-NRLF Sbt, v'C'.'Crv i£v~i >. Lj^i ^S2Suiwicvlr2: 0* LIB R ARY OF THE UNIVERSITY OF CALIFORNIA. GIFT OF BIOLOGY I K/V^> *GAW Received fiCT 29 1892 Accessions No.l{f{Qi^\ Shelf No. THE NEW SIDE N HAM SOCIETY. INSTITUTED MDCCCLVIII. VOLUME LVII. MANUAL OF HUMAN AND COMPARATIVE HISTOLOGY. EDITED BY S. STRJCKER. ASSISTED BY J. ARNOLD, BABUCHIN, O. BECKER, BIESIADECKI, F. BOLL, E. BRUCKE, CHROBAK, COHNHEIM, EBERTH, TH. W. ENGELMANN, GERLACH, GRUNWALD, IWANOFF, KESSEL, E. KLEIN, W. KUHNE, LANGER, V. LA VALETTE, LEBER, LUDWIG, SIGMUND MAYER, MEYNERT, W. MULLER, OBERSTEINER, PFLUGER, PREYER, V. RECKLINGHATJSEN, REITZ, A. ROLLETT, RUDINGER, MAX SCHULTZE, F. E. SCHULZE, SCHWALBE, SCHWEIGGER - SEIDEL, LUDWIG, STIEDA, C. TOLDT, E. VERSON, WALDEYER, AND OTHERS. VOLUME III. TRANSLATED BY HENRY POWER, M.B., LOND, F.R.C.S, SENIOR OPHTHALMIC SURGEON TO ST. BARTHOLOMEW'S HOSPITAL, EXAMIKER IN PHYSIOLOGY AND COMPARATIVE ANATQMY IN THE UNIVERSITY OF LONDON. THE NEW SYDENHAM SOCIETY, LONDON. 1873. Watson and Hazell, Printers, London and Aylesbury. OP THE uirn Y PREFACE, BY PROFESSOR STRICKER. THE Science of Histology rests on more numerous and more exact observations than any other department of knowledge. The microscope effects the enlargement of the image falling upon the retina, and by thus diminishing the extent of surface that can be examined at once, we gain proportionately in sharpness. Constant practice enables us to raise the acuteness of our perception of luminous rays to an extraordinary degree. We place ourselves in a convenient position ; we put away from us all extraneous disturbing impressions on our senses, and even concentrate the sensation of light upon one eye. Nay, more, we even endeavour to save this organ every secondary or subsidiary effort, neither permitting it to roll nor allowing any accommodation to be effected. We take, SQ to speak, the eyeball into our very hands, we accommodate it by a screw, and turn it about by means of a mechanical stage. Our region of observation, thanks to the improvements in the microscope, has not only waxed in breadth during the last ten years, it has also gained in depth and clearness through the distribution of the " lights " of careful obser- vation. In yet another direction, too, is our sphere bein^- enlarged. Histology is constantly and steadily advancing to the dignity of a comparative Science. Each worker conse- VI PREFACE. quentiy finds it more and more difficult to acquire such a grasp of the whole subject as is requisite to enable him to give a scientific description of it. It was with feelings of this kind that I undertook the Editorship of the present collection ; and the willing co-opera- tion I have obtained from the best workers of the day, on the one hand, and the liberality of the publishers on the other, have enabled me to bring it to a happy conclusion. A review of the whole work, however, compels me to admit that it does not present the same uniformity that it would otherwise have done had it been the outcome of a single master mind. Some pages glow with the results of the long-continued industry of the best investigators of our time, and sometimes again these nodal points, so to speak, appear joined together by the labour of younger hands. It lacks, however, that white- wash with which our master builders, following the usual custom, are wont to cover their constructions in order to hide from the eye of the observer all the piece-work of their men — the good bits equally with the bad. My collaborateurs will, however, suffer no detriment by aiding in the construction of this fabric, how rude soever it may be. The more experienced and advanced certainly not, for light is never darkened by a less light, whilst the younger . ones will assuredly not complain that their participation is manifest. It can only then remain a question whether the reader, and above all, whether Science, has gained anything by this pro- ceeding. The two questions are really reducible to one ; for the interests of the reader cannot be better promoted than by presenting to him whatever best responds to the demands of the advance of Science. It requires no further argument to prove that the true features are better seen in proportion as the use of paint is avoided. PBEFACE. Vll It cannot be denied that in the composition of Manuals on Histology the colour-top still plays a prominent role ; our knowledge of this subject is still of the nature of a mosaic, and in the exposition of the whole we eagerly cover the mosaic with our paint. This is no doubt perceptible, to some extent, even in this work ; but it is less apparent in proportion as the several chapters approximate the characters of mono- graphs ; it is moreover all the less injurious, inasmuch as the whole is not pervaded by any one style. On the contrary, the many and various modes of treatment observable in our work form not the least of its excellencies. It thereby comes nearer that goal towards which all handbooks should strive ; viz., to draw a picture of the condition of ^theories at a given period. Such a picture will the more closely approximate truth the more completely the predominance of each individual is suppressed. The variety of the mode of treatment nevertheless has an attendant evil. The various co-workers are opposed to one another in questions that are not altogether unessential. This evil will however only trouble those who place the con- venient arrangement of their knowledge higher than truth. The learned, and those who would become such, will, I feel sure, be satisfied that I have given space to conflicting views. " Durch den Widerspruch wird der Geist der Pr lifting genahrt." (Controversy is the mother of inquiry.) S. STRICKER. TABLE OF CONTENTS. CHAPTER XXXIII. THE ORGANS OF TASTE. BY TH. W. ENGELMANN, OF UTRECHT. PAGE A. ORGANS OF TASTE IN MAN AND MAMMALS .... 1 Seat of Gustatory Impressions . . . . 1 Gustatory Papillae ....... 3 Gustatory Lamina of Rabbit and Hare ... 5 Gustatory Bulbs 7 Termination of the Gustatory Nerves . . .12 B. ORGANS OF TASTE IN AMPHIBIA . . . . .14 Gustatory Papillae .... 14 Nerve Cushion ....... 15 Gustatory Disks . . . . . . .16 Goblet Cells ... .... 16 Columnar Cells . . . . . . .18 Forked Cells .18 c. ORGANS OF TASTE IN FISH . .... 20 Cupshaped Organs . . . . . . .21 Method of Research 22 Bibliography 24 X CONTENTS. CHAPTER XXXIV. THE ORGAN OF HEARING. I. THE EXTERNAL AND MIDDLE EAR, EXCLUDING THE EUSTACHIAN TUBE. BY J. KESSEL. PAGE A. THE EXTERNAL EAR 27 Auricle 27 External Auditory Meatus ..... 29 Ceruminous Glands ....... 29 Vessels and Nerves ....... 30 Membrana Tympani ...... 30 Internal Layer 31, 38 External Layer 33 Membrana Propria 34 Vessels ........ 42 Lymphatics ........ 44 Nerves . . . . . . . . .46 B. THE MIDDLE EAR ........ 51 The Tympanic Cavity . . . . . .51 Mucous Membrane . . . . . . .51 Peculiar Corpuscles . . . . . .53 Vessels and Lymphatics ...... 56 Nerves ......... 57 Ossicula ......... 61 Mastoid Cells .62 Bibliography ......... 63 II. THE EUSTACHIAN TUBE. BY PROFESSOR DR. RUDINGER, OF MUNICH. Osseous and Cartilaginous Portion of the Eustachian Tube . 67 The Muscular or Membranous Segment ..... 70 CONTENTS. XI PAGE The Mucous Membrane .... . .72 Nerves .......... 83 Vessels .......... 83 Bibliography ....... .84 III. THE MEMBRANOUS LABYRINTH. BY PROF. DR. RUDINGER. Topographical Description 85 Ligamenta Labyrinthi . . . . . , 88 Wall of the Labyrinth 94 Membranous Labyrinth of Birds . . . • . . .100 of Fish 102 ,, ,, of Batrachia ..... 106 Vessels 107 Nerves and Epithelium ........ 108 Aquaeductus Vestibuli 120 Canalis Reuniens ......... 121 Otoliths 121 Fenestra Ovalis and Articulation of the Stapes . . . .123 Bibliography 128 IV. THE AUDITORY NERVE AND COCHLEA. BY W. WALDEYER, Comparative Anatomy and Development .... 131 Osseous Capsule and Membrana Propria of the Ductus Cochlearis 140 Crista Spiralis ......... 145 Organ of Corti 151 Auditory Nerve, and its Relations to the Organ of Corti . .168 Cochlea of Birds and Amphibia . . . . . .180 Comparative Anatomy and Phsyiology 182 Comparison between the Organ of Corti and the Retina . .184 Xli CONTENTS. PAGE Historical Notices . . .186 Measurements ......... 193 Bibliography ......... 195 CHAPTER XXXV. THE OLFACTORY ORGAN. BY PROF. BABUCHIN. Characters of the Mucous Membrane in the Olfactory Region . 201 Bowman's Glands 203 Olfactory Cells 206 Olfactory Nerves .210 Bibliography .217 CHAPTER XXXVL THE EYE. I. THE RETINA. BY MAX SCHULTZE. General Structure of the Retina .... .218 The Nervous Constituents of the Retina ..... 221 Optic Nerve-fibre Layer ...... 223 Ganglion- cell Layer , . . . . . . 228 Internal Granulated Layer 232 Internal Granule Layer . . . . . .234 Intergranule Layer . . . . . . 236 External Granule Layer .... . 236 External Limiting Membrane ..... 237 Bacillar Layer ....... 243 Pigment Layer . . . . . . .269 The Connective-tissue Framework of the Retina . . . 272 Membrana Limitans Interna ... . 275 Externa . • . .277 Stratum Intergranulosum Fenestratum . . . 279 CONTENTS. Xlll PAGE Macula Lutea and Fovea Centralis . ... 280 Ora Serrata and Pars Ciliaris . . 288 Development of the Retina . . 293 II. THE TUNICA VASCULOSA. BY PROF. A. IWANOFF. The Choroid 299 Ciliary Processes ... . 300 Vitreous Membrane ...... 302 Vascular Layer 303 Ciliary Muscle .304 Ciliary Nerves .307 Stroma of the Choroid 308 Suprachoroid Membrane ...... 309 The Iris 310 Epithelium of 310 Uvea 310 Vessels of 311 Sphincter iridis ..... .311 Dilatator iridis 312 Nerves ......... 314 Stroma 315 HI. THE BLOODVESSELS OF THE EYE. BY TH. LEBER. Vascular System of the Retina ... .316 Choroid 320 Sclerotic 323 Margin of the Cornea . . . .331 Conjunctiva ..... 332 XIV CONTENTS. PAGE IV. LYMPHATICS OF THE EYE. BY G. SCHWALBE. Posterior Lymphatic System of the Eye . Lymphatics of the Retina .... Anterior Lymphatic System of the Eye . Lymphatics of the Conjunctiva Bibliography ...... 3,34 337 339 342 343 V. THE VITREOUS HUMOUR. BY PROF. A. IWANOFF. General Form and Position Canal of Petit . Historical and Controversial Points . Cells of the Vitreous Zonule of Zinn 345 345 347 352 353 General Characters Anterior Layer Posterior Layer Fibres of the Lens Capsule of the Lens VI. THE LENS. BY PROF. BABUCHIN. 357 358 360 366 370 VII. THE CORNEA. BY ALEXANDER ROLLETT. Layers of the Cornea Tissue of the Cornea Proper 372 375 CONTENTS. XV PAGE Migrating Cells of the Cornea 376 Fixed Corpuscles of the Cornea .... 380 Matrix of the Cornea 391 Anterior Lamina of the Cornea .... 398 Relation of Corneal Cells to Matrix .... 402 Vessels of the Cornea 417 Posterior Elastic Lamina ...... 418 Endothelium of the Cornea ..... 421 Development of the Cornea ....... 422 Epithelium of the Cornea ..... 424 Nerves of the Cornea ........ 428 Peripherie Region of the Cornea ...... 435 VIII. THE CONJUNCTIVA AND SCLEROTIC. BY STRICKER, STIEDA, AND KLEIN. Structure of Eyelids 439 Meibomian Glands ....... 445 Structure of Conjunctiva ....... 447 Palpebral Conjunctiva . . . . . .447 Lymph Follicles 449 Fornix of the Conjunctiva ..... 452 Conjunctiva of the Globe ...... 452 Nerves of the Conjunctiva 453 Structure of Sclerotic 459 IX. THE LACHRYMAL GLANDS. BY FRANZ BOLL. General Structure ; . . . . . . . .464 The Alveoli 464 The Interstices of the Alveoli 468 The Excretory Ducts 470 The Nerves 472 Bibliography 472 XVI CONTENTS. PAGE CHAPTER XXXVII. UTERUS, PLACENTA, AND FALLOPIAN TUBES. L UTEKUS. BY DK. R. CHROBAK. Attachments of Peritoneum 474 Layers of Muscular Tissue ....... 475 Mucous Membrane ........ 477 Glandulse Utriculares ........ 478 Distribution of Nerves ........ 490 Bloodvessels and Lymphatics . . . . . . .491 Methods of Research 492 II. PLACENTA, BY DR. REITZ. Maternal Villi , .494 Foetal Villi ... . .495 Matrix . 496 Membrana Intermedia 497 III, THE OVIDUCTS, OR FALLOPIAN TUBES. BY GRUNWALD AND STRICKER. Position and Course ... . . . 498 In Birds .... . .499 In Amphibia ........ 499 In Mammals and Man . . . . . .499 Structure 500 CONTENTS. xvii PAGE CHAPTER XXXVIII. DEVELOPMENT OF THE SIMPLE TISSUES. BY S. STRICKER. Structure of Ovum ........ 504 Disappearance of Original Nucleus ...... 504 Nuclear Cavity 505 Appearance of Second Nucleus 505 Amoeboid Movements of Germ 505 Process of Cleavage in Batrachian Ovum 506 Baer's " Cleavage Cavity " 507 Rusconi's Fissure . , , . . . . . . 5C9 Ecker's " Vitelline Plug" 509 Laminae of the Germ ........ 510 Process of Development in Ovum of Fowl . . . . 517 Method of Research by Imbedding 519 Process of Cleavage in Ovum of Bird ..... 520 Historical Facts in Embryology ...... 522 Account given by Wolff . .. . . . 522T ,, „ by Pander • 523 „ „ by v. Baer 523 ,, ,, by Reichert ..... 524 „ ,, byRemak. 524 „ by His 525 ,, „ by Hensen . . . . 525 „ „ by Dursy 525 byWaldeyer . . . . . 526 Formation of Laminae in Ovum of Bird . . . . ' . 526 of Fish 530 ,, ,, of Mammal .... 533 Morphological Value of the Germinal Laminae . . . .535 Development of the Simple Tissues 538 Development of the Blood 539 Structure of Transversely Striated Muscle .... 543 Size of Fibres 544 Sarcolemma ........ 544 Muscle Corpuscles ....... 544 Fibrillae 544 Bowman's Sarcous Elements 545 XV111 CONTENTS. PAGE Cohnheim's Areas ....... 546 Hensen's Median Disk ...... 547 Krause's Muscle-Compartments .... 547 Development of Striated Muscle ...... 552 Development of the Nervous System ... . 553 APPENDIX. I. THE STRUCTURE OF THE SYNOVIAL MEMBRANES. BY EDWAKD ALBERT. Bichat's division of Synovial Membranes . . .555 Endothelium . 556 Serous Canals ....... • 559 Synovial Sheaths of the Tendons . . 560 Mucous Sacs • 560 II. THE NON-PEDUNCULATED HYDATID. BY DE. ERNST FLEISCHL. Position Structure .562 OF THR uiriT 7 CHAPTER XXXIII. THE ORGANS OF TASTE. BY TH. W. ENGELMANN, OF UTRECHT. a. ORGANS OF TASTE OF MAN AND MAMMALS. FOR some time past physiologists have recognized the principal regions in Man in which the peripheric terminal apparatus of the gustatory nerves must be situated, and have concluded that they are represented by the superior surface of the root of the tongue (especially the papillse circumvallatse), the borders and apex of the tongue, and probably also the anterior portion of the soft palate. Observations and experiments have rendered it also probable that various kinds of terminal apparatus exist ; and that these are not equably distributed over the gustatory regions. In accordance with this, microscopic anatomy has recently made us acquainted with special organs in Mammals which must be regarded as the terminal apparatus of the gus- tatory nerves. Chr. Loven and G. Schwalbe, independently of each other, discovered in the laminated pavement epithelium which covers the papillae cir cum vail at 83 of the Mammalian tongue, numerous microscopic bud-like cell groups, which form the terminations of the branches of the nervus glossopharyn- geus, named by Loven gustatory bulbs (Geschmacks knospen and Geschmackszwiebeln), and by Schwalbe, gustatory cups (Schmeckbecher). These organs have already been demonstrated in Man, the Bog, VOL. III. B 2 THE GUSTATORY ORGANS, BY TH. W. ENGELMANN. Cat, Ox, Sheep, Roedeer, Horse, Pig, Hare, Rabbit, Guineapig, Rat, and Mouse. The gustatory bulbs (fig. 269) occupy cavities in the lingual mucous membrane, which they completely fill. As a general rule, the form of the spaces is that of a round- bellied flask (Bulb). The bottom of the flask rests upon the surface of the fibrous layer of the membrana mucosa ; the slender and for the most part short neck of the flask perforates the corneal lamina of the epithelium, and opens on the surface with a circular opening, which may be termed the gustatory pore. The length Fig. 269. Fig. 269. Gustatory bulbs from the lateral gustatory organ of the Rabbit. Magnified 450 diameters. of the bulb, which constantly exceeds its greatest breadth, amounts in Man to 0'077 — O'OSl of a millimeter ; the greatest breadth is about 0'039G of a millimeter ; the width of the gus- tatory pore is from 0'0027 to 0'0045 of a millimeter (Schwalbe). The gustatory bulbs present somewhat diverse forms in different animals. In some, as the Ox and Pig, they are slender and quite three times as long as broad ; whilst in others, as in the Rabbit and Roedeer, they are compressed and but little longer than broad. The most slender are usually the largest. Their size likewise varies, and is not constant in the same species or even in the same individual. In many instances larger and smaller bulbs are arranged in juxta- position, apparently without any regularity. Subjoined are a few measurements taken for the most part from Schwalbe : GUSTATORY ORGANS OF MAN AND MAMMALS. DOG. OX. PIG. RABBIT. Length of the bulbs in millimeters . Greatest breadth of the bulbs in millimeters Diameter of the gustatory pores in millimeters 0-072 0-0306 0-0045 0-172 j 0-055—0-130 0-043 0-020—0-052 0^002— 9-009 ! 0-0027 1 0-045—0-070 0-03—0-045 0-003—0-0045 The lateral portions of the papillae circumvallatae are pre- eminently the regions of the lingual mucous membrane where the gustatory bulbs are found. They here, numbering often many hundreds, form a broad girdle around each papilla. They are found also, though in general more sparsely distri- buted and isolated, upon the papillae fungiformes. In the Hare and Rabbit, each, side of the root of the tongue exhibits also a large oval elevation, divided into from ten to fourteen thin folds — the gustatory laminae— b}7 a corresponding number of parallel transverse grooves or fissures, which contain thousands of gustatory bulbs. Apart from the fungiform papillae which now and then bear gustatory papillae on their free surfaces, we find the organs in question always occupying protected portions of the lingual mucous membrane, such as furrows and the bottoms of fissures. Hence they are never seated upon the epithelium of the plateau, in the papillae circumvallataa, but upon the lateral portions of those papillae, and are therefore protected by the circular wall, and in like manner they never occupy the projecting portions of the laminae in these gustatory folds of the lateral gustatory organ of the Rabbit, but are always seated upon their sides. Structure of the gustatory papilla awl ifiixttitory folds. The papilla nmiuii-iillata. — The papillae circumvallatae (fig.. 270), into a descrip- tion of the manifold variations in form of which we shall not h sre enter, consist usually of a truncated conical body, composed of connective tissue which is invested by a laminated pavement epithe- lium. According to Loven, "The papilla itself i< beset upon its upper part with a great number of conical or more or less elongated, and sometimes forked, secondary papilla- ; whilst the border of the B 2 4 THE GUSTATORY ORGANS, BY TH. W. ENGELMANN. upper surface and the sides present low perpendicular folds, i.e., folds running parallel to the axis of the papilla, with intervening furrows." He also observes " that these furrows are completely filled with epithelium, so that the surface of the papilla is everywhere perfectly smooth, and exhibits no trace of the subjacent inequalities. The epithelial layer is considerably thicker upon the upper surface and that portion of the papilla which is not protected by the circular wall, than upon the protected lateral portions ; but even in the former situations it is far thinner than upon the remainder of the surface of the tongue. The epithelium is also very thin upon the external wall of the vallecula. The gustatory bulbs are situated in the thin epithelium at the sides of the papilla, and indeed there usually form a zone that extends from the bottom of the fossa upwards to about the level at which the papilla is no longer protected by the lateral wall (Schwalbe). The Fig. 270. Fig. 270. Transverse section through a papilla circumvallata of a Calf. Showing the arrangement and distribution of the gustatory bulbs. Magnified 25 diameters. zone, like the wall, entirely encircles the papilla. If the fossa be deep, as in the Sheep and Pig, the zone is broad ; if, as in the Horse, it be shallow, it is narrow. In Man, however, even when the fossa is deep, the upper half of the lateral wall of the papilla appears to be destitute of gustatory bulbs (Schwalbe). The number of the gustatory bulbs is very great, since as a rule they stand in close contiguity to one another, and most so in Man, where, according to Schwalbe, they are in absolute contact. Schwalbe estimated the number present in one papilla of the Sheep, of moderate size, at 480 ; in one from the Ox, at 1,760 ; in the Pig, which only possesses two circumvallate papilla?, each has about 4,760 bulbs. This would give a total number of bulbs in the Sheep, of 9,600 ; in the Ox, of 35,200 ; in the Pig, of 9,520. In Man and in the Dog, according to Schwalbe, and in the Rat and Rabbit, according to Loven, a few bulbs usually appear to be scattered on the outer wall of the vallecula, or that which looks towards the GUSTATORY ORGANS OF MAN AND MAMMALS. 5 papilla. The relations of the nerves found in the papillae to the gustatory apparatus will receive consideration hereafter. Papilla fungiformes. — The papillae fungiformes, between which and the papillae' circumvallatae are many transitional forms, present also essentially similar structural characters. They, however, do not possess the mantle of gustatory bulbs. On the other hand, Loven discovered gustatory cups in the Calf, distributed on their upper free surface, between the secondary papillae. In the Kabbit and in the Rat he found them upon every papilla fungiformis ; though there was only one in each of the small papillae. Schwalbe doubted at first their presence upon the fungiform papillae, but he subsequently found them (especially in the Pig). I have also seen them in vertical sections of the papillae in the Mouse and Cat. In Man, and in the Dog and Calf, they occur, according to Loven, much more rarely upon the fungiform papillae than in the animals just mentioned. The two lateral yustatory oryans of the Rabbit and Hare, to which allusion has just been made, appear, notwithstanding their size, to have escaped observation.* Yet they constitute gustatory organs Fig. 271. Fig. 271. Transverse section through a few of the gustatory lamellae of the lateral gustatory organ of the Rabbit. Magnified 25 dia- meters. of the first rank. Each consists of an oval slightly prominent elevation at the side of the root of the tongue, traversed by from ten to fourteen parallel grooves. In Rabbits, the length of the organ from before backwards is about 5 — 6, and in breadth from 2*5 — 3-5 * They are not mentioned in W. Krause's work on the anatomy of the Rabbit. They were discovered and described, independently of myself, by Hans von Wyss, " On a new Gustatory Organ in the Tongue of the Rabbit." Centralblatt fur die medizinische Wissenschaften, 1869, No. 35, p. 548, and in more detail in the Archiv fur Mikroskopische Anatomie, 1870. The account given by v. Wyss is in complete accordance with my own, which last, I may remark incidentally, had already been sent to press in the summer of 1869. 6 THE GUSTATORY ORGANS, BY TH. W. LNGELMANN. millimeters. In the Hare it is somewhat larger. Fig. 271 shows the appearances presented by a vertical section carried at right angles to the direction of the furrows through the middle of the organ. Here four gustatory lamellae are seen in complete section, and two in half- section. They are separated from one another by deep grooves, at the bottom of which an acinous gland here and there opens. These folds present a body composed of connective tissue, dividing into three secondary folds, of which the centre one is broader than the two lateral. The connective-tissue matrix is invested by laminated pavement epithelium, which completely occupies the groove Fig. 272. Fig. 272. Upper half of the epithelial framework of the gustatory bulbs. Four cavities, from which the bulbs have fallen out, are here seen from the side of the mucous membrane. In the centre of the bottom of each is the gustatory pore. The specimen was taken from the lateral gustatory organ of the Rabbit. Magnified 450 diameters. between the secondary folds, and is much thicker on their free surface than laterally, where they form the boundaries of the grooves. The gustatory bulbs are placed laterally along the whole length of each lamella. They there form a broad stria, which extends down- wards to about the middle cf the depth of each furrow, and upwards to near the opening of the furrow. The gustatory bulbs are so closely arranged (figs. 271 and 272) as to be in absolute contact. In the Rabbit they usually stand in four tiers or ranks, one above another. Each tier may contain in its whole length about eighty bulbs. Each gustatory fold may perhaps be approximately held to contain GUSTATORY ORGANS OF MAN AND MAMMALS. 7 620 bulbs, and the two gustatory organs together (estimating them to have twelve lamellee apiece) would thus have 14,880 gustatory bulbs. According to the statements of Schwalbe, two similar organs are present in the Pig. They contain, however, only isolated gustatory bulbs. As has been already stated, the gustatory bulbs (see fig. 269) occupy flask-like cavities of the epithelium, which they com- pletely fill. The walls of these cavities, with the exception of the floor, which rests on the connective tissue of the mucous membrane, are formed by the epithelial cells themselves. At the level of the belly of the flask the epithelium is composed of cells of many different shapes, which present the characteristics of the elements of the rete Malpighii in their finely granular protoplasm, relatively large nucleus, and indistinct cell wall. The Fig. 273. Fig. 273. A gustatory bulb exposed in consequence of the detach- ment of the upper half of the epithelial framework, seen from above. From the lateral gustatory organ of the Rabbit. Magnified 450 dia- meters. innermost of these cells, which are cemented to the wall of the flask-like space, have a concavo-convex shape, like fragment** of a watch-glass. When seen in transverse section, they are falciform (fig. 272). Around the neck of the flask and its opening, the gustatory pore, the epithelium presents the characters of the horny epithelial layer of the oral mucous membrane, the cells having a flattened form, a thick cell mem- brane, homogeneous contents, and flat nucleus. In those regions that are occupied by the gustatory bulbs, the horny lamina is, as a rule, only O'Ol — 0 02 of a millimeter in thickness, and its TTSIVEESITY 8 THE GUSTATORY ORGANS, BY TH. W. ENGELMANN. inferior surface is not very sharply defined from the stratum Malpighii. The margin of the gustatory pore is generally formed by the apposition of several cells, but sometimes by a single cell, which then appears as if it were perforated by a round hole. The border of the hole often presents an annular thickening (fig. 272). Figs. 269, 272, and 273 may serve to further elucidate this de- scription ; all three figures being taken from the gustatory lamellae of the Rabbit. Fig. 269 shows a section carried perpendicularly through the thickness of the gustatory epithelium. The gustatory bulbs are seen occupying the flask-shaped spaces. Fig. 272 exhibits the upper half of the epithelial framework which surrounds the space for the gustatory bulbs, as seen from below. This half of the Fig. 274. Fig. 274. Isolated gustatory bulb, from the lateral gustatory organ of the Rabbit. Magnified 600 diameters. epithelium has raised itself as a continuous lamina from the sub- jacent layer in the course of the preparation of the specimen. The gustatory bulbs remain with this last seated upon the mucous membrane. The figure gives the appearances presented to the observer as seen on looking into the open and empty spaces from below ; at the bottom of each may be seen the sharply defined gustator}'' pore, surrounded by a thickened ring. Fig. 273 completes fig. 272. It represents a gustatory bulb still attached to the mucous membrane, with the surrounding inferior half of the epithelial framework, as seen from above. The gustatory bulbs, or taste cups (Geschmacksknospen oder Schmeckbecher), (fig. 274,) which occupy the above- GUSTATORY ORGANS OF MAN AND MAMMALS. 9 described spaces, consist of a number — varying, according to the size of the bulbs, from fifteen to thirty — of long, thin cells, that are arranged like the leaves of a bud. They stand in several closely compressed rows around the axis of the bud. The outermost, which are applied to the wall of the space, and are curved concentrically to it (their concavities being directed inwards), enclose those situated more internally, which are less and less curved as they approach the axis. All gustatory bulbs, it would appear, are composed of at least two principal kinds of cells ; of these, one does not differ very essentially from ordinary epithelial cells, and is not in direct connection with nerves. The cells of the second kind are peculiar, highly differentiated structures, that in all probability are directly continuous with nerves, and are to be regarded as the proper gustatory cells. The former, which may be termed investing cells (Deckzellen), as Loven and Schwalbe suggest, are usually the most numerous, and form the external layers of the bulb ; the second appear to be chiefly situated near the axial region of the bulb. Fig. 275. Fig. 275. Isolated investing cells, from the gustatory bulbs of the Rabbit. Magnified 600 diameters. The investing cells (fig. 275) are long, rather slender, and in general somewhat fusiform structures with an ellipsoidal vesicular nucleus, which is situated either near the centre or towards one end. They consist of clear protoplasm quite free from granules. Towards the gustatory pore they gradually be- come attenuated to a fine point; inferiorly they either diminish but slightly, so that they still remain of considerable breadth where they come into contact with the connective-tissue surface 10 THE GUSTATORY ORGANS, BY TH. W. ENGELMANN. of the mucous membrane to which they are firmly adherent, or they gradually diminish in size, and suddenly break up into several processes that often undergo subdivision, but in many instances do not reach the surface of the membrane. In preparations obtained from the Sheep, and treated with perosmic acid, Schwalbe found a circlet of fine short hairs at the apex of the bulb, the points of which converged towards the interior of that structure, and he was then led to the conclusion that they sprang from the apices of the investing cells. These small hairs did not undergo solution in caustic potash lye, even after long maceration, but were no longer distinctly visible after isolation of the bulbs in solutions of chromic acid. Their presence could not be distinctly demonstrated either in other animals or in Man. Investing cells, whose inferior extremities were prolonged into slender processes, were easily obtained by Loven and Schwalbe from the gustatory bulbs of Man and of the Calf. The processes were never varicose, but often presented a capitate enlarge- ment at their extremity. Some of the investing cells depicted by Loven * call to mind the forked cells of the Frog, hereafter to be described ; and, like these, are possibly peculiar forms of true gustatory cells. The long axis of the investing cells is usually parallel to that of the bulb, and varies within the same limits as these — in Rabbits, for example, between ^-045 and 0-065 of a millimeter. The investing cells of the same bulb are not all of equal size ; but those of the outermost layer are usually the largest and widest, and at the same time the flattest. Those of the inner layer are shorter and more cylindrical. The gustatory cells (fig. 276, a and 6) are long and thin organs, that are always homogeneous and highly refractile. Each consists of an elliptical body prolonged at its upper pole into a moderately broad, arid at its inferior pole into a slender, process. The body is formed by a vesicular nucleus surrounded by a very thin layer of homogeneous substance or "protoplasm." The superior broader (peripheries) process is in the Rabbit quite cylindrical, somewhat attenuated towards the apex, in general about two and a half to three times longer, and at its middle about half as broad, as the nucleus of the cell. The apex is usually obliquely truncated and prolonged into a short hair or cilium (fig. 276, a). * Loc. cit., infra, fig. 6, e, g, and h, i, j. GUSTATORY ORGANS OF MAN AND MAMMALS. 11 The apices of these hairs appear scarcely to reach in the normal state to the level of the gustatory pore. The inferior (central) process is thin, cylindrical, and even at a small distance from the nucleus is about three times more slender than the above-described peripheric process. At a distance of O006 to 0'0012 of a millimeter from the nucleus it usually divides into two but slightly thinner branches which extend to the surface of the mucous membrane. Before this happens, however, it divides once or several times in quick succession. The chemical relations of the central process appear to be those of a nerve fibril. Fig. 276. Fig. 276. a, Isolated gustatory cells, from the lateral organ of the Rabbit, magnified 600 diameters ; b, an investing and two gustatory cells, isolated but still in connection with one another, from the same, magnified 600 diameters. Loven found that the gustatory cells of the Calf were somewhat differently constructed. In these the peripheric outrunner is cylindrical and rod-like, but supports no hair. The centric process is a long fine thread, frequently beset with various enlargements and short branches that are apparently abruptly broken off and are directed outwards. In the case of Man, Loven found that the peripheric processes are shorter and somewhat pointed at the extremity, though in other respects they resemble those of the Calf. Schwalbe distinguished two kinds of gustatory cells in Man and the Sheep — pin or pe."> Gustatory Nerve of the Frog.) Vorl. Mitth. Centralbl. f. d. med. Wiss., 1867, No. 50. TH. WILH. ENGELMANN, Ueber die Endigungen der Geschmacks- nerven in der Zunge des Frosches, Zeitschr. f. wiss. ZooL, Bd. xviii., p. 142, Taf. ix., 1867. Hollandisch erschienen als : — , Over de uiteinden der smaakzenuwen in te tong van den kikvorsch. (Appearing in Dutch as Researches on the terminations of the Nerves in the Tongue of the Frog.) Arch, voor Natuur- en Geneesk. iii., p. 387. Met plaat. — S. a. Onderzoekingen gadaan in het physiol. laborat. des Utrecht'sche hoogeschool. Tweede reeks, i., 1867-68, p. 193. G. SCHWALBE, Ueber das Epithel der Papillae vallatae. (On the Epithelium of the Papillae vallatae : provisional communi- cation.) Vorl. Mitth. Arch. f. Mikr. Anat. iii., 1867, p. 504. CHR. LOVEN, Beitrage zur Kenntniss vom Bau der Geschmackswarz- chen der Zunge. (Essays on the structure of the Gusta- tory Papillse of the .Tongue.) Arch. f. mikr. Anat. iv., 1868, p. 96., Taf. vii. Uebersetzung aus dem schwedischen Original, das mir nicht zuganglich. (Translation from the Swedish original, which I was unable to obtain.) G. SCHWALBE, Ueber die Geschmacksorgane der Saugethiere und des Menschen. (On the Gustatory Organs of Mammals and of Man.) Arch. f. mikr. Anat. iv., 1868, p. 154, Taf. xii. u. xiii. , Zur Kenntniss der Papillae fungiformes der Saugethiere. (On the Papilla fungiformes of Mammals.) Centralbl. f. d. med. Wiss., 1868, No. 28. L. LETZERICH, Ueber die Endapparate der Geschmacl^snerven. (On the terminal apparatus of the Gustatory Nerves : provisional communication.) Yorl. Mitth. Centralbl. f. d. med. Wiss., 1868, No. 32. , Virchow's Arch., Bd. xlv., p. 9, Taf. i. L. S. BEALE, New Observations on the Minute Anatomy of the Frog's Tongue. Quart. Journ. of Microsc. Science, 1869, p. 1, PI. i._iv. R. L. MADDOX, A Contribution to the Minute Anatomy of the Fungi- form Papillae and terminal arrangement of Nerve to striped Muscular Tissue in the Tongue of- the common Frog. Monthly Microsc. Journ., 1869, p. 1, PI. i. 26 THE GUSTATORY ORGANS, BY TH. W. ENGELMANN. H. VON WYSS, Ueber ein neues Geschmacksorgan auf der Zunge des Kaninchens. (On a new Gustatory Organ in the Tongue of the Rabbit.) ' Centralbl. f. d. med. Wis'sench., 1869, No. 35, p. 548. , Die becherformigen Organe der Zunge. (The cup- shaped Organs of the Tongue.) Arch. f. mikr. Anat., Bd. vi., 1870, p. 237, Taf. xv. F. E. SCHULZE, Die Geschmacksorgane der Froschlarven. (The Gusta- tory Organs of the Tadpole.) Ibidem, p. 407, Taf. xxii. CHAPTER XXXIV. THE ORGAN OF HEARING. I. THE EXTERNAL AND MIDDLE EAR, EXCLUDING THE EUSTACHIAN TUBE. BY J. KESSEL. IN the auditory organ of the more highly organised Vertebrata we may distinguish a sound-conducting and a .sound-perceiving apparatus. The conducting apparatus includes the external and middle ear, whilst the sensory apparatus is contained ID the vestibule, the semicircular canals, and the cochlea. a. THE EXTERNAL EAR. This is represented by the auricle or concha, the external auditory meatus and the membrana tympani. AURICLE. — The auricle, with the exception of the lobulus, is essentially formed of elastic cartilage, the complex moulding of which confers upon it its peculiar shape. The cartilage itself belongs to the group of reticular cartilages ; it is from one to two millimeters thick, and is invested by a perichondrium which contains a large number of elastic fibres. The fibres penetrate into the matrix of the cartilage, and form fine plexuses inter- weaving with one another, in the meshes of which small cartilage corpuscles are imbedded. (See Rollett, vol. i., p. 106, of this Manual.) In regard to the muscles that are in connection with the concha, only those need here be mentioned tha^t run between its several regions. These are small thin striated muscles that are inserted by means of short tendons into the perichondrium. The cutis of the concha, which is continuous with that of the 28 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. face and Lead, invests the cartilage, and at its inferior extremity forms a simple duplication known as the lobulus. Its whole surface is covered by lanuginous hairs, into the sacs of which sebaceous glands, having a diameter of from 0'5 to 2'0 millimeters, open. These last attain their greatest size in the interior of the concha, where, in comparison to the size of the hairs, they are very large and numerous, so that their openings are visible to the naked eye as minute fossae. This relation is altered in many individuals at the entrance of the external meatus, where the woolly hairs are remarkably developed, on which account they have been named " tragal " hairs. Small sweat glands, of 0*15 of a millimeter, are chiefly found upon that surface of the auricle that is turned towards the skull. The subcutaneous tissue of the external skin of the auricle does not everywhere present exactly the same features. It contains numerous elastic fibres which may be traced passing through the perichondrium as far as to the fibres of the reticu- lar cartilage. On the concave surface of the auricle this tissue forms a thin lamina firmly attached to the perichondrium, on which account the skin is not here moveable. On the concave surface the subcutaneous tissue is more abundant, and the skin can consequently be moved hither and thither to some extent, and in the lobule and lower parts it contains fat cells in its meshes in gradually increasing proportion, by which means the form and thickness of the lobule, whicji it is well known pos- sesses no supporting cartilage, is essentially determined. The auricle derives its blood from various sources. The capillary plexuses proceeding from the arterial trunks ramify around the hair follicles and glands of the cutis and in the cartilage. A few of the vessels, according to Pareidt (31), traverse the cartilage obliquely from the inner to the outer side, whilst others remain in the perichondrium. Some of the latter, according to Meyer (28), give off minute branches that pene- trate the cartilage, and ramify in its substance. Nerves are found most abundantly on the convex surface of the concha. They are less numerous on the concave surface and in the lobule. The larger trunks accompany the larger vessels, and penetrate the mesial surface of the cartilage in order to reach the skin of the lateral surface. THE EXTERNAL EAR. 29 EXTERNAL AUDITORY MEATUS. — The external auditory meatus presents a cartilaginous and a bony division, which together have an average length of twenty-four millimeters (Troeltsch, 45), of which eight millimeters belong to the first, and sixteen to the latter. The width of the meatus is subject to individual varia- tions. The cartilaginous portion extends from the auricular cartilage and the tragus, and forms a channel or groove open be- hind and above, which is completed into a tube by fibrous tissue. It is moveably connected with the osseous portion of the meatus by a slender band of connective tissue. The cartilage itself pre- senting the same characters as that of the auricle, has, with a view to its greater moveability, up wards and backwards, towards the anterior and inferior wall, two fissures, the spaces of which are occupied by connective tissue. The cutis of the external auditory meatus is a continuation of that of the auricle and of the tragus. It is not everywhere alike, but exhibits differences in different parts, both in regard to its thickness and its internal structure. In the cartilaginous portion of the meatus the cutis is one millimeter and a half thick, is covered with woolly hairs, with which sebaceous and ceruminous glands are connected, and contains but little fat in the subcutaneous connective tissue ; in the osseous portion the cutis rapidly alters, its thickness dimi- nishing to 0*1 of a millimeter, the woolly hairs becoming finer and fewer in number, and the ceruminous glands, except upon the posterior and superior wall, are continued (though not in all instances) as far as the transition into the tympanic membrane. Beneath the epidermis are low papillae arranged in longitudinal rows, and a corium containing much elastic tissue, the deeper layers of which represent the periosteum. The ceruminous glands agree both in the time and mode of their development, as well as in their external form and in their minute anatomy, with the sudoriparous glands. The same may be said of the contents of the ceruminous glands, so far as we may judge from a micro- scopical examination, except that the cerumen often contains confusedly aggregated pigment granules. (See this Manual, vol. ii., p. 597.) The ceruminous and sebaceous glands to- gether furnish a whitish yellow, more or less fluid, secretion, that essentially consists of various-sized fat molecules, and a conglomerate of colouring particles and cells, in which last a 30 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. few fat molecules and pigment granules are imbedded ; with these are mingled hairs and epidermis scales from the lining of the meatus, with particles of very various nature derived from without. When accumulated in considerable quantity, and allowed to remain for a long period in the meatus, the cerumen becomes altered in colour, and in consequence of the evapora- tion of its watery portion forms consistent masses, the so-called ceruminous plugs. The larger arterial vessels run to the upper and posterior wall of the auditory meatus, and from these a large branch is given off, which is distributed to the membrana tympani. The principal nerve trunks that were previously found in the cutis of the cartilaginous portion of the meatus break up in the osseus meatus into numerous branches, so that at the end of this passage the surface of expansion of the nerves, as compared with the outer parts, is considerably increased, which is in accordance with the great sensitiveness of these parts. The membrana tympani is expanded like a septum between the external auditory meatus and the tympanum. This membrane usually presents the form of an ellipse, the regula- rity of which is broken by the Kivinian hiatus or gap, which is situated anteriorly and to the upper part. The longer axis of this ellipsoid extends from behind and above, downwards and forwards, the shorter is directed from before and above, backwards and downwards. Cor- responding to this, the diameter of the membrana tympani should be measured in the direction of the axes of the ellipsoid, and not, as is usually done, in the vertical and horizontal diameter. Different values are obtained in the two cases ; in the former, when the longer axis of the ellipsoid is measured, it amounts to 9*5 — 10 millimeters, whilst the shorter is 8 millimeters ; in the other case, the horizontal diameter is from 8 — 8'5, and the vertical 8'5 — 9 millimeters. The planes of attachment of the tympanic membranes of opposite sides are inclined to one another ; their inclination is indicated by angles opening above and posteriorly, the former divergence amount- ing to 180 — 185°, the latter having not as yet been satisfactorily determined. The membrana tympani itself does not lie in the plane of its attachment, but presents a curved surface, so that it forms a kind of funnel, the apex of which is situated at the lower part of the handle THE EXTERNAL EAR. 31 of the malleus, and the ineridianal lines of which are arched in a convex manner towards the cavity. The examination of the intact membrane with low powers of the microscope will be found very serviceable in under- standing the topography of its several constituent elements. With this object in view, the membrane should be pre- pared with the bony margins and the ossicula in situ, de- tached from the temporal bone, and placed for a few hours in water, when the cuticle which obstructs the view can be in great measure removed. The preparation is then to be de- prived of water by immersion in absolute alcohol, rendered transparent by oil of turpentine, and allowed to dry. With the aid of low powers, three layers may now be distinguished, an external, a middle, and an internal, which are adherent by means of a thickened border, the tendinous ring, t6 a bony groove, which fails only at the Rivinian hiatus. The external layer, which is to be regarded as a continuation of the cutis of the auditory meatus, agrees essentially with this in its struc- ture. The middle layer, which is the thickest of the three, consists of sharply defined fibres of various breadth, the greater number of which run either in a radial or circular direction to the malleus ; only a small portion diverges between the two former in the most various directions. The radial layer lies externally beneath the cutis ; the circular internally beneath the mucous membrane. The internal, or muco-membranous layer of the membrana tympani, is an immediate prolongation of the mucous mem- brane of the tympanic cavity. It is very thin, and, on ac- count of its complex structure, can only be distinguished with high powers. Although it is easy to demonstrate the different arrangement of the elements composing the tympanic mem- brane, an exception occurs at one spot, the Rivinian hiatus, respecting which there is still much difference of opinion. The bony groove into which the membrana tympani is inserted does not return into itself. A notch occurs in the bone, in the form of a more or less flattened abscission of the circle, the chord of which, having a length of 2*5 to 3 millimeters, is represented by the connecting line of the two ends of the 32 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. groove — the Bivinian hiatus. This notch is filled up by the tissue of the cutis and the mucous membrane of the tympanic membrane. The tendinous ring of the membrana tympani curves away, with the greater part of its fibres, from its direction at the two angles of the notch, and turns to the deeper-lying apex of the processus brevis into which it is inserted, whilst the remainder of the tendinous fibres of the ring extend upwards, and are lost in the connective tissue of the periosteum. In this way an irregular triangular space is formed, which is bounded above by the Rivinian notch, and on the two sides by two ligaments, by means of which the malleus, or rather the apex of its pro- cessus brevis, is attached to the anterior and posterior angles of the groove of attachment. The anterior ligament is 1'5 of a mil- limeter, the posterior 2 millimeters in length. The three points of insertion of these ligaments do not lie in a vertical plane, but the inferior point, which is connected with both the others, pro- jects as far laterally beyond them as the short process of the malleus at this point pushes the membrana tympani towards the auditory meatus, so that a perpendicular struck from the Rivinian foramen downwards would cut off the malleus nearly at its neck. The distance from the highest point of the notch to the apex of the short process amounts to 2'5 — 3 millimeters. The tissue which fills the just-described foramen, and which has been named the membrana flaccida by Odo Schrapnell (40), is less tensely stretched than the rest of the membrana tym- pani, and sometimes even projects like a pocket towards the tympanic cavity (Henle, 12). It consists of two thin layers, one of which is the continuation of the cutis, and the other of the mucous membrane of the membrana tympani. The cutis consists of an epidermis, beneath which are sinuous fasciculi of connective tissue, which extend obliquely over the triangular space from the posterior segment of the auditory meatus, to become continuous with the circular fibres of the anterior and superior segment, together with vessels and nerves. The layer of mucous membrane extends as far as to the osseous margin of the Rivinian perforation, and passes from this point to the neck of the malleus opposite to it. The statement that the existence of a Rivinian foramen is quite THE EXTERNAL EAR. 33 normal, is positively denied by Hyrtl (16) and others, who regard it as a consequence of inflammation. I have satisfied myself, in company with Dr. Gruber, of its occurrence both in the dead body, and also directly during life. After this general account of the topographical relations of the membrana tympani, I proceed to the description of its finer microscopical characters. The cutis of the bony meatus is continued upon the mem- brana tympani at all points of its circumference. The small hairs and glands sparingly present in the cutis are entirely absent over the membrana tympani ; the papillse extend only to the tendinous ring, except in the posterior superior part, where they reach as far as to the processus brevis. The rete Malpighii in the remaining segments of the membrana tym- pani exhibits a plane and only here and there wavy course. In a fresh membrana tympani, treated with perosmic acid, the corneal layer, just as in the meatus externus, becomes stained of a black colour precisely as far as to the epidermic layer of cells (a proof of the fatty nature of their ceruminous con- tents— Williams). The corneal cells and variously thick cuticle, as well as the corium, gradually diminish in thickness from the periphery towards the handle of the malleus, but attain their greatest thickness over its external edge. This is caused by the circumstance that the vessels and nerves of the cutis and of the membrana propria, accompanied by strong bands of connective tissue, extend towards the handle of the malleus in an oblique direction from the posterior and superior wall of the auditory meatus, and having reached it, cover it. Part of the bands of connective tissue encircles the handle of the malleus, and joins on the anterior side with that which invests the ascending veins of the malleal plexus. Independently of the just-described general characters of the membrana tympani, the thickness of the epidermis is subject to mani- fold individual variations. It is a fact of general experience that the cells of the horny layer quickly become cloudy, and readily separate after death, so that in many instances we are not in a position to determine whether we have still all the layers before us, or whether VOL. III. D 34 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. some of the more superficial have not become detached. It is obvious also that we must bear in mind the frequent occurrence of patho- logical alterations, in order to avoid forming an erroneous estimate of the normal thickness. Independently, however, of these sources of error, I have satisfied myself by numerous measurements, that the thickness of the cuticle varies to a considerable extent in adults. How far the greater or less development of the cuticle of the membrana tympani affects the sensi- bility and the normal discharge of the physiological functions, cannot at present be stated with certainty. From analogy to the skin generally, we may however presume that the thinner the cuticle the greater the sensibility. The thickness of the cuticle of the membrana tympani in the new-born child favours the same view. The membrana propria is composed of sharply defined, strongly refractive fusiform fibres, flattened laterally, and having a diameter of 0'0036 — O0108 of a millimeter. Under certain circumstances these appear to be homogeneous, though they are in reality fibrillated, as may be clearly demonstrated by the addition of various reagents, as chromic acid, chloride of gold, perosmic acid, etc. The fibres most closely resemble tendinous fibres, and present the same chemical characters, swelling up in solutions of potash and acetic acid, and becoming isolated by the solution of their cement in baryta and lime water. If the membrana tympani be boiled in dilute solution of potash, it dissolves, only a small quantity of elastic tissue remaining behind, of which part evidently belongs to the vessels, whilst part appears in the form of a continuous and very thin sheet, which probably forms the basement membrane of the mucous layer on the inner surface of the membrana tympani (Helmholtz, 11). The foetal membrana tympani is particularly well adapted for the investigation of these fibrillated bands. We here find that the membrana propria is represented by distinct fasciculi of fibrils which pre- sent all stages of development. No distinct limits exist, in the earlier periods of development, between the connective tissue of the cutis and the fibres representing the subsequently developed membrana propria ; the difference is first distinctly expressed towards the close of foetal life. The latter therefore (membrana propria) may be regarded THE EXTERNAL EAR. 35 " as a deep layer of the curium favourably arranged and meta- morphosed for physiological purposes." We may also see, in sections of the membrana tympani of adults, how the highly refractile fasciculi radiate out, and are continuous with the thin layer of fibrillar tissue of the cutis, and with the matrix of the mucous membrane. In consequence of the intimate connection of the fibrils by their cement, and their arrangement into strong broad bands, the latter offer a strong resistance to ex- tension, and form, in the mode hereafter to be mentioned, an almost inextensible membrane, which as a mechanical arrange- ment for auditory purposes is, as Helmholtz (11) has shown, of the greatest importance. These fibres run in the several already mentioned layers, either parallel to one another, or decussating at very acute angles, and frequently communicate (Gerlach, 7), leaving everywhere lacunae and larger spaces between them. The lacunae are usually empty, and are then bright and clear, or are covered at their borders with finely granular material. Sometimes nerve cells, in addition to the nerve fibres hereafter to be described, may be seen within them, exactly filling their cavities. These cells, called by v. Troeltsch (44) "tympanic membrane corpuscles," appear, according to the plane in which they are seen, sometimes in the form of fusiform, sometimes of stellate, bodies ; in the former case being seen in profile, in the latter in face. The larger lacunae have nuclei attached to their walls, and are frequently filled with amoeboid cells. By means of injec- tions and the chloride of gold method, it may be demonstrated that such appearances are due to transversely and obliquely divided bloodvessels. Near the periphery of the membrane the three layers of the membrana propria interweave with one another, leaving variously sized spaces for the passage of vessels between them, and by their further connection with the tissues of the cutis, of the external auditory meatus, and of the mucous membrane lining the tympanic cavity, form a thick swelling, " the ten- dinous ring," which is attached to the annulus tyrnpanicus by means of a thin layer of periosteum. Between the highly refracting fasciculi of fibrils are found, besides the vessels, D 2 36 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. fusiform nucleated elements, and not unfrequently small carti- lage cells, either scattered or arranged in rows. From the above description it appears that all the layers of the mem'brana propria are intimately connected with the tendinous ring. I must therefore corroborate Gruber (8) in his recently made statement, that the circular fibres can be distinctly followed into the tendinous ring; but may add, that they run at some distance from each other, and are severally given off at very acute angles from the latter. The fibres, as they are given off collectively in the vicinity of the ring, form groups, the thickness of which is equal to that of the epidermis, cutis, and mucous membrane collectively ; by the tension of these fibres the radii of the surface of the tympanic membrane are rendered convex towards the auditory meatus. Towards the centre of the tympanic membrane the circular fibres diminish again in thickness, and are altogether absent at the lower third of the handle of the malleus and the adjoining parts. The circular fibrous layer is particularly well marked at the periphery of the anterior and superior segment, because the fibres here present, which proceed from the tendinous ring, become associated with those which come in an oblique direc- tion from the posterior and superior wall of the auditory meatus, and extend across the already described triangular space below the Bivinian fissure. Thus, with the exception of the above-mentioned neutral portion, the circular layer is everywhere present. The varying diameter of the circular layer, like the varying thickness of the cutis, which, as above stated, is most strongly expressed at the periphery and along the handle of the malleus, renders it impossible to give an average thickness to the membrana tyrnpani. It amounts, in the two last-named spots, to about 01 of a millimeter ; whilst in the intervening parts, where the cutis diminishes in thickness, and the circular fibres become thinner or are altogether absent, it is only half as much as this, or still less. Moreover, the membrana propria is attached to the handle of the malleus, but the views that are held upon the mode and nature of this attachment are widely divergent. According to v. Troeltsch (45), the handle of the malleus is introduced between the two fibrous layers (radial and circular THE EXTERNAL EAR. 37 layers), the former proceeding from it, the latter lying behind it, yet in such a manner that the uppermost part of the an- nulus of circular fibres runs outwards from the malleus, and passes along its outer side. Gruber (8) subjected the mode of attachment of the malleus to the membrana tympani to fresh examination, and described a till then unknown cartilaginous structure which commences above the short process, and ex- tends for half a millimeter below the handle. The cartilage is firmly attached to the lower two-thirds of the manubrium; but above, where the processus brevis is present, it is not attached } but forms a kind of joint, the cavity of which is filled with a synovian-like fluid. Still more recent examinations of this part made by Prussak (36), myself (17), and Moos (29), agree in showing that a third part of the processus brevis consists of cartilage, which, however, passes uninterruptedly into the osseous portion. According to Prussak and Moos, a thin layer of cartilage cells is also to be found beneath the entire peri- phery of the periosteum of the manubrium, not only in the new-born child, but in adults and old persons. I have very recently repeatedly studied this part in tympanic membranes that were still in connection with the malleus, and taken from persons of different ages. In embryoes, from the third to the ninth month, the ossicula are still in the condition of cartilage, and have the advantage of being fit for section without preparation, whilst those of newly born children and of adults require to be first subjected, to some decalcifying process. If sections be so made as to exhibit the membrar.a tympani and the malleus in their natural connec- tion, the malleus appears (with especial distinctness in em- bryoes) to be invested by a periosteum quite independently of the membrana propria, and to be only in connection with the latter by a duplicature of the mucous membrane, having a breadth of 0*2 to OS of a millimeter. At the point where the processus brevis is subsequently developed, a cluster of highly retractile nucleated cells occurs, lying above the periosteum, and in the substance of the duplicature. These elements, persisting throughout life as cartilage cells, form a mass inti- mately connected with the bony part of the processus brevis, which develops towards the end of foetal life with coincident 38 THE EXTERNAL AND MIDDLE EAll, BY J. KESSEL. ossification of the periosteum at the point of fusion. About this time also the connection of the malleus with the membrana tympani is very intimate, though only at two points ; namely, at the processus brevis, where the ligaments extending from the borders of the Rivinian gap are inserted into it, and at the lower third of the manubrium, where a portion of the radial fibres give additional strength to the periosteum, whilst the others decussate in front of the manubrium, in order to become continuous with the irregular layer found between the radial and circular fibres. The membrana propria is only connected with the periosteum of the upper part of the manubrium by means of loose connective tissue, so that a slight capability of move- ment exists at this part also, without any kind of articulation being present. The mucous membrane as it passes from the inner surface of the membrana tympani to the malleus is scarcely perceptible at its attachment to the former. The statement that the tympanic cavities are filled throughout the whole of intra-uterine life with young connective tissue requires corro- boration, as I have frequently found them filled with fluid in old embryoes and new-born children, their mucous membrane being at the same time coated with epithelium. The mucous membrane of the membrana tympani is composed of an epithelium resting on a fibrous matrix. The epithelium which has hitherto been described as consisting of a simple layer of pavement epithelium, by no means presents this cha- racter throughout, but has the same peculiarities of form as that described by Ludwig and Schweigger-Seidel (48) in the epithelium of the abdominal surface of the diaphragm in the Rabbit. After treatment with nitrate of silver, polygonal areas of various size, enclosed by dark sinuous lines, come into view on the surface of the mucous membrane, as is seen in fig. 280. Where these lines meet, more or less round or angular spots appear (d) which give the impression of openings, an impres- sion that is strengthened by the circumstance that they appear to be homogeneous after treatment with iodine-serum. The polygons may be distinguished as large (a), small (6), and smallest (c) ; the latter lying in particular along the manubrium and towards the periphery, and enclosing the most homogeneous THE EXTERNAL EAR. 39 spaces. The colouring of the cells under the influence of solu- tion of nitrate of silver varies, some scarcely appearing to be at all stained, whilst others are black and opaque, the latter chiefly occurring in the smaller polygons. The nuclei are here, as is common after treatment with nitrate of silver, invisible, though a few scattered ones are sometimes perceptible, usually occupying an excentric position. Fig. 280. d Fig. 280. Epithelium of the mucous membrane of the membrana tympani of Man. Silvered preparation. The fibrous framework or matrix of the mucous membrane is subjacent to the just-described epithelium, and on the other hand rests upon the membrana propria. The arrangement or disposition of the fasciculi in the membrana tympani of Man is subject to variation. Fig. 281 consequently only gives a repre- sentation of the form of the framework as it is most frequently met with in the posterior segment of the membrana tympani. Between the manubrium and the tendinous ring the membrane is composed of very fine fibres, forming more or less broad trabe- culse of similar structure that run in various directions. The membrane varies in thickness. It usually extends on the one side as far as to the manubrium, with the mucous membrane of which it is continuous, or it already terminates at some dis- tance from it, and is then continued by means of several trabecular processes over the radial fibres, which two last inter- weave together. I have usually observed a few trabecula? of the framework extend to the processus brevis. On the other side, towards the tendinous ring, trabeculre pass from the cen- 40 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. tral membranous expansion to the periphery, and streaming out over the circular fibres like a fan interweave with one an- other. Owing to the radiation of the adjoining trabeculse, the margin of the middle membranous expansion forms a series ol curves, the concavities of which are directed towards the peri- phery. Owing to their peripheric attachment, these arches leave hiatuses varying in their number, form, and position. The central membranous expansion may also exhibit similar gaps. The structure of the framework is further rendered Fig. 281. Fig. 281. Part of the posterior segment of the membrana tympani, seen with a low power, a, The membrane itself lying beneath the epithelium, with its processes stretching towards b, the tendinous ring ; the dark plexus represents bloodvessels. From a specimen stained with chloride of gold. complicated by the circumstance that the above-mentioned radiating trabeculse do not all lie in the same plane ; some, in- stead of going towards the tendinous ring, penetrate deeply between the radial and circular fibres into the above-described free spaces remaining between the circular fibres, and expanding here form a trabecular tissue, so as to leave a number of spaces THE EXTERNAL EAR. 41 or " lacunae" which intercommunicate with one another. These again, by means of spaces existing between the circular fibres, may stand in connection with the upper system of cavities. These spaces are all lined with an endothelium, the form and instability of which renders it most comparable with the epi- thelium lining the layer of Descemet on the posterior surface of the cornea. After treatment with solutions of silver and of gold, dark- coloured looped lines forming meshes are brought into view, similar to those characterising the interior of the lymphatics. The relations of the framework to the remaining parts of the membrana tympani, it is to be observed, are such that the anterior part normally presents a similar configuration to that just described, whilst it only appears as a foraminated membrane in the lower parts. Yet, even here, the already- described variations in the arrangement of the fibres may also occur. Gruber, in a monograph (8), attributes a dendritic structure to a fibrous framework, the position of which indeed corresponds with ours, but the minuter details of which he has not sufficiently described. In connection with the fibrous framework, and especially in children, at the marginal zone of the mucous membrane, villous processes, 0'220 of a millimeter in length, and O088 of a milli- meter broad, were first described by Gerlach. (These villi occur also in the purse of Troeltsch and at the malleus.) They are in- vested with pavement epithelium, and are composed internally of connective tissue in which are seen capillary loops. In regard to the nerves, the bloodvessels, and the lymphatics of the membrana tympani, the relations of the bloodvessels alone are known through the labours of Gerlach (7), v. Troeltsch (45), and Rudinger (38). In reference to the nerves, v. Troeltsch states that they are chiefly or almost entirely dis- tributed in the cutis, without, however, giving any further