NORMAL HISTOLOGY AND MICROSCOPICAL ANATOMY NORMAL HISTOLOGY AND MICROSCOPICAL ANATOMY BY JEREMIAH S. FERGUSON, All.Sc., M.D. INSTRUCTOR IN NORMAL HISTOLOGY, CORNELL UNIVERSITY MEDICAL COLLEGE, NEW YORK CITY WITH FOUR HUNDRED AND SIXTY-TWO ILLUSTRATIONS IN THE TEXT, MANY IN COLOR Hi NEW YORK AND LONDON D. APPLETON AND COMPANY 1905 COPYRIGHT, 1904, BY D. APPLETON AND COMPANY PRINTED AT THE APPLETON PRESS NEW YORK, U. S. A. PREFACE THE appearance of a new text-book in a field which is so inade- quately covered as that of normal histology and microscopical anat- omy, needs no apology. The rapid development of medical science, by the extensive application of the exact methods of the laboratory, has steadily increased the importance of an accurate and somewhat extended knowledge of microscopical anatomy, until now the medi- cal student finds a ready command of the minute anatomy of the human body to be essential to the satisfactory comprehension of the sciences of physiology, pathology, bacteriology, and clinical medi- cine. Thus the work of the histological laboratory in American medical colleges has developed within the last two decades from comparative insignificance to an importance which bids fair to rival that of the dissecting room. The aim of the present volume has been to present to the reader a sufficiently comprehensive view of the subject to briefly cover the entire field in which the medical student must now become proficient. To this end unusual space has been devoted to the microscopical anatomy of those organs which serve as a field for the specialist in medicine. This is especially true of the chapters on the central nervous system, the extreme importance of the histology of these organs, as the very foundation of neurological science, being con- sidered a sufficient warrant for their extended consideration. In the selection of the illustrations, the aim has been to present exact pictures of actual sections as viewed with known magnifica- tion. Unless distinctly described as diagrams, the illustrations invariably represent actual fields in actual preparations, the greater vi PEEFACE portion of which have been used for laboratory demonstration in the class room. The magnification in each case is precisely stated. The original drawings, of which there are about one hundred, have been prepared by the author with the aid of the camera lucida. The photomicrographs, of which one hundred and twenty-two are original, were made, under the author's direction, by Mr. J. N. Lett, and a few by Mr. F. E. Ives. My thanks are due these gentlemen for their able assistance. The illustrations in color have also been drawn by the author with the aid of the camera lucida, and have been reproduced by a process specially devised for the purpose. . I desire at this time to acknowledge my indebtedness for numer- ous illustrations which have been reproduced from the literature. The author's name has in each case been appended to the legends of these figures, and a reference to the bibliography will serve as a more precise acknowledgment of their source. The list of literature has been arranged in accordance with the main subdivisions of the text, to facilitate ready reference to special topics, and in the hope that the earnest student maybe tempted to search beyond the confines of the text-book, and thus acquire a broader appreciation of the subject. To much of the recorded literature the author has been frequently indebted during his experience as a teacher, and it is a pleasure to be able to grate- fully acknowledge his indebtedness to these sources. A limited chapter on technique has been inserted at the end. The limits of the work do not permit an extended treatise on this subject, a science by itself, but it is hoped that the few fundamental facts which have been briefly stated may serve to give the student a more exact idea of the methods by which tissues are prepared for examination, and the means by which the more important results have been obtained. Finally, it is a pleasure to acknowledge the repeated courtesies which have been frequently received at the hands of the publishers. JEREMIAH S. FERGUSON. NEW YORK. CONTENTS CHAPTER PAGE I. — INTRODUCTION — PROTOPLASM — THE CELL 1 II. — EPITHELIAL TISSUES 16 III.— CONNECTIVE TISSUES 32 IV. — CARTILAGE . 48 V.— THE MUSCULAR TISSUES 53 VI.-BLOOD 67 VII. — THE VASCULAR SYSTEM 84 VIII.— THE NERVOUS TISSUES 103 IX. — PERIPHERAL NERVE TERMINATIONS — END ORGANS . . . 123 X. — THE LYMPHATIC SYSTEM ........ 140 XI. — BONE AND BONE MARROW 167 XII. — Mucous MEMBRANES — SECRETING GLANDS 184 XIIL— THE SKIN . 197 XIV.— THE RESPIRATORY SYSTEM 226 XV.— THE DIGESTIVE SYSTEM 251 XVI. — THE DIGESTIVE SYSTEM (Continued) 271 XVII. — THE SALIVARY GLANDS AND PANCREAS 304 XVIII.— THE LIVER 321 XIX.— THE URINARY SYSTEM 336 XX. — THE MALE REPRODUCTIVE ORGANS 366 XXI. — THE FEMALE REPRODUCTIVE ORGANS 393 XXII.— THE DUCTLESS GLANDS 443 XXIII. — THE NERVOUS SYSTEM — ITS TISSUES AND DEVELOPMENT . . 462 XXIV. — THE NERVOUS SYSTEM (Continued] — HISTOLOGICAL MORPHOL- OGY 478 XXV. — THE NERVOUS SYSTEM (Continued] — THE CONDUCTION PATHS OF THE CENTRAL NERVOUS SYSTEM 522 vii viii CONTENTS PAGE XXVI. — THE NERVOUS SYSTEM (Continued) — THE CENTRAL PATHS OF THE CRANIAL NERVES 543 XXVII. — THE NERVOUS SYSTEM (Continued) — THE MENINQES AND BLOOD SUPPLY 557 XXVIIL— THE EYE 563 XXIX.— THE EAR . . . .-.. 607 XXX.— TECHNIQUE 639 BIBLIOGRAPHY \ . .. v 671 INDEX , 719 LIST OF ILLUSTRATION FIG. PAGE 1. Diagram illustrating various theories of cell structure . . 2 2. Spheroidal cells 3 3. Epithelial cells containing a nebenkern 3 4. Alveolar structure of protoplasm ...... 4 5. Developing fat cells ......... 5 6. Ciliate and flagellate cells 7 7. Synctimn in a villus of the human placenta .... 7 8. Intercellular bridges in epithelial cells of the Malpighian layer of the skin 8 9. Leucocyte from human blood in active amoeboid motion . . 9 10. Various forms of cells 10 11. Direct cell division . . . . . . . . .11 12. Diagram of prophase of mitosis 12 13. Metaphase and telaphase of mitosis . . . . .13 14. Epidermis of salamander, showing cells in process of division by mitosis . . . . . . / . . . .14 15. Secretory capillaries of the gastric glands 17 16. Secretory capillaries of the pancreas . . . . . .18 17. " Terminal bars " in the epithelium of the pyloric glands . . 18 18. Polyhedral epithelium from the human liver . . . .21 19. Squamous epithelium or endothelium ...... 22 20. Columnar epithelium from pyloric region of the human stomach 22 21. Cuboidal epithelium from the rete testis of a rabbit ... 23 22. Columnar ciliated epithelium from the epididymis of a rabbit . 23 23. Glandular epithelium 24 24. Goblet cells of Lieberkiihn's crypts ...... 25 25. Diagram showing arrangement of cells in the preceding figure . 25 26. Stratified epithelium from human esophagus .... 27 27. Keratized epithelium of the skin 28 28. Transitional epithelium from the ureter of an infant ... 29 29. Isolated cells of human urine ....... 29 30. Pseudo-stratified columnar ciliated epithelium from a bronchial tube of man .......... 30 31. Diagram showing connection of epithelial cells of pseudo-stratified ciliated epithelium with the basement membrane . . .30 32. Embryonic connective tissue, early stage ..... 32 33. Embryonic connective tissue, later stage 32 34. Areolar connective tissue 33 ix x LIST OF ILLUSTRATIONS FIG. PAGE 35. Plasma cells of connective tissue 34 36. Spindle-shaped connective tissue cells . . . . . . 34 37. Pigmented connective tissue cells 35 38. Granule cells of connective tissue ....... 35 39. Gelatinous connective tissue from the umbilical cord . . . 37 40. Dense fibrous tissue from the tendon of an ocular muscle . . 39 41. Coarse elastic fibres from the ligamentum nuchse of an ox . . 40 42. Transection of a fasciculus of the ligamentum nuchae of an ox . 40 43. Adipose tissue . . ' 41 44. Fat cells from a teased preparation of adipose tissue . . 42 45. Adipose tissue, treated by osmium tetroxid . . . .42 46. Developing adipose tissue ........ 43 47. Reticular tissue of a lymphatic node ...... 44 48. Reticular tissue from the gastric mucosa ..... 45 49. Lymphatic nodules and cords, low magnification .... 46 50. Lymphoid tissue, high magnification . . .... 47 51. Hyaline cartilage, from the trachea of a child .... 49 52. Cells and matrix of hyaline cartilage . ... . . 50 53. Elastic cartilage from the human epiglottis . .... ... 51 54. White fibrocartilage • . .... . . . . 52 55. Smooth muscle fibres, isolated . .... . . 54 56. Smooth muscle fibres from wall of the human intestine, longi- tudinal section . . . . . . ;. ... 55 57. Smooth muscle fibres from wall of the human intestine, tran- section . ...-.- . . .- . . . . . 55 58. Cardiac muscle cells . . . . . . . . .56 59. Human cardiac muscle, longitudinal section . . . .57 60. The same, more highly magnified . ... . . .58 61. Transection of a papillary muscle of the human heart ... 58 62. Developing cardiac muscle from a human embryo at the seventh month . . . . . 58 63. Developing muscle fibres^ striated, from the buccal muscles of a fetal pig . . . 4 . . ... . .59 64. Striated muscle fibres, showing the sarcolemma . . . .60 65. Isolated fragments of striated muscle fibres . . . . .61 66. Striated muscle fibres of dog, transection 61 67. Striated muscle fibre, longitudinal section 62 68. Muscle fibre of a crab, showing ultimate fibrillae ... 62 69. Muscle fibrils from the wing muscles of a wasp . . .63 70. Striated muscle fibres of the dog, injected, longitudinal section . 64 71. Striated muscle fibres of the cat, injected, transection ... 64 72. Portion of a transection of a large tendon 65 73. Freshly prepared, unstained specimen of human blood ... 68 74. Blood cells from a specimen of freshly drawn, unstained human blood . 69 75. Red blood cells, showing action of water 70 76. " Vaso-formative " cells from the mesentery of a rabbit . . 72 LIST OF ILLUSTRATIONS xi FIG. PAGE 77. " Vaso-formative cell " 72 78. Nucleated red cells from the blood of a frog . Plate, facing 74 79. Nucleated red blood cells from the marrow of a human rib. Plate, facing 74 80. Group of cells from normal human blood . . Plate, facing 74 81. Leucocytes in mitosis . . . . . . . . .76 82. Group of platelets from the human blood ..... 80 83. Fibrils of fibrin 82 84. Hemoglobin crystals ......... 83 85. Hemin crystals 83 86. A small artery . . . . . . . . .85 87. External carotid artery of a child 86 88. Transection of the wall of a child's aorta . . . ^ . .87 89. Transection of the coeliac axis of man . . . ... .88 90. Group of small blood vessels . . . . . .89 91. Capillary network connecting an arteriole and venule of the omentum . . . . . . . .... 90 92. Capillary vessel of frog's mesentery . . . . ; .91 93. " Sinusoids " . .... 92 94. Precapillary arteriole and venule .« . 93 95. Transection of the human vena cava . . . . . . 94 96. Transection of an arteriole and venule . . . ... 96 97. Parietal pericardium of a child . . . ... .98 98. The human endocardium . . . . . ... 98 99. Radial sections of the human mitral valve . . . - . . 99 100. Diagram of a neurone ......... 104 101. Unipolar ganglion of a frog ........ 105 102. Isolated nerve cells from the human spinal cord . . . . 105 103. Arkyochrome nerve cell . . 106 104. Stichochrome nerve cell . . . . . . . . 107 105. Apyknomorphous stichochrome nerve cell 108 106. A nerve cell of Purkinje, arkyostichochrome variety . . . 108 107. Arkyochrome, caryochrome, and cytochrome nerve cells of the cerebellar cortex . . . . . . . 109 108. A nerve cell .110 109. Intracellular network Ill 110. Golgi cell, type I 112 111. Golgi cell, type II . . . 113 112. Nerve fibres in transection . . . . . . • .115 113. Nerve fibres, in longitudinal and transverse section . .116 114. Transection of the sciatic nerve . . . . . . .118 115. Portion of human Gasserian ganglion ...... 120 116. Nerve cell of the Gasserian ganglion of man .... 121 117. Schematic representation of a spinal ganglion .... 121 118. Nerve endings in the epithelium of the larynx .... 123 119. Tactile cells in epithelium ..124 120. Schematic representation of a taste bud 125 xii LIST OF ILLUSTKATIONS FIG. 121. Taste bud from human tongue . . 120 122. Tactile corpuscle of Meissner 127 123. Nerve endings of a tactile corpuscle of Meissner . . . . 128 124. Rumni's end organ . , •-..-- . ... ' . . . . 128 125. End bulb of Krause . ... . . . . . 128 126. Genital corpuscles . ' . . . . . ... 127. Pacinian corpuscle from the mesentery of a cat . . . . 129 128. Nerve endings of a Pacinian corpuscle . . . . . . 130 129. Pacinian corpuscle whose axial fibre has lateral processes . . 130 130. Pacinian corpuscle, showing network of spiral elastic fibres . .131 131. Corpuscle of Herbst . ... . . . . . 131 132. Corpuscle of Grandry . . . * 132 133. Golgi-Mazzoni corpuscles 133 134. Motor nerve endings in striated muscle . . . . .134 135. Muscle spindle in transection . ... . . . 135 136. Nerve endings of a muscle spindle . ... . 136 137. Neuro-tendinous end organ or tendon spindle of Golgi . . . 137 138. Nerve endings in cardiac muscle . » ; . » . . 139 139. Nerve endings in smooth muscle . '. • . .. . . . 139 140. Subcutaneous lymphatic vessel of a fetal pig .... 142 141. Growing end of a developing lymphatic vessel .... 143 142. Lymphatic and blood vessels in the hilum of a human lymphatic node . . ...../, . . . . 143 143. Lymphatic capillary, showing nerve endings ..... 144 144. Transection of the pericardium . , , . . . . 145 145. A vascular synovial villus . . . . . • . . . . 14*3 146. A lymphatic nodule . . ; . . ; . . .147 147. Transection of a cervical lymphatic node ..... 149 148. Transection of mesenteric lymphatic node . . . . .150 149. Diagram of the blood vessels of a lymphatic node .... 152 150. A hemolymph node . . .• * , . . . . 154 151. Horizontal section through the faucial tonsil of a child . . 155 152. Epithelium of a crypt of the tonsil ... . . .156 153. Lingual tonsil of man . . 157 154. Section through several lobules of the thymus .... 158 155. A corpuscle of Hassal . . . . . . . 159 156. From the spleen of a child . 161 157. Types of cells from a smear preparation of the pulp of the human spleen . . . •*••,'• • . Plate, facing 162 158. Types of cells from a smear preparation of the marrow of a human rib Plate, facing 162 159. Three Malpighian corpuscles of the human spleen . . .163 160. Diagram of a lobule of the spleen 164 161. Origin of a vein in the splenic pulp 165 162. Transection of compact bone 169 163. Longitudinal section of compact bone 169 164. A section of red marrow of human bone 172 LIST OF ILLUSTRATIONS xiii FIG. PAGE 165. Group of cells from red marrow of a human rib . . . . 173 166. Primary changes in intracartilaginous bone formation . . 176 167. Developing bone 178 168. Transection of a developing rib . . . . . .180 169. Intramembranous bone formation ....... 182 170. Diagram of a mucous membrane . . . . . . .185 17.1. Mucous and serous secreting tubules . . . . . .187 172. Simple tubular glands 190 173. Convoluted tubular glands (coil glands) 191 174. Reconstruction of a compound tubular gland . . . .192 175. Reconstruction of tubulo-alveolar gland ..... 192 176. Reconstruction of the terminal ducts of a tubulo-acinar or race- mose gland .......... 192 177. Compound saccular glands . . . . . . . .194 178. The epidermis 198 179. Transection of the skin of the human finger ..... 200 180. Epidermis, showing " epidermal fat " 202 181. Abdominal integument of an infant ...... 206 182. Sudoriparous gland of human finger ...... 207 183. Finger nail in longitudinal section ...... 208 184. Transection through .the margin of a finger nail .... 209 185. Five stages in the development of a human hair .... 212 186. Skin of infant's arm, showing small immature hair follicles in transection 213 187. The human scalp 217 188. Transection of a hair near the middle of the root sheath . . 217 189. The human scalp, showing hairs in longitudinal and oblique section . . . . . . . . . . .218 190. Regeneration of hair 221 191. Sebaceous glands . . . 222 192. Reconstruction of cutaneous blood vessels 224 193. Respiratory mucosa of the human nose . . . . . 227 194. Olfactory mucosa of a cat ........ 229 195. Olfactory mucosa of man 230 196. Nerve endings in the olfactory mucosa . . . . .231 197. Vertical section through lateral wall of the human larynx . . 232 198. Transection of the wall of a child's trachea 234 199. Reconstruction of a tubulo-alveolar gland of the human trachcal mucosa ........... 235 200. Large bronchus .236 201. Bronchus from the human lung 238 202. Section of child's lung, alveoli and bronchioles .... 240 203. Section of child's lung, small bronchi and bronchioles . . . 241 204. Section of child's lung, terminal bronchioles .... 242 205. Two alveoli of a child's lung 243 206. Transection of the pleura .... .244 207. Section of pleura of man, elastic tissue 244 XIV LIST OF ILLUSTRATIONS FIG. PAGE 208. Diagram of a lobule of the lung 245 209. Lung of child, origin of a pulmonary venule .... 246 210. Injected lung of a dog . . 247 211. From the central portion of the preceding figure .... 248 212. The lip of an infant ........ .252 213. Axial section of human molar tooth . . . . . . 254 214. Longitudinal section of the neck of a child's tooth and the adjacent alveolus .......... 255 215. Dentine and enamel . . . 256 216. Enamel prisms in transection ....... 258 217. Dentine and cementum ......... 259 218. Developing tooth from a human embryo 260 219. Dental anlages from a human fetus . . . . . .261 220. Developing tooth from a human fetus 262 221. Developing tooth from an infant's jaw ..... 263 222. A portion of the preceding figure, more highly magnified . . 264 223. Lateral half of a coronal section of dog's tongue .... 266 224. Filiform papillae of dog's tongue . . . . . . 267 225. Circumvallate papillae of human tongue . . . . . 268 226. Surface view of Auerbach's plexus . . • . . . . 272 227. Longitudinal section of the human esophagus .... 274 228. Superficial glands of the human esophagus 276 229. Transection of the wall of the human stomach near the pyloric orifice . " . 277 230. Longitudinal section of the fundus glands of man . . . 279 231. Mucosa of the fundus region of the dog's stomach . . . 280 232. Transection of three secreting glands of the fundus region of the human stomach . . . . . . . . . 281 233. Secretory capillaries of the fundus glands of the dog's stomach 282 234. Mucosa of the pyloric region of the human stomach . . . 283 235. Blood vessels of the stomach . . 285 236. Longitudinal section of the human small intestine . . . 287 237. Central portion of a Peyer's patch . ' ." . . . 289 238. Villi from the small intestine of a dog 291 239. The human pylorus . . . 293 240. Reconstruction model of a Brunner's gland 294 241. Brunner's glands in the duodenum of man . . . . . 295 242. Blood vessels of the small intestine ...... 296 243. Intestinal mucosa of the frog during absorption of f at . . . 298 244. Apex of an intestinal villus during absorption of fat . . . 299 245. Mucosa of the large intestine of man . . . . .' . 300 246. Transection of the vermiform appendix . . . . . 302 247. A small mucous gland from the oral mucosa 304 248. Corrosion model of an interlobular duct and branches, from the human submaxillary gland . 305 249. Intercalary ducts and acini of the human submaxillary gland, reconstruction . 306 LIST OF ILLUSTRATIONS xv FIG. PAGE 260. Group of serous acini, from the human submaxillary gland . 307 251. Acini and ducts of the sublingual gland of man .... 309 252. Secretory capillaries in mucous acini 310 253. Diagram of a mixed salivary gland 310 254. From the human parotid gland 311 255. Duct and acini of the human submaxillary gland . . . 312 256. A section of the sublingual gland of man 313 257. Reconstruction of a duct and acini of the sublingual gland of man 314 258. Nerve endings in a salivary gland . . . . . .314 259. Several lobules of the human pancreas 315 260. Reconstruction of a terminal duct and its acini, from the human pancreas ........... 316 261. Acini of human pancreas . . . . . . . .317 262. Cells from the pancreas of necturus in various stages of secretion 318 263. From the human pancreas . . . . . . . .319 264. A lobule of the pig's liver, transection . . . . .321 265. From a section of turtle's liver 322 266. Reticulum of dog's liver 323 267. Stellate cells of von Kupfer 323 268. A lobule of a pig's liver in longitudinal section .... 325 269. A lobule of the human liver 326 270. Bile capillaries . ' 327 271. Intralobular and interlobular bile ducts ..... 327 272. Types of cells from the normal human liver .... 328 273. A portal canal of the human liver ...... 329 274. Rabbit's liver, injected 331 275. A sublobular vein 332 276. Intralobular nerve fibres 333 277. From section through the wall of the gall bladder . . . 334 278. Reconstruction of the wall of the gall bladder .... 335 279. Diagram of the structure of the kidney 338 280. Reconstruction of uriniferous tubule ...... 340 281. Reconstruction of a glomerulus of the human kidney . .341 282. The cortical labyrinth of the human kidney 342 283. Transection of a medullary ray ....... 344 284. Longitudinal section of a convoluted tubule ..... 345 285. Group of tubules from a transection of a Malpighian pyramid . 347 286. Cortex of the human kidney, medullary ray in oblique section . 349 287. Ducts of Bellini 350 288. Distribution of the left renal artery . . . . . .353 289. Cortex of an injected human kidney ...... 354 290. Transection of an injected kidney 355 291. Nerve endings in a convoluted tubule of a frog's kidney . . 357 292. Cast of pelvis, infundibula, and calices of the kidneys of man . 358 293. Transection of a human ureter 359 294. Transection of the wall of a child's bladder 361 295. The mucosa of a child's bladder . 362 xvi LIST OP ILLUSTRATIONS FIG. PAGE 296. Transection of the female urethra . . . . . . 364 297. Transection of a child's penis ....... 367 298. A helicine artery 368 299. Erectile tissue of the penis 369 300. Human semen 370 301. Human spermatosomes . . . ' . . . . . .371 302. Spermatozoa of various animals . ... . . . 372 303. Testicle, with its system of efferent passages . . - ... . 373 304. Tortuous seminiferous tubules . . .. v' . . . 374 305. Diagram of successive stages of spermatogenesis . •'••'. . . 376 306. Seminal tubule of man in transection 377 307. Three phases of spermatogenesis ....... 378 308. Dorsal surface of a rabbit's testis . . . . . . .381 309. Portion of the wall of an efferent ductule 381 310. Efferent ductules of the epididymis . . . . . .382 311. Tubules of the epididymis in transection . . . ... 383 312. Transection of the vas deferens . 385 313. The pampiniform plexus 386 314. A section through the wall of the seminal vesicle of man . . 387 315. Reconstruction of the prostate gland of man . . . . 389 316. Alveoli of the human prostate gland . .. . , . 390 317. Prostatic genital corpuscles . ' . : -. , ... . 391 318. Reconstruction of Cowper's gland . . . . " , . 392 319. A section of Cowper's gland . . . . . . . .392 320. From the ovarian cortex of an infant . . . . . . 395 321. Ovum containing yolk nucleus ... . . . . 396 322. Diagram of reduction during maturation of the ovum . . . 398 323. -Ovarian cortex of a new-born kitten . ... . . 399 324. Graafian follicle of the human ovary . . ... . 401 325. Graafian follicle of the human ovary, somewhat more advanced than the preceding ......... 402 326. A nearly mature Graafian follicle 403 327. A mature Graafian follicle 404 328. The peripheral portion of a corpus luteum . . . . . 406 329. Corpora lutea 407 330. A corpus albicans 408 331. The epoophoron 409 332. The Wood vessels of the ovary . . . . . . .410 333. Transections of the human oviduct 412 334. The ampulla of the human oviduct 413 335. The mucosa of the oviduct ........ 414 336. Transection of the uterus of an ape 416 337. Transection through the body of the human uterus . . .417 338. Uterine mucosa of a girl of sixteen years 418 339. Transection of the uterine mucosa 419 340. Cervix uteri of a girl of sixteen years 420 341. A gland of the cervix uteri in longitudinal section . . . 421 LIST OF ILLUSTRATIONS xvii FIG. PAGE 342. Mucosa of the menstruating uterus 422 343. Diagram of the structure of the human placenta .... 425 344. Transection of the wall of the human uterus, with the placenta in situ 427 345. The amnion and chorion at the fifth month 428 346. Chorion of human placenta at the seventh month .... 429 347. Chorionic villi from the human placenta at full term . . . 430 348. Human decidua serotina at the seventh month . . . .431 349. Margin of the human placenta at full term ..... 432 350. Transection of the umbilical cord 433 351. Section of the vaginal wall . . . . . . . 435 352. Labium minus of an infant . . 436 353. Human mammary gland, active . . . . . . . 439 354. Reconstruction of an intralobular duct and its acini, from the active mammary gland . . . . . . . . 440 355. Mammary gland in the resting condition 441 356. Transection of the human adrenal . . . . . . 444 357. Same as above, more highly magnified . . . . . 446 358. The blood vessels of the adrenal . . . . . . .449 359. Vesicles of the human thyroid gland ...... 452 360. Aberrant thyroid tissue . . . . . . . .455 361. Transection of a parathyroid gland . . . . . 456 362. Central portion of above, more highly magnified . . . . 457 363. The carotid gland .459 364. The coccygeal gland •. . - : .459 365. The hypophysis cerebri . . . . . .... 460 366. Neuroglia from spinal cord ........ 463 367. A long-rayed astrocyte .......... 464 368. A short-rayed astrocyte, or mossy cell ...... 465 369. Neuroglia cells and fibres . . • 466 370. Diagram of a neurone 467 371. Golgi cell, type I .471 372. Golgi cell, type II 472 373. Cerebral vesicles of a chick . . . ... . . .473 374. Diagram of the migration of neuroblasts toward the marginal veil and dorsal nerve root, early stage . . . .. . 476 375. Transection of the spinal cord of a human embryo of four weeks 476 376. Transection of the spinal cord of an embryo chick . . . 477 377. Transection of the spinal cord, third sacral segment . . . 482 378. Transection of the spinal cord, fifth lumbar segment . . . 483 379. Transection of the spinal cord, eighth thoracic segment . . 484 380. Transection of the spinal cord, seventh cervical segment . . 484 381. Transection of the spinal cord, fourth cervical segment . . 486 382. Transection of the medulla oblongata, at the level of the motor decussation 489 383. Transection of the medulla oblongata at level of the inferior olivary body .......... 491 1* xviii LIST OF ILLUSTRATIONS FIG. PAGE 384. Transection of the medulla oblongata at the mid-level of the inferior olivary bodies ........ 493 385. Section through the lower border of the pons Varolii . . . 495 386. Section through the middle of the pons Varolii .... 497 387. Section of the pons Varolii at the level of the trigeminus nerve . 498 388. Section of the brain stem at the level of the cerebral border of the pons Varolii . . .-•.•' . .*'. ". . . . . 500 389. Section of the brain stem at the level of the posterior corpora quadrigeraina . ..-•» . v . . . . . . . 501 390. Section of the brain stem at the level of the posterior border of the red nucleus 503 391. Section of the brain stem at the mid-level of the red nucleus . 504 392. Section of the brain stem at the mid-level of the optic thalamus 505 393. Frontal section through the internal capsule and corona radiata 507 394. Scheme of the motor area of the cerebral cortex, showing the effect of various staining methods ... . . . 508 395. Cortex cerebri, motor area " . . 511 396. Cortex cerebri, parietal lobe . . . . . . . ... 512 397. Cortex cerebri, olfactory region . ... . . . 513 398. Transection of the hippocampal gyrus ...... . .514 399. Diagram of the cornu Ammonis, Golgi's stain . . . .515 400. Cortex cerebelli . .. , . C . . . . . ... .517 401. A Purkinje cell of the cerebellar cortex ... . .518 402. A Purkinje cell, highly magnified . . . . . .519 403. Diagram of the internal capsule . . . . . . . 523 404. Motor paths of the spinal cord as shown in a case of descending degeneration . . . . . ... . . . 524 405. Ganglion of a dorsal nerve root, Golgi's stain .... 526 406. Bifurcation of central processes of the peripheral sensory neu- rones of the vestibular nerve 527 407. Dorsal root zones of the spinal cord 529 408. Diagrammatic representation of the tracts of the spinal cord and their relation to the paths of the medulla oblongata . . 530 409. Reconstruction of the medulla oblongata and mid-brain of a child 532 410. Diagram of the origin and relations of the peripheral motor and sensory neurones ......... 534 411. Sagittal section of the medulla oblongata and midbrain . . 539 412. Diagram of the fibre paths of the spinal cord . . . .541 413. Section of the brain stem, at the level of the superior corpora quadrigemina 553 414. Section of the brain stem, at the level of the optic chiasm . . 554 415. Olfactory lobe and bulb . . 555 416. Diagram of the relations of the neurones of the olfactory nerve and olfactory bulb 556 417. Anterior segment of a child's eye .... . . . 564 418. Meridional section of the cornea 566 419. Corneal corpuscles . . 567 LIST OF ILLUSTRATIONS xix FIG. PAGE 420. Corneal corpuscles, isolated ........ 568 421. Meridional section of the choroid coat of the eye . . . .571 422. Ciliary body and adjacent structures, meridional section . . 573 423. Developing eye in section, diagrammatic ..... 579 424. Schematic reconstruction of the developing eye- .... 579 425. Retina of a child's eye, meridional section ..... 580 426. Pigmented epithelium of the retina ...... 580 427. Isolated rod and cone cells ........ 582 428. Rod and cone bipolars of the human retina 583 429. The layers of the retina near the margin of macula lutea . . 584 430. The layers of the retina midway between the macula lutea and the ora serrata ......... 585 431. Horizontal cell of the retina 587 432. Amacrine cells or spongioblasts ....... 588 433. A nerve cell of the large ganglion cell layer of the retina . . 589 434. A fibre cell of Muller 590 435. Transection through the fovea centralis retinae .... 592 436. Entrance of the optic nerve 593 437. Lens fibres 594 438. Nuclear zone at the margin of the crystalline lens . . . 595 439. The intrinsic blood vessels of the eye 598 440. Vertical section through the upper eyelid ..... 602 441. A lobule of the lachrymal gland . . . . . . . 605 442. Transection of the lobule of the external ear .... 608 443. External auditory canal 609 444. The middle and internal ear of a guinea-pig 610 445. Transection of the tympanic membrane ..... 612 446. The margin of the tympanic membrane ..... 613 447. The auditory ossicles 614 448. Cavity and ligaments of the tympanum, viewed from above . 615 449. Transection of the Eustachian tube, diagrammatic . . . 617 450. The bony labyrinth 619 451. The membranous labyrinth ........ 620 452. The margin of the macula sacculi 621 453. Nerve endings in the macula . . . . . . .621 454. Transection of a semicircular canal 623 455. Axial section of the cochlea ........ 624 456. Axial section through a turn of the cochlea ..... 627 457. Radial section through Corti's organ 630 458. Diagram of Corti's organ ........ 633 459. Axial section through Corti's organ, showing terminal nerve fibrils 635 460. Scheme of the vascular supply of the internal ear .... 636 461. Scheme of the vascular terminations in the wall of the cochlear canals 637 462. Method of preparing a paper box for parafin embedding . . 651 0 NORMAL HISTOLOGY CHAPTEE I INTRODUCTION-PROTOPLASM— THE CELL Histology is concerned with the finer structure of living tis- sues. It may thus include the study of both animal and vegetable tissue. Animal histology, which deals with the structure of animal tissues, is closely allied to the science of microscopical anatomy, which considers the structure of the organs. All tissues are composed of a living substance called proto- plasm, which is of very complex structure. It can usually be considered as being made up of certain structural units. These structural units are the animal cells. Protoplasm is capable of all the functions of life — metabolism, motion, growth, development, and reproduction. Thus all proto- plasm owes its existence, as does the individual organism also, to a primitive cell mass, the germ cell. This germ cell assumes a more or less definite form, which we may consider as the true cell type — the typical cell. The description of the ovum, the germ cell of man, will serve to present those structures which characterize the typical animal cell. THE TYPICAL CELL.— The term cell, as thus applied, com- prises a circumscribed mass of protoplasm. It is enclosed by a membrane of somewhat denser consistence, the cell wall or cell membrane, which is thickened by a narrow outlying, and often radiating, zone of condensed or otherwise altered protoplasmic substance, the exoplasm. The inner portion of protoplasm, that which surrounds the nucleus and is contained within the cell wall, in contradistinction to the peripheral exoplasm, is called endoplasm. The term cytoplasm, though used by Kolliker as synonymous with protoplasm, is now limited, in accordance with the usage of Strasburger, to the entire protoplasmic substance of the cell, ex- clusive of its nucleus. 2 1 INTRODUCTION— PROTOPLASM— THE CELL The cytoplasm consists of a fluid matrix in which a finely granular reticulum may be demonstrated. Other though less constant structures are found within the cytoplasm. Such are the microsomes, coarse gran- ules which probably belong to the structure of the proto- plasm itself; vacuoles, which occur as spherical inclosures of a more fluid substance; paraplasm,* a generic term which, in various cells, may include all sorts of foreign bodies, pigment, bacteria, in- gested particles of nutritive material, etc. The nucleus is inclosed by a highly chromatic nuclear membrane, within which is an achromatic ground sub- stance or nuclear matrix, a THEORIES OF CELL STRUCTURE. fine network of achromatic 1, alveolar structure; granules occur only &'»*» fibrils, and a COarse at the angles formed by the alveoli. £, filar network of cJiromatin fibrils, structure, showing filar and interfilar mass. The cnromatin fibrils here Ine centrosome (a diplosome) is represented in this portion; it is surrounded by a clear at- and there present Small knot- traction sphere. 3, granular structure; coarse like thickenings, Or JcaryO- microsomes irregularly disposed. This portion -, • -, contains three foreign bodies which have been somes'> wmc especially included by the cell, a streptococcus, a crystal, prone to OCCUr just within and a spheroidal pigment mass. 4, the alveolar ^e nuclear walls are formed by regularly arranged micro- somes; a vacuole is shown in this section. 5, reticular structure. The cell is inclosed by a cell membrane, and contains a central nucleus in which are shown the nuclear membrane, indistinct linin fibrils, ic Substance, the deeply stained chromatin in coarse threads and which is closely related Fio. 1. — DIAGRAM ILLUSTRATING THE VARIOUS membrane, at . , „ . tne periphery Ol the nucleus. Within the nucleus is also a o-nhprnlp of rhrnmat to irregular masses (karyosomes), and a centrally ,, , . -, situated rmoipniiis m- nias™™™™ the chromatic nuclear net- situated nucleolus or plasmosome. work. The typical cell also includes, usually at some point near the nucleus, a small chromatic dot or centrosome, which is surrounded by a clearer area, the attraction sphere. These bodies are closely * This term has been used by von Kupffer in an entirely different sense, as synonymous with exoplasm. THE TYPICAL CELL FIG. 2. — VARIOUS SPHE- ROIDAL CELLS. 1, ovuin, from the ovary of a child ; #, spermatocyte ; and 3, spermatid, from the testicle of a rabbit. Hema- tein and eosin. x 750. connected with the processes of reproduction by cell division, karyokinesis or mitosis. In fact, as the nucleus is to be considered as the controlling center of cell activity, growth, and development — in short, of con- structive metabolism — so also is the centro- some, in all probability, to be considered as the dynamic center of the cell, controlling the formation of those mitotic figures which finally result in cell division. A small, spheroidal, distinctly chromatic body is also frequently seen in the cyto- plasm in the vicinity of the nucleus. This is the true u nebenkern " of Biitschli, which has been shown by Platner and La Valette St. George to be the remains of the mitotic nuclear spindle. At times it has a dis- tinctly fibrillar structure. Protoplasm. — The finer structure of pro- toplasm, while certain fundamental facts may be readily observed, is open to varied interpretation by differ- ent observers. These interpretations have evolved several theories to explain the minute structure of this substance. It is certain that protoplasm, though at times perfectly homogeneous and appar- ently structureless, upon careful examination usually presents a fine reticulum. It is equally certain that this reticulum is not merely the product of coagulation by strong fixing reagents, for it has been fre- quently observed in living cells. Protoplasm may therefore be said to consist of a reticular net- work and an intervening, fluid, ground substance. To the former Leydig gave the name spongioplasm, to the latter hyaloplasm.* Neither of these structures is, how- ever, of homogeneous, nor even of constant composition. The * Filar mass and interfilar mass, according to Fleming's theory of the fibril- lar structure of protoplasm. The terms mitome and paramitome are also equivalent. FIG. 3. — EPITHELIAL CELLS FROM THE AMPHIBIAN PANCREAS. N, nebenkern. Highly magnified. (After Matthews.) INTKODUCTION— PROTOPLASM— THE CELL spongioplasm frequently presents a finely granular appearance, which is so universal in its occurrence as to have led to the pro- mulgation of the now discarded granular theory of protoplasmic structure, so ably supported by Altmaim. These fine granules, termed microsomes by Hanstein, as well as the coarser granules of paraplasm, appear to be strictly confined to the spongioplasmic reticulum, the larger and therefore more frequently observed granules occurring at the intersections of this network (Biitschli).* There is still some doubt as to the exact character of the reticulum and its matrix, and as to the microscop- ical substances of which they are the optical expression. All observers are now practically agreed upon the fluid nature of the matrix, or hyaloplasm ; the interpretation of the network is still the subject of discussion. The fibrous nature of this network, though not explaining all the pecul- iarities of protoplasmic structure, had come to be quite generally ac- cepted, until the convincing studies of Biitschli upon the structure of protoplasm as related to that of cer- tain microscopic oil foams, coagulated proteid solutions, etc., showed that the reticular structure of protoplasm could be almost exactly simulated by the artificial combination of fluids of different consistence to produce a microscopic foam. Biitschli there- fore regards protoplasm as composed of fluid alveoli of not over 0.001 millimeter in diameter, between and surrounding which is a denser fluid coating, whose section produces the characteristic optical appearance of a true reticulum. That this theory possesses at least a considerable essence of truth is evident from the very able and conclusive demonstrations of its author. Jfe FlG. 4. — AN EPIDERMAL SUPPORTING CELL OF LUMBBICUS TERRE9TUIS, ILLUSTRATING THE ALVEOLAR STRUCTURE OF PROTOPLASM. c, cuticle. Very highly magnified. (After Biitschli.) * London, 1894. THE TYPICAL CELL 5 Nevertheless, distinct fibrils are often to be found in proto- plasm, and frequently form an essential part of the cell structure. In this list one finds the neurofibrils of nerve cells which Apathy and Bethe have demonstrated to be frequently continuous from one nerve cell to another ; the longitudinal contractile fibrillae of muscle fibers ; the intercellular bridge fibrils of epithelium, which can often be traced through two or three adjacent cells ; and finally the intracellular " rod fibrils " of many epithelial cells. J IIG. 5.— DEVELOPING Protoplasm frequently also contains spherical FAT CELLS. vacuoles, which are formed by the accumulation The fat droplets, of fluid droplets whose consistence differs from after extraction with that of the surrounding protoplasm. These ^^ ±££ droplets may be the result of metabolic activity Hematein and eosin. within the protoplasm itself ; they are frequently x 55°- of a fatty nature. Other products of cellular metabolism which appear within the cell protoplasm are the secretory granules — zymogen, mucinogen, glycogen, etc. — which are formed within the protoplasm of secret- ing cells. The nucleus differs somewhat in structure from the surround- ing cytoplasm. It contains a fluid nuclear matrix, or nuclear sap, embedded in which are a chromatic and an achromatic nuclear network. The achromatic reticulum is composed of very fine linin threads, which form an exceedingly delicate mesh. The nuclear chromatin may or may not exist in the form of a network. Its condition is very variable, and apparently is more or less dependent upon the state of cellular activity as regards the processes of reproduction. The chromatin may thus form a single thread-like fibril of considerable length, which, under high mag- nification, is seen to be composed of small discoid granules, the chromomeres of Fol. During mitosis the chromatin thread is broken into a given number of V-shaped segments or chromosome* ; the number of these chromosomes varies in different animals, but is definite for each species. In the resting stage, the phenomena of karyoki- nesis having been completed, the daughter segments are capable of reuniting to form a single thread, or, on the other hand, they may disintegrate into still smaller granular particles. The gran- ules thus formed are frequently scattered along the linin threads, 6 INTKODUCTIOX— PEOTOPLASM— THE CELL and often accumulate in knot-like groups to form the karyosomes, the larger of which closely simulate the plasmosomes, or true nucleoli. The chromatin granules are also prone to collect be- neath the nuclear membrane, to the inner surface of which they adhere. Chromatin possesses a strong affinity for basic dyes.* Its gran- ules and threads are often so closely packed as to give to the nucleus the appearance of a solid basophile mass. This condition, however, is only found in the resting nucleus; in those nuclei which are undergoing mitotic changes the chromatin granules are less abundant, less closely packed, and the achromatic portions form a proportionately larger part of the nucleus. The nucleolus closely resembles the chromatin in its staining properties. It forms a small spherical but solid basophile mass. The nucleolus is described as a plasmosome, to distinguish it from its simulacra, the larger karyosomes. The nucleolus entirely dis- appears during cell division. The nuclear wall is likewise only found during the resting stage of the cell as regards the phenomena of karyokinesis. It closely resembles the chromatin, and, though somewhat variable in its staining properties, is, as a rule, strongly basophile. It is said to be composed of amphipyrenin (Schwarz f ). Cell Growth, Development, and Differentiation.— The germ cell is not only capable of reproducing itself by karyokinesis, but, in the multicellular animals, is also capable of forming the tissue cells which are so specialized or differentiated as to be no longer capable, like the germ cell, of reproducing the animal species, but which may produce other similar cells to form the various tissues of the body. In such tissue cells there occur many modifications of the typical cell structure. The exoplasm may be arranged as fibrillae to form cilia, flagella, intercellular bridges, etc. The shape of the cell may also be altered from its typical contour to a squamous, columnar, polyhedral, fusiform, or even a stellate form, and the cell may be subject to great variations in size. The endoplasm likewise presents great variations in structure. * Heidenhain describes the basophile chromatin as basichromatin, in contra- distinction to the slightly acidophile properties of the exceedingly fine granules which he demonstrated as forming the linin threads, and which he described as oxychromaiin or lanthanin. f Breslau, 1887. THE TYPICAL CELL FlG. 6. — ClLIATE AND FLAGELLATE CELLS. A, ciliated cells isolated from the trachea of a cat ; £, human spermatozoa — ./, in surface view ; 2, in profile. Ex- amined fresh in normal saline solution, x 550. It may be reticular, alveolar, or homogeneous ; it may also con- tain fibrillae of considerable length, either straight or coiled, which may even be continued through the exoplasm and into adjacent cells. The nucleus is also subject to great variations in size, in shape, and in the arrangement of its chromatic fibrils. These changes are in great measure dependent upon the processes of karyoki- nesis. As a result of the processes of cell multiplication, which begin with the germ cell, new tissue cells are formed, which exist either as isolated cells, in relation with their neighbors by contact only, or as a continuous protoplasmic mass or syncytium, which is formed by fusion of the exoplasm of adjacent cells (Studnicka *). The true syncytium is usually found in embryonic tissues ; the mature tis- sues, on the other hand, possess a distinctly cellular character. The differentiation of cells in the course of development results in the formation of special tissue groups, the protoplasm of each group presenting certain common char- acteristics. These tissue groups form the primary tissues of the body. Thus we distinguish : (1) epithelial tissues, (2) connective tissues, (3) muscular tissues, (4) nervous tissues, (5) blood, (6) lymph. Still further differentiation may occur within each group. Thus, for example, connective tissue may be fibrous, elastic, areolar, reticular, cartilaginous, bony, etc. These changes, apparently taking place The connective tissue inclosed / by the syncytium contains under the influence of the nucleus, are three capillary vessels. Hema- more pronounced at the periphery of the cell. The most marked protoplasmic dif- ferentiation is therefore found in the exoplasm — it results in the formation of cilia, intercellular bridges, and the fibrillae of epithe- FlG. 7. — A VILLUS OF THE HU- MAN PLACENTA, SHOWING A PERIPHERAL SYNCYTIUM OF IRREGULAR THICKNESS. *Anat. Anz., 1903. 8 INTKODUCTIOX— PEOTOPLASM— THE CELL LAYER OF THE SKIN. The intercellular bridges are very distinct. and eosin. x 1,000. Hematein Hum, muscle, and connective tissue. Similar differential changes acting upon the endoplasm result in the formation of such struc- tures as the contractile fibrils of muscle cells, the neurofibrils of nerve cells, the mu- cin, zymogen and secretory granules of epithelial cells, and the fat of con- nective tissue cells. These develop- mental phenomena are, however, not the only evidence of the vital nature of protoplasm. It pre- r^r sents certain other phenomena, some FIG. 8. — GROUP OF EPITHELIAL CELLS FROM THE MALPIGHIAN Q£ \^hich ma\T be Qli- croscopically dem- onstrated, which are accompanied by characteristic histological changes. The vital properties which thus concern the histologist are motion, secretion, growth, and reproduction. Motion. — Cell motion is that evidence of excitability which results in change of the cell form or position. Three varieties may be recognized in animal cells. (a) Amoeboid Motion. — This form of cell motion is evidenced by a change of shape of the cell by which protoplasmic processes, pseudopodia, are ^ pushed out in one or more directions. These processes may then be either with- drawn or they may unite with one an- other, and thus, per- haps, inclose a for- eign particle ; or, again, the cell body may flow into the pseudopodium, which is thus increased in size, the cell body becoming correspondingly FlG. 9. — A LEUCOCYTE FROM HUMAN BLOOD IN ACTIVE AMCEBOID MOTION. The figures indicate the successive forms assumed by the cell. Drawings were made at intervals of one minute, x 500. THE TYPICAL CELL * smaller, until the whole cell finally occupies the position of its former process. The cell has thus changed its position — locomo- tion has heen accomplished. (b) Ciliary Motion. — This is a rapid waving motion of fine hair-like cilia which project from the free border of certain cells, as, for example, the ciliated epithelium of the respiratory tract. The rapid undulatory vibrations of the flagellum attached to cer- tain other cells — e. g., the spermatozoa — is closely allied to ciliary motion. The ciliary vibrations are exceedingly rapid, occurring many times to the second. (c) Molecular Motion. — This is a peculiar dancing movement of the finer granules, which occur within cell protoplasm. These granules may be microsomes, various forms of paraplasm, pigment granules, etc. A closely allied form is pigmentary motion in which pigment granules, which are at first equally distributed throughout the cell, are collected into a group, which usually sur- rounds the nucleus ; the reverse then occurs, the pigment granules becoming again equally distributed through the cell protoplasm. Molecular motion is readily 'observed in the pigment granules of the plasmodium malariae, a parasite occurring in the blood of persons afflicted with malarial fever. Molecular motion is closely simulated by Brownian motion, a peculiar dancing movement occurring when fine granular particles of inert substance are sus- pended in a fluid of nearly equal density. Secretion, — Changes in the appearance of cells may be due to secretory activity. Thus, during rest, glandular cells become dis- tended with their secretion ; they appear swollen, and their nuclei are obscured and pushed toward the attached margin of the cell. During activity secreting cells become shrunken and regain their ordinary protoplasmic appearance; their nuclei again approach the center, or even the free margin of the cell. In other types of secreting gland, as in the sebaceous glands, the secretion is produced by a disintegration of the cell protoplasm, which, in most of these cases, undergoes a fatty metamorphosis. Growth. — This process involves changes in the size, shape, and consistence of the cell. The increase in size in most cells is not marked. It is, however, frequently sufficient to produce an in- creased pressure upon surrounding cells, which is to a certain extent accountable for the varying shapes assumed by those cells which are closely packed within the organs of the body. Most cells in their early embryological condition are nearly spherical in 10 INTRODUCTION— PROTOPLASM— THE CELL shape. If expansion during the growth of such cells is limited or resisted by surrounding tissues, pressure will be applied to the cell in many directions, and it consequently assumes a poly- hedral shape. If, on the other hand, the pressure is excessive in two opposing directions, the cell gradually becomes flattened or squamous. If, again, the pressure on its four sides should exceed FIG. 10. — VARIOUS FORMS OF CELLS. a, squamous epithelium from the tongue; 6, a columnar cell from the small intestine; c, a polyhedral or spheroidal cell from the liver ; d, a smooth muscle cell from the mus- cular coat of the stomach, x 550. that applied to the poles of the cell, it would necessarily assume an elongated, prismatic, or columnar shape. Reproduction. — Two forms of cell division may be observed within the human body : direct division or fission, and indirect division, karyokinesis or mitosis. Direct Division (amitosis, fragmentation, fission). — This method of cell division is the least common. It occurs in some of the epithelial cells of the urinary bladder, in certain cells of red bone marrow, and perhaps occasionally in leucocytes and in glandular epithelium. The process, according to Nemiloff,* commences by an elonga- tion, followed by constriction, and finally fission of the nucleolus. These changes are accompanied by a similar elongation of the nucleus, followed by constriction and cleavage along such a median plane that a daughter nucleolus is included within each daughter nucleus. The daughter nuclei then travel toward opposite poles of the cell, and constriction and cleavage of the cell protoplasm complete the process. * Anat. Anz., 1903. THE TYPICAL CELL 11 Indirect Cell Division (karyokinesisi* mitosis\}. — This is the usual form of cell division. It consists of a series of changes which chiefly concern the centrosome and nucleus, and which are followed by constriction of the cytoplasm and its final separation into two daughter cells, each of which contains a daughter nucleus and centrosome. That condition of any cell during which it is not undergoing mitotic change is described as its resting stage. In this condition the nucleus is surrounded by a distinct nuclear membrane, within which its chromatic fibrils are irregularly disposed. Xear the nucleus is the centrosome, a minute chromatic point which is surrounded by a lighter radiate area, the so-called attraction sphere. It is about the centrosome that the earliest mitotic changes appear. In fact, division of the centrosome itself is fre- FIG. 11. — DIRECT CELL DIVISION, SHOWING SUCCESSIVE STAGES IN ORDER FROM LEFT TO RIGHT. (After Nemiloff.) Diagrammatic. quently the last occurrence in the formation of a daughter nucleus, a " precocious preparation " for future division. The mitotic changes which accompany indirect cell division may be conveniently considered under four heads: prophase, metaphase, anaphase, and telophase. PropJiase. — The preparatory changes which indicate the ap- proach of cell division begin with the early cleavage of the centro- some, which often even precedes the resting stage. With begin- ning mitotic activity the daughter centrosomes move apart, each surrounded by its clear radiate, or "astral" attraction sphere. * Meaning nuclear change. f A thread, referring to the appearance of the nucleus. 12 INTRODUCTION— PROTOPLASM— THE CELL The two asters thus formed may occasionally retain their connec- tion with one another, by means of fine achromatic fibrils which pass from one aster to the other, thus early forming the achro- FIG. 12. — DIAGRAM OF THE PROPHASE OF MITOSIS. a, achromatic spindle ; c, centrosome ; e p, equatorial plate ; A-F, successive stages of tho prophase of mitosis. (After Wilson.) matic spindle. More frequently the asters become either partially or entirely separated from each other, after which they continue THE TYPICAL CELL 13 their divergent migration until they finally reach opposite poles- of the nucleus. From these points achromatic fibrils, (astf'al rays) push into the nucleus, and, by union with their fellows of the opposite pole, form the achromatic spindle. Meanwhile changes have taken place within the nucleus. The nuclear wall and nucleolus disappear, and the entire chromatin FIG. 13. — METAPHASE AND TELOPHASE OF MITOSIS. G-H, metaphuse ; J-J, telophase ; e p, equatorial plate ; i/, interzonal fibres ; n, neben- kern. (After Wilson.) mass, now even more intensely chromatic, unites to form a single coarse, thread-like, convoluted fiber, the chromatic skein or spi- reme. The spireme soon breaks into a definite number of seg- ments or chromosomes, the number of which varies as between different animal species, but, as regards the individuals of each 14 INTRODUCTION— PROTOPLASM— THE CELL species, it is fixed and unchangeable. In man the number of chromosomes is sixteen. The termination of the prophase is marked by the approach of the chromosomes toward the equator of the achromatic spindle. Metaphase. — The chromosomes now come to lie in the equator of the achromatic spindle, and are so arranged that each segment forms a U or V, whose apex is directed toward the axis of the spin- dle. When viewed from the nuclear pole, this peculiar arrange- a FIG. 14.— EPIDERMIS OF THE SALAMANDER. Three cells are in process of division by mitosis. o, prophase ; 6, inetaphase. The second cell above 6, whose cell body is in process of fission, presents a stage of the telophase. (After Wilson. ) ment of the chromosomes produces a wreath-like appearance, the monaster. The chromosomes now divide by longitudinal cleavage into two exactly equal portions, which promptly begin a migration THE TYPICAL CELL 15 toward the opposite poles of the spindle. The two daughter nuclei thus receive from the mother cell precisely equivalent por- tions of chromatic substance. The cleavage of the chromatin segments frequently occurs at a very early period, and may even antedate the formation of the chromosomes by making its appear- ance in the spireme stage. Anaphase. — The daughter chromosomes are now drawn toward the opposite poles of the achromatic spindle, about which they are again arranged in a wreath-like manner to form the diaster. The daughter chromosomes are apparently connected with each other during their migration by the fine achromatic connecting or inter- zonal fibers of the central spindle. Minute chromatic thickenings in the equator of this spindle (cell plate, mid-body) indicate the future plane of cytoplasmic cleavage. Telophase. — The cytoplasm of the cell divides along the cell plate or equatorial plane of the achromatic spindle. Thus each daughter cell not only receives equivalent portions of chromatin through the daughter chromosomes, but the achromatic structures are likewise equally divided, one centrosome, with its surrounding aster or attraction sphere, going to each daughter cell. Thus a portion at least of the achromatic spindle persists as the attraction sphere of the resting nucleus. Other portions go to form the " nebenkern " which is present in many cells. The daughter chromosomes now become thickened, convoluted, and finally crowded or fused together to form the daughter skein or spireme. The nuclear wall and nucleolus reappear, though the manner of their origin is not yet understood. As a final change, and a preparation for future division, the centrosome frequently divides. In this case the double centro- some (diplosomc) persists throughout the resting stage. V- CHAPTER II EPITHELIAL TISSUES EPITHELIAL tissues, the epithelia, include all those cellular membranes which cover the free surfaces of the body, either exter- nal or internal, together with the cellular portions of the secreting glands directly connected with, or developed from, these free sur- faces. They thus include the epidermis of the skin, the mucous membranes of the digestive, respiratory, and geni to-urinary tracts, the cellular structures of the salivary glands, pancreas, liver, ovary, testicle, kidney, and all other glands connected with these systems. Portions of the organs of special sense — the nose, eye, and ear — are also included within the scope of the term. The epithelial tissues are composed of cells which vary greatly in their shape and histological characters, and which may be arranged either en masse as in the Graafian follicles of the ovary, or in tubules or acini as in most secreting glands, or as membranes consisting of a variable number of cell layers. These membranes are either mucous or serous. Mucous mem- branes include all those which are connected, directly or indi- rectly, with external surfaces of the body, such as those of the esophagus, stomach, bronchial tubes, bladder, etc. Their epithe- lium is of epiblastic origin. Serous membranes, construing the term in its broadest sense, include those cellular layers which line all of the closed cavities of the body, viz., the arachnoid mem- branes of the brain and spinal column, the pleurae, pericardium, peritoneum, tunica vaginalis of the testicle, and the synovial mem- branes, bursae, and sheaths of the tendons. The epithelial cells which line these latter structures, together with those forming the lining membranes of the circulatory system — heart, arteries, capil- laries, veins, and lymphatic vessels — are of mesoblastic origin and are classified as endotlielium, the term referring to their distribu- tion within the closed cavities of the body. When epithelial cells are arranged to form a membrane, they may occur either as a 16 EPITHELIAL TISSUES 1? single layer of cells placed side by side, or the membrane may be several cells in thickness, in which case those cells upon the sur- face usually differ in structure and appearance from those of the deeper layers. When but a single layer of cells is present, the tissue may be called single or pavement epithelium ; when com- posed of several cell layers, the epithelium may be said to be complex, compound, or stratified. All epithelial membranes rest upon a subjacent supporting connective tissue, the tunica propria, upon the free surface of which a distinct basement membrane or membrana propria is usually developed. This basement membrane is formed by fine reticular connective tissue fibers, many of which are elastic, and are flattened connective tissue cells. In the stratified epithelial tissues the superficial cells — those nearest the free surface — usually arise by cell division in the deeper layers, and, if they become detached by abrasion, disintegration, or by other physiological or pathological processes, they may be replaced by cell reproduction occurring in the deeper layers. When but a single layer of cells is present, as in the simple epithelial tis- sues, abrasion or disintegration of the cells over large areas will obviously become more difficult of replacement by cell division. Hence it is that repair of extensively destructive pathological con- ditions involving such epithelial tissues becomes exceedingly diffi- cult, and often impossible. Each epithelial cell is to some extent a secreting cell. Some- times this is its chief function, as is the case with goblet cells, which might well be called " unicellular glands," and which secrete an abundant sup- ply of m ucus. The same is true of those cells which form the psuvn- chyma of secreting ESffii ^ Wk l[ flUf u a subsidiary function. ^ lumen of the ffland . ^ seereting ceiis ; sc, secretory The cells of an epi- capillaries. (After Sobotta.) thelial membrane are maintained in proper juxtaposition, one to another, by means of a delicate cement substance which is apparently a product of their 18 EPITHELIAL TISSUES FIG. 16.— SECRETORY CAPILLARIES IN THE HUMAN PANCREAS. Z, glandular lumen ; sc, secretory capillaries ; 2, secreting cells. (Af- ter Sobotta.) x 375. exoplasm. This cement substance is pierced by numerous minute canals, the secretory or nutrient canaliculi, which are either con- nected with the tissue spaces of the membrana propria, or open upon the free surface of the epithe- lium, to which they convey the secre- tion of the cells. The nutrient canals so occasionally are continued directly into the cytoplasm of the cell. At the surface of the membrane this cement substance, from exposure to unusual mechanical and chemical influence, becomes altered in consist- ence, and is readily demonstrated by certain staining methods (silver nitrate, hematein, etc.). These condensed por- tions, when viewed from the free sur- face, form a network of " terminal bars," the meshes of which are occupied by the free surfaces of the epithelial cells. In the case of many epithelial cells — i. e., the polyhedral cells in the deeper layers of stratified epithelium, and many cells of columnar epithelium, the in- tercellular cement substance is . bridged across by numer- ous fine protoplasmic threads, which, arising within the sub- stance of one cell, become lost .in the cytoplasm of its neigh- bors. The peculiar spinous appearance produced by these so-called intercellular bridges has caused such cells to be described as "prickle cells" (Fig. 8). The intercellular bridges are more than the name im- plies, for they can often be traced not only from one cell to another, but may even pass entirely through an intermediate cell and enter a third or even a fourth cell. These protoplasmic processes usually follow regular curves with a convexity toward the cell nuclei, so that in passing through a cell they frequently FIG. 17. — " TERMINAL BARS" OF CEMENT SUB- STANCE AS SEEN BETWEEN THE EPITHELIAL CELLS OF A TUBULAR SECRETING GLAND IN THE PYLORIC REGION OF THE HUMAN STOMACH. The columnar epithelium is seen in profile at a ; at 6, the free ends of the cells are seen. Hematein. x 550. EPITHELIAL TISSUES 19 subdivide it into three or four segments, in the center of which is the nucleus. They are probably exoplasmic derivatives of the cell protoplasm. Similar fibrils, though less pronounced, have also been found in other tissues than epithelium — i. e., in smooth muscle and in nerve cells. CLASSIFICATION OF EPITHELIA I. SIMPLE EPITHELIA — those which occur en masse, or composing a mem- brane but one cell in thickness. Ovum. (d) Spherical cells. Graafian 1. Spheroidal, composed of. 2. Bquamous, composed of flat- tened, scaly cells. Embryonal cells. f Liver cells. (b) Polyhedral cells, -j Deeper layers of com- [ plex epithelium. ' Serous membranes, synovial membranes, bursse, and tendon sheaths; heart, arter- ies, capillaries, veins, closed (a) Lining cavities. Pavement epitheli- um or, endothe- lium. and sels. lymphatic ves- 3. Columnar. (b) Lining the alveoli of the lungs, some tu- bules of the kidney, the anterior chamber of the eye, and the membranes of the mid- dle and internal ear. (c) As the superficial cells of stratified epithe- lium (vide infra). (a) Lining the mucous membrane of the ali- mentary tract — stomach, small intestines, large intestines. (b) Lining the ducts of all secreting glands — liver, pancreas, salivary, lachrymal, and mammary glands, testicle, prostate, etc. (c) The deejpest layer of cells in stratified epi- thelium is composed of columnar-shaped cells, which, however, differ in structure from the true columnar type. (a) Lining the uterus and Fallopian tubes. (b) Lining portions of the ventricles of the brain and central spinal canal of the em- l bryo and infant, f (O Pyramidal or [ The secreting cells of all tubular glands- \ / » J \7if\rm\T » lt> » i , . !•, 1.1 L: caliirat*\r nrionHc r>wr\TG f\T (A) Simple (£) Ciliated, glandular." (D) Goblet, (E) Neuro-epithe- lium. •j kidney, pancreas, salivary glands, crypts of [ the intestines, etc. {(a) Respiratory tract — nasal, pharyngeal, tra- cheal. and bronchial mucous membranes. (b) Alimentary tract — stomach, small and large intestines. f (a) Eye — the rod and cone cells of the retina. I (6) Ear— in the maculse of the labyrinth and Iin Corti's organ. (c) Nose— in the olfactory mucous membrane. (d) Tongue — in the taste buds. 20 EPITHELIAL TISSUES 1. Stratified (" stratified •{ squamous"). fSuperficial cells, II. COMPLEX EPITHELIA— those whose cells form several superimposed layers. f Forms the epidermis of the skin, and covers the free surface of those mucous membranes which clothe all orifices in direct connection therewith — viz., the conjunctiva and cornea ; the external auditory canal ; part of the nasal mucous membrane ; mouth, pharynx, and esophagus; epiglottis and vocal cords ; anus, as high as the internal sphincter ; vagina and external por- tion of the urethra. squamous; deeper, polyhedral ; the deepest, columnar in shape. 2. Transitional.^ 3. Pseudo-strati- fied columnar. Superficial cells only somewhat flat- tened; next deeper layer, pear-shaped ; deepest layers, polyhedral. ( Superficial cells, co- Ilumnar ; || deeper cells, polyhedral «{ or spindle-shaped, (a) Non-ciliated (rare). [ (b) Ciliated. Found only in the urinary system — viz., pelvis of the kidney, ureter, bladder, and first portion of the urethra. (a) Part of vas deferens. (b) Respiratory tract; nasal mucous membrane and passages connected therewith, tear-ducts, Eustachian tube, etc., larynx, trachea, and bronchi. Genital tract ; epididymis and vas deferens. * Usually designated "columnar" by way of abbreviation. Short columnar cells are often called "cubical" or " cuboidal" and are included under this head. f In later life these cells lose their cilia. \ Cells whose protoplasm has been converted into mucinogen. They maybe considered unicellular, mucus-secreting glands. § Differentiation of this variety of epithelial tissue, though neglected by some authors, becomes most important in the clinical examination of urine where it is necessary to determine the origin of individual cells. Transitional cells from the bladder are easily distinguished from the stratified cells of the vagina, urethra, or epidermis. I The " superficial " cells of this variety extend throughout the entire thick- ness of the membrane. Hence this form of epithelium may in one sense be called " simple " rather than " stratified." SPHEROIDAL EPITHELIUM.— In their early embryological condition all epithelial cells are nearly spherical in shape, but, apparently from pressure during growth or development, or from other unknown causes, they are distorted according to the direc- tion of the pressure applied, and according to the number of points of application. Pressure unequally applied on many sides natu- rally produces a polyhedral shape. SQUAMOUS EPITHELIUM 21 Such is the condition of the epithelial cells which compose the parenchyma of the liver. The liver cell may therefore be con- sidered as exhibiting the typical struc- ture of spheroidal epithelium. These cells are polyhedral in shape ; in profile, polygonal. They consist of soft, finely granular protoplasm, whose surface is slightly condensed to form an indistinct limiting membrane. Within the cell a distinct spherical nucleus — sometimes two nuclei — may be observed. The nu- FIG. 18.— POLYHEDRAL EPITHE- cleus is deeply chromatic. Small fat LIUM' FROM A SECTTON OF r J . . THE HUMAN LIVER. globules or vacuoles, pigment, and secre- ^ The central blood capillary tory granules (zymogen, glycogen, etc.) contains one leucocyte, and its are found within the cytoplasm. Such wal1 contains the nucleus of cells are often surrounded by a network L" dlt^ "'" of lymphatic spaces, nutrient canals, or secretory canaliculi, and from these minute canals, still finer off- shoots penetrate the cytoplasm of the cell. SQTTAMOUS EPITHELIUM (pavement epithelium). — The cells of this variety vary much, according to their location. Those lying within the body (endothelium) are of soft consistence, highly elastic, and form minute plate-like masses of protoplasm, joined edge to edge by cement substance, to form a continuous yet ex- tremely thin membrane. Within each cell is a large oval nucleus, which, like the cell body, is much flattened. The nucleus, how- ever, forms the thickest portion of the cell, and is usually found near its center. In those cells which are exposed upon the free surface of the body, such as the superficial cells of the epidermis or of the mucous membrane of the mouth or pharynx, the cell cytoplasm becomes changed in consistence as it changes its relative position in the cell layer. A peculiar horny material, known as "keratin," is developed within the superficial squamous cells of stratified epi- thelium, which obscures their nucleus and changes the cell proto- plasm into a firm horny substance. By the action of alkalis, such cells may be softened and the nucleus again brought into view. These cells, when seen " on the flat " — their broad surfaces pre- senting— are irregularly polygonal in outline, and have serrated margins and sharp angles. When viewed in profile, however — viz., their edges presenting — as frequently occurs in transections 22 EPITHELIAL TISSUES of endothelial membranes, squamous epithelial cells appear either as mere lines or as spindle-shaped bodies whose bulging center incloses the flattened nucleus. Fio. 19. — SQUAMOUS EPITHELIUM OR ENDOTHELIUM (surface view). From the mesentery of a rat. 'Silver nitrate and hematein. x 550. SIMPLE COLUMNAR EPITHELIUM.— Simple columnar cells occur as cylindrical bodies of varying length. Their deeper or attached extremity often tapers nearly to a point, and is frequently bifid. A surface view of a mem- brane consisting of columnar cells shows the free extremity of each cell to be of polygonal outline, the cells collectively forming a beautiful mosaic (Fig. 17). Each cell consists of finely granular cytoplasm and con- tains an oval nucleus, the long axis of which corresponds with that of its cell. The free extremity of these cells has frequently a peculiarly fine striated border, the cuticular mar- gin ; it is distinguished from the body of the cell by a very deli- cate membrane. When present, this peculiar striated border or cuticle is characteristic of the columnar type of cell, and is specially typical of those columnar cells which occur in the digestive tract. Fio. 20. — COLUMNAR EPITHELIUM FROM THE PTLORIC REGION OF THE HUMAN STOMACH. (Profile view.) Hematein and eosin. x 550. CILIATED CELLS TESTIS OF THE RABBIT. a, epithelium ; 6, connective tissue, and eosin. x 550. Hematein The attached extremity of the columnar epithelial cells fre- quently presents a longitudinally striated appearance. Such " rodded epithelium "is specially characteristic of +** * * ^ O^ ^ the ducts of the salivary * JE^' *^* glands and pancreas, and '"^ •* of certain of the urinifer- J" * # ous tubules of the kidney. Short Columnar cells, FlG- 21.— CUBOIDAL EPITHELIUM FROM THE BETE those whose three axes are approximately equal, are frequently described as cubical or cuboidal epithelium, but these cells do not differ either in structure or in distribution from the ordinary columnar type. CILIATED CELLS, — Many cells carry upon their free surface a group of delicate hair-like processes called cilia, or a single flagellum, which during life are capable of a rapid vibratory or undulating motion. The direc- tion of this ciliary motion is con- stant, and is such as to produce a definite current within the fluids which bathe the surface of these cells, whose direction is in- variably from within outward — v*z*> toward the external surface of the body. In the human body cilia occur almost exclusively upon the free extremities of columnar-shaped cells. In some of the lower animals, as, for ex- ample, in the mouth of the frog, cilia are also found upon poly- hedral or pear-shaped cells. The cilia are evidently extensions of the cytoplasm of the cell body, and may be regarded as modifica- tions of its exoplasm. The ciliated cell border is differentiated from the protoplasm of the cell body by a fine chromatic line which is divisible into a number of knob-like segments. The cytoplasm and nucleus of ciliated epithelium, except for the peculiarities dependent upon FIG. 22. — COLUMNAR CILIATED EPITHE- LIUM FROM THE EPIDIDYMIS OF A RABBIT. a, epithelium; 6, connective tissue; c, cilia. A leucocyte is seen between the bases of the columnar cells. Hematein and eosin. x 550. 24 EPITHELIAL TISSUES the formation of cilia, is similar to that of the simple non-ciliated columnar cells. Their cytoplasm, as in other types, may con- tain vacuoles, pigment granules, paraplasm, and even secretory granules. PYRAMIDAL CELLS—" GLANDULAR EPITHELIUM."— This variety of the columnar cell occurs in the secreting glands. It is, perhaps, unnecessary to distinguish it from the simple columnar ^^ cell, there being but little differ- ence in the structure of their 44ft protoplasm. The peculiar shape ^ which characterizes these cells re- ^^ $1 • suits from their disposition to form the wall of secreting tubules, sacular acini, etc. The greater area of their base as compared with that of their free extremity °f FIG. 23.-A GROUP OF CELLS FROM A TRANSECTION OF AN ACINUS OF THE cated pyramid. A cuticular bor- HUMAN PANCREAS; GLANDULAR EPI- £er jg no^ usually present. The THELIUM. ,, . . ,, cells are partially or completely Hematem and eosin. x ooO. . \ J J loaded with secretory granules. Pyramidal or glandular epithelium is found in tubules of the kidney, salivary glands, and pancreas, in the secreting glands of the gastric and intestinal mucous membrane, in the mucous glands of the esophagus, pharynx, bronchial tubes, and oral and nasal cavities, and in the secreting glands of the skin. GOBLET CELLS.— These cells are derivatives of the columnar variety, and may occur among either the plain or ciliated colum- nar cells. Goblet cells are most abundant in the intestinal tract, but are also to be found in the stomach, bronchial tubes, trachea, nasal mucous membrane, and in the ducts and tubules of mucus- secreting glands. In such epithelial membranes certain columnar cells, if not indeed all of these cells, are destined to secrete mucus. The cytoplasm of such cells is converted into a clear, poorly chromatic mass of a peculiar glassy or vitreous appearance, which occupies an increasing proportion of the free extremity of the cell. This "mucinogen" when acted upon -by alcohol, is pre- cipitated within the cell, and then forms fine basophile fibrils or granules, which stain deeply with the muchematein and muci- carmine solutions of P. Mayer. At the base of the goblet cell its nucleus is embedded in a minute mass of unaltered granular cyto- NEURO-EPITHELIAL CELLS 25 plasm and is often flattened against the basement membrane, the amount of flattening being proportionate to the volume of its mucous content. The accumulation of mucinogen within its cytoplasm expands the cell, finally ruptures its wall in the direction of least resistance, and thus permits its mucous content to exude upon the free surface, leaving behind the small granular protoplasmic cell remnant at- tached to the basement membrane. The further history of these cell remnants is somewhat doubtful. They are possibly absorbed, removed, and finally replaced by mitotic division of adjacent cells. There is, however, some evidence to show that they are still FIG. 24. — GOBLET CELLS AS SEEN IN A TBANSECT10N OF A CRYPT OF THE LARGE INTESTINE OF MAN. Sections of five goblet cells are seen among the columnar cells which line the tubule. Muchematein and eosin. x 550. FIG. 25. — DIAGRAM SHOWING THE ARRANGE- MENT OF THE COLUMNAR AND GOBLET CELLS OF THE PRECEDING FIGURE. The goblet cells are represented as being empty ; their unaltered basal portions con- taining the nucleus are distinctly seen. capable of further growth, whereby they may regain their original form and become again capable of passing through the same stages of secretory activity. NEURO-EPITHELIAL CELLS.— These cells are derivatives of columnar epithelium which are specially differentiated to form nerve end-organs. They are usually elongated cells having a bulging nucleated center, their free extremity either projecting beyond the epithelial surface as a bundle of fine cilia or as a slender non-ciliated process which terminates within a pore-like opening directly connected with the free surface. Their at- tached extremity, tapering to a fine process, is in relation with the terminal arborization of the axis cylinder of a nerve fibre. Neuro-epithelium is found only in the several organs of special 26 EPITHELIAL TISSUES sense, and will be more fully described as a part of these several organs.* STRATIFIED EPITHELIUM.— This variety of epithelium oc- curs as a membrane of varying thickness but always comprising several cell layers. A straight line perpendicular to its free sur- face would penetrate from five to thirty or more epithelial cells. But while there is a wide diversity in the thickness of the epithe- lial layers, the character of the cells at any given level is very nearly constant. Thus the deeper cells, those nearest the basement mem- brane, are nucleated, of soft consistence, and may contain mitotic figures, indicating that it is at this level that cell reproduction is most active. Toward the surface of the membrane the cells be- come progressively of firmer consistence, so that the most super- ficial ones present a horny appearance as a result of the gradual keratization of the cytoplasm during the progress of the cell to- ward the surface. The keratization is apparently dependent upon surrounding mechanical conditions, for it is much more marked in the skin, which from constant and rapid evaporation is compara- tively dry, than in the mouth, esophagus, or conjunctiva, where the epithelium is constantly moistened by glandular secretions : the margins of the lips, eyelids, etc., present an intermediate state of keratization. With these chemical changes in the composition of the cyto- plasm there are corresponding changes in its nucleus. In the deeper cells, the nucleus is oval or spherical and highly chromatic. Toward the surface, the nucleus becomes more and more flattened and more and more obscured by the cornification of the cell proto- plasm. In the most superficial cells it is usually impossible to demonstrate the nuclei, except by acting upon their protoplasm with strong reagents such as the caustic alkalis, soda or potassa. But the most characteristic change in the cells of stratified epithelium is the progressive transition in shape during their pas- sage from the deeper layers to the free surface. Kew cells, result- ing from indirect division of the cells in the deeper layers, are, by continued reproduction, gradually pushed toward the surface, whence they are constantly being desquamated in small scaly masses. The pressure exerted in this process tends to gradually flatten these cells so that their vertical diameter, that perpendic- ular to the surface, becomes progressively shorter the nearer they *See chapters on the Eye, the Ear, the Olfactory Organ, the Tongue, and on Nerve End-organs. STKATIFIED EPITHELIUM 27 approach the free surface; on the other hand, their transverse diameter, that parallel to the surface of the epithelial membrane, is correspondingly increased. The deepest cells of stratified epi- thelium— those which rest upon the basement membrane— are elongated in their vertical diameter, and possess an irregularly columnar shape.* Their nuclei are likewise elongated, oval or & & & «B> >" :• 0 <*» ~Q ^ — ^ *•"• -^ •' @® ® ^ ' © ®@ s> • •• -*•' *®- «** e» © © ® ct -^ „© 6> 65 '^m&&$& **<*Y* «;v® ** • 2S-islV&^VrV*"' ;•*•;.--»•• 5?: *£ . ,» '-• ^ * «• . »% • -*• > FIG. 26. — STRATIFIED EPITHELIUM FROM THE HUMAN ESOPHAGUS. a, basement membrane ; 6, connective tissue. Hematein and eosin. x 410. elliptical in shape. Superficial to these, but still in the deeper layers, are polyhedral cells with spherical nuclei, which are known as prickle cells because of their prominent intercellular bridges. Superficial to the prickle cells, the epithelial cells become progres- sively more flattened, until at the surface they are mere scales. This gradual transition from columnar and polyhedral cells below, * In the skin of brunettes and the dark-skinned races, and in the epithelium of the skin of the scrotum, peri-anal region, and areolae of the breasts, these cells contain small granules of the pigment to which the color of the cuticle is due. This columnar cell layer is then described as the layer of pigment epithelium. 28 EPITHELIAL TISSUES to thin flat scales on the surface is characteristic of all stratified epithelium. The thin superficial scales resemble very closely in shape and appearance the squamous epithelium previously described. The FIG. 27. — EPIDERMIS OF THE SKIN OF THE FINGER TIP, SHOWING EXTREME KERATIZA- TION OF THE EPITHELIUM. o, keratized epithelium ; 6. Malpighian or germinal layer ; c, connective tissue. Hematein and eosin. x 50. deeper cells have a finely granular cytoplasm and distinct nuclei except when obscured by the appearance of keratin within their protoplasm. Many of these cells contain coarse granules of eleiclin and Jceratohyalin — substances chemically intermediate between the unaltered and the keratized protoplasm. As stated, the formation of keratin within these cells is more active in those membranes which are comparatively dry from ex- posure to the air. Consequently, it is most active in the epidermis of the skin. If stratified epithelium is at all times well moistened, as, for example, in the mouth and esophagus, the formation of keratin is slight, and the soft polyhedral cells compose the major portion of the epithelial membrane which then has only a thin superficial covering of flattened scaly cells. In the comparatively dry epidermis, on the other hand, the flattened horny cells fre- quently occupy more than half the thickness of the epithelial layer. In the superficial squamous cells of moist membranes the nucleus can always be readily demonstrated, even in the keratized cells of the extreme surface. TKANSITIO^AL EPITHELIUM TRANSITIONAL EPITHELHIM.— This variety of epithelium resembles the preceding, in that it is composed of several cell layers, the deeper cells of which are more nearly polyhedral but are somewhat flat- tened upon the free surface. It differs, however, in the num- ber of cell layers, ^» v ^ ^ , . , . , W il ^ ©A BK ^* which is much less than is usual in the preceding variety, and in the character of the superficial cells. Transitional epithelium is not usually more than from three to ten cells deep, four to six being the rule. The numerical as well as the actual thickness of epithelial membranes is to a certain extent depend- ent upon their state of tension during life ; thus the transitional epithelium of the urinary bladder is much thicker when the organ is collapsed than during distention. FIG. 28. — TRANSITIONAL EPITHELIUM FROM A TRANSEC- TION OF THE URETER OF AN INFANT. a, epithelium; ft, connective tissue. Hematein and eosin. x 550. B FIG. 29.— ISOLATED CELLS OF THE HUMAN URINE. A, from the vagina of a woman (stratified squamous epithelium) ; B, from the ureter of a child (transitional epithelium); a, cells from the deep layers; 6, superficial cell- Moderately magnified. 30 EPITHELIAL TISSUES The deepest cells are polyhedral, and these form the greater portion of the membrane. Only the more superficial layers differ therefrom. Those polyhedral cells which lie in the mid-region of the epithelial layer possess a peculiar flask or pear-shape, with well- rounded bodies and a broad tapering process which is embedded between the adjacent cells of the deeper layers. The rounded ex- tremities of the pear-shaped cells fit into peculiar indentations in the deeper surface of the superficial layer of epithelial cells, producing peculiar concave facets, which are particularly char- acteristic of the detached superficial cells of transitional epi- thelium. The superficial cells, while somewhat flattened, usually have a thickness equal to one-sixth to one-third their transverse diameter. In this respect they differ markedly from the superficial scaly cells FIG. 31. — DIAGRAM SHOWING THE MANNER IN WHICH ALL THE EPITHELIAL CELLS OF PSEUDO-STRATIFIED CILIATED EPI- THELIUM REACH THE BASEMENT MEM- BRANE. Letters as in the preceding figure. FIG. 30. — PSEUDO-STRATIFIED COLUMNAR CILIATED EPITHELIUM FROM A BRON- CHIAL TUBE OF MAN. a, a goblet cell; 6, cilia; c, superficial cytoplasmic layer; d, deeper nucleated layer, the nuclei of the columnal cells are somewhat more deeply stained than those of the basal cells ; e, basement membrane ; /, connective tissue. Hematein and eosin. x 550. of stratified epithelium and are easily distinguished therefrom, even in the isolated condition in which they are frequently found in the urine. The concave facets on their under surface, as well as the peculiar pear-shape and small size of the deeper cells, are sufficient to distinguish the transitional cells from those of strati- fied epithelium. There is little, if any, formation of keratin in transitional epi- thelium. This is possibly explained by the fact that, as it occurs PSEUDO-STKATIFIED COLUMNAR EPITHELIUM 31 only in the urinary system, this form of epithelium is always well moistened. PSEUDO-STEATIFIED COLUMNAR EPITHELIUM.— The su- perficial cells only of this variety of epithelium are columnar in shape, and except in one or two unimportant places are always ciliated. The deeper extremities of these columnar cells taper to a point, and extend all the way to the basement membrane. Between the tapering ends of these cells small spindle-shaped and spheroidal cells are closely packed. The several varieties of cells thus appear to be superimposed, though all actually rest upon the basement membrane. The distribution of this variety of the epi- thelium is practically identical with that of ciliated cells. The deeper extremities of the columnar cells are occasionally bifid or even somewhat varicose in order the more closely to fit between the spindle-shaped and spheroidal cells of the deeper portion. The nucleus of these latter cells is usually situated a little below the middle of the columnar cell, so that all the nuclei of the epithelial membrane lie within its deeper half, thus giving to this portion a more deeply chromatic appearance when observed in stained sections under low magnification. The superficial half of the epithelial layer contains only the cytoplasmic portion of the columnar cells with their ciliated borders. CHAPTER III CONNECTIVE TISSUES WHILE in the epithelial tissues the cells are chiefly developed at the expense of the intercellular elements, in the connective tissues the conditions are the reverse. The intercellular elements are here developed out of all proportion to the connective tissue cells. The cells of these tissues, therefore, are scanty, the ground substance considerable, and within the latter a new element, the connective tissue fibre, makes its appearance. The fibres are of three varieties : white connective tissue fibres, yellow elastic fibres, and reticulum. In any given location either of these varieties may predominate to such an extent as to determine the character of the mature tissue, while in the immature forms of connective tissue it is the cellular elements which attain the greatest promi- nence. The minute structure of connective tissue is subject to great and important changes during its development. Beginning, as it ^:P • ^m^ & ^.j&? -. -*«.** .,-. i^e^p^ig- FIG. 32. — EMBRYONIC CONNECTIVE TISSUE, FIG. 33. — EMBRYONIC CONNECTIVE TISSUE AT EARLY STAGE. Highly magnified. A LATER STAGE THAN is REPRESENTED (After Mall.) IN FlG- 32- (After Mall.) does, with the primitive mesoblast, connective tissue is originally a cellular structure. The mesoblastic germ cells of connective tissue not only increase in number, by cell division but also secrete an intercellular ground substance of semifluid consistence. The 32 CONNECTIVE TISSUES 33 mesodermic cells, according to Studnida,* by fusion with each other finally form a syncytial tissue, in which there promptly occurs a differentiation of the cytoplasm with the formation of an endoplasm and an exoplasm, and within the latter the fine fibrils FIG. 34. — ABEOLAK CONNECTIVE TISSUE OF THE MATURE TYPE, FROM THE REGION OF THE KIDNEY OF MAN. a, fat cells, the one at a' is so cut as to show the surface of the spheroidal cell (the fat has been removed) ; 6, connective tissue cells of the lamellar type ; c, coarse bundle of white fibres ; d, elastic fibres, most of them very obliquely cut. Hematein, picrc-acid fuohsin, and Weigert's elastic tissue stain, x 750. soon make their appearance. This process progresses, new ground substance and fibres being constantly formed at the expense of the endoplasm, until finally the latter again forms isolated cells. * Anat. Anz., 1903. 34 CONNECTIVE TISSUES The culmination of these changes results in the mature fibrillar connective tissue in which the cells are shrunken and scarce, though still apparently capable of assuming renewed activity when occasion requires. Embryonic connective tissue is therefore typically cellular as compared with the mature type ; its ground substance is abundant, but the fibres, whose development is as yet incomplete, are scanty. Such embryonic connective tissue is found not only in the fetus, but also in early childhood, and in the adult especially during re- generation of destroyed areas of connective tissue, and in other more or less pathological conditions. Connective Tissue Cells.— Connective tissue cells not only vary in number as they -approach maturity, but in their structure and appearance as well. The cells of embryonic connective tissue are comparatively large, are frequently stellate «r^ from the presence of numerous interlacing and sometimes anastomosing branches, and their cytoplasm has a typical reticular or granular appearance. In the later stages of their development ameboid motion has been observed in such cells, and, within the limits of the tissue in which they are developed, they are presumably endowed with the power of locomotion. In the neighborhood of developing blood- vessels plasma cells of large size and irregular shape are frequently seen. The cytoplasm of these cells is of considerable volume, and is prolonged into broad protoplasmic branches of considerable length. Both in the cell body and in the processes vacuoles are so numerous as to give the cell a typically reticular appearance, a peculiarity which is emphasized by the removal of the contents of the vacuoles, as frequently happens in the preparation of microscopical specimens. In the denser forms of mature connective tissue, where the cells are apparently subjected to more or less compression between the firm bundles of fibres, the connective tissue cells lose their typical embryonal stellate form and become somewhat fusiform ; they are then known as the spindle cells of connective tissue. Such FIG. 35.— PLASMA CELLS OF CONNECTIVE TIS- SUE FROM THE HU- MAN BREAST. Hematein and eosin. x 750. FIG. 36. — SPINDLE-SHAPED CON- NECTIVE TISSUE CELLS FROM THE STROM A OF THE HUMAN OVARY. Hematein and eosin. x 550. CONNECTIVE TISSUES 35 cells occur in great abundance in the stroraa of the ovary and the mucosa of the uterus and oviduct. In the mature tissue of the adult many of the cells become more or less flattened, and are often closely applied to, or even wrapped around, the fibre bundles. These lamellar cells have a small nucleus, a considerable rim of cytoplasm, which frequently has a shrunken appearance, and sometimes a few short cytoplasmic processes. The branching stellate forms, how- ever, are characteristic of the younger connective tissues. In certain locations a de- posit of pigment granules oc- curs within the connective tis- sue cells. Such pigment cells are usually found where pro- tection from light seems de- sirable, and are most abundant in the choroid coat and iris of the eye. The pigment gran- ules are entirely confined to the cytoplasm of the cell ; the nucleus is never invaded by the deposit. The cytoplasm of certain connective tissue cells contains coarse basophile granules, which stain with dahlia and similar basic dyes. This type is known as granule cells, or Mast cells (Mastzellen of the German authors). The gran- ules of other granule cells are readily stained with acid dyes, such as eosin (eosinopMle or acido- phile granule cells). According to the observa- tions of H. B. Shaw,* certain of the granule cells abound in those locations where fat is deposited, and have a special relation to the development of ihefat cells of adipose tissue. All the forms of connective tissue cells so far enumerated have their origin within the tissue area in which they lie, hence they are termed FlG. 37. — PlGMENTED CELLS FROM THE CHO- BOID COAT OF THE ox's EYE. (Unstained ; hence, only the pigment granules appear in the figure. ) 1, granules contained within the cyto- plasm ; I?, free granules which have escaped from cells injured during the process of teasing ; S, the non-pigmented nuclei. FIG. 38.— GRANULE CELLS FROM THE FIBROUS CONNEC- TIVE TISSUE OF THE HUMAN MAM- MARY GLAND. A, a basophile cell ; B, an eosinophile cell. Hematein and eosin. x Y50. * J. Anat. and Physiol., 1901. 36 CONNECTIVE TISSUES fixed or Mstogenic connective tissue cells in centra-distinction to the leucocytes which wander out from the blood into the tissue spaces of the connective tissues, and which are then called the wandering or hematogenic connective tissue cells. These latter cells may pre- sent the same varieties as the white blood cells from which they are derived. The several varieties of connective tissue cells may be classified as follows : (a) Lamellar cells. I. HlSTOGENIC or FIXED. - (b) Spindle cells. (c) Plasma cells. (d) Granule cells. (e) Fat cells. (/) Pigment cells. . (g) Embryonic stellate cells. II. HEMATOGENIC or wAN-(/7X T \ (Ji) Leucocytes. DEEING. ( v ' Types of Connective Tissue. — The proportions and character of the cells and fibres present in any given connective tissue, to a certain extent, determine its character. If the white fibres of con- nective tissue are closely packed in dense parallel bundles, the elastic fibres being comparatively insignificant in number, the type of connective tissue may then be said to be dense fibrous or white fibrous tissue. In elastic tissue, on the other hand, the yellow elastic fibres are highly developed, the white fibres forming only insignificant and very delicate sheaths, which inclose the coarser elastic fibres. Again, it is the variety of delicate connective tissue fibre known as reticulum which preponderates in reticular tissue, and if the meshes of this reticular network become infiltrated by leucocytes, which then multiply by division until they exceed the other tissue elements, the connective tissue is then said to be of the lymphoid or adenoid variety. In all we distinguish the following varieties of connective tissue : 1, embryonic; 2, gelatinous ; 3, areolar ; 4, dense white fibrous ; 5, elastic ; 6, adipose ; 7, reticular ; 8, lymphoid. Embryonic connective tissue (Figs. 32 and 33) occurs not only in fetal and infantile life, but also during the regeneration of de- stroyed connective tissue areas and in pathological neoplasms. It is distinctly cellular in character. Its cells are spindle-shaped and stellate, are much branched, and, through their larger processes, they frequently anastomose. CONNECTIVE TISSUES 37 The fibres are extremely fine ; they are not usually arranged in bundles, but form a delicate network which permeates the ground substance in every direction. In the very immature types the fibres are all of the white fibrous variety ; fine elastic fibres appear later. The fluid ground substance forms an abundant mass of tissue juice which occupies the meshes of the fibrous net. Gelatinous connective tissue (mucous or mucoid connective tis- sue) occurs only in the umbilical cord, where it forms the " jelly of Wharton," and in the vitreous humor of the eye. Its semifluid FIG. 39. — GELATINOUS CONNECTIVE TISSUE FROM TUB UMBILICAL CORD OF A MEW-BORN INFANT. Safrauin and water blue, x 410. ground substance is of a gelatinous consistence, and forms the greater portion of the tissue; in the vitreous humor there is little else. The cells are mostly of the branched lamellar variety, are few in number in the vitreous, but more abundant in the umbilical cord. In the vitreous humor, also, there are very few fibres ; those which are present are very fine, and form a delicate reticulum. In the umbilical cord the fibres are more abundant, and possess a tendency to form bundles, which are disposed in parallel cylin- drical layers around the large blood vessels. Areolar connective tissue (Fig. 34) is the most widely distributed of all the varieties ; it fills all otherwise unoccupied spaces within 38 CONNECTIVE TISSUES the body, and in all microscopical sections areolar tissue is almost invariably to be found. This tissue connects the skin with the underlying structures, maintains the position and relation of ad- joining muscles, surrounds the heart and its great vessels, envelops the abdominal viscera, occupies the spaces of the mediastinum, and fills similar intervals between the various organs in all parts of the body. The ground substance of areolar tissue is a coagulable fluid, the tissue juice. Solutions of silver nitrate injected into the inter- stices of areolar tissue coagulate its tissue juice or ground sub- stance and darken it slightly. It is then seen to be permeated by broad lymphatic channels, which are lined by delicate endothelial cells (W. G. MacCallum*). Both white fibrous and yellow elastic fibres occur in areolar tissue, the former being far in excess of the latter. The compara- tively loose reticular arrangement of the fibres of areolar tissue affords a most favorable opportunity for the study of these con- nective tissue elements. The white fibres in mature tissues are invariably arranged in bundles which interlace with one another to form an open net- work. Each bundle consists of a number of very fine fibres, whose course is characteristically wavy or undulating. Though the indi- vidual fibres rarely branch, the fibre bundles frequently anastomose with one another. The white fibres are readily stained with most " acid " dyes, and possess a special affinity for acid f uchsin. On boiling they yield gelatin, and are readily dissolved by boiling in dilute acids or alkalis ; they are digested by artificial gastric juice in five or ten minutes, but are scarcely altered after several hours when acted upon by solutions of pancreatin. After boiling, how- ever, white fibres are readily digested by pancreatin. The elastic fibres of areolar tissue, in comparison with the white fibres, are few in number. They occur as isolated fibres — never in bundles — which frequently branch and anastomose, forming in this way a very fine net with wide meshes, within which are the inter- lacing bundles of white fibres. The elastic fibres exist under a cer- tain tension during life, so that their course, under favorable con- ditions, is invariably straight. When areolar tissue is removed from the body this tension is frequently relieved, and the elastic fibres then curl up, especially at their free ends. Under these *Arch. f. Anat., 1902; also Bui. J. Hop. Hosp., 1903. CONNECTIVE TISSUES 39 conditions they are no longer straight, but present a gracefully curved contour. The elastic fibres also possess a glassy, shining, or highly refractive appearance, the white fibres by comparison looking dull and opaque. Elastic fibres stain but slightly with most dyes ; they are readily colored by orcein and by Weigert's elastic tissue stain, both of which serve as specific dyes for these fibres. Elastic fibres are not dissolved by dilute acids or alkalis, even when boiled, and are only digested by artificial gastric juice after a lapse of several hours ; they are, however, readily digested in faintly alkaline solu- tions of pancreatin. The cells of areolar tissue are few in number, but may include any of the several varieties, though lamellar and spindle cells together with leucocytes form the more common types. Many of the lamellar cells are closely applied to, or even wrapped around FIG. 40. — DENSE FIBROUS TISSUE FROM THE TENDON OF ONE OF THE OCULAR MUSCLES OF A CHILD. Hematein and eosin. x 550. the bundles of white fibres. Fat cells occur in considerable num- bers in all areolar tissue and in some places are aggregated into large groups which form lobules of fatty tissue. CONNECTIVE TISSUES Dense White Fibrous Tissue. — In dense fibrous tissue the ground substance is comparatively deficient. Large bundles of white fibres are arranged in approximately parallel rows, and are so closely packed as to form a dense, firm, highly resistant tissue. Its scanty connective tissue cells are of the lamellar variety and are usually arranged in rows which occupy the interstices between the parallel fibre bundles. Dense white fibrous tissue occurs in tendons ; in these the con- nective tissue cells often have a peculiar quadrate shape and are arranged in rows of exceptional regularity. It also forms the liga- ments, the fasciae, the muscular sheaths, and the enveloping cap- sules of many of the viscera. Thus it surrounds the liver, kidney, lymphatic nodes, and other organs; it also forms the valves of the heart, the tendinous rings which surround the cardiac orifices, and the chordae tendinae which are attached to its valves; and, in general, it is found wherever great firmness and resistance are required. Elastic fibres in this tissue are relatively few in number and are so obscured by the dense bundles of white fibres as to be scarcely demonstrable except by means of the specific stains. FIG. 41. — COARSE ELASTIC FIBRES FROM THE LIGAMEUTUM NUCH^E OF THE OX ; ISOLATED BY TEASING. Partly diagrammatic, x about 250. FIG. 42. — TRANSECTION OF A FASCICULUS OF THE LIGAMENTUM NUCH,£ OF THE OX, SHOWING THE VERY LARGE ELASTIC FIBRES EMBEDDED IN A VERY DELI- CATE NETWORK OF WHITE FIBRES. Picro-fuchsin. x 550. Elastic Tissue. — In this form of tissue the elastic fibres are developed at the expense of the white fibres. The ground sub- CONNECTIVE TISSUES 41 stance is insignificant in amount, and the connective tissue cells are scanty and are confined to the white fibrous sheaths in which the elastic fibres are enveloped. The elastic fibres are of very large size (10 to 15 /x) as compared with those of other forms of connective tissue. But, except for their larger size, these fibres have the same peculiar characteristics as the elastic fibres of areo- lar tissue. In their straight course, frequent branches, and their FIG. 43. — ADIPOSE TISSUE OF MAN. The fat has been removed and only the cell membranes and investing connective tissue remain. Hematein and eosin. Photo, x 150. glistening, highly refractive appearance, as also in their charac- teristic reactions to specific dyes and other reagents, these fibres are identical with the elastic fibres of the other types of connec- tive tissue. The elastic fibres are bound together by delicate sheaths of very fine white fibres, and are united into bundles by coarser bands of fibrous tissue. Elastic tissue is found in the ligamentum sub- CONNECTIVE TISSUES FIG. 44. — FAT CELLS FROM A TEASED PREPARATION OF ADIPOSE TISSUE OF MAN. X 110. flava, and in the ligamentum nuchae of quadrupeds. In these locations it occurs in considerable quantity and has a peculiar yellowish color; it is for this reason that it is fre- quently described as yellow elastic tissue. Adipose Tissue (fatty tissue, fat}. — Wherever areolar tissue occurs, adi- pose tissue may also be found ; its distribution is therefore identical with that of areolar tissue. It forms a considerable mass, panniculus adiposus, be- neath the skin of many parts ; in it are embedded the kidneys, adrenals, and many lymphatic nodes; the mesentery and omentum are freely supplied with fat. The same tissue is found in the grooves of the heart wall, and it also occupies the spaces of the mediastinum. Adipose tissue is composed of lob- ules or groups of fat cells which are sup- ported by fibrous bands and septa and are abundantly supplied with small blood-vessels. The fat cells arise from the con- nective tissue cells by a deposit of fat droplets within the cytoplasm of the lat- ter. These droplets continue to increase in number and fuse with each other to form globules of increasing size, until the cytoplasm finally becomes so excavated as to form a mere limiting FIG. 45. — ADIPOSE TISSUE. The fat cells have been blackened by osmium tetroxid. x 110. CONNECTIVE TISSUES 43 membrane or cell wall. The nucleus is pushed to one side in this process and is flattened against the cell membrane ; it is usually embedded in a remnant of granular cytoplasm. Being thus dis- tended with fluid fat, the cell acquires a spheroidal shape. During periods of starvation or malnutrition, at which time fat decreases greatly in volume, many of the fat cells return to a con- dition which approximates their former state. As the fat is removed the cytoplasm of the cell increases in amount, but assumes a peculiar fluid appearance and is not readily colored by the usual dyes. These cells, which still contain a number of fat droplets, are known as " serous " fat cells. The origin of the fat cell is still somewhat in doubt. It was formerly thought that it might result from a deposit of fat within any of the connective tissue cells. A second theory con- siders that it arises only from a special fat-forming connective tissue cell. The demonstration of large numbers of peculiar ovoid granular cells with- in areas where fat cells were undoubtedly form- FIG. 46. — DEVELOPING ADIPOSE TISSUE FKOM THE SUBCUTANEOUS TISSUE OF AN INFANT. The fat has been removed by immersion in alco- hol and ether. The polygonal outlines of the fat cells arc well shown. Within many of them is seen the finer cytoplasmic network by which the inclosed droplets of fat were invested ; this network had not been completely replaced by the accumulation of fat. Hematein and eosin. Photo, x 325. ing in fetal and young subjects, and the demonstration of similar cells in areas showing fat formation in adult tissues, has lent support to the hypothesis that these granular cells are the only progenitors of the fat cells (Shaw *). Reticular Tissue (reticulated tissue, reticulum). — Reticular tis- sue occurs as the stroma of adenoid tissue in the lymphatic glands and other lymphoid organs, and, according to Mall,f is also found in the membrana propria of the secreting tubules of the stomach, intestine, kidney, testis, and thyroid, and in the marrow of bone and walls of the pulmonary air sacs. * J. Anat. and Physiol., 1901. f Johns Hop. Hosp. Rep., 1896. 