cAn Americanized Fourth Edition Rewritten and Revised M. A Comple Consulting , Lecturer < Middlesex Examine* Durham^ , For the omists have revise sectic important r the United !: its widening students. Among t R. J. Terry, Bardeen an< W. H. A. Ja The text will be fou clature (BN to the illust] been very m Conta Hands $7.00, PART I. PART II. PART III. PART IV. MEDICAL SCHOOL VON WERTHERN LEL10RIAL 1.50. $2.00. ^v-ivwuo Astern, wigctus ui opeciai ^ense. inaex. $1.50. Organs of Digestion; of Voice and Respiration. Urinary PART and Reproductive Organs. Ductless Glands. Skin and Mammary Glands. Index. $1.50. V. Surgical and Topographical Anatomy. Index. $1.00. P. BLAKISTON'S SON & CO., Publishers and Booksellers 5-4 09 1012 WALNUT STREET, PHILADELPHIA 'TYSON. The Practice of Medicine. Fourth Revised Editltn. A Text-Book for Physicians and Students, with Special Reference to Diagnosis and Treatment. By JAMES TYSON, M.D., Professor of Medicine in the University of Pennsylvania, and Physician to the Hospital of the University ; Physician to the Pennsylvania Hospital, etc. Fourth Edition, Revised and Enlarged. Colored Plates and 240 other Illustrations, 1 3 of which are in Colors. 8vo. Just Ready. Cloth, $5.50; Leather or Half Morocco, $6.50 edition contains 100 new illustrations and has been increased in size by 65 pages. It includes a Special Article on Animal Parasites and the Conditions Caused by them, by ALLEN J. SMITH, M.D., Professor of Pathology, University of Pennsylvania. BY THE SAME AUTHOR. Blight's Disease and Diabetes. New Edition. Colored Plates. Including Articles on Ocular Manifestations in these Diseases by G. E. DE SCHWEINITZ, A.M., M.D., Professor of Ophthalmology in the University of Pennsylvania ; Ophthalmic Surgeon to the Philadelphia Hospital. Second Edition, Revised and Rewritten. 7 Colored Plates and other Illustrations. Octavo. Cloth, $4.00 ; Half Morocco, $5.00 Guide to the Examination of Urine. Tenth Edition. For the Use of Physicians and Students. With Colored Plate and Numerous Illustrations Engraved on Wood. Tenth Edition, Revised, Enlarged and partly Rewritten. I2mo. Cloth, $1.50 Handbook of Physical Diagnosis. Fourth Edition. Fourth Edition, Revised and Enlarged. With two Colored Plates and 5 5 other Illustrations. 298 pages. 1 2mo. Cloth, $1.50 Cell Doctrine. Its History and Present State. Second Edition. Cloth, $1.50 P. BLAKISTON'S SON & CO., Publishers and Booksellers 1012 WALNUT STREET, PHILADELPHIA JS^T BASED ON RECENT MEDICAL LITERATURE. The Standard Medical Reference Books. Dictionaries. 25 0,000 HAVE: BEEN SOLD INCLUDING THE PRONUNCIATION, ACCENTUATION, DERI- VATION, AND DEFINITION OF THE TERMS USED IN MEDI- CINE AND THOSE SCIENCES COLLATERAL TO IT. WITH MANY USEFUL TABLES. By GEORGE M. GOULD. A.M.. M.D.. Editor of American Medicine. The Illustrated Dictionary of Medicine, Biology and Allied Sciences. 1633 pages. Fifth Edition. Sheep or Half Morocco, $10.00; with Thumb Index, $11.00 Half Russia, Thumb Index, $12.00 Dictionary of New Medical Terms. Being a Supplement to " Gould's Illustrated Dictionary," consisting of upwards of 571 double-column pages and containing many thousand new terms and definitions. Sheep or Half Morocco, $5.00; with Thumb Index, $6.00 Half Russia, Thumb Index, $7.00 The Above Two Books bound in One Volume, Hal} Morocco, $15.00 The Practitioner's Medical Dictionary. Illustrated. Octavo, xvi + 1043 pages. Just Ready. Flexible Leather, Gilt Edges, $5.00; Thumb Index, $6.00 The Medical Student's Dictionary. Eleventh Edition. Enlarged and illustrated with a large number of Engravings. 840 pages. Half Morocco, $2.50; with Thumb Index, $3.00 Flexible Leather, Burnished Edges, Thumb Index, $3.50 The Pocket Pronouncing Medical Lexicon. (30,000 Medical Words Pronounced and Defined.) Fourth Edition, Revised and Enlarged. 838 pages. Flexible Leather, Gilt Edges, $1.00; Thumb Index, $1.25 250,000 Copies of Gould's Dictionaries Have Been Sold. P. BLAKISTON'S SON & CO., Publishers and Booksellers 1012 WALNUT STREET. PHILADELPHIA HISTOLOGY RADASCH From The Southern Clinic: " We know of no series of books issued by any house that so fully meets our approval as these ? Quiz-Compends ?. They are well arranged, full, and concise, and are really the best line of text-books that could be found for either student or practitioner." BLAKISTON'S ? QUIZ-COMPENDS ? The Best Series of Manuals for the Use of Students. Price of each, Cloth, $1.00 net. Interleaved, for taking Notes, $1.25 net. ng advantage. ge. Can be used by students of any college. They contain over 900 Illustrations. They contain information nowhere else collected in such a condensed, l shae. practical shape. Illustrated Circular Free. POTTER'S ANATOMY. Seventh Revised and Enlarged Edition. Including Vis- ceral Anatomy. Can be used with either Morris' or Gray's Anatomy. 138 Illus- trations and 1 6 Plates of Nerves and Arteries, with Explanatory Tables, etc. BRUBAKER. PHYSIOLOGY. Twelfth Edition, with Illustrations and a Table of Physiological Constants. Enlarged and Revised. LANDIS. OBSTETRICS. Eighth Edition. Revised and Edited by WM. H. WELLS. M. i)., Instructor Jefferson Medical College, Philadelphia. 56 Illustrations. POTTER. MATERIA MEDICA, THERAPEUTICS, AND PRESCRIPTION WRIT- ING. Seventh Revised Edition. WELLS. GYNECOLOGY. Third Edition. With 145 Illustrations. GOULD and PYLE. DISEASES OF THE EYE AND REFRACTION. Including Treatment and Operations and a Section on Local Therapeutics. With formula and 109 Illustrations, several of which are in Colors. Third Edition. HORWITZ'S SURGERY, Minor Surgery, and Bandaging. Sixth Edition. Enlarged and Improved. With 104 Formulae and 195 Illustrations. LEFFMANN. CHEMISTRY, Inorganic and Organic. Fifth Edition. Including Urinalysis, Animal Chemistry, Chemistry of Milk, Blood, Tissues, the Secre- tions, etc. STEWART. PHARMACY. Seventh Edition. Based upon Prof. Remington's Text-book of Pharmacy. BALLOU. VETERINARY ANATOMY AND PHYSIOLOGY. With 29 graphic Illustrations. WARREN. DENTAL PATHOLOGY AND DENTAL MEDICINE. Fourth Edition. Illustrated. Containing all the most noteworthy points of interest to the Dental Student, and a Section on Emergencies. HATFIELD. DISEASES OF CHILDREN. Colored Plate. Third Edition. Revised and Enlarged. ST. CLAIR. MEDICAL LATIN. Second Edition. SCHAMBERG. DISEASES OF THE SKIN. Fourth Edition. Revised and En- larged. 1 08 Illustrations. RADASCH. HISTOLOGY. Second Edition. With 107 Illustrations. THAYER. SPECIAL PATHOLOGY. With 34 Illustrations. KYLE. EAR, NOSE, AND THROAT. 85 Illustrations. HIRSCH. GENITO-URINARY AND VENEREAL! DISEASES AND SYPHILIS. 71 Illustrations. PITTFIELD. BACTERIOLOGY. 136 Illustrations. BLAKISTON'S ? QUIZ-COMPENDS.? A COMPEND OF . HISTOLOGY BY HENRY ERDMANN|RADASCH, M.S., M. D. ASSOCIATE IN HISTOLOGY AND EMBRYOLOGY AND DEMONSTRATOR OP VISCERAL ANATOMY IX THE JEFFERSON MEDICAL COLLEGE; ADJUNCT PROFESSOR OF PHYSIOLOGY AND INSTRUCTOR IN HISTOLOGY IN THE PENNSYLVANIA COLLEGE OF DENTAL SURGERY SECOND EDITION, REVISED AND ENLARGED WITH ONE HUNDRED AND SEVEN ILLUSTRATIONS _., ^ PHILADELPHIA P. BLAKISTON'S SON & CO. 1012 WALNUT STREET 1909 COPYRIGHT, 1909, BY P. BLAKISTON'S SON & Co. Printed by The Maple Press, York, Pa. TO PROFESSOR W. M. L. COPLIN THIS VOLUME IS AFFECTIONATELY DEDICATED 47016 PREFACE TO SECOND EDITION. The call for a second edition has made it possible to make changes arid additions in the text. In the Circulatory System additions were made, among the most important of which are the Bundle of His, Hemo- lymphnodes and the Parasympathetic Bodies. Part of the chapter on the Nerve System was rewritten and several cuts were added. In order to make this book of greater use to the dental students, the Histology of the Tooth was rewritten and en- larged upon, and a new chapter on the Development of the Face and Teeth, with appropriate cuts, was added. The writer desires to thank the teachers and students who have seen fit to use this work, and he hopes that the present edition will meet with the same satisfaction. 914 SOUTH FORTY- SEVENTH STREET, PHILADELPHIA, October, 1909. Vll PREFACE TO FIRST EDITION. IT has been the author's purpose to supply a volume more complete than the existing compends, and yet not so voluminous as a Text-book. An effort has been made to present the matter in a clear and concise manner, and as up-to-date as possible. The subject of Embryology has been touched upon only in so far as it bears directly upon the Histology. The chapter on Technic has been made as complete as is necessary for routine histologic and pathologic work. The Connective Tissues have been grouped in what seems a simple and also characteristic manner. The Blood Cells have also been arranged in a simple and readily-compre- hended form. The chapter on Placenta and Umbilical Cord has, how- ever, been written somewhat in detail, as the embryology of these organs is essential for a thorough knowledge of their structure. The illustrations are from the works of Prof. Minot, to whom the writer is indebted for their use. The forty-seven new cuts were prepared ^nder the direction of Dr. H. H. Cushing. Of these, twenty-seven are from slides, while the remainder represent modifications of current Text-book figures. The writer desires to thank Dr. R. C. Rosenberger for his assistance in proof-reading and suggestions, and the publishers for their many kindnesses and courtesies. 914 SOUTH FORTY-SEVENTH STREET, PHILADELPHIA. CONTENTS. CHAPTER I. Technic . CHAPTER II. The Cell ' 3 1 CHAPTER III. The Tissues Epithelial Tissues 45 CHAPTER IV. Connective Tissues 58 CHAPTER V. Muscle Tissues . . . 78 CHAPTER VI. Nerve Tissues 84 CHAPTER VII. Circulatory System 96 CHAPTER VIII. Lymphatic System 112 CHAPTER IX. Alimentary Tract 1 18 CHAPTER X. Digestive Glands 148 xi xii CONTENTS. CHAPTER XL PAGE Respiratory System and Thyroid Body 159 CHAPTER XII. Urinary System and Adrenal 171 CHAPTER XIII. Male Genital System 186 CHAPTER XIV. Female Genital System 201 CHAPTER XV. Placenta and Umbilical Cord 217 CHAPTER XVI. Skin and Its Appendages 230 CHAPTER XVII. Nerve System ' 245 CHAPTER XVIII. Eyeball and Lacrimal Apparatus 274 CHAPTER XIX. The Ear 298 CHAPTER XX. The Senses of Smell, Taste and Touch 311 CHAPTER XXI. Development of Face and Teeth 318 INDEX 333 LIST OF ILLUSTRATIONS. 1. The Cell 32 2. Karyokinesis,' Close Coil 35 3. Karyokinesis, Loose Coil 36 4. Karyokinesis, Equatorial Plate 37 5. Karyokinesis, Nuclear Spindle 38 6. Karyokinesis, Daughter Stars 39 7. Karyokinesis, Daughter Cells 39 8. Unripened Ovum of a Young Guinea-pig 41 9. Simple Squamous and Cuboidal Epithelial Cells 46 10. Squamous Cells of Frog's Skin (surface view) 46 11. Squamous Cell, Isolated 46 12. Stratified Squamous Epithelium 46 13. Simple Columnar, Ciliated and Goblet Cells 47 14. Isolated Columnar and Ciliated Cells; Goblet Cells in Various Stages 47 1 5. Pseudostratified Cells 48 1 6. Stratified Columnar, Ciliated and Goblet Cells 49 17. Transitional Cells 49 1 8. Various Forms of Endothelial Cells 50 19. Simple Tubular Gland from Large Intestine 54 20. Diagram of Tubular Glands 55 21. Diagram of Alveolo-tubular Glands 55 22. Diagram of Alveolar Glands 56 23. Varieties of Connective Tissue 60 24. White Fibrous Tissue 63 2 5. Varieties of Cartilage 68 26. Cross-section of Compact Bone 71 27. Cross- section of Developing Bone 76 28. Varieties of Muscle Tissue 80 29. Nerve Cells and Fibres 88 30. Tactile Cells 90 31. Corpuscle of Meissner 91 32. Pacinian Body 92 xiii XIV LIST OF ILLUSTRATIONS. FIGURE PAGE 33. Tendon-spindle 93 34. Motor Nerve-endings 94 35. Cross-section of a Medium-sized Artery 100 36. Cross-section of a Vein 103 37. Forms of Blood Cells 105 38. Hemin Crystals 109 39. Hemoglobin Crystals iog 40. Section of a Human Lymph Node 113 41. Section of the Spleen 115 42. Section of the Thymus Body 117 43. Longitudinal Section of a Tooth 121 44. Cross-section of the Tongue 128 45. Vertical Section of a Human Tonsil 130 46. Cross-section of a Human Esophagus . . . 132 47. Section of the Cardiac End of the Stomach 135 48. Section of the Pyloric End of the Stomach . 137 49. Section of the Duodenum 139 50. Longitudinal Section of a Villus 140 51. Cross- section of the Ileum 141 52. Cross-section of the Colon 143 53. Cross- section of the Human Appendix 14 ^ 54. Section of Pig's Liver 1 4MI:S (Stohr's Histology). When a nerve system is present, this presides over such changes which are then secondary. Reproduction is the process by means of which a cell or an organism propagates itself and continues its life history. Without this or an analogous process, life would soon cease to exist. It is of two varieties, DIRECT, AMITOSIS or BUDDING and INDIRECT, MITOSIS or KARYOKINESIS. Of these, the latter is the more common. In Amitosis, the cell-body is marked by a constriction that gradually deepens and is imparted to the nucleus. CELL-DIVISION. 37 As tnis deepens, the protoplasm and nucleus are- finally divided into two small but practically equal cells, which have the same structure as the parent cell. By growth, these cells, which are called daughter cells, increase in size, until that of the parent, or mother, cell is attained. This form of division is seen in the bladder epithelium in mammals and in the cells of Sertoli of the testicle. Mitosis is a very complex process, in which the nucleus plays a very important part. The protoplasm is almost Polar radiation. Central spindle. FIG. 4. SCHEME OF THE MOTHER STAR, OR EQUATORIAL PLATE (Stohr's Histology). passive until the late stages of the process. The various stages are the PROPHASE, METAPHASE, ANAPHASE and TELOPHASE. These are not absolutely separable from one another. The changes that occur may be grouped under three heads nuclear, centrosomic and protoplasmic. PROPHASE. The nuclear changes are quite complex. Whereas the chromatin is ordinarily arranged as an ir- regular network, when division begins the irregular twigs of the network gradually become smooth, and form, usually, a single thin closely-convoluted thread, called the SPIREM, or SKEIN. The thread becomes thicker and shorter, 30 HISTOLOGY. and soon separates into a number of segments called CHROMOSOMES. This sometimes occurs before the spirem is formed. The chromosomes become U- or V-shaped, and arrange themselves along the equator of the cell w r ith the closed ends directed toward a common center, called the polar field. This arrangement is termed the EQUATORIAL PLATE, or MONASTER, and practically ends the chromatin changes during the PROPHASE. FIG. 5. SCHEME OF METAKINESIS, SHOWING THE NUCLEAR SFINDI i: (Stohr's Histology'). The CHROMOSOMES are always even in number, and the same number is always formed in each cell of the same species. In man, the number is said to be sixteen or twenty-four. The nuclear membrane, during these changes, has gradu- ally become more and more hazy, and finally disappears. The achromatin is released, and mixes with the protoplasm. The nucleolus likewise gradually fades and disappears. The centrosome is the dynamic center of * the cell. It di- vides into two portions (if within the nucleus, it passes first into the protoplasm), each of which becomes surrounded by its own attraction sphere. These centrosomes gradually move apart, through an arc of 90, to opposite poles of the cell. During this change, some of the intervening rays remain in KARYOKINESIS. 39 contact, forming a spindle of delicate threads, which is com- plete when the centrosomes reach their polar position. This is the CENTRAL, or ACHROMATIC SPINDLE, and the threads are of the utmost importance, and become attached to the chromosomes of the equatorial plate. With the formation of the equatorial plate and central spindle, the PROPHASE ends. Variations, too numerous to describe, occur, but the above is the usual course in this stage of mitosis. FIG. 6. SCHEME OF THE DAUGHTER FIG. 7. SCHEME OF DIVISION OF STARS THE PROTOPLASM FORMING DAUGHTER CELLS. (Stohr's Histology}. METAPHASE. This is the stage during which the chromo- somes divide and separate. It concerns the chromatin chiefly. The chromosome divide longitudinally into two equal portions. This cleavage occurs at the closed end first, and as it proceeds, the daughter chromosomes become separated, one-half being drawn toward the one centrosome, and the other toward the second. This gives rise to a second spindle, the NUCLEAR, or CHROMATIC SPINDLE. The separation is affected by the traction exerted upon the daughter chromosomes by the threads of the central spindle. ANAPHASE. This is the stage of complete separation of 40 HISTOLOGY. the chromosomes. The latter collect around their respect- ive centrosome, and remain connected to the opposite set, for some time, by the central spindle threads. The figures thus formed are the DIASTERS, or DAUGHTER STARS. TELOPHASE. This stage is concerned with the protoplas- mic changes and the formation of a resting nucleus. Up to this time, the protoplasm has been practically quiescent. The chromosomes collect around the centrosomes, and unite to form a close skein. Lateral twigs are developed that anastomose to form the nuclear network, a nuclear membrane is formed and a nucleolus appears. The hitherto inert protoplasm shows changes. A double row of vacuoles appears at the equator of the cell, and separation occurs in the intervening space until two sepa- rate masses are formed; these are the DAUGHTER CELLS. The above changes are usually succeeded by a period of rest. Although apparently a long process, only about one-half hour is consumed in the division of human cells, but the cells of lower animals require a longer period. In the case of giant cells, the nucleus divides and redivides, while the protoplasm remains unchanged. They may also be formed by the fusion of the protoplasm of a number of cells with the retention of the individuality of the nuclei. As all cells are developed from preexisting elements, it is but natural that the original cell of the body, the Ovum, should be of greatest interest. It is the most characteristic cell of the body, and is secreted by the ovary. It is the largest cell, and illustrates the individual parts well. The Ovum consists of a limiting wall, the vitelline mem- brane, that is well developed. Within this is the proto- plasm, vitellus, which consists of two parts the DEUTO- PLASM, or NUTRITIVE YOLK, and the ANIMAL PROTOPLASM, or FORMATIVE YOLK. This is of importance, embryologically. MATURATION. 41 Within the vitellus is found the nucleus, or germinal vesicle, which contains a deeply stained nucleolus, or germinal spot. The centrosome is to be seen in unripened ova. After maturation this body disappears. In what might be termed an embryologic ovum, there are two layers external to the vitelline membrane, the ZONA PELLUCIDA and the CORONA RADIATA. Of these, the former is the more important, because of the part which it plays in the early stages of development. FIG. 8. UNRIPENED OVUM FROM A YOUNG GUINEA-PIG. A, Nucleus; B, nucleolus; C, centrosomes in the attraction sphere. There are a number of processes that occur in the ovum before it can develop into an offspring. Of these, the most important are MATURATION and FERTILIZATION. The former occurs, usually, in the ovary, and the latter, as a rule, in the Fallopian tube. Maturation is the process by which part of the chromatin and a small portion of the protoplasm are extruded in the form of two minute structures called POLAR BODIES. It is a modified karyokinesis, and its object is unknown. All ova must pass through this process before they can be fertilized. 42 HISTOLOGY. Fertilization is the process in which the male and female elements unite to form a complete and perfect cell, which, by division, gives rise to the cells that ultimately form the whole body. The male element, or spermatozoon, or spermium, consists of HEAD, MIDDLE-PIECE and TAIL. Of these the HEAD and MIDDLE-PIECE, representing the NUCLEUS and CENTROSOME, respectively, of a cell of the testicle, enter the ovum and form eight * chromosomes. The chromatin of the germinal vesicle of the ovum also forms eight. By longitudinal cleavage thirty-two are formed of which sixteen enter into each diaster and, consequently, each daughter cell. By this process the descendants of the fertilized ovum contain double the number of chromosomes that existed in either of the original cells before fertilization. After fertilization the ovum divides and redivides, forming an irregular mass of cells called the Morula, or Mulberry Mass. Certain of these cells form a complete layer that surrounds the remainder, which constitutes an irregular mass. The layer is the OUTER CELL-MASS and the latter the INNER CELL-MASS. This structure constitutes the Blastula, or one-layered vesicle. Of these two structures the inner is the more important as it persists and forms the whole body while the outer is said to disappear. The INNER CELL-MASS forms two layers, an outer, several cells in thickness, the ECTODERM, or EPIBLAST, and an inner, composed of but a single layer, the ENTODERM, or HYPOBLAST. This is the Gastrula, or Diploblast. The ectoderm and entoderm each set aside a number of cells which by multiplication form a third layer, the MESODERM, or MESOBLAST, that lies between the two. This structure receives the name of Blastodermic Vesicle, or Triploblast. * Some writers claim the somatic cell contains sixteen chromosomes while others say there are twenty-four. DERIVATIVES OF THE TRIPLOBLAST. 43 From these three primitive layers all the orgens and tissues of the body are formed as follows: ECTODERM. The nerve system (cerebrospinal and sympathetic) the retina, the bulk of the crystalline lens, the muscle of the iris and part of the vitreous humor of the eyeball, the epi- thelium of the cornea and conjunctiva, the epithelium of the internal ear and of the olfactory organ, the medulla of the adrenal. The epithelial lining of the anterior portion of the male urethra, the labia of the female and the glands leading thereto. The epithelial lining of the mouth and salivary glands, epithelial lobe of the pituitary body, the enamel of the teeth, the cells of the nasal tract and glands leading thereto, to the pharynx, and the lining of the anus. The epidermis and appendages of the skin, muscles of the sweat glands. The syncytium of the placenta. ENTODERM. The epithelial lining of the bladder, the prostate and glands of Cowper, of the first and second portions of the male and entire female urethra, vestibule and glands of Bartholin. The epithelium of the tongue, thymus and thyroid bodies of the parathyroids, middle ear and Eustachian tube. The epithelium of the alimentary and respiratory tracts from the mouth and posterior nares down and the epithelium of all glands opening into these structures. The notochord. MESODERM. The vascular system. The lymphatic system including the large serous cavities, spleen and thymus body (except the corpuscles of Hassal). 44 HISTOLOGY. The muscle tissues (except the muscles of the sweat- glands and iris). The connective tissues. Testicle, vas, seminal vesicles, ejaculatory duct, ovary, oviducts, uterus and vagina. Kidneys, ureters and cortex of adrenal. CHAPTER III. THE TISSUES. From the preceding table it will be seen that all tissues are developed from the three layers of the triploblast. These tissues are grouped, histologically, under four classes, Epithelial, Connective, Muscle and Nerve. A Tissue consists of similarly differentiated cells held to- gether by intercellular cement, and performing a definite function. The intercellular substance varies with the different tissues. The cells of a tissue may be so arranged as to form an organ or merely a supporting structure. Epithelium. The Epithelial Tissues are characterized by the small amount of the intercellular cement. The cellular elements are usually prominent, and rich in granular protoplasm. They are found lining cavities that communicate normally with the air and usually secrete, although they may also have an excretory, absorptive, or protective function. They are avascular and may be derived from any of the layers of the triploblast. The cells very in size, form and arrangement, as will be seen later. For convenience of description, the cells are classified as follows : 1. Squamous. 3. Ciliated. a. SIMPLE. e. SIMPLE. b. STRATIFIED. f. STRATIFIED. 2. Columnar. 4. Prickle cells. c. SIMPLE. 5. Goblet cells. d. STRATIFIED. 6. Transitional cells. Modified. 4 6 THE TISSUES. 7. Pigmented. Specialized. 8. Neuro -epithelial. 9. Glandular. i. Squamous. a. The SIMPLE SQUAMOUS cells consist of a single layer of flattened elements, each containing a FIG. 9. a. Simple squamous cells, b. Simple cuboidal cells. large nucleus. This is usually in the center, and has an oval, or round form. They occur in the descending limb of Henle's loop, the capsule of Bowman in the kidney, the FIG. ii. SQUAMOUS CELL ISOLATKD. FIG. 10. SURFACE VIEW OF SQUAM- FIG. 12. STRATIFIED SQUAMOUS ous CELLS OF FROG'S SKIN. EPITHELIUM. alveoli of the lungs, and in parts of the ventricles of the brain. b. The STRATIFIED SQUAMOUS variety consists of many layers of cells that are unlike in form. The lowest layer, EPITHELIAL CELLS. 47 the germinal stratum, is columnar, while those ceils just above are polygonal. The succeeding cells become more and more flattened, forming the squames, or scales, from which this variety receives its name. It is found covering the body as the epidermis, lining the mouth, pharynx, FIG. 13. a. Simple Columnar showing Cuticular Border, b. Simple Ciliated Cells. c. Simple Columnar and Goblet Cells. esophagus, epiglottis, vocal cords and the anus and vagina. 2. Columnar, c. SIMPLE COLUMNAR cells are tall, cylindric elements arranged in a single layer. The nucleus is usually oval, and found nearer the base than the center of the cell. The variety is found in the stomach and intestinal tract, FIG. 14. 0. Isolated Columnar Cells, b. Isolated Ciliated Cells, c. Three Stages of Goblet Cells. the penile portion of the urethra, glands of Cowper, and Bartholin, prostate, gall-bladder and seminal vesicles, and in many gland ducts. In the intestine these cells, upon their exposed surface, have a layer of differentiated protoplasm forming a partial membrane; this is called a cniicular border. Low columnars are often called cuboidal. 48 THE TISSUES. PSEUDOSTRATIFIED cells are simple columnar, or ciliated, cells, in which the nuclei are not all basal, but occupy differ- ent levels, thus giving the appearance of several layers of cells, where, in reality, but a single layer exists. These are found as ciliated elements in the oviducts, uterus and middle ear and as non-ciliated elements in the seminal vesicles (maybe simple) and prostate, according to some writers. d. STRATIFIED COLUMNAR cells consist of a number of layers of columnar elements superimposed upon one FIG. 15. PSEUDOSTRATIFIED CELLS. another. The cells are not as large as the preceding. They occur in the vas deferens, membranous urethra and the ducts of some glands. 3. Ciliated cells, e. SIMPLE CILIATED cells are simple columnar elements, which bear, upon their exposed surface, a varying number of hair-like processes called cilia. These possess a motion that is directed toward the outlet of the organ in which these cells are found. They line the smaller bronchioles, spinal canal, accessory spaces of the nasal fossae and the ventricles of the brain. f . The STRATIFIED CILIATED cells are practically stratified columnar cells, of which the exposed layer alone possesses cilia. They are found in the epididymis, first part of the vas, Eustachian tube, upper part of the pharynx, in the larynx, trachea and nasal tract. 4. Prickle cells are polygonal elements that possess little spines, which project from the sides of the cells. These, EPITHELIAL CELLS. 49 meeting the spines of other cells, prevent the ce41-bodies from touching. In this way, a series of intercellular bridges and spaces is formed. These cells are found in the epidermis, just above the genetic layer. FIG. 16. a. Stratified Columnar Cells, b. Stratified Ciliated Cells. Columnar Cells showing Goblet Cells. c. Stratified 5. Goblet cells are cells of the cylindric type, distended with a peculiar secretion called mucin. When filled, they resemble a goblet, hence the name. When the secretion has been discharged, the cells are long and slender, the part con- taining the nucleus projecting on either side. Such cells are met with in the gastro-intestinal and respiratory tracts. FIG. 17. TRANSITIONAL CELLS. 6. Transitional cells are peculiar stratified elements that are neither columnar nor squamous. They occupy an intermediate position, as all the cells are polygonal. They occur in the pelvis of the ureter, in the ureter, bladder, the 4 50 THE TISSUES. first portion of the male and the greater portion of the female urethra. 7. Pigmented cells are polygonal or columnar cells, in which the protoplasm contains a varying number of pig- ment granules. The former shape is found in the epidermis of colored races, and around the nipple and genitals of Caucasians; the latter occurs in the retina of the eye, and the pigment granules obscure the various parts of the cell. 8. Neuro -epithelial cells are epithelial cells that have become so differentiated as to perform a special sense function. They differ according to location, and will be described under each special sense. They occur in the retina (rods and cones), in the internal ear (hair cells), in the olfactory mucous membrane, in the taste-buds and as tactile cells. 9. Glandular cells also vary according to the nature of the gland in which they are found, as in the liver, pancreas, etc. Mucous Membranes. The epithelial surfaces within the body are termed Mucous membranes. Glands, which are evaginations of such surfaces, are also classed with mucous membranes. Such membranes are complexes of all four varieties of tissues. They are lined by EPITHELIAL CELLS, of any of the varieties above mentioned, that rest upon a delicate BASEMENT MEMBRANE, beneath which is found a layer of fibro-elastic tissue called the TUNICA PROPRIA. Here are seen nerves, capillary blood-vessels, lymphatic channels or spaces, and, in certain organs, glands and lymph- oid tissue. The structure is limited, peripherally, by a layer of involuntary, nonstriated muscle tissue, the MUS- CULARIS MUCOS^. The latter is not always present, as will be seen when the various organs are studied in detail. These membranes line cavities that communicate normally with the air and usually secrete. MUCOUS AND SEROUS MEMBRANES. 51 As some writers classify Endothelial cells as epithelial, it is well to consider them at this time, so as to contrast them. Endothelial, or, better, Mesothelial, cells are thin, flat- tened elements possessing a large projecting nucleus. They are irregular in outline, and are held together by inter- FIG. 18. A. ABDOMINAL EXDOTHELIUM. a. Endothelial cell; b. nucleus of cell; c. cell boundary; d. stigmata; e. endothelial cells of stomata; /. sto- mata. B. MESENTERIC ENDOTHELIUM. C. ARTERIAL ENDOTH- ELIUM. D. PERIVASCULAR LYMPHATICS, a. Endothelial cells of lymphatics; b. blood-vessel (arteriole). cellular cement. They never occur in more than a single layer, and form, with fibro-elastic supportive tissue, the subendothelial connective tissue, a Serous Membrane. A Serous Membrane possesses neither basement membrane nor muscularis miicosa, and lines cavities that do not com- municate normally with the air and never secretes. Such 5 2 THE TISSUES. membranes are smooth, moist, glistening and transparent, and subject to inflammations different from those of the foregoing. Openings called stomata are said to exist, but these are now considered artifacts. Serous membranes are found lining joint-cavities, bursae, tendon sheaths, the circulatory and lymphatic systems and the larger serous cavities, the pleural, periton- eal and pericardial. CHARACTERISTICS. MUCOUS MEMBRANES. SEROUS MEMBRANES. Where found Lined by Secrete . Structure . Represents . Lining cavities that communicate nor- mally with the air. Epithelial cells of any variety. With few exceptions- Epithelial cells, base, ment membrane, tu- nica propria, muscu- laris mucosae. All four varieties of tissue. In cavities that do not normally communi- cate with the air (fe- male peritoneal cav- ity excepted). Endothelial (Meso- thelial) cells, one layer. Do not. Endothelial cells, sub- endothelial connec- tive tissue. But two varieties (nei- ther muscle nor epi- thelial tissues). GLANDS. A description of epithelial tissues would not be complete without a consideration of Glands. Glands may be UNICELLULAR, as the GOBLET-CELL, Or MULTICELLULAR, as those that will be considered below. A Gland is an evagina- tion of a mucous surface, consists of epithelial cells, ar- ranged in definite groups, and performs a physiologic GLANDS. 53 function. These groups are the secretory units of the organ. Glands may be classified in several ways: i, as to Structure, 2, as to Secretion, and 3, as to Outlet. i. Structure. As the secretory units are of different shapes we have the following divisions and subdivisions : Tubular Glands. SIMPLE. BRANCHED. COILED. COMPOUND. Tubulo -alveolar Glands. Alveolar, or Racemose Glands. SIMPLE. COMPOUND. Tubular. SIMPLE TUBULAR glands are mere cylindric depressions in the mucous membrane. They are lined, usually, by simple columnar cells. They occur in the cardiac end of the stomach, and in the small and large intestines. The branched tubular are like the above, except that the lower end is divided into two or more secretory units. The lining cells may be columnar, or ciliated, as in the uterus. These glands are found in the fundus and pyloric portion of the stomach, in the duodenum (Brunner's glands), in the uterus, and in the prostrate. Coiled tubular glands are really simple tubes, the secre- tory portion of which has become coiled and convoluted to occupy as small a space as possible. The lining cells are columnar or cuboidal (low columnar). Examples are the sweat and ceruminous glands. Compound tubular glands are those in which the prim- tive tubules have divided and redivided until an enormous 54 THE TISSUES. number of divisions has resulted. Pure examples of this variety are the liver (also called reticular), testicle, kid- FIG. 19. GLAND OF LIEBERKUEHN FROM A SECTION OF THE LARGE INTESTINE. a. Lumen; b. secretion of cells; c, nucleus and protoplasm of cell; dfundus cells at the beginning of secretion; e. f. goblet cells in later stage; g. dying goblet cells (Stohr's Histology'). ney, thyroid, lacrimal and serous glands of the mucous membranes. GLANDS. 55 Tubulo -alveolar glands are those in which the terminal tubules possess sac-like evaginations along the walls. Such glands are the sub maxillary, sublingual, mammary and the lungs. FIG. 20. DIAGRAMS OF TUBULAR GLANDS (Stohr's Histology}. A. Simple tubular; B. branched tubular; a. excretory duct; C. compound tubular. FIG. 21. ALVEOLO-TUBULAR GLANDS (Stohr's Histology}. Branched alveolo-tubular; 2. compound alveolo-tubular ; a. excretory duct. Alveolar. The SIMPLE ALVEOLAR, or saccular, glands are sac-like depressions extending from the free surface. They are comparatively few in number, and occur as the smallest sebaceous glands. The COMPOUND RACEMOSE glands are like the compound tubular, except that the terminal portions are saccular, 56 THE TISSUES. instead of tubular. Such glands are the pancreas, parotid, and the large sebaceous glands. 2. Secretion. The function of a gland is to give rise to a substance to be used by the body in some of its many processes. This substance is called a secretion, and it may be liquid or cellular (ovum). The liquid secretions may Fig. 22. Alveolar Glands (Stoh^s Histology). i. Alveolar system; 2. compound alveolar gland; a. excretory duct. be serous, mucous, or mixed. These terms, applied to the respective glands as well, have reference to the salivary glands alone. SEROUS glands are those which form a thin albuminous secretion. The glandular cells respond well to stains. The parotid and pancreas belong to this class. Mucous glands are those that give rise to a thick viscid substance. The cells here stain but lightly with the GLANDS. 57 ordinary stains. Such are the small glands found in the mouth, esophagus, trachea and the sublingual, according to some writers. MIXED glands are those in which both varieties of secre- tion are formed. The secretory areas are stained darkly or lightly, according to whether they are serous or mucous. The sublingual and submaxillary glands are examples, and of these, the latter is the more characteristic. The minute structure of these glands will be considered under the Alimentary Tract. The excretory glands are the kidneys, lungs and sweat glands. Each will be considered in detail, under its re- spective system. 3. Outlet. As a rule, all glands, at some period in their development, are connected with the mucous surface by a tube called a duct. This connection, in most instances, persist, but where it disappears, the gland becomes isolated, and the term ductless gland is applied. Such are the ad- renals, hypophysis and thyroid bodies, parathyroid, carotid and coccygeal glands, the ovary and the areas of Langer- hans in the pancreas. These form an internal secretion that is absorbed by the circulatory or lymphatic system. Those with ducts pour their secretions or excretions into the various tracts with which they are connected. CHAPTER IV. CONNECTIVE TISSUES. The Connective Tissues are the supportive tissues of the body. They are characterized by the predominance of the intercellular substance over the cellular elements. This intercellular substance varies in the different forms, as will be seen when each is considered. Connective tissues are usually vascular and are derived entirely from the mesoderm. For the convenience of description, this class has been subdivided into the following varieties: Fibrous. Modified. 1. WHITE. 6. ADIPOSE. a. Loose. 7. LYMPHOID. b. Dense. 8. CARTILAGE. 2. YELLOW ELASTIC. 9. BONE. 3. Mucous. 10. DENTIN. 4. RETIFORM. n. BLOOD. 5. MIXED. The Fibrous varieties are characterized by the fibrous or semi-solid intercellular substance. The cellular elements are comparatively few, and are found scattered among the fibrils. There are several varieties of cells found in con- nective tissues. These are the TRUE, or FIXED, the WANDER- ING and the PLASMA cells. The TRUE, or FIXED, connective tissue cell is a flattened, stellate element with many proc- esses that extend in all directions, and anastomose with those of other cells. These cells may be pigmented as 58 FIBROUS TISSUE. 59 seen in the iris and choroid. Within the network thus formed lies the intercellular substance. In young tissue, the cells are not all of the above form. Some are round, others are spindle-shaped ; these gradually become converted into the stellate variety. The WANDERING cell passes into the tissue from the blood- vessels. It may return, or remain and become a fixed, or true connective tissue cell. PLASMA cells are large, granular, fixed elements, especially noticeable in areolar tissue. They are at first oval or ob- long, and later change to the stellate type. The INTERCELLULAR substance is soft, and, in most varieties, fibrous. These fibrils react characteristically to certain stains, as will be pointed out later. They vary in thickness, and are arranged in bundles which may be paral- lel, or may interlace. These bundles lie in a more or less homogeneous ground substance that varies in quantity in the different varieties. The origin of the intercellular substance is still in dispute. Two theories are advanced. According to some writers, it is of intracellular origin , while others claim it to be inter- cellular in derivation; in other words, it is formed in the homogeneous, semi-solid intercellular or ground substance, which exists before the fibrils appear. The real origin is probably by a combination of these two processes. It seems that the intercellular substance is formed from the peripheral protoplasm of the cell, which becomes fibrillar in character. This small amount of differentiated proto- plasm is then supposed to increase itself, and so give rise to the remainder of the fibrils. The origin of the elastic fibres is not so plain, both of the above views being held in regard to them. In elastic carti- lage, they are of intercellular origin, but still the intra- cellular formation must not be lost sight of. 6o CONNECTIVE TISSUES. b FIG. 23. A. Mucous Connective Tissue, a. Spindle cells; 5. stellate cell; c. inter- cellular substance. B. Cross Section of Tendon, a. Epitendineum; b. peritendineum; c. tendon fasciculi; d. interfascicular space. C. Part of B, highly magnified, a. Epitendineum; b. cell in a; c. peri- tendineum; d. tendon fasciculus; e. interfascicular space. D. Tendon Cells from Interfascicular Spaces. E. Elastic Tissue, Cross-sec- tion of Ligamentum Nuchae. a. Elastic fibres; b white fibrous WHITE FIBROUS TISSUE. 6l i. WHITE FIBROUS tissue consists of fine or coarse bundles of inelastic fibrils, either parallel or forming a deli- cate mesh work. Its two subdivisions are, a, loose, and b, dense. a. Loose fibrous connective tissue is a minute network of small bundles of fibrils formed for the support of capil- lary blood-vessels. The fibrils are delicate, less than i micron in diameter, do not branch or anastomose and are held in bundles by a small amount of cement substance. The cellular elements are of the types named above, and are few in number. Upon boiling, it yields gelatin, is not, or only slowly, digested by pancreatin, and is swollen by acetic acid. It forms the capsules of organs, and is found as the tu- nica propria and submucosa of the alimentary and respi- ratory tracts. b. In the dense variety, the fibrils are coarser, and ar- ranged in larger bundles, which are usually parallel. TENDONS are dense white fibrous tissues, in which all the fibril bundles have a parallel course. The whole structure is surrounded by a sheath of looser tissue, called the epi- tendineum, from the inner surface of which septa are sent in that divide the tendon fibres into large secondary bun- dles. These latter are further subdivided into primary bundles, each of which is surrounded by a minute sheath, the peritendineum. Between the individual bundles, lie the peculiar tendon cells. These are flattened, rectangular elements arranged end to end upon the tendon bundles. supportive tissue. F. E highly magnified, a. Elastic fibres; b. white fibrous supportive tissue. G. Areolar Tissue, a. White fibre bundles; b. elastic fibres; c. spindle cell; d. granule cell; e. plasma cell;/, stellate cell. H. Adipose Tissue, a. Interlobular connective tissue; b. fat cells; c. nucleus and protoplasm and of the cell. I. H highly magni- fied, a. Fat cell; b. protoplasm and nucleus of cell. K. Lymphoid Tissue, a. Leukocytes; b. stellate connective tissue cells; c. reticulum. L. Pigmented Connective Tissue Cell from a Pike. 62 CONNECTIVE TISSUES. The nuclei are peculiarly arranged. In two adjoining cells they will be seen near the line of junction, but in the cells on either side of these, they are separated by nearly the length of the two cells. In FASCIA and the DURA the bundles are large, dense, interwoven and closely packed. 2. ELASTIC tissue, as its name indicates, has the peculiar property of elasticity. The fibres are yellow in color, refractile, and coarser than those of the white variety, averaging 1-5 microns in diame- ter. In AREOLAR tissue, they are branched, while in other places bands and even membranes are formed (arteries). When separated and ruptured, the torn ends curl. This occurs in no other tissue. According to Mall, each fibre consists of a delicate sheath, surrounding the elastic sub- stance; the latter stains deeply with magenta. This variety occurs in the ligamentum nuchae, where the fibres are very heavy, and are surrounded by white inelastic fibres, in the ligamentum subflava, in blood-vessels, and in the true skin. Elastic tissue is digested by pancreatin and somewhat by pepsin, but not by acetic acid; upon boiling it yields elastin. 3. Mucous, or EMBRYONIC, connective tissue is that variety in which the intercellular substance is semi-fluid. The cellular elements are mostly of the spindle-shaped variety, although numerous stellate cells are present. Round cells are also frequently seen. The intercellular substance is semi-solid in the youngest tissue, and takes a peculiar homogeneous stain. As the tissue becomes older fibrils begin to develop, and of these, the white are formed into bundles, while the elastic are usually individual. Mucous connective tissue is found in the umbilical cord, RETIFORM CONNECTIVE TISSUES. 63 in embryos, in the vitreous humor of the eye and* in the pulp of the teeth. 4. RETIFORM connective tissues, or RETICULUM, is the supportive tissue of glands and gland-like organs. It con- sists of delicate bundles of fibrils forming a network, in the meshes of which are found the functionating cells of the organ. The cells are chiefly stellate in form, and their processes anastomose around the fibril bundles. FIG. 24. INTERMUSCULAR CONNECTIVE TISSUE BUNDLES OF MAN. a. Fat drop; b. fat cells; c. bundles of white fibres; d. nucleus of a cell; e. elastic fibres (Stohr's Histology}. This tissue is more resistant to those reagents that dis- solve the white variety (hydrochloric acid and potassium hydrate) and does not yield elastin upon boiling, but a mixture of gelatin and reticulin, nor is it digested by pancreatin. 64 CONNECTIVE TISSUES. 5. MIXED, or AREOLAR, connective tissue is a combination of the white and elastic varieties. The white tissue is present in the form of delicate bundles, and these form a loose network with the elastic fibres, which are usually thin and branched. The stellate and wandering cells are well represented, but the plasma cells are more numerous than in any other variety of tissue. This variety is found binding the skin to the fascia be- neath and between muscles. Modified. In these varieties of connective tissue, the intercellular substance varies from liquid (blood) to the hard, unyielding material found in bone and dentin. The cellular elements also differ, as will be seen when each variety is discussed. 6. ADIPOSE tissue, or FAT, is white fibrous tissue, in which the cells have become repositories for fat globules. These cells are quite numerous, but the stellate shape is lost. The minute globules unite to form a single large drop that distends the delicate cell-membrane. By this coalescence, the protoplasm and nucleus of the cell are forced to one side, and are seen as a thin band, or crescent. The nucleus may contain vacuoles. Fat cells are spherical, when not closely packed, as the fat is liquid at the body temperature. After death, margarin crystals are seen in the protoplasm. The cells are collected into groups called lobules, and these form large masses called lobes. Blood-vessels, nerves and lymphatics are present in considerable number. The first named are especially numerous, as there is a close relation between fat deposition and the vascularity of the part. According to some writers, fat cells are specialized con- nective cells that exist in no other form. This seems doubtful, however, as experiments have shown that when animals are starved, the spherical, fat-containing cells re- LYMPHOID TISSUE. 65 turn to the stellate form as the fat is removed. Fram this, it would seem that these cells act merely as storage cells. When adipose tissue is studied, after ordinary prepara- tion, merely a network of fibres and cell boundaries is seen. This is due to the fact that the fat has been removed by the alcohol leaving* the insoluble white fibrous supportive tissue. In such sections, the nucleated crescents of protoplasm are readily observable. In sections of osmicated fat, the peripheral cells are circular in outline, while the deeper ones are irregular and black, due to the action of the osmic acid, which is a characteristic reagent for fat. Sudan III, also used as a test for fat, stains the globules dark red. Adipose tissue is found widely distributed over the body, except in the penis, scrotum, ear and eyelid. From the orbit and around the kidneys it never entirely disappears, though death be due to starvation. 7. LYMPHOID tissue is a special form of the connective variety consisting of a network of reticulum, in the meshes of which are found leukocytes, or white blood-cells. These cells are usually the small lymphocytes, although varying numbers of the large lymphocytes (hyalin cells) and polynuclear cells are to be seen. For a description of these cells, see Blood (p. 107). For readiness of comprehension, LYMPHOID tissue is divided into four varieties: a. DIFFUSE; b'. SOLITARY FOL- LICLE; c. PEYER'S PATCH, or AGMINATED FOLLICLE; and d. LYMPH NODE. a. DIFFUSE LYMPHOID tissue is an indefinite collection of leukocytes in an organ. The cells are not especially arranged, neither is there a special supportive tissue present, as in the last two varieties. It is found in the tunica propria of the alimentary and respiratory tracts, and the cells are merely scattered be- tween the bundles of white fibrous tissue. It forms the 66 CONNECTIVE TISSUES. medulla of the thymus body, and the bulk of the tonsil and spleen, and is transient in character. b. SOLITARY FOLLICLES are small, dense collections of leukocytes in white fibrous tissue, as above. There is no special supportive tissue present; although the outline may be slightly irregular, it is sharp. Each follicle usually shows a lighter center in which the cells are fewer and younger. This is called the germinal center, and here the new cells are formed by karyokinetic division. Solitary follicles are found in the alimentary and respira- tory tracts, the spleen and tonsil. They, like the diffuse variety, are transient structures. (See Fig. 41, page 115.) c. A PEYER'S PATCH is a more or less regular collection of solitary follicles sharply outlined from the surrounding tissue. Each patch consists of ten to sixty solitary follicles, each of which usually shows a germinal center. (See Fig. 51, p. 141). Peyer's patches are found in the ileum. d. LYMPH NODES (Lymph Glands) are small, bean- shaped bodies interposed in the pathways of the lymphatic vessels. As they are closely related to the Lymphatic System, their structure will be there considered. 8. The CARTILAGES are characterized by a solid inter- cellular substance. The cellular elements also differ from those previously cl escribed. Three varieties are found in man: the HYALIN, WHITE FIBRO and YELLOW ELASTIC. The general structure will first be considered, under />rn- chondrium, cells and intercellular substance. The perichondrium is a fibrous sheath that surrounds cartilage and gives rise to its cellular elements. It is composed of white fibrous tissue, and is divided, functionally, into two parts. This division is not apparent under the microscope, as the layers fade into each other. CARTILAGE. 67 The outer part is the fibrous layer, and contains lew cells. The inner portion, or chondro genetic layer, is rich in cells that are not of the stellate type, but flattened and elongated, or spindle-shaped. These are the chondroblasts, which become cartilage cells. Blood-vessels also are present. The cartilage cells, or chrondroblasts, vary in the different portions of the cartilage. Just beneath the perichondrium, they are flat and 'thin, indicating an early stage. Toward the center, they gradually become broader until, finally, they are oval or round in form. Each cell is rich in pro- toplasm, which contains one or more vacuoles. The nucleus is usually prominent. The cell is sharply outlined from the surrounding substance by a thick wall, the capsule. This is a product of secretion of the cell, and it is cast off, as a rule, every time the cell divides. Each cell may be individual, or several may be seen within one capsule, which is due to the fact that the new cells did not form capsules for themselves. This is seen especially in ossi- fication of cartilage. Between the cell and the capsule is usually a space called the lacuna. The intercellular substance varies. In the HYALIN variety, it is apparently homogeneous; in -white fibro, it is composed mainly of white fibrous tissue, while in the yellow fibro it consists of yellow elastic fibres. HYALIN CARTILAGE is a peculiar bluish or pearly tissue, which is elastic, and readily cut with a knife. The cellular elements are as above. They are quite numerous, and close together just beneath the perichon- drium. Further down, a number are usually found within one lacuna and capsule. The intercellular substance or matrix, is apparently homo- geneous. Upon very careful study, and treatment with special reagents, it shows a fibrillar character, in the meshes of which is seen the ground substance, which is homogeneous. 