoas Minor 467 Iliacus 467 Variations 467 The Muscles and Fascice of the Thigh. The Anterior Femoral Muscles .... 467 Superficial Fascia 468 Deep Fascia 468 The Fossa Ovalis 469 Sartorius 470 Variations 470 Quadriceps Femoris 470 Rectus Femoris 470 Vastus Lateralis 470 Vastus Medialis 471 Vastus Intermedius 471 Articularis Genu 471 The Medial Femoral Muscles .... 471 Gracilis 471 Pectineus 472 Adductor Longus 472 Adductor Brevis 473 Adductor Magnus 473 Variations 474 The Muscles of the Gluteal Region . . . 474 Gluteus Maximus 474 Bursae 474 Glutaeus Medius 474 Variations 475 Glutseus Minimus 475 Variations 475 Piriformis 476 Variations 476 Tensor Fasciae Latae 476 Obturator Membrane 477 Obturator Internus 477 Gemelli 477 Gemellus Superior 477 Gemellus Inferior 477 Quadratus Femoris 477 Obturator Externus 477 The Posterior Femoral Muscles .... 478 Biceps Femoris 478 Variations 479 Semitendinosus 479 Semimembranosus .... . 479 Variations .... 479 The Muscles and Fascice of the Leg. The Anterior Crural Muscles 480 Deep Fascia 480 Tibialis Anterior 480 Variations 480 16 CONTENTS The Anterior Crural Muscles — Extensor Hallucis Longus . . . .481' Variations 481 Extensor Digitorum Longus .... 481 Variations 482 PeroniEus Tertius 482 The Posterior Crural Muscles .... 482 The Superficial Group 482 Gastrocnemius ..... 482 Variations 483 Soleus 483 Variations 483 Tendo Calcaneus 483 Plantaris 483 The Deep Group 483 Deep Transverse Fascia . . . 483 Popliteus 484 Variations 485 Flexor Hallucis Longus .... 485 Variations 485 Flexor Digitorum Longus . . . 485 Variations 485 Tibialis Posterior 485 The Lateral Crural Muscles 486 Peronseus Longus 486 Peronseus Brevis 486 Variations 487 The Fascia Around the Ankle. Transverse Crural Ligament 488 Cruciate Crural Ligament 488 Laciniate Ligament , 489 Peroneal Retinacula 489 The Mucous Sheaths of the Tendons Around the Ankle The Muscles and Fasciae of the Foot. I 489 The Dorsal Muscle of the Foot .... 490 Extensor Digitorum Brevis .... 490 Variations 490 The Plantar Muscles of the Foot . . . 490 Plantar Aponeurosis 490 The First Layer 491 Abductor Hallucis 491 Variations 491 Flexor Digitorum Brevis . . .491 Variations 492 Fibrous Sheaths of the Flexor Tendons 492 Abductor Digiti Quinti .... 492 Variations 492 The Second Layer 493 Quadratus Plantse 493 Variations 493 Lumbricales 493 Variations 493 The Third Layer 493 Flexor Hallucis Brevis .... 493 Variations 493 Adductor Hallucis 493 Variations 494 Flexor Digiti Quinti Brevis . . 494 The Fourth Layer 495 Interossei 495 Interossei Dorsales .... 495 Interossei Plantares . . . 495 ANGIOLOGY. Structure of Arteries 498 Capillaries 499 Sinusoids 501 Structure of Veins 591 The Blood. General Composition of the Blood . . 503 Blood Corpuscles 503 Colored or Red Corpuscles . . . 503 Colorless Corpuscles or Leukocytes 504 Development of the Vascular System. Further Development of the Heart . . . 508 The Valves of the Heart 514 Further Development of the Arteries . 515 The Anterior Ventral Aortae . . . 516 The Aortic Arches 516 The Dorsal Aortse 517 Further Development of the Veins . . . 518 The Visceral Veins 518 The Parietal Veins 520 Inferior Vena Cava 520 Venous Sinuses of the Dura Mater . . 522 The Thoracic Cavity. The Cavity of the Thorax 524 The Upper Opening of the Thorax . . . 524 The Lower Opening of the Thorax . 524 The Pericardium. Structure of the Pericardium 525 The Heart. Size 526 Component Parts 526 Right Atrium 628 Sinus Venarum 628 Auricula 628 Right Ventricle 631 Left Atrium 633 Auricula 533 Left Ventricle 635 Ventricular Septum 535 Structure of the Heart ...... 535 The Cardiac Cycle and the Actions of the Valves 538 Peculiarities in the Vascular System in the Fetus. Fetal Circulation 540 Changes in the Vascular System at Birth . 542 THE ARTERIES. The Pulmonar Relations yA rtery . 543 . 545 The Aorta. The Ascending Aorta. Relations . 546 Branches . 646 Branches of the Ascending Aorta — The Coronary Arteries 546 Right Coronary Artery .... 546 Left Coronary Artery .... 547 Peculiarities 547 The Arch of the Aorta. Relations 547 Peculiarities 548 CONTENTS 17 Branches 548 Peculiarities 548 The Innominate Artery 548 Relations 548 Branches 549 Thyreoidea Ima 549 Collateral Circxilation 549 The Arteries of the Head and Neck. The Common Carotid Artery. Relations 549 Peculiarities 551 Collateral Circulation 551 The External Carotid Artery 551 Relations 552 Branches 552 Superior Thyroid Artery . . . 552 Relations 552 Branches 552 Lingual Artery 553 Relations 553 Branches 553 External Maxillary Artery . . 553 Relations 554 Branches 554 Peculiarities 556 Occipital Artery 556 Course and Relations . 556 Branches 556 Posterior Auricular Artery . 557 Branches 557 Ascending Pharj-ngeal Artery . . 557 Branches 558 Superficial Temporal Artery 558 Relations 558 Branches 558 Internal Maxillary Artery . 559 Branches 560 The Triangles of the Neck 562 Anterior Triangle 563 Inferior Carotid or Muscular Tri- angle 563 Superior Carotid or Carotid Tri- angle 564 Submaxillary or Digastric Tri- angle 564 Suprahyoid Triangle .... 565 Posterior Triangle 565 Occipital Triangle 565 Subclavian Triangle 565 The Internal Carotid Artery 566 Course and Relations 567 Cervical Portion 567 Petrous Portion 567 Cavernous Portion 567 Cerebral Portion 567 Peculiarities 567 Branches _ 568 Caroticotympanic 568 Artery of the Pterygoid Canal . 568 Cavernous 568 Hypophyseal 568 Semilunar 568 Anterior Meningeal 568 Ophthalmic artery 568 Branches 568 Anterior Cerebral Artery . . 571 Branches 571 Middle Cerebral Artery . . 572 Branches 573 Posterior Communicating Artery . 573 Anterior Choroidal Artery . . 574 The Arteries of the Brain. The Ganglionic System The Cortical Arterial System 2 575 575 The Arteries of the Upper Extremity. The Subclavian Artery, First Part of the Right Subcla\'ian Artery . 576 Relations 576 First Part of the Left Subclavian Artery . 577 Relations 577 Second and Third Parts of the Subclavian Artery 577 Relations 577 Relations 577 Peculiarities 577 Collateral Circulation 578 Branches 578 Vertebral Artery 578 Relations 578 Branches ........ 579 Thyrocer\acal Trunk . . . . 581 Branches 581 Peculiarities 583 Internal Mammarj' Artery .... 584 Relations 584 Branches 584 The Costocervical Trunk .... 585 The Axilla. Boundaries 585 Contents 686 The Axillary Artery 586 Relations 586 Collateral Circulation 587 Branches 587 The Highest Thoracic Artery . 587 The Thoracoacromial Artery . 588 The Lateral Thoracic Artery . 588 The Subscapular Artery . . . 588 The Posterior Humeral Circumflex Artery 589 The Anterior Humeral Circumflex Artery 589 Peculiarities 589 The Brachial Artery 589 Relations 589 The Anticubital Fossa 589 Peculiarities 690 Collateral Circulation 690 Branches 690 The Arteria Profunda Brachii . 591 The Nutrient Artery . . . .591 The Superior Ulnar Collateral Artery 591 The Inferior Ulnar Collateral Artery 592 Muscular Branches 592 The Anastomosis Around the Elbow-joint 592 The Radial Artery 592 Relations 592 Peculiarities 594 Branches 594 Radial Recurrent Artery . . . 594 Muscular 594 Volar Carpal 594 Superficial Volar 594 Dorsal Carpal . . . . . 694 Arteria Princeps PoUicis . . . 595 Arteria Volaris Indicis Radialis . 595 Deep Volar Arch 595 Volar Metacarpal Arteries . 696 Perforating 595 Recurrent 596 The Ulnar Artery 595 Relations 595 Peculiarities 596 Branches 696 Anterior Ulnar Recurrent Artery . 596 Posterior Ulnar Recurrent Artery . 596 Common Interosseous Artery . . 596 Muscular 598 Volar Carpal 698 Dorsal Carpal 698 Deep Volar 598 Superficial Volar 598 Relations 598 18 CONTENTS The Arteries of the Trunk. The Descending Aorta. The Thoracic Aorta 598 Relations 599 Peculiarities 599 Branches 600 Pericardial 600 Bronchial 600 Esophageal 600 Mediastinal 600 Intercostal Arteries 600 Branches ... . 601 Subcostal Arteries 601 Superior Phrenic 601 The Abdominal Aorta 602 Relations 603 Collateral Circulation 603 Branches 603 The Celiac Artery 603 Relations 603 The Superior Mesenteric Artery . 606 Branches 607 The Inferior Mesenteric Artery . 609 Branches 610 The Middle Suprarenal Arteries . 610 The Renal Arteries 610 The Internal Spermatic Arteries . 611 The Ovarian Arteries . . . .611 The Inferior Phrenic Arteries . . 612 The Lumbar Arteries .... 612 The Middle Sacral Artery ... 613 The Cominon Iliac Arteries. Peculiarities 614 Collateral Circulation 614 The Hypogastric Artery 614 Relations 614 Peculiarities 615 Collateral Circulation 615 Branches 615 Superior Vesical Arterj' . . . .615 Middle Vesical Artery .... 615 Inferior Vesical Artery .... 615 Middle Hemorrhoidal Artery . . 615 Uterine Artery 615 Vaginal Artery 616 Obturator Artery 616 Branches 616 Peculiarities ...... 617 Internal Pudendal Artery- . . . 617 Relations 618 Peculiarities 618 Branches 618 Inferior Gluteal Arterj- .... 620 Branches 620 Lateral Sacral Arteries . . . .621 Superior Gluteal Artery . . . 622 The External Iliac Artery 622 Relations 622 Collateral Circulation 622 Branches 622 Inferior Epigastric Artery . . . 623 Branches 623 Peculiarities 623 Deep Iliac Circumflex Artery . . 623 The Arteries of the Lower Extremity. The Femoral Artery. The Femoral Sheath 6251 The Femoral Triangle 628i The Adductor Canal 627 Relations of the Femoral Artery .... 627 Peculiarities of the Femoral Artery . . . 629 Collateral Circulation 629 Branches 629 Superficial Epigastric Artery . 629 Superficial Iliac Circumflex Artery . . 629 Superficial External Pudendal Artery . 629 Deep External Pudendal Artery . 629 Muscular . 629 Profunda Femoris Artery .... 629 Relations 630 Peculiarities 630jb!^^ Branches . 63(«l|^| Highest Genicular Artery .... 631^fff3B The Popliteal Fo.ssa 031 Boundaries 631 Contents 632 The Popliteal Artery 632 Relations 632 Peculiarities ....... 633 Branches 633 Superior Muscular 633 Sural Arteries 633 Cutaneous Branches .... 633 Superior Genicular Arteries . 633 Middle Genicular Artery . 033 Inferior Genicular Arteries . . 633 The Anastomosis Around the Knee- joint . . 634 The Anterior Tibial Artery 634 Relations 635 Peculiarities 635 Branches 635 Posterior Tibial Recurrent Artery . 635 Fibular Artery 635 Anterior Tibial Recurrent Arterj- . 635 Muscular Branches 635 Anterior Medial Malleolar Artery . 035 Anterior Lateral Malleolar Arterv . 635 The Arteria Dorsalis Pedis . . . . " . 636 Relations 636 Peculiarities 636 Branches 637 Lateral Tarsal Artery .... 637 Medial Tarsal Artery .... 637 Arcuate Artery 637 Deep Plantar Arterj- .... 637 The Posterior Tibial Artery 637 Relations 637 Peculiarities 638 Branches 638 Peroneal Artery 638 Peculiarities^ 638 Branches 638 Nutrient Artery 638 Muscular Branches 639 Posterior Medial Malleolar Artery 639 Communicating Branch .... 639 Medial Calcaneal 639 Medial Plantar Artery .... 039 Lateral Plantar Arterj .... 639 Branches 640 The Pulmonary Veins The Systemic Veins. THE VEINS. . 642 The Veins of the Heart. Coronary Sinus 642 Tributaries 642 The Veins of the Head and Neck. The Veins of the Exterior of the Head and Face 644 The Frontal Vein 644 The Veins of the Exterior of the Head and Face — The Supraorbital Vein 645 The Angular Vein 645 The Anterior Facial Vein 645 Tributaries .... 645 The Superficial Temporal Vein 645 Tributaries .... 645 The Pterygoid Plexus 645 The Internal Maxillary Vein . 646 The Posterior Facial Vein 646 The Posterior Auricular Vein 646 The Occipital Vein 646 CONTENTS 19 The Veins of the Neck The External Jugular Vein Tributaries The Posterior External Jugular Vein The Anterior Jugular Vein The Internal Jugular Vein Tributaries The Vertebral Vein Tributaries The Diploic Veins . The Veins of the Brain The Cerebral Veins The External Veins The Superior Cerebral Vein The Middle Cerebral Vein . The Inferior Cerebral Vein . The Internal Cerebral Veins The Great Cerebral Vein The Cerebellar Veins .... The Sinuses of the Dura Mater. Ophthalmic Veins and Emissary Veins The Superior Sagittal Sinus . The Inferior Sagittal Sinus . The Straight Sinus .... The Transverse Sinuses The Occipital Sinus .... The Confluence of the Sinuses The Cavernous Sinuses The Ophthalmic Veins The Superior Ophthalmic Vein The Inferior Ophthalmic Vein The Intercavernous Sinuses The Superior Petrosal Sinus The Inferior Petrosal Sinus The Basilar Plexus The Emissary Veins The The The The Veins of the Upper Extremity and Thorax. Superficial Veins of the Upper Extremity Digital Veins The Cephalic Vein .... The Accessory Cephalic Vein The Basilic Vein .... The Median Antibrachial Vein Deep Veins of the Upper Extremity Deep Veins of the Hand . Deep Veins of the Forearm The Brachial Veins The Axillary Vein The Subclavian Vein Tributaries Veins of the Thorax The Innominate Veins The Right Innominate Vein The Left Innominate Vein Tributaries .... Peculiarities The Internal Mammary Veins The Inferior Thyroid Veins . The Highest Intercostal Vein The Superior Vena Cava Relations The Azygos Vein .... Tributaries .... The Hemiazygos Veins 646 646 647 647 647 648 648 649 650 651 652 652 652 652 652 652 653 653 653 654 654 655 655 657 658 658 658 658 659 659 659 659 659 660 660 660 660 661 662 662 662 663 663 663 663 663 664 664 664 664 664 666 666 666 666 666 666 666 667 667 667 667 The Veins of the Thorax — The Azygos Vein — The Accessory Hemiazygos Veins 667 The Bronchial Veins 667 The Veins of the Vertebral Column . . . 667 The External Vertebral Venous Plexuses 668 The Internal Vertebral Venous Plexuses 668 The Basivertebral Veins 668 The Intervertebral Veins ... 669 Th« Veins of the Medulla Spinalis . 669 The Veins of the Lower Extremity, Abdomen, and Pelvis. The Superficial Veins of the Lower Extremity 669 The Dorsal Digital Veins 669 The Great Saphenous Vein .... 669 Tributaries 670 The Small Saphenous Vein .... 670 The Deep Veins of the Lower Extremity . 671 The Plantar Digital Veins .... 671 The Posterior Tibial Veins .... 672 The Anterior Tibial Veins .... 672 The Popliteal Vein 672 The Femoral Vein 672 The Deep Femoral Vein 672 The Veins of the Abdomen and Pelvis . 672 The External Iliac Vein 672 Tributaries 672 The Hypogastric Veins 673 Tributaries 673 The Hemorrhoidal Plexus .... 676- The Pudendal Plexus 676 The Vesical Plexus 676. The Dorsal Veins of the Penis . . . 676 The Uterine Plexuses 676 The Vaginal Plexuses 677 The Common Iliac Veins .... 677 The Middle Sacral Veins ... 677 Peculiarities 677 The Inferior Vena Cava 677 Relations 678 Peculiarities 678 Applied Anatomy 678 Tributaries 678 Lumbar Veins 678 Spermatic Veins .... 678 Ovarian Veins 679 Renal Veins 679 Suprarenal Veins .... 679 Inferior Phrenic Veins . . . 679 Hepatic Veins 680 The Portal System of Veins. The Portal Vein 681 Tributaries 681 The Lienal Vein 681 Tributaries 681 The Superior Mesenteric Vein . . 682 Tributaries 682 The Coronary Vein 682 The Pyloric Vein 682 The Cystic Vein 682 The Parumbilical Veins .... 682 THE LYMPHATIC SYSTEM. The Development of the Lymphatic Vessels Lymphatic Capillaries Distribution Lymphatic Vessels Structure of Lymphatic Vessels . . . . The Lymph Glands Structure of Lymph Glands . . . . Hemolymph Nodes Lymph The Thoracic Duct. The Cistema Chyli . . Tributaries The Right Lymphatic Duct Tributaries 683 684 684 687 687 688 688 690 690 691 691 691 692 The Lymphatics of the Head, Face, Neck. The Lymph Glands of the Head . The Occipital Glands . The Posterior Auricular Glands The Anterior Auricular Glands The Parotid Glands . . . The Facial Glands The Deep Facial Glands . The Lingual Glands The Retropharyngeal Glands The Lymphatic Vessels of the Scalp The Lymphatic Vessels of the Auricul and External Acoustic Meatus The Lymphatic Vessels of the Face 692 692 693 693 693 694 694 694 694 694 694 695 20 CONTENTS The Lymph Glands of the Head— The Lymphatic Vessels of the Nasal Cavities 695 The Lymphatic Vessels of the Mouth . 695 The Lymphatic Vessels of the Palatine Tonsil 695 The Lymphatic Vessels of the Tongue 696 The Lymph Glands of the Neck .... 697 The Submaxillary Glands .... 697 The Submental or Suprahyoid Glands . 697 The Superficial Cervical Glands . . ' . 697 The Anterior Cervical Glands . . 697 The Deep Cervical Glands . . . .697 The Lymphatic Vessels of the Skin and Muscles of the Neck 698 The Lymphatics of the Upper Extremity. The Lymph Glands of the Upper Extremity 699 The Superficial Lymph Glands . . . 699 The Deep Lymph Glands .... 699 The Axillary Glands .... 699 The Lymphatic Vessels of the Upper Extremity 700 The Superficial Lymphatic Vessels . . 700 The Deep Lymphatic Vessels . . 701 The Lymphatics of the Lower Extremity. The Lymph Glands of the Lower Extremity 701 The Anterior Tibial Gland .... 701 The Popliteal Glands 701 The Inguinal Glands 702 The Lymphatic Vessels of the Lower Extremity 703 The Superficial Lymphatic Vessels . 703 The Deep Lymphatic Vessels . 703 The Lymphatics of the Abdomen and Pelvis. The Lymph Glands of the Abdomen and Pelvis 703 The Parietal Glands 703 The External Iliac Glands ... 703 The Common Iliac Glands . . 704 The Epigastric Glands .... 704 The Iliac Circumflex Glands . . 704 The Hypogastric Glands . . . 704 The Sacral Glands 704 The Lumbar Glands .... 705 The Lymphatic Vessels of the Abdomen and Pelvis 706 The Superficial Vessels 706 The Deep Vessels 706 The Lymphatic Vessels of the Perineum and External Genitals 706 The Visceral Glands 706 706 706 706 709 709 709 709 710 The Gastric Glands . The Hepatic Glands The Pancreaticolienial Glands The Superior Mesenteric Glands The Mesenteric Glands . The Ileocolic Glands The Mesocolic Glands . The Inferior Mesenteric Glands The Lymphatic Vessels of the Abdominal and Pelvic Viscera 710 The Lymphatic Vessels of the Abdomina and Pelvic Viscera — The Lymphatic Vessels of the Subdia- phragmatic Portions of the Digestive Tube The Lymphatic Vessels of the Stomach 710 The Lymphatic Vessels of the Duodenum 710 The Lymphatic Vessels of the Jejunum _^^H and Ileum ^^41^1 The Lymphatic Vessels of the Vermiform !■ ^H Process and Cecum 710 The Lymphatic Vessels of the Colon . 711 The Lymphatic Vessels of the Anus, ^. ^^ Anal Canal, and Rectum .... ''^l^l^H The Lymphatic Vessels of the Liver ^^^^1^1 The Lymphatic Vessels of the Gall- ^B^H bladder '^^flH The Lymphatic Vessels of the Pancreas 71^H^H The Lymphatic Vessels of the Spleen and ^H^l Suprarenal Glands 7lU^B The Lymphatic Vessels of the Urinary Organs . 712 The Lymphatic Vessels of the Kidney 712 The Lymphatic Vessels of the Ureter 712 The Lymphatic Vessels of the Bladder 712 The Lymphatic Vessels of the Prostate 713 The Lymphatic Vessels of the Urethra 713 The Lymphatic Vessels of the Repro- ductive Organs 713 The Lymphatic Vessels of the Testes 713 The Lymphatic Vessels of the Ductus Deferens 713 The Lymphatic Vessels of the Ovary 714 The Lymphatic Vessels of the Uterine Tube 714 The Lymphatic Vessels of the Uterus 714 The Lymphatic Vessels of the Vagina 714 The Lymphatics of the Thorax. The Parietal Lymph Glands 715 The Sternal Glands 715 The Intercostal Glands 715 The Diaphragmatic Glands . . .715 The Superficial Lymphatic Vessels of the Thoracic Wall 715 The Lymphatic Vessels of the Mamma. 715 The Deep Lymphatic Vessels of the Thoracic Wall 716 The Visceral Lymph Glands . . .717 The Anterior Mediastinal Glands . . 717 The Posterior Mediastinal Glands . .717 The Tracheobronchial Glands . . . 717 The Lymphatic Vessels of the Thoracic Viscera 718 The Lymphatic Vessels of the Heart . 718 The Lymphatic Vessels of the Lungs . 718 The Lymphatic Vessels of the Pleura 719 The Lymphatic Vessels of the Thymus 719 The Lymphatic Vessels of the Eso- phagus 719 NEUROLOGY. Structure of the Nervous System. Neuroglia 722 Nerve Cells 722 Nerve Fibers 724 Wallerian Degeneration 727 Non-medullated Fibers 728 Structure of the Peripheral Nerves and Ganglia , .v • • • ' Z^^ Origins and Terminations of Nerves . . . 729 Ganglia Neuron Theory Fasciculi, Tracts or Fiber Systems 730 732 732 Development of the Nervous System. The Medulla Spinalis 733 The Spinal Nerves 735 The Brain 736 CONTENTS 21 The Brain — The Hind-brain or Rhombencephalon . 738 The Mid-brain or Mesencephalon . 741 The Fore-brain or Prosencephalon 741 The Diencephalon 742 The Telencephalon 743 The Commissures 746 Fissures and Sulci 747 The Cranial Nerves ". 748 The Spinal Cord or Medulla Spinalis. Enlargements 751 Fissures and Sulci 752 The Anterior Median Fissure 752 The Posterior Median Sulcus . 752 The Internal Structure of the Medulla Spinalis 753 The Gray Substance 753 Structure of the Gray Substance 755 The White Substance 758 Nerve Fasciculi 759 Roots of the Spinal Nerves 764 The Anterior Nerve Root .... 764 The Posterior Root 764 The Brain or Encephalon. General Considerations and Divisions 766 The Hind-brain or Rhombencephalon. The Medulla Oblongata 767 The Anterior Median Fissure . 767 The Posterior Median Fissure . . . 767 Internal Structure of the Medulla Oblongata 775 The Cerebrospinal Fasciculi 775 Gray Substance of the Medulla Oblongata 779 Inferior Peduncle 782 Formatio Reticularis .... 784 The Pons 785 Structure 785 The Cerebellum 788 Lobes of the Cerebellum 788 Internal Structure of the Cerebellum 791 The White Substance . . . .791 Projection Fibres .791 The Gray Substance .... 794 Microscopic Appearance of the Cortex 794 The Fourth Ventricle ....!!! 797 Angles 797 Lateral Boundaries 797 Choroid Plexuses 798 Openings in the Roof 798 Rhomboid Fossa 798 The Mid-brain or Mesencephalon. The Cerebral Peduncles 800 Structure of the Cerebral Peduncles . 801 The Gray Substance .... 802 The White Substance .... 803 The Corpora Quadrigemina 805 Structure of the Corpora Quadrigemina 806 The Cerebral Aqueduct 806 The Fore-brain or Prosencephalon. The Diencephalon 807 The Thalamencephalon 808 Structure 810 Connections 810 The Metathalamus 811 The Epithalamus 812 The Hypothalamus 812 The Optic Chiasma 814 The Optic Tracts 814 The Third Ventricle 815 The Interpeduncular Fossa . . . .816 The Telencephalon 817 The Cerebral Hemispheres 817 The Longitudinal Cerebral Fissure . 818 The Surfaces of the Cerebral Hemi- spheres 818 The Lateral Cerebral Fissure . . 819 The Central Sulcus 819 The Parietooccipital Fissure .... 820 The Calcarine Fissure 820 The Cingulate Sulcus 820 The Collateral Fissure 820 The Sulcus Circularis 821 The Lobes of the Hemispheres . . . 821 The Frontal Lobe 821 The Parietal Lobe 822 The Occipital Lobe 823 The Temporal Lobe 823 The Insula 825 The Limbic Lobe 825 The Rhinencephalon 826 The Olfactory Lobe ..... 826 The Interior of the Cerebral Hemi- spheres 827 The Corpus Callosum .... 828 The Lateral Ventricles .... 829 The Fornix 838 The Interventricular Foramen . 840 The Anterior Commissure . 840 The Septum Pellucidum .... 840 The Choroid Plexus of the Lateral Ventricle 840 Structure of the Cerebral Hemi- spheres ■. . 842 Structure of the Cerebral Cortex . 845 Special Types of Cerebral Cortex . . 847 Weight of Encephalon 848 Cerebral Localization 849 Composition and Central Connections of the Spinal Nerves. The Intrinsic Spinal Reflex Paths . . 850 Sensory Pathways from the Spinal Cord to the Brain 851 Composition and Central Connections of the Cranial Nerves. The Hypoglossal Nerve 855 The Accessory Nerve 855 The Vagus Nerve 855 The Glossopharyngeal Nerve 856 The Acoustic Nerve 857 The Vestibular Nerve 860 The Facial Nerve 861 The Abducens Nerve 861 The Trigeminal Nerve 862 The Trochlear Nerve . 863 The Oculomotor Nerve 863 The Optic Nerve 864 The Olfactory Nerves 866 Pathways from the Brain to the Spinal Cord. The Motor Tract 870 The Meninges of the Brain and Medulla Spinalis. The Dura Mater 872 The Cranial Dura Mater .... 872 Processes 873 Structure 875 The Spinal Dura Mater 875 Structure 876 The Arachnoid . 876 The Cranial Part 876 The Spinal Part 876 Structure 876 The Subarachnoid Cavity .... 876 The Subarachnoid Cistemse .... 876 The Arachnoid Villi 878 Structure 878 The Pia Mater 878 The Cranial Pia Mater 879 The Spinal Pia Mater 879 The Ligamentum Denticulatum . 880 22 CONTENTS The Cerebrospinal Fluid The Cranial Nerves. The Olfactory Nerves The Optic Nerve. The Optic Chiasma The Optic Tract The Oculomotor Nerve The Trochlear Nerve . The Trigeminal Nerve. The Semilunar Ganglion . The Ophthalmic Nerve The Lacrimal Nerve . The Frontal Nerve The Nasociliary Nerve The Ciliary Ganglion . The Maxillary Nerve . Branches .... The Middle Meningeal Nerve The Zygomatic Nerve . The Sphenopalatine . The Posterior Superior Alveolar The Middle Superior Alveolar The Anterior Superior Alveolar The Inferior Palpebral . The External Nasal . The Superior Labial The Sphenopalatine Ganglion The Mandibular Nerve .... Branches . . . The Nervus Spinosus The Internal Pterygoid Nerve The Masseteric Nerve . The Deep Temporal Nerves The Buccinator Nerve . The External Pterygoid Nerve The Auriculotemporal Nerve The Lingual Nerve . The Inferior Alveolar Nerve The Otic Ganglion . The Submaxillary Ganglion Trigeminal Nerve Reflexes The Abducent Nerve The Facial Nerve. 880 881 883 884 885 886 887 887 887 888 890 890 891 891 891 891 891 891 893 894 894 894 894 895 895 895 895 895 896 897 898 899 899 The Greater Superficial Petrosal Nerve . . 903 The Nerve to the Stapedius 904 The Chorda Tympani Nerve 904 The Posterior Auricular Nerve .... 905 The Digastric Branch 905 The Stylohyoid Branch 905 The Temporal Branches 905 The Zygomatic Branches 905 The Buccal Branches 905 The Mandibular Branch 905 The Cervical Branch 905 The Acoustic Nerve. The Cochlear Nerve 906 The Vestibular Nerve 906 The Ganglion Nodosum — The Meningeal Branch . The Auricular Branch The Pharyngeal Branch . The Superior Laryngeal Nerve The Recurrent Nerve The Superior Cardiac Branches The Inferior Cardiac Branches The Anterior Bronchial Branches The Posterior Bronchial Branches The Esophageal Branches The Gastric Branches The Celiac Branches The Hepatic Branches The Accessory Nerve, The Cranial Part The Spinal Part The Hypoglossal Nerve. The Glossopharyngeal Nerve. The Superior Ganglion .... The Petrous Ganglion The Tympanic Nerve The Carotid Branches The Pharyngeal Branches 908 908 909 909 909 The Muscular Branches 909 The Tonsillar Branches 909 The Lingual Branches 909 The Vagus Nerve. The Jugular Ganglion 911 The Ganglion Nodosum 911 Branches of Communication Branches of Distribution . The Meningeal Branches The Descending Ramus The Thyrohyoid Branch The Muscular Branches The Spinal Nerves. Nerve Roots The Anterior Root The Posterior Root The Spinal Ganglia Structure Connections -with Sympathetic . Structure Divisions of the Spinal Nerves .... The Posterior Divisions The Cervical Nerves .... The Thoracic Nerves .... The Lumbar Nerves .... The Sacral Nerves The Coccygeal Nerve .... The Anterior Divisions The Cervical Nerves .... The Cervical Plexus Great Auricular Nerve Cutaneous Cervical Nerve Supraclavicular Nerves . Communicantes Cervicales Phrenic Nerve .... The Brachial Plexus Relations Dorsal Scapular Nerve . Suprascapular Nerve . Nerve to Subclavius . Long Thoracic Nerve Anterior Thoracic Nerves Subscapular Nerves . Thoracodorsal Nerve . Axillary Nerve Musculocutaneous Nerve Medial Antibrachial Cuta- neous Nerve Medial Brachial Cuta- neous Nerve Median Nerve . Ulnar Nerve Radial Nerve . The Thoracic Nerves First Thoracic Nerve Upper Thoracic Nerves Lower Thoracic Nerves The Lumbosacral Plexus The Lumbar Nerves The Lumbar Plexus Iliohypogastric Nerve Ilioinguinal Nerve Genitofemoral Nerve Lateral Femoral Cuta- neous Nerve Obturator Nerve 911 911 911 912 912 912 912 913 913 913 913 913 913 913 913 915 916 916 916 916 916 916 916 916 917 917 920 920 921 921 921 923 924 924 925 925 925 925 926 927 928 928 928 930 931 932 932 933 933 933 933 934 934 935 937 937 938 939 943 944 945 945 948 948 948 949 950 952 953 953 953 CONTENTS 23 Divisions of the Spinal Nerves — The Anterior Divisions — The Lumbosacral Plexus — The Lumbar Nerves — The Lumbar Plexus — Accessory Obturator Nerve .... 955 Femoral Nerve . 955 Saphenous Nerve. 956 The Sacral and Coccygeal Nerves 957 The Sacral Ple.xus 957 Relations . 957 Nerve to Quadratus Femoris and Gemellus Inferior 957 Nerve to Obturator Internus and Ge- mellus Superior . 958 Nerve to Piriformis 959 Superior Gluteal Nerve .... 959 Inferior Gluteal Nerve .... 959 ; Posterior Femoral j Cutaneous Nerve 959 j Sciatic Nerve . . 960 Tibial Nerve . . 960 Lateral Plantar Nerve 963 Common Peroneal Nerve .... 964 Deep Peroneal Nerve 965 Superficial Peroneal Nerve .... 966 The Pudendal Plexus 966 Perforating Cuta- neous Nerve . . 967 Pudendal Nerve . 967 Anococcygeal Nerve 968 The Sympathetic Nerves. The Cranial Sympathetics 970 The Sacral Sympathetics 973 The Thoracolumbar Sympathetics . . . 974 The Sympathetic Trunks 976 Connections with the Spinal Nerves . 976 Development 977 The Cephalic Portion of the Sympathetic System. The Internal Carotid Plexus The Cavernous Plexus 977 978 The Cervical Portion of the Sympathetic System. The Superior Cervical Ganglion Branches The Middle Cervical Ganglion Branches The Inferior Cervical Ganglion Branches 978 978 979 979 980 981 The Thoracic Portion of the Sympathetic System. The Greater Splanchnic Nerve .... 981 The Lesser Splanchnic Nerve .... 981 The Lowest Splanchnic Nerve .... 981 The Abdominal Portion of the Sympathetic System .... 982 The Pelvic Portion of the Sympathetic System .... 984 The Great Plexuses of the Sympathetic System. The Cardiac Plexus 984 The Celiac Plexus 985 , Phrenic Plexus 985 * Hepatic Plexus 986 Lienal Plexus 986 Superior Gastric Plexus 987 Suprarenal Plexus 987 Renal Plexus 987 Spermatic Plexus 987 Superior Mesenteric Plexus . . . 987 Abdominal A^tic Plexus .... 987 Inferior Mesenteric Plexus .... 987 The Hypogastric Plexus 987 The Pelvic Plexuses 987 The Middle Hemorrhoidal Plexus . . 988 The Vesical Plexus 988 The Prostatic Plexus 988 The Vaginal Plexus 989 The Uterine Plexus 989 THE ORGANS OF THE SENSES AND THE COMMON INTEGUMENT. The Peripheral Organs of the Special Senses. The Organs of Taste. Structure 991 The Organ of Smell. The External Nose 992 Structure 992 The Nasal Cavity 994 The Lateral Wall 994 The Medial Wall 995 The Mucous Membrane .... 996 Structure 996 The Accessory Sinuses of the Nose . 998 The Frontal Sinuses 998 The Ethmoidal Air Cells .... 998 The Sphenoidal Sinuses 998 The Maxillary Sinus 999 The Organ of Sight. Development 1001 The Tunics of the Eye 1005 The Fibrous Tunic 1005 The Sclera 1005 Structure 1006 The Cornea 1006 Structure 1007 The Tunics of the Eye — The Vascular Tunic 1009 The Choroid 1009 Structure 1010 The Ciliary Body 1010 Structure 1011 The Iris 1012 Structure 1013 Membrana Pupillaris .... 1014 The Retina 1014 Structure 1015 The Refracting Media 1018 The Aqueous Humor 1018 The Vitreous Bodv 1018 The Crystalline Lens 1019 Structure 1020 The Accessory Organs of the Eye . 1021 The Ocular Muscles 1021 Levator PalpebrEe Superioris . 1021 The Recti 1022 Obliquus Oculi Superior . . . 1022 Obliquus Oculi Inferior . . . 1023 The Fascia Bulb 1024 The Orbital Fascia 1025 The Eyebrows 1025 The Eyelids 1025 The Lateral Palpebral Commis- sure 1025 The Eyelashes 1025 Structure of the Eyelids . . 1025 The Tarsal Glands 1026 24 CONTENTS The Accessory Organs of the Eye — Structure of the Tarsal Glands The Conjunctiva The Palpebral Portion The Bulbar Portion The Lacrimal Apparatus The Lacrimal Gland Structure The Lacrimal Ducts The Lacrimal Sac Structure The Nasolacrimal Duct The Organ of Hearing. 1026 1026 1027 1027 1028 1028 1028 1028 1028 1029 1029 Development 1029 The External Ear 1033 The Auricula or Pinna 1033 Structure 1034 The External Acoustic Meatus . . 1036 Relations 1037 The Middle Ear or Tympanic Cavity . . 1037 The Tegumental Wall or Roof . . . 1038 The Jugular Wall or Floor .... 1038 The Membranous or Lateral Wall . 1038 The Tympanic Membrane .... 1039 Structure 1039 The Labyrinthic or Medial Wall . . 1040 The Mastoid or Posterior Wall . . 1042 The Carotid or Anterior Wall . . . 1042 The Auditory Tube 1042 The Auditory Ossicles 1044 The Malleus X044 The Incus 1044 The Stapes 1045 Articulations of the Auditory Ossicles 1045 Ligaments of the Ossicles .... 1045 The Muscles of the Tympanic Cavity 1046 The Tensor Tympani .... 1046 The Stapedius . . , . . . . 1046 The Internal Ear or Labyrinth .... 1047 The Osseous Labyrinth 1047 The Internal Ear or Labyrinth — The Osseous Labyrinth — The Vestibule The Bony Semicircular Canals The Cochlea . . . The Membranous Labyrinth The Utricle .... The Saccule .... The Semicircular Ducts Structure The Ductus Cochlearis The Basilar Membrane The Spiral Organ of Corti Hair Cells .... 1047 1049 1050 1051 1051 1052 1052 1052 1054 1056 1056 1057 Peripheral Terminations of Nerves of General Sensations. Free Nerve-endings 1059 Special End-organs 1059 End-bulbs of Krause 1060 Tactile Corpuscles of Grandry .... 1060 Pacinian Corpuscles 1060 Corpuscles of Golgi and Mazzoni . . . 1061 Tactile Corpuscles of Wagner and Meissner 1061 Corpuscles of Ruffini 1061 Neurotendinous Spindles 1061 Neuromuscular Spindles 1061 The Comon Integument. The Epidermis, Cuticle, or Scarf Skin . . 1062 The Corium, Cutis Vera, Dermis, or True Skin 1065 Development 1066 The Appendages of the Skin. The Nails 1066 The Hairs 1067 The Sebaceous Glands 1069 The Sudoriferous or Sweat Glands . . . 1070 I SPLANCHNOLOGY. The Respiratory Apparatus. Development 1071 The Larynx. The Cartilages of the Larynx .... 1073 The Thyroid Cartilage . 1073 The Cricoid Cartilage 1074 The Arytenoid Cartilage 1075 The Corniculate Cartilages 1075 The Cuneiform Cartilages 1075 The Epiglottis . . . 1075 Structure 1076 The Ligaments of the Larynx 1076 The Extrinsic Ligaments 1076 The Intrinsic Ligaments 1077 The Interior of the Larynx . 1078 The Ventricular Folds 1079 The Vocal Folds . . . 1079 The Ventricle of the Larynx 1080 The Rima Glottidis . . 1080 The Muscles of the Larynx . 1081 Cricothyreoideus 1081 Cricoarytsenoideus Posterior 1082 Cricoarytsenoideus Lateralis 1082 Arytsenoideus .... 1082 Thyreoarytsenoideus 1083 The Trachea and Bronchi. Relations 1084 The Right Bronchus 1085 The Left Bronchus ....... 1085 Structure 1086 The Pleurce. Reflections of the Pleura 1088 Pulmonary Ligament 1090 Structure of Pleura 1090 The Mediastinum. Superior Mediastinum 1090 Anterior Mediastinum 1092 Middle Mediastinum . 1092 Posterior Mediastinum 1093 The Lungs. The Apex of the Lungs 1094 The Base of the Lungs 1094 Surfaces of the Lungs 1094 Borders of the Lungs 1096 Fissures and Lobes of the Lungs . . . 1096 The Root of the Lung 1097 Divisions of the Bronchi 1097 Structure of the Lungs 1098 The Digestive Apparatus. The Digestive Tube 1100 The Development of the Digestive Tube 1101 The Mouth 1101 The Salivary Glands .... 1102 The Tongue 1102 The Palatine Tonsils .... 1103 The Further Development of the Digestive Tube 1103 The Rectum and Anal Canal . . 1 108 CONTENTS 25 The Mouth. The Abdomen. The Vestibule of the Mouth 1110 The Mouth Cavity Proper 1110 Structure 1110 The Lips 1111 The Labial Glands 1111 The Cheeks 1112 Structure 1112 The Gums 1112 The Palate 1112 The Hard Palate 1112 The Soft Palate 1112 The Teeth 1112 General Characteristics 1114 The Permanent Teeth 1115 The Canine Teeth 1117 The Premolar or Bicuspid Teeth . 1118 The Molar Teeth 1118 The Deciduous Teeth 1118 Structure of the Teeth 1118 Development of the Teeth .... 1121 Development of the Deciduous Teeth 1122 Development of the Permanent Teeth 1124 Eruption of the Teeth . . . . 1124 The Tongue 1125 The Root of the Tongue .... 1125 The Apex of the Tongue . . . 1125 The Dorsum of the Tongue . . . 1125 The Papilla; of the Tongue . . . . 1126 The Muscles of the Tongue . . . 1128 Genioglossus 1129 Hyoglossus 1129 Chondroglossus 1130 Styloglossus 1130 Longitudinalis Linguae Superior 1130 Longitudinalis Linguae Inferior 1130 Transversus Linguae . . . . 1130 Verticalis Linguae 1131 Structure of the Tongue . . 1131 Glands of the Tongue 1131 The Salivary Glands 1132 The Parotid Gland 1132 Structures within the Gland . . 1134 The Parotid Duct 1134 Structure 1134 The Submaxillary Gland .... 1135 The Submaxillary Duct . . 1135 The Sublingual Gland 1136 Structure of the Salivary Gland . 1136 Accessory Glands 1137 The Fauces. The Glossopalatine Arch 1137 The Pharyngopalatine Arch . 1137 The Palatine Tonsils . . . 1137 Structure 1139 The Palatine Aponeurosis 1139 The Muscles of the Palate 1139 Levator Veli Palatini 1139 Tensor Veli Palatini 1139 Musctilus Uvulae 1139 Glossopalatinus 1139 Paryngopalatinus 1139 The Pharynx. The Nasal Part of the Pharynx .... 1141 The Oral Part of the Pharynx . . 1142 The Laryngeal Part of the Pharynx 1142 The Muscles of the Pharynx 1142 Constrictor Pharyngis Inferior . 1142 Constrictor Pharyngis Medius . 1142 Constrictor Pharyngis Superior 1142 Stylopharyngeus 1142 Salpingopharyngeus . 1142 Structure of the Pharynx 1143 The Esopfiagus. Relations 1145 1146 Structure Boundaries of the Abdomen ..... 1147 The Apertures in the Walls of the Abdomen 1147 Regions of the Abdomen 1147 The Peritoneum 1149 Vertical Dispositions of the Main Peri- toneal Cavity 1150 Vertical Disposition of the Omental Bursa 1152 Horizontal Disposition of the Peri- toneum 1153 In the Pelvis . . . . 1153 In the Lower Abdomen 1154 In the Upper Abdomen . . 1155 The Omenta 1156 The Mesenteries 1157 The Peritoneal Recesses or Fossae . . 1158 The Duodenal Fossae .... 1159 The Cecal Fossae 1160 The Intersigmoid Fossa . . . 1161 Th^ Stomach. Openings of the Stomach 1161 Curvatures of the Stomach 1162 Surfaces of the Stomach 1162 Component Parts of the Stomach . . . 1163 Position of the Stomach 1163 Interior of the Stomach 1164 Pyloric Valve * . . . 1164 Structure of the Stomach 1164 The Gastric Glands 1166 The Small Intestine. The Duodenum 1169 Relations . 1169 The Jejunum and Ileum 1170 Meckel's Diverticulum 1172 Structure 1172 The Large Intestine. The Cecum 1177 The Vermiform Process or Appendix . 1178 Structure 1179 The Colic Valve 1179 The Colon 1180 The Ascending Colon 1180 The Transverse Colon 1180 The Descending Colon 1181 The Iliac Colon 1182 The Sigmoid Colon 1182 The Rectum 1183 Relations of the Rectum .... 1184 The Anal Canal 1184 Structure of the Colon 1184 The Liver. Surfaces of the Liver 1188 Fossae of the Liver 1191 Lobes of the Liver 1191 Ligaments of the Liver 1192 Fixation of the Liver 1193 Development of the Liver 1 193 Structure of the Liver . . . . 1195 Excretory Apparatus of the Liver . . . 1197 The Hepatic Duct 1197 The Gall-bladder 1197 Relations . 1197 Structure 1198 The Common BUe Duct .... 1198 Structure 1199 The Pancreas. Relations 1200 The Pancreatic Duct 1202 Development of the Pancreas .... 1202 Structure 1203 26 CONTENTS The Urogenital Apparatus. Development of the. Urinary and Generative Organs The Pronephros and Wolffian Duct . . 1205 The Mesonephros, Milllerian Duct, and Genital Gland 1205 The Miillerian Ducts 1206 Genital Glands 1207 The Ovary 1207 The Testis 1210 Descent of the Ovaries 1211 The Metanephros and the Permanent Kidney 1211 The Urinary Bladder 1212 The Prostate 1213 External Organs of Generation . 1213 The Urethra 1215 The Urinary Organs. The Kidneys 1215 Relations 1215 Surfaces 1215 Borders 1218 Extremities 1219 Fixation of the Kidney .... 1220 General Structure of the Kidney . 1220 The Ureters 1225 The Ureter Proper 1226 Structure . , 1227 Variations ' 1227 The Urinary Bladder 1227 The Empty Bladder 1227 The Distended Bladder 1228 The Bladder in the Child .... 1229 The Female Bladder 1230 The Ligaments of the Bladder . . . 1231 The Interior of the Bladder . . . 1231 Structure 1232 Abnormalities 1233 The Male Urethra 1234 The Prostatic Portion 1234 The Membranous Portion .... 1235 The Cavernous Portion 1235 Structure 1235 Congenital Defects 1235 The Female Urethra 1236 Structure 1236 Th Male Genital Organs. The Testes and their Coverings .... 1236 The Scrotum 1237 The Intercrural Fascia 1238 The Cremaster Muscle 1238 The Infundibuliform Fascia . . . 1239 The Tunica Vaginalis 1239 The Inguinal Canal 1239 The Spermatic Cord 1239 Structure of the Spermatic Cord . 1239 The Testes 1240 The Epididymis 1242 Appendages of the Testis and Epi- didymis 1242 The Tunica Vaginalis . 1242 The Tunica Albuginea . 1242 The Tunica Vasculosa . 1243 Structure 1243 Peculiarities 1245 The Ductus Deferens 1245 The Ductuli Aberrantes .... 1246 Paradidymis 1246 Structure 1246 The Vesiculse Seminales 1246 Structure 1247 The Ejaculatory Ducts ...... 1247 Structure 1247 The Penis 1247 The Corpora Cavernosa Penis . . . 1248 The Corpus Cavernosum Urethrse . 1248 Structure of the Penis 1250 The Prostate . . . ^^^^^^H" . 1251 Structure . . . ^^^^^^K • 1253 The Bulbourethral Glands 1253 Structure 1253 The Female Genital Organs. The Ovaries 1254 The Epoophoron 1255 The Paroophoron 1255 Structure 1255 Vesicular Ovarian Follicles .... 125& Discharge of the OvuVn 1256 Corpus Luteum 1256 The Uterine Tube 1257 Structure 1257 The Uterus 1258 The Body 1259 The Cervix 1259 The Interior of the Uterus .... 1260 The Cavity of the Body . . . 1260 The Canal of the Cer\ax . . . 1260 The Ligaments of the Uterus . . . 1260 Structure 1262 The Vagina 1264 Relations 1264 Structure 1264 The External Organs 1264 The Mons Pubis 1265 The Labia Majora 1265 The Labia Minora 1265 The Clitoris 1266 The Vestibule 1266 The Bulb of the Vestibule .... 1266 The Greater Vestibular Glands . 1266 The Mammae 1267 The Mammary Papilla or Nipple . 1267 Development 1267 Structure 1267 The Ductle.ss Glands. The Thyroid Gland. Development 1270 Structure 1271 The Parathyroid Glands. Development . 1272 Structure 1273 The Thymus. Development 1273 Structure 1274 The Hypophysis Cerebri. Development 1276 The Pineal Body. Structure 1277 The Chromaphil and Cortical Systems. Development 1277 The Suprarenal Glands 1278 Development 1278 Relations 1278 Accessory Suprarenals 1279 Structure 1279 Glomus Caroticum 1281 Glomus Coccygeum 1281 The Spleen. Development 1282 Relation 1282 Structure 1283 STENTS 27 SURFACE ANATOMY AND SURFACE MARKINGS. Surface Anatomy of the Head and Neck. The Bones 1287 The Joints and Muscles 1288 THe Arteries 1290 Surface Markings of Special Regions of the Head and Meek. The Cranium 1291 The Scalp 1291 Bony Landmarks 1291 The Brain 1292 Vessels 1294 The Face 1294 External Maxillary Artery .... 1294 Trigeminal Nerve 1295 Parotid. Gland 1295 The Nose 1296 The Mouth 1296 The Eye 1299 The Ear 1300 The Tympanic Antrum 1301 The Neck 1301 Muscles 1302 Arteries 1302 Veins 1303 Nerves 1303 Submaxillary Gland 1303 Surface Anatomy of the Back. Bones 1303 Muscles 1304 Surface Markings of the Back. Bony Landmarks 1305 Medulla Spinalis 1306 Spinal Nerves 1307 Surface Anatomy of the Thorax. Bones 1307 Muscles 1307 Mamma \ 1308 Surface Markings of the Thorax. Bony Landmarks 1308 Diaphragm [ ] I309 Surface Lines I3O9 Pleurae ' " 1309 Lungs '.'.'. 1310 Irachea 1311 Esophagus [ [ 1311 Heart 1311 Arteries \ 1312 Veins '\ 1312 Surface Anatomy of the Abdomen. |^'° 1313 ?oiies 1313 Musces 1313 ^?ssels 1313 Viscera I313 Surface Markings of the Abdomen. Bony Landmarks 1315 Muscles 1315 Surface Lines 1315 Stomach 1317 Duodenum 1319 Small Intestine 1319 Cecum and Vermiform Process .... 1319 Ascending Colon 1319 Transverse Colon 1319 Descending Colon 1320 Iliac Colon 1320 Liver 1320 Pancreas 1320 Spleen 1320 Kidneys 1320 Ureters 1321 Vessels 1321 Nerves 1322 Surface Anatomy of the Perineum. Skin 1322 Bones 1322 Muscles and Ligaments 1322 Surface Markings of the Perineum. Rectum and Anal Canal 1322 Male Urogenital Organs . . . . 1323 Female Urogenital Organs 1323 Surface Anatomy of the Upper Extremity. Skin 1325 Bones 1326 Articulations 1327 Muscles 1327 Arteries 1331 Veins 1331 Nerves 1331 Surface Markings of the Upper Extremity. Bony Landmarks 1331 Articulations 1331 Muscles 1332 Mucous Sheaths 1334 Arteries 1334 Nerves 1335 Surface Anatomy of the Lower Extremity. Skin 1336 Bones 1336 Articulations 1338 Muscles 1338 Arteries 1341 Veins 1342 Nerves 1342 Surface Markings of the Lower Extremity. Bony Landmarks 1342 Articulations 1343 Muscles 1343 Mucous Sheaths 1343 Arteries 1343 Veins ] . 1345 Nerves 1346 ^^K^ ANATOMICAL BIBLIOaRAPHY. ^M ^^^^^ INDEXES. ^M Anatomical Bibliography of the Concilium Bibliographiciim, ^^^| Bibliographic Service; Wistar Institute of Anatomy, 1917- . ^^^H Bibliographie Anatomique, 1893- . fl Index Medicus, 1879- I Index Catalogue of the Library of the Surgeon-General's Office, U. S. ArnB 1880- \ Jahresberichte iiber die Fortschritte der Anatoraie und Physiologic, 1856-1894. Jahresberichte iiber die Fortschritte der Anatomic mid Entwicklungsgeschichte, 1895- JOURNALS. The Anatomical Record, 1906- The American Journal of Anatomy, 1901- Anatomische Hefte, 1892- Anatomischer Anzeiger, 1886- Archives d 'Anatomic Microscopique, 1897- Archiv fiir Anatomic und Physiologic, 1795- Archiv fiir Entwicklungsmechanik der Organismen, 1894- Archiv fiir Microskopische Anatomic, 1865- Archivo Italiano di Anatomia e di Embriologia, 1902- Biological Bulletin, 1900- Brain, 1878- Bibliographie Anatomique, 1893- Contributions to Embryology, Carnegie Institution of Washington, 1914-- Comptcs Rendus de 1' Association des Anatomistes, 1899- Gegenbaur's Morphologischcs Jahrbuch, 1876- International Monatsschrift fiir Anatomic und Histologic, 1884- The Journal of Anatomy and Physiology, 1867- Journal of Comparative Neurology, 1891- . Journal de 1 'Anatomic et de Physiologic, etc., 1864- Journal of Experimental Zoology, 1904- Journal of Morphology, 1887- Le Nevraxe, 1900- Morphologischc Arbciten, 1892-1898. Petrus Camper Nederlandschc Bijdragen tot de Anatomic, 1902- Proceedings of the Royal Society, Scries B. Quarterly Journal of Microscopical Science, 1853- Zcitschrift fiir Morphologic und Anthropologic, 1899- Zeitschrift fiir Wissenschaftliche Mikroskopie, 1884- XXV iii ) ANATOMY OF THE HUMAN BODY INTRODUCTION. THE term human anatomy comprises a consideration of the various structures which make up the human organism. In a restricted sense it deals merely with the parts which form the fully developed individual and which can be ren- dered evident to the naked eye by various methods of dissection. Regarded from such a standpoint it may be studied by two methods: (1) the various structures may be separately considered— systematic anatomy; or (2) the organs and tissues may be studied in relation to one another — topographical or regional anatomy. It is, however, of much advantage to add to the facts ascertained by naked- eye dissection those obtained by the use of the microscope. This introduces two fields of investigation, viz., the study of the minute structure of the various component parts of the body — histology — and the study of the human organism in its immature condition, i. e., the various stages of its intrauterine develop- ment from the fertilized ovum up to the period when it assumes an independent existence — embryology. Owing to the difficulty of obtaining material illustrating all the stages of this early development, gaps must be filled up by observations on the development of lower forms — comparative embryology, or by a consideration of adult forms in the line of human ancestry — comparative anatomy. The direct application of the facts of human anatomy to the various pathological conditions which may occur constitutes the subject of applied anatomy. Finally, the appre- ciation of structures on or immediately underlying the surface of the body is frequently made the subject of special study — smiace anatomy. Systematic ANATOMY.^The various systems of which the human body is composed are grouped under the following headings: 1. Osteology — the bony system or skeleton. 2. Syndesmology — the articulations or joints. 3. Myology — the muscles. With the description of the muscles it is convenient to include that of the fasciae which are so intimately connected with them. 4. Angiology — the vascular system, comprising the heart, bloodvessels, lymphatic vessels, and lymph glands. 5. Neurology — the nervous system. The organs of sense may be included in this system. 6. Splanchnology — the visceral system. Topographically the viscera form two groups, viz., the thoracic viscera and the abdomino-pelvic viscera. The heart, a thoracic viscus, is best considered with the vascular system. The rest 3 (33) 34 INTRODUCTION I of the viscera may be grouped according to their functions: (a) the respiratory apparatus; (6) the digestive apparatus; and (c) the urogenital apparatus. Strictly speaking, the third subgroup should include only such components of the urogenital apparatus as are included within the abdomino-pelvic cavity, but it is convenient to study under this heading certain parts which lie in relation to the surface of the body, e. g., the testes and the external organs of generation. For descriptive purposes. the body is supposed to be in the erect posture, with the arms hanging by the sides and the palms of the hands directed forward. The median plane is a vertical antero-posterior plane, passing through the center of the trunk. This plane will pass approximately through the sagittal suture of the skull, and hence any plane parallel to it is termed a sagittal plane. A vertical plane at right angles to the median plane passes, roughly speaking, through the central part of the coronal suture or through a line parallel to it; such a plane is known as a frontal plane or sometimes as a coronal plane. A plane at right angles to both the median and frontal planes is termed a transverse plane. The terms anterior or ventral, and posterior or dorsal, are employed to indicate the relation of parts to the front or back of the body or limbs, and the terms superior or cephalic, and inferior or caudal, to indicate the relative levels of different structures; structures nearer to or farther from the median plane are referred to as medial or lateral respectively. The terms superficial and deep are strictly confined to descriptions of the relative depth from the surface of the various structures; external and internal are reserved almost entirely for describing the walls of cavities or of hollow viscera. In the case of the limbs the words proximal and distal refer to the relative distance from the attached end of the limb. EMBRYOLOGY. THE term Embryology, in its widest sense, is applied to the various changes ^^ which take place during the growth of an animal from the egg to the adult ^Hj condition: it is, however, usually restricted to the phenomena which occur before ^" birth. Embryology may be studied from two aspects: (1) that of ontogeny, which j^ deals only with the development of the individual; and (2) that of phylogeny, which concerns itself with the evolutionary history of the animal kingdom. In vertebrate animals the development of a new being can only take place when a female germ cell or ovum has been fertilized by a male germ cell or spermatozoon. The ovum is a nucleated cell, and all the complicated changes by which the various tissues and organs of the body are formed from it, after it has been fertilized, are the result of two general processes, viz., segmentation and differentiation of cells. Thus, the fertilized ovum undergoes repeated segmentation into a number of cells which at first closely resemble one another, but are, sooner or later, differentiated into two groups: (1) somatic cells, the function of which is to build up the various tissues of the body; and (2) germinal cells, which become imbedded in the sexual glands — the ovaries in the female and the testes in the male — and are destined for the perpetuation of the species. Having regard to the main purpose of this work, it is impossible, in the space available in this section, to describe fully, or illustrate adequately, all the phenom- ena which occur in the different stages of the development of the human body. Only the principal facts are given, and the student is referred for further detaUs to one or other of the text-books^ on human embryology. THE ANIMAL CELL. All the tissues and organs of the body originate from a microscopic structure (the fertilized ovum), which consists of a soft jelly-like material enclosed in a membrane and containing a vesicle or small spherical body inside which are one or more denser spots. This may be regarded as a complete cell. All the solid tissues consist largely of cells essentially similar to it in nature but differing in external form. In the higher organisms a cell may be defined as "a nucleated mass of proto- plasm of microscopic size." Its two essentials, therefore, are: a soft jelly-like material, similar to that found in the ovum, and usually styled cytoplasm, and a small spherical body imbedded in it, and termed a nucleus. Some of the unicellular protozoa contain no nuclei but granular particles which, like true nuclei, stain with basic dyes. The other constituents of the ovum, viz., its limiting membrane and the denser spot contained in the nucleus, called the nucleolus, are not essential ta the type cell, and in fact many cells exist without them. Csrtoplasm (protoplas7n) is a material probably of variable constitution during life, but yielding on its disintegration bodies chiefly of proteid nature. Lecithin and cholesterin are constantly found in it, as well as inorganic salts, chief among 1 Manual of Human Embryology, Keibel and Mall; Handbuch der vergleichenden und experimentellen Entwickel- ungslehre der Wirbeltiere, Oskar Hertwig; Lehrbuch der Entwickelungsgeschichte, Bonnet; The Physiology of Reproduction, Marshall. (36) 36 EMBRYOLOGY which are the phosphates and chlorides of potassium, sodium, and calcium. It is of a semifluid, viscid consistence, and probably colloidal in nature. The living cjloplasm appears to consist of a homogeneous and structureless ground-substance in which are embedded granules of ^'arious t\'pes. The mitochondria are the most constant type of granule and vary in form from granules to rods and threads. Their function is unknown. Some of the granules are proteid in nature and prob- ably essential constituents; others are fat, glycogen, or pigment granules, and are regarded as adventitious material taken in from without, and hence are styled cell-inclusions or paraplasm. When, however, cells have been "fixed" by reagents a fibrillar or granular appearance can often be made out under a high power of the microscope. The fibrils are usually arranged in a network or reticulum, to which the term spongioplasm is applied, the clear substance in the meshes being termed hyaloplasm. The size and shape of the meshes of the spongioplasm vary in different cells and in different parts of the same cell. The relative amounts of spongioplasm and hyaloplasm also vary in different cells, the latter preponderating in the young cell and the former increasing at the expense of the hyaloplasm as the cell grows. Such appearances in fixed cells are no indication whatsoever of the existence of Cell wall NvcUar membrane Vacuole Centrosome consisting of cen- trosphere enclosing ttvo cen- trioles Nucleolus Net-knot of chromatin form- ing a pseudo-nucleolus Chromatin network Cell-inclusions {paraplasm) Fig. 1. — Diagram of a cell. (Modified from Wilson.) similar structures in the living, although there must have been something in the living cell to give rise to the fixed structures. The peripheral layer of a cell is in all cases modified, either by the formation of a definite cell membrane as in the ovum, or more frequently in the case of animal cells, by a transformation, probably chemical in nature, which is only recognizable by the fact that the surface of the cell behaves as a semipermeable membrane. Nucleus. — The nucleus is a minute body, imbedded in the protoplasm, and usually of a spherical or oval form, its size having little relation to that of the cell. It is surrounded by a well-defined wall, the nuclear membrane; this encloses the nuclear substance {nuclear matrix), which is composed of a homogeneous material in which is usually embedded one or two nucleoli. In fixed cells the nucleus seems to consist of a clear substance or karyoplasm and a network or karyomitome. The former is probably of the same nature as the hyaloplasm of the cell, but the latter, which forms also the wall of the nucleus, differs from the spongioplasm of the cell substance. It consists of fibers or filaments arranged in a reticular manner. These filaments are composed of a homogeneous material known as linin, which stains with acid dyes and contains embedded in its substance particles which have a strong affinity for basic dyes. These basophil granules have been named chromatin THE ANIMAL CELL 37 or basichromatin and owe their staining properties to the presence of nucleic acid. Within the nuclear matrix are one or more highly refracting bodies, termed nucleoli, connected with the nuclear membrane by the nuclear filaments. They are regarded as being of two kinds. Some are mere local condensations ("net-knots") of the chromatin; these are irregular in shape and are termed pseudo-nucleoli ; others are distinct bodies differing from the pseudo-nucleoli both in nature and chemical composition; they may be termed true nucleoli, and are usually found in resting cells. The true nucleoli are oxis-phil, i. e., they stain with acid dyes. Most living cells contain, in addition to their protoplasm and nucleus, a small particle which usually lies near the nucleus and is termed the centrosome. In the middle of the centrosome is a minute body called the centriole, and surrounding this is a clear spherical mass known as the centrosphere. The protoplasm surround- ing the centrosphere is frequently' arranged in radiating fibrillar rows of granules, forming what is termed the attraction sphere. Reproduction of Cells. — Reproduction of cells is effected either by direct or by indirect division. In reproduction by direct division the nucleus becomes constricted in its center, assuming an hour-glass shape, and then divides into two. This is fol- lowed by a cleavage or division of the whole protoplasmic mass of the cell; and thus two daughter cells are formed, each containing a nucleus. These daughter cells are at first smaller than the original mother cell; but they grow, and the process may be repeated in them, so that multiplication may take place rapidly. Indirect divsion or karyokinesis (karyomitosis) has been observed in all the tissues — genera- tive cells, epithelial tissue, connective tissue, muscular tissue, and nerve tissue. It is possible that cell division may always take place by the indirect method. The process of indirect cell division is characterized by a series of complex changes in the nucleus, leading to its subdivision; this is followed by cleavage of the cell protoplasm. Starting with the nucleus in the quiescent or resting stage, these changes may be briefly grouped under the four following phases (Fig. 2). 1. Prophase. — The nuclear network of chromatin filaments assumes the form of a twisted skein or spirem, while the nuclear membrane and nucleolus disappear. The convoluted skein of chromatin divides into a definite number of V-shaped segments or chromosomes. The number of chromosomes varies in different animals, but is constant for all the cells in an animal of any given species; in man the number is given by Flemming and Duesberg as twenty-four.^ Coincidently with or pre- ceding these changes the centriole, which usually lies by the side of the nucleus, undergoes subdivision, and the two resulting centrioles, each surrounded by a centrosphere, are seen to be connected by a spindle of delicate achromatic fibers the achromatic spindle. The centrioles move away from each other — one toward either extremity of the nucleus — and the fibrils of the achromatic spindle are cor- respondingly lengthened. A line encircling the spindle midway between its ex- tremities or poles is named the equator, and around this the V-shaped chromosomes arrange themselves in the form of a star, thus constituting the mother star or monaster. 2. Metaphase. — Each V-shaped chromosome now undergoes longitudinal cleavage into two equal parts or daughter chromosomes, the cleavage commencing at the apex of the V and extending along its divergent limbs. 3. Anaphase. — The daughter chromosomes, thus separated, travel in opposite directions along the fibrils of the achromatic spindle toward the centrioles, around which they group themselves, and thus two star-like figures are formed, one at either pole of the achromatic spindle. This constitutes the diaster. The daughter chromosomes now arrange themselves into a skein or spirem, and eventually form the network of chromatin which is characteristic of the resting nucleus. Dr. J. Duesberg, Anat. Anz., Band xxviii. S. 475. 38 EMBRYOLOGY 4. Telophase. — The cell protoplasm begins to appear constricted around the equator of the achromatic spindle, where double rows of granules are also sometimes seen. The constriction deepens and the original cell gradually becomes divided into two new cells, each with its own nucleus and centrosome, which assume the ordinary positions occupied by such structures in the resting stage. The nuclear membrane and nucleolus are also differentiated during this phase. I . -, II . - """•••-. I ni iim '. Fia. 2.— Diagram showing the changes which occur in the centrosomes and nucleus of a cell in the process of mitotic division. (Schafer.) / to ///, prophase; IV, metaphase; V and VI, anaphase; VII and VIII, telophase. THE OVUM. The ova are developed from the primitive germ cells which are imbedded in the substance of the ovaries. Each primitive germ cell gives rise, by repeated divisions, to a number of smaller cells termed oogonia, from which the ova or primary oocjrtes are developed. Human ova are extremely minute, measuring about 0.2 mm. in diameter, and are enclosed within the egg follicles of the ovaries; as a rule each follicle contains THE OVUM 39 single ovum, but sometimes two or more are present. "^ By the enlargement and subsequent rupture of a follicle at the surface of the ovary, an ovum is liberated and conveyed by the uterine tube to the cavity of the uterus. Unless it be fertilized it undergoes no further development and is discharged from the uterus, but if fertilization take place it is retained within the uterus and is developed into a new being. In appearance and structure the ovum (Fig. 3) differs little from an ordinary cell, but distinctive names have been applied to its several parts; thus, the cell substance is known as the yolk or ooplasm, the nucleus as the germinal vesicle, and the nucleolus as the germinal spot. The ovum is enclosed within a thick, trans- • 3;~Human ovum examined fresh in the liquor folliculi. (Waldeyer.) The zona pellucida is seen as a thick clear girdle surrounded by the cells of the corona radiata. The egg itself shows a central granular deutoplasmie area and a peripheral clear layer, and encloses the germinal vesicle, in which is seen the germinal spot. parent envelope, the zona striata or zona pellucida, adhering to the outer surface of which are several layers of cells, derived from those of the follicle and collectively constituting the corona radiata. Yolk.— The yolk comprises (1) the cytoplasm of the ordinary animal cell with its spongioplasm and hyaloplasm; this is frequently termed the formative yolk; (2) the nutritive yolk or deutoplasm, which consists of numerous rounded granules of fatty and albuminoid substances imbedded in the cytoplasm. In the mammalian ovum the nutritive yolk is extremely small in amount, and is of service in nourish- See description of the ovary on a future page. m ^^^B EMBRYOLOGY . ^^M ing the embryo in the early stages of its development only, whereas in the egg of the bird there is sufficient to supply the chick with nutriment throughout the whole period of incubation. The nutritive yolk not only varies in amount, but in its mode of distribution within the egg; thus, in some animals it is almost uniformly distributed throughout the cytoplasm; in some it is centrally placed and is surrounded by the cytoplasm; in others it is accumulated at the lower pole of the ovum, while the cytoplasm occupies the upper pole. A centrosome and centriole are present and lie in the immediate neighborhood of the nucleus. ■ Germinal Vesicle. — The germinal vesicle or nucleus is a large spherical body which at first occupies a nearly central position, but becomes eccentric as the growth of the ovum proceeds. Its structure is that of an ordinary cell-nucleus, viz., it consists of a reticulum or karyomitome, the meshes of which are filled with karyoplasm, while connected with, or imbedded in, the reticulum are a number of chromatin masses or chromosomes, which may present the appearance of a skein or may assume the form of rods or loops. The nucleus is enclosed by a delicate nuclear membrane, and contains in its interior a well-defined nucleolus or germinal spot. Coverings of the Ovum. — The zona striata or zona pellucida (Fig. 3) is a thick membrane, which, under the higher powers of the microscope, is seen to be radially striated. It persists for some time after fertilization has occurred, and may serve for protection during the earlier stages of segmentation. It is not yet determined whether the zona striata is a product of the cytoplasm of the ovum or of the cells of the corona radiata, or both. The corona radiata (Fig. 3) consists or two or three strata of cells; they are derived from the cells of the follicle, and adhere to the outer surface of the zona striata when the ovum is set free from the follicle; the cells are radially arranged around the zona, those of the innermost layer being columnar in shape. The cells of the corona radiata soon disappear; in some animals they secrete, or are replaced by, a layer of adhesive protein, which may assist in protecting and nourishing the ovum. The phenomena attending the discharge of the ova from the follicles belong more to the ordinary functions of the ovary than to the general subject of embry- ology, and are therefore described with the anatomy of the ovaries.^ Maturation of the Ovum. — Before an ovum can be fertilized it must undergo a process of maturation or ripening. This takes place previous to or immediately after its escape from the follicle, and consists essentially of an unequal subdivision of the ovum (Fig. 4) first into two and then into four cells. Three of the four cells are small, incapable of further development, and are termed polar bodies or polocytes, while the fourth is large, and constitutes the mature ovum. The process of maturation has not been observed in the human ovum, but has been carefully studied in the ova of some of the lower animals, to which the following description applies. It was pointed out on page 37 that the number of chromosomes found in the nucleus is constant for all the cells in an animal of any given species, and that in man the number is probably twenty-four. This applies not only to the somatic cells but to the primitive ova and their descendants. For the purpose of illustrating the process of maturation a species may be taken in which the number of nuclear chromosomes is four (Fig. 5) . If an ovum from such be observed at the beginning of the maturation process it will be seen that the number of its chromosomes is apparently reduced to two. In reality, however, the number is doubled, since each chromosome consists of four granules grouped to form a tetrad. During the metaphase (see page 37) each tetrad divides into two dyads, which are equally ' See description of the ovary on a future page. THE OVUM 41 distributed between the nuclei of the two cells formed by the first division of the ovum. One of the cells is almost as large as the original ovum, and is named the secondary oocyte; the other is small, and is termed the first polar body. The f.jm Fig. 4. — Formation of polar bodies in Asterias glacialis. (Slightly modified from Hertwig.) In / the polar spindle (sp) has advanced to the surface of the egg. In // a small elevation (p6') is formed which receives half of the spindle. In III the elevation is constricted off, forming the first polar body (p6'), and a second spindle is formed. In IV is seen a second elevation which in V has been constricted off as the second polar body (p6'). Out of the remainder of the spindle (/.p» in VI) the female pronucleus is developed. secondary oocyte now undergoes subdivision, during which each dyad divides and contributes a single chromosome to the nucleus of each of the two resulting cells. Priviary oocyte Primary oocyte (commencing maturation) ( f ] First polar V J body Secondary oocyte Mature f *@ \ /^\ /*S\ /*0\ V^ WV_^ I Polar bodies ' FiQ. 5. — Diagram showing the reduction in number of the chromosomes in the process of maturation of the ovum. This second division is also unequal, producing a large cell which constitutes the mature ovum, and a small cell, the second polar body. The first polar body fre- quently divides while the second is being formed, and as a final result four cells 42 EMBRYOLOGY are produced, viz., the mature ovum and three polar bodies, each of which con- tains two chromosomes, i. e., one-half the number present in the nuclei of the somatic cells of members of the same species. The nucleus of the mature ovum is termed the female pronucleus. THE SPERMATOZOON. dl The spermatozoa or male germ cells are developed in the testes and are present in enormous numbers in the seminal fluid. Each consists of a small but greatly modified cell. The human spermatozoon possesses a head, a neck, a connecting, piece or body, and a tail (Fig. 6). Head Connecting piece •Perforator ) Neck Tail! End-piece > I ^ Head-cap J ■-•A nterior centriole ""Posterior centriole -—'Spiral thread Mitochondria sheath Terminal disc Axial filament I Fig. 6. — Human spermatozoon. Diagrammatic. A. Surface view. B. Profile view. In C the head, neck, and connecting piece are more highly magnified. The head is oval or elliptical, but flattened, so that when viewed in profile it is pear-shaped. Its anterior two-thirds are covered by a layer of modified proto- plasm, which is named the head-cap. This, in some animals, e. g., the salamander, is prolonged into a barbed spear-like process or perforator, which probably facilitates the entrance of the spermatozoon into the ovum. The posterior part of the head exhibits an affinity for certain reagents, and presents a transversely striated appear- ance, being crossed by three or four dark bands. In some animals a central rod- like filament extends forward for about two-thirds of the length of the head, while in others a rounded body is seen near its center. The head contains a mass of THE SPERMATOZOON 43 chromatin, and is generally regarded as the nucleus of the cell surrounded by a thin envelope. The neck is less constricted in the human spermatozoon than in those of some of the lower animals. The anterior centriole, represented by two or three rounded particles, is situated at the junction of the head and neck, and behind it is a band of homogeneous substance. The connecting piece or body is rod-like, and is limited behind by a terminal disk. The posterior centriole is placed at the junction of the body and neck and, like the anterior, consists of two or three rounded particles. From this centriole an axial filament, surrounded by a sheath, runs backward through the body and tail. In the body the sheath of the axial filament is encircled by a spiral thread, around which is an envelope containing mitochondria granules, and termed the mitochondria sheath. The tail is of great length, and consists of the axial thread or filament, sur- rounded by its sheath, which may contain a spiral thread or may present a striated appearance. The terminal portion or end-piece of the tail consists of the axial filament onlv. Primary oocyte Primary spermatocyte Secondary ( \ oocyte K J Mature O O Secondary spermatocytes Oooooo oo Polar bodies Spermatids FiQ. 7. — Scheme showing analogies in the process of maturation of the ovum and the development of the spermatids (young spermatozoa). Krause gives the length of the human spermatozoon as between 52 /x and 62 /x, the head measuring 4 to 5m, the connecting piece G^t, and the tail from 41 ^i to 52 fx. By virtue of their tails, which act as propellers, the spermatozoa are capable of free movement, and if placed in favorable surroundings, e. g., in the female pas- sages, will retain their vitality and power of fertilizing for several days. In certain animals, e. g., bats, it has been proved that spermatozoa retained in the female passages for several months are capable of fertilizing. The spermatozoa are developed from the primitive germ cells which have become imbedded in the testes, and the stages of their development are very similar to those of the maturation of the ovum. The primary germ cells undergo division and produce a number of cells termed spermatogonia, and from these the primary spermatocytes are derived. Each primary spermatocyte divides into two secondary spermatocytes, and each secondary spermatocyte into two spermatids or young spermatozoa; from this it will be seen that a primary spermatocyte gives rise to four spermatozoa. On comparing this process with that of the maturation of the ovum (Fig. 7) it will be observed that the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the primary oocyte to two cells, the secondary oocyte and the first polar body. Again, the two secondary sperma- EMBRYOR tocytes by their subdivision give origin to four spermatozoa, and the secondary oocyte and first polar body to four cells, the mature ovum and three polar bodies. In the development of the spermatozoa, as in the maturation of the ovum, there is a reduction of the nuclear chromosomes to one-half of those present in the primary spermatocyte. But here the similarity ends, for it must be noted that the four spermatozoa are of equal size, and each is capable of fertilizing a mature ovum, whereas the three polar bodies are not only very much smaller than the mature ovum but are incapable of further development, and may be regarded as abortive ova. I FERTILIZATION OF THE OVUM. Fertilization consists in the union of the spermatozoon with the mature ovum (Fig. 8). Nothing is known regarding the fertilization of the human ovum, but II 1. Polar bodies- Female pronucleus Male pronucleus Female pronudetis Male pronucleus 5. Segmentation nucleus Female promtcleus Male pronucleus ~ Fused pronuclei Segmentation nucleus {commencing division) Fio. 8. — The process of fertilization in the ovum of a mouse. (After Sobotta.) the various stages of the process have been studied in other mammals, and from the knowledge so obtained it is believed that fertilization of the human ovum takes place in the lateral or ampullary part of the uterine tube, and the ovum is then conveyed along the tube to the cavity of the uterus — a journey probably occupy- ing seven or eight days and during which the ovum loses its corona radiata and zona striata and undergoes segmentation. Sometimes the fertilized ovum is arrested in the uterine tube, and there undergoes development, giving rise to a tubal preg- nancy; or it may fall into the abdominal cavity and produce an abdominal preg- nancy. Occasionally the ovum is not expelled from the follicle when the latter ruptures, but is fertilized within the follicle and produces what is known as an ovarian pregnancy. Under normal conditions only one spermatozoon enters the yolk and takes part in the process of fertilization. At the point where the sperma SEGMENTATION OF THE FERTILIZED OVUM 45 tozoon is about to pierce, the yolk is drawn out into a conical elevation, termed the cone of attraction. As soon as the spermatozoon has entered the yolk, the per- ipheral portion of the latter is transformed into a membrane, the vitelline membrane which prevents the passage of additional spermatozoa. Occasionally a second spermatozoon may enter the yolk, thus giving rise to a condition of polyspermy: when this occurs the ovum usually develops in an abnormal manner and gives rise to a monstrosity. Having pierced the yolk, the spermatozoon loses its tail, while its head and connecting piece assume the form of a nucleus containing a cluster of chromosomes. This constitutes the male pronucleus, and associated with it there are a centriole and centrosome. The male pronucleus passes more deeply into the yolk, and coincidently with this the granules of the cytoplasm surrounding it become radially arranged. The male and female pronuclei migrate toward each other, and. meeting near the center of the yolk, fuse to form a new nucleus, the segmentation nucleus, which therefore contains both male and female nuclear substance; the former transmits the individualities of the male ancestors, the latter those of the female ancestors, to the future embryo. By the union of the male and female pronuclei the number of chromosomes is restored to that which is present in the nuclei of the somatic cells. Fig. 9. — First stages of segmentation of a mammalian ovum. Semidiagrammatic. (From a drawing by Allen liomson.) z.p. Zona striata, p.gl- Polar bodies, a. Twocell stage, h. Four-cell stage, c. Eight-cell stage. t. Morula stage. SEGMENTATION OF THE FERTILIZED OVUM. The early segmentation of the human ovum has not yet been observed, but judging from what is known to occur in other mammals it may be regarded as certain that the process starts immediately after the ovum has been fertilized, i. e., while the ovum is in the uterine tube. The segmentation nucleus exhibits the usual mitotic changes, and these are succeeded by a division of the ovum into two cells of nearly equal size.^ The process is repeated again and again, so that > In the mammalian ova the nutritive yolk or deutoplasm is small in amount and uniformly distributed through- out the cytoplasm; such ova undergo complete division during the process of segmentation, and are therefore termed holoblashc. In the ova of birds, reptiles, and fishes where the nutritive volk forms by far the larger portion of the ^K^k' t '^'^^^'i^Se IS limited to the formative yolk, and is therefore only partial; such ova are termed meroblastic. Again, It has been observed, in some of the lower animals, that the pronuclei do not fuse but merely lie in apposition. At the commencement of the segmentation process the chromosomes of the two pronuclei group themselves around the equator of the nuclear spindle and then divide ; .in equal number of male and female chromosomes travel to the opposite poles of the spindle, and thus the male and female pronuclei contribute equal shares of chromatin to the nuclei of the two cells which result from the subdivision of the fertilized ovum 46 EMBRYOLOGY the two cells are succeeded by four, eight, sixteen, thirty-two, and so on, with the result that a mass of cells is found within the zona striata, and to this mass the term morula is applied (Fig. 9). The segmentation of the mammalian ovum may not take place in the regular sequence of two, four, eight, etc., since one of the two first formed cells may subdivide more rapidly than the other, giving rise to a three- or a five-cell stage. The cells of the morula are at first closely aggregated, but soon they become arranged into an outer or peripheral layer, the trophoblast, which Inner cell-mass Entoderm Blastodermic vesicle Trophoblast Fig. 10. — Blastodermic vesicle of Vespertilio miirinus. (After van Beneden. Inner cell-mass TrofhMast Embryonic ectoderm Entoderm Fig. 11. — Section through embryonic disk of Vespertilio murinus. (After van Beneden.) #1 Maternal bloodvessels Amniotic cavity Syncytiotrcphoblast CyMrcpTioblast Embryonic ectoderm Entoderm Fig. 12. — Section through embryonic area of Vespertilio murinus to show the formation of the amniotic cavity. (After van Beneden,) does not contribute to the formation of the embryo proper, and an inner cell-mass, from which the embryo is developed. Fluid collects between the trophoblast and the greater part of the inner cell-mass, and thus the morula is converted into a vesicle, the blastodermic vesicle (Fig. 10). The inner cell-mass remains in con- tact, however, with the trophoblast at one pole of the ovum; this is named the embryonic pole, since it indicates the situation where the future embryo will be developed. The cells of thf. trophoblast become differentiated into two strata: an SEGMENTATION OF THE FERTILIZED OVUM 47 I outer, termed the syncytium or s3mcytiotrophoblast, so named because it consists of j a layer of protoplasm studded with nuclei, but showing no evidence of subdivision into cells; and an inner layer, the cytotrophoblast or layer of Langhans, in which the cell outlines are defined. As already stated, the cells of the trophoblast do not contribute to the formation of the embryo proper; they form the ectoderm of the chorion and play an important part in the development of the placenta. On the deep surface of the inner cell-mass a layer of flattened cells, the entoderm, is differ- entiated and quickly assumes the form of a small sac, the yolk-sac. Spaces appear between the remaining cells of the mass (Fig. 11), and by the enlargement and coalescence of these spaces a cavity, termed the amniotic cavity (Fig. 12), is gradually ^^ developed. The floor of this cavity is formed by the embryonic disk composed ^■1 of a layer of prismatic cells, the embryonic ectoderm, derived from the inner cell- ^H mass and lying in apposition with the entoderm. ^■1 The Primitive Streak; Formation of the Mesoderm. — The embryonic disk ^H becomes oval and then pear-shaped, the wider end being directed forward. Near !■' the narrow, posterior end an opaque streak, the primitive streak (Figs. 13 and 14), makes its appearance and extends along the middle of the disk for about one-half of its length; at the anterior end of the streak there is a knob- like thickening termed Hensen's knot. A shallow groove, the primitive groove, appears on the surface of the streak, and the anterior end of this groove communicates by means of an aperture, the blastophore, with the yolk-sac. The primitive streak is produced by a thickening of the axial part of the ectoderm, the cells of which multiply, grow downward, and blend with those of the subjacent entoderm (Fig. 15). From the sides of the primitive streak a third layer of cells, the mesoderm, extends lateralward I between the ectoderm and entoderm; the caudal end of Hi the primitive streak forms the cloacal membrane. " ■ The extension of the mesoderm takes place throughout the whole of the embry- onic and extra-embryonic areas of the ovum, except in certain regions. One of these is seen immediately in front of the neural tube. Here the mesoderm extends » forward in the form of two crescentic masses, which meet in the middle line so as Hi to enclose behind them an area which is devoid of mesoderm. Over this area the r ectoderm and entoderm come into direct contact with each other and constitute a thin membrane, the buccopharyngeal membrane, which forms a septum between the primitive mouth and pharynx. In front of the buccopharyngeal area, where the lateral crescents of mesoderm fuse in the middle line, the pericardium is afterward developed, and this region is therefore designated the pericardial area. A second region where the mesoderm is absent, at least for a time, is that imme- diately in front of the pericardial area. This is termed the proamniotic area, and is the region where the proamnion is developed; in man, however, a proamnion is apparently never formed. A third region is at the hind end of the embryo where the ectoderm and entoderm come into apposition and form the cloacal membrane. The blastoderm now consists of three layers, named from without inward: ectoderm, mesoderm, and entoderm; each has distinctive characteristics and gives rise to certain tissues of the body.^ Ectoderm. — ^The ectoderm consists of columnar cells, which are, however, somewhat flattened or cubical toward the margin of the embryonic disk. It forms the whole of the nervous system, the epidermis of the skin, the lining cells of the sebaceous, Fig. 13. — Surface view of embryo of a rabbit. (After KoUiker.) arg. Embryonic disk. pr. Primiti%'e streak. I ' The mode of formation of the germ layers in the human ovum has not yet been observed; in the youngest known human ovum (viz., that described by Bryce and Teacher), all three layers are already present and the mesoderm is split into its two layers. The extra-embryonic celom is of considerable size, and scattered mesodermal strands are seen stretching between the mesoderm of the yolk-sac and that of the chorion. Amnion Allantois in body-stalk EMBRYO! Yolk-sac - — Y } Notochord Amnion -f — -gf • Neurenteric canal Primitive streak ' Fig. 14. — Surface view of embrj'o of Hylobates concolor. (After Selenka.) The amnion has been opened to expose the embryonic disk. m HI Fig. 15. — Series of transverse sections through the embryonic disk of Tarsius. (After Hubrecht ) Section / passes through the disk, in front of Hensen's knot and shows only the ectoderm and entoderm. Sections //, III, and IV pass through Hensen's knot, which is seen in V tapering away into the primitive streak. In III, IV, and V the mesoderm is seen springing from the keel-like thickening of the ectoderm, which in III and IV is observed to be continuous into the entoderm. SEGMENTATION OF THE FERTILIZED OVUM 49 sudoriferous-, and mammary glands, the hairs and nails, the epithelium of the nose and adjacent air sinuses, and that of the cheeks and roof of the mouth. From it also are derived the enamel of the teeth, and the anterior lobe of the hypophysis cerebri, the epithelium of the cornea, conjunctiva, and lacrimal glands, and the neuro-epithelium of the sense organs. Entoderm. — The entoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of the whole of the digestive tube excepting part of the mouth and pharynx and the terminal part of the rectum (which are lined by involutions of the ectoderm), the lining cells of all the glands I, which open into the digestive tube, including those of the liver and pancreas, HL IV. ^ 8m sp Fig. 16. — A series of transverse sections through an embryo of the dog. (After Bonnet.) Section I is the most anterior. In V the neural plate is spread out nearly flat. The series shows the uprising of the neural folds to form the neural canal, a. Aortse. c. Intermediate cell mass. ect. Ectoderm, ent. Entocferm. h, h. Rudiments of endothelial heart tubes. In ///, IV, and V the scattered cells represented between the entoderm and splanchnic layer of meso- derm are the vasoformative cells which give origin in front, according to Bonnet, to the heart tubes, h; l.p. Lateral plate still undivided in 7, II, and III; in IV and V split into somatic (sm) and splanchnic (sp) layers of mesoderm. mea. Mesoderm, p. Pericardium, so. Primitive segment. the epithelium of the auditory tube and tympanic cavity, of the trachea, bronchi, and air cells of the lungs, of the urinary bladder and part of the urethra, and that which lines the follicles of the thyroid gland and thymus. Mesoderm. — ^The mesoderm consists of loosely arranged branched cells sur- rounded by a considerable amount of intercellular fluid. From it the remaining tissues of the body are developed. The endothelial lining of the heart and blood- vessels and the blood corpuscles are, however, regarded by some as being of ento- dermal origin. As the mesoderm develops between the ectoderm and entoderm it is separated into lateral halves by the neural tube and notochord, presently to be described. A 4 50 EMBRYOLOGY I longitudinal groove appears on the dorsal surface of either half and divides it into a medial column, the paraxial mesoderm, lying on the side of the neural tube, and a lateral portion, the lateral mesoderm. The mesoderm in the floor of the groove connects the paraxial with the lateral mesoderm and is known as the intermediate cell-mass; in it the genito-urinary organs are developed. The lateral mesoderm splits into two layers, an outer or somatic, which becomes applied to the inner surface of the ectoderm, and with it forms the somatopleure ; and an inner or splanchnic, which adheres to the entoderm, and with it forms the splanchnoplem-e (Fig. IG). The space between the two layers of the lateral mesoderm is termed the celom. THE NEURAL GROOVE AND TUBE. ^1 In front of the primitive streak two longitudinal ridges, caused by a folding up of the ectoderm, make their appearance, one on either side of the middle line (Fig. 16). These are named the neural folds; they commence some little distance Ydksac Amnion Neural groove Neurenteric canal Primitive streak Body-stalk f IG. 17. — Human embryo — length, 2 mm. Dorsal view, with the amnion laid open. X 30. (After Graf Spee.) ' behind the anterior end of the embryonic disk, where they are continuous with each other, and from there gradually extend backward, one on either side of the anterior end of the primitive streak. Between these folds is a shallow median groove, the neural groove (Figs. 16, 17) . The groove gradually deepens as the neural folds become elevated, and ultimately the folds meet and coalesce in the middle line and convert the groove into a closed tube, the neural tube or canal (Fig. 18), the ectodermal wall of which forrns the rudiment of the nervous system. After the coalescence of the neural folds over the anterior end of the primitive streak, the blastopore no longer opens on the surface but into the closed canal of the neural tube, and thus a transitory communication, the neurenteric canal, is established between the neural tube and the primitive digestive tube. The coalescence of the neural folds occurs first in the region of the hind-brain, and from there extends forward and backward; toward the end of the third week the front opening (anterior neuropore) of the tube finally closes at the anterior end of the future brain, and forms a recess which is in contact, for a time, with the overlying ectoderm; the hinder part of the neural groove presents for a time a rhomboidal shape, and to this THE NEURAL GROOVE AND TUBE 51 expanded portion the term sinus rhomboidalis has been applied (Fig. 18). Before the neural groove is closed a ridge of ectodermal cells appears along the prominent margin of each neural fold ; this is termed the neural crest or ganglion ridge, and from it the spinal and cranial nerve ganglia and the ganglia of the sympathetic nervous system are developed. By the upward growth of the mesoderm the neural tube is ultimately separated from the overlying ectoderm. .Head fold of amnion partly covering the fore-brain Mid-brain -' Hind-brain Nerve ganglion Auditory vesicle Vitelline vein Fourteenth 'primitive -7 segment Paraxial mesoderm -%_ Neural fold f Sinus rhomboidalis - Htnvains of primitive streak - Heart Fig. 18. — Chick embryo of thirty-thi' (From Dm ion, viewed from the dorsal aspect. X 30. u Embrj'ologie.") The cephalic end of the neural groove exhibits several dilatations, which, when the tube is closed, assume the form of three vesicles; these constitute the three primary cerebral vesicles, and correspond respectively to the future fore-brain (pros- encephalon), mid-brain (mesencephalon), and hind-brain (rhombencephalon) (Fig. 18). The walls of the vesicles are developed into the nervous tissue and neuroglia of the brain, and their cavities are modified to form its ventricles. The remainder IBRYOLOGY I of the tube forms the medulla spinalis or spinal cord; from its ectodermal wall the nervous and neuroglial elements of the medulla spinalis are developed while the cavity persists as the central canal. THE NOTOCHORD. '■ The notochord (Fig. 19) consists of a rod of cells situated on the ventral aspect of the neural tube ; it constitutes the foundation of the axial skeleton, since around it the segments of the vertebral column are formed. Its appearance synchronizes with that of the neural tube. On the ventral aspect of the neural groove an axial thickening of the entoderm takes place; this thickening assumes the appearance of a furrow — the chordal furrow — the margins of which come into contact, and so convert it into a solid rod of cells — the notochord — which is then separated from the entoderm. It extends throughout the entire length of the future vertebral Ectoderm .. Neural canal Primitive Wolffian segment duct Celom Somatic mesoderm Entoderm >' _ Notochord Aorta Splanchnic mesoderm Fig. 19. — Transverse section of a chick embryo of forty-five hours' incubation. (Balfour.) column, and reaches as far as the anterior end of the mid-brain, where it ends in a hook-like extremity in the region of the future dorsum sellse of the sphenoid bone. It lies at first between the neural tube and the entoderm of the yolk-sac, but soon becomes separated from them by the mesoderm, which grows medial- ward and surrounds it. From the mesoderm surrounding the neural tube and notochord, the skull and vertebral column, and the membranes of the brain and medulla spinalis are developed. THE PRIMITIVE SEGMENTS. Toward the end of the second week transverse segmentation of the paraxial mesoderm begins, and it is converted into a series of well-defined, more or less cubical masses, the primitive segments (Figs. 18, 19, 20), which occupy the entire length of the trunk on either side of the middle line from the occipital region of the head. Each segment contains a central cavity — myocoel — which, however, is soon filled with angular and spindle-shaped cells. Thef primitive segments lie immediately under the ectoderm on the lateral aspect of the neural tube and notochord, and are con- nected to the lateral mesoderm by the inter- mediate cell-mass. Those of the trunk may Yolk: Cut edge of amnion Primitive segments FlQ. Neural folds Neurenteric canal 20. — Dorsum of human embryo, 2.11 mm. in length. (.\fter Eternod.) SEPARATION OF THE EMBRYO 53 f be arranged in the following groups, viz. : cervical 8, thoracic 12, lumbar 5, sacral 5, and coccygeal from 5 to 8. Those of the occipital region of the head are usually described as being four in number. In mammals primitive segments of the head can be recognized only in the occipital region, but a study of the lower vertebrates leads to the belief that they are present also in the anterior part of the head, and that altogether nine segments are represented in the cephalic region. SEPARATION OF THE EMBRYO. The embryo increases rapidly in size, but the circumference of the embryonic disk, or line of meeting of the embryonic and amniotic parts of the ectoderm, is of relatively slow growth and gradually comes to form a constriction between the embryo and the greater part of the yolk-sac. By means of this constriction, which corresponds to the future umbilicus, a small part of the yolk-sac is enclosed within the embryo and constitutes the primitive digestive tube. Villi of chorion Amnion Embryonic disk Rudiment of heart Chorion Mesoderm. Body-stalk Primitive streak Mesoderm Bloodvessel Fia. 21. — Section through the embryo which is represented in Fig. 17. (After Graf Spee.) The embryo increases more rapidly in length than in width, and its cephalic and caudal ends soon extend beyond the corresponding parts of the circumference of the embryonic disk and are bent in a ventral direction to form the cephalic and caudal folds respectively (Figs. 26 and 27). The cephalic fold is first formed, and as the proamniotic area (page 47) lying immediately in front of the pericardial area (page 47) forms the anterior limit of the circumference of the embryonic disk, the forward growth of the head necessarily carries with it the posterior end of the pericardial area, so that this area and the buccopharyngeal membrane are folded back under the head of the embryo which now encloses a diverticulum of the yolk-sac named the fore-gut. The caudal end of the embryo is at first connected to the chorion by a band of mesoderm called the body-stalk, but with the formation of the caudal fold the body-stalk assumes a ventral position; a diverticulum of the \'olk-sac extends into the tail fold and is termed the hind-gut. Between the fore-gut EMBRYOLOGY and the hind-gut there exists for a time a wide opening into the yolk-sac, but the-i latter is gradually reduced to a small pear-shaped sac (sometimes termed the) umbilical vesicle), and the channel of communication is at the same time narrowed ^ and elongated to form a tube called the vitelline duct. THE YOLK-SAC. The yolk-sac (Figs. 22 and 23) is situated on the ventral aspect of the embryo; i it is lined by entoderm, outside of which is a layer of mesoderm. It is filled with fluid, the vitelline fluid, which possibly may be utilized for the nourishment of the embryo during the earlier stages of its existence. Blood is conveyed to the wall of the sac by the primitive aortse, and after circulating through a wide-meshed capil- lary plexus, is returned by the vitelline veins to the tubular heart of the embryo. This constitutes the vitelline circulation, and by means of it nutritive material is absorbed from the yolk-sac and conveyed to the embryo. At the end of the fourth week the yolk-sac presents the appearance of a small pear-shaped vesicle (umbilical vesicle) opening into the digestive tube by a long narrow tube, the vitelline duct. The vesicle can be seen in the after-birth as a small, somewhat oval-shaped body Amnion Heart Yolk-sac Heart HTjoid arch Mandibular arch- Maxillary process Eye Fore-limb Body-stalk Fig. 22. — Human embryo of 2.6 mm. (His.) Fig. 23. Hind-limb -Human embryo from thirty-one to thirty-four days. (His.) whose diameter varies from 1 mm. to 5 mm.; it is situated between the amnion and the chorion and may lie on or at a varying distance from the placenta. As a rule the duct undergoes complete obliteration during the seventh week, but in about three per cent, of cases its proximal part persists as a diverticulum from the small intestine, Meckel's diverticulum, which is situated about three or four feet above the ileocolic junction, and may be attached by a fibrous cord to the abdominal wall at the umbilicus. Sometimes a narrowing of the lumen of the ileum is seen opposite the site of attachment of the duct. DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA. The Allantois (Figs. 25 to 28). — The allantois arises as a tubular diverticulum of the posterior part of the yolk-sac; when the hind-gut is developed the allantois is carried backward with it and then opens into the cloaca or terminal part of the hind-gut: it grows out into the body-stalk, a mass of mesoderm which lies below and around the tail end of the embryo. The diverticulum is lined by entoderm and covered by mesoderm, and in the latter are carried the allantoic or umbilical vessels. )EVELOPMENT OF THE FETAL MEMBRANES AXD THE PLACENTA 55 In reptiles, birds, and many mammals the allantois becomes expanded into d, "vesicle which projects into the extra-embryonic celom. If its further development be traced in the bird, it is seen to project to the right side of the embryo, and, gradually expanding, it spreads over its dorsal surface as a flattened sac between the amnion and the serosa, and extending in all directions, ultimately surrounds the yolk. Its outer wall becomes applied to and fuses with the serosa, which lies immediately inside the shell membrane. Blood is carried to the allantoic sac by Amniotic cavity FlQ. Amniotic cavity Yolk-sac Chorion 2i. — Diagram showing earliest observed stage of human ovum. FlQ Body-stalk Allantois Yolk-sac - Chorion 25. — Diagram illustrating early formation allantois and dififerentiation of body-stalk. the two allantoic or umbilical arteries, which are continuous with the primitive aortse, and after circulating through the allantoic capillaries, is returned to the primitive heart by the two umbilical veins. In this way the allantoic circulation, which is of the utmost importance in connection with the respiration and nutrition of the chick, is established. Oxygen is taken from, and carbonic acid is given up to the atmosphere through the egg-shell, while nutritive materials are at the same time absorbed by the blood from the yolk. Amniotic cavity Embryo Body-stalk Placental villi Placental villi Allantois Yolk-sac Chorion Body-stalk Allantois Yolk-sac Heart Heart Fig. 26 — Diagram showing later stage of allan- toic development with commencing constriction of the yolk-sac. Fore-gut Embryo Amniotic cavity Fio. 27. — Diagram showing the expansion of amnion and delimitation of the umbilicus. In man and other primates the nature of the allantois is entirely different from that just described. Here it exists merely as a narrow, tubular diverticulum of the hind-gut, and never assumes the form of a vesicle outside the embryo. With the formation of the amnion the embryo is, in most animals, entirely separated from the chorion, and is only again united to it when the allantoic mesoderm spreads over and becomes applied to its inner surface. The human embryo, on the other hand, as was pointed out by His, is never wholly separated from the chorion, its 56 EMBRYOLOGY tail end being from the first connected with the chorion by means of a thick bana of mesoderm, named the body-stalk (Bauchstiel) ; into this stalk the tube of th(! allantois extends (Fig. 21). The Amnion. — The amnion is a membranous sac which surrounds and protects the embryo. It is developed in reptiles, birds, and mammals, which are hence called "Amniota;" but not in amphibia and fishes, which are consequently termed "Anamnia." In the human embryo the earliest stages of the formation of the amnion have not been observed; in the youngest embryo which has been studied the amnion was already present as a closed sac (Figs. 24 and 32), and, as indicated on page 46, appears in the inner cell-mass as a cavity. This cavity is roofed in by a single stratum of flattened, ectodermal cells, the amniotic ectoderm, and its floor consists of the prismatic ectoderm of the embryonic disk — the continuity between the roof and floor being established at the margin of the embryonic disk. Outside the amniotic ectoderm is a thin layer of mesoderm, which continuous with that of the Placental villi IS Yolk-sac Umbilical cord Allantois Heart Digestive tvbe Embryo Amniotic cavity Fio. 28. — Diagram illustrating a later stage in the development of the umbilical cord. somatopleure and is connected by the body-stalk with the meso- dermal lining of the chorion. When first formed the amnion is in contact with the body of the embryo, but about the fourth or fifth week fluid {liquor amnii) be- gins to accumulate within it. This fluid increases in quantity and causes the amnion to expand and ultimately to adhere to the inner surface of the chorion, so that the extra-embryonic part of the celom is obliterated. The liquor amnii increases in quantity up to the sixth or seventh month of preg- nancy, after which it diminishes somewhat; at the end of preg- nancy it amounts to about 1 liter. It allows of the free movements of the fetus during the later stages of pregnancy, and also protects it by diminishing the risk of injury from without. It contains less than 2 per cent, of solids, consisting of urea and other extractives, inorganic salts, a small amount of protein, and frequently a trace of sugar. That some of the liquor amnii is swallowed by the fetus is proved by the fact that epidermal debris and hairs have been found among the contents of the fetal alimentary canal. In reptiles, birds, and many mammals the amnion is developed in the following manner: At the point of constriction where the primitive digestive tube of the embryo joins the yolk-sac a reflection or folding upward of the somatopleure takes place. This, the amniotic fold (Fig. 29), first makes its appearance at the cephalic extremity, and subsequently at the caudal end and sides of the embryo, and grad- ually rising more and more, its different parts meet and fuse over the dorsal aspect of the embryo, and enclose a cavity, the amniotic cavity. After the fusion of the edges of the amniotic fold, the two layers of the fold become completely separated, the inner forming the amnion, the outer the false anmion or serosa. The space between the amnion and the serosa constitutes the extra-embryonic celom, and for a time communicates with the embryonic celom. I DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 57 The Umbilical Cord and Body-stalk. — ^The umbilical cord (Fig. 28) attaches the fetus to the placenta; its length at full time, as a rule, is about equal to the Fig. 29. — Diagram of a transverse section, showing the mode of formation of the amnion in the chick. The amniotic folds have nearly united in the middle line. (From Quain's Anatomy.) Ectoderm, blue; mesoderm, red; entoderm and notochord, black. Umbilical cord Chorion Placenta Amnion Umbilical cord Yolk^ac Vitelline duct Fig. 30. — Fetua of about eight weeks, enclosed in the amnioa. Magnified a little over two diameters. (Drawn from stereoscopic photographs lent by Prof. A. Thomson, Oxford.) length of the fetus, i. e., about 50 cm., but it may be greatly diminished or increased. The rudiment of the umbilical cord is represented by the tissue which connects- the rapidly growing embryo with the extra-embryonic area of the ovum. Included in this tissue are the body-stalk and the vitelline duct— the former containing the allantoic diverticulum and the umbilical vessels, the latter forming the communica- tion between the digestive tube and the yolk-sac. The body-stalk is the posterior segment of the embryonic area, and is attached to the chorion. It consists of a plate of mesoderm covered by thickened ectoderm on which a trace of the neural groove can be seen, indicating its continuity with the embryo. Running through its mesoderm are the two umbilical arteries and the two umbilical veins, together with the canal of the allantois — the last being lined by entoderm (Fig. 31). Its dorsal] surface is covered by the amnion, while its ventral surface is bounded b}^ the extra- embryonic celom, and is in contact with the vitelline duct and yolk-sac. With the rapid elongation of the embryo and the formation of the tail fold, the body stalk comes to lie on the ventral surface of the embryo (Figs. 27 and 28), where Splanchnic mesoderm Entoderm, Vitelline veins Somatic iriesodemi Amniotic cavity Amniofi Neural groove Body-stalk Fig. 31. — Model of human embryo 1.3 mm. long, (.\fter Eternod.) its mesoderm blends with that of the yolk-sac and the vitelline duct. The lateral leaves of somatopleure then grow round on each side, and, meeting on the ventral aspect of the allantois, enclose the vitelline duct and vessels, together with a part of the extra-embryonic celom; the latter is ultimately obliterated. The cord is covered by a layer of ectoderm which is continuous with that of the amnion, and its various constitutents are enveloped by embryonic gelatinous tissue, jelly of Wharton. The vitelline vessels and duct, together with the right umbilical vein, undergo atrophy and disappear; and thus the cord, at birth, contains a pair of umbilical arteries and one (the left) umbilical vein. Implantation or Imbedding of the Ovum. — As described (page 44), fertilization of the ovum occurs in the lateral or ampullary end of the uterine tube and is immediately followed by segmentation. On reaching the cavity of the uterus the segmented ovum adheres like a parasite to the uterine mucous membrane, destroys the epithelium over the area of contact, and excavates for itself a cavity in the mucous membrane in which it becomes imbedded. In the ovum described by DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 59 IBryce and Teacher^ the point of entrance was visible as a small gap closed by a mass of fibrin and leucocytes; in the ovum described by Peters^ the opening was covered by a mushroom-shaped mass of fibrin and blood-clot (Fig. 32), the narrow stalk of which plugged the aperture in the mucous membrane. Soon, however, ^ all trace of the opening is lost and the ovum is then completely surrounded by the It uterine mucous membrane. The structure actively concerned in the process of excavation is the trophoblast • of the ovum, which possesses the power of dissolving and absorbing the uterine tissues. The trophoblast proliferates rapidly and forms a network of branching processes which cover the entire ovum and invade and destroy the maternal ^^ tissues and open into the maternal bloodvessels, with the result that the spaces ^■( in the trophoblastic network are filled w ith maternal blood ; these spaces com- 1^^ municate freely with one another and become greatly distended and form the intervillous space. TTi.v. tr. a.Q. tr. II F^o. 32. — Section through ovum imbedded in the uterine decidua. Semidiagrammatic. (After Peters.) am. Ammotic cavity, h.c. Blood-clot. h.s. Body-stalk, ect. Embryonic ectoderm, ent. Entoderm, mes. Mesoderm. m.x. Maternal vessels, tr. Trophoblast. u.e. Uterine epithelium, u.g. Uterine glands, j/.s. Yolk-sac. The Decidua. — Before the fertilized ovum reaches the uterus, the mucous membrane of the body of the uterus undergoes important changes and is then known as the decidua. The thickness and vascularity of the mucous membrane are greatly increased; its glands are elongated and open on its free surface by funnel-shaped orifices, while their deeper portions are tortuous and dilated into irregular spaces. The interglandular tissue is also increased in quantity, and is crowded with large round, oval, or polygonal cells, termed decidual cells. These changes are well advanced by the second month of pregnancy, when the mucous membrane consists of the following strata (Fig. 33): (1) stratum compactum, next > Contribution to the study of the early development and imbedding of the human ovum, 1908. ' Die Einbettung des menschlichen Eies, 1899. 60 EMBRYOLOGY MvxMus membrane Muscular fibers Stratum compactum the free surface; in this the uterine glands are only slightly expanded, and arej lined by columnar cells; (2) stratum spongiosum, in which the gland tubes are greatly dilated and very tortuous, and are ultimately separ-ated from one another by only a small amount of interglandular tissue, while their lining cells are flattened or' cubical; (3) a thin unaltered or boundary layer, next the uterine muscular fibers, containing the deepest parts of the uterine glands, which are not dilated, and are lined with columnar epithelium; it is from this epithelium that the epithelial lining of the uterus is re- generated after pregnancy. Distinc- tive names are applied to different portions of the decidua. The part which covers in the ovum is named the decidua capsularis; the portion which intervenes between the ovum and the uterine wall is named the decidua basalis or decidua placentalis ; it is here that the placenta is subsequently developed. The part of the decidua which lines the remainder of the body of the uterus is known as the decidua vera or decidua parietaUs. Coincidently with the growth of the embryo, the decidua capsularis is thinned and extended (Fig. 34) and the space between it and the decidua vera is gradually obliterated, so that by the third month of pregnancy the two are in contact. By the fifth month of pregnancy the decidua cap- sularis has practically disappeared, while during the succeeding months the decidua vera also undergoes atrophy, owing to the increased press- ure. The glands of the stratum com- pactum are obliterated, and their epithelium is lost. In the stratum spongiosum the glands are compressed and appear as slit-like fissures, while their epithelium undergoes degener- ation. In the unaltered or boundary layer, however, the glandular epithe- lium retains a columnar or cubical form. The Chorion (Figs. 23 to 28) .—The chorion consists of two layers : an outer formed by the primitive ectoderm or trophoblast, and an inner by the soma- tic mesoderm; with this latter the amnion is in contact. The trophoblast is made up of an internal layer of cubical or prismatic cells, the c3rtotrophoblast or layer of Langhans, and an external layer of richly nucleated protoplasm devoid of cell boundaries, the syncytiotrophoblast. It undergoes rapid proliferation and forms numerous processes, the chorionic villi, which invade and destroy the uterine decidua and at the same time absorb from it nutritive materials for the growth Stratum spongiosum Unaltered or boundary layer Muscular fibers Fig. 33. — Diagrammatic sections of the uterine mucous membrane: A. The non-pregnant uterus. B. The preg- nant uterus, showing the thickened mucous membrane and the altered condition of the uterine glands. (Kundrat and Engelmann.) I DEVELOPMENT OP THE FETAL MEMBRANES AND THE PLACENTA 61 of the embryo. The chorionic villi are at first small and non-vascular, and consist of trophoblast only, but they increase in size and ramify, while the mesoderm, carrying branches of the umbilical vessels, grows into them, and in this way they are vascularized. Blood is carried to the villi by the branches of the umbilical Placeyital villi imbedded in the ^Decidua placentalis Uterine tvhe Allantois Umbilical cord with its con- tained vessels Non-placental villi im- bedded in the decidua capsularis Cavity of uterus Yolk-sac Cavity of amnion Decidua vera or parietalis Plug of rnucus in the cervix uteri Fig. 34. — Sectional plan of the gravid uterus in the third and fourth month. (Modified from Wagner.) arteries, and after circulating through the capillaries of the villi, is returned to the embryo by the umbilical veins. Until about the end of the second month of pregnancy the villi cover the entire chorion, and are almost uniform in size (Fig. 25), but after this they develop unequally. The greater part of the chorion Trophoblast esoderm Branches of umbilical i Fig. 35. — Transverse section of a chorionic villus is in contact with the decidua capsularis (Fig. 34), and over this portion the villi, with their contained vessels, undergo atrophy, so that by the fourth month scarcely . a trace of them is left, and hence this part of the chorion becomes smooth, and is named the chorion Iseve; as it takes no share in the formation of the placenta, it 62 EMBRYOLOGY is also named the non-placental part of the chorion. On the other hand, the villi on that part of the chorion which is in contact with the decidua placentalis increase greatly in size and complexity, and hence this part is named the chorion frondosum (Fig. 28). Uterine vessels Uterine glands Syncytiolroj)h6blast Cytolrophoblast Mesoderm Intervilloiis space Fig. 36. — Primary chorionic villi. Diagrammatic. (Modified from Bryce. The Placenta. — The placenta connects the fetus to the uterine wall, and is the organ by means of which the nutritive, respiratory, and excretory functions of the fetus are carried on. It is composed of fetal and maternal portions. Fetal Portion. — The fetal portion of the placenta consists of the villi of the chorion frondosum; these branch repeatedly, and increase enormously in size. These greatly ramified villi are suspended in the intervillous space, and are bathed Uterine glands Uterine vessels Syncytiotrophoblast Cytolrophoblast Core of mesoderm with fetal vessels Mesoderm Intervillous space Fig. 37. — Secondary chorionic villi. Diagrammatic. (Modified from Bryce.) in maternal blood, which is conveyed to the space by the uterine arteries and carried away by the uterine veins. A branch of an umbilical artery enters each villus and ends in a capillary plexus from which the blood is drained by a tributary of the umbilical vein. The vessels of the villus are surrounded by a thin layer of mesoderm consisting of gelatinous connective tissue, which is covered by two DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 63 strata of ectodermal cells derived from the trophoblast : the deeper stratum, next the mesodermic tissue, represents the cytotrophoblast or layer of Langhans; the fiuperficial, in contact with the maternal blood, the syncytiotrophoblast (Figs. 3(3 and 37). After the fifth month the two strata of cells are replaced by a single layer of somewhat flattened cells. Maternal Portion. — The maternal portion of the placenta is formed by the decidua placentalis containing the intervillous space. As already explained, this space is produced by the enlargement and intercommunication of the spaces in the trophoblastic network. The changes involve the disappearance of the greater portion of the stratum compactum, but the deeper part of this layer persists and is condensed to form what is known as the basal plate. Between this plate and the uterine muscular fibres are the stratum spongiosum and the boundary layer ; Wall of uterus Umbilical cord Cervix uteri Fio. 38. — Fetus in utero, between fifth and sixth months. through these and the basal plate the uterine arteries and veins pass to and from the intervillous space. The endothelial lining of the uterine vessels ceases at the point where they terminate in the intervillous space w^hich is lined by the syncytio- trophoblast. Portions of the stratum compactum persist and are condensed to form a series of septa, which extend from the basal plate through the thickness of the placenta and subdivide it into the lobules or cotyledons seen on the uterine surface of the detached placenta. The fetal and maternal blood currents traverse the placenta, the former passing through the bloodvessels of the placental villi and the latter through the inter- I villous space (Fig. 39). The two currents do not intermingle, being separated from each other by the delicate walls of the villi. Nevertheless, the fetal blood is able 64 EMBRYOLOGY I maternal blood, and give up to the latter its waste products. The blood, so purified , is carried back to the fetus by the umbilical vein. It will thus be seen that the placenta not only establishes a mechanical connection between the mother and the fetus, but subserves for the latter the purposes of nutrition, respiration, and ex- cretion. In favor of the view that the placenta possesses certain selective powers may be mentioned the fact that glucose is more plentiful in the maternal than in the fetal blood. It is interesting to note also that the proportion of iron, and of lime and potash, in the fetus is increased during the last months of pregnancy. Further, there is evidence that the maternal leucocytes may migrate into the fetal blood, since leucocytes are much more numerous in the blood of the umbilical vein than in that of the umbilical arteries. The placenta is usually attached near the fundus uteri, and more frequently on the posterior than on the anterior wall of the uterus. It may, however, occupy a lower position and, in rare cases, its site is close to the orificium internum uteri, which it may occlude, thus giving rise to the condition known as placenta previa. Stratum spongiosum Limiting or boundary layer Maternal vessels Placental septum ViUiLs Chorion Marginal sinus Fig. 39. — Scheme of placental circulation. Separation of the Placenta. — ^After the child is born, the placenta and membranes are expelled from the uterus as the after-birth. The separation of the placenta from the uterine wall takes place through the stratum spongiosum, and necessarily causes rupture of the uterine vessels. The orifices of the torn vessels are, however, closed by the firm contraction of the uterine muscular fibers, and thus postpartum hemorrhage is controlled. The epithelial lining of the uterus is regenerated by the proliferation and extension of the epithelium which lines the persistent portions of the uterine glands in the unaltered layer of the decidua. The expelled placenta appears as a discoid mass which weighs about 450 gm. and has a diameter of from 15 to 20 cm. Its average thickness is about 3 cm., but this diminishes rapidly toward the circumference of the disk, which is continu- ous with the membranes. Its uterine surface is divided by a series of fissures into lobules or cotyledons, the fissures containing the remains of the septa which extended between the maternal and fetal portions. Most of these septa end in irregular or pointed processes; others, especially those near the edge of the placenta, pass THE BRANCHIAL REGION 65 through its thickness and are attached to the chorion. In the early months these septa convey branches of the uterine arteries which open into the intervillous space on the surfaces of the septa. The fetal surface of the placenta is smooth, being closely invested by the amnion. Seen through the latter, the chorion presents a mottled appearance, consisting of gray, purple, or yellowish areas. The umbilical cord is usually attached near the center of the placenta, but may be inserted anywhere between the center and the margin; in some cases it is inserted into the membranes, i. e., the velamentous insertion. From the attach- ment of the cord the larger branches of the umbilical vessels radiate under the amnion, the veins being deeper and larger than the arteries. The remains of the vitelline duct and yolk-sac may be sometimes observed beneath the amnion, close to the cord, the former as an attenuated thread, the latter as a minute sac. , On section, the placenta presents a soft, spongy appearance, caused by the Ugreatly branched villi; surrounding them is a varying amount of maternal blood giving the dark red color to the placenta. Many of the larger villi extend from the chorionic to the decidual surface, while others are attached to the septa which separate the cotyledons; but the great majority of the villi hang free in the inter- villous space. Mid-brain Fore-brain Stomodeum andibtdar arch Heart Hind-brain Auditory vesicle Visceral arches Olfactory pit Maxillary process Amnion (cut) Mandibular arch Hyoid arch Third arch Body-stalk Fio. 40. — Embryo between eighteen and twenty-one days. (His.) Fig. 4t. — Head end of human embryo, about the end of the fourth week. (From model by Peter.) THE BRANCHIAL REGION. The Branchial or Visceral Arches and Pharyngeal Pouches. — In the lateral walls of the anterior part of the fore-gut five pharyngeal pouches appear (Fig. 42) ; each of the upper four pouches is prolonged into a dorsal and a ventral diverticulum. Over these pouches corresponding indentations of the ectoderm occur, forming what are known as the branchial or outer pharjnageal grooves. The intervening mesoderm is pressed aside and the ectoderm comes for a time into contact with the ento- dermal lining of the fore-gut, and the two layers unite along the floors of the grooves to form thin closing membranes between the fore-gut and the exterior. Later the mesoderm again penetrates between the entoderm and the ectoderm. In gill-bearing animals the closing membranes disappear, and the grooves become 5 66 EMBRYOLOGY I Lateral tongue Thyroid, elevations diverticvium complete clefts, the gill-clefts, opening from the pharynx on to the exterior; p^ ration, however, does not occur in birds or mammals. The grooves separate a series of rounded bars or arches, the branchial or visceral arches, in which thickening of the mesoderm takes place (Figs. 40 and 41). The dorsal ends of these arches are attached to the sides of the head, while the ventral extremities ultimately meet in the middle line of the neck. In all, six arches make their appearance, but of these only the first four are visible externally. The first arch is named the mandibular, and the second the hyoid; the others have no distinctive names. In each arch a cartilaginous bar, consisting of right and left halves, is developed, and with each of these there is one of the primitive aortic arches. Ml The mandibular arch lies between the first^^ branchial groove and the stomodeum; from it are developed the lower lip, the mandible, the muscles of mastication, and the anterior part of the tongue. Its cartilaginous bar is formed by what are known as Meckel's carti- lages (right and left) (Fig. 43) ; above this the incus is developed. The dorsal end of each cartilage is connected with the ear-capsule and is ossified to form the malleus; the ventral ends meet each other in the region of the symphysis menti, and are usually regarded as undergoing ossification to form that portion of the mandible which contains the incisor teeth. The intervening part of the cartilage disappears; the portion immediately adjacent to the malleus is replaced by fibrous membrane, which constitutes the spheno-mandibular ligament, Malleus Entrance to larynx Fia. 42. — Floor of pharynx of embryo shown in Fig. 40. Incus Tympanic ring ' Mandible • — Meckel's cartilage Hyoid bone Fia. 43. — Head and neck of a human embryo eighteen weeks old, with Meckel's cartilage and hyoid bar exposed (After Kolliker.) while from the connective tissue covering the remainder of the cartilage the greater part of the mandible is ossified. From the dorsal ends of the mandibular arch a triangular process, the maxillary process, grows forward on either side and forms the cheek and lateral part of the upper lip. The second or hyoid arch assists in forming the side and front of the neck. From its cartilage are developed the styloid process, stylohyoid ligament, and lesser cornu of the hyoid bone. The stages prob- 1 THE BRANCHIAL REGION 67 ably arises in the upper part of this arch. The cartilage of the third arch gives origin to the greater cornu of the hyoid bone. The ventral ends of the second and third arches unite with those of the opposite side, and form a transverse band, from which the body of the hyoid bone and the posterior part of the tongue are devel- oped. The ventral portions of the cartilages of the fourth and fifth arches unite to form the thyroid cartilage; from the cartilages of the sixth arch the cricoid and arytenoid cartilages and the cartilages of the trachea are developed. The mandibular and hyoid arches grow more rapidly than those behind them, with the result that the latter become, to a certain extent, telescoped within the former, and a deep depression, the sinus cervicalis, is formed on either side of the neck. This sinus is bounded in front by the hyoid arch, and behind by the thoracic wall; it is ultimately obliterated by the fusion of its walls. From the first branchial groove the concha auriculae and external acoustic meatus are developed, while around the groove there appear, on the mandibular and hyoid arches, a number of swellings from which the auricula or pinna is formed. The first pharyngeal pouch is prolonged dorsally to form the auditory tube and the tympanic cavity; the closing membrane between the mandibular and hyoid arches Membranous capsule over cerebral 7iemisj)here Fronto-nasal process Stomodeum Lateral nasal process Eye Globular process Maxillary process Mandibular arch Hyomandibvlar deft Fig. 44. — Under surface of the head of a human embryo about twenty-nine days old. (After His.) is invaded by mesoderm, and forms the tympanic membrane. No traces of the second, third, and fourth branchial grooves persist. The inner part of the second pharyngeal pouch is named the sinus tonsillaris; in it the tonsil is developed, above which a trace of the' sinus persists as the supratonsillar fossa. The fossa of Rosen- miiller or lateral recess of the pharynx is by some regarded as a persistent part of the second pharyngeal pouch, but it is probably developed as a secondary forma- tion. From the third pharyngeal pouch the thymus arises as an entodermal diver- ticulum on either side, and from the fourth pouches small diverticula project and become incorporated with the thymus, but in man these diverticula probably never form true thymus tissue. The parathyroids also arise as diverticula from the third and fourth pouches. From the fifth pouches the ultimobranchial bodies originate and are enveloped by the lateral prolongations of the median thyroid rudiment; they do not, however, form true thyroid tissue, nor are any traces of them found in the human adult. The Nose and Face. — During the third week two areas of thickened ectoderm, the olfactory areas, appear immediately under the fore-brain in the anterior wall of the stomodeum, one on either side of a region termed the fronto-nasal process (Fig. 44). By the upgrowth of the surrounding parts these areas are converted into pits, 68 EMBRYOLOGY the olfactory pits, which indent the fronto-nasal process and divide it into a medial and two lateral nasal processes (Fig. 45). The rounded lateral angles ol the medial process constitute the globular processes of Plis. The olfactory pits form I Future apex of nose Medial nasal frocesa Oljactory -pit Lateral rmsal process Olcbular ^ocess Maxillary process Stomodeura Mandibular arch Future apex of nose Medial nasal process Olfactory pit Lateral nasal process Globular process Maxillary process Rocf of pharynx Hypophyseal diverticulum Dorsal wall of pharynx Fig. 45. — Head end of human embryo of about thirty to thirty-one days. (From model by Peters.) Fig. 46. — Same embryo as shown in Fig. 45, with front wall of pharynx removed. the rudiments of the nasal cavities, and from their ectodermal lining the epithe- lium of the nasal cavities, with the exception of that of the inferior meatuses, is derived. The globular processes are prolonged backward as plates, termed the nasal laminae : these laminse are at first some distance apart, but, gradually approach- Lateral nasal pro- cess Olobvlar processes Fig. 47. — Head of a human embryo of about eight weeks, in which the nose and mouth are formed. (His.) Fig. 48. — Diagram showing the regions of the adult face and neck related to the fronto-nasal process and the branchial arches. ing, they ultimately fuse and form the nasal septum; the processes themselves meet in the middle line, and form the premaxillse and the philtrum or central part of the upper lip (Fig. 48). The depressed part of the medial nasal process THE BRANCHIAL REGION 69 )etv\'een the globular processes forms the lower part of the nasal septum or columella; while above this is seen a prominent angle, which becomes the future apex (Figs. 45, 46), and still higher a flat area, the future bridge, of the nose. The lateral nasal processes form the alse of the nose. ' Continuous with the dorsal end of the mandibular arch, and growing forward from its cephalic border, is a triangular process, the maxillary process, the ventral extremity of which is separated from the mandibular arch by a > shaped notch Narea Primitive palate Nasal cavity Bucconasal membranes Fig. 49. — Primitive palate of a human embryo of thirty-seven to thirty-eight days. (From model by Peters.) On the left side the lateral waU of the nasal cavity has been removed. (Fig. 44). The maxillary process forms the lateral wall and floor of the orbit, and in it are ossified the zygomatic bone and the greater part of the maxilla; it meets with the lateral nasal process, from which, however, it is separated for a time by a groove, the naso-optic furrow, that extends from the furrow encircling the eyeball to the olfactory pit. The maxillary processes ultimately fuse with the ateral nasal and globular processes, and form the lateral parts of the upper lip Gldbvlar 'process Mouth of olfactory pit, or naris Palatine process of globular process Palatine part of maxillary process Maxillary process Pharynx Fig. 50. — The roof of the mouth of a human embryo, aged about two and a half months, showing the mode of formation of the palate. (His.) I and the posterior boundaries of the nares (Figs. 47, 48). From the third to the fifth month the nares are filled by masses of epithelium, on the breaking down and disappearance of which the permanent openings are produced. The maxillary process also gives rise to the lower portion of the lateral wall of the nasal cavity. The roof of the nose and the remaining parts of the lateral wall, viz., the ethmoidal labyrinth, the inferior nasal concha, the lateral cartilage, and the lateral crus of the alar cartilage, are developed in the lateral nasal process. By the fusion of the 70 EMBRYOLOGY I maxillary and nasal processes in the roof of the stomodeum the primitive palate (Fig. 49) is formed, and the olfactory pits extend backward above it. The pos- terior end of each pit is closed by an epithelial membrane, the bucco-nasal membrane, formed by the apposition of the nasal and stomodeal epithelium. By the rupture^! of these membranes the primitive choanse or openings between the olfactory pits and the stomodeum are established. The floor of the nasal cavity is completed by the development of a pair of shelf-like palatine processes which extend medial- ward from the maxillary processes (Figs. 50 and 51); these coalesce with each other in the middle line, and constitute the entire palate, except a small part in front which is formed by the premaxillary bones. Two apertures persist for a time between the palatine processes and the premaxillse and represent the permanent channels which in the lower animals connect the nose and mouth. The union of the parts which form the palate commences in front, the premaxillary and palatine processes joining in the eighth week, while the region of the future hard palate Lateral part of_ nasal capsule Inferior concha Inferior meatus Vomeronasal ^^-a^- 'S^-v cartilage ' ' Palatine process Cartilage of '^!