account of their mode of termination; he was never able to discover them in the mucous membrane ; but Gerlach (7) once or twice recognized in the latter region a few fine, non- medullated nerve fibres. The membrana propria, in accordance with the observations of all who have hitherto studied its anatomy, is destitute of 42 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. nerves and vessels ; a few capillary vessels only, according to Gerlach (7), forming anastomoses at the periphery between the mucous membrane and the cutis. As far as I am aware, no other description of the lymphatics exists besides that published by me in the Centralblatt fur die Medicinische Wissenschaften. The results of my observations show that nerves, bloodvessels, and lymphatics are discoverable in all the three principal layers forming the membrana tympani — the cutis, the mem- brana propria, and the mucous membrane. The bloodvessels of the cutis (and membrana propria) are chiefly supplied by an artery which runs from the posterior superior wall of the auditory meatus on to the membrana tympani, ascends at its posterior part along the manubrium, and gives off a successive series of small branches in a radial direction. The artery crosses the lower extremity of the manubrium, and then divides into two branches, of which one supplies the anterior inferior quadrant. The branches running in a centrifugal direction in the cutis, and here and there connected by transverse or oblique anastomoses, termi- nate in capillaries, which on the one hand unite to form the smaller veins accompanying the arteries, and on the other hand pass straight into two venous plexuses, of which one encircles the manubrium, and conveys its blood into the pos- terior superior veins of the cutis of the auditory meatus, whilst the other lies at the border of the membrana tympani, and likewise conveys its blood in an outward direction. In addition to this main artery, other smaller ones pass, at tolerably regular distances from the periphery, with the cutis, upon the membrana tympani, where they quickly break up into capillaries that join with those above described. The capillary plexus lying centrally in the membrana propria com- municates both with that of the mucous membrane, and with the more external one just mentioned ; it is distributed between the radial and circular fibrous layers, as well as in the lacunar system, being everywhere closely attached to the walls of the latter. At the middle and internal parts lying between the manubrium and the tendinous ring, where the radial fibres become more and more aggregated together in their course towards the manubrium, and the circular fibres are deficient, THE EXTERNAL EAR. 43 the capillaries pass more transversely or obliquely from the exterior between the radial fibres to the internal plexus of the mucous membrane, so that this spot appears to be the least vascular part of the membrana tympanum. Towards the periphery the radial fibres diverge from one another, leaving grooves or channels between them that are filled by capillaries which quickly increase in size ; the vessels themselves, there- fore, also run in a radial direction and at regular distances from each other. These vessels also pour their contents into the marginal plexus. If the cutis and the mucous membrane be detached from the membrana propria, the transversely and obliquely traversing vessels are torn through, and then the above-mentioned spaces with adherent nuclei come into view. The inner blood vascular plexus of the mucous membrane consists essentially of capillaries, and is chiefly distributed as a close plexus of vessels around the manubrium and about the tendinous ring. The plexus of the last-named part is to be regarded as a prolongation of the capillaries of the mucous membrane of the tympanic cavity. These run on to the membrana tympani, there form loops around or entirely encircle the foramina between the trabeculse, and then turn back to the vessels of the tympanic mucous membrane, or extend to the borders of the tunnel -like passages, or penetrate directly into the deeper layers in order to anastomose with the capillaries of the membrana propria. The plexus surrounding the manu- brium, and also connected with the median and the above- described plexus, obtains its blood from 'a few small arteries which run from above downwards in nearly the same direction as the arteries of the cutis. As we have just seen, the blood of the tympanic mucous membrane is carried off in two ways — by the veins of the tympanic cavity, and by those of the external auditory meatus. The chief proportion of the blood traversing the arteries of the membrana tympani and the capil- laries may therefore enter the larger veins by very different routes ; by a shorter path into the plexus of the malleus, and by a longer path over the membrana tympani into the marginal plexus. The path traversed by the blood during life will obviously depend upon the nature of the resistance with which it meets hi the different veins. It 44 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. may however be said with certainty that the arterial blood always returns by the shortest route through the plexus around the manu- brium, when no special obstacle is presented to its course, in the veins into which the vessels of this plexus discharge themselves (Prussak, 37). I have satisfied myself of the accuracy of this last statement, which was advanced by Prussak from the results of his carefully performed injection experiments. As I cannot here enter into any details re- specting the means and methods which have led me to this conclusion, I shall content myself with a statement of the method I have employed to demonstrate the circulation of the membrana tympani. I subjected frogs to the influence of woorara, and having divided the masseters, drew back the lower jaw as far as possible. The animal was then so placed between moist cushions upon a glass plate, that the external surface of the membrana tympani to be examined lay upon the plate, and was then pinned down to the stage of the microscope. Owing to the short and wide Eustachian tube of the Frog, the circulation of the various portions of the membrana tympani may then, by judicious turning of the head, be very well studied. In regard to the lymphatics it may be broadly stated that, like the bloodvessels, they are arranged in three layers. The first belongs to the cuticular investment ; the second to the membrana propria ; and the third to the mucous membrane. In the cutis they form an extremely fine plexus lying imme- diately beneath the rete Malpighii, the vessels of which accompany and frequently arch over the blood capillaries. They gradually pass into wider capillaries, which often cross the blood capillaries, and ultimately collect into separate larger trunks, which either run backwards and upwards, or extend like the bloodvessels at various parts towards the peri- phery and the auditory meatus. In the mucous membrane a sparingly distributed subepithelial plexus is found chiefly in the vicinity of the tendinous ring, which is distinguishable from the bloodvessels of equal width by its manifold, dilatations. The vessels penetrate into the lacunar system through the above-described spaces in the fibrous framework, and there form large spherical and saccular dilatations. (See fig. 282.) These last again are continuous with capillaries of small diameter presenting valve-like constrictions, which either com- municate with the above-mentioned deeper-lying funnel-shaped THE EXTERNAL EAR. 45 trunks, or pass straight through the membrana propria, so that by this means all the three layers of lymphatics belonging to the membrana tympani intercommunicate with each other and with those distributed in the cutis of the external auditory meatus. It is further to be remarked, that after brushing off the epithelium of the mucous membrane, and treatment with nitrate Fig. 282. Fig. 282. Lymphatics with their saccular dilatations lying imme- diately subjacent to the fibrous framework of the mucous membrane. From a specimen prepared with solution of nitrate of silver. of silver, a system of serous canals comes into view, both upon the immediately subjacent membranes and trabeculse, and upon the depressions and tunnel-like passages lying between them, as was first described by Recklinghausen in the diaphragm of the Rabbit. (See vol. i., p. 304.) This is distributed over the whole surface of the membrana tympani, but especially over those parts where the membrane is covered with small -celled 46 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. epithelium, and therefore along the manubrium and towards the tendinous ring. Here they frequently increase in size and number at the expense of the brown-coloured masses,, and form light spaces communicating with each other. I found in the clear spaces of the membrana tympani of the Dog and Cat, as in that of Man, strongly looped fine lines, thickened at certain points, which, becoming progressively finer by dichotomous division, run outwards in all directions, and consequently into the brown masses. (See fig. 283.) Similar markings, indicating the presence of serous canals, have been described by Koster,* and used by him as corroborating his view, that the serous canals are formed of epithelial cells. The light spaces are here and there seen bounding one or both sides of the vessels, and communicating with the attenuated extremities of adjoining serous canals. What relation exists be- tween the serous canal system and the epithelium of the mucous membrane, or rather between it and the above-described openings between the epithelial cells, I have not hitherto been able to dis- cover; and shall here only mention the interesting fact in a phy- siological point of view, that in the Dog I effected the most beautiful and complete injection of the lymphatics of the mem- brana tympani from the tympanic cavity, by the method first adopted by von Recklinghausen, and subsequently by Ludwig and Schweigger-Seidel, in the case of the diaphragm. It follows, therefore, from the above injection experiment showing the arrangement of the lymphatic system, that every alteration of tension of the membrana tympani must exert a suction action on the contents of the tympanic cavity, and eventually also aid the propulsion of the same within the lymphatics. The nerves of the membrana tympani are distributed like the vessels in the cutis, membrana propria, and mucous mem- brane. The larger trunks accompany the principal blood- vessels, divide like these, and frequently intercommunicate like the capillaries. They extend with the latter into the regions supplied by them, and consequently form close plexuses both * Ueber die feinere structur der menschliche Nabdschnur. " On the Minute Anatomy of the Umbilical Cord of Man." Inaugural Dissertation. Wiirzburg, 1868. THE EXTERNAL EAR. 47 beneath the cuticle of the derails and the epithelium of the mucous membrane. We may thus distinguish here a basal, a capillary, and a subepithelial plexus. A principal nerve trunk, which consists of medullated fibres provided with the sheath of Schwann, and lies between the cutis and the membrana propria, passes from the auditory meatus to the membrane at the upper part of the posterior segment close to and behind the artery, giving off branches Fig. 283. Fig. 283. Serous canals of the membrana tympani of the Dog. which accompany the vascular twigs. In correspondence with the forking of the artery over the manubrium of the malleus, the nerve divides into two branches, of which one supplies the anterior, and the other the posterior and lower part of the membrana tympani. Besides this main trunk, several smaller nerves accompany vessels passing to the membrane from various parts of the periphery. The coarse branches of all these nerves which lie between the cutis and membrana propria, I have named the "fundamental plexus of the membrana tympani." The branches given off from the trunks break up into numerous fibres, which, though non-medullated, are yet pro- vided with sheaths, and these form wide plexuses around the 48 THE EXTEENAL AND MIDDLE EAE, BY J. KESSEL. vessels, as well as in the interstices between the capillaries. If we inspect such a plexus more minutely, we see that the several fibres are closely adherent to the capillaries, but occasionally run at some distance from them, so that a small clear space becomes apparent between the margins of the nerve and vessel. In its further course the nerve may leave the vessel altogether and join with the plexus found beneath the rete Malpighii, or it may break up at once into very fine fibres which encircle the capillaries. Lipmann* and Tomsaf have given a similar account, but, like myself, have been unable to trace any connection between the nerve fibrils and the nuclei of the capillary wall. Fig. 284. Fig. 284. Nucleated nerve fibre which is attached to the capillary wall at d, by a pyriform enlargement. From a specimen taken from Man, and prepared with chloride of gold. A second kind of nerve fibres do not present the above detailed characters, but appear as simple axis-cylinders which are enlarged at many points of their course into nodal swell- * Inavg. Dissert. Berlin, 1869. t CentralUatt fur die medecin. Wissenschaften, No. 39. THE EXTERNAL EAR. 49 ings containing a distinct nucleus. From such an enlarge- ment two or more fibres may be given off, in the latter case giving it the appearance of a small ganglion cell. I have seen such fibres enter into close relation with the cells of the rete Malpighii, and also with the vessels lying close beneath the rete. In successful preparations we may see these nerves lying as above described, with their nucleated enlargements closely applied to the capillaries, and again becoming detached and running at some distance from them (fig. 284). Elsewhere they may be traced into fine fibres which in their further course sometimes exhibit pyriform enlargements. These last, after treatment with chloride of gold, assume a darker tint, whilst the neighbouring nuclei of the capillaries usually remain clear. In gold preparations it appears as if the pyriform enlargement were situated in the angle of a forked division of the nerve, so that one arm terminates by a capitate extremity in the dilatation, whilst the other forms a delicate thread on the side turned towards the capillary wall, and terminates on the vascular wall in a manner that is still un- known (fig. 284, d). Hitherto, therefore, no satisfactory evidence has been adduced to show that these dilatations constitute the ends of the vascular nerves, since they themselves give off fibrils which are lost on the vascular walls. The relations just given can indeed only be perfectly demonstrated in a few instances ; for the long course the nerve fibres pursue to the point where they expand into a brush of extremely fine fibres, permits satisfactory evidence of their continuity with the pyriform en- largement to be furnished only in very fortunate preparations. It has been remarked above, that only a part of the nerve fibres are distributed upon the bloodvessels, another part becoming connected with the plexus lying in the rete Mal- pighii. This last forms a plexus provided with bi- and multipolar cells, situated immediately beneath the deepest layer of the epidermis. From these plexuses extremely fine but distinctly recognisable fibrils are given off, which often run directly between the cells, so that a doubt may arise whether we are looking at a cell border or a fibre of this kind, but which may also be frequently traced without any confusion VOL. III. E 50 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. over the cell margins, as well as over the nuclei, to reach adjoining or more distant cell- layers. I am unable to make any positive statement as to their mode of termination. Before passing to the consideration of the middle layers of the membrana propria, it may here be mentioned that nume- rous nerve fibres proceeding from the basal plexus penetrate between the fibres of the membrana tympani, and either pursuing a tortuous course, or undergoing continual dichoto- mous division, apply themselves to the tendinous fibres, or traversing the spaces and lacunae between these, are distri- buted as nerves of the mucous membrane. In these territories of distribution nucleated nodal enlargements similar to those above described also occur. Thus we have found in the membrana propria certain fissures and vascular openings, with their just-mentioned contents, and in addition a large number of nucleated enlargements provided with two or more processes which are connected with the nerves there distributed, and are placed over and between the several layers of fibres. I once more adduce these facts, because up to the present time all cellular ele- ments found between the fibres of the membrana propria have been considered to be connective tissue, whilst in truth, as the above description shows, only a small number of them belong to that tissue, and the greater part must be regarded as belonging to the blood and lymphatic, or to the nervous system. Lastly, in regard to the nerves of the mucous membrane of the membrana tympani, I must first observe that they are by no means so sparingly distributed to it as has been hitherto maintained. Here also we find a vascular plexus and a sub- epithelial plexus. The former accompanying the lymphatics earlier than the bloodvessels, obtains its fibres partly from the plexus tympanicus, by means of twigs which pass to the mem- brana tympani at various points of the periphery together with the mucous membrane of the tympanic cavity, and partly from those nerves which lie in the cutis, by means of fibres that perforate the membrana propria. It distributes its branches on the one hand to the capillary bloodvessels and lymphatics, and on the other hand to the subepithelial plexus. THE MIDDLE EAR. 51 The latter forms a fine plexus immediately beneath the epithelium, supplying this last also with fibrils. 6. THE MIDDLE EAR. The term middle ear includes (1) the tympanic cavity, with the ossicula contained in it, and their muscles and ligaments ; (2) the cells of the mastoid process ; and (3) the Eustachian tube. THE TYMPANIC CAVITY. — The bony walls of this cavity, the structures found in it, as well as the inner surface of the mem- brana tympani, are covered by mucous membrane, which is continuous with that lining the Eustachian tube, and at the same time passes through the antrum mastoideum into the cells of the mastoid process. The mucous membrane of the tym- panic cavity of Man is, speaking generally, composed of an epithelium and a subjacent layer of connective tissue. The epithelium presents various forms. On the floor and lower portion of the anterior, internal, and posterior walls of the cavity it consists chiefly of ciliated columnar cells ; on the pro- montory, the roof, the membrana tympani, and the ossicula, it is tesselated (v. Troeltsch, 45). The transition of the former into the latter is gradual, the ciliated columnar cells becoming lower, and passing into tesselated ciliated epithelium, and finally into non-ciliated pavement cells. If the columnar epithelium be separated from the subjacent tissue, and an attempt be made to isolate the cells, cup-cells are found resembling those of the intestinal mucous membrane, together with columnar cells both with and without nuclei, of which the non-nucleated possess an extremely slender and often rod-shaped body, and a slender brush of cilia which are often adherent to each other. Both forms are continuous below with homogeneous strongly refrac- tile fibres. They are sometimes forked at their lower extremity, and are then in connection with two such fibres. In a speci- men prepared by teazing, I have succeeded in isolating a cell with two processes, of which one still remained in connection with a fibre three times the length of the cell, which could be traced beyond this for some distance into the connective tissue. B 2 52 THE EXTEKNAL AND MIDDLE EAR, BY J. KESSEL. On moving the covering glass, the cell with the fibre floated freely in the mounting fluid, so that it was impossible to enter- tain any doubt of their connection. Riidinger also described fibres in the mucous membrane of the tuba Eustachii, conti- nuous on the one hand with the epithelial cells, and on the other hand with the tissue of the submucosa. Besides these forms of columnar cells, there is another fusi- form variety characterised by the nucleated body of the cell becoming attenuated as it extends both upwards and down- wards. The upper process extends to the epithelial margin ; whilst the lower is columnar, with a bright highly refractile fibre, which is lost in the subjacent tissue, and not unfrequently presents a nodal enlargement near the cell from which it proceeds. In regard to the pavement epithelium, it may here be ob- served that wherever it occurs it presents the same peculiarities of form as that which has been already described as covering the mucous membrane of the membrana tympani. If the epithelium be detached, and the mucous membrane be treated by the silver method, serous canals come into view ; but if the epithelium be not removed, and a solution of chloride of gold or perosmic acid be poured over it, dark red or bla.k stellate intercommunicating lines appear (with especial distinctness in the Dog and Cat) immediately beneath the epithelium, which are here and there continuous with broad and similarly dark- coloured striae that are lost in the deeper layers of the tissue. The question whether these last are to be regarded as identical with those brought into view by nitrate of silver, and whether like them they may be in intimate relation with the lymphatics, must at present remain open, as I am unable to adduce any positive evidence in favour of either view. Two layers can be distinguished in the subjacent stratum of connective tissue, an upper lying immediately beneath the epithelium, and a lower, which represents the periosteum, and at the same time gives off fibres to the sheaths of the nerves running in the grooves of the bone, as well as in the tunica adventitia of the vessels of the bone. The upper layer forms a fibrous framework, which is to be regarded as the prolonga- tion of that I have more minutely described in the membrana THE MIDDLE EAR. 53 tympani, and which here presents the same relations to the periosteum as it there does to the membrana propria. Here also it consists of extremely minute fibrils, which collectively form a framework of trabecuke and a foraininated membrane, which, like the periosteum, includes large spaces filled with nerves, bloodvessels, and lymphatics. At various points of the cavity this fibrous framework becomes detached from the periosteum, in order to stretch across the cavity from one bony prominence to another. These bridges serve at the same time as supports for numerous capillaries running from point to point, and are everywhere covered by an epithelium which is ' continuous, where they are attached, with that of the mucous membrane. Thereto belong the ligamentum mallei superius, the ligamentum mallei externum et posterius, and the posterior pocket of the membrana tympani. The liga- mentum mallei anterius is composed of thick bundles of fibrils resembling those of tendinous' tissue, and forms with the ligamentum mallei posterius the so-called axial cord, which at the same time constitutes the axis of revolution of the malleus (Helmholtz, 11). Moreover certain trabeculae which are stretched between the numerous bony processes on the floor of the tympanic cavity belong to the same category. A trabecular framework which I have very frequently found in the vicinity of the stapes is deserving of special mention. This passes from the eminentia pyramidalis, which is a bony projection, to the semi-canal of the tensor tympani — projecting sometimes strongly into the free space of the tympanic cavity — and forms a more or less deep groove or nick with the posterior superior margin of that canal. Proceeding from the free border of this band I frequently saw several trabeculae, often communicating with each other, span the groove, and pass to be inserted either at the base or into the posterior crus of the stapes. Peculiar bodies, differing considerably from each other in external form and size, but upon the whole exhibiting the same structure, present themselves in this framework, as well as on the floor of the tympanum and in the ligamentum mallei superius, which extends from the tegmen tympani to the caput of the malleus. In the more simple forms of these 54 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. bodies we may recognize on the one Land a central axial band, and on the other a series of capsules arranged concentrically round it. The axial band appears in the form of a smooth round cord, which, after running; free for a variable distance, enters at one pole of the lemon-shaped body, and emerges again at the opposite, to expand immediately in a fan-like manner in the above-described foraminated membrane of the mucous membrane. Without the addition of coloured substances, this shows an extremely fine fibrillar structure, with a cloudy finely granular material between the fibrils ; but if it be treated with solutions of silver or gold, it becomes more deeply tinted than the tissues of the capsules. The capsules arranged concentri- cally around the axial band have likewise a fibrillar structure. Between the several capsular layers are spaces which either appear homogeneous or are filled with fusiform elements. The margins of the spaces are frequently covered with a finely granular cloudy material. The outermost of the capsules often presents a regularly wavy course, and possesses a delicate pave- ment epithelium on its external surface. At one pole of the body this capsule forms a circular highly refractile ring, which leads into a funnel-shaped depression occupied by the axial band at its point of entry ; at the other pole the capsule is continued upon the axial band as it emerges. The description just given corresponds to the simpler types of the bodies, which, apart from the structure of the axial band, present the appearance of a Vater's corpuscle. But other forms are also met with ; a structure of similar character may be so constructed as to present a figure of 8, whilst it may either be .straight or bent at an angle. In both cases it gives the impression of two of the above-described bodies being so connected together that the two capsules are continuous with one another at the point of union. In other instances, again, we may see the axial band divide into several branches after its emergence, which may again bear other smaller corpuscles of the same kind. Fig. 285 is an illustration of a body of this kind, which I found stretched between the base of the stapes and the band proceeding from the eminentia pyramidalis. These organs, as we shall hereafter see, occur also in the mucous membrane lining the mastoid cells, but never attain so remarkable a size THE MIDDLE EAR. 55 in that position as in the tympanic cavity. The corpuscles may be either roundish, or elongated, or fusiform, and are found of all sizes, from microscopic minuteness, O08 to as much as 0'5 of a millimeter in length. Though I am not in a position to determine the histological significance of these corpuscles, in a physiological point of view their presence in the trabeculse, and the intimate con- Fig. 285. V e Fig. 285. a, Point of entrance of the axial cord ; 6, point of passage into a membrane ; at c and d, branches of the angularly bent axial cord are shown with smaller corpuscles. nection of the latter with each other, as well as with the mechanical apparatus for the conduction of sound of the middle ear, seems to indicate that they participate to a certain extent in the auditory processes ; but the precise determination of this must be referred to the experimental physiologists. These corpuscles were first discovered by v. Troeltsch* in the * Virchow's ArcMv, Band 56 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. mucous membrane of the tympanic membrane of an old and deaf woman, and were regarded by him as pathological formations. Their importance as physiological structures was first recognized from my own researches and those of Politzer (34 and 35). The mucous membrane of the tympanic cavity receives its supply of nourishment from various quarters and from different arteries. The principal artery pursues a very tortuous course on the floor and over the promontory. The branches it gives off often form circular and elliptical loops, and then break up into a plexus of capillaries lying beneath the epithelium, which transmits the blood traversing it into a subjacent capillary plexus, the vessels of which rapidly increase in size, and again discharge their contents into the comparatively large veins of the periosteum. The arterial branches do not always present these relations, since many run straight and undivided till they suddenly break up into capillaries, which often pass in considerable numbers between the fibres of the foraminated membrane, in the same direction, and at equal distances from one another, transmitting their contents into large veins lying on the floor of the above-described system of cavities. The lymphatics of the mucous membrane lining the tympanic cavity exhibit the same relations as those of the membrana tympani. They form in Man, in some parts, a system of tubes, either presenting spherical dilatations, or large lateral diver- ticula, which is chiefly situated in the periosteum, or which, after presenting saccular expansions, opens out into the Jacunar system. This tubular system is not however everywhere present, but is in some parts, as upon the upper bony walls and roof of the cavity, replaced by funnel-shaped or spherical and intercommunicating spaces, which are again traversed by a fine plexus ; appearances that are also presented in the tympanic cavity of the Dog, as shall presently be more fully described. I have frequently found these spaces clogged with white blood corpuscles, which makes them resemble the follicles of a gland. These appearances have probably led to the statement made by Nasiloff, to the effect that he had discovered a lymphatic gland in the mucous membrane of the tympanum, at the part where it passes from the upper wall of the cavity to the THE MIDDLE EAR. 57 membrana tympani. As to any other relations of the lympha- tics to the epithelium of the mucous membrane, I have no further information than that above given, respecting the figures which make their appearance beneath the epithelium after treatment with solutions of silver and gold. The nerves which are distributed in the mucous membrane of the tympanic cavity, and of the membrana tympani, and which may also be followed into that of the Eustachian tube, and into the cells of the mastoid process, proceed from the plexus tympaiiicus, which is an anastomosis between the otic ganglion, the petrosal ganglion of the glossopharyngeal nerve, and the carotid plexus ; that is to say, the superior cervical ganglion of the sympathetic nerve (Bischoff, 3). The principal nerve trunks forming the tympanic plexus are composed of medullated fibres, which run in the perios- teum covering the lower and inner walls of the tympanic cavity. They give off small branches to the upper wall, which lie in the stratum of connective tissue subjacent to the epi- thelium, where they form by their intercommunication a wide irregular network. Non-medullated fibres proceed from this last, which form a delicate plexus immediately beneath the epithelium. Ganglion cells of variable diameter, enclosed in capsules, are found either applied to the surface or imbedded in the substance of the principal trunks, as well as of the branches given off from them, and are seen both in their course and at their points of division. They occur either singly or in clusters and groups. In regard to this point I can only corroborate the statements of Pappenheim (32), Kolliker (22) and Krause (23), and maintain the wide distribution of ganglia, in opposition to the observation of E. Bischoff (3), who regarded them as limited to the branches passing from the tympanic nerve to the fenestra ovalis. I may further add, that in the Dog and Cat I have found a few ganglion cells provided with sheaths, lying immediately beneath the epithelium of the mucous membrane where the fine nerve plexuses are situated. The mucous membrane in the Dog and Cat presents analogous structural characters to that of Man. The epithe- lium exhibits the same forms, and beneath it there is a fibrous 58 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. layer that presents the same relations to the periosteum as those that have been above more minutely detailed. The principal nerve trunks exhibit at certain points deep con- strictions/ caused by highly retractile bands, whilst at others they form fusiform enlargements. Ganglion cells are distri- buted, often in considerable numbers, both in and on the trunks. I found such ganglion-bearing trunks lying close beneath the epithelium, where the cells are columnar, and show the forms mentioned above. These columnar cells are prolonged into slender processes that run towards the nerves, and may be traced into their sheaths, but I am unable to give their further relations. The nerves themselves exhibit remarkable relations in another point of view. I have been able to demonstrate by injection the presence of capillary bloodvessels, which form, both in the nerve sheaths and amongst the nerve fibres them- selves, a narrow-meshed basket-like plexus that may also be rendered apparent by the chloride of gold method. If injected preparations, after previous hardening in alcohol, be treated with solution of chloride of gold, a second system of tubes becomes visible under favourable circumstances, which is not filled with the injection. This usually accompanies the nerve sheaths, or even lies in their substance, and is distinguishable from the blood vascular system by the presence of the sphe- roidal and fusiform enlargements that are characteristic of the lymphatics. I have succeeded in following branches of this system through the nerve sheaths as far as to the nerve fibres, but have been unable to trace their ultimate distribution in the interior of the nerves. The statements of v. Troeltsch (44), respecting the .presence of mucous glands in the tympanic cavity of Man, have up to the present time remained uncorroborated, though I can sub- stantiate their existence in Dogs and Cats, where they form simple follicles lined by columnar epithelium. As the further relations of the nerves and lymphatics in these animals are precisely similar to those of Man, I need only add a few remarks on the mucous membrane of the bulla ossea. The membrane here alters its characters ; the medul- lated nerve fibres become fewer in number, and ganglion cells THE MIDDLE EAR. '59 resembling those of the rest of the membrane lining the tympanic cavity are only sparsely scattered, but are invested by sheaths lying immediately beneath the epithelium. If the epithelium be stripped off from the subjacent very thin layer of connective tissue, an adenoid plexus appears, which in certain regions is very compact, though large openings occur between the groups. The openings lead into funnel-shaped or spheroidal cavities, which again intercommunicate by spaces in the tissue, and are finally continuous with tubes of various width. These Fig. 286. Fig. 286. Mucous membrane of the bulla ossea of the Dog. Spaces are visible in the tissue, which at a and 6 are continuous with lymphatics ; c, bloodvessels filled with gelatine. The pre- paration was stained with chloride of gold. cavities are traversed by a fine plexus, and are lined by a very delicate epithelium. They may either be empty or filled with lymph corpuscles. They almost invariably contain fat drops of. various size, which more or less run together. After macera- tion in a solution of perosmic acid, these last become black, and then sharply define the course of the tubes and the situation of the cavities. I have, however, also seen fat drops in the veins. However full the bloodvessels may become in con- sequence of injections made from the aorta, the fluid never penetrates into these cavities and tubes. This circumstance, as 60 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. well as their form and contents, justifies us in considering tliat they belong to the lymphatic system. . I have in vain sought, in works devoted to this subject, for any statements relating to the lymphatics of the tympanic cavity. Prussak (37), who investigated the minute anatomy of these parts in the Dog, denied their existence altogether. He maintained that, owing not only to the mode of formation of the numerous large veins from capillary plexuses, but to the direct connections between small arteries and veins, and to the passing away of large veins at various points, the circulation is carried on under a low pressure, and with great rapidity, by no means favouring exsudations which might have been expected to occur on account both of the loose nature of the soft parts separating the bloodvessels from the tympanic cavity, and of the absence of lymphatics. Now, although the arrangements in the blood vascular system of the mucous membrane in the Dog, described by Prussak, may be admitted to exist, we must nevertheless here also seek, in the presence of lymphatics, the principal reason for the non- occurrence of such pathological results ; and indeed it may easily be demonstrated that the absorbing surface of the lymphatics exceeds collectively that of the bloodvessels. From the position the lymphatics occupy in the -above-described system of cavities, imme- diately beneath the thin elastic, but easily compressible membranes, we may admit in these cases, besides the ordinary causes effecting the movement of the lymph, the frequent alterations of pressure occurring in the tympanic cavity, since these appear, together with the above- given mechanical arrangements of the lymphatic system, to be well adapted to exercise, sometimes a suction power on the contents of the tympanic cavity, and sometimes a pressure forcing them forward. The statements of Voltolini (46), that a small quantity of clear fluid is constantly present in the tympanic cavity of Man, I can only cor- roborate in the case of the mastoid cells. Peculiar cells still require to be noticed, which for the most part lie between the bloodvessels and lymphatics of the deep- est layers of the periosteum of the bulla ossea, but are also distributed through the more superficial stratum of connective tissue as far as to the epithelium. In the corpuscles themselves may be distinguished a discoid or more spherical or oval body and several processes. The body of the cell usually exhibits a large vesicular nucleus with a distinct nucleolus, or sometimes THE MIDDLE EAR. 61 several nuclei, each of which may again contain several distinct nucleoli. Amongst the processes there are usually one larger and from two to five smaller ones. The former, after running a variable distance, usually joins with another similar body, or gives off branches that unite with the processes of other cells, and these lead to the formation of plexuses. The smaller processes branch in a tree-like manner, and ultimately run out into fine processes that under favourable circumstances may be seen to join with nucleated cells. Both the body of the cell and the cell processes, but especially the former, appear to be finely striated and invested by a finely granular mass. Whilst those cells provided with a single nucleus resemble in form the ganglion cells of the spinal cord, those which contain several nuclei are very similar to rayeloplaxes. If the latter make the multiplication of nuclei highly probable, this will be rendered certain where disk- shaped appear to be converted into globular cell bodies by the multiplication of nuclei. Before we now leave the tympanic cavity, we may still add a few words respecting the ossicula, their connection with one another, and the muscles attached to them. The ossicula are invested with mucous membrane and in adults with a very thin periosteum. Externally they are composed of compact and internally of cancellous tissue. The latter is traversed by numerous bloodvessels, which, passing through the compact layer, communicate with the vessels of the periosteum or of the mucous membrane. In the head and cervix of the malleus, as well as in the body of the incus, the cancellous tissue increases at the expense of the cortical layer; whilst the converse occurs •in the long and short processes of the incus and in the maiiu- brium of the malleus. The articulations of the ossicula agree in their structure with other true joints, having capsular liga- ments, whilst a layer of hyaline cartilage covers the articular surfaces. The mode of attachment of the stapes to the fenestra ovalis will be more minutely described when the soft parts of the vestibule are under consideration. The muscles of the ossicula are transversely striated, and their tendons, where they traverse the interior of the tympanic cavity, are covered by the mucous membrane by which it is 62 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. lined. The tensor tympani is connected with the dilatator tubse, not only by tendinous fasciculi, as Majer (27) asserts, but also by muscular fibres, as I have already had an opportunity of stating. At the point of its attachment to the malleus, cartilage cells may frequently be found imbedded in its tendon. THE CELLS OF THE MASTOID PROCESS. The mastoid cells are lined by a very thin mucous mem- brane, which is continued into them from the tympanic cavity, and, speaking generally, preserves the same anatomical characters in both regions. The epithelium is composed of smooth cells presenting the features that have already been described as characterising those of the membrana tympani. Beneath them is a layer of connective tissue, and beneath this again a second layer of connective tissue representing the periosteum, and containing numerous nerves, bloodvessels, and lymphatics. The upper layer of connective tissue frequently projects in the form of membranes at the free borders of the cells, which extend to adjoining bony processes where they are inserted, and owing to which not unfrequently the cavities of two adjoining cells are shut off from each other. In the larger cell cavities these membranes are stretched horizontally, so as to form a kind of tent, by means of trabeculse proceeding from them. In the trabeculse of the membranes the peculiar organs with concentric striation, formerly described, occur with great frequency (I have counted as many as seven). They never attain here to the same size as those of the tympanic cavity, but nevertheless present a much greater variety of interesting forms. They vary from the small fusiform variety to the large spheroidal, clavate, and finger-biscuit form. I have repeatedly noticed membranes with their processes and the corpuscles adherent to them in the aditus ad cellulas, and have also seen trabeculee in direct connection with the pro- cessus brevis of the incus. BIBLIOGRAPHY OF THE EAR. 63 BIBLIOGRAPHY. 1. ARNOLD, FR., Icones organ, scnsuum. Turici, 1839. 2. , Handbuch der Anat. des Menschen, Bd. ii., 1851. 3. BISCHOFF, E., Microscopische Analyse der Kopfnerven. (Micro- scopic analysis of the cerebral nerves.) Miinchen, 1865. 4. BOCHDALEK, Otologische Beitrage. (Otological essays.) Prager Vierteljahrschr., Bd. i., pp. 33—46. 5. BOCHDALEK, junior, Beitrage zur Anatomie des Gehororgans. (Essays on the anatomy of the auditory organ.) Oesterr. Zeitschr. f. pract. Heilkunde, 1866, No. 32. 6. BUCHANAN, Phys. illust. of the organ of hearing. London, 1828. (MECKEL'S Arch., 1828.) 7. GERLACH, Microsc. Studien aus d. Gebiete der menschl. Morpho- logic. (Microscopic studies in the department of human morphology.) Erlangen, 1858. 8. GRUBER, Jos., Anatomisch-physiol. Studien iiber das Trommelfell und die Gehorknochelchen. (Anatomico-physiological in- vestigations on the membrana tympani and the ossicula auditus.) Wien, 1867. 9. , Ueber den feineren Bau des Ringwulstes am Trommelfell. (On the minute anatomy of the annular swelling of the membrana tympani.) Monatsschr. f. Ohrenheilkunde, 1869, No. 2. 10. , Lehrbuch der Ohrenheilkunda. Wien, 1870. 11. HELMHOLTZ, Die Mechanik der Gehorknochelchen und des Trom- melfells. (The mechanics of the ossicula auditus and of the membrana tympani.) PFLUGER'S Archivf. gesammte Physiol., 1868, Heft i. 12. HENLE, Handbuch der system. Anat. d. Menschen. Bd. ii. Gehorapparat. Braunschw., 1866. 13. HOME, Ev., On the structure and uses of the membr. tymp. of the ear. Phil. Transact., Vol. xc., 1800. 14. , On the difference of the structure between the human membr. tymp. and that of the Elephant. Phil. Transact., 1823. 15. HUSCHKE, Bearbeitung des menschl. Gehororganes in Sommer- ing's Anatomie, Bd. v. 16. HYRTL, Jos., Handbuch der topogr. Anat. Wein, 1853. 17. KESSEL, J., Ueber einige anat. Verhaltn. des Mittelohres. (On 64 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. some anatomical features of the middle ear.) Archiv fur Okrheilkunde, Bd. iii., Hft. iv., 1867. 18. - — , Nerven- und Lymphgefasse des menschl. Trommelf. (On the nerves and lymphatics of the membrana tympani of Man.) Centralbl. fiir med. Wissenchaft., No. 23 u. 24, 1868. 19. , Beitrag zur Anat. d. Schleimhaut der Paukenhohle und der Zellen d. Warzenfortsatzes. (Essay on the anatomy of the mucous membrana of the tympanic cavity, and of the mastoid cells.) Centralbl. fiir medic. Wissensch., No. 57, 1869. 20. , Beitrag zuin Baue der Paukenhohlenschleimhaut des Hundes und der Katze. (Essay on the structure of the mucous membrane of the tympanic cavity of the Dog and Cat.) Centralbl. f. medic. Wissenschaft., No. 6, 1870. 21. , Ueber Form- und Lageverhaltnisse eigenthiimlicher an der Schleimhaut des menschl. Mittelohres vorkomrnender Organe. (On the form and position of certain organs in the mucous membrane of the middle ear of Man.) Archiv f. Ohrenheilkunde v. TROELTSCH, Bd. v., Hft. iv:, 1870. 22. KOLLIKER, Microsc. Anatomie, ii., 1855. 23. KRAUSE, Ueber d. Nerv. tymp. u. Nerv. petrosus superf. min. Zeitschr. f. ration. Medic, von HENLE, Bd. xxviii., Hft. i., 1866. 24. LEYDIG, Lehrbuch der Histol. des Mensch. u. d. Thiere, 1867. 25. LUSCHKA, Anatomie des Menschen. 26. MAGNUS, Beitrage zur Anat. des mittleren Ohres. (Essay on the anatomy of the middle ear.) VIRCH. Archiv, xx., 1860. 27. MAJEK, LUDW., Studien iiber die Anatomie des Canalis Eustachii. Miinchen, 1846. 28. MEIER, Ueber das Othaematom, VIRCH. Archiv, Bd. xxxiii., 3 Folge, Bd. iii. 29. Moos, Untersuchungen iiber die Beziehungen zwischen Hammer- griff und Trommelfell. (Researches on the relations existing between the manubrium and membrana tympani.) Arch. f. Augen- u. Ohrenheilkunde von KNAPP, Bd. i., 1869. 30. NASILOFF, Ueber eine Lymphdriise in der Schleimhaut der Trom- melhohle. (On a lymphatic gland in the mucous membrane of the tympanic cavity.) Centralbl. f. medic. Wissenschaft., No. 17, 1869. 31. PAREIDT, De Chondromalacia. Hallis, 1864. Dissert, inaug. 32. PAPPENHEIM, Die specielle Gewebelehre des Gehdrorgane. (The minute anatomy of the tissues of the auditory organs.) Breslau, 1840. BIBLIOGRAPHY OF THE EAR. 65 33. POPPER, Die Gefasse u. Nerven des Trommelfelles. (The vessels and nerves of the membrana tympani.) Monatsschrift f. Ohrenheilkunde, No. 5 u. 6, 1869. 34. POLITZER, Ueber gestielte Gebilde im Mittelohre des menschlichen Gehororganes. (On pedunculated structures in the middle ear of Man.) Vorlaufige Mittheilg. Wiener medic. Wochen- schrift, 20 Nov., 1869. 85. , Ueber gestielte Gebilde im Mittelohre des menschl. Gehororg. Arch. f. Ohrenheilkunde von TROELTSCH, Bd. v., Hft. iii. 36. PRUSSAK, Zur Anatomie des menschl. Trommelf. (On the anatomy of the membrana tympani of Man.) Arch. f. Ohrenheilkunde v. TROELTSCH, Bd. iii., Hft. iv. 37. , Zur Physiologic u. Anatomie des Blutstromes in der Trom- nielhohle. (On the physiology and anatomy of the circula- tion in the membrana tympani.) Barichte der Kon. Sachs. Gesellsch. d. Wissensch., 1868. 38. RUDINGER, Atlas d. menschl. Gehororg. Miinchen, 1867. 89. , Notizen iiber die Histologie der Gehorknochelchen. (Notices of the histology of the ossicula.) Monatsschrift f. Ohren- heilkunde, No. 4, 1869. 40. SHRAPNELL, On the structure of the membrana tympani. London Med. Gaz., April, 1832. 41. TOYNBEE, Jos., On the structure of the membrana tympani in the human ear. Philosoph. Transact., 1851. 42. , On the structure of the ear. London, 1853. 43. , Beitrage zur Anatomie des menschl. Tromrnelfells. (Essays on the anatomy of the membrana tympani of Man.) Zeit- schrift f. wissenschaftl. Zoologie, Bd. ix., 1858. 44. v. TROELTSCH, Die Anatomie des Ohres in ihrer Anwendung auf die Praxis. (The anatomy of the ear in relation to practice.) Wiirzburg, 1861. 45. _ _, Lehrbuch der Ohrenheilk., 1868. 46. VOLTOLTNI, Die Zerlegung u. Untersuchung des Gehororgans an der Leiche. (The mode of examining the auditory organ in the dead body.) Breslau, 1862. 47. WHARTON JONES, Organs of hearing, in Todd's Cyclopedia of Anatomy and Physiology, Vol. ii., 1839. 48. LUDWIG and SCHWEIGGER-SEIDEL, Arbeiten aus den physiolo- gischen Aiistalt zu Leipzig, 1866. VOL. Til. F it THE EUSTACH[AN TUBE. BY PROFESSOR' RUDINGER, OF MUNICH. THE Eustachian tube of Man and of the various species of animals, is constructed on the same general plan, but in different instances presents minor modifications of structure. And however close may be the resemblance of the tubse of various animals, the more minute differences in form they present are so characteristic, that a practised observer can tell, from the examination of a transverse section alone, the name of the animal from which it was obtained. The Eustachian tube, forming a mechanical apparatus, with cartilaginous and muscular tissues entering into its com- position, obviously stands in intimate physiological relation with the tympanic cavity. In addition to the office of carry- ing off its own secretion and that of the highly vascular mucous membrane of the tympanum, it is capable of effecting, in consequence of its peculiar mechanism, the ventilation oi this cavity. Whether the Eustachian tube plays any im- portant physiological part in the conduction of sound into the tympanic cavity, and whether it possesses any relations to the voice of the individual, and if any, what kind of relation, are questions that receive no satisfactory elucidation from researches in comparative anatomy. Conclusive responses to such inquiries have still to be obtained from experimental investigations. OSSEOUS PORTION OF THE EUSTACHIAN TUBE. (J7 1. OSSEOUS AND CARTILAGINOUS PORTIONS OF THE EUSTACHIAN TUBE. The osseous portion of the Eustachian tube of Man forms an elongated triangular fissure, the greatest diameter of which is almost vertical. The base of the triangle is above, and is bounded by the thin bony lamella which sometimes completely separates the Eustachian tube from the rounded semi-canal of the tensor tympani. If the bony lamella happens to be broad, it curves somewhat upwards anteriorly, in consequence of which the upper end of the tube is of smaller diameter, and comes to occupy a position anterior to the bony semi-canal. As the bony end of the median tubal opening appears dentated and obliquely cut at its point of junction with the cartilage, it is more largely bounded by osseous substance mesially and posteriorly than anteriorly and laterally, an arrangement which, as Henle has already remarked, is deserving of notice, to enable us to understand the mode of attachment of the cartilage to the bone. If a temporal bone, in which the connection with the Eus- tachian tube is preserved uninjured, be carefully deprived of its salts, and then be divided through the middle of the tympanic cavity, so that successive sections may be made towards the Eustachian tube, dividing this at right angles, the gradual transition of the tympanic cavity into the bony portion of the tuba, and the relations of this to the cartilaginous por- tion, may be clearly seen, each section aiding the observer to understand the succeeding one. By this means it may be shown that the cartilage of the Eustachian tube interdigitates with the dentated margin oi the bony portion, and is a direct continuation of the walls of the osseous tuba Eustachii, yet in such a mode, that the hyaline cartilage substance does not immediately succeed to the bone, but that a connection is established between the two by means of nbro-cartilaginous tissue. This is prolonged for some distance into the substance of the cartilage, so that C. F. Th. Krause arrived at the conclusion that the upper end of the Eustachian tube was composed of nbro-cartilage ; and it r2 68 THE EUSTACHIAN TUBE, BY PROFESSOR RUDINGER. must be admitted that the two kinds of tissue at this point are not very sharply differentiated from each other, since the basilar nbro-cartilage is partially continued into the Eustachian cartilage. The cartilage close to the bony portion of the tube presents the form of a lamina, bent at right angles, with a horizontal Fig. 287. Fig. 287. Transverse section of the Eustachian tube and the ad- joining parts. 1, Median plate of the cartilage ; 2, lateral hook of the cartilage ; 3, dilatator muscle of the tube ; 4, levator palati ; 5, basilar nbro-cartilage ; 6 and 7, acinous glands ; 8, layer of fat on the lateral wall ; 9, safety tube (Sicherheitsrohre) ; 10, accessory fissure (Hilfsspalte) ; 11, fold of the mucous membrane ; 12, tissue bounding the tube laterally. and a gradually attenuating vertical and lateral limb. No carti- lage is as yet present on the median side, because the median and posterior wall of the osseous tuba is longer than the lateral, and therefore here forms its boundary, whilst the opposite part of the wall is already composed of the lateral cartilaginous lamina. CARTILAGINOUS SEGMENT OF THE EUSTACHIAN TUBE. 69 It further appears from such transverse sections, that the transition of the osseous into the cartilaginous tuba Eustachii is very gradual. Cartilage cells appear in the dense fibrous tissue at some distance from the bony tube, at first scat- tered, but subsequently in larger numbers. The curved hook-like portion of cartilage of the Eustachian tube in Man, which is attached by means of the so-called fibro-cartilago basilaris to the base of the skull, is of moderate thickness, and consists of non-vascular cartilage, which, as Kolliker states, belongs to the same series of structures as hyaline cartilage. Its hyaline matrix, containing a few fibres, includes isolated groups of rounded and oval cartilage cells, of various size. The larger cells contain two or more nuclei, the smaller cells only one. Near the surface the cells become gradually smaller, and there is here a layer of nucleated connective tissue, which represents a perichondrium. No well-defined line exists be- tween the perichondrium and the proper substance of the cartilage, but the one kind of tissue runs gradually into the other. At a few points this vascular tissue dips more or less deeply into the cartilage, so as to form little islands in trans- verse section, which i-nclude, in the Ox, small acinous glands. The fibrous layer is much more strongly developed at the lateral truncated extremity of the cartilaginous hook than elsewhere, which is partly caused by the attachment of the tendon of the musculus dilatator tubse to it. In the Quadrumana, as well as in Cheiroptera, the cartilage of the Eustachian tube is hyaline, and very similar to that of Man, the fibrous substance, especially in Bats, being almost suppressed, whilst the hyaline cartilage, containing moderately large cells, greatly preponderates. The same remarks apply to the Eustachian tube of Rodcntia, Pachydermata, and Rumi- nants. In the latter the cartilage cells are small, and the whole cartilage appears to be composed of several segments. Remarkable differences occur in the external form of the cartilage in different animals. In Talpa Europsea, Arctomys marmota, Canis vulgaris, Mustela martes, and Lutra, there is a simple lamella or cylindrical rod of cartilage on the median side of the tuba, which in Lutra contains a considerable amount of calcareous deposit. In the Dog, Marten, and Otter, the 70 THE EUSTACHIAN TUBE, BY PROFESSOR RUDINGER. tissue surrounding the cartilage consists of alternate layers of connective tissue and elastic fibres. In Felis domestica, Felis leo, and Felis tigris, the cartilage is essentially limited to a hook at the end of the tubal fissure. The remaining portion of the tuba of these animals is enclosed by dense fibrous tissue, containing small lamellae of cartilage on its median side. I once saw a large amount of fat infiltrated into the tubal cartilage of Man, conferring an unusual appearance upon it, by rendering it two or three times larger than natural in all its dimensions ; both cartilages projected to a considerable extent from the wall of the pharynx. 2. THE MUSCULAR (MEMBRANOUS) SEGMENT. I have already had an opportunity of remarking that the expression, " membranous portion of the tube," is very indeter- minate. It immediately suggests the mucous membrane to the mind, which however by no means belongs to one segment of the Eustachian tube alone, but lines this throughout its whole extent, and is connected both with the cartilage and with the muscles. If the expression is to be used, it should be understood to indicate that part of the tube which is not invested by cartilage, and there is then no objection to its use, since these two parts can be demonstrated in the Eustachian tube of many animals. In the meanwhile, though disposed in general to be exceed- ingly precise in reference to nomenclature, we still think it may be found advantageous for Man and many animals to give up the term at present in use, and to name the segment of the tuba in question the " muscular segment!' I am well aware that muscles are here present which do not exclusively belong to the tuba, and that this term does not express the complete morphological characters of the segment of the Eustachian tube in question. No absolute necessity, however, exists that all the characteristic features should be expressed in the nomenclature, and it appears to me that it will be convenient to derive the name of this segment from the muscles which both morphologically and physiologically stand in such intimate relation with it. MUSCULAR SEGMENT OF THE EUSTACHIAN TUBE. 71 As I regard the layer of tissue between the muscles and the mucous membrane as the submucosa, only a few points require to be mentioned respecting the histology of the muscular seg- ment. If it be desired to obtain a general view of the relations of the voluntary musculus dilatator tubse to the cartilage, transverse sections must be carried through the tuba with its decalcified osseous investment in such a manner that the sec- tions run parallel to the muscular fibres. It may be incontes- tably shown from an examination of such sections, which ought to be rather thick, that the musculus dilatator tubee is attached exclusively to the truncated extremity of the lateral cartila- ginous lamina along the whole length of the Eustachian tube. (See fig. 287.) Its flat tendon limits the submucosa in the tuba of Man, receives transversely striated muscular fibres on its outer side, and coalesces above with the perichondrium of the uncinate extremity. There can be no doubt that in Man the dilatator tubse exhibits no direct transition into the mucous membrane. Even in those cases where it appears as though in the vicinity of the cartilage the muscle is continuous with the mucous membrane, sections demonstrate that an isolated fragment of cartilage is connected with the apex of the hook by means of dense tissue. I am able from transverse sections and surface views to corroborate the statement made by v. Troeltsch and L. Mayer, that a direct passage of the musculus dilatator tubse takes place into the tensor tyrnpani, and this is true not only in regard to the tendons, but also for the transversely striated fibres of the two muscles. In Monkeys the muscular segment of the tuba, and especially the musculus dilatator tubse, which is attached exclusively to the truncated extremity of the lateral cartilage, are strongly developed. I have also decalcified the cranial bones of Monkeys, and made transverse sections through the tubse and their investment, and have found that the musculus dilatator tubse does not extend beyond the limits of the lateral cartilage. The muscle holds similar relations to the cartilage in the Pig, Horse, Stag, Reindeer, etc. An exception to this dis- position of parts however occurs in those animals in which no lateral cartilage of the tuba exists, as in the Marmot, Dog, Marten, Otter, and Cat ; in these animals the dilatator tuba? is 72 THE EUSTACHIAN TUBE, BY PROFESSOR RUDINGER. directly continuous with the dense submucous tissue. In the case of the Horse it is to be remarked that two voluntary muscles, the so-called levator and tensor palatini, are inserted into the lateral part of the cartilage.* The musculus levator veil palatini has a peculiar topograph- ical relation to the Eustachian tube, as it ascends from the bot- tom of the tubal fissure in immediate contact with the mucous membrane, as far as to the pars petrosa, where it is attached, not only to the bones, but also, with a few fibres, to the dense submucosa of the mucous membrane. A special transversely striated muscle, which is situated on the median side of the Eustachian tube, occurs in the Stag. It is strongly deve- loped in the Buck, its several fasciculi, surrounded by fat, extending to the median portion of the mucous membrane, with which they are intimately connected, whilst its tendon is continued directly into the fibrous layer of the submucosa. It is destined for the fixation of that part of the mucous membrane which is free from cartilage, and I have named it the dilatator tubse medialis.f 3. THE Mucous MEMBRANE. The mucous membrane of the osseous portion of the Eusta- chian tube, which dips to a variable depth into the inequalities of the osseous surface, varies in diameter between O'OSO and 0'112 of a millimeter. Transverse sections of the osseous por- tion of the tuba exhibit no well-defined line of demarcation between the periosteum and the mucous membrane. A finely fibrous nucleated connective tissue is intimately blended with the osseous tissue, and processes are given off from it which dip into the bone. At a little distance from the bone the con- nective tissue becomes somewhat looser in texture, and supports a coarsely meshed vascular plexus, the branches of which are distributed, not only to the mucous membrane, but also in the bone. This layer is remarkably thick on the processes of the bone and at the bottom of the osseous portion of the Eustachian * S. Riidinger, Beitrdge zur Anatomie und Histologie der Ohrtrompete. t S. Riidinger, loc. cit., figs. 42 and 43. MUCOUS MEMBRANE OF THE EUSTACHIAN TUBE. 73 tube, where trunks of considerable size, which in part run towards the cartilaginous tuba, are met with in transverse section. At a few points the basement membrane, with its ciliated epithelium, is in contact with the loose submucosa; at other points of the mucous membrane, and most frequently beneath the osseous lamella which divides the Eustachian Fig. 288. Fig. 288. Transverse section of the osseous portion of the Eusta- chian tube. 1, Laminated ciliated epithelium ; 2, conglobate gland tissue ; 3, periosteum ; 4, bone. Magnified 184 diameters. tube from the semicanal's tensoris tympanj, lymph corpuscles occur, -closely aggregated in a fibrous reticulum, and we have here that layer of tissue under inspection which has been described under the term conglobate gland substance in the pharynx and in the intestinal canal. It forms a layer, the thick- ness of which varies from 0'056 to 0'040 of a millimeter, and to it is applied the basal membrane with the ciliated epithelium. (See fig. 288.) This has a thickness of 0'028 of a millimeter. The pale thin- walled Vessels have still to be mentioned, which traverse the submucosa in a plexiform manner, and in transverse sections of injected ( specimens never contain any of the injection, on which account they have been regarded as lymphatics. All other large spaces and fissures which inter- communicate with one another in the submucosa appear in such injected specimens as blood-conveying vessels. At the 74 THE EUSTACHIAN TUBE, BY PROFESSOR RUDINGER. bottom of the osseous portion of the tube, as I have already elsewhere had an opportunity of describing, delicate folds ap- pear of various height, which, when seen in transverse section, present the form of villous processes. In the cartilaginous portion of the tube, the mucous mem- Fig. 289. Fig. 289. Transverse section of the Eustachian tube of Man, in its upper third. 1, Median cartilage ; 2, lateral cartilaginous hook ; 3, perichondrium ; 4, submucous layer ; 5 attachment of the dilatator tubse ; 6, safety tube (Sicherheits-rohre) ; 7, lateral projection of the mucous membrane ; 8, median projection of the mucous mem- brane ; 9, accessory fissure (Hilfs-spalte). Magnified 184 diameters. brane and the cavity it encloses present many points of differ- ence from that of the osseous portion, since in it acinous mucous glands and peculiar foldings occur, which are intimately con- nected with the mechanism of the tube. In the adult Man I have distinguished two divisions in the tubal fissure. I have applied the term " safety tube " (Sicher- MUCOUS MEMBRANE OF THE EUSTACHIAN TUBE. 75 heits-rohre) to the semi-cylindrical space beneath the cartila- ginous hook, and the fissure connected therewith I have called the " accessory" or " auxiliary fissure " (Hilfs-spalte). These two names sufficiently express their physiological significance. The two divisions are caused by the peculiar configuration Fig. 290. Fig. 290. Transverse section of the Eustachian tube of Man, through its upper third. 1, 2, Cartilage ; 3, musculus dilatator tuba? ; 4, lateral submucous layer ; 5, median projection of the mucous membrane, with its vessels ; 6, lateral projection of the mucous membrane, with its vessels ; 7, large vessel on the roof of the tuba ; 8, safety tube, with the mucous membrane ; 9, accessory tube. Mag- nified 184 diameters. of the cartilage, and are separated from each other by pro- jections of the mucous membrane. Whilst the mucous mem- brane at the concavity of the hook behaves itself, in all essential respects, like that of pneumatic canals generally,— that is to say, it is closely adherent to the surrounding parts, and is 76 THE EUSTACHIAN TUBE, BY PROFESSOR RUDINGER. only folded at certain definite points, — at that part where the auxiliary fissure commences, folds of the membrane project be- tween it and the safety tube, which present individual varia- tions both in form and size. In the greater number of cases the lateral fold is stronger than the median ; but the opposite Fig. 291. Transverse section from the middle third of the Eusta- chian tube of Man. 1, 2, Cartilage ; 3, musculus dilatator tubse ; 4, mucous membrane in folds beneath the hook of the cartilage ; 5, slightly elevated mucous folds of the accessory fissure ; 6, sub- mucosa. condition may also be met with, and so far as regards these folds they are incapable of effecting the complete closure of the safety tube. This first becomes possible at that part where the curvature of the uncinate process becomes sharp, and the mucous membrane is no longer so intimately connected with the cartilage. This point is situated at about the middle of the length of the Eustachian tube; here the mucous membrane MUCOUS MEMBRANE OF THE EUSTACHIAN TUBE. 77 has a slightly wavy character, as is shown in fig. 291. The configuration of the cartilage at this part renders it possible for the surfaces of the mucous membranes to be immediately applied to one another without any special apparatus, when the cartilaginous lamellse, owing to their elasticity and the re- laxation of the muscles, are approximated. In reference to this point it is to be observed that where a fissure is visible in the middle portions of the tube with high magnifying powers, this is to be clearly distinguished from the oval or semi-cylindrical openings which appear in transverse sections through the upper third beneath the uncinate process of the cartilage. The safety tube is well marked in the Cat tribe and in the Horse, Roedeer, Sheep, Goat, Calf, Ox, Rabbit, and Hare. On the other hand, it does not present this form in Monkeys, Marmots, Dogs, Martens, Pigs, and Otters. In the Sheep, Stag, Goat, and Calf, there is a delicate series of folds of the mucous membrane on the concavity of the carti- lage, which I described in 1867 and 1868. It does not extend, however, through the whole length of the tube, but is limited to the upper part. The folds are most numerous in the Sheep, Goat, and Calf, whilst in the Ox they have coalesced to form a single projection. In the Calf the greatest projection measures from base to apex 0-042—0-064 of a millimeter; and in the Ox, 0*080— 0'096 of a millimeter. From these measurements, then, it appears that the same structure presents considerable differences in relation to the age of the animal, and it is highly probable that the presence of folds at the concavity of the cartilage is intended to facilitate its movements. At the same time we may reasonably admit that they never attain the same size during life as they present in the dead subject. In the accessory fissure, where the surfaces of the mucous membrane, when the muscles are not acting, come into contact, numerous regularly opposed folds occur in the pharyngeal segment of the Eustachian tube, which have already been described as they appear in Man by Huschke and F. Arnold. These are also connected with the mechanism of the tuba ; for they are most numerous at that part where the median lamella of cartilage attains its greatest amount of mobility. 