68 CONNECTIVE TISSUES. This ground substance is formed by a fusion of the cast-off capsules, and responds very well to hematoxylin, showing a peculiar bluish color. This variety of cartilage is found covering articular sur- faces, lining joint-cavities, as the costal, tracheal and most > r '-}, ABC FIG. 25. SECTIONS OF CARTILAGE. A. HYALIN CARTILAGE, a. Fibrous layer of perichondrium; b. genetic layer of perichondrium; c. youngest chondroblasts; d. older chondro- blasts; e. capsule; /. cells; g. lacuna. B. ELASTIC CARTILAGE. C. WHITE FIBRO-CARTILAGE. of the laryngeal cartilages. It precedes, with a few excep- tions, all the bones of the body, and may ossify in old age. WHITE FIBRO CARTILAGE consists of islands of the hyalin variety, separated by an intercellular substance made up of delicate bundles of white fibrous tissue. This form may calcify or ossify in old age. CARTILAGE. 69 It is not very abundant, and is found deepening joint- cavities, as inter-articular fibro-cartilages, and as the inter- vertebral discs. YELLOW FIBRO, or ELASTIC CARTILAGE is that variety in which the intercellular substance is composed of elastic fibres. It is practically hyalin cartilage in which the hyalin matrix has been replaced by elastic tissue. The cartilage cells are found in small groups, surrounded by only a small amount of the hyalin substance. This variety never ossifies or calcifies, and is to be looked for in regions where elasticity is required, as in the epiglottis, ear, Eustachian tube and small laryngeal cartilages. Cartilage contains no blood-vessels, except in the perichon- drium, and during the developing stage. Lymph channels are said to be absent, so that its nutrition is not of a very high order. 9. BONE is the most highly differentiated of the connect- ive tissues. It is characterized by the presence of a very hard, unyielding intercellular substance that has a char- acteristic arrangement. BONES, like cartilage, are surrounded by a fibrous sheath, the periosteum, beneath which is the bone substance proper; the latter consists of cells and intercellular substance. The periosteum is composed of two layers outer, or fibrous, and inner, or genetic. The outer layer consists of white fibrous tissue, support- ing a large number of blood-vessels, and containing but few cells. The inner, or genetic, layer is rich in cells and capil- laries. These cells are the future osteoblasts that secrete the osseous tissue. From its inner surface, it sends in bundles of fibres that pierce the layer of bone at right angles, and bind them together. These are Sharpey's fibres. 70 CONNECTIVE TISSUES. The cells are all of the irregular stellate type, and consist of flattened bodies and short processes that extend into small canals, to be described later. The protoplasm is not very abundant, and the nuclei are oval, and often vesicular. The intercellular substance is hard and resistant. It con- sists of osseous material that is secreted by the cells, and is peculiarly arranged in the compact variety. It contains spaces, or lacuna, from which extend minute canals, or canaliculi. Beside these, there are a great number of canals that vary in length and diameter. These are the Haversian canals. BONE is composed of inorganic and organic salts; the former are soluble in mineral acids, by which they may be removed and the tissue cut. The latter are removed by burning, after which process the inorganic substance re- mains as a porous mold of the bone. There are two varieties CANCELLOUS, or SPONGY, and COMPACT, or SOLID. CANCELLOUS BONE consists of spicules forming a network resembling a sponge. These spicules have a fibrillar structure, and contain little spaces, called lacuna. In the living condition, these lacunae are occupied by bone-making cells, termed osteoblasts. This variety is found around the medullary cavity and in the heads of the long bones, and forming the central portion of the flat bones. The meshes of the network are covered by the endosteum and are rilled with marrow. COMPACT BONE has a characteristic structure. The os- seous matter is arranged in layers, or lamella, between which lie the lacuna. There are four. varieties of lamellae: a. Periosteal, peripheral, or circumferential; b. Haversian, or concentric; c. Intermediate, ground, or irregular; and d. Perimedullary, or Internal. a. The peripheral, periosteal, or external lamellae are BjONE. 71 those formed directly from the periosteum. They are few in number, and several are required to complete the cir- cumference. Between them are a number of irregular spaces, lacunae, from which little canals extend, the canal- iculi. The external layer has a number of small depressions called Howship's fovece, or lacuna. These are occupied by large bone-destroying cells called osteoclasts. Haversian FIG. 26. CROSS-SECTION OF HUMAN COMPACT BONE. a. Periosteum; b. peripheral lamellae; c. Haversian canals; d. lacunae; e. interstitial lamellae;/, perimedullary lamelhe; g. marrow; h. Haversian lamellae (Stb'hr's Histology}. canals are not present, but larger canals, containing blood- vessels from the periosteum, are seen. These are Volk- mann's canals. b. The Haversian lamellae, which are probably the most numerous, are thin layers circularly arranged around a small central canal called the Haversian canal. These layers are separated by the lacunae, and pierced by the canaliculi. The lamellae of a system are parallel to one another, but the different systems usually run at various angles. 72 CONNECTIVE TISSUES. An Haversian system consists of the lamellae, canal, lacunae arid canaliculi. The canals are occupied by blood-vessels, nerves and lymphatics. Those nearest the marrow cavity contain marrow. The canals are generally parallel to the long axis of the bone, and anastomose freely with one another. c. The intermediate, interstitial, or irregular lamellae lie between the Haversian system, and are irregular in size and form. They are the remains of Haversian and periosteal lamellae, altered by the growth of the bone in diameter. No canals are found here, but lacunae and canaliculi are present between the lamellae. d. The perimedullary, or internal, lamellae are not very regular, and are found surrounding the medullary, or mar- row cavity. The lacuna are small, irregular spaces found between the various lamellae throughout the bone, and occupy a portion of each of the adjacent lamellae, and do not lie in one alone. These spaces are said to be lined by a delicate membrane. They contain the osteoblasts. Extending in all directions, are small canals, or canalicuh, that communicate with those of other lacunae, so that a series of intercommunicating spaces results. Those lacunae lying nearest the Haversian canals, communicate with them, but the peripheral ones of a system do not com- municate, to any great extent, with those of the interstitial lacunae. The canaliculi serve as supports for the processes of the osteoblasts. The compact portions of the heads of bones contain no Haversian systems and no large lacunae so that pressure can more readily be borne. Vessels do not enter the bone here. The MEDULLARY CAVITY, which contains the nutrient marrow, is a large space, in the shafts of the long bones; it BONE-MARROW. 73 is lined by the endosteum which is analogous in structure and function to the periosteum. The MARROW is of two varieties, red and yellow. The red is found in young persons, while the yellow occurs in those above the prime of life. The difference is due to the pres- ence of a great deal of fat in the yellow, whereby the color becomes changed. It is not a blood-making tissue as the cellular elements 'are few or may be entirely wanting. In disease, however, it may again become red. MARROW consists of a delicate network of reticulum, derived from the endosteum, supporting a close capillary plexus and a number of different cells. These cells are: MYELOCYTES, Or MARROW CELLS; NUCLEATED RED BLOOD CELLS, Or ERYTHROBLASTS, WHITE BLOOD CELLS, OR LEUKO- CYTES, and MYELOPLAXES. MYELOCYTES are large nucleated masses of granular pro- toplasm. The nucleus is usually large and oval or round in shape; the chromatin is small in quantity. The proto- plasma contains fine granules that may or may not react to acid stains; pigment granules are not infrequently found. These cells may show ameboid movements, and are found in the blood in certain diseases. ERYTHROBLASTS, or NUCLEATED RED CELLS. These cells differ from the ordinary red cells in possessing a nucleus, and may show mitotic figures. They vary somewhat in size, but are seldom over 9.5 microns in diameter. By a loss of the nucleus, these cells become the erythrocytes, or normal red cells. The LEUKOCYTES are usually the finely and coarsely granular eosinophiles, and the bas ophites; lymphocytes are usually not numerous. MYELOPLAXES, or OSTEOCLASTS, are very large, irregular cells. The protoplasm is abundant, and a number of nuclei may be seen. These cells are of great importance in bone 74 CONNECTIVE TISSl KS. destruction, from which the term osteoclast is derived. They may be capable of ameboid movements and are phagocytic. The functions of red marrow are to make erythrocytes, granular leukocytes in large numbers and to store fat. Bones are nourished by blood-vessels that enter through the nutrient foramen and pass to the marrow cavity. From here, branches are sent to the various parts by way of the Haversian canals. Other vessels, derived from the periosteum, lie in Volkmann's canals, which are found in the circumferential lamellae. Nerves and lymphatics accompany the blood-vessels. Development of Bone. Bone is not a primary, but a secondary tissue. It is preceded by cartilage or by fibrous tissue. Bone developed from hyalin cartilage is called ENDOCHONDRAL, while that developed in fibrous tissue is re- ferred to as INTRA-MEMBRANOUS bone. ENDOCHONDRAL bone formation is the process by which the hyalin cartilage is converted into SPONGY bone. It is, in reality, a combined process, for so soon as the spongy bone is formed, this is changed to the compact variety by the intra-membranous, or periosteal method. When OSSIFICATION begins, the cartilage cells in that vicinity begin to multiply rapidly, and arrange themselves in rows parallel with the long axis of the bone. Multiplica- tion is most rapid in the center of the area, and, as a result, the new cells are unable to form new capsules for themselves ; in consequence, a large number are seen in one space called a primary areola, or marrow space. In the cartilage be- tween these spaces, calcareous matter is deposited, and the cells above and below arrange themselves into parallel rows. The cells within the areolae either disappear, be- come osteoblasts, or osteoclasts; the latter dissolve the car- tilaginous and calcareous partitions between the spaces. BONE DEVELOPMENT. 75 As a result of the latter, larger spaces are formed, and these are the secondary areola. Those cells that become osteo- blasts, lay down a thin layer of osseous tissue upon the re- maining partitions, so that, at first, these consists of a core of calcific material covered by a thin veneer of true bone. As the process continues, the calcareous matter is entirely removed and is replaced by bone. While these changes have been in progress, the perichon- drium has become the periosteum, which now forms osteo- blasts. These, with trabeculae of the periosteum and blood- vessels, pass inward toward the center of ossification, and enter the areolae. This vascularization forms the first marrow. The blood-vessels pass upward and downward from the center, following the process of calcification. Gradually, the delicate rod of cartilage is converted into a rod of spongy bone. The articular portions are separated from the shaft by an interposed disc, the epiphyseal cartilage. Periosteal bone formation now begins. The inner sur- face of the periosteum becomes converted into a thin layer of osseous tissue, and the osteoblasts remain surrounded by a small space that is continued along its processes. This space and its continuations are the lacuna and canaliculi. As the inner surface is changed to bone, the outer surface has a corresponding amount added to it, so that the thick- ness of the periosteum is proportionately the same. With the formation of periosteal bone, the various lamella are formed. The peripheral are merely the con- verted periosteum. The Haversian system and lamella are formed in the following manner. From the inner sur- face of the periosteal layer, projections are formed at various angles. These meet other projections, thereby enclosing a small space, the primitive Haversian canal. Osteoclasts gain access and make this space regular and 7 6 CONNECTIVE TISSUES. larger. Then osteoblasts lay down layer upon layer of osseous matter until only a small channel, the Haversian FIG. 27. CROSS-SECTION OF A DEVELOPING BONE OF A HUMAN FETUS OF FOUR MONTHS. a. Periosteum; b. boundary between endochondral and periosteal bone; c. perichondral bone; d. remains of area of calcification; e. endochondral bone; f, F. blood-vessel; g. g f . developing Ha versian spaces; h. marrow; i. blood-vessel (Stohr's Histology}. canal, is left. The remains of the peripheral lamellae be- tween the various systems go to make up the interstitial lamella. BONE DEVELOPMENT. 77 With the formation of the peripheral lamellae,* ^.he net- work of spongy bone is removed from the center by osteo- clasts. This leads to the formation of a marrow cavity. As the bone increases in size, the cavity increases in proportion, by the destruction of the surrounding bone. During the prime of life, bone formation exceeds cavity formation, but in old age, the reverse is the case, so that the shaft becomes thinner, and the cavity larger. The bone increases in diameter by the continued addition of peripheral lamellae, as a tree grows in thickness. It grows in length by the interposition of a disc of cartilage between the shaft and head of the bone. In this disc, new cartilage is formed as rapidly as ossification occurs. This is the cambium layer, and should it ossify, that end of the bone would no longer increase in length. This change occurs normally when full height is reached. This method of bone formation occurs in all bones except those of the face and of the vault of the cranium. Intra-membranous bone formation is the process whereby white fibrous tissue becomes converted directly into bone. Two periosteal layers are present, and between these, the bone is formed. Upon the fibrous bundles connecting them, osteoblasts deposit osseous material until all are con- verted at the same time the formation of Haversian systems occurs. Such bones increase, in thickness, as above, and laterally, by the maintenance of a layer of fibrous tissue at their edges. This is the cambium layer, and when full growth is attained, this layer ossifies, and union occurs between the various bones. 10. DENTIN will be considered under the TEETH. -II. BLOOD is the only liquid connective tissue. As it is part of the CIRCULATORY SYSTEM, it will be considered when that is described. CHAPTER V. MUSCLE TISSUES. Muscle tissues are those which produce the various movements of the body, whether voluntary or involuntary. Like epithelial tissues, they consist chiefly of cellular elements, the intercellular substance being small in amount. The varieties are voluntary striated, involuntary non- striated and involuntary striated. Voluntary striated muscles are characterized by being under the control of the will and are called skeletal muscles. Each MUSCLE consists of a large number of units called fibres, bound together by white fibrous tissue. Each fibre, or cell, is a long, narrow cylinder. It varies from one to five inches in length, and exhibits cross and longitudinal striations. It is composed of a large number of fibril I mY . . ; The ADVENTITIA, or EXTERNALS a thick fibre-elastic coat, IOO CIRCULATORY SYSTEM. and protects the vessel from undue dilatation. In some vessels, as renal and splenic arteries, longitudinal muscle fibres are found. This coat contains the larger trunks that h- FIG. 35. CROSS-SECTION OF A MEDIUM-SIZED ARTERY. a. Intima; b. media; c. adventitia; d. endothelial cells; e. subendothclial tissue; /. internal elastic lamina; g. circular muscle tissue; h. elastic fibres; i. external elastic lamina; k. white fibrous tissue; /. arteriole; m. venule, vasa vasorum. nourish the vessels, the vasa vasorum. The nervi vasorum are present also, and form branches that pass to the iriusclf ' coa't. " ' lit I.ARGE ARTERIES the iNTiMA is not so distinct and ARTERIES. 101 gradually fades into the media. The inter ml elastic lamina is usually not present as such, but the elastic fibres have fused with the elastic tissue of the intima to form the fenestrated membrane of Henle. The media is not very muscular, as it contains a predominance of elastic fibres that give it an elastic, but not a contractile, character. The same is true of the large branches of the aorta as the iliacs, innominate,- and common carotids. The adventitia differs but slightly. In SMALL ARTERIES, the intima is proportionately thinner, and the elastic lamina quite prominent and thick. The media is proportionately thicker than in the other vessels. It contains very little elastic tissue, and^ no jdastic lamina. As the vessels become reduced, the intima is the first to suffer; the subendothelial tissue disappears, and the endo- thelial cells are seen to rest upon the elastic lamina. The media becomes attenuated so that only a single layer of muscle fibres is seen. This soon becomes reduced to a few stray fibres. The adventitia becomes greatly reduced, and is represented by a few bundles of fibrous tissue. This is practically the PRECAPILLARY VESSEL. It is succeeded by the Capillary. 2. The Connecting vessels (Capillaries) are merely delicate tubes consisting of a single layer of endothelial cells placed end to end, and held together by intercellular cement. The endothelium is held by some to be phagocytic. They are the smallest vessels, and anastomose freely to form loose or dense plexuses. The loosest mesh is found in muscles. At times they are very irregular, possessing dilatations. They are practically very thin animal membranes, and through their walls the. liquid portion of the blood and the ameboid white blood cells have no difficulty in passing into the surrounding tissues. Small capillaries average 5 to 7 microns in diame- 102 CIRCULATORY SYSTEM. ter, and cross-sections show that they are encircled by two endothelial cells. Large capillaries average 8 to 13 mi- crons and are encircled by three to four endothelial cells. Stohr claims that capillaries can contract as nerve endings are found in the cells. In muscles, the capillaries run parallel to the course of the fibres, and are connected to one another by dilated vessels, or ampulla. In the liver, adrenal, spleen and carotid gland, the endothelium of the capillaries is usually attached to the functionating epithelium or parenchyma. Such vessels are termed sinusoids (Minot). In the kidney are seen little arterial capillary tufts interposed between two arterioles. Such structures are termed rctia mirabilui. In the penis, the arterioles empty into cavernous spaces, or sinuses without forming capillaries. In exposed regions, nose, ear, toes, kidneys and membranes of the nervous system, direct connections between arteries and veins exist. They are called anastomoses. The Afferent vessels (Veins) have the same general structure as arteries, though the coats are all thinner, and collapse more readily; they carry the blood toward the heart. The INTIMA often shows no internal elastic lamina; when present, it is not prominent. At intervals, this coat is thrown into folds called VALVES. These are duplications of the intima, and are usually arranged in pairs. At the place in which they are located, the vessels are usually slightly dilated. Valves occur in all the veins except the portal, pulmonary, hepatic, innominate, common iliacs, mesenteric, splenic and renal veins. The MEDIA contains a very small amount of muscle tissue, but is reinforced by fibre-elastic tissue. In some veins, the muscle tissue is entirely wanting (brain and bones), while in others, longitudinal muscle fibres are present in this coat. VEINS. 103 The lack of muscle tissue accounts for the collapsibility of these vessels. The ADVENTITIA is the most prominent coat, and may possess longitudinal muscle fibres. It is similar, in struc- ture, to that of the arteries. Blood-vessels are nourished by vessels that pierce the d FIG. 36. PORTION OF A CROSS-SECTION OF A HUMAN VEIN. A. Intima; B. Media; C. Adventitia a. internal elastic lamina; b. smooth muscle fibres; c. white fibrous connective tissue; d. smooth muscle fibres in the adventitia (Stohr's Histology}. adventitia and send branches to the media, the vasa vasorum. The intima is nourished by the blood that flows over it. The NERVES are chiefly sympathetic, and are dis- tributed to the media and adventitia. They are the nervi vasorum. Vessels are often the centers of extensive lymphatic chan- nels that lie in the adventitia. 104 CIRCULATORY SYSTEM. Table of comparison of arteries and veins : CHARACTER. ARTERIES. VEINS. Coats. Three. Three. Size. Thick. Thin. Intim. Elastic lamina promi- Not prominent; may be nent. absent. Media. Mainly smooth muscle. Little muscle, mainly white fibrous tissue. When empty. Do not collapse readily. Collapse readily. Valves. Absent. Usually present. Course of the blood. From the heart. Toward the heart. Character of Oxygenated (with ex- Deoxygenated (with ex- the blood. ception of that in the ception of that in the pulmonary artery). pulmonary veins). The Blood is the only liquid connective tissue. It is com- posed of CELLULAR ELEMENTS, THE CORPUSCLES, and the INTERCELLULAR SUBSTANCE, the LIQUOR SANGUINIS. The CELLULAR ELEMENTS are of three varieties, the RED CELLS, WHITE CELLS and PLATELETS. The RED CELLS, or ERYTHROCYTES, are non-nucleated, bell-shaped elements averaging 7 to 8.5 microns in diameter. The bell-shape is not seen unless the necessary precautions are exercised, that is to fix the blood before it becomes exposed to the air (see Blood Technic, p. 27). These cells have been studied under various conditions by Weiden- reich and Lewis and the author has found that they are to be readily studied in fetal tissues. Upon exposure to air these bell-shaped cells collapse and this accounts for the usual description as that of a biconcave disc. In the normal blood these cells form rouleaux and this is said to be due to the cells fitting into one another. When exposed to air these cells collapse and resemble rolls of coins on edge. RED BLOOD CELLS. 105 Under the microscope each cell is pale straw-colored or greenish. It consists of a framework, the stroma, that contains an inorganic compound that carries the oxygen; this is the hemoglobin. The presence of a cell membrane is still a matter of dispute. Some cells average from 5.5 to 7.5 microns, and are called microcytes, while those over 8.5 microns are macro- -, FIG 37. BLOOD CELLS. Red blood cells i, 2, 3 and 4 i, Bell-shaped red blood cell of man; 2, surface view of collapsed bell-shaped cell; 3, side view of 2; 4, surface view of red blood cell of the frog. White cells 5, 6 and 7. 5, Small lymphocyte; 6, hyalin cell; 7, finely granular oxyphil. cytes. Bethe found the various red cells in the following proportions: 6.92 microns, 42 per cent.; 7.26 microns, 28 per cent. ; 8.58 microns, 16 per cent. ; 6.6 microns, 8 per cent. ; 9.24 microns, 6 per cent. In normal blood, the cells tend to form rolls, or rouleaux. Under the same condition, 5,000,000 corpuscles are found, 106 CIRCULATORY SYSTEM. per cubic mm., in the male, and about 4,500,000 in the female. Nucleated red cells, or erythroblasts, are found in the fetus, in bone-marrow and the spleen. The cell of average size is called a normoblast, the smaller, a microblast, and the larger, a macroblast. In fishes, reptiles, birds and amphib- ians, the red cells are nucleated. In all mammals, they are circular, except in the camel family, in which they are oval. In the frog, the red cells are very large, oval, biconcave, nucleated discs that are far larger than the same cells in man. The size of the red cell is by no means proportionate to that of the animal. The musk deer possesses one of the smallest (2.4 microns), while the proteus has about the largest (62.5 microns). That of the elephant is but 9.2 microns in diameter, and beside it stands that of the hum- ming bird, with a diameter of nearly 9.4 microns. The red cells are more numerous in carnivorous than in herbivorous animals, while in birds they are larger in size. In the amphibians, where the size is great, the number is small. According to Malassez and Hayem, each cu. mm. of goat's blood contains 18 to 19 millions of red cells; birds 2 to 3 millions; reptiles 0.5 to 1.6 millions; frogs 400,000; proteus 36,000; bony fishes i to 2 millions; torpedo 140,000. WHITE BLOOD CELLS, or LEUKOCYTES, are large, pale cells readily distinguished from the above. About 5,000 to 8,000 are found in each cubic mm. of blood, and some of the varieties have the powers of motion and phagocytosis. They are classified as follows: 1. LYMPHOCYTES (SMALL LYMPHOCYTES). 2. HYALIN CELLS (LARGE LYMPHOCYTES). 3. POLYMORPHONUCLEAR LEUKOCYTES, Or FINELY GRANU- LAR OXYPHILS (Formerly neutrophil). WHITE BLOOD CELLS. 107 4. COARSELY GRANULAR OXYPHILS (Formerly acidophil). 5. FINELY GRANULAR BASOPHILS. 6. COARSELY GRANULAR BASOPHILS. 1. The LYMPHOCYTES average 5 to 11 microns. Each consists of a large darkly staining nucleus surrounded by a narrow rim of faintly stained protoplasm. It is both ameboid and phagocytic, and constitutes about 15 to 30 per cent, of all the white cells. 2. The HYALIN CELL averages 11 to 15 microns. Both nucleus and protoplasm stain but faintly, hence the name. In the protoplasm some basophilic granules are occasionally seen. It is actively ameboid and phagocytic. It represents 2 to 6 per cent, of the white cells. 3. POLYMORPHONUCLEAR LEUKOCYTES, Or FINELY GRANU- LAR OXYPHILS, F. G. ACIDOPHILS, Or F. G. EOSINOPHILS, average 7.5 to n microns. The nucleus has many shapes, as U, V, W, etc., and may even be divided in a number of segments (polynuclear) . The protoplasm contains a num- ber of fine granules that take the acid stain deeply. These granules were at one time regarded as neutrophilic, and the cells were called neutrophils. They are actively ameboid and phagocytic, and represent 60 to 72 per cent, of all leukocytes. 4. The COARSELY GRANULAR OXYPHIL, C. G. ACIDOPHIL, or EOSINOPHIL, is about 7 to 10 microns in diameter. The protoplasm contains a few large granules that take the acid stain deeply. It was formerly called acidophil, or eosino- phil, and is actively ameboid, but not phagocytic. It repre- sents .1 to 4 per cent, of the leukocytes, though rarely over 2 per cent, except in childhood. 5. The FINELY GRANULAR BASOPHiL resembles GROUP 3, except that the granules take a basic stain, and are present to the extent of .1 to i per cent., but usually under .25 per cent. 108 CIRCULATORY SYSTEM. 6. The COARSELY GRANULAR BASOPHiL is said to be absent from normal blood. It is a relatively large cell, and is also called the mast cell. Another cell that is usually described among the leuko- cytes is the myelocyte, or marrow cell. This cell is not a normal constituent of the blood, but is found there in certain blood diseases. (See Bone-marrow, p. 73.) The BLOOD PLATELETS, or THROMBOCYTES, are small (2 to 4 microns), oval or circular discs, capable of ameboid move- ment. They number about 200,000 to 300,000 per cubic mm. Their function and origin are unknown. They can readily be found in blood fixed in a i per cent, osmic acid solution. In certain diseases the platelets are increased while in others they are diminished. According to Helber, platelets are not found in the blood of frogs or birds. The INTERCELLULAR SUBSTANCE, Or LIQUOR SANGUINIS, contains the salts of the blood. Its density is such that the cells retain their normal shape. If, however, solutions are added that differ in density, the action upon the cells is characteristic. Upon the addition of strong salt solution, the cells become irregular in outline, and are crenated. If water be added, it dissolves the hemoglobin, and the cells swell and become spherical, but, as a rule, are not destroyed. The action of acetic acid is important. The addition of a .3 per cent, solution decolorizes the red cells and renders the 1 white cells more distinct. This is made use of in Hema- tology for the purpose of counting the white cells, in a fresh condition. When blood clots, fibrin is precipitated, and this entangles the corpuscles. HEMOGLOBIN is an organic compound of iron, and, as it HEMAL GLANDS. I I0 9 exists in the blood, it cannot be readily studied. Its con- version into the crystalline state is not difficult. HEMOGLOBIN CRYSTALS will be formed if a drop of de- fibrinated blood be mixed with a drop of Canada balsam, or clove oil, and covered with a cover-glass. They are large, red, tetrahedral crystals. HEMIN CRYSTALS may be prepared by adding a small crystal of salt arid two drops of glacial acetic acid to a little dried blood, and heating until the mixture boils. During this process it should be covered. When cool, small FIG. 38. i. Hemin crystals of man ( X56o); 2. crystals of common salt; 3. hematoid crystals of man (Stohr's Histology}. FIG. 39. HEMOGLO- BIN CRYSTALS OF A DOG (Xioo); a crystal separating into fibres (Stohr's Histology). brownish crystals will be found. These may be single or grouped in the form of rosettes, and are known as Teich- mann's crystals. Among the blood-making organs are placed the COCCY- GEAL and CAROTID GLANDS. The former, LUSCHKA'S GLAND, is found in front of the coccyx, and is joined to the middle sacral artery. It is surrounded by a fibrous sheath, which sends in septa that divide the organ irregularly into areas, or compartments. The latter contain groups of polyhedral cells surrounded by dense plexuses of capillaries. Nonmyelinated nerve fibres are numerous. HO CIRCULATORY SYSTKM. The CAROTID GLAND is found at the bifurcation of the com- mon carotid artery, and its structure is the same as that of Luschka's gland. HEMOLYMPH NODES. These organs vary in size from a pin head to a large bean and are found in abundance in the re- troperitoneal and cervical regions and less numerous else- where. Each is surrounded by a capsule of white fibrous and yellow elastic tissues, containing a little smooth muscle tissue; trabeculae pass in and form the framework of the organ. In the framework are found red and white blood- cells. Of the latter, the lymphocytes are the most numer- ous; besides these hyalin, finely granular oxyphils and basophils are found in varying numbers. In addition, mononuclear phagocytes that contain pigment and disinte- grating red cells are seen. Beneath the capsule and following the trabeculae to the hilus are seen sinuses that do not contain lymph but blood. These organs usually possess no lymphatics. The blood- vessels enter at the hilus and form capillaries within the organ; these capillaries communicate with the blood sinuses. The larger views are in the trabeculae and end in thin-walled lacunae that possess perforated walls, by means of which they communicate with the blood sinuses. Certain atypic organs possess lymphatics. Nerves are present and probably pass to the smooth muscle tissue. Some of these structures resemble the spleen in structure, others the marrow and still others ordinary lymph nodes. Parasympathetics, or Aortic Bodies. These are two to four brownish bodies found in the neighborhood of the inferior mesenteric artery and closely related with the aortic sympathetic plexus. Each is surrounded by a capsule of white fibrous connective tissue that sends in trabeculae that form the framework of the organ. In the meshes of this framework are found the epithelium which consists of BLOOD VESSELS AND NERVES. Ill groups of polygonal or cuboidal cells closely packed and of the chromaffin type. The blood-vessels derived from the aorta, or inferior mesenteric artery, follow the trabeculae and form a rich capillary plexus around the epithelial cell-groups. The nerves are from the sympathetics and their relation and arrangement is similar to the nerves of medulla of the adrenal. These organs are found chiefly in childhood. CHAPTER VIII. THE LYMPHATIC SYSTEM. The Lymphatic System includes the Lymphatic and Thoracic Ducts, capillaries and intermediate vessels, and a number of organs, Lymph Node (Lymphatic Gland), Spleen and Thymus Body. The ducts resemble veins more than arteries. Their walls are thin, and they possess valves. The arrangement of the muscle, and the distribution of the nerves, are like those of an artery. Lymph capillaries are much larger than those of the vascular system, measuring 30 to 60 microns in diameter. Lymphoid tissue is arranged in four ways, DIFFUSE, SOLITARY FOLLICLES, AGMINATED FOLLICLES AND LYMPH NODES, or LYMPHATIC GLANDS. The first three have been considered under Lymphoid Tissue. (See Connective Tis- sues, p. 66). Lymph Nodes, or Glands, are small, bean-shaped organs, surrounded by a CAPSULE, and composed of CORTEX, ME- DULLA and HILUS. The CAPSULE consists of white fibrous tissue and contains some yellow elastic and smooth muscle tissues; beneath is a lymph space or sinus. From the inner surface of the capsule, trabeculcB are sent into the cortex, and these divide the latter into a number of masses called secondary follicles, or nodules. The lymph space continues along the trabeculae. The CORTEX contains the secondary nodules and tra- beculcz. The former consist of dense lymphoid tissue, and 112 LYMPH NODE. 113 contain a germinal center. The cells are chie'fiy lympho- cytes, which are arranged in concentric layers around the periphery. Other cells of the hyalin variety are found in the central portion. During gestation, nucleated red cells may be present. The follicles continue into the center of the node as the medullary cords. FIG. 40. LONGITUDINAL SECTION OF A LYMPH NODE. a. Hilus; b. arteriole; c. venous sinuses; d. adipose tissue; e. secondary nodule of cortex; /. vein in medulla; g. subcapsular lymph sinus; h. germinal center of secondary nodule; i, i. trabeculae; k. capsule; /. lymph sinus; m. medullary cord. The trabecula separate the follicles from one another, and pass into the medulla surrounded by the lymph space. The MEDULLA consists of the medullary cords and trabeculce. The cords are the band-like continuations of the second- ary follicles, and are separated from the trabeculae by the lymph spaces that accompany the latter. They consist of dense lymphoid .tissue, supported by reticulum. At the hilus, the medulla comes to the surface. 114 THE LYMPHATIC SYSTEM. The HILUS is a scar-like depression at one side, where the vessels enter and leave. At this place, the secondary nodules are wanting, and the medulla comes to the surface. The arterial vessels, to a great extent, enter at the per- iphery of the node. Their branches continue into the trabeculae, and then pass into the follicles. Those that enter at the hilus also follow the trabeculae, and bridge the sinuses to enter the lymphoid tissue. The venous radicals all pass toward the hilus, where one or more vessels may be formed that carry all the blood away. The afferent lymph vessels pierce the capsule at different points, and empty into the capsular sinus. The lymph passes down along the trabeculae, and niters through the organ. All the lymph is collected into one or more efferent vessels that leave at the hilus. Lymph nodes are the highest form of lymphoid tissue. They are scattered throughout the lymphatic system, in the pathways of the vessels. They are often collected into groups, as in the axillary, inguinal and femoral regions. Lymph nodes are uncertain structures, as they may disappear early, or change from place to place. They make the white blood-cells, filter the lymph, are the centers of cell destruction, and may possibly give rise to red blood-cells, as in the female during pregnancy. SPLEEN. The Spleen is a lymphoid structure, surrounded by a capsule of dense white fibrous tissue that contains invol- untary non-striated muscle fibres, and limits the splenic substance. The capsule sends in trabeculce that divide the organ ir- regularly into compartments. At one side is a depression, the HILUS, at which the vessels enter and leave. SPLEEN. 115 The splenic substance consists of two main portions, the PULP and MALPIGHIAN Or SPLENIC CORPUSCLES. The PULP is composed of diffuse lymphoid tissue, dis- integrating red cells, nucleated red cells and some large polynuclear elements. To the red cells the peculiar color is due, and the organ has been called the " grave-yard of the red cells." The cells are supported by retiform connective tissue. FIG. 41. SECTION OF SPLEEN. fl . Capsule; b. trabeculae, longitudinal section; c. pulp; d. splenic corpuscle; e. germinal center of corpuscle; /. eccentric arteriole in corpuscle; g. trabecula, cross-section; h. blood-vessel. The SPLENIC CORPUSCLES are solitary follicles and consist of dense lymphoid tissue. They differ from the ordinary follicle in possessing an eccentric ally- placed arteriole. This lymphoid tissue is held to be in the adventitial sheath of the arteriole, and forms a spherical mass at the bifurcation of the vessel. These follicles usually show germinal centers. Il6 THE LYMPHATIC SYSTEM. The circulatory system of the spleen is peculiar in being an open one. Capillaries, as such, do not exist, and the arterioles and venules are connected by blood spaces, or ampulla. The splenic artery enters at the hilus, and breaks into branches that follow the trabeculae. Of these, some quickly pass into the pulp, while others follow the tra- beculae to their smallest divisions. The spleen is divided into lobules, about one mm. in diameter, each one of which is further subdivided into histologic units, one for each termi- nal artery, or ampulla. These terminal vessels are covered by a lymphatic sheath, the ellipsoidal sheaths. The terminal ampullae are porous, and continue as veins. The spleen is subject to rhythmic contractions, one per minute, and about 18 per cent, of its volume is lost at each contraction. These are produced by the involuntary muscle in the capsule and trabeculae. When the cardiac impulse sends the blood into the arteries, the blood passes into the ampullae, and through the porous walls into the pulp. When the rhythmic contractions occur, the blood is forced into the veins, and, at the same time, the arteries are closed. This shows an open circulation (Mall). Lymphatics occur in the capsule and trabeculae only. THYMUS BODY. The Thymus Body is essentially a lymphoid structure, though it undergoes peculiar changes in its life history. It -originates as a true gland (epithelial organ), but soon leukocytes infiltrate it, and cause the disappearance of the epithelium, except small islands. After the sixth year, it generally undergoes further change. The lymphoid tissue is gradually replaced by adipose tissue, so that an old thy m us will show but little lymphoid tissue. This organ is surrounded by a capsule of white fibrous THYMUS BODY. 1 17 tissue that sends in septa, which divides the.organ into LOBES and LOBULES. Each LOBULE consists of cortex and medulla. The CORTEX is composed of dense lymphoid tissue, and stains deeply, owing to the large number of leukocytes present. The MEDULLA consists of diffuse lymphoid tissue, and takes, therefore, a lighter stain. The supportive tissue is reticulum. FIG. 42. SECTION OF THE THYMUS BODY OF A CHILD. a. Capsule; b. interlobular connective tissue; c, c. adipose tissue; d. blood- vessels in interlobular tissue; e. cortex; /. mzdulla; g. blood-vessel in lobule; h, h. corpuscle of Hassal; i. corpuscle of Hassal magnified. In the medulla, are found small, peculiar bodies, con- sisting of concentrically arranged epithelial cells; these are the thymic corpuscles, or corpuscles of Hassal. They are sup- posed to represent the remains of the epithelium, though some hold that they represent endothelium of blood-vessels. These bodies are encapsulated, and may be compound. The blood-vessels pierce the capsule, and form branches in the interlobular connective tissue. From these, capil- laries enter the lobules and are distributed to the lymphoid tissue. CHAPTER IX. ALIMENTARY TRACT. The Alimentary Tract starts at the lips, and extends to the anus. It receives the food, digests it and casts off that which is undigested. The various portions perform differ- ent functions, and the lining cells differ accordingly. The inner coat is a mucous membrane that gives rise to glands, which are devices of nature for increasing the secretory surface. The absorptive surface is increased by prolon- gations of the mucosa into the lumen of the organ (villi of the small intestine). The Lip is covered externally by SKIN, and internally by MUCOUS MEMBRANE. Between these, are found connective tissue and muscle. The SKIN consists of two portions, the epithelial, or epidermis, and the connective tissue portion, or derma. The epidermis is composed of stratified squamous cells, of which two layers, the stratum corneum and stratum Mal- pighii are distinct. The stratum corneum is the outer, and consists of nonnucleated scales; the stratum Malpighii is the genetic portion. Its lowest cells rest upon a basement membrane, and are columnar in shape. Those above are polyhedral; the latter become more flattened as the corneum is approached. The derma consists of white fibrous con- nective tissue supporting blood-vessels, nerves and lym- phatics. Beneath the epithelium it is thrown into waves called papillce. The mucous surface is also lined by stratified squamous cells, that differ from the outer, however, in being larger 118 TKKTII. 119 and less readily stained. The cells rest upon a basement membrane, beneath which is the tunica propria, composed of papillated, delicate fibro-elastic tissue. Between the tunica propria and skin, are found connec- tive tissue and voluntary striated muscle. Near the tunica propria are to be seen small, compound tubular glands that open upon the mucous surface. At the margin of the lip these two surfaces join, and this is the muco-cutaneous junction; here the epithelial layer is quite thick, and the cells are larger and bladder-like, resembling the epitrichial cells of the fetus. Blood-vessels are found in great abundance, and form dense plexuses, especially around the glands. The Mouth is'lined by a MUCOUS MEMBRANE, consisting of stratified squamous cells resting upon a basement mem- brane and tunica propria. Here and there are found small glands of the same nature as those found in the lips. THE TEETH. The Teeth are the chief organs of mastication and are adapted for cutting, grinding, holding, etc. Each consists, anatomically, of CROWN, that portion above the gum; ROOT or FANG, that portion in the jaw; NECK, the narrow portion between the preceding, covered by the gum. Histologically considered, there is the ENAMEL that covers the crown; the DENTIN that forms the bulk and gives the shape of the tooth; the CEMENTUM that covers the den tin of the fang; the PERIDENTAL MEMBRANE that surrounds the root and holds the tooth in place; the PULP that occupies the pulp cavity and is the nutritive and sensitive portion of the organ. In the root of the tooth is a canal that leads into the PULP CHAMBER; this is the ROOT CANAL. The enamel is the hardest substance in the body and 120 ALIMENTARY TRACT. forms a cap-like covering, of varying thickness, of the dentin. It is thickest at the cutting or occlusal surface of the teeth and diminishes in thickness as the root is ap- proached. It is said to consist of 97 per cent., or more, of inorganic matter and 3 per cent., or less, of organic matter. The enamel consists of hexagonal enamel prisms that are arranged perpendicular to the surface of the dentin, and represent modified epithelial cells. Each ENAMEL PRISM or FIBRE has a wavy or tortuous course with its inner end fitting into a slight depression in the dentin. The prism is of the same diameter throughout, though the sides may not be straight and even. As a result, near the surface of the tooth shorter additional prisms are found and these are the SUPPLEMENTAL PRISMS. The prisms seem to be held together by a transparent cement which is apparently inorganic in composition. In a prepared section of the tooth are seen some brown striations that run almost parallel to the surface of enamel or dentin and in the latter instance may run the entire extent of the crown. These are the "brown striae of Retzius. " The cause of these striae is still in dispute. Tomes believes that they represent successive positions of the enamel cap. When studied with reflected light the "lines of Schreger" are seen in the enamel. These are apparently due to various directions taken by the different bundles of enamel prisms, and are well marked near the surface of the dentin and less so toward the surface of the enamel. Dentin. This portion forms the bulk of the tooth and gives it its shape. It is yellowish-white in color, harder than bone, and represents ivory. It is everywhere covered by either enamel or cementum. It is composed of about 72 per cent, of inorganic matter and of about 28 per cent, of organic matter. The parts of importance are the DENTINAL SHEATHS, TEETH. 121 MATRIX, and DENTINAL FIBRES. The DENTINAL SHEATHS, or NEUMANN'S SHEATHS, are delicate tube-like masses of 4 -. FIG. 43. LONGITUDINAL SECTION OF AN INCISOR TOOTH A. Crown; B. Neck; C. Fang; i. enamel; 2. dentin; 3. pulp-cavity; 4. ce- mentum; 5. root-canal (after Stohr's Histology}. dense dentin that seem indestructible and will persist when the matrix has been destroyed. They extend in a curved 122 ALIMENTARY TRACT. or spiral course from the pulp cavity to the enamel or cementum, diminishing in diameter as they pass outward. Within the sheaths are spaces called DENTINAL TUBULES or CANALICULI. They radiate from the pulp cavity to the periphery and have the same curved or spiral course of the sheaths. They diminish in diameter from within outward, and terminate at the enamel or cemental surface either by anastomosing with one another, ending bluntly or opening into the interglobular spaces. The pulp cavity end is usually funnel-shaped and the tubules here are closely packed so that there is very little matrix. The tubules branch toward the enamel or cementum. The curvatures of the tubules are long and short, or primary and secondary, respectively. The DENTINAL FIBERS, or TOME'S FIBRES, represent the processes of the odontoblasts and they occupy the dental tubules, branching as the latter do and diminishing in size as the tubules become smaller. Some claim that they do not belong to the odontoblasts, but represent nerve tissue surrounded by connective tissue. The MATRIX occupies the space between the dentinal sheaths. It consists of a more or less homogeneous dentin that is not so hard as that surrounding the canaliculi in the form of the dentinal sheaths. It is less abundant near the pulp cavity, as the sheaths here are very close together. Farther out, as the sheaths become smaller in diameter, the matrix increases along the margin of the dentin near the enamel, a varying number of small irregu- lar spaces, the interglobular spaces, are seen; these repre- sent areas of imperfect calcification and they are filled with a gelatinous substance. Between dentin and cementum these spaces are smaller, and under low power give a granular appearance to the area; this represents " Tome's granular layer." TEETH. 123 Cementum. This is a bone-like substance tfyat covers the root of the tooth. It consists of about 66 per cent, inor- ganic matter and 34 per cent, organic matter. It is thickest at the apex of the tooth and becomes gradually thinner as the cervix or neck is approached and ends at the lower margin of the enamel. It resembles bone very closely, contains LACUNA CANALICULI and LAMELLA, but no Haversian systems. The LAMELLA are about the same in number but thicker at the apex than near the cervix. This applies to young teeth. In older teeth the layers are not only much thicker near the apex but are also more numerous, the shorter added lamellae constituting sup- plemental lamella. The layers may or may not run parallel to the den tin. Passing through the lamellae at varying inter- vals are fibres that seem to bind the layers together, resem- bling the fibres of Sharpey. Between the lamellae are irregu- lar spider-like spaces that resemble, but vary in size, shape and number of canaliculi, those of bone; they lie partially in one layer and partially in another and their long axes are parallel to the surface of the tooth. Extending out from the lacunae are the CANALICULI which usually are directed peripherally, though some are seen extending in all directions. The CEMENTOBLASTS occupy the lacunae. They are oval, stellate, or elongated elements and usually correspond in direction to the lacunae. The processes vary in length and form, and most of them extend toward the periphery, following the canaliculi. Dental Pulp. The Pulp is the highly vascular and sensi- tive mucous connective tissue that occupies the pulp cavity, or chamber and root canals and is concerned with the nutrition and growth of the tooth. It is composed of cells and intercellular substance and contains blood- vessels and nerves. 124 ALIMENTARY TRACT. The cells are of various varieties, the most important of which are the ODONTOBLASTS. These cells are found upon the surface of the pulp and form a continuous layer of cells one layer deep. The cells are elongated flask- shaped elements from which three sets of processes extend. These are dentinal, pulpal and lateral. The dentinal process or processes arise from the peripheral end of the cell and extend into the dentinal tubules, and they have been described under the dentin. The lateral processes pass from the sides of the cells to the neighboring cells, while the pulpal processes extend from the central ends of the odontoblasts to the deeper cellular elements of the pulp. The nucleus occupies the end of the cell next the pulp reticulum. Beneath the layer of odontoblasts there is a narrow layer of tissue almost devoid of cells, then an area of which the cells are quite numerous, and again a region, the center of the pulp, in which there are very few cellular elements. The cells are spindle-shaped, stellate and spheroid in form and possess many or few hair-like processes that pass in all directions. The ARTERIES, apical, of the pulp are derived from a branch that enters the root canal of the tooth; as this vessel passes toward the pulp chamber it gives off branches that form plexuses parallel to the long axis of the tooth; ultimately forming rich capillary plexuses in the neighbor- hood of the odontoblastic layer. The blood is collected by venous channels that anastomose freely and empty into one channel that leaves through the root canal. The NERVES, one or more, pass through the root canal giving off a few fibres here; in the pulp chamber branches are distributed in every direction forming arch plexuses, after losing their myelin sheaths, beneath the layer of odontoblasts. From this plexus fibres are said to pass between the odontoblasts to end in bulbous enlargements TEETH. 125 within the central ends of the dentinal tubules. Magitot claims, however, that the dentinal fibres are continuations of the nerve fibres. The Peridental, or Alveolodental membrane, is a highly vascular and sensitive white fibrous tissue membrane that lines the alveolar processes of the jaw and covers the roots of the teeth. It is thickest at gum and apical portions and thinnest in the middle. The fibrous elements are bundles of white fibrous tissue that pass into the cemental layers on the one hand and into the bony tissue of the jaw on the other hand, resembling Sharpey's fibres. In general around the apex of the tooth the fibre bundles are arranged fan-like and are directed upward and outward. In the body of the tooth the fibre bundles pass directly outward from the cementum to the alveolar wall and are largest and strongest here. At the gum margin the fibre bundles pass outward and are lost in the fibrous tissue of the gum, or pass toward the adjacent tooth as the case may be. Upon the inner surface of the membrane are found the cementoblasts; these are irregular flattened elements possess- ing a clearly defined nucleus and numerous delicate irregular processes that extend in various directions. They are evenly distributed. Upon the opposite (alveolar) surface of this membrane are the osteoblasts that form the bone of the jaw. In the meshes of the fibre bundles are found fibroblasts or connective-tissue cells and some osteoclasts or bone-destroying cells. The latter are large, fairly regular, oval or round cells that possess several nuclei and usually have no processes. The arteries are derived from the apical artery and pass up parallel to the long axis of the tooth, giving off branches at intervals; these form capillary plexuses beneath the alveolar and cemental side of the membrane. The blood 126 . \I.I.MK.