^ nasal septum Vomeronasal organ of Jacobson Inferior meatus Cavity of mouth Fig. 51. — Frontal section of nasal cavities of a human embryo 28 mm. long. (Kollmann.) is completed by the ninth, and that of the soft palate by the eleventh week. By the completion of the palate the permanent choanse are formed and are situated a considerable distance behind the primitive choanse. The deformity known as cleft palate results from a non-union of the palatine processes, and that of hare- lip through a non-union of the maxillary and globular processes (see page 199). The nasal cavity becomes divided by a vertical septum, which extends downward and backward from the medial nasal process and nasal laminae, and unites below with the palatine processes. Into this septum a plate of cartilage extends from the under aspect of the ethmoid plate of the chodrocranium. The anterior part of this cartilaginous plate persists as the septal cartilage of the nose and the medial crus of the alar cartilage, but the posterior and upper parts are replaced by the vomer and perpendicular plate of the ethmoid. On either side of the nasal septum, at its lower and anterior part, the ectoderm is invaginated to form a blind pouch or diverticulum, which extends backward and upward into the nasal septum and is supported by a curved plate of cartilage. These pouches form the rudiments of THE BRANCHIAL REGION 71 le vomero-nasal organs of Jacobson, which open below, close to the junction [of the premaxillary and maxillary bones. The Limbs. — The limbs begin to make their appearance in the third week as [small elevations or buds at the side of the trunk (Fig. 52). Prolongations from [the muscle- and cutis-plates of several primitive segments extend into each bud, and carry with them the anterior divisions of the corresponding spinal nerves. The nerves supplying the limbs indicate the number of primitive segments which contribute to their formation — the upper limb being derived from seven, viz., fourth cervical to second thoracic inclusive, and the lower limb from ten, viz., twelfth thoracic to fourth sacral inclusive. The axial part of the mesoderm of the limb-bud becomes condensed and converted into its cartilaginous skeleton, and by the ossification of this the bones of the limbs are formed. By the sixth week the three chief divisions of the limbs are marked off by furrows — the upper into arm, forearm, and hand; the lower into thigh, leg, and foot (Fig. 53). The limbs are at first directed backward nearly parallel to the long axis of the trunk. Heart Hyoid arch Mandibvlar arch Maxillary process Auricula - Fore-limb —Hind-limb Hg. 52. — Human embryo from thirty-one to thirty- four days. (His.) Umbilical cord Fig. 53. — Embryo of about six weeks. (His. and each presents two surfaces and two borders. Of the surfaces, one— the future flexor surface of the limb — is directed ventrally; the other, the extensor surface, dorsally; one border, the preaxial, looks forward toward the cephalic end of the embryo, and the other, the postaxial, backward toward the caudal end. The lateral epicondyle of the humerus, the radius, and the thumb lie along the preaxial border of the upper limb ; and the medial epicondyle of the femur, the tibia, and the great toe along the corresponding border of the lower limb. The preaxial part is derived from the anterior segments, the postaxial from the posterior segments of the limb- bud; and this explains, to a large extent, the innervation of the adult limb, the nerves of the more anterior segments being distributed along the preaxial (radial or tibial), and those of the more posterior along the postaxial (ulnar or fibular) border of the limb. The limbs next undergo a rotation or torsion through an angle of 90° around their long axes the rotation being effected almost entirely at the limb girdles. In the upper limb the rotation is outward and forward; in the lower b, inward and backward. As a consequence of this rotation the preaxial (radial) Htlim 72 EMBRYOLOGY border of the fore-limb is directed lateralward, and the preaxial (tibial) borde of the hind-limb is directed medialward; thus the flexor surface of the fore-limb is turned forward, and that of the hind-limb backward. DEVELOPMENT OF THE BODY CAVITIES. «l In the human embryo described by Peters the mesoderm outside the embryonic disk is split into two layers enclosing an extra-embryonic coelom; there is no trace of an intra-embryonic coelom. At a later stage four cavities are formed within the embryo, viz., one on either side within the mesoderm of the pericardial area, and one in either lateral mass of the general mesoderm. All these are at first independent of each other and of the extra-embryonic celom, but later they become continuous. The two cavities in the general mesoderm unite on the ventral aspect of the gut and form the pleuro-peritoneal cavity, which becomes continuous with the remains of the extra-embryonic celom around the umbilicus; the two cavities in the peri- cardial area rapidly join to form a single pericardial cavity, and this from two lateral diverticula extend caudalward to open into the pleuro-peritoneal cavity (Fig. 54). y'^^K Mesentery Pleural cavity \^ lAi/ng. Pleuro- pericardial opening Pericardium Mesoderm surrounding duct ofCuvier "-^Dorsal mesocardium ~^Heart Fig. 64. — Figure obtained by combining several successive sections of a human embryo of about the fourth week (From KoUmann.) The upper arrow is in the pleuroperitoneal opening, the lower in the pleuropericardial. Between the two latter diverticula is a mass of mesoderm containing the ducts of Cuvier, and this is continuous ventrally with the mesoderm in which the umbili- cal veins are passing to the sinus venosus. A septum of mesoderm thus extends across the body of the embryo. It is attached in front to the body-wall between the pericardium and umbilicus; behind to the body-wall at the level of the second cervical segment; laterally it is deficient where the pericardial and pleuro-peri- toneal cavities communicate, while it is perforated in the middle line by the fore- gut. This partition is termed the septum transversum, and is at first a bulky plate of tissue. As development proceeds the dorsal end of the septum is carried grad- ually caudalward, and when it reaches the fifth cervical segment muscular tissue with the phrenic nerve grows into it. It continues to recede, however, until it reaches the position of the adult diaphragm on the bodies of the upper lumbar vertebrae. The liver buds grow into the septum transversum and undergo development there. The lung buds meantime have grown out from the fore-gut, and project laterally into the forepart of the pleuro-peritoneal cavity; the developing stomach and liver are imbedded in the septum transversum; caudal to this the intestines project into the back part of the pleuro-peritoneal cavity (Fig. 55) . Owing to the descent of I DEVELOPMENT OF THE BODY CAVITIES 73 the dorsal end of the septum transversum the lung buds come to lie above the septum and thus pleural and peritoneal portions of the pleuro-peritoneal cavity (still, however, in free communication with one another) may be recognized; the pericardial cavity opens into the pleural part. Left due of Cuvier Hsopluxgus Right duct of Cuvier Omental bursa Stomach 2Iesoderm surrounding duct Pleuro-pericardial opening Ridge growing across opening Dorsal mesentery Peritoneal recess Fia. 55. — Upper part of celom of human embryo of 6.8 mm., seen from behind. (From model by Piper.) The ultimate separation of the permanent cavities from one another is effected by the growth of a ridge of tissue on either side from the mesoderm surrounding Bsophagua Aorta Pleural cavity Lung Inferior vena cava Body wall Pericardium Fig. 56. — Diagram of transverse section through rabbit embryo. (After Keith.) the duct of Cuvier (Figs. 54, 55). The front part of this ridge grows across and obliterates the pleuro-pericardial opening; the hinder part grows across the pleuro- 1^ peritoneal opening. ■ With the continued growth of the lungs the pleural cavities are pushed forward ki 74 EMBRYOLOGY in the body-wall toward the ventral median line, thus separating the pericardium from the lateral thoracic walls (Fig. 53) . The further development of the peritoneal cavity has been described with the development of the digestive tube (page 168 et seq.). Spken Colon Suprarenal gland Eleventh rib Twelfth rib Sternn-costal part of Diaphragma Central tendon of Diaphragma Inferioi- vena cava (Esophagus Vertebral part of Diaphragma T Posterior mediastinal cavity -Aorta — Spino-costal hiattis Left pleura Eight pleura Fig. 57. — The thoracic aspect of the diaphragm of a newly born child in which the communication between the peritoneum and pleura haa not been closed on the left side; the position of the opening is marked on the right side by the spinocostal hiatus. (After Keith.) THE FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH. First Week. — During this period the ovum is in the uterine tube. Having been fertilized in the upper part of the tube, it slowly passes down, undergoing segmentation, and reaches the uterus. Peters^ described a specimen, the age of which he reckoned as from three to four days. It was imbedded in the decidua on the posterior wall of the uterus and enveloped by a decidua capsularis, the central part of which, however, consisted merely of a layer of fibrin. The ovum was in the form of a sac, the outer wall of which consisted of a layer of trophoblast; inside this Heart Amnion Fig. 58.- Body-stalk Chorion -Human embryo about fifteen days old. (His.) was a thin layer of mesoderm composed of round, oval, and spindle-shaped cells. Numerous villous processes — some consisting of trophoblast only, others possessing a core of mesoderm — projected from the surface of the ovum into the surrounding decidua. Inside this sac the rudi- ment of the embryo was found in the form of a patch of ectoderm, covered by a small but com- ' Die Einbettung des menschlichen Eies, 1899. M WRM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH 75 pletely closed amnion. It possessed a minute yolk-sac and was surroimded by mesoderm, which was connected by a band to that lining the trophoblast (Fig. 32).^ Second Week. — By the end of this week the ovum has increased considerably in size, and the majority of its villi are vascularized. The embryo has assumed a definite form, and its cephaUc and caudal extremities are easily distinguished. The neural folds are partly united. The embryo Mid-brain Fore-brain Stomodeum Mandibular arch Heart Hind-brain Auditory vesicle Amnion {cut) Body-stalk Fig. 59. — Human embryo between eighteen and twenty-one days old. (His. more completely separated, from the yolk-sac, and the paraxial mesoderm is being divided into Jthe primitive segments (Fig. 58). Third Week. — By the end of the third week the embryo is strongly curved, and the primitive segments number about thirty. The primary divisions of the brain are visible, and the optic Heart Fore-limb ki Byoid arch Mandibular arch Maxillary process Eye-i Olfactory pit Chorion' Hind-limb Fig. 60. — Human embryo, twenty-seven to thirty days old. (His.) and auditory vesicles are formed. Four branchial grooves are present: the stomodeum is well- marked, and the bucco-pharyngeal membrane has disappeared. The rudiments of the hmba are seen as short buds, and the Wolffian bodies are visible (Fig. 59). ■ Br>-ce and Teacher {Early Deielopment and Imbedding of the Human Ovum, 1908) have described an ovum which they regard as thirteen to fourteen days old. In it the two vesicles, the amnion and yolk-sac, were pre.sent, but there was no trace of a layer of embryonic ectoderm. They are of opinion that the age of Peters' ovum has been understated, and estimate it as between thirteen and one-half and fourteen and one-half days. f was no trace < ■^> and estimate 76 EMBRYOLOGY Fourth Week. — The embryo is markedly curved on itself, and when viewed in profile is almost circular in outline. The cerebral hemispheres appear as hollow buds, and the elevations whica form the rudiments of the auricula are visible. The limbs now appear as oval flattened projec- tions (Fig. 60). Heart I Hyoid Mandibular arch Maxillary process Eye limb Hind-limb Fig. 61. — Human embryo, thirty-one to thirty-four days old. (His.) Fifth Week. — The embryo is less curved and the head is relatively of large size. DifTerentiation of the limbs into their segments occurs. The nose forms a short, flattened projection. The cloaca! tubercle is evident (Fig. 61). Auricula Fore-limb Hind-limb Umbilical cord Fio. 62. — Human embryo of about six weeks. (His.) Fio. 63. — Human embryo about eight and a half weeks old. (His.) Sixth Week. — The curvature of the embryo is further diminished. The branchial grooves— except the first — have disappeared, and the rudiments of the fingers and toes can be recognized (Fig. 62). Seventh and Eighth Weeks. — The flexure of the head is gradually reduced and the neck is somewhat lengthened. The upper lip is completed and the nose is more prominent. The nostrils I FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH 77 are directed forward and the palate is not completely developed. The eyelids are present in the shape of folds above and below the eye, and 'the different parts of the auricula are distinguish- able. By the end of the second month the fetus measures from 28 to 30 mm. in length (Fig. 63). Third Month. — The head is extended and the neck is lengthened. The eyelids meet and fuse, remaining closed until the end of the sixth month. The limbs are well-developed and nails appear on the digits. The external generative organs are so far differentiated that it is possible to dis- tinguish the sex. By the end of this month the length of the fetus is about 7 cm., but if the legs be included it is from 9 to 10 cm. Fourth Month. — The loop of gut which projected into the umbilical cord is withdrawn within the fetus. The hairs begin to make their appearance. There is a general increase in size so that by the end of the fourth month the fetus is from 12 to 13 cm. in length, but if the legs be included it is from 16 to 20 cm. Fifth Month. — It is during this month that the first movements of the fetus are usually ob- Berved The eruption of hair on the head commences, and the vemix caseosa begins to be deposited. I By the end of this month the total length of the fetus, including the legs, is from 25 to 27 cm J Sixth Month. — The body is covered by fine hairs (lanugo) and the deposit of vernix caseosa Is considerable. The papillae of the skin are developed and the free border of the nail projects from the corium of the dermis. Measured from vertex to heels, the total length of the fetus at the end of this month is from 30 to 32 cm. Seventh Month. — The pupillary membrane atrophies and the eyehds are open. The testis descends with the vaginal sac of the peritoneum. From vertex to heels the total length at the end of the seventh month is from 35 to 36 cm. The weight is a little over three pounds. Eighth Month. — The skin assumes a pink color and is now entirely coated with vemix caseosa, and the lanugo begins to disappear. Subcutaneous fat has been developed to a considerable extent, and the fetus presents a plump appearance. The total length, i. e., from head to heels, at the end of the eighth month is about 40 cm., and the weight varies between four and one-half and five and one-half pounds. Ninth Month. — The lanugo has largely disappeared from the trunk. The umbilicus is almost in the middle of the body and the testes are in the scrotum. At full time the fetus weighs from aix and one-half to eight poimds, and measures from head to heels about 50 cm. Il BIBLIOGRAPHY. I Broman: Normale und abnorme Entwicklung des Menschen, 1911. Bryce, Teacher and Kerr: Contributions to the Study of the Early Development and Imbedding of the Human Ovum, 1908. Hertwig, O.: Handbuch der Vergleichenden und ExperimenteUen Entwicklungslehre der Wirbeltiere, 1906. His, W. : Anatomie menschlicher Embryonen, 1880-1885. • Hochstetter, F.: Bil der der ausserenKoperformeiniger menschlicher Embryonen aus den beiden ersten Monaten der Entwicklung, 1907. Keibel and Elze: Normentafel zur Entwicklimgsgeschichte des Menschen, 1908. Keibel and Mall: Manual of Human Embryology, 1910-1912. KoLLMANN, J.: Handatlas der Entwicklimgsgeschichte des Menschen, 1907. tKoLLMANN, J.: Lehrbuch der Entwicklungsgeschichte des Menschen, 1898. Mall: Contribution to the Study of the Pathology of the Human Embryo, Jour, of Morph., 908. See also contributions to Embryology of the Carnegie Institution of Washington. Mall: Development of the Human Coelom, Jour, of Morph., 1897. Peters, H.: Ueber die Einbettung des menschlichen Eies und das frviheste bisher bekannte menschliche Placentationsstadium, 1899. OSTEOLOGY. ^ rriHE general framework of the body is built up mainh' of a series of bones, -'- supplemented, however, in certain regions by pieces of cartilage; the bony part of the framework constitutes the skeleton. In the skeleton of the adult there are 206 distinct bones, as follows: — Axial Skeleton Appendicular Skeleton Vertebral column Skull .... Hyoid bone . Ribs and sternum f Upper extremities \ Lower extremities Auditory ossicles ^ Total 26 22 1 25 — 74 64 62 — 126 6 206 The patellse are included in this enumeration, but the smaller sesamoid bones are not reckoned. Bones are divisible into four classes: Long, Short, Flat, and Irregular, Long Bones. — The long bones are found in the limbs, and each consists of a body or shaft and two extremities. The body, or diaphysis is cylindrical, with a central cavity termed the medullary canal; the ^all consists of dense, compact tissue of considerable thickness in the middle part of the body, but becoming thinner toward the extremities; within the medullary canal is some cancellous tissue, scanty in the middle of the body but greater in amount toward the ends. The extremities are generally expanded, for the purposes of articulation and to afford broad surfaces for muscular attachment. They are usually developed from sep- arate centers of ossification termed epiphyses, and consist of cancellous tissue surrounded by thin compact bone. The medullary canal and the spaces in the cancellous tissue are filled with marrow. The long bones are not straight, but curved, the curve generally taking place in two planes, thus affording greater strength to the bone. The bones belonging to this class are: the clavicle, humerus, radius, ulna, femur, tibia, fibula, metacarpals, metatarsals, and phalanges. Short Bones. — Where a part of the skeleton is intended for strength and com- pactness combined with limited movement, it is constructed of a number of short bones, as in the carpus and tarsus. These consist of cancellous tissue covered by a thin crust of compact substance. The patellae, together with the other . sesamoid bones, are by some regarded as short bones. Flat Bones. — Where the principal requirement is either extensive protection or the provision of broad surfaces for muscular attachment, the bones are expanded into broad, flat plates, as in the skull and the scapula. These bones are composed ^ of two thin layers of compact tissue enclosing between them a variable quantity of cancellous tissue. In the cranial bones, the layers of compact tissue are famili- \ arly known as the tables of the skull; the outer one is thick and tough; the inner is thin, dense, and brittle, and hence is termed the vitreous table. The intervening (79) JTEOLOGY I I cancellous tissue is called the diploe, and this, in certain regions of the skull, becomes absorbed so as to leave spaces filled with air (air-sinuses) between the two tables. The flat bones are: the occipital, parietal, frontal, nasal, lacrimal, vomer, scapula, os coxae {Jiip hone), sternum, ribs, and, according to some, tht- patella. Irregular Bones. — The irregular bones are such as, from their peculiar form] cannot be grouped under the preceding heads. They consist of cancellous tissue enclosed within a thin layer of compact bone. The irregular bones are: the vertebrae, sacrum, coccjrx, temporal, sphenoid, ethmoid, zygomatic, maxilla, mandible, palatine, inferior nasal concha, and hyoid. _d^m Surfaces of Bones. — If the surface of a bone be examined, certain eminence^iJH and depressions are seen. These eminences and depressions are of two kinds: ' articular and non-articular. Well-marked examples of articular eminences are found in the heads of the humerus and femur; and of articular depressions in the glenoid cavity of the scapula, and the acetabulum of the hip bone. Non-articular eminences are designated according to their form. Thus, a broad, rough, uneven elevation is called a tuberosity,' protuberance, or process, a small, rough prominence, a tubercle ; a sharp, slender pointed eminence, a spine ; a narrow, rough elevation, running some way along the surface, a ridge, crest, or line. Non-articular depres- sions are also of variable form, and are described as fossae, pits, depressions, grooves, furrows, fissures, notches, etc. These non-articular eminences and depressions serve to increase the extent of surface for the attachment of ligaments and muscles, and are usually well-marked in proportion to the muscularity of the subject. A short perforation is called a foramen, a longer passage a canal. DEVELOPMENT OF THE SKELETON. The Skeleton. — The skeleton is of mesodermal origin, and may be divided into (a) that of the trunk (axial skeleton), comprising the vertebral column, skull, ribs, and sternum, and (6) that of the limbs (appendicular skeleton). The Vertebral Column.- — The notochord (Fig. 19) is a temporary structure and forms a central axis, around which the segments of the vertebral column are devel- oped.^ It is derived from the entoderm, and consists of a rod of cells, which lies on the ventral aspect of the neural tube and reaches from the anterior end of the mid-brain to the extremity of the tail. On either side of it is a column of paraxial mesoderm which becomes subdivided into a number of more or less cubical seg- ments, the primitive segments (Figs. 19 and 20). These are separated from one another by intersegmental septa and are arranged symmetrically on either side of the neural tube and notochord: to every segment a spinal nerve is distributed. At first each segment contains a central cavity, the myoccEl, but this is soon filled ■with a core of angular and spindle-shaped cells. The cells of the segment become differentiated into three groups, which form respectively the cutis-plate or derma- tome, the muscle-plate or myotome, and the sclerotome (Fig. 64). The cutis-plate is placed on the lateral and dorsal aspect of the myoccel, and from it the true skin of the corresponding segment is derived ; the muscle-plate is situated on the medial side of the cutis-plate and furnishes the muscles of the segment. The cells of the sclerotome are largely derived from those forming the core of the myocoel, and lie next the notochord. Fusion of the individual sclerotomes in an antero-posterior direction soon takes place, and thus a continuous strand of cells, the sclerotogenous layer, is formed along the ventro-lateral aspects of the neural tube. The cells of this layer proliferate rapidly, and extending medialward surround the notochord; at the same time they grow backward on the lateral aspects of the neural tube and eventually surround it, and thus the notochord and neural tube are enveloped ' In the amphioxus the notochord persists and forms the only representative of a skeleton in that animal. DEVELOPMENT OF THE SKELETON 81 i I by a continuous sheath of mesoderm, which is termed the membranous vertebral column. In this mesoderm the original segments are still distinguishable, but each is now differentiated into two portions, an anterior, consisting of loosely arranged cells, and a posterior, of more condensed tissue (Fig. 65, A and B) . Between the two portions the rudiment of the intervertebral fibro- cartilage is laid down (Fig. 65, C). Cells from the pos- terior mass grow into the intervals between the myo- tomes (Fig. 65, B and C) of the corresponding and suc- ceeding segments, and extend both dorsally and ventrally; the dorsal extensions sur- round the neural tube and represent the future verte- bral arch, while the ventral extend into the body-wall as the costal processes. The hinder part of the posterior mass joins the anterior mass of the succeeding segment to form the vertebral body. Each vertebral body is there- fore a composite of two segments, being formed from the posterior portion of one segment and the anterior part of that immediately behind it. The vertebral Fio. 64. — Transverse section of a human embryo of the third week to show the dififerentiation of the primitive segment. (Kollmann.) ao. Aorta. m.p. Muscle-plate, n.c. Neural canal, sc. Sclerotome, s p. cutis-plate. Myotome Anterior portion of sclerotome Notochord Posterior portion of sclerotome. Intermyolomic septum Costal process '?\ Ml it Intervertebral fibrocartilage Notochord Centr ISJiii; iv;:j ::*.:: m^ "tiiiVrr?) ;;;:: / tUli»4i .«»'»«jL AV. ••«.... I. i.\ /1 1 1 • I i r: t r : !! J V, 1 ' >?••.".'.*.♦• i • • u j » (., . .'. « .V.V,\ .•; \\ I /•.•:;.v/....;.'.,<3 B FiQ. 65. — Scheme showing the manner in which each vertebral centrum is developed from portions of two adjacent segments. I and costal arches are derivatives of the posterior part of the segment in front of the intersegmental septum with which they are associated. 6 OSTEOLOGY I This stage is succeeded by that of the cartilaginous vertebral column. In the fourth week two cartilaginous centers make their appearance, one on either side o^^ the notochord; these extend around the notochord and form the body of the cartil-^U aginous vertebra. A second pair of cartilaginous foci appear in the lateral parts of the vertebral bow, and grow backward on either side of the neural tube to form ^ ,_ the cartilaginous vertebral arch, and a separate cartilaginous center appears foilMfl each costal process. By the eighth week the cartilaginous arch has fused with the body, and in the fourth month the two halves of the arch are joined on the dorsal aspect of the neural tube. The spinous process is developed from the junction of the two halves of the vertebral arch. The transverse process grows out from the, vertebral arch behind the costal process. In the upper cervical vertebrae a band of mesodermal tissue connects the ends of the vertebral arches across the ventral surfaces of the intervertebral fibrocartilages. This is termed the hypochordal bar or brace; in all except the first it is transitory and disappears by fusing with the fibrocartilages. In the atlas, however, the entire bow persists and undergoes chondrification; it develops into the anterior arch of the bone, while the cartilage representing the body of the atlas forms the dens or odontoid process which fuses with the bod}^ of the second cervical vertebra. Anterior longitudiiial ligamevt Posterior lo7igiludinal ligament Cartilaginous end of vertebral body Nucleus puljmsus Intervertebral fibro- cartilage Slight enlargement of notochord in the cartilaginous vertebral body Fig. 66. — Sagittal section through an intervertebral fibrocartilage and adjacent parts of two vertebrae of an advanced sheep's embryo. (KoUiker.) The portions of the notochord which are surrounded by the bodies of the verte- brae atrophy, and ultimately disappear, while those which lie in the centers of the intervertebral fibrocartilages undergo enlargement, and persist throughout life as the central nucleus pulposus of the fibrocartilages (Fig. 66). The Ribs. — The ribs are formed from the ventral or costal processes of the primitive vertebral bows, the processes extending between the muscle-plates. In the thoracic region of the vertebral column the costal processes grow lateralward to form a series of arches, the primitive costal arches. As already described, the transverse process grows out behind the vertebral end of each arch. It is at first connected to the costal process by continuous mesoderm, but this becomes differ- entiated later to form the costotransverse ligament; between the costal process and the tip of the transverse process the costotransverse joint is formed by absorption. The costal process becomes separated from the vertebral bow by the development of the costocentral joint. In the cervical vertebroB (Fig. 67) the trans- verse process forms the posterior boundary of the foramen transversarium, while the costal process corresponding to the head and neck of the rib fuses with the I DEVELOPMENT OF THE SKELETON 83 body of the vertebra, and forms the antero-lateral boundary of the foramen. The distal portions of the primitive costal arches remain undeveloped; occasionally the arch of the seventh cervical vertebra undergoes greater development, and by the formation of costovertebral joints is separated off as a rib. In the lumbar region the distal portions of the primitive costal arches fail ; the proximal portions fuse with the transverse processes to form the transverse processes of descriptive anatomy. Occasionally a movable rib is developed in connection with the first lumbar vertebra. In the sacral region costal processes are developed only in connection with the upper three, or it may be four, vertebrae; the processes of adjacent segments fuse with one another to form the lateral parts of the sacrum. The coccygeal vertebrcs are devoid of costal processes. CERVICAL LUMBAR THORACIC SACRAL I Fig. 67. — Diagrams showing the portions of the adult vertebrse derived respectively from the bodies, vertebral arches, and costal processes of the embrj'onic vertebrse. The bodies are represented in yellow, the vertebral arches in red, and the costal processes in blue. The Sternum. — The ventral ends of the ribs become united to one another by a longitudinal bar termed the sternal plate, and opposite the first seven pairs of ribs these sternal plates fuse in the middle line to form the manubrium and body of the sternum. The xiphoid process is formed by a backward extension of the sternal plates. The Skull. — Up to a certain stage the development of the skull corresponds with that of the vertebral column; but it is modified later in association with the expan- sion of the brain-vesicles, the formation of the organs of smell, sight, and hearing, and the development of the mouth and pharynx. 84 OSTEOLOGY I Fossa hypophyseos Mesoderm of base of skull Parachordal cartilage The notochord extends as far forward as the anterior end of the mid-brain, and becomes partly surrounded by mesoderm (Fig. 68) . The posterior part of this meso- dermal investment corresponds with the basilar part of the occipital bone, and show s a subdivision into four segments, which are separated by the roots of the hypo- glossal nerve. The mesoderm then extends over the brain-vesicles, and thus the entire brain is enclosed by a mesodermal investment, which is termed the membran- ous cranium. From the inner layer of this the bones of the skull and the membranes of the brain are developed ; from the outer laj^er the muscles, bloodvessels, true skin, and subcutaneous tissues of the scalp. In the shark and dog-fish this membranous cranium undergoes complete chondrifi- cation, and forms the cartilaginous skull or chondrocranium of these animals. In mammals, on the other hand, the process of chondrification is limited to the base of the skull — ^the roof and sides being covered in by membrane. Thus the bones of the base of the skull are preceded by cartilage, those of the roof and sides by membrane. The posterior part of the base of the skull is developed around the notochord, and exhibits a segmented condition analogous to that of the vertebral column, while the anterior part arises in front of the notochord and shows no regular segmentation. The base of the skull may therefore be divided into (a) a chordal or vertebral, and (b) a prechordal or prevertebral portion. SitvMion of olfactory pit Ethmoid plate and nasal Olfactory organ Anterior arch of atlas Notochord Body of axis Third cervical vertebra Fio. 68. — Sagittal section of ceplialic end ot chord. (Keibel.) Fossa hypophyseos Trabecvla cranii SitvMion of avditory vesicle Parachordal cartilage Notochord Extension around 7 olfactory organ Foramina for olfactory nerves . Eyeball Fossa ~ hypophyseos — Basilar plate --Auditory vesicle •Notochord Fig. 69. — Diagrams of the cartilaginous cranium. (Wiedersheim. In the lower vertebrates two pairs of cartilages are developed, viz., a pair of parachordal cartilages, one on either side of the notochord; and a pair of pre- chordal cartilages, the trabeculse cranii, in front of the notochord (Fig. 66). The parachordal cartilages (Fig. 69) unite to form a basilar plate, from which the car- tilaginous part of the occipital bone and the basi-sphenoid are developed. On the lateral aspects of the parachordal cartilages the auditory vesicles are situated, I DEVELOPMENT OF THE SKELETON 85 and the mesoderm enclosing them is soon converted into cartilage, forming the cartilaginous ear-capsules. These cartilaginous ear-capsules, which are of an oval shape, fuse with the sides of the basilar plate, and from them arise the petrous and mastoid portions of the temporal bones. The trabeculse cranii (Fig. 69) are two curved bars of cartilage which embrace the hypophysis cerebri; their posterior ends soon unite with the basilar plate, while their anterior ends join to form the ethmoidal plate, which extends forward between the fore-brain and the olfactory pits. Later the trabeculse meet and fuse below the hypophysis, forming the floor Crista gain Cribriform plate Meckel's cartilage Malleus I71CUS Jnt. acoustic meat. Jugular foramen Tossa svbarcuata janal for hypoglossal nerve Small wing of sphenoid Optic foramen -Great wing of sphenoid Sella turcica Dorsum seUce Canal for facial nerve Ear capsule Ihictus endal. Foramen magnum FiQ. 70. — Model of the chondrocranium of a human embryo, 8 cm. long. not represented. (Hertwig.) The membrane bones are of the fossa hypophyseos and so cutting off the anterior lobe of the hypophysis from the stomodeum. The median part of the ethmoidal plate forms the bony and cartilaginous parts of the nasal septum. From the lateral margins of the trabeculse cranii three processes grow out on either side. The anterior forms the ethmoidal labyrinth and the lateral and alar cartilages of the nose; the middle gives rise to the small wing of the sphenoid, while from the posterior the great wing and lateral pterygoid plate of the sphenoid are developed (Figs. 70, 71). The bones of the vault are of membranous formation, and are termed dermal or covering bones. They are partly developed from the mesoderm of the membranous OSTEOLOGY I cranium, and partly from that which lies outside the entoderm of the fore- gut. They comprise the upper part of the occipital squama (interparietal), th(^ squamse and tympanic parts of the temporals, the parietals, the frontal, the vomer, the medial pterygoid plates, and the bones of the face. Some of them remain distinct throughout life, e. g., parietal and frontal, while others join with the bones of the chondrocranium, e. g., interparietal, squamae of temporals, and medial pterygoid plates. Recent observations have shown that, in mammals, the basi-cranial cartilage, both in the chordal and prechordal regions of the base of the skull, is developed as a single plate which extends from behind forward. In man, however, its posterior part shows an indication of being developed from two chondrifying centers which fuse rapidly in front and below. The anterior and posterior thirds of the cartilage surround the notochord, but its middle third lies on the dorsal aspect of the noto- chord, which in this region is placed between the cartilage and the wall of the pharynx. Optic foramen Small wing of sphenoid Great wing of sphenoid Nasal capsiUe Vomer Palattne bone Mandible Cricoid cart. Thyroid cart. Styloid process Fen. cochlew Canal for hypoglossal nerve Fio. 71. — The same model as shown in Fig. 70 from the left side. Certain of the membrane bones of the right side are represented in yellow. (Hertwig.) BONE Structure and Physical Properties. — Bone is one of the hardest structures of the animal body; it possesses also a certain degree of toughness and elasticity. Its color, in a fresh state, is pinkish-white externally, and deep red within. On examining a section of any bone, it is seen to be composed of two kinds of tissue, one of which is dense in texture, like ivory, and is termed compact tissue; the other consists of slender fibers and lamellae, which join to form a reticular structure; this, from its resemblance to lattice-work, is called cancellous tissue. The compact tissue is always placed on the exterior of the bone, the cancellous in the interior. The relative quantity of these two kinds of tissue varies in different bones, and in different parts of the same bone, according as strength or lightness is requisite. Close examination of the compact tissue shows it to be extremely porous, so that the difference in structure between it and the cancellous tissue depends merely upon the different amount of solid matter, and the size and number of spaces in each; the cavities are small in the compact tissue and the solid matter between I BONE 87 them abundant, while in the cancellous tissue the spaces are large and the solid matter is in smaller quantity. Bone during life is permeated by vessels, and is enclosed, except where it is coated with articular cartilage, in a fibrous membrane, the periosteum, by means of which many of these vessels reach the hard tissue. If the periosteum be stripped from the surface of the living bone, small bleeding points are seen which mark the entrance of the periosteal vessels; and on section during life every part of the bone exudes blood from the minute vessels which ramify in it. The interior of each of the long bones of the limbs presents a cylindrical cavity filled with marrow and lined by a highly vascular areolar structure, called the medullary membrane. The Strength of Bone Compared with other Materials Substance. Weight in pounds per cubic foot. Ultimate strength. Pounds per square inch. Tension. Compression. Shear. I Medium steel 490 65,000 | 60,000 Granite 170 1,500 15,000 Oak, white 46 12,500^ 7,000^ Compact bone (low) 119 13,200^ 18,000i Compact bone (high) I i 17,700^ ; 24,000i 40,000 2,000 4,0002 11,800'' 7,1601 Periosteirai. — ^The periosteum adheres to the surface of each of the bones in nearly every part, but not to cartilaginous extremities. When strong tendons or ligaments are attached to a bone, the periosteum is incorporated with them. It consists of two layers closely united together, the outer one formed chiefly of connective tissue, containing occasionally a few fat cells; the inner one, of elastic fibers of the finer kind, forming dense membranous networks, which again can be separated into several layers. In young bones the periosteum is thick and very vascular, and is intimately connected at either end of the bone with the epiphysial cartilage, but less closely with the body of the bone, from which it is separated by a layer of soft tissue, containing a number of granular corpuscles or osteoblasts, by which ossification proceeds on the exterior of the young bone. Later in life the periosteum is thinner and less vascular, and the osteoblasts are converted into an epithelioid layer on the deep surface of the periosteum. The periosteum serves as a nidus for the ramification of the vessels previous to their distribution in the bone; hence the liability of bone to exfoliation or necrosis when denuded of this membrane by injury or disease. Fine nerves and lymphatics, which generally accompany the arteries, may also be demonstrated in the periosteum. Marrow. — The marrow not only fills up the cylindrical cavities in the bodies of the long bones, but also occupies the spaces of the cancellous tissue and extends into the larger bony canals (Haversian canals) which contain the bloodvessels. It differs in composition in different bones. In the bodies of the long bones the marrow is of a yellow color, and contains, in 100 parts, 96 of fat, 1 of areolar tissue and vessels, and 3 of fluid with extractive matter; it consists of a basis of connective tissue supporting numerous bloodvessels and cells, most of which are fat cells but some are "marrow cells," such as occur in the red marrow to be immediately described. In the flat and short bones, in the articular ends of the long bones, in the bodies of the vertebrae, in the cranial diploe, and in the sternum and ribs the marrow is of a red color, and contains, in 100 parts, 75 of water, and 25 of solid matter consisting of cell-globulin, nucleoprotein, extractives, salts, and only a small proportion of fat. The red marrow consists of a small quantity of connective tissue, bloodvessels, and numerous cells (Fig. 72), some few of which are fat cells, 1 Indicates stresses with the grain, j. e., when the load is parallel to the long axis of the material, or parallel to the direction of the fibers of the material. 2 Indicates unit-stresses across the grain, i. e., at right angles to the direction of the fibers of the material. OSTEOLOGY but the great majority are roundish nucleated cells, the true "marrow cells' of Kolliker. These marrow cells proper, or myelocjrtes, resemble in appearance' lymphoid corpuscles, and like them are ameboid; they generally have a hyalin- — Myelocyte ' Faf [__ Eosinophil cell 11- Normoblasts .L_ Myelocyte dividing " Myelocyte FiQ. 72. — Human bone marrow. Highly magnified. Vessels and Nerves of Bone. — The bloodvessels of bone are very numerous. Those of the compact tissue are derived from a close and dense network of vessels ramify- ing in the periosteum. From this membrane vessels pass into the minute orifices in the compact tissue, and run through the canals which traverse its substance. The cancellous tissue is supplied in a similar way, but by less numerous and larger vessels, which, perforating the outer compact tissue, are distributed to the cavities of the spongy portion of the bone. In the long bones, numerous apertures may be seen at the ends near the articular surfaces; some of these give passage to the arteries of the larger set of vessels referred to; but the most numerous and largest apertures are for some of the veins of the cancellous tissue, which emerge apart from the arteries. The marrow in the body of a long bone is supplied by one large artery (or sometimes more), which enters the bone at the nutrient foramen (situated in most cases near the center of the body), and perforates obliquely the compact structure. The medullary or nutrient artery, usually accompanied by one or two veins, sends branches upward and downward, which ramify in the medul- lary membrane, and give twigs to the adjoining canals. The ramifications of this I BONE 89 ^ vessel anastomose with the arteries of the cancellous and compact tissues. In most of the flat, and in many of the short spongy bones, one or more large apertures are observed, which transmit to the central parts of the bone vessels corresponding to the nutrient arteries and veins. The veins emerge from the long bones in three places (Kolliker) : (1) one or two large veins accompany the artery; (2) numerous large and small veins emerge at the articular extremities; (3) many small veins pass out of the compact substance. In the flat cranial bones the veins are large, very numerous, and run in tortuous canals in the diploic tissue, the sides of the canals being formed by thin lamellae of bone, perforated here and there for the passage of branches from the adjacent cancelli. The same condition is also found in all cancellous tissue, the veins being enclosed and supported by osseous material, and having exceedingly thin coats. When a bone is divided, the vessels remain patulous, and do not contract in the canals in which they are contained. L3miphatic vessels, in addition to those found in the periosteum, have been traced by Cruikshank into the substance of bone, and Klein describes them as running in the Haversian canals. Nerves are distributed freely to the periosteum, and accom- pany the nutrient arteries into the interior of the bone. They are said by Kolliker to be most numerous in the articular extremities of the long bones, in the vertebrae, and in the larger flat bones. t Fig. 73. — Transverse section of compact tissue bone. Magnified. (Sharpey.) Minute Anatomy. — A transverse section of dense bone may be cut with a saw and ground down until it is sufficiently thin. If this be examined with a rather low power the bone will be seen to-be mapped out into a number of circular districts each consisting of a central hole surrounded by a number of concentric rings. These districts are termed Haversian systems; the central hole is an Haversian canal, and the rings are layers of bony tissue arranged concentrically around the central canal, and termed lamellae. More- over, on closer examination it will be found that between these lamellae, and therefore also arranged concentrically around the central canal, are a number of little dark spots, the lacimae, and that these lacunae are connected with each other a,nd with the central Haversian canal by a number of fine dark lines, which radiate Uke the spokes of a wheel and are called canaliculi. Filling in the irregular intervals which are left between these circular systems are other lamellae, with their lacunae and canaliculi running in various directions, but more or less curved (Fig. 73); they are termed interstitial lamellae. Again, other lamellae, found on the surface f the bone, are arranged parallel to its circumference; they are termed circum- 90 OSTEOLOGY I ferential, or by some authors primary or fundamental lamellae, to distinguish them from those laid down around the axes of the Haversian canals, which are then termed secondaiy or special lamellae. The Haversian canals, seen in a transverse section of bone as round holes at or about the center of each Haversian system, may be demonstrated to be true canah if a longitudinal section be made (Fig. 74). It will then be seen that the canals run parallel with the longitudinal axis of the bone for a short distance and then branch and communicate. They vary considerably in size, some being as much as 0.12 mm. in diameter; the average size is, however, about 0.05 mm. Near the medullary cavity the canals are larger than those near the surface of the bone. Each canal contains one or two bloodvessels, with a small quantity of delicate connective tissue and some nerve filaments. In the larger ones there are also lymphatic vessels, and cells with branching processes which communicate, through the canalculi, with the branched processes of certain bone cells in the substance of the bone. Those canals near the surface of the bone open upon it by minute orifices, and those near the medullary cavity open in the same way into this space, so that the whole of the bone is permeated by a system of bloodvessels running through the bony canals in the centers of the Haversian systems. The lamellae are thin plates of bony tissue encircling the central canal, and may be com- pared, for the sake of illustration, to a number of sheets of paper pasted one over another around a central hollow cylinder. After macerating a piece of bone in dilute mineral acid, these lamellae may be stripped off in a Fig. 74. — Settion parallel to the surface from the body of the femur. X 100. o, Haver- sian canals; b, lacunffi seen from the side; c, others seen from the surface in lamellae, which are cut horizontally. FiQ. 75. — Perforating fibers, human parietal bone, decalcified. (H. Muller.) o, perforating fibers in situ; b, fibres drawn out of their sockets; c, sockets. longitudinal direction as thin films. If one of these be examined with a high power of the microscope, it will be found to be composed of a finely reticular structure, made up of very slender transparent fibers, decussating obliquely; and coalescing at the points of intersection ; these fibers are composed of fine fibrils identical with those of white connective tissue. The intercellular matrix between the fibers is impregnated by calcareous deposit which the acid dissolves. In many places the various lamellae may be seen to be held together by tapering fibers, which run obliquely through them, pinning or bolting them together; they were first de- scribed by Sharpey, and were named by him perforating fibers (Fig. 75). The Lacunae are situated between the lamellae, and consist of a number of oblong I BONE 91 ^ ¥ ta spaces. In an ordinary microscopic section, viewed by transmitted light, tliey appear as fusiform opaque spots. Each lacuna is occupied during life by a branched cell, termed a bone-cell or bone-corpuscle, the processes from which extend into the canaliculi (Fig. 76). The Canaliculi are exceedingly minute channels, crossing the lamellae and con- necting the lacunae with neighboring lacunae and also with the Haversian canal. From the Haversian canal a number of canaliculi are given off, which radiate from it, and open into the first set of lacunae between the first and second lamellae. From these lacunae a second set of canaliculi is given off; these run outward to the next series of lacunae, and so on until the periphery of the Haversian system is reached; here the canaliculi given off from the last series of lacunae do not communi- cate with the lacunae of neighboring Haversian systems, but after passing outward for a short distance form loops and return to their own lacunae. Thus every part of an Haversian system is supplied with nutrient fluids derived from the vessels in the Haversian canal and distributed through the canaliculi and lacunae. The bone cells are contained in the lacunae, which, however, they do not completely fill. They are flattened nucleated branched cells, homologous with those of connective tissue; the branches, especially in young bones, pass into the canaliculi from the lacunae. In thin plates of bone (as in the walls of the spaces of cancellous tissue) the Haversian [ canals are absent, and the canaliculi open into the spaces of the cancellous tissue (medullary spaces), which thus have the same function as the Haversian canals. Chemical Composition. — Bone consists of an animal and an earthy part intimately com- bined together. I The animal part may be obtained by immersing a bone for a considerable time in dilute mineral acid, after which process the bone comes out exactly the same shape as before, but perfectly flexible, so that a long bone (one of the ribs, for example) can easily be tied in a knot. If now a transverse section is made (Fig. 77) the same general arrangement of the Haversian canals, lamellae, lacunae, and canaliculi is seen. The earthy part may be separately obtained by calcination, by which the animal matter is completely burnt out. The bone will still retain its original form, but it will be white and brittle, will have lost about one-third of its original I weight, and will crumble down with the slightest force. The earthy matter is I composed chiefly of calcium phosphate, about 58 per cent, of the weight of the I bone, calcium carbonate about 7 per cent., calciimi fluoride and magnesium phos- " phate from 1 to 2 per cent, each and sodium chloride less than 1 per cent. ; they confer on bone its hardness and rigidity, while the animal matter (ossein) determines its I tenacity. Ossification. — Some bones are preceded by membrane, such as those forming the roof and sides of the skull; others, such as the bones of the limbs, are preceded by rods of cartilage. Hence two kinds of ossification are described: the intra- membranous and the intracartilaginous. (Intramembranous Ossification. — In the case of bones which are developed in membrane, no cartilaginous mould precedes the appearance of the bony tissue. The membrane which occupies the place of the future bone is of the nature of con- nective tissue, and ultimately forms the periosteum; it is composed of fibers and granular cells in a matrix. The peripheral portion is more fibrous, while, in the Fig. 76. — Nucleated bone cells and their processes, contained in the bone lacunae and their canaliculi respectively. From a section through the vertebra of an adult mouse. (Klein and Noble Smith.) 92 OSTEOLOGY I interior the cells or osteoblasts predominate; the whole tissue is richly supplied with bloodvessels. At the outset of the process of bone formation a little network of spicules is noticed radiating from the point or center of ossification. These rays consist at their growing points of a network of fine clear fibers and granular Haversian canal Bone corpuscle Bone corpuscle between inter- stitial lamellee Fig. 77. — Transverse section of body of human fibula, decalcified. X 250. corpuscles with an intervening ground substance (Fig. 78). The fibers are termed osteogenetic fibers, and are made up of fine fibrils differing little from those of white fibrous tissue. The membrane soon assumes a dark and granular appearance from the deposition of calcareous granules in the fibers and in the intervening matrix, Union of adjacent ~~' spicules Osteoblasts^^ Osteogenetic fibers Calcified deposit between the fibers Bony spicvlea FiQ. 78. — Part of' the growing edge of the developing parietal bone of a fetal cat. (After J. Lawrence.) and in the calcified material some of the granular corpuscles or osteoblasts are enclosed. By the fusion of the calcareous granules the tissue again assumes a more transparent appearance, but the fibers are no longer so distinctly seen. The involved osteoblasts form the corpuscles of the future bone, the spaces in I BONE 93 ■ which they are enclosed constituting the lacunae. As the osteogenetic fibers grow out to the periphery they continue to calcify, and give rise to fresh bone spicules. Thus a network of bone is formed, the meshes of which contain the bloodvessels and a delicate connective tissue crowded with osteoblasts. The bony trabeculse thicken by the addition of fresh layers of bone formed by the osteoblasts on their surface, and the meshes are correspondingly encroached upon. Subsequently, successive layers of bony tissue are deposited under the periosteum and around the larger vascular channels which become the Haversian canals, so that the bone increases much in thickness. Intercartilaginous Ossification. — Just before ossification begins the mass is entirely cartilaginous, and in a long bone, which may be taken as an example, the process commences in the center and proceeds toward the extremities, which for some time remain cartilaginous. Subsequently a similar process commences in one or more places in those extremities and gradually extends through them. The extremities do not, however, become joined to the body of the bone by bony tissue until growth has ceased ; between the body and either extremity a layer of cartilaginous tissue termed the epiphysial cartilage persists for a definite period; The first step in the ossification of the cartilage is that the cartilage cells, at the point where ossification is com- mencing and which is termed a center of ossification, enlarge and arrange themselves in rows (Fig. 79). The matrix in which they are imbedded increases in quantity, so that the cells become further separated from each other. A deposit of calcareous material now takes place in this matrix, between the rows of cells, so that they become separated from each other by longi- tudinal columns of calcified matrix, presenting a granular and opaque ap- pearance. Here and there the matrix between two cells of the same row also becomes calcified, and transverse bars of calcified substance stretch across from one calcareous column to another. Thus there are longitudinal groups of the cartilage cells enclosed in oblong cavities, the walls of which are formed of calcified matrix which cuts off all nutrition from the cells; the cells, in consequence, atrophy, leaving spaces called the primary areolae. At the same time that this process is going on in the center of the solid bar of cartilage, certain changes are I taking place on its surface. This is I covered by a very vascular membrane, I the perichondrium, entirely similar to the embryonic connective tissue already described as constituting the basis of membrane bone; on the inner surface of this — that is to say, on the surface in contact with the cartilage — are gathered the formative cells, the osteoblasts. By the agency of these cells a thin layer of bony tissue is formed between the peri- vnu Fig. 79. — Section of fetal bone of cat. tV. Irruption of the subperiosteal tissue, p. Fibrous layer of the pierios- teum. o. Layer of osteoblasts, im. Subperiosteal bony deposit. (From Quain's "Anatomy," E. A. Schafer.) OSTEOLOGY I chondrium and the cartilage, by the intramembranons mode of ossification just described. There are then, in this first stage of ossification, two processes going on simultaneously: in the center of the cartilage the formation of a number of oblong spaces, formed of calcified matrix and containing the withered cartilage cells, and on the surface of the cartilage the formation of a layer of true mem- brane bone. The second stage consists in the prolongation into the cartilage of processes of the deeper or osteogenetic layer of the perichondrium, which has now become periosteum (Fig. 79, ir). The processes consist of bloodvessels and cells — osteoblasts, or bone-formers, and osteoclasts, or bone-destroyers. The latter are similar to the giant cells (myeloplaxes) found in marrow, and they excavate passages through the new-formed bony layer by absorption, and pass through it into the calcified matrix (Fig. 80). Wherever these processes come in con- tact with the calcified walls of the primary areolae they absorb them, and thus cause a fusion of the original cavities and the formation of larger spaces, which are termed the secondary areolae or medullary spaces. These secondary spaces become filled with embryonic marrow, consisting of osteoblasts and vessels, derived, in the manner described above, from the osteogenetic layer of the periosteum (Fig. 80) . Thus far there has been traced the forma- tion of enlarged spaces (secondary areolae), the perforated walls of which are still formed by calcified cartilage matrix, containing an embryonic marrow derived from the processes sent in from the osteogenetic layer of the periosteum, and consisting of bloodvessels and osteoblasts. The walls of these secondary areolae are at this time of only inconsiderable thickness, but they become thickened by the deposition of layers of true bone on their sur- face. This process takes place in the follow- ing manner: Some of the osteoblasts of the embryonic marrow, after undergoing rapid division, arrange themselves as an epithelioid layer on the surface of the wall of the space (Fig. 81). This layer of osteoblasts forms a bony stratum, and thus the wall of the space becomes gradually covered with a layer of Osteoclasts ^f''"^' Fig. 80. — Part of a longitudinal section of the developing femur of a rabbit, a. Flattened cartilage cells, h. Enlarged cartilage cells, c, d. Newly formed bone. e. Osteoblasts. /. Giant cells or osteoclasts. g, h. Shrunken cartilage cells. (From "Atlas of Histology," Ivlein and Noble Smith.) Osteoblasts ug^!,;^^.:3^^W Fig. 81. — Osteoblasts and osteoclasts on trabecula of lower jaw of calf embryo. (KoUiker.) true osseous substance in which some of the bone-forming cells are included as bone corpuscles. The next stage in the process consists in the removal of these primary bone spicules by the osteoclasts. One of these giant cells may be found lying in a Howship's foveola at the free end of each spicule. The removal of the I BONE ^^^^^^^K 95 Pi primary spicules goes on pari passu with the formation of permanent bone by the periosteum, and in this way the medullary cavity of the body of the bone is formed. This series of changes has been gradually proceeding toward the end of the body of the bone, so that in the ossifying bone all the changes described above may be seen in different parts, from the true bone at the center of the body to the hyaline cartilage at the extremities. While the ossification of the cartilaginous body is extending toward the articular ends, the cartilage immediately in advance of the osseous tissue continues to grow until the length of the adult bone is reached. During the period of growth the articular end, or epiphysis, remains for some time entirely cartilaginous, then a bony center appears, and initiates in it the process of intracartilaginous ossification; but this process never extends to any great distance. The epiphysis remains separated from the body by a narrow cartilaginous layer for a definite time. This layer ultimately ossifies, the distinc- tion between body and epiphysis is obliterated, and the bone assumes its completed form and shape. The same remarks also apply to such processes of bone as are separately ossified, e. g., the trochanters of the femur. The bones therefore con- tinue to grow until the body has acquired its full stature. They increase in length by ossification continuing to extend behind the epiphysial cartilage, w^hich goes on growing in advance of the ossifying process. They increase in circumference by deposition of new bone, from the deeper layer of the periosteum, on their exter- nal surface, and at the same time an absorption takes place from within, by which I the medullary cavities are increased. } The permanent bone formed by the periosteum when first laid down is cancellous In structure. Later the osteoblasts contained in its spaces become arranged in jthe concentric layers characteristic of the Haversian systems, and are included [as bone corpuscles. The number of ossific centers varies in different bones. In most of the short bones ossification commences at a single point near the center, and proceeds toward ^_ the surface. In the long bones there is a central point of ossification for the body ^|[or diaphysis: and one or more for each extremity, the epiphysis. That for the ^f -body is the first to appear. The times of union of the epiphyses with the body W vary inversely with the dates at which their ossifications began (with the exception of the fibula) and regulate the direction of the nutrient arteries of the bones. Thus, I the nutrient arteries of the bones of the arm and forearm are directed toward rthe elbow, since the epiphyses at this joint become united to the bodies before jthose at the opposite extremities. In the low^er limb, on the other hand, the Inutrient arteries are directed away from the knee: that is, upward in the femur, [downward in the tibia and fibula; and in them it is observed that the upper epiphysis of the femur, and the lower epiphyses of the tibia and fibula, unite first with the bodies. Where there is only one epiphysis, the nutrient artery is directed toward the other end of the bone; as toward the acromial end of the clavicle, toward the P distal ends of the metacarpal bone of the thumb and the metatarsal bone of the fereat toe, and toward the proximal ends of the other metacarpal and metatarsal bones. Parsons^ groups epiphyses under three headings, viz.: (1) pressure epiphyses, appearing at the articular ends of the bones and transmitting "the weight of the r, body from bone to bone;" (2) traction epiphyses, associated with the insertion lof muscles and "originally sesamoid structures though not necessarily sesamoid bones;" and (3) atavistic epiphyses, representing parts of the skeleton, which at one time formed separate bones, but which have lost their function, " and only appear as separate ossifications in early life." ..,..., ....„., P...,™,.. „„..„..... 96 OSTEOLOGY THE VERTEBRAL COLUMN (COLUMNA VERTEBRALIS ; SPINAL COLUMN). The vertebral column is a flexuous and flexible column, formed of a series o! bones called vertebrae. The vertebrae are thirty-three in number, and are grouped under the names cervical, thoracic, lumbar, sacral, and coccygeal, according to the regions they occupy; there are seven in the cervical region, twelve in the thoracic, five in the lumbar, five in the sacral, and four in the coccygeal. This number is sometimes increased by an additional vertebra in one region, or it may be diminished in one region, the deficiency often being supplied by an additional vertebra in another. The number of cervical vertebrae is, however, very rarely increased or diminished. The vertebrae in the upper three regions of the column remain distinct through- out life, and are known as true or movable vertebrae; those of the sacral and coccygeal regions, on the other hand, are termed false or fixed vertebrae, because they are united with one. another in the adult to form two bones — five forming the upper bone or sacrum, and four the terminal bone or coccyx. With the exception of the first and second cervical, the true or movable vertebrae present certain common characteristics which are best studied by examining one from the middle of the thoracic region. GENERAL CHARACTERISTICS OF A VERTEBRA. A typical vertebra consists of two essential parts — viz., an anterior segment, the body, and a posterior part, the vertebral or neural arch; these enclose a foramen, the vertebral foramen. The vertebral arch consists of a pair of pedicles and a pair of laminae, and supports seven processes — viz., four articular, two transverse, and one spinous. Costal fovea Pedicle or roof of vertebral arch Lamina Superior articular process Fig. 82. — A typical thoracic vertebra, viewed from above. When the vertebrae are articulated with each other the bodies form a strong pillar for the support of the head and trunk, and the vertebral foramina constitute a canal for the protection of the medulla spinalis {spinal cord), while between every pair of vertebrae are two apertures, the intervertebral foramina, one on either side, for the transmission of the spinal nerves and vessels. Body (corpus vertebrce). — ^The body is the largest part of a vertebra, and is more or less cylindrical in shape. Its upper and lower surfaces are flattened and THE CERVICAL VERTEBRA rough, and give attachment to the intervertebral fibrocartilages, and each presents a rim around its circumference. In front, the body is convex from side to side and concave from above downward. Behind, it is flat from above downward and slightly concave from side to side. Its anterior surface presents a few small apertures, for the passage of nutrient vessels; on the posterior surface is a single large, irregular aperture, or occasionally more than one, for the exit of the basi- vertebral veins from the body of the vertebra. Pedicles {radices arci vertebroe). — The pedicles are two short, thick processes, which project backward, one on either side, from the upper part of the body, at the junction of its posterior and lateral surfaces. The concavities above and below the pedicles are named the vertebral notches; and when the vertebrae are articulated, the notches of each contiguous pair of bones form the intervertebral foramina, already referred to. Laminae. — The laminae are two broad plates directed backward and medialward from the pedicles. They fuse in the middle line posteriorly, and so complete the posterior boundary of the vertebral foramen. Their upper borders and the lower parts of their anterior surfaces are rough for the attachment of the ligamenta flava. Processes. — Spinous Process {processus spinosus). — The spinous process is directed backward and downward from the junction of the laminae, and serves for the attachment of muscles and ligaments. Articular Processes. — The articular processes, two superior and two inferior, spring from the junctions of the pedicles and laminae. The superior project upward, and their articular surfaces are directed more or less backward; the inferior project downward, and their surfaces look more or less forward. The articular surfaces are coated with hyaline cartilage. Transverse Processes {processus transversi). — ^The transverse processes, two in number, project one at either side from the point where the lamina joins the pedicle, between the superior and inferior articular processes. They serve for 'the attachment of muscles and ligaments. Stnictore of a Vertebra (Fig. 83). — The body is composed of cancellous tissue, covered by a thin coating of compact bone; the latter is perforated by numerous orifices, some of large size I for the passage of vessels; the interior of the bone is traversed by one or two large canals, for the [reception of veins, which converge toward a single large, irregular aperture, or several small apertures, at the posterior part of the body. The thin bony lamellae of the cancellous tissue are more pronounced in lines perpendicular to the upper and low^er surfaces and are developed in response to greater pressure in this direction (Fig. 83). The arch and processes projecting from it have thick coverings of compact tissue. The Cervical Vertebrae (Verte- brae Cervicales). The cervical vertebrae (Fig. 84) are the smallest of the true vertebrae, and can be readily distinguished from those of the thoracic or lumbar regions by the presence of a foramen in each transverse process. The first, second, and seventh present excep- tional features and must be separately described ; the following characteristics are k common to the remaining four. The body is small, and broader from side to side than from before backward The anterior and posterior surfaces are flattened and of equal depth; the former Fig. 83. — Sagittal section of a lumbar vertebra. ^ 98 OSTEOLOGY is placed on a lower level than the latter, and its inferior border is prolongeo downward, so as to overlap the upper and forepart of the vertebra below. The upper surface is concave transversely, and presents a projecting lip on either side ; the lower surface is concave from before backward, convex from side to side, and presents laterally shallow concavities which receive the corresponding projecting lips of the subjacent vertebra. The pedicles are directed lateralward and l3ackward, and are attached to the body midway between its upper and lower borders, so that the superior vertebral notch is as deep as the inferior, but it is, at the same time. Anterior tubercle of transverse 'process Foramen iransversarium Posterior tvbercle of—^ transverse process Transverse process Superior articular process Inferior articular process I Spinmis process Fig. 84. — A cervical vertebra. narrower. The laminse are narrow, and thinner above than below; the vertebral foramen is large, and of a triangular form. The spinous process is short and bifid, the two divisions being often of unequal size. The superior and inferior articular processes on either side are fused to form an articular pillar, which projects lateral- ward from the junction of the pedicle and lamina. The articular facets are flat and of an oval form: the superior look backward, upward, and slightly medial- ward: the inferior forward, downward, and slightly lateralward. The transverse processes are each pierced by the foramen transversarium, which, in the upper six Body Anterior tubercle of transverse process Svlcusfor nerve Superior articular surface Articular pillar Fig. 85. Posterior tubercle of transverse process ■Side view of a typical cervical vertebra. Spinous process vertebrae, gives passage to the vertebral artery and vein and a plexus of sympa- thetic nerves. Each process consists of an anterior and a posterior part. The anterior portion is the homologue of the rib in the thoracic region, and is there- fore named the costal process or costal element: it arises from the side of the body, is directed lateralward in front of the foramen, and ends in a tubercle, the anterior tubercle. The posterior part, the true transverse process, springs from the vertebral arch behind the foramen, and is directed forward and lateralward; it ends in a flattened vertical tubercle, the posterior tubercle. These two parts I THE CERVICAL VERTEBRA 99 are joined, outside the foramen, by a bar of bone which exhibits a deep sulcus on its upper surface for the passage of the corresponding spinal nerve. ^ First Cervical Vertebra. — The first cervical vertebra (Fig. 86) is named the atlas because it supports the globe of the head. Its chief peculiarity is that it has no body, and this is due to the fact that the body of the atlas has fused with that of the next vertebra. Its other peculiarities are that it has no spinous process, is ring-like, and consists of an anterior and a posterior arch and two lateral masses. The anterior arch forms about one-fifth of the ring: its anterior surface is convex, and presents at its center the anterior tubercle for the attachment of the Longus colli muscles; posteriorly it is concave, and marked by a smooth, oval or circular facet (fovea dentis), for articulation with the odontoid process (dejis) of the axis. The upper and lower borders respectively give attachment to the anterior atlanto- occipital membrane and the anterior atlantoaxial ligament; the former connects it with the occipital bone above, and the latter with the axis below. The posterior arch forms about two-fifths of the circumference of the ring : it ends behind in the posterior tubercle, which is the rudiment of a spinous process and gives origin to the Recti capitis posteriores minores. The diminutive size of this process pre- vents any interference with the movements between the atlas and the skull. The posterior part of the arch presents above and behind a rounded edge for Anterior tvbercle Outline of section of odontoid process Outline cf section of trans- verse atlantal ligament Foramen transver- sarium Groove for vertebral artery and first cervical nerve I Posterior tiibercle Fig. 86. — First cervical vertebra, or atlas. the attachment of the posterior atlantooccipital membrane, while immediately behind each superior articular process is a groove (sulcus arteriw wrtchralis), (sometimes converted into a foramen by a delicate bony spiculum which arches backward from the posterior end of the superior articular process. This groove represents the superior vertebral notch, and serves for the transmission of the vertebral artery, which, after ascending through the foramen in the transverse process, winds around the lateral mass in a direction backward and medialward; it also transmits the suboccipital (first spinal) nerve. On the under surface of the posterior arch, behind the articular facets, are two shallow grooves, the inferior vertebral notches. The lower border gives attachment to the posterior atlanto- axial ligament, which connects it with the axis. The lateral masses are the most bulky and solid parts of the atlas, in order to support the weight of the head. (Each carries two articular facets, a superior and an inferior. The superior facets are of large size, oval, concave, and approach each other in front, but diverge behind: they are directed upward, medialward, and a little backward, each forming a cup for the corresponding condyle of the occipital bone, and are admirably adapted to the nodding movements of the head. Not infrequently they are ' The costal element of a cervical vertebra not only includes the portion which spriags from the side of tlje body, but ^the anterior and posterior tubercles and the bar of bone which connects them (rig. 67). 100 OSTEOLOGY partially subdivided by indentations which encroach upon their margins. The inferior articular facets are circular in form, flattened or slightly convex and directed downward and medialward, articulating with the axis, and permitting the rotatory movements of the head. Just below the medial margin of each superior facet is a small tubercle, for the attachment of the transverse atlantal ligament which stretches across the ring of the atlas and divides the vertebral foramen into two unequal parts — the anterior or smaller receiving the odontoid process of the axis, the posterior transmitting the medulla spinalis and its membranes. This part of the vertebral canal is of considerable size, much greater than is required for the accommodation of the medulla spinalis, and hence lateral displacement of the atlas may occur without compression of this structure. The transverse processes are large; they project lateralward and downward from the lateral masses, and serve for the attachment of muscles which assist in rotating the head. They are long, and their anterior and posterior tubercles are fused into one mass; the foramen transversarium is directed from below, upward and backward. Dens For alar ligaments For trans, ligament of atlas Superior artiadar surface Foramen transversarium Spinous process Fia. 87. — Second cervical vertebra, or epistropheus, from above. Second Cervical Vertebra. — ^The second cervical vertebra (Fig. 87 and 88) is named the epistropheus or axis because it forms the pivot upon which the first vertebra, carrying the head, rotates. The most distinctive characteristic of this bone is the strong odontoid process which rises perpendicularly from the upper surface of the body. The body is deeper in front than behind, and prolonged downward anteriorly so as to overlap the upper and fore part of the third vertebra. It pre- sents in front a median longitudinal ridge, separating two lateral depressions for the attachment of the Longus colli muscles. Its under surface is concave from before backward and covex from side to side. The dens or odontoid process exhibits a slight constriction or neck, where it joins the body. On its anterior surface is an oval or nearly circular facet for articulation with that on the anterior arch of the atlas. On the back of the neck, and frequently extending on to its lateral surfaces, is a shallow groove for the transverse atlantal ligament which retains the process in position. The apex is pointed, and giAes attacliment to the apical odontoid ligament; below the apex the process is somewhat enlarged, and pre- sents on either side a rough impression for the attachment of the alar ligament; these ligaments connect the process to the occipital bone. The internal structure I THE CERVICAL VERTEBRA 101 of the odontoid process is more compact than that of the body. The pedicles are broad and strong, espe;cially in front, where they coalesce with the sides of the body and the root of the odontoid process. They are covered above by the superior articular surfaces. The laminae are thick and strong, and the vertebral Odontoid process Rough surface for alar ligament Groove for transverse atlantal ligament Spinous process"^ Articular facet for anterior arch of Body Post, root I Transverse process Inferior articular process Fig. 88. — Second cervical vertebra, epistropheus, or axis, from the side. foramen large, but smaller than that of the atlas. The transverse processes are very small, and each ends in a single tubercle; each is perforated by the foramen transversarium, which is directed obliquely upward and lateralward. The superior articular surfaces are round, slightly convex, directed upward and lateralward, and are supported on the body, pedicles, and transverse processes. ^'^^^ [The inferior articular surfaces have the same direction as those of the other cervical vertebrae. The supe- rior vertebral notches are very shal- low, and lie behind the articular k)rocesses; the inferior lie in front of the articular processes, as in the other cervical vertebrae. The spinous process is large, very strong, deeply channelled on its under surface, and presents a bifid, tuberculated extremity. The Seventh Cervical Vertebra (Fig. 89). — The most distinctive characteristic of this vertebra is the existence of a long and promi- nent spinous process, hence the name vertebra prominens. This pro- cess is thick, nearly horizontal in direction, not bifurcated, but ter- minating in a tubercle to which the lower end of the ligamentum nuchse is attached. The transverse processes are of considerable size, their posterior roots are large and prominent, while the anterior are small and faintly marked; the upper surface of each has usually a shallow sulcus for the eighth spinal nerve, and its extremity seldom presents more than a trace of bifurcation. The foramen Spinous process Fig. 89. — Seventh cervical vertebra. 102 OSTEOLOGY I transversarium may be as large as that in the other cervical vertebrae, but is generally smaller on one or both sides; occasionally it is double, sometimes it is absent. On the left side it occasionally gives passage to the vertebral artery; more frequently the vertebral vein traverses it on both sides; but the usual arrangement is for both artery and vein to pass in front of the transverse pro- cess, and not through the foramen. Sometimes the anterior root of the trans- verse process attains a large size and exists as a separate bone, which is known as a cervical rib. The Thoracic Vertebrae (Vertebrae Thoracales). The thoracic vertebrae (Fig. 90) are intermediate in size between those of the cervical and lumbar regions; they increase in size from above downward, the upper vertebrae being much smaller than those in the lower part of the region. They are distinguished by the presence of facets on the sides of the bodies for articulation with the heads of the ribs, and facets on the transverse processes of all, except the eleventh and twelfth, for articulation with the tubercles of the ribs. Superior articular process Demi-facet for head of rib Facet for articular part of tubercle of rib Demi-facet for head of rib Inferior articular process Fig. 90. — A thoracic vertebra. The bodies in the middle of the thoracic region are heart-shaped, and as broad in the antero-posterior as in the transverse direction. At the ends of the thoracic region they resemble respectively those of the cervical and lumbar vertebrae. They are slightly thicker behind than in front, flat above and below, convex from side to side in front, deeply concave behind, and slightly constricted laterally and in front. They present, on either side, two costal demi-facets, one above, near the root of the pedicle, the other below, in front of the inferior vertebral notch; these are covered with cartilage in the fresh state, and, when the vertebrae are articulated with one another, form, with the intervening intervertebral fibro- cartilages, oval surfaces for the reception of the heads of the ribs. The pedicles are directed backward and slightly upward, and the inferior vertebral notches are of large size, and deeper than in any other region of the vertebral column. The laminae are broad, thick, and imbricated — that is to say, they overlap those of subjacent vertebrae like tiles on a roof. The vertebral foramen is small, and of a circular form. The spinous process is long, triangular on coronal section, directed obliquely downward, and ends in a tuberculated extremity. These processes I THE THORACIC VERTEBRAE 103 overlap from the fifth to the eighth, but are less oblique in direction above and below. The superior articular processes are thin plates of bone projecting upward from the junctions of the pedicles and laminse; their articular facets are practi- cally flat, and are directed backward and a little lateralward and upward. The inferior articular processes are fused to a considerable extent with the laminse. An entire facet above; a demi-facet below A demi-facet above — One entire facet One entire facet. No facet on trans, proc. which is rudimentary One entire facet. (No facet on trans- I verse process, -[ Infer.artic.process I convex and turned \lateralivard3 Fio. 91. — Peculiar thoracic vertebrse. I and project but slightly beyond their lower borders; their facets are directed forward and a little medialward and downward. The transverse processes arise from the arch behind the superior articular processes and pedicles; they are thick, strong, and of considerable length, directed obliquely backward and lateralward, and each ends in a clubbed extremity, on the front of which is a small, concave surface, for articulation with the tubercle of a rib. 104 OSTEOLOGY The first, ninth, tenth, eleventh, and twelfth thoracic vertebrae present certaiai pecuHarities, and must be specially considered (Fig. 91). The First Thoracic Vertebra has, on either side of the body, an entire articular facet for the head of the first rib, and a demi-facet for the upper half of the head of the second rib. The body is like that of a cervical vertebra, being broad trans- versely; its upper surface is concave, and lipped on either side. The superior articular surfaces are directed upward and backward; the spinous process is thick, long, and almost horizontal. The transverse processes are long, and the upper vertebral notches are deeper than those of the other thoracic vertebrae. The Ninth Thoracic Vertebra may have no demi-facets below. In some sub- jects however, it has two demi-facets on either side; when this occurs the tenth has only demi-facets at the upper part. The Tenth Thoracic Vertebra has (except in the cases just mentioned) an entire articular facet on either side, which is placed partly on the lateral surface of the pedicle. In the Eleventh Thoracic Vertebra the body approaches in its form and size to that of the lumbar vertebrae. The articular facets for the heads of the ribs are of large size, and placed chiefly on the pedicles, which are thicker and stronger in this and the next vertebra than in any other part of the thoracic region. The spinous process is short, and nearly horizontal in direction. The transverse processes are very short, tuberculated at their extremities, and have no articular facets. The Twelfth Thoracic Vertebra has the same general characteristics as the- eleventh, but may be distinguished from it by its inferior articular surfaces being convex and directed lateralward, like those of the lumbar vertebrae; by the general form of the body, laminae, and spinous process, in which it resembles the lumbar vertebrae; and by each transverse process being subdivided into three elevations, the superior, inferior, and lateral tubercles: the superior and inferior correspond to the mammillary and accessory processes of the lumbar vertebrae. Traces of similar elevations are found on the transverse processes of the tenth and eleventh thoracic vertebrae. Superior articular process Fig. 92. — A lumbar vertebra seen from the side. The Lumbar Vertebrae (Vertebrae Lumbales). The lumbar vertebrae (Figs. 92 and 93) are the largest segments of the movable part of the vertebral column, and can be distinguished by the absence of a foramen in the transverse process, and by the absence of facets on the sides of the body. The body is large, wider from side to side than from before backward, and a little thicker in front than behind. It is flattened or slightly concave above and I THE LUMBAR VERTEBRA 105 below, concave behind, and deeply constricted in front and at the sides. The pedicles are very strong, directed backward from the upper part of the body; Transverse process Inferior articular process Superior articular process Mamillary process Accessory process FiQ. 93. — A lumbar vertebra from above and behind. consequently, the inferior vertebral notches are of considerable depth. The laminse are broad, short, and strong; the vertebral foramen is triangular, larger Fio. 94. — Fifth lumbar vertebra, from above. than in the thoracic, but smaller than in the cervical region. The spinous process is thick, broad, and somewhat quadrilateral; it projects backward and ends in I 106 OSTEOLOGY a rough, uneven border, thickest below where it is occasionally notched. Tht5^ superior and inferior articular processes are well-defined, projecting respectively upward and downward from the junctions of pedicles and laminae. The facets on the superior processes are concave, and look backward and medial ward; thos(3 on the inferior are convex, and are directed forward and lateral ward. The former are wider apart than the latter, since in the articulated column the inferior articular processes are embraced by the superior processes of the subjacent vertebra. The transverse processes are long, slender, and .horizontal in the upper three lumbar vertebrae; they incline a little upward in the lower two. In the upper three verte- brae they arise from the junctions of the pedicles and laminae, but in the lower two they are set farther forward and spring from the pedicles and posterior parts of the bodies. They are situated in front of the articular processes instead of behind them as in the thoracic vertebrae, and are homologous with the ribs. Of the three tubercles noticed in connection with the transverse processes of the lower thoracic vertebrae, the superior one is connected in the lumbar region with the back part of the superior articular process, and is named the mammillary process; the inferior is situated at the back part of the base of the transverse process, and is called the accessory process (Fig. 93). The Fifth Lumbar Vertebra (Fig. 94) is characterized by its body being much deeper in front than behind, which accords with the prominence of the sacro- vertebral articulation; by the smaller size of its spinous process; by the wide interval between the inferior articular processes; and by the thickness of its transverse processes, which spring from the body as well as from the pedicles. The Sacral and Coccygeal Vertebrae. The sacral and coccygeal vertebrae consist at an early period of life of nine separate segments which are united in the adult, so as to form two bones, five entering into the formation of the sacrum, four into that of the coccyx. Some- times the coccyx consists of five bones; occasionally the number is reduced to three. The Sacrum {os sacrum). — The sacrum is a large, triangular bone, situated in the lower part of the vertebral column and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones; its upper part or base articulates with the last lumbar vertebra, its apex with the coccyx. It is curved upon itself and placed very obliquely, its base projecting forward and forming the prominent sacrovertebral angle when articulated with the last lumbar vertebra; its central part is projected backward, so as to give increased capacity to the pelvic cavity. Pelvic Surface {jades pelvina). — The pelvic surface (Fig. 95) is concave from above downward, and slightly so from side to side. Its middle part is crossed by four transverse ridges, the positions of which correspond with the original planes of separation between the five segments of the bone. The portions of bone intervening between the ridges are the bodies of the sacral vertebrae. The body of the first segment is of large size, and in form resembles that of a lumbar vertebra; the succeeding ones diminish from above downward, are flattened from before backward, and curved so as to accommodate themselves to the form of the sacrum, being concave in front, convex behind. At the ends of the ridges are seen the anterior sacral foramina, four in number on either side, somewhat rounded in form, diminishing in size from above downward, and directed lateralward and forward; they give exit to the anterior divisions of the sacral nerves and entrance to the lateral sacral arteries. Lateral to these foramina are the lateral parts of the sacrum, each consisting of five separate segments at an early period of life; in the adult, these are blended wdth the bodies and with each other. Each lateral part is tra- I THE SACRAL AND COCCYGEAL VERTEBRAE 107 versed by four broad, shallow grooves, which lodge the anterior divisions of the sacral nerves, and are separated by prominent ridges of bone which give origin to the Piriformis muscle. If a sagittal section be made through the center of the sacrum (Fig. 99), the bodies are seen to be united at their circumferences by bone, wide intervals being left centrally, which, in the fresh state, are filled by the intervertebral fibro- cartilages. In some bones this union is more complete between the lower than the upper segments. Dorsal Surface (fades dorsalis). — The dorsal surface (Fig. 96) is convex and narrower than the pelvic. In the middle line it displays a crest, the middle sacral crest, surmounted by three or four tubercles, the rudimentary spinous processes Promontory FiQ. 95. — ^Sacrum, pelvic surface. rof the upper three or four sacral vertebrae. On either side of the middle sacral 'crest is a shallow groove, the sacral groove, which gives origin to the Multifidus, the floor of the groove being formed by the united laminae of the corresponding vertebrs. The laminae of the fifth sacral vertebra, and sometimes those of the fourth, fail to meet behind, and thus a hiatus or deficiency occurs in the posterior wall of the sacral canal. On the lateral aspect of the sacral groove is a linear series of tubercles produced by the fusion of the articular processes which together form the indistinct sacral articular crests. The articular processes of the first sacral vertebra are large and oval in shape; their facets are concave from side to side, look backward and medialward, and articulate with the facets on the inferior processes of the fifth lumbar \ertebra. The tubercles which represent the inferior articular processes of the fifth sacral vertebra are prolonged downward as rounded 108 OSTEOLOGY I processes, which are named the sacral comua, and are connected to the corni:a of the coccyx. Lateral to the articular processes are the four posterior sacral foramina; they are smaller in size and less regular in form than the anterior, and transmit the posterior divisions of the sacral nerves. On the lateral side of the posterior sacral foramina is a series of tubercles, which represent the transverse processes of the sacral vertebrse, and form the lateral crests of the sacrum. The transverse tubercles of the first sacral vertebra are large and very distinct; they, together with the transverse tubercles of the second vertebra, give attachment to the horizontal parts of the posterior sacroiliac ligaments; those of the third vertebra give attachment to the oblique fasciculi of the posterior sacroiliac liga- ments; and those of the fourth and fifth to the sacrotuberous ligaments. Saerospinalis Latissimus dor si Saerospinalis er half of fifth posterior sacral foramen Fig. 96. — Sacrum, dorsal surface. Lateral Surface. — The lateral surface is broad above, but narrowed into a thin edge below. The upper half presents in front an ear-shaped surface, the auricular surface, covered with cartilage in the fresh state, for articulation with the ilium. Behind it is a rough surface, the sacral tuberosity, on which are three deep and uneven impressions, for the attachment of the posterior sacroiliac ligament. The lower half is thin, and ends in a projection called the inferior lateral angle; medial to this angle is a notch, which is converted into a foramen by the trans- verse process of the first piece of the coccyx, and transmits the anterior division of the fifth sacral nerve. The thin lower half of the lateral surface gives attachment to the sacrotuberous and sacrospinous ligaments, to some fibers of the Glutseus maximus behind, and to the Coccygeus in front. Base {basis oss. sacri). — The base of the sacrum, which is broad and expanded, is directed upward and forward. In the middle is a large oval articular surface, I THE SACRAL AND COCCYGEAL VERTEBRA 109 the upper surface of the body of the first sacral vertebra, which is connected with the under surface of the body of the last lumbar vertebra by an intervertebral Articular process Medial sacral crest Cornu of sacrum/ Cornu of coccyx Fig. 97. — Lateral surfaces of sacrum and coccyx. Sacral canal Articular procesa Fig 98.— Base of sacrum. 110 OSTEOLOGY I fibrocartilage. Behind this is the large triangular orifice of the sacral canal, whicb is completed by the laminae and spinous process of the first sacral vertebra. The superior articular processes project from it on either side; they are oval, concave;, directed backward and medialward, like the superior articular processes of a lumbar vertebra. They are attached to the body of the first sacral vertebra and to the alae by short thick pedicles; on the upper surface of each pedicle is a vertebral notch, which forms the lower part of the foramen between the last lumbar and first sacral vertebrae. On either side of the body is a large triangular surface, which supports the Psoas major and the lumbosacral trunk, and in the articulated pelvis is continuous with the iliac fossa. This is called the ala; it is slightly concave Cornua Anterior Surface Posterior surface Fia. 99. — Mediaa sagittal section of the sacrum. Fig. 100.- from side to side, convex from before backward, and gives attachment to a few of the fibers of the Iliacus. The posterior fourth of the ala represents the trans- verse process, and its anterior three-fourths the costal process of the first sacral segment. Apex {a'pex oss. sacri). — ^The apex is directed downward, and presents an oval facet for articulation with the coccyx. Vertebral Canal (canalis sacralis; sacral canal). — The vertebral canal (Fig. 99) runs throughout the greater part of the bone; above, it is triangular in form; below, its posterior wall is incomplete, from the non-development of the laminae and spinous processes. It lodges the sacral nerves, and its walls are perforated by the anterior and posterior sacral foramina through which these nerves pass out. THE SACRAL AND COCCYGEAL VERTEBRA 111 ^^m- Structure. — The sacrum consists of cancellous tissue enveloped by a thin layer of compact bone. Articulations. — The sacrum articulates with four bones; the last lumbar vertebra above, the coccyx below, and the hip bone on either side. Differences in the Sacrum of the Male and Female. — In the female the sacrum is shorter and wider than in the male; the lower half forms a greater angle with the upper; the upper half is nearly straight, the lower half presenting the greatest amount of curvature. The bone is also directed more obliquely backward; this increases the size of the pelvic cavity and renders the sacrovertebral angle more prominent. In the male the curvature is more evenly distributed over the whole length of the bone, and is altogether greater than in the female. Variations. — The sacrum, in some cases, consists of six pieces; occasionally the number is reduced to four. The bodies of the first and second vertebra may fail to unite. Sometimes the uppermost transverse tubercles are not joined to the rest of the ala on one or both sides, or the sacral canal may be open throughout a considerable part of its length, in consequence of the imperfect development of the laminse and spinous processes. The sacrum, also, varies con- siderably with respect to its degree of curvature. The Coccyx (os coccygis). — The coccyx (Fig. 100) is usually formed of four rudimentary vertebrae; the number may however be increased to five or diminished to three. In each of the first three segments may be traced a rudimentary body and articular and transverse processes; the last piece (sometimes the third) is a mere nodule of bone. All the segments are destitute of pedicles, laminae, and spinous processes. The first is the largest; it resembles the lowest sacral vertebra, and often exists as a separate piece; the last three diminish in size from above (downward, and are usually fused with one another. Surfaces. — ^The anterior surface is slightly concave, and marked with three trans- verse grooves which indicate the junctions of the different segments. It gives attachment to the anterior sacrococcygeal ligament and the Levatores ani, and H|.$upports part of the rectum. The posterior surface is convex, marked by transverse ^" grooves similar to those on the anterior surface, and presents on either side a linear row of tubercles, the rudimentary articular processes of the coccygeal vertebrae. 3f these, the superior pair are large, and are called the coccygeal comua; they project upward, and articulate with the cornua of the sacrum, and on either side complete the foramen for the transmission of the posterior division of the fifth sacral nerve. Borders. — ^The lateral borders are thin, and exhibit a series of small eminences, which represent the transverse processes of the coccygeal vertebrae. Of these, the first is the largest; it is flattened from before backward, and often ascends to join the lower part of the thin lateral edge of the sacrum, thus completing the foramen for the transmission of the anterior division of the fifth sacral nerve; the others diminish in size from above downward, and are often wanting. The borders of the coccyx are narrow, and give attachment on either side to the sacro- tuberous and sacrospinous ligaments, to the Coccygeus in front of the ligaments, and to the Glutaeus maximus behind them. jM , Base. — The base presents an oval surface for articulation with the sacrum. ^1 ' Apex. — The apex is rounded, and has attached to it the tendon of the Sphincter ani externus. It may be bifid, and is sometimes deflected to one or other side. ■ Ossification of the Vertebral Column. — Each cartilaginous vertebra isossified from three primary centers (Fig. 101), two for the vertebral arch and one for the body.' Ossification of the vertebral arches begins in the upper cervical vertebrae about the seventh or eighth week of fetal hfe, and grad- ually extends down the column. The ossific granules first appear in the situations where the trans- verse processes afterward project, and spread backward to the spinous process forward into the pedicles, and lateralward into the transverse and articular processes. Ossification of thebodies begins about the eighth week in the lower thoracic region, and subsequently extends upward and down- ward along the column. The center for the body does not give rise to the whole of the body of the adult vertebra, the postero-lateral portions of which are ossified by extensions from the verte- ^bral arch centers. The body of the vertebra during the first few years of life shows, therefore, !».* u ^^"^bra is occasionally found in which the body consists of two lateral portions — a condition which proves that I Be body IS sometimes ossified from two primary centers, one on either side of the middle line. 112 OSTEOLOGY two synchondroses, neurocentral synchondroses, tr the three centers (Fig. 102). In the thoracic region, Fig. 101. — Ossification of a vertebra By 3 primary centers 1 for body {Sth week) I Ifor each vertebral arch [llh or Sth week) Fig. 102. By 3 secondary centers Neurocentral synchondrosis 1 for each trans, process 16th year aversing it along the planes of junction of the facets for the heads of the ribs lie behhid the neurocentral synchondroses and are ossified from the centers for tlie vertebral arch. At birth the vertebra consists of three pieces, the body and the halves of the vertebral arch. Dur- ing the first year the halves of tlie arch unite behind, union taking place first in the lumbar region and them extending upward through the thoracic and cervical regions. About the third year the bodies of the upper cervical vertebrae are joined to the arches on either side; in the lower lumbar verte- brae the union is not completed until the sixth year. Before puberty, no other Additional centers for costal elements * At birth 1 for spinous process (16fA year) Fig. 103. By 2 additional plates 1 for upper surface' of body 1 for under surface of body I6th year Fig. 104.— Atlas. By 3 centers for anter. arch {end of 1st year) \ llh week _1 for each lateral mass Fig. 105.— Axis. By 7 centers 2nd year 6th month 1 for each vertebral arch (7 th or Sth week) 1 for body (4th month) 1 for under surface of body a Fig. 106. — Lumbar vertebra. 2 additional centers for mammillary processes Fig. 107 At ^ yrs. Fig. 108 Two epiphysial plates for each lateral surface * At 25th year Fig. 107-109. — Ossification of the sacrum. changes occur, excepting a gradual increase of these primary centers, the upper and under sur- faces of the bodies and the ends of the transverse and spinous processes being cartilaginous. I THE SACRAL AND COCCYGEAL VERTEBRA 113 About the sixteenth year (Fig. 102), five secondary centers appear, one for the tip of each transverse process, one for the extremity of the spinous process, one for the upper and one for the lower surface of the body (Fig. 103). These fuse with the rest of the bone about the age of twenty-five. Exceptions to this mode of development occur in the first, second, and seventh cervical verte- bra;, and in the lumbar vertebrae. Atlas.^ — The atlas is usually ossified from three centers (Fig. 104). Of these, one appears in each lateral mass about the seventh week of fetal life, and extends backward; at birth, these portions of bone are separated from one another behind by a narrow interval filled with cartilage. Between the third and fourth years they unite either directly or through the medium of a separate center developed in the cartilage. At birth, the anterior arch consists of cartilage; in this a separate center appears about the end of the first year after birth, and joins the lateral masses from the sixth to the eighth year — the lines of union extending across the anterior portions of the superior articular facets. Occasionally there is no separate center, the anterior arch being formed by the forward extension and ultimate junction of the two lateral masses; sometimes this arch is ossified from two centers, one on either side of the middle line. Epistropheus or Axis. — The axis is ossified from five primary and two secondary centers (Fig. 105). The body and vertebral arch are ossified in the same manner as the corresponding parts in the other vertebrae, viz., one center for the body, and two for the vertebral arch. The centers for the arch appear about the seventh or eighth week of fetal life, that for the body about the fc irth or fifth month. The dens or odontoid process consists originally of a continuation upward of the cartilaginous mass, in which the lower part of the body is formed. About the sixth month of fetal life, two centers make their appearance in the base of this process: they are placed laterally, and join before birth to form a conical bilobed mass deeply cleft above; the interval between the sides of the cleft and the summit of the process is formed by a wedge-shaped piece of cartilage. The base of the process is separated from the body by a cartilaginous disk, which gradually becomes ossified at its circumference, but remains cartilaginous in its center until advanced age. In this cartilage, rudiments of the lower epiphysial lamella of the atlas and the upper epiphysial lamella of the axis may sometimes be found. The apex of the odontoid process has a separate center which appears in the second and joins about the twelfth year; this is the upper epiphysial lamella of the atlas. In addition to these there is a secondary center for a thin epiphysial plate on the under surface of the body of the bone. The Seventh Cervical Vertebra. — The anterior or costal part of the transverse process of this vertebra is sometimes ossified from a separate center which appears about the sixth month of fetal life, and joins the body and posterior part of the transverse process between the fifth and sixth years. Occasionally the costal part persists as a separate piece, and, becoming lengthened lateralward and forward, constitutes what is known as a ceruical rib. Separate ossific centers have also been found in the costal processes of the fourth, fifth, and sixth cervical vertebrae. Lumbar Vertebrae. — The lumbar vertebrae (Fig. 106) have each two additional centers, for [the mammillary processes. The transverse process of the first lumbar is sometimes developed as a separate piece, which may remain permanently ununited with the rest of the bone, thus form- ing a lumbar rib — a peculiarity, however, Center for neural a Center for neural arch. N jOostal element. body. Lateral epiphysis. Fig. 110. — Base of young sacrum Lateral epiphysis. ^ rarely met with. Sacrum (Figs. 107 to 110).— The body of each sacral vertebra is ossified from a primary center and tivo epiphysial plates, one for its upper and another for its under surface, while each vertebral arch is ossi- fied from two centers. The anterior portions of the lateral parts have six additional centers, two for each of the first three vertebrae; these represent the costal elements, and make their ap- pearance above and lateral to the anterior sacral foramina (Figs. 107, 108). On each lateral surface two epiphysial plates are developed (Figs. 109, 1 10) : one for the auric- ular surface, and another for the remaining part of the thin lateral edge of the bone.^ Periods of Ossification. — About the eighth or ninth week of fetal life, ossification of the central part of the body of the first sacral vertebra commences, and is rapidly foUowed by deposit of ossific matter in the second and third ; ossification does not commence in the bodies of the lower two segments imtil between the fifth and eighth months of fetal hfe. Between the sixth ' The ends of the spinous processes of the upper three sacral vertebrae are sometimes developed from separate epiphyses, and Fawcett (Anatomischer Anzeiger, 1907, Band xxx) states that a number of epiphysial nodules may be seen in the sacrum at the age of eighteen years. These are distributed as follows: One for each of the mammillary pro- cesses of the first sacral vertebra ; twelve — six on either side — in connection with the costal elements (two each for the first and second and one each for the third and fourth) and eight for the transverse processes— four on either side — one each for the first, third, fourth, and fifth. He is further of opinion that the lower part of each lateral surface of the sacrum is formed by the extension and union of the third and fourth "costal" and fourth and fifth "transverse" epiphyses. ■ 114 ^^^^^^^ OSTEOLOGY and eighth months ossification of the vertebral arches takes place; and about the same time the costal centers for the lateral parts make their appearance. The junctions of the vertebral arches with the bodies take place in the lower vertebrae as early as the second year, but are not effected in the uppermost until the fifth or sixth year. About the sixteenth year the epiphysial plates for the upper and under surfaces of the bodies are formed; and between the eighteenth and twentieth years, those for the lateral surfaces make their appearance. The bodies of the sacral vertebrae are, during early life, separated from each other by intervertebral fibrocartilages, but about the eighteenth year the two lowest segments become united by bone, and the process of bony union gradually extends upward, with the result that between the twenty-fifth and thirtieth years of life all the segments are united. On examining a sagittal section of the sacrum, the situa- tions of the intervertebral fibrocartilages are indicated by a series of oval cavities (Fig. 99). Coccyx. — The coccyx is ossified from four centers, one for each segment. The ossific nuclei make their appearance in the following order: in the first segment between the first and fourth years; in the second between the fifth and tenth years; in the third between the tenth and fifteenth years; in the fourth between the fourteenth and twentieth years. As age advances, the segments unite with om another, the union between the first and second segments being frequently delayed until after the age of twenty-five or thirty. At a late period of life, especially in females, the coccyx often fuses with the sacrum. THE VERTEBRAL COLUMN AS A WHOLE. The vertebral column is situated in the median line, as the posterior part of the trunk; its average length in the male is about 71 cm. Of this length the cervical part measures 12.5 cm., the thoracic about 28 cm., the lumbar 18 cm., and the sacrum and coccyx 12.5 cm. The female column is about 61 cm. in length. Curves.- — Viewed laterally (Fig. Ill), the vertebral column presents several curves, which correspond to the different regions of the column, and are called cervical, thoracic, lumbar, and pelvic. The cervical curve, convex forward, begins at the apex of the odontoid process, and ends at the middle of the second thoracic vertebra; it is the least marked of all the curves. The thoracic curve, concave for- ward, begins at the middle of the second and ends at the middle of the twelfth thoracic vertebra. Its most prominent point behind corresponds to the spinous process of the seventh thoracic vertebra. The lumbar curve is more marked in the female than in the male; it begins at the middle of the last thoracic vertebra, and ends at the sacrovertebral angle. It is convex anteriorly, the convexity of the lower three vertebrse being much greater than that of the upper two. The pelvic curve begins at the sacrovertebral articulation, and ends at the point of the coccyx; its concavity is directed downward and forward. The thoracic and pelvic curves are termed primary curves, because they alone are present during fetal life. The cervical and lumbar curves are compensatory or secondary, and are developed after birth, the former when the child is able to hold up its head (at three or four months), and to sit upright (at nine months), the latter at twelve or eighteen months, when the child begins to walk. The vertebral column has also a slight lateral curvature, the convexity of which is directed toward the right side. This may be produced by muscular action, most persons using the right arm in preference to the left, especially in making long-continued efforts, when the body is curved to the right side. In support of this explanation it has been found that in one or two individuals who were left- handed, the convexity was to the left side. By others this curvature is regarded as being produced by the aortic arch and upper part of the descending thoracic aorta — a view which is supported by the fact that in cases where the viscera are transposed and the aorta is on the right side, the convexity of the curve is directed to the left side. Surfaces. — Anterior Surface. — When viewed from in front, the width of the bodies of the vertebrse is seen to increase from the second cervical to the first thoracic; there is then a slight diminution in the next three vertebrse; below this there is again a gradual and progressive increase in width as low as the sacrovertebral angle. From this point there is a rapid diminution, to the apex of the coccyx. I I THE VERTEBRAL COLUMN AS A WHOLE 115 I Posterior Surface. — The posterior surface of the vertebral cokimn presents in the median line the spinous processes. In the cervical region (with the exception of the second and seventh vertebrae) these are short and horizontal, with bifid extremities. In the upper part of the thoracic region they are directed obliquely downward; in the middle they are almost vertical, and in the lower part they are nearly horizontal. In the lumbar region they are nearly hori- zontal. The spinous processes are separated by considerable intervals in the lumbar region, by narrower intervals in the neck, and are closely approximated in the middle of the thoracic region. Occasionally one of , these processes deviates a little from the median line — a fact to be remembered in practice, as irregularities of this sort are attendant also on fractures or displacements of the vertebral column. On either side of the spinous processes is the vertebral groove formed by the laminae in the cervical and lumbar regions, where it is shallow, and by the laminae and transverse processes in the thoracic region, where it is deep and broad ; these grooves lodge the deep muscles of the back. Lateral to the vertebral grooves are the articular processes, and still more later- ally the transverse processes. In the tho- racic region, the transverse processes stand backward, on a plane considerably behind that of the same processes in the cervical and lumbar regions. In the cervical region, I the trans^•erse processes are placed in front 'of the articular processes, lateral to the pedicles and between the intervertebral foramina. In the thoracic region they are posterior to the pedicles, intervertebral foramina, and articular processes. In the lumbar region they are in front of the articular processes, but behind the inter- vertebral foramina. Lateral Surfaces. — ^The lateral surfaces are separated from the posterior surface by the articular processes in the cervical and lum- bar regions, and by the transverse processes in the thoracic region. They present, in I front, the sides of the bodies of the verte- I brae, marked in the thoracic region by the r facets for articulation with the heads of the ribs. jNIore posteriorly are the inter- vertebral foramina, formed by the juxta- position of the vertebral notches, oval in Fia. 111. — Lateral view of the vertebral column. 116 OSTEOLOGY shape, smallest in the cervical and upper part of the thoracic regions, and gradually] increasing in size to the last lumbar. They transmit the spinal nerves and 'ar«3 situated between the transverse processes in the cervical region, and in front of them in the thoracic and lumbar regions. Vertebral Canal. — The vertebral canal follows the different curves of the column; it is large and triangular in those parts of the column which enjoy the greatest freedom of movement, viz., the cervical and lumbar regions; and is small and rounded in the thoracic region, where motion is more limited. Abnormalities. — Occasionally the coalescence of the laminae is not completed, and conse- quently a cleft is left in the arches of the vertebrae, through which a protrusion of the spinal membranes (dura mater and arachnoid), and generally of the medulla spinaUs itself, takes place, constituting the malformation known as spina bifida. This condition is most common in the lumbosacral region, but it may occur in the thoracic or cervical region, or the arches throughout the whole length of the canal may remain incomplete. First thoracic Fig. 112. — The thorax from in front. (Spalteholz.) THE THORAX. The skeleton of the thorax or chest (Figs. 112, 113, 114) is an osseo-cartilaginous cage, containing and protecting the principal organs of respiration and circulation. I THE THORAX 117 It is conical in shape, being narrow above and broad below, flattened from before backward, and longer behind than in front. It is somewhat reniform on trans- verse section on account of the projection of the vertebral bodies into the cavity. First thoracic Fia. 113. — The thorax from behind. (Spalteholz.) Boundaries. — The posterior surface is formed by the twelve thoracic vertebrae and the posterior parts of the ribs. It is convex from above downward, and pre- sents on either side of the middle line a deep groove, in consequence of the lateral and backward direction which the ribs take from their vertebral extremities to their angles. The anterior surface, formed by the sternum and costal cartilages, is flattened or slightly convex, and inclined from above downward and forward. The lateral surfaces are convex; they are formed by the ribs, separated from jcach other by the intercostal spaces, eleven in number, which are occupied by fthe Intercostal muscles and membranes. The upper opening of the thorax is Teniform in shape, being broader from side ko side than from before backward. It is formed by the first thoracic vertebra [behind, the upper margin of the sternum in front, and the first rib on either side. 118 OSTEOLOGY It" slopes downward and forward, so that the anterior part of the opening is on a lower level than the posterior. Its antero-posterior diameter is about 5 cm., and its transverse diameter about 10 em. The lower opening is formed by the twelftli thoracic vertebra behind, by the eleventh and twelfth ribs at the sides, and in front by the cartilages of the tenth, ninth, eighth, and seventh ribs, which ascend on either side and form an angle, the subcostal angle, into the apex of which the First thoTi ■Sternum Twelfth thoracic' First lumbar Fig. 114. — The thorax from the right. (Spalteholz.) xiphoid process projects. The lower opening is wider transversely than from before backward, and slopes obliquely downward and backward, it is closed by the diaphragm which forms tlie floor of the thorax. The thorax of the female differs from that of the male as follows: 1. Its capacity is less. 2. The sternum is shorter. 3. The upper margin of the sternum is on a level with the lower part of the body of the third thoracic vertebra, whereas in the male it is on a level with the lower part of the body of the second. 4. The upper ribs are more movable, and so allow a greater enlargement of the upper part of the thorax. THE STERNUM The Sternum (Breast Bone). 119 Tlie sternum (F'igs. 115 to 117) is an elongated, flattened bone, forming the middle portion of the anterior wall of the thorax. Its upper end supports the clavicles, and its margins articulate with the cartilages of the first seven pairs STEENOCLEIDOMASTOIDEUS S0BCLAVIDS \ '^i placed laterally forfouHh) ^ * for fifth Fig. 120. — Peculiaritiea. Arrest of ossification of lateral ineces. producing : Sternal fissure, and Sternal foramen Fig. 121 I THE RIBS Wl^m 123 ^ Wh present, they are generally situated one above the other, the upper being the larger; the second piece has seldom more than one; the third, fourth, and fifth pieces are often formed from two centers placed laterally, the irregular union of which explains the rare occurrence of the sternal foramen (Fig. 121), or of the vertical fissure which occasionally intersects this part of the bone constituting the malformation known as fissura sterni; these conditions are further explained by the manner in which the cartilaginous sternum is formed. More rarely still the upper end of the sternum may be divided by a fissure. Union of the various centers of the body begins about puberty, and proceeds from below upward (Fig. 119) ; by the age of twenty-five they are all imited. The xiphoid process may become joined to the body before the age of thirty, but this occurs more frequently after forty; on the other hand, it sometimes remains ununited in old age. In advanced life the manubrium is occasionally joined to the body by bone. When this takes place, however, the bony tissue is generally only superficial, the central portion of the intervening cartilage remaining unossified. Articulations. — The sternum articulates on either side with the clavicle and upper seven costal cartilages. The Ribs (Costae). The ribs are elastic arches of bone, which form a large part of the thoracic skeleton. They are twelve in number oh either side; but this number may be increased by the development of a cervical or lumbar rib, or may be diminished to eleven. The first seven are connected behind with the vertebral column, and in front, through the intervention of the costal cartilages, with the sternum (Fig. 115); they are called true or vertebro-stemal ribs.^ The remaining five are false ribs ; of these, the first three have their cartilages attached to the cartilage of the rib above (vertebro-chondral) : the last two are free at their anterior extremities and are termed floating or vertebral ribs. The ribs vary in their direction, the upper ones being less oblique than the lower; the obliquity reaches its maximum at the ninth rib, and gradually decreases from that rib to the twelfth. The ribs are situated one below the other in such a manner that spaces called intercostal spaces are left between them. The length of each space corresponds to that of [the adjacent ribs and their cartilages; the breadth is greater in front than behind, and between the upper than the lower ribs. The ribs increase in length from the first to the seventh, below which they diminish to the twelfth. In breadth they decrease from above downward; in the upper ten the greatest breadth is at the sternal extremity. { Common Characteristics of the Ribs (Figs. 122, 123). — A rib from the middle of the series should be" taken in order to study the common characteristics of these bones. Each rib has two extremities, a posterior or vertebral, and an anterior or sternal, and an intervening portion — the body or shaft. Posterior Extremity. — The posterior or vertebral extremity presents for examination a head, neck, and tubercle. The head is marked by a kidney-shaped articular surface, divided by a hori- zontal crest into two facets for articulation with the depression formed on the bodies of two adjacent thoracic vertebrae; the upper facet is the smallier; to the crest is attached the interarticular ligament. ^ The neck is the flattened portion which extends lateralward from the head; it is about 2.5 cm. long, and is placed in front of the transverse process of the lower of the two vertebrae with which the head articulates. Its anterior surface is flat and smooth, its posterior rough for the attachment of the ligament of the neck, nd perforated by numerous foramina. Of its two borders the superior presents a rough crest (crista colli costoe) for the attachment of the anterior costotransverse ligament; its inferior border is rounded. On the posterior surface at the junction of the neck and body, and nearer the lower than the upper border, is an eminence _ 1 Sometimes the eighth rib cartilage articulates with the sternum; thi-s coaditioa occurs more frequently on the right than on the left side. km 124 OSTEOLOGY — the tubercle ; it consists of an articular and a non-articular portion. The articuiar portion, the lower and more medial of the two, presents a small, oval surface lor I Angle •Costal groove S Sf •Body Non-articular part of tubercle Articular part of tubercle ■^ Fig. 122.