78 THE EUSTACHIAN TUBE, BY PROFESSOR RUDINGER. They occur with more or less modification in the greater number of animals examined, attaining their highest develop- ment in the Eustachian tube of the Marmot and Otter, in which only a single sinuous fissure, without any safety tube, is present. Fig. 292. Fig. 292. Transverse section of the cartilaginous portion of the Eustachian tube of the Ox. 1, Median lamella of cartilage ; 2, mesially directed long process ; 3, uncinate process of cartilage ; 4, lateral extremity of the cartilage ; 5, musculus dilatator tubse ; 6, safety tube, with the fold of the mucous membrane ; 7, dilated portion of the Eustachian tube at the commencement of the accessory fissure ; 8, accessory fissure. Magnified 184 diameters. The Eustachian tube of the Bat and of the Horse presents a peculiar structure, the mucous membrane forming a lateral dilatation like an air sac, which is surrounded by muscles and glands. (See fig. 294.) In the Bat this sac is of an elongated quadrangular form, owing to the disposition of the glands and muscles in relation with it externally. MUCOUS MEMBRANE OF THE EUSTACHIAN TUBE. 79 In the Horse, the wide safety tube is separated from the accessory fissure by a thick process of the mucous membrane. The latter opens into the air sac. This stretches throughout almost the whole length of the Eustachian tube, and the air Fig. 293. Fig. 293. Mucous membrane of the accessory fissure of Man, showing the- parietal folds and glands. 1, Prominent folds of the mucous membrane, with an epithelium and a subjacent fibrous layer, which last contains many nuclei ; 2, submucous fibrous layer ; 3, acinous glands ; 4, excretory ducts of the glands, lined by transitional epithelium ; 5, ciliated epithelium on the lateral wall. sacs of the two tubes reach to the middle line in front of the vertebral column, and are bounded by the base of the skull and the transverse processes of the two first cervical vertebrae. 80 THE EUSTACHIAN TUBE, BY PROFESSOR RUDINGER. The histological characters of the raucous membrane are as follows : Its internal surface is lined throughout by a lami- nated ciliated epithelium, which has an average diameter of O020 of a millimeter. In this, as well as in the osseous portion of the tube, two kinds of cells may be distinguished : (1) Those Fig. 294. Fig. 294. Transverse section of the Eustachian tube of Vespertilio murinus . 1, Median cartilaginous lamina ; 2, thinner uncinate pro- cess ; 3, oral-shaped safety tube ; 4, auxiliary fissure ; 5, elongated quadrangular air sac ; 6, musculus levator veli palatini ; 7, thick glandular layer ; 8, excretory duct of a gland. which stand in close order on the free surface, and which when they possess cilia are broad, and dip with their attenuated extremities (2) into the deeper layer of cells. The cells forming the latter layer rest by a broad base on the basement mem- brane, and s.nd their attenuated extremities between the cells of the superficial layer. The nuclei of the former are elon- gated, those of the latter more spheroidal, as well as smaller THE MUCOUS MEMBRANE OF THE EUSTACHIAN TUBE. 81 and more gelatinous. F. E. Schulze has also described cup- cells in the epithelium of the Eustachian tube, and on exa- mining my finest sections with a view of discovering these cells, I observe between the columnar cells, and situated at definite distances from one another, moderately wide spaces, a disposition that approximatively coincides with that described and pictured as cup-cells. Subjacent to the epithelium and the basement membrane is a fibrous layer, containing nume- rous nuclei, and presenting different characters in the osseous and cartilaginous tuba. The layer of connective tissue corre- sponding to the cartilaginous portion of the Eustachian tube, is developed inversely to the glandular layer; where the glandular tissue is thick, as in the neighbourhood of the tubal fissure, this fibrous layer is thin ; but where the glands are entirely absent, as in the safety tube, the fibrous layer attains its maximum. A dense layer of connective tissue of considerable thickness makes its appearance above, in the bony tuba be- neath the lateral portion of the cartilage, and here the tendinous fibres of the musculus dilatator tubse are partially interwoven with it. At this part, dense connective tissue is also present at the bottom of the tubal fissure, partly produced by the tendi- nous fibres of the levator palati muscle. It may be said that the upper end of the Eustachian tube receives from this dense tissue a compact investment in addition to the above-described bone and rectangular plate of cartilage, on which the muscles can exert but a very small influence. If the transverse section be made somewhat lower down, a sharp line of demarcation becomes apparent between the flat tendons of the dilatator tubse and the submucous connective tissue, and still deeper is a layer of fat. Mucous glands are entirely absent in the membrane of the safety tube throughout the whole length of the Eustachian tube. In the middle segment of the tubal fissure the acinous glands form a distinct layer, becoming thicker inferiorly be- tween the median cartilaginous lamella and the superimposed mucous membrane. Gland vesicles also occur laterally between the dilatator tubse and the epithelium, and extend at some points as far as to the truncated extremity of the lateral car- tilage. The mucous glands are similar in structure to those of VOL. III. G 82 THE EUSTACHIAN TUBE, BY PROFESSOR RUDINGER. the pharynx and oesophagus ; the several acini become aggre- gated into larger masses, the moderately wide excretory tubes of which open into the tuba at various points. The epithe- lium of the ducts presents the characters of a transitional form between tha't of the mucous membrane and that of the gland Fig. 29f . Fig. 295. The cartilage represented in connection with the mucous membrane of the safety tube. 1, Ciliated epithelium ; 2, sub- mucosa ; 3, dense fibrous layer ; 4, perichondrium ; 5, cartilage cells with small elongated nuclei ; 6, groups of fibres with cartilage cells. Magnified 170 diameters. vesicles. The several spheroidal or elongated acini are filled by cuneiform epithelial cells, which leave only a small cavity in the centre. The acinous mucous glands exhibit great variations in their NERVES AND VESSELS OF THE EUSTACHIAN TUBE. 83 size and number in the different classes of animals. Whilst in the Quadrumana, in Bats and Marmots, and in the Sheep and Goat, they form a thick layer either limited to certain spots or completely invest the tuba on its central and median side, they appear to be reduced in all the other animals I .have examined to a thin layer in the submucous layer. The only histoiogical difference I have been able to distinguish between them is in regard to their size. 4. NERVES. I have already described ganglion cells as occurring in the nerves of the mucous glands of the Eustachian tube of Man. The nerve fasciculi consist of double-contoured fibres, and ori- ginate in the plexus tympanicus and the plexus pharyngeus, forming a coarse network which contains a variable number of ganglion cells at those points where the fasciculi meet. The cells vary in size, and their processes are continuous with primitive fibres. The ganglia agree with those that occur in the branches of the plexus promontorii (E. Bischoff) ; and since the nerves of the Eustachian tube essentially originate in this plexus, while they also contain sympathetic nerves, we cannot well deny their morphological relation to the tympanic plexus, although their possible functional importance in re- gard to the mucous glands is on this account by no means excluded. 5. VESSELS. The vessels of the Eustachian tube arise from two different sources; namely, from the vessels of the tympanic cavity, and from those supplying the wall of the pharynx : the latter pre- sent no peculiar features in their arrangement, but agree in their characters with the pharyngeal vessels. The former, on the other hand, run in the first place as large arterial trunks in the direction of the long axis of the tube, both upon its lower part and upon the safety tube, and in transverse sections constantly appear at certain definite points. Thus, in the processes of the mucous membrane situated be- tween the safety tube and the accessory fissure, two vessels of different size become apparent, of which one arises upon G 2 84 THE EUSTACHIAN TUBE, BY PROFESSOR RUDINGER. the lateral, the other upon the median side, forming capillary plexuses that do not astomose with the plexus of a third in the middle third of the safety tube. (See fig 290.) This third vessel forms a distinct capillary network in the submucosa, which is extended over the roof of the tuba for a definite dis- tance only. BIBLIOGRAPHY. HUSCHKE, S. SOEMMERING, Vom Baue des menscklichen Korpers. ARNOLD, F., Handbuch der Anatomie des Menschen. Freiburg, 1847. KRAUSE, C. F. Th., Handbuch der menschlichen Anatomie. Hannover, 1842. PAPPENHEIM, Die specielle Gewebelehre des Gehororganes. Breslau, 1840. HENLE, Handbuch der systematiscken Anatomie des Menschen. Braunschweig, 1866. KOLLIKER, Handbuch der Gewebelehre. v. TROELTSCH, Archiv fiir Ohrenheilkunde, 1864, ss. 16^-21. MAYER, L., Studien iiber die Anatomie des Canalis Eustachii. Miinchen, 1866. BISCHOFF, E., Mikroskopische Analyse der Anastomosen der Kopf- nerven. Gekronte Preisschrift. Miinchen, 1865. KRAUSE, W., Ueber den Petrosus superficial major, Zeitschr. fiir wissenschaft. Medecin. von HENLE und PFEUFFER. RUDINGER, Ein Beitrag zur Anatomie und Histologie der Tuba Eustachii. Miinchen, 1865. , Beitrage, zur vergleicbenden Anatomie und Histologie der Ohrtrompete. Miinchen, 1870. III. THE MEMBRANOUS LABYRINTH. BY PROFESSOR RUDINGER, OF MUNICH. 1. TOPOLOGICAL AND HlSTOLOGICAL ACCOUNT. IN consequence of experimental observations, some doubt has been thrown on the functional importance of the membranous labyrinth for the faculty of hearing ; it must still, however, be considered an integral part of the inner ear, by virtue of its being the supporter of the acoustic percipient apparatus. Its topographico-histological relations present numerous dif- ferences in the various classes of animals. In many Inverte- brata, as in Mollusca and Crustacea, a vesicular structure appears as the representative of the labyrinth, which is usually seated on the nerve centre, or on one of its branches. In the > Achetidse and Locustidse, amongst Insecta, it is placed nearj the knee-joint; and in the Acrididse, over the origin of the last) pair of feet. In almost all Vertebrata the membranous laby- rinth forms a division of the auditory apparatus, that is found to be enclosed more or less completely in a cartilaginous or osseous capsule, of which it forms an attenuated protrusion. The elongated sac, or utricle,, with its ampullae and semi- circular passages, as well as the more rounded sacculus, are in direct contact with the osseous or cartilaginous capsule, and are not, as has hitherto been erroneously believed, completely surrounded by fluid (perilymph). These topographical relations of the labyrinth are already i \ f -(ltv^ 86 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. recognizable in the embryo.* Sections made through the temporal bone at various stages of development show that the cavity of the vestibule arid of the semicircular canals is filled with a gelatinous substance, which becomes con- Fig. 296. Fig. 296. Membranous labyrinths of various vertebrate animals. A, from Man ; B, from the Calf ; C, from the Pike ; D, from Vultur fulvus ; E, from Rana esculenta. 1, Canalis semicircularis horizon- tails ; 2, can. sem. superior; 3, can. sem. posterior; 4, canalis com- munis ; 5, ampulla-form termination of the can. sem. horizontalis ; 6, utriculus ; 7, sacculus rotundus. densed near the cartilaginous wall, and that the parts of the labyrinth are connected with this somewhat denser fibrous layer. The vessels that develop in this part traverse the * Kolliker first gave an illustration of the relations of the semicircular canals in the foetus, in his Eiitwickhnufsyescliichte, or History of Development. HISTOLOGY OF THE MEMBRANOUS LABYRINTH. 87 gelatinous tissue in such a manner that the larger branches appear in sections made in the direction of the long axis of a semicircular canal, whilst the secondary branches run in a more or less transverse or oblique direction. Of the two larger vessels (see fig. 297) which constantly run with some interval between them, I regard the smaller as the artery and the larger as the vein. In the formation of the cavities or lumina of the tubes, the periosteum and the nucleated connective tissue surrounding the vessels which traverse the cavity, may be regarded as the results of the regressive metamorphosis Fig. 297. Fig. 297. Transverse section of a cartilaginous and membranous semicircular canal of a foetus. 1, Cartilaginous semicircular canal ; 2, gelatinous tissue, which completely fills the space between the two canals; 3, vein ; 4, artery ; 5, wall of the membranous semicircular canal. of the gelatinous tissue, and as constituting the ultimate products of its development. In the adult human subject the periosteum lining the osseous labyrinth is a moderately thick layer of connective tissue inter- mingled with fine elastic fibres. Both it and the vessels it encloses are continuous with those of the bone, so that it is difficult to detach it from the bone. The internal surface of the periosteum in the semicircular canals is uneven. Rather large nuclei are scattered through its substance, which become more numerous, and are less regularly arranged, near the free than 88 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. the attached surface. In specimens that have been hardened in chromic acid or in chromate of ammonia, these nuclei some- times form regular rows, so as to present many of the charac- teristic appearances of a pavement epithelium. After repeated observations recently made on carefully prepared specimens, I am inclined to think that, as Henle and Hasse have already stated, there is really no epithelium here, but that the appearances presented are simply due to the numerous nuclei of the perios- teum. Henle finds the periosteum of the labyrinth analogous to the sub-arachnoideal tissue, the pigment cells, however, being very few in number. The calcareous particles described by Kolliker and Henle as existing in the periosteum are absent in some cases, whilst in others they are very numerous. If an attempt be made with the aid of a chisel to dissect out the labyrinth, it will soon be discovered that not only the two sacculi in the vestibule, but also the membranous semicircular canals, are at certain points closely connected with the perios- teum. A clear view of the histological relations of the osseous and of the membranous labyrinths respectively, can therefore only be obtained by making transverse sections through the temporal bone decalcified in chromic acid. In reference to the sacculi it may be observed that the utriculus is more closely attached to the bones of the median wall of the vestibule, than the sacculus rotundus. This, as Ode- nius has already pointed out, is separated from the recessus hemisphericus by a moderately thick and loose layer of con- nective tissue, which surrounds the nerve fibres and vessels traversing it. The two sacculi occupy about two-thirds of the cavity of the vestibule. The utriculus extends farther laterally than the sacculus rotundus, but neither of the two touches the lateral wall of the vestibule or footplate of the stapes ; topographical relations that I had already described in 1866 * The membranous semicircular canals are attached to the periosteum on the convex side of the osseous canals by mode- rately broad bands of connective tissue, which I call the liga- menta labyrinthi canaliculorum et sacculorum. At the points * Aerztliches Intelligenzblatt, Juni. HISTOLOGY OF THE MEMBRANOUS LABYRINTH. 89 where the membranous canals adhere to the bones, the perios- teum is feebly developed ; in the angular spaces, on the other hand, where the canals separate from the bones, strong nu- cleated fasciculi of connective tissue pass from the periosteum to the external fibrous layer of the membranous semicircular canals, and these ligamenta labyrinthi canaliculorum form the essential means by ivhich the semicircular canals are retained in position. In some cases there are two or more bands Fig. 298. Fig. 298. Utriculus and sacculus rotundus, drawn with the camera lucida. 1, Utriculus ; 2, sacculus rotundus ; 3, macula acustica ; 4, ampulla ; 5, canalis communis . which enclose variously shaped spaces between them. These spaces appear to be the transverse sections of small canals which run along the ligaments to the principal membranous canal. They may even be found in the neighbourhood of the ampullae, but I do not think that any particular mor- phological or physiological importance is to be attributed to them. In the sacculi and ampullse, these ligaments, or rather 90 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. means of fixation, are feebly developed in those angles where the former separate from the bones. Vessels are constantly met with in transverse sections of the ligaments. The moderately tense and finely fibrous fasciculi of connective tissue traversing the cavity of a semicircular canal (see fig. Fig. 299. Fig. 299. Transverse section of an osseous and membranous semi- circular canal of Man. 1, Osseous wall ; 2, fasciculi of connective tissue, with vessels enclosed within them ; 3, point of j unction of the fasciculus with the periosteum ; 4, membranous semicircular canal, with its three layers ; 5, ligamenta canaliculorum, with their spaces or cavities ; 6, point where the membranous semicircular canal coalesces with the periosteum. 299), which are attached on the one hand to the periosteum, and on the other to the free wall of the labyrinth, are to be re- garded as essentially the carriers of vessels, and also as means of fixation for the free wall of the membranous semicircular canal. They for the most part run at right angles to the longitudinal HISTOLOGY OF THE MEMBRANOUS LABYRINTH. 91 axis of the semicircular canals, give off secondary branches to the periosteum, and are attached to the most diverse points by their gradually expanding extremities. The two sacculi are attached in a very similar manner, except that the finely fibrous connective tissue (the ligamenta labyrinthi sacculo- ruiri) is much more feebly developed at those angles where the sacculi separate from the bone. In the Quadrumana and other Mammals, the labyrinth, which upon the whole is very thin-walled, appears to be as firmly attached as in Man. The connection with the periosteum and the vessels with their Fig. 300. Fig. 300. Transverse section of an osseous and membranous semi- circular canal of a Rat. 1, Osseous semicircular canal ; 2, plexiform fibrous tissue ; 3, wall of the membranous semicircular canal ; 4, con- nective-tissue corpuscles ; 5, pigment cells. delicate investing tissue, is only so far different that the ligamenta labyrintjii canaliculorum appear to be less sharply defined. In the Rat the interior of the osseous canals is every- where traversed by plexiform bands of connective tissue and scattered pigment cells, and is quite half filled by the mem- branous excentric membranous canal, so that here there is quite a different proportion in point of size between the osseous and membranous canals to that observed in Man. No difference 92 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. exists in the mode of attachment to the bone of the two vestibular sacculi. In the osseous semicircular canals of Birds, according to Hasse's and my own observations, the position of the utriculus and of the' membranous semicircular canals is also excentric. The membranous ampullae, on the other hand, certainly appear to be the outlets of the osseous canals, being in con- tact with the periosteum of the bone throughout their whole extent. The membranous canals are applied to the periosteum of the convex side of the osseous canals, though they do not Fig. 301. Fig. 301. Transverse section of an osseous and membranous semi- circular canal from the Goose. ], Superior osseous semicircular canal ; 2, connecting fibres stretching from the periosteum to the membranous semicircular canal ; 3, membranous semicircular canal with epithelial lining ; 4, attachment of the thinner part of the mem- branous semicircular canal to the periosteum. appear to be imbedded in the periosteum in the manner I have described above as occurring in Man. Their free wall is connected with the rest of the periosteum by means of a fine plexus, and in the Rat, as well as especially in Birds, Fishes, and the Anourous Batrachia, it may be demonstrated that the space which bounds the free surface of the membranous semi- circular canals and the utriculus is not enclosed by any serous layer lined by epithelium. In Fishes also the membranous canals are adherent to the HISTOLOGY OF THE MEMBRANOUS LABYRINTH. 93 solid wall. The relatively wide cartilaginous or osseous canal is here partially filled by a plexus of broad fibrous trabecula?, which enclose a system of cavities filled with mucus. The rest of the space is occupied by the membranous canal which is loosely adherent to the wall, and by a fine fibrous plexus that does not essentially differ from the above-mentioned gelatinous tissue in the canals of the human foetus and of the Frog. In his first communications on the Frog, Hasse made the following statement, that he had observed certain markings on the outer surface of the membranous canals in this animal, which gave the impression of the presence of an epithelial investment. But transverse sections made through the mem- branous labyrinth whilst still adherent to the bone show histological relations (especially well marked in the osseous semicircular canals) which thoroughly negative the existence of a serous layer; for if successful sections be examined, we may perceive that the anastomosing connective-tissue cor- puscles which completely fill the canal, and which in the human embryo we have termed gelatinous tissue, are persistent in the Frog. Whether they remain in this condition throughout the whole of life I am unable to say, since my researches have only been made on Frogs at the end of the winter. In the gelatinous tissue in the Frog I find also many large pigment cells, of which a few adhere intimately to the outer side of the membranous canals. A still richer deposit of pig- ment exists in the neighbourhood of the utriculus and of the otolithic sac in the vestibule, so that the point of entrance of the nerves and vessels into the utricular wall is rendered some- what obscure. In regard to the support received by the walls of the membranous labyrinth of the Frog, it is to be remarked that the utriculus, the otolithic sac, the ampullae, and the com- mencement of the membranous canals lie tolerably close to the dense capsule ; but, on the other hand, it cannot be denied that the membranous semicircular canals, where they are most, re- mote from the vestibule, become detached from the wall of the osseous canal, so that they appear to be everywhere surrounded by nucleated finely fibrous connective tissue. Should any one be disposed to regard this as a result of manipulation, he should not forget that the connection between the entire membranous 94 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. labyrinth and the periosteum in the Frog is by no means so intimate as in Birds, Mammals, and Man ; a relation that may possibly be regarded as dependent upon the degree of regressive metamorphosis undergone by the gelatinous tissue. -2. WALL OF THE LABYRINTH. The histology of the wall of the labyrinth is most advan- tageously studied in transverse sections. The semicircular canal, which is oval or transverse in s-ection, appears to be of unequal Fig. 302. Fig. 302. from Man. Transverse section of a membranous semicircular canal 1, Free portion of the wall, with the fibrous layer and connective-tissue corpuscles ; 2, tunica propria ; 3, papillse, with their epithelium ; (4, omitted ;) 5, portion of the wall free from pa- pillae, with a thin layer of the tunica propria ; 6, strongly developed papillse at the boundary of the portion destitute of papillse ; 7, liga- menta labyrinthi canaliculorum. thickness. (See fig. 302.) In the semicircular canals of Man, the thickness of the wall where attached to the bone, exclusive of the periosteum, is 0*016 of a millimeter ; the free wall measures 0'028, and 'at the points where it is fixed by the ligamenta labyrinthi canaliculorum it has a diameter of 0'060 — O'OSO of a millimeter. Four layers of tissue may be distinguished in the wall of the STRUCTURE OF THE WALL OF THE LABYRINTH. 95 semicircular canals. (1) The layer of connective tissue ; (2) the hyaline tunica propria; (3) the papilliform or villus-like pro- cesses, and (4) the epithelium. The outer fibrous layer is composed of connective tissue with numerous nuclei scattered through its substance, which for the most part runs circularly around the canal, and presents no particular marks distinguishing it either from the above- described ligaments, or from the periosteum. Where the canal is in contact with the periosteum, the outer fibrous layer is very thin ; but it becomes thicker where the wall is free and attains its greatest development ; that is to say, at the point where the ligamenta labyrinthi canaliculorum are attached. The large and for the most part rounded nuclei, owing to their mode of arrangement on the outer surface of the free wall of the canal, quite give the appearance of an epithelial investment. The nuclei, however, have a similar disposition in the ligaments of the labyrinth, and on the side of the periosteum ; so that in good imbibition preparations it may be clearly seen that the outer surface of the membranous canals are not really invested by a layer of pavement epithelium.* If an examination be made of the entire semicircular canal which, with the periosteum and the ligaments, has been withdrawn from its natural position, another fibrous plexus comes into view near the vessels, of the nature of which I am still doubtful. The trabeculse of this plexus are pale and moderately broad, and form regularly . arranged meshes. At the nodal points they become much broader, exhibit their fibrous nature more distinctly, and contain large nucleated cells in their substance. At first sight this plexus presents precisely the aspect of nerves with intercalated ganglion cells (fig. 303). Whether they really are nerves or some other kind of tissue, I &m unable at present to state with certainty. It need scarcely be remarked that it would prove of great interest if these turned out to be the nerves of the membranous semi- * According to Schwalbe and F. E. Weber, the space between the membranous and the osseous labyrinth filled with perilymph is a lymph space, since injections into the cavity of the arachnoid penetrate into it through the poms acusticus. 9C THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. circular canals, the existence of which has up to the present time been doubted. In the sacculi the fibrous layer is thin, except where the nerves penetrate the osseous wall. At these points the sacculi are not very intimately connected with the osseous wall (the utriculus, however, more closely than the sacculus rotundus), but are separated from it by a wide-meshed connective tissue enclosing vessels and nerves. Fig. 303. Fig. 303. Fibrous network adjoining the vessels of the semicircular canals of Man, with its cells. The second layer, the vitreous-like tunica propria, likewise varies in thickness. At the attached parts of the membranous canals it appears in transverse sections as a very thin layer, which increases in thickness towards the free portion of the wall, and acquires considerable dimensions at the points of attachment of the ligaments of the labyrinth. In fresh speci- mens it forms a hyaline substance that appears sharply de- fined both externally towards the fibrous layer, and internally towards the papillae. After the application of colouring agents STRUCTURE OF THE WALL OF THE LABYRINTH. 1)7 and other tests, it presents the appearance of a granular slightly striated membrane. It is demonstrable in the utriculus, but is there reduced to an extremely thin uniform layer. The papilliform processes* iagram 01 tue inoue or termination ot the auditory nerve. 1, Cartilage of the wall of the ampulla ; 2, structureless basement membrane ; 3, doubly contoured nerve fibre ; 4, axis-cylin- der traversing the basement membrane ; 5, plexiform union of fine nerve fibres with interspersed nuclei ; 6, fusiform cells with nucleus and dark fibre in their interior ; 7, supporting cells ; 8, auditory hairs. quently observed these appearances in the ampullae of the Cy- prinoids; and the reaction occurring in these fusiform cells on the application of the above-named acid admits only of the inter- pretation that they are nervous structures. These observations are in accordance with the statements very recently made by i 2 116 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. v. Grimm,* who has also observed the black coloration of the fusiform cells of the ampullae of Cats, on the application of perosmic acid. A dark tinting of the nucleus is sometimes ob- servable in the simple columnar cells, but I have never been able to see the dark striae in these. I am still doubtful in regard to the presence of the basal cells resting on the structureless border of the tunica propria described by Max Schultze, as I have been unable to bring them into view in situ in very thin sections. In one instance only in a large Salmon I thought I perceived striae indicating a series of cells resting on the basement membrane. If the whole epithelial layer be detached from the tunica propria, no regular series of cells can be perceived resting upon the basement membrane, nor can several regular series of cells be dis- tinguished in the detached layer of nerve-epithelium. M. Schultze has already made the observation that the basal cells do not occur through the whole extent of the ridge of the crista acustica, but are for the most part situated in the marginal regions. As soon as the fine nerve fibres which it is impossible to dis- tinguish from the isolated axis-cylinders have penetrated into the loose epithelial layer, they form frequent anastomoses, and thus produce a plexus which both at the points of intersection, as well as in the course of the fine fibrils, exhibits numerous enlargements. I have occasionally been able to bring this net- work very clearly into view. The nature of the swellings, however, still remains doubtful ; for I am unable to regard them as ganglion cells, as Reich has done, notwithstanding that many recent observations tend to prove that nucleated enlarge- ments in fine nerve fibres are to be considered as ganglionic elements, as in the case of the granule layers of the retina. Fibres proceed from the fine nervous plexus, which run verti- cally in the epithelium; and, from the results of numerous observations, I believe it may be admitted that the fibres which enter into the fusiform cells represent the continuation of the nerves. And if, on account of their assuming a black tint in perosmic acid, the dark striae and the nucleus of the fusiform cells are to be regarded as nervous structures, we may * Bulletin de V Academic imperial des Sciences de St. Petersbourg. NERVES AND EPITHELIUM OF AMPULLA AND SACCULI. 117 also consider the auditory hairs as gradually attenuating processes of the flask-cells. These run up between the colum- nar epithelial cells by which the latter are supported, occupy- ing the angular interspaces between their borders. It may further be remarked that though the auditory hairs do not become black in perosmic acid, yet they assume a brown tint earlier than any other tissue in the walls of the ampullae. The nerve epithelium of the ampullae and sacculi thus presents a number of columnar supporting cells, between which are spaces and fine canals for the reception of the fusiform nerve cells, which last are to be regarded as bearing the terminal organs of the vestibular nerves. The observations of F. E. Schulze on a transparent fish (Gobius niger ?) may here be mentioned, according to which the primitive nerve fibres are directly continuous with the auditory hairs. The stage of development of the animal from which his drawing was taken is such that the epithelial cells are probably not yet apparent. According to Max Schultze and C. Hasse, stellate and par- tially pigmented cell forms occur in various classes of animals, situated between the simple columnar cells, in the neighbour- hood of the nerve eminence of the crista acustica and of the macula acustica. The details of the special disposition of these cells is to be found in the beautiful treatises of those authors. As regards the auditory hairs, the first observations upon the presence of ciliated epithelium in the membranous labyrinth were made by Ecker, Reich, and Leydig; but the true nature of the auditory hairs was first pointed out by Max Schultze. This observer described them as forming long stiif fibres which, gradually becoming more and more attenuated, are attached by their base to the nerve epithelium, and project into the fluid of the endolymph by their fine-pointed extremities, unless in- deed, as I imagine, their extremity is covered by a peculiarly organised cap. That structure, which was observed and has been depicted by Leydig in the ampullae of the Pigeon, I, with Max Schultze, regard as the detached epithelial investment of the crista acustica and its vicinity. In Fishes and Birds, however, I have observed a delicate structure composed of remarkably fine cells in that tract of the ampulla on which the auditory 118 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. hairs are seated, but into its precise relations I have gained no satisfactory insight. The length of the auditory hairs amounts, according to Max Schultze, in the Ray tribe to 0'04 Prussian lines. They are disposed at definite distances from each other, and undergo Fig. 314. Fig. 314. Longitudinal section of the ampulla of a Bird. 1, Osseous wall ; 2, periosteum ; 3, space between the osseous and membra- nous canal ; 4, roof of the ampulla adjoining the bone ; 5, thicken- ing of the crista acustica ; 6, nerve fibres contained in it ; 7, columnar cells of the floor in the vicinity of the nerve eminence ; 8, line of demarcation between columnar and pavement cells ; 9, pavement epithelium ; 10, transition of the ampulla into the membranous canal. very rapid changes in their form and appearance on the ad- dition of various reagents. I have found the basal portion of the hair, both in Mammals as well as in Fishes and Frogs, even with the most careful manipulation, somewhat thicker than Schultze has described and pictured. NERVES AND EPITHELIUM OF AMPULLA AND SACCULI. 119 A difference in the course of the nerves in the very slightly thickened tunica propria of the macula acustica of the sacculus, as Henle has already pointed out, exists in the circumstance that Fig. 315. Fig. 315. Transverse section of the ampulla of Cyprinus carpio. 1, Roof of the ampulla ; 2, lateral wall of the ampulla ; 3, thickening of the lateral wall corresponding to the planum semilunare ; 4, 5, 6, thickened floor of the ampulla, with the nerves ; 7, nerve epithelium ; 8, columnar cells ; 9, planum semilunare ; 10, the structureless bodies seated upon the epithelium ; 11, pavement epithelium ; 12, cupula terminalis. they do not pursue the same linear course as in the ampullary crest ; in other respects similar histological relations may be observed between the nerve and epithelium as in the ampullae. 120 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. The vesicular structureless bodies which occur both upon the auditory hairs of the crista acustica, as well as closely com- pressed upon the epithelium of the planum senilunare, are particularly striking objects. I have observed them best in specimens of Cyprinus that have been macerated in perosmic acid. They here form an Uneven layer covering the whole extent of the inner surface of the epithelium. (See fig. 315.) In these Fishes the auditory hairs appear sometimes to be held together by a glutinous material, a regularly shaped conical process (cupula terminalis) being observable on the epithelial surface of the ampullary crest (fig. 315), which in some of my preparations occupies more than two-thirds of the ampullary cavity. This is faintly striated, the striae converging from the base towards the apex. The striae, however, do not appear to be present in all parts of the eminence; for if the centre be brought into focus, a finely granular substance comes into view. Occasionally I have thought I have observed a cap upon its apex, composed of delicate cells. Lang has denied the exist- ence of auditory hairs in the Cyprinoids, and in place of them has described the eminence itself as the terminal apparatus of the ampullary crest. I believe I can recognise in this the adherent auditory hairs. This subject is certainly worthy of further investigation. Finally, two parts connected with the sacculus require to be mentioned, namely : — (1) The aquceductus vestibuli. (2) The canalis reuniens. Bb'ttcher has recently directed attention to the former. The process which extends from the posterior surface of the pars petrosa towards the vestibule, and lies in the so-called aquse- ductus vestibuli, has already long been known, and has been described at a remote period as the aqueduct of the vestibule. Bottcher has recognised the existence in this process of an epithelial canal, which is surrounded by nucleated connective tissue, and is lined on its uneven internal surface by vascular (?) tesselated epithelium exhibiting great similarity to the stria vascularis of the cochlear canal. The simple canal lying in the aquseductus terminates at the posterior surface of the pars OTOLITHS. 121 petrosa by a cgecal dilatation, and divides near the sacculus into two hollow ducts, of which one is continuous with the sacculus rotundus, whilst the other joins the utriculus; by this means the cavities of the two sacculi appear to be connected. On making a transverse section of the aquseductus vestibuli I have observed a moderately large convolute of vessels on one portion of its wall, and must therefore support the statement of Hyrtl, that it is destined for the reception of veins. The canalis reuniens is limited to the sacculus rotundus. It was discovered by Hensen, and its existence corroborated by Reichert, Henle, and myself; it is attached to the periosteum, and is distinguished histologically from the wall of the saccu- lus only by the greater delicacy of its structure. This little canal brings the sacculus rotundus into connection with the ductus cochlearis, so that this forms the blind vestibular end of the most important cochlear segment of the labyrinth, just as the utriculus forms the blind vestibular end of the membranous labyrinth. 5. OTOLITHS. The otoliths contained in the albuminous endolymph of the membranous labyrinth present many variations in different animals, in regard to their consistence, size, and form. They adhere tolerably firmly together by means of a clear tenacious substance. In Reptiles and osseous Fishes the delicately formed otoliths attain a considerable size, whilst in Birds, Mammals, and Man they either appear to be amorphous or are crystallized in the form of small rhombs, hexahedra, or octahedra. Oto- liths of various size and form may however be found in the same animal. Three or four otoliths of exceedingly pretty form occur in the osseous Fishes, where they are found both in the sacculi and in the ampullae. In Man and Mammals they form the white spots of the maculse acusticse, and both here and in other animals they are maintained in position by a tenacious gelatinous sub- stance, which Lang has described in the Cyprinoids as a peculiar fenestrated membrane (but which is regarded by Kolliker as a cuticular formation). Deiters and Hasse admit the presence of a fenestrated outi- 122 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. cular formation on the inner surface of the columnar epithelial cells in the otolithic sac of the Frog, by means of which its contact with the otoliths is prevented. I have observed this means of fixation of the otoliths very beautifully in transverse sections through the auditory organ of the Frog. Otoliths are essentially composed of carbonate of lime ; according to Henle, however, after treatment with acids, there is a residue which is composed of organic substances (otolith cartilage). Leydig Fig. 316 Fig. 316. Otoliths of different classes of animals. 1, From the Goat ; 2, from the Herring ; 3, from the Angler Fish ; 4, from the Mackerel ; 5, from Pterois volitans (after Breschet) ; 6, from the Pike ; 7, from Cyprinus carpio ; 8, from the Ray (after Leydig) ; 9, from Scymnus lichia (after Leydig) ; 10, from the Grouse (after Leydig). has observed in the otolith of the Grouse, that, after treatment with bichromate of potash, peculiar lines occur at the two poles, which converge towards the centre (fig. 316, 10). It still remains to be mentioned that in Man and Birds, even when the vestibule is quite uninjured, otoliths may be observed in considerable numbers in the membranous semicircular canals, especially in the horizontal one, and according to Hyrtl in the fluid of the cochlea. In these cases it is impossible to admit ATTACHMENT OF THE STAPES TO THE FENESTRA OVALIS. 123 that they have escaped into the semicircular canals from the utriculus. 6. THE FENESTRA OVALIS, AND ITS CONNECTION WITH THE BASE OF THE STAPES. The majority of authors describe the insertion of the base of the stapes into the fenestra ovalis as being of a very simple nature, whilst I, on the contrary, find that it is rather complicated. That Soemmering* had already noticed this, is evident from his remark, "that the basis of the stapes is attached to the fenestra ovalis by a delicate articular capsule." But it is impossible to determine from this brief expression whether Soemmering meant to indicate by the term articular capsule the existence of a proper joint, or only the presence of a fibrous layer resembling a fibrous articular capsule. Several writers speak of a simple fibrous union, to which they apply the term Ligamentum orbiculare baseos stapedis. It was reserved for the active Englishman, Toy nbee, to furnish an exact description of the mode of connection of the base of the stapes with the fenestra ovalis. The difference in form between the anterior and the poste- rior border of the base of the stapes, which in a physiological point of view is certainly of importance, was first noticed by Toy nbee, f by whom also the hyaline cartilage between the fenestra ovalis and the base of the stapes was first described. If in a successful horizontal section the anterior extremity of the base of the stapes be compared with the posterior, it is ob- servable that besides the thickening which exists at these spots, the moderately broad posterior surface of contact forms almost a right angle with the vestibular surface of the base of the stapes, and that the base towards the posterior limb of the stapes runs off into a kind of process (fig. 317). The surface of contact at the anterior margin of the base is somewhat narrower than at the posterior, and forms an acute angle with its vestibular surface, so that the whole anterior extremity which projects beyond the corresponding limb appears somewhat longer than the * VomBau des menschlichen Korpers. Frankfort, 1796. Theil ii., p. 12. t British and Foreign Medico-C'hiruryical Hevieu; 1853. 124 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. posterior ; and it is very conceivable that, owing to the obliquity of the surfaces, and the greater length of the anterior margin of the base of the stapes, a certain amount of resistance is opposed to the action of the voluntary musculus stapedius. The above-mentioned moderately thick borders of the base of the stapes are invested by a lamella of hyaline cartilage, Fig. 317. Fig. 317. Horizontal transverse section through the base of the stapes at its insertion into the posterior border of the fenestra ovalis. 1, Bony margin of the base, with its investment of hyaline cartilage ; 3, thin osseous lamella of the basis ; 4, angle between the crus of the stapes and the projecting border of the base ; 5, posterior border of the fenestra ovalis, with its investment of hyaline cartilage ; 6, car- tilage on the vestibular surface of the base, with its perichondrium ; 7, ligamentum baseos stapedis vestibulare ; 8, Ligamentum baseos stapedis tympanicum ; 9, layer of elastic fibres ; 10, spaces between the fibres ; 11, osseous trabeculse ; 12 and 13, musculus fixator baseos lis. which varies in thickness from O012 — 0*024 of a millimeter. The hyaline cartilage dips into the inequalities of the bone, in order that here, as in other osseous junctions of the body, the opposite surfaces may be uniformly applied to each other. It is not, however, the anterior and posterior borders of the base of the stapes that are alone invested with cartilage, but a layer of this substance covers the whole vestibular surface of the stapes- ATTACHMENT OF THE STAPES TO THE FENESTRA OVALIS. 125 The cartilage at the last-named part is invested by nucleated fibrous tissue, constituting the perichondrium, which is con- tinuous with the lining membrane of the vestibule. The homogeneous matrix of the cartilage is distinguished from the adjoining osseous tissue by its yellowish tint, and in tinted specimens the rounded cartilage cells are brought clearly into view in consequence of the intense colour of their nuclei, as compared with the colourless matrix. The cartilage cells undergo a change in form near the centre of the vestibular surface of the base of the stapes, be- coming elongated, with their longest diameter running from before backwards. The margin of the fenestra ovalis also possesses a cartilagi- nous investment. The thickness of this at the posterior border is equal to that covering the opposite surface of the base of the stapes : anteriorly it measures from 0'040 to 0*048 of a milli- meter. The cartilage terminates more abruptly towards the tympanic cavity than in the vestibule, where it reaches beyond the margin of the fenestra ovalis, and becoming thinner extends for some distance upon the surface of the vestibule. A layer essentially composed of elastic tissue, and equal in thickness to the hyaline cartilage, is continuous with this both at the fenestra ovalis and at the border of the base of the stapes ; the layer is of very close texture, and it becomes very conspicuous in macerated specimens, in consequence of strongly imbibing the colouring material. The fibres run from one car- tilage towards the other, and at the point where the opposite sets meet a system of lacunae is formed by their plexiform inter communication, which is filled with fluid. Towards both the vestibule and the tympanic cavity this dense elastic tissue extends from the one cartilage to the other, forming a ligamen- tum orbiculare baseos stapedis vestibulare, and in the tympanic cavity a weaker ligamentum orbiculare baseos stapedis tym- panicum. The latter is continuous with the mucous membrane of the tympanic cavity, without however being so sharply defined at its circumference, as is shown in fig. 318. At the upper and lower borders of the base of the stapes the nature of the connection chaiges in consequence of the uniformly thick circumference of the base being bevelled off 126 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. towards the tympanic cavity, so that the surfaces of contact are somewhat smaller than at the already described anterior and posterior extremities. A cartilaginous investment is, however, here also present, which augments in thickness to some extent towards the middle of the vestibular surface of the basis. The connection with the cartilaginous investment of the margin of the fenestra ovalis is established by means of a layer of Fig. 318. Fig. 318. Horizontal section through the anterior margin of the base of the stapes at its attachment to the fenestra ovalis. 1, acute angle made by the margin of the basis with the cartilage ; 2, base of the stapes ; 3, anterior crus ; 4, margin of the fenestra ovalis invested by hyaline cartilage ; 5, ligamentum baseos stapedis tympanicum ; 6, ligamentum baseos stapedis vestibulare ; 7, elastic fibrous layer of the fenestra ovalis ; 8, the same at the base of the stapes ; 9, lacunar system in the centre of the fibrous layer. The two ligaments at the base of the stapes are not so sharply defined in the preparations themselves as in the figure. elastic fibres, in the middle of which intercommunicating spaces occur, though more sparingly than in that of the anterior and posterior margin. The articulation of the stapes with the fenestra ovalis is consequently neither a pure syndesmosis nor a synch ondrosis, but constitutes a mode of connection that, if rightly placed in the category of the other joints, would be included in the am- phiarthroses, from which it differs only in the circumstance ATTACHMENT OF THE STAPES TO THE FEXESTRA OVALIS. 127 that there are a large number of intercommunicating cavities, whilst in the amphiarthroses generally there is only a single irregularly shaped cavity. If we altogether disregard mere nomenclature, it appears from our description that the base of the stapes is attached to, or inserted into, the fenestra ovalis in quite a peculiar manner, a fact which indeed Hel.mholtz has established experimentally. This observer has demonstrated that the mobility of the base of the stapes is very small, the greatest excursion it can make not exceeding 1-lSth to l-24th of a millimeter. According to the ear- lier accounts of the mode of attachment of the base of the stapes with the fenestra ovalis, a considerable degree of mobility occurs between them. All the diameters of the osseous fenestra ovalis are, however, so far diminished by the elastic cushion of the hyaline cartilage that the base of the stapes, which is also covered with cartilage, is received into it, and but little room for movement consequently remains. I have still to call atten- tion to a structure on the tympanic surface of the base of the stapes, which, from the observations I have hitherto made, I must regard as a muscle of vegetative life — the musculus fixator baseos stapedis. At about the distance of a millimeter from the fenestra ovalis, a narrow crest of bone, with a transverse diameter of about O'OSO of a millimeter, springs from the posterior and inferior border of the base of the stapes, and projects into the tympanic cavity. In surface views this appears in the form of a low sinuous elevation which terminates with a blunt point that is opposite the projecting border of the base of the stapes. Its importance is only recognizable in transverse sections. The mucous membrane presents the same relation to this crest of bone as to the others that project into the tympanic cavity. Forming a direct continuation of this ridge is a yellowish dense tissue, which is attached to the angle between the crus of the base of the stapes and the somewhat everted part of the base. This tissue is connected and continuous, however, not only with the bone, but also with the cartilaginous invest- ment (fig. 317). In macerated transverse sections which have been subjected to imbibition, long coloured stride are visible, which, in isolated 128 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. specimens, appear in the form of fusiform cells, and which I at present regard as contractile fibre cells. This fixator baseos stapedis is confined not only to the posterior extremity of the base of the stapes, where it is thickest, but it is continued towards the upper border, and the direction of its action is consequently antagonistic to the volun- tary musculus stapedius ; for it fixes the basis at that part which is pressed towards the vestibule by the unilateral action of the musculus stapedius. LITERATURE. SCARPA, A., Anatomicae disquisitiones de auditu et olfactu. Ticini, 1789. E. H. WEBER, De aure et auditu hominis et animalium. Lipsiae, 1820. BRESCHET, G., Recherches anatomiques et physiologiques sur 1'organ del'ouie des Poissons. (Anatomical and physiological researches on the organ of hearing in Fishes.) Paris, 1838. STEIFENSAND, KARL, Untersuchungen iiber die Ampullen des Gehoror- ganes. (Researches on the ampullae of the auditory organ.) MULLER'S Archiv fiir Anatomic und Physiologic. 1835. Seite 171. ECKER, A., Ueber Flimmerbewegung im Gehororgan von Petromyzon marinus. (On ciliary motion in the auditory organ of Petromy- zon marinus.) MULLER'S Archiv fiir Anatomic und Physiologic. 1844. HYRTL, Vergleichend anatomische Untersuchungen iiber das innere Gehororgan. (Comparative anatomical researches on the internal ear.) Prag, 1845. REICH, H., Ueber den feineren Bau des Gehororganes von Petromyzon und Ammocoetes. (On the minute anatomy of the auditory organ of Petromyzon and Ammocoetes.) In ECKER'S Unter- suchungen zur Ichthyologie. 1857. LEYDIG, F., Lehrbuch der Histologie des Menschen und der Thiere. 1857. M. SCHULTZE, Ueber die Endigungsweise des Hornerven im Labyrinth. (On the mode of termination of the auditory nerve in the laby- rinth.) J. MULLER'S Archiv fiir Anatomie und Physiologic. 1858. REICHERT, Beitrag zur feineren Anatomie der Gehorschnecke. (Essay on the minute anatomy of the cochlea.) Berlin, 1864. BIBLIOGRAPHY OF THE MEMBRANOUS LABYRINTH. 120 VOLTOLINI, VIRCHOW'S Archiv fiir pathologische Anatomie, Bande xxii., xxvii., und xxxi. RUDINGER, Ueber das runde Sackchen. (On the sacculus rotundus.) Sitzungsberichte der k. k. Academie der Wissensch. zu Miinchen, Jahrgang 1863, Bd. ii., p. 55. , Ueber die Zotten in den hautigen halbc. Canalen. (On the villi in the membranous semicircular canals.) Archiv fiir Ohren- heilkunde, Bd. ii. , Ueber das hautige Labyrinth im menschlichen Ohre. (On the membranous labyrinth in the ear of Man.) Aerztliches In- telligenzblatt. Juni, 1866. , Vergleichend anatornische Studien iiber das hautige Laby- rinth. (Comparative anatomical researches on the membranous labyrinth.) Monatsschrift fiir Ohrenheilkunde, No. 2. 1867. KOLLIKER, A., Handbuch der Gewebelehre des Menschen. 1867. LUCAE, A., Ueber eigenthiimliche Gebilde in den hautigen Canalen. (On some peculiar structures in the membranous canals.) VIR- CHOW'S Archiv, Bd. xxxv. DEITERS, 0., Ueber das innere Gehororgan der Amphibien. (On the internal ear of Amphibia.) Archiv fiir Anatomie und Physiologie, von REICHERT und E. DU BOIS-REYMOND. 1862. SCHULZE, FRANZ EILHARD, Zur Kenntniss der Endigungsweise des Hornerven bei Fischen und Amphibien. (On the mode of termi- nation of the auditory nerves in Fishes and Amphibia.) Archiv fiir Anatomie und Physiologie, von REICHERT und DU BOIS-REYMOND. 1862. HARTMAXN, R., Die Endigungsweise des Gehornerven im Labyrinthe d3r Knochenfische. (The mode of termination of the auditory nerves in the labyrinth of the osseous Fishes.) Ebenda, 1862. LANG, GUSTAV, Das Gehororgan der Cyprinoiden, mit besonderer Beriicksichtigung der Nervenendapparate. (The auditory organ of the Cyprinoid Fishes, with special reference to the mode of termination of the nerves.) v. SIEBOLD und KOLLIKER' s Zeitschrift fiir wiss. Zoologie. 1863. HENSEN, V., Studien iiber das Gehororgan der Decapoden. (Re- searches on the auditory organ of the Decapod Crustaceans.) v. SIEBOLD und KOLLIKER' s Zeitschiift fiir wissensch. Zoologie. 1863. Qw^ HENLE, Allgemeine Anatomie. Leipzig, 1841. , Handbuch der systematischen Anatomie. 1866. ODEMUS, M. V., Ueber das Epithel der Maculae acusticae beim Men- VOL. III. K -C 130 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. schen. (On the epithelium of the maculae acusticae in Man.) Archiv fur mikroskopische Anatomie. 1867. HASSE, C., Der Bogenapparat der Vogel. (The semicircular-canal apparatus of the Bird.) v. SIEBOLD und KOLLIKER'S Zeitschr. fiir wissensch. Zoologie. Bd. xvii., Heft iv. — , Bemerkungen iiber das Gehororgan der Fische, der Frosche, und die Histologie des Steinsackes der Frosche. (Remarks on the auditory organ of the Fish and the Frog, with the histology of the otolithic sac of the Frog.) Zeitschr. fiir wissench. Zoo- logie, Bd. xviii. v. GRIMM, 0., Der Bogenapparat der Katze. (The semicircular canal apparatus of the Cat.) Bulletin de 1'academie imperiale des Sciences de St. Petersbourg. 1869. BOTTCHER, Ueber den Aquaeductus vestibuli. (On the aquaeductus vestibuli.) Du BOIS-REYMOND und REICHERT'S Archiv. 1869. IV. THE AUDITORY NERVE AND COCHLEA. BY W. WALDEYER. GENERAL VIEW OF THEIR COMPARATIVE ANATOMY AND DEVELOPMENT. WHILST the auditory apparatus treated of in the preceding chapter — the ssmicircular canals and utriculus — already attain their complete development in the majority of Fishes, the second division of the membranous auditory labyrinth — the cochlear apparatus — is essentially developed as a constituent of the organ of hearing in the higher classes of animals. The cochlear apparatus includes the sacculus, the histological characters of which are analogous to those of the utriculus (see the preceding chapter), and a csecal prolongation of the sacculus — the ductus cochlearis. The first trace of a ductus cochlearis is exhibited by the os- se >us Fishes, in which, according to the excellent description of Hasse (25), a small projection of the sacculus (fig. 319, 1 0), called by Breschet (5) the cysticula, is to be regarded a.s the rudiment of the cochlea. Amongst Amphibia, several portions of the sacculus can be distinguished as belonging to the cochlea, though, with the exception of a small and more independent projection which corresponds to the cysticula of the Fish and the lagena of the Bird, they scarcely rise above the level of the wall of the sac- culus (otolith sac), and rather resemble thickenings of the saccular walls provided with peculiar nerve ends (Deiters, 15; Hasse, 24). The cochlear apparatus of Reptiles and Birds is still further developed. In Reptiles, the several divisions of the K 2 132 THE AUDITORY NERVE AND COCHLEA, BY W. WALDEYER, cochlea appear in the form of a cone projecting beyond the plane of the sacculus, especially well marked in the Crocodile, which most nearly approximates Birds. In the latter, as Hasse (68) has shown to be probable, the sacculus and utri- culus are fused into an alveus communis (fig. 319 II., US. Fig. 319. Fig. 319. Three diagrams to show the relations of the auditory labyrinth in the Vertebrate series. I. Type of the labyrinth in the Fish. U, Utriculus with the semi- circular canals ; S, sacculus ; C, cysticula ; E, aquseductus vestibuli. II. Type of the labyrinth in the Bird. US, alveus communis ; C, cochlea ; UC, commencement of the cochlea ; L, lagena ; Or, canalis reuniens ; E, aquseductus vestibuli. III. Type of the labyrinth in the Mammal. U, S, Or, as before ; E, aquseductus vestibuli, dividing into two crura for the utriculus and the sacculus ; C, ductus cochlearis, with F, the caecal pouch of the vestibule, and K, the csecal sac of the cupola. The cochlear passage (C) is considerably elongated, and several divisions or segments may be distinguished in it, as the commencement or cochlea proper (U(T) and the flask-shaped terminal segment or lagena (L) of Windischmann. Here is seen also the first indication of a spiral course in the cochlear canal. The communication of the latter with the alveus is effected by a narrow passage, the canalis reuniens of Hensen, which, cording to the observations of Hasse, appears frequently to VIEW OF THEIR ANATOMY AND DEVELOPMENT. 133 undergo obliteration in adult Birds. I have myself frequently found only a narrow tube at this point. Fig. 319 III. represents the type of the labyrinth in Mam- mals ; here the semicircular canals and the cochlear portion communicate with one another only through the intermedia- tion of the aquceductus. vestibuli (R) (Bottcher, 3). See the preceding chapter. The ductus cochlearis ((7) has undergone extraordinary development, and forms the principal part of the labyrinth ; as is already seen in Birds, it has become entirely distinct from the sacculus, and is only in connection with it by the narrow canalis reuniens (Cr). The canalis reunions pro- ceeds from the wall of the ductus — the membrana Reissneri (see below) ; it opens into the cochlear passage almost at a right angle, so that a small caeca! sac exists beyond its point of at- tachment— the vestibular caecal sac (F) (Reich ert). The other end of the duct likewise terminates blindly, forming the ccecal sac of the cupola (K) (Reichert). The canalis reuniens and the two csecal sacs are lined by a short columnar epithelium, and receive no fibres from the auditory nerve. The cochlear canal, which here properly answers to its name, is wound spi- rally around a bony axis, the modiolus. The number of turns varies in different animals from one and a half to five. They sometimes lie nearly in one plane, like the shell of the Planorbis (Cetacea); sometimes, on the other hand, they may coil steeply around the modiolus, as in Clausilia (Guinea-pigs) ; we may thus have flat and steep coiled cochleae. Whilst I refer to the preceding chapter for an account of the sacculus, I consider it to be advantageous in regard to the somewhat complicated structure of the cochlea to precede its histological description by,a short account of the bony cap- sale and of the position of the ductus cochlearis, together with a sketch of its development. I shall commence with the cochlea of Mammals and of Man. A median section carried through the axis of the human cochlea, as in fig. 320, exhibits a tubular canal imbedded in the hard mass of the temporal bone, which, constantly becoming narrower, runs spirally to the apex of an also gradually attenu- ating axis, and terminates by a blind extremity in the so-called cupola. This canal is traversed throughout its whole length by 134 THE AUDITORY NERVE AND COCHLEA, BY W. WALDEYER. a partly osseous and partly cartilaginous septum, the lamina spi- ralis, which divides externally into two laminae that pass to the osseous walls of the cochlea, and enclose the ductus coch- learis between them (fig. 320, L Sp). In this way the osseous canal of the cochleais divided by the ductus cochlearis and its two attachments — the osseous at the modiolus, and the membranous towards the outer wall — into two chambers, the scala tympani (ST), and the Scala vestibuli ($F), which only communicate with one another at the cupola of the cochlea by a fine aperture, the helicotrema of Breschet. The scala tympani terminates crecally, being cut off by the membrane of the fenestra rotunda from the tympanic cavity; the scala vestibuli communicates directly with the perilymphatic space of the vestibular sac- culus. The situation of the ductus cochlearis in the cochlear mass corresponds therefore to the semicircular canals and sac- culi in the other part of the labyrinth (see the preceding chapter). Like these, it is attached excentrically to the exter- nal wall of the canal, and indeed by its opposite sides. The median lamina of attachment, (with reference to the axis,) which at the same time supports the nerves, is here very much elongated and ossified (lamina spiralis ossea) ; the lateral lamina of adhesion, which especially supports the vessels (fig. 320, the connective tissue between h and b ; figs. 321 and 322, e e), forms a thick cushion of connective tissue, which is semi- lunar on section (ligamentum spirale, Kolliker). See below. The ductus cochlearis (fig. 320, e— e4; figs. 321 and 322, D (7) forms in adults a tubular cavity, which is triangular in section, and is enclosed by a connective-tissue membrana propria ; towards the tympanum it is bounded by the membrana basilaris (f L sp\ which is continuous with the crista spiralis (E — Or, figs. 321 and 322), in the sulcus spiralis internus (S. sp. i), (the entire tympanal wall is included between the letters E and L sp,) towards the vestibule, by the mem- brane of Eeissner (f f, fig. 320; E Rlt fig. 321); laterally it is bounded by a vascular layer of connective tissue, which is continuous with the periosteum .of the cochlea by means of the above-mentioned semilunar cushion of connective tissue (e e, figs. 321 and 322). Towards the inner side the membrana Reissneri and crista spiralis join at a more or less acute angle. VIEW OF THEIR ANATOMY AND DEVELOPMENT. 135 Fig. 320. Fig 320. Section of the cochlea in a human embryo of four months, magnified thirty diameters, a a a, Cartilaginous capsule of the cochlea ; 66, perichondrium ; c, mucous-tissue matrix of the modiolus ; dd, cartilaginous septa of the several turns of the cochlea ; e — «4, sections of the ductus cochlearis ; //,, membrane of Reissner ; g, meni- brana tectoria, slightly separated from the subjacent tissue ; A, rudi- ment of stria vascularis ; i, rudiment of the later appearing organ of 136 THE AUDITOKY NERVE AND COCHLEA, BY W. WALDEYER. In the subsequent pages we shall call the surface looking towards the modiolus of the cochlea the "internal" (mesial), and that turned to the external wall of the osseous cochlear canal as the " external " (lateral). Everything that runs in the direction from the axis to the external wall, we name "radial," and, on the contrary, everything follow- ing the course of the cochlear walls, " spiral " (Henle). Lastly, those surfaces which are turned towards the vestihular scala, or towards the tympanal scala, are termed " vestibular " or " tympanic." * Touching the development of the cochlea, to which I can here only devote a few remarks, it may be stated, that in human embryoes of from eight to ten weeks of age, three several textural constituents are distinctly visible in the region of what subsequently undergoes development into the pars petrosa of the temporal bone ; externally is a cartilaginous mass, which is at this period continuous with the rest of the cartilaginous basis cranii ; next, enclosed by the cartilage, is a large spheroidal mass of embryonal mucous tissue, within which, again, the epithelial labyrinth-vesicle is imbedded. From the -same part of the latter that subsequently corre- sponds to the sacculus, a hollow epithelial projection is thrust out, even before the eighth week, which, gradually becoming wider, penetrates into the mucous tissue, and, owing to the presence of the surrounding denser capsule, is compelled to wind spirally in its soft bed. At one point the cartilaginous capsule is incomplete, and here the.ramus cochlearis of the auditory nerve enters. Human embryoes of three months exhibit the hollow epithelial projection, and the rudiment of the ductus cochlearis, with its several coils. In embryoes of Corti ; L sp, lamina spiralis ; Gfl, Gh, ganglion spirale with various afferent and efferent nerve fasciculi ; ST, scala tympani ; SV, scala vestibuli ; ST1, SP}, ST^, mucous tissue of the subsequently forming scales in the last turn of the cochlea. * There is scarcely any region of the body so small in extent as that of the cochlea which possesses so rich and complicated a nomenclature. The confusion is not diminished by the practice, little worthy of com- mendation, but adopted by many authors who have given a fresh descrip- tion of long-known structures, of inventing a series of new names. Perhaps the terms now employed may not appear to be inappropriate to my fellow-workers. Scarcely any new ones have been added, whilst many superfluous and duplicate terms have been simplified. VIEW OF THEIR ANATOMY AND DEVELOPMENT. 