44 CONNECTIVE TISSUES Like the other connective tissues, reticular tissue consists of cells, fibres, and ground substance ; the latter, however, is no more than a fluid tissue juice which, at least in the lymphoid organs, is identical with the lymph. The fibres are extremely fine and are arranged in slender bun- dles, which jfreely anastomose to form a delicate close-meshed reticulum. Individual fibres can be readily demonstrated in these bundles only after the action of alkalis, digestion by artificial gastric juice, or by other methods of dissociation, yet on careful examination in- dications of fibrillar structure can be seen in the reticulum of fresh tissue and in ordina- ry microscopical preparations. The chemical reactions of the reticular fibres are similar to those of white fibres except that the former are much less readily digested by artificial gastric juice. Flattened connective tissue cells clasp the bundles of reticular fibers ; they are mostly found at the intersections of the anasto- mosing bundles. This fact was accountable for the former theory, which regarded reticular tissue as formed by the anastomosing branches of stellate cells. The careful investigations of Carlier * and others have shown the true nature of the lamellar cells and their underlying fibre bundles. The fibres of reticular tissue very closely resemble the white fibres of areolar tissue, but differ from them in having a clearer, more highly refractive appearance. Their digestion in pepsin begins only after an interval of two hours, while white fibres are digested in a few minutes ; they also stain less readily than white fibres, and yield reticulin, which differs somewhat from the gelatin of fibrous tissue. The intimate histologic relation between reticu- lar and white fibrous tissue is shown by the fact that the two tis- sues are frequently continuous, * 3. Anat, and Physiol., 1895. FIG. 47. — RETICULUM OF A CERVICAL LYM- PHATIC NODE OF MAN, FROM A THIN SEC- TION FROM WHICH THE LYMPHATIC COR- PUSCLES HAD BEEN PARTIALLY WASHED OUT. a, polynuclear lymphatic corpuscle ; &, large mononuclear cell ; c, connective tissue cells of the reticular tissue ; d, fibrous bundle of the reticulum ; e, small mononuclear lym- phatic cell. Hematein and eosin. x 500. CO]STXECTIVE TISSUES 45 Mall * has recently attempted to show that reticular tissue should be considered as that form of connective tissue which has been least differentiated from the embryonic mesenchymal type. He accordingly considers the cells of the reticulum as formed by the FIG. 48. — EETIOULUM FROM THE MUCOSA OF THE FUNDUS REGION OF THE DOG'S STOMACH. The section was made parallel to the surface and the glandular tissue removed by shaking in water. Picro-carmin. x 125. (After Mall.) undifferentiated endbplasm, and the reticular fibres as representing the specialized exoplasm of this most primitive type of connective tissue. Lymphoid Tissue (adenoid tissue).— Lymph oid tissue is a retic- ular tissue the meshes of whose network are occupied by a closely packed mass of small spheroidal cells, the lymphatic corpuscles. These cells have a prominent ovoid nucleus which is richly sup- plied with chromatin and is occasionally indented, constricted, or * Am. J. of Anat., 1902. 46 CONNECTIVE TISSUES even polymorphous. In the latter case it consists of two or more lobules united by a chromatin filament. The amount of cytoplasm which surrounds the nucleus is variable, but never very great. The lymphatic corpuscles* are so closely packed that it is almost impossible to distinguish the fine lines of the reticular stroma, except in those portions where some of the lymphatic cells have been washed out or displaced in the preparation of the specimen. The density of the lymphoid tissue varies much, however, in different organs and even in different portions of the same organ. The denser accumulations of lymphoid corpuscles may form either ovoid lymphatic nodules or follicles, or long dense trabeculae, the lymphatic cords, which are surrounded by looser portions of lymphoid tissue. Lymphatic corpuscles are frequently infiltrated into the con- nective tissue of the mucous membranes, where they form irregular a FlG. 49. — A LYMPHATIC NODE OF A DOG, SHOWING LYMPHATIC NODULES AND CORDS. The lymphatic corpuscles have been partially removed from the medulla, a, me- dulla ; 6, cortex ; c, nodules in the cortex ; d, cords in the medulla ; e, a fibrous trabecula. Hematein and eosin. Photo, x 20. collections, which may be termed diffuse lymphoid tissue, in con- tradistinction to compact lymphoid tissue, which occurs in the lym- phatic glands, tonsils, thymus, and spleen, and in Peyer's patches and the solitary follicles of the intestinal tract. Diffuse lymphoid tissue is found in the mucous membranes of (A) the respiratory tract — nose, naso-pharynx, larynx, trachea, and bronchi ; and (B) the alimentary tract — mouth, tongue, pharynx, esophagus, stom- ach, and intestines. * For the several types of lymphatic corpuscles see Chapter X. CONNECTIVE TISSUES Blood and Nerve Supply of the Connective Tissues.— The connec- tive tissues, but especially the areolar variety, form a supporting substance through which the various blood and lymphatic vessels and nerve trunks are distributed to all portions of the body. Within the con- nective tissues these vessels are everywhere present, and from them the connective tis- sue itself receives its supply of capillary vessels and ter- minal nerve fibrils. The vascular supply of the connective tissues is very abundant. Small arteries, which are derived from the main trunks, form a capillary plexus throughout the tissue, the capillaries finally reunit- ing to form the venules. It is in this capillary plexus that the fluid portions of the blood exude into the surrounding perivascular lym- phatic or tissue spaces of the connective tissue. The tissue juices which arise in this man- ner are most active agents in the physiological processes of assimilation. From the tissue juice spaces, lymph re-enters the abundant capillary lymphatic vessels to be finally returned to the venous blood. Of the several varieties of connective tissue, the adipose possesses the most abundant blood supply ; the lymphoid, on the other hand, is most richly supplied with lymph. Abundant nerves are distributed to the connective tissues, some of which supply its blood vessels while others terminate in special forms of sensory nerve end organs. FIG. 50. — FROM A SECTION THROUGH THE ME- DULLA OF A CERVICAL LYMPHATIC NODE OF MAN. a, a "cord" of dense lymphoid tissue; 6, looser lymphoid tissue of the medullary sinuses ; c, the margin of a fibrous trabecula ; d, nucleus of the connective tissue reticulum ; e, endothelial lining of the lymphatic sinus. Hematein and eosin. x 475. CHAPTER IV CARTILAGE CARTILAGE is a dense, firm, but elastic substance, resembling connective tissue in that it is developed from similar mesoblastic cells. It contains a ground substance, the cartilage matrix, and at times fibres, which may be either white fibres or yellow elas- tic. The presence, absence, or character of these fibres determines the variety of cartilage. Three varieties are thus distinguished : hyaline cartilage, in which no fibres can be demonstrated within the matrix ; elastic cartilage, whose matrix is permeated by yellow elastic fibres; and fibrocartilage, whose matrix contains white fibers. HYALINE CARTILAGE.— This is the most abundant of the three varieties. It is found in the respiratory system, forming the cartilages of the nose, larynx, trachea, and bronchial tubes; in the costal cartilages of the ribs; as articular cartilages cover- ing the ends of long bones ; and in embryo, where, in the course of development of the bones, the entire skeleton, except- ing only the flat bones of the skull and face, at .first consists of hyaline cartilage. In most of these locations the cartilage occurs as plate-like masses, which are surrounded or encapsulated by a vascular membrane of dense fibrous and ^elastic tissue. This membrane is the perichondrium. The inner portion of this mem- brane is richly supplied with small cells, and it is from this cell layer that the cartilage is presumably developed. These chondro- genetic cells multiply, and deposit about themselves the structure- less mass which first forms merely a capsule to the cell, but which, as it increases in amount, separates the various cells by wider areas and becomes the cartilage matrix. The cells, which in the perichon- drium are small and decidedly flattened, likewise increase in size during this process, and become more nearly spherical, so that those cartilage cells which lie near the center of the cartilaginous plates are spheroidal in shape, while those toward the surface are 48 HYALINE CARTILAGE 49 more and more flattened or elongated, their long axes gradually revolving from a perpendicular in the center of the plate until at the surface it becomes parallel with the perichondrium. Each cartilage cell is inclosed within a small space or lacuna, which during life it entirely fills. Cell multiplication within the cartilage is peculiar in that cell division occurs within a firm capsule and results in the forma- FIG. 51. — TRANSECTION OF A PLATE OF HYALINE CARTILAGE, FROM THE TRACHEA OF A CHILD. The margin of the fibrous perichondrium can be seen on either side of the plate of cartilage, in the upper right hand corner and lower left hand corner of the figure. Hem- atein and eosin. Photo, x 400. tion of two daughter cells, which at first lie within the same encapsuled space. These two cells may each again undergo division within the same space with formation of four new cells. As a result of this peculiar method of cell division the cartilage cells are arranged in groups of two, four, or even eight cells. Each of the cells in the group deposits its capsule, and thus forms a 50 GAKTILAGE matrix about itself, so that the increasing space thus produced between the cells of a group may separate them until they become completely isolated cartilage cells each within its own lacuna. In this way the matrix of the cartilage is produced. The matrix of hyaline cartilage is devoid of fibrous or cellular structure. During life, or if the tissue is examined in the fresh state, the cartilage cell entirely fills the lacuna in which it lies. But shortly after death shrinkage of these cells begins, so that after some hours a considerable space intervenes between the cell and the wall of its lacuna. It has been supposed that this space was occupied during life by lymph. It would, however, seem more probable that it is partially the result of post-mortem shrinkage of the cell. Frequently, and espe- cially in developing carti- lage, concentric lines may be seen surrounding each lacuna. These lines have been described as the " cell capsule." They appear only to indicate the successive layers of material which have been deposited by the cell, and which have fused together to form its surrounding matrix. Recent investigations on the development of the connective tissues suggest that cartilage arises from a mesenchymal syncytium in which the matrix is formed from the exoplasm of the syncytial tissue, the cartilage cell representing its endoplasm. The so-called capsule of the cartilage cell would accordingly represent the par- tially modified border line between the original endo- and exo- plasm, and would thus correspond to similar conditions which are observed in other forms of developing connective tissue. Cartilage cells frequently contain small droplets of fat, and these may coalesce until the cell is completely transformed into a fat cell. Isolated masses of adipose tissue, resulting from the FIG. 52. — CELLS AND MATRIX or HYALINE CARTI- LAGE FROM THE WALL OF A LARGE BRONCHUS OF MAN. The grouping in pairs and fours, and the ten- dency to produce a so-called " capsule," are espe- cially noticeable. Hernateiu. x 550. ELASTIC CARTILAGE 51 transformed groups of cartilage cells, thus make their appearance within the cartilaginous plates. This fatty metamorphosis is most marked in the elastic variety of cartilage. By coloration with iodin, glycogen granules may also be demon- strated in the cartilage-cells (Ranvier *). THE PEBICHONDBIITM is a dense fibrous membrane which surrounds each individual plate-like mass of cartilage. It is con- tinuous with the surrounding connective tissue, and is well sup- plied with bloodvessels and lymphatics; it may also contain terminal nerve fibrils. The cartilage itself is an absolutely bloodless and nerveless tissue. Neither are lymphatic channels demonstrable within the cartilage matrix. After long maceration or artificial digestion the matrix assumes a granular or fibrous appearance, and small channels have been demonstrated within it, which have been said to connect the various lacunae ; but it is evident that these appear- ances were possibly the re- sult of artificial destructive processes, and could not therefore be considered as evidences of the presence of such structure in living cartilage. ELASTIC CARTILAGE (net cartilage, reticular car- tilage) . — Elastic cartilage occurs within the human body in the external ear, and in the epiglottis and cartilages of Wrisberg and Santorini in the larynx. It resembles hyaline carti- lage in the presence of large spheroidal cartilage cells and a homogeneous matrix, but the matrix is everywhere permeated by a dense inter- lacing network of fine elastic fibres. These plates of cartilage, like those of the hyaline variety, are surrounded by a dense fibrous perichondrium. Neither blood vessels, nerves, nor lymphatics are distributed within the matrix of elastic cartilage. * Traite technique d'histologie, 2 ed., page 235. •i FIG. 53. — ELASTIC CARTILAGE FROM THE HUMAN EPIGLOTTIS, SHOWING THE LARGE OVOID CARTI- LAGE CELLS AND THE VERY DELICATE RETICU- LVM OF ELASTIC FIBRES. Ehrlich's triacid stain, x 550. CAETILAGE FIG. 54. — WHITE FIBROCARTILAGE, SHOWING A GROUP OF OVAL CAR- TILAGE CELLS. From the semilunar cartilage of the knee of man. Hematein and eosin. x 550. FIBROCARTILAGE. — This tissue forms the interarticular car- tilages of the lower jaw, the clavicle, and the knee ; composes the intervertebral disks and the other cartilaginous symphyses of the body ; lines the tendon grooves of the bones, and forms the glenoid ligament of the shoulder and the cotyloid liga- ment of the hip. Fibrocartilage is intermediate in structure between hyaline cartilage and such very dense white fibrous tissue as occurs in the tendons of muscles. At the attached margin of the cartilaginous plates its tissue is continued by imperceptible gradations into the surrounding fibrous connective tissues. Like the other forms of cartilage, this variety is also non-vascular and devoid of nerves. Microscopically, fibrocartilage differs from such dense white fibrous tissue as is found in the ligaments and tendons, in that the meshes of the dense fibrous tissue of fibrocartilage are everywhere permeated by a hyaline matrix, in which, here and there, are small groups of ovoid cartilage cells. Each cartilage cell is occasionally surrounded by a characteristic, concentric, lamellar appearance of the adjacent matrix, the so-called " capsule." Plates of fibrocartilage, unlike the other varieties, are not sur- rounded by a perichondrium. CHAPTEE V THE MUSCULAR TISSUES THE musculature of the body includes not only the skeletal muscles, but certain portions of the wall of the hollow viscera, such as the respiratory, alimentary, and urinary tracts. The skeletal muscles contain the most highly developed type of muscle cell, the visceral organs the lowest or least differentiated type ; the muscle of the heart is intermediate between these, and stands in a class by itself. Thus we distinguish threejfcypes of muscular tissue, the xolun-. tary or striated, the involuntary smooth or plain, and the cardiac. These types are all of mesoblastic origin, the first muscular tissue to make its appearance being the " myotomes " from which the striated fibres of the skeletal muscles are developed. Cardiac muscular tissue next appears, the anlages of the visceral muscu- lature being formed at a still later period. The completed devel- opment of the three types of muscle may be said to correspond, in a way, to the priority of their appearance, the smooth muscle cells being the least and the striated cells the most altered or differen- tiated from the primitive cell type. The physiological classification of muscle into the voluntary and involuntary varieties, while it corresponds quite closely with the striated and smooth types of muscle cell, is not exactly coinci- dent with this histological division. Inasmuch as the terms vol- untary and involuntary refer not to any structural peculiarity of the cell, but rather to the form and mechanism of its nervous con- trol, it is not to be expected that such a classification based upon its physiological relation to the nervous system would be identical with the histological types of muscle cell. Nevertheless, the stri- ated type of muscle is found to be usually under voluntary, and the smooth and cardiac types under involuntary control. SMOOTH MUSCLE TISSUE (plain, non-striated, or involun- tary).— This type of muscular tissue consists of small fusiform 53 54 THE MUSCULAK TISSUES cells which are either directly united by cement substance or are held together by very delicate membranous lines of connective tissue. In the former case adjacent cells are frequently connected by very delicate protoplasmic fibrils, intercellular bridges. Each muscle cell (muscle fibre) consists of a much elongated fusiform mass of finely granular cytoplasm which incloses a rod- shaped nucleus. The peculiar shape of this nucleus, together with its distinct nuclear wall and the distribution of its chromatin in coarse granules, separated by wide intervals of achromatic sub- stance, is characteristic of this variety of muscular tissue. These FIG. 55. — SMOOTH MUSCLE FIBRES FROM THE PIG'S STOMACH, ISOLATED IN EQUAL PARTS OF ALCOHOL, GLYCERIN, AND WATER. Unstained. X 410. peculiarities of the nucleus in connection with the affinity of the cytoplasm of the muscle fibres for certain acid dyes, e. g., eosin, serve to distinguish this variety of muscle from white fibrous con- nective tissue, with which it might otherwise be easily confounded. The cytoplasm of smooth muscle cells presents fine longitudinal striations indicative of a subdivision into ultimate fibrillce, a re- arrangement of the cell protoplasm which is more characteristic- ally developed in the higher types of muscle. Transverse stria- tions are not seen. The nucleus is found in the center of the cell. The surface of the cytoplasm is somewhat condensed, though a true cell membrane, comparable to the sarcolemma of the striated muscle cell, is wanting. The size of the smooth muscle cell is SMOOTH MUSCLE TISSUE 55 variable. Its greatest diameter in the region of the centrally sit- uated nucleus is from 5 to 10 /A, about the diameter of a red blood corpuscle. The length of the cell varies from 50 to 500 /A. As seen in transverse section these fibres vary in size from a mere FIG. 56. — SMOOTH MUSCLE FIBRES FROM THE WALL OF THE HUMAN INTESTINE. Longitudinal section. Hematein and eosin. x 665. point up to their maximum diameter, according as the section hap- pens to pass through the end or through the middle of a fibre. Because of its central location, the nucleus is onlv found in the larger transections. Smooth muscle fibers may be joined together in interlacing groups as in the wall of the uterus or bladder; or they may form broad membranous layers as in the wall of the alimentary tract ; or again, they may $ form small isolated bundles, as in the skin. & 9 * In any case, the muscle bundles are united 9 by a delicate network of connective tissue. $ Smooth muscular tissue occurs chiefly in • the walls of the hollow or tubular viscera. • Its distribution may be classified as follows : jtr (1) In the alimentary tract: lower por- tion of the esophagus, stomach, small and large intestines. (2) In the respiratory system : trachea and bronchial tubes. (3) In the genito-urinary system : ureter, bladder, urethra, penis, prostate, vagina, uterus, oviduct, and ovary. (4) In the vascular system : arteries, veins, and the larger lymphatic vessels. (5) In the ducts of all secreting glands : gall ducts and gall bladder, and the ducts of the pancreas, salivary glands, testicle, etc. (6) It is also found in the capsules of the spleen and lymphatic nodes, in the skin, and in the intrinsic muscles of the eye. FIG. 57. — SMOOTH MUSCLE FIBRES FROM THE WALL OF THE HUMAN INTES- TINE. Transection. Hcmatein and eosin. x 750. 56 THE MUSCULAK TISSUES CARDIAC MUSCLE. — The muscular tissue of the heart is inter- mediate in its phylogenic position between smooth and striated muscle. Its cells consist of a granular cytoplasm which presents distinct longitudinal fibrillations, but only indistinct transverse striation. The latter appearance indicates an incomplete differ- entiation of its ultimate fibrillae into alternate disks of light and dark (isotropic and anisotropic) substance, a differentiation which is much more highly developed in the striated variety of muscle. The cardiac muscle cell is short and broad as compared with that of smooth muscle, and is joined to its neighbors at either end. FIG. 58. — CARDIAC MUSCLE CELLS FROM THE PIG'S HEART, ISOLATED IN EQUAL PARTS OF ALCOHOL, GLYCERIN, AND WATER. Unstained. (The nuclei are somewhat darker than they actually appear.) x 410. This firm union by abutment produces long bands, cardiac muscle fibres, which are united into bundles, and as such may be fol- lowed, by careful dissection, for long distances through the cardiac wall, their course maintaining a peculiar figure-of-eight direction. The union of cells end to end to form these fibres is accom- plished by means of a cement substance, which is occasionally bridged across by fine protoplasmic fibrils. A cell membrane is wanting. The cardiac muscle cell frequently branches, and its processes anastomose with those of adjacent cells to form a coarse network of muscle fibres, which insures harmony in physiological contrac- CAKDIAC MUSCLE 57 most tion. The numerous branches of its cells constitute the prominent histologic characteristic of the heart muscle. The nucleus of the cardiac muscle cell is oval in shape, and is situated in its center. Like that of smooth muscle, its nuclear FIG. 59. — CARDIAC MUSCLE OF THE HUMAN HEART; THE ABUNDANT BRANCHES ARE PLAINLY SHOWN. Longitudinal section. Hematein and eosin. Photo, x 120. wall is distinct and its chromatin is distributed in coarse, widely separated karyosomes. The cytoplasm can be differentiated into a clear sarcoplasm and dim fibril bundles. The sarcoplasm is extremely translucent, which accounts for its apparently lighter color, and occurs most abun- dantly in the neighborhood of the nucleus. The fibrils, less trans- lucent, and therefore darker in appearance than the sarcoplasm, 58 THE MUSCULAR TISSUES are prone to arrange themselves in rows, which, as seen in transec- tion, appear to radiate more or less distinctly, from the central axis in which the nucleus lies, and toward the periphery of the cell. Heart muscle fibres occur in groups or bun- dles which are united by delicate membranes of connective tissue, — Nuc the endomysium, whose finer fibres penetrate between the individual muscle cells. The normal amount of connective tissue occur- ring among the heart muscle fibres is, however, never very large. The bundles of muscle fibres, from the peculiar figure- of-eight arrangement of the fibrous bands, characteristically inter- lace with one another, so that in sections from small pieces of the cardiac wall individual muscle fibres will be cut in all conceivable directions. \ a en FIG. 60. — THE CENTRAL PORTION OF THE PRECEDING FIGURE, MORE HIGHLY MAGNIFIED. a, cement substance uniting the ends of the mus- cle cells ; this can also be seen at several other points and even in the preceding section if carefully studied ; en, endothelium of the blood vessels ; Nuc, nucleus of the cardiac muscle cell. Hematein and eosin. x 500. t • FIG. 61. — TRANSECTION OF A GROUP OF CARDIAC MUSCLE FIBRES FROM A PAPILLARY MUSCLE OF THE HUMAN HEART. Hematein and eosiu. x 550. • ^ FIG. 62. — DEVELOPING MUSCLE FIBRES FROM THE HEART OF A HUMAN EMBRYO AT SEVEN MONTHS. Fibrillae are well developed at the periphery ; the undifferentiated cyto- plasm in the center presents a clear appearance and in some cases is partially occupied by the nucleus. Hematein and eosin. x 750. STKIATED MUSCLE TISSUE 59 In certain heart muscle cells which are found just beneath the endocardium, and are more abundant in some of the lower mam- mals than in man (Purkinje's muscle fibres), the central mass of undifferentiated sarcoplasm is exceptionally abundant, the fibril bundles occurring only at the periphery of the cell. In many heart muscle cells a small number of very fine brownish pigment granules may be found in the sarcoplasm adjoining the nucleus. STRIATED MUSCLE TISSUE (voluntary muscle). — The trans- versely striated cells of this form of muscle are the most highly differentiated of any of the three varieties. Their earliest an- lages are found in the myotomes of the body segments, in which the tissue consists of small elongated cells with a finely granular cytoplasm and a single centrally situated nucleus. These cells enlarge and soon present faint longitudinal striations. Coincident with these changes fibril bundles make their appearance at the periphery of the cell. At this stage the primitive muscle cell somewhat resembles the mature type of smooth muscle. A FIG. 63. — DEVELOPING MUSCLE FIBRES OF THE STRIATED VARIETY, FROM THE BUCCAL MUSCLES OF A FETAL PIG. A, early stage, a " myoblast " ; B, later stage, fibrillation has already begun at the periphery, but the central portion of the fibre is as yet undifferentiated ; the fibre has been cut off at one end, the left. Hematein and congo-red. x 540. Further changes include the continued differentiation of the cytoplasm into fibril bundles, and the rapid multiplication of the cell nucleus without a corresponding division of the cytoplasm. During these changes, which are accompanied by differentiation of the primitive fibrils into light and dark disks, the muscle cells frequently resemble the mature cardiac muscle fibres with their in- distinct striations. The progress and final consummation of these embryonic changes, with the consequent increase in the size of the cell, produce the mature striated muscle cell with its distinct membrane, its many nuclei, and its highly differentiated fibrillar cytoplasm. The striated muscle cell is surrounded by a highly developed cell wall, the sarcolemma. This structure may be seen in transec- tions of the muscle fibre, but is more clearly demonstrated in 60 THE MUSCULAE TISSUES teased preparations of fresh muscle fibres, in which the cell has been ruptured by gentle but firm pressure. The cytoplasm is frequently torn by this means, while the cell membrane, being of a more resistent nature, spans the interval between the rup- tured ends of the cytoplasm. Within the cell membrane the cytoplasm forms what may be termed a syncytium ; the cell frequently attains an enormous size, being, as a rule, several centimeters in length but only 30 to 80 //, in breadth. Its shape is that of a long cylinder with rounded or very bluntly pointed ends. The many nuclei, sometimes numbering hundreds for each muscle cell, are found at the surface of the fibre, lying just beneath the sarcolemma. The nuclei are ovoid in shape and possess a distinct nuclear wall and abundant chromatin. They are fre- quently surrounded by a narrow rim of un- differentiated cytoplasm, which is more abundant about the poles of the nucleus. The nuclei are also prone to accumulate at the ends of the fibre, at its insertion into the fibrous tissue of the tendon. The cytoplasm of the striated cells is the most distinctly fibrillated of the several types of muscle fibre. The ultimate fibritta are arranged in small bundles, which are separated by intervals of clear undiffer- entiated sarcoplasm. As seen in cross sec- tion this arrangement of the fibril bundles gives rise to polygonal areas within the muscle cell, the dark ends of the cut fibrils being surrounded by lighter intervals of sarcoplasm. These peculiar polygonal out- lines are described as the areas or fields of Cohnheim. The distribution of the fibrils in bundles gives rise to distinct longitudinal striations, which are visible even with the aid of very •ij FIG. 64. — STRIATED MUSCLE FIBRES RUPTURED BY TEASING, SHOWING THE SARCOLEMMA. a, ruptured end of the muscle fibre ; jB, a bundle of fibrils projecting from the torn end ; m, a muscle fibre ; w', a nucleus of the muscle cell ; at p, the mus- cle substance has shrunken away from the sarcolem- ma ; s, sarcolemma. Mod- erately magnified. (After Eanvier.) u FIG. 65.— ISOLATED FRAGMENTS OF STRIATED MUSCLE FIBRES, UNSTAINED. The one above is from the end of a fibre; that on the right shows at one end a tendency to cleavage into transverse disks, x 360. FIG. 66.— STRIATED MUSCLE FIBRES OF THE DOG, SEEN IN TRANSEOTION. The areas of Cohnheiui are indistinctly outlined. Hematein and eosin. x 490. 61 THE MUSCULAR TISSUES low magnification and even in living muscle fibres. When examined under higher magnification, after teasing, or in thin sections, the fibril bundles can be seen to consist of nu- merous still finer fibrils, the ultimate fibrillw (sarcous element of Bowman, sarcostyle of Schafer). These ultimate fibrillae are also seen to consist of alternate light and dark disks. When examined under polarized light the dark disks are found to be anisotropic or doubly refracting, the light disks isotropic or singly refracting. The alternate light and dark disks are so disposed within the muscle cell that the corresponding disks of adjacent fibrillse lie in the same transverse plane. This arrangement produces alternate light and dark composite disks whose diameter corresponds with that of the muscle cell. These larger alternate light and dark disks, each composed of the corresponding portions of innumerable ultimate fibrillae, give rise to an appearance of transverse striation which is so readily visible under either low or high mag- nification as to become the most prominent characteristic of this type of muscle cell. Regarding the minute structure of the ulti- mate fibrillse, there is still much discussion. That the alternate light and dark disks are more than mere optical illusions is evidenced by the fact that they react differently to stains, notably to gold chlorid. Bisecting the middle of the dark disk, Hensen in 1868 described a fine light line, Henseri*s line, and it is possible by the action of certain reagents, e. g., acids, alkalis, and artificial gastric juice, to produce transverse cleavage of the muscle cell along this line (Ranvier *). z h FlG. 67. — A BIT OF A STRI- ATED MUSCLE FIBRE SEEN IN LONGITUDINAL SECTION. The alternate light and dark cross striations are well shown, ft, light line, Hensen's line, in the mid- dle of the dark disk Q. z, dark line, Krause's membrane or Dobie's line, in the middle of the light disk. Hematein. x 1200. (After Bohm and von Davidoff.) FlG. 68. — A SMALL POR- TION OF A MUSCLE FIBRE OF A CRAB SHOWING BEGINNING SEPARATION INTO FI- BRILS. Drawn from a photo- graph, x 600. (After Schafer.) * Traits technique d'histologie. STRIATED MUSCLE TISSUE At about the same time Krause described a dark transverse line which bisected the light disk. This line, the membrane of Krause (Dobie's line), may be readily seen under ordinarily high magnification. The interpretation of this appearance, however, is somewhat doubtful. Following its description by Amici in 1859 and Krause in 1868, it was considered that a complete mem- brane bisected the light disk, but this conclusion was discredited by the observations of Dobie, Kuhne, and others, and is strenuously opposed by Scha- fer, who regards Krause's membrane as the optical ex- pression of a row of dark dots or granules disposed in one transverse plane, each dot ly- ing in the angle between adja- cent areas of un differentiated sarcoplasm. Striated muscle cells rarely branch, yet in those locations where its fibres are inserted into the subcutaneous or sub- mucous connective tissue, e. g., the face, scrotum, tongue, etc., branching fibres frequently occur. Within the muscles the individual cells are united by a delicate connective tissue endomysinm which penetrates between the fibres and sup- ports a liberal supply of capil- lary vessels. The muscle fibres are, however, unequally dis- tributed within the muscle, numbers of muscle cells being united to form fibre bundles or fasciculi, which are surrounded by thicker membranes of con- nective tissue, the perimysium. The fasciculi are in turn united by bands of connective tissue derived from a firm fibrous mem- brane, i\\j)f£gimysium, which surrounds the entire muscle. FIG. 69.— FIBRILS FROM THE WING MUSCLES OF A WASP. A, contracted; #, stretched; (7, uncon- tracted. The alternate dark and light disks are prominent ; the membrane of Krause in the light disk, and the line of Hensen in the dark disk are well shown. Very highly magnified. (After Schafer.) 3, J\\p£&m 64 THE MUSCULAR TISSUES Blood and Nerve Supply. — The muscular tissues are richly supplied with nerves, blood vessels, and lymphatics. The larger FIG. TO. — STRIATED MUSCLE FIBRES OF THE DOG. The blood vessels have been filled by injection with a gelatinous mass and are rep- resented in black. One whole fasciculus and one fibre from an adjacent fasciculus have been included, a, perimysium ; 6, endomysium ; c, a large vein seen in transection. The section was not stained, x 80. .-. .-• •• • f_ -< fl FIG. 71. — STRIATED MUSCLE OF A CAT SEEN IN TRANSECTION. The blood vessels have been injected and are black in the figure. At a an artery is contracted and empty. The heavy black vessels are veins and arterioles ; the small black dots are capillaries in transection. One whole fasciculus is represented and is sur- rounded by a delicate perimysium of connective tissue. Between the muscle fibres is the still more delicate endomysium. The larger vessels are almost exclusively found in the perimysium. The section was not stained, x '80. STRIATED MUSCLE TISSUE 65 nerve trunks are found in the loose connective tissue which sur- rounds the muscle, and in the epimysium and perimysium. From these trunks fine branches enter between the muscle fibres and break up into a plexus of delicate fibrils. The terminations of the nerve fibres are found within the sarcolemma of the muscle cell as the motor end plates and, in striated muscle, as the terminal filaments of special sensory endings, the muscle spindles* The blood vessels also distribute their larger trunks within the connective tissue of the epimysium. The smaller branches pene- trate the endomysium and supply a rich capillary plexus with long rectangular meshes. This network of capillaries surrounds the c FlG. T2. — POBTION OF A TRANSECTION OF A LARGE TENDON. a, fibrous capsule with circular, and at &, longitudinal bundles of connective tissue ; c, d, and e, fibrous septa between the fasciculi of the tendon ; Z, lymphatic cleft. Moder- ately magnified. (After Schafer.) muscle cells so completely that each cell is placed in relation with four or five capillary vessels which run parallel with the long axis of the cell. Numerous lymphatics occur in the perivascular connective tis- sue. These lymphatic vessels are especially abundant in the car- diac muscle. The distribution of the blood and nerve supply of cardiac and smooth muscle closely resembles that of the striated variety. The larger trunks are found only in the thicker connective tissue membranes, but the smaller nerve trunks and capillary vessels * See chapter on the Peripheral Nerve Terminations. 6 66 THE MUSCULAK TISSUES penetrate between the individual fibres of the cardiac muscle and between the smaller fibre bundles of smooth muscle. The TENDONS of the striated muscles consist of parallel bands of dense white fibrous tissue, between whose bundles are found rows of flattened connective tissue cells, which are frequently much enlarged and have a peculiar oblong shape. At the junction of the tendon with muscle each small bundle of tendon fibres becomes continuous with the sarcolemma of a muscle cell, the end of the tendon bundle being concave to receive the rounded end of the muscle fibre. At this end of the cell the muscle nuclei are especially abundant. Table showing the more important differential characteristics of the several varieties of muscle cells. STRIATED. SMOOTH. HEART. Longitudinal fibrillae . Transverse striations. ! Number Marked. Marked. Numerous. Present. Absent. One. Distinct. Present. One (or two). Shape Ovoid Rod-shaped Ovoid Situation . . Branches Peripheral. Rare Central. Rare Central. Numerous Htt&f" Shape Several cm. 40 to 100 A*. Long cylinders. Short (and slender). 5 to 10 /*. Fusiform. Short (and broad). 30 to 50 /x. Short prisms (uni- Sarcolemma Present Absent ted to form long fibres). Absent CHAPTEE VI BLOOD THE blood is a bright red, semi-opaque fluid, which circulates within a closed system of vessels, the circulatory system. The blood may be considered as a primary tissue, whose peculiar cell elements are the blood corpuscles, and whose intercellular sub- stance is the fluid blood plasma. Its corpuscles, according to their color, are of two varieties : those which are colored, the red blood cells, and those which are colorless, the white blood cells. To these must now be added the blood platelets, minute protoplasmic masses of definite form which are constantly present, and are therefore true structural elements of the blood, but which can as yet scarcely be classed as tissue cells. When blood is removed from the body it immediately assumes a viscid consistence, and in a short time will solidify into a jelly- like mass, the blood clot. This peculiar property is part of the phenomenon of coagulation — a phenomenon which results from a rearrangement of the chemical constituents of the blood with the formation of a new histological element, the fibrin. Coagulated blood consists of corpuscles, fibrin, and a fluid serum which differs from the plasma in its chemical composition, though the two fluids are very similar in their histological appearance. RED BLOOD CORPUSCLES (colored blood corpuscles, red blood cells, erythrocytes). — The red blood cells are minute circular disks with biconcave surfaces and rounded or convex edges. The color of the corpuscle differs according as they are viewed by reflected or by transmitted light. By reflected light they have a bright red color, by transmitted light a faint greenish-yellow or amber shade. This color is entirely due to the presence of hemoglobin within the corpuscle ; the so-called shadows which remain after the hemo- globin has been dissolved out of the cell are absolutely devoid of color, and possess very little affinity for stains. Since all the hemoglobin of the blood is contained within these red cells, the 67 68 BLOOD familiar red color of the blood is due to reflection of light from the surface of its innumerable colored corpuscles. The suspen- sion in the blood plasma of a multitude of transparent disks which act in part as biconcave — center of the corpuscle — and in part as biconvex circular lenses — corpuscular rim — accounts in great measure for the opacity of thick layers of blood. The average diameter of a red blood cell is 7.5 /A (-j^W inch) ; its thickness varies from 2 to 4 /*. These cells vary but little in size. Seventy-five per cent of the red cells in human blood will measure 7.5 /A, the remainder are either a little smaller or a little larger than the average, the normal extremes being about 6 /* and 8 fji respectively. Those of extreme size are called megalocytes, while the smallest are microcytes. FIG. 73. — FROM A FRESHLY PREPARED, UNSTAINED SPECIMEN OF HUMAN BLOOD. Three leucocytes, an eosinophile, a polynuclear, and a lymphocyte, are represented. Many red blood cells, some " on the flat," some in rouloux and in profile, are also shown, x 1200, but reduced somewhat in reproduction. (After Schafer.) The number of red corpuscles in the blood is subject to con- stant variation between wide limits. Many physiological condi- tions influence their total number, as well as the relative proportion of red cells to the white. The average number of red blood cells in the adult male is about 5,000,000 per cubic millimeter. In EED BLOOD CORPUSCLES 69 young robust persons the number may be considerably higher. The number may also be much reduced by considerable hemor- rhages or by the imbibition of large quantities of fluid. Profuse perspiration tends to produce concen- tration of the blood and an apparent increase in the number of its corpuscles. The number of red blood cells in the female is slightly less than in the male, about 4,500,000 per cubic millimeter. The red blood cell consists of a com- pound of hemoglobin with a colorless mass, the "stroma" of Rollett. The precise manner in which the hemo- globin is contained within this stroma has been the subject of considerable discussion. The recent investigations of G. K. Stewart * on the effect of lak- ing reagents on the blood would tend to show that the hemoglobin is in part held in solution in the stroma, and in part in more intimate combination. That this stroma is not, as Rollett sup- posed, a structureless mass, may now be considered as satisfactorily demon- strated. Much evidence lately ad- vanced tends to show that the red cell, though not possessed of a distinct cell membrane in the sense of Schwann, is nevertheless supplied with an external limiting layer, a thickened exoplasm, which is homogeneous in appearance, is insoluble in water, permits free osmotic currents, and probably contains the traces of lecithin and cholesterin which are found in the red blood cells. Important information concerning the internal structure of the stroma is furnished by the fact that the large nucleated red blood cells of amphibians, as well as the early nucleated cells, erythroblasts, of man and mammals, have been shown to possess a reticular or alveolar structure. However, the living red blood cells of human blood under ordinary conditions show no trace of inter- FIG. 74. — BLOOD CELLS FROM A SPECIMEN OF FRESHLY DRAWN UNSTAINED HUMAN BLOOD. A, red blood cells, deep focus, showing a light center and dim margin ; B, the same with a high- er focus ; the center, being slightly out of focus, is dim while the margin is light; (7, crenated red cells from the margin of the prepa- ration ; a, deep focus ; 6, higher focus ; D, two polynuclear leuco- cytes ; E, large mononuclear leu- cocyte, x 750. * J. of Physiol., 1899 ; also J. of Med. Research, 1902. 70 BLOOD rial structure, and in their mature form possess no semblance of a nucleus. Nucleated red blood cells in man are only found as pre- mature forms in the hemopoietic tissues and in the circulating blood in early embryonic life. In the later periods of fetal life, and even in the first year of childhood, an occasional nucleated red cell may be demonstrated in the blood current. Diseased con- ditions, involving rapid regeneration of blood cells, are, however, frequently accompanied by the appearance within the general blood current of nucleated red cells, erythroblasts, in considerable numbers. Effect of Reagents upon the Red Blood Cells.— The effect of certain reagents upon the red cells throws much light upon their finer structure, and especially upon their relation to osmotic proc- esses. The red cells apparently exist within the blood, floating free in its plasma, in a state of osmotic stability ; the plasma is then an isotonic solution as regards the red cell. Should the spe- cific gravity of the blood plasma be in any way increased, it imme- diately becomes hyperisotonic for the red cell ; should, on the other hand, the specific gravity be diminished, the plasma becomes hyp- isotonic. It should be borne in mind that osmotic flow occurs in a direction from the lighter toward the heavier fluid. Water. — The addition of water to the blood plasma diminishes the specific gravity of the latter, and produces an osmotic flow into the red cells. The corpuscles promptiv a I c d e ,, , ,, . , . 5 8ft & fb r*} swell, lose their biconcave shape, and fj gp \ir v_y finally, from the extreme distention, Fio. 75.— SHOWING THE ACTION their limiting membranes apparently or WATER UPON THE RED rupture ^ permit the escape of the BLOOD CELL. • , ' . » a, the cell in profile; 6-,, hemoglobin; the remaining colorless various stages in the transfer- stroma of the red cells forms the so- mation which leaves only a caned " blood-shadows." The rapidity "shadow" e\ diagrammatic. , , , , . ,. , , (After Schafer.) °* these changes is apparently dependent upon the amount of water added to the plasma, and therefore upon the degree of hypisotonicity produced in the latter. Saline Solutions (hyperisotonic). — Solutions of sodium chlorid, magnesium sulfate, etc., whose specific gravity is greater than that of the blood plasma, when added to the blood produce a con- dition of hyperisotonicity. The consequent osmosis takes place from the corpuscle to the plasma ; the corpuscular wall promptly collapses and presents an irregular spinous or serrated profile — EED BLOOD CORPUSCLES 7J becomes crenated. The rapidity and extent of the collapse and consequent crenation appear to be dependent upon the degree of hyperisotonicity produced, and the consequent volume of the out- ward osmotic flow. Normal Saline Solution (isotonic). — It is possible to produce a saline solution whose specific gravity corresponds with that of the plasma, and which is isotonic for the corpuscles. An aqueous solution of this character contains about 0.9 per cent of sodium chlorid. The exact strength of such a solution can not be accu- rately stated, for the reason that the tonicity of the blood plasma not only varies somewhat in different individuals, but also in the same individual at different times and under varying conditions of diet, absorption, excretion, etc. An isotonic solution, when added to the blood, will be found to produce no visible change in the appearance of the blood cells. Certain reagents, as well as extremes of heat and cold, have the property of rapidly dissolving out the hemoglobin, laking the blood, either by rupture or by solution of the corpuscular envelope. Such reagents are dilute acids or alkalis, bile, and the serum from a different species of animal ; the last-mentioned reagent possesses a certain forensic value in determining the animal species of a given specimen of blood. These reagents, when mixed with human blood, produce a rapid destruction of its corpuscles — hemolysis. These osmotic peculiarities, taken in connection with other facts — e. g., the presence of a cell membrane in the red blood cells of animals beneath the mammalian type ; the extreme elasticity of the corpuscle, which can be distorted into almost any conceivable shape, but returns immediately to its original form ; and the tend- ency of the corpuscles in undiluted blood to adhere to each other in the form of moniliform piles, rouleaux, like rolls of coin, their cohesion being apparently due to the presence in their envelope of cholesterin and lecithin, which possess the physical properties of a fat — would seem to demonstrate beyond a doubt the presence in the red blood cell of an outer exoplasmic envelope differing in structure and in composition from its contained endoplasm. Development of the Red Blood Cell.— The earliest embryonic origin of the red blood corpuscle is a much disputed point. Ac- cording to van der Stricht,* however, they first appear in the * Compt. rend. soc. de biol., 1895. BLOOD " blood islands " of the extra-embryonic vascular area of the meso- blast. Their mode of origin in this location is essentially intra- cellular, through the medium of the " vow-formative cells." This process consists essential- ly in the enlargement and 7i excavation of the vaso- formative cell groups, their nuclei undergoing division by mitosis, some- times without corre- sponding division of the cytoplasm, the daughter nuclei forming in some cases primitive nucleated blood cells, and in others the nuclei of the endo- thelial wall. According to Ranvier, minute par- ticles of the vaso-forma- tive cytoplasm may sepa- rate from the parent mass to float free as non- nucleated, hemoglobin containing cells within the primitive blood vessel. Similar vaso-formative processes occur throughout the meso- blastic tissues in the early periods of fetal life. They have been carefully studied in the subcutaneous tissue and the omentum by Schafer, Ranvier, Minot, Nicolaides, et als. ; but more recent ob- servations by S. Mayer, E. Neumann, Spuler and Fuchs tend to throw discredit upon the previous conclusions, inasmuch as these FIG. 76. — "VASO-FORMATIVE" CELLS FROM THE MES- ENTERY OF A BABBIT SEVEN DAYS OLD. gr.s., red blood cells; w, nucleus of the vascular endothelium ; p, points of growth, at which extension occurs. Highly magnified. (After Eanvier.) FlG. 77. A " VASO-FORMATIVE CELL.7 a, isolated red blood cell. Note the apparent disintegration of the red blood cells shown in the middle of the figure. (After Fuchs.) observers maintain that the vaso-formative cells instead of being developing cells are in reality in a state of degeneration, they hav- ing been separated from the general vascular current by occlusion of the lumen. The small, hemoglobin containing, protoplasmic RED BLOOD CORPUSCLES 73 masses found within such cells and described by Ranvier as true microcytes are taken by these authors to be minute portions of the included red cells. Fuchs, especially, (see Fig. 77) describes the disintegration not only of the cytoplasm, but of the nuclei of oc- cluded erythroblasts as well. The formation of red blood cells within the " vaso-formative " cells of the mesoblastic tissues, in the later periods of fetal life at least, must be considered as somewhat doubtful. With the appearance of the fetal liver, at a very early period, the bulk of the hemopoietic function seems to be transferred to this organ, in the " blood-islands " of which, nucleated erythroblasts are rapidly formed by karyokinesis. The primitive spleen also as- sumes a small portion of the blood forming function. In neither of these organs, however, does this function appear to persist much beyond the term of intra-uterine life. The appearance of the red marrow of fione marks the transfer of a steadily increasing portion of the hemogenic function to this tissue. Moreover, bone marrow seems to be the sole tissue in which the function persists throughout adult life. In this tissue the red blood cells are developed by mitosis, occurring within hemoglobin containing erythroblasts. This process is, however, confined to the marrow tissue proper, the red cells, after the dis- appearance of their nucleus, only secondarily gaining admission to the vascular channels* (Swaen et Brachetf). The disappearance of the nucleus of the daughter erythroblasts may possibly be the result of extrusion (Rindfleisch {), or more probably of solution (Kolliker |j). In the latter case the nucleus is said to disappear by karyotysis ; if during this process the chromatin becomes collected into a small compact mass, the nucleus is said to disappear by pylcnosis. The more important histological deductions from the foregoing facts may be stated as follows : 1. All red blood cells are in their primitive condition nucle- ated, viz., erythroblasts, and consequently biconvex rather than biconcave. * In this connection the observation of Ascoli (Giorn. d. R. Accad. di Med. di Torino, 1899), that nucleated red blood cells are constantly present in the efferent tibial vein of the dog, is of interest. f Arch, de biol., 1902. % Arch. f. mik. Anat, 1879. j Handbuch der Anat. 74 BLOOD 2. In fetal life — and in certain diseased conditions — blood for- mation occurs with sufficient rapidity to permit the immature erythroblasts to gain entrance into the general circulation. The red blood cells of the earliest fetal circulation are therefore all nucleated, those of later fetal life are nucleated in constantly decreasing proportion, while in healthy extra-uterine life only mature non-nucleated forms occur in the general blood current. 3. The primitive nucleated red cells, the type having been once firmly established in the early fetus, are reproduced by mitotic division of similar parent cells. 4. Though the size of the primitive cells varies considerably, and is for the most part larger than that of the mature forms, yet prior to their entrance into the general circulation of the adult, all erytlirocytes closely approximate a constant diameter of 7.5/x. WHITE BLOOD CORPUSCLES (white blood cells, leucocytes, colorless corpuscles). — The white blood cells are nucleated granular masses of protoplasm usually of spherical form but possessing a remarkable tendency to undergo active amoeboid motion, They are of a distinctly viscid consistence, adhering more or less closely to the vascular walls, and therefore lying at the periphery of the blood stream, while in circulation. In microscopical preparations of freshly drawn blood they adhere quite firmly to the glass slide or cover. With moderately high magnification the cytoplasm of the white blood cell is seen to possess fine granules which vary in number and in size in different cells. The greater portion of these cells possess numerous fine granules (neutrophiles) ; a smaller portion show no cytoplasmic granules in freshly prepared speci- mens (the non-granular, "hyaline" or mononuclear leucocytes); occasional cells show very coarse granules throughout their cyto- plasm (eosinophiles). All forms of white blood cells possess a nucleus which, how- ever, is only faintly visible in the living cell, but is readily brought into view by the action of dilute acids, which also cause the cyto- plasmic granules to accumulate about the nucleus. The nucleus is likewise brought into view by other laking reagents — water, bile, electricity, etc., as well as by hyperisotonic solutions — heavy solutions of sodium chlorid, etc. Normal blood contains 6,000 to 8,000 white blood corpuscles per cubic millimeter. They are therefore present in the propor- tion of 1 to 600 or 800 red corpuscles. This ratio is, however, -/v / * FIG. 78. FlVE NUCLEATED BED CELLS FROM THE BLOOD OF A FROG. Eosin-methylen blue. Basting's method. x 1200. FIG. 79. THREE NUCLEATED RED BLOOD CELLS FROM THE MARROW OF A HUMAN RIB. Eosin-methylen blue. Jfocht method. x 1200. FIG. 80. A GROUP OF CELLS FROM NORMAL HUMAN BLOOD. 7, red blood corpuscles in rouleau formation ; 2, red blood corpuscles, surface view ; 3, lymphocyte ; 4, large mononuclear leucocyte ; 5, polynuclear, finely granular leucocyte ; 6, eosinophile leucocyte ; 7, a group of blood platelets ; 8, basophile leucocyte. Eosin- methylen blue. Hasting's method, x 1200. WHITE BLOOD CORPUSCLES 75 subject to constant variations from physiological causes, e. g., digestion, absorption, etc. Varieties of White Blood Corpuscles.— After fixation and stain- ing the nucleus, as well as the cytoplasmic granules, is found to present characteristic differences in the several varieties of white blood corpuscle. The nuclei of the non-granular cells — mono- nuclear leucocytes — are spheroidal in shape, have a fairly distinct nuclear membrane, and possess a varying amount of irregularly distributed chromatin. The size of the nuclei of these cells is also variable, and upon these differences two cell types are recog- nized, the large and the small mononuclear. The small mononuclear leucocytes — lymphocytes — possess a highly chromatic and therefore deeply staining nucleus of small size which occupies nearly the entire cell, the encircling rim of cytoplasm being extremely narrow and at times scarcely demon- strable. The large mononuclear cells — " spleenocytes " of Virchow —possess a wider cytoplasmic rim and a large nucleus with a dis- tinct nuclear wall ; the nucleus in contradistinction to that of the lymphocyte is deficient in chromatin, and therefore is- but lightly stained with nuclear (basic) dyes. The cytoplasm of the mononuclear cells under moderate mag- nification presents a hyaline structureless appearance, but with higher magnifying power a delicate reticulum and at times, especially in the large mononuclear forms, very fine neutrophile granules can be demonstrated. The nucleus of the mononuclear forms, but much more fre- quently that of the larger variety only, occasionally deviates from its typical spheroidal form, being notched, indented, or even of almost a horseshoe shape. In this latter form these nuclei some- what resemble those of the polynuclear cells to be described, yet they are readily distinguished therefrom by their characteristic deficiency in nuclear chromatin and cytoplasmic granules. The finely granular white blood cetts— polynuclear leucocytes— after fixation and staining, present a highly chromatic, deeply basophilic nucleus which varies greatly in form. Thus it may be indented, horseshoe-shaped, S-shaped, elongated and twisted upon itself, or separated into distinct lobes which are connected together by means of fine chromatic filaments. It is thus characteristically polymorphous, but in all its varying forms it is readily distinguish- able from the mononuclear types by its extreme depth of stain, its intense cJiromatophilia. 76 BLOOD The cytoplasm of these cells is considerable in amount and presents an extremely delicate reticulum, at the intersections of whose meshes are the minute neutrophile granules, which give the cell its finely granular appearance as seen in the freshly prepared specimen. The characteristic finely granular protoplasm and the polymorphous nucleus are the distinguishing peculiarities of these cells, the so-called "polynuclear neutrophile leucocytes." P. Ehrlich in a series of communications announced that by coloring the leucocytes with various stains he was able to distinguish by their reaction, sev- eral types of granules. These he called (a) oxyphile or acidophile, which were deeply stained by eosin, acid fuchsin, etc. ; ()8) amphophile, which were stained both by eosin, and by dahlia and like dyes ; (7) basophile, which were stained deeply by dahlia, thionin, etc.; (5) certain cells which neither after stain- ing with eosin, etc., nor with dahlia, etc., could be made to show any granules other than the nodes of the cytoreticulum ; (e) neutrophile, which can be stained only by a due admixture of acid and basic dyes, as of fuchsin and methylen blue, or the so-called " triacid mixture " of Ehrlich. The demonstration of these characteristics presupposed a division of dyes into three primary classes : 1. Acid — e. g., eosin, orange-G, acid fuchsin, aurantia, erythrosin. 2. Basic— e. g., methylen blue, dahlia, thionin, hematein. • 3. Neutral — which are only formed by the interreaction of examples of each of the two preceding classes ; the neutral dye is supposed to arise de novo in such mixtures, as a result of 'chemical reaction. The application of such a classification of stains to other tissues than the blood has, however, been found to present considerable difficulties. Centrosomes and mitotic figures have been repeatedly demon- strated in the polynuclear neutrophiles of the lower vertebrates and in those of human blood by Fleming,* Gulland,f and others. The meshes of their cytoplasmic reticulum — exclusive of the neu- trophile granules — present a very slightly aci- dophile character, so that by overstaining in eosin, erythrosin, etc., the cytoplasm of these FIG 81 —LEUCOCYTES ce^s "takes on a distinctly red tint. That this IN PROCESS OF reaction is not due to the presence of hemo- MTOSIS- globin is evidenced by the fact -that red blood From the red mar- n contajnea jn the same specimen will in- row of a guinea-pig. * (After Demarbaix.) variably stain much more deeply with the acid dye than any of the leucocytes. The coarsely granular leucocytes of the blood — eosinophiles — possess a nucleus which presents the same polymorphous form * Arch. f. mik. Anat., 1891. t <*• of Physiol., 1896. WHITE BLOOD CORPUSCLES 77 and highly chromatic, deeply staining character as that of the polynuclear neutrophile type. Their cytoplasm differs, however, in that the intersections of the meshes of its cytoplasmic retic- ulum are occupied by very coarse spheroidal granules which are highly acidophile, and therefore stain deeply with such dyes as eosin, erythrosin, and acid fuchsin. The cytoplasm of these cells, exclusive of its specific granules, possesses a slightly acidophile nature similar to that of the polynuclear neutrophile type ; this peculiarity can be readily demonstrated, as in the former case, by overstaining with acid dyes. Centrosomes and mitotic figures have also been repeatedly demonstrated in these cells. Other coarsely granular cells — basophile leucocytes — possess a considerable rim of cytoplasm containing very coarse basophile granules. They are usually mono-, though frequently polynuclear. They form about 0.5 per cent of the white blood cells, and can therefore be disregarded' as a normal constituent of human blood. In certain diseased conditions, notably in myelogenous leukemia, they appear in the circulation in considerable numbers. None of the several forms of white blood cells possess a cell membrane, and in marked contradistinction to most other cells of the body the presence of a peripheral condensation of the cyto- plasm (exoplasm) can not be demonstrated with any degree of cer- tainty. The several varieties of white blood corpuscles found in normal blood, with their prominent characteristics, may be summed up as follows : . 1. Small mononuclear leucocytes or lymphocytes, with a non- granular basophile cytoplasmic rim of insignificant breadth, and a spheroidal deeply staining nucleus whose abundant chromatin is characteristically clumped to form even more deeply staining karyosomes. These cells are the smallest of the several types of leucocyte, and they form from 22 to 25 per cent of the white blood corpuscles in human blood.* 2. Large mononuclear leucocytes with a considerable rim of non-granular cytoplasm in which a slightly basophile reticulum can be demonstrated. These cells possess a faintly staining vesic- ular nucleus which is poor in chromatin ; it is typically sphe- roidal in shape, but may be notched, indented, or even horseshoe- * These figures are those originally given by Ehrlich. In infancy the rela- tive percentage of small mononuclear leucocytes is often greatly increased (50 per cent) at the expense of the polynuclear neutrophiles (40 per cent). 78 BLOOD shaped. This is the largest of the several types of leucocyte : they form 2 to 4 per cent of the white corpuscles of the blood. 3. Polynuclear neutropMle leucocytes (" polymorphonuclear " neutrophiles, polynuclear leucocytes) possess a broad rim of cyto- plasm, which contains fine neutrophile granules, and a deeply staining polymorphous nucleus consisting frequently of three or four ovoid lobes united by a delicate chromatin thread. These are relatively large cells : they form 70 to 72 per cent of the white blood cells, and are therefore the most abundant of the several types of leucocyte. 4. Eosinophile leucocytes (polynuclear eosinophiles, acidophiles, or oxyphiles) have a broad rim of cytoplasm with very coarse, highly acidophile granules, and a highly chromatic polymorphous nucleus which resembles that of the neutrophiles and consists usually of several distinct lobes united by chromatin threads. In relative size they are similar to the neutrophiles. Eosinophile cells form 2 to 4 per cent of the white blood corpuscles. 5. Basophile leucocytes (" mast-cells ") are provided with a con- siderable cytoplasmic rim containing coarse basophile granules; they may be either mono- or polynuclear, the nucleus in either case not being richly supplied with chromatin. In size these cells resemble the neutrophiles. They are the least frequent of the several types of leucocytes, but form at least 0.5 per cent of the white blood cells. Development of the White Blood Cell.^-The primary origin of the embryonic white blood cells is still a matter of some obscurity. They make their appearance considerably later in fetal life than the red blood cells. According to Saxer,* the first white blood cells are derived by reproduction and differentiation of those same ances- tral mesoblastic cells which at first form only red blood cells, but later the white cells as well. These primitive wandering cells gain admission to the blood vessels by their amoeboid activity. Kostianecki,* however, thinks that these ancestral cells are formed within the dilated portions of the primitive vessels,, and that the earliest white blood cells are therefore formed within the vessel and probably stand in intimate genetic relation with the primitive endothelium.f *Anat. Hefte, 1896. f The recent studies of Beard have thrown some doubt upon the former conception. This observer finds that there are no leucocytes in the blood prior to the appearance of the anlage of the thymus. He also finds that in the earliest WHITE BLOOD COKPUSCLES 79 In later fetal life, as in the adult, the formation of white blood cells takes place actively in all the lymphoid organs and tissues. Those cells which are found in the germinal centers of the lym- phatic nodules are especially active ; their cell reproduction is by mitosis, the daughter cell, according to Fleming, being of the lymphocyte type. The presence of centrosomes and mitotic figures in all varieties of leucocytes, both in the adenoid tissues and under certain con- ditions in the blood as well, has been so constantly found as to indicate that this, rather than amitosis as was formerly supposed, is perhaps the only method of cell division by which white blood cells are reproduced. The same fact would indicate that each variety of leucocyte when once established is capable of repro- ducing itself. As soon as leucocytes appear in the fetal blood current all of the several varieties can be distinguished. It is therefore doubt- ful if one variety can in any way be regarded as a more mature form than the other. While in fetal life all varieties of leucocyte may be formed in any lymphoid organ, yet with the appearance of the bone marrow the formation of the granular varieties, eosinophiles, neutrophiles, and basophiles, appears to become most active in this tissue. It is possible that the marrow is the only tissue in which these cells are reproduced in adult life (Ehrlich). The mononuclear non- granular types — lymphocytes and large mononocular cells — con- tinue to be actively regenerated in the lymphoid organs, i. e., the lymphatic nodes, lymphatic nodules, and spleen. The finding of large giant cells, megakaryocytes, — resembling the osteoclasts, but differing therefrom in that the former pos- sess a single polylobar nucleus, whereas the osteoclast is multinu- clear, each nucleus being of ellipsoid shape and of approximately equal size — in all hemopoietic tissues, has been taken to indicate anlage of the thymus primitive leucocytes are formed by mitotic division of cells which are apparently derived from the epithelium of the gill clefts. Working independently, Nussbaum also found that the anlage of the thymus in fishes was derived from the epithelium of the primitive gill clefts. These observa- tions would therefore indicate a possible ectoblastic origin for the leucocytes, and that the earliest cells of this type, as later in life, are derived from the lym- phoid organs, and only by their characteristic nomadic tendency do they gain admission to the primitive blood vessels to be thereby distributed to distant portions of the fetal body. These observations, however, lack further con- firmation. 80 BLOOD a relation between these giant cells and the formation of blood corpuscles. It seems probable, however, that these cells are more concerned with degenerative processes, e. g., the absorption of the nuclei of erythroblasts, than with the regeneration of blood cells. THE BLOOD PLATELETS (third corpuscles, Uood plaques or plates, hematoUasts of Hay em, tlirombocytes). — The blood platelets are minute ovoid or ellipsoid, colorless, granular bodies much smaller than the red blood cells. They vary considerably in size, but are mostly from 2 to 4/A in diameter. Blood platelets can be demon- strated in living blood, and therefore form a constant structural element of the blood. It is FIG. 82.— A GROUP OF BLOOD PLATELETS, f ound that after drawing blood from the vessels FROM THE HUMAN these elements increase rapidly in number for a short period, and as their number is subject Veryhighlymagmfied. . . * . (After Eisen.) to constant variation from other causes it is impossible to assign them a definite numerical relationship to the red and white blood cells. The number of blood platelets has been variously estimated at from 200,000 to 600,000 per cubic millimeter. The blood platelets present a remarkable tendency to collect into masses containing considerable numbers of these elements. It is in the vicinity of such accumulations that the first fibrils of fibrin make their appearance during coagulation, and for this reason the platelets have been assumed to bear an important rela- tion to the production of fibrin in shed blood. Blood platelets as a rule present but little appearance of finer cell structure. They are usually non-nucleated globular masses of finely granular protoplasm which have a slight affinity for most basic dyes and are deeply stained by gentian violet, thionin, etc. Under favorable conditions they can be observed to execute amoe- boid movements, sending out long and very slender protoplasmic processes. Nuclei can also be demonstrated in at least a portion of the platelets, and some observers (Deetjen,* Kopsch f) are in- clined to consider them as being typically nucleated blood cells. The development of the platelets is still obscure. They were formerly supposed, because of their basophile properties, to be products of degeneration or of disintegration of the white blood corpuscles. This theory has not received further corroboration. * Arch, f . path. Anat., 1901. f Anat. Anz., 1901. OTHER ELEMENTS OF THE BLOOD si On the other hand, the platelets undoubtedly stand in relation to the red blood cells, since the latter can frequently be seen in the apparent act of extruding from their substance globular elements closely resembling the platelets in appearance and staining reaction. More or less apparent confusion of the subject has arisen from the supposed analogy of the true blood platelets of human blood with certain other structures found in the blood of the lower ver- tebrates, especially the " spindle-cells " of amphibians. Eisen * has cleared the matter considerably by demonstrating the presence in batrachian blood of true platelets in addition to the characteristic " spindle-cells." He has also shown that in at least one species the true platelets represent the survival of the extruded centro- some and archoplasm of the red blood cells. These platelets he finds to be at first nucleated and amosboid (plasmocytoblasts) ; by mitotic division the plasmocytoblasts of Eisen produce plate- lets which lose their nucleus and in every way resemble the true blood platelets (plasmocytes of Eisen). It is thus possible that the nucleated platelets of mammalian blood are premature types, and that the true platelets are genetically related to the disap- pearance of the nuclei of the erythrocytes with the possible sur- vival of certain of its achromatic portions. OTHER ELEMENTS OF THE BLOOD.— Under certain condi- tions the blood contains a considerable proportion of fat globules. These are most abundant a few hours after a hearty meal, especially if it contain an undue proportion of fatty food. The fat globules which are thus found are of small size and float free in the plasma. In addition to fat the blood has been found to contain other fine granular particles which mostly represent the detritus from disintegration of the blood cells. The "Wood-dust" and the " hemoconia " of Miiller are of this nature. Plasma and Serum. — Plasma is a clear colorless fluid in which the formed elements of the blood are suspended. It is therefore devoid of histological structure. Serum is likewise of a fluid nature, but differs histologically from the plasma in that it contains in solution or suspension the products of that disintegration of blood cells which is concomi- tant with coagulation. Serum is therefore of a faint amber color from the presence of hemoglobin in solution, and in addition to * Proc. Calif. Acad. of Sc., 1897; also, J. of Morphol., 1899. 7' 82 BLOOD the corpuscular clot it contains fragments of red and white cor- puscles and of fibrin. Fibrin. — If a specimen of freshly drawn blood be allowed to remain in the field of the microscope, it will be noticed, after some time, that fine colorless fibrils appear within the spaces be- tween the corpuscular elements. This forma- tion of fibrin takes place first in the more exposed portions of the specimen at the edge of the cover glass, but in course of time ex- tends throughout the entire specimen. The fine filaments thus formed produce a dense network of interlacing fibrils. This fibrin net eventually contracts, FIG. J. — FIBRILS OF FIBRIN. Drawn from the same preparation as is represented in Fig. T4, but only after an interval of several Lours. x 1065. drawing with it the corpuscles, which are thus crowded into groups to form with the fibrin the denser clot, the fluid serum being expressed into the interval between adjacent masses of clot. Careful observation of the earliest formed fibrils of fibrin will show that they can be first recognized about the margins of the groups of blood platelets and in relation to the white blood cor- puscles. This appearance is taken to indicate a close physiolog- ical relation between these elements and the formation of fibrin. Hemoglobin. — The coloring matter of the blood is a compound of iron with a globulin. This hemoglobin is held either in solu- tion or in loose chemical combination by the cytoplasm of the red blood corpuscles. It escapes from these cells after rupture of their limiting membrane and is then capable of being crystallized in the form of minute brownish-yellow prisms. The color of the blood is entirely due to the presence of hemo- globin in its red cells. When examined by transmitted light, so- lutions of hemoglobin — and likewise the red blood corpuscles — have a faint greenish-yellow or amber color; by reflected light OTHER ELEMENTS OF THE BLOOD 83 they possess the familiar crimson tint of freshly drawn blood. In thin layers solutions of hemoglobin are quite transparent, in thicker layers they become more and more opaque. Various crystalline and amorphous substances may be obtained by decomposition of hemoglobin. The iron of the coloring matter may be thus obtained in the form of hematin, a soluble amorphous compound of a brownish-red color. If hematin is combined with hydrochloric acid the chlorid of hematin, hemin, is produced. Hemin occurs in deep brownish-red crystals which differ some- what according to the animal species from which they are ob- tained ; those of human blood take the form of triclinic plates. Hemin crystals derive a certain importance as a forensic test for the pres- ence of blood, and they may be obtained from old and dried-up specimens as readily as from fresh blood. The hemin crystals ob- tained from human blood, however, are identical with those from the blood of other mammals. > m w FIG. 84. — HEMOGLOBIN CRYSTALS. a and 6, from human blood ; c, from the cat ; d, from the guinea-pig ; e, from the hamster ; /, from the squirrel. (After Ranvier.) FIG. 85. — CRYSTALS OF CHLORID OF HEMATIN OR HEMIN. (After Kanvier.) When extravasations of blood occur within the tissues of the body the coloring matter is frequently deposited as hematoidin, an iron-free derivative of hemoglobin which forms stellate groups of yellowish needle-like crystals. CHAPTER YII THE VASCULAR SYSTEM THIS system includes the heart, arteries, capillaries, veins, and lymphatic vessels. These structures form a continuous set of branching tubes, which convey the blood from the heart, through the arteries and capillaries, and back again through the veins to the heart. In the capillaries a portion of the blood plasma trans- udes into the tissue spaces, where it forms the " tissue juices," and from which it is returned to the blood by the lymphatic vessels, the terminal branches of which empty into the subclavian veins. This entire vascular system is completely lined by a single layer of flattened epithelial cells, endothelimn, which are united edge to edge by an intercellular cement substance, to form a continuous membrane throughout the entire system. The blood vessels include the arteries, capillaries, and veins, and these, together with the heart, will form the subject of the present chapter ; the lymphatic vessels will be described in connection with the lymphatic system. ARTERIES. — The arteries convey the blood from the heart to all the tissues of the body. They are therefore almost universally present, but vary in size from the aorta down to minute unnamed vessels of microscopic caliber. They are divisible, according to size, into the large, medium sized, and small arteries, the arterioles, and what may be termed the arterial capillaries, or " precapillary arteries." The large arteries include only the aorta and the largest of its immediate branches ; the medium-sized arteries comprise nearly all the remaining named arteries of the body ; small arter- ies, arterioles, and precapillary arteries include those unnamed arteries which are to be found in nearly all of the organs and tissues of the body. A medium-sized artery will be first described, as presenting the typical arterial structure. Such a vessel consists of three coats : 1. The internal coat — tunica intima. 2. The middle coat — tunica media. 3. The external coat — tunica adventitia. 84 AETERIES 85 / The internal coat, tunica intima, presents three layers, the innermost being the layer of endothelial cells, the outermost a layer of elastic tissue, ^ the fenestrated coat ^r ^*ll-l- --'----{ J of Henle, or internal '-^^. kWx^\Y ' elastic membrane ; be- tween these is a deli- cate fibrous mem- brane, which consti- tutes the middle layer. The endothelium comprises only a single layer of flattened or -Mi-,6' v° ' ^->-%;j-vc- ^-^-;^;^- .,• squamous cells, placed \ ^xxxc>i;?;c -:>--\--5'''t--^ ' edge to edge to form a - " '* FlG. 86. — A SMALL ARTERY FROM THE CONNECTIVE TIS- SUE OF THE ANTERIOR CERVICAL REGION OF MAN. a, tunica adventitia; i, tunica intima; w, tunica media; n, a small non-medullated nerve trunk; •», a minute venule. Hematein and eosin. x 370. continuous membrane of simple pavement epi- thelium. These cells are irregularly polygo- nal in outline, and are somewhat elongated in the direction of the axis of the vessel. They are loosely attached to the elastic membrane by the middle layer of fine fibrillar connective tissue, in whose ground substance small branching connective tissue cells are found. The thickness of this connective tissue layer varies proportionately to the size of the vessel. The internal elastic membrane is a layer of elastic tissue, con- sisting of an intimately united fibrous mass, which completely en- circles the artery. In the smaller vessels the elastic fibres of this layer form only a reticulated structure, but in the larger arteries they are so abundant and so closely interwoven as to form a com- plete membrane, which can be readily stripped from the subjacent tissue. If the membrane thus prepared is examined microscopic- ally, it will be found to present numerous small openings at points where the elastic tissue is deficient. It is this appearance which led to its description as a " fenestrated membrane." The internal elastic membrane is intimately united to the tunica media, upon which it rests ; in fact, it may perhaps be better considered as the innermost layer of this tunic, for, in the larger arteries, e. g., the aorta, it can only with difficulty be distinguished from the adjacent layers of elastic tissue which form a large portion of the tunica media of these vessels. 86 THE VASCULAR SYSTEM The tunica media, or middle coat, contains smooth muscle, sheets of elastic tissue, and a very delicate fibrous connective tis- sue. The proportion of these elements present in any given artery varies with the size of the vessel. Muscular tissue usually pre- dominates, but in the larger arteries elastic tissue is so abundant as to appear quite in excess of the muscular ; in the smaller ar- teries, however, the muscular tissue is by far the more abundant. The smooth muscle fibres are circularly disposed in the wall of the vessel ; they are short, of irregularly serrated outline, and are intimately united with one another. Quite frequently the muscle fibres possess short branches which interdigitate with those of neighboring fibres. In the larger vessels they are arranged in layers which alternate with the sheets of elastic tissue. Small bundles of longitudinal smooth muscle fibres are occasionally found in the outer portion of the tunica media. The elastic tissue of the mid- dle coat is disposed in membra- nous sheets which, in the larger vessels, are embedded in a fine fibrillar connective tissue. In these vessels, also, the fibro-elas- tic membranes thus formed alter- nate with the layers of smooth a, tunica intinia, the internal elastic muscle, throughout the entire membrane is prominent ; 6, tunica media, thickness of the tunica media, containing smooth muscle and several T „ , , . . wavy layers of elastic tissue; c, tunica In consequence of the relaxation adventitia, containing many transversely of the normal arterial tone and and obliquely cut elastic fibres and much the contraction of the HlUSCUlar wavy connective tissue. Photo. (Alter Magrath.) wall in rigor mortis, as seen in the usual preparations, these elas- tic layers, as well as the internal elastic membrane, are thrown into wavy folds. The external coat, tunica adventitia, consists chiefly of fibrous connective tissue. Relatively few elastic fibres occur in this coat, and these for the most part lie in its inner portion, adjoining the tunica media. In the larger arteries, when especially abundant, the elastic fibres form an incomplete layer, which may be termed the external elastic membrane. Like the internal elastic membrane, FIG. 87. — THE EXTERNAL CAROTID ARTERY OF A CHILD. ARTERIES 87 this layer might well be considered as belonging to the tunica media, of which coat it would then form the outermost stratum. The white fibres of the tunica adventitia are disposed in dense interlacing bundles, to form a firm, unyielding coat. At the periphery of the artery the connective- tissue bundles of the adventitia inter- mingle with those of the adjacent areolar connective tissue, in which the blood vessels are nearly always embed- ded, hence the outer boundary of this coat is usually more or less ill-defined. The fibrous bundles of the adven- titia are disposed somewhat obliquely or diagonally about the artery, thus forming a closely felted connective- tissue network. Small blood vessels, both arteries and veins (vasa vasorum), and minute nerve trunks with occa- sional ganglia, occur in this coat. From these vasa et nervi vasorum capillaries and fine nerve fibres are distributed to the muscular coat. No blood vessels are found in the tunica intima. General Characteristics of the Arte- rial Wall. — The tunica media is almost invariably the thickest of the arterial coats. In the larger vessels the adven- titia is often of nearly equal thickness, but in the medium sized and small vessels it is much thinner. The arterial wall, as a whole, also, is very thick as compared with the lumen of the vessel, and is much thicker than that of a vein of corresponding size. The wall of the larger arteries is relatively thinner as compared with the lumen than is the case with the smaller arteries ; in these latter vessels the thickness of the arterial wall often exceeds the diameter of their lumen. In certain small arteries, e. g., those of the liver, even this ratio is exaggerated, the excess of muscular tissue in these vessels resulting in a breadth of wall which may be as much as two or three times that of the lumen. The arterial wall contracts firmly in rigor mortis, hence the FIG. 88. — TBANSECTION OF THE WALL OF THE AORTA OF A CHILD. The elastic tissue is deeply stained. 1, tunica intima; #, tunica media; 3, tunica adven- titia. Weigert's elastic stain and picro-fuchsin. Photo, x 64. 88 THE VASCULAE SYSTEM arteries after death contain but little blood, and, because of the density of the tissues which compose their wall, these vessels retain, as a rule, their cylindrical form. The Large Arteries.— The largest arteries differ from the me- dium-sized type in the excess of elastic tissue and relative defi- ciency of muscle in their media, the extreme thinness of their adventitia, and the relative thinness of their wall, as a whole, when compared with their lumen. Elastic tissue is especially abundant in all of these vessels ; in the media it exceeds in volume the mus- cular tissue, in the adventitia it forms a dense network of elastic fibres. The adventitia of the largest arteries is extremely thin, that of the thoracic aorta being not much thicker than its fibrous tunica intima ; this coat, therefore, forms but a small portion of the vas- cular wall in vessels of this type. In the medium-sized vessels, e. g., the iliac arteries, the tunica adventitia more nearly approaches the media in thickness. In the small arteries the elas- tic tissue is relatively decreased and the smooth muscle notice- ably increased. The tunica in- tima of these vessels is thin, and is limited externally by an in- ternal elastic membrane, which stands out prominently because of the relative deficiency of elas- tic tissue in the tunica media. In the tunica media of these vessels the plates of elastic tissue which characterize the larger arteries are scarcely to be found. This coat in the small arteries contains very little tissue other than smooth muscle. The external elastic membrane is indistinct, and the adventitia is not more than one-half to two-thirds as thick as the tunica media. The arterioles possess a relatively thicker wall than any other vessel of the arterial system. Their tunica intima is thin, but little fibrous tissue being contained within it, and the internal FIG. 89. — TKANSECTION OF THE CCELIAC AXIS OF MAN. a, tunica intima with a prominent in- ternal elastic membrane ; 6, tunica media, consisting chiefly of smooth muscle ; c, external elastic membrane in the inner portion of the tunica adventitia. Photo. (After Magrath.) AETERIES 89 elastic membrane is represented only by a very incomplete layer of elastic fibres. The tunica media of the arteriole forms two- thirds to three-fourths of its wall, and consists almost entirely of firmly united smooth muscle fibres. The adventitia, much thinner than the media, contains bundles of white fibres and delicate inter- lacing elastic fibrils. The smallest arfcerioles pass into what may be termed the precapillary arteries. In these minute vessels the wall consists of scarcely more than the endothelial lining, about which is an in- complete layer of circular muscle fibres, interspersed with occa- sional white fibrous and elastic fibres. On approaching the capil- laries the endothelial tube is gradually laid bare. It is the smooth A A GROUP OF SMALL BLOOD VESSELS. .4, small artery obliquely cut; B, arteriole and venule, the latter filled with blood; o, fat cells. A and B are from the connective tissue of the anterior cervical region. Hema- tein and eosin. A, x 110; 5, x 550. (7, a small arteriole near the descending aorta of man ; the internal and external elastic membranes are rendered distinct by the stain. Hematein, Weigert's elastic tissue stain, and picro-fuchsin. x 550. muscle which is the last of the tissues to disappear from the arte- rial wall, whereas beyond the capillaries it is the fibrous tissues which are first added to the endothelial tube to form the wall of the smallest venules (Fig. 94). Comparison of Large and Small Arteries. — The larger arteries are typically elastic, the smaller typically muscular. In the larger vessels the elastic tissue forms about one-half of the entire wall ; toward the smaller arteries this tissue progressively diminishes until, in the arterioles, it is limited to an incomplete internal 90 THE VASCULAR SYSTEM elastic membrane, the homologue of the complete elastic coat or fenestrated coat of Henle, which is found only in larger vessels. The smooth mus- cle, on the other hand, increases in relative amount from the larger to the smaller arteries. While in the largest vessels it forms not more than one- third, in the arte- rioles it represents about three-fourths of the arterial wall. In the largest arteries the adven- titia is relatively very thin. That of the medium sized vessels is somewhat thicker, and the ra- tio of connective tis- sue as found in the wall of these vessels remains fairly con- stant down to the arterioles. In the wall of the precapil- lary arteries con- nective tissue is very scanty. CAPILLARIES. — The capillaries are minute tubes, 5 to 13/x in diameter, which, in nearly ail the tissues of the body, connect the arteries with the veins. Their wall FIG. 91. — THK CAPILLARY NETWORK CONNECTING AN AR- TERIOLE AND VENULE OF THE OMENTUM OF A YOUNG RABBIT. The blood vessels have been injected. The discolora- tions at I and I are due to the presence of lacteals beneath the endothelium ; at V and V these are surrounded by the capillary network, a, arteriole; v, venule. Considerably magnified. (After Eanvier.) CAPILLARIES 91 is formed by a layer of endothelial cells which on the one hand is continuous with the endothelial lining of the arteries, on the other hand with that of the veins. As a rule there are neither muscle fibres nor connective tissue in the wall of the true capillaries ; occasionally, however, very fine isolated circumferential elastic fibres encircle the endothelial tube. In the minute arfcerioles and venules, which are about to terminate in or take origin from the true capillaries and which have been described as precapillary arterioles and venules, a very thin layer of muscle fibres or of connective tissue is added to the endothelial wall of the capillary. On the arterial side the muscle is the first tissue to be thus added, on the venous side the fibrous connective tissue is the first to appear. The endothelium of the capillary wall consists of flattened plate-like cells which are joined edge to edge by cement sub- FIG. 92. — CAPILLARY VESSEL OF THE FROG'S MESENTERY. Treated with nitrate of silver to show the outlines of the endothelial cells. Highly magnified. (After Kan vier.) stance. These cells are somewhat elongated in the axis of the vessel, the shape of the cell, as in the arteries and veins, depend- ing upon the size of the vessel — the smaller the vessel the more elongated its endothelial cells. The margins of these cells are extremely irregular, hence they present a wavy or serrated outline. Although the endothelial cells of the capillary wall appear to be firmly united to one another, yet they are capable of being separated sufficiently to permit the ready passage of white blood cells though the capillary wall, by means of diapedesis. The capillary wall does not appear to be an inactive factor in this process, for inert pigment granules may also penetrate the wall of these vessels, the endothelial cells immediately closing the aperture which is thus formed. Nevertheless, purely mechanical means, e. g., increased blood pressure, appear also to favor this process. The openings which are formed between the endothelial cells by the process of diapedesis are very transitory ; they are almost immediately closed by the activity of the endothelium. Such transitory breeches of the capillary wall are termed stigmata. THE VASCULAR SYSTEM The capillaries branch and anastomose with one another to form networks, the outlines of whose meshes vary according to the tissue in which they occur. In such fibrous tissues as muscle and nerve they form elon- gated meshes whose long axes are parallel to those of the muscle or nerve fibres ; in the looser, more areolar tissues they form large meshes of irregular form; while in the capil- lary membranes, as in the walls of the pulmonary alveoli, they are disposed in a close net the diameter of whose meshes scarcely exceeds that of the capil- laries. With but few excep- tions capillaries occur in all the tissues of the body. In epithelium and in carti- lage there are no blood vessels of any kind, and in the splenic pulp it is doubtful if true capillaries occur. In certain tissues large vascular spaces occur, which are comparable to the capillaries in that their wall consists of scarcely FIG. 93. — Two SINUSOIDAL VESSELS FROM THE . , -1,11-1 MEDULLA OF THE HUMAN ADRENAL. ^10™ ^0,11 the Cndothelial Each contains the outline of a single red blood tube> but which differ from cell for comparison of size. At a, a small vein is the true Capillaries in the 8hT;JVS fil1^ ffth f^d /f P°ssesse8/ extreme size of their lu- much thicker wall than that of the sinusoids. Hemateiu and eosin. x 410. men. These vessels have been described by Minot * as sinusoids. They are found in the erectile tissues, adrenals, coccygeal gland, parathyroids, and heart, in the maternal placenta, and in the fetal liver, pronephros, and Wolffian body. * J. Bost. Soc. of Med. So., 1900. VEINS 93 VEINS. — The blood having passed the capillaries, enters the smallest radicals of the venous system, the precapillary venules, and passes thence through the venules to the larger veins. The pro- gressive increase in the caliber of these successive vessels is ac- companied by a corresponding increase in the thickness of their wall. Thus, while the endothelial tube alone com- poses the capillary wall, the endothe- lium of the precapillary venule is en- circled by a delicate connective tissue membrane. In the venule occasional smooth muscle fibres are added to the wall of the smaller vessel, and in the vessels of this caliber the fibrous tis- sues have been so increased that the vascular wall, as in the artery, can be said to possess three coats. The wall of the precapillary venule consists of the endothelial lining, which is surrounded by a very delicate connective tissue membrane in which are very few elastic and white fibres. In the venule the tunica intima consists of little more than the endo- thelial lining. Its media and adventitia are not as yet distinctly diiferentiated, the former being distinguished only by the incom- plete layer of circularly disposed smooth muscular fibres. The extremely thin adventitia is composed almost wholly of white fibres, the greater part of whicli are circularly disposed. Very few elastic fibres occur even in vessels of this size. In the small veins the three coats are fairly distinct, the vas- cular wall being, however, much thinner than in the artery of corresponding size. The endothelium of the tunica intima is supported by a very delicate connective-tissue membrane which as yet contains but few elastic fibres. The tunica media consists of a thin layer of circularly arranged smooth muscle fibres intermingled with a delicate fibrous tissue ; elastic fibres are relatively scarce. The adventitia, though considerably the thickest of three coats, is as yet a thin membrane. It consists of fibrous connective PRECAPILLARY ARTERI- OLE AND VENULE. The lighter nuclei are those of the endothelium. The darker nuclei in the venule are in con- nective tissue cells ; in the arte- riole they are in the muscle cells. A, venule ; B, arteriole. Partly diagrammatic. Highly magnified. 94 THE VASCULAK SYSTEM tissue, elastic fibres being scarcely demonstrable except by means of the specific stains for this tissue. The wall of the larger veins closely resembles that of the cor- responding artery, except that the venous wall is much thinner and contains far less elastic tissue. The tunica intima of the medium and large veins presents a lining endothelium, a thin layer of delicate connective tissue fibres, and an incomplete in- ternal elastic membrane. The last named is never so prominent as in the artery. The tunica media contains smooth, muscle fibres, the most of which are circularly arranged. A somewhat smaller proportion of delicate connective tissue completes this coat. The adventitia of the larger veins consists of interlacing bundles of dense white fibres, among which is a network of fine elastic fibres. Occasional small bundles of longitudinal smooth muscle fibres occur in the adventitia of the largest veins. In these vessels also, a very incomplete external elastic membrane may be demonstrated by the specific stains for elastic tissue. '- '-. •„,' - -^i ; ^ ---- ^3 ;.- FIG. 95. — TRANSECTION OF THE WALL OF THE HUMAN VENA CAVA. a, tunica intima ; 6, tunica media ; c, tunica adventitia. The inner portion of which contains numerous bundles of longitudinal smooth muscle fibres which have been cut across. Hematein and eosin. x 90. Nerve fibres and minute blood vessels, vasa vasorum, occur in this coat and distribute their terminal branches to the two outer coats of the vessel. The intima of the vein, as in the artery, is non-vascular. \b VEINS 95 In certain tissues the veins present noticeable departures from the typical structure. Longitudinal muscle fibres are found in many of the larger veins of the abdominal and thoracic cavities. The adrenal veins contain, almost exclusively, longitudinal muscle fibres, and in the renal and phrenic veins and the vena cava these fibres form the greater portion of the tunica adventitia. In the pulmonary veins the circular muscle fibres are highly developed,, the tunica media of these veins almost equaling in thickness that of the corresponding pulmonary artery. As in other large veins, however, elastic tissue is notably deficient in the tunica media of the pulmonary vessels. The tunica media of the largest veins, e. g., the vena cava, con- tains much fibrous and considerable elastic tissue, the latter often forming incomplete membranous layers, which alternate with the muscle, as in the arteries. Such structure is, however, limited to the very largest of the veins. The cranial veins are conspicuous for the almost entire absence of muscle from their walls, the large meningeal sinuses being sur- rounded by a dense fibrous coat derived from the dura mater, and lined by the usual endothelium. The venous spaces of the erectile tissues have already been mentioned as presenting to some extent the sinusoidal type of structure, these large venous cavities possessing an extremely thin wall, in structure scarcely more than an endothelial lining. The afferent artery projects into the broad vascular lumen, from which the efferent vein makes its exit. Comparison of the Larger and the Smaller Veins. — Comparing the larger with the smaller veins, the excess of elastic and mus- cular tissue in the former is most noticeable; In the absence of specific stains, elastic tissue can scarcely be recognized in the venules and smaller veins. In the medium sized vessels it is scanty, but is present in considerable quantity in the largest vessels. The precapillary veins and venules contain scarcely any smooth muscle. This tissue becomes more distinct in the small veins and steadily increases proportionately to the size of the vessel ; in the largest veins it is again relatively deficient. Comparison of the Vein with the Artery of Corresponding Size.