- central rib of the left side. Inferior aspect. articulation with the end of the transverse pro- cess of the lower of the two vertebrae to which the head is connected. The non-articular por- tion is a rough elevation, and affords attach- ment to the ligament of the tubercle. The tubercle is much more prominent in the upper than in the lower ribs. Body. — The body or shaft is thin and flat, with two surfaces, an external and an internal ; and two borders, a superior and an inferior. The external surface is convex, smooth, and marked, a little in front of the tubercle, by a prominent line, directed downw^ard and lateral- ward; this gives attachment to a tendon of the Iliocostalis, and is called the angle. At this point the rib is bent in tw^o directions, and at the same time twisted on its long axis. If the rib be laid upon its lower border, the portion of the body in front of the angle rests upon this border, while the portion behind the angle is bent medial ward and at the same time tilted upw-ard; as the result of the twist- ing, the external surface, behind the angle, looks downward, and in front of the angle, slightly upward. The distance between the angle and the tubercle is progressively greater from the second to the tenth ribs. The por- tion between the angle and the tubercle is rounded, rough, and irregular, and serves for the attachment of the Longissimus dorsi. The internal surface is concave, smooth, directed a little upward behind the angle, a little down- ward in front of it, and is marked by a ridge which commences at the lower extremity of the head; this ridge is strongly marked as far as the angle, and gradually becomes lost at the junction of the anterior and middle thirds of the bone. Between it and the inferior border is a groove, the costal groove, for the intercostal vessels and nerve. At the back part of the bone, this groove belongs to the I THE RIBS 125 inferior border, but just in front of the angle, where it is deepest and broadest, it is on the internal surface. The superior edge of the groove is rounded and serves for the attachment of an Intercostalis internus; the inferior edge corresponds to the lower margin of the rib, and gives attachment to an Intercostalis externus. Within the groove are seen the oriifices of numerous small foramina for nutrient vessels which traverse the shaft obliquel}' from before backward. The superior border, thick and rounded, is marked by an external and an internal lip, more distinct behind than in front, which serve for the attachment of Intercostales externus and internus. The inferior border is thin, and has attached to it an Inter- costalis externus. Anterior Extremity. — The anterior or sternal extremity is flattened, and presents a porous, oval, concave depression, into which the costal cartilage is received. Peculiar Ribs.— The first, second, tenth, eleventh, and twelfth ribs present certain variations from the common characteristics described above, and require special consideration. ' Demifacet for vertebra Jnterarticular crest Demifacet for vertebra A central rib of the left aide, viewed from behind. First Rib. — The first rib (Fig. 124) is the most curved and usually the shortest )f all the ribs; it is broad and flat, its surfaces looking upward and downward, ■ md its borders inward and outward. The head is small, rounded, and possesses -felly a single articular facet, for articulation with the body of the first thoracic ' \^ertebra. The neck is narrow and rounded. The tubercle, thick and prominent, s placed on the outer border. There is no angle, but at the tubercle the rib is slightly bent, with the convexity upward, so that the head of the bone is directed downward. The upper surface of the body is marked by two shallow grooves, separated from each other by a slight ridge prolonged internally into a tubercle, the scalene tubercle, for the attachment of the Scalenus anterior; the anterior groove transmits the subclavian vein, the posterior the subclavian artery and the lowest trunk of the brachial plexus.^ Behind the posterior groove is a rough area for the attachment of the Scalenus medius. The under surface is smooth, and destitute of a costal groove. The outer border is convex, thick, and rounded, and at its posterior part gives attachment to the first digitation of the Serratus anterior; the inner border is concave, thin, and sharp, and marked about its center by the scalene tubercle. The anterior extremity is larger and thicker than that of any of the other ribs. Second Rib. — ^The second rib (Fig. 125) is much longer than the first, but has a ...... .,„„...„.^, ' Anat. Anzeiger, 1910, Band xxxvi. 126 OSTEOLOGY I only feebly marked. The angle is slight, and situated close to the tubercle. Tlie body is not twisted, so that both ends touch any plane surface upon which it may be laid; but there is a bend, with its convexity upward, similar to, though smaller than that found in the first rib. The body is not flattened horizontally like that of the first rib. Its external surface is convex, and looks upward and a little outward ; near the middle of it is a rough eminence for the origin of the lower part of the FiQ. 124 Fig. 125 Angi FiQ. 126 Single articular facet — FiQ. 127 Single articular facet Fia. 128 Single articular facet Figs. 124 to 128. — Peculiar ribs. first and the whole of the second digitation of the Serratus anterior; behind and above this is attached the Scalenus posterior. The internal surface, smooth, and concave, is directed downward and a little inward: on its posterior part there is a short costal groove. Tenth Rib. — ^The tenth rib (Fig. 126) has only a single articular facet on its head. Eleventh and Twelfth Ribs. — The eleventh and twelfth ribs (Figs. 127 and 128) have each a single articular facet on the head, which is of rather large size; they I THE COSTAL CARTILAGES ^^^K 127 have no necks or tubercles, and are pointed at their anterior ends. The eleventh has a slight angle and a shallow costal groove. The twelfth has neither; it is much shorter than the eleventh, and its head is inclined slightly downward. Sometimes the twelfth rib is even shorter than the first. Structure. — The ribs consist of liighly vascular cancellous tissue, enclosed in a thin layer of compact bone. Ossification. — Each rib, with the exception of the last two, is ossified from four centers; a primary center for the body, and three epiphysial centers, one for the head and one each for the articular and non-articular parts of the tubercle. The eleventh and twelfth ribs have each only two centers, those for the tubercles being wanting. Ossification begins near the angle toward the end of the second month of fetal life, and is seen first in the sixth and seventh ribs. The epiphyses for the head and tubercle make their appearance between the sixteenth and twentieth years, and are united to the body about the twenty-fifth year. Fawcett^ states that "in all probabihty there is usually no epiphysis on the non-articular part of the tuberosity below the sixth or seventh rib. PThe Costal Cartilages (Cartilagines Costales). The costal cartilages (Fig. 115) are bars of hyaline cartilage which serve to prolong the ribs forward and contribute very materially to the elasticity of the walls of the thorax. The first seven pairs are connected with the sternum; the next three are each articulated with the lower border of the cartilage of the pre- ceding rib; the last two have pointed extremities, which end in the wall of the abdomen. Like the ribs, the costal cartilages vary in their length, breadth, and direction. They increase in length from the first to the seventh, then gradually decrease to the twelfth. Their breadth, as well as that of the intervals between them, diminishes from the first to the last. They are broad at their attachments to the ribs, and taper toward their sternal extremities, excepting the first two, which are of the same breadth throughout, and the sixth, seventh, and eighth, v.hich are enlarged where their margins are in contact. They also vary in direc- tion: the first descends a little, the second is horizontal, the third ascends slightly, ^,'hile the others are angular, following the course of the ribs for a short distance, find then ascending to the sternum or preceding cartilage. Each costal cartilage I)resents two surfaces, two borders, and two extremities. Surfaces. — The anterior surface is convex, and looks forward and upward: that of the first gives attachment to the costoclavicular ligament and the Subclavius muscle; those of the first six or seven at their sternal ends, to the Pectoralis major. The others are covered by, and give partial attachment to, some of the flat muscles of the abdomen. The posterior surface is concave, and directed backward and downward; that of the first gives attachment to the Sternothyroideus, those of the third to the sixth inclusive to the Transversus thoracis, and the six or seven inferior ones to the Transversus abdominis and the diaphragm. Borders. — Of the two borders the superior is concave, the inferior convex; they afford attachment to the Intercostales interni: the upper border of the sixth gives attachment also to the Pectoralis major. The inferior borders of the sixth, seventh, eighth, and ninth cartilages present heel-like projections at the points of greatest convexity. These projections carry smooth oblong facets which articulate respec- tively with facets on slight projections from the upper borders of the seventh, (eighth, ninth, and tenth cartilages. ^ Extremities. — The lateral end of each cartilage is continuous with the osseous tissue of the rib to which it belongs. The medial end of the first is continuous with the sternum; the medial ends of the six succeeding ones are rounded and are received into shallow concavities on the lateral margins of the sternum. The medial ends of the eighth, ninth, and tenth costal cartilages are pointed, and are connected each with the cartilage immediately above. Those of the eleventh and twelfth are pointed and free. In old age the costal cartilages are prone to undergo superficial ossification. 1 Journal of Anatomy and Physiology, vol. xlv. ■ 128 OSTEOLOGY I Cervical ribs derived from the seventh cervical vei'tebra (page 83) are of not infrequent occur- rence, and are important clinically because they may give rise to obscure nervous or vascular symptoms. The cervical rib may be a mere epiphysis articulating only with the transverse process of the vertebra, but more commonly it consists of a defined head, neck, and tubercle, with or without a body. It extends lateralwaixl, or forward and lateralward, into the posterior triangle of the neck, where it may terminate in a free end or may join the first thoracic rib, the first costal cartilage, or the sternum. ^ It varies much in shape, size, direction, and mobility. If it ret.ch far enough forward, part of the brachial plexus and the subclavian artery and vein cross o^er it, and are apt to suffer compression in so doing. Pressure on the artery may obstruct the circula- tion so much that arterial thrombosis results, causing gangrene of the finger tips. Pressure on the nerves is commoner, and affects the eighth cervical and first thoracic nerves, causing paralysis of the muscles they supply, and neuralgic pains and paresthesia in the area of skin to which they are distributed : no oculopupillary changes are to be found. The thorax is frequently found to be altered in shape in certain diseases. In rickets, the ends of the ribs, where they join the costal cartilages, become enlarged, giving rise to the so-called "rickety rosary," which in mild cases is only found on the internal surface of the thorax. Lateral to these enlargements the softened ribs sink in, so as to present a groove passing downward and lateralward on either side of the sternum. This bone is forced forward by the bending of the ribs, and the antero-posterior diameter of the chest is increased. The ribs affected are the second to the eighth, the lower ones being prevented from falling in by the pres- ence of the liver, stomach, and spleen; and when the abdomen is distended, as it often is in rickets, the lower ribs may be pushed outward, causing a transverse groove (Harrison's sulcus) just above the costal arch. This deformity or forward projection of the sternum, often asymmetrical, is known as pigeon breast, and may be taken as evidence of active or old rickets except in cases of primary spinal curvature. In many instances it is associated in children with obstruction in the upper air passages, due to enlarged tonsils or adenoid growths. In some rickety children or adults, and also in others who give no history or further evidence of having had rickets, an opposite condition obtains. The lower part of the sternum and often the xiphoid process as well are deeply depressed backward, producing an oval hollow in the lower sternal and upper epigastric regions. This is known as funnel breast (German, Trichterbrust) ; it never appears to produce the least disturbance of any of the vital functions. The phthisical chest is often long and narrow, and with great obliquity of the ribs and projection of the scapula?. In pulmonary emphysema the chest is enlarged in all its diameters, and presents on section an almost circular outline. It has received the name of the barrel-shaped chest. In severe cases of lateral curvature of the vertebral column ■ the thorax becomes much distorted. In consequence of the rotation of the bodies of the vertebrae which takes place in this disease, the ribs opposite the convexity of the dorsal curve become extremely convex behind, being thrown out and bulging, and at the same time flattened in front, so that the two ends of the same rib are almost parallel. Coincidently with this the ribs on the opposite side, on the concavity of the curve, are sunk and depressed behind, and bulging and convex in front. THE SKULL. The skull is supported on the summit of the vertebral column, and is of an oval shape, wider behind than in front. It is composed of a series of flattened or irregular bones which, with one exception (the mandible), are immovably jointed together. It is divisible into two parts: (1) the cranium, which lodges and protects the brain, consists of eight bones, and (2) the skeleton of the face, of fourteen, as follows : Cranium, 8 bones Occipital. Two Parietals. Frontal. Two Temporals. Sphenoidal. Ethmoidal. Skull, 22 bones ] ^ ^^.^ ^^^^^^ Two Maxillae. Two Lacrimals. Two Zygomatics. Two Palatines. Two Inferior Nasal Conchse. Vomer. 1^ Mandible. 1 W. Thorburn, The Medical Chronicle, Manchester, 1907, 4th series, xiv. No. 3 . Face, 14 bones I THE OCCIPITAL BONE 129 In the Basle nomenclature, certain bones developed in association with the nasal capsule, viz., the inferior nasal conchse, the lacrimals, the nasals, and the vomer, are grouped as cranial and not as facial bones. The hyoid bone, situated at the root of the tongue and attached to the base of the skull by ligaments, is described in this section. THE CRANIAL BONES (OSSA CRANE). The Occipital Bone (Os Occipitale). ^H The occipital bone (Figs. 129, 130), situated at the back and lower part of the cranium, is trapezoid in shape and curved on itself. It is pierced by a large oval aperture, the foramen magnum, through w^hich the cranial cavity communicates with the vertebral canal. Constrictor pharyngis superior Fig. 129. — Occipital bone. Outer surface. The curved, expanded plate behind the foramen magnum is named the squama; the thick, somewhat quadrilateral piece in front of the foramen is called the basilar part, whilst on either side of the foramen is the lateral portion. The Squama {squama occipitalis). — ^The squama, situated above and behind the foramen magnum, is curved from above downward and from side to side. Surfaces. — The external surface is convex and presents midway between the summit of the bone and the foramen magnum a prominence, the external occipital protuberance. Extending lateralward from this on either side are two curved ines, one a little above the other. The upper, often faintly marked, is named le highest nuchal line, and to it the galea aponeurotica is attached. The lower 9 130 OSTEOLOGY I is termed the superior nuchal line. That part of the squama which Hes above the highest nuchal lines is named the planum occipitale, and is covered by the Occipitalis muscle; that below, termed the planum nuchale, is rough and irregular for the attachment of several muscles. From the external occipital protuberance a ridge or crest, the median nuchalline, often faintly marked, descends to the fora- men magnum, and affords attachment to the ligamentum nuchae; running from the middle of this line across either half of the nuchal plane is the inferior nuchal line. Several muscles are attached to the outer surface of the squama, thus: the superior nuchal line gives origin to the Occipitalis and Trapezius, and insertion to the Sternocleidomastoideus and Splenius capitis: into the surface between Sufieri'of Am. Fia. Inferior A ngle 130. — Occipita bone. Inner surface. the superior and inferior nuchal lines the Semispinalis capitis and the Obliquus capitis superior are inserted, while the inferior nuchal line and the area below it receive the insertions of the Recti capitis posteriores major and minor. The posterior atlantooccipital membrane is attached around the postero-lateral part of the foramen magnum, just outside the margin of the foramen. The internal surface is deeply concave and divided into four fossae by a cruciate eminence. The upper two fossse are triangular and lodge the occipital lobes of the cerebrum; the lower two are quadrilateral and accommodate the hemispheres of the cerebellum. At the point of intersection of the four divisions of the cruciate eminence is the internal occipital protuberance. From this protuberance the upper division of the cruciate eminence runs to the superior angle of the bone, and on I THE OCCIPITAL BONE 131 ^ one side of it (generally the right) is a deep groove, the sagittal sulcus, which lodges the hinder part of the superior sagittal sinus; to the margins of this sulcus the falx cerebri is attached. The lower division of the cruciate eminence is prominent, and is named the internal occipital crest; it bifurcates near the foramen magnum and gives attachment to the falx cerebelli; in the attached margin of this falx is the occipital sinus, which is sometimes duplicated. In the upper part of the internal occipital crest, a small depression is sometimes distinguishable; it is termed the vermian fossa since it is occupied by part of the vermis of the cerebellum. Transverse grooves, one on either side, extend from the internal occipital protuber- ance to the lateral angles of the bone; those grooves accommodate the transverse sinuses, and their prominent margins give attachment to the tentorium cerebelli. The groove on the right side is usually larger than that on the left, and is continuous with that for the superior sagittal sinus. Exceptions to this condition are, however, not infrequent; the left may be larger than the right or the two may be almost equal in size. The angle of union of the superior sagittal and trans- verse sinuses is named the confluence of the sinuses {torcular Herophili^), and its position is indicated by a depression situated on one or other side of the protuberance. Lateral Parts (pars lateralis). — The lateral parts are situated at the sides of the foramen magnum; on their under surfaces are the condyles for articulation with the superior facets of the atlas. The condyles are oval or reniform in shape, and their anterior extremities, directed forward and mediahvard, are closer together than their posterior, and encroach on the basilar portion of the bone; the posterior extremities extend back to the level of the middle of the foramen magnum. The articular surfaces of the condyles are convex from before backward and from side to side, and look downward and lateralward. To their margins are attached the capsules of the atlantooccipital articulations, and on the medial side of each is a rough impression or tubercle for the alar ligament. At the base of either condyle the bone is tunnelled by a short canal, the hypoglossal canal {anterior Icondyloid foramen) . This begins on the cranial surface of the bone immediately [above the foramen magnum, and is directed lateralward and forward above the j*condyle. It may be partially or completely divided into two by a spicule of bone ; it gives exit to the hypoglossal or twelfth cerebral nerve, and entrance to a meningeal branch of the ascending pharyngeal artery. Behind either condyle is a depression, Ithe condyloid fossa, which receives the posterior margin of the superior facet of the atlas when the head is bent backward; the floor of this fossa is sometimes perforated by the condyloid canal, through which an emissary vein passes from the I ttransverse sinus. Extending lateralward from the posterior half of the condyle lis a quadrilateral plate of bone, the jugular process, excavated in front by the jugvdar Ixiotch, which, in the articulated skull, forms the posterior part of the jugular fora- men. The jugular notch may be divided into two by a bony spicule, the intra- jugular process, which projects lateralward above the hypoglossal canal. The ■under surface of the jugular process is rough, and gives attachment to the Rectus •capitis lateralis muscle and the lateral atlantooccipital ligament; from this surface an eminence, the paramastoid process, sometimes projects downward, and may be of sufficient length to reach, and articulate with, the transverse process of the atlas. Laterally the jugular process presents a rough quadrilateral or tri- ( angular area which is joined to the jugular surface of the temporal bone by a plate of cartilage; after the age of twenty-five this plate tends to ossify. The upper surface of the lateral part presents an oval eminence, the jugular tubercle, which overlies the hypoglossal canal and is sometimes crossed by an oblique groove for the glossopharyngeal, vagus, and accessory nerves. On the ' The columns of blood coming in different directions were supposed to be pressed together at this point (torcular, wine press). 132 OSTEOLOGY upper surface of the jugular process is a deep groove which curves medial ward and forward and is continuous with the jugular notch. This groove lodges the terminal part of the transverse sinus, and opening into it, close to its medial margin, is the orifice of the condyloid canal. Basilar Part (pars hasilaris) .■ — The basilar part extends forward and upward from the foramen magnum, and presents in front an area more or less quadrilateral in outline. In the young skull this area is rough and uneven, and is joined to the body of the sphenoid by a plate of cartilage. By the twenty-fifth year this cartil- aginous plate is ossified, and the occipital and sphenoid form a continuous bone. Surfaces. — On its lower surface, about 1 cm. in front of the foramen magnum, is the pharyngeal tubercle which gives attachment to the fibrous raphe of the pharynx. On either side of the middle line the Longus capitis and Rectus capitis anterior are inserted, and immediately in front of the foramen magnum the anterior atlantooccipital membrane is attached. The upper surface presents a broad, shallow groove which inclines upward and forward from the foramen magnum; it supports the medulla oblongata, and near the margin of the foramen magnum gives attachment to the membrana tectoria. On the lateral margins of this surface are faint grooves for the inferior petrosal sinuses. Foramen Magnum. — The foramen magnum is a large oval aperture with its long diameter antero-posterior; it is wider behind than in front where it is encroached upon by the condyles. It transmits the medulla oblongata and its membranes, the accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, and the membrana tectoria and alar ligaments. Angles. — The superior angle of the occipital bone articulates with the occipital angles of the parietal bones and, in the fetal skull, corresponds in position with the posterior fontanelle. The inferior angle is fused with the body of the sphenoid. The lateral angles are situated at the extremities of the grooves for the transverse sinuses: each is received into the interval between the mastoid angle of the parietal and the mastoid part of the temporal. Borders. — The superior borders extend from the superior to the lateral angles: they are deeply serrated for articulation with the occipital borders of the parietals, and form by this union the lambdoidal suture. The inferior borders extend from the lateral angles to the inferior angle; the upper half of each articulates with the mastoid portion of the corresponding temporal, the lower half with the petrous part of the same bone. These two por- tions of the inferior border are separated from one another by the jugular process, the notch on the anterior surface of which forms the posterior part of the jugular foramen. Fio. 131. — Occipital bone at birth. Structure. — The occipital, like the other cranial bones, consists of two compact lamellae, called the outer and inner tables, between which is the cancellous tissue or diploe; the bone is especially- thick at the ridges, protuberances, condyles, and anterior part of the basilar part; in the inferior fossse it is thin, semitransparent, and destitute of diploe. Ossification (Fig. 131). — The planum occipitale of the squama is developed in membrane, and may remam separate throughout life when it constitutes the interparietal bone; the rest of Planum occipitale Planum nv£hale Kerckring^s center Lateral part Basilar part THE PARIETAL BONE 133 the bone is developed in cartilage. The number of nuclei for the planum occipitale is usually- given as four, two appearing near the middle hne about the second month, and two some little distance from the middle line about the third month of fetal life. The planum nuchale of the scjuama is ossified from two centers, which appear about the seventh week of fetal Ufe and soon unite to form a single piece. Union of the upper and lower portions of the squama takes place in the third month of fetal life. An occasional center (Kerckring) appears in the posterior margin of the foramen magnum during the fifth month; this forms a separate ossicle (sometimes double) which unites with the rest of the squama before birth. Each of the lateral parts begins to ossify from a single center during the eighth week of fetal Ufe. The basilar portion is ossified from two centers, one in front of the other; these appear about the sixth week of fetal life and rapidly coalesce. Mall^ states that the planum occipitale is ossified from two centers and the basilar portion from one. About the fourth year the squama and the two lateral portions unite, and about the sixth year the bone consists of a single piece. Between the eighteenth and twenty- fifth years the occipital and sphenoid become united, forming a single bone. Articulations. — The occipital articulates with six bones : the two parietals, the two temporals, the sphenoid, and the atlas. The Parietal Bone (Os Parietale). The parietal bones form, by their union, the sides and roof of the cranium. Each bone is irregularly quadrilateral in form, and has two surfaces, four borders, and four angles. Articulates with opposite parietal bone ticvlates rental Fig. 132. — Left parietal bone. With mastoid portion of tetniDoral bone Outer surface. Surfaces. — The external surface (Fig. 132) is convex, smooth, and marked near le center by an eminence, the parietal eminence (tuber parietale), which indicates le point where ossification commenced. Crossing the middle of the bone in an • American Journal of Anatomy, 1906, vol. v. 134 OSTEOLOGY arched direction are two curved lines, the superior and inferior temporal lines; the former gives attachment to the temporal fascia, and the latter indicates the upper limit of the muscular origin of the Temporalis. Above these lines the bone is covered by the galea aponeurotica; below them it forms part of the temporal fossa, and affords attachment to the Temporalis muscle. At the back part and close to the upper or sagittal border is the parietal foramen, which transmits a vein to the superior sagittal sinus, and sometimes a small branch of the occipital artery; it is not constantly present, and its size varies considerably. The internal surface (Fig. 133) is concave; it presents depressions corresponding to the cerebral convolutions, and numerous furrows for the ramifications of the middle meningeal vessel;^ the latter run upward and backward from the sphenoidal angle, and from the central and posterior part of the squamous border. Along the upper margin is a shallow groove, which, together with that on the opposite Ul^^^^^^^'h. I Occipital angle Mastoid angle Frontal ' angle noidal anple Fig. 133. — Left parietal bone. Inner surface. parietal, forms a channel, the sagittal sulcus, for the superior sagittal sinus; the edges of the sulcus afford attachment to the falx cerebri. Near the groove are several depressions, best marked in the skulls of old persons, for the arachnoid granulations {Pacchionian bodies). In the groove is the internal opening of the parietal foramen when that aperture exists. Borders. — The sagittal border, the longest and thickest, is dentated and articu- lates with its fellow of the opposite side, forming the sagittal suture. The squamous border is divided into three parts: of these, the anterior is thin and pointed, bevelled at the expense of the outer surface, and overlapped by the tip of the great wing of the sphenoid; the middle portion is arched, bevelled at the expense of the outer surface, and overlapped by the squama of the temporal ; the posterior part is thick and serrated for articulation with the mastoid portion of the temporal. The ' Journal of Anatomy and Physiology, 1912, vol xlvi I THE FRONTAL BONE ^^^B 135 IN frontal border is deeply serrated, and bevelled at the expense of the outer surface above and of the inner below; it articulates with the frontal bone, forming one- half of the coronal suture. The occipital border, deeph' denticulated, articulates with the occipital, forming one-half of the lambdoidal suture. Angles. — The frontal angle is practically a right angle, and corresponds with the point of meeting of the sagittal and coronal sutures; this point is named the bregma; in the fetal skull and for about a year and a half after birth this region is membranous, and is called the anterior fontanelle. The sphenoidal angle, thin and acute, is received into the interval between the frontal bone and the great wing of the sphenoid. Its inner surface is marked by a deep groove, sometimes a canal, for the anterior divisions of the middle meningeal artery. The occipital angle is rounded and corresponds with the point of meeting of the sagittal and lambdoidal sutures — a point which is termed the lambda; in the fetus this part of the skull is membranous, and is called the posterior fontanelle. The mastoid angle is truncated; it articulates with the occipital bone and with the mastoid portion of the temporal, and presents on its inner surface a broad, shallow groove which lodges part of the transverse sinus. The point of meeting of this angle ith the occipital and the mastoid part of the temporal is named the asterion. Ossification. — The parietal bone is ossified in membrane from a single center, which appears t the parietal eminence about the eighth week of fetal life. Ossification gradually extends in n radial manner from the center toward the margins of the bone; the angles are consequently he parts last formed, and it is here that the fontanelles exist. Occasionally the parietal bone iS divided into two parts, upper and lower, by an antero-posterior suture. Articulations. — The parietal articulates with five bones: the opposite parietal, the occipital, frontal, temporal, and sphenoid. The Frontal Bone (Os Frontale). The frontal bone resembles a cockle-shell in form, and consists of two portions -a vertical portion, the squama, corresponding with the region of the forehead; |fcnd an orbital or horizontal portion, which enters into the formation of the roofs of the orbital and nasal cavities. Squama {squama frontalis). — Surfaces. — The external surface (Fig. 134) of this portion is convex and usually exhibits, in the lower part of the middle line, the remains of the frontal or metopic suture ; in infancy this suture divides the bone into I two, a condition which may persist tlu-oughout life. On either side of this suture, jiibout 3 cm. above the supraorbital margin, is a rounded elevation, the frontal emi- I iience {tuber frontale) . These eminences vary in size in different individuals, are occasionally unsymmetrical,.and are especially prominent in young skulls; the sur- iace of the bone above them is smooth, and covered by the galea aponeurotica. teelow the frontal eminences, and separated from them by a shallow groove, are Itwo arched elevations, the superciliary arches; these are prominent medially, and fare joined to one another by a smooth elevation named the glabella. They are larger in the male than in the female, and their degree of prominence depends to some extent on the size of the frontal air sinuses;^ prominent ridges are, how- ever, occasionally associated with small air sinuses. Beneath each superciliary arch is a curved and prominent margin, the supraorbital margin, which forms the upper boundary of the base of the orbit, and separates the squama from the orbital [portion of the bone. The lateral part of this margin is sharp and prominent, laffording to the eye, in that situation, considerable protection from injury; the Imedial part is rounded. At the junction of its medial and intermediate thirds is 1 Some confusion is occasioned to students commencing the study of anatomy by the name "sinus" having been • given to two different kinds of space connected with the skull. It may be as well, therefore, to state here that the "sinuses" in the interior of the cranium which produce the grooves on the inner surfaces of the bones are venous channels which convey the blood from the brain, while the "sinuses" external to the cranial cavity (the frontal, sphenoidal, ethmoidal, and maxillary) are hollow spaces in the bones themselves; they communicate with the nasal savities and contain air. ■ 136 OSTEOLOGY a notch, sometimes converted into a foramen, the supraorbital notch or foramen, which transmits the supraorbital vessels and nerve. A small aperture in the uppeT part of the notch transmits a vein from the diploe to join the supraorbital vein. The supraorbital margin ends laterally in the zygomatic process, which is strong and prominent, and articulates with the zygomatic bone. Running upward and backward from this process is a well-marked line, the temporal line, which divid(!S into the upper and lower temporal lines, continuous, in the articulated skull, with the corresponding lines on the parietal bone. The area below and behind the tem- poral line forms the anterior part of the temporal fossa, and gives origin to the Temporalis muscle. Betw^een the supraorbital margins the squama projects down- ward to a level below that of the zygomatic processes; this portion is known as the nasal part and presents a rough, uneven interval, the nasal notch, which articulates I Zygomatic process Frontal i spine Fig. 134. — Frontal bone. Outer surface. on either side of the middle line with the nasal bone, and laterally with the frontal process of the maxilla and with the lacrimal. The term nasion is applied to the middle of the frontonasal suture. From the center of the notch the nasal process projects downw^ard and forward beneath the nasal bones and frontal processes of the maxilla^, and supports the bridge of the nose. The nasal process ends below in a sharp spine, and on either side of this is a small grooved surface which enters into the formation of the roof of the corresponding nasal cavity. The spine forms part of the septum of the nose, articulating in front with the crest of the nasal bones and behind with the perpendicular plate of the ethmoid. The internal surface (Fig. 135) of the squama is concave and presents in the upper part of the middle line a vertical groove, the sagittal sulcus, the edges of which unite below to form a ridge, the frontal crest; the sulcus lodges the superior sagittal sinus, w'hile its margins and the crest afford attachment to the falx cerebri. J THE FRONTAL BONE 137 The crest ends below in a small notch which is converted into a foramen, the fora- men cecum, by articulation with the ethmoid. This foramen varies in size in different subjects, and is frequently impervious; when open, it transmits a vein from the nose to the superior sagittal sinus. On either side of the middle line the bone presents depressions for the convolutions of the brain, and numerous small furrows for the anterior branches of the middle meningeal vessels. Several small, irregular fossae may also be seen on either side of the sagittal sulcus, for the reception of the arachnoid granulations. Orbital or Horizontal Part {yars orbitalis). — This portion consists of two thin triangular plates, the orbital plates, which form the vaults of the orbits, and are separated from one another by a median gap, the ethmoidal notch. Supraorbital foramen With maxilla With nasal Frontal sinus \vm nasal, • i \ jj,,^^^ surface of nasal process With ■perpendicular plate of ethmoid || forming part of roof of nose * I Fig. 135. — Frontal bone. Inner surface. Surfaces. — The inferior surface (Fig. 135) of each orbital plate is smooth and concave, and presents, laterally, under cover of the zygomatic process, a shallow depression, the lacrimal fossa, for the lacrimal gland; near the nasal part is a depres- sion, the fovea trochlearis, or occasionally a small trochlear spine, for the attach- ment of the cartilaginous pulley of the Obliquus oculi superior. The superior surface is convex, and marked by depressions for the convolutions of the frontal Llobes of the brain, and faint grooves for the meningeal branches of the ethmoidal rvessels. The ethmoidal notch separates the two orbital plates; it is quadrilateral, and filled, in the articulated skull, by the cribriform plate of the ethmoid. The margins of the notch present several half-cells which, when united with corresponding half-cells on the upper surface of the ethmoid, complete the ethmoidal air cells. Two grooves cross these edges transversely; they are converted into the anterior 138 OSTEOLOGY I and posterior ethmoidal canals by the ethmoid, and open on the medial wall of tlie orbit. The anterior canal transmits the nasociliary nerve and anterior ethmoidal vessels, the posterior, the posterior ethmoidal nerve and vessels. In front of tlie ethmoidal notch, on either side of the frontal spine, are the openings of the frontal air sinuses. These are two irregular cavities, which extend backward, upward, and lateralward for a variable distance between the two tables of the skull; th<;y are separated from one another by a thin bony septum, which often deviates to one or other side, with the result that the sinuses are rarely symmetrical. Absent at birth, they are usually fairly well-developed between the seventh and eighth years, but only reach their full size after puberty. They vary in size in different persons, and are larger in men than in women. ^ They are lined by mucous mem- brane, and each communicates with the corresponding nasal cavity by means of a passage called the frontonasal duct. Borders. — The border of the squama is thick, strongly serrated, bevelled at the expense of the inner table above, where it rests upon the parietal bones, and at the expense of the outer table on either side, where it receives the lateral pressure of those bones; this border is continued below into a triangular, rough surface, which articulates with the great wing of the sphenoid. The posterior borders of the orbital plates are thin and serrated, and articulate with the small wings of the sphenoid. Structure. — The squama and the zygomatic processes are very thick, consisting of diploic tissue contained between two compact laminae; the diploic tissue is absent in the regions occupied by the frontal air sinuses. The orbital portion is thin, translucent, and composed entirely of compact bone; hence the facility with which instruments can penetrate the cranium through this part of the orbit; when the frontal sinuses are exceptionally large they may extend backward for a considerable distance into the orbital portion, which in such cases also consists of onlj"^ two tables. Ossification (Fig. 136). — The frontal bone is ossified in membrane from two primary centers, one for each half, which appear toward the end of the second month of fetal life, one above each supraorbital margin. From each of these centers ossification extends upward to form the corresponding half of the squama, and backward to form the orbital plate. The spine is ossified from a pair of secondary centers, « on either side of the middle line; similar * centers appear in the nasal part and zN'go- matic processes. At birth the bone consists of two pieces, separated by the frontal suture, which is usually obliterated, except at its lower part, by the eighth year, but occasionally persists throughout life. It is generally maintained that the development of the frontal sinuses begins at the end of the first or beginning of the second year, but Onodi's researches indicate that de- velopment begins at birth. The sinuses are of considerable size by the seventh or eighth year, but do not attain their full proportions until after puberty. Articulations. — The frontal articulates with twelve bones: the sphenoid, the eth- moid, the two parietals, the two nasals, the two maxillse, the two lacrimals, and the two zygomatics. Nasal part Zygomatic process Spine Fia. 136. — Frontal bone at birth. The Temporal Bone (Os Temporale). The temporal bones are situated at the sides and base of the skull. Each consists of five parts, viz., the squama, the petrous, mastoid, and tympanic parts, and the styloid process. • Aldren Turner (The Accessory Sinuses of the Nose, 1901) gives the foljowirig measurements for a sinus of average size: height, \}/i inches; breadth, 1 inch; depth from before backward, 1 inch. THE TEMPORAL BONE 139 The Squama (squama temporalis). — The squama forms the anterior and upper part of the bone, and is scale-like, thin, and translucent. Surfaces.— Its outer surface (P'ig. 137) is smooth and convex; it affords attach- ment to the Temporalis muscle, and forms part of the temporal fossa; on its hinder part is a vertical groove for the middle temporal artery. A curved line, the tem- poral line, or supramastoid crest, runs backward and upward across its posterior part; it serves for the attachment of the temporal fascia, and limits the origin of the Temporalis muscle. The boundary between the squama and the mastoid portion of the bone, as indicated by traces of the original suture, lies about 1 cm. below this line. Projecting from the lower part of the squama is a long, arched process, the zygomatic process. This process is at first directed lateralward, its two surfaces looking upward and downward; it then appears as if twisted inward Groove for middle temporal artery Parietal notch Swprameatal triangle Occipitalis Occipital groove Tympanic part Stylohyoideds Styloid process Fig. 137. — Left temporal bone. Outer surface. ipon itself, and runs forward, its surfaces now looking medial ward and lateralward. ?he superior border is long, thin, and sharp, and serves for the attachment of the _ smporal fascia; the inferior, short, thick, and arched, has attached to it some fibers of the Masseter. The lateral surface is convex and subcutaneous; the medial is concave, and affords attachment to the Masseter. The anterior end is deeply serrated and articulates with the zygomatic bone. The posterior end is connected I to the squama by two roots, the anterior and posterior roots. The posterior root, a prolongation of the upper border, is strongly marked; it runs backward above the External acoustic meatus, and is continuous with the temporal line. The anterior root, continuous with the lower border, is short but broad and strong; it is directed medialward and ends in a rounded eminence, the articular tubercle (eminentia articidaris). This tubercle forms the front boundary of the mandibular fossa, h 140 OSTEOLOGY I and in the fresh state is covered with cartilage. In front of the articular tubenQe is a small triangular area which assists in forming the infratemporal fossa; this area is separated from the outer surface of the squama by a ridge which is continu- ous behind with the anterior root of the zygomatic process, and in front, in the articulated skull, with the infratemporal crest on the great wing of the sphenoid. Between the posterior wall of the external acoustic meatus and the posterior root of the zygomatic process is the area called the suprameatal triangle (Macewen), or mastoid fossa, through which an instrument may be pushed into the tympanic antrum. At the junction of the anterior root with the zygomatic process is a pro- jection for the attachment of the temporomandibular ligament; and behind the anterior root'is an oval depression, forming part of the mandibular fossa, for the reception of the condyle of the mandible. The mandibular fossa {glenoid fossa) ctctl ho9ie Eminentia arcuata Mastoid foramen Aquceductus vestihuli Aquceducttis cochlcce Internal acoustic yneatua Fig. 138. — Left temporal bone. Inner surface. is bounded, in front, by the articular tubercle; behind, by the tympanic part of the bone, which separates it from the external acoustic meatus; it is divided into two parts by a narrow slit, the petrotympanic fissure (Glaserian fissure). The anterior part, formed by the squama, is smooth, covered in the fresh state with cartilage, and articulates with the condyle of the mandible. Behind this part of the fossa is a small conical eminence; this is the representative of a prominent tubercle which, in some mammals, descends behind the condyle of the mandible, and prevents its backward displacement. The posterior part of the mandibular fossa, formed by the tympanic part of the bone, is non-articular, and sometimes lodges a portion of the parotid gland. The petrotympanic fissure leads into the middle ear or tympanic cavity; it lodges the anterior process of the malleus, and transmits the tympanic branch of the internal maxillary artery. The chorda i THE TEMPORAL BONE 141 tympani nerve passes through a canal (canal of Huguier), separated from the an- terior edge of the petrotympanic fissure by a thin scale of bone and situated on the lateral side of the auditory tube, in the retiring angle between the squama and the petrous portion of the temporal. The internal surface of the squama (Fig. 138) is concave; it presents depressions corresponding to the convolutions of the temporal lobe of the brain, and grooves for the branches of the middle meningeal vessels. Borders. — ^The superior border is thin, and bevelled at the expense of the internal table, so as to overlap the squamous, border of the parietal bone, forming with it the squamosal suture. Posteriorly, the superior border forms an angle, the parietal notch, with the mastoid portion of the bone. The antero-inferior border is thick, serrated, and bevelled at the expense of the inner table above and of the outer below, for articulation with the great wing of the sphenoid. Mastoid Portion {yars mastoidea). — The mastoid portion forms the posterior part of the bone. Tympanic antrum Tegmen tympani Prominence, of lateral semicircular canal Prominence of facial canal Fenestra vestibuli Bristle in semicanal for Tensor tympani Septum canalis muscviotubarii Bristle m hiatus of facial canal Carotid canal Bony part of auditory tube Promontory Bristle in pyramid Fenestra cochleae Sulcus tympanicus Mastoid cells ^''''^^ *^ stylomastoid foramen Fia. 139. — Coronal section of right temporal bone. Surfaces. — Its outer surface (Fig. 137) is rough, and gives attachment to the Occipitalis and Auricularis posterior. It is perforated by numerous foramina; one of these, of large size, situated near the posterior border, is termed the mastoid foramen; it transmits a vein to the transverse sinus and a small branch of the occipi- tal artery to the dura mater. The position and size of this foramen are very ■^variable; it is not always present; sometimes it is situated in the occipital bone, pr in the suture between the temporal and the occipital. The mastoid portion is continued below into a conical projection, the mastoid process, the size and form of which vary somewhat; it is larger in the male than in the female. This process serves for the attachment of the Sternocleidomastoideus, Splenius capitis, and Longissimus capitis. On the medial side of the process is a deep groove, the astoid notch (digastric fossa) , for the attachment of the Digastricus; medial to is is a shallow furrow, the occipital groove, which lodges the occipital artery. OSTEOLOGY I The inner surface of the mastoid portion presents a deep, curved groove, the sigmoid sulcus, which lodges part of the transverse sinus; in it may be seen the opening of the mastoid foramen. The groove for the transverse sinus is separated from the innermost of the mastoid air cells by a very thin lamina of bone, and even this may be partly deficient. Borders. — The superior border of the mastoid portion is broad and serrated, for articulation with the mastoid angle of the parietal. The posterior border, also serrated, articulates with the inferior border of the occipital between the lateral angle and jugular process. Anteriorly the mastoid portion is fused with the descending process of the squama above; below it enters into the formation of the external acoustic meatus and the tympanic cavity. A section of the mastoid process (Fig. 139) shows it to be hollowed out into a number of spaces, the mastoid cells, which exhibit the greatest possible variety as to their size and number. At the upper and front part of the process they are large and irregular and contain air, but toward the lower part they diminish in size, while those at the apex of the process are frequently quite small and contain marrow; occasionally they are entirely absent, and the mastoid is then solid throughout. In addition to these a large irregular cavity is situated at the upper and front part of the bone. It is called the tympanic antrum, and must be distin- guished from the mastoid cells, though it communicates with them. Like the mas- toid cells it is filled with air and lined by a prolongation of the mucous membrane of the tympanic cavity, with which it communicates. The tympanic antrum is bounded above by a thin plate of bone, the tegmen tympani, which separates it from the middle fossa of the base of the skull; below by. the mastoid process; later- ally by the squama just below the temporal line, and medially by the lateral semi- circular canal of the internal ear which projects into its cavity. It opens in front into that portion of the tympanic cavity which is known as the attic or epitympanic recess. The tympanic antrum I's a cavity of some considerable size at the time of birth; the mastoid air cells may be regarded as diverticula from the antrum, and begin to appear at or before birth; by the fifth year they are well-marked, but their development is not completed until toward puberty. Petrous Portion {pars petrosa [pyramis]). — The petrous portion or pyramid is pyramidal and is wedged in at the base of the skull between the sphenoid and occipital. Directed medialward, forward, and a little upward, it presents for examination a base, an apex, three surfaces, and three angles, and contains, in its interior, the essential parts of the organ of hearing. Base. — The base is fused with the internal surfaces of the squama and mastoid portion. Apex. — ^The apex, rough and uneven, is received into the angular interval between the posterior border of the great wing of the sphenoid and the basilar part of the occipital; it presents the anterior or internal orifice of the carotid canal, and forms the postero-lateral boundary of the foramen lacerum. Surfaces. — ^The anterior surface forms the posterior part of the middle fossa of the base of the skull, and is continuous with the inner surface of the squamous portion, to which it is united by the petrosquamous suture, remains of which are distinct even at a late period of life. It is marked by depressions for the convolu- tions of the brain, and presents six points for examination: (1) near the center, an eminence (eminentia arcuata) which indicates the situation of the superior semi- circular canal; (2) in front of and a little lateral to this eminence, a depression indi- cating the position of the tympanic cavity : here the layer of bone which separates the tympanic from the cranial cavity is extremely thin, and is known as the tegmen tympani; (3) a shallow groove, sometimes double, leading lateralward and backward to an oblique opening, the hiatus of the facial canal, for the passage of the greater superficial petrosal nerve and the petrosal branch of the middle men- I THE TEMPORAL BONE 143 ingeal artery; (4) lateral to the hiatus, a smaller opening, occasionally seen, for the passage of the lesser superficial petrosal nerve; (5) near the apex of the bone, the termination of the carotid canal, the wall of which in this situation is deficient in front; (6) above this canal the shallow trigeminal impression for the reception of the semilunar ganglion. The posterior surface (Fig. 138) forms the front part of the posterior fossa of the base of the skull, and is continuous with the inner surface of the mastoid portion. Near the center is a large orifice, the internal acoustic meatus, the size of which varies considerably; its margins are smooth and rounded, and it leads into a short canal, about 1 cm. in length, which runs lateralward. It transmits the facial and acoustic nerves and the internal auditory branch of the basilar artery. The lateral end of the canal is closed by a vertical plate, which is divided by a horizontal crest, the crista falciformis, into two unequal portions (Fig. 140). Each I)ortion is further subdivided by a vertical ridge into an anterior and a posterior ])art. In the portion beneath the crista falciformis are three sets of foramina; one group, just below the posterior part of the crest, situated in the area cribrosa media, consists of several small openings for the nerves to the saccule; below and behind this iirea is the foramen singulare, or opening for the nerve to the posterior semicircular duct; in front of and below the first is the tractus spiralis foraminosus, consisting of a number of small spirally arranged openings, which encircle the canalis centralis cochleae; these openings together with this central canal transmit the nerves to the cochlea. The portion above the crista falciformis presents behind, the area cribrosa superior, pierced by a series of small openings, for the passage of the nerves to the utricle and the superior and lateral semicircular ducts, and, in front, the area facialis, with one large opening, the com- mencement of the canal for the facial nerve (aquaeductus Fallopii). Behind the internal acoustic meatus is a small slit almost hidden by a thin plate of bone, leading to a canal, the aquaeductus vestibuli, which transmits the ductus endolymphaticus together with a small artery and vein. Above and between these two openings is an irregular depression which lodges a process of the dura mater and transmits a small vein; in the infant this depression is repre- sented by a large fossa, the subarcuate fossa, which extends backward as a blind jtunnel under the superior semicircular canal. '" The inferior surface (Fig. 141) is rough and irregular, and forms part of the exterior f>i the base of the skull. It presents eleven points for examination: (1) near the apex is a rough surface, quadrilateral in form, which serves partly for the attachment of the Levator veli palatini and the cartilaginous portion of the audi- tory tube, and partly for connection with the basilar part of the occipital bone through the intervention of some dense fibrous tissue; (2) behind this is the large circular aperture of the carotid canal, which ascends at first vertically, and then, making a bend, runs horizontally forward and medialward; it transmits into the cranium the internal carotid artery, and the carotid plexus of nerves; (3) medial to the opening for the carotid canal and close to its posterior border, in front of the jugular fossa, is a triangular depression; at the apex of this is a small opening, the Fig. 140. — Diagrammatic view of the fundus of the right internal acoustic meatus. (Testut.) 1. Crista falciformis. 2. Area facialis, with (2') internal opening of the facial canal. 3. Ridge separating the area facialis from the area crib- rosa superior. 4. Area cribrosa superior, with (4') openings for nerve filaments. 5. Anterior inferior cribriform area, with (5') the tractus spiralis foraminosus, and (5") the canalis cen- tralis of the cochlea. 6. Ridge separating the tractus spiralis foraminosus from the area crib- rosa media. 7. Area cribrosa media, with (7') orifices for nerves to saccule. 8. Foramen singulare. II 144 OSTEOLOGY I aquaeductus cochleae, which lodges a tubular prolongation of the dura mater establish- ing a communication between the perihinphatic space and the subarachnoid space, and transmits a vein from the cochlea to join the internal jugular; (4) behind these openings is a deep depression, the jugular fossa, of variable depth and size in different skulls; it lodges the bulb of the internal jugular vein; (5) in the bony ridge dividing the carotid canal from the jugular fossa is the small inferior tympanic canaliculus for the passage of the tympanic branch of the glossopharyngeal nerve; (6) in the lateral part of the jugular fossa is the mastoid canaliculus for the entrance of the auricular branch of the vagus nerve; (7) behind the jugular fossa is a quadrilateral area, the jugular surface, covered with cartilage in the fresh state, and articulating with the jugular process of the occipital bone; (8) extending backward from the carotid canal is the vaginal process, a sheath-like plate of bone, which divides Semicanals for auditory tube a lid Tensor tympani StylopJiaryngeua Lev. vdi palatini Rough quadrilaieral surface Openiitg of carotid canal Inferior tympanic canaliculus Aquceductiis cochlew Mastoid canalicvlus Jugular fossa Vaginal process Styloid process Stylomastoid foramen J^igUlar surface Tympanomastoid fissure Fia. 141. — Left temporal bone. Inferior surface. behind into two laminae; the lateral lamina is continuous with the tympanic part of the bone, the medial with the lateral margin of the jugular surface; (9) between these laminae is the styloid process, a sharp spine, about 2.5 cm. in length; (10) between the styloid and mastoid processes is the stylomastoid foramen; it is the termination of the facial canal, and transmits the facial nerve and stylomastoid artery; (11) situated between the tympanic portion and the mastoid process is the tympanomastoid fissure, for the exit of the auricular branch of the vagus nerve. Angles. — ^The superior angle, the longest, is grooved for the superior petrosal sinus, and gives attachment to the tentorium cerebelli; at its medial extremity is a notch, in which the trigeminal nerve lies. The posterior angle is intermediate in length between the superior and the anterior. Its medial half is marked by a sulcus, which forms, with a corresponding sulcus on the occipital bone, the channel for the inferior petrosal sinus. Its lateral half presents an excavation — the jugular fossa — which, with the jugular notch on the occipital, forms the THE TEMPORAL BONE 145 t jugular foramen ; an eminence occasionally projects from the center of the fossa, and divides the foramen into two. The anterior angle is divided into two parts — a lateral joined to the squama by a suture (petrosquamous), the remains of which are more or less distinct; a medial, free, which articulates with the spinous process of the sphenoid. At the angle of junction of the petrous part and the squama are two canals, one above the other, and separated by a thin plate of bone, the septum canalis musculotubarii {processus cochleariformis) ; both canals lead into the tympanic cavity. The upper one (semicanalis m. tensoris tympani) transmits the Tensor tympani, the lower one (semicanalis tubcB auditivw) forms the bony part of the auditory tube. The tympanic cavity, auditory ossicles, and internal ear, are described with the organ of hearing. Tympanic Part (jmrs tympanica). — The tympanic part is a curved plate of bone lying below the squama and in front of the mastoid process. Surfaces. — Its postero-superior surface is concave, and forms the anterior wall, the floor, and part of the posterior wall of the bony external acoustic meatus. ]Medially, it presents a narrow furrow, the tympanic sulcus, for the attachment of the tympanic membrane. Its antero-inferior surface is quadrilateral and slightly concave; it constitutes the posterior boundary of the mandibular fossa, and is in contact w^ith the retromandibular part of the parotid gland. Borders. — Its lateral border is free and rough, and gives attachment to the car- tilaginous part of the external acoustic meatus. Internally, the tympanic part is fused with the petrous portion, and appears in the retreating angle between it and the squama, where it lies below and lateral to the orifice of the auditory tube. Posteriorly, it blends with the squama and mastoid part, and forms the anterior boundary of the tympanomastoid fissure. Its upper border fuses laterally with the back of the postglenoid process, w^hile medially it bounds the petro- tympanic fissure. The medial part of the lower border is thin and sharp; its lateral part splits to enclose the root of the styloid process, and is therefore named the vaginal process. The central portion of the tympanic part is thin, and in a consid- I arable percentage of skulls is perforated by a hole, the foramen of Huschke. The external acoustic meatus is nearly 2 cm. long and is directed inward and slightly forward: at the same time it forms a slight curve, so that the floor of the canal is convex upward. In sagittal section it presents an oval or elliptical shape • with the long axis directed downward and slightly backward. Its anterior wall land floor and the lower part of its posterior wall are formed by the tympanic part; the roof and upper part of the posterior wall by the squama. Its inner end is closed, in the recent state, by the tympanic membrane; the upper limit of its outer orifice is formed by the posterior root of the zygomatic process, imme- diately below which there is sometimes seen a small spine, the suprameatal spine, situated at the upper and posterior part of the orifice. Styloid Process {processus styloideus) . — The styloid process is slender, pointed, and of varying length; it projects downward and forw^ard, from the under surface ■ of the temporal bone. Its proximal part (tympanohyal) is ensheathed by the 'vaginal process of the tympanic portion, while its distal part (stylohyal) gives attachment to the stylohyoid and stylomandibular ligaments, and to the Stylo- glossus, Stylohyoideus, and Stylopharyngeus muscles. The stylohyoid ligament extends from the apex of the process to the lesser cornu of the hyoid bone, and in some instances is partially, in others completely, ossified. Structure. — The structure of the squama is like that of the other cranial bones: the mastoid portion is spongy, and the petrous portion dense and hard. Ossification. — The temporal bone is ossified from eight centers, exclusive of those for the internal ear and the tympanic ossicles, viz., one for the squama including the zygomatic process, one for k 10 146 OSTEOLOGY I the tympanic part, four for the petrous and mastoid parts, and two for the styloid process. Just before the close of fetal Hfe (Fig. 142) the temporal bone consists of three principal parts: 1. The squama is ossified in membrane from a single nucleus, which appears near the root of tlie zygomatic process about the second month. 2. The petromastoid part is developed from four centers, which make their appearance in the cartilaginous ear capsule about the fifth or sixth month. One (prootic) appears in the neighborhood of the eminentia arcuata, spreads in front and above the internal acoustic meatus and extends to the apex of the bone; it forms part of the Septum canalis musculotvbarii Fenestra vestibuli Tympanic antrum. Sulcus tym,panicus Bristle in facial canal Lateral wall of tympanic antrum Fig. 142. -The three principal parts of the tempora bone at birth. 1. Outer surface of petromastoid part. 2. Outer surface of tympanic ring. 3. Inner surface of squama. cochlea, vestibule, superior semicircular canal, and medial wall of the tympanic cavity. A second (opisthotic) appears at the promontory on the medial wall of the tympanic cavity and surrounds the fenestra cochlea?; it forms the floor of the tympanic cavity and vestibule, surrounds the carotid canal, invests the lateral and lower part of the cochlea, and spreads medially below the internal acoustic meatus. A third (pterotic) roofs in the tympanic cavity and antrum; while the fourth Squ/ima Squama Petrosquamous suiure Petrosquamous suture Eminentia arcuaia Tympanic ring Petromastoid portion Fig. 143. — Temporal bone at birth. Outer aspect. Fossa suharcuata Internal acoustic meatus Fig. 144. — Temporal bone at birth. Inner aspect. (epiotic) appears near the posterior semicircular canal and extends to form the mastoid process (Vrolik). 3. The tympanic ring is an incomplete circle, in the concavity of which is a groove, the tympanic sulcus, for the attachment of the circumference of the tympanic membrane. This ring expands to form the tympanic part, and is ossified in membrane from a single center which appears about the third month. The styloid process is developed from the proximal part of the cartilage of the second branchial or hyoid arch by two centers: one for the proximal part, the iympanohyal, appears before birth; the other, comprising the rest of the process, is named the J THE SPHENOID BONE HHP 147 I I stylohyal, and does not appear until after birth. The tympanic ring unites with the squama shortly before birth; the petromastoid part and squama join during the first year, and the tym- panohyal portion of the styloid process about the same time (Figs. 143, 144). The stylohyal does not unite with the rest of the bone until after puberty, and in some skulls never at all. The chief subsequent changes in the temporal bone apart from increase in size are: (1) The tympanic ring extends outward and backward to form the tympanic part. This extension does not, however, take place at an equal rate all around the circumference of the ring, but occurs most rapidly on its anterior and posterior portions, and these outgrowths meet and blend, and thus, for a time, there exists in the floor of the meatus a foramen, the foramen of Huschke; this foramen is usually closed about the fifth year, but may persist throughout life. (2) The mandibular fossa is at first extremely shallow, and looks lateralward as well as downward; it becomes deeper and is ultimately directed downward. Its change in direction is accounted for as follows. The part of the squama which forms the fossa lies at first below the level of the zygomatic process. As, however, the base of the skull increases in width, this lower part of the squama is directed hori- zontally inward to contribute to the middle fossa of the skull, and its surfaces therefore come to look upward and downward; the attached portion of the zygomatic process also becomes everted, and projects like a shelf at right angles to the squama. (3) The mastoid portion is at first quite flat, and the stylomastoid foramen and rudimentary styloid process lie immediately behind the tympanic ring. With the development of the air cells the outer part of the mastoid portion grows downward and forward to form the mastoid process, and the styloid process and stylomastoid foramen now come to lie on the under surface. The descent of the foramen is necessarily accompanied by a corresponding lengthening of the facial canal. (4) The downward and forward growth of the mastoid process also pushes forward the tympanic part, so that the portion of it which formed the original floor of the meatus and contained the foramen of Huschke is ultimately found in the anterior wall. (5) The fossa subarcuata becomes filled up and almost obliterated. Articulations. — The temporal articulates with five bones : occipital, parietal, sphenoid, mandible and zygomatic. I The Sphenoid Bone (Os Sphenoidale). The sphenoid bone is situated at the base of the skull in front of the temporals and basilar part of the occipital. It somewhat resembles a bat with its wings extended, and is divided into a median portion or body, two great and two small wings extending outward from the sides of the body, and two pterygoid processes which project from it below\ [ Body {corpus syhenoidale) . — The body, more or less cubical in shape, is hollowed out in its interior to form two large cavities, the sphenoidal air sinuses, which are separated from each other by a septum. Surfaces. — The superior surface of the body (Fig. 145) presents in front a promi- ent spine, the ethmoidal spine, for articulation with the cribriform plate of the ithmoid; behind this is a smooth surface slightly raised in the middle line, and grooved on either side for the olfactory lobes of the brain. This surface is bounded behind by a ridge, which forms the anterior border of a narrow, transverse groove, the chiasmatic groove {optic groove), above and behind which lies the optic chiasma; Ihe groove ends on either side in the optic foramen, which transmits the optic nerve and ophthalmic artery into the orbital cavity. Behind the chiasmatic groove is an elevation, the tuberculum sellae; and still more posteriorly, a deep depression, the sella tiu'cica, the deepest part of which lodges the hypophysis cerebri and is known as the fossa hypophyseos. The anterior boundary of the sella turcica is completed by two small eminences, one on either side, called the middle clinoid processes, while the posterior boundary is formed by a square- shaped plate of bone, the dorsum sellae, ending at its superior angles in two tubercles, the posterior clinoid processes, the size and form of which vary considerably in different individuals. The posterior clinoid processes deepen the sella turcica, and give attachment to the tentorium cerebelli. On either side of the dorsum sellse is a notch for the passage of the abducent nerve, and below the notch a sharp process, the petrosal process, which articulates with the apex of the petrous portion of the temporal bone, and forms the medial boundary of the foramen lacerum. 148 OSTEOLOGY I Behind the dorsum sellse is a shallow depression, the clivus, which slopes obliquely backward, and is continuous with the groove on the basilar portion of the occipii:al bone; it supports the upper part of the pons. Middle Clinoid j)rocess Posterim- Clinoid process Ethmoidal spine Groove for olfactorji lobe Optic foramen Superior orbital fissure Forainen rotundum Foramen Vesalii Foramen ovale Foramen spinosum Spina angularis With jialatine Fig. 145. — Sphenoid bone. Upper surface. The lateral surfaces of the body are united with the great w ings and the medial pterygoid plates. Above the attachment of each great wing is a broad groove, curved something like the italic letter /; it lodges the internal carotid artery and the cavernous sinus, and is named the carotid groove. Along the posterior part Tensor vel palatini Medial pteryijoid plat, Hamiilu. Fig. 146. — Sphenoid bone. Anterior and inferior surfaces. of the lateral margin of this groove, in the angle between the body and great wing, is a ridge of bone, called the lingula. The posterior surface, quadrilateral in form (I'ig. 147), is joined, during infancy and adolescence, to the basilar part of the occipital bone by a plate of cartilage. THE SPHENOID BONE 149 Between the eighteenth and twenty-fifth years this becomes ossified, ossification commencing above and extending downward. The anterior surface of the body (Fig. 146) presents, in the middle line, a vertical crest, the sphenoidal crest, which articulates with the perpendicular plate of the ethmoid, and forms part of the septum of the nose. On either side of the crest is an irregular opening leading into the corresponding sphenoidal air sinus. These sinuses are two large, irregular cavities hollowed out of the interior of the body of the bone, and separated from one another by a bony septum, which is commonly bent to one or the other side. They vary considerably in form and size,^ are seldom symmetrical, and are often partially subdivided by irregular bony laminae. Occasionally, they extend into the basilar part of the occipital nearly as far as the foramen magnum. They begin to be developed before birth, and are of a consid- erable size by the age of six. They are partially closed, in front and below, by two thin, curved plates of bone, the sphenoidal conchse (see page 152), leaving in the articulated skull a round opening at the upper part of each sinus by which it com- ierygoid canal Lateral pterygoid lamina Medial -pterygoid lamina Hamulus V Rostrum Fig. 147 — Sphenoid bone. Upper and posterior surfaces. unicates with the upper and back part of the nasal cavity and occasionally with the posterior ethmoidal air cells. The lateral margin of the anterior surface is serrated, and articulates with the lamina papyracea of the ethmoid, completing the posterior ethmoidal cells; the lower margin articulates with the orbital process of the palatine bone, and the upper with the orbital plate of the frontal bone. The inferior surface presents, in the middle line, a triangular spine, the sphenoidal rostrum, which is continuous with the sphenoidal crest on the anterior surface, and is received in a deep fissure between the alee of the vomer. On either side of the rostrum is a projecting lamina, the vaginal process, directed medialward from he base of the medial pterygoid plate, with which it will be described. The Great Wings (alee viagnoe). — The great wings, or ali-sphenoids, are two strong processes of bone, which arise from the sides of the body, and are curved upward, lateralward, and backward; the posterior part of each projects as a tri- angular process which fits into the angle between the squama and the petrous ' Aldren Turner (op. cit.) gives the following as their average measurements: vertical height, '/s inch; antero-posterior orders. H _ Surfaces. — The nasal surface exhibits at its lower part a broad, shallow depres- ^sion, which forms part of the inferior meatus of the nose. Immediately above this is a well-marked horizontal ridge, the conchal crest, for articulation with the inferior nasal concha; still higher is a second broad, shallow depression, which forms part of the middle meatus, and is limited above by a horizontal crest less prominent than the inferior, the ethmoidal crest, for articulation with the middle nasal concha. Above the ethmoidal crest is a narrow, horizontal groove, which forms part of the superior meatus. i 168 OSTEOLOGY The maxillary surface is rough and irregular throughout the greater parTo extent, for articulation with the nasal surface of the maxilla; its upper and back part is smooth where it enters into the formation of the pterygopalatine fossa; it is also smooth in front, where it forms the posterior part of the medial A^all of the maxillary sinus. On the posterior part of this surface is a deep vertical groove, converted into the pterygopalatine canal, by articulation with the maxilla; this canal transmits the descending palatine vessels, and the anterior palatine nerve. Borders. — The anterior border is thin and irregular; opposite the conchal crest is a pointed, projecting lamina, the maxillary process, which is directed forward, and closes in the lower and back part of the opening of the maxillary sinus. The posterior border (Fig. 169) presents a deep groove, the edges of which are serrated for articulation with the medial pterygoid plate of the sphenoid. This border is continuous above with the sphenoidal process; below it expands into the pyramidal process. The superior border supports the orbital process in front and the sphenoidal process behind. These processes are separated by the sphenopalatine notch, which is converted into the sphenopalatine foramen by the under surface of the body of the sphenoid. In the articulated skull this foramen leads from the pterygopalatine fossa into the posterior part of the superior meatus of the nose, and transmits the sphenopalatine vessels and the superior nasal and nasopalatine nerves. The inferior border is fused with the lateral edge of the horizontal part, and immediately in front of the pyramidal process is grooved by the lower end of the pterygopalatine canal. The Pyramidal Process or Tuberosity (processus pyrmnidalis) . — The pyramidal process projects backward and lateralward from the junction of the horizontal and vertical parts, and is received into the angular interval between the lower extremities of the pterygoid plates. On its posterior surface is a smooth, grooved, triangular area, limited on either side by a rough articular furrow. The furrows articulate with the pterygoid plates, while the grooved intermediate area completes the lower part of the pterygoid fossa and gives origin to a few fibers of the Ptery- goideus internus. The anterior part of the lateral surface is rough, for articulation with the tuberosity of the maxilla; its posterior part consists of a smooth triangular area which appears, in the articulated skull, beWeen the tuberosity of the maxilla and the lower part of the lateral pterygoid plate, and completes the lower part of the infratemporal fossa. On the base of the pyramidal process, close to its union with the horizontal part, are the lesser palatine foramina for the transmis- sion of the posterior and middle palatine nerves. The Orbital Process (processus orbitalis). — The orbital process is placed on a higher level than the sphenoidal, and is directed upward and lateralward from the front of the vertical part, to which it is connected by a constricted neck. It presents five surfaces, which enclose an air cell. Of these surfaces, three are articu- lar and two non-articular. The articular surfaces are: (1) the anterior or maxillary, directed forward, lateralward, and downward, of an oblong form, and rough for articulation with the maxilla; (2) the posterior or sphenoidal, directed backward, upward, and medialward; it presents the opening of the air cell, w^hich usually communicates with the sphenoidal sinus; the margins of the opening are serrated for articulation with the sphenoidal concha; (3) the medial or ethmoidal, directed forward, articulates with the labyrinth of the ethmoid. In some cases the air cell opens on this surface of the bone and then communicates with the posterior ethmoidal cells. ]More rarely it opens on both surfaces, and then communicates with the posterior ethmoidal cells and the sphenoidal sinus. The non-articular surfaces are: (1) the superior or orbital, directed upward and lateralward; it is triangular in shape, and forms the back part of the floor of the orbit; and (2) the lateral, of an oblong form, directed toward the pterygopalatine fossa; it is separated THE INFERIOR NASAL CONCHA 169 from the orbital surface by a rounded border, which enters into the formation of the inferior orbital fissure. The Sphenoidal Process {processus sphenoidalis) . — The sphenoidal process is a thin, compressed plate, much smaller than the orbital, and directed upward and mediahvard. It presents three surfaces and two borders. The superior surface articulates with the root of the pterygoid process and the under surface of the sphenoidal concha, its medial border reaching as far as the ala of the vomer; it presents a groove which contributes to the formation of the pharyngeal canal. The medial surface is concave, and forms part of the lateral wall of the nasal cavity. The lateral surface is divided into an articular and a non-articular portion: the former is rough, for articulation with the medial pterygoid plate; the latter is smooth, and forms part of the pterygopalatine fossa. The anterior border forms the posterior boundary of the sphenopalatine notch. The posterior border, ser- rated at the expense of the outer table, articulates with the medial pterygoid plate. The orbital and sphenoidal processes are separated from one another by the sphenopalatine notch. Sometimes the two processes are united above, and form between them a complete foramen (Fig. 168), or the notch may be crossed by one or more spicules of bone, giving rise to two or more foramina. Ossification. — The palatine bone is ossified in membrane from a single center, which makes its appearance about the sixth or eighth week of fetal life at the angle of junction of the two parts O" the bone. From this point ossification spreads medialward to the horizontal part, downward into the pyramidal process, and upward into the vertical part. Some authorities describe the bone as ossifying from four centers: one for the pyramidal process and portion of the vertical part behind the pterygopalatine groove; a second for the rest of the vertical and the horizontal parts; a third for the orbital, and a fourth for the sphenoidal process. At the time of birth the height of the vertical part is about equal to the transverse width of the horizontal part, whereas ill the adult the former measures about twice as much as the latter. Artictllations. — The palatine articulates with six bones: the sphenoid, ethmoid, maxilla, inferior nasal concha, vomer, and opposite palatine. "|i fthe Inferior Nasal Concha (Concha Nasalis Inferior; Inferior Turbinated Bone). The inferior nasal concha extends horizontally along the lateral wall of the lasal cavity (Fig. 170) and consists of a lamina of spongy bone, curled upon itself ike a scroll. It has two surfaces, two borders, and two extremities. The medial surface (Fig. 171) is convex, perforated by numerous apertures, jid traversed by longitudinal grooves for the lodgement of vessels. The lateral nrface is concave (Fig. 172), and forms part of the inferior meatus. Its upper lorder is thin, irregular, and connected to various bones along the lateral wall >f the nasal cavity. It may be divided into three portions: of these, the anterior urticulates with the conchal crest of the maxilla; the posterior with the conchal rest of the palatine; the middle portion presents three well-marked processes, ihich vary much in their size and form. Of these, the anterior or lacrimal process k small and pointed and is situated at the junction of the anterior fourth with ihe posterior three-fourths of the bone: it articulates, by its apex, with the descend- ing process of the lacrimal bone, and, by its margins, with the groove on the back of the frontal process of the maxilla, and thus assists in forming the canal for the nasolacrimal duct. Behind this process a broad, thin plate, the ethmoidal process, ascends to join the uncinate process of the ethmoid; from its lower border a thin lamina, the maxillary process, curves downward and lateralward; it articulates '.vith the maxilla and forms a part of the medial wall of the maxillary sinus. The inferior border is free, thick, and cellular in structure, more especially in the middle of the bone. Both extremities are more or less pointed, the posterior being the ore tapering. I 170 OSTEOLOGY 1 Ossification. — The inferior nasal concha is ossified from a single center, which appears' alout the fifth month of fetal life in the lateral wall of the cartilaginous nasal capsule. Articulations. — The inferior nasal concha articulates with four bones: the ethmoid, maxilla, lacrimal, and palatine. . Uncinate process oj ethmoid Openings into maxillary sinus Medial pterygoid plate Pterygoid hamulus Fig. 170. — Lateral wall of right naaal cavity showing inferior concha in situ. .1- Fig. 171. — Right inferior nasal concha. Medial surface. Fig. 172. — Right inferior nasal concha. Lateral surface. The Vomer. The vomer is situated in the median plane, but its anterior portion is frequently bent to one or other side. It is thin, somewhat quadrilateral in shape, and forms the hinder and lower part of the nasal septum (Fig. 173) ; it has two surfaces and four borders. The surfaces (Fig. 174) are marked by small furrows for blood- vessels, and on each is the nasopalatine groove, which runs obliquely downward and forward, and lodges the nasopalatine nerve and vessels. The superior border, the thickest, presents a deep furrow, bounded on either side by a horizontal pro- jecting ala of bone; the furrow receives the rostrum of the sphenoid, while the margins of the alse articulate with the vaginal processes of the medial pterygoid plates of the sphenoid behind, and with the sphenoidal processes of the palatine bones in front. The inferior border articulates with the crest formed by the maxillae THE VOMER 171 and palatine bones. The anterior border is the longest and slopes downward and forward. Its upper half is fused with the perpendicular plate of the ethmoid; its lower half is grooved for the inferior margin of the septal cartilage of the nose. The posterior border is free, concave, and separates the choanse. It is thick and bifid above, thin below. Rostrum of sphenoid Crest of nasal hones Frontal spine Space for triangular cartilage of septum Crest of palatines Crest of maxiUoe Fig. 173. — Median wall of left nasal cavity showing vomer in situ. Ossification. — At an early period the septum of the nose consists of a plate of cartilage, the iQimovomerine cartilage. The postero-superior part of this cartilage is ossified to form the per-, [endicular plate of the ethmoid; its antero-inferior portion persists as the septal cartilage, while the vomer is ossified in the membrane covering its postero-inferior part. Two ossific centers, one on either side of the middle Une, appear about the eighth week of fetal life in this part of llhe membrane, and hence the vomer consists primarily of two lamellae. About the third month 174. — The vomer. Fig 175. — Vomer of infant. these unite below, and thus a deep groove is formed in which the cartilage is lodged. As :^owth proceeds, the union of the lamellae extends upward and forward, and at the same time the intervening plate of cartilage undergoes absorption. By the age of puberty the lamelte are almost completely united to form a median plate, but evidence of the bilaminar origin of the bone is Iaeen in the everted alae of its upper border and the groove on its anterior margin. I 172 OSTEOLOGY I Articulations. — The vomer articulates with six bones: two of the cranium, the sphenoid and ethmoid; and four of the face, the two maxillaj and the two palatine bones; it also articuUtes with the septal cartilage of the nose. The Mandible (Mandibula ; Inferior Maxillary Bone; Lower Jaw). The mandible, the largest and strongest bone of the face, serves for the reception of the lower teeth. It consists of a curved, horizontal portion, the body, and two perpendicular portions, the rami, which unite with the ends of the body nearly at right angles. The Body {corpus mandibuloe) . — The body is curved somewhat like a horseshoe, and has two surfaces and two borders. Surfaces. — The external surface (Fig. 176) is marked in the median line by a faint ridge, indicating the symphysis or line of junction of the two pieces of which the bone is composed at an early period of life. This ridge divides below and encloses a triangular eminence, the mental protuberance, the base of which is de- Goronoid process Condyle TEMPORALIS ""■■"li'KllUl///' jif' V ^^" Body ^^^f" ^^ntal m^ "^^y - ■ ..^^^^^-^^ protvherance-W^^^^^^^':^' J Qrocme. for external maxillary artery Fig. 176. — Mandible. Outer surface. Side view. Am. ale pressed in the center but raised on either side to form the mental tubercle. On either side of the symphysis, just below the incisor teeth, is a depression, the incisive fossa, which gives origin to the Mentalis and a small portion of the Orbicularis oris. Below the second premolar tooth, on either side, midway between the upper and lower borders of the body, is the mental foramen, for the passage of the mental vessels and nerve. Running backward and upward from each mental tubercle is a faint ridge, the oblique line, which is continuous with the anterior border of the ramus; it affords attachment to the Quadratus labii inferioris and Triangularis; the Platysma is attached below it. The internal surface (Fig. 177) is concave from side to side. Near the lower part of the symphysis is a pair of laterally placed spines, termed the mental spines, which give origin to the Genioglossi. Immediately below these is a second pair of spines, or more frequently a median ridge or impression, for the origin of the Geniohyoidei. In some cases the mental spines are fused to form a single eminence, in others they are absent and their position is indicated merely by an irregularity of the surface. Above the mental spines a median foramen and furrow are some- times seen; they mark the line of union of the halves of the bone. Below the mental THE MANDIBLE 173 spines, on either side of the middle line, is an oval depression for the attachment of the anterior belly of the Digastricus. Extending upward and backward on either side from the lower part of the symphysis is the mylohyoid line, which gives origin to the Mylohyoideus ; the posterior part of this line, near the alveolar margin, gives attachment to a small part of the Constrictor pharyngis superior, and to the pterygomandibular raphe. Above the anterior part of this line is a smooth triangular area against which the sublingual gland rests, and below the hinder part, an oval fossa for the submaxillary gland. Borders. — The superior or alveolar border, wider behind than in front, is hollowed into cavities, for the reception of the teeth; these cavities are sixteen in number, and vary in depth and size according to the teeth which they contain. To the outer lip of the superior border, on either side, the Buccinator is attached as far forward as the first molar tooth. The inferior border is rounded, longer than the superior, and thicker in front than behind; at the point where it joins the lower border of the ramus a shallow groove; for the external maxillary artery, may be present. ..,|1v '^'^■"'/'o. Oenio- glossus Genio- hyoideus Mylohyoid line BODY Fig. 177. — Mandible. Inner surface. Side view. \ The Ramus {ramus mandibulcp; perpeiidicular portion). — The ramus is quadri- lateral in shape, and has two surfaces, four borders, and two processes. Surfaces.^ — The lateral surface (Fig. 176) is flat and marked by oblique ridges at its lower part; it gives attachment throughout nearly the whole of its extent tc the Masseter. The medial surface (Fig. 177) presents about its center the oblique mandibular foramen, for the entrance of the inferior alveolar vessels and nerve. The margin qf this opening is irregular; it presents in front a prominent ridge, surmounted by a sharp spine, the lin6:ula mandibulae, which gives attachment to the sphenomandibular ligament ; at its lower and back part is a notch from which the mylohyoid groove runs obliquely downward and forward, and lodges the mylo- hyoid vessels and nerve. Behind this groove is a rough surface, for the insertion ol the Pterygoideus internus. The mandibular canal runs obliquely downward and forward in the ramus, and then horizontally forward in the body, where it is placed under the alveoli and communicates with them by small openings. On arriving at the incisor teeth, it turns back to communicate with the mental foramen, giving off two small canals which run to the cavities containing the incisor teeth. ■ 174 I In the posterior two-thirds of the bone the canal is situated nearer the internal surface of the mandible; and in the anterior third, nearer its external surface. It contains the inferior alveolar vessels and nerve, from which branches are dis- tributed to the teeth. The lower border of the ramus is thick, straight, and con- tinuous W'ith the inferior border of the body of the bone. At its junction with the posterior border is the angle of the mandible, which may be either inverted or everted and is marked by rough, oblique ridges on each side, for the attachment of the Masseter laterally, and the Pterygoideus internus medially; the stylomandibular ligament is attached to the angle between these muscles. The anterior border is thin above, thicker below, and continuous with the oblique line. The posterior border is thick, smooth, rounded, and covered by the parotid gland. The upper border is thin, and is surmounted by two processes, the coronoid in front and the condyloid behind, separated by a deep concavity, the mandibular notch. The Coronoid Process (processus coronoideus) is a thin, triangular eminence, which is flattened from side to side and varies in shape and size. Its anterior border is convex and is continuous below with the anterior border of the ramus; its posterior border is concave and forms the anterior boundary of the mandibular notch. Its lateral surface is smooth, and affords insertion to the Temporalis and Masseter. Its medial surface gives insertion to the Temporalis, and presents a ridge which begins near the apex of the process and runs downward and forward to the inner side of the last molar tooth. Between this ridge and the anterior border is a grooved triangular area, the upper part of which gives attachment to the Temporalis, the lower part to some fibers of the Buccinator. The Condyloid Process (processus condyloideus) is thicker than the coronoid, and consists of two portions : the condyle, and the constricted portion which sup- ports it, the neck. The condyle presents an articular surface for articulation with the articular disk of the temporomandibular joint; it is convex from before back- ward and from side to side, and extends farther on the posterior than on the ante- rior surface. Its long axis is directed medialward and slightly backward, and if prolonged to the middle line will meet that of the opposite condyle near the ante- rior margin of the foramen magnum. At the lateral extremity of the condyle is a small tubercle for the attachment of the temporomandibular ligament. The neck is flattened from before backward, and strengthened by ridges which descend from the forepart and sides of the condyle. Its posterior surface is convex; its anterior presents a depression for the attachment of the Pterygoideus externus. The mandibular notch, separating the two processes, is a deep semilunar depres- sion, and is crossed by the masseteric vessels and nerve. Ossification. — The mandible is ossified in the fibrous membrane covering the outer surfaces of Meckel's cartilages. These cartilages form the cartilaginous bar of the mandibular arch (see p. 66), and are two in number, a right and a left. Their proximal or cranial ends are connected with the ear capsules, and their distal extremities are joined to one another at the symphysis by mesodermal tissue. They run forward immediately below the condyles and then, bending downward, lie in a groove near the lower border of the bone; in front of the canine tooth they incUne upward to the symphysis. From the proximal end of each cartilage the malleus and incus, two of the bones of the middle ear, are developed; the next succeeding portion, as far as the lingula, is replaced by fibrous tissue, which persists to form the sphenomandibular ligament. Between the lingula and the canine tooth the cartilage disappears, while the portion of it below and behind the incisor teeth becomes ossified and incorporated with this part of the mandible. Ossification takes place in the membrane covering the outer surface of the ventral end of Meckel's cartilage (Figs. 178 to 181), and each half of the bone is formed from a single center which appears, near the mental foramen, about the sixth week of fetal life. By the tenth week the portion of Meckel's cartilage which lies below and behind the incisor teeth is surrounded and invaded by the membrane bone. Somewhat later, accessory nuclei of cartilage make their appear- ance, viz., a wedge-shaped nucleus in the condyloid process and extending downward through the ramus; a small strip along the anterior border of the coronoid process; and smaller nuclei in the front part of both alveolar walls and along the front of the lower border of the bone. These accessory nuclei possess no separate ossific centers, but are invaded by the siu-rounding membrane THE MANDIBLE 175 boae and undergo absorption. The inner alveolar border, usually described as arising from a sejjarate ossific center (splenial center), is formed in the human mandible by an ingrowth from the main mass of the bone. At birth the bone consists of two parts, united by a fibrous symphysis, in which ossification takes place during the first year. The foregoing description of the ossification of the mandible is based on the researches of Low' and Fawcett,- and differs somewhat from that usually given. Articulations. — The mandible articulates with the two temporal bones. Mental nerve Mylohyoid nerve Fio. 178. — Mandible of human embryo 24 mm. long. Outer aspect. (From model by Low.) Lingual nerve Inf. alveolar n. Mylohyoid nerve Chorda tympani Stapes Facial nervi ReicherVs cartilage Fig. 179. — Mandible of human embryo 24' mm. long. Inner aspect. (From model by Low.) Mandibular nerve Meckel's cartilage Mental nerve Anterior process of nuii.i.,^ Fig. 180. — Mandible of human embryo 95 mm. long. Outer aspect. Nuclei of cartilage stippled. (From model by Low.) AuriciUotem/poral nerve Ant. process of malleus Chorda tympani Symphysis stylohyoid nerve Fig. 181.- -Mandible of human embryo 95 mm. long. Inner aspect. (From model by Low.) Nuclei of cartilage stippled. CHANGES PRODUCED IN THE MANDIBLE BY AGE. At birth (Fig. 182) the body of the bone is a mere shell, containing the sockets of the two incisor, the canine, and the two deciduous molar teeth, imperfectly partitioned off from one another. The mandibular canal is of large size, and runs near the lower border of the bone; the mtid artery, the latter being surrounded by a plexus of sympathetic nerves. The lateral parts of the middle fossa are of considerable depth, and support the temporal lobes of the brain. They are marked by depressions for the brain convolutions and traversed by furrows for the anterior and posterior branches of the middle meningeal vessels. These furrows begin near the foramen spinosiim, and the anterior runs forward and upward to the sphenoidal angle of the parietal, where it is sometimes converted into a bony canal; the posterior runs lateral ward and backward across the temporal squama and passes on to the parietal near the middle of its lower border. The following apertures are also to be seen. In front is the superior orbital fissure, bounded above by the small wing, below, by the great wing, and medially, by the body of the sphenoid; it is usually completed laterally by the orbital plate of the frontal bone. It transmits to the orbital cavity the oculomotor, the trochlear, the ophthalmic division of the trigeminal, and the abducent nerves, some filaments from the cavernous plexus of the sympathetic, and the orbital branch of the middle meningeal artery; and from the orbital cavity a recurrent branch from the lacrimal artery to the dura mater, and the ophthalmic veins. Behind the medial end of the superior orbital fissure is the foramen rotundum, for the passage of the maxillary nerve. Behind and lateral to the foramen rotundum is the foramen ovale, which transmits the mandibular nerve, the accessory meningeal artery, and the lesser superficial petrosal nerve.^ Medial to the foramen ovale is the foramen Vesalii, which varies in size in different individuals, and is often absent; when present, it opens below at the lateral side of the scaphoid fossa, and transmits a small vein. Lateral to the foramen ovale is the foramen spinosum, for the passage of the middle meningeal vessels, and a recurrent branch from the mandibular nerve. Medial to the foramen ovale is the foramen lacerum; in the fresh state the lower part of this aperture is filled up by a layer of fibrocartilage, while its upper and inner parts transmit the internal carotid artery surrounded by a plexus of sympathetic nerves. The nerve of the pterygoid canal and a meningeal branch from the ascending pharyngeal artery pierce the layer of fibrocartilage. On the anterior surface of the petrous portion of the temporal bone are seen the eminence caused by the projection of the superior semicircular canal; in front of and a little lateral to this a depression corresponding to the roof of the tympanic cavity; the groove leading to the hiatus of the facial canal, for the transmission of the greater superficial petrosal nerve and the petrosal branch of the middle meningeal artery ; beneath it, the smaller groove, for the pas- sage of the lesser superficial petrosal nerve; and, near the apex of the bone, the depression for the semilunar ganglion and the orifice of the carotid canal. The Posterior Fossa (fossa cranii posterior). — -The posterior fossa is the largest and deepest of the three. It is formed by the dorsum sellse and clivus of the sphenoid, the occipital, the petrous and mastoid portions of the temporals, and the mastoid angles of the parietal bones; it is crossed by the occipitomastoid and the parietomastoid sutures, and lodges the cerebellum, pons, and medulla oblongata. It is separated from the middle fossa in and near the median line by the dorsum sellse of the sphenoid and on either side by the superior angle of the petrous por- tion of the temporal bone. This angle gives attachment to the tentorum cerebelli, is grooved for the superior petrosal sinus, and presents at its medial end a notch upon which the trigeminal nerve rests. The fossa is limited behind by the grooves for the transverse sinuses. In its center is the foramen magnum, on either side of which is a rough tubercle for the attachment of the alar ligaments; a little above this tubercle is the canal, which transmits the hypoglossal nerve and a meningeal branch from the ascending pharyngeal artery. In front of the foramen magnum ' See footnote, page 150. THE INTERIOR OF THE SKULL 193 the basilar portion of the occipital and the posterior part of the body of the sphenoid form a grooved surface which supports the medulla oblongata and pons; in the young skull these bones are joined by a synchondrosis. This grooved surface is separated on either side from the petrous portion of the temporal by the petro- occipital fissure, which is occupied in the fresh state by a plate of cartilage; the fissure is continuous behind with the jugular foramen, and its margins are grooved for the inferior petrosal sinus. The jugular foramen is situated between the lateral part of the occipital and the petrous part of the temporal. The anterior portion of this foramen transmits the inferior petrosal sinus; the posterior portion, the transverse sinus and some meningeal branches from the occipital and ascending pharyngeal arteries; and the intermediate portion, the glossopharyngeal, vagus, and accessory nerves. Above the jugular foramen is the internal acoustic meatus, for the facial and acoustic nerves and internal auditory artery; behind and lateral Palatine bone Fig. 194. — Sagittal section of skull. this is the slit-like opening leading into the aquseductus vestibuli, which lodges the ductus endolymphaticus; while between these, and near the superior angle of the petrous portion, is a small triangular depression, the remains of the fossa sub- arcuata, which lodges a process of the dura mater and occasionally transmits a small ivein. Behind the foramen magnum are the inferior occipital fossae, which support the hemispheres of the cerebellum, separated from one another by the internal occipital crest, which serves for the attachment of the falx cerebelli, and lodges the occipital sinus. The posterior fossae are surmounted by the deep grooves for the transverse sinuses. Each of these channels, in its passage to the jugular foramen, grooves the occipital, the mastoid angle of the parietal, the mastoid portion of the temporal, and the jugular process of the occipital, and ends at the back part of the jugular foramen. Where this sinus grooves the mastoid portion of the temporal, the orifice of the mastoid foramen may be seen; and, just previous to its termina- I tion, the condyloid canal opens into it; neither opening is constant. 13 194 OSTEOLOGY The Nasal Cavity {camim. nasi; nasal fossa). — The nasal cavities are two irregu spaces, situated one on either side of the middle line of the face, extending from the base of the cranium to the roof of the mouth, and separated from each other by a thin vertical septum. They open on the face through the pear-shaped anterior nasal aperture, and their posterior openings or choanse communicate, in the fresh state, with the nasal part of the pharynx. They are much narrower above than below, and in the middle than at their anterior or posterior openings: their depth, which is considerable, is greatest in the middle. They communicate with the frontal, ethmoidal, sphenoidal, and maxillary sinuses. Each cavity is bounded by a roof, a floor, a medial and a lateral wall. The roof (Figs. 195, 196) is horizontal in its central part, but slopes do\An- ward in front and behind; it is formed in front by the nasal bone and the spine of the frontal; in the middle, by the cribriform plate of the ethmoid; and behind, Crest of nasal hones Frontal spine Space for triangular cartilage of septum Crest of palatines Crest of maxilla Fig. 195. — Medial wall of left nasal fossa. by the body of the sphenoid, the sphenoidal concha, the ala of the vomer and the sphenoidal process of the palatine bone. In the cribriform plate of the ethmoid are the foramina for the olfactory nerves, and on the posterior part of the roof is the opening into the sphenoidal sinus. The floor is flattened from before backward and concave from side to side. It is formed by the palatine process of the maxilla and the horizontal part of the palatine bone; near its anterior end is the opening of the incisive canal. The medial wall (septum nasi) (Fig. 195), is frequently deflected to one or other side, more often to the left than to the right. It is formed, in front, by the crest of the nasal bones and frontal spine; in the middle, by the perpendicular plate of the ethmoid; behind, by the vomer and the rostrum of the sphenoid; below, by the crest of the maxillae and palatine bones. It presents, in front, a large, triangular notch, which receives the cartilage of the septum; and behind, the free edge of the vomer. Its surface is marked by numerous furrows for vessels THE INTERIOR OF THE SKULL 195 and nerves and by the grooves for the nasopalatine nerve, and is traversed by sutures connecting the bones of which it is formed. The lateral wall (Fig. 196) is formed, in front, by the frontal process of the maxilla and by the lacrimal bone; in the middle, by the ethmoid, maxilla, and inferior nasal concha; behind, by the vertical plate of the palatine bone, and the medial pterygoid plate of the sphenoid. On this wall are three irregular antero- posterior passages, termed the superior, middle, and inferior meatuses of the nose. The superior meatus, the smallest of the three, occupies the middle third of the lateral wall. It lies between the superior and middle nasal conchse; the spheno- palatine foramen opens into it behind, and the posterior ethmoidal cells in front. The sphenoidal sinus opens into a recess, the sphenoethmoidal recess, which is placed above and behind the superior concha. The middle meatus is situated between the middle and inferior conchse, and extends from the anterior to the posterior end of Nasal bone Frontal spine Cribriform plate of ethmoid Sphenoid Probe passed through nasolacrimal canal Bristle passed through infundibulum Frontal prpe. of maxilla Lacrimal Ethmoid Uncinate proc. of ethmoid Inferior nasal concha Palatine Superior meatus Middle meatus Inferior meatus Anterior nasal spine Palatine proc. of maxilla Ryrizontal part of palatini Posterior nasal spine Incisive canal- Fig. 196. — Roof, floor, and lateral wall of left nasal cavity. 't,he latter. The lateral wall of this meatus can be satisfactorily studied only after t;he removal of the middle concha. On it is a curved fissure, the hiatus semilunaris, limited below by the edge of the uncinate process of the ethmoid and above by an elevation named the bulla ethmoidaUs; the middle ethmoidal cells are contained within this bulla and open on or near to it. Through the hiatus semilunaris i:he meatus communicates with a curved passage termed the infundibulum, which <3ommunicates in front with the anterior ethmoidal cells and in rather more than Sfty per cent, of skulls is continued upward as the frontonasal duct into the frontal air-sinus; when this continuity fails, the frontonasal duct opens directly into the anterior part of the meatus. Below the bulla ethmoidalis and hidden by the unci- nate process of the ethmoid is the opening of the maxillary sinus (ostium maxillare) ; an accessory opening is frequently present above the posterior part of the inferior nasal concha. The inferior meatus, the largest of the three, is the space between the inferior concha and the floor of the nasal cavitv. It extends almost the entire I 196 OSTEOLOGY length of the lateral wall of the nose, is broader in front than behind, and presents anteriorly the lower orifice of the nasolacrimal canal. The Anterior Nasal Aperture (Fig. 181) is a heart-shaped or pyriform opening, whose long axis is vertical, and narrow end upward; in the recent state it is much contracted by the lateral and alar cartilages of the nose. It is bounded above by the inferior borders of the nasal bones; laterally by the thin, sharp margins which separate the anterior from the nasal surfaces of the maxillae; and below by the same borders, where they curve medialward to join each other at the anterior nasal spine. The choanse are each bounded above by the under surface of the body of the sphenoid and ala of the vomer; below, by the posterior border of the horizontal part of the palatine bone; laterally, by the medial pterygoid plate; they are separated from each other by the posterior border of the vomer. DIFFERENCES IN THE SKULL DUE TO AGE. At birth the skull is large in proportion to the other parts of the skeleton, but its facial portion is small, and equals only about one-eighth of the bulk of the cranium as compared with one-l?aK in the adult. The frontal and parietal eminences are prominent, and the greatest width of the skull is at the level of the latter; on the other Frontal fontanel hand, the glabella, superciliary arches, and mastoid processes are not developed. Ossi- fication of the skuU bones is not completed, and many of them, e. g., the occipital, temp- orals, sphenoid, frontal, and mandible, consist of more than one piece. Unossified mem- branous intervals, termed Jontanelles, are seen at the angles of the parietal bones; these fontaneUes are six in number: two, an ante- rior and a posterior, are situated in the middle hne, and two, an antero-lateral and a postero- lateral, on either side. The anterior or bregmaiic fontanelle (Fig. 197) is the largest, and is placed at the junc- tion of the sagittal, coronal, and frontal sutures; it is lozenge-shaped, and measiu-es about 4 cm. in its antero-posterior and 2.5 cm. in its transverse diameter. The posterior fontanelle is triangular in form and is situated at the junction of the sagittal and lambdoidal sutures. The lateral fontaneUes (Fig, 198) are small, irregular in shape, and correspond re- spectively with the sphenoidal and mastoid angles of the parietal bones. An additional fontanelle is sometimes seen in the sagittal suture at the region of the obehon. The fontaneUes are usually closed by the growth and extension of the bones which surround them, but sometimes they are the sites of separate ossific centers which develop into sutural bones. The posterior and lateral fon- taneUes are obliterated within a month or two after birth, but the anterior is not completely closed until about the middle of the second year. The smallness of the face at birth is mainly accounted for by the rudimentary condition of the maxillae and mandible, the non-eruption of the teeth, and the small size of the maxillary air sinuses and nasal cavities. At birth the nasal cavities He almost entirely between the orbits, and the lower border of the anterior nasal aperture is only a httle below the level of the orbital floor. With the eruption of the deciduous teeth there is an enlargement of the face and jaws, and these changes are still more marked after the second dentition. The skull grows rapidly from birth to the seventh year, by which time the foramen magnum and petrous parts of the temporals have reached their full size and the orbital cavities are only a httle smaller than those of the adult. Growth is slow from the seventh year until the approach Occipital fontanel FiQ. 197. — Skull at birth, showing frontal and occipital fonticuli. CRANIOLOGY 197 of jjuberty, when a second period of activity occurs : this results in an increase in all directions, but it is especially marked in the frontal and facial regions, where it is associated with the develop- ment of the air sinuses. Obhteration of the sutures of the vault of the skull takes place as age advances. This process may commence between the ages of thirty and forty, and is first seen on the inner surface, and some ten years later on the outer surface of the skull. The dates given are, however, only approxi- mate, as it is impossible to state with anything hke accuracy the time at which the sutures are closed. Obhteration usually occurs first in the posterior part of the sagittal suture, next in the coron. 1, and then in the lambdoidal. In old age the skull generally becomes thinner and Ughter, but in a small proportion of cases it increases in thickness and weight, owing to an hypertrophy of the inner table. The most strik- ing feature of the old skull is the diminution in the size of the maxillaj and mandible consequent on the loss of the teeth and the absorption of the alveolar processes. This is associated with a marked reduction in the vertical measurement of the face and with an alteration in the angles of the mandible. Frontal fontanel Mastoid fontanel Sphenoidal fontanel Fia. 198. — Skull at birth, showing sphenoidal and mastoid fonticuli. SEXUAL DIFFERENCES IN THE SKULL. ^" Until the age of puberty there is Httle difference between the skull of the female and that of the male. The skull of an adult female is, as a rule, lighter and smaller, and its cranial capacity about 10 per cent, less, than that of the male. Its walls are thinner and its muscular ridges less st:ongly marked; the glabella, supercihary arches, and mastoid processes are less prominent, aid the corresponding air sinuses are small or rudimentary. The upper margin of the orbit is sharp, the forehead vertical, the frontal and parietal eminences prominent, and the vault some- wiat flattened. The contour of the face is more rounded, the facial bones are smoother, and the maxillae and mandible and their contained teeth smaller. From what has been said it will be seen that more of the infantile characteristics are retained in the skull of the adult female than in that of the adult male. A well-marked male or female skull can easily be recognized as such, but in some cases the respective characteristics are so indistinct that the determination of the sex may hv difficult or impossible. ■ CRANIOLOGY. Skulls vary in size and shape, and the term craniology is applied to the study of these varia- tions. The capacity of the cranial cavity constitutes a good index of the size of the brain which it contained, and is most conveniently arrived at by fiUing the cavity with shot and measuring the contents in a graduated vessel. Skulls may be classified according to their capacities as follows: 1. Microcephalic, with a capacity of less than 1350 c.cm. — e. g., those of native Austrahans arid Andaman Islanders. 2. Mesocephalic, with a capacity of from 1350 c.cm. to 1450 c.cm. — e. g., those of African negroes and Chinese. 3 Megacephalic, with a capacity of over 1450 c.cm. — e. g., those of Europeans, Japanese, and ikimos. I 198 OSTEOLOGY In comparing the shape of one skull with that of another it is necessary to adopt some definite position in which the skulls should be placed during the process of examination. They should be so placed that a line carried through the lower margin of the orbit and upper margin oi' the external acoustic meatus is in the horizontal plane. The norma? of one skull can then be com- pared with those of another, and the differences in contour and surface form noted. Further, it is necessary that the various linear measurements used to determine the shape of the tikuU should be made between definite and easily localized points on its surface. The principal points may be divided into two groups: (1) those in the median plane, and (2) those on either side of it. The Points in the Median Plane are the: Mental Point. The most prominent point of the chin. Alveolar Point or Prosthion. The central point of the anterior margin of the upper alveolar arch. Subnasal Point. The middle of the lower border of the anterior nasal aperture, at the l^ase of the anterior nasal spine. Nasion. The central point of the frontonasal suture. Glabella. The point in the middle line at the level of the superciliary arches. Ophryon. The point in the middle line of the forehead at the level where the temporal lines most nearly approach each other. Bregma. The meeting point of the coronal and sagittal sutures. Obelion. A point in the sagittal suture on a level with the parietal foramina. Lambda. The point of junction of the sagittal and lambdoidal sutures. Occipital Point. The point in the middle line of the occipital bone farthest from the glabella. Inion. The external occipital protuberance. Opisthion. The mid-point of the posterior margin of the foramen magnum. Basion. The mid-point of the anterior margin of the foramen magnum. The Points on Either Side of the Median Plane are the: Gonion. The outer margin of the angle of the mandible. Dacryon. The point of union of the antero-superior angle of the lacrimal with the frontal bone and the frontal process of the maxilla. Stephanion. The point where the temporal line intersects the coronal suture. Pterion. The point where the great wing of the sphenoid joins the sphenoidal angle of the parietal. Auricular Point. The center of the orifice of the external acoustic meatus. Asterion. The point of meeting of the lambdoidal, mastooccipital, and mastoparietal sutures. The horizontal circumference of the cranium is measured in a plane passing through the glabella (Turner) or the ophryon (Flower) in front, and the occipital point behind; it averages about 50 cm. in the female and 52.5 cm. in the male. The occipitofrontal or longitudinal arc is measm-ed from the nasion over the middle line of the vertex to the opisthion: while the basinasal length is the distance between the basion and the nasion. These two measurements, plus the antero-posterior diameter of the foramen magnum, represent the vertical circumference of the cranium. The length is measured from the glabella to the occipital point, while the breadth or greatest transverse diameter is usually found near the external acoustic meatus. The proportion of , (breadth X 100) . , , , ,. . , • , ^ ^ ^., breadth to length , -r is termed the cephalic index or index of breadth. The height is usually measured from the basion to the bregma, and the proportion of height , (height X 100) . , . , , . ^, . ^ to length , — r, constitutes the vertical or height index. length In studying the face the principal points to be noticed are the proportion of its length and breadth, the shape of the orbits and of the anterior nasal aperture, and the degree of projection of the jaws. The length of the face may be measured from the ophryon or nasion to the chin, or, if the mandible be wanting, to the alveolar point; while its width is represented by the distance between the zygomatic arches. By comparing the length with the width of the face, skulls may be divided into two groups; dolichofacial or leptoprosope (long faced) and brachy facial or chemoprosope (short faced). The orbital index signifies the proportion which the orbital height bears to the orbital width, thus: orbital height X 100 orbital width The nasal index expresses the proportion which the width of the anterior nasal aperture bears to the height of the nose, the latter being measured from the nasion to the lower margin of the nasal aperture, thus: nasal width X 100 nasal height CRANIOLOGY 199 The degree of projection of the jaws is determined by the gnathic or alveolar index, which repre- sents the proportion between the basialveolar and basinasal lengths, thus: basialveolar length X 100 basinasal length The following table, modified from that given by Duckworth, i illustrates how these different indices may be utilized in the classification of skuUs: Index. Classification. Nomenclature. Examples. 1. Cephahc Below 75 Between 75 and 80 Above 80 Dolichocephalic Mesaticephalic BrachycephaUc Microseme Mesoseme Megaseme Leptorhine Mesorhine Platyrhine Orthognathous Mesognathous Prognathous Kaffirs and Native Australians. Europeans and Chinese. Mongolians and Andamans. 2. Orbital Below 84 Between 84 and 89 Above 89 Tasmanians and Native Austra- lians. Europeans. Chinese and Polynesians. 8. Nasal P ft. Gnathic Below 48 Between 48 and 53 Above 53 Below 98 Between 98 and 103 Above 103 Europeans. Japanese and Chinese. Negroes and Native Australians. Europeans. Chinese and Japanese. Native Australians. The chief function of the skull is to protect the brain, and therefore those portions of the skull \7hich are most exposed to external violence are thicker than those which are shielded from injury by overlying muscles. Thus, the skull-cap is thick and dense, whereas the temporal squamae, being protected by the temporales muscles, and the inferior occipital fossa;, being shielded by the muscles at the back of the neck, are thin and fragile. Fracture of the skull is further prevented by its elasticity, its rounded shape, and its construction of a number of secondary elastic arches, each made up of a single bone. The manner in which vibrations are transmitted through the bones of the skull is also of importance as regards its protective mechanism, at all events as far JLS the base is concerned. In the vault, the bones being of a fairly equal thickness and density, vibrations are transmitted in a uniform manner in all directions, but in the base, owing to the varying thickness and density of the bones, this is not so; and therefore in this situation there are special buttresses which serve to carry the vibrations in certain definite directions. At the iront of the skull, on either side, is the ridge which separates the anterior from the middle fossa of the base; and behind, the ridge or buttress which separates the middle from the posterior fossa; and if any violence is appHed to the vault, the vibrations would be carried along these buttresses io the sella turcica, where they meet. This part has been termed the "center of resistance," and here there is a special protective mechanism to guard the brain. The subarachnoid cavity at the base of the brain is dilated, and the cerebrospinal fluid which fills it acts as a water cushion 1.0 shield the brain from injury. In hke manner, when violence is applied to the base of the skull, as in falls upon the feet, the vibrations are carried backward through the occipital crest, and i orward through the basilar part of the occipital and body of the sphenoid to the vault of the skull. In connection with the bones of the face a common malformation is cleft palate. The cleft usually starts posteriorly, and its most elementary form is a bifid uvula; or the cleft may extend ihrough the soft palate; or the posterior part of the whole i)f the hard palate may be involved, the cleft extending as :'ar forward as the incisive foramen. In the severest forms, :he cleft extends through the alveolus and passes between ;he incisive or premaxillary bone and the rest of the max- -11a; that is to say, between the lateral incisor and canine ^eeth. In some instances, the cleft runs between the central and lateral incisor teeth; and this has induced some anatomists to beheve that the premaxillary bone is devel- oped from two centers (Fig. 199) and not from one, as was stated on p. 163. The medial segment, bearing a central incisor, is called an endognathion; the lateral segment, bear- ing the lateral incisor, is called a mesognathion. The cleft may affect one or both sides; if the latter, the central part is frequently displaced forward and re- ^ mains united to the septum of the nose, the deficiency in the alveolus being complicated with a cleft ' Morphology and Anthropology, by W. L. H. Duckworth. M.A., Cambridge University Press. Endognathion Mesognathion Exognathion Fig. 199.- -The premaxilla and its sutures. (After Albrecht.) 200 ^^^^^^^ OSTEOLOGY I in the lip (hare-lip). On examining a cleft palate in which the alveolus is not implicated, the cleft will generally appear to be in the median line, but occasionally is unilateral and in some cases bilat- eral. To understand this it must be borne in mind that three processes are concerned in the format ion of the palate — the palatine processes of the two maxillse, which grow in horizontally and unite in the middle line, and the ethmovomerine process, which grows downward from the base of the skull and frontonasal process to unite with the palatine processes in the middle line. In those cases where the palatine processes fail to unite with each other and with the medial process, the cleft of the palate is median; where one palatine process unites with the medial septum, the other faiUng to do so, the cleft in the palate is unilateral. In some cases where the palatine pro- cesses fail to meet in the middle, the ethmovomerine process grows downward between them and thus produces a bilateral cleft. Occasionally there may be a hole in the middle line of the hard palate, the anterior part of the hard and the soft palate being perfect; this is rare, because, as a rule, the union of the various processes progresses from before backward, and therefore the posterior part of the palate is more frequently defective than the anterior. THE EXTREMITIES. The bones by which the upper and lower limbs are attached to the trunk con- stitute respectively the shoulder and pelvic girdles. The shoulder girdle or girdle of the superior extremity is formed by the scapulae and clavicles, and is imperfect in front and behind. In front, however, it is completed by the upper end of the sternum, with which the medial ends of the clavicles articulate. Behind, it is widely imperfect, the scapulae being connected to the trunk by muscles only. The pelvic girdle or girdle of the inferior extremity is formed by the hip bones, which articulate with each other in front, at the symphysis pubis. It is imperfect behind, but the gap is filled in by the upper part of the sacrum. The pelvic girdle, with the sacrum, is a complete ring, massive and comparatively rigid, in marked contrast to the lightness and mobility of the shoulder girdle. THE BONES OF THE UPPER EXTREMITY (OSS A EXTREMITATIS SUPERIORIS). The Clavicle (Clavicula; Collar Bone). The clavicle (Figs. 200, 201) forms the anterior portion of the shoulder girdle. It is a long bone, curved somewhat like the italic letter/, and placed nearly horizon- tally at the upper and anterior part of the thorax, immediately above the first rib. It articulates medially with the manubrium sterni, and laterally with the acromion of the scapula.