\T.\RY TRACT; is collected by venous channels that ultimately empty into the apical vein. The veins are likewise derived from those at the apex and are distributed somewhat like the arteries. The functions of the alveolodental membrane are physical and sensor. It holds the tooth in place, returns it to its normal position when slightly rotated or displaced; upon one side it forms cementum and upon the other it forms bone. Nasmyth's Membrane. This is a thin indestructible membrane covering the enamel of the tooth. It is said by some to be the remains of the enamel organ, while others claim it is a continuation of the cementum. The former seems the more probable origin. THE TONGUE. The Tongue, like the Teeth, occupies part of the mouth cavity. It is covered by a MUCOUS MEMBRANE that con- sists of stratified squamous cells, basement membrane and tunica propria, which, along the sides and base, is papilla ted. The upper surface, or dor sum, is characteristic. Its apical two-thirds is covered by minute projections, called papillce; of these there are three varieties, FILIFORM, FUNGIFORM and CIRCUMVALLATE. The central portion consists chiefly of voluntary striated muscle. The FILIFORM PAPILLA are cone-shaped projections of the tunica propria, covered by the stratified squamous cells, the outer ones of which are hard and horny. The central part of a papilla consists of white fibrous tissue, which is thrown into small secondary papilla that are not visible externally. These papillae are the most numerous, and are scattered over the whole of the apical two-thirds. They are directed backward, and are the ones that produce the TONGUE. 127 scratching sensation when the hand is lickea by a lower animal. The FUNGIFORM PAPILLA are flat- topped, table-like structures, in which the sides are parallel. They have secondary papillae, and are scattered like the filiform variety, but are less numerous. The CIRCUMVALLATE PAPILLA are the most important. While the top is flat, the sides usually converge and give this variety a narrow base. SECONDARY PAPILLA are found only on the upper portion. Each papilla is sur- rounded by a little -vallum, or ditch, hence-the name. These papillae are the least numerous, and are found only in one area. Ten to fifteen arrange themselves like a letter V, with the apex at the foramen cecum, a little de- pression that lies at the boundary of the apical two-thirds and basal one- third of the tongue. These papillae contain TASTE-BUDS along their sides. The TASTE-BUDS are the organs of taste, lie in the epithelial portion of the sides, and have a definite structure. They are barrel-shaped, and open at the exposed ends. Each consists of two kinds of cells, outer (stave-like), the sustentacular , or supporting cells, and the inner, neuro- epithelial elements. The SUSTENTACULAR cells are flat and stave-like elements possessing a prominent nucleus. The neuro -epithelial elements are spindle-shaped, and each ends in a minute, hair-like process, the gustatory hair, that projects through an opening in the barrel, the gustatory pore. The nerve fibre that extends to each bud forms branches, one of which is supplied to each neuro-epithelial cell. Beneath the mucosa is found the MUSCULATURE of the tongue. This consists of the voluntary striated variety, arranged longitudinally, vertically and transversely. The longitudinal fibres are arranged in bundles that lie beneath 128 ALIMENTARY TRACT. FIG. 44. CROSS-SECTION OF TONGUE. a. Stratified squamous cells; b. basement membrane; c. tunica propria; d. serous glands; e. mucous glands; /.^venule; g. longitudinal muscle fibres; h. vertical muscle fibres; i. transverse muscle fibres; /. septum; m. filiform papilla; n. secondary papillae; r. adipose tissue. A. Filiform papilla. B. Fungiform papilla. C, D. Circumvallate papillae m, m. taste-buds; w, n. glands. E. Taste-bud o. nucleus of neuro-epithelial cell; r. nerve fibre; s. gustatory hair; t. sustentacular cell; v. neuro- epithelial cell. TONSILS. 129 the tunica propria and extend around the tongue. They are separated by small bundles of vertical fibres. In the center, the fibres are vertical, oblique and transverse, and are separated in the middle line by a little partition, or septum. This consists of white fibrous tissue, and arises at the base, but does not reach the tip. It varies in height, being higher in the middle than at either end. In the muscular portion, small glands afe often found. Occasionally, branched muscle fibres are found. The true base of the tongue, the posterior one-third, possesses no papilla. It contains small salivary glands and collections of lymphoid tissue called the lingual tonsils. The blood-vessels are quite numerous; the capillaries ex- tend into the papillae and between the muscle fibres and form plexuses around the glands. The lymphatics are in the base, and are found quite numerous in the tunica propria, where they receive branches from the papillae. THE TONSILS. The Tonsils are found just between mouth and pharynx, and are essentially lymphoid structures. They are covered, upon their exposed surface, by strati- fied squamous cells that dip down into the organ in the form of irregular tubes called the tonsillar crypts. The organ is separated from the surrounding tissue by a layer of white fibrous tissue, the capsule, that sends in trabeculae, which form the main framework of the organ. Th/bulk of the tonsil consists of lymphoid tissue, in the form of the diffuse variety and solitary follicles. The latter show germinal cen- ters, and are found chiefly around the crypts. The support- ive tissue is of the retiform -variety. Leukocytes may be seen on their way to the crypts, where they become the salivary corpuscles. 9 130 ALIMENTARY TRACT. Blood-vessels, and especially lymphatics, are numerous. The vascular capillaries ramify the lymphoid tissue, while the lymph channels surround the follicles and form a peripheral vessel beneath the fibrous capsule. '/ ; 4 FIG. 45. VERTICAL SECTION OF HUMAN TONSIL. a. Stratified squamous epithelium; b. basement membrane; c. tunica propria; d. trabecuke; e. diffuse lymphoid tissue; /. adipose tissue; h, capsule; /. glands; k. muscle; /. blood-vessel; ;;/. epithelium of crypts: (/, q. crypts. THE PHARYNX. The Pharynx is a musculo -membranous bag that connects the mouth cavity and the esophagus. It has three coats, MUCOUS, FIBROUS and MUSCULAR. The MUCOUS COAT is lined, in the lower, or alimentary portion, by stratified squamous cells. The upper, or res- piratory, part is lined by stratified ciliated cells. These all rest upon a basement membrane, beneath which is the tunica propria, that is thrown into waves or papilla?. The tunica ESOPHAGUS. 131 propria contains a considerable amount of difTase lymphoid tissue. The FIBROUS COAT is composed of large bundles of white fibrous tissue, and serves as a support to the larger vessels and the small pharyngeal glands. It also serves as an attach- ment for the muscle fibres. The MUSCULAR COAT consists of voluntary striated muscle, surrounded externally by loose areolar tissue. The blood-vessels and lymphatics are numerous. The cap- illaries are found in the mucous and muscular coats, around the glands and between the muscle fibres. ESOPHAGUS. The remainder of the Alimentary Tract is tubular, and possesses four coats, MUCOUS, SUBMUCOUS, MUSCULAR and FIBROUS. The MUCOSA is further subdivided into four layers, epithelium, basement membrane, tunica propria and muscularis mucoscz. In the Esophagus, the MUCOUS COAT is lined by stratified sqamous cells. These rest upon the basement membrane, beneath which is the papillated tunica propria. The latter consists of yellow elastic and white fibrous tissues, in which the capillary vessels form a delicate network beneath the epithelium; the ducts of the glands pass through this layer on their way to the surface. The muscularis mucoscz con- sists of involuntary, nonstriated muscle fibres, circularly and longitudinally arranged. In the upper portion of the esophagus, this layer is often wanting, but in the lower part it is always present. In the relaxed condition, the mucous and submucous coats are thrown into longitu- dinal folds. The SUBMUCOUS COAT is composed of coarser bundles of white fibrous tissue, which forms a loose network for the 132 ALIMENTARY TRACT. support of the large blood-vessel trunks. In this coat are seen a number of glandular structures, the esophageal glands, which are apparently mucous, as they stain lightly. They send their ducts through the mucous coat. As the FIG. 46. CROSS-SECTION ESOPHAGUS. a. Stratified squamous epithelium; b. basement membrane; c. tunica propria: d. muscularis mucosae; e. esophageal gland; /. blood-vessel; g. sub- mucosa; k. outer longitudinal muscle; /. fibrous coat; n. inner circular muscle. stomach is approached, these glands become more numerous, and may even be found in the mucosa. The MUSCULAR COAT consists of muscle fibre, arranged in two layers, inner circular and outer longitudinal. In the STOMACH. 133 upper third, these fibres are of the voluntary striated variety, in the lower third, smooth, and in the middle portion, mixed. The involuntary variety continues throughout the remainder of the tract. The FIBROUS COAT consists of fibre-elastic tissues, and connects the organ with surrounding tissues. It sends in bundles between the muscle bundles, of which they are said to form the perimysium. The blood-vessels pass directly to the submucosa, where branches are formed, and sent to the mucous and muscu- lar coats. Here they form longitudinal plexuses. The lymphatics follow the same general course. The nerves end in the muscular coat and beneath the epithelial cells. Others surround the glands. STOMACH. The Stomach is the first part of the tract in which the food rests for any length of time, and in which active diges- tion and absorption occur. Although very large, it still represents a tube, and has the four coats above mentioned. It is divided into three portions, the CARDIA, FUNDUS and PYLORIC END. They pass into one another insensibly, and the structure of the first two parts is practically the same. The MUCOUS COAT presents a great change over that of the esophagus, showing a higher degree of specialization. In it are seen, with the naked eye, a number of minute depressions, the gastric crypts, or pits, from which the gas- tric glands extend into the deeper portions. Between or bounding the pits, are the inter glandular projections. Each gland consists of mouth, neck and fundus, or secretory por- tion, and is lined by simple epithelial cells. The cells rest upon a basement membrane, which, in turn, 134 ALIMENTARY TRACT. rests upon the tunica propria. The latter forms the core of the interglandular projeetions that form the boundaries of the pits. Between the glands, the tunica propria consists of narrow bands of the fibrous tissue, which contains a great deal of diffuse lymphoid tissue, bundles of muscle fibres from the muscularis mucosae, and capillaries, both vascular and lymphatic, in great numbers. In places, the lymphoid tissue is collected into solitary follicles that are lens-shaped, and are called the lenticular follicles, or glands. These are numerous in the pyloric end. The MUCOSA is bounded ex- ternally by the muscularis mucosce, which consists of two layers of smooth muscle fibres, arranged as inner circular and outer longitudinal bands. In the cardiac and fundal portions, the secretory portions of the glands are chiefly of the simple tubular variety. The mouth is short, with the neck and fundus of about the same length. In the neck and fundus, are found two varieties of low columnar cells, the chief, peptic, or adelomorphous cells, and the large delomorphous, acid, oxyntic, or acid cells. The peptic cells are low columnar elements, and are found more numerous in the fundus than in the neck. The nucleus is usually circular or oval, and takes the stain very well. These cells, in the glands, have an affinity for the hematoxylin, and appear bluish when characteristically stained. They also line the mouth and pits, and cover the interglandular projections. In these places, the cells be- come very much longer, and take the stain but faintly. They form a broad band of palely stained protoplasm, in which the darkly stained nuclei have a basal location, forming a row of closely-placed bodies. The lateral bound- aries are not distinct, but the nuclei indicate the breadth of the cell. Altogether, they give a feather-like appearance to the interglandular projections. Besides the peptic cells, a few goblet cells are found in the latter region. STOMACH. The acid cells are readily distinguished frorfl the others by their size, shape, and affinity for acid stains. They are very large, oval, or triangular elements, most numerous in the FIG. 47. CROSS-SECTION OF SEGMENT OF STOMACH. A. Cardiac Region a. mucous coat; b. submucous coat; c. muscular coat; d. fibrous coat; e. epithelium;/, interglandular projection; g. basement membrane; h. gastric pit; i. neck of gland; k. acid cell; /. tunica propria; m, n. layers of muscularis mucosae; o. submucosa; p. circular layer of muscular coat; q. longitudinal layer of muscular coat; r. oblique layer of muscular coat; s. white fibrous tissue layer containing the nerve plexus of Auerbach. B. Gland of Cardiac Region of Stomach a. gastric pit; b. columnar epithelium; c. goblet cell; d. basement membrane; e. tunica propria of interglandular projection; /. neck of gland; g. acid cell; h. peptic cell. necks, but also scattered in the fundus. They are found along the wall of the tubule, and usually beneath the peptic 136 ALIMENTARY TRACT. cell, hence the term parietal,- or wall, cell. The nucleus is quite large, and centrally located, and the protoplasm con- tains minute canals. The affinity for acid stains is pro- nounced. With eosin, they are distinctly red, while with acid fuchsin they are colored a very much deeper red. These cells are supposed to form the hydrochloric acid. In the first portion of the FUNDUS, the glands are chiefly of the simple tubular variety. As the PYLORIC end is ap- proached, the branched tubulars begin to increase, so that they form the predominating variety in this end. There is also a marked change in the lining cells. The acid cells be- come rapidly fewer in number, and, in the pyloric end, are but seldom seen. One can, therefore, be safe in saying that a section containing a number of acid cells is from the FUNDUS, Or CARDIA. In the PYLORIC END, the glands are different. The mouth becomes longer and wider, and the fundus and iurk comparatively shorter. The lumen of the fundus is broader, and the cells are only of the peptic -variety. These cells are usually longer and broader than those in the cardiac glands, and have distinct cell boundaries and prominent basal nuclei. The protoplasm, however, does not respond well to the stain, but is always pale. As the pylorico-duodenal junction is reached, the glands become shorter and less numerous, and some may even extend into the submucosa. The inter glandular projections become longer, and resemble, somewhat, the VILLI of the small intestine. The MUCOSA and SUBMUCOSA are thrown into large folds, the rug(E. These folds and glands increase greatly the ab- sorptive and secretory surfaces. The SUBMUCOUS COAT consists of loosely arranged white fibrous tissue, in which the larger blood-vessels are seen. The MUSCULAR COAT is composed of smooth muscle ar- ranged into three layers. Of these, the inner is oblujm ; STOMACH. 137 the middle, circular, and the outer, longitudinal. At both openings of the stomach, the circular fibres are more numerous, and form sphincters. Of these the sphincter pylori is the more prominent. The FIBROUS, SEROUS or PERITONEAL COAT is composed of a thin layer of white fibrous tissue, covered by a reflection of the peritoneum. FIG. 48. LONGITUDINAL SECTION OF SEGMENT OF PYLORIC REGION OF STOMACH. a. Mucous coat; b. submucous coat; c. muscular coat; d. fibrous coat; e. interglandular projection; /. epithelium; g. basement membrane; h. gastric pit; i. pyloric glands; k. tunica propria; /. muscularis mucosae; m. blood-vessel; n. connective tissue in muscular coat; o. inner circular layer of muscle; p. outer longitudinal layer of muscle. Throughout the alimentary tract, the chief vessels are found in the submucosa, and from this coat, the branches are sent to the mucosa and muscularis. In the stomach, the vascular and lymphatic capillaries are very numerous in the tunica propria. The lymphatics empty into larger vessels in the submucosa, in which the veins also are formed. 138 ALIMENTARY TRACT. The nerves are chiefly sympathetic, and are arranged in two plexuses, one in the submucosa, and the other in the muscular coat. (See Intestine, p. 146). SMALL INTESTINE. The Intestinal Tract consists of two main portions, the Small and Large Intestines. These each have their sub- divisions, which usually differ from one another. The Small Intestine is divided into DUODENUM, JEJUNUM and ILEUM. They all have the same general structure. This will first be described, and then the differences studied. There are four coats, mucosa, submucosa, muscularis and fibrosa, or serosa. The MUCOSA has four layers, epithelium, basement mem- brane, tunica propria and muscularis mucosce. It contains a large number of simple tubular glands, the crypts of Lieber- kuehn, or intestinal crypts. Above the level of the glands, the mucosa is thrown into an immense number of small, finger-like projections, the mlli. The epithelium is chiefly of the simple columnar variety, with varying numbers of goblet cells. Those within the gland are nearly conical in shape, and stain darkly. The protoplasm is granular, and the nucleus basal. Upon the villi, the cells are columnar, and the protoplasm granular and reticular, while the exposed margin is differentiated into a cuticular border. Some hold that the cells in the glands secrete a fluid used in digestion; others consider them goblet cells in different stages of secretory activity. The goblet cells are distinctly columnar elements, in which the position of the nucleus varies with the state of secretion. They form the mucin. The protoplasm is granular and reticular, and, when mucin is forming, shows small clear areas; these fuse to form a single large drop of mucin that SMALL INTESTINE. 139 forces the protoplasm and nucleus to the basal portion of the cell. The sides are curved, producing the goblet form. When the cuticular border ruptures, and the mucin is discharged, the cell becomes slender and irregular. These cells are found mostly upon the villi, and become more numerous as the large intestine is approached. The tunica propria consists of delicate white fibrous tissue 657 W 4 FIG. 49. CROSS-SECTION OF DUODENUM. i. Mucous coat; 2. submucous coat; 3. muscular coat; 4. fibrous coat; 5, 6. villi; 7. epithelium of villus; 8. muscularis mucosae; 9. glands of Brunner. that forms the core of the villi. It contains diffuse lym- phoid tissue and capillary vessels, both lymphatic and vascular. The muscularis mucosce consists of two layers of smooth muscle fibres arranged circularly and longitudinally. From it bundles are sent up into the villi. A VILLUS is a finger-like projection of the tunica propria, covered by a basement membrane- and epithelial cells of the simple columnar and goblet varieties. The tunica propria 140 ALIMENTARY TRACT. forms the core, and contains considerable diffuse lymphoid tissue, a large number of capillary blood-vessels, muscle fibres and a space in the center called the lacteal. It is by FIG. 50. LONGITUDINAL SECTION OF THE UPPER PART OF A VILLUS OF A DOG. a. Epithelium; b. tunica propria; c. capillary; d. cuticular border of the epithelium; e. nucleus of wandering leukocyte; /. section of goblet cell; g. mucoid area of goblet cell; h. lacteal; i. smooth muscle fibre (Stohr's Histology). the villi that nature increases enormously the absorptive surface. The lacteal is the starting point of the lymphatic system of the intestine. SMALL INTESTINE. 141 The lymphoid tissue is often collected* into solitary follicles that are usually present in the mucosa, and in such areas the glands and villi are generally absent. FIG. 51. CROSS-SECTION OF ILEUM. (7. Villus; b. epithelium; c. tunica^ propria of villi; d. intestinal gland; e tunica propria;/,/. muscularis mucosae; g. blood-vessel; h. submucosa; i. circular muscle layer; k. longitudinal muscle layer; /. peritoneal layer; w. fibrous coat; ;/. follicles of the Peyer's patch. The mucosa and submucosa are thrown into circular folds. These are the valvula conniventes, or folds of Kerk- 142 ALIMENTARY TRACT. ring. They are seen upon longitudinal section of the bowel. The SUBMUCOSA consists of loose bundles of white fibrous tissue, and here are to be found the main vascular and lymphatic trunks. It enters into the formation of the valvulce conniventes, and contains the duodenal glands of the duodenum, and the Peyer's patches of the ileum. The MUSCULAR COAT is composed of inner circular and outer longitudinal layers. These are well developed in the duodenum, but become thinner as the colon is approached. The fibrous coat is thin, and nearly the whole of the intestine is covered by peritoneum, forming a serous coat. The JEJUNUM contains no special structures. The ILEUM is characterized by agminated follicles, or Peyer's patches. These are collections of solitary follicles (10 to 60), generally found in both the mucosa and submu- cosa. Each follicle usually shows a germinal center. The DUODENUM is characterized by the presence of a large number of branched tubular glands in its submucosa. The excretory ducts open at the bases of the villi, and pour their secretion into the lumen of the intestine. These are the duodenal glands, or glands of Brunner, and they give rise to the succus entericus. LARGE INTESTINE. This consists of Cecum, Colon, Rectum and Appendix. The structure of all is practically the same. The MUCOSA contains simple tubular glands, crypts of Lieberkuehn, which are usually short, and broader than those of the small intestine. The cells lining these are goblet cells. The tunica propria contains a great deal of diffuse lymphoid tissue that is often collected into solitary follicles that show germinal centers. Vahnlcr connivcntcs and mill are absent. LARGE INTESTINE. 143 The outer three coats are like those of the small intestine, except for difference in the muscular coat. The longitu- dinal fibres are usually arranged into three bands, the t&nicecoli, which are about one-sixth shorter than the bowel. These act as a purse string to the intestine, and cause it to be thrown into a number of speculations. If the bands be removed, the sacculations disappear. FIG. 52. CROSS-SECTION OF SEGMENT OF COLON. a. Mucous coat; b. submucous coat; c. muscular coat; d. fibrous coat; e. columnar cell;/, goblet cell; g. basement membrane; h. tunica propria; /. inner circular layer of muscularis mucosae; k. outer longitudinal layer of muscularis mucosae; /. inner circular layer of muscular coat; m. outer longitudinal layer of muscular coat. The Rectum has its mucous and submucous coats formed into folds called the rectal valves. These contain a continua- tion of the muscular coat, by means of which the valves may be protruded into the lumen. At the lower end, the ANUS, stratified squamous cells replace the simple columnar, and this marks another muco -cutaneous junction as in the lips. The Appendix is a continuation of the cecutn. It has the 144 ALIMENTARY TRACT. four coats, MUCOSA, SUBMUCOSA, MUSCULARIS and FIBROSA, or SEROSA. The MUCOSA is usually irregular, and consists of simple columnar epithelial cells that rest upon a basement mem- brane; beneath the latter lies the tunica propria, which is bounded by the muscularis mucosce. In the MUCOSA are a large number of tube-like depressions, the glands of Lieberkuehn. These possess an equal diameter throughout, and are quite regularly distributed. The cells of the mucosa are the simple columnar variety, interspersed with many goblet cells. They are quite distinct, and usually possess a basal border. The cells in the base of the glands supply the parts higher up, and are consequently the young- est. The glands are about 25,000 (Kelly and Hurdon) in number, and are absent where the solitary follicles are found. The tunica propria consists of a delicate fibre-elastic stroma containing many capillaries, considerable diffuse lymphoid tissue and solitary follicles (often 300 to 400 in num- ber). The solitary follicles contain germinal" centers, and may extend into the submucosa. Immediately over them, the glands are usually absent. The muscularis mucosa is not always present. It consists of smooth muscle fibres forming a thin band separating the mucosa from the submucosa. The SUBMUCOSA consists of loose white fibrous tissue, and supports the larger blood-vessels. In older subjects, it becomes thicker and denser, and passes into the tunica propria. The MUSCULAR coat is usually separable into two distinct layers, inner circular and outer longitudinal. The former is the more prominent, and extends to the blind end, where the fibres form a dome-like collection of interlacing fibres. The longitudinal fibres are less prominent than the circular. Both layers are pierced, at intervals, by large vessels. Such APPENDIX. an opening, of which one especially exists at the blind end, is called an HIATUS (Kelly and Hurdon). FIG. 53. CROSS-SECTION OF HUMAN APPENDIX. a. Lumen; b. epithelium; c. basement membrane; d. glands; e. tunica propria; /. diffuse lymphoid tissue; g. muscularis mucosae; h. solitary follicle; i. adipose tissue; k. submucosa; / circular muscle fibres; m. longitudinal muscle fibres; n. fibrous coat. The SEROUS coat consists of white fibrous tissue, sur- rounded by the peritoneum. The lumen tends to disappear more frequently than sup- posed; this change occurs during the ages ranging from 20 to 80. The older the individuals, the higher the percent- 146 ALIMENTARY TRACT. age of occlusions. The glands are gradually destroyed by the thickening of the submucosa, this process beginning at the blind extremity and proceeding toward the bowel. Occasionally, in this process of occlusion, quite an abun- dance of adipose tissue is seen in the submucosa. The chief blood-vessels of the intestines pass from between the layers of the mesentery into the submucosa. From these trunks, branches are sent to the various coats. In the villi, dense capillary plexuses are formed around the lacteals, and, lower down in the mucosa, around the gland. The blood is returned to the submucosa through venous channels, and . these unite here to form the main venous trunks that leave the intestine to pass between the layers of the mesentery. The lymphatics of the intestine start as the lacteals. These pass from the apices of the villi to the bases, where they open into a set of vessels near the muscularis mucosae. From this plexus, vessels connect with another network in the submucosa. The latter receives lymph through other vessels that encircle the solitary follicles and patches. From this submucous plexus, vessels pierce the muscular coat to pass between the layers of the mesentery, receiving, at the same time, branches from the muscularis itself. Ulti- mately, these channels empty into the receptaculum chyli. The chyle vessels, or lacteals, are usually guarded, at the base, by a valve that prevents regurgitation, and aids in producing a vacuum in the lacteals, thus aiding absorption. The nerves are chiefly sympathetic and, as in the stomach, two plexuses are formed. The plexus of Meissner lies in the submucosa, and that of Auerbach in the muscular coat, be- tween the circular and longitudinal layers. Where the plexus fibres join, little collections of multipolar cells, called ganglia, are formed. The plexus of Meissner seems to be a derivative of the plexus of Auerbach. The mucosa is sup- plied by fibres from the former. CELLS LINING ALIMENTARY TRACT. 147 The cells lining the various portions of the Alimentary Tract are as follows. LIPS .............. Stratified squamous. MOUTH ............. Stratified squamous. TONGUE ............. Stratified squamous. PHARYNX ............ Stratified squamous. ESOPHAGUS ........... Stratified squamous. ( Acid cells. Peptic cells. STOMACH CARDIAC END ...>> . Tall columnar. [ Goblet cells (a few) . f Peptic cells. PYLORIC END ...-< Tall columnar. Goblet cells. f Simple columnar. SMALL INTESTINE . ( Goblet cells. f Goblet cells. LARGE INTESTINE . . . < . [ Simple columnar. ANUS ............. Stratified squamous. The differences between the Small and Large Intestines are as follows : SMALL. LARGE. GLANDS. LONG AND NARROW. BROAD. CELLS. CHIEFLY CHIEFLY GLANDULAR. GOBLET. VILLI. PRESENT. ABSENT. VALVUL^. PRESENT. ABSENT. BRUNNER'S GLANDS. PRESENT. ABSENT. PEYER'S PATCHES. PRESENT. ABSENT. LONGITUDINAL ABSENT. PRESENT. BANDS. SACCULATIONS. ABSENT. PRESENT. CHAPTER X. THE DIGESTIVE GLANDS. The Digestive Glands are the Liver, and Salivary Glands, the Parotid, Pancreas, Sublingual and Submaxillary. LIVER. The Liver, the largest gland in the body, is compound tubular in structure. It is surrounded by a sheath of white fibrous tissue, the capsule of Glisson, which is covered by peritoneum. On the under surface of the organ, the capsule follows the blood-vessels at the portal or transverse fissure into the gland, and forms the interlobular connective tissue. Folds and bands form the various ligaments, suspensory, coronary and lateral. The round ligament is formed by the persistent, closed umbilical vein. The Liver is divided into LOBES and LOBULES, of which the latter represent the UNITS. A description of a lobule will suffice for that of the whole liver. Each Lobule consists of a collection of RADIATING CHAINS of HEPATIC CELLS, the TUBULES, that start from the CENTRAL, or INTRALOBULAR VEIN. These CHAINS are separated from one another by reticulum, which supports the cells and the INTRALOBULAR BLOOD CAPILLARIES; these capillaries are of the sinusoidal variety; that is, the endothelium is attached to the epithelium of the tubules. Each CHAIN consists of two or three cells side by side, enclosing a small capillary space called the BILE CAPILLARY. Peripherally, the lobules are not separated from one another by connective tissue, except in the pig and camel. In these animals, the lobules 148 LIVER. 149 are sharply outlined by bands of connectiw tissue. This FIG. 54. LIVER OF PIG. a. Interlobular connective tissue containing a portal system consisting of ' b. Interlobular branch of hepatic artery. c. Interlobular branch of portal vein. v d. Interlobular branch of bile duct. e. chains of hepatic cells;/, central vein; g. chain of cells highly magnified. occurs somewhat imperfectly in the human liver under pathologic conditions (chronic interstitial hepatitis). 150 TIIK DIGESTIVE GLANDS. According to Mall,* the lobule, as now considered, is not the structural unit of the liver; the structural unit refers to all the tissue that surrounds each terminal branch of the portal vein. The HEPATIC CELLS are large, mononuclear masses of pro- toplasm, although occasionally two nuclei may be present. The protoplasm is granular, and may contain droplets of fat, glycogen and even pigment granules. The cells are traversed by minute canals, SECRETORY CAPILLARIES, that open into the bile capillaries lying between the cells. These cells are arranged in irregular chains that consist of two or three cells, in cross-section, and extend from the central vein to the periphery of the lobule. Such are the HEPATIC TUBULES. The BILE CAPILLARIES, that lie between the cells, are merely notches in the apposed cells. They start blindly at the central vein, pass to the periphery, and empty into INTERLOBULAR VESSELS that possess a low columnar epithelial lining supported by basement membrane and tunica propria. These unite to form larger vessels that are lined by tall columnar cells. The interlobular ducts that lie between the lobules are lined by the same, and possess, in addition, some muscular tissue. The INTERLOBULAR CONNECTIVE TISSUE is seen in abun- dance, at times, at the junction of several lobules. In such areas will be found branches of the hepatic artery and -vein, portal -vein and bile duct. These vessels, with the connective tissue, form a PORTAL SYSTEM, or CANAL. The CIRCULATION of the liver is more peculiar and inter- esting than that of any other organ in the body. Two systems bring blood, yet it leaves through one. In other organs, the vessel that supplies the functionating tissue is an ARTERY, but here it is a VEIN, the PORTAL VEIN. *Jour. of Anat, Vol. V, No. 3. PORTAL CIRCULATION. 151 The PORTAL VEIN is made up of the superior and inferior mesenteries, coronary (stomach) and splenic veins. It enters at the portal or transverse fissure of the liver, and forms two main branches, RIGHT and LEFT, one for each main lobe. These rapidly form INTERLOBULAR BRANCHES that give rise to the INTRALOBULAR CAPILLARIES, found in the lobules, where they converge at the center and empty into the CENTRAL, OK INTRALOBULAR VEIN. The circulation of the liver might be outlined as follows: PORTAL VEIN. I LOBAR BRANCHES. I INTERLOBULAR VEINS. *0sf Hepatic artery. i Lobar branches. i Interlobular arteries. j Interlobular capillaries. \ * INTRALOBULAR CAPILLARIES Central vein. i Sublobular vein. j Interlobular vein. i Hepatic \eins. 152 THE DIGESTIVE GLANDS. The HEPATIC ARTERY enters the transverse fissure, and forms LOBAR and INTERLOBULAR branches. The latter rapidly form capillaries that lie in the interlobular connective tissue and nourish it, and the vessels found here. These are the INTERLOBULAR CAPILLARIES, some of which enter the outer third of the lobule and empty into the portal vein capillaries. The remainder of the hepatic artery capillaries empty into the interlobular branch of the portal vein, or form small venules that ultimately empty into these. The blood that has entered the CENTRAL VEIN, from the portal vein and the hepatic artery, passes into the SUBLOBU- LAR VEINS, which are formed by a union of the centrals, and then into the INTERLOBULAR branches of the hepatic veins. The INTERLOBULARS are formed by a union of the SUBLOBULARS, and these, in turn, unite to form the HEPATIC VEINS that empty the blood into the postcava, or inferior vena cava. As the portal vein blood comes into intimate relation with the hepatic cells, the latter remove the products re- quired for nutrition, also the excess of glucose, which is converted into liver sugar, or glycogen, and, in addition, take out the constituents of the bile; it is now considered the seat of urea formation. The lymphatics are superficial and deep. The superficial drain into either the celiac and hepatic lymph nodes on the one hand, or through the diaphragm into the ventral mediastinal nodes. The deep pass out either through the portal fissure to hepatic and celiac nodes, or along the hepatic vein pass through diaphragm to nodes around the postcava. The blood-vessels are surrounded by lymph spaces that communicate with the capillaries and with similar spaces in the periphery of the lobule, and in the interlobular con- nective tissue. The sympathetic nerves form the chief source of enerva- SALIVARY GLANDS. 153 tion of the liver. They lie in the interlobular connective tissue as plexuses, and from these some fibres pass to the bile ducts, and others penetrate the lobules to pass beneath the cells. The Excretory Apparatus consists of the Gall-bladder, Hepatic, Cystic and Common Ducts. They all possess three coats, MUCOUS, MUSCULAR and FIBROUS. In the Gall-bladder, the MUCOUS COAT consists of simple columnar cells, basement membrane and tunica propria; the latter is thrown into folds, in which the muscular coat also is included. In this layer, a few mucous glands may be found, diffuse lymphoid tissue is usually abundant, and solitary follicles are not infrequently found. The MUSCULAR coat consists of a mixture of smooth muscle and white fibrous tissue, the latter predominating near the mucous coat. In the fibrous tissue are found the chief vessels that supply the other coats with branches. The fibrous coat consists of white fibrous tissue, covered in part by the peritoneum. The lymphatics are connected to those of the liver by the subserous plexus, into which the vessels from the muscular coat empty. The nerves are sympathetic and cerebro spinal, the former passing to the blood-vessels and muscles, and the latter ending in the mucosa, near large arteries. The Ducts have somewhat the same structure, containing a few mucous glands in the mucosa. The muscle fibres are quite distinct. They are arranged as circular, longitu- dinal and oblique layers. The circular fibres of the common duct form a sphincter at its entrance into the duodenum. SALIVARY GLANDS. The Salivary Glands are the Parotid, Pancreas (the ab- dominal salivary gland), Sublingual and Submaxillary 154 THE DIGKSTIYi; GLANDS. glands. In addition, there are a large number of small unnamed glands in the lips, mouth, tongue, pharynx, base of the epiglottis, and esophagus. According to SECRETION, they are divided into MUCOUS, SEROUS and MIXED. The MUCOUS glands are distinguished by their large secretory units that stain lightly. These are the acini, alveoli or tubules, and they give rise to a thick viscid secre- tion. Such glands are the small glands of the mouth, pharynx and esophagus. The SUBLINGUAL is almost a pure mucous gland. SEROUS glands are those in which the acini stain darkly, owing to the presence of secretory granules in the protoplasm, which retain the stain. These glands secrete a thin al- buminous fluid. Such are the PAROTID and PANCREAS. The MIXED glands are those that stain both lightly and darkly, and secrete a mixed fluid, as the SUBMAXILLARY and SUBLINGUAL. As all of these glands have the same general structure, this will be first considered, and the special points then noted. Each is surrounded by a CAPSULE of white fibrous tissue that limits it from the surrounding organs or tissues. The CAPSULE sends in prolongations that divide the gland into LOBES and LOBULES. The LOBULES, or STRUCTURAL UNITS, consist of the functionating units that are composed of a single layer of glandular epithelial cells, supported by a basement membrane. External to the basement membrane, is the interstitial, or intertubular connective tissue, which is composed of reticulum, and in which the blood-vessels, nerves and lymphatics are found. It corresponds to the tunica propria of a mucous membrane. The SECRETORY UNITS lead into minute INTERMEDIATE, or INTERCALATED TUBULES that unite to form INTRALOBU- PAROTID AND PANCREAS. 155 LAR DUCTS, which pass into the interlobular connective tissue. Here they unite to form the INTERLOBULAR DUCTS; these, by union, form the lobars, and then the SINGLE EX- CRETORY DUCT. The INTERMEDIATE TUBULES are lined by simple squamous or low columnar cells, supported by base- ment membrane and interstitial tissue; the INTRALOBULAR branches contain simple columnar s, the INTERLOBULARS and INTERLOBARS are lined by pseudo- stratified columnars, and the EXCRETORY DUCT usually by stratified columnars. In the latter the muscle coat is distinct. The blood-vessels follow the divisions of the ducts, and form plexuses of capillaries around the units, and in close proximity to the epithelium. The nerves pass down in the same manner, and, after penetrating the basement membrane, end around the cells. The Parotid Gland, a compound alveolar gland, consists of small, serous acini, lined by cells adapted to fit these alveoli. The actively secreting cell has a very granular protoplasm, but that of the resting cell contains but few granules. As the granules increase, the protoplasm decreases, until expulsion of the secretion, and then the protoplasm again increases. Secretory capillaries exist between the cells. This gland is not so definitely limited as the others, and, as a consequence, adipose tissue may be seen in the inter- lobular connective tissue, and the ductular system is said to be more highly differentiated than in any other. The PAROTID DUCT is the excretory duct. o-^ C The Pancreas, the other SEROUS GLAND, is also compound alveolar in structure. It is also called the abdominal sali- vary gland. The ACINI are usually distinct and sharply out- lined. In these, occasionally, a small flat cell is seen occupy- ing a central position; this is a centro-acinar cell, and is supposed to be one of the cells lining the intermediate tubules that extends into the acini. In addition to the acini, 156 THE DIGESTIVE GLANDS. certain peculiar collections of lightly-staining cells are seen. These are oval or circular in outline, and surrounded by a capsule of white fibrous tissue. The cells are divided into groups, each of which seems to be environed by a collection of capillaries. These are the pancreatic islands, or areas, or islands of Langerhans, and possess no outlet for the FIG. 55. SECTION OF HUMAN PANCREAS SHOWING PANCREATIC ISLANDS. a. Interlobular connective tissue; b. capillary; c. interlobular duct; d. in- tralobular duct; c. cells of acini; /. area of Langerhans. secretion they are supposed to form, which is, therefore, supposed to be absorbed by the blood-vessels. Such is an internal secretion. These islands are considered of pathologic importance in a certain form of glycosuria. The EXCRETORY DUCT, the DUCT OF WIRSUNG, is lined by simple columnar cells. SUBLINGUAL GLAND. 157 The Sublingual, a tubule-alveolar gland, according to some is purely mucous, and differs from the above in pos- sessing lightly-staining cells in the secretory units. These cells are large and clear during secretory activity, but smaller and cloudy after expulsion of the contents. The *&&* O-* ri >~ >ir H^x - c^J ; ' /v f'- : B^s<^-v i if !> 4 :S^r- srt ^&&M^: y FIG. 56. SECTION OF SUBMAXILLARY GLAND OF A Fox. a. Connective tissue; b. serous acinus; c. intralobular ducts; d. lumen of a mucous acinus; e. mucous cells; /. demilune of Heidenhain; g. capillary. nucleus is usually peripheral, in the former condition. Besides the above cells, there are certain darkly-staining cells or cell-groups, at the periphery of the tubules, lying between the mucous cells and the basement membrane. These are crescent-shaped, and are, therefore, called the 158 nil'. DIGKSTIYI; GLANDS. cresents of Gianuzzi, or demilunes of Heidenhain. Accord- ing to Stohr, they represent stages of secretory activity, in which the cells have expelled their secretion. Others hold them to be separate SEROUS cells, and that accounts for their dark stain. Secretory canals are said to exist in them, and this would seem to point to a serous character. There are usually several ducts, called the SUBLINGUAL DUCTS or DUCTS OF RIVINUS. If but one is present it is called the DUCT OF BARTHOLIN. The Submaxillary is a MIXED gland in secretion, and tubulo-alveolar in structure. The SEROUS and MUCOUS UNITS may be separated into lobules or lobes, or may be found side by side in the same lobule. The serous are the more numer- ous in man. In the mucous tubules, demilunes are present. The ducts are unusually numerous, forming a distinguishing feature of this gland. The excretory duct is the SUB-MAXILLARY DUCT, or DUCT OF WHARTON. CHAPTER XI. RESPIRATORY SYSTEM. This System comprises the Nares, upper part of the Pharynx, the Larynx, Trachea, Bronchi and Lungs. Al- though there is no connection, the Thyroid and Parathyroids are included in this Chapter. The Nares are lined by a mucous membrane, which differs according to the function of the part. The FIRST portion is lined by stratified squamous cells, continued from the skin surface. Here are found some large hairs, sweat and sebaceous glands. Within this area, the TRUE RESPIRATORY portion is lined by stratified ciliated cells, with a few goblet cells scattered here and there. Beneath the basement membrane, the tunica propria is represented by a delicate fibrous tissue containing some diffuse lymphoid tissue and some glands of the mucous and serous types. Above this area, the OLFACTORY MUCOUS MEMBRANE is found. The RESPIRATORY portion of the PHARYNX, continuous with the nares, is lined by stratified ciliated cells. In the tunica propria, glands resembling those found in the nares are seen. LARYNX. The Larynx is a hollow, cartilaginous organ connecting the pharynx with the trachea. It consists of EPIGLOTTIS, VOCAL CORDS and LARYNX PROPER. The EPIGLOTTIS is a projecting flap that protects the GLOTTIS during deglutition. It is covered by stratified 159 l6o RKSI'IRATORY SVSTKM. squamous cells upon both sides, and these are continuous at the edges, and rest upon basement membrane and papil- lated tunica propria. The latter is composed of fibro-elastic tissue, and contains diffuse lymphoid tissue, and, also, some glands, near its attachment. In the epithelial portion of the ventral surface, taste-buds are found. Beneath the tun- ica propria is the submucosa, which consists of loose white fibrous connective tissue. In it is found a plate of elastic cartilage that gives the stiffness, and also the elasticity, to this organ. The VOCAL CORDS comprise the TRUE and the FALSE. The FORMER are the functionating structures, while the latter are merely heavy folds that seem to resemble the former. The TRUE CORDS alone are of importance. The TRUE VOCAL CORDS, PLic^: VOCALES, are covered by stratified squamous cells that are supported by basement membrane and tunica propria. The central portion consists of a band of elastic tisssue. They contain no glands. Between the two sets of cords, there is a space, or recess, upon each side, called the ventricle of the larynx. The remainder of the larynx consists of MUCOUS, SUB- MUCOUS and FIBROUS coats. The MUCOUS coat, including that of the ventricles, is lined by stratified ciliated epithelial cells. The tunica propria contains a great deal of diffuse lymphoid tissue. That por- tion of the SUBMUCOSA adjacent to the tunica propria possesses a number of small mucous glands. In its outer portion, the cartilage masses are found. The form of the larynx is given by the cartilages, which are chiefly hyalin. Those of Wrisberg and Santorini y middle of the thyroid and the apices of the arytenoids are elastic cartilage. External to the cartilage is the fibrous coat, which is com- posed of white fibrous tissue, supports the other coats, TRACHEA. l6l and connects the larynx to the surrounding organs or tissues. The blood-vessels, nerves and lymphatics are numerous. The circulatory system is represented by several networks of large vessels, and a plexus of capillaries in the tunica propria. The lymphatics closely follow the blood-vessels. The nerves are distributed to the mucosa, where they end near and within the epithelial layer, or in the taste-buds. TRACHEA. The Trachea connects the larynx with the lungs, its lower end bifurcating to form the Bronchi. It has THREE COATS, MUCOUS, SUBMUCOUS and FIBROUS. The MUCOUS coat is a continuation of that of the larynx. It is composed chiefly of stratified ciliated and goblet cells that rest upon the basement membrane and tunica propria. The basement membrane is usually quite prominent, and the tunica propria contains considerable diffuse lymphoid tissue. It consists of fibre-elastic tissue, in which the fibres have chiefly a longitudinal direction. That portion of the mucosa opposite to the attachment to the esophagus is lined, at times, by stratified squamous cells, and is usually irregular. The SUBMUCOSA is made up of white fibrous tissue, and supports the large blood-vessels and a large number of mucous glands, the tracheal glands. These lie in that portion near the tunica propria. In the outer part are found the cartilage rings. These so-called rings are C-shaped masses of hyalin car- tilage, with the open portion at the attachment of the organ to the esophagus. These masses are thickest in front, and taper as the ends are reached. Although the cartilages are 162 RESPIRATORY SYSTI.M. supposed to consist of one piece, they are commonly made up of a number of plates. The ends of the C's are con- nected by traversely and longitudinally arranged smooth -,vv,-ii s-- r^x- FIG. 57. CROSS-SECTION OF SK<;MK.\T OK THK TRACHKA. a. Mucous coat; b. submucous coat; r, d. fibrous coat containing sonic vol- untary striated muscle, /, m; e. stratified ciliated epithelium;/, basement membrane; g. goblet cells; h. mucous glands; i. blood-vessel; k. elastic- tissue and perichondrium; /. longitudinal, and ;;?, cross-sections of voluntary muscle fibres. muscle fibres, which are attached to the inner and outer perichondriums, and then bridge the spaces between the ends of the cartilage. This strip of muscle extends the length of the trachea, but no complete muscularis is present. LUNGS. 163 The rings are sixteen to eighteen in number, and are separated from one another by white fibrous tissue. The FIBROUS coat lies outside of the cartilage rings, and consists of white fibrous and yellow elastic tissues. The blood-vessels and lymphatics have their larger branches in the submucosa, from which smaller vessels ex- tend to the other coats, and form capillaries. The nerves are chiefly sympathetic. The Bronchi have the same general structure as the trachea. Usually the C-shaped ring of cartilage is re- placed by a number of plates. LUNGS. The Lungs resemble compound racemose glands, the BRONCHI corresponding to the excretory ducts. Each Lung is invested by & fibrous sheath, covered almost entirely by serous membrane, the VISCERAL LAYER OF THE PLEURA, which is reflected over the inside of the pleural cavity, as the parietal layer of the pleura. Between these two layers is the so-called pleural cavity, but as the lungs fill it in the living condition, it does not exist as a cavity. In it is found a small amount of lymph that lubricates the membranes. The Pleurae have the same structure as other serous membranes. Each consists of endothelial cells and subendo- thelial connective tissue that pass from the lung over to the body wall. The sub endothelial tissue is continuous with the interlobular connective tissue of the lung. Upon the internal surface of the lung is an area, in which the vessels and tubes enter and leave the organ; this is the ROOT of the lung, and here no serous membrane exists. The LUNGS, like other glands, are merely systems of tu- bules that branch and rebranch, and are lined by different 1 64 RESPIRATORY SYSTEM. varieties of cells. Each is an aheolo-tubular gland, and al- though no liquid secretion or excretion is formed, it plays an important part in the excretion of gases and organic matter from the blood and in the oxygenation of the blood. The Bronchi divide like the ducts of any gland, and, FIG. 58. SECTION OF HUMAN LUNG. a. Pleura; b. alveolar septum; c. alveus, or air sac; d. alveolus; e. intralobular blood-vessel; /. interlobular blood-vessel; g. interlobular bronchial tube; h. cartilage; i. branch of pulmonary artery; k. gland. ultimately, the small divisions called BRONCHIOLES are reached. Each BRONCHIOLE forms a system separate and closed from its neighbors. The BRONCHIOLE (0.5 mm. in diameter) divides into the RESPIRATORY BRONCHIOLES (0.3 to 0.4 mm. in diameter); these, in turn, give rise to LUNGS. 