— The lumen of any given artery is always much smaller than the total lumen of its venas comites, the ratio being about one to three. Hence, of any two vessels in close proximity to each other, 96 THE VASCULAR SYSTEM the vein would more likely possess the larger caliber ; the artery, on the hand, would have the thicker wall. As compared with the arteries, the veins are notably deficient in elastic and muscular tissue. In the wall of most veins the white fibrous is in excess of all other tissues. For this reason the adven- titia is almost invariably the thickest of the three coats of the vein, whereas in the artery the media is always the thickest coat. The internal elastic membrane, which can be readily recog- nized even in the smaller arteries, is limited to the large veins. Alternating layers of elastic and muscular tissues are to be seen even in the medium sized arteries, but this arrangement is like- wise confined to the largest of the veins. The wall of the vein as a whole is much thinner in proportion to its lumen than that of the corresponding artery ; it is also less FIG. 96. — TRANSECTION OF AN ARTERIOLE AND VENULE. x 250. (After Schafer.) rigid. For this reason the wall of the vein is much more likely to collapse after death than is the thicker and more rigid arterial wall. Because of the preponderance of muscle in the wall of the artery its contraction in rigor mortis is more powerful than that of the vein ; the vein therefore is apt to be distended with blood while the artery contains but little. A certain number of blood cells can usually be found in almost any type of blood vessel. Valves occur at intervals of considerable length along the course of the larger veins. These are not found in the arteries. Each valve consists of one, two, or more crescentic folds or redupli- HEART 97 cations of the tunica intima between which is a slightly increased amount of connective tissue. The valves therefore are suspended free in the lumen of the vessel and are covered on either side with a layer of endothelium which is continuous with that lining the vein. The fact should be borne in mind that it is because of their relative infrequency that valves are not often met with in those transections of the smaller veins which are seen in nearly all microscopical preparations. HEART. — The wall of the heart consists of interlacing bundles of cardiac muscle fibres, the myocardium, which are covered ex- ternally by the epicardium, a serous membrane which forms the visceral layer of the pericardium. Internally the muscular wall of the heart is lined by the endocardium, which resembles the serous membranes in that it consists of pavement endothelium supported upon a layer of connective tissue. The endocardium lines all the cavities of the heart, and its endothelium is directly continuous with that of those arteries and veins which are connected with the cavity of the heart. Thus the entire vascular system — heart, ar- teries, capillaries, lymphatics, and veins — may be said to be lined by an uninterrupted sheet of pavement epithelial cells, the endo- thelium. Myocardium. — The muscle cells of the myocardium are so dis- posed as to form long fibrous bundles which by their figure-of-8 arrangement are interwoven with one another to form a dense in- terlacing mass of muscle bundles. The structure of these cardiac muscle cells has already been described. Because of the irregu- larity of their disposition, transections of the cardiac wall present sections of muscle fibres which have been cut in every conceivable direction. Between the muscle fibres is a very delicate framework of fibrous connective tissue, the endomysium, which surrounds the muscle fibres and supports the abundant capillaries, arterioles, and venules, with which they are supplied. The proportion of connective tissue in the normal myocardium as compared with the muscle is, nevertheless, very small. In certain portions of the myocardium connective tissue is more abundant. Thus it is slightly increased in the vicinity of the endocardium, in the papillary muscles, and near the bases of the cardiac valves. At the surface of the heart, beneath the epi- cardiurn, and especially in the various grooves on the surface of 8 98 THE VASCULAR SYSTEM the heart, the connective tissue is still more abundant, and may contain groups of fat cells. It is through these accumulations of connective tissue that the larger blood vessels are distributed to the myocardium. Epicardium. — The epicardium, like the other serous mem- branes, consists of a layer of pavement cells, so joined edge to edge as to form a complete endothelial coat. Here and there the endothelium pre- sents small openings at the angles between its cells ; these stomata are surround- ed by minute, finely granu- lar cells and are connected with the lymphatic vessels. The endothelium of the a, endothelium ; 6, connective tissue, and eosin. Photo, x 500. FIG. 97. — THE PARIETAL LAYER OF THE PERI- CARDIUM OF A CHILD. Hematein epicardium is supported upon a thin layer of dense areolar tissue in which are many small blood vessels and lymphatics. Fibres from the deeper surface of this layer are prolonged into the myocardium to become continuous with its endomysial connective tissue. The larger of these connective tissue trabeculae accompany the branches of the larger arteries and veins which are distributed to the muscular wall of the heart. FIG. 98. — THE ENDOCARDIUM. From the ventricular wall of the heart of man. Hematein and eosin. Photo, x 469. Endocardium. — The endocardium consists of a lining mem- brane of polygonal endothelial cells supported upon a thin layer HEAET 99 of delicate fibrous connective tissue. In this membrane is a net- work of elastic fibres. The endothelium of this membrane is con- tinuous with that of those blood vessels which open from the cav- ities of the heart. Its connective tissue also forms a continuous layer with that of the tunica intima of these vessels : in fact, the three coats of the cardiac wall — endocardium, myocardium, and epicardium — might well be compared with the corresponding three coats of the arterial and venous walls — the intima, media, A FIG. 99. — RADIAL SECTIONS OF THE MITRAL VALVE, FROM THE HEART OF A MAN. A, from the base of the valve showing the extension into it of cardiac muscle fibres from the wall of the heart; B, from the mid-region of the valve, a, auricular endo- cardium ; 6, muscle fibres ; c, dense fibrous tissue ; d, ventricular endocardium, llcma- tein and eosin. Photo, x 800. and adventitia. In either organ, the inner coat consists of a lining membrane of endothelinm, and a supporting membrane of connective tissue; muscle in large part composes the middle coat, while the outer coat is typically a connective tissue layer. 100 THE VASCULAR SYSTEM Valves. — At the cardiac orifices the entire thickness of the en- docardium is folded upon itself to form a double layer, between the folds of which an intervening stratum of dense fibrous tissue is inserted. These endocardial folds are the cardiac valves. The number and shape of their cusps are dependent upon the location. The semilunar valves of the aortic and pulmonary orifices consist of three crescentic endocardial folds ; at the auriculo-ventricular orifices the tricuspid valve consists of three large cusps, the mitral of two, together with an equal number of small intervening folds of the endocardium. The margin of the valvular cusp is extremely thin ; just within the margin, however, the central mass of dense fibrous tissue is somewhat thickened to form, in each cusp, a dense rim which during valvular closure secures the firm and accurate approxima- tion of the free margins of adjacent cusps. At the apex of the valvular cusp, where the adjacent fibrous margins of the valve meet, the dense connective tissue, particularly in the semilunar valves, is considerably thickened to form the corpus Aurantii. These corpora, in the aged, are frequently subject to calcareous infiltration. Muscular fibres are frequently continued from the adjacent cardiac or arterial wall into the dense fibrous tissue at the base of the valve. The base of the valve is also surrounded by a ring of fibrous tissue, the annula fibrosa, whose interlacing bundles are so closely packed as to give them an almost cartilaginous feel. At the auriculo-ventricular orifices, these fibrous rings are continuous with the auriculo-ventricular septum, from which the muscle bands of the myocardium take their origin. Chordae tendinese. — These are firm, unyielding cords, composed of parallel bundles of dense white fibres, and covered with a very thin endocardium continuous with that of the ventricular wall and cardiac valve. These fibrous bands unite the apices of the papillary muscles to the ventricular surfaces of the mitral and tricuspid valves. At the apex of the papillary muscle the fibrous bundles of the chordae intermingle with the muscle fibres, and are continued into the endomysial connective tissue, which is especially abundant in those portions of the myocardium. At their valvular attachment the fibrous bundles of the chordae tendinese turn almost at right angles, and spread out, in a somewhat radial manner, to become continuous with the dense fibrous tissue which forms the interior of the valve. NERVE SUPPLY 101 The columnse carnae are columelliform projections of the myo- cardium into the ventricular cavity. They consist of cardiac muscle fibres, which are disposed in their long axis, and are cov- ered by reflections and reduplications of the endocardium. The irregular contour of the ventricular cavities appears to be entirely due to the projecting columnae carnae. These muscular columns may present any one of three modes of attachment to the myocardium : (1) They may be attached along their entire extent ; (2) they may be attached only at their two ends, the mid-portion being free ; (3) they may be attached to the myocardium at one end only, the other end projecting into the ventricular cavity as a papillary muscle, from whose apex chordae tendinae pass to the auric ulo-ventricular valves. Either of the last two forms may, in transections of the ventricles, appear as isolated islands of muscular tissue surrounded by endocardium and lying apparently free within the cavity of the ventricle. Blood vessels. — The heart is supplied with blood through the coronary arteries. The larger branches of these vessels pursue their course beneath the epicardium in the superficial grooves of the cardiac wall. From these large arteries, smaller branches are distributed to the epicardium and to the muscular wall, the latter vessels penetrating as far as the endocardium, in whose connective tissue they form a meager capillary plexus. The capillaries of the myocardium are extremely abundant. They form elongated meshes between the muscle fibres, the cir- cumference of each muscle fibre being in relation with several capillary vessels. The veins return the blood from these rich capillary plexuses and pursue a course similar to that of the arter- ies, the larger veins being always found in the broader connect- ive tissue septa. NEEVE SUPPLY,— The nerve supply of the vascular system is by means of fine branches derived from the cerebro-spinal and sympathetic systems. In the heart these minute nerve trunks end in the various cardiac ganglia, most of which are found in the connective tissue of the heart, e. g., the coronal plexuses about the orifices of the aorta and pulmonary artery. From these ganglia sensory nerve fibres are distributed to the endocardium and epicar- dium, and motor fibres to the myocardium. The most of the former are connected with the vagus, the latter with the sympathetic trunks. From the cardiac ganglia branches pass to form a coarse plexus 102 THE VASCULAR SYSTEM in the connective tissue between the muscle bundles, the peri- mysial plexus, from the branches of which a fine plexus is dis- tributed to the endomysium. The terminal branches end in re- lation with the surface of the muscle fibres. The blood vessels are similarly supplied, minute ganglia occur- ring here and there in the adventitia or adjacent connective tis- sue. Erom these ganglia sensory branches are distributed to the adventitia and intima and motor branches to the tunica media. Naked nerve fibrils can be traced to the smallest blood vessels, and even in the capillaries terminal fibrillae are found in relation with the endothelial wall. tots CHAPTER VIII THE NERVOUS TISSUES THE nervous tissues include those tissue elements which are peculiar to the nervous system. The essential unit of structure, comparable to the cell of other tissues, is here the neurone. A neurone is a nerve cell in the broadest sense of the term. It con- sists of the cell body (nerve cell of the older writers, perikaryon), together with all of its processes. These latter are divisible into two varieties, the neuraxone and ihe.dendrites. The neurones are among the largest cells of the body. Their cell body is of variable size, in some cases extremely minute, at other times sufficiently large to be readily observed with the naked eye. Their processes, usually of considerable number, vary in length from a millimeter or less, up to half the height of man. It is therefore obviously impossible to study microscopically at one time the entire course of these longer processes. This circum- stance renders it advisable to retain the term nerve fibre of the older writers to designate, not as was the former conception, a his- tological entity, but rather that portion of those long processes of the nerve cell which pursues its course, as a rule, outside of the grey matter of the central nervous system. On this basis we may divide the neurone into the nerve cell and the nerve fibre. The former term includes the cell body with its dendrites and the proximal portion of its neuraxone, the distal portion of the neuraxone forming the essential part of a long nerve fibre. The nerve cells are found throughout the grey mat- ter of the central nervous system and in the ganglia of the pe- ripheral cerebro-spinal and sympathetic systems. Nerve fibres occur in the white matter of the central nervous system and in the nerve trunks and ganglia of the peripheral system. In the peripheral nervous system the nervous tissues are chiefly supported by the connective tissues, but in the central nervous 103 104 THE NERVOUS TISSUES system a special form of sup- porting tissue, the neuroglia, is also found.* THE NERVE CELL (cell body, perikaryon, ganglion cell). — This term, as already stated, includes the cell body with its dendrites and the proximal portion of its long neuraxis. The cell bodies vary in size from 4 to 200/x, in diameter. Their shape is chiefly dependent upon the number of their processes. Unipolar nerve cells, with but a single process, are flask- shaped or pyriform; bipolar cells, whose processes are usu- ally derived from opposite extremities, are most fre- quently fusiform ; multipolar nerve cells, from the con- siderable number of their processes, are irregularly stellate. Nucleus. — The cytoplasm of the cell is finely granular, and contains a large vesicular nucleus which, as a rule, is eccentrically situated. The appearance of this large nu- cleus is quite characteristic of the nerve cell, as distin- guished from the cells of FIG. 100. — DIAGRAM or A NEURONE. a Jt, axone hillock ; a x, neuraxis ; c, cytoplasm, the Nissl granules have been stained; d, dendrites ; m, myelin sheath of the nerve fibre ; m', muscle fibre ; n, nucleus ; n', nu- cleolus ; n of w, nucleus of the neurilemma of the nerve fibre ; n .R, node of Ranvier ; s /, collateral ; s L, segment of Lantermann ; tel, telodendrion or terminal arborization which here forms a motor end-plate. (After Barker.) See chapter xxiii. THE NERVE CELL 105 other tissues. The nuclear membrane is distinct and high- ly chromatic. The contents of the nucleus, however, except for the large spherical nucleolus which is quite constantly present, is noticeably deficient in chromatin. Those few small karyosomes which are present are mostly adherent to the inner surface of the nu- clear membrane. The achromatic nucleo- plasm forms the greater portion of the nucleus. Occasionally the chromatin forms still finer granules, and is more equally distributed throughout the nucle- us. A large, chromatic, centrally situ- ated nucleolus is nearly always present. Cytoplasm. — The finer structure of the cytoplasm of the nerve cell is the FIG. 102. — ISOLATED NERVE CELLS FKOM THE SPINAL CORD OF MAN. .r, m-uraxis. ('aniiin. x 160. (After Sobotta.) b a FlG. 101. — A UNIPOLAR GANGLION CELL OF A FROG. a, cell body ; 6, neuraxis ; c, dendrite. Methylen blue. High- ly magnified. (After von Smir- now.) subject of considerable difference of opinion. The studies of Xissl have shown that it is divisible into a substance which is readily stained by methylen blue, thionin, etc. (the stainable sub- stance of Nissl,tigroid of von Lenhossek), and an apparently homogeneous substance which is not so readily stained (the unstainable substance of Nissl). 106 THE NEEVOUS TISSUES Nissl's substance, or tigroid, occurs in the form of flake-like granules of varying size and irregular shape. Their disposition within the cytoplasm is subject to considerable variations in dif- FIG. 103. — NERVE CELL FROM THE OLFACTORY BULB OF A RABBIT. An arkyochrome nerve cell in the parapyknomorphous condition. Highly magnified. (After Nissl.) ferent nerve cells. Yet it has been found that nerve cells occu- pying the same position in any given animal species always present the same type of structure as regards the disposition of their Nissl granules. According to Nissl, the following types may be distin- guished : A. SOMATOCHKOME NEEYE CELLS, in which the nucleus is sur- rounded by a considerable cytoplasmic body. 1. Ar Icy o chrome nerve cells, whose stainable substance occurs in the form of an irregular network. These cells are widely distrib- uted among the sensory nuclei of the spinal cord and medulla. 2. Stichochrome nerve cells, whose stainable substance presents a linear arrangement, the rows of granules being more or less nearly THE NEKVE CELL 107 parallel either to the nuclear membrane or to the surface of the cell. These cells are most abundant in the motor nuclei of the spinal cord and brain. 3. Gryochrome nerve cells, whose stainable granules present a tendency to agglutinate into clumps or threads. These cells are less numerous, but may be found in the corpus striatum. 4. Arkyostichochrome nerve cells, whose stainable granules, while presenting a delicate network, show at the same time a dis- Fio. 104. — MOTOR NERVE CELL FROM THE VENTRAL HORN OF THE SPINAL CORD OF A RABBIT. Of the three lower processes, the middle one represents the neuraxis. All the other processes are dendrites. The margins of the cell and of the masses of stainable sub- stance appear too sharp in the reproduction. At the angle of division of the large dendrite at the left superior angle of the cell is shown one of the " wedges of division." This is classed as a stichochrome nerve cell in the apyknomorphous condition. Highly magnified. (After Nissl.) 108 THE NERVOUS TISSUES tinctly linear arrangement. The Purkinje cells of the cerebellar cortex are offered as the only example of this type. Even these cells have lately been considered as belonging more distinctly to the ar- kyochrome variety (Xissl *). B. CYTOCHEOME NERVE CELLS, which present but very little cyto- FIG. 105. — NERVE CELL FROM A GANGLION ON THE DORSAL ROOT OF A CERVICAL NERVE OF A BABBIT. Stichochrome nerve cell in the apyknomorphous con- dition. Highly magnified. (After Nissl.) V FIG. 106.— PURKINJE CELL FROM THE CEREBELLAR CORTEX OF THE RABBIT. - Arkyostichochrome nerve cell in the apyknomorphous condition. Highly magnified. (After Nissl.) plasm, and whose nucleus is small, being only about the size of the ordinary leucocyte. Examples of this type are found in the granular layers of the cerebral and cerebellar cortex. *Allg. Zeitschr. f. Psychiat., 1898. THE NERVE CELL 109 C. KARYOCHROME NERVE CELLS, which also present but little cytoplasm, but whose nucleus is large, being equal in size to that of the average nerve cell. Such cells are also found in the granular layer of the cerebellar cortex. Those nerve cells in which the Mssl substance is abundant are said to be in a pyknomorphous, those in which it is scanty in an apyknomorpJious condition. The Nissl granules are apparently used up during functional activity of the nerve cell. The majority of the coarse granules of stainable substance of Xissl present an irregular spindle shape ; this is particularly true of those which show a linear ar- rangement. They are sometimes so grouped as to form two characteristic structures, the nuclear caps and the division wedges. Nuclear caps, as their name indicates, are accumula- tions of Nissl substance, which occur at the poles of the nucleus ; one, two, or three of these caps may be in re- lation to a given nucleus. Division wedges occur in the dendrites, at the point of their division. The wedges are of a triangular shape, their con- cave base spanning the angle formed by the two subdivisions of the den- dritic process. Concerning the finer structure of the unstainable substance of Nissl comparatively little is known. With varying methods of fixation this por- tion of the cellular cytoplasm has been found to show very fine fibrils (Schultze, Flemming, Apathy, Bethe) and fine acidophile granules (neurosomes of Held). Besides these structures there remains a homogeneous ground substance or hyaloplasm, which, though of extreme physiological importance, in the usual histological prepa- rations presents no structure. Centrosomes and attraction spheres have been frequently observed in the nerve cells of the lower vertebrates, and occasionally in those of mammals. The cytoplasm of many nerve cells contains a characteristic brownish-yellow pigment, whose fine granules have a tendency to FIG. 107. — NERVE CELLS OF THE CEREBELLAE CORTEX. 1, cell of Purkinje ; arkyochrome type ; #, nerve cell of the granular layer ; caryochrorae type with a large nucleus ; #, a granule cell of the granular layer ; cytochronie type with a small nucleus equal in size to that of a leucocyte. Nissl's stain, x 1200. 110 THE NEBVOUS TISSUES accumulate in the vicinity of the nucleus. End fibrils of other nerve cells have been demonstrated within the cytoplasm of the nerve cell. Apathy has likewise demonstrated that fibrils occa- sionally pass from one neurone to another, so that we no longer consider that a neurone, though a structural unit, is in all cases anatomically independent of all other neurones. The present status of this much discussed question seems to be comparable to that of the cell, as a histological unit of structure, which, though formerly thought to exist independently of other cell units, has since been found to be frequently connected, as by the intercellular bridges of epithelium and of smooth muscle, the syncytial tissues, etc. The neurones of the nervous system, therefore, while being usually related to one another by contiguity or by contact only, FlG. 108. — A NERVE CELL FROM THE TRAPEZOID NUCLEUS IN THE MIDBRAIN OF A RABBIT. a, neuraxis ; 6, neuraxes of other nerve cells which terminate in relation and appar- ently fuse with the cytoplasm of the cell body ; c, points of fusion or zones of concres- cence ; d, dendrites which have been cut off close to the cell body ; e, neuroglia. Iron hematoxylin. Very highly magnified. (After Held.) may occasionally be more directly connected by fibrillge, which pass from the processes of one neurone to the cell body or processes of a second neurone (Apathy, Bethe), or by "concrescence," as de- scribed by Held. The nerve cells are surrounded by a narrow interval which THE NERVE CELL 111 FIG. 109. — INTRACELLULAR NETWORK WITHIN A PlJR- KINJE CELL OF THE CERE- BELLUM or " STRIX FLAM- MEA." Golgi's stain. (After Golgi.) separates them from the surrounding tissue. This is presumably a lymphatic or tissue juice space. Holmgren has recently demon- strated, also, the presence, within the cytoplasm of the nerve cell, of minute canaliculi which form an intra- cellular network, more abundant near the surface of the cell, and which he has termed juice canaliculi (Saftkancilchen). These canaliculi may possibly account for the pe- culiar intracellular network which Golgi has recently demonstrated in the periph- ery of the nerve cell by a modification of his rapid silver impregnation method. The processes of the nerve cell are of two varieties : the one, broad, granular, and rapidly dividing in the vicinity of the cell body into a number of branching sub- divisions, is the dendrite ; the other, long, slender, and finely fibrillar, arises from the cell body direct, or from the base of a dendrite, and, passing for a consider- able distance from the cell body, finally enters the nerve fibre as its axis cylinder, or terminates in relation to some distant nerve cell. This latter process is the neuraxis. Each cell body usually possesses a single neuraxis and several den- drites. Cells without a neuraxis are found in the retina and in the olfactory bulb ; except for these, all nerve cells in the body of man possess a neuraxis and usually but one such process. The subdivision of nerve cells into uni-, bi-, and multi-polar cells is, therefore, chiefly based upon the number of their dendrites. Dendrites (protoplasmic processes). — The dendrites of a nerve cell vary from one to a considerable number. They arise from the cell body by a broad stem, and quickly break into branches which can be traced for a considerable distance — in fact, the arbor- ization of the dendrites is usually so extensive that it can be fol- lowed for only a short portion of its course. Occasionally dendrites do not branch until they have arrived at a considerable distance from their parent cell body. The structure of the dendrite is, to all appearances, similar to that of the cell body. The stainable substance of Xissl is con- tinued for some distance into the arborizing dendrites, which often possess a finely fibrillar appearance. In Golgi-stained prepa- 112 THE NEEVOUS TISSUES rations the dendrites frequently present a thorny appearance, due to the clustering along their borders of minute lateral projections, the gemmules. The terminal filaments of the dendritic arborization are fre- quently in relation with the cell bodies or neu raxes of other neu- rones, less frequently with the dendrites of other neurones. The neuraxis (neuraxon, dendron, neurite, axone, axis cylinder process). — This process, in contradistinction to the dendrite, is long and slender, as a rule does not arborize near its parent cell body, is of smooth and regular contour in Golgi preparations, and con- tains no stainable substance of Nissl. It arises from the cell body, or less frequently from the base of a dendrite, by a conical, clear area, the axone hillock, which, like the process itself, is devoid of Nissl's stainable granules. At some little distance from the parent cell body the neuraxis gives off very fine lateral branches, the collaterals, which leave the FIG. 110. — GOLGI CELL, TYPE i, FROM THE SPINAL CORD OF A HUMAN FETUS. At * is the relatively straight neuraxis which has already given off one collateral. Golgi's stain. (After von Lenhossek.) parent stem at nearly right angles. These delicate branches finally terminate by a sudden end arborization, or end brush, by which each neuraxis is placed in relation with a large number of neurones. THE NERVE FIBRE 113 FlG. 111. — GoLGI CELL, TYPE II. a, neuraxis, which immediately breaks into a network of fine col- laterals. Golgi's stain. (After Andriezen, from Obersteiner.) The parent stem of the neuraxis may be finally exhausted in its collaterals, or it may in turn end in a terminal arborization. Col- laterals are said to be more frequent in the proximal than in the distal portion of the neuraxis. According to the length of their neuraxis, neurones were divided by Golgi into two types : 1. Golgi cells, Type I (Deiter's cells). 2. Golgi cells, Type II (Golgi's cells). The cells of Type I possess a long neuraxis which passes beyond the con- fines of the grey matter in which it arises and usually becomes the axis cylinder of a nerve fibre. The cells of Type II possess a short neuraxis which forms its terminal ar- borization in the vicinity of its parent cell body. The cells of this type are usually association neurones; they place in conduction relation other not very remote neurones. The cells of Type I, on the other hand, are more frequently projection neurones; they are distributed from the nerve centers to other and perhaps very different tissues, their course lying in the long projection tracts and nerve trunks of the nervous system. The cells of Type II are therefore most frequently intrinsic or endogenous neurones, their whole course lying in one division of the central nervous system, e. g., the grey matter of the spinal cord. The cells of Type I are more frequently extrinsic or exoge- nous ; they arise in one part of the nervous system to be distributed to a distant portion, e. g., they arise in the peripheral ganglia and enter the spinal cord to terminate in its grey matter, or vice versa. THE NERVE FIBRE.— The origin of the nerve fibre and its relation to the other portions of the neurone will be appreciated by tracing the course of the neuraxis of a motor nerve cell of the ventral horn of grey matter in the spinal cord. This process, ari- sing in the central grey matter, is at first a naked neuraxis. It soon leaves the grey matter to traverse the white matter and makes its exit from the spinal cord as the axis cylinder of one of the fibres of an anterior nerve root. On leaving the grey matter 114 THE NERVOUS TISSUES the neuraxis acquires a cylindrical sheath of myelin substance, the medullary sheath, myelin sheath, or white substance of Scliwann. On entering the anterior nerve root, which lies outside of the white matter of the spinal cord, the neuraxis receives a connective tissue sheath, the neurilemma or ideated sheath of Scliwann. The neuraxis retains these two sheaths until near its termination, when the sheaths suddenly stop, the neuraxis becoming again naked as it breaks into terminal fibrils. Not all nerve fibres are medullated, nor do they all possess a nucleated sheath of Schwann. The neuraxes of the central nerv- ous system are not supplied with a neurilemma until they pierce the meninges to enter the nerve roots. Those of the grey matter also have no appreciable medullary sheath. The neuraxes of the peripheral nerve trunks and ganglia are all supplied with a neuri- lemma except at their terminals, as already explained. Yet some of the peripheral neuraxes have a medullary sheath, while others have none. A neuraxis with its enveloping sheaths constitutes a nerve fibre, and upon the presence or absence of these sheaths nerve fibres "nay be classified as follows : A. Medullated nerye fibres a 2. Without a neurilemma. B. Non-medullated nerve fibres.. j 3' With a neurilemma. ( 4. Without a neurilemma. 1. Medullated Nerve Fibres with a Neurilemma. — Nearly all the nerve fibres of the cerebro-spinal nerve trunks and ganglia and some of those of the sympathetic nerves are of this type. These nerve fibres consist essentially of three cylindrical structures : the axis cylinder, which is the continuation of the neuraxis of a nerve cell, and which forms the central portion or core of the nerve fibre ; the medullary sheath, which forms a hollow cylinder inclosing the axis cylinder, and which suffers frequent interruptions, as will be described ; and the neurilemma, which is an extremely thin invest- ing sheath of connective tissue origin, and forms an uninterrupted envelope from the point where the nerve fibre leaves the central nervous system to a point near the end of the fibre where the axis cylinder breaks into its terminal fibrils. To these structures an investing sheath of connective tissue, the sheath of Henle. is sometimes added. It is derived from the connective tissue endo- neurum in which the nerve fibres are embedded. It serves to support the capillary blood vessels destined for the supply of the nerve fibres. THE NERVE FIBRE 115 FlG. 112. — A SMALL PORTION OF A TRANSECTION OF THE SCIATIC NERVE OF A DOG. Nerve fibres are seen in transection ; their myelin sheaths are black, their neuraxes unstained, tetroxid. Photo, x VOO. Osmium The The axis cylinder presents a finely fibrillar structure. The nature of these fibrils is not well understood. In certain nerve fibres of the lower animals these fibrils have a tendency to collect into the center of the axis cylinder, leaving a peripheral clear zone ; this distribu- tion is especially char- acteristic of those fibres which are not supplied with a med- ullary sheath. In mammals, however, the fibrillae occupy a large portion of the axis cylinder, the clear peripheral area being corresponding- ly diminished until in man it can scarcely be recognized, fibrils of the lower animals are also coarser. Apathy, studying chiefly the lower animals, has considered these ? ultimate fibrtifo" to be the conducting element of the nerve fibre. Others, however, lay greater stress upon the intervening clear portion, the neuroplasm of Schiefferdecker, as containing the active conducting element of the fibre. The axis cylinder is, under certain conditions, at least, found to be inclosed by an extremely delicate membrane, the axilemma of Kiihne. The existence of this membrane as an integral part of a living axis cylinder has been denied by others. The medullary sheath (white substance of Schwann, myelin sheath] forms a cylindrical investment for the axis cylinder. It appears to be retained in position by the neurilemma, for when the latter is ruptured the myelin exudes in the form of " myelin drops." The myelin thus obtained possesses the physical proper- ties of a fat. It is also capable of being blackened by osmium tetroxid. By extraction with ether the myelin can be removed, leaving behind a network of neurolceratin. It has not yet been proved that this network exists in the living nerve fibre. At frequent intervals in the course of the nerve fibre its myelin sheath suffers complete interruption, thus forming the annular constrictions or nodes of Ranvier. At these points the neuri- 116' THE NERVOUS TISSUES of fibre lemma dips in until it is in contact with the axis cylinder. Both axis cylinder and neurilemma are continued past the node without interruption. The successive nodes Ranvier divide the nerve into interannular Within each interannular seg- ment the medullary sheath, on blackening with osmium tet- roxid, presents clear intervals which penetrate the myelin sheath in such manner as to give the appearance of obliquely disposed clear lines or incisions. These incisures of Schmidt (Schmidt - Lantermann lines) have not been satisfactorily ex- plained and can not be demon- strated in the living fibre, yet they present a constant form and are always present in osmic preparations.* These incisures subdivide the interannular seg- ments of the medullary sheath into medullary segments. In preparations of fresh nerve fibres which have been treated with silver nitrate ac- cording to the method of Ran- vier, the solution is found to enter the fibre most readily at the nodes of Ranvier, so that if blackened by exposure to the sunlight, minute +- like appear- ances are seen at each node. By prolonged maceration in weak solutions of silver nitrate FIG. 113. — NERVE FIBRES. A and B, from the sciatic nerve of a rabbit, isolated by teasing, and viewed in profile ; (7, a group of nerve fibres in tran- saction, from the sciatic nerve of a dog. a, neuraxis ; &, neurilemma projecting be- yond the torn end of the fibre ; d, nucleus ; ft, endoneurium or fibrous sheath of Henle ; J, Schmidt-Lantermann lines ; n, nodes of Ranvier. Osmium tetroxid. A and .B, x 670 ; (7, x 900. * Schmidt originally considered them to be the optical expression of folds in the outer fibrous coats. Lantermann and others have shown that they are within the neurilemma. THE NERVE FIBRE . 117 the solution penetrates still farther and the blackened axis cylin- der is found to possess spiral transverse markings which are quite characteristic. The true meaning of these appearances has not been satisfactorily explained.* Because of the apparent greater permeability of the fibre at these points, these peculiarities have been taken to indicate a certain relation of the annular constric- tions to the nutrition of the fibre. The neurilemma (nucleated sheath of Schwanri) is the outer- most of the nerve fibre sheaths. It is -of distinctly mesoblastic origin and makes its appearance prior to the medullary sheath. It forms a very delicate membrane, which incloses the myelin sub- stance, and at each node of Ranvier comes into contact with the axis cylinder. Attached to the inner surface of the neurilemma in each inter- node, and usually but one for each internodal segment, is an oval nucleus. The nucleus is surrounded by a minute amount of finely granular cytoplasm. This structure is taken to indicate that the embryonal neurilemma is formed by connective tissue cells which become spread out over the surface of the primitive fibre, one cell, as a rule, supplying each internodal segment, and its nu- cleus with a minute amount of undifferentiated protoplasm is, according to this hypothesis, considered to remain as a perma- nent part of the neurilemma. 2. Medullated Nerve Fibres without a Neurilemma, — This type of nerve fibre composes the white matter of the central nervous system. The axis cylinder does not, of course, differ in the least from those of the previous variety and will need no further de- scription. The medullary sheath is, also, similar in its finer structure to that of the previous type, but since no neurilemma is present, these fibres possess no nodes of Ranvier. The medullary sheath of the fibres found in the white matter of the brain and spinal cord is, therefore, uninterrupted. Its surface is in direct contact with the neuroglia network, which forms the supporting tissue of these organs. 3. Non-medullated Nerve Fibres with a Neurilemma (sympa- thetic nerve fibres, Remotes fibres). — The most of the fibres of the sympathetic system are of this type. The axis cylinder does not differ from that of the previous types. The medullary sheath is * They have been usually considered to be artifacts. 118 THE NEKVOUS TISSUES either entirely absent or, at most, very insignificant in these fibres. The neurilemma is perhaps incomplete at times, but exhibits fre- quent nuclei along the course of the fibre. Fibres of this type are of quite frequent occurrence in the cranial nerves of the cere- bro-spinal system. Other cerebro-spinal nerve fibres lose their medullary sheath and finally also their neurilemma prior to their termination. 4. Non-medullated Nerve Fibres without a Neurilemma. — These fibres are naked axis cylinders and as such are found at the cyto- proximal end of the neuraxis in the grey matter of the central nervous system, and at the cytodistal end prior to the termination of the neuraxis in its arborization of terminal fibrils. In man nerve fibres are of this type throughout their entire course, only in the olfactory nerves. NERVE TRUNKS.— The nerve fibres of the peripheral nervous system are united into bundles to form the nerve trunks or nerves. Each nerve is sur- b rounded by a heavy connective tissue sheath, the epineu- rium, which sends trabeculum-like sep- ta into the nerve. These septa subdi- 'vide the nerve trunk into smaller bundles of nerve fibres, the funiculi. The fu- niculus forms a compact bundle of nerve fibres, and is in turn invested with a sheath of dense connective tissue, the perineurium. Hence the perineurium stands in the same re- lation to the funiculus as does the epineurium to the whole nerve trunk. From the inner surface of the perineurium, septa pass into the funiculus and break up to form a fine connective tissue framework between the individual nerve fibres. Thus the nerve fibres are embedded in a delicate connective tissue sheath. On teasing the FIG. 114.— TRANSECTION OF THE SCIATIC NERVE OF A DOG. The fat cells and the myelin sheaths of the nerve fibres have been blackened by osmium tetroxid. a, fat cells ; 6, &', blood vessels, that at &' lies within a funiculus ; c, epineurium ; d, perineurium ; e, coarser bands of the endo- neurium. Osmium tetroxid. Photo, x 30. GAXGLIA 119 nerve fibres with needles this fibrous endoneurium remains adher- ent to the surface of the nerve fibre and gives the appearance of an outermost fibrous sheath, the so-called connective tissue sheath of Henle. Nerve trunks frequently branch, the branches being formed either by an individual funiculus or by groups of funiculi. In the smaller nerve trunks the funiculi are further subdivided. It is by anastomosis of the funiculi that most of the nerve plexuses are formed. Individual nerve fibres of the medullated type do not branch except in those portions which are naked axis cylin- ders, viz., at the cytoproximal portion of the neuraxis by means of collaterals, and at the cytodistal portion by means of end arborizations. Occasionally also the nerve fibre divides at a node of Ranvier. Vascular Supply. — The nerve trunks are well supplied with Uood vessels. The larger of these are found in the epineurium, and from them branches of considerable size enter the septa to be distributed through the perineurium to the funiculi. The coarser septa of the endoneurium contain minute arteries and veins. A capillary network with elongated meshes occupies the finer di- visions of the endoneurium, its vessels being thus brought into contact with the nerve fibres. Perivascular lymphatic vessels abound in the epineurium and its septa, and lymphatic tissue spaces are found throughout the connective tissue of the nerve trunk. Where the cerebro- spinal nerve trunks penetrate the meninges these lymphatic vessels are said to be continuous with the similar vessels of the dura mater. Minute nerve fibre bundles, nervi nervorum, are also found in the epineurium ; their fibres are mostly, if not entirely, distributed to the blood vessels. GANGLIA.— A ganglion may be described as a group of nerve cells occurring in the course of a peripheral nerve trunk. The largest of the ganglia form fusiform swellings in the course of the nerve, which are visible to the naked eye. The smallest, on the other hand, contain not more than half a dozen nerve cells, and these must be sought with the aid of the microscope and can only be found by the most careful observation. Whatever may be their size, all ganglia appear to have a simi- lar structure, except for those differences which characterize the sympathetic as distinguished from the cerebro-spinal type. The 120 THE NERVOUS TISSUES essential elements of structure are the nerve cells, nerve fibres, and a supporting framework of rather dense connective tissue. Many of the nerve cells of the adult mammal are unipolar in the cerebro-spinal ganglia, but are usually multipolar in the sympa- thetic. The spinal ganglia of the lower vertebrates and of the embryo mammal, however, contain bipolar ganglion cells. In mam- FlG. 115. — A SMALL PORTION OF A HUMAN GASSERIAN GANGLION. a, funiculi derived from the nerve trunk ; &, nerve cells. Hematein and eosin. Photo. x 60. mals the two processes fuse to form a single one which branches in a Y- or T-like manner soon after leaving the parent cell body. The nerve cells of all ganglia are surrounded by a peculiar connective tissue capsule. It is composed of flattened endothe- lioid connective tissue cells which form a complete investment for the nerve cell and are continued on to its processes, possibly be- coming continuous with the neurilemma. The capsule is not, as a rule, closely applied to the cell, but leaves a narrow interval which is occupied by lymph or " tissue juice." GANGLIA FlG. 116. — A NERVE CELL FROM A SECTION OF A HUMAN GASSERIAN GANGLION. (7, capsule. Nissl's stain, x 500. other, especially in sympathetic system, where they were formerly but little understood. In the spinal ganglia Dogiel * describes two types of gan- glion cells: (1) in which the processes are thick and pass out of the gan- glion to become the axis- cylinder of a medullated nerve fibre, and (2) cells with slender processes which break up within the ganglion and whose terminal branches form a pericapsular plexus around the cell capsule ; from this plexus fine end branches penetrate the capsule to form a pericel- lular arborization about the nerve cell itself. The cells of this latter type might be said to serve as In its finer structure the ganglionic neurones do not appear to differ in any way from other neurones. The large vesicular nucleus with its distinct nu- cleolus readily distinguishes these cells from those of neighboring tissues. Recent studies of the ganglion cells by * Dogiel, Eanvier, and Cajal have done much to explain the re- lations of these cells to each the FIG. 117. — SCHEMATIC REPRESENTATION OF THE RE- LATIONS OF THE STRUCTURES COMPOSING A SPINAL GANGLION. A and B, ventral and dorsal spinal nerve roots ; 0, a spinal nerve ; D and J£, its ventral and dorsal divisions ; F, its ramus coramunicans. a, nerve cells of the first type, whose neuraxes divide and form the axis cylinder of a peripheral and a central nerve fibre ; 6, nerve cells of the second type, whose neuraxes, n, end in a felt work about the cells of the first type ; s, sympathetic nerve fibres which termi- nate in a basket work about the cell bodies of the second type of ganglion cells. (After Dogiel.) * Anat. Anz., 1896. 122 THE NERVOUS TISSUES association neurones within the ganglion. Nerve fibres from the sympathetic ganglia also enter the spinal ganglia and form peri- cellular arborizations about the cells of the second type. Dogiel also finds that multipolar ganglion cells occur in the spinal gan- glia of the adult as well as of the embryo. In the sympathetic ganglia Dogiel * likewise recognizes two cell types : (1) small multipolar fusiform or stellate nerve cells with 5 to 20 dendrites and a neuraxis which enters the nerve trunks as a non-medullated fibre, but may later acquire a thin med- ullary sheath ; (2) larger spheroidal nerve cells with 1 to 16 den- drites and a single neuraxis which also enters the nerve trunk as a non-medullated nerve fibre, but may later acquire a very thin medullary sheath. The dendrites of Type II are distinguished from those of Type I by being very long and slender and also by entering the nerve trunks, to pass, presumably, to neighboring ganglia. The dendrites of the first cell type, on the other hand, are shorter, thicker, and end in relation with other cells within the same ganglion. The ganglionic cell group is eccentrically placed as regards the axis of the nerve trunk, some funiculi apparently passing the ganglion without being in any way connected with its nerve cells. The sympathetic differ from the cerebro-spinal ganglia chiefly in the preponderance of non-medullated nerve fibres in the former and of the medullated type in the latter. Just as the cerebro- spinal ganglia receive a few non-medullated sympathetic fibres, so also the sympathetic ganglia receive, through the medium of the rami communicantes, a certain number of medullated nerve fibres from the cerebro-spinal system. Moreover, with the intense stain- ing method of Weigert very thin medullary sheaths may now be demonstrated where formerly they were not suspected. The ganglia are supplied with blood vessels and lymphatic vessels in a manner similar to the nerve trunks in whose course they occur. *Anat. Anz., 1896. CHAPTER IX PERIPHERAL NERVE TERMINATIONS: END ORGANS ALL peripheral nerve fibres end either as terminal fibrils or in relation to a highly specialized end organ. The function of these latter bodies is apparently included in the changing of ordinary stimuli — mechanical, thermal, chemical, etc. — into a nerve im- pulse, or, vice versa, the changing of a nerve impulse to a cell stimulus which results in motion, secretion, etc., according to the nature of the tissue cells which are thus stimulated. Some of the nerve end organs are connected with centrifugal (motor) fibres, others with centripetal (sensory) fibres. Nerve endings are found in nearly all the tissues of the body with the exception of carti- lage and the calcareous tissue of the bones. NERVE ENDINGS IN EPITHELIUM Intra-epithelial nerve fibrils are derived from nerve fibre plex- uses in the subjacent connective tissue ; the epithelium usually receives a very abundant nerve supply. The follow- ing types of intra-epithelial nerve endings have to be considered. I. END FIBRILS.— This form of nerve termination has been demonstrated in all the varieties of epithe- lium. Terminal nerve fibres enter the epithelial tissue as naked fibrils, often some- what varicose, which form a delicate plexus between the epithelial cells. The terminal fibrils of this plexus frequently end in minute knob-like enlargements 123 FIG. 118. — NERVE ENDINGS IN THE EPITHELIUM OF THE LARYNX. On the left a taste bud ; on the right, nerve endings in the stratified epithelium are repre- sented. (After Ketzius.) 124 PERIPHERAL NERVE TERMINATIONS FIG. 119. — TACTILE CELLS IN THE EPITHELIUM OF THE GROIN OF A GUINEA-PIG. a, tactile cell ; c, epithelial cell ; m, tactile men- iscus, at the end of a nerve fibril; w, nerve fibre. Chlorid of gold. Highly magnified. (After Ean- vier.) which are in contact with the surface, but rarely, if ever, pene- trate the interior of the epithelial cells. The " trefoil plates " of Bethe represent unusually large end knobs. II. TACTILE CELLS (Merkel).— These are modified epithelial cells, with clear cytoplasm and a slightly vesicular nucleus, which are found in the deeper layers of the stratified epi- thelium of the epidermis and in the root sheaths of hairs. These cells are recognized by their vesicu- lar character and by the fact that they occur most abundantly in the inter- papillary portions of the epidermis. The deeper » » ,1 , .n -,, surface of the tactile cell rests in a cup-like expan- sion of a terminal nerve fibril which is known as the tactile meniscus. III. NETTRO-EPITHELITTM.— The cells of some types of neuro- epithelium, e. g., the olfactory cells, are true nerve cells ; others are modified epithelial cells, in relation to which the nerves termi- nate by intercellular end fibrils. The neuro-epithelium of the eye and the ear will be described in the chapters devoted to these organs, that of the gustatory organ forms typical nerve end organs, the taste buds. IV. TASTE BUDS (gustatory organ). — These end organs ap- pear to be concerned with the special sense of taste. They occur in the stratified epithelium of the base of the tongue, uvula, soft palate, and epiglottis. Disse has also found similar structures in the nasal mucous membrane. They are most abundant on the lateral surfaces of the circumvallate papillae of the tongue and on the walls of the sulci in the foliate papillae which are most highly developed in the rabbit. They are occasionally found on the fungiform papillae of the tongue, where they occur in consid- erable numbers in fetal life but mostly disappear before birth, and in the lateral walls of the sulci about the circumvallate papillae. Taste buds are ovoid, ellipsoidal, or spheroidal masses which occupy almost the entire depth of the epithelial layer. Their NERVE EXDIXGS IN EPITHELIUM 125 broad base rests upon the basement membrane, their narrower apex extends nearly to the surface of the epithelium. The apex of the bud is thus covered by the superficial squamous epithelial cells except for a narrow tubular opening which overlies the su- perficial pole of the end organ. This canal presents an external and an internal ostium, respectively designated the outer and inner taste pore. The inner taste pore leads into a goblet-shaped depression in the apex of the taste bud, into which the cuticular processes of the gustatory cells pro- ject (von Ebner *). The taste buds con- sist essentially of two varieties of cells, the gus- tatory and the susten- tacular. The latter in- clude the broad outer sustentacular or tegmen- tal cells at the surface of the bud, the inner sustentacular cells with- in, and the basal cells which lie near the base- ment membrane. The gustatory cells are slender neuro-epithe- lial structures whose nucleus causes a fusiform enlargement near their center or toward the basal end. Their cytoplasm is finely granular; their nucleus stains deeply and is ovoid or rod-shaped. The distal end of the " cell carries a delicate, highly refractive cuticular process which projects beyond the apices of the susten- tacular cells and as far as the inner taste pore. Their proximal end is often bifid, forked, or so flattened as to form a foot-like extremity which is connected with the basal cells by fine processes. The outer and inner sustentacular cells are elongated epithe- lioid cells, having an ovoid or spheroidal vesicular nucleus which causes no bulging of the protoplasm, and a coarsely reticular and frequently vacuolated cytoplasm. The distal ends of the cells Cone. *- Supporting cell. Neuro-epithelial cell. . Rod cell. •Nerve fibrils. FIG. 120. — SCHEMATIC REPRESENTATION OF A TASTE BCD. (After Hermann, from Bohm and von Davidoff.) * Kiilliker's Handbuch. 126 PERIPHERAL NERVE TERMINATIONS taper to blunt points, which collectively form the lateral wall of v. Ebner's goblet-shaped cavity at the apex of the taste bud. 'The proximal end is broad, often blunt or serrated, and, like the gustatory cells, it is connected with the basal cells by proto- plasmic processes. Sp FIG. 121. — TASTE BUD FROM THE HUMAN TONGUE. A, in longitudinal section ; B, transaction through the deeper third ; (7, transection through the base. Bz, basal cells ; Ez, extra-bulbar cells ; Gz, gustatory cell ; L, leuco- cytes, in A one of these is seen in the pore; P0, perigemraal space; Sg, Subgemmal spaces ; Sp, connective tissue of the tunica propria ; Sz, sustentacular cells ; x, ceils of the adjacent epithelium. (After Graberg.) The basal cells (Hermann) are flattened bodies with small ovoid vesicular nuclei and a relatively small amount of cytoplasm which is prolonged into numerous processes that appear to be continuous with the sustentacular and gustatory cells. These cells have been considered as having a similar function to the sustentacular cells. The nerve fibrils of the taste buds are derived from a sub- epithelial plexus which distributes terminal fibrils to the gustatory NERVE ENDINGS IN CONNECTIVE TISSUE 127 and sustentacular cells — intragemmal fibres — and to the interven- ing portions of the stratified epithelium — intergemmal fibres — where they terminate in end fibrils. Von Lenhossek * states that the intragemmal and intergemmal fibres are never derived from the same nerve fibre. Circumgemmal fibres, distributed as vari- cose fibrils to the surface of the taste bud, may, however, arise from the same nerve fibre as the intragemmal branches. Those nerve fibres which enter the taste buds form fine vari- cose fibrils which are closely applied to, but are not continuous with, the gustatory and the sustentacular cells. The terminal twigs of these fibrils end by minute end knobs which are scarcely distinguishable from the varicosities (Fig. 118). NERVE ENDINGS IN CONNECTIVE TISSUE The nerve fibres form extensive plexuses in the connective tissues from which terminal branches are distributed to the epi- thelium, the walls of the blood and lymphatic vessels, and to the numerous sensory end organs which occur in great abundance in most of the connective tissues. Nerves also terminate in con- nective tissue by free end fibrils some of which, as in the epithelial tissues, possess minute end knobs. Free nerve endings of this nature occur in the tendons, the lungs, the stomachial and intestinal mucous mem- branes, the meninges, and in the superficial layer of the corium of the skin and the hair follicles (terminaisons hederiformes of Ean- vier). The following types of nerve end organs are found in connective tissue : I. TACTILE CORPUSCLES (touch cor- puscles of Meissner). — These organs are formed by the terminal expansion of a nerve fibre, which forms a varicose plexus inclosed within a delicate connective tissue sheath. The nerve fibre, or its primary branches, prior to its ultimate division makes several spiral turns about the corpuscle. The course FIG. 122. — TACTILE COR- PUSCLE OF MEISSNER FROM THE SKIN OF THE HUMAN TOE. Bl, blood vessel; N, medullated nerve fibre. Highly magnified. (After Schiefferdecker.) * Anat, Anz., 1892. 128 PERIPHERAL NERVE TERMINATIONS of the nerve fibre gives the corpuscle a peculiar spirally striated appearance. Within the corpuscle the nerve fibre breaks into a plexus of varicose fibrils, many of which end in knobbed extrem- ities. The corpuscles also contain many flattened or cuneiform epithelioid cells which are interspersed among the nerve fibrils. FIG. 123. — TACTILE CORPUSCLE OF MEISSNER. a, nerve fibrils which enter the corpuscle and supply its nerve skein. Methylen blue. Very highly magnified. (After Dogiel.) FIG. 125. — END BULB OF KRAUSE FROM THE MARGIN OF THE OCULAR CONJUNCTIVA. The neuraxis -forms a dense skein within the encapsulated bulb. Methylen bl ue. High- ly magnified. (After Dogiel.) n L FlG. 124. — EUFFINI'S END ORGAN. A single nerve fibre breaks up to form the tangle of nerve fibrils within the organ. gH, medullary sheath ; il, terminal fibrils of the axis cylinder ; L, connective tissue capsule. (After Ruffini.) NERVE ENDINGS IN CONNECTIVE TISSUE 129 Tactile corpuscles occur in large numbers in the cutaneous papilla of the finger tips and less abundantly in other portions of the skin; they have also been found in the conjunctiva FIG. 126. — GENITAL CORPUSCLES FROM THE CLITORIS OF A RABBIT. A single neuraxis from the nerve plexus enters each corpuscle. Methylen blue. Highly magnified. ( After Eetzius. ) (Dogiel*). They appear to be concerned with the finer tactile sensations. II. RUFFINrS END ORGANS.— These bodies resemble the tactile corpuscles in structure but possess a definite, though thin, connective tissue sheath within which the terminal arborization FIG. 127. — A PACINIAN CORPUSCLE FROM THE MESENTERY OF A CAT. A, a nearly axial section ; 5, a transection. Hematein and orange G. x 410. of the nerve fibre is embedded in a granular core. They occur in the deeper part of the true skin near its junction with the sub- cutaneous tissue and in the connective tissue septa of the latter, whereas the tactile corpuscles are found in the papillary layer of 10 * Arch. f. mik. Anat., 1891. 130 PERIPHERAL NERVE TERMINATIONS the skin. Ruffini * states that they occur in large numbers in the skin of the finger tips, where they rival in number the rather more deeply placed Pacinian corpuscles. /^ ^>x The Ruffini organs are cylindrical in shape and their nerve fibres usually enter at the side of the organ, though occasionally at its end. Now and then a single branching nerve fibre is dis- tributed to several of these end organs. III. END BULBS (Krause).— These structures, together with those which follow, form the so-called encapsulated nerve end organs. In the end bulbs the nerve forms a terminal arboriza- tion of varicose and knobbed fibrils which freely anastomose (Dogiel, Ruf- fini). The bulb is invested with a distinct connective tissue capsule. On entering the bulb the nerve fibre loses its sheaths and the perineu- rium becomes con- tinuous with the capsule of the bulb. Within the capsule the nerve fibrils are embedded in a granular inner bulb. The end bulbs vary much in both size and shape. They may be either spheroidal, ovoid, twisted or convoluted, branched or compound, or cylindroid. They are abundantly found in the conjunctiva, but also occur in the corium , . o'-i 1-111 The nerve fibre shows of the skin. Similar, though more highly de- lateral processes, many veloped, end bulbs form the so-called genital of which are knobbed. corpuscles which are found in considerable •r FIG. 128. — A PACINIAN CORPUSCLE FROM THE PLEURA OF A CHILD. a, lamellae ; 6, nerve fibre ; c, nerve. Methylen blue. Moder- ately magnified. (After Dogiel.) FIG. 129. — PACINIAN COR- PUSCLE FROM THE MESENTERY OF A KITTEN. numbers in the connective tissue of the glans saia.) Methyien biu& Motor- ately magnified. (After * Arch. ital. de biol., 1894. NERVE ENDINGS IN CONNECTIVE TISSUE 131 penis, prepuce, and clitoris. In some of the smaller end bulbs found in the tendons, the mucous membranes, and in certain por- tions of the skin, the nerve fibre fails to divide but ends near the distal extremity of the bulb in a small fusiform end knob. IV. PACINIAN CORPUSCLES ( Vater's corpuscles, Vater-Pa- cinian corpuscles, lamellar corpuscles). — These are among the largest of the nerve end organs. ^^jjjj^-^- They assume the form of a large ffit ovoid thickening, placed upon ^^| 1;^ the end of a nerve fibre. The Pacinian corpuscle consists of a thick lamellated connective tissue FIG. 130. — A PACINIAN CORPUSCLE IN LONGITUDINAL SECTION, SHOWING A NETWORK OF SPIRAL ELASTIC FIBRES. Weigert's elastic tissue stain. Highly magnified. (After Sala.) a FIG. 131.— AXIAL SECTION OF A CORPUSCLE OF HERBST FROM A DUCK'S TONGUE. a, medullated nerve fibre ; 6, naked axial nerve fibre with a bulbous end ; c, niu-k-i uf the core ; d, inner concentric capsule ; e, nu- clei of the outer lamellated capsule, x 380. (After Sobotta.) coat, and a central granular protoplasmic core which is pierced by the nerve fibre. The medullated nerve fibre enters the axis of the corpuscle, its perineurium becoming continuous with the superficial capsule of connective tissue. The nerve fibre on en- tering the core loses its medullary sheath, and after traversing a greater or less portion of the core divides into two to five branches which end near the distal pole in a disk-like expansion. 132 PERIPHERAL NERVE TERMINATIONS In its course through the core, the nerve fibre gives off fine lateral twigs (Sala, Retzius). The connective tissue sheath consists of a granular protoplasm which is permeated by densely felted spiral fibres (Sala) and is divided into ten to fifty concentric lamellae by lines of flattened connect- ive tissue cells and fibres. Accord- ing to Schwalbe, however, these cells form an endothelial coat on either surface of each lamella. Pacinian corpuscles are occasionally com- pound, two or more adjacent cor- puscles being supplied by branches of the same nerve fibre. Pacinian corpuscles are found in large numbers in the subcutaneous tissue of the finger tips and of the penis, as well as in the skin of other parts, in the mesentery and the con- nective tissue of neighboring organs (e. g., the pancreas), in the pre verte- bral connective tissue of the abdomen and mediastinum near the walls of the large blood vessels, in the serous membranes — pleura,pericardium,per- itoneum — in the peri-articular con- nective tissue and periosteum, in the sheaths of the larger nerve trunks, and in the connective tissue of the thyroid gland and of the skeletal muscles. The corpuscles of Herbst (Key-Retzius corpuscles) are similar in structure to the Pacinian corpuscles except that the core which surrounds the axial nerve fibre contains cuboidal tactile cells. They occur only in the cere of aquatic birds. The corpuscles of Grandry (MerkeVs corpuscles), also found only in aquatic birds, contain several tactile cells of ectoblastic origin similar to those found in the epidermis. Each cell is in relation with a ring or meniscus formed by the expanded end of a nerve fibre. The whole is included within a thin connective tissue capsule and may be regarded as a compound tactile cell oc- curring in connective tissue. FlG. 132. — A PAPILLA OF THE DUCK'S TONGUE, CONTAINING A CORPUS- CLE OF GRANDRY. The corpuscle contains four large cells, between which are the tactile menisci of the nerve ending. n, nerve. Highly magnified. (After Merkel, from Kolliker.) NERVE ENDINGS IN CONNECTIVE TISSUE 133 The Golgi-Mazzoni corpuscles, described by Ruffini,* somewhat resemble the Pacinian corpuscles in that they possess a lamellar, though relatively very thin, connective tissue sheath and a cen- Fio. 133. — GOLGI-MAZZONI CORPUSCLES FROM THE SUBCUTANEOUS TISSUE OF THE TIP OF THE FINGER. (After Ruffini.) tral granular core. The core, however, is relatively excessive in size, and the entering nerve fibre breaks into a number of branches with discoid terminal expansions similar to those found in the nerve endings of Golgi in the tendons. Arch. ital. de biol., 1894. 134 PERIPHERAL NERVE TERMINATIONS NERVE ENDINGS IN MUSCLE AND TENDON A. Striated Muscle I. MOTOR END PLATES.— These organs form the intramus- cular endings of peripheral motor neurones whose cell bodies are found in the ventral horns of the grey matter of the spinal cord. They reach the muscle through the many cerebro-spinal nerve trunks. On entering the muscle these nerves form a plexus in __ a FIG. 134. — MOTOR NERVE ENDINGS IN STRIATED MUSCLE. A, from a lizard ; B, from the guinea-pig ; (7, from the hedgehog. A and C are sur- face views ; in B the end plate is seen in profile, a, muscle fibre ; 6, nerve fibre ; c, nerve ending in the form of a " brush " ; d, the sole plate ; e, sarcolemma. A, x 160 ; B, x 700 ; C, x 1200. (After Bohm and von Davidoff.) the perimysium from which nerve fibres are distributed within the muscle bundles. Here they form an abundant plexus of branching nerve fibres within the endomysium, the ultimate branches being of sufficient number to supply one or more termi- nal nerve fibres to each muscle cell, NEKVE ENDINGS IN MUSCLE AND TENDON 135 At the surface of the muscle cell the nerve fibre loses its med- ullary sheath, its neurilemma becomes continuous with the sar- colemma of the muscle cell, and its naked axis cylinder divides into two to five branches, which end, often after repeated subdi- vision, in flattened terminal disks, distributed in mammals over a limited, in amphibians over a broad area, but which never com- pletely encircle the cylindrical muscle cell. The terminal expansions of the neuraxis rest upon a granular sole plate which contains many ovoid nuclei, the sole nuclei. The nature of these nuclei is somewhat uncertain. By those who consider, as is now generally accepted, that the nerve endings lie within the sarcolemma of the muscle fibre, the nuclei are pre- sumed to be derived from the muscle cell and the granular sub- stance of the sole plate is regarded as a modified portion of the sarcoplasm. Some authors (Kolliker, Krause) regard the end plates as lying on the muscle cell rather than within the sarco- lemma, but the studies of Huber and De Witt, * as also those of many other observers, would seem to have satisfactorily settled this question in favor of the intramuscular interpretation. In this connection it is interesting to observe that motor end plates were discovered by Doyere in those muscle cells of insects which are not provided with a sarcolemma. In these cells, as in the muscles of many verte- brates, the entrance of the nerve produces a distinct eminence on the surface of the muscle fibre which is known as the eminence, elevation, or hillock of Doyere. II. MUSCLE SPINDLES (Neuro-muscular spindles, neuro- muscular end organs). — These are sensory nerve endings which are concerned with the so-called muscle sense and are found in nearly all the skeletal muscles. FlO. 135. — A MUSCLE SPINDLE FROM THE PSOAS MAGNUS OF MAN. Jf, intrafusal muscle fibres; 2, nerve fibres ; 3, axial shealh ; h connective tis- sue capsule ; 5, muscle fibres of an adja- cent fasciculus ; 6, peri-axial lymphatic spaces ; 7, blood vessel. Hematein and eosiii. x 470. * J. of Comparat. Neurol., 1898. 136 PEEIPHERAL NERVE TERMINATIONS They are especially numerous in the extrinsic muscles of the tongue, in the small muscles of the hand and foot, and in the intercostal muscles (Huber*). A muscle spindle contains from five to twenty striated muscle fibres of small size, and an almost equal number of nerve fibres. The whole is inclosed within a connective tissue capsule of con- siderable thickness. The bundle of intrafusal muscle fibres is again surrounded by a delicate axial sheath of connective tissue which is united to the capsule by bands of fine fibrous tissue FIG. 136. — MIDDLE THIRD OF A TERMINAL PLAQUE IN THE MUSCLE SPINDLE OF AN ADULT CAT. A, rings ; F, dendritic branchings ; S, spirals. Chloride of gold preparation. Highly magnified. (After Ruffini.) which span the broad periaxial lymphatic space. The larger of these fibrous bands support the nerve fibres, on their way to the intrafusal muscle cells, together with several small blood vessels. The muscle spindles form long fusiform bodies whose muscle fibres at the pole of the spindle may be connected with the ten- don, or they may join other muscle fibre bundles. The muscle spindles are usually found in the fibrous septa of the peri- mysium. * Am. J. of Anat., 1902. 138 PERIPHERAL NERVE TERMINATIONS Either one or several nerve trunks enter the spindle, usually near its equator rather than at its poles. The nerve fibres branch repeatedly in the intracapsular connective tissue, and finally pierce the axial sheath as naked processes which form a rich arboriza- tion of terminal fibrils about the intrafusal muscle fibres. Ruf- fini distinguishes three types of terminal nerve fibrils : (1) an- nular, which form rings around the muscle fibres; (2) spiral, which are spirally twisted about the intrafusal fibres ; and (3) dendritic branchings (terminaisons a fleurs), in which the neu- raxes break into numerous irregular processes with laminate ex- pansions. Motor end plates for the muscle fibres of the spindle as well as sympathetic vase-motor nerves for its blood vessels have also been demonstrated within the muscle spindles. That the muscle spindles are sensory and not motor organs has been demonstrated by Sherington,* who found that they were not affected by the muscular atrophy following section of the pe- ripheral motor neurones, and by Horsley f and others who have found that the muscle spindles are unaffected in cases of extreme muscular atrophy in man. III. NEUROTENDINOUS END ORGANS (Golgi end organs, tendon spindles}. — These organs occur in the tendons of mus- cles near the junction of the tendon bundles with the muscle fibres. They are fusiform in shape and consist of a thin lamellar capsule of connective tissue which incloses several intrafusal tendon bundles of dense fibrous tissue. A narrow lymphatic space intervenes between the capsule and the intrafusal tendon bundles. Nerve fibres enter the spindle and give off several medullated branches which run between the tendon bundles near the axis of the spindle. These finally form naked end fibrils with branching end plates, which surround the tendon bundles in an annular or spiral manner (Ciacio J). Since the structure of the Golgi ten- don spindles closely resembles that of the muscle spindles, they are undoubtedly of similar function. IV. In addition to the special motor and sensory end organs described above, Pacinian corpuscles and end bulbs of Krause are also found in the connective tissue of striated muscles. * J. Physiol., 1894. f Brain, 1897. I Arch. ital. de biol., 1891. NEKVE ENDINGS IN MUSCLE AND TENDON 139 FIG. 138. — NERVE ENDINGS IN CARDIAC MUSCLE, FROM THE HEART OF A CAT. a, muscle cells ; 6, nerve fibre. Methylen blue. Highly magnified. (After Huber and De Witt.) B. Cardiac and Smooth Muscle The nerves of the heart are distributed to the cardiac ganglia, whence non-medullated fibres pass to all portions of the organ and form a very rich plexus in the intermuscular con- nective tissue. Fine ter- minal fibrils are distributed from this plexus to the * muscle fibres, upon whose surface they end in vari- cose swellings and end knobs. While most of these fibrils are probably motor in function, others which, end in the intermuscular con- nective tissue are more probably centripetal. In smooth muscle plexuses of sympathetic nerve fibres occur in the intervals between the bundles of muscle fibres. Secondary plexuses of naked fibrils are found among the mus- cle cells, and from this plexus fine lateral fibrils are distributed to the muscle cells, upon whose surface they end in small terminal gran- ules or end knobs. Many of the nerve fibres in smooth muscle are undoubtedly of sensory function. FIG. 139. — NERVE ENDINGS IN SMOOTH MUSCLE, FROM THE INTESTINE OF A CAT. o, muscle cell ; 6, nerve fibre. Methylen blue. Highly mag- nified. (After Huber and De Witt.) The nerve endings and the distribution of the peripheral nerve fibres in the various organs of the body are more fully described in the several chapters devoted to those organs. CHAPTER X THE LYMPHATIC SYSTEM THE lymphatic series includes a system of lymphatic chan- nels which collect the lymph from the various tissues of the body and return it to the large veins of the neck, where it mixes with the blood. In the course of this lymph vascular system are various aggregations of lymphoid or adenoid tissue which occur in the form of lymphoid nodules or follicles, lymphatic glands or nodes, and the lymphoid organs. These organs are the tonsils, thymus, and spleen. The lymphatic vessels also stand in intimate relation if not in direct communication with the serous and synovial mem- branes and the bursae. LYMPH. — Like the blood, the lymph may be considered as a primary tissue whose intercellular elements are entirely of a fluid nature. In most portions of the body, lymph is a colorless fluid which is scantily provided with corpuscular elements, the lym- phatic corpuscles. The lymphatic corpuscles are identical with the leucocytes of the blood. In the lymph most of these cells are of the mononuclear form, the small mononuclears or lymphocytes being the most abundant. Lymph also contains a small propor- tion of polynuclear cells, which not only are derived from the lymphoid tissues, but as wandering cells find their way into the lymphatic vessels from the tissues generally. In addition to the leucocytes lymph contains fat globules and glycogen. These are mostly the products of absorption from the intestinal tract, in which process the lymphatic vessels play an important role. In the lymphatic vessels of the intestine during absorption fat globules are so abundant as to impart to the lymph a milky white color ; this variety of lymph is termed the chyle. These fat globules are rapidly removed by the lymphoid organs, since even in the presence of abundant chyle only comparatively few fat globules escape into the general blood current. The lymph of other portions of the body than the abdominal region, therefore, contains relatively little fat. 140 LYMPHATIC VESSELS 141 The lymph, unlike the blood, circulates in but one direction, viz., toward the heart. It must therefore be formed in the tissues generally. The blood plasma constantly escapes through the walls of the capillary vessels into the surrounding lymphatic spaces of the tissues. It is these tissue spaces which have been consid- ered as forming the beginning of the lymphatic system. Recent evidence, however, goes to show that the tissue spaces are not directly connected with the lymphatic vessels, but that just as the plasma exudes into the tissue spaces by processes of secretion, osmosis, and nitration, so the tissue juices, as the predecessors of lymph, enter the lymphatic vessels by similar processes of secre- tion, osmosis, and filtration. Lymph is also formed by absorption, which occurs chiefly in the alimentary tract. Under similar conditions the lymph as well as the blood will coagulate, the fibrin forming a firm, colorless clot in which the leucocytes are entangled. Because of their tendency to adhere to the sides of the vessel — thus circulating at the periphery of the current — the lymphatic corpuscles are most likely to be found at the periphery in those post-mortem clots which occur within the lymphatic vessels. LYMPHATIC VESSELS (lymphatics).— The lymphatic vessels vary in size from that of the smallest capillary vessels up to that of the thoracic duct. The smaller vessels, lymphatic capillaries, form anastomosing meshes in all tissues where blood capillaries are found. They are most abundant in the perivascular connect- ive tissues, where they form a dense plexus about the wall of the blood vessels. The wall of the lymphatic capillary, like that of the blood capillary, consists of a single layer of endothelium. This endo- thelium probably forms a complete lining for the lymphatic capillary and is continuous through larger and larger vessels with that of the veins, from which, according to Sabin,* the lymphatics are originally developed. The relation of the lymphatic capillaries to the tissue spaces is not as yet definitely settled. It was formerly thought that these spaces were continuous with the lymphatic capillaries, but the more recent observations, represented by those of MacCallum,f seem to show that the capillaries of the lymphatic system, like * Amer. J. Anat, 1902. f Johns Hop. Hosp. Bull., 1903 ; and Arch. f. Anat., 1902. 142 THE LYMPHATIC SYSTEM those of the blood vascular system, form a series of branching channels which are open only toward the veins. According to this conception, therefore, the tissue juices, formerly also consid- ered as lymph, are contained within a separate series of channels, the tissue spaces and lymphatic canaliculi, and they enter the true FIG. 140. — SUBCUTANEOUS LYMPHATIC VESSEL OF A PETAL PIG. At the right is a small blood vessel. Hematein and eosiu. Highly magnified. (After MacCallum.) lymphatics only by processes of osmosis and the secretory activity of the lymphatic endothelia. The lymphatic capillaries are of rather irregular caliber and possess frequent sinus-like dilatations, which peculiarity is also characteristic of the larger lymphatic vessels. The lymphatic capillaries soon acquire an adventitial sheath of fibro-elastic tissue and pass into the smaller lymphatic vessels, On attaining a size of from 0.2 to 0.8 mm. their wall is differen- FIG. 141. — THE GROWING END OF A DEVELOPING LYMPHATIC VESSEL IN THE SUBCU- TANEOUS TISSUE OF A FETAL PIG. The lumen of the vessel has been filled with a dark injection mass. Highly magnified. (After MacCallum.) FIG. 142.— LYMPHATIC AND BLOOD VESSELS IN THE HILUM OK A HUMAN LYMPHATIC NODE. a, lymphatic vessels ; 6, blood vessels. Henmtein and eosin. * Photo, x 160. 143 144 THE LYMPHATIC SYSTEM tiated into the same three coats which are found in the veins. Except for the fact that they contain lymph instead of blood, these vessels closely resemble the small veins, and like the latter vessels they possess frequent valves. The tunica intima of the lymphatic vessel consists of an endo- thelial lining with a thin delicate fibro-elastic membrane. The FIG. 143. — LYMPHATIC CAPILLARY FROM THE SPERMATIC CORD OF A DOG, SHOWING NERVE ENDINGS. o, nerve fibres. Methylen blue. Highly magnified. (After Kytmanof.) tunica media is thin and contains circular smooth muscle fibres. The adventitia is the thickest coat of the lymphatic vessel. It consists of fibrous connective tissue and longitudinally disposed bundles of smooth muscle fibres. The wall of the lymphatic vessels is supplied with small blood- vessels and nerves, in the same manner as the veins. The nerves form a plexus in the adventitia from which branches are distributed to the media and intima. Kytmanof * has traced the fine nerve fibrils to the smallest lymphatic capillaries, where, as in the intima of the larger vessels, they end in close relation to the endothelial cells. To summarize : the lymphatic capillaries arise by one of three methods : 1. As lymphatic plexuses in all connective tissue; the most abundant of these are the perivascular lymphatics. * Anat. Anz., 1901. THE SEROUS MEMBRANES 145 2. As dilated pouches having blind extremities, as in the villi of the small intestine. 3. By direct communication with the stomata of the serous membranes. The lymph is derived from the tissue juices and by absorption from the alimentary tract, and is conveyed by the lymphatic capil- laries to larger and larger lymphatic vessels, which resemble the small veins in their structure, and which finally empty into the subclavian veins of the neck. THE SEROUS MEMBRANES.— The serous membranes form closed sacs which line the great cavities of the body and are re- flected over the viscera to form a double covering, the two layers of which are freely movable over one another. Of these two layers the one, the parietal layer, is attached to the wall of the body cavity, the other, the visceral layer, covers the surface of the in- closed organ. The serous membranes consist of an endothelial lining and a supporting membrane of areolar connective tissue which is richly supplied with capillary blood vessels and lymphatics. The eudo- thelium consists of large flat cells, pavement epithelium, whose serrated margins are firmly united by an intercellular cement sub- stance. Here and there minute openings are seen which are sur- rounded by very small endothelial cells ; these stomata have been found to be in certain instances directly connected with the lym- phatic vessels. ___^ Tunica Propria. — The endothelium rests upon a layer of areolar tissue which is richly supplied with small blood vessels and lymphat- ics, forming an abundant vascular plexus beneath the endothelium. The SerOUS pIG> 144.— TRANSECTION OF THE PERICARDIUM membrane is either directly OF A CHILD. United to the Wall Of the «-*i endothelium; 6-6, subendothelial con- ., - nective tissue. Hematein and eosin. Photo. cavity and the surface of " 500 the organ which it envelops, or it may be attached by a looser layer of " su ^endothelial con- nective tissue" The thickness of the endothelial cells varies in different por- tions of the serous membranes and is somewhat dependent upon 11 146 THE LYMPHATIC SYSTEM the age of the individual. In most portions it is no more than a pavement epithelium, but over the surface of the functionally active ovary these cells are much thickened and acquire a cuboidal shape ; thus it forms the " germi- nal epithelium " of the ovary. In young individuals, viz., in fetal life and early child- hood, the cuboidal cell type is found in many portions of the peritoneum, pleura, and peri- cardium. The synovial membranes resem- ble the serous in their structure. They are lined by a single layer of pavement cells which is said to be incomplete in places. Its endothelium is supported upon a layer of firm fibrous tissue richly supplied with both lymphatic and blood capillaries. In the recesses of the joints the synovial mem- branes are frequently thrown into small villous folds, which are chiefly formed by the inner portion of the fibrous coat and are covered with endothelium ; these are the synovial villi. The bursae and the synovial sheaths of the tendons are of simi- lar structure. Both the serous and the synovial membranes are moistened by fluid which contains leucocytes in small numbers, and closely re- sembles the lymph and tissue juice in its composition. LYMPHATIC FOLLICLES (Lymphatic Nodules).— The lym- phatic follicle is a structural unit of lymphoid tissue which may exist independently, as in the solitary follicles of the intestinal tract, or may form groups or accumulations consisting of a greater or less number of f ollicular units. In this latter condition they occur in the mucous membrane of the small intestine as FIG. 145. — SECTION OF A VASCULAR SYNOVIAL VILLUS FROM THE KNEE JOINT OF A CHILD. Hematein and eosin. Photo, x 200. LYMPHATIC FOLLICLES 147 Peyer's patches, in the tongue as the lingual tonsil, in the fauces as the faucial tonsils, in the pharynx as the pharyngeal tonsil, in the wall of the laryngeal cavity, in the spleen as the Malpighian corpuscles, in the lymphatic glands as the peripheral lymphatic follicles, and in the thymus, where we may consider the lobule of the organ as being the structural equivalent of a lymphatic fol- licle. The lymphatic follicle consists of a mass of lymphoid tissue, usually of ovoid form, which is surrounded by or embedded in FlG. 146. — A LYMPHATIC NODULE, SOLITARY FOLLICLE, FROM THE LARGE INTESTINE OF MAN. In the upper part of the figure the edge of the intestinal mucosa is shown ; it con- tains many secreting tubules which have been cut in transverse or oblique section and are lined by columnar epithelium and goblet cells. Photo, x 80. connective tissue. In those locations where it exists independ- ently the follicle is completely surrounded by the connective tissue in which it lies. In other places, as in the lymphatic glands, 148 THE LYMPHATIC SYSTEM the follicle is only partially surrounded by the connective tissue trabeculae of the organ. Not only do fine branches from the sur- rounding connective tissue bundles penetrate the periphery of the follicle, but the reticulum of the follicle is continuous with these trabeculae, thus forming a supporting stroma in which the lym- phatic corpuscles are embedded. The lymphatic corpuscles are loosely packed in the center of the follicle, and in this portion cell division by mitosis is most active. This central portion is the germinal center of Fleming. The germinal center is surrounded by a denser circumferential layer of lymphoid tissue in which karyokinesis is less active. Be- tween this denser portion and the surrounding connective tissue the lymphatic corpuscles are again more loosely packed, and over a greater portion of the follicle are separated from the trabeculae by a lacuna-like space, the peripheral lymphatic sinus. The follicle is usually supplied with a thin-walled artery, occa- sionally two, which penetrates to the middle of the follicle to form a wide meshed capillary plexus. The capillaries, at the periphery of the follicle unite to form two or more veins, which are con- tained in the adjacent connective tissue. The lymphatic corpuscles are mostly of the mononuclear type of leucocyte, the small mononuclear or lymphocyte type being the most abundant. Polynuclear and acidophile leucocytes are also found in the lymphatic follicles, though in much smaller numbers. Mitosis is most frequently observed in the large mononuclear type. Because of the nomadic tendencies of the leucocytes the bounda- ries of the lobule are not always sharp, the lymphatic corpuscles frequently infiltrating the surrounding connective tissue so as to render it most difficult to distinguish the latter from the true lymphoid tissue of the follicle. THE LYMPHATIC NODES (Lymphatic Glands* Lympho- glandulce). — These structures occur in the course of the lymphatic circulation in various parts of the body. They are found in the neighborhood of the large joints, as in the axilla, the groin, the popliteal space, in the prevertebral and mediastinal connective tissue of the abdominal and thoracic cavities, and in the mesen- tery. They are frequently in relation with the large arteries, e. g., the renal, internal and external carotids, etc. * Since the lymphatic glands are in no sense true secreting glands after the manner of the serous and mucous secreting glands, this name is most ill-chosen. THE LYMPHATIC NODES 149 Each lymphatic node consists of a mass of follicular lymphoid tissue inclosed within a fibro-elastic connective tissue capsule. The capsule also contains a little smooth muscle tissue, but this is never so abundant as to form any considerable portion of the fibrous membrane ; in fact, as compared with the somewhat similar capsule of the spleen, that of the lymphatic node is notably defi- cient in smooth muscle. An afferent lymphatic vessel, pursuing its course within the capsule, enters the lymphatic node by a number of subdivisions which penetrate the deeper layers of the capsule and open into a FIG. 147. — TRANSECTION or A CERVICAL LYMPHATIC NODE OF A DOG. The denser portions of lymphoid tissue are light in the figure, a, medullary cord of dense lymphoid tissue ; 6, looser lymphoid tissue of the cavernous medulla ; c, capsule ; F, dense lymphoid follicle of the cortex ; HF, fibrous tissue containing the large vr--t -Is of the hilum ; s, peripheral lymphatic sinus ; V, blood vessel. Magnified several diam- eters. (After Kauvier.) peripheral lacunar space, the lymphatic sinus, which separates the inner surface of the capsule from the adjacent lymphoid tissue, but which is bridged across at frequent intervals by the fine strands of lymphatic reticulum. The lymphoid tissue, which forms the substance of the node, consists of a dense peripheral portion, the cortex, formed by closely packed lymphatic follicles, and a looser medulla in which are co- lumnar accumulations of dense lymphoid tissue, the lymphatic cords. Cortex.— The follicles of the cortex are partially separated from each other by septum-like trabeculas which extend inward from the fibrous capsule, and along which the peripheral lymphatic sinuses are continued into the substance of the node to partially surround its lymphatic follicles. Each lymphatic follicle is thus surrounded, except at its central pole, by a peripheral lymphatic sinus, into which the afferent lym- 150 THE LYMPHATIC SYSTEM phatic vessels pour their contents. The lymph on entering the gland is thus permitted to enter the spaces of the reticulum and percolate through the lymphatic follicles of the cortex before it can reach the looser portions of the medulla. Each of the follicles of the cortex contains a germinal center in which lymphatic cor- puscles are actively formed by mitosis, and from which the leuco- cytes readily escape along the lymphatic channels of the reticulum into the more open meshes of the medulla. Medulla. — The medulla occupies the center of the gland, and at one point, the hilum, it reaches the surface. At this point a considerable mass of fibrous trabecula6 enters the medulla, carry- ing with it the larger blood vessels to be distributed to all portions of the gland. The finer ramifications of these medullary trabeculae are continuous with those of the cortex. The lymphoid tissue of the medulla is divisible into the denser branching lymphatic cords, in which the leucocytes are closely FIG. 148. — TKANSECTION OF A MESENTERIC LYMPHATIC NODE or MAN. Hematein and eosin. Photo, x 38. packed, and the intervening pulp spaces, in which leucocytes are less numerous, and the reticulum of which is continuous with that of the cortical follicles. The pulp spaces are broad channels, which are occupied by a reticulum whose meshes are partially filled with lymphatic cor- THE LYMPHATIC NODES 151 puscles. They are bounded by a layer of endothelioid cells which everywhere incloses the denser lymphatic cords. The function of these cords would seem to be comparable to that of the peripheral lymphatic follicles. The pulp spaces are open toward the cortex, whence they re- ceive the afferent lymph after it has percolated through the folli- cles, but toward the hilum the spaces are continued into the effer- ent radicles of the lymphatic vessels which, in the connective tissue of this part, unite into larger trunks, and finally form several efferent, lymphatic vessels of considerable size. The reticulum of the lymphatic gland is a close-meshed net- work of interlacing fibrillar bundles, which are here and there clasped by flattened endothelioid connective tissue cells. Retic- ulum is but poorly stained with either acid or basic dyes, is de- stroyed by acids and bases, but is not digested by pancreatin. After prolonged action of Weigert's specific stain for elastic tissue it is but slightly colored. Lymphatic Corpuscles. — The great majority of these cells are of the small mononuclear or lymphocyte type. Large mononuclear cells with a considerable cytoplasmic body are also very numerous. Polynuclear neutrophile leucocytes, though of frequent occur- rence, are less abundant than the previous varieties. Eosinophile cells are present in small numbers, and large basophilic mast-cells are occasionally seen, though according to Carlier * they are mostly confined to the connective tissue. Drummond f also found large multinuclear giant cells, megakaryocytes, similar to those of the bone marrow ; these were, however, very rare. Many of these cells, after proper fixation, show mitotic figures. This mitosis has been most frequently observed in the large mono- nuclear type, and is most abundant in the germinal centers of the follicles. The small mononuclear and polynuclear types have also been shown to be capable of cell reproduction by indirect division. Reproduction by direct division of leucocytes appears to be rare, if indeed it ever actually occurs. The mononuclear as well as the polynuclear forms appear to be phagocytic. Among the inclusions which have been found within these cells are fat globules, pigment granules, red blood corpuscles in partial disintegration, insoluble pigments, such as carbon gran- ules, etc., and bacteria. * J. Anat. and Physiol., 1893. f J« Anat. and Physiol., 1900. FIG. 149. — DIAGRAM OF THE BLOOD VESSELS OF A LYMPHATIC NODE. A composite section of three follicles and the medullary cords of a mesenteric lym- phatic node of the dog. A, artery ; £, medullary artery ; C, follicular vein ; £", artery going to the capsule ; F, capillaries in the periphery of a cord ; (?, medullary vein ; H, follicular artery ; J, arterial capillaries in a follicle ; J, vein from capsule ; K, cord ; X, trabecula ; V, vein, x 501. (After Calvert.) 153 HEMOLYMPH NODES 153 Blood vessels.— The arteries enter the lymphatic node at its hilum, and, following the trabeculae within which they lie, are dis- tributed to all portions of the organ. In the medulla branches are distributed to the lymphatic cords, in which they form a wide- ineshed capillary plexus. The terminal branches of the primary divisions of the afferent artery are distributed to the follicles of the cortex. A single fol- licular branch (Calvert*) enters the follicle and passes straight toward its center, where it breaks into a plexus of divergent cap- illaries which unite at the surface of the follicle to form small venous radicals. The veins follow the interfollicular trabeculae in their course toward the medulla, where they enter the medullary trabeculae, are augmented by venous radicals from the capillary plexuses of this portion of the gland, and thence follow the trabeculae to the hilum, where they unite to form the efferent vein. Certain of the arteries also pass from the medulla through the interfollicular trabeculae to the capsule of the gland, to which they supply a capillary plexus. The blood is returned through veins which retrace the course of the arteries and enter the large veins of the medullary trabeculae. HEMOLYMPH NODES.— These structures, which closely re- semble the lymphatic nodes, were first described by H. Gibbs,f in 1884. He found them in the connective tissue, between the renal artery and vein, in the human subject. They have since been found in the prevertebral connective tissue, and in the mediasti- num and mesentery. They are larger and more numerous in the ruminants, ox, sheep, etc., than in man. Their size varies from that of a millet seed to that of a pea. In color they closely re- semble a minute extravasation of blood. These organs are essentially lymphatic structures in which the lymphoid tissue is arranged in the form of cords rather than in follicles. The node is inclosed by a fibrous capsule, beneath which is a broad sinus filled with blood. In this fact lies the chief distinguishing feature of these glands. The peripheral Uood sinus, which is analogous to the peripheral lymphatic sinus of a lymphatic node, sends into the interior of the organ a greater or less number of secondary sinuses. Based largely upon the abundance of these secondary sinuses, the hemo- * Anat. Anz., 1897. f Quart. J. Mic. Sc. 154 THE LYMPHATIC SYSTEM lymph nodes have been divided into two varieties, which were named hy Warthin * the " spleenolymph glands " and the " mar- rowlympli glands" FIG. 150. — HEMOLYMPH NODE OF THE SHEEP. The dark areas are blood sinuses ; the lighter portion within is lymphoid tissue. Photo, x 35. (After Warthin.) In the spleenolymph type, which is the more abundant, the gland is of small size and is well filled with secondary blood sinuses. The lymphoid tissue is supported by a similar reticulum, and con- tains the same varieties of lymphatic corpuscles as in the lym- phatic nodes. In the marrowlymph glands a somewhat similar structure is found. The blood sinuses are less numerous and lymphatic folli- cles do not occur (Vincent, Warthin). The eosinophile leucocytes are more numerous than in the spleenolymph type, and the mar- rowlymph glands as a rule are the larger. * J. Bost. Soc. Med. Sc., 1901. THE TOXSIL 155 Intermediate types between the lymphatic nodes and the spleenolymph (Vincent*) on the one hand, and between the spleenolymph gland and the spleen and marrowlymph type on the other hand, are of frequent occurrence. Blood supply. — The afferent artery, according to Drummond, f enters the hilum with the connective tissue, and through the tra- beculae reaches all parts of the gland. In the lymph oid tissue its branches form a capillary plexus whose vessels open into the blood sinuses. All the sinuses, peripheral and secondary, communicate with each other, and from them the blood is ultimately collected into two or more thin-walled veins. In the center of the gland these vessels unite to form an efferent vein which passes out at the hilum. THE TONSIL (the Faucial Tonsil, Palatine Tonsil, Amygdala). — The tonsil consists of a mass of lymphoid tissue which projects slightly from either side into the cavity of the fauces, and is cov- a - tf •^.'•;--.C .' i^> 'v ,. >?-••• /":."f- ' ' •" < '•^*&$JM?!A FIG. 151. — HORIZONTAL SECTION THROUGH THE FAUCIAL TONSIL OF A CHILD. Semi-diagrammatic, a, stratified epithelium ; 6, crypts ; c, lymphoid nodule ; d, mucous secreting gland. Hematein and eosin. x about 20. ered by a layer of stratified epithelium continuous with that which lines the oral and pharyngeal cavities. The lymphoid follicles which compose the tonsil immediately underlie the epithelial coat, and are embedded in areolar connective tissue. The epithelial coat here and there penetrates the substance of * J. Anat. and Physiol., 1897. f J. Anat. and Physiol., 1900. 156 THE LYMPHATIC SYSTEM the organ in. the form of invaginated funnel-shaped depressions, the crypts ("follicles" of the tonsils). The ducts of many mucous glands open into the recesses of these branching crypts. The mucus secreting glands lie in the loose connective tissue which surrounds the tonsil on all but its faucial surface. The crypts are lined throughout by a layer of stratified epithelium, which is con- tinuous with that on the free surface of the tonsil, but which becomes progressively thinner as it recedes into the deeper recesses of the crypts. Many of the lymphatic corpuscles migrate into the intercellu- lar spaces of the epithelial layer, and even penetrate to the free surface ; thus they find their way into the oral cavity, where they are found in large numbers in the saliva, as " salivary corpuscles" If such salivary corpuscles are examined in a drop of saliva, freshly prepared, the fine intracellular granules of the polynuclear leuco- cytes will be seen to undergo an active dancing movement, Brow)i- ian motion. The salivary corpuscles are derived not only from FIG. 152. — FROM A CRYPT OF A DOG'S TONSIL. a, stratified epithelium ; 6, basal margin of the epithelium ; c, infiltration of the epi- thelium by leucocytes ; d, spaces in the epithelium filled with leucocytes and epithelial cells ; e, blood vessel ; /, lymphoid tissue, x 150. (After Bohrn and von Davidofi'J the faucial tonsils but from the other lymphoid tissue which is in relation with the oral mucous membrane, e. g., the lingual and pharyngeal tonsils. The passage of leucocytes through the epithelial surface of the faucial tonsil is so very active that at times the epithelium becomes completely filled with these cells, and it is then difficult to distin- guish it from the adenoid tissue beneath. THE THYMUS 157 The Lingual Tonstt.— A collection of lymphatic follicles is also found at the base of the tongue in the median line, between the circumvallate papillae and the epiglottis. This, because of its FIG. 153. — THE LINGUAL TONSIL OF MAN. a, a crypt ; 6, von Ebner's glands. Hematein and eosin. x 45. similarity in appearance and in structure to the faucial tonsil, is called the lingual tonsil. In the lingual tonsil, however, the follicles are grouped about a single wide-mouthed crypt, the foramen ccecum lingui. This crypt is frequently branched, and into it the many mucous glands of the neighboring lingual mucosa pour their secretion. The Pharyngeal Tonsil. — The posterior wall of the naso-pharynx is supplied with a similar accumulation of lymphatic follicles, the pharyngeal tonsil. It lies in the median line and extends down- ward from between the orifices of the Eustachian tubes for a dis- tance of three centimetres (Klein). It contains a considerable number of lymphatic follicles and several small crypts. The pharyngeal tonsil is prone to hypertrophy in youth, in which case it forms the adenoid growths which are so common in strumous children. THE THYMUS.— The thymus is an organ of fetal and infantile life, attaining its maximum development during the second year 158 THE LYMPHATIC SYSTEM of childhood. After this time it is gradually replaced by adipose tissue, its retrograde metamorphosis becoming complete at about the age of puberty. At its maximum the thymus forms a large lymphoid mass, embedded in areolar connective tissue, the trabeculas of which divide the organ into several lobes and innumerable minute Mules. Each lobule is surrounded by a thin fibrous capsule, by which it is loosely united to its neighbors. The lobule consists of a mass of lymphoid tissue, which is dense at the periphery but looser in the central portion. It is thus di- visible into a dense cortex and a loose medulla, both composed essentially of lymphoid tissue, but between which, because of the difference in density, there is a sharp line of demarcation. Fre- quently, at some point on its circumference, the medulla reaches d FIG. 154. — A SECTION THROUGH SEVERAL LOBULES OF THE THYMUS OF AN INFANT. o, loose fibrous septum between the lobules ; 6, cortex, and c, medulla of the lobule ; d, blood vessels in the connective tissue. Hematein and eosin. Photo, x 60. the surface of the lobule, and at such locations a narrow column of medullary lymphoid tissue connects it with the adjoining lobule. A close-meshed reticulum, within the narrow meshes of which are closely packed lymphatic corpuscles, composes the lymphatic tissue of the lobule. That of the cortex and the medulla is alike, THE THYMUS 159 FIG. 155. — A CORPUSCLE OF HASSAL FROM THE THYMUS OF AN INFANT. Hematein and eosin. x 665. except for the fact that the meshes of the reticulum in the cortex are much more crowded with leucocytes than are those of the medulla. The medulla of each lobule is also characterized by the presence of several groups of concentrical- ly arranged epithelioid cells, the concentric cor- puscles of Hassal. Each concentric cor- puscle consists of a large central cell or group of cells, which is surrounded by two to five layers of con- centrically arranged flat epithelioid cells. These groups or cell nests are strongly acidophile in their staining reactions, and therefore stand out in marked contrast to the basophilic nuclei of the surrounding lymphoid tissue. Since no similar structure occurs elsewhere in the body, the concentric corpuscles are absolutely characteristic of the thymus lobule. The nature of the concentric corpuscles is not satisfactorily understood. According to one hypothesis they represent blood vessels whose lumen has been obliterated by proliferation of its endothelial cells. Another theory regards them as remains of the epithelial columns from which the organ arises in the embryo. The types of lymphatic corpuscle which are found in the thymus are similar to those of the lymphatic glands, though polynuclear leucocytes are rather more frequent here, and giant cells, polynu- clear or multinuclear in form, may be readily found in the medulla of this organ. Eosinophile cells have been found in the thymus even at a very early period of embryonic life (Schaffer*), and Beard f has ascribed the first formation of embryonic leucocytes to this organ. Blood supply.— The larger arteries of the thymus are distributed within the interlobular connective tissue. They supply branches * Centralbl. f. d. raed. Wissensch., 1891. f Lancet, 1899 ; and Anat. Anz., 1900. 160 THE LYMPHATIC SYSTEM to the lobule which penetrate to the medulla, where the}' form a plexus of sinusoidal capillaries with elongated meshes, and also distribute radiating capillaries to the cortical portion of the lobule. These sinusoidal vessels are highly characteristic of the medulla of the thymus lobule. They unite to form venous radicals of con- siderable caliber, which leave the lobule to join the interlobular veins in the loose connective tissue between the lobules. Lymphatic vessels are of frequent occurrence in the interlob- ular connective tissue, and their branches occasionally penetrate to the medulla of the lobule. Small nerve trunks are also found in the interlobular connective tissue, but seem to be chiefly distrib- uted to the walls of the larger blood vessels. THE SPLEEN.— The spleen contains a pulp which closely resembles adenoid tissue, and is surrounded by a well-developed, fibro-muscular capsule. The spleen pulp, as indeed the entire structure of the organ, is intimately related to its blood supply. The framework of the organ includes a capsule, numerous tra- beculae, and a delicate reticulum. The spleen is also inclosed by a reflection of the peritoneum which supplies a serous coat to all portions of the surface of the organ, except at the attachments of the gastro-splenic omentum and the phreno-splenic and lieno-renal ligaments. The capsule of the organ, to which its serous coat is loosely attached, comprises two layers, an outer fibrous and an inner mus- cular. In some animals — e. g., the ox — these layers are much more highly developed than in man. The outer layer consists of dense interlacing bundles of fibrous tissue, in which is an abun- dant network of elastic fibres. The inner layer contains, in addi- tion to the fibro-elastic membrane, a considerable amount of smooth muscle which forms interlacing bundles. In the ox, in which ani- mal this coat is most highly developed, two layers, the fibres of which cross each other at right angles, may be distinguished in the muscular portion of the capsule. From the inner surface of the capsule trabeculse extend into the interior of the organ and penetrate to all its portions. These trabeculae consist of fibrous and elastic tissue, with which bundles of smooth muscle fibres are intermingled. At the hilum a large mass of trabecular tissue is carried into the interior of the organ along with the larger blood vessels. Those trabeculae which arise in this manner serve as sheaths for the larger arteries and veins. THE SPLEEX 161 From the borders of the trabeculae, as well as from the inner surface of the capsule, a delicate reticulum is continued into the spleen pulp. This reticular tissue is similar in structure to that a a FIG. 156. — FROM THE SPLEEN OF A CHILD. a, splenic pulp ; 6, Malpighiaa corpuscle ; c, capsule ; d, vascular trabeculas. Hematein and eosin. Photo, x 28. of the lymphatic glands though consisting of rather coarser fibrous bundles. Mall * states that the splenic reticulum is readily dis- solved in acids and alkalis, but that, unlike that of lymphoid tissue, it is also digested by pancreatin. The meshes of this retic- ulum are occupied by the splenic cells. Splenic cells. — Besides the endothelioid cells of the reticulum and the epithelium of the small blood vessels, the following cell types can be distinguished in the splenic pulp. 1. Large mononuclear leucocytes. These are the most numer- ous of the several cell types of the spleen. They possess a broad rim of cytoplasm, and frequently exhibit karyokinetic figures. 2. Small mononuclear leucocytes or lymphocytes, with a deeply staining nucleus and narrow cytoplasmic rim. 12 * Johns Hop. Hosp. Bull., 1898. 162 THE LYMPHATIC SYSTEM 3. Polynuclear neutrophile leucocytes, similar to those of the blood. 4. EosinopTiile leucocytes, with numerous coarse acidophile granules and a polylobular nucleus. This variety is more fre- quent than in any other lymph oid tissue except the bone marrow. 5. Basophile leucocytes, mononuclear or polynuclear, but with a considerable basophilic rim of cytoplasm. 6. Phagocytes, either mononuclear or polynuclear, with a broad ring of cytoplasm, within which are found coarse pigment granules, fragments of disintegrated red blood cells and even entire blood corpuscles, fat droplets, and in diseased conditions bacteria. 7. Giant cells, megakaryocytes, with a polylobular nucleus and a very broad rim of cytoplasm. Bed blood corpuscles and fat droplets have also been found in these cells. 8. Red Uood corpuscles, erythrocytes, occur in great abundance ; they are derived from the blood. They are found not only within the thin-walled vessels of the pulp but also in the spaces of the reticulum, where, if the slightest congestion of the organ is pres- ent, they are so numerous as to outnumber the other cell types. 