^ It presents a double curvature, the convexity being directed forward at the sternal end, and the concavity at the scapular end. Its lateral third is flattened from above downward, while its medial two-thirds is of a rounded or prismatic form. Lateral Third. — The lateral third has two surfaces, an upper and a lower; and two borders, an anterior and a posterior. Surface.^ — The upper surface is flat, rough, and marked by impressions for the attachments of the Deltoideus in front, and the Trapezius behind; between these impressions a small portion of the bone is subcutaneous. The under surface is flat. At its posterior border, near the point where the prismatic joins with the flattened portion, is a rough eminence, the coracoid tuberosity {conoid tubercle)', this, in the natural position of the bone, surmounts the coracoid process of the scapula, and gives attachment to the conoid ligament. From this tuberosity an oblique ridge, the oblique or trapezoid ridge, runs forward and lateralward, and afford attachment to the trapezoid ligament. ' The clavicle acts especially as a fulcrum to enable the muscles to give lateral motion to the arm. It is accordingly absent in those animals whose fore-limbs are used only for progression, but is present for the most part in animals whose anterior extremities are clawed and used for prehension, though in some of them — as, for instance, in a large number of the carnivora — it is merely a rudimentary bone suspended among the muscles, and not articulating with (either the scapula or sternum. THE [VI CLE Borders. — The anterior border is concave, thin, and rough, and gives attachment to the Deltoideus. The posterior border is convex, rough, thicker than the anterior, and gives attachment to the Trapezius. Medial Two-thirds. — The medial two-thirds constitute the prismatic portion of the bone, which is curved so as to be convex in front, concave behind, and is marked by three borders, separating three surfaces. Borders.^ — The anterior border is continuous with the anterior margin of the flat portion. Its lateral part is smooth, and corresponds to the interval between the attachments of the Pectoralis major and Deltoideus; its medial part forms the lower boundary of an elliptical surface for the attachment of the clavicular portion Sternal extremity Acromial extremity Fig. 200. — Left clavicle. Superior surface. of the Pectoralis major, and approaches the posterior border of the bone. The superior border is continuous with the posterior margin of the flat portion, and separates the anterior from the posterior surface. Smooth and rounded laterally, it becomes rough toward the medial third for the attachment of the Sternocleido- raastoideus, and ends at the upper angle of the sternal extremity. The posterior or subclavian border separates the posterior from the inferior surface, and extends from the coracoid tuberosity to the costal tuberosity; it forms the posterior boun- dary of the groove for the Subclavius, and gives attachment to a layer of cervical lascia which envelops the Omohyoideus. Articular capsule Inferior surface. Surfaces. — The anterior surface is included between the superior and anterior borders. Its lateral part looks upward, and is continuous with the superior sur- face of the flattened portion; it is smooth, convex, and nearly subcutaneous, being covered only by the Platysma. Medially it is divided by a narrow subcutaneous area into two parts! a lower, elliptical in form, and directed forward, for the attachment of the Pectoralis major; and an upper for the attachment of the Sternocleidomastoideus. The posterior or cervical surface is smooth, and looks backward toward the root of the neck. It is limited, above, by the superior border; below, by the subclavian border; medially, by the margin of the sternal extremity ; and laterally, by the coracoid tuberosity. It is concave medio-laterally, I 202 OSTEOLOGY ■I and is in relation, by its lower part, with the transverse scapular vessels. This surface, at the junction of the curves of the bone, is also in relation with the brachial plexus of nerves and the subclavian vessels. It gives attachment, near the sternal extremity, to part of the Sternohyoideus; and presents, near the middle, an obliciue foramen directed lateralward, which transmits the chief nutrient artery of the bone. Sometimes there are two foramina on the posterior surface, or one on the posterior and another on the inferior surface. The inferior or subclavian surface is bounded, in front, by the anterior border; behind, by the subclavian border. It is narrowed medially, but gradually increases in width laterally, and is contin- uous with the under surface of the flat portion. On its medial part is a broad rough surface, the costal tuberosity {rhomboid impression), rather more than 2 cm. in length, for the attachment of the costoclavicular ligament. The rest of this surface is occupied by a groove, which gives attachment to the Subclavius; the coracoclavicular fascia, which splits to enclose the muscle, is attached to the margins of the groove. Not infrequently this groove is subdivided longitudinally by a line which gives attachment to the intermuscular septum of the Subclavius. The Sternal Extremity {extremitas sternalis; internal extremity). — The sternal extremity of the clavicle is triangular in form, directed medialward, and a little downward and forward; it presents an articular facet, concave from before back- ward, convex from above downward, which articulates with the manubrium sterni through the intervention of an articular disk. The lower part of the facet is con- tinued on to the inferior surface of the bone as a small semi-oval area for articula- tion with the cartilage of the first rib. The circumference of the articular surface is rough, for the attachment of numerous ligaments; the upper angle gives attach- ment to the articular disk. The Acromial Extremity (extremitas acromialis; outer extremity). — The acromial extremity presents a small, flattened, oval surface directed obliquely downward, for articulation with the acromion of the scapula. The circumference of the articular facet is rough, especially above, for the attachment of the acromio- clavicular ligaments. In the female, the clavicle is generally shorter, thinner, less curved, and smoother than in the male. In those persons who perform considerable manual labor it becomes thicker and more curved, and its ridges for muscular attachment are prominently marked. Structure. — The clavicle consists of cancellous tissue, enveloped by a compact layer, which is much thicker in the intermediate part than at the extremities of the bone. Ossification. — The clavicle begins to ossify before any other bone in the body; it is ossified from three centers — viz., two primary centers, a medial and a lateral, for the body,i which appear during the fifth or sixth week of fetal Ufe; and a secondary center for the sternal end, which appears about the eighteenth or twentieth year, and imites with the rest of the bone about the twenty-fifth year. The Scapula (Shoulder Blade). The scapula forms the posterior part of the shoulder girdle. It is a flat, trian- gular bone, with two surfaces, three borders, and three angles. Surfaces. — The costal or ventral surface (Fig. 202) presents a broad concavity, the subscapular fossa. The medial two-thirds of the fossa are marked by several oblique ridges, which run lateralward and upward. The ridges give attachment to the tendinous insertions, and the surfaces between them to the fleshy fibers, of the Subscapularis. The lateral third of the fossa is smooth and covered by the fibers of this muscle. The fossa is separated from the vertebral border by smooth triangular' areas at the medial and inferior angles, and in the interval between these by a narrow ridge which is often deficient. These triangular areas and the intervening ridge afford attachment to the Serratus anterior. At the upper part of the fossa is a transverse depression, where the bone appears to be bent on itself 1 Mall, American Journal of Anatomy, vol. v; Fawcett, Journal of Anatomy and Physiology, vol. xlvii. * I THE SCAPULA flHJHK ^^^ along a line at right angles to and passing through the center of the glenoid cavity, forming a considerable angle, called the subscapular angle; this gives greater strength to the body of the bone by its arched form, while the summit of the arch serves to support the spine and acromion. The dorsal surface (Fig. 203) is arched from above downward, and is subdivided into two unequal parts by the spine; the portion above the spine is called the supraspinatous fossa, and that below it the infraspinatous fossa. The supraspinatous fossa, the smaller of the two, is concave, smooth, and broader at its vertebral than at its humeral end; its medial two-thirds give origin to the Supraspinatus. The infraspinatous fossa is much larger than the preceding; toward its vertebral margin a shallow concavity is seen at its upper part ; its center presents a promi- nent convexity, while near the axillary border is a deep groove which runs from the upper toward the lower part. The medial two-thirds of the fossa give origin to the Infraspinatus; the lateral third is covered by this muscle. The dorsal surface is marked near the axillary border by an elevated ridge, which runs from the lower part of the glenoid cavity, downward and backward to the vertebral border, about 2.5 cm. above the inferior angle. The ridge serves for the attachment of a fibrous septum, which separates the Infraspinatus from the Teres major and Teres minor. The surface between the ridge and the axillary border is narrow in the upper two-thirds of its extent, and is crossed near its center by a groove for the passage of the scapular circumflex vessels; it affords attachment to the Teres minor. Its lower third presents a broader, somewhat triangular surface, which gives origin to the Teres major, and over which the Latis- simus dorsi glides; frequently the latter muscle takes origin by a few fibers from this part. The broad and narrow portions above alluded to are separated by an oblique line, which runs from the axillary border, downward and backward, to meet the elevated ridge: to it is attached a fibrous septum which separates the Teres muscles from each other. The Spine (spina scapuloB). — The spine is a prominent plate of bone, which crosses obliquely the medial four-fifths of the dorsal surface of the scapula at its upper part, and separates the supra- from the infraspinatous fossa. It begins at the vertical border by a smooth, triangular area over which the tendon of inser- tion of the lower part of the Trapezius glides, and, gradually becoming more ele- vated, ends in the acromion, which overhangs the shoulder-joint. The spine is triangular, and flattened from above downward, its apex being directed toward the vertebral border. It presents two surfaces and three borders. Its superior surface is concave; it assits in forming the supraspinatous fossa, and gives origin to part of the Supraspinatus. Its inferior surface forms part of the infraspinatous fossa, gives origin to a portion of the Infraspinatus, and presents near its center the orifice of a nutrient canal. Of the three borders, the anterior is attached to the dorsal surface of the bone; the posterior, or crest of the spine, is broad, and presents two lips and an intervening rough interval. The Trapezius is attached to the supe- rior lip, and a rough tubercle is generally seen on that portion of the spine which receives the tendon of insertion of the lower part of this muscle. The Deltoideus is attached to the whole length of the inferior lip. The interval between the lips is subcutaneous and partly covered by the tendinous fibers of these muscles. The lateral border, or base, the shortest of the three, is slightly concave; its edge, thick and round, is continuous above with the under surface of the acromion, below with the neck of the scapula. It forms the medial boundary of the great scapular notch, which serves to connect the supra- and infraspinatous fossae. The Acromion. — The acromion forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first lateralward, and then curving forward and upward, so as to overhang the 204 OSTEOLOGY glenoid cavity. Its superior surface, directed upward, backward, and lateral war( is convex, rough, and gives attachment to some fibers of the Deltoideus, and in the rest of its extent is subcutaneous. Its inferior surface is smooth and conca\'e. Its lateral border is thick and irregular, and presents three or four tubercles for the tendinous origins of the Deltoideus. Its medial border, shorter than the lateral, is concave, gives attachment to a portion of the Trapezius, and presents about its center a small, oval surface for articulation with the acromial end of the clavicle. Articular capsule Coracoacromial _L_li ligament rticular capsule Fig. 202. — Left scapula. Costal surface. Its apex, which corresponds to the point of meeting of these two borders in front, is thin, and has attached to it the coracoacromial ligament. Borders. — Of the three borders of the scapula, the superior is the shortest and thinnest; it is concave, and extends from the medial angle to the base of the cora- coid process. At its lateral part is a deep, semicircular notch, the scapular notch, THE SCAPULA 205 formed partly by the base of the coraeoid process. This notch is converted into a foramen by the superior transverse Hgament, and serves for the" passage of the suprascapular nerve; sometimes the ligament is ossified. The adjacent part of the superior border affords attachment to the Omohyoideus. The axillary border Coracohumeral ligament Coraco-acromial ligament ^«Co Trapezoid ligament Conoid ligament FiQ. 203. — Left scapula. Dorsal surface. I is the thickest of the three. It begins above at the lower margin of the glenoid :avity, and inclines obliquely downward and backward to the inferior angle. Immediately below the glenoid cavity is a rough impression, the infraglenoid tuberosity, about 2.5 cm. in length, which gives origin to the long head of the Tri- ceps brachii; in front of this is a longitudinal groove, which extends as far as the 206 OSTEOLOGY lower third of this border,. and affords origin to part of the Subscapularis. The inferior third is thin and sharp, and serves for the attachment of a few fibers of the Teres major behind, and of the Subscapularis in front. The vertebral border is the longest of the three, and extends from the medial to the inferior angle. It is arched, intermediate in thickness between the superior and the axillary borders, and the portion of it above the spine forms an obtuse angle with the part below. This border presents an anterior and a posterior lip, and an intermediate narrow area. The anterior lip affords attachment to the Serratus anterior; the posterior lip, to the Supraspinatus above the spine, the Infraspinatus below; the area Fig. 204. — Posterior view of the thorax and shoulder girdle. (Morris.) between the two lips, to the Levator scapulae above the triangular surface at the commencement of the spine, to the Rhomboideus minor on the edge of that surface, and to the Rhomboideus major below it; this last is attached by means of a fibrous arch, connected above to the lower part of the triangular surface at the base of the spine, and below to the lower part of the border. Angles. — Of the three angles, the medial, formed by the junction of the superior and vertebral borders, is thin, smooth, rounded, inclined somewhat lateralward, and gives attachment to a few fibers of the Levator scapulae. The inferior angle, thick and rough, is formed by the union of the vertebral and axillary borders; its dorsal surface affords attachment to the Teres major and frequently to a few THE SCAPULA 207 Coracoid process Acromion Infraglenoid tubercle fibers of the Latissimus dorsi. The lateral angle is the thickest part of the bone, and is sometimes called the head of the scapula. On it is a shallow pyriform, articular surface, the glenoid cavity, which is directed lateralward and forward and articulates with the head of the humerus; it is broader below than above and its vertical diameter is the longest. The surface is covered with cartilage in the fresh state; and its margins, slightly raised, give attachment to a fibro- cartilaginous structure, the glenoidal labrum, which deepens the cavity. At its apex is a slight elevation, the SUpraglenoid tuberosity, to which Supragleru>id tubercJe the long head of the Biceps brachii is attached. The neck of the scapula is the slightly constricted portion which sur- rounds the head; it is more dis- tinct below and behind than above and in front. The Coracoid Process (processus coracoideus) . — The coracoid pro- cess is a thick curved process at- tached by a broad base to the u])per part of the neck of the scapula; it runs at first upward and medialward; then, becoming smaller, it changes its direction, and projects forward and lateral- ward. The ascending portion, flattened from before backward, presents in front a smooth con- cave surface, across which the S ibscapularis passes. The hori- zontal portion is flattened from al)ove downward; its upper sur- face is convex and irregular, and g ves attachment to the Pector- ais minor; its under surface is smooth; its medial and lateral borders are rough; the former g ves attachment to the Pectoralis n inor and the latter to the cora- coacromial ligament; the apex is embraced by the conjoined tendon o ' origin of the Coracobrachialis aid short head of the Biceps brachii and gives attachment to the coracoclavicular fascia. On the medial part of the root of the coracoid process is a rough im- pression for the attachment of the conoid ligament; and running from it obliquely forward and lateralward, on to the upper surface of the horizontal portion, is an elevated ridge for the ai:tachment of the trapezoid ligament. Fig. 205. -Inferior angle -Left scapula. Lateral view. I Structure.— The head, processes, and the thickened parts of the bone, contain cancellous ssue; the rest consists of a thin layer of compact tissue. The central part of the supraspinatous 208 OSTEOLOGY fossa and the upper part of the infraspinatous fossa, but especially the former, are usually so thin as to be semitransparent; occasionally the bone is found wanting in this situation, and the adjacent muscles are separated only by fibrous tissue. Ossification (Fig. 206). — The scapula is ossified from seven or more centers: one for the body, two for the coracoid process, two for the acromion, one for the vertebral border, and one for the inferior angle. Ossification of the body begins about the second month of fetal life, by the formation ol' an irregular quadrilateral plate of bone, immediately behind the glenoid cavity. This plate exte^nds so as to form the chief part of the bone, the spine growing up from its dorsal surface about the third month. At birth, a large part of the scapula is osseous, but the glenoid cavity, the coraooid process, the acromion, the vertebral border, and the inferior angle are cartilaginous. From the fifteenth to the eighteenth month after birth, ossification takes place in the middle of the coraooid process, which as a rule becomes joined with the rest of the bone about the fifteenth year. Between the fourteenth and twentieth years, ossification of the remaining parts takes place in quick succes- sion, and usually in the following order; first, in the root of the coracoid process, in the form of a broad scale; secondly, near the base of the acromion; thirdly, in the inferior angle and contiguous part of the vertebral border; fourthly, near the extremity of the acromion; fifthly, in the vertebral border. The base of the acromion is formed by an extension from the spine; the two separate nuclei of the acromion unite, and then join with the extension from the spine. The upper third ..<^5 Fia. 206. — Plan of ossification of the scapula. From seven centers. of the glenoid cavity is ossified from a separate center (subcoracoid), which makes its appear- ance between the tenth and eleventh years and joins between the sixteenth and the eighteenth. Further, an epiphysial plate appears for the lower part of the glenoid cavity, while the tip of the coracoid process frequently presents a separate nucleus. These various epiphyses are joined to the bone by the twenty-fifth year. Failure of bony union between the acromion and spine sometimes occurs, the junction being effected by fibrous tissue, or by an imperfect articulation; in some cases of supposed fracture of the acromion with ligamentous union, it is probable that the detached segment was never united to the rest of the bone. THE HUMERUS ^^^^^K 209 The Humerus (Arm Bone). The humerus (Figs. 207, 208) is the longest and largest bone of the upper extremity; it is divisible into a body and two extremities. Upper Extremity. — The upper extremity consists of a large rounded head joined to the body by a constricted portion called the neck, and two eminences, the greater and lesser tubercles. The Head (caput humeri). — The head, nearly hemispherical in form,^ is directed upward, medialward, and a little backward, and articulates with the glenoid cavity of the scapula. The circumference of its articular surface is slightly constricted and is termed the anatomical neck, in contradistinction to a constriction below the tubercles called the surgical neck which is frequently the seat of fracture. Fracture of the anatomical neck rarely occurs. The Anatomical Neck (collum anatomicum) is obliquely directed, forming an obtuse angle with the body. It is best marked in the low^er half of its circum- ference; in the upper half it is represented by a narrow groove separating the head from the tubercles. It affords attachment to the articular capsule of the shoulder- joint, and is perforated by numerous vascular foramina. The Greater Tubercle (tuberculum majus; greater tuberosity). — The greater tubercle is situated lateral to the head and lesser tubercle. Its upper surface is rounded and marked by three flat impressions : the highest of these gives insertion to the Supraspinatus; the middle to the Infraspinatus; the lowest one, and the body of the bone for about 2.5 cm. below it, to the Teres minor. The lateral surface of the greater tubercle is convex, rough, and continuous with the lateral surface of the body. The Lesser Tubercle {tuberculum minus; lesser tuberosity). — The lesser tubercle, although smaller, is more prominent than the greater: it is situated in front, and hi directed medialward and forward. Above and in front it presents an impression for the insertion of the tendon of the Subscapularis. The tubercles are separated from each other by a deep groove, the intertubercular groove (bicipital groove), which lodges the long tendon of the Biceps brachii and transmits a branch of the anterior humeral circumflex artery to the shoulder-joint. It runs obliquely downward, and ends near the junction of the upper with the middle third of the bone. In the fresh state its upper part is covered with a thin layer of cartilage, lined by a prolongation of the synovial membrane of the shoulder-joint; its lower portion gives insertion to the tendon of the Latissimus (lorsi. It is deep and narrow above, and becomes shallow and a little broader J is it descends. Its lips are called, respectively, the crests of the greater and lesser tubercles (bicipital ridges), and form the upper parts of the anterior and medial borders of the body of the bone. The Body or Shaft (corpus humeri). — The body is almost cylindrical in the upper lialf of its extent, prismatic and flattened below, and has three borders and three surfaces. Borders. — The anterior border runs from the front of the greater tubercle above t;o the coronoid fossa below, separating the antero-medial from the antero-lateral surface. Its upper partis a prominent ridge, the crest of the greater tubercle; it serves for the insertion of the tendon of the Pectoralis major. About its center it forms the anterior boundary of the deltoid tuberosity; below, it is smooth and rounded, affording attachment to the Brachialis. The lateral border runs from the back part of the greater tubercle to the ' Though the head is nearly hemispherical in form, its margin, as Humphry has shown, is by no means a true circle. Its greatest diameter is, from the top of the intertubercular groove in a direction downward, medialward, and back- ward. Hence it follows that the greatest elevation of the arm can be obtained by rolling the articular surface in this direction — that is to say, obliquely upward, lateralward, and forward. 14 ■ 210 OSTEOLOGY Articular capavle Surqi4HjU Neek- Brachioradialis Common origin of" Flexor carpi radialis Palmaris longua "'^ Flexor digitorum svblimis Flexor carpi vlnaria Capit- ulum -v^ Extensor carpi radialis 1 longtis , Articular capsule ■ Common origin of Extensor carpi rad. brev. ,, digitorum convmunia ,, digiti quinti prop. , , carpi idnaris Supinator Fig. 207. — Left humerus. Anterior view. THE HUMERUS 1 I I lateral epicondyle, and separates the antero- lateral from the posterior surface. Its upper half is rounded and indistinctly marked, serv- ing for the attachment of the lower part of the insertion of the Teres minor, and below this giving origin to the lateral head of the Triceps brachii; its center is traversed by a broad but shallow oblique depression, the radial sulcus (musculospiral groove). Its lower part forms a prominent, rough margin, a little curved from behind forward, the lateral supracondylar ridge, which presents an anterior lip for the origin of the Brachioradialis above, and Extensor carpi radialis longus below, a posterior lip for the Triceps brachii, and an intermediate ridge for the attachment of the lateral intermuscu- lar septum. The medial border extends from the lesser tubercle to the medial epicondyle. Its upper third consists of a prominent ridge, the crest of the lesser tubercle, which gives insertion to the t(3ndon of the Teres major. About its center is a slight impression for the insertion of the C!oracobrachialis, and just below this is the entrance of the nutrient canal, directed down- ward; sometimes there is a second nutrient canal at the commencement of the radial sulcus. T'he inferior third of this border is raised into a slight ridge, the medial supracondylar ridge, v/hich becomes very prominent below; it pre- sents an anterior lip for the origins of the IJrachialis and Pronator teres, a posterior lip for the medial head of the Triceps brachii, {.nd an intermediate ridge for the attachment of the medial intermuscular septum. Surfaces. — The antero-lateral surface is di- rected lateralward above, where it is smooth, rounded, and covered by the Deltoideus; for- ^vard and lateralward below, where it is slightly concave from above downward, and gives origin 1.0 part of the Brachialis. About the middle )f this surface is a rough, triangular elevation, [the deltoid tuberosity for the insertion of the Deltoideus; below this is the radial sulcus, directed obliquely from behind, forward, and downward, and transmitting the radial nerve and profunda artery. The antero-medial surface, less extensive than the antero-lateral, is directed medialward above, i'orward and medialward below; its upper part is narrow, and forms the floor of the intertuber- cular groove which gives insertion to the tendon of the Latissimus dorsi; its middle part is .slightly rough for the attachment of some of '%.. la f K (^ =^ f 1 1 1'^ U n f H 1 a > 1 o 1 — ■* 1 o 1 PI '^ 1 ■0 §, W J' M. 1 1 a 1 e^ 1 f » 1 f "> 1 i "^ 1 ■. il « I 1 n \ Articular capsule Articular capsule 1 /Vo cA i Fig. 208. — Left humerus. Posterior view. 212 OSTEOLOGY the fibers of the tendon of insertion of the Coracobrachialis; its loweT part is smooth, concave from above downward, and gives origin to the BrachiaHs.^ The posterior surface appears somewhat twisted, so that its upper part is directed a Httle medialward, its lower part backward and a Httle laterahvard. Nearly the whole of this surface is covered by the lateral and medial heads of the Triceps brachii, the former arising above, the latter below the radial sulcus. The Lower Extremity. — The lower extremity is flattened from before backward, and curved slightly forward; it ends below in a broad, articular surface, which is divided into two parts by a slight ridge. Projecting on either side are the latt^ral and medial epicondyles. The articular sm-face extends a little lower than the epicondyles, and is curved slightly forward; its medial extremity occupies a lower level than the lateral. The lateral portion of this surface consists of a smooth, rounded eminence, named the capitulum of the humerus; it articulates with the cup- shaped depression on the head of the radius, and is limited to the front and lower part of the bone. On the medial side of this eminence is a shallow groove, in which is received the medial margin of the head of the radius. Above the front part of the capitulum is a slight depression, the radial fossa, which receives the anterior border of the head of the radius, when the forearm is flexed. The medial portion of the articular surface is named the trochlea, and presents a deep depression be- tween two well-marked borders; it is convex from before backward, concave from side to side, and occupies the anterior, lower, and posterior parts of the extremity. The lateral border separates it from the groove which articulates with the margin of the head of the radius. The medial border is thicker, of greater length, and consequently more prominent, than the lateral. The grooved portion of the artic- ular surface fits accurately within the semilunar notch of the ulna; it is broader and deeper on the posterior than on the anterior aspect of the bone, and is inclined obliquely downward and forward toward the medial side. Above the front part of the trochlea is a small depression, the coronoid fossa, which receives the coronoid process of the ulna during flexion of the forearm. Above the back part of the troch- lea is a deep triangular depression, the olecranon fossa, in which the summit of the olecranon is received in extension of the forearm. These fossae are separated from one another by a thin, transparent lamina of bone, which is sometimes perforated by a supratrochlear foramen; they are lined in the fresh state by the synovial membrane of the elbow-joint, and their margins afford attachment to the anterior and posterior ligaments of this articulation. The lateral epicondyle is a small, tuberculated eminence, curved a little forward, and giving attachment to the radial collateral ligament of the elbow-joint, and to a tendon common to the origin of the Supinator and some of the Extensor muscles. The medial epicondyle, larger and more prominent than the lateral, is directed a little backward; it gives attach- ment to the ulnar collateral ligament of the elbow-joint, to the Pronator teres, and to a common tendon of origin of some of the Flexor muscles of the forearm ; the ulnar nerve runs in a groove on the back of this epicondyle. The epicondyles are continuous above with the supracondylar ridges. Structure. — The extremities consist of cancellous tissue, covered with a thin, compact layer (Fig. 209) ; the body is composed of a cylinder of compact tissue, thicker at the center than toward the extremities, and contains a large medullary canal which extends along its whole length. 1 A small, hook-shaped process of bone, the supracondylar process, varying from 2 to 20 mm. in length, is not infre- quently found projectmg from the antero-medial surface of the body of the humerus 5 cm. above the medial epicondjle. It is curved downward and forward, and its pointed end is connected to the medial border, just above the medial epicondyle, by a fibrous band, which gives origin to a portion of the Pronator teres; through the arch completed by this fibrous band the median nerve and brachial artery pass, when these structures deviate from their usual course. Sometimes the nerve alone is transmitted through it, or the nerve may be accompanied by the ulnar artery, in cases of high division of the brachial. A well-marked groove is usually found behind the process, in which the nerve and artery are lodged. This arch is the homologue of the supracondyloid foramen found in many animals, and probably serves in them to protect the nerve and artery from compression during the contraction of the muscles in this region. THE HUMERUS 213 Ossification (Figs. 210, 211). — The htimerus is ossi- fied from eight centers, one for each of the following parts: the body, the head, the greater tubercle, the les.ser tubercle, the capitulum, the trochlea, and one for each epicondyle. The center for the body appears near the middle of the bone in the eighth week of fetal life, and soon extends toward the extremities. At birth the humerus is ossified in nearly its whole length, only the extremities remaining cartilaginous. During the first year, sometimes before birth, ossification commences in the head of the bone, and during the third year the center for the greater tubercle, and during the fifth that for the lesser tubercle, make their appearance. By the sixth year the centers for the head and tubercles have joined, so as to form a single large epiphysis, which fuses with the body about the twentieth year. The lower end of the humerus is ossified as follows. At the end of the second year ossification begins in the capitulum, and extends medialward, to form the chief part of the articular end of the bone; the center for the medial part of the trochlea appears about the age of twelve. Ossifi- cation begins in the medial epicondyle about the fifth year, and in the lateral about the thirteenth or four- teenth year. About the sixteenth or seventeenth year, the lateral epicondyle and both portions of the articu- lating surface, having already joined, unite with the body, and at the eighteenth year the medial epicon- dyle becomes joined to it. Epiphysial line Fia. 209. — Longitudinal section of head of left humerus. Epiphyses of head and' t ubercles blend at fifth year, and unite with body at twentieth year Unites with body\ -S I i at eighteenth year J ^ Bleni of, i^t Fia. 210. — Plan of ossification of the humerus. Fig. 211. — Epiphysial lines of humerus in a young adult. Anterior aspect. The lines of attachment of the articular capsules are in blue. JSTEOLOGY Olecranons. The Ulna (Elbow Bone).i The ulna (Figs. 212, 213) is a long bone, prismatic in form, placed at the maiial side of the forearm, parallel with the radius. It is divisible into a body and two extremities. Its upper extremity, of great thickness and strength, forms a large part of the elbow-joint; the bone diminishes in size from above downward, its lower extremity being very small, and excluded from the wrist-joint by the interposition of an articular disk. The Upper Extremity {proximal extremity) (Fig. 212). — The upper extremity presents two curved processes, the olecranon and the coronoid process; and two concave, articular cavities, the semilunar and radial notches. The Olecranon {olecranon process). — The olecra- non is a large, thick, curved eminence, situated at the upper and back part of the ulna. It is bent forward at the summit so as to present a promi- nent lip which is received into the olecranon fossa of the humerus in extension of the forearm. Its base is contracted where it joins the body and the narrowest part of the upper end of the ulna. Its posterior surface, directed backward, is triangular, smooth, subcutaneous, and covered by a bursa. Its superior surface is of quadrilateral form, marked behind by a rough impression for the insertion of the Triceps brachii; and in front, near the margin, by a slight transverse groove for the attachment of part of the posterior ligament of the elbow-joint. Its anterior surface is smooth, concave, and forms the upper part of the semilunar notch. Its borders present continuations of the groove on the margin of the superior surface; they serve for the attach- ment of ligaments, viz., the back part of the ulnar collateral ligament medially, and the posterior ligament laterally. From the medial border a part of the Flexor carpi ulnaris arises; while to the lateral border the Anconseus is attached. The Coronoid Process {processus coronoideus) . — The coronoid process is a triangular eminence projecting forward from the upper and front part of the ulna. Its base is continuous with the body of the bone, and of considerable strength. Its apex is pointed, slightly curved upward, and in flexion of the forearm is received into the coronoid fossa of the humerus. Its upper surface is smooth, concave, and forms the lower part of the semilunar notch. Its antero-inferior surface is concave, and marked by a rough impression for the insertion of the Brachialis. At the junction of this surface w ith the front of the body is a rough eminence, the tuberosity of the ulna, which gives insertion to a part of the Brachialis; to the lateral border of this tuberosity the oblique cord is attached. Its lateral surface presents a narrow, oblong, articular depression, the radial notch. Its medial surface, by its prominent, 1 In the anatomical position, the forearm ia placed in extension and supination with the palm looking forward and the thumb on the outer side. Fig. 212. — Upper extremity of left ulna. Lateral aspect. THE ULNA 215 free margin, serves for the attachment of part of the ulnar collateral ligament. At the front part of this surface is a small rounded eminence for the origin of one head of the Flexor digitorum sublimis; behind the eminence is a depression for part of the origin of the Flexor digitorum profundus; descending from the eminence is a ridge which gives origin to one head of the Pronator teres. Fre- quently, the Flexor pollicis longus arises from the lower part of the coronoid process by a rounded bundle of muscular fibers. The Semilunar Notch {incisura semilunaris; greater sigmoid cavity). — ^The semi- lunar notch is a large depression, formed by the olecranon and the coronoid process, and serving for articulation with the trochlea of the humerus. About the middle of either side of this notch is an indentation, which contracts it somewhat, and indicates the junction of the olecranon and the coronoid process. The notch is concave from above downward, and divided into a medial and a lateral portion by a smooth ridge running from the summit of the olecranon to the tip of the coronoid process. The medial portion is the larger, and is slightly concave transversely; the lateral is convex above, slightly concave below. The Radial Notch (incisura radialis; lesser sigmoid cavity). — The radial notch is a narrow, oblong, articular depression on the lateral side of the coronoid process ; it receives the circumferential articular surface of the head of the radius. It is concave from before backw^ard, and its prominent extremities serve for the attach- ment of the annular ligament. The Body or Shaft (corpus ulnce). — The body at its upper part is prismatic in form, and curved so as to be convex behind and lateral ward; its central part is straight; its lower part is rounded, smooth, and bent a little lateralward. It tapers gradually from above downward, and has three borders and three surfaces. Borders. — The volar border (margo volaris; anterior border) begins above at the jDrominent medial angle of the coronoid process, and ends below in front of the styloid process. Its upper part, well-defined, and its middle portion, smooth and i-ounded, give origin to the Flexor digitorum profundus; its lower fourth serves 'or the origin of the Pronator quadratus. This border separates the volar from the medial surface. The dorsal border (margo dorsalis; posterior border) begins above at the apex of I the triangular subcutaneous surface at the back part of the olecranon, and ends below at the back of the styloid process; it is well-marked in the upper three- fourths, and gives attachment to an aponeurosis which affords a common origin to the Flexor carpi ulnaris, the Extensor carpi ulnaris, and the Flexor digitorum pro- I fundus; its lower fourth is smooth and rounded. This border separates the medial I from the dorsal surface. The interosseous crest (crista interossea; external or interosseous border) begins above by the union of two lines, which converge from the extremities of the radial notch and enclose between, them a triangular space for the origin of part of the Supinator; it ends below at the head of the ulna. Its upper part is sharp, its lower fourth smooth and rounded. This crest gives attachment to the interosseous mem- brane, and separates the volar from the dorsal surface. Surf aces. -^-The volar surface (fades volaris; anterior surface), much broader I above than below, is concave in its upper three-fourths, and gives origin to the Flexor digitorum profundus; its lower fourth, also concave, is covered by the Pronator quadratus. The lower fourth is separated from the remaining portion by a ridge, directed obliquely downward and medialward, which marks the extent of origin of the Pronator quadratus. At the junction of the upper with the I middle third of the bone is the nutrient canal, directed obliquely upward. The dorsal surface (fades dorsalis; posterior surface) directed backward and lateralward, is broad and concave above; convex and somewhat narrower in the I middle; narrow, smooth, and rounded below. On its upper part is an oblique 216 OSTEOLOGY Articular capsule Flexor digilorum sublimis Prcmator teres Occasional origin of Flexor pollicis longus Articular capsule Styloid process Radial origin of Flexor digitorum sublimis Brachioradialis Groove for Abductor pollicis longus and Extensor pollicis brevis Styloid process Fig. 213. — Bones of left forearm. Anterior aspect. THE ULNA 217 C Abductor pollicis ForJ longus (Extensor pollicis brevis RADIUS Articular capsule Flexor digitorum sublimit Articular capsule For Ext. carpi radialis longus For Extensor carpi radialis brevia For Extensor pollicis longus Fia. 214. — Bones of left forearm Fen" Extensor carpi vlnaris For Extensor digiti quinti projyrius For^ Extensor indicis proprius Extensor digitorum communis Posterior aspect. 218 OSTEOLOGY ridge, which runs from the dorsal end of the radial notch, downward to the dorsal border; the triangular surface above this ridge receives the insertion of the Anconseus, while the upper part of the ridge affords attachment to the Supinator. Below this the surface is subdivided by a longitudinal ridge, sometimes called the perpendicular line, into two parts: the medial part is smooth, and covered by the Extensor carpi ulnaris; the lateral portion, wider and rougher, gives origin from above downward to the Supinator, the Abductor pollicis longus, the Extensor pollicis longus, and the Extensor indicis proprius. The medial surface {fades medialis; internal surface) is broad and concave above, narrow and convex below. Its upper three-fourths give origin to the Flexor digitorum profundus; its lower fourth is subcutaneous. Olecranon Appears at ,^^^^__ Joins body at tenth year ^^^^ sixteenth year Appears at t fourth year Joins body at twentieth year Inferior extremity Fio. 215. — Plan of ossification of the ulna. From three'centers. FiQ. 216. — Epiphysial lines of ulna in a young ridult. Lateral aspect. The lines of attachment of the articular capsules are in blue. The Lower Extremity {distal extremity). — The lower extremity of the ulna is small, and presents two eminences; the lateral and larger is a rounded, articular eminence, termed the head of the ulna; the medial, narrower and more projecting, is a non-articular eminence, the styloid process. The head presents an articular surface, part of which, of an oval or semilunar form, is directed downward, and articulates with the upper surface of the triangular articular disk which separates it from the wrist-joint; the remaining portion, directed lateralward, is narrow, convex, and received into the ulnar notch of the radius. The styloid process projects from the medial and back part of the bone; it descends a little lower than the head, and its rounded end affords attachment to the ulnar collateral ligament of the wrist-joint. The head is separated from the styloid process by a depression for the attachment of the apex of the triangular articular disk, and behind, by a shallow groove for the tendon of the Extensor carpi ulnaris. THE RADIUS WKKKKK ^^^ Structure. — The long, narrow medullary cavity is enclosed in a strong wall of compact tissue which is thickest along the interosseous border and dorsal surface. At the extremities the compact layer thins. The compact layer is continued onto the back of the olecranon as a plate of close spongy bone with lamellae parallel. From the inner surface of this plate and the compact layer below it trabeculae arch forward toward the olecranon and coronoid and cross other trabeculse, passing backward over the medullary cavity from the upper part of the shaft below the coronoid. Below the coronoid process there is a small area of compact bone from which trabecule curve ui)ward to end obliquely to the surface of the semilunar notch which is coated with a thin layer of compact bone. The trabecular at the lower end have a more longitudinal direction. Ossification (Figs. 215, 216). — The ulna is ossified from three centers: one each for the body, the inferior extremity, and the top of the olecranon. Ossification begins near the middle of the body, about the eighth week of fetal life, and soon extends through the greater part of the bone. At birth the ends are cartilaginous. About the fourth year, a center appears in the middle of the head, and soon extends into the styloid process. About the tenth year, a center appears in the olecranon near its extremity, the chief part of this process being formed by an upward extension of the body. The upper epiphysis joins the body about the sixteenth, the lower about the twentieth year. Articulations. — The ulna articulates with the humerus and radius. The Radius. The radius (Figs. 213, 214) is situated on the lateral side of the ulna, which exceeds it in length and size. Its upper end is small, and forms only a small part of the elbow-joint; but its low^er end is large, and forms the chief part of the wrist- joint. It is a long bone, prismatic in form and slightly curved longitudinally. It has a body and two extremities. The Upper Extremity {yroximal extremity). — The upper extremity presents a head, neck, and tuberosity. The head is of a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum of the humerus. The circumference of the head is smooth; it is broad medially where it articulates \Aith the radial notch of the ulna, narrow in the rest of its extent, which is embraced by the annular ligament. The head is supported on a round, smooth, and con- stricted portion called the neck, on the back of which is a slight ridge for the inser- tion of part of the Supinator. Beneath the neck, on the medial side, is an eminence, the radial tuberosity; its surface is divided into a posterior, rough portion, for the i isertion of the tendon of the Biceps brachii, and an anterior, smooth portion, on v/hich a bursa is interposed between the tendon and the bone. The Body or Shaft {corpus radii). — The body is prismoid in form, narrower above than below, and slightly curved, so as to be convex lateralward. It presents three borders and three surfaces. Borders. — The volar border {mar go volaris; anterior border) extends from the lower part of the tuberosity above to the anterior part of the base of the styloid process below, and separates the volar from the lateral surface. Its upper third is promi- iient, and from its oblique direction has received the name of the oblique line of the radius ; it gives origin to the Flexor digitorum sublimis and Flexor pollicis longus ; the surface above the line gives insertion to part of the Supinator. The middle third of the volar border is indistinct and rounded. The lower fourth is prominent, and gives insertion to the Pronator quadratus, and attachment to the dorsal carpal ligament; it ends in a small tubercle, into which the tendon of the Brachioradialis is inserted. The dorsal border {margo dorsalis; posterior border) begins above at the back of the neck, and ends below at the posterior part of the base of the styloid process; it separates the posterior from the lateral surface. It is indistinct above and below, but well-marked in the middle third of the bone. The interosseous crest {crista interossea; internal or interosseous border) begins above, at the back part of the tuberosity, and its upper part is rounded and indis- tinct; it becomes sharp and prominent as it descends, and at its lower part divides into two ridges which are continued to the anterior and posterior margins of the ulnar notch. To the posterior of the two ridges the lower part of the interosseous OSTEOLOGY membrane is attached, while the triangular surface between the ridges gives inser- tion to part of the Pronator quadratus. This crest separates the volar from the dorsal surface, and gives attachment to the interosseous membrane. Surface. — The volar surface (fades volaris; anterior surface) is concave in its upper three-fourths, and gives origin to the Flexor pollicis longus; it is broad and flat in its lower fourth, and affords insertion to the Pronator quadratus. A prominent ridge limits the insertion of the Pronator quadratus below, and between this and the inferior border is a triangular rough surface for the attachment of the volar radiocarpal ligament. At the junction of the upper and middle thirds of the volar surface is the nutrient foramen, which is directed obliquely upward. The dorsal surface (fades dorsalis; posterior surface) is convex, and smooth in the upper third of its extent, and covered by the Supinator. Its middle third is broad, slightly concave, and gives origin to the Abductor pollicis longus above, and the Extensor pollicis brevis below. Its lower third is broad, convex, and covered by the tendons of the muscles which subsequently run in the grooves on the lower end of the bone. The lateral surface (fades lateralis; external surface) is convex throughout its entire extent. Its upper third gives insertion to the Supinator. About its center is a rough ridge, for the insertion of the Pronator teres. Its lower part is narrow, and covered by the tendons of the Abductor pollicis longus and Extensor pollicis brevis. The Lower Extremity. — The lower extremity is large, of quadrilateral form, and provided with two articular surfaces — one below, for the carpus, and another at the medial side, for the ulna. The carpal articular surface is triangular, concave, smooth, and divided by a slight antero-posterior ridge into two parts. Of these, the lateral, triangular, articulates with the navicular bone; the medial, quadri- lateral, with the lunate bone. The articular surface for the ulna is called the ulnar notch (sigmoid cavity) of the radius; it is narrow, concave, smooth, and articulates with the head of the ulna. These two articular surfaces are separated by a promi- nent ridge, to which the base of the triangular articular disk is attached ; this disk separates the wrist-joint from the distal radioulnar articulation. This end of the bone has three non-articular surfaces — volar, dorsal, and lateral. The volar surface, rough and irregular, affords attachment to the volar radiocarpal ligament. The dorsal surface is convex, affords attachment to the dorsal radiocarpal ligament, and is marked by three grooves. Enumerated from the lateral side, the first groove is broad, but shallow, and subdivided into two by a slight ridge; the lateral of these two transmits the tendon of the Extensor carpi radialis longus, the medial the tendon of the Extensor carpi radialis brevis. The second is deep but narrow, and bounded laterally by a sharply defined ridge ; it is directed obliquely from above downward and lateralward, and transmits the tendon of the Extensor pollicis longus. The third is broad, for the passage of the tendons of the Extensor indicis proprius and Extensor digitorum communis. The lateral surface is prolonged obliquely downward into a strong, conical projection, the styloid process, which gives attachment by its base to the tendon of the Brachioradialis, and by its apex to the radial collateral ligament of the wrist-joint. The lateral surface of this process is marked by a flat groove, for the tendons of the Abductor pollicis longus and Extensor pollicis brevis. Structure. — The long narrow medullary cavity is enclosed in a strong wall of compact tissue which is thickest along the interosseous border and thinnest at the extremities except over the cup-shaped articular surface (fovea) of the head where it is thickened. The trabecular of the spongy tissue are somewhat arched at the upper end and pass upward from the compact layer of the shaft to the fovea capituli; they are crossed by others parallel to the surface of the fovea. The arrangement at the lower end is somewhat similar. Ossification (Figs. 217, 218). — The radius is ossified from three centers: one for the body, and one for either extremity. That for the body makes its appearance near the center of the bone, during the eighth week of fetal hfe. About the end of the second year, ossification commences THE CARPUS in the lower end; and at the fifth year, in the upper end. The upper epiphysis fuses with the body at the age of seventeen or eighteen years, the lower about the age of twenty. An additional center sometimes found in the radial tuberosity, appears about the fourteenth or fifteenth year. Herid Appears at fifth year Unites with body about pvherty Unites with body about ttoentieth year Lower extremity Fig. 217.- -Plan of ossification of the radius. From three centers. Fig. 218. — Epiphysial lines of radius in a young adult. Anterior aspect. The line of attachment of the articular capsule of the wrist-joint is in blue. THE HAND. I ^H The skeleton of the hand (Figs. 219, 220) is subdivided into three segments: the ^■carpus or wrist bones; the metacarpus or bones of the palm; and the phalanges or ^■bones of the digits. ^M The Carpus (Ossa Carpi). ^H The carpal bones, eight in number, are arranged in two rows. Those of the ^■|)roximal row, from the radial to the ulnar side, are named the navicular, lunate, ^^triangular, and pisiform ; those of the distal row, in the same order, are named the greater multangular, lesser multangular, capitate, and hamate. Common Characteristics of the Carpal Bones. — Each bone (excepting the pisi- form) presents six surfaces. Of these the volar or anterior and the dorsal or posterior surfaces are rough, for ligamentous attachment; the dorsal surfaces being the broader, except in the navicular and lunate. The s^ijjerior or proximal, and inferior or distal surfaces are articular, the superior generally convex, the inferior concave; the medial and lateral surfaces are also articular where they are in contact with contiguous bones, otherwise they are rough and tuberculated. The structure in all is similar, viz., cancellous tissue enclosed in a layer of compact bone. Bones of the Proximal Row {upper row). — The Navicular Bone (os naviculare manus; scaphoid bone) (Fig. 221), — The navicular bone is the largest bone of the proximal row, and has received its name from its fancied resemblance to a boat. It is situated at the radial side of the carpus, its long axis being from above downward, lateralward, and forward. The superior surface is convex, smooth, of triangular shape, and artic- 222 OSTEOLOGY ulates with the lower end of the radius. The inferior surface, directed downwaiv lateralward, and backward, is also smooth, convex, and triangular, and is divided by a slight ridge into two parts, the lateral articulating with the greater multangu- lar, the medial with the lesser multangillar. On the dorsal surface is a narrow, rough groove, which runs the entire length of the bone, and serves for the attach- ment of ligaments. The volar surface is concave above, and elevated at its lower and lateral part into a rounded projection, the tubercle, which is directed forward Carpus Flexor carpi ulnakis Flexor digiti quinti bkevis OpPONENS I>IQITI QUINTl Metacarpus Groove for tendon of Flexor carpi radialis Opponens pollicis Flexor polucis brkvis //Abductor pollicis Flexor brevis'\ AND I Abductor J "' digiti QniNTI. / Sesamoid bones Abductor pollicis brevis Flexor digitorum sublimis Flexor digitorum profundus FiQ. 219. — Bones of the left hand. Volar surface. I THE CARPUS 223 and gives attachment to the transverse carpal ligament and sometimes origin to a few fibers of the Abductor pollicis brevis. The lateral surface is rough and narrow, and gives attachment to the radial collateral ligament of the wrist. The medial surface presents two articular facets; of these, the superior or smaller is flattened of semilunar form, and articulates with the lunate bone; the inferior or larger is concave, forming with the lunate a concavity for the head of the capitate bone. CARPI RADIALIS LONG0S BXT. CARPI RADIALIS BREVIS sr-fjiffw Fig. 220. — Boaes of the left hand. Dorsal surface. 224 OSTEOLOGY Articulations. — The navicular articulates with five bones: the radius proximally, greater and lesser multangulars distally, and capitate and lunate medially. The Lunate Bone (os lunatum; semilunar bone) (Fig. 222). — The lunate bone may be distinguished by its deep concavity and crescentic outHne. It is situated in the center of the proximal row of the carpus, between the navicular and triangul ar. The superior surface, convex and smooth, articulates with the radius. The inferior surface is deeply concave, and of greater extent from before backward than trans- For radius For lunate Tubercle \ For greater multangular For capitate For lesser multangular Fig. 221. — The left navicular bone. versely: it articulates with the head of the capitate, and, by a long, narrow facet (separated by a ridge from the general surface), with the hamate. The dorsal and volar surfaces are rough, for the attachment of ligaments, the former being the broader, and of a somewhat rounded form. The lateral surface presents a For triangular For radius For navicular For Iiamate For capitate Fig. 222.— The left lunate bone. narrow, flattened, semilunar facet for articulation with the navicular. The medial surface is marked by a smooth, quadrilateral facet, for articulation with the triangular. Articulations. — The lunate articulates with five bones: the radius proximally, capitate and hamate distally, navicular laterally, and triangular medially. For pisiform For lunate For triangular For hamate Fig. 223.— The left triangular bone. Fig. 224. — The left pisiform bone. The Triangular Bone (os triquetum; cuneiform hone) (Fig. 223). — The triangular bone may be distinguished by its pyramidal shape, and by an oval isolated facet for articulation with the pisiform bone. It is situated at the upper and ulnar side of the carpus. The superior surface presents a medial, rough, non-articular portion, and a lateral convex articular portion which articulates with the triangular articular disk of the wrist. The inferior surface, directed lateralward, is concave, sinuously curved, and smooth for articulation with the hamate. The dorsal surface is rough for the attachment of ligaments. The volar surface presents, on its medial part, THE CARPUS 225 an oval facet, for articulation with the pisiform; its lateral part is rough for liga- mentous attacliment. The lateral surface, the base of the pyramid, is marked by a fiat, quadrilateral facet, for articulation with the lunate. The medial surface, the summit of the pyramid, is pointed and roughened, for the attachment of the » ulnar collateral ligament of the wrist. Ar^'culations. — The triangular articulates with three bones: the lunate laterally, the pisiform in front, the hamate distaUy; and with the triangular articular disk which separates it from the lower end of the ulna. The Pisiform Bone (os pisiforme) (Fig. 224). — The pisiform bone may be known by its small size, and by its presenting a single articular facet. It is situated on a plane anterior to the other carpal bones and is spheroidal in form. Its dorsal surface presents a smooth, oval facet, for articulation with the triangular : this facet approaches the superior, but not the inferior border of the bone. The volar surface is rounded and rough, and gives attachment to the transverse carpal ligament, and to the Flexor carpi ulnaris and Abductor digiti quinti. The lateral and medial surfaces are also rough, the former being concave, the latter usually convex. Articulation. — The pisiform articulates with one bone, the triangular. Bones of the Distal Row {lower row). — The Greater Multangular Bone (os mul- tangulum majus; trapezium) (Fig. 225). — The greater multangular bone may be distinguished by a deep groove on its volar surface. It is situated at the radial side of the carpus, between the navicular and the first metacarpal bone. The superior surface is directed upward and medialward; medially it is smooth, and articulates with the navicular ; laterally it is rough and continuous with the lateral surface. The inferior surface is oval, concave from side to side, convex from before backward, so as to form a saddle-shaped surface for articulation with the base For lesser vivitangtdar Groove For navicular For 2nd metacarpal Ridge For \st metacarpal Fig. 225. — The left greater multangular bone For lesser mvltanguMT For 2)id metacarpal )f the first metacarpal bone. The dorsal surface is rough. The volar surface is barrow and rough. At its upper part is a deep groove, running from above obliquely pownward and medialward; it transmits the tendon of the Flexor carpi radialis, ^nd is bounded laterally by an oblique ridge. This surface gives origin to the Opponens pollicis and to the Abductor and Flexor pollicis brevis; it also affords attachment to the transverse carpal ligament. The lateral surface is broad and rough, for the attachment of ligaments. The medial surface presents two facets; the upper, large and concave, articulates with the lesser multangular; the lower, small and oval, with the base of the second metacarpal. ; Articulations. — The greater multangular articulates with four bones : the navicular proximally, [ the first metacarpal distally, and the lesser multangular and second metacarpal medially. The Lesser Multangular Bone (os multangulum minus; trapezoid hone) (Fig. 226). -The lesser multangular is the smallest bone in the distal row. It may be known llby its wedge-shaped form, the broad end of the wedge constituting the dorsal, l^he narrow end the volar surface; and by its having four articular facets touching ich other, and separated by sharp edges. The superior surface, quadrilateral, 15 226 OSTEOLOGY For navicular Volar surface For greater multangular smooth, and slightly concave, articulates with the navicular. The inferioT'surFace articulates with the proximal end of the second metacarpal bone; it is convex from side to side, concave from before backward and subdivided by an elevated ridge into two unequal facets. The dorsal and volar surfaces are rough for the attachment of ligaments, the former being the larger of the two. The lateral surface, con\'ex and smooth, articulates with the greater multangular. The medial surface is con- cave and smooth in front, for artic- ulation with the capitate; rough behind, for the attachment of an interosseous ligament. For capitate Dorsal surface Fig. 226. — The left lesser multangular bone. For 2nd vielacarpal Articulations. — The lesser multangular articulates with /our bones: the navicular proximally, second metacarpal distally, greater multangular laterally, and capitate medially. The Capitate Bone {os capitatum; os magnum) (Fig. 227). — The capitate bone is the largest of the carpal bones, and occupies the center of the wrist. It presents, above, a rounded portion or head, which is received into the concavity formed by For lunate For navicular For lesser multangular For hamate For 3rd For 2nd metacarpal metacarpal For 4ih metacarpal Fig. 227.— The left capitate bone. Volar surface the navicular and lunate; a constricted portion or neck; and below this, the body. The superior surface is round, smooth, and articulates with the lunate. The inferior surface is divided by two ridges into three facets, for articulation with the second, third, and fourth metacarpal bones, that for the third being the largest. The dorsal surface is broad and rough. The volar surface is narrow, rounded, and rough, for the attachment of ligaments and a part of the Adductor pollicis obliquus. For lunate For triangular For capitate For Ath metacarpal For 5th metacarpal Hamulus Fig. 228.— The left hamate bone. For 5th metacarpal The lateral surface articulates with the lesser multangular by a small facet at its anterior inferior angle, behind which is a rough depression for the attach- ment of an interosseous ligament. Above this is a deep, rough groove, forming part of the neck, and serving for the attachment of ligaments; it is bounded supe- riorly by a smooth, convex surface, for articulation with the navicular. The medial I THE METACARPUS I surface articulates with the hamate by a smooth, concave, oblong facet, which occupies its posterior and superior parts; it is rough in front, for the attachment of an interosseous ligament. Articulations. — The capitate articulates with seven bones : the navicular and lunate proximally, the second, third, and fourth metacarpals distally, the lesser multangular on the radial side, and the hamate on the ulnar side. The Hamate Bone {os hamaium; unciform bone) (Fig. 228). — The hamate bone may be readily distinguished by its wedge-shaped form, and the hook-like process which projects from its volar surface. It is situated at the medial and lower angle of the carpus, with its base downward, resting on the fourth and fifth metacarpal bones, and its apex directed upward and lateralward. The superior surface, the ai)ex of the wedge, is narrow, convex, smooth, and articulates with the lunate. The inferior surface articulates with the fourth and fifth metacarpal bones, by concave facets which are separated by a ridge. The dorsal surface is triangular and rough for ligamentous attachment. The volar surface presents, at its lower and ulnar side, a curved, hook-like process, the hamulus, directed forward and lateralward. This process gives attachment, by its apex, to the transverse carpal ligament and the Flexor carpi ulnaris; by its medial surface to the Flexor brevis and Opponens digiti quinti; its lateral side is grooved for the passage of the Flexor tendons into the palm of the hand. It is one of the four eminences on the front of the carpus to which the transverse carpal ligament of the wrist is attached; tlie others being the pisiform medially, the oblique ridge of the greater multangular and the tubercle of the navicular laterally. The medial surface articulates with tlie triangular bone by an oblong facet, cut obliquely from above, downward and medial ward. The lateral surface articulates with the capitate by its upper and posterior part, the remaining portion being rough, for the attachment of ligaments. Articulations. — The hamate articulates with five bones: the lunate proximally, the fourth fth metacarpals distally, the triangular medially, the capitate laterally. ^f The Metacarpus. I The metacarpus consists of five cylindrical bones which are numbered from the iteral side {ossa metacarpalia I-V) ; each consists of a body and two extremities. Common Characteristics of the Metacarpal Bones.— The Body (corpus; shaft). — ?he body is prismoid in form, and curved, so as to be convex in the longitudinal lirection behind, concave in front. It presents three surfaces: medial, lateral, iid dorsal. The medial and lateral surfaces are concave, for the attachment of he Interossei, and separated from one another by a prominent anterior ridge. ^[Tie dorsal surface presents in its distal two-thirds a smooth, triangular, flattened jea which is covered in the fresh state, by the tendons of the Extensor muscles. This surface is bounded by two lines, which commence in small tubercles situated >n either side of the digital extremity, and, passing upward, converge and meet bme distance above the center of the bone and form a ridge which runs along the test of the dorsal surface to the carpal extremity. This ridge separates two 'oping surfaces for the attachment of the Interossei dorsales. To the tubercles »n the digital extremities are attached the collateral ligaments of the metacarpo- phalangeal joints. The Base or Carpal Extremity (basis) is of a cuboidal form, and broader behind lian in front: it articulates with the carpus, and with the adjoining metacarpal >ones; its dorsal and volar surfaces are rough, for the attachment of ligaments. [ The Head or Digital Extremity (capitulum) presents an oblong surface markedly 'convex from before backward, less so transversely, and flattened from side to side; it articulates with the proximal phalanx. It is broader, and extends farther up- 228 For greater multangular For greater multangular FiQ. 229. — The first metacarpal. (Left.) ward, on the volar than on the dorsal aspect, and is longer in the antero-post(;rior than in the transverse diameter. On either side of the head is a tubercle for the attachment of the collateral ligament of the metacarpophalangeal joint. The dorsal surface, broad and flat, supports the Extensor tendons; the volar smface is grooved in the middle line for the passage of the Flexor tendons, and mai-ked on either side by an articular eminence continuous with the terminal articular surface. Characteristics of the Individual Metacarpal Bones. — The First Metacarpal Bone {os vietacarpale I; metacarpal bone of the thumb) (Fig. 229) is shorter and stouter than the others, diverges to a greater degree from the carpus, and its volar surface is directed toward the palm. The body is flattened and broad on its dorsal surface, and does not present the ridge which is found on the other metacarpal bones; its volar surface is concave from above downward. On its radial border is inserted the Opponens pollicis; its ulnar border gives origin to the lateral head of the first Interosseus dorsalis. The base presents a concavo-convex surface, for articulation with the greater multangular; it has no facets on its sides, but on its radial side is a tubercle for the insertion of the Abductor pollicis longus. The head is less convex than those of the other metacarpal bones, and is broader from side to side than from before backward. On its volar surface are two articular eminences, of which the lateral is the larger, for the two sesamoid bones in the tendons of the Flexor pollicis brevis. The Second Metacarpal Bone (os metacarpale II; metacarpal bone of the index finger) (Fig. 230) is the longest, and its base the largest, of the four remaining bones. Its base is prolonged upward and medialward, forming a prominent ridge. It presents four articular facets: three on the upper surface and one on the ulnar side. Of the facets on the upper surface the intermediate is the largest and is concave from side to side, convex from before backward for articulation with the lesser multangular; the lateral is small, flat and oval for articulation with the greater multangular; the medial, on the summit of the ridge, is long and narrow for articu- lation with the capitate. The facet on the ulnar side articulates with the third metacarpal. The Extensor carpi radialis longus is inserted on the dorsal surface and the Flexor carpi radialis on the volar surface of the base. The Third Metacarpal Bone {os metacarpale III; metacarpal bone of the middle finger) (Fig. 231) is a little smaller than the second. The dorsal aspect of its base presents on its radial side a pyramidal eminence, the styloid process, which extends upward behind the capitate; immediately distal to this is a rough surface for the attachment of the Extensor carpi radialis brevis. The carpal articular facet is concave behind, flat in front, and articulates with the capitate. On the radial side is a smooth, concave facet for articulation with the second metacarpal, and on the ulnar side two small oval facets for the fourth metacarpal. The Fourth Metacarpal Bone {os metacarpale IV; metacarpal bone of the ring finger) (Fig. 232) is shorter and smaller than the third. The base is small and quadrilateral; its superior surface presents two facets, a large one medially for articulation with the hamate, and a small one laterally for the capitate. On the radial side are two oval facets, for articulation with the third metacarpal ; and on the ulnar side a single concave facet, for the fifth metacarpal. The Fifth Metacarpal Bone {os metacarpale V; metacarpal bone of the little finger) (Fig. 233) presents on its base one facet on its superior surface, which is concavo- THE METACARPUS 229 convex and articulates with the hamate, and one on its radial side, which articulates with the fourth metacarpal. On its ulnar side is a prominent tubercle for the inser- tion of the tendon of the Extensor carpi ulnaris. The dorsal surface of the body For greater For '6rd Fo '• lesser multangxdar metacarpal For For lesser mt Uangular capitate mult- angular Fio. 230. — The second metacarpal. (Left.) Styloid Far 2nd process meta- carpal Fig. 231. — The third metacarpal. (Left.) For capitate For ^th metacarpal is divided by an oblique ridge, which extends from near the ulnar side of the base to the radial side of the head. The lateral part of this surface serves for the attach- mjnt of the fourth Interosseus dorsalis; the medial part is smooth, triangular, and covered by the Extensor tendons of the little finger. •f For capitate For 3rd For For 5th metO' carpal metacarpal hamate Fig. 232.— The fourth metacarpal. (Left.) For 4:th metacarpal For hamate Fig. 233. — The fifth metacarpal. (Left.) Articulations. — Besides their phalangeal articulations, the metacarpal bones articulate as follows: the first with the greater multangular; the second with the greater multangular, lesser multangular, capitate and third metacarpal; the third with the capitate and second and fourth metacarpals; the fourth with the capitate, hamate, and third and fifth metacarpals; and the fifth with the hamate and fourth metacarpal. 230 OSTEOLOGY The Phalanges of the Hand (Phalanges Digitonim Manus). The phalanges are fourteen in number, three for each finger, and two for the thumb. Each consists of a body and two extremities. The body tapers from above downward, is convex posteriorly, concave in front from above downward, flat from side to side; its sides are marked by rough ridges which give attachment to the fibrous sheaths of the Flexor tendons. The proximal extremities of the bones of the first row present oval, concave articular surfaces, broader from side to side than from before backward. The proximal extremity of each of the bones of the second and third rows presents a double concavity separated by a median ridge. The distal extremities are smaller than the proximal, and each ends in two condyles separated by a shallow groove; the articular surface extends farther on the volar than on the dorsal surface, a condition best marked in the bones of the first row. The ungual phalanges are convex on their dorsal and flat on their volar surfaces; they are recognized by their small size, and by a roughened, elevated surface of a horseshoe form on the volar surface of the distal extremity of each which serves to support the sensitive pulp of the finger. One center for each hone : All cartilaginous at birth METACARPALS OF FINGERS Tloo centers for each bone . One for body One for head PHALANOZIS Two centers for each bone One for body One for proximal extremity ajifieari /^-S*r y t- \ unite 18 ZO'^yZ. FiG. 234. — Plan of ossification of the hand. Articulations. — In the four fingers the phalanges of the first row articulate with those of the second row and with the metacarpals; the phalanges of the second row with those of the first and third rows, and the ungual phalanges with those of the second row. In the thumb, which has only two phalanges, the first phalanx articulates by its proximal extremity with the meta- carpal bone and by its distal with the ungual phalanx. Ossification of the Bones of the Hand. — The carpal bones are each ossified from a single center, and ossification proceeds in the following order (Fig. 234) : in the capitate and hamate, during 1 THE HIP BONE 231 the first year, the former preceding the latter; in the triangular, during the third year; in the lunate and greater multangular, during the fifth year, the former preceding the latter; in the navicular, during the sixth year; in the lesser multangular, during the eighth year; and in the pisiform, about the twelfth year Occasionally an additional bone, the os centrale, is found on the back of the carpus, lying between the navicular, lesser multangular, and capitate. During the second month of fetal life it is represented by a small cartilaginous nodule, which usually fuses with the cartilaginous navic- ular. Sometimes the styloid process of the third metacarpal is detached and forms an additional ossicle. The metacarpal bones are each ossified from two centers: one for the body and one for the distal extremity of each of the second, third, fourth, and fifth bones; one for the body and one for the base of the first metacarpal bone.^ The first metacarpal bone is therefore ossified in the same manner as the phalanges, and this has led some anatomists to regard the thumb as being made up of three phalanges, and not of a metacarpal bone and two phalanges. Ossification com- mences in the middle of the body about the eighth or ninth week of fetal life, the centers for the second and third metacarpals being the first, and that for the first metacarpal, the last, to appear; about the third year the distal extremities of the metacarpals of the fingers, and the base of the metacarpal of the thumb, begin to ossify; they unite with the bodies about the twentieth year. The phalanges are each ossified from two centers: one for the body, and one for the proximal extremity. Ossification begins in the body, about the eighth week of fetal life. Ossification of the proximal extremity commences in the bones of the first row between the third and fourth y(!ars, and a year later in those of the second and third rows. The two centers become united in each row between the eighteenth and twentieth years. In the ungual phalanges the centers for the bodies appear at the distal extremities of the phalanges, instead of at the middle of the bodies, as in the other phalanges. Moreover, of all the bones of the hand, the ungual phalanges are the first to ossify. THE BONES OF THE LOWER EXTREMITY (OSSA EXTREMITATIS INFERIORIS). The Hip Bone (Os Coxae; Innominate Bone). The hip bone is a large, flattened, irregularly shaped bone, constricted in the center and expanded above and below. It meets its fellow on the opposite side ill the middle line in front, and together they form the sides and anterior wall of tie pelvic cavity. It consists of three parts, the ilium, ischium, and pubis, which are distinct from each other in the young subject, but are fused in the adult; t tie union of the three parts takes place in and around a large cup-shaped articular cavity, the acetabulum, which is situated near the middle of the outer surface of the lone. The ilium, so-called because it supports the flank, is the superior broad and expanded portion which extends upward from the acetabulum. The ischium is the lowest and strongest portion of the bone; it proceeds downward from the acetab- ilum, expands into a large tuberosity, and then, curving forward, forms, with the pubis, a large aperture, the obturator foramen. The pubis extends medialward and downward from the acetabulum and articulates in the middle line with the I one of the opposite side: it forms the front of the pelvis and supports the external crgans of generation. ' The niiim {os ilii). — ^The ilium is divisible into two parts, the body and the ala; the separation is indicated on the internal surface by a curved line, the arcuate Ime, and on the external surface by the margin of the acetabuluni. The Body {corpus oss. ilii). — The body enters into the formation of the acetab- jlum, of which it forms rather less than two-fifths. Its external surface is partly articular, partly non-articular; the articular segment forms part of the lunate surface of the acetabulum, the non-articular portion contributes to the acetabular fossa. The internal surface of the body is part of the wall of the lesser pelvis and gives origin to some fibers of the Obturator internus. Below, it is continuous with the pelvic surfaces of the ischium and pubis, only a faint line indicating the place of union. an ■ Allen Thomson demonstrated the fact that the first metacarpal bone is often developed from three centers: that is say, there is a separate nucleus for the distal end, forming a distinct epiphysis visible at the age of seven or eight ®*,'^, . .° stated that there are traces of a proximal epiphysis in the second metacarpal bone, Journal of Anatomy and Physiology, 1869. 232 OSTEOLOGY The Ala {ala oss. ilii). — The ala is the large expanded portion which bounds the greater pelvis laterally. It presents for examination two surfaces — an extei-nal and an internal — a crest, and two borders — an anterior and a posterior. The external surf ace (Fig. 235), known as the dorsum ilii, is directed backward and lateral- ward behind, and downward and lateralward in front. It is smooth, convex in front, Posterior superio spine Posterior inferior spine Oemellus superior JSpine of ischium Qemdlus inferior Ant. superior spine -Anterior inferior spine Articular capsule Ligamentum teres _ o/\ Rectus Fuhia]^^ abdominis Pyramidalis Adductor longus Fig. 235. — Right hip bone. External surface. deeply concave behind; bounded above by the crest, below by the upper border of the acetabulum, in front and behind by the anterior and posterior borders. This surface is crossed in an arched direction by three lines — the posterior, anterior,, and inferior gluteal lines. The posterior gluteal line {superior curved line), the short- est of the three, begins at the crest, about 5 cm. in front of its posterior extremity; it is at first distinctly marked, but as it passes downward to the upper part of the THE HIP BONE 233 greater sciatic notch, where it ends, it becomes less distinct, and is often altogether lost. Behind this line is a narrow semilunar surface, the upper part of which is rough and gives origin to a portion of the Glutseus maximus ; the lower part is smooth and has no muscular fibers attached to it. The anterior gluteal line {middle curved line), the longest of the three, begins at the crest, about 4 cm. behind its anterior extremity, and, taking a curved direction downward and backward, ends Levator dm Constrictor urethroe Cms penis Via. 236. — Right hip bone. Internal surface. Transversus perincei superfic Ischiocavemosus at the upper part of the greater sciatic notch. The space between the anterior and posterior gluteal lines and the crest is concave, and gives origin to the Glutseus medius. Near the middle of this line a nutrient foramen is often seen. The inferior gluteal line {inferior curved line), the least distinct of the three, begins in front at the notch on the anterior border, and, curving backward and downward, ends near the middle of the greater sciatic notch. The surface of bone included 234 OSTEOLOGY ^IHR" between the anterior and inferior gluteal lines is concave from above downward, convex from before backward, and gives origin to the Glutseus minimus. Betwtien the inferior gluteal line and the upper part of the acetabulum is a rough, shallow groove, from which the reflected tendon of the Rectus femoris arises. The internal surface (Fig. 236) of the ala is bounded above by the crest, below, by the arcuate line; in front and behind, by the anterior and posterior borders. It presents a large, smooth, concave surface, called the iliac fossa, which gives origin to the Iliacus and is perforated at its inner part by a nutrient canal; and below this a smooth, rounded border, the arcuate line, which runs downward, for- ward, and medialward. Behind the iliac fossa is a rough surface, divided into two portions, an anterior and a posterior. The anterior surface {auricular surface), so called from its resemblance in shape to the ear, is coated with cartilage in the fresh state, and articulates with a similar surface on the side of the sacrum. The posterior portion, known as the iliac tuberosity, is elevated and rough, for the attachment of the posterior sacroiliac ligaments and for the origins of the Sacrospinalis and Multifidus. Below^ and in front of the auricular surface is the preauricular sulcus, more commonly present and better marked in the female than in the male; to it is attached the pelvic portion of the anterior sacroiliac ligament. The crest of the ilium is convex in its general outline but is sinuously curved, being concave inward in front, concave outward behind. It is thinner at the center than at the extremities, and ends in the anterior and posterior superior iliac spines. The surface of the crest is broad, and divided into external and internal lips, and an intermediate line. About 5 cm. behind the anterior superior iliac spine there is a prominent tubercle on the outer lip. To the external lip are attached the Tensor fasciae latse, Obliquus externus abdominis, and Latissimus dorsi, and along its whole length the fascia lata; to the intermediate line the Obliquus internus abdominis; to the internal lip, the fascia iliaca, the Transversus abdominis, Quadratus lumborum, Sacrospinalis, and Iliacus. The anterior border of the ala is concave. It presents two projections, separated by a notch. Of these, the uppermost, situated at the junction of the crest and anterior border, is called the anterior superior iliac spine; its outer border gives attachment to the fascia lata, and the Tensor fasciae latse, its inner border, to the Iliacus; while its extremity affords attachment to the inguinal ligament and gives origin to the Sartorius. Beneath this eminence is a notch from which the Sartorius takes origin and across which the lateral femoral cutaneous nerve passes. Below the notch is the anterior inferior iliac spine, which ends in the upper lip of the acetabulum; it gives attachment to the straight tendon of the Rectus femoris and to the iliofemoral ligament of the hip-joint. Medial to the anterior inferior spine is a broad, shallow groove, over which the Iliacus and Psoas major pass. This groove is bounded medially by an eminence, the iliopectineal eminence, which marks the point of union of the ilium and pubis. The posterior border of the ala, shorter than the anterior, also presents two projections separated by a notch, the posterior superior iliac spine and the posterior inferior iliac spine. The former serves for the attachment of the oblique portion of the posterior sacroiliac ligaments and the Multifidus; the latter corresponds with the posterior extremity of the auricular surface. Below the posterior inferior spine is a deep notch, the greater sciatic notch. The Ischium {os ischii). — The ischium forms the lower and back part of the hip bone. It is divisible into three portions — a body and two rami. The Body {corpus oss. ischii). — The body enters into and constitutes a little more than two-fifths of the acetabulum. Its external surface forms part of the lunate surface of the acetabulum and a portion of the acetabular fossa. Its internal surface is part of the wall of the lesser pelvis; it gives origin to some fibers of the THE HIP BONE 235 Obturator mternus. Its anterior border projects as the posterior obturator tubercle; from its posterior border there extends backward a thin and pointed triangular eminence, the ischial spine, more or less elongated in different subjects. The external surface of the spine gives attachment to the Gemellus superior, its internal surface to the Coccygeus, Levator ani, and the pelvic fascia; while to the pointed extremity the sacrospinous ligament is attached. Above the spine is a large notch, the greater sciatic notch, converted into a foramen by the sacrospinous ligament; it transmits the Piriformis, the superior and inferior gluteal vessels and nerves, the sciatic and posterior femoral cutaneous nerves, the internal pudendal vessels, and nerve, and the nerves to the Obturator internus and Quadratus femoris. Of these, the superior gluteal vessels and nerve pass out above the Piriformis, the other structures below it. Below the spine is a smaller notch, the lesser sciatic notch; it is smooth, coated in the recent state with cartilage, the surface of which presents two or three ridges corresponding to the subdivisions of the tendon of the Obturator internus, which winds over it. It is converted into a foramen by the sacrotuberous and sacrospinous ligaments, and transmits the tendon of the Obturator internus, the nerve which supplies that muscle, and the internal pudendal vessels and rterve. The Superior Ramus {ramus superior oss. ischii; descending ramus). — The superior ramus projects downward and backward from the body and presents for examination three surfaces: external, internal, and posterior. The external surface is quadrilateral in shape. It is bounded above by a groove which lodges the tendon of the Obturator externus; below, it is continuous with the inferior ramus; in front it is limited by the posterior margin of the obturator foramen; behind, a prominent margin separates it from the posterior surface. In front of this margin the surface gives origin to the Quadratus femoris, and anterior to this to some of the fibers of origin of the Obturator externus; the lower part of the sur- iace gives origin to part of the Adductor magnus. The internal surface forms part of the bony wall of the lesser pelvis. In front it is limited by the posterior margin of the obturator foramen. Below, it is bounded by a sharp ridge which gives attachment to a falciform prolongation of the sacrotuberous ligament, and, more anteriorly, gives origin to the Transversus perinsei and Ischiocavernosus. Poste- liorly the ramus forms a large swelling, the tuberosity of the ischium, which is divided into two portions: a lower, rough, somewhat triangular part, and an upper, smooth, juadrilateral portion. The lower portion is subdivided by a prominent longitudinal :*idge, passing from base to apex, into two parts; the outer gives attachment to "he Adductor magnus, the inner to the sacrotuberous ligament. The upper portion s subdivided into two areas by an oblique ridge, which runs downward and out- ward; from the upper and outer area the Semimembranosus arises; from the lower and inner, the long head of the Biceps femoris and the Semitendinosus. The Inferior Ramus {ramus inferior oss. ischii; ascending ramus). — The inferior ramus is the thin, flattened part of the ischium, which ascends from the superior ramus, and joins the inferior ramus of the pubis — the junction being indicated in the adult by a raised line. The outer surface is uneven for the origin of the Obturator externus and some of the fibers of the Adductor magnus; its inner surface forms part of the anterior wall of the pelvis. Its medial border is thick, rough, slightly everted, forms part of the outlet of the pelvis, and presents two ridges and an intervening space. The ridges are continuous with similar ones on the inferior tamus of the pubis : to the outer is attached the deep layer of the superficial peri- heal fascia {fascia of Colles), and to the inner the inferior fascia of the urogenital diaphragm. If these two ridges be traced downward, they will be found to join i«^^ith each other just behind the point of origin of the Transversus periniei; here She two layers of fascia are continuous behind the posterior border of the muscle. ^o the intervening space, just in front of the point of junction of the ridges, the 236 ^^^^^^^ OSTEOLOGY Transversus perinan is attached, and in front of this a portion of the cms penis vel clitoridis and the Ischiocavernosus. Its lateral border is thin and sharp, and forms part of the medial margin of the obturator foramen. The Pubis {os imbis) . — The pubis, the anterior part of the hip bone, is divisible into a body, a superior and an inferior ramus. The Body {corpus oss. pubis). — The body forms one-fifth of the acetabulum, contributing by its external surface both to the lunate surface and the acetabular fossa. Its internal surface enters into the formation of the wall of the lesser peh'is and gives origin to a portion of the Obturator internus. The Superior Ramus {ramus superior oss. pubis; ascending ramus) . — The superior ramus extends from the body to the median plane where it articulates with its fellow of the opposite side. It is conveniently described in two portions, viz., a medial flattened part and a narrow lateral prismoid portion. The Medial Portion of the superior ramus, formerly described as the body of the pubis, is somewhat quadrilateral iil shape, and presents for examination two surfaces and three borders. The anterior surface is rough, directed downward and outward, and serves for the origin of various muscles. The Adductor longus arises from the upper and medial angle, immediately below the crest; lower down, the Obturator externus, the Adductor brevis, and the upper part of the Gracilis take origin. The posterior surface, convex from above downward, concave from side to side, is smooth, and forms part of the anterior wall of the pelvis. It gives origin to the Levator ani and Obturator internus, and attachment to the puboprostatic ligaments and to a few muscular fibers prolonged from the bladder. The upper border presents a prominent tubercle, the pubic tubercle {pubic spine), which pro- jects forward; the inferior crus of the subcutaneous inguinal ring {external abdominal ring), and the inguinal ligament {Pouparfs ligament) are attached to it. Passing upward and lateralward from the pubic tubercle is a well-defined ridge, forming a part of the pectineal line which marks the brim of the lesser pelvis: to it are attached a portion of the inguinal falx {conjoined tendon of Obliquus internus and Transversus), the lacunar ligament {Gimbernafs ligament), and the reflected inguinal ligament {triangular fascia). Medial to the pubic tubercle is the crest, which extends from this process to the medial end of the bone. It affords attach- ment to the inguinal falx, and to the Rectus abdominis and Pyramidalis. The point of junction of the crest with the medial border of the bone is called the angle ; to it, as well as to the symphysis, the superior crus of the subcutaneous inguinal ring is attached. The medial border is articular; it is oval, and is marked by eight or nine transverse ridges, or a series of nipple-like processes arranged in rows, separated by grooves; they serve for the attachment of a thin layer of cartilage, which intervenes between it and the interpubic fibrocartilaginous lamina. The lateral border presents a sharp margin, the obturator crest, which forms part of the circumference of the obturator foramen and affords attachment to the obturator membrane. The Lateral Portion of the ascending ramus has three surfaces : superior, inferior, and posterior. The superior surface presents a continuation of the pectineal line, already mentioned as commencing at the pubic tubercle. In front of this line, the surface of bone is triangular in form, wider laterally than medially, and is covered by the Pectineus. The surface is bounded, laterally, by a rough eminence, the iliopectineal eminence, which serves to indicate the point of junction of the ilium and pubis, and below by a prominent ridge which extends from the acetabular notch to the pubic tubercle. The inferior surface forms the upper boundary of the obturator foramen, and presents, laterally, a broad and deep, oblique groove, for the passage of the obturator vessels and nerve; and medially, a sharp margin, the obturator crest, forming part of the circumference of the obturator foramen, and giving attachment to the obturator membrane. The posterior surface consti- THE HIP BONE lutes part of the anterior boundary of the lesser pelvis. It is smooth, convex from above downward, and affords origin to some fibers of the Obturator internus. The Inferior Ramus {ramus inferior oss. pubis; descending ramus). — The inferior ramus is thin and flattened. It passes lateralward and downward from the medial end of the superior ramus; it becomes narrower as it descends and joins with the inferior ramus of the ischium below the obturator foramen. Its anterior surface is rough, for the origin of muscles — the Gracilis along its medial border, a portion of the Obturator externus where it enters into the formation of the obturator foramen, and between these two, the Adductores brevis and magnus, the former being the more medial. The posterior surface is smooth, and gives origin to the Obturator internus, and, close to the medial margin, to the Constrictor urethra?. The medial border is thick, rough, and everted, especially in females. It presents two ridges, separated by an intervening space. The ridges extend downward, and are continuous with similar ridges on the inferior ramus of the ischium; to the external is attached the fascia of Colles, and to the internal the inferior fascia of the urogenital diaphragm. The lateral border is thin and sharp, forms part of the circumference of the obturator foramen, and gives attachment to the obturator membrane. The Acetabulum (cotyloid cavity) . — The acetabulum is a deep, cup-shaped, hemi- spherical depression, directed downward, lateralward, and forward. It is formed medially by the pubis, above by the ilium, laterally and below by the ischium; a little less than two-fifths is contributed by the ilium, a little more than two- lifths by the ischium, and the remaining fifth by the pubis. It is bounded by a ])rominent uneven rim, which is thick and strong above, and serves for the attach- ment of the glenoidal labrum (cotyloid ligament), which contracts its orifice, and deepens the surface for articulation. It presents below a deep notch, the acetabular notch, which is continuous with a circular non-articular depression, the acetabular riossa, at the bottom of the cavity: this depression is perforated by numerous [apertures, and lodges a mass of fat. The notch is converted into a foramen by l^e transverse ligament; through the foramen nutrient vessels and nerves enter [the joint; the margins of the notch serve for the attachment of the ligamentum teres. The rest of the acetabulum is formed by a curved articular surface, the lunate surface, for articulation with the head of the femur. The Obturator Foramen (foramen ohturatum; thyroid foramen). — The obturator foramen is a large aperture, situated between the ischium and pubis. In the male it is large and of an oval form, its longest diameter slanting obliquely from before backward; in the female it is smaller, and more triangular. It is bounded by a thin, uneven margin, to which a strong membrane is attached, and presents, I superiorly, a deep groove, the obturator groove, which runs from the pelvis obliquely medialward and downward. This groove is converted into a canal by a ligamentous band, a specialized part of the obturator membrane, attached to two tubercles: one, the posterior obturator tubercle, on the medial border of the ischium, just in front of the acetabular notch; the other, the anterior obturator tubercle, on the obturator crest of the superior ramus of the pubis. Through the canal the 1 obturator vessels and nerve pass out of the pelvis. Structure. — The thicker parts of the bone consist of cancellous tissue, enclosed between two [layers of compact tissue; the thinner parts, as at the bottom of the acetabulum and center of [the ihac fossa, are usually semitransparent, and composed entirely of compact tissue. Ossification (Fig. 237). — The hip bone is ossified from eight .centers: three primary — one each for the ihum, ischium, and pubis; and ^ye secondary — one each for the crest of the ilium, the anterior inferior spine (said to occur more frequently in the male than in the female), the tuberosity lof the ischium, the pubic symphysis (more frequent in the female than in the male), and one or Imore for the Y-shaped piece at the bottom of the acetabulum. The centers appear in the foUow- ling order: in the lower part of the ihum, immediately above the greater sciatic notch, about I the eighth or ninth week of fetal life; in the superior ramus of the ischium, about the third month; 238 OSTEOLOGY k in the superior ramus of the pubis, between the fourth and fifth months. At birth, the three primary centers are quite separate, the crest, the bottom of the acetabulum, the ischial tuberosity, and the inferior rami of the ischium and pubis being still cartilaginous. By the seventh or eighth year, the inferior rami of the pubis and ischium are almost completely united by bone. About the thirteenth or fourteenth year, the three primary centers have extended their growth into the bottom of the acetabulum,' and are there separated from each other by a Y-shaped portion of cartilage, which now presents traces of ossification, often by two or more centers. One of these, the OS acetabuli, appears about the age of twelve, between the ilium and pubis, and fuses with them about the age of eighteen; it forms the pubic part of the acetabulum. The iUum and ischium then become joined, and lastly the pubis and ischium, through the intervention of this Y-shaped portion. At about the age of puberty, ossification takes place in each of the remaining porti(ms, and they join with the rest of the bone between the twentieth and twenty-fifth years. Separate centers are frequently found for the pubic tubercle and the ischial spine, and for the crest and angle of the pubis. Articulations. — The hip bone articulates with its fellow of the opposite side, and with the sacrum and femur. By eight centers \ ^^''^^ primary {Ilium. lacUum. and Pvhia) . " " I Five secondary (J. ^^^''^^i* i'.Tui'*' Fig. 237. — Plan of ossification of the hip bone. The three primary centers unite through a Y-shaped piece about puberty. Epiphyses appear about puberty, and unite about twenty-fifth year. The Pelvis. The pelvis, so called from its resemblance to a basin, is a bony ring, interposed between the movable vertebrae of the vertebral column which it supports, and the lower limbs upon which it rests; it is stronger and more massively constructed than the wall of the cranial or thoracic cavities, and is composed of four bones: the two hip bones laterally and in front and the sacrum and cocc3rx behind. The pelvis is divided by an oblique plane passing through the prominence of the sacrum, the arcuate and pectineal lines, and the upper margin of the symphysis pubis, into the greater and the lesser pelvis. The circumference of this plane is termed the linea terminaUs or pelvic brim. The Greater or False Pelvis (pelvis major). — The greater pelvis is the expanded portion of the cavity situated above and in front of the pelvic brim. It is bounded on either side by the ilium; in front it is incomplete, presenting a wide interval between the anterior borders of the ilia, which is filled up in the fresh state by THE PELVIS 239 the parietes of the abdomen; behind is a deep notch on either side between the ilium and the base of the sacrum." It supports the intestines, and transmits part of their weight to the anterior wall of the abdomen. The Lesser or True Pelvis {pelvis minor). — The lesser pelvis is that part of the pelvic cavity which is situated below and behind the pelvic brim. Its bony walls are more complete than those of the greater pehis. For convenience of descrip- tion, it is divided into an inlet bounded by the superior circumference, and outlet bounded by the inferior circumference, and a cavity. The Superior Circumference. — The superior circumference forms the brim of the pelvis, the included space being called the superior aperture or inlet (apertura pelvis [yninoris] superior) (Fig. 238). It is formed laterally by the pectineal and arcuate lines, in front by the crests of the pubes, and behind by the anterior margin of the base of the sacrum and sacrovertebral angle. The superior aperture is somewhat heart-shaped, obtusely pointed in front, diverging on either side, and encroached upon behind by the projection forward of the promontory of the sacrum. It has three principal diameters: antero-posterior, transverse, and oblique. The antero- posterior or conjugate diameter extends from the sacrovertebral angle to the sym- fi I I Fig. 238. — Diameters of superior aperture of lesser pelvis (female). physis pubis; its average measurement is about 110 mm. in the female. The t'ansverse diameter extends across the greatest width of the superior aperture, from the middle of the brim on one side to the same point on the opposite; its aver- age measurement is about 135 mm. in the female. The oblique diameter extends from the iliopectineal eminence of one side to the sacroiliac articulation of the pposite side; its average measurement is about 125 mm. in the female. The cavity of the lesser pelvis is bounded in front and below by the pubic sym- 'hysis and the superior rami of the pubes; above and behind, by the pelvic surfaces of the sacrum and coccyx, which, cijrving forward above and below, contract the superior and inferior apertures of the cavity; laterally, by a broad, smooth, quadrangular area of bone, corresponding to the inner surfaces of the body and superior ramus of the ischium and that part of the ilium which is below the arcuate line. From this description it will be seen that the cavity of the lesser pelvis hi a short, curved canal, considerably deeper on its posterior than on its anterior v/all. It contains, in the fresh subject, the pelvic colon, rectum, bladder, and some of the organs of generation. The rectum is placed at the back of the pelvis, in the curve of the sacrum and coccyx; the bladder is in front, behind the pubic sym- physis. In the female the uterus and vagina occupy the interval between these viscera. 240 OSTEOLOGY The Lower Circumference. — The lower circumference of the pelvis is very irregu ar; the space enclosed by it is named the inferior aperture or outlet {apertura pelvis [minoris] inferior) (Fig. 239), and is bounded behind by the point of the coccyx, and laterally by the ischial tuberosities. These eminences are separated by three notches: one in front, the pubic arch, formed by the convergence of the inferior Fia. 239. — Diameters of inferior aperture of lesser pelvis (female). rami of the ischium and pubis on either side. The other notches, one on either side, are formed by the sacrum and coccyx behind, the ischium in front, and the ilium above; they are called the sciatic notches; in the natural state they are converted into foramina by the sacrotuberous and sacrospinous ligaments. When the ligaments are in situ, the inferior aperture of the pelvis is lozenge-shaped, bounded, in front, by the pubic arcuate ligament and the inferior rami of the pubes and ischia; later- ally, by the ischial tuberosities; and behind, by the sacrotuberous ligaments and the tip of the coccyx. The diameters of the outlet of the pelvis are two, antero-posterior and transverse. The antero-posterior diameter extends from the tip of the coccyx to the lower part of the pubic symphysis; its measurement is from 90 to 115 mm. in the female. It varies with the length of the coccyx, and is capable of increase or diminution, on account of the mobility of that bone. The transverse diameter, measured between the posterior parts of the ischial tuberosities, is about 115 mm. in the female.* Axes (Fig. 240). — A Hne at right angles to the plane of the superior aperture at its center would, if prolonged, pass through the umbilicus above and the middle of the coccyx below ; the axis of the superior aperture is therefore directed downward and backward. The axis of the inferior aperture, produced upward, would touch the base of the sacrum, and is also directed downward, and slightly backward. The axis of the cavity — i. e., an axis at right angles to a series of planes between those of the superior and inferior apertures ' The measurements of the pelvis given above are fairly accurate, but different figures are given by various authors no doubt due mainly to differences in the physique and stature of the population from whom the measurements have been taken. Fia. 240. -Median sagittal section of pelvis. — is curved like the cavity itself: this curve corresponds to the concavity of the sacrum and coccyx, the extremities being indicated by the central points of the superior and inferior apertures. A knowledge of the direction of these axes serves to explain the course of the fetus in its passage through the pelvis during parturition. Position of the Pelvis (Fig. 240). — In the erect posture, the pelvis is placed obliquely with regard to the trunk : the plane of the superior aperture forms an angle of from 50° to 60°, and that of the inferior aperture one of about 15° with the horizontal plane. The pelvic surface of the symphysis pubis looks upward and backward, the concavity of the sacrum and coccyx downward and forward. The position of the pelvis in the erect posture may be indicated by holding it so that the anterior superior iliac spines and the front of the top of the symphysis pubis are in the same vertical plane. Fig. 241. — Male pelvis. Differences between the Male and Female Pelves. — The female pelvis (Fig. 1'42) is distinguished from that of the male (Fig. 241) by its bones being more ing at a distance from the neutral axis. This conforms to the requirement of mechanics I ■or economy, as a minimum of material is provided for resisting shearing stresses where these I .stresses are a minimum. 2. Economy for resisting bending moment. "The bending moment increases from a minimum [.it section 4 to a maximum between sections 16 and 18, then gradually decreases almost uniformly X) near section 75." "To resist bending moment stresses most effectively the material should 06 as far from the neutral axis as possible." It is evident that the hollow shaft of the femur is in efficient sti-ucture for resisting bending moment stresses, all of the material in the shaft being •elatively at a considerable distance from the neutral axis. It is evident that the hollow shaft jrovides efficiently for resisting bending moment not only due to the load on the femur-head, but Tom any other loads tending to produce bending in other planes. 3. Economy for resisting axial stress. The inner architecture of the shaft is adapted to resist in the most efficient manner the com- oined action of the minimal shearing forces and the axial and maximum bending stre.sses. The structure of the shaft is such as to secure great strength with a relatively small amount of Jiaterial. The Distal Portion of the Femur.— In frontal section (Fig. 249) in the distal 6 inches of the "emur "there are to be seen two main systems of trabeculse, a longitudinal and a transverse [;jystem. The trabeculse of the former rise from the inner wall of the shaft and continue in per- "ectly straight lines parallel to the axis of the shaft and proceed to the epiphyseal line, whence phey continue in more or less curved lines to meet the articular surface of the knee-joint at right kiingles at every point. Near the center there are a few thin, delicate, longitudinal trabecula; rjehich spring from the longitudinal trabeculse just described, to which they are joined by fine jiiransverse filaments that lie in planes parallel to the sagittal plane. "The trabeculse of the transverse sj'stem are somewhat lighter in structure than those of the longitudinal system, and consist of numerous trabeculse at right angles to the lattef. "As the distal end of the femur is approached the shaft gradually becomes thinner until the [iirticular surface is reached, where there remains only a thin shell of compact bone. With the radual thinning of the compact bone of the shaft, there is a simultaneous increase in the amount [of the spongy bone, and a gradual flaring of the femur which gives this portion of the bone a radually increasing gross area of cross-section. "There is a marked thickening of the shell of bone in the region of the intercondyloid fossa [where the anterior and posterior crucial ligaments are attached. This thickened area is about 254 OSTEOLOGY Appears at 4:th year ; joins body about ISth yr. Appears at end of 1st yr. ; joins body about ISth yr. Appears ISth-lith year ; joins body about 18th year Joins body at 20th year Appears at 9th month of fetal life Lower extremity Fig. 252. — Plan of ossification of the femur. five centers. From 0.4 inch iri diameter and consists of compac bone from which a number of thick trabeci Uae'' pass at right angles to the main longitudinal system. The inner structure of the bone is here evidently adapted to the efficient distribution of the stresses arising from this ligamentary at- tachment. "Near the distal end of the femur the longi- tudinal trabecular gradually assume curved paths and end perpendicularly to the articular surface at every point. Such a structure is in accordance with the principles of mechanics, as stresses can be communicated througli a frictionless joint only in a direction perpendic- ular to the joint surface at every point. "With practically no increase in the amount of bony material used, there is a greatly increased stability produced by the expansion of the lower femur from a hollow shaft of compact bone to a structure of much larger cross-section almost entirely composed of spongy bone. "Significance of the Inner Architecture of the Distal Part of the Femur. — The function of the lower end of the femur is to transmit through a hinged joint the loads carried by the femur. For stability the width of the bearing on which the hinge action occurs should be relatively large. For economy of material the expansion of the end bearing should be as lightly constructed as is consistent with proper strength. In accordance with the principles of mechanics , Fig. 253. — Epiphysial lines of femur in a young adult. Anterior aspect. The lines of attachment of the articular capsules are in blue. Fig. 254. — Epiphysial lines of femur in a young adult. Posterior aspect. The lines of attachment of the articular capsules are in blue. THE PATELLA 255 The Patella (Ejiee Cap). the most efficient manner in which stresses are transmitted is by the arrangement of the resist- ing material in lines parallel to the direction in which the stresses occur and in the paths taken b}' the stresses. Theoretically the most efficient manner to attain these objects would be to pro- long the innermost filaments of the bone as straight lines parallel to the longitudinal axis of the bone, and gradually to flare the outer shell of compact bone outward, and continuing to give ofr filaments of bone parallel to the longitudinal axis as the distal end of the femur is approached. Tliese filaments should be well-braced transversely and each should carry its proportionate part of the total load, parallel to the longitudinal axis, transmitting it eventually to the articular surface, and in a direction perpendicular to that surface." Referring to Fig. 249, it is seen that the large expansion of the bone is produced by the gradual transition of the hollow shaft of compact bone to cancellated bone, resulting in the production of a much larger volume. The trabecular are given off from the shaft in lines parallel to the longitudinal axis, and are braced transversely by two series of trabeculae at right angles to each other, in the same manner as required theoretically for economy. Although the action of the muscles exerts an appreciable effect on the stresses in the femur, it is relatively small and very complex to analyze and has not been considered in the above analj'sis. Ossification (Figs. 252, 253, 254). — The femur is ossified from jive centers: one for the body, one for the head, one for each trochanter, and one for the lower extremity. Of all the long bones, except the clavicle, it is the first to show traces of ossification; this commences in the middle of the body, at about the seventh week of fetal life, and rapidly extends upw^frd and downward. The centers in the epiphyses appear in the following order : in the lower end of the bone, at the ninth month of fetal life (from this center the condyles and epicondyles are formed) ; in the head, at the end of the first year after birth; in the greater trochanter, during the fourth year; and in the lesser trochanter, between the thirteenth and fourteenth years. The order in which the epiphyses are joined to the body is the reverse of that of their appearance; they are not united uritil after puberty, the lesser trochanter being first joined, then the greater, then the head, and, lastly, the inferior extremity, which is not united until the twentieth year. The patella (Figs. 255, 25G) is a flat, triangular bone, situated on the front of tj e knee-joint. It is usually regarded as a sesamoid bone, developed in the tendon of the Quadriceps femoris, and resembles these bones (1) in bresents a deep notch form.ed by the commencement of the peroneal sulcus. The posterior surface is smooth, triangular, and concavo-convex, for articulation with the anterior surface of the calcaneus; its infero-medial angle projects backward as a process which underlies and supports the anterior end of the calcaneus. The anterior surface, of smaller size, but also irregularly triangular, is divided by a vertical ridge into two facets: the medial, quadrilateral in form, articulates with the fourth metatarsal; the lateral, larger and more triangular, articulates with the fifth. The medial surface is broad, irregularly quadrilateral, and presents at its middle and upper part a smooth oval facet, for articulation with the third I 270 OSTEOLOGY cuneiform; and behind this (occasionally) a smaller facet, for articulation with the navicular; it is rough in the rest of its extent, for the attachment of strong interosseous ligaments. Articulations. — The cuboid articulates with /our bones: the calcaneus, third cuneiform, jind fourth and fifth metatarsals; occasionally with a fifth, the navicular. The Navicular Bone {os naviculare pedis; scaphoid bone) (Figs. 276, 277). — The navicular bone is situated at the medial side of the tarsus, between the talus behind and the cuneiform bones in front. For 1st cuneijorm For 2iid cuneiforvi For 3rd cuneiform Fig. 276.— The left naviciilar. Occasional facet for cvboid Antero-lateral view. For talus Tuberosity Fig. 277. — Theleft navicular. Postero-niedialview. Surfaces. — The anterior surface is convex from side to side, and subdivided by two ridges into three facets, for articulation with the three cuneiform bones. The posterior surface is oval, concave, broader laterally than medially, and articulates with the rounded head of the talus. The dorsal surface is convex from side to side, and rough for the attachment of ligaments. The plantar surface is irregular, and also rough for the attachment of ligaments. The medial surface presents a rounded tuberosity, the lower part of which Fcr 2nd For gives attachment to part of the For 1st metatarsal metatarsal 2nd cuneiform tendon of the Tibialis posterior. The lateral surface is rough and irregular for the attachment of ligaments, and occasionally pre- sents a small facet for articula- tion with the cuboid bone. Articulations. — Thenavicular articu- lates with four bones: the talus and the three cuneiforms; occasionally with a fifth, the cuboid. For tendon of Tibialis anterior For navicular Fig. 278. — The left first cunei- form. Antero-medial view. The First Cuneiform Bone {os cvneiform privium; internal ciinei- ''form.''-roSrifii\?;fi vTw'- fomi) (Figs. 278, _279).-The first cuneiform bone is the largest of the three cuneiforms. It is situated at the medial side of the foot, between the navicular behind and the base of the first metatarsal in front. Surf aces.^ — ^Tlie medial surface is subcutaneous, broad, and quadrilateral ; at its anterior plantar angle is a smooth oval impression, into which part of the tendon of the Tibialis anterior is inserted; in the rest of its extent it is rough for the attachment of ligaments. The lateral surface is concave, presenting, along its superior and posterior borders a narrow F-shaped surface, the vertical limb and posterior part of the horizontal limb of which articulate with the second cuneiform, while the anterior part of the horizontal limb articulates with the second metatarsal THE TARSUS 271 bone : the rest of this surface is rough for the attachment of ligaments and part of the tendon of the Peronaeus longus. The anterior surface, kidney-shaped and much larger than the posterior, articulates with the first metatarsal bone. The posterior surface is triangular, concave, and articulates with the most medial and largest of the three facets on the anterior surface of the navicular. The plantar surface is rough, and forms the base of the wedge; at its back part is a tuberosity for the insertion of part of the tendon of the Tibialis posterior. It also gives insertion in front to part of the tendon of the Tibialis anterior. The dorsal surface is the narrow end of the wedge, and is directed upward and lateralward; it is rough for the attachment of ligaments. Articulations. — The first cuneiform articulates with four bones: the navicular, second cunei- form, and first and second metatarsals. The Second Cuneiform Bone (os cuneiforme secundum; middle cuneiform) (Figs. 280, 281).— The second cuneiform bone, the smallest of the three, is of very reg- ular wedge-like form, the thin end being directed downward. It is situated between the other two cuneiforms, and articulates with the navicular behind, and the second metatarsal in front. - Surfaces. — The anterior surface, triangular in form, and narrower than the pos- terior, articulates with the base of the second metatarsal bone. The posterior sur- face, also triangular, articulates with the intermediate facet on the anterior surface of the navicular. The medial surface carries an L-shaped articular facet, running along the superior and posterior borders, for articulation w^ith the first cuneiform, and is rough in the rest of its extent for the attachment of ligaments. The lateral For 1st cuneiform For navicular For 2nd metatarsal For 3rd cuneiform Fig. 280.— The left second ctineiform. An t ero-media 1 vi 'w. Fig. 281.— The left second cuneiform. Pos- tero-lateral view. surface presents posteriorly a smooth facet for articulation with the third cuneiform bone. The dorsal surface forms the base of the wedge; it is quadrilateral and rough for the at- tachment of ligaments. The plantar surface, sharp and tuberculated, is also rough for the attachment of ligaments, and for the insertion of a slip from the tendon of the Tibialis posterior. Articulations. — The second cuneiform articulates with four bones: the navicular, first and tl ird cuneiforms, and second metatarsal. The Third Cuneiform Bone {os cuneiforme iertium; external cuneiform) (Figs. 282, 2S3). — The third cuneiform bone, intermediate in size between the two preceding, is wedge-shaped, the base being uppermost. It occupies the center of the front row ol the tarsal bones, between the second cuneiform medially, the cuboid laterally, the navicular behind, and the third metatarsal in front. Surfaces. — The anterior surface, triangular in form, articulates with the third metatarsal bone. The posterior surface articulates with the lateral facet on the anterior surface of the navicular, and is rough below for the attachment of liga- mentous fibers. The medial surface presents an anterior and a posterior articular facet, separated by a rough depression: the anterior, sometimes divided, articulates with the lateral side of the base of the second metatarsal bone; the posterior skirts tl e posterior border, and articulates with the second cuneiform; the rough depres- sion gives attachment to an interosseous ligament. The lateral surface also pre- sents two articular facets, separated by a rough non-articular area; the anterior facet, situated at the superior angle of the bone, is small and semi-oval in shape, and articulates with the medial side of the base of the fourth metatarsal bone; 272 OSTEOLOGY the posterior and larger one is triangular or oval, and articulates with the cuboid; the rough, non-articular area serves for the attachment of an interosseous ligament. The three facets for articulation with the three metatarsal bones are continuous with one another; those for articulation with the second cuneiform and navicular are also continuous, but that for articulation with the cuboid is usually separate. The dorsal surface is of an oblong form, its postero-lateral angle being prolonged backward. The plantar surface is a rounded margin, and serves for the attachment of part of the tendon of the Tibialis posterior, part of the Flexor hallucis brevis, and ligaments. Articulations. — ^The third cuneiform articulates with six bones: form, cuboid, and second, third, and fourth metatarsals. the navicular, second cunei- For navicular For 2nd cuneiform For cuboid Fig. 282. — The left third cuneiform, view. For 2nd metatarsal Postero-medial Fig. Forird metatarsal 283. — The third left cuneiform, lateral view. Antero- The Metatarsus. The metatarsus consists of five bones which are numbered from the medial side {ossa metatarsalia I.-V.); each presents for examination a body and two extremities. Common Characteristics of the Metatarsal Bones. — The body is prismoid in form, tapers gradually from the tarsal to the phalangeal extremity, and is curved longitudinally, so as to be concave below, slightly convex above. The base or posterior extremity is wedge-shaped, articulating proximally with the tarsal bones, and by its sides with the contiguous metatarsal bones: its dorsal and plantar surfaces are rough for the attachment of ligaments. The head or anterior extremity presents a convex articular surface, oblong from above downward, and extend- ing farther backward below than above. Its sides are flattened, and on each is a depression, surmounted by a tubercle, for ligamentous attachment. Its plantar surface is grooved antero-posteriorly for the passage of the Flexor tendons, and marked on either side by an articular eminence continuous with the terminal articular surface. Characteristics of the Individual Metatarsal Bones. — The First Metatarsal Bone (os metatarsale I; metatarsal bone of the great toe) (Fig. 284). — The first metatarsal bone is remarkable for its great thickness, and is the shortest of the metatarsal bones. The body is strong, and of well-marked prismoid form. The base presents, as a rule, no articular facets on its sides, but occasionally on the lateral side there is an oval facet, by which it articulates with the second metatarsal. Its proximal articular surface is of large size and kidney-shaped; its circumference is grooved, for the tarsometatarsal ligaments, and medially gives insertion to part of the tendon of the Tibialis anterior; its plantar angle presents a rough oval prominence for the insertion of the tendon of the Peronseus longus. The head is large; on its plantar surface are two grooved facets, on which glide sesamoid bones; the facets are separated by a smooth elevation. THE METATARSUS 273 The Second Metatarsal Bone {os metatarsale II) (Fig. 285). — The second meta- tarsal bone is the longest of the metatarsal bones, being prolonged backward For sesamoid bones For 1st For PeroruBfua CU7ieiform Umgus Fig. 284.— The first metatarsal. (Left.) Fm 1st cuneiform For 2nd For 'Srd cuneiform cuneiform Fig. 285. — The second metatarsal. (Left.) For 2nd metatarsal I For 2nd For meta- 3rd tarsal cuneiform For Ath metatarsal Fig. 286.