165 ALVEOLAR DUCTS (0.2 mm.), which end as large spaces, the ALVEI, ALVEOLAR SACS or AIR SACS (0.3 by 5 mm.); along the walls of these divisions, are found small depressions the ALVEOLI, or SACCULES (0.05 to o.i mm.), and these are the final divisions. A LOBULE, or STRUCTURAL UNIT, consists of the divisions of a bronchiole, and varies from 0.3 cm. to 3 cm. in diameter. It is surrounded by white fibrous tissue containing larger vessels and ducts, which are called interlobular, are over 0.5 mm. in diameter, and contain cartilage. The alvei, or air sacs, are separated from one another by yellow elastic tissue, in which a dense capillary plexus is found. As the BRONCHUS divides and redivides, the tubules con- tain less and less cartilage. The first important change is the formation of a complete investment of cartilage, com- posed of a number of plates. As this occurs, the muscle tissue begins to increase, so that soon a distinct layer is seen internal to the cartilage. The lining cells are stratified cili- ated, but the whole mucosa becomes irregular and corru- gated, due to the formation of longitudinal folds; as the divisions become smaller, the cartilage diminishes. The glands disappear when a diameter of i mm. is reached. The cartilage is retained until a diameter of 0.5 mm. is attained. Such a tubule is a BRONCHIOLE. It is lined by simple ciliated epithelial and goblet cells, supported by a basement membrane and an elastic tunica propria. External to this, the circular muscle fibres are quite prominent, and as a re- sult, folds are formed. The fibrous tissue external contains elastic fibres, as well as vessels and nerves. The RESPIRATORY BRONCHIOLES arise by a division of the above tubules. They are lined partially by simple ciliated and partially by nonciliated cells. The former are of the simple variety, and few in number. The nonciliated cells l66 RESPIRATORY SYSTEM. at first are columnar, but quickly give way to low cuboidal and flattened cells. The last named are called respiratory epithelium. Along the walls of the tubules, little depres- sions, the alveoli, are seen, and here the respiratory epithe- lium is marked. Muscle fibres are found beyond the tunica propia, and elastic tissue becomes more abundant. The ALVEOLAR DUCTS contain many alveoli lined by respiratory epithelium, which consists of thin, nonnucleated plates of various sizes, arranged individually or in groups. The smaller cells are derived from the cuboidal cells and are flattened by inspiration, and the larger are formed by a fusion of the smaller ones. The walls of these ducts consist of tunica propria, muscle tissue (which disappears when the end of this tubule is reached) and considerable elastic tissue circularly arranged. The alveolar ducts lead into the ALVEUS, AIR SAC, or ALVE- OLAR SAC. On the walls of this part are the small depres- sions, the ALVEOLI or SACCULES. These are separated from one another by minute partitions, or septa, that consist of elastic tissue covered by simple squamous cells, the respiratory epithelium. The ALVEOLI of a system com- municate with one another by means of small channels, or pores. At the base of the alveolus, the elastic tissue is formed into a thick ring. In the meshwork of the elastica of an alveolus is found a dense plexus of blood-capillaries. The amount of elastica allows a great increase in size of the air sacs (2 to 3 times). From W. S. Miller's careful studies on the structure of the lungs, the terminal bronchioles terminate as follows: Each respiratory bronchiole divides into one or more alve- olar ducts, which widen at their outer ends. Each duct opens into several vestibula; from each vestibulum, a num- ber of atria open, which, in turn, communicate with the air sacs, or alvei, on the walls of which are the alveoli. LUNGS. 167 The circulatory system is peculiar. As in the liver, two sets of vessels enter, the pulmonary and bronchial, but, un- like those of the liver, they do not unite to form a single system, but remain individual. There is some anastomosis between the two systems of vessels. The pulmonary artery conveys the blood to be oxygenated and is the nutrient vessel of the functionating epithelial cells. It branches at the root, and the divisions follow those of the bronchus very closely. Between the lobules, its branches are the interlobular divisions, and these penetrate the lobules to form the densest capillary plexus of the body, within the elastica of the alveoli. Here the endothelial cells of the capillary, and the squamous epithelial cell of the alveolus, separate the blood from the air. Such an exceed- ingly thin membrane allows the interchange of oxygen and effete gases, and also the absorption of nutrient matter by the epithelial cells, and the outward passage of the waste matter. The blood is collected by the venous radicals of the pulmonary vein, and these unite to form the inter- lobular branches, that ultimately form the pulmonary veins. The bronchial artery branches somewhat as the pulmonary artery, but its divisions do not penetrate to the same degree. They enter the lobule and form capillaries around the vessels and ducts here and nourish them, but not the respiratory epithelium. The capillaries lie in the interlobular connect- ive tissue, and supply the vessels there with nutrient material. Between these two sets of vessels, the pulmonary and bronchial arteries, there is some anastomosis, so that the pulmonary veins carry some of the bronchial artery blood from the lungs. The bulk of the bronchial blood, however, is collected by the divisions of the bronchial veins that finally empty into the vena azygos, right and left (or left superior intercostal). The lymphatics are superficial and deep; the former lie l68 RESPIRATORY SYSTEM. beneath the pleurae and connect with the deep plexus. The latter consists of vessels that follow the blood-vessels and lie in the interlobular connective tissue; these have a number of bronchial lymph nodes (incorrectly called bron- chial glands) in their course. The nerves are mainly sympathetic, though the vagus sends branches to the lungs. They end chiefly in the blood- vessels. The following are the epithelial cells that line the various portions of the Respiratory Tract: ^. f FIRST PART .... Stratified squamous. \ SECOND PART .... Stratified ciliated. PHARYNX Stratified ciliated. f EPIGLOTTIS .... Stratified squamous. LARYNX -j VOCAL CORDS . . . Stratified squamous. ( REMAINDER OF LARYNxStratified ciliated. TRACHEA Stratified ciliated. BRONCHI Stratified ciliated. BRONCHIAL TUBES Stratified ciliated. ( Simple ciliated. BRONCHIOLES i Simple columnar. [ Simple squamous (respiratory). ALVEOLAR DUCTS Simple squamous (respiratory). ALVEOLI Simple squamous (respiratory). THYROID BODY. The Thyroid Body is a ductless, compound tubular gland, and consists of two large lateral lobes united by a narrow band, the middle lobe, or isthmus. The organ is surrounded by a capsule that sends in trabec- ulae, which divide the gland into lobes and lobules. These divisions are irregular, and the lobules are composed of a number of short tubules, sometimes called follicles. Each tubule is lined by cuboidal epithelial cells that rest upon a basement membrane; outside of this is the intralobular, or in- THYROID BODY. 169 /( 'r tubular , connective tissue that supports the blood-vessels. In the tubules is seen a peculiar, homogeneous substance, the colloid substance, that is supposedly the result of the activity of the cells. It has a yellowish color, and as blood- cells are frequently seen in it, the color may be due to the hemoglobin from these. Sometimes, the colloidal material is shrunken, and then its edges are crenated; in such tubules, FIG. 59. SECTION OF HUMAN THYROID GLAND. a. Epithelium; b. basement membrane; c. colloid substance; d. interlobular connective tissue; e. interlobular vein. the epithelial cells are drawn away from the basement membrane. Gulland and Goodall found granules of iron in the interlobular tissue cells and in the epithelial cells of the tubules. These granules were most abundant in those tubules in which the colloid substance was small in amount. It is not unusually found that the colloid substance in the same tubule is of different reaction, most of it responding to protoplasmic stains, while a smaller amount, centrally 170 RESPIRATORY SYSTCM. located and surrounded by the preceding, responds to the nuclear stain. Blood-vessels are numerous, and dense plexuses are formed around the tubules. It is thought that the colloid material may represent an internal secretion that is absorbed by the blood-vessels, or perhaps the lymphatics. The lymphatics are numerous, and lie between the tubules. They often contain some of the colloid substance. PARATHYROIDS. The Parathyroids are usually four in number, two of which lie in close relation with each lateral lobe of the THYROID. They are small, and the epithelial cells are usually of the glandular type, and are arranged in groups, or chains, forming a network, or even tubules. These cells respond very readily to the protoplasmic stains and are usually quite deeply stained, in marked contrast to the cells of the thyroid body. Between the cells is white fibrous connective tissue that supports quite a capillary plexus. Occasionally, colloid material is seen in the tubules. When the thyroids are removed and the parathyroids remain, they hypertrophy and carry on the function of the removed organs. According to some investigators, the parathyroids do not assume the function of the thyroids. Removal of the parathyroids is fatal within a short time. CHAPTER XII. THE URINARY SYSTEM. The Urinary Organs comprise the Kidneys, Ureters, Bladder and Urethra. On account of its proximity to the kidney, the Adrenal will also be considered. The Kidney is a compound tubular gland, and, next to the liver, the largest in the body. It lies in a mass of adipose tissue, the perirenal fat, from which it is readily separated. Some of this fat persists even when the animal dies of starvation. The kidney is surrounded by a thin CAPSULE of white fibrous tissue that normally strips readily from the organ. This is of great importance, when the organ is studied pathologically. Beneath the capsule is the kidney PAREN- CHYMA that consists of a great number of tubules, the uriniferous tubules, that have a very irregular course. Along the internal margin is a depression or notch, the HILUS, at which the vessels enter and leave. When the organ is sectioned, upon microscopic examina- tion it is seen to consist of an outer margin, the cortex, and an inner broader portion, the medulla. Just within the hilus is seen a space, the SINUS, containing the PELVIS and the main branches of the renal artery and vein. The cortex constitutes the outer third of the organ, and is further subdivided into MEDULLARY RAYS and LABYRINTH. This division is represented by the alternating dark and light bands, which are at right angles to the capsule, and gives a striated appearance to the cortex. 172 THE URINARY SYSTK.M. The MEDULLARY RAYS, or PYRAMIDS OF FERREIN, Consist, microscopically, of the straight portions of the tubules that FIG. 60. SECTION OF HUMAN KIDNEY SHOWING CORTEX AND MEDULLA. a. Capsule; b. cortex; c. medulla; d. labyrinth; e. medullary ray;/, renal bodies; g. area in which renal body has dropped out; h. capsule of Bowman; i. glomerulus; k. afferent arteriole; /. neck of uriniferous tubule; m. tubules of labyrinth; n. longitudinal sections of collecting tubules; o. cross-sections of collecting tubules. extend from the medulla into the cortex, surrounded by the intertubular, or interstitial reticulum. They never extend KIDNEY. 173 to the capsule, but diminish in width as the outer portion of the cortex is approached. The LABYRINTH lies between the medullary rays, and is composed of the MALPIGHIAN, or RENAL, CORPUSCLES, the starting points of the tubules, and the convoluted portions of the uriniferous tubules. These are supported by the interstitial connective tissue that contains the blood-vessels. The RENAL CORPUSCLES are found only in the cortex, and here are limited to the labyrinth. Each one consists of a tuft of arterial capillaries, the GLOMERULUS, or RENAL TUFT, surrounded immediately by a delicate double mem- brane of simple squamous cells, resting upon a basement membrane. The inner layer lies upon the tuft, and the outer forms the wall of the tubule. This membrane is BOWMAN'S CAPSULE, and, with the tuft, comprises the RENAL CORPUSCLE. The tuf t itself is not a simple structure. The arteriole, upon entering, divides into a number of branches, each of which forms a set of capillaries. This apparent lobulation is quite distinct. As these capillaries unite to form an efferent arteriole, this arrangement is called a retia mirabilia. The medulla is sharply outlined from the cortex, micro- scopically, by the absence of renal corpuscles and the regularity of the tubules. At the junction are to be found the great vessels, and this portion is called the boundary zone. The medulla consists of the MEDULLARY, or MAL- PIGHIAN PYRAMIDS, separated from one another by the COLUMNS of BERTIN. The MEDULLARY PYRAMIDS are ten to sixteen in number. Their bases continue with the cortex, and their apices are directed toward the hilus and project into the sinus. Each consists of a large number of straight tubules that become fewer in number as the apex is reached, where but fifteen to twenty are present. These are the PAPILLARY DUCTS, 174 THE URINARY SYSTKM. OR DUCTS OF BELLINI. The tubules are supported by reticulum, in which the capillaries are found. The PYRAMIDS are separated from one another by a narrow band of tissue, that, near the apices, is chieily white fibrous; toward the bases, the parenchyma begins to enter into its formation. This is the column of Berlin, and within it are the large vessels that pass from the sinus to the boundary zone. The PYRAMIDS represent the embryonal condition when the whole organ consisted of lobes. At birth, usually, the bases of the lobes have fused to form the cortex, but the inner ends never reach that condition. The columns of Berlin then represent the interlobar connective tissue and spaces. In some animals the lobulation never disappears. The uriniferous tubule has a very peculiar and convoluted course. It starts in the cortex, and passes into the medulla, to return to the cortex for its final passage through the medulla. It originates at the RENAL CORPUSCLE, which is merely the invaginated end of the tubule, containing a tuft of capillaries. From this, the presence of a double capsule can be readily understood. The corpuscle is succeeded by a narrow constricted portion, the NECK, lined by simple squamous cells lying upon a basement membrane, and supported by interstitial connective tissue, which continues throughout. The next portion, the PROXI- MAL, OR FIRST CONVOLUTED tubule, as its name indicates, is very convoluted and irregular. This part lies in the labyrinth, and is lined by cuboidal cells, in which the protopasm is granular and the cell boundaries are indistinct. That part of the cell near the lumen is striated. This continues as the DESCENDING LIMB of HENLE'S LOOP, which passes into the medulla and is succeeded by the LOOP and the ASCENDING LIMB. The descending limb and the loop, at times, are lined by simple squamous cells, KIDNEY. 175 which are so flat that the nuclei project. The ascending limb, and, according to some, the loop, contains simple cuboidal cells, which may begin as flat cells. The proto- plasm of these is striated. The continuation of the ascend- ing is the SECOND, or DISTAL, CONVOLUTED tubule, and here the cells are cuboidal and irregular, and the protoplasm granular and striated. This portion lies in the labyrinth, and is succeeded by a short, curved portion, the ARCHED CONNECTING tubule, that connects the irregular with the STRAIGHT COLLECTING tubule. These are lined by simple columnar cells that become longer as the papillae are approached. The protoplasm of these is clear, and not striated. The STRAIGHT TUBULES, as these approach the apex of the pyramid, unite to form fifteen to eighteen large excretory tubules, the DUCTS OF BELLINI, or PAPILLARY DUCTS. These are lined by long columnar cells. The various portions of the URINIFEROUS TUBULE are distributed as follows: Cortex. In the LABYRINTH are found the renal corpus- cles, neck, first and second convoluted tubules. In the MEDULLARY RAYS, the upper ends of the descending and ascending limbs of Henle's loop and straight collecting tubules, and the arched connecting tubule. Medulla. The lower ends of the descending and ascend- ing limbs and the loop of Henle and the straight collecting tubules and papillary ducts. The diameter of the different parts of the tubule varies. The RENAL CORPUSCLE is large, measuring 120 to 200 microns. The NECK averages about 15 microns, and the PROXIMAL CONVOLUTED TUBULE is quite irregular, but the average is about 40 microns. The DESCENDING LIMB is quite narrow, 10 to 13 microns, and the ASCENDING LIMB about 25. In the SECOND CONVOLUTED TUBULE, the diameter again increases, averaging 40 to 45 microns. i 7 6 Till; URINARY SYSTEM. From the beginning of the STRAIGHT TUBULE to the end, the diameter progressively increases, so that the PAPILLARY DUCTS may have a diameter of 200 microns. The blood-vessels have a characteristic distribution. The RENAL ARTERY passes through the HILUS and enters the SINUS, where it divides into a number of branches, of - 5 FIG. 61. SECTION OF INJECTED KIDNEY OF GUINEA-PIG. i. Interlobular (cortical) artery; 2. afferent vessel; 3. efferent vessel; 4. capillary network in medullary ray; 5. capillary network in labyrinth; 6. interlobular (cortical) vein (Stbhr's Histology). which the greater number supply the ventral pyramids, and the ventral portions of the dorsal pyramids. The branches that go to the ventral pyramids carry the greater part of this blood. The rest of the kidney is supplied by the dorsal branches. The branch that supplies each pole, derived KIDNEY. 177 from the ventral division, divides into ventral, middle and dorsal branches, which are in no way united. The trunks pass up through the columns of Berlin, where small branches are given off to the vessels and tissues, as the INTERLOBAR BRANCHES. These branches pass to the boundary zone, where they arch between the cortex and medulla, form- ing the ARTERIAL ARCHES, or ARCADE. From the cortical side of the arch, the CORTICAL, or INTERLOBULAR, arteries are sent toward the capsule; from these, small arterioles, AFFERENT, pass to the RENAL corpuscles, enter and form several smaller branches, each of which breaks into a capillary tuft. From this, it will be seen that the renal tuft consists of several bunches of capillaries. Each capillary group is separate, and the vessels unite to form arterioles that leave the tuft as a single vessel, the EFFERENT arteriole. The blood is still arterial. The EFFERENT arteri- oles soon form DENSE PLEXUSES OF CAPILLARIES around the tubules of the labyrinth and medullary rays. Those capillaries near the boundary zone pass into the medulla and surround the tubules there. The CAPILLARIES become VENOUS in character, and unite with others to form the INTERLOBULAR VEINS. The CORTICAL ARTERY continues to the capsule, where it forms a star-shaped mass of venules, the VEN/E STELLATE. These are, in reality, the starting-points of the INTERLOBULAR VEINS, which run parallel to the arteries of the same name, and empty into a VENOUS ARCADE that is formed at the boundary zone by the union of the large vessels. Such is the blood supply of the CORTEX. The MEDULLA receives its blood from the concave surface of the arterial arch. The arterioles given off have a straight course, and are the ARTERIOLE RECIVE. They very soon break up into CAPILLARIES that surround the tubules of the medulla. These continue as VENOUS radicals that unite to 178 THE URINARY SYSTEM. form straight veins, VEN^ RECT^:, which empty into the VENOUS ARCH on its concave surface. The VENOUS ARCHES unite at the columns of Bertin, and pass down these, parallel to the arteries, as the INTER- LOBAR VEINS. In the sinus, they unite to form the renal 'vein. The vessels of the kidney communicate with those of the perirenal fat, through the vessels of the capsule. This is of importance. Direct anastomoses between arterial and venous vessels occur in this organ. The lymphatics comprise a capsular set, cortical and medullary plexuses. The capsular vessels empty into those of the cortical plexus. These, in turn, empty into those of the medullary plexus, the vessels of which follow the blood- vessels, emerge at the hilus, and pass to the neighboring lymph nodes. The nerves are derived from both systems. They follow the vessels and envelop them in networks to the smallest divisions. Some supply the pelvis, and others pass to the tubules, and, apparently, enter the epithelium. THE EFFERENT APPARATUS. The Efferent Apparatus consists of the Pelvis, Ureter, Bladder and Urethra. The Pelvis is the upper, expanded portion of the ureter, and lies in the sinus. It is very irregular and is divided into two or three main portions, the INFUNDIBULA, or CALYCES MAJOR, which are arranged in little cup-like structures around the apices of medullary pyramids. These are the CALYCES MINOR, and they are equal in number to the pyramids. The three coats, MUCOUS, MUSCULAR and FIBROUS, extend throughout the ureter and bladder. The MUCOUS membrane consists of transitional cells, basement membrane and tunica propria. The epithelial cells PELVIS OF THE URETER. 179 are not all regular, as those of the transitional variety are supposed to be. The upper cells are usually somewhat flattened, and almost squamous. Beneath these, they are somewhat larger, and more or less pear-shaped, while the lowest cells are polyhedral. The tunica propria con- FIG. 62. A. Cross-section of Human Ureter a. lumen; 6. epithelium; c. basement membrane; d. longitudinal fold of mucosa; e. tunica propria; /. inner longitudinal muscle; g. outer circular muscle; h. vessels; i. fibrous coat. B. Cross Section of Segment of Human Bladder a. mucous coat; b. muscular coat; c. fibrous coat; d. transitional epithelium; e. basement membrane;/, tunica propria; g. blood-vessels; h. white fibrous tissue; i. inner longitudinal muscle; k. middle circular muscle; /. white fibrous tissue; m. outer longitudinal muscle; n. venule; o. arteriole; p. adipose tissue. sists of delicate fibre-elastic tissue, in which lymphoid tissue may be seen. The MUSCULAR coat consists of smooth muscle fibres that are not distinctly arranged into layers. The FIBROUS coat is the supportive coat, and is composed of white fibrous tissue. l8o THE URINARY SYSTEM. URETER. The Ureter is the small tube connecting the kidney and the bladder, which organ it enters at an acute angle. Its coats are quite distinct. The MUCOSA resembles that of the pelvis, with which it is continuous. The epithelial cells have the same appear- ance, but the tunica propria sometimes sends delicate fibres up into the epithelial layer. These fibres lie between the cells. In it are found diffuse lymphoid tissue and some racemose glands. The whole coat is usually thrown into longitudinal folds. The MUSCULAR coat consists of smooth muscle tissue, arranged in definite layers. The inner consists of longi- tudinal, and the outer of circular fibres. Occasionally, at the lower end, there is added an external longitudinal layer, which continues into the bladder. The FIBROUS coat does not differ from that of the pelvis. BLADDER. The Bladder is a muscular sac that acts as a reservoir for the urine. It consists of fundus or body, and a small con- stricted portion, the neck, which continues as the urethra. The MUCOUS coat resembles that of the ureter in structure. The cells may be somewhat flatter. Often, in the ureter and bladder of children at birth, and older fetuses, the cells are all of the polyhedral type, and represent a typic layer of transitional cells. In urinary examinations, it is prac- tically impossible to tell the cells of the pelvis, ureter and bladder from one another. The tunica propria contains diffuse lymphoid tissue, and even solitary follicles, also racemose glands, at times. The mucosa is loosely attached to the muscular coat, ex- cept at a small triangular area near the neck. This space BLADDER. l8l has for its apex the urethral opening, and for its basal angle, the ureteral orifices. A line, connecting the two latter, forms the base. This area is the trigonum vesicce. The MUSCULAR coat is composed of smooth muscles. This is arranged as inner longitudinal, middle circular and outer longitudinal layers. All of the layers interlace, more or less, thereby giving a peculiar appearance to this coat. At the neck, the circular fibres become quite pronounced and constitute the sphincter of the bladder. The FIBROUS coat supports the others, and prevents undue dilatation. The blood-vessels lie in the outer portion of the tunica propria of the above organs, and from these a very close network of capillaries is formed beneath the epithelium, and in the muscular coat. These vessels are accompanied by the lymphatics. The nerves are chiefly sympathetic, and ganglia are not uncommon. Many of the nerve fibres end beneath the epithelium. The male Urethra is many times longer than that of the female. In the female, the structure is quite simple, and it will be first considered. The female Urethra is lined by transitional cells, except at its outer end, where the stratified squamous cells of the skin enter into its structure. The transitional cells are sometimes quite flattened. Some writers describe a simple columnar layer in the middle portion. The basement membrane rests upon a papillated tunica propria, in which are found the glands of Littre; these, in the female, are not very numerous. The MUSCULAR coat consists of smooth muscles, arranged as inner longitudinal and outer circular layers, separated by an intermuscular layer of white fibrous tissue. The male Urethra is more complex, and is divided into 182 THE URINARY SYSTEM. three portions, PROSTATIC, the continuation of the bladder; the MEMBRANOUS, that portion beneath the symphysis pubis, and the PENILE. The PROSTATIC part is lined by transitional cells that are continued from the bladder. In the MEMBRANOUS portion, stratified columnar cells are present, and these become simple in the PENILE division. Just before the outlet, or meatus, is reached, the urethra dilates, and this portion is called the fossa navicularis. It is lined by stratified squamous cells. The cells are all supported by basement membrane and tunica propria, which consists of white fibrous tissue, in which the glands of Littre are very numerous. The MUSCLE tissue is like that of the female urethra, and continues to the penile portion, where it disappears. In the membranous part, the muscular coat is reinforced by the compressor urethrce muscle, which tapers toward the prostatic and penile divisions. The FIBROUS coat consists of white fibrous tissue, and strengthens the urethra. Capillaries are numerous in the mucosa, and the vessels are followed by the nerves and lymphatics. The nerves end in the tunica propria, just beneath the epithelium. The various portions of the Urinary System are lined by the following cells: KIDNEY. URINIFEROUS TUBULE: RENAL CORPUSCLE Simple squamous. NECK Simple squamous. FIRST CONVOLUTED TUBULE . Cuboidal to columnar. DESCENDING LIMB Simple squamous. LOOP OF HENLE Simple squamous or low cuboidal. ASCENDING LIMB Low cuboidal. SECOND CONVOLUTED TUBULE Cuboidal to columnar. ADRENAL. 183 ARCHED CONNECTING TUBULE Cuboidal STRAIGHT COLLECTING TUBULE Columnar PAPILLARY DUCTS Tall columnar. PELVIS Transitional. URETER Transitional. BLADDER Transitional. / Transitional. URETHRA. .FEMALE < Oj ,. .. \ Stratified squamous. MALE FIRST PART Transitional. SECOND PART Stratified columnar. THIRD PART Simple columnar. FOSSA NAVICULARIS .... Stratified squamous. ADRENAL. The Adrenal, or Suprarenal Body is a ductless gland. It lies at the upper pole of the kidney, and has a yellow color. Upon section, it shows a yellow external layer, and a dark centrum. The organ is surrounded by a capsule of white fibrous tissue, in which involuntary, nonstriated muscle may be found. Beneath this is the parenchyma, which consists of Cortex and Medulla. The Cortex consists of three zones of epithelial cells, the ZONA GLOMERULOSA, ZONA FASCICULATA and ZONA RETICU- LARIS. The ZONA GLOMERULOSA lies just beneath the capsule, and is composed of several rows of cell-groups, oval or cir- cular in outline, surrounded by capillaries and reticulum. The cells, mostly large and polyhedral, contain a consider- able number of fat globules. Beneath this zone, the cells are arranged in columns of twos, called the ZONA FASCICULATA. These cells resemble the above, but the nuclei are on the capillary side of the cells. The columns are separated from one another by reticulum, supporting many capillaries. 1 84 THE URINARY SYSTI.M. The ZONA RETICULARIS is composed of an irregular in l work of cells formed by the anastomosis of the columns. These cells are usually smaller and outlines distinct. The nuclei are large, and the protoplasm pigmented. The Medulla is usually separated from the cortex by a layer of large, smooth cells. Beneath this layer, the cells are arranged in irregular groups, and chains surrounded by I'v^.v'':-" FIG. 63. SECTION OF HUMAN ADRENAL. a, Capsule; b, zona glomerulosa; c, zona fasciculata; d, zona reticularis; e, chromaffin cells of the medulla; /, medullary vein reticulum and capillaries. These cells are small, and their outlines are indistinct. They color very deeply with chromium salts and are called chromaffin cells. These are found in other ductless glands as the hypophysis. Nerve cells are also present. The blood-vessels are quite numerous, and apparently ab- sorb the secretion of the gland. They form a plexus in the ADRENAL. 185 capsule, from which the arterial branches penetrate the cor- tex, where they form many capillaries that surround the cells quite closely. These capillaries empty into thin- walled venous radicals in the outer portion of the medulla, and from them veins are formed that do not anastomose with one another, but empty into the central veins. The medullary capillaries are derived from the capsular vessels that pass to the medulla through the cortex without branch- ing. They unite to form the above-named veins, which are two or four in number. The lymphatics follow the blood-vessels closely. They lie between the cell-groups, and even penetrate the columns, and end between the cells. The nerves, both myelinated and amyelinated, are numerous. A plexus in the capsule sends branches into the cortex, where plexuses are formed around the vessels. Branches pass from the capsular plexus to the medulla, where rich plexuses are formed around the cells and veins. Sympathetic ganglia are also present. CHAPTER XIII. THE MALE GENITAL SYSTEM. The Male Generative Organs form a very complex sys- tem They comprise the Testicle, Epididymis, Vas Defer- ens, Seminal Vesicles, Ejaculatory Duct, Prostate, Glands of Cowper and the Penis. The Testicle is another compound tubular gland. It is surrounded by an unusually thick CAPSULE called the TUNICA ALBUGINEA, which is composed of bundles of white fibrous tissue that interlace so as to form a very tough and prominent covering. From its inner surface, prolonga- tions, or trabeculce, pass into the center of the organ to divide it irregularly into compartments. These trabeculae all converge at the dorsal portion of the organ, where the capsule is very thick, forming, at this point, a thickened mass called the CORPUS HIGHMORI, OR MEDIASTINUM TESTIS. Here a number of tubules, to be described later, are found. The TUNICA VAGINALIS TESTIS is a SEROUS MEMBRANE that, at one time, was continuous with the peritoneum. It covers almost the entire organ, and is attached to the tunica albuginea, and constitutes the visceral layer of the tunica vaginalis. It is reflected over the inner surface of the scrotum as the parietal layer. Some writers consider this membrane part of the tunica albuginea, and describe it as such, but as it is genetically different, it should be considered a separate covering. The PARENCHYMA of the testicle is made up of TUBULES, 186 TESTICLE. I8 7 which, like those of the kidney, are very convoluted, and consist of secretory and conductive portions. These tubules are the SEMINIFEROUS TUBULES, and are collected into groups which correspond to lobules. These groups, limited by the connective tissue of the tunica albuginea FIG. 64. HUMAN TESTICLE. A. Peripheral portion of the testicle showing the capsule and tubules a. tunica albuginea; b. blood-vessel; c. membrana propria of tubule; d. interstitial cells; e. spermiogenetic cells; /. lumen of longitudinal tubule. B. Single seminiferous tubule highly magnified a. tunica propria; b. basement membrane; c. spermiogonia; d. cells of Sertoli; e. mother and daughter cells; /. spermids; g. spermia. C. Sper- mia highly magnified. D. Tubule of the epididymis. that extends to the corpus, constitute the COMPARTMENTS of the testicle. The COMPARTMENTS contain a large number of very convoluted tubules, in which the SPERMIA are formed; these 1 88 THE MALE GENITAL SYSTEM. are the SEMINIFEROUS TUBULES proper, and they are supposed to end blindly beneath the capsule. According to some, however, they anastomose, and so form a set of communicating tubules, which pass toward the apex of a compartment. There are said to be three to four con- voluted tubules in each compartment, or about 600 in the testicle. When straightened each measures about 2 feet in length. At the apex of a compartment these convoluted tubules unite to form a smaller number of straight tubules that are conductive in function. These are the TUBULI RECTI, which pass into the mediastinum, where they anasto- mose to form a network called the RETE TESTIS. In the upper portion of the mediastinum, these tubules join to form a few, ten to fifteen, vessels that pass toward the edge of the corpus Highmori, as the VASA EFFERENTIA. As these leave the testicle, they become convoluted and dilated into cone-shaped structures called the CONI VASCULOSA, or GLOBUS MAJOR, of the epididymis. The CONI VASCULOSA unite to form a single tubule that runs a very convoluted course, forming a narrow continuation of the above, called the BODY of the epididymis. At the lower pole of the testicle, the mass formed by the continuation of the body is somewhat larger, and is named the GLOBUS MINOR. The tubule that continues from this point into the abdomen is called the VAS DEFERENS. The SEMINIFEROUS TUBULES are from 140 to 200 microns in diameter, and form the bulk of the testicle. Each con- sists of a small amount of tunica propria, and a basement membrane, upon which is found a number of layers of cells. The basal layer consists of two varieties, the SPERMIO- GONIA, which are the more numerous, and the SUSTENTACU- LAR CELLS, Or COLUMNS OF SERTOLI. The SPERMIOGONIA are rather large cells, in which the nuclei are mostly in the resting stage. The cells just within TESTICLE. 189 these are derived from the spermiogonia, and are the MOTHER CELLS. Each mother cell divides in two daughter cells, which, in turn, give rise to the SPERMIDS, from which the SPERMIA are developed. These layers are not regular, as the space within the lumen is gradually filled by the reproducing cells. The COLUMN of SERTOLI, or SUSTENTACULAR CELL is a less distinct element. It is pyramidal in shape, and extends up through the various layers, and serves as a support for the cells that are being transformed into spermia. For this reason, it has received the name of SUSTENTACULAR CELL. Its protoplasm is usually clear, though it may contain pigment granules. Its nucleus is pale, but the nucleolus is quite prominent. These cells are said to divide amitotic- ally. It plays an important part in spermiogenesis. Between the tubules lies the INTERSTITIAL CONNECTIVE TISSUE that supports the blood-vessels, nerves and lymph- atics. It is the variety of connective tissue called reticulum, and here and there are found groups of large cells that con- tain coarse granular protoplasm. These are the INTERSTI- TIAL CELLS, or CELLS OF LEYDic. The protoplasm often contains pigment, fat and crystalloids. These cells are probably embryonal remains. They are most numerous before and after the period of sexual activity. The EXCRETORY SYSTEM starts with the TUBULI RECTI. These are from 25 to 50 microns in diameter, and extend to the apex of the compartment. They are lined by simple cuboidal, or squamous, cells that rest upon a basement membrane. The RETE TESTIS consists of a network formed from the tubuli recti, and lies in the MEDIASTINUM. These tubes have a somewhat larger diameter than the foregoing, but are lined by the same variety of cells. The VASA EFFERENTIA are few in number, and are formed \()0 TIIK MALI; GENITAL SNSTK.M. by a union of the tubules of the rete testis. The lining cells are rather peculiar in that in some areas they are simple ciliated, while in others, nonciliated. The basement mem- brane is further supported by interstitial tissue that contains some circularly arranged nonstriated muscle tissue. The Epididymis consists of a mass of convoluted tubules that lie outside of the testicle. It is divided into three por- tions, the globus major, or head, the body, and the globus minor, or tail. The globus major consists of 10 to 15 large, cone-shaped tubules that are very convoluted . These tubules are the continuations of the vasa efferentia. The cilia are the largest in the body. The body and tail consist of a single long tubule that is very convoluted; if straightened it would measure 19 to 20 feet in length. The epididymis is surrounded by a dense sheath, or cap- sule of white fibrous tissue that divides it into compart- ments. In the globus major, the tubules in a compart- ment represent the convolutions of one of the coni vasculosa. The tubules are lined by STRATIFIED CILIATED CELLS that rest upon a basement membrane, outside of which is a dis- tinct tunica propria. External to this a're two layers of smooth muscle tissue, one circularly, and the other (thin) longitudinally, arranged. The vessels of the testicle enter the corpus Highmori and inner layer of the tunica albuginea, and send branches around the convoluted tubules, especially, forming dense plexuses. The lymphatics originate in the capsule and around the seminiferous tubules, and pass to the corpus, and leave the testicle from that point. The nerves are chiefly sympathetic, but possess no ganglia. These form plexuses around the vessels and the tubules. Occasionally, ganglia are found in the epididymis. SPERMATOZOON. 191 The Spermatozoon, or Spermium, consists of three main parts, head, middle -piece and tail (see Fig. 65). The head is somewhat pear-shaped when viewed from the side and is 4 to 5 microns long and 2 to 3 microns wide. It consists of the condensed chromatin of the spermium con- FIG 65. DIAGRAM OF THE DEVELOPMENT OF SPERM IA (Stohr after Meves). a.c., Anterior centrosome; a./., axial filament; c. p., middle piece; ch,p., tail; n, nucleus; nk, neck; p, protoplasm; p. c., posterior centrosome. stituting 8 or 12 chromosomes. It is surrounded by a delicate layer of protoplasm. In some mammals a little body is seen at the front part of the head just beneath the enveloping protoplasm; this is the acrosome and it represents the attraction sphere of a centrosome. This end of the spermium represents, apparently, a cutting edge, and in IQ2 THE MALE GENITAL SYSTEM. some lower forms it possesses a spiral or barbed projection that assists in the entrance of the spermium into the ovum. The middle-piece is composed of several portions, the END-KNOB, AXIAL FIBRE, SPIRAL FIBRE and ENVELOP. The END-KNOB connects the head with the middle-piece and is also called the NECK. Here is seen the divided centrosome, one part of which becomes a flattened mass at the junction of head and middle-piece; the other elon- gates into the AXIAL FIBRE with its front end enlarged to a disc-like mass that ultimately separates from the axial fibre to surround it as a darkly staining ring. Surround- ing the axial fibre is a delicate SPIRAL FILAMENT that is probably derived from the protoplasm. The ENVELOP is a thin layer of protoplasm that surrounds the middle-piece and is continued over the head and tail portions of the spermium. The tail consists of AXIAL FIBRE and ENVELOP. The AXIAL FIBRE is the continuation of the axial fibre of the middle-piece, but is not so prominent. It represents an elongated centrosome. It forms the motile portion of the organism and its origin from a centrosome is not difficult to understand when we consider that in ameboid, flagel- lated and ciliated cells the centrosome presides over the property of motion. It is about 5 microns longer than the envelop. The ENVELOP represents a thin protoplasmic covering of the axial fibre and is continuous with that of the middle-piece. The tail is about 40 to 50 microns long and about i micron in diameter. Spermiogenesis is that peculiar change by which spermia are formed from cells several generations removed from the spermiogonia, or original cells. The spermiogonia, with the columns of Sertoli, form the basal layer of cells of the seminiferous tubule. Up to the age of puberty, these tubes are usually solid, or nearly so. SPERMATOGENESIS. 193 The Spermiogonia represent the primordial cells, and by division give rise to the mother cells, or spermiocytes. These latter give rise to the daughter cells, and these form the spermids, which, by a direct change, become spermia. In this last division, the chromosomes are reduced from twenty-four to twelve (or from sixteen to eight) . Upon fertili- zation, these twelve unite with the twelve within the ovum, reduced from twenty-four to form the twenty-four found in all cells that are derived from the segmenting ovum. In the formation of spermia, the spermids are of the most importance. According to some authors, the nucleus forms the whole organism, while others hold the head and middle-piece are of nuclear origin, and the tail protoplasmic. These cells become crowded or drawn to the columns of Sertoli, to which they apparently attach themselves. At the same time, the shape of the cell becomes modified by elongation. The CHROMATIN of the nucleus becomes denser and migrates toward the attached, or peripheral end, while the protoplasm draws toward the central end. At the attached, or peripheral end, the nucleus has a small promi- nence developed that indicates the future head. The proto- plasm becomes clear and draws centrally, forming a slender vesicle, in the middle of which a delicate line appears. This line joins the head, and, growing backward, breaks through the membrane to form the TAIL of the spermium. The CENTROSOMES, usually two in number, become differ- ent in shape; the attraction sphere of the smaller passes to the head of the spermium to become the ACROSOME. The smaller centrosome then becomes disc-shaped and attaches itself to head at its junction with the middle-piece; the larger is cone-shaped, and differentiates into two portions, the larger of which passes toward the nucleus, and develops a flattened extremity just behind the preceding; the remain- 194 TH E MALE GENITAL SYSTEM. der elongates into the axial fibre of the middle-piece and tail. The ENVELOP is held to be protoplasmic in origin. As the spermia continue to develop, the column of Sertoli increases in length, and when development is com- plete, the organisms lie in the lumen of the tubule. The column of Sertoli, with the attached spermids, is called a SPERMIOBLAST. Loisel believes that these columns secrete a substance that attracts the spermids (positive chemiotaxis) . The Semen consists principally of spermia suspended in a fluid derived from the various portions of the genital tract. The spermia are practically amotile until mixed with the FIG. 66. HUMAN SPERMIA. i. Surface view; 2. side view; 3. looped seminal filament; 4. spermium of an ox; a. head; b. middle piece; c. tail. secretion of the prostate, when they become actively motile. Beside the PROSTATIC FLUID, other secretion is added by the seminal vesicles, glands of Cowper and urethral glands (Littre). In addition to the spermia, crystals and amyloid bodies from the prostate, fat globules and epithelial cells are seen in the semen. There are said to be about 60,000 spermia in each cu. mm. of semen. Motility may be exhibited by the spermia twenty-four hours after death. They have been kept alive for two weeks, under proper conditions, and this may readily occur in the female genital tract. Water, acids and metallic VAS DEFERENS AND SEMINAL VESICLES. 195 salts cause cessation of action, while alkaline and normal salt solutions aid it. Batelli, in 1902, found by experi- ments that the spermia travel better against than with the current. The Vas Deferens connects the testicle with the urethra. It passes into the body through the inguinal canal, and is accompanied, to the internal ring, by the spermatic artery and vein, the deferential artery, cremaster muscle and fibrous connective tissue. These form the SPERMATIC CORD. THE VAS DEFERENS. The Vas has three coats, MUCOUS, MUSCULAR and FIBROUS. The MUCOUS coat consists of stratified columnar cells resting upon basement membrane and tunica propria. It is usually thrown into longitudinal folds. The cells in the first portion may be stratified ciliated continued from the epididymis. The MUSCULAR coat is composed of smooth muscle tissue usually arranged as inner and outer longitudinal and middle circular layers. These are not always distinct, as they may interlace, more or less. The FIBROUS coat consists of fibro-elastic tissue, and gives strength to the organ. THE SEMINAL VESICLES. The Seminal Vesicles lie beneath the bladder, and empty into the vas through the SEMINAL DUCTS. They consist of three coats, MUCOUS, MUSCULAR and FIBROUS. The MUCOUS coat is lined by simple columnar, or pseudo- stratified, cells that possess yellow pigment granules. These cells rest upon basement membrane and tunica propria. The whole coat is thrown into waves, or folds, to which an apparent stratification of the cells is due. 196 THE MALE GENITAL SYSTEM. The MUSCULAR coat consists of inner circular and outer longitudinal layers of the smooth variety. The FIBROUS coat is indistinct. These organs act as reservoirs for spermia, at times, besides secreting a fluid that helps to make up the semen. The Ejaculatory Ducts are, in reality, the continuation of the vas. They are lined by simple columnar cells, like the seminal vesicles. The muscle tissue is chiefly longitudinally arranged. THE PROSTATE. The Prostate is a branched tubular gland. It is sur- rounded by a CAPSULE, and is composed of three main lobes. The CAPSULE consists, externally, of a thin layer of white fibrous tissue, beneath which is a thick layer of smooth muscle tissue. From the latter, trabeculae pass into the center of the organ, and converge at the urethra. They possess thick bases, but taper as the center is approached. These partitions form COMPARTMENTS in which the GLANDS are found. The GLANDS are of the branched tubular variety, and the ALVEOLI, or SECRETORY, PORTIONS are lined by simple colum- nar cells, and are separated from one another by the mus- cular trabeculcE. The basal portions of the cells contain granules that have an affinity for the acid stains. The ducts are a dozen or so in number, and are lined by simple columnar cells, except at their outer ends, where transitional cells of the urethra are found. These ducts empty into the floor of the urethra. The alveoli contain a varying number of structures called amyloid bodies; these are few in youth and numerous in old age. The vessels that supply the tubules, ramify in the muscu- lar septa, and form plexuses of capillaries that surround the PROSTATE. 197 tubules. The veins run toward the periphery, and form a network in the capsule. The lymphatics originate in the septa, and follow the vessels. FIG. 67. SECTION OF THE PROSTATE GLAND. a. Interstitial tissue and muscular trabecula; b. capsule; c. glands; d. prostatic bodies; e. secretion;/, blood-vessel; g. duct. Nerve fibres are numerous, and some special sensor organs are present. The Glands of Cowper are racemose glands that empty into the penile portion of the urethra. They are surrounded by a capsule of white fibrous tissue that divides the gland into lobes and lobules. The alveoli that make up a lobule 198 THE MALE GENITAL SYSTEM. are lined by low columnar mucous cells. These rest upon basement membrane and tunica propria. The smaller ducts are lined by cuboidal cells, while the larger possess stratified columnar cells. Bundles of muscle fibres are present. THE PENIS. The Penis is a peculiar organ surrounded by a loosely attached skin. The latter contains no adipose tissue. The skin extends over the end of the organ as the PREPUCE, which is covered, upon both surfaces, by stratified squam- ous cells. The inner surface possesses the characteristics of a mucous membrane. The organ consists of two main portions, the glans and the body. The glans is covered by stratified squamous cells, and is separated from the body by a narrow constricted area, the CERVIX. At this point, the squamous cells of prepuce and glans are continuous. The body consists of two CORPORA CAVERNOSA and the single CORPUS SPONGIOSUM. The CORPORA CAVERNOSA lie side by side, forming the dorsal' portion of the penis, and are bound together by a thick sheath of white fibrous tissue called the tunica albu- ginea. From the inner surface of this, trabecula pass in- ward and form a series of communicating spaces, or caverns. These are venous blood spaces. The trabeculae contain tor- tuous arteries, the helicine arteries, which, when engorged, become straightened as the organ increases in size. The spaces become filled with blood, and, with the vascular trabeculae, constitute true erectile tissue. This engorgement produces the erection. False erectile tissue depends for its action upon smooth muscle tissue. PENIS. 199 The CORPUS SPONGIOSUM has a thin tunic, and consists of two portions, urethral and peripheral. The urethral part is quite dense and rich in veins, while the peripheral part re- sembles, somewhat, the cavernous portion. The glans is a continuation of the corpus spongiosum, and consists of a delicate network of connective tissue en- closing a number of small spaces. It is covered by a deli- cate skin, which is continuous with the prepuce, or foreskin. In the cervix are located a number of glands that secrete the smegma. These are the glands of Tyson, or glandule oderiferce. The blood-vessels and spaces are numerous. The arterial branches follow the septa, in which they run such a convo- luted course as to receive the name of helicine arteries. They form capillary plexuses in the trabeculae, some of which empty into the spaces, while others pass over into the veins. The branches within the tunica form capillaries that empty into the spaces. Anastomoses between arterial and venous capillaries are numerous. The emissary veins receive blood from the tunica and superficial vessels, and partly from the deeper tissues and vessels; they pass through the tunica to empty into the dorsal vein of the penis that lies in a groove between the corpora cavernosa. These veins are pressed upon when the superficial vessels are filled with blood, in that way pre- venting egress, but not ingress, of the blood. Nerve organs include corpuscles of Meissner, bulbs, genital corpuscles, Pacinian bodies and intra-epithelial free be- ginnings. The Paradidymis, or organ of Giraldes, is found in the epididymis. It consists of a number of tubules, in which the lining cells are low columnar or even ciliated. The tubules are closed, and are separated from one another by vascular connective tissue. 200 THE MALE GENITAL SYSTEM. The cells that line the various portions of the male genital tract are as follows: Testicle. ( Spermiogonia \ > Basal layer. Sustentacular J Spermiocvtes, or mother cells. SEMINIFEROUSTUBULE . . becond layer. Daughter cells, Third layer. [ Sperm ids, Fourth layer. TUBULI RECTI Cuboidal or squamous. RETE TESTIS Cuboidal or squamous. VASA EFFERENTIA Columnar or ciliated. Epididymis Stratified ciliated. ,, T. . / Stratified columnar. VasDeferens { _ [ Stratified cdiated (some). Seminal Vesicles Simple or pseudostratified col- umnar. Ejaculatory Duct Simple columnar. CHAPTER XIV. THE FEMALE GENITAL SYSTEM. This system consists of the Ovary, Oviduct, Uterus, Vagina, Glands of Bartholin and Genitalia. The Ovary, the distinctive female organ, lies upon the dorsal surface of the broad ligament and projects into the pelvic cavity. It is surrounded by a CAPSULE of white fibrous connective tissue called the TUNICA ALBUGINEA. This is not so prominent as that of the testicle. The free surface of the capsule is covered by low columnar cells called the GERMINAL EPITHELIUM. The organ consists of Cortex and Medulla. The Cortex is the outer part, and surrounds the medulla, except at one point, at which the vessels enter and leave; this is the HILUM, and here the medulla comes to the surface. The cortex is the glandular portion, where the cellular elements of the secretion, the OVA, are formed. It consists of a delicate reticulum, the STROMA, in which the GRAAFIAN FOLLICLES are found, CORPORA LUTEA in various stages, and occasionally groups of large, polygonal epithelial cells, called the INTERSTITIAL CELLS. The free surface of the stroma is covered by the modified mesothelial cells, the GERMINAL EPITHELIUM, from which the ova are derived. These cells are low columnar elements. The Graafian follicles are characteristic structures. They vary in size; the smallest are just beneath the tunica albuginea, the medium-sized near the medulla, and the largest extend from the medulla to the capsule, and cause a projection upon the surface of the organ. 