9. Nucleated red Uood corpuscles, erythrollasts. The embry- onic spleen contains true " blood islands " in which erythroblasts are actively formed. In the normal spleen of adult man, as well as of other mammals, nucleated red blood cells appear to be quite constantly present, though in relatively small numbers. 10. Blood platelets, thrombocytes and thromboblasts, are of fre- quent occurrence. They are probably derived from the blood. Blood supply. — The further structure of the spleen is closely connected with its blood supply. The arteries enter the hilum of the organ in a group, and fol- lowing the branching trabeculae reach all portions of the organ. The arterial bifurcations are not always coincident with the sub- division of a trabecula, so that the latter, instead of including a blood vessel, form solid columns of fibro-muscular tissue. The wall of the trabecular arteries of the spleen is rich in smooth muscle, the fibres of which are circularly disposed. The adventitia is loose, thin, and firmly adherent to the substance of the trabecula in which the vessel lies : it contains a system of perivascular lymphatics and tissue spaces. The smaller branches of these arteries finally leave the trabec- ulae to pass directly into the spleen pulp. Within this tissue their muscular coat becomes much thinner, and their adventitia is re- FIG. 157.— TYPES OF CELLS FROM A SMEAR PREPARATION OF THE PULP OF THE HUMAN SPLEEN. a, lymphocytes ; 6, polynuclear neutrophile leucocytes whose granules are not stained by the method used ; c, large mononuclear leucocyte ; d, eosinophile cells ; e, basophile cell ; /, red blood cells. Hematein and eosin. x 1200. Fio. 158.— TYPES OF CELLS FROM A SMEAR PREPARATION OF THE MARROW OF A Hl'MAN RIB. J, red blood cells ; #, nucleated red blood cells, erythroblasts ; £, lymphocytes ; J^ large mononuclear cells with m-.utrophile granules ; 5, polynia-lour ncutrophile ; 5, eosinophile cells ; 7, a basophile cell. Eosin and methylen blue. Noch's stain, x 1200. THE SPLEEN 163 placed by an investment of adenoid tissue. In the spleen pulp of some animals the adenoid tissue forms a complete investment of considerable thickness with occasional slender fusiform enlarge- ments. In other mammals and in man this sheath is incomplete, but here and there forms ovoid accumulations of lymphoid tissue,, the Malpighian corpuscles, which inclose the arterial twigs. These FIG. 159. — THREE MALPIGHIAN CORPUSCLES OF THE HUMAN SPLEEN. Each lymphoid nodule contains one or more arterioles ; a branch of one of these is seen in longitudinal section. Hcmatein and eosin. Photo, x 338. lymphatic follicles are eccentrically placed as regards the artery, and are most frequently situated at the bifurcations of the vessel. They differ from the lymphatic follicles of other organs in that they frequently contain no germinal center, and invariably possess one or more small arteries with distinct muscular walls, which are rarely ever situated in the axis of the corpuscle. The Malpighian corpuscle is therefore characteristic of the spleen. 164 THE LYMPHATIC SYSTEM Within the Malpighian corpuscle the artery gives off capillary twigs which pass radially to the adjacent spleen pulp, and there enter the small veins. At the circumference they are in close relation with the splenic ellipsoids, which are formed by minute condensations of the splenic reticulum (Schafer). Within the Malpighian corpuscle also, or in the adjacent splenic pulp, the small artery breaks into a minute brush of terminal ves- FIG. 160. — DIAGRAM OF A LOBULE OF THE SPLEEN. A, artery lying in the center of the lobule ; Am, a terminal ampulla of the artery ; C, intralobular vein ; L, a Malpighian corpuscle ; P, venous plexus within the pulp of the spleen ; Tr, fibro-muscular trabeculae within the lobule ; F, interlobular vein, lying in a large trabecula. (After Mall.) sels, the penicilli of Ruysch. The ultimate destiny of these vessels is still in doubt, some observers claiming that they open free into the reticular meshes of the spleen pulp, others that they form a system of closed capillaries within the pulp, by which the blood is transferred directly to the veins. THE SPLEEN 165 Mall* has shown that each terminal artery enters a lobular compartment which is partially outlined by coarser trabeculae, and within which is a mass of spleen pulp supported by the finer tra- becular processes and the still more delicate reticulum. This schematic structural unit he has termed the lobule of the spleen. The terminal artery enters its axis through that margin which is directed toward the hilum. Within the lobule the artery gives off its terminal twigs, which end in minute dilatations, the ampullce of Thoma. From some of these end twigs, capillary spaces direct the blood current into the broad venous radicals. Elsewhere the blood seems to be poured directly into wide pulp channels, com- parable to the sinuses of the lymphatic glands, by which the blood current under ordinary conditions is directed into the venules, but which under conditions of very slightly increased blood pressure permit the extravasation of considerable quantities of blood into the meshes of the surrounding splenic reticulum. The veins begin as wide sinusoidal channels within the splenic pulp. At first, and for a considerable distance, they follow an independent course through the pulp, receiving at the same time frequent acces- sions of blood from other ve- nous radicals. Finally, how- ever, the veins enter the larger trabeculse, but are still devoid of more complete coats than the thin mem- brane of fibro-elastic tissue which surrounds the endo- thelial tube, but which is now ensheathed by the tra- becular tissue. Henceforth the path of the veins lies within the trabeculae, and is directed toward the hilum. On approaching the hilum the larger veins acquire the usual venous coats. Having arrived at the hilum they form several efferent vessels which, in the outlying connective tissue, form by their union the splenic vein. The spleen is poorly supplied with lymphatics. These vessels FIG. 161. — THE ORIGIN OF A VEIN IN THE SPLENIC PULP. a, venous endothelium ; 6, leucocytes ; c, red blood cells (appearing rather too dark in the reproduction) ; d, a mesh of the splenic pulp. Highly magnified. (After Bannwarth.) * Johns Hop. IIosp. Bull., 1898. 166 THE LYMPHATIC SYSTEM form a plexus within the capsule and larger trabeculae, and a peri- vascular plexus in the walls of the blood vessels. The nerves of the spleen form a plexus of nonmedullated nerve fibres about the larger arteries at the hilum. From this plexus fine branches are distributed to the muscular tissue of the tra- beculae and to the arterial branches down to their finest ramifica- tions. Nerve fibres have not as yet been demonstrated within the splenic pulp. CHAPTEE XI BONE AND BONE MARROW BONE is a firm calcareous tissue which is found only in the skeletal system. In the flat bones it forms a double layer of dense bony tissue between which is a narrow space, bridged across at frequent intervals and thus subdivided into a number of com- partments, the marrow cavities. This central stratum presents a spongy appearance as compared with the denser periphery ; it is therefore said to contain spongy or cancellous tone, while the more superficial lamellae contain compact bone. In the long bones a similar condition exists i-n the epiphyses, which consist of a wall of compact bone within which the marrow cavity is subdivided by bony partitions into numerous compart- ments ; the epiphysis consists, therefore, of spongy bone. The shaft or diaphysis of the bone, however, contains a single large marrow cavity whose walls, except for a thin layer at either end, consist entirely of compact bone. A little spongy structure is present at either end of the shaft, in that portion which adjoins the marrow cavity. The ends and facets of the bones are covered by a disk of hya- line cartilage, which forms the articulating surfaces of those bones which enter into the formation of the movable joints. These articular cartilages are peculiar in that they are not covered by a perichondrium, and their deeper cells, which adjoin the bone, are so arranged that their long axes are perpendicular to the free sur- face, as is the case in the central portion of free cartilaginous plates. Toward the free surface of the cartilage the long axis of the cell lies more nearly parallel to the surface, as is likewise the case at the surface of cartilaginous plates elsewhere. In the long bones of younger individuals a plate of hyaline cartilage is also found at the epiphyseal lines between the epiphyses and the dia- physis. This plate, which extends through the entire axis of the bone, becomes ossified later in life. It represents the line ^*^ 4tb cells have been found within them. The giant cells have therefore been thought to take some part in the formation w » of red blood cells. Whether this hypothesis be true or not, the megakaryocyte variety is characteristic of the blood- forming organs, and is also Fl°- 165.— A GROUP OF CELLS FROM THE RED found in the fetal liver and MABEOW op A """^ K1B' spleen during the period of 7i!±' ""i^' their hematopoietic activity. 4. Nucleated Red Blood Cells (ErytUrollasts of Lowit f).— These cells possess a hemoglobin-containing cytoplasm and a small, sphe. roidal, very deeply staining nucleus. Most of them are of about the size of the red blood corpuscle, normoblasfs ; others, micro- blasts^ are somewhat smaller ; still others, megaloblasts, are larger than the red blood cells. Many of the erythroblasts contain cen- * J. of Morph., 1890. f Arch- f- mik- Anat., 1891. 174 BONE AND BONE MAREOW trosomes and centrosphere, and reproduce themselves by mitosis. Their nucleus finally disappears either by extrusion or by karyo- lysis, and in this way mature red blood cells are formed. Under normal conditions this process is confined to the marrow, but in certain diseases, and also in the healthy infant, a few erythroblasts escape into the blood current prior to the disappearance of their nucleus. 5. Red Blood Corpuscles (Erythrocytes). — These cells differ in no wise from those of the blood, from which many of them, as well as some of the leucocytes, are derived. The walls of the smaller blood vessels of the marrow are pervious to the red as well as to the white blood cells. Many of the erythrocytes, however, are formed within the marrow by the erythroblasts. Blood platelets are also present in the marrow, and occur in such abundance as to suggest that they may arise during the nuclear karyolysis from the achromatic portions of the erythroblastic nucleus as described by Eisen.* 6. Fat Cells.— These cells arise by the fatty infiltration of the connective tissue cells, and their number is subject to great varia- tion. In fetal red marrow they are scanty, but as growth and development proceed the proportion of fat cells progressively in- creases until in the shafts of most of the mature bones the fat greatly predominates over all other tissue elements ; the bone is then said to contain yellow marrow. 7. Osteoblasts. — The marrow of developing bones contains large numbers of small round or ovoid cells which are specially con- cerned with the formation of bony tissue. They contain a single oval or spheroidal nucleus, and are distinguished with difficulty from the mononuclear leucocytes, except when they are charac- teristically arranged in a membranous coat upon the surface of the bony walls of the marrow cavities. These osteoblasts not only occur in fetal bone, but are also found beneath the periosteum, and in relation to the endosteum of the marrow cavity in mature bone. In addition to the above types, Jolly f describes certain very small cells with a polymorphous nucleus and a clear cytoplasm which occur in the red marrow, and are possibly identical with the leucoUasts of Lowit. J These cells are thought to be early types of leucocytes. * Proc. Cal. Acad. Sc., 1897; and Jour. Morph., 1899. f Loc. cit. \ Loc. cit. DEVELOPMENT OF BONE 175 Blood Supply. — Marrow, and especially the red variety, is richly supplied with blood. The nutrient arteries penetrate to the mar- row cavity of the bone and supply an abundance of small arteries to all portions of the medulla. The arteries terminate in broad capillary vessels whose wide lumen and delicate endothelial walls determine their character as sinusoids. It was formerly thought that the endothelial walls of these vessels were here and there defi- cient, and, although recent investigations discredit the former observations, the all-important fact remains, that the endothelial walls are pervious to both red and white blood cells, neither is this the only location where the red as well as the white cells may, under certain conditions at least, penetrate the endothelial walls of the blood capillaries. Efferent veins return the blood from the sinusoidal capillaries of the marrow. These veins, as also those of the bony tissue, are not supplied with valves. The lymphatics of bone occur in great abundance in the peri- osteum, and as perivascular spaces penetrate the canals of Havers and Volkman and thus reach the medullary cavity. The exist- ence of lymphatics within the marrow, other than in the sheaths of the blood vessels, is doubtful. The nerves accompany the blood vessels in all portions of the * bone and marrow, and form a rich perivascular plexus which is distributed to the walls of the vessels ; occasional side fibrils are also distributed to the marrow. Nerve endings have not been demonstrated in compact bone. In the periosteum terminal nerve fibrils are supplied to the musculature of the blood vessels, and other sensory fibrils end in Paccinian corpuscles. DEVELOPMENT OF BONE.— Bone makes its appearance very early in fetal life. The long bones are mapped out by masses of fetal hyaline cartilage as early as the embryo begins to acquire its typical form. The entire skeleton, with the exception of the flat bones of the trunk and those of the vault of the skull and face, are thus primarily formed by plates of fetal cartilage. The pro- cess by which these cartilaginous plates are formed into bone is known as intracartilaginous ossification. The flat bones, together with most of those of the face, are formed directly from the mesoblastic connective tissue without the intervention of cartilage. This method of bone formation (litters somewhat from the above and is known as intramemlranous ossification. 176 BONE AND BONE MAKKOW INTRACARTILAGINOUS OSSIFICATION.— This process be- gins with the formation of plates of hyaline cartilage whose shape corresponds more or less closely with that of the future bone. This type of fetal cartilage differs from the hyaline cartilage of the adult only in the irregular form and distribution of its carti- lage cells. Each plate of fetal cartilage is enveloped by a layer of pre- fibrous tissue, the fetal perichondrium. The outer portion of the fibrocellular layer is destined to become the periosteum of the future bone ; its innermost portion contains many small round cells, which, from their intimate relation to bone production, are known as osteoblasts. The inner portion of the perichondrium forms the osteogenic layer of the future periosteum. C FIG. 166. — THE PRIMARY CHANGES IN INTRACARTILAGINOUS BONE FORMATION. A, metatarsus ; B and C, phalanges, of human embryo. In A, the earliest enlarge- ment of cartilage cells at the center of ossification is shown. B and C are successively later stages. The bones are cut in longitudinal section. Carmin hematoxylin stain. x 27. (After Toldt.) Ossification of the cartilage begins at one or more points which are called centers of ossification. In the long bones, in which the process of bone formation can be most readily traced, there are usually three such centers, one near the middle of the cartilagi- nous plate, from which the diaphysis is formed, and one epiphysial center at each extremity. The centers for the epiphyses make their appearance much later than that for the shaft of the bone. INTRACARTILAGIXOUS OSSIFICATION 177 The first indication of beginning bone formation is evidenced by an enlargement of the cartilage cells which promptly arrange themselves in rows or columns that radiate from the center of ossification. This process is accompanied by absorption of the adjacent cartilage matrix, so that the enlarged cartilage cells are contained within broad spaces or lacunce. The cartilage cells now appear to undergo a gradual but progressive absorption; their cytoplasm becomes shrunken and granular and finally disappears, even the nucleus at last succumbs to the process. The absorption of the cartilaginous matrix proceeds more rap- idly in those portions which separate the individual cells in the columns than in those other portions which intervene between the adjacent rows of cartilage cells. While the former portions are entirely absorbed, remnants of the latter remain, and in them cal- cium salts are deposited in an irregular manner. Calcified carti- lage, the most primitive of the calcareous tissues, is thus formed. The absorption of the cartilage matrix results in the formation of broad spaces into which osteogenic buds of primitive marrow tissue push their way from the perichondrium. Thus the primor- dial marrow cavities are formed. The fetal marrow which now occupies these cavities is derived from the osteogenic layer of the primitive periosteum. The osteogenous tissue of this layer, con- taining osteoblasts, osteoclasts, and developing blood vessels, grows into the cartilage in the form of bud-like cords which are preceded by absorption of the adjacent cartilage matrix. This so-called " eruptive tissue " promptly reaches the center of ossification and burrows its way into the enlarged cartilage lacunas whose cells are now replaced by primary osteogenic marrow. The osteoblasts, which thus gain access to the primary marrow cavities, now arrange themselves along the surface of the remnants of calcified cartilage and begin the deposit of the fibrous tissue and calcareous salts which compose the primary bone. Many of the osteoblasts apparently become entangled in this newly formed and form the bone corpuscles. The fetal cartilage is thus transformed into a spongy mass of primary osseous tissue whose spicules are formed by a core of calcified cartilage upon which are deposited successive layers of bony tissue with their included lacuna' and bone corpuscles. Axial sections of long bones at this stage of ossification show all the above changes in regular succession from the fetal hyaline cartilage at the extremities to the primary bone with its marrow 13 FIG. 167. — DEVELOPING BONE IN A PHALANX OF A FIVE MONTHS HUMAN FETUS. a, Fetal cartilage ; 6, enlarged cartilage cells ; c, primary bone ; d, periosteum ; e, peri- osteal bone ; /, a thin-walled blood vessel within the marrow cavity ; g, the line points to an osteoclast. Hematein and Congo red. Photo, x 69. 178 INTRACARTILAGINOUS OSSIFICATION 179 cavities in the center. The process of ossification steadily pro- gresses at the periphery, the line of enlarged cartilage cells con- stantly advancing farther and farther from the original center of ossification. It is at this stage, however, that the giant cell osteoclasts be- come most active and the absorption of the newly formed bone pro- gresses rapidly. The osteoclasts collect along the surface of the spicules of primary bone in considerable numbers and appear to sink into little recesses which they form within the bony tissue. The little bays which are thus formed in the primary bone are the lacunae of Howslip. The continued absorption soon breaks down and removes the trabeculae and partitions of spongy bone and forms a central medullary cavity of constantly increasing size. Coincident with these changes within the cartilage the osteo- genic tissue which forms the inner layer of the periosteum produces successive layers of bony tissue upon the surface of the fetal carti- lage. This process of periosteal ossification proceeds in a manner similar to that by which enchondral bone is formed. Osteoblasts arrange themselves upon the surface of the cartilage and deposit successive layers of bony tissue, between which many of these cells are included as bone corpuscles. At irregular intervals the osteo- clasts collect and the primary periosteal bone is absorbed. Into these cavities buds of vascular osteogenic tissue push their way to form canals of considerable length. Upon the surface of the canals which are thus hollowed out of the periosteal bone, the osteoblasts deposit successive concentric layers of bony tissue and the Haversian systems make their appearance. Finally, upon the surface of the periosteal bone successive layers of newly formed bony tissue compose the outer circumferential lamella, while upon the wall of the- medullary cavity a similar endosteal layer of bone- forming cells deposits the inner circumferential lamella. With the formation of the periosteal bone the lateral expansion of the organ by enchondral bone formation necessarily ceases. Henceforth increase in diameter of the bone is only produced by continued absorption of the compact bony wall and the formation of new bone beneath the periosteum by frequent repetitions of the processes of periosteal ossification as already described. The rem- nants of those Haversian and circumferential lamellae which are only partially absorbed in this process form the interstitial lamellcB of the mature bone. During the processes of enchondral and periosteal ossification 180 BOXE AND BONE MARBOW within the shaft of the bone, the epiphysial cartilages continue to grow. Finally, however, ossification begins in the epiphysis, and, FIG. 168. — TRAN SECTION OF A RIB OF AN INFANT. Developing bone. Hematein and eosin. Photo, x 67. proceeding in the same manner as in the shaft, results in the for- mation of primary spongy bone, some of which is absorbed and INTKAMEMBRANOUS OSSIFICATION 181 replaced by more compact bony tissue, as occurs in the wall of the epiphysis. In its central portions the tissue retains its spongy arrangement and but few Haversian systems are formed. It is thus that the cancellous bone of this part, as also of the ends of the diaphysis, is formed. At the point where the expanding centers of ossification of the shaft and epiphysis are about to meet, a line of unossified carti- lage, the epipJiysial line, persists until growth of the bone is com- plete. It is by growth of this cartilaginous disk, with continued formation of cartilage on its surface, that the bone increases its length. The following is a resume of the various stages of enchondral ossification : 1. Formation of the fetal cartilages. 2. Enlargement of the cartilage cells with a rearrangement into radiating cell rows at the center of ossification. 3. Absorption of the cartilage matrix and finally also of the cartilage cells. Appearance of calcified remnants of the cartilage matrix. 4. Eruption of the subperiosteal osteogenetic tissue and the formation of primary marrow cavities at the center of ossification. 5. Gradual extension of the above processes followed by a de- posit of primary bone by the osteoblasts upon the calcified carti- lage. Coincident osteoblastic deposit of periosteal bone beneath the perichondrium of the cartilage plate. 6. Absorption of portions of the primary bone by the osteo- clasts to form the large central marrow cavity or medulla. The absorption involves both the enchondral and the periosteal bone and is accompanied by a further deposit of new bone at the periph- ery. In the periosteal bone cylindrical axial channels are formed, in which the deposit of new bone produces the Haversian systems of the compact bony tissue. INTRAMEMBRANOUS OSSIFICATION.— In this type of bone formation, ossification occurs directly within the preconnective tissue of the mesoblast without the preliminary formation of car- t ilaire. The earliest evidence of ossification consists in an enlarge- ment of the mesenchymal cells which arrange themselves in the form of a membrane at the site of the future bone. Certain of these cells produce the periosteum ; others increase greatly in size, acquire a considerable cytoplasmic body, and assume the functions of the osteoblasts. The osteoblasts which are thus formed, not 182 BONE AND BONE MABROW only line the primitive periosteum but also form budding processes which project into the adjacent connective tissue. Bone tissue is now formed by the osteoUasts. The deposit of the fibrous stroma precedes calcification and in this way brushes of radiating fibres frequently project from the osteogenic buds c FIG. 169. — INTRAMEMBRANOUS BONE FORMATION IN THE LOWER JAW OF AN EMBRYO SHEEP. a, bone ; &, primary marrow cavity ; c, osteoblasts ; eZ, growing point of the primitive bone, beyond which primary marrow is developing in the connective tissue of the meso- blast. x 300. (After Bohm and von Davidoff.) beyond the limit of the calcareous deposit. The bony processes thus formed are covered by a layer of osteoblasts which continue to deposit bony lamellae, with their bone corpuscles and lacunae, in the same manner as in enchondral bone formation : a mass of spongy bone results. The ma/rroiv spaces of the cancellous bone are occupied by embryonic connective tissue in which are many small and thin- walled blood vessels. This primitive marrow differs from that of INTRAMEMBRAXOUS OSSIFICATION 183 the enchondral bone in the scarcity of its cellular elements ; other- wise the process of intramembranous bone formation is identical with that which forms the periosteal layers of the enchondral bone. The after absorption of the bony spicules and partitions in intramembranous bone is very active, the osteoclasts appearing in considerable numbers. The contour of these bones is subject to frequent changes as a result of the continued absorption and new formation of bony tissue. The cancellous bone which is developed during these processes forms the mid-portion of the bone or diploe, the outer walls of the flat bone being formed by periosteal ossifi- cation as in the enchondral bones. .ft CHAPTEE XII MUCOUS MEMBRANES— SECRETING GLANDS THE histologic structures which are necessary for the forma- tion of a secretion include an epithelial surface, and a tunica pro- pria of connective tissue which supports the requisite blood and lymphatic vessels and the controlling nerve supply. These struc- tures may either form smooth membranous surfaces or apparent epithelial invaginations. The former are found on the surface of the mucous membranes, the latter are the secreting glands. MUCOUS MEMBRANES,— The mucous membranes may be said to include all those secreting surfaces which are directly or indi- rectly connected with the surface of the body, hence their epithe- lial clothing is continuous with that of the skin. The mucous membranes form the lining coat of the respiratory and alimentary systems, together with the ducts of their secreting glands : in the nose this membrane is continuous through the tear ducts with the conjunctiva of the eye and through the Eustachian tubes with the lining membrane of the middle ear. The broad expanse thus formed is known as the gastro-pneumonic mucous membrane. A second membranous sheet, the genito-urinary mucous membrane, clothes the organs of the genital and urinary systems : it thus forms the lining membrane of the vagina, uterus, and Fallopian tubes, of the urethra, bladder, and pelvis of the kidney, of the ducts and tubules of the prostate gland, the testis, and the smaller secreting glands which are connected with the genital system. A mucous membrane consists of a superficial layer of epithe- lium of varying type, which rests upon a basement membrane (membrana propria) and is in turn supported by an investment of connective tissue, the tunica propria, or corium. The tunica pro- pria is richly supplied with small blood vessels and lymphatics ; its nerve fibrils are not only distributed to the walls of the blood vessels but in many cases send terminal filaments which enter the epithelial layer and terminate in contact with the secreting cells. The mucous membranes are mostly contained within hollow organs 184 SECRETING GLANDS 185 which are subject to alternate collapse and distention ; hence the membranes are frequently much folded. The deeper portion of the mucous membrane usually contains a more or less well- defined layer of smooth muscle fibres, the muscularis mucosce. The mucous membranes, as their name indicates, are nearly all moistened by a mucus containing secretion. The relative amount of mucus which its secretion contains, and consequently the viscidity of the secretion, bears a close physiologic relation to the in- tensity of the mechanical irri- tation to which the membrane is subjected. Thus the mucus secreting goblet cells of the gastro-pneumonic membrane are here and there reinforced by numerous mucus secreting glands of considerable size ; these are especially abundant in the oral cavity, pharynx, and esophagus, and in the nose, trachea, and bronchi ; in the urinary system even the goblet cells are absent. The basement membranes, upon which the epithelium of the mucous membranes and the secreting glands is supported, are con- nective tissue structures. They are sometimes formed by inter- lacing bundles of delicate white fibres intermingled with numerous elastic fibres. Frequently, however, they consist of reticular tissue. Basement membranes of this nature have been demonstrated by Mall and his pupils in the mucous membranes and glandular tubules of the stomach, intestine, liver, salivary glands, kidney, testis, and thyroid. Occasionally basement membranes are homogeneous or hyaline in structure and present a more or less clear or glassy appearance. SECRETING GLANDS.— The secreting glands may be quite properly considered as invaginations of the epithelial surfaces of the mucous membranes. They appear as such in the embryo. Their earliest anlage is formed by a solid or funnel-shaped process a y FIG. 170. — DIAGRAM OF A MUCOUS MEMBRANE HAVING SIMPLE TUBULAR GLANDS. a, artery ; 6-6, basement membrane ; C, connective tissue ; d, duct of the gland, lined by cuboidal cells ; J£, epithelium of the free surface, clear, columnar cells ; (?, lumen of the fundus of the gland, lined by granular, serous secreting, columnar cells surrounded by se- cretory capillaries; V, veins. The arteries are striped, the capillaries and veins, black. Nerves are not represented. 186 MUCOUS MEMBKANES of epithelium, in which a distinct lumen soon appears, and which grows into the surrounding mesoblast, carrying with it its embry- onal tunica propria. The form of the glandular invaginations is subject to great variation. They may be straight and simple, more or less branched and compound, convoluted or coiled, or the tubules may terminate in minute ampullary enlargements, the acini. The invaginations may also be distinctly tubular and of approximately equal diameter throughout, or they may form pouch-like saccules. According to the form of the organ, it is thus possible to distinguish the following HISTOLOGIC TYPES OF SECRETING GLANDS: 1. Simple. 2. Convoluted. I. Tubular , free extremity; c, eponychium; d, hyponychium; e, nail; /, stratum mucosum of the nail ; g, nail bed ; A, bone. Hematein and eosin. Photo, x 23. THE NAILS. — The nails are produced by a peculiar modifica- tion of the epidermis by which the stratum lucidum becomes greatly thickened while the horny layer is at the same time want- ing. The nail is divisible into the nail ~body and nail root ; the THE KAILS former comprising the exposed, the latter the hidden portion of the organ. The root of the nail is overhung by a fold of the skin, the thickened horny layer at the margin of which forms an adher- ent border, the eponychium. The nail groove or sulcus is included between the overhanging skin and the root of the nail. It is deep at its proximal end but is shallow at the lateral margins of the nail. The distal or free border of the nail projects over the skin at the tip of the finger and the thickening of the horny layer of the subjacent epidermis forms the so-called hy pony Mum. Finer Structure. — The nail consists of two layers, the superficial stratum lucidum and the deeper Malpighian layer. These are continuous at the border of the nail with the corre- sponding layers of the epi- dermis which lines the nail groove. At the distal bor- der, however, the nail prop- er or thickened stratum lucidum ends in a free mar- gin. The finer structure of these two layers does not essentially differ from that of the corresponding layers of the epidermis. The stratum lucidum in the body of the nail is very thick and its cells are so completely blended with each other through the ex- cessive eleidin production that it is impossible to dis- tinguish their outlines. By maceration in alkaline solu- tions, however, the outlines of both cells and nuclei may be caused to reappear. In the nail root the stratum lucidum increases rapidly in thick- ness as it grows distal ward ; in the body of the nail this layer is not very materially thickened as it approaches the distal or free margin. 15 FIG. 184. — TRANSECTION THROUGH THE MARGIN OF A FINGER NAIL. On the left is the skin, on the right the nail, a, a', horny layer ; ft, ft', germinal layer ; c, c', corium ; d, margin of the nail. Moderately magnified. (After von Brunn.) 210 THE SKIN The stratum mucosum is of nearly equal thickness in all por- tions of the nail body. In the nail root it is somewhat thicker and forms the nail matrix of Ranvier. In this portion also is a dis- tinct stratum granulosum, a layer which is absent or rudimentary beneath the body of the nail. It is the presence within this layer of numerous keratohyalin granules which renders the root of the nail opaque and thus forms the dull white lunula which contrasts with the transparent, eleidin containing, stratum lucidum, which latter layer alone, covers the Malpighian layer of the nail body (Unna). The Nail Bed. — The nail rests upon a very vascular corium or nail bed (matrix of authors) which is continuous with the corium or derma of the skin. The nail bed at the margins of the nail is provided with papillae as in other portions of the skin, but beneath the body of the nail its surface is raised into longitudinal ridges which possess only very minute secondary papillae. Nail Growth. — The growth of the nail occurs almost entirely in the matrix of the nail root. The cells of the stratum ger- minativum of this portion, having been once formed by active mitosis push obliquely forward and outward toward the nail body. It is thus that the more advanced are constantly carried onward toward the free border. The growth of the nail occurs at the rate of about one thirty-second of an inch per week (Schafer). Development. — In the fetus the nail appears as a direct forma- tion of the epidermis, which is very early evidenced by a thicken- ing of the stratum lucidum in the nail area. The nail is therefore at first covered by the superficial epitrichial cells of the cuticle. The nail groove is rapidly formed by an invasion of the mesoblast by the epidermal cells which become piled up at the margin of the groove to form an excessive horny layer or eponychium. At the distal extremity of the nail the superficial cells are also accumu- lated into a considerable mass which forms a prominent hypony- chium. Further growth of the nail pushes its distal margin for- ward over the eponychium so that the border becomes free shortly prior to birth. The epitrichial cells are then shed and the nail body finally presents, at about the time of birth, its naked stratum lucidum. THE HAIR, — The structure of the hair will be most readily appreciated if preceded by a brief introductory sketch of its development. DEVELOPMENT OF THE HAIE 211 The Hair Germ. — The hairs arise at any time after the third month of fetal life, their earliest anlage appearing as a slightly increased proliferation of the cells of the germinal layer of the epidermis. The further multiplication of the cylindrical cells produces a solid columnar ingrowth of the epidermis which pene- trates into, and sometimes through, the primitive derma. The spheroidal cells of the intermediate layer of the epidermis increase in size, assume a vesicular character, and finally by fatty degenera- tion form the epidermal hair canal through which the future hair reaches the surface. The Hair Column. — The columnar epidermal ingrowths, hair columns or hair pegs, come into early relation with the anlage of the hair papilla which is formed by a proliferation of the mesen- chymal cells at the tip of the hair column. Further development of the papilla produces an indentation of the advancing hair column and gives rise to a true dermal papilla of considerable size. The Hair Bulb. — Coincident with the formation of the papilla there is an increased proliferation of the cells of the hair column by which it is surrounded, and which therefore represents the future hair bulb. Two other swellings appear in the hair column ; one, the more superficial, forming the anlage of the sebaceous gland, and the other, the deeper, forming the so-called matrix of the hair which stands in close relation with the future regenera- tion of the hair. The development of the hair papilla produces a slight evagi- nation of the epithelium of the hair bulb, which is just sufficient to redirect the growth of central cells of the hair column toward the cutaneous surface. It is thus that the younger cells which arise by mitosis in the germinal layers of the hair bulb are pushed outward along the axis of the hair column where they form the shaft of the future hair. The growth of the hair from the germi- nal cells of the hair bulb is accompanied by beginning cornification of the newly formed cells of the primitive hair shaft and of the intermediate cells of the hair column. The growth of the shaft is, however, preceded by enlargement, vesiculation, and fatty de- generation of the central cells of the hair column, thus producing a central canal through which the hair may grow, and which later becomes continuous with the hair canal of the epidermis. The Hair Follicle. — At this stage the hair column has been differentiated into a peripheral follicle, the primitive root sheath, Ill IV rfudi \ * \fr*v ^ ***s&s ^«£**'*^ *^- e i FIG. 185. — FIVE STAGES IN THE DEVELOPMENT OF A HUMAN HAIR. a, papilla ; J, arrector pili ; c, the line is directed toward the primordial shaft ; rf, cells which form the hair canal ; e, sebaceous gland ; /, hair germ ; , sebaceous gland; c, hair follicles in oblique section; d, horny layer of the epidermis; e, Malpighian layer; /, derma; g, blood vessel. Hematein and eosin. Photo, x 83. saccules are connected with the long excretory duct by means of a short intercalary duct. The fatty secretion of the sebaceous glands, sebum, is formed by the direct disintegration of the proto- plasm of the glandular epithelium. The saccules of the sebaceous glands are invested by a thin connective tissue tunic and a delicate basement membrane. They BLOOD SUPPLY 223 are embedded in the subcutaneous fat or in the deeper part of the corium near the hair follicle. The glands are so disposed as to be included within a triangular space beneath the corium,, which is bounded by the arrector pili muscle and the hair follicle. The saccules are lined by several layers of polygonal epithelial cells the outermost of which are cylindrical and rest upon the basement membrane. In the peripheral layers the lining epithelial cells multiply so actively that the daughter cells are pushed inward until they fill the entire saccule. During this excursion they are progressively farther and farther removed from their source of nutrition, and as they approach the outlet or duct of the saccule a process of fatty degeneration appears within the cell, by which its protoplasm becomes changed into a granulo-fatty mass. The accumulated product of this degeneration and final disintegration of the epi- thelial cells forms the secretion of the gland. Continued cell multiplication at the periphery maintains the integrity of the organ. Development. — The sebaceous glands are developed as minute epithelial buds from the sides of the hair columns or from the deeper surface of the epidermis. These buds soon assume the characteristic flask-like shape and later become hollowed out by fatty degeneration of their central cells. By this process also their lumen is eventually made continuous with that of the follicle. Secondary saccules of the sebaceous glands are developed in a similar manner by outgrowing germs which appear near the con- stricted neck portion of the primary saccule. BLOOD SUPPLY OF THE SKIN The larger arteries supplying the skin lie in the subcutaneous tissue. From these vessels branches pass toward the surface, giving off lateral twigs to the rich capillary plexuses in the sub- cutaneous connective and adipose tissues and about the sweat glands, hair follicles, and sebaceous glands. These arteries con- tinue their course to the deeper part of the corium, where they form an anastomosing plexus of small vessels. Branches from this plexus pass to the papillary layer, where they form a second plexus from which terminal arteries are distributed to the capil- laries of the papillae. The distribution of the veins is similar to that of the arteries. The primary plexus is found in the papillary layer ; occasionally 224 THE SKIN a second plexus immediately underlies the first, and from these, venules pass to the deeper part of the corium, whence after free anastomosis they proceed to the subcutaneous tissue, collecting on the way the venules returning from the hair follicles and FIG. 192. — KECONSTRUCTION OF THE CUTANEOUS BLOOD VESSELS. a, epidermis ; J, derma ; c, subcutaneous tissue ; d, deep, and e, superficial arterial plexus;/-*, successive venous plexuses, x 9i. (After Spalteholz.) secreting glands, and from the subcutaneous connective tissue. The very rich capillary network in the papilla of the hair bulb is worthy of special mention. The lymphatic vessels of the skin begin as a terminal lymphatic plexus in the corium, which collects the lymph from the tissue spaces of both derma and epidermis. The vessels of this plexus communicate with a subcutaneous lymphatic plexus of larger ves- sels which follow the course of the blood vessels on their way to reach the neighboring groups of superficial lymphatic glands. NERVE SUPPLY.— The skin is abundantly supplied with large nerve trunks which find their way along the subcutaneous fat and send branches directly to the larger blood vessels, the hair follicles, the sebaceous and sudoriparous glands, to the corpuscles Pacini, Ruffini, and Golgi-Mazzoni, and to the end bulbs of Krause, which lie in the connective tissue. In the cutis vera the nerve trunks form a plexus of delicate fibre bundles in the reticular layer, with a secondary, more closely NERVE SUPPLY 325 meshed plexus of finer nerve bundles in the papillary layer. From these plexuses fibrils are distributed to the smaller blood vessels and to the papillae, where many of them end in tactile corpuscles. Still other fibrils penetrate the epidermis, and, becoming more- or less varicose, terminate as naked fibrils between the cells of the stratum germinativum, many of them being distributed to the tactile cells of Meissner. In the region of the hair follicle small branches form a net- work of fibrils in the dermal root sheath, which surrounds the follicle as far outward as the opening of the sebaceous glands. Branches (pilomotor nerves) are also distributed to the arrector pili muscles. In the sudoriparous glands the nerves form a fine plexus about the membrana propria (epilamellar plexus), from which naked axis cylinders penetrate the basement membrane and terminate between the secreting cells. CHAPTER XIV THE RESPIRATORY SYSTEM THE respiratory system may be said to comprise a true respi- ratory organ, the pulmonary alveoli, in which the interchange of gases between the air and the blood occurs, and a system of duct- like passages leading thereto, which, beginning with the nasal cavityr successively includes the naso-pharynx, larynx, trachea, and bronchi of gradually diminishing caliber, and which finally ends in the terminal bronchioles leading to the pulmonary alveoli or air saccules. The arrangement of these several portions of the respiratory system has been frequently compared to the structure of the tubulo-acinar secreting glands. From this point of view the larynx and trachea form the duct stem of the gland, the bronchi form the branching interlobular ducts, and the terminal bronchi- oles end in the numerous acinar air saccules of the lung. THE NASAL CAVITY. — This cavity is bounded by a cartila- ginous and bony wall and is lined by a mucous membrane which, according to the nature of its epithelium, may be divided into three portions : (1) the vestibule, (2) the respiratory portion, and (3) the olfactory portion. The VESTIBULE of the nose corresponds very closely to the cartilaginous portion of the nasal wall. Its mucous membrane is continuous anteriorly with the skin and posteriorly with the mucous membrane of the respiratory portion. The vestibule is lined by stratified squamous epithelium, which offers a gradual transition from the moist respiratory epithelium to the dense horny epidermis of the skin. Near its external orifice are numer- ous coarse stiff hairs, vibrissae, connected with which are many sebaceous glands. Some of these glands also open directly upon the surface of the mucous membrane. The fibrous tunica propria of the vestibule is continuous with the corium of the skin, and in it are embedded the deeper portions 226 THE NASAL CAVITY 22? of the vibrissae and the secreting portions of the sebaceous glands. By its deeper surface the tunica propria is closely attached to the perichondrium of those plates of hyaline cartilage which form the septum and alas of the nose. The RESPIRATORY PORTION of the nasal mucous membrane (Schneiderian membrane) clothes the middle and inferior meatus of the nose. It is continuous anteriorly with the mucous membrane of the vestibule, above with the olfactory mucous membrane, and posteriorly with that of the naso-pharynx. The respiratory region is lined by columnar ciliated epithelium of the pseudo-stratified type, which also contains many mucus secreting, goblet cells. FIG. 193. — FROM A SECTION OF THE MUCOUS MEMBRANE OF THE RESPIRATORY REGION OF THE HUMAN NOSE. o-«, ciliated epithelium ; ft, ft, secreting glands ; c, blood vessel. Henmtein and Congo red. Photo, x 185. The epithelium rests upon a distinct basement membrane which reacts to the specific stains for elastic tissue. The tunica propria consists of a very vascular connective tissue ; it varies much in thickness in different portions. It is thinnest in the 228 THE RESPIRATORY SYSTEM accessory sinuses and is thickest where it covers the turbinal bones and the adjacent portions of the nasal septum. The tunica pro- pria is richly supplied with both mucous and serous glands. The smaller ones, in the thinner portions of the mucous membrane, are somewhat convoluted ; the larger and more numerous are tubulo- acinar glands. Many of the latter are mixed glands containing both mucous and serous acini. They produce an abundant secre- tion. The Schneiderian membrane is in all portions extremely vas- cular, many of its vessels having very thin walls. The thicker portions over the turbinals and the septum are typically erectile. The dense connective tissue of these portions is permeated with broad venous channels which are surrounded by bands of smooth muscle. Other muscular bundles are longitudinally distributed. The small arteries are contained within the fibro-muscular stroma. The subepithelial portion of the tunica intima contains fine interlacing bundles of connective tissue and many capillary blood vessels. Here and there it is also infiltrated with leucocytes and occasional very minute lymphoid nodules are found. The lym- phatics of the Schneiderian membrane lead posteriorly to the lymphatic nodules of the naso-pharynx. The OLFACTORY PORTION of the nasal mucous membrane, THE OLFACTORY ORGAN, lines the superior meat us, and its irregular border here and there invades the upper portion of the middle meatus. It consists of a fibrous tunica propria and a cloth- ing of neuro-epithelium. The tunica propria contains elastic as well as white connective tissue fibres, and many small tubulo- acinar secreting glands, the olfactory glands of Bowman. Beneath the epithelium is an indistinct basement membrane. The neuro-epithelium contains three intermingled cell types, the sustentacular, olfactory, and basal cells. The Sustentacular Cells are columnar ciliated epithelial cells which possess a distinct cuticular margin. Their nuclei are ovoid, and, since they lie at the same level, they form a continuous su- perficial zone of oval nuclei. The deep ends of the cells are often branched ; they interlace with one another and with the processes of the olfactory and basal cells. The cytoplasm of the susten- tacular cells is finely granular and contains a yellow pigment. The Olfactory Cells occupy a unique position among neuro- epithelial cells in that they are true nerve or ganglion cells. They THE OLFACTORY O&GAN 229 possess a small cytoplasmic body and two processes, a distal and a central. Their nuclei are spherical and are disposed in several rows beneath the nuclear zone of the sustentacular cells; thus they form a broad zone of spherical nuclei. The distal process of FIG. 194. — THE OLFACTORY MUCOSA OF A CAT. a, epithelium ; &, basement membrane ; c, corium ; d. cuticle ; e, sustentacular cell layer; /, olfactory cell layer; , dentine ; P, pulp cavity ; &, enamel, x 8. (After Sobotta.) THE TEETH 255 9 the odontoblasts interlace with each other and firmly unite the cells into a membranous layer. Other processes are given off from the base of these cells and intermingle with the fibres of the pulp, so that if this tissue is forcibly separated from the dentine the odontoblasts remain adherent to the connective tissue of the pulp. The nuclei of the odontoblasts are found near their inner or basal ex- tremity. Their cytoplasm is of con- siderable extent as compared with that of the other connective tissue cells of the pulp. The dental pulp is richly sup- plied with blood vessels, derived from a nutrient artery which enters through the root canal, its branches forming a network of minute arterioles and capillary ves- sels in the center of the pulp cavity, and a peripheral f close-meshed capil- lary network which is in close rela- tion with the layer of odontoblasts. There are no lym- phatic vessels in the tissue of the dental pulp. A rich nerve supply is derived from fine branches which also enter by the root canal. Most of the nerve fibres lose their myelin sheaths soon after they enter the pulp. They form a primary plexus in the connective tissue from which FIG. 214. — FROM A LONGITUDINAL SECTION OF THE NECK OF A CHILD'S TOOTH AND THE ADJACENT ALVEOLUS. a, enamel ; J, cementum ; c, dentine ; d, bone ; «, peri- osteum ; /*, corium ; g, lymphoid tissue ; A, stratified epithe- lium of the gum ; i, circular dental ligament ; £, epithelial remnants ; Z, blood vessels, x 25. (After Kolliker.) 256 THE DIGESTIVE SYSTEM fine fibres pass to the periphery and form a network of terminal fibrils which end among the odontoblasts. Boll,* though suggest- ing that the terminal nerve fibrils enter the dentinal canals, was yet unable to demonstrate the theory. More recent observers (Eet- zius,f et als.) have likewise been unable to recognize any nerve fibrils beyond the layer of odontoblasts. Boll's theory of nerve fibrils within the dentinal canals, therefore, still lacks satisfactory confirmation. Dentine. — The dentine surrounds the entire pulp cavity except at the opening of the root canal. It is a fine calcareous substance which resembles bone in that it consists of a fibrous matrix and is infiltrated with lime salts. The matrix is a fine fibrous network of dense connective tissue, the majority of whose fibres are dis- posed in a longitudinal direction. The meshes of the matrix are almost completely filled by a deposit of calcareous salts which gives the dentine its bony consistence. Here and there, especially toward its peripheral border and near the apex of the tooth, the dentinal matrix fails to become calcified. Such uncalcified areas, interglobular spaces, are en- croached upon by the rounded or globular margins of the adjacent calcified matrix which forms the so-called dental globules. The dentine is everywhere permeated by a system of canaliculi, the dentinal tubules or canals, which extend in a radial manner from the pulp cavity outward to the cementum and enamel. b c FIG. 215. — FROM A SECTION OF A HUMAN TOOTH WHICH HAD BEEN GROUND TO EXTREME THINNESS. a, dentine ; b, granular layer of Thomes ; c, enamel. Photo, x 150. Their course is characteristically curved, resembling the letter /. The cavity of the dentinal tubules is partially occupied by the dentinal processes of the odontoblasts, an arrangement which may * Arch. f. mik. Anat., 1868. f Biol. Untersuch., 1894, N. F., vol. vi. THE TEETH 257 be compared to the bone corpuscles and canaliculi of bone. At their inner extremity the dentinal tubules are 2 to 4 /A in diameter, but they taper very gradually, especially in the outer portion of their course, where they finally reach a diameter of no more than 0.5 to 1 ^ Throughout their course the dentinal tubules give off very fine lateral twigs, which at first leave the parent tubule nearly at right angles, but later are slightly inclined outward. At their distal end most of the dentinal tubules divide into a group of terminal branches, some of the arborizations being very extensive, others consisting of but two or three subdivisions. The coarser branches are frequently looped, the distal end of the loop often anasto- mosing with adjacent tubules. In their course through the den- tine those canaliculi which enter the interglobular spaces are con- tinued through these spaces without interruption. The walls of the dentinal tubules are formed by extremely dense calcareous dentinal sheaths which are very resistant to the action of acids. The curvatures in the course of the dentinal tubules, occurring with extreme regularity, give rise to certain parallel lines in the substance of the dentine which follow the contour of the dentinal surface. These are known as the incre- mental lines of Schreger. The superficial portion of the dentine is formed by the granu- lar layer of Thomes, in which there are no dentinal tubules, but instead there are in this layer numerous small interglobular spaces from which minute canaliculi radiate in various directions. Many of these canaliculi are connected, on the one hand with the denti- nal tubules, and on the other with the canaliculi and bony lacunas of the cementum. The canaliculi of the granular layer are readily distinguished from the adjacent dentinal tubules by the extreme irregularity of their course, which contrasts sharply with the straight or regularly curved course of the dentinal tubules. The granular layer is relatively thick in the root of the tooth, but becomes much thinner toward the neck. Beneath the enamel it becomes so thin that toward the apex of the tooth it is scarcely demonstrable. At this point, also, occasional dentinal tubules are continued for a short distance into the enamel, though this con- dition is more characteristically developed in some of the lower mammals (e. g., Rodentia) than in man. Enamel. — The enamel, which covers the exposed crown of the tooth, is the hardest tissue of the body. It consists of many cal- ls 258 THE DIGESTIVE SYSTEM careous cylinders, the enamel prisms. These radiate outward from the dentine and are disposed after the manner of a mosaic. They are firmly united to each other by a very thin layer of calcified cement substance. Strangely enough the enamel prisms are developed from epithelial cells, by which they are apparently deposited as a calca- reous cuticular formation, the calcification pro- ceeding from within outward. The uncalcified cytoplasm of the outer portion of these, cells FIG. 2i 6.— ENAMEL becomes highly cornified, so that the free sur- PKISMS IN THAN- face of a recently erupted tooth is covered by a thin horny cuticle, the cuticular membrane of a cFai?m !f ^(Af- ^asmytn- The cuticular covering which is thus ter Kolliker.) formed by the horny uncalcified portions of the enamel cells is, however, removed by mechanical violence in a relatively short time after the final eruption of the tooth. The enamel prisms are grouped into bundles within which the constituent prisms are parallel. The course of the prism bundles, however, is variable, so that, though following a more or less radial course through the enamel, the prism bundles frequently cross one another at acute angles. In the thicker portions of the enamel this peculiarity gives rise to an apparently laminated condition of this tissue. Ground sections of dried tooth show brownish lines having a general radial direction, but which are somewhat inclined toward the apex of the tooth. These lines of Retzius are explained by von Ebner as being the result of air-filled fissures in the dried enamel. They are also said to be the result of the wavy direction of the enamel prisms. Cementum. — The dental cement, crusta petrosa, is a thin layer of bony tissue which invests the root of the tooth. It forms a very thin layer at the neck of the tooth, but gradually increases in thickness as it approaches the tip of the fang. The cement um consists of parallel layers of bony lamellae be- tween which many lacunae with their bone corpuscles are included. Bone canaliculi radiate from the lacunae and frequently open into the interglobular spaces of the granular layer. There are no Haversian systems in the cementum, but the thicker portions are frequently penetrated by vascular canals which, like Volkmann's canals, are not accompanied by concentric lamellae. The cement- DEVELOPMENT OF THE TEETH 259 urn is firmly united to the granular layer of the dentine, the matrix of the two tissues being continuous. The cementum is invested with a periosteal coat, the peri- odontium, alveolar periosteum, or root membrane, of dense fibrous tissue which, at the neck of the tooth, unites with the dense con- nective tissue of the gum to form an annular thickening of very « be FIG. 217.— FROM A SECTION OF A HUMAN TOOTH WHICH HAD BEEN GROUND TO EXTREME THINNESS. a, dentine ; ft, granular layer of Thomes ; c, cementum. Photo, x 140. dense fibrous tissue which encircles the tooth and is known as the circular dental ligament. The root membrane contains no elastic fibres, but sends considerable numbers of slender white fibrous bands (Sharpey's fibres) into the cementum. DEVELOPMENT OF THE TEETH The teeth arise partly from the epithelium of the oral cavity and partly from the connective tissue of the alveolar processes. In the seventh week of fetal life there appears upon the surface of the maxillary ridges a thickening of the epithelium which grows into the subjacent connective tissue in the form of a longi- tudinal ridge or shelf, the dental ridge, whose position is indicated by a dental groove which indents the epithelial surface. The dental ridge forms the earliest anlage of the enamel, and at this early stage it shows no indication of the future subdivisions which correspond to the several temporary teeth. On its inner side is a similar ingrowth of epithelial cells which is destined to form the vallum between the lips and the alveolar processes. At the beginning of the third month the dental ridge shows upon its deep margin slight indentations, one for each of the tern- 260 THE DIGESTIVE SYSTEM porary teeth, which are produced by a growth and thickening of the mesenchymal connective tissue cells at the site of each tooth germ. This thickening of the connective tissue forms the anlage .fs9 . of the dental papilla. ->' v-v"/\::y.*-X':""- "•'/:-. ;: "/ ... That portion of the dental ridge which spreads out laterally to cover the dental papilla of each tooth forms its enamel germ, from which the dental en- amel is eventually pro- duced. Further devel- opment of the enamel germ and dental papil- la causes the former to surround the papilla like a cap. During the third month of fetal life the anlages of all the prim- itive teeth are formed in the above manner. At about the same time, also, a lateral growth from the lingual side of the thin portion of the dental ridge which still connects the enamel germs with the oral epithelium, forms the anlages of the permanent teeth. The molars arise at a later period and in a similar manner by a dorsal extension of the dental ridge which grows backward through the connective tissue of the alveolar process as a solid cell column from which the enamel germs are formed and into which the dental papillae grow. Further development of the dental anlage includes the differ- entiation of the enamel germ on the one hand and of the dental papilla on the other. From the former the enamel and the cuticu- lar membrane arise ; the latter produces the dental pulp and the dentine. FIG. 218. — DEVELOPING TOOTH FROM A HUMAN EMBRYO 17 MM. LONG. LF, dental groove ; M, oral cavity ; OK, m.esoblast of upper jaw; 6>Z, epithelium of the primitive upper lip, and UL, of the lower lip; ZL, dental ridge. x 120. (After C. Eose.) DEVELOPMENT OF THE TEETH 261 The Enamel Germ. — The enamel germ or enamel organ soon differentiates into three layers : 1, an inner enamel epithelium which forms the enamel prisms ; 2, an outer enamel epithelium which lines the dental sac ; and 3, an intervening enamel pulp. The Inner Enamel Epithelium. — The innermost cells of the enamel organ, viz., those which rest directly upon the dental pa- pilla, soon become elongated and attain a cylindrical form. A cuticular border appears upon the inner extremities, and as the ZL Pn LFL- •-' LF- LFL :• Pf, FIG. 219. — DENTAL ANLAGES FROM A HUMAN FETUS 40 MM. LONG. Letters as in the preceding figure. ZFZ, anlage of the groove between the lip and the mandibular process ; Pp, dental papilla ; Z, outline of the margin of the tongue. x 60. (After C. Rose.) calcareous substance of the enamel begins to be deposited fine processes are seen extending inward from the extremities of the enamel cells, Thomes* processes. It is around these processes that the permanent enamel is deposited to form the enamel prisms. 262 THE DIGESTIVE SYSTEM The deposit of lime salts by the cylindrical cells of the inner enamel layer, adamantoblasts, occurs earliest at the apex of the dental germ. Thus, it is the enamel of the face of the tooth crown $ FIG. 220. — DEVELOPING TOOTH FROM A HUMAN FETUS 30 CM. LONG. />, dentine; K, bone of the jaw ; RM, Malpighian layer of the oral nmcosa; S, en- amel organ ; /SX2, enamel anlage of the permanent tooth ; VB, epithelial bridge still uniting the anlages of the temporary and permanent teeth ; ZZ, disintegrating dental ridge, x 30. (After C. Kose.) which is first formed, and this is therefore its thickest portion. The enamel on the sides of the tooth crown appears later and hence it gradually tapers in thickness as it approaches the neck of the tooth, in which latter place the last formed enamel is found. The nucleated bases of the cylindrical cells of the inner enamel epithelium are also marked by a sharp cuticular margin and rest upon the adjacent cells of the enamel pulp, the innermost cells of which retain a characteristic epithelial appearance. The thin layer formed by the uncalcified bases of the adamantoblasts, which DEVELOPMENT OF THE TEETH 263 still cover the free surface of the enamel at the eruption of the tooth, remains as the cuticular membrane of Xasmyth. The Outer Enamel Epithelium.— The outermost cells of the enamel germ are immediately in contact with the mesenchymal FlO. 221. — A DEVELOPING TOOTH FROM AN INFANT'S JAW. a, papilla; 6, crown ; c, outer enamel epithelium. Ilematein and eosin. Photo, x 65. connective tissue of the primitive jaw. This connective tissue forms, toward the end of the third month, an investing sheath or 264 THE DIGESTIVE SYSTEM - ft**** dental sac, which incloses the entire dental germ and finally, by gradually encroaching upon the narrow neck which still connects the enamel germ with the dental ridge, severs the connection of these organs so that the primitive tooth lies free within the dental sac. The outer enamel epithelium, which lines all portions of the dental sac except at the base of the dental pa- pilla, forms several layers of flattened epithelial cells. Remnants of this cell layer frequently persist, in rela- tion to the inner margin of the bony alveolus whose wall is produced by intra- membranous ossification in the connective tissue sur- rounding the embryonic dental sac. / The Enamel Pulp.— This structure is produced by a most remarkable differen- tiation which occurs within the mid-portion of the en- amel organ. The epithe- lial cells of this region, which at first appear to form a delicate syncytium, become separated by wider and wider in- tercellular spaces, and are thus drawn out into stellate forms with long anastomosing processes. The resulting cells closely resemble in form the connective tissue cells of embryonic or gelatinous con- nective tissue. They are, however, inclosed on all sides by the epithelial cells of the inner and outer enamel epithelium and, like other epithelial tissues, are never penetrated by blood vessels. The enamel pulp appears to serve a purely mechanical func- tion, it being a soft tissue through which the growing tooth readily pushes its way to the surface. THE DENTAL PAPILLA, — The dental papilla is a connective tissue structure which is invested by and grows into the enamel FIG. 222. — A PORTION OF FIG. 221, NEAR THE APEX OF THE DEVELOPING TOOTH. a, enamel epithelium; 6, adamantoblasts ; c, enamel; d, dentine; e, odontoblasts;/, border of the dental pulp. Hematein and eosin. x 550. THE TONGUE 265 organ. Coincident with the appearance of the adamantoblasts in the enamel organ, the superficial cells of the dental papilla become enlarged, elongated, and so arranged as to form a continuous layer of odontoblasts on the surface of the papilla. These cells appar- ently secrete a thin homogeneous layer, membrana praeformativa (Raschkow), which serves as a basement membrane upon which the adamantoblasts deposit the enamel prisms ; it also forms the anlage of the granular layer of Thomes. The odontoblasts now form the dentine in a manner entirely analogous to the deposit of bone by the osteoblasts, processes of the odontoblasts being included within the deposit of dentine to form the dentinal fibres. Irregular spaces, occurring in the den- tine and granular layer, in which no calcification occurs produce the interglobular spaces. The central mass of the dental papilla develops the embryonic connective tissue of the tooth pulp. The blood vessels and nerves enter the pulp through the base of the papilla, which thus becomes the anlage of the root canal. The cementum is formed by intramembranous ossification oc- curring in the connective tissue which invests the base of the dental papilla and the primitive root of the tooth. THE TONGUE The tongue is formed by a reflection of the oral mucous mem- brane which incloses a mass of muscular tissue. The fibres of this striated muscle are separated into two lateral halves by a median septum of dense connective tissue which extends from the base to the tip of the organ, and is known as the lingual septum. The muscle fibres are disposed in three planes and are so ar- ranged that the bundles cross one another at right angles. They thus form : 1, saggital or vertical fibre bundles which are slightly inclined outward from the septum linguae and are derived from the lingualis muscle ; 2, longitudinal fibres running from the base to the apex of the tongue, which are derived from the lingualis, styloglossus, hyoglossus, genioglossus ; 3, transverse or horizontal fibres extending laterally from the septum linguae, which are also derived from the lingualis muscle. The interlacing bundles of muscle fibres are embedded in loose areolar and adipose tissue. The muscle fibres are inserted into the corium of the lingual mucous membrane, their sarcolemma be- ing firmly adherent to the connective tissue of the mucosa, which 266 THE DIGESTIVE SYSTEM invests the rounded blunt extremity of the muscle cell. Many of these muscle fibres are branched. The mucous membrane of the tongue consists of a thick corium, and an epithelial covering. The deeper part of the corium, con- sisting of loose areolar tissue, is intimately connected with the FIG. 223. — ONE LATERAL HALF OK A CORONAL SECTION OF A DOG'S TONGUE. The dorsal surface presents numerous large filiform papillae, a, lingual papillae ; 6, corium ; c, the fibro-muscular substance of the tongue. Hematein and eosin. Photo, x 6. muscle. The superficial portion of the corium, containing denser areolar tissue, carries upon its surface papillce of unusually large size which project into the epithelial coat. The surface of the larger of these papillae is not smooth, but is covered with small secondary papillce. The epithelium of the tongue is of the stratified variety. Upon the under surface and margins of the organ its surface is smooth, but on the dorsum of the tongue the stratified epithelium forms tall projections, which correspond with the papillae of the corium, and which constitute the so-called lingual papillce. These papillae are of three varieties : 1, conical or filiform ; 2, f ungif orm ; and 3, circumvallate. THE TONGUE 267 The Conical or Filiform Papillae.— These papillae consist of flat- tened and elongated epithelial cells which are often so arranged as to produce a slender conical projection or epithelial tuft of FIG. 224. — FILIFOBM PAPILLAE OF THE DOG'S TONGUE. a, papillae ; b, corium ; c, insertion of the muscular fibres into the border of the corium. Hematein and eosin. Photo, x 60. variable height, which covers the apex of each connective tissue papilla. This type is the most abundant of the three varieties of lingual papillae ; they are found upon all portions of the dorsum of the tongue. The fungiform papillae are formed by a large connective tissue papilla or core which projects above the general level of the epithelial surface and is covered by a smooth layer of stratified epithelium in which occasional taste buds are found. This variety, though much less abundant than the former, is still very numerous and may be found upon any or all portions of the dorsum of the tongue, where they are irregularly scattered among the fili- form papillae. The fungiform variety are most abundant near the margin of the tongue on its dorsal surface. The circmnvallate papillae form a group of from eight to twelve elevations which are situated at the base of the tongue, and are 268 THE DIGESTIVE SYSTEM arranged in the form of an inverted V, the apex being directed toward the larynx. These papillae are much larger than either of the former varieties. They extend slightly above the general level of the epithelial surface, are of an inverted conical shape, and are covered by a smooth layer of stratified epithelium. Their base is surrounded by a deep circular excavation, lined by an invagination A B FlG. 225. — ClRCUMVALLATE PAPILLAE OF THE HUMAN TONGUE. A, axial section ; B, section through the side of a papilla. The serous glands of von Ebner occupy the lower portion of the figure. Hematein and eosin. Photo, x 40. of the layer of stratified epithelium, which thus forms a deep trench or vallum about the base of the papilla. The epithelium which covers the sides of the circumvallate papillae, as well as that forming the lateral wall of the vallum, con- tains large numbers of taste buds.* The large central connective * See Chapter IX. THE TONGUE tissue papilla carries upon its surface many small secondary papillae of the corium, which project into the epithelial coat of the circum- vallate papilla upon its free surface, but are not found upon its lateral margins. Mucous and serous glands occur in the deeper portion of the corium of the tongue and among its muscle bundles ; they open upon its epithelial surface between the papillae. These glands are most abundant at the base of the organ but are also found along its margins as far forward as the tip, where a pair of small tubulo- acinar mucous glands lie on either side of the median septum and open upon the ventral surface of the tongue ; these are the anterior lingual glands of Nuhn.* The serous glands of von Eb- ner are confined to the region of the circumvallate papillae at the base of the tongue. They pour their secretion into the val- lum which surrounds the base of the papilla or into the crypts of the lingual tonsil. Other lingual glands, also of the small tubulo-acinar type, occur at various portions of the dorsal surface of the tongue. The lingual tonsil (Fig. 153, page 157) is a considerable col- lection of lymphoid nodules which is found at the base of the tongue in and about the median line. These nodules are grouped about a large funnel-shaped crypt, the foramen ccecum, which opens at the apex of the V formed by the group of circumvallate papillae and which in the embryo forms the lingual extremity of the so-called duct of the thyroid gland (thyreo-glossal duct). Several smaller crypts are also included in the region of the lingual tonsil. The lymphoid nodules are embedded in the mucosa or corium of the tongue and are surrounded by mucous glands many of whose ducts penetrate between the nodules to open into the branching crypts. Lymphatic corpuscles, apparently derived from the nod- ules, infiltrate the surrounding connective tissue and epithelium and find their way into the lumen of the follicular crypts. In other portions of the lingual mucous membrane diffuse col- lections of lymphatic corpuscles are of frequent occurrence, and small nodules occur in many parts of the dorsal mucous membrane toward the base of the tongue. The blood vessels of the tongue are supplied by large arteries which, with the corresponding veins, are embedded in the muscular portion of the organ and supply capillary vessels to this tissue. * Mannheim, 1845. 270 THE DIGESTIVE SYSTEM From these arteries, also, small arterial branches enter the deeper portion of the coriuni and form a capillary plexus which supplies the connective tissue and whose terminal ramifications extend to the very apex of the connective tissue papillae. The blood is re- turned by veins which pursue a similar course. The Lymphatics form a superficial set of small vessels and tissue spaces beneath the epithelial layer, which are especially abundant in the region of the lingual tonsil at the base of the tongue. The lymphatic vessels of this superficial plexus frequently encircle the lymphoid nodules. A deeper plexus of lymphatics in the loose connective tissue of the submucosa receives the lymph from the superficial plexus and conveys it by efferent lymphatic vessels to the deep cervical lymphatic glands. The Nerves of the tongue are derived from the lingual, glosso- pharyngeal, and chorda tympani. The larger trunks accompany the arteries, lying near the median line on the under surface of the tongue, and are embedded in the connective and adipose tissue between the muscle bundles of this portion of the organ, small ganglia occurring along their course. From these nerve trunks, fibres are distributed to the muscular tissue and to the corium. The former terminate in muscle plates in the striated muscle fibres, in the walls of the larger blood vessels to which both sensory and motor fibres are distributed, and in sensory endings in the muscle spindles and connective tissue. The smaller nerves of the corium supply the blood vessels of this tissue and send minute fibrils to the epithelium, which terminate in delicate knobbed extremities between the epithelial cells. At the base of the tongue small nerve bundles are distributed to the circumvallate papillae, and form a subepithelial plexus from which fibrils are distributed : 1, to the interior of the taste buds where they end in relation with the gustatory cells, intragem- mal fibres ; 2, to the surface of the taste buds, perigemmal fibres ; and 3, to the intervening portions of the epithelial layer, where they end between the epithelial cells as in other parts of the tongue, intergemmal fibres (Fig. 120, page 125). CHAPTEK XVI THE DIGESTIVE SYSTEM (Continued) . THE ALIMENTARY TRACT IT is convenient to consider collectively under this head the pharynx, esophagus, stomach, and the small and large intestines. This tract forms a continuous tube whose wall has, throughout its entire extent, many common characteristics. Thus the wall in all portions consists of four coats which are respectively known, from within outward, as the mucous, submucous, muscular, and fibro- serous. The three outermost coats are of very similar structure in all portions of the tract. The Fibro-serous Coat. — In the abdominal cavity the outermost coat is derived from the peritoneum, by which the stomach and intestines are invested. In the upper portion of the tract, pharynx and esophagus, the serous coat is replaced by a layer of areolar connective tissue which usually contains much fat. In the abdo- men the homologous subserous connective tissue is covered by a layer of endothelium. The connective tissue of the outer fibro- serous coat contains the larger blood and lymphatic vessels whose branches are distributed to the three inner coats. The Muscular Coat, situated next within the fibro-serous, is divisible into two layers, an outer longitudinal the direction of whose fibres is parallel to the long axis of the tract, and an inner transverse layer whose fibres are circularly disposed. The two layers are united by a thin septum of areolar connective tissue which serves for the support of the larger blood vessels and lym- phatics, whose capillaries are distributed to the muscular coat. This septum also contains a coarse-meshed nerve plexus, consisting of small anastomosing nerve trunks which are composed in large part of non-medullated fibres, at whose intersections are numer- ous small sympathetic ganglia. This is the nerve plexus of Auerbach. Below the level of the junction of the middle and lower third 271 272 THE DIGESTIVE SYSTEM of the esophagus, and including the musculature of the stomach and intestines, the muscle is entirely of the non-striated or smooth variety. In the pharynx and upper third of the esophagus, the striated or voluntary type of muscle is exclusively found. In the mid-portion of the esophagus both striated and non-striated muscle occur in varying proportions, occasional striated fibres being found even in the lower third of the organ. The Submucous Coat consists of loose areolar tissue, and serves for the support of the larger blood and lymphatic vessels which supply this coat and the mucosa. A second plexus of nerve fibres, similar in structure to the intra- muscular plexus, is found in the deeper layers of the submucosa, and is known as the plexus of Meissner. Its nerve trunks and gan- glia are somewhat smaller than those of the plexus of Auerbach. The plexus of Meissner supplies the muscular and glandular tissues of the mucous membrane. The Mucous Membrane or mucosa of the gastro-intestinal tract contains four typical structures, (1) an internal lining epithelium; (2) the muscularis mucosse which forms the outermost layer ; be- tween these is (3) a tunica propria or corium of diffuse lymphoid or areolar tissue, which serves chiefly for the support of (4) the secreting glands. The muscularis mucosce usually consists of a double layer of involuntary or smooth muscle, the outer being longitudinally, the inner transversely or circularly disposed. This layer is most highly developed in the esophagus. The tunica propria consists of loose areolar or reticular tissue whose volume is in inverse proportion to that of the secreting glands. It is most abundant in the esophagus. In the stomach and intestines it is considerably infiltrated by lymphatic corpuscles and often contains diffuse lymphoid tissue. Small lymphatic nodules are also found in the deeper part of this membrane ; they FIG. 226. — SURFACE VIEW OF AUERBACH'S INTRA- MUSCULAR NERVE PLEXUS, FROM THE ESOPHAGUS OF A CAT. Methylen blue, x 40 to 50. (After De Witt.) ESOPHAGUS 273 progressively increase in size toward the lower portion of the tract, where they form the solitary follicles of the intestine. The nature of the lining epithelium and the type of the secret- ing glands differs in each succeeding portion of the tract, and must therefore, together with the other peculiarities of the several sub- divisions of the tract, be separately considered. THE PHARYNX The pharynx may be subdivided, upon histological as well as physiological grounds, into (1) an upper respiratory portion, or naso-pharynx, and (2) a lower portion, oro-pharynx and laryngo- pharynx; only the latter of these properly belongs to the ali- mentary tract. The naso-pharynx has already been described as a part of the respiratory system (see Chapter XIV). The mucous membrane of the lower portion of the pharynx is lined by stratified squamous epithelium which rests upon a thick corium of areolar tissue. The tunica propria is well supplied with thin-walled blood vessels and lymphatics, and contains many mucus secreting glands of the tubulo-acinar type whose secreting portions lie deeply embedded in the connective tissue of the muscular coat. There is no muscularis mucosse in the mucous membrane of the pharynx ; its place is taken by a layer of connective tissue which is exceedingly rich in longitudinal elastic fibres. This layer lies immediately upon the muscular coat, into which processes of fibro- elastic tissue extend between the muscular bundles; hence this fibro-elastic layer also serves as a submucosa. The superficial layer of the corium contains diffuse collections of lymphoid tissue and occasional small lymphatic nodules. The muscular coat of the pharynx is formed by its constrictor muscles. Their striated fibres mostly pursue an oblique course. Where these muscles are not immediately attached to the peri- osteum of the v.ertebrae, the pharynx is invested with an outer coat of areolar connective tissue by which it is loosely united to adja- cent organs. ESOPHAGUS The wall of the esophagus contains the usual four coats : 1, the outer fibrous ; 2, muscular ; 3, submucous ; and 4, mucous. THE OUTER FIBROUS COAT envelops the wall of the esoph- agus and unites it to the adjacent organs. It consists of loose fibrous tissue, and contains the blood and lymphatic vessels and nerve trunks which supply the three inner coats. 19 274 THE DIGESTIVE SYSTEM THE MUSCULAR COAT contains an outer longitudinal and an inner circular layer of muscle fibres, which are separated by a narrow septum of loose fibrous tissue. In the upper and middle thirds of the esophagus the muscle is of 'the striated variety, in FIG. 227. — FROM A LONGITUDINAL SECTION AT THE JUNCTION OF THE MIDDLE AND LOWER THIRD OF THE HUMAN ESOPHAGUS. a, epithelium; 6, corium, and c, muscular layer of the mucosa; d, fibrous tissue, and e, mucous glands of the submucosa : y, inner, and ^, outer layer of the muscular coat, the former partly of smooth and partly of striated fibres ; A, edge of the outer fibrous coat. Hematein and eosin. Photo, x 42. the lower third it is largely smooth or involuntary muscle. The distribution of the muscle in the lower third is, however, subject to great individual variation, and occasional striated fibres are often found all the way down to the diaphragmatic opening. ESOPHAGUS 275 The fibrous septum between the muscular layers contains the larger blood vessels and the nerve plexus of Auerbach. THE SUBMTJCOUS COAT forms a layer of areolar connective tissue which firmly unites the muscular and the mucous coats. It contains those blood and lymphatic vessels, together with the nerve plexus of Meissner, whose branches supply the mucous membrane. It also contains a considerable number of tubulo- acinar mucous glands whose ducts enter the mucous membrane and open upon the free epithelial surface. The secreting acini of these glands are short branching tubules with ampullary dilata- tions ; they possess a characteristic, tortuous form. Their col- umnar secreting cells have a strong affinity for muchematein and other mucous stains. This basophile reaction, together with the situation of their isolated groups of secreting acini within the submucosa, sharply distinguishes the esophageal mucous glands from the secreting glands of the stomach and intestine. THE MUCOUS COAT (mucosa) of the esophagus consists of a tunica propria or corium of areolar tissue which rests upon a well- developed muscularis mucosae and is covered on its free surface by stratified squamous epithelium. The muscularis mucosae contains considerable bundles of smooth muscle whose general direction is a longitudinal one in its outer, and circular in its inner portion. This layer forms tho outermost layer of the mucous coat, and is penetrated by the ducts of the deep mucous glands whose secreting acini lie in the submucosa. The inner portion of the tunica propria carries on its surface many tall connective tissue papillae which project well into the epithelial coat and which closely resemble the vascular papillae of the skin. The mid-portion of the corium is penetrated by the ducts of the mucous glands. These are at first lined by low columnar cells which, as they approach the epithelial surface are changed into several layers of flattened cells, which thus form a thin stratified lining, continuous with the superficial stratified squamous epithe- lium of the esophageal mucosa. Many of these ducts possess small cystic dilatations which are found in the connective tissue of the corium or occasionally in the submucosa. Superficial Glands. — At about the level of the cricoid cartilage the esophageal mucous membrane presents two lozenge-shaped depressions, one on either side, whose diameter varies from 1 cm. down to a microscopical size. These areas mark the site of the 276 THE DIGESTIVE SYSTEM superficial glands of the esophagus (Hewlett *) or upper cardiac glands (Schafferf). These are short branched tubular glands which closely resemble those of the cardiac region of the stomach. They are confined to the mucous membrane ; their tubules, in marked contrast to those of the deep mucous glands of the eso- ^ phagus, never pene- ' trating the muscu- laris mucosae,which, however, is consid- _ <***-._ &f erably thinned be- •?^ neath the super- ficial glands. These ^'r glands secrete a mucinous fluid, but their cells are not so strongly baso- phile as those of true mucous glands such as the deep glands of the eso- phagus. The ducts of the superficial glands, as well as their secreting portions, and also the lining epithelium of the esopha- gus upon which they open, are clothed with columnar epithelial cells. Many of the secreting tubules contain parietal cells similar to those of the f undus glands of the stomach. Both ducts and secreting tubules contain small, cystic dilatations. At the lower end of the esophagus a similar group of superficial glands, the cardiac glands of the esophagus, frequently mark the beginning transition to the structure of the cardiac portion of the stomach, with whose secreting glands they are continuous. The lining epithelium of the esophagus is of the stratified squamous variety. Its attached surface is indented by the papillae of the corium ; its free surface is smooth. In the collapsed state of the organ its mucous membrane is thrown into longitudinal folds or rugae and its lumen is obliterated. The small isolated areas of FIG. 228. — FROM A SECTION OF THE SUPERFICIAL GLANDS OF THE HUMAN ESOPHAGUS. a, esophageal epithelium ; £, superficial glands ; c, mucous glands; rf, tunica propria; e, muscularis mucosae. Hemat- oxylin and eosin. Photo, x 17. (After Hewlett.) * Jour. Exper. Med., 1901. f Sitz. d. Wien. Akad., 1897. THE STOMACH 277 columnar or ciliated epithelium, which occur in occasional indi- viduals on the surface of the esophageal mucosa, especially in its upper third, are to be regarded as examples of irregular develop- ment. THE STOMACH THE SEROUS COAT of the stomach is derived from the peri- toneum. It is formed by a thin layer of subserous connective tissue which is covered by endothelium. The serous coat supports Fli.. 'Jli'.t. — KKOM A TKAV-l-.i II"N »K THK \\.VI.I. <>F THK HUMAN STOMACH NEAU THE PYLOKIC ORIFICE. a, secretion ; 6, mucosa; c, submucosu ; , neck region, and c, fundus por- tions of the secreting glands, the parietal cells being much more abundant in the former; d, muscularis mu- thre zones m*J ^Q distinguished- GLANDS OF STOMACH. THE DOG'S Golgi stain. (After Miiller, from Oppel.) . 233.-SECKETOKY LABIES OF THE FUNDUS a superficial, middle, and deep. The superficial zone is narrow and contains the wide-mouthed crypts or foveolae which are lined by tall columnar cells similar to those of the fundus crypts. The middle zone contains the narrowed portion of the ducts and is the broadest of the three zones. Several of the narrow ducts open into each foveola and further branching of the secret- ing tubules occurs to a limited extent. The epithelium of the ducts is of the low columnar variety, whose deeply stained basal nuclei are spheroidal or ovoid, and are progressively flattened as the secreting portion is approached. The superficial cytoplasm of these cells stains readily with muchematein and often has a coarsely granular or reticular appearance. The deepest zone contains the convoluted secreting portions and is sharply demarked from the adjacent ducts, since in a transec- tion of the stomach wall its tubules, owing to their convolution, are nearly all cut across, while the ducts are in longitudinal sec- tion ; the clear tall columnar epithelium and broad lumen of the fundus, also, contrast strongly with the low finely granular epithe- lium and narrow lumen of the duct. It is this narrow zone of THE STOMACH 283 peculiar convoluted tubules, lying just within the muscularis mu- cosae, by which the pyloric mucous membrane is most readily distin- guished from all other regions of the alimentary tract. FIG. 234. — THE MUCOSA OF THE PYLORIC REGION OF THE HUMAN STOMACH. a, ft, and c, respectively the crypt, neck, and fundua zones of the secreting glands ; i among the crypts ; c, artery to the villus ; d, coat» bufc most oi them pass venules in the deeper part of the mucosa; ) the lymphoid tissue, and (c) the central lacteal. In the epithelium fat is contained in the form of fine droplets which are most numerous in the distal or free ends of the cells. They are also found in the intercellular spaces. During absorp- tion the epithelial cells of the villi become much swollen and elongated. As the process subsides they return to their former size, relatively they are shrunken. When most distended the intracellular fat droplets are the most abundant; as the cells shrink the intercellular droplets relatively increase in number (Drago*). The relative size of the epithelial cells and the abun- dance of intra-epithelial fat is apparently dependent upon the ac- tivity of the processes of absorption. * Richerche d. lab. anat. norm. d. r. univ. d. Roma, 1900. INTESTINAL ABSORPTION 299 As to the manner in which the fat enters the epithelium there is some doubt. Schafer * suggested that the leucocytes by their amoeboid activity inclose the emulsified droplets in the intestinal lumen and convey them into the substance of the villi. It seems more probable that the fats are saponified in the intestinal tract, and, as such, enter the epithelium in solution. Here they are again synthetized into neutral fat by the activity of the epithe- lium (Pfliigerf). Such a process accounts for the abundance of fat within the distal portions of the cells. The droplets are then secreted into the intercellular and subjacent tissue spaces. The second phase of absorption includes the transference of the fat particles to the lacteal. This process appears to depend partially, at least, upon the activity of the leucocytes, as suggested by Schafer, the particles of fat thus finding their way through the diffuse lymphoid tissue. According to ReuterJ fat drop- lets are found in the tissue spaces as well as in the lymphatic cor- puscles of the diffuse lymphoid tissue, a fact which would seem to in- dicate that other agen- cies aid in the transit of the fat from the epithe- lium to the lacteal than are accounted for by the purely mechanical the- ory of Schafer. The third phase in- cludes the secretion of the fat into the lumen of the lacteal. This is, at least partially, accom- plished by the disinte- gration of fat-laden leu- cocytes which, by amoeboid motion, have found their way into the lacteal. Other fat particles may possibly find their way into the lacteal without the aid of the leucocytes, a process which may be FIG. 244. — APEX OF AN INTESTINAL VILLUS OF A RAB- BIT WHICH HAD BEEN FED WITH MILK. The fat droplets have been blackened by fixation with picric acid and osmium tetroxid. The figure shows the distribution of fat during certain stages of absorption. Alum carmin stain. Highly mag- nified. (After K. Heidenhain, from Oppel.) * Internat Monatsch. f. Anat. u. Physiol., 1885. f Arch. f. d. ges. Physiol., 1900. % Anat. Hefte, 1902. 300 THE DIGESTIVE SYSTEM more or less dependent upon the vital properties of the lining epithelium. The absorption of the products resulting from the digestion of the starches, sugars, albumins, etc., probably proceeds along similar lines. The peptones enter the epithelium in solution and are then secreted, as albumins and globulins, into the tissue spaces, whence they find their way into the lacteal and capillaries. Thus the lac- teals become widely distended even in the absence of the digestion and absorption of fat. THE LAKGE INTESTINE The three outer coats of this portion of the alimentary canal are identical in structure with those of the small intestine, with a FIG. 245.— THE MUCOSA )F THE LARGE INTESTINE OF MAN. At a, the crypts are in longitudinal section ; at ft, owing to a fold of the mucosa, they are very obliquely cut, some of them being almost in transection. A single solitary nodule of lymphoid tissue is embedded in the superficial portion of the submucosa; c, c, the vascular submucosa. Hematein and eosin. Photo, x 48. single exception in the irregular distribution of the outer layer of the muscular coat, which in the large intestine forms three dis- tinct longitudinal ridges or thickenings. At other parts of the THE LARGE INTESTINE .301 circumference of the organ the outer muscular layer is slightly thinner than in the small intestine. The mucous membrane of the large intestine may be best de- scribed by comparison with that of the small intestine. If the mucosa of the latter organ contains two zones, a superficial layer of villi and a deeper glandular layer, that of the large intestine may be said to consist of only the deeper of these zones. It there- fore possesses no villi, and its simple tubular crypts of Lieberkiihn extend from the free surface almost to the muscularis mucosae. The lining epithelium of the large intestine is of the simple columnar variety and has only an indistinct cuticular margin. That of the crypts of Lieberkiihn contains both columnar and goblet cells, the latter being far more numerous than in the small intestine. The lymphoid tissue of the large intestine occurs in the form of diffuse lymphoid tissue in the corium, and as solitary follicles, which frequently break through the muscularis mucosae and lie in the submucosa. The fundus of such crypts of Lieberkiihn as may occasionally be inclosed within the lymphatic follicles are fre- quently prolonged into the superficial portion of the submucosa where they often possess alveolar dilatations. Elsewhere the mus- cularis mucosae forms a complete membrane which is nowhere penetrated by the simple tubular glands of Lieberktihn. Lymphatic nodules are especially abundant in the rectum and in the vermiform appendix. In the latter the nodules are more or less confluent, a condition which is not found elsewhere in the large intestine. In the appendix the greater portion of the mucous membrane is invaded by the lymphoid tissue and the crypts are much diminished in both number and size (Fig. 246). The vascular and nerve supply of the large intestine is identical in its arrangement with that of the small intestine. The mucous membrane contains a capillary plexus of blood and lymphatic vessels in the corium about the crypts. The nerves of the large intestine supply its muscular coats and blood vessels and, in the mucosa, end in naked varicose or knobbed fibrils beneath the epi- thelium of the glands of Lieberkiihn. In the rectum the lining epithelium is continuous at the anus with the stratified squamous epithelium of the skin. In this region, also, the circular fibres of the inner layer of the muscular coat are much thickened to form the internal rectal sphincter. Lymphoid tissue abounds in the rectal mucous membrane. 302 THE DIGESTIVE SYSTEM The ileo-caecal valve, which guards the orifice hy which the small intestine opens into the caecum, is formed by a reduplication of the mucous membrane, which is strengthened by a thickening and overlapping of the circular muscular layers of both small and large intestines. The outer longitudinal muscular layer is continued directly from the wall of the ileum to that of the caecum, and therefore FIG. 246. — TRANSECTION OF THE VERMIFORM APPENDIX OF MAN. The submucosa contains much adipose tissue, and a number of large lymphoid nodules, each with a dense periphery and a large, lighter, germinal center. Photo, x 10. pursues a relatively shorter course than either the internal muscu- lar layer or the mucous membrane. Section of only the outer layer of the muscular coat permits one to straighten the fold of the intestinal wall and thus obliterate the valve. In other words the outer muscular layer is not included in the valvular reduplication. The muscularis mucosae is slightly thickened at the margin of the valve. At this point, also, the villi become shorter and at the margin of the caecal surface of the valve they entirely disappear. The following tabulated statement of the more important characteristics of the several portions of the alimentary tract may be of assistance to the student in the differential diagnosis of these organs. THE LAEGE INTESTINE 303 • W £ ll M 0) ^ j ft ,d S g s S> a > §o a< ^ O •— ' o3 § G- !J |1 i 1 | '1 o3 W E O 6 a a ^ ILEUM AND JEJUNUM. Columnar ind goblet. || t| 5"3 M 5 Mucosa. |*| Smooth. c 02 CQ * DUODENUM. Columnar and goblet. Columnar, muco- albuminous. Branched tubulo-acinar. Mucosa and submucosa. Many, large, confluent. Smooth. Present. CB • , ej *" S pM PYLORIC STOMACH Columna •|ti Convolut tubular Mucosa co Smooth e o ;_,' .*2 'S T3 , J w U 11 Columna 11° Branche tubular 1 0) | cc 0) | Sg 03 ^ . 13 . S S o3 - p ^ o5 § ** g 'c O 2 * i 8 o .g CJ ^ j! 1 If § a CO c 0 ^^ ^^ ESOPHAGUS. Stratified squamous. Columnar, mucous. Branched tubulo-acinar. Mucosa and submucosa. 1 I Striated or smooth. oJ i ft S d j s • 0 CO 1 3 & 1 s 1 cu O) H 35 a 1 OH b > y — -i o fcJD 3 tn M r^ PO OH 9 a 1 5 3 4" 1 1 1 CHAPTER XVII SALIVARY GLANDS AND PANCREAS THE salivary glands include the smaller secreting glands of the oral cavity and three pairs of large compound tubulo-acinar glands, the parotid, submaxillary, and sublingual glands. All these are of the tubulo-acinar type, but certain ones secrete a mucous fluid while others produce an albuminous secretion which contains no mucous. The former are collectively known as the mucous, the latter as the serous salivary glands. Still other salivary glands secrete a fluid which is inter- mediate in composition, and as these glands contain certain alveoli which resemble those of the mucous, and others which are similar to those of the serous glands, this type is known as mixed salivary glands. The salivary glands may therefore be subdivided into : I. Mucous glands: sublingual, glands of Nuhn, and the mucous glands of the mucosa of the lips, cheeks, and tongue. II. Mixed glands : submaxillary. III. Serous glands : parotid, and v. Ebner's glands at the base of the tongue. The form of the salivary glands will be appreciated by the accompany- ing diagram (Fig. 247) which repre- sents one of the smaller glands of this FIG. 247.— SEMIDIAGRAMMATIC REP- RESENTATION OF A SMALL MU- COUS GLAND FROM THE ORAL MUCOSA OF A RABBIT. a, mucous alveoli ; «, epithelium of the oral mucosa ; m, mouth of the glandular duct* x 70. (After Kolliker.) 304 SALIVARY GLANDS 305 type. The larger ones are constructed in the same manner, the larger number of their secreting alveoli or acini arising through a more complex duct system. FIG. 248. — CORROSION MODEL OF AN INTERLOBULAR DUCT AND ITS BRANCHES, FROM THE HUMAN SUBMAXILLARY GLAND. C, intcrlobular duct; Z>, large intralobular duct; E, small intralobular duct; ^inter- calary duct, x 12. (After Flint.) The larger ducts of the gland are lined by columnar cells, which, as they approach their termination, become superposed and thus offer a gradual transition to the stratified epithelium upon whose surface they open. The epithelium rests upon a base- 21 306 SALIVAEY GLANDS AND PANCREAS ment membrane which, in the larger ducts, is invested with a fibro- elasfcic coat containing a few longitudinal smooth muscle fibres. The ducts divide and subdivide in an arborescent manner, the larger branches lying in the connective tissue which invests the lobules into which the gland is subdivided, while the smaller branches are found within the lobule. The duct system is thus divisible into interlobular and intralobular ducts ; the latter in- clude the " salivary " and intercalary ducts. In the smaller glands of the mouth the number of subdivisions of the duct system is relatively small, but in the larger salivary glands the small ducts are innumerable. Thus, in the submaxil- lary gland, Flint * found that the interlobular duct system formed 1,500 terminal branches, each of which entered a lobule and was further subdivided into intralobular and intercalary ducts before terminating in the secreting acini. The larger glands may therefore be said to bear to the smaller ones represented in Fig. 247, a relation which is comparable with that of a full-grown tree to the youngest sapling. The smaller interlobular ducts are lined by columnar epithe- lium whose cells contain two zones, one on either side of the cen- trally situated nucleus. The distal zone or free extremity of the cell is finely granular, the proximal zone or base pre- sents a characteristic striated appearance which is apparently due to a fibrillar structure of the cytoplasm in this portion of the cell. The epithelium is easily de- tached from its basement membrane by the artificial contraction of the tissues during fixation and hardening. The lumen of the ducts is of consider- FIG. 249. — INTERCALARY DUCTS diameter and contains the reticulated AND ACINI OF THE HUMAN SUBMAXILLARY GLAND, COR- or granular particles of the secretion. duct; The *"&* d^S ^ ™ ^ Connective G, intercalary duct ; JJ, acini. tissue sePta whlch mvest the Highly magnified. (After groups of acini. Each of these groups is derived from the ramifications of the terminal branch of an interlobular duct which enters the lobule to divide into numerous intralobular ducts, and secondarily, through a short intermediate or intercalary portion, into the * Am. J. of Anat., 1902. SALIVARY GLANDS 307 secreting alveoli or acini. The intercalary ducts are lined by low cuboidal epithelium and are the smallest tubules of the gland. As the duct passes into the acinus the tubule is increased in size, and its secretory epithelium becomes taller. The tubular acinus k more or less tortuous and possesses a sacculated or alveolar appearance. The epithelium differs accordingly as it secretes a mucous or a serous fluid. Thus the acini are either mucous or serous secreting. The serous acini contain pyramidal epithelial cells of sufficient height to almost completely fill the tubule; hence the lumen is •^mpr FIG. 250. — A GROUP OF SEROUS ACINI, FROM THE HUMAN SUBMAXILLARY GLAND. a-a, interlobular connective tissue. Hematein and eosin. Photo, x 510. very narrow. The form of the secreting cells is somewhat irregu- lar, a fact which apparently depends upon their crowded condi- tion within the acinus. The nucleus is situated in the central portion or in the proximal end of the cell and is spheroidal in shape. The cytoplasm is finely granular, the granules being more prominent in the distal portion of the cell. The epithelium rests upon a basement membrane within which, beneath the bases of the secreting epithelial cells, are certain flat- tened " "basket cells " which here and there send short processes be- tween the cells of the secretory epithelium and thus provide cup- 308 SALIVARY GLANDS AND PANCREAS like depressions which receive the bases of the secreting cells. The function and origin of these " basket cells " is not at present known. They are readily recognized by their deeply stained and flattened nuclei which are contained within the thin cytoplasmic cell body. The appearance of the secreting epithelium varies with its activity. During rest the granular secretion accumulates within the cell, until the non-granular zone is reduced to a narrow rim at its basal extremity and the nucleus is obscured and pushed somewhat basalward. The cell therefore becomes much swollen and the alveolar lumen almost obliterated. During activity the zymogen granules are discharged into the lumen, the cell shrinks and becomes clearer, the nucleus appears more distinct, and the granular zone becomes progressively narrower, the basal non- granular zone being correspondingly increased in breadth. In this basal zone elongated granules have been demonstrated, which are possibly to be regarded as prozymogen (" basal filaments " of Solger*). The serous cells are provided with systems of secretory canal- iculi which, beginning at the glandular lumen, invest the cell with a network of canals which lie in the intercellular substance and may even send short offshoots into the body of the cell itself. These canaliculi are considered to be characteristic of the serous acini and are not found in relation with the cells of thp mucous acini (Fig. 252). The mucous acini may contain only mucus secreting epithelium, or they may also include certain finely granular cells which resemble the epithelium of the serous glands. The former variety of acinus is found in the mucous glands at the base of the tongue and in the soft palate ; the latter in the sublingual gland, in the glands of N"uhn, and in the mucous glands of the lips and cheeks. The serous appearing cells of the latter form of mucous acinus are frequently arranged as crescentic groups bordering upon the adjacent mucous cells. Such groups are known as the demilunes of Haidenhain or crescents of Gianuzzi. They occur at the periphery of the acinus, their base being applied to the membrana propria, their inner margin sometimes reaching the glandular lumen, but more frequently separated therefrom by the overlapping of the ad- jacent mucus cells. The demilunes are frequently found at the , blind extremity of the secreting acinus, but they may also occur along its sides. * Festschr. f. C. Gegenbaur, 1896. SALIVAEY GLANDS 309 The nature of the demilunes is the subject of considerable dis- cussion. Haidenhain * first advanced the theory that the mucous cells were destroyed during secretion, and that the function of the demilunes was therefore to replace the disintegrated mucinous FIG. 251.