137 four months, the development of the scalse commences; as well as of the parts contained in the duct (fig. 320). The former originate in the retreat (Verfliissigung) of the mucous tissue, to the two sides of the ductus cochlearis (see fig. 320, where this tissue still remains in the last coil), whilst, in order to form a septum between the two coils, it undergoes ossification, the cartilaginous capsule however, participating to some extent in the process (fig. 320, d). Moreover a cord proceeding from the duct, and extending to the axis of mucous tissue, remains persistent, in which at a very early period the fibres and ganglion cells of the auditory nerve are visible (L sp and Gl in fig, 320). This cord partly ossifies near the axis, forming the lamina spiralis ossea, and always continues to be fused in a peculiar manner with the fibrous menibrana propria of the canal, which is already capable of being demonstrated as a special layer. The membrana propria is developed in exactly the same manner out of the mucous tissue around the ingrowing epithelial tube, as is the theca of the Graafian follicle, or the fibrous wall of t*he utriculus and semicircular canals. We find here a recurrence of the same process as that stated by His (69) to occur in the develop- .ment of epithelial masses in a matrix of connective tissue. The epithelial structures appear to exert a formative stimulus upon the fibrous investment, resulting in an abundant cell proliferation immediately around the epithelial tube, from which at a subsequent period the membranse proprise of the originally naked epithelial masses are developed. We learn these facts, especially in reference to the ductus cochlearis, from the illustrations of E. Rosenberg (49), the correctness of whose fig. 1, in plate ii., I can entirely confirm. Ultimately the mucous-tissue axis of the cochlea, in which the nerve fibres are imbedded, also ossifies. In all the ossified parts remains of the mucous tissue persist in the form of a delicate periosteum. A proper perichondrium is indeed visible at an early period on the inner wall of the cochlear capsule, and with this the remains of the mucous tissue of the scalse subse- quently coalesce. The epithelium of the ductus cochlearis (fig. 320, e — 220 Narrowest point. Can. reun., thickness of the walls . J5 15 2. Lamina spiralis mem- branacea, total length in two adult men . . WALDEYER (28 or (31 Mm. fin the neighbour- •< hood of the organ (of Corti. 3. Ductus cochlearis, width from the com- mencement of the crista spiralis to the lig. spirale, 1st turn . j) 800 700 360—400 2nd turn . ,, 700 700 350 4. Ductus cochlearis, greatest height, 1st turn . »j 500 400 -450 400 2nd turn. 500 350 260 5. Length of the Reiss- uerian Membrane, 1st turn . ji 900 2nd turn . ,, 700 • 6. Width of crista spira- lis . . . 1st turn . n 300 150 140—150 2nd turn . ,, 200—250 7. Length of the auditory teeth .... HENLE 30 Breadth 12 8. Sulcus spiralis inter- » nus, greatest height . WALDEYER 60—70 60—70 100—120 194 THE AUDITOEY NERVE AND COCHLEA, BY W. WALDEYER. Name of the part. Observer. Man. Dog. Vesperugo. Remarks. 9. Distance between the basis of the pillars of WALDEYER 66—70 80—90 40 In hardened sec- Corti tions between the 10. Height of the arches „ 12 40 21—24 ^Ist & 2nd turn. at centre 11. Length of the inter- nal pillars measured /"Sections measured on their dorsal surface in hardened speci- from the foot to the 50 60—70 45 ' meus. The acces- apex of the arch . . 12. Length of the outer | sory lamina is com- pletely omitted in pillars taken in the 55 60—66 90 50 \this measurement. same manner . . . 13. Thickness of the ^From the new- bodies of the pillars, 55 4-5 90 50 born child ; the inner . 55 3 90 50 length is to a cer- outer . tain extent ap- 14. Cell bodies of the in- 5J 18 90 50 proximatively ner hair cells, length . 55 6—9 90 50 given, since the breadth . determination of the point of at- tachment of the 15. External hair cells, ^process is arbitrary total length with basilar process . . breadth . 55 J5 55 48 6—7 4 45 6—7,5 ( The process is \ about half the (length. 16. Length of the cilia . 1 K. 17. Phalanges, average 55 10 length 18. Rings,average diame- 55 6 ter 19. Epithelium of the membrane of Reiss- 55 9 ner, thickness . . . 20. Thickness of the epithelium in the 55 15 sulcus spiralis ext. . 21. Greatest (radial) breadth of the mem- 55 200—230 brana tectoria . . . 55 50 Greatest thickness-' . 22. Nuclei of the granule 55 3-5—4-5 cells K6LLIKER WALDEYER 24—35 3,000 / In the first turn there are about \ 110 to one milli- 23. Ganglion cells of the ganglion spirale . . 24. Number of the fora- mina nervina . . . 25. Number of the in- ternal pillars . . . 55 6,000 meter ; at the \hamulus about 80. 26. Number of the ex- ternal pillars . . . 55 4,500 27. Number of the in- ternal hair cells . . 28. Number of the ex- ternal hair cells 55 5> 3,300 18,000 (In each row 4,500, •I as many as there (are external pillars BIBLIOGRAPHY. 195 RECENT LITERATURE. 1. BOTTCHER, Observationes microscopicae de ratione qua nervus cochleae mammalium terminatur. Dorpati Liv., 1856. Dissert. 2. , Weitere Beitrage zur Anatomie der Schnecke. (Additional observations on the anatomy of the cochlea.) VIRCHOW'S Arch, fur patholog. Anat., Bd. xvii^'p. 243. 1859. 3. - — , Ueber den aquaeductus vestibuli bei Katzen und Menschen. (On the aquasductus vestibuli in Cats and Man.) REICHERT und Du BOIS-REYMOND'S Archiv, p. 372. 1869. Bottcher in this communication refers to a larger work upon the cochlea, which will appear in the 35th volume of the Trans- actions of the kaiserl. Leopoldino-Carol. Akademie. 4. — — , Bau und Entwickelung der Schnecke. (Structure and de- velopment of the cochlea.) Petersburger medic. Zeitschr. Bd. xiv., p. 60. Known to- the author only from the reference made by Schweigger-Seidel in the Jahresberichte von VIR- CHOW und HiRscnr p. 40. Berlinr 1869. 5. BRESCHET, Recherches sur Forgane de 1'ouie dans 1'Homme et les animaux vertebres. (Researches on the organ of hearing in Man and Vertebrate animals.) Paris, 1840. 2ieme edit. 6. CLAUDIUS, M. , Bemerkungen iiber den Bau der hautigen Spiralleiste der Schnecke. (Remarks on the structure of the mem- branous spiral band of the cochlea.) v. SIEBOLD und KOL- LIKER'S Zeitschr. fur wissensch. Zoologie, Bd. vii., p. 154. 1856. 7. .-, Physiologische Bemerkungen iiber das Gehororgan der Ce- taceen und das Labyrinth der Saugethiere. (Physiological remarks on the auditory organ of C'etacea, and the labyrinth of Mammals.) Kiel, 1858. 8. 8. , Das Gehorlabyrinth von Dinotherium giganteum nebst Be- merkungen iiber den "Werth der Labyrinthformen fiir die Systematik der Saugethiere. (The auditory labyrinth of Dinotherium giganteum, with remarks on the taxonomic value of the different forms of the labyrinth in Mammals.) Cassel, 1864. 4to. 9. , Das Gehororgan von Rhytina Stelleri. (The auditory or- gan of Rhytina Stelleri.) Memoires de 1'Acad. imper. des Scienc. de St. Petersbourg, Ser. vii., T. xi., Nro. 5. St. Petersbourg, 1867. o 3 196 THE AUDITORY NERVE AND COCHLEA, BY W. WALDEYER. 10. CORTI, A., Recherches sur 1'organe de 1'ou'ie des Mammiferes. (Researches on the organ of hearing in Mammals.) Premiere partie. Liinacon. v. SIEBOLD und KOLLIKER'S Zeitschr. fiir wissensch. Zoologie, Bd. iv., p. 109. 1851. 11. CZERMAK, Verastelungen der Primitivfasern des N. acusticus. (Ramifications of the primitive fibres of the auditory nerve.) Ibid., Bd. ii., p. 105. 1850. 12. DEITERS, Beitrage zur Kenntniss der Lamina spiralis membranacea der Schnecke. (Essays on the lamina spiralis membranacea of the cochlea.) Ibid., Bd. x., p. 1. 1860. 13. - — , Untersuchungen iiber die Lamina spiralis membranacea, etc. (Remarks on the lamina spiralis membranacea.) Bonn, 1860. 8. 14. , Untersuchungen iiber die Schnecke der Vogel. (Remarks on the cochlea of Birds.) REICHERT und Du Bois- REYMOND'S Archiv, p. 409. 1860. 15. - — , Ueber das innere Gehororgan der Amphibien. (On the internal ear of Amphibia.) Ibid., p. 277. 1862. 16. , Untersuchungen iiber das Gehirn und Riickenmark. (Re- searches on the brain and spinal cord.) Herausgegeben von MAX SCHULTZE. Braunschweig, 1865. 8vo. (N. acusticus.) 17. HARLESS, Artikel "Htiren" in R. WAGNER'S Handworterbuche der Physiologie, Bd. iv., p. 811. 1853. 18. HASSE, De cochlea avium. Dissert, inaug. Kiliae, 1866. 4to. 19. - — , Die Endigungsweise des N. acusticus im Gehororgane der Vogel. (The mode of termination of the auditory nerve in the ear of the Bird.) Gottinger Nachrichten, 1867. Nro. 11. 20. - — , Die Schnecke der Vogel. (The cochlea of the Bird'.) Von SIEBOLD und KOLLIKER'S Zeitschrift fiir wissench. Zoologie, Bd. xvii., p. 56. 1867, 21. , Beitrage zur Entwickelung der Gewebe der hautigen Vogel- schnecke. (Essays on the development of the tissue of the membranous cochlea of the Bird.) Ibid., p. 381. 22. , Nachtriige zur Anatoniie der Vogelschnecke. (Essays on the anatomy of the cochlea of the Bird.) Ibid., p. 461. 23. , Zur Histologie des Bogenapparates und des Steinsackes der Frosche. (On the histology of the semicircular canals and of the otolithic sac of the Frog.) Ibid., Bd. xviii., p. 72. 1868. 24. - — , Das Gehororgan der Frosche. (The auditory organ of the Frog.) Ibid., p. 359. BIBLIOGRAPHY. 197 25. HASSE, Bemerkungen liber das Gehororgan der Fische. (Re- marks on the ear of Fishes.) Verhandl. der physikalisch- medic. Gesellsch. in Wiirzburg. Neue Folge. Bd. i., Hft. 2, p. 92. 1868. 26. HENLE, Eingeweidelehre, p. 762 et seq. Braunschweig, 1866. 27. HENSEN, Zur Morphologic der Schnecke des Menschen und der Saugethiere. (The morphology of the cochlea of Man and Mammals.) V. SIEBOLD und KOLLIKER'S Zeitschr. f. wis- sench. Zoologie, Bd. xiii., p. 481. 1863. 28. HUSCHKE : FRORIEP'S Notizen, 1832. — Isis, 1833. — SOEMMERING'S Anatomie, "Eingeweidelehre." 29. HYRTL, Ueber das innere Gehororgan des Menschen und der Saugethiere. (The internal ear of Man and Mammals.) Prag, 1845. 30. KOLLIKER, Handbuch der Gewebelehre. 5th Edition, p. 714. Leipzig, 1867. 31. , Mikroskopische Anatomie, Bd. ii., p. 743. Leipzig, 1854. 32. - — , Zeitschr. fiir wissench. Zoologie, Bd. i., p. 55. 1849. (Musculus cochlearis.) 33. - — , Ueber die letzten Endigungen des N. cochleae. (The ulti- mate terminations of the nerve of the cochlea.) Gratula- tionsschrift an TIEDEMANN. Wiirzburg, 1854. 34. , Der embryonale Schneckenkanal und siene Beziehung zu den Theilen der fertigen Cochlea. (The embryonal coch- lear canal, and the relations of its parts to the perfect cochlea.) Wiirzburger naturwissench. Zeitschr., Bd. ii., p. 1. 1861. 35. LAN.G, G., Ueber das Gehororgan der Cyprinoiden. (The ear of the Cyprinoid Fish.) v. SIEBOLD und KOLLIKER'S Zeitschr. fiir wissenschaftl. Zoologie, Bd. xiii. 1863. 36. LEYDIG, Lehrbuch der Histologie, p. 262. Frankfurt- a- M., 1857. 37. LOWENBERG, Etudes sur les membranes et les canaux du limacon. (Researches on the membranes and canals of the cochlea.) Gaz. hebdom. Nro. 42, p. 694. 1864. 38. , Beitrage zur Anatomie der Schnecke. (Essays on the anatomy of the cochlea.) Arch. f. Ohrenheilk., Bd i., p. 175. 39. , La lame spirale du lirnagon de 1'oreille de 1'Homrae et des Mammiferes. (The lamina spiralis of the cochlea of Man and Mammals.) Paris, Bailliere, 1867. 8. et : Journal de 1' Anatomie et de la Physiologic par M. Ch. ROBIN, 1867 et 1868, p. 626. (Nos. 37 — 39 form a continuous series.) 40. MIDDENDORP, Het vliezig slakkenhuis in zijne woerding en in den <*r~ l ^ ' 198 THE AUDITORY NERVE AND COCHLEA, BY W. WALDEYER. ontwikkelden Toestand. Groeningen, 1867. 4. Three plates. (Extracts from the same will be found in the Monatsschrift fiir Ohrenheilk. von GRUBER, VOLTOLINI, RUDINGER und WEBER. 1868. Nro. 11 und 12.) 41. PAPPENHEIM, Die specielle Gewebelehre des Gehororganes. (The histology of the ear.) Breslau, 1840. 42. REICHERT, Bulletin de la classe Mathemat. de 1'Acad. des Sciences de St. Petersbourg, T. x., Nr. 222. 1851. 43. - — , Jahresbericht liber die Fortschritte der mikroskopischen Anatomie im Jahre, 1855. J. MULLER'S Archiv, p. 85. 1856. 44. , Monataberichte der Berliner Akademie, p. 479. 1864. 45. - — , Beitrag zur feinern Anatomie der Gehorschnecke des Men- schen und der Saugethiere. (Essay on the minute anatomy of the ear in Man and Mammals.) Abhandlungen der Konigl. Akad. der "Wissench. zu Berlin, 1864. 4. Extract from the Monatsschrift fiir Ohrenheilkunde von VOLTOLINI, etc. 1869. Nro. 1. 46. REISSNER, E., De auris internae formatione. Dissert, inaug. Dorpati Liv., 1851. (In commission bei Reyher in Mitau.) 47. - — , Zur Kenntniss der Schnecke im Gehororgane der Saugethiere und des Menschen. (On the cochlea of the ear of Mammals and Man.) J. MULLER'S Archiv fiir Anatomie, etc., p. 420. 1854. 48. - — , Ueber die Schwimmblase uiad den Gehcrapparat der Silu- roiden. (On the swimming bladder and the ear of Siluroids.) Ibid., p. 421. 1849. 49. ROSENBERG, E., Untersuchungen iiber die Entwickelung des Cana- lis cochlearis der Saugethiere. (Researches on the develop- ment of the canalis cochlearis of Mammals.) Dissert, inaug. Dorpat, 1868. 4. Two plates. 50. SCHULTZE, MAX, Ueber die Endigungsweise der Hornerven im Labyrinth. (On the mode of termination of the auditory nerves in the labyrinth.) J. MULLER'S Archiv fiir Anatomie, p. 343. 1858. 51. STIEDA, L., Studien iiber das Central-Nervensystem der Knochen- fische. (Researches on the central nervous system of Osseous Fishes.) v. SIEBOLD und KOLLIKER'S Zeitschrift fiir wissench. Zoologie, Bd. xviii., p. 1. 1868. 52. , Studien iiber das centrale Nervensystem der Vogel und Saugethiere. (Researches on the central nervous system of Birds and Mammals.) Ibid., Bd. xix., p. 1. BIBLIOGRAPHY. 199 53. STIEDA, L., Studien iiber das centrale Nervensystem der Wirbel- thiere. (Remarks on the central nervous system of Ver- tebrata.) Ibid., Bd. xx., p. 273. 54. TODD and BOWMAN, The physiological anatomy of Man, Vol. ii., p. 54. London, 1856. 55. VIETOR, Ueber den Canalis ganglionaris der Schnecke der Siiuge- thiere und des Menschen. (On the canalis ganglionaris of the cochlea of Mammals and Man.) See HENLE'S and v. PFEUFFER'S Zeitschr. fiir rationelle Med., 3te Reihe., Bd. xxiii., p. 236. 1865. 56. WHARTON JONES, " The organ of hearing," TODD'S Cyclopaedia, Vol. ii. 57. v. WINIWARTER, Sitzungsberichte der k. k. AkademiederWissench. Mathem. natw. Klasse. Nro. 13., p. 107. 1870. (Vor- lau^^o Mittheilung.) (The following works may also be consulted on the development of the cochlea.) 58. VAN BAMBEKE, Recherches sur le developpement du Pelobate brun. (Researches on the development of the Pelobatis brunus.) Mem. de 1'Acad. Belgiqua des Sciences, des Lettres, et des Beaux Arts, T. xxxiv. 1868. (Separate copy.) 59. GRAY, The development of the Retina and the Labyrinth. Lond. Philos. Transact., Part 1. 1850. 60. GUNTHER, Beobachtungen iiber die Entwickelung des Gehororgans bei Menschen und hoheren Saugethieren. (Observations on the development of the ear in Man and the higher Mammals.) Leipzig, 1842. Englemann. 8. 61. REMAK, Untersuchungen iiber die Entwickelung der Wirbelthiere. (Researches on the development of the Vertebrata.) Berlin, 1855. Fol. 62. KOLLIKER, Entwickelungsgeschichte des Menschen und der hoheren Thiere. (History of the development of Man and the higher animals.) Leipzig, 1861. 8. 63. SCHENK, MOLESCHOTT'S Untersuchungen zur Naturlehre, Bd. ix. 64. STRICKER, Zeitschrift fiir wissenschaftl. Zoologie, Bd. x. 65. TOROK. MOLESCHOTT'S Untersuchungen zur Naturlehre, Bd. x. APPENDIX. 66. GOTTSTEIN, J., Beitrage zurn feineren Bau der Gehorschnecke. (Essays on the minute anatomy of the cochlea.) Central- 200 THE AUDITORY NERVE AND COCHLEA, BY W. WALDEYER. blatt ftir die medicinischen Wissenschaften. 1870. Nro. 40, 10 September. (Provisional communication.) 67. BOTTCHER, A., Einige Bemerkungen zu den neuesten Entdeckun- gen in der Gehorschnecke. (A few observations on the most recent investigations into the structure of the cochlea.) (Fliegendes Blatt, Dorpat, 6 November, 1870. — Bottcher states that the greater number of facts recently published by Gottstein (66) are already contained in his treatise in the September part of the Leopoldinic Academy for 1868, which has not, however, as yet appeared (No. 3). The author laments that, in view of this satisfactory agreement between two completely independent works, Bottcher's essay could not be made use of for the foregoing account, which it was impossible to keep back, to trace the development of the cochlea. At least, the latter subject appears to be consi- dered in Bottcher's paper, from a report I have received through Bottcher's kindness — ''Melanges Biologiques tires du Bulletin de FAcad. imperial, des Sci. de St. Petersbourg," T. vii., April 23, 1870, — in which is contained a short abstract by Kolliker of Bottcher's manuscript. 68. HASSE, Zeitschrift fiir wissenschaft. Zoologie, Band xvii., p. 631. 69. His, Entwickelung des Hiihnchens. Leipzig, 1868.' 70. LUSCHKA, Struktur der serosen Haute. Tubingen, 1851. 71. SCHWALBE, Centralblatt fiir die medizinische Wissenschaften. 1869. 72. VIRCHOW and HIRSCH'S Jahresbericht fiir 1868. 73. HENSEN, Zeitschrift fiir wissensch. Zoologie, Bd. xiii., p. 319 et seq. 1863. 74. , Centralblatt fiir die medizinische Wissenschaften, No. 40. 1870. 75. , Zeitschrift fiir die rationelle Medizin, Bd. xx. 1863. 76. , Archiv fiir Mikroskop. Anatomie, Bd. v., p. 164. 18'69. CHAPTER XXXV. THE OLFACTORY ORGAN. BY PROFESSOR BABUCHIN. THREE parts must be distinguished in the organ of smell, (a) The apparatus for receiving the impressions of odours ; (6) the conducting apparatus ; and (c) the central organ to which the odorous impressions are carried by the conducting apparatus. The first, and a part also of the second apparatus are imbed- ded in the mucous membrane which, amongst the higher ani- mals, covers the uppermost and the deepest parts of the nasal cavities ; whilst in some of the lower Vertebrata (naked Am- phibia) it extends as a kind of elevation on this or that wall of the simple nasal passage ; and in others, as in Fishes, forms manifold but regularly arranged folds rising from the floor of the olfactory furrows, between or on which the odour-perceiving elements occur. It is impossible to give here an elaborate de- scription of all the peculiarities of the external modifications of the olfactory organ in all animals ; this rather belongs to the domain of comparative anatomy. Our duty is to furnish an account of the physiologically active elements of this organ, and their different relations to one another. The mucous membrane which contains the odour-perceiving elements, presents certain peculiarities, by means of which it can be distinguished, even with the naked eye, from the rest of the nervous mucous membrane. It either possesses a yellow- ish colour, as in Man, the Sheep and Calf, or is of a brownish tint, as in the Guinea-pig, Rabbit, Dog, and other Mammals. On this account the term locus luteus has been applied to it. But inasmuch as this spot is not characterized in all animals by a peculiar colour, another name, the regie olfactoria, is per- haps preferable, which, however, only indicates that part of ' ii 202 THE OLFACTOKY ORGAN, BY PROFESSOR BABUCHIN. the nasal mucous membrane where the olfactory nerves branch and terminate. Were it, however, desired to indicate the pecu- liarity of this spot by a feature characterizing it throughout the whole of the Vertebrata, it would be not so much its colour, but its greater thickness, softness, and, so to speak, greater succulency, as compared with the rest of the membrane. Even this, however, varies in degree in different animals ; for whilst Fig. 337. Fig. 337. Vertical section of the septum nasi of the Guinea-pig. The specimen was prepared by maceration in solution of chloride of gold, a, Medullary tissue of bone ; 6, osseous lamina ; c, periosteum ; d, gland layer, not filled up, that it may be more distinctly seen ; e, branches of the olfactory nerves ; /, epithelial layer. ill Birds, for example, the membrane is tolerably dense at this part, and scarcely presents any peculiarity recognizable to the naked eye, in the Plagiostomata it is so soft as to resemble thick mucus. The works of Todd and Bowman (1), Eckhardt (2), Ecker (3), and others, certainly contributed much to our knowledge of the structure of the olfactory region ; but the first really accurate information was furnished by the extremely careful investiga- tions of Schultze, and future research, though it may possibly affect points of detail, will not shake the essential facts that he discovered. Some attempts have, however, been made, with this object in view. An idea of the general relations of the olfactory region may best be obtained from fine vertical sections carried CHARACTERS OF THE OLFACTORY REGION. 203 through the whole thickness of the membrane, and these, I think, may best be made in specimens of the membrane which have been hardened in solutions of chloride of gold whilst still adherent to the bones. The various structures are thus retained in their normal position, and appear sharply defined. In fine sections of a nasal septum thus prepared from the Guinea-pig, we find that the osseous portion of the septum is invested by periosteum, which is immediately covered by a thick layer of numerous and closely arranged glands (fig. 337). These glands, named the "glands of Fig. 338. Fig. 338. Section of the olfactory mucous membrane of the Frog, a, Gland of Bowman; 6, its orifice; c, fasciculus of nerve fibrils which run between the epithelial cells. Bowman " by Kb'lliker, are elongated tubes, which, according to the species of animal, are sometimes simple and more flask- shaped than tubular ; and at others are multiform, and charac- terized by pullulations, and by the sinuous course of their blind extremities. Hence it rarely occurs, as the adjoining woodcuts show, that, in vertical sections of the membrane of the higher animals, any simple gland can be followed through- out its whole length ; in general, only transverse sections of the several parts, at different heights, are seen. Better prepara- tions are obtained from the lower animals. The glands contain an epithelium, which at the fundus consists of large granular, nearly spherical cells, which in some animals have yellowish 204 THE OLFACTORY ORGAN, BY PROFESSOR BABUCHIN. or brownish pigment in their interior. Chloride of gold stains them of a deep black colour. Towards the excretory duct the epithelium assumes a more polygonal form, and becomes less granular. The excretory ducts finally reach the surface between the elements of the next following external layer (fig. 338). The orifice sometimes opens at the bottom of a funnel-shaped depression of the membrane. Amongst the lower animals, as in the Frog, it may be very easily demonstrated that the ex- cretory duct is lined, from its commencement to its termination on the surface of the mucous membrane, with smaller cells. Immediately in front of the orifice slender epithelial cells are situated, which are elongated in the direction of the axis of the excretory duct. At the point where the olfactory region passes into the ordi- nary mucous membrane, the glands become fewer in number, and ultimately vanish altogether, being replaced by the ordi- nary mucous glands. According to Kolliker, even in the olfactory region of the human subject, instead of the just- described glands, we meet only with the ordinary mucous glands. Schultze, however, considers that in Man they pro- perly constitute a transitional form, and resemble in appearance Meibomian glands.* In Fishes, the glands are entirely absent, but are replaced by numerous cells. The glands are separated from one another by ordinary con- nective tissue, which is continuous on the one hand with the periosteum, and on the other extends as far as to the epithe- lium. I have not been able to discover the basement mem- brane described by Hoffman. The appearance of a membrane is caused by the contour line of the connective tissue in contact with the epithelium. Both here and in the deeper layers of the connective tissue are many fusiform cells provided with processes, and especially in the lower animals, containing black pigment. M. Schultze has also observed free masses of pig- ment, as well as pigment cells, in the higher animals. Lastly, imbedded in the connective tissue are vessels and the ramifica- * More recently, Schultze (5) has observed acinous mucous glands in the olfactory region of Man. EPITHELIUM OF THE OLFACTORY REGION. 205 tions of the olfactory nerves, which come out with remarkable distinctness in specimens prepared with chloride of gold. The superficial layer of the olfactory mucous membrane is an epithelium which in specimens prepared with chloride of gold (as is shown in fig. 337) is divisible into two, an external, which Fig. 339. Fig. 339. A group of olfac- tory cells from the Proteus, with an epithelial cell lying within them. From a speci- men prepared with Miiller's fluid, a. An isolated olfac- tory cell, after treatment with a diluted solution of sulphuric acid. Fig. 340. Fig. 340. A a, Epithelial cells from the olfactory region of the Proteus (from a specimen prepared with Miiller's fluid) ; d, the processes apparently connected with them ; c, olfactory cells. -B, Epithe- lial and olfactory cells from Man ; after Max Schultze. is finely striated transversely, and an internal granular layer. It was formerly considered to be a laminated epithelial layer. Eckhardt and Ecker to some extent indicated its nature cor- rectly, but we are indebted to the beautiful researches of Max Schultze for. the full details of its structure. From these it 206 THE OLFACTORY ORGAN, BY PROFESSOR BABUCHIN. appears that the epithelial portion of the olfactory organ is constructed upon one and the same type in all Vertebrata, so that the description of its structure in any one animal is applicable to all. We shall therefore select an animal whose epithelial cells are large and easily isolable, as the Proteus, in which the histological elements attain an almost colossal size, and have nevertheless been as yet but little examined. If now the entire olfactory organ of a Proteus be macerated for a day in Miiller's fluid, then be transferred for the same space of time to distilled water, and finally a fragment be torn away from the olfactory region, we shall see distinctly how the epithelial cells split up into distinct cell groups (fig. 339). In these groups we distinguish an external half, composed apparently of extremely fine fibrils, which at their outer extremities terminate in long fine cilia, and an internal half, composed of large closely com- pressed nuclei, of which one is larger than the remainder, presents an elongated oval form, and is for the most part situated ex- ternally. Further manipulation with needles shows that each of the above-described groups consists of two kinds of cells, some few of which are large, whilst the greater number have a large round nucleus and very long fine processes (fig. 340). One of these processes, and indeed the thicker of the two, runs outwards, the other is very fine, is directed inwards, and can be followed to the margin of the subepithelial connective tissue. These are the olfactory cells of Max Schultze which conduct the impressions of smell. Their outer extremity bears the above-named long and fine cilia,* and appears in pre- parations which have been macerated in Miiller's fluid sinu- ously curved, and as it were in zigzags. In specimens prepared with chloride of gold, or in those which have been treated with sulphuric acid, these processes present the appearance of very fine and varicose fibres. By the use of high powers it may be demonstrated that a continuous fine fibre runs through all the * The apparent difference of the above from Max Schultze's observa- tions, according to whom the cilia are absent in the Proteus, and as in branchiated animals, must necessarily be absent, can only arise from the circumstance that this most careful inquirer had only animals at his com- mand that had long been preserved in solution of chromic acid. CHARACTERS OF THE OLFACTORY CELLS. 207 enlargements, and from thence we may conclude that the ex- ternal process of the olfactory cells is composed of two sub- stances throughout its whole length, an external, which swells up under the influence of certain reagents, and an internal thread which remains unaffected. The central process of the olfactory cells presents the same relations, with this difference only, that it is considerably finer, and in many instances is immeasurable. In Tritons I have found that the length of these processes, taken together with the other portions of the olfactory cells, sometimes exceeds by many times Fig. 341. Fig. 341. A, an epithelial and two olfactory cells from the point of transition of the olfactory region into the ordinary mucous mem- brane (from the Triton) ; B, peculiar epithelial cells faom the olfac- tory mucous membrane ; a, from the Raja clavata, after Max Schultze ; 6, from the Proteus. the thickness of the epithelial layer (fig. 341). They must consequently either penetrate into the subepithelial layer, or run in a horizontal direction along the line of demarcation be- tween it and the epithelial layer. I have actually observed the latter course in the Proteus. The cells that have just been described everywhere surround the above-mentioned large cells that possess a large oval nucleus, and extend through the whole thickness of the epithelial layer ; their external half appears to be more or less cylindrical in the Triton and Proteus, is trans- parent, and often distinctly striated longitudinally (fig. 340). I have been able to satisfy myself that this striation is not to 208 THE OLFACTORY ORGAN, BY PROFESSOR BABUCHItf. be regarded as the optical expression of the surrounding olfactory cells. Moreover, it does not affect the whole thick- ness of the cell, but is limited to the surface. At the external extremities of the cells, which are free from cilia, a row of minute points can be distinguished, which encircle the entire extremity, and do not call to mind the appearances presented by the ordinary columnar epithelial cells at the surface. The inner half of the cells in question are not so uniform as the external, yet I very much doubt the statements made by several authors, that they consist of branching processes. They exhibit a great variety of forms, and we may represent- these halves as more or less thick cylinders, composed of a soft and transparent mass, in which the round bodies and granules of the olfactory cells are everywhere imbedded. Folds thus originate, the borders of which, sharper than the remaining substance, project, giving rise to the appearance of figures that simulate the processes of authors. But by staining with anilin it may be shown that a very delicate transparent and longitu- dinally striated substance is stretched between these processes. The independency of this striation comes still more clearly into view at the base, where it altogether fails to give the impres- sion of the presence of fibrous elements. The internal process gradually enlarges in a cone-like manner towards the subjacent connective tissue, and breaks up into numerous very short fibrils. It is very remarkable that the internal process pre- sents a different appearance under the influence of many reagents. If for example the epithelial cells of the Proteus be treated with Muller's fluid or with iodized serum, and be then placed for a short time in diluted glycerine, all traces of the transparent substance vanish, and the above-mentioned folds make their appearance in the form of branched processes. If the mucous membrane of the olfactory region of an animal which does not exhibit any decided coloration of this part be treated with nitrate of potash, we obtain a very delicate pic- ture, which shows distinctly how the olfactory cells are topo- graphically related to those just described. Annular figures, which appear to be the ends of large cells, come into view, surrounded by a number of black dots, which are more or less closely arranged in different animals, and which are simply OLFACTORY CELLS. 209 the extremities of the olfactory cells (fig. 342). The rela- tions just described are found to occur with very unimportant modifications in all animals, and even amongst the Invertebrata, as in the Cephalopoda (Sernoff). Max Schultze, however, states that in Man, as well as in Mammals generally, the olfactory cells have no cilia, or, as he terms it, no olfactory hairs ; in other words, he maintains that these hairs form no necessary conditionfor the perception of smell, and therefore are not deserving of any special name. When the olfactory hairs are present (as in Birds and Amphibia), they appear either «in the form of stiff hairs, of which only one is supported by each cell, or of a bundle of fine cilia. In some few animals olfactory cells occur possessing both kinds of hairs. Occasionally that portion of the olfactory cell where the nu- cleus lies is fusiform. In some animals the external processes Fig. 342. Fig. 342. Surface view of the epithelial layer of the olfactory region, after treatment with nitrate of silver. From the Proteus. are remarkably thick, in others they are delicate, and become varicose under the influence of macerating fluids. Max Schultze has further demonstrated that the large epithelial cells are, in many Mammals, more or less strongly pigmented, the yellow pigment lying either near the outer surface or nearer their centre, and that to the presence of this pigment the above-mentioned tint of the olfactory region is due. Both in Man and Mammals generally, epithelium, free from olfactory hairs, occurs in this region ; and although in the former ordinary ciliated epithelium occurs here and there, no true olfactory cells can be found interspersed amongst the others. In the Plagiostomata, on the contrary, the parts capable of per- ceiving odours are especially covered with ciliated epithelium. Besides the two kinds of cells just described, another kind exists in the Plagiostomata (Max Schultze), in the Proteus and Triton (Babuchin), and perhaps also in many other animals, VOL. in. p 210 THE OLFACTORY ORGAN, BY PROFESSOR BABUCHIX. which are likewise intercalated in the epithelial layer, and which call to mind the forked cells of Engelmann. Their form is very various, and is represented in fig. 340, B. They are in immediate contact, by their central extremity, with the sub- epithelial layer, and here frequently break up into very fine short fibrils. Their peripheric extremity does not reach to the surface of the epithelial layer, and is either conically pointed or branched. Their form, moreover, as above mentioned, is very variable, so that in the Proteus, for example, we meet Avith cells that, owing to their ramification, are very similar to the multipolar nerve-cells. Lastly, it is not uncommon in young animals, and in the deeper part of the epithelial layer, to meet with round cells, destitute of any processes, which we may no doubt regard as destined to develop into the olfactory and epithelial cells. The conducting apparatus of the olfactory organ is composed of the so-called olfactory nerves, which, as is well known, arise from the two bulbi olfactorii, and, according to the animal, either constitute a single nerve trunk, or form several strands, and then ramify in the mucous membrane of the olfactory region. The trunks of the olfactory nerve, which .may be very readily broken up into fasciculi, run either horizontally or obliquely, in the glandular layer. From these trunks nu- merous branches are given off, which, undergoing further subdivision at different angles, run outward to the epithelial layer, and in specimens prepared with chloride of gold may be distinctly followed to its deep surface. On the other side the branches of the nerves run to the base of Bowman's glands. The minute anatomy of these nerves has been sufficiently examined by Max Schultze, and has been already discussed at pp. 162, et seq., of the first volume of this work. I am unable, however, to agree with the statement of this observer, that the olfactory nerves contain primitive nerve fibres, which are constructed on the type of those of Remak, that is to say,, of a nucleated sheath of Schwann and fibrillar contents. Max Schultze states that the funiculi of the olfactory nerves split up into fasciculi of primitive fibres, and that in some few animals these fasciculi consist of fibrils, and are enclosed in a nucleated sheath, which he names the sheath of Schwann; MINUTE ANATOMY OF THE OLFACTORY NERVES. 211 whilst in others the fasciculi of primitive fibres split into pri- mitive fibres within their sheath, and these again are composed of fibrils and a sheath of Schwann. So far as my observation has extended, however, the fasciculi in question, whether they are provided with a sheath or not, consist in all animals of extremely fine fibrils kept in position by a finely granular mass. In some animals nuclei are sometimes seen in addition, disposed in regular rows between the fibrils, in consequence of which the whole fasciculus is divisible into secondary fasciculi destitute of a sheath. The sheath of the primitive fasciculi cannot represent the sheath of Schwann, but is rather to be compared, from a morphological point of view, with the neu- rilemma, with which also its peculiarities- and structure may perhaps agree. We may also reasonably admit this even where the fibrils contain no nuclei between them, or form no second- ary fasciculi, as occurs for example, according to Max Schultze, in the Pike. If in this case we were to regard the sheath as Schwann's sheath, we must do so also when the fibrils split into secondary fasciculi within the sheath, which fasciculi, according to Max Schultze, are again provided with a Schwann's sheath ; wre should be obliged to admit, in other words, that the nerve fibres possessing a nerve sheath, are again enclosed in a com- mon sheath of Schwann. I may also remark in addition that I was unable to satisfy myself that the primitive-fibre fasci- culi in many animals, especially in Plagiostomata, possess any sheath at all. The history of the development of the peri- pheric nervous system suggests that the olfactory nerves are to be regarded as embryonal structures that remain persistent at the second grade of their development, whilst the fibres of Remak attain the ultimate stage. The nuclei found between the fibrils of the olfactory nerves are, for the most part, true cells. They are not unfrequently fusiform, and in this case adhere, by means of their fine processes, very firmly to the nerve fibrils. I shall have an opportunity of entering into fuller details respecting them in another part of this work. The question that now arises is, what becomes of the nerve fibrils when they have reached the epithelial layer ? Unfortu- nately it can only be answered hypothetical!}'. Examinations instituted on specimens stained with chloride of gold by no p 2 212 THE OLFACTORY ORGAN, BY PROFESSOR BABUCHIN. means prove that the nerve fibrils end in the same mode as has been observed in the transparent cornea, though this might, indeed, be presupposed. After my discovery, that the large epithelial cells present throughout their whole length delicate longitudinal strise, which, however, are only visible under favourable circumstances, may we not presume that the finest fibrils of the olfactory nerves, after they have penetrated the epithelial layer, everywhere closely embrace the large epithelial cells, and thus reach the surface of the epithelium ? This pre- sumption gains in strength, if we take into consideration that the conical internal extremities of the large epithelial cells break up into short delicate fibrils. I believe, however, that such a statement would at the present time be a little premature ; for the number of instances of striated cells recorded increases daily. Thus, for example, it has long been known that the fibres of the lens are frequently longitudinally striated. Pfluger has observed striation in nearly all the cells composing the salivary cells. 1 have myself seen that a regularly disposed striation may be produced by the action of certain reagents on the crystalline lenses of some Crabs. Lastly, T have observed that even the contents of the cup cells 'sometimes appear to consist of very fine fibrils. This admonishes us to regard the stride with con- siderable caution, and not to consider everything that is striated to be a nervous structure. I must also call attention to the fact that in the Triton, at the point where the epithelium of the olfactory region passes into the ordinary epithelium, where both the olfactory and epithelial cells become shorter and thicker, the internal extremities of the epithelial cells are enormously broad, and yet exhibit no indication of striae (fig 340). Max Schultze long ago advanced the hypothesis that the fibrils of the olfactory nerves enter into connection with the inner extremities of the olfactory cells. As essentially supporting this hypothesis, he referred to the very complete analogy which obtains, both in a chemical and in a morpho- logical point of view, between the central extremities of the cells in question and the nerve fibrils. As additional evidence in favour of this hypothesis, I may add that under the influ- ence of chloride of gold the olfactory nerves constantly assume a blackish violet colour, and although very rarely, still in sue- MINUTE ANATOMY OF THE OLFACTORY NERVES. 213 cessfully coloured specimens the processes of the olfactory cells also become distinctly stained, whilst the nucleus remains pale and transparent. I possess a preparation made from a tortoise, unique amongst many hundred sections, in which the direct passage of the nerve fibrils into the epithelial layer is observable. In this instance branches arise from the deeper- lying trunks of the olfactory nerves, and run nearly vertically towards the epithelial layer. These branches are fibrillated, and are beset with nuclei subdividing as they continue their course to the attached surface of the epithelium ; they here break up into fibrils and extremely fine fasciculi, which spread out horizontally for a very short distance, like a fan, and then run perpendicularly, but in an irregularly sinuous manner, into the epithelial layer itself, where they may be followed as far as to the nuclei of the olfactory cells. M. Schultze's hypo- thesis would become matter of fact if in the chloride of gold we possessed an agent that stained nervous elements alone, and was less capricious in its action, so as to produce no illusory appearances. We find also, as mentioned above, in the epi- thelial layer of the olfactory region, the peculiar cells which very closely resemble the forked cells of Engelmann. Whether we should regard these as constituting the terminations of the nerves is questionable. In many instances appearances are presented which render it quite evident how the secondary fibrils, united into fasciculi, penetrate into the epithelial layer, and ran for a considerable distance outwards between the epithelial cells, which is obvi- ously suggestive of their terminating with free extremities (tig. 338, 0). This is in apparent contradiction to what has been said in our earlier statements respecting the termination of the nerves, but the opposition is only apparent. If we admit that, as I have satisfied myself with the adoption of every pre- caution, the olfactory region is sensitive, if we further consider it to be highly probable that sensibility and smell are communicated by separate nerves, it immediately suggests itself to consider the free nerve ends I have observed as belonging to the fibres of simple sensation. Max Schultze has moreover already ob- served medullated between the non-medullated fibres. The question in regard to the relation of the olfactory fibrils 214 THE OLFACTORY ORGAN, BY PROFESSOR BABUCHIN. to the central part of the olfactory organ is not less difficult to answer. It has long been known, through the researches of Walter (6), Leydig (7), Max Schultze (4), and has recently been confirmed by Meynert (8), that the fibrils of the olfactory nerve arise by fasciculi from the large spherical bodies which are imbedded in the bulbus olfactorius. Still, as Kolliker states in his work, the minute anatomy of these structures has not been thoroughly investigated. The best results are obtained by the investigation of their various relations in Plagiostomata, where they possess the same constituent parts as in the central apparatus of higher animals, though isolated and far apart from each other. In the Torpedo, for example, the bulbus olfactorius lies immediately upon the olfactory fossa, and is united by means of the long and slender tractus olfactorius with the olfactory lobes (?) (Scheinlappen), whilst the sheath of the tractus is continuous with that of the bul- bus, in which the above-named spheroidal structures are dis- tributed without any definite arrangement. They are separated from one another by nerve fibres and vessels, appear in the form of a finely granular structure, and are apparently beset externally with nuclei. In the Torpedo it may easily be demonstrated that these apparent nuclei are unquestionably very small cells, some of which are bipolar, whilst the majority are multipolar. One of the processes of these cells is some- times smooth, and runs towards the tractus olfactorius, where it becomes invested with medullary substance. The other pro- cesses are at first thick, but subsequently divide into an infinite number of branches, which penetrate the spherical corpuscles. In the bipolar nerve cells the more delicate pro- cess passes into the tractus olfactorius ; but the other, which is of distinctly fibrillar structure, penetrates into a spherical body, where it breaks up into extremely fine fibrils. The fibrils in some instances enter divergingly into a spherical body, without any definite arrangement, and emerge again from one side, united into a fasciculus ; in other instances they already unite in the spherical body itself into a fasciculus which forms a kind of spire or coil, and then associates itself with the other fasciculi of the olfactory nerves (fig. 343). What morphological significance are we to attribute to the MINUTE ANATOMY OF THE OLFACTORY NERVES. 215 spherical bodies in question ? Are they special and peculiar structures, or do they find their analogues in the nervous system ? Although at first sight they appear to be finely granular, extremely thin sections present precisely the same appearance as the so-called molecular layer of the retina. It would not however, it appears to me, be quite correct to admit that we have here a reticular or spongy tissue before us. It is rather a convolute of extremely fine fibrils, the origin of which we are already acquainted with, and between which is a considerable quantity of finely granular substance. Similar relations are met with wherever there are only naked nerve Fig. 343. Fig. 343. a, An isolated corpuscle or spherule, with adherent nerve cells, from the olfactory bulb of the Torpedo ; b, isolated nerve cells, from the same. fibrils, or it may be the finest axis-cylinders, or in other words, where the nerves have not reached the higher grades of de- velopment. When such fibrils run parallel to each other, as is the case in embryonal and in the olfactory nerves, the fasci- culi of fibrils offer a striated granular aspect. The smallest granules, or perhaps a substance which only changes into granules under the influence of certain reagents, cleaves so strongly to the fibrils, and glues them so firmly together as to render their isolation very difficult. But when the fibrils as- sume an irregularly convoluted course, we obtain the appear- ance presented by the reticular connective tissue, which is 216 THE OLFACTORY ORGAN, BY PROFESSOR BABUCHIN. chiefly occasioned by the granules ; and the isolation of the several nerve fibrils then becomes almost an impossibility, as we find to be the case in the spherules of the regio olfactoria. I am very much inclined to believe that the same relations are repeated in the retina, and perhaps in other parts of the nervous system. The tractus olfactorius consists exclusively of medullated nerve fibres, which have no sheath of Schwann. After they have reached one of the two projections, which in the Torpedo are placed at the sides of the great hemispheres, they pene- trate into the reticular substance, gradually lose their medullary layer, and unite there with numerous small nerve cells, of which some again are bipolar, whilst others are multipolar. This is the essential fact I have discovered from my re- searches upon the Plagiostomata. I am unable to pursue the examination of the other constituents of this apparatus. All the relations just described respecting the origin of the ner- vus olfactorius are present also in the higher Vertebrata, however different their structure may at first sight appear to be. The fibres of the olfactory tract arise directly from a finely granular reticular mass, whether in the form of sphe- rules or otherwise. This mass is everywhere surrounded by small nerve cells. The processes which run inwards into the olfactorius and the cerebrum everywhere undergo conversion into medullated nerve fibres, which here and there unite again with fresh nerve cells. A difference consequently only exists in a topographical point of view, which must obviously be regarded as of merely secondary importance, and belongs to another chapter of this work. [During the final revision of these sheets Exner has published in the Wiener Sitzungsberichte the results of his researches upon the olfactory mucous membrane of the Frog. According to what I can learn from his short provisional communication, the branches of the olfactory nerves break up into a plexus* between the connective tissue of the mucous membrane and the epithelial layer, and from this the central processes both of the so-called olfactory cells and of the epi- thelial cells arise. The trigeminal fibres form a wide-meshed plexus in the connective tissue of the mucous membrane. — STRICKER.! LITERATURE. 217 LITERATURE. 1. TODD and BOWMAN, Physiological Anatomy, Vol. ii. 2. ECKHARDT, Beitrage zur Anatomie und Physiologie, Heft i. 1855. 3. ECKER, Bericht iiber die Verhandlung., 3 Bef. d. Naturwissen- schaft. zu Freiburg, 1855, No. 12 ; Zeitscbrift fiir wissen- scliaft. Zoologie, Band 1856. 4. MAX SCHULTZE, Untersuchungen iiber die Nasenschleimhaut. 1862. 5. , Ceritralblatt fiir die medizin. Wissenschaften, No. 25. 1864. 6. WALTER, Virchow's Archiv, Band xxii. 7. LEYDIG, Lehrbuch der Histologie. 1857. 8. MEYNERT, Vierteljahrschrift fiir Psychiatrie., Band ii. ; Jahrgang 1, Heft iv., p. 102. CHAPTER XXXVI. THE EYE. THE RETINA. BY MAX SCHULTZE. THE retina is the membrane-like terminal expansion of the optic nerve lining the posterior part of the globe of the eye. In addition to nerve fibres, it contains various forms of nerve cells, which are intercalated in the course of these fibres before they reach their peripheric extremity. The extremity itself is characterized by a peculiar terminal apparatus, forming the layer of rods and cones, which are invested by pigment. The nerve fibres and nerve cells of the retina are imbedded in a spongy connective-tissue substance, which may be regarded as a continuation of that of the optic nerve, and presents great similarity to the connective tissue of the central organs of the nervous system. A part of this connective tissue is formed by bloodvessels, and probably also by lymphatics. The textural elements of the retina are arranged in layers parallel to the surface of the spherical external membrane. The innermost of these, in immediate contact with the vitreous, is formed by the limiting layer of the spongy connective tissue which is often intimately connected with the surface of the vitreous, and is named the membrana limitans interna; its adhesion to the vitreous sometimes renders the detachment of the retina in the vicinity of the ora serrata, in fresh or well- preserved specimens, extraordinarily difficult. The most ex- ternal of the layers is that of the rods and cones, including the pigment sheaths, which are formed by a special cell-layer — the pigment cell-layer of the retina. This rests upon the choroid, and, indeed, upon the vitreous connective substance of the chorio-capillaris, to which, on separation of the retina, it GENERAL STRUCTURE OF THE RETINA. 219 often remains adherent, in which case the layer of rods and cones drawn out of their pigment sheaths constitutes the most external layer of the retina. A part, however, even of these not unfrequently remains behind with the pigment of the choroid, Fig. 344. Fig. 344. General view of the layers of the retina of Man. Mag- nified 400 diameters. The numbers refer to the explanation given in the text. so that in well-preserved specimens we find the pigment sheaths do not easily permit the detachment of the enclosed portion of the rods, the latter adhering with the pigment to the choroid, whilst the inner portion of the rods cleaves to the retina. 220 THE RETINA, BY MAX SCHULTZE. The retina is composed of several layers, the synonyms of which threaten to perplex ophthalmological literature. It is therefore of importance to name the various layers in the sim- plest manner possible. The terms employed by Heinrich Muller in all his publications upon the retina have proved the most serviceable, and with a few modifications may still be retained. The only terms I have introduced are my membrana limitans externa and the division of the intergranule layer of H. Muller into two layers. I indeed first called attention to the necessity of making this division, and whilst preserving the name of intergranule layer to that constantly present layer of finely granulated substance which lies between the internal and external granules, have dissociated from it that portion of the external granule ]ayer composed of the rod and cone fibres, which is particularly strongly developed at the yellow spot in Man, and which was included by Muller (1) in his inter- granule layer. Henle calls the intergranule layer, as I define it, the external granulated layer, and thus expresses its similarity in structure with the molecular or internal granulated layer ; the radially fibrillated division of the ex- ternal granule layer, on the other hand, he terms the outer fibrous layer. In order to obviate misapprehension in the ex- planation of the name intergranule layer, which, it will be seen from the above, in consequence of H. M tiller's publications, differs somewhat from mine, we shall hereafter term it Henle's exter- nal granulated layer instead of the " intergranule layer." In accordance with the nomenclature here employed, the layers of the retina from within outwards are as follows : — 1. Membrana limitans interna. 2. Optic-fibre layer. 3. Ganglion-cell layer. 4. Internal granulated (molecular) layer. 5. Internal granule layer. 6. External granulated (intergranule) -layer. 7. External granule layer, including the external fibre layer, which is present in certain parts of the retina. 8. Membrana limitans externa. 9. Layer of rods and cones. 10. Pigment layer. GENERAL STRUCTURE OF THE RETINA. 221 All the layers of the retina lying between the two limiting layers are composed of the two different elementary parts which have already been named dements of the nerve tissue, and elements of the connective tissue. This is admitted on all hands. The differences of opinion that exist relate to which of the two groups of tissues this or that fibre, this or that cell, belongs. This disagreement, as our researches on the mode of termination of the nerves at the periphery and in the centres show, depends on the extremely embarrassing circumstance that very fine non medullated nerve fibres are indistinguish- able by any absolutely certain characteristic, even where high powers are used, from other kinds of fibres, especially where both kinds are intimately interwoven with each other, as un- doubtedly occurs in many parts of the retina. In order to obtain a starting-point to enable us to determine the distinction between these two kinds of fibres, we shall commence our con- sideration of the minute anatomy of the retina with that of the undoubted nerve fibres which spread out divergingly from the optic nerve, and form the layer of optic-nerve fibres immedi- ately succeeding the membrana limitans interna. With the knowledge thus gained we ^shall proceed to investigate, and endeavour to distinguish, the nerve fibres of other layers, which cannot be shown to be continuous with true nervous elements. We shall then describe the supporting connective tissue in a special section, as well as the modifications of structure pre- sented by the retina at the macula lutea, the fovea centralis, and ora serrata. The vessels of the retina will be elsewhere described. THE NERVOUS ELEMENTS OF THE RETINA. The optic nerve, at the point where it reaches the external sur- face of the globe of the eye, consists, just as in its whole course through the orbit, (independently of its sheaths, bloodvessels, and lymphatics,) of medullated fibres, which are grouped into fasciculi, and are imbedded in relatively dense connective tissue. On breaking up small portions, we meet, when examined in the fresh condition, and in indifferent fluids, with short pieces of nerve fibres and with rounded and cylindrical masses of nerve •2-2'2 THE EETINA, BY MAX SCHULTZE. medulla, which resemble the elements of the white substance of the brain.* Longer portions of medullated nerve fibres may be isolated by teazing out fine longitudinal sections of the optic nerve preserved in hardening fluids. These also resemble the medullated fibres of the white substance of the brain, when subjected to similar treatment, in the circumstance of their sur- face being beset with knots and varicosities.f It would there- fore appear that the fibres of the optic nerve resemble those of the brain in being destitute of the sheath of Schwann. The superior firmness of the optic nerves to the brain substance is sufficiently explained by the large amount of dense connecting substance they contain, the presence of which can be demon- strated in fine transverse sections of the hardened nerves. Each fasciculus of nerve fibres is separated from the adjoining ones by a thick layer of highly vascular fibrillar connective tissue. £ Extremely instructive specimens may be obtained from sec- tions of this kind, if taken from optic nerves which have been hardened for a short time in a strong solution of per- osmic acid, or, as F. E. Schulze recommends, in chloride of palladium, or from fine sections otherwise hardened, coloured with chloride of gold (Leber), and explain how Klebs§ could maintain that the quantity of connective tissue in the optic nerves is often still more abundant than that depicted in fig. 5 of Plate xix. of the Icones physiologies. The differ- ences existing between normal and atrophic optic nerves have been very exactly described elsewhere by Leber, so that at a rough guess the fasciculi of nerve fibres constitute about one half of the mass of the optic nerve. In every fasciculus, * This similarity of the fibres of the optic nerves with those of the brain, and their difference from other peripheric nerves, was first de- scribed and illustrated with many drawings by Ehrenberg, Abhandlungcn der Acad. der Wissenschaften zu Berlin aus dem Jahre, 1854, p. 665 Taf. i._v. t See this Manual, p. Ill, fig. 19. t See the description and illustrations of transverse and longitudinal sections of these nerves given by Bonders, in Griife's Archiv, Band i. , Abtheil. 2, Taf. ii., figs. 2 and 3 ; by Henle, in his Anatomic dcs Menschen, Eingeweidelehre, p. 583 ; and by Leber, in Grafe's Archiv, Band xiv.,— ii , Taf. v., fig. 1. § Virchow's Archiv, Band xix., p. 324. GENERAL STRUCTURE OF THE RETINA. 223 nerve fibres of very various diameter are mingled together, the finer ones preponderating. As the nerve perforates the sclero- tic at the so-called lamina cribrosa, all the nerve fibres, except in a few instances that will hereafter be mentioned, lose their medullary sheath. The diminution in the diameter of the nerve, thus occasioned, is rather sudden, and is accompanied also, according to Lowig,* by the internal connective tissue of the nerves becoming continuous with that of the sclerotic and choroid. What now remains of the nerve fibres is the extremely delicate axis-cylinder, completely deprived of its medullary sheath. These, enclosing the arteria and vena cen- tralis, and always invested by a certain quantity of connective tissue, pass through the choroid, and as they radiate outward in all directions, bound the shallow crater of excavation of the optic diskf into the plane of the internal surface of the retina, where they form the optic-fibre layer situated immediately external to the membrana limitans interna, and the thickness of which gradually diminishes towards the ora serrata, so that at this latter line only isolated fibres or small fasciculi of fibres are demonstrable. At the yellow spot of the retina the layer of nerve fibres, considered as a continuous layer, suffers an in- terruption. The rest of the connective tissue of the optic nerve passes into the substance of the supporting fibres of the retina.^: The nature of the nerve fibres forming the layer in question may best be examined under the microscope in the perfectly fresh state by placing portions of the retina taken from the still warm bulb in vitreous humour, with the internal surface looking upwards. Under these circumstances we may some- times, in the vicinity of the ora serrata, where the optic-nerve fibres run separately, obtain very well-marked specimens, pro- * Studien des Physiolog. Institute zu Breslau, herausgegeben von Reichert, 1858, p. 125. t H. Miiller treats of the so-called physiological excavation of the entrance of the optic nerve in Grafe's Archiv fur Ophthalmoloyie, Band iii. , Abtheil. ii. , p. 86. L. Mauthner refers in a more extended manner to the recent literature upon the subject in his Lehrbuch der Ophthalmm- copie, 1868, p. 252. £ Klebs, in Virchow's Archiv, Band xix., p. 321, Taf. vii. 224< THE RETINA, BY MAX SCHULTZE. vided the granular coagulation which occurs soon after death in most of the cellular elements of the retina has not occurred. The isolation of the soft fibres by needles can only be very imperfectly accomplished in the fresh condition and in in- different fluids, but may be effected in retinae macerated in hardening fluids, as, for example, after preservation for some time in iodine serum, and in dilute solutions of chromic acid and of bichromate of potash. The nerve fibres of the retina thus brought into view vary considerably in diameter, many being only just capable of measurement, and therefore under half a micromillimeter, whilst the thickest have a diameter of from three to five micromillimeters. None of them present any traces of attached or imbedded nuclei, and very slight traces of any isolable sheath, or of a differentiation into cortex and medulla. They appear in the form of pale, pliable, very soft fibres, in which no further structure is perceptible than some indication of fibrillation and here and there a cluster of fine granules. All exhibit a great tendency to the formation of fusiform varicosities. In fresh preparations examined in situ, such varicosities however are almost entirely absent, and their formation can be retarded by the application of iodine serum or addition of common salt to serum, but is ac- celerated by dilution of serum with water, and is therefore un- doubtedly a phenomenon of imbibition. The number, size, and form of the varicosities exhibit many varieties, but the appear- ances are always quite different from those presented by the medullated fibres of the brain or spinal cord. In the latter the surface is beset with varicosities, and rendered knotty by the partial escape of the strongly refractile medulla. No trace of such escape is perceptible in the retinal fibres; but the fusiform varicosities they present, correspond to those observed in axis-cylinders from which the medullary sheath has been detached, as may be seen for example in the. fibres of the auditory nerve.* That a change occurs in the texture of the optic fibres in the places where varicosities develop, is demonstrated by the fact that the varicosities, especially of the thicker fibres, exhibit * M. Schultze's Observationes de retina structura 2>enitiori, 1859, fig. 1. NERVOUS CONSTITUENTS OF THE RETINA. 225 for the most part in their interior, a granular change of the fibre-substance, whilst the parts which have not become swollen by imbibition remain homogeneous, and permit the fibrillar structure to be more or less distinctly recognized. That phe- nomena of imbibition here play an important part is shown by the behaviour of the nerve fibres of the retina in solutions of chromic acid, which when sufficiently concentrated prevent the formation of varicosities, whilst when rendered more and more dilute the number and size of the varicosities progressively increase, till at length the fibre, beset with enlargements till Fig. 345. Fig. 345. Nerve fibres of the retina, with and without varicosities. a, From the Ox ; the remainder from Man. Magnified 800 diameters. it resembles a string of beads, altogether breaks up.* This occurs in the case of the finest fibres, the varicosities of which are relatively the largest from the very commencement, and are in more close proximity with one another, whilst they make their appearance earlier than in the thicker fibres. Dichotomous divisions of the nerve fibres have been de- scribed and depicted by Corti-f- and Gerlach.^ These occur as a rule in the optic-fibre layer, but are only exceptionally met with ; the cases that have been described may possibly have been instances of the bifurcation of processes of ganglion cells. * More precise statements in regard to the solutions in which varicosi- ties occur, will be found in my Essay in the Monatsberichten der Academic der Wissenschaften zu Berlin, 1856, p. 511. t Mliller's Archiv, 1850, Taf. vi., fig. 3. £ Handbuch, der Gewebelehre, 1854, p. 498. VOL. III. Q THE RETINA, BY MAX SCHULTZE. The concordant statements of Michaelis, H. Miiller, Henle, Kolliker, and others, show that at the yellow spot an inter- ruption to the regular radiating course of the nerve fibres in the retina occurs, a continuous fibre layer being here defective, and the fibres losing themselves in the thick ganglion-cell layer, in order to enter into which freely, they form a series of arches in the vicinity of the yellow spot. Liebreich* has recently called attention to another peculiarity, namely, that many more nerve fibres proceed directly upwards and down- wards from the point of entrance of the optic nerve, than outwards, though far larger tracks of the retina require to be innervated in the latter direction. The fibres accompanying the larger vessels, and running outwards, form arches around the macula lutea where they terminate. On microscopic examination of an uninjured retina from the inner surface, the nerve fibres may frequently be seen to be grouped into fasciculi, between which are elongated fusiform spaces.