— The third metatarsal. (Left.) For Srd metatarsal For cuboid For 3rd cuneiform For 5th metatarsal Fig. 287. — The fourth metatarsal. (Left.) into the recess formed by the three cuneiform bones. Its base is broad above, narrow and rough below. It presents four articular surfaces: one behind, of a triangular form, for articulation with the second cuneiform; one at the upper part IS 274 OSTEOLOGY I of its medial surface, for articulation with the first cuneiform; and two on its lat(;ral surface, an upper and lower, separated by a rough non-articular interval. Each of these lateral articular surfaces is divided into two by a vertical ridge; the two anterior facets articulate with the third metatarsal; the two posterior (sometiraes continuous) with the third cuneiform. A fifth facet is occasionally present for articulation with the first metatarsal; it is oval in shape, and is situated on the medial side of the body near the base. The Third Metatarsal Bone {os metatarsale III) (Fig. 286). — The third meta- tarsal bone articulates proximally, by means of a triangular smooth surface, with the third cuneiform; medially, by two facets, with the second metatarsal; and laterally, by a single facet, with the fourth metatarsal. This last facet is situated at the dorsal angle of the base. iir P. For Uk metatarsal For cuboid Tuberosity Fia. 288.— The fifth metatarsal. (Left.) The Fourth Metatarsal Bone {os metatarsale IV) (Fig. 2 According to Bruch, the sternal end of the clavicle is covered by a tissue which is fibrous rather than cartilaginous in structure. 314 SYNDESMOLOGY part of the sternal end of the clavicle, and, passing obliquely downward and medialward, is fixed below to the back of the upper part of the manubrium sterni. It is in relation, in front, with the articular disk and synovial membranes; behind, ^- with the Sternohyoideus and Sternothyreoideus. H The Interclavicular Ligament (ligamentum inierclaviculare) . — This ligament is a ™ flattened band, which varies considerably in form and size in diflferent individuals, it passes in a curved direction from the upper part of the sternal end of one clavicle to that of the other, and is also attached to the upper margin of the sternum. It is in relation, in frojit, with, the integument and Sternocleidomastoidei ; behind, with the Sternothyreoidei. H The Costoclavicular Ligament (ligamentum costoclavicular e; rhomboid ligament). — ^| This ligament is short, flat, strong, and rhomboid in form. Attached below to the upper and medial part of the cartilage of the first rib, it ascends obliquely backward and lateralw ard, and is fixed above to the costal tuberosity on the under surface of the clavicle. It is in relation, in front, with the tendon of origin of the Subclavius; behind, with the subclavian vein. m\ Fig. 325. — Sternoclavicular articulation. An terior view. The Articular Disk (discus articularis) . — The articular disk is flat and nearly circular, interposed between the articulating surfaces of the sternum and clavicle. It is attached, above, to the upper and posterior border of the articular surface of the clavicle; below, to the cartilage of the first rib, near its junction with the sternum; and by its circumference to the interclavicular and anterior and posterior sterno- clavicular ligaments. It is thicker at the circumference, especially its upper and back part, than at its center. It divides the joint into two cavities, each of which is furnished with a synovial membrane. Synovial Membranes. — Of the two synovial membranes found in this articulation, the lateral is reflected from the sternal end of the clavicle, over the adjacent sui-face of the articular disk, and around the margin of the facet on the cartilage of the first rib ; the medial is attached to the margin of the articular surface of the sternum and clothes the adjacent surface of the articular disk; the latter is the larger of the two. Movements. — This articulation admits of a limited amount of motion in nearly every direc- tion — upward, downward, backward, forward, as well as circumduction. When these move- ments take place in the joint, the clavicle in its motion carries the scapula with it, this bone gliding on the outer surface of the chest. This joint therefore forms the center from which all movements of the supporting arch of the shoulder originate, and is the only point of articulation of the shoulder girdle with the trunk. The movements attendant on elevation and depression of the shoulder take place between the clavicle and the articular disk, the bone rotating upon the ligament on an axis drawn from before backward through its own articular facet; when the shoulder is moved forward and backward, the clavicle, with the articular disk rolls to and fro on the A C ROM IOC LA VIC ULAR ARTIC ULA TION 315 articular surface of the sternum, revolving, with a sliding movement, around an axis drawn nearly vertically through the sternum; in the circumduction of the shoulder, which is compounded of these two movements, the clavicle revolves upon the articular disk and the latter, with the clavicle, rolls upon the sternum.^ Elevation of the shoulder is limited principally by the costoclavicular hgament; depression, by the interclavicular ligament and articular disk. The muscles which raise the shoulder are the upper fibers of the Trapezius, the Levator scapulae, and the clavicular head of the Sternocleidomastoideus, assisted to a certain extent by the Rhomboidei, which pull the vertebral border of the scapula backward and upward and so raise the shoulder. The depres- sion of the shoulder is principally effected by gravity assisted by the Subclavius, Pectoralis minor and lower fibers of the Trapezius. The shoulder is drawn backward by the Rhomboidei and the middle and lower fibers of the Trapezius, and forward by the Serratus anterior and Pectoralis n. Acromioclavicular Articulation (Articulatio Acromioclavicularis ; Scapulo- clavicular Articulation) (Fig. 326). The acromioclavicular articulation is an arthrodial joint between the acromial end of the clavicle and the medial margin of the acromion of the scapula. Its ligaments are: The Articular Capsule. The Articular Disk. The Superior Acromioclavicular. rr-i /^ i • i /Trapezoid and ^ Ihe Coracociavicular i >^_ -j The Inferior Acromioclavicular. I Conoid. The Articular Capsule {capsula articularis; capsular ligament). — The articular capsule completely surrounds the articular margins, and is strengthened above and below by the superior and inferior acromioclavicular ligaments. The Superior Acromioclavicular Ligament (ligamentum acromioclamculare) . — This ligament is a quadrilateral band, covering the superior part of the articula- tion, and extending between the upper part of the acromial end of the clavicle and the adjoining part of the upper surface of the acromion. It is composed of parallel fibers, which interlace with the aponeuroses of the Trapezius and Deltoideus; below, it is in contact with the articular disk when this is present. The Inferior Acromioclavicular Ligament. — This ligament is somewhat thinner than the preceding; it covers the under part of the articulation, and is attached to the adjoining surfaces of the two bones. It is in relation, above, in rare cases with the articular disk ; below, with the tendon of the Supraspinatus. The Articular Disk (discus articularis). — The articular disk is frequently absent in this articulation. When present, it generally only partially separates the artic- ular surfaces, and occupies the upper part of the articulation. More rarely, it completely divides the joint into two cavities. The Synovial Membrane. — There is usually only one synovial membrane in this articulation, but when a complete articular disk is present, there are two. The Coracoclavicular Ligament (ligamentum coracoclaviculare) (Fig. 326). — This ligament serves to connect the clavicle with the coracoid process of the scapula. It does not properly belong to this articulation, but is usually described with it, since it forms a most efficient means of retaining the clavicle in contact with the acromion. It consists of two fasciculi, called the trapezoid and conoid ligaments. The Trapezoid Ligament (ligamentum trapezoidewn) , the anterior and lateral fas- ciculus, is broad, thin, and quadrilateral: it is placed obliquely between the cora- coid process and the clavicle. It is attached, below, to the upper surface of the coracoid process; above, to the oblique ridge on the under surface of the clavicle. Its anterior border is free; its posterior border is joined with the conoid ligament, the two forming, by their junction, an angle projecting backward. The Conoid Ligament (ligamentum conoideum), the posterior and medial fasciculus, is a dense band of fibers, conical in form, with its base directed upward. It is 1 Humphry, On the Human Skeleton, page 402. 316 SYNDESMOLOGY attached by its apex to a rough impression at the base of the coracoid process, medial to the trapezoid ligament; above, by its expanded base, to the coracoid tuberosity on the under surface of the clavicle, and to a line proceeding medial- ward from it for 1.25 cm. These ligaments are in relation, in front, with the Subclavius and Deltoideus ; behind, with the Trapezius. Fig. 326. — The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula. Movements. — The movements of this articulation are of two kinds: (1) a gliding motion of the articular end of the clavicle on the acromion; (2) rotation of the scapula forward and back- ward upon the clavicle. The extent of this rotation is limited by the two portions of the coraco- clavicular Ugament, the trapezoid limiting rotation forward, and the conoid backward. The acromioclavicular joint has important functions in the movements of the upper extremity. It has been well pointed out by Humphry, that if there had been no joint between the clavicle and scapula, the circular movement of the scapula on the ribs (as in throwing the shoulders back- ward or forward) would have been attended with a greater alteration in the direction of the shoulder than is consistent with the free use of the arm in such positions, and it would have been impossible to give a blow straight forward with the fuU force of the arm; that is to say, with the combined force of the scapula, arm, and forearm. "This joint," as he happily says, "is so adjusted as to enable either bone to turn in a hinge-Uke manner upon a vertical axis drawn through the other, and it permits the surfaces of the scapula, hke the baskets in a roundabout swing, to look the same way in every position, or nearly so." Again, when the whole arch formed by the clavicle and scapula rises and falls (in elevation or depression of the shoulder), the joint between these two bones enables the scapula still to maintain its lower part in contact with the ribs. THE LIGAMENTS OF THE SCAPULA. The ligaments of the scapula (Fig. 326) are : Coracoacromial, Superior and Inferior Transverse. The Coracoacromial Ligament {ligamentum coracoacromiale) . — This ligament is a strong triangular band, extending between the coracoid process and the acromion. HUMERAL ARTICULATION OR SHOULDER-JOINT 317 It is attached, by its apex, to the summit of the acromion just in front of the articular surface for the clavicle; and by its broad base to the whole length of the lateral border of the coracoid process. This ligament, together with the coracoid process and the acromion, forms a vault for the protection of the head of the humerus. It is in relation, above, with the clavicle and under surface of the Del- toideus; beloiv, with the tendon of the Supraspinatus, a bursa being interposed. Its lateral border is continuous with a dense lamina that passes beneath the Del- toideus upon the tendons of the Supraspinatus and Infraspinatus. The ligament is sometimes described as consisting of two marginal bands and a thinner inter- vening portion, the two bands being attached respectively to the apex and the base of the coracoid process, and joining together at the acromion. When the Pectoralis minor is inserted, as occasionally is the case, into the capsule of the shoulder-joint instead of into the coracoid process, it passes between these two bands, and the intervening portion of the ligament is then deficient. The Superior Transverse Ligament (ligamentum transversum scapulcB swperius; transverse or suprascapular ligavient). — This ligament converts the scapular notch into a foramen. It is a thin and flat fasciculus, narrower at the middle than at the extremities, attached by one end to the base of the coracoid process, and by the other to the medial end of the scapular notch. The suprascapular nerve runs through the foramen; the transverse scapular vessels cross over the ligament. The ligament is sometimes ossified. The Inferior Transverse Ligament {ligamentum transversum scapula' inferius; spinoglenoid ligament).— This ligament is a weak membranous band, situated behind the neck of the scapula and stretching from the lateral border of the spine to the margin of the glenoid cavity. It forms an arch under which the transverse scapular vessels and suprascapular nerve enter the infraspinatous fossa. in. Humeral Articulation or Shoulder- joint (Articulatio Humeri) (Fig. 326). The shoulder-joint is an enarthrodial or ball-and-socket joint. The bones entering into its formation are the hemispherical head of the humerus and the shallow glenoid cavity of the scapula, an arrangement which permits of very considerable movement, while the joint itself is protected against displacement by the tendons which surround it. The ligaments do not maintain the joint sur- faces in apposition, because when the}' alone remain the humerus can be separated to a considerable extent from the glenoid cavit}'; their use, therefore, is to limit the amount of movement. The joint is protected above by an arch, formed by the coracoid process, the acromion, and the coracoacromial ligament. The artic- ular cartilage on the head of the humerus is thicker at the center than at the cir- cumference, the reverse being the case with the articular cartilage of the glenoid cavity. The ligaments of the shoulder are: 'I ^ The Articular Capsule. The Coracohumeral. The Glenohumeral. The Transverse Humeral. The Glenoidal Labrum.^ The Articular Capsule (capsula articularis; capsular ligament) (Fig. 327). — The articular capsule completely encircles the joint, being attached, above, to the circumference of the glenoid cavity beyond the glenoidal labrum; below, to the anatomical neck of the humerus, approaching nearer to the articular cartilage above than in the rest of its extent. It is thicker above and below than elsewhere, and is so remarkably loose and lax, that it has no action in keeping the bones in contact, but allows them to be separated from each other more than 2.5 cm., an ' The long tendon of origin of the bicejjs Ijrachii also acts as one of the ligaments of this joint. See the observations on page 287, on the function of the muscles passing over more than one joint. 318 SYNDESMOLOGY evident provision for that extreme freedom of movement which is pecuHar to this articulation. It is strengthened, above, by the Supraspinatus; below, by the long head of the Triceps brachii ; behind, by the tendons of the Infraspinatus and Teres minor; and in front, by the tendon of the Subscapularis. There are usually three openings in the capsule. One anteriorly, below the coracoid process, establishes a communication between the joint and a bursa beneath the tendon of the Sub- scapularis. The second, which is not constant, is at the posterior part, where an opening sometimes exists between the joint and a bursal sac under the tendon of the Infraspinatus. The third is between the tubercles of the humerus, for the passage of the long tendon of the Biceps brachii. The Coracohmneral Ligament {ligamentum coracohwnerale) . — This ligament is a broad band which strengthens the upper part of the capsule. It arises from the lateral border of the coracoid process, and passes obliquely downward and lateralward to the front of the greater tubercle of the humerus, blending with the Superior transverse Ligament m Transverse humeral ligament Prolongation of synovial mem- brane on tendon of Biceps brachii m i Bursa under Svbscapularia Fia. 327. — Capsule of shoulder-joint (distended). Anterior aspect. tendon of the Supraspinatus. This ligament is intimately united to the capsule by its hinder and lower border; but its anterior and upper border presents a free edge, which overlaps the capsule. Glenohumeral Ligaments. — In addition to the coracohumeral ligament, three supplemental bands, which are named the glenohumeral ligaments, strengthen the capsule. These may be best seen by opening the capsule at the back of the joint and removing the head of the humerus. One on the medial side of the joint passes from the medial edge of the glenoid cavity to the lower part of the lesser tubercle of the humerus. A second at the lower part of the joint extends from the under edge of the glenoid cavity to the under part of the anatomical neck of the humerus. A third at the upper part of the joint is fixed above to the apex of the glenoid cavity close to the root of the coracoid process, and passing down- ward along the medial edge of the tendon of the Biceps brachii, is attached below to a small depression above the lesser tubercle of the humerus. In addition to HUMERAL ARTICULATION OR SHOULDER-JOINT 319 CONOID LIGAMENT TRAPEZOID LIGAMENT RACOIO PROCESS these, the capsule is strengthened in front by two bands derived from the tendons of the PectoraHs major and Teres major respectively. The Transverse Humeral Ligament (Fig. 327) is a broad band passing from the lesser to the greater tubercle of the humerus, and always limited to that portion of the bone which lies above the epiphysial line. It converts the intertubercular groove into a canal, and is the homologue of the strong process of bone which connects the summits of the two tubercles in the musk ox. The Glenoidal Labrum {labrimn glenoidale; glenoid ligament) is a fibrocartilaginous rim attached around the margin of the glenoid cavity. It is triangular on section, the base being fixed to the circumference of the cavity, while the free edge is thin and sharp. It is continuous above with the tendon of the long head of the Biceps brachii, w^hich gives off two fasciculi to blend with the fibrous tissue of the labrum. It deepens the articular cavity, and protects the edges of the bone. Synovial Membrane. — The synovial membrane is reflected from the margin of the glenoid cavity over the labrum; it is then reflected over the inner surface of the capsule, and covers the lower part and sides of the anatomical neck of the humerus as far as the articular cartilage on the head of the bone. The tendon of the long head of the Biceps brachii passes through the capsule and is enclosed in a tubular sheath of synovial membrane, which is reflected upon it from the summit of the glenoid cavity and is continued around the tendon into the intertubercular groove as far as the surgical neck of the humerus (Fig. 327). The tendon thus traverses the articulation, but it is not contained within the synovial cavity. Bursse. — The bursse in the neighborhood of the shoulder-joint are the following: (1) A constant bursa is situated between the tendon of the Subscapularis muscle and the capsule; it communicates with the synovial cavity thi'ough an opening in the front of the capsule; (2) a bursa which occasionally communicates with the joint is sometimes found between the tendon of the Infraspinatus and the capsule; (3) a large bursa exists between the under surface of the Deltoideus and the capsule, but does not communicate with the joint; this bursa is prolonged under the acromion and coraco- acromial ligament, and intervenes between these structures and the capsule; (4) a large bursa is situated on the summit of the acromion; (5) a bursa is frequently found between the cora- coid process and the capsule; (6) a bursa exists beneath the Coracobrachialis; (7) one lies between the Teres major and the long head of the Triceps brachii; (8) one is placed in front of, and another behind, the tendon of the Latissimus dorsi. The muscles in relation with the joint are, above, the Supraspinatus; below, the long head of the Triceps brachii; in front, the Subscapularis; behind, the Infraspinatus and Teres minor; within, the tendon of the long head of the Biceps brachii. The Deltoideus covers the articulation in front, behind, and laterally. The arteries supplying the joint are articular branches of the anterior and posterior humeral circumflex, and transverse scapular. The nerves are derived from the axillary and suprascapular. Movements. — The shoulder-joint is capable of every variety of movement, flexion, extension, abduction, adduction, circumduction, and rotation. The humerus is flexed (drawn forward) by the PectoraUs major, anterior fibers of the Deltoideus, Coracobrachialis, and when the fore- arm is flexed, by the Biceps brachii; extended (drawn backward) by the Latissimus dorsi, Teres major, posterior fibers of the Deltoideus, and, when the forearm is extended, by the Triceps brachii; it is abducted by the Deltoideus and Supraspinatus; it is adduded by the Subscapularis, PectoraUs major, Latissimus dorsi, and Teres major, and by the weight of the limb; it is rotated outward by the Infraspinatus and Teres minor; and it is rotated inward by the Subscapularis, Latissimus dorsi, Teres major, Pectoralis major, and the anterior fibers of the Deltoideus. The most striking peculiarities in this joint are: (1) The large size of the head of the humerus in comparison with the depth of the glenoid cavity, even when this latter is supplemented by the glenoidal labrum. (2) The looseness of the capsule of the joint. (3) The intimate connection of the capsule with the muscles attached to the head of the humerus. (4) The peculiar relation of the tendon of the long head of the Biceps brachii to the joint. Fig. 328. — Glenoid fossa of right side. 320 SYNDESMOLOGY It is in consequence of the relative sizes of the two articular surfaces, and the looseness Oi the articular capsule, that the joint enjoys such free movement in all directions. When thes& movements of the arm are arrested in the shoulder- joint by the contact of the bony surfaces, and by the tension of the fibers of the capsule, together with that of the muscles acting as accessory ligaments, the arm can be carried considerably farther by the movements of the scapula, involv- ing, of course, motion at the acromio- and sternoclavicular joints. These joints are therefore to be regarded as accessory structures to the shoulder-joint (see pages 314 and 316). The extent of the scapular movements is very considerable, especially in extreme elevation of the arm, u movement best accomphshed when the arm is thrown somewhat forward and outward, because; the margin of the head of the humerus is by no means a true circle; its greatest diameter is from the intertubercular groove, downward, medialward, and backward, and the greatest elevation of the arm can be obtained by rolling its articular surface in the direction of this measurement. The great width of the central portion of the humeral head also allows of very free horizontal movement when the arm is raised to a right angle, in which movement the arch formed by the acromion, the coracoid process and the coracoacromial ligament, constitutes a sort of supple- mental articular cavity for the head of the bone. The looseness of the capsule is so great that the arm will fall about 2.5 cm. from the scapula when the muscles are dissected from the capsule, and an opening made in it to counteract the atmospheric pressure. The movements of the joint, therefore, are not regulated by the capsule so much as by the surrounding muscles and by the pressure of the atmosphere, an arrangement which "renders the movements of the joint much more easy than they would otherwise have been, and permits a swinging, pendulum-hke vibration of the limb when the muscles are at rest" (Humphry). The fact, also, that in all ordinary positions of the joint the capsule is not put on the stretch, enables the arm to move freely in all directions. Extreme movements are checked by the tension of appropriate portions of the capsule, as well as by the interlocking of the bones. Thus it is said that "abduction is checked by the contact of the great tuberosity with the upper edge of the glenoid cavity; adduction by the tension of the coracohumeral ligament" (Beaunis et Bouchard). Cleland' maintains that the limitations of movement at the shoulder-joint are due to the structure of the joint itself, the glenoidal labrum fitting, in different positions of the elevated arm, into the anatomical neck of the humerus. The scapula is capable of being moved upward and downward, forward and backward, or, by a combination of these movements, circumducted on the wall of the chest. The muscles which raise the scapula are the upper fibers of the Trapezius, the Levator scapula", and the Rhomboidei; those which depress it are the lower fibers of the Trapezius, the Pectoralis minor, and, through the clavicle, the Subclavius. The scapula is drawn backward by the Rhomboidei and the middle and lower fibers of the Trapezius, and forward by the Serratus anterior and Pectoralis minor, assisted, when the arm is fixed, by the Pectoralis major. The mobility of the scapula is very considerable, and greatly assists the movements of the arm at the shoulder-joint. Thus, in raising the arm from the side, the Deltoideus and Supraspinatus can only lift it to a right angle with the trunk, the fvuther elevation of the limb being effected by the Trapezius and Serratus anterior moving the scapula on the wall of the chest. This mobility is of special importance in ankylosis of the shoulder- joint, the movements of this bone compensating to a veiy great extent for the immobility of the joint. Cathcart^ has pointed out that in abducting the arm and raising it above the head, the scapula rotates throughout the whole movement with the exception of a short space at the beginning and at the end; that the humerus moves on the scapula not only while passing from the hanging to the horizontal position, but also in travelling upward as it approaches the vertical above; that the clavicle moves not only during the second half of the movement but in the first as well, though to a less extent — i. e., the scapula and clavicle are concerned in the first stage as well as in the second; and that the humerus is partly involved in the second as well as chiefly in the first. The intimate union of the tendons of the Supraspinatus, Infraspinatus, Teres minor and Subscapularis with the capsule, converts these muscles into elastic and spontaneously acting ligaments of the joint. The pecuhar relations of the tendon of the long head of the Biceps brachii to the shoulder- joint appear to subserve various purposes. In the first place, by its connection with both the shoulder and elbow the muscle harmonizes the action of the two joints, and acts as an elastic ligament in all positions, in the manner previously discussed (see page 287). It strengthens the upper part of the articular cavity, and prevents the head of the humerus from being pressed up against the acromion, when the Deltoideus contracts; it thus fixes the head of the humerus as the center of motion in the glenoid cavity. By its passage along the intertubercular groove it assists in steadying the head of the humerus in the various movements of the arm. When the arm is raised from the side it assists the Supraspinatus and Infraspinatus in rotating the head of the humerus in the glenoid cavity. It also holds the head of the bone firmly in contact with the glenoid cavity, and prevents its slipping over its lower edge, or being displaced by the action of the Latissimus dorsi and Pectoralis major, as in climbing and many other movements. ' Journal of Anatomy and Physiology, 1867, i, 85. »Ibid.. 18S4, vol. xviii. ELBOW-JOINT 321 IV. Elbow-joint (Articulatio Cubiti) (Figs. 329, 330). The elbow-joint is a ginglymus or hinge-joint. The trochlea of the humerus is received into the semilunar notch of the ulna, and the capitulum of the humerus articulates with the fovea on the head of the radius. The articular surfaces are connected together by a capsule, which is thickened medially and laterally, and, to a less extent, in front and behind. These thickened portions are usually described as distinct ligaments under the following names: The Anterior. The Ulnar Collateral. The Posterior. The Radial Collateral. Fig. 329. — Left elbow-Joint, showing anterior and ulnar collateral ligaments. FiQ. 330. — Left elbow-joint, showing posterior and radial collateral ligaments. The Anterior Ligament (Fig. 329). — The anterior ligament is a broad and thin fibrous layer covering the anterior surface of the joint. It is attached to the front of the medial epicondyle and to the front of the humerus immediately above the coronoid and radial fossse; helow, to the anterior surface of the coronoid process of the ulna and to the annular ligament (page 324), being continuous on either side with the collateral ligaments. Its superficial fibers pass obliquely from the medial epicondyle of the humerus to the annular ligament. The middle fibers, vertical in direction, pass from the upper part of the coronoid depression and become partly blended with the preceding, but are inserted mainly into the anterior surface of the coronoid process. The deep or transverse set intersects these at right angles. This ligament is in relation, in front, with the Brachialis, except at its most lateral part. 21 322 ^^^^Br SYNDESMOLOGY The Posterior Ligament (Fig. 330). — This posterior ligament is thin ana mem branous, and consists of transverse and oblique fibers. Above, it is attached to the humerus immediately behind the capitulum and close to the medial margin of the trochlea, to the margins of the olecranon fossa, and to the back of the lateral epicondyle some little distance from the trochlea. Below, it is fixed to the upper and lateral margins of the olecranon, to the posterior part of the annular ligament, and to the ulna behind the radial notch. The transverse fibers form a strong band which bridges across the olecranon fossa; under cover of this band a pouch of synovial membrane and a pad of fat project into the upper part of the fossa when the joint is extended. In the fat are a few scattered fibrous bundles, which pass from the deep surface of the transverse band to the upper part of the fossa. This ligament is in relation, behind, with the tendon of the Triceps brachii and the Anconeus. The Ulnar Collateral Ligament (ligamentum collaterale ulnare; internal lateral ligament) (Fig. 329) . — This ligament is a thick triangular band consisting of two portions, an anterior and posterior united by a thinner intermediate portion. The anterior portion, directed obliquely forward, is attached, a6o«e, by its apex, to the front part of the medial epicondyle of the humerus; and, below, by its broad base to the medial margin of the coronoid process. The posterior portion, also of trian- gular form, is attached, above, by its apex, to the lower and back part of the medial epicondyle; below, to the medial margin of the olecranon. Between these two bands a few intermediate fibers descend from the medial epicondyle to blend with a transverse band which bridges across the notch between the olecranon and the coronoid process. This ligament is in relation with the Triceps brachii and Flexor carpi ulnaris and the ulnar nerve, and gives origin to part of the Flexor digitorum sublimis. The Radial Collateral Ligament {ligamentum collaterale radiate; external lateral ligament) (Fig. 330). — ^This ligament is a short and narrow fibrous band, less dis- tinct than the ulnar collateral, attached, above, to a depression below the lateral epicondyle of the humerus; below, to the annular ligament, some of its most pos- terior fibers passing over that ligament, to be inserted into the lateral margin of the ulna. It is intimately blended with the tendon of origin of the Supinator. Synovial Membrane (Figs. 331, 332). — The synovial membrane is very extensive. It extends from the margin of the articular siu"face of the humerus, and lines the coronoid, radial and olec- ranon fossae on that bone; it is reflected over the deep surface of the capsule and forms a pouch between the radial notch, the deep surface of the annular ligament, and the circumference of the head of the radius. Projecting between the radius and ulna into the cavity is a crescentic fold of synovial membrane, suggesting the division of the joint into two; one the humeroradial, the other the humeroulnar. Between the capsule and the synovial membrane are three masses of fat: the largest, over the olecranon fossa, is pressed into the fossa by the Triceps brachii during the flexion ; the second, over the coronoid fossa, and the third, over the radial fossa, are pressed by the Brachialis into their respective fossae during extension. The muscles in relation with the joint are, in front, the Brachiahs; behind, the Triceps brachii and Anconajus; laterally, the Supinator, and the common tendon of origin of the Extensor muscles; medially, the common tendon of origin of the Flexor muscles, and the Flexor carpi ulnaris. The arteries supplying the joint are derived from the anastomosis between the profunda and the superior and inferior ulnar collateral branches of the brachial, with the anterior, posterior, and interosseous recurrent branches of the ulnar, and the recurrent branch of the radial. These vessels form a complete anastomotic network around the joint. The nerves of the joint are a twig from the ulnar, as it passes between the medial condyle and the olecranon; a filament from the musculocutaneous, and two from the median. Movements. — The elbow-joint comprises three different portions — viz., the joint between the ulna and hmnerus, that between the head of the radius and the himierus, and the proximal radioulnar articulation, described below. AU these articular surfaces are enveloped by a common synovial membrane, and the movements of the whole joint should be studied together. The com- bination of the movements of flexion and extension of the forearm with those of pronation and supination of the hand, which is ensured by the two being performed at the same joint, is essential to the acciu-acy of the various minute movements of the hand. I ELBOW-JOINT 323 The portion of the joint between the ukia and humerus is a simple hinge-joint, and allows of movements of flexion and extension only. Owing to the obUquity of the trochlea of the humerus, this movement does not take place in the antero-posterior plane of the body of the humerus. When the forearm is extended and supinated, the axes of the arm and forearm are not in the same line; the arm forms an obtuse angle with the forearm, the hand and forearm being directed lateral- ward. During flexion, however, the forearm and the hand tend to approach the middle line of the body, and thus enable the hand to be easily carried to the face. The accurate adaptation of the trochlea of the humerus, with its prominences and depressions, to the semilunar notch of the ulna, prevents any lateral movement. Flexion is produced by the action of the Biceps brachii and Brachialis, assisted by the BrachioradiaUs and the muscles arising from the medial condyle of the humerus; extension, by the Triceps brachii and Ancona?us, assisted by the Extensors of the wrist, the Extensor digitorum commimis, and the Extensor digiti quinti proprius. Fio. 331. — Capsule of elbow-joint (distended). Anterior aspect. Fig. 332. — Capsule of elbow-joint (distended). Posterior aspect. The joint between the head of the radius and the capitulum of the humerus is an arthrodial joint. The bony surfaces would of themselves constitute an enarthrosis and allow of movement in all directions, were it not for the annular ligament, by which the head of the radius is boimd to thr radial notch of the ulna, and which prevents any separation of the two bones laterally. It is to the same ligament that the head of the radius owes its security from dislocation, which would otherwise tend to occur, from the shallowness of the cup-Uke surface on the head of the radius. In fact, but for this ligament, the tendon of the Biceps brachii would be hable to pull the head of the radius out of the joint. The head of the radius is not in complete contact with the capitulum of the humerus in all positions of the joint. The capitulima occupies only the anterior and inferior surfaces of the lower end of the humerus, so that in complete extension a part of the radial head can be plainly felt projecting at the back of the articulation. In full flexion the movement of the radial head is hampered by the compression of the surrounding soft parts, so that the freest rotatory movement of the radius on the humerus (pronation and supina- tion) takes place in semiflexion, in which position the two articular surfaces are in most intimate 524 SYNDESMOLOGY contact. Flexion and extension of the elbow-joint are limited by the tension of the structures on the front and back of the joint; the limitation of flexion is also aided by the soft structures of the arm and forearm coming into contact. In any position of flexion or extension, the radius, carrying the hand with it, can be rotated in the proximal radioulnar joint. The hand is directly articulated to the lower surface of the radius only, and the ulnar notch on the lower end of the radius travels around the lower end of the ulna. The latter bone is excluded from the wrist-joint by the articular disk. Thus, rotation of the head of the radius around an axis passing through the center of the radial head of the humerus imparts circular movement to the hand through a very considerable arc. V. Radioulnar Articulations (Articulatio Radioulnaris). The articulation of the radius with the ulna is effected by ligaments which co nect together the extremities as well as the bodies of these bones. The ligaments may, consequently, be subdivided into three sets: 1, those of the proximal radio- ulnar articulation; 2, the middle radioulnar ligaments; 3, those of the distal radio- ulnar articulation. Proximal Radioulnar Articulation (articulatio radioulnaris proximalis; superior radioulnar joint).— This articulation is a trochoid or pivot-joint between the circumference of the head of the radius and the ring formed by the radial notch of the ulna and the annular ligament. Head of radius Quadrate Semilunar (cut) ligament notch Annular ligament Radial Olecranon (ciii) Fig. 333. — Annular ligament of radius, from above. The head of the radius has been sawn off and the bone dislodged from the ligament. The Annular Ligament {ligamentum annulare radii; orbicular ligament) (Fig. 333). — This ligament is a strong band of fibers, which encircles the head of the radius, and retains it in contact with the radial notch of the ulna. It forms about four- fifths of the osseo-fibrous ring, and is attached to the anterior and posterior margins of the radial notch ; a few of its lower fibers are continued around below the cavity and form at this level a complete fibrous ring. Its upper border blends with the anterior and posterior ligaments of the elbow, while from its lower border a thin loose membrane passes to be attached to the neck of the radius; a thickened band which extends from the inferior border of the annular ligament below the radial notch to the neck of the radius is known as the quadrate ligament. The superficial surface of the annular ligament is strengthened by the radial collateral ligament of the elbow, and affords origin to part of the Supinator. Its deep surface is smooth, and lined by synovial membrane, which is continuous with that of the elbow-joint. I I II RADIOULNAR ARTICULATIONS 325 Movements. — The movements allowed in this articulation are limited to rotatory movements of the head of the radius within the ring formed by the annular ligament and the radial notch of the ulna; rotation forward being called pronation; rotation backward, supination. Supination is performed by the Biceps brachii and Supinator, assisted to a slight extent by the Extensor muscles of the thumb. Pronation is performed by the Pronator teres and Pronator quadratus. Middle Radioulnar Union. — The shafts of the radius and ulna are connected by the Oblique Cord and the Interosseous Membrane. The Oblique Cord {chorda ohliqua; oblique ligament) (Fig. 329). — The oblique cord is a small, flattened band, extending downward and lateral ward, from the lateral side of the tubercle of the ulna at the base of the coronoid process to the radius a little below the radial tuberosity. Its fibers run in the opposite direction to those of the interosseous membrane. It is sometimes wanting. The Interosseous Membrane {membrana interossea antebrachii) . — The interosseous membrane is a broad and thin plane of fibrous tissue descending obliquely down- ward and medialward, from the interosseous crest of the radius to that of the ulna; the lower part of the membrane is attached to the posterior of the two lines into which the interosseous crest of the radius divides. It is deficient above, commencing about 2.5 cm. beneath the tuberosity of the radius; is broader in the middle than at either end ; and presents an oval aperture a little above its lower margin for the passage of the volar interosseous vessels to the back of the forearm. This mem- brane serves to connect the bones, and to increase the extent of surface for the attachment of the deep muscles. Between its upper border and the oblique cord is a gap, through which the dorsal interosseous vessels pass. Two or three fibrous bands are occasionally found on the dorsal surface of this membrane; they descend obliquely from the ulna toward the radius, and have consequently a direction contrary to that of the other fibers. The membrane is in relation, in front, by its upper three-fourths, with the Flexor pollicis longus on the radial side, and with the Flexor digitorum profundus on the ulnar, lying in the interval between which are the volar interosseous vessels an(J nerve; by its lower fourth with the Pronator quadratus; behind, with the Supinator, Abductor pollicis longus. Extensor pollicis brevis. Extensor pollicis longus, Extensor indicis proprius; and, near the wrist, • with the volar interosseous artery and dorsal interosseous nerve. Distal Radioulnar Articulation (articidatio radioulnaris distalis; inferior radio- ulnar joint). — This is a pivot-joint formed between the head of the ulna and the uhiar notch on the lower end of the radius. The articular surfaces are connected together by the follo'^ving ligaments: The Volar Radioulnar. The Dorsal Radioulnar. The Articular Disk. The Volar Radioulnar Ligament {anterior radioulnar ligament) (Fig. 334). — This ligament is a narrow band of fibers extending from the anterior margin of the ulnar notch of the radius to the front of the head of the ulna. The Dorsal Radioulnar Ligament {posterior radioulnar ligament) (Fig. 335). — This ligament extends between corresponding surfaces on the dorsal aspect of the articulation. The Articular Disk {discus articularis; triangular fibrocartilage) (Fig. 336). — The articular disk is triangular in shape, and is placed transversely beneath the head of the ulna, binding the lower ends of the ulna and radius firmly together. Its periphery is thicker than its center, which is occasionally perforated. It is attached by its apex to a depression between the styloid process and the head of the ulna; and by its base, which is thin, to the prominent edge of the radius, which separates the ulnar notch from the carpal articular surface. Its margins are united to the ligaments of the wrist-joint. Its upper surface, smooth and concave, articulates with the head of the ulna, forming an arthrodial joint; its under surface, also con- I- 326 SYNDESMOLOGY cave and smooth, forms part of the wrist-joint and articulates with the trianguh bone and medial part of the lunate. Both surfaces are clothed by synovial mem-^ brane; the upper, by that of the distal radioulnar articulation, the under, by that of the wrist. Distal radio-vXnar articulation Wrist-joint IrUercarpal artictdaiions Pisohamate ligament Pisometacarpal ligament Carpometacar'pal articulaiions Fig. 334. — Ligaments of wrist. Anterior view Synovial Membrane (Fig. 336). — The synovial membrane of this articulation is extremely loose, and extends upward as a recess {recessus sacciformis) between the radius and the ulna. Distal radio-vlnar, articulation Wrist-joint Inlercarpal articvlations Carpometacarpcd articidationa Fig. 335. — Ligaments of wrist. Posterior view. Movements. — The movements in the distal radioulnar articulation consist of rotation of the lower end of the radius around an axis which passes through the center of the head of the ulna. When the radius rotates forward, 'pronation of the forearm and hand is the result; and when back- ward, supination. It will thus be seen that in pronation and supination the radius describes the RADIOCARPAL ARTICULATION WRIST-JOINT segment of a cone, the axis of which extends from the center of the head of the radius to the middle of the head of the ulna. In this movement the head of the ulna is not stationary, but describes a curve in a direction opposite to that taken by the head of the radius. This, however, is not to be regarded as a rotation of the ulna — the curve which the head of this bone describes is due to a combined antero-posterior and rotatory movement, the former taking place almost entirely at the elbow-joint, the latter at the shoulder-joint. Wrist-joint Madial collateral ligament Distal radioulnar articulation Articular disc Ulnar collateral ligament — Pisiform Fig. 336. — Vertical section through the articulations at the wrist, showing the synovial cavities. VI. Radiocarpal Articulation or Wrist-joint (Articulatio Radiocarpea) (Figs. 334, 335). The wrist-joint is a condyloid articulation. The parts forming it are the lower end of the radius and under surface of the articular disk above; and the navicular, lunate, and triangular bones below. The articular surface of the radius and the under surface of the articular disk form together a transversely elliptical concave surface, the receiving cavity. The superior articular surfaces of the navicular, lunate, and triangular form a smooth convex surface, the condyle, which is received into the concavity. The joint is surrounded by a capsule, strengthened by the following ligaments: The Volar Radiocarpal. The Dorsal Radiocarpal. The Ulnar Collateral. The Radial Collateral. The Volar Radiocarpal Ligament (ligamentum radiocarpeum volare; anterior liga- ment) (Fig. 334). — This ligament is a broad membranous band, attached above to the anterior margin of the lower end of the radius, to its styloid process, and to the front of the lower end of the ulna; its fibers pass downward and medialward to be inserted into the volar surfaces of the navicular, lunate, and triangular bones, some being continued to the capitate. In addition to this broad mem- brane, there is a rounded fasciculus, superficial to the rest, which reaches from the base of the styloid process of the ulna to the lunate and triangular bones. The ligament is perforated by apertures for the passage of vessels, and is in relation, in front, with the tendons of the Flexor digitorum profundus and Flexor pollicis 328 SYNDESMOLOGY longus; behind, it is closely adherent to the anterior border of the articular disk of the distal radioulnar articulation. _■ The Dorsal Radiocarpal Ligament iligamentum radiocarpeiim dorsale; 'posteriorWm ligament) (Fig. 335). — The dorsal radiocarpal ligament less thick and strong than the volar, is attached, above, to the posterior border of the lower end of the radius; its fibers are directed obliquely downward and medialward, and are fixed, 6eZo2/;,M| to the dorsal surfaces of the navicular, lunate, and triangular, being continuous with those of the dorsal intercarpal ligaments. It is in relation, behind, with the Extensor tendons of the fingers; m front, it is blended with the articular disk. The Ulnar Collateral Ligament (ligamentum collaterale carpi ulnar e; internal lateral ligament) (Fig. 334). — The ulnar collateral ligament is a rounded cord, attached above to the end of the styloid process of the ulna, and dividing below into two fasciculi, one of which is attached to the medial side of the triangular bone, the other to the pisiform and transverse carpal ligament. The Radial Collateral Ligament {ligamentum collaterale carpi radiale; external lateral ligament) (Fig. 335). — The radial collateral ligament extends from the tip of the styloid process of the radius to the radial side of the navicular, some of its fibers being prolonged to the greater multangular bone and the transverse carpal ligament. It is in relation with the radial artery, which separates the ligament from the tendons of the Abductor pollicis longus and Extensor pollicis brevis. Sjoiovial Membrane (Fig. 33G). — The synovial membrane lines the deep surfaces of the hga- ments above described, extending from the margin of the lower end of the radius and articular disk above to the margins of the articular surfaces of the carpal bones below. It is loose and lax, and presents numerous folds, especially behind. The wrist-joint is covered in front by the Flexor, and behind by the Extensor tendons. The arteries supplying the joint are the volar and dorsal carpal branches of the radial and ulnar, the volar and dorsal metacarpals, and some ascending branches from the deep volar arch. The nerves are derived from the ulnar and dorsal interosseous. Movements. — The movements permitted in this joint are flexion, extension, abduction, adduc- tion, and circumduction. They will be studied with those of the carpus, with which they are combined. Vn. Intercarpal Articulations (Articulationes Intercarpeae ; Articulations of the Carpus). These articulations may be subdivided into three sets: 1. The Articulations of the Proximal Row of Carpal Bones. 2. The Articulations of the Distal Row of Carpal Bones. 3. The Articulations of the Two Rows with each Other. Articulations of the Proximal Row of Carpal Bones. — These are arthrodial joints. The navicular, lunate, and triangular are connected by dorsal, volar, and interosseous ligaments. The Dorsal Ligaments (ligamenta intercarpea dorsalia). — The dorsal ligaments, two in number, are placed transversely behind the bones of the first row; they connect the navicular and lunate, and the lunate and triangular. The Volar ligaments {ligamenta intercarpea volaria; palmar ligaments). — The volar ligaments, also two, connect the navicular and lunate, and the lunate and trian- gular; they are less strong than the dorsal, and placed very deeply behind the Flexor tendons and the volar radiocarpal ligament. The Interosseous Ligaments {ligamenta intercarpea interossea) (Fig. 336). — The interosseous ligaments are two narrow bundles, one connecting the lunate with the navicular, the other joining it to the triangular. They are on a level with the superior surfaces of these bones, and their upper surfaces are smooth, and form part of the convex articular surface of the wrist-joint. INTERCARPAL ARTICULATIONS 32? The ligaments connecting the pisiform bone are the articular capsule and the two volar ligaments. The articular capsule is a thin membrane which connects the pisiform to the triangular; it is lined by synovial membrane. The two volar ligaments are strong fibrous bands; one, the pisohamate ligament,- IB connects the pisiform to the hamate, the other, the pisometacarpal ligament, joins the pisiform to the base of the fifth metacarpal bone (Fig. 334). These ligaments are, in reality, prolongations of the tendon of the Flexor carpi ulnaris. IH Articulations of the Distal Row of Carpal Bones. — These also are arthrodial ^■joints; the bones are connected by dorsal, volar, and interosseous ligaments. The Dorsal Ligaments {ligamenta intercarpea dorsalia). — The dorsal ligaments, three in number, extend transversely from one bone to another on the dorsal surface, connecting the greater with the lesser multangular, the lesser multangular with the capitate, and the capitate with the hamate. The Volar Ligaments {ligamenta intercarpea volaria; palmar ligaments). — The volar ligaments, also three, have a similar arrangement on the volar surface. The Interosseous Ligaments (ligamenta intercarpea interossea). — The three inter- osseous ligaments are much thicker than those of the first row; one is placed be- tween the capitate and the hamate, a second between the capitate and the lesser multangular, and a third between the greater and lesser multangulars. The first is much the strongest, and the third is sometimes wanting. Articulations of the Two Rows of Carpal Bones with Each Other. — The joint between the navicular, lunate, and triangular on the one hand, and the second row of carpal bones on the other, is named the midcarpal joint, and is made up of three distinct portions: in the center the head of the capitate and the superior surface of the hamate articulate with the deep cup-shaped cavity formed by the navicular and lunate, and constitute a sort of ball-and-socket joint. On the radial side the greater and lesser multangulars articulate with the navicular, and on the ulnar side the hamate articulates with the triangular, forming gliding joints. The ligaments are: volar, dorsal, ulnar and radial collateral. The Volar Ligaments {ligamenta intercarpea volaria; anterior or palmar ligaments). — The volar ligaments consist of short fibers, which pass, for the most part, from the volar surfaces of the bones of the first row to the front of the capitate. The Dorsal Ligaments {ligamenta intercarpea dorsalia; posterior ligaments). — The dorsal ligaments consist of short, irregular bundles passing between the dorsal surfaces of the bones of the first and second rows. The Collateral Ligaments (lateral ligaments) .—The collateral ligaments are very short; one is placed on the radial, the other on the ulnar side of the carpus; the former, the stronger and more distinct, connects the navicular and greater mul- tangular, the latter the triangular and hamate; they are continuous with the collateral ligaments of the wrist-joint. In addition to these ligaments, a slender interosseous band sometimes connects the capitate and the navicular. Synovial Membrane. — The synovial membrane of the carpus is very extensive (Fig. 336), and bounds a synovial cavity of very irregular shape. The upper portion of the cavity inter- venes between the under surfaces of the navicular, lunate, and triangular bones and the upper surfaces of the bones of the second row. It sends two prolongations upward — between the navic- ular and lunate, and the lunate and triangular — and three prolongations downward between the four bones of the second row. The prolongation between the greater and lesser multangulars, or that between the lesser multangular and capitate, is, owing to the absence of the interosseous ligament, often continuous with the cavity of the carpometacarpal joints, sometimes of the second, third, fourth, and fifth metacarpal bones, sometimes of the second and third only. In the latter condition the joint between the hamate and the fourth and fifth metacarpal bones has a separate synovial membrane. The synovial cavities of these joints are prolonged for a short distance between the bases of the metacarpal bones. There is a separate synovial mem- brane between the pisiform and triangular. 330 -^^^ SYNDESMOLOGY Movements. — The articulation of the hand and wrist considered as a whole involves four articular surfaces: (a) the inferior surfaces of the radius and articular disk; (6) the superior surfaces of the navicular, lunate, and triangular, the pisiform having no essential part in the movement of the hand; (c) the S-shaped surface formed by the inferior surfaces of the navicular, lunate, and triangular; (d) the reciprocal surface formed by the upper surfaces of the bones of the second row. These four surfaces form two joints: (1) a proximal, the wrist-joint proper; and (2) a distal, the mid-carpal joint. 1. The wrist-joint proper is a true condyloid articulation, and therefore all movements but rotation are permitted. Flexion and extension are the most free, and of these a greater amount of extension than of flexion is permitted, since the articulating surfaces extend farther on the dorsal than on the volar surfaces of the carpal bones. In this movement the carpal bones rotate on a transverse axis drawn between the tips of the styloid processes of the radius and ulna. A certain amount of adduction (or ulnar flexion) and abduction (or radial flexion) is also permitted. The former is considerably greater in extent than the latter on account of the shortness of the styloid process of the ulna, abduction being soon Hmited by the contact of the styloid process of the radius with the greater multangular. In this movement the carpus revolves upon an antero- posterior axis drawn through the center of the wrist.^ Finally, circumduction is permitted by the combined and consecutive movements of adduction, extension, abduction, and flexion. No rotation is possible, but the effect of rotation is obtained by the pronation and supination of the radius on the ulna. The movement oi flexion is performed by the Flexor carpi radiaUs, the Flexor carpi ulnaris, and the Palmaris longus; extension by the Extensores carpi radiales longus and brevis and the Extensor carpi ulnaris; adduction (ulnar flexion) by the Flexor carpi ulnaris and the Extensor carpi ulnaris; and abduction (radial flexion) by the Abductor poUicis longus, the Extensors of the thumb, and the Extensores carpi radiales longus and brevis and the Flexor carpi radiaUs. When the fingers are extended, flexion of the wrist is performed by the Flexores carpi radialis and ulnaris and extension is aided by the Extensor digitorum communis. When the fingers are flexed, flexion of the wrist is aided by the Flexores digitorum sublimis and profundus, and extension is performed by the Extencores carpi radiales and ulnaris. 2. The chief movements permitted in the mid-carpal joint are flexion and extension and a slight amount of rotation. In flexion and extension, which are the movements most freely enjoyed, the greater and lesser multangulars oh the radial side and the hamate on the ulnar side glide forward and backward on the navicular and triangular respectively, while the head of the capitate and the superior surface of the hamate rotate in the cup-shaped cavity of the navicular and lunate. Flexion at this joint is freer than extension. A very trifling amount of rotation is also permitted, the head of the capitate rotating around a vertical axis drawn through its own center, while at the same time a sUght ghding movement takes place in the lateral and medial portions of the joint. Vm. Carpometacarpal Articulations (Articulationes Carpometacarpese). Carpometacarpal Articulation of the Thumb {articulatio carpometacarpea pollicis). — This is a joint of reciprocal reception between the first metacarpal and the greater multangular; it enjoys great freedom of movement on account of the configuration of its articular surfaces, which are saddle-shaped. The joint is sur- roimded by a capsule, which is thick but loose, and passes from the circumference of the base of the metacarpal bone to the rough edge bounding the articular surface of the greater multangular; it is thickest laterally and dorsally, and is lined by synovial membrane. Movements. — In this articulation the movements permitted are flexion and extension in the plane of the palm of the hand, abduction and adduction in a plane at right angles to the palm, circumduction, and opposition. It is by the movement of opposition that the tip of the thumb is brought into contact with the volar surfaces of the slightly flexed fingers. This movement is effected through the medium of a small sloping facet on the anterior Up of the saddle-shaped articular surface of the greater multangular. The Flexor muscles pull the corresponding part of the articular surface of the metacarpal bone on to this facet, and the movement of opposition is then carried out by the Adductors. Flexion of this joint is produced by the Flexores poUicis longus and brevis, assisted by the Opponens pollicis and the Adductor pollicis. Extension is effected mainly by the abductor pollicis longus, assisted by the Extensores polhcis longus and brevis. Adduction is carried out by the Adductor; abduction mainly by the Abductores polhcis longus and brevis, assisted by the Extensors. > H. M. Johnaton (Journal of Anatomy and Physiology, vol. xli) maintains that n ulnar and radial flexion only slight lateral movement occurs at the radiocarpal joint, and that in cornglete flexion and extension of the hand there is a small degree of ulnar flexion at the radiocarpal joint. ^V ISSTEtCMETAfJAKlrAL AlCTlLuLATlUNS 661 Articulations of the Other Four Metacarpal Bones with the Carpus {articulationes carpometacarpecp). — The joints between the carpus and the second, third, fourth, and fifth metacarpal bones are arthrodial. The bones are united by dorsal, volar, and interosseous ligaments. The Dorsal Ligaments {ligamenta carpometacarpea dorsalia) . — The dorsal ligaments, the strongest and most distinct, connect the carpal and metacarpal bones on their dorsal surfaces. The second metacarpal bone receives two fasciculi, one from the greater, the other from the lesser multangular; the third metacarpal receives two, one each from the lesser multangular and capitate; the fourth two, one each from the capitate and hamate; the fifth receives a single fasciculus from the hamate, and this is continuous with a similar ligament on the volar surface, forming an incomplete capsule. The Volar Ligaments (ligamenta carpometacarpea volaria; palmar ligaments). — The volar ligaments have a somewhat similar arrangement, with the exception of those of the third metacarpal, which are three in number : a lateral one from the greater multangular, situated superficial to the sheath of the tendon of the Flexor carpi radialis; and intermediate one from the capitate; and a medial one from the hamate. The Interosseous Ligaments. — The interosseous ligaments consist of short, thick fibers, and are limited to one part of the carpometacarpal articulation; they con- nect the contiguous inferior angles of the capitate and hamate with the adjacent surfaces of the third and fourth metacarpal bones. Synovial Membrane. — The synovial membrane is a continuation of that of the intercarpal joints. Occasionally, the joint between the hamate and the fourth and fifth metacarpal bones has a separate synovial membrane. The synovial membranes of the wrist and carpus (Fig. 336) are thus seen to be five in number. The first passes from the lower end of the ulnar to the ulnar notch of the radius, and fines the upper surface of the articular disk. The second passes from the articular disk and the lower end of the radius above, to the bones of the first row below. The third, the most extensive, passes between the contiguous margins of the two rows of carpal bones, and sometimes, in the event of one of the interosseous ligaments being absent, between the bones of the second row to the carpal extremi- ties of the second, third, fourth, and fifth metacarpal bones. The fourth extends from the margin of the greater multangular to the metacarpal bone of the thvunb. The fifth runs between the adjacent margins of the triangular and pisiform bones. Occasionally the fourth and fifth carpo- metacarpal joints have a separate synovial membrane. Movements. — The movements permitted in the carpometacarpal articulations of the fingers are limited to slight gliding of the articular surfaces upon each other, the extent of which varies in the different joints. The metacarpal bone of the little finger is most movable, then that of the ring finger; the metacarpal bones of the index and middle fingers are almost immovable. DC. Intermetacarpal Articulations (Articulationes Intermetacarpese; Articulations of the Metacarpal Bones with Each Other). The bases of the second, third, fourth and fifth metacarpal bones articulate with one another by small surfaces covered with cartilage, and are connected together by dorsal, volar, and interosseous ligaments. The dorsal (ligamenta basium oss. metacarp. dorsalia) and volar ligaments (liga- menta hasium oss. metacarp. volaria; palmar ligaments) pass transversely from one bone to another on the dorsal and volar surfaces. The interosseous ligaments (ligamenta hasium oss. metacarp. interossea) connect their contiguous surfaces, just distal to their collateral articular facets. The synovial membrane for these joints is continuous with that of the carpometacarpal articulations. The Transverse Metacarpal Ligament (ligamentum capitulorum [oss. metacarpalium] transversum) (Fig. 337). — This ligament is a narrow fibrous band, which runs across the volar surfaces of the heads of the second, third, fourth and fifth meta- carpal bones, connecting them together. It is blended with the volar (glenoid) 332 SYNDESMOLOGY ligaments of the metacarpophalangeal articulations. Its volar surface is concave where the Flexor tendons pass over it; behind it the tendons of the Interossei pass to their insertions. X. Metacarpophalangeal Articulations (Articulationes Metacarpophalangese ; Metacarpophalangeal Joints) (Figs. 337, 338). These articulations are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cavities on the proximal ends of the first phalanges, with the exception of that of the thumb, which presents more of the characters of a ginglymoid joint. Each joint has a volar and two collateral ligaments. Metacarpal bone Transverse metacarpal ligament Groove for Flexor tendons let phalange Volar ligament Volar ligament Metacarpal __\ bone 3rd phalanx I Collateral ligament Collateral ligament 2nd phalanx Collateral ligament Fig. 337. — Metacarpophalangeal articulation and articulations of digit. Volar aspect. Fig. 338. — Metacarpophalangeal articulation and articulations of digit. Ulnar aspect. The Volar Ligaments (glenoid ligaments of Cruveilhier; palmar or vaginal ligaments) . — The volar ligaments are thick, dense, fibrocartilaginous structures, placed upon the volar surfaces of the joints in the intervals between the collateral ligaments, to which they are connected ; they are loosely united to the metacarpal bones, but are very firmly attached to the bases of the first phalanges. Their volar surfaces are intimately blended with the transverse metacarpal ligament, and present grooves for the passage of the Flexor tendons, the sheaths surrounding which are connected to the sides of the grooves. Their deep surfaces form parts of the articular facets for the heads of the metacarpal bones, and are lined by synovial membranes. The Collateral Ligaments {ligamenta collateralia; lateral ligaments). — The col- lateral ligaments are strong, rounded cords, placed on the sides of the joints; I I COXAL ARTICULATION OR HIP- JOINT 333 each is attached by one extremity to the posterior tubercle and adjacent depres- sion on the side of the head of the metacarpal bone, and by the other to the contiguous extremity of the phalanx. The dorsal surfaces of these joints are covered by the expansions of the Extensor tendons, together with some loose areolar tissue which connects the deep surfaces of the tendons to the bones. Movements. — The movements which occur in these joints are flexion, extension, adduction, abduction, and circumduction; the movements of abduction and adduction are very Umited, and cannot be performed when the fingers are flexed. XI. Articulations of the Digits f Articulationes Digitorum Manus ; Interphalangeal Joints) (Figs. 337, 338). The interphalangeal articulations are hinge-joints; each has a volar and tw^o collateral ligaments. The arrangement of these ligaments is similar to those in the metacarpophalangeal articulations. The Extensor tendons supply the place of posterior ligaments. Movements. — The only movements permitted in the interphalangeal joints are flexion and extension; these movements are more extensive between the first and second phalanges than between the second and third. The amount of flexion is very considerable, but extension is limited by the volar and collateral ligaments. Muscles Acting on the Joints of the Digits. — Flexion of the metacarpophalangeal joints of the fingers is eff'ected by the Flexores digitorum subUmis and profundus, Lumbricales, and Interossei, assisted in the case of the little finger by the Flexor digiti quinti brevis. Extension is produced by the Extensor digitorvun communis. Extensor indicis proprius, and Extensor digiti quinti pro- prius. Flexion of the interphalangeal joints of the fingers is accomplished by the Flexor digitorum profundus acting on the proximal and distal joints and by the Flexor digitorum sublimis acting oil the proximal joints. Extension is effected mainly by the Lumbricales and Interossei, the long Extensors having little or no action upon these joints. Flexion of the metacarpophalangeal joint of the thumb is effected by the Flexores pollicis longus and brevis; extension by the Extensores pollicis longus and brevis. Flexion of the inter- phalangeal joint is accomplished by the Flexor poUicis longus, and extension by the Extensor pollicis longus. ARTICULATIONS OF THE LOWER EXTREMITY. The articulations of the Lower Extremity comprise the following: V. Intertarsal. VI. Tarsometatarsal. VII. Intermetatarsal. VIII. Metatarsophalangeal. IX. Articulations of the Digits. I. Coxal Articulation or Hip-joint (Articulatio Coxae). his articulation is an enarthrodial or ball-and-socket joint, formed by the reception of the head of the femur into the cup-shaped cavity of the acetabulum. The articular cartilage on the head of the femur, thicker at the center than at the circumference, covers the entire surface with the exception of the fovea capitis femoris, to which the ligamentum teres is attached ; that on the acetabulum forms an incomplete marginal ring, the lunate surface. Within the lunate surface there is a circular depression devoid of cartilage, occupied in the fresh state by a mass of fat, covered by synovial membrane. The ligaments of the joint are: I. Hip. II. Knee. III. Tibiofibular, IV. Ankle. The Articular Capsule. The Iliofemoral. The Ischiocapsular. The Pubocapsular. The Ligamentum Teres Femoris. The Glenoidal Labrum. The Transverse Acetabular 334 SYNDESMOLOGY The Articular Capsule {capsula articularis; capsular ligament) (Figs. 339, 340). — The articular capsule is strong and dense. Above, it is attached to the margin of the acetabulum 5 to 6 mm. beyond the glenoidal labrum behind; but in front, it is attached to the outer margin of the labrum, and, opposite to the notch where the margin of the cavity is deficient, it is connected to the transverse ligament, and by a few fibers to the edge of the obturator foramen. It surrounds the neck of the femur, and is attached, in front, to the intertrochanteric line; above, to the base of the neck; behind, to the neck, about 1.25 cm. above the intertrochanteric crest; below, to the lower part of the neck, close to the lesser trochanter. From its femoral attachment some of the fibers are reflected upward along the neck as longitudinal bands, termed retinacula. The capsule is much thicker at the upper and forepart of the joint, where the greatest amount of resistance is required; Ani. inf. iliuc 3pine I I JrUertrocharUeric line Fig. 339. — Right hip-joint from the front. (Spalteholz.) behind and below, it is thin and loose. It consists of two sets of fibers, circular and longitudinal. The circular fibers, zona orbicularis, are most abundant at the lower and back part of the capsule (Fig. 342), and form a sling or collar arourd the neck of the femur. Anteriorly they blend with the deep surface of the iliofemoral ligament, and gain an attachment to the anterior inferior iliac spine. The longi- tudinal fibers are greatest in amount at the upper and front part of the capsule, where they are reinforced by distinct bands, or accessory ligaments, of which the most important is the iliofemoral ligament. The other accessory bands are known as the pubocapsular and the ischiocapsular ligaments. The external surface of the capsule is rough, covered by numerous muscles, and separated in front from the Psoas major and Iliacus by a bursa, which not infrequently communicates by a circular aperture with the cavity of the joint. COXAL ARTICULATION OR HIP-JOINT The Iliofemoral Ligament (ligamentum iliofemorale; Y-ligameni; ligament of Bigeloic) (Fig. 339). — The iliofemoral ligament is a band of great strength which lies in front of the joint; it is intimately connected with the capsule, and serves to strengthen it in this situation. It is attached, above, to the lower part of the anterior inferior iliac spine; below, it divides into two bands, one of which passes downward and is fixed to the lower part of the intertrochanteric line; the other is directed downward and lateralward and is attached to the upper part of the same line. Between the two bands is a thinner part of the capsule. In some cases there is no division, and the ligament spreads out into a flat triangular band which is attached to the whole length of the intertrochanteric line. This ligament is frequently called the Y-shaped ligament of Bigelow; and its upper band is some- times named the iliotrochanteric ligament. Horizontal fibers Ischiofemoral ligament w (Quain.) The Pubocapsular Ligament (ligamentum pubocapsulare; pubofemoral ligament). — This ligament is attached, above, to the obturator crest and the superior ramus of the pubis; below, it blends with the capsule and with the deep surface of the vertical band of the iliofemoral ligament. The Ischiocapsular Ligament (ligamentum ischiocapsulare; ischiocapsular band; ligament of Berlin).- — The ischiocapsular ligament consists of a triangular band of strong fibers, which spring from the ischium below and behind the acetabulum, and blend with the circular fibers of the capsule (Fig. 340). 336 SYNDESMOLOGY The Ligamentum Teres Femoris (Fig. 341), — The ligamentum teres femoris is a triangular, somewhat flattened band implanted by its apex into the antero-superior part of the fovea capitis femoris ; its base is attached by two bands, one into either side of the acetabular notch, and between these bony attachments it blends with the transverse ligament. It is ensheathed by the synovial membrane, and varies greatly in strength in different subjects; occasionally only the synovial fold exists, and in rare cases even this is absent. The ligament is made tense when the thigh is semiflexed and the limb then adducted or rotated outward; it is, on the other hand, relaxed when the limb is abducted. It has, however, but little influence as a ligament. Spine of ischium Ant, inf. iliac spine Fovea capitis Iliofemoral ligament II Lesser trochanter Fig. 341. — Left hip-joint, opened by removing the floor of the acetabulum from within the pelvis. The Glenoidal Labnim (labrum glenoidale; cotyloid ligament). — The glenoidal labrum is a fibrocartilaginous rim attached to the margin of the acetabulum, the cavity of which it deepens; at the same time it protects the edge of the bone, and fills up the inequalities of its surface. It bridges over the notch as the transverse ligament, and thus forms a complete circle, which closely surrounds the head of the femur and assists in holding it in its place. It is triangular on section, its base being attached to the margin of the acetabulum, while its opposite edge is free and sharp. Its two surfaces are invested by synovial membrane, the external one being in contact with the capsule, the internal one being inclined inward so as to narrow the acetabulum, and embrace the cartilaginous surface of the head of the femur. It is much thicker above and behind than below and in front, and consists of compact fibers. The Transverse Acetabular Ligament {ligamentum transversum acetabuli; transverse ligament) .—This ligament is in reality a portion of the glenoidal labrum, though differing from it in having no cartilage cells among its fibers. It consists of strong, COXAL ARTICULATION OR HIP-JOINT 337 Fia. 342. — Hip-joint, front view. The capsular ligament has been largely removed. Spine of ischium Capsvie Greater trochanter FiQ. 343. — Capsule of hip-joint (distended). Posterior aspect. 22 338 SYNDESMOLOGY flattened fibers, which cross the acetabular notch, and convert it into a foramen through which the nutrient vessels enter the joint. Synovial Membrane (Fig. 343). — The synovial membrane is very extensive. Commencing at the margin of the cartilaginous surface of the head of the femur, it covers the portion of the neck which is contained within the joint; from the neck it is reflected on the internal surface of the capsule, covers both surfaces of the glenoidal labrum and the mass of fat contained in the depression at the bottom of the acetabulum, and ensheathes the ligamentum teres as far as the head of the femur. The joint cavity sometimes communicates through a hole in the capsule between the vertical band of the iliofemoral hgament and the pubocapsular ligament with a bursa situated on the deep surfaces of the Psoas major and Iliacus. The muscles in relation with the joint are, in front, the Psoas major and Iliacus, separated from the capsule by a bursa; above, the reflected head of the Rectus femoris and Glutajus minimus, the latter being closely adherent to the capsule; medially, the Obturator extemus and Pectineus; behind, the Piriformis, Gemellus superior, Obturator intemus, Gemellus inferior, Obturator extemus, and Quadratus femoris (Fig. 344). Femoral artery Femoral nerve | Femoral vein Iliofemoral ligament Rectus femoris Ligamentum, teres Obturator nerve Piriformis \ Sciatic nerve Obturator intermu Fig. 344. — Structures surrounding right hii>-joint. The arteries supplying the joint are derived from the obturator, medial femoral circumflex, and superior and inferior gluteals. The nerves are articular branches from the sacral plexus, sciatic, obturator, accessory obturator, and a filament from the branch of the femoral supplying the Rectus femoris. Movements. — The movements of the hip are very extensive, and consist of flexion, extension, adduction, abduction, circvunduction, and rotation. The length of the neck of the femvur and its inclinations to the body of the bone have the^ effect of converting the angular movements of flexion, extension, adduction, and abduction par- tially into rotatory movements in the joint. Thus when the thigh is flexed or extended, the head of the femur, on account of the medial incUnation of the neck, rotates within the acetabulum with only a slight amount of gliding to and fro. The forward slope of the neck similarly affects the movements of adduction and abduction. Conversely rotation of the thigh which is permitted by the upward inclination of the neck, is not a simple rotation of the head of the femur in the acetabulum, but is accompanied by a certain amount of gliding. THE KNEE-JOINT 339 The hip-joint presents a very striking contrast to the shoulder-joint in the much more com- plete mechanical arrangements for its security and for the limitation of its movements. In the shoulder, as has been seen, the head of the humerus is not adapted at all in size to the glenoid cavity, and is hardly restrained in any of its ordinary movements by the capsule. In the hip- joint, on the contrary, the head of the femur is closely fitted to the acetabulimi for an area extend- ing over nearly half a sphere, and at the margin of the bony cup it is still more closely embraced by the glenoidal labrum, so that the head of the femur is held in its place by that ligament even when the fibers of the capsule have been quite divided. The iliofemoral ligament is the strongest of all the ligaments in the body, and is put oi) the stretch by any attempt to extend the femur beyond a straight line with the trunk. That is to say, this ligament is the chief agent in main- taining the erect position without muscular fatigue; for a vertical Une passing through the center of gravity of the trunk falls behind the centers of rotation in the hip-joints, and therefore the pelvis tends to fall backward, but is prevented by the tension of the iUofemoral ligaments. The security of the joint may be provided for also by the two bones being directly united through the ligamentum teres ; but it is doubtful whether this ligament has much influence upon the mechanism of the joint. When the knee is flexed, flexion of the hip-joint is arrested by the soft parts of the thigh and abdomen being brought into contact, and when the knee is extended, by the action of the hamstring muscles; extension is checked by the tension of the iliofemoral ligament; adduc- tion by the thighs coming into contact; adduction with flexion by the lateral band of the ilio- femoral ligament and the lateral part of the capsule; abduction by the medial band of the iliofemoral ligament and the pubocapsular ligament ; rotation outward by the lateral band of the iliofemoral ligament; and rotation inward by the ischiocapsular hgament and the hinder part of the capsule. The muscles which ^ex the femur on the pelvis are the Psoas major, Iliacus, Rectus femoris, Sartorius, Pectineus, Adductores longus and brevis, and the anterior fibers of the Glutaei medius and minimus. Extension is mainly performed by the Glutseus maximus, assisted by the hamstring muscles and the ischial head of the Adductor magnus. The thigh is adducted by the Adductores magnus, longus, and brevis, the Pectineus, the Gracilis, and lower part of the Glutseus maximus, and abducted by the Glutaei medius and minimus, and the upper part of the Glutseus maximus. The muscles which rotate the thigh inward are the Glutseus minimus and the anterior fibers of the Glutajus medius, the Tensor fascise latae and the lUacus and Psoas major; while those which rotate it outward are the posterior fibers of the Glutseus medius, the Piriformis, Obturatores extemus and intem\is, Gemelli superior and inferior, Quadratus femoris, Glutseus maximus, the Adductores longus, brevis, and magnus, the Pectineus, and the Sartorius. n. The Knee-joint (Articulatio Genu). The knee-joint was formerly described as a ginglymus or hinge-joint, but is really of a much more complicated character. It must be regarded as consisting of three articulations in one: two condyloid joints, one between each condyle of the femur and the corresponding meniscus and condyle of the tibia; and a third between the patella and the femur, partly arthrodial, but not completely so, since the articular surfaces are not mutually adapted to each other, so that the movement is not a simple gliding one. This view of the construction of the knee- joint receives confirmation from the study of the articulation in some of the lower mammals, where, corresponding to these three subdivisions, three synovial cavities are sometimes found, either entirely distinct or only connected together by small communications. This view is further rendered probable by the existence in the middle of the joint of the two cruciate ligaments, which must be regarded as the collateral ligaments of the medial and lateral joints. The existence of the patellar fold of synovial membrane would further indicate a tendency to separa- tion of the synovial cavity into two minor sacs, one corresponding to the lateral and the other to the medial joint. The bones are connected together by the following ligaments: The Articular Capsule. The Ligamentum Patellae. The Oblique Popliteal. The Tibial Collateral. The Fibular Collateral. The Anterior Cruciate. The Posterior Cruciate. The Medial and Lateral Menisci. The Transverse. The Coronary. 340 SYNDESMOLOGY ■^ The Articular Capsule {capsula articularis; capsular ligamenf) (Fig. 345).— The articular capsule consists of a thin, but strong, fibrous membrane which is strength- ened in almost its entire extent by bands inseparably connected with it. Above and in front, beneath the tendon of the Quadriceps femoris, it is represented only by the synovial membrane. Its chief strengthening bands are derived from the fascia lata and from the tendons surrounding the joint. In front, expansions from the Vasti and from the fascia lata and its iliotibial band fill in the intervals between the anterior and collateral ligaments, constituting the medial and lateral patellar retinacula. Behind the capsule consists of vertical fibers which arise from the condyles and from the sides of the intercondyloid fossa of the femur; the posterior part of the capsule is therefore situated on the sides of and in front of the cruciate ligaments, which are thus excluded from the joint cavity. Behind the cruciate ligaments is the oblique popliteal ligament which is aug- mented by fibers derived from the tendon of the Semimembranosus. Laterally, a prolongation from the iliotibial band fills in the interval be- tween the oblique popliteal and the fibular collat- eral ligaments, and partly covers the latter. Medially, expansions from the Sartorius and Semimembranosus pass upward to the tibial collateral ligament and strengthen the capsule. The Ligamentimi Patellae {anterior ligament) (Fig. 345) . — The ligamentum patellfe is the cen- tral portion of the common tendon of the Quad- riceps femoris, which is continued from the patella to the tuberosity of the tibia. It is a strong, flat, ligamentous band, about 8 cm. in length, attached, above, to the apex and adjoin- ing margins of the patella and the rough depres- sion on its posterior surface; helaio, to the tuberosity of the tibia; its superficial fibers are continuous over the front of the patella with those of the tendon of the Quadriceps femoris. The medial and lateral portions of the tendon of the Quadriceps pass down on either side of the patella, to be inserted into the upper extremity of the tibia on either side of the tuberosity; these portions merge into the capsule, as stated above, forming the medial and lateral patellar retinacula. The posterior surface of the ligamentum patellae is separated from the synovial membrane of the joint by a large infrapatellar pad of fat, and from the tibia by a bursa. The Oblique PopUteal Ligament (ligamentum popliteum ohliquum; posterior liga- ment) (Fig. 346). — This ligament is a broad, flat, fibrous band, formed of fasciculi separated from one another by apertures for the passage of vessels and nerves. It is attached above to the upper margin of the intercondyloid fossa and posterior surface of the femur close to the articular margins of the condyles, and below to the posterior margin of the head of the tibia. Superficial to the main part of the ligament is a strong fasciculus, derived from the tendon of the Semimembranosus and passing from the back part of the medial condyle of the tibia obliquely upward and iateralward to the back part of the lateral condyle of the femur. The oblique popliteal ligament forms part of the floor of the popliteal fossa, and the popliteal artery rests upon it. Fig. 345. — Right knee-joint, view. Anterior THE KNEE-JOINT 341 The Tibial Collateral Ligament (ligamentum collaterale tibiale; internal lateral liga- ment) (Fig. 345).— The tibial collateral is a broad, flat, membranous band, situated nearer to the back than to the front of the joint. It is attached, above, to the medial condyle of the femur immediately below the adductor tubercle; below, to the medial condyle and medial surface of the body of the tibia. The fibers of the posterior part of the ligament are short and incline backward as they descend; they are inserted into the tibia above the groove for the Semimembranosus. The anterior part of the ligament is a flattened band, about 10 cm. long, which inclines forward as it descends. It is inserted into the medial surface of the body of the tibia about 2.5 cm. below the level of the condyle. It is crossed, at its lower part, by the tendons of the Sartorius, Gracilis, and Semitendinosus, a bursa being interposed. Its deep surface covers the inferior medial genicular vessels and nerve and the anterior portion of the tendon of the Semimembranosus, with which it is connected ■■ by a few fibers; it is intimately adherent to the medial meniscus. I Posterior view. Fig. 347. — Right knee-joint, from the front, showing interior ligaments. The Fibular Collateral Ligament (ligamentum collaterale fibular e; external lateral or long external lateral ligament) (Fig. 348).— The fibular collateral is a strong, rounded, fibrous cord, attached, above, to the back part of the lateral condyle of the femur, immediately above the groove for the tendon of the Popliteus; below, to the lateral side of the head of the fibula, in front of the styloid process. The greater part of its lateral surface is covered by the tendon of the Biceps femoris; the tendon, however, divides at its insertion into two parts, which are separated by the liga- ment. Deep to the ligament are the tendon of the Popliteus, and the inferior lateral genicular vessels and nerve. The ligament has no attachment to the lateral meniscus. 342 SYNDESMOLOGY An inconstant bundle of fibers, the short fibular collateral ligament, is placed behind and parallel with the preceding, attached, above, to the lower and back part of the lateral condyle of the femur; below, to the summit of the styloid process of the fibula. Passing deep to it are the tendon of the Popliteus, and the inferior lateral genicular vessels and nerve. The Cruciate Ligaments {ligamenia cruciata genu; crucial ligaments). — The cru- ciate ligaments are of considerable strength, situated in the middle of the joint, nearer to its posterior than to its anterior surface. They are called cruciate because they cross each other somewhat like the lines of the letter X; and have received the names anterior and posterior, from the position of their attachments to the tibia. The Anterior Cruciate Ligament {ligamentum cruciatum anterius; external crucial ligament) (Fig. 347) is attached to the depression in front of the intercondyloid eminence of the tibia, being blended with the anterior extremity of the lateral meniscus; it passes upward, backward, and lateralward, and is fixed into the medial and back part of the lateral condyle of the femur. H Ant. cruciateligament Tendon of Poplitetis Lateral meniscus Fibular collateral ligament Fia. 348. — ^Left knee-joint from behind, showing interior ligaments. The Posterior Cruciate Ligament {ligamentum cruciatum posterius; internal crucial ligament) (Fig. 348) is stronger, but shorter and less oblique in its direction, than the anterior. It is attached to the posterior intercondyloid fossa of the tibia, and to the posterior extremity of the lateral meniscus; and passes upward, forward, and medialward, to be fixed into the lateral and front part of the medial condyle of the femur. The Menisci {semilunar fihrocartilages) (Fig. 349). — The menisci are two crescentic lamellae, which serve to deepen the surfaces of the head of the tibia for articulation with the condyles of the femur. The peripheral border of each meniscus is thick, convex, and attached to the inside of the capsule of the joint ; the opposite border THE KNEE-JOINT 343 is thin, concave, and free. The upper surfaces of the menisci are concave, and in contact with the condyles of the femur; their lower surfaces are flat, and rest upon the head of the tibia; both surfaces are smooth, and invested by synovial membrane. Each meniscus covers approximately the peripheral two-thirds of the corresponding articular surface of the tibia. The medial meniscus {meniscus medialis; internal semilunar fibrocartilage) is nearly semicircular in form, a little elongated from before backward, and broader behind than in front; its anterior end, thin and pointed, is attached to the anterior intercondyloid fossa of the tibia, in front of the anterior cruciate ligament; its posterior end is fixed to the posterior intercondyloid fossa of the tibia, between the attachments of the lateral meniscus and the posterior cruciate ligament. Anterior cruciate ligament Transverse ligament Ligament of Wrisberg Posterior cruciate ligament Fig. 349. — Head of right tibia seen from above, showing menisci and attachments of ligaments. The lateral meniscus {meniscus lateralis; external semilunar fibrocartilage) is nearly circular and covers a larger portion of the articular surface than the medial one. It is grooved laterally for the tendon of the Popliteus, which separates it from the fibular collateral ligament. Its anterior end is attached in front of the intercon- dyloid eminence of the tibia, lateral to, and behind, the anterior cruciate ligament, with which it blends; the posterior end is attached behind the intercondyloid eminence of the tibia and in front of the posterior end of the medial meniscus. The anterior attachment of the lateral meniscus is twisted on itself so that its free margin looks backward and upward, its anterior end resting on a sloping shelf of bone on the front of the lateral process of the intercondyloid eminence. Close to its posterior attachment it sends off a strong fasciculus, the ligament of Wrisberg (Figs. 348, 349), which passes upward and medialward, to be inserted into the medial condyle of the femur, immediately behind the attachment of the posterior cruciate ligament. Occasionally a small fasciculus passes forward to be inserted into the lateral part of the anterior cruciate ligament. The lateral meniscus gives off from its anterior convex margin a fasciculus which forms the transverse ligament. The Transverse Ligament {ligamentum transversum genu). — The transverse liga- ment connects the anterior convex margin of the lateral meniscus to the anterior end of the medial meniscus ; its thickness varies considerably in different subjects, and it is sometimes absent. The coronary ligaments are merely portions of the capsule, which connect the periphery of each meniscus with the margin of the head of the tibia. 344 SYNDESMOLOGY Synovial Membrane. — The synovial membrane of the knee-joint is the largest and most exten- sive in the body. Commencing at the upper border of the patella, it forms a large cul-de-sac beneath the Quadriceps femoris (Figs. 3.50, 3.51) on the lower part of the front of the femur, and frequently communicates with a bursa interposed between the tendon and the front of the femur. The pouch of synovial membrane between the Quadriceps and front of the femur is supported, during the movements of the knee, by a small muscle, the Articularis genu, which is inserted into it. On either side of the patella, the synovial membrane extends beneath the aponeuroses of the Vasti, and more especially beneath that of the Vastus medialis. Below the patella it is separated from the ligamentum patella; by a considerable quantity of fat, known as Oblique poplitea ligament Medial meniscus ^ — Adipose tissue -1 — . Bursa under Quadriceps femoris Medial meniscus Ligamentum patellce I _ Bursa between tibia arid ligamentum patellae Fia. 350. — -Sagittal section of right knee-joint. the infrapatellar pad. From the medial and lateral borders of the articular surface of the patella, reduplications of the synovial membrane project into the interior of the joint. These form two fringe-like folds termed the alar folds ; below, these folds converge and are continued as a single band, the patellar fold {ligamentum mucosum), to the front of the intercondyloid fossa of the femur. On either side of the joint, the synovial membrane passes downward from the femur, lining the capsule to its point of attachment to the menisci; it may then be traced over the upper surfaces of these to their free borders, and thence along their under sm-faces to the tibia (Figs. 351, 352). At the back part of the lateral meniscus it forms a cul-de-sac between the groove on its surface and the tendon of the Popliteus; it is reflected across the front of the cruciate ligaments, which are therefore situated outside the synovial cavitj'. THE KNEE-JOINT Bursse. — The burs£E near the knee-joint are the following: In front there are four bursae: a large one is interposed between the patella and the skin, a small one between the upper part of the tibia and the ligamentum patella;, a third between the lower part of the tuberosity of the tibia and the skin, and a fourth between the anterior surface of the lower part of the femur and the deep surface of the Quadriceps femoris, usually communicating with the knee-joint. Laterally there are four bursse: (1) one (which sometimes communicates with the joint) between the lateral head of the Gastrocnemius and the capsule; (2) one between the fibular collateral ligament and the tendon of the Biceps; (3) one between the fibular collateral ligament and the tendon of the PopUteus (this is sometimes only an expansion from the next bursa); (4) one between the tendon of the Pophteus and the lateral condyle of the femiu", usually an extension from the synovial membrane of the joint. ]Medially, there are five bursa?: (1) one between the medial head of the Gastrocnemius and the capsule; this sends a prolongation between the tendon of the Quadriceps femoris Fibular collateral ligament Tendon of PopUteus Lateral meniscus Ligamentum patella Fia. 351. — Capsule of right knee-joint (distended). Lateral aspect. medial head of the Gastrocnemius and the tendon of the Semimembranosus and often communi- cates with the joint; (2) one superficial to the tibial collateral ligament, between it and the tendons of the Sartorius, Gracilis, and Semitendinosus; (3) one deep to the tibial collateral ligament, between it and the tendon of the Semimembranosus (this is sometimes only an expansion from the next bursa) ; (4) one between the tendon of the Semimembranosus and the head of the tibia; (5) occasionally there is a bursa between the tendons of the Semimembranosus and Semitendinosus. Structures Around the Joint. — In front, and at the sides, is the Quadriceps femoris; laterally the tendons of the Biceps femoris and Popliteus and the common peroneal nerve; medially, the Sartorius, Gracilis, Semitendinosus, and Semimembranosus; behind, the popliteal vessels and the tibial nerve, Popliteus, Plantaris, and medial and lateral heads of the Gastrocnemius, some lymph glands, and fat. The arteries supplying the joint are the highest genicular (anastomotica magna), a branch SYNDESMOLOGY of the femoral, the genicular branches of the ]:)opUteal, the recurrent branches of the anterior tibial, and the descending branch from the lateral femoral circumflex of the profunda femoris. The nerves are derived from the obturator, femoral, tibial, and common peroneal. Movements. — The movements which take place at the knee-joint are flexion and extension, and, in certain positions of the joint, internal and external rotation. The movements of flexion and extension at this joint differ from those in a typical hinge-joint, such as the elbow, in that (a) the axis around which motion takes place is not a fixed one, but shifts forward during extension and backward during flexion; (6) the commencement of flexion and the end of extension are accompanied by rotatory movements associated with the fixation of the limb in a position of great stabiUty. The movement from full flexion to full extension may therefore be described in three phases: 1. In the fully flexed condition the posterior parts of the femoral condyles rest on the corre- sponding portions of the meniscotibial surfaces, and in this position a slight amount of simple ' rolling movement is allowed. Posterior cruciate ligament Medial menisciis — ^ Tibial collateral ligament rUerior cruciate ligament Lateral meniscus Fibular collateral ligament Fia. 352. — Capsule of right knee-joint (distended). Posterior aspect. 2. During the passage of the limb from the flexed to the extended position a gUding movement is superposed on the rolling, so that the axis, which at the commencement is represented by a line through the inner and outer condyles of the femur, gradually shifts forward. In this part of the movement, the posterior two-thirds of the tibial articular surfaces of the two femoral condyles are involved, and as these have similar curvatures and are parallel to one another, they move forward equally. 3. The lateral condyle of the femur is brought almost to rest by the tightening of the anterior cruciate ligament; it moves, however, shghtly forward and medialward, pushing before it the anterior part of the lateral meniscus. The tibial surface on the medial condyle is prolonged farther forward than that on the lateral, and this prolongation is directed lateralward. When, therefore, the movement forward of the condyles is checked by the anterior cruciate ligament, continued muscular action causes the medial condyle, dragging with it the meniscus, to travel backward and medialward, thus producing an internal rotation of the thigh on the leg. When the position of full extension is reached the lateral part of the groove on the lateral condyle is pressed against the anterior part of the corresponding meniscus, while the medial part of the ARTICULATIONS BETWEEN THE TIBIA AND FIBULA 347 groove rests on the articular margin in front of the lateral process of the tibial intercondyloid eminence. Into the groove on the medial condyle is fitted the anterior part of the medial meniscus, while the anterior cruciate ligament and the articular margin in front of the medial process of the tibial intercondyloid eminence are received into the forepart of the intercondyloid fossa of the femur. This third phase by which all these parts are brought into accurate apposition is known as the "screwing home," or locking movement of the joint. The complete movement of flexion is the converse of that described above, and is therefore preceded by an external rotation of the femur which unlocks the extended joint. The axes around which the movements of flexion and extension take place are not precisely at right angles to either bone; in flexion, the femur and tibia are in the same plane, but in exten- sion the one bone forms an angle, opening lateralward with the other. In addition to the rotatory movements associated with the completion of extension and the initiation of flexion, rotation inward or outward can be effected when the joint is partially flexed; these movements take place mainly between the tibia and the menisci, and are freest when the leg is bent at right angles with the thigh. Movements of Patella. — The articular surface of the patella is indistinctly divided into seven facets — upper, middle, and lower horizontal pairs, and a medial perpendicular facet (Fig. 353). When the knee is forcibly flexed, the medial perpendicular facet is in contact with the semilunar surface on the lateral part of the mediaL condyle; this semilunar surface is a pro- longation backward of the medial part of the patellar surface. As the leg is carried from the flexed to the extended position, first the highest pair, then the middle pair, and lastly the lowest pair of horizontal facets is successively brought into contact with the patellar surface of the femur. In the ex- tended position, when the Quadriceps femoris is relaxed, the patella lies loosely on the front of the lower end of the femur. During flexion, the ligamentum patella? is put upon the stretch, and in extreme flexion the posterior cruciate ligament, the obhque popliteal, and collateral hgaments, and, to a sUght extent, the anterior cruciate ligament, are relaxed. Flexion is checked during life by the contact of the leg with the thigh. 'When the knee-joint is fuUy extended the oblique popliteal and collateral ligaments, the anterior cruciate ligament, and the posterior cruciate in the act of extending the knee, the ligamentum patellae femoris, but in full extension with the heel supported it is relaxed. Rotation inward is checked by the anterior cruciate ligament; rotation outward tends to uncross and relax the cruciate liga- ments, but is checked by the tibial collateral ligament. The main function of the cruciate liga- ment is to act as a direct bond between the tibia and femur and to prevent the former bone from being carried too far backward or forward. They also assist the collateral ligaments in resisting any bending of the joint to either side. The menisci are intended, as it seems, to adapt the surfaces of the tibia to the shape of the femoral condyles to a certain extent, so as to fill up the intervals which would otherwise be left in the varying positions of the joint, and to obviate the jars which would be so frequently transmitted up the limb in jumping or by falls on the feet; also to permit of the two varieties of motion, flexion and extension, and rotation, as explained above. The patella is a great defence to the front of the knee-joint, and distributes upon a large and tolerably even surface, during kneeling, the pressure which would otherwise fall upon the prominent ridges of the condyles; it also affords leverage to the Quadriceps femoris. When standing erect in the attitude of "attention," the weight of the body falls in front of a line carried across the centers of the knee-joints, and therefore tends to produce overextension of the articulations; this, however, is prevented by the tension of the anterior cruciate, oblique pophteal, and collateral Hgaments. Extension of the leg on the thigh is performed by the Quadriceps femoris; flexion by the Biceps femoris, Semitendinosus, and Semimembranosus, assisted by the Gracilis, Sartorius, Gastroc- nemius, Popliteus, and Plantaris. Rotation outward is effected by the Biceps femoris, and rota- tion inward by the Popliteus, Semitendinosus, and, to a sUght extent, the Semimembranosus, the Sartorius, and the Gracihs. The PopUteus comes into action especially at the commencement of the movement of flexion of the knee; by its contraction the leg is rotated inward, or, if the tibia be fixed, the thigh is rotated outward, and the knee-joint is unlocked. Fio. 353. — Posterior surface of the right patella, showing diagrammatically the areas of contact with the femur in different positions of the knee. ligament, are rendered tense; is tightened by the Quadriceps m. Articulations between the Tibia and Fibula. I \^m . The articulations between the tibia and fibula are effected by ligaments which ^^K connect the extremities and bodies of the bones. The ligaments may consequently 348 be subdivided into three sets: (1) those of the Tibiofibular articulation; (2) the interosseous membrane; (3) those of the Tibiofibular syndesmosis. Tibiofibular Articulation {articulatio iibiofibularis; superior tibiofibular articula- tion). — This articulation is an arthrodial joint between the lateral condyle of the tibia and the head of the fibula. The contiguous surfaces of the bones present flat, oval facets covered with cartilage and connected together by an articular capsule and by anterior and posterior ligaments. The Articular Capsule {caysula articularis; capsular ligament). — The articular capsule surrounds the articulation, being attached around the margins of the articular facets on the tibia and fibula; it is much thicker in front than behind. The Anterior Ligament {anterior superior ligament). — The anterior ligament of the head of the fibula (Fig. 347) consists of two or three broad and flat bands, which pass obliquely upward from the front of the head of the fibula to the front of the lateral condyle of the tibia. The Posterior Ligament (posterior superior ligament). — The posterior ligament of the head of the fibula (Fig. 348) is a single thick and broad band, which passes obliquely upward from the back of the head of the fibula to the back of the lateral condyle of the tibia. It is covered by the tendon of the Popliteus. Sjoiovial Membrane. — A synovial membrane lines the capsule; it is continuous with that of the knee-joint in occasional cases when the two joints communicate. Interosseous Membrane (membrana interossea cruris; middle tibiofibular liga- ment). — An interosseous membrane extends between the interosseous crests of the tibia and fibula, and separates the muscles on the front from those on the back of the leg. It consists of a thin, aponeurotic lamina composed of oblique fibers, which for the most part run downward and lateralward ; some f cav fibers, however, pass in the opposite direction. It is broader above than below. Its upper margin does not quite reach the tibiofibular joint, but presents a free concave border, above which is a large, oval aperture for the passage of the anterior tibial vessels to the front of the leg. In its lower part is an opening for the passage of the anterior peroneal vessels. It is continuous below with the interosseous ligament of the tibio- fibular syndesmosis, and presents numerous perforations for the passage of small vessels. It is in relation, in front, with the Tibialis anterior, Extensor digitorum longus. Extensor hallucis proprius, Peronseus tertius, and the anterior tibial vessels and deep peroneal nerve; behind, with the Tibialis posterior and Flexor hallucis longus. Tibiofibular Syndesmosis {syndesmosis tibiofibularis; inferior tibiofibular articu- lation). — This syndesmosis is formed by the rough, convex surface of the medial side of the lower end of the fibula, and a rough concave surface on the lateral side of the tibia. Below, to the extent of about 4 mm. these surfaces are smooth, and covered with cartilage, which is continuous with that of the ankle-joint. The ligaments are: anterior, posterior, inferior transverse, and interosseous. The Anterior Ligament {ligamentum malleoli lateralis anterius; anterior inferior ligamejit) .—The anterior ligament of the lateral malleolus (Fig. 355) is a flat, triangular band of fibers, broader below than above, which extends obliquely downward and lateralward between the adjacent margins of the tibia and fibula, on the front aspect of the syndesmosis. It is in relation, in front, with the Peronseus tertius, the aponeurosis of the leg, and the integument; behind, with the interosseous ligament; and lies in contact with the cartilage covering the talus. The Posterior Ligament (ligamentum malleoli lateralis posterius; posterior inferior ligament). — The posterior ligament of the lateral malleolus (Fig. 355), smaller than the preceding, is disposed in a similar manner on the posterior surface of the syndesmosis. TALOCRURAL ARTICULATION OR ANKLE-JOINT 349 I The Inferior Transverse Ligament. — The inferior transverse ligament lies in front of the posterior ligament, and is a strong, thick band, of yellowish fibers which passes transversely across the back of the joint, from the lateral malleolus to the posterior border of the articular surface of the tibia, almost as far as its malleolar process. This ligament projects below the margin of the bones, and forms part of the articulating surface for the talus. The Interosseous Ligament. — The interosseous ligament consists of numerous short, strong, fibrous bands, which pass between the contiguous rough surfaces of the tibia and fibula, and constitute the chief bond of union between the bones. It is continuous, above, with the interosseous membrane (Fig. 356). Synovial Membrane. — The synovial membrane associated with the small arthrodial part of this joint is continuous with that of the ankle-joint. IV. Talocrural Articulation or Ankle-joint (Articulatio Talocruralis ; Tibiotarsal Articulation). The ankle-joint is a ginglymus, or hinge-joint. The structures entering into its formation are the lower end of the tibia and its malleolus, the malleolus of the ^^ Post, talotibial ligament , Medial talocalcaneal lig. Post, talocalcaneal lig. tr capsule Medial cuneonavic. lig. \ Calcaneocuboid ligament ' Plantar calcaneonaoic. liaament Long plantar ligament Fig. 354. — Ligaments of the medial aspect of the foot. (Quain.) fibula, and the transverse ligament, which together form a mortise for the recep- tion of the upper convex surface of the talus and its medial and lateral facets. The bones are connected by the following ligaments: The Articular Capsule. The Deltoid. The Anterior Talofibular. The Posterior Talofibular. The Calcaneofibular. 350 SYNDESMOLOGY The Articular Capsule (capsula articularis; capsular ligament). — The articular ca^ sule surrounds the joints, and is attached, above, to the borders of the articular surfaces of the tibia and malleoli ; and below, to the talus around its upper articular surface. The anterior part of the capsule (anterior ligament) is a broad, thin, membranous layer, attached, above, to the anterior margin of the lower end of the tibia; below, to the talus, in front of its superior articular surface. It is in relation, in front, with the Extensor tendons of the toes, the tendons of the Tibialis anterior and Peronseus tertius, and the anterior tibial vessels and deep peroneal nerve. The posterior part of the capsule (posterior ligament) is very thin, and consists principally of transverse fibers. It is attached, above, to the margin of the articular surface of the tibia, blending with the transverse ligament; below, to the talus behind its superior articular facet. Laterally, it is somewhat thickened, and is attached to the hollow on the medial surface of the lateral malleolus. i Post. lot. malleol. Eg Dorsal talonavic. lia. \ Calcaneonavic, parl\r,-, I Calcaneocuboid part]^^^'^'"^^^'^ ^'O- I Dorsal cuboideonavic. tig. Dorsal navicular cuneif. lig, \ Dorsal cuneocuboid lig. .1 \Dorsal intercuneif, Uq, /y Dorsal tarsometat. lig Post, talofibular lig Dorsal \calcaneocub lig. Long plantar lig. \ ]Interos. talocalcan. lig I Ant. talofibular lig, Caicaneofibular lig. Dorsal intermet. lig. Dorsal tarsomet. lig. Fig. 355. — The ligaments of the foot from the lateral aspect. (Cjuain.) I The Deltoid Ligament (ligamentum deltoideum; internal lateral ligament) (Fig. 331). — The deltoid ligament is a strong, flat, triangular band, attached, above, to the apex and anterior and posterior borders of the medial malleolus. It consists of two sets of fibers, superficial and deep. Of the superficial fibers the most anterior (tibionavicular) pass forward to be inserted into the tuberosity of the navicular bone, and immediately behind this they blend with the medial margin of the plantar calcaneonavicular ligament; the middle (calcaneotibial) descend almost perpendicularly to be inserted into the w^hole length of the sustentaculum tali of the calcaneus; the posterior fibers (posterior talotibial) pass backward and lateralward to be attached to the inner side of the talus, and to the prominent TALOCRURAL ARTICULATION OR ANKLE-JOINT 351 11^^ ercle on its posterior surface, medial to the groove for the tendon of the Flexor hallucis longus. The deep fibers {anterior talotibial) are attached, above, to the tip of the medial malleolus, and, below, to the medial surface of the talus. The deltoid ligament is covered by the tendons of the Tibialis posterior and Flexor digitorum longus. The anterior and posterior talofibular and the calcaneofibular ligaments were formerly described as the three fasciculi of the external lateral ligament of the ankle-joint. The Anterior Talofibular Ligament {lig amentum talofibulare anterius) (Fig. 355). The anterior talofibular ligament, the shortest of the three, passes from the anterior margin of the fibular malleolus, forward and medially, to the talus, in front of its lateral articular facet. The Posterior Talofibular Ligament (ligamentum talofibulare posterius) (Fig. 355). The posterior talofibular ligament, the strongest and most deeply seated, runs almost horizontally from the depression at the medial and back part of the fibular malleolus to a prominent tubercle on the posterior surface of the talus immediately lateral to the groove for the tendon of the Flexor hallucis longus. The Calcaneofibular Ligament {ligamentum calcaneqfibulare) (Fig. 355). — The calcaneofibular ligament, the longest of the three, is a narrow, rounded cord, run- ning from the apex of the fibular malleolus downward and slightly backward to a tubercle on the lateral surface of the calcaneus. It is covered by the tendons of the Peronsei longus and brevis. Anterior talofibular ligament Posterior ialofihular ligament Calcaneofibtdar ligament Lateral kUocalcaneal ligament II Anterior talocalcaneal ligament Fig. 356. — Capsule of left talocrura articulation (distended). Lateral aspect. Synovial Membrane (Fig. 356). — The synovial membrane invests the deep surfaces of the ligaments, and sends a small process upward between the lower ends of the tibia and fibula. Relations. — The tendons, vessels, and nerves in connection with the joint are, in front, from the medial side, the Tibialis anterior, Extensor hallucis proprius, anterior tibial vessels, deep peroneal nerve. Extensor digitorum longus, and Perona^us tertius; behind, from the medial side, the Tibialis posterior, Flexor digitonma longus, posterior tibial vessels, tibial nerve, Flexor hallucis longus; and, in the groove behind the fibular malleolus, the tendons of the Peromei longus and brevis. The arteries supplying the joint are derived from the malleolar branches of the anterior tibial and the peroneal. The nerves are derived from the deep peroneal and tibial. Movements. — When the body is in the erect position, the foot is at right angles to the leg. The movements of the joint are those of dorsiflexion and extension; dorsiflexion consists in the 352 -^^^^™r SYNDESMOLOGY approximation of the dorsum of the foot to the front of the leg, while in extension the heel 'is drawn up and the toes pointed downward. The range of movement varies in different individuals from about 50° to 90°. The transverse axis about which movement takes place is slightly oblique. The malleoli tightly embrace the talus in all positions of the joint, so that any slight degree of side-to-side movement which may exist is simply due to stretching of the ligaments of the talo- fibular syndesmosis, and slight bending of the body of the fibula. The superior articular surface of the talus is broader in front than behind. In doisiflexion, herefore, greater space is required between the two malleoU. This is obtained by a slight outward rotatory movement of the lower end of the fibula and a stretching of the ligaments of the syndesmosis; this lateral movement is faciUtated by a slight gliding at the tibiofibular articulation, and possibly also by the bending of the body of the fibula. Of the Ugaments, the deltoid is of very great power — so much so, that it usually resists a force which fractures the process of bone to which it is attached. Its middle portion, together with the calcaneofibular Ugament, binds the bones of the leg firmly to the foot, and resists displacement in every direction. Its anterior and posterior fibers limit extension and flexion of the foot respectively, and the anterior fibers also limit abduction. The posterior talofibular ligament assists the calcaneofibular in resisting the displacement of the foot back- ward, and deepens the cavity for the reception of the talus. The anterior talofibular is a security against the displacement of the foot forward, and hmits extension of the joint. The movements of inversion and eversion of the foot, together with the minute changes in form by which it is appUed to the ground or takes hold of an object in cUmbing, etc., are mainly effected in the tarsal joints; the joint which enjoys the greatest amount of motion being that be- tween the talus and calcaneus behind and the navicular and cuboid in front. This is often called the transverse tarsal joint, and it can, with the subordinate joints of the tarsus, replace the ankle- joint in a great measure when the latter has become ankylosed. Extension of the foot upon the tibia and fibula is produced by the Gastrocnemius, Soleus, Plantaris, Tibiahs posterior, Peronai longus and brevis. Flexor digitorum longus, and Flexor hallucis longus; dorsiflexion, Ijy the TibiaUs anterior, Peronseus tertius, Extensor digitorum longus, and Extensor hallucis proprius.^ V. Intertarsal Articulatdons (Articulationes Intertarseae ; Articulations of the Tarsus). Talocalcaneal Articulation (articulatio talocalcanea; articulation of the calcaneus and astragalus; calcaneo-astragaloid articulation). — The articulations between the calcaneus and talus are two in number — anterior and posterior. Of these, the anterior forms part of the talocalcaneonavicular joint, and will be described with that articulation. The posterior or talocalcaneal articulation is formed betw^een the posterior calcaneal facet on the inferior surface of the talus, and the posterior facet on the superior surface of the calcaneus. It is an arthrodial joint, and the two bones are connected by an articular capsule and by anterior, posterior, lateral , medial, and interosseous talocalcaneal ligaments. The Articular Capsule (capsula articularis) . — The articular capsule envelops the joint, and consists for the most part of short fibers, which are split up into distinct slips; betw^een these there is only a weak fibrous investment. The Anterior Talocalcaneal Ligament {ligamentum talocalcaneum anterius; anterior calcaneo-astragaloid ligament) (Figs. 356, 359). — The anterior talocalcaneal liga- ment extends from the front and lateral surface of the neck of the talus to the superior surface of the calcaneus. It forms the posterior boundary of the talocalcaneonavicular joint, and is sometimes described as the anterior interosseous ligament. The Posterior Talocalcaneal Ligament {ligamentum talocalcaneum posteriiis; posterior calcaneo-astragaloid ligament) (Fig. 354). — The posterior talocalcaneal ligament connects the lateral tubercle of the talus with the upper and medial part of the calcaneus; it is a short band, and its fibers radiate from their narrow attach- ment to the talus. The Lateral Talocalcaneal Ligament (ligamentum talocalcaneum laterale; external calcaneo-astragaloid ligament) (Figs. 356, 359).— The lateral talocalcaneal ligament 1 The student must bear in mind that the Extensor digitorum longus and Extensor hallucis proprius are extenaora of the toes, but flexors of the ankle: and that the Flexor digitorum longus and Flexor hallucis longus are flexors of the toes, but extensors of the ankle INTERTARSAL ARTICULATIONS 353 IS a short, strong fasciculus, passing from the lateral surface of the talus, imme- diately beneath its fibular facet to the lateral surface of the calcaneus. It is placed in front of, but on a deeper plane than, the calcaneofibular ligament, with the fibers of which it is parallel. The Medial Talocalcaneal Ligament (ligamentum talocalcaneum mediale; internal calcaneo-astragaloid ligament). — The medial talocalcaneal ligament connects the medial tubercle of the back of the talus with the back of the sustentaculum tali. Its fibers blend with those of the plantar calcaneonavicular ligament (Fig. 354) . Interosseous ligament of tibia fibular syndesmosis Medial malleolus - Deltoid ligament • Tibialis posterior' l^lexor digitorum longus Flexor fiallucis longus Med. plantar nerve and vessels Quadratus plantCB Abductor hallucis Lat. plantar nerve and vessels Flexor digitorum brevis Lateral malleolus Calcaneofibular ligament ,terosseou6 ligament Peroncetcs brevis PeroncBus longus Abductor digiti quinti Fig. 357. — Coronal section through right talocrural and talocalcaneal joints. The Interosseous Talocalcaneal Ligament (ligamentum talocalcaneum interosseum) (Figs. 357, 359). — The interosseous talocalcaneal ligament forms the chief bond of union between the bones. It is, in fact, a portion of the united capsules of the talocalcaneonavicular and the talocalcaneal joints, and consists of two partially united layers of fibers, one belonging to the former and the other to the latter joint. It is attached, above, to the groove between the articular facets of the under surface of the talus; below, to a corresponding depression on the upper surface of the cal- caneus.' It is very thick and strong, being at least 2.5 cm. in breadth from side to side, and serves to bind the calcaneus and talus firmly together. Synovial Membrane (Fig. 360). — The synovial membrane lines the capsule of the joint, and is distinct from the other synovial membranes of the tarsus. Movements. — The movements permitted between the talus and calcaneus are limited to glid- ing of the one bone on the other backward and forward and from side to side. Talocalcaneonavicular Articulation {articulatio talocalcaneonacicularis) . — This articulation is an arthrodial joint: the rounded head of the talus being received into the concavity formed by the posterior surface of the navicular, the anterior articular surface of the calcaneus, and the upper surface of the plantar calcaneo- 23 354 SYNDESMOLOGY navicular ligament. There are two ligaments in this joint: the articular capsule] and the dorsal talonavicular. The Articular Capsule (capsula articularis) . — The articular capsule is imperfectly developed except posteriorly, where it is considerably thickened and forms, with a part of the capsule of the talocalcaneal joint, the strong interosseous ligament which fills in the canal formed by the opposing grooves on the calcaneus and talus, as above mentioned. The Dorsal Talonavicular Ligament {ligamentum talonaviculare dorsale; superior astragalonavicular ligament) (Fig. 354).— This ligament is a broad, thin band, which connects the neck of the talus to the dorsal surface of the navicular bone; it is covered by the Extensor tendons. The plantar calcaneonavicular supplies the place of a plantar ligament for this joint. Synovial Membrane. — The synovial membrane lines all parts of the capsule of the joint Movements. — This articulation permits of a considerable range of ghding movements, and some rotation; its feeble construction allows occasionally of dislocation of the other bones of the tarsus from the talus. Calcaneocuboid Articulation (articulatio calcaneocuhoidea; articulation of the calcaneus with the cuboid). — The ligaments connecting the calcaneus with the cuboid are five in number, viz., the articular capsule, the dorsal calcaneocuboid, part of the bifurcated, the long plantar, and the plantar calcaneocuboid. The Articular Capsule {capsula articularis). — The articular capsule is an imper- fectly developed investment, containing certain strengthened bands, which form the other ligaments of the joint. The Dorsal Calcaneocuboid Ligament {ligamentum calcaneocuhoideum dorsale; supe- rior calcaneocuboid ligament) (Fig. 355). — The dorsal calcaneocuboid ligament is a thin but broad fasciculus, which passes between the contiguous surfaces of the calcaneus and cuboid, on the dorsal surface of the joint. The Bifurcated Ligament {ligamentum bifurcatum; internal calcaneocuboid; inter- osseous ligament) (Fig. 355, 359). — The bifurcated ligament is a strong band, attached behind to the deep hollow on the upper surface of the calcaneus and divid- ing in froi^t in a Y-shaped manner into a calcaneocuboid and a calcaneonavicular part. The calcaneocuboid part is fixed to the medial side of the cuboid and forms one of the principal bonds between the first and second rows of the tarsal bones. The calcaneonavicular part is attached to the lateral side of the navicular. The Long Plantar Ligament {ligamentum plantare longum; long calcaneocuboid ligament; superiicial long plantar ligament) (Fig. 358) . — The long plantar ligament is the longest of all the ligaments of the tarsus : it is attached behind to the plantar surface of the calcaneus in front of the tuberosity, and in front to the tuberosity on the plantar surface of the cuboid bone, the more superficial fibers being con- tinued forward to the bases of the second, third, and fourth metatarsal bones. This ligament converts the groove on the plantar surface of the cuboid into a canal for the tendon of the Peronseus longus. The Plantar Calcaneocuboid Ligament {ligamentum calcaneocuboideum plantare; short calcaneocuboid ligament; short plantar ligament) (Fig. 358). — The 'plantar calcaneocuboid ligament lies nearer to the bones than the preceding, from which it is separated by a little areolar tissue. It is a short but wide band of great strength, and extends from the tubercle and the depression in front of it, on the forepart of the plantar surface of the calcaneus, to the plantar surface of the cuboid behind the peroneal groove. Synovial Membrane. — The synovial membrane lines the inner surface of the capsule and is distinct from that of the other tarsal articulations (Fig. 360). Movements. — The movements permitted between the calcaneus and cuboid are limited to slight ghding. movements of the bones upon each other. The transverse tarsal joint is formed by the articulation of the calcaneus with the cuboid, and INTERTARSAL ARTICULATIONS 355 the articulation of the talus with the navicular. The movement which takes place in this joint is more extensive than that in the other tarsal joints, and consists of a sort of rotation by means of which the foot may be sUghtly flexed or extended, the sole being at the same time carried medially (inverted) or laterally (everted). The Ligaments Connecting the Calcaneus and Navicular. — Though the calcaneus and navicular do not directly articulate, they are connected by two ligaments: the calcaneonavicular part of the bifurcated, and the plantar calcaneonavicular. The calcaneonavicular part of the bifurcated ligament is described on page 354. Plantar intermetatar . lig. irdar calcaneocub. lig. —— Tendon peronanis longus muscle Long plantar ligament Tendon peronceus ^ longus muscle --•^ Plantar tarsometatar. lig. Tendon tibialis anticua nvuscle 'Plantar cuneonavic. lig, '^"Plantar cuboideonavic, ligament ^i_ Plantar calcaneonavic. ligament Tendon tibialis posticus muscle Fig. 358.