201 202 THE FEMALE GENITAL SYSTEM. Externally the FOLLICLE is covered by a layer of condensed stroma called the THECA FOLLICULI; the outer portion of this is called the TUNICA FIBROSA, and the inner the TUNICA VAS- CULOSA. The THECA is lined by a number of layers of granular cells termed the ZONA GRANULOSA, within which is FIG. 68. CROSS-SECTION OF OVARY OF A CAT. The Graafian follicles are so numerous that but little of the medulla is seen. a. Germinal epithelium; b. tunica albuginea; c. immature Graafian follicle; d. ovum; e. cortical stroma; /. interstitial cells; g. theca folliculi; h. zona granulosa; i. antrum containing liquor folliculi; k. discus proligerus; /. corona radiata; m. zona pellucida; n. vitellus; o. germinal vesicle; p. follicle without ovum; r. hilum; s. medulla showi g the tubules of the parovarium; t. arteriole; u. venule. a space, the ANTRUM, filled by a liquid, the LIQUOR FOLLIC- ULI. At one point, the granule layer projects into the antrum, and this mass contains the ovum. This projection is called the DISCUS PROLIGERUS, or CUMULUS OVIGERUS. Just within the granule cells of the discus is seen a layer of OVARY. 203 long columnar cells, the CORONA RADIATA. These cells rest upon a thick homogeneous membrane called the ZONA PELLUCIDA, which is separated from the ovum by a small space, called the PERIVITELLINE SPACE. This space is disputed by some writers. The corona is supposed to give rise to the zona pellucida. The OVUM that lies just within the space consists of a cell- wall, the VITELLINE MEMBRANE, and cell-body, the VITELLUS. In the vitellus is seen the nucleus, or GERMINAL VESICLE, which contains the prominent nucleolus, or GERMINAL SPOT. The Ovum is the most characteristic and largest cell in the body. Its diameter varies from .2 to .3 mm. The zona pellucida that surrounds it is quite thick, measuring from 7 to 10 microns. It is said to contain small radial canals called micropyles, through which the spermium gains en- trance to the ovum in fertilization. The protoplasm con- sists of yolk granules, the NUTRITIVE YOLK, or DEUTOPLASM, and the FORMATIVE YOLK. The nucleus averages about 30 microns, is eccentrically placed and sharply outlined by a membrane that possesses a double contour. The chroma- tin is rather scant, but the nucleolus is quite large and prominent. The centrosome may be seen in ova that have not undergone maturation. If this process has been com- pleted the centrosome disappears. Hertwig states that they are found in ova of rabbits up to six or seven weeks of age, and in young guinea-pigs. The Graafian follicles, of which there are about 36,000 in each ovary, are developed during intrauterine life, and all are usually present at birth. Not all of these develop, by any means. The smallest consist of the OVUM, surrounded closely by a few layers of small GRANULE CELLS and a delicate THECA. They lie just beneath the tunica albu- ginea, and show no antrum. The medium-sized follicles lie near the medulla, and present an antrum. The GRANULE 204 THE FEMALE GENITAL SYSTEM. CELLS are more numerous, and the OVUM larger. The fully- developed follicles extend from the medulla through the cortex beyond the original surface level, projecting varying distances. cr zp y FIG. 69. OVUM OF A WOMAN THIRTY YEARS OF AGE, (McMnrrick). cr, Corona radiata; zp, zona pellucida; p, protoplasmic zone of ovum; ps, perivitelline space; y, yolk (deutoplasm) ; n, nucleus (germinal vesicle) showing germinal spot. The FOLLICULAR CELLS are derived from the germinal epi- thelium, and grow into the stroma in long columns during the developmental period, as the EGG-TUBES OF PFLUEGER. In such a column will be found several large, and a great MATURATION. 205 number of small cells. These columns become separated into a number of groups of cells consisting of one or more large, and many small cells. The large are the OOGENETIC, and the small the GRANULE cells. Gradually, the large cells fuse to form a single mass of protoplasm, and all the nuclei, except one, disintegrate. The single cell resulting is called the OOCYTE. The egg-tubes are separated into these groups by the stroma that grows into the columns. This stroma further condenses around each group to form the PRIMITIVE THECA. Toward the age of puberty, these follicles begin to develop, though they may start sooner. The granule cells increase rapidly in number, and some of the more central ones disappear by disintegration or lique- faction. This gives rise to the space, or ANTRUM, which be- comes filled by a liquid, the LIQUOR FOLLICULI. The latter is probably derived from the blood-vessels. As the follicle develops and is about to rupture, the OVUM (OOCYTE) undergoes a process called Maturation. Maturation is the process by which the POLAR BODIES are formed and extruded. The germinal vesicle migrates toward the periphery, and undergoes mitotic change. When the NUCLEAR SPINDLE is formed parallel to one of the radii, the PERIPHERAL HALF, surrounded by a small amount of protoplasm, is thrust out of the cell. This is the FIRST POLAR BODY. Without rest, the remaining chromosomes immediately undergo division again, and the extrusion process is repeated. This is the SECOND POLAR BODY. The remaining chromosomes form a new nucleus called the GERM-NUCLEUS. By this change, the number of chromo- somes is reduced from twenty-four, in the oocyte, to twelve, in the matured ovum. The first polar body often divides into two, and, as a result of maturation, four cells are formed. Of these four, the ovum is the only one capable of producing an offspring. The three polar bodies disintegrate and dis- 206 THE FEMALE GENITAL SYSTEM. appear. This is entirely different from the change in the testicle. In that oigan, the SPERMIOCYTE gives rise to FOUR CELLS, each of which becomes a SPERMIUM, capable of fertilization. As the follicle increases in size, it approaches the tunica albuginea, and causes it to protrude. The stroma inter- vening between the ovum and the tunica gradually dimin- ishes until merely the tunica albuginea remains. As the follicle increases and the pressure within becomes greater, the tunica becomes progressively thinner, until it is no longer able to withstand the pressure. Then it ruptures, and the liquor folliculi and the ovum, surrounded by the granule cells, are cast out of the ovary. The vessels of the tunica vasculosa rupture, and the follicle fills with blood. When this occurs, the body is called the CORPUS HEMORRHAGICUM. The cells of the theca penetrate the clot, and cause this to organize. In addition to these cells, there are certain other large cells that possess a yellowish pigment. These are the LUTEIN CELLS, and their function is unknown. These are derived from the theca. If the ovum has not been fertilized, this body is called a CORPUS LUTEUM SPURIUM, which rapidly undergoes atrophy; in a few weeks, it leaves a white scar called the CORPUS ALBICANS. If fertilization has occurred, then the body persists until near the end of pregnancy, and is termed the CORPUS LUTEUM VERUM. The CORPUS LUTEUM seems to be a gland of short duration. It seems to secrete a substance that causes the second suc- ceeding menstrual flow, that is, of the next month. Experi- mental study upon animals, in which the follicles were de- stroyed, showed an almost invariable absence of the second succeeding period. The preceding flow was caused by the follicle preceding the experiment. This secretion also stimulates the uterus, and aids the implantation of the OVULATION. 207 ovum in the uterine mucosa, providing fertilization has occurred (Frankel). Of all the follicles formed, but few are ever fertilized. A great number atrophy; in the remainder, MATURATION occurs. Of these ova, there are those which are cast into the abdominal cavity and absorbed by the peritoneum; those which pass down the genital tract and are cast out, or disintegrate, and lastly, those that become fertilized. Ovulation includes the delivery of the ovum from the follicle and its passage through the genital apparatus. In the lower animals, in which the young are developed from eggs outside of the body (OVIPAROUS), this process is evinced by the "laying of the egg." In the VIVIPAROUS ANIMALS, or those in which the offspring is developed within the mother, this process is not accompanied by any outward signs or manifestations. In the temperate climate, it begins at about the twelfth to the fifteenth year, and continues until about the forty-fifth to the fiftieth year. At this time ovulation ceases, and fertilization cannot occur thereafter. The Medulla consists of a loose network formed by large, coarse bundles of white fibrous tissue, in which strands of SMOOTH MUSCLE TISSUE are found. These latter are limited to the medulla. In the meshes of the stroma are seen the INTERSTITIAL CELLS, which are more numerous than in the cortex. In this part of the ovary are found the large blood- vessel trunks which are very numerous. The 'vessels enter the ovary at the hilus, and form a large number of branches in the medulla. From these, smaller ones are sent to the cortex, some passing to the follicles, where they form a dense surrounding plexus, while others pass to the tunica vasculosa of the tunica albuginea. The lymphatics follow the vessels closely. 208 THE FEMALE GENITAL SYSTEM. Nerve fibres accompany the vessels, and surround the follicles. Ganglia occur in the medulla. The Parovarium, or Epoophoron, lies near the hilus of the ovary, and consists of a number of short vertical tubules united to a single horizontal tube. The vertical tubules are short, and are lined by low columnar cells. The horizontal tubule has a larger diameter than the preceding, and is lined by the same variety of cells. It often lies deep in the broad ligament. The Paroophoron lies in the broad ligament, between the ovary and uterus, and consists of a number of short, closed tubules lined by low columnar cells. The tubes re- semble the vertical tubes of the epoophoron. THE OVIDUCT. Although the ovary possesses no excretory apparatus like other glands, the Oviduct, or Fallopian Tube, acts as such. The Fallopian Tube consists of the outer FIMBRIATED END, the middle, or AMPULLA, and the inner UTERINE END, or ISTHMUS. It has three coats, MUCOUS, MUSCULAR and FIBROUS. The MUCOUS coat consists of simple ciliated cells that lie upon a basement membrane and tunica propria. A muscu- laris mucosce is absent. The tunica propria is thrown into longitudinal folds that are high in the fimbriated end, but diminish in height as the uterus is approached. These folds are the VILLI, which possess a very narrow base, but the part lying in the lumen of the tube is greatly branched. The tunica propria consists of white fibrous and yellow elastic tissues, in which diffuse lymphoid tissue is found. The MUSCULAR coat consists of involuntary nonstriated muscle tissue arranged in inner circular and outer longitudi- nal layers. Near the uterine end, an inner longitudinal layer is added. This corresponds to a muscularis mucosse. OVIDUCT. 209 The FIBROUS coat consists of white fibrous tissue, and is surrounded by peritoneum. The blood-vessels lie in the deeper portion of the tunica propria. From these, smaller ones are sent into the villi, and into the muscular and fibrous coats. The vessels are usually quite tortuous. FIG. 70. CROSS-SECTION OF THE HUMAN OVIDUCT. a. Epithelium; b. tunica propria; c. villi; d, muscular coat, inner circular layer; e. muscular coat, outer longitudinal layer; /. blood-vessels in the fibrous coat; g. blood-vessels in villus; h. fibrous coat; k. epithelium of fimbria; /. tunica propria of fimbria. The lymphatics accompany the blood-vessels. The nerves are both myelinated and amyelinated. They accompany the blood-vessels, which they supply, and then pass to the mucosa, where they end in relation with the cells. 14 210 THE FEMALE GENITAL SYSTEM. THE UTERUS. The Uterus is a flattened, pear-shaped organ that con- sists of BODY and CERVIX. It is an important organ, as within it develops the offspring, in viviparous animals. All parts consist of MUCOUS, MUSCULAR and FIBROUS coats. The MUCOUS coat of the body is about i mm. in thickness, and is composed of simple ciliated cells, basement mem- brane and tunica propria. Within the latter are found a rich capillary plexus and diffuse lymphoid tissue. The surface is not smooth, but is broken by the formation of GLANDS. These are tube-like depressions lined by the simple ciliated cells, and are of the branched tubular -variety. They are the UTERINE GLANDS and extend to the muscular coat, but do not penetrate it. They are often so long that When they reach the muscular coat, they turn and extend parallel to it for some distance. The MUCOSA of the CERVIX is a little different. The uterine end is lined by simple ciliated cells, and glands are present. The -vaginal end is lined by stratified squamous cells, and gland-like depressions are present. The orifices often closed, causing them to become distended with secre- tion. In this condition, they produce globular projections called the OVULI NABOTHI. The cervical mucosa is thrown into folds called the PLIC.E PALMATE. The vaginal portion of the cervix is covered by stratified squamous cells. The MUSCULAR coat consists of three layers of smooth muscle, inner longitudinal, middle circular and outer longi- tudinal. The inner longitudinal probably represents an hypertrophied muscularis mucosoz. It is separated from the middle layer by a very thin layer of connective tissue. This muscle layer is called the STRATUM MUCOSUM. The middle layer is the thickest, and contains the large vessels. It is called the STRATUM VASCULARE. The outer longitudi- UTERUS. 211 nal layer lies just beneath the fibrous coat, and is often called the STRATUM SUPRA VASCULARE. In the CERVIX, the circular fibres are more pronounced, forming a dense band or ring. t mm FIG. 71. RESTING UTERINE MUCOSA. a. Mucosa; b. epithelium; c. gland tubule (Stohr's Histology, after Bohm and Davidojf}. The muscle fibres average 50 to 60 microns in length; but, during pregnancy, they lengthen to from 300 to 600 microns. The FIBROUS, or SEROUS, coat is quite thin. It is com- pletely invested by peritoneum in the BODY. 212 THE FEMALE GENITAL SYSTEM. Menstruation is the periodic change that occurs in the uterine mucosa, every twenty-eight days, during the child- bearing period (13 th to 50 th year). It is divided into stages, the HYPERTROPHIC, DESQUAMATIVE, REPARATIVE and RESTING stages. During the HYPERTROPHIC, or CONSTRUCTIVE stage, the mucosa increases to 2 or 3 mm. in thickness, and the sur- face becomes irregular. This is due to the increase in size and number of the blood-vessels, and to cell proliferation in the tunica propria. The glands become broader, deeper and more tortuous. This change requires four to six days, and is succeeded by the DESQUAMATIVE, or destructive, stage. The DESQUAMATIVE, or DESTRUCTIVE, stage is character- ized by the appearance of the FLOW, or FLUX. It is caused by the diapedesis of some of the blood from the capillaries of the tunica propria. The blood passes into this layer beneath the epithelium, and cuts off the nutrition of the overlying cells, causing them to undergo a fatty degenera- tion. These cells then disintegrate, exposing the vessels, which rupture and allow the blood to pass into the uterine cavity. The surface is thus left without an epithelial covering, and the thickness of the mucosa becomes reduced. Hoppe-Seyler states that the average amount of blood lost is from 26 to 52 cu. cm. This stage, lasting three to five days, is followed by repair. The REPARATIVE stage is that in which the mucosa re- turns to the normal condition. The hyperemia disappears, and the disintegrated epithelium is replaced by epithelial cells from the glands. This stage requires about five to eight days. The RESTING stage constitutes the remaining twelve to fourteen days of the period. During this stage, the uterine mucosa is quiescent. Should fertilization occur at the time VAGINA. 213 of the constructive stage, the other three stages may not take place. The blood-vessels are important. Two arteries, the uter- ine and ovarian, supply the organ. The main branches of these arteries pass to the middle circular layer of muscle, which plays the part of submucosa. Smaller branches are sent into the mucosa, and there form plexuses around the glands. The large trunks are very tortuous, to allow for the increase in the size of the uterus during pregnancy. The lymphatics originate in the mucosa; these vessels empty into a set of larger vessels in the middle layer of the muscular coat. From here the vessels pass into the serous coat. The nerve fibres are both myelinated and amyelinated. The former pass into the mucosa, some ending in the epi- thelial layer. The latter pass chiefly to the muscular tissue. THE VAGINA. The coats of the Vagina are the same as those of the uterus. The MUCOUS coat consists of stratified squamous cells, supported by basement membrane and tunica propria. The subepithelial portion of the tunica propria is papillated. The deeper portion contains many large elastic fibres and considerable diffuse lymphoid tissue. Occasionally, some simple tubular glands are met with, and the lining cells are of the simple ciliated variety. The MUSCULAR coat varies in thickness, that nearer the outlet being the thicker. The layers are not sharply sepa- rated from one another, but the general direction is inner circular and outer longitudinal. The mucous and muscular coats are thrown into folds that are called RUG^E. The FIBROUS coat consists of dense fibrous tissue, and 214 THE FEMALE GENITAL SYSTEM. serves to connect, the vagina with the surrounding tissues and organs. The larger vessels lie in the deeper portion of the mucosa, and send branches into the mucosa and muscularis. The *?-V FIG. 72. CROSS-SECTION OF SEGMENT OF HUMAN VAGINA. a. Stratified squamous epithelium; b. tunica propria; c. inner circular muscle fibres; d. outer mixed muscle fibres. capillaries of the mucosa pass chiefly to the papillae. The veins form dense plexuses beneath the fibrous coat. Large vessels occur in the lower part of the mucosa, causing it to resemble cavernous tissue. GENITALIA. 215 The lymphatics follow the same course as the blood- vessels. The nerves are both myelinated and amyelinated. Genital corpuscles may be found in the mucosa. THE GENITALIA. The VAGINAL ORIFICE is guarded by a delicate annular, or crescentic membrane called the Hymen. This consists of white fibrous tissue covered upon its external and internal surfaces by stratified squamous cells. Occasionally, it is very vascular. Just outside of this fold, the primitive uro-genital sinus spreads to form the Vestibule of the vagina. This is a triangular space, with the apex formed by the junction of the labia minora, the sides by these folds and the base by the vaginal orifice. It contains the opening of the urethra. This space is lined by stratified squamous cells. In the tunica propria, are found a great many elastic fibres and mucous and sebaceous glands, especially near the opening of the urethra. The lower portion of the tunica propria contains so many large venous channels that it is practically ERECTILE TISSUE. Opening into the vestibule upon each side is a gland, the analog of the gland of Cowper of the male. This is the GLAND OF BARTHOLIN, which is a compound racemose gland, and the acini are lined by large, clear, mucous cells. The ducts are lined by low columnar cells. Covering the vaginal orifice, to a greater or less extent, are seen the Labia Minora, or Nymphae. These consist of a central mass of loose connective tissue, in which the blood-vessels are abundant, especially the veins. In the tissue between the veins, smooth muscle tissue exists, and this with the vascularity, forms to ERECTILE TISSUE. The 2l6 . THE FEMALE GENITAL SYSTEM. folds are covered upon both sides by stratified squamous cells that rest upon a papillated tunica propn'a. In these papillae, capillary plexuses are seen. Schaccons glands are numerous, but hairs and sweat-glands arc absent. The Glans Clitoris lies in the tissue formed by the junction of the labia minora. It is covered by stratified squamous cells. The central part consists of ERECTILE TISSUE, and many large and small vascular papillae are present. Genital corpuscles and sebaceous glands are found. The Glans is covered by a fold of skin, the PREPUCE, in which the seba- ceous glands are quite numerous. The Labia Majora are merely folds, or pouches of skin. Their outer surfaces are covered by ordinary skin. In the subcutaneous tissue are seen numerous vessels, nerves, glands, bundles of smooth muscle and an abundance of adipose tissue. Along a median line, they come in contact with each other, and the skin surface is somewhat modified. Here elastic and muscle tissues are abundant, but adipose tissue is wanting. The skin of the labia majora is some- what darker than that in the immediate neighborhood, due to the presence of pigment in the epithelial layers. Over the pubis, the two labia meet and form a prominent mass, the Mons Veneris. The various portions of the female genital tract are lined by the following cells: OVIDUCT Simple ciliated. UTERUS. BODY Simple ciliated. CERVIX, UTERINE END. . . . Simple ciliated. VAGINAL END . . . Stratified squamous. VAGINA Stratified squamous. VESTIBULE Stratified squamous. LABIA Stratified squamous. CHAPTER XV. THE PLACENTA AND UMBILICAL CORD. A description of the formation of the Placenta and Cord must be given in order to understand their structure at term. Should the ovum become fertilized, it is passed down the oviduct by the ciliated cells, as fertilization usually occurs in this portion of the genital system. It is sur- rounded by the zona pellucida and corona, or zona radiata. The mucous membrane of the uterus becomes thickened, as for menstruation, and the ovum becomes lodged, usually in the fundus. The mucosa of the uterus is divided into regions: that immediately beneath the ovum is the PLACENTAL DECIDUA, or DECIDUA SEROTINA; the ovum becomes covered by a portion called the OVULAR, or REFLEX DECIDUA; the re- mainder is the UTERINE DECIDUA, Or DECIDUA VERA. The ovum divides and redivides, and passes down the oviduct toward the uterus. These cells form an irregular mass, the MORULA. The outer cells of this mass arrange themselves beneath the zona pellucida as the SUB- ZONAL ECTODERM, or OUTER CELL MASS, while the remainder constitute the INNER CELL MASS. The entire structure grows rapidly, and, as a result, a cavity is formed around the inner mass, except at one point, where it is attached to the subzonal layer. The cavity is filled with liquid, under pressure. This mass is called the BLASTULA, or ONE- LAYERED VESICLE. The point of attachment is called the 217 2l8 THE PLACENTA AND UMBILICAL CORD. EMBRYONIC AREA. In this condition, the ovum usually reaches the uterus. The OUTER MASS, at the point of union with the inner mass, becomes greatly thickened, its upper portion being called the TROPHODERM (Minot), and its under portion the ecto- derm. The trophoderm extends all around the zona pellucida, and is closely applied to it. The innermost cells of the INNER MASS then arrange themselves as a single layer of cuboidal cells that extend into the cavity of the blastula and form, by meeting, a little vesicle, the ento- FIG. 73. DIAGRAM OF SUPPOSED DEVELOPMENT OF PRIMATES (Minot}. Tro. Trophoderm; EC. ectoderm; Mes. mesoderm; Ent. entoderm; Coe. ccelom. dermal 'vesicle. By this formation, the GASTRULA, or DIPTOBLAST, in which two distinct layers, ectoderm and entoderm, are seen, is completed. From these two layers, the 'mesoderm is derived. This constitutes the TRIPLOBLAST, or THREE-LAYERED VESICLE. The mesoderm lies between the ectoderm and entoderm, and where these layers separate, it splits into two layers, one of which accompanies the ectoderm around the triploblast to form the SOMATO- PLEURE, and the other accompanies the entoderm to form the SPLANCHNOPLEURE. The mass increases in size, and the trophoderm in the embryonic area thickens greatly. TRIPOBLAST. 2IQ At the same time, the cells at the junction of trophoderm and ectoderm disappear, leaving a space, the AMNIOTIC CAVITY. This cavity is now bounded by trophoderm above and the combined ectoderm, mesoderm and entoderm be- neath, these latter constituting the EMBRYONIC SHIELD. At the edges of the cavity, the mesoderm continues with the trophoderm, forming the PROCHORION. At what are to be the cephalad and caudad regions of the future embryo, transverse depressions appear in the FIG. 74. DIAGRAM OF EARLY DEVELOPMENT OF PRIMATES. Later Stage of 73 (Minot). a. Aminotic cavity; b. ectoderm; c and d. mesoderm; e. entoderm. somatopleure (one at each end) ; these are called the head and tail folds of the amnion, respectively. The lateral folds appear on each side in the same manner. All these grooves deepen, and the somatopleure extends ventrally from all directions (less from caudad) to form the body-wall; its re- turn folds pass dor sally over the embryo to unite, forming an inner membrane next to the embryo, the true amnion, and an outer above the embryo, the FALSE AMNION, or PRIMI- TIVE CHORION. The prochorion consists of trophoderm (ectoderm called also the placentoblast) and mesoderm; the amnion, of mesoderm and ectoderm, and the body-wall of 220 THE PLACENTA AND UMBILICAL CORD. ectoderm and mesoderm, respectively. At all points, like layers are opposed to like layers. In the formation of the body-wall and amnion, the SPLANCHNOPLEURE has been pushed before the somatopleure to form a tube within the body, the GUT-TRACT and a sac outside, the YOLK SAC and VITELLINE DUCT. In the formation of the amnion, the embryo loses its connection with the chorion at all points, except caudally, where the mesoderm and ectoderm of the two are continuous, forming the BELLY-STALK. By this time, the ovum has become lodged in the uterine mucosa. This process is accomplished by the aid of the trophodermal cells, that have the power of phagocytosis (destruction of tissue) and erode the superficial tissues of the mucosa, forming a cavity into which the ovum sinks. The epithelium of the uterus is lost in this region and also in the glands and the superficial vessels are exposed. The tropho- derm, or placentoblast becomes thrown into little proc- esses, or mlli (present as early as the fifth day, Peters), due to actual growth and the disappearance of cells in the trophoderma' layer. As a result, there are formed a series of intercommunicating spaces, the trophodermal lacuna. The villi are composed of trophoderm and mesoderm. When the vessels of the mucosa are exposed, they rupture into the glandular spaces, and from these, the maternal blood gains access to the trophodermal lacuna, or spaces. Thus does the embryo receive nourishment from the mother, before the umbilical vessels are present. The area of the ovum left uncovered when the ovum becomes lodged, is covered by mucosa that is reflected from the lining at the sides of the ovum. This is, therefore, called DECIDUA REFLEXA, Or OVULAR DECIDUA. We must remember that the BELLY-STALK connects the embryo with the prochorion. This belly-stalk is of OVIPAROUS. 221 importance, because it represents that part of the embryonic disc that does not lose connection with the prochorion during the formation of the body-wall and gut-tract. Into the belly-stalk the allantoic evagination of the gut-tract extends for a short distance, while the allan- toic vessels pass along the entire extent of the stalk to the forming chorion. With the passage of the allantoic vessels FIG. 75. DIAGRAM OF EARLY DEVELOPMENT OF PRIMATES. Later than FIG. 74. (Minot). a. Amnion; b. chorion; c. embryo; d. yolk-sac; e. body-stalk; /. allantois; g. entodermal cavity of embryo; h. entoderm; i. chorionic villi. to vascularize the chorion, the belly-stalk becomes the so- called extra- embryonic portion of the allantois. In some animals, the OVIPAROUS, the allantois loses connection with the belly-stalk, and is free. It remains as a dilated sac, and serves as a receptacle for urine. In the viviparous animals, it remains connected with the belly-stalk, and is said to connect the embryo with the uterus, becoming the 222 THE PLACENTA AND UMBILICAL CORD. organ of nutrition and respiration. As a matter of fact, it seems to be the belly-stalk that forms the link between fetus and chorion; the chorion becomes the fetal portion of the placenta, while the belly-stalk becomes the umbilical cord by the addition of the vessels. It would seem that the allantois proper has nothing to do with the formation of the placenta and cord in the higher types. In this mesoderm, four main vessels develop, two arteries and two veins. Later but one vein is found, due either to a fusion of the two veins, or more probably to the atrophy of the right vein. The two veins enter the body and proceed toward the heart, while the other two vessels pass into the body, and connect with the aorta. The distal ends of all the vessels pass into the chorion, and divide to ramify all the villi. These villi are still covered by the trophoderm, consisting usually of two layers. Of these, the outer becomes con- verted into a thin layer of protoplasm, in which the original nuclei remain and the cell-boundaries are lost. This pro- toplasm constitutes the SYNCYTIUM. The villi do not long remain simple, but branch and re- branch; the vessels follow these branches, and penetrate to the very ends. Some of the villi enter the uterine glands, in which the epithelium becomes denuded by about the sixth week, and the surface cells by the fourth week, and are the floating villi; others become attached, and form the fixed villi. When the epithelium of the uterus is lost, the engorged superficial capillaries of the placental decidua become connected with the glands, and the blood enters these, and then the trophodermal spaces. These channels are the later intervillous spaces. From these cavities, the blood is returned to the venous channels of the mucosa, but no direct connection is established between the fetus and the mother. These villi are very abundant, and may be scattered all CHORION. 223 over te ovum or be limited to the equator of the mass- Up to his time, all are equal in size. Soon a difference is noted i size, those at the place of attachment of the ovum increar in number and size, forming^the chorionf rondo sum, FIG. ; i \<;KAMMATIC OUTLINE OF A DORSO- VENTRAL SECTION I:RUS CONTAINING AN EMBRYO OF ABOUT FIVE WEEKS. a. Veni a dorsal surface; g. outer limit of decidua; s, s. limits of the placen j decidua; ch. chorion, within which is the embryo enclosed by and attached to the chorion by the umbilical cord; from the coi hangs the pedunculated yolk-sac; r, r. ovular decidua (Minot). while th< remainder disappear and constitute the chorion latter do not become vascularized. At abot the fifth month, a villus has the following ap- pearance Of the trophodermal cells, the outer do not re- 224 THE PLACENTA AND UMBILICAL CORD. main large, distinct elements, but become flattened, and represent a mere layer of nucleated protoplasm that covers the villi; this is the syncytium, and it is the covering of the embryonic connective tissue that constitutes the core of the villi and supports the vessels. In the inner layer, the cells remain distinctly outlined, and persist for a short time as the cell-layer of Langhans. From the fifth month on, they disappear so that ultimately only the syncytium remains. Here and there on the villi are seen groups of cells that rep- resent collections of syncytial cells, the cell knots. These, like the other syncytium, contain nuclei that are small, but stain deeply. The protoplasm responds well to the acid stains. The Langhans cells, however, contain large nuclei, but neither these nor the protoplasm respond well to stains. After the third month, the number of villi that become attached to the mucosa rapidly increases, so that after that time the fetal and maternal portions become more and more fixed to each other. This is the beginning of the formation of the placenta as it is seen at birth. The villi branch repeatedly, and the whole structure grows rapidly, causing the child to do the same. Any disturbance that will retard the growth of the placenta will also retard the growth of the fetus in greater proportion. The difference between the placenta at the fourth or fifth month and at birth is merely in size. This is due to the increase in number and branches of the villi. The villi are separated into groups by connective-tissue septa that are derived from the uterine tunica propria. These are the placental septa. At birth the Placenta is a flesh-like, saucer-shaped mass, the attached surface of which is divided into lobes, or cotyledons. The fetal surface is covered by the amnion, a continuation of the sac in which the fetus lies, and shows the vessels as they enter and leave the organ; the opposite PLACENTA. 225 surface is divided into lobes, or cotyledons, covered by the decidua serotina. The weight of the placenta is about si xl3 FIG. 77. HUMAN PLACENTA AT TERM. A. Vertical section at margin; D. decidua; Cho. chorion; Fib. fibrin; Vi. placental villi; Si. marginal sinus; vi. aborted extra-placental villi; b. decidual tissue. B. Portion of decidual tissue at b highly magnified; v. blood-vessels; d. decidual cells with one nucleus; d'. multinucleated decidual cells (Minoi). one-sixth that of the child. It consists of two portions, the fetal and maternal. This organ consists of a fleshy mass lying between two 226 THE PLACENTA AND UMBILICAL CORD. membranes. Upon the fetal surface, we find the AMNION and CHORION. The AMNION consists of a single layer of cuboidal epithelial cells that rest upon the mesodermal tissue. These epithelial cells possess prominent, deeply- staining nuclei, but the protoplasm does not react well to the stain. The mesodermal tissue is somewhat fibrillar, and few cells are present. It is avascular. The CHORION is composed of mesodermal tissue in which the fibrils are more or less distinct. This mesoderm is covered by trophodermal (ectodermal) cells that later be- come the syncytium. From the side opposite to the amnion are seen projections. These may vary from small simple villi to those resembling a tree possessing an enormous number of twigs. Along this surface of the chorion, may be seen masses of a fibrillar substance that are called canalized fibrin. The bulk of the placenta consists of villi. These form a reddish spongy mass, divided into masses called cotyledons. The main stems contain two or more vessels surrounded by mesodermal tissue. Peripherally, each villus is covered by a thin layer of nucleated proto- plasm, the syncytium. The small twigs consist of a core of mucous connective tissue supporting several small capil- laries. The syncytium surrounds each twig. In places are seen collections of nuclei representing the cell-knots. The cavities between the villi are the intermllous spaces con- taining the maternal blood and, at times, canalized fibrin. From this, it is readily seen that the fetal and maternal blood currents do not intermingle. They are separated from each other, the endothelium of the fetal capillaries on the one hand, and the syncytium of the villi on the other. The maternal side of the placenta is covered by the DECIDUA SEROTINA, or the STRATUM COMPACTUM of the mucosa. It is less than a millimeter thick, and possesses a number of short oblique channels. These are the remains MEMBRANES. 227 of the uterine glands; they now represent blood sinuses, which contain maternal blood. The serotina extends into the fetal portion as the placen- tal septa, and divides it into the cotyledons. At the edge of the placenta, it becomes attached to the chorion, and continues as the DECIDUA VERA. At this junction there is a considerable space that extends all around the edge of the placenta. This is the marginal sinus, and is prominent be- cause few or no villi have developed here. The MEMBRANES consist of the AMNION and the uterine lining, or the STRATUM COMPACTUM. The latter is thin, and contains neither glands nor epithelium. When the fetus increases in size and causes a dilatation of the uterus, the amniotic sac is forced against the uterine lining, and causes an atrophy of the glands and cells of the stratum compactum. As a result, a mere fibrinous membrane, that has a loose connection with the amnion, is produced, due entirely to pressure. Fossati, by means of the Golgi method, found a peculiar network of fibres surrounding the blood-vessels of the placenta and umbilical cord; this network also seemed to come into relation with the epithelium. He considered this network nerve tissue. The Umbilical Cord is the connecting link between the fetus and the placenta, and represents the early belly- stalk. It is surrounded by one or more layers of cuboidal epithelial cells, continuous on the one hand with epithelium of the amnion, and on the other with the ectodermal cells of the body, supported by a little subepithelial fibrous tissue. Within this covering is the peculiar tissue called WHARTON'S JELLY. This is embryonic connective tissue in which the cells are chiefly spindle-shaped; some round and stellate cells, however, are seen. The intercellular sub- stance is semi-solid, and takes a peculiar homogeneous stain. 228 THE PLACENTA AND UMBILICAL CORD. During the early months of pregnancy, the intercellular substance contains a great deal of water, and the cellular elements are few. At the end of pregnancy the intercellu- lar substance is more or less fibrillar, though the semi-solid portion predominates. At this time the cells are mostly of the stellate type, but not numerous. At the body end, occasionally, traces of allantoic cavity and yolk sac are found. The VESSELS contained are the single UMBILICAL VEIN and two UMBILICAL ARTERIES. These are thick-walled and well- FIG. 78. CROSS-SECTION OF HUMAN UMBILICAL CORD (Minot). A, A'. Umbilical arteries; V. umbilical vein; Y. remains of allantois. developed, and the muscle fibres run both circularly and longitudinally. The wall of the arteries is thicker than that of the vein. The insertion of the cord into the placenta is usually eccentric, and at this point the vessels branch rapidly and spread out in all directions. The circulation of the placenta is a closed one. The blood is carried from the iliac arteries to the umbilicus through the hypogastric arteries, which continue in the cord as the um- bilical arteries. These branch to follow the villi and ulti- mately terminate in tufts of capillaries in the terminal villous twigs. The blood at this point receives the oxygen and nutritive matter from the maternal blood that circulates FETAL CIRCULATION. 22Q in the intervillous spaces in which the villi lie. There is no direct communication between the feted and maternal blood, for they are separated from each other by the endothelium of the capillaries and the syncytium covering the villi. As the oxygen and nutritious substances pass into the fetal blood, the effete matter and gases pass out into the maternal blood. The principle is the same as in the lung, where the blood is oxygenated. Red cells never pass from one system to another, but leukocytes that have the power of ameboid motion may. The blood is collected by the radicals of the umbilical -vein and carried into the body to the under sur face of the liver, where a portion enters the portal vein through the continuation of the umbilical vein, is dis- tributed to the liver and collected by the hepatic veins and emptied into the postcava; the remainder is carried to the postcava (inferior vena cava) by the ductus venosus. The blood passes to the right auricle, then through {.he foramen ovale to the left auricle, from which it passes, through the auriculo-ventricular orifice, into the left ventricle. The blood then passes into the aorta chiefly to the upper ex- tremities and head, is collected by the radicals of the precava (superior vena cava), and emptied into the right auricle. From this chamber it passes through the auric- ulo-ventricular orifice into the right ventricle, from which it passes into the pulmonary artery toward the lungs. As these organs do not functionate at this time, most of the blood is sent to the aorta through the ductus arteriosus. The blood then passes toward the lower extremities, and, as it reaches the internal iliac arteries, most of it is sent to the placenta through the arterial trunks, which inside of the body are called the hypogastric arteries, and in the cord the umbilical arteries. CHAPTER XVI. THE SKIN AND ITS APPENDAGES. The Skin covers the external surface of the body and is its most extensive organ. It consists of two portions, the Epidermis, or Cuticle, and the Cutis Vera, or Corium. The Epidermis is the epithelial portion of which the appen- dages are modifications. It consists of stratified squamous cells, which, over the general body surface, are divisible into two layers, STRATUM MALPIGHII and STRATUM CORNEUM. The STRATUM MALPIGHII, or RETE MUCOSUM, is composed of a number of layers of cells. The basal part consists of columnar elements, and is called the GENETIC LAYER. The cells stain deeply, and under certain conditions show pig- ment granules. The layer is uneven in its course, as it conforms to the waves of the corium. The upper cells of the stratum Malpighii are large polyhedral elements that do not touch one another, but are separated by intercellular spaces. Each cell is provided with a number of delicate spines, or prickles, that meet those of other cells, and thus prevent the cell-bodies from coming into contact with one another. These are the PRICKLE CELLS. As the upper part of this stratum is approached, the cells become flattened and have an even course. The STRATUM CORNEUM ordinarily forms a thin layer. Its cells are very thin and scale-like and usually possess no nuclei. They are derived from the cells beneath, but differ from them in consisting of keratin that gives them their hard and horny characteristic. These cells are constantly cast off, and the cells below increase to replace them. Be- 230 DERMA. 231 tween these two layers an irregular STRATUM GRANULOSUM is often seen. In certain parts of the body, sole and palm, the STRATUM GRANULOSUM and another, the STRATUM LUCIDUM, are well developed. The STRATUM GRANULOSUM lies external to the stratum Malpighii, and is composed of two or three layers of flattened, spindle-shaped cells that contain a deeply-staining nucleus and coarsely granular protoplasm. The granules are keratohyalin that later form the horny matter of the stratum corneum. These granules are quite large and prominent, and respond well to hematoxylin. They seem to be modified protoplasm, but some hold that they represent products of the degenerating nucleus. The STRATUM LUCIDUM lies external to the stratum granulosum, and separates this from the stratum corneum. It forms a narrow, glistening band of cells, two or three layers broad, in which the keratohyalin granules have fused to form a homogeneous substance, called eleidin. This substance reacts well to eosin. The nuclei are not promi- nent nor are the cell-bodies distinct. The Derma, True Skin, or Cutis Vera, is composed of connective tissue arranged in two or more less distinctly separated layers. These are the STRATUM PAPILLARE, or outer, and the STRATUM RETICULARE, or inner. The STRATUM PAPILLARE consists of delicate bundles of small white fibrils forming a close network with elastic fibres. The upper portion of this stratum is thrown into small waves called the papilla, to which the stratum Malpighii conforms. Over the general skin surface, these papillae do not extend through the stratum Malpighii, but in the palmar and plantar regions they are visible externally, and cause the peculiar markings seen in these areas. These papillae 232 THE SKIN AND ITS APPENDAGES. are important, as they contain either capillary plexuses or special sensor nerve beginnings. The lower portion of the papillare consists of a looser network, in which the vessels FIG. 79. CROSS-SECTION OF SKIN OF SOLE OF FOOT. a. Stratum corneum; b. stratum lucidum; c. stratum granulosum; d. stratum Malpighii; e. derma; /. panniculus adiposis; g. duct of sweat gland; h. prickle cells; i. genetic layer; k. cross-section of a smooth muscle fibre; /. duct of sweat gland; m. Pacinian body; n. secretory portion of sweat gland; o. muscle of tubule; p. blood-vessel; q. adipose tissue. form plexuses parallel with the surface. It gradually passes into the STRATUM RETICULARE. The STRATUM RETICULARE is not distinctly separable from the preceding. It is composed of larger bundles of coarser DERMA. 233 fibrils of white fibrous tissue, and contains some yellow elastic tissue, as will be seen below. Here are found the larger blood-vessels and the appendages and special sensor nerve beginnings. In the corium of the scrotum, penis and nipple, smooth muscle fibres are found. When these bundles contract, "goose-flesh" is produced. The elastica is often separated into layers, of which there are four, the subepithelial, papillary, reticular and sub- cutaneous elastic layers. Beneath the stratum reticulare is usually a layer of adipose tissue that separates the skin from the fascia. This is the PANNICULUS ADIPOSUS, and it varies in thickness in the different regions. The color of the skin is due to the presence of pigment granules in the lower layers of the stratum Malpighii. Such granules have been found even in the corium. In the white races, this pigmentation is limited to the nipple and genital region. Whether the pigment is due to the vital activity of the cells, or whether it is brought here and deposited, is not definitely settled. The former seems to be the origin of that of the retinal cells and probably of that of the skin. The skin is the protective organ, and varies in thickness in the different regions. It is thinner on the less exposed sur- faces, as the inner surfaces of the thighs and arms, and thicker on the exposed regions, as back, sole and palm. Upon the palmar and plantar surfaces the epithelium is thrown into ridges. These are arranged in definite patterns characteristic of each individual. Recorded impressions of these surfaces have been used as means of identification for various purposes. Wilder considers the plantar patterns more characteristic than the palmar patterns. The blood-vessels of the skin vary in size and number, according to the location; in the gluteal, plantar and palmar regions, they are greater, while in the most movable parts 234 THE SKIN AND ITS APPENDAGES. they are most branched. The larger trunks lie in the reticulare, parallel to the surface, and form a capillary plexus in the papillare. From this plexus, capillary tufts enter the various papillae. The latter vessels continue as venous cap- illaries, that form a plexus just beneath the papillae. This empties into another in the lower portion of the derma that communicates with a subdermal plexus; the latter lies be- tween the derma and the panniculus adiposus, and its vessels possess valves. The long nerve trunks are found in the reticulare, and from these branches form a subpapillary plexus. Myelin- ated fibres extend toward the surface, and form the special beginnings. The sensor organs are very numerous in the skin. These comprise the free beginnings, or those in which the naked axis cylinder pierce the epithelial layer, branch and send these divisions between epithelial cells. The higher forms of beginnings comprise tactile corpuscles of Meissner, most numerous in the palmar and plantar skin of the ringers and toes; bulbs of the conjunctiva and genitalia; Pacinian bodies especially in the palms and soles; and the organs of Ruffini, resembling the neuro -muscular beginnings. For a detailed description, see Nerve Tissue (p. 90). In addition, there is the usual nerve supply to the blood-vessels. The lymphatics of the skin consist of superficial, or papil- lary plexus, which receives the lymph from the spaces in the papillae, and a deeper, or subcutaneous plexus that con- sists of larger trunks, that anastomose with the above, and communicate with the special plexuses of the appendages. THE APPENDAGES. The Appendages of the skin are the Hairs, Nails, Se- baceous, Sweat and Mammary Glands. These are all de- rived from the epidermis. HAIRS. THE HAIRS. 235 The Hairs are protective organs limited to certain por- tions of the body. Each consists of a ROOT, that portion within the skin, and a SHAFT, that part seen above the surface. FIG. 80. FROM A SECTION OF SCALP (Stohr's Histology). i. Hair-shaft; 2. hair-root; 3. sebaceous gland; 4. arrector pili muscle; 5. root sheaths; 6. follicular sheath; 7. hair-bulb; 8. papilla; 9. fat cells. The ROOT is somewhat flask-shaped, the lower end being enlarged to form the HAIR-BULB. This, on its under surface, is indented and invaginated by a little mass of connective tissue, the HAIR PAPILLA, that contains a small tuft of capillaries, upon which the nourishment of the hair solely depends. The root is surrounded by a condensation 236 THE SKIN AND ITS APPENDAGES. of the derma, in which the connective tissue bundles are arranged into two layers. In the outer, the fibres have a longitudinal course, while in the inner, they run circularly. Within this circular layer is a prominent homogeneous band, the glassy membrane. This represents a greatly hypertrophied basement mem- brane. These layers constitute the FOLLICULAR SHEATH. Internal to it are found the epithelial cells, which are continuous with the epidermis. These are arranged into layers that are the ROOT SHEATHS, of which there are two, OUTER and INNER. The OUTER ROOT SHEATH is the direct cont'nuation of the stratum Malpigh.'i. These cells are the same as elsewhere, and continue to the bottom of the root, where they blend with those of the inner root sheath. Throughout the greater part of the follicle, this layer consists of several rows of cells. Toward the bulb, it gradually becomes reduced to a single layer. The INNER ROOT SHEATH begins at the lower edge of the orifice of the sebaceous gland that opens into the hair follicle. Above the duct it is replaced by the stratum corneum. This sheath consists of two portions, the outer of which is called the LAYER OF HENLE. This lies next to the outer root sheath, and is composed of a single layer of flattened cells. Within this layer is the sheath, or LAYER OF HUXLEY, which consists of two or three layers of large irregular cells. In the bulb all of these layers, including the outer root sheath, are inseparable, and gradually pass over into the hair itself. The Hair occupies the central portion of the follicle, and is composed of three parts, CUTICLE, CORTEX and MEDULLA. The CUTICLE is composed of a single layer of irregular, nonnucleated scales. These are very thin and overlap. Within the follicle they lie closely applied to the layer of -NAILS. 