-)- These are occupied by fasciculi of the radiating sup- porting fibres of the retina, which terminate in the membrana limitans interna. Where, as at the ora serrata, the nerve fibres are sparingly present ; or as at the macula lutea, are altogether absent as a continuous layer, the ganglion cells come to be in immediate contact with the membrana limitans interna. In exceptional cases in the human subject the medullary sheath of certain portions of the optic nerve is retained beyond the limits of the optic disk, and extends for some distance into the retina. This con- sequently is rendered opaque, and when examined by direct light appears white, as is well shown in the excellent ophthalmoscopic illus- trations given by Liebreich in his Atlas of Ophthalmoscopy, Taf. xii., figs. 1 and 2. Virchow:}: first established this fact in a man aged forty-six, in whose eyes, after death, he found medullated fibres around both disks, in one eye presenting the appearance of four diverging radii ; in the other a hazy white annulus ; and since that date a series of similar cases have been observed and examined both anatomically * Zehender, Klinische Monatsblcitter fur Augenheilkunde. Jahrgang, vii., p. 457. t See H. Miiller and Kolliker, Retina-tafel in Eckers' "Icones," etc., fig. 14. I Virchow's Archiv, Band x., p. 190. NERVOUS CONSTITUENTS OF THE RETINA. 'I'll and optbalmoscopically. Two varieties have been noticed, in one of vliich the medullated fibre tract is continuous with the optic disk,* •\\hilst in the other and less common case isolated white spots appear upon the retina at some distance from the disk, so that here the medulla, after disappearing at the point of entrance of the optic nerve, reappears after the fibres have run for a certain distance.! Amongst Mammals it has been known since the time of Bowman that medullated nerve fibres were prolonged into the retina in the Rabbit and Hare.J In these animals two white fasciculi run diverg- ingly outwards in opposite directions, which render the retina mode- rately opaque, but perhaps are not altogether incapable of perceiving light, since, as I have satisfied myself, the bacillar layer is well de- veloped behind them. A small quantity of medullary substance, which however scarcely interferes with the transparency of the optic-fibre layer, is found, as Leydig has pointed out, around the nerve fibres of the retina in many Fishes, and he remarks that the primitive nerve fibres of Sharks and Rays are " sharply contoured and varicose. § H. Miiller also men- tions the fact that some of the fibres within the globe of the eye in Fish are composed of axis-cylinder and medullary sheath. || A some- what similar appearance may also be seen in Birds. A very remarkable deviation from the normal condition is exhibited in the thickenings of the nerve fibres of the retina, which in cases of Bright's disease were regarded as the cause of certain white spots occurring in this affection, and were considered to be bipolar ganglion cells. These varicosities resembling bipolar ganglion cells were first described by Zenker and Virchow, and their true nature was recog- nized by H. Miiller.^" They are formed of fusiform thickenings and * Donitz (Reichert and Du-Bois Reymond's Archiv, p. 741, 1864), by whom this persistence of medulla was first demonstrated ophthalmoscopi- cally, established the fact that in his own eye the part in question was, like the disk itself, blind; i.e., is either quite incapable of transmitting light, or that there is no layer of rods and cones behind it. t See for example the cases given by v. Recklinghausen in Virchow's Archiv, Band xxx. , p. 375. J See H. Miiller, Zcitschrift far ivissenschaftliche Zoologie, Band viii., p. 64. § Beit-rage zur Mikroskop. Anat. und Entwicklungsgeschichte tier Rochen n,td Haie, p. 24, 1852. j| Zdtschrift fiir ivissenschaftliche Zoologie, Band viii., p. 22. IT v. Grafe's Archiv fiir Ophthalmologie, Band iv., 2, p. 41. Q2 228 THE RETINA, BY MAX SCHULTZE. condensations of the non-medullated fibres ; their substance is firmer and more lustrous than the healthy axis-cylinder, and is capable of resisting decomposition for a longer period. Section of the optic nerve in the orbit in animals is followed by atrophy of the nerve-fibre layer (Lehmann), and this, according to Krause, is preceded by a deposit of fat molecules in the transparent pale fibres, which form of degeneration extends to the elements of the following layer, to wit, the ganglion-cell layer. On the outer side of the nerve-fibre layer, and extending over the greatest part of the retina, is a simple layer of nerve, cells or corpuscles, separated by interspaces of various size, which is designated the layer of ganglion cells. Near the macula lutea of Man, two or three such cells are superimposed upon one another, whilst at the yellow spot itself, with sup- pression of the nerve-fibre layer, the ganglion cells come to be arranged in a single layer. The size of these cells varies to an extraordinary extent in the same retina; so that sir all ones not exceeding fifteen micromillimeters are found in close proximity with others of double that size or more. All have the peculiar finely granular appearance of the cell substance presented by the nerve corpuscles of the ganglia of the central organs, and are for the most part without yellow pigment,* which it is well known often occurs in other nerve cells ; they contain a relatively large homogeneous transparent nucleus, with the large nucleoli that all ganglion cells possess, and in the interior of this again, is here and there a small vesicle or granule. Notwithstanding the difficulty of isolating perfect specimens of these cells, a large number of observations have been made on the long and branched processes, which, like the ganglion celL of the nervous centres, they give off. A particular condition of maceration of the retina, not easily hit upon, appears to be requisite in order to permit the isolation of these cells to be satisfactorily accomplished; at least, we can only thus explain the circumstance that the best preserved processes of these cells that have hitherto been observed, were obtained * According to Corti, the ganglion cells of the retina of the Elephant have a yellowish or yellowish-brown colour. . NERVOUS CONSTITUENTS OF THE RETINA. '1'1\) from the eyes of an Elephant, that were not removed from the body until seven days after death * Ganglion cells, with their processes, may be observed in the perfectly fresh retina, if portions taken from the neighbourhood of the ora serrata, and from the surface of which the vitreous has been removed, are examined in serum, with this sur- face upwards. Lying among the decussating nerve fibres, and immediately beneath the membrana limitans interna, in the same plane with the capillary bloodvessels, numerous gan- glion cells may be then seen, which, by cautious manipulation, the production of a cloudy appearance by coagulation being avoided, and the pressure of the covering glass being gradually increased, become more and more distinct, and well adapted for observation, even with the highest powers. Such, so to say, living ganglion cells (fig. 346, A) present an extraordinary de- gree of transparency, since they contain only very small gra- nules in their cell substance, and are composed essentially of an almost hyaline mass, in which the perfectly transparent nu- cleus, with its lustrous and often finely dentated nucleoli, lies imbedded. Dead ganglion cells which in such preparations may be found at the margin of the section, or where the retina has been otherwise injured, present a totally different aspect, be- coming, by coagulation, coarsely granular and perfectly opaque. More minute examination of the former with higher powers, shows that the fine granules of the cell substance lie to some extent in rows, and are grouped in parallel striae, whilst the non-granular cell substance appears also differentiated into bands. This character is precisely similar to that which I first described as occurring in the ganglion cells of the brain and spinal cord.f The cell substance is hence probably fibrillar, and contains, in addition, an interfibrillar granular substance ; but the transparency of the cells of the retina during life is so great, and the fibrils are so fine, that the image they present is less distinct than that, for instance, of the cells of the spinal cord. In the next place, the fibrils around the nucleus possess an approximatively concentric arrangement, whilst at the peri- * Corti, Zeitschrift fur wiss. Zooloyie, Band v., p. 90, Taf. v., 1854. t In this Manual, Vol. i., p. 171 et seq. 230 THE RETINA, BY MAX SCHULTZE, phery they pass into the processes springing from the ganglion cells. Several such processes may often be seen in fresh pre- parations, of considerable thickness, and undergoing more or less ramification. If a process runs out unbranched and straight, it cannot, either by its refractile power or its intimate struc- ture, be distinguished from the fibres of the optic nerve, since the latter, as has been mentioned above, likewise possess a fibrillar structure. This extremely delicate fibrous structure of Fig. 34G. . Fig. 346. A, Ganglion cells from the fresh retina of the Ox, taken from the neighbourhood of the ora serrata, in situ • a, nerve-fibre process passing into a fasciculus of optic fibres ; 6 6, processes which lose themselves in the granulated layer ; c, small ganglion cells, very commonly found near the larger ones. B, Ganglion cells of the macula lutea of Man ; a, their central ; 6, their peripheric pro- cess. Magnified 500 diameters. the ganglion-cell substance cannot be rendered more distinct by the aid of reagents; but, on the contrary, it rather tends to disappear with the occurrence of granular coagulation. Even iodized serum and perosmic acid destroy the transparency of the cells. Surface views of still living retinas are obviously not well adapted to enable a correct estimate to be formed of the number of processes given off by the ganglion cells. In many NERVOUS CONSTITUENTS OF THE RETINA. 231 of the cells it is scarcely possible to see whether any processes are given off at all, either on account of their being so closely compressed against one another, or because they are covered by the fibres of the optic layer. The results of the examination of teazed-out preparations and sections, so far as they have been at present used for the study of the ganglion cells, show that the number of these processes, like those of the ganglion cells of the central organs of the nervous system, varies con- siderably. Cells with many processes have been most com- monly depicted, but many cells also occur with only two processes, as at the yellow spot (fig. 346, J5), and unipolar cells have also been described. In 1850, Corti* pointed out the similarity of the appearance of some of the ganglion-cell processes to fibres of the optic nerve layer, and, relying essentially upon the above-described fusiform varicosities, which occur in both, came to the con- clusion that the optic-nerve fibres were directly continuous with the ganglion cells. Attention has been called to the agreement in character of the ganglion-cell processes with the nerve fibres of the retina, by Remak, Hannover, H. Miiller, Kolliker, and many others. The cells lie in immediate contact with the layer of nerve fibres, and are, in fact, interposed be- tween the fasciculi of the latter, whilst their processes may be followed for considerable distances, and agree in all points with the fibres of the optic-nerve layer ; under these circumstances it is impossible to doubt that the fibres are directly continuous with the cells. Another question is, whether all optic-nerve fibres are connected with ganglion cells before they reach the external layers of the retina. It is possible that a part of those differences in the function of the several optic-nerve fibres which we are compelled to admit on physiological grounds, stand in direct relation to the presence or absence of a connection between the fibres and the ganglion cells. Upon this point, however, no positive statement can at present be made. According to a method suggested by Manz,f the optic layer * Mliller's Archiv, 1850, p. 273, Taf . vi. t Zeitscfirift fur rationelle Medizin, Band xxviii. , p. 231, 1866. 232 THE RETINA, BY MAX SCHULTZE. of the retina of the Frog can be so detached in specimens pre- pared with alcohol, that the ganglion cells come away with them,* and the connection of the latter with the optic fibres can thus be most distinctly brought into view. The majority of the cells then appear to be unipolar. Manz nevertheless admits that the numerous and probably peripherically directed processes of these cells, demonstrable by other methods, are broken off in this mode of preparation. We only know, there- fore, in respect to these processes of the ganglion cells of the retina which do not disappear in the optic-fibre layer, that -a portion run towards the granulated layer. Anastomoses of the cells with each other, effected by thick processes, have been depicted by Corti in the Elephant. It remains to be shown whether such connecting processes, which have not been again observed, are to be regarded as normal. As in the optic-fibre layer, so also between the ganglion cells, the radiating supporting fibres form a kind of framework, which will be subsequently described. Section of the optic nerve in animals is followed, according to W. Krause, by fatty degeneration of the ganglion cells.'f' In the eyes of blind persons in whom the disappearance of the layer of nerve fibres of the optic nerve can be anatomically demonstrated, there is usually also atrophy or complete absence of the ganglion cells, as is seen especially in glaucoma resulting from an increase of the intra-ocular pressure. The peculiar appearance of the internal granulated (mole- cular) layer of the retina is due to the admixture of a very fine plexus of spongy connective tissue, given off from the hereafter-to-be-described radial supporting fibres, with im- measurably minute nerve fibrils. The latter, as Pacini J and Remak § first pointed out, form an essential constituent of this layer. They may be isolated in properly macerated retinae * H. Miiller (Zeitschrift fur wiss. Zool. , Band viii. , p. 21), even at that date (1856), remarked in regard to the retina of Fishes, that " if the ner- vous fibre layer were raised from the inner surface of the retina with forceps, a portion of the cells was easily detached with them." t Membrana fenestrata, p. 38. I Nuove ricerche sulla tessitura intima della retina. Bologna, 1844. § Medicinische Centralzeituny, 1854. No. 1. NERVOUS CONSTITUENTS OF THE RETINA. 233 for short distances, when they appear as extremely delicate and very tortuous fibres, beset with distinct fusiform varicosities, but otherwise smooth. The thicker and branched ganglion-cell processes which dip into this layer, or belong to it from their first origin from the cells, can be still more distinctly followed, though little is known in respect to their mode of termination. Some are continuous with immeasurably fine fibrils, which, after a circuitous path, at length reach the outer layers of the retina, whilst others, especially at the yellow spot, enter the inner granule layer in the form of thick fibres. Such state- ments have been made, amongst others, by H. Muller * and K6lliker,-f- Gerlach,! Manz,§ and Merkel.|| The macula lutea, on account of its less resistant connective tissue, appears to be the part of the human retina best adapted to follow to their termination the nerve fibres running in the granulated layer. But inasmuch as the ganglion cells are here almost all bipolar, whilst they are elsewhere multipolar, it becomes a question whether great differences do not also exist in regard to the course pursued by these processes. Speaking generally, the same differences of opinion are held respecting the nature of this granulated layer as of the grey granulated substance of the cortex of the cerebrum.^I In particular, it is doubtful whether, besides the fine and the very finest nerve fibres and the plexuses of the connective substance, a certain number of minute granules of unknown nature are not also present, as appears to be the case, or whether the nerve fibrils and spongy connective substance give rise by their peculiar disposition to the finely granular appearance. In regard to the course and ultimate destiny of the processes of the ganglion cells and the fine nerve fibres of this layer, we must admit the impossibility of giving any positive statement * Zeitschrift fur wiss. Zoologie, Band viii. , p. 61. t Icones Physiologicce, Taf. xix., fig. 12. X. I Gewebelehre, 2nd edition, p. 498; fig. 220. § Zeitschrift fur rationelle Medizin, Band xxviii., p. 237. j| Macula lutea, p. 11, fig. 9. IT See inter aliosH. Miiller, Zeits. fur ivissenschaft. Zoologie, Band viii., p. 115 ; and Henle and Merkel, Zeitschrift fur rat. Med., Band xxxiv. p. 49, 1869. 234 THE RETINA, BY MAX SCHULTZE. on the basis of the preceding observations, and with the ex- ception of those at the yellow spot. The internal granulated layer interrupts our knowledge of the course of the nerve fibres, which again become visible in the outer layers of the retina. The thickness of the internal granulated layer in Man varies, accord- ing to H. Miiller, between 0 03 and O04 of a millimeter. The cause of the appearance, in sections of the retina of many animals, of dark strise, which run parallel to the surface, and give indications of a lamination of the granulated substance concentric with the tunics of the eye, has not as yet been satis- factorily ascertained. G. Wagner* states that he has counted eight such layers. The spongy connective tissue, as my in- vestigations on the retinae of Sharks show, takes some share in its formation, the meshes being somewhat smaller in the darker bands.f The layer of internal granules which succeeds externally to the granulated layer contains, as VintschgauJ and H. Muller were already aware, two distinct kinds of cellular elements which are connected with two different kinds of fibres that pursue an essentially radial course. Besides the radial sup- porting fibres, which occupy a considerable space in this layer, and intercommunicate by numerous bridges and intercalated plexuses, there are numerous similarly radiating nerve fibres, the course of which only in some few instances differs from that of the supporting fibres, in being directed obliquely towards the surface of the retina.§ These exactly resemble the fibres of the optic layer, and are distinguished by their fusiform varicosi- ties and smooth surface from the rough finely dentated sup- porting fibres. In both kinds of fibres nucleated spots are imbedded, and these represent the so-called internal granules. * Sitzungsberichte der Marburger naturforsch. Gesellschaft,Juli, 1868, No. 5, p. 47. t De retina structura penitiori, fig. 5. * Hicer che sulla structura microgr. della retina dell' uomo, degli animali vertebrati e di Ceptialopodi. Sitzwigsberichte der Wiener Acad. d. Wissen- schaften, Band xi., 1853, figs. 1, 5, 6, 9. § In Falco buteo. Max Schultze, Archiv fur Microscopische Anatomie, Band ii., p. 262. And, according to Hulke, in the yellow spot of Man, Philosoph. Transact., 1868, p. 112. NERVOUS CONSTITUENTS OF THE RETINA. 235 Those of the supporting fibres, which are far less numerous than the others, will be subsequently described ; whilst those which are introduced in the course of the nervous radial fibres, and which, in consequence of the large number of these last, are arranged in several superimposed layers, resemble small bipolar ganglion cells. But the quantity of their very finely granu- lated substance is small, and the nucleus is therefore relatively larger than in the case of the true ganglion cells ; the nucleolus is very apparent in the homogeneous nucleus, but is again rela- Fig. 347. Fig. 347. Internal granules of the retina of Man. Magnified 800 diameters. tively smaller than in the true ganglion cells. Of the two pro- cesses possessed by the inner granules, and which represent the nervous radial fibres, those that are peripherically directed, as described by Merkel,* from the vicinity of the macula lutea, are usually thicker than the central one. In animals also the inner granules appear to have usually two processes,! though it is only by a happy accident they can be clearly isolated, and we are therefore still far from having an exact knowledge of the ner- vous inner granules and their processes in various regions of the retina, either of Man or of animals. A few inquirers, as Ritter, J have described more than two processes. Great variations occur amongst the inner granules. II. Miiller states that in * Loc. cit., p. 11. t M. Schultze, Archiv. fiir Mik. Anat., Taf. xiv., fig. 96, from the Cat. Hasse, loc. cit., p. 257. I Wallfischauge, p. 37. 236 THE RETINA, BY MAX SCHULTZE. Man, as amongst the Yertebrata generally, the innermost layer frequently contains somewhat larger granules. Besides these two forms and the nuclei of the supporting fibres, W. Krause* distinguishes a fourth kind of internal granules, which form the outermost layer, and project into the external granulated layer (Krause's membrana fenestrata). These he believes are unipolar, and have no connection with the outer layers of the retina,f but form the terminal organs of the optic fibres. A structural difference exists in some animals, especially amongst Fishes, in regard to the cells projecting into the inner granule layer, which unite with the layer I have termed the fenestrated intergranule layer (stratum intergranulosum fenes- tratum).^ I consider these to be formed by a special develop- ment of the connective tissue of the next layer. The thickness of the internal granule layer in Man amounts, according to H. Miiller, to 0*03 or 0'04 of a millimeter, dimi- nishing towards the ora serrata, where, at most, three tiers of granules lie superimposed upon one another, to O02 of a milli- meter, but increasing at the yellow spot to about 0'06 of a millimeter. The layer of internal granules is separated from the layer of external granules by an intergranule layer, which consists of a thin layer of fine plexiform tissue enclosing a few nuclei and smooth cells, with coarser fibres running parallel to the surface of the retina, which are capable of being raised in the form of thin laminye. In Man and the higher Vertebrata this appears in sections of the retina as a finely punctated granular layer, which, though much thinner, presents a very close resemblance to the internal granulated layer. On this account Henle designated it the external granulated layer, a term that, as already stated (p. 220), we shall adopt in order to avoid con- fusion with H. Muller's intergranule layer. W. Krause has re- cently employed the term membrana fenestrata to indicate it. The external granule layer, in its simplest form, as seen in Man and Mammals, consists of a thin layer of granulated * Membrana fenestrata, p. 42. t See W. Krause's Schema, loc. cit. , Taf . ii. , fig. 21, gri. $ De Retime structura, 1859, p. 13. NERVOUS CONSTITUENTS OF THE RETINA. 237 substance of tolerably equable thickness in Man, amounting to about ten micro-mill, through the whole retina. In the finely striated matrix of the connective tissue, extraordinarily fine fibrils are imbedded, which run without branching for consider- able distances, either obliquely or parallel to the surface of the retina, and are to be regarded, like the similar ones of the internal granule layer, as nerve fibres, on account of the fine fusiform varicosities they present, and their otherwise smooth surfaces. These fibres are in part developed from the peripheric processes of the internal granules, and in part from the fibres of the rods and cones. Isolated nuclei are scattered generally in this layer, but probably all belong to the connective tissue, which at this spot presents many modifications in different animals that will be hereafter described. We possess no more information of the nervous fibres of this layer than of those of the internal granule layer. Their course deviates from the radial ; and although, in occasional instances, fibres may be seen passing straight through it,* the greater number appear to form a fine plexus in the plane of the retina, so fine and complex, indeed, as to be equalled only by the grey substance of the central organs. TJte rod and cone fibres, which form an essential constituent of the external granule layer, are rooted by their inner ends in the external granulated layer. All the so-called external gra- nules are nucleated swellings of these fibres. The layer of the rods and cones is immediately superimposed upon the external granules, owing to the above-named fibres being in direct continuity with the latter. A sharp contour- line which in transverse sections of the retina divides the external granules from the rods and con;s, constitutes the external limiting membrane. In most parts of the retina of Man, and almost everywhere in animals, the space intervening between the limitans externa and the external granulated layer is not larger than is necessary for the disposition of the external granules (a single nucleus corresponding to each rod and cone) and the fibres belonging to them, putting aside the small quantity of connective tissue which * Hasse, Zeitschrift fur rat. Medicin, Band xxix., p. 255. 238 THE KETINA, BY MAX SCHULTZE. is present in this layer. In this case, which is "by far the most common, the external granulated layer forms a true intergranu- lar layer. In the posterior part of the fundus of the eye, and sometimes in the vicinity of the macula lutea of Man, the space intervening between the limitans externa and the external granulated layer becomes much more considerable. Instead, Fig. 348. Fig. 348. From the posterior part of the fundus of the human retina. 6, External granulated layer ; 7, external granule layer ; 8, limitans externa ; 9, rods and cones, the external segments of which are sharply differentiated from the internal cylinders. Magnified 800 diameters. The supporting fibres of the connective tissue are omitted in this figure. however, of the external granules separating from one another, they remain in close apposition to the limitans externa, form- ing a multiple layer, whilst internally a free space appears, in which are no granules, and which is essentially occupied by the fibres of the rods and cones running to the external granu- NERVOUS CONSTITUENTS OF THE RETINA. 239 lated layer. If the whole space between the limitans externa and the external granulated layer is to be named the " external granule layer," it is still to be noted that an internal division of the external granule layer exists here which is free from granules, and has been named by Henle the external fibrous layer. It must be observed, however, that rod and cone fibres occur everywhere in the external granule layer, and therefore in that part also where the special name of external fibrous layer is not applied to it. As the adjoining figure shows, the cone fibres are thicker Fig. 349. Fig. 349. Cone 'and cone fibre, the latter presenting varicosities, from the vicinity of the yellow spot of the retina of Man. Magnified 500 diameters. than the rod fibres. Both are pale, with a smooth surface, and especially in the case of the thin rod fibres are very easily broken down. Their disappearance in dilute solution of chromic acid or of perosmic acid stands in direct relation with the above- mentioned occurrence of varicosities, since the more dilute the solution the larger do these become, and the fibres ultimately swelling in every part are destroyed. These appearances agree completely with those we have observed in the nerve fibres of the retina. The thicker and somewhat more resistant cone fibres undergo similar metamor- phoses to the rod fibres, the distinctness with which this may be seen being proportionate to their length ; it is therefore most obvious at the macula lutea. When moderately hardened, they appear as pale perfectly smooth fibres which never branch, or anastomose, or pass into spongy plexuses, and are thus sharply differ entiated from the radial supporting fibres and the connect- ing substance that surrounds them. In fluids in which the optic fibres exhibit strongly marked varicosities, distinct vari- cosities also usually occur in the cone fibres, leading ultimately to their complete swelling and solution (fig. 349). Lastly, they exactly resemble the thicker fibres of the optic layer, in the circumstance that, under high powers, they present 240 THE RETINA, BY MAX SCHULTZE. the appearance of being finely striated longitudinally, and therefore give some indication of being composed of fine fibrils, which we regard as characteristic of all the thicker axis- cylinders (fig. 350). On reaching the external granulated layer, the cone fibres present a peculiar modification ; each forming at the outer sur- face of this layer a conical triangular enlargement (fig. 348, 6), beyond which it is impossible to follow the fibre continuously.* These are so firmly imbedded in the substance of the exter- nal granulated layer as to give the impression that they are continuous with it. The cone-fibre spheroids, when isolated, have for the most part fragments of the granulated substance still adherent to them, supporting the view of their continuity. It is true that the conical enlargements in question here break up into fine fibrils, but these are different from those of the plexus. In successfully made preparations of the retina of Man, mace- rated in iodized serum, I have seen the conical enlargement break up into a brush of numerous and extremely fine fibrils, which were not joined together in a plexiform manner. f If we com- pare with this appearance that of the network of the external granulated layer, similarly hardened and isolated, the difference between the two kinds of fibres becomes exceedingly evident. This is further evidenced, on the one hand, by the ease with which the continuity of the plexus with the radial supporting fibres can be demonstrated ; and on the other, by the manifold differences in appearance between the latter and the cone fibres, especially in the disposition to form varicosities, exhibited by the latter and* the nerve fibres on their side, but which does not occur in the radial supporting fibres, whilst these, on the other hand, are characterized by their peculiarly rough surface. With these facts, the relation of the cone-fibre enlargement to the external granulated layer cannot, as is believed to be the * H. Miiller, Zeits. fur wissenschaft. Zoologie, Band viii., Taf. i., figs. 1 and 3 ; Henle, Eingeweidelehre, p. 650 ; M. Schultze, Archiv fur Mikros- kop. Anatomie, Band ii., Taf. xxxi. t Hasse (Zeitschrift fiir rat. Med., Band xxix., p. 252), believed that in all instances three of such fibrils emanated from each conical en- largement, whilst Merkel, loc. cit., p. 7, considers that (at the macula lutea at least) a bifurcate division normally occurs. NERVOUS CONSTITUENTS OF THE RETINA. 241 case by W. Krause,* constitute a counterproof against the nervous nature of the cone fibres. The rod fibres, again, can only be followed as far as, or just into, the external granulated layer. Our knowledge of their mode of termination is, however, still more imperfect than in regard to the cone fibres. The great delicacy and destructi- bility of the internal portion of the rod fibres in Mammals and Man only permit them to be exceptionally preserved through- out their whole course to the external granulated layer. Very frequently, and especially where numerous and large varicosi- Fig. 350. Fig. 350. Cone fibres, with and without varicosities, from the inner part of the external granule layer of the macula lutea of Man. Magnified 1,000 diameters. ties appear in the course of the rod fibre, it terminates just above the external granulated layer with a clavate enlarge- ment.f This gives the impression of being a diminutive re- presentative of the cone-fibre enlargement, though I have not been able to observe any division of the rod fibres into the fine fibrils so characteristic of the cone-fibre spherule. In Fishes, however,:}: and still more in Birds and Amphibia,§ there is no doubt upon the point. The external granule layer in the last- named animal's consists, for the most part, of only two layers * Membrana, fenestrata. t Max Schultze, Archivfiir Mikroskop. Anatomie, Band ii., Taf. x., fig. 1 ; Hasse, loc. cit., p. 248. t Max Schultze, Archiv fur Mikroskop. Anatomic, Band ii., Taf. xi., figs. 8 and 9. § Idem, figs. 18 and 19. VOL. III. 11 242 THE RETINA, BY MAX SCHULTZE. of granules, which are connected with the external granulated layer by very short fibres. The rod granules and cone granules, and the fibres belonging to them, are here very similar, and break up at the outer granulated layer in the same manner into fine fibres. In Fishes, where the difference in the thick- ness of the more elongated rod and cone fibres is again very apparent, the conical enlargement of the rod fibres is also very similar to that of the cone fibres. In short, everything favours the view that no other essential difference exists between the rod and cone fibres than in their thickness, and that the rod fibre probably always breaks up into a number of fibrils at the external granulated layer, and thus also, like the cone fibre, is in reality a fasciculus of fibrils. In Mammals and in Man the rod fibres are very delicate, but are always several times thicker than the finest fibrils of the optic nerve. This is especially true of the external peripheric part which is turned towards the limitans externa, and which constantly and considerably exceeds the thickness of the internal central portion that extends from the external granule to the external granulated layer. Every rod and cone fibre is connected with one of the so- called external granules ; that is to say, each of these fibres has at some point in its course an enlargement in which a nucleus is imbedded, and this is named a rod or cone granule (see fig. 347). If the fibres in question are nerve fibres, the granules must be comparable to small bipolar nerve or ganglion cells. The quantity of the cell substance, however, is very small, yet still somewhat greater in the constantly larger granules of the cones than in those of the rods. The nucleus fills the interior of the granule almost completely, is of hyaline appearance, and contains a bright nucleolus, which is larger in a cone than in a rod granule. Except at the yellow spot, the rod nuclei are much more numerous than those of the cones ; they are superimposed in several tiers upon one another, and are so closely arranged as to be in contact. The cone granules lie just beneath the membrana limitans externa, except where, as at the macula lutea, the cones are so closely placed that the granules belonging to them are necessarily in several layers.* * Exceptionally in the more peripheric parts of the retina the interval NERVOUS CONSTITUENTS OF THE RETINA. 243 Thus it appears that the'cone fibres are not, properly speaking, interrupted by the cone granule, but originate in it ; for in most instances the cone itself is attached to the outer surface of the cone granule, whilst in the case of the rod granules, in conse- quence of their not lying immediately beneath the limitans externa, the connection of the rods is effected by a portion of the rod fibre, of similar nature, only somewhat thicker than the portion which extends to the external granulated layer. This last-named internal division of the rod fibre must ob- viously become shortened to a minimum, whilst the outer division must be proportionately elongated in those rod granules which are closely applied to the external granulated layer. The rod and cone granules are perfectly transparent during life, the difference in the refractive power for light of the cell substance, nucleus, and nucleolus being scarcely perceptible ; granular cloudiness becomes apparent in them after death, either in consequence of spontaneous coagulation, or owing to the action of reagents. In like manner it appears that the occurrence of transverse striae or bands in the rod granules, described by Henle,* which can be observed sooner or later after death in Man and Mammals, and which may be rendered very distinct by the action of dilute acids,t is a post-mortem appearance depending on a partition of the nucleus or of the contents of the nucleus.^ If the external granules represent a peculiar form of nerve cell introduced in the course of the nervous rod and cone fibres, the rods and cones themselves must constitute the nervous between the cone and the cone granule is also increased. The peripheric part of the cone fibre is then always thicker than the central part, extend- ing from the granule to the granulated layer. (See below, fig. 355.) * Gottinger Nachrichten, May and November, 1864, No. 7. t Max Schultze, Archiv fur Mikroskop. Anatomic, Band ii., p. 219. According to W. Krause (Membrana fenestrata, p. 32), they may also be observed in the cone granules. £ W. Krause, Anatomie d. Kaninchens, p. 129. See also, in regard to the still unexplained appearance of transverse striae, Hitter in Grafe's Archiv, Band xi., Abtheil i., p. 89. G. Wagener (Sitzungsberichtc der J\V turwissenschaft. Gesellschaft zu Marburg, 1868, No. 5) remarks in regard to the transverse striation, that in fresh preparations it is more distinctly visible with low, than with high powers. R 2 244 THE KETINA, BY MAX SCHULTZE. terminal organs of the optic nerve. The anatomical connection is perfectly clear, since it may be seen that each flask-shaped cone situated outside the membrana limitans externa is con- tinuous with a granule, whilst each rod-fibre is continuous with a rod, which either springs directly from a rod granule, Fig. 351. Fig. 351. From the posterior part of the retina of Man. 6, External granulated layer ; 7, external granule layer ; 8, limitans "externa ; 9, rods and cones, the external segments of which are sharply denned from the internal. Magnified 800 diameters. The supporting fibres of connective tissue are omitted in this drawing. if the granule be placed just beneath the membrane, or if not, with the intervention of a thicker portion of the fibre. The layer of rods and cones thus covers like a wood of close- set palisades the outer surface of the external granule layer, and completes the formation of the retina as a nervous ex- pansion. The conversion of luminous waves into nerve move- NERVOUS CONSTITUENTS OF THE RETINA. 245 ment, which is the fundamental condition of the visual act, must take place at this spot. The rods are cylindrical bodies with a length at the back part of the eye in Man of fifty to sixty micromillimeters, and a thickness of two micromillimeters ; more anteriorly, near the ora serrata, they are somewhat shorter, though equally thick. They stand in close apposition, so that there is not much more space between them than results from their cylin- drical form. Distributed at regular intervals between the rods, except at the macula lutea and the ora serrata, are the flask- shaped cones. The distance between two cones amounts on an average to eight or ten micromillimeters, the intervening space being occupied by three or four rods in a straight line. The average thickness of the cones at their base, with the exception of those of the macula lutea, varies from six to seven micromillimeters. Externally they diminish like a wine flask, and are not unfrequently slightly distended just above the base ; they terminate in a conical point, the extremity of which is in a plane anterior to that of the rods, so that the cones are shorter than the adjoining rods. Like the rods, the cones also become shorter towards the ora serrata, and still earlier increase in thickness. In both structures two essentially different segments are distinguishable, which have been named respectively the ex- ternal and the internal segment, by W. Krause.* The dis- tinction is most marked, and has been longes.t known, in the cones, in which the conical point characterized by its higher refractive power had previously been indicated by H. Miiller as the cone-rod. The rods present a similar structure, except that the external segment is not conical in form, but for the most part regularly cylindrical.! The junction between the external and the internal segment in the rods of Man is situ- * Gottinger Nachrichten, 1861, No. 2. Zeitschrift fur rat. Medidn, Bandxi., p. 175. 1861. t In Amphibia only (Frog, Triton, Axolotl) does the diameter of the external segment of the rod slightly decrease towards the outer extremity. This is particularly observable in young animals (A rchiv fur Mikroskop. Anatomic, Band iii., Taf. xiii., fig. 14), and may in some instances ren- der it impossible to distinguish the rods from the cones. 246 THE KETINA, BY MAX SCHULTZE. ated in the posterior part of the fundus, at about the middle of their length. I estimate the length of each segment in this region at about twenty-five or twenty-seven mieromillimeters. The boundary line between the external and the internal segment of adjoining rods lies, for the most part, in one and the same plane. The plane of junction of the two segments in the cones, however, is different, being situated more anteriorly both in Man and Mammals. The inner segment of the cones (the body of the Fig. 352. Fig. 352. Cones and rods, 9 ; limitans externa, 8 ; and part of tlie external granule layer, 7 ; from the posterior part of the retina of the Pig. Each of the cones, which are in very close apposition, contains in its inner segment a highly refractile body, the function of which is unknown. Magnified 800 diameters. cone) is consequently always shorter than that of the adjoining rods; the difference in length between the inner segments of the rods and of the cones at the posterior part of the eye amounting in Man, upon the average, to six mieromillimeters. On account of the great difficulties encountered in obtaining a view of the fresh and uninjured cones, it is by no means easy to ascertain their exact length. It appears, however, to be the rule that where rods and cones occur mingled together, the outer segments of the cones are always shorter than those of the rods. In Man I estimate the length of the conical outer NERVOUS CONSTITUENTS OF THE RETINA. 24)7 segment of the cones, which have been taken from the back part of the eye, and preserved as perfectly as possible, to be twelve micromillimeters. This is about one half of the length of the corresponding part of the adjoining rods. Great differ- ences in this respect exist amongst animals. Thus, for example, in the Pig, the retina of which contains an extraordinarily large number of cones, the small length of the latter in comparison with the rods is very striking. At certain points the cones, with their external segments, scarcely reach the line of junction of the outer and inner segments of the rods. (See the adjoin- ing woodcut.) The difference in the refractive powers of the two segments of the rods and cones is apparent even in perfectly fresh specimens, but becomes still more distinct after death, coincidently with the occurrence of post-mortem changes that then rapidly take place, even with the most careful treatment. These changes consist partly in the originally homogeneous substance of the somewhat less strongly refractile internal segment becoming cloudy and finely granular, whilst the outer segment remains homogeneous and highly refractile. As a consequence of this, the line of junc- tion of the two segments is rendered more distinct. Whilst the rods can be preserved for some time in indifferent fluids without undergoing further alteration, a process of coagulation usually occurs in the inner segments of the cones, rendering them coarsely granular and progressively more and more opaque, their outer segments soon becoming wholly unrecognizable. In these last alterations set in almost unavoidably immediately after the preparation of the fresh specimen, resulting in the arching and curvation of the whole structure with division into disks, which after remaining connected for some time ultimately become swollen up and disappear. The same changes are undergone, though more slowly, by the outer segments of the rods. The peculiar alterations that have long been known to occur in them when floating in serous fluids, especially after dilution with water, and which have been regarded as a kind of coagulation, depend, as I have shown,* upon imbibition of fluid, which in the first instance produces * Archivfiir Mikroskop. Anatomie, Band iii., p. 224. 248 THE RETINA, BY MAX SCHULTZE. a very apparent and regular transverse striation, and leads quickly to a separation of the substance into disks. As the process of imbibition in many instances does not occur with uniformity,, curvatures, crook-like archings, and various other alterations of form, are occasioned in the outer segment, the final result of which is a spheroidal body resembling certain myelin drops. The larger rods of the fresh retina of the Frog, isolated in serum, always exhibit in parts a very fine transverse striation when examined with centric illumination and a magnifying power of from 500 to 800 diameters. When this is not at first observable, it can be rendered distinct by very oblique illumina- tion* As soon as swell ing 'takes place in the substance of the outer segment, in consequence of imbibition, disks may be seen to separate, and these again undergo further change, especially in serum diluted with water, swelling up and becoming ulti- mately totally unrecognizable. The rods of the retina, both of Man and animals, undergo precisely similar changes. The highest powers of the microscope and very oblique illumina- tions are however indispensable at an early period, before swelling with prolongation of the external segment has taken place. The external segment of the rods of Man and Mammals which whilst still warm have been placed in a one or two per cent, solution of perosmic acid, and have been thus preserved absolutely unaltered in form, exhibit, when examined with a power magnifying 1,000 diameters and very oblique illumina- tion, a striation which is as sharp as a hair line drawn on copper, and is about as fine as the markings of Nitschia sig- moides, which is one of the most difficult test objects to resolve amongst the Diatomaceae. This would correspond to a distance between the lines of 0.3 to 0.4 of a micromillimeter. In the cones the disks are somewhat thicker.f * Max Schultze, Archiv fur Mikroskop. Anatomic, Band v., p. 380. Note. t Direct measurements may be found in Schultze's paper in the Archiv fur Mikroskop. Anatomic, Band iii., p. 228, and in that of Zenker, idem, p. 259. By the application of a more perfect system of lenses, I now obtain somewhat smaller numbers than those given in the above. W. Krause's objections are contained in his Essay on the Membrana fenes- trata, p. 23. NERVOUS CONSTITUENTS OF THE RETINA. 240 Besides this structure, so characteristic of the outer segments fresh or well-preserved specimens also exhibit a longitudinal striation.* This, as Hensen first recognized, depends upon the presence of a number of folds running in the direction of the long axis, or in elongated spirals which at the same time vary in depth. As it frequently occurs that in rods preserved in osmic acid, friction or pressure causes the separation of disks of varying thickness, which turn their flat surfaces to the f Fig. 353. Outer segments of rods and cones, a — d, Rods from the Frog ; e, from Man ; /, twin-cone from a Fish (Perch) ; a, fresh rod still connected with the internal segment (s', lenticular body) ; 6, first stage of imbibition in serum ; c, the same stage in dilute solution of potash, magnified 500 diameters ; d, disintegration of a rod into disks in serum, magnified 1,000 diameters ; e, appearance presented by a rod from the retina of Man immersed in strong solution of per osmic acid immediately after enucleation, and macerated for twenty-four hours, magnified 1,000 diameters ; /, fresh rod examined in serum. observer, it is easy to obtain a clear image of the relief of the surface. In such disks, shown in fig. 354, besides the grooving of the surface, there is some indication of radial cleavage of the substance of the rod proceeding from the bottom of the grooves. Fresh rods examined in serum exhibit here and there longitu- dinal fissures. The appearances presented by the surface of the disks, which call to mind blood corpuscles, the edges of * Hensen in Virchow's Archiv, Band xxxix., Taf. xii., fig. 7. Max Schultze, Archivfiir Mikroskop. Anatomic, Band v., Taf. xxii. 250 THE RETINA, BY MAX SCHULTZE. which have become serrated, are not caused by a process of shrinking. The form of the natural transverse section of the o outer segment in the fresh state is exactly the same. I have shown that the longitudinal striation, which is more easily seen in Amphibia and Fishes on account of the larger size of the outer segments, is also present in Man and Mammals, and here also probably depends upon a channelling of the surface. It is a highly remarkable circumstance that the transverse section Fig. 354. ooO o QCPQ Fig. 354. a, External segment of a Triton examined in the fresh condition in serum ; b, thin disk of the same, broken off after treat- ment with a two-per-cent. solution of perosmic acid, seen some- what laterally. The remaining figures represent similar or even still thinner disks, seen from the surface, with fissures penetrating to a variable depth. Magnified 1,000 diameters. of the large external segments of Amphibia (Triton) and Fish (Syngnathus) often differs considerably from the circular form, and may present an irregular dentated border, or even be of semilunar shape. Several observers have expressed themselves in favour of the existence of an axis fibre running in the interior of the external segment. Hitter's* first description, as well as the corroborating observations of Manz and Scliiess,")* lead to the supposition that we are here 'dealing with appearances that owe their origin to the action of the preserving fluids ; but if in a perfectly fresh Mammalian retina we obtain a surface view of * Grafe's Archiv fur Ophtlialmologie, Band v., Abtheil ii., p. 101, Taf. iv. t Zeitschrift fur rationelle Median, Band x., p. 305. 1860. J Idem, Band xviii., p. 128. 1863. NERVOUS CONSTITUENTS OF THE RETINA. 251 the still well preserved extremities of the rods in their natural state, it will be found that, by careful focussing, a black point or short line becomes occasionally visible in the centre of the rods,* and this may be attributed to the presence of an axis fibre. Hensenf firmly maintains, in opposition to Krause,^: that the ap- pearance in question is really caused by a pre-existent structure. A perfectly satisfactory explanation of its occurrence has not yet been given ; for no one has hitherto demonstrated the presence, by isolating it, of an axial fibre in the outer segment. It is to be observed also, that no trace of an axis fibre or of an axial canal can be discovered in the detached disks even of the thick rods of Amphibia, however perfectly they may be pre- served. (See the above figures:) On the other hand, it must be admitted that, according to the observations of Zenker,§ there is a difference in the refractive index between the investing layer and the central portion of the rods, which in all proba- bility furnishes an explanation of the appearance in question. These indices are estimated by Zenker to be 1*5 for the maxi- mum, and T33 for the minimum. In the rods of the Frog, || when slightly swollen in perosmic acid, Hensen believed he saw indications of the presence of three axial fibres lying in close apposition.^! Hensen** also, with a few other observers, bslieves that an axial fibre may be distinguished in the inner segment of the rods. W. Krauseft first depicted this in the cones of Birds, when he made it terminate in an ellipsoidal body, to which he applied the term optic ellipsoid. We shall return to the consideration of these bodies when speaking of the rods and cones of Birds and other animals ; nothing whatever of them can be distin- * Max Schultze, Archiv fiir Mikroskop. Anatomic, Band ii., p. 219, Taf. xiv., fig. -5. Hensen, in Virchow's Archiv, Band xxxix.,p. 486, Taf. xii., fig. 4 A. t Archiv fiir Mikroskop. Anatomie, Band iv., p. 347. J Membrana Fenestrata, p. 23. § Archiv fiir Mikroskop. Anatomic, Band iii., p. 259. || Krause more recently estimates the refractive index of the rods to be from 1*45 to 1'47. Membrana fenestrata, p. 25. IT Virchow's Archiv, Band xxxix., p. 489, Taf. xii., fig. 8. ** Loc. cit, fig. 6. +f Anatom. Untcrsuch., 1860, Taf. ii., figs. 5 and 6. 252 THE KETINA, BY MAX SCHULTZE. guished in the rods of Man or of Mammals. The existence of an axial fibre in the inner segment leading up to the ellipsoidal body like the supposed fibre of the outer segment, is however very doubtful. I have myself been unable to discover any axial fibre in the rods of Man. The internal segments of the rods and cones in Man and many animals, on the other hand, exhibit, when very completely preserved in perosmic acid, and carefully examined with the highest powers, a fine longitudinal striatlon on the surface, * which recals that above mentioned of the outer segments of Amphibia, and is in fact, partially at least, continued on the latter. f Even if in these last, however, it is impossible to demonstrate that the striae ar& independent structures by iso- lating them in the form of fibres, the impression given being due rather to simple channelling of the surface (see above), it is nevertheless certain that there are points at which fine fibrils producing the appearance of striation are capable of being strip- ped off the internal segments. In the large cones of the human retina, the striation of the surface is under certain circumstances very distinct. The striae run longitudinally or in long spirals, and are from forty to fifty in number ; they are placed at equal distances from one another, and this amounts at the widest part of the cones to about half a micromillimeter. At the apex of the internal segment they become so crowded, that with the optical means at present at our disposal it is impos- sible to distinguish them. 'Yet the impression is given that the striae are continued in the form of a conical tube on the surface of the outer segment ; for a delicate sheath proceeding from or continuous with the striated cortex of the internal segment may be isolated for a variable distance on the outer. Like those of the cones, the inner segments of the rods of Man and of Mammals present a striated surface. The striae, which are eight or ten in number, run in the form of extremely fine lines placed at equal distances around the internal segment, and parallel to its long axis, or, as in the cones, in elongated * Max Sclmltze, Archiv fur Mikroskop. Anatomic, Band v. , p. 394, Taf. xxii. f Hensen made the first observation on this point in the Frog. Virchow's Archiv, Band xxxix., p. 489. NERVOUS CONSTITUENTS OF THE RETINA. 253 spirals, as far as to the boundary line between the inner and the outer segments. If the latter have become detached whilst still well preserved in perosmic acid, it may be observed that fine fibrils which are continuous with the strise of the internal segment project free from the end, forming a kind of basket by Fig. 355. Fig. 355. Rod and cone from the retina of Man, preserved in a two-per- cent, solution of perosmic acid, to show the fine fibres of the surface, and the different lengths of the internal segment. The outer seg- ment of the cone is broken up into disks, which, however, are still adherent to one another. . Magnified 1,000 diameters. which the outer segment was previously enclosed. In short, it may be said that here, as in the cones, a fibrous investment for the outer segment is formed from the striae of the inner segment, and that this to some extent at least can be isolated. It is possible also, notwithstanding their delicacy, to perceive 254 THE RETINA, BY MAX SCHULTZE. extremely fine longitudinal lines running either in a straight direction, or in easy spirals, upon the highly refractile external segments of the rods of Man. * As has already been stated, these fibres are capable of being partially isolated. At the base of the cones in particular they are easily separable for a certain constant length, and remain, forming by their continuity a short tube composed of stiff fibrils, seated on the membrana lirnitans externa, where the cones have themselves become detached from this membrane. f Examined from the surface, the limitans externa then appears to be finely punctated in circles, the diameter of which corre- sponds with that of the cones, J and gives the impression that the fibrils, of which we considered the cone fibres in the outer granule layer to be composed, here run separately upon the surface of the bodies of the cones. In this event the fibrils would be nerves. Nevertheless, this does not appear to be the case. The fine fibrils can only be followed backwards into the outer granule layer with very great difficulty. I have, however, ascertained this much with certainty, that they are continuous with the tissue intervening between the rod and cone fibres. As this can only be considered to be connective tissue, the fibres in question must represent a prolongation of the delicate and already finely fibrillated or striated connective tissue of the outer granule layer, and form to this extent isolable " supporting basketworks" or cradles for the bases of the cones and rods, § (see below, fig. 360). The further superficial relations of these fibres, especially in the case of the cones of Man, are rendered doubtful by a fresh complication of structure * Max Schultze, loc. cit., Taf. xxii., figs. 7 — 16. -f I have depicted very incomplete portions of these fibres in the Ar- chivfiir Mikroskop. Anatomie, Band ii., Taf. xi., fig. 13a, and they have been described by W. Krause, who has applied the term "needles" to them, as forming a distinct constituent of the retina. Membrana fenes- trata, figs. 4, 5, 21. J Archivfiir Mikroskop. Anatomie, Band v., Taf. xxii., fig. 6. § Landolt has recently described, in the Archivfiir Mikroskop. Anatomie, Band vii. , p. 94, a sheath-like prolongation of the connecting substance over the rods in Amphibia, which must in all essential respects agree with the above-named " fibre-baskets " of the cones of Man. NERVOUS CONSTITUENTS OF THE RETINA. 255 in the interior of the body of the cones. For my observations show that we here find a compact mass of extremely fine fibres kr. 356. O" if -«vf « ?•?" ° v- -.'•GV&SZ Fig. 356. From Man, showing the inner segments of the rods, s s s, and cones, z z', the latter in connection with the cone granules and fibres as far as to the outer granulated layer, 6. The cone zf is cha- racterised by an unusually long bridge between the body and the cone granule (the thicker peripheric part of the cone fibre). The fibrillar structure of the interior of the inner segments of the rods and cones is represented, magnified 800 diameters. B, Inner seg- ment of a cone, with cone granule, and commencement of the cone fibre in which the inner fibrillar portion does not extend so far to- wards the limitans extema, magnified 1,200 diameters ; 0, isolated fibre-cone from the interior of a cone, still shorter than the preceding one, taken from a cone situated near the ora serrata. running longitudinally, which occupy -and form the entire sub- stance of the body of the cone from the surface inwards, so that 25G THE RETINA, BY MAX SCHULTZE. no distinction has hitherto at least been made out between the superficial and the deep fibres. The internal fibrils (which I have already imperfectly depicted in the Archiv fur Mikroakop- Anatomic, Band ii., Taf. x., fig. 8) do not extend quite down to the limitans externa, but cease abruptly at a certain distance from it. At any rate, they here become invisible, and if they extend any further towards the cone fibre, change their nature. Cones are found containing small spheroidal particles like fat drops at the point where the internal fibrils appear to cease, whilst there are others that have snapped across at this point. In the fresh condition the fibrillated portion of the cones appears as a brilliant strongly refractile body. By careful maceration the fibrils may even be isolated. They cease at the point where the outer segment commences. The connection of the outer with the internal segment appears also to be effected by a sheath investing the fibrillar substance. I have been able to recognize a very similar structure, com- posed of short stiff fibrils, in the interior of the inner segments of the rods in Man (fig. 356, A, s s). The appearances presented are precisely similar to those of the cones, and corroborate the view, otherwise well established, that independently of the different thickness of the nerve fibres belonging to them, no essential difference exists between the rods and cones beyond that of form and size, and that thus these two forms of perci- pient elements are only modifications of a type common to both. With the rods and cones we have arrived at the end of the expansion of the optic fibres in the retina, and if we now take a general view of the connection of the nervous elements of the retina of Man, as we are justified by our present knowledge in stating it, we find, in the first place, (see the adjoining schematic representation,) that the non-medullated nerve fibres of the optic layer are directly continuous with ganglion cells. At the macula lutea, where this connection is particularly obvi- ous, all the ganglion cells are bipolar. The peripheric process is the thicker of the two, and enters the internal granulated layer, where it divides. In other parts of the retina the gan- glion cells appear to be for the most part multipolar, in which case there is probably one central process given off into the NERVOUS CONSTITUENTS OF THE EETINA. 257 optic-nerve layer, whilst the remainder run peripherically into the internal granulated layer, where they become exceedingly attenuated by division. The nature and course of the fine gan- glion-cell processes of the internal granulated layer resemble in every respect those of the finest primitive nerve fibrils of the grey substance of the cortex of the cerebrum. During their intricate course they form an extremely close-meshed plexus, and lie imbedded in the tenacious spongy connective tissue, which prevents their isolation for any considerable distance. There is consequently but little prospect that the communication of these ganglion-cell processes with the nervous fibres of the fol- lowing layers will ever be demonstrated. In the layer of the inner granules, nerve fibres are found running perpendicularly to the surface of the retina. But at the macula lutea there are also oblique fibres. Each of these fibres is interrupted by a small cell, an internal granule, or a bipolar ganglion cell, the central process of which (that part of the radial nerve fibre which ascends from the internal granulated layer) is very deli- cate, whilst the peripheric is thick. This probably always loses itself by branching in the external granulated layer, which resembles the internal, and permits as little as the former the course of the fine nerve fibrils that pass through it to be exactly followed. From it the rods and cones arise, standing perpen- dicularly to its surface, except at the macula lutea, where they are oblique. The cone fibres arise by the coalescence of a great number of fine fibrils, each forming a large fasciculus of such fibrils, which resembles a thick fibre of the optic-fibre layer, and is continuous with the nucleated cone granule ; this is a bipolar ganglion cell, the peripheric process of which is usually the cone body itself. If, as often happens, especially at the macula lutea, there is a long intervening space between the cone gra- nule and cone corpuscle or body, this part, which constitutes the peripheric portion of the cone fibre, is again thicker than the other or central portion. The rod fibres are very much smaller than the cone fibres. Whether they also are composed of several fibrils cannot be determined from actual observation, though it is on various grounds probable. The peripheric part of the rod fibres, again, is far thicker than the centric ; each one begins at the external granulated layer with a dilatation which VOL. in. s Fig. 357. Fig. 357. Diagrammatic representation of the con- nections of the nerve fibres in the retina. The num- bers are the same as in the diagram, fig. 344, p. 219. 2, Optic fibres ; 3, gan- glion cells; 4, internal granulated layer ; 5, inner granule layer ; 6, exter- nal granulated layer; 7, outer granule layer ; 8, layer of rods and cones. NERVOUS CONSTITUENTS OF THE RETINA. 250 is comparable to that of the rod fibres, and is in many animals ] >recisely similar. In the rods and cones themselves we see the terminal organs of the optic-nerve fibres. Whether the fibrils in the interior of the inner segments stand in connection with the nerve fibrils of the fibres in question, and form their modi- fied extremities, must remain undecided, as well as the question of the relations of the outer segments to the nerve substance. It is highly probable that the internal and external segments have a common sheath or investing membrane, but that they are in any other way continuous, as, for example, by means of nervous fibres in their interior, is at present a pure matter of theory. Hence it is possible that the nervous substance may terminate at or in the internal segment, and the outer segment may represent a non -nervous physical accessory apparatus. The relation presented in fig. 357 appears to be very note- worthy and important for the explanation of the significance of nerve cells in general; namely, that the processes of the nervous cells of the retina always become thicker towards the periphery than towards the centre. If this difference in thickness depends on a difference in the number of the element- ary nerve fibrils, the latter must become more numerous at the periphery than at the centre, which can only be explained by an augmentation of the number of fibrils within the nerve cells. That the most minute peculiarities of structure presented by the rods and cones of the retina claim our attentive consideration, is obvious when we reflect that we have here to deal with structures that are capable of converting the undulations on which light depends into nerve force. We may and indeed must suppose that the structure of the terminal organs is appropriate to their function, whilst the hope of discovering something artificial in the rods and cones is rightly grounded and supported on the fact that the more exact the research, and the sharper the definition of the instruments employed, the more delicate and the more remarkable are the details brought into view. No doubt but that many persons, in consideration of the extreme shortness of the waves of light, will regard this as too bold a statement. Yet if we bear in mind that the length of these waves amounts to 0'7 of a micromillimeter at the red end of the spectrum, and C'4 at the violet end, which ar«v s 2 260 THE RETINA, BY MAX SCHULTZE. magnitudes that are not beyond the limits perceptible and measurable by the microscope, the statements above made will scarcely appear to be too venturesome. Comparative anatomical investigations will obviously prove of the very greatest value in this research. Whatever modifications the eyes of animals may present in regard to their structure and development, we may presume there is just such an agreement between the structure of the terminal organs of the nerves and the acessory apparatus, adapting them for the conversion of luminous waves into nerve force, as that which we see in the auditory organ, where delicate hairs — auditory hairs — project into a fluid. We shall here therefore endeavour to give a short resume of the state of our information respecting the terminal apparatus of the optic nerves in animals, with a reference at the same time to the physiological value of the differences observed. All Vertebrata that are able to see, with the single exception perhaps of the Amphioxus, the eyes of which present a much lower grade of development, possess a retina with a layer of rods and cones similar to that of Man. Now, although as a general rule the cones are recog- nizable by their ventricose internal segment and conical outer segment, and are mingled with rods, as in the retina of Man, there being no difficulty in distinguishing between the two either in him or in the Monkeys, Pig, Ruminants, and most Osseous Fishes ; still cases occur in which the rods and cones resemble each other much more closely, as in the Guinea-pig and Rabbit, where the inner segments of the cones are scarcely thicker or in any other way unlike the rods, so that they can only be distinguished by the characters of their outer segments. Transitional forms are moreover seen in the Tritons* and in a less de- gree in the Frog, in both of which the outer segments of the rods are conical. In Birds the cones are very slender and rodlike. The ex- ternal segment is much elongated, and is not always very distinctly conical. Though it would appear from this that the distinction between the rods and cones is not always sharply marked in the animal kingdom, there are nevertheless always other characteristics by which the two structures may be distinguished from one another. Amongst these special characteristics are the highly refractile spheroids of fatty substance found in the Birds, which for the most part have a red or yellow colour, and are present in all the cones, whilst they are absent in the rods. They are situated in the internal segment, at the point of its junction with the outer segment, and are so large, and so completely fill each cone at this point, that it * Max Schultze, Archiv fur Mikroskop. Anatomie, Band iii., p. 237. NERVOUS CONSTITUENTS OF THE RETINA. 