— FROM THE SUBLINGUAL GLAND OF MAN. a, intralobular duct ; F THE HUMAN PANCREAS. The acinus at a is connected with an intercalary duct, cut in tengential section, and occupying the center of the figure. Hematein and eosin. Photo, x 950. carefully studied by Mathews. f This is a spheroidal basophile body which lies near the nucleus and is frequently surrounded by a clear area of cytoplasm. Its origin and function are somewhat doubtful and it is possible that several distinct bodies have been * Arch. f. mik. Anat, 1885. fJ. of Morph., 1899. 318 SALIVAEY GLANDS AND included under this name. Ogata* considers that ft is derived from the nucleus by the extrusion of its plasmosome, aft opinion" which seems to be shared by von Ebner. f The studies of FIG. 262. — CELLS FROM THE PANCREAS or NECTURUS IN VARIOUS STAGES OF SECRETION. A and .2?, show the appearance of cells which are nearly filled with secretion after a period of rest ; (7, after active secretion. Highly magnified. (After Math ews.) Mathews, however, show that at least in certain instances it is distinctly fibrillar and that it is concerned with the mechanism of secretion (see Fig. 3, page 3). ISLANDS OF LAN GERHANS.— Most of the lobules of the pan- creas contain, in addition to the acini and ducts, certain minute collections of spheroidal or polyhedral cells which lie in the inter- acinar connective tissue and which, though they possess the appearance of secreting cells, are in no way connected with the duct system. These cell groups are known as the islands of Lan- gerhans (intraldbular cell groups). They are most abundant in the splenic end of the gland (Opie). J The insular cells form a spheroidal group which is abundantly supplied with blood capillaries. Occasionally the cells form col- umnar strands between the capillary vessels but more frequently they are irregularly disposed. Still more rarely they are so grouped about a capillary vessel as to give a false impression of a tubular structure. These cells possess a finely granular or retic- ular cytoplasm and a central spheroidal nucleus. It is supposed * Arch. f. Physiol., 1883. f Kolliker's Handbuch 1902, Bd. iii, S. 250. % Johns Hop. Hosp. Bull., 1900. ISLANDS OF LANGERHANS 319 that they form an internal secretion which enters the blood ves- sels and exerts an influence upon carbohydrate metabolism. Ontogenetically the islands of Langerhans are derived from the tubular acini but are separated therefrom during the third month of fetal life (Pearce). * In the adult they appear to have no connection whatever with the acini. In perfectly impregnated specimens prepared by Dogiel f by the method of Golgi, no secre- FIG. 263. — FROM THE HUMAN PANCREAS. a, acini; ft, is placed above an interlobular duct; c, an island of Langerhans ; a second island, circular in outline, lies near the center of the figure. Hematein and eosin. Photo, x 330. tory capillaries could be demonstrated connecting the cells of the islands with the lumen of the acini. Blood Supply. — The large blood vessels of the pancreas accom- pany the interlobular ducts, but after repeated subdivision these * Amer. J. of Anat., 1903. f Arch. f. Anat., 1893. 320 SALIVAEY GLANDS AND PANCKEAS vessels part company and the smaller arteries pursue a separate course through the interlobular connective tissue. Thus they reach all portions of the gland and supply capillaries to the intra- lobular connective tissue about the acini. Certain arterial branches also enter the islands of Langerhans and form a specially rich plexus of broad capillaries within these cell groups. The veins return by a similar course. The lymphatics are mostly confined to the interlobular tissue, where they are in relation with the blood vessels. The nerves are derived from the sympathetic, and occur as small trunks within the interlobular connective tissue. Numerous small ganglia occur in their course. As in the salivary glands the nerves supply the vascular walls. About the secreting acini they form a delicate network of naked fibrils from which end branches pene- trate the basement membrane and terminate upon the secreting cells. Paciniau corpuscles are occasionally found in the inter- lobular connective tissue of the pancreas. Resum6. — Finally the attention of the student should be speci- ally directed to the presence of the islands of Langerhans, the centro-acinar cells, the very distinct inner and outer zones of the secreting cells, the thick walls of the interlobular ducts, the absence of intralobular ducts except of the intercalary type, and the loose character of the interlobular tissue as the distinguishing characteristics of the pancreas. CHAPTEE XVIII THE LIVER THE liver is the largest secreting gland of the body, and may be classed as a peculiar form of compound tubular gland whose ! FIG. 264. — A LOBULE OF THE PIG'S LIVER; THE CENTRAL VEIN LIES IN THE MIDDLE OF THE FIGURE. a, capsule of Glisson. Hematein and eosin. Photo, x 115. cells resemble the serous secreting type. The organ is invested with a connective tissue sheath the greater portion of which is 22 321 322 THE LIVES clothed with peritoneal epithelium. From this connective tissue capsule, fibrous bands or septa are continued into the substance of the organ and permeate to all its portions. These processes of connective tissue, collectively forming the capsule of Glisson, are most abundant at the transverse fissure, where they contain the large blood vessels and hepatic ducts, this fissure serving as a hilum for the organ. The liver is dependent for its structural peculiarities upon the peculiar disposition of the connective tissue of Glisson's capsule, as also of the blood vessels whose branches it contains, for by these tissues the substance of the liver is extensively subdivided into minute collections of hepatic cells, each group forming an ana- tomical unit, the hepatic lobule, which in addition to the hepatic cells contains a connective tissue reticulum and the smaller blood vessels and secretory capillaries (bile canaliculi). The hepatic lobules are analogous to the lobules of compound tubulo-acinar glands, inasmuch as they contain the secreting parenchyma of the organ, but are very different from the latter in the arrangement of the secreting cells which, in the human liver, do not present either a tubular or acinar structure, but form more solid cell col- umns. Thus in the human d liver the tubular character of the gland is scarcely ap- parent, yet in the liver of many of the lower animals, notably in that of the turtle and frog, the cells form typical tubules within the indistinct hepatic lobules. The bile formed by the liver cells is conveyed to the duodenum by an excretory system, beginning with in- numerable interlobular bile ducts which receive the in- tralobular secretory capil- laries, and, leaving the lobule from all its sides, find their way through the interlobu- lar connective tissue of the capsule of Glisson, unite with their fellows to form larger and larger bile ducts, and finally leave the FIG. 265. — FROM A SECTION OF THE TURTLE'S LIVER, SHOWING THE TUBULAR ARRANGE- MENT OF THE PARENCHYMA. a, blood capillary, partially filled with clotted blood ; ft, vascular endothelium ; c, darkened central portions of the hepatic cells ; d, periph- eral portion of the hepatic cells. Osmium tetroxid; carmin. x 400. (After Shore and Jones.) THE HEPATIC CONNECTIVE TISSUE 323 organ at the hepatic duct, thus reaching the gall bladder and intestine by means of the cystic and common bile ducts. In all their course the bile ducts are in close relation with the radicals of the por- tal vein and of the hepatic artery, the group of vessels forming the so- called portal canals. THE HEPATIC CONNECTIVE TIS- SUE.— The hepatic connective tissue, or the supporting tis- sue of the liver, in- a- cludes the capsule of the organ and the capsule of Glisson, —the latter form- ing a framework throughout the liver and inclosing its hexagonal lobules — together with the more delicate intralobular reticulum. These tissues convey the blood vessels, lymphatics, nerves, and bile ducts. The fibrous framework, which forms both the outer fibrous capsule of the liver and the capsule of Glisson, contains both fibrous and elastic tissue, the latter being FIG. 266. — THE RETICULUM OF THE DOG'S LIVER. a, central vein ; 6, capsule of Glisson at the margin of the lobule. Gold chlorid. x 120. (After Bohm and von Davidoff.) FIG. 267.— STELLATE CELLS OF VON KUPFEB fairly abundant, a fact which IN THE LIVER OF A DOG. sharply contrasts with the <7, capillary blood vessel; J, hepatic cells; complete absence of elastic st, stellate cells. Goldchlorid. x 200. (After „, ,, . , . , Koiiiker.) fibres from the interior of the hepatic lobules. The intralobular connective tissue is extremely delicate, and consists of very fine Jjbrils an(L stellate cells (von Kupfer) which form a delicate reticulum in which the capillary blood vessels and 324 THE LIVER columns of liver cells are suspended. The anastomosing strands of reticulum converge from the periphery toward the center of the lobule, thus following the course of the blood capillaries and cell columns. This reticular tissue (Mall) exists in so small a quantity and is so extremely delicate that although it can be readily studied after removal of the liver cells, as by artificial digestion, in ordinary preparations, except those of extreme thin- ness, it can scarcely be discovered in the minute clefts between the cell columns and the blood capillaries. The volume of the interlobular connective tissue which forms Glisson's capsule varies greatly in different animals. In the liver of the pig this tissue is very extensive and forms a complete investment for each lobule. In man it is very limited in amount and is confined to minute areas between the .adjacent angles of the lobules, with an occasional fragment separating the lateral surfaces of neighboring lobules. It is in the latter portions, viz., between the opposed surfaces of the lobules, that the branches of the hepatic veins (sublobular veins) are found. The interlobular veins, the subdivisions of the portal vein, together with the bile ducts and the branches of the hepatic artery are found at the angles of adjacent lobules ; hence the portal canals, which contain these vessels, should always be sought in this location, while the sublobular veins, which run alone and form no part of the portal canals, will be found between the opposed surfaces of the lobules. The capsule of Glisson also contains many lymphatic vessels and non-medullated nerve fibres. THE HEPATIC LOBULE.— The lobule is the structural unit of the liver and consists chiefly of hepatic cells which are arranged in radiating columns. In shape the lobule is an irregularly hex- agonal pyramid, the exact number of its faces being extremely variable. The periphery of the lobule is outlined by the connect- ive tissue of Glisson's capsule which either completely invests each lobule, as in the pig's liver, or forms only a very incomplete investment, as in the liver of man. Blood enters the lobule from the vessels of the portal canals and finds its way, through converging capillaries, from the periph- ery to the center of the lobule. Here it enters the intralobular or central vein, which occupies the axis of the lobule and conveys the blood thence to the sublobular veins, which again lie in the interlobular connective tissue of Glisson's capsule. THE HEPATIC LOBULE 325 The hepatic cells occupy the meshes of the intralobular capil- laries and are arranged in columns which radiate from the central vein toward the periphery. The frequent anastomoses of the capillaries as they approach the central vein produce great irregu- larities in the arrangement and length of the cell columns. Each FIG. 268. — A LOBULE OF THE PIG'S LIVER IN LONGITUDINAL SECTION, SHOWING THE RELATION OF THE CENTRAL AND SUBLOBULAR VEINS AND THE ARRANGEMENT OF THE HEPATIC CELLS. a, sublobular vein ; J, capsule of Glisson. Hematein and eosin. Photo, x 68. column, however, reaches the periphery of the lobule after a more or less tortuous course, and it is here that the secretory bile capil- laries, which are found within the cell columns, become continu- ous with the minute bile ducts of the portal canals. The bile capillaries occur as secretory canaliculi between the opposed surfaces of the hepatic cells. They are thus found with- 326 THE LIVER in the cell columns and stand in the same relation to the hepatic cells as though each cell column formed a tubule whose capillary lumen, the bile canaliculus, was surrounded by only two secreting cells, whereas in other tubular glands a larger number of cells encircle the lumen of the secreting tubule. Hence the bile capil- laries and the blood capillaries are never in contact, but are always separated by at least one-third to one-half the diameter of a hepatic FIG. 269. — A LOBULE OF THE HUMAN LIVER, SEEN IN TRANSECTION. It is outlined by three small portal canals and contains a single central vein. Ilematein and eosin. Photo, x 50. cell. The bile capillary occurs on that surface of the hepatic cell which is in contact with other cells within the column; the blood j capillary, on the other hand, is in relation with that surface of! the hepatic cell which forms the periphery of the cell column. The blood capillaries are suspended in the fine meshes of the delicate reticulum which has already been described as the intra- lobular connective tissue, and which also invests the columns of hepatic cells. This connective tissue is of relatively insignificant volume. THE HEPATIC LOBULE 327 The bile capillaries are true secretory canaliculi by which the bile, after secretion by the hepatic cells, finds its way along the b jv?-rvV ^ • sST'^' a ^Wfe-? V£W^&Wv £? V? ^K^^- r^^>/ 'i ~Vt> ' ^ -^ K K ' S?S\V ^^ ~^ f 'ft 1 ^5>VA FIG. 270. — BILE CAPILLARIES OF THE HEPATIC LOBULE, FROM THE LIVER OF A CAT. a, a portal canal ; 6, a small interlobular bile duct. Golgi's stain and hematein. Moder- ately magnified. (After Geberg.) anastomosing cell columns to some point at the periphery of the lobule, where the cell column becomes continuous with a minute bile duct, the secreting cells within the lobule presenting a rapid Fio. 271. — SHOWING THE CONNECTION BETWEEN THE INTRALOBULAR AND INTERLOBULAR BILE DUCTS IN THE CAT'S LIVER. a, interlobular vein; 6, interlobular bile duct; c, intralobular bile capillaries. Golgi stain and hematein. Highly magnified. (After Geberg.) 328 THE LIVEE transition to the very low columnar or flattened epithelium of the interlobular bile duct. THE HEPATIC CELLS.— These are large polyhedral cells which possess one, or very frequently two, spherical nuclei and a coarsely granular cytoplasm. A true cell membrane may be regarded as being absent, yet there is often a sharply defined exoplasm which forms the surface of the cell and simulates a true membrane. The nuclei of the hepatic cells are rich in chromatin, and stain deeply. They are situated well within the cell, but usually in an eccentric position. Frequently they contain a distinct nucleolus. The cytoplasm of the hepatic cell is finely reticular, the meshes being filled with coarse granules of irregular size. Many of these are undoubtedly glycogenic gran- ules, and show a decided reaction when acted upon by Lugol's solu- tion of iodin after alcoholic fixa- tion. The amount of glycogen present varies with the diet. After digestion and absorption of a carbohydrate meal it is greatly increased, but disappears during fasting. Even when glycogen is quite deficient, the hepatic cells still present a granular appearance from the presence of other substances, possibly zymogens. Fat globules occur in the hepatic cells in limited numbers, and appear to be a normal constituent. The globules vary much in size, but are all very small. Their number is also dependent upon diet and digestion. During absorption of a fatty meal, fat globules occur in considerable numbers, and are most numerous in those hepatic cells which are at the periphery of the lobule. They are not normally found in the vicinity of the central vein. The hepatic cells also frequently contain brown or yellowish- brown granules of ferruginous pigment, which are more prone to occur in the interior of the lobule near the central vein. When present in considerable amount this pigment can no longer be considered a normal constituent of the hepatic cell. THE PORTAL CANALS.— The portal canals are formed by the ramifications of the portal vein, hepatic artery, and hepatic FIG. 272. — TYPES OF CELLS FROM A SEC- TION OF THE NORMAL HUMAN LIVER. A, the usual type of liver cell; B, fatty, and C, pigmented cells. Types B and C were very scarce. Hematein and eosin. x 900. THE PORTAL CAXALS 329 duct, and are characteristic of the liver, the peculiarity consisting not so much in the structure of the tissue, as in the combination of artery, duct, and vein occurring in close relation, in the connect- ive tissue at the angles of the hepatic lobules. The largest vessel in the canal is invariably the vein, the smallest the artery. The Interlobular Veins, branches of the portal, are extremely thin-walled vessels. They are formed by scarcely more than the endothelial lining, which is supported by the connective tissue of Glisson's capsule. Their wall contains very little or no smooth muscle. The Interlobular Arteries, branches of the hepatic, are very small and are noted for their highly developed muscular coat and distinct elastic membrane. They give off minute vaginal branches which supply capillaries to the tissue of Glisson's capsule. * - .-,-* V - " ^ »^ FIG. 273. — A PORTAL CANAL OF THE HUMAN LIVER. The large thin- walled vessel in the center of the connective tissue is the interlobular vein ; at its left are two ducts in oblique and longitudinal section ; at the right of the vein, a duct and an artery are seen in transection. Hematein and eosin. Photo, x 375. The Interlobular Ducts, radicals of the hepatic duct, receive the bile from the intralobular bile canaliculi and convey it, through larger and larger branches, to the hepatic duct. They are more numerous than the interlobular veins and much more numerous 330 THE LIVER than the interlobular arteries. The ducts are lined by columnar epithelium whose height varies with the size of the tubule, the smallest ducts being lined by low columnar or cuboidal, the largest by tall columnar cells ; the lining epithelium of the hepatic and common bile ducts is very tall. The epithelial cells of the ducts possess characteristic spherical or ovoid nuclei which are heavily loaded with chromatin. Their cytoplasm is clear or finely reticu- lar. The largest ducts contain a few goblet cells ; small mucous glands are found in the hepatic and common bile duct. The epithelium of the interlobular bile ducts rests upon a thin basement membrane, which is surrounded by a thick fibro- elastic coat. The larger ducts are also supplied with circular smooth muscle fibres, which, in the largest branches, form a con- siderable coat (Fig. 239, page 293). Outside of the liver longitu- dinal muscle fibres also appear in the walls of the excretory ducts, and so accumulate in the wall of the gall bladder and common bile duct as often to form a distinct layer. BLOOD SUPPLY. — The liver is supplied with blood from two independent sources, the hepatic artery and the portal vein. That supplied by the artery is of minor importance and is destined only for the nutrition of the connective tissue framework of the organ. On entering the liver at the transverse fissure the hepatic artery gives off numerous capsular branches which ramify in the capsule of the liver and supply capillaries to its connective tissue. Other branches, the direct continuation of the hepatic artery, enter the portal canals and by repeated division form the inter- lobular arteries, which ramify in the tissue of Glisson's capsule, and whose vaginal branches supply capillaries to this connective tissue. These capillaries, as well as those from the capsular branches, become continuous, at the periphery of the lobule, with the intralobular capillaries which are derived from the branches of the portal vein. The Portal Vein likewise enters at the transverse fissure, bring- ing to the liver the blood collected from the capillaries of the organs of digestion and absorption. It divides into numerous branches which follow the portal canals, in which they are known as the interlobular veins, and in this way reach all portions of the organ. The interlobular veins throughout all their course give off small branches which at once enter the periphery of the hepatic lobules and immediately break into a brush of capillary vessels. BLOOD SUPPLY 331 These intralobular capillaries converge toward the center of the lobule and anastomose to form a capillary network, in the elon- gated meshes of which are the columns of hepatic cells. These capillaries approach the center of the lohule where they unite to form the intralobular or central vein. The central vein frequently FIG. 274. — FROM A SECTION OF THE BABBIT'S LIVER WHOSE BLOOD VESSELS HAD BEEN INJECTED WITH A GELATINOUS, CARMIN STAINED, MASS ; SOMEWHAT MORE THAN A SINGLE LOBULE IS REPRESENTED. a, interlobular veins; 6, central vein ; c, central vein from which the injection mass had fallen out ; the capillaries are dark. Photo, x 70. begins in the form of a Y, its two or more branches finally uniting to form a single vessel which pursues its course through the axis of the lobule. The central vein makes its exit at the periphery of the lobule and enters the interlobular connective tissue where it unites with its fellows to form larger sullobular veins. The sub- 332 THE LIVER lobular are easily distinguished from the interlobular veins by their thicker walls and by the fact that the former pursue an independent course through the tissue of Glisson's capsule, being nowhere in relation with either artery or duct. The sublobular veins are, as a rule, vessels of considerable size, and by frequent union with their fellows become constantly larger. In their general direction they tend toward the dorsal surface of the liver and finally make their exit as four or five large hepatic veins which enter the inferior vena cava. FlG. 275. — A SUBLOBULAR VEIN OF THE Fid's LIVER. a, capsule of Glisson between adjacent lobules. Hematein and eosin. Photo, x 60. The blood supply of the liver is peculiar in that: 1, the greater portion of its blood has already passed through the capil- laries of the digestive organs before entering the liver; 2, its arterial supply is extremely insignificant, and supplies only the connective tissue framework, intermingling with the portal blood at the periphery of the lobule ; 3, its intralobular capillaries are extremely abundant and are in intimate relation with the hepatic cells, each cell coming into contact with four to six capillary vessels. NERVES 333 The course of the blood through the vessels of the liver will be readily appreciated by reference to the following table which indi- cates the succession of the hepatic blood-vessels : 1. Portal vein. 1. Hepatic artery. 2. Interlobular veins. 2. Interlobular arteries. 3. Branches to lobule. 3. Vaginal branches and capil- laries in Glisson's capsule. 4. Intralobular capillaries. 5. Central vein (intralobular). 6. Sublobular veins. 7. Hepatic veins. 8. Vena cava inferior. The three classes of veins, interlobular, central, and sublobular are readily differentiated by the fact that the two latter lie alone, while the interlobular veins are always in company with ducts or arteries within the portal canals. Moreover the central vein has almost no connective tissue wall until near its exit from the lob- ule where it passes into the sublobular branches ; the sublobular veins, on the other hand, possess a relatively thick connective tissue wall and even some smooth muscle, except in the very smallest, which are to be regarded as mere interlobular continua- tions of central veins which soon unite to form the larger sublob- ular vessels. LYMPHATICS. — The lymphatics of the liver may be consid- ered as consisting of a superficial set which supplies the hepatic peritoneum and the capsule of the liver, and which is continuous with a deeper set in Glisson's capsule. The lymphatics of the deep set begin as perivascular spaces within the lobule, from which the lymph enters larger lymphatic vessels in the interlobular connective tissue, which follow the vessels of the portal canals to their exit from the liver; the larger lymphatics pass to the ab- Fl»- 276.— INTRALOBULAR dominal lymphatic glands. Other lymphat- RABBIT'S*" ics follow the sublobular and hepatic veins a? hepatic cells ; J, and pass to the mediastinal lymphatic glands, nerve fibre. Goigi stain. NERVES.— The nerves of the liver are JSSidSlf" (Af" mostly of the non-medullated variety. They follow the portal canals and are distributed to the walls of the blood vessels, the walls of the bile ducts, and to the capsule of the 334 THE LIYEE liver. Naked fibrils from these trunks also enter the lobules and form a plexus among the hepatic cells (Korolkow*) in relation with which they form fine terminal brushes and varicose end knobs (Berkley!). THE GALL BLADDEK The wall of the gall bladder consists of three coats : 1, mucous ; 2, muscular ; 3, fibro-serous. The mucous membrane is markedly folded or corrugated, the irregularly polygonal depressions being relatively broad at the fundus but becoming narrower toward the neck of the organ. The lining epithelium is of the tall columnar variety, with spheroidal or ovoid nuclei which lie near the base of b FIG. 277.— FROM A SECTION THROUGH THE WALL OF A DOG'S GALL BLADDER. a, epithelium ; i, lymphatic nodule ; 0, serous coat, x 80. (After Sudler.) the cell. The free extremity of the epithelial ce]ls presents an indistinct cuticular border. The epithelium follows all the folds of the mucosa and lines the intervening depressions. The corium of the mucosa consists of delicate connective tissue and contains a few smooth muscle fibres derived from the mus- cular coat. It is connected with the muscularis by a thin layer of denser connective tissue which contains blood and lymphatic vessels and which simulates a submucosa. The gall bladder possesses a distinct muscular wall, consisting of numerous interlacing smooth muscle bundles the most of which *Anat. Anz., 1893. f Johns Hop. Hosp. Rep., 1895. THE GALL BLADDER 335 are circularly disposed. Occasionally they form fairly distinct cir- cular and longitudinal layers. The fibro-serous coat consists of loose areolar tissue, which con- tains the larger blood vessels with which the organ is abundantly supplied. The free surface of the gall bladder also receives a peritoneal investment. FIG. 278. — KECONSTRUCTION OF THE WALL OF A DOG'S GALL BLADDER. a, vein ; 6, artery ; c, lymphatic vessel ; d, epithelium, x 60. (After Sudler.) Occasional mucous glands occur in the mucosa of the gall bladder. These are mostly of small size and widely separated, but toward the neck of the organ they increase in both number and size. They form short, branched, convoluted tubules. The blood vessels form a plexus just outside the muscular coat, from which branches are distributed to the peritoneal coat and to a plexus in the depth of the mucosa from which capillaries are supplied to the muscular layers and to a subepithelial plexus. The nerves are distributed to the blood vessels and to the mus- cular wall. Minute ganglia occur in the muscular coat. ': CHAPTER XIX THE URINARY SYSTEM THIS system includes the kidneys, which are two large secret- ing glands, together with their excretory passages, the ureters, which conduct the urine to the urinary bladder, whence it is voided through the urethra. THE KIDNEY Each kidney is a large secreting gland of the compound tubu- lar type. Its secretion, the urine, is produced by the uriniferous tubules, which are long tortuous canals beginning near the surface of the kidney and finally ending at the hilum of the organ where they pour their secretion into the calyces of the renal pelvis. The uriniferous tubules are in intimate relation with the renal blood- vessels which supply rich capillary plexuses to the entire extent of the tubules. Each uriniferous tubule consists of both tortuous and straight portions, and these are so regularly disposed as to produce macroscopical variations in the appearance of the differ- ent portions of the renal parenchyma according as the tortuous or the straight portions of the tubules predominate. These varia- tions result in the following topographical subdivisions. TOPOGRAPHY OF THE KIDNEY (Figs. 288 and 290).— If the kidney be divided parallel to its long axis by an incision extending from its convex surface to the hilum, the cut surface shows that the parenchyma is divisible into a superficial cortex and a central medulla. The hilum of the organ forms a deep excavation which is occupied by the renal pelvis and its subdivisions, the infundiv- ula and calyces, into which the medulla projects in the form of several conical pyramids. The pelvis of the kidney, the expanded funnelform beginning of the ureter, toward the renal parenchyma divides into two or three infundibula, which in turn subdivide into several calyces, each of which incloses the conical apex of a projecting medullary or Malpighian pyramid. TOPOGRAPHY OF THE KIDNEY 337 The Medulla of the kidney consists of a number of these coni- cal Malpighian pyramids (usually twelve to fifteen) each of whose apices, as already stated, is received into the extremity of a renal calyx. The base of each Malpighian pyramid is embedded in the adjacent renal cortex, and that portion of the cortex which is interposed between the bases of adjacent pyramids, and thus brought into relation with the fibrous and adipose tissue which envelopes the pelvis and calyces at the hilum of the organ, com- poses the cortical columns of Bertini. Each Malpighian pyramid may be subdivided into a central free portion, the apical or papillary zone of the medulla, which is received into a calyx, and an outer or basal portion, which is embedded in the renal cortex and is known as the boundary zone of the medulla. These two portions of the medulla, the papillary and boundary zones, can be readily distinguished, since the latter con- tains only narrow tubules and is highly vascular, while the former, relatively deficient in blood vessels, contains the broad termina- tions of the uriniferous tubules, the so-called ducts of Bellini, which converge toward the apex of the Malpighian pyramid where they open into the calyces. The Cortex of the kidney, on careful observation, presents numerous dark lines or delicate columns which radiate from the base of the Malpighian pyramids outward toward the surface of the organ. These radiating columns are the medullary rays * (pyra- mids of Ferrein). They contain straight portions of the urinife- rous tubules, only these are continuous with the similar tubules in the boundary zone of the medulla. That portion of the cortex which invests the medullary rays, and which includes all the remaining cortical portions of the organ, consists of extremely tortuous tubules, and is characterized by the presence of small globular bodies, each of which contains a tuft of capillary vessels. These are the Malpighian bodies (renal corpuscles) which are characteristic of the kidney. The portion of the cortex in which they occur includes the entire cortical sub- stance with the exception of the medullary rays, and is known as the TQ^^Jab^rinth. The labyrinth is subdivided into : 1, the columns of Bertini, already mentioned ; 2, the intercolumnar * These columns lie within the cortex and not, as their name might be taken to indicate, in the medulla. They are termed medullary rays because of their peculiar relation to the medulla, from which they extend outward in a radial direction. 338 THE URINARY SYSTEM portions, oT^labyrinth proper, which include that portion of the labyrinth which invests the medullary rays, and which, in sections cut parallel to these columns (longitudinal sections) appears as a portion of cortex inserted between the adjacent medullary rays ; 3, a narrow boundary zone of the cortex, " cortex corticis" of Hyrtl, which is included between the fibrous capsule of the organ and the tips of the medul- lary rays, and in which 10 the Malpighian bodies, though present, are rela- tively few in number. The Renal Lobule.— In fetal and infantile life the kidney is distinctly lobulated. This condition is permanent in some ani- mals, each lobe consisting of a Malpighian pyramid with its related portion of cortical substance. In man, after the first year, the renal lobes completely fuse and eventually leave scarcely a trace of the early lobar con- dition. The term renal lobule or a \ \\\\\iiuiiiii///y reniculus, as applied to the adult human kidney, refers to a still smaller subdivi- sion of the organ, one which includes a single medul- lary ray together with that medulla ; c, cortex ; 1, apex of a Malpighian pyra- portion of the Cortical laby- mid ; #, capsule ; •/.*! .*< '\\w %-v ^4 « •*»••, ;-:\< • -•.:*{"--t:^ ^.- • • w ^^ ^ % ^^ Vsi^'%/ ^fii ^iV^S**.*'^ •^tvicfiv^S^w Fio. 286. — FROM THE CORTEX OF THE HUMAN KIDNEY; A MEDULLARY RAY IN OBLIQUE SECTION. a, labyrinth ; ft, spiral tubule ; c, c, collecting tubules ; .->• * TT i > .L t, i THE MEDULLA 1 Ascending limb of Henle's tubule. 1UJS IVliiDULLiA I CM • i L IT j.- ±' ( Straight collecting portion. f Descending limb of Henle's tubule. PAPILLARY ZONE OF J Loop of Henle's tubule. THE MEDULLA ] Straight collecting portion. [ Duct of Bellini. 352 THE URINARY SYSTEM The following tabular resume may be of service by emphasizing the more important peculiarities of the several portions of the uri- niferous tubule. PORTION OF TUBULE. EPITHELIUM. LOCATION. Malpighian body. Flattened, endothelial. Cortical labyrinth. Neck. Changing from flattened Cortical labyrinth. to low columnar. Proximal convoluted. Low columnar, granular, Cortical labyrinth. and rodded. Spiral portion of above. Low columnar, granular, Medullary rays of cortex. and rodded. Descending limb. Low cuboidal or flat- Medulla (boundary and Loop. tened, granular. Varies ; like either the papillary zones). Medulla (boundary and ».-. preceding or following. papillary zones). Ascending limb. Cuboidal or low colum- Boundary zone of me- nar, granular, imbri- dulla and medullary cated. rays of cortex. Distal convoluted. Low columnar or pyram- Cortical labyrinth. idal, granular, and rodded. Arched collecting. Cuboidal, clear cyto- Cortical labyrinth. plasm, dark nucleus. Straight collecting. Cuboidal, changing to Medullary rays of cortex, columnar. and both zones of me- dulla. Duct of Bellini. Cuboidal, tall columnar. Papillary zoneof medulla. BLOOD SUPPLY. — The kidney receives its blood supply from the renal artery, which, as it enters the hilum, divides into two sets of principal branches, of which the ventral set supply one-fourth, the dorsal set three-fourths of the renal substance. These princi- pal branches, the arterice proprice renales, are embedded in the connective tissue of the hilum and follow the walls of the infundi- bula and calyces, upon which they lie, thus reaching the columns of Bertini between the renal calyces. Here they enter the cortical substance and divide, each branch passing in a curved or arched manner beneath the base of the adjacent Malpighian pyramids. These vessels form an incomplete arterial arcade which lies in the margin of the cortex at the outer border of the medullary bound- ary zone. From the arterial arcade, branches are given to the medullary tissue of the Malpighian pyramids on the one hand, and on the other to the cortical substance. Those branches which enter the medulla are slender vessels which pursue a characteristically straight course between the parallel tubules of this region and are THE PEMS 369 axis of the corpus spongiosum from its bulb forward to the urinary meatus at the tip of the glans penis. This canal has already been sufficiently described in the preceding chapter. The skin of the glans penis is peculiar in the relatively moist character of its epidermis and the consequent imperfect develop- ment of its superficial horny layer. Its dermal papillae are con- spicuously developed. In the region of the corona the derma contains a ring of large sebaceous glands, the glands of Tyson, which open on the free epithelial surface. Their secretion forms the smegma, a peculiarly odoriferous sebum. •— FIG. 299. — THE ERECTILE TISSUE OF THE PENIS. c r, peripheral capillary plexus ; t a, tunica albuginea ; v s, venous spaces ; s, bands of smooth muscle and vascular connective tissue, x 30. (After Kolliker.) The nerves of the penis are abundantly supplied with special nerve end organs. In the skin they form free varicose endings among the epithelial cells, and are connected with tactile corpus- cles of Meissner in the dermal papillae. Deeper in the skin are many end bulbs of Krause, while still deeper are the peculiar genital corpuscles. Pacinian corpuscles are also found in the loose connective tissue and in the tunica albuginea of the corpora cavernosa. Nerve fibres are abundantly supplied to the walls of the blood vessels. 25 370 THE MALE REPRODUCTIVE ORGANS The lymphatics of the penis form an abundant superficial set in the subcutaneous tissue ; these follow the larger blood vessels and empty into the inguinal lymphatic glands. A less abundant deep set of lymphatics in the erectile tissue, also, accompanies the blood vessels of these parts, but are distributed to the pelvic lym- phatic glands. THE SEMEN AND SPERMATOZOA The essential constituent of the semen is the spermatozoon (spermatosome, spermatozo'id), a body which is developed in the seminiferous tubules of the testes by the metamorphosis of the I I FIG. 300.— HUMAN SEMEN. Hematein and eosin. Photo, x 850. cells of the lining epithelium. They are very numerous, a cubic millimeter of semen being said to contain as many as 60,876 sper- matozoa (Lode*). In addition to the spermatozoa the semen * Arch, f . Anat. u. Physiol., 1896. THE SEMEN AND SPEEMATOZOA 371 contains the fluid secretions of the accessory genital glands and many coarse protoplasmic seminal granules. When first formed the spermatozoa are motionless, but when the secretion of the testes is diluted with the secretions of the seminal vesicles and prostate they become very active and re- tain their motility for a long time even under the most unfavorable conditions. The spermatozoa are flagellate bodies which consist of a head, a middle piece, and a tail. Each of these subdivisions is a composite structure. The head of the human spermatozoon is an ovoid body about 4.5 to 5 ^ long, 3 to 3.5 /x, broad, and 0.5 to 1 ^ thick. When seen " on the flat " (surface view) its outline is oval but when viewed in profile it has a pyriform shape. It is united to the middle piece by a slight- ly constricted neck and its anterior ex- tremity forms a blunt point analogous to the " lance " of the spermatosomes of cer- tain of the lower vertebrates. The head of the human spermatozoon consists of two distinct portions, a posterior solid mass of chromatin which stains deeply with nuclear dyes, and an anterior clear portion or head cap. This head cap in some of the mammalian species contains a rounded chromatic body, the acrosome. At the posterior pole of the nuclear chromatin, where it joins the middle piece, is a small dark dot, the inner centrosome, from which the axial filament, beginning with a minute end knob, is continued backward through the mid- dle and tail pieces and is inclosed by a dedicate cytoplasmic en- velope. At the tip of the tail piece the axial fibre is no longer surrounded by cytoplasm but projects as a naked end piece. The flagellum varies in diameter from a breadth of about 1 /*. in the middle piece, to the immeasurably delicate end piece ; in length it is about 45 to 50 //,. In the spermatozoa of the lower animals still other structures may be demonstated in the flagellum, chief among which are (1) FIG. 301. — SPERMATOSOMES FROM THE SEMEN OF MAN. A, usual type ; 5, " giant " double spermatozoon. Hem- atein and eosiii. x 1200. 372 THE MALE REPRODUCTIVE ORGANS the spiral cytoplasmic fin of the flattened spermatozoa of amphib- ians, whose border contains a second filament, the marginal fibre ; (2) the faintly chromatic ring or spiral which sometimes occurs near the posterior end of the middle piece or entwined about its axial filament. These structures have not, however, been demon- strated in the spermatosomes of man. The spermatozoa may be regarded as metamorphosed germ cells which arise by the direct transformation of the spermatids in the seminiferous tubules of the testicle. As a result of this transformation, so far as has been satisfactorily demonstrated, the nu- cleus of the spermatid becomes the chromatic body or nucleus of the spermatozoon : the centrosome of the spermatid, usually double, enters the middle piece, the inner centrosome forming the end knob of the axial filament, the outer centrosome either forming the ring body of the middle piece or, like the inner, entering into the formation of the end knob and axial filament ; the arcoplasm (attraction sphere, idiosome of Meves) leaves the centro- somes of the spermatid and in part at least wanders around the nucleus to the opposite pole where it forms the acrosome, the re- mainder of the arcoplasm probably entering into the formation of the cytoplasmic por- tion of the middle piece : the axial filament arises under the influence of the centrosomes (Meves*) or possibly by the direct trans- formation of the outer of these bodies (Korff,f Suzuki I) : and finally, the envelope of the tail piece, and probably also that of the middle piece, arises by the direct transformation of a part of the cytoplasm of the sperma- tid; the remaining portion of the cytoplasm of the spermatid does not enter into the structure of the spermatozoon but is sepa- rately cast off and degenerates. FIG. 302. — SPERMATOZOA OF VARIOUS ANIMALS. A, from the badger; 5, from the bat. Eedrawh after Ballowitz. x 1200. (7, from the rat. Hema- tein andeosin. 'x 1200. Arch. f. inik. Anat., 1897. f Ibid., 1899. \ Anat. Anz., 1898. THE TESTIS 373 THE TESTIS (Testicle) Each testis is inclosed within a serous sac, its tunica vaginalis, whose visceral layer is closely applied to the organ. Its parietal layer forms a lining membrane for the scrotum, within which the testicle is suspended. The tunica vaginalis is developed as an invagination of the peritoneum and is a true serous membrane. Its visceral endothelium rests upon a dense connective tissue layer, the tunica albuginea, which serves as a capsule for the organ. The deep surface of the membrane contains many blood vessels which are held in place by a somewhat looser type of connective tissue ; hence this innermost coat is frequently termed the tunica vasculosa testis. At the posterior border of the testis its connective tissue cap- sule presents a considerable thickening which indents the organ Ductus deferens Lobuli epididymidis-c Ductuli efferentes testis Ductus epi- didymidis ^Ductulus aberrans (superior) Corpus epi- didymidis 'Ductulus aberrans (inferior) FIG. 303. — THE TESTICLE WITH ITS SYSTEM or EFFERENT PASSAGES. Natural size. (After Toldt.) and extends well into its interior to form the mediastinum testis or body of Highmore, in which are the ducts of the rete testis. From the mediastinum testis fibrous septa radiate in all directions to become continuous at the surface of the organ with the con- nective tissue of the tunica albuginea. Thus the organ is sub- 374 THE MALE KEPKODUCTIVE ORGANS divided into a number of pyramidal lobules whose bases rest upon the capsule and whose apices are directed toward the mediastinum. Each of these lobules contains numerous seminiferous tubules which are tortuous throughout the greater part of their course, FIG. 304. — TORTUOUS SEMINIFEROUS TUBULES OF THE RABBIT'S TESTIS. Hematein and eosin. Photo, x 214. but become straight, tubuli recti, toward the apex of the lobule, where they enter the mediastinum to become continuous with the canals of the rete testis. The seminiferous tubules are invested with a delicate con- nective tissue which forms an intralobular framework. This THE TESTIS 375 interstitial tissue is characterized by the presence of many pecul- iar ovoid interstitial cells of large size, whose significance is not yet determined. They contain a large nucleus which has a distinct nuclear membrane, a reticular chromatin network, and many karyosmes. Their cytoplasm is reticular and finely vacuolated. The seminiferous tubules begin at the periphery of the organ with either a blind extremity or very frequently a peripheral loop formed by the anastomosis of adjacent tubes. They pursue their way through the lobule in an extremely tortuous manner (tortuous or serpentine tubule), and finally near the apex of the lobule become relatively straight (tubuli recti). They then enter the mediastinum and by frequent anastomoses form the rete testis. The tortuous portion of the seminiferous tubule is relatively long, its straight portion very short. It is the former which is of the greater physiological importance and which is to be considered as the true seminiferous tubule, for it is here that the spermatozoa, the essential elements of the semen, are produced. The straight tubules mark the beginning of a system of excretory ducts which include the ductuli efferentes, epididymis, vas deferens, ejactula- tory duct, and urethra. The tortuous seminiferous tubules are lined by a peculiar form of epithelium, which, since it consists of several layers of sphe- roidal cells, might be described as a stratified spheroidal type. The tubule is invested by a very delicate tunica propria upon whose homogeneous basement membrane the epithelium rests. The cells of the lining epithelium are divisible into three types, which are from without inward : 1, a single layer of small cuboidal spermatogonia ; 2, one or two rows of very large sperma- tocytes ; 3, and three to five rows of spheroidal spermatids. Besides these a fourth type of cell occurs at fairly regular intervals in the circumference of the tubule ; these are the so-called Sertoli's cells. These last cells are of columnar form, rest upon the membrana propria and extend inward for a variable distance, sometimes penetrating as far as the innermost cell layers. The developing spermatozoa are, at a certain stage, intimately united with the central ends of the Sertoli cells, the resulting group — a supporting cell of Sertoli with its attached spermatozoa — forming the so- called spermatoblasts * of von Ebner \. * Much confusion has arisen through the use of this term by certain authors as synonymous with the term spermatid. f Untersuch. a. d. Inst. f. Physiol. u. Hist., Graz., 1871. 376 THE MALE REPRODUCTIVE OBGAKS The four types of epithelial cells enumerated ahove may also be con- sidered as typifying the four prin- cipal stages in the origin and develop- ment of the spermatozoa. Spermato- genesis begins with the spermatogonia which, by reproduction, differen- tiation, and development, pass suc- cessively through the spermatocyte, spermatid, and spermatoblast stages to finally produce the mature sper- matozoa. In the course of this de- velopment great changes are pro- duced in the character of the lining ^ epithelium, each of the several cell types presenting many intermediate phases (Fig. 305). Hence, in a given lobule of the testis, tubules may be found which present over and over again all of the successive phases of spermatogenesis, and scarcely any two neighboring tubules, nor the suc- cessive portions of a given tubule, will at the same time present the same phases of spermatogenesis. It is estimated that in every 32 mm. of the length of a tortuous tubule the several phases of spermatogenesis are repeated (von Ebner*). The spermatogonia are small cu- boid or spheroidal cells which rest upon the membrana propria. They have an ovoid nucleus, rich in chro- matin, and a small amount of cyto- FIG. 305. — DIAGRAM OF THE SUCCESSIVE STAGES OF SPER- MATOGENESIS IN THE RAT. A-H, the grouping of associated stages ; O-S®, the suc- cessive steps, in numerical order, from the spermatogonia to the discharge of the spermatosomes. (After Kolliker.) * Kolliker's Handbuch, III, 428. THE TESTIS 377 plasm. Their cell outlines are often indistinct. These cells by mitotic division produce two daughter cells, one of which retains the structure and position of the mother cell, the other increases greatly in size and, assuming a more central position, becomes a spermatocyte. The subdivision of the spermatogonium marks the initial phase of spermatogenesis. The spermatocytes, which arise by the division of the sperma- togonia, are large cells. Their cytoplasm is finely granular, their nucleus large, and its rich supply of chromatin is arranged in a more or less skein-like manner. Because of the active mitosis oc- '•&&ffi° :&&£>*; *5.r. v" >^*Jl o *-**-- -->;•• ; r :* ' - . R» . A <§ WS •-* ;V: #^ .*;•>?*'< y. ^sf:, -•'S**-*.^**''' «;-'.'.'., t '" FIG. 306. — SEMINAL TUBULE OF A MAN IN TRANSACTION. a and 6, interstitial cells, the latter containing coarse granules ; c, connective tissue cells ; d, a mast-cell of the connective tissue. Within the tubule, several phases of sper- matogenesis are well shown. Highly magnified. (After Spangaro.) curring in these cells their nuclear membrane is usually absent or indistinct. ' Mitotic figures are frequently observed in the sperma- tocytes. As a rule two divisions, resulting in two generations, occur in these cells ; hence the frequency of the double row of large spermatocytes.. 378 THE MALE REPRODUCTIVE ORGANS Mitotic division of the cells of the second generation or inner row of spermatocytes results in the formation of two spermatids. Hence each spermatocyte of the first order, producing two sper- matocytes of the second generation, ultimately forms four sper- matids, each of which is finally transformed into a spermatozoon. A peculiar fact in connection with this process is that in one of the mitotic divisions of the spermatocyte the chromosomes fail to divide in the ordinary manner, thus producing one-half the usual number of daughter chromosomes. This results in a reduc- tion of the chromosomes during the spermatocyte stage to one- half the number elsewhere characteristic of the species. This " reduction " in the male germ, which is paralleled in the female during the development of the ovum, is of great importance in its relation to the proc- esses of fertilization and maturation of the germ cell. The spermatids formed by the division of the second generation of spermatocytes, are FIG. 307. — THREE PHASES OF SPERMATOGENESIS IN THE SEMINIFEROUS TUBULES OF THE RAT'S TESTICLE. A, the formation of spermatosomes ; 5, discharge of the spermatosomes ; (7, formation of the spermatoblast ; /, fat droplets, blackened by the use of a fixative which contained osmium tetroxid ; fc, fat and stainable granules ; m, basement membrane ; s, spermato- somes ; sc, spermatocytes ; sg, spermatogonia, in mitosis at sg'; sp, spermatids ; St, cells ofSertoli. Saffranin. x 540. (After Kolliker.) THE TESTIS 379 small spheroidal cells with little cytoplasm and large spherical nuclei. Unlike the nucleus of the spermatocytes, that of the spermatid has a well defined nuclear membrane and its chromatin is distributed in irregular karyosomes. Mitosis is at an end ; and each spermatid continues its development by direct transformation into a spermatozoon. At first the spermatids form an innermost group of independent cells ; later they arrange themselves about the extremities of the Sertoli cells to which they become firmly united. In this way they enter into the formation of the sper- matoblast of von Ebner. The Sertoli cells are of large size and irregular columnar form. They possess an ovoid vesicular nucleus with a distinct nuclear wall and prominent nucleolus, but are otherwise poor in chromatin, a fact by which they can usually be distinguished from the neigh- boring cells, all of which are relatively rich in nuclear chromatin. The cytoplasm of the Sertoli cell is finely granular, toward the inner extremity often somewhat fibrillar ; and the base of the cell frequently contains minute fat droplets. When first formed from the primordial cells, which also give rise to the spermatogonia, the Sertoli cells are cuboidal in shape and are relatively low; moreover, the long axis of their ovoid nucleus is nearly parallel to the basement membrane. As development proceeds and they unite with the spermatids to form the spermatoblasts, the Sertoli cells become greatly elongated, and their nucleus revolves until its long axis is nearly at right angles to its former position ; it also becomes more centrally placed. The surface of their cytoplasm is indented by the attached spermatids and often presents short lateral processes by which the cell is placed in relation with a large number of the spermatid cells. As the spermatids develop into spermatozoa the heads of the latter cells become deeply em- bedded in the cytoplasm of the Sertoli cell, which is thus enabled to contribute to the cytoplasm of the spermatosomes. The tail pieces of the latter project centralward into the lumen of the tubule. Finally when the transformation of the group of sperm- atids into a corresponding number of spermatozoa is complete, the newly formed germ cells break away from the Sertoli cell and become free in the lumen of the seminiferous tubule. The spermatids become spermatozoa by a process of direct transformation, the nucleus of the former producing the nucleus, and its cytoplasm the middle and tail pieces of the latter. In this process the nuclear chromatin becomes much condensed and 380 THE MALE KEPKODUCTIVE OKGANS in the spermatozoon it forms a very dense compact mass. At the same time the cytoplasm is at first collected at one pole of the spermatid and then elongated to form the long flagellate tail of the spermatozoon. The middle piece of the spermatozoon seems to arise partly from the attraction sphere and partly from the cytoplasm of the spermatid. The lumen of the seminiferous tubules is occupied by either the fully formed spermatozoa or by the developing tails of such of them as are still attached to the Sertoli cells, together with a scanty fluid secretion in which they are suspended, and numerous particles of granular debris which result from the degeneration of many spermatids which for some reason fail to develop into spermatozoa. TUBULI RECTI At the apex of the testicular lobule the tortuous seminiferous tubules pass into the rete testis of the mediastinum. At this point the tubule becomes straight and is abruptly narrowed. Thus the short straight tubules, tubuli recti, are formed. In the straight tubules the stratified epithelium of the tortuous portions is abruptly exchanged for a very low columnar or flattened type of epithelium with which the Sertoli cells of the tortuous tubules seem to be continuous. The straight tubules are very short and are soon transformed into the irregular anastomosing canals of the rete testis. EETE TESTIS The connective tissue of the mediastinum is permeated by a network of irregular channels of varying diameter which present frequent dilatations and often have the appearance of broad cleft- like spaces. These are the canals of the rete testis which form a dense network of anastomosing channels. On the one hand they receive the straight tubules, and on the other they pass into the ductuli efferentes, which convey the secretion onward to the globus major of the epididymis. The canals of the rete testis are lined by cuboidal or flattened epithelium, which rests upon a delicate basement membrane. This in turn is supported by the connective tissue of the medias- tinum. The broad but irregular lumen of the canals is occupied by the secretion from the seminiferous tubules and contains many spermatozoa. DUCTULI EFFEBENTES 381 FIG. 308. — FROM THE DORSAL SURFACE OF A RABBIT'S TESTIS. a, seminiferous tubules ; 6, mediastinum testis ; c, rete testis ; d!, ductuli efferentes. Hematein and eosin. Photo, x 50. DUCTULI EFFEBENTES As the tubules of the rete testis leave the mediastinum they are abruptly transformed into peculiar efferent ducts, which pass into the globus major of the epididymis and by means of spiral windings form coni- cal masses, coni vasculosi, whose apex projects into the globus major. The epi- thelium of these tubules is peculiar in that it contains two varieties of cells, and in that it is thrown into FlG. 309. — A SMALL PORTION OF THE WALL OF AN EFFERENT DUCTULE OF THE TESTICLE. d, " glands " in longitudinal section ; result- ing from the rupture of the largest Graafian follicles, a phenome- non which marks the climax of the process of ovulation. The stroma of the ovarian cortex is a connective tissue structure which contains relatively few elastic fibres and, except near the medulla, very little if any smooth muscle. It is, however, abun- dantly supplied with connective tissue cells of large size, most of which are ovoid, fusiform, or even considerably elongated in shape. Many of these cells closely simulate smooth muscle on superficial examination, but are readily distinguished by careful study, espe- cially if specimens are prepared by the various differential staining methods. In the vicinity of the Graafian follicles the stroma is specially rich in cellular elements and is otherwise modified to form a con- centric coat for each of these bodies. This coat, the tkeca foUicuU, consists of (a) an outer layer, or tunica externa, composed chiefly of connective tissue whose interlacing bundles are concentrically disposed, (#) an inner layer, tunica interna, which is peculiarly rich in large ovoid cells, and (c) an innermost membrana propria, upon which the epithelial cells of the follicle directly rest. At the surface of the ovary the cortical stroma forms a dense layer of fine connective tissue fibres whose delicate bundles inter- lace in a close-meshed network. This layer, which immediately underlies the germinal epithelium at the surface of the ovarian cortex, is known as the tunica albuginea. It differs greatly in thickness in different mammalian species, in different individuals of the same species, and even in different portions of the same ovary. Its deeper surface blends insensibly with the underlying stroma of the cortex. The general appearance of the ovary varies according to the number, size, and stage of development of its ova and Graafian follicles. At birth the cortex is packed with large numbers of newly formed ova, all of which are in approximately the same stage of development. During childhood the formation of larger follicles goes forward at an unequal rate, some ova rapidly ap- proaching maturity, others apparently remaining almost stationary, THE OVARY 393 and still others undergoing retrograde development, so that at the age of puberty the ovary contains germ cells and follicles in all stages of development. After puberty the ripe follicles succes- sively rupture and result in the formation of many corpora lutea which promptly degenerate, and are finally replaced by dense con- nective tissue in the form of small scar-like masses known as the corpora albicantia. Hence throughout the menstrual epoch the FIG. 320. — FROM THE OVARIAN CORTEX OF AN INFANT, SHOWING MANY OVA WHICH HAVE AS YET SCARCELY DEVELOPED TO EVEN THE EARLY STAGE OF A GRAAFIAN FOLLICLE. The portion above and to the right is near the free surface ; that below and to the left adjoins the medulla. Hematein and eosin. Photo, x 200. ovarian cortex contains many corpora lutea and corpora albicantia in addition to ova and follicles in various earlier stages of develop- ment. It is doubtful, however, if during this period of life new ova are formed within the germinal epithelium, as occurs in in- fancy and childhood as well as during fetal life. After the climac- 396 THE FEMALE KEPKODUCTIVE OKGANS teric the remaining follicles degenerate and the process of ovula- tion gradually ceases. We shall now discuss the structure of the ovum or female germ cell and shall then successively trace its development and matura- tion, the formation of its Graafian follicle, the rupture of the follicle, and the subsequent history of the corpus luteum. THE OVUM. — The ovum is a spherical cell of large size (200 to 300 /x). When fully developed it is surrounded by a thick layer of exoplasm, the zona pellucida, which is probably derived from the cytoplasm of the follicular epithelium by which the ovum is closely invested. The ovum itself consists of a mass of cytoplasm, the vitellus, and a large vesicular nucleus or germinal vesicle, within which is frequently a single prominent nucleolus or germinal spot. The cytoplasm of the mature ovum is inclosed by a very delicate cell membrane, known as the vitaline membrane, which is not demonstrable in the primitive ova of the younger follicles. The cytoplasm of the ovum at first appears finely reticular, but as its development advances a fatty material is deposited within its meshes, usually in the form of minute irregular spheroids, by the accumulation of which the reticular cytoplasm is in great part '-. . replaced by a granulo-fatty mass of faint yellowish color known as deutoplasm. Fre- J| quently this metamorphosis is not quite re complete, a remnant of the original cyto- %*(X-£J--H A plasm persisting beneath the vitaline mem- yV ti brane and in the vicinity of the nucleus. /p Numerous cy toplasmic structures have ! been described in these cells, chief among which are the accessory nucleus (Nebenkerri), FIG. 321.— OVUM, CONTAIN- an(j the yolk nucleus (Dotterlcern). The ac- (D°OTOKERN) TTTHE cessory nuclei, occasionally chromatinic and LEFT AND ABOVE THE therefore basophile, more frequently stain NUCLEUS. with cytoplasmic dyes and are at times at- The peripheral nuclei tached at other times separate from the are derived from the adja- r . cent stroma. iron-herna- true nucleus. The yolk nuclei of mamma- toxyiin. Highly magni- ijan ova most frequently take the form of ^' crescentic masses of lightly staining chroma- tin which partially surround the nucleus, forming a so-called nuclear cap. They are often found in various stages of disintegration, and the fragments may be transported to the peripheral portions of the cytoplasm, or may be irregularly THE OVUM 397 scattered as small round chromatin granules, which occur throughout the cytoplasm. The physiological interpretation of these bodies is uncertain. The nucleus of the ovum is a large spheroidal vesicle, the vol- ume and distribution of whose chromatin is subject to great varia- tion. Chromatin is present in greatest amount during the period of most active cell growth, in which the cytoplasm of the ovum is enormously increased in volume. At this time the nucleus often appears as a solid mass of chromatin. Later the chromatin is diminished in volume, portions of its substance being possibly extruded into the surrounding cytoplasm; the nucleus then acquires a characteristic vesicular appearance. The nuclear membrane is sharply defined and is at most times prominent, except, as in other cells, during "mitosis, a process which marks the final maturation of the germ cell. The nuclear matrix or nuclear sap abounds in the vesicular type of nucleus and the chromatin is scattered in small particles which adhere to the inner surface of the nuclear wall or to the delicate achromatic linin threads. Each ovum as a rule contains a single nucleus (germinal vesicle), though occasionally two nuclei occur. The latter con- dition is presumed to arise either by the fusion of two ova within a single follicle or from incomplete cell division during develop- ment. Each nucleus, during its vesicular stage, usually contains a single nucleolus (germinal spot), which forms a spherical mass of chromatin, situated, like the nucleus itself, eccentrically rather than centrally. The staining properties of the nucleoli vary re- markably. Usually they take the basic (nuclear) dyes to a greater or less depth ; occasionally they exhibit an affinity for the acid (cytoplasmic) dyes ; still other nuclei take a metachromatic or ir- regular tint with the ordinary nuclear stains. Many nuclei even in the absence of mitosis contain no nucleolus. In the development of the ovum from the germinal epithelium, whose cells from their homology with the spermatogonia have been termed oogonia, there occur several mitoses which result in so-called oocytes ; these later develop into the complete ovum. At about the time of its extrusion from the Graafiah follicle a final series of mitoses occur, which distinguish the maturation of the ovum. In this process there is a series of two mitoses which result in the appearance of the polar bodies and produce a reduc- THE FEMALE REPRODUCTIVE ORGANS tion in the number of chromosomes to one-half the number which is characteristic of the somatic cells.* By the first mitosis the FIG. 322. — DIAGRAM OF REDUCTION DURING THE MATURATION OF THE OVUM. A-H, successive stages ; one-half of the cell, only, has been .represented, c, centro- some ; w, cell membrane ; n, nucleus ; pl and p2, polar bodies formed in successive mito- ses ; F, germinal vesicle, which, at F1, has nearly disappeared. The somatic number of chromoses in the diagram is four ; after reduction the germinal number is two. * Body cells as distinct from the germ cells. DEVELOPMENT OF THE GRAAFIAN FOLLICLE 399 cell produces what may be termed a daughter ovum, together with the first polar body, a minute cell of insignificant size. The second mitosis is irregular in that the chromosomes separate without split- ting, one-half going to the second polar body, the other to the mature ovum, thus effecting the reduction of the chromosomes, a deficiency which is compensated for in the event of fertilization by the entry and. fusion of an equal number of chromosomes derived from the male sperm nucleus of the spermatozoon. The second mitosis may or may not be accompanied by mitotic division of the first polar body; in the former case three, in the latter only two polar bodies arise in connection with the process of maturation of the ovum. DEVELOPMENT OF THE GKAAFIAN FOLLICLE The development of the Graafian follicle goes hand in hand with that of the ovum and can be readily followed in ovaries from individuals of different ages, children and adults, the mature fol- SV-H* FIG. 323. — FUOM A SECTION OF THE OVARIAN CORTEX OF A NEW-BOBN KITTEN. jBT, Pfluger's tubes ; Ke, germinal epithelium ; w, mitosis ; Str, ovarian stroma ; Ubt primitive follicles. Moderately magnified. (After Kolliker.) licles and corpora lutea appearing only after puberty. The process begins in the germinal epithelium in which certain cells so increase in size that they may be readily distinguished as future ova. More 400 THE FEMALE REPRODUCTIVE ORGANS frequently, however, the earliest step in the process consists in the growth of solid cell columns from the layer of germinal epi- thelium into the cortical stroma of the ovary. These cell columns are known as P finger's tubes, though, except occasionally at the extreme surface of the organ, they lack a true tubular form and possess no vestige of a lumen. Certain cells in these columns, by their increased size and prominent nucleus, become very early distinguished as the primi- tive ova ; their differentiation is rapidly followed by the constric- tion of the columns, through the activity of the surrounding tissue of the stroma, in such a manner that one, rarely two or more ova, and several undifferentiated epithelial cells are included in each portion whose connection with the layer of germinal epithelium is thus severed. In this way the primitive follicles (egg nests, or Ei- ballen) are formed. In the ovary of the new-born hundreds of such immature follicles occur in all portions of the cortex (Fig. 320). They are also found in large numbers in the ovary of the adult, though it is asserted that during adolescence their forma- tion gradually ceases. Many follicles never go beyond this primary stage of develop- ment, but after a time undergo retrograde metamorphosis either by gradual atrophy or by a process, known as atresia of the fol- licle, in which the chromatolysis in the ovum and its surrounding f ollicular cells is followed by growth and organization of the theca f olliculi, the connective tissue which is thus formed finally replac- ing the atresic follicle. After remaining stationary for a long period, often for years, certain of the primitive follicles enter upon a period of rapid growth. This process first affects the ovum and results in the appearance of the deutoplasm, zona pellucida, and other accessory structures, as already described under the development of the germ cell. Cell multiplication now occurs in the surrounding epithelial cells, so that, instead of the single row of epithelium which surrounds the ovum of the primitive follicle, the ripening follicle soon acquires a layer of follicular epithelium several cells deep. The rapid multiplication of the epithelial cells is soon followed by active secretion, resulting in the formation of a clear fluid by which the cells are more and more separated, and the cytoplasm of adjacent cells is then readily seen to be firmly joined together by numerous delicate processes which may be regarded as intercelr DEVELOPMENT OF THE GKAAFIAN FOLLICLE 401 lular bridges. Similar processes unite the neighboring cells to the zona pellucida which has already formed about the ovum. The accumulation of the fluid liquor folliculi within the fol- licle soon appears to tear apart certain of the epithelial cells, and a fluid-filled space, the antrum folliculi, is thus formed. This space is characteristic of the true Graafian follicle. The epithelial cells are separated by the antrum into two layers : the one, adher- ent to the membrana propria of the follicle, is known as the FIG. 324. — A GRAAFIAN FOLLICLE OF THE HUMAN OVARY. From within outward are seen the germinal spot, germinal vesicle, vitellus, vitelline membrane, zona pellucida, granule cell layer, membrana propria, and theca folliculi. The ovarian stroma forms the border of the figure. Hematein and eosin. Photo, x 575. membrana or stratum granulosum ; the other, adherent to the zona pellucida of the ovum, is designated the discus proligerus. The two layers remain in contact at one point, and as the liquor folliculi increases in volume, the attached discus proligerus with its contained ovum comes to occupy a more and more eccentric position, and the cells of the stratum granulosum, where the two layers are in contact, appear to pile up about the ovum in the form of a hillock, the so-called cumulus oophorus. 27 402 THE FEMALE EEPEODUCTIVE OKGANS The cells of the discus proligerus, which adjoin the zona pellu- cida, become somewhat elongated and in this way they form a radi- ate investment consisting of one or two rows of columnar cells which surround the zona pellucida of the ovum and are known as FIG. 325. — A GRAAFIAN FOLLICLE OF THE HUMAN OVARY, SOMEWHAT MORE ADVANCED THAN THE PRECEDING. The accumulation of liquor folliculi has separated the granular cells into a discus proligerus and a membrana granulosa. The membrana propria is very sharp, aud the theca folliculi is almost divisible into an inner cellular and an outer fibrous layer. Hema- tein and eosin. Photo, x 460. the corona radiata. With the increase of the liquor folliculi the discus proligerus with its contained ovum is soon separated from its attachment to the stratum granulosum and the development of the folliculi is complete. During this period of rapid growth and development the folli- cle has increased in size from a diameter which scarcely exceeded that of its ovum (about 300 /*) to such a size that it occupies DEVELOPMENT OF THE GKAAFIAN FOLLICLE 403 the entire breadth of the ovarian cortex. It is now ready for the final steps in the maturation of its ovum and for the rup- ture of the follicle coincident with the approach of the menstrual period. The forces which lead to the rupture of the follicle are not fully determined. They are undoubtedly varied, and, in addition to the gradual attenuation of the layer of cortical stroma which covers the free surface of the follicle and is known as the stigma, they FlG. 326. — A NEARLY MATURE GRAAFIAN FOLLICLE FROM THE OVARY OF A DOG. a, fibrous, and 6, cellular layer of the theca folliculi ; c, membrana propria ; d, mem- brana gramilosa, which, as a result of contraction during hardening, has retracted from the nicmbnina propria, leaving a broad artificial space; .E, liquor folliculi; /, discus proligerus; f/, /ona pellucida; ft, vitelline membrane ; i, vitellus ; fc, the germinal spot, lying within the germinal vesicle. Hematein and eosin. Photo, x 150. include the gradual accumulation of liquor folliculi under increas- ing tension, the marked congestion of the ovary at the approach of the menstrual period, which is accompanied by the determina- tion of an undue proportion of blood to the theca of the ripe fol- 404 THE FEMALE REPRODUCTIVE ORGANS licle (Clark *), and possibly the contraction of the smooth muscle contained in the stroma of the deeper part of the cortex and adja- cent portions of the medulla. In any event, as a result of the independent or combined action of these, or other unknown forces, FIG. 327. — A MATURE GRAAFIAN FOLLICLE OF THE DOG'S OVARY. Two smaller follicles are partially included in the figure. Hemateiu and eosin. Photo, x 110. the follicle ruptures in the direction of least resistance, viz., at the attenuated stigma, and the liquor folliculi gushes forth, carrying with it the detached ovum invested with its discus proligerus. The ovum" is now free to enter the oviduct and prepare itself for fertilization and the development of the future embryo. The following table is offered for the benefit of the student as a resume of the several structural layers of the mature Graafian follicle. The structures are enumerated in order from without inward : * Contributions to the Sc. of Med., 1900. DEVELOPMENT OF THE GKAAFIAN FOLLICLE 405 f tunica externa 1. Theca folliculi -! tunica interna ( membrana propria. 2. Stratum (seu membrana) granule-sum. 3. Liquor folliculi — occupying the atrium folliculi. 4. Discus proligerus. 5. Corona radiata. 6. Zona pellucida. 7. Perivitelline space (possibly an artefact). 8. Vitelline membrane. 9. Vitellus. 10. Nucleus or germinal vesicle. 11. Nucleolus or germinal spot (if present). The Corpus Luteum. — The rupture of the follicle is accom- panied by sudden relief of the intrafollicular tension and conse- quent hemorrhage from the thin-walled capillaries of the theca folliculi. Thus the cavity of the follicle is filled with blood ; the ruptured follicle is then known as a corpus hemorrhagicum. This is the first stage in the formation of the corpus luteum. Promptly succeeding the formation of the corpus hemorrhagi- cum, lutein cells appear at the periphery of the body. They are large, ovoid or polyhedral cells having a clear finely granular cyto- plasm and a peculiar yellow color due to the presence of a pigment known as lutein. Moreover, the cytoplasm of the lutein cells becomes very rapidly infiltrated with droplets of fat, likewise deeply colored by the lutein pigment which is apparently held in solution. The origin of these cells is somewhat obscure. By certain observers they have been thought to result from the growth and multiplication of those cells of the stratum granulosum which remain after the rupture of the follicle (Bischoff, Pfliiger, Sobotta) ; by others they are derived from the connective tissue cells in the tunica interna of the theca folliculi (Kolliker, His, Palladino). The lutein cells increase rapidly both in number and in size, and gradually encroach upon the margin of the blood clot whose progressive absorption precedes the advance of the lutein cells. But not only does the lutein mass grow centralward, it also, and especially in the event of fertilization of the discharged ovum with the consequently increased vascularity of the reproductive organs, grows at the periphery and in this way greatly increases the diame- ter of the corpus luteum. 406 THE FEMALE KEPKODUCTIVE ORGANS Minute vascular sprouts of embryonic connective tissue now penetrate the lutein mass from the adjacent stroma of the theca folliculi, and growing centralward in septa-like processes, finally penetrate as far as the central blood clot. Hence the corpus luteum at this stage presents a more or less radiate structure. The central ends of the embryonic connective tissue septa fre- FIG. 328. — SECTION THROUGH THE PERIPHERAL PORTION OF A CORPUS LUTEUM, SHOWING LUTEIN CELLS. a, the fibrous coat of the corpus luteum ; 6, lutein cells with bands of newly formed connective tissue ; c, central blood clot, partially organized. Moderately magnified. (After Williams.) quently unite to inclose the remnant of the central blood clot, or by further proliferation they may entirely replace the clot by a mass of newly formed gelatinous connective tissue. The absorption of the blood clot usually proceeds slowly. Rem- nants of the disintegrating blood in the form of a central stellate mass, which often contains hematoidin crystals, frequently persist until the corpus luteum has become well organized with connect- ive tissue. The formation of new connective tissue is followed by its con- traction. That this process occurs very early in the connective tissue first formed at the periphery of the body, may possibly be DEVELOPMENT OF THE GRAAFIAN FOLLICLE 407 held to account for the fatty infiltration and final degeneration of the lutein cells, because of the consequent interference with their vascular supply. By continued development the entire mass of lutein cells is FlG. 329. — OUGANIZED COKPOKA LUTEA IN THE OVARY OF A DOG. a, a, corpora lutea ; 6, 6, remnants of the ovarian cortex ; c, c, blood vessels, one of which is filled with blood. Hematein and eosin. Photo, x 12. 408 THE FEMALE REPRODUCTIVE ORGANS gradually replaced by connective tissue, which, by further con- traction, finally produces a dense white fibrous scar, no longer containing lutein pigment, known as a corpus albicans. This body persists for a long period, but undergoes progressive contraction FIG. 330. — A CORPUS ALBICANS, FROM A SECTION OF THE HUMAN OVARY. x 75. (After Williams.) until only a minute scar of almost microscopical size remains to mark the site of the ruptured corpuscle and the highly developed corpus luteum. Such scars persist for years in the stroma of the ovarian cortex. The function of the corpus luteum is practically unknown. A glandular function resulting in the formation of an internal secre- tion has recently been attributed to it (Born,* Cohn f ). Finally it must be stated that there are no recognizable histo- logical differences, other than those of size and duration, between the corpora lutea vera of pregnancy and the corpora lutea spuria whose formation accompanies the extrusion of the unfertilized ovum. The true corpora lutea are of relatively large size and per- sist for many months, the spurious are somewhat smaller and are of shorter duration ; yet both pass through the same histological process of development and degeneration and both leave their scars in the substance of the ovarian stroma. Ovarian scars also arise through atresia of the larger follicles, the degeneration of whose epithelium is followed by an ingrowth of tissue derived from the theca folliculi, and the gradual develop- * Arch, f . mik. Anat., 1894. flbid., 1903. THE EPOOPHORON 409 ment, organization, and final contraction of the connective tissue, forming, as it were, a minute but imperfect corpus albicans, in the center of which is often the shrunken degenerating remains of the ovum. THE EPOOPHORON". — In the margin of the mesovarium at its attachment to the medulla of the ovary, lies a peculiar struc- ture which is variously known as the epodphoron, organ of Rosen- muller, or parovarium. This structure is at present without FIG. 331. — THE EPOOPHORON OF A DOG. o-a, margin of the ovary. Hematein and eosin. Photo, x 130. known function ; it apparently represents the remains of the fetal Wolffian body and is homologous with a portion of the epididymis in the male. The peritoneal epithelium in the region of the epoophoron is 410 THE FEMALE REPRODUCTIVE ORGANS ....d .A again thickened so as to acquire a columnar form, and from its sur- face, tubules and irregu- lar imaginations extend into the substance of the mesovarium as far as its attachment to the broad ligament. Occa- sionally they extend well into the interior of the ligament and there form c a group of anas- -"/" tomosing channels, — -b a rete ovarii. The tubules of the epoophoron are lined by cuboidal or colum- nar epithelium whose cells are sometimes provided with cilia. The epithelium rests upon a delicate mem- a brana propria and a r thin connective tissue 1 tunic. Blood Supply.— The blood vessels of the ovary are derived from the branches of the ovarian and uterine arteries. These vessels enter the ovary through the mesovarium and divide FIG. 332. — FROM A THICK SECTION OF THE OVARY OF A WOMAN. The blood vessels have been injected. A, a, and a', arteries ; 6, corpus luteum, partially organized ; c, point where rup- ture of the follicle occurred ; d, tangential section of a follicle ; e, corpora lutea which have organized and are already retrogressive. (After Clark.) THE OVIDUCT 411 into numerous branches which pursue a peculiar spiral or cork- screw course through the stroma of the medulla, and finally enter the cortex. They possess thick muscular walls containing bundles of longitudinal smooth muscle fibres. In the cortex they supply capillaries to the stroma, and in the theca folliculi of the Graafian follicles they form rich plexuses of broad capillaries and thin-walled venules. As the follicle approaches maturity these plexuses become enormously developed and apparently bear an important relation to the rupture of the follicle and the rapid development of the corpus luteum (Clark*). The veins, which take origin from the venules of these capillary plexuses, converge toward the medulla, where they form a plexus of large thin-walled vessels, the plexus venosus ovarii or pampiniform plexus, which is im- bedded in the connective tissue of the medulla, the mesovarium, and the adjacent portions of the broad ligament. The lymphatics arise in the cortical stroma by anastomosing canals and capillaries of irregular caliber, which are especially abundant in the walls of the Graafian follicles. These vessels con- verge toward the medulla, where they enter lymphatics which are supplied with valves, and find their way to the lymphatic nodes of the pelvic and lumbar regions. The nerves are chiefly derived from the ovarian plexus. They enter the hilum and are distributed to the walls of the blood vessels, and to the stroma of the ovary ; here they form a rich ter- minal plexus in the walls of the follicles. Whether or not the naked fibrils are distributed to the epithelial cells within the follicle has not been satisfactorily determined, THE OVIDUCT The oviduct or Fallopian tube is a narrow duct leading from the ovary to the cavity of the uterus. It consists of a broad, funnel-shaped, fringed or fimbriated extremity, a constricted neck, an intermediate ampulla of considerable diameter, and a slender isthmus by which the oviduct communicates with the uterine cavity. Throughout the entire tube its wall consists of three coats — mu- cous, muscular and serous — but the character of its mucous mem- brane differs somewhat in its several portions. In the isthmus it is relatively smooth and usually presents four longitudinal ridges which have few secondary or accessory folds ; in the ampulla the * Contributions to Sc. of Med,, 1900. FIG. 333. — TRANSECTIONS OF THE HUMAN OVIDUCT. A, uterine ; .B, isthmic ; and (7, ampullar portions, x 15. (After Williams.) 412 THE OVIDUCT 413 mucosa is greatly folded, the primary rugae possessing small sec- ondary folds which extend in all directions, and by their very com- plexity nearly obliterate the otherwise broad lumen. In the fimbriated portion the folds of the mucosa are continued into the fimbriae, at the margin of which the columnar epithelium of the oviduct becomes directly continuous with the serous endothelium of the peritoneum investing the outer surface of the tube. FIG. 334. — FROM A TIIANSECTION OF THE AMPULLA OF THE HUMAN OVIDUCT. One of the four major folds is included in the figure, a, mucosa ; J, muscular coat. Hematein and eosin. Photo, x 33. The mucosa is lined by columnar epithelium, arranged either in a simple or pseudo-stratified manner, the greater portion of whose cells are provided with cilia. The ciliary motion is directed toward the uterus. The epithelial layer covers all the folds of the mucosa 414 THE FEMALE REPRODUCTIVE ORGANS and, extending deeply into the crevices, forms invaginations which, in transections of the tube, simulate glandular structures. There are, however, no true secreting glands in the oviduct. Here and there groups of non-ciliated cells with clear cyto- plasm occur among the more numerous ciliated cells of the mucosa. This arrangement reminds one of the epithelium of the early por- tion of the epididymis with which the oviduct is homologous. The epithelium rests upon a thin homogeneous basement mem- brane beneath which is a tunica propria consisting of a cellular FIG. 335. — FROM A TRANSECTION OF THE AMPULLA OF THE OVIDUCT, SHOWING THE STRUCTURE OF THE MUCOSA. x 280. (After Williams.) type of connective tissue. Many of the connective tissue cells are of fusiform shape, and, unless specially stained or carefully exam- ined, they closely resemble smooth muscle cells. The mucosa, however, contains no muscle except at the bases of the largest folds, into which occasional fibres from the adjacent muscular coat penetrate. The muscular wall of the oviduct is formed by two layers of smooth muscle, — a broad inner circular layer, and an outer longi- tudinal coat, which is very unequally developed at different por- tions of the circumference, but is relatively thin in all parts, and is THE UTEEUS 415 entirely wanting at frequent intervals. The outer layer is usually broadest at the free margin of the oviduct and at its opposite side where the tube is attached to the broad ligament. The inner cir- cular fibres are more or less obliquely disposed, and, toward the mucosa, the muscular bundles fuse insensibly with the cellular connective tissue of the mucous membrane. The serous coat of the oviduct is continuous with the perito- neum. It consists of an outermost layer of endothelium which rests upon a subepithelial layer of connective tissue, by which it is firmly united to the muscular wall. This portion of the serous coat contains the larger vessels and nerves, which are distributed to the inner coats. Blood Supply. — The arteries of the oviduct are derived from the uterine and ovarian vessels. The larger divisions find their way through the connective tissue of the serosa whence they send smaller branches inward to form a plexus between the layers of the muscular wall and among the bundles of circular muscle fibres. From this plexus capillaries are distributed to the muscular coat, and to the mucous membrane in which they form a rich subepithe- lial capillary plexus. The veins follow a similar course, and like the arteries, form an extensive plexus in the muscular coat. The abundance of vessels in the muscular wall of the oviduct has led to the description of this coat as the vascular layer of the organ. The lymphatics arise by anastomosing plexuses in the mucosa, from which vessels pass to the serous coat and enter valved lym- phatics by which the lymph is conveyed to the lymphatic nodes of the lumbar region. The nerves are distributed from a plexus in the serous coat, to the muscular wall, and to the mucosa, in which they form a ter- minal subepithelial plexus. THE UTEKUS The wall of the uterus consists of a mucous membrane, a mus- cular coat, and an outermost serous coat which is derived from the peritoneum and invests the body of the organ. The cervix uteri projects into the vaginal canal and the serous coat is there replaced by a reflection of the vaginal mucosa. The serous coat of the uterus consists of endothelium which rests upon a thin subepithelial layer of connective tissue. It pre- sents no peculiarities. 416 THE FEMALE REPRODUCTIVE ORGANS The muscular coat of the uterus consists of smooth muscle whose fibres are of large size (40 to 60 /* in length) and which are dis- posed in interlacing bundles. In the lower mammals these form quite regular layers — an outer longitudinal, a thick inner layer, most of whose fibres are circular, and an innermost, but less dis- FIG. 336. — TRANSECTION OF THE UTERUS OF AN APE. a, mucosa ; 6, circular muscle ; c, longitudinal muscle ; d, serous coat ; e, lateral ligament; /, Wolffian tube ; g, blood vessels. . x 4. (After Sobotta.) tinct, submucous portion containing oblique and longitudinal fibres. The outer longitudinal and circular layers are separated by a fibro-muscular stratum containing a rich plexus of large blood vessels. THE UTEKUS 417 In the human uterus the arrangement of muscle fibres is much less regular, but follows a similar plan, though there is no distinct subdivision into layers. Nevertheless, careful examina- tion reveals three indistinct strata which are intimately blended with one another. The outermost of these indistinct layers con- sists of irregularly disposed longitudinal fibres, the stratum supra- vasculare. This layer is in most parts very thin, and is best developed opposite the margin of the lateral ligament and in the cervix uteri. Within this is a broad layer of interlacing bundles of more or less circular fibres, which, from the slight obliquity of their course, frequently cross each other at acute angles. Inter- mingled with these circular bundles are many large blood vessels, Fio. 337. — TRANSECTION THROUGH THE BODY OF THE HUMAN UTERUS. <7, blood vessels ; Z, lumen ; W, broad ligament ; Im, longitudinal muscle ; w, circular muscle (the fibres are mostly oblique) ; », serous coat ; tp, mucosa. Hematoxylin and eosin. x 2. (After Sobotta.) from which both the mucous and muscular coats are supplied. This broad middle layer is therefore known as the stratum vas- culare. The inner portion of this second layer passes insensibly into a thin innermost stratum submucosum, which again contains many longitudinal fibres, and upon which the mucosa directly rests. The uterine mucosa is of considerable thickness (1 to 3 mm.). It is clothed with epithelium, and its tunica propria contains numerous tubular glands. 28 418 THE FEMALE EEPEODUCTIVE OKGANS The epithelium is of the ciliated columnar type, and consists of a single row of cells. Apparently not all of its cells are pro- vided with cilia, areas of ciliated, alternating with groups of non- ciliated epithelium. The epithelial layer is continuous with the epithelium of the uterine glands ; in the region of the external os FIG. 338. — FROM THE UTERINE MTJCOSA OF A GIRL OF SIXTEEN YEARS, SHOWING THE GLANDS OF THE BODY OF THE ORGAN. o-«, lining epithelium. Hematein and eosin. Photo, x 115. uteri it is replaced by the stratified squamous epithelium of the vaginal mucosa. Ofttimes, and especially in multiparae, the strati- fied squamous epithelium of the vagina is continued for some little distance within the canal of the cervix uteri ; it never clothes more than the lower one-half to two-thirds of the cervical canal. The current resulting from the vibration of the intra- uterine cilia is directed toward the vagina (Hofmeier,* Mandl f ). The tunica propria of the mucosa consists of a peculiar em- bryonal type of connective tissue, similar to that of the oviducts, which contains very few white and no elastic fibres, but which is richly supplied, in fact is literally packed, with cellular elements. These cells are ovoid or fusiform in shape, and many of them are branched; their nuclei, also, are ovoid and somewhat vesicular. * Centralbl. f. Gynakol, 1893. \ Ibid., 1898. THE UTEEUS 419 Many leucocytes are found in the tunica propna, but these mostly occur in the vicinity of the lymphatics and smaller blood vessels with which the uterine mucosa is abundantly supplied. In the mucosa of the cervix uteri the development of the connective tissue appears to be more advanced, the cellular elements being relatively fewer ; it also contains many fine fibres which appear to form a delicate network. At the external os uteri the tunica propria is continuous with the similar, though still more fibrous, layer of the vaginal mucosa. The uterine glands are divisible into two types — those of the body of the organ, and those of its cervix. The former are, per- haps, to be regarded as tubular invaginations of the lining epithe- FIG. 339. — FROM A TRANSECTION OF THE UTERINE MUCOSA. x 16. (After Williams.) lium, whose function is one of epithelial regeneration rather than of glandular secretion. The tubules of the cervix uteri are true mucus secreting glands. The uterine glands proper, those of the body of the organ, are slightly branched or forked tubules which traverse the entire breadth of the mucosa, presenting a characteristic spiral or cork- screw course their blind extremities are often bent or turned to 420 THE FEMALE REPRODUCTIVE ORGANS one side, apparently from the proximity of the adjacent muscular coat. The glandular epithelium is of the columnar type and, like that of the free surface, is frequently provided with cilia, especially near the mouth of the gland. The epithelium rests directly upon the connective tissue of the tunica propria. The cervical glands (glandulce uterince cervicales) resemble those of the body of the organ in their tubular form and the columnar shape of their epithelium, but here the resemblance FIG. 340. — FROM THE CERVIX UTERI OF A GIRL, OF SIXTEEN YEARS, SHOWING THE CERVICAL GLANDS IN SECTION. a-a, lining epithelium. Hematein and eosin. Photo, x 102. ceases. The cervical glands are much branched, and their tubules present frequent dilatations, some of which, apparently from occlusion of their outlet, attain a macroscopic size, and are then known as NabotMan follicles (ovula Ndbothii) ; they are filled with a tenacious, mucous secretion. The glandular epithelium near THE UTEKUS 421 the crypt-like ducts is usually ciliated, like that of the surface, but in the secreting portions it consists of tall, clear, columnar cells which are in various stages of secretory activity, their product being a viscid glairy mucus, strings and granules of which are found within the lumen of the glands, as well as within the canal of the cervix uteri. The uterine cavity is a rela- tive term. In the virgin, the mucosa is considerably folded and its surfaces are almost in apposition, being only sepa- rated by a very limited amount of desquamated epithelium and cellular debris, to which, in the canal of the cervix uteri, the mucous secretion is added. During pregnancy, the devel- opment of the fetus within the uterine cavity distends its walls and so dilates the canal that it at last forms a sac of sufficient size to contain the fetus, which floats within the amniotic fluid inclosed by its membranes. The blood vessels of the uterus enter through the folds of the lateral ligament and find their way, through the subepi- thelial connective tissue of the serous coat and the muscular wall, to all portions of the organ. In the vascular layer of the muscular coat they form an extensive plexus from which branches are dis- tributed to the musculature and to the mucosa, the branches to the latter penetrating nearly to the surface, where they form rich, subepithelial, capillary and venous plexuses. The uterine arteries, like those of the ovary, possess a peculiar, spirally tortuous course. The veins accompany the arteries, but are less tortuous. The lymphatics of the uterus arise by anastomosing channels in the mucous and muscular coats. They form a vascular plexus FlO. 341. — A. GLAND OF THE HUMAN CERVIX UTERI IN LONGITUDINAL SECTION. x 90. (After Williams.) ±22 THE FEMALE REPEODUCTIVE ORGAXS in the serous coat and lead outward, through the lateral ligaments and pelvic connective tissue, to the lower lymphatic nodes of the lumbar region. The nerves of the uterus are very numerous. They enter the serous coat from the ganglionic pelvic plexus, and are distributed to the vascular layer of the muscular coat. They there form a rich plexus, from which fibres are distributed to the musculature and to the walls of the blood vessels. The distribution of nerves within the mucosa has not yet been thoroughly worked out. According to von Gawronsky * and Kostlin f nerve fibrils penetrate nearly to the surface and form a scanty subepithelial plexus, whence are derived fibrils which ter- minate between the epithelial cells. THE MENSTRUATING UTERUS The appearance of the phenomena of menstruation is accom- panied by decided alterations in the structure of the uterine FIG. 342. — FROM A SECTION OF THE HUMAN UTERINE MUCOSA AT THE FIRST DAY OF MENSTRUATION. e, epithelium ; d, disintegrating layer ; 0, gland ; «, blood vessel ; m, muscular coat, x 44. (After Minot.) mucosa. In spite of the difficulty of obtaining sufficiently fresh and well preserved material, certain changes which characterize the menstruating uterus are now definitely known. These chiefly * Arch. f. Gynakol., 1894. f Fortschr. d. Med., 1894. THE GRAVID UTERUS 423 consist in increased vascularity, hypertrophy of the elementary tissues of the mucosa, epithelial desquamation, and rupture of the blood vessels, with consequent hemorrhages. These changes are followed by a process of regression and later of regeneration, by which the uterine mucosa rapidly returns to its former condition. The first or hypertrophic stage involves the epithelium, whose cells are elongated, and the tunica propria, in which many of the connective tissue cells undergo multiplication and enlargement. Thus the mucous membrane becomes greatly thickened ; its glands, also, are increased in both length and breadth, becoming at the same time even more tortuous than before. The glandular hyper- trophy involves both the uterine and the cervical glands ; the secre- tion of the latter is much increased. At the same time, the blood vessels become widely dilated, especially those near the surface, and broad thin-walled sinuses are formed beneath the epithelium. Finally these vessels rupture and hemorrhages occur into the substance of the mucosa as well as into the cavity of the organ ; desquamation and disintegration of the superficial portions of the mucosa result. The menses which are thus formed contain blood, epithelium, connective tissue cells, and many leucocytes, which wander out from the blood vessels of the mucosa in large numbers. The greatly thickened and hemor- rhagic mucosa is known as the decidua menstrualis. Regression and regeneration follow rapidly upon one another, the mucosa gradually regaining its former condition. During this process fat droplets appear in. many of the connective tissue cells. The epithelium is rapidly regenerated, the new cells arising from the epithelial remnants at the mouths of the uterine glands. In the course of a few days the mucosa regains its former quiescent condition. THE GKAYID UTERUS In the event of conception the uterine changes are even more pronounced than during menstruation. These alterations include the same processes of hypertrophy and thickening as occur in the decidua menstrualis ; they involve the musculature as well as the mucosa but are not followed by regressive changes, — hemorrhage, desquamation, etc. — until parturition occurs. The muscular wall undergoes an enormous increase both in the number and size of its fibres. The relatively short (30 to 60 /A) smooth muscle fibres of the uterine wall gradually increase in size to as much as eleven times their former length and two to 424 THE FEMALE KEPKODUCTIVE ORGANS five times their breadth (Kolliker *). The connective tissue of the muscular coat also increases in volume and becomes more dis- tinctly fibrous. After parturition, fat droplets appear within the muscle cells, and the muscular wall by gradual atrophy returns to its former condition. In the mucosa the formation of a decidual membrane goes for- ward in a manner similar to the development of the decidua men- strualis, but the process is exaggerated. The tunica propria soon becomes divisible into two distinct, though not sharply defined, layers, a deeper cavernous portion which is permeated by broad vascular channels together with the atrophied remains of the uterine glands, and a superficial compact layer in which the vascu- lar channels, except for the thin-walled venous spaces, are smaller and the connective tissue cells more closely packed. Many of the connective tissue cells attain a large size and their nuclei are frequently multiple, or they may acquire an irregular polymorphonuclear form. Giant cells are thus produced in the compact layer of the mucosa of the gravid uterus ; they are highly characteristic of this tissue and are known as decidual cells. Though it is frequently asserted that similar cells occur in the decidua menstrualis, this is denied by Minot,f who states that in a considerable number of menstrual decidua examined, no such cells were ever found. The superficial epithelium is soon desquamated and the tunica propria comes into contact with the fetal chorion. The glandu- lar epithelium is also partially degenerated, often becoming flat- tened and of irregular shape. It is frequently desquamated into the glandular lumen; this lumen is thus reduced to a narrow crevice, which is so elongated during the dilatation of the uter- ine wall that the axis of the glandular remnant becomes nearly parallel to the surface of the decidua. The decidual membrane which is thus formed is divisible into three portions, according to its relation to the tissues of the em- bryo : 1, that portion upon which the developing ovum directly rests, which is known as the decidua serotina or decidua basalis but later forms the placenta uterina or maternal portion of the placenta ; 2, at the margins of the implanted ovum the decidual tissues grow up around the ovum which is thus surrounded by the so-called decidua reflexa or decidua capsularis, which, after * Handbuch, iii, 574. f Laboratory Text-book of Embryology, 1903. THE PLACENTA 425 the early months of pregnancy, is gradually obliterated by the in- creasing growth of the fetus, and is finally replaced, its functions being progressively usurped by the newly formed placental tis- sues ; 3, all the remaining portions of the decidual mucosa, those which line the greater part of the uterine cavity, collectively form the decidua vera, with whose surface, in the later months of preg- nancy, the fetal chorion is intimate in relation. The mucosa of the cervix uteri meanwhile becomes greatly hypertrophied and its glands much enlarged. This portion of the uterine mucosa does not, however, enter into the formation of the decidua vera ; the changes occurring in its tissues, though similar, are much less pronounced. THE PLACENTA The human placenta at full term is formed partly by fetal and partly by maternal tissues, the former of which may be said to be implanted in the superficial layers of the latter. Hence on the fetal side the organ is limited by the fetal membranes, amnion FIG. 343. — DIAGRAM SHOWING THE STRUCTURE OF THE HUMAN PLACENTA AS SEEN IN TRANSECTION. The fetal blood vessels and maternal arteries are black ; the maternal veins and inter. villous blood spaces are white, a, amnion; 6, chorion; c, chorionic villi; d, decidua; e, glandular layer of the uterine mucosa ; /, muscular wall of the uterus. 426 THE FEMALE EEPEODUCTIYE ORGANS and chorion, on the maternal side by the tissues of the decidua serotina, while between these boundaries is a broad interval which is occupied by a forest of arborizing processes of the fetal chorion, some of which, the main stems, completely span the interval, their tips being firmly embedded in the surface of the decidua, while others, the free branches m floating villi, pass from the lateral sur- faces of the main stems and repeatedly subdivide, the tips of their branches floating free in maternal blood spaces which are therefore known as intervillous spaces. Where the fetal chorion and maternal decidua are in direct contact at the margin of the placenta, the decidual cells extend inward to meet the opposed surface of the chorion, upon which they then expand to form the so-called decidua subcliorialis (Fig. 349, page 432). THE AMNION.