237 Huxley. The CORTEX consists of a great many layers of long, spindle-shaped elements. The nuclei are rod-shaped. The MEDULLA, when present, is composed of several rows of cuboidal cells that do not extend the length of the hair. They contain granules of keratohyalin, and frequently have a dark appearance; this is due to the presence of small air-bubbles. The heaviest hairs are found on the scalp and pubis, in the axilla, and upon the face of males. Delicate hairs oc- cur all over the body surface, and these are like the LANUGO HAIRS of the fetus. The color of the hair is due to pigment granules in the cortex. These cells may even contain pigment in solution. Diffuse pigment is abundant in dark and red hairs, but ab- sent in white. Opening into the hair follicles are the SEBACEOUS GLANDS. This is usually upon the side toward which the hair leans, and here is also seen the muscle of the hair follicle, the ARRECTOR PiLi muscle. This is smooth muscle, and is at- tached above to the derma, just beneath the stratum Mal- pighii, and below to the hair bulb. When it contracts it causes the hair to "stand on end" THE NAILS. The Nails are peculiar appendages that serve for the protection of the ends of the fingers and toes, and consist of the ROOT and the NAIL-BODY. The ROOT is the proximal end at which the organ grows. Here the epithelial cells are transformed into the hard sub- stance that gives the nail its character. Along the sides, the nail is protected by an overhanging ledge of skin, which constitutes, at the root, the NAIL-FOLD, and at the sides, the NAIL-WALL. The angle formed by the nail and wall is the 2 3 8 THE SKIN AND ITS APPENDAGES. NAIL-GROOVE. The stratum corneum continues into the angle over the edge of the nail as the EPONYCHIUM. The NAIL-BODY consists of the NAIL PROPER and the NAIL- BED upon which the najl rests. The NAIL represents a greatly hypertrophied stratum lucidum. The cells are flattened elements, in which the nuclei are indistinct, and the protoplasm clear. At the proximal end is the root, and at this place alone the nail grows. It is marked by a white area, the LUNULA. Here the epithelial layer is so thick that the underlying capil- FIG. 81. CROSS- SECTION OF NAIL. i. Nail; 2. corium; 3. epithelium; 4. nail-wall; 5. nail groove; 6. bone of phalanx; 7. eponychium. laries are invisible. The cells also are said to contain keratohyalin granules. At the distal end, the nail projects as the FREE EDGE. The NAIL BED consists of the stratum Malpighii and the corium. The stratum Malpighii resembles that of the skin surface, and rests upon the papillated corium. That portion beneath the lunula is termed the MATRIX. The corium is composed of bundles of white fibrous and yellow elastic tissues that have a general longitudinal direction. Between the bundles are vertical fibres that pass from the periosteum toward the nail. The PAPILLAE of the bed are GLANDS. 239 not like those of the skin, but consist of long RIDGES that extend from the root to the end of the nail. They are small beneath the root, but increase *n height as the free edge is approached, and end abruptly at that point. THE GLANDS. The Glands comprise the Sweat, Sebaceous and Mam- mary Glands. The Sweat-glands are of the coiled tubular variety. Each consists of a secretory portion that lies in the stratum reticulare, and an excretory duct that passes up through the derma and cuticle to open upon the surface. The SECRETORY PORTION consists of a single layer of cu- boidal cells lining the tubule. These are separated from the basement membrane by a layer of smooth muscle fibres. The protoplasm is granular and may contain pigment granules and fat globules. The nucleus is usually quite distinct. The secretory tubule is coiled upon itself, and the various convolutions are separated from one another by interstitial tissue that corresponds to the tunica propria. The DUCT that leads from the secretory part to the sur- face has usually one-half the diameter of the secretory tubule, and is lined by two layers of cells that rest upon a basement membrane and tunica propria. In the epidermis its course is spiral, and no separate wall is present, the epi- thelial cells of the epidermis acting in this capacity. The diameter of this portion is greater than that of the corium. Its opening upon the surface is large and trumpet-shaped, and is called the SWEAT-PORE. These glands are generally distributed, except on the margins of the lips, glans penis and inner surface of the prepuce. They are most numerous in the palm and largest in the axilla. The average diameter is i mm., but 240 THE SKIN AND ITS APPENDAGES. in the latter region they may attain a size of 3 or 4 mm. In this region the secretory tubule may be branched. The normal secretion is an oil that keeps the skin soft and pliable. When the innervation becomes disturbed, the secretion becomes thin and watery, and is then termed sweat. The GLANDS of MOLL, of the eyelid, and the CERU- MINOUS GLANDS, of the external ear, are coiled tubular glands that secrete oil alone. The Sebaceous Glands are racemose structures. They are usually found in connection with the hair follicles; the largest hairs possess small glands, while the smallest hairs are appendages of the attached sebaceous glands. Each is surrounded by a capsule of white fibrous tissue that forms the supportive structure. The ALVEOLI are lined by cells that are a continuation of the cells of the stratum Malpighii, and which rest upon a basement membrane and tunica propria. These cells are very large, and completely fill the alveolus. Those in the center, where the lumen should be, are further advanced in changes than the basal cells. The entire protoplasm be- comes converted into oil, which constitutes the secretion, and is called SEBUM. The death of the cell is necessary to the formation of this secretion. The transformed cell is immediately replaced by another. The excretory duct is lined by several layers of cells that do not take part in the secretory activity, and are derived from the outer root sheath of the hair follicle. Sebaceous glands are found in regions devoid of hairs, as in the margins of the lips, glans penis, prepuce, glans clitoris and labia minor a. THE MAMMARY GLAND. The Mammary Gland is an alveolo-tubular organ. Ac- cording to some writers, it is a modified sweat gland, while MAMMARY GLANDS. 241 others hold it to be a modified sebaceous structure. It is a compound organ, if such a term may be used, as it is composed of from fifteen to twenty individual compound glands. Each of these possesses its own excretory duct, that has its own opening in the nipple. The entire organ is covered by skin. m FIG. 82. SECTION OF LACTATING HUMAN MAMMARY GLAND (Stohr's Histology} . a. Alveolo-tubule; b. tubule; c. duct; d. connective tissue. Each gland consists of lobes and lobules separated and supported by white fibrous and adipose tissues. All of the individual glands are further bound together in the same manner. The ducts converge and end in the nipple, which forms a small projecting mass. 16 242 THE SKIN AND ITS APPENDAGES. Each lobule consists of a number of acini, which are tubular or alveolar in structure. The number of these depends upon the state of activity. In the gland of pregnancy, the acini are very numerous, and are lined by simple columnar, or cuboidal cells, in which are accumulated the fat globules that form the important constituent of the milk. These cells rest upon a basement membrane, but in places are separated therefrom by peculiar elements called basket cells, which are compared to the smooth muscle tissue of the sweat glands. The ducts are lined by simple columnar cells that rest upon a basement membrane, outside of which circular bundles of white fibrous tissue are to be found. These ducts unite to form the main secretory duct of the individual glands; each main duct dilates to form a small AMPULLA, or SINUS LACTIFEROUS, before the nipple is reached. The nonlactating gland consists chiefly of white fibrous and adipose tissues, in which are seen a number of ducts, but few acini. The bulk of the organ consists of the fibrous and adipose tissues. When pregnancy occurs, the ducts divide and redivide, and the terminal portions dilate to form the acini. This increase in the glandular part causes the increase in the size of the organ, and the tingling sensation that occurs at that time. After lactation has ceased, most of the acini undergo retrogression, atrophy, and disappear. Some of the ducts undergo the same change. As a result, the gland becomes somewhat smaller and flabby. In old age, or after the child-bearing period has passed, the glandular and ductular portions retrograde and disappear in the same manner, until in old age, they may be entirely absent. The glands are then represented by fibrous and adipose tissues. Milk consists of minute globules of fat, o.i to 0.5 mm. in diameter, surrounded by a thin layer of CASEIN. This MILK. 243 prevents them from coalescing. They are formed in the protoplasm of the cells of the acini, but the cell, after discharging them, does not die, as formerly supposed. At first, COLOSTRUM is present in the glands; this consists of fat and COLOSTRUM CORPUSCLES, which are either degen- erated gland cells, or leukocytes. The NIPPLE, or MAMMILLA, consists of an outer covering of pigmented skin, and within it the individual ducts are found. These are separated from one another by fibrous tissue and involuntary, nonstriated muscle. The muscle tis- sue is arranged circularly and vertically, extending to the apex of the mammilla. By its contraction, an erection is produced. Such tissue is called false erectile tissue. At the base of the nipple is a pigmented area called the AREOLA, which contains a ring of sebaceous glands called the GLANDS OF MONTGOMERY. In addition to the general blood-vessels, the various ap- pendages have special supplies. From the sub papillary ar- terial plexus, branches pass to the hair follicles, to form one plexus beneath the hyalin membrane, and another in the papilla. The venous radicals formed, empty into subpapil- lary plexus of veins. Around the sebaceous and sweat glands, the subpapillary arterial plexus forms a close net- work of capillaries which form venous branches that empty into the subpapillary venous plexus. The blood-vessels of the mammary gland converge to- ward it, and pass into the organ in the partitions between the lobules. From these vessels, branches extend into the lobules, and form close plexuses around the acini. The appendages are supplied with nerves from both sym- pathetic and cerebrospinal systems. The hair follicles receive myelinated fibres that branch freely, and end in spoon-shaped masses upon the glassy membrane. The sweat glands are supplied with sympathetic fibres, that 244 THE SKIN AND ITS APPENDAGES. form a close network beneath the basement membrane, which they pierce, to end upon the gland cells. The mammary gland has both varieties of nerves. The sym- pathetic are the more numerous; these pass to the blood- vessels on the one hand, and to the acini on the other. In the latter, they form a plexus beneath the basement mem- brane, and from this plexus, branches end upon the gland cells. The nerve beginnings in the nipple are numerous. The glands and hair follicles are surrounded by separate lymphatic plexuses that empty into the subcutaneous ves- sels. In the mammary gland, plexuses are found between the individual lobes, around the ampullae and in the nipple. These empty into the axillary lymphatics. CHAPTER XVII. THE NERVE SYSTEM. The Nerve System consists of the Cerebrum, Cerebellum, Pons, Oblongata and Spinal Cord. It is surrounded by three membranes, the Dura, Arachnoid and Pia. The Dura is a tough membrane composed of interlacing bundles of white fibrous and yellow elastic tissues that con- tain lymph spaces between them. Within the skull, it forms the inner periosteum of the cranium, which relation ceases at the foramen magnum, the entrance into the vertebral canal. In the latter, it is not connected with the bone, but hangs like a bag and contains the spinal cord. This membrane is lined by endothelial cells, and forms the outer boundary of the SUBDURAL LYMPH SPACE. It is quite vascular, and a few nerves, that pass to the blood spaces are found. The Arachnoid is a thin, delicate, web-like membrane composed of loosely interwoven bundles of w r hite fibrous tissue. It lies closely applied to the dura, and is separated from the pia by the SUBARACHNOIDEAN LYMPH SPACE. This is also lined by endothelial cells. It forms the PAC- CHIONIAN BODIES and VILLI, but contains neither blood- vessels nor nerves. The Pia is the vascular membrane. Its outer portion contains the bulk of the vessels, while the inner enters into close relation with the nerve tissue. Its blood-vessels lie in the fibro-elastic network, surrounded by PERIVASCULAR LYMPHATICS. Its arachnoidean surface is covered by 245 246 THE NERVE SYSTEM. endothelial cells. Only a few nerve fibres are present. The pia is the only one of these membranes that follows the fissures and depressions of the nerve system. The Nerve System consists of Gray and White Substances. The Gray Substance consists of NERVE CELLS, their PROCESSES and NEUROGLIA, MYELINATED and AMYELINATED nerve fibres. The NERVE CELLS are of various forms, unipolar, bipolar and multipolar. The first possess but one process, the second, two, and the third, three or more. The CELL-BODY may be of any shape, and consists of granular protoplasm that has a fibrillar structure. The NUCLEUS is usually large, but does not take a deep stain. The NUCLEOLUS is very large and stains deeply. The PROCESSES are DENDRITIC and AXIS CYLINDER. The DENDRITES are minor processes that are subdivided into a great many smaller processes, the teledendrites; in certain instances, sensor cells, the dendrites may be myelinated (see Nerve Tissue, p. 84). The AXIS CYLINDER process, or NEURIT, is the main process. In cells of the FIRST TYPE, or DEITER CELLS, the neurit leaves the gray substance to become the center of a nerve fibre. In those of the SECOND TYPE, or GOLGI CELLS, the axis-cylinder never leaves the gray substance. The NEUROGLIA consists of NEUROGLIA, or GLIA CELLS, and a fibrillar intercellular substance. The cells are either spider or mossy. For a detailed description of these, see the chapter on Nerve Tissues (p. 86). The White Substance consists of MYELINATED NERVE FIBRES held together by NEUROGLIA and some white fibrous connective tissue. In the Cerebrum and Cerebellum, the Gray Substance is external, and constitutes the CORTEX. The White Sub- stance is internal, and is called the MEDULLA. In the THE CEREBRUM. 247 Spinal Cord, the Gray Substance is surrounded by the White Substance. In the Oblongata and Pons, there is no distinct arrangement. CEREBRUM. Beside the Cerebrum, there are other masses of nerve tissue to be considered here. These are the Olfactory Lobes, the Pituitary and Pineal Bodies. The GRAY SUBSTANCE, orCortexof the Cerebrum, is divided into layers that are not sharply limited from one another. In some regions, five can be made out, in others three, while four form the average number. The Cortex is made irregular by the formation of tissues and convolutions. The latter consist of a central mass of white substance, Medulla, covered by the gray substance, or Cortex. The CORTICAL LAYERS are, from without inward, the I, MOLECULAR, 2, SMALL PYRAMIDAL, 3, LARGE PYRAMIDAL and 4, MIXED or POLYMORPHOUS LAYERS. 1. The MOLECULAR layer consists mainly of neuroglia and cell-processes. The latter are derived from the next two layers, and are chiefly dendrites. The neuroglia forms a network within which the dendrites and myelinated nerve fibres lie. The latter run parallel to the surface, and are therefore called tangential fibres. Among the cellular elements are some of the second type, or Golgi cells. The axis cylinders of these cells remain in the gray substance. They are polygonal, stellate and spindle-shaped cells, in which the dendrites run parallel to the surface, and are -called the CELLS OF CAJAL. 2. The LAYER OF SMALL PYRAMIDAL Cells is Composed of several layers of cells, the dendrites of which extend into the molecular layer, while some of the axis cylinders par- tially pass to the molecular layer (second type) and others 248 THE NERVE SYSTEM. pass into the medulla (first type, or Deiter cell)'. In the latter case, the axis cylinders give off branches called FIG. 83. VERTICAL SECTION OF HUMAN CEREBRAL CORTEX. a. Pia; b. molecular layer; c. small pyramidal cells; d. large pyramidal cells; e. layer of polymorphous cells; /. layer of fusiform cells'; g. medulla; //. radial bundles of myelinated fibres in cortex; i. pial process; k. large pyramidal cell. collaterals. The CELLS themselves are small, measuring 10 to 12 microns in diameter, and triangular in outline. The THE CEREBRUM. 249 DENDRITES arise from the angles, while the AXIS CYLINDER, or NEURIT, has its origin at the middle of the base. 3. The LAYER OF LARGE PYRAMIDAL cells constitutes the widest and most important layer. The CELLS are usually 20 to 50 microns in diameter, though some may exceed this. The dendrites pass to the molecular layer, while the neurit becomes myelinated nerve fibre. These cells are, therefore, cells of the first type. Their outline is triangular, and the nucleus is large and prominent. 4. The LAYER OF POLYMORPHOUS cells contains cells of various shapes; these are large and small pyramidal, spindle- shaped, oval and polygonal. The latter predominate. The dendrites pass to the upper layers of the cortex, while the axis cylinders, in some instances remain in the cortex, and in others pass into the medulla. In the last three layers, bundles of myelinated nerve fibres having a radial course are seen. They begin in the small pyramidal layer, increase in number as they ap- proach the medulla, and contain, beside those fibres de- rived from the immediate cortical cells, others whose origin is not definite. In addition there are other myelinated nerve fibres that form layers practically parallel with the surface. The STRIATION OF BAiLLARGER is composed of such fibres that lie in the large pyramidal cell layer. The STRIATION OF BECHTEREFF consists of myelinated fibres between molecu- lar and small pyramidal cell layers. The Medulla consists of MYELINATED NERVE FIBRES from various sources; those that pass to the periphery of the body from the pyramidal and polymorphous cells (PRO- JECTION FIBRES) ; others from the pyramidal cells that pass from one hemisphere to the other (COMMISSURAL FIBRES) ; those that connect different areas of the same side (pyramidal cells), and whose axis cylinders are U T" 250 THE NERVE SYSTEM. branched, and pass into the cortex sooner or later (AS- SOCIATION FIBRES); lastly, fibres that come from distant parts of the same or the other hemisphere, or other parts of the nerve system (CENTRIPETAL FIBRES). OLFACTORY LOBE. The Olfactory Lobe, that portion of the nerve system devoted to the sense of smell, is comparatively small in man. There are. five layers present, which are best marked in the central part of the organ. These are the LAYER OF PERIPHERAL FIBRES, the GLOMERULAR LAYER, the MOLECU- LAR LAYER, the LAYER OF MITRAL CELLS and the GRANULE LAYER. The LAYER OF PERIPHERAL FIBRES consists of a plexus formed by the fibres of the OLFACTORY NERVES. The GLOMERULAR LAYER lies beneath the above, and is made up of peculiar round, or oval, bodies 100 to 300 microns in diameter. They are said to be masses of inter- lacing telodendria of the olfactory and mitral cells. The MOLECULAR LAYER is made up of large and small spindle-shaped ganglion cells whose dendrites end in the glomeruli, and whose axis cylinders pass to the FIFTH, or GRANULE LAYER. The LAYER OF MITRAL CELLS consist mainly of large PYRAMIDAL cells varying in size from 30 to 50 microns. Their dendrites pass to the glomeruli and the axis cylinders to the granule layer. The GRANULE LAYER consists of nerve cells and fibres. The cells are stellate, ganglion elements, and peculiar gran- ule cells; the latter appear to have no axis cylinders. Some of the nerve fibres are derived from the mitral cells, some from the molecular layer, and others from the outside. The deeper bundles enclose granule and stellate cells. THE HYPOPHYSIS. 251 THE HYPOPHYSIS. The Hypophysis or Pituitary Body, is a small organ con- sisting of a NEURAL, or CAUDAL LOBE, the Posthypophysis and an EPITHELIAL, or FRONTAL LOBE, the Prehypophysis. Both are surrounded by a common capsule of fibrous tissue. The PREHYPOPHYSIS, however, is divided into a number of tubular alveoli lined by polygonal epithelial cells. These cells are of two varieties, acidophilic and basophilic; the latter are the more numerous. Some contain large nuclei surrounded by a clear and slightly granular protoplasm, while others contain a similar nucleus buried in a coarsely granular protoplasm. These are irregularly arranged so that a small lumen remains; this may contain colloid substance. The nerves of this lobe consist of very few fibres with numerous branchlets and ramifications that follow the arteries to be distributed mainly to acini. Here they terminate in ball-like enlargements. According to Berkley, the POSTHYPOPHYSIS consists of an outer layer of gray substance similar to that of the infun- dibulum, composed of slightly irregular endymal cells three to four layers deep; this tissue, however, is not found on the surface where the two lobes are in contact. The central part of this lobe consists of a few acini, that may contain colloid substance; these acini constitute about one-third of the cellular elements; the remaining two-thirds of the cellu- lar elements are nerve cells of various forms as follows: i. Flask-shaped cells with short axones and knob- tipped den- drites. These cells are widely distributed and the branches end freely between the other structures. 2. Cells whose processes end in the endymal layer; these are large ganglion cells the axones of which traverse the entire organ and end in the infundibular area. Large oval cells higher up also 252 THE NERVE SYSTEM. belong to this group. 3. Small elements with short den- drites of a prickly appearance; these cells are unlike any other cells in the body. To this group belongs another small cell with an apical tuft of wavy processes. The two lobes, although surrounded by an apparently common capsule, are absolutely distinct and are separated by a fibrous lamella. The posthypophysis alone is connected with the infundibulum. The arteries reach the organ by means of the infun- dibulum. As they reach the fibrous septum between the two lobes branches pass to the prehypophysis and form plexuses between the acini. The capillary plexuses of the posthypophysis are likewise numerous. The veins have a corresponding return course. The lymphatics are found in the lamella between the two lobes and consist of a network of spaces lined by simple ciliated cells; these probably represent endymal cells derived from the cavity of the infundibulum. THE EPIPHYSIS. The Epiphysis, or Pineal Body, is a small, apparently unimportant organ in man. In some lower animals, it is a visual organ. This rudimentary structure consists of a number of tubules lined by polygonal cells supported by fibrous tissue and neuroglia in the lower part. These tubules contain the BRAIN SAND, or ACERVULUS CEREBRI, peculiar concretions of phosphate and carbonate of mag- nesium, ammonium and calcium, which are not limited to this body, however, but may be found in other portions of the nerve system. CEREBELLUM. The Cerebellum, or Little Brain, has a characteristic gross appearance, when sectioned. Its Cortex and Medulla THE CEREBELLUM. 253 are so colored and arranged as to give the appearance of a TREE, called the ARBOR VITAE, or TREE OF LIFE. FIG. 84. VERTICAL SECTION OF THE HUMAN CEREBELLUM. A. Cerebellum, low power; B. cerebellum highly magnified; a. molecular and ganglionic 1 yers; b. granule layer; c. medulla; d. pia; e. cell of Pur- kinje; /. cell of molecular layer; g. cells of the granule layer; C. cell of Purkinje. The Cortex consists of three sharply-marked layers, the I, MOLECULAR, r the 2, GANGLIONIC and 3, GRANULE LAYERS, from without inward. 254 THE NERVE SYSTEM. 1. The MOLECULAR LAYER consists of a network of neuro- glia, in which the dendritic branches of the cells of the lower layers are found. They are mostly those of the GANGLIONIC CELLS. In addition, there are small and large multipolar cells; the axis cylinders of the former remain in this layer, while those of the latter pass toward the second layer and form a network, of branches around the ganglionic cells. They are therefore called the BASKET CELLS. Fibres from the MEDULLA pass into this layer and break into a great number of delicate terminal twigs. 2 . The GANGLIONIC LAYER, Or LAYER OF PURKIN JE CELLS, is very characteristic. The bodies of these cells are very big, measuring 30 to 70 microns. A large nucleus and a dis- tinct nucleolus are present. The protoplasm is fibrillar, but contains no pigment granules. Two main processes extend from the body; the LOWER, or NEURIT, passes to the medulla and becomes a myelinated nerve fibre. The UPPER, or DENDRITIC, quickly breaks into two, that run at right angles to the main stem. From the upper sides of these two branches, an immense number of small, delicate branches are formed. These cells are called ANTLER CELLS, from their appearance. The cells are more numerous at the top than at the bottom of the convolutions. 3. The GRANULE LAYER IS Composed of GREAT and SMALL GRANULE CELLS. The SMALL CELLS possess large nuclei and a small amount of protoplasm. The DENDRITIC PROCESSES remain mostly in this layer, while the NEURIT passes to the molecular layer, forming U T" branches that run parallel to the surface. The LARGER CELLS resemble the cells of the ganglionic layer, but the AXIS-CYLINDER forms a network of branches, being a . cell of the second type. Besides the neuroglia present, there are some fibres of the myelinated variety. This layer is thicker at the summit of the convolu- tion, and diminishes as the base is reached. THE PONS. 255 The Medulla consists of myelinated nerve fibres, sup- ported by neuroglia and connective tissue; of these fibres, some form the inferior peduncles; others the middle (pontile), and the remainder the superior peduncles, which connect the cerebellum with the corpora quadrigemina. THE PONS. The Pons can conveniently be divided into two portions, the VENTRAL PART or PONS PROPER, that can readily be distinguished by the naked eye, and the DORSAL or TEG- MENTAL PART, which is continuous with the oblongata, and hence called PREOBLONGATA. The ventral portion consists mainly of FIBRES running in various directions and separated by masses of gray sub- stance, the PONTILE NUCLEI. The FIBRES course trans- versely and longitudinally. The transverse fibres, at the caudal portion of the pons lie superficial to the pyramids; at a higher level the fibres hv crease in number and are often described in three groups: a. Ventral superficial fibres, those that pass ventral to the pyramids; b. dorsal, or deep, fibres,. those that pass dorsal to the pyramid; c. penetrating, or middle, those that pass right through the pyramids and break into a number of smaller bundles. At the cephalic level of the pons all the transverse fibres again form a single mass. At the lateral border of the pons these transverse fibres pass into the cerebellum as the medipeduncles. As to origin these fibres are of two kinds : i . those that arise in the cerebellar cortex and end in the pon tile nuclei and, 2. those that arise in the pontile nuclei and end in the cerebellar cortex. The longitudinal fibres are those that constitute the pyramid ; at the upper and lower portions of the pons these fibres form a single compact bundle, while in the middle 256 THE NERVE SYSTEM. region they are separated into smaller bundles by the transverse penetrating fibres. The gray substance of this portion of the pons consists of FIG. 85. DIAGRAM OF TRANSVERSE SECTION OF CEPHALAD PORTION OF PONS (Morris, after Schwalbe}. i, Mesencephalic root of trigeminal nerve; 2, prepeduncle; 3, Median longi- tudinal bundle; 4, lateral lemniscus; 5, formatio reticularis; 6, medial lemniscus; 7, trigeminal nerve; 8, pyramidal fasciculi; 9, transverse fibers of pons; 10, raphe; n, fourth ventricle; 12, metatela. many collections of nerve cells in -the spaces between the fibre bundles; these are the pontile nuclei. At the boundary zone between pons and preoblongata lies a bundle of transverse fibres that arise from cells in the nuclei of termination of the cochlear division of the auditory nerve; these fibres cross to the opposite side of the organ THE PONS. 257 and form here in the mesial region, by their decussation, the trapezium. From the trapezium the fibres continue toward the side of the preoblongata and form here the lateral lemniscus, which will be described later. The PREOBLONGATA, or TEGMENTAL PORTION of the pons, lies dorsal to the preceding structures and includes the FIG. 86 DIAGRAM OF TRANSVERSE SECTION OF CAUDAL PORTION OF PONS (Morris, after Schwalbe) . i, Nucleus of abducens (6th) nerve; 2, lateral nucleus of vestibular nerve; 3, formatio reticularis; 4, nucleus of facial (yth) nerve; 5, spinal tract of trigeminal (5th) nerve; 6, root of vestibular nerve; 7, superior olive; 8, root of abducens (6th) nerve; 9, pyramid; 10, trapezium; n, raphe; 12, descending root of facial (yth) nerve; 13, genu of facial cephalic portion of the floor of the fourth ventricle. The gray substance is found mainly as a layer just beneath the endyma of the ventricle; at various levels it forms nuclei of origin (motor) or termination (sensor) of the trigeminal, abducens, facial and auditory nerves. Between these nuclei and the trapezium is found the FORMATIO RETICU- 17 258 THE NERVE SYSTEM. LARIS. Beneath the ventricle gray and near the midline is a bundle of fibres, the MEDIAN LONGITUDINAL BUNDLE. Laterally is formed a bundle of ascending fibres constituting the continuation of the fibres of the trapezium, called the LATERAL LEMNISCUS. The MEDIAL LEMNISCUS continued cephalad from the oblongata is seen near the midline in the lower part of preoblongata, but higher up it is pushed laterad by other structures, so that it lies here in relation with the lateral lemniscus, but is not connected therewith. The PREPEDUNCLE, Or SUPERIOR CEREBELLAR PEDUNCLE, is found only in the middle and upper portions of the preoblongata, occupying a superficial position in the dorso- lateral area; higher up it becomes covered by the lateral lemniscus. In addition to the cranial nerve-nuclei several other gray masses of importance are seen in the preoblongata. The NUCLEUS OF THE LATERAL LEMINSCUS is seen at the side of the organ and represents a nucleus of termination of some of the fibres of the trapezium; its cells give rise to fibres that continue cephalad in the lateral lemniscus. This nucleus seems to be connected with the succeeding nucleus. The SUPERIOR OLIVARY NUCLEUS lies just laterad of the trapezium and many of the fibres of the trapezium end here; its cells give rise to fibres that aid in the formation of the lateral lemniscus. This nucleus lies at a lower level (caudad) than the preceding, but seems connected with it. THE OBLONGATA. The Oblongata, or Postoblongata, consists of halves like the spinal cord, but here the resemblance ceases, as the ar- rangement of gray and white substances is different. The H-shape of the gray substance is no longer retained; that THE OBLONGATA. 259 portion in relation with the canal still remains about the same, but the horns are modified and broken by the PYRAMIDAL DECUSSATION and the FORMATIO RETICULARIS. As the canal is followed upward and is seen to broaden into the fourth ventricle, or METEPICELE, the gray substance that surrounded the canal becomes merely the floor of the ventricle. The remaining gray is seen as isolated masses forming nuclei, as the GRACILE, CUNEATE, OLIVARY, ARCUATE and PYRAMIDAL NUCLEI. The SUBSTANTIA GELATINOSA ROLANDI continues from the spinal cord as the same mass forming a cellular mass at the side of the oblongata, the TUBERCULUM ROLANDI. The cause of the rearrangement of the ventral gray sub- stance is the PYRAMIDAL DECUSSATION. As the motor fibres that compose the pyramid are about to enter the cord, 85 to 90 per cent, take an oblique course from the ventral to the lateral portion of the opposite side of spinal cord, con- tinuing here as the crossed pyramidal tract. In crossing, the ventral horn of gray substance is cut into two portions, that around the canal the basal part and the isolated ventral mass that is pushed laterad. The ventral ground bundle of the oblongata becomes covered by the pyramid so that the bundle becomes more dorsally placed as the oblongata is ascended. In the caudal portion of the oblongata other marked changes are noted dorsally. As the funiculus gracilis (Goll) and the funiculus cuneatus (Burdach) enter the oblongata from the spinal cord they form two broad masses that con- sequently force the dorsal gray horns laterad so that ultimately these gray masses lie opposite each other at the sides of the oblongata. Ultimately the basal (canal) and lateral portions of the gray substance become separated from each other by nerve fibers that run in various direc- tions, constituting the FORMATIO RETICULARIS. Thus, as 260 THE NERVE SYSTKM. ventrally, the gray substance of the dorsal horn becomes separated into a basal (canal) portion (connected with the ventral basal gray) and an isolated lateral mass, that is associated with the spinal root of the trigeminal nerve. FIG. 87. SECTION OF THE OBLONGATA AT ABOUT THE MIDDI.K OF THE OLIVARY BODY (Gordinier, ajter Schwalbe}. j.l.a., Ventro-median fissure; n.ar, arcuate nucleus; p, pyramid; A"II, hypoglossal nerve; j.a.e., external arcuate fibers: n ./., nucleus lateralis; g, substantia gelatinosa; a.V., ascending root of fifth nerve; X, vagus nerve; /.r., formatio reticularis;O., restis being formed; n.c., nucleus cunealus; f.s., funiculus solitarius; n.X, and n.X', two portions of vagal nucleus; nXIT, hypoglossal nucleus; r, raphe; A, beginnings of ventral column of the spinal cord; o f o", accessory olivary nuclei; p.o.L, peduncle of olive; n.am, nucleus ambiguus. In connection with this dorsal basal gray arise two new gray masses, the NUCLEUS GRACILIS and NUCLEUS CUNEATUS. The NUCLEUS GRACILIS is a mass of gray substance that lies close to the dorso-median groove and increases in size as the funiculus gracilis ends. It represents the nucleus of THE OBLONGATA. 261 termination of the fibres of the funiculus gracilis, or column of Goll. The cephalic end of this nucleus is connected with the gray substance of the canal area. The NUCLEUS cuNEATUvS lies laterad of the preceding; FIG. 88. TRANSVERSE SECTION OF THE OBLONGATA THROUGH THE MOTOR DECUSSATION. (Goedinier, after Henle) . Fpy, Ventral pyramid; Cga, ventral horn; Fa, beginning of ventral column of spinal cord; Ng, nucleus gracilis; g, substantia gelatinosa; XI, spinal accessory nerve. at its origin it is connected with, and represents an offshoot of, the central gray substance. It is the nucleus of termina- tion of the fibres of the funiculus cuneatus. Cephalad to the motor, or pyramidal decussation, is a second crossing of fibres involving those of sensor function, 262 THE NERVE SYSTEM. tllC SICNSOK I)ECrSSATH)\, or DECUSSATION OF 1IIK FILLET, After crossing the midline the fibres form a bundle called the FILLET, or MEDIAL LEMNiSCUS. These ascending fibres arise in the nuclei gracilis cuneatus, and in crossing have also been termed the DEEP, or INTERNAL ARCUATE FIBRES. The INFERIOR OLIVARY NUCLEUS, or BODY, is an isolated mass of gray and white substances located in the ventro- lateral region of the oblongata. The gray substance is peripherally placed in the form of a thick wavy lamina that is wanting at the mesial side of the body; this space is the hilum. The central part of the body consists of myelinated nerve fibres that leave or enter through the hilum. In the immediate neighborhood of the olive are two smaller gray masses, the dorsal and mesial accessory olivary nuclei. The ARCUATE NUCLEUS is found along the ventral portion of the oblongata cephalad to the pyramidal decussation. It is a flattened mass of gray substance; here end some of the fibres of the superficial arcuate band, while other fibres of this band arise from the cells of this nucleus. The FORMATIO RETICULARIS lies in the lateral area of the oblongata and consists of a network of gray and white sub- stances. The gray is more abundant laterally and this portion thence receives the name formatio reticularis grisea. The cells are associative in function and serve to connect the various levels of the oblongata with one another. The formatio near the midline is almost devoid of nerve cells and is called the formatio reticularis alba. The fibers of the formatio have both a transverse course (deep ^arcuate fibres] and a longitudinal direction. The RESTIS, RESTIFORM BODY, or inferior CEREBELLAR PEDUNCLE, is found in the dorsal portion of the oblongata. It is composed of the direct cerebellar fibres of the spinal cord; fibres from the nuclei gracilis and cuneatus of the same side, the dorsal superficial arcuate fibres; fibres from the oppo- THE SPINAL CORD. 263 site nuclei gracilis and cuneatus, the -ventral superficial arcuate fibres; fibres from the opposite olivary body, the olivo-cere- bellar fibres. The last seem to form the bulk of the restis. The LATERAL TRACT consists of fibres of the lateral ground bundle of the spinal cord and fibres of the lateral columns, not including the direct cerebellar and crossed pyramidal tracts. The ground bundle fibres enter into the formation of the formatio reticularis, while the remaining fibres continue toward the cerebrum. The VENTRAL PYRAMID, or pYRAMis, consists of motor fibres from higher centers to the spinal cord. THE SPINAL CORD. This portion of the nerve system is the longest. It is characterized by possessing the gray substance internally and the white substance externally. Its form varies in the different regions; in the cervical and lumbar areas, it is enlarged, and these enlargements are termed the IN- TUMESCENITA CERVICALIS and LUMBALis, respectively. The outline in the cervical region is oval, in the thoracic region almost circular, and in the lumbar portion oval. The cord ends in the neighborhood of the upper border of the second lumbar vertebra, and its termination is cone- shaped. This is called the CONUS MEDULLARIS. Owing to the fact that the cord is shorter than the vertebral canal, the lower lumbar, the sacral and coccygeal nerves pass down for varying distances before reaching their respective fora- mina. This produces a mass of fibres in the lower part of the canal called the CAUDA EQUINA. In the center of the latter is a fibrous band that extends toward the end of the canal. It is the FILUM TERMINALE. The Cord consists of two hemispheres separated ventrally by the VENTRAL, or ANTERIOR MEDIAN FISSURE, in which is 264 THE NERVE SYSTEM. seen a process of the pia. Dorsally, no fissure exists, but a SEPTUM is present. This is the DORSAL, or POSTERIOR MEDIUM SEPTUM, Or RAPHE. The gray substance of the cord is arranged in the form of a letter H, the two side bars constituting the HORNS, and FIG. 89 A COMPOSITE DIAGRAM OF ALL LEVELS OF THE SPINAL CORD. i, Sulco-marginal tract; 2, direct pyramidal tract (Tiirck); 3, ventral ground bundle; 4, vestibulo-spinal tract (Loewenthal); 5, ventro-median group of cells; 6, central group of cells; 7, spino-olivary tract (Helweg); 8, ven- tro-lateral group of cells; 9, tract of Gowers; 10, lateral ground bundle; n, dorso-median group of cells; 12, mixed lateral tract; 13, spino-thal- amic tract; 14, rubro-spinal tract; 15, dorsal nucleus (Clarke); i6 3 crossed pyramidal tract; 17, cell group of dorsal horn; 18, direct cere- bellar tract; 19, dorsal (sensor) root; 20, tract of Spitzka (marginal); 21, dorsal ground bundle; 22, dorso-external column (Burdach); 23, cornu- commissural tract; 24, dorso-internal column (Goll); 25, comma tract of Schutze; 26, septomarginal tract (Bruce); 27, oval bundle of Flechsig. the cross-bar the GRAY, DORSAL, or POSTERIOR COMMISSURE. The HORNS are further subdivided into VENTRAL, or ANTERIOR, and DORSAL, or POSTERIOR. In the thoracic region a LATERAL HORN is described. THE SPINAL CORD. 265 The VENTRAL HORNS are large and blunt, and do not ex- tend to the periphery. In them are found collections of large, multipolar ganglion cells having a MOTOR function. The axis cylinders of the cells pass out of the ventral portion of the cord as the VENTRAL ROOT OF THE SPINAL NERVE. These cells average 60 to 120 microns, and are quite numerous. Each is surrounded by a distinct lymph space. They are collected into various groups which vary according to the region of the cord. The following are the most important: i. CERVICAL REGION: VENTRO-MEDIAN, DORSO- MEDIAN, VENTRO-LATERAL, INTERMEDIATE, DORSO-LATERAL. 2. THORACIC REGION: VENTRAL, INTERMEDIATE. 3. LUM- BAR REGION: VENTRO-MEDIAN, CENTRAL, VENTRO-LATERAL, DORSO-LATERAL (see Fig. 89). The DORSAL, or POSTERIOR HORNS are sharp and pointed, and usually extend to the edge of the cord. The cells here are small in number and size, averaging from 15 to 20 mi- crons, and are scattered along the external margin. They comprise 'marginal cells whose axis cylinders pass into the lateral columns after passing through the substantia gelatin- osa; spindle-shaped cells, the neurits of which pass into the dorsal columns; stellate cells, the axis cylinders of which pass into the dorsal columns of Burdach. The LATERAL HORNS are most marked in the thoracic and upper cervical and third and fourth sacral regions. Each is formed, chiefly, by the intermediate cell group. The axones of these cells probably do not pass into the ventral roots but terminate within the cord at various levels of the same and opposite sides. They are probably closely connected with the sympathetic system and vasomotor and sweat-gland nerves. Along the median edge of the horn, near its junction with the gray commissure, lies a group of cells that extends from the cervical to the mid-lumbar region. This is the VESICU- 266 THE NERVE SYSTEM. II 10 13 12 FIG. 90. CROSS-SECTION OF HUMAN SPINAL CORD AT LOWER CERVICAL REGION. From Decapitated Criminal (Dr. H. H. Gushing). i. Ventral spinal artery; 2. pial process in ventral fissure; 3. dura; 4. nerve fibres from ventral horn (motor root fibres); 5. stellate cells of ventral horn; 6. ventral horn; 7. dorsal horn; 8. nerve fibres of dorsal horn (sensor root fibres); 9. dorsal septum; 10. dorsal spinal artery and vein (arteria et vena fissurae posterioris) ; n. fibres of the column of Goll; 12. tissue separating the columns of Goll and Burdach; 13. column of Burdach; 14. traces of the lateral horn; 15. fibres of the lateral columns; 17. central canal in the gray commissure; 18. ventral, or white com- missure; 19. fibres of the ventral columns; 20. arteria et vena fissurae anterioris. THE SPINAL CORD. 267 LAK COLUMN OF CLARK. A similar collection, though less distinct, lies just ventral of Clark's column and extends through a greater part of the cord. This is the NUCLEUS OF STILLING and is represented in the oblongata by the accessory cuneate nucleus. The neurits of these cells of the DORSAL HORNS pass into the DORSAL COLUMNS; those of the VESICULAR COLUMN OF CLARK pass into the DIRECT CEREBELLAR TRACT, on the same side and into the VENTRAL (ANTERIOR) COMMISSURE. In the dorsal horn is the SUBSTANTIA GELATINOSA ROLANDI, which consists of cells of the second type (Golgi). The GRAY COMMISSURE consists of myelinated and amyelinated commissural fibres separated into VENTRAL (smaller) and DORSAL (larger) bands by the CENTRAL CANAL of the cord. The ventral portion is called the VENTRAL, or ANTERIOR GRAY COMMISSURE, while the other receives the name of DORSAL, or POSTERIOR GRAY COM- MISSURE. The whole is the GRAY, or DORSAL COMMISSURE, in contradistinction to the VENTRAL, or WHITE COMMISSURE. The CANAL of the cord is the remains of the embryonal cavity within this portion of the nerve system. In child- hood, it is lined by simple ciliated elements, the ENDYMAL CELLS. Above, it communicates with the fourth ventricle, and its form varies in the different portions of the cord. It becomes more or less obliterated with increasing age, par- tially by increased growth of the lining ENDYMAL cells and partially by the ingrowth of neuroglial processes. Besides the nerve cells, processes and fibres, the gray matter contains that peculiar supportive tissue found only in the nerve system, called NEUROGLIA. This substance is ectodermal in origin. NEUROGLIA consists of two varieties of cells, or astrocytes, SPIDER and MOSSY. The SPIDER cells are composed of thin, flat bodies from which extend long, slender processes. The 268 THi: NERVE SYSTEM. MOSSY cells have short, heavy processes. In addition to these, there are some cells that possess large bodies and few processes. Fibres that, apparently, have no connection with any cell are seen passing over or under cell bodies. These processes all interlace to form a network for the sup- port of the nerve cells and their processes. This substance is the SUBSTANTIA SPONGIOSA. Around the central canal of the cord, the subs tan tia spongiosa becomes more modified, and is called the SUBSTANTIA GELATINOSA CENTRALIS. The network is much closer in this region. Around the dorsal horns, it forms a homogeneous, striated mass, in which a few nerve cells are found. This is the SUBSTANTIA GELATINOSA ROLANDI, CAPUT GLIOSIUM, Or GLIOSA CORNUALIS. The WHITE SUBSTANCE consists of myelinated nerve fibers, connective tissue, and neuroglia. Spider cells are especially numerous here. The nerve fibres possess no neurilemma, and are grouped into columns. Ventrally, they are separated by the fissure, and dorsally, by the septum, into the hemispheres. Ventrally, they are connected by a band of white substance that lies between the bottom of the fissure and the gray commissure. This is the WHITE, or VENTRAL (ANTERIOR) commissure. The MOTOR fibres are usually large, measuring 15 to 20 microns in diameter. The SENSOR are smaller. The following columns are not found in any one section of the cord but represent all that are definitely bounded. Fig. 89 represents merely a diagramatic section locating all the columns. The VENTRO-MEDIUM columns that lie between the ventro-median fissure and the ventral roots of the spinal nerves; the LATERAL, that lie between the ventral and dorsal roots, and are subdivided into VENTRO-LATERAL, or those ventral to the transverse midline, and the DORSO- LATERAL, or those behind the same line. The DORSO- THE SPINAL CORD. 269 MEDIAN columns lie between the septum and the dorsal roots of the spinal nerves, subdivided into DORSO-INTER- NAL and DORSO-EXTERNAL. These areas are further subdivided into individual columns. In the VENTRO-MEDIAN region, there are several groups : i . the DIRECT PYRAMIDAL TRACT (TURCK) . This is a narrow band of fibres that lies along the fissure, and represents the nondecussating fibres from the motor regions of the brain. The bundle lies next to fissure in thoracic region and disappears in the lumbar part of the cord. A descending tract. 2 . The SULCO-M ARGINAL TRACT is f ound only in the cervical part of the cord and consists of fibres from opposite quadri- gemina and represents a descending tract. It lies next to the fissure. 3. The VENTRAL VESTIBULO-SPINAL TRACT (Loewen thai' s) lies at ventral surface of the cord in cervical and thoracic portions and consists of descending fibres. 4. VENTRAL GROUND BUNDLE. This consists of fibres that arise in the cord and end in the cord, extending up and down for short distances in order to connect the various segments of the cord. These fibres are associative in function. In the LATERAL region of the cord are the following tracts : 1. SUPERFICIAL VENTRO-LATERAL, or SPINO-CEREBELLAR (GOWERS) lies in the superficial ventral portion of the lateral area. The fibres probably arise from cells on both sides of cord in visceral and partly ventral regions and are ascending. 2. SPINO-OLIVARY, or HELWEG'S TRACT, lies just lateral to the ventral root and is found only in cervical and upper thoracic portions of the cord and represents ascending fibres. 3. DIRECT SPINO-CEREBELLAR TRACT lies in the superficial 270 TIIK NERVE SYSTKM. dorso-lateral area and consists of ascending fibres from the cells of the column of Clark. This tract is not found in the lower lumbar region of the cord. 4. CROSSED PYRAMIDAL TRACT, is in the dorso-lateral region of the cord and is composed of fibres that descend. In the cervical region it is internal to the direct cerebellar tract but in the thoracic area of the cord it comes partially to the surface, and in the lumbar region, where the direct cerebellar tract is absent, the crossed pyramidal tract lies entirely superficial. 5. LATERAL GROUND BUNDLE lies against the gray sub- stance and consists of associative fibres of both descending and ascending courses. 6. LATERAL MIXED TRACT occupies the remainder of the lateral columns and in it several tracts have been more or less completely outlined as follows (see Fig. 89) : a. RUBRO-SPINAL, descending. b. CEREBELLO-SPINAL, descending. c. Lateral VESTIBULO-SPINAL, descending. d. OLIVO-SPINAL, descending. These collectively are also termed the FASCICULUS INTERMEDIUS. In the DORSAL region are seen the following tracts : 1. FASCICULUS GRACILIS (COLUMN OF GOLL) lies adjacent to the dorso-median septum and consists of ascending fibres that arise in the cells of the spinal ganglia (the axonic processes). These fibres end in the nucleus gracilis. 2. FASCICULUS CUNEATUS (COLUMN OF BURDACH) lies peripheral to the preceding, and likewise consists of fibres (axones derived from the cells of the spinal ganglia that ascend). 3. The DORSAL GROUND BUNDLE lies next to the gray substance of the dorsal horn and consists of short fibres that ascend and descend; they are associative in function. THE SPINAL CORD. 271 4. The COMMA TRACT of SCHUTZE occupies a position in the tract of Burdach at the boundary line with the tract of Goll. Its fibres are descending. 5. The MARGINAL TRACT, Or TRACT OF SPITZKA, Or LISSAUER, is located along the dorsal root or among its fibres. It consists of some of the axones, of cells of the spinal ganglia, which traverse not more than three or four segments and end around the cells in the gliosa cornualis. It is sensor in function and is probably concerned with transmission of pain sense. All of the above tracts are found in all levels of the cord. 6. The DORSAL CORNUCOMMISSURAL TRACT is associative in function, consisting of both ascending and descending fibres. 7. The SEPTOMARGINAL TRACT (Bruce) consists also associative in function and lies along the postseptum. Its fibres ascend and descend. Both of these tracts are most distinct in the lumbar region of the cord. The gray substance of the cord can be subdivided functionally into the following categories: i. SOMATO- MOTOR; 2. VISCERO-MOTOR; 3. VISCERO-SENSOR; 4. SOMATO- SENSOR, as shown in Fig. 91. The course of the various components of the nerve-roots is likewise shown. The SPINAL NERVES Consist Of VENTRAL, MOTOR, Or EFFERENT, and DORSAL, SENSOR, Or AFFERENT ROOTS. Before these unite to form the nerve, a mass of gray substance is seen upon the dorsal root. This is the SPINAL GANGLION. The fibres of the DORSAL ROOT are derived from the cells that lie in the ganglia, and where they enter the cord, a distinct depression is noted. The fibres peripheral to the ganglion represent myelinated dendrites and those that enter the dorsal root of the spinal cord represent the myelinated axones. Upon examining Fig. 91 it will be that the dorsal root is not purely sensor, but also con- 272 THE NERVE SYSTEM. tains mscero -motor fibres. The VENTRAL ROOT is made up of fibres derived from the cells in the ventral horn, and where they emerge only a slight incurving of the surface is seen. The circulation of the nerve system is carried on chiefly by the vessels in the pia. In the CEREBRUM, the vessels of FIG. 91. A DIAGRAM OF THE COUPON KM ELEMENTS OF THE SPINAL CORD AND ITS NERVE-ROOTS IN A TRUNK-SEGMENT ILLUSTRATING THE FOUR FUNCTIONAL DIVISIONS OF THE NERVE SYSTEM. (After Johnston.} ss, Somatic sensor; vs, visceral sensor; VM, visceral motor; SM, somatic motor. The arrow heads indicate the directions of the impulses. Note that visceral motor impulse passes out through the dorsal root. the cortex enter vertically, and form a close plexus of capillaries most plentiful where the cells are. Those in- tended for the medulla are larger, and, passing through the cortex, form capillary networks between the fibres and parallel to them. In the CEREBELLUM, the capillaries are few in the outer THE SPINAL CORD. 273 portion of the molecular layer, but in the granule layer and around the cells of Purkinje, close meshes are formed. In the SPINAL CORD, there are two sets of vessels, those that enter at all points of the periphery and supply chiefly the white matter, and those derived from the artery lying in the ventro-median fissure; the latter set goes to the gray substance. The smaller peripheral vessels remain in the white substance, and run parallel to the fibres, while the larger penetrate the gray substance and supply the outer part. The artery in the fissure sends branches into the gray commissure; these divide right and left, and form dense plexuses in the gray substance. The blood is collected by venous radicals that have the same general course. The SUBARACHNOIDEAN LYMPH SPACE continues as the PERIVASCULAR LYMPHATICS that accompany the blood- vessels. 