- -Ligaments of the sole of the foot, with the tendons of the Peronseus longus. Tibialis posterior and Tibialis anterior muscles. (Quain.) The Plantar Calcaneonavicular Ligament (ligamentum ealcaneonaviculare plantare; inferior or internal calcaneonavicular ligament; calcaneonavicular ligament) (Figs. 354, 358) . — The plantar calcaneonavicular ligament is a broad and thick band of fibers, which connects the anterior margin of the sustentaculum tali of the calca- IB neus to the plantar surface of the navicular. This ligament not only serves to H connect the calcaneus and navicular, but supports the head of the talus, forming 356 SYNDESMOLOGY part of the articular cavity in which it is received. The dorsal surface of the ligament presents a fibrocartilaginous facet, lined by the synovial membrane, and upon this a portion of the head of the talus rests. Its plantar surface is supported by the tendon of the Tibialis posterior; its medial border is blended with the forepart of the deltoid ligament of the ankle-joint. Tibialis 'posterior Interosseous talocalcaneal ligament Lateral talocalcaneal ligament Anterior talocalcaneal ligament Fio. 359. — Talocalcaneal and talocalcaneonavicular articulations exposed from above by removing the talus. The plantar calcaneonavicular ligament, by supporting the head of the talus, is principally concerned in maintaining the arch of the foot. When it yields, the head of the talus is pressed downward, medialward, and forward by the weight of the body, and the foot becomes flattened, expanded, and turned lateralward, and exhibits the condition known as flal-foot. This ligament contains a considerable amount of elastic fibers, so as to give elasticity to the arch and spring to the foot; hence it is sometimes called the "spring" ligament. It is supported, on its plantar surface, by the tendon of the Tibialis posterior, which spreads out at its insertion into a number of fasciculi, to be attached to most of the tarsal and metatarsal bones. This prevents undue stretching of the ligament, and is a protection against the occurrence of flat-foot; hence muscular weakness is, in most cases, the primary cause of the deformity. Cuneonavicular Articulation (articulatio cuneonavicularis; articulation of the navicular with the cuneiform bones). — The navicular is connected to the three cuneiform bones by dorsal and plantar ligaments. The Dorsal Ligaments (ligamenta navicularicuneiformia dorsalia). — The dorsal ligaments are three small bundles, one attached to each of the cuneiform bones. The bundle connecting the navicular with the first cuneiform is continuous around the medial side of the articulation with the plantar ligament which unites these two bones (Figs. 354, 355) . The Plantar Ligaments {ligamenta navicularicuneiformia plantaria) . — The plantar ligaments have a similar arrangement to the dorsal, and are strengthened by slips from the tendon of the Tibialis posterior (Fig. 358). Sjmovial Membrane. — The sjTiovial membrane of these joints is part of the great tarsal synovial membrane (Fig. 360). Movements. — Mere gliding movements are permitted between the navicular and cuneiform bones. Cuboideonavicular Articulation. — The navicular bone is connected with the cuboid by dorsal, plantar, and interosseous ligaments. INTERTARSAL ARTICULATIONS 357 II The Dorsal Ligament {ligamentum cuboideonaviculare dorsale) . — The dorsal ligament extends obliquely forward and lateralward from the navicular to the cuboid bone (Fig. 355). The Plantar Ligament (ligavientum cuboideonaviculare plantare). — The plantar ligament passes nearly transversely between these two bones (Fig. 358), The Interosseous Ligament. — The interosseous ligament consists of strong trans- verse fibers, and connects the rough non-articular portions of the adjacent surfaces of the two bones Fig. 360). Ssmovial Membrane. — The synovial membrane of this joint is part of the great tarsal synovial membrane (Fig. 360). Movements. — The movements permitted between the navicular and cuboid bones are limited to a slight gliding upon each other. Deltoid ligament Ankle-joint Talofibular ligament Interosseous talocalcaneal ligament Metatarsals Fig, 360. — Oblique section of left intertarsal and tarsometatarsal articulations, showing the synovial cavities. Intercuneiform and Cuneocuboid Articulations. — The three cuneiform bones and the cuboid are connected together by dorsal, plantar, and interosseous ligaments. The Dorsal Ligaments (ligamenta intercuneiformia dorsalia). — The dorsal liga- ments consist of three transverse bands : one connects the first with the second cuneiform, another the second with the third cuneiform, and another the third cuneiform with the cuboid. The Plantar Ligaments (ligamenta intercuneiformia plantaria). — The plantar liga- ments have a similar arrangement to the dorsal, and are strengthened by slips from the tendon of the Tibialis posterior. The Interosseous Ligaments (ligamenta intercuneiformia interossea). — The inter- osseous ligaments consist of strong transverse fibers which pass between the rough non-articular portions of the adjacent surfaces of the bones (Fig. 360) . 358 SYNDESMOLOGY Synovial Membrane. — The synovial membrane of these joints is part of the great tarsal synovial membrane (Fig. 360). Movements. — The movements permitted between these bones are limited to a slight gUding upon each other. VI. Tarsometatarsal Articulations (Articulationes Tarsometatarseae). These are arthrodial joints. The bones entering into their formation are the first, second, and third cuneiforms, and the cuboid, which articulate with the bases of the metatarsal bones. The first metatarsal bone articulates with the first cunei- form; the second is deeply wedged in between the first and third cuneiforms articulating by its base with the second cuneiform; the third articulates with the third cuneiform; the fourth, with the cuboid and third cuneiform; and the fifth, with the cuboid. The bones are connected by dorsal, plantar, and interosseous ligaments. The Dorsal Ligaments {ligamenta tarsometatarsea dorsalia) . — The dorsal ligaments are strong, flat bands. The first metatarsal is joined to the first cuneiform by a broad, thin band; the second has three, one from each cuneiform bone; the third has one from the third cuneiform; the fourth has one from the third cuneiform and one from the cuboid; and the fifth, one from the cuboid (Figs. 354, 355). The Plantar Ligaments (ligamenta tarsometatarsea plantaria) .—The plantar liga- ments consist of longitudinal and oblique bands, disposed with less regularity than the dorsal ligaments. Those for the first and second metatarsals are the strongest; the second and third metatarsals are joined by oblique bands to the first cuneiform; the fourth and fifth metatarsals are connected by a few fibers to the cuboid (Fig. 358). The Interosseous Ligaments (ligamenta cuneometatarsea interossia). — The inter- osseous ligaments are three in number. The first is the strongest, and passes from the lateral surface of the first cuneiform to the adjacent angle of the second meta- tarsal. The second connects the third cuneiform with the adjacent angle of the second metatarsal. The third connects the lateral angle of the third cuneiform with the adjacent side of the base of the third metatarsal. Synovial Membrane (Fig. 360). — The synovial membrane between the first cuneiform and the first metatarsal forms a distinct sac. The synovial membrane between the second and third cuneiforms behind, and the second and third metatarsal bones in front, is part of the great tarsal synovial membrane. Two prolongations are sent forward from it, one between the adjacent sides of the second and third, and another between those of the third and fourth metatarsal bones. The synovial membrane between the cuboid and the fourth and fifth metatarsal bones forms a distinct sac. From it a prolongation is sent forward between the fourth and fifth metatarsal bones. Movements. — The movements permitted between the tarsal and metatarsal bones are limited to slight ghding of the bones upon each other. Nerve Supply. — The intertarsal and tarsometatarsal joints are supphed by the deep peroneal nerve. VII. Intermetatarsal Articulations (Articulationes Intermetatarsese). The base of the first metatarsal is not connected with that of the second by any ligaments; in this respect the great toe resembles the thumb. The bases of the other four metatarsals are connected by the dorsal, plantar, and interosseous ligaments. The Dorsal Ligaments (ligamenta hasium [oss. metatars.] dorsalia) pass transversely between the dorsal surfaces of the bases of the adjacent metatarsal bones. The Plantar Ligaments (ligamenta hasium [oss. metatars] 'plantaria) . — The plantar ligaments have a similar arrangement to the dorsal. The Interosseous Ligaments (ligamenta hasium [oss. metatars.] interossea). — The interosseous ligaments consist of strong transverse fibers which connect the rough non-articular portions of the adjacent surfaces. II ARTICULATIONS OF THE DIGITS 359 Synovial Membranes (Fig. 360). — The synovial membranes between the second and third, and the third and fourth metatarsal bones are part of the great tarsal synovial membrane; that between the fourth and fifth is a prolongation of the synovial membrane of the cuboideometatarsal joint. Movements. — The movement permitted between the tarsal ends of the metatarsal bones is Hmited to a shght gUding of the articular surfaces upon one another. The heads of all the metatarsal bones are connected together by the transverse metatarsal ligament. The Transverse Metatarsal Ligament. — The transverse metatarsal ligament is a narrow band which runs across and connects together the heads of all the meta- tarsal bones; it is blended anteriorly with the plantar (glenoid) ligaments of the metatarsophalangeal articulations. Its plantar surface is concave where the Flexor tendons run below it; above it the tendons of the Interossei pass to their insertions. It differs from the transverse metacarpal ligament in that it connects the metatarsal to the others. The Synovial Membranes in the Tarsal and Tarsometatarsal Joints (Fig. 360). — The synovial membranes found in the articulations of the tarsus and metatarsus are six in number: one for the talocalcaneal articulation; a second for the talocalcaneonavicular articulation; a third for the calcaneocuboid articulation; and a fourth for the cuneonavicular, intercuneiform, and cimeo- cuboid articulations, the articulations of the second and third cuneiforms with the bases of the second and third metatarsal bones, and the adjacent surfaces of the bases of the second, third, and fourth metatarsal bones; a fifth for the first cuneiform with the metatarsal bone of the great toe; and a sixth for the articulation of the cuboid with the fourth and fifth metatarsal bones. A small synovial cavity is sometimes foimd between the contiguous surfaces of the navicular and cuboid bones. VIII. Metatarsophalangeal Articulations (Articulationes Metatarsophalangese). The metatarsophalangeal articulations are of the condyloid kind, formed by the reception of the rounded heads of the metatarsal bones in shallow cavities on the ends of the first phalanges. The ligaments are the plantar and two collateral. The Plantar Ligaments {ligamenta accessoria plantaria; glenoid ligaments of Cru- veilhier). — The plantar ligaments are thick, dense, fibrous structures. They are placed on the plantar surfaces of the joints in the intervals between the collateral ligaments, to which they are connected ; they are loosely united to the metatarsal bones, but very firmly to the bases of the first phalanges. Their plantar surfaces are intimately blended with the transverse metatarsal ligament, and grooved for the passage of the Flexor tendons, the sheaths surrounding which are connected to the sides of the grooves. Their deep surfaces form part of the articular facets for the heads of the metatarsal bones, and are lined by synovial membrane. The Collateral Ligaments {ligamenta collateralia; lateral ligaments) .—The collat- eral ligaments are strong, rounded cords, placed one on either side of each joint, and attached, by one end, to the posterior tubercle on the side of the head of the metatarsal bone, and, by the other, to the contiguous extremity of the phalanx. The place of dorsal ligaments is supplied by the Extensor tendons on the dorsal surfaces of the joints. Movements. — The movements permitted in the metatarsophalangeal articulations are flexion, extension, abduction, and adduction. IX. Articulations of the Digits (Articulationes Digitorum Pedis; Articulations of the Phalanges). The interphalangeal articulations are ginglymoid joints, and each has a plantar and two collateral ligaments. The arrangement of these ligaments is similar to that in the metatarsophalangeal articulations: the Extensor tendons supply the places of dorsal ligaments. 360 ^^^^^^m. SYNDESMOLOGY Movements. — The only movements permitted in the joints of the digits are flexion and exten- sion; these movements are more extensive between the first and second phalanges than between the second and third. The amomit of flexion is very considerable, but extension is hmited by the plantar and collateral ligaments. Arches of the Foot. In order to allow it to support the weight of the body in the erect posture with the least expenditure of material, the foot is constructed of a series of arches formed by the tarsal and metatarsal bones, and strengthened by the ligaments and tendons of the foot. The main arches are the antero-posterior arches, which may, for descriptive purposes, be regarded as divisible into two types — a medial and a lateral. The medial arch (see Fig. 290, page 276) is made up by the calcaneus, the talus, the navicular, the three cuneiforms, and the first, second, and third metatarsals. Its summit is at the superior articular surface of the talus, and its two extremities or piers, on which it rests in standing, are the tuberosity on the plantar surface of the calcaneus posteriorly and the heads of the first, second, and third metatarsal bones anteriorly. The chief characteristic of this arch is its elasticity, due to its height and to the number of small joints between its component parts. Its weakest part, i. e., the part most liable to yield from overpressure, is the joint between the talus and navicular, but this portion is braced by the plantar calcaneonavicular ligament, which is elastic and is thus able to quickly restore the arch to its pristine condition when the disturbing force is removed. The ligament is strengthened medially by blending with the deltoid ligament of the ankle-joint, and is supported inferiorly by the tendon of the Tibialis posterior, which is spread out in a fan- shaped insertion and prevents undue tension of the ligament or such an amount of stretching as would permanently elongate it. The arch is further supported by the plantar aponeurosis, by the small muscles in the sole of the foot, by the tendons of the Tibialis anterior and posterior and Peronseus longus, and by the ligaments of all the articulations involved. The lateral arch (see Fig. 291, page 277) is com- posed of the calcaneus, the cuboid, and the fourth and fifth metatarsals. Its summit is at the talocalcaneal articulation, and its chief joint is the calcaneocuboid^ which possesses a special mechanism for locking, and allows only a limited move- ment. The most marked features of this arch are its solidity and its slight eleva- tion; two strong ligaments, the long plantar and the plantar calcaneocuboid, together with the Extensor tendons and the short muscles of the little toe, preserve its integrity. While these medial and lateral arches may be readily demonstrated as the component antero-posterior arches of the foot, yet the fundamental longitudinal arch is contributed to by both, and consists of the calcaneus, cuboid, third cunei- form, and third metatarsal: all the other bones of the foot may be removed without destroying this arch. In addition to the longitudinal arches the foot presents a series of transverse arches. At the posterior part of the metatarsus and the anterior part of the tarsus the arches are complete, but in the middle of the tarsus they present more the characters of half-domes the concavities of which are directed downward and medialward, so that when the medial borders of the feet are placed in apposition a complete tarsal dome is formed. The transverse arches are strengthened by the interosseous, plantar, and dorsal ligaments, by the short muscles of the first and fifth toes (especially the transverse head of the Adductor hallucis), and by the Peronseus longus, whose tendon stretches across between the piers of the arches. BIBLIOGRAPHY. R. Fick: Handbuch der Anatomie und Mechanik der Gelenke (Bardeleben 's Handbuch der Anatomie). I II myology; THE Muscles are connected with the bones, cartilages, ligaments, and skin, either directly, or through the intervention of fibrous structures called tendons or aponeuroses. Where a muscle is attached to bone or cartilage, the fibers end in blunt extremities upon the periosteum or perichondrium, and do not come into direct relation with the osseous or cartilaginous tissue. Where muscles are con- nected with its skin, they lie as a flattened layer beneath it, and are connected with its areolar tissue by larger or smaller bundles of fibers, as in the muscles of the face. The muscles vary extremely in their form. In the limbs, they are of considerable length, especially the more superficial ones; they surround the bones, and constitute an important protection to the various joints. In the trunk, they are broad, flattened, and expanded, and assist in forming the walls of the trunk cavities. Hence the reason of the terms, long, broad, short, etc., used in the description of a muscle. There is considerable variation in the arrangement of the fibers of certain muscles with reference to the tendons to which they are attached. In some muscles the fibers are parallel and run directly from their origin to their insertion; these are quadrilateral muscles, such as the Thyreohyoideus. A modification of these is found in the fusiform muscles, in which the fibers are not quite parallel, but slightly curved, so that the muscle tapers at either end; in their actions, however, they resemble the quadrilateral muscles. Secondly, in other muscles the fibers are convergent; arising by a broad origin, they converge to a narrow or pointed inser- tion. This arrangement of fibers is found in the triangular muscles — e. g., the Temporalis. In some muscles, which otherwise would belong to the quadrilateral or triangular type, the origin and insertion are not in the same plane, but the plane of the line of origin intersects that of the line of insertion; such is the case in the Pectineus. Thirdly, in some muscles (e. g., the Peronei) the fibers are oblique and converge, like the plumes of a quill pen, to one side of a tendon which runs the entire length of the muscle; such muscles are termed unipennate. A modification of this condition is found where oblique fibers converge to both sides of a central tendon; these are called bipennate, and an example is afforded in the Rectus femoris. Finally, there are muscles in which the fibers are arranged in curved bundles m one or more planes, as in the Sphincters. The arrangement of the fibers is of con- siderable importance in respect to the relative strength and range of movement of the muscle. Those muscles where the fibers are long and few in number have great range, but diminished strength; where, on the other hand, the fibers are short and more numerous, there is great power, but lessened range. The names applied to the various muscles have been derived: (1) from their situation, as the Tibialis, Radialis, Ulnaris, Peronaeus; (2) from their direction, as the Rectus abdominis, Obliqui capitis, Transversus abdominis; (3) from their uses, as Flexors, Extensors, Abductors, etc.; (4) from their shape, as the Deltoideus, 1 The muscles and fasciae are described conjointly, in order that the student may consider the arrangement of the latter in his dissection of the former. It is rare for the student of anatomy in this country to have the opportunity of dissecting the fascise separately; and it is for this reason, as well as from the close connection that exists between the muscles and their investing sheaths, that they are considered together. Some general observations are first made on the anatomy of the muscles and fascis, the special descriptions being given in connection with the different regions. (361) 362 ^^^^^^^- MYOLOGY Rhomboideus; (5) from the number of their divisions, as the Biceps and Triceps; (6) from their points of attachment, as the Sternocleidomastoideus, Sternohyoideus, ._ Sternothyreoideus. ll In the description of a muscle, the term origin is meant to imply its more fixed or central attachment; and the term insertion the movable point on which the force of the muscle is applied; but the origin is absolutely jBxed in only a small number MM of muscles, such as those of the face which are attached by one extremity to immov- ■■ able bones, and by the other to the movable integument; in the greater number, the muscle can be made to act from either extremity. MM In the dissection of the muscles, attention should be directed to the exact origin, H insertion, and actions of each, and to its more important relations with surrounding parts. While accurate knowledge of the points of attachment of the muscles is of great importance in the determination of their actions, it is not to be regarded as conclusive. The action of the muscle deduced from its attachments, or even by pulling on it in the dead subject, is not necessarily its action in the living. By pulling, for example, on the Brachioradialis in the cadaver the hand may be slightly supinated when in the prone position and slightly pronated when in the supine position, but there is no evidence that these actions are performed by the muscle during life. It is impossible for an individual to throw into action any one muscle; in other words, movements, not muscles, are represented in the central nervous system. To carry out a movement a definite combination of muscles is called into play, and the individual has no power either to leave out a muscle from this com- bination or to add one to it. One (or more) muscle of the combination is the chief moving force; when this muscle passes over more than one joint other muscles (synergic muscles) come into play to inhibit the movements not required; a third set of muscles (fixation muscles) fix the limb — i. e., in the case of the limb-movements — and also prevent disturbances of the equilibrium of the body generally. As an example, the movement of the closing of the fist may be considered: (1) the prime movers are the Flexores digitorum. Flexor pollicis longus, and the small muscles of the thumb; (2) the synergic muscles are the Extensores carpi, which prevent flexion of the wrist; while (3) the fixation muscles are the Biceps and Triceps brachii, which steady the elbow and shoulder. A further point which must be borne in mind in considering the actions of muscles is that in certain positions a movement can be effected by gravity, and in such a case the muscles acting are the antagonists of those which might be supposed to be in action. Thus in flexing the trunk when no resistance is interposed the Sacrospinales contract to regulate the action of gravity, and the Recti abdominis are relaxed.^ By a consideration of the action of the muscles, the surgeon is able to explain the causes of displacement in various forms of fracture, and the causes which pro- duce distortion in various deformities, and, consequently, to adopt appropriate treatment in each case. The relations, also, of some of the muscles, especially those in immediate apposition with the larger bloodvessels, and the surface mark- ings they produce, should be remembered, as they form useful guides in the application of ligatures to those vessels. MECHANICS OF MUSCLE.^ In studying the mechanical action of muscles the individual muscle cannot always be treated as a single unit, since different parts of the same muscle may have entirely different actions, as with the Pectoralis major, the Deltoid, and the Trapezius where the nerve impulses control and stimulate different portions of the ' Consult in this connection the Croonian Lectures (1903) on "Muscular Movements and Their Representation in the Central Nervous System," by Charles E. Beevor, M.D. 2 R. Fick. Bd. ii, in Bardeleben's Handbuch der Anatomie des Menschen. MECHANICS OF MUSCLE 363 muscle in succession or at different times. Most muscles are, however, in a mechanical sense units. But in either case the muscle fibers constitute the elementary motor elements. Fio. 361 The Direction of the Muscle Pull. — In those muscles where the fibers always run in a straight line from origin to insertion in all positions of the joint, a straight line joining the middle of the surface of origin with the middle of the insertion surface Fig. 362 w^ill give the direction of the pull (Fig. 361). If, however, the muscle or its tendon is bent out of a straight line by a bony process or ligament so that it runs ove:: a pulley-like arrangement, the direction of the muscle pull is naturally bent out of Fig. 363 line. The direction of the pull in such cases is from the middle point of insertion to the middle point of the pulley where the muscle or tendon is bent. Muscles or tendons of muscles which pass over more than one joint and pass through more than 364 MYOLOGY one pulley may be resolved, so far as the direction of the pull is concerned, into two or more units or single-joint muscles (Fig. 362). The tendons of the Flexor pro- fundus digitorum, for example, pass through several pulleys formed by fibrous sheaths. The direction of the pull is different for each joint and varies for each joint according to the position of the bones. The direction is determined in each case, however, by a straight line between the centers of the pulleys on either side of the joint (Fig. 363). The direction of the pull in any of the segments would not be altered by any change in the position or origin of the muscle belly above the proximal pulley. The Action of the Muscle Pull on the Tendon. — 'WTiere the muscle fibers are parallel or nearly parallel to the direction of the tendon the entire strength of the muscle contraction acts in the direction of the tendon. In pinnate muscles, however, only a portion of the strength of contraction is effi- cient in the direction of the tendon, since a portion of the pull would tend to draw the tendon to one side, this is mostly annulled by pressure of surrounding parts. In bipinnate muscles this lateral pull is counterbalanced. If, for example, the muscle fibers are inserted into the tendon at an angle of 60 degrees (Fig. 364), it is easy to determine by the parallelogram of forces that the strength of the pull along the direction of the tendon is equal to one-half the muscle pull. T = tendon, m = strength and direction of muscle pull. t = component acting in the direction of the tendon. = angle of insertion of muscle fibers into tendon. t ^ y^ cos (^ = 0.5 = ^ m cos z 60° 0.50000 t = If 72'* 41° 90° 0° _ 1 — 1 30' 20' m cos = 1" cos = f cos = = 1 Fia. 364 cos = The more acute the angle ^, that is the smaller the angle, the greater the component acting in the direction of the tendon pull. At 41° 20' three-fourths of the pull would be exerted in the direction of the tendon and at 0° the entire strength. On the other hand, the greater the angle the smaller the tendon component; at 72° 30' one-third the muscle strength would act in the direction of the tendon and at 90° the tendon component would be nil. The Strength of Muscles. — The strength of a muscle depends upon the number of fibers in what is known as the physiological cross-section, that is, a section which passes through practically all of the fibers. In a muscle with parallel or nearly parallel fibers which have the same direction as the tendon this corresponds to the anatomical cross-section, but in unipinnate and bipinnate muscles the physiological cross-section may be nearly at right angles to the anatomical cross-section as shown in Fig. 365. Since Huber has shown that muscle fibers in a single fasciculus of a given muscle vary greatly in length, in some fasciculi from 9 mm. to 30.4 mm., it is unlikely that the physiological cross-section will pass through all the fibers. Estimates have been made of the strength of muscles and it is probable that coarse- fibered muscles are somewhat stronger per square centimeter of physiological MECHANICS OF MUSCLE 365 cross-section than are the fine-fibered muscles. Fick estimates the average strength as about 10 kg. per square cm. This is known as the absolute muscle strength. The total strength of a muscle would be equal to the number of square centimeters in its physiological cross-section X 10 kg. -PCS PCS A B c Fig. 365 — A, fusiform; B, unipinnate; C, bipinnate; P.C.S., physiological cross-section. The Work Accomplished by Muscles. — For practical uses this should be expressed in kilogr ammeters. In order to reckon the amount of work which a muscle can perform under the most favorable conditions it is necessary to know (1) its physio- logical cross-section (2) the maximum shortening, and (3) the position of the joint ■ when the latter is obtained. Work = lifted weight X height through which the weight is lifted; or Work = tension X distance; tension = physiological cross-section X absolute ^ muscle strength. ^b If a muscle has a physiological cross-section of 5 sq. cm, its tension strength = ^■5 X 10 or 50 kg. If it shortens 5 cm. the work = 50 X .05 = 2.5 kilogrammeters. ^P If one determines then the physiological cross-section and multiplies the absolute muscle strength, 10 kg, by this, the amount of tension is easily obtained. Then one must determine only the amount of shortening of the muscle for any particular position of the joint in order to determine the amount of work the muscle can do, since work = tension X distance. The tension of a muscle is, howevsr, not constant during the course of contraction but is continually decreasing during contraction. It is at a maximum at the begin- ■ ning and gradually decreases. This can be illustrated by the work diagram Fig. 366. AMD (ordinate) = tension. A V X (abscissa) = shortening. A D = tension of muscle in extended or antagonistic position. A V = amount of actual shortening. A M = tension in midposition = absolute muscle strength. D V = shows how the tension sinks from maximum (in the extended position of the muscle) where it is about double that in the midposition {M) to nothing on complete contraction. 366 MYOLOGY A A D V = work diagram, in reality the hypothenose is not straight but has a concave curve. The A has the same area as the rectangle A M M' V. A M = the average tension. Work = A M X A V kilogrammeters if the size of the ordinate as expressed in kilograms and the abscissa in meters. ^ SHORTENING Although the muscle works with a changing tension, yet the accomplishment is the same as if it were contracting with the tension of the midposition. In reality the amount of work is somewhat greater since even in extreme con- traction the muscle still retains a certain amount of tension so that the maximum amount of work is more nearly like A D X. We know that a muscle may have an extreme actual shortening of about 80 per cent, of its length when the tendon of insertion is cut. The trapezoid A D S V represents more nearly the amount cf wox'k, but since there are only approximate values and AD S Vis not much larger than AM M' F, we may use the latter. Only the tension and amount of shortening are needed to determine the amount of work of the muscle. Neither the lever arm nor the fiber angle in pinnate muscles need be considered." The diagram Fig. 367 shows that the lever arm is of no importance for deter- mining the amount of work the muscle performs. J B and J B^ = two bones jointed at J. CD and E F = the direction of the pull of two muscles of equal cross-section, each having a muscle tension of 1000 gms. The centers of the attachments are such that perpendiculars / c and J e to C D and E F are equal to 40 and 23 mm. respectively, J c = 40 mm. and J e = 23 mm. The static moments are equal to 1000 X 40 and 1000 X 23, therefore the first muscle can hold a much larger load (L) on the bone J B^ at H^ (100 mm. from J) than the second muscle whose load can be designated as L^. Equilibrium exists for the first muscle if i X 100 = 1000 X 40 or L = ^^^qq ^^ = 400 gms. For the second muscle D X 100 = 1000 X 23. 1000 X 23 D = ^ = 230 gms. If we suppose J JS to be fixed and J B^ to move in the plane of the paper about J and the muscle C D to shorten 5 mm. C d = C D — 5 mm. and with the tension of 1000 gms., J B^ will take the position J B^ and the load (L) will be lifted from H' to H\ MECHANICS OF MUSCLE 367 H the second muscle likewise shortens 5 mm. then E f = E F — 5 mm., and with the tension of 1000 gms. the bone J B^ will take the position J B^ and the weight or load (D) will be lifted from H^ to H^. The question now is to prove that the work done is the same in both cases, namely, 5 X 1000 grammillimeters. If so, 400 X H'W- = 230 X H' H^ = 5000 grammillimeters. Since the two radii Cd and C d' are very long as compared with the arc d d' we may consider this short arc as a line J_ to C Z) at d', likewise the arc //' may be considered as a straight line \_to E F. In the same manner we can consider the short arcs F f, D d, H' H'- and H' H' ± to the line J B\ The sides D d' and Ff of the A D d d' and F ff are each 5 mm. The lever arm D J = 60 mm. and J F = 30 mm. Fig. 367 The A D d d' k similar to the A D c J hence D d also H' m 5 :: 60 : 40 Dd :: 100 : 60 300 Dd = 40 :: 100 : 60 H' H'- = 300 40 300 24 The AFff is similar to F e J Ff =i-'^ ^ J OQ 30 : 23 [ hence F f : 5 also H'H' :Ff :: 100 : 30 150 mm-.— :: 100: 30 H' H' = . 400 X f = 230 X 1-|0 . 5000 Thus we see that the work of the two muscles depends on the size of the contrac- tion and on the tension and not on the lever arm in very small contractions or in 23 1500 69 368 MYOLOGY the summation of such contractions and therefore for large contractions. In the first muscle a large load is moved through a short distance and in the second muscle a lighter load is moved through a greater distance. The amount of work accomplished by pinnate muscles is not dependent upon the angle of insertion of the muscle fibers into the tendon, as will be seen b\' the following diagram Fig. 368. T' T = direction of the tendon pull. w a = direction of muscle fiber before con- traction. m' = direction of muscle fiber after contrac- tion. V = amount of contraction. m = tension of the muscle. (^ = angle of insertion of muscle fiber. t = tendon component = m X cos (/> = the weight carried by the tendon to balance the muscle tension. d = distance tendon is drawn up. (1) TO X V = work done by the muscle fiber. (2) t X d = work done by the movement of the tendon. If we consider the distance v as being very short then the line b c can be dealt with as though it were perpendicular to a c. then V = d X cos ^ or d I since t = m X cos or m = cos (p t m X v = t cos (f) X d X COS (f) = t X d T' o Fig. 368 COS If this is true for very minute contractions it is likewise true for a series of such contraction and hence for larger contractions. If we assume that <^ = 60°, m = 10 kg. and v = 5 mm., the work done by the contracting muscle fiber = m v or lOX 5 kilogrammilli- meters. cos z 60° = I; hence t = ^ m; and d = j == 2 v; ^ m = 5 kg.; and 2 v = 10 mm. hence t d = 50 kilogrammillimeters or the work done by the movement of the tendon in lifting the load of 5 kg. a distance of 10 mm., and is exactly the same as that done by the muscle fiber. The load on the tendon is but one-half the tension of the muscle, but the distance through which the load is lifted is twice that of the amount of shortening of the muscle. If (^ = 41° 20' then cos (^ = f hence t = f w and d = ^ v and t d = m v In pinnate muscles, then, we have the rather unexpected condition in which the same amount of movement of the tendon can be accomplished with less contrac- tion of the muscle than in muscles where the fibers have the same direction as the tendon. The Action of Muscles on Joints. — If we consider now the action of a single muscle extending over a single joint in which one bone is fixed and the other movable, we MECHANICS OF MUSCLE 369 will find that muscle pull can be resolved into two components, a turning com- ponent and a friction or pressure component as shown in Fig. 369. D F = the fixed bone from which the muscle takes its origin. D K = the movable bone. 01 = a line from the middle of origin to the middle of insertion. / M = size and direction of the muscle pull. If the parallelogram is constructed with / t and M h \_to D K, \hen 1 1 = the turning component and 7 6 = the component which acts against the joint. The size of the two components depends upon the insertion angle 4>. The smaller this angle the smaller the turning component, and ^he nearer this angle 4> is to 90° the larger the turning component. / i = I il/ X sin (^ lb = I M X cos <}> li <}> = 90^* cos o. — Muscles of tne neck, l^ateral view. m. THE SUPRA- AND INFRAHYOID MUSCLES (Figs. 385, 386). The suprahyoid muscles are : Digastricus. Stylohyoideus. Mylohyoideus. Geniohvoideus. The Digastricus (Digastric muscle) consists of two fleshy belHes united by an intermediate rounded tendon. It lies below the body of the mandible, and extends, in a curved form, from the mastoid process to the symphysis menti. The posterior belly, longer than the anterior, arises from the mastoid notch of the temporal bone and passes downward and forward. The anterior belly arises from a depression on the inner side of the lower border of the mandible, close to the symphysis, and passes downward and backward. The two bellies end in an intermediate tendon which perforates the Stylohyoideus muscle, and is held in connection with the side of the body and the greater cornu of the hyoid bone hy a fibrous loop, which is 392 MYOLOGY sometimes lined by a mucous sheath. A broad aponeurotic layer is given off from the tendon of the Digastricus on either side, to be attached to the body and greater cornu of the hyoid bone; this is termed the suprahyoid aponeurosis. Variations are numerous. The posterior belly may arise partly or entirely from the styloid process, or be connected by a slip to the middle or inferior constrictor; the anterior belly may be double or extra slips from this belly may pass to the jaw or Mylohyoideus or decussate with a simUar slip on opposite side; anterior belly may be absent and posterior belly inserted into the middle of the jaw or hyoid bone. The tendon may pass in front, more rarely behind the Stylo- hoideus. The Mentohyoideus muscle passes from the body of hyoid bone to chin . The Digastricus divides the anterior triangle of the neck into three smaller triangle (1) the submaxillary triangle, bounded above by the lower border of the body of the mandible, and a line drawn from its angle to the Stemocleidomastoideus, below by the posterior belly of the Digastricus and the Stylohyoideus, in front by the anterior belly of the Digastricus; (2) the carotid triangle, bounded above by the posterior belly of the Digastricus and Stylohyoideus, behind by the Stemocleidomastoideus, below by the Omohyoideus; (3) the suprahyoid or sub- mental triangle, bounded laterally by the anterior belly of the Digastricus, medially by the middle line of the neck from the hyoid bone to the symphysis menti, and inferiorly by the body of the hyoid bone. Fig. 386. — Muscles of the neck. Anterior view. '^, 1 The Stylohyoideus (Stylohyoid muscle) is a slender muscle, lying in front of, and above, the posterior belly of the Digastricus. It arises from the back and lateral surface of the styloid process, near the base; and, passing downward and forward, is inserted into the body of the hyoid bone, at its junction with the greater cornu, and just above the Omohyoideus. It is perforated, near its insertion, by the tendon of the Digastricus. Variations. — It may be absent or doubled, lie beneath the carotid artery, or be inserted into the Omohyoideus, Thyreohyoideus, or Mylohyoideus. The Stylohyoid Ligament (ligamentuvi stylohyoideus). — In connection with the Stylohyoideus muscle a ligamentous band, the stylohyoid ligament, may be THE SUPRA- AND INFRAHYOID MUSCLES 393 described. It is a fibrous cord, which is attached to the tip of the styloid process of the temporal and the lesser cornii of the hyoid bone. It frequently contains a little cartilage in its center, is often partially ossified, and in many animals forms a distinct bone, the epihyal. The Mylohyoideus (Mylohyoid muscle), flat and triangular, is situated imme- diately above the anterior belly of the Digastricus, and forms, with its fellow of the opposite side, a muscular floor for the cavity of the mouth. It arises from the whole length of the mylohyoid line of the mandible, extending from the symphysis in front to the last molar tooth behind. The posterior fibers pass medialward and slightly downward, to be inserted into the body of the hyoid bone. The middle and anterior fibers are inserted into a median fibrous raphe extending from the sym- physis menti to the hyoid bone, where they join at an angle with the fibers of the opposite muscle. This median raphe is sometimes wanting; the fibers of the two muscles are then continuous. Variations. — It may be united to or replaced by the anterior belly of the Digastricus; accessory slips to other hyoid muscles are frequent. The Geniohyoideus {Geniohyoid muscle) is a narrow muscle, situated above the medial border of the Mylohyoideus. It arises from the inferior mental spine on the back of the symphysis menti, and runs backward and slightly downward, to be inserted into the anterior surface of the body of the hyoid bone; it lies in con- tact with its fellow of the opposite side. Variations. — It may be blended with the one on opposite side or double; slips to greater cornu of hyoid bone and Genioglossus occur. Nerves. — The Mylohyoideus and anterior belly of the Digastricus are supplied by the mylo- hyoid branch of the inferior alveolar; the Stylohyoideus and posterior belly of the Digastricus, by the facial; the Geniohyoideus, by the hypoglossal. Actions. — These muscles perform two very important actions. During the act of deglutition they raise the hyoid bone, and with it the base of the tongue; when the hyoid bone is fixed by its depressors and those of the larynx, they depress the mandible. During the first act of degluti- tion, when the mass of food is being driven from the mouth into the pharynx, the hyoid bone and with it the tongue, is carried upward and forward by the anterior bellies of the Digastrici, the Mylohyoidei, and Geniohyoidei. In the second act, when the mass is passing through the pharynx, the direct elevation of the hyoid bone takes place by the combined action of aU the muscles; and after the food has passed, the hyoid bone is carried upward and backward by the posterior bellies of the Digastrici and the Stylohyoidei, which assist in preventing the return of the food into the mouth. The infrahyoid muscles are : Sternohyoideus. Thyreohyoideus. Sternothyreoideus. Omohyoideus. The Sternohyoideus {Sternohyoid muscle) is a thin, narrow muscle, which arises from the posterior surface of the medial end of the clavicle, the posterior sterno- clavicular ligament, and the upper and posterior part of the manubrium sterni. Passing upward and medialward, it is inserted, by short, tendinous fibers, into the lower border of the body of the hyoid bone. Below, this muscle is separated from its fellow by a considerable interval; but the two muscles come into contact with one another in the middle of their course, and from this upward, lie side by side. It sometimes presents, immediately above its origin, a transverse tendinous inscription. Variations. — Doubling; accessory slips (Cleidohyoideus) ; absence. The Sternothyreoideus {Sternothyroid muscle) is shorter and wider than the preceding muscle, beneath which it is situated. It arises from the posterior surface of the manubrium sterni, below the origin of the Sternohyoideus, and from the edge of the cartilage of the first rib, and sometimes that of the second rib, it is inserted MYOLOGY into the oblique line on the lamina of the thyroid cartilage. This muscle is in close contact with its fellow at the lower part of the neck, but diverges somewhat as it ascends; it is occasionally traversed by a transverse or oblique tendinous inscription. Variations.— Doubling; absence; accessory slips to Thyreohyoideus, Inferior constrictor, or carotid sheath. The Thyreohyoideus (Thyrohyoid muscle) is a small, quadrilateral muscle appearing like an upward continuation of the Sternothyreoideus. It arises from the oblique line on the lamina of the thyroid cartilage, and is inserted into the lower border of the greater cornu of the hyoid bone. The Omohyoideus (Omohyoid muscle) consists of two fleshy bellies united by a central tendon. It arises from the upper border of the scapula, and occasionally from the superior transverse ligament which crosses the scapular notch, its extent of attachment to the scapula varying from a few millimetres to 2.5 cm. From this origin, the inferior belly forms a flat, narrow fasciculus, which inclines forward and slightly upward across the lower part of the neck, being bound down to the clavicle by a fibrous expansion; it then passes behind the Sternocleidomastoideus, becomes tendinous and changes its direction, forming an obtuse angle. It ends in the superior belly, which passes almost vertically upward, close to the lateral border of the Sternohyoideus, to be inserted into the lower border of the body of the hyoid bone, lateral to the insertion of the Sternohyoideus. The central tendon of this muscle varies much in length and form, and is held in position by a process of the deep cervical fascia, which sheaths it, and is prolonged down to be attached to the clavicle and first rib; it is by this means that the angular form of the muscle is maintained. Variations. — Doubling; absence; origin from clavicle; absence or doubling of either belly. The inferior belly of the Omohyoideus divides the posterior triangle of the neck into an upper or occipital triangle and a lower or subclavian triangle, while its superior belly divides the anterior triangle into an upper or carotid triangle and a lower or muscular triangle. Nerves. — The Infrahyoid muscles are supplied by branches from the first three cervical nerves. From the first two nerves the branch joins the hypoglossal trunk, runs with it some distance, and sends off a branch to the Thyreohyoideus; it then leaves the hypoglossal to form the descendens hypoglossi and unites with the communicantes cervicalis from the second and third cervical nerves to form the ansa hypoglossi from which nerves pass to the other Infrahyoid muscles. Actions. — These muscles depress the larynx and hyoid bone, after they have been drawn up with the pharynx in the act of deglutition. The Omohyoidei not only depress the hyoid bone, but carry it backward and to one or the other side. They are concerned especially in prolonged inspiratory efforts; for by rendering the lower part of the cervical fascia tense they lessen the inward suction of the soft parts, which would otherwise compress the great vessels and the apices of the lungs. The Thyreohyoideus may act as an elevator of the thyroid cartilage, when the hyoid bone ascends, drawing the thyroid cartilage up behind the hyoid bone. The Sterno- thyreoideus acts as a depressor of the thyroid cartilage. IV. THE ANTERIOR VERTEBRAL MUSCLES (Fig. 387). The anterior vertebral muscles are : Longus colli. Rectus capitis anterior. Longus capitis. Rectus capitis lateralis. The Longus colli is situated on the anterior surface of the vertebral column, between the atlas and the third thoracic vertebra. It is broad in the middle, narrow and pointed at either end, and consists of three portions, a superior oblique, an inferior oblique, and a vertical. The superior oblique portion arises from the anterior tubercles of the transverse processes of the third, fourth, and fifth cervical vertebrae; and, ascending obliquely with a medial inclination, is inserted by a narrow i THE ANTERIOR VERTEBRAL MUSCLES 395 tendon into the tubercle on the anterior arch of the atlas. The inferior oblique portion, the smallest part of the muscle, arises from the front of the bodies of the first two or three thoracic vertebrae; and, ascending obliquely in a lateral direction, is inserted into the anterior tubercles of the transverse processes of the fifth and sixth cervical vertebrae. The vertical portion arises, below, from the front of the bodies of the upper three thoracic and lower three cervical vertebrae, and is in- serted into the front of the bodies of the second, third, and fourth cervical vertebrge. The Longus capitis (Rectus capitis anticus major), broad and thick above, narrow below, arises by four tendinous slips, from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical vertebrae, and ascends, converging toward its fellow of the opposite side, to be inserted into the inferior surface of the basilar part of the occipital bone. Fig. 387. — The anterior vertebral muscles. The Rectus capitis anterior {Rectus capitis anticus minor) is a short, flat muscle, situated immediately behind the upper part of the Longus capitis. It arises from the anterior surface of the lateral mass of the atlas, and from the root of its transverse process, and passing obliquely upward and medialward, is inserted into the inferior surface of the basilar part of the occipital bone immediately in front of the foramen magnum. The Rectus capitis lateralis, a short, flat muscle, arises from the upper surface of the transverse process of the atlas, and is inserted into the under surface of the jugular process of the occipital bone. Nerves. — The Rectus capitis anterior and the Rectus capitis lateralis are supplied from the loop between the first and second cervical nerves; the Longus capitis, by branches from the 396 ^^ MYOLOGY first, second, and third cervical; the Longus colli, by branches from the second to the seventh cervical nerves. Actions. — The Longus capitis and Rectus capitis anterior are the direct antagonists of the muscles at the back of the neck, serving to restore the head to its natural position after it has been drawn backward. These muscles also flex the head, and from their obhquity, rotate it, BO as to turn the face to one or the other side. The Rectus lateralis, acting on one side, bends the head laterally. The Longus colli flexes and slightly rotates the cervical portion of the vertebral column. V. THE LATERAL VERTEBRAL MUSCLES (Fig. 387). The lateral vertebral muscles are : Scalenus anterior. Scalenus medius. Scalenus posterior. The Scalenus anterior {Scalenus anticus) lies deeply at the side of the nee behind the Sternocleidomastoideus. It arises from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical vertebrae, and descending, almost vertically, is inserted by a narrow, flat tendon into the scalene tubercle on the inner border of the first rib, and into the ridge on the upper surface of the rib in front of the subclavian groove. The Scalenus medius, the largest and longest of the three Scaleni, arises from the posterior tubercles of the transverse processes of the lower six cervical vertebrae, and descending along the side of the vertebral column, is iriserted by a broad attachment into the upper surface of the first rib, between the tubercle and the subclavian groove. The Scalenus posterior (Scalenus posticus), the smallest and most deeply seated of the three Scaleni, arises, by two or three separate tendons, from the posterior tubercles of the transverse processes of the lower two or three cervical vertebrae, and is inserted by a thin tendon into the outer surface of the second rib, behind the attachment of the Serratus anterior. It is occasionally blended with the Scalenus medius. Variations. — The Scaleni muscles vary considerably in their attachments and in the arrange- ment of their fibers. A slip from the Scalenus anticus may pass behind the subclavian artery. The Scalenus posticus may be absent or extend to the third rib. The Scalenus pleuralis muscle extends from the transverse process of the seventh cervical vertebra to the fascia supporting the dome of the pleura and inner border of first rib. Nerves. — The Scaleni are supplied by branches from the second to the seventh cervical nerves. Actions. — When the Scaleni act from above, they elevate the first and second ribs, and are, therefore, inspiratory muscles. Acting from below, they bend the vertebral column to one or other side; if the muscles of both sides act, the vertebral column is slightly flexed. THE FASCLffi AND MUSCLES OF THE TRUNK. The muscles of the trunk may be arranged in six groups: I. Deep Muscles of the Back. IV. Muscles of the Abdomen. II. Suboccipital Muscles. V. Muscles of the Pelvis. III. Muscles of the Thorax. VI. Muscles of the Perineum. L THE DEEP MUSCLES OF THE BACK (Fig. 388). The deep or intrinsic muscles of the back consist of a complex group of muscles extending from the pelvis to the skull. They are: Splenius capitis. Multifidus. Splenius cervicis. Rotatores. Sacrospinalis. Interspinales. Semispinalis. Intertransversarii . THE DEEP MUSCLES OF THE BACK 397 The Lumbodorsal Fascia (fascia lumbodorsalis; lumbar aponeurosis and vertebral fascia). — The lumbodorsal fascia is a deep investing membrane which covers the deep muscles of the back of the trunk. Above, it passes in front of the Serratus posterior superior and is continuous with a similar investing layer on the back of the neck — the nuchal fascia. In the thoracic region the lumbodorsal fascia is a thin fibrous lamina which serves to bind down the Extensor muscles of the vertebral column and to separate them from the muscles connecting the vertebral column to the upper extremity. It contains both longitudinal and transverse fibers, and is attached, medially, to the spinous processes of the thoracic vertebrae ; laterally to the angles of the ribs. In the lumbar region the fascia (lumbar aponeurosis) is in two layers, anterior and posterior (Figs. 388, 409). The posterior layer is attached to the spinous processes of the lumbar and sacral vertebrae and to the supraspinal ligament ; the anterior layer is attached, medially, to the tips of the transverse processes of the lumbar vertebrae and to the intertransverse ligaments, below, to the iliolumbar ligament, and above, to the lumbocostal ligament. The two layers unite at the lateral margin of the Sacrospinalis, to form the tendon of origin of the Transversus abdominis. The aponeurosis of origin of the Serratus posterior inferior and the Latissimus dorsi are intimately blended with the lumbodorsal fascia. ^Obliquus externus Mbliquus intemus Transversus Fascia on Qtuid. Lumb. lAimbod(yrsal\^'^^^^ ^V^ [ Posterior layer , Fia. 388. — Diagram of a transverse section of the posterior abdominal wall, to show the disposition of the lumbodorsal fascia. The Splenius capitis (Fig. 409) arises from the lower half of the ligamentum nuchae, from the spinous process of the seventh cervical vertebra, and from the spinous processes of the upper three or four thoracic vertebrae. The fibers of the muscle are directed upward and lateralward and are inserted, under cover of the Sternocleidomastoideus, into the mastoid process of the temporal bone, and into the rough surface on the occipital bone just below the lateral third of the superior nuchal line. The Splenius cervicis (Splenius colli) (Fig. 409) arises by a narrow tendinous band from the spinous processes of the third to the sixth thoracic vertebrae; it is inserted, by tendinous fasciculi, into the posterior tubercles of the transverse processes of the upper two or three cervical vertebrae. Variations. — The origin is frequently moved up or down one or two vertebrae. Accessory slips are occasionally found. Nerves. — The Splenii are supplied by the lateral branches of the posterior divisions of the middle and lower cervical nerves. Actions. — The Splenii of the two sides, acting together, draw the head directly backward, assisting the Trapezius and Semispinahs capitis; acting separately, they draw the head to one side, and shghtly rotate it, turning the face to the same side. They also assist in supporting the head in the erect position. The Sacrospinalis (Erector spines) (Fig. 389), and its prolongations in the thoracic and cervical regions, lie in the groove on the side of the vertebral column. 398 MYOLOGY They are covered in the lumbar and thoracic regions by the lumbodorsal fascia,| and in the cervical region by the nuchal fascia. This large muscular and tendinous Occipital bom Multibus First thoracic vertebra First lumbar vertebra First sacral vertebra Fig. 389. — Deep musclea of tlie back. THE DEEP MUSCLES OF THE BACK 399 mass varies in size and structure at different parts of the vertebral column. In the sacral region it is narrow and pointed, and at its origin chiefly tendinous in structure. In the lumbar region it is larger, and forms a thick fleshy mass which, on being followed upward, is subdivided into three columns; these gradually diminish in size as they ascend to be inserted into the vertebrae and ribs. The Sacrospinalis arises from the anterior surface of a broad and thick tendon, which is attached to the medial crest of the sacrum, to the spinous processes of the lumbar and the eleventh and twelfth thoracic vertebrae, and the supraspinal ligament, to the back part of the inner lip of the iliac crests and to the lateral crests of the sacrum, where it blends with the sacrotuberous and posterior sacro- iliac ligaments. Some of its fibers are continuous with the fibers of origin of the Glutseus maximus. The muscular fibers form a large fleshy mass which splits, in the upper lumbar region into three columns, viz., a lateral, the Iliocostalis, an intermediate, the Longissimus, and a medial, the Spinalis. Each of these consists from below upward, of three parts, as follows: Lateral Column. Intermediate Column. Medial Column. Iliocostalis. Longissimus. Spinalis, (a) I. lumborum. (a) L. dorsi. (a) S. dorsi. (6) I. dorsi. (6) L. cervicis. (b) S. cervicis. (c) I. cervicis. (c) L. capitis. (c) S. capitis. The Iliocostalis lumborum (Iliocostalis muscle; Sacrolumbalis muscle) is inserted, by six or seven flattened tendons, into the inferior borders of the angles of the lower six or seven ribs. The Iliocostalis dorsi (Musculus accessorius) arises by flattened tendons from the upper borders of the angles of the lower six ribs medial to the tendons of insertion of the Iliocostalis lumborum; these become muscular, and are inserted into the upper borders of the angles of the upper six ribs and into the back of the transverse process of the seventh cervical vertebra. The Iliocostalis cervicis {Cermcalis ascendens) arises from the angles of the third, fourth, fifth, and sixth ribs, and is inserted into the posterior tubercles of the trans- verse processes of the fourth, fifth, and sixth cervical vertebrae. The Longissimus dorsi is the intermediate and largest of the continuations of the Sacrospinalis. In the lumbar region, where it is as yet blended with the Ilio- costalis lumborum, some of its fibers are attached to the whole length of the pos- terior surfaces of the transverse processes and the accessory processes of the lumbar vertebrae, and to the anterior layer of the lumbodorsal fascia. In the thoracic region it is inserted, by rounded tendons,' into the tips of the transverse processes of all the thoracic vertebrae, and by fleshy processes into the lower nine or ten ribs between their tubercles and angles. The Longissimus cervicis {Transversalis cervicis), situated medial to the Longis- simus dorsi, arises by long thin tendons from the summits of the transverse pro- cesses of the upper four or five thoracic vertebrae, and is inserted by similar tendons into the posterior tubercles of the transverse processes of the cervical vertebrae from the second to the sixth inclusive. The Longissimus capitis ( Trachelomastoid muscle) lies medial to the Longissimus cervicis, between it and the Semispinalis capitis. It arises by tendons from the transverse processes of the upper four or five thoracic vertebrae, and the artic- ular processes of the lower three or four cervical vertebrae, and is inserted into the posterior margin of the mastoid process, beneath the Splenius capitis and Sterno- cleidomastoideus. It is almost always crossed by a tendinous intersection near its insertion. The Spinalis dorsi, the medial continuation of the Sacrospinalis, is scarcely separable as a distinct muscle. It is situated at the medial side of the Longissimus MYOLOGY dorsi, and is intimately blended with it ; it arises by three or four tendons from the spinous processes of the first two lumbar and the last two thoracic vertebrae : these, uniting, form a small muscle which is inserted by separate tendons into the spinous processes of the upper thoracic vertebrse, the number varying from four to eight. It is intimately united with the Semispinalis dorsi, situated beneath it. The Spinalis cervicis {Spinalis colli) is an inconstant muscle, which arises from the lower part of the ligamentum nuchae, the spinous process of the seventh cer- vical, and sometimes from the spinous processes of the first and second thoracic vertebrse, and is inserted into the spinous process of the axis, and occasionally into the spinous processes of the two vertebrse below it. The Spinalis capitis {Biventer cervicis) is usually inseparably connected with the Semispinalis capitis (see below). The Semispinalis dorsi consists of thin, narrow, fleshy fasciculi, interposed between tendons of considerable length. It arises by a series of small tendons from the transverse processes of the sixth to the tenth thoracic vertebrse, and is inserted, by tendons, into the spinous processes of the upper four thoracic and lower two cervical vertebrse. The Semispinalis cervicis (Semispinalis colli), thicker than the preceding, arises by a series of tendinous and fleshy fibers from the transverse processes of the upper five or six thoracic vertebrae, and is inserted into the cervical spinous processes, from the axis to the fifth inclusive. The fasciculus connected with the axis is the largest, and is chiefly muscular in structure. The Semispinalis capitis (Complexus) is situated at the upper and back part of the neck^ beneath the Splenius, and medial to the Longissimus cervicis and capitis. It arises by a series of tendons from the tips of the transverse processes of the upper six or seven thoracic and the seventh cervical vertebrse, and from the articular processes of the three cervical above this. The tendons, uniting, form a broad muscle, which passes upward, and is inserted between the superior and inferior nuchal lines of the occipital bone. The medial part, usually more or less distinct from the remainder of the muscle, is frequently termed the Spinalis capitis; it is also named the Biventer cervicis since it is traversed by an imperfect tendinous inscription. The Multiiidus (Multifidvs spince) consists of a number of fleshy and tendinous fasciculi, which fill up the groove on either side of the spinous processes of the ver- tebrse, from the sacrum to the axis. In the sacral region, these fasciculi arise from the back of the sacrum, as low as the fourth sacral foramen, from the aponeu- rosis of origin of the Sacrospinalis, from the medial surface of the posterior superior iliac spine, and from the posterior sacroiliac ligaments; in the lumbar region, from all the mamillary processes; in the thoracic region, from all the transverse processes; and in the cervical region, from the articular processes of the lower four vertebrse. Each fasciculus, passing obliquely upward and medialward, is inserted into the whole length of the spinous process of one of the vertebrse above. These fasciculi vary in length: the most superficial, the longest, pass from one vertebra to the third or fourth above; those next in order run from one vertebra to the second or third above; while the deepest connect two contiguous vertebrse. The Rotatores (Rotatores spince) lie beneath the Multifidus and are found only in the thoracic region; they are eleven in number on either side. Each muscle is small and somewhat quadrilateral in form; it arises from the upper and back part of the transverse process, and is inserted into the lower border and lateral surface of the lamina of the vertebra above, the fibers extending as far as the root of the spinous process. , The first is found between the first and second thoracic vertebrse; the last, between the eleventh and twelfth. Sometimes the number of these muscles is diminished by the absence of one or more from the upper or lower end. The Interspinales are short muscular fasciculi, placed in pairs between the THE SUBOCCIPITAL MUSCLES 401 spinous processes of tlie contiguous vertebrae, one on either side of the interspinal ligament. In the cervical region they are most distinct, and consist of six pairs, the first being situated between the axis and third vertebra, and the last between the seventh cervical and the first thoracic. They are small narrow bundles, attached, above and below, to the apices of the spinous processes. In the thoracic region, they are found between thq first and second vertebrae, and sometimes be- tween the second and third, and between the eleventh and twelfth. In the lumbar region there are four pairs in the intervals between the five lumbar vertebrae. There is also occasionally one between the last thoracic and first lumbar, and one between the fifth lumbar and the sacrum. The Extensor coccygis is a slender muscular fasciculus, which is not always present; it extends over the lower part of the posterior surface of the sacrum and coccyx. It arises by tendinous fibers from the last segment of the sacrum, or first piece of the coccyx, and passes downward to be inserted into the lower part of the coccyx. It is a rudiment of the Extensor muscle of the caudal vertebrae of the lower animals. The Intertransversarii (Intertransversales) are small muscles placed between the transverse processes of the vertebrae. In the cervical region they are best developed, consisting of rounded muscular and tendinous fasciculi, and are placed in pairs, passing between the anterior and the posterior tubercles respectively of the transverse processes of two contiguous vertebrae, and separated from one another by an anterior primary division of the cervical nerve, which lies in the groove between them. The muscles connecting the anterior tubercles are termed the Intertransversarii anteriores; those between the posterior tubercles, the Inter- transversarii posteriores; both sets are supplied by the anterior divisions of the spinal nerves (LickleyO- There are seven pairs of these muscles, the first pair being between the atlas and axis, and the last pair between the seventh cervical and first thoracic vertebrae. In the thoracic region they are present between the transverse processes of the lower three thoracic vertebrae, and between the trans- verse processes of the last thoracic and the first lumbar. In the lumbar region they are arranged in pairs, on either side of the vertebral column, one set occupy- ing the entire interspace between the transverse processes of the lumbar vertebrae, the Intertransversarii laterales; the other set, Intertransversarii mediales, passing from the accessory process of one vertebra to the mammillary of the vertebra below. The Intertransversarii laterales are supplied by the anterior divisions, and the Intertransversarii mediales by the posterior divisions of the spinal nerves (Lichley, op. cit). n. THE SUBOCCIPITAL MUSCLES (Fig. 389). The suboccipital group comprises: Rectus capitis posterior major. Obliquus capitis inferior. Rectus capitis posterior minor. Obliquus capitis superior. The Rectus capitis posterior major (Rectus capitis posticus major) arises by a pointed tendon from the spinous process of the axis, and, becoming broader as it ascends, is inserted into the lateral part of the inferior nuchal line of the occipital bone and the surface of the bone immediately below the line. As the muscles of the two sides pass upward and lateralward, they leave between them a triangular space, in which the Recti capitis posteriores minores are seen. The Rectus capitis posterior minor (Rectus capitis posticus minor) arises by a narrow pointed tendon from the tubercle on the posterior arch of the atlas, and, widening as it ascends, is inserted into the medial part of the inferior nuchal line of the occipital bone and the surface between it and the foramen magnum. '■ Journal of Anatomy and Physiology, 1904, vol. xxxix. 26 402 '^^^^^^^ MYOLOGY The Obliquus capitis inferior (Obliquus inferior), the larger of the two Oblique muscles, arises from the apex of the spinous process of the axis, and passes lateral- ward and slightly upward, to be inserted into the lower and back part of the transverse process of the atlas. The Obliquus capitis superior {Ohliqnus superior), narrow below, wide an expanded above, arises by tendinous fibers from the upper surface of the transversa process of the atlas, joining with the insertion of the preceding. It passes upward and medialward, and is inserted into the occipital bone, between the superior and inferior nuchal lines, lateral to the Semispinalis capitis I I ^1 The Suboccipital Triangle. — Between the Obliqui and the Rectus capitis posterior major is the suboccipital triangle. It is bounded, above and medially, by the Rectus capitis posterior major; above and laterally, by the Obliquus capitis superior; below and laterally, by the Obliquus capitis inferior. It is covered by a layer of dense fibro-fatty tissue, situated beneath the Semi- spinalis capitis. The floor is formed by the posterior occipito-atlantal membrane, and the posterior arch of the atlas. In the deep groove on the upper surface of the posterior arch of the atlas are the vertebral artery and the first cervical or suboccipital nerve. Nerves. — The deep muscles of the back and the suboccipital muscles are supplied by the posterior primary divisions of the spinal nerves. Actions. — The Sacrospinalis and its upward continuations and the Spinales serve to main- tain the vertebral column in the erect posture; they also serve to bend the trunk backward when it is required to counterbalance the influence of any weight at the front of the body — as, for instance, when a heavy weight is suspended from the neck, or when there is any great abdominal distension, as in pregnancy or dropsy; the peculiar gait under such circumstances depends upon the vertebral column being drawn backward, by the counterbalancing action of the Sacrospinales. The muscles which form the continuation of the Sacrospinales on to the head and neck steady those parts and fix them in the upright position. If the IHocostalis lumborum and Longissimus dorsi of one side act, they serve to draw down the chest and vertebral column to the correspond- ing side. The Iliocostales cervicis, taking their fixed points from the cervical vertebriE, elevate those ribs to which they are attached; taking their fixed points from the ribs, both muscles help to extend the neck; while one muscle bends the neck to its own side. When both Longissimi cervicis act from below, they bend the neck backward. When both Longissimi capitis act from below, they bend the head backward; while, if only one muscle acts, the face is turned to the side on which the muscle is acting, and then the head is bent to the shoulder. The two Recti draw the head backward. The Rectus capitis posterior major, owing to its obliquity, rotates the skull, with the atlas, arovmd the odontoid process, turning the face to the same side. The Multifidus acts successively upon the different parts of the column; thus, the sacrum furnishes a fixed point from which the fasciculi of this muscle acts upon the lumbar region; which in tui'n becomes the fixed point for the fascicuU moving the thoracic region, and so on throughout the entire length of the column. The Multifidus also serves to rotate the column, so that the front of the trimk is turned to the side opposite to that from which the muscle acts, this muscle being assisted in its action by the Obliquus extemus abdominis. The Obliquus capitis superior draws the head backward and to its own side. The Obliquus inferior rotates the atlas, and with it the skull, around the odontoid process, turning the face to the same side. When the Semispinals of the two sides act together, they help to extend the vertebral column; when the muscles of only one side act, they rotate the thoracic and cervical parts of the column, turning the body to the opposite side. The Semispinales capitis draw the head directly backward; if one muscle acts, it draws the head to one side, and rotates it so that the face is turned to the opposite side. The Interspinales by approximating the spinous processes help to extend the column. The Inter- transversarii approximate the transverse processes, and help to bend the column to one side. The Rotatores assist the Multifidus to rotate the vertebral column, so that the front of the trunk is turned to the side opposite to that from which the miiscles act. III. THE MUSCLES OF THE THORAX. The muscles belonging to this group are the Intercostales externi. Levatores costarum. Intercostales interni. Serratus posterior superior, Subcostales. Serratus posterior inferior. Transversus thoracis. Diaphragm. Intercostal Fasciae. — In each intercostal space thin but firm layers of fascia cover the outer surface of the Intercostalis externus and the inner surface of the THE MUSCLES OF THE THORAX 403 Intercostalis internus; and a third, more delicate layer, is interposed between the two planes of muscular fibers. They are best marked in those situations where the muscular fibers are deficient, as between the Intercostales externi and sternum in front, and between the Intercostales interni and vertebral column behind. The Intercostales (Intercostal muscles) (Fig. 411) are two thin planes of muscular and tendinous fibers occupying each of the intercostal spaces. They are named external and internal from their surface relations — the external being superficial to the internal. The Intercostales extern! {External intercostals) are eleven in number on either side. They extend from the tubercles of the ribs behind, to the cartilages of the ribs in front, where they end in thin membranes, the anterior intercostal membranes, which are continued forward to the sternum. Each arises from the lower border of a rib, and is inserted into the upper border of the rib below. In the two lower spaces they extend to the ends of the cartilages, and in the upper two or three spaces they do not quite reach the ends of the ribs. They are thicker than the Intercostales interni, and their fibers are directed obliquely downward and lateral- ward on the back of the thorax, and downward, forward, and medialward on the front. Variations. — Continuation with the ObHquus externus or Serratus anterior: A Supracostalis muscle, from the anterior end of the first rib down to the second, third or fourth ribs occasionally occurs. The Intercostales interni (Internal intercostals) are also eleven in number on either side. They commence anteriorly at the sternum, in the interspaces between the cartilages of the true ribs, and at the anterior extremities of th6 cartilages of the false ribs, and extend backward as far as the angles of the ribs, whence they are continued to the vertebral column by thin aponeuroses, the posterior intercostal membranes. Each arises from the ridge on the inner surface of a rib, as well as from the corresponding costal cartilage, and is inserted into the upper border of the rib below. Their fibers are also directed obliquely, but pass in a direction opposite to those of the Intercostales externi. The Subcostales (Infracostales) consist of muscular and aponeurotic fasciculi, which are usually well-developed only in the lower part of the thorax; each arises from the inner surface of one rib near its angle, and is inserted into the inner surface of the second or third rib below. Their fibers run in the same direction as those of the Intercostales interni. The Transversus thoracis (Triangidaris sterni) is a thin plane of muscular and tendinous fibers, situated upon the inner surface of the front wall of the chest (Fig. 390). It arises on either side from the lower third of the posterior surface of the body of the sternum, from the posterior surface of the xiphoid process, and from the sternal ends of the costal cartilages of the lower three or four true ribs. Its fibers diverge upward and lateralward, to be inserted by slips into the lower borders and inner surfaces of the costal cartilages of the second, third, fourth, fifth, and sixth ribs. The lowest fibers of this muscle are horizontal in their direc- tion, and are continuous with those of the Transversus abdominis; the intermediate fibers are oblique, while the highest are almost vertical. This muscle varies in its attachments, not only in different subjects, but on opposite sides of the same subject. The Levatores costamm (Fig. 389), twelve in number on either side, are small tendinous and fleshy bundles, which arise from the ends of the transverse pro- cesses of the seventh cervical and upper eleven thoracic vertebrae; they pass obliquely downward and lateralward, like the fibers of the Intercostales externi, and each is inserted into the outer surface of the rib immediately below the vertebra from which it takes origin, between the tubercle and the angle (Levatores costamm breves). Each of the four lower muscles divides into two fasciculi, one MYOLOGY The Obliquus capitis inferior (Obliquus inferior), the larger of the two Oblique muscles, arises from the apex of the spinous process of the axis, and passes lateral- ward and slightly upward, to be inserted into the lower and back part of the transverse process of the atlas. The Obliquus capitis superior {Obliquus superior), narrow below, wide and expanded above, arises by tendinous fibers from the upper surface of the transverse process of the atlas, joining with the insertion of the preceding. It passes upward and medialward, and is inserted into the occipital bone, between the superior and inferior nuchal lines, lateral to the Semispinalis capitis The Suboccipital Triangle. — Between the Obliqui and the Rectus capitis posterior major is the suboccipital triangle. It is bounded, above and medially, by the Rectus capitis posterior major; above and laterally, by the Obliquus capitis superior; below and laterally, by the ObMquus capitis inferior. It is covered by a layer of dense fibro-fatty tissue, situated beneath the Semi- spinahs capitis. The floor is formed by the posterior occipito-atlantal membrane, and the posterior arch of the atlas. In the deep groove on the upper surface of the posterior arch of the atlas are the vertebral artery and the first cervical or suboccipital nerve. Nerves. — The deep muscles of the back and the suboccipital muscles are supplied by the posterior primary divisions of the spinal nerves. Actions. — The Sacrospinalis and its upward continuations and the Spinales serve to main- tain the vertebral column in the erect posture; they also serve to bend the trunk backward when it is required to counterbalance the influence of any weight at the front of the body — as, for instance, when a heavy weight is suspended from the neck, or when there is any great abdominal distension, as in pregnancy or dropsy; the peculiar gait under such circumstances depends upon the vertebral column being drawn backward, by the counterbalancing action of the Sacrospinales. The muscles which form the continuation of the Sacrospinales on to the head and neck steady those parts and fix them in the upright position. If the Iliocostalis lumborum and Longissimus dorsi of one side act, they serve to draw down the chest and vertebral column to the correspond- ing side. The Ihocostales cervicis, taking their fixed points from the cervical vertebra?, elevate those ribs to which they are attached; taking their fixed points from the ribs, both muscles help to extend the neck; while one muscle bends the neck to its own side. When both Longissimi cervicis act from below, they bend the neck backward. When both Longissimi capitis act from below, they bend the head backward; while, if only one muscle acts, the face is turned to the side on which the muscle is acting, and then the head is bent to the shoulder. The two Recti draw the head backward. The Rectus capitis posterior major, owing to its obliquity, rotates the skull, with the atlas, around the odontoid process, turning the face to the same side. The Multifidus acts successively upon the different parts of the column; thus, the sacrum furnishes a fixed point from which the fasciculi of this muscle acts upon the lumbar region ; which in tm-n becomes the fixed point for the fasciculi moving the thoracic region, and so on throughout the entire length of the column. The Multifidus also serves to rotate the column, so that the front of the trunk is turned to the side opposite to that from which the muscle acts, this muscle being assisted in its action by the Obliquus extemus abdominis. The Obliquus capitis superior draws the head backward and to its own side. The Obhquus inferior rotates the atlas, and with it the skull, aroimd the odontoid process, turning the face to the same side. When the Semispinales of the two sides act together, they help to extend the vertebral column; when the muscles of only one side act, they rotate the thoracic and cervical parts of the column, turning the body to the opposite side. The Semispinales capitis draw the head directly backward; if one muscle acts, it draws the head to one side, and rotates it so that the face is turned to the opposite side. The Interspinals by approximating the spinous processes help to extend the column. The Inter- transversarii approximate the transverse processes, and help to bend the column to one side. The Rotatores assist the Multifidus to rotate the vertebral column, so that the front of the trxmk is turned to the side opposite to that from which the muscles act. ra. THE MUSCLES OF THE THORAX. The muscles belonging to this group are the Intercostales externi. Levatores costarum. Intercostales interni. Serratus posterior superior. Subcostales. Serratus posterior inferior. Transversus thoracis. Diaphragm. Intercostal Fasciae. — In each intercostal space thin but firm layers of fascia cover the outer surface of the Intercostalis externus and the inner surface of the THE MUSCLES OF THE THORAX 403 Intercostalis internus; and a third, more delicate layer, is interposed between the two planes of muscular fibers. They are best marked in those situations where the muscular fibers are deficient, as between the Intercostales externi and sternum in front, and between the Intercostales interni and vertebral column behind. The Intercostales (Intercostal muscles) (Fig. 411) are two thin planes of muscular and tendinous fibers occupying each of the intercostal spaces. They are named external and internal from their surface relations — the external being superficial to the internal. The Intercostales externi (External intercostals) are eleven in number on either side. They extend from the tubercles of the ribs behind, to the cartilages of the ribs in front, where they end in thin membranes, the anterior intercostal membranes, which are continued forward to the sternum. Each arises from the lower border of a rib, and is inserted into the upper border of the rib below. In the two lower spaces they extend to the ends of the cartilages, and in the upper two or three spaces they do not quite reach the ends of the ribs. They are thicker than the Intercostales interni, and their fibers are directed obliquely downward and lateral- ward on the back of the thorax, and downward, forward, and medialward on the front. Variations. — Continuation with the Obhquus externus or Serratus anterior: A Supracostalis muscle, from the anterior end of the first rib down to the second, third or fourth ribs occasionally occurs. The Intercostales interni (Internal intercostals) are also eleven in number on either side. They commence anteriorly at the sternum, in the interspaces between the cartilages of the true ribs, and at the anterior extremities of th6 cartilages of the false ribs, and extend backward as far as the angles of the ribs, whence they are continued to the vertebral column by thin aponeuroses, the posterior intercostal membranes. Each arises from the ridge on the inner surface of a rib, as well as from the corresponding costal cartilage, and is inserted into the upper border of the rib below. Their fibers are also directed obliquely, but pass in a direction opposite to those of the Intercostales externi. The Subcostales (Infracostales) consist of muscular and aponeurotic fasciculi, which are usually well-developed only in the lower part of the thorax; each arises from the inner surface of one rib near its angle, and is inserted into the inner surface of the second or third rib below. Their fibers run in the same direction as those of the Intercostales interni. The Transversus thoracis ( Triangularis sterni) is a thin plane of muscular and tendinous fibers, situated upon the inner surface of the front wall of the chest (Fig. 390). It arises on either side from the lower third of the posterior surface of the body of the sternum, from the posterior surface of the xiphoid process, and from the sternal ends of the costal cartilages of the lower three or four true ribs. Its fibers diverge upward and lateralward, to be inserted by slips into the lower borders and inner surfaces of the costal cartilages of the second, third, fourth, fifth, and sixth ribs. The lowest fibers of this muscle are horizontal in their direc- tion, and are continuous with those of the Transversus abdominis; the intermediate fibers are oblique, while the highest are almost vertical. This muscle varies in its attachments, not only in different subjects, but on opposite sides of the same subject. The Levatores costarum (Fig. 389), twelve in number on either side, are small tendinous and fleshy bundles, which arise from the ends of the transverse pro- cesses of the seventh cervical and upper eleven thoracic vertebrae; they pass obliquely downward and lateralward, like the fibers of the Intercostales externi, and each is inserted into the outer surface of the rib immediately below the vertebra from which it takes origin, between the tubercle and the angle (Levatores costarum breves) . Each of the four lower muscles divides into two fasciculi, one 404 MYOLOGY of which is inserted as above described; the other passes down to the seconc rib below its origin (Levatores costaramlongi). The Serratus posterior superior {Serratus 'posticus superior) is a thin, quadri-j lateral muscle, situated at the upper and back part of the thorax. It arises bj a thin and broad aponeurosis from the lower part of the ligamentum nuchae,' from the spinous processes of the seventh cervical and upper two or three thoracic vertebrae and from the supraspinal liga- ment. Inclining downward and lateral-^^— ward it becomes muscular, and is in-^| serted, by four fleshy digitations, into the upper borders of the second, third, fourth, and fifth ribs, a little beyond their angles. Variations. — Increase or decrease in size and number of slips or entire absence. The Serratus posterior inferior {Ser- ratus posticus inferior) (Fig. 409) is sit- uated at the junction of the thoracic and lumbar regions: it is of an irreg- ularly quadrilateral form, broader than the preceding, and separated from it by a wide interval. It arises by a thin aponeurosis from the spinous processes of the lower two thoracic and upper two or three lumbar vertebrae, and from the supraspinal ligament. Passing obliquely upward and lateral ward, it becomes fleshy, and divides into four flat digitations, w^hich are inserted into the inferior borders of the lower four ribs, a little beyond their angles. The thin aponeurosis of origin is intimately blended with the lumbodorsal fascia, and aponeurosis of the Latissimus dorsi. Sternal origin of Diaphragm Fig. 390. — Posterior surface of sternum and costal cartilages, showing Transversus thoracis. Variations. — Increase or decrease in size and number of slips or entire absence. Nerves. — The muscles of this group are supplied by the intercostal nerves. The Diaphragm (Fig. 391) is a dome-shaped musculofibrous septum which separates the thoracic from the abdominal cavity, its convex upper surface forming the floor of the former, and its concave under surface the roof of the latter. Its peripheral part consists of muscular fibers which take origin from the circumference of the thoracic outlet and converge to be inserted into a central tendon. The muscular fibers may be grouped according to their origins into three parts — sternal, costal, and lumbar. The sternal part arises by two fleshy slips from the back of the xiphoid process ; the costal part from the inner surfaces of the car- tilages and adjacent portions of the lower six ribs on either side, interdigitating with the Transversus abdominis; and the lumbar part from aponeurotic arches, named the lumbocostal arches, and from the lumbar vertebrae by two pillars or crura. There are two lumbocostal arches, a medial and a lateral, on either side. The Medial Lumbocostal Arch (arcus lumbocostalis medialis [Halleri]; internal arcuate ligament) is a tendinous arch in the fascia covering the upper part of the Psoas major; medially, it is continuous with the lateral tendinous margin of the corresponding crus, and is attached to the side of the body of the first or second THE MUSCLES OF THE THORAX 405 lumbar vertebra; laterally, it is fixed to the front of the transverse process of the first and, sometimes also, to that of the second lumbar vertebra. The Lateral Lumbocostal Arch (arcus lumbocostalis lateralis [Halleri]; external arcuate ligament) arches across the upper part of the Quadratus lumborum, and is attached, medially, to the front of the transverse process of the first lumbar vertebra, and, laterally, to the tip and lower margin of the twelfth rib. The Crura. — At their origins the crura are tendinous in structure, and blend with the anterior longitudinal ligament of the vertebral column. The right cms, larger and longer than the left, arises from the anterior surfaces of the bodies and intervertebral fibrocartilages of the upper three lumbar vertebrae, while the left cms arises from the corresponding parts of the upper two only. The medial ten- dinous margins of the crura pass forward and medialward, and meet in the middle line to form an arch across the front of the aorta; this arch is often poorly defined. Xiphoid process Opening for Lesser Splanchnic Nerve FiQ. 391. — The diaphragm. Under surface. From this series of origins the fibers of the diaphragm converge to be inserted into the central tendon. The fibers arising from the xiphoid process are very short, and occasionally aponeurotic; those from the medial and lateral lumbocostal arches, and more especially those from the ribs and their cartilages, are longer, and describe marked curves as they ascend and converge to their insertion. The fibers of the crura diverge as they ascend, the most lateral being directed upward and lateralward to the central tendon. The medial fibers of the right crus ascend on the left side of the esophageal hiatus, and occasionally a fasciculus of the left crus crosses the aorta and runs obliquely through the fibers of the right crus toward the vena caval foramen (Low^). ' Journal of Anatomy and Physiology, vol. xlii. 406 The Central Tendon. — The central tendon of the diaphragm is a thin but strong aponeurosis situated near the center of the vault formed by the muscle, but some- what closer to the front than to the back of the thorax, so that the posterior muscu- lar fibers are the longer. It is situated immediately below the pericardium, with which it is partially blended. It is shaped somewhat like a trefoil leaf, consisting of three divisions or leaflets separated from one another by slight indentations.] The right leaflet is the largest, the middle, directed toward the xiphoid process," the next in size, and the left the smallest. In structure the tendon is composed of several planes of fibers, which intersect one another at various angles and unite into straight or curved bundles — an arrangement which gives it additional strength. Openings in the Diaphragm. — The diaphragm is pierced by a series of apertures to permit of the passage of structures between the thorax and abdomen. Three large openings— the aortic, the esophageal, and the vena caval— and a series of smaller ones are described. The aortic hiatus is the lowest and most posterior of the large apertures; it lies at the level of the twelfth thoracic vertebra. Strictly speaking, it is not an aperture in the diaphragm but an osseoaponeurotic opening between it and tbe vertebral column, and therefore behind the diaphragm ; occasionally some tendinous fibers prolonged across the bodies of the vertebrae from the medial parts of the lower ends of the crura pass behind the aorta, and thus convert the hiatus into a fibrous ring. The hiatus is situated slightly to the left of the middle line, and is bounded in front by the crura, and behind by the body of the first lumbar vertebra. Through it pass the aorta, the azygos vein, and the thoracic duct; occasionally the azygos vein is transmitted through the right crus. The esophageal hiatus is situated in the muscular part of the diaphragm at the level of the tenth thoracic vertebra, and is elliptical in shape. It is placed above, in front, and a little to the left of the aortic hiatus, and transmits the esophagus, the vagus nerves, and some small esophageal arteries. The vena caval foramen is the highest of the three, and is situated about the level of the fibrocartilage between the eighth and ninth thoracic vertebrae. It is quad- rilateral in form, and is placed at the junction of the right and middle leaflets of the central tendon, so that its margins are tendinous. It transmits the inferior vena cava, the wall of which is adherent to the margins of the opening, and some branches of the right phrenic nerve. Of the lesser apertures, two in the right crus transmit the greater and lesser right splanchnic nerves; three in the left crus give passage to the greater and lesser left splanchnic nerves and the hemiazygos vein. The gangliated trunks of the sympathetic usually enter the abdominal cavity behind the diaphragm, under the medial lumbocostal arches. On either side two small intervals exist at which the muscular fibers of the diaphragm are deficient and are replaced by areolar tissue. One between the sternal and costal parts transmits the superior epigastric branch of the internal mammary artery and some lymphatics from the abdominal wall and convex surface of the liver. The other, between the fibers springing from the medial and lateral lumbocostal arches, is less constant; when this interval exists, the upper and back part of the kidney is separated from the pleura by areolar tissue only. Variations. — The sternal portion of the muscle is sometimes wanting' and more rarely defects occur in the lateral part of the central tendon or adjoining muscle fibers. Nerves. — The diaphragm is supplied by the phrenic and lower intercostal nerves. Actions. — The diaphragm is the principal muscle of inspiration, and presents the form of a dome concave toward the abdomen. The central part of the dome is tendinous, and the peri- cardium is attached to its upper surface; the circumference is muscular. During inspiration the lowest ribs are fixed, and from these and the crura the muscular fibers contract and draw down- ward and forward the central tendon with the attached pericardium. In this movement the curvature of the diaphragm is scarcely altered, the dome moving downward nearly parallel THE MUSCLES OF THE THORAX 407 to its original position and pushing before it the abdominal viscera. The descent of the abdominal viscera is permitted by the elasticity of the abdominal wall, but the hmit of this is soon reached. The central tendon applied to the abdominal viscera then becomes a fixed point for the action of the diaphragm, the effect of which is to elevate the lower ribs and through them to push forward the body of the sternum and the upper ribs. The right cupola of the diaphragm, lying on the liver, has a greater resistance to overcome than the left, which lies over the stomach, but to compensate for this the right crus and the fibers of the right side generally are stronger than those of the left. In all expulsive acts the diaphragm is called into action to give additional power to each expulsive effort. Thus, before sneezing, coughing, laughing, crying, or vomiting, and previous to the expulsion of urine or feces, or of the fetus from the uterus, a deep inspiration takes place. The height of the diaphragm is constantly varying during respiration; it also varies with the degree of distension of the stomach and intestines and with the size of the hver. After a forced expiration the right cupola is on a level in front with the fourth costal cartilage, at the side with the fifth, sixth, and seventh ribs, and behind with the eighth rib; the left cupola is a little lower than the right. Halls Dally ^ states that the absolute range of movement between deep inspira- tion and deep expiration averages in the male and female 30 mm. on the right side and 28 mm. on the left; in quiet respiration the average movement is 12.5 mm. on the right side and 12 mm. on the left. Skiagraphy shows that the height of the diaphragm in the thorax varies considerably with the position of the body. It stands highest when the body is horizontal and the patient on his back, and in this position it performs the largest respiratory excursions with normal breathing. When the body is erect the dome of the diaphragm falls, and its respiratory movements become smaller. The dome falls still lower when the sitting posture is assumed, and in this position its respiratory excursions are smallest. These facts may, perhaps, explain why it is that patients suffering from severe dyspnoea are most comfortable and least short of breath when they sit up. When the body is horizontal and the patient on his side, the two halves of the diaphragm do not behave alike. The uppermost half sinks to a level lower even than when the patient sits, and moves little with respiration; the lower half rises higher in the thorax than it does when the patient is supine, and its respiratory excursions are much increased. In unilateral disease of the plem'a or lungs analogous interference with the position or movement of the diaphragm can generally be observed skiagraphically. It appears that the position of the diaphragm in the thorax depends upon three main factors, viz.: (1) the elastic retraction of the lung tissue, tending to pull it upward; (2) the pressure exerted on its under surface by the viscera; this naturally tends to be a negative pressure, or down- ward suction, when the patient sits or stands, and positive, or an upward pressure, when he lies; (3) the intra-abdominal tension due to the abdominal muscles. These are in a state of contrac- tion in the standing position and not in the sitting; hence the diaphragm, when the patient stands, is pushed up higher than when he sits. The Intercostales interni and externi have probably no action in moving the ribs. They con- tract simultaneously and form strong elastic supports which prevent the intercostal spaces being pushed out or drawn in during respiration. The anterior portions of the Intercostales interni probably have an additional function in keeping the sternocostal and interchondral joint sur- faces in apposition, the posterior parts of the Intercostales externi performing a similar function for the costovertebral articulations. The Levatores costarum being inserted near the fulcra of the ribs can have little action on the ribs; they act as rotators and lateral flexors of the vertebral column. The Transversus thoracis draws down the costal cartilages, and is therefore a muscle of expiration. The Serrati are respiratory muscles. The Serratus posterior superior elevates the ribs and is therefore an inspiratory muscle. The Serratus posterior inferior draws the lower ribs down- ward and backward, and thus elongates the thorax; it also fixes the lower ribs, thus assisting the inspiratory action of the diaphragm and resisting the tendency it has to draw the lower ribs upward and forward. It must therefore be regarded as a muscle of inspiration. Mechanism of Respiration. — The respiratory movements must be examined dm-ing (a) quiet respiration, and {h) deep respiration. Quiet Respiration. — The first and second pairs of ribs are fixed by the resistance of the cervical structures; the last pair, and through it the eleventh, by the Quadratus lumborum. The other ribs are elevated, so that the first two intercostal spaces are diminished while the others are increased in v/idth. It has already been shown (p. 304) that elevation of the third, fourth, fifth, and sixth ribs leads to an increase in the antero-posterior and transverse diameters of the thorax; the vertical diameter is increased by the* descent of the diaphragmatic dome so that the lungs __ are expanded in all directions except backward and upward. Elevation of the eighth, ninth, !■ and tenth ribs is accompanied by a lateral and backward movement, leading to an increase in II the transverse diameter of the upper part of the abdomen; the elasticity of the anterior abdominal W II II ' Journal of Anatomy and Physiology, 1908, vol. xliii. MYOLOGY ones being attached close to the cartilages of the corresponding ribs, the lowest to the apex of the cartilage of the last rib, the intermediate ones to the ribs at some distance from their cartilages. The five superior serrations increase in size from above downward, and are received between corresponding processes of the Serratus anterior; the three lower ones diminish in size from above downward and receive between them corresponding processes from the Latissimus dorsi. From these attachments the fleshy fibers proceed in various directions. Those from the lowest ribs pass nearly^ vertically downward, and are inserted into the anterior half of the outer lip of the iliac crest; the middle and upper fibers, directed downward and forward, end in an aponeurosis, opposite a line drawn from the prominence of the ninth costal cartilage to the anterior superior iliac spine. The aponeurosis of the Obliquus extemus abdominis is a thin but strong mem- branous structure, the fibers of which are directed downward and medialward. It is joined with that of the opposite muscle along the middle line, and covers the whole of the front of the abdomen; above, it is covered by and gives origin to the lower fibers of the Pectoralis major; belotv, its fibers are closely aggregated together, and extend obliquely across from the anterior superior iliac spine to the pubic tubercle and the pectineal line. In the middle line, it interlaces with the aponeurosis of the opposite muscle, forming the linea alba, which extends from the xiphoid process to the symphysis pubis. That portion of the aponeurosis which extends between the anterior superior iliac spine and the pubic tubercle is a thick band, folded inward, and continuous below with the fascia lata; it is called the inguinal ligament. The portion which is reflected from the inguinal ligament at the pubic tubercle is attached to the pectineal line and is called the lacunar ligament. From the point of attachment of the latter to the pectineal line, a few fibers pass upward and medialward, behind the medial crus of the subcutaneous inguinal ring, to the linea alba; they diverge as they ascend, and form a thin triangular fibrous band which is called the reflected inguinal ligament. In the aponeurosis of the Obliquus extemus, immediately above the crest of the pubis, is a triangular opening, the subcutaneous inguinal ring, formed by a separation of the fibers of the aponeurosis in this situation. The following structures require further description, viz., the subcutaneous inguinal ring, the intercrural fibers and fascia, and the inguinal, lacunar, and reflected inguinal ligaments. The Subcutaneous Inguinal Ring (annulus inguinalis suhcutaneus; external abdominal ring) (Fig. 393). — The subcutaneous inguinal ring is an interval in the aponeurosis of the Obliquus externus, just above and lateral to the crest of the pubis. The aperture is oblique in direction, somew^hat triangular in form, and corresponds with the course of the fibers of the aponeurosis. It usually measures from base to apex about 2.5 cm., and transversely about 1.25 cm. It is bounded below by the crest of the pubis; on either side by the margins of the opening in the aponeurosis, which are called the crura of the ring ; and above, by a series of curved Intercrural fibers. The inferior crus {external 'pillar) is the stronger and is formed by that portion of the inguinal ligament which is inserted into the pubic tubercle; it is curved so as to form a kind of groove, upon which, in the male, the spermatic cord rests. The superior crus {internal 'pillar) is a broad, thin, flat band, attached to the front of the symphysis pubis and interlacing with its fellow of the opposite side. The subcutaneous inguinal ring gives passage to the spermatic cord and ilio- inguinal nerve in the male, and to the round ligament of the uterus and the ilioinguinal nerve in the female; it is much larger in men than in women, on account of the large size of the spermatic cord. The Intercrural Fibers {fibra; intercr urates; intercolumnar fibers) . — The intercrural fibers are a series of curved tendinous fibers, which arch across the lower part of THE ANTERO-LATERAL MUSCLES OF THE ABDOMEN 411 the aponeurosis of the ObHquus externus, describing curves with the convexities downward. They have received their name from stretching across between the two crura of the subcutaneous inguinal ring, and they are much thicker and stronger at the inferior crus, where they are connected to the inguinal ligament, than supe- riorly, where they are inserted into the linea alba. The intercrural fibers increase the strength of the lower part of the aponeurosis, and prevent the divergence of the crura from one another; they are more strongly developed in the male than in the female. As they pass across the subcutaneous inguinal ring, they are connected together I by delicate fibrous tissue, forming a fascia, called the intercrural fascia. This inter- Superficial iliac circumflex vein Subcutaneous inguinal ring Fig. 393. — The subcutaneous inguinal ring. jrural fascia is continued down as a tubular prolongation around the spermatic cord and testis, and encloses them in a sheath; hence it is also called the external spermatic fascia. The subcutaneous inguinal ring is seen as a distinct aperture only after the intercrural fascia has been removed. The Inguinal Ligament (ligamentuvi inguinale [Pouparti] ; Poupart's ligament) (Fig. 394) . — The inguinal ligament is the lower border of the aponeurosis of the Obliquus externus, and extends from the anterior superior iliac spine to the pubic tubercle. From this latter point it is reflected backward and lateralward to be attached to the pectineal line for about 1.25 cm., forming the lacunar ligament. Its general direction is convex downward toward the thigh, where it is continuous with the fascia lata. Its lateral half is rounded, and oblique in direction; its 412 MYOLOGY medial half gradually widens at its attachment to the pubis, is more horizontal in direction, and lies beneath the spermatic cord. The Lacunar Ligament {ligamentum lacunare [Gimbernati] ; Gimhernafs ligament) (Fig. 394) . — The lacunar ligament is that part of the aponeurosis of the Obliquus externus which is reflected backward and lateralward, and is attached to the pecti- neal line. It is about 1.25 cm. long, larger in the male than in the female, almost horizontal in direction in the erect posture, and of a triangular form with the base directed lateralward. Its base is concave, thin, and sharp, and forms the medial boundary of the femoral ring. Its apex corresponds to the pubic tubercle. Its posterior margin is attached to the pectineal line, and is continuous with the pectineal fascia. Its anterior margin is attached to the inguinal ligament, surfaces are directed upward and downward. Ant. sup. iliac spine. Symphysis pubis Its I Transverse acetabular ligainent Fig. 394. — The inguinal and lacunar ligaments. The Reflected Inguinal Ligament {ligamentum inguinale reflexum [ Collesi] ; trian- gular fascia) . — The reflected inguinal ligament is a layer of tendinous fibers of a triangular shape, formed by an expansion from the lacunar ligament and the inferior cms of the subcutaneous inguinal ring. It passes medialward behind the spermatic cord, and expands into a somewhat fan-shaped band, lying behind the superior crus of the subcutaneous inguinal ring, and in front of the inguinal aponeurotic falx, and interlaces with the ligament of the other side of the linea alba (Fig. 396). Ligament of Cooper. — This is a strong fibrous band, which was first described by Sir Astley Cooper. It extends lateralward from the base of the lacunar ligament (Fig. 394) along the pectineal hne, to which it is attached. It is strengthened by the pectineal fascia, and by a lateral expansion from the lower attachment of the hnea alba {adminiculum linece alhce). Variations. — The Obliquus externus may show decrease or doubling of its attachments to the ribs; addition slips from lumbar aponeurosis; doubling between lower ribs and ilium or inguinal ligament. Rarely tendinous inscriptions occur. The Obliquus intemus abdominis {Internal or ascending oblique muscle) (Fig. 395), thinner and smaller than the Obliquus externus, beneath which it lies, is of THE ANTERO-LATERAL MUSCLES OF THE ABDOMEN 413 an irregularly quadrilateral form, and situated at the lateral and anterior parts of the abdomen. It arises, by fleshy fibers, from the lateral half of the grooved upper surface of the inguinal ligament, from the anterior two-thirds of the middle lip of the iliac crest, and from the posterior lamella of the lumbodorsal fascia. From this origin the fibers diverge; those from the inguinal ligament, few in number and paler in color than the rest, arch downward and medialward across the sper- matic cord in the male and the round ligament of the uterus in the female, and, becoming tendinous, are inserted, conjointly with those of the Transversus, into the crest of the pubis and medial part of the pectineal line behind the lacunar ligament, forming what is known as the inguinal aponeurotic falx. Those from the Inguinal apo- neurotic falz Cremaster Fia. 395. — The Obliquua internua abdominis. [anterior third of the iliac origin are horizontal in their direction, and, becoming tendinous along the lower fourth of the linea semilunaris, pass in front of the Rectus abdominis to be inserted into the linea alba. Those arising from the middle third of the iliac origin run obliquely upward and medialward, and end in an aponeurosis; this divides at the lateral border of the Rectus into two lamellse, which are con- tinued forward, one in front of and the other behind this muscle, to the linea alba: the posterior lamella has an attachment to the cartilages of the seventh, eighth, and ninth ribs. The most posterior fibers pass almost vertically upward, to be inserted into the inferior borders of the cartilages of the three lower ribs, being continuous with the Intercostales interni. 414 MYOLOGY Variations.— Occasionally, tendinous inscriptions occur from the tips of the tenth or eleventh cartilages or even from the ninth; an additional slip to the ninth cartilage is sometimes found;' separation between iliac and inguinal parts may occur. The Cremaster (Fig. 396) is a thin muscular layer, composed of a number of fasciculi which arise from the middle of the inguinal ligament where its fibers- are continuous with those of the Obliquus internus and also occasion- ally with the Transversus. It passes along the lateral side of the spermatic cord, descends with it through the sub- cutaneous inguinal ring upon the front and sides of the cord, and forms a series of loops which differ in thickness and length in different subjects. At the upper part of the cord the loops are short, but they become in succession longer and longer, the longest reaching down as low as the testis, where a few are inserted into the tunica vaginalis. These loops are united together by areolar tissue, and form a thin cover- ing over the cord and testis, the cremas- teric fascia. The fibers ascend along the medial side of the cord, and are inserted by a small pointed tendon into the tubercle and crest of the pubis and into the front of the sheath of the Rectus abdominis. The Transversus abdominis (Trans- versalis vmscle) (Fig. 397), so called from the direction of its fibers, is the most internal of the flat muscles of the abdomen, being placed imme- diately beneath the Obliquus internus. It arises, by fleshy fibers, from the lateral third of the inguinal ligament, from the anterior three-fourths of the, inner lip of the iliac crest, from the inner surfaces of the cartilages of the lower six ribs, interdigitating with the diaphragm, and from the lumbodorsal fascia. The muscle ends in front in a broad aponeurosis, the lower fibers of w^hich curve downward and medial ward, and are inserted, together with those of the Obliquus internus, into the crest of the pubis and pectineal line, forming the ingui- nal aponeurotic falx. Throughout the rest of its extent the aponeurosis passes horizontally to the middle line, and is inserted into the linea alba; its upper three-fourths lie behind the Rectus and blend with the posterior lamella of the aponeurosis of the Obliquus internus; its lower fourth is in front of the Rectus. Variations. — It may be more or less fused with the Obliquus internus or absent. The spermatic cord may pierce its lower border. Slender muscle slips from the ileopectineal line to transversalis fascia, the aponeurosis of the Transversus abdominis, or the outer end of the linea semicircularis and other slender slips are occasionally found. The inguinal aponeurotic falx {falx aponeurotica inguinalis; conjoined tendon of Internal oblique and Transversalis muscle) of the Obliquus internus and Trans- versus is mainly formed by the lower part of the tendon of the Transversus, and is inserted into the crest of the pubis and pectineal line immediately behind the subcutaneous inguinal ring, serving to protect what would otherwise be a Fig. 396.— The Cremaster. THE ANTERO-LATERAL MUSCLES OF THE ABDOMEN 415 weak point in the abdominal wall. Lateral to the falx is a ligamentous band con- nected with the lower margin of the Transversus and extending down in front of the inferior epigastric artery to the superior ramus of the pubis ; it is termed the inter- foveolar ligament of Hesselbach (Fig. 398) and sometimes contains a few muscular fibers. 397. — The Transversus abdominis, Rectus abdominis, and Pyramidalis. The Rectus abdominis (Fig. 397) is a long flat muscle, which extends along the whole length of the front of the abdomen, and is separated from its fellow of the opposite side by the linea alba. It is much broader, but thinner, above than below, and arises by tw^o tendons; the lateral or larger is attached to the crest of the pubis, the medial interlaces with its fellow of the opposite side, and is con- nected with the ligaments covering the front of the symphysis pubis. The muscle is inserted by three portions of unequal size into the cartilages of the fifth, sixth, and seventh ribs. The upper portion, attached principally to the cartilage of the 416 MYOLOGY fifth rib, usually has some fibers of insertion into the anterior extremity of the rib itself. Some fibers are occasionally connected with the costoxiphoid ligaments, and the side of the xiphoid process. ^_l The Rectus is crossed by fibrous bands, three in number, which are named the fl tendinous inscriptions; one is usually situated opposite the umbilicus, one at the extremity of the xiphoid process, and the third about midway between the xiphoid process and the umbilicus. These inscriptions pass transversely or obliquely across the muscle in a zigzag course; they rarely extend completely through its substance and may pass only halfway across it; they are intimately adherent in front to the sheath of the muscle. Sometimes one or tM^o additional inscriptions, generally incomplete, are present below the umbilicus. Linea semicircularis Transmrsus Beetus abdominis Inferior epigastric artery arid vein Obliquus intemus Inguinal aponeurotic falx Interjoveolar ligament Fig. 398. — The interfoveolar ligament, seen from in front. (Modified from Braune.) The Rectus is enclosed in a sheath (Fig. 399) formed by the aponeuroses of the Obliqui and Transversus, which are arranged in the following manner. At the lateral margin of the Rectus, the aponeurosis of the Obliquus intemus divides into two lamellae, one of which passes in front of the Rectus, blending with the aponeurosis of the Obliquus externus, the other, behind it, blending with the aponeurosis of the Transversus, and these, joining again at the medial border of the Rectus, are inserted into the linea alba. This arrangement of the aponeurosis exists from the costal margin to midway between the umbilicus and symphysis pubis, where the posterior wall of the sheath ends in a thin curved margin, the linea semicircu- laris, the concavity of which is directed downward : below this level the aponeuroses of all three muscles pass in front of the Rectus. The Rectus, in the situation where its sheath is deficient below, is separated from the peritoneum by the transversalis fascia (Fig. 400). Since the tendons of the Obliquus intemus and Transversus only reach as high as the costal margin, it follows that above this level the sheath of the Rectus is deficient behind, the muscle resting directly on the cartilages of the ribs, and being covered merely by the tendon of the Obliquus externus. The Pyramidalis (Fig. 397) is a small triangular muscle, placed at the lower part of the abdomen, in front of the Rectus, and contained in the sheath of that THE ANTERO-LATERAL MUSCLES OF THE ABDOMEN 417 muscle. It arises by tendinous fibers from the front of the pubis and the anterior pubic ligament; the fleshy portion of the muscle passes upward, diminishing in size as it ascends, and ends by a pointed extremity which is inserted into the linea alba, midway between the umbilicus and pubis. This muscle may be wanting on one or both sides; the lower end of the Rectus then becomes proportionately increased in size. Occasionally it is double on one side, and the muscles of the two sides are sometimes of unequal size. It may extend higher than the level stated. Linea alba Ohliquus intemug > TransverstiS Fig. 399. — Diagram of sheath of Rectus. Besides the Rectus and Pyramidalis, the sheath of the Rectus contains the superior and inferior epigastric arteries, and the lower intercostal nerves. Variations. — The Rectus may insert as high as the fourth ot third rib or may fail to reach the fifth. Fibers may spring from the lower part of the linea alba. Nerves. — The abdominal muscles are supphed by the lower intercostal nerves. The Obliquus internus and Transversus also receive filaments from the anterior branch of the iliohypogastric and sometimes from the iUoinguinal. The Cremaster is suppUed by the external spermatic branch of the genitofemoral and the PyramidaUs usually by the twelfth thoracic. The Linea Alba. — The linea alba is a tendinous raphe in the middle line of the abdomen, stretching between the xiphoid process and the symphysis pubis. It is placed between the medial borders of the Recti, and is formed by the blending of the aponeuroses of the Obliqui and Trans- versa It is narrow below, corresponding to the hnear interval existing between the Recti; but broader above, where these muscles diverge from one another. At its lower end the Unea alba has a double attachment — its superficial fibers passing in front of the medial heads of the Recti to the symphysis pubis, while its deeper fibers form a triangular lamella, attached behind the Recti to the posterior lip of the crest of the pubis, and named the adminiculum lines albse. It presents apertures for the passage of vessels and nerves; the umbihcus, which in the fetus exists as an aperture and transmits the umbiHcal vessels, is closed in .the adult. Obliquug extemua . Obliquus internus - Transversusy Fig. 400. — Diagram of a transverse section through the anterior abdomina wall, below the linea semicircularis The Linese Semilunares. — The hneae semilimares are two curved tendinous fines placed one on either side of the hnea alba. Each corresponds with the lateral border of the Rectus, extends from the cartilage of the ninth rib to the pubic tubercle, and is formed by the aponeurosis of the Obliquus internus at its line of division to enclose the Rectus, reinforced in front by that of the Obhquus extemus, and behind by that of the Transversus. Actions. — When the pelvis and thorax are fixed, the abdominal muscles compress the abdominal viscera by constricting the cavity of the abdomen, in which action they are materially assisted by the descent of the diaphragm. By these means assistance is given in expelling the feces from the rectmn, the urine from the bladder, the fetus from the uterus, and the contents of the stomach in vomiting. If the pelvis and vertebral column be fixed, these muscles compress the lower part of the thorax, materially assisting expiration. If the pelvis alone be fixed, the thorax is bent directly forward, when the muscles of both sides act; when the muscles of only one side contract, the trunk is bent toward that side and rotated toward the opposite side. 27 418 MYOLOGY If the thorax be fixed, the muscles, acting together, draw the pelvis upward, as in climbing; or, acting singly, they draw the pelvis upward, and bend the vertebral column to one side or the other. The Recti, acting from below, depress the thorax, and consequently flex the vertebral column ; when acting from above, they flex the pelvis upon the vertebral column. The Pyramidales are tensors of the linea alba. The Transversalis Fascia. — The transversalis fascia is a thin aponeurotic membrane which lies between the inner surface of the Transversus and the extraperitoneal fat. It forms part of the general layer of fascia lining the abdominal parietes, and is directly continuous with the iliac and pelvic fasciae. In the inguinal region, the transversalis fascia is thick and dense in structure and is joined by fibers from the aponeurosis of the Transversus, but it becomes thin as it ascends to the dia- phragm, and blends with the fascia covering the under surface of this muscle. Behind, it is lost in the fat which covers the posterior surfaces of the kidneys. Below, it has the following attachments: posteriorly, to the whole length of the iliac crest, between the attachments of the Transversus and Iliacus; between the ante- rior superior iliac spine and the femoral vessels it is connected to the posterior margin of the inguinal ligament, and is there continuous with the iliac fascia. Medial to the femoral vessels it is thin and attached to the pubis and pectineal line, behind the inguinal aponeurotic falx, with which it is united; it descends in front of the femoral vessels to^rm the anterior wall of the femoral sheath. Beneath the inguinal ligament it is strengthened by a band of fibrous tissue, which is only loosely connected to the ligament, and is specialized as the deep crural arch. The spermatic cord in the male and the round ligament of the uterus in the female pass through the transversalis fascia at a spot called the abdominal inguinal ring. This opening is not visible externally, since the transversalis fascia is prolonged on these structures as the infundibuliform fascia. The Abdominal Inguinal Ring (annulus inguinalis abdominis; internal or deep abdominal ring). — The abdominal inguinal ring is situated in the transversalis fascia, midway between the anterior superior iliac spine and the symphysis pubis, and about 1.25 cm. above the inguinal ligament (Fig. 401). It is of an oval form, the long axis of the oval being vertical; it varies in size in different subjects, and is much larger in the male than in the female. It is bounded, above and laterally, by the arched lower margin of the Transversus ; below and medially, by the inferior epigastric vessels. It transmits the spermatic cord in the male and the round ligament of the uterus in the female. From its circumference a thin funnel-shaped membrane, the infundibuliform fascia, is continued around the cord and testis, enclosing them in a distinct covering. The Inguinal Canal (canalis inguinalis; spermatic canal). — The inguinal canal contains the spermatic cord and the ilioinguinal nerve in the male, and the round ligament of the uterus and the ilioinguinal nerve in the female. It is an oblique canal about 4 cm. long, slanting downward and medialward, and placed parallel with and a little above the inguinal ligament; it extends from the abdominal inguinal ring to the subcutaneous inguinal ring. It is bounded, m front, by the integument and superficial fascia, by the aponeurosis of the Obliquus externus throughout its whole length, and by the Obliquus internus in its lateral third; behind, by the reflected inguinal ligament, the inguinal aponeurotic falx, the trans- versalis fascia, the extraperitoneal connective tissue and the peritoneum; above, by the arched fibers of Obliquus internus and Transversus abdominis; below, by the union of the transversalis fascia with the inguinal ligament, and at its medial end by the lacunar ligament. Extraperitoneal Connective Tissue.— Between the inner surface of the general layer of the fascia which lines the interior of the abdominal and pelvic cavities, and the peritoneum, there is a considerable amount of connective tissue, termed the extraperitoneal or subperitoneal connective tissue. THE POSTERIOR MUSCLES OF THE ABDOMEN 419 I The parietal portion lines the cavity in varying quantities in different situations. It is especially abundant on the posterior wall of the abdomen, and particularly around the kidneys, where it contains much fat. On the anterior wall of the abdo- men, except in the pubic region, and on the lateral wall above the iliac crest, it is scanty, and here the transversalis fascia is more closely connected with the peritoneum. There is a considerable amount of extraperitoneal connective tissue in the pelvis. The visceral portion follows the course of the branches of the abdominal aorta between the layers of the mesenteries and other folds of peritoneum which connect the various viscera to the abdominal wall. The two portions are directly con- tinuous with each other. bdominal inguinal ring Inf. epigastric artery -4 — Fia. 401. — The abdominal inguinal ring. The Deep Crural Arch. — Curving over the external iliac vessels, at the spot where they become femoral, on the abdominal side of the inguinal ligaments and loosely connected with it, is a thickened band of fibers called the deep crural arch. It is apparently a thickening of the transversalis fascia joined laterally to the center of the lower margin of the inguinal ligament, and arching across the front of the femoral sheath to be inserted by a broad attachment into the pubic tubercle and pectineal line, behind the inguinal aponeurotic falx. In some subjects this structure is not very prominently marked, and not infrequently it is altogether wanting. 