— This is a thin membrane, of fetal origin, con- sisting of an epithelial coat and a thin layer of mesenchymal con- nective tissue. Its epithelium, whose surface is directed toward' the fetus, consists of cuboidal or flattened epithelial cells which are derived from the ectoderm ; they are firmly united with one another by means of intercellular bridges (Minot*). The connect- ive tissue forms a thin transparent layer of embryonic tissue in which are many cells. From the inner surface of this layer deli- cate processes pass to the surface of the chorion, to which mem- brane the amnion is loosely attached. THE CHORION. — This tissue includes a membranous portion which is in relation with the amnion, and a villous portion which forms the forest of placental villi already described as lying between the fetal membranes, on the one hand, and the maternal decidua on the other. That portion of the chorion which enters into the formation of the placenta is known as the chorion f rondo- sum, in contradistinction to the remaining portion of the chorionic membrane which is loosely attached to the decidua vera and is called the chorion Iceve. The membranous portion of the chorion may be said to consist of two layers, — an inner or fetal layer of embryonic connective tissue, which is continuous with the similar tissue of the amnion and serves for the transmission of the fetal blood vessels on their way from the umbilical cord to the placental villi, and an outer layer which consists of intermingled groups of large cells, collect- * Loc. cit. '- FIG. 344. — TRANSECTION OF THE WALL OF THE HUMAN UTERUS AT THE SEVENTH MONTH OF PREGNANCY, WITH THE PLACENTA IN SITU. Am, aranion ; Cho, chorion ; J2, main stem of a chorionic villus ; ct, villi in section ; D, D', decidua serotina ; .Me, muscular wall of the uterus ; Ve, uteriue artery. The fetal vessels are black, the maternal white. The glandular remnants in the decidua are dark, x 6. ( After Minot.) 427 428 THE FEMALE REPRODUCTIVE ORGANS ively forming the trophoblast, together with masses of canalized fibrin. The trophoblast consists of large ovoid cells. It presents a homogeneous appearance, not unlike that of the maternal decidua serotina, and is derived from the fetal ectoderm. Its cells form FIG. 345. — HUMAN PLACENTAL TISSUES (AMNION AND CHOBION) AT THE FIFTH MONTH. Ep, epithelium of the amnion ; Am, amnion ; c, cellular layer of the chorion ; Fib, fibrillar layer; Fbr, canalized fibrin ; Str, stroma ; Fi, chorionic villi. x 71. (After Minot.) the larger part of the outer portion of the membranous chorion and are continued into the main stems of the chorionic villi. In the early months of pregnancy they occur in all the primitive villi of the placenta, where they are found on the surface of the connective tissue core, beneath the syncytium, and are known as the cells of Langerhans. Later they appear to degenerate, and are of less frequent occurrence in the chorionic villi. The canalized fibrin is of doubtful origin. It forms irregular plate-like masses which either invade the substance of the mem- branous chorion or here and there clothe the placental surface of the mass of trophoblastic cells. Occasionally, and especially upon the surface of the chorionic villi, it apparently replaces portions of the syncytial membrane which elsewhere covers the villi, lines the maternal surface of the membranous chorion, and therefore forms the proper wall of the intervillous or maternal blood spaces. THE PLACENTA 429 Canalized fibrin consists of a granular eosinophilic mass which is pierced by many narrow clefts, hence the name. The Chorionic Villi. — These innumerable processes form the greater portion of the placental tissues. They vary in size from the broad main stems to the very slender terminal branches of the floating villi. In the early condition of the placenta (fourth or fifth month of pregnancy) the villi are clothed with a double epi- thelial layer, of which the superficial takes the form of a syn- ?:'•*•" :--.v': 1TIES FIG. 346. — THE CHORION OF THE HUMAN PLACENTA AT THE SEVENTH MONTH. 4 cellular layer ; ep, remnants of the epithelial layer ; /ft, canalized fibrin ; mes, meso- dermal stroma. x 445. (After Minot) cytium, derived, according to Keibel,* from the endothelium of the maternal blood vessels ; the deeper consists of a cellular layer, the cells of Langerhans. At later periods (seventh month to full * Anat. Anz., 1889. 430 THE FEMALE REPRODUCTIVE ORGANS term) the syncytium is found to have undergone a peculiar altera- tion, having become much thinner, and having even completely disappeared from considerable portions of the villi, it being re- placed by canalized fibrin; at other points the syncytial cyto- FIG. 347. — CHORIONIC VILLI FKOM THE HUMAN PLACENTA AT FULL TERM. Heraatein and eosin. Photo, x 114. plasm is much thickened and the nuclei appear to be bunched or grouped within the thickened portions; these areas are known as cell-knots or 'proliferation islands. Here and there the degen- erated cell-knots have been replaced by canalized fibrin. Wherever the main stems are inserted into the decidua the epithelium which formerly covered their tips appears to have also degenerated into a peculiar hyaline border zone. Within its syncytium the substance of the villus consists of the superficial cells of Langerhans with their large ovoid nuclei, and a THE DECIDUA SEROTINA 431 core of connective tissue of a delicate embryonic type, in which are the fetal blood vessels. Even the smallest villi contain capil- lary loops of broad calibre, which are supplied by fetal arteries, derived from the umbilic,al arteries, which distribute their branches throughout the chorionic connective tissue. The fetal veins accom- pany the arteries. THE DECIDUA SEROTINA (Decidua £asalis).—This portion of the maternal decidua receives the insertion of the chorionic villi; its superficial compact portion belongs rather to the pla- centa than to the uterine mucosa, since it separates from the uter- ine wall along with the chorionic tissues when the placenta is dis- lodged at parturition. The substance of this layer is formed by Vi me 348. — THE HUMAN DECIDUA SEROTINA AT THE SEVENTH MONTH. D', cavernous layer of the decidua ; D", compact layer ; me, margin of the muscular coat of the uterus ; Fi, chorionic villi, the spaces between which were filled with maternal blood. (After Minot.) the decidual connective tissue in which the enlarged decidual cells are specially numerous. It transmits the maternal blood vessels, and with its surface the main stems of the chorionic villi, at their occasional points of attachment, are intimately blended. Here and there the decidual connective tissue is continued inward for some distance between the chorionic villi to form incomplete septa 432 THE FEMALE REPRODUCTIVE ORGANS which mark off the outer surface of the detached placenta into macroscopical areas or lobules, the placental cotyledons. The distribution of the blood vessels of this part is specially interesting. The arteries enter from the muscular coat of the uterus and follow a spirally tortuous course through the decidua, until they arrive near the surface of the compact layer. Here their lumen suddenly broadens and their walls become relatively si FIG. 349. — THE MARGIN or THE HUMAN PLACENTA AT FULL TERM. A, the placental margin; D, decidua subchorialis ; Cho, cho- rion; Fib, canalized fibrin; Fi, placental villi ; vi, aborted villi outside of the placenta. (After Minot.) xl3 thin, consequently they are with difficulty distinguished from the veins. These arterial spaces at last turn suddenly and enter the placental tissues, pouring their contents directly into the lumen of the intervillous spaces ; hence these are to be regarded as mater- nal blood spaces. The maternal veins also open directly from the intervillous spaces and, though much less tortuous, they retrace the course of the arteries to the vascular layer of the uterine mus- culature. We may liken the intervillous spaces to an enormously dilated capillary space, a great lake, as it were, within which the chorionic villi are suspended and of which the many maternal arteries form the inlets and the corresponding veins of the decidua THE UMBILICAL CORD 433 serotina, the outlets. At the margin of the placenta the border of this great intervillous lake is relatively free from villi and forms the so-called circular sinus, a space which is obviously not a true sinus, in that, not having a proper wall, it can not be said to pos- sess definite boundaries. Since the fetal blood vessels of the placenta are everywhere contained within the connective tissue of the chorionic villi, while the maternal blood circulates only in the intervillous spaces, it is obvious that there can be no direct communication between the fetal and the maternal blood channels, nor can there be any inter- change whatsoever of fetal and maternal blood cells. The course of the fetal blood can be traced from the umbilical arteries to the arteries of the villi, thence through the blood capillaries to the venous radicals within the villi; these return the fetal blood, through veins in the connective tissue of the chorion, to the larger venous branches in the membranous chorion, which finally unite to form the um- bilical vein. THE UMBILICAL COED This organ trans- mits the two umbilical A arteries which are spi-r! rally wound about the umbilical vein. These vessels are embedded in a non-vascular, gel- atinous, connective tissue, known as the jelly of Wharton, which is rich in cells and ground substance. The fibres, as in all embryonic tissue, are poorly developed and form only a loose net of very delicate fibrils. 29 FIG. 350. — TRANSECTION OF THE UMBILICAL CORD OF A NEW-BORN HUMAN INFANT. A, artery ; F, F, veins. Hematein and eosin. Photo, x 10. 434 THE FEMALE REPRODUCTIVE ORGANS The connective tissue cells and fibres are frequently arranged in membranous bands which extend lengthwise of the cord and in transections present a peculiar concentric arrangement, the deli- cate membranes alternating with broad tissue spaces, and often inclosing the blood vessels or forming incomplete concentric lamellae about the circumference of the cord. The surface of the cord is clothed with an ectodermal layer of flattened epithelium which occasionally forms several layers of cells. The umbilical vessels, the veins as well as the arteries, are peculiar in that they possess unusually thick muscular walls. Their smooth muscle fibres are disposed both longitudinally and circularly. In transection the endothelial lining of the vessels is seen to be thrown into prominent folds by the contraction of the thick muscular wall. Remnants of the allantois, and occasionally of the yolk sac as well, are found in the fetal end of the umbilical cord even at full term. These appear in the form of indistinct epithelial tubes or columns, whose cells often show evidences of degenerative changes. THE VAGINA The vagina is a fibro-muscular sheath whose wall is divisible into three coats — mucous, muscular, and serous. The mucous membrane is clothed by a layer of stratified squamous epithelium, and is thrown into numerous folds or rugae. The epi- thelium rests upon a fibrous basement membrane. The tunica pro- pria is formed by a close-meshed areolar tissue which, in its deeper and looser portion, is permeated by vascular channels of consider- able size. This deep vascular layer is frequently described as a submucosa; it rests directly upon the muscular wall. The sur- face of the mucosa presents numerous conical papillae which pro- ject well into the epithelial layer. The musculature of the vagina contains smooth or involuntary fibres, and is divisible into an inner circular and an outer longi- tudinal layer. The muscle fibres are long and slender. Consid- erable connective tissue is distributed among the muscle bundles. The latter are arranged in more or less parallel layers which are united by the delicate bands of connective tissue. The outer fibrous coat consists of dense areolar tissue which is well supplied with elastic fibres. It loosely unites the vaginal wall to the surrounding tissues. In this coat is a plexus of blood- vessels and lymphatics, from which branches pass to the muscular THE VAGINA 435 coat, and to the mucosa, in which they form an abundant plexus. An extensive nerve plexus, in which are many small ganglia, is FIG. 351. — FROM A SECTION THROUGH THE WALL OF THE VAGINA OF A GIRL SIXTEEN YEARS OLD. o, mucosa ; 6, muscular coat ; c, fibrous coat, containing large thin-walled vascular spaces. Hematein and eotdn. Photo, x 47. 436 THE FEMALE EEPEODUCTIVE OKGANS also found in the fibrous coat; it distributes motor branches to the muscular wall and to the blood vessels, and sensory fibres to the mucosa, in which they end in relation with the cells of the lining epithelium. The vaginal mucosa is reflected upon the outer wall of the cervix uteri, and at or near the external os it is continuous with the mucosa of the uterine cavity. Though occasional glands have been found in the vaginal mucous membrane, lined either by mucus secreting or by ciliated cells, these glands would seem to be prop- erly considered as anomalies, since they are usually absent, the mucoid secretions of the vaginal canal being chiefly provided by the abundant supply of mucus from the cervical glands of the uterus. The vaginal mucosa is continuous below with that of the vestibule. THE EXTERNAL GENITALS The vestibule is supplied with a mucosa which offers a gradual transition from the vagina, on the one hand, to the skin on the other. Its stratified squamous epithelium becomes in this way gradually more and more like that of the skin, eleidin granules first, and keratin later appearing on the outer surface of the labia minora. The epithe- lium of the labia ma- jora is identical with that of the skin. The labia minora are formed by a fold of the mucosa which is provided with ex- ceptionally tall papil- lae. Small sebaceous glands open directly upon the surface of the stratified squamous . 352— TKANSECTION OF A LABIUM MINUS OF AN epithelium. There are INFANT- no hair follicles in a, labium minus; 6, border of the labium majus ; -i f irif"h +VIPCP c, adipose tissue of the latter. Hematein and eosin. Photo, x 12. glands, and the labia THE MAMMAKY GLANDS 437 minora contain no adipose tissue. They are richly supplied with blood vessels. The labia majora are formed by similar folds whose inner sur- face resembles the adjacent portion of the labia minora, but whose outer surface is cutaneous and is supplied with sebaceous and sudoriparous glands and with numerous hair follicles. The sub- epithelial areolar tissue is very dense and its deeper portion con- tains much fat. The clitoris consists of a mass of erectile tissue, homologous with the corpora cavernosa and glans penis of the male ; it is covered by a fold of the mucosa. It is well supplied with nerves, which terminate in tactile corpuscles, end bulbs, and genital cor- puscles. In this vicinity also, as well as in the region of the labia, Pacinian corpuscles are occasionally found. The hymen is formed by a reduplication of the vestibular mu- cosa. Its inner surface is similar to that of the labia minora and vagina ; its outer is like that of the cutaneous surface, except that it contains no hair follicles. The glandulae vestibulares minor es are a group of small mucus secreting glands, similar in structure to the glands of Littre in the male, which occur in the vestibular mucosa in the vicinity of the meat us urethrae. The glandulae vestibulares majores (glands of BartJiolin) form a paired tubulo-alveolar mucus secreting gland which opens by a narrow duct into the groove between the hymen and labium minus. The tubular alveoli are lined by columnar mucus secreting cells ; the ducts are clothed with columnar epithelium, which, as they approach their termination, becomes double-rowed, and finally changes to a stratified squamous epithelium similar to that of the surface upon which they open. These ducts frequently pre- sent saccular dilatations. THE MAMMAEY GLANDS From a strictly histogenic standpoint the mammary glands should be considered as appendages of the skin, and as such should more properly have been considered in the chapter devoted to that subject. Yet these glands are so closely related to the reproductive functions, attaining their full development only in the lactating female, that it seems equally proper^to consider them at this time as accessory reproductive organs. Each mammary gland consists of fifteen to twenty -four (Kolli- 438 THE FEMALE EEPKODUCTIVE ORGANS ker*) lobes, each of which is of itself a tubulo-acinar gland whose lactiferous duct opens on the surface of the nipple near its apex. The mouths of these ducts are narrow : their terminal portions in the deeper part of the mammilla are much broader, thus forming in each lobar duct a sort of terminal saccule or lactiferous sinus. The main lactiferous ducts subdivide in an 'arborescent manner into many interlobular ducts, about which are clustered the groups of secreting alveoli, each group forming one of the many lobules included in a lobe of the gland. The structure of the lobule, as well as the general appearance of microscopical sections of the gland, varies much according to the stage of development and the condition of activity of the organ. THE ACTIVE GLAND.— During lactation the glandular alve- oli are so numerous as to form by far the most prominent portion of the gland. Each lobule consists of a cluster of saccular alveoli which open by short alveolar ducts into the interlobular ducts of the connective tissue which invests the lobules of the gland. The alveoli are closely packed within the lobule. In form, except for the regularity of their epithelium and the distinctness of their cell outlines, they might well be compared with the intralobular alveoli of the salivary glands. They possess, however, a broader lumen. The actively secreting alveoli are lined by cuboidal or low col- umnar cells which vary much in height even within the same alveolus, and are often considerably flattened. Their secretory activity is indicated by the appearance of fat droplets, which ac- cumulate within the distal portion of their cytoplasm. These droplets apparently push toward the free surface of 'the cell, gain- ing somewhat in size as well as in number, until they finally occupy the greater part of the distal end of the cell and are separated from each other by only a narrow interval of albuminous cyto- plasm. At last they are discharged into the broad lumen of the alveolus, where they apparently still retain a thin albuminous envelope which prevents their cohesion and consequent fusion, and thus permits their suspension in the albuminous, fluid portion of the milk. The spheroidal nuclei of the secreting cells during this process are crowded to the base of the cell, and after the discharge of the secretion the shrunken but nucleated cell remnants remain in situ ; after a period of rest, the cells apparently resume their secretory function. It appears probable that each cell in its life * Handbuch, iii, 590. THE MAMMARY GLANDS 439 history may repeatedly pass through the cycle of secretory changes, though the exact number of such cycles which an individual cell may present obviously does not admit of demonstration. As a rule, the active epithelium consists of a single row of cells, though here and there they appear as if piled upon one another b I FIG. 353. — FROM THE ACTIVELY SECRETING MAMMARY GLAND OF A WOMAN. Several lobules are included, a, interlobular duct ; 6, iuterlobular connective tissue. Hematein and eosin. Photo, x 52. to form a double layer. The epithelium rests upon a reticular or homogeneous basement membrane, within which are occasional basket cells (Korbzellen). The alveoli of the active gland are so closely packed that a connective tissue tunica propria is no more than scarcely demonstrable. The thin tunica propria is, however, richly supplied with blood capillaries, lymphatic vessels, and nerve fibres. 440 THE FEMALE REPRODUCTIVE ORGANS The ducts of the mammary gland are lined by either a single or double row of low columnar cells. They possess a relatively broad lumen. Their membrana propria is supported by a thin connective tissue wall, containing both circular and longitudinal elas- tic fibres but no muscle (Kolliker,* Schaferf). The elastic fibres of the smaller ducts are poorly devel- oped, but in suitable specimens the longitudinal fibres are readily seen even in very small branches. Be- yond the lactiferous sinus the duct epithelium changes to a stratified squamous variety which is continu- ous with that of the cutaneous sur- face- of the nipple. The glandular lobules are firmly united by strong septa derived from the dense areolar tissue in which they are embedded. In the deeper parts of the gland occasional lobules of fat are found in this tissue. Within the nipple and beneath the adjacent portions of the areola, smooth muscle fibres are also found. These are arranged in circular bundles at the base of the nipple, with longitudinal fibres within its substance which, at the base of the mammilla, diverge in radiating bundles into the sub- cutaneous tissue of the areolar zone. Contraction of these fibres elevates and hardens the nipple, thus stimulating the action of the erectile tissues. Embedded in the subcutaneous tissue of the areola are also a number of small accessory lactiferous glands known as the Glands of Montgomery (Areolar Glands of Duval). THE RESTING GLAND.— With the cessation of lactation the glandular alveoli undergo a rapid atrophy, and are replaced by connective tissue derived from the interlobular stroma. The ducts contract and the epithelium piles up to form a two-rowed, or even thicker, layer. The alveoli are reduced to mere buds from the terminal ducts, and their lumen is almost obliterated ; their epithelium is similarly massed into a double layer of small cells. The lobules are reduced in size and consist only of a few FIG. 354. — MODEL OF A RECONSTRUC- TION OF AN INTRALOBULAR DUCT AND ITS ACINI FROM THE ACTIVE MAMMARY GLAND OF A WOMAN. x 200. (After Maziarski.) * Handbuch, iii, 591. f Quain's Anat., iii, pt. iv. THE MAMMARY GLAXDS 441 a shrunken alveoli clustered about the termination of an interlobu- lar duct. The lumen of the alveoli, if any, contains no secretion, and that of the ducts, except for a little granular albuminous material and an occasional leucocyte, is empty. The connective tissue stroma is much increased in volume, and in places shows a marked infiltration with fat. The alveolar tissue of the mam- mary gland at all times contains wan- dering leucocytes, and many granule cells, both acidophile and basophile in character. C With the appearance of pregnancy the gland promptly re-enters a state of activity ; its alveoli multiply ; its connective tissue becomes relatively diminished in volume ; its lobules are reformed and their alveoli finally begin secretion, a process which is heralded by the formation of a granulo-fatty co- lostrum, a rather serous fluid in which are suspended large numbers of colos- trum corpuscles, large spheroidal cells, resembling leucocytes in their general form and in the character of their nuclei, but which possess a broad rim of cytoplasm often containing numbers of fat globules of varying size. Their cytoplasm has also been shown to con- tain neutrophile granules of Ehrlich similar to those of the polynuclear leucocytes (Michaelis *). The origin of the colostrum corpus- cles is still somewhat in doubt, though modern technique has gradually dis- credited the theory of their origin from desquamated remnants of the alveolar epithelium, and shows them to be more probably enlarged leu- cocytes which have wandered through the alveolar wall and have *Arch. f. mik. Anat, 1898. FIG. 355. — FROM A SECTION OF THE HUMAN MAMMARY GLAND IN THE RESTING CONDITION. a, remnants of the glandular alveoli ; 6, duct ; c, connective tissue ; d, adipose tissue. Hema- tein and eosin. Photo, x 10. 442 THE FEMALE EEPRODUCTIVE ORGANS thus found their way into the lumen, where they take on a phago- cytic activity and continue their growth. The following facts may be mentioned in support of this theory : #, leucocytes can be read- ily found between the cells of the alveolar epithelium as well as in the lumina of the saccules ; #, the colostrum corpuscles examined in a fresh condition on a warmed slide have been repeatedly shown to possess the property of amoeboid motion ; e, the colostrum cor- puscles, when stained, present the same granular and non-granular varieties as do the leucocytes of the blood ; d, finally, the colostrum corpuscles have been shown to undergo mitotic cell division (Biz- zozero and Ottolenghi *), a phenomenon which we should hardly ex- pect to find in degenerated and desquamated epithelial cell remnants. The Uood vessels of the mammary gland are specially abun- dant. They form rich capillary plexuses about the walls of the active alveoli. Many of the venules coming from these plexuses converge toward the areola, where they form an incomplete venous circle (circulus venosus of Holler) from which the efferent veins take their origin. The lymphatics of the mammary gland are also numerous. They take origin from broad channels among the alveoli and enter a rich plexus about the interlobular ducts. From here several vessels pass to the lymphatic nodes of the axilla. The nerves of the mammary gland are distributed to the vas- cular walls, to the smooth muscle of the areola and nipple, to the alveolar epithelium, and in the connective tissue of the nipple and areola they occasionally terminate in tactile and Pacinian corpuscles. Among the secreting alveoli the nerve fibres form an epilemmal plexus beneath the membrana propria, from which fibrils pene- trate between the epithelial cells, upon which they end in minute granular varicosities ( Arnstein f ). MILK Milk, secreted by the active mammary gland, consists of an emulsion, in which fat droplets, varying in size from 2 ft to 20 /A or more, are suspended in a watery albuminous fluid. Each fat droplet is presumably invested with a thin coat of casein, derived from the cytoplasm of the secreting epithelium. Occasionally leucocytes occur in the milk, but never in large numbers, and like the similar colostrum corpuscles, they are mostly confined to the -earlier periods of lactation. * Ergeb. d. Anat. u. Entwickl., 1899. f Anat. Anz., 1895. CHAPTER XXII THE DUCTLESS GLANDS UNDER this heading it will be convenient to consider the supra- renal, thyroid, parathyroid, carotid, and coccygeal glands, and the hypophysis cerebri. I. THE SUPRARENAL GLANDS The suprarenal glands (adrenals) are two glandular masses situ- ated above but in close relation with the upper extremity of each kidney. On section the adrenal is seen to be readily divisible into a bright yellow or brownish-yellow cortex and a more vascular, and^ hence darker and somewhat reddish, medulla, whose central portion transmits several large veins which make their exit from an indentation in the anterior surface of the organ, known as the Jiilum. The organ is inclosed by a connective tissue capsule of consid- erable thickness. From the inner surface of the capsule delicate fibrous trabeculae pass inward and subdivide the epithelial paren- chyma of the organ into cell groups and columns, which vary in their appearance according to the distribution of the connective tissue trabeculae. The organ may be thus divided into a central medulla and a peripheral cortex. In the medulla the connective tissue presents an irregular areolar arrangement ; the more regu- lar, though varying form of the areolae in the cortex, subdivides this portion of the organ into three more or less distinct layers, which were first described by Arnold * as the zona glomerulosa, zona fasciculata, and zona reticularis. In the zona glomerulosa the connective tissue trabeculae sub- divide the epithelium into spheroidal groups of cells, many of which are continuous with the cell columns of the adjacent zona fasciculata. The glomerulate layer is relatively thin and lies close beneath the capsule. * Arch, f . path. Anat., 1866. 443 444 THE DUCTLESS GLANDS The stroma of the zona fasciculata is continued inward from the glomerulosa, but is so drawn out as to form elongated areolae, inclosing cell columns of considerable length, which are disposed -b FIG. 356. — FROM A SECTION THROUGH THE HUMAN ADRENAL. a, central vein ; 6, capsule ; c, zona glomerulosa ; rZ, zona fasciculata ; e, zona reti- cularis ; /, medulla ; gr, peri-adrenal adipose and areolar tissue. Hematein and eosin. Photo, x 45. in a radial manner. This is the broadest of the three cortical zones and is interposed between the glomerulosa and reticularis. THE SUPRARENAL GLANDS 445 At the inner border of the zona fasciculata the connective tis- sue bundles pass insensibly from the regular columnar arrange- ment of this layer into a reticular maze. The resulting cell groups are of very irregular form and compose the innermost cor- tical layer, the zona reticularis. This layer is the thinnest and least distinct of the three zones of the cortex. It can often be more readily distinguished by the highly pigmented condition of its cells, than by the mere form of its cell columns. In man it passes almost insensibly into the medulla ; in many animals — e. g., the dog, cat, and pig — there is a sharp demarcation between the zona reticularis and the medulla, produced by a thin membranous layer of connective tissue which apparently results from the fusion of the central ends of the fibrous bands in the cortical stroma. Such a membranous septum is usually wanting in the human adrenal. The connective tissue stroma of the adrenal consists of a deli- cate vascular network, which in the cortex contains very few if any elastic fibres. Flint * has shown that this connective tissue is, in large part, at least, a reticular tissue. The capsule consists of dense bundles of white fibrous tissue among which are many elas- tic fibres. The stroma of the medulla is also richly supplied with elastic tissue. The epithelium of the zona glomerulosa is arranged in sphe- roidal groups or in hooked or slightly coiled columns which are continuous with the straight columns of the fascicular zone. The cells of the zona glomerulosa are closely packed within the con- nective tissue meshes and the cell outlines are very indistinct. Wherever their outlines can be readily distinguished the cells are seen to be of columnar shape and are arranged in slender columns whose cells are often grouped about an indistinct central lumen. The cytoplasm of the cells of this zone is finely granular and stains readily with acid dyes. Occasional minute fat droplets appear in the innermost cells of the group, but these are never so abundant as in the more internal portions of the cortex. The nuclei in this zone are spheroidal in shape and rich in chromatin ; they present frequent mitoses (Canalis f),but these are more abundant in early life than in the adult. The cells of the zona fasciculata are highly characteristic. They are arranged in long straight columns which extend from the zona * Contrib. to the Sc. of Med. ded. to W. H. Welch, 1900. f Internat. Monatschr. f . Anat. u. Physiol., 1877. FIG. 357. — FROM A TRANSECTION OF THE HUMAN ADRENAL. The figure includes one half the breadth of the organ ; it extends from the central veins in the middle of the medulla to the capsule on the free surface, a, peri-adrenal connective tissue ; 6-6, capsule ; c, zona glomerulosa ; d, zona fasciculata ; e, zona retic- ularis ; /, medulla ; g, central vein in transection. Hematein and eosin. Photo, x 60. 446 THE SUPRARENAL GLANDS 447 glomerulosa inward to the zona reticularis. The cells are colum- nar or polyhedral in shape ; many of them contain minute fatty droplets in great abundance. This fat is readily blackened by os- mic acid. Arnold,* by extraction with ether, obtained crystals of palmatin and stearin from the suprarenal gland. Plecnik,f how- ever, considers that the adrenal fat differs in its ultimate chemical properties from the other fat of the body. Each columnar group consists of cells which are, as a rule, in approximately the same stage of fatty metamorphosis, and the cell columns of this zone may be divided into those which are distinctly acidophile and those which are distinctly fatty, though between these extremes there are many intermediate stages. The acidophile cells are ovoid or polyhedral elements which possess one or two highly chromatic spheroidal nuclei and a finely granular cytoplasm. On careful examination with high magnifi- cation, extremely minute fat droplets may often be demonstrated even in the most characteristic of these cells ; with lower magnifi- cation these are frequently invisible. The fatty cells possess a spheroidal nucleus which is usually vesicular in character ; occasionally it is highly chromatic. Fre- quently the apparent chromatolysis seems to progress in exact ratio to the accumulation of fat ; those cells in which the fatty meta- morphosis is more advanced present the more typically vesicular nucleus. With the progress of the fatty metamorphosis the cell outlines are again lost and the granular acidophile cytoplasm gradually replaced. The presence of fat in the broad zona fas- ciculata is partially responsible for the bright yellow color of the cortex of the organ. The cells of the zona reticularis are similar to those of the zona fasciculata, though the fatty metamorphosis is less pronounced. In one particular, however, the cells of this layer are remarkable. They contain an abundance of a peculiar brownish-yellow pigment which occurs both in the form of coarse granules and as a diffuse coloration of the cytoplasm. The spherical nuclei, highly chro- matic or only slightly vesicular in character, are not invaded by the pigmentation. The volume of pigment varies greatly in differ- ent individuals ; it is usually absent in young persons, but is, as a rule, present after the twentieth year of life (Maass J). The epithelial cells of the medulla are ovoid elements with one or two spherical nuclei, which in many cases possess a vesicular * Loc. cit. f Arch. f. mik. Anat., 1902. \ Arch. f. mik. Anat, 1889. 448 THE DUCTLESS GLAXDS character ; in other cells they consist of a dense, almost solid, mass of chromatin. The shape of the cell groups in the medulla varies greatly; usually they form small spheroidal masses or short col- umns. The cells are frequently arranged in a more or less tubular form but without a distinct lumen. Frequently they surround a minute capillary vessel. The medullary cells presumably pour their secretion into the blood vessels, whose broad capillaries or sinusoids (Minot *) permeate the delicate connective tissue bands which inclose the cell groups. Felicine f claims to have demon- strated the presence of minute intra- and intercellular secretory canaliculi which open directly or indirectly through broader lacunce, into the blood vessels. The cell groups of the medulla, like those of the cortex, are divisible into the acidophile and the fatty types ; the former are the more abundant, but the fatty metamorphosis is scarcely ever so advanced as in the cortex. There is, however, great variation in the size of the medullary cells. The larger ovoid elements form the typical groups ; between these groups are narrow cell columns consisting of much smaller and less highly acidophile cells, which are arranged in slender columns and scattered irregular masses. In the vicinity of the central veins, small nerve trunks are found, and occasional minute ganglia or isolated nerve cells occur along their course. These are not to be confused with the large ovoid epithelial cells of the medulla. BLOOD SUPPLY. — The arteries which supply the suprarenal glands form a plexus of vessels in the capsule of the organ and in the neighboring connective tissue. Some of the smaller branches of this plexus, the capsular arteries, supply the capsule itself, others enter the organ and are distributed to the cortex and to the medulla. The blood supplied to the capsular arteries, after traversing the capillaries, enters small venules which are tributary to the lumbar and phrenic veins. The course of the cortical and medullary vessels has been exhaustively studied by Flint. £ The cortical arteries enter the zona glomerulosa where they abruptly break up to form a capillary plexus which occupies the connective tissue between the cell columns. Capillary vessels are continued from this plexus through the intercellular connective tissue of the zona fasciculata, where they are in intimate relation * Proc. Bost. Soc. of Nat. Hist., 1900. f Anat. Anz., 1902 ; also Arch. f. mik. Anat., 1904. \ Loc. cit. u 3D 450 THE DUCTLESS GLANDS with the epithelial cells, and reach the zona fasciculata. Here the capillaries are collected into thin-walled venules or sinusoids. These vessels, after some anastomoses, form venous stems which are continued, without further anastomosis, through the medulla to the central veins. The venules of the cortex possess no walls other than their endothelium. The medullary arteries are also derived from the capsular plexus. They penetrate the cortex, and at the border of the medulla abrrptly terminate in a plexus of capillary vessels which lie in the connective tissue stroma and come into intimate relation with the medullary cells. These vessels possess extremely thin walls, their endothelium often being in direct contact with the adjacent epithelium, whose cells frequently impinge upon the lumen of the capillary vessel (see Fig. 93, page 93). The capil- lary plexus pervades the entire medulla, its vessels being here and there collected into small venules which unite to form the central veins. These form two, or sometimes four, main stems (Flint) which make their exit at the hilum and enter the lumbar or renal vein, or, on the right side, enter the inferior vena cava. 'All of the efferent veins of the adrenal are characterized by a peculiar distribution of their smooth muscle fibres, which occur in considerable abundance, but are nearly all disposed in the axis of the vessel ; the circular muscle fibres are confined to a very thin coat beneath the endothelium, or are often entirely absent. Fre- quently, and especially in the central veins of the adrenal, the coarse bundles of longitudinal muscle fibres project into the lumen of the vessel in a somewhat rugose manner. Whenever two veins unite to form a larger vessel, and at the junction of a central vein with any of its branches, these protuberant muscular bundles are especially prominent. Moreover, the author has frequently ob- served anomalous vessels of a venous nature which arise in the medulla, penetrate the cortex, and enter the venous plexus of the capsule; and in these instances the same peculiar distribu- tion of the muscle has been observed in the veins of the capsular plexus. LYMPHATICS.— The lymphatics of the suprarenal gland, according to Stilling,* form rich plexuses in ttfe zona glomeru- losa and in the medulla ; elsewhere they are less abundant. They follow the course of the blood vessels and are especially well devel- oped in the vicinity of the central veins. * Arch. f. path. Anat., 1887. THE THYEOID GLAND 451 NERVES. — The adrenal is well supplied with small sympa- thetic nerve trunks; in fact, the ontogenetic relations between the adrenal and the large sympathetic ganglia of the solar plexus are extremely intimate, the cells of the medulla apparently taking their origin, in embryos about 3 cm. in length, from the primitive anlages of the sympathetic ganglia. The sympathetic nerves form a plexus in the capsule from which branches are distributed to the cortex and to the medulla. In the cortex they invest the blood vessels with a delicate plexus, but have not been found within the epithelial cell columns. In the medulla they are also distributed to the blood vessels and are supplied with occasional small ganglia. From the plexus of sym- pathetic nerve fibres which invests the groups of medullary epithe- lium, Dogiel * demonstrated delicate fibrils, supplied with minute varicosities, which penetrate between the epithelial cells and ter- minate in a manner very similar to that which is characteristic of the epithelial parenchyma of other secreting glands. II. THE THYKOID GLAND. The thyroid consists of a mass of glandular tubules or follicles, supported by a connective tissue stroma and supplied with a thin but dense fibrous capsule which closely invests the surface of each of its lobes. The Connective Tissue Framework. — The capsule of the thyroid consists of dense white fibrous and elastic tissue, from which tra- beculae, containing the larger blood vessels, pass inward and pro- duce an indistinct lobular subdivision. A network of delicate fibres, among which are very few if any elastic fibres, passes from the trabeculae and invests the glandular follicles, forming a deli- cate basement membrane for their epithelium. Flint f has shown that much of this interf ollicular connective tissue is of the reticu- lar variety. In it are contained the smaller blood vessels and lymphatics. It also contains a few leucocytes, which are scattered about in a diffuse manner. The follicles of the thyroid are ovoid saccules or short branched tubules with frequent diverticula (Streiff {). They vary greatly in diameter and in the calibre of their lumen. Many of them pre- sent scarcely any lumen, others appear, from their extreme size * Arch. f. Anat., 1894. f Johns Hop. Hosp. Bull., 1903. J Arch. f. mik. Anat., 1897. 452 THE DUCTLESS GLANDS (100 to 500 //.), to simulate small cysts. All follicles which possess any considerable lumen contain a peculiar acidophile substance, known as colloid, which is apparently formed by the secretory activity of the glandular epithelium lining the follicles. Colloid is a homogeneous or very finely granular substance which stains readily with eosin, taking a very bright tint closely b FIG. 359. — FROM A SECTION OF THE HUMAN THYROID GLAND. a, thyroid follicles in transaction ; 6, tangential section of the follicular wall. Hematein and eosin. Photo, x 110. resembling that acquired by the hemoglobin of the red blood cells. Frequently, and especially in specimens which have been fixed and hardened in alcohol, it presents a vacuolated appearance. As a rule the lumen of the follicle is not completely filled with THE THYEOID GLAND 453 the colloid mass, which is then adherent to the surface of the lining epithelium by delicate thread-like processes; the colloid thus acquires a deceptive appearance of extreme contraction, as if its surface, except for occasional delicate strands, had been drawn away from the epithelium. Occasionally a single large vacuole, often containing basophile granules or crystalloid particles, occupies the center of the colloid mass in the larger follicles ; at other times the colloid material appears to be broken into minute spherules. In general, the ratio of colloid content within the follicle, roughly stated, is in propor- tion to the age of the individual. The follicles at the periphery of the lobes of the gland are less fully distended than those in the interior. Embedded in the colloid mass within the follicle, even in the apparently normal thyroid, red blood cells and desquamated fol- licular epithelium are frequently found, but never in large quan- tity. Leucocytes are of less frequent occurrence and are more rarely found in the human thyroid than in that of the lower mammals. The follieular epithelium is typically cuboidal in shape ; in young individuals it is somewhat taller than broad. In those fol- licles which are distended with colloid secretion the epithelium is relatively short ; in those which are empty it is taller. Each cell contains a single spheroidal nucleus which lies in the center of the cell, or somewhat toward its basal extremity. This orderly disposition causes the nuclei, when seen in sections of the follicle, to appear as a continuous row in the wall of the alveolus, a dispo- sition which is noticeable for its exceptional regularity. The cytoplasm of the epithelium is finely granular and de- cidedly acidophile. It usually contains some coarse granules and very small fatty droplets, which are prone to occupy the extremi- ties of the cells. Minute spheroidal granules which give the color reactions of colloid are also found in the cytoplasm of the epithe- lial cells. Hiirthle,* by staining with the Biondi-Ehrlich mixture, succeeded in differentiating two types of cell, one lightly staining, the " chief cells," the other a darker colloid-containing type which he designated as " colloid cells." These variations probably only represent different stages of secretion in the same epithelial cell type. Minute intercellular canaliculi occur at the angles between adjacent cells. * Arch. f. d. ges. Physiol., 1894. 454 THE DUCTLESS GLANDS The epithelium rests upon a very delicate reticular basement membrane and is in close relation with the capillaries and lym- phatic vessels of the interfollicular stroma. Colloid material, similar to that within the follicles, has been repeatedly found within the lymphatic vessels (Baber,* Langendorf, f HiirthleJ) and may be readily demonstrated in most sections of the thyroid. Undoubtedly this does not, however, represent the entire " inter- nal secretion " of the gland. Blood Supply. — The arteries form a rich plexus in and about the capsule of the thyroid, from which numerous branches pene- trate the organ, lying in the connective tissue trabeculae between the lobules ; they are distributed to all parts of the gland. They supply a rich capillary plexus in the walls of the follicles. The veins retrace the course of the arteries. The walls of the smaller venules consist only of endothelium, with a very thin coat of elastic connective tissue. Lymphatics. — The thyroid is very abundantly supplied with lymphatic vessels. These form a plexus of very broad lacunar capillaries in the interfollicular connective tissue, where they stand in intimate relation with the follicular epithelium. From this plexus vessels pass to the interlobular connective tissue, in which they form a second plexus, whence lymphatic vessels pass out of the thyroid in company with the blood vessels and enter the deep cervical lymphatic nodes. Nerves. — The nerves of the thyroid are derived from the sym- pathetic and are mostly non-medullated. They accompany the arteries and form a delicate terminal plexus in the walls of the follicles. The finer fibrils of this plexus end in contact with the epithelium. Berkley § found occasional fibrils which apparently penetrated between the epithelial cells, but his observations have not yet been corroborated. ACCESSOEY OR ABERRANT THYROIDS These bodies, first described by Zuckerkandl, || are widely dis- tributed through the connective tissue of the cervical region. They are most frequently found in the course of the embryonic thyreo-glossal duct and in the immediate vicinity of the lateral lobes of the thyroid. They present the appearance of embryonal * Phil. Trans., 1876. f Arch. f. Physiol., 1889, Suppl. Bd. \ Loc, cit. § Johns Hop. Hosp. Rep., 1895. i Stuttgart, 1879. ACCESSORY OR ABERRANT THYROIDS 455 " rests " or remnants of thyroid tissue, but are found in nearly all individuals. The colloid follicles of the aberrant thyroids are usually small, though, in the larger specimens of these bodies, they may attain as great a size as those of the thyroid itself. The cell columns without colloid are more numerous than in the thyroid gland, giving to the aberrant bodies a decidedly cellular appearance. Fia. 360. — FROM THE BORDER OF A MASS OF ABERRANT THYROID TISSUE OF MAN, OCCURRING IN THE REGION OF THE PARATHYROID GLANDS. Hematein and cosin. Photo, x 204. Each aberrant mass is usually inclosed by a very thin connective tissue capsule which sends delicate processes between the cell groups. The epithelial cells retain all the characteristics of those of the thyroid gland, and can be readily distinguished from the epithelium of the parathyroid glands with which the accessory 456 THE DUCTLESS GLANDS thyroid bodies have been frequently confused. They are also much less vascular than the parathyroids. III. THE PAKATHYROID GLANDS The parathyroids are small glandular bodies of irregular distri- bution, usually found in relation with the posterior margin of the lateral lobes of the thyroid gland. Frequently they occur in rela- tion with the tracheal or laryngeal wall and may be found as high Fie. 361. — TRANSECTION or A PARATHYROID GLAND OF MAN. Heinatein and eosin. Photo, x 10, as the hyoid bone or as low as the border of the thymus. In man they are asymmetrical in their distribution, no more than two being present on either side. They also vary greatly in size and shape, but usually -are of ovoid form and about 3 to 5 mm. in diameter. Each parathyroid is invested by a thin capsule of dense con- nective tissue and consists of a mass of epithelial cells supported by a delicate fibrous reticulum. The epithelial cells are of two chief types, designated by Welsh* as the "principal" and the " oxyphile " or acidophile cells. The principal cells are the more abundant. They are ovoid or spheroidal elements, with a clear vesicular cytoplasm, a distinct cell membrane, and a large spherical nucleus, whose chromatin is irregularly distributed and often gives the nucleus, a somewhat vesicular character. * J. Anat. and Physiol., 1898. THE PARATHYROID GLANDS 457 The acidophile cells are of similar shape but are provided with a small spherical nucleus, which is very rich in chromatin, and a granular acidophile cytoplasm. The acidophile are less numerous than the principal cells. The distribution of the epithelial cells is subject to considera- ble variation. Most frequently they form an almost solid epithe- lial mass, in which capillary vessels are here and there found, the larger blood vessels occupying the coarser bands of the fibrous stro- FIG. 362. — FROM A CENTRAL PORTION OF THE PRECEDING FIGURE, SHOWING THE AP- PEARANCE OF THE CELLS OF THE HUMAN PARATHYROID GLAND UNDER MODERATE MAGNIFICATION. Several blood vessels are included. Capillary vessels can scarcely be recognized with this magnification. Hematein and eosin. Photo, x 300. ma. In such glands the two cell varieties are either intermingled irregularly, or the acidophile cells may occur in scattered groups which are interspersed among the more numerous principal cells. 458 THE DUCTLESS GLANDS In certain instances the epithelial cells are arranged in small alveolar groups which are surrounded by a network of capillary vessels. This arrangement appears to be more frequent in young individuals. The cell groups in this type of gland frequently form branching columns. Occasionally, epithelial cells surround a central lumen, in which are small masses of an acidophile substance which re- sembles colloid in its reactions. In the experience of the author this colloidal material is less abundant in the human parathyroid than in that of the lower mammals. Likewise the cystic ducts, lined by columnar or ciliated columnar epithelium, which have been described by Kohn,* though of frequent occurrence in the lower mammals are rarely, if ever, found in the human parathyroid. The connective tissue of the gland is of variable quantity. It forms a thin but dense capsule ; occasionally trabeculae extend inward and partially outline indistinct lobules. In many instances a hilum transmits the larger bloodvessels by means of vascular trabeculae which radiate to all portions of the organ. A delicate fibrous or reticular stroma invests the individual cells, or the cell groups, when these are present. Occasionally the cells are so closely packed that the stroma is scarcely demonstrable. The blood supply of the parathyroid is exceedingly rich. Arteries enter from the capsule, or at the hilum, and rapidly break up into a plexus of broad capillary or sinusoidal vessels which follow the fibrous bands of the stroma and are in intimate relation with the epithelium. They are collected into thin-walled venules which retrace the course of the arteries. IV. THE CAROTID GLAND This body was first carefully described by Luschka f and, from its intimate relation to the blood vessels and nerves, is also known as the glomus caroticum or ganglion inter car oticum. It consists of scattered masses of epithelial cells, usually grouped in small spheroidal clumps or "cell balls" embedded in the connective tissue. Kohn { has described four types of the gland according to the density of its parenchyma — the type found in man consists of scattered cell groups ; in the rabbit they are even more diffuse. The carotid gland of a cat consists of a single cell mass, while that of the ape is intermediate between that of the cat and man. * Arch. f. mik. Anat., 1897. f Arch. f. Anat., 1862. J Arch. f. mik. Anat., 1900. THE CAEOTID AND COCCYGEAL GLANDS 459 The nature and genesis of the glandular cells is somewhat doubtful. They are ovoid elements with finely granular cyto- plasm and a spheroid- al, somewhat vesicu- s lar nucleus. Many of \ ,/ them contain a yellow- ^ >.' ish pigment which is intensified by fixation . ~~ in solutions of potas- £*J sium bichromate ''m/f'^ (Kohn). This is the jff;*ff so-called chromofine reaction which is like- wise exhibited by the / medullary cells of the Suprarenal glands and FlG' ^.-CAROTID GLAND OF AN APE. hv man v TIPT-VP ppll* Chr9> a " chromofine cel1 " J *i connective tissue sep- UJ l "v 1 turn. Portions of two adjacent lobules are included in The Carotid gland the figure, x 200. (After Kohn.) is richly supplied with capillary blood vessels and small non-medullated nerve trunks. The capillaries are in intimate relation with the glandular epithelium. V. THE COCCYGEAL GLAND This small body — 2.5 mm. in diameter (Eberth) — was discov- ered by Luschka * in 1860. Its structure closely resembles that of the carotid gland. It usually consists of several minute / • ' \ groups of epitheli- / ' >, Ibid cells which are / in relation with the / °rt'-; '"I terminal branches ; / of the middle sac- ral artery. It is richly supplied with broad capillaries or sinusoids and hence is also known as FIG. 364.-FROM A SECTION OF THE COCCYOKAL GLAND OF the ffhmUS COCCy- MAN. Highly magnified. (After Sertoli.) * Arch. f. path. Anat., 1860. 460 THE DUCTLESS GLANDS The parenchymal cells of the organ are ovoid elements which are closely packed about the walls of the blood vessels in groups or short columns inclosed by delicate sheaths of connective tis- sue. The origin and function of these cells are unknown. The organ is embedded in the dense connective tissue at the tip of the coccyx. VI. HYPOPHYSIS CEKEBKI (Pituitary Body) This body consists of two distinct lobes, an anterior and a posterior. The posterior is largely composed of nerve elements ; the anterior is more distinctly glandular. This difference in structure is doubtless depend- ent upon the genesis of the organ, the posterior lobe being developed as an outgrowth from the second cerebral ves- icle or diencephalon, the an- terior arising as a diverticulum from the oral cavity of the fetus. The cellular elements of the posterior lobe include ependyma cells, neuroglia cells, small nerve cells, and a few epithelioid cells (Berkley *). The anterior lobe consists of epithelial cells which occur in small groups and irregular strands, between which are broad sinusoidal capillaries. The cells are ovoid in shape, of a finely granular appearance, and possess large spheroidal nuclei. Some of them, the chromophile cells, are somewhat acido- phile and granular ; the chief cells, on the other hand, show no special affinity for acid dyes. In this they resemble the cells of the parathyroid gland. Occasionally the cell columns of the pituitary gland assume a tubular or follicular character and in FIG. 365.— FROM A SECTION OF THE HY- POPHYSIS CEREBUI OF A DOG. a, blood vessels ; 6, endothelium of the vascular wall ; c, glandular epithelium, x 300. (After Szyuionowicz.) Johns Hop. Hosp. Rep., 1895. HYPOPHYSIS CEREBRI 461 these cases the lumen often contains a colloid mass resembling that found in the thyroid follicles. The organ is richly supplied with blood vessels, which form an extensive capillary plexus among the cell columns and are thus brought into intimate relation with the glandular epithelium. The nerves of the anterior lobe, according to Berkley, are derived from the sympathetic, and terminate in varicose end fibrils which are in contact with the epithelial cells. The nerve supply is relatively scanty. CHAPTER XXIII THE NERVOUS SYSTEM A. ITS TISSUES AND DEVELOPMENT THE nervous system is readily divisible into two anatomical portions, the central and the peripheral. The central nervous system (cerebro-spinal axis) includes, as its more important gross divisions, the cerebrum or telencephalon, its large basal nuclei (optic thalmi, etc.) or diencephalon, the crura cerebri and corpora quadrigemina or mesencephalon, the pons Varolii and cerebellum or metencephalon, the medulla oblongata or myelencephalon, all of which lie within the cranial cavity and are collectively called the brain, and the spinal cord or myelon which is contained within the medullary cavity of the vertebral column. The peripheral nervous system includes the cranial and spinal nerve trunks with their cerebro-spinal ganglia, and the sympa- thetic nerve trunks and ganglia, together with their peripheral nerve endings, the motor and sensory end organs. These portions have been already described in Chapters VIII and IX. Though the above anatomical divisions are macroscopically distinct and are of great convenience in description, it must be borne in mind that the histological elements, the cell units called neurones, are not confined to any one gross division, but may, as a nerve cell with its many processes, be traced in direct anatomical continuity through several such gross divisions. Some neurones, for example, whose cell bodies lie in the posterior root ganglia of the spinal nerves may be followed throughout a peripheral nerve trunk on the one hand, while on the other it sends a process cen- tralward which enters the spinal cord and passes all the way to the medulla oblongata. The central nervous system is said to consist of grey and white matter, the grey matter being composed chiefly of nerve cells with NEUEOGLIA 463 their non-medullated processes, the white matter containing only the medullated processes of the nerve cells, which are known as nerve fibres. THE 'SUPPORTING TISSUES OF THE CENTRAL NERVOUS SYSTEM.— Both the grey and the white matter of the central nervous system contain a peculiar supporting tissue, the neuroglia, which consists of two elements, the glia cells and the glia fibres. 464 THE NEKVOUS SYSTEM The latter are very probably produced by the glia cells, of which they were formally considered to be processes. The glia cells, as seen in Golgi preparations, are divisable into two distinct types, the ependyma cells and the astrocytes. The ependyma cells may be considered as undifferentiated relics of the embryonal cells, from which both glia and true nerve or ganglion cells were presumably developed. These cells line the central canal of the spinal cord and the ventricles of the brain, in which latter organ they also form the covering or outer coat of the telae choroidei. The ependyma consists of long nucleated columnar cells whose free ends, in fetal and early life, carry a tuft of cilia ; in adult life FlG. 367. — A LONG-RATED ASTBOCYTE. Golgi's stain. Highly magnified. (After Berkley.) they are usually non-ciliated. The attached ends of these cells are embedded in the surrounding gelatinous tissue, and are fre- quently prolonged for some distance as a fine branched process. In this way the ependyma of the spinal cord enters into the for- mation of the substantia gelatinosa centralis, in which the branched processes of its cells ramify in a glia-like manner. In the fetus the filamentous processes extend from the central canal all the way to the periphery of the spinal cord. In the adult the epen- dyma cells are prone to so multiply as to almost occlude the central canal ; their processes have apparently become shorter, and now reach the surface of the spinal cord only at its posterior median sulcus. NEUROGLIA 465 The astrocytes (Belter's cells), when stained by the Golgi method, apparently consist of a small cell body and an innumera- ble number of long slender processes. Two varieties of these cells are recog- nized; the spider cell or long-rayed astrocyte, with a small cell body and very many exceptionally long and slen- der processes; and the mossy cells or short-rayed astrocytes, whose processes are shorter and somewhat thicker but decidedly more varicose than those of the long-rayed tvpe. Fi»- 368.— A SHORT-RAYED ASTRO- Recent investigations by means of OYTE' OB MOSSY CELU the staining methods of Weigert, Mai- Golgi's lory, and Benda, have demonstrated that the astrocytes, as seen in the Golgi preparations, probably in- clude two distinct structures, the glia cells and the glia fibres. Olia cells, as seen in sections prepared according to these meth- ods, appear as small cytoplasmic cells with large and deeply staining nuclei. In the small glia cells the cytoplasm is so slight as to form scarcely more than a mere rim about the nucleus ; in the larger cells the cytoplasm is more abundant and the processes larger and more numerous. The presence of cytoplasmic proc- esses gives the cell an irregularly stellate appearance. In Golgi preparations these processes can not be distinguished from the dense network of glia fibres with which they are surrounded. The glia fibres comprise numerous filiform fibrils which occur as a dense network around the glia cells, from which they radiate in all directions. They pass alongside of, over, or under the glia cells ; their filaments have even been described as passing entirely through the cytoplasm of the cell. Nevertheless they appear at all points to be anatomically distinct from the cell body. The relation of the glia cells to the fibres of neuroglia is perhaps comparable to the arrangement in fibrous or reticular tissue. The fibres of each of these tissues appear to be ontogenetically derived either directly or indirectly from its cells, yet when fully formed they often exist as anatomically distinct elements. Neuroglia cells and fibres occur in both the grey and white matter of the central nervous system, though perhaps more abun- dant in the latter. The fibres radiate for considerable distances from their glia cells, and thus form a supporting tissue for the 31 466 THE NEKVOUS SYSTEM nerve elements. They are frequently in intimate relation with the blood vessels, on the walls of which many of the glia fibres, particularly the thicker or mossy cell variety, terminate in ex- FIG. 369. — NEDKOGLIA CELLS AND FIBRES FROM THE SPINAL CORD OF AN ELEPHANT. The letters indicate various types of neuroglia cells. Z, a leucocyte. Beiida's stain. x 940. (After Hardesty.) panded plates, which, in some parts, form an almost complete outer membranous coat of the vessel. The astrocytes are ontogenetic derivatives of the embryonic ependyma cells. From their point of origin around the neural canal they wander to all portions of the central nervous system, and even into the optic and olfactory tracts, which are embryonic outgrowths from the fetal cerebral vesicles. Thus neuroglia oc- curs throughout the brain and spinal cord, and also in the olfac- tory nerves, the optic chiasm, and the retina of the adult. The supporting tissues of the central nervous system include, besides the neuroglia, numerous bands or trabeculae of fibrous connective tissue, which push inward from the pia mater, carrying with them the vascular branches for the supply of the nervous tissues, and which penetrate deeply into the substance of the spinal cord and brain. THE NEURONE 467 THE NEURONE.— The nerve elements of the central, as well as the peripheral, nerv- ous system include the nerve cells and the nerve cell proc- esses; the latter are usually called nerve fibres. This sub- division, which has been hand- ed down from former times, when it was considered that nerve cells and nerve fibres were independent elements, is still useful for descriptive pur- poses. However, it must be constantly borne in mind, and can not be too often empha- sized, that these two terms are merely descriptive of two portions of the same anatom- ical unit, the neurone. Thus the neurone forms the structural unit of the en- tire nervous system. This unit has already been dis- cussed in its relation to the nervous tissues,* but the im- portance of a correct impres- sion of its bearing on the structure of the central nerv- ous system as at present in- terpreted, makes it advisable at this time to briefly review its structure. A neurone is an animal cell. It consists of a cell body (nerve cell, ganglion cell, perikaryori) with all of its va- rious processes. These proc- esses include the dendrites, which are considered as usu- FIG. 370. — DIAGRAM OF A NEURONE. aft, axone hillock ; ax, neuraxis ; c, cyto- plasm ; d, dendrites ; TO, myelin sheath of the nerve fibre ; m', muscle fibre ; n, nucleus ; w', nucleolus ; n. of n, nucleus of the neurilemma ; nR, node of Ranvier ; s/, collateral ; sL, seg- ment of Lanterinann ; tel, telodendrion. (After Barker.) * See Chapter VIII. 468 THE KffRVOUS SYSTEM ally transmitting cellulipetal impulses, and the neuraxes and col- laterals, which transmit cellulifugal impulses. The cell body or nerve cell has already been sufficiently described.* The dendrite is a broad arborizing process whose substance closely resembles the cytoplasm of the cell body in its microscop- ical appearance and in its staining reactions. It branches freely, but always dicotymously, and usually ends at a point not very remote from its cell body. The neuraxis (nerve fibre, axis cylinder process, axon, dendron, neurite, etc.) is a long and slender process. It arises either directly from the cell body or indirectly from the trunk of one of its den- drites. It gives off numerous collaterals at right angles to the parent fibre throughout the greater part of its course, and finally terminates, as do also its collaterals, in an end brush (terminal arborization, felt work, basket work, etc.), or in one of the several forms of peripheral nerve end organs, The end brushes are apparently formed by the rapid separation of the fibre into its component fibrillae. The neuraxis is usually a much longer process than are the dendrites. Unlike the latter, it extends not merely to other por- tions of the grey " nucleus" in which its cell body lies, but fre- quently it passes without interruption of its anatomical continuity to other and even very distant parts. The wide radius through which these fibres are distributed is well illustrated by the passage of neuraxes, coming from nerve cells of the cerebral cortex, to the grey matter of the spinal cord ; other nerve cells in the spinal cord send their neuraxes through the entire length of the spinal nerve, to supply even the most remote tissues of the body. While, there- fore, the cell bodies and dendrites are measured in millimetres or micromillimetres, the neuraxis is often to be measured only in centimetres and decimetres. There are very few cells in the body which are in any way comparable to the nerve cell or neurone for the large size of its cell body and the extensive area of distribu- tion of its processes. All portions of the neurone, its neuraxis and collaterals as well as its dendrites, are dependent upon the cell body for nutrition ; hence each nerve cell becomes the so-called trophic center for all of its processes. The entire nervous system may be considered as an enormous tangle, formed by the interlacing processes of an innumerable * Chapter VIII. THE NEURONE 469 number of neurones whose complex fibre paths place all portions of the body in communication with all other portions. Nerve cells are unequally distributed throughout the central nervous system; they therefore occur in more or less distinct groups or nuclei, from each cell of which a neuraxis is frequently distributed along the same path. The larger bundles thus formed are called tracts; the smaller ones, funiculi, fasciculi, or fibre bundles. Since each fibre of such a tract is dependent for nutrition upon the nerve cell from which it arises, the tract as a whole must de- pend upon its nucleus of origin for its nutrition. Each nucleus therefore becomes the trophic center for the fibre tract to which it gives origin. It may be readily demonstrated that if any such group of neu- raxes be cut or otherwise separated from its trophic center, that tract will promptly degenerate. If these neuraxes happen to be the axis cylinders of medullated nerve fibres, as is often the case, their myelin sheaths become rapidly altered in composition and acquire a tendency to disintegrate into small globular granules, which stain deeply with osmic acid when used according to the method of Marchi. For the experimental demonstration of this form of partial cell death occurring in that portion of the neurone which has been cut off from its cell of origin, we were originally indebted to the eminent English physiologist Waller ; the result- ing changes are therefore called Wallerian degeneration. Obviously that portion of a neurone or of a fibre tract which, after injury or disease involving its path, still retains its connec- tion with its cell body or trophic center, will not degenerate. This part of the neurone is called its central portion, in contradistinction to its distal portion, the latter of which has been severed from its trophic center and is consequently degenerated. To the study of the various types of Wallerian degeneration we are indebted for many of the facts by means of which the intri- cate tangles of neuraxes composing the various fibre tracts of the central nervous system have been partially unraveled. The Anatomic Relations of the Neurone. — The many neurones in the nervous system are in relation with one another through their neuraxes, collaterals, and dendrites, and by their peripheral proc- esses are closely connected with all the organs and tissues of the body. Our former conception regarded the processes of any one neurone as being nowhere in direct anatomical connection with 470 THE NEKVOUS SYSTEM those of any other neurone nor with any other tissue within the body ; their relation to one another is as a rule one of contiguity rather than of anatomical continuity. The observations of Apathy, Bethe, Held, and others, have demonstrated that neurofibrils are at times continued from one neurone to another. But while these observations serve as an important addition to our knowledge of the histology of the nerv- ous tissues, they do not materially alter our conception of the neurone as an anatomical unit of the nervous system, any more than the occasional occurrence of a syncytium modifies our views of the cell as an anatomical unit of body structure. The neurone is a nerve cell in the broadest sense of the term. The connection existing between the several tissue elements of the body and the peripheral neuraxes of the nervous system takes place through the intervention of the nerve end organs, motor and sensory, in nearly all the tissues of the body, at the peripheral terminations of the nerve fibres. These end organs have been described in a previous chapter, and will not need further discus- sion at this time. The contiguous relationship of different neurones within the nervous system occurs in any one of several ways. The terminal arborizations or end brushes of one neurone may interlace with : — a. the end brushes of neuraxes belonging to other neurones, b. the end brushes of collaterals of other neurones, c. the dendrites of other neurones, or d. the terminal arborization may surround, basket-like, the cell body of other neurones. Golgi Cell Types. — The length of the neuraxis varies greatly in different neurones. Dependent upon this fact, as demonstrated in preparations by the staining method of Golgi, nerve cells have been classified into two cell types, Golgi cells, Type I, and Type II. a. Golgi cells, Type 7, viz., those having long neuraxes. The neurones of this type send their neuraxes beyond the con- fines of the grey nucleus in which their cell bodies lie and in which their dendrites are distributed. Such, for example, are the periph- eral motor neurones whose cells lie in the spinal cord, and whose neuraxes are distributed to the various muscles of the body ; such also are the central motor neurones whose cells lie in the cerebral cortex, and the end brushes of whose neuraxes surround the cell GOLGI CELL TYPES 471 bodies of the peripheral motor neurones in the spinal cord. Cells of this type are familiarly known as the " Deiters' cells." FIG. 371. — GOLGI CELL, TYPE i. c, collaterals ; w, neuraxis. Golgi's stain. (After Kolliker.) b. Golgi cells, Type II (Golgi cells), viz., those having short neuraxes. The neuraxes of cells of this type do not leave the grey nucleus in which they take origin. Their branching begins almost imme- diately and their end brushes are found in the immediate vicinity of their cell body. These cells undoubtedly serve to place neigh- boring neurones in close physiological relation, whereas the cells of the first type connect distant parts. The size of a nerve cell is thought to bear a general relation to the length of its neuraxis, the larger cells possessing the longer neuraxes. The cells of Golgi's Type I are therefore larger than those of Type II. Likewise the cells of the motor tracts, whose 472 THE NEBVOTTS SYSTEM neuraxes are as a rule much longer than those of the sensory tracts, are characterized by their large size as compared with the sensory cells. FIG. 372.— GOLGI NERVE CELL, TYPE n. a, neuraxis ; #, dendrite. (After Kolliker.) DEVELOPMENT OF THE NERVOUS SYSTEM A familiarity with the principal stages in the course of the development of the nervous system is necessary for the proper appreciation of its histology. The appearance of the first anlage of the nervous system occurs DEVELOPMENT OF THE NERVOUS SYSTEM 473 at a very early stage of embryonic life ; is, in fact, the first differ- entiation which can be observed after the subdivision of the blas- toderm into its three primary layers. The epiblast very early pre- sents a shallow longitudinal groove bordered on either side by a slight ridge; this is the neural groove, bounded by its neural ridges. The ectodermal cells forming the neural ridges multiply much more rapidly than those lying in the bottom of the groove ; conse- Headfold Neuro- pores Head plate Foregut Yolk vei Medullary groover-- Somite. FIG. 373. — RECONSTRUCTION OF THE ANTERIOR PORTION OF THE BODY OF A CHICK, THE HEAD DISTINCTLY DIFFERENTIATED, SEEN FROM THE SURFACE. (After Kolllliann.) quently the ridges come more and more to overhang the groove, and by continued growth they finally meet along the median line. The opposed surfaces of the two lateral ridges then fuse together and the former groove becomes a tube, the neural canal, which is at first much flattened from side to side, its ventro-dorsal being considerably greater than its transverse diameter. At this stage the neural canal resembles a long axial slit bounded upon all sides by epiblastic cells. The caudal portion of the neural canal is destined to become 474 THE NEBVOtTS SYSTEM the central canal of the spinal cord, its cephalic portion forms the cerebral vesicles. The former portion retains an approximately equal caliber throughout ; the latter soon presents three character- istic dilatations, the three primary cerebral vesicles, whose walls respectively develop the prosencephalon, mesencephalon, and rJiom- bencephalon. The first and third of these primary cerebral vesicles soon subdivide into two each, five secondary vesicles being thus formed. These five vesicles are the telencephalon, diencephalon, mesencepha- lon, met encephalon } and myelencephalon. The following table exhibits the relation of the several primi- tive vesicles to each other as well as to the gross divisions of the central nervous system : (I. TELENCEPHALON (endbrain) II. DIENCEPHALON (interbrain or ' ENCEPHALON (brain) NEURAL CANAL II. MESEN- CEPHALON MYELON (spinal cord) III. MESENCEPHALON % (midbrain) ( <™^™») III. RHOMBEN- f IV. METENCEPHALON CEPHALON I (hindbrain) (rhomboid \ brain) ( V. MYELENCEPHALON (afterbrain) The encephalon develops the various portions of the brain, the cranial nerves and their ganglia. The myelon forms the spinal cord, the spinal nerves and their ganglia. The sympathetic nerves and ganglia are outgrowths from the cerebro-spinal nerve roots. The following lists will show more definitely the destination of the several portions of the encephalon and the parts of the brain formed from each of the cerebral vesicles. 1. From the Telencephalon, — The anterior end of the third ven- tricle, the lateral ventricles, the foramen of Monroe, the cerebral hemispheres with their cortex or pallium, the olfactory bulb and its tracts (sometimes called the rhinencephalon), the corpora stri- ata, the corpus callosum, and the fornix. 2. From the Diencephalon. — The third ventricle, the optic nerve and retina, the optic tracts (pars optica hypothalmi), the optic DEVELOPMENT OF THE XEKVOUS SYSTEM 475 thalamus, the cerebral portion of the pituitary gland, the pineal gland, and the corpora mamillaria. 3. From the Mesencephalon. — The corpora quadrigemini, the crura cerebri (pedunculi cerebri), and the aqueduct of Sylvius. 4. From the Metencephalon. — The isthmus rhombencephali, pons Variolii, and cerebellum. 5. From the Myelencephalon. — The medulla oblongata. The Ependyma. — The epiblastic cells which line the lateral walls of the slit-like neural canal become elongated or columnar in shape, and are called ependyma cells. Many of these are germinal cells, exhibiting the various stages of mitosis ; the resulting cells promptly differentiate into two distinct varieties, the spongioblast and the neuroblast. The spongioUasts are long cells whose expanded bases line the neural canal and whose elongated bodies are directed outward toward the surrounding mesoblastic tissue. The interlacing proc- esses of these cells, together with those from the neuroblasts, form a network or neurospongium. The spongioblasts are destined to develop the neuroglia. The neuroblasts are small ovoid or fusiform cells, which, though usually bipolar, very early develop a long peripheral process directed away from the neural canal ; this process is the primitive neuraxis. In those cells which are to form the nerve roots and the peripheral ganglia this process grows outward into the sur- rounding mesoblast, the cell gradually migrating along the same course, but leaving in its wake the developing central process which in some cases is dendritic in character, but in others is des- tined to form a second centrally directed branch of the neuraxis. It is by means of this property of locomotion that these cells reach their destination in the various cell groups or nuclei in the brain and spinal cord or in the peripheral ganglia. In this way the fibre paths or tracts of the central nervous system as well as the cranial and spinal nerves and their ganglia are formed. Since, during the period that the neuroblast is performing this migration, it is also developing its neuraxis and dendrites, by the time it reaches its permanent location its principal portions, cell body, neuraxis, and dendrites are already formed and are ready to functionate. The further history of the neuroblast is merely one of continued growth, pushing forward its neuraxis to still more distant and more complex relations. 476 THE NEKVOUS SYSTEM The development of the posterior nerve root ganglia forms a striking example of the history of the neuroblast, as above de- scribed. The manner in which these cells are derived from cells lying in the wall of the neural canal can be readily appreciated by examining successively Figures 374 to 376. After their develop- ment has been completed each of these neurones comprise a nerve cell situated in the posterior nerve root ganglion of a spinal nerve, from which one branch of its T-shaped process passes through the spinal nerve toward the periphery, while the other branch, through the posterior root, enters the spinal cord to terminate in its cen- tral grey matter either at or near the level at which it enters, or possibly at a much higher and more remote level. FIG. 374. — DIAGRAM OF A TRANSECTION OF THE SPINAL CORD OF AN EARLY EMBRYO, SHOWING THE MIGRATION OF NEUROBLASTS TOWARD THE MAR- GINAL VEIL AND THE DORSAL NERVE ROOT. a, neural canal ; 6, dorsal root. (After His.) FIG. 375. — TRANSECTION OF THE SPINAL CORD OF A HUMAN EMBRYO OF FOUR WEEKS. The central canal is immediately sur- rounded by ependyma cells. The peripheral nerve cells are shown on the left of the figure. The nerve roots are already pushing out- ward from the primitive cord, d, dorsal ; t>, ventral nerve roots. (After His.) Myelinization. — Having attained its full area of distribution, the last change in the neurone to mark the completion of its development is the appearance of its myelin or medullary sheath. The period at which this sheath is obtained varies with the differ- ent tracts of fibres in the nervous system, and seems to be syn- DEVELOPMENT OF THE NERVOUS SYSTEM 477 chronous with the appearance of their function. Thus those neu- rones, e. g., the peripheral sensory neurone, which in the fetus are first acted upon by stimuli from without, are the first to obtain a roe. post. FIG. 376. — TRANSECTION OF THE SPINAL COED OF AN EMBRYO CHICK. c. rad. ant., neuraxes to the ventral roots ; c. rad. post., neuraxes to the dorsal roots ; col, collateral from a neuraxis back to the grey matter ; gg, dorsal root ganglion ; rac. ant., ventral root ; rac. post., dorsal root. (After van Gehuchten.) myelin sheath. Following these, medullary sheaths are formed in the peripheral motor neurones, and reflex movements begin ; still later, myelin sheaths appear in the intrinsic neurones of the paths of the spinal and cranial nerves which conduct sensory im- pulses toward the brain ; and finally, the cerebral sensory and motor neurones receive their myelin sheaths, and consciousness and voluntary movements are manifested. To this peculiarity in the formation of the medullary sheaths, as well as to the phenomena of Wallerian degeneration, we are in- debted for much of our knowledge of the course of the fibre tracts in the central nervous system. If, for example, sections from the spinal cord of embryos of suitable age be stained to show their myelin sheaths, certain tracts or fibre bundles will be found to have already acquired their medullary coat, while in other bundles the myelin has not yet made its appearance. Thus in a fetus at the seventh or eighth month the sensory paths of the spinal cord will be found to be well medullated, while the adjoining motor paths show scarcely any myelinization. This method of study, the myelinization method, together with the degeneration method and the staining methods of Golgi, have supplied most of our knowledge concerning the course of the intricate fibre paths of the brain and spinal cord. CHAPTEE XXIV THE NERVOUS SYSTEM {Continued) B. HlSTOLOGICAL MORPHOLOGY THE spinal cord and brain collectively form a long slender mass consisting of conduction paths or fibre tracts, which are for the most part axially disposed and connect more or less distant groups of nerve cells. Each cell group controls the functions of a limited portion of the body, to which its neuraxes pass in bundles that follow definite paths. These paths are the so-called tracts, and the cell group which gives origin to the fibres of any one tract is its center or nucleus. The cerebro-spinal axis is thus composed of many series of such nuclei with their connecting tracts ; the nuclei collectively forming the grey, and the tracts the white matter. Except for the cortex of the cerebrum and of the cerebellum the grey matter is, as a rule, centrally, and the white matter peripherally disposed. Thus in the spinal cord the grey matter consists of a central H -shaped mass extending from the filum terminale upward to the medulla. Above this level the continuity of the central grey mass suffers frequent interruption from the irregular and oblique disposition of the fibre tracts of this region, so that above the medulla the grey matter is only represented by a series of islands (nuclei), each containing one or more cell groups. In the cerebrum and cerebellum these central nuclei are sepa- rated from the grey matter of the cortex by an intervening stratum of white matter ; in these locations the larger mass of grey matter is found on the surface of the white medulla. The peculiar disposition of the grey matter of the brain is ex- plained by the progress of its development. In the early embryo the cerebral vesicles are at first surrounded by a cell mass only. From these cells the fibre processes grow out, and in so doing the excessive formation of fibres at the cephalic end cuts off the grey matter of the cortex (pallium) from the more caudal portions. 478 THE SPINAL CORD 479 This separation is increased by the growth into the cerebrum of the centripetal fibre paths coming into the brain from the more caudal parts. The grey matter of the cerebral cortex may thus be said to represent a cephalic mantle or covering, which, by its stem of nerve fibres, is supported above the cephalic end of a grey axis of nerve centers which extends from the base of the cerebrum through the midbrain and medulla oblongata to the spinal cord. This cerebro-spinal axis is developed in two symmetrical halves, which are more or less completely separated from each other by two series of deep sulci or fibrous septa, the one dorsal and the other ventral. In the brain the dorsal is a deep sulcus, the ven- tral a mere fibrous septum or raphe. In the spinal cord the con- dition is reversed, the anterior or ventral median fissure forming a deep sulcus, while the posterior is a shallow groove deepened by a prominent median septum. The cerebro-spinal axis will be best appreciated by a study of its several regions, in succession, from below upward. The fol- lowing subdivisions are convenient for purposes of description : (1. Sacral region 2. Lumbar region * rru • /J ix 8. Thoracic (dorsal) region 4. Cervical region a. Myelencephalon — 5. Medulla oblongata ( 6. PonsVarolii BRAIN (cepha- lon) . b. Metencephalon j ?> Cerelbelum c. Mesencephalon — 8. Region of the crurse cerebri (brain-stein) d. Diencephalon — 9. Region of the optic thalami (basal nuclei) ^ e. Telencephalon — 10. Cerebral cortex (pallium) THE SPINAL CORD (Figs. 377 to 381).— The spinal cord con- sists of a considerable mass of central grey matter which is sur- rounded by a layer of nerve fibres, the white matter. The grey matter consists of two lateral portions united by a central commissure (grey commissure, posterior commissure). Each lateral portion includes an anterior and a posterior horn with an intervening deeper portion, the central mass or "intermediate zone " of Golgi. The anterior is somewhat broader than the posterior horn. Its cells supply neuraxes, which, after uniting into bundles, pass ventral ward through the white matter to form the ventral (ante- rior) nerve roots. 480 THE NERVOUS SYSTEM The spinal cord may be considered as consisting of ontogenetic segments whose number corresponds to the number of the spinal nerves. Hence each segment contains the anterior horn cells whose neuraxes form the ventral root of the corresponding spinal nerve. In an entirely similar manner the posterior horns of the grey matter receive a large portion of the incoming fibres of the pos- terior roots, which in large part form end brushes around the cells of the dorsal horns and the intermediate zone. The dorsal roots enter through a distinct longitudinal groove, the postero-lateral sulcus. At the exit of the ventral roots there is, however, only a broad shallow indentation, these roots making their exit in isolated bundles distributed through a vertical plane of considerable width. The dorsal root fibres of each segment, on the other hand, enter in a single compact mass. The grey matter consists of a dense tangle of nerve cells and fibrils, together with neuroglia and blood vessels. The fibrils of a given area are derived not only from nerve cells in their imme- diate vicinity, but also include many processes which come from very distant regions. The grey reticulum is thus supplied from fibres of the ventral and dorsal nerve roots, together with innu- merable collaterals, not only from the root fibres, but more espe- cially from those fibres which collectively form the many large tracts passing up and down the spinal cord and placing each seg- ment in communication with many other levels of both the spinal cord and brain. The center of the grey commissure contains the central canal which lies in the axis of the spinal cord and is continuous above with the ventricles of the brain. It represents the remains of the fetal neural canal ; and in the young subject is still patent, filled with cerebro-spinal fluid, and lined by columnar cells which are frequently ciliated. In older subjects the cells of the lining epithe- lium have usually lost their cilia, and the lumen of the canal is more or less filled by cell proliferation which involves not only the lining epithelium but also the surrounding glia cells and fibroblasts. The central canal is immediately surrounded by a peculiar gelatinous tissue in which are many glia cells. This mass is called the substantia gelatinosa centralis. A similar area of gelatinous tissue occurs near the dorsal extremity of the posterior horns, and is called the substantia gelatinosa posterior or gelatinous substance of Rolando. THE SPINAL COED 481 The white matter forms a covering or shell around the central grey mass. It increases in thickness from below upward. This peculiarity is the result of the constant addition of centripetal fibres, and a corresponding loss of centrifugal fibres, through the spinal nerves of each successive segment. The posterior median septum extends inward from the shallow sulcus on the dorsal surface of the spinal cord to the central grey commissure, and divides the posterior mass of white matter into two dorsal white columns, lying on either side of the median line, and bounded laterally by the dorsal horns of grey matter and the dorsal nerve roots. The anterior median sulcus in a similar man- ner, splits the ventral portion of white matter into the two ante- rior white columns. This sulcus, however, does not penetrate all the way to the grey commissure but leaves an interval of white matter containing many transverse and obliquely disposed nerve fibres. The ventral or white commissure thus formed connects the two anterior columns of white matter. The spinal cord is thus divided into two lateral and symmetrical halves by a plane passing through the anterior and posterior me- dian fissures and the central canal. Each lateral half includes a central mass of grey matter completely surrounded, except at the grey commissure, by the white matter. The latter is subdivided into an anterior, lateral, and posterior column, each of which ex- tends the entire length of the spinal cord and is apparently (to the naked eye only) continuous above with a similar column in the medulla oblongata. The anterior white column is included between the anterior median sulcus and the ventral grey horns and nerve roots; the lateral columns extend from the ventral roots in front, around the lateral surface of the spinal cord, to the dorsal roots ; the dorsal or posterior columns are included between the dorsal horns of grey matter and dorsal nerve roots, and the posterior median septum. Each of these columns of white matter is again subdivided by connective tissue septa of variable size and number, which extend inward from the pia mater for a considerable distance. Such septa may even penetrate all the way to the central grey matter. One of these septa, more constant than the others, subdivides the posterior column into two portions, a poster o-internal and a postero- external column. The larger blood vessels are distributed along the fibrous septa, taking their origin from the vessels of the pia mater ; the most of 482 THE NERVOUS SYSTEM them are distributed to the white matter, but to some extent they also supply the grey matter. The entire surface of the spinal cord presents, just beneath the pia mater, a thin superficial layer or marginal veil of glia tissue. In the brain this layer is somewhat exaggerated in thickness. THE REGIONS OF THE SPINAL CORD.— The varying num- ber of fibres which are given off at different parts of the spinal cord results in considerable differences in size in its several por- tions. By means of these peculiarities, as well as by the spinal nerve roots to which they give origin, we distinguish a sacral, lum- bar, thoracic, and cervical region. Each of these regions presents certain more or less important morphological characteristics. In the sacral region the investment of white matter is very thin, the grey matter — though actually less in amount than in the more cephalad regions — appearing large by comparison. Both the ven- tral and dorsal horns of grey matter are short and thick. The substantia gelatinosa of Rolando is of consider- able volume. The cell groups in the ventral horns of this region are a ventro-medial and a dor so-lateral. The cord as a whole is small and its transection nearly circular in out- line. The five segments of this re- gion contain the neurone centers for the urinary bladder, the anus, some of the musculature of the lower limbs, and the sensory reflexes of the perineum and genito-urinary organs. Below the sacral region the spinal cord tapers rapidly (conus medullaris) and is continued downward for a considerable distance as the filum terminate. The fibrous membranes which surround the spinal cord continue even farther downward in the medullary canal to form the central ligament, which is finally attached to the sacrum or coccyx. , In the lumbar region there is a distinct enlargement,* chiefly involving the grey substance, which here includes the immense number of cells of the anterior horns whose " motor " fibres enter the large lumbar nerve trunks for the supply of the lower limbs. * In those vertebrates which have no limbs— e. g., the reptiles — the cervical and lumbar enlargements are not found. FIG. 377. — TRANSECTION OF THE SPI- NAL CORD OF A CHILD, THIRD SACRAL SEGMENT. "Weigert stain, x 7. THE REGIONS OF THE SPINAL CORD 483 FIG. 378. — TRANSECTION OF THE SPINAL COBD OF A CHILD, FIFTH LUMBAR SEGMENT. Weigert stain, x 7. These nerve trunks also supply to the cord a great number of centripetal or sensory fibres which enter the dorsal and, later (through secondary neu- rones), the lateral col- umns; thus both of these columns are of large size in and above the lumbar region. The postero-in- ternal column in this re- gion attains an appreci- able size, and a distinct pial septum marks its lateral boundary. The spinal cord is now nearly circular in tran- section, its ventrodorsal being perhaps slightly greater than its transverse diameter. The grey commissure lies very near the middle of the spinal cord, and the anterior median fissure is, therefore, quite as deep as the posterior median septum. Both the ventral and dorsal grey horns are long and thick. Each dorsal horn contains a large area of gelatinous substance, is somewhat longer on its lateral than on its median side, and reaches nearly to the dorsal surface of the spinal cord, opposite the postero- lateral sulcus. The dorsal nerve roots entering at this level are apparently directed toward the middle of the tips of the dorsal horns of grey matter ; once within the spinal cord they pass around to the median side of the dorsal horns. The ventral horns, somewhat larger than the dorsal, present two short and broad protuberances, the one at the antero-mesial, and the other and more prominent at the antero-lateral angle. A similar though less prominent protuberance is seen at the base of the ventral horn, on its lateral aspect. Each of these projections contains a more or less well-defined group of motor nerve cells. The cell groups of the anterior horns in the lumbar region are therefore a ventro-medial, ventro-lateral, and dor so-lateral, together with an ill-defined central group occupying the deeper " interme- diate zone " of grey matter. The nerve centers contained in the lumbar region control the reflexes and musculature of the lower limbs and the lower part of the abdominal wall. 484 THE NEKVOUS SYSTEM FIG. 379. — TRANSECTION OF THE SPINAL CORD OF A CHILD, EIGHTH THORACIC SEGMENT. Weigert stain, x 7. A transection of the spinal cord in the thoracic region is of small diameter, and is very nearly circular in outline. The white matter, since it contains the many nerve fibres going to and coming from the lumbar enlargement, is much more voluminous than the grey matter. The latter is reduced to a comparatively insignificant central mass. The postero-internal col- umn attains a considerable size in this region, and is distinctly marked off from the adjacent postero-lateral column by a fibrous septum derived from the pia mater. The posterior and the lateral columns, having been much augmented by the influx of fibres from the large poste- rior roots of the lumbar nerves, form the larger part of the white matter. The grey matter consequently appears to be pushed forward, its grey commissure lies considerably ventral to the center of the spinal cord, the anterior median fissure is shorter than the posterior median septum, and the tips of the dorsal grey horns are far removed from the surface, being only connected with the postero-lateral sulcus by the slender dorsal nerve roots. In fact, the dorsal horns of grey matter in this region are reduced to a minimum size ; they are short and slender and contain com- paratively few nerve cells. At the base of each dorsal horn, on its mesial side, there is a distinctly outlined cell group whose transection is of oval or cir- cular outline. Indeed, this cell group, the cell column of Clarke, begins in the second or third lumbar segment, and is continued upward to the second or third thoracic — at times even into the lowermost cervical segments — at which level it has dwindled to a relatively insignificant group.* The ventral grey horns are very short and narrow, and their cells can not be subdivided into groups as in the other regions of the spinal cord. In the upper part of the dorsal region a distinct * In the lower lumbar region an ill-defined group of cells occupying a simi- lar position and having the same function is known as the nucleus of Stilling. THE BEGIONS OF THE SPINAL COED 485 protuberance makes its appearance at the base of the anterior horn, on its lateral aspect. This is the precursor of the larger lateral horn of the cervical region. In the upper dorsal region it contains a small cell group, the dorso-lateral. The nerve centers of the dorsal segments control the upper abdominal region, the thorax, and the viscera. In the lower half of the cervical region the spinal cord presents a distinct enlargement, within the grey matter of which are the nuclei for the upper limbs. The spinal cord in this region is somewhat flattened, its transverse diameter considerably exceeding its antero-posterior. The major portion of the white matter is still contained within its dorsal rather than its ventral portion, the grey commissure appearing to lie somewhat in front of the center. The posterior median septum dips inward for a much greater distance than does the anterior median fissure. The posterior columns are decidedly larger than the anterior, and a distinct groove, from which a fibrous septum is continued FIG. 380. — TRANSECTION OF THE SPINAL CORD OF A CHILD, SEVENTH CERVICAL SEGMENT. Weigert stain, x 7. inward, separates the postero-internal from the postero-lateral column. The dorsal grey horns are long, relatively slender, and more divergent than in the lower levels. They do not reach the sur- face of the spinal cord, but are connected therewith by the long, slender dorsal nerve roots. The grey matter of the dorsal horns in this region is more or less invaded by bundles of nerve fibres derived from the lateral and posterior columns ; the tips of the 486 THE NERVOUS SYSTEM dorsal horns are thus almost cut off from the deeper portions of grey matter. The ventral horns are both long and broad. They present three noticeable promontories or processes — a ventral (ventro- medial), a medial (ventro-lateral), and a lateral. The lateral, because of its special prominence, is frequently called the lateral horn, it is one of the noticeable characteristics of the cervical region. Each of these processes contains a corresponding cell group ; hence we distinguish in the cervical enlargement a mesial, a ven- tral, and a lateral group, together with a small intermedia-lateral, which is partially or completely detached from the dorsal por- tion of the lateral group. There is also a small disseminated central group of nerve cells occupying the deeper portion of the anterior horn. The nuclei of the segments included in the cervical enlarge- ment contain the centers for the musculature and sensory reflexes of the upper limbs. The partial control of the pupillary move- ments in the eye is also located in the lowermost segments of this region. In the upper half of the cervical region a transection of the spinal cord, except for its larger size, resembles very closely that of the thoracic re- ^^ gion. The larger size is due to an increase in the white matter of the posterior and lateral columns, consequent upon the acquisition of new fibres which enter the subja- cent segments from the nerves supplying the up- per extremities, together with an increased number of centrifugal fibres from the cerebrum which are distributed to the grey matter of this region. The anterior columns are also much increased in size by the FIG. 381. — TRANSECTION OF THE SPINAL CORD OF A CHILD, FOURTH CERVICAL SEGMENT. Weigert stain, x 7. THE MEDULLA OBLOXGATA AND BEAIN STEM 487 addition of many fibres coming down from the medulla and cere- bellum, which place the nerve centers of the spinal cord in close relation with those of the cranial nerves and with the association centers of the cerebellum. In addition to the large size of its white columns, a noticeable characteristic of the upper cervical region is the prominence of its lateral horns of grey matter. Just dorsal to the lateral horns is also a peculiar reticular formation which results from an invasion of the adjacent portions of the lateral white columns by bands of grey matter. The grey matter thus forms a coarse network whose meshes inclose isolated bundles of longitudinal nerve fibres. The ventral horn cells of this region are scarcely divisible into groups, but a large and distinct cell group, the inter medio-lateral cell column^ occupies the so-called lateral horn. The nuclei of the upper cervical region enervate the skin and muscles of the neck and shoulder, they also supply the diaphragm. The nerve cells of this region not only supply the cervical spinal nerves, but they also send root bundles to the spinal accessory or eleventh cranial nerve. THE MEDULLA OBLONGATA AND BRAIN STEM.— Passing from the first cervical segment of the spinal cord to the lower portion of the medulla, a remarkable rearrangement of the central grey mass is noticed, the change being apparently dependent upon three prime factors, as follows : 1. The passage of numerous bundles of white fibres between .the lateral columns of the spinal cord and the anterior columns or pyramids of the medulla, cuts off the ventral horns of the grey matter ; the detached ventro-lateral portion with its lateral cell groups is thus displaced lateral ward, while the base of the ventral horns with their mesial cell groups remain adherent to the grey commissure near the region of the central canal. Between these two portions of the ventral horns is an irregularly disposed and interlacing mass of nerve fibres, interspersed with fragments of grey matter, which forms the formatio reticularis of the medulla oblongata. 2. The anterior median fissure in this region becomes merely a shallow and deep raphe across which many nerve fibres decussate. Those long fibre bundles which in the spinal cord occupied the lateral and posterior columns are now found in the anterior or ventral portion (pyramids, formatio reticularis, and fillet) of the medulla oblongata. 