261 is impossible for the light to reach the outer segment without tra- versing the spheroid in question. (See fig. 358, «.) There are some colourless spheroids of this nature, but the majority are chrome, Naples yellow, gamboge, or greenish-yellow and orange, between which others are scattered at regular distances, of a ruby tint. Their spheroidal form must exert a refractile influence upon the course of the light traversing them, whilst certain portions cf the rays corresponding to their colour must be absorbed. Their presence, as Hensen * first pointed out, renders it highly probable that it is by the external segments that perception is accomplished, since only in this case can the object of the selective absorption be understood. The circumstance that they are only present in the cones, and not in the rods, proves that the former have more to do with the perception of colour than the rods, which is also probable on other grounds for Mammals and Man.f That these spheroids occupy the whole thickness of the internal segment, demonstrates further r as Krause j has stated, that we have here a solution of continuity, and that the outer seg- ments are not of a nervous nature, even if this be true in regard to the inner segments. As a result of my discovery,- that there are fibres running upon the surface of the internal segments, which are prolonged upon the outer ones, and are not interrupted by the fat spheroids, I believed that I might be able to point out the mode in which the outer segments take part in the process of perception. § The fresh complications, however, resulting from the discovery of the internal fibre system of the rods and cones, does not at present allow us to draw any definite conclusions upon the subject. As in Birds, so also in Reptiles, oil globules are found in the cones ; in the Chelonia, in addition to a few colourless globules, there are others that are red, orange, and yellow. Lastly, the very small cones of the Anourous Batrachians are each characterized by presenting a strongly refractive spheroid which is either colourless or of a clear yellow hue. They are not present in Fishes, unless we may consider them to be indicated by certain bodies observed by Leydig in the Sturgeon. || Many of the cones in Birds (Pigeon) and Lizards contain besides the coloured spheroid some diffused red or yellow colouring * Yirchow's Archiv, Band xxxiv., p. 405. t Max Schultze, Archiv fur Mikroskop. Anatomic, Band ii., p. 253. £ Membrana fenestrata, p. 48. § Archiv fur Mikroskop. Anatomic, Bandv., p. 400. || Anatom. Histoloyische Untersuchungen iiber Fische und Reptilicn, p. 0, 1853. THE RETINA, BY MAX SC'HULTZE. matter, which must consequently assist the selective absorption of the spheroids. Moreover another structure adapted to exercise an influence upon the course of the luminous rays, is to be found in the internal segments of the cones in Birds, Reptiles, and Amphibia, and also in the rods of Birds and Amphibia ; namely, a lenticular body of higher refractive power than the substance by which it is surrounded. This occupies the extremity of the inner segment in the rods, and is flattened pos- teriorly towards the outer segments, but anteriorly it presents a spherical or elliptic surface ; in the cones containing spherical oil drops, it is situated immediately in front of and in contact with the drop. W. Krause first observed this body in the cones of the Fowl, and considered Fig. 358. M \ t 2 J 4 J Fig. 358. 1, 2, 3, Rods of the retina of the Falcon : s', internal seg- ment, with highly refractile lenticular bodies ; s", external segment invested by lineally arranged pigment granules, as they may be seen to adhere to the surface of the outer segments in many specimens hardened in perosmic acid. 4, Rod and cone (z) from the Fowl : fc, yellow flat spheroid in the internal segment of the cone, situated in front of which is an ellipsoidal refractile body. 5, Rod from the Triton : c, plano-concave ; c', biconvex lens in the internal segment. Magnified 800 diameters. it must be regarded as the clavate extremity of a nervous central fibre of the internal segment, naming it at the same time the " optic ellipsoid." * I have termed it the lenticular body.f * Gottinger Naehrichten, No. 37. 1867. t Max Schultze, ArcMvfur Mikroskop. Anatomie, Band iii., p. 221. NERVOUS CONSTITUENTS OF THE RETINA. 263 Perosmic acid applied to the fresh retina of Birds and Reptiles hrings out the lenticular body with extraordinary distinctness, pre- serving the sharpness of its outline, and at the same time scarcely altering its colour. No structure similar to this can be discovered in the cones and rods of Man, either in the fresh state, or when acted on by perosmic acid. It is particularly worthy of notice that in some animals the lenticular body of the rods is composed of two segments that react differently to this acid, and present also different refractive powers.* In the rods of Birds a small anterior segment often be- comes separated from the point of the ellipsoidal lens, appearing in the form of a short pointed process, possessing a strong lustre t (fig. 358, s) ; and in Tritons the posterior segment presents a spherical concavity in front, in which the anterior segment lies (fig. 358, 5 c). We may reasonably suppose that we have here to do with arrangements which refract in a very definite way the rays of light passing to the outer segment. The peculiar " twin or double cones,'1 first described by Hannover, are quite enigmatical from a physiological point of view. { They have not up to the present time been discovered in Mammals or in Man,§ but they exist in Birds and Reptiles, Amphibia and Fishes. In Fishes, where they attain the largest size, and are the most numerous, and where consequently they are most easily examined, they consist of two apparently exactly similar coalesced cones, the outer segments of which, however, as well as the cone fibres, are separate and distinct, so that it might almost be said they were cones multiplying by longi- tudinal fission. It is different in other classes of animals ; for, as I have shown, there are essential points of distinction between- the two halves of the twin-cones, which must possess some physiological signi- fication. In Birds, Tortoises, Lizards, and in the Frog, in which each ordinary cone contains a coloured or colourless globule, such a globule is found in only one of the halves of the twin-cones, the other half possessing merely the ellipsoidal lenticular body, which in many * Max Sclmltze, Archiv fiir Mikroskop. Anatomic, Band v. , pp. 401, 403, figs. 2 and 17. f I formerly stated that this pointed body, as seen in swollen internal segments, might possibly be a persistent and resistant axis fibre. Archiv fur Mikroskop. A natomie, Band iii. , p. 245, fig. 6. J Hannover, Rechcrchcs microscopiqucs, etc., 1841. A more minute de- scription of them, by Max Schultze, will be found in the Archiv fur Mikroskop. Anatomic, Band iii., p. 231. § Hannover, indeed, believed he had found them in both Man and Mammals, but his observations were incorrect. 264 THE RETINA, BY MAX SCHULTZE. Birds is coloured yellow, but which even in them always presents an essentially different form and refractive power from the coloured oil globules of the other half of the cone.* Moreover there is often a difference in the length of the two halves, so that the one containing the oil globule extends farther back than the other, whilst the planes of junction of the outer and inner segments of the two halves do not coincide. If we regard the outer segment as the seat of distinct vision, there would be a necessity for different accommodation for the two halves of the twin-cones, supposing them to have the same function, and to receive the rays of light under otherwise identical conditions. This last, however, does not really occur, inasmuch as there is an essential difference between the refractile lenticular body of the internal segments of the two halves. From all this we may draw the conclusion that the lenticular bodies are destined to give to the luminous rays a direction fitting them for undergoing their final changes in the outer segment, which, it would seem, cannot be given to them by the coarser refracting apparatus. The different distribution of the rods and cones met icitJi in the animal kingdom is well worthy of note. Both kinds of percipient elements can be replaced or represented by the other. Thus the cones are entirely absent in the retina of Sharks and Rays, the Lamprey (Flussneunaugen), and probably in the Sturgeon ;f amongst * Archiv fur Mikroskop. Anatomic, Band iii., Taf. xiii., fig. 6, c. t The Petromyzon demands closer investigation than it has as yet re- ceived. In the river Lamprey (Flussneunauge) an opportunity presented itself long ago, in which I found that in the fresh condition it possesses only one kind of element in the bacillar layer, and these, on account of the form of their outer segment, I termed rods. According to a provisional communication by H. Mtiller (Auge des Chamaleon, p. 25), both rods and cones occur mixed together in the Petromyzon. In the Sturgeon, ac- cording to Bowman (on the Eye, p. 89) and Leydig (Fishes and Amphibia, p. 9), only one kind of percipient element is present, and these in Leydig's drawings resemble the rods in the form of their outer segments. In the osseous Fishes, rods and cones as a rule both occur. Amongst a large collection of Fishes of the Baltic which I examined in the fresh state in reference to the distribution of the rods and cones, and which included species of Pleuronectes, Gadus, Gasterosteus, Trachurus, Cottus, Crenila- brus and Syngnathus, I found in the latter genus alone any remarkable deviation from the ordinary type. The rods are here very thick and short as in Amphibia, the cones are much less conspicuous, and the disks into which the rods break up after short maceration in perosmic acid have in some instances a very well-marked semihmar form resembling that which I have described as occurring in the Triton. NERVOUS CONSTITUENTS OF THE RETINA. 205 Mammals, in the Bat, the Hedgehog, and Mole ; * whilst the bacillar layer of the retina of many Lizards, Snakes, and Tortoises, and pro- bably indeed of all Keptiles, is altogether destitute of rods, and is therefore c.cclusircb/ composed of cones.^ In Birds the number of cones is in general far greater than that of the rods, whilst in Mammals the reverse obtains. In the retina of Man and the Monkeys, as is well known, it is only at the yellow spot that the cones exceed the rods in number ; at the centre of this acutely perceptive area the rods en- tirely fail. The retina of Birds resembles consequently the macula lutea of Man throughout its whole extent, in the relative proportion of the cones to the rods, and this similarity is still further increased by the circumstance that the yellow oil globules in the outer segments of the cones of Birds correspond to the presence of yellow pigment in the most sensitive area of the human retina. It is very remarkable that the number of the cones in the dusk or night-flying Owls is re- markably less, so that in these birds the rods again predominate, whilst at the same time the intensity of the yellow pigment in the cones is con- siderably smaller than in the day Birds, and the red pigment is wholly absent. J In Mammals that roam by night or in the twilight the pro- portionate number of the cones likewise diminishes, or they altogether fail, as in the Bat and other genera already mentioned. The cones in the Rat, Mouse, Dormouse, Guinea-pig, though present, are quite rudimentary as compared with those of Man, the Pig, Ruminants, and the Dog. Cats have distinct but slender cones ; those of Rabbits are not so well marked. § It is also a remarkable circumstance that the absolute length of the outer segments of' the rods of most nocturnal animals is very con- siderable. || With the length of the outer segments, the number of * Archiv fitr Mikroskop. Anatomic, Band ii. , p. 198, Band iii. ; p. 238. t Archiv fur Mikroskop. Anatomie, Band ii. , p. 209. The statement made by Krause, that in Lacerta agilis both rods and cones are present, is erroneous. Hulke, as I have shown, has not been able to distinguish the rods from the cones in Reptiles, so that his statements must be received with caution. £ See my statements in the A rchiv f. Mikrosk. A nat. , Band ii. , p. 208, the accuracy of which, after repeated re-investigation, I must still maintain, notwithstanding the opposition of W. Krause (Membrana fenestrata, p. 29). § Max Schultze, Archiv fur Mikroskop. Anatomie, Band ii., p. 197. For the conflicting statements of W. Krause, see his Anatomy of the Rabbit, p. 129, and Membrana fenestrata, p. 30. || Max Schultze, Archiv fur Mikroskop. Anatomie, Band ii., p. 199, Taf. xiv., fig. 7 (Rat) ; p. 208, Taf. ix., figs. 10 and 11 (Owl) ; Band iii., p. 243. W. Krause, Membrana fenestrata, p. 31. 266 THE RETINA, BY MAX SCHULTZE. the disks placed one behind the other increases, whilst their thickness varies, though only to a slight extent. It would therefore seem tha the reflection and modifications of the luminous waves resulting from the disks, and having relation to perception on the part of the outer segments, must necessarily, from their greater length, be here mud more complete. In correspondence with their entirely different modt of development, the structure of the retina of Invertebrata differs es- sentially from that of Vertebrata. This is particularly noticeable ii the layer of the perceptive elements, or bacillar layer, In Mollusks Articulate animals, and Vermes, the extremities of the optic nerve form as in the Vertebrata, a layer of palisade-like structures. Apparently however, these are more favourably placed in relation to the light than amongst the Yertebrata ; they are directed forward towards the lens, whilst the bacillar layer in the Vertebrata is in contact with the choroid. This difference is explained by the mode of development of the retina in the two cases, being formed in the Vertebrata by an e version of the central vesicle (see below), whilst in the Invertebrata it originates from an inversion of the skin.* Amongst the Mollusca the structure of the retina is most exactly known in the Cephalopoda and Heteropoda.f The innermost layer of the retina, which is separated from the external layers by brownish- black pigment, is formed by rod-like palisades that are of considerable length in the Cephalopoda, and. are visible even to the naked eye as a reddish lamina. The rod-like layer is composed — 1. Of lamellated palisades resembling the outer segment of the rods of Vertebrata, though much more variable in the form they present on transverse section, which may be semilunar, annular, quadrangular, or quite irregular. Adjoining palisades may so coalesce with one another as to form a continuous mass, traversed by vertical tubes. The laminae that form these palisades, according to * Semper, according to a communication by Heiisen, Archiv fiir Mikros- kop. Anatomic, Band ii., p. 416. t See Babuchin, Wiirzburg. Nat. Zeit,scfirift} Band v., p. 125, 1864 ; Heiisen, Ueber das auge einiger Cephalopoda, " On the eyes of some Ce- phalopods," Zeitschrift fur urissenschaft. Zoologie, Band xv. ; and Bronn, Klassen und Ordnungen der Thier. Molusken, Taf. cxv. Steinlin, Beitrdge zur Anatomie der fietina, St. Gallen, 1865-66, p. 70. Max Schultze, Archiv fiir M'ikroskop. Anatomie, Band v., p. 1, Ueber die . Netzliant anderer Mollusken, " On the retina of various Mollusks," etc. Babuchin, Sitzungsberichte der Acad. zu VI ien, Juni, 1865 ; and Hensen, Archiv fiir Mikroskop. Anatomie, Band ii., p. 399, in which last paper the literature of the subject is fully given. NERVOUS CONSTITUENTS OF THE RETINA. 267 my measurement, have almost the same thickness as in Vertebrata, i.e. about 0'5 of a microinillimeter. 2. In the intervening spaces between these palisades, and upon their surface, are fine fibrils, the extremities of the optic fibres. These, proceeding from a layer of nucleated fusiform bodies comparable to an external granule layer, enter the bacillar layer, whilst the nucleated fusiform bodies that terminate by one of their extremities in the fibres of the bacillar layer break up at their other extremity into fibrils which proceed from the optic layer. 3. In this layer the granular brownish-black pigment is also to be included. This is never absent at the outer extremities of the rods, and here separates these last from the fusiform bodies. This pig- ment, like the nerve fibres, lies external to the lamellated palisades which it invests, then extends further in the intervening spaces occu- pied by nerve fibres between the palisades, and frequently forms at the inner ends of the rods, where these are separated from the vitreous by a homogenous membrane, a dense accumulation filling up the spaces between the palisades. Light can penetrate into the latter, but is excluded by the thick layer of pigment from the canals containing nerve fibrils, or reaches these only by a circuitous path through the lamellar palisades." It is evident that if the fine fibrils running in Vertebrata upon the surface of the outer segments of the rods and cones are nerve fibrils, their position on the one hand in relation to the lamellated substance, and on the other to the pigment of the pigmented epithelial cells of the retina, would be precisely identical] with that of the analogous structures of the retina of the Cephalopoda. In the eyes of Articulata the structure of the retina is complicated in accordance with the circumstances of these organs, being here composed of many single eyesf united into one ; but here also lamellated rods J are found behind the refractile bodies comparable with the cornea, lens, and vitreous, with extraordinary powers of reflexion, and very often of considerable length. They also are invested by dark pigment, and stand in close relation to nerve fibrils, which enter at their posterior extremity, and terminate either * See especially Max Schultze, Archiv fur Mikroskop. Anatomie, Band v., pp. 15 — 18. f Leydig, Das Auge der Gliederthiere, " The Eyes of Articulata." | Max Schultze, Untermchungen ueber die zusammengesetzten Augen dcr Krebse und Insecten, " Researches on the compound eyes of Crabs and Insects." Bonn, 1868. 268 THE RETINA, BY MAX SCHULTZE. in them or at them. The lamination is here often recognizable with low power, as in the Crabs, since the finest disks do not here exceed 0-5 of a micromillimeter, and are united into groups that possess a different aspect, and in the River Crab can even be distinguished by their colour. The exact relation of the nerve fibrils to the lamellated rods is however less known in this case than in the Mollusks. Finally, amongst the Yermes, at least in the large-eyed Alciope, the structure of the bacillar layer presents some analogy with that of the higher animals. The rods first observed by Krohn, so far as can be observed in my Neapolitan preparations preserved in various fluids, appear in the form of highly refractile, finely transversely striated, and easily transversely fracturing palisades, which are partly tubuliform, and anteriorly surrounded by pigment. In what manner the nerve fibres of the optic layer situated externally to the palisades terminate in this pigmented bacillar layer, is reserved for future research to determine. It may here, however, be mentioned that recently much doubt has been expressed as to the rods and cones really constituting the terminal organs of the optic-nerve fibres. The rod and cone fibres may be of the nature of connective tissue, and may stand in connec- tion with the connective-tissue cells and fibres of the internal layers of the retina. This opinion is maintained by W. Krause, * with whom Landoltf in a certain sense agrees, so far as regards the Amphibia. In Frogs, Tritons, and Salamanders, the external granule layer, as already stated, is so thin, and contains, besides the fusiform rod and cone granules, only such short fibres proceeding from these, that it does not appear to be by any means well adapted to settle the point in question. Landolt moreover admits that these fibres may contain nerve fibres in their interior. This is true also in the case of Birds and Reptiles. In Mammals and in Man, to which Krause's state- ments refer, the difference between the fibres of the connecting sub- stanceand those of the nerve fibres is, in accordance with the description given above, so great, whilst on the other hand the agreement of the rod and cone fibres with nerve fibres is so complete, that it is impossible on anatomical grounds to doubt the nervous nature of the rods and cones. Further researches are required to furnish an explanation of the reason why, after section of the optic nerve, as was first shown by Krause in animals, and in various cases of atrophy of the optic nerve and of the ganglion cells in Man, these bodies do not undergo degene- * Membrana fenestrata, p. 48. t Arckivfur Mikroskop. Anatomie, Band vii., p. 84. PIGMENT LAYER OF THE RETINA. 2 GO ration ; but the fact of their persistence cannot shake the anatomically and physiologically well-grounded fact that the rods and cones represent the terminal organs of the optic-nerve fibres. The same argument also holds against the statements which have recently been made by Manz in a very valuable essay on the eyes of acephalous monstrosities against the nature of the rods and cones.* Their pre- sence in heniicephalic foetuses only proves that the elements of the external layers of the retina can under certain circumstances become developed independently of those of the inner layers, which, if the rods and cones are terminal nerve organs, is in complete accordance with that which is found in other nerves, the peripheric terminal organs of which may be found well developed when the central organs are absent. 2. THE PIGMENT LAYER OF THE RETINA. Although, so far as we know, not directly continuous with the nerve fibres, the layer of pigment cells, ordinarily termed the pigment epithelium of the choroid, still belongs, both phy- siologically and morphologically, to the retina. It is formed during the period of embryonic development from the outer lamina of the primary eye vesicle, which itself proceeds from a protrusion of the foetal brain, and the inner layer of which is metamorphosed into the remaining layers of the retina. At a later period the rods and cones proceeding from the inner layer of the primary eye vesicle grow into the pigment layer, and thus the well-known and very intimate connection between the two is brought about. The pigment cells resemble the hexagonal pieces of stone in ' a mosaic, united to form a membrane, the several cells of which however are still capable of being isolated. The external part of each cell adjoining the choroid is poor in pigment or perfectly colourless, and usually contains the spheroidal nucleus, as well as in many animals, the Frog for example, intensely yellow fat globules. The inner portion of the cells contains the peculiar granular colouring matter, and is prolonged in the form of numerous extremely destructible processes between the outer segments of the rods and cones, which last thus come to be imbedded in a pigmented sheath. These sheath-like processes * Virchow's Archiv, Band li. 270 THE RETINA, BY MAX SCHULTZE. of the pigment cells break up at their extremities again into innumerable fine fibres, which are often quite colourless, and present no distant resemblance to a brush of cilia. They extend at least as far as the line of junction of the outer and inner segments of the rods and cones, and in many animals as far as to the region of the limitans externa. They closely embrace the rods and cones, but soon break down after death, owing to which the connection between the pigment cells and rods becomes less firm, After the perfectly fresh retina has been hardened in perosmic acid, the outer segments, even in Man, however, usually adhere so firmly to the pigment cells, that they rather separate from the internal segments, or fracture through their substance, than become detached from the pig- ment cells. The intensity of the pigment varies ; it is least in blonde individuals, greatest in the negro. It is always darker behind Fig. 359. Fig. 359. Cells from the pigment layer of the retina of Man. a. Seen in situ from the surface. 6. Seen in profile with the long hair-like processes partly pigmented, partly free from pigment, c. A cell also seen in profile, to which the outer segments of several rods are still adherent. the macula lutea than in any other part of the retina. The retina of Albinoes is almost or entirely free from pigment, and it is absent in those parts of the retina of Mammals, where the choroid presents a highly reflecting tapetum. The hair-like ciliaform processes of the cells which invest the rods like a sheath are nevertheless well developed in these colourless cells.* The pigment granules themselves, which appear for the most * Max Schultze, Archie fur Mikroskop. Anatomic, Band ii., Taf. xiv., fig. 9, b. PIGMENT LAYER OF THE RETINA. 271 part to be not spheroidal, but elliptical and rod-like* are, accord- ing to the statements of A. Frisch, small crystals, which when perfectly fresh are recognizable under very high powers by their sharp' angles and borders.! They are placed with their long diameter at right angles to the surface of the retina, and therefore, when seen from this surface in profile, are of a rod- like form. Rosow and Frisch found that the largest measured from four to five micromillimeters in length. The pathological pigmentation of the retina, known to ophthalmo- logists under the name of Retinitis piymentosa, which is accompanied by diminished sharpness of vision, and leads ultimately to loss of sight, is highly remarkable. In typical cases of such pigmentary degenera- tion we have probably to deal with a partial degeneration of the pig- ment epithelium, and a more or less extended pigmentation of the other layers of the retina, together with a degeneration of the rods and cones, and finally with atrophy of the nervous constituents of the retina. The granular pigment set free by the breaking of some of the pigment epithelial cells makes its way into the other layers of the retina. This, however, is clearly only possible after previous destruction of certain parts of the bacillar layer and of the limitans externa, as well as of the external granule layer. Having reached the deeper layers of the retina, the granular pigment follows the adventitia of the bloodvessels, and thus probably the perivascular lymph sheaths, and thus becomes deposited far and wide in the form of diffused masses. Inasmuch as this either occurs as a congenital condition, or takes place in early infancy as a result of hereditary influence, especially in the offspring of blood relations, who, as is well known, furnish a rich contingent of malformations, we may conclude that we have- here a defective development in the outer lamina of the primary eye vesicle, which undergoes conversion (see below, "Development of the Retina,") into the pigment epithelium of the retina. Owing to the intimate relation existing between the pigment cells and the rods and cones, it is inevitable that processes of softening taking place in the pigment cells, and, implicating the bacillar layer, will by regressive extension also come to affect the other layers of the retina. Precise anatomical investigations upon this kind of degeneration, which has been admira- * Rosow in Grafe's Archiv, Band ix., Heft, iii., p. 65. t A. Frisch, Gestatten des Chorioidalpigmentes, "Forms presented by the choroidal pigment." Sitzungsberichte d. AcacL zu Wien, 18G9, Juli heft. 272 THE RETINA, BY MAX SCHULTZE. bly followed out ophtlialmoscopically, are still only sparingly present.* In addition to this form of pigmentation, leading to impairment of vision, is another of a less serious nature, which consists in the development of stellate pigment cells (pigmented connective-tissue cells) in the supporting tissue and adventitia of the vessels, which is a fre- quent occurrence in animals, as has been particularly observed by me in the case of Ruminants. 3. THE CONNECTIVE-TISSUE FRAMEWORK OF THE RETINA. In addition to the nervous tissues that have hitherto been under consideration, almost all the layers of the retina are interpene- trated by a tissue occupying a considerable space in many parts, and this is the supporting connective tissue. Though continu- ous with that of the optic nerve,-f- it forms a very peculiar kind of framework in the retina, varying in its character according to the various nervous constituents of the several layers by which it is surrounded. This form of connective tissue is closely allied structually to that of the brain and spinal cord, and has, like it, been named Neuroglia by Virchow. We have applied the term " spongy connective tissue " to it, and distinguish as several parts belonging to it the two limiting layers — limitans interna and externa ; the radial fibrous bands, or supporting fibres, in opposition to the radial nerve fibres ; and 'the finer and coarser plexuses connecting the supporting fibres, which, from their resemblance to a sponge, have given their name to the whole tissue. The membrana limitans interna (limitans hyaloidea of Henle) immediately invests the vitreous humour, to which it is often intimately connected ; whilst the limitans externa divides the layer of the external granules from the bacillar layer. Stretched between these two limiting layers, as columns between a floor and a ceiling, stand in great numbers the radial supporting fibres. * Donders, in Grafe's Archiv, Band iii., p. 139. Schweigger-Seidel, ibidem, Band v., Heft i., p. 96. Leber, ibidem, Band xv., 1869, Heft iii., p. 1. There is also an excellent illustration of the affection in Leibreich's Atlas, Taf. vi., fig. 1. Iwanoff describes, in Grafe's Archiv, Band xi., Heft, i., p. 153, a deposition of pigment along the radial fibres. t. Klebs, Virchow's Archiv, Band xix., p. 321. THE CONNECTIVE-TISSUE FRAMEWORK OF THE RETINA. 273 Whilst in all the layers of the retina these supporting fibres are continuous by means of lateral processes or branches with Fig. 360. Fig. 360. Diagrammatic representation of the con- nective tissue of the re- tina, in correspondence with the characters it pre- sents near the ora serrata. 1. Limitaiis interna; 3, ganglion-cell region ; 4, internal granulated, or molecular layer ; 5, inter- nal granule layer ; 6, exter- nal granulated or mole- cular layer; 7, external granule layer ; 8, limitans externa, beyond which the cradles of fibres which em- brace the bases of the rods and cones project. Magnified 800 diameters. the intermediate spongy connective tissue, they are really merely a part of the same, and are distinguishable from it only VOL. III. T 274 THE KETINA, BY MAX SCHULTZE. by a somewhat greater degree of resistance, permitting themto be isolated, whilst the intervening spongy tissue becomes broken down or destroyed. Small tags or fragments of the spongy tissue, or at least lateral processes, always remain attached here and there to the radial supporting fibres, and give rise to the peculiar and quite characteristic roughness of their surface. But the plexus, which, like a sponge, consists not only of fibres, but of membranous plates, forming shells and sheaths around the nervous elements, varies in thickness in accordance with that of the different layers of the retina, contains large spaces for the reception of the ganglion cells, smaller ones for the internal granules, and still finer ones for the nerve fibres of the two granulated layers.* The radial fibres are often seen to break up completely into spongy tissue, and thus it comes to pass that many of them which maybe folJowed outwards from the limitans interna through all the layers, ceasef in the external granulated layer, and therefore do not reach the outer granule layer. On the other hand, many radial fibres which may be followed into it from the outer layers, disappear in the plexus of the internal granulated layer.:}: Lastly, radial fibres may also be met with, which reach neither of the membranse limitantes. The radial supporting fibres are most constantly found in the internal granule layer. The greater number of them here also contain in their substance oval homogeneous nuclei, with distinct nucleoli. In general it is impossible to discover any * In opposition to the different views that have been advanced in regard to the structure of the young tissue of the granulated layers (see Henle and Merkel in the Zeitschrift fur rat. Med., Band xxxiv., 1869, p. 51, et seq.), I can only repeat what I have already stated in my Unter- suchungen uber den Ban der Nasenschleimhaut, ("Researches on the Structure of the Mucous Membrane of the Nose,") p. 29, Halle, 1862. I willingly admit that our microscopes and methods of preparation are in- sufficient for the investigation of the granulated substance of the cerebral cortex, but the spongy substance of the retina in the granulated layers is distinctly resolvable into a plexus of fibres, if due care be taken in its preparation, and if its examination be undertaken with our best immer- sion-lenses. t Max Schultze, Archiv fur Mikroskop. Anatomie, Taf. xiv., fig. 6, 8 b, 8 c, 10 6. J Ibidem, Taf. xi., fig. 13. THE COXXECTIVE-TISSUE FRAMEWORK OF THE RETINA. 275 granular protoplasm around the nucleus. These nuclei of the radial supporting fibres form the second kind of internal granules mentioned above. The supporting fibres themselves usually traverse the layer of optic-nerve fibres with great re- gularity, in order to take part in the formation of the limitans interna. They are here arranged serially, the direction and fascicular mode of grouping* of the fibres corresponding for the most part with that of the nerve fibres, whilst they are pro- longed into conical flattened enlargements, or after undergoing division, like roots of a tree, are continuous with several such terminal dilatations, f which ultimately coalesce to form a smooth membrane on.the side turned towards the vitreous — the frequently mentioned membrana limitans interna. J At many points the connection of the ends of the radial fibres with the membrane is deficient, in which case a fine fibrous plexus occupies the intervals between the truncated cones, and the limitans is per- forated in a filigree-like manner. Such an appearance is pre- sented by surface views of this membrane in Rabbits. At the yellow spot, where the optic fibres no longer form a special layer, and the ganglion cells occupy the inner surface of the retina, even the extremities of the thicker radial fibres fail to join the limitans interna. The radial supporting fibres are in point of fact commonly absent at this very soft portion of the retina ; at the same time the limitans interna is by no means absent, but, on the contrary, is very resistant, and can easily be detached as a separate membrane. As in other parts of the retina, it appears as a denser membranous portion of the sup- porting connective tissue, but becomes detached from them and from the spongy substance between the ganglion cells, the more readily the greater the difference in the consistence of the two. The external surface of the limitans interna presents a very distinctly rough appearance at the yellow spot, owing to the remains of innumerable ruptured fibres, and demonstrates in this way its continuity with the adjoining portions of the con- nective tissue, which is at the same time doubtless very differ- * Kolliker, Gewebdehre, 5th Edit., p. 680, fig. 488. t M. Schultze, De Eetin. Structura penit. , fig. 3. J Schelske in Virchow's Archiv, Band xxviii., p. 482. 276 THE RETINA, BY MAX SCHULTZE. ent in character from the radially directed rows of fibres seen in the more peripherally situated parts of the retina. Some differences of opinion prevail respecting the membrana limitans interim, which I believe depend on the different thick- ness and resistance it presents at various parts of the retina in Man and different animals, and its frequent coalescence with the vitreous. Kolliker* observes, in regard to this point, that the remarkable softness and destructibility of the radial fibres in contrast to the resistance of the limitans, is opposed to the idea of their identity of structure, and he consequently consi- ders the limitans as a special tissue to be ranked amongst the vitreous membranes. In opposition to this, however, it may be remarked that other vitreous membranes, as the anterior elastic lamina of the cornea, or the internal layer of the choroid, also fuse with their supporting tissue, and may be held to originate with and out of this, though presenting essential differences in their relations to solvents. I am unable to discover any other kind of membrana limitans interna besides the above described, on which account I place its identity of structure with the sup- porting reticular or spongy connective tissue in the foreground, though fully recognizing the importance of the separability of the limitans, and the difference in resistance between it and the spongy subjacent layer, especially at the yellow spot. Henle also regards the limitans interna as an independent membrane, to the outer surface of which the radial supporting fibres, with their expanded extremities, are applied, f He calls it the limitans hyaloidea, to show that it is identical with the special membrane of the vitreous, described by many au- thors. The conditions of hypertrophy of the connecting sub- stance which take place in atrophy of the nervous constituents of the retina are very instructive for the purpose of demon- strating the connection of the supporting fibres with the limitans interna, as they have been described in one case by Iwanoff, J where the hypertrophy of the radial fibres occasioned circumscribed enlargements extending into the vitreous. * Geu-ebelehre, 5th Edition, p. 681. t Eingeu-eidelehre, p. 658. $ Grafe's Arcfiiv, Band xi., Abtheil i., p. 141, Taf. 3 and 4. THE CONNECTIVE-TISSUE FRAMEWORK OF THE RETINA. 277 The limitans externa is not to be regarded as an isolable membrane. Like the interna, it is composed either of a mem- branous expansion of the radial fibres, or, where such isolable fibres are deficient in the granule layer, of the connective sub- stance investing in manifold-wise the external granules, with their nerve fibres. The connecting substance of the outer gra- nule layer is never absent,* not even at the macula lutea, where it was unobserved besides the long cone fibres, until Merkel demonstrated its existence in the form of delicate sheaths invest- ing these fibres. (See his ' Macula lutea,' p. 7.) Where, as in Birds, the radial supporting fibres can be readily observed to pass from the inner into the outer granule layer, each fibre may be observed to branch and form membranous capsules around the external granules and their nerve fibres. If after moderate hardening these granules, and with them the rods and cones, are removed as completely as possible by agita- tion from small fragments of the retina, the supporting tissue alone remains, forming a system of sheaths which only becomes in some measure intelligible on the application of very high magnifying powers. The sheaths themselves exhibit a fine parallel striation, indicating a ftbrillar structure, which does not cease at the membrana limitans externa, which they help to form. For beyond the latter an indefinite number of fine stiff fibrils project (fig. 360, 8), which, grouped into the form of circles, form fibre-crates, cradles or basketworkfr, from which the cones fall out, as has been above described. The appearance pre- sented is just as if these fibrils were continuous with the fibrous sheaths that invest the outer granules. f It was obviously por- tions of these fibrous crates which I formerly depicted^ in specimens prepared from the Fowl as fibres exhibiting a certain connection with the connective-tissue sheaths of the external granule layer, and which were also described by W. Krause under the name of needles,^ who considered them to be a constant element of the bacillar layer. The illustration of M. * W. Krause's Widerspruch membrana fenestrata, p. 19. t See the illustration in the Archiv fur Mikroskop. Anatomic, Band v., Plate xxii., fig. 4, from Man. J Ibidem, Band ii., Taf. xi., fig. 13. § Membrana fenestrata, p. 6, Plate i., figs. 5 and 7. 278 THE RETIXA, BY MAX SCHULTZE. Iwanoff, taken from a human retina, macerated by suppurative inflammation,* in which the nervous elements were collectively destroyed, whilst the supporting framework alone remained, exhibits similar appearances. This fibrous basketwork, which is isolable in the above - desciibed 'mode, appears to be present in all Vertebrata, as well as in Man. Further researches, however, are required to show how far it is prolonged over the surface of the outer segments.f Besides the nuclei which ^are present within the internal granule layer in the radial supporting fibres, others are found, though for the most part more sparingly distributed in other layers of the retina, and especially in the two molecular layers.} The importance of these increases in those pathological processes which advance pari passu with an increase of the cells of the connective tissue. Even if the statements respecting a proliferation of these cells by fission are to be admitted with caution, it may nevertheless be regarded as established that under certain circumstances a finely or coarsely granular proto- plasm containing fat molecules, collects around the pale oval nuclei of the connective substance, and that the number of these cells can augment materially in excess of all that we know of them in their normal state. Fatty degeneration of the retina does not limit itself to the immediate neighbourhood of the nuclei of the connecting substance, but may also, as for example in morbus Brightii, occur in the form of delicate rows of granules along the whole length of the supporting fibres, especially towards the inner layers of the retina, so that these fibres might be imagined to be hollow. In the external granule layer, also, I have observed cells that have undergone fatty degeneration, and which from the characters of their nuclei I must regard as elements of the connecting substance, so that it is impossible to deny the presence of nuclei of the connective substance under normal conditions in the external granule layer, however closely its nervous cells are compressed together. It is a matter of importance in regard to the question of the origin of those tumours of the retina that have been termed * Grafe's Archiv, Band xv., Abtheil ii., Plate ii., fig. 2. t In an essay published in the 7th Vol. of the Archiv fur Mikroskop. Anatomie, p. 81, E. Landolt maintains, on the ground of his personal observation, that in Amphibia the outer segments of the rods and cones lie in a sheath belonging to the supporting connective substance. $ See inter alias Nagel in Grafe's Archiv, Band vi. , p. 218. THE CONNECTIVE-TISSUE FRAMEWORK OF THE RETINA. 279 glioina by Virchow,* to point out that one of their essential con- stituents coincides with the spongy substance (neuroglia), and that it may also proceed from the external granule layer.f We are indebted to H. Miiller for our knowledge of peculiar smooth stellate and anastomosing cells forming a double layer in the Perch and Ruff or Pope (Acerina cernua), which lie on the inner side of the external granulated layer (intergranule layer), and are not ganglion cells. They may be found in many other animals, though, perhaps, not always so easily isolable, and form, where they attain their greatest development, as in Fishes, a special layer lying to the inner side of the external molecular layer, to which I have given the name of the stratum in tergranulosum fenestratum.$ The substance of the nucleated laminaB anastomosing together by means of processes resembling sheets of perforated iron, frequently possesses the structure of striated plexiform (Plagiostomata), or fibrillar (Perca), connective tissue,§ and is often directly continuous, as I have shown, with that of the radial supporting tissue. In Perca fluviatilis I find this foraminated intergranular layer to be composed of three separate layers. The middle one includes the flat stellate cells, which frequently anastomose, but the processes of which may be as broad as the cells, so that the layer rather resembles a plexus of broad nucleated fibres. These are covered on one side by a plexus of delicate fibres resembling the branched and interwoven elastic fibres, which form a single layer of wide- meshed tissue. On the other surface is a thin lamina of appa- rently finely granular substance of great delicacy, containing scattered nuclei, and perforated by round holes. W. Krausel) has recently described the external granulated layer of the retina in Man and Mammals as being composed of * Vorlesungen uber Geschwulste, Band ii. , p. 158. t See Iwanoff in Graf e's A rchiv, Band xv. , Heft ii. , p. 84. Iwanoff clearly goes too far in maintaining that in no case can glioma develop from the external granule layer ; for neuroglia — that is to say, spongy connective tissue — is, as I showed as long ago as 1859 in my treatise, De structura penitiori, unquestionably present in this layer. Zeitschrift fur wissenschaftliche Zoologie, Band viii., p. 17. De EetituK structura penitiori, p. 13, fig. 5, /, fig. 6. Die Membrana fenestrata der Retina, pp. 7 — 19. Leipzig, 1868. 280 THE RETINA, BY MAX SCHULTZE. a layer of flat cells of remarkably large superficial area. These cells, which anastomose by means of their processes, and thus form a fenestrated membrane, he considers to be at the same time in connection with the fibres of the rods and cones ; the conical terminal enlargements of the latter being continuous with the substance of the cells, or of their processes. On the other hand, the radial supporting fibres which terminate at the limitans interna, end in this fenestrated membrane, and never reach the limitans externa. The holes of the membrana fenestrata are occupied by peculiarly formed internal granules, which, accord- ing to Krause, are the terminal cells of the optic fibres, with which, therefore, the rods and cones are not continuous, since these pass by means of their fibres into the fenestrated mem- brane formed by the connective tissue. I am unable to bring the results of my researches into harmony with these views. Lastly, the bloodvessels of the retina, which in Man are dis- tributed through all the inner layers, as far as to the external granulated layers throughout the whole extent of the retina, with the exception of the fovea centralis, are to be included amongst the connective tissue. The connection of their exter- nal walls with the reticular connecting substance resembles that observed in the lymphatic and lymphoid glands. Peri- vascular lymphatic passages are, as His supposed,* probably here present. The course of the vessels is elsewhere given. 4. MACULA LUTEA AND FOVEA CENTRALIS. The elementary parts of the retina that have now been described undergo essential modification in their form and arrangement at the macula lutea and fovea centralis in Man and Quadrumana. Nearly in the axis of vision, and at some distance to the side of the optic-nerve entrance, an intensely yellow pigment is deposited between the elements of the differ- ent layers, with the exception of those of the bacillar and external granule layers. The centre of the yellow spot is de- pressed on the surface looking towards the vitreous, to form the * Verhandlungen der natur. Gesellschaft. zu Basel, Band iv., Heft ii., p. 256. MACULA. LUTEA AND FOVEA CENTRALIS. 281 fovea centralis. The colouring material, which is most intense in the fossa, and becomes gradually paler towards the margin of the spot, dees not present a granular appearance, but is com- pletely hyaline, and in consequence only so far disturbs the transparency of the retina at this part, that it absorbs a consi- derable portion of the violet and blue rays before these reach the layer of cones.* With the aid of Browning's spectroscope I have very dis- tinctly perceived the shortening at the violet end of the spec- trum under the microscope. I have not, however, by this mode of observation discovered any special absorption-bands. According to Huschke,f the intensity of the colour of the yellow spot is subject to variation, being brighter in blue-eyed than in dark-eyed men. The retina is thicker at the macula lutea, of course excepting at the fovea centralis, than in the adjoining parts ; but is at the same time softer and more prone to post-mortem changes. It is probably owing to its greater capacity for imbibition, that it usually swells up at this part soon after death, forming the so-called plica centralis. It is well known that the attenuated centre of the yellow spot tears with great facility, and then appears as a hole in the substance (Foramen centrale). The high degree of softness and destructibility of the substance of the yellow spot receives explanation from the circumstance that the delicate nervous elements far preponderate in this part over the widely distributed plexuses and fibres of the sup- porting tissue found in other parts of the retina. The nervous elements are very numerous and closely packed at the macula lutea, which is in accordance with its physiological importance as the most sensitive spot of the retina. The layer of the ganglion cells and internal division of the external granule layer, which Henle designated external fibrous layer, are the layers that are most obviously thickened. On the other hand, there is no continuous layer of nerve fibres beneath the limitans * According to Preyer (Pfliiger's Archiv, Band i., p. 299), the first ob- servations on this point were made by Maxwell. See also Max Schultze, Ueber den gelben Fleck der Eetina. Bonn, 1866. t Eingeweidelehre in Soemmering's Anatomie, p. 727. 282 THE RETINA, BY MAX SCHULTZE. interim. In the percipient layer the rods already begin to fail, even at the outermost edge of the macula lutea, their place being taken by the cones, and they ultimately altogether disappear. The cones, which are closely arranged, become more and more slender towards the border of the fovea cen- tralis, so that they here resemble the rods. Thus it comes to pass that in the fovea a much greater number of cones find room than in any other corresponding area in the vicinity. The thickness of the cone fibres which are attached to the slender cones of the fovea centralis, and traverse the external granule layer, is, however, not much less than that of the thick cones of the more peripheric parts of the retina. Each slender cone of the fovea terminates also in as large a number of primitive nerve fibrils as the thick cones of the periphery. The arrangement of the cones at the yellow spot is surpris- ingly regular.* They are disposed in curved lines, which con- verge towards the centre of the yellow spot, and produce the appearance of shagreen, or that presented by the engine turned back of many watches. This arrangement, which on physio- logical grounds had been predicted by Hensen,f is perfectly regular, the cones successively diminishing in diameter from the periphery of the yellow spot to the margin of the fovea ; at this point, however, — that is to say, in the fovea itself, — the curves are less regular, and the cones in an area of about 0'2 of a millimeter in diameter are all of equal thickness. As the thickness of the cones diminishes towards the fovea, their length increases. The outer segments, which at the more peripheric parts of the retina are concealed amongst and are somewhat shorter than the rods, become at the yellow spot, where they gradually supplant them, equal to or even longer than the rods, especially when, as in the fovea, the remaining layers of the retina retreat somewhat towards the vitreous, as though in order to make room for the longer cones.J In one case I found the longest cones above 100 micromillimeters in * Max Schultze, Archiv fur Mikroskop. Anatomic, Band ii., Taf. xii. t Vircliow's Archiv, Band xxxv., p. 403. J Max Schultze, Archiv fur Mihroskop. Anatomic, Band ii., p. 229, Taf. xiii., fig. 1. MACULA LUTEA AND FOVEA CENTRALIS. 283 length. H. Miiller and Hulke have also found that the cones of the fovea are longer than those of the rest of the yellow spot.* The thinnest cones of the fovea are 3 ft in thickness at their base. These are distributed over a circular area of about 200 fji in diameter, which, as has been stated, is the diameter of the fovea eentralis, if this be determined by the extent of distribution of the smallest percipient elements. Taking several diameters of this area, and in the perfectly fresh retina of Man, I counted in each fifty cones, all of equal slender- ness. According to this, each cone would have a thickness of about four micromillimeters .; but the fine intervening spaces between the cones ought to be deducted. In hardened speci- mens, measurements made of isolated cones often appear under three micromillimeters. In specimens preserved in alcohol, Henle found that they did not exceed two micromillimeters. Welcker, to whom we are indebted for some very exact measurements of these elements from the examinations of the retina of a criminal, estimated the thickness of the cones of the fovea between 3'1 and 8'6 micromillimeters, or upon the average 3'3.f The long conical external segments, as they run outwards to the choroid, become attenuated to one micro- millimeter or less. They are invested by the pigment sheaths of the coloured cells of the pigment layer, which are for the most part darker at the macula lutea than in the adjoining part of the retina, and reach as far as the uncoloured outer part of these cells. We are in consequence probably able to perceive in Man, as I have already diagrammatically repre- sented in an earlier work J in animals, and -especially in Birds in the perfectly fresh macula lutea, still covered with undis- turbed pigment cells, the natural extremities of the cones as bright spots surrounded by dark pigment. As already stated, no remarkable difference is observable in * Hulke, Philosophical Transactions, 1857, p. 110. t Zeitschrift fur rationelk Medicin, Band xx., p. 176, 1863. For other measurements the reader may be referred to Max Schultze in Reichert and Dubois-Reymond's Archiv, 1861, p. 784, and H. Miiller in the Wurz- burg. Nat. Zeitschrift, Band ii., p. 219, 1861. t Archiv fur Mikroskop. Anatomic, Band ii., Taf. xii., fig. 1. 284 THE RETINA, BY MAX SCHULTZE. the size of the external granules, or in the thickness of the cone fibres between those of the area of the macula lutea in question, and the more peripheric regions of the retina. On the other hand, the course pursued by the cone fibres is quite dif- ferent. From the date of Bergmann's observations on this point it has been known that in the external granule layer, and especially in the subsequent inner division of this layer, which contains no cells, but free fibres alone, the course of the fibres even external to the borders of the macula lutea, change from a radial to a horizontal direction, which, coincidently with the thickening of this layer towards the border of the fovea, becomes constantly more and more oblique, so that in fact some fibres even run parallel to the surface of the retina. The rod and cone fibres, and afterwards the cone fibres alone, form curves which, prolonged backwards, all diverge from the fovea or from the visual axis, which if prolonged would pass through the fovea, and thus reach the outer granulated layer ; though not by that shortest path which is pursued by the more peripheric fibres of the external granule layer. In consequence of the gradual and necessary prolongation of the cone fibres, a layer of horizontal fibres is produced, extending for some distance around the fovea, the beginnings and endings of which are no doubt radially directed ; but which at a certain plane stream out like radii from the central fovea.* The explanation of this is found in the very existence of the fovea. At this point all the layers of the retina, with the exception of the cones and external granules, diminish to a minimum. The cone fibres of this region, in order to reach their destination, must diverge from one another in all directions. Beyond the fovea are the inter- nal granules belonging to them, the internal granulated or molecular substance, and the ganglion cells. But from the uninterrupted cone layer fresh masses of cone fibres still come in order to seek their connections. And, although the ganglion- cell layer becomes considerably increased in thickness at the macula lutea, this is not the case with that of the internal granules. The fibres thus press outwards, till ultimately external to the yellow spot the direct radial course of the * Merkel, loc. cit, Taf. i, fig. 11. Fig. 361. Diagrammatic section through the macula lutea and fovea centralis of the retina of Man. Mag- nified 110 diameters. 2, optic - nerve fibres ; 3, ganglion cells ; 4, internal granulated layer ; 5, in- ternal granule layer; 6, external granulated layer ; 7 'a, external fibrous layer ; 7, external granule layer ; 9, rods and cones ; 10, pig- ment layer. 286 THE RETINA, BY MAX SCHULTZE. cone and rod fibres, such as they pursue in other parts of the human retina, and in the retina of animals that do not possess a fovea cent-rails, is re-established. An oblique direction, as Hulke has observed, is pursued also by the nerve fibres of the internal granule layer. In transverse sections carried through the macula lutea and fovea centralis, I found that the rod and cone fibres pursue an oblique course outwards on every side from the fovea for two millimeters in the horizontal meri- dian, but only for about 1*5 millimeters in the vertical meri- dian. According to Hud. Schirmer^s observations on the oph- thalmoscopic appearance of the macula lutea in healthy eyes, it is always of a tranversely oval form ; its horizontal in relation to its vertical diameter being as 4 : 3.* The ganglion cells of the yellow spot are for the most part bipolar, as has been stated by various observers, and recently by Merkel. The connective substance at the yellow spot, as has been already mentioned, is particularly tender and delicate, and has no thick radial supporting fibres. On the other hand, the membrana limitans interna becomes quite thick and strong. According to Merkel, it attains a thickness of three micro- millimeters, though it again becomes attenuated at the fovea centralis. It separates with extraordinary facility from the deli- cate spongy connective tissue that occupies the interspaces between the ganglion cells. A macula lutea and fovea centralis are only present in Quaclrumana amongst Mammals, but here entirely agree in their anatomical charac- ters with the corresponding parts in Man. Kernak and H. Miiller^: have pointed out the existence of an area centralis, with a structure similar to the yellow spot in the retina of several Mammals ; but we possess no precise information on the point. That in the retina of some Birds, not only one, but two fossae are present at some distance from each other, was discovered by H. Miiller,§ though he gave no details in regard to the principal elements of these parts. According to my * Grafe, Archiv, Band x., 1, p. 150. f Max Schultze, Sitzungsberichte der Nieder-rheinische Gesellschaft zu Bonn, Juli, 1861. $ Wurzburg naturwiss. Zeitschrift, Band ii., p. 140, 1861. § Loc. tit., and in his- treatise Ueber das Auge des Chamaleon, p. 11. MACULA LUTEA AND FOVEA CENTRALIS. 287 observations, the percipient elements in the two fossae centralis of the Falcon consist of cones of smaller thickness than in the adjoining parts, which possess only yellow, but no red pigment spheroids, though both are present in the other portions of the retina. The rods are entirely absent.* The retina of the Chamaeleon presents a very well-marked fovea, the minute anatomy of which has been given with great exactness by H. Miillerf and Hulke.J As appears to be the general rule in Reptiles, cones alone are found in the percipent layer of the entire retina of the Chamaeleon. These, however, in the fovea centralis are only about one-fifth as thick as in the peripheric regions, but at the same time are much longer, so that the line of the liinitans externa is here more distant from the choroid, just as I have depicted it in Man. To these cones, obliquely running cone fibres are attached, also closely resembling those of Man. But, whilst in Man the connective tissue of the external granule and cone fibre layers follows these fibres, H. Miiller has demonstrated the presence in the Chamaeleon of a peculiar kind of radial supporting fibres, which decussate at an acute angle with those of the cones. The delicacy of the individual cones of the Chamaeleon, as seen in preserved eyes of this animal, surpasses that of every other animal. In other Reptiles, as in Ophidia and Chelonia, it appears from the statements of Knox and Hulke,§ that a fovea is present, though not very well marked. On the other hand, in Amphibia and Fishes no indica- tions of either a macula lutea or of a fovea centralis have been observed. I have directed attention to the circumstance that the yellow screen, which in the macula lutea is situated in front of the per- cipent elements, must exercise an important influence on the amount of violet and blue that we see in the spectrum, || and it naturally sug- gests itself, that an increase in the intensity of the yellow pigment of the retina must produce yellow vision, or violet blindness. In consider- ing the effects of santonin, I overlooked, as I here desire to be particu- larly noted, the fact that objects appear yellow, not only by direct, but * Archivfur Mikroskop. Anatomie, Band ii., p. 206. t Wiirzburg naturwiss. Zeitschrift, Band iii., p. 10, 1862. J Journal of A natomy and Physiology, No. 1, p. 104, 1866. § Loc. cit.j pp. 103 and 104. || See my treatise above cited, Ueber den gelben Fleck der Retina; seinen Einfluss auf normales Sehen und auf Farbenblindheit. (" On the yellow spot of the Retina : its influence on normal vision, and upon colour- blindness.") 288 THE RETINA, BY MAX SCHULTZE. also by indirect vision. I therefore retract my earlier view, which I consider to be no longer tenable. We, however, habitually see through another yellow screen present throughout the whole extent of the retina, namely, the narrow -meshed plexus of its capillary vessels, which lie in front of all the percipient elements, that is to say, between the limitans interna and the external granulated layer. The quantity of the rays of the spectrum which a single layer of corpuscles sometimes standing on their edges, and disposed like rouleaux of coin, absorbs is very considerable, as an examination with Browning's spectroscope shows. The hoernoglobin lines are visible, and a considerable portion of the rays at the violet end of the spectrum are lost. With thicker layers of blood corpuscles, like those circulating in the larger retinal vessels, the absorption effects would clearly be much more considerable. And, although there are many holes in this screen of bloodvessels through which we may see, and of which, on account of the constant movements of the eye, we are unconscious ; yet the plexus of blood- vessels, especially if it be projected from the various layers of the retina into one plane, is too thick for its influence to be entirely dis- regarded. Alterations in the blood affecting this absorption power for certain luminous rays must necessarily lead to unusual perceptions of colour.* 5. ORA SERRATA AND PARS CILIARIS. The neighbourhood of the ora serrata of the human retina, in opposition to the area surrounding the macula lutea, is characterized by the gradual disappearance of the nervous elements, whilst the connective tissue, on the contrary, is pro- gressively more and more developed. The radial supporting fibres, with the spongy network connecting them, form the principal portion of the tissue at the ora serrata ; and ulti- mately, though in a somewhat modified condition, appear to constitute that continuation of the retina over the ciliary pro- cesses which no longer participates in the perception of visual images. H. Muller has made such extensive researches upon this sub- ject, that little remains for subsequent inquirers to add. His results show essentially that the " several layers of the retina * Zeitsclirift fur wissenscliaft. Zooloyie, Band viii., p. 91. ORA SERRATA AND PARS CILIARIS. 289 have undergone such diminution in the vicinity of the ora serrata, that their united thickness only amounts to 012 to 014 of a millimeter. The nerve and ganglionic spheroids become very sparingly scattered, so that they can only be found quite isolated between the internal extremities of the radial fibres ; the granular layer, in consequence of the preponderating amount of the latter, has likewise become more vertically striated, so that ultimately its inner boundary disappears. The internal granule layer consists of only two or three not very closely arranged tiers of granules, and not unfrequently simple nuclei appear to occupy their place in the fibrous mass which extends through the slender intergranule layer to the external granules. The rods and cones are distinct, though they have become somewhat shorter. Just before the point of greatest attenuation, the retinal layers severally lose their peculiar characters to a still greater degree, and pass into an obscurely vertically striated mass, in which numerous roundish or oval nuclei are distributed. The bacillar layer is alone excepted from this general fusion or indifference of tissue, remaining to the last a separate layer, the elements of which rapidly diminish in size, and finally cease. As soon as this takes place the remaining layers form a single tier of cells, which con- stitutes the pars ciliaris, and is the immediate prolongation of the retina proper. The ''cells resemble in general those of columnar epithelium, but vary in height in different animals. H. M tiller examined this region, particularly in the Pig, Ox, Rabbit, Pigeon, and Fowl. In the Rabbit their height amounts to 0'025 of a millimeter." H. Miiller regards these cells as a continuation of the indifferent supporting apparatus of the retina, " whence, as it appears, the inner extremities of the radial fibres are perhaps to be reckoned as belonging to such of the inner granules as correspond to the — in most animals — distinctly different nucleated radial fibres . . ." More- over the form of the cells in question is in some parts in Man such as to render their epithelial nature doubtful. They are isolated, frequently not rounded at the extremities, but provided with one or with several dentations and short processes, which are given off also from the longer side, so that they might be considered to belong to the group of connective tissues, against VOL. III. 0? TJ1TI7BRSXT7 290 THE RETINA, BY MAX SCHULTZE. which view the rounded cell forms occurring elsewhere certainly constitute no objection. Kolliker* completed these observations in so far that he directly states he has seen the gradual transi- tion of the shortened radial fibres into the cells of the pars ciliaris. He admits also the presence of a membrana limitans interna at this part. On the other hand, we miss an exact description of the isolated cells, the forms of which, as H. Miiller has already pointed out, may, owing to the presence of processes and dentations, be very various, and respecting which Klebsf from his investigations admits that they pass directly into the fibres of the zonula. Two regions, however, are to be distinguished here, the smooth posterior and the plaited anterior division, the plaits or folds of the latter forming the processus ciliares. SchwalbeJ respectively designates these two the zone of the orbiculus ciliaris and the zone of the ciliary processes. He was able to isolate a limitans interna in both ; but at the zone of the ciliary processes, after removal of the vitreous, he found that it remains in part adherent to the zonula Zinnii, especially at the points corresponding to the depressions between the processes, which also remain covered with the cells of the pars ciliaris retinae and the pigment, in consequence of which the well-known form of the black-rayed zonula originates. Schwalbe, however, does not, like Kolliker, con- sider that the membrana limitans interna arises from the cells of the pars c^iaris, but describes it — together with certain reti- cular externalVprocesses, observed also by Merkel,§ which extend between the cells of the pars ciliaris, and correspond to the radial supporting fibres — as a prolongation of the connecting substance of the retina. II By this means the transition of the radial fibres of the retina into the cells of the pars ciliaris, which Kolliker considered to be an ascertained fact, is again rendered doubtful.