2. The Posterior Muscles of the Abdomen. Psoas major. Psoas minor. Iliacus. Quadratus lumborum. The Psoas major, the Psoas minor, and the Iliacus, with the fasciae covering them, will be described with the muscles of the lower extremity (see page 466). The Fascia Covering the Quadratus Lumborum. — This is a thin layer attached, medially, to the bases of the transverse processes of the lumbar vertebrae; below, 420 MYOLOGY to the iliolumbar ligament; above, to the apex and lower border of the last rib. The upper margin of this fascia, which extends from the transverse process of the first lumbar vertebra to the apex and lower border of the last rib, constitutes the lateral lumbocostal arch (page 405). Laterally, it blends with the lumbodorsal fascia, the anterior layer of which intervenes between the Quadratus lumborum and the Sacrospinalis. The Quadratus lumborum (Fig. 389, page 398) is irregularly quadrilateral in shape, and broader below than above. It arises by aponeurotic fibers from the iliolumbar ligament and the adjacent portion of the iliac crest for about 5 cm., and is inserted into the lower border of the last rib for about half its length, and by four small tendons into the apices of the transverse processes of the upper four lumbar vertebrae. Occasionally a second portion of this muscle is found in front of the preceding. It arises from the upper borders of the transverse processes of the lower three or four lumbar vertebrae, and is inserted into the lower margin of the last rib. In front of the Quadratus lumborum are the colon, the kidney, the Psoas major and minor, and the diaphragm; between the fascia and the muscle are the twelfth thoracic, ilioinguinal, and iliohypogastric nerves. Variations. — The number of attachments to the vertebrae and the extent of its attachment to the last rib vary. Nerve Supply. — The twelfth thoracic and first and second lumbar nerves supply this muscle. Actions. — The Quadratus lumborvun draws down the last rib, and acts as a muscle of inspira- tion by helping to fix the origin of the diaphragm. If the thorax and vertebral column are fixed, it may act upon the pelvis, raising it toward its own side when only one muscle is put in action; and when both muscles act together, either from below or above, they flex the trunk. V. THE MUSCLES AND FASCIA OF THE PELVIS. Obturator internus. Levator ani. Piriformis. Coccygeus. The muscles within the pelvis may be divided into two groups : (1) the Obturator internus and the Piriformis, which are muscles of the lower extremity, and will be described with these (pages 476 and 477) ; (2) the Levator ani and the Coccygeus, which together form the pelvic diaphragm and are associated with the pelvic viscera. The classification of the two groups under a common heading is convenient in connection with the fasciae investing the muscles. These fasciae are closely related to one another and to the deep fascia of the perineum, and in addition have special connections with the fibrous coverings of the pelvic viscera ; it is customary there- fore to describe them together under the term pelvic fascia. Pelvic Fascia. — The fascia of the pelvis may be resolved into: (a) the fascial sheaths of the Obturator internus. Piriformis, and pelvic diaphragm; (b) the fascia associated with the pelvic viscera. The fascia of the Obturator internus covers the pelvic surface of, and is attached around the margin of the origin of, the muscle. Above, it is loosely connected to the back part of the arcuate line, and here it is continuous with the iliac fascia. In front of this, as it follows the line of origin of the Obturator internus, it gradually separates from the iliac fascia and the continuity between the two is retained only through the periosteum. It arches beneath the obturator vessels and nerve, com- pleting the obturator canal, and at the front of the pelvis is attached to the back of the superior ramus of the pubis. Below, the obturator fascia is attached to the falciform process of the sacrotuberous ligament and to the pubic arch, where it becomes continuous with the superior fascia of the urogenital diaphragm. Behind, it is prolonged into the gluteal region. The internal pudendal vessels and pudendal nerve cross the pelvic surface of I THE MUSCLES AND FASCIA OF THE PELVIS 421 the Obturator internus and are enclosed in a special canal — Alcock's canal — formed by the obturator fascia. The fascia of the Piriformis is very thin and is attached to the front of the sacrum and the sides of the greater sciatic foramen; it is prolonged on the muscle into the gluteal region. At its sacral attachment around the margins of the anterior sacral foramina it comes into intimate association with and ensheathes the nerves emerging from these foramina. Hence the sacral nerves are frequently described as lying behind the fascia. The internal iliac vessels and their branches, on the other hand, lie in the subperitoneal tissue in front of the fascia, and the branches to the gluteal region emerge in special sheaths of this tissue, above and below the Piriformis muscle. ,_. , (Srtperior Diaphragmatic I layer part of pelvic J fascia Inferior \ layer Tendinous arch Fascia endopelvina Vesicida seminalie Ductus deferens Rectovegical layer Fig. 402. — Coronal section of pelvis, showing arrangement of fasciae. Viewed from behind. (Diagrammatic.) The diaphragmatic part of the pelvic fascia (Fig. 402) covers both surfaces of the Levatores ani. The inferior layer is known as the anal fascia; it is attached above to the obturator fascia along the line of origin of the Levator ani, while below it is continuous with the superior fascia of the urogenital diaphragm, and with the fascia on the Sphincter ani internus. The layer covering the upper surface of the pelvic diaphragm follows, above, the line of origin of the Levator ani and is there- fore somewhat variable. In front it is attached to the back of the symphysis pubis about 2 cm. above its lower border. It can then be traced laterally across the back of the superior ramus of the pubis for a distance of about L25 cm., when it reaches the obturator fascia. It is attached to this fascia along a line which pursues a somewhat irregular course to the spine of the ischium. The irregularity of this line is due to the fact that the origin of the Levator ani, which in lower forms is from the pelvic brim, is in man lower down, on the obturator fascia. Tendinous fibers of origin of the muscle are therefore often found extending up toward, and in some cases reaching, the pelvic brim, and on these the fascia is carried. It will be evident that the fascia covering that part of the Obturator internus which lies above the origin of the Levator ani is a composite fascia and includes the following: (a) the obturator fascia; (b) the fascia of the Levator ani; (c) degenerated fibers of origin of the Levator ani. 422 MYOLOGY The lower margin of the fascia covering the upper surface of the pelvic diaphragm is attached along the line of insertion of the Levator ani. ^i At the level of a line extending from the lower part of the symphysis pubis"' to the spine of the ischium is a thickened whitish band in this upper layer of the diaphragmatic part of the pelvic fascia. It is termed the tendinous arch or white line of the pelvic fascia, and marks the line of attachment of the special fascia (pars endopelvina fascice pelvis) which is associated with the pelvic viscera. Peritoneum Vesical layer Fascia 0/ {^^^^ urogenital -> j^l.,.^ diaphragm y ^^^^ Vesicula "seminalis Rectovesical layer ! _ Capsule of prostate Rectal layer Transverstis perincei superficialis Collet fascia Urogenital diaphragm Fig. 403. — Median sagittal section of pelvis, showing arrangement of fascise. The endopelvic part of the pelvic fascia is continued over the various pelvic viscera (Fig. 403) to form for them fibrous coverings which will be described later (see section on Splanchnology). It is attached to the diaphragmatic part of the pelvic fascia along the tendinous arch, and has been subdivided in accordance with the viscera to which it is related. Thus its anterior part, known as the vesical layer, forms the anterior and lateral ligaments of the bladder. Its middle part crosses the floor of the pelvis between the rectum and vesiculse seminales as the rectovesical layer; in the female this is perforated by the vagina. Its posterior portion passes to the side of the rectum; it forms a loose sheath for the rectum, but is firmly attached around the anal canal ; this portion is known as the rectal layer. The Levator ani (Fig. 404) is a broad, thin muscle, situated on the side of the pelvis. It is attached to the inner surface of the side of the lesser pelvis, and unites THE MUSCLES AND FASCIA OF THE PELVIS 423 with its fellow of the opposite side to form the greater part of the floor of the pelvic cavity. It supports the viscera in this cavity, and surrounds the various structures which pass through it. It arises, in front, from the posterior surface of the superior ramus of the pubis lateral to the symphysis; behind, from the inner surface of the spine of the ischium; and between these two points, from the obturator fascia. Posteriorly, this fascial origin corresponds, more or less closely, with the tendinous arch of the pelvic fascia, but in front, the muscle arises from the fascia at a vary- ing distance above the arch, in some cases reaching nearly as high as the canal Superior glutccal vessels Obturator nerve and vessels Left lobe of prostate (cut) Anococcygeal raphe Fia. 404. — Left Levator ani from within. for the obturator vessels and nerve. The fibers pass downward and backward to the middle line of the floor of the pelvis; the most posterior are inserted into the side of the last two segments of the coccyx; those placed more anteriorly unite with the muscle of the opposite side, in a median fibrous raphe (anococcygeal raphe), which extends between the coccyx and the margin of the anus. The middle fibers are inserted into the side of the rectum, blending with the fibers of the Sphincter muscles; lastly, the anterior fibers descend upon the side of the prostate to unite beneath it with the muscle of the opposite side, joining with the fibers of the Sphincter ani externus and Transversus perinsei, at the central tendinous point of the perineum. 424 MYOLOGY The anterior portion is occasionally separated from the rest of the muscle by connective tissue. From this circumstance, as well as from its peculiar relation with the prostate, which it supports as in a sling, it has been described as a distinct muscle, under the name of Levator prostatse. In the female the anterior fibers of the Levator ani descend upon the side of the vagina. The Levator ani may be divided into iliococcygeal and pubococcygeal parts. The Iliococcygeus arises from the ischial spine and from the posterior part of the tendinous arch of the pelvic fascia, and is attached to the coccyx and anococcygeal raph6; it is usually thin, and may fail entirely, or be largely replaced by fibrous tissue. An accessory slip at its posterior part is sometimes named the Iliosacralis. The Pubococcygeus arises from the back of the pubis and from the anterior part of the obturator fascia, and "is dii-ected backward almost horizontally along the side of the anal canal toward the coccyx and sacrum, to which it finds attachment. Between the termination of the vertebral column and the anus, the two Pubococcygei muscles come together and form a thick, fibromuscular layer lying on the raphe formed by the Ihococcygei" (Peter Thompson). The greater part of this muscle is inserted into the coccyx and into the last one or two pieces of the sacrum. This insertion into the vertebral column is, however, not admitted by all observers. The fibers which form a sling for the rectum are named the Pubo- rectalis or Sphincter recti. They arise from the lower part of the symphysis pubis, and from the superior fascia of the urogenital diaphragm. They meet with the corresponding fibers of the opposite side around the lower part of the rectum, and form for it a strong sUng. Nerve Supply. — The Levator ani is suppUed by a branch from the fourth sacral nerve and by a branch which is sometimes derived from the perineal, sometimes from the inferior hemor- rhoidal division of the pudendal nerve. The Coccygeus (Fig. 404) is situated behind the preceding. It is a triangular plane of muscular and tendinous fibers, arising by its apex from the spine of the ischium and sacrospinous ligament, and inserted by its base into the margin of the coccyx and into the side of the lowest piece of the sacrum. It assists the Levator ani and Piriformis in closing in the back part of the outlet of the pelvis. Nerve Supply. — The Coccygeus is supplied by a branch from the fourth and fifth sacral nerves. Actions. — The Levatores ani constrict the lower end of the rectum and vagina. They elevate and invert the lower end of the rectum after it has been protruded and everted during the expul- sion of the feces. They are also muscles of forced expiration. The Coccygei pull forward and support the coccyx, after it has been pressed backward during defecation or parturition. The Levatores ani and Coccygei together form a muscular diaphragm which supports the pelvic viscera. VI. THE MUSCLES AND FASCMJ OF THE PERINEUM. The perineum corresponds to the outlet of the pelvis. Its deep boundaries are — in front, the pubic arch and the arcuate ligament of the pubis; behind, the tip of the coccyx; and on either side the inferior rami of the pubis and ischium, and the sacrotuberous ligament. The space is somewhat lozenge-shaped and is limited on the surface of the body by the scrotum in front, by the buttocks behind, and laterally by the medial side of the thigh. A line drawn transversely across in front of the ischial tuberosities divides the space into two portions. The pos- terior contains the termination of the anal canal and is known as the anal region; the anterior, which contains the external urogenital organs, is termed the urogenital region. The muscles of the perineum may therefore be divided into two groups: 1. Those of the anal region. 2. Those of the urogenital region: a, In the male; b. In the female. L The Muscles of the Anal Region. Corrugator cutis ani. Sphincter ani externus. Sphincter ani internus. The Superficial Fascia. — The superficial fascia is very thick, areolar in texture, and contains much fat in its meshes. On either side a pad of fatty tissue extends THE MUSCLES OF THE ANAL REGION 425 i deeply between the Levator ani and Obturator internus into a space known as the ischiorectal fossa. The Deep Fascia. — The deep fascia forms the lining of the ischiorectal fossa; it comprises the anal fascia, and the portion of obturator fascia below the origin of Levator ani. Ischiorectal Fossa {fossa ischioredalis) (Fig. 405). — The fossa is somewhat pris- matic in shape, with its base directed to the surface of the perineum, and its apex at the line of meeting of the obturator and anal fasciae. It is bounded medially by the Sphincter ani externus and the anal fascia ; laterally, by the tuberosity of the ischium and the obturator fascia; anteriorly, by the fascia of Colles covering the Transversus perinsei superficialis, and by the inferior fascia of the urogenital diaphragm; posteriorly, by the Glutseus maximus and the sacrotuberous ligament. Crossing the space transversely are the inferior hemorrhoidal vessels and nerves; Fig. 405. — The perineum. The integument and superficial layer of superficial fascia reflected. at the back part are the perineal and perforating cutaneous branches of the pudendal plexus; while from the forepart the posterior scrotal (or labial) vessels and nerves emerge. The internal pudendal vessels and pudendal nerve lie in Alcock's canal on the lateral wall. The fossa is filled with fatty tissue across which numerous fibrous bands extend from side to side. The Comigator Cutis Ani.— Around the anus is a thin stratum of involuntary muscular fiber, which radiates from the orifice. Medially the fibers fade off into the submucous tissue, while laterally they blend with the true skin. By its contrac- tion it raises the skin into ridges around the margin of the anus. The Sphincter ani externus {External sphincter ani) (Fig 405) is a flat plane of muscular fibers, elliptical in shape and intimately adherent to the integument surrounding the margin of the anus. It measures about 8 to 10 cm. in length, from its anterior to its posterior extremity, and is about 2.5 cm. broad opposite the anus. It consists of two strata, superficial and deep. The superficial, constituting 426 MYOLOGY the main portion of the muscle, arises from a narrow tendinous band, the anococcy- geal raphe, which stretches from the tip of the coccyx to the posterior margin offll the anus; it forms two flattened planes of muscular tissue, which encircle the anus™' and meet in front to be inserted into the central tendinous point of the perineum, joining with the Transversus perinsei superficialis, the Levator ani, and the Bul- bocavernosus. The deeper portion forms a complete sphincter to the anal canal. Its fibers surround the canal, closely applied to the Sphincter ani internus, and in front blend with the other muscles at the central point of the perineum. In a considerable proportion of cases the fibers decussate in front of the anus, and are continuous with the Transversi perinaei superficiales. Posteriorly, they are not attached to the coccyx, but are continuous with those of the opposite side behind the anal canal. The upper edge of the muscle is ill-defined, since fibers are given off from it to join the Levator ani. Nerve Supply. — A branch from the fourth sacral and twigs from the inferior hemorrhoidal branch of the pudendal supply the muscle. Actions. — The action of this muscle is pecuUar. (1) It is, like other muscles, always in a state of tonic contraction, and having no antagonistic muscle it keeps the anal canal and orifice closed. (2) It can be put into a condition of greater contraction under the influence of the will, so as more firmly to occlude the anal aperture, in expiratory efforts unconnected with defecation. (3) Taking its fixed point at the coccyx, it helps to fix the central point of the perineum, so that the Bulbocavernosus may act from this fixed point. The Sphincter ani internus (Internal sphincter ani) is a muscular ring which surrounds about 2.5 cm. of the anal canal; its inferior border is in contact with, but quite separate from, the Sphincter ani externus. It is about 5 mm. thick, and is formed by an aggregation of the involuntary circular fibers of the intestine. Its lower border is about 6 mm. from the orifice of the anus. Actions. — Its action is entirely involuntary. It helps the Sphincter ani externus to occlude the anal aperture and aids in the expulsion of the feces. 2. A. The Muscles of the Urogenital Region in the Male (Fig. 406). Transversus perinaei superficialis. Ischiocavernosus. Bulbocavernosus. Transversus perinsei profundus. Sphincter urethrse membranacese. Superficial Fascia. — The superficial fascia of this region consists of two layers, superficial and deep. The superficial layer is thick, loose, areolar in texture, and contains in its meshes much adipose tissue, the amount of which varies in different subjects. In front, it is continuous with the dartos tunic of the scrotum; behind, with the subcuta- neous areolar tissue surrounding the anus; and, on either side, with the same fascia on the inner sides of the thighs. In the middle line, it is adherent to the skin on the raphe and to the deep layer of the superficial fascia. The deep layer of superficial fascia {fascia of Colles) (Fig. 405) is thin, aponeurotic in structure, and of considerable strength, serving to bind down the muscles of the root of the penis. It is continuous, in front, with the dartos tunic, the deep fascia of the penis, the fascia of the spermatic cord, and Scarpa's fascia upon the anterior wall of the abdomen; on either side it is firmly attached to the margins of the rami of the pubis and ischium, lateral to the crus penis and as far back as the tuberosity of the ischium; posteriorly, it curves around the Transversi perinsei superficiales to join the lower margin of the inferior fascia of the urogenital dia- phragm. In the middle line, it is connected with the superficial fascia and with the median septum of the Bulbocavernosus. This fascia not only covers the muscles in this region, but at its back part sends upward a vertical septum from its deep surface, which separates the posterior portion of the subjacent space into two. THE MUSCLES OF THE UROGENITAL REGION IN THE MALE 427 The Central Tendinous Point of the Perineum. — This is a fibrous point in the middle line of the perineum, between the urethra and anus, and about 1.25 cm. in front of the latter. At this point six muscles converge and are attached: viz., the Sphincter ani externus, the Bulbocavernosus, the two Transversi perinsei super- ficiales, and the anterior fibers of the Levatores ani. Fio. 406. — Muscles of male perineum. The Transversus perinsei superficialis ( Transversus yerinaei; Suyerficial transverse perineal muscle) is a narrow muscular slip, which passes more or less transversely across the perineal space in front of the anus. It arises by tendinous fibers from the inner and forepart of the tuberosity of the ischium, and, running medialward, is inserted into the central tendinous point of the perineum, joining in this situa- tion with the muscle of the opposite side, with the Sphincter ani externus behind, and with the Bulbocavernosus in front. In some cases, the fibers of the deeper layer of the Sphincter ani externus decussate in front of the anus and are con- tinued into this muscle. Occasionally it gives off fibers, which join with the Bulbocavernosus of the same side. ^H Variations are numerous. It may be absent or double, or insert into Bulbocavernosus or I 428 MYOLOGY Actions. — The simultaneous contraction of the two muscles serves to fix the central tendinous point of the perineum. The Bulbocavemosus (Ejaculator urince; Accelerator urince) is placed in the middle line of the perineum, in front of the anus. It consists of two symmetrical parts, united along the median line by a tendinous raphe. It arises from the cen- tral tendinous point of the perineum and from the median raphe in front. Its fibers diverge like the barbs of a quill-pen; the most posterior form a thin layer, which is lost on the inferior fascia of the urogenital diaphragm; the middle fibers encircle the bulb and adjacent parts, of the corpus cavernosum urethrae, and join with the fibers of the opposite side, on the upper part of the corpus cavernosum urethrae, in a strong aponeurosis; the anterior fibers, spread out over the side ^| of the corpus cavernosum penis, to be inserted partly into that body, anterior to HI the Ischiocavernosus, occasionally extending to the pubis, and partly ending in a tendinous expansion which covers the dorsal vessels of the penis. The latter fibers are best seen by dividing the muscle longitudinally, and reflecting it from the surface of the corpus cavernosum urethrse. Actions. — This muscle serves to empty the canal of the urethra, after the bladder has expelled its contents; during the greater part of the act of micturition its fibers are relaxed, and it only comes into action at the end of the process. The middle fibers are supposed by Krause to assist in the erection of the corpus cavernosum urethra?, by compressing the erectile tissue of the bulb. The anterior fibers, according to Tyrrel, also contribute to the erection of the penis by compressing the deep dorsal vein of the penis as they are inserted into, and continuous with, the fascia of the penis. The Ischiocavernosus {Erector penis) covers the crus penis. It is an elongated muscle, broader in the middle than at either end, and situated on the lateral bound- ary of the perineum. It arises by tendinous and fleshy fibers from the inner sur- face of the tuberosity of the ischium, behind the crus penis; and from the rami of the pubis and ischium on either side of the crus. From these points fleshy fibers succeed, and end in an aponeurosis which is inserted into the sides and under surface of the crus penis. Action. — The Ischiocavernosus compresses the crus penis, and retards the return of the blood through the veins, and thus serves to maintain the organ erect. Between the muscles just examined a triangular space exists, bounded medially by the Bulbo- cavemosus, laterally by the Ischiocavernosus, and behind by the Transversus perinai super- ficialis; the floor is formed by the inferior fascia of the urogenital diaphragm. Running from behind forward in the space are the posterior scrotal vessels and nerves, and the perineal branch of the posterior femoral cutaneous nerve; the transverse perineal artery courses along its posterior boundary on the Transversus perinaei superficialis. The Deep Fascia. — The deep fascia of the urogenital region forms an investment for the Transversus perinsei profundus and the Sphincter urethrse membranacese, but within it lie also the deep vessels and nerves of this part, the whole forming a transverse septum which is known as the urogenital diaphragm. From its shape it is usually termed the triangular ligament, and is stretched almost horizontally across the pubic arch, so as to close in the front part of the outlet of the pelvis. It consists of two dense membranous laminae (Fig. 407), which are united along their posterior borders, but are separated in front by intervening structures. The superficial of these two layers, the inferior fascia of the urogenital diaphragm, is tri- angular in shape, and about 4 cm. in depth. Its apex is directed forward, and is separated from the arcuate pubic ligament by an oval opening for the transmission of the deep dorsal vein of the penis. Its lateral margins are attached on either side to the inferior rami of the pubis and ischium, above the crus penis. Its base is directed toward the rectum, and connected to the central tendinous point of the perineum. It is continuous w ith the deep layer of the superficial fascia behind the Transversus perinaei superficialis, and with the inferior layer of the diaphragmatic THE MUSCLES OF THE UROGENITAL REGION IN THE MALE 429 I part of the pelvic fascia. It is perforated, about 2.5 cm. below the symphysis pubis, by the urethra, the aperture for which is circular and about 6 mm. in diameter by the arteries to the bulb and the ducts of the bulbourethral glands close to the urethral orifice; by the deep arteries of the penis, one on either side close to the pubic arch and about halfway along the attached margin of the fascia; by the dorsal arteries and nerves of the penis near the apex of the fascia. Its base is also perfor- ated by the perineal vessels and nerves, while between its apex and the arcuate pubic ligament the deep dorsal vein of the penis passes upward into the pelvis. If the inferior fascia of the urogenital diaphragm be detached on either side, the following structures will be seen between it and the superior fascia: the deep dorsal vein of the penis; the membranous portion of the urethra; the Transversus perinsei profundus and Sphincter urethrse membranacese muscles; the bulbo- urethral glands and their ducts; the pudendal vessels and dorsal nerves of the penis; the arteries and nerves of the urethral bulb, and a plexus of veins. urogenitaU j^y^.^ diaphragm [ ^^^^^ Ischiocavernostis Bulbocavemosus IFio. 407. — Coronal section of anterior part of pelvis, through the pubic arch. Seen from in front. (Diagrammatic.) I The superior fascia of the urogenital diaphragm is continuous with the obturator fascia and stretches across the pubic arch. If the obturator fascia be traced medially after leaving the Obturator internus muscle, it will be found attached by some of its deeper or anterior fibers to the inner margin of the pubic arch, while its super- ficial or posterior fibers pass over this attachment to become continuous with the superior fascia of the urogenital diaphragm. Behind, this layer of the fascia is continuous with the inferior fascia and with the fascia of Colles ; in front it is con- tinuous with the fascial sheath of the prostate, and is fused with the inferior fascia to form the transverse ligament of the pelvis. The Transversus perinsei profundus arises from the inferior rami of the ischium and runs to the median line, where it interlaces in a tendinous raphe with its fellow of the opposite side. It lies in the same plane as the Sphincter urethrse membran- acese; formerly the two muscles were described together as the Constrictor urethrse. The Sphincter urethrae membranacese surrounds the whole length of the mem- branous portion of the urethra, and is enclosed in the fasciae of the urogenital dia- phragm. Its external fibers arise from the junction of the inferior rami of the pubis 430 mHKm MYOLOGY ;'T, ,.'-; X- and ischium to the extent of 1.25 to 2 em., and from the neighboring fasciae. They arch across the front of the urethra and bulbourethral glands, pass around the urethra, and behind it unite with the muscle of the opposite side, by means of a tendinous raphe. Its innermost fibers form a continuous circular investment for the membranous urethra. ^1 Nerve Supply. — The perineal branch of the pudendal nerve supplies this group of muscles. Actions. — The muscles of both sides act together as a sphincter, compressing the membranous portion of the urethra. During the transmission of fluids they, hke the Bulbocavernosus, are, relaxed, and only come into action at the end of the process to eject the last drops of the fluid. ^ 2. B. The Muscles of the Urogenital Region in the Female (Fig. 408). Transversus perinsei superficialis. Ischiocavernosus. Bulbocavernosus. Transversus perinjsi profundus. Sphincter urethrse membranacese. The Transversus perinaei superficialis {Transversus perinosi; Superficial trans- verse perineal muscle) in the female is a narrow muscular slip, which arises by a small tendon from the inner and forepart of the tuberosity of the ischium, and is inserted into the central tendinous point of the perineum, joining in this situa- tion with the muscle of the opposite side, the Sphincter ani externus behind, and the Bulbocavernosus in front. Action. — The simultaneous contraction of the two muscles serves to fix the central tendinous point of the perineum. The Bulbocavernosus (Sphincter vaginoe) surrounds the orifice of the vagina. It covers the lateral parts of the vestibular bulbs, and is attached posteriorly to the central tendinous point of the perineum, where it blends with the Sphincter ani externus. Its fibers pass forward on either side of the vagina to be inserted into the corpora cavernosa clitoridis, a fasciculus crossing over the body of the organ so as to compress the deep dorsal vein. Actions. — The Bulbocavernosus diminishes the orifice of the vagina. The anterior fibers contribute to the erection of the clitoris, as they are inserted into and are continuous with the fascia of the clitoris, compressing the deep dorsal vein during the contraction of the muscle. The Ischiocavernosus {Erector clitoridis) is smaller than the corresponding muscle in the male. It covers the unattached surface of the crus clitoridis. It is an elongated muscle, broader at the middle than at either end, and situated on the side of the lateral boundary of the perineum. It arises by tendinous and fleshy fibers from the inner surface of the tuberosity of the ischium, behind the crus clitoridis; from the surface of the crus; and from the adjacent portion of the ramus of the ischium. From these points fleshy fibers succeed, and end in an aponeurosis, which is inserted into the sides and under surface of the crus clitoridis. Actions. — The Ischiocavernosus compresses the crus clitoridis and retards the return of blood through the veins, and thus serves to maintain the organ erect. The fascia of the urogenital diaphragm in the female is not so strong as in the male. It is attached to the pubic arch, its apex being connected with the arcuate pubic ligament. It is divided in the middle line by the aperture of the vagina, with the external coat of which it becomes blended, and in front of this is perfor- ated by the urethra. Its posterior border is continuous, as in the male, with the deep layer of the superficial fascia around the Transversus perinsei superficialis. Like the corresponding fascia in the male, it consists of two layers, between which are to be found the following structures : the deep dorsal vein of the clitoris, a portion of the urethra and the Constrictor urethra muscle, the larger vestibular THE MUSCLES AND FASCIA OF THE UPPER EXTREMITY 431 glands and their ducts; the internal pudendal vessels and the dorsal nerves of the clitoris; the arteries and nerves of the bulbi vestibuli, and a plexus of veins. The Transversus perinsei profundus arises from the inferior rami of the ischium and runs across to the side of the vagina. The Sphincter urethrse membranacese '.Constrictor urethras), like the corresponding muscle on the male, consists of external Clitoris Sphincter ani extemus Fig. 408. — Muscles of the female perineum. (Modified from a drawing by Peter Thompson.) and internal fibers. The external fibers arise on either side from the margin of the inferior ramus of the pubis. They are directed across the pubic arch in front of the urethra, and pass around it to blend with the muscular fibers of the opposite side, between the urethra and vagina. The innermost fibers encircle the lower end of the urethra. Nerve Supply. — The muscles of this group are supplied by the perineal branch of the pudendal. I THE MUSCLES AND FASCLffi OF THE UPPER EXTREMITY. The muscles of the upper extremity are divisible into groups, corresponding with the different regions of the limb. I. Muscles Connecting the Upper Extremity to the Vertebral Column. II. Muscles Connecting the Upper Extremity to the Anterior and Lateral Thoracic Walls. III. Muscles of the Shoulder. V. Muscles of the Forearm. IV. Muscles of the Arm. VI. Muscles of the Hand. 432 MYOLOGY I. THE MUSCLES CONNECTING THE UPPER EXTREMITY TO THE VERTEBRAL COLUMN. The muscles of this group are : Trapezius. Rhomboideus major. Latissimus dorsi. Rhomboideus minor. Levator scapulae. Superficial Fascia. — The superficial fascia of the back forms a layer of con- siderable thickness and strength, and contains a quantity of granular fat. It is continuous with the general superficial fascia. fli Deep Fascia, — The deep fascia is a dense fibrous layer, attached above to the superior nuchal line of the occipital bone; in the middle line it is attached to the ligamentum nuchse and supraspinal ligament, and to the spinous processes of all the vertebrae below the seventh cervical ; laterally, in the neck it is continuous with the deep cervical fascia; over the shoulder it is attached to the spine of the scapula and to the acromion, and is continued downward over the Deltoideus to the arm ; on the thorax it is continuous with the deep fascia of the axilla and chest, and on the abdomen with that covering the abdominal muscles; below, it is attached to the crest of the ilium. The Trapezius (Fig. 409) is a flat, triangular muscle, covering the upper and back part of the neck and shoulders. It arises from the external occipital protu- berance and the medial third of the superior nuchal line of the occipital bone, from the ligamentum nuchse, the spinous process of the seventh cervical, and the spinous processes of all the thoracic vertebrae, and from the corresponding portion of the supraspinal ligament. From this origin, the superior fibers proceed downward and lateralward, the inferior upward and lateralward, and the middle horizontally; the superior fibers are inserted into the posterior border of the lateral third of the clavicle; the middle fibers into the medial margin of the acromion, and into the supe- rior lip of the posterior border of the spine of the scapula; the inferior fibers con- verge near the scapula, and end in an aponeurosis, which glides over the smooth triangular surface on the medial end of the spine, to be inserted into a tubercle at the apex of this smooth triangular surface. At its occipital origin, the Trapezius is connected to the bone by a thin fibrous lamina, firmly adherent to the skin. At the middle it is connected to the spinous processes by a broad semi-elliptical aponeurosis, which reaches from the sixth cervical to the third thoracic vertebrae, and forms, with that of the opposite muscle, a tendinous ellipse. The rest of the muscle arises by numerous short tendinous fibers. The two Trapezius muscles together resemble a trapezium, or diamond-shaped quadrangle: two angles corre- sponding to the shoulders; a third to the occipital protuberance; and the fourth to the spinous process of the twelfth thoracic vertebra. Variations. — The attachments to the dorsal vertebrae are often reduced and the lower ones are often wanting; the occipital attachment is often wanting; separation between cervical and dorsal portions is frequent. Extensive deficiencies and complete absence occur. The clavicular insertion of this muscle varies in extent; it sometimes reaches as far as the middle of the clavicle, and occasionally may blend with the posterior edge of the Sternocleidomastoideus, or overlap it. The Latissimus dorsi (Fig. 409) is a triangular, flat muscle, which covers the lumbar region and the lower half of the thoracic region, and is gradually con- tracted into a narrow fasciculus at its insertion into the humerus. It arises by tendinous fibers from the spinous processes of the lower six thoracic vertebrae and from the posterior layer of the lumbodorsal fascia (see page 397), by which it is attached to the spines of the lumbar and sacral vertebrae, to the supraspinal ligament, and to the posterior part of the crest of the ilium. It also arises by I I MUSCLES OF THE UPPER EXTREMITY 433 Fia 409. — Muscles connecting the upper extremity to the vertebral column. 28 434 VHaBHaV MYOLOGY muscular fibers from the external lip of the crest of the ilium lateral to the margin j of the Sacrospinalis, and from the three or four lower ribs by fleshy digitations^ ' which are interposed between similar processes of the Obliquus abdominis externus j (Fig. 392, page 409). From this extensive origin the fibers pass in different direc- [ tions, the upper ones horizontally, the middle obliquely upward, and the lower vertically upward, so as to converge and form a thick fasciculus, which crosses the inferior angle of the scapula, and usually receives a few fibers from it. The muscle curves around the lower border of the Teres major, and is twisted upon itself, so that the superior fibers become at first posterior and then inferior, and the vertical fibers at first anterior and then superior. It ends in a quadrilateral tendon, about 7 cm, long, which passes in front of the tendon of the Teres major, and is inserted into the bottom of the intertubercular groove of the humerus; its insertion extends higher on the humerus than that of the tendon of the Pectoralis major. The lower border of its tendon is united with that of the Teres major, the surfaces of the two | being separated near their insertions by a bursa; another bursa is sometimes inter- posed between the muscle and the inferior angle of the scapula. The tendon of the muscle gives off an expansion to the deep fascia of the arm. Variations. — The number of dorsal vertebrae to which it is attached vary from four to seven or eight; the number of costal attachments varies; muscle fibers may or may not reach the crest of the ilium. \ A muscular slip, the axillary arch, varying from 7 to 10 cm. in length, and from 5 to 15 mm. in breadth, occasionally springs from the upper edge of the Latissimus dorsi about the middle of the posterior fold of the axilla, and crosses the axilla in front of the axillary vessels and nerves, to join the under surface of the tendon of the Pectoralis major, the Coracobrachialis, or the fascia over the Biceps brachii. This axillary arch crosses the axillary artery, just above the spot usually selected for the apphcation of a hgature, and may mislead the surgeon during the operation. It is present in about 7 per cent, of subjects and may be easily recognized by the transverse direction of its fibers. A fibrous slip usually passes from the lower border of the tendon of the Latissimus dorsi, near its insertion, to the long head of the Triceps brachii. This is occasionally muscular, and is the representative of the Dorsoepitrochlearis brachii of apes. The lateral margin of the Latissimus dorsi is separated below from the Obliquus externus abdominis by a small triangular interval, the lumbar triangle of Petit, the base of which is formed by the iliac crest, and its floor by the Obliquus internum abdominis. Another triangle is situated behind the scapula. It is bounded above by the Trapezius, below by the Latissimus dorsi, and laterally by the vertebral border of the scapula; the floor is partly formed by the Rhomboideus major. If the scapula be drawn forward by folding the arms across the chest, and the trunk bent forward, parts of the sixth and seventh ribs and the interspace between them become subcutaneous and available for auscultation. The space is there- fore known as the triangle of auscultation. Nerves. — The Trapezius is supplied by the accessory nerve, and by branches from the third and fourth cervical nerves; the Latissimus dorsi by the sixth, seventh, and eighth cervical nerves through the thoracodorsal (long subscapular) nerve. The Rhomboideus major (Fig. 409) arises by tendinous fibers from the spinous processes of the second, third, fourth, and fifth thoracic vertebrae and the supra- spinal ligament, and is inserted into a narrow tendinous arch, attached above to the lower part of the triangular surface at the root of the spine of the scapula; below ^o the inferior angle, the arch being connected to the vertebral border by a thin membrane. When the arch extends, as it occasionally does, only a short distance, the muscular fibers are inserted directly into the scapula. The Rhomboideus minor (Fig. 409) arises from the lower part of the ligamentum nuchse and from the spinous processes of the seventh cervical and first thoracic vertebrae. It is inserted into the base of the triangular smooth surface at the root of the spine of the scapula, and is usually separated from the Rhomboideus major ■■^^P MUSCLES OF THE UPPER EXTREMITY 435 by a slight interval, but the adjacent margins of the two muscles are occasionally united. Variations. — The vertebral and scapular attachments of the two muscles vary in extent. A small slip from the scapula to the occipital bone close to the minor occasionally occurs, the Rhom- boideus occipitalis muscle. The Levator scapulae* (Levator anguli scapulce) (Fig. 409) is situated at the back and side of the neck. It arises by tendinous slips from the transverse pro- cesses of the atlas and axis and from the posterior tubercles of the transverse processes of the third and fourth cervical vertebrae. It is inserted into the verte- bral border of the scapula, between the medial angle and the triangular smooth surface at the root of the spine. Variations.— The number of vertebral attachments varies; a slip may extend to the occipital or mastoid, to the Trapezius, Scalene or Serratus anterior, or to the first or second rib. The muscle may be subdivided into several distinct parts from origin to insertion. Levator claviculce from the transverse processes of one or two upper cervical vertebrae to the outer end of the clavicle corre- sponds to a muscle of lower animals. More or less union with the Serratus anterior. Nerves. — The Rhomboidei are supplied by the dorsal scapular nerve from the fifth cervical; the Levator scapula? by the third and fourth cervical nerves, and frequently by a branch from the dorsal scapular. Actions. — The movements effected by the preceding muscles are numerous, as may be con- ceived from their extensive attachments. When the whole Trapezius is in action it retracts the scapula and braces back the shoulder; if the head be fixed, the upper part of the muscle will elevate the point of the shoulder, as in supporting weights; when the lower fibers contract they assist in depressing the scapula. The middle and lower fibers of the muscle rotate the scapula, causing elevation of the acromion. If the shoulders be fixed, the Trapezii, acting together, will draw the head directly backward; or if only one act, the head is drawn to the corresponding side. When the Latissimus dorsi acts upon the humerus, it depresses and draws it backward, and at the same time rotates it inward. It is the muscle which is principally employed in giving a downward blow, as in felling a tree or jn sabre practice. If the arm be fixed, the muscle may act in various ways upon the trunk; thus, it may raise the lower ribs and assist in forcible inspira- tion; or, if both arms be fixed, the two muscles may assist the abdominal muscles and Pectorales in suspending and drawing the trunk forward, as in cUmbing. If the head be fixed, the Levator scapula; raises the medial angle of the scapula; if the shoulder be fixed, the muscle inclines the neck to the corresponding side and rotates it in the same direc- tion. The Rhomboidei carry the inferior angle backward and upward, thus producing a shght rotation of the scapula upon the side of the chest, the Rhomboideus major acting especially on the inferior angle of the scapula, through the tendinous arch by which it is inserted. The Rhom- boidei, acting together with the middle and inferior fibers of the Trapezius, will retract the scapula. 4) n. THE MUSCLES CONNECTING THE UPPER EXTREMITY TO THE ANTERIOR AND LATERAL THORACIC WALLS. The muscles of the anterior and lateral thoracic regions are: Pectoralis major. Subclavius. Pectoralis minor. Serratus anterior. Superficial Fascia.— The superficial fascia of the anterior thoracic region is con- tinuous with that of the neck and upper extremity above, and of the abdomen below. It encloses the mamma and gives off numerous septa which pass into the gland, supporting its various lobes. From the fascia over the front of the mamma, fibrous processes pass forward to the integument and papilla; these were called by Sir A. Cooper the ligamenta suspensoria. Pectoral Fascia. — The pectoral fascia is a thin lamina, covering the surface of the Pectoralis major, and sending numerous prolongations between its fasciculi: it is attached, in the middle line, to the front of the sternum; above, to the clavicle; laterally and below it is continuous with the fascia of the shoulder, axilla, and thorax. It is very thin over the upper part of the Pectoralis major, but thicker 436 MYOLOGY in the interval between it and the Latissimus dorsi, where it closes in the axillarjf space and forms the axillary fascia ; it divides at the lateral margin of the Latis- simus dorsi into two layers, one of which passes in front of, and the other behind it; these proceed as far as the spinous processes of the thoracic vertebrae, to which they are attached. As the fascia leaves the lower edge of the Pectoralis major to cross the floor of the axilla it sends a layer upward under cover of the muscle; this lamina splits to envelop the Pectoralis minor, at the upper edge of which it is continuous with the coracoclavicular fascia. The hollow of the armpit, seen when the arm is abducted, is produced mainly by the traction of this fascia on the axillary floor, and hence the lamina is sometimes named the suspensory ligament of the axilla. At the lower part of the thoracic region the deep fascia is well-developed, and is continuous with the fibrous sheaths of the Recti abdominis. n Fia. 410. — Superficial muscles of the chest and front of the arm. m The Pectoralis major (Fig. 410) is a thick, fan-shaped muscle, situated at the upper and forepart of the chest. It arises from the anterior surface of the sternal half of the clavicle; from half the breadth of the anterior surface of the sternum, as low down as the attachment of the cartilage of the sixth or seventh rib ; from the I MUSCLES OF THE UPPER EXTREMITY 437 cartilages of all the true ribs, with the exception, frequently, of the jBrst or seventh, or both, and from the aponeurosis of the Obliquus externus abdominis. From this extensive origin the fibers converge toward their insertion; those arising from the clavicle pass obliquely downward and lateralward, and are usually separated from the rest by a slight interval; those from the lower part of the sternum, and the cartilages of the lower true ribs, run upward and lateralward; while the middle fibers pass horizontally. They all end in a flat tendon, about 5 cm. broad, w^hich is inserted into the crest of the greater tubercle of the humerus. This tendon con- l^psists of two laminae, placed one in front of the other, and usually blended together ^^^below. The anterior lamina, the thicker, receives the clavicular and the uppermost sternal fibers; they are inserted in the same order as that in which they arise: that is to say, the most lateral of the clavicular fibers are inserted at the upper part of the anterior lamina; the uppermost sternal fibers pass down to the lower part of the lamina which extends as low as the tendon of the Deltoideus and joins with it. The posterior lamina of the tendon receives the attachment of the greater part of the sternal portion and the deep fibers, i. e., those from the costal cartilages. These deep fibers, and particularly those from the lower costal cartilages, ascend I^_ the higher, turning backward successively behind the superficial and upper ones, ^Bso that the tendon appears to be twisted. The posterior lamina reaches higher on the humerus than the anterior one, and from it an expansion is given off which covers the intertubercular groove and blends with the capsule of the shoulder- joint. From the deepest fibers of this lamina at its insertion an expansion is given off which lines the intertubercular groove, while from the lower border of the tendon a third expansion passes downward to the fascia of the arm. I^B Variations. — The more frequent variations are greater or less extent of attachment to the ribs I ^m and sternum, varying size of the abdominal part or its absence, greater or less extent of separation of sternocostal and clavicular parts, fusion of clavicular part with deltoid, decussation in front of the sternum. Deficiency or absence of the sternocostal part is not uncommon. Absence of the clavicular part is less frequent. Rarely the whole muscle is wanting. Costocoracaideus is a muscular band occasionally found arising from the ribs or aponeurosis of the External oblique between the Pectoralis major and Latissimus dorsi and inserted into the coracoid process. Chondro-epitrochlearis is a muscular slip occasionally found arising from the costal cartilages or from the aponeurosis of the External oblique below the Pectoralis major or from the Pectoralis major itself. The insertion is variable on the inner side of the arm to fascia, intermuscular septum or internal condyle. ISternalis, in front of the sternal end of the Pectoralis major parallel to the margin of the sterniun. It is supplied by the anterior thoracic nerves and is probably a misplaced part of the pectoralis. Coracoclavicular Fascia {fascia cora^oclavicularis; costocoracoid membrane; clavi- pedoral fascia). — The coracoclavicular fascia is a strong fascia situated under cover of the clavicular portion of the Pectoralis major. It occupies the interval between the Pectoralis minor and Subclavius, and protects the axillary vessels ^H and nerves. Traced upward, it splits to enclose the Subclavius, and its two layers ^fare attached to the clavicle, one in front of and the other behind the muscle; the latter layer fuses with the deep cervical fascia and with the sheath of the axillary , vessels. Medially, it' blends with the fascia covering the first two intercostal spaces, and is attached also to the first rib medial to the origin of the Subclavius. "^Laterally, it is very thick and dense, and is attached to the coracoid process. The portion extending from the first rib to the coracoid process is often whiter and denser than the rest, and is sometimes called the costocoracoid ligament. Below this it is thin, and at the upper border of the Pectoralis minor it splits into two layers to invest the muscle; from the lower border of the Pectoralis minOr it is continued downward to join the axillary fascia, and lateralward to join the fascia over the short head of the Biceps brachii. The coracoclavicular fascia is pierced by the cephalic vein, thoracoacromial artery and vein, and external anterior thoracic nerve. 438 MYOLOGY The Pectoralis minor (Fig. 411) is a thin, triangular muscle, situated at the upper part of the thorax, beneath the Pectoralis major. It arises from the upper margins and outer surfaces of the third, fourth, and fifth ribs, near their cartilage and from the aponeuroses covering the Intercostalis; the fibers pass upward and lateralward and converge to form a flat tendon, which is inserted into the medial border and upper surface of the coracoid process of the scapula. Variations. — Origin from second, third and fourth or fifth ribs. The tendon of insertion may extend over the coracoid process to the greater tubercle. May be split into several parts. Absence rare. Pectoralis minimus, first rib-cartilage to coracoid process. Rare. Badius Fig. 411. — Deep musclea of the chest and front of the arm, with the boundariea of the axilla. The Subclavius (Fig. 411) is a small triangular muscle, placed between the clavicle and the first rib. It arises by a short, thick tendon from the first rib and its cartilage at their junction, in front of the costoclavicular ligament; the fleshy fibers proceed obliquely upward and lateralward, to be inserted into the groove on the under surface of the clavicle between the costoclavicular and conoid ligaments. Variations. — Insertion into coracoid process instead of clavicle or into both clavicle and coracoid process. Sternoscapular fasciculus to the upper border of scapula. Sternoclavicularis from manu- brium to clavicle between Pectoralis major and coracoclavicular fascia. The Serratus anterior {Serratus magnus) (Fig. 411) is a thin muscular sheet, situated between the ribs and the scapula at the upper and lateral part of 1^ ■s THE MUSCLES AND FASCIA OF THE SHOULDER 439 tne chest. It arises by fleshy digitations from the outer surfaces and superior borders of the upper eight or nine ribs, and from the aponeuroses covering the intervening Intercostales. Each digitation (except the first) arises from the corresponding rib ; the first sprjngs from the first and second ribs ; and from the fascia covering the first intercostal space. From this extensive attachment the fibers pass backward, closely applied to the chest-wall, and reach the vertebral border pf the scapula, and are inserted into its ventral surface in the following manner, he first digitation is inserted into a triangular area on the ventral surface of the tnedial angle. The next two digitations spread out to form a thin, triangular sheet, the base of which is directed backward and is inserted into nearly the whole length of the ventral surface of the vertebral border. The low^er five or six digita- tions converge to form a fan-shaped mass, the apex of which is inserted, by muscular and tendinous fibers, into a triangular impression on the ventral surface of the inferior angle. The lower four slips interdigitate at their origins with the upper five slips of the Obliquus externus abdominis. Variations. — ^Attachment to tenth rib. Absence of attachments to first rib, to one or more of he lower ribs. Division into three parts; absence or defect of middle part. Union with Levator scapulae, External intercostals or External oblique. Nerves. — The Pectoralis major is suppUed by the medial and lateral anterior thoracic nerves; through these nerves the muscle receives filaments from all the spinal nerves entering into the formation of the brachial plexus; the Pectoralis minor receives its fibers from the eighth cervical and first thoracic nerves through the medial anterior thoracic nerve. The Subclavius is suplied by a filament from the fifth and sixth cervical nerves; the Serratus anterior is supplied by the long thoracic, which is derived from the fifth, sixth, and seventh cervical nerves. Actions. — If the arm has been raised by the Deltoideus, the Pectorahs major will, conjointly with the Latissimus dorsi and Teres major, depress it to the side of the chest. If acting alone, it adducts and draws forward the arm, bringing it across the front of the chest, and at the same time rotates it inward. The Pectoralis minor depresses the point of the shoulder, drawing the scapula downward and medialward toward the thorax, and throwing the inferior angle back- ward. The Subclavius depresses the shoulder, carrying it downward and forward. When the arms are fixed, all three of these muscles act upon the ribs; drawing them upward and expand- ing the chest, and thus becoming very important agents in forced inspiration. The Serratus anterior, as a whole, carries the scapula forward, and at the same time raises the vertebral border of the bone. It is therefore concerned in the action of pushing. Its lower and stronger fibers move forward the lower angle and assist the Trapezius in rotating the bone at the sternoclavicular joint, and thus assist this muscle in raising the acromion and supporting weights upon the shoulder. It is also an assistant to the Deltoideus in raising the arm, inasmuch as during the action of this latter muscle it fixes the scapula and so steadies the glenoid cavity on which the head of the humerus rotates. After the Deltoideus has raised the arm to a right angle with the trunk, the Serratus anterior and the Trapezius, by rotating the scapula, raise the arm into an almost vertical position. It is possible that when the shoulders are fixed the lower fibers of the Serratus anterior may assist in raising and everting the ribs; but it is not the important inspiratory muscle it was formerly beheved to be in. THE MUSCLES AND FASCMl OF THE SHOULDER. I In this group are included: Deltoideus. Infraspinatus. Subscapularis. Teres minor. Supraspinatus. Teres major. Deep Fascia. — The deep fascia covering the Deltoideus invests the muscle, and sends numerous septa between its fasciculi. In front it is continuous with the fascia covering the Pectoralis major; behind, where it is thick and strong, with that covering the Infraspinatus; above, it is attached to the clavicle, the acromion, and the spine of the scapula; below, it is continuous with the deep fascia of the arm. The Deltoideus {Deltoid muscle) (Fig. 410) is a large, thick, triangular muscle, which covers the shoulder- joint in front, behind, and laterally. It arises from the anterior / 440 MYOLOGY I border and upper surface of the lateral third of the clavicle; from the lateral margm and upper surface of the acromion, and from the lower lip of the posterior border of the spine of the scapula, as far back as the triangular surface at its medial end.iH From this extensive origin the fibers converge toward their insertion, the middle-™ passing vertically, the anterior obliquely backward and lateralward, the posterior obliquely forward and lateralward; they unite in a thick tendon, which is inserted into the deltoid prominence on the middle of the lateral side of the body of the humerus. At its insertion the muscle gives off an expansion to the deep fascia of the arm. This muscle is remarkably coarse in texture, and the arrangement of its fibers is somewhat peculiar; the central portion of the muscle — that is to say, the part arising from the acromion — consists of oblique fibers; these arise in a bipenniform manner from the sides of the tendinous intersections, generally four in number, which are attached above to the acromion and pass downward parallel to one another in the substance of the muscle. The oblique fibers thus formed are inserted into similar tendinous intersections, generally three in number, which pass upward from the insertion of the muscle and alternate with the descending septa. The portions of the muscle arising from the clavicle and spine of the scapula are not arranged in this manner, but are inserted into the margins of the inferior tendon. Variations. — Large variations uncommon. More or less splitting common. Continuation into the Trapezius; fusion with the Pectoralis major; additional slips from the vertebral border of the scapula, infraspinous fascia and axillary border of scapula not uncommon. Insertion varies in extent or rarely is prolonged to origin of Brachioradialis. Nerves. — The Deltoideus is suppUed by the fifth and sixth cervical through the axillary nerve. Actions. — The Deltoideus raises the arm from the side, so as to bring it at right angles with the trunk. Its anterior fibers, assisted by the Pectoralis major, draw the arm forward; and its posterior fibers, aided by the Teres major and Latissimus dorsi, draw it backward. Subscapular Fascia (fascia subscapularis) . — The subscapular fascia is a thin membrane attached to the entire circumference of the subscapular fossa, and affording attachment by its deep surface to some of the fibers of the Sub- scapularis. The Subscapularis (Fig. 411) is a large triangular muscle which fills the sub- scapular fossa, and arises from its medial two-thirds and from the lower two- thirds of the groove on the axillary border of the bone. Some fibers arise from tendinous laminae which intersect the muscle and are attached to ridges on the bone; others from an aponeurosis, which separates the muscle from the Teres major and the long head of the Triceps brachii. The fibers pass lateralward, and, gradually converging, end in a tendon which is inserted into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint. The tendon of the muscle is separated from the neck of the scapula by a large bursa, which communicates with the cavity of the shoulder-joint through an aperture in the capsule. Nerves. — The Subscapularis is supplied by the fifth and sixth cervical nerves through the upper and lower subscapular nerves. Actions. — The Subscapularis rotates the head of the humerus inward; when the arm is raised, it draws the humerus forward and downward. It is a powerful defence to the front of the shoulder- joint, preventing displacement of the head of the humerus. Supraspinatous Fascia (fascia supraspinata) . — ^The supraspinatous fascia com- pletes the osseofibrous case in which the Supraspinatus muscle is contained; it affords attachment, by its deep surface, to some of the fibers of the muscle. It is thick medially, but thinner laterally under the coracoacromial ligament. The Supraspinatus (Fig. 412) occupies the whole of the supraspinatous fossa, arising from its medial two-thirds, and from the strong supraspinatous fascia. The muscular fibers converge to a tendon, which crosses the upper part of the I THE MUSCLES AND FASCIA OF THE SHOULDER 441 fder-joint, and is inserted into the highest of the three impressions on the greater tubercle of the humerus; the tendon is intimately adherent to the capsule of the shoulder-joint. Infraspinatous Fascia (fascia infraspinata). — The infraspinatous fascia is a dense fibrous membrane, covering the Infraspinatous muscle and fixed to the circumfer- ence of the infraspinatous fossa; it affords attachment, by its deep surface, to some fibers of that muscle. It is intimately attached to the deltoid fascia along the over- lapping border of the Deltoideus. Fig. 412. — Muscles on the dorsum of the scapula, and the Triceps brachii. The Infraspinatus (Fig. 412) is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa; it arises by fleshy fibers from its medial two- thirds, and by tendinous fibers from the ridges on its surface; it also arises from the infraspinatous fascia which covers it, and separates it from the Teretes major and minor. The fibers converge to a tendon, which glides over the lateral border of the spine of the scapula, and, passing across the posterior part of the capsule of the shoulder-joint, is inserted into the middle impression on the greater tubercle of the humerus. The tendon of this muscle is sometimes separated from the capsule of the shoulder-joint by a bursa, which may communicate with the joint cavity. The Teres minor (Fig, 412) is a narrow, elongated muscle, which arises from the dorsal surface of the axillary border of the scapula for the upper two-thirds of its extent, and from two aponeurotic laminae, one of which separates it from the Infraspinatus, the other from the Teres major. Its fibers run obliquely upward and lateralward; the upper ones end in a tendon which is inserted into the lowest of the three impressions on the greater tubercle of the humerus; the lowest fibers are inserted directly into the humerus immediately below this impression. The 442 MYOLOGY tendon of this muscle passes across, and is united with, the posterior part of capsule of the shoulder-joint. Variations. — It is sometimes inseparable from the Infraspinatus. The Teres major (Fig. 412) is a thick but somewhat flattened muscle, which arises from the oval area on the dorsal surface of the inferior angle of the scapula, and from the fibrous septa interposed between the muscle and the Teres minor and Infraspinatus; the fibers are directed upward and lateralward, and end in a flat tendon, about 5 cm. long, which is inserted into the crest of the lesser tubercle of the humerus. The tendon, at its insertion, lies behind that of the Latissimus dorsi, from which it is separated by a bursa, the two tendons being, however, united along their lower borders for a short distance. Nerves. — The Supraspinatus and Infraspinatus are suppUed by the fifth and sixth cervical nerves through the suprascapular nerve; the Teres minor, by the fifth cervical, through the axillary; and the Teres major, by the fifth and sixth cervical, through the lowest subscapular. Actions. — The Supraspinatus assists the Deltoideus in raising the arm from the side of the trunk and fixes the head of the humerus in the glenoid cavity. The Infraspinatus and Teres minor rotate the head of the humerus outward; they also assist in carrying the arm backward. One of the most important uses of these three muscles is to protect the shoulder-joint, the Supra- spinatus supporting it above, and the Infraspinatus and Teres minor behind. The Teres major assists the Latissimus dorsi in drawing the previously raised humerus downward and backward, and in rotating it inward; when the arm is fixed it may assist the Pectorales and th^ Latissimus dorsi in drawing the trunk forward. IV. THE MUSCLES AND FASCLffl OF THE ARM. The muscles of the arm are: Coracobrachialis. Brachialis. Biceps brachii. Triceps brachii. Brachial Fascia (fascia brachii; deep fascia of the arm) . — The brachial fascia is continuous with that covering the Deltoideus and the Pectoralis major, by means of which it is attached, above, to the clavicle, acromion, and spine of the scapula; it forms a thin, loose, membranous sheath for the muscles of the arm, and sends septa between them ; it is composed of fibers disposed in a circular or spiral direc- tion, and connected together by vertical and oblique fibers. It differs in thickness at different parts, being thin over the Biceps brachii, but thicker where it covers the Triceps brachii, and over the epicondyles of the humerus: it is strengthened by fibrous aponeuroses, derived from the Pectoralis major and Latissimus dorsi medially, and from the Deltoideus laterally. On either side it gives off a strong intermuscular septum, which is attached to the corresponding supracondylar ridge and epicondyle of the humerus. The lateral intermuscular septmn extends from the lower part of the crest of the greater tubercle, along the lateral supra- condylar ridge, to the lateral epicondyle; it is blended with the tendon of the Del- toideus, gives attachment to the Triceps brachii behind, to the Brachialis, Brachio- radialis, and Extensor carpi radialis longus in front, and is perforated by the radial nerve and profunda branch of the brachial artery. The medial intermuscular septum, thicker than the preceding, extends from the lower part of the crest of the lesser tubercle of the humerus below the Teres major, along the medial supra- condylar ridge to the medial epicondyle; it is blended with the tendon of the Coracobrachialis, and affords attachment to the Triceps brachii behind and the Brachialis in front. It is perforated by the ulnar nerve, the superior ulnar collateral artery, and the posterior branch of the inferior ulnar collateral artery. At the elbow, the deep fascia is attached to the epicondyles of the humerus and the olecranon of the ulna, and is continuous with the deep fascia of the forearm. THE MUSCLES AND FASCIA OF THE ARM 443 Tust below the middle of the arm, on its medial side, is an oval opening in the deep fascia, which transmits the basilic vein and some lymphatic vessels. The Coracobrachialis (Fig. 411), the smallest of the three muscles in this region, is situated at the upper and medial part of the arm. It arises from the apex of the coracoid process, in common with the short head of the Biceps brachii, and from the intermuscular septum between the two muscles ; it is inserted by means of a flat tendon into an impression at the middle of the medial surface and border of the body of the humerus between the origins of the Triceps brachii and Brachialis. lit is perforated by the musculocutaneous nerve. Biceps brachii M Cephalic vein-. Brachialis 'M. Radial nerve- Dorsal antihrachial, cutaneous nerve Radial collateral arteri/ Lateral intermuscular septum of humerus Lateral antibrachial cutaneous nerve Brachial artery and veins Median nerve ^Medial antibrachial V cutaneous nerve l^ ^'-Basilic vein . >,.. Ulnar nerve Superior ulnar collateral artery Medial intermuscular septum of humerus -Humerus ''Triceps brachii M. Fig. 413. — Cross-section through the middle of upper arm. (Eycleshymer and Schoemaker.O Variations. — A bony head may reach the medial epicondyle; a short head more rarely foimd ly insert into the lesser tubercle. The Biceps brachii {Biceps; Biceps flexor cuhiti) (Fig. 411) is a long fusiform muscle, placed on the front of the arm, and arising by two heads, from which circumstance it has received its name. The short head arises by a thick flattened tendon from the apex of the coracoid process, in common with the Coracobrachialis. The long head arises from the supraglenoid tuberosity at the upper margin of the glenoid cavity, and is continuous with the glenoidal labrum. This tendon, enclosed ,in a special sheath of the synovial membrane of the shoulder-joint, arches over the head of the humerus; it emerges from the capsule through an opening close to the humeral attachment of the ligament, and descends in the intertubercular groove; it is retained in the groove by the transverse humeral ligament and by a fibrous prolongation from the tendon of the Pectoralis major. Each tendon is succeeded by an elongated muscular belly, and the two bellies, although closely applied to each other, can readily be separated until within about 7.5 cm. of the elbow-joint. Here they end in a flattened tendon, which is inserted into the rough posterior portion of the tuberosity of the radius, a bursa being interposed between the tendon and the front part of the tuberosity. As the tendon of the muscle approaches the radius it is twisted upon itself, so that its anterior surface becomes 1 A Cross-section Anatomy, New York, 1911. 444 ^^MAMJa^^ MYOLOGY lateral and is applied to the tuberosity of the radius at its insertion. Opposrte the bend of the elbow the tendon gives off, from its medial side, a broad aponeu- rosis, the lacertus fibrosus (bicipital fascia) which passes obliquely downward and medial ward across the brachial artery, and is continuous with the deep fascia j^ covering the origins of the Flexor muscles of the forearm (Fig. 410). H Variations. — A third head (10 per cent.) to the Biceps brachii is occasionally found, arising at the upper and medial part of the Brachialis, with the fibers of which it is continuous, and inserted into the lacertus fibrosus and medial side of the tendon of the muscle. In most cases this additional slip lies behind the brachial artery in its coarse down the arm. In some instances the third head consists of two slips, which pass down, one in front of and the other behind the artery, concealing the vessel in the lower half of the arm. More rarely a fourth head occurs arising from the outer side of the humerus, from the intertubercular groove, or from the greater tubercle. Other heads are occasionally found. Slips sometimes pass from the inner border of the muscle over the brachial artery to the medial intermuscular septum, or the medial epicondyle; more rarely to the Pronator teres or Brachialis. The long head may be absent or arise from the intertubercular groove. The Brachialis (Brachialis anticus) (Fig. 411) covers the front- of the elbow-joint and the lower half of the humerus. It arises from the lower half of the front of the humerus, commencing above at the insertion of the Deltoideus, which it embraces by two angular processes. Its origin extends below to within 2.5 cm. of the margin of the articular surface. It also arises from the intermuscular septa, but more extensively from the medial. than the lateral; it is separated from the lateral below by the Brachioradialis and Extensor carpi radialis longus. Its fibers converge to a thick tendon, which is inserted into the tuberosity of the ulna and the rough depression on the anterior surface of the coronoid process. Variations. — Occasionally doubled; additional slips to the Supinator, Pronator teres, Biceps, lacertus fibrosus, or radius are more rarely found. Nerves. — The Coracobrachialis, Biceps brachii and Brachialis are supplied by the musculo- cutaneous nerve; the Brachiahs usually receives an additional filament from the radial. The Coracobrachialis receives its supply primarily from the seventh cervical, the Biceps brachii and Brachialis from the fifth and sixth cervical nerves. Actions. — The CoracobrachiaUs draws the humerus forward and medialward, and at the same time assists in retaining the head of the bone in contact with the glenoid cavity. The Biceps brachii is a flexor of the elbow and, to a less extent, of the shoulder; it is also a powerful supinator, and serves to render tense the deep fascia of the forearm by means of the lacertus fibrosus given off from its tendon. The Brachialis is a flexor of the forearm, and forms an impor- tant defence to the elbow-joint. When the forearm is fixed, the Biceps brachii and Brachialis flex the arm upon the forearm, as in efforts of climbing. The Triceps brachii {Triceps; Triceps extensor cubiti) (Fig. 412) is situated on the back of the arm, extending the entire length of the dorsal surface of the humerus. It is of large size, and arises by three heads (long, lateral, and medial), hence its name. The long head arises by a flattened tendon from the infraglenoid tuberosity of the scapula, being blended at its upper part with the capsule of the shoulder- joint; the muscular fibers pass downward between the two other heads of the muscle, and join with them in the tendon of insertion. The lateral head arises from the posterior surface of the body of the humerus, between the insertion of the Teres minor and the upper part of the groove for the radial nerve, and from the lateral border of the humerus and the lateral intermus- cular septum; the fibers from this origin converge toward the tendon of insertion. The medial head arises from the posterior surface of the body of the humerus, below the groove for the radial nerve; it is narrow and pointed above, and extends from the insertion of the Teres major to within 2.5 cm. of the trochlea: it also arises from the medial border of the humerus and from the back of the whole length of the medial intermuscular septum. Some of the fibers are directed downward to the olecranon, while others converge to the tendon of insertion. The tendon of the Triceps brachii begins about the middle of the muscle: it con- THE Vi jAR :m m I II sists of two aponeurotic laminae, one of which is subcutaneous and covers the back of the lower half of the muscle; the other is more deeply seated in the substance of the muscle. After receiving the attachment of the muscular fibers, the two lamellae join together above the elbow, and are inserted, for the most part, into the posterior portion of the upper surface of the olecranon; a band of fibers is, however, continued downward, on the lateral side, over the Anconseus, to blend with the deep fascia of the forearm. The long head of the Triceps brachii descends between the Teres minor and Teres major, dividing the triangular space between these two muscles and the humerus into two smaller spaces, one triangular, the other quadrangular (Fig. 412). The triangular space contains the scapular circumflex vessels; it is bounded by the Teres minor above, the Teres major below, and the scapular head of the Triceps laterally. The quadrangular space transmits the posterior humeral circumflex vessels and the axillary nerve; it is bounded by the Teres minor and capsule of the ehoulder-joint above, the Teres major below, the long head of the Triceps brachii medially, and the humerus laterally. Variations. — A fourth head from the inner part of the humerus; a slip between Triceps and Latissimus dorsi corresponding to the Dorso-epitrochlearis. The Subanconaeus is the name given to a few fibers which spring from the deep surface of the lower part of the Triceps brachii, and are inserted into the posterior Ugament and synovial membrane of the elbow-joint. Nerves. — The Triceps brachii is supplied by the seventh and eighth cervical nerves through the radial nerve. Actions. — The Triceps brachii is the great extensor muscle of the forearm, and is the direct antagonist of the Biceps brachii and Brachialis. When the arm is extended, the long head of the muscle may assist the Teres major and Latissimus dorsi in drawing the humerus backward and in adducting it to the thorax. The long head supports the under part of the shoulder-joint. The Subanconseus draws up the synovial membrane of the elbow-joint during extension of the forearm. V. THE MUSCLES AND FASCMl OF THE FOREARM. Antibrachial Fascia (fascia antibrachii; deep fascia of the forearm). — The anti- brachial fascia continuous above with the brachial fascia, is a dense, membranous investment, which forms a general sheath for the muscles in this region; it is at- tached, behind, to the olecranon and dorsal border of the ulna, and gives off from its deep surface numerous intermuscular septa, which enclose each muscle separately. Over the Flexor tendons as they approach the wrist it is especially thickened, and forms the volar carpal ligament. This is continuous with the transverse carpal liga- ment, and forms a sheath for the tendon of the Palmaris longus which passes over the transverse carpal ligament to be inserted into the palmar aponeurosis. Behind, near the wrist-joint, it is thickened by the addition of many transverse fibers, and ■forms the dorsal carpal ligament. It is much thicker on the dorsal than on the volar surface, and at the lower than at the upper part of the forearm, and is strengthened above by tendinous fibers derived from the Biceps brachii in front, and from the Triceps brachii behind. It gives origin to muscular fibers, especially at the upper part of the medial and lateral sides of the forearm, and forms the boundaries of a series of cone-shaped cavities, in which the muscles are contained. Besides the vertical septa separating the individual muscles, transverse septa are given off both on the volar and dorsal surfaces of the forearm, separating the deep from the superficial layers of muscles. Apertures exist in the fascia for the passage of vessels and nerves; one of these apertures of large size, situated at the front of the elbow, serves for the passage of a communicating branch between the superficial and deep veins. The antibrachial or forearm muscles may be divided into a volar and a dorsal group. 1. The Volar Antibrachial Muscles. These muscles are divided for convenience of description into two groups, superficial and deep. The Superficial Group (Fig. 414). Pronator teres. Palmaris longus. Flexor carpi radialis. Flexor carpi ulnaris. Flexor digitorum sublimis. The muscles of this group take origin from the medial epicondyle of the humerus by a common tendon; they receive additional fibers from the deep fascia of the fore- arm near the elbow, and from the septa which pass from this fascia between the individual muscles. The Pronator teres has two heads of origin — humeral and ulnar. The humeral head, the larger and more superficial, arises immediately above the medial epi- condyle, and from the tendon common to the origin of the other muscles; also from the intermuscular septum between it and the Flexor carpi radialis and from the antibrachial fascia. The ulnar head is a thin fasciculus, which arises from the medial side of the coronoid process of the ulna, and joins the preceding at an acute angle. The median nerve enters the forearm between the two heads of the muscle, and is separated from the ulnar artery by the ulnar head. The muscle passes ob- liquely across the forearm, and ends in a flat tendon, which is inserted into a rough impression at the middle of the lateral surface of the body of the radius. The lateral border of the muscle forms the medial boundary of a triangular hollow situated in front of the elbow-joint and containing the brachial artery, median nerve, and tendon of the Biceps brachii. Variations. — Absence of ulnar head; additional slips from the medial intermuscular septum, from the Biceps and from the Brachialis anticus occasionally occur. The Flexor carpi radialis lies on the medial side of the preceding muscle. It arises from the medial epicondyle by the common tendon; from the fascia of the forearm; and from the intermuscular septa between it and the Pronator teres laterally, the Palmaris longus medially, and the Flexor digitorum sublimis beneath. Slender and aponeurotic in structure at its commencement, it increases in size, and ends in a tendon which forms rather more than the lower half of its length. This tendon passes through a canal in the lateral part of the transverse carpal ligament and runs through a groove on the greater multangular bone; the groove is converted into a canal by fibrous tissue, and lined by a mucous sheath. The ten- don is inserted into the base of the second metacarpal bone, and sends a slip to the base of the third metacarpal bone. The radial artery, in the lower part of the forearm, lies between the tendon of this muscle and the Brachioradialis. Variations. — Slips from the tendon of 'the Biceps, the lacertus fibrosus, the coronoid, and the radius have been found. Its insertion often varies and may be mostly into the annular ligament, the trapezium, or the fourth metacarpal as well as the second or third. The muscle may be absent. The Palmaris longus is a slender, fusiform muscle, lying on the medial side of the preceding. It arises from the medial epicondyle of the humerus by the common tendon, from the intermuscular septa between it and the adjacent muscles, and from the antibrachial fascia. It ends in a slender, flattened tendon, which passes over the upper part of the transverse carpal ligament, and is inserted into the central part of the transverse carpal ligament and lower part of the palmar aponeurosis, frequently sending a tendinous slip to the short muscles of the thumb. Variations. — One of the most variable muscles in the body. This muscle is often absent about (10 per cent.), and is subject to many variations; it may be tendinous above and muscular below; or it may be muscular in the center with a tendon above and below; or it may present two muscular bimdles with a central tendon; or finally it may consist solely of a tendinous band. The muscle may be double. Slips of origin from the coronoid process or from the radius have been seen. i THE VOLAR ANTIBRACHIAL' MUSCLES 447 Partial or complete insertion into the fascia of the forearm, into the tendon of the Flexor carpi ulnaris and pisiform bone, into the navicular, and into the muscles of the little finger have been observed. The Flexor carpi ulnaris lies along the uhiar side of the forearm. It arises by two heads, humeral and ulnar, connected by a tendinous arch, beneath which the ulnar nerve and posterior ulnar recurrent artery pass. The humeral head arises from the Fig. 414.— Front of the left forearm. Superficial muscles. FiQ. 415. — Front of the left forearm. Deep muscles. MYOLOGY medial epicondyle of the humerus by the common tendon; the uhiar head arises from the medial margin of the olecranon and from the upper two-thirds of the dorsal border of the ulna by an aponeurosis, common to it and the Extensor carpi ulnaris and Flexor digitorum profundus ; and from the intermuscular septum between it and the Flexor digitorum sublimis. The fibers end in a tendon, which occupies the anterior part of the lower half of the muscle and is inserted into the MM pisiform bone, and is prolonged from this to the hamate and fifth metacarpal"" bones by the pisohamate and pisometacarpal ligaments; it is also attached by a few fibers to the transverse carpal ligament. The ulnar vessels and nerve lie on the lateral side of the tendon of this muscle, in the lower two-thirds of the forearm- Variations. — Slips of origin from the coronoid. The Epitrochleo-anconceus, a small muscle oftea present runs from the back of the inner condyle to the olecranon, over the ulnar nerve. The Flexor digitorum sublimis is placed beneath the previous muscle; it is the largest of the muscles of the superficial group, and arises by three heads — humeral, ulnar, and radial. The humeral head arises from the medial epicondyle of the humerus by the common tendon, from the ulnar collateral ligament of the elbow-joint, and from the intermuscular septa between it and the preceding muscles. The ulnar head arises from the medial side of the coronoid process, above the ulnar origin of the Pronator teres (see Fig. 213, page 216). The radial head arises from the oblique line of the radius, extending from the radial tuberosity to the insertion of the Pronator teres. The muscle speedily separates into two planes of muscular fibers, superficial and deep: the superficial plane divides into two parts which end in tendons for the middle and ring fingers; the deep plane gives off a muscular slip to join the portion of the superficial plane which is asso- ciated with the tendon of the ring finger, and then divides into two parts, which end in tendons for the index and little fingers. As the four tendons thus formed pass beneath the transverse carpal ligament into the palm of the hand, they are arranged in pairs, the superficial pair going to the middle and ring fingers, the deep pair to the index and little fingers. The tendons diverge from one another in the palm and form dorsal relations to the superficial volar arch and digital branches of the median and ulnar nerves. Opposite the bases of the first phalanges each tendon divides into two slips to allow of the passage of the corresponding tendon of the Flexor digitorum profundus ; the two slips then reunite and form a grooved channel for the reception of the accompanying tendon of the Flexor digitorum profundus. Finally the tendon divides and is inserted into the sides of the second phalanx about its middle. Variations. — Absence of radial head, of little finger portion; accessory slips from ulnar tuberosity to the index and middle finger portions; from the inner head to the Flexor profundus; from the ulnar or annvilar ligament to the little finger. The Deep Group (Fig. 415). Flexor digitorum profundus. Flexor pollicis longus. Pronator quadratus. The Flexor digitorum profundus is situated on the ulnar side of the forearm, immediately beneath the superficial Flexors. It arises from the upper three- fourths of the volar and medial surfaces of the body of the ulna, embracing the insertion of the Brachialis above, and extending below to within a short distance of the Pronator quadratus. It also arises from a depression on the medial side of the coronoid process ; by an aponeurosis from the upper three-fourths of the dorsal border of the ulna, in common with the Flexor and Extensor carpi ulnaris; and from the ulnar half of the interosseous membrane. The muscle ends in four tendons which run under the transverse carpal ligament dorsal to the tendons of the Flexor I THE VOLAR ANTI BRACHIAL MUSCLES 449 digitorum sublimis. Opposite the first phalanges the tendons pass through the openings in the tendons of the Flexor digitorum sublimis, and are finally inserted into the bases of the last phalanges. The portion of the muscle for the index finger His usually distinct throughout, but the tendons for the middle, ring, and little fingers are connected together by areolar tissue and tendinous slips, as far as the palm of the hand. Fibrous Sheaths of the Flexor Tendons. — After leaving the palm, the tendons of the Flexores digitorum sublimis and profundus lie in osseo-aponeurotic canals (Fig. 427), formed behind by the phalanges and in front by strong fibrous bands, which arch across the tendons, and are attached on either side to the margins of the phalanges. Opposite the middle of the proximal and second phalanges the bands (digital vaginal ligaments) are very strong, and the fibers are transverse; but opposite the joints they are much thinner, and consist of annular and cruciate ligamentous fibers. Each canal contains a mucous sheath, which is reflected on I^« the contained tendons. H Within each canal the tendons of the Flexores digitorum sublimis and profundus are connected to each other, and to the phalanges, by slender, tendinous bands, called vincula tendina (Fig. 416). There are two sets of these; (a) the vincula brevia, which are two in number in each finger, and consist of triangular bands of fibers, one connecting the tendon of the Flexor digitorum sublimis to the front of the first interphalangeal joint and head of the first phalanx, and the other the tendon of the Flexor digitorum profundus to the front of the second interphalan- geal joint and head of the second phalanx; (6) the vincula longa, which connect the under surfaces of the tendons of the Flexor digitorum profundus to thos j of the • subjacent Flexor sublimis after the tendons of the former have passed through the latter. ^^B Variations. — The index finger portion may arise partly from the upper part of the radius. Slips from the inner head of the Flexor sublimis, medial epicondyle, or the coronoid are found. Connec- tion with the Flexor pollicis longus. I^P Four small muscles, the Lumbricales, are connected with the tendons of the Flexor profundus in the palm. They will be described with the muscles of the ■hand (page 464). The Flexor pollicis longus is situated on the radial side of the forearm, lying in the same plane as the preceding. It arises from the grooved volar surface of the body of the radius, extending from immediately below the tuberosity and oblique line to within a short distance of the Pronator quadratus. It arises also from the adjacent part of the interosseous membrane, and generally by a fleshy slip from the medial border of the coronoid process, or from the medial epicondyle of the humerus. The fibers end in a flattened tendon, which passes beneath the transverse carpal ligament, is then lodged between the lateral head of the Flexor pollicis brevis and the oblique part of the Adductor pollicis, and, entering an osseo- aponeurotic canal similar to those for the Flexor tendons of the fingers, is inserted into the base of the distal phalanx of the thumb. The volar interosseous nerve and vessels pass downward on the front of the interosseous membrane between the Flexor pollicis longus and Flexor digitorum profundus. Variations.— Slips may connect with Flexor sublimis, or Profimdus, or Pronator teres. An addi- [■tional tendon to the index finger is sometimes found. The Pronator quadratus is a small, flat, quadrilateral muscle, extending across [the front of the lower parts of the radius and ulna. It arises from the pronator ridge on the lower part of the volar surface of the body of the ulna; from the medial part of the volar surface of the lower fourth of the ulna; and from a strong apon- eurosis which covers the medial third of the muscle. The fibers pass lateral ward 29 450 MYOLOGY and slightly downward, to be inserted into the lower fourth of the lateral borS5 and the volar surface of the body of the radius. The deeper fibers of the muscle are inserted into the triangular area above the ulnar notch of the radius — aa attachment comparable with the origin of the Supinator from the triangular area below the radial notch of the ulna. Tendon of Ext. carpi rod. longus Tendon of Ext. digitorum communis Tendon of Extensor indicis proprius First Lumbricalis Vincula hrevia Tendon of Ahdv^tor poinds longus Cheater multangular bone Radial artery Tendon of Ext. pollicis hrevis -Tendon of Ext. pollicis longus 'lexor digitorum suhlimis Flexor digitorum profundus FiQ. 416. — Tendons of forefinger and vincula tendina Variations. — Rarely absent; split into two or three layers; increased attachment upward or downward. Nerves. — All the muscles of the superficial layer are supplied by the median nerve, excepting the Flexor carpi ulnaris, which is supplied by the ulnar. The Pronator teres, the Flexor carpi radialis, and the Palmaris longus derive their supply primarily from the sixth cervical nerve; the Flexor digitorum subUmis from the seventh and eighth cervical and first thoracic nerves, and the Flexor carpi ulnaris from the eighth cervical and first thoracic. Of the deep layer, the Flexor digitorum profundus is supplied by the eighth cervical and first thoracic through the ulnar, and the volar interosseous branch of the median. The Flexor pollicis longus and Pronator quadratus are supplied by the eighth cervical and first thoracic through the volar interosseous branch of the median. Actions. — These muscles act upon the forearm, the wrist, and hand. The Pronator teres rotates the radius upon the ulna, rendering the hand prone; when the radius is fixed, it assists in flexing the forearm. The Flexor carpi radialis is a flexor and abductor of the wrist; it also assists in pronating the hand, and in bending the elbow. The Flexor carpi ulnaris is a flexor and adductor of the wrist; it also assists in bending the elbow. The Palmaris longus is a flexor of the wrist-joint; it also assists in flexing the elbow. The Flexor digitorum subMmis flexes first the middle and then the proximal phalanges; it also assists in flexing the wrist and elbow. The Flexor digitorum profundus is one of the flexors of the phalanges. After the Flexor sublimis has bent the second phalanx, the Flexor profundus flexes the terminal one; but it cannot do so until after the contraction of the superficial muscle. It also assists in flexing the wrist. The THE DORSAL ANTIBRACHIAL MUSCLES 451 Flexor pollicis longus is a flexor of the phalanges of the thumb; when the thumb is fixed, it assists in flexing the wrist. The Pronator quadratus rotates the radius upon the ulna, rendering the hand prone. Flexor carpi radialis M Antibrachial interos- seous membrane Lateral antibrachial cutaneous nerve Radial artery and nerve Median nerve Palmaris longus M. Medial antibrachial cutaneous nerve [volar branch] Flexor digitorum sublimis M. Cephalic vein~~, Brachioradialis Af ... Flexor pollicis longus M.' Radius - Tendo m. pronatoris,^ teretis Hxtensores carpi radiales, longus and brevis Mm Extensor digitorum.- ■ communis M. ,, Ulnar artery and nerve Flexor digitorum profundus M. -Flexor carpi ulnaris "Basilic vein '' Ulna Abductor pollicis / longus M. i Volar interosseous artery and volar antibrachial interosseous nerve Extensor carpi ulnaris M. j Extensor pollicis S longus M. Extensor digiti quinti proprius M. and dor- sal interosseous artery Fig. 417. — Cross-section through the middle of the forearm. (Eycleshymer and Schoemaker.) 2. The Dorsal Antibrachial Muscles. These muscles are divided for convenience of description into two groups, superficial and deep. The Superficial Group (Fig. 418). Brachioradialis. Extensor digitorum communis. Extensor carpi radialis longus. Extensor digiti quinti proprius. Extensor carpi radialis brevis. Extensor carpi ulnaris. Anconseus. The Brachioradialis {Supinator longus) is the most superficial muscle on the radial side of the forearm. It arises from the upper two-thirds of the lateral supracondylar ridge of the humerus, and from the lateral intermuscular septum, being limited above by the groove for the radial nerve. Interposed between it and the Brachialis are the radial nerve and the anastomosis between the anterior branch of the profunda artery and the radial recurrent. The fibers end above the middle of the forearm in a flat tendon, which is inserted into the lateral side of the base of the styloid process of the radius. The tendon is crossed near its insertion by the tendons of the Abductor pollicis longus and Extensor pollicis brevis; on its ulnar side is the radial artery. Variations. — Fusion with the Brachialis; tendon of insertion may be divided into two or three slips; insertion partial or complete into the middle of the radius, fasciculi to the tendon of the Biceps, the tuberosity or oblique line of the radius; slips to the Extensor carpi radialis longus or Abductor pollicis longus; absence; rarely doubled. 452 ^^^^^^^ MYOLOGY The Extensor carpi radialis longus {Exiemor carpi radialis longior) is placed partly beneath the Brachioradialis. It arises from the lower third of the lateral supracon- dylar ridge of the humerus, from the lateral intermuscular septum, and by a few fibers from the common tendon of origin of the Extensor muscles of the forearm. The fibers end at the upper third of the forearm in a flat tendon, which runs along the lateral border of the radius, beneath the Abductor pollicis longus and Extensor pollicis brevis ; it then passes beneath the dorsal carpal ligament, where it lies in a groove on the back of the radius common to it and the Extensor carpi radialis brevis, immediately behind the styloid process. It is inserted into the dorsal surface of the base of the second metacarpal bone, on its radial side. The Extensor carpi radialis brevis {Extensor carpi radialis brevior) is shorter and thicker than the preceding muscle, beneath which it is placed. It arises from the lateral epicondyle of the humerus, by a tendon common to it and the three following muscles; from the radial collateral ligament of the elbows-joint; from a strong aponeurosis which covers its surface; and from the intermuscular septa between it and the adjacent muscles. The fibers end about the middle of the forearm in a flat tendon, which is closely connected with that of the preceding muscle, and accompanies it to the wrist; it passes beneath the Abductor pollicis longus and Extensor pollicis brevis, then beneath the dorsal carpal ligament, and is inserted into the dorsal surface of the base of the third metacarpal bone on its radial side. Under the dorsal carpal ligament the tendon lies on the back of the radius in a shallow groove, to the ulnar side of that which lodges the tendon of the Extensor carpi radialis, longus, and separated from it by a faint ridge. The tendons of the two preceding muscles pass through the same compartment of the dorsal carpal ligament in a single mucous sheath. Variations. — Either muscle may split into two or three tendons of insertion to the second and third or even the fourth metacarpal. The two muscles may unite into a single belly with two tendons. Cross slips between the two muscles may occur. The Extensor carpi radialis inter- medius rarely arises as a distinct muscle from the humerus, but is not uncommon as an accessory slip from one or both muscles to the second or third or both metacarpals. The Extenscrr carpi radialis accessorius is occasionally found arising from the humerus with or below the Extensor carpi radialis longus and inserted into the first metacarpal^ the Abductor pollicis brevis, the First dorsal interosseous, or elsewhere. The Extensor digitorum communis arises from the lateral epicondyle of the humerus, by the common tendon; from the intermuscular septa between it and the adjacent muscles, and from the antibrachial fascia. It divides below into four tendons, which pass, together with that of the Extensor indicis proprius, through a separate compartment of the dorsal carpal ligament, within a mucous sheath. The tendons then diverge on the back of the hand, and are inserted into the second and third phalanges of the fingers in the following manner. Opposite the meta- carpophalangeal articulation each tendon is bound by fasciculi to the collateral ligaments and serves as the dorsal ligament of this joint; after having crossed the joint, it spreads out into a broad aponeurosis, which covers the dorsal surface of the first phalanx and is reinforced, in this situation, by the tendons of the Inter- ossei and Lumbricalis. Opposite the first interphalangeal joint this aponeurosis divides into three slips; an intermediate and two collateral: the former is inserted into the base of the second phalanx; and the two collateral, which are continued onward along the sides of the second phalanx, unite by their contiguous margins, and are inserted into the dorsal surface of the last phalanx. As the tendons cross the interphalangeal joints, they furnish them with dorsal ligaments. The tendon to the index finger is accompanied by the Extensor indicis proprius, which lies on its ulnar side. On the back of the hand, the tendons to the middle, ring, and little fingers are connected by two obliquely placed bands, one from the third tendon passing downward and lateralward to the second tendon, and the other THE DORSAL ANTIBRACHIAL MUSCLES 453 Fig. 419. — Posterior surface of the forearm. Deep muscles. 454 ^BBBRSi^r MYOLOGY passing from the same tendon downward and medialward to the fourth. Occa- sionally the first tendon is connected to the second by a thin transverse band. Variations. — An increase or decrease in the number of tendons is common; an additional slip- to the thumb is sometimes present. The Extensor digit! quinti proprius {Extensor minimi digiti) is a slender musck; placed on the medial side of the Extensor digitorum communis, with which it is generally connected. It arises from the common Extensor tendon by a thin tendinous slip, from the intermuscular septa between it and the adjacent muscles. Its tendon runs through a compartment of the dorsal carpal ligament behind the distal radio-ulnar joint, then divides into two as it crosses the hand, and finally joins the expansion of the Extensor digitorum communis tendon on the dorsum of the first phalanx of the little finger. Variations. — An additional fibrous slip from the lateral epicondyle; the tendon of insertion may not divide or may send a slip to the ring finger. Absence of muscle rare; fusion of the beUy with the Extensor digitorum commimis not uncommon. The Extensor carpi ulnaris lies on the ulnar side of the forearm. It arises from the lateral epicondyle of the humerus, by the common tendon; by an aponeu- rosis from the dorsal border of the ulna in common with the Flexor carpi ulnaris and the Flexor digitorum profundus; and from the deep fascia of the forearm. It ends in a tendon, which runs in a groove between the head and the styloid process of the ulna, passing through a separate compartment of the dorsal carpal ligament, and is inserted into the prominent tubercle on the ulnar side of the base of the fifth metacarpal bone. Variations. — Doubling; reduction to tendinous band; insertion partially into fourth metacarpal. In many cases (52 per cent.) a slip is continued from the insertion of the tendon anteriorly over the Opponens digiti quinti, to the fascia covering that muscle, the metacarpal bone, the capsule of the metacarpophalangeal articulation, or the first phalanx of the little finger. This slip may be replaced by a muscular fasciculus arising from or near the pisiform. The Anconseus is a small triangular muscle which is placed on the back of the elbow-joint, and appears to be a continuation of the Triceps brachii. It arises by a separate tendon from the back part of the lateral epicondyle of the humerus; its fibers diverge and are inserted into the side of the olecranon, and upper fourth of the dorsal surface of the body of the ulna. The Deep Group (Fig. 419). Supinator. Extensor pollicis brevis. Abductor pollicis longus. Extensor pollicis longus. Extensor indicis proprius. The Supinator (Supinator brevis) (Fig. 420) is a broad muscle, curved around the upper third of the radius. It consists of two planes of fibers, between which the deep branch of the radial nerve lies. The two planes arise in common^ — the superficial one by tendinous and the deeper by muscular fibers — from the lateral epicondyle of the humerus; from the radial collateral ligament of the elbow-joint, and the annular ligament; from the ridge on the ulna, which runs obliquely down- ward from the dorsal end of the radial notch ; from the triangular depression below the notch; and from a tendinous expansion which covers the surface of the muscle. The superficial fibers surround the upper part of the radius, and are inserted into the lateral edge of the radial tuberosity and the oblique line of the radius, as low down as the insertion of the Pronator teres. The upper fibers of the deeper plane I THE DORSAL ANTIBRACHIAL MUSCLES 455 the neck of the radius above the tuber- its medial surface; the greater part of the dorsal and lateral surfaces of the oblique line and the head of the bone. Lateral epicondyle Radial collateral I ig. Annular ligament Deep branch of radial nerve Interosseous recurrent art. Deep "branch of radial nerve Dorsal interosseous art. form a sling-like fasciculus, which encircles osity and is attached to the back part of this portion of the muscle is inserted into body of the radius, midway between the The Abductor pollicis longus {Ex- tensor OSS. metacarpi pollicis) lies im- mediately below the Supinator and is sometimes united with it. It arises from the lateral part of the dorsal surface of the body of the ulna below the insertion of the Anco- nseus, from the interosseous mem- brane, and from the middle third of the dorsal surface of the body of the radius. Passing obliquely downward and lateralward, it ends in a tendon, which runs through a groove on the lateral side of the lower end of the radius, accompanied by the tendon of the Extensor pollicis brevis, and is inserted into the radial side of the base of- the first metacarpal bone. It occasionally gives off two slips near its insertion : one to the greater multangular bone and the other to blend with the origin of the Abduc- tor pollicis brevis. Variations. — More or less doubling of muscle and tendon with insertion of the extra tendon into the first metacarpal, the greater multangular, or into the Abductor pollicis brevis or Opponens pollicis. The Extensor pollicis brevis {Ex- tensor primi internodii pollicis) lies on the medial side of, and is closely connected with, the Abductor pollicis longus. It arises from the dorsal surface of the body of the radius below that muscle, and from the interosseous membrane. Its direction is similar to that of the Abductor pollicis longus, its tendon passing through the same groove on the lateral side of the lower end of the radius, to be inserted into the base of the first phalanx of the thumb. Variations. — Absence; fusion of tendon with that of the Extensor pollicis longus. The Extensor pollicis longus {Extensor secundi internodii pollicis) is much larger than the preceding muscle, the origin of which it partly covers. It arises from the lateral part of the middle third of the dorsal surface of the body of the ulna below the origin of the Abductor pollicis longus, and from the interosseous mem- brane. It ends in a tendon, which passes through a separate compartment in the dorsal carpal ligament, lying in a narrow, oblique groove on the back of the lower end of the radius. It then crosses obliquely the tendons of the Extensores carpi radialis longus and brevis, and is separated from the Extensor brevis pollicis by a triangular interval, in which the radial artery is found; and is finally inserted into the base of the last phalanx of the thumb. The radial artery is crossed by the Fig. 420.— The Supinator. 456 Tdi^Mn^^ MYOLOGY tendons of the Abductor pollicis longus and of the Extensores pollicis lon^^nl brevis. The Extensor indicis proprius (Extensor indicis) is a narrow, elongated muscle, placed medial to, and parallel with, the preceding. It arises, from the dorsal sur- face of the body of the ulna below the origin of the Extensor pollicis longus, and from the interosseous membrane. Its tendon passes under the dorsal carpal ligament in the same compartment as that which transmits the tendons of the Extensor digitorum communis, and opposite the head of the second metacarpal bone, joins the ulnar side of the tendon of the Extensor digitorum communis which belongs to the index finger. Variations. — Doubling; the ulnar part may pass beneath the dorsal carpal ligament with the Extensor digitorum communis; a slip from the tendon may pass to the index finger. Nerves. — The Brachioradialis is supphed by the fifth and sixth, the Extensores carpi radialis longus and brevis by the sixth and seventh, and the Anconajus by the seventh and eighth cervical nerves, through the radial nerve; 'the remaining muscles are innervated through the deep radial nerve, the Supinator being supplied by the sixth, and all the other muscles by the seventh cervical. Actions. — The muscles of the lateral and dorsal aspects of the forearm, which comprise all the Extensor muscles and the Supinator, act upon the forearm, wrist, and hand; they are the direct antagonists of the Pronator and Flexor muscles. The Anconeus assists the Triceps in extending the forearm. The Brachioradialis is a flexor of the elbow-joint, but only acts as such when the movement of flfexion has been initiated by the Biceps brachii and Brachialis. The action of the Supinator is 'suggested by its name; it assists the Biceps in bringing the hand into the supine position. The Extensor carpi radialis longus extends the wrist and abducts the hand. It may also assist in bending the elbow-joint; at all events it serves to fix or steady this' articula- tion. The Extensor carpi/radialis brevis extends the wrist, and may also act slightly as an abductor of the hand. The Extensor carpi ulnaris extends the wrist, but when acting alone inclines the hand toward the ulnar side; by its continued action it extends the elbow-joint. The Extensor digitorum communis extends the phalanges, then the wrist, and finally the elbow. It acts prin- cipally on the proximal phalanges, the middle and terminal phalanges being extended mainly by the Interossei and Lumbricales. It tends to separate the fingers as it extends them. The Extensor digiti quinti proprius extends the little finger, and by its continued action assists in extending the wrist. It is owing to this muscle that the little finger can be extended or pointed while the others are flexed. The chief action of the Abductor pollicis longus is to carry the thumb laterally from the palm of the hand. By its continued action it helps to extend and abduct the wrist. The Extensor poUicis brevis extends the proximal phalanx, and the Extensor pollicis longus the terminal phalanx of the thumb; by their continued action they help to extend and abduct the wrist. The Extensor indicis proprius extends the index finger, and by its continued action assists in extending the wrist. VI. THE MUSCLES AND FASCM) OF THE HAND. The muscles of the hand are subdivided into three groups: (1) those of the thumb, which occupy the radial side and produce the thenar eminence ; (2) those of the little finger, which occupy the ulnar side and give rise to the hypothenar eminence ; (3) those in the middle of the palm and between the metacarpal bones. Volar Carpal Ligament (ligamentum carpi volare). — The volar carpal ligament is the thickened band of antibrachial fascia which extends from the radius to the ulna over the Flexor tendons as they enter the wrist. Transverse Carpal Ligament (ligamentum carpi transversum; anterior annular ligament) (Figs. 421, 422). — The transverse carpal ligament is a strong, fibrous band, which arches over the carpus, converting the deep groove on the front of the carpal bones into a tunnel, through which the Flexor tendons of the digits and the median nerve pass. It is attached, medially, to the pisiform and the hamulus of the hamate bone; laterally, to the tuberosity of the navicular, and to the medial part of the volar surface and the ridge of the greater multangular. It is continuous, above, with the volar carpal ligament; and below, with the palmar aponeurosis. It is crossed by the ulnar vessels and nerve, and the cutaneous branches of the median and ulnar nerves. At its lateral end is the tendon of the I THE MUSCLES AND FASCIA OF THE HAND 457 lexor carpi radialis, which Hes in the groove on the greater multangular between the attachments of the ligament to the bone. On its volar surface the tendons of the Palmaris longus and Flexor carpi ulnaris are partly inserted; below, it gives origin to the short muscles of the thumb and little finger Median nerve _, , , . . Palmaris longus | Flexor dig. svbhmts __ . \ I A XJlTiar artery raimans Longus Flex. poll. long. \ Flex. carp. rod. \,-\- JRadial artery ~ ^^^"Z^^P^ r' Abd. poll. long. Ext poll brev. Ext. carp. rad. long. Ulnar nerve Flex. carp, vln. Flex. dig. profundus. Ext. carp. rad. brev. ." , ~\ " V \ Ext. carp. vln. Ext. poll. long. \ \ \ Distal radio-ulnar artic. Ext, indicis. prop. \ Ext. dig. quinfi prop. Ext. dig. commun. Fia. 421. — Transverse section across distal ends of radius and ulna. The Mucous Sheaths of the Tendons on the Front of the Wrist. — Two sheaths envelop the tendons as they pass beneath the transverse carpal ligament, one for the Flexores digitorum sublimis and profundus, the other for the Flexor pollicis longus (Fig. 423). They extend into the forearm for about 2.5 cm. above the transverse carpal ligament, and occasionally communicate with each other under Median nerve Transverse carpal ligament Flex. poll. long. \ \ Palmaris longus Flex, carpi rad. \ \ \ Flex. dig. sublimis 2Iusdes of thumb \ \ \ \ \ // Ulnar art. and nerve _ \__— - ^ \ \ - \ — \ // £_^ Muscles of little finger Abd.poU. long. Ext. poll. brev. Flex, dig, profundus Bxt. carp. rad. long, Badial artery Ext. carp. rad. brev. Ext, poll, long. Ext. carp. uln. Ext. dig. quinti prop. Ext. dig. communis Ext. indicis prop. Fig. 422. — Transverse section across the wrist and digits. the ligament. The sheath which surrounds the Flexores digitorum extends down- ward about half-way along the metacarpal bones, where it ends in blind diverticula around the tendons to the index, middle, and ring fingers. It is prolonged on the tendons to the little finger and usually communicates with the mucous 458 MYOLOGY ■ sheath of these tendons. The sheath of the tendon of the Flexor polHcis longus is continued along the thumb as far as the insertion of the tendon. The mucous sheaths enveloping the terminal parts of the tendons of the Flexores digitorum have been described on page 449. Sheaths of terminal parts of Flexores digitorum Muscles of thenar eminence Sheath of Flexor poinds longus SJieath of Flexor carpi radialis Muscles of hypo- thenar emirteiux Common sheath of Flexores digitorum sublimis and profundus Flexor carpi idnaris FiQ. 423. — The mucous sheaths of the tendons on the front of the wrist and digits. Dorsal Carpal Ligament (ligamentum carpi dorsale; posterior annular ligament) (Figs. 421, 422). — The dorsal carpal ligament is a strong, fibrous band, extending obliquely downward and medialward across the back of the wrist, and consisting of part of the deep fascia of the back of the forearm, strengthened by the addition of some transverse fibers. It is attached, medially, to the styloid process of the ulna THE MUSCLES AND FASCIA OF THE HAND 459 and to the triangular and pisiform bones; laterally, to the lateral margin of the radius; and, in its passage across the wrist, to the ridges on the dorsal surface of the radius. ^^.) T. CXTCS jlTOP Abd. poll. long. Ext. carp. rod. long. Ext. carp. rad. hrev. Fia. 424. — The mucous sheaths of the tendons on the back of the wrist. The Mucous Sheaths of the Tendons on the Back of the Wrist. — Between the dorsal carpal ligament and the bones six compartments are formed for the passage of tendons, each compartment having a separate mucous sheath. One is found in each of the following positions (Fig. 424) : (1) on the lateral side of the styloid pro- cess, for the tendons of the Abductor pollicis longus and Extensor pollicis brevis; (2) behind the styloid process, for the tendons of the Extensores carpi radialis 460 MYOLOGY longus and brevis; (3) about the middle of the dorsal surface of the radius, for the tendon of the Extensor pollicis longus; (4) to the medial side of the latter, for the tendons of the Extensor digitorum communis and Extensor indicis proprius; (5) opposite the interval between the radius and ulna, for the Extensor digiti quinti proprius; (6) between the head and styloid process of the ulna, for the tendon of the Extensor carpi ulnaris. The sheaths lining these compartments extend from above the dorsal carpal ligament; those for the tendons of Abductor pollicis longus, Extensor brevis pollicis, Extensores carpi radialis, and Extensor carpi ulnaris stop immediately proximal to the bases of the metacarpal bones, while the sheaths for Extensor communis digitorum. Extensor indicis proprius, and Extensor digiti quinti proprius are prolonged to the junction of the proximal and intermediate thirds of the metacarpus. Proper digital artery and nerve I Ulnar artery and nerve Fig. iJ'j 1 In ij.il.ii.u aponeurosis. Palmar Aponeurosis {aponeurosis palmaris; palmar fascia) (Fig. 425). — The palmar aponeurosis invests the muscles of the palm, and consists of central, lateral, and medial portions. The central portion occupies the middle of the palm, is triangular in shape, and of great strength and thickness. Its apex is continuous with the lower margin of the transverse carpal ligament, and receives the expanded tendon of the Pal THE LATERAL VOLAR MUSCLES 461 maris longus. Its base divides below into four slips, one for each finger. Each slip gives off superficial fibers to the skin of the palm and fihger, those to the palm joining the skin at the furrow corresponding to the metacarpophalangeal articula- tions, and those to the fingers passing into the skin at the transverse fold at the bases of the fingers. The deeper part of each slip subdivides into two processes, which are inserted into the fibrous sheaths of the Flexor tendons. From the sides of these processes offsets are attached to the transverse metacarpal ligament. By this arrangement short channels are formed on the front of the heads of the metacarpal bones; through these the Flexor tendons pass. The intervals between the four slips transmit the digital vessels and nerves, and the tendons of the Lum- bricales. At the points of division into the slips mentioned, numerous strong, transverse fasciculi bind the separate processes together. The central part of the palmar aponeurosis is intimately bound to the integument by dense fibroareolar tissue forming the superficial palmar fascia, and gives origin by its medial margin to the Palmaris brevis. It covers the superficial volar arch, the tendons of the Flexor muscles, and the branches of the median and ulnar nerves; and on either side it gives off a septum, which is continuous with the interosseous aponeurosis, and separates the intermediate from the collateral groups of muscles. The lateral and medial portions of the palmar aponeurosis are thin, fibrous layers, which cover, on the radial side, the muscles of the ball of the thumb, and, on the ulnar side, the muscles of the little finder; they are continuous with the central portion and with the fascia on the dorsum of the hand. The Superficial Transverse Ligament of the Fingers is a thin band of transverse fasciculi (Fig. 425) ; it stretches across the roots of the four fingers, and is closely attached to the skin of the clefts, and medially to the fifth metacarpal bone, forming a sort of rudimentary web. Beneath it the digital vessels and nerves pass to their destinations. 1. The Lateral Volar Muscles (Figs. 426, 427). Abductor pollicis brevis. Flexor pollicis brevis. Opponens pollicis. Adductor pollicis (obliquus). Adductor pollicis (transversus). The Abductor pollicis brevis (Abductor pollicis) is a thin, flat muscle, placed immediately beneath the integument. It arises from the transverse carpal liga- ment, the tuberosity of the navicular, and the ridge of the greater multangular, frequently by two distinct slips. Running lateralward and downward, it is inserted by a thin, flat tendon into the radial side of the base of the first phalanx of the thumb and the capsule of the metacarpophalangeal articulation. The Opponens pollicis is a small, triangular muscle, placed beneath the pre- ceding. It arises from the ridge on the greater multangular and froih the trans- verse carpal ligament, passes downward and lateralward, and is inserted into the whole length of the metacarpal bone of the thumb on its radial side. The Flexor pollicis brevis consists of two portions, lateral and medial. The lateral and more superficial portion arises from the lower border of the transverse carpal ligament and the lower part of the ridge on the greater multangular bone; it passes along the radial side of the tendon of the Flexor pollicis longus, and, becoming tendinous, is inserted into the radial side of the base of the first phalanx of the thumb; in its tendon of insertion there is a sesamoid bone. The medial and deeper portion of the muscle is very small, and arises from the ulnar side of the first metacarpal bone between the Adductor pollicis (obliquus) and the lateral head of the first Interosseous dorsalis, and is inserted into the ulnar side of the base of the first phalanx with the Adductor pollicis (obliquus). The medial part of the Flexor brevis pollicis is sometimes described as the first Interosseous volaris. 462 MYOLOGY The Adductor pollicis (obliquus) {Adductor ohliquus j^ollicis) arises by several slips from the capitate bone, the bases of the second and third metacarpals, the intercarpal ligaments, and the sheath of the tendon of the Flexor carpi radialis. From this origin the greater number of fibers pass obliquely downward and con- verge to a tendon, which, uniting with the tendons of the medial portion of the Flexor pollicis brevis and the transverse part of the Adductor, is inserted into the ulnar side of the base of the first phalanx of the thumb, a sesamoid bone being present in the tendon. A considerable fasciculus, however, passes more obliquely beneath the tendon of the Flexor pollicis longus to join the lateral portion of the Flexor brevis and the Abductor pollicis brevis. I Piaometacarpal lig. Fia. 426. — The muscles of the thumb. The Adductor pollicis (transversus) (Adductor transversus pollicis) (Fig. 426) is the most deeply seated of this group of muscles. It is of a triangular form arising by a broad base from the lower two-thirds of the volar surface of the third metacarpal bone; the fibers converge, to be inserted with the medial part of the Flexor pollicis brevis and the Adductor pollicis (obliquus) into the ulnar side of the base of the first phalanx of the thumb. Variations. — The Abductor pollicis brevis is often divided into an outer and an inner part; accessory slips from the tendon of the Abductor pollicis longus or Palmaris longus, more rarely from the Extensor carpi radialis longus, from the styloid process or Opponens pollicis or from the skin over the thenar eminence. The deep head of the Flexor poUicis brevis may be absent or enlarged. The two adductors vary in their relative extent and in the closeness of their connection. The Adductor obliquus may receive a slip from the transverse metacarpal ligament. Nerves. — The Abductor brevis, Opponens, and lateral head of the Flexor pollicis brevis are supplied by the sixth and seventh cervical nerves through the median nerve; the medial head of the Flexor brevis, and the Adductor, by the eighth cervical through the ulnar nerve. Actions. — The Abductor pollicis brevis draws the thumb forward in a plane at right angles to that of the palm of the hand. The Adductor pollicis is the opponent of this muscle, and approxi- mates the thumb to the palm. The Opponens polUcis flexes the metacarpal bone, i. e., draws it medialward over the palm; the Flexor pollicis brevis flexes and adducts the proximal phalanx. 