488 THE NERVOUS SYSTEM 3. The posterior median septum rapidly becomes a deep sulcus which soon broadens out to form the fourth ventricle, thus push- ing the diminished remains of the posterior columns, with the adjacent dorsal horns, farther and farther lateral and ventralward until the dorsal horns finally come to occupy a position in which their long axis is directed, from the grey commissure, lateralward and but slightly dorsal ward. The fibre paths of the posterior columns, consisting now of secondary neurones, having crossed, almost in a body, to the fillet of the opposite side in the ventral portion of the medulla, uncovers the dorso-mesial surface of the dorsal grey horns, leaving them exposed in the floor of the fourth ventricle, which is formed by the much expanded central canal and posterior median fissure. It will thus be seen that the nuclei of the centripetal cranial nerve fibres (sensory nuclei), whose homologues in the spinal cord were found in the dorsal horns, in the medulla oblongata are to be found in the floor of the fourth ventricle, the grey matter which forms this region being both homologous, and nearly continuous, with the dorsal horns of the spinal cord. The nuclei of the centripetal paths (motor nuclei), which in the spinal cord included the various cell groups of the ventral horns, are found in the medulla oblongata in two regions : first, a median group near the anterior median raphe, which, in the lower levels of the medulla oblongata, lies just ventro-lateral to the central canal and grey commissure, but higher in the medulla is found on either side of the median line beneath the floor of the fourth ventricle, from which it is separated by a layer of grey matter continued upward from the grey commissure of the spinal cord ; and second, a lateral group representing the detached tips of the ventral horns, which is now found well toward the lateral surface of the medulla oblongata, and which in the lower part of the medulla forms the lateral nucleus, but higher up becomes the nucleus ambiguus of the ninth and tenth cranial nerves. The laterally displaced dorsal horns are now separated from the detached portions of the ventral by an insignificant column of white fibres, the upward continuation of the lateral columns of the spinal cord. It will later be shown that the motor fibres of the twelfth, sixth, fourth, and third cranial nerves take their origin from the medial group of nuclei, while the motor portions of the tenth, ninth, seventh, and fifth nerves arise from the lateral group. The THE MEDULLA OBLONGATA AND BRAIN STEM 489 sensory portions of this latter group of cranial nerves arise, or rather their peripheral neurones terminate, in the medulla oblon- gata in the cell groups of the dorsal horns which lie in the floor of the fourth ventricle and not far removed from the median line ; this is the case with the tenth, ninth, and a part of the ves- tibular portion of the eighth nerves. In the upper rhomben- cephalon, at the level of the pons Varolii, the dorsal grey nuclei, though more laterally situated, are displaced somewhat ventral- FIG. 382. — TKANSECTION OF THE LOWER MEDULLA OBLONGATA OF MAN, AT THE LEVEL OF THE MOTOR DECUSSATION. (7a', anterior horn ; Cac, central canal ; Dpy, motor decussation ; FcV, accompanying tracts of the trigeminus; /we, column of Burdach ; fng, column of Goll ; fsla, anterior median fissure ; JET, Helwig's fasciculus ; J5T/S, direct cerebellar tract ; Ncu, nucleus of Bur- dach ; Ng, nucleus of Goll ; NXId, dorsal nucleus of the spinal accessory nerve ; P, Pick's bundle ; Py, pyramid ; Sgl, substantia gelatinosa of Eolando ; /SW, lateral reticular sub- stance ; Trs, the rubro-spinal tract, Monakow's bundle ; Tscv, antero-lateral ascending (Gower's) tract ; Fa, bundle of Vicq d'Azyr ; VG, anterior ground bundle ; XI, spinal accessory nerve. Weigert's stain, x 5. (After Marburg.) ward. In this region is the lateral group of sensory nuclei of the cranial nerves, which includes a portion of the vestibular group, the acoustic nuclei, and the sensory nucleus of the trigeminus. Besides the grey nuclei which are thus continued up from the spinal cord, several additional centers occur in the rhomben- cephalon as isolated masses of grey matter which are without homologues in the lower segments of the cerebro-spinal axis. The first of these are the nuclei of Goll and Burdach, in which the postero-internal and postero-external columns of the spinal cord 490 THE NEBVOUS SYSTEM respectively terminate. The central neurones, whose cell bodies form these nuclei, send their neuraxes ventralward and toward the anterior median raphe, which they cross to the opposite side, and enter the tract of the mesial fillet (mesial lemniscus, laqueus). Thus it is that the posterior columns of the spinal cord disappear in the medulla, and the dorsal horns of grey matter are in this way brought into direct relation with the layer of ependymal cells which lines the floor of the fourth ventricle. The Inferior Olivary Body. — Another and still larger isolated grey nucleus, beginning at a slightly higher level than the above and extending farther cephalad, is the inferior olivary body. This nucleus is inserted between the ventrally situated pyramids on the one hand, and the lateral columns, lateral nucleus, and forma- tio reticularis on the other. The inferior olivary body is a large ovoid mass with a central core of white fibres and a crinkled shell of grey matter ; its convoluted surface presents a ribbon-like ap- pearance when seen in transection. The olivary nucleus extends from near the spinal border of the medulla oblongata upward to the lower portion of the pons Varolii. The white matter of the medulla oblongata presents two prominent decussations of long fibre tracts, which have already been mentioned as cutting off the lateral from the medial cell groups of the ventral horns. The more spinalward of these is the motor decussation, the more cephalad is the great sensory decussation of the mesial fillet. The motor decussation occurs at the junction of the first cervi- cal segment and spinal border of the medulla oblongata; it is found at the level of the lower portions of the nuclei of Goll and "Burdach. The greater portion of the nerve fibres composing the pyramids of the medulla decussate through the median raphe at this level, and pass obliquely downward to the opposite lateral column of the spinal cord. The sensory decussation occurs at a slightly higher level, its fibres chiefly coming from the nuclei of Goll and Burdach, to pass cephalad in an obliquely ventro-mesial direction, piercing the me- dian raphe just dorsal to and a little above the motor decussation. Having reached the opposite side they immediately turn cephal- ward to form the mesial fillet, a large flattened bundle of longitu- dinal white fibres lying next the median raphe" and just dorsal to the pyramidal tracts. The interlacing of these fibres as they approach the raphe forms a reticular mass of white matter which THE MEDULLA OBLONGATA AND BRAIN STEM 491 is distinguished from the more lateral grey reticular formation (formatio reticularis grised) ; in contradistinction this is known as the white reticular formation (formatio reticularis alba). At the mid-level of the medulla oblongata a small portion of the lateral column moves obliquely dorsal ward to enter the cere- ffiul FIG. 383. — TRANSECTION OF THE HUMAN MEDULLA OBLONGATA AT THE LEVEL OF THE LOWER MARGIN OF THE INFERIOR OLIVARY BODY. Cac, central canal ; cH, central tract of the tegmentum ; do, dorso-olivary fibres ; faed, the dorsal external arcuate fibres ; faev, the ventral external arcuate fibres ; /a?', the internal arcuate fibres ; Fe V, accompanying tracts of the trigeminus ; IXa, spinal root of., the glosso-pharyngeus ; IXa', accessory bundle of the same ; KS, direct cerebellar tract ; Lm, mesial lemniscus ; Na, nucleus ambiguus ; NarcP, arcuate nucleus of the pyramids ; Nee, external nucleus of Burdach ; Ncu, nucleus of Burdach ; Ng, nucleus of Goll ; Nit, nucleus of the lateral column ; Nmd, dorso-marginal nucleus of Ziehen ; No, inferior olive ; NX, dorsal vago-glosso-pharyngeal nucleus ; NXId, dorsal spinal accessory nu- cleus ; NXII, hypoglossal nucleus ; Oae, accessory olivary nuclei ; Py, pyramids ; Sgl, gelatinous substance of Rolando ; Trs, rubro-spinal tract (Monakow's bundle); Tscv, an- tero-lateral ascending tract of Gowers ; Tst, spino-tectal and thalamic tract ; VNo, olivary capsule ; vo, ventro-olivary fibres ; XII, hypoglossal nerve. Weigert's stain, x 5. (After Marburg.) bellum. These fibres are reinforced by a considerable bundle com- ing from the cerebellum to enter the inferior olivary body. To- gether these bundles form a projecting column of white matter in close relation to the substantia gelatinosa of Rolando in the tips of the dorsal grey horns ; this mixed tract is the restiform body 492 THE NERVOUS SYSTEM or inferior peduncle of the cerebellum. At the mid-level of the medulla the gelatinous substance of Rolando is so increased in amount as to form a slight protuberance, tubercle of Rolando, which is seen on the ventral border of the restiform body. The Nucleus of the Twelfth Cranial Nerve. — The four lower cra- nial nerves are given off from this portion of the rhombencepha- lon. The twelfth, a motor nerve, arises from a grey nucleus on either side of the raph6 just ventral to the grey commissure. Its nucleus extends from a point just above the motor decussation upward to the level of the caudal margin of the pons Varolii. Fibres pass ventralward from this nucleus and emerge from the medulla oblongata through a groove between the pyramid and the olivary body. The eleventh cranial nerve (motor) arises from the intermedio- lateral cell group in the ventral horns of the six upper cervical segments and from the lateral nucleus of the medulla. Fibres pass from these nuclei through the lateral columns, from which they make their exit, and passing upward unite with each other to form the trunk of the spinal accessory. The tenth cranial nerve arises in two main divisions, the motor and the sensory. The motor portion takes its origin from the nucleus ambiguus which, toward the spinal cord, is continuous with the lateral nucleus and the ventral horns. Higher in the medulla the nucleus ambiguus also gives origin to the peripheral neurones of the ninth nerve. The motor fibres of the tenth 'and ninth nerves make their exit from the lateral surface of the medulla oblongata, ventral to the restiform body. The sensory roots of these nerves enter the medulla in com- pany with the outgoing motor fibres; they pass to a triangular area of grey matter in the floor of the fourth ventricle. This is the chief nucleus of the vagus. It is continuous above with the similar nucleus of the ninth nerve. Descending branches from the fibres of the ninth and tenth nerves form a small but prominent tract which lies in the margin of the grey matter, and ventro-lateral from the chief nuclei of these nerves. This is the tractus solitarius or spinal root of the ninth and tenth nerves. It is continued downward as far as the cervical region, and its path is surrounded by a thin shell of grey matter (nucleus of the tractus solitarius) in which its fibres terminate. The ninth or glossopharyngeal nerve is very similar to the tenth in its origin and its exit from the medulla. The root bundles THE MEDULLA OBLONGATA AND BRAIN STEM 493 of the tenth nerve, however, are rather coarser and form larger bundles than those of the ninth. At the level of the ninth nerve the dorsal and medial accessory olivary nuclei make their appearance. They form, on either side, two isolated flattened grey masses. The dorsal accessory nucleus is flattened antero-posteriorly, and lies just behind the mesial half FIG. 384. — TRANSECTION OF THE HUMAN MEDULLA OBLONGATA AT THE MID-LEVEL OF THE INFERIOR OLIVARY BODIES. cH, central tract of the tegmentura ; do, dorso-olivary fiures ; faev, ventral external arcuate fibres ; Fc V, accompanying tracts of the trigeminus ; Ftp, posterior longitudinal bundle ; Hil, hilum of the olivary body ; io, intraolivary fibres ; it, arcuate trigeminal fibres ; IXa, spinal root of the glossopharyngeus ; IXa', accessory bundle of same ; Lm, mesial lemniscus ; m, dorsal longitudinal bundle of Schutz ; Na, nucleus ambiguus ; NarcP, arcuate nucleus of the pyramids ; Ncu, nucleus of Burdach ; Nft, nucleus of the eminentia teres ; NiS, intercalate nucleus of Staderini ; Nit, nucleus of the lateral column ; No, inferior olivary body ; NB, nucleus of Roller ; Nvtd, chief nucleus of the vestibular nerve ; NX, dorsal or chief nucleus of the vagus ; NXII, hypoglossal nucleus ; Oaa, me- sial, and Oae, dorsal accessory olivary nuclei ; Plchm, mesial choroid plexus ; Pol, pontic- ulus ; pt, trigeminal arcuate fibres ; pt', marginal trigeminal arcuate fibres ; Py, pyr- amids ; Ra, raphe ; rt, retrogeminal arcuate fibres ; Sgl, gelatinous substance of Rolando ; Sri, lateral reticular substance ; Trs, rubro-spinal tract of von Monakow ; Tscv, Gowers' tract ; Tst, spino-tectal and thalamic tract ; TVIII, acoustic tubercle ; vcpl, ventral col- lateral plexus ; Villa, spinal root of the auditory nerve ; VIIIc, cochlear nerve ; VIV, the fourth ventricle ; X, vagus nerve ; XII, hypoglossal nerve. Weigert's stain, x 5. (After Marburg.) 494 THE NERVOUS SYSTEM of the inferior olivary body. The mesial accessory olivary nucleus is transversely flattened, and lies between the mesial surface of the olivary body and the median raphe. Just below the spinal border of the pons Varolii the anterior pyramids present a thin layer of grey matter on their ventral sur- face ; this is the arcuate nucleus (nucleus of the external arcuate fibres, nucleus arcuatus). Opposite the upper end of the chief glossopharyngeal nucleus the medulla comes into relation ventrally with the pons Varolii, but is covered dorsally by the overhanging cerebellum. At the lower border of the pons Varolii the eighth, seventh, and sixth cranial nerves are given off, the sixth from the groove between the pyramid and the cephalic end of the inferior olivary body, the seventh lateral to the olivary body, and the eighth still farther lateral and somewhat dorsal from the seventh. The twelfth, sixth, and later the third cranial nerves may be collectively considered as a ventral group which are given off in a ventral plane near the median line ; the eleventh, tenth, ninth, eighth, seventh, and fifth form a lateral group, having their super- ficial origin from the lateral surface of the nervous system and in nearly the same vertical plane. The fourth nerve, since it makes its exit from the dorsal surface, is without a homologue. The sec- ond and first cranial nerves are for many reasons considered as diminutive lobes of the cerebrum itself, and as such are not homolo- gous with the other cranial nerves. THE PONS VAROLII The pons Varolii or metencephalon occupies a region corre- sponding to the upper half of the fourth ventricle. The lateral walls of the ventricle approach each other in this region, finally uniting in the median line and thus surrounding a central canal, the aqueduct of Sylvius, which extends cephalward through the mesencephalon to the third ventricle. These cavities are not only homologous, but at the spinal end of the fourth ventricle are also continuous with the central canal of the spinal cord. In the metencephalon the morphological structures of the medulla oblongata or myelencephalon are continued upward in the dorsal half of the organ, known as its tegmentum, with the single exception of the pyramids, which, as longitudinally disposed fibre bundles, enter the ventral portion to interlace with the transverse fibre bundles of the pons Varolii. This reticular mass of nerve THE PONS VAROLII 495 fibres forms the ventral portion or crusta of the pons. Since the transverse fibres of the pons Varolii pass directly into the cere- bellum, these fibres may be considered as forming the middle peduncles of this organ. Fie. 385. — A SECTION THROUUH THE LOWER BOKDER OF THE PONS VAROLII OF THE HUMAN BRAIN. Brcj, brachium conjunctivum ; BPo, middle peduncle of the cerebellum ; ell, central tract of the tegmentum ; Crst, restiform body ; Decl, declive ; Dca, anterior cerebellar commissure; Emb, nucleus emboliformis;/c/b, cerebello-pontine fibres ; flst, peduncle of the flocculus; glob, globular nucleus; Lm, mesial lemniscus; NaB, von Bechterew's nucleus; Ndt, dentate nucleus of the cerebellum; Nod, nodulus cerebelli; Not, superior olivary nucleus ; AY, nucleus tecti; NVII, facial nucleus; Nvm, motor nucleus of the trigeminus; Nrtg, reticular nucleus of the tegmentum; Plchl, lateral choroid plexus ; Po, pons Varolii; Py, pyramid ; Tr, trapezoid body; Va, bundle of Vicq d'Azyr; F7, abducens nerve ; Vila, first portion of the root of the facial nerve ; VIII, auditory nerve ; VIV, fourth ventricle; VNdt, capsule of the dentate nucleus. Weigert's stain, x 2§. (After Marburg.) In addition to those structures which are continued upward from the medulla oblongata, the metencephalon contains the cen- tral paths and nuclei of those cranial nerves which enter this region. 496 THE NEKVOUS SYSTEM Thus the floor of the fourth ventricle in its upper half contains that dorsal grey matter which is continued upward from the chief nuclei of the ninth and tenth nerves ; it is thus homologous with the dorsal horns of the spinal cord. This grey mass at the lower border of the pons forms the chief or mesial nucleus of the eighth cranial nerve. Just ventral to this nucleus is an ovoid compact group of large motor nerve cells, the nucleus of the sixth or abducens nerve. The nuclei of the sixth pair are thus in the same vertical plane as those of the twelfth, but are somewhat more separated from one another by a median longitudinal fibre bundle, the medial or pos- terior longitudinal fasciculus, which, in its upward course, curves dorsalward in the medulla oblongata, so that in the pons Varolii it lies on either side of the median raph6 and beneath the grey matter of the floor of the fourth ventricle. The deeper part of the pontal tegmentum contains a continua- tion of the formatio reticularis of the medulla. Ventral to this and separating it from the pons fibres are the longitudinal fibre bundles of the mesial fillet, which in transection form an oval bundle with its long axis at nearly a right angle to the median raph6. Lateral to the formatio reticularis and above, but in the same vertical plane as the inferior olivary body, is the superior olivary nucleus, a small oval mass of grey matter which forms a cell station in the path of the cochlear division of the auditory nerve. In some of the lower mammals this nucleus is more highly developed than in man. Connecting the superior olivary body with a similar region of the opposite side is a transverse bundle of fibres, the trapezoid body, which crosses the pons just ventral to the mesial fillet, but dorsal to the pyramidal tracts and transverse fibres of the pons Varolii. In close proximity to the superior olivary nucleus, on its dorso- lateral side, is the nucleus of the seventh cranial nerve, a slender rounded cell column whose position is above but homologous with that of the nucleus ambiguus, the lateral nucleus, and the ventral horns of the spinal cord. The eighth cranial nerve enters just lateral to the nucleus of the seventh, its vestibular division lying at a somewhat lower level than its cochlear portion. The vestibular nerve near its point of entrance is surrounded by a ganglionic mass of grey matter which lies in the extreme lateral portion of the metencephalon. This THE PONS VAROLII 497 nucleus, being penetrated by the cochlear nerve, is thus divided into two portions, a ventral or accessory nucleus, and a dorsal nucleus or tuber culum acusticum. Between the cochlear nuclei FIG. 386. — A SECTION THROUGH THE MIDDLE OF THE HUMAN PONS VAROLII. BPo, middle cerebellar peduncle ; cH, central tract of the tegmentum ; Crst, restiform body ; Fc V, the accompanying tracts of the trigeminus ; Flp, posterior longitudinal bundle ; fist, peduncle of the flocculus ; fpPo, longitudinal pontine fibres ; fprd, predor- sal bundle ; Lm, mesial lemniscus ; m, dorsal longitudinal bundle of Schutz ; NaB, nu- cleus of von Bechterew ; Nft, nucleus of the eminentia teres ; Nrtg, reticular nucleus of the tegmentum; NTr, trapezoid nucleus; NVI, abducens nucleus; NVIac, accessory nucleus of the abducens; NVII, facial nucleus; Nvm, motor nucleus of the trigeminus; Nvt, triangular or chief nucleus of the vestibular nerve ; Py, pyramid ; Sgl, gelatinous substance of Rolando ; so, peduncle of the superior olive ; Strap, striae acusticae ; Strc, middle, Strp, deep, and Sirs, superficial layer of the pons ; Ten, nucleo-cerebellar tract ; TV,. trapezoid body; Trs, rubro-spinal tract of von Monakow ; Tscv, Gowers' tract ; Tst\ spino-tectal and thalamic tract; F, trigeminus ; t>a, bundle of Vicq d'Azyr ; F/, abdu- cens ; Vllb, second ; and VHc, third portion of the facial root ; Villa, spinal vestibular root. Weigert's stain, x 3J. (After Marburg.) and the ventro-lateral wall of the fourth ventricle the grey matter of the formatio reticularis appears to be directly continued later- alward into the substance of the cerebellum. Just at this point is a disseminated group of very large nerve 33 498 THE NERVOUS SYSTEM cells, Deifers' nucleus. Still more lateral and just at the margin of the central grey matter of the cerebellum, is the small-celled nucleus of von Bechterew. These two nuclei, together with the FIG. 387. — A SECTION OF THE HUMAN PONS VAROLII AT THE LEVEL OF THE TRIGEMINUS NERVE. BPo, middle cerebellar peduncle ; cH, central 4ract of the tegmentum ; dlH, dorso- lateral tract of the tegmentum ; Flp, posterior longitudinal bundle ; fist, peduncle of the flocculus ; fpPo, longitudinal pontine fibres ; Fprd, predorsal fasciculus ; LI, lateral lem- niscus; Lm, mesial lemniscus; m, dorsal longitudinal bundle of Schiltz; mPy, cortico- pontine tract; NaB, nucleus of von Bechterew; Nft, nucleus of the eminentia teres; Nos, superior olivary nucleus ; Nrtg, reticular nucleus of the tegmentum; NVm, motor trigeminal nucleus; NVs, sensory trigeminal nucleus; Po, pons; R Tr, radial fibres of the trapezoid body ; So, peduncle of the superior olive ; Strc, middle layer of the pons ; Strp, deep layer of the pons; Strs, superficial layer of the poiis; Tr, trapezoid body ; Trs, rubro-spinal tract ; Tscv, Gowers' bundle ; Tst, spino-tectal and thalamic tract; V, trigeminus ; Vc, cerebral root of the trigeminus ; Vllb, second portion of the facial root ; VIIc, third portion of same ; Vs, crossed root of the trigeminus. Weigert's stain, x 3£. (After Marburg.) chief or mesial auditory nucleus, are connected with the path of the vestibular nerve. In the lateral wall of the fourth ventricle is a transversely flat- tened oval bundle of nerve fibres, which arises from the central grey matter of the cerebellum and passes, as the brachium con- THE MESENCEPHALON 499 junctivum or superior peduncle of the cerebellum, in a convergent cephalad course, at the same time approaching the median line to decussate in the mesencephalon with its fellow of the opposite side. On the ventro-mesial aspect of the superior peduncle, near its origin, is the superior end of the restiform body or inferior peduncle of the cerebellum, which here approaches its termination in the vermis cerebelli. The roof of the fourth ventricle at this level is formed by the vermis of the cerebellum. On its ventral surface and near the median line is a small group of cells, the nucleus fastigius. Dorsal to this nucleus are the convolutions of the superior vermis, while farther lateral is the dentate nucleus of the cerebellum, in section a ribbon-like mass of grey matter whose general appearance closely simulates that of the inferior olivary body. The dentate nucleus is embedded within the central white matter of the cerebellum. At the mid-level of the pons Yarolii the fifth nerve penetrates the organ from its lateral surface and passes inward to the teg- mentum. On the ventro-mesial side of the trigeminal fibres is its chief motor nucleus, a small group of motor cells ; on its dorso- lateral side is the larger, triangular, sensory nucleus of the trigem- inus, whose apex extends downward through the pons, and beyond which the spinal root of the fifth nerve is continued into the medulla oblongata. In the upper part of the pons the superior cerebellar peduncles have passed to a more ventral plane, and now lie in the lateral wall of the much narrowed fourth ventricle. Mesial to the peduncles, in relation to the ventro-lateral angle of the ventricle, is a small bundle of scattered nerve fibres, the descending cerebral root of the fifth nerve. The ventral margin of the grey matter on the inner side of this root contains a group of pigmented nerve cells which, as the substantia ferruginea or locus cceruleus, extends cerebralward into the midbrain. The central portion of the pontal tegmentum in its upper part still consists of the f ormatio reticularis, which is continued upward through the isthmus rhombencephali and midbrain. THE MESENCEPHALON Entering the mesencephalon, at the isthmus rhombencephali, the decussation of the fourth nerve can be seen forming the roof of the aqueduct of Sylvius, which canal represents the cephalic continuation of the fourth ventricle and occupies the axis of the 500 THE NERVOUS SYSTEM organ ; it is therefore homologous with the central canal of the spinal cord. At a slightly higher level, lateral to the grey matter FIG. 5. — A SECTION OF THE HUMAN BKAIN STEM AT THE BORDER OF THE PONS VAROLII. LEVEL OF THE CEREBRAL Brcj, brachium conjunctivum ; cH, central tract of the tegmentura ; DBrcj, decussa- tion of the brachium conjunctivum; DIV, decussation of the trochlearis nerve; Fpl, lat- eral pontine bundle; Flp, posterior longitudinal fasciculus \fpLl, perforating fibres of the lateral lemniscus ; fpPo, longitudinal pontine fibres; Fprd, predorsal bundle ; IVb, descending root, and /Fc, point of exit of the trochlearis nerve; Leo, locus coeruleus; LI, lateral lemniscus ; Lm, mesial lemniscus ; LmP, bundle from the fillet to the crusta ; m, dorsal longitudinal fasciculus of Schtitz ; mPy, cortico -pontine tract ; Nca, superior central nucleus ; NdR, dorsal nucleus of the raphe' ; NLl, nucleus of the lateral lemnis- cus; Po, pons; Srt, substantia reticularis alba; Strc, middle, Sirp, deep, and Strs, su- perficial layers of the pons ; Trs, rubro-spinal tract ; Tst, spino-tectal and thalamic tract ; vH, ventral field of the tegmentum; F/F, fourth ventricle; Vlma, anterior medullary velum ; F«, crossed root of the trigeminus. Weigert's stain, x 3. (After Marburg.) surrounding the aqueduct and lying just mesial to the cerebral root of the fifth nerve, is a small circular bundle of coarse nerve fibres, the cerebral or descending root of the fourth cranial nerve. THE MESEKCEPHALON 501 On the dorsal aspect of the mesencephalon, just cephalad from the decussation of the fourth pair of nerves, are the inferior corpora quadrigemina (inferior colliculi). Transections at this level show a large oval grey mass, corresponding to the prominence on either side. These are the nuclei of the inferior corpora quadrigemina. FIG. 389. — A SECTION OF THE HUMAN BRAIN STEM, AT THE LEVEL OF THE POSTERIOR CORPORA QUADRIGEMINA. Aq, aqueductus Fallopii; Brqp, peduncle of the posterior corpora quadrigemina, cH, central tract of the tegmentum ; Coqp, commissure of the posterior corpora quadri- gemina ; Cpbg, parabigeminal body ; DBrcjd, dorsal, and DBrcjv, ventral portion of the decussation of the brachium conjunctivum; Fcoea, anterior perforated space \fFp, fron- tal pontine tract; Flp, posterior longitudinal bundle ; Fpl, lateral pontine bundle ; Fprd, predorsal bundle ; fr, straight fibres of the midbrain ; fTp, temporo-pontine tract ; Glp, globus pallidus of the lenticular nucleus; Gml, lateral ganglion of the midbrain ; Hg, central grey matter; IH, lateral bundle of the tegmentum ; Lmp, bundle from the lem- niscus to the crusta; Ndtg\ accessory dorsal tegmental nucleus; NIV, nucleus of the trochlearis ; NlAq, lateral nucleus of the aqueduct ; NQp, nucleus of the posterior cor- pora quadrigemina ; pern, peduncle of the mammillary body ; Po, pons ; Ppbg, parabi- geminal fibres ; prP, propons ; Py, pyramid ; Spp, posterior perforated space ; SnS, sub- stantia nigra ; Srt, substantia reticularis alba ; Stri, intermediate layer ; 7Vs,rubro-spinal tract; Tst, spino-tectal and thalamic tract; Vc, cerebral, and F«, crossed root of the trigeminus. Weigert's stain, x 3i. (After Marburg.) 502 THE NERVOUS SYSTEM The lateral and mesial fillets, superior cerebellar peduncles, pyramidal tracts, and posterior longitudinal fasciculi are continued upward through the mesencephalon. The mesial fillet lies rather more lateral from the median raphe than in the lower levels, and its outer border is blended with the lateral fillet. The superior cerebellar peduncles approach the median line and soon decussate. This decussation occurs in the cephalic end of the midbrain. The pyramidal tracts form the large bundle of longitudinal fibres which compose the columns of the crurae cerebri. The fibres of the pos- terior longitudinal fasciculus on either side of the median line, form a deep longitudinal trough in which rests the grey matter which incloses the aqueduct of Sylvius. In this grey matter sev- eral groups of large motor cells mark the beginning of the nuclei of the third pair of cranial nerves. These nuclei extend cephalad for a considerable distance. The nuclei of the fourth cranial nerves form, on either side, a group of large pigmented cells which indent the dorsal margin of the posterior longitudinal fasciculus. Opposite the anterior corpora qiiadrigemina the third nerve makes its exit. At this level the grey matter, which was continued upward from the medulla oblongata and dorsal half of the pons Varolii, is reduced to a comparatively thin cylindrical mass which surrounds the aqueduct of Sylvius. The nucleus of the third cranial nerve, which is embedded in this grey matter, presents a median and a lateral cell group. The median nucleus lies in the median line, in the angle of the trough formed by the posterior longitudinal fasciculi ; the lateral nucleus indents the dorsal sur- face of these bundles. In the ventral portion of the organ at this level, and on either side of the median line, is a large oval reddish-grey mass of nerve cells, the red nucleus (nucleus ruber). This nucleus occurs at the level of the decussation of the superior cerebellar peduncles, and in it the fibres of these tracts terminate immediately after their decussation. Ventral to the red nucleus, but separated from it by a dark mass of nerve cells, the substantia nigra of Sommering, is the free portion of the crus cerebri, which contains the continuation of the pyramidal tracts. The optic tracts at this level pass dorsal ward around the lateral surface of the mesencephalon to reach the medial geniculate bodies in the angle between the optic thalamus and the brain stem. Above the border of the pons Varolii the crura cerebri diverge, THE DIENCEPHALON 503 leaving a deep but broad sulcus in the median line, in the floor of which is the posterior perforated space. The root bundles of the third cranial nerves pass ventral ward from their nuclei of FIG. 390. — A SECTION OF THE HUMAN BRAIN STEM, AT THE LEVEL OF THE POSTERIOR BORDER OF THE RED NUCLEUS. Cgl, lateral geniculate body ; Cgm, mesial geniculate body ; Girl, internal capsule ; Cop, posterior commissure; EW, Edinger-Westphal nucleus; Fcop, fasciculus of the posterior commissure ; Fe Qa, efferent fibres from the roof of the mesencephalon ; Ftp, posterior longitudinal bundle ; fp, perforating fibres of the crusta ; frtf. fasciculus retro- tiexus of Meynert ; Glp, pineal gland ; H, Forel's field ; ///, oculomotor nerve ; LM, Wernicke's field ; Nc, caudate nucleus ; Ncop, nucleus of the posterior commissure ; NQa, nucleus of the superior corpora quadrigemina; Mg, red nucleus; Pcm, peduncle of the mammillary body : Pp, crusta ; Pal, pulvinar ; 8n&, substantia nigra ; Stri, intermediate layer; 777, optic tract; Tpt, transverse tract of the peduncle; Tst, spino-tectal and thalamic tract. Weigert's stain, x Ij. (After Marburg.) origin, penetrate the region of the red nuclei, and emerge through the posterior perforated space at the mesial border of the crura cerebri. THE DIENCEPHALON,— With the next step cerebralward the aqueduct of Sylvius opens into the third ventricle and the mesen- cephalic nuclei are replaced by the large basal nuclei of the cere- brum. This group of nuclei include the optic thalamus, caudate nucleus, lenticular nucleus, hypothalmic nucleus, and the nucleus of the posterior longitudinal fasciculus (Darkschewitsch's nucleus). The nucleus of the posterior longitudinal fasciculus (Darksche- witscli) lies on either side of the median line, ventral and some- what cephalad from the oculo-motor nuclei. In it the posterior longitudinal fasciculus, in part, at least, terminates. 504 THE NEKVOUS SYSTEM On either side of the third ventricle, dorso-lateral from the red nucleus, is the large ovoid group of nuclei which collectively form the optic tlialamus. The group of thalamic nuclei include the FIG. 391. — A SECTION OF THE HUMAN BRAIN STEM, AT THE MID-LEVEL OF THE RED NUCLEUS. Cm, mammillary body; Cop. posterior commissure; Csth, subthalamic body of Luys; FeQa, efferent fibres from the roof of the mesencephalon ; fp, perforating fibres of the crusta ; frtf, Meynert's bundle ; Gem, ectomarnmillary ganglion ; Gb, ganglion habenulse ; Glp, pineal gland ; glp, globus pallidus ; ///, oculomotor nerve ; ImL lateral medullary layer of the thalamus; Narc, arcuate nucleus of the thalamus; Nc, caudate nucleus; Ncop, nucleus of the posterior commissure; Nl, centre median of Luys; Nlve, external latero- ventral nucleus of the thalamus; Ntg, red nucleus; Ntgd, dorsal portion of same; Pcm, peduncle of the mammillary body; Pp, crusta; Pu, putamen; Pul. pulvinar; Stri, intermediate layer ; Til, optic tract ; Tpt, transverse tract of the peduncle ; Tri, inter- crural trigone ; VIII, third ventricle ; VS, bundle of Vicq d'Azyr. Weigert's stain, x If. (After Marburg.) " centre median" or nucleus of Luys, a small oval cell group lying just dorso-lateral from the red nucleus, and separated from it by a narrow interval of white matter; the lateral cell mass or lateral nucleus ; a ventral group of cells ; a small anterior nucleus ; a dorsal cell group ; a large rounded posterior extremity, the pul- vinar ; together with several nuclei of minor importance.* The * The limited space at our disposal, and the indeterminate state of our pres- ent knowledge of the relations of these several cell groups to the fibre paths of the brain, does not warrant a detailed description of the subdivisions of the optic thalamus. For its minute structure, so far as it is at present known, the reader is referred to the excellent text-books of Barker and Obersteiner, and to the works of Nissl, von Monakow, and Marburg. THE DIE]VCEPHALON 505 optic thalami of the two hemispheres are united with each other by the posterior commissure, which bridges across the third ven- tricle. The caudate nucleus lies dorso-lateralward from the optic thal- amus, which latter body it partially encircles. It projects into the wall of the lateral ventricle, and is separated from the optic thalamus by a thin band of white matter. The optic thalamus and caudate nucleus, on the mesial side, are separated from the more laterally situated lenticular nucleus by a broad band of white matter, the cerebral continuation of the pyramids, fillet, and other long fibre tracts of the mesencephalon. FIG. 392. — A SECTION OF THE HUMAN BRAIN STEM AT THE MID-LEVEL OF THE OPTIC THALAMUS. Cfe, external capsule; Cex, capsula extrema; £7*', internal capsule; ::••••:••:• \ _ii£i.- v • ••••.•.: FIG. 397. — HUMAN COKTKX CEREBBI, OLFACTORY REGION". o, tangential fibre layer ; 6, white matter of the medulla. Nissl's stain. Moderately magnified. (After Schlapp.) 514 THE NERVOUS SYSTEM 1. Molecular or tangential fibre layer. 2. Outer polymorphous cell layer. 3. Small pyramidal cell layer. 4. The layer of granule and large pyramidal cells. 5. The outer stripe of Baillarger (great pyramidal plexus). 6. The granule cell layer. 7. The inner stripe of Baillarger (polymorphous plexus). 8. Inner polymorphous cell layer. The special characteristics of this visual area are the abundance of tangential fibres,* as evidenced by the prominent stripes of Bail- '1 rfy-y occ. temp.' inf. " I.- -... '• . i- -^ FIG. 398. — TRANSECTION OF THE HIPPOCAMPAL GYRUS. (After Edinger.) * The corresponding abundance of granule cells and tangential fibres is suggestive of a close relation between these elements, the tangential fibres prob- ably arising in large part from the terminal division of centripetal neuraxes. N THE HIPPOCAMPAL GYRUS 515 larger, the thick fibre layer in the deeper part of the molecular stratum, the abundance of granule cells, the paucity and irregular form of the pyramidal cells, and finally the presence in the inner stripe of Baillarger and in the outer portion of the deep poly- morphous cell layer of numerous large isolated multipolar cells, the giant " solitary cells " of Meynert. IN THE AUDITORY AREA— temporal lobe— the seven layer type is found. Its structure in this area is apparently identical with that previously described for the seven layer type in the parietal lobe. IN THE RHINENCEPHALON several peculiarities of cell formation are found. That occurring in the olfactory bulbs will be briefly considered in connection with the course of the olfac- FIG. 399. — DIAGRAM OF THE CORNU AMMONIS AS SHOWN BY THE GOLGI STAIN. al, collaterals of the pyramidal cells ; (7, Ammon's horn ; F, dentate fascia ; H, hippo- campal gyrus. 1-8, typical cells of the several layers ; 1, fusiform ; #, 3, small poly- morphous; 4i 5, pyramidal ; 6, small polymorphous; and 7, 8, cells of the dentate fascia. (After K. Schaffer, from Piersol.) tory tracts (page 555). The olfactory area of the hippocampal gyrus and the peculiar formation of the cornu Ammonis deserve mention at this time. IN THE HIPPOCAMPAL GYRUS the outer polymorphous cells exhibit a special tendency to group formation. The pyramidal cells form a tier of considerable thickness, but are of irregular shape. The cortex as a whole is comparatively thin. It presents the following layers : 516 THE NERVOUS SYSTEM 1. The molecular fibre layer. 2. The grouped polymorphous cell layer. 3. The layer of irregular pyramidal cells. 4. The inner polymorphous cell layer. Ammon's horn presents a peculiar formation, which may he considered as forming a transition area between the cerebral cortex and the very thin fascia dentata. The cornu Ammonis is charac- terized by the special prominence of but one cell type, the py- ramidal, this cell layer forming the greater part of its thickness. Its basal layer, the alveus — homologue of the cerebral medulla — is continuous with the white matter of the gyrus hippocampus. Within the alveus is a thin molecular layer, the stratum oviens, homologous with the polymorphous cell layer ; it contains a very few small fusiform cells. The basal processes of the pyramidal cells penetrate this layer to spread out within the alveus. Next to the stratum oviens is the broad pyramidal cell layer, its cells lying in the basal portion of the layer and sending their processes toward the alveus. From the apices of these cells a second set of processes pass toward the outer molecular layer, their thicker stem portions producing the radial appearance from which this part has been called the stratum radiatum. The small pyramidal and outer polymorphous cell layers are merely represented by an unusually vascular, molecular layer con- taining a very few small nerve cells. The abundance of small anastomosing blood vessels in this layer gives it a lacunar appear- ance, hence its name — the stratum lacunosum. The true molecular layer is the next beyond the lacunar stratum, and is similar in structure to its homologue in other parts of the cerebral cortex. On the surface of this layer, replacing the pia mater, is the lamina medullaris involuta, which contains the ter- minal dendrites of the pyramidal cells ; it is therefore homologous with the superficial tangential fibres of the molecular layer in other portions of the cerebral cortex. To recapitulate, the layers of Ammon's horn are as follows : 1. Lamina medullaris involuta. 5. Pyramidal cell layer. 2. Molecular layer. 6. Stratum oviens. 3. Stratum lacunosum. 7. Alveus. 4. Stratum radiatum. THE CEREBELLUM. — The cortex of the cerebellum, like other portions of grey matter, consists of nerve cells with their naked processes, together with their supporting neuroglia. The grey THE CEBEBELLUM 517 matter is distributed over the surface of the convolutions, and incloses the medullary white matter. The latter consists of medul- lated nerve fibres passing to or from the cortical cells. In section the cortex presents two distinct layers separated by a border line of large pyrif orm nerve cells, the cells of Pur- kinje. The outer layer, molecular stratum, contains many cell b c c c FIG. 400.— FROM A SECTION OF THE CEREBELLAK CORTEX OF MAN. o-a, pia mater ; ft-i, molecular layer ; c-c, granular layer ; d-d, white matter of the medulla. Nissl's stain. Photo, x 38. processes but few cell bodies. The inner, granular or nuclear layer, on the other hand, consists almost entirely of small nerve cells with prominent nuclei, together with glia cells. The Nuclear Layer. — The nerve cells of the granular or nuclear layer contain large spherical nuclei which are surrounded by the 518 THE NEKVOUS SYSTEM narrowest possible rim of cytoplasm. From the cytoplasm of each cell a few short and slender dendrites and a very fine neu- raxis are given off. The dendrites interlace among the neigh- boring cells of the granular layer. The neuraxes pass outward to the molecular layer, in the middle and outer portion of which they divide, in a T-like manner, to form two terminal branches which are distributed in the long axis of the cerebellar convolution. Many glia cells also occur in the granular stratum, their radi- ating fibres extending through the entire depth of the layer. This stratum is penetrated by the neuraxes of the Purkinje cells on their way to the medulla, and by nerve fibres coming from the medulla which lose their medullary sheath on entering the granu- FIG. 401. — A PURKINJE CELL FROM THE HUMAN CEREBELLAR CORTEX. Moderately magnified. Photo. (After Berkley.) lar layer, and terminate by end brushes in relation either to the granule cells or to the cells of Purkinje. The granular layer is thickest at the apex of the convolution, and thinnest opposite the bottom of the sulci. This peculiarity ap- parently results from the infolding of the cortex in the course of that portion of its development during which the sulci are formed. THE CEREBELLUM 519 Those portions of the cortex which are thus carried in with the sulci are necessarily attenuated. The cells of Purkinje form the characteristic element of the cerebellar cortex. These are very large pyrif orm nerve cells, placed between the nuclear and the molecu- lar layers, with their long axis nearly perpendicular to the adjacent surface of the convolutions. From their in- ner pole a neuraxis arises, and, pene- trating the nuclear layer, enters the white medulla, where it acquires a medullary sheath. In its passage through the nuclear layer the neur- axis gives off recurrent collaterals which return into the molecular layer to terminate in relation to neighbor- ing cells of Purkinje. A thick-stemmed dendrite arises from the outer pole of the Purkinje cell, but immediately divides into two primary branches. Occasionally the two branches are given off directly from the cell body. From these pri- mary branches smaller processes pass into the molecular layer and dicoty- mously divide into an innumerable number of fine terminal fibrils. This arborization is peculiar in the absence of anastomoses, and in the fact that it lies entirely within the limits of a plane whose diameter is no greater than that of the cell body, a plane which is found in the transverse axis of the cerebellar convolution. It is therefore impossible to demonstrate this arborization in sections which are cut parallel to the long axis of the convolution. The bodies of the Purkinje cells are closely surrounded by a basketwork of terminal fibrils derived from the cells of the molecular layer. FIG. 402. — A PURKINJE CELL FROM THE CEREBELLAR CORTEX OF THE RABBIT. Highly magnified. (After Nissl.) 520 THE NEKVOUS SYSTEM The molecular layer consists chiefly of the processes of cells which are found in the deeper layers ; it possesses but few cells of its own. Such nerve cells as it may possess, though all of small size, fall under two types, the one whose processes spread out lateralward and interlace with the dendrites of Purkinje's cells, and the other whose processes pass transversely through the cere- bellar convolutions and give off collaterals which dip inward to form end baskets around the bodies of the Purkinje cells. The neuraxes of these latter cells, in the tangential portion of their course, form a stratum of fibres which occupies the deeper third of the molecular layer and overlies the outer poles of the Purkinje cells. Glia cells also occur in the molecular layer, many of them dis- tributing their processes in planes perpendicular to the surface of the convolutions. These glia fibres penetrate the entire depth of the molecular layer, and on the surface of the convolutions beneath the pia mater form a superficial " basal membrane.'99 The greater part of the molecular layer is composed of fibres which, however, are not only derived from the intrinsic cells of this layer, but also include processes from Purkinje's cells and from the granule cells of the nuclear layer, together with certain fibres which enter from the white matter of the medulla and terminate in a network about the chief dendrites of Purkinje's cells. According to the classification of Nissl, nearly all the nerve cells of the cerebellar cortex, with the exception of Purkinje's cells, are of the cytochrome variety ; their nucleus stains deeply, and corresponds in size to that of a leucocyte ; mere traces of cyto- plasm are present. Nevertheless, a few cells of the granular layer possess a much larger nucleus, one which equals in size that of the average nerve cell ; they are therefore of the karyochrome type of Mssl. Purkinje's cells come under the arkyo-stichochrome or arkyo- chrome variety (Mssl *), their large granules of stainable substance being arranged in the form of an indistinct network whose meshes are more or less parallel to the nuclear membrane and to the surface of the cell. These coarse granules are continued out- ward into the dendrites; they also frequently form a "nuclear cap " for that pole of the nucleus which adjoins the stem of the dendrite. * Allg. Zeitschr. f. Psychiat., 1898. THE CEREBELLUM 521 It is a remarkable fact that the only cells of the cerebellar cor- tex which send their neuraxes into the white medulla are those of Purkinje. All the other nerve cells appear to be so arranged as to serve as association paths only, whereas the neuraxes of the Purkinje cells may be said to form the projection paths of the cerebellar cortex. CHAPTER XXV THE NERVOUS SYSTEM (Continued) C. THE CONDUCTION PATHS OF THE CENTRAL NERVOUS SYSTEM THE functions of the central nervous system, as well as the in- terpretation of its lesions, all center around its capacity for the transmission of nerve impulses, the process of conduction. Hence the importance of tracing with certainty the histological paths by which these impulses are conveyed. These paths are divisible into three general classes : 1. Centrifugal or " motor" tracts. 2. Centripetal or "sensory" tracts. 3. Association tracts. The centrifugal tracts are so arranged as to conduct nerve im- pulses in a direction from the cerebral cortex toward the peripheral nerve endings ; the centripetal conduct from the periphery toward the cerebral cortex ; while the association paths connect not only the opposite sides of the central organs by commissural fibres, but pass between different levels of the spinal cord and brain and may even unite very remote parts — e. g., the nuclei of the midbrain and the ventral horns of the spinal cord. A. The Motor Paths The centrifugal or motor paths begin in the motor area of the cerebral cortex and include the neuraxes of all those pyramidal nerve cells which occur in the grey matter of this area. These neuraxes penetrate the deeper layers of the cortex and as projection fibres enter the corona radiata of the cerebral medulla. Here, they converge toward the knee of the internal capsule, which they enter in a compact bundle. They then pass beneath the optic thalamus to enter the crusta of the midbrain as the large pyramidal bundles. In the midbrain and pons the pyramidal tracts coming from the two cerebral hemispheres converge toward the median line. In 522 THE MOTOE PATHS 523 the pons, however, they are broken up by the transverse pontal fibres into numerous small bundles of large medullated fibres. At the lower border of the pons these bundles reunite to form a com- pact bundle, on either side of the median line, which enters the pyramids of the medulla oblongata. Thus far the course of the motor tracts has been entirely ven- tral. In the lower part of the medulla a marked change in this condition is produced as a result of the motor decussation. About ninety per cent of the motor fibres which have been traced into the pyramids of the medulla now change their direction, pass obliquely inward, dorsalward, and spinalward, de- cussate in the median line with their fel- low of the opposite side, and enter the lateral columns of the spinal cord, where they form the crossed pyramidal tracts. Not more than ten per cent of the fibres of the pyramidal tracts in the medulla,* on the other hand, continue straight into the ventral columns of the spinal cord as the direct or uncrossed pyramidal tract. This uncrossed fasciculus takes a position on either side of the anterior median fissure. However, the fibres of this tract constantly decussate through the ventral or white commissure of the spinal cord in the cervical region, so that the tract be- comes progressively smaller and smaller in its passage down the cervical cord, and below this region is seldom found. Its fibres end in arborizations about the ven- tral horns of the opposite side. Thus all the fibres of the motor paths to the spinal cord reach the opposite side as compared with the cerebral hemisphere in which they arise. The fibres of the crossed as well as those of the direct pyramidal tracts end in arborizations about the ventral horn cells of the spinal cord. The neuraxes of the motor cells of the ventral horns in each * Usually less than ten per cent ; the volume of decussation within the me- dulla oblongata is subject to very great individual variation. FIG. 403.— DIAGRAM OF THE INTERNAL CAPSULE. No, caudate nucleus; Nl, lenticular nucleus ; Th, optic thalamus ; 77A«, anterior stalk of the thalamus; 1, fronto- pontal path ; 2, cortico-bulbar path ; , ventral roots, medullated ; v W, ven- tral root zone of dorsal funiculi. (After Flechsig.) longata. The group of dorsal root fibres which thus follows the tract of Goll to the medulla oblongata ends by terminal arborizations about 35 12 T FIG. 408. — DIAGRAMMATIC REPRESENTATION OF THE TRACTS OF THE SPINAL CORD AND THEIR RELATION TO THE PATHS OF THE MEDULLA OBLONGATA. • (7, cervical, Z, lumbar, and 7*, thoracic segments of the spinal cord ; the prefixed number indicates more exactly the level ; LM, lower, and UM, upper segments of the medulla ; io, inferior olivary body ; in the lower medulla the lateral nuclei are shown just behind the olive ; in the upper medulla the accessory olivary nuclei are shown. Column of Goll. Column of Burdach. Anterior ground bundle, continu- ous in the medulla with the pos- terior longitudinal bundle. Pyramidal (motor) tracts. Spinal root of the. trigeminus (seen only in LM and UM). 530 F "1 Lateral ground bundles, and tract H-' * of Gowers. Direct cerebellar tract. Spinal root of the auditory nerve, and the cerebello-olivary fibres. Mesial fillet, interolivary portion. Grey matter. THE SENSOKY PATHS 531 the cells of the nucleus of Goll. They convey the nerve impulses of muscular sensation and are chiefly derived from those nerves which come from the limbs. The column of Goll, therefore, first attains an appreciable size in the lumbar region, but adds to its volume in each successive spinal segment through which it passes. In the cervical region, this influx of fibres is so great that the en- tire volume can scarcely be contained within the limits of the pos- tero-internal column, and many are forced to continue their course in the column of Burdach until they reach the medulla oblongata where they end by arborization about the nerve cells of the nucleus of Burdach. From the nuclei of Goll and Burdach, neurones of the second order send their neuraxes ventralward toward the opposite side, the larger portion taking a direct course as internal arcuate fibres through the formatio reticularis alba to the raphe, where they de- cussate to the opposite side and immediately turn upward between the inferior olivary bodies to form the first portion of the mesial fillet or lemniscus. This early portion of the lemniscus, because of its position, is known as the inter olivary fillet. The smaller portion of the neurones of the second order from the nucle of Goll and Burdach follow the indirect course, as external arcuate fibres, first passing dorsalward to reach the surface of the medulla oblongata, which they then follow ventralward, keep- ing close beneath the pia mater until they reach the margin of the pyramidal tracts, where they divide, a small portion passing between the pyramids and the olivary body, a larger portion passing around the ventral and mesial borders of the pyramids to reach the median raphe. Here the two bundles reunite, join the internal arcuate fibres, decussate to the opposite side, and enter the interolivary portion of the mesial fillet. The mesial fillet in this portion forms a flattened band on either side of the median line, its dorsal margin blending with the poste- rior longitudinal fasciculus, a similar though smaller bundle of association fibres which will be described under a later heading. The longitudinal fibres of the fillet are spread over a sectional area which extends from the mid-region of the inferior olives dorsalward nearly to the hypoglossal nucleus, the posterior longitudinal fascic- ulus being interposed between this nucleus and the dorsal margin of the fillet. The mesial fillet begins at the level of the nucleus of Goll and increases rapidly in size in its upward course by the constant addi- Sup. Cap. Red. Nuc. Mey. Bun. L. L, L. L. to Sup. Cereb. Fed. Post. Long. Fas..... Form. Ret. Alb. -,. Sup. Ol. Nuc N.VII. Nuc. VI Str. Acust Dor. Nuc. N. Cock. N. Vest. T. B./ N. Coch. Inf. OL Nuc. Nuc. Burd.. Col. Goll to Form. Ret Nuc. Goll Sup. 01. uc. FIG. 409.— RECONSTRUCTION OF THE MEDULLA OBLONGATA AND MIDBRAIN OF A CHILD. Ac. Ol. Nuc., accessory olivary nucleus ; 3 tile corpuscle of Meissner. (After von Lenhossek.) Called " nucleus of Still- FIG. 410. — DIAGRAM or THE ORIGIN AND RELATIONS OF THE PERIPHERAL MOTOR AND SENSORY NEU- RONES. A cylindrical section of the spinal cord, with its ventral and dorsal nerve roots, is shown, a, nerve cell of the ventral horn whose neuraxis passes through the ventral nerve root, J, to its peripheral termination, c; at rf, is a unipolar sensory nerve cell in the dorsal root ganglion : its process imme- diately divides into a peripheral and a central branch. The central branch enters the spinal cord and at 0, divides into an ascending, /, and a de- THE SEXSORY PATHS 535 ing."* Its cells possess similar connections and are similar in function to those of Clarke's column. About the cells of these nuclei the third division of the dorsal root fibres have their terminal arborizations. The central neurone of this path, sensory neurone of the second order, begins with the cells of Clarke's column, and to a much less extent from those of Stilling's nucleus ; their neuraxes pass obliquely outward and up- ward to reach a point near the surface of the lateral white col- umns. Here they form a thin ribbon-like superficial zone which spreads forward from the dorsal nerve roots to a point opposite the central grey commissure. This superficial fibre bundle is the dorso-lateral or direct cerebellar tract, so called because of its loca- tion in the spinal cord and because of the distribution of its fibres, which pass directly cephalad to the medulla oblongata, and thence through the superficial zone of the restif orm body of the same side to the vermis of the cerebellum. It is therefore, as are all other paths from the spinal cord to the cerebellum, an uncrossed or direct tract. Those fibres of the direct cerebellar tract which enter at the lower levels naturally assume the more superficial position. More- over, since Clarke's column is not found as a distinct nucleus above the thoracic region, the direct cerebellar tract does not appreciably increase in size above this level. The neurones of this path proba- bly transmit impulses which are chiefly derived from the abdominal and thoracic viscera, hence it receives few fibres in the cervical portion of the spinal cord. In the vermis cerebelli the terminal arborizations of fibres coming from the direct cerebellar tract are undoubtedly in relation, either directly or by collaterals, with the cerebellar cortex. How- ever, the majority at least of its impulses leave the cerebellum through the superior cerebellar peduncles by means of neurones of the third order, decussate in the mesencephalon, and in great part terminate in the red nucleus of the opposite side. It is thought, however, that some of the neurones of the supe- rior cerebellar peduncles extend beyond the red nucleus without interruption. These uninterrupted fibres are joined by the nerve fibres of those sensory neurones of the fourth order, whose cell bodies lie in the red nucleus, and together they continue the path through " Forel's field," enter the posterior limb of the internal capsule in relation with the fillet tract, and travel thence through the corona radiata to the cortex cerebri. •Cassel, 1859. 536 THE NEKVOUS SYSTEM PATH "IV."— The fourth and last division of the dorsal root fibres follows a somewhat more uncertain course. The neuraxes of its peripheral neurones end in arborizations about the many small cells in the dorsal horns of the spinal cord, on the same, and possi- bly also to some extent on the opposite side. Thence they pass up the spinal cord by neurones of higher orders, which form associa- tion bundles in the lateral columns and thus connect the dorsal horn cells of successively higher levels. In the brain these paths have been traced into the formatio reticularis. A considerable number of dorsal horn cells in the spinal cord send their neuraxes into a narrow superficial zone in the anterior half of the lateral column to form the ventro-lateral ascending column or tract of Gowers. This tract, increasing in size, continues up the spinal cord to the lateral column of the medulla oblongata. Its further course is somewhat uncertain, though it undoubtedly con- tinues upward through the lateral portion of the formatio reticu- laris in the pons, where some of its fibres turn sharply backward and enter the vermis cerebelli through the middle, and possibly also the superior, cerebellar peduncles ; other fibres continue up- ward through the formatio reticularis to the optic thalamus (Hoche*). From this point its impulses probably reach the cor- tex of the cerebral hemisphere after the same manner and in com- pany with the fibres of the preceding division (PATH " III "). C. The Association Paths Besides the motor and sensory paths of the central nervous sys- tem there are certain other tracts which connect the nuclei of vari- ous levels. Some of these are tracts of ascending, some of descend- ing degeneration. Many of them, however, contain both ascending and descending fibres and may be called mixed fibre tracts. Some of the above tracts contain long fibres, e. g., the sulco- marginal fasciculus, while others, e. g., the antero-lateral ground bundles of the spinal cord, consist chiefly of short fibres. The course of many of these association fibres is so difficult to follow that they are not yet well known. We shall only attempt, there- fore, to trace briefly the course of the more important fasciculi, first those of the spinal cord and later those of the brain. The comma tract of Schultze in the middle root zone of the pos- terior white column has already been mentioned as probably con- * Arch. f. Psychiat., 1896. THE ASSOCIATION PATHS 537 taining association fibres which connect the posterior horn cells of adjacent levels. This tract is most prominent in the cervical region. It is absent from the lower portions of the spinal cord. The posterior white column in the sacral region of the spinal cord contains a small bundle which, with its fellow of the opposite side, forms an oval or cuneate area which incloses the posterior median septum. This short tract is the fasciculus dorso-medialis (dor so-medial sacral bundle, triangle median, Flechsig's oval field). Though part of its fibres are thought to come from the dorsal roots and are therefore exogenous, yet many are undoubtedly derived from the more cephalad regions of the spinal cord. This fascicu- lus is therefore homologous with those fibres which at higher levels are found in the comma tract. In the lateral white column are four distinct tracts, the inter- medio-lateral fasciculus, the lateral border zone, the lateral ground bundle, and Helwig's fasciculus. The intermedio-lateral fasciculus (rubro-spinal tract, von Mona- kow's bundle) occupies a small area at the ventral margin of the crossed pyramidal tract. The fibres of this bundle probably arise in the optic thalamus and red nucleus of the opposite side. They decussate in the tegmentum and reach the spinal cord through the formatio reticularis of the pons and medulla. The fasciculus ex- tends the entire length of the spinal cord, its collaterals being distributed to the ventral horns. The lateral border zone is a thin area adjoining the lateral sur- face of the grey matter of the spinal cord. Its short fibres connect the nerve cells of neighboring spinal segments. The lateral ground bundle includes many fibres, some ascending and some descending, which connect more distant segments of the spinal cord, and in the medulla oblongata blend with the anterior ground bundle to enter the formatio reticularis alba and posterior longitudinal fasciculus. Helwig's fasciculus is a short tract, found only in the cervical region. It is triangular, or at times crescentic in section, and lies in front of the broad apices of the ventral horns at the ventral margin of the lateral white columns. The origin and destination of these fibres is not yet known. The anterior white column contains the sulco-marginal fasciculi and an anterior or ventral ground bundle. The descending sulco-marginal fasciculus (Lowenthal's tract) in the cervical region occupies an area just ventral to the direct py- 538 THE NERVOUS SYSTEM ramidal tract. As the size of this latter path diminishes with its passage caudalward, the sulco- marginal fasciculus moves backward along the anterior median sulcus into the position thus vacated. In the thoracic and lumbar regions the tract under discussion occu- pies the narrow area on either side of the anterior median fissure which in the cervical region contains the direct pyramidal tract. The fibres of the fasciculus take origin in the anterior corpus quadrigeminum of the opposite side, decussate through Meynert's commissure, pass caudad in a position which is ventral to the aque- duct of Sylvius and the posterior longitudinal fasciculus, and enter the anterior column of the spinal cord. The bundle in passing receives many neuraxes from the cells of Deiters* nucleus in the rhombencephalon. The fibres derived from Deiters' nucleus, there- fore, form a large portion of those which form this tract. The fas- ciculus sulco-marginalis extends the entire length of the spinal cord, its collaterals being probably distributed to the ventral horns. The ventral portion of this fasciculus also contains many ascend- ing fibres which are thought to arise in the nerve cells of the dorsal horns and intermediate zone of the opposite side. They then decus- sate through the anterior commissure and pass cephalad either as scattered fibres among those of the descending sulco-marginal fas- ciculus or as a small bundle in the ventral margin of this tract. These fibres form the ascending sulco-marginal fasciculus. The anterior ground bundle forms a large portion of the anterior white columns. Like the lateral ground bundle, it connects neigh- boring segments of the spinal cord and is similarly continued into the medulla oblongata. In fact, the course of these two bundles is so entirely comparable that they may be, and frequently are, col- lectively described as the antero-lateral ground bundle. The formatio reticularis alba of the medulla oblongata receives, among its many fibre bundles, certain fibres from the antero-lateral ground bundles of the spinal cord which continue cephalad through the reticular formation of the pons and midbrain for a varying dis- tance. In the medulla and midbrain they are probably connected with a small cell group which in each of these locations lies in or near the median line : these are the superior and inferior central nuclei. The ultimate destination of this group of fibres is, how- ever, still obscure. The Posterior Longitudinal Fasciculus.— Certain other fibres from the antero-lateral ground bundles of the spinal cord, as they enter the formatio reticularis of the medulla oblongata, unite to THE ASSOCIATION PATHS 539 form a compact fibre bundle, the posterior or median longitudinal fasciculus. This fasciculus presents a gentle dorsal curve in its passage through the medulla oblongata, in the upper part of which lear nerve. Decussation of the Posterior trochlear longitudinal nerve. fasciculus Nucleus of the \ troch- ' Posterior commissure- Pineal gland. Oculo-motor nucleus. ~~~A Facial root Hypoglossal (internal knee). nucleus. Glossopharyngeal nucleus. Nucleus of Goll. Mammillary body. Decussation of the brachium conjunctivum. Deep trans- verse fibres of the pons. Super- ficial transverse fibres of the pons. Mesial lemniscus. FlG. 411. — A SAGITTAL SECTION OF THE MEDULLA OBLONGATA, PONS, AND MESENCEPHALON PARALLEL AND CLOSE TO THE MIDDLE LINE, FROM A CHILD AGED THREE MONTHS. The posterior longitudinal fasciculus and its relation to the antero-lateral ground bundle of the spinal cord are particularly well shown. Weigert's stain. (After Bruce.) it reaches a position near the median raphe, and just in front of the dorsal grey matter of the hypoglossal nucleus. Here it blends with the dorsal margin of the interolivary portion of the mesial fillet. As it enters the pons Varolii the posterior longitudinal bundle separates from the fillet, thus attaining a still more dorsal position, in which it continues its course through the pons. In the midbrain it lies ventral to the aqueduct of Sylvius, but makes a gradual ven- tral curve which corresponds to the increased depth of the grey matter surrounding the aqueduct at this level. The fasciculi of either side, together form a median trough in which the nuclei of the oculo-motor nerve are found. 540 THE NERVOUS SYSTEM In the diencephalon the posterior longitudinal fasciculus appar- ently ends in the nucleus of Darkschewitsch or nucleus of the poste- rior longitudinal fasciculus. Though we have traced the course of this fasciculus from the spinal cord cephalward, it must be borne in mind that it contains fibres which run both cephalad and caudad, and that it is therefore subject to both ascending and descending degeneration. In its course through the brain the posterior longitudinal fas- ciculus receives many fibres from the sensory nuclei of the cranial nerves, especially from those of the ocular group with which it is in close relation. By these connections the several groups of ocular nuclei are brought into intimate relation with one another as well as with those nuclei of closely related function which occur in the cervical region of the spinal cord. The cerebellum possesses at least three important association paths, the one placing this organ in relation with the opposite infe- rior olivary body through the cerebello-olivary tract, the second connecting it with the opposite cerebral hemisphere through the superior cerebellar peduncles, and the third placing the cerebellum in communication with the medulla oblongata and midbrain through the middle cerebellar peduncles. The cerebello-olivary tract arises from nerve cells in the vermis cerebelli, and, passing caudad through the restiform body, enters the medulla oblongata. Its fibres here turn sharply inward and ventralward in small discrete bundles and penetrate the formatio reticularis, lying more lateral but parallel to the internal arcuate fibres. Most of the bundles decussate to the opposite side and enter the inferior olivary body, many of them first traversing the surface of this nucleus. The fibres which thus surround the inferior olive form for it an encapsulating sheath of medullated nerve fibres. A few fibres of the cerebello-olivary tract end without decussation in the inferior olivary body of the same side. The superior cerebellar peduncle (jbrachium conjunctivum) takes origin from the cells of the vermis cerebelli and enters the mesen- cephalon as a large round bundle of fibres which, at first, forms the lateral roof of the fourth ventricle, but gradually sinks ventral- ward, thus passing obliquely around the lateral border of the grey matter which surrounds the aqueduct of Sylvius. The bundle finally makes a sharp mesial curve toward its decussation at the cephalic end of the mesencephalon. Its position is thus mesial and dorsal to that of the mesencephalic portion of the fillet. THE ASSOCIATION PATHS 541 After decussation the fibres of the brachinm conjunctivum are immediately lost in the red nucleus of the opposite side. A few of its fibres, however, are said to continue past the red nucleus with- out interruption. These, together with neuraxes from the cells of the nucleus ruber, enter ForePs field, and pass lateralward either to the optic thalamus or to the lenticular nucleus. Their further course is uncertain, but it seems probable that from these points new neurones continue the path through the corona radiata to the cerebral cortex. Each cerebellar hemisphere is thus placed in inti- mate relation with the opposite half of the cerebrum. The path of the branchium conjunctivum, like all the other association tracts, contains fibres which run in both directions. It is therefore a tract of more or less mixed degeneration. The Middle Cerebellar Peduncles. — Fibres from the cerebellum also enter the middle cerebellar peduncles and pass to the crusta of FIG. 412. — DIAGRAM OF THE FIBRE PATHS OF THE SPINAL CORD. The black cells are of the sensory or centripetal paths, those on the left are spinal ganglion cells whose branches may be traced to their several terminations within the spinal cord. The motor cells of anterior horn on the right are white ; commissural cells are vertically striped ; the small cells of the dorsal horns are horizontally striped ; a small " Golgi cell " of the dorsal horn is stippled. (Redrawn after the scheme of von Lenhossek.) the pons, where they end in terminal arborizations about those nerve cells, of the same and opposite sides, which are scattered 542 THE NEKVOUS SYSTEM through this portion of the pons Varolii. Through these pontal nuclei the cerebellum is brought into relation with the association paths of the mes- and rhombencephalon. The more important conduction paths of the spinal cord may at this time be summarized as follows : DESCENDING ASCENDING In the posterior column. Comma tract, f Dorso-lateral sacral bun- dle.f Goll's tract, f Burdach's tract, f In the lateral column. Crossed pyramidal tracts.* Intermedio-lateral fascic- ulus.f Dorso - lateral cerebellar tract, f Ventro-lateral cerebellar tractf In the anterior column. Direct pyramidal tract.* Descending sulco - margi- nal fasciculus. J Helwig's fasciculus4 Ascending sulco - margi- nal fasciculus.:}: * In the motor pathway. f In the sensory pathway. \ Association paths. CHAPTER XXVI THE NERVOUS SYSTEM (Continued) D. THE CENTRAL PATHS OF THE CRANIAL NERYES THE course of the spinal nerves has already been sufficiently described in tracing the course of the great motor and sensory paths of the spinal cord. Each spinal segment was found to con- tain the nuclei of a ventral or motor nerve root, whose centrifugal peripheral neurones begin in its ventral horns, together with cer- tain cell groups of the posterior horns and intermediate zone which serve as sensory nuclei, receive the end arborizations of peripheral sensory neurones whose nerve cells lie in the spinal ganglion of a dorsal nerve root, and send their neuraxes cephalad in one of the various centripetal tracts of the spinal cord. In the medulla these centripetal paths unite in the fillet, by which, with the aid of neu- rones of higher orders, the centripetal impulses are finally con- veyed to the cerebral cortex. The course of the cranial nerves, while conforming quite closely to the same general arrangement, presents slight deviations from this type which result in the appearance of special nuclear groups and centripetal pathways. These peculiarities warrant a brief out- line of the central paths of the several cranial nerves. The twelfth or hypoglossal nerve (Figs. 383 and 384) contains only centrifugal or " motor" fibres. This nerve takes its origin in the large-celled hypoglossal nucleus, which is ovoid in shape, and is situated in the medulla oblongata on either side of the me- dian line and just dorsal to the posterior longitudinal fasciculus (Fig. 383). The nucleus can be traced through the lower half of the medulla, and if it is stained according to the method of Wei- gert, it can be readily distinguished by the many coarse medullated fibres which it contains. The central neurones of the hypoglossal nerve come down from the cerebrum in the pyramidal tracts. Having arrived at the level 543 544 THE NERVOUS SYSTEM of the nucleus they turn sharply dorsalward along the median raphe", pass between the interolivary fillets, and thus reach the region of the hypoglossal nucleus, where they turn sharply out- ward, to end by arborization around its cells. The peripheral neurones of the twelfth cranial nerve begin with the large cells of the hypoglossal nucleus. Their neuraxes pass directly ventralward in large bundles and make their exit from an antero-lateral groove between the pyramid and the inferior olivary body. The eleventh or spinal accessory nerve (Fig. 382), like the twelfth, is a centrifugal or motor nerve trunk. Its fibres arise from the nerve cells of the ventral horns of the six upper cervical segments and, in the lower part of the medulla, from that detached portion of the ventral horns which forms the so-called lateral nucleus. Its central neurones probably reach these nuclei after the same manner as those of the spinal nerves. Its peripheral neurones take origin from the large cells of these nuclei, leave the grey matter at the dorso-lateral angle of the ventral horns, pass lateralward through the white matter, and make their exit from the lateral surface of the spinal cord and medulla in a vertical plane midway between the ventral and dorsal nerve roots of the spinal cord. Outside of the7 central nervous system they form small root bundles, which pass cephalad and unite to form the spinal accessory nerve trunk. The tenth, pneumo gastric, or vagus nerve (Figs. 383 and 384) contains both centrifugal and centripetal fibres. The neuraxes of its centrifugal or motor fibres arise from the large scattered nerve cells of the nucleus ambiguus, which are homologous with the more caudad group forming the lateral nucleus, and also with the nerve cells of the ventral horns of the spinal cord. The neuraxes from the scattered cells of the nucleus ambiguus pass at first dorsalward until they reach the neighborhood of the tractus solitarius, where they join the centripetal bundles, pass lateralward and slightly ventralward, and make their exit from the side of the medulla just ventral to the margin of the restiform body. Outside of the medulla the several bundles unite to form the median portion of the vagus. The central motor neurones of the vagus reach the medulla ob- longata through the pyramidal tracts, and, having arrived at the proper level, turn dorsalward along the median raphe — in which they promptly decussate — and terminate by arborization about the cells of the nucleus ambiguus. PATHS OF THE CKANIAL NERVES 545 The peripheral neurones of the centripetal or sensory portion of the vagus, whose cell bodies lie in the jugular ganglion, enter the medulla along with its motor fibres. They pass inward toward the dorsal grey matter, at the border of which each fibre divides into a short ascending and a long descending branch. The long descending branches collectively form a small compact bundle of medullated fibres, the tractus solitarius (fasciculus solitarius, tractus spinalis nervi vagi). The fibres of this tract, after passing caudad for a considerable distance, terminate about a group of small nerve cells in the grey matter which surrounds the fasciculus, the nucleus of the solitary tract. The cells of this nucleus acting as neurones of the second order send their fibres, after the manner of the internal arcuates, to join the mesial fillet of the opposite side. The short ascending branches, together with many collaterals from the descending processes, terminate about the small nerve cells of the triangular or chief vagus nucleus in the floor of the fourth ventricle. The cells of this nucleus, also acting as neurones of the second order, send their neuraxes, in a manner similar to those coming from the nucleus of the solitary tract, to the oppo- site mesial fillet, and are continued through neurones of higher orders to the cerebral cortex.* The ninth or glossopharyngeal nerve (Figs. 383 and 384).— The course of the neuraxes of this nerve is exactly similar to those of the vagus. Its peripheral motor nerves begin as nerve cells of the cephalic end of the nucleus ambiguus, those belonging to the glossopharyngeal nerve not being in any way distinguishable from those of the vagus except by their superior position. Their neu- raxes pass dorsalward to meet the incoming sensory neurones, in company with which they make their exit through the small lateral columns of the medulla oblongata. The central motor neurones from the cerebral cortex arrive in the nucleus ambiguus after traversing the corona radiata, internal capsule, and pyramidal tracts ; they then decussate in the median raphe, to terminate in arborizations about the nerve cells of the opposite side in the same manner as do the central neurones of the vagus path. The peripheral sensory (centripetal) neurones of the glosso- pharyngeus begin as cell bodies in the petrosal ganglion, which, like the other root ganglia of the cranial nerves, is homologous with * For the course of the mesial fillet, see page 531. 36 546 THE NERVOUS SYSTEM the dorsal root ganglia of the spinal nerves. Thus, the nerve cells of the petrosal ganglion send one process peripheralward, while the other enters the medulla through the sensory portion of the glosso- pharyngeal nerve roots. These fibres pass toward the dorsal grey matter and divide into a long ascending and a short descending branch. The former enters the tractus solitarius and ends about the adjacent cells of its nucleus in the manner already described for the vagus nerve. The latter, with some collaterals from the descending branches, passes to the triangular or chief nucleus of the glossopharyngeus just above but continuous with the similar nucleus of the vagus, in the floor of the fourth ventricle. From both of these nuclei new neurones of the second order continue the path cerebralward, decussating as internal arcuate fibres to enter the mesial fillet of the opposite side. The glossopharyngeal roots are peculiar as compared with those of the vagus in that the root fibres of the former form finer bundles in their passage through the lateral columns to reach their sensory nuclei ; also in the fact that the glossopharyngeus distributes the larger part of its fibres to the tractus solitarius, while the vagus sends the larger portion to the triangular or chief sensory nucleus. The intermediate nerve of Wrisberg has its peripheral neurone cells in the geniculate ganglion of the facial nerve. Their central processes on entering the medulla pass to the tractus solitarius to terminate after the same manner as the similar fibres of the glosso- pharyngeus. Its fibres thus form the most cephalic portion of the solitary tract, the more caudad portions of the bundle being formed from fibres of the glossopharyngeus and vagus, respectively. The eighth or auditory nerve (Figs. 384, 385, and 386), cen- tripetal in direction, consists of two distinct divisions which differ in origin, distribution, and function. These are the pars cochlearis (cochlear nerve, true auditory nerve) and the pars vestibularis (vestibular nerve). The peripheral neurones of the vestibular nerve arise from the nerve cells of the ganglion vestibulare (ganglion of Scarpa) in the internal auditory meatus. They enter the medulla oblongata at the lower margin of the pons and in the same vertical plane as the ninth and tenth cranial nerves. On approaching the grey matter in the floor of the fourth ventricle these neuraxes divide into a short ascending and a long descending branch. The terminals of these fibres, together with those of their col- laterals, end in one of several cell groups. 1. A large number end PATHS OF THE CRANIAL NEKVES 547 about the cells of the mesial or chief nucleus, a large area in the floor of the fourth ventricle containing small scattered nerve cells ; it is comparable to the chief nuclei of the ninth and tenth nerves. 2. Other fibres, probably for the most part ascending branches, pass to the superior vestibular nucleus (von Bechterew's nucleus), which is situated in a more dorsal and lateral plane and somewhat cephal- ad, from the mesial nucleus. 3. Other fibres end about the large cells of the lateral vestibular nucleus (Deiters' nucleus). 4. Still other fibres, mostly descending branches, pass caudad, as the de- scending or spinal root of the vestibular nerve, which passes down the medulla in the restiform body, following a course parallel, but lateral, to the tractus solitarius. The fibres of the spinal root end in relation to the nerve cells of the adjacent grey matter. From the nerve cells of the descending root, as well as from the median and superior nucleus, neurones of the second order send their neuraxes as internal arcuate fibres to the fillet of the opposite side, through which they are continued toward the cerebrum. Neurones of the second order, which include the cells of Deiters' nucleus, send their neuraxes caudad in a fairly compact bundle, which finally joins the fasciculus sulco-marginalis of the spinal cord, as already described. , The vestibular nerve is also directly connected with the cere- bellum by paths which can only be followed with considerable difficulty. Some neurones from the superior vestibular nucleus (von Bechterew's) are thought to enter the cerebellum through the superior peduncles. This group may, however, also contain per- ipheral neurones which pass without interruption to the ver- mis cerebelli. A second bundle enters the cerebellum through the corpus restiforme and is probably derived from the cells of Deiters' nucleus. The cochlear nerve, the path of the acoustic impulses, contains neurones which begin as the bipolar nerve cells of the ganglion spirale in the internal ear. The distal processes of these cells are distributed to Corti's organ, their proximal branches collectively form the root of the cochlear nerve. This nerve enters the medulla oblongata at the caudal margin of the pons, along with, but somewhat dorsal to the vestibular nerve. Near its entrance it passes into the cochlear nucleus, which it thus divides into a dorso-lateral portion (dorsal cochlear nucleus or tuber culum acusticum) and a ventro-mesial portion (acoustic nu- cleus, ventral or chief cochlear nucleus). Its fibres divide into 548 THE NERVOUS SYSTEM ascending and descending branches in the usual manner, and most if not all of them terminate in one of these two nuclei. A few fibres, however, are undoubtedly continued past the cochlear nu- clei without interruption. The ventral cochlear nucleus probably receives the unusually short ascending branches, while most of the descending branches end in the tuberculum acusticum, which is continued spinalward for a considerable distance. From the ventral nucleus neurones of the second order send their neuraxes in a ventro-mesial and somewhat cephalad direction to collectively form the trapezoid body, a compact fibre bundle which decussates behind the mesial fillet and enters the superior olivary nucleus of the opposite side. This nucleus is closely ap- plied to the dorsal surface of the trapezoid body. The neurones of the second order which arise in the dorsal cochlear nucleus or tuberculum acusticum, reach the opposite su- perior olive by a more circuitous route. They first pass dorsalward to the lateral margin of the floor of the fourth ventricle ; in this grey matter they turn toward the median line, forming superficial coarse groups, the striae acusticce, which appear as macroscopic transverse ridges in the ventricular floor. At the lateral margin of the abducens these fibre bundles suddenly dip into the substance of the pons, pass ventral to the nucleus of the sixth nerve, decus- sate through the median raphe, and reach the opposite superior olivary body in which most of these fibres terminate. Some fibres from the tuberculum acusticum and striae acus- ticae, as also some from the mesial nucleus and trapezoid body, are continued past the superior olives and enter the lateral fillet with- out interruption. The lateral fillet, however, consists chiefly of neurones of the third order, which arise in the superior olive of the same side. This tract is continued cephalad, lying at first near the lateral margin of the tegmental portion of the pons and dorso-lat- eral from the mesial fillet. The lateral fillet soon blends with the lateral margin of the mesial fillet to form a continuous sheet of longitudinal fibres. In the mesencephalon some at least of the neurones from the lateral fillet are interrupted at the inferior corpora quadrigemina, their neuraxes terminating by arborization about the scattered nerve cells of these bodies. From this point the auditory path is continued cerebral ward by fibres which prob- ably accompany the mesial fillet. The seventh or facial nerve (Figs. 385, 386, and 387).— The peripheral neurones of this nerve, which in man is a purely centri- PATHS OF THE CRANIAL NEKVES 549 fugal or motor nerve, begin in the nerve cells of the facial nucleus, a small oval group of large motor cells placed on the dorsal side of the trapezoid body, just dorso-lateral from the superior olive. Their neuraxes soon collect into a compact tract, which, in its first portion, passes dorsalward in the region of the abducens nucleus, around which it makes a sharp turn, the internal genu. It then passes somewhat cephalad, and finally takes a lateral, yet slightly ventral and caudad course, toward its exit at the lower margin of the pons Varolii, just dorsal to the root of the auditory nerve. The facial tract thus presents three portions: (a) the proximal, whose direction is dorso-mesial and slightly cephalad ; (b), the in- ternal genu, whose course is first dorso-mesial and cephalad, but later ventro-lateral and cephalad, and (c) the distal, which is directed lateralward, but slightly ventralward, and caudad. The central neurones of the facial reach its nucleus in the pons through the pyramidal tracts, probably by passing dorsalward along the median raphe, until at a point dorsal to the trapezoid body, where they decussate and pass directly to the facial nucleus. The sixth or abducens nerve (Figs. 385 and 386) is entirely centrifugal or motor. Its peripheral neurones arise from the cells of the compact ovoid abducens nucleus which lies beneath the grey matter of the floor of the fourth ventricle on either side of the median line. It is in close relation to the fasciculus longitudinalis posterior, which lies on its ventro-mesial side, and with the tract of the facial nerve whose internal genu encircles the dorso-mesial angle of the abducens nucleus. The neuraxes of the large nerve cells of this nucleus form bundles of considerable size, which pass almost directly ventral- ward, through the tegmentum and crusta of the pons, and emerge at the inferior margin of the rhombencephalon near the median line, where they unite to form the trunk of the abducens nerve. The central neurones of the sixth nerve are derived from the pyramidal tracts. Having reached the pons Varolii, they pass dor- salward along the median raphe until near the abducens nucleus, where they decussate and immediately end about the nerve cells of the peripheral neurones. The fifth or trigeminus nerve (I ri facial nerve) (Fig. 387) con- tains a large sensory or centripetal, and a smaller motor or cen- trifugal root. Both make their entrance or exit at the lateral sur- face of the pons Varolii, plunging together into the substance of the middle cerebellar peduncles to reach the dorsal half of the tegmen- 550 THE XEKVOUS SYSTEM turn in the mid-region of the pons Varolii. The motor root occu- pies a slightly cephalad position as compared with the sensory. Though the path of the central neurones which supply this root is not definitely known, from analogy it is reasonable to suppose that from the motor cortex their fibres start down the pyramidal tracts, as in the case of the central motor neurones of the other cranial nerves, but unlike these, they leave the pyramidal tracts at a level considerably cephalad from the nerve trunk for which they are destined. They probably decussate through the median raphe, and many of them then end about the nerve cells of the substantia fer- ruginea or locus ceruleus (nuclei minores nervi trigemini), a scat- tered group of large cells lying near the median line and ventral to the grey matter surrounding the aqueduct of Sylvius. Some of the central motor neurones, however, are continued past this nucleus without interruption ( Vs, Fig. 387, and Vc, Fig. 414), and these fibres, together with the neu raxes from the cells of the substantia ferruginea, pass caudal ward as the descending or mesen- cephalic root of the trigeminus. This root above the trochlear decussation is lateral to the descending root of the fourth or troch- lear nerve. Caudad to the trochlear decussation it is .continued downward in the same plane and is thus found just dorso-lateral to the substantia ferruginea and resting upon the ventral surface of the grey matter which surrounds the aqueduct and forms the floor of the fourth ventricle. At the level of the fifth nerve its mesencephalic root turns lateralward, many of its neuraxes (probably those coming from the cells of the substantia ferruginea) entering the motor root, and passing between the bundles of transverse pons fibres to their exit in the portio minor of the trigeminus. Other fibres of the descend- ing root of the fifth (probably those central neurones which come from above the locus ceruleus) terminate in the motor nucleus of the trigeminus (chief motor nucleus, nucleus princeps nervi trigemini), a group of large nerve cells in the dorso-lateral part of the pontal tegmentum. This motor nucleus is ventro-mesial from the chief sensory nucleus and the incoming centripetal root (sensory root, portio major) of the trigeminus. The nerve cells of the chief motor trigeminal nucleus are en- veloped by an intricate network of collaterals derived from the neurones of the pyramidal tracts and of the minor trigeminal nuclei. The neuraxes of the cells of the chief nucleus, together with those from the cells of the locus ceruleus, form the motor root PATHS OF THE CRANIAL NERVES 551 of the trigeminus, and through this nerve trunk are distributed to the muscles of mastication. The sensory root of the trigeminus, larger than the motor, enters the lateral portion of the pons Varolii slightly caudad to the motor root. Its fibres pass in a dorso-lateral direction until near the grey matter, where they divide into very short ascending and very long descending bundles. The latter form the long spinal root of the trigeminus, which is continued downward on the inner side of the restiform body to the cervical region of the spinal cord. Its fibres and collaterals successively end about the small nerve cells contained in the adjacent substantia gelatinosa of Rolando, which is continued upward from the tips of the dorsal horns in the spinal cord. The neuraxes of these cells — sensory trigeminal neu- rones of the second order — decussate as internal arcuate fibres and pass cerebralward in the mesial fillet. The short ascending branches, together with many collaterals from the descending divisions, end in the chief sensory nucleus of the trigeminus, which begins in the extreme lateral portion of the pontal grey matter somewhat cephalad from the trigeminal root, and by a tapering extremity is continued spinalward as far as the gelatinous substance of Rolando in the medulla oblongata, with which portion of the grey matter it appears to be continuous. The path of the central neurones from this nucleus is still un- certain. They probably pass, after the mariner of the internal arcuate fibres, to the mesial fillet of the opposite side. The Fourth or Trochlear Nerve (Figs. 388 and 389).— The peripheral neurones of the trochlear nerve begin in the large motor nerve cells of the trochlear nucleus, which lies in the grey matter between the aqueduct of Sylvius and the posterior longitudinal fasciculus at the level of the cephalic border of the inferior corpora quadrigemina and the decussation of the superior cerebellar pedun- cles. The nucleus comprises a compact group of large stichochrome nerve cells, which are in close relation to the dorsal surface and lat- eral margin of the posterior longitudinal fasciculus. These nuclei are characteristically asymmetrical in size, shape, and position. From the nerve cells of this nucleus neuraxes pass spinalward in a small compact bundle lying in the ventro-lateral angle of the grey matter surrounding the aqueduct. This descending root of the trochlear nerve is placed dorso-mesial to the descending or mesen- cephalic root of the fifth nerve, and dorso-lateral to the posterior longitudinal fasciculus. 552 THE NEEVOUS SYSTEM At the level of the spinal border of the inferior corpora quadri- gemina and isthmus rhombencephali the root of the fourth nerve makes a sharp dorsal turn, passes around the lateral margin of the grey matter to its dorsal surface, where it enters the anterior medul- lary velum, decussates with its fellow of the opposite side, and makes its exit from the dorsal surface. The fourth nerve is peculiar in that it is the only cranial nerve to leave the dorsal surface of the central nervous system, and is pos- sibly the only one whose decussation is on the distal side of the trophic center for its peripheral neurones. It is also the only cra- nial nerve whose decussation is dorsal to the axial central canal. As to the manner in which the central motor neurones reach the trochlear nucleus but little is known. We should, however, expect to find no decussation in the paths of the central neurones to this nerve. The trochlear nucleus is known to receive fibres from the region of the posterior longitudinal fasciculus, but whether these are central motor neurones or collaterals from the other ocu- lar paths is at present uncertain. The latter deduction would appear to be the more probable. The Third or Oculomotor Nerves (Figs. 390 and 413).— The nuclei of the oculomotor nerves form a series of cell groups in the mesencephalon. They lie in the grey matter between the aqueduct of Sylvius and the posterior longitudinal fasciculus and occupy the deep median trough which is formed by these fasciculi. The nuclei of the oculomotorius include a median cell group (median nucleus, nucleus impar) which is also the most ventral portion, and a lateral group on either side of the median line which has been variously subdivided by diiferent observers. It may be said to contain a ventro-medio-anterior nucleus (the Westphal- Edinger nucleus) and a dorso-latero-posterior portion (ventral and dorsal lateral nuclei}. The nerve fibres coming from the anterior two-thirds of the group of oculomotor nuclei are uncrossed, but those from the pos- terior or spinal third decussate to the opposite side and enter the lateral fasciculi of the oculomotor nerve roots. The root bundles from the various nuclei of the third nerve pass ventralward through the posterior longitudinal fasciculus, and through or around the red nucleus, to converge to a point near the median line ; they make their exit at the posterior perforated space. The course of the central neurones of the oculomotor nerves is not yet known. The nuclei of these nerves are closely connected PATHS OF THE CRANIAL NERVES 553 with each other and with the posterior longitudinal fasciculus. Through this fasciculus they are placed in intimate relation with the ocular centers of the lower cranial nerves. The second or optic nerves differ markedly in their arrangement from the lower cranial nerves. From the standpoint of embryology and comparative anatomy the retina of the eye represents, in part, OF THE HUMAN B11A1N STEM, AT THE LEVEL OF THE SUPERIOR CORPORA QUADRIGEMINA. Aq, aqueductus Fallopii ; Brga, arm of the anterior corpora quadrigemina ; Brgp, arm or peduncle of the inferior corpora quadrigemina ; Cgl, lateral geniculate body ; Cgm, mesial geniculate body; Cgma, accessory nucleus of same; Coqa, commissure of the su- perior corpora quadrigemina ; Fcop, bundle to the posterior commissure ; Flp, posterior longitudinal bundle; Fpl, lateral pontine bundle ; Fprd, predorsal bundle; ( iVa&M". FIG. 452. — TRANSECTION OF THE MARGIN OF THE MACULA SACCULI OF A GUINEA-PIG. a, otolithic membrane; i, cilia; 0, cuticular membrane; d,hair cells; e, sustentacular cells ; /, epithelium of the saccule ; <7, tunica propria ; A, nerve fibres ; *, bone. Hema- toxylin and eosin. x 325. (After Kulliker.) lies the macula, and into which the hair-like processes project, though not essentially different in microscopic appearance in fresh tissues, appears to possess a somewhat gelatinous consistence, and in it are suspended various forms of crystals of calcium carbonate which are known as otoliths. The free surface of the neuro-epithelium is also provided with a reticulated cuticular membrane which presumably is formed by the amalgamation of the free ends of the sustentacular cells. Through the openings in this reticular membrane the ciliary tufts of the hair cells project. The central ends of the hair cells, beneath the nucleated enlargement which is found near the middle of the epithelial layer, FIG. 453. — NERVE ENDINGS IN THE MACULA OF A GUINEA-PIG. a, epithelium ; 5, tunica propria ; c, three terminal nerve fibres. Golgi stain, x about 200. (After Ketzius.) 622 THE EAK are prolonged outward between the nucleated portions of the sus- tentacular cells and frequently terminate in small knobbed extrem- ities. This portion of the cells is in intimate relation with the ter- minal fibrils of the vestibular nerve, which, coming from nerve plexus in the fibrous wall of the saccule, forms an intra-epithelial plexus of delicate varicose fibrils. Frequently the epithelial coat contains coarse granules of a brownish pigment which, at times, also produces a diffuse coloration of the cells. The epithelial coat of the saccule rests upon a thin homo- geneous basement membrane and is further supported by a delicate fibrous coat or tunica propria. The connective tissue of this coat forms interlacing bundles the most of which are distributed in a circular manner about the wall of the ovoid saccule. At the macula this coat is much thickened by the entrance of the nerve fibres from the vestibular nerve. It also contains the minute blood vessels which supply the organ. As is the case with the other divisions of the membranous laby- rinth, the fibrous wall of the saccule is in contact on one aspect of its surface with the periosteum which lines the osseous labyrinth ; elsewhere it is separated from the periosteum by the perilymphatic cavity. The utricle is somewhat larger than the saccule. It lies behind and somewhat above the saccule, is of a very irregular oblong form, and receives the insertions of the semicircular canals. Its anterior portion is provided with a macula and the structure of its wall differs in no wise from that of the saccule; both of these mem- branous sacs are contained within the irregular cavity of the vesti- bule. The structure of the utricle, therefore, requires no further description. The Semicircular Canals. — The semicircular canals are three in number, the posterior, superior, and external. The last is also horizontal in its position ; the first two are vertical, but are so placed as to form a right angle with one another. The superior lies in the long axis of the petrous bone and its plane is therefore more nearly coronal, while that of the posterior canal is more nearly sagittal. Each canal forms something more than half a circle, its two ends opening separately into the cavity of the vesti- bule, with the exception of the posterior and superior canals whose inserted ends open by a common orifice, the canalis communis. The unjoined orifices of the posterior and superior canals, as also the outer extremity of the external canal, present a marked dila- THE INTERNAL EAE 623 tation at their termination in the vestibule. These dilatations are known as the ampullae. The osseous and membranous canals are of similar shape; the latter is, of course, contained within the former. The membranous semicircular canals open into the utricle. They do not entirely fill their bony canal, but, like the utricle and FIG. 454. — TRANSECTION OF A HUMAN SEMICIRCULAR CANAL. 1, bone ; #, retiform connective tissue membranes ; ', Z*, three rows of Betters' cells; H, cells of Hensen ; *.&., inner border cell ; i.h., inner hair cell ; i.p., inner pillar cell ; n, terminal branch of the cochlear nerve; o.h.-l, 2, 3, three rows of outer hair cells; o.p., outer pillar cell; p., phalangeal process of the outer sustentacular process. Very highly magnified. (After Held.) hair cells of the organ of Corti, the maculae, and the cristae, is essentially the same. The ganglia contain the cell bodies of the peripheral sensory neurones of the eighth cranial nerve. These are bipolar cells, of which the central process or neuraxis enters a medullated nerve fibre of the auditory nerve, while the peripheral process is distributed to the hair cells of the several areas of special- ized neuro-epithelium, as above described. BLOOD SUPPLY.— The internal ear is supplied by the internal auditory artery, which enters the labyrinth along with the auditory nerve, and at once divides into two main stems, the vestibular and the cochlear (arteria cochlearis communis, Siebenmann *). The vestibular branch accompanies the branches of the vestibular nerve to the saccule, utricle, and semicircular canals, supplying these structures in the posterior portion of the vestibule, and forming a rich plexus in the connective tissue of the maculae and cristae, and * Handbuch der Anat, Bardeleben, Bd. v, Abth. II. 636 THE EAR a more scanty network in the remaining portions of the membran- ous labyrinth. The cochlear division of the internal auditory artery, according to Siebenmann, promptly subdivides into the cochlear artery d f FIG. 460. — SCHEME OF THE VASCULAR SUPPLY OF THE INTERNAL EAR. <7i, first turn of the cochlea; /S, saccule; Sup. S.C., Ext. S.C., and Post. S.C., superior, external, and posterior semicircular canals ; £7", utricle. The arteries are in heavy black, the veins somewhat lighter : a, central vein, and &, central artery of the cochlea ; c, ves- tibular artery; rf, vestibulo-cochlear artery; 0, arteria proprise cochleae; /, vena aque- ductus cochlese ; g, vena aqueductus vestibuli. proper, which appears as the continuation of the vessel, and the vestibulo-cochlear artery, which supplies the macula sacculi, the posterior ampulla, and the adjacent portions of the utricle and posterior semicircular canal. This vessel also supplies the early portion of the first turn of the spiral cochlea. The true cochlear artery enters the modiolus and supplies a branch to the remaining portion of the first cochlear turn, and a terminal branch which passes as far as the apex of the cochlea, distributing its branches to the last two turns. All of these vessels are characterized by their peculiarly tortuous course. They dis- BLOOD SUPPLY 637 tribute terminal branches to the limbus spiralis and to the con- nective tissue of the membranous scala vestibuli, extending as far around this canal as the spiral ligament. No vessels cross in the basal membrane. The veins collect the blood from the liinbus spiralis and the wall of the scala tympani and form venous trunks within the modiolus, which correspond more or less closely with the arteries. Those veins coming from the wall of the scala tympani unite to form anterior and posterior spiral veins in the limbus and inner wall of the scala tympani. These vessels chiefly empty into the vena aqueductus cochleae which finds its way through the aqueduct to the internal jugular vein. Other branches from the interior of the cochlea unite to form the central vein of the cochlea, which FIG. 461. — SCHEME OF THE VASCULAK TERMINATIONS IN THE WALL OF THE COCHLEAB CANALS. ., IX, 593. Ruzicka, V. 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Ueber die feinere Structur des normalen Knochengewebes. Arch. f. PhysioL, 1882, 428; also, Arch. f. mik. Anat., 1882, XXI, 695. Czermak, N. Vergleichende Studien liber die Entwicklung des Knochen- und Knorpelgewebes. Anat. Anz., 1888, III, 470. Demarbaix, H. Division et de"gene>escence des cellules g£antes de la moelle des os. La cellule, 1888, V, 27. Denys, J. La structure de la moelle des os et la genese du sang chez les osseaux. La cellule, 1887, IV, 203. Bizzozero, G. Neue Untersuchungen iiber den Bau des Knochenmarks bei den Vogeln. Arch. /. mik. Anat., 1890, XXV, 424. von Ebner, V. Sind die Fibrillen des Knochengewebes verkalkt oder nicht? Arch. f. mik. Anat., 1887, XXIX, 213. Enderlen, E. Fasern im Knochenmarke. Anat. Anz., 1891, VI, 489. Frattin, G. Sulla struttura degli osteoblasti. Anat. Anz., 1902, XXII, 21. Gies, W. J. A new constituent of bone. Am. Med., 1901, II, 820. Hammar, J. A. Primares und rotes Knochenmark. Anat. Anz., 1901, XIX, 567. 