18 CHAPTER XVIII. THE EYEBALL AND LACRIMAL SYSTEM. The Eyeball is one of the most important organs of the special senses. It is composed of THREE COATS, and contains FOUR REFRACTIVE MEDIA. The COATS are the External, or Corneo-sclera; the Middle, or Choroid, Ciliary Body and Iris ; and the Internal, or Retina. The REFRACTIVE MEDIA are the CORNEA, the AQUEOUS and VITREOUS HUMORS and the LENS. Of these, the cornea and lens alone are of importance. The Corneo-sclera is the protective and transparent coat of the eyeball. The Sclera constitutes about five-sixths of this coat. It is composed of coarse bundles of white fibrous tissue that interlace to form a dense, tough coat. These bundles are arranged chiefly longitudinally and transversely. Between the bundles are spaces that contain large, stellate cells. These spaces communicate with the lymph spaces within the cornea. On its external surface, the sclera is in relation with the CAPSULE OF TENON, and, anteriorly, the CON- JUNCTIVA. To it are attached the ocular muscles. Between the sclera and choroid is a lymph space called the SUBSCLERAL SPACE. Here the tissue is loosely arranged and lined by endothelial cells. At the exit of the optic nerve, the sclera is pierced by the nerve fibres so as to form a sieve-like area, the LAMINA CRIBROSA. Pigmentation oc- curs here, as well as at the corneo-scleral junction. Its presence in the subscleral tissue gives rise to the LAMINA FUSCA. 274 THK CORNEA. 275 The Cornea is a specialized portion of the sclera modified for the transmission of light. It consists of FIVE LAYERS: ANTERIOR EPITHELIUM, ANTERIOR LIMITING MEMBRANE, SUBSTANTIA PROPRIA, POSTERIOR LIMITING MEMBRANE, and POSTERIOR ENDOTHELIUM. The ANTERIOR EPITHELIUM is a continuation of the epi- thelium of the conjunctiva. This is of the stratified squam- ous variety, and the tunica propria beneath is not papillated. The layers of cells are more numerous at the corneo-scleral junction than in the center. The basal cells are long and columnar, and possess processes that extend into the an- terior elastic lamina, while the external cells are squamous. The middle layers are prickle-cells, and the spaces between are lymph channels. The ANTERIOR ELASTIC LAMINA, or BOWMAN'S MEMBRANE, is a clear, prominent band serving as a basement membrane to the epithelial cells. Although called elastic, it does not consist of elastic tissue. It is thickest in the center, and becomes thinner as the junction is approached, where it disappears entirely. The SUBSTANTIA PROPRIA forms the bulk of the cornea, and consists of a number of layers (about sixty) of white fibrous tissue arranged parallel to one another. It is due to this arrangement that this organ is transparent. In addi- tion to these fibres, there are others that penetrate the organ at a right angle to the layers, and bind all together. These are the perforating fibres. Between the various layers are a large number of irregular spaces called the CORNEAL LA- CUNA. These contain large stellate cells that are the original connective-tissue cells of the organ. They are the CORNEAL CORPUSCLES. The spaces communicate with one another by means of little canals called CANALICULI, into which their processes extend. These spaces are readily shown by the gold chlorid method of staining. 276 THE EYEBALL AND LACRIMAL SYSTEM. The POSTERIOR LIMITING MEMBRANE, OF MEMBRANE OF DESCEMET, is analogous to the anterior membrane; unlike this one, however, it is thicker peripherally than centrally, and seems more independent of the substantia propria than the anterior. It does not respond to the elastica stain, and, consequently, is not made up of elastic tissue, as its name would seem to indicate. It becomes the pectinate ligament. The ENDOTHELIAL LAYER consists of a single layer of well- defined regular cells, which cover the posterior surface of this organ, and continues over the anterior surface of the iris. These cells are hexagonal, and possess a fibrillar protoplasm that seems to extend through several layers. The cornea possesses blood-vessels during the develop- mental period; these, however, disappear before birth, so that none are then present. Lymph, which circulates through the many spaces and canaliculi, nourishes the cornea. The sclera possesses but few vessels, and these are found chiefly at the corneo-scleral junction, where a circular net- work is formed. The nerves are SENSOR; at the corneo-scleral junction a circular plexus is formed, from which fibres pass into the substantia propria, while others penetrate the anterior elastic lamina to pass into the epithelial layer. Some of these fibres extend almost to the surface. The Middle Coat, or tunic, also called the Uveal Tract, is the vascular coat. It contains the main vessels of the eyeball, except the central artery of the retina, and consists of the Choroid, Ciliary Body and Iris. The Choroid is the vascular portion, and is divided into three layers, the STROMA LAYER, the CHORIO-CAPILLARIS, and the GLASSY MEMBRANE, from without, inward. The STROMA LAYER is sometimes referred to as the layer of large vessels, as they are found only in this portion. It THE CHOROID. 277 consists, externally, of delicate fibres that connect with those of the subscleral tissue and form a complete space, the SUPRACHOROIDAL, Or SUBSCLERAL LYMPH SPACE. In this tissue are found pigmented connective-tissue cells, and it has received the name of LAMINA SUPRACHOROIDEA. The main portion of the stroma layer consists of bundles that are closely arranged. The network formed by these are the FlG. 92. CORNEO-SCLERAL JUNCTION OF MAN. i. Epithelium; 2. connective tissue of conjunctiva; 3. sclera; 4, 5, 6, 7 and 8. ciliary body; 4. meridional; 5. radial; 6. circular fibres of ciliary muscle; 7. ciliary process; 8. pars ciliaris retinae; 9. pars iridica retinae; 10. stroma of iris; n. posterior elastic lamina of cornea; 12. substantia propria; 13. epithelium; 14. canal of Schlemm; 15. angle of iris, or infiltration angle (Stohr's Histology). -venous trunks, externally, and the arterial trunks, internally; the latter are accompanied by bundles of smooth muscle tissue. Pigmented cells exist between the bundles. The inner portion of this layer is called the BOUNDARY ZONE; the bundles are arranged into several layers in her- bivorous animals, so as to give a peculiar metallic reflex, and constitutes the TAPETUM FIBROSUM. This area is usually 278 THE EYEBALL AND LACRIMAL SYSTEM. free from pigment cells. In the carnivorous animals t la- fibres are replaced by distinct cells that contain crystals. The metallic reflex, however, is the same. This' forms the TAPETUM CELLULOSUM. The CHORIO-CAPILLARIS contains little stroma, and is composed chiefly of a dense capillary plexus. No pigment cells are seen. The capillaries are most numerous around the macula latea. The GLASSY MEMBRANE lies at the inner boundary of the choroid, and consists of refractile, homogeneous tissue. It is a very thick basement membrane, and supports the pig- mented cells of the retina. The choroid extends to the ORA SERRATA, a peculiar, serrated line, at which the neural portion of the retina ceases. At this point, the choroid continues as the Ciliary Body. The Ciliary Body is composed of three main portions, the Ciliary Ring, the Ciliary Processes and the Ciliary Muscle. It is thicker than the choroid, which is due especially to the addition of the muscle tissue. The Ciliary Ring is practically the continuation of the stroma layer of the choroid and the boundary membrane, and consists of dense white fibrous tissue, which forms a circular band about 4 mm. in breadth. The vessels have a longitudinal course. The Ciliary Processes are projections of the stroma, covered by pigmented epithelial cells, from 60 to 80 in number. They arise at the junction with the choroid, and extend toward the iris, increasing in height, ending abruptly at that point. At this place they are about i mm. in height. Each process consists of a core of stroma (connective tissue) supporting blood-vessels and covered by the pigmented epithelial cells of the retina, the PARS CILIARIS RETINA. These cells rest upon a continuation of the glassy mem- THE CILIARY MUSCLE. 279 brane. There are two layers, the outer, or basal of which consists of low columnar or cuboidal elements that are the continuation of the true pigmented cells of the retina. The inner layer is composed of cells that are columnar, possess little or no pigment, and are the representative of the optical portion of the retina. The Ciliary Muscle is of the nonstriated variety, and lies external to the ciliary ring, just beneath the sclera. The fibres are arranged in MERIDIONAL, RADIAL and CIRCULAR sets. The MERIDIONAL are the outermost, and extend from the canal of Schlemm, in the corneo-scleral junction, to the ciliary ring. These are the tensor muscles of the choroid. The RADIAL fibres, which compose the middle layer, extend peripherally, and, spreading fan-like, are inserted into the ciliary ring and processes. The CIRCULAR fibres are the inner ones, and their direction is equatorial. They consti- tute MUELLER'S RING-MUSCLE. The ciliary region is indicated, externally, by a band about one-fourth of an inch broad, starting at the corneo- scleral junction. It is called the danger zone of the eyeball, as injuries here usually result fatally to sight. The Iris is the continuation of the stroma layer and glassy membrane of the choroid. It receives also the posterior lamina and the endothelium of the cornea, and consists of the ANTERIOR ENDOTHELIUM, STROMA LAYER, POSTERIOR LAMINA and PIGMENT LAYERS. The ANTERIOR ENDOTHELIUM is a continuation of that of the cornea, and covers the anterior surface of the iris. The cells are neither so regular nor distinct as those of the cornea. The STROMA LAYER is composed chiefly of a coarse net- work of white fibrous tissue, some of which is circularly arranged around the blood-vessels, which possess no muscu- lar coat. Anteriorly, this stroma is very much reticulated 280 THE EYEBALL AND LACRIMAL SYSTEM. and forms a support for the endothelial cells. According to some authors, this portion constitutes an anterior limiting membrane. In the stroma layer, pigment cells are found in varying quantities; in gray eyes, very few are seen; as the color passes to blue, brown and black, the number increases, the last possessing the most. In albino eyes not only are the pigmented connective cells of the stroma layer absent, but the pigment that is usually present in the posterior epithelial cells continued from the retina is also absent. As a result of this, the retinal blood-vessels cause a peculiar red reflex, the retinal reflex. In the other eyes the pigment obscures it. In the stroma, is found muscle tissue of the involuntary nonstriated variety. This is arranged CIRCULARLY and RADIALLY. The CIRCULAR fibres are near the anterior part of the iris, and contract the pupil when stimulated; these form the SPHINCTER PUPILL^ muscle. The RADIAL fibres lie near the posterior part, and when they contract, the pupil is dilated; they constitute the DILATOR PUPILL^ muscle. The POSTERIOR LIMITING MEMBRANE, or MEMBRANE OF BRUCH, is a continuation of the glassy membrane. It sup- ports the pigmented cells, the PARS IRIDICA RETINA. The PIGMENTED LAYER, a continuation of the pars ciliaris retinae, and called the PARS IRIDICA RETINA, is usually pigmented, and consists of two layers of cells. It continues to the anterior margin of the pupil. The PUPIL is the aperture in the iris. Its size is regulated automatically by the amount of light entering. The Corneo-scleral junction is the region in which cornea, sclera, ciliary body and iris come together. The sclera passes over into the cornea, but the line of transition is not abrupt, but gradual, and forms an oblique line that extends from before, backward and inward. Beneath the posterior THE RETINA. . 281 margin, usually within the sclera, is a circidar canal, the CANAL OF SCHLEMM, which extends around the corneo- scleral junction. In this region, the membrane of Descemet is seen to divide into a large number of fibres that extend to the base of the iris. Between the fibres are found many intercommunicating spaces called the SPACES OF FONTANA. These spaces lie around the angle formed by the cornea and iris, called the INFILTRATION ANGLE, and communicate with the anterior chamber and the canal of Schlemm. The network is called the PECTINATE LIGAMENT, and is covered by endothelial cells. THE RETINA. The Retina forms the INTERNAL, or NEURAL COAT of the eyeball. It may be divided into two portions, the PARS OPTICA, that portion capable of vision, and the PARS CECA, or the blind part, possessing no nerve elements. The latter portion is further subdivided into PARS CILIARIS and PARS IRIDICA RETINA. The simplest division of the retina, however, is PARS OPTICA, PARS CILIARIS and PARS IRIDICA RETIN/E. The PARS OPTICA lines almost the entire optic cup, and extends forward to the end of the choroid. Here the neu- ral portion ceases, and the coat becomes abruptly thinner, and forms an irregular serrated line, the ORA SERRATA. From this point, the last two portions of the retina continue. The optical portion consists of eleven layers, counting the pigmented layer. These layers are classed as NEURO-EPI- THELIAL and CEREBRAL. The NEURO-EPITHELIAL portion consists of the first five layers within the pigment layer, and the CEREBRAL portion the remaining divisions. The pig- mented part is derived from the outer layer of the optic cup, and the other parts from the inner layer. 282 THE EYEBALL AND LACRIMAL SYSTEM. Optic Vesicle. Retinal Layer. Classes. 1. Outer Layer. PIGMENTED LAYER . . . PIGMENT LAYER. f LAYER OF RODS AND CONES. I EXTERNAL LIMITING MEMBRANE .... NEURO-EPITHELIAL LAYER. OUTER GRANULAR LAYER. HENLE'S FIBRE LAYER. 2. Inner Layer \ OUTER RETICULAR (MOLECULAR). OUTER GANGLIONIC (INNER GRANULE). INNER RETICULAR (MOLECULAR) CEREBRAL. INNER GANGLIONIC. NERVE FIBRES. INTERNAL LIMITING MEMBRANE. 1. The PIGMENT LAYER consists of polyhedral cells con- taining a black, granular, mobile pigment. The position occupied by this pigment depends upon the presence or absence of the light. The nonpigmented nuclei occupy the basal portion of the cells. These cells continue over the ciliary body and iris as the PARS CILI ARIS and IRIDICA RETINA. In the iris, both layers are pigmented, but not in the ciliary region. This layer is derived from the outer layer of the optic cup. The nerve structures are supported by NEUROGLIA, of which a great deal is present and unevenly distributed. 2. The LAYER OF RODS AND CONES is the most important portion of the retina. The CONES consist of CELL-BODY and CONE-FIBRE. The CELL-BODY is about 30 microns in length, and is divided into two segments, outer and inner. The outer is conical, may be striated, rests upon the limiting membrane, and is ap- parently composed of discs. The inner segment is striated and flask-shaped. At its junction with the outer segment, it is granular, and the other part is fibrillar. The cone-fibre THE RETINA. 28 3 ends in the outer reticular layer, and has a nucleus near its junction with the body. c H FIG. 93. SECTION OF HUMAN RETINA (after Pier sol). A, Part of pigment layer; B, layer of rods and cones; C, external limiting membrane; D, (outer) nuclear layer; E, outer reticular layer; F, outer ganglionic layer; G, inner reticular layer; H, inner ganglionic layer; 7, layer of nerve fibers; K, inner limiting membrane. Henle's fiber- layer is not represented. The RODS are longer than the cones, averaging about 50 microns. They have somewhat the same structure as the preceding and are almost uniform in size. The different 284 THE EYEBALL AND LACRIMAL SYSTEM. segments react differently to stains. The outer segment possesses prominent cross and faint longitudinal striations. In this portion of the cell, the RHODOPSIN, or VISUAL PURPLE, is located. The inner segment is spindle-shaped, granular, and fibrillar like the above. The rod fibres terminate in the outer reticular layer, where they are en- larged. The nuclei lie in the outer granular layer. They may be irregularly placed, and in lower animals may even be striated. Usually three or four rods are seen to each cone. In the central portion of the yellow spot the cones alone are present. 3. The EXTERNAL LIMITING MEMBRANE Consists of the outer ends of the fibres of Miiller. These run radially, and extend through almost the entire thickness of the retina. The outer ends of these fibres are enlarged, and lie so close together that they form a membrane, the OUTER LIMITING MEMBRANE. These fibres do not penetrate the rod and cone layer, but give branches to all of the other layers. Each fibre possesses a nucleus that lies in the inner nuclear layer. At their internal ends, they are again enlarged, and form the INTERNAL LIMITING MEMBRANE. Glia cells are also present. 4. The GRANULE, or NUCLEAR LAYER consists of several layers of oval nuclei, which are the granules. These are the nuclei of the rod and cone-fibres. The former are the more numerous. 5. HENLE'S FIBRE LAYER is best developed in the macular region, from which area it diminishes peripherally. It is made up of the inner segments of the red and cone-fibres. 6. The OUTER MOLECULAR, Or RETICULAR LAYER is COm- posed of the inner ends of the rod and cone cells, which are branched, and fibrillar, and proceed from the inner nuclear layer. THE RETINA. 285 7. The OUTER GANGLIONIC, Of INNER GRANULAR LAYER is made up of several varieties of closely packed cells, the most numerous of which are OVAL, BIPOLAR ELEMENTS. These are placed vertically, and the small amount of proto- plasm present continues as an inner process that passes to the inner molecular layer; here it breaks into many branches that form a network around the ganglion cells. The outer processes of these oval cells surround the ends of the rod- fibres in the form of a delicate rete, or mesh of fibrillae. -f t FIG. 94. CELLS FROM RETINA OF AN APE (Stohr's Histology}. i. Cell of ganglionic of layer. 2. Cells of inner granule layer. 3. Rod- cells: a. outer egment; b. inner segment; k. rod-granule; x. fibre appara- tus. Below are rod-cells and fragments. 4. Cone-visual cells: a. outer segment; i. inner segment; k. cone-granule;/, cone-fibre; x. fibre appa- ratus; 5. Radial fibre, Muller's fibre: k. nucleus; r. pyramidal base. Other cell-processes pass to the cone-fibres and to the inner molecular layer. Another kind of cell is present, the AMAKRINE CELL, which forms a layer near the inner boundary of this nuclear layer. These cells possess no axis cylinders, but other processes extend into the inner molecular layer. A third variety possesses a cell-body, the long diameter of which lies parallel to the surface of the retina. The proc- esses pass into the outer molecular layer. Some connect with the rod-fibres; these are larger and lie internally, 286 THE EYEBALL AND LACRIMAL SYSTEM. while the others that pass to the cone-fibres are smaller and have an external position. In addition to the above, there are some cells present in this layer that send their axis cylinders into the optic nerve. The nuclei of Miiller's fibres lie in this layer. 8. The INNER RETICULAR, or MOLECULAR 'LAYER consists of fibrils of cells of the preceding layer and from cells of the inner ganglionic layers. The fibres lie at different levels, which gives them a striated appearance. 9. The GANGLIONIC (INNER) LAYER is composed of a single layer of multipolar ganglion cells. The cell-bodies are flask-shaped, and the axis cylinders pass into the layers of nerve fibres. The dendritic processes extend into the inner molecular layer at different levels, and, supposedly, do not communicate with those of other cells. In the region of the macula lutea, these cells become increased in number, forming, often, eight layers. 10. The LAYER OF NERVE FIBRES is the expanded optic nerve. These fibres pierce all the layers, except the internal limiting membrane. They arise, mainly, from the cells of the inner ganglionic layer, converge at the blind spot, pass through the cribriform lamina of the sclera and become myelinated. As most of the fibres pass from the ganglion cells toward the brain, it would be better to say that they converge at the optic nerve exit, where the LAYER OF NERVE FIBRES is thickest, and decreases as the ora serrata is approached. 11. The INTERNAL LIMITING MEMBRANE is formed by the fusion of the inner ends of Miiller's fibres. There are three important areas in the retina: i. the OPTIC NERVE EXIT, OPTIC PAPILLA, or BLIND SPOT; 2, the MACULA LUTEA, or YELLOW SPOT, and 3, the ORA SERRATA. i. In the BLIND SPOT, only the layer of nerve fibres is pres- THE OPTIC NERVE. 287 ent. It lies about one-eighth of an inch to the nasal side, and about one-tenth of an inch below the optic axis. In the center is usually a shallow depression; around the edge it is raised and forms the PAPILLA NERVI OPTIONS. 2. The YELLOW SPOT is not in the direct visual axis. The color is due to the presence of a diffuse yellow pigment. Its edge is raised, owing to the great thickness of the inner ganglionic layer. From the edge to the center, all the layers decrease and disappear, so that in the center, the FOVEA CENTRALIS, the cones alone are present. Here vision is most acute. 3. At the ORA SERRATA all of the neural layers end ab- ruptly, and are continued as a single layer of cuboidal or columnar cells. Beyond this point, there is no vision. The light rays falling upon the retina are not transmitted to the brain by a direct route. The impressions are re- ceived by the rods and cones, which send impulses to the outer reticular layer; here the impulses are received by the processes of the outer ganglionic layer, conveyed through the bodies of the cells of that layer to the inner reticular layer; here they are relayed to the processes of the cells of the inner ganglionic layer and to its cells and thence to the nerve fibre layer; the latter makes up the optic nerve by means of which the impulses are then conveyed to various parts of the brain. The Optic Nerve consists of a single bundle of nerve fibres that possess no neurilemmae. It is said to contain from 450,000 to 800,000 nerve fibers. It is surrounded by the dura, arachnoid, and pia, continued from the brain. The lymph spaces included within these, communicate with those of the eyeball. The dura and pia pass over into the sclera, but the arachnoid, as such, is lost before this occurs; as a result, the two lymph spaces between these three layers become one. The nerve fibres penetrate the sclera through 288 THE EYKBALL AM) LACRIMAL SYSTEM. the LAMINA CRIBROSA. As they pass through this coat, they lose the myelin sheath, so that they become amyel- inated fibres when they connect with the retina. VITREOUS BODY AND LENS. Of the REFRACTIVE MEDIA of the eyeball, the Vitreous and Aqueous Humors and the Lens are yet to be described. The Vitreous Humor, or Body, occupies the optic cup, or VITREOUS CHAMBER. This body consists of a fine limiting membrane, the HYALOID MEMBRANE, a delicate homogeneous structure enclosing the substance of the organ, which is composed of about 98 per cent, water and 2 per cent, solid elements. The latter comprise connective tissue and wandering cells, and some fibrils. This organ is traversed by a small canal, called the CANAL OF STILLING, or HYALOID CANAL. This extends from the optic nerve to the lens, and in intrauterine life is occupied by a branch of the retinal artery, the HYALOID ARTERY, that passes to the lens. The Aqueous Humor is practically lymph. It occupies the anterior and posterior chambers, and as a refractive medium is unimportant. The Crystalline Lens is a solid body, and the most im- portant refractive medium of the eyeball. It possesses two curvatures, of which the posterior is the greater. It lies in a depression of the vitreous humor, called the PATELLAR FOSSA, and is held in position by the SUSPENSORY LIGAMENT. The LENS consists of a capsule, within which lies the lens substance. The capsule is composed of delicate white fibrous tissue, and to it are attached the ligaments. This is thicker anteriorly, and seems composed of layers. The SUBSTANCE OF THE LENS is of epithelial origin, and THE CHAMBERS OF THE EYEBALL. 289 consists of LENS FIBRES that are greatly elongated cells. Upon the anterior surface, just beneath the capsule, is a single layer of cuboidal cells called the LENS EPITHELIUM. At the equator of the lens, these cells lengthen, forming the LENS FIBRES, which are hexagonal, nucleated structures. The nuclei are large and oval, and lie near the middle of the fibres. Peripherally, the fibres are harder than those of the center. No cells are found posteriorly. The Suspensory Ligament of the lens is really a continua- tion of the hyaloid membrane, reinforced by a large number of fibres that pass from the anterior and posterior layers of the capsule. Those from the anterior layer pass into depressions between the ciliary processes, while those from the posterior layer are attached to the summits of the processes. Between these two layers of fibres is a small space, the CANAL OF PETIT. This region constitutes the ZONE OF ZINN. The Chambers of the eyeball are Anterior, Posterior and Vitreous. The Anterior lies between the iris and cornea, the Posterior between the lens and vitreous humor, and the Vitreous is occupied by the vitreous body. These are large lymph spaces, and are connected with one another, and with the other spaces of the eyeball. The circulation of the eyeball is carried on by the CENTRAL ARTERY OF THE RETINA, the LONG and SHORT POSTERIOR and the ANTERIOR CILIARY ARTERIES. The RETINAL ARTERY passes into the eyeball through the center of the optic nerve, and forms a whorl of branches upon its entrance. These vessels extend to the ora serrata. The layer of rods and cones and the macula lutea possess no blood-vessels. The blood is collected by venous stems, which form the central vein of the retina that has a course parallel to the artery. The SHORT POSTERIOR CILIARY arteries are about twenty 19 2 90 THE EYEBALL AND LACRIMAL SYSTEM. Cornea ,S r Ora Ciliary Serrata. Processes. a Anterior ciliary artery. d Anterior ciliary vein. /? connection with circulus iridicus major. 7 Connection with chorio-capillaris. d Arterial episcleral branches. 5' Venous episcleral branches. e Arterial conjunctival branches. ~- tq <^ ^i x x j -6 -^- fts ^ J/T ^^ /* 1--' I ' 1 55 01 1 u 1 li S ' /-^ i >> c g t- & . . -i X5 ^P o a G ^4 D *r u ^ ;*^- U "! e- A * A -^ f, -^" O g "^ C/5 -M - -^---^ H "P -ft'C . I oj i rt'aj/f I |8s -, -^ ^" - s a-j O gj c/3 7^ 6 6 I? s -|| "S -^ U 'H'o 'S-^2 T ^0 = tfl ^ U 3 . ^, J ^c eti 3 ., rr - c '5, SW. w Y * S fe ^ CJ C - ^ ffi.S "^ <* ^3 C "** rt ~ RsS s^|^ 2 J2 fl ^ 3u E . d u ^-<^ THE ORGAN OF CORTI. 309 are longer and narrower than the INNER, and more numer- ous. Usually one hair cell is present for each two pillar cells. The outer hair cells are found in three or four rows, which are separated by the ends or phalanges of Deiter's cells and the membrana reticularis. The inner row rests upon the outer pillar cells; the cells of the next row lie opposite to the rods, and the third row alternates, produc- ing a peculiar checker-board appearance, the ends of the hair cells being separated from one another by the ends of the Deiter cells. The SUSTENTACULAR, or DEITER CELLS are INTERNAL and EXTERNAL. Each cell consists of a thin PYRAMIDAL PROC- ESS and a large BASAL part that contains the nucleus. The INTERCELLULAR SPACES OF NUEL, between the cells of the organ of Corti, contain a substance like that in the tunnel of Corti. Internally, DEITER'S cells pass through the entire layer, and are continuous with the cells of the sulcus. Externally, they form the phalanges that help produce the membrana reticularis. A surface view will show both sustentacular and neuro-epithelium; a basal view, however, will show only sustentacular elements. Just external to the Deiter cells are other sustentacular elements, the CELLS OF HENSEN. These extend to and continue with those of Claudius. Extending over the organ of Corti and arising from the upper lip of the limbus is a membrane composed of delicate fibres and interfibrillar substance. This is the MEMBRANA TECTORIA, or CORTI'S MEMBRANE. At one time this was part of the cells beneath, those of the sulcus and auditory teeth; it represents a cuticular border. The divisions of the auditory nerve are vestibular and cochlear. The vestibular arises from the sacculus, utriculus, macula and the semicircular canals (crisis). The cochlear portion arises in the cochlea, and is made up as follows: 310 THE EAR. In a little bony canal in the lamina spirale is a strip of gray substance that is called the GANGLION SPIRALE. This consists of bipolar cells, one branch, the dendrite of which passes outward into the organ of Corti, while the other, the axis cylinder, passes through a minute canal in the axis to the central canal, where it meets other fibres from different levels. These pass to the base and to the internal auditory meatus, as the COCHLEAR BRANCH, and then to the oblongata. The dendritic branches of these ganglion cells form a plexus in the minute canal of the spiral shelf. Toward the organ of Corti the lamina is pierced by many canals called the FORAMINA NERVOSA through which numerous fibres, the myelinated dendritic branches, pass, along its inner epithe- lium, to the organ of Corti. Upon entering these canals, the myelin sheaths and neurilemmae are lost, and the naked dendrites, in bundles, continue. Each bundle separates into two, one of which remains at the inner sur- face and the other passes along the outer side of the pillar cells. The latter lies in the tunnel. Other dendrites cross the tunnel and pass to the outer side of the outer pillar cells and form several bundles between the Deiter cells. From these various bundles, fibrillse connect with the hair cells. The blood-vessels follow the nerves, those of the utriculus and sacculus follow the vestibular branch and those of the cochlea the cochlear division. After giving off branches to the first turn, the main trunk enters the canal of the axis, from which the branches form the peculiar GLOMERULI COCHLEA. Branches of the latter penetrate the scala vestibuli, and supply, the limbus and neighboring tissues. Other branches continue over the vestibule to the ligamen- tum spirale, the stria vasculare, and basillar membrane sur- rounding the scala vestibuli. The veins surround the scala tympani and form a trunk below the spiral ganglion. CHAPTER XX. THE SENSES OF SMELL, TASTE, AND TOUCH. THE ORGAN OF SMELL. The Nasal Mucosa is divided into RESPIRATORY and OL- FACTORY portions. The lower portion of the RESPIRATORY area, called the VESTIBULE, is lined by stratified squamous cells to the inferior turbinate bone. Here a great many hairs, sebaceous and mucous glands that extend for a short distance, are encountered. Above the turbinate, the epithe- lium is of the stratified ciliated variety, and many goblet cells are present. The tunica propria contains much lym- phoid tissue and a large venous plexus. Mucous and serous glands are also present in great numbers in the region of the inferior turbinate and nasal septum. The mucosa is 4 mm, thick in this area. The OLFACTORY MUCOSA is usually prominent on account of its yellow color, but this does not indicate the entire olfactory membrane. It is very thick, and ciliated cells no longer exist. The epithelium is of three varieties, the SUSTENTACULAR, NEURO-EPITHELIAL ELEMENTS and BASAL cells. The SUSTENTACULAR cells are irregular, and possess an OUTER SEGMENT, peripheral, which is cylindrical, and an INNER, basal, that is narrow and irregular. The OUTER SEGMENTS form a row of columnar elements. The oval nuclei form a regular band or row\ The protoplasm con- tains granules and pigment near the inner end, the former 3 I2 THE SENSE OF SMI,!. I.. being arranged in rows. A cuticular border is present, and forms the MEMBRANA LIMITANS OLFACTORIA. The inner segments are irregular, and usually branch at their internal ends. The NEURO-EPITHELIAL ELEMENTS consist of peculiar, inconspicuous strips of protoplasm possessing an enlarge- ment near the middle, in which lies a large, round nucleus. The latter form a band or zone of spherical elements. The outer ends of the rods extend to the free surface, between the supportive cells, while the inner ends pass to the base- ment membrane. FIG. ioo. DIAGRAM OF OLFACTORY MUCOSA. a. Sustentacular cells; b. neuro-epithelial elements; c. basal cells; d. basement membrane. The BASAL cells are small and irregular elements that send processes between the upper layers and, internally, rest upon the basement membrane. The tunica propria consists of a loose network of fibro- elastic tissue. This supports the mucous (BOWMAN'S) glands, whose functionating epithelium possesses a brown- ish pigment. These glands are numerous, forming a con- tinuous layer. The Accessory Cavities possess a lining of ciliated cells. The mucosa is very thin, .02 mm., and it is firmly attached to the periosteum. Glands are very few in the mucosa of these cavities. THE ACCESSORY CAVITIES. The blood-vessels are numerous. The arterial branches form a dense subepithelial plexus, including a network around the glands. The veins are large in number and size, especially upon the inferior turbinate. The lymphatics lie in the lower part of the tunica propria; in the olfactory area, an extra set of vessels occurs in the superficial portion. These communicate with the channels around the nerves. FIG. 1 01. ISOLATED ELEMENTS OF THE OLFACTORY MUCOSA. a. Neuro-epithelial cell; b. sustentacular cells showing cuticular border. The nerves are those of ordinary and special sensation. The former are derived from the trigeminus and do not connect with the cells. The latter form the olfactory nerves. The fibres of the olfactory nerves arise from the neuro-epithelial elements in the form of delicate fibrillae; the latter join together, beneath the epithelial layer, to form small bundles that are surrounded by perineural lymphatic sheaths; from this position in the tunica propria they pass through the openings in the cribriform plate of the ethmoid bone and terminate around the glomerular cells of the olfactory lobe. These fibres possess neither myelin sheaths nor neurilemmae. 314 THE SENSE OF TASTE. THE SENSE OF TASTE. The Sense of Taste is due to the Taste-buds. These arc- not restricted to the circumvallate papilla of the tongue, but are found in the papilla foliata, in the ventral surface of the epiglottis, at times in the fungiform papilla and in the soft palate and uvula. The organs are barrel-shaped, and consist of two varieties of cells, the SUSTENTACULAR and the NEURO-EPITHELIAL. The SUSTENTACULAR CELLS are the OUTER, and are com- posed of a cell-body and a pointed end. The latter, with its c - b FIG. 102. TASTE-BUD FROM A PAPILLA FOLIATA OF A RABBIT. i. Epithelium; 2. tunica propria; a. taste-bud; b. gustatory hairs; c. gustatory pore. neighbors, forms an opening at the exposed end of the organ called the GUSTATORY PORE. The cell-body varies in its thickness and the enlargement may be central or proximal. In this enlargement is seen the large nucleus. The NEURO-EPITHELIAL elements are peculiar, long, spindle-shaped cells possessing a nuclear enlargement. This is more pronounced than that of the preceding. The peripheral end of each cell is continued as a hair-like pro- jection through the gustatory pore; this projection is the GUSTATORY HAIR. The nerve fibres of the nerves of taste arise between or upon the neuro-epithelial elements and represent the dendrites of cells in the ganglia of the glossopharyngeal THE SENSE OF TOUCH. 315 nerve and the geniculate ganglion that lies in relation with the facial nerve. These dendrites pass into the subepi- thelial tissue and unite to form bundles of fibres that become myelinated and join the glossopharyngeal and chorda tympani nerves. Other sensor beginnings lie in the epithelium around the taste-buds. THE SENSE OF TOUCH. The Sense of Touch is not limited to any special region, but it is best developed in certain areas, as the PALM and SOLE. It is restricted to the skin, and represents a modifi- FIG. 103. CORPUSCLE OF MEISSNER FROM GREAT TOE OF MAN. n. Myelinated nerve fibre; h. connective-tissue sheath; e. varicosities. The nuclei are invisible (Stohr's Histology}. cation of general sensibility. In the papillae of the skin, especially that of the sole and palm, are found the TACTILE CORPUSCLES OF MEISSNER. These are elongated structures, about 50 by 150 microns, and possess transverse striations that seem due to cells with transversely placed nuclei. These are encapsulated by white fibrous tissue, and are pierced at the lower end by nerve fibres whose myelin sheaths blend with the capsule. The dendrites arise from telodendria between the cells 3 i6 THE SENS!-: OF TOITH. and possess enlargements at intervals. They pass to the bottom of the organ, and as they leave they become myelin- ated and covered by a neurilemma. These myelinated den- drites pass to the ganglia of the spinal and cranial nerves. The corpuscles of Vater, or Pacinian bodies, are very large, oval structures. Each consists of a CAPSULE, an INNER BULB and a KNOB. The CAPSULE consists of many layers of white fibrous tis- sue, each separated from its neighbor by a lymph space FIG. 104. PACINIAN BODY FROM MESENTERY OF A CAT. i. Fat cells; 2. artery; 3. nerve fibre; 4. inner bulb; 5. dendrite; 6. layers of the capsule (Stohr's Histology). lined by endothelial cells. These lamellae are held to- gether by an INTRA-CAPSULAR LIGAMENT that pierces all. The INNER BULB is a cylindric mass of almost homogeneous protoplasm possessing nuclei and a slight enlargement called the KNOB. The knob represents the point of origin of the dendrite that leaves this organ as a nerve fibre as in the preceding organ. THE SENSE OF TOUCH. 317 The CONJUNCTIVAL CORPUSCLES, Or CORPUSCLE OF KRAUSE, are also tactile corpuscles. These are surrounded by a delicate fibrous CAPSULE, which is surrounded and lined by endothelium. The center of the corpuscle seems occupied by the divisions of the dendrite that arises here, and by lymph. Such corpuscles are found in the con- junctiva, edges of the eyelids, in the lips and epiglottis. The GENITAL CORPUSCLES are more complex than the preceding. They may resemble the Pacinian body, or may be composed of several simple corpuscles fused into one. They are found in the glans penis and glans clitoris. CHAPTER XXI. DEVELOPMENT OF FACE AND TEETH. The development of the face is a complicated process, a number of different fetal structures taking part therein. At about the twelfth day of intrauterine life there appears a depression upon the ventral surface of the blunt head- process called the ORAL DEPRESSION, or STOMODEUM. The floor of this depression sinks deeper, forming the pharyngeal membrane, and the margins become more pronounced. At about the fifteenth day the lower boun- dary of the depression becomes formed upon each side into a finger-like process, called the FIRST VISCERAL ARCH, that soon divides into a shorter upper portion, the MAXILLARY DIVISION, and a lower part, the MANDIBULAR DIVISION. The upper division forms now the lateral boundary and the lower the inferior boundary of the oral depression. At about the same time the tissues in the frontal region become pro- jected in the form of a blunt mass between the maxillary divisions of the first arch, constituting the NASO-FRONTAL PROCESS. Thus the stomodeum has become a pentagonal fossa. At about the eighteenth day a second finger-like process makes its appearance beneath the mandibular por- tion of the first arch; this is followed by a third arch about the twenty-first day, a fourth by about the twenty-fourth day, and the fifth and last arch is formed by the twenty- eighth day. The last are less highly developed than the first, and while the lower ones are forming the upper ones are undergoing metamorphosis into their adult structures. The changes that occur in the VISCERAL ARCHES will be 318 VISCERAL ARCHES. 319 considered first: Each arch consists of a core of mesoderm containing a rod of cartilage and a blood-vessel called the visceral arch vessel; externally the arch is covered by ectoderm and internally by entoderm. The arches are separated from each other by a groove or depression, inter- nally, and externally, and spanning the groove is the vis- ceral cleft membrane consisting merely of ectoderm and entoderm, so that no real complete cleft exists in the early stages of development; in aquatic animals these membranes do rupture to form the gill-clefts. On each side there are four external and four internal visceral grooves or, better, branchial pouches. The first arch, as previously mentioned, divides into two portions, maxillary and mandibular; the maxillary part unites with naso-frontal process to complete the upper jaw; it itself gives rise to the bulk of the upper jaw and most of the palate. The upper jaw is completed by about the fortieth to the forty-seventh day. The mandibular process unites with its fellow of the opposite side to form the complete lower jaw, union being completed by the end of the fifth week, or thirty-fifth day. In addition, the cartilage of the mandibular process gives rise to incus and malleus, and stylomandibular ligament. The rod of cartilage of the second arch gives rise to the stapes, styloid process, stylohyoid ligament and lesser cornu of the hyoid bone. The cartilage of the third arch forms the body and greater cornu of the hyoid bone. The cartilages of the fourth and fifth arches unite and form a single mass, the thyroid cartilage of the larynx. The first external branchial pouch persists only at its dorsal end to form here the external auditory canal. From both first and second arches in this region the ear is developed. The remaining pouches are lost as the arches 320 DKVKLOPMKNT OF I'AC'K AND TEETH. overlap each other from above downward. Occasionally part of a pouch persists as an enclosed cyst of ectoderm and this is called a branchial cyst. In case a pouch mem- brane ruptures and permits of a passage-way from the out- side to the gut-tract it is called a cervical fistula. The first internal pouch is formed into a tube with its outer end dilated into an irregular cavity, the tympanic cavity; the tube-like portion connecting this with the pharynx is called the Eustachian tube. That part of the first pouch membrane separating the external auditory canal from the tympanic cavity is the future tympanic membrane, or ear drum. In the middle of the ventral portion of the first pouch is found a projection, the tuber- culum impar, which later becomes the anterior, or apical two-thirds of the tongue. From the region of the second pouch (representing second and third arches) we find the tonsil and lateral recess of the pharynx developed, dorsally, while ventrally in the median line the middle lobe of the thyroid body is formed, and just lateral of this the dorsal, or basal one- third of the tongue by two masses (one on each side). In the third pouch region (third and fourth arches) the thymus body, as two lobes, appears and also the inferior parathyroids and the carotid bodies. From the fourth pouch (fourth and fifth arches) the lateral lobes of the thyroid body with the superior para- thyroids. The NASO-FRONTAL PROCESS is at first a blunt mass of tissue projecting from che frontal region. As it grows down between the maxillary divisions of the first visceral arch, it becomes thickened along its margins, forming here the globular processes; each process contains a little depres- sion that constitutes the nasal pit. In addition, two masses, the lateral nasal processes, develop from the NASO-FRONTAL PROCESS. 3 2I naso-frontal process, at the orbital region, to form the lateral boundary of the nasal pits. Usually by the fortieth or forty -second day the naso-frontal process has filled the gap between the two maxillary processes of the first arch, and union of these parts is completed. As a result the nasal pits are separated from the mouth cavity. The derivatives of the naso-frontal process are the middle of the FIG. 105. FACE OF AN EMBRYO OF 8 MM. (McMurrich, after His), pg, Globular process of naso-frontal process; np, nasal pit bounded exter- nally by the lateral nasal process; os, oral pit; mxp, maxillary process of first visceral arch. upper jaw (intermaxillary bones) the middle of the upper lip, the tip, septum, alae and briuge of the nose and the vomer. The crevice between lateral nasal processes and the maxillary division of the first arch extends from the orbit to the nose cavity. When this crevice is closed a cord of epithelium is inclosed, and by hollowing out this cord of cells forms the naso-lacrimal duct. If the lip por- 322 DEVELOPMENT OF FACE AND TEETH. tions of the naso-frontal process and first arch fail to unite, a malformation, unilateral , or bilateral hare-lip, is produced. If the bony parts within are affected, various forms of cleft- palate result. The palate is developed in the form of three shelves, two lateral from the maxillary processes of the first arch and one frontal, triangular, from the naso-frontal process. At about the eighth week union between the lateral shelves at the front end and the naso-frontal portions be- gin; by the ninth week union as far as the posterior border of the future hard palate is completed, by the eleventh week the soft palate is finished and by the end of the third month the uvula is complete. Various malformations may occur here, as partial, or complete cleft-palate and bifid uvula. Then after the upper jaw is completed two ridges appear upon each jaw, the inner represents the gum and the outer the lip. The Teeth. The teeth are developed partially (enamel) from the ectoderm and partially (dentin, cementum, pulp, and peridental membrane) from the mesoderm. There are two sets of teeth in the mammals, TEMPORARY, or DECIDUOUS, or MILK TEETH, and PERMANENT, or suc- CEDANEOUS TEETH. Such animals are diphyodonts. Ani- mals that may develop teeth successively without regard to number are polyphyodonts. In the former case the teeth are unlike, and the animals are heterodonts, while in the latter case the teeth are all alike and the class is that of homodonts. The teeth begin to develop during the sixth -week (shortly after the completion of the lower jaw). From the under surface of the thickened epithelium of the jaw a band of epithelial cells grows into the mesodermal core of the jaw. This is the DENTAL SHELF, the earliest indica- tion of the developing teeth. Shortly after the formation THE TEETH. 3 2 3 Ill^fpP^* FIG. 1 06 FOUR STAGES OF TOOTH DEVELOPMENT (After Bohm, Davidoff and Huber). A, Formation of the enamel from the dental shelf; B, later stage with early formation of the dental papilla; C, later stage showing enamel sac with its layers differentiating and the dental paiplla well advanced; D, enamel sac completed (just preceding enamel formation) connected to dental shelf; dental papilla completed, i, i, i, i, oral epithelium; 2, 2, 2, 2, basal layer of same; 3,3,3, 3, mesoderm of jaw; 4, 4, 4, 4, outer layer of enamel organ; 5, 5, 5, 5, middle layer; 6, 6, 6, inner layer; 7, 7, 7, dental papilla; 8, layei of odontoblasts; 9, dental shelf; 10, follicular sheath. 324 DEVELOPMENT OF FACE AND TEETH. of this shelf the epithelium at the area of thickening sinks in forming the dental groove. The dental shelf extends from one end of the jaw to the other and leans toward the median plane of the head, and from the outer free or labial surface ten little germs or buds develop, called the ENAMEL GERMS. There are ten in each jaw, and they represent enamel organs of the temporary teeth. These buds appear successively: those for the central incisors first, then lateral incisors, first molars, canine, and second molars. The earliest buds appear during the seventh or eighth week. The enamel bud is at first flask-shaped, and its connection with dental shelf becomes smaller. Gradu- ally the surface opposite to the dental shelf connection be- comes invaginated by condensing mesoderm; the con- cavity deepens and a sac is thus formed, while at the same time the dental shelf connection becomes more attenuated. The sac consists of three layers, inner, middle, and outer. The mass of condensed mesoderm that has caused the sac formation of the enamel, but which lies now in the enamel sac, constitutes the dental papilla. During about the tenth week mesoderm in the immediate neighborhood of the enamel sac condenses to form a sheath for the whole structure, and this is called the dental follicle. Meanwhile the dental shelf becomes attenuated and tends to disappear. The succeeding changes will be described under Enamel Formation, Dentin Formation and Cementum Formation. Enamel Formation. The enamel organ now consists of three layers: the OUTER LAYER is composed of simple columnar epithelial cells continuous with the inner layer of cells at the base of the organ. They play no part in the formation of enamel. The MIDDLE LAYER consists of a mass of stellate cells varying in thickness as Fig. 107 shows; these cells make up the bulk of the enamel organ and the meshwork formed by them is filled with a fluid. This ENAMEL FORMATION. 3 2 5 layer likewise has nothing to do with the direct formation of enamel, but seems to have a nutrient function. Along the innermost portion of this reticular mass is a group of FIG. 107. SECTION OF A DEVELOPING TOOTH OF A CAT EMBRYO. (After Pier sol.} A, Outer, B, middle, C, inner layers of enamel organ; D, formed enamel; E, formed dentin; F, layer of odontoblasts; G y follicular sheath; H, dental papilla, mesoderm cells forming a layer called the STRATUM INTERMEDIUM. This layer consists chiefly of spherical cells mixed with some columnar elements. Apparently the spherical cells have elongated to the columnar type, probably for the 326 DEVELOPMENT OF FACE AND TEETH. purpose of replacing cells that fail in the innermost layer. This stratum intermedium is looked upon as the reserve layer to the enamel-forming cells; the cells of this stratum are most numerous where enamel formation is most active. The INNER LAYER is composed of a single row of tall slender, columnar elements; these form a closely packed unbroken layer surrounding the dental papilla and are termed the ameloblasts. The nuclei lie in the peripheral portion of the cells. Enamel deposition begins during the sixteenth week of intrauterine life, in the temporary teeth. According to Tomes and others, the inner ends of the enamel cells become calcified and converted directly into enamel. An organic matrix is formed in which the enamel is deposited, probably in the form of calcoglobulin globules. The organic matter disappears, leaving the homogeneous, inorganic material representing, no doubt, the fused globules of calcoglobulin. According to Andrews and others, the enamel is secreted from the cell in some form (calcoglobulin) , and this solidifies and forms outside of the cell. The first, however, seems to be the more acceptable explanation. Enamel is formed from within outward, so that the youngest enamel is upon the surface while the oldest is next to the dentin. Capillary blood-vessels have been noted in the enamel organ by Bromell. It seems that before calcification be- gins that vessels are absent; with the formation of enamel vascularization of the enamel organ begins and is said to persist until the tooth erupts. By the time that the tooth begins to erupt, or, at the latest, when completely erupted, the enamel is fully formed. Between the enamel organ and the surface of the dentinal papilla is a layer of homogeneous substance called the membrana preformativa. Reference to this will be made later. DENTIN FORMATION. 