2. The Medial Volar Muscles (Figs. 426, 427). Palmaris brevis. Flexor digiti quinti brevisi Abductor digiti quinti. Opponens digiti quinti. THE MEDIAL VOLAR MUSCLES 463 The Palmaris brevis is a thin, quadrilateral muscle, placed beneath the integu- ment of the ulnar side of the hand. It arises by tendinous fasciculi from the transverse carpal ligament and palmar aponeurosis; the fleshy fibers are inserted skin on the ulnar border of the palm of the hand. 1^ 427. — The muscles of the left hand. Palmar surface. The Abductor digiti quinti (Abductor minimi digiti) is situated on the ulnar border of the palm of the hand. It arises from the pisiform bone and from the iendon of the Flexor carpi ulnaris, and ends in a flat tendon, which divides into two slips ; one is inserted into the ulnar side of the base of the first phalanx of the little finger; the other into the ulnar border of the aponeurosis of the Extensor digiti quinti proprius. K— 464 MYOLOGY I The Flexor digit! quinti brevis {Flexor brevis minimi digiti) lies on the sane plane as the preceding muscle, on its radial side. It arises from the convex surface of the hamulus of the hamate bone, and the volar surface of the transverse carpal ligament, and is inserted into the ulnar side of the base of the first phalanx of tlie little finger. It is separated from the Abductor, at its origin, by the deep branches of the ulnar artery and nerve. This muscle is sometimes wanting; the Abductor is then, usually, of large size. The Opponens digiti quinti {Opponens minimi digiti) (Fig. 426) is of a tri- angular form, and placed immediately beneath the preceding muscles. It arises from the convexity of the hamulus of the hamate bone, and contiguous portion of the transverse carpal ligament ; it is inserted into the whole length of the meta- carpal bone of the little finger, along its ulnar margin. Variations. — The Palmaris brevis varies greatly in size. The Abductor digiti quinti may be divided into two or three slips or united with the Flexor digiti quinti brevis. Accessory head from the tendon of the Flexor carpi ulnaris, the transverse carpal ligament, the fascia of the forearm or the tendon of the Palmaris longus. A portion of the muscle may insert into the metacarpal, or separate slips the Pisimetacarpus, Pisiuncinatus or the Pisianmdaris muscle may exist. Nerves. — All the muscles of this group are supplied by the eighth cervical nerve through the ulnar nerve. v Actions. — The Abductor and Flexor digiti quinti brevis abduct the little finger from the ring finger and assist in flexing the proximal phalanx. The Opponens digiti quinti draws forward the fifth metacarpal bone, so as to deepen the hollow of the palm. The Palmaris brevis corrugates the skin on the ulnar side of the palm. 3. The Intermediate Muscles. Lumbricales. Interossei. The Lumbricales (Fig. 427) are four small fleshy fasciculi, associated with the tendons of the Flexor digitorum profundus. The first and second arise from the radial sides and volar surfaces of the tendons of the index and middle fingers respectively; the third, from the contiguous sides of the tendons of the middle and ring fingers; and the fourth, from the contiguous sides of the tendons of the ring and little fingers. Each passes to the radial side of the corresponding finger, and opposite the metacarpophalangeal articulation is inserted into the tendinous expansion of the Extensor digitorum communis covering the dorsal aspect of the finger. Variations. — The Lumbricales vary in niunber from two to five or six and there is considerable variation in insertions. The Interossei (Figs. 428, 429) are so named from occupying the intervals between the metacarpal bones, and are divided into two sets, a dorsal and a volar. The Interossei dorsales {Dorsal interossei) are four in number, and occupy the intervals between the metacarpal bones. They are bipenniform muscles, each arising by two heads from the adjacent sides of the metacarpal bones, but more exten- sively from the metacarpal bone of the finger into which the muscle is inserted. They are inserted into the bases of the first phalanges and into the aponeuroses of the tendons of the Extensor digitorum communis. Between the double origin of each of these muscles is a narrow triangular interval ; through the first of these the radial artery passes ; through each of the other three a perforating branch from the deep volar arch is transmitted. The first or Abductor indicis is larger than the others. It is flat, triangular in form, and arises by two heads, separated by a fibrous arch for the passage of the radial artery from the dorsum to the palm of the hand. The lateral head arises from the proximal half of the ulnar border of the first metacarpal bone; the medial head, from almost the entire length of the radial border of the second metacarpal bone; the tendon is inserted into the radial side of the index finger. The second THE MUSCLES AND FASCIA OF THE LOWER EXTREMITY 465 and third are inserted into the middle finger, the former into its radial, the latter into its ulnar side. The fourth is inserted into the ulnar side of the ring finger. The Interossei volares {Palmar interossei), three in number, are smaller than the Interossei dorsales, and placed upon the volar surfaces of the metacarpal bones, rather than between them. Each arises from the entire length of the metacarpal bone of one finger, and is inserted into the side of the base of the first phalanx and aponeurotic expansion of the Extensor communis tendon to the same finger. The first arises from the ulnar side of the second metacarpal bone, and is inserted into the same side of the first phalanx of the index finger. The second arises from the radial side of the fourth metacarpal bone, and is inserted into the same side of the ring finger. The third, arises from the radial side of the fifth metacarpal bone, and is inserted into the same side of the little finger. From this account it may be seen that each finger is provided with two Interossei, with the exception of the little finger, in which the Abductor takes the place of one of the pair. As already mentioned (p. 461), the medial head of the Flexor pollicis brevis is sometimes described as the Interosseus volaris primus. Fig. 428. — The Interossei dorsales of left hand. Fig. 429. — The Interossei volares of left hand. Nerves. — The two lateral Lumbricales are supplied by the sixth and seventh cervical nerves, through the third and fourth digital branches of the median nerve; the two medial Lumbricales and all the Interossei are supphed by the eighth cervical nerve, through the deep palmar branch of the ulnar nerve. The third Lumbricahs frequently receives a twig from the median. Actions. — The Interossei volares adduct the fingers to an imaginary line drawn longitudinally through the center of the middle finger; and the Interossei dorsales abduct the fingers from that line. In addition to this the Interossei, in conjunction with the Lumbricales, flex the first phalanges at the metacarpophalangeal joints, and extend the second and third phalanges in consequence of their insertions into the expansions of the Extensor tendons. The Extensor digitorum communis is believed to act almost entirely on the first phalanges. THE MUSCLES AND FASCLffi OF THE LOWER EXTREMITY. The muscles of the lower extremity are subdivided into groups corresponding with the different regions of the limb. I. Muscles of the Iliac Region. II. Muscles of the Thigh. III. Muscles of the Leg. IV. Muscles of the Foot. 466 3.^] h^i ri ' ''^\ Fig. 430 — Muscles of the iliac and anterior femoral regions. MYOLOGY I. THE MUSCLES AND FASCLffi OF THE ILIAC REGION (Fig. 430). Psoas major. Psoas minor. Iliacus The Fascia Covering the Psoas and Iliacus is thin above, and becomes gradually thicker below as it approaches the inguinal ligament. The portion covering the Psoas is thickened above to form the medial lumbocostal arch, which stretches from the transverse process of the first lumbar vertebra to the body of the second. Medially, it is attached by a series of arched processes to the intervertebral fibro- cartilages, and prominent margins of the bodies of the vertebrae, and to the upper part of the sacrum; the intervals left, opposite the con- stricted p>ortions of the bodies, transmit the lumbar arteries and veins and filaments of the sympathetic trunk. Laterally, above the crest of the ilium, it is continuous with the fascia covering the front of the Quadratus lumborum (see page 419), while below the crest of the ilium it is continuous with the fascia covering the Iliacus. The portions investing the Iliacus {fascia iliaca; iliac fascia) is connected, laterally to the whole length of the inner lip of the iliac crest; and medially, to the linea terminalis of the lesser pelvis, where it is continuous with the peri- osteum. At the iliopectineal eminence it re- ceives the tendon of insertion of the Psoas minor, when that muscle exists. Lateral to the femoral vessels it is intimately connected to the posterior margin of the inguinal ligament, and is continuous with the transversalis fascia. Immediately lateral to the femoral vessels the iliac fascia is prolonged backward and medial- ward from the inguinal ligament as a band, the iliopectineal fascia, which is attached to the iliopectineal eminence. This fascia divides the space between the inguinal ligament and the hip bone into two lacunae or compart- ments, the medial of which transmits the femoral vessels, the lateral the Psoas major and Iliacus and the femoral nerve. Medial to the vessels the iliac fascia is attached to the pectineal line behind the inguinal apo- neurotic falx, where it is again continuous with the transversalis fascia. On the thigh the fasciae of the Iliacus and Psoas form a single sheet termed the iliopectineal fascia. Where the external iliac vessels pass into the thigh, the fascia descends behind them, forming the pos- terior wall of the femoral sheath. The portion of the iliopectineal fascia which passes behind ■ THE ANTERIOR FEMORAL MUSCLES 467 the femoral vessels is also attached to the pectineal line beyond the limits of the attachment of the inguinal aponeurotic falx; at this part it is continuous with the pectineal fascia. The external iliac vessels lie in front of the iliac fascia, but all the branches of the lumbar plexus are behind it; it is separated from the peri- toneum by a quantity of loose areolar tissue. The Psoas major {Psoas magnns) (Fig. 430) is a long fusiform muscle placed on the side of the lumbar region of the vertebral column and brim of the lesser pelvis. It arises (1) from the anterior surfaces of the bases and lower borders of the transverse processes of all the lumbar vertebrae; (2) from the sides of the bodies and the corre- sponding intervertebral fibrocartilages of the last thoracic and all the lumbar verte- brae by five slips, each of which is attached to the adjacent upper and lower margins of two vertebrae, and to the intervertebral fibrocartilage; (3) from a series of tendinous arches which extend across the constricted parts of the bodies of the lumbar vertebrae between the previous slips; the lumbar arteries and veins, and filaments from the sympathetic trunk pass beneath these tendinous arches. The muscle proceeds downward across the brim of the lesser pelvis, and diminishing gradually in size, passes beneath the inguinal ligament and in front of the capsule of the hip-joint and ends in a tendon; the tendon receives nearly the whole of the fibers of the Iliacus and is inserted into the lesser trochanter of the femur. A large bursa w^hich may communicate with the cavity of the hip-joint, separates the tendon from the pubis and the capsule of the joint. The Psoas minor (Psoas parvus) is a long slender muscle, placed in front of the Psoas major. It arises from the sides of the bodies of the twelfth thoracic and first lumbar vertebrae and from the fibrocartilage between them. It ends in a long flat tendon which is inserted into the pectineal line and iliopectineal eminence, and, by its lateral border, into the iliac fascia. This muscle is often absent. The Iliacus is a flat, triangular muscle, which fills the iliac fossa. It arises from the upper two-thirds of this fossa, and from the inner lip of the iliac crest; behind, from the anterior sacroiliac and the iliolumbar ligaments, and base of the sacrum; in front, it reaches as far as the anterior superior and anterior inferior iliac spines, and the notch between them. The fibers converge to be inserted into the lateral side of the tendon of the Psoas major, some of them being prolonged on to the body of the femur for about 2.5 cm. below and in front of the lesser trochanter.^ Variations. — The Iliacus minor or Iliocapsidaris, a small detached part of the Iliacus is frequently present. It arises from the anterior inferior spine of the ilium and is inserted into the lower part of the intertrochanteric line of the femur or into the iliofemoral ligament. Nerves. — The Psoas major is supphed by branches of the second and third lumbar nerve; the Psoas minor by a branch of the first lumbar nerve; and the lUacus by branches of the second and third lumbar nerves through the femoral nerve. Actions. — The Psoas major, acting from above, flexes the thigh upon the pelvis, being assisted by the Iliacus; acting from below, with the femur fixed, it bends the lumbar portion of the verte- bral column forward and to its own side, and then, in conjunction with the Iliacus, tilts the pelvis forward. When the muscles of both sides are acting from below, they serve to maintain the erect posture by supporting the vertebral column and pelvis upon the femora, or in continued action bend the trunk and pelvis forward, as in raising the trunk from the recimibent posture. The Psoas minor is a tensor of the ihac fascia. n. THE MUSCLES AND FASCIA OF THE THIGH. 1. The Anterior Femoral Muscles (Fig. 430) ' Rectus femoris. o , . Quadriceps S^^tonus. femoris Articularis genu. Vastus lateralis. Vastus medialis. Vastus intermedins. 1 The Psoas major and iliacus are sometimes regarded as a single muscle named the Ilioptoai. 468 MYOLOGY Superficial Fascia. — The superficial fascia forms a continuous layer over the whole of the thigh; it consists of areolar tissue containing in its meshes much fat, and may be separated into two or more layers, between which are found the superficial vessels and nerves. It varies in thickness in different parts of the limb ; in the groin it is thick, and the two layers are separated from one another by the superficial inguinal lymph glands, the great saphenous vein, and several smaller vessels. The superficial layer is continuous above with the superficial fascia of the abdomen. The deep layer of the superficial fascia is a very thin, fibrous stratum, best marked on the medial side of the great saphenous vein and below the inguinal ligament. It is placed beneath the subcutaneous vessels and nerves and upon the surface of the fascia lata. It is intimately adherent to the fascia lata a little below the inguinal ligament. It covers the fossa ovalis (saphenous opening), being closely united to its circumference, and is connected to the sheath of the femoral vessels. The portion of fascia covering this fossa is perforated by the great saphenous vein and by numerous blood and lymphatic vessels, hence it has been termed the fascia cribrosa, the openings for these vessels having been likened to the holes in a sieve. A large subcutaneous bursa is found in the superficial fascia over the patella. Deep Fascia. — ^The deep fascia of the thigh is named, from its great extent, the fascia lata ; it constitutes an investment for the whole of this region of the limb, but varies in thickness in different parts. Thus, it is thicker in the upper and lateral part of the thigh, where it receives a fibrous expansion from the Glutseus maximus, and where the Tensor fasciae latse is inserted between its layers; it is very thin behind and at the upper and medial part, where it covers the Adductor muscles, and again becomes stronger around the knee, receiving fibrous expansions from the tendon of the Biceps femoris laterally, from the Sartorius medially, and from the Quadriceps femoris in front. The fascia lata is attached, above and behind, to the back of the sacrum and coccyx; laterally, to the iliac crest; in front, to the inguinal ligament, and to the superior ramus of the pubis; and medially, to the inferior ramus of the pubis, to the inferior ramus and tuberosity of the ischium, and to the low^er border of the sacrotuberous ligament. From its attachment to the iliac crest it passes down over the Glutseus medius to the upper border of the Glutseus maximus, where it splits into two layers, one passing superficial to and the other beneath this muscle; at the lower border of the muscle the two layers reunite. Laterally, the fascia lata receives the greater part of the tendon of insertion of the Glutseus maximus, and becomes proportionately thickened. The portion of the fascia lata attached to the front part of the iliac crest, and corresponding to the origin of the Tensor fasciae latae, extends down the lateral side of the thigh as two layers, one superficial to and the other beneath this muscle ; at the lower end of the muscle these two layers unite and form a strong band, having first received the insertion of the muscle. This band is continued downward, under the name of the iliotibial band (tradus iliotihialis) and is attached to the lateral condyle of the tibia. The part of the iliotibial band which lies beneath the Tensor fasciae latse is prolonged upward to join the lateral part of the capsule of the hip-joint. Below, the fasciae lata is attached to all the prominent points around the knee- joint, viz., the condyles of the femur and tibia, and the head of the fibula. On either side of the patella it is strengthened by transverse fibers from the lower parts of the Vasti, which are attached to and support this bone. Of these the lateral are the stronger, and are continuous with the iliotibial band. The deep surface of the fascia lata gives off two strong intermuscular septa, which are attached to the whole length of the linea aspera and its prolongations above and below; the lateral and stronger one, which extends from the insertion of the Glutseus maximus to the lateral condyle, separates the Vastus lateralis in front from the short head of the Biceps femoris behind, and gives partial origin to these mus- cles; the medial and thinner one separates the Vastus medialis from the Adduc- THE ANTERIOR FEMORAL MUSCLES 469 tores and Pectineus. Besides these there are numerous smaller septa, separating the individual muscles, and enclosing each in a distinct sheath. The Fossa Ovalis (saphenous opening) (Fig. 431). — At the upper and medial part of the thigh, a little below the medial end of the inguinal ligament, is a large oval-shaped aperture in the fascia lata; it transmits the great saphenous vein, and other, smaller vessels, and is termed the fossa ovalis. The fascia cribrosa, which is pierced by the structures passing through the opening, closes the aperture and must be removed to expose it. The fascia lata in this part of the thigh is described as consisting of a superficial and a deep portion. Fig. 431. — The fossa ovalia. The superficial portion of the fascia lata is the part on the lateral side of the fossa ovalis. It is attached, laterally, to the crest and anterior superior spine of the ilium, to the whole length of the inguinal ligament, and to the pectineal line in con- junction with the lacunar ligament. From the tubercle of the pubis it is reflected downward and lateralward, as an arched margin, the falciform margin, forming the lateral boundary of the fossa ovalis; this margin overlies and is adherent to the anterior layer of the sheath of the femoral vessels : to its edge is attached the fascia cribrosa. The upward and medial prolongation of the falciform margin is named the superior comu ; its downward and medial prolongation, the inferior comu. The latter is well-defined, and is continuous behind the great saphenous vein with the pectineal fascia 4 The deep portion is situated on the medial side of the fossa ovalis, and at the lower margin of the fossa is continuous with the superficial portion; traced upward. 470 MYOLOGY it 'covers the Pectineus, Adductor longus, and Gracilis, and, passing behind the sheath of the femoral vessels, to which it is closely united^ is continuous with the iliopectineal fascia, and is attached to the pectineal line. From this description it may be observed that the superficial portion of the fascia lata lies in front of the femoral vessels, and the deep portion behind them, so that an apparent aperture exists between the two, through which the great saphenous passes to join the femoral vein. The Sartorius, the longest muscle in the body, is narrow and ribbon-like; it arises by tendinous fibers from the anterior superior iliac spine and the upper half of the notch below it. It passes obliquely across the upper and anterior part of the thigh, from the lateral to the medial side of the limb, then descends vertically, as far as the medial side of the knee, passing behind the medial condyle of the femur to end in a tendon. This curves obliquely forward and expands into a broad apon- eurosis, which is inserted, in front of the Gracilis and Semitendinous, into the upper part of the medial surface of the body of the tibia, nearly as far forward as the anterior crest. The upper part of the aponeurosis is curved backward over the upper edge of the tendon of the Gracilis so as to be inserted behind it. An offset, from its upper margin, blends with the capsule of the knee-joint, and another from its lower border, with the fascia on the medial side of the leg. Variations. — Slips of origin from the outer end of the inguinal ligament, the notch of the ilium, the ilio-pectineal line or the pubis occur. The muscle may be split into two parts, and one part may be inserted into the fascia lata, the femur, the ligament of the patella or the tendon of the Semitendinosus. The tendon of insertion may end in the fascia lata, the capsule of the knee- joint, or the fascia of the leg. The muscle may be absent. The Quadriceps femoris (Quadriceps extensor) includes the four remaining muscles on the front of the thigh. It is the great extensor muscle of the leg, forming a large fleshy mass which covers the front and sides of the femur. It is subdivided into separate portions, which have received distinctive names. One occupying the middle of the thigh, and connected above with the ilium, is called from its straight course the Rectus femoris. The other three lie in immediate connection with the body of the femur, which they cover from the trochanters to the condyles. The portion on the lateral side of the femur is termed the Vastus lateralis; that covering the medial side, the Vastus medialis ; and that in front, the Vastus intermedius. The Rectus femoris is situated in the middle of the front of the thigh; it is fusi- form in shape, and its superficial fibers are arranged in a bipenniform manner, the deep fibers running straight down to the deep aponeurosis. It arises by two tendons: one, the anterior or straight, from the anterior inferior iliac spine; the other, the posterior or reflected, fro;n a groove above the brim of the acetabulum. The two unite at an acute angle, and spread into an aponeurosis which is prolonged downward on the anterior surface of the muscle, and from this the muscular flbers arise. The muscle ends in a broad and thick aponeurosis which occupies the lower two-thirds of its posterior surface, and, gradually becoming narrowed into a flat- tened tendon, is inserted into the base of the patella. The Vastus lateralis (Vastus externus) is the largest part of the Quadriceps femoris. It arises by a broad aponeurosis, which is attached to the upper part of the intertrochanteric line, to the anterior and inferior borders of the greater tro- chanter, to the lateral lip of the gluteal tuberosity, and to the upper half of the lateral lip of the linea aspera; this aponeurosis covers the upper three-fourths of the muscle, and from its deep surface many fibers take origin. A few additional fibers arise from the tendon of the Gluta^us maximus, and from the lateral inter- muscular septum between the Vastus lateralis and short head of the Biceps femoris. The fibers form a large fleshy mass, which is attached to a strong aponeurosis, placed on the deep surface of the lower part of the muscle: this aponeurosis becomes 41 THE MEDIAL FEMORAL MUSCLES 471 ^B I contracted and thickened into a flat tendon inserted into the lateral border of the patella, blending with the Quadriceps femoris tendon, and giving an expansion to the capsule of the knee-joint. ■I The Vastus medialis and Vastus intermedins appear to be inseparably united, but when the Rectus femoris has been reflected a narrow interval will be observed extending upward from the medial border of the patella between the two muscles, and the separation may be continued as far as the lower part of the intertrochan- teric line, where, however, the two muscles are frequently continuous. ■I The Vastus medialis {VaMus internus) arises from the lower half of the inter- " trochanteric line, the medial lip of the linea aspera, the upper part of the medial supracondylar line, the tendons of the Adductor longus and the Adductor magnus and the medial intermuscular septum. Its fibers are directed downward and for- ward, and are chiefly attached to an aponeurosis which lies on the deep surface of the muscle and is inserted into the medial border of the patella and the Quad- ra riceps femoris tendon, an expansion being sent to the capsule of the knee-joint. Hp The Vastus intermedius (Crureus) arises from the front and lateral surfaces of the ' body of the femur in its upper two-thirds and from the lower part of the lateral "intermuscular septum. Its fibers end in a superficial aponeurosis, which forms ■■the deep part of the Quadriceps femoris tendon. The tendons of the different portions of the Quadriceps unite at the lower part of the thigh, 80 as to form a single strong tendon, which is inserted into the base of the patella, some few fibera passing over it to blend with the ligamentum patellae. More properly, the patella may be regarded aa a sesamoid bone, developed in the tendon of the Quadriceps; and the ligamentum patellae, which is continued from the apex of the patella to the tuberosity of the tibia, as the proper tendon of insertion of the muscle, the medial and lateral patellar retinacula (see p. 338) being expan- sions from its borders. A bursa, which usually communicates with the cavity of the knee-joint, is situated between the femur and the portion of the Quadriceps tendon above the patella; another is interposed between the tendon and the upper part of the front of the tibia; and a third, the irepatellar bursa, is placed over the patella itself. f The Articularis genu (Subcrureus) is a small muscle, usually distinct from the astus intermedius, but occasionally blended with it; it arises from the anterior surface of the lower part of the body of the femur, and is inserted into the upper part of the synovial membrane of the knee-joint. It sometimes consists of several separate muscular bundles. 11. Nerves. — The muscles of this region are supplied by the second, third, and fourth lumbar erves, through the femoral nerve. Actions. — The Sartoriua flexes the leg upon the thigh, and, continuing to act, flexes the thigh upon the pelvis; it next abducts and rotates the thigh outward. When the knee is bent, the Sartorius assists the Semitendinosus, Semimembranosus, and Popliteus in rotating the tibia inward. Taking its fixed point from the leg, it flexes the pelvis upon the thigh, and, if one muscle acts, assists in rotating the pelvis. The Quadriceps femoris extends the leg upon the thigh. The Rectus femoris assists the Psoas major and Iliacus in supporting the pelvis and trunk upon the femur. It also assists in flexing the thigh on the pelvis, or if the thigh be fixed it will flex the pelvis. The Vastus medialis draws the patella medialward as well as upward. 2. The Medial Femoral Muscles. Gracilis. Adductor longus. Adductor magnus. Pectineus. Adductor brevis. P The Gracilis (Fig. 430) is the most superficial muscle on the medial side of the thigh. It is thin and flattened, broad above, narrow and tapering below. It arises by a thin aponeurosis from the anterior margins of the lower half of the symphysis pubis and the upper half of the pubic arch. The fibers run vertically downward, and end in a rounded tendon, which passes behind the medial condyle of the femur, curves around the medial condyle of the tibia, where it becomes flat- MYOLOGY tened, and is inserted into the upper part of the medial surface of the body of thfl tibia, below the condyle. A few of the fibers of the lower part of the tendon are prolonged into the deep fascia of the leg. At its insertion the tendon is situated immediately above that of the Semitendinosus, and its upper edge is overlapped by the tendon of the Sartorius, with which it is in part blended. It is separated from the tibial collateral ligament of the knee-joint, by a bursa common to it and the tendon of the Semitendinosus. Rectus femoris M. Femur Vasttis intermedius M Linea aspera Deep femoral artery and vein Sartorius M. ^.Saphenous nerve Femoral vein and artery Intermediate ... cutancjus nerve Great saphenous vein ^Adductor longus M. ^Gracilis M. Intermuscular septum of f'cdian femoral .Perforating artery arid vein Vastus lateralis Al. Intermuscular septu m , of lateral femoral ^"^ Semimembranosus M. Biceps femoris M. \ [captit breve] ', Biceps femoris M. [caput longum] Semitendinosus M Isch I 1 'usitnur femoral cutaneous nerve Adductor magnus M. Fig. 432. — Cross-section through the middle of the thigh. (Eycleshymer and Schoemaker.) •1 The Pectineus (Fig. 430) is a flat, quadrangular muscle, situated at the anterior part of the upper and medial aspect of the thigh. It arises from the pectineal line, and to a slight extent from the surface of bone in front of it, between the iliopectineal eminence and tubercle of the pubis, and from the fascia covering the anterior surface of the muscle; the fibers pass downward, backward, and lateral- ward, to be inserted into a rough line leading from the lesser trochanter to the linea aspera. The Adductor longus (Fig. 433), the most superficial of the three Adductores, is a triangular muscle, lying in the same plane as the Pectineus. It arises by a flat, narrow tendon, from the front of the pubis, at the angle of junction of the crest THE MEDIAL FEMORAL with the symphysis; and soon expands into a broad fleshy belly. This passes downward, backward, and lateralward, and is inserted, by an aponeurosis, into the linea aspera, between the Vastus medialis and the Adductor magnus, with both of which it is usually blended. The Adductor brevis (Fig. 433) is situ- ated immediately behind the two preceding muscles. It is somewhat triangular in form, and arises by a narrow origin from the outer surfaces of the superior and inferior rami of the pubis, between the Gracilis and Obturator externus. Its fibers, passing backward, lateralward, and downward, are inserted, by an aponeurosis, into the line leading from the lesser trochanter to the linea aspera and into the upper part of the linea aspera, immediately behind the Pectin- eus and upper part of the Adductor longus. The Adductor magnus (Fig. 433) is a large triangular muscle, situated on the medial side of the thigh. It arises from a small part of the inferior ramus of the pubis, from the inferior ramus of the ischium, and from the outer margin of the inferior part of the tuberosity of the ischium. Those fibers which arise from the ramus of the pubis are short, horizontal in direction, and are inserted into the rough line leading from the greater trochanter to the linea aspera, medial to the Glutseus maximus; those from the ramus of the ischium are directed downward and lat- eralward with different degrees of obliquity, to be inserted, by means of a broad aponeu- rosis, into the linea aspera and the upper part of its medial prolongation below. The medial portion of the muscle, composed principally of the fibers arising from the tuberosity of the ischium, forms a thick fleshy mass consisting of coarse bundles which descend almost vertically, and end about the lower third of the thigh in a rounded tendon which is inserted into the adductor tubercle on the medial condyle of the femur, and is connected by a fibrous expansion to the line leading upward from the tubercle to the linea aspera. At the insertion of the muscle, there is a series of osseoaponeurotic openings, formed by tendi- nous arches attached to the bone. The upper four openings are small, and give passage to the perforating branches of the profunda femoris artery. The lowest is of large size, and transmits the femoral vessels to the popliteal fossa. ^^°- ^^S-Deep musdes^of the medial femoral 474 i^^^^^^m MYOLOGY Variations. — The Pectineus is sometimes divided into an outer part supplied by the femoral nerve and an inner part supplied by the obturator nerve. The muscle may be attached to or inserted into the capsule of the hip-joint. The Adductor longus may be double, may extend to the , knee, or be more or less united with the Pectineus. The Adductor brevis may be divided into two ' or three parts, or it may be united to the Adductor magnus. The Adductor magnus may be more or less segmented, the anterior and superior portion is often described as a separate muscle, the Adductor minimus. The muscle may be fused with the Quadratus femoris. Nerves. — The three Adductores and the Gracilis are supplied by the third and fourth lumbar nerves through the obturator nerve; the Adductor magnus receiving an additional branch from the sacral plexus through the sciatic. The Pectineus is suppHed by the second, third, and fourth lumbar nerves through the femoral nerve, and by the third lumbar through the accessory obturator - when this latter exists. Occasionally it receives a branch from the obturator nerve.^ * Actions. — The Pectineus and three Adductores adduct the thigh powerfully; they are especially used in horse exercise, the sides of the saddle being grasped between the knees by the contraction of these muscles. In consequence of the obliquity of their insertions into the Unea aspera, they rotate the thigh outward, assisting the external Rotators, and when the limb has been abducted, they draw it medialward, carrying the thigh across that of the opposite side. The Pectineus and Adductores brevis and longus assist the Psoas major and Iliacus in flexing the thigh upon the pelvis. In progression, all these muscles assist in drawing forward the lower hmb. The Gracilis assists the Sartorius in flexing the leg and rotating it inward; it is also an adductor of the thigh. If the lower extremities be fixed, these muscles, taking their fixed points below, may act upon the pelvis, serving to maintain the body in an erect posture; or, if their action be continued, flex the pelvis forward upon the femur. 3. The Muscles of the Gluteal Region (Fig. 434). Glutseus maximus. Obturator internus. Glutseus medius. Gemellus superior. Glutseus minimus. Gemellus inferior. Tensor fasciae latae. Quadratus femoris. Piriformis. Obturator externus. The Glutseus maximus, the most superficial muscle in the gluteal region, is a broad and thick fleshy mass of a quadrilateral shape, and forms the prominence of the nates. Its large size is one of the most characteristic features of the muscular system in man, connected as it is with the power he has of maintaining the trunk in the erect posture. The muscle is remarkably coarse in structure, being made up of fasciculi lying parallel with one another and collected together into large bundles separated by fibrous septa. It arises from the posterior gluteal line of the ilium, and the rough portion of bone including the crest, immediately above and behind it; from the posterior surface of the lower part of the sacrum and the side of the coccyx; from the aponeurosis of the Sacrospinalis, the sacrotuberous ligament, and the fascia (gluteal aponeurosis) covering the Glutaeus medius. The fibers are directed obliquely downward and lateralward; those forming the upper and larger portion of the muscle, together with the superficial fibers of the lower portion, end in a thick tendinous lamina, which passes across the greater trochanter, and is inserted into the iliotibial band of the fascia lata; the deeper fibers of the lower portion of the muscle are inserted into the gluteal tuberosity between the Vastus lateralis and Adductor magnus. Bursse. — Three bursse are usually found in relation with the deep surface of this muscle. One of these, of large size, and generally multilocular, separates it from the greater trochanter; a second, often wanting, is situated on the tuberosity of the ischium; a third is found between the tendon of the muscle and that of the Vastus lateralis. The Glutaeus medius is a broad, thick, radiating muscle, situated on the outer surface of the pelvis. Its posterior third is covered by the Glutaeus maximus, its ' The Pectineus may consist of two incompletely separated strata; the lateral or dorsal stratum, which is constant, is supplied by a branch from the femoral nerve, or in the absence of this branch by the accessory obturator nerve; the medial or ventral stratum, when present, is supplied by the obturator nerve. — A. M. Paterson. Journal of Anatomy and Physiology, xxvi, 43. I ^Banterlor two-thirds by the gluteal aponeurosis, which separates it from the superficial fascia and integument. It arises from the outer surface of the ilium between the iliac crest and posterior glu- teal line above, and the anterior gluteal line below; it also arises Pfrom the gluteal aponeurosis covering its outer surface. The fibers converge to a strong flat- tened tendon, which is inserted ^^ into the oblique ridge which runs ^B downward and forward on the ^■lateral surface of the greater tro- chanter. A bursa separates the tendon of the muscle from the • surface of the trochanter over [which it glides. I Variations. — The posterior border Imay be more or less closely vmited to the Piriformis, or some of the fibers end on its tendon. The Glutseus minimus, the small- est of the three Glutaji, is placed immediately beneath the preced- ing. It is fan-shaped, arising from the outer surface of the ilium, between the anterior and inferior gluteal lines, and behind, from the margin of the greater sciatic notch. The fibers converge to the deep surface of a radiated aponeurosis, and this ends in a tendon which is inserted into an impression on the anterior border of the greater trochanter, and gives an expansion to the capsule of the hip-joint. A bursa is interposed between the tendon and the greater trochanter. Be- tween the Glutseus medius and Glutseus minimus are the deep branches of the superior gluteal vessels and the superior gluteal nerve. The deep surface of the Glutseus minimus is in relation with the reflected tendon of the Rectus femoris and the capsule of the hip-joint. Variations. — The muscle may be di- vided into an anterior and a posterior part, or it may send slips to the Piri- formis, the Gemellus superior or the outer part of the origm of the Vastus lateralis. THE MUSCLES OF THE GLUTEAL REGION 475 P t II Medial hamstring tendons Sartorius Cfracilis Semitendinosus Semi- membranosus Lateral ^^hamstring tendon Biceps femoris Fia. 434. — Muscles of the gluteal and posterior femoral regions. 476 MYOLOGY The Tensor fasciae latae {Tensor fascice femoris) arises from flie~ anterior "pari of the outer lip of the iliac crest; from the outer surface of the anterior superior iliac spine, and part of the outer border of the notch below it, between the Glutaeus medius and Sartorius; and from the deep surface of the fascia lata. It is inserted between the two layers of the iliotibial band of the fascia lata about the junction of the middle and upper thirds of the thigh. The Piriformis is a flat muscle, pyramidal in shape, lying almost parallel with the posterior margin of the Glutseus medius. It is situated partly within the pelvis against its posterior wall, and partly at the back of the hip-joint. It arises from the front of the sacrum by three fleshy digitations, attached to the portions of bone between the first, second, third, and fourth anterior sacral foramina, and to the grooves leading from the foramina : a few fibers also arise from the margin of the greater sciatic foramen, and from the anterior surface of the sacrotuberous ligament. The muscle passes out of the pelvis through the greater sciatic fora- men, the upper part of which it fills', and is inserted by a rounded tendon into the upper border of the greater trochanter behind, but often partly blended with, the common tendon of the Obturator internus and Gemelli. Variations. — It is frequently pierced by the common peroneal nerve and thus divided more or less into two parts. It may be luiited with the Glutaeus medius, or send fibers to the Glutaeus minimus or receive fibers from the Gemellus superior. It may have only one or two sacral attach- ments or be inserted in to the capsule of the hip-joint. It may be absent. Ant. sup. iliac spine- Symphysis pubis Transverse acetabular ligament Fig. 435. — The obturator membrane. ^ Obturator Membrane (Fig. 435). — The obturator membrane is a thin fibrous sheet, which almost completely closes the obturator foramen. Its fibers are arranged in interlacing bundles mainly transverse in direction; the uppermost bundle is attached to the obturator tubercles and completes the obturator canal for the pas- sage of the obturator vessels and nerve. The membrane is attached to the sharp margin of the obturator foramen except at its lower lateral angle, where it is fixed THE MUSCLES OF THE GLUTEAL REGION 477 I to the pelvic surface of the inferior ramus of the ischium, i. e., within the margin. Both obturator muscles are connected with this membrane. The Obturator intemus is situated partly within the lesser pelvis, and partly at the back of the hip-joint. It arises from the inner surface of the antero-lateral wall of the pelvis, where it surrounds the greater part of the obturator foramen, being attached to the inferior rami of the pubis and ischium, and at the side to the inner surface of the hip bone below and behind the pelvic brim, reaching from the upper part of the greater sciatic foramen above and behind to the obturator fora- men below and in front. It also arises from the pelvic surface of the obturator membrane except in the posterior part, from the tendinous arch which completes the canal for the passage of the obturator vessels and nerve, and to a slight extent from the obturator fascia, which covers the muscle. The fibers converge rapidly toward the lesser sciatic foramen, and end in four or five tendinous bands, which are found on the deep surface of the muscle; these bands are reflected at a right angle over I the grooved surface of the ischium between its spine and tuberosity. This bony II surface is covered by smooth cartilage, which is separated from the tendon by a [bursa, and presents one or more ridges corresponding with the furrows between the tendinous bands. These bands leave the pelvis through the lesser sciatic fora- men and unite into a single flattened tendon, which passes horizontally across the capsule of the hip-joint, and, after receiving the attachments of the Gemelli, is inserted into the forepart of the medial surface of the greater trochanter above the trochanteric fossa. A bursa, narrow and elongated in form, is usually found I between the tendon and the capsule of the hip-joint; it occasionally communicates I with the bursa between the tendon and the ischium. I The Gemelli are two small muscular fasciculi, accessories to the tendon of the I Obturator internus which is received into a groove between them. I The Gemellus superior, the smaller of the two, arises from the outer surface of I the spine of the ischium, blends with the upper part of the tendon of the Obturator I internus, and is inserted with it into the medial surface of the greater trochanter. I It is sometimes wanting. I The Gemellus inferior arises from the upper part of the tuberosity of the ischium, : immediately below the groove for the Obturator internus tendon. It blends with - the lower part of the tendon of the Obturator internus, and is inserted with it H I it into the medial surface of the greater trochanter. Rarely absent. HI The Quadratus femoris is a flat, quadrilateral muscle, between the Gemellus ■ ■inferior and the upper margin of the Adductor magnus; it is separated from the ' latter by the terminal branches of the medial femoral circumflex vessels. It arises from the upper part of the external border of the tuberosity of the ischium, and is inserted into the upper part of the linea quadrata — that is, the line which extends vertically downward from the intertrochanteric crest. A bursa is often found between the front of this muscle and the lesser trochanter. Sometimes absent. The Obturator extemus (Fig. 436) is a flat, triangular muscle, which covers ^ the outer surface of the anterior wall of the pelvis. It arises from the margin ■ I of bone immediately around the medial side of the obturator foramen, viz., from the rami of the pubis, and the inferior ramus of the ischium; it also arises from the medial two-thirds of the outer surface of the obturator membrane, and from the tendinous arch which completes the canal for the passage of the obturator vessels and nerves. The fibers springing from the pubic arch extend on to the inner sur- face of the bone, where they obtain a narrow origin between the margin of the foramen and the attachment of the obturator membrane. The fibers converge and pass backward, lateralward, and upward, and end in a tendon which runs across the back of the neck of the femur and lower part of the capsule of the hip- joint and is inserted into the trochanteric fossa of the femur. The obturator vessels lie between the muscle and the obturator membrane; the anterior branch of the l_ 478 MYOLOGY by passing in front of the muscle, anc obturator nerve reaches the thigh posterior branch by piercing it. Nerves. — The Glutseus maximus is supplied by the fifth lumbar and first and second sacra nerves through the inferior gluteal nerve; the Gluta?i medius and minimus and the Tensor fascdae latge by the fourth and fifth lumbar and first sacral nerves through the superior gluteal; the Piri- formis is supplied by the first and second sacral nerves; the Gemellus inferior and Quadrat us femoris by the last lumbar and first sacral nerves; the Gemellus superior and Obturator internus by the first, second, and third sacral nerves, and the Obturator externus by the third and fourth lumloar nerves through the obturator. Obturator nerve Ant. inf. iliac spine Fig. 436. — The Obturator externus. Actions. — When the Glutaeus maximus takes its fixed point from the pelvis, it extends the femur and brings the bent thigh into a line with the body. Taking its fixed point from below, it acts upon the pelvis, supporting it and the trunk upon the head of the femur; this is especially obvious in standing on one leg. Its most powerful action is to cause the body to regain the erect position after stooping, by drawing the pelvis backward, being assisted in this action by the Biceps femoris, Semitendinosus, and Semimembranosus. The Glutaeus maximus is a tensor of the fascia lata, and by its connection with the ihotibial band steadies the femur on the articular surfaces of the tibia during standing, when the Extensor muscles are relaxed. The lower part of the muscle also acts as an adductor and external rotator of the hmb. The Glutsei medius and minimus abduct the thigh, when the limb is extended, and are principally called into action in supporting the body on one hmb, in conjunction with the Tensor fasciae latae. Their anterior fibers, by drawing the greater trochanter forward, rotate the thigh inward, in which action they are also assisted by the Tensor fasciae latae. The Tensor fasciae latae is a tensor of the fascia lata; continuing its action, the oblique direction of its fibers enables it to abduct the thigh and to rotate it inward. In the erect posture, acting from below, it will serve to steady the pelvis upon the head of the femur; and by means of the iliotibial band it steadies the condyles of the femur on the articular surfaces of the tibia, and assists the Glutaeus maximus in supporting the knee in the extended position. The remaining muscles are powerful external rotators of the thigh. In the sitting posture, when the thigh is flexed upon the pelvis, their action as rotators ceases, and they become abductors, with the exception of the Obturator externus, which still rotates the femur outward. 4. The Posterior Femoral Muscles (Hamstring Muscles) (Fig. 434). Biceps femoris. Semitendinosus. Semimembranosus. The Biceps femoris (Biceps) is situated on the posterior and lateral aspect of the thigh. It has two heads of origin ; one, the long head, arises from the lower and inner 1 THE POSTERIOR FEMORAL MUSCLES 479 impression on the back part of the tuberosity of the ischium, by a tendon common to it and the Semitendinosus, and from the lower part of the sacrotuberous liga- ment; the other, the short head, arises from the lateral lip of the linea aspera, between the Adductor magnus and Vastus lateralis, extending up almost as high as the insertion of the Glutgeus maximus; from the lateral prolongation of the linea aspera to within 5 cm. of the lateral condyle; and from the lateral inter- muscular septum. The fibers of the long head form a fusiform belly, which passes obliquely downward and lateralward across the sciatic nerve to end in an aponeu- rosis which covers the posterior surface of the muscle, and receives the fibers of the short head; this aponeurosis becomes gradually contracted into a tendon, which is inserted into the lateral side of the head of the fibula, and by a small slip into the lateral condyle of the tibia. At its insertion the tendon divides into two portions, which embrace the fibular collateral ligament of the knee-joint. From the posterior border of the tendon a thin expansion is given off to the fascia of the leg. The tendon of insertion of this muscle forms the lateral hamstring; the common peroneal nerve descends along its medial border. Variations. — The short head may be absent; additional heads may arise from the ischial tuberosity, the linea aspera, the medial supracondylar ridge of the femur or from various other parts. A slip may pass to the Gastrocnemius. The Semitendinosus, remarkable for the great length of its tendon of insertion, is situated at the posterior and medial aspect of the thigh. It arises from the lower and medial impression on the tuberosity of the ischium, by a tendon common to it and the long head of the Biceps femoris; it also arises from an aponeurosis which connects the adjacent surfaces of the two muscles to the extent of about 7.5 cm. from their origin. The muscle is fusiform and ends a little below the middle of the thigh in a long round tendon which lies along the medial side of the popliteal fossa; it then curves around the medial condyle of the tibia and passes over the tibial collateral ligament of the knee-joint, from which it is separated by a bursa, and is inserted into the upper part of the medial surface of the body of the tibia, nearly as far forward as its anterior crest. At its insertion it gives off from its lower border a prolongation to the deep fascia of the leg and lies behind the tendon of the Sartorius, and below that of the Gracilis, to which it is united. A tendinous intersection is usually observed about the middle of the muscle. The Semimembranosus, so called from its membranous tendon of origin, is situ- ated at the back and medial side of the thigh. It arises by a thick tendon from the upper and outer impression on the tuberosity of the ischium, above and lateral to the Biceps femoris and Semitendinosus. The tendon of origin expands into an aponeurosis, which covers the upper part of the anterior surface of the muscle; from this aponeurosis muscular fibers arise, and converge to another aponeurosis which covers the lower part of the posterior surface of the muscle and contracts into the tendon of insertion. It is inserted mainly into the horizontal groove on the posterior medial aspect of the medial condyle of the tibia. The tendon of insertion gives off certain fibrous expansions : one, of considerable size, passes upward and lateralward to be inserted into the back part of the lateral condyle of the femur, forming part of the oblique popliteal ligament of the knee-joint ; a second is continued downward to the fascia which covers the Popliteus muscle; while a few fibers join the tibial collateral ligament of the joint and the fascia of the leg. The muscle overlaps the upper part of the popliteal vessels. Variations. — It may be reduced or absent, or double, arising mainly from the sacrotuberous ligament and giving a slip to the femur or Adductor magnus. The tendons of insertion of the two preceding muscles form the medial ham- strings. 480 ^^^SSBKI^ MYOLOGY Nerves. — The muscles of this region are supplied by the fourth and fifth lumbar and the-ffifst second, and third sacral nerves; the nerve to the short head of the Biceps femoris is derived frona the common peroneal, the other muscles are supplied through the tibial nerve. Actions. — The hamstring muscles flex the leg upon the thigh. When the knee is semiflexed, the Biceps femoris in consequence of its oblique direction rotates the leg slightly outward; and the Semitendinosus, and to a slight extent the Semimembranosus, rotate the leg inward, assist- ing the Popliteus. Taking their fixed point from below, these muscles serve to support the pelvis upon the head of the femur, and to draw the trunk directly backward, as in raising it from the stooping position or in feats of strength, when the body is thrown backward in the form of an arch. As already indicated on page 285, complete flexion of the hip cannot be effected unless the knee-joint is also flexed, on account of the shortness of the hamstring muscles. m. THE MUSCLES AND FASCMl OF THE LEG. The muscles of the leg may be divided into three groups: anterior, posterior, and lateral. 1. The Anterior Crural Muscles (Fig. 437). Tibialis anterior. Extensor digitorum longus. Extensor hallucis longus. Peronseus tertius. Deep Fascia {fascia cruris) . — The deep fascia of the leg forms a complete invest- ment to the muscles, and is fused with the periosteum over the subcutaneous surfaces of the bones. It is continuous above with the fascia lata, and is attached around the knee to the patella, the ligamentum patellae, the tuberosity and con- dyles of the tibia, and the head of the fibula. Behind, it forms the popliteal fascia, covering in the popliteal fossa; here it is strengthened by transverse fibers, and perforated by the small saphenous vein. It receives an expansion from the tendon of the Biceps femoris laterally, and from the tendons of the Sartorius, Gracilis, Semitendinosus, and Semimembranosus medially; in front, it blends with the peri- osteum covering the subcutaneous surface of the tibia, and with that covering the head and malleolus of the fibula; below, it is continuous with the transverse crural and laciniate ligaments. It is thick and dense in the upper and anterior part of the leg, and gives attachment, by its deep surface, to the Tibialis anterior and Extensor digitorum longus; but thinner behind, where it covers the Gastroc- nemius and Soleus. It gives off from its deep surface, on the lateral side of the leg, two strong intermuscular septa, the anterior and posterior peroneal septa, which enclose the Peronsei longus and brevis, and separate them from the muscles of the anterior and posterior crural regions, and several more slender processes which enclose the individual muscles in each region. A broad transverse intermuscular septum, called the deep transverse fascia of the leg, intervenes between the super- ficial and deep posterior crural muscles. The Tibialis anterior {Tibialis anticus) is situated on the lateral side of the tibia; it is thick and fleshy above, tendinous below. It arises from the lateral condyle and upper half or two-thirds of the lateral surface of the body of the tibia; from the adjoining part of the interosseous membrane; from the deep surface of the fascia; and from the intermuscular septum between it and the Extensor digitorum longus. The fibers run vertically downward, and end in a tendon, which is apparent on the anterior surface of the muscle at the lower third of the leg. After passing through the most medial compartments of the transverse and cruciate crural ligaments, it is inserted into the medial and under surface of the first cuneiform bone, and the base of the first metatarsal bone. This muscle overlaps the anterior tibial vessels and deep peroneal nerve in the upper part of the leg. Variations. — A deep portion of the muscle is rarely inserted into the talus, or a tendinous slip may pass to the head of the first metatarsal bone or the base of the first phalanx of the great toe. The Tibiofascialis anterior, a small muscle from the lower part of the tibia to the transverse or cruciate crural ligaments or deep fascia. THE ANTERIOR CRURAL MUSCLES 481 The Extensor hallucis longus {Extensor proprius hallucis) is a thin muscle, situated between the Tibialis anterior and the Extensor digitorum longus. It arises from the anterior surface of the fibula for about the middle two-fourths of its extent, medial to the origin of the Extensor digi- torum longus; it also arises from the interosseous membrane to a similar extent. The anterior tibial vessels and deep peroneal nerve lie between it and the Tibialis anterior. The fibers pass downward, and end in a tendon, which occupies the anterior border of the muscle, passes through a distinct compartment in the cruciate crural ligament, crosses from the lateral to the medial side of the anterior tibial vessels near the bend of the ankle, and is inserted into the base of the distal phalanx of the great toe. Opposite the metatarso- phalangeal articulation, the tendon gives off a thin prolongation on either side, to cover the surface of the joint. An expansion from the medial side of the tendon is usually inserted into the base of the proximal phalanx. Variations. — Occasionally united at its origin with the Extensor digitorum longvis. Extensor ossis metatarsi hal- lucis, a small muscle, sometimes found as a slip from the Extensor hallucis longus, or from the Tibialis anterior, or from the Extensor digitorum longus, or as a distinct mus- cle; it traverses the same compartment of the transverse ligament with the Extensor hallucis longus. The Extensor digitonim longus is a penniform muscle, situated at the lateral part of the front of the leg. It arises from the lateral condyle of the tibia; from the upper three-fourths of the anterior surface of the body of the fibula; from the upper part of the interosseous membrane; from the deep surface of the fascia; and from the intermuscular septa between it and the Tibialis anterior on the medial, and the Peronsei on the lateral side. Between it and the Tibialis anterior are the upper portions of the anterior tibial vessels and deep peroneal nerve. The tendon passes under the transverse and cruciate crural ligaments in company with the Peronseus tertius, and divides into four slips, which run forward on the dorsum of the foot, and are inserted into the second and third phalanges of the four lesser toes. The ten- dons to the second, third, and fourth toes are each joined, opposite the metatarsophalangeal articulation, on the lateral side by a tendon of the Extensor digitorum brevis. The tendons are inserted in the following manner: each receives a fibrous expansion from the Interossei and Lum- bricalis, and then spreads out into a broad apon- eurosis, which covers the dorsal surface of the \ri6li xentt Fia. 437. — Muscles of the front of the leg. k: 482 MYOLOGY ^1 e second first phalanx: this aponeurosis, at the articulation of the first with the phalanx, divides into three slips — an intermediate, which is inserted into the base of the second phalanx; and two collateral slips, which, after uniting on the dorsal surface of the second phalanx, are continued onward, to be inserted into the base of the third phalanx. Variations. — This muscle varies considerably in the modes of origin and the arrangement of itsi various tendons. The tendons to the second and fifth toes may be found doubled, or extra slips are given off from one or more tendons to their corresponding metatarsal bones, or to the short extensor, or to one of the interosseous muscles. A slip to the great toe from the innermost tendon has been found. The Peronseus tertius is a part of the Extensor digitorum longus, and might be described as its fifth tendon. The fibers belonging to this tendon arise from the lower third or more of the anterior surface of the fibula; from the lower part of the interosseous membrane; and from an intermuscular septum between it and the Peronseus brevis. The tendon, after passing under the transverse and cruciate crural ligaments in the same canal as the Extensor digitorum longus, is inserted into the dorsal surface of the base of the metatarsal bone of the little toe. This muscle is sometimes wanting. Nerves. — These muscles are supplied by the fourth and fifth lumbar and first sacral nerves through the deep peroneal nerve. Actions. — The Tibialis anterior and Peronajus tertius are the direct flexors of the foot at the ankle-joint; the former muscle, when acting in conjunction with the Tibialis posterior, raises the medial border of the foot, i. e., inverts the foot; and the latter, acting with the Perona?i brevis and longus, raises the lateral border of the foot, i. e., everts the foot. The Extensor digitorum longus and Extensor hallucis longus extend the phalanges of the toes, and, continuing their action, flex the foot upon the leg. Taking their fixed points from below, in the erect posture, all these muscles serve to fix the bones of the leg in the perpendicular position, and give increased strength to the ankle-joint. 2. The Posterior Crural Muscles. The muscles of the back of the leg are subdivided into two groups — superficial and deep. Those of the superficial group constitute a pcf^verful muscular mass, forming the calf of the leg. Their large size is one of the most characteristic features of the muscular apparatus in man, and bears a direct relation to his erect attitude and his mode of progression. The Superficial Group (Fig. 438). Gastrocnemius. Soleus. Plantaris. The Gastrocnemius is the most superficial muscle, and forms the greater part of the calf. It arises by two heads, which are connected to the condyles of the femur by strong, flat tendons. The medial and larger head takes its origin from a depression at the upper and back part of the medial condyle and from the adjacent part of the femur. The lateral head arises from an impression on the side of the lateral condyle and from the posterior surface of the femur immediately above the lateral part of the condyle. Both heads, also, arise from the subjacent part of the capsule of the knee. Each tendon spreads out into an aponeurosis, which covers the posterior surface of that portion of the muscle to which it belongs. From the anterior surfaces of these tendinous expansions, muscular fibers are given off; those of the medial head being thicker and extending lower than those of the lateral. The fibers unite at an angle in the middle line of the muscle in a tendinous raphe, which expands into a broad aponeurosis on the anterior surface of the muscle, and into this the remaining fibers are inserted. The aponeurosis, gradually contracting, unites with the tendon of the Soleus, and forms with it the tendo calcaneus. I^^^^^^H THE POSTERIOR CRURAL MUSCLES 483 P \^Miafions.-^^-X1osence of the outer head or of the entire muscle. Extra slips from the popliteal [surface of the femur. I The Soleus is a broad flat muscle situated immediately in front of the Gastroc- nemius. It arises by tendinous fibers from the back of the head of the fibula, and from the upper third of the posterior surface of the body of the bone; from the popliteal line, and the middle third of the medial border of the tibia; some fibers ■1 also arise from a tendinous arch placed between the tibial and fibular origins |of the muscle, in front of which the popliteal vessels and tibial nerve run. The fibers end in an aponeurosis .which covers the posterior surface of the muscle, and, gradually becoming thicker and narrower, joins with the tendon of the Gastroc- Inemius, and forms with it the tendo calcaneus. Variations. — Accessory head to its lower and inner part usually ending in the tendocalcaneus, or [the calcaneus, or the laciniate ligament. The Gastrocnemius and Soleus together form a muscular mass which is occa- sionally described as the Triceps surse; its tendon of insertion is the tendo calcaneus. Tendo Calcaneus {tendo Achillis) . — The tendo calcaneus, the common tendon of the Gastrocnemius and Soleus, is the thickest and strongest in the body. It is about 15 cm. long, and begins near the middle of the leg, but receives fleshy fibers on its anterior surface, almost to its lower end. Gradually becoming contracted below, it is inserted into the middle part of the posterior surface of the calcaneus, a bursa being interposed between the tendon and the upper part of this surface. The ten- don spreads out somewhat at its lower end, so that its narrowest part is about 4 cm. above its insertion. It is covered by the fascia and the integument, and is separated from the deep muscles and vessels by a considerable interval filled up with areolar and adipose tissue. Along its lateral side, but superficial to it, is the small saphenous vein. The Plantaris is placed between the Gastrocnemius and Soleus. It arises from the lower part of the lateral prolongation of the linea aspera, and from the oblique popliteal ligament of the knee-joint. It forms a small fusiform belly, from 7 to 10 cm. long, ending in a long slender tendon which crosses obliquely between the two muscles of the calf, and runs along the medial border of the tendo calcaneus, to be inserted with it into the posterior part of the calcaneus. This muscle is some- times double, and at other times wanting. Occasionally, its tendon is lost in the laciniate ligament, or in the fascia of the leg. Nerves. — The Gastrocnemius and Soleus are suppUed by the first and second sacral nerves, and the Plantaris by the fourth and fifth lumbar and first sacral nerves, through the tibial nerve. Actions. — The muscles of the calf are the chief extensors of the foot at the ankle-joint. They possess considerable power, and are constantly called into use in standing, walking, dancing, and leaping; hence the large size they usually present. In walking, these muscles raise the heel from the ground; the body being thus supported on the raised foot, the opposite limb can be carried forward. In standing, the Soleus, taking its fixed point from below, steadies the leg upon the foot and prevents the body from falling forward. The Gastrocnemius, acting from below, serves to flex the femur upon the tibia, assisted by the PopUteus. The Plantaris is the rudiment of a large muscle which in some of the lower animals is continued over the calcaneus to be inserted into the plantar aponeurosis. In man it is an accessory to the Gastrocnemius, extending the ankle if the foot be free, or bending the knee if the foot be fixed. ki ir The Deep Group (Fig. 439). Popliteus. Flexor digitorum longus. Flexor hallucis longus. Tibialis posterior. Deep Transverse Fascia. — The deep transverse fascia of the leg is a transversely placed, intermuscular septum, between the superficial and deep muscles of the back of the leg. At the sides it is connected to the margins of the tibia and 484 MYOLOGY fibula. Above, where it covers the PopHteus, it is thick and dense, and receives an expansion from the tendon of the Semimembranosus; it is thinner in the middle Tendons of Peronae longus et brevis Fig. 438. — Muscles of the back of the leg. Superficial layer. Fig. 439. — Muscles of the back of the leg. Deep layer. of the leg; but below, where it covers the tendons passing behind the malleoli, it is thickened and continuous with the laciniate ligament. The Popliteus is a thin, flat, triangular muscle, which forms the lower part of THE POSTERIOR CRURAL MUSCLES 485 ^Bithe floor of the popliteal fossa. It arises by a strong tendon about 2.5 em. long, from a depression at the anterior part of the groove on the lateral condyle of the femur, and to a small extent from the oblique popliteal ligament of the knee-joint; ^■Eand is inserted into the medial two-thirds of the triangular surface above the pop- ^■' liteal line on the posterior surface of the body of the tibia, and into the tendinous expansion covering the surface of the muscle. ■I Variations. — Additional head from the sesamoid bone in the outer head of the Gastrocnemius. ' Popliteus minor, rare, origin from femur on the inner side of the Plantaris, insertion into the pos- terior ligament of the knee-joint. Peroneotibialis, 14 per cent., origin inner side of the head of the fibula, insertion into the upper end of the oblique line of the tibia, it lies beneath the Popliteus. The Flexor hallucis longus is situated on the fibular side of the leg. It arises from the inferior two-thirds of the posterior surface of the body of the fibula, with the exception of 2.5 cm. at its lowest part; from the lower part of the interosseous embrane; from an intermuscular septum between it and the Peronsei, laterally, and from the fascia covering the Tibialis posterior, medially. The fibers pass obliquely downward and backward, and end in a tendon which occupies nearly ;he whole length of the posterior surface of the muscle. This tendon lies in a groove which crosses the posterior surface of the lower end of the tibia, the posterior surface of the talus, and the under surface of the sustentaculum tali of the calca- neus; in the sole of the foot it runs forward between the two heads of the Flexor hallucis brevis, and is inserted into the base of the last phalanx of the great toe. The grooves on the talus and calcaneus, which contain the tendon of the muscle, are converted by tendinous fibers into distinct canals, lined by a mucous sheath. As the tendon passes forward in the sole of the foot, it is situated above, and crosses from the lateral to the medial side of the tendon of the Flexor digitorum longus, to which it is connected by a fibrous slip. Variations. — -rsualiy a slip runs to the Flexor digitorum and frequently an additional slip runs from the Flexor digitorum to the Flexor hallucis. Peroneocalcaneus internus, rare, origin below or outside the Flexor hallucis from the back of the fibula, passes over the sustentaculvun tali with ihe Flexor hallucis and is inserted into the calcaneum. ■^ ir The Flexor digitorum longus is situated on the tibial side of the leg. At its origin it is thin and pointed, but it gradually increases in size as it descends. It arises from the posterior surface of the body of the tibia, from immediately below the popliteal line to within 7 or 8 cm. of its lower extremity, medial to the tibial origin of the Tibialis posterior; it also arises from the fascia covering the Tibialis posterior. The fibers end in a tendon, which runs nearly the whole length of the posterior surface of the muscle. This tendon passes behind the medial malleolus, in a groove, common to it and the Tibialis posterior, but separated from the latter by a fibrous septum, each tendon being contained in a special compartment lined by a separate mucous sheath. It passes obliquely forward and lateral ward, super- ficial to the deltoid ligament of the ankle-joint, into the sole of the foot (Fig. 444), where it crosses below the tendon of the Flexor hallucis longus, and receives from it a strong tendinous slip. It then expands and is joined by the Quadratus plants, and finally divides into four tendons, which are inserted into the bases of the last phalanges of the second, third, fourth, and fifth toes, each tendon passing through an opening in the corresponding tendon of the Flexor digitorum brevis opposite the base of the first phalanx. Variations. — Flexor accessorius longus digitorum, not infrequent, origin from fibula, or tibia, or the deep fascia and ending in a tendon which, after passing beneath the laciniate ligament, joins the tendon of the long flexor or the Quadratus plantse. The Tibialis posterior ( Tibialis posticus) lies between the two preceding muscles, and is the most deeply seated of the muscles on the back of the leg. It begins above by two pointed processes, separated by an angular interval through which » I- 486 ^^ MYOLOGY I the anterior tibial vessels pass forward to the front of the leg. It arises from the whole of the posterior surface of the interosseous membrane, excepting its lowest part; from the lateral portion of the posterior surface of the body of the tibia, between the commencement of the popliteal line above and the junction of the middle and lower thirds of the body below; and from the upper two-thirds of the medial surface of the fibula ; some fibers also arise from the deep transverse fascia, and from the intermuscular septa separating it from the adjacent muscles. In the lower fourth of the leg its tendon passes in front of that of the Flexor digitorum longus and lies with it in a groove behind the medial malleolus, but enclosed in a separate sheath; it next passes under the laciniate and over the deltoid ligament into the foot, and then beneath the plantar calcaneonavicular ligament. The tendon contains a sesamoid fibrocartilage, as it runs under the plantar calcaneo- navicular ligament. It is inserted into the tuberosity of the navicular bone, and gives off fibrous expansions, one of which passes backward to the sustentaculum tali of the calcaneus, others forward and lateralward to the three cuneiforms, the cuboid, and the bases of the second, third, ^nd fourth metatarsal bones. Nerves. — The Popliteus is supplied by the fourth and fifth lumbar and first sacral nerves, the Flexor digitorum longus and Tibiahs posterior by the fifth lumbar and first sacral, and the Flexor haUucis longus by the fifth lumbar and the first and second sacral nerves, through the tibial nerve. Actions. — The PopHteus assists in flexing the leg upon the thigh; when the leg is flexed, it will rotate the tibia inward. It is especially called into action at the beginning of the act of bending the knee, inasmuch as it produces the slight inward rotation of the tibia which is essential in the early stage of this movement. The Tibialis posterior is a direct extensor of the foot at the ankle- joint; acting in conjunction with the Tibialis anterior, it turns the sole of the foot upward and medialward, i. e., inverts the foot, antagonizing the Peronai, which turn it upward and lateral- ward (evert it). In the sole of the foot the tendon of the TibiaUs posterior lies directly below the plantar calcaneonavicular hgament, and is therefore an important factor in maintaining the arch of the foot. The Flexor digitorum longus and Flexor hallucis longus are the direct flexors of the phalanges, and, continuing their action, extend the foot upon the leg; they assist the Gastroc- nemius and Soleus in extending the foot, as in the act of walking, or in standing on tiptoe. In consequence of the oblique direction of its tendons the Flexor digitorum longus would draw the toes medialward, were it not for the Quadratus plantae, which is inserted into the lateral side of the tendon, and draws it to the middle line of the foot. Taking their fixed point from the foot, these muscles serve to maintain the upright posture by steadying the tibia and fibula perpendicularly upon the talus. 3. The Lateral Crural Muscles (Fig. 439). Peronseus longus. Peronseus brevis. The Peronseus longus is situated at the upper part of the lateral side of the leg, and is the more superficial of the two muscles. It arises from the head and upper two-thirds of the lateral surface of the body of the fibula, from the deep surface of the fascia, and from the intermuscular septa between it and the muscles on the front and back of the leg; occasionally also by a few fibers from the lateral condyle of the tibia. Between its attachments to the head and to the body of the fibula there is a gap through which the common peroneal nerve passes to the front of the leg. It ends in a long tendon, which runs behind the lateral malleolus, in a groove common to it and the tendon of the Peronseus brevis, behind which it lies; the groove is converted into a canal by the superior peroneal retinaculum, and the tendons in it are contained in a common mucous sheath. The tendon then extends obliquely forward across the lateral side of the calcaneus, below the troch- lear process, and the tendon of the Peronaeus brevis, and under cover of the inferior peroneal retinaculum. It crosses the lateral side of the cuboid, and then runs on the under surface of that bone in a groove which is converted into a canal by the long plantar ligament; the tendon then crosses the sole of the foot obliquely, and is inserted into the lateral side of the base of the first metatarsal bone and the lateral THE LATERAL CRURAL MUSCLES 487 side of the first cuneiform. Occasionally it sends a slip to the base of the second metatarsal bone. The tendon changes its direction at two points : first, behind the lateral malleolus; secondly, on the cuboid bone; in both of these situations the ten- don is thickened, and, in the -latter, a sesamoid fibrocartilage (sometimes a bone), is usually developed in its substance. Tibialis anterior M.- Interosseous membram '■ Tibia Extensores longi digi- toTum et hallucis Mm. Flexor digitorum / longus M. Deep peroneal nen and anterior tihi' artery and vein Peroncei longzis and brevis Mm Superficial peroneal •- ' \ nerve V' Fibula'' Peroneal artcri and vein Great saphenous vein and saphenous nerve ^Posterior tibial vein and artery -Tibial nerve Soleus M. Tendo m. plantaris Gastrocnemius M. Gastrocnemius M/ ^Median cutaneous nerve isinuil saphenous vein Fig. 440. — Cross-section through middle of leg. (Eycleshymer and Schoemaker.) Lateral cuiuncuu^ nerve The Peronaeus brevis lies under cover of the Peronseus longus, and is a shorter and smaller muscle. It arises from the lower two-thirds of the lateral surface of the body of the fibula; medial to the Peronaeus longus; and from the intermuscular septa separating it from the adjacent muscles on the front and back of the leg. The fibers pass vertically downward, and end in a tendon which runs behind the lateral malleolus along with but in front of that of the preceding muscle, the two tendons being enclosed in the same compartment, and lubricated by a common mucous sheath. It then runs forward on the lateral side of the calcaneus, above the trochlear process and the tendon of the Peronaius longus, and is inserted into the tuberosity at the base of the fifth metatarsal bone, on its lateral side. On the lateral surface of the calcaneus the tendons of the Peronsei longus and brevis occupy separate osseoaponeurotic canals formed by the calcaneus and the perineal retinacula; each tendon is enveloped by a forward prolongation of the common mucous sheath. Variations. — Fusion of the two peronsei is rare. A slip from the Peronaeus longus to the base of the third, fourth or fifth metatarsal bone, or to the Adductor hallucis is occasionally seen. Peronaeus accessarius, origin from the fibula between the longus and brevis, joins the tendon of the longus in the sole of the foot. PeroncBus quinti digiti, rare, origin lower fourth of the fibula imder the brevis, insertion into the Extensor aponeurosis of the little toe. More common as a slip of the tendon of the Perona;us brevis. Peronaeus quartus, 13 per cent. (Gniber), origin back of fibula between the brevis and the Flexor hallucis, insertion into the peroneal spine of the calcaneum, {peroneocalcaneus externum), or less frequently into the tuberosity of the cuboid (peroneocuboideus). Nerves. — The Peronaei longus and brevis are supplied by the fourth and fifth lumbar and first sacral nerves through the superficial peroneal nerve. 488 MYOLOGY Actions. — The Peronacf longus and brevis extend the foot upon fhe leg, in conjuncfion with the Tibialis posterior, antagonizing the Tibiahs anterior and Peronajus tertius, which are flexors of the foot. The Peronajus longus also everts the sole of the foot, and from the obhque direction of the tendon across the sole of the foot is an important agent in the maintenance of the trans- verse arch. Taking their fixed points below, the Perona^i serve to steady the leg upon the foot. This is especially the case in standing upon one leg, when the tendency of the superincumbent weight is to throw the leg medialward ; the Peronajus longus overcomes this tendency by drawing on the lateral side of the leg. THE FASCIA AROUND THE ANKLE. Fibrous bands, or thickened portions of the fascia, bind down the tendons front of and behind the ankle in their passage to the foot. They comprise three ligaments, viz., the transverse crural, the cruciate crural and the laciniate; and the superior and inferior peroneal retinacula. IS m^^ Tibialis anterior / Extensor dig. longus Ext. hall. long. Ext. dig. brevis Tendo calcaneus Peronaua longus PerontBus brevis Peronoetia tertius Fia. 441. — The mucous sheaths of the tendons around the ankle. Lateral aspect. Transverse Crural Ligament (ligamentum transversum cruris; upper part of anterior annular ligament) (Fig. 441). — The transverse crural ligament binds down the tendons of Extensor digitorum longus, Extensor hallucis longus, Peronseus tertius, and Tibialis anterior as they descend on the front of the tibia and fibula; under it are found also the anterior tibial vessels and deep peroneal nerve. It is attached laterally to the lower end of the fibula, and medially to the tibia; above it is con- tinuous with the fascia of the leg. Cruciate Crural Ligament (ligamentum cruciatum cruris; lower part of anterior annular ligament) (Figs. 441, 442). — The cruciate crural ligament is a Y-shaped band placed in front of the ankle-joint, the stem of the Y being attached laterally to the upper surface of the calcaneus, in front of the depression for the interosseous talocalcanean ligament; it is directed medialward as a double layer, one lamina passing in front of, and the other behind, the tendons of the Peronseus tertius and Extensor digitorum longus. At the medial border of the latter tendon these two layers join together, forming a compartment in which the tendons are enclosed. From the medial extremity of this sheath the two limbs of the Y diverge : one is directed upward and medialward, to be attached to the tibial malleolus, passing over the Extensor hallucis longus and the vessels and nerves, but enclosing THE FASCIA AROUND THE ANKLE ^■the Tibialis anterior by a splitting of its jSbers. The other limb extends downward ^*and medialward, to be attached to the border of the plantar aponeurosis, and passes over the tendons of the Extensor hallucis longus and Tibialis anterior and also the vessels and nerves. ^^ Laciniate Ligament (ligamentum laciniatum; internal annular ligament). — The ^■Jaciniate ligament is a strong fibrous band, extending from the tibial malleolus ^^ above to the margin of the calcaneus below, converting a series of bony grooves in this situation into canals for the passage of the tendons of the Flexor muscles and the posterior tibial vessels and tibial nerve into the sole of the foot. It is ■ continuous by its upper border with the deep fascia of the leg, and by its lower |)order with the plantar aponeurosis and the fibers of origin of the Abductor hallucis muscle. Enumerated from the medial side, the four canals which it forms transmit the tendon of the Tibialis posterior; the tendon of the Flexor digitorum longus; the posterior tibial vessels and tibial nerve, which run through a broad space beneath the ligament; and lastly, in a canal formed partly by the talus, the tendon of the Flexor hallucis longus. The mucous sheaths of the tendons around the ankle. Bursa Tendocalcaneus Medial aspect. 1 a Peroneal Retinacula. — The peroneal retinacula are fibrous bands which bind down the tendons of the Peronsei longus and brevis as they run across the lateral side of the ankle. The fibers of the superior retinaculum {external annular ligament) are attached above to the lateral malleolus and below to the lateral surface of the calcaneus. The fibers of the inferior retinaculum are continuous in front with those of the cruciate crural ligament; behind they are attached to the lateral surface of the calcaneus; some of the fibers are fixed to the peroneal trochlea, forming a septum between the tendons of the Peronsei longus and brevis. The Mucous Sheaths of the Tendons Aroimd the Ankle. — All the tendons crossing the ankle-joint are enclosed for part of their length in mucous sheaths which have an almost uniform length of about 8 cm. each. On the front of the ankle (Fig. 441) ;he sheath for the Tibialis anterior extends from the upper margin of the trans- verse crural ligament to the interval between the diverging limbs of the cruciate ligament; those for the Extensor digitorum longus and Extensor hallucis longus reach upward to just above the level of the tips of the malleoli, the former being the higher. The sheath of the Extensor hallucis longus is prolonged on to the base of the first metatarsal bone, while that of the Extensor digitorum longus reaches 490 ^^^^^^^- MYOLOGY only to the level of the base of the fifth metatarsal. On the medial side of the ankle (Fig. 442) the sheath for the Tibialis posterior extends highest up — to about 4 cm. above the tip of the malleolus — while below it stops just short of the tuber- osity of the navicular. The sheath for Flexor hallucis longus reaches up to the level of the tip of the malleolus, while that for the Flexor digitorum longus is slightly higher; the former is continued to the base of the first metatarsal, but the latter stops opposite the first cuneiform bone. On the lateral side of the ankle (Fig. 441) a sheath which is single for the greater part of its extent encloses the Peronsei longus and brevis. It extends upward for about 4 cm, above the tip of the malleolus and downward and forward for about the same distance. •^ IV. THE MUSCLES AND FASCLffi OF THE FOOT. 1. The Dorsal Muscle of the Foot. Extensor digitorum brevis. The fascia on the dorsum of the foot is a thin membranous layer, continuous above with the transverse and cruciate crural ligaments; on either side it blends with the plantar aponeurosis; anteriorly it forms a sheath for the tendons on the dorsum of the foot. The Extensor digitorum brevis (Fig. 441) is a broad, thin muscle, which arises from the forepart of the upper and lateral surfaces of the calcaneus, in front of the groove for the Peronseus brevis; from the lateral talocalcanean ligament; and from the common limb of the cruciate crural ligament. It passes obliquely across the dorsum of the foot, and ends in four tendons. The most medial, which is the largest, is inserted into the dorsal surface of the base of the first phalanx of the great toe, crossing the dorsalis pedis artery; it is frequently described as a separate muscle — the Extensor hallucis brevis. The other three are inserted into the lateral sides of the tendons of the Extensor digitorum longus of the second, third, and fourth toes. Variations. — ^Accessory slips of origin from the talus and navicular, or from the external cunei- form and third metatarsal bones to the second slip of the muscle, and one from the cuboid to the third slip have been observed. The tendons vary in number and position; they may be reduced to two, or one of them may be doubled, or an additional slip may pass to the little toe. A super- numerary slip ending on one of the metatarsophalangeal articulations, or joining a dorsal inter- osseous muscle is not uncommon. Deep slips between this muscle and the Dorsal interossei occur. Nerves. — It is suppUed by the deep peroneal nerve. Actions. — The Extensor digitorum brevis extends the phalanges of the four toes into which it is inserted, but in the great toe acts only on the first phalanx. The obhquity of its direction counteracts the obUque movement given to the toes by the long Extensor, so that when both muscles act, the toes are evenly extended. 2. The Plantar Muscles of the Foot. Plantar Aponeurosis {aponeurosis plantaris; plantar fascia). — The plantar apo- neurosis is of great strength, and consists of pearly white glistening fibers, disposed, for the most part, longitudinally: it is divided into central, lateral, and medial portions. The central portion, the thickest, is narrow behind and attached to the medial process of the tuberosity of the calcaneus, posterior to the origin of the Flexor digitorum brevis; and becoming broader and thinner in front, divides near the heads of the metatarsal bones into five processes, one for each of the toes. Each of these processes divides opposite the metatarsophalangeal articulation into two strata, superficial and deep. The superficial stratum is inserted into the skin of THE PLANTAR MUSCLES OF THE FOOT 491 the transverse sulcus which separates the toes from the sole. The deeper stratum divides into two slips which embrace the side of the Flexor tendons of the toes, and blend with the sheaths of the tendons, and with the transverse metatarsal ligament, thus forming a series of arches through which the tendons of the short and long Flexors pass to the toes. The intervals left between the five processes allow the digital vessels and nerves and the tendons of the Lumbricales to become superficial. At the point of division of the aponeurosis, numerous transverse fasciculi are superadded ; these serve to increase the strength of the aponeurosis at this part by binding the processes together, and connecting them with the integu- ment. The central portion of the plantar aponeurosis is continuous with the lateral and medial portions and sends upward into the foot, at the lines of junction, two strong vertical intermuscular septa, broader in front than behind, which separate the intermediate from the lateral and medial plantar groups of muscles; from these again are derived thinner transverse septa which separate the various layers of muscles in this region. The upper surface of this aponeurosis gives origin behind to the Flexor digitorum brevis. The lateral and medial portions of the plantar aponeurosis are thinner than the central piece, and cover the sides of the sole of the foot. The lateral portion covers the under surface of the Abductor digiti quinti; it is thin in front and thick behind, where it forms a strong band between the lateral process of the tuberosity of the calcaneus and the base of the fifth metatarsal bone; it is continuous medially with the central portion of the plantar aponeurosis, and laterally with the dorsal fascia. The medial portion is thin, and covers the under surface of the Abductor hallucis; it is attached behind to the laciniate ligament, and is continuous around the side of the foot with the dorsal fascia, and laterally with the central portion of the plantar aponeurosis. The muscles in the plantar region of the foot may be divided into three groups, in a similar manner to those in the hand. Those of the medial plantar region are connected with the great toe, and corrrespond with those of the thumb; those of the lateral plantar region are connected with the little toe, and correspond with those of the little finger; and those of the intermediate plantar region are connected with the tendons intervening between the two former groups. But in order to facilitate the description of these muscles, it is more convenient to divide them into four layers, in the order in which they are successively exposed. Abductor hallucis. The First Layer (Fig. 443). Flexor digitorum brevis. Abductor digiti quinti. [■ The Abductor hallucis lies along the medial border of the foot and covers the origins of the plantar vessels and nerves. It arises from the medial process of the tuberosity of the calcaneus, from the laciniate ligament, from the plantar aponeu- rosis, and from the intermuscular septum between it and the Flexor digitorum brevis. The fibers end in a tendon, which is inserted, together with the medial tendon of the Flexor hallucis brevis, into the tibial side of the base of the first phalanx of the great toe. Variations. — Slip to the base of the first phalanx of the second toe. The Flexor digitorum brevis lies in the middle of the sole of the foot, imme- diately above the central part of the plantar aponeurosis, with which it is firmly united. Its deep surface is separated from the lateral plantar vessels and nerves 492 MYOLOGY by a thin layer of fascia. It arises by a narrow tendon, from the medial process of the tuberosity of the calcaneus, from the central part of the plantar aponeurosis, and from the intermuscular septa between it and the adjacent muscles. It passes forward, and divides into four tendons, one for each of the four lesser toes. Oppo- site the bases of the first phalanges, each tendon divides into two slips, to allow of the passage of the corresponding tendon of the Flexor digitorum longus; the two portions of the tendon then unite and form a grooved channel for the reception of the accompanying long Flexor tendon. Finally, it divides a second time, and is inserted into the sides of the second phalanx about its middle. The mode of division of the 7UUWIM tendons of the Flexor digitorum brevis, and of their insertion into the phalanges, is analogous to that of the tendons of the Flexor digitorum sublimis in the hand. Variations. — Slip to the little toe frequently wanting, 23 per cent.; or it may be replaced by a small fusiform muscle arising from the long flexor tendon or from the Quadratus plantse. Fibrous Sheaths of the Flexor Tendons. — The terminal portions of the tendons of the long and short Flexor muscles are contained in osseoaponeurotic canals similar in their ar- rangement to those in .the fingers. These canals are formed above by the phalanges and below by fibrous bands, which arch across the tendons, and are attached on either side to the margins of the phalanges. Opposite the bodies of the proximal and second pha- langes the fibrous bands are strong, and the fibers are transverse; but opposite the joints they are much thinner, and the fibers are directed obliquely. Each canal contains a mucous sheath, which is reflected on the con- tained tendons. The Abductor digiti quinti {Abductor minimi digiti) lies along the lateral border of the foot, and is in relation by its medial margin with the lateral plantar vessels and nerves. It arises, by a broad origin, from the lateral process of the tuberosity of the calcaneus, from the under surface of the calcaneus between the two pro- cesses of the tuberosity, from the forepart of the medial process, from the plantar aponeu- rosis, and from the intermuscular septum between it and the Flexor digitorum brevis. Its tendon, after gliding over a smooth facet on the under surface of the base of the fifth metatarsal bone, is inserted, with the Flexor digiti quinti brevis, into the fibular side of the base of the first phalanx of the fifth toe. Variations. — Slips of origin from the tuberosity at the base of the fifth metatarsal Abdvctor osm metatarsi quinti, origin external tubercle of the calcaneus, insertion into tuberosity of the fifth metatarsalbone in common with or beneath the outer margin of the plantar fascia. I Fig. 443. — Muscles of the sole of the foot. First layer. I THE PLANTAR MUSCLES OF THE FOOT 493 The Second Layer (Fig. 444). Quadratus plantae. Lumbricales. The Quadratus plantse (Flexor accessoriiis) is separated from the muscles of the first layer by the lateral plantar vessels and nerve. It arises by two heads, which are separated from each other by the long plantar ligament: the medial or larger head is muscular, and is attached to the medial concave surface of the calcaneus, below the groove which lodges the tendon of the Flexor hallucis longus; the lateral head, flat and tendinous, arises from the lateral border of the inferior surface of the calcaneus, in front of the lateral process of its tuberosity, and from the long plantar ligament. The two portions join at an acute angle, and end in a flattened band which is inserted into the lateral margin and upper and under sur- t faces of the tendon of the Flexor digitorum longus, forming a kind of groove, in which the tendon is lodged. It usually sends slips to those tendons of the Flexor digitorum longus which pass to the second, third, and fourth toes. Variations. — Lateral head often wanting; entire muscle absent. Variation in the number of digital tendons to which fibers can be traced. Most frequent offsets are sent to the second, third and fourth toes; in many cases to the fifth as well; occasionally to two toes only. The Lumbricales are four small muscles, accessory to the tendons of the Flexor digitorum longus and numbered from the medial side of the foot; they arise from these tendons, as far back as their angles of division, each springing from two tendons, except the first. The muscles end in tendons, which pass forward on the medial sides of the four lesser toes, and are inserted into the expansions of the tendons of the Extensor digitorum longus on the dorsal surfaces of the first phalanges. Variations. — Absence of one or more; doubling of the third or fourth. Insertion partly or wholly into the first phalanges. The Third Layer (Fig. 445). r Flexor hallucis brevis. Adductor hallucis. Flexor digiti quinti brevis. The Flexor hallucis brevis arises, by a pointed tendinous process, from the medial part of the under surface of the cuboid bone, from the contiguous portion of the third cuneiform, and from the prolongation of the tendon of the Tibialis posterior which is attached to that bone. It divides in front into two portions, which are inserted into the medial and lateral sides of the base of the first phalanx of the great toe, a sesamoid bone being present in each tendon at its insertion. The medial portion is blended with the Abductor hallucis previous to its insertion; the lateral portion with the Adductor hallucis; the tendon of the Flexor hallucis longus lies in a groove between them; the lateral portion is sometimes described as the first Interosseous plantaris. Variations. — Origin subject to considerable variation; it often receives fibers from the calcaneus lor long plantar ligament. Attachment to the cuboid sometimes wanting. Slip to first phalanx I of the second toe. The Adductor hallucis {Adductor ohliquus hallucis) arises by two heads — oblique and transverse. The oblique head is a large, thick, fleshy mass, crossing the foot obliquely and occupying the hollow space under the first, second, third, and fourth metatarsal bones. It arises from the bases of the second, third, and fourth meta- tarsal bones, and from the sheath of the tendon of the Peronseus longus, and is inserted, together with the lateral portion of the Flexor hallucis brevis, into the lateral side of the base of the first phalanx of the great toe. The transverse head ( Transversus pedis) is a narrow, flat fasciculus which arises from the plantar meta- 494 MYOLOGY tarsophalangeal ligaments of the third, fourth, and fifth toes (sometimes^fy from the third and fourth), and from the transverse ligament of the metatarsus. It is inserted into the lateral side of the base of the first phalanx of the great toe, its fibers blending with the tendon of insertion of the oblique head. I Fig. 444.— Muscles of the sole of the foot. Second layer. Fia. 445. — Muscles of the sole of the foot. Third layer. Opponens hallucis, occasional Variations. — Slips to the base of the first phalanx of the second toe. slips from the adductor to the metatarsal bone of the great toe. The Abductor, Flexor brevis, and Adductor of the great toe, like the similar muscles of the thumb, give off, at their insertions, fibrous expansions to blend with the tendons of the Extensor digitorum longus. The Flexor digiti quinti brevis (Flexor brevis minimi digiti) lies under the metatarsal bone of the little toe, and resembles one of the Interossei. It arises from the base of the fifth metatarsal bone, and from the sheath of the Peronseus longus; its tendon is inserted into the lateral side of the base of the first phalanx of the fifth toe. Occasionally a few of the deeper fibers are inserted into the lateral part of the distal half of the fifth metatarsal bone; these are described by some as a distinct muscle, the Opponens digiti quinti. THE PLANTAR MUSCLES OF THE FOOT 495 The Fourth Layer. Interossei. The titerossei in the foot are similar to those in the hand, with this exception, that they are grouped around the middle line of the second digit, instead of that of the third. They are seven in number, and consist of two groups, dorsal and plantar. The Interossei dorsales (Dorsal interossei) (Fig. 446), /owr in number, are situated between the metatarsal bones. They are bipenniform muscles, each arising by two heads from the adjacent sides of the metatarsal bones between which it is placed ; their tendons are inserted into the bases of the first phalanges, and into the aponeurosis of the tendons of the Extensor digitorum longus. In the angular interval left between the heads of each of the three lateral muscles, one of the perforating arteries passes to the dorsum of the foot; through the space between the heads of the first muscle the deep plantar branch of the dorsalis pedis artery enters the sole of the foot. The first is inserted into the medial side of the second toe; the other three are inserted into the lateral sides of the second, third, and fourth toes. Fig. 446. — The Interossei dorsales. Left foot. Fio. 447. — -The Interossei plantares. Left foot. The Interossei plantares {Plantar interossei) (Fig. 447), three in nimiber, lie beneath rather than between the metatarsal bones, and each is connected with but one metatarsal bone. They arise from the bases and medial sides of the bodies of the third, fourth, and fifth metatarsal bones, and are inserted into the medial sides of the bases of the first phalanges of the same toes, and into the aponeuroses of the tendons of the Extensor digitorum longus. Nerves. — The Flexor digitorum brevis, the Flexor hallucis brevis, the Abductor hallucis, and the first Lumbricalis are supphed by the medial plantar nerve; all the other muscles in the sole of the foot by the lateral plantar. The first Interosseous dorsahs frequently receives an extra filament from the medial branch of the deep peroneal nerve on the dorsum of the foot, and the second Interosseous dorsahs a twig from the lateral branch of the same nerve. Actions. — AU the muscles of the" foot act upon the toes, and may be grouped as abductors, adductors, flexors, or extensors. The abductors are the Interossei dorsales, the Abductor hallucis, 496 ^^^MSmSm MYOLOGY ■ and the Abductor digiti quinti. The Interossei dorsales are abductors from an imaginary line passing through the axis of the second toe, so that the first muscle draws the second toe medijil- ward, toward the great toe, the second muscle draws the same toe lateralward, and the third and fourth draw the third and fourth toes in the same direction. Like the Interossei in the hand, each assists in flexing the first phalanx and extending the second and third phalanges. Tlie Abductor hallucis abducts the great toe from the second, and also flexes its proximal phalanx. In the same way the action of the Abductor digiti quinti is twofold, as an abductor of this toe from the fourth, and also as a flexor of its proximal phalanx. The adductors are the Interossei plantares and the Adductor hallucis. The Interossei plantares adduct the third, fourth, and fifth toes toward the imaginary Une passing through the second toe, and by means of their inser- tions into the aponeuroses of the Extensor tendons they assist in flexing the proximal phalanges and extending the middle and terminal phalanges. The oblique head of the Adductor hallucis is chiefly concerned in adducting the great toe toward the second one, but also assists in flexing this toe; the transverse head approximates all the toes and thus increases the curve of the trans- verse arch of the metatarsus. The ^xors are the Flexor digitorum brevis, the Quadrat us planta?, the Flexor hallucis brevis, the Flexor digiti quinti brevis, and the Lumbricales. The Flexor digitorum brevis flexes the second phalanges upon the first, and, continuing its action, flexes the first phalanges also, and brings the toes together. The Quadratus plants) assists the Flexor digi- torum longus and converts the obhque puU of the tendons of that muscle into a direct backward puU upon the toes. The Flexor digiti quinti brevis flexes the Uttle toe and draws its metatarsal bone downward and medialward. The Lumbricales, like the corresponding muscles in the hand, assist in flexing the proximal phalanges, and by their insertions into the tendons of the Extensor digitorum longus aid that muscle in straightening the middle and terminal phalanges. The Extensor digitorum brevis extends the first phalanx of the great toe and assists the long Extensor in extending the next three toes, and at the same time gives to the toes a lateral direction when they are extended. BIBLIOGRAPHY. Bardeen, C. R.: Development and Variation, etc., of the Inferior Extremity, etc.. Am. Jour. Anat., 1907, vi. Bardeen and Lewis: Development of the Back, Body Wall and Limbs in Man, Am. Jour. Anat., 1901, i. EiSLER, P.: Die Muskeln des Stammes, v. Bardeleben's Handbuch der Anatomic des MenscKen, Bd. ii, Abt. ii, Teil 1. FiCK, R.: Anatomie und Mechanik der Gelenke unter Benicksichtigimg der bewegenden Muskeln, v. Bardeleben's Handbuch der Anatomie des Menschen, Bd. ii, Abt. i, Teil 2 and 3. Frohse and Frankel: Die Muskeln des Menschlichen Beines; Die Muskeln des Menschlichen Armes, Handbuch der Anatomie des Menschen, von Bardeleben, Bd. ii, Abt. ii, Teil 2, A and B. Henle, J.: Handbuch der Systematischen Anatomie des Menschen, 1871-79. Koch, J. C: The Laws of Bone Architecture, Am. Jour. Anat., 1917, xxi. Le Double: Traits des Variations du Systeme Musculaire de L'Homme, 1897. Lewis, W. H.: Development of the Arm in Man, Am. Jour. Anat., 1901, i. Lewis, W. H.: Development of the Muscular System, Keibel and Mall, Manual of Human Embryology. PoiRiER, P., et Charpy, a.: Traits d' Anatomie, 1899-1901. TbsTUT, L. : Traite d' Anatomie Humaine. 1893-94. Wolff, J. : Das Gesetz der Transformation der Knochen, Berlin, 1892. ANGIOLOGY. ''PHE vascular system is divided for descriptive purposes into (a) the blood J- vascular system, which comprises the heart and bloodvessels for the circula- tion of the blood; and (6) the Ijrmph vascular system, consisting of lymph glands and lymphatic vessels, through which a colorless fluid, the lymph, circulates. It must be noted, however, that the two systems communicate with each other and |9,re intimately associated developmentally. t The heart is the central organ of the blood vascular system, and consists of a hollow muscle; by its contraction the blood is pumped to all parts of the body through a complicated series of tubes, termed arteries. The arteries undergo enormous ramification in their course throughout the body, and end in minute vessels, called arterioles, which in their turn open into a close-meshed network of microscopic vessels, termed capillaries. After the blood has passed through the capillaries it is collected into a series of larger vessels, called veins, by which it is returned to the heart. The passage of the blood through the heart and blood- vessels constitutes what is termed the circulation of the blood, of which the following is an outline. The human heart is divided by septa into right and left halves, and each half is further divided into two cavities, an upper termed the atrium and a lower the ventricle. The heart therefore consists of four chambers, two, the right atrium and right ventricle, forming the right half, and two, the left atrium and left ventricle the left half. The right half of the heart contains venous or impure blood; the left, arterial or pure blood. The atria are receiving chambers, and the ventricles dis- tributing ones. From the cavity of the left ventricle the pure blood is carried into a large artery, the aorta, through the numerous branches of which it is distributed to all parts of the body, with the exception of the lungs. In its passage through the capillaries of the body the blood gives up to the tissues the materials necessary for their growth and nourishment, and at the same time receives from the tissues the waste products resulting from their metabolism. In doing so it is changed from arterial into venous blood, which is collected by the veins and through them returned to the right atrium of the heart. From this cavity the impure blood passes into the right ventricle, and is thence conveyed through the pulmonary arteries to the lungs. In the capillaries of the lungs it again becomes arterialized, and is then carried to the left atrium by the pulmonary veins. From the left atrium it passes into the left ventricle, from which the cycle once more begins. The course of the blood from the left ventricle through the body generally to the right side of the heart constitutes the greater or systemic circulation, while its passage from the right ventricle through the lungs to the left side of the heart is termed the lesser or pulmonary circulation. It is necessary, however, to state that the blood which circulates through the spleen, pancreas, stomach, small intestine, and the greater part of the large intes- tine is not returned directly from these organs to the heart, but is conveyed by the portal vein to the liver. In the liver this vein divides, like an artery, and ultimately ends in capillary-like vessels (sinusoids), from which the rootlets of a series of veins, called the hepatic veins, arise; these carry the blood into the inferior vena cava, 32 (497) 498 ANGIOLOGY I whence it is conveyed to the right atrium. From this it will be seen that the blood contained in the portal vein passes through two sets of vessels: (1) the capillaries in the spleen, pancreas, stomach, etc., and (2) the sinusoids in the liver. The blood in the portal vein carries certain of the products of digestion : the carbo- hydrates, which are mostly taken up by the liver cells and stored as glycogen, and the protein products which remain in solution and are carried into the general circulation to the various tissues and organs of the body. Speaking generally, the arteries may be said to contain pure and the veins impure blood. This is true of the systemic, but not of the pulmonary vessels, since it has been seen that the impure blood is conveyed from the heart to the lungs by the pulmonary arteries, and the pure blood returned from the lungs to the heart by the pulmonary veins. Arteries, therefore, must be defined as vessels which convey blood from the heart, and veins as vessels which return blood to the heart. Structure of Arteries (Fig. 448). — The arteries are composed of three coats: an internal or endothelial coat {tunica intima of Kolliker); a middle or muscular coat {tunica media); and an external or connective-tissue coat {tunica adventitia). The two inner coats together are very easily separated from the external, as by the ordinary operation of tying a ligature around an artery. If a fine string be tied forcibly upon an artery and then taken off, the external coat will be found undivided, but the two inner coats are divided in the track of the ligature and can easily be further dissected from the outer coat. The inner coat {tunica intima) can be separated from the middle by a little maceration, or it may be stripped off in small pieces; but, on account of its friability, it cannot be separated as a complete mem- brane. It is a fine, transparent, colorless structure which is highly elastic, and, after death, is commonly corrugated into longitudinal wrinkles. The inner coat consists of: (1) A layer of pavement endothelium, the cells of which are polygonal, oval, or fusiform, and have very distinct round or oval nuclei. This endothelium is brought into view most distinctly by staining with nitrate of silver. (2) A subendothelial layer, consisting of deUcate connective tissue with branched cells lying in the interspaces of the tissue; in arteries of less than 2 mm. in diameter the sub- endothelial layer consists of a single stratum of stel- late cells, and the connective tissue is only largely developed in vessels of a considerable size. (3) An elastic or fenestrated layer, which consists of a mem- brane containing a net-work of elastic fibers, having principally a longitudinal direction, and in which, imder the microscope, small elongated apertures or perforations may be seen, giving it a fenestrated ap- pearance. It was therefore called by Henle the fenes- trated membrane. This membrane forms the chief thickness of the inner coat, and can be separated into several layers, some of which present the appearance of a net-work of longitudinal elastic fibers, and others a more membranous character, marked by pale lines having a longitudinal direction. In minute arteries the fenestrated membrane is a very thin layer; but in the larger arteries, and especially in the aorta, it has a very considerable thickness. The middle coat {tunica media) is distinguished from the inner by its color and by the trans- verse arrangement of its fibers. In the smaller arteries it consists principally of plain muscle fibers in fine bundles, arranged in lamellae and disposed circularly around the vessel. These lamellae vary in number according to the size of the vessel; the smallest arteries having only a single layer (Fig. 449), and those slightly larger three or four layers. It is to this coat that the thickness of the wall of the artery is mainly due (Fig. 448^, m). In the larger arteries, as the Fig. 448. — Transverse section through a small artery and vein of the mucous membrane of the epiglottis of a child. X 350. (Klein and Noble Smith.) A. Artery, showing the nucleated endo- thelium, e, which lines it; the vessel being con- tracted, the endothelial cells appear very thick. Underneath the endothelium is the wavy elastic lamina. _ The chief part of the wall of the vessel is occupied by the circular muscle coat m; the rod-shaped nuclei of the muscle cells are well seen. Outside this is o, part of the adventitia. This is composed of bundles of connective tissue fibers, shown in section, with the nuclei of the connec- tive tissue corpuscles. The adventitia gradually merges into the surrounding connective tissue. V. Vein showing a thin endothelial membrane, e, raised accidentally from the intima, which on account of its delicacy is seen as a mere line on the media m. This latter is composed of a few circular unstriped muscle cells o. The adventitia, similar in structure to that of an artery. STRUCTURE OF ARTERIES 499 I iliac, femoral, and carotid, elastic fibers unite to form lamellae which alternate with the layers of muscular fibers; these lamellae are united to one another by elastic fibers which pass between the muscular bundles, and are connected with the fenestrated membrane of the inner coat (Fig. ■ 450). In the largest arteries, as the aorta and innominate, the amount of elastic tissue is very JBonsiderable; in these vessels a few bundles of white connective tissue also have been found in the middle coat. The muscle fiber cells are about oOu in length and contain well-marked, rod- shaped nuclei, which are often slightly curved. The external coat (tunica adventitia) consists mainly of fine and closely felted bundles of white connective tissue, but also contains elastic fibers in all but the smallest arteries. The elastic tissue is much more abundant next the tunica media, and it is sometimes described as forming here, between the adventitia and media, a special layer, the tunica elastica externa of Henle. This layer is most marked in arteries of medium size. In the largest vessels the external coat is relatively thin; but in small arteries it is of greater proportionate thickness. In the smaller arteries it consists of a single layer of white connec- tive tissue and elastic fibers; while in the smallest arteries, just above the capillaries, the elastic fibers are wanting, and the connective tissue of which the coat is composed becomes more nearly homogeneous tlie nearer it approaches the capillaries, and is grad- ually reduced to a thin membranous envelope, which finally disappears. Some arteries have extremely thin walls in propor- tion to their size; this is especially the case in those situated in the cavity of the cranium and vertebral canal, the difference depending on the thinness of the external and middle coats. The arteries, in their distribution throughout the body, are included in thin fibro-areolar investments, which form their sheaths. The vessel is loosely con- nected with its sheath by delicate areolar tissue; and the sheath usually encloses the accompanying veins, and sometimes a nerve. Some arteries, as those in the cranium, are not included in sheaths. All the larger arteries, like the other organs of the body, are supplied with bloodvessels. These nutrient vessels, called the vasa vasorum, arise from a branch of the artery, or from a neighbor- ing vessel, at some considerable distance from the point at which they are distributed; they ramify in the loose areolar tissue connecting the artery with its sheath, and are distributed to the external coat, but do not, in man, penetrate the other coats; in some of the larger mammals a few vessels have been traced into the middle coat. Minute veins return the blood from these vessels; they empty themselves into the vein or veins accompanying the artery. Lymphatic H ^essels are also present in the outer coat. m W Arteries are also supplied with nerves, which are derived from the sympathetic, but may pass through the cerebrospinal nerves. They form intricate plexuses upon the surfaces of the larger trunks, and run along the smaller arteries as single filaments, or bundles of filaments which twist around the vessel and unite with each other in a plexiform manner. The branches derived from these plexuses penetrate the external coat and are distributed principally to the muscular tissue of the middle coat, and thus regulate, by causing the contraction and relaxation of this tissue the amount of blood sent to any part. H ■ The Capillaries. — The smaller arterial branches (excepting those of the cavernous structure ■ fof the sexual organs, of the splenic pulp, and of the placenta) terminate in net-works of vessels which pervade nearly every tissue of the body. These vessels, from their minute size, are termed capillaries. They are interposed between the smallest branches of the arteries and the commenc- ing veins, constituting a net-work, the branches of which maintain the same diameter throughout; the meshes of the net-work are more uniform in shape and size than those formed by the anasto- moses of the small arteries and veins. The diameters of the capillaries vary in the different tissues of the body, the usual size being about 8,u. The smallest are those of the brain and the mucous membrane of the intestines; and the largest those of the skin and the marrow of bone, where they are stated to be as large as 20/x in diameter. The form of the capillary net varies in the different tissues, the meshes being generally rounded or elongated. The rounded form of mesh is most common, and prevails where there is a dense network, as in the lungs, in most glands and mucous membranes, and in the cutis; the meshes are not of an absolutely circular outhne, but more or less angular, sometimes nearly quadrangular, or polygonal, or more often irregular. Fia. 449. — Small artery and vein, pia mater of sheep. X 250. Surface view above the inter- rupted line; longitudinal section below. Artery in red; vein in blue, I- 500 ANGIOLOGY I Elongated meshes are observed in the muscles and nerves, the meshes resembling parallelograms in form, the long axis of the mesh running parallel with the long axis of the nerve or muscle. Sometimes the capillaries have a looped arrangement; a single vessel projecting from the common net-work and returning after forming one or more loops, as in the papillse of the tongue ar.d skin. The number of the capillaries and the size of the meshes determine the degree of vascularity of a part. The closest network and the smallest interspaces are found in the lungs and in the choroid coat of the eye. In these situations the interspaces are smaller than the capillary vessels themselves. In the intertubular plexus of the kidney, in the conjunctiva, and in the cutis, the interspaces are from three to four times as large as the capillaries which form them; and in the brain from eight to ten times as large as the capillaries in their long diameters, and from four to six times as large in their transverse diameters. In the adventitia of arteries the width of the meshes is ten times that of the capillary vessels. As a general rule, the more active the funo tion of the organ, the closer is its capillary net and the larger its supply of blood; the meshes of the network are very narrow in all growing parts, in the glands, and in the mucous membranes, wider in bones and Ugaments which are comparatively inactive; bloodvessels are nearly alto- gether absent in tendons, in which very little organic change occurs after their formation. In the liver the capillaries take a more or less radial course toward the intralobular vein, and their walls are incomplete, so that the blood comes into direct contact with the liver cells. These vessels in the liver are not true capillaries but "sinusoids;" they are developed by the growth of columns of liver cells into the blood spaces of the embryonic organ. Endothelial and svb- endothelial layer of inner coat Elastic layer Innermost layers of middle coat Outermost layers of middle coat Innermost part of outer coat Outermost part of outer coat Fig. 450. — Section of a medium-sized artery. (After Grilnstein.) Structure. — The wall of a capillary consists of a fine transparent endothelial layer, composed of ceUs joined edge to edge by an interstitial cement substance, and continuous with the endo- thelial cells which hne the arteries and veins. When stained with nitrate of silver the edges which boimd the epithehal ceUs are brought into view (Fig. 451). These cells are of large size and of an irregular polygonal or lanceolate shape, each containing an oval nucleus which may be dis- played by carmine or hematoxyhn. Between their edges, at various points of their meeting, roundish dark spots are sometimes seen, which have been described as stomata. though they are closed by intercellular substance. They have been beUeved to be the situations through which the colorless corpuscles of the blood, when migrating from the bloodvessels, emerge; but this view, though probable, is not universally accepted. Kolossow describes these cells as having a rather more complex structvu-e. He states that I STRUCTURE OF VEINS 501 each consists of two parts: of hyaline ground plates, and of a protoplasmic granular part, in which is imbedded the nucleus, on the outside of the ground plates. The hyaline internal coat of the capillaries does not form a complete membrane, but consists of "plates" which are inelastic, tand though in contact with each other are not continuous; when therefore the capillaries are sub- jected to intravascular pressure, the plates become separated from each other; the protoplasmic portions of the cells, on the other hand, are united together. In some organs, e. g., the glomeruH of the kidneys, intercellular cement cannot be demonstrated in the capillary wall and the cells are beheved to form a syncytium. In many situations a delicate sheath or envelope of branched nucleated connective tissue cells is found around the simple capillary tube, particularly in the larger ones; and in other places, especially in the glands, the capillaries are invested with retiform connective tissue. Sinusoids. — In certain organs, viz., the heart, the Uver, the suprarenal and parathyroid glands, the glomus caroticum and glomus coccygeum, the smallest bloodvessels present various differences from true capillaries. They are wider, with an irregular lumen, and have no connective tissue covering, their endothehal cells being in direct contact with the cells of the organ. Moreover, they are either arterial or venous and not intermediate as are the true capillaries. These vessels have been called sinusoids by Minot. They are formed by columns of cells or trabeculae pushing their way into a large bloodvessel or blood space and carrying its endothe- lium before them; at the same time the wall of the vessel or space grows out between the cell columns. Structure of Veins.— The veins, like the arteries, are com- posed of three coats: internal, middle, and external; and these coats are, with the necessary modifications, analogous to the coats of the arteries; the internal being the endo- thehal, the middle the muscular, and the external the connective tissue or areolar (Fig. 452). The main differ- ence between the veins and the arteries is in the compara- tive weakness of the middle coat in the former. In the smallest veins the three coats are hardly to be dis- tinguished (Fig. 449). The endothelium is supported on a membrane separable into two layers, the outer of which is the thicker, and consists of a delicate, nucleated mem- brane (adventitia) , while the inner is composed of a network of longitudinal elastic fibers (media). In the veins next above these in size (0.4 mm. in diameter), according to Kolhker, a connective tissue layer containing numerous muscle fibers circularly disposed can be traced, forming the middle coat, while the elastic and connective tissue elements of the outer coat become more distinctly perceptible. In the middle-sized veins the typical structure of these vessels becomes clear. The endothelium is of the same character as in the arteries, but its cells are more oval and less fusiform. It is supported by a connective tissue layer, consisting of a deUcate net-work of branched cells, and external to this is a layer of elastic fibers disposed in the form of a net-work in place of the definite fenestrated membrane seen in the arteries. This constitutes the internal coat. The middle coat is composed of a thick layer of con- nective tissue with elastic fibers, intermixed, in some veins, with a transverse layer of muscular tissue. The white fibrous element is in considerable excess, and the elastic fibers are in much smaller proportion in the veins than in the arteries. The outer coat consists, as in the arteries, of areolar tissue, with longitudinal elastic fibers. In the largest veins the outer coat is from two to five times thicker than the middle coat, and contains a large number of longitudinal muscular fibers. These are most distinct in the inferior vena cava, especially at the termination of this vein in the heart, in the trunks of the hepatic veins, in all the large tnmks of the portal vein, and in the external iliac, renal, and azygos veins. In the renal and portal veins they extend through the whole thickness of the outer coat, but in the other veins mentioned a layer of con- nective and elastic tissue is found external to the muscular fibers. All the large veins which open into the heart are covered for a short distance with a layer of striped muscular tissue continued on to them from the heart. Muscular tissue is wanting: (1) in the veins of the maternal part of the placenta; (2) in the venous sinuses of the dura mater and the veins of the pia mater of the brain and medulla spinaUs; (3) in the veins of the retina; (4) in the veins of the cancellous tissue of bones; (5) in the venous spaces of the corpora cavernosa. The veins of the above-men- tioned parts consist of an internal endothehal lining supported on one or more layers of areolar tissue. Most veins are provided with valves which serve to prevent the reflux of the blood. Each valve is formed by a reduplication of the inner coat, strengthened by connective tissue and elastic Fig. 451.— Capillaries from the mesen- tery of a guinea-pig, after treatment with solution of nitrate of silver, a. Cells. b. Their nuclei. 502 ANGIOLOGY I fibers, and is covered on both surfaces with endothehum, the arrangement of which differs on the two surfaces. On the surface of the valve next the wall of the vein the cells are arran^^ed transversely; while on the other surface, over which the current of blood flows, the cells are arranged longitudinally in the direction of the current. Most commonly two such valves are found placed opposite one another, more especially in the smaller veins or in the larger trunks at the point where they are joined by smaller branches; occasionally there are three and some- times only one. The valves are semilunar. They are attached by their convex edges to the wall of the vein; the concave margins are free, directed in the course of the venous current, and Ue in close apposition with the wall of the vein as long as the current of blood takes its natural course; if, however, any regurgitation takes place, the valves become distended, their opposed edges are brought into contact, and the current is interrupted. The wall of the vein on the cardiac side of the point of attachment of each valve ia expanded into a pouch or sinus, which gives to the vessel, when injected or distended with blood, a knotted appearance. The valves are very numerous in the veins of the extremities, especially of the lower extremities, these vessels Endothelium • - . Elastic layer x-^' Middle coat — — rft '0^'::% Ovier coat ?^ Fig. 452. — Section of a medium-sized vein. having to conduct the blood against the force of gravity. They are absent in the very small veins, i. e., those less than 2 mm. in diameter, also in the venae cavse, hepatic, renal, uterine, and ovarian veins. A few valves are found in each spermatic vein, and one also at its point of junc- tion with the renal vein or inferior vena cava respectively. The cerebral and spinal veins, the veins of the cancellated tissue of bone, the pulmonary veins, and the umbihcal vein and its branches, are also destitute of valves. A few valves are occasionally found in the azygos and intercostal veins. Rudimentary valves are found in the tributaries of the portal venous system. The veins, like the arteries, are supplied with nutrient vessels, vasa vasortun. Nerves also are distributed to them in the same manner as to the arteries, but in much less abundance. THE BLOOD. The blood is an opaque, rather viscid fluid, of a bright red or scarlet color when it flows from the arteries, of a dark red or purple color when it flows from the veins. It is salt to the taste, and has a peculiar faint odor and an alkaline reaction. Its specific gravity is about 1.06, and its temperature is generally about 37° C, though varying slightly in different parts of the body. THE BLOOD 503 I General Composition of the Blood. — Blood consists of a faintly yellow fluid, the plasma or liquor sanguinis, in which are suspended numerous minute particles, the blood corpuscles, the majority of which are colored and give to the blood its ;red tint. If a drop of blood be placed in a thin layer on a glass slide and examined under the microscope, a number of these corpuscles will be seen floating in the plasma 6 of Fig. 453. — Human red blo