45 690 BIBLIOGRAPHY Hawk, P. B., and W. J. Gies. Chemical studies of osseomucoid. Am. J. Physiol, 1901, V, 387. Howell, W. H. Observations upon the occurrence, structure, and function of the giant cells of the marrow. J. MorphoL, 1890, IV, 117. Jackson, C. L. Zur Histologie und Histogenese des Knochenmarks. Arch. f. Anat., 1904, 33. Jolly, M. J. Recherches sur la division indirecte des cellules lymphatiques granuleuses de la moelle des os. Arch, d'anat. mic., 1900, III, 168. Kolliker, A. Ueber den feineren Bau des Knochengewebes. Sitz. d. phys- . med. Gesellsch. z. Wiirzb., 1886, 33. Den feineren Bau des Knochengewebes. Zeitschr. f. wissen. Zool., 1886, XLIV, 644. Malassez, L. Sur 1'origine et la formation des globules rouges dans la moelle des os. Arch, de physiol. norm, et path., 1882, ser. 2, IX, 1. Pappenheim, A. Kleinere Mitteilungen. Arch. f. path. Anat., 1901, CLXIV, 374. Retzius, G. Zur Kenntnis der Riezenzellen und der Stutzsubstanz des Knochenmarks. Biol. Untersuch., 1903, .V. F. X, 37. Rindfleisch, G. E. Ueber Knochenmark und Blutbildung. Arch. f. mik. Anat., 1879, XVII, 21. Schulz, K. Das elastische Gewebe der Periost und Knochen. Anat. Hefte, 1896, VI, 117. Van der Stricht, O. Recherches sur la structure de la substance fundamentale du tissu osseux. Arch, de biol., 1889, IX, 27. Wendelstadt. Experimentelle Studie iiber Regenerationsvorgange am Knochen und Knorpel. Arch. f. mik. Anat., 1904, LXIII, 766. Williams, E. T. Marrow cells and spleen cells, considered in their relation to blood cells. Am. Med., 1902, III, 684. CHAPTER XII.— MUCOUS MEMBRANES— SECRETING GLANDS Arnstein, C. Zur Morphologic der sekretorischen Nervenendapparate. Anat. Anz., 1895, X, 410. Cajal, S. Ram6n y. Nuevas aplicaciones del metodo de coloracion de Golgi. Gac. med. Catal., 1889, XII, 613, 643. Flemming, W. Ueber Bau und Einteilung der Driisen. Arch. f. Anat., 1888, 287. Galeotti, G. Ueber die Granulation in den Zellen. Internal. Monatschr. f.Anat. u. Physiol, 1895, XII, 440, 461, 513. Gamier, C. 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Anat., 1898, LII, 546. CHAPTER XIII.— THE SKIN Bkschko, A. Beitrage zur Anatomic der Oberhaut. Arch. /. mik. Anat., 1887, XXX, 495. Ueber den Verhornungsprocess. Arch. f. PhysioL, 1889, 366, 539. von Brunn, A. Haut. Bardeleben's Handbuch der Anat. des Menschen, Bd. V, Abth. I, Jena, 1897. Buzzi, Keratohyalin und Eleidin. Monatschr. /. prakt. DermatoL, 1888, VII, 761, 896, 963. Calef. Studio istologico e morfologico di un appendice epitheliale del pelo nella pelle del Mus decumanus var. albina e del Sus scropha. Anat. Am., 1900, XVII, 509. Dogiel, A. S. Die Nervenendigungen im Nagelbett des Menschen. Arch. f. mik. Anat., 1904, LXIV, 173. Flemming, W. Zellteilungen in den Keimschichten des Haares. Monatschr. f. prakt. DermatoL, 1884, III, 129. Zur Kenntnis der Regeneration der Epidermis beim Saugetier. Arch. f. mik. Anat., 1884, XXIII, 148. Giovannini, S. De la regeneration des poils apres 1'epilation. Arch. f. mik. Anat., 1890, XXXVI, 528. Herxheimer, K. Ueber die Structur des Protoplasmas der menschlichen Epidermiszelle. Arch. f. mik. Anat., 1899, LIII, 510. Huber, G. C., and E. W. Adamson. A contribution on the morphology of sudoriparous and allied glands. Contrib. Med. Sc., dedic. to V. C. Vaughan, Ann Arbor, 1903, 365. Karg. Studien iiber transplantirte Haut: 1. Entwicklung und Bedeutung des Hautpigments. Arch. f. Anat., 1888, 369. Kodis. Epithel und Wanderzelle in der Haut des Froschlarvenschwanzes. Arch. f. PhysioL, 1889, Suppl. Bd., 1. Kolliker, A. Ueber die Entstehung des Pigments in den Oberhautgebilden . Zeitschr. f. wissensch. ZooL, 1887, XLV, 743. Die Entwicklung des menschlichen Nagels. Zeitschr. f. vrissensch. ZooL, 1888, XL VII, 129. Ueber die Entwicklung der Nagel. Sitz. d. phys.-med. Gesellsch. z. Wiirzburg, 1888, 53. 692 BIBLIOGRAPHY List, J. H. Der Herkunft des Pigments in der Oberhaut. Anat. Anz., 1889, IV, 596. Mertsching, A. Beitrage zur Histologie des Haares und Haarbalges. Arch. f. mik. Anat., 1887, XXXI, 32. Rabl, H. Ueber die Herkunft des Pigments in der Haut der Larven der urodelen Amphibien. Anat. Anz., 1895, X, 12. Ranvier, L. Histologie de la peau. Arch, d'anat. mic., 1900, III, 1. Smith, F. Histology of the skin of the horse. J. Anat. and Physiol., 1888, XXII, 142. Spalteholz, W. Die Verteilung der Blutgefasse in der Haut. Arch. /. Anat., 1893, 1. Spencer, B., and G. Sweet. The structure and development of the hairs of Monotremes and Marsupials. Quart. J. Mic. Sc., 1899, XLI, 549. Spuler. Ueber Regeneration der Haare. Verhandl. d. anat. Gesellsch., 1899, XVI, 18. Stbhr, P. Entwicklungsgeschichte des menschlichen Wollhaares. Anat. Hefte, 1903, XXI, 1. Ueber Intercellularbriicken zwischen ausserer und innerer Wurzel- scheide. Verhandl. d. anat. Gesellsch., 1903, XX, 24. Ueber die Entwicklung der Glashaut des menschlichen Haarbalges. Verhandl. d. anat. Gesellsch., 1903, XX, 26. Unna, P. G. 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Anat., 1887, XXIX, 617. Jagodowski, K. P. Zur Frage nach der Endigung des Geruchsnerven bei den Knochenfischen. Anat. Am., 1901, XIX, 257. Kanthack, A. A. Studien iiber die Histologie der Larynxschleimhaut. Arch. f. path. Anat., 1889, CXVIII, 137; 1890, CXIX, 326; 1890, CXX, 273. Kblliker, A. Zur Kenntnis des Baues der Lunge des Menschen. Verhandl. d. phys.-med. Gesellsch. z. Wurzburg, 1881, N. F., XVI, 1. Linser, P. Ueber den Bau und die Entwicklung des elastischen Gewebes in der Lunge. Anat. Hefte, 1900, XIII, 307. Lubosch, W. Ueber den Bau und die Entwicklung des Geruchsorganes von Petromyzon. Verhandl. d. anat. Gesellsch., 1904, XVIII, 67. Merkel, F. Atmungsorgane. von Bardeleben's Handbuch d. Anat., Bd: VI, Abth. I, Jena, 1902. Meyer, W. Beitrage zur Kenntnis der Anatomic und Histologie der lateralen " Nasendriise. Anat. Anz., 1904, XXIV, 369. Miller, W. S. The lobule of the lung and its blood vessels. Anat. Anz., 1892, VII, 181. The structure of the lung. J. Morph., 1893, VIII, 165. The lymphatics of the lung. Anat. Anz., 1896, XII, 95. Das Lungenlappchen seine Blut-und Lymph-gefasse. Arch. /. Anat., 1900, 197. Most. Ueber die Lymphgefasse und Lymphdriisen des Kehlkopfes. Anat. Anz., 1899, XV, 387. 694 BIBLIOGRAPHY Oppel, A. Atmungs-Apparat. Ergebn. d. Anat. u. EntwickL, 1902, XII, 134. Ploschko, A. Die Nervenendigungen und der Ganglien der Respirations- organe. Anat. Am., 1897, XIII, 12. Retzius, G. Die Endigungsweise des Reichnerven. Biol. Untersuch., 1892, N. F., Ill, 25. Zur Kenntnis der Nervenendigungen in den Lungen. Biol. Un- tersuch., 1893, AT. F., V, 41. Schultze, M. Untersuchungen iiber den Bau der Nasenschleimhaut. Abhandl. d. Naturf. Gesellsch. z. Halle, 1862, VII, 1. Spiess, G. Ueber den Blutstrom in der Schleimhaut des Kehlkopfes und des Kehldeckels. Arch. f. Physiol., 1894, 503. Zuckerkandl, E. Ueber die Anastomosen der Venae pulmonales mit den Bronchialvenen und mit dem mediastinalen Venennetze. Sitz. d. k.Akad. d. Wissensch., Wien, 1882, LXXXIV, 110. CHAPTER XV.— THE DIGESTIVE SYSTEM MOUTH AND TEETH Adloff, P. Zur Entwicklungsgeschichte des Zahnsystems von Sus scrofa domest. Anat. Am., 1901, XIX, 481. Boll, F. Untersuchungen iiber die Zahnpulpa. Arch. f. mik. Anat., 1868, IV, 73. von Brunn, A. Beitrage zur Kenntnis der Zahnentwicklung. Arch. /. mik. Anat., 1891, XXXVIII, 142. Collaud, A. Etude sur le ligament alveolo-ctentaire. Internal. Monatschr. f. Anat. u. Physiol, 1890, VII, 32. Columbini. Ueber einige fettsecernierende Drusen der Mundschleimhaut des Menschen. Monatschr. f. prakt. Dermatol, 1902, XXXIV, 423. Czermak, J. H. Beitrage zur mikroskopischen Anatomic der menschlichen Zahne. Zeitschr. f. ivissensch. Zool, 1850, II, 295. Hohl, E. Beitrag zur Histologie der Pulpa und des Dentins. Arch. f. Anat., 1896, 31. Kallius, E. Beitrage zur Entwicklung der Zunge. Anat. Hefte, 1901, XVI, 531. Morgenstern, M. Ueber die Innervation des Zahnbeines. Arch. f. Anat., 1896, 378. Neumann, E. F. C. Beitrage zur Kenntnis des normalen Zahnbein- und Knochengewebes. Leipzig, 1863. Nuhn. Ueber eine bisjetzt noch nicht naher beschriebene Druse im Innern der Zungenspitze. Mannheim, 1845. Retzius, G. Zur Kenntnis der Endigungsweise der Nerven in den Zahnen der Saugetiere. Biol. Untersuch., 1894, N. F., VI, 64. Robertson, W. G. A. On the relation of nerves to odontoblasts, and on the growth of dentine. Trans. Roy. Soc., Edinburgh, 1892, XXXVI, 321. Rose, C. Ueber die Entwicklung der Zahne des Menschen. Arch. /. mik. Anat., 1891, XXXVIII, 447. Contribution to the histogeny and histology of bony and dental tissues. Dental Cosmos, 1893, XXXV, 1189, 1273. BIBLIOGRAPHY 695 Ruffer, A. On the phagocytes of the alimentary canaA. Quart. J. Mic. Sc., 1890, XXX, 481. Schaffer, J. Beitrage zur Histologie menschlicher Organe. IV. Zunge. V. Mundhole-Schlundkopf. VI. Oesophagus. VII. Cardia. Site. d. k. Akad. d. Wissensch., Wien, 1897, CVI, 353. Stieda, L. Ueber die Foveolse palatinae (Gaumengriibchen). Verhandl. d. anat. Gesellsch., 1902, XVI, 130. Tomes, C. S. Upon Rose's proposed classification of the forms of dentine. Anat. Anz.-, 1898, XIV, 343. A manual of dental anatomy. London, 6th ed., 1904. Walkhoff, O. Die normale Histologie menschlicher Zahne, einschliesslich der mikroskopischen Technik. Leipzig, 1901. Williams, J. L. On the formation and structure of dental enamel. Dental Cosmos, 1896, XXXVIII, 101, 269, 453. CHAPTER XVI.— THE DIGESTIVE SYSTEM (Continued) PHARYNX AND ESOPHAGUS De Witt, L. M. Arrangement and terminations of nerves in the esophagus of mammalia. J. Comparat. Neurol., 1900, X, 382. Hammar, J. A. Studien uber die Entwicklung des Vorderdarms und einiger angrenzenden Organe. Arch. f. mik. Anat., 1902, LXI, 404. Hewlett, A. W. The superficial glands of the esophagus. J. Exper. Med., 1901, V, 319. Ruckert. Ueber die sogenannten oberen Cardialdrusen der Oesophagus. Arch. /. path. Anat., 1904, CLX^V, 16. Schaffer, J. Ueber die Driisen der menschlichen Speiserohre. Sitz. d. k. Akad. d. Wissensch., Wien, 1897, CVI, 175. Schridde, H. Ueber Magenschleimhaut-Inseln vom Bau der Cardialdrii- senzone und Fundusdriisenregion und den unteren, oesophagealen Car- dialdrusen gleichende Driisen im obersten Oesophagusabschnitt. Arch, f. path. Anat., 1904, CLXXV, 1. Smirnow, A. Ueber die Nervenendigungen im Oesophagus des Frosches. Internat. Monatschr. f.Anat. u. Physiol., 1893, X, 248. STOMACH Bensley, R. R. The structure of the mammalian cardiac glands. Quart. J. Mic. Sc., 1898, N. S., XLI, 361. The cardiac glands of mammals. Am. J. Anat., 1902-3, II, 105. — The differentiation of the specific elements of the gastric glands of the pig^ Am. J. Anat., 1902-3, II, Proc. Assoc. Am. Anat., in. Cade, A. Etudes de la constitution histologique normale, et de quelques variations fonctionelles et experimentelles des elements se"cre*teurs des glandes gastriques du fond. Arch, d'anat. mic., 1901, IV, 1. Capparelli, A. Die nervosen Endigungen in der Magenschleimhaut. Biol. Centralbl, 1891, XI, 27. Dekhuyzen, M. C., und Vennaet, P. Ueber das Epithel der Oberflache des Magens. Verhandl. d. anat. Gesellsch., 1903, XVII, 145. 696 BIBLIOGEAPHY De Witt, L. M. Morphology of the pyloric glands as shown by reconstruc- tion. Am. J. Anat., 1902, I, 514, Proc. Assoc. Am. Anal. On the morphology of the pyloric glands of vertebrates. Contrib. Med. Research, dedic. to V. C. Vaughan, Ann Arbor, 1903, 188. Edinger, L. Zur Kenntnis der Driisenzellen des Magens besonders beim Menschen. Arch. f. mik. Anat., 1880, XVII, 193. Glassner, K. Ueber die Vorstufen der Magenfermente. Beitr. z. chem. Physiol., 1901, I, 1. Golgi, C. Sur la fine organization des glandes peptiques des mammiferes. Arch. ital. de biol, 1893, XIX, 448. Greenwood, M. Observations on the gastric glands of the pig. J. Physiol., 1884-5, V, 195. Heidenhain, R. Untersuchungen iiber den Bau der Labdriisen. Arch. f. mik. Anat., 1870, VI, 368. von Kupffer, C. Epithel und Driisen des menschlichen Magens. Munchen, 1883. Langley, J. N. On the changes in pepsin-forming glands during secretion. J. Physiol., 1879-80, II, 281. On the histology of the mammalian gastric glands, and the relation of pepsin to the granules of the chief cells. J. Physiol., 1880-81 , III, 269. Mall, F. The vessels and walls of the dog's stomach. Johns Hop. Hosp. Rep., 1896, I, 1. Peiser, A. Ueber die Form der Driisen des menschlichen Verdauungs- ' apparates. Arch. f. mik. Anat., 1902, LXI, 391. Stohr, P. Zur Kenntnis des feineren Baues des menschlichen Magenschleim- haut. Arch. f. mik. Anat., 1882, XX, 221. Theohari, A. Etude sur la structure fine des cellules principales de bordure et pyloriques de Pestomac a 1'etat de repos et a 1'etat d'activite secre'toire. Arch, d'anat. mic., 1899, III, 11. INTESTINE Arnold, J. Weitere Beispiele granularer Fettsynthese (Zungen- und Darm- schleimhaut). Anat. Anz., 1904, XXIV, 389. Bensley, R. R. On the histology of the glands of Brunner. Am. J. Anat., 1902-3, II, Proc. Assoc. Am. Anat., xi. Concerning the glands of Brunner. Anat. Anz., 1903, XXIII, 497. Berry, R. J. A. The true csecal apex, or the vermiform appendix ; its minute and comparative anatomy. J. Anat. and Physiol., 1901, XXXV, 83. Bizzozero, G. Ueber die schlauchformigen Driisen der Magendarmkanals und die Beziehungen ihres Epithels zu dem Oberflachenepithel der Schleimhaut. Arch. f. mik. Anat., 1893, XLII, 82. Bizzozero, G., und Vassale, G. Ueber der Erzeugung und die physiologische Regeneration der Driisenzellen bei den Saugetieren. Arch. /. path. Anat., 1887, CX, 155. Bogomoletz, A. A. Beitrag zur Morphologic und Mikrophysiologie der Brun- nerschen Driisen. Arch. f. mik. Anat., 1903, LXI, 656. Cooke, A. B. A study of the rectal valve, experimental and clinical. Phila. Med. J., 1900, V, 964. BIBLIOGKAPHY 697 von Davidoff, M. Untersuchungen iiber die Beziehungen des Darmepithels zum lymphoiden Gewebe. Arch. f. mik. Anat., 1887, XXIX, 237. Drago, U. Cambiamenti di forma e di struttura dell' epitelio intestinali du- rante 1'assorbimento del grassi. Richerche lab. di anat. norm. d. r. univ. di Roma, 1900, VIII, 65. DuBois, C. C. Granule cells in the mucosa of the pig's intestine. Anat. Anz., 1904, XXV, 6. Haidenhain, M. Ueber die Struktur der Darmepithelzellen. Arch. f. mik. Anat., 1899, LIV, 184. Heidenhain, R. Beitrage zur Histologie und Physiologic der Dimndarm- schleimhaut. Arch. f. d. ges. Physiol., 1888, XLIII, Suppl. 1. Klein, S. The nature of the granule cells of Paneth. Am. J. Anat., 1902-3, II, Proc. Assoc. Am. Anat., IV. Kultschitzky, N. Zur Frage iiber den Bau des Darmkanals. Arch. /. mik. Anat., 1897, XLIX, 7. Loevenhart, A. S. On the relation of lipase to fat metabolism — lipogenesis. Am. J. Physiol, 1902, VI, 331. Majewsky, A. Ueber die Veranderungen der Becherzellen im Darmkanal wah- rend der Secretion. Internal. Monatschr. f. Anat. u. Physiol., 1894, XI, 177. Mall, F. Die Blut- und Lymph wege im Diinndarm des Hundes. Abhandl. d. math.-phys. Kl. d. k. sachs. Gesellsch. d. Wissensch., 1888, XIV, 153. Mingazzini, P. Cambiamenti morfologici dell' epitelio intestinale durante lo assorbimento delle sostanze alimentari. Richerche lab. di anat. norm. d. r. univ. di Roma, 1902, XII, 97. Munk, I. Weiteres zur Lehre von der Spaltung und Resorption der Fette. Arch. f. Physiol., 1890, 581. Oppel, A. Verdauungs-Apparat. (Speicheldriisen, Darmkanal.) Ergebn. d. Anat. u. Entwickl., 1902, XII, 61. Paneth, J. Ueber die secernierenden Zellen des Diinndarm-Epithels Arch. /. mik. Anat., 1888, XXXI, 113. Ein Beitrag zur Kenntnis der Lieberkiihnsches Krypten. Centralbl. /. Physiol., 1888, I, 255. Pfluger, E. Der gegenwartige Zustand der Lehre von der Verdauung und Resorption der Fette. Arch. f. d. ges. Physiol., 1900, LXXXII, 303. Fortgesetzte Untersuchungen iiber die Resorption der kiinstlich gefarbten Fette. Arch. f. d. ges. Physiol., 1901, LXXXV, 1. Ueber Kalkseifen als Beweise gegen die in wasseriger Losung sich vollziehende Resorption der Fette. Arch. f. d. ges. Physiol., 1902, LXXXIX, 211. Ramond, M. F. La desquamation de l'epithe"lium de 1'intestin grele au cours de la digestion. Compt. rend. soc. de biol., 1904, LVI, 171. Renter, K. Zur Frage der Darmresorption. Anat. Anz., 1901 , XIX, 198. Ein Beitrag zur Frage der Darmresorption. Anat. Hefte, 1903, XXI, 121. Schafer, E. A. On the part played by amoeboid cells in the process of intes- tinal absorption. Internat. Monatschr. f. Anat. u. Physiol., 1885, II, 6. Schaffer, J. Beitrage zur Histologie menschlicher Organe. I. Duodenum. II. Diinndarm. III. Mastdarm. Sitz. d. k. Akad. d. Wissensch., Wien, 1891, C, 440. 698 BIBLIOGRAPHY Spalteholz, W. Das Bindegewebsgeriist der Diinndarmschleimhaut. Arch. f.Anat., l897,Suppl. Bd., 373. Ssobolew, L. W. Zur Frage iiber die Folgen der Unterbindung des Wurm- fortsatzes. Arch. f. mik. Anat., 1903, LXII, 122. CHAPTER XVII.— THE SALIVARY GLANDS AND PANCREAS SALIVARY GLANDS Berkley, H. J. The intrinsic nerves of the submaxillary gland of Mus mus- culus. Johns Hop. Hosp. Rep., 1895, IV, 275. Flint, J. M. The ducts of the human submaxillary gland. Am. J. Anat., 1902, I, 269. The blood vessels of the submaxillary gland and their development. J. Med. Research, 1902, VII, 464. The development of the reticulated basement membranes in the submaxillary gland. Am. J. Anat., 1902-3, II, 1. Hammar, J. A. Notiz iiber die Entwicklung der Zunge und der Mundspei- cheldriisen beim Menschen. Anat. Anz., 1901, XIX, 570. Hebold, O. Ein Beitrag zur Lehre von der Sekretion und Regeneration der Schleimzellen. Bonn, 1879. Huber, G. C. Observation on the innervation of the sublingual and sub- maxillary glands. J. Exper. Med., 1896, I, 281. Klein, E. Histological notes. Quart. J. Mic. Sc., 1881, XXI, 114. On the lymphatic system and the minute structure of the salivary glands and pancreas. Quart. J. Mic. Sc., 1882, XXII, 153. Krause, R. Zur Histologie der Speicheldriisen. Arch. f. mik. Anat., 1895, XLV, 93. Beitrage zur Histologie der Speicheldriisen. Arch. f. mik. Anat., 1897, XLIX, 707. Beitrage zur Histologie der Speicheldriisen. Arch. f. mik. Anat., 1901, LIX, 407. Kultschitzky. Zur Lehre vom feineren Bau der Speicheldriisen. Zeitschr. f. wissensch. Zool, 1885, XLI, 99. Lange, A. Ueber den Bau und die Funktion der Speicheldriisen bei den Gas- tropoden. Anat. Hefte, 1902, XIX, 85. Langley, J. N. On the histology of the mucous salivary glands, and on the behavior of their mucous constituents. /. Physiol., 1889, X, 433. Launoy, L. Sur la presence de formations ergastoplasmiques dans les glandes salivares des Ophidiens. Compt. rend. soc. de biol., 1901, LIII, 742. Lavdowsky, M. Zur feineren Anatomic und Physiologic der Speicheldriisen. Arch. f. mik. Anat., 1877, XIII, 281. Maximow, A. Beitrage zur Histologie und Physiologic der Speicheldriisen. Arch. f. mik. Anat., 1901, LVIII, 1. Noll, A. Ueber die Bedeutung der Giannuzzi'schen Halbmonde. Anat. Am., 1902, XXI, 139. Das Verhalten der Driisengranula bei der Sekretion der Schleimzelle und die Bedeutung der Giannuzzi'schen Halbmonde. Arch. f. Physiol., 1902, Suppl. Bd., 166. BIBLIOGRAPHY 699 Ranvier, L. Etude anatomique des glandes connues sous les noms de sous- maxillaire et sublinguale chez les mammiferes. Arch, de physiol. norm. et path., 1886, ser. 3, VIII, 223. Retzius, G. Ueber die Anfange der Driisengange und die Nervenendigungen in den Speicheldriisen des Mundes. Biol. Untersuch., 1892, N. F., Ill, 59. Sainte-Hilaire, C. Ueber die Membrana propria der Speicheldriisen bei Mol- lusken und Wirbeltieren. Anat. Am., 1901, XIX, 478. Solger, B. Zur Kenntnis der secernierenden Zellen der Glandula submaxil- laris des Menschen. Anat. Anz., 1894, IX, 415. Ueber den feineren Bau der Glandula submaxillaris des Menschen mit besonderer Beriicksichtigung der Driisengranula. Festschr. f. C. Gegenbaur, 1896, II, 179. PANCREAS Dogiel, A. S. Zur Frage iiber die Ausfiihrungsgange des Pancreas des Men- schen. Arch. /. Anat., 1893, 117. Eberth, C. J. Zur Kenntnis der Verbreitung glatter Muskeln. Zeitschr. /. wissensch. Zool, 1863, XII, 360. Gentes. Note sur les terminaisons nerveuses des ilots de Langerhans du pancreas. Compt. rend. soc. de biol., 1902, LIV, 202. Glinski, L. K. Zur Kenntnis des Nebenpancreas und verwandter Zustande. Arch. f. path. Anat., 1901, CLXIV, 132. Hansemann. Ueber die Structur und das Wesen der Gefassinseln des Pan- creas. Verhandl. d. deutschen path. Gesellsch., 1902, 187. Kiister, H. Zur Entwicklungsgeschichte der Langerhans'schen Inseln im Pancreas beim menschlichen Embryo. Arch. /. mik. Anat., 1904, LXIV, 158. Laguesse, E. et A. G. de la Roche. Les ilots de Langerhans dans le pancreas du cobaye apres ligature. Compt. rend. soc. de biol., 1902, LIV, 854. Matthews, A. P. The changes in structure of the pancreas cell. «/. Morph., 1899, XV, Suppl, 171. Nussbaum, M. Ueber die Teilbarkeit der lebendigen Materie. Arch. f. mik. Anat., 1886, XXVI, 485. Ogata, M. Die Veranderungen der Pancreaszellen bei der Secretion. Arch. f. Physiol., 1883, 405. Opie, E. L. On the histology of the islands of Langerhans of the pancreas. Johns Hop. Hosp. Bull., 1900, XI, 205. On the relation of chronic interstitial pancreatitis to the islands of Langerhans and to diabetes mellitus. /. Exper. Med., 1901, V, 397. The relation of diabetes mellitus to lesions of the pancreas. J. Exper. Med., 1901, V, 527. The anatomy of the pancreas. Am. Med., 1903, V, 996. Also, Johns Hop. Hosp. Bull., 1903, XIV, 229. Pearce, R. M. The development of the islands of Langerhans in the human embryo. Am. J. Anat., 1903, II, 445. Also, Univ. Pa. Med. Bull., 1903, XVI, 341. Renaut, J. Le pancreas de deux Ophidiens. Arch, d'anat. mic., 1903, VI, 1. Revell, D. G. The pancreatic ducts in the dog. Am. J. Anat., 1902, I, 443. 700 BIBLIOGRAPHY CHAPTER XVIII.— THE LIVER Arnold, J. Zur Kenntnis der Granula der Leberzellen. Anat. Anz., 1901, XX, 226. Berkley, H. J. Studies in the histology of the liver. Johns Hop. Hosp. Rep., 1895, IV, 211. Browicz. Die Beziehungen zwischen den intraacinosen Blutkapillaren und der intracellularen Ernahrungskanalchen der Leberzelle. Anat. Anz., 1902, XXII, 157. Ciechanowski, S. Weigert's Markscheidenmethode als Gallenkapillarenfar- bung. Anat. Anz., 1902, XXI, 426. Fraser, J. W., and E. H. Fraser. Preliminary note on inter- and intra-cellular passages in the liver of the frog. J. Anat. and Physiol., 1894-5, XXIX, 240. Geberg, A. Ueber die Gallengange in der Saugetierleber. Internal. Monat- schr. f.Anat. u. Physiol., 1893, X, 15. Zur Verstandigung iiber den Driisenbau der Leber der Saugetiere. Intemat. Monatschr. f. Anat. u. Physiol., 1897, IV, 8. Helly, K. K. Die Schliessmuskulatur an den Miindungen der Gallen- und der Pancreasgange. Arch. f. mik. Anat., 1899, LIV, 614. Hendrickson, W. F. The development of the bile capillaries as revealed by Golgi's method. Johns Hop. Hosp. Bull., 1898, IX, 220. Hildebrandt, W. Die erste Leberentwicklung beim Vogel. Anat. Hefte, 1902, XX, 73. Holmgren, E. Ueber die "Trophospongien" der Darmepithelzellen, nebst einer Bemerkung in Betreff einer von Prof. Browicz neulich publicirten Abhandlung iiber die Leberzellen. Anat. Anz., 1902, XXI, 477. — Ueber die "Saftkanalchen" der Leberzellen und der Epithelzellen der Nebenniere. Anat. Anz., 1902, XXII, 9. Ueber die "Trophospongien" der Nebenhodenzellen und der Le- bergangzellen von Helix pomatia. Anat. Anz., 1902, XXII, 260. Jade", N. Normale und pathologische Histologie der Gallenkapillaren. Beitr. z. path. Anat. u. z. ally. Path., 1903, XXXIII, 302. Korolkow, P. Ueber die Nervenendigungen in der Leber. Anat. Anz., 1893, VIII, 751. von Kupffer, C. Ueber die sogenannten Sternzellen der Saugetierleber. Arch'. f. mik. Anat., 1899, LIV, 254. Mall, F. P. On the origin of the lymphatics in the liver. Johns Hop. Hosp. Bull., 1901, XII, 146. Piper, H. Die Entwicklung von Magen, Duodenum, Schwimmblase, Leber, Pancreas und Milz bei Amia calva. Arch. f. Anat., 1902, Suppl. Bd., 1. Retzius, G. Ueber die Gallenkapillaren und den Driisenbau der Leber. Biol. Untersuch., 1892, N. F., Ill, 65. Weiteres liber die Gallenkapillaren und den Driisenbau der Leber. Biol. Untersuch., N. F., IV, 67. Schafer, E. A. On the existence, within the liver cells, of canaliculi which are in direct communication with the blood capillaries. J. Physiol., 1902, XXVII, Proc. Physiol. Soc., xxxiv. BIBLIOGRAPHY 701 Schlater, G. Kritisches zur Frage vom Bau der Leberzelle. Anat. Am., 1902, XXII, 249. Schmaus, H. Ueber Fixationsbilder von Leberzellen im normalen Zustande und bei Arsenikvergiftung. CentralbL /. allg. Path. u. path. Anat., 1903, XIV, 212. Shore, T. W., and H. L. Jones. On the structure of the vertebrate liver. J. Physiol., 1889, X, 408. Sudler, M. T. The architecture of the gall bladder. Johns Hop. Hosp. Bull, 1901, XII, 126. CHAPTER XIX.— THE URINARY ORGANS Berkley, H. J. The intrinsic nerves of the kidney. J. Path, and Bacterial., 1893, I, 406. Castaigne, J., et F. Rathery. Action exercee "in vitro" par les solutions de chlorure de sodium sur 1'epithelium renal. Arch, de med. exper. et d'anat. path., 1903, XV, 669, 678. Courant. Ueber die Praputialdrusen des Kaninchens. Arch. f. mik. Anat., 1903, LXII, 175. Disse, J. Ueber die Veranderungen der Nierenepithelien bei der Sekretion. Anat. Hefte, 1892, II, 141. Harnorgane. Handbuch d. Anat. d. Menschen, Bardeleben, Bd. VII, Teil I, Jena, 1902. Dogiel, A. S. Zur Frage iiber das Epithel der Harnblase. Arch. f. mik. Anat., 1890, XXXV, 389. Gerota, D. Ueber die Anatomic und Physiologic der Harnblase. Arch. /. Physiol., 1897, 428. Golgi, C. Annotazioni interne all' istologia dei reni dell' uomo e di altri mam- miferi e sull' istogenesi dei canalicoli oriniferi. Rend. d. r. accad. d. Lincei, 1889, ser. I, V, 334. Golobew, W. Z. Ueber die Blutgefasse in der Niere der Saugetiere und des Menschen. Internal. Monatschr. f. Anat. u. Physiol., 1893, X, 541, 547. Goodall, J. S. The comparative histology of the urethra. J. Anat. and Physiol., 1902, XXXVI, 405. Hamburger, A. Zur Histologie des Nierenbeckens und des Harnleiters. Arch. f. mik. Anat., 1880, XVII, 14. Hamburger, O. Ueber die Entwicklung der Saugetierniere. Arch. /. Anat., 1890, Suppl. Bd., 15. Hauch, E. Ueber die Anatomic und Entwicklung der Nieren. Anat. Hefte, 1903, XXII, 153. Heidenhain, R. Mikroskopische Beitrage zur Anatomic und Physiologic der Nieren. Arch. f. mik. Anat., 1874, X, 1. Herring, P. T. The development of the Malpighian bodies of the kidney, and its relation to pathological changes which occur in them. J. Path. and Bacteriol., 1900, VI, 459. Herzog, F. Beitrage zur Entwicklungsgeschichte und Histologie der mann- lichen Harnrohre. Arch. f. mik. Anat., 1904, LXIII, 710. Johnston, W. B. 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Station in Neapel, 1897, XII, 495. Barker, L. F. The nervous system and its constituent neurones. New York, 1901. von Bechterew, W. Die Leitungsbahnen im Gehirn und Riickenmark. Leip- zig, 1899. Berkley, H. J. A treatise on mental diseases. New York, 1900. Braunig, K. Ueber Chromatolyse in den Vorderhornzellen des Riicken- marks. Arch. f. PhysioL, 1903, 251. Cajal, S. Ram6n y. Sur 1'origine et la direction des prolongations nerveuses de la couche mole'culaire du cervelet. Internat. Monatschr. f. Anat. u. PhysioL, 1889, VI, 158. — Comparative study of the sensory areas of the human cortex. Clark Univ. Decennial Celebration, Worcester, 1899, 311. Cramer, A. Das hintere Langsbundel, Fasciculus longitudinalis dorsalis, nach Untersuchungen am menschlichen Fotus, Neugeborenen und 1 bis 3 Monate alten Kindern. Anat. Hefte, 1900, XIII, 97. Cushing, H. The taste fibres and their independence of the nervus trigeminus. Johns Hop. Hosp. Bull., 1903, XIV, 71. BIBLIOGRAPHY 711 Dixon, A. F. On the course of the taste fibres. Edinb. Med. J., 1897, N. S., I, 395. Flechsig, P. Die Leitungsbahnen im Gehirn und Riickenmark des Menschen. Leipzig, 1876. 1st die Tabes dorsalis eine "System-Erkrankung." N enrol. Cen- tralbl, 1890, IX, 33, 72. Forel, A. Untersuchungen iiber die Haubenregion und ihre oberen Ver- kniipfungen im Gehirn des Menschen und einige Saugetiere. Arch. f. Psychiat., 1877, VII, 393. Ueber das Verhaltniss der experimentellen Atrophie und Degenera- tionsmethode zur Anatomic und Histologie des Centralnervensystems. Festschr. von Ndgeli u. von Kolliker, Zurich, 1891. Fowler, H. A. Model of the nucleus dentatus of the cerebellum and its ac- cessory nuclei. Johns Hop. Hosp. Bull., 1901, XII, 151. Fusari, R. Untersuchungen iiber die feinere Anatomic des Gehirns der Teli- ostier. Internal. Monalschr. f. Anat. u. Physiol., 1887, IV, 275. Goldstein, K. Beitrnge zur Entwicklungsgeschichte des menschlichen Gehirns. Arch. /. Anat., 1903, 29. Hardesty, I. The neuroglia of the spinal cord of the elephant, with some preliminary observations upon the development of neuroglia fibres. Am. J. Anat., 1902-3, II, 81. Hatschek, R. Ein vergleichend-anatomisches Beitrag zur Kenntnis der Haubenfaserung und zur Frage des centralen Trigeminusverlaufes. Arbeit, a. d. neurol. Inst. Wiener Univ., 1902, IX, 279. Hatschek, R., und H. Schlesinger. Der Hirnstamm des Delphins. Arbeit. a. d. neurol. Inst. Wiener Univ., 1902, IX, 1. Held, H. Die centralen Bahnen des Nervus acusticus bei der Katze. Arch. f.Anat., 1891,271. Die centrale Gehorleitung. Arch. f.Anat., 1893, 201. Ueber den Bau der grauen und weissen Substanz. Arch f. Anat., 1902, 189. His, W. Ueber das frontale Ende des Gehirnrohres. Arch. f. Anat., 1893, 157. Vorschlage zur Einteilung des Gehirns. Arch. f. Anat., 1893, 172. Hoche, A. Ueber secundare Degeneration, speciell des Gowers'schen Bundels. Arch. f. Psychiat., 1896, XXVIII, 510. Jakob, C. An atlas of the normal and pathological nervous systems. Transl. by J. Collins. New York, 1896. von Lenhosse'k, M. Beitrage zur Histologie des Nervensystems und der Sinnesorgane. Wiesbaden, 1894. Lewis, F. T. The gross anatomy of a 12 mm. pig. Am. J. Anat., 1902-3, II, 211. Lissauer, H. Beitrag zum Faserverlauf im Hinterhorn des menschlichen Ruckenmarks und zum Verhalten desselben bei Tabes dorsalis. Arch. f. Psychiat., 1886, XVII, 377. Lubosch, W. Drei kritische Beitrage zur vergleichenden Anatomic des Nervus accessorius. Anat. Anz., 1901, XIX, 461. Marburg, O. Mikroskopisch-topographischer Atlas des menschlichen Central- nervensystems. Leipzig und Wien, 1904. 712 BIBLIOGRAPHY Mellus, E. L. On the origin and destination of fibres of the occipito-temporo- pontine bundle (Tiirck's bundle, Meynert). Am. J. Anat., 1904, III, Proc. Assoc. Am. Anat., xvi. On a hitherto undescribed nucleus lateral to the fasciculus solitarius. Am. J. Anat., 1903,11,361. von Monakow, C. Experimented und pathologisch Untersuchungen iiber die Haubenregion, den Sehhiigel und die Regio subthalamica. Arch. f. Psychiat., 1895, XXVII, 386. Mott, F. W. Microscopical examination of Clarke's column in man, the monkey, and the dog. J. Anat. and Physiol, 1888, XXII, 479. The bipolar cells of the spinal cord and their connections. Brain, 1890, XIII, 433. Obersteiner, H. Anleitung beim Studium des Baues der nervosen Central- organe. Leipzig und Wien, 1901. Paton, S. A study of the neurofibrils in the ganglion cells of the cerebral cortex. J. Exper. Med., 1901, V, 21. Patrick, H. T. On the course and destination of Gowers' tract. J. Nerv. and Ment. Dis., 1896, XXIII, 85. Peter, K. Der Einfluss der Entwicklungsbedingungen auf die Bildung des Centralnervensystems und der Sinnesorgan bei den verschiedenen Wir- beltierklassen. Anat. Anz., 1901, XIX, 176. Probst, M. Experimentelle Untersuchungen iiber die Anatomic und Physi- ologic der Leitungsbahnen des Gehirnstammes. Arch. f. Anat., 1902, Suppl. Bd., 147. Renaut, J. Recherches sur les centres nerveux, amyeliniques. La nevroglie et 1'ependyme. Arch, de Physiol., 1882, ser. 2, IX, 593. Ris, F. Ueber den Bau des Lobus opticus der Vogel. Arch. f. mik. Anat., 1899, LIII, 106. Rothmann, M. Ueber die Endigungen der Pyramidenbahnen im Riicken- mark. Arch. f. Physiol., 1903, Suppl. Bd., 509. Sabin, F. R. On the anatomical relation of the nuclei of reception of the cochlear and vestibular nerves. Johns Hop. Hosp. Bull., 1897, VIII, 253. An atlas of the medulla and mid-brain. Bait., 1901. Also, Contrib. Sc. Med., dedic. to W. H. Welch, Bait., 1900. Schlapp, M. G. Der Zellenbau der Grosshirnrinde des Affen Macacus cynomol- gus. Arch. f. Psychiat., 1898, XXX, 583. The microscopical structure of the cortical areas in man and some mammals. Am. J. Anat., 1902-3, II, 259. Sippy, B. W. Lesions of the conus medullaris and cauda equina. J. Am. Med. Assoc., 1902, XXXVIII, 1195. von Smirnow, A. E. Ueber eine besondere Art von Nervenzellen der Molecu- larschicht des Kleinhirnes bei erwachsene Saugetieren und beim Men- schen. Anat. Anz., 1897, XIII, 636. Smith, G. E. The connection between the olfactory bulb and the hippocampus. Anat. Anz., 1895, X, 470. Stilling, B. Neue Untersuchungen iiber den feineren Bau des Riickenmarks. Cassel, 1859. BIBLIOGRAPHY 713 Streeter, G. L. Anatomy of the floor of the fourth ventricle. Am. J. Anat., 1903, II, 299. Tarasewitsch, J. Zum Studium der mit den Thalamus opticus und Nucleus lenticularis in Zusammenhang stehenden Faserzuge. Arbeit, a. d. neurol. Inst. Wiener Univ., 1902, IX, 251. Terterjanz, M. Die obere Trigeminuswurzel. Arch. f. mik.Anat., 1899, LIII, 732. Vincenzi, L. Sulla fina anatomia del nucleo ventrale dell' acustico. Anat. Am., 1901, XIX, 33. Di alcuni nuovi fatti risguardanti la fina anatomia del nucleo del corpo trapezoide. Anat. Anz., 1901, XIX, 359. Di molte mie ricerche sulP origine di alcuni nervi cerebrali rimaste affatto ignote. Anat. Anz., 1901, XIX, 601. Sulla mancanza di cellule monopolari nel midollo allungato. Anat. Anz., 1903, XII, 557. Wallenberg, A. Die secundare Balm des sensibiler Trigeminus. Anat. Anz., 1896, XII, 95. Das basale Reichbiindel des Kaninchens. Anat. Anz., 1901, XX, 175. Eine centrifugal leitende direkte Verbindung der frontalen Vorder- hirnbasis mit der Oblongata (u. Riickenmark?) bei der Ente. Anat. Anz., 1902, XXII, 289. CHAPTER XXVIII.— THE EYE Agababow, A. Ueber die Nerven" der Sclera. Arch. /. mik. Anat., 1904. LXIII, 701. Barbadoro, L. Gli strati della retina nello sviluppo della rana. Anat. Anz., 1901, XIX, 597. Berger, E. Anatomic normale et pathologique de Pceil. Paris, 1893. Bernard, H. M. Studies in the retina. Quart. J. Mic. Sc., 1902, XL VI, 25, and 1903, XL VII, 303. Bird, C. H. G., and E. A. Schafer. Observations on the structure of the cen- tral fovea of the human eye. Inter nat. Monatschr. f. Anat. u. Physiol., 1895, XII, 1. Buchanan, L. The glands of the ciliary body, 262. Cajal, S. Ram6n y. Le retine des verte'bre's. La cellule, 1893, IX, 119. Carlson, A. J. Changes in the Nissl's s bstance of the ganglion and the bipolar cells of the retina of the Brandt cormorant, Phalacrocorax penicillatus, during prolonged normal stimulation. Am. J. Anat., 1903, II, 341. Chievitz, J. H. Die Area und Fovea centralis retinae beim menschlichen Fotus. Internat. Monatschr. f. Anat. u. PhysioL, 1887, IV, 201. Cirincione. Ueber die Genese des Glaskorpers bei Wirbeltieren. Verhandl. d. anat. Gesellsch., 1903, XVII, 51. Dogiel, A. S. Ueber die nervosen Elemente in der Retina des Menschen. Arch. f. mik.Anat., 1891, XXXVIII, 317. Die Nervenendkorperchen (Endkolber, W. Krause) in der Cornea und Conjunctiva bulbi des Menschen. Arch. f. mik.Anat., 1891, XXXVII, 602. 714 BIBLIOGKAPHY Dogiel, A. S. Ein besonderer Typus von Nervenzellen in der mittleren gan- gliosen Schicht der Vogel-Retina. Anat. Anz., 1895, X, 750. Die Structur der Nervenzellen der Retina. Arch. f. mik. Anat., 1895, XLVI, 394. Embden, G. Primitivfibrillenverlauf in der Netzhaut. Arch. f. mik. Anat., 1901, LVII, 570. Fischel, A. Ueber die Regeneration der Linse. Anat. Hefte, 1900, XIV, 1. Fuchs, E. Text-book of ophthalmology. Transl. by A. Duane, New York, 1895. Herzog, H. Ueber einen neuen Lidmuskel. Anat. Anz., 1904, XXIV, 332. Kallius, E. Sehorgan. Ergebn. d. Anat. u. Entwickl., 1902, XII, 348. Koch, R. Epithelstudien am dritten Augenlide einiger Saugetiere. Arch. f. mik. Anat., 1904, LXIII, 417. Kb'lliker, A. Ueber die Entwicklung und Bedeutung des Glaskorpers. Ver- handl. d. anat. Gesellsch., 1903, XVII, 49. Krause, W. Die Retin . Internat. Monatschr. f. Anat. u. Physiol., 1895, XII, 46, 105. Lewis, W. H. Wandering pigmented cells arising from the epithelium of the optic cup. Am. J. Anat., 1903, II, 405. Experimental studies on the development of the eye in amphibia. Am. J. Anat., 1904, III, Proc. Assoc. Am. Anat., xm. Lbwenthal, N. Zur Kenntnis der Glandula infraorbitalis einiger Saugetiere. Anat. Anz., 1895, X, 123. Onodi, A. Das Ganglion ciliare. Anat. Anz., 1901, XIX, 118. Pfitzner, W. Das Epithel der Conjunctiva. Zeitschr. f. biol., 1897, N. F., XVI, 397. Piersol, G. A. Beitrage zur Histologie der Harder'schen Driisen der Am- phibien. Arch. f. mik. Anat., 1887, XXIX, 594. Rabl, C. Zur Frage nach der Entwicklung des Glaskorpers. Anat. Anz., 1903, XXII, 573. Reichel, P. Ueber die morphologischen Veranderungen der Thranendriise bei ihre Thatigkeit. Arch. f. mik. Anat., 1880, XVII, 12. Sala, G. Beitrag zum Studium der feineren Struktur der Netzhaut. Anat. Anz., 1904, XXV, 246. Stohr, P. Beitrage zur mikroskopischen Anatomic des menschlichen Kor- pers. Retina. Verhandl. d. phys.-med. Gesellsch. z. Wiirzburg, 1887, N. F., XX, 1. Ueber die Querschichtung in den Kernen der menschlichen Stabchen- sehzellen. Anat. Anz., 1899, XVI, 197. von Szily, A. Zum Glaskorperfrage. Anat. Anz., 1904, XXIV, 417. Tartuferi, F. Sull' anatomia della retina. Internat. Monatschr. f. Anat. u. Physiol, 1887, IV, 421. Wolfrum, M. Beitrage zur Entwicklungsgeschichte der Cornea der Sauger. Anat. Hefte, 1903, XXII, 59. Ziirn, J. Vergleichend histologische Untersuchungen iiber die Retina und die Area centralis retinae der Haussaugetiere. Arch. f. Anat., 1902, Suppl. Bd., 99. BIBLIOGBAPHY 715 CHAPTER XXIX.— THE EAR Alaxander, G. Das Labyrinthpigment des Menschen und der hoheren Sau- getiere. Arch. f. mik. Anat., 1901, LVIII, 134. Bulle, H. Beitrage zur Anatomic des Ohres. Arch. f. mik. Anat., 1887, XXIX, 237. Dench, E. B. Diseases of the ear. New York, 1895. Denis, P. Recherches sur le developpement de 1'oreille interne chez les mam- miferes. Arch, de biol, 1902, XVIII, 377. Denker, A. Zur vergleichenden Anatomic des Gehororgans der Saugetiere. Ergebn. d. Anat. u. Entwickl., 1899, IX, 297. Driiner, L. Ueber die Anatomic und Entwicklungsgeschichte des Mittelohres beim Menschen und bei der Maus. Anat. Am., 1904, XXIV, 257. Eschweiler. Zur vergleichenden Anatomic der Muskeln und der topographic des Mittelohres verschiedener Saugetiere. Arch. f. mik. Anat., 1899, LIII, 558. Kaiser, O. Das Epithel der CristaB und Maculae acusticse. Arch. f. Ohren- heilk., 1891, XXXII, 181. Kishi, J. Ueber den peripheren Verlauf und die Endigung des Nervus coch- leae. Arch. f. mik. Anat., 1902, LIX, 144. Krause, R. Die Entwicklung des Aqueductus vestibuli seu Ductus endolym- phaticus. Anat. Am., 1901, XIX, 49. von Lenhosse"k, M. Die Nervenendigungen im Gehororgans. Verhandl. d. anat. Gesellsch., 1893, VII, 199. Norris, H. W. Studies on the development of the ear in Amblystoma. J. Morph., 1892, VII, 23. Prussak, A. Zur Physiologic und Anatomic des Blutstroms in der Trommel- hohle. Arch. /. Ohrenheilk., 1869, IV, 290. Retzius, G. Die Endigungsweise des Gehornerven. Biol. Untersuch., 1892, N. F., Ill, 29. Weiteres iiber die Endigungsweise des Gehornerven. Biol. Un- tersuch., 1893, N. F., V, 35. Rickenbacher, O. Untersuchungen iiber die embryonale Membrana tectoria des Meerschweinchens. Anat. Hefte, 1901, XVI, 381. Rudinger, N. Zur Anatomic und Entwicklung des inneren Ohres. Monat- schr. f. Ohrenheilk., 1888, XXII, 1. Schwalbe, G. Lehrbuch der Anatomic der Sinnesorgane. Erlangen, 1887. Smith, G. The middle ear and columella of Birds. Quart. J. Mic. Sc., 1904, XL VIII, 11. Weigner, K. Experimenteller Beitrag zur Frage vom zentralen Verlaufe der Nervus cochlearis beim Spermophilus citellus. Arch. f. mik. Anat., 1903, LXII, 251. Zuckerkandl, E. Beitrage zur vergleichenden Anatomic der Ohrtrompete. Arch. f. Ohrenheilk., 1886, XXIII, 201. 716 BIBLIOGRAPHY CHAPTER XXX.— TECHNIQUE Arnold, J. Ueber vitale und supravitale Granulafarbung der Nierenepi- thelien. Anat. Anz., 1902, XXI, 417. Weitere Mitteilungen iiber vitale und supravitale Granulafarbung (Epithelien, Endothelien, Bindegewebszellen, Mastzellen, Leukocyten, Gefasse, glatte Muskelf asern) . Anat. Anz., 1903, XXIX, 1. Bardeen, C. R. A new carbon-dioxide freezing microtome. Johns Hop. Hosp. Bull, 1901, XII, 112. Bern's method of reconstruction by means of wax plates. Johns Hop. Hosp. Bull, 1901, XII, 148. Bethe, A. Eine neue Methode der Methylenblaufixation. Anat. Anz., 1896, XII, 438. Daddi, L. Nouvelle methode pour colorer la graisse dans les tissus. Arch. ital. de biol., 1896, XXVI, 143. Durig, A. Das Formalin als Fixirungsmittel anstatt der Osmiumsaure bei der Methode Ramon y Cajals. Anat. Anz., 1895, X, 659. Ehrlich, P. Ueber die Methylenblaureaction der lebenden Nervensubstanz. Deutsche med. Wochenschr., 1886, XII, 49. Feinberg. Ueber die Anwendung der Romano wski'schen (Methylenblau, Eosin) Farbemethode in den Gewebsschnitten. Berl. klin. Wochenschr., 1902, XXXIX, 1048. Fischer, A. Zur Kritik der Fixirungsmethoden und der Granula. Anat. Anz., 1894, IX, 678. Neue Beitrage zur Kritik der Fixirungsmethoden. Anat. Anz., 1895, X, 769. Flint, J. M. A new method for the demonstration of the framework of organs. Johns Hop. Hosp. Bull., 1902, XIII, 48. Gurwitsch, A. Ein schnelles Verfahren der Eisenhamatoxylinfarbung. Zeit- schr. f. wissensch. Mik., 1902, XVIII, 291. Hardesty, I. Neurological technique. Chicago and London, 1902. Harris, H. F. A new method of staining elastic tissue. Zeitschr. f. wissensch. Mik., 1902, XVIII, 290. Hastings, T. W. A modified Nocht's stain. Johns Hop. Hosp. Bull, 1904, XV, 122. Jenner, L. A new preparation for rapidly fixing and staining blood. Lancet, 1899, I, 370. Kaplan, I. Nervenfarbungen. Arch. f. Psychiat., 1902, XXXV, 825. Kollmann. Die Herstellung der Teichmann'schen Injectionsmassen. Ver- handl. d. anat. Gesellsch., 1895, IX, 77. Kolossow, A. Ueber eine neue Methode der Bearbeitung der Gewebe mit Osmiumsaure. Zeitschr. /. wissensch. Mik., 1892, IX, 38. Langley, J. N. On the preservation of mucous granules in secretory cells. J. Physiol, 1889, X, Proc. Physiol. Soc., iv. Lee, A. B. The microtomist's vade-mecum. London, 1896. Mallory, F. B. A contribution to staining methods. 1. A differential stain for connective tissue fibrillae and reticulum. 2. Chlorid of iron hema- toxylin for nuclei and fibrin. 3. Phosphotungstic acid hematoxylin for neuroglia fibres. J. Exper. Med., 1900, V, 15. BIBLIOGRAPHY 717 Mann, G. Physiological histology. Oxford, 1902. Mayer, P. Ueber Schleimfarbung. Mitt. a. d. zool. Station in Neapel, 1897, XII, 303. Michaelis, L. Ueber Fett-Farbstoffe. Arch. f. path. Anat., 1901, CLXIV 263. Beitrag zur Theorie des Farbeprocesses. Arch. /. d. ges. Physiol., 1903, XCVII, 634. Pollack, B. Die Farbetechnik des Nervensy stems. Berlin, 1897. Schaffer, J. Die Methodik der histologischen Untersuchung der Knochenge- webes. Zeitschr. /. wissensch. Mik., 1893, X, 167. Tandler, J. Mikroskopische Injectionen mit kaltfliissiger Gelatine. Zeitschr. /. wissensch. Mik., 1901, XVIII, 22. Tellyesniczky, K. Ueber die Fixirungs- (Hartungs-) Fliissigkeiten. Arch. /. mik. Anat., 1898, LII, 202. Thoma, R. Eine Entkalkungsmethode. Zeitschr. f. wissensch. Mik., 1891, VIII, 191. Van Wart, R. McL. On a rapid method of staining neuroglia. Johns Hop. Hosp. Bull., 1903, XIV, 246. Weigert, C. Ueber eine Methode zur Farbung elastischer Fasern. Centralbl. /. ally. Path. u. path. Anat., 1898, IX, 289. 7/f INDEX Abducens nerve, 549; nucleus, 496. Aberrant thyroid, 454. Absorption, intestinal, 298. Accessory, lachrymal gland, 604; nucleus, 396; olivary nuclei, 493; thyroids, 454. Achromatic spindle, 13. Acid dyes, 655. Acid hematein, Mann's, 657. Acidophile granule cells, 35; leuco- cytes, 78. Acini, of pancreas, 316; of salivary glands, mucous, 308; of salivary glands, serous, 307; secreting, 193. Acrosome of spermatozoon, 371. Adamantoblasts, 262. Adelomorphous cells, 280. Adenoid tissue, 45. Adipose tissue, 42; developing, 43. Adrenal, see suprarenal glands, 443; bibliography of, 707. Adrenal veins, structure of, 95. Afterbrain, 474. Agminated follicles, 289. Air saccules of lung, 241. Albumin, Mayer's, 654. Alcohol, for fixation, 642; graded, 642; for hardening tissues, 649. Alimentary tract, 271; characteris- tics of, 303. Allantois, 434. Alum carmin, 658. Alum hematein, 656. Alveolar ducts of lung, 241. Alveoli, pulmonary, 242. Alveus, 516. Amacrine cells, 587. Ammon's horn, 516. Amnion, 426. Amosboid motion, 8. Amphipyrenin, 6. Ampullae of Thoma, 165. Amygdala, 155. Anaphase of mitosis, 15. Anisotropic disks of striated mus- cle, 62. Annula fibrosa of the cardiac valves, 100. Annulus tympanicus, 610, 612. Anterior, basal membrane of cornea, 566; chamber of eye, 571, 577; col- umn, of spinal -cord, 481; commis- sure, of brain, 506 ; ground bundle, 538; lingual glands, 269. Antrum of Graafian follicles, 401. Appendages, of eye, 601 ; of the skin, 205. Appendix epididymis, 384; testis, 384; vermiformis, 301. Apyknomorphous condition of nerve cells, 109. Aqueduct of Sylvius, 494, 499. Aqueductus Fallopii, 611. Aqueous humor, 593. Arborization, terminal, 468. Arachnoid, membrane, 558; villi of, 558. Arch of Corti, 631. Arched collecting tubules of kidney, 348. Arcuate nucleus, 494. Area, motor, of cerebrum, 510. Areolar connective tissue, 37. Arkyochrome nerve cells, 106. Arkyostichochrome nerve cells, 107. Arteria centralis retinae, 597. Arteries, 84; coats of, 84; compari- son of large and small, 89 ; general characteristics, 87 ; helicine, 367 ; large, 88; medium-sized, 84; pre- capillary, 89; small, 88; arteries and veins, comparison of, 95. Arterioles, 88. Articular cartilages, 167. Ascending sulco-marginal fasciculus, 538. Association, amacrines, 588; centers, 509; paths, of nervous system, 536; tracts, 522. Astrocytes, 465. 719 720 INDEX Atria of lung, 241. Attraction sphere, 2. Auditory, area of cerebrum, cortex of, 515; canal, external, 607; nerve, 546, 634; nerve, nuclei of, 496, 497; ossicles, 614. Auerbach's plexus, of esophagus, 27 1 ; of intestine, 297 ; of stomach, 286. Auricle of ear, 607. Axial, filament, of spermatozoon, 371; sheath, of muscle spindles, 136. Axilemma of nerve fibres, 115. Axis cylinder of nerve fibres, 115; cylinder process, 112, 468. Axone, 112, 468. B Bacillary layer of retina, 581. Baillarger, stripes of, 513. Balsam for mounting sections, 669. Bartholin, glands of, 437. Basal, cells of retina, 586; cells of taste buds, 126; filaments of serous secreting cells, 308; membrane of cerebellum, 520; membrane of Cor- ti's organ, 628. Basement membrane, 17, 185. Basic dyes, 655. Basichromatin, 6. Basket cells, of lachrymal gland, 605; of mammary glands, 439; of pancreas, 316; of salivary glands, 307. Basophile, granule cells, 35; leuco- cytes, 78. von Bechterew's, nucleus of, 498, 547. Bellini, ducts of, 337, 350. Bergamot oil for clearing sections, 669. Berlin blue for injection, 648. Bertini, columns of, 337. Bethe, trefoil plates of, 124. Bibliography, 671; of blood, 677; of blood vessels, 681; of bone and bone marrow, 689; of cartilage, 675; of cells and protoplasm, 672; of central nervous system, 710; of connective tissue, 674; of digestive system, 694; of ductless glands, 707; of ear, 715; of epithelum, 674; of eye, 713; of female reproductive organs, 704; of liver, 700; of lym- phatic system, 686; of male repro- ductive organs, 702; of mucous membranes, 690; of muscle, 675; of nervous tissues, 681 ; of pan- creas, 699; of peripheral nerve end- ings, 684; of respiratory system, 692; of salivary glands, 698; of secreting glands, 690; of skin, 691; of technique, 716; of text- books, 671; of urinary organs, 701. Bichromate of potassium for fixa- tion, 643. Bipolar cells of retina, 587. Bizzozero, wander theory of, 292. Bladder, gall, 334;" urinary, 361. Blast for injection, pressure by, water, 649. Blood, 67; bibliography of, 677; col- oring matter of, 82; examination of, 639; fixation of, 646; capillar- ies, 90; Hasting's stain for, 664; infrequent elements of, 81. Blood corpuscles, colored, 67 ; color- less, 74; red, 67; red, development of, 71; red, effect of reagents upon, 70; red, number of, 68; red, stroma of, 69; red, structure of, 69; white, 74; white, development of, 78; white, number of, 74; white, vari- eties of, 75. Blood fibrin, 82. Blood dust, 81. Blood islands, 72. Blood plasma, 81. Blood platelets, 80; development of, 80; number of, 80. Blood serum, 81. Blood shadows, 70. Blood supply, see blood vessels. Blood vessels, bibliography of, 681 ; of connective tissue, 47; of cornea, 569; of eye, 597; ganglia of, 102; of heart, 101 ; of hemolymph nodes, 155; of internal ear, 634; of intes- tine, 296 ; of kidney, 352 ; of liver, 330; of liver, course of, 333; of lungs, 245; of lymphatic nodes, 153; of mammary gland, 442; of middle ear, 617; of muscle, 64; of nerve trunks, 119; of nervous sys- tem, 561 ; of olfactory organ, 230 ; of ovary, 410; of oviduct, 415; of pancreas, 319; of parathyroid glands, 458; precapillary, 93; of salivary glands, 313; of sclera, 570; of skin, 223; of spleen, 162: of stomach, 285; of suprarenal glands, 448; of thymus, 159; of thyroid gland, 454; of tongue, 269; of tooth, 255; of ureter, 360; of uterus, 421. Bohmer's hematoxylin, 656. Bone and bone marrow, bibliography of, fiS9. $3one, 167J cancellous, 167; cancel- lous, formation of, 181; compact, INDEX 721 167; compact, structure of, 168; corpuscles, 167; corpuscles, forma- tion of, 177; decalcification of, 647; development of, 175; marrow, for- mation of red blood corpuscles in, 73; marrow, structure of, 170; pri- mary, 177; spongy, 167. Borax carmin, 658. Bottcher, cells of,j632. Bowman, capsule of, 341; membrane of, 566; olfactory glands of, 228. Box for embedding, 651. Brachium conjunctivum, 498, 540. Brain stem., 487. Branched, saccular glands, 194; tu- bular glands, 191. Bridges, intercellular, 18. Bronchi, 236. Bronchial arteries, 248 ; tubes, 235. Bronchiole, terminal, 240. Bronchioles, 239. Brownian motion, 9, 156. Bruch, membrane of, 572. Brunner, glands of, 294. Bulbo-urethral glands, 392. Burdach, nucleus of, 489; tract of, 528. Bursae, 146. Caecum vestibulare, 625. Cajal, amacrine cells of, 587. Cajaput oil for clearing sections, 669. Calcined cartilage, 177. Calyces of kidney, 336. Canada balsam for mounting, 669. Canal, of Corti, 631 ; external audi- tory, 607; Haversian, 169; neural, 473; portal, 323; of Petit, 597; of Schlemm, 570; semicircular, 622; utriculo-saccular, 619; of Volkmann, 170. Canaliculi, of bone, 170; of nerve cells, 111; secretory, 18. Canalis, communis, 622; hyaloideus, of Stilling, 599. Canalized fibrin, 428. Cancellous bone, formation of, 181. Capillaries, blood, 90; lymphatic, 141 ; secretory, 18, 189. Capsule, of Bowman, 341 ; of cartilage cells, 50; of Glisson, 322; internal, 506; of kidney, 339; of lens, 594; of Tenon, 563. Carbo-xylol for clearing sections, 669. Cardiac, ganglia, 101; glands of esophagus, 276; glands of stomach, 284; glands, upper, 276; muscle, 47 56; muscle fibres, 56; muscle, nerve endings in, 139; valves, 100. Carmin, 658. Carotid gland, 458; bibliography of, 709. Cartilage, 48; articular, 167; bibli- ography of, 675; of bronchi, 237; calcified, 177; cells of, 48; elastic, 51; fetal, 176; fibro-, 52; hyaline, 48; of larynx, 231; net, 51; reticu- lar, 51; of trachea, 235; varieties of, 48; white fibrous, 52. Caudate nucleus, 505. Cell, typical, 1; differentiation, 6; division, 10; growth, 6; membrane, 1 ; motion, 8. Cell balls of carotid gland, 458. Cell knots of placenta, 430. Celloidin, adhesive, 654; embedding in, 650; for fastening parafin sec- tions, 654. Cells, amacrine, 587; of areolar tis- sue, 39; bibliography of, 672; of bone marrow, 171; of Bottcher, 632 ; of cardiac muscle, 56 ; of carti- lage, 48 ; chromofine, 459 ; of Claud- ius, 632; colloid, 453; of connective tissue, 34; decidual, 424; of Deit- ers, 465, 471; development of white blood, 78; ependyma, 464, 560; fat, 35, 42; fibre of Miiller, 590; ganglion, 104; glia, 464, 465; glia of retina, 590; goblet, 24; of Golgi, 471; granule, 35; gustatory, 125; of Hensen, 632; horizontal, of retina, 586; lamellar, 35; of Lan- gerhans, 428, 429; of liver, 328; lutein, 405; Mast, 35; mastoid, 611; mitral olfactory, 556; mucus, secreting, 187; nerve, 104, 467; olfactory, 228, 555; of Paneth, 292, 293; pigmented, 35; plasma, 34; prickle, 27; of Purkinje, 517; of Purkinje, structure of, 519; pyramidal, of cerebrum, 511; red blood, 67; red blood, development of, 71; reproduction of, 10; serous secreting, 188; of Sertoli, 379; smooth muscle, 54; solitary, of Meynert, 515; spindle, 34; of spleen, 161; of striated muscle, 59; of thyroid, chief, 453; vaso- forma- tive, 72; white blood, 74. Cement substance, 17. Cementum, 258. Center of ossification, 176. Center, trophic, 468. Central cells of gastric glands, 280. Central nervous system, bibliography of, 710. 722 INDEX Center median of Luys, 504. Centrifugal tracts, 522. Centripetal paths, 525; tracts, 522. Centro-acinar cells of pancreas, 316. Centrosome, 2; of spermatozoon, 371. Cerebello-olivary tract, 540. Cerebellum, 516; association paths of, 540; inferior peduncle of, 492; middle peduncle of, 495, 541; su- perior peduncle of, 499, 540. Cerebral root of fourth cranial nerve, 500. Cerebral vesicles, primary, 474; secondary, 474. Cerebrum, 509. Ceruminous glands, 608. Cervical glands of uterus, 420. Cervical region of spinal cord, lower half, 485; upper half, 486. Chief cells, of gastric glands, 280; of thyroid, 453. Chief nucleus, of eighth cranial nerve, 496, of vagus nerve, 492. Chlorid of gold stain, 665. Chordae tendinae, 100. Chorio-capillaris, 572. Chorion, 426; frondosum, 426; laeve, 426. Chorionic villi, 429. Choroid coat of eye, 571. Chromatic ring of spermatozoon, 372. Chromatin, 2. Chromofine, cells, 459; reaction, 459. Chromomeres, 5. Chromosomes, 5. Chyle, 140. Cilia, 23. Ciliary, arteries, 599; body, 572; body, pigment layer of, 575 ; epithelium, 575; motion, 9, 23; muscle, 572. Ciliated epithelium, 23. Circle of Zinn, 599. Circular sinus of placenta, 433. Circulus, major and minor, of iris, 577; venosus of Haller, 442. Circumgemmal nerve fibres, 127. Circumvallate papillae, 267. Clarification of sections, 669. Clarke, column of, 484, 534. Classification of dyes, 655. Claudius, cells of, 632. Claustrum, 506. Clean slides, how to, 639. Clitoris, 437. Clove oil for clearing sections, 669. Coats of alimentary tract, 271; of eye, 563. Coccygeal gland, 459; bibliography of, 709. Cochlea, 624. Cochlear, duct, 625; nerve, 547. Cohnheim, areas or fields of, 60; ter- minal arteries of, 562. Coil glands, 190. Collaterals of nerve fibres, 112, 468. Collecting tubules of kidneys, 348. Colliculi, inferior, 501. Colloid, 452; cells of thyroid, 453. Colostrum corpuscles, 441. Column, of Clarke, 484, 534; inter- medio lateral, of spinal cord, 487. Columnae carnae, 101. Columnar epithelium, 22. Columns of Bertini, 337. Comma tract of Schultze, 528, 536. Commissure, anterior, of brain, 506; grey, 479; posterior, of brain, 505; white, of spinal cord, 481. Compound, saccular glands, 194; tubular glands, 192; tubulo-alve- olar glands, 192. Concretions, prostatic, 391. Conduction paths of nervous system, 522. Cone, bipolars, 587; fibres of retina, 583; foot, 583. Cones of retina, 582. Congo red, 660. Coni vasculosi testis, 381. Conjunctiva, corneal, 565; divisions of, 601; fornix of, 604; palpebral, 603. Connective tissue, 32; adenoid, 45; adipose, 42; areolar, 37; bibli- ography of, 674; blood supply of, 47; cells, 34; cells, classification of, 36 ; cells, fixed or histogenic, 36 ; cells, wandering or hematogenic, 36; compact lymphoid, 46; devel- opment of, 32; diffuse lymphoid, 46 ; elastic, 40 ; elastic fibres of, 38 ; embryonic, 32, 36 ; fatty, 42 ; fibro- glia of, 206 ; gelatinous, 37 ; of kid- ney, 339; of liver, 323; lymphoid, 45; Mallory's stain for, 667; mu- coid, 37; nerve endings in, 127; nerve supply of, 47; reticular, 43; teased, 640; types of, 36; varieties of, 32, 36 ; white fibres of, 38 ; white fibrous, 40. Conus medullaris, 482. Convoluted tubular glands, 190. Convoluted tubules of kidney, prox- imal, 343; distal, 348. Cord, umbilical, 433. Cords, lymphatic, 150. INDEX 723 Corium, of gastric mucosa, 284; of mucous membranes, 184; of skin, 202. Cornea, 565; anterior epithelium of, 565; blood vessels of, 569; nerves of, 569; posterior epithelium of, 568. Corneal, corpuscles, 568; endothe- lium. 568; epithelium, 565; sub- stance, 567. Corona radiata, 401, 506. Corpora, albicantia, 395; cavernosa penis, 366; lutea, 394, 408; lutea spuria, 408; quadrigemina, in- ferior, 501, 548. Corpus, albicans, 408; Aurantii, 100; cavernosum urethrse, 366; ciliare, 572; hemorrhagicum, 405; luteum, 405; spongiosum urethrae, 366. Corpuscles, of bone, 169; corneal, 568; of Golgi-Mazzoni, 133; of Grandry, 132; of Hassal, 159; of Herbst, 132; lymphatic, 151; of Merkel, 132; red blood, 67; white blood, 74. Corrosive, acetic mixture for fixa- tion, 643; sublimate, see mercuric chlorid, 642. Cortex cerebelli, 517. Cortex cerebri, 509; eight-layer type, 514; five-layer type, 510; seven- layer type, 513; six-layer type, 513. Cortex, of kidney, 337; corticis of kidney, 338. Corti, arch of, 631; canal of, 631; membrane of, 628; organ of, 625, 629. Cotyledons of placenta, 432. Cover glass, applying of, 640. Cowper's glands, 392. Cranial nerve, eighth, 546; eleventh, 544; fifth, 549; first, 555; fourth, 551 ; ninth, 545; nucleus of twelfth, 492; second, 553; seventh, 548; sixth, 549; tenth, 544; third, 552; twelfth, 543. Cranial nerves, central paths of, 543 ; veins, structure of, 95. Crescents of Gianuzzi, 188, 308. Crista acustica, 624. Crusta, of Pons Varolii, 495. Crypts, of Lieberkiihn, 292; of lin- gual tonsil, 269; mucous, 292; of faucial tonsil, 156. Crystalline lens, 594; nucleus of, 596. Cumulus oophorus, 401. Cupola, of cochlea, 624; of crista acustica, 624. Cuboidal epithelium, 23. Curved tubules of kidney, 348. Cuticle of epithelium, 22. Cuticular membrane of Nasmyth, 258. Cutis vera, 202. Cytochrome nerve cells, 108. Cytoplasm, 1. Darkschewitsch's nucleus, 503. Daughter, skein, 15; spireme, 15. Decalcification, 647. Decidua, basalis, 424, 431 ; capsularis, 424; menstrualis, 423; reflexa, 424; serotina, 424, 431; subchorialis, 426; vera, 425. Decidual cells of uterus, 424. Decussation, of fourth cranial nerve, 499 ; motor, 490, 523 ; sensory, 490. Decussations in medulla oblongata, 487. Degeneration of nerve fibres, Wal- lerian, 469. Degeneration method, 477. Deiters', cells, 113, 465, 471; cells of Corti's organ, 632; nucleus, 498, 547. Dehydration of tissues, 649. Delafield's hematoxylin, 657. Delomorphous cells, 281. Demilunes of Heidenhain, 187, 308. Dendrite, 111, 468. Dendron, 112, 468. Dense white fibrous tissue, 40. Dental, groove, 259; ligament, circu- lar, 259 ; nerves, 255 ; papilla, 260, 264; pulp, 253; ridge, 259; sac, 264. Dentate nucleus of cerebellum, 499. Dentine, 256. Dentinal, sheaths, 257; tubules, 256. Derma, 202. Dermal root sheath of hair, 218. Descending root of fourth cranial nerve, 500; of trigeminus nerve, 550; of trochlear nerve, 551. Descending sulco-marginal fascicu- lus, 537. Deutoplasm, 396. Diaster, 15. Diencephalon, 474, 503. Digestive system, 251; bibliography of, 694. Dilator muscle of iris, 577. Diplosome, 15. Direct cerebellar tract, 535. Discus proligerus, 401. Dissociation of tissues, 640. 724 INDEX Division of cells, direct, 10; indirect, 11. Division wedges, 109. Dobie's line, 63. Dogiel, ganglion cell types of, 121, 122. Dorsal horns of spinal cord, 479. Dorsal nucleus of auditory nerve, 497. Dorsal region of spinal cord, see tho- racic region, 484. Dorso-medial sacral bundle, 537. Dorso-lateral cerebellar tract, 535. Dotterkern of ovum, 396. Double staining, 660. Doyere, hillock of, 135. Duct, cochlear, 625; excretory, 193; of gland, 186; intercalary, 193; in- terlobular, 193; intralobular, 193. Ductless glands, 195, 443; bibliogra- phy of, 707. Ducts, of Bellini, 337, 350; efferent, of testis, 381; ejaculatory, 388; of lachrymal gland, 606; of pancreas, 315; of salivary glands, 305; of tubulo-alveolar glands, 192. Ductules, efferent, of testis, 381. Ductus deferens, 384. Ductus endolymphaticus, 619. Dura mater, 557. Duval, areolar glands of, 440. Dyes, classification of, 655; Ehrlich's classification of, 76. E Ear, 607; bibliography of, 715; blood vessels of internal, 634; blood ves- sels of middle, 618; external, 607; internal, 618; ligaments of, 616; lymphatics of internal, 638; mid- dle, 609; muscles of, 615; nerves of internal, 634; ossicles of, 614. von Ebner, glands of, 269; spermato- blasts of, 375. Efferent ductules of testis, 381. Egg nests, 400. Ehrlich's, classification of granules, 76 ; triacid stain, 668. Eiballen, 400. Eighth cranial nerve, 546. Eisen, plasmocytes of, 81. Ejaculatory ducts, 388. Elastic, cartilage, 51; fibres, 38; fibres of cartilage, 51; tissue, 40; tissue, Weigert's stain for, 666. Eleidin, 28, 201. Eleventh cranial nerve, 544; nucleus of, 492. Elipsoids, splenic, 164. Embedding, box for, 651 ; in celloidin, 650; in parafin, 650; tissues, 049. Embryonic connective tissue, 32, 36. Enamel, 257; epithelium, inner, 261; epithelium, outer, 263; germ, 260, 261; organ, 261; prisms, 258; pulp, 264. Encephalon, 474. Enchondral ossification, 176. End, arborizations, 112; brush, 468; bulbs of Krause, 130; fibrils of nerves, 123 ; organs of nerves, 123 ; organs neuro-muscular, 135; or- gans of Rufrini, 129 ; plates, motor, 134. Endbrain, 474. Endocardium, 98. Endolymph of ear, 619. Endolymphatic duct of ear, 619. Endomysium, of cardiac muscle, 58, 97; of striated muscle, 63. Endoneurium, 114, 119. Endoplasm, 1. Endothelium, 16, 21 ; of blood capil- laries, 91; of iris, 576; of the vas- cular system, 84. Eosin, 659. Eosin and hematein stain, 660. Eosin and methyl blue, Mann's stain, 667. Eosinate of methylen blue stain, 664. Eosinophile granule cells, 35; leuco- cytes, 78. Ependyma, 475; cells, 464, 560. Epicardium, 98. Epidermal fat, 201. Epidermis, 197 ; keratization of, 28. Epididymis, 383. Epidural space, 557, 560. Epilemmal plexus, of salivary glands, 314; of kidney, 357. Epimysium of striated muscle, 63. Epineurium, 118. Epiphyseal line, 167. Epiphysis, ossification in, 180. Epithelia, the, 16; classification of, 19. Epithelial tissues, 16. Epithelium, bibliography of, 674; ciliary, 575; ciliated, 23; cuboidal, 23; cuticle of, 22; dissociation of, 641 ; examination of, 639 ; glandu- lar, 24; of iris, 577; lenticular, 594; nerve endings in, 123; neuro-, 25; pavement, 17, 21; pigment of retina, 580; pseudo-stratified col- umnar, 31; pyramidal, 24; rodded, 23; silvering, 665; simple col- umnar, 22; spheroidal, 20; squam- INDEX 725 ous, 21; stratified, 17, 26; transi- tional, 29. Epitrichium, 204. Epitympanic cavity, 610. Eponychium, 209. Epoophoron, 409. Erectile tissue of penis, 366. Ergastoplasm, 281. Erythroblasts, 70, 73; of Lowit, 173. Erythrocytes, 67. Esophagus, 273; bibliography of, (i!)o; superficial glands of, 275. Eustachian tube, 616. Excretory passages of kidney, 358. Exoplasm, 1. External, auditory canal, 607; ear, 607; elastic membrane of arteries, 86; genitals, 436; limiting mem- brane of retina, 585. Eye, 563; anterior chamber of, 577; appendages of, 601; bibliography of, 713; blood vessels of, 597; con- tents of, 593; development of, 579; external coat of, 565 ; internal coat of, 578; lymphatics of, 600; mid- dle coat of, 571; nerves of, 600; posterior chamber of, 578. Eyeball, 563. Eyelids, 601. Facial nerve, 548; nucleus of, 496; relation to tympanum, 611. Fallopian tube, see oviduct, 411. Fasciculi of striated muscle, 63. Fasciculus, dorso-medialis, 537; pos- terior longitudinal, 496. Fat, 42. Fat, absorption of, 298; of liver cells, 328. Fat cells, 35; isolated by teasing, 640; serous, 43. Female reproductive organs, 393; bibliography of, 704; urethra, 363. Fenestra ovalis, 611; rotunda, 611. Fenestrated membrane of arteries, 85. Ferrein, pyramids of, 337. Fibre, cells of Retzius, 620; layer of Henle, 586. Fibres, glia, 465; of Muller, 590; nerve, 467; of Sharpey, perforat- ing, 170. Fibrillae of striated muscle, struct uro of ultimate, 62. Fibrin of blood, 82; canalized, 428. Fibrocartilage, 52. Fibroglia, 206. Fields of Cohnheim, 60. Fifth cranial nerve, 549; nuclei of, 499. Filar mass, 3. Fillet, 487 ; lateral, 502, 533, 548 ; in- terolivary, 531; mesial, 490, 531. Filum terminale, 482. Finger nails, 208. First cranial nerve, 555. Fixation of tissues, 641 ; by injection, 647 ; by vapors, 646. Flagellum, 23. Flechsig, oval field of, 537. Flemming, germinal center of, 148. Flemming's solution, 644. Follicle, development of Graafian, 399; Graafian, 394; Follicles, lymphatic, 46, 146; Nabo- thian, 420; of small intestine, ag- minated, 289; of small intestine, solitary, 288; of thyroid gland, 451; of tonsil, 156. Fontana, spaces of, 570, 577. Foramen caecum lingui, 157, 269. Foramina nervosa of cochlea, 634. Forebrain, 474. Forel's field, 535. Formalin for fixation, 643; vapor of, 646. Formatio, reticularis alba, 491; reti- cularis grisea, 491. Fornix, of brain, 556; conjunctive, 604. Fourth cranial nerve, 551 ; cerebral or descending root of, 500; decus- sation of, 499. Fovea centralis, 579; structure of, 591. Fresh tissues, examination of, 639; staining of, 641. Frontal lobe of cerebrum, cortex of, 512. Fuchsin, 660. Fundus, of gland, 186; glands of stomach, 279. Fungiform papillae, 267. Funiculi of nerve fibres, 118, 469. G Gage, isolation of nerve cells, method of, 641. Gall bladder, 334. Ganglia, 119; of blood vessels, 102; cell types of spinal, 121; cHl types of sympathetic, 122; of heart, 101. Ganglion, cell, 104, 467 ; cell layer of retina, 588; geniculate, 546; habe- 726 INDEX nulae, 556; intercaroticum, 458; interpeduncular, 556; jugular, 545; nervi optici, 554, 578, 588; petrosal, 545; of retina, 554, 578, 586; of Scarpa, 546, 634; spiral, 547, 634; vestibular, 546. Gastro - pneumonic mucous mem- brane, 184. van Gehuchten's fluid, 645. Gelatin mass for injection, 648. Gelatinous, connective tissue, 37; substance of spinal cord, 480. Generative organs, female, 393; male, 366. Geniculate, bodies, 506; body, lateral, 555; ganglion, 546. Genital corpuscles, 130; of prostate, 391. Genitals, external, 436. Genito-urinary mucous membrane, 184. Germ cell, 1. Germinal, center of Flemming, 148; spot, 396; vesicle, 396. Giant cells in marrow, 172; in spleen, 162. Gianuzzi, crescents of, 188, 308. Glands, accessory lachrymal, 604; agminated, 289; anterior lingual, 269; of Bartholin, 437; of Bow- man, 228; branched saccular, 194; branched tubular, 191; of Brun- ner, 294; bulbo-urethral, 392; car- diac, of stomach, 284; carotid, 458; ceruminous, 608; coccygeal, 459; coil, 190; compound saccular, 194; compound tubular, 192; com- pound tubulo-alveolar, 192; con- voluted tubular, 190; Cowper's, 392; ductless, 195, 443; ductless, bibliography of, 707; of Duval, areolar, 440; of von Ebner, 269; of esophagus, cardiac, 276; of esophagus, superficial, 275; fun- dus, 279; of Harder, 606; histolo- gic types of secreting, 186; intes- tinal, 292 ; of Krause, 604 ; lachry- mal, 604; large vestibular, 437; lenticular, 284; of Lieberkiihn, 292; of Littre", 365; lymphatic, 148; mammary, 437; of Meibom, 603; mixed secreting, 187; of Moll, 602; of Montgomery, 440; of mouth, 252; of Nuhn, 269; olfac- tory, 228; parathyroid, 456; paro- tid, 311; peptic, 299; physiologic types of secreting, 186; pituitary, 460; posterior tarsal of Waldeyer, 604; prostate, 388; pyloric, 282; racemose, 192; salivary, 304; sali- vary, bibliography of, 698; sebace- ous, 220; secreting, 184; secreting, bibliography of, 690; simple saccu- lar, 193; simple tubular, 189; small vestibular, 437; of stomach, car- diac, 284; of stomach, fundus, 279; sublingual, 312 ; submaxillary, 312 ; sudoriparous, 205 ; suprarenal, 443 ; sweat, 205; tarsal, 603; thyroid, 451 ; of trachea, 235 ; tubulo-acinar, 192; of Tyson, 369; upper cardiac, 276; uterine, 419; of uterus, cervi- cal, 420. Glandules vestibulares, ma j ores, 437 ; minores, 437. Glandular epithelium, 24. Glassy membrane of hair, 219. Glia cells, 464, 465 ; of retina, 590. Glia fibres, 465. Glisson, capsule of, 322. Globe of eye, 563. Globus pallidus, 506. Glomerulus, of kidney, 341; olfac- tory, 556. Glomus, caroticum, 458; coccygeum, 459. Glossopharyngeal nerve, 545. Glossopharyngeus, nucleus of, 492. Glycogen in liver cells, 328; fixation of in tissues, 642. Goblet cells, 24. Gold chlorid stain, 665. Golgi, cell types, 113, 470; cells of, ' 113, 471; end organs of, 138; stain for nerve cells, 664. Golgi-Mazzoni corpuscles, 133. Goll, nucleus of, 489; tract of, 528. Gowers, tract of, 536. Graafian follicle, 394 ; layers of, 405 ; development of, 399. Graded alcohol, 642. Grandry, corpuscles of, 132. Granular layer of epidermis, 200; of Thomes, 257. Granulations arachnoidales, 559. Granule cells, 35. Granules, secretory, 5. Gravid uterus, 423. Grey, commissure, 479; matter of spinal cord, 480; reticular forma- tion, 491. Groove, neural, 473. Ground bundles of spinal cord, 538. Ground substance of areolar tissue, 38. Growth, 9. Gryochrome nerve cells, 107. Gustatory, cells, 125 ; organ, 124. Gyrus, hippocampal, 515; insulse, 506; uncinate, 556. INDEX 727 H Hair, 210; cells of Corti's organ, 629; cells of maculae of ear, 620; cortex of, 214; cuticle of, 214; dermal root sheath of, 218; development of, 210; epidermal root sheath of, 216; follicles, atypical, 219; inner root sheath of, 216; medulla of, 214; outer root sheath of, 217; pa- pilla of, 220; regeneration of, 220; root of, 214; shaft of, 214. Haller, circulus venosus of, 442. Hamulus of cochlea, 624. Hardening tissues, 649. Harder, gland of, 606. Hassal, corpuscles of, 159. Hasting's stain, 664. Haversian, lamellae, 169; systems, 168; systems, formation of, 179. Hayem, hematoblasts of, 80. Heart, 97; ganglia of, 101; muscle of, 56; nerve endings in muscle of, 139; valves of, 100. Heat for fixation, 646. Heidenhain, demilunes of, 187, 308; iron hematoxylin, 661. Helicine arteries, 367. Helicotrema, 626. Helwig's fasciculus, 537. Hematein, 656; Mann's, 657; stains, application of, 657. Hematein and eosin stain, 660. Hematoxylin, Bohmer's, 656; Dela- field's, 657 ; Heidenhain's iron, 661. Hematin, 83. Hematoblasts, 80. Hematoidin, 83. Hematopoiesis, 71. Hemin, 83. Hemoconia, 81. Hemoglobin of blood, 82. Hemolymph glands or nodes, 153. Hemolysis, 71. Henle, fibre layer of, 586; layer of, 216; loop of, 346; sheath of, 119; tubule of, 346. Hensen, cells of, 632. Hensen's line, 62. Hepatic, artery, 330; cells, 328; cir- culation, course of, 333; lobule, 324. Herbst, corpuscles of, 132. Hermann, basal cells of, 126. Hillock of DoySre, 135. Hindbrain, 474. Hippocampal gyrus, 515. Hippocampus, 556. Hone, use of, 653. Horizontal nerve cells of retina, 586. Horn of Ammon, 516. Horns of spinal cord, anterior or ventral, 479; posterior or dorsal. 479. Horny layer of epidermis, 198. Howslip, lacunae of, 179. Humor, aqueous, 593; vitreous, 596. Huxley, layer of, 216. Hyaline cartilage, 48. Hyaloid membrane, 596. Hyaloplasm, 3. Hymen, 437. Hypoglossal, nerve, 543; nucleus, 492. Hypolemmal plexus, 314; of kidney, 358. Hyponychium, 209. Hypophysis cerebri, 460. Hypothalamic nucleus, 506. Ileo-caecal valve, 302. Incisures of Schmidt, 116. Incremental lines of Schreger, 257. Incus, 614. Irido-corneal angle, 577. Iris, 575; dilator muscle of, 577; ex- ternal epithelium of, 576. Iron hematoxylin stain, 661. Island of Reil, 506. Islands of Langerhans, 318. Isotropic disks of striated muscle, 62. Inferior, central nucleus, 538; colli- culi, 501; corpora quadrigeniina, 501; olivary body, 490; peduncle of cerebellum, 492. Infundibula of lung, 241 ; of kidney, 336. Injection, apparatus for, 649; of tis- sues, 647. Insula of cerebrum, cortex of, 512. Interannular segments of nerve fibres, 116. Interbrain, 474. Intercalary tubule of kidney, 348. Intercellular bridges, 18; in epider- mis, 199; in Graafian follicle, 400. Intercellular secretory canaliculi, 189. Intergemmal nerve fibres, 127, 270. Interglobular spaces of tooth, 256. Interlobular, arteries of liver, 329; ducts of liver, 329; veins of liver, 329. Intermediate, nerve of Wrisberg, 546 ; tubule of kidney, 348; zone of spinal cord, 479. 728 INDEX Intermedio-lateral cell column, 487; fasciculus, 537. Internal, capsule, 506; ear, 618; elas- tic membrane of arteries., 85; lim- iting membrane of retina, 590; se- cretion. 195. Interolivary fillet, 531. Interstitial cells of testicle, 375. Interstitial tissue of kidney, 339. Intestinal, absorption, 298; glands, 292 ; villi, 290. Intestine, bibliography of, 696 ; blood vessels of, 296; large, 300; lym- phatics of, 297; nerves of, 297; small, 286. Intracellular canals, 189. Intrafusal muscle fibres, 136. Intragemmal nerve fibres, 127, 270. Intramembranous ossification, 181. Intravitam methylen blue stain, 663. Jelly of Wharton, 433. Juices, tissue, 141. Jugular ganglion, 545. Junctional tubules of kidney, 348. Karyochrome nerve cells, 109. Karyo kinesis, process of, 11. Karyolisis in erythroblasts, 73. Karyosomes, 2, 6. Keratin, 28, 201. Keratohyalin, 28, 200. Key-Retzius corpuscles, 132. Kidney, 336; blood vessels of, 352; capsule of, 339; connective tissue of, 339; cortex of, 337; excretory passages of, 358; interstitial tissue of, 339; lobule of, 338; lymphatics of, 357 ; medulla of, 337 ; nerves of, 357; pelvis of, 358; topography of, 336. Kleinenberg's fluid, 645. Knife, method for sharpening, 653. Kdlliker, spongioblasts of, 587. Korbzellen, 316; of lachrymal gland, 605; of mammary gland, 439. Krause, end bulbs of, 130; membrane of, 63. von Kupfer, stellate cells of, 323. Labia, majora, 437 ; minora, 436. Labyrinth, of ear, 618; of kidney, 337. Lachrymal gland, 604; accessory, 604. Lacteals, 290. Lactiferous sinus, 438. Lacunae of bone, 169; of cartilage cells, 50; of Howslip, 179. Lagena, 625. Lamella?, Haversian, 169. Lamellae of bone, cicumferential, 168, 170; circumferential, formation of, 179; concentric, 168; ground, 168; interstitial, 168, 170; interstitial, formation of, 179. Lamellar cells, 35; corpuscles, 131. Lamina, basalis of choroid, 572 ; basi- laris of cochlea, 624; capillaris of choroid, 572 ; chorio-capillaris, 572 ; fusca scleras, 569; reticularis of Corti's organ, 632 ; spiralis of coch- lea, 624; suprachoroidea, 571; vasculosa of choroid, 572. Langerhans, cells of, 428, 429; cen- tro-acinar cells of, 316; islands of, 318. Lantermann lines, Schmidt-, 116. Lanthanin, 6. Laqueus, 490. Large intestine, 300; blood vessels of, 301; nerves of, 301. Larynx, 231; cartilages of, 231; vo- cal cords of, 233. Lateral, border zone, 537; column of spinal cord, 481; fillet, 502, 533, 548; geniculate body, 506; ground bundle, 537, 538; horn of spinal cord, 486; nucleus of medulla ob- longata, 488; nucleus of third cranial nerve, 502. Lemniscus, mesial, 490. Lens, crystalline, 594. Lenticular glands, 284; nucleus, 506. Leucoblasts of Lowit, 174. Leucocytes, 74; basophile, 78; eo* sinophile, 78; large mononuclear, 77; polynuclear neutrophile, 78; small mononuclear, 77. Lid, third, 606. Lieberkiihn, crypts or glands of, 292, 301. Ligament, circular dental, 259; spi- ral, 627; suspensory, of lens, 597. Ligaments of ear, 616. Ligamentum dentatum, 558; pecti- natum, 570, 577. Limbus, lutea, 579, 591 ; spiralis, 628. Lines of Retzius, 258. Lingual, papillae, 266; septum, 265; tonsil, 157, 269. Linin, 2. Lip, 252. Liquor folliculi, 401. INDEX 729 Littre, glands of, 365. Liver, 321; bibliography of, 700; blood vessels of, 330; cells of, 328; connective tissue of, 323; forma- tion of red blood corpuscles in, 73 ; lobule of, 324; lymphatics of, 333; nerves of, 333. Lobule, of kidney, 338 ; of liver, 324 ; of lung, 244; of spleen, 165. Lobus insula^ 506. Locomotion, 9. Locus coeruleus, 499, 550. Loop of Henle, 346. Lowenthal's tract, 537. Lowit, erythroblasts of, 173; leuco- blasts of, 174. Lumbar region of spinal cord, 482. Lung, blood vessels of, 245; lobule of, 244; lymphatics of, 249; nerves of, 249. Lutein, 405; cells, 405. Lymph, 140. Lymphatic, capillaries, 141 ; capil- laries, origin of, 144; cords, 46, 150; corpuscles, 151; corpuscles of spleen, 161 ; corpuscles of thy- mus, 159; follicles, 46, 146; glands, 148; nodes, 148; nodules, 46, 146; sinus, 148; system, 140; system, bibliography of, 686; vessels, 141, 142. Lymphatics, 141 ; of bone marrow, 175; of eye, 600; of internal ear, 638; of intestine, 297; of kidney, 357; of liver, 333; of lung, 249; of mammary gland, 442; of mus- cle, 65; of olfactory organ, 231; of ovary, 411; of oviduct, 415; of pancreas, 320; of salivary glands, 314; of skin, 224; of spleen, 165; of stomach, 286; of suprarenal glands, 450; of thyroid gland, 454; of tongue, 270; of ureter, 360; of uterus, 421. Lymphocytes, 77. Lympho-glandula?, 148. Lymphoid tissue, 45; compact, 46; diffuse, 46. M Macula, of saccule and utricle, 620; lutea, 579; lutea, structure of, 591. Male, reproductive organs, 366; re- productive organs,, bibliography of, 702; urethra, 364. Malleus, 614. Mallory's connective tissue stain, 667 ; fixation for, 643. Malpighi, corpuscles of, in spleen, 163. Malpighian, bodies, 337; body, 341; corpuscles of spleen, 163; pyramid of kidney, 336. Mammary gland, 437; active, 438; blood vessels of, 442; lymphatics of, 442; nerves of, 442; resting, 440. Mammillary bodies, 556. Mann's, eosin and methyl blue stain, 667; hematein, 657. Marginal, veil of spinal cord, 482; fibre of spermatozoon, 372. Marrow, 167; bibliography of, 689; cavities, primordial, 177; cells, 171; formation of red blood cor- puscles in, 73; red, 171; structure of, 170. Marrowlymph glands, 154. Mast cells, 35; of blood, 78; of mar- row, 172. Mastoid cells, 611. Matrix of cartilage, 48. Mayer's, hematein, 656; albumin, 654; muchematein, 661; mucicar- min, 662; triacid stain, 668. Medial geniculate body, 506, 555. Median nucleus of third cranial nerve, 502. Mediastinum testis, 373. Medulla, of kidney, 337; oblongata, 487. Medullary cavity of bone, formation of, 179; rays of kidney, 337; seg- ments, 116; sheath of nerve fibres, 114, 115. Medullated nerve fibres, with a neu- rilemma, 114; without a neurilem- ma, 117. Megakaryocytes, 173; in spleen, 162. Megaloblasts, 173. Megalocytes, 68. Meibomian glands, 603. Meissner, touch corpuscles of, 127. Meissner's plexus, of esophagus, 272; of intestine, 297; of stomach, 286. Membrana, basilaris of Corti's organ, 628; granulosum of Graafian folli- cle, 401 ; limitans externa of reti- na, 585; limitans interna of retina, 598; nictitans, 606; propria, see basement membrane, 17, 185; tec- toria, 625, 628. Membrane, basal, of cochlea, 624; basement, 17, 185; of Bowman, 566; of Bruch, 572; of Corti, 628; of Descemet, 568; hyaloid, 596; mucous, 184; of Reissner, 625, 626; Schneiderian, 227 ; Schrapnell's, 730 INDEX 614; serous, 145; synovial, 146; tympanic, 612. Meninges, 557. Menstruating uterus, 422. Mercuric chlorid for fixation, 642. Merkel, corpuscles of, 132; tactile cells of, 124. Mesencephalon, 474, 475, 499. Mesial, fillet, 490, 531; lemniscus, 490; longitudinal fasciculus, 496. Mesovarium, 393. Metaphase of mitosis, 14. Metencephalon, 474, 475. Methods of staining, special, 661. Methyl blue, and eosin, Mann's stain, 667; and safranin, 660. Methyl green, 658. Methylen blue, 657; for nerve tis- sues, 663. Meynert, solitary cells of, 515. Microblasts, 173. Microcytes, 68. Microsomes, 2, 4. Microtomes, 652. Midbrain, 474. Middle, cerebellar peduncles, 541 ; ear, 609; peduncle of cerebellum, 495. Milk, 442. Mitome, 3. Mitosis, anaphase of, 15; diagrams of, 12, 13; metaphase of, 14; proc- ess of, 11; telophase of, 15; in white blood cells, 76. Mitral olfactory cells, 556. Modiolus of cochlea, 624. Molecular motion, 9. Moll, glands of, 602. von Monakow's bundle, 537. Monaster, 14. Mononuclear leucocytes, 77. Montgomery, glands of, 440. Mordants, 656. Morgagni, hydatid of, 384. Mossy cells, 465. Motion, amoeboid, 8; Brownian, 9, 156; ciliary, 9, 23; molecular, 9. Motor, area of cerebrum, 510; decus- sation, 490, 523; end plates, 134; nucleus of trigeminus, 499; oculi nerve, 552; oculi nerve, nuclei of, 502; paths of nervous system, 522. Mounting of sections, 668. Mouth, 251; bibliography of, 694. Muchematein, Mayer's, 661. Mucicarmin, Mayer's, 662. Mucinogen, 24. Mucoid connective tissue, 37. Mucosa, of alimentary tract, 272; of esophagus, 275; of large intestine, •301; of small intestine, 288; of stomach, 278; of tympanum, 61 1; of uterus, 417. Mucous, acini of salivary glands, 308; crypts, 292; membranes, 184; membranes, bibliography of, 690; secreting cells, 187. Mucus, 188; secreted by goblet cells, 24. Miiller, fibres of, 590. Miiller-formol, for fixation, 644. Miiller's solution, 643. Muscle, 53; bibliography of, 675; blood vessels of, 64; cell, of smooth muscle, 54; involuntary, 53; fibre, of smooth muscle, 54; fibres, dis- sociation of, 641; lymphatics of, 65; nerve endings in, 134; nervea of, 64; non-striated, 53; plain, 53; spindles, 135; striated, 59; vari- eties, characteristics of, 66; volun- tary, 59. Muscular tissue, 53 ; blood vessels of, 64; involuntary, 53; lymphatics of, 65; nerves of, 64; non-striated, 53; smooth, 53; smooth, distribu- tion of, 55; types of, 53; varieties, characteristics of, 66; voluntary, 59. Muscularis mucosae, 185; of ali- mentary tractj 272. Myelencephalon, 474, 475. Myelin, 115; sheath of nerve fibres, 114, 115. Myelinization, 476; method, 477. Myelocytes, 171. Myelon, 474. Myeloplaxes, 172. Myocardium, 97. N Nabothian follicles, 420. Nails, 208. Nail bed, 210; body, 208; develop- ment of, 210; groove, 209; growth of, 210; matrix, 210; root, 208. Nasal cavity, 226. Nasmyth, cuticular membrane of, 258. Naso-pharynx, 231. Nebenkern, 3. Nebenkern of ovum, 396; of pancre- atic cells, 317. Neck, of secreting glands, 191. Nerve, abducens, 549; auditory, 546, 634; cochlea, 547; eighth cranial, 546; eleventh cranial, 544; facial, 548; fifth cranial, 549; first cra- nial, 555; fourth cranial, 551; glos- INDEX 731 sopharyngeal, 545 ; hypogloss"al, 544; ninth cranial, 545.; optic, 553; oculomotor, 552; olfactory, 555; pneumogastric, 544; roots, 479; second cranial, 553; seventh cra- nial, 548; sixth cranial, 549; spinal accessory, 544; supply, see Nerves; tenth cranial, 544; third cranial, 552; trifacial, 549; tri- geminus, 549; trochlear, 551; twelfth cranial, 543; vagus, 544; vestibular, 546. Nerve cell layer of retina, 588. Nerve cells, 104, 467; apyknomor- phous, 109; arkyochrome, 106; arkyostichochrome, 107; axis cyl- inder, processes of, 112; canaliculi of, 111; collaterals of, 112; cyto- chrome, 108 ; dissociation of, 641 ; Golgi's types, 113; gryochrome, 107; karyochrome, 109; minute structure of, 109; neuraxis of, 112; Nissl's stain for, 663; protoplasmic processes of, 111; pyknomorphous, 109; somatochrome, 106; sticho- chrome, 106. Nerve end organs, 123. Nerve end plates, motor, 134. Nerve endings, bibliography of per- ipheral, 684; in cardiac muscle, 139; in connective tissue, 127; en- capsulated, 130; in epithelium, 123; in muscle and tendon, 134; in muscle spindles, types of, 138; in smooth muscle, 139; of Ruffini, 129. Nerve fibre, relation to the neurone, 103. Nerve fibre layer of retina, 589. Nerve fibres, 113, 467; varieties of, 114; Weigert-Pal stain for, 662. Nerve plexus, of Auerbach, 271; of Meissner, 272. Nerve terminations, peripheral, 123; peripheral, bibliography of, 684. Nerve tissues, 103; stains for, 662, 663, 664. Nerve trunks, 118. Nerves, 118; blood vessels of, 119; of blood vessels, 102; of bone marrow, 175; of connective tissue, 47 ; of cornea, 569 ; of eye, 600 ; of heart, 101; of internal ear, 634; of intestine, 297; of kidney, 357; of liver, 333 ; of lung, 249 ; of mam- mary gland, 442 ; of muscle, 64 ; of olfactory organ, 230; of ovary, 411; of oviduct, 415; of pancreas, 320; of pituitary gland, 461; of salivary glands, 314; of skin, 224; of spleen, 166; of stomach, 286; of suprarenal glands, 451; of taste buds, 270; of thyroid gland, 454; of tongue, 270; of tooth, 255; of ureter, 360; of uterus, 422; teased, 640. Nervi nervorum, 119. Nervous system, central, bibliogra- phy of, 710; conduction paths of, 522; blood vessels of central, 561; development of, 472; histological morphology of, 478 ; supporting tis- sues of, 463. Nervous tissues, 103; bibliography of, 681. Net cartilage, 51. Neural, canal, 473; groove, 473; ridge, 473. Neuraxis, see axis cylinder, 115, 468. Neuraxon, 112. Neurilemma of nerve fibres, 114, 117. Neurite, 112. Neuroblasts, 475. Neuro-epithelium, 25, 124; of ear, 620; of retina, 578. Neuroglia, 463. Neurokeratin, 115. Neuro-muscular spindles, 135. Neurone, 103, 467; an anatomical unit, 110; relations of, 469; ter- minations of, 470. Neuroplasm, 115. Neurospongium of retina, 588. Neurotendinous end organs, 138. Neutral, balsam, 669; dyes, 655. Neutrophile leucocytes, 78. Ninth cranial nerve, 545. Nissl's, classification of nerve cells, 106; stain for nerve cells, 663; sub- stance, 106. Nitrate of silver for staining, 665. Nodes, lymphatic, 148; of Ranvier, 115. Nodules, lymphatic, 146. Non-medullated nerve fibres, with a neurilemma, 117; without a neu- rilemma, 118. Normal saline solution, 639. Normoblasts, 173. Nose, mucosa of, 226; olfactory por- tion of, 228 ; respiratory portion of, 227 ; vestibule of, 226. Nuclear cap, 109, 396; skein, 13; spi- reme, 13. Nucleated red blood cells in marrow, 173; sheath of Schwann, 117. Nuclei, accessory olivary, 493; of cochlear nerve, 547; of eighth cra- nial nerve, 496, 497 ; of fifth cranial nerve, 499; of glossopharyngeal 732 INDEX nerve, 546 ; of inferior corpora quadrigemina, 501 ; of medulla ob- longata, 488; of tenth cranial nerve, 492; of third cranial nerve, 502; of vagus nerve, 545; of vesti- bular nerve, 547. Nucleolus, 2. Nucleus, 2; accessory, 396; ambigu- ous, 488, 492, 545 ; arcuate, 494 ; of von Bechterew, 498, 547; of Bur- dach, 489; caudate, 505; of crys- talline lens, 596; dentate, of cere- bellum, 499; of Deiters, 498, 547; of Darkschewitsch, 503, 540; of eleventh cranial nerve, 492; facial, 549; fastigius, 499; of Goll, 489; hypothalamic, 506; impar, 552; lenticular, 506; of nervous system, 468; of ninth cranial nerve, 492; of posterior longitudinal fasciculus, 503, 540; ruber, 502; of seventh cranial nerve, 496; of sixth cranial nerve, 496; of the solitary tract, 492, 545; of Stilling, 484, 534; structure of, 5; superior olivary, 496; trochlear, 551; of twelfth cra- nial nerve, 492 ; of Westphal-Edin- ger, 552; yolk, 396. Nuel's space, 631. Nuhn, glands of, 269. Occipital lobe of cerebrum, cortex of, 512. Ocular contents, 593. Oculomotor nerve, 552; nuclei of, 502. (Esophagus, see Esophagus, 273. Oils for clearing sections, 669. Olfactory, bulb, 556; cells, 228, 555; glands, 228; glomeruli, 556; nerve, 230, 555; organ, 228. Olivary body, inferior, 490; nucleus, superior, 496, 548. Olive, inferior, 490; superior, 496, 548 Oocytes, 397. Oogonia, 397. Optic cup, 579; nerve, 553, 592; pa- pilla, 592; thalamus, 504; tracts, 502. Optical axis, 564. Oral mucosa, 251. Orange G, 660. Ora serrata, 578, 593. Organ of Corti, 625, 629; of Rosen- miiller, 409. Origanum oil, for clearing sections, 669. Osmium tetroxid for fixation, 645; vapor of, 646. Ossicles, auditory, 614. Ossification, center of, 176; intracar- tilaginous, 176; intracartilaginous, resume of, 181; intramembranous, 181; periosteal, 179. Osteoblasts, 168; in intracartilagin- ous ossification, 177, 179; in intra- membranous ossification, 182; in marrow, 174. Osteoclasts, 173. Otoliths, 621, 624. Oval field of Flechsig, 537. Ovary, 393; blood vessels of, 410; cortex of, 394; lymphatics of, 411; medulla of, 393; nerves of, 411. Oviduct, 411; blood vessels of, 415; lymphatics of, 415; nerves of, 415. Ovula Nabothii, 420. Ovum, 396. Oxychromatin, 6. Oxyntic cells of gastric glands, 281. Pacinian corpuscles, 131. Pal, staining method of Weigert, 662. Pallium, 478, 509. Palpebral, conjunctiva, 602; fascia, 602; muscle, 604. Pampiniform plexus, 386; of ovary, 411. Pancreas, 314; bibliography of, 699; blood vessels of, 319; lymphatics of, 320; nerves of, 320. Paneth, cells of, 292, 293. Panniculus adiposus, 42. Papilla, optic, 592; of hair, 220; of tooth, 260, 264. Papillae, circumvallate, 267; fungi- form, 267; filiform, 267; lingual, 266; of skin, 203; of tongue, 266; of tongue, conical, 267. Papillary ducts of kidney, 350. Paradidymis, 386. Paraffin, embedding in, 650. Paraffin sections, fixation to slide, 654. Paraplasm, 2. Parathyroid glands, 456; bibliogra- fthy of, 708; blood vessels of, 458. Parietal, cells of gastric glands, 281 ; fobe of cerebrum, cortex of, 512. Parotid glandL3LL__ — Parovarium, 409. Pars, choroidalis iridis, 576; ciliaris retinae, 575; iridis retinae, 577; op- tica retinae, 578. INDEX 733 Patches of Peyer, 289. Paths, of cranial nerves, 543; of spi- nal cord, table of, 542. Pavement epithelium, 17, 21. Peduncle of cerebellum, inferior, 492 ; middle, 495, 541; superior, 499, 540. Pelvis, of kidney, 336, 358 ; ovalis of tympanum, 611. enicilli Penicilli of Ruysch, 164. Penis, 366. Peptic glands, 280; of stomach, 279. Periaxial lymphatic space of muscle spindles, 136. Pericardium, 97; visceral, see epicar- dium, 98. Perichondrium, 48, 51. Perigemmal nerve fibres, 270. Perikaryon, 104, 467. Perimysium of .striated muscle, 63. Peripheral nerve terminations, bibli- ography of, 684. Perilymph of ear, 619. Perineurium, 118. Periosteal ossification, 179. Periosteum, 168. Petit, canal of, 597. Petrosal ganglion, 545. Peyer's patches, 289. Pfluger's tubes, 400. Phagocytes in spleen, 162. Phalanges of Corti's organ, 632. Pharyngeal tonsil, 157. Pharynx, 273; bibliography of, 695. Phrenic veins, structure of, 95. Pia mater, 559. Picro-carmin, 658. Picro-fuchsin stain, 666. Pigment, cells, 35 ; of liver cells, 328 ; in nerve cells, 109. Pillar cells of Corti's organ, 631. Pituitary, body, 460; gland, bibliog- raphy of, 709. Placenta, 425; cotyledons of, 432; uterina, 424. Plaques, blood, .80. Plasma, of blood, 81 ; cells, 34. Plasmocytes, 81. Plasmocytoblasts, 81. Plasmosomes, 6. Platelets, blood, 80. Pleura, 243. Plexus, of Auerbach, 271; of Meiss- ner, 272; pampiniform, 386; pam- piniform, of ovary, 411; venosus ovarii, 411. Pneumogastric nerve, 544. Polar bodies, 399. Polykarocytes, 173. Polynuclear leucocytes, 78. Pons Varolii, 494. Portal, canals, 323, 328; vein, 330. Porus opticus, 592. Posterior, basal membrane of cornea, 568 ; chamber of eye, 570, 578 ; col- umn of spinal cord, 481; commis- sure of brain, 505; commissure of spinal cord, 479 ; epithelium of iris, 577; longitudinal fasciculus, 496, 538; longitudinal fasciculus, nu- cleus of, 503; perforated space, 503. Postero-external column of spinal cord, 481. Postero-internal column of spinal cord, 481. Potassium bichromate for fixation, 643. Precapillary arteries, 89; venules, 93. Pressure for injection, 649. Prickle cells, 27 ; of epidermis, 199. Primary bone^ 177. Primordial marrow cavities, 177. Prisms, enamel, 258. Processes, of nerve cells, axis cylin- der, 112; of nerve cells, protoplas- mic, 111; of Thomes, 261. Processus cochleariformis, 611, 615. Progressive staining, 655. Proliferation islands, 430. Projection centers, 509. Promontory of tympanum, 611. Prophase of mitosis, 11. Prosencephalon, 474. Prostate gland, 388; genital corpus- cles of, 391. Prostatic concretions, 391. Protoplasmic processes of nerve cells, 111. Protoplasm, 1, 3; bibliography of, 672. Prozymogen, 281 ; of salivary glands, 308. Pseudo- stratified columnar epitheli- um, 31. Pulmonary, alveoli, 242 ; artery, 245 ; lobules, 244; lymphatics, 249; nerves, 249; veins, 95, 247. Pulp, of dental enamel, 264; spaces of lymphatic nodes, 150. Pulvinar, 555. Purkinje, cells of, 517, 519. Purkinje's muscle fibres, 59. Putamen, 506. Pyknomorphous condition of nerve cells, 109. Pyknosis in erythroblasts, 73. Pyloric glands of stomach, 282. Pyramids of Ferrein, 337 ; of medul- 734 INDEX la oblongata, 487; of tympanum, 611. Pyramidal, cells of motor area, 511; epithelium, 24; tracts, paths of, 522. Racemose glands, 192. Ranvier, nodes of, 115; terminaisons hederiformes of, 127. Rectum, 301. Red, blood corpuscles, nucleated, in marrow, 173; blood corpuscles, nu- cleated, in spleen, 162; marrow, 171; nucleus, 502. Reduction in ovum, 397. Reniculus, 338. Reflex, path of spinal cord, 534; tracts of spinal cord, 528. Regions of spinal cord, 482. Regressive staining, 655. Reil, island of, 506. Reissner, membrane of, 625, 626. Remak's fibres, 117. Renal, circulation, course of, 356 ; lob- ule, 338; pelvis, 358; veins, struc- ture of. 95. Reproductive organs, female,. 393; fe- male, bibliography of, 704; male, 366; male, bibliography of, 702. Respiratory, bronchioles, 240 ; system, 226; system, bibliography of, 692. Restiform body, 491. Rests, thyroid, 455. Rete, Malpighii of epidermis, 198; mirabile, 341; mucosum of epider- mis, 198; ovarii, 410; testis, 373; testis, structure of, 380. Reticular, cartilage, 51 ; formation of spinal cord, 487 ; tissue, 43. Reticulum, 43; of lymphatic nodes, 151; of spleen, 161; of suprarenal glands, 445; of thyroid gland, 451. Retina, 578; bacillary layer of, 581; external limiting membrane of, 585; fibre layer of Henle of, 586; ganglion cell layer of, 588; inner ganglionic layer of, 588; inner granular layer of, 586 ; inner mole- cular layer of, 588; inner nuclear layer of, 586; inner plexiform layer of, 588; inner reticular layer of, 588; internal limiting mem- brane of, 590; large nerve cell layer of, 588 ; layers of, 580 ; nerve fibre layer of, 589; neurospongium of, 588; outer ganglionic layer of, 586; outer granular layer of, 585; outer molecular layer of, 586; outer nuclear layer of, 585; outer reticular layer of, 586; pigment epithelium of, 580; pigmentary layer of, 580; rod and cone layer of, 581; supporting tissues of, 590. Retzius, fibre cells of, 620; lines of, 258. Rhinencephalon, 474; cortex of, 515. Rhodopsin, 581. Rhombencephalon, 474. Ridge, neural, 473. Rod bipolars, 587. Rod and cone, layer of retina, 581 ; sockets, 591. Rod fibres of retina, 582. Rods of retina, 581. Rolando, substantia gelatinosa of, 551; gelatinous substance of, 480; tubercle of, 492. Rosenmuller, organ of, 409. Root, membrane of tooth. 259 ; sheath of hair, dermal, 218; sheath of hair, epidermal, 216. Roots, nerve, of spinal cord, 479. Rubro-spinal tract, 537. Ruffini, end organs of, 129. Ruysch, penicilli of, 164. S Saccule of ear, 618, 619. Saccus endolymphaticus, 638. Sacral region of spinal cord, 482. Safranin, 659. Saftkanalchen, 111. Saline solutions, action upon red blood corpuscles, 70; normal, 639. Salivary corpuscles, 156. Salivary glands, 304; bibliography of, 698; blood vessels of, 313, 314; nerves of, 314; types of, 304. Sarcolemma, 59. Sarcoplasm of cardiac muscle, 57. Sarcostyle, 62. Sarcous element, 62. Scala, media, 625 ; tympani, 625 ; ves- tibuli, 625. Scarpa, ganglion of, 546, 634. Schachowa, spiral tubule of, 344. Schlemm, canal of, 570. Schmidt, incisures of, 116. Schmidt-Lantermann lines, 116. Schneiderian membrane, 227. Schrapnell's membrane, 614. Schreger, incremental lines of, 257. Schwann, nucleated sheath of, 114, 117; white substance of, 114, 115. Schultze, comma tract of, 536. Sclera, 569; blood vessels of, 570. Sclero-corneal junction, 570. Sclerotic coat of eye, 569. INDEX 735 Sebaceous glands, 220; development of, 223. Second cranial nerve, 553. Secreting glands, 184; bibliography of, 690. Secretion, 9; internal, 195. Secretory, canaliculi, 18; canaliculi of gastric glands, 282; capillaries, 18, 189; granules, 5. Sectioning, 652. Sections, paraffin, fixation to slide, 654. Segments of spinal cord, 480. Sensory, decussation, 490; nucleus of trigeminus, 499; paths, 525. Semen, 370. Semicircular canals, 622. Seminal, granules, 371; vesicles, 386. Seminiferous tubules, 375. Septum, lingual, 265. Serous, acini of salivary glands, 307 ; fat cells, 43; glands of von Ebner, 269; membranes, 145; secreting cells, 188. Serpentine tubules of testis, 375. Sertoli's cells of testis, 379. Serum of blood, 81. Seventh cranial nerve, 548; nucleus of, 496. Sharpey, perforating fibres of, 170. Sheath of Henle, 119. Silver, nitrate of, for staining, 665. Simple, saccular glands, 193; tubular glands, 189. Single stains, with cytoplasmic dyes, 659; with nuclear dyes, 656. Sinus, circular, of placenta, 433 ; lac- tiferous, 438; lymphatic, 149. Sinusoidal vessels, 92. Sinusoids, 92; in marrow, 175. Sixth cranial nerve, 549; nucleus of, 496. Skein, nuclear, 13. Skin, 197; appendages of, 205; bib- liography of, 691 ; blood vessels of, 223 ; coil glands of, 205 ; cuticle of, 197; development of, 204; epider- mis of, 197; growth of, 204; layers of, 197; lymphatics of, 224; nerves of, 224. Slides, cleaning of, 639; fixing paraf- fin sections upon, 653. Small intestine, 286; blood vessels of, 296 ; lymphatics of, 297 ; nerves of, 297. Smegma, 369. Smooth muscle, 53; distribution of, 55; nerve endings in, 139. Sole, nuclei, 134; plate, 134. Solitary, cells of Meynert, 515; folli- cles, 288; tract, 492, 545. Somatochrome nerve cells, 106. Sommering, substantia nigra of, 502. Spaces of Fontana, 570, 577. Space, Nuel's, 631. Spatia zonularis, 597. Special staining methods, 661. Specific dyes, 655. Spermatic cord, 385. Spermatids, 378. Spermatoblasts of von Ebner, 375. Spermatocytes, 377. Spermatogenesis, 376. Spermatogonia, 376. Spermatosomes, 370. Spermatozoa, 370. Spermatozoid, 370. Spheroidal epithelium, 20. Spider cells, 465. Spinal accessory, nerve, 544; nucleus, 492. Spinal cord, 479; columns of, 481; regions of, 482; tracts of, table, 542. Spinal ganglia, 121; neurones of, 526. Spinal root, of ninth and tenth cran- ial nerves, 492; of trigeminus, 551; of vestibular nerve, 547. Spinal segments, 480. Spinal tract of vagus nerve, 545. Spindles, achromatic, 13. Spindles, neuro-muscular, 135. Spindle-cells, 34; of amphibian blood, 81. Spiral, ganglion, 547, 634; tubuli of kidney, 344; ligament, 627. Spireme, nuclear, 13. Spleen, 160; blood vessels of, 162; cells of, 161; elipsoids of, 164; for- mation of red blood corpuscles in, 73; nerves of, 166; lobule of, 165; lymphatics of, 165. Spleenolymph glands, 154. Spongioblasts, 475 ; of Kolliker, 587. Spongioplasm, 3. Squamous epithelium, 21. Staining, 653; in bulk, 654; of fresh tissues, 641 ; methods, special, 661 ; progressive, 655; regressive, 655. Stains, Ehrlich's classification of, 76. Stapedius muscle, 611, 615. Stapes, 614. Stellate, cells of von Kupfer, 323; veins of kidney, 355. Stichochrome nerve cells, 106. Stigma of Graafian follicle, 403. Stigmata, 91. 736 INDEX Stilling, canalis hyaloideus of, 599; nucleus of 484, 533. Stomach, 277; bibliography of, 695; blood vessels of, 285; cardiac § lands of, 284; fundus glands of, 79; lenticular glands of, 284; lymphatics of, 286; mucosa of, 278; nerves of, 286; pyloric glands of, 282. Stomata of serous membranes, 145. Straight tubules of kidney, 348. Stratified epithelium, 17, 26. Stratum, corneum of epidermis, 198; 201 ; cylindricum of epidermis, 198 ; disjunctum of epidermis, 201; ger- minativum of epidermis, 199; granulosum of epidermis, 200; in- termedium of epidermis, 205; lu- cidum of epidermis, 201. Striae acusticse,, 548. Stria vascularis, 628. Striated muscular tissue, 59. Stripes of Baillarger, 513. Stroma of red blood corpuscles, 69. Strop, use of, 653. Subarachnoid space, 558, 561. Subcutaneous tissue, 204. Subdural space, 558. Sublingual gland, 312. Sublobular veins of liver, 331. Submaxillary gland, 312. Substantia, ferruginea, 499, 550 ; gela- tinosa, 480; gelatinosa of Rolan- do, 551; lentis, 594; nigra of Som- mering, 502; propria of cornea, 567. Sudoriparous glands, 205. Subdural space, 560. Sulco-marginal fasciculus, 537. Sulcus, of lamina spiralis, 625; spir- alis, 625, 628. Superficial glands of esophagus, 275. Superior, central nucleus, 538; cere- bell ar peduncle, 540; olivary nu- cleus, 496, 548; peduncle of cere- bellum, 499. Suprachoroid layer, 571. Suprarenal glands, 443 ; bibliography of, 707 ; blood vessels of, 448 ; lym- phatics of, 450; nerves of, 451. Suprarenal veins, structure of, 95. Suspensory ligament of lens, 597. Sweat glands, 205. Sylvius, aqueduct of, 494, 499. Sympathetic, ganglia, 122; nerve fibres, 117. Syncytium, 7. Synovial, membranes, 146; villi, 146. Systems. Haversian, 168. Table, of characteristics of alimentary tract, 303; of renal circulation, 356 ; of tracts of spinal cord, 542. Tactile, cells, 124; cells, compound, 132; cells of Herbst's corpuscles, 132; corpuscles, 127; meniscus, 124; papillae of skin, 203. Tarsal glands, 603; of Waldeyer, posterior, 604. Tarsus, 603. Taste buds, 124; of circumvallate pa- pillae, 268; nerve fibres of, 270. Taste pore, 125. Teasing of tissues, 640. Technique, 639; bibliography of, 716. Teeth, 253; bibliography of, 694; de- velopment of, 259. Tegmentum of pons Varolii, 494. Telse choroidea% 560. Telencephalon, 474. Tellyesniczky's fluid, 644. Telophase of mitosis, 15. Temporal lobe of cerebrum, cortex of, 512. Tendon, nerve endings in, 134; spin- dles, 138. Tendons, structure of, 66. Tenon, capsule of, 563. Tensor tympani muscle, 611, 615. Tenth cranial nerve, 544; nucleus of, 492. Terminaisons hederiformes, 127. Terminal, arteries of Cohnheim, 562; bars, 18; bronchioles, 240. Testicle, 373; interstitial cells of, 375. Testis, 373. Text-books, bibliography, 671. Third cranial nerve, 552; nuclei of, 502. Third lid, 606. Thoma, ampullae of, 165. Thomes, granular layer of, 257; processes of, 261. Thoracic region of spinal cord, 484. Thrombocytes, 80. Thymus, 157 ; blood vessels of, 159. Thyreo-glossal duct, 269. Thyroid, aberrant, 454; accessory, 454; gland, 451; gland, bibliogra- phy of, 708; gland, blood vessels of, 454; gland, lymphatics of, 454; gland, nerves of, 454; rests, 455. Tigroid, 106. Tissue juices, 38, 141. Tissues, dissociation of, 640; epithe- lial, 16; examination of fresh, 639; primary, 7. INDEX 737 Tongue, 265; blood vessels of, 269; lymphatics of, 270; nerves of, 270. Tonsil, 155; lingual, 157, 269; phar- yngeal, 157; tubal, 617. Tooth, blood vessels of, 255; crown of, 253; fangs of, 253; neck of, 253; nerves of, 255; papilla of, 260; root membrane of, 259. Touch corpuscles, 127. Trachea, 234. Trachealis muscle, 235. Tract of Gowers, 536. Tracts of nervous system, 469; of spinal cord, table of, 542. Tractus solitarius, 492, 545, 546. Transitional epithelium, 29. Trapezoid body, 496, 548. Trifoil plates of Bethe, 124. Triacid stain, Ehrlich's, 668. Triangle median, 537. Triangular nucleus, of eighth cranial nerve, see chief nucleus, 496; of vagus, see chief nucleus, 492. Trifacial nerve, 549. Trigeminus, descending or mesen- cephalic root of, 550; nerve, 549; nuclei of, 499. Trochlear nerve, 551. Trophic center, 468. Trophoblast, 428. Tubal tonsil, 617. Tube, Eustachian, 616. Tubercle of Rolando, 492. Tuberculum acusticum, 497. Tubes, Pfluger's, 400. Tubule of Henle, 346. Tubules, uriniferous, 339. Tubuli recti of testicle, 373, 380. Tubulo-acinar glands, 192. Tubulo-alveolar glands, 192. Tubulus contortus of kidney, 343. Tunnel fibres of Corti's organ, 634. Tunica, adventitia of arteries, 86; al- buginea of ovary, 394; albuginea of penis, 366; albuginea of testi- cle, 373; choroidea, 571; intima of arteries, 85; media of arteries, 86; propria, 17, 184; propria of alimentary tract, 272 ; Ruyschiana, 572 ; vaginalis of testicle, 373 ; vas- culosa of testicle, 373. 'Tweenbrain, 474. Twelfth cranial nerve, 543. Tympanic membrane, 612. Tympanum, 609; mucosa of, 611. Types, of cartilage, 48 ; of nerve cells, Golgi's, 113; of salivary glands, 304; of secreting glands, 186. Tyson, glands of, 369. 48 U Ultimate fibrillae, of nerve fibres, 115; of striated muscle, 60; of stri- ated muscle, structure of, 62. Umbilical cord, 433. Umbo of tympanic membrane, 612. Uncinate gyrus, 556. Urinary system, 336. Upper cardiac glands, 276. Ureter, 358; blood vessels of, 360; epithelium of, 29; lymphatics of, 360; nerves of, 360. Urethra, female, 363; male, 364. Urinary, bladder, 361; organs, bib- liography of, 701. Urine, epithelial cells from, 29. Uriniferous tubules, 339; location of divisions of, 351; resume of, 352. Uro-genital canal, 366. Uterine glands, 419. Uterus, 415; blood vessels of, 421; gravid, 423; lymphatics of, 421; menstruating, 422; nerves of, 422; in pregnancy, 423. Utricle of ear, 618, 622. Utriculo-saccular canal, 619. Uvea, 571. Uveal tract, 571. Vacuoles, 2. Vagina, 434. Vagus nerve, 544. Vagus, nuclei of, 492. Valve, ileo-caecal, 302. Valves, of heart, 100 ; of veins, 96. Van Gehuchten's fluid, 645. Van Gieson's picro-fuchsin stain, 666. Varieties of muscle, table of charac- teristics, 66. Vas abberans, 384. Vas deferens, 384, Vasa vasorum, 94. Vascular, papillae of skin, 203; sys- tem, the, 84. Vaso-formative cells, 72. Vater's corpuscles, 131. Veins, 93; adrenal, 95; and arteries, comparison of, 95; atypical, 95; comparison of large and small, 95; cranial, 95 ; large, 94 ; phrenic, 95 ; pulmonary, 95; renal, 95; valves of, 96. Vena cava, 95. Venae, stellulae of kidney, 355; vor- ticosae, 599. Venous spaces, 95. Ventral, horns of spinal cord, 479; nucleus of auditory nerve, 497. 738 INDEX Ventro-lateral cerebellar tract, 536. Venules, 93; precapillary, 93. Verheyn, stellate veins of, 355. Vermiform appendix, 301. Vesicles, seminal, 386. Vesicular cell column of Clarke, 534. Vestibular nerve, 546. Vestibule of vagina, 436. Vibrissae, nasal, 226. Villi, arachnoidal, 558; chorionic, 429; of placenta, 426; of small in- testine, 288, 290; synovia!, 146. Visual, area of cerebrum, cortex of, 513; axis, 564; purple, 581. Vitaline membrane, 396. Vitellus, 396. Vitreous humor, 596. Vocal cords, 233. Voluntary muscle, 59. Volkmann's canals, 170. W Waldeyer, glands of, 604. Wallerian degeneration, 469. " Wander theory " of Bizzozero, 292. Wasser blau and safranin stain, 660. Water blast for injection,' pressure by, 649. Weigert's elastic tissue stain, 666. Weigert-Pal staining method, 662. Westphal-Edinger nucleus, 552. Wharton, jelly of, 433. White, blood corpuscles, 74; commis- sure of spinal cord, 481 ; fibres, 38 ; fibrocajtilage, 52; fibrous tissue, dense, 40; matter of spinal cord, 481; reticular formation, 491. Wrisberg, intermediate nerve of, 546. Xylol, for clearing sections, 669. Xylol-balsam for mounting, 669 ; neu- tral, 669. Yellow, elastic fibres, 38; spot, 591. Yolk nucleus, 396. Zenker's solution, 644; for fixation, choice of, 643. Zinn, circle of, 599 ; zonula of, 597. Zona, incerta, 506; pellucida, 396. Zonula of Zinn, 597. Zymogen of liver cells, 328; of pan- creas, 316. (1) THE END 0 University of Toronto library Acme Library Card Pocket U«der Pat. "Rei. Ind«* Flit" Made by LIBRARY BUREAU