^" * G-eivebelehre Aufl. v., p. 685. t Virchow's Archiv, Band xxi. p. 187, 1861. J Archiv fur Mikroskop. Anatomic, Band vL, p. 326. § Die Zonula ciliaris, Taf . i. , fig. 9. Leipzig, 1870. IJ Ibidem, p. 303. ^T See also the essay of Manfredi, Sulla struttura della parte cigliare della Retina, in the Gaz. Med. Ital-Lombard, Ser. vi., Tom. iii., 1870. ORA SERRATA AND PARS CILTARIS. 291 According to my observations made on fresh human eyes which had been preserved for twenty-four hours, or for a some- what longer period, in solutions of perosmic acid of various degrees of concentration, the cells of the pars ciliaris offer very diverse appearances. In general they form elongated prisms resembling tall columnar epithelial cells. At their outer ex- tremities they are smoothly truncated, and are in contact with a pigment cell ; at their inner extremities they either become enlarged or attenuated, and cleave firmly to the surface of the vitreous, which is here distinctly fibrous (zonula Zinnii). Many of these cells here terminate distinctly as radial sup- porting fibres of the retina, presenting either a conical enlarge- ment, or undergoing division ; each of the branches again ceasing abruptly like a column upon its pedestal. Other cells intercalated between these reach the surface of the vitreous by a pointed extremity, or break up into fine fibres, so that it ap- pears as though the ends pass into the fibres of the zonula. I have never, however, observed a direct transition of the one into the other. The whole surface of the cells of the pars cili- aris is not unfrequently beset with fine elevations and rough- nesses, those of the adjoining cells interlocking with each other. The substance of the cells is not homogeneous, but appears finely striated longitudinally, though not divisible into fibres. Their nucleus is oval, hyaline, relatively large, very pale, like the nuclei of the radial supporting fibres, and is sometimes placed nearer to the one end, and sometimes to the other. Small quantities of dark-brown granular pigment are not un- frequently found in the substance of the cells, which is most- closely disposed towards the exterior, so that it is doubtful whether these are peculiar pigment cells (the pigmentary layer of the retina), or whether the pigment cells themselves have not grown out in a fibrous manner. Upon the whole, that view appears to me to be the most correct, according to which the cells of the pars ciliaris correspond to the radial supporting- fibres. They agree generally in the nature of their substance, which is in both cases finely striated, and, as it were, fibrillated; in the form and refractive properties of the nucleus ; in their relation to perosmic acid, which confers upon both a clear brownish colour, whilst the adjoining vitreous becomes of a u 2 292 THE RETINA, BY MAX SCHULTZE. bluish-black colour after long maceration ; and lastly, in the rough prickly surface, and the mode of ending at the vitreous. It is maintained by various authors that the cones of the human retina continuously diminish in number in relation to the rods from the macula lutea to the ora serrata. This, how- ever, is not correct, as I* have already shown. The relative distribution of the rods and cones remains unaltered from a certain line surrounding the yellow spot to the ora serrata, so that three or four rods are always interposed in the direct line between two cones. At the ora serrata the number of the rods suddenly diminishes, and empty spaces occur between the cones. These last, which appear to increase in number, resem- ble, in a surface view, irregularly circumscribed circles, lose their lustre, and ultimately disappear in the tissue of the pars ciliaris. As was stated by H. Mliller, the height of the rods and cones is less near the ora serrata than in the fundus of the eye or near the equator.t Merkel made similar observations in Man, the Ox, Fowl, and Pike. The condition which Iwanoff and I have named oedema of the retina, associated with atrophy of the nerve tissue at the ora serrata, and to which the latter has recently devoted an ex- tended essay, j: presents a very remarkable departure from the normal state. According to Merkel § and Iwanoff, it especially occurs in elderly people, consequently may be considered as a senile metamorphosis, || being characterised by the formation of spaces filled with serous fluid, which, intercommunicating with each other, can detach the retina to a not inconsiderable extent, and lead to atrophy of the nerve tissue at the points in question. The radial supporting fibres, however, become * A rchiv fur Mikroskop. Anatomie, Band ii., p. 225, Taf. xii., figs. 3, 4. t See Max Schultze, Archiv fur Mikroskop. Anatomie, Band v., Taf. xxii., fig. 5, taken from the anterior border; fig. 14, from the neigh- bourhood of the equator ; and fig. 11, from the yellow spot of Man. t Grafe, Archiv fur Ophthalmologie, Band xv., Heft, ii., p. 88, 1869. § Macula lutea, etc., p. 17. || Iwanoff, who observed a large number of these cases, saw the oedema in only six amongst fifty eyes of adults between twenty and forty years of age ; on the other hand, it was present twenty-six times in forty-eight eyes of adults between fifty and eighty years of age. DEVELOPMENT OF THE RETINA. 203 compressed into columnar fasciculi, which remain stretched between the two limitantes, or between the limitans interna and the external granulated layer. Though it was originally described by H. Muller* under the impression that the infiltra- tion was a post-mortem change, it was first depicted by Blessig,f and first stated to be of frequent occurrence by Henle.J When transverse sections of such cedematous spots of the retina are made, cavities are seen in the region of the granule layers, or there may be extensive degeneration of the tissues between the limitans externa and interna,. bounded by closely com- pressed columns of radial fibres, in which are many nuclei, and which form arches near the limiting membranes. Degenera- tions of this kind, however, are not exclusively limited to the ora serrata. I have myself observed a case where a portion of the retina, the size of a pea, was so infiltrated as to form a pro- minent tumour near the equator of the eye. Transverse section showed that there was a well-marked state of cedema confined to this spot. The retina was here about one millimeter in thick- ness. The rods and cones which, in minor degrees of oedema, appear to be unaltered disappear in the more completely dis- tended parts. § Merkel also observed cedematous swelling of the retina in old Dogs. 6. DEVELOPMENT OF THE RETINA. To form the retina a vesicle is protruded from the brain of the embryo, termed the primitive eye vesicle, which very soon after its appearance becomes changed with coincident develop- ment of the lens into a doubly laminated cup. This occurs in Fowls at the end of the second day of incubation. The two laminae of the primitive retina which originates from the eye vesicle are, in the first instance, of equal thickness ; but the anterior lamina, which is in contact with the vitreous, soon * Zeitschrift fur wissenschaft. Zoologie, Band viii., p. 71. t De Retinae, structura, fig. 3, p. 47. Dorpat, 1855. £ Eingeweidelehre, p. 669. § See Iwanoff, loc. cit., Taf. iv. and v., figs. 11 and 12. 294 THE KETINA, BY MAX SCHULTZE. increases considerably, whilst the posterior remains unchanged.* The former consists, on the fifth day of incubation, of very numerous small fusiform cells, arranged vertically to the sur- face ; the latter of a single layer of short prismatic cells con- taining dark pigment. Remak was disposed, in consequence, to recognize in these the first rudiment of the choroid, as well as of the retina. By Kolliker/f1 however, and more recent inquirers,^: it has been demonstrated that the deve- lopment of the pigmented connective tissue and of the ves- sels of the choroid proceeds independently of the pigmented layer of the primary eye vesicle. The posterior lamina of the latter goes exclusively to form the pigment epithelium of the retina, whilst the anterior lamina forms the remaining layers of this membrane. The rods and cones are the last to appear. Prior to their development the embryonal retina is very sharply defined towards the pigmented epithelium by a limitans externa. This "is much more distinct than the limitans interna at the same period of development. It corresponds in regard to its position, lining as it does the cavity of the primary eye vesicle to the inner surface of the cerebral ventricle,§ which in embryoes of the same age I find to be lined by an equally sharply defined membrane. It ori- ginates from a conical expansion of fibrils and fusiform cells arranged vertically to the surface, the truncated extremities of which lie in one plane, and are intimately attached to one another to form a membrane. There is thus a complete simi- larity of structure between the retina and the cerebral ventricles. At this period no epithelial investment exists in either place. From the seventh to the tenth day of incubation in Chickens, * See Remak, Entwickelung der Wirbelthiere, p. 35, Taf. v., fig 60 ; Hensen, Virchow's Archiv, Band xxx., p. 181 ; and my detailed account of the development of the retina in the Chick, Archiv fur Mikroskop. Anatomie, Band ii., p. 239, Taf. viii. f Entwickelungsgeschichte der Wirbelthiere, p. 288, 1861, for Mammals. * Babuchin, Wurzburg not. Zeitschrift, Band iv., p. 71, 1863, for Mam- mals, the Chick, and Frog ; Max Schultze in idem, for the Chick and for Mammals ; Schenk, Sitzungsberichte der Akad. zu Wien, 1867 ; April part, for Fishes. See also Hensen, Archiv fur Mikroskop. Anatomie, Band ii , p. 421. § Max Schultze, Archiv fur Mikroskop. Anatomie, Band ii., p. 265. DEVELOPMENT OF THE RETINA. 295 a very distinct lamination becomes apparent in what was ori- ginally the homogeneous mass of the (anterior) retina. This lamination consists in the differentiation of an internal fibrous layer, of the two granulated layers, and of distinct differences in the size of the cells in the several layers of the granules and ganglion cells ; at the same time the rudiments of the rods and cones project posteriorly beyond the membrana limitans ex- terna in the form of homogeneous hemispherical elevations of very small diameter. As these increase in length and thick- ness the internal segment is first formed, and then subsequently the external segment. These consequently grow into the pig- mented epithelial cells of the posterior lamina of the retina, which on their side form the pigment sheaths. On the eighteenth day of incubation, coloured, but at first very small, red and subsequently yellow oil globules appear in the cones, so that the retina of the Chick just escaped from the egg is already provided with completely developed percipient elements, which do indeed increase in length and thickness, but not in number. It is moreover worthy of notice that in Chickens the rods and cones appear from the first as distinct structures, and that the cones, which are originally smaller than the rods, immediately after hatching become considerably thicker, and, with their coloured globules, occupy a much larger space than at an earlier period. The relation of the developing rods and cones to the external granules has been ascertained by Babuchin from his researches on the retina of the Tadpole.* The large size of the element- ary parts permits it to be seen that the rods and cones owe their origin to an outgrowth of the substance of the outer gra- nules, and although when fully developed the rods and cones appear very distinct, the difference, according to Babuchin, in the early stages of development is but slight. The results of the investigations made by Schenk on Fishes agree well with these observations on the development of the rods and cones from the anterior lamina of the primary eye vesicle. This process, so far as it is connected with the pro- duction of cells on one side of a substance differentiated from * Loc. cit.j p. 77. 296 THE RETINA, BY MAX SCHULTZE. protoplasm may be associated with the production of the so- called cuticular formations, at least, so far as regards the outer segments, and the refractile bodies of the internal segments.* As in Chickens, previous to hatching, the rods and cones are already developed, though they are then of smaller size than in the adult animal, so is it also at the time of birth in Man and in many Mammals, as, for example, in Ruminants. In the new-born Child and in the Calf the rods and cones are well developed, and divided into internal and external segments, though these are much more slender and shorter than in adults. It is different in the blind litters of Cats and Rabbits ; here, the percipient elements develop subsequent to birth .f Either at the period of birth the limitans externa is still perfectly smooth, or the first indications of rods and cones begin to pro- ject beyond the limiting membrane in the form of rounded elevations ; the formation of distinct rod-like elements follows a few days later, and proceeds as in Fowls, so that the internal segment is first formed, and then the external segment. The first distinctly perceptible laminae of the latter occur at about the fifth or sixth day after birth. At the ninth day, that is to say, at the period when the eyelids open, the length of the external segments in the Cat amounts to scarcely more than four micromillimeters, whilst in the adult animal their length amounts to seventeen micromillimeters. In the Rabbit the proportions are similar.! The laminae consequently increase, not in thickness but in number. § At what period antecedent * Hensen long held the opinion that the rods, or the outer part of their substance, develop coincidently with the pigment from the outer lamina of the primary eye vesicle (Virchow's Archiv, Band xxx. , p. 181, and Archiv fiir Mikroskop. Anatomie, Band ii., p. 421), but he has lately given up this view (Ibidem, Band iv. , p. 349). t Max Schultze, Archiv fiir Mikroskop. Anatomie, Band ii., p. 246, and Band iii., p. 373. Steinlin, Anatomie der Retina, St. Gallen, p. 99. J Max Schultze, loc. cit., Band iii., p. 375. § For a different view, by W. Krause, see his Membrana fenestrata, p. 33. I may here state, that satisfactory conclusions respecting the development of the rods and cones can only be obtained from the borders of folds of absolutely fresh specimens of retinae, preserved in aqueous humour or iodine of serum, and that all my statements rest on the •DEVELOPMENT OF THE RETIXA. 297 to birth in Man the development of the rods and cones begins from the outer granule layer has not been accurately ascer- tained. In an embryo of the twenty-fourth week, which I obtained perfectly fresh, I found the membrana limitans interna still quite smooth. Hitter, however, believes he has seen well- developed rods in younger embryoes.* In the early stages of its development the retina extends forwards as far as to the border of the lens. In consequence of a difference in the process of development of its several parts, arise the retina proper, its pars ciliaris, and lastly the pigment lying behind the iris, which is covered by only a rudiment of the tissue proceeding from the internal lamina of the primary eye vesicle, which is, it would appear, a variable prolongation of the limitans interna. Inasmuch as during the development of the retina the rudiment of the palpebral fissure of the embryo is indicated by a non-pigmented stria which extends from behind forwards over the whole extent of the retina,f the rudiment of this not unfrequently occasions a persistent absence of pigment as an arrest of development (coloboma), which affects the pigment behind the iris equally with that before the choroid. Coloboma, as Schb'lerJ has already demonstrated, is primarily an arrest of development of the retina, and not of the choroid. § Information as to how far the tissues of the latter membrane and of the iris, apart from the pigment epithelium, take part in the frequently occurring examination of such specimens. W. Krause macerates the eyes of young Rabbits in bichromate of potash, and finds that the existence of rods and cones can be demonstrated with extraordinary facility, when I am unable to discover them in the fresh state. * Grafe's Archiv, Band x., Heft i., p. 75, Heft ii., p. 142. Die Structur der Retina, etc., pp. 32 and 52. t See Archiv fur Mikroskop. Anatomie, Band ii., Taf. viii., fig 7. J De oculi evolutione. Dissert, inaugural. Mitau, 1849. § We cannot possibly regard the fovea centralis as a remains of the foetal palpebral fissure, on account of its position, as Hensen has recently pointed out (Archivfur Mikroskop. Anatomie, Band iv., p. 350). On the other hand, the pecten of Birds, and what corresponds to this in Fishes and Reptiles, are situated in the vicinity of the fissure, whilst they originate from the growth of the choroid into it. Schenk, Wiener Stizwngsberichte, 1867. 298 THE KETINA, BY MAX SCHULTZE. coloboma, must be obtained from numerous and exact ophthal- moscope examinations of cases in which this arrest of develop- ment has occurred. Here also there are relations in respect to the development of the pigment epithelium from the external lamina of the primary eye vesicle to the development of the choroidal tissue that are quite unknown. II. TUNICA VASCULOSA. BY PROF. A. IWANOFF. THE tunica vasculosa, or tunica uvea, lines the sclerotic, and lies between it and the retina. At a distance of one millimeter from the margin of the cornea it makes a sharp curve inwards towards the axis of the eye, and rests on the anterior surface of the lens, forming by means of this rectangularly bent part the posterior wall of the anterior chamber of the eye. The posterior part of the tunica vasculosa, lining the sclerotic, is termed the choroid ; whilst the anterior part, which appears during life behind the transparent cornea, is named the iris, and is perforated at its centre by an opening, the pupil. These two membranes are together named the tunica vasculosa, because both are richly supplied with vessels, and because both sets of vessels freely intercommunicate with one another. The other term common to the choroid and iris, of tunica uvea, was conferred upon them from their remote resemblance to the skin of a dark-coloured grape, in which the hole for the pedicle corresponds to the pupil.* Many anatomists now limit the term uvea to the layer of pigment that lines the posterior surface of the iris. I. The choroid forms a thin vascular membrane, having a thickness of 0'08 to 016 of a millimeter, which is firmly attached to the sclerotic in two places, posteriorly at the point of entrance of the optic nerve, where its inner layers are con- tinuous with a ring that embraces the nerve, and from which fine fibres are given off that penetrate the nerve itself ;f * Briicke, Anatomische Beschreibung des menschlichen Augapfds, p. 2, 1847. t H. Miiller, Anatomische Beitrage zur Ophthalmologie, Archiv ftir Ophthalmologie, Band ii., Abtheilung ii., p. 24. 300 TUNICA VASCULOSA, BY PROF. A. IWANOFF. and anteriorly at the point of transition of the sclerotic into the cornea (annular tendon of the circular muscle). These two coats are elsewhere connected by arteries and nerves, which perforate the sclerotic in order to enter the choroid, and by veins Avhich pass in the opposite direction. The external surface, which is turned towards the sclerotica, is of fibrous structure, and brownish colour ; where the choroid is attached in front to the sclerotica, there is an annular grey thickening, having a breadth of from three to four millimeters, which encircles the anterior part of the vascular membrane, and is termed the ciliary muscle. The internal surface of the choroid looks towards the retina, and is very loosely connected with it as far as the ora serrata, though sufficiently firmly to cause the whole external layer of the retina (namely, the pigmented epithelial layer) to remain adherent to it in the greater number of cases, which has led to the belief that this layer belongs to the choroid. Starting from the ora serrata, these membranes are much more intimately united, since from this point forwards the pigmentary layer, forming a bond of union between the ciliary portion of the retina and the choroid; increases considerably; on which ac- count also the separation of the retina from the choroid at this spot does not always, and then only partially, take place. If the pigment be removed, the inner surface of the choroid, as far as to the ora serrata, appears perfectly smooth, and of a grey colour ; behind the ora serrata its surface becomes rough, and in front of it is a series of folds, arranged in a meridianal direction, and separated from one another by deep furrows, which are the so-called ciliary processes. The ciliary processes, from seventy to eighty in number, have the aspect of a regularly plaited frill, and as they project more and more anteriorly their apices ultimately reach the ciliary border of the iris. The entire internal surface and all the folds as far as their anterior margin, are covered with a thick layer of pigment and with the cells of the ciliary portion of the retina (pars ciliaris retinae). The anterior part of the choroid, commencing from the ora serrata, together with the ciliary processes and the ciliary muscle, are collectively termed the corpus ciliare. THE CHOROID COAT. 301 The anterior part of the choroid has long had a special name applied to it. Thus, Vesalius named it the tunica ciliaris, and subsequent anatomists distinguished in this tunica ciliaris a pars plicata and a pars non plicata. Fallopius was, however, the first who applied the term corpus ciliare to this part of the choroid. Henle only names the most anterior part of the choroid the corpus ciliare, including under this term the ciliary processes and the ciliary muscle. . The zone lying between the ora serrata and the corpus ciliare he terms the orbiculus ciliaris, without maintaining, however, that any well-defined line can be drawn between the corpus ciliare and the orbiculus ciliaris. Under the name corona ciliaris, Luschka describes that portion of the membrane which is connected with the zonula Zinnii, and extends from the ora serrata to beyond the margin of the lens ; the ciliary muscle he names the annulus ciliaris. We believe that it would be of advan- tage in facilitating the comprehension of the ordinary terminology to keep to one system of nomenclature, even if this did not express all the anatomical peculiarities of this part of the choroid. We have selected the term corpus ciliare, not because we consider it to be the best, but because it is most generally employed ; in this sense Kolliker uses the term corpus ciliare in his Manual, as well as H. Miiller in all his treatises on the eye. The vessels form the chief constituent of the choroid, and on this account this membrane has from a remote period been considered to exert a powerful influence on the nutrition of the eye. Its rich -supply of vessels explains also, without doubt, the very important part it plays in the various patho- logical processes taking place within this organ. The smooth muscles form another constituent of this mem- brane, playing an important part in the functions of the eye. The larger part of them is accumulated in the corpus ciliare, but they are by no means altogether absent in the posterior segment of the choroid. Lastly, the choroid is abundantly supplied with nerves. All these constituents are connected together by a stroma, characterized by the presence of a large number of stellate pig- ment cells. The five following layers are usually distinguished in the choroid — the pigment layer ; the vitreous layer ; the membrana chorio-capillaris ; the layer formed by the larger arteries and veins ; and lastly, the membrana supra-chorioidea. The history 302 TUNICA VASCULOSA, BY PROF. A. IWANOFF. of the development of the pigment layer from the external lamella of the secondary eye vesicle, shows, however, that it must be reckoned as belonging to the retina ; so that there only remain four layers. But inasmuch as this division of the choroid into four layers is not based on any facts of struc- ture or position, we shall not adhere to it in the following account. 1. Vitreous membrane (Glashaut), (lamina vitrea of F. Arnold,* elastic layer of Kolliker,t basal membrane of Henle,|) was origi- nally described by Bruch,§ by whom it was named membrana pigmenti. In the posterior segment of the choroid it forms a very thin (0'0006— 0'0008 of a millimeter) structureless, or slightly fibrous (Kolliker) membrane, which, except by the application of artificial means, is indissolubly connected with the stroma of the choroid. The surface in contact with the pigmented epithelium is perfectly smooth as far as to the ora serrata. Solutions of potash and of sulphuric acid bring its folds into view, because these reagents act differently on the vitreous layer and the external layers of the choroid connected with it. For since the protracted action of these reagents causes a part of the stroma attached to the vitreous membrane to break down ; so also, in concentrated acids and alkalies, it frequently separates from the other layers of the choroid in the form of isolated shreds. If the choroid be macerated for some time in a ten-per-cent. solution of common salt, the fibrous structure of the vitreous layer is very clearly brought into view. Even then, however, it presents no trace of nuclei. The nuclei described as existing in it by Bruch and Henle unquestionably belong to the capillaries. In the anterior portion of the choroid — the corpus ciliare — the characters of the vitreous layer undergo a marked change. It here becomes paler, thicker, and is more amenable to the action of alkalies and acids. It here also loses its smoothness, its inner surface presenting microscopical elevations and de- * Anatomic, Band ii. , p. 1020. f Handbuch der Gewebelehre, p. 661, 1867. $ Handbuch der Systematischen Anatomic des Menschen, Band ii., p. 620, 1866. § Korniges pigment, 1844. VESSELS OF THE CHOROID. 303 pressions, which form the so-called reticulum of the ciliary body.* This reticulum is produced by small elevations anas- tomosing with one another, and enclosing depressions which contain pigment. The meshes of this reticulum are smaller in proportion to their distance from the ora serrata. The plexi- form character of the vitreous layer is preserved as far as to the iris. 2. The vessels of the choroid, as has been already stated, form two layers : the chorio-capillary layer, known also as the membrana Ruyschiana, which reaches only as far as to the ora serrata, and the layer composed of the larger arterial and venous trunks, which has also been termed the tunica vasculosa Halleri. The ramification of these vessels will be hereafter separately described, but a few remarks may here be made in respect to some peculiarities of their structure. The capillaries are so intimately connected with the vitreous membrane by means of a very thin connective-tissue stroma, that their separation can only be effected by the application of reagents which dissolve the stroma. The walls of the capillaries present no points of difference in their structure from the capillaries of other regions of the human body. Contrary to the opinion of Henle, their walls contain nuclei ; and this not only in young persons, as H. Miiller admits, but also in those of advanced age. In old persons, how- ever, the nuclei are somewhat atrophied, become flattened, whilst at the same time the vascular walls are thickened, rendering their observation more difficult. In many instances we see in the eyes of persons apparently in perfect health elongated cells placed by the side of the capillary wall, from which extremely delicate processes, visible only under the highest powers, extend to the wall ; but these cells and their processes, which join to form a plexus, are brought very clearly into view in inflammation of the choroid. In such cases these processes extend themselves also into the interspaces of the capillaries. The arterise ciliares breves are characterized by the great development of their circular muscles. They are accompanied * H. Miiller, Archiv fur Ophthalmologie, Band ii., Heft ii., Anatomische Beitrage zur Ophthalmologie. 304 TUNICA VASCULOSA, BY PROF. A. IWANOFF. on either side by a longitudinal fasciculus of smooth muscular fibres, the size of which varies considerably in different in- stances.* Moreover, the thickness of the muscular fasciculus is not alike on the two sides of the vessel. The smooth muscles only accompany the short ciliary arteries as far as to the posterior portion of the choroid ; the farther they are traced forward in the direction of the ora serrata, the fewer are the muscles. Detached muscles in the form of thin fasciculi are found also distributed in the stroma of the choroid. 3. The principal mass of the smooth muscular fibres of the choroid is imbedded in the most anterior part of this membrane, and constitutes the ciliary muscle (tensor choroideae, Brucke). The ciliary muscle (fig. 362) resembles a prism, bent into the form of a circle, with its sharp border turned backwards. Fig. 362. Fig. 362. Section of the ciliary region of the eye of Man. a, Meridianal muscular fasciculus of the musculus ciliaris ; b, deeper- seated radiating fasciculi ; c c c, annular plexus ; d, annular muscle of Miiller ; /, muscular lamina on the posterior surface of the iris ; g, muscular plexus at the ciliary border of the iris ; e, annular tendon of the musculus ciliaris ; h, ligamentum pectinatum. Its position is in the anterior and external part of the ciliary body. The ciliary muscle is separated from the sclerotic by a thin layer, the lamina fusca; and from the pigment which covers the surface of the ciliary processes, by connective tissue. * H. Miiller, Verhandlung. der physikalisch-medicinischen Gesellschaft in Wurzburg, Band x., Abtheil. ii., iii., p. 179. CILIARY MUSCLE. 305 In meridianal sections the ciliary muscle exhibits the form of a rectangular triangle, the shortest side of which is turned forwards, and forms a right angle with the outer side. The thickness of the muscle is about 0*8 of a millimeter. The greater part of the muscle is composed of meridianally running fasciculi (fig. 362, a), forming a compact mass, which constitutes the thick external portion, and makes up its larger third. The deeper-lying fasciculi (6), which, like the preceding, arise at the anterior external angle of the muscle, run diverg- iiigly in a radiating manner to the inner side of the triangle. In this course the radiating fasciculi frequently anastomose with one another ; after they have reached the inner side they become circular, and thus form a thick circular web along the whole internal muscular surface (c). Moreover, the anterior side, and, to a certain extent, the internal anterior angle of the ciliary muscle, include tolerably thick fasciculi of circular fibres, the so-called circular or annular muscle of Muller (d). The posterior fasciculi are formed of those longitudinal fibres which have changed their direction, the anterior represent a completely independent muscle. All the meridianal and radiating fasciculi arise from the anterior external angle of the muscle, and they are continuous with a dense flattened expansion of connective tissue which forms its annular tendon (e). This is directed forwards, lies on the inner side of the canal of Schlemm, and is ultimately itself continuous with the tissue of the cornea. That meridianal portion of the muscle which is in imme- diate contact with the sclerotic consists anteriorly of regularly arranged parallel laminae. In proportion, however, as we pass farther backwards, this regularity of disposition disappears, so that at a distance of three millimeters from the origin of the muscle the fasciculi separating and anastomosing with one another, form a series of loops, with their convexities turned backwards, in which a part of the muscle terminates. The other portion of the meridianally running fibrils preserves its primary direction, and may be followed to a distance of from five to six millimeters from the origin of the muscle, in the x • '* "( 306 TUNICA VASCULOSA, BY PROF. A. IWANOFF. form of extremely fine fasciculi, which are lost amongst the pigment cells in the stroma of the ciliary body. The further course of these fasciculi can only be followed on the temporal and nasal sides of the choroid, where, united into two fasciculi, they lie on either side of the long ciliary arteries. H. Muller observed that in many eyes these fasciculi not only accompany the ciliary arteries throughout their whole length, but also accompany them for some distance in the scleral canal. Fig. 363. Fig. 363. Section of the ciliary region of a hypermetropic (long or far-sighted) eye. The ciliary muscle was discovered in 1846, by Briicke,* and soon after, independently, by Todd and Bowman. Briicke and Todd and Bowman only described the meridianal fasciculi. The most complete description of the muscle was given by H. MiUler,f in the year 1857. In this essay he first described the circular fasciculi running parallel to the border of the cornea, which constitute the anterior and inner portion of the ciliary muscle ; and were termed by him the compressor lentis. Coincidently ArltJ also discovered the circular fibres of this muscle, and described them as being only processes of the radiating fibres. Finally, in the year 1867, F. E. Schulze discovered, with the aid of * Midler's ArcMv, 1846. t Archw fiir Ophthalmologie, Band iii. J Archiv fur Mikroskop. Anatomic, Band iii., p. 477. CILIARY MUSCLE. 307 chloride of palladium, the annular plexus which is expanded over the whole internal side of this muscle. The size of the muscle, its texture, and the relative development of its meridianal and circular fibres, are subject to considerable individual variations. These variations are in immediate relation to the length of the optic axis, on which the refraction of the eye, that is to say, its long or short-sightedness, depends. In hypermetropic persons,* whose optic axis is generally short, the anterior part of the muscle, that is to say, Miiller's annular muscle, is relatively largely developed ; in consequence of which the muscle projects anteriorly in the direction of the anterior chambers of the eye, and is upon the whole of smaller size. Fig. 364. Fig. 364. Section from the ciliary region of a myopic (short-sighted) eye. In myopics (whose optic axis is considerably longer) the anterior circular muscular fasciculi are very feebly developed ; the muscle itself consists chiefly of meridianal and radiating fasciculi, and the anterior part of the muscle consequently appears to be displaced backwards to a considerable extent ; and the whole muscle is longer. In the domestic animals the muscle consists exclusively of longi- tudinal fasciculi. In the Pig, however, circular fasciculi are found in the posterior part.t 4. The nerves of the choroid (nervi ciliares) belong to the third and fifth pairs, and to the sympathetic. The long set, * A. Iwanoff, Beitrage zur Anatomic des Ciliarmuskels in the Archiv fur Ophthalmoloyie, Band xv., Abtheil iii., p. 284. f A. Iwanoff and A. Rollett, Archiv fur Ophthalmologie, Band xv., Abtheil i. x 2 308 TUNICA VASCULOSA, BY PROF. A. iWANOFF. (nervi ciliares longi) two, or more rarely three in number, proceed from the ramus naso-ciliaris trigemini ; the short set (nervi ciliares breves), fourteen to eighteen in number, proceed from the ganglion ciliare. Both sets perforate the sclerotic near the entrance of the optic nerve, and having gained the interior of the eye, run upon the external surface of the choroid. After they have given off a considerable number of branches to the posterior portion of the membrane, they pass forward to the ciliary muscle, on which, dividing dichotomously, they form a close plexus. H. Miiller* found ganglion cells in the angles of the first divisions of these nerves, with a dia- meter of 0'0016 — 0'025 of a millimeter, and containing two or three nuclei. In the deep layers of this plexus, lying in the interior of the muscle, we find, in addition, nodal swellings, closely resembling bipolar cells. The peculiarity of the structure of the nerve plexus in the posterior portion of the choroid is, that the ciliary nerves, im- mediately after their exit from the sclerotic, and as they run forwards to the ciliary muscle, give off lateral branches, which are composed partly of dark-edged and partly of pale nerve fibres. These lateral branches, after repeated divisions and anastomoses, form a plexus lying between the vessels and the sclerotic. From this plexus delicate filaments may be traced to the arteries, in the smooth muscular fibres of which they appear to terminate. Ganglion cells are also found in this plexus occupying the points of intersection. True ganglia likewise occur in the trunks of the ciliary nerves. It is worthy of note that both the development of the pos- terior nerve-plexus, as well as the number of ganglion cells to be met with in this part, undergoes considerable individual variation, and it is also to be remarked that these variations stand in close relation to the development of the smooth mus- cular fibres in the posterior portion of the choroid. 5. The stroma of the choroid is formed of a close plexus of branched fibres, in the interspaces of which, especially of the outer layers, considerable numbers of stellate pigment cells are imbedded. * Verliandlungen der phys. med. Gesellschaft in Wilrzburg, Band x., p. 108. STEOMA OF THE CHOROID. 309 The fibres of this plexus, anastomosing with each other, run for the most part in a direction parallel to the surface of the sclerotic, giving off at the same time but few processes into the adjoining layers; it thus appears as if the fibres were inter- woven into several distinct membranes, of which one, the lamina fusca of authors, usually adheres to the sclerotic, and the other thicker one to the choroid. The latter again splits into several superimposed laminae, which, commencing at the posterior part of the ciliary body, extend to the entrance of the optic nerve (membrana suprachoroidea). The fibrillar stroma which occupies the interspaces between the vessels is in immediate relation with this membrana suprachoroidea. The stroma of the choroid contains numerous cells ; the most characteristic of these are the stellate pigment cells, which differ somewhat in their form in the superficial and deep layers of the membrane. The cells in the superficial layers are stellate, with short, broad, and flat surfaces ; their dark-brown pigment is absent in the immediate vicinity of the nucleus, which is consequently always sharply defined. The deep-lying stellate cells, which completely fill the interspaces between the vessels, are thicker than they are broad, and are pro- vided with long thin processes, which frequently anastomose and form a close plexus with the processes of the adjoining cells. These cells are usually of darker colour than the super- ficial ones. Besides pigmented cells, we also meet with the most diverse forms of non-pigmented cells in the choroid. Amongst these the spheroidal cells deserve special notice, which in size and form closely resemble the white blood or the lymph corpuscles.* These are met with in all the layers of the choroid, but chiefly in the deepest layers between the capillaries. Like the white blood corpuscles, they can change their form, and move from place to place. They vary considerably in number, according to age and the healthy state or otherwise of the eye. They are very numerous in children, but are met with in dispropor- tionately small number in adults, in whom, however, their * Hasse, Archiv fur Ophthalmologie, Band iv., p. 57. 310 TUNICA VASCULOSA, BY PROF. A. IWANOFF. number varies to a considerable extent. They are abundant in certain intraocular pathological conditions. The external surface of the suprachoroid coat, according to the recent researches of Schwalbe, is covered with an endo- thelium. The question of the nature and kind of tissue of which the choroid is composed cannot be determined exclusively on his- tological grounds, but requires also an histogenetic investiga- tion. The defective character of the latter has led some to classify the strorna of the choroid with connective tissue, and others with elastic tissue. II. THE IRIS. — In the iris we distinguish the pupillary border, margo pupillaris, bounding the central opening or pupil; and the ciliary border, margo ciliaris, by which it is attached to the ciliary body and the cornea. It has also an anterior and a posterior surface. On the anterior surface of the iris is a dentated ridge which divides it into two zones : the internal or pupillary zone, about one millimeter broad, is beset with radiating folds in close apposition to each other ; the external or ciliary zone has a breadth of about three millimeters (with an average diameter of the pupil of four millimeters in the dead body), and presents in its peripheric half from five to seven concentrically arranged folds, which always — but especially when the pupil is dilated — project sharply denned. The anterior surface of the iris is covered by an epithelium, which is really the continuation of the epithelium of the mem- brane of Descemet, but differs somewhat from this in being composed of smaller cells which are granular, not quite so dis- tinctly hexagonal, and not so sharply differentiated from one another. The posterior surface of the iris is black, consequent on the presence of a thick layer of pigment. This is the uvea of authors. The uvea begins at the margin of the pupil, which when contracted is distinctly bordered by it (whilst when dilated it vanishes entirely), and terminates at the ciliary border, where it becomes continuous with the pigmentary layer of the ciliary processes. The contour line between these two pig- THE IRIS. 311 ments is always well defined, since that of the ciliary processes is provided, as far as to its point of contact with the uvea, with a layer of the ciliary portion of the retina. Histologically the uvea is composed of cells, the protoplasm of which is infiltrated with pigment granules, which completely conceal the nucleus. In specimens teazed out with needles, clumps with rough surfaces, and of the most various size, are commonly met with under the microscope. It is impossible from these fragments to determine the form of the cells. The nuclei, when completely freed from pigment, are spheroidal and slightly granular. The free surface of the uvea possesses a series of radiating slightly projecting folds, which extend from the pupillary to the ciliary border in the form of regularly arranged straight lines ; their number is from 70 to 80. In Man there is no investing membrane for this pigment layer. That which was at one time described under the names of the membrana limitans Pacini, Jacobi, pigmenti, is, accord- ing to Kolliker, " the coalesced external cell walls of the pigment cells ; " according to Henle, it is the border of the cementing substance which holds the pigment granules together, a view which appears so much the more probable, as no walls can be perceived in the cells of these layers. The tissue of the iris, like that of the choroid, is composed of vessels, muscles, nerves, and stroma. The vessels of the iris are characterized, speaking generally, by the extraordinary thickness of their walls (Arnold), and especially of their adventitia (Henle), which is considerably thicker than all the rest of their coats put together. The mus- culature of the vascular walls is also remarkably developed (Arnold and Hiittenbrenner). The movements of the iris are effected by means of two muscles, — the sphincter, by which the pupil is contracted, and the dilatator, by which it is enlarged. The sphincter of the pupil (fig. 365, a) occupies the pupillary zone of the iris, and extends outwards to a distance of from 0*9 — 1'3 millimeters. At the pupillary border it is thin (having a thickness of 0' 10 of a millimeter) ; but further outwards it becomes thicker, and not far from its external margin it attains 312 TUNICA VASCULOSA, BY PKOF. A. IWANOFF. a thickness of 0'25 of a millimeter. It is situated towards the posterior surface of the iris, and is separated from the uvea only by a thin layer of connective tissue, and some extremely delicate muscular fasciculi belonging to the dilatator. The dilatator pupillse (fig. 365, 6) is developed from the fasci- culi of the sphincter, of which it constitutes the unbroken continuation. It commences in a series of arcuate interwoven fasciculi that are partly situated in the interior of the sphincter, and partly lie on its posterior surface, between it and the pigment layer. These several fasciculi, after they have passed beyond the boundary of the sphincter, unite to form a continuous muscular lamina, extending over the whole posterior surface of the iris (fig. 362, /), all the fibres of which lie parallel to one another, and are all directed radially from the pupillary to the ciliary border. Fig. 365. Fig. 365. Segment of the iris, seen from the surface, a, Sphincter ; 6, dilatator. At a distance of half a millimeter from its insertion, the muscle breaks up into separate fasciculi, which are arranged in two layers, one lying upon the other (fig. 366, a a). The fibres of these fasciculi having arrived at the ciliary border, imme- diately change their direction, curve round (6), and form by their interlacement a thin muscular plexus (c), which runs cir- cularly round the ciliary border of the iris (fig. 362, g). The literary history of the dilatator pupillse leads ns irresistibly to the conclusion that, up to the time of Henle, the existence of this muscle in Man was admitted rather in obedience to urgent physiological re- quirements than from its having been actually demonstrated. That it THE IRIS. 313 had been seen in animals by the greater number of authors is indis- putable, and it is equally probable that they then transferred the results of their observations directly to Man, yet this is certainly not feasible on the ground of the peculiarities which the whole arrangement of the accommodation and the muscular mechanism exhibit in Man. The peculiarities in the structure of the dilatator in Man compel Henle himself to make the correct statement that no agreement exists between the object of his description, and that which has been described as the dilatator by Briicke and Henle. Kolliker* does not attempt to conceal the fact that his account is taken from that of the dilatator of the Rabbit. According to him, the dila- tator consists of several thin fasciculi which lie between the vessels, and Fig. 366. Disposition of the muscular fasciculi of the iris. The lettering explained in the text. consequently in the substance of the iris. Henlef refers to a special layer of fibres which he finds on the internal surface of the iris, and is of opinion that in this homogeneous and continuous, though very thin, layer of radial fibres extending from the pupillary to the ciliary border he has discovered the muscle, the contraction of which effects the dilatation of the pupil. This statement led to further researches upon the dilatator. Ac- cording to Hiittenbrenner,J the dilatator in Rabbits is formed by the continuous layer of muscular fibres described by Henle, lying imme- diately behind the epithelium, which in that animal represents the * Handbuch der Gewebelehre des Menschen, 1867, § 667. t Handbiich der systematischen Anatomie des Menschen, Bandii., p. 635. £ Sitzungsberichte d. K.-Akademie der Wissenschaften zu Wien, Ab- theilungi., 1868. 314 TUNICA VASCULOSA, BY PROF. A. IWANOFF. pigment layer. This muscle extends to the ciliary border, and some of its fibres can easily be followed as far as to the ligamentum pectmatum. It is obvious that this is not the muscle seen in Rabbits by Kolliker. In Hiittenbrenner's opinion, the dilatator in Man is similarly disposed. Thus it appears that this author, with the single exception of the passage of muscular fibres into the ligamentum pectmatum, corrobo- rates the views of Henle, not only in the case of Man, but in that of animals. The account of the dilatator given by Merkel,* on the other hand, is more in accordance with Kolliker 's definition ; he does not describe a continuous layer unbroken by perforations, such as Henle saw, but a number of isolated fasciculi, which however, as Henle states, are placed immediately behind the pigment. Dogielf described a muscle which answers to the descriptions given by Briicke and Kolliker ; it commences at the sphincter, on the anterior surface of the iris ; then, divided into separate fasciculi, runs outwards between, the vessels, and is attached to the ciliary ring. In view of these conflicting statements, I suggested to Herr Jerop- heeff to examine the dilatator in Man. The results of his investigation are given above, and are in complete accordance with Henle' s de- scription. Herr Jeropheef has also been successful in discovering circular fasciculi at the ciliary border. The nerves of the human iris, in consequence of the great difficulties that oppose themselves to their investigation, have as yet been very unsatisfactorily examined. The best account is that given by Arnold,;}: which, however, treats only of the nerves of the Rabbit. The nerves of the iris are branches of the ciliary nerves of the choroid. On reaching the iris, they divide dichotomously in its external parts ; form arches, and then break up into a plexus consisting of medium-sized branches of nerves. In this plexus an interchange of fibres takes place between the nerve- trunks, which strongly resembles the grouping of the fibres in the chiasma nervorum opticorum. Three kinds of nerve fibrils proceed from these points of * Zeitschrift fur rat. Medicin, Bande xxxi. and xxxiv. t Archiv fur Mikroskopische Anatomie, Band vi., p. 95. | Archiv fur pathol. Anatomie und Physiologie, Band xxvii, Ueber die Nerven und das Epitlid der Iris. THE IRIS. 315 decussation : a. Pale fibres, in all probability belonging to the sympathetic, which run towards the posterior surface of the iris (consequently to the dilatator), on which they form a very fine plexus, b. Medullated fibres, which pass to the anterior surface, and there break up into a close plexus of fine fibres ; these are the sensory fibres of the iris. c. Lastly, a third plexus is distributed within the sphincter ; its delicate nerves are for the most part motor. The vessels, muscles, and nerves of the iris are imbedded in a stroma, which is chiefly composed of connective-tissue fibrils and cells. The connective tissue accompanies the vessels in the form of thin fasciculi of fibrils ; but fibres are also met with in the interspaces, most of which run in a longitudinal direction. In black eyes the principal portion of the stroma is composed of pigmented stellate cells, which form close anastomoses with each other. These cells are most closely arranged in the most superficial layers of the iris. In black eyes we meet also with many free, round, strongly pigmented cells. In light-coloured eyes, non-pigmented stellate cells, with long thin processes, are met with, and, in addition, a great num- ber of round cells resembling the lymph corpuscles. III. THE BLOODVESSELS OF THE EYE. BY TH. LEBER. THE bloodvessels of the globe of the eye form two com- pletely separate systems; the vascular system of the retina, and the choroidal or ciliary vascular system, which are only connected with each other by means of a number of small branches at the point of entrance of the optic nerves. The vascular system of the retina, in addition to supplying the retina, supplies also a portion of the trunk of the optic nerve ; whilst the ciliary vascular system, besides supplying the vascular membrane of the eye (including the choroid, ciliary body, and iris), gives branches also to the sclerotic, the margin of the cornea, and the immediately adjoining portion of the scleral conjunctiva. The remaining portions of the conjunctiva receive special vessels, which proceed from those of the lids, and form the conjunctival vascular system. 1. VASCULAR SYSTEM OF THE RETINA. The vascular system of the retina is formed by the arteria and vena centralis retinse. The artery is one of the first branches of the ophthalmic artery, and penetrates obliquely into the trunk of the optic nerve, at a distance of fifteen to twenty millimeters from the eye, the vein entering a little nearer to the globe. The latter, as a rule, opens directly into the sinus cavernosus, previously communicating by means of a few large branches with the V. ophthalmica superior, but sometimes opening directly into the latter. More rarely it opens into the VASCULAR SYSTEM OF THE RETINA. 317 V. ophthalmica inferior.* The arteria and vena centralis retinae (fig. 367, e e) run close to one another in the axis of the optic nerve, surrounded by some connective tissue as far as to the intra- ocular extremity of the nerve. In their course they give off small branches to the trunk of the optic nerve, which run in the plexiform trabeculae of connective tissue that invest the nerve fasciculi. In addition to the branches of the central vessels, the optic nerve also receives many twigs from the vessels supplying the internal sheath, /, (or proper neurilemma of the nerve,) and, though in smaller number, from those of the external sheath, g. These vessels are branches of the ophthalmic artery, and of its primary divisions. The intra-cranial portion of the optic nerves, the chiasma and the tractus opticus, are supplied by the vessels running in the adjoining parts of the pia mater and brain, the branches of which communicate with those of the intra-orbital part of the nerve. At its point of entrance into the eye, the optic nerve receives also branches from a few (two or three) of the posterior short ciliary arteries, 7c. These form a complete vascular circle, named the circle of Zinn or Haller* which gives off numerous fine branches into the optic nerves, that anastomose with the branches of the central artery. Veins corresponding to these branches of the ciliary arteries, there are none ; on the other hand, the small arteries, veins, and capillaries of the choroid communicate directly at the margin of the optic disk with the corresponding vessels of the papilla and of the external sheath of the optic nerve, so that a toler- ably ultimate connection is here established between the retinal and ciliary vascular systems, I. No other communication exists between the two. At the ora serrata the vascular system of the retina ceases with the formation of capillary loops, without communicating at any point with that of the choroid. * Waller, De venis oculi, Berol, 1778. Sesemann, Die Orbitalvenen des Menschen und ihr Zusammenhang mit den oberflachlichen Venen des Kopfes (The orbital veins of Man and their communications with the superficial veins of the head), in Reichert and Dubois-Reymond's Archiv, 1869, p. 2. * Illustrations of which will be found in Jayer ueber die Einstellungen des dioptric. Apparats, Taf iii. , figs. 34 — 36 (Wien, 1861) ; and Th. Leber, Denkschrift. d. Wien. Akad., Band xxiv., Taf. iv. 318 THE BLOODVESSELS OF THE EYE, BY TH. LEBER. Fig. 367. Fig. 367. Diagrammatic representation of the course of the vessels in the eye ; horizontal section ; the veins represented black, the arteries clear, a, Arterise ciliares posteriores breves ; 6, arteriae ciliares posteriores longae ; c'c, arteriae et venae ciliares anteriores ; d d', art. et ven. conj. posteriores ; e'e, arteriae et ven. centrales retinae ; /, vessels of the internal, and g, of the external optic sheath ; 7i, vena VASCULAR SYSTEM OF THE RETINA. 319 The arteria and vena centralis run in the axis of the optic nerve, to the surface of the papilla, at which point, or some- what earlier, they break up into their principal branches, the vein usually dividing somewhat earlier than the artery. The mode of branching is dichotomous. A main branch, both of the artery and vein, runs upwards ; the others downwards, and these again quickly subdivide and diverge at different angles from one another. The veins pursue approxirnatively the same direction as the arteries, at least in their larger branches, and are usually of larger size. Numerous variations, within certain limits, occur in different individuals. No large vessel ever runs outwards towards the temple, and over the macula lutea, except in extremely rare cases (Mauthner) ; all the larger vessels curve round the yellow spot, to reach the peripheric portions of the retina, and send small branches from all sides into the macula. Similar small vessels pass to it also directly from the papilla. These supply the macula, but all terminate at the border of the fovea centralis by means of capillary loops, so that this last is quite destitute of vessels. The capillary plexus of the retina is distinguished from that of the choroid by its much wider meshes, the capillaries them- selves are finer and very thin- walled. The mode of ramifica- tion of the retinal vessels closely resembles that of the central organs of the nervous system. According to His, peri vascular lymph spaces surround the retinal vessels very similar to those of the vessels of the brain and spinal cord. The larger branches of the central vessels all run in the nerve-fibre layer of the retina, and become smaller in propor- tion as they are situated more externally in the successive layers of the retina. The smaller branches penetrate as far as vorticosa ; i, vense ciliares posteriores breves ; kt branch of the art. cil. post. brev. to the optic nerve ; I, anastomoses of the choroidal vessels with those of the optic nerve ; m, chorio-capillaris ; n, episcleral branches ; o, arteria recurrens choroidalis ; p, circulus arteriosus iridis major (transverse section) ; q, vessels of the iris ; r, of the ciliary pro- cess ; s, branch to the vena vorticalis from the ciliary muscle ; t, branch to the anterior ciliary vein, proceeding from the ciliary muscle ; u, circulus venosus ; v, marginal loop-plexus of the cornea ; iv, arteria et vena conjunctivalis anterior. 320 THE BLOODVESSELS OF THE EYE, BY TH. LEBER. to the intergranule layer ; the external granule layer and the bacillar layer are, like the fovea centralis, destitute of vessels. In the foetus the central artery gives off the arteria hyaloidea, which runs forwards from the papilla, through a canal in the vitreous, to the posterior surface of the lens which it covers with vessels. In the new- born child it is already completely atrophied, the artery being very rarely visible after birth, and even then being generally in an obliterated state. In many animals the retinal vessels are absent, or are only distributed to a definite portion of the retina. In Birds, many Amphibia, and Fishes, they are altogether absent ; but are here for the most part, though not always, replaced by the vessels of the hyaloidea, which are distributed to the inner surface of the retina (Huschke, Hyrtl, H. Muller). Amongst Mammals, the Rabbit possesses vessels only in that portion of the retina characterized by the presence of medullated nerve-fibres. In the Horse there are only very small vessels, which break up to form a circle of capillary loops not more than from three to six millimeters in diameter.* In the Guinea-pig, very fine vessels are occasionally seen on the papilla of the nerve, which, however, cannot be followed upon the retina. 2. CILIARY OR CHOROIDAL VASCULAR SYSTEM. The entire choroidal tract, the sclerotic with the margin of the cornea, and the immediately adjoining parts of the scleral conjunctiva, are supplied by the so-called ciliary vessels. They are the following : — a Arteries. 1. The short posterior ciliary arteries (arterice ciliares pos- teriores breves, figs. 367 and 368, a,) form from four to six small trunklets, that spring from the ophthalmic artery or its first branches. Pursuing the same course as the optic nerve, they divide into a great number of branches (about twenty), which perforate the posterior segment of the sclerotic in a nearly straight direction from without inwards. The most numerous as well as the largest branches occur in the vicinity of the pos- terior pole of the eye, internal to the entrance of the optic nerve * H. Muller, Notiz uber die Netzliautgefasse beimanchem Thieren (Ob- servations on the retinal vascular system in various animals), Wiirzburg Naturwissenscliaft. Zeitschrift, Band ii., p. 64. ARTERIES OF THE CHOROID AND IRIS. 321 and its immediate neighbourhood. The latter are usually of smaller calibre. Some give off the branches already mentioned to the optic-nerve entrance. Fig. 368. Fig. 368. Semi-diagrammatic representation of the choroidal ves- sels. At Chorioidea ; B, pars non-plicata of the ciliary body, orbiculus ciliaris ; C, ciliary processes (the ciliary muscle is supposed to have been removed) ; D, ciliary muscle ; E, iris ; a, arteries ciliaris posteriores breves ; 6, arteria ciliaris posterior longa ; c, arteria? ciliares anteriores ; cp venae ciliares anteriores ; h, vense vorticosse ; o, arterise recurrentis choroidese ; p, circulus arteriosus iridis major. 2. The long posterior ciliary arteries (arterice ciliares pos- teriores longce, 6,) have the same origin as the short. They are two in number, and perforate the sclerotic in the horizontal meridian of the eye, somewhat more anteriorly than the latter, Y 322 THE BLOODVESSELS OF THE EYE, BY TH. LEBER. the one on the median, the other on the temporal side. They perforate the sclerotic very obliquely, so that the artery runs in a canal, in the substance of the sclerotic, of as much as four millimeters in length. 3. The anterior ciliary arteries (arterice ciliares anteriores, c). These are not direct branches of the ophthalmica, but pro- ceed from the arteries of the four recti muscles. Generally speaking, two arteries arise from each muscle, though as a rule only one comes from the rectus externus. They pass from the insertion of the tendons on to the sclerotic, run for the most part, with many curves, towards the cornea, and after giving off delicate superficial branches, penetrate the sclerotic with their perforating branches rather obliquely, not far from the margin of the cornea. b. The veins of the ciliary vascular system are — 1. The so-called vence vorticosce, h, of which there are usually four trunks, that either open directly into the vena ophthalmica, or into the muscular branches. They perforate the sclerotic near the sequator of the bulb, just as obliquely as the long ciliary arteries. One or more of them frequently divide before their entrance into the sclerotic, in consequence of which the number of perforating branches is increased to six, but seldom more. During and just after their passage through the sclerotic, again, divisions frequently occur; and thus, besides the four or six larger ones, a variable number of smaller vessels pass into the choroid. 2. The small venulce ciliares posteriores breves (fig. 367, i\ which, like the corresponding arteries, emerge from the sclerotic in the neighbourhood of the optic nerves, but correspond only to the scleral branches of the latter, and receive no branches from the choroid. They are consequently much less numerous and much smaller than the corresponding arteries. 3. The vence ciliares anteriores. These, like the correspond- ing arteries, are branches of the veins of the recti muscles, but are smaller than the arteries, because the region in which their perforating branches ramify is much more limited in extent. There are no veins that correspond in their course with poste- rior long ciliary arteries. VESSELS OF THE SCLEROTIC AND CHOROID. 