327 Dentin Formation. The dentin is derived from the dental papilla; this structure is composed of embryonic connective tissue in which four different kinds of cells are found. Upon the surface of the papilla will be found a single layer of flask-shaped cells, the odontoblasts. These form the membrana eboris from which the dentin is derived. The basal portion of each cell is directed toward the papilla, or centrally, and contains the nucleus. Each cell possesses processes; those which are directed toward the enamel organ constitute the ultimate dental fibres. These cells are differentiated shortly before the formation of dentin begins. Just beneath the layer of odontoblasts the papilla is practically devoid of cells; beneath this, however, there is a cellular area of mixed cells and then again a central area containing but few cells. Dentin is first formed at the cutting, or occlusal surface and during the sixteenth week of intrauterine life. The dentin seems to be a secretion from the peripheral ends of the odontoblasts so that the processes in this region are surrounded by the lime salts, thus forming the dental sheaths and tubules; the odontoblasts are constantly out- side of the dentin that is formed. The dentin is laid down from without inward, and in areas where dentin formation is incomplete spaces, that are called the interglobular spaces, remain. As the dentin becomes thicker (by encroach- ment upon the dental papilla) the dental fibres elongate and the tubules become correspondingly longer. The dentin in the crown portion is formed first, the root portion being completed last. When the teeth begin to erupt their roots are partially formed; by the time that the whole crown is exposed the fang is usually completed. In the case of the incisor teeth the roots are usually completed by the time that the tooth begins to erupt. Cementum Formation. The cementum is also of mesoder- 328 DEVELOPMENT OF FACE AND TEETH. mal origin. As the enamel organ becomes in vagina ted by the dental papilla the mesoderm immediately surrounding the enamel organ condenses to form a sac-like covering, the DENTAL FOLLICLE. This structure gives rise to the cemen- tum and the alveolar process of the jaw and its remains constitute the PERIDENTAL MEMBRANE. The follicle is formed shortly after the tenth week. During the earlier stages of development the dental follicle covers the entire enamel organ and is connected with the dental papilla at its base. The follicle upon its outer surface forms bone, and upon its inner surface forms the cementum of the tooth. As the enamel organ grows the follicle seems to recede from the cutting edge until the neck portion is reached; at this point it remains, and as the root is formed by the dental papilla the follicle forms the cementum until the full length of the root is reached. The process of cementum formation is like that of bone, a secretion, and layer are formed as described in the section on the structure of cementum. The cementum and bone of the jaw are de- veloped from the dental follicle, or peridental membrane, at the expense of the latter, it becoming thinner as the cementum and alveolar bone increase in thickness. The temporary teeth begin to erupt from the sixth to the eighth month after birth and the set is usually completed by the twenty-fourth to the thirtieth or thirty-sixth month. The order of eruption is as follows: Central incisors, sixth to eighth month. Lateral incisors, seventh to ninth month. First molars, twelfth to fourteenth month. Canines, sixteenth to eighteenth month. Second molars, twenty-fourth to thirty-sixth month. The permanent teeth are thirty-two in number. The difference in number of the two sets and later appearance THE PERMANENT TEETH. 329 of added teeth is due to the fact that the jaw at certain periods will accommodate only a certain number of teeth, and any attempt to hurry their appearance will interfere with the dental arch. Of these permanent teeth, the molars, twelve in number, are not succedaneous teeth at all, but primary teeth as will be explained later. The germs for most of the permanent teeth are formed during intrauterine life. During the sixteenth week a bud appears at each end of the dental shelves; these buds are the germs for the first permanent molar teeth. During the seventeenth week the germs for the central incisors appear from the lingual sur- face of the dental shelf, opposite the point of formation of the corresponding temporary tooth; the remaining suc- cedaneous teeth follow in order of their eruption. The enamel organs undergo the same changes as previously described, with the exception that the process is somewhat slower, making their eruption somewhat later. As was stated above, the germs for the first permanent molars appear at the ends of the dental shelves and so have no forerunners; the germs for the second molars are developed from the neck of the enamel organs of the first molar during the third to the fifth month after birth; the enamel sacs for the third permanent molars appear from the neck of the enamel sacs of the second molars during the third to the fifth year after birth. All of the molar teeth, therefore, have no forerunners, and, are then, primary and not suc- cedaneous teeth. The first permanent molar tooth is the first one of the second set to appear; the order and times are as follows: First molar, sixth year. Central incisors, seventh year. Lateral incisors, eighth year. 330 DEVELOPMENT OF FACE AND TEETH. First premolars, ninth year. Second premolars, tenth year. Canines, eleventh to twelfth year. Second molars, twelfth to thirteenth year. Third molars, seventeenth to twenty-fifth year. The eruption and succession of the teeth are by no means simple processes. As the tooth germs develop they at first lie in a groove of the jaw, covered merely by the gum; gradually transverse partitions of bone form so that the entire tooth is ultimately incased in the bone of the jaw. The bone intervening between the tooth and the gum amounts to but a thin lamella that is completed shortly before the tooth is to erupt, except in the region where the gubernaculum passes to the gum. As eruption is to take place, that bone which is last formed (toward the gum) is resorbed so that there is no interference with eruption. The process of eruption is as follows: The bone covering the labial surface of the crown is resorbed until fully one- half of the surface is exposed; this is followed by the re- sorption of the bone on the lingual surface but here the process is slower and less complete, leaving some bone to protect the germs of the permanent teeth underneath. As a result of this process the crown apparently grows through the gum when in reality the gum becomes stretched over the tooth by the disappearance of the bone beneath. As the resorption continues until the crown is exposed new bone is laid down about the base of the tooth to strengthen its position. According to some writers the tooth erupts by the growth of the root forcing the crown above the gum surface. When one considers that in the temporary and permanent cuspid teeth the roots are completed by the time eruption occurs, this force cannot be counted upon as a THE PERMANENT TEETH. 331 factor in the eruption of the teeth. It might play some part in the eruption of the other teeth, but even this is doubtful. From the eruption of the second temporary molar tooth until the fourth year the teeth are practically quiescent. From the fourth year on the temporary teeth begin to decalcify and drop out to make room for the permanent teeth. The process of decalcification is one of absorption; it begins in the apical portion of the tooth and advances to the enamel line. The central incisors are the first af- fected, at about the fourth year, and the others follow in order of their eruption. As a result of this process the root becomes absorbed and the hold of the tooth upon the jaw becomes weakened; ultimately merely an enamel cap remains; this process extends over a period of about three years for each tooth, going on simultaneously or success- ively in the various teeth. Some claim that the process of resorption of the roots is due to the pressure exerted upon the root by the permanent tooth beneath. This does not, however, seem to be the cause, for in cases of absence of the succedaneous tooth the process of absorption of the root of the temporary tooth occurs as usual. The permanent teeth follow the temporary successively as the latter are lost. As the jaw gradually increases in length there is a second permanent molar added at the twelfth to the fourteenth year and a third one at the eigh- teenth to the twenty-fifth year. The permanent teeth erupt in the same manner as the temporary organs; that is, by the absorption of the bone from the crown portion. As this process of absorption occurs during the eruption of both sets the jaws would become thinner from above downward; to offset this nature adds below more than is absorbed above so that the dimension from above downward increases up to the prime of life. 332 DEVELOPMENT OF FACE AND TEETH. As the second set is gradually lost bone is not replaced as rapidly as lost so that in an old jaw the alveolar processes are lost (showing the absorption from above downward) and the vertical dimension decreases. Connected with the permanent tooth is a structure, the GUBERNACULUM DENTis, that seems to be of importance. It is a fibrous, cord-like structure attached to the apex of the tooth-sac and ends at the epithelium of the gum. It seems to direct the follicle by its tension and also to indicate the direction of eruption, and to maintain the tooth in position. In regard to malformation of the teeth, both sets may fail to appear, or the succedaneous teeth alone may not develop; again individual teeth may be absent, or a third set may appear after the second has been lost. What is more common than the latter is a duplication of some of the permanent teeth forming a row within the normal set; a fourth molar may appear if the jaw is long enough to accommodate it. Malformations of the root may be in the form of an additional root or the fusion of several to form one massive root. Again, the teeth may be united by fusion (if before birth) or concrescence (if after birth). If two teeth are found in a single sac the condition is known as geminous teeth. INDEX. Accessory cavities, 312 Acervulus cerebri. 252 Achromatic spindle, 39 Achromatin, 33 Acid cells, 14. 135 Acidophil, see Eosinophil Acrosome, 191 Adelomorphous cells, 137 Adipose tissue, 64 Adrenal, 183 Adventitia of artery, 99 of vein, 103 Agminated follicles, 66 Air-sacs, 166 Albumen, Mayer's, 28 Alcohol for clearing, absolute and ether, 9 for fixation, absolute, 4 absolute and ether, 5 absolute and formalin, 5 ninety-five per cent., 5 Alimentary tract, 118 Allantois, 221 Alum carmin, 15 Alvei, 1 66 Alveolar ducts, 166 Alveoli of lungs, 166 Alveolo-tubular glands, 55 Amakrine cell, 285 Ameboid motion of leukocytes, 106 Ameloblasts, 326 Amitosis, 36 Amnion, false, 219 true, 226 Amniotic cavity, 219 folds, 219 Amphipyrenin, 33 Ampullae capillary, 102 of ear, 303 of oviduct, 208 of spleen, 116 Amyloid bodies, 196 Anabolism, 35 Anaphase, 39 Anastomoses, 102 Angle of infiltration, 281 Angles, leaden, 7 Anilin oil-xylol, 23 Anisotropic disc, 77 Annuli fibrosi, 96 Annulus fibrosus, 299 Antrum of follicle, 202 Aortic bodies, no Appendix, follicles of, 144 glands of, 144 occlusion of, 145 Aqueous humor, 288 Arantii, corpus, 97 Arachnoid, 245 Arches, visceral, 318, 319, 320 Arcuate fibres of the pons, 263 Arcus tarseus externus, 295 internus, 295 Area of Langerhans, 156 Areola, 243 Areolar tissue, 64 Arrectores pilorum, 237 Arteries, large, 100 medium, 99 small, 101 Astrocyte, 86 Astrosphere, 34 Atria, 166 Atrio ventricular bundle, 97 Attraction sphere, 33 Auditory hairs, 303 nerve, 309 ossicles, 299 teeth, 306 Auerbach, plexus of, 146 Axial fibre, 192 Axis-cylinder, 84 Axilemma, 87 Basal border, 144 Balsam, 23 Basement membrane, 50 Basic stains, 12 Basilar membrane, 306 Basket cells, 254 Basophil, 107, 108 Belly-stalk, 220 Bensley's solution, 3 Benzol, 7, 22 Berlin blue, 24 Bertin, columns of, 173 Bile capillaries, 150 Bipolar cells, 85 Bismarck brown, 14 Bladder, 180 Blastodermic vesicle, 42 Blastula, 40, 217 Blind spot, 286 Blocking, 8 Blood cells of, erythroblasts, 26, 106 erythrocytes, 104 333 334 INDEX. Blood cells of, leukocytes, 106 platelets, 26, 108 crystals, 32 films, 25 fixation, 26 hemoglobin, 105, 109 platelets, 26, 108 technic, fixation, 26 spreads, 26 stains, 16, 26, 27 Blood-forming organs carotid gland, no coccygeal gland, 109 hemolymph nodes, no marrow, 73 Blood-vessels arteries, 99 capillaries, 101 heart, 98 nerves of, 100 veins, 103 Bone canaliculi, 72 cells, 70 compact, 70 composition, 70 corpuscles, 69 decalcification, n development endochondral, 74 endosteum, 70 growth, 77 intramembranous, 77 Haversian canal, 70 lamellae, 71 system, 70 lacunas, 72 Howship's, 71 lamellae, 70 lymphatics of, 74 marrow cavity, 72 cells, 73 red, 73 yellow, 73 nerves of, 74 osteoblasts, 69 osteoclasts, 73 perichondral, 74 periosteum, 69 Sharpey's fibres of, 69 structure of, 69 Volkmann's canals, 71 vessels of, 74 Bone-cells, 70 Bone-marrow cells of, 73 red, 73 serous, 73 yellow, 73 Bones of ear, 99 Bony cochlea, 303 labyrinth, 301 Borax carmin, 14 Boundary zone of choroid, 277 of kidney, 173 Bowman's capsule, 173 glands, 312 Bowman's membrane, 275 Brain, see Cerebrum sand, 252 Bronchi, 163 Bronchiole respiratory, 165 terminal, 165 Bruecker's lines, 78 Brunner's glands, 142 Bulb, hair, 235 Bulbus.oculi, see Eyeball Bundle of His, 97 Burdach's columns, 270 Cajal, cells of, 247 Calyces, 180 Cambium layer, 77 Canada balsam, 23 Canal, hyaloid, 288 of Petit, 259 of Schlemm, 281 of Stilling, 288 of spinal cord, 267 semicircular, 303 Canaliculi, of bone, 72 of eyelid, 296 Canalized fibrin, 226 Capillaries, bile, 150 blood, 101 lymph, 112 secretory of acid cells, 136 of demiliunes, 158 of hepatic cells, 150 of parotid, 155 Capsule of Bowman, 173 of Glisson, 148 of lens, 288 of Tenon, 297 suprarenal, 183 Carbol-xylol, 22 Cardia, 136 Cardiac muscle, 82 Carmin, borax, 15 alum, 15 injection mass, 24 Carminic acid, 16 Carotid gland, no Cartilage calcification of, 74 capsule, 67 cells, 67 chrondroblasts, 67 costal, 68 elastic, 69 fibro, 68 hyalin, 67 ossification of, 74 perichondrium, 66 vessels of, 69 Caruncle, lacrimal, 295 Cauda equina, 263. Cecum, foramen, 127 Cedar oil, 6, 22 Cell, the, 31 Cellodin infiltration, 9 Cells acid, 14, 35 INDEX. 335 Cells acidophilic, 107 adelomorphous, 134 amakrine, 285 basket, 254 basophilic, 107 bipolar, 85 blood red, 104 white, 105 bone, 70 Cajal, 247 cartilage, 67 centro-acinar, 155 chief, 134 chromaffin, 184, 251 ciliated, 48 Claudius, 306 columnar, 47 cone- visual, 282 connective tissue, 59 crystals (eye), 278 decidual, 206 definition of, 31 Deiter's 86, 309 delomorphous, 135 egg, 40 ectodermal, 218 enamel, 325 endothelial, 51 entodermal, 218 endymal, 267 epithelial, 245 eosinophil, 107 fat, 64 form, 34 follicular, 203 ganglion, 89 giant, 40 glia, 79 glycogen in, 32, 150 goblet, 49, 134, 138, 142 granule (cerebellum), 254 Golgi, 86 gustatory, 314 hair, 302, 307 Hensen's 306 hepatic, 150 interstitial, of ovary, 201 of testicle, 189 Langhans, 224 liver, 150 lutein, 206 marginal, 238 marrow, 73 mast, 107 mesothelial, 51 mitral, 250 mossy, 86 mother, 174 mucin, 49, 134 multipolar, 86 muscle cardiac, 82 smooth, 8 1 voluntary, 78 Cells nerve, 84, 86 neuro-epithelial, 50 neuroglia, 86 of Claudius, 306 of Clark's column, 266 of Golgi, 87 of Hensen, 306 of Langhans, 224 of Leydig, 189 of Purkinje, 254 of Sertoli, 189 olfactory, 312 oxyntic, 135 parietal, 135 peptic, 134 pigmented, 48 pillar, 307 plasma, 59 polymorphous, 249 polynuclear, 107 prickle, 48, 211 properties of, 34 pseudostratified, 48 pyramidal large, 247 small, 249 reproduction of, 36 rod-visual, 283 seminiferous, 188 sexual fertilization, 42 maturation, 41, 205 shape of, 34 size of, 34 spider, 86 squamous, 45 stain reaction of, 32 structure of, 3 1 stellate bone, 70 connective tissue, 59 sustentacular of ear, 301, 309 of olfactory membrane, 311 of retina, 284 of taste-bud, 127, 314 tactile, 90 tendon, 61 transitional, 49 trophodermal, 219 wandering, 59 Cell-body, 31 Cell-division a mitosis, 36 mitosis, 37 time of, 40 Cell-knots, 224 Cell-mass, inner, 42, 217 outer, 42, 217 Cell membrane (wall), 34 Celloidin casting, 9 hardening, 10 infiltration, 9 sectioning, n solutions, 9 Cell-spaces of Nuel, 309 336 INDEX. Cementoblasts, 328 Cementum formation of, 327 structure of, 123 Central artery of retina, 289 nerve system, 245 spindle, 39 Centro-acinar cells, 155 Centrosomes, 33, 41 Cerebellar columns, direct, 269 cortex, 253 basket cells of, 254 capillaries of, 272 cells of Purkinje, 254 ganglionic layer, 254 granule layer, 254 medullary substance, 255 molecular layer, 254 peduncles, 262 Cerebral cortex, 247 capillaries of, 272 cells of Cajal, 247 medullary substance, 249 molecular layer, 247 polymorphous cells of, 249 pyramidal cells of, 247, 249 radial bundles, 249 striations of Baillarger, 249 of Bechtereff, 249 tangential layer of, 249 Ceruminous glands, 298 Cervix, 210 Chambers anterior, 289 posterior, 289 vitreous, 289 Chief cells, 134 Chloroform for clearing, 7 Chordae tendineae, 97 Chorio-capillaris, 278 Chorion, 222, 226 frondosum, 223 laeye, 223 primitive, 220 Chorionic villi, 223 Choroid coat arteries of, 277 boundary zone, 277 glassy membrane, 278 lamina vasculosa, 277 stroma of, 276 tapetum cellulosum, 278 fibrosum, 277 Chromatic spindle, 39 Chromatin, 33 Chromosomes, 38 number of, 38 Chyli, receptaculum, 146 Cilia of eyelid, 294 Ciliary body, 278 muscle, 279 processes, 278 ring, 278 Ciliated cells, 48 Circulus ridicus major, 291 minor, 291 Circulatory system, 96 Circumferential lamellae, 70 Circumvallate papilhc, 127 Clark, column of, 269 Claudius, cells of, 306 Clearing blocks, 6 sections, 22 Clefts, visceral, 319 Clitoris, 196 Coccygeal gland, 109 Cochlea bony, 303 perilymph, 303 spiral ganglion of, 310 Cohnheim's fields, 79 Coiled glands, 53, 298 Colloid substance, 169, 170, 251 Colostrum corpuscles, 243 Columns of Bertin, 173 of Sertoli, 189 of spinal cord, 269 Commissure, gray, 267 white, 268 Compact bone, 70 Cone-fibres, 283 Cone-granules, 283 Coni vasculosa, 188 Conjunctiva corpuscles of, 91, 295, 317 palpebral, 295 scleral, 274 Connective tissues adipose, 64 areolar, 64 blood, 77 bone, 69 cartilage, 66 cells of, 58 classification of, 58 dentin, 77 elastic, 62 embryonic, 63 fibrous, 58 intercellular substance of, 59 lymphoid, 65 modified, 64 mucous, 63 origin of, 59 reticulum, 63 retiform, 63 varieties of, 58 Conus medullaris, 263 Convoluted tubules of kidney, 174, 175 Cord, umbilical, 227 Cords, medullary, 113 Corium, 231 Cornea, 275 Corneal corpuscles, 275 lacunae, 275 Corneo-scleral junction, 280 Corona radiata, 203 Corpora cayernosa, 198 Corpus albicans, 206 Arantii, 97 hemorrhagicum, 206 Highmori, 186 luteum spurium, 206 verum, 206 INDEX. 337 Corpus spongiosum, 199 Corpuscles blood, red, 104 white, 1 06 bone, 69 colostrum, 243 conjunct! val, 91, 317 corneal, 275 Smital, 91, 317 assal's, 117 Krause, 317 lamellar, 91, 316 Malpighian, 115 Meissner's, 91, 315 Pacinian, 91, 316 renal, 173 splenic, 115 tactile, 90, 315 Vater, 91, 316 Wagner, 91, 315 Corrosive sublimate fixative, i, 2 Corti's membrane, 309 organ, 307 tunnel, 307 Cowper's gland, 197 Cotyledons, 226 Creosote, 22 Crescents of Gianuzzi, 158 Crista basilaris, 305 Cristas acusticae, 303 Crossed pyramidal tract, 270 Crown, 119 Crypts, gastric, 133 Lieberkuehn's, 138 tonsillar, 129 Crystalline lens, 288 Crystals hematoidin, 108 hemin, 109 hemoglobin, 109 in the choroid, 278 Teichmann's, 109 Cumulus ovigerus, 202 Cup, imbedding, 8 Cupola, 302 Cuticular border, 134 Cuticle of hair, 236 Cutis vera, 231 Cytoplasm, 31 Dammar, 23 Daughter cells, 140 nuclei, 40 stars, 40 Decalcification, n Decidua ovular, 217, 220 placental, 217 reflexa, 217, 220 serotina, 217 uterine, 217 vera, 217 Decidual cell, 226 Dehydration, 5 Deiter's cells, 86, 309 Delafield's hematoxylin, 13 Delomorphous cells, 134 Demilunes of Heidenhain, 158 Dental follicle, 324, 328 groove, 324 papilla, 324 shelf, 322 Dentin formation of, 327 structure of, 107 Dentinal canals, 122 fibres, 122 tubes, 122 sheaths, 120 Derivatives of triploblast, 43 Derma, 212 Deutoplasm, 203 Development of face, 318 of teeth, 322 Diaster, 40 Diffuse lymph oid tissue, 65 Digestive glands, 148 Dilator pupillae, 280 Diphyodonts, 322 Diploblast, 42, 218 Direct cell-division, 36 cerebellar tract, 269 pyramidal tract, 269 Discus proligerus, 202 Dobie's globules, 79 Duct alveolar, 165 Bartholin, 158 cochlear, 303 ejaculatory, 196 endolymphatic, 301 pancreatic, 156 Rivini, 158 Wharton's, 158 Wirsungian, 156 Duodenum, 142 Dura, 245 Ear external, 298 internal, 300 middle, 299 Ear, bones of, 299 Ear-stones, 302 Ectoderm, 42, 218 derivatives of, 43 Egg-tubes of Pflueger, 184 Ehrlich-Biondi-Heidenhain stain, iO Ehrlich, fixation of blood, 26 Ejaculatory duct, 196 Elastic cartilage, 69 lamina anterior, 275 internal, 99 external, 99 posterior, 276 Elastin, 62 Ellipsoidal sheaths, 116 Embedding celloidin, 9 paraffin, 7 Embryonic area, 218 shield, 219 tissue, 62 Emissary veins, 199 INDEX. Enamel, 120 formation, 324 organ, 324 prisms, 120 Endocardium, 96 Endochondral bone, 74 Endolymph, 301 Endomysium, 81 Endoneurium, 89 Endothelial cells, 5 1 membrane, 51 End-plate, 95 Endymal cells, 268 Entoderm, 42, 218 derivatives, 43 Entpdermal vesicle, 218 Eosin, 14 Eosinophyl coarsely granular, 107 finely granular, 107 Epiblast, 41 Epicardium, 98 Epidermis, 230 Epididymis, 190 Epiglottis, 159 Epimysium, 81 Epineurium, 89 Epiphysis, 252 Epitendineum, 61 Epithelium basal border of, 144 ciliated, 48 classification, 45 columnar, 47 cuticular border of, 138 germinal, 201 glandular, 50 goblet, 9, 138, 142, 144 modified, 46 neuro-epithelial, 50 of mucous membrane, 50 pigmented, 50 prickle, 48 pseudostratified, 48 respiratory, 166 secretory canals of, 136, 150, 155 squampus, 46 transitional, 49 Eponychium, 238 Epoophpron, 208 Equatorial plate, 38 Erectile tissue, 198, 216 Erlicki's solution, 3 Erythroblasts, 106 Erythrocytes, 104 Esophagus coats of, 131 glands of, 132 muscle of, 132 vessels of, 133 Eustachian tube, 300 Excretion, 35 Exoplasm, 32 External ear, 298 Eyeball angle of infiltration, 281 blood-vessels of, 289 canal of Petit, 289 Eyeball cnnal of, Schlemm 281 Stilling, 288 chambers of, 289 chproid, 276 ciliary body, 278 muscle, 279 processes, 278 ring, 278 cornea, 275 hyaloid canal, 288 iris, 279 lens, 288 lymph channels of, 292 optic nerve, 287 refractive media, 288 retina, 281 sclera, 274 venae vorticosae, 291 vitreous humor, 288 Eyelashes, 294 Eyelid blood supply, 295 caruncle, 295 cilia, 294 conjunctiva, 295 glands, 294 lymphatics, 295 nerves of, 295 plica semilunaris, 295 tarsus, 293 third, 295 Fallopian tube, 208 Farrant's solution, 24 Fascia, 62 Fat, 64 cells, 64 crystals, 64 stains for, 65 Female genital system, 201 Fenestra rotunda, 300 Fenestrated membrane of Henle, 101 Ferrein, pyramids of, 172 Fertilization, 42 Fetal circulation, 228 Fibre-layer of Henle, 284 Fibres cone, 283 dentinal, 122 Mueller's, 284 muscle cardiac, 82 intrafusal, 92 smooth, 8 1 voluntary, 78 nerve, amyelinated, 89 myelinated, 87 neuroglia, 87 rod, 282 Sharpey's, 69 Fibro cartilage, 68 Fibrous tissue, 58 Filar mass, 31 Filiform papillae, 126 Films, blood, 26 Filum terminale, 263 Fimbriated end of Fallopian tube, 208 INDEX. 339 Fissure of spinal cord, 263 Fixation, i Fixatives, see Fixing solutions Fixing sections on slides, 28 Fixing solutions alcohol absolute, 4 absolute and ether, 5, 26 absolute and formalin, 5, 26 ninety-five per cent., 5 Bensley's, 3 chromic acid, 3 Erlicki's, 3 Flemming's, 3 formalin, 4 Golgi's, 4 Heidenhain, i Kopsch's, 3 Mueller's, 2 nitric acid, 4 Orth's, 3 osmic acid, 3 potassium bichromate, 2 Tellyesnicky's, 2 Zenker's, 2 Flemming's solution, 3 Fluids, see Fixing solutions Folds of Kerkring, 141 Foliate papillae, 314 Follicles agminated, 66, 142 Graafian, 201 hair, 235 lenticular, 134 solitary, 66, 116 Folliculi, theca, 201 Fontana, spaces of, 280 Foramen cecum, 127 Foramina nervosa, 310 Formaldehyde, 4 Formalin, 4 Formative yolk, 203 Formatio reticularis, 257, 262 Fovea centralis, 287 Howship's, 71 Freezing tissue, 10 Fungiform papillae, 127 Gall-bladder, 153 Ganglia, 89 spinal, 243 Ganglion cells, 89 bipolar, 85 multipolar, 86 unipolar, 85 Ganglion spirale, 310 Gastric glands, 134 pits, 133 Gastrula, 42, 218 Gelatin injection mass, 24 Genital corpuscles, 91, 317 organs, female, 201 male, 186 Genitalia, 215 Germinal center, 66 epithelium, 201 spot, 40, 203 vesicle, 40, 203 Germ-nucleus, 205 Giant cells, 40 Gianuzzi, crescents of, 158 Giraldes, organ of, 199 Glacial acetic acid, i Glands accessory tear, 294 alveolar, 55 alveolo- tubular, 55 arterial, 109 Bartholin's, 215 Bowman's, 312 Brunner's, 142 cardiac, 134 carotid, no ceruminous, 298 coccygeal, 109 coiled, 53 Cpwper's, 197 digestive, 148 ductless, 57 duodenal, 142 excretory, 57 fundus, 136 intestinal, 138 Krause's, 294 labial, 118 lacrimal, 296 lenticular, 134 Lieberkuehn, 138 lingual, 129 Litre's, 181, 182 Luschka's, 109 mammary, 240 Meibomian, 294 mixed, 57, 154 Moll, 294 Montgornmery's, 243 mucous, 56, 154 olfactory, 312 pancreas, 155 parathyroids, 170 parotid, 155 peptic, 136 pineal, 252 pituitary, 251 preputial, 199 prostate, 196 pyloric, 136 racemose, 55 saccular, 55 salivary, 153 sebaceous, 240 serous, 56, 154 structure of, 154 sublingual, 157 submaxillary, 158 sudoriparous, 239 suprarenal, 183 sweat, 239 tarsal, 294 tear, 296 thymus, 116 thyroid, 168 tubular, 53 tubulo-alveolar, 55 Tyson's, 199 unicellular, 52 urethral, 181 340 INDEX. Glands uterine, 210 varieties according to outlet, 57 secretion, 56 structure, 53 Glandular cells, 50 Glans, clitoris, 216 penis, 199 Glassy membrane, 278 Glisson's capsule, 148 Globular process, 320 Glomerular layer of olfactory lobe, 250 adrenal, 183 Glomerulus, 173 Glomus caroticum, no coccygeum, 109 Glycerin albumen, 29 jelly, 24 Glycogen, 32, 150 Goblet cells, 9, 134, 138, 142 Gold chlorid, 17 stain, 17 Golgi cells, 86 fixing solution, 4 silver stain, 17 Goll, columns of, 270 Gower, columns of, 269 Graafian follicles, 201 Granular cells of cerebellum, 234 Granule cells of Graafian follicle, 201 Gray commissure, 267 substance, 84, 246 Ground substance of cartilage, 67 of bone, 70 Growth, 35 Gubernaculum dentis, 332 Gum, 10 Gustatory hair, 127 organ, 127 pore, 127 Hair auditory, 303 bulb, 235 color of, 237 follicle, 235 lanugo, 237 layers of, 236 muscle, 237 olfactory, 281 papilla, 235 root, 235 root-sheaths, 236 . shaft, 235 Hair-cells, 301, 307 Hardening agent, 5 Hassal's corpuscles, 117 Haversian canals, 71 lamellae, 71 Heart, 88 annuli fibrosi, 96 blood-vessels of, 98 bundle of His, 97 chordae tendineae, 97 corpus Arantii, 97 elastic tissue, 96 endocardium, 96 epicardium, 98 Heart lymphatics, 98 muscle, 82 myocardium, 98 nerves of, 98 pericardium, 98 structure of, 96 valves, 97 Heidenhain, demilunes of, 158 solution, i Helicine arteries, 199 Hematoidin crystals, 109 Hematoxylin, acid, 13 Delaneld's, 13 Harris', 12 Weigert's, 19 Hemin crystals, 109 Hemaglobin crystals, 109 Hemolymph nodes, no Henle's, fenestrated membrane of, 101 fibre layer, 284 layer, 236 loop, 174 limbs, 174 Hensen's cells, 306 disc, 78 Hiatus, 145 Howship's lacunae, 71 Humor, aqueous, 288 vitreous, 288 Huxley's layer, 236 Hyaloid artery, 288 canal, 288 membrane, 288 Hyalin cartilage, 67 cells, 107 Hyaloplasm, 31 Hymen, 215 Hypoblast, 41 Hypophysis, 251 Ileum, 142 Indirect division, 36 Infiltration angle, 281 celloidin, 9 gum, 10 paraffin, 7 Injection, 24 Inner cell-mass, 42, 217 Inner bulb, 92, 285 Intercellular bridges (spines), 48, 230 substance, 59, 62, 67, 70, 86 Interfilar mass, 31 Interglandular projection, 133 Interglobular spaces, 122 Intermediate disc, 79 Internal ear, 300 elastic lamina, 99 Interstitial cells of ovary, 201 of testicle, 189 Intervillous spaces, 226 Intestine agminated follicles of, 142 blood-vessels of, 146 Brunner's glands, 142 crypts of, 138 epithelium of. 138 goblet cells of, 138, 142, 144 folds of Kerkring, 141 INDEX. 341 Intestine large, 142 lymphatics, 146 mucosa of large, 142 of small, 138 muscular coat of large, 143 of small, 142 nerves of, 146 Peyer's patches of, 142 plica circulates, 141 solitary follicles, 141 submucosa of large, 143 of small, 142 valyulae conniventes, 141 villi, 139 Intima of artery, 99 of vein, 102 Intra-cartilagenous bone, 74 Intrafusal muscle fibres, 92 Intra-membranous bone, 77 Intumescentia cervicalis, 263 lumbalis, 263 lodin, 29 Iris anterior endothelium, 279 lamina, 280 muscle, 280 pigment, 280 posterior epithelium, 280 lamina, 280 strorna, 279 Irritability, 36 Islands, pancreatic, 156 Isotropic, 78 Jejunum, 142 Jelly, glycerin, 24 Wharton's, 208 Karyokinesis, 37 Karyolymph, 33 Karyosomes, 33 Katabolism, 35 Keratohyalin, 231 Kerkring, folds of, 141 Kidney arched tubules, 175 arches, arterial, 177 venous, 178 blood-vessels of, 176 Bowman's capsule, 173 capsule of, 171 columns of Bertin, 173 of Ferrein, 172 convoluted tubules, 174 cortex, 171 ducts of Bellini, 175 Henle's limbs, 174 loops, 174 hilus, 171 interjobular arteries, 177 veins, 177 labyrinth, 173 lymphatics, 178 pyramids, 173 medulla, 173 medullary pyramids, 173 rays, 172 Kidney nerves of, 178 papillary ducts, 175 pyramids, medullary, 173 of Ferrein, 172 renal corpuscle, 173 sinus of, 171 straight collecting tubules, 175 tubules, 174 diameter of, 173 uriniferous, 174 venae stellatae, 177 Kopsch's fluid, 3 Krause, corpuscles of, 317 gland of, 294 membrane of, 79 Labia majora, 216 minora, 215 Labyrinth, bony, 301 membranous, 301 of kidney, 173 Lacrimal apparatus, 296 canaliculi, 296 caruncle, 295 gland; 296 accessory, 294 sac, 296 Lacteal, 140 Lacunae, bone, 72 corneal, 275 Howship's, 67 trophodermal, 222 Lamellae of bone circumferential, 70 concentric, 71 external, 70 ground, 72 Haversian, 71 intermediate, 72 internal, 72 perimedullary, 72 periosteal, 70 peripheral, 70 Lamellar corpuscles, 91, 3,16 Lamina cribrpsa, 274 elastic, anterior, 275 external, 99 internal, 99 posterior, 276 fusca, 274 spiralis, 305 suprachoroidea, 277 Langerhans, areas of, 156 Langhans, layer of, 224 Lantermann, clefts of, 87 Lanugo hairs, 237 Large intestine, 142 Larynx blood-vessels of, 161 cartilages of, 160 coats of, 159 epiglottis, 159 nerves of, 161 ventricles, 160 vocal cords, 160 Lateral discs, 73 342 INDEX. Lateral lemniscus, 258 Lens, crystalline, 288 capsule of, 288 epithelium of, 289 fibres of, 289 ligaments of, 289 Lenticular glands (follicles), 134 Leukocytes classification of, 105 Leydig's cells, 189 Lieberkuehn's glands, 138 Ligamentum nuchae, 62 pectinatum, 276 spirale, 305 suspensorium, 259 Limbus, 306 Limiting membrane of retina external, 284 internal, 286 of vessels of arteries, 99 of veins, 102 Lingual glands, 129 papillae, 127 septum, 129 tonsil, 129 Lines of Schreger, 120 Linin, 33 Lip, 118 Liquor folliculi, 204 sanguinis, 108 Lithium carbonate, 19 Litre", glands of, 181, 182 Liver bile-capillaries, 150 blood-vessels, of, 150 capsule, 148 cells, 150 circulation of, 151 function of, 152 hepatic duct, 153 interlobular ducts, 150 tissue, 150 vessejs, 150 lobule, 148 lymphatics, 152 nerves of, 152 pig's, 148 portal system, 150 vein, 151 reticulum of, 148 Loop, Henle's, 174 Lungs air-sacs, 166 alveolar ducts, 166 alvei, 1 66 alveoli, 166 blood-vessels of, 167 circulation of, 167 lobules, 165 lymphatics, 167 nerves of, 168 pleura, 163 respiratory bronchiole, 165 epithelium, 165 terminal bronchiole, 165 vestibulum, 166 Lunula, 97, 238 Luschka's gland, 109 Lutein cells, 201 Lymphatic system, 112 Lymph capillaries, 112 ducts, 112 vessels, 112 Lymph follicles agminated, 66, 142 germinal center of, 66, 142 of appendix, 144 of intestine, 141, 142 of pharynx, 131 of tongue, 129 of tonsil, 129 solitary, 66, 129 Lymph node blood-vessels of, 114 cortex, 112 hilus, 114 lymph sinuses, 114 medulla, 113 medullary cords, 113 nerves, 114 structure of, 112 Lymphocytes, 107 Lymphoid tissue dense, 66, 112 diffuse, 65, 112 M. Macroblast, 106 Macrocyte, 105 Macula acustica, 301 lutea, 287 Male genital organs, 186 Malformations of face, 322 of palate, 322 of teeth, 332 Malpighian body, 173 corpuscles, 115 pyramid. 174 Mammary gland ampulla, 242 areola, 243 cells of, 242 colostrum, 243 glands of Montgommery, 243 lactating and nonlactating, 242 nerves of, 243 nipple, 243 structure of, 241 Mammilla, 243 Margarin crystals, 64 Marrow cells of, 73 cavity, 72 red, 73 serous, 73 spaces, 74 yellow, 73 Marrow cells, 73 Mast-cells, 108 Matrix of nail, 238 cartilage, 67 Maturation of ovum, 40, 204 Mayer's albumen, 28 solution, ii INDEX. 343 Media, of artery, 99 of vein, 102 Medial lemniscus, 258 Median disc of Hensen, 78 Median longitudinal bundle, 258. Mediastinum testis, 186 Medullary cavity, 72 cords, 113 pyramids, 173 rays, 172 sheaths, 87 Medulla of adrenal, 184 of bone, 72 of cerebellum, 255 of cerebrum, 249 of hair, 237 of kidney, 173 of lymph node, 113 of ovary, 207 Meibomian glands, 294 Meissner's corpuscles, 91, 315 plexus, 146 Membrana basilaris, 306 nictitans, 295 olfactoria limitans, 312 preformativa, 326 reticularis, 307 tectoria, 309 Membrane basement, 50 basilar, 306 Bowman's, 275 Corti's, 309 Descemet's, 276 fenestrated, of Henle, 101 glassy, 278 hyaloid, 288 Krause, 79 mucous, 50 Nasmyth's, 126 otolith, 271 peridental, 125, 328 of cell, 34 of retina external limiting, 284 internal limiting, 286 Reissner, 304 serous, 51 tympanic, 298 vitelline, 40, 203 Menisci, 90 Menstruation, changes of, 212 Mesoblast, 42 Mesoderm, 42, 218 derivatives, 43 Mesothelium, 51 Metabolism, 35 Metaphase, 39 Methylene blue, 14 Methyl green, 14 Microblast, 106 Microcyte, 105 Microsome, 32 Middle ear, 299 Milk, 242 Mitosis, 37 Mitral cells, 250 Mixed connective tissue, 64 Mixed glands, 57, 154 Modiolus, 303 Molecular layer of cerebellum, 254 of cerebrum, 247 of olfactory bulb, 250 of retina, 284, 286 Moll, glands of, 294 Monaster, 38 Mons veneris, 216 Montgommery's glands, 243 Morula, 42 Mossy cells, 86 Mother cell, 189 star, 38 Motion, 35 Motor cells, 265 endings, 94 nerves, 87 roots, 271 Mounting, 29 Mouth, 119 Mucin, 49, 138 Mucous connective tissue, 62 glands, 56, 154 membrane, 50 Mulberry mass, 42 Mueller's fibres, 284 lid muscle, 294 ring muscle, 279 solution, 2 Muscle nerves of, 83, 94 of blood-vessels, 81 structure of a, 81 vein, 1 02 Muscle fibre branched, 82 cardiac, 82 Cohnheim's fields, 79 fibrillae of, 75 involuntary, 81 nuclei, 79, 80, 82 pigment in, 82 red, 79 sarcolemma, 79 sarcoplasm, 78 sarcous elements, 78 smooth, 8 1 striations, 79, 81, 82 voluntary, 78 white, 79 Muscle-spindle, 92 Muscularis mucosae, 50 Myelin sheath, 87 stain, 19, 20 Myelocyte, 73, 108 Myeloplaxes, 73 Myocardium, 98 Nabothi, ovuli, 210 Nails bed, 238 body, 238 eponychium, 238 fold, 237 groove, 238 lunula, 238 344 INDEX. Nails matrix, 238 root, 237 wall, 237 Nares, 159 Nasal mucosa blood-vessels of, 313 Bowman's glands, 312 lymphatics, 313 nerves of, 313 olfactory area, 311 respiratory portion, 311 Nasmyth's membrane, 126 Nasof rental process, 320 Nerve cells axis-cylinder, 84 bipolar, 85 Deiter's, 86 dendrites, 84 first type, 86 Golgi's, 86 multipolar, 86 neurit, 84 neuron, 84 second type, 86 structure, 84 telodendrites, 85 unipolar, 85 Nerve-organs bulbs, 90 classification, 90 conjunctival, 91, 317 corpuscles of Meissner, 91, 315 of Vater, 91, 316 of Wagner, 91, 315 genital, 91, 317 in epithelium, 90 smooth muscle, 95 voluntary muscle, 94 motor, 94 neuro-muscular, 92 neuro-tendinous, 94 Pacinian body, 91, 315 sensor, 90 tactile cells, 90 corpuscles, 90, 315 Nerve fibre amyelinated, 89 axis-cylinder, 87 functional varieties, 87 internode, 87 myelin, 87 myelin sheath, 87 myelinated, 87 neurilemma, 87 nodes of Ranvier, 87 sheath of Schwann, 87 sympathetic, 89 white substance of Schwann, 87 Nerve trunk blood-vessels of, 89 endoneurium, 89 epineurium, 89 sympathetic, 89 lymphatics, 89 perineurium, 89 system, 245 tissues, 84, 246 Nerve nervorum, 89 yasorum, 100 Neurilemma, 87 Neuro-epithelium of ear, 301, 307 of eye, 282 of nose, 312 of retina, 282 of taste buds, 127, 314 Neurofibrils, 84 Neuroglia, 86, 246 cells of, 86 fibres, 86 Neuron, 84 Neutrophil, 97 Nissl's bodies, 84 Nitric acid, 4 Nodes of Ranvier, 87 Nodules cortical, 112 lymph, 66, 112 secondary, 112 solitary, 66, 112 Normoblasts, 106 Nuclear division, 37 matrix, 33 membrane, 33 sap 33 spindle, 39 Nucleolus, 34 Nucleus, 32 achromatin, 33 arcuate, 262 chromatin, 33 cuneatus, 261 gracillis, 260 olivary, inferior, 262 superior, 258 of lateral lemniscus, 258 Stilling, 267 Nuel, spaces of, 309 Nutritive yolk, 203 Nymphae, 214 Oblongata, 258 Odontob lasts, 124, 327 Oils for clearing anilin, 23 anilin-xylol, 23 bergamot, 22 benzol of, 22 cedar-wood, 6, 22 clove, 22 creosote, 22 origanum, 22 turpentine, 6 toluol, 7, 22 xylol, 6, 22 Olfactory lobe glomerular layer, 250 granular layer, 250 mitral cells, 250 molecular layer, 250 peripheral fibres, 250 Olfactory mucosa blood-vessels of, 313 INDEX. 345 Olfactory mucosa cells of, 311 glands of, 312 Olivary bodies, 262 nucleus, 258, 262 Oocyte, 204 Optic nerve, 287 papilla, 287 Orange, 15 Ora serrata, 287 Oral cavity, 119 depression, 318 Organ of Corti, 307 Orth's solution, 3 Osmic acid fixative, 3 stain for fat, 21, 65 Osteoblasts, 70 Osteoclasts, 73 Ossicles, auditory, 299 Ossification endochondral, 74 intra-membranous, 77 Otolith membrane, 302 Otoliths, 302 Outer cell-mass, 217 Ovary antrum of follicle, 202 blood-vessels of, 207 corpus albicans, 206 hemorrhagicum, 206 luteum, 206 cortex, 201 egg tubes of Pflueger, 204 germinal epithelium, 201 Graafian follicle, 201 hilus, 201 interstitial cells, 207 lymphatics, 207 medulla, 207 muscle tissue of, 207 nerves of, 208 tunica albuginea, 201 Oviduct, 208 Ovulation, 207 Ovuli Nabothi, 210 Ovum dentoplasm, 40, 203 embryologic, 41 escape of, 206, 207 fertilization, 41 formative yolk, 40, 207 maturation, 40, 205 nutritive yolk, 40, 207 segmentation, 42 structure, 40, 207 Oxyntic cell, 134 Oxyphil, see Eosinophil Pacchpnian bodies, 245 villi, 245 Pacinian bodies, 91, 316 Palate, development of, 322 Palatine tonsils, 129 Pancreas areas of Langerhans, 156 blood-vessels of, 155 cells of, 154 centro-acinar cells, 155 Pancreas ducts, 154 nerves of, 155 zympgen granules, 154 Pancreatic duct, 156 Panniculus adiposus, 233 Papilla circumvallate, 127 filiform, 126 foliate, 314 fungiform, 127 hair, 235 of mucosa of tongue, 126 esophagus, 131 optic, 287 tactile, 232 vascular, 232 Paracarmin, 16 Paradidymis, 199 Paraffin fixation of, sections, 28 infiltration, 7 removal from sections, 29 sectioning, 10 Parathyroids, 170 Parasympathetics, no Paroophoron, 208 Parotid gland, 155 Parovarium, 208 Pars ciliaris retinas, 278 iridica retinae, 280 pptica retinae, 281 Pectinate ligament, 281 Pellicula, 34 Pelvis of ureter, 170 Penis arteries of, 199 corpora cavernosa, 198 corpus spongiosum, 199 emissary veins, 199 erectile tissue, 198 glands of Tyson, 199 glans, 199 helicine arteries, 199 nerves, 199 tunica albuginea, 198 veins, 199 Peptic cells, 14, 134 glands, 136 Perforating fibers of cornea, 275 of Sharp ey, 69 Pericardium, 98 Perichondrium, 66 Peridental membrane, 125 Perimysium, 81 Perineurium. 89 Periosteal lamellae, 70 Periosteum, 69 Peripheral nerve organs, 82 Peritendineum, 61 Perivitelline space, 203 Petit's canal, 289 Peyer's patches, 66, 142 Pflueger's egg tubes, 204 Phagocytes, 107 Phalangeal plates, 307 process, 307 Pharynx, 130 346 INDEX. Phloroglucin nitric acid, n Pia, 245 Picric acid stain, 14 Picro-carmin, 16 Picro-fuchsin, 15 Pigment cells, 50 of hair, 237 of iris, 280 of retina, 282 of skin, 233 Pig's liver, 148 Pillar cells, 307 Pineal body, 252 Pinna, 298 Pits, gastric, 133 Pituitary body, 251 Placenta canalized fibrin, 226 cell-knots, 224 chorion, 226 decidua, 217 development of, 219 intervillous spaces, 226 septa of, 224 syncytium, 222 villi of, 223 Placentoblast, 219 Plasma cells, 59 Plastids, 32 Platelets of blood, 108 Pleura, 163 Plexus of Auerbach, 146 of Meissner, 146 Plica circulares, 141 palmatae, 210 semilunaris, 295 Polar bodies, 42, 204 field, 38 Polynuclear cells, 106 Polyphyodonts, 322 Pons, 255 Pontile nuclei, 255 Portal circulation, 150 system, 1.50 vein, 150 Posthypophysis, 251 Postoblongata, 258 Potassium bichromate, 2 Pouches, visceral, 319 Precapillary vessels, 101 Prehypophysis, 251 Preoblongata, 257 Prepuce, 198 Prickle cells, 4, 230 Primary marrow cells, 75 spaces, 75 Prochorion, 219 Prominentia spiralis, 305 Prophase, 37 Prostate blood-vessels, 196 capsule, 196 glands, 196 nerves, 197 Prostatic bodies, 196 Protoplasm, 31 Prussian blue, 24 Pseudostratified cells, 48 Pulp cavity, 119 splenic, 115 tooth, 123 Pupil, 280 Purkinje cells, 254 Pyramidal cells of cerebrum, 249 columns, direct, 269 crossed, 270 Pyramids Malpighian, 173 medullary, 173 of Ferrein, 172 Pyramidal decussation, 359 Pyramis, 263 Pyrenin, 34 Ranyier, nodes of, 87 Rapid technic, 28 Receptaculum chyli, 146 Rectum, 143 valves of, 143 Red blood cells, 102 bone marrow, 73 Reissner's membrane, 304 Remak's fibres, 89 Renal corpuscles, 173 Reproduction, 36 Respiratory bronchiole, 165 organs, 159 Restiform bodies, 262 Rete Malpighii, 230 testis, 189 Retia mirabilia, 102 Reticular connective tissue, 63 gland, 58 Reticulum, 63 Retina amakrine cells, 285 blind spot, 286 blood-vessels, 289 central artery, 289 cone-cells, 282 cone-fibres, 282 fovea centralis, 287 ganglion cells, 285, 286 Henle's fibre layer, 284 limiting membrane, inner, 286 outer, 284 macula lutea, 287 molecular layer, inner, 286 outer, 284 nerve fibre layer, 286 optic, 281 optic nerve papilla, 287 ora serrata, 287 pars ciliaris, 278 iridica, 280 optica, 281 pigment layer, 282 rhodopsin, 284 rod-cells, 283 fibres, 284 visual purple, 284 INDEX. 347 Rod-cells, 283 fibres, 284 Rolandi, substantia gelatinosa, 268 Root sheaths, 236 Rouleaux, 105 Sacculations of colon, 142 Sacculus, 301 Safranin, 14 Salivary corpuscles, 129 glands, 153 Sarcolemma, 79 Sarcoplasm, 78 Scala media, 303 tympani, 303 vestibuli, 303 Schlemm's canal, 281 Schwann, sheath of, 87 white substance of, 87 Sclera, 274 Scleral conjunctiva, 295 Sebaceous glands, 240 Sebum, 240 Secondary marrow spaces, 75 Secretion, 56 Secretory canals, 136, 150, 155 Sectioning celloidin, n paraffin, 10 Sections, staining of, 29 Semen, 194 Semi-circular canals, 303 Seminiferous tubules, 188 Seminal vesicles, 195 Sense of smell, 311 taste, 314 touch, 315 Sensor decussation, 262 nerves, 87 organs, 90 Septa, placental, 205 Septum linguali, 129 posterior median, 238 Serous glands, 56, 154 membranes, 51 Sertoli's columns, 189 Sharpey's fibres, 69 Sheath, Henle's, 217 Huxley's, 217 myelin, 87 Silver staining blood-vessels, 19 lymphatics, 19 nerve tissue, 17 Sinus lactiferous, 243 marginal, 227 lymph, 114 of kidney, 171 Sinusoids, 102 Skein, daughter, 40 mother, 37 Skin appendages, 234 arrector pili muscle, 237 blood-vessels of, 233 color of, 233 corium, 231 derma, 231 epidermis, 230 Skin glands, 239 layers of, 230 lymphatics, 234 panniculus adiposus, 233 pigment, 233 Slide technic, 28 Slides, 28 Small intestine, 138 Smell, 311 Smooth muscle, 81 Sole-plate, 95 Solitary follicles, 66 Somatopleure, 218 Spaces of Fontana, 281 of Nuel, 309 Spermid, 193 Spermioblast, 194 Spermiocyte, 193 Spermiogenesis, 192 Spermiogonia, 188, 192 Spermatozoon, 42 Spider cell, 86 Spinal cord blood-vessels of, 273 canal, 267 cells, 265 commissures, 267, 268 columns, 269 fissure, 263 functional divisions of, 271 gray substance, 264 horns, 265 membranes of, 245 nerves, 271 septum, 264 white substance, 268 Spindle, central, 39 nuclear, 39 Spinal ganglion, 271 Spirem, 37 Splanchnopleure, 218 Spleen capsule, 114 circulation, 116 corpuscles, 115 lobules, 104 Malpighian corpuscles, 115 pulp, 115 trabeculas, 115 Spongioplasm, 31 Spongy bone. 70 Spot, germinal, 41 Staining of sections, 12, 29 Stains acid, 14 acid hematoxylin, 13 alum carmin, 15 anilin dyes, 13, 14 basic, 12 Bismarck brown, 14 borax carmin, 15 carmin, 15 Delafield's hematoxylin, 13 Ehrlich-Biondi-Heidenhain, 16 elastica, 21 eosin, 14 eosin-methylene blue, 27 348 INDEX. Stains for adipose tissue, 59 gold, 17 Harris' hematoxylin, 12 hematoxylin acid, 13 Delafield's 13 Harris', 12 methylene blue-eosin, 27 methyl green, 14 myelin, 19, 20 nuclear, 12 orange, 15 osmic acid for fat, 21, 65 paracarmin, 16 picric acid, 14 picro-carmin, 16 protoplasmic, 14 silver, 17 safranin, 14 Sudan III for fat, 21, 65 Van Gieson, 15, 21 Weigert's elastica, 21 myelin, 17 Weigert-Pal, 20 Wright's blood, 26 Stars, daughter, 40 mother, 38 Stellate cells, 58 Stomach, acid cells, 135 blood-vessels, 137 cardiac end, 134 coats, 133 glands, 133 lymphatics, 137 mucous membrane, 133 nerves, 138 peptic cells, 134 pyloric end, 136 Stratum corneum, 230 germinativum, 230 granulosum, 231 of ovary, 202 intermedium, 325 lucidum, 231 Malpighii, 230 mucosum, 230 papillare, 231 reticulare, 232 supra vasculare, 211 vasculare, 210 Stria vascularis, 305 Striae of Retzius, 120 Striations of Baillarger, 247 of Bechtereff, 247 Stilling canal of, 288 nucleus of, 240 Stomodeum, 318 Subarachnoid space, 245 Subdural space, 245 Subscleral, 274 Sublingual gland, 157 Submaxillary gland, 158 Substantia gelatinosa, 259, 267 grisea centralis, 268 propria, 275 spongiosa, 268 Subzonal ectoderm, 217 Succus entericus, 142 Sudan III, 21, 65 Sudoriparous glands, 239 Sulcus spiralis, 306 Suprarenal body blood-vessels, 184 cells, 183 cortex, 185 medulla, 184 nerves, 185 zones, 183 Suspensory ligaments of lens, 289 Sustentacular cells, 127, 189, 302, 309, 3ii, 3i4 Sweat-glands blood-vessels, 243 cells of, 239 lymphatics, 244 modified, 240 nerves, 243 pore, 239 Syncytium, 226 Tactile cells, 90 corpuscles, 90, 315 menisci, 90 papillae, 231 Taenia coli, 143 Tapetum cellulosum, 278 fibrosum, 277 Tarsal glands, 294 plates, 293 Taste-buds, 127, 159, 314 pore, 127 sense of, 314 Tear gland, 296 accessory, 294 Technic, general, i rapid, 28 slide, 28 Teeth, auditory, 306 cementum, 123 crown, 119 dentin, 120 development of, 322 enamel, 120 fang, 119 nerves, 124 pulp, 123 root, 119 root canal, 119 vessels of, 124 Teichmann's crystals, 109 Tellyesnicky's solution, 2 Telophase, 40 Tendon, 61 cells, 6 1 Tenon, capsule of, 297 space of, 292 Terminal bronchioles, 166 Testicle blood-vessels, 190 excretory tubules, 189 interstitial cells, 189 lobules of, 1 86 lymphatics, 190 mediastinum, 186 INDEX. 349 Testicle nerves, 190 seminiferous tubules, 188 tunica albuginea, 186 vaginalis, 186 Theca folliculi, 202 Third eyelid, 295 Thrombocytes, 108 Thymus blood-vessels, 117 changes in, 116 corpuscles of Hassal, 117 cortex, 117 medulla, 117 Thyroid body blood-vessels, 170 colloid substance, 169 lymphatics, 170 Tigroid bodies, 84 Tissue areolar, 64 adipose, 64 connective, 58 definition of, 45 elastic, 62 embryonic, 62 epithelial, 45 erectile, 198, 215 fibrous, 58 lymphoid, 63 mucous, 62 muscle cardiac, 82 smooth, 8 1 voluntary, 78 nerve, 84 retiform, 63 Toluol, 8, 22 Tome's granular layer, 122 Tongue blood-vessels, 129 glands, 129 lymphoid tissue, 129 muscle, 126 papillae, 126 taste-buds, 127 Tonsil crypts of, 129 lingual, 129 palatine, 129 Touch, 315 Trachea, 161 Transitional cells, 49 Trichloracetic acid, n Trigonum vesicae, 181 Triploblast, 42, 217 Trophoderm, 218 Trophodermal lacunas, 220 Tuberculum Rolandi, 259. Tubular glands coiled, 53 compound, 53 branched, 53 reticular, 54 simple, 50 Tubules dentinal, 122 intercalated, 15 Tubules intermediate, 154 secretory, 154 seminiferous, 188 uriniferous, 174 Tubuli recti, 189 Tubulo-alveolar glands, 55 Tunica adyentitia, 99 albuginea ovary, 2-01 testicle, 186 externa artery, 99 eye, 274 vein, 102 interna artery, 99 eye, 274 vein, 102 media artery, 99 eye, 274 vein, 102 propria, 50 vaginalis, 186 Tunica vasculosa, 202 Tunnel of Corti, 307 Turpentine, 6 Tympanic cavity, 299 lamella, 306 membrane, 298 Tympanum, 299 Tyson's glands, 199 Umbilical cord, 227 Units, functionating, 154 secreting, 154 structural, 154 Ureter, 180 Urethra female, 181 male, 181 Urinary bladder, 180 organs, 171 Uriniferous tubule, 174 Uterus blood-vessels of, 213 cervix, 210 glands, 210 lymphatics, 213 menstrual changes, 212 mucosa, 210 nerves, 213 ovuli Nabothi, 210 Utriculus, 301 Uveal tract, 276 Vacuoles, 32 Vagina, 213 Valves of heart, 97 veins, 102 Valvulae conniventes, 141 Van Gilson's stain, 15, 21 Vasa efferentia, 189 vasorum, 100 Vascular papillae, 232 Vas deferens, 195 Vater-Pacinian body, 91, 316 Veins central, 148 coats of, 102 INDEX. Veins portal, 150 valves of, 102 Venae archiformes, 178 rectae, 178 stellatae, 177 vprticosae, 201 Ventricles of larynx, 160 Vermiform appendix, 143 Vesicle blastodermic, 42 entodermal, 218 germinal, 40, 203 seminal, 195 Vestibule of vagina, 2 1 5 Villi chorionic, 223 of oviduct, 208 of placenta, 226 Pacchionian, 245 of small intestine, 139 Visceral arches changes in, 318, 319, 320 derivatives of, 319, 320 Visceral pouches, 319, 320 Visual cells, 284 Visual purple, 284 Vital phenomena, 34 Vitelline membrane, 40, 203 Vitellus, 40, 203 Vitreous humor, 288 Vocal cords, 160 Volkmann's canals, 71 Voluntary muscle, 78 Wagner, corpuscles of, 91, 315 Wandering cells, 59 Weigert's elastica stain, 21 Weigert's myelin stain, 19 Weigert-Pal myelin stain, 20 Wharton's duct, 158 jelly, 27 White blood-cells, 105 commissure, 268 fibrous tissue, 58 substance, 86, 246 substance of Schwann, 87 Wirsung's duct, 158 Wright's blood stain, 26 Xylol, 6, 22 anilin oil, 23 balsam, 23 carbol, 22 Yellow bone marrow, 73 elastic tissue, 62 fibre-cartilage, 68 spot, 287 Yolk, formative, 203 nutritive, 203 Zenker's fluid, 2 Zinn, zone of 289 Zona fasciculata, 183 glomerulosa, 183 granulosa, 202 pellucida, 203 reticularis, 184 Zone, boundary of choroid, 277 kidney, 173 of Zinn, 289 cA Companion Volume io Gould's ^Pocket 'Dictionary A POCKET CYCLOPEDIA OF MEDICINE ^ SURGERY EDITED BY GEORGE M. GOULD, A.M., M.D. Author of " Gould's Medical Dictionarie. , " Editor of " Amrican Medicine " AND WALTER L. PYLE, A.M., M.D. Assistant Sturgeon Wills Eye Hospital, Philadelphia > formerly Editor 44 International Medical Magazine/' etc. BBINO BASED UPON GOULD AND PYLE'S LARGE " CYCLOPEDIA OF PRACTICAL MEDICINE AND SURGERY" Vnlfform with Gould's Pocket Dictionary. 64mo. Flexible Leather. Gilt Edges. Hound Corners, net $1.00 ; with Thumb Index. $1.25 TIHIS book bears to Gould and Pyle's large "Cyclopedia of Medicine I and Surgery ' ' a relation similar to that which the Pocket Die* tionary bears to Gould's complete "Illustrated Dictionary." A* the Dictionary gives the derivation, pronunciation, and definition of medical words, the Cyclopedia is designed to furnish general information concerning medical subjects. Every subject, concerning which the student may desire a brief and thorough description, supplementing the mention which may be given in lectures or a general text-book, is taken up and treated thoroughly and concisely. To those desiring concise authoritative information on medical or surgical themes or who wish to look up any new term or matter of recent discovery and use, the book will prove invaluable. It includes articles on Emergencies, Hygiene, Poisons, Nursing, etc. ; describes Drugs and their Uses ; gives Treatment of Diseases ; explains Surgical Oper- ations ; contains many Prescriptions and Formulae, Tables of Differential Diagnosis, Dose Table in both English and Metric Systems, etc. P. BLAKISTON'S SON ns, 00. IE. hly .D., gist, 2.50 ion. rcrf So t ons. 50 CO., Publf.her. and Booli..ller, BRUBAKER. A TEXT-BOOK OF HUMAN PHYSIOLOGY. By ALBERT P. BRUBAKER, A.M., M.D., Professor of Physiology anu Hygiene, Jefferson Medical College; Professor of Physiology, Penna. College of Dental Surgery, Philadelphia, etc. With Colored Plates and 383 Illustrations. Octavo. Third Edition. Cloth, net, $3.00 HANSELL AND SWEET. DISEASES OP THE EYE. A Treatise on the Principles and Practice of Ophthalmic Medicine and Surgery. By HOWARD F. HANSELL, A.M., M.D., Clinical Professor of Ophthalmology, Jefferson Medical College ; Professor of Diseases of the Eye, Philadelphia Polyclinic and College for Graduates in Medicine ; Ophthalmic Surgeon, Philadelphia Hospital, etc., and WILLIAM M. SWEET, M.D., Instructor in Ophthalmology, Jefferson Medical College; Assistant Attending Surgeon and Chief of Eye Clinic, Jefferson Medical College Hospital ; Associate in Ophthalmology, Philadelphia Polyclinic, etc. With 253 Illustrations. Cloth, net, 4.00 KYLE. MANUAL OF DISEASES OF THE EAR, NOSE, AND THROAT. By JOHN JOHNSON KYLE, B.S., M.D., Clinical Professor of Otology, Rhinology and Laryngology in the Medical College of Indiana, Department of Medicine of Purdue University, Indianapolis, etc. Second Edition. With 169 Illustrations. I2mo. xxx-f- 610 pages. Flexible Leather, Gilt Edges and Round Corners, $3.0 WILLIAMS. MANUAL OF BACTERIOLOGY. By HERBER-J WILLIAMS, M.D., Professor of Pathology and Bacteriology, Medica" partment, University of Buffalo. Fifth Edition, Revised and ~ With 113 Illustrations. I2mo. Cloth,y HAWK. PRACTICAL PHYSIOLOGICAL CHEMJ PHILIP B. HAWK, M.S., PH.D., Professor of Physiolo University of Illinois. Second Edition. Octavo. 6 Color Plates and 126 other Illustrations. BLAKISTON'S MANIKINS. Twelve Manikr Throat, Eye, Lungs, Heart, Head, Liver, K#- Foot, with Descriptions. Bound in one vojr GORDON. DISEASES OF THE N7 ALFRED GORDON, A.M., M.D., AssociaX Medical College, Philadelphia. Ocj/ trations. GREENE. MEDICAL DIAG' Practitioners. By CHARLES ' fessor of the Theory and Minnesota ; Ex-Presidep' Examining Surgeons, Plates and 241 Illu- FJ STITT. PRAC" ANIMAL ' f T ur f? ( ^ 4 7 4 o I . M D Medicine! Illustrations. A * Cloth > *-so and Booksellers. .LPHIA