323 A. THE SCLEROTIC. This coat receives small branches from all the vessels just described. They are not, however, very numerous, and form a wide-meshed plexus chiefly upon the surface, in which, as a rule, two veins, one on either side of it, accompany each artery. The relations of the episcleral vessels in the anterior segment of the sclerotic, adjoining the margin of the cornea, are differ- ent from this, and will receive subsequent consideration in con- nection with the vessels of the margin of the cornea and of the conjunctiva. B. THE CHOROID. The choroid is supplied by a very large number of vessels, which very freely branch and interweave. This rich plexus of vessels, which attains its fullest development in the ciliary processes, appears to be destined to secrete the fluid that pre- serves the intraocular pressure which would otherwise rapidly undergo diminution, owing to filtration through the fibrous capsule. The vessels of the choroid may also, perhaps, be destined for the nutrition of the external non-vascular layers of the retina ; and this is rendered so much the more probable by the circumstance mentioned above > that in many animals the whole retina is destitute of vessels, in which case its nutrition must necessarily be maintained by the cboroid. Prom the preceding enumeration of the vessels of the ciliary vascular system, it is obvious that there is by no means a com- plete correspondence between the arteries and veins of the choroid. The choroidal tract in relation to its arterial supply is divisible into two tolerably separate districts ; one of which, formed by the choroid proper, receives its supply from the short posterior ciliary arteries, whilst the other, consisting of the ciliary body and iris, is supplied by the long posterior and the anterior ciliary arteries. The most anterior part of the choroid, however, receives in addition a number of recurrent branches from the anterior district, whereby a communication is effected between the latter and the district supplied by the posterior arteries. The efflux of venous blood is differently provided for- The greater part of the venous blood of the entire choroid (including the iris and ciliary processes), has a common outlet Y 2 324 THE BLOODVESSELS OF THE EYE, BY TH. LEBER. through the vence vorticosce, a portion only of the blood of the ciliary muscle discharging itself externally through the small anterior ciliary veins; which portion is far inferior to the other in importance. (1.) ARTERIES OF THE CHOROID. The small trunks of the short ciliary arteries in the pos- terior segments of the choroid lie at first in the most superficial layers of the membrane, surrounded by a loose, and for the most part darkly pigmented tissue. As they pass forwards they are very tortuous, and, dividing dichotomously, gradu- ally dip into the deeper layers. The finest branches break up into the capillary plexus which covers uniformly the whole internal surface of the choroid, forming the so-called chorio- capillaris. The ramifications which run forward are differ- entiated from the veins by their straighter course, whilst the finer branches found in the neighbourhood of the optic nerves are, like those of the veins, very tortuous. This circumstance, •together with the large number of vessels here present, gives the whole membrane the appearance, in well injected specimens, of being an inextricable convolute of minute vessels. Besides the branches which break up into capillaries, there are no other branches,* as was formerly admitted, which directly discharge themselves into the veins. The belief in the pre- sence of the latter was dependent on illusory appearances, which were easily produced in the methods of opaque injection formerly employed, but which are completely removed by the use of coloured transparent injections. f The short ciliary arteries break up completely into the capillary plexus of the choroid, and give off no branches for- * Briicke, Anatomische Beschreibung des menschlichen Augapfels (Anato- mical description of the Eye of Man), p. 14. Berlin, 1847. f Th. Leber, Anatomische Untersuchungen uber die Blutgefasse des menschlichen Auge (Anatomical researches on the bloodvessels of the Eye of Man), Denkschrift der A kademie zu Wien, Band xxiv. ; Math. Naturwissensch. Classe, p. 301 ; also Untersuchungen uber den Verlauf und Zusammerihang der Gefdsse im menschlichen Auge (Researches on the course and communications of the vessels of the Eye in Man), Arcliiv fur Optiihalmologie, Band xi., p. 15. ARTERIES OF THE CILIARY BODY AND IRIS. :j:>5 wards to the ciliary processes and the iris. The admission formerly made of the presence of such branches depends on the veins that pass from the ciliary processes to the venae vorti- cosae having been mistaken for them. On the other hand, the most anterior portion of the choroid receives a number of recurrent branches* from the ciliary body, which proceed from the long posterior and anterior ciliary arteries. These, varying in number and size, run backwards at considerable distances from each other, between the numerous parallel veins of the orbiculus ciliaris, supplying the most anterior portion of the choroid with capillaries, and also partially anastomosing with the terminal branches of the short posterior ciliary arteries. The capillary plexus forms a uniform layer covering the whole internal surface of the choroid from the optic-nerve entrance to the margin of the orbiculus ciliaris (which corre- sponds to the ora serrata of the retina), and here terminates with an irregularly dentated margin. Near the optic nerves the meshes are irregularly rounded and very small; but in proportion as they are more distant from, the nerve they become more elongated in form, the long diameter ulti- mately becoming from eight to ten times longer than the short. Moreover, the diameter of the capillaries themselves becomes somewhat greater. There are no true capillaries in the orbi- eulus ciliaris. (2.) ARTERIES OF THE CILIARY BODY AND OF THE IRIS. The two long posterior ciliary arteries, after their passage through the sclerotic, are situated on the external surface of the choroid, and run without dividing horizontally forwards to the ciliary muscle. Here they divide into two branches, which separate at an acute angle, and penetrate into the substance of the muscle, and having reached the anterior border curve round, so that the two branches of each artery together encircle the * These recurrent branches were first described and depicted by Haller, (Tabulae arteriarum oculi, Tab. vi.,fig. 4), and subsequently by Zinn (De- xcr't[>tio anatom. ocul. human, ed. by H. A. Wrisberg, Gottingen, 1780, p. 39), whose account, however, had fallen into oblivion until I rediscovered it (loc. cit.j pp. 303 and 306, Taf. ii., fig. 12). 326 THE BLOODVESSELS OF THE EYE, BY TH. LEBER. globe of the eye. The vascular circle thus formed is completed by branches of the anterior ciliary arteries, which pass directly from the sclerotic to the ciliary muscle. By this means a complete arterial circle is produced at the anterior border of the muscle, termed the circulus arteriosus iridis major, which is distributed chiefly to the iris and the ciliary processes, whilst the arteries of the ciliary muscle and the rami recur- rentes of the choroid are given off directly to it by the ciliary arteries. In many animals in which the ciliary processes advance farther upon the posterior surface of the iris, as for example in the Rabbit, the circulus iridis major does not lie in the ciliary muscle, but in the iris at a small distance from the ciliary border. In addition to the circulus iridis major, the long and anterior ciliary arteries form still further backwards in the ciliary muscle an incomplete circle of anastomoses. The arteries of the ciliary muscle branch in an arborescent manner, and following the direction of the muscular fasciculi, form a tolerably dense trellis-like plexus, which differs in a very marked manner from the plexus of the subjacent ciliary processes. The arteries of the ciliary processes proceed from the cir- culus iridis major, and must all therefore, like those of the iris, first pass through the ciliary muscle. They are small brandies, which quickly break up into a large number of branches that frequently anastomose with each other, and gradually dilating become continuous with the commencement of the veins. Owing to their frequent anastomoses, these capil- lary veins form a very rich vascular plexus that constitutes the principal portion of the ciliary processes. The remarkable increase in the extent of surface caused by the numerous larger and smaller lamelliform processes and the intervening channel-like depressions, the great width of the capillary veins, the resulting retardation of the current of the blood, and the thinness of the walls of the vessels, co-operate in rendering the ciliary processes the chief agents for the secretion of the intraocular fluids. The arteries of the iris spring from the anterior border of the circulus arteriosus major, in the form of numerous and VEINS OF THE CHOROID. 327 rather tortuous trunklets, which divide dichotomously in the substance of the iris. Their walls are thick in proportion to their calibre. Their ramifications appear upon the anterior surface of the iris as radially running vessels, anastomosing in a plexiform manner, and of the same colour as the iris itself, except in Albinos, in whom the colour of the blood shines through the walls. Not far from the pupillary margin the arteries form a circle of anastomoses, the so-called circulus iridis minor. The capillary plexus of the iris has much wider meshes than that of the choroid ; at the pupillary margin the finest arterial twigs bend round in loops to become continuous with the commencement of the veins. The sphincter pupillse is traversed by a peculiarly fine capillary plexus. (3.) VEINS OF THE CHOROID. The vence vorticosce (h), numbering as a rule from four to six large, with frequently a variable number of small vessels (in some instances amounting to as many as ten), are characterized by the whorl-like arrangement of their branches, which radiate outwards in all directions. The smaller vessels form incomplete vortices ; receiving vessels from certain directions only. The larger ones, on the other hand, collect their branches from every side, and receive the blood from the choroid proper, the ciliary body, and the iris. Their ramifications form very numerous anastomoses, which, lying on a superficial plane, decussate, for the most part at very acute angles, with the straighter ciliary arteries. Between each two adjoining whorls, loop-like anas- tomoses wander over the posterior segment of the choroid, which sometimes also receives a number of straighter branches from the fore part. The veins of the iris, of the ciliary pro- cesses, and a portion of the veins of the ciliary muscle, form numerous parallel and frequently anastomosing vessels of nearly equal size, which run backwards through the orbiculus ciliaris (pars non-plicata) to the choroid. In the region of the ciliary body they all lie upon the inner surface of the mem- brane, but pass to the outer surface of the choroid at the ora serrata. They gradually unite to form larger vessels, and having reached the choroid, receive branches from that mem- 328 THE BLOODVESSELS OF THE EYE, BY TH. LEBER. brane, and there constitute the anterior branches of the vente vorticosse. These parallel veins of the orbiculus ciliaris, between which, at great distances from each other, the arteria3 recurrentes run, were formerly considered to consist for the most part of arteries, and gave occasion for the admission of the so-called anterior branches of the arterise ciliares posteriores breves. A part only of the veins of the ciliary muscle unite to form the small vense ciliares ant. (c), which perforate the sclerotic near the margin of the cornea, and discharge themselves into the veins of the recti muscles. These veins communicate with the venous vascular circle (V), discovered by Schlemm, which is situated in the deepest layers of the sclerotic, close to the corneal margin, and which is usually termed the canalis Schlemmii, circulus or sinus venosus cornese, and by me the plexus ciliaris venosus* This is in reality by no means a simple canal, but a plexiform circle of yeins/f" which nevertheless presents certain differences in different eyes, and in different parts of the circumference of the same eye. As a rule, -it appears in correspondence with the ordinary description as a large (one-fourth of a millimeter wide), flattened, and very thin- walled vein, but is almost always ac- companied by one or more small veins, which branch off from it, and after a short course again open into it. At many points the larger vein splits up into two, three, or more correspondingly fine branches, which anastomose, and gradually reunite to form a large vessel. Very frequently the two branches resulting from a division immediately reunite, so that the course of a large vein is as it were interrupted by a small island. Less frequently a large number (from five to seven) of small, frequently anastomosing veins, either running close to one another, or partially overlapping, occur, which then form a delicate plexus, or may gradually again coalesce to form a large vessel. * Loc. cit., p. 19. For illustrations see Taf. iii. and the Archiv fur Ophthalmologie, Band xi., Heft, i., Taf. ii., fig 2. + Rouget, Comptes rendus et Memoires de la Societe de Biologie, 1856, p. 118. VEINS OF THE CHOROID. 329 The plexiform character of this vascular circle is not equally well marked in all eyes ; it occurs especially in those parts of the circumference where the veins proceeding from the ciliary muscle join it. These pass at the anterior extremity of the muscle to the internal surface of the sclerotic (in one case I counted from twelve to fourteen of them), divide near the venous circle into several anastomosing branches, which partly perforate the sclerotic obliquely, in order to join with the episcleral venous plexus (see below) and the veins of the recti muscles, and partly enter the circulus venosus itself. At these points the latter often appears to be dilated, whilst it is prolonged directly into the plexus of the veins emerging from the ciliary muscle, or forms itself a circular venous plexus. Moreover in vertical sections made in the region of the mar- gin of the cornea, especially in injected specimens, we almosi) always find, besides the single large vascular lumen, one or more smaller ones, or we may meet with two or more lumina, which not unfrequently anastomose with each other. The venous circle of Schlemm appears to constitute a kind of reservoir for the blood of the ciliary muscle in the varying conditions of its contractions. The position of the channel in regard to the muscle is such that the contraction of the latter may occasion a dilatation of the vessels forming it. In most animals a circular venous plexus occurs at the same point. (Rouget, G. Meyer, IwanofT, and Rollett.) In the preceding description I trust I have avoided the objection raised by Henle* to my former account, that I laid too much stress upon the plexiform character of the circulus venosus. I certainly never thought, as Henle appears to believe,t that the circle is always composed of a large number of small vessels. The confounding of the circulus venosus with the so-called canal of Fontana (which is present in the Ox, but not in Man), formerly led to great confusion, which has recently been revived by Pelechin,| but the distinction between * Jahresbericht iiber d. Fortschritte der Anatomie fur 1865, Zeitschrift fur rat. Med., Ser. iii., Band xxvii., pp. 96 and 97. f Handbuch der Anatomie, Band iii., Heft i. (Gefdsskhre), p. 344, note. J Ueber den sogenannte Kanal von Fontana oder Schlemm (On the so- 330 THE BLOODVESSELS OF THE EYE, BY TH. LEBER. them was long ago pointed out by Briicke * and Rouget, f and more recently by Iwanoff and Rollett. J An analogous structure to the peculiar trabecular tissue which fills the canal of Fontana, occurs, according to these observers, in Man also, though in small amount ; this is the so- called ligamentum pectinatum, that extends from the border of the membrane of Descemet over the circulus venosus, towards the insertion of the ciliary muscle and the origin of the iris. The circulus venosus may be injected both from the ophthalmic artery and vein, though not readily, without extra- vasation^ Owing to such extravasations the plexiform struc- ture of the venous circle is more or less concealed, but the extravasations are recognized easily by their having no sharply defined contour. Extravasations are produced still more readily by direct injection through simple penetration with the point of the canula, for which purpose mercury was formerly em- ployed. I have recently found, however, that Prussian blue and glycerine can be thus injected with great facility, and, in part at least, without extravasation, into the vascular circle, and that the fluid penetrates by this means at a low pressure into the finest branches of the episcleral veins, and into those of the ciliary muscle. These experiments with injection fluids, the presence of blood in the dead body, especially in those who have been hanged (Schlemm), and the demonstration of a thin vascular wall which may be made with facility in transverse sections, may be collectively regarded as finally proving the blood- vascular nature (still doubted by many) of the circulus venosus. || called Canal of Fontaiia or of Schlemm), in the Archiv fur Ophthalmology, Band xiii., Heft ii. , p. 425, et seq. * Anatomiscfie Beschreibung d. menschlichen Augapfels, pp. 52 and 53. + Loc. cit., p. 117. J Iwanoff and Rollett, Bemerkungen zur Anatomic der Irisanheftung (Remarks on the anatomy of the attachment of the Iris, etc.), Archiv fur Ophthalmologie, Band xv., Heft i., p. 23, et seq. § Though Pelechin was not able to effect this, I may adduce my own experience in opposition ; for I found, when the injections were otherwise successful, the vessels of the circulus venosus were, as a rule, filled. || The essay of Schwalbe on the Lymphatics of the Eye and their limits, VESSELS AT THE MARGIN OF THE CORNEA. 331 c. THE MARGIN OF THE CORNEA. At the anterior part of the sclerotic, where it is invested by the conjunctiva, as far as to the corneal margin, two vascular layers may be distinguished ; a deep episcleral or sub-con- junctival layer, formed by the branches of the anterior ciliary vessels, and a superficial or conjunctival vascular layer, which only communicates with the former at the margin of the cornea. The anterior ciliary arteries, after their emergence from the muscles, run very tortuously towards the margin of the cornea, near which they give off a number of fine episcleral branches, whilst their principal branches perforate the sclerotic. As a rule, two vessels proceed from each muscle, with the exception of the rectus externus, from which only one is given off. In many cases an artery to the temporal side proceeds from the palpebral vessels, and running in the connective tissue, per- forates the sclerotic near the margin of the cornea. The anterior- ciliary veins are distinguished from the arte- ries by their smaller size (consequent on their much more insignificant perforating branches) and the straighter course of their coarser branches. Their episcleral branches, on the other hand, are larger than those of the arteries, as is usually the case where the two sets of vessels supply the same region. They communicate by a very rich plexus of fine veins with rather small polygonal meshes, which, on account of its position, has been named the episcleral venous plexus, and surrounds the cornea, forming a zone of about four millimeters in breadth. The episcleral branches of the arteries and veins nearly cor- respond in their ramifications, the arteries being constantly finer, and running straighter than the veins in opposition to the relations of the trunks. After giving off small branches to the sclerotic, they run with frequent subdivision and numerous arched communications in the second part of which (Max Schultze's Archiv, Band vi., pp. 261 — 362) the author maintains that the canal of Schlemm is a lymphatic cavity, and has no connection with the ciliary plexus, appeared after the above account was written. I must decidedly support my own view in opposition to that of M. Schwalbe. 332 THE BLOODVESSELS OF THE EYE, BY TH. LEBER. to the margin of the cornea, and here give off fine branches at regular distances to the cornea, forming the Anterior conjunctival arteries and veins. These pursue a recurrent course in the conjunctiva, supply the innermost zone of the conjunctiva, which has a breadth of from three to four millimeters, and anastomose with the peripheric or posterior conjunctival vessels. One or two veins constantly accompany each artery, in the latter case one being situated on either side of the artery. The terminal branches of the episcleral vessels, frequently subdividing and anastomosing, run beyond and over the mar- gin of the cornea, forming the looped marginal plexus of the cornea, which extends for a distance of one or at most two millimeters over the periphery of this membrane, and usually advance to a somewhat greater extent above and below than at the sides. In the capillary loops we may discern a more slender ascend- ing arterial limb, and a descending gradually widening venous limb. In Man, after birth, no vessels penetrate into the substance of the cornea beyond this zone. In the foetus, J. Miiller found vessels distributed over the whole anterior surface of the cornea. In many animals, as for example in the Sheep and Ox, vessels extend to a considerably greater distance over the surface of the cornea. In Oxen the superficial marginal loops, with flattened arches, can be very clearly distinguished from the vascular loops accompanying. the nerves which penetrate much more deeply into the cornea. In the Sheep, Coccius saw these last extend as far as to the middle of the cornea. In Keratitis, newly formed vessels very frequently make their appearance, which may be situated in this membrane at all parts of its thickness. 3. CONJUNCTIVAL VASCULAR SYSTEM. The larger peripheric portion of the scleral conjunctiva, the sulcus, and the tarsal portion, are supplied by the vessels of the lids, the arteriae palpebrales medians et laterales, and the cor- responding veins. To the scleral conjunctiva pass numerous small arborescent branched vessels, arteries and venae conjunctive posticse (fig. VESSELS OF THE CONJUNCTIVA. 333 367, d d'). As is the case with the anterior conjunct! val ves- sels, the arterial ramifications are here accompanied by one or two veins. They ultimately join the anterior conjunctival vessels. The meshes of the capillary plexus are tolerably wide, but become progressively finer towards the sinus palpebralis, and attain their highest development in the small papilliform elevations of the palpebral conjunctiva. The posterior conjunctival vessels, and the veins in particular, are visible in the living eye of Man, forming small vessels capable of being moved with the conjunctiva, and distinguishable from the anterior ciliary arteries, not only by their course but by their brighter colour and their smaller callibre ; the latter being of a more carmine tint, and not moveable with the conjunctiva. The difference in colour is due to the circumstance of the latter vessels being covered by the cloudy whitish conjunctiva. The anterior conjunctival vessels, like the anterior ciliary veins, are scarcely perceptible on account of their minute size, but come distinctly into view on irritation of tne eye; when they undergo remarkable dilatation. The injection of the episcleral venous plexus produces a diffused bluish redness around the margin of the cornea, which in pathological states indicates a condition of irritation of the parts supplied by the ciliary vascular system ; that is to say, of the uveal tract or of the cornea. IV. THE LYMPHATICS OF THE EYE. BY G. SCHWALBE. THE lymph formed in the tissues of the eye is discharged from them in three directions. That portion which proceeds from the iris and ciliary processes -collects in the anterior chamber of the eye, and finds its point of exit through the canal of Schlemm. With this system the canal of Petit is in direct communication; and these passages, together with the lymph- atics of the conjunctiva and the canalicular plexus of the cornea, may be termed the anterior lymphatic system of the eye. All those parts of the globe that are situated behind the ciliary body discharge their lymph by two other tracts ; the lymph proceeding from the choroid and sclerotic escaping at the points of emergence of the vense vorticosa from the bulb, and that from the retina quite independently by a tract within the nervus opticus. The two last-named tracts may be collectively regarded as constituting the posterior lymphatic system of the globe ; and with these we may include still another lymphatic space which exists between the two optic sheaths. 1. THE POSTERIOR LYMPHATIC SYSTEM OF THE EYE. A. The Canals for the discharge of the Lymph formed in the Choroid and Sclerotic. The lymphatics of the proper tissue of the sclerotic are deve- loped to no greater an extent than are those of the vascular choroid. The lymph formed in these membranes passes into two large lacuniform spaces which are in direct communica- POSTERIOR LYMPHATIC SYSTEM OF THE EYE. 335 tion with each other (fig. 369). One of these spaces (p) is situated between the sclerotic and cornea throughout the whole extent of these membranes, from the ciliary body to near the point of entrance of the optic nerve into the bulb. On account of its investing the choroid it has been termed the pericho- roidal space. In Birds it forms a kind of lacuna, resembling the serous cavities in being bounded by two smooth walls. In Mammals the space is usually traversed by numerous trabeculse, Fig. 369. Fig. 369. Diagrammatic representation of the posterior lymphatic tracts of the eye of the Pig, with the exception of the lymphatics of the retina. On the left the relation of the tendons inserted into the bulb, to the ' cavity of Tenon,' t, is exhibited; on the right, the latter is also shown near the insertion of the muscles. The lettering is for the most part referred to and explained in the text, but in addition a indicates a layer of fat between the retractor muscle and the supra- vaginal space ; c, conjunctiva ; ra r, musculi recti ; m retr, musculus retractor bulbi ; v, external or fibrous sheaths of the optic nerve. which in some instances, as in the eye of Man and of the Dog, may form quite a plexiform tissue, that has been named the membrana suprachoroidea. The portion of this tissue which remains attached to the sclerotic after detachment of the choroid has also been termed the lamina fusca. The peculiarity of struc- ture of the plexiform tissue of the suprachoroidea is that it is 336 THE LYMPHATICS OF THE EYE, BY G. SCHWALBE. composed of numerous very flat lamellae, the basis of which is formed of a rich plexus of elastic fibres. Closely connected with this plexiform tissue are numerous very flat and more or less branched pigment cells, which, when numerous, lie in close apposition, and resemble an epithelium. In many animals, as for example, in the Pig, in addition to these pigment cells, small flat colourless cells are constantly found to be pre- sent on both sides of the elastic lamella thus formed, or where this is firmly attached to the tissue of the sclerotic, on one side only, is a very thin glass-clear membrane, present- ing at certain points ellipsoidal nuclei projecting beyond the general plane of the lamella. If these membranes are treated with solutions of nitrate of silver, containing from one-fourth to one per cent, of the salt, a beautiful plexus of dark sil- vered lines is brought into view, each mesh of which corre- sponds to one of the ellipsoidal nuclei. The elastic lamella of the supra-choroidea is then, it appears, covered by an endo- thelium, which differs but little from that of the lymphatic canals. Its presence may be demonstrated both on the outer surface of the choroid and upon the inner surface of the scle- rotic, covering uniformly the whole perichoroidal system of cavities. If injections be forced into the perichoroidal space, it will be found that the fluid passes into the second of the above- mentioned lacuniform lymphatic spaces at four points which lie close behind the points of emergence of the vense vorticosse. A careful examination of this region shows that the lymphatic vessel at first invests the vein as it passes obliquely through the sclerotic like a sheath (fig. 370), but shortly before reach- ing the external surface it separates from it, and lies on the inner and inferior side of the vessel. Its passage through the sclerotic is thus for the most part perivascular. Having reached the surface of the bulb, the injected fluid passes into a lymphatic cavity which exists between the sclerotic and the fascia .of Tenon, and may be termed Tenon's space or cavity (fig. 369, Q. This is lined throughout by an endothelial layer of cells resembling that which lines the perichoroidal space. A net- work of dark silvered lines may easily be shown to exist- on LYMPHATICS OF THE RETINA. 337 the surface of the choroid with solutions of nitrate of silver. At those points where the ocular muscles are attached to the bulbus the continuity of the cavity of Tenon is interrupted ; it is not, however, continued into the sheaths of the tendons, but is on that side completely closed. In Mammals, owing to the attachment of the musculus retractor bulbi (fig. 369, m retr), it is divided into an anterior larger, and a posterior smaller cavity. Fig. 370. Fig. 370. Diagrammatic representation of the passage of a vena vorticosa, with its perivascular space, through the sclerotic, as seen in the Pig. r, Retina ; c/i, choroid ; pch, perichoroidal space filled with injection ; scl, sclerotica ; £, Tenon's space ; v, vena vorticosa. At the posterior pole of the eye, and around the point of entrance of the optic nerve, the cavity of Tenon communicates with another lymphatic space which, like a sheath, invests the external fibrous sheath of the optic nerve, and on account of its position may be termed the supravaginal space (fig. 369, spv). This finally opens through the canalis opticus into the arach- noid space of the brain, which last, as is shown by injections beneath the dura mater, communicates directly with the lymph- atics of the neck. t B. The Lymphatics of the Retina. The lymphatics of the retina, as His (7, 8) discovered, form sheaths to the bloodvessels of this membrane. They are peri- VOL. III. Z 338 THE LYMPHATICS OF THE EYE, BY G. SCHWALBE. vascular canals of the same nature as those demonstrated by the same author in the brain and spinal cord. The veins and capillaries are completely invested by these lymphatic sheaths, whilst the arteries are probably only surrounded by them through a definite portion of their course. The injection of the retinal lymphatics may be accomplished by driving the fluid with considerable force into the bloodvessels. The latter give way at certain points, and the fluid then escapes through the rents into the perivascular canals. The discharge of the retinal lymph takes place in the optic nerve through the lamina cribrosa. According to His, the outer portion of the optic nerve contains a rich plexus of lymphatics, which, however, are here no longer perivascular. A cavity which was described by Henle and Merkel (9), and which is situated between the membrana limitans interna and the optic-fibre layer of the retina, probably communicates with the perivascular canals of the retina. Lymph corpuscles are found in this position, but no injection of it has hitherto been successfully made. The relation of the tissue of the vitreous to the lymphatic system is still unknown. Stilling (11) found that in the eye of the Pig a central vessel, perforating the vitreous from .be- hind forwards, could easily be shown by dropping a solution of carmine upon the posterior surface of the latter, and this he re- garded as a lymphatic canaL The perivascular canals of the hyaloid of the Frog, described by v. Iwanoff (10), are the ana- logues of the perivascular canals of the retina of Mammals. c. A lymphatic cavity which does not communicate with either of the two systems just described is found between the two optic sheaths throughout their whole extent from the bulb to the canalis opticus. On account of its position beneath the fibrous sheaths of the optic nerves, it may be termed the sub- vaginal cavity (fig. 369, sbv). It opens directly into the arachnoidal space. At the point of entrance of the optic nerve into the globe of the eye it extends to close beneath the choroid, though without entering into communication with the perichoroidal space. Its walls are lined by an endothelium, which is very easily separable in the form of small nucleated scales. The space is traversed by a rich plexus of delicate THE ANTERIOR LYMPHATICS OF THE EYE. 339 connective -tissue trabeculse, which are also enclosed by an endothelial sheath. Such sheaths may often be completely detached, and then appear as glass-clear membranes beset with elliptic nuclei. 2. THE ANTERIOR LYMPHATIC SYSTEM OF THE EYE. A. The system of the anterior chamber of the Eye. The anterior chamber of the eye is a general receptacle for the lymph coming from the iris and ciliary processes, which flows into it at two points : from the canal of Petit through the capillary fissure between the pupillary border of the iris and the anterior surface of the lens ; and from the ciliary body through the spaces between the trabeculse of the ligamentum pectinatum. The canal of Petit runs circularly round the margin of the lens, and extends laterally in the form of a narrow fissure, as far as to the ora serrata. Its lumen communicates by a series of fine fissures, which exist in the zonula ciliaris, close to the border of the lens, with the posterior, and through this with the anterior chamber of the eye. It may be easily injected from the anterior chamber, especially in the eye of the Pig. Under normal conditions, however,- a current can only set in from the canal of Petit towards the anterior chamber of the eye, and not in the opposite direction, because in the latter case the iris forms a valve-like septum to the anterior cham- ber, which can only be overcome by such' a change of form of the globe of the eye as results from increased intraocular pressure, which may be artificially produced by injections into the anterior chamber of the eye. The principal channels discharging themselves into the anterior chamber of the- eye open into this through the spaces between the trabeculs& of the ligaua>entum pectinatum, and con- duct to it the lymph of a large portion of the ciliary body, and probably also of the iris. It is only in the eye of the Pig that a portion of this spongy region has been successfully in- jected with solution of Prussian blue thrown into the anterior chamber, and this has consisted of a fissure traversed by a plexus of connective tissue which extends circularly from z 2 340 THE LYMPHATICS OF THE EYE, BY G. SCHWALBE. Fontana's canal, as far as to the posterior border of the ciliary body, and lies in this between the ciliary muscle and the pars 'ciliaris retinae. In the eye of Man also fluids, when injected, penetrate at this point for some distance into the ciliary body. The trabeculse of the canal of Fontana in Mammals, as well as the trabeculse of the ligamentum pectinatum of Man corre- sponding to them, are everywhere invested by endothelial sheaths exactly resembling those which cover the trabeculse of the. sub vaginal space. The anterior chamber of the eye is lined throughout in front by the epithelium of the membrane of Descemet ; behind, by the epithelium of the anterior surface of the iris, .the two being continuous with each other in the angle of the chamber on the trabeculse of the ligamentum pectinatum, yet so that fissures are here present, by means of which the plexiform system of Fontana's canal communicates with the anterior chamber of the eye. The 'latter discharges itself near the border of the membrane of Descemet, through the canal of Schlemm, into the vense ciliares anticse (15). This is shown by the fact that on injecting a solution of Prussian blue into the anterior chamber of the eye, these veins are always filled, but the lymphatics never. This repletion of the veins by injec- tion occurs in the fresh eye of the Pig with a pressure not exceeding twenty millimeters of quicksilver, and demonstrates that the injection must reach the veins in well beaten paths, and that its entrance into the bloodvessels is not in any way rendered possible by rupture of the tissues. Nor can the intense blue injection of the veins be attributed to filtration, since the blue injection fluid never filtrates, as such, through vascular walls. In order to ascertain the mode in which the communication of the anterior chamber of the eye in man with the veins is effected, it is necessary to examine meridianal sections of such eyes, made through the corpus ciliare, in which the veins have been filled by an injection driven into the anterior chamber. In such sections it may be observed that a short stria of the blue injection fluid extends from the anterior chamber of the eye just behind the margin of the membrane of Descemet, obliquely backwards and outwards to the canal of Schlemm. THE ANTERIOR LYMPHATICS OF THE EYE. 341 The latter is also completely filled by the injection. In many preparations, injected vessels may also be observed in the sclerotic, which run from the canal of Schlemm, backwards and outwards through the fibrous membrane. Careful observa- tion shows that these vessels are indubitably veins. Never- theless, the canal of Schlemm must still be regarded as a lymph space, since the characters of its walls are essentially different from those of a vein. It communicates with the anterior chamber of the eye by means of a system of fine fissures. These fissures occur between the elastic €ircular fibres and fenestrated membranes, which extend from the margin of the membrane of Descemet, and form a modified prolongation of this membrane as far as to the posterior point of insertion of the ciliary muscle, and are continuous internally with the trabecular ineshwork of the canal of Fontana. This peculiar tissue bridges over a groove situated on the inside of the anterior border of the sclerotic, where it joins the cornea, and converts this groove into a lacuniform circular canal, which is, in fact, the canal of Schlemm. The ciliary plexus of Leber is situated, as he himself states," in the compact tissue of the sclerotic, just external to this groove. In many cases, instead of one patent orifice, there are two or more, and thus a transition is effected to the eyes of Mammals, in which several small lumina are present at the same point, but which are always placed internally to the groove of the sclerotic. The manner in which the canal of Schlemm is connected with the veins in its vicinity is still unknown. In all probability certain valvular arrangements exist, which prevent the pas- sage of venous blood into the canal of Schlemm, under the normal conditions of pressure. If we consider what the con- sequences would be if the anterior chamber of the eye were to have in the lymphatics its proper discharge pipes,, we shall readily understand the meaning of the above-described * Anatomische Untersuchungen iiber die Blutgefdsse des menschlichen Auges. (Anatomical researches upon the bloodvessels of the eye of Man.) Denkschriften der Kaiserlichen Akad.. der Wissenschaften zu Wien. Math,- Naturwissensch. Classe^ Band xxiv., p. 316. 342 THE LYMPHATICS OF THE EYE, BY G. SCHWALBE. relations. Were the lymphatics the discharge pipes of the aqueous humour, it would be clearly impossible to preserve the relatively considerable pressure which exists in the anterior chamber of the eye, since with the low pressure of the fluids contained in the lymphatics a rapid discharge of the aqueous humour would occur, which could not be compensated for by the transudation of fresh fluid through the walls of the vessels, and the anterior chamber would collapse. This, how- ever, is avoided by the opening of the lymphatics into the veins, through the intervention of the canal of Schlemm. Thus, owing to the circumstance that in the small veins the pressure is considerably higher than in the corresponding lymphatics, and further, owing to the resistance which the fluids have to overcome in their passage from the anterior chamber of the eye to the canal of Schlemm, in the narrow system of fissures, i,t becomes possible for the pressure in the anterior chamber of the eye to be preserved at its normal height, and for the entrance and discharge of fluid to be equalized. B. The account of the cornea in this book may be referred to for a description of its canalicular system. c. The Lymphatics of the Conjunctiva. The lymphatics of the conjunctiva were discovered by F. Arnold (5), and were more exactly described by Teichmann (6). They arise at the margin of the cornea, where they form a delicate plexus of about one millimeter in breadth ; more ex- ternally they are continuous with the wide-meshed lymphatic plexus of the sclerotic conjunctiva. The trunklets here soon be- come stronger, and usually run in a meridianal direction, anas- tomosing by means of numerous short, thin, transverse branches. According to Teichmann, a few branches proceed from the close plexus at the border of the cornea, in a meridianal direction towards its centre, forming a zone of about 0*1 of a millimeter wide. These perhaps correspond to the lymph-like structures described as lymphatic by Kolliker (3), His (1), and Samisch (2). According to Lightbody (4), the capillaries at the margin of the cornea are invested by lymphatic sheaths. I have not, however, been able in any case to satisfy myself of their presence. BIBLIOGRAPHY. 343 BIBLIOGRAPHY. CONJUNCTIVA. 1. His, Beitrage zur normalen und pathologischen Anatomie der Cornea, p. 71. Basel, 1856. 2. SAMISCH, Beitrage zur normalen und pathologischen Anatomie des Auges. Leipzig, 1862. 3. KOLLIKER, Gewebelehre, 5 Aufl. 1867. — Mikroskopische Anatomie, Bd. ii., p. 621. 1854. 4. LIGHTBODY, On the anatomy of the cornea of Vertebrates, Journal of Anat. and Physiol., i. 1867. 5. F. ARNOLD, Handbuch der Anatomie, Bd. ii., p. 986. 6. TEICHMANN, Das Saugadersystem, p. 65. Leipzig, 1861. RETINA UND GLASKORPER. 7. His, Ueber ein perivasculiires Canalsystem in den nervosen Central - organen und dessen Beziehungen zum Lymphsystem. (On a perivascular canal system in the central organs of the nervous system and on its relations to the lymphatic system.) Zeitschr. f. wissensch. Zoologie. 1865. 8. Lymphgefasse der Retina. (Lymphatics of the retina.) Verhandlungen der naturforschenden Gesellschaffc in Basel, iv., p. 256. 1866. 9. HENLE und MERKEL, Ueber die sogenannte Bindesubstanz der Centralorgane des Nervensystem. (On the so-called con- necting substance of the central organs of the nervous system.) Zeitschr. f. ration. Medicin (3), Bd. xxxiv. 10. IWANOFF, Beitrage zur normalen und pathologischen Anatomie des Frosch-Glaskorpers. (Essays on the normal and patho- logical anatomy of the vitreous of the Frog.) Medicin. Centralblatt, No. 9, p. 129. 1868. 11. STILLING, Zur Theorie des Glaucoms. (On the theory of Glau- coma.) Archiv. f. Ophthalrnologie. 1868. ALLGEMEINES. 2. G. SCHWALBE, Ueber ein mit Endothel bekleidetes Hohlensystem zwischen Chorioidea und Sclerotica. (On a cavitary system lined with an endothelium between the choroid and the sclerotic.) Medicin. Centralblatt, No. 54. 1868. 344 THE LYMPHATICS OF THE EYE, BY G. SCHWALBE. 13. G. SCHWALBE, Der Arachnoidalraum ein Lymphraum und sein Zusammenhang mit dem Perichorioidalraum. (The arach- noidal space a lymph space, and on its relations to the perichoroidal space.) Ibid., No. 30. 1869. 14. Untersuchungen iiber die Lymphbahnen des Auges und ihre Begrenzungen. (Researches on the lymphatic canals of the eye and their boundaries.) M. SCHULTZE'S Archiv, Bd. vi., p. 1. 1870. 15. Untersuchungen iiber die Lymphbahnen des Auges, etc. (Researches on the lymphatic canals of the eye, etc.) Theil. ii., M. SCHULTZE'S Archiv, Bd. vi., p. 261. 1870. V. THE VITREOUS HUMOUR. BY PROFESSOR A. IWANOFF. THE vitreous humour occupies the greater part of the cavity of the globe of the eye, and is surrounded posteriorly and laterally by the retina. The anterior surface is hollowed out into a slight fossa, in which lies the lens enclosed by its capsule. It presents a free surface from the margin of the lens to the apices of the ciliary processes, and this part looks towards the zonule of Zinn. The supposed interspace between this free part of the vitreous and the zonule of Zinn is termed the canal of Petit, which surrounds the whole free sequatorial border of the lens. The dimensions and relations of this canal during life (canal godronne of Petit) have not been very accurately ascertained. Briicke describes the canal of much smaller size than is in accordance with the original description by Petit. Henke goes still further, and denies generally the presence of such an open space in the living eye. "It is not," he says,* " to be regarded as an open space, any more than the pleura, peritoneum, or articulations ; but, like- them, as a fissure between two free (serous) surfaces, m-oveable over one- another, and without an intermediate space." Henle- holds the same opinions; whilst Kolliker, on the other hand, believes that although, the canal is cer- tainly very narrow, it yet has a distinct lumen in the living eye, and contains a fluid. My own researches support th*e view entertained by Henle, as in frozen eyes, at least, I was unable to discover any ice in the canal. The vitreous is not, as has been hitherto generally admitted, * Grafe's Archiv, Band vi., Heft ii.} p. 61. 346 THE VITREOUS HUMOUR, BY PROF. A. IWANOFF. surrounded by a special membrane, the so-called membrana hyaloidea. This membrane is in reality identical with the membrana limitans retinse. It is a constituent of the retina, and is consequently applied immediately to the vitreous only so far as the retina extends, that is, to the ora serrata. From thence the membrana limitans is continuous with the pars ciliaris retinae, but here meridianally running fibres lie between the vitreous and the limitans, which are known under the name of the zonula Zinnii, and these are intimately united both with the limitans and with the vitreous. Near the ciliary processes the vitreous and the zonula separate from one another, so that the whole anterior surface of the vitreous which looks toward the canal of Petit and the lens is not covered by any special membrane, nor by a pro- longation of the limitans, as Henle maintains, nor by a special membrana hyaloidea, as was formerly supposed. Henle* has demonstrated the non-existence of the hyaloidea. In the meanwhile ' the name limitans hyaloidea is also not quite satis- factory in a strictly anatomical sense. That the limitans is an integral constituent of the retina is demonstrated in the clearest manner by pathological processes taking place in the vitreous : in consequence of which this last shrivels, and becomes detached from the retina.t In such cases the membrana limitans always remains attached to the retina. In perfectly fresh specimens of the vitreous, and better still in those that have been hardened, the peripheric part exhibits distinct points of difference from the central. In the former a more or less obvious laminated structure is perceptible, whilst the latter appears to be homogeneous. Stilling termed the central part the nucleus, and the peri- pheric the cortex. The homogeneous central portion, or nucleus, does not occupy the centre of the mass, so as to be uniformly invested by the concentric laminated cortex, but is pressed forwards towards the lens in such a way that the cortical substance becomes progressively thinner from behind forwards, * Eingeweidelehre, p. 661. t A. Iwanoff, Beitrage zur normal und pathologische Anatomic desAuges, Archivfur Ophthalmologie, Band xv., Heft ii., p. 51. HISTOLOGY OF THE VITREOUS HUMOUR. 347 and at the ora serrata the several concentric layers are so closely compressed together that the surface of the nucleus is here separated from the limitans only by a very thin but distinctly fibrous layer. The fibres of this layer run parallel to the surface of the vitreous, forming wavy fasciculi bearing some resemblance to the fibres of connective tissue. This entire layer thus modified ultimately curves inwards towards the optic axis, and covers the whole anterior surface of the vitreous. Now, since we have here presented to us, not a single, but several compressed layers, though these are only loosely con- nected with each other, it is intelligible how easily we may come to the conclusion that there is a special membrane covering the vitreous and lying behind the lens, especially since the most superficial of these layers is perfectly smooth. The deeper-seated layers may sometimes in hardened eyes be separated from each other, — a circumstance that has led Hannover and Finkbeiner* to the conclusion that the hyaloid divides at the anterior surface of the vitreous into two laminae in such a manner that behind the canal of Petit there is a second canal, the canal of Hannover. In addition to the above-mentioned fibres resembling those of connective tissue that are met with in the anterior part of the vitreous, there are a considerable number of others like elastic fibres. They commence as early as .at the sequator of the eye, in the form of extremely fine looped fibres, but are first seen in large numbers at the ora serrata; from this point, lying in close apposition to the limitans, they curve round into the pars ciliaris retinae, and here form the commencement of the zonule of Zinn. A. canal of about two millimeters in diameter runs forward through the vitreous from the papilla optica to the posterior surface of the capsule of the lens. The difficulties that accompany the examination of the fresh vitreous induced all the earlier anatomists, who paid particular attention to this * Vergleichende Untersuchungen der Starke des Glaskorpers bei den Wirbelthieren, (Comparative researches on the density of the vitreous humour in the Vertebrata,) Zeitschrift fur wssenschaft. Zoologie, Band vi., p. 335. 348 THE VITREOUS HUMOUR, BY PROF. A. IWANOFF. subject, to adopt various methods of hardening. It was even believed that the diverse action of chemical reagents on the stroma and the mucous fluid occupying its meshes was capable of effecting their separation. Pappenheim* was the first who adopted this plan. On hardening the vitreous in carbonate of potash, he found that the stroma of the organ consisted of lamina running parallel to the surface, composed of very fine fibres and a homogeneous substance. Briicket found that after the action of acetate of lead the vitreous appeared to be composed of a large number of very fine structureless membranes which were superimposed on one another like the layers of an onion, and ran parallel to the surface. According to Hannover, J such a structure occurs only in Mammals. In Man the vitreous consists, according to him, of segments arranged radially around the optic axis, having some resemblance therefore to those of an orange. These appearances, however, are observed only in eyes that have been macerated for a long time in diluted chromic acid. The observations of Hannover have been corroborated by Finkbeiner from the examination of hyaloids that had been treated with corrosive sublimate. On the other hand, Bowman, § Doncan, Yirchow, Kolliker, and Henle obtained only negative results. Bowman and Doncan, in endeavouring to repeat and confirm or otherwise the observations of Hannover and Briicke, were unable to discover any membranes in the vitreous ; in their opinion, as both state-, the membranes and their arrangement are to be regarded as merely artificial products, resulting from the action of different reagen-ts ; Doncan entertained somewhat similar views to those held by Virchow and K611ikerrthe former of whom considered the vitreous to be analogous to mucous tissue, and the latter to the connective tissues. At the same time he did not deny that this did not sufficiently explain either the existence of fluid and solid constituents in the vitreous or the entoptic phenomena. Henle also was unable to see any membranes, and simply describes the vitreous as a homogeneous substance of tenacious or cell-like nature. * Spezielle Gewebelehre d. Auges, p. 182. Breslau, 1842. t Miiller's Archiv, p. 345, 1843. J Miiller's Archiv, p. 467, 1845. Das Auge, Beitrdge zur Anatomic, Physiologic, und Pathologic dieses Organs, p. 18, Leipzig, 1852. § Froriep's Notiven, No, 238, December, 1849, p. 274, HISTOLOGY OF THE VITREOUS HUMOUR. 349 It is clear from this that the hyaloid membrane is nothing else than the limitans, which passes without interruption upon the pars ciliaris retinae in front of the ora serrata, and Kolliker also holds this opinion. The limitans may be easily seen in ineridianal sections through the pars ciliaris retinae, supposing that the section runs exactly parallel to the course of the fibres of the zonula. In such preparations the limitans appears as a distinctly doubly contoured line, which divides by a very sharp line the pars ciliaris retinae from the zonula. In carefully made preparations the limitans may be detached for some distance as a fine membrane., both upon the zonula and on the pars ciliaris retinae. The views of Weber are quite peculiar, and unlike those of any other author. In his opinion the whole vitreous is composed of anastomosing cells forming a network, in the meshes of which a mucous fluid is contained. Dr. Smith* has lately stated that the vitreous humour of Man, ma- cerated for several days in water, and treated with carbolic acid, shows a concentrically laminated structure in its peripheric portions, whilst the central portion is radiated; the concentric laminae, according to his account, are composed of coarse fibres, and the nucleus of stellate anastomosing cells. He observed also an open canal extending from the papilla optica to the posterior surface of the lens. Bowman had already made similar statements in regard to the central portion. If the method adopted by Smith be pursued, it is difficult to determine what is and what is not to be regarded as an artificial product. The great diversities of opinion on this subject held by different authors, as shown by this short historical account, are explicable on the one hand by the difficulties that 'present themselves in the exami- nation of the fresh vitreous ; and on the other by the differences that are presented by the various methods of artificially hardening it. The membranes are the principal cause of discord, some maintaining that all the layers of the vitreous are separated from ons another by membranes, whilst others, being unable to discover the membranes, deny in consequence the correctness of all the other observations. Now, although the membranes are really .absent, this does not preclude the possibility of the existence of a laminated structure. Thin trans- * D. Smith, Structure of the adult Human Vitreous Humour, Lancet, 19th Sept., Vol. ii., 18G8, pp. 376—378. 350 THE VITEEOUS HUMOUR, BY PROF. A. IWANOFF. verse sections of the vitreous of eyes hardened in Mailer's fluid, split into layers which run parallel to the surface, and with the aid of high powers, after tinting with carmine, a finely granular mass makes its appearance in these layers, in the posterior part of this organ, together with a few scattered fine fibres. Anteriorly, towards the ora serrata the fibres become more abundant, and pursue a wavy course parallel to the surface. Even here, however, no traces of membranes are visible. These statements respecting the structure of the vitreous have received fresh confirmation from the researches of Stilling,! which possess the advantage of having been exclusively made on the fresh vitreous, and are not therefore open to the objection that the conclusions arrived at are due to appearances artificially produced. According to Stilling, if sections be made through the fresh vitreous parallel to the optic axis, and a few drops of carmine be allowed to fall on the cut surface, a number of concentric furrows, varying from six to twelve, are formed in the periphery, whilst the centre, or nucleus, remains free from colour. The furrow forming the boundary between the cortex and the nucleus is, as a rule, the deepest, and is most quickly filled. Stilling does no-t give the relations of the cortex and nucleus quite correctly, since he was only aible to apply his method to the determination of the coarser anatomy of the parts. He states that the cortex invests that part of the nucleus situated behind the ora serrata, so that the lens and zonula lie npon the latter alone. But, as we have seen above, the cortical portion, the several layers of which are closely compressed at the ora serrata, completely surrounds the nucleus, as is correctly shown in the illustrations of Hannover and Finkbeiner. After Henle had demonstrated that mo hyaloid membrane existed, he endeavoured to explain the existence of the membrane that, in his opinion, is found in the shallow groove covering the vitreous at this point, by assuming that the limitans, before it reaches the ora serrata, increases in thickness, and at the same time becomes altered in struc- ture. He considered that it partially breaks up into fibres, which either pursue an irregularly tortuous course, like those of elastic tissue, or are parallel and wavy, like those of connective tissue ; in either case, how- ever, being always remarkable for their extraordinary tenuity : and further, wiiilst the principal portion of these fibres or fasciculi of fibres * Stilling, Eine Studie uber den Bau des Glaskorpers, Archiv fiir Anatomie, Band xv., Heft iv. HISTOLOGY OF THE VITREOUS HUMOUR. 351 extend over the surface of the vitreous, a few penetrate into its interior, where they are soon(lost. According to the same author, the superficial fibrous tissue of the limitans hyaloidea divides at the point where the orbicularis ciliaris begins to enlarge into the corpus ciliare, into two laminae, of which one passes inwards to form the hyaloidea of the shallow groove, whilst the other passes outwards to the pars ciliaris retinae, in order to form the zonula. The researches above given show, in opposition to those of Henle, that all those changes to which the limitans is subjected, take place in the peripheric layers of the vitreous, whilst the limitans itself remains unaltered, and becoming progressively thinner, passes simply from the ora serrata to the pars ciliaris retina. It thus not only takes no part in the formation of the urceolate groove of the hya- loidea, which, as has been above shown, does not exist, but the part it takes in the formation of the zonula is more than doubtful. I at least have never been able to discover this relation, whilst the origin of the zonula from the vitreous may be very easily observed. It only remains therefore to determine whether the limitans is actually continuous with the pars ciliaris retinas. Henle himself admits that if we consider the fibrous layer of the zonula as the an- terior lamina of the limitans, the latter again splits into two layers at the apices of the ciliary processes, and that in some cases he has even seen the hyaloid membrane extend beyond the origin of the fibres of the zonula on the orbiculus ciliaris, As regards the development of the zonula, we now know that it does not exist in the embryo, so long as the vessels investing the capsule are present, although at this period the limitans is already completely developed. The zonula first appears at the time when the capsular vessels atrophy, and as their atrophy proceeds becomes progressively more and more distinct. But if the limitans passes unaltered from the ora serrata over the pars ciliaris retinas, it is self-evident that it cannot possibly form a quantity of fibres of the zonula, and beyond this, by further division, the membrane of the quoit-like groove. All this confusion originates in the fact being overlooked, that the superficial layers of the vitreous become already altered in their structure in front of the ora serrata, and are intimately fused with the limitans and the retina. At the same time the coalesced parts are not altogether inseparable since, in some pathological cases, and even in healthy eyes, treatment with alkalies will very often effect S52 THE VITREOUS HUMOUR, BY PROF. A. IVVANOFF. the detachment of the vitreous with the zomila from the membrana lirnitans. In the year 1814, Martegiani described a funnel-shaped depression in the vitreous at the point of entrance of the optic nerve, which he named the " area." This " area Martegiani " is really the commencement of the canal which has been incorrectly designated the canalis hyaloideus Cloqueti. Cloquet never saw and never depicted the canal in adults ; he only describes the course of the capsular artery in the foetal vitreous. Hannover describes the canal better, but states expressly that he has never found it open, and thus really knew nothing of the existence of a proper canal. The account given by Finkbeiner * is not clear ; of the existence of an open canal in any fully developed eye of Mammal or Man he really says nothing. He describes at length only the eye of the Ox, in which two elongated arese unite to form a solid cord traversing the vitreous. The presence of this canal as a patent tube existing throughout life in the eye all Mammals and of Man, and gradually increasing to the period of complete development of the whole eye, was first demon- strated by Stilling, who described the method by means of which it can be demonstrated in the fresh eye. The cells of the vitreous are situated only in its external superficial layers ; in the deeper layers we meet only with derivatives from them, that is to say, with nuclei and shrivelled vesicles. Though their form is very various, they can all be classed under three principal groups. 1. Round cells with large nuclei, the latter surrounded by coarsely granular protoplasm. These occur chiefly in the ante- rior portions of the vitreous, especially in children, in whom they often contain several nuclei. 2. Fusiform and stellate cells. These are met with through- out the peripherical portions of the vitreous. The stellate cells usually possess long, fine, ramified processes, which are. beset with varicose dilatations. 3. A very characteristic form of round cells, which contain in their interior a large, round, and perfectly transparent * Loc. ctf., p. 332. HISTOLOGY OF THE VITREOUS HUMOUR. 353 vesicle. In fully developed cells of this kind a single vesicle only exists, which completely fills the entire cavity, and only leaves a little space at the periphery for a nucleus surrounded by a small quantity of protoplasm. Sometimes two vesicles occur, separated from each other by a straight line. In other cases there are several vesicles which appear to be surrounded by a common sheath, the contour of which is perfectly spherical. The vesicles just described are not only found in the round cells, but are seated also on the processes of the stellate cells ; where they sometimes attain a colossal size, exceeding that of the cells themselves. We meet with these at all periods of life, though chiefly in old people, and in the posterior, por- tions of the vitreous. All these cells possess the property of contractility. They change their form and perhaps also their place. The contracti- lity of the round cells containing vesicles is less in proportion to the size of the vesicles, and the more consequently the pro- toplasm has diminished. The views in respect to the existence and the nature of the cells are as various as those on the structure of the stroraa. We are indebted to Virchow for the first special investigations that were made upon the cells. In the embryo of a Pig four inches in length he found, distributed at tolerably regular distances through the homogeneous intercellular substance, round, nucleated, sometimes multinucleated and coarsely granular cells. According to Kolliker, the cells occur especially in young persons ; he saw them indeed in some adults, but scattered and indistinct, and chiefly near the lens and hyaloid membrane. Weber, on the other hand, found stellate anastomosing cells throughout the whole vitreous. Hannover and Finkbeiner describe an epithelium covering the hyaloid membrane, and this, according to the last-named author, invests also the several septa in its interior. The same view is also entertained by Coccius. Ritter observed an epithelium with ramified cells only on tbe internal surface of the hyaloid, but no cells, on the other hand, within the vitreous. The fibres of the zonula, as has been already stated, spring from the vitreous, and from that part of it which has not yet reached the ora serrata retinae. The zonula-fibres arise near VOL. III. A A 354 THE VITREOUS HUMOUR, BY PROF. A. IWANOFF. this latter, and, lying at first beneath the surface of the vitreous, ascend towards the ora serrata, and become applied in the form of extremely fine fibrils to the membrana limitans retinae, -with which they are in close contact ; in this way the vitreous and limitans are so intimately connected at the ora serrata that it is impossible to separate the retina from the vitreous, por- tions of the vitreous remaining constantly adherent at the ora. But just as on the one hand it may be clearly demonstrated that the zonula-fibres arise from the substance of the vitreous behind the ora serrata, so, on the other hand, it may be shown that the territory of origin of the zonula does not terminate at this line. The origin of the zonula-fibres from the corpus vitreum may also be shown to take place for some distance in front of the ora, and consequently towards the ciliary processes, so that here also the zonula and the vitreous do not form isolated structures. The zonula Zinnii first appears to be completely differentiated from the vitreous at a distance of from four to five millime- ters from the ora. As it passes towards the lens it is separated from the pigment layers of the smooth portion of the corpus ' <• <•', conjunctiva and sclerotic. Drawing taken from the eye of a child, very perfectly injected with gelatine and Prussian blue. E E 2 420 THE CORNEA, BY ALEXANDER ROLLETT. Portions of the membrane detached either from the fresh cornea or from a cornea treated in the above-mentioned manner are characterized by the rolling inwards of the opposite edges, like paper that has been long rolled up. The borders of a detached portion of the membrane of Descemet are very sharply defined under the microscope ; and as, on account of its great transparency, the foreshortened image of "all angles is visible, a glass-like appearance is pro- duced. All these peculiarities are common to the membrane of Descemet and the capusle of the lens. When fresh, the membrane of Descemet presents no structure recognizable under the microscope. In rare instances only an indistinct and interrupted striation may be perceived on frac- tured surfaces.* Henlet saw the membrane of Descemet of the eye of the Ox, after thirty hours' boiling, break up into a number of extremely fine, somewhat inrolled, glass-like laminae. Tamamscheff J noticed that fine sections of dried cornese, when submitted for twenty-four hours to the action of solution of iodide of potassium containing, iodine (3:1: 500), become striated in the direction of the surface, and divisible into extremely fine fibrils. Schweigger-Seidel§ describes and depicts some peculiar appearances, and also states that, a ten per cent, solution of common salt brings into view a distinctly fibrillar striation in the membrane, but whether in the superficial or side view is not specified. Wart-like projections of the posterior surface of the mem- brane of Descemet occur in Man at the margin of the cornea.] | These are not present in the early years of life, but between twenty and thirty they have a diameter of O'Ol of a millimeter at their base, are a,bout half this height, and stand in from two to * Briicke, loc. cit., p. 606. Mensonides, Nederlandisch Lancet, Mai, 1849, p. 694. Leydig, Zeitschrift fur wissenschaftliche Zoologie, Band v., p. 41. t Canstatt's Jahresbericht, 1853, p. 26, and loc. cit, p. 606. J Centralblatt fur die medicin. Wissenschaften, 1869, p. 353. § Schweigger-Seidel, loc. cit., pp. 311 and 312, figs. 7, 8, 9, and 10. || Hassall, Mikroskopische Anatomic, translated into German by Kohl- schiitter, Band ii., Taf. Ixiii., fig. 11, p. 393. Leipzig, 1852. H. Miiller, Archiv fur Ophthalmologie, Band ii., Abtlieil. ii., p. 48. ENDOTHELIUM OF THE CORNEA. 4^1 four rows, at distances from each other that are about equal to the diameter of their bases. In old people they are about O02 of a millimeter wide at their base, and O'Ol of a millimeter high, and form a broad zone. In rare cases they extend as far as the centre of the cornea (H. M tiller). The connections formed by the membrane of Descemet at its border will be 'subsequently considered. THE ENDOTHELIUM OF THE MEMBRANE OF DESQEMET. Internal Epithelium of the Cornea. The endothelium of the membrane of Descemet consists, in the eye of Man and of adult animals, of a layer of polygonal cells, having a diameter of O025 of a millimeter.* The cells have a flattened appearance, and possess round nuclei, with a diameter of O'OOS of a millimeter. t In perfectly fresh eyes the endothelium may be stripped off in the form of a continuous membrane. This layer of cells situated at the back of the cornea is not to be included amongst the true epithelia, but amongst the endothelia.J In the endothelial cells of the membrane of Descemet of the irritated cornea of the Frog, Klebs§ observed the occurrence of a series of alterations of form, which under certain circumstances are as lively as those of the lymph corpuscles, and lead to detachment of the cells. Norris and Strieker]] also saw move- ments take place in the endothelial cells of the membrane of Descemet in inflamed cornese, and state that they observed an increase in the number of the nuclei, and a proliferation of the cells. If the freshly excised and healthy cornea of the Frog be moistened with aqueous humour as rapidly as possible, be brought under the microscope, and the endothelium of the membrane of Descemet be examined whilst in accurate focus, it will frequently appear as if composed of two kinds of * Henle, loc. tit., p. 607. t Henle, loc. cit. 4. His, Haute und Hohlen des Korpers (Membranes and cavities of the body), p. 18. -Basel, 1865. § Centmlblatt fur die, medicin. Wissenschaften, 1864, pp. 513 — 510. || Norris and Strieker, loc. cit., pp. 16 and 17. 422 THE CORNEA, BY ALEXANDER ROLLETT. cells. Some of the cells appear granular, and contain a round nucleus with a more or less well-defined contour; whilst others, on the other hand, appear perfectly smooth and without any indication of a nucleus. These two kinds of cells either occur isolated or connected together into irregular figures, the variations in the distribution of the two occasioning very diverse markings of the endothelial membrane. DEVELOPMENT OF THE CORNEAL LAYERS BELONGING TO THE CONNECTIVE TISSUE. The histogenesis of the cornea requires to be again worked over, especially with the aid of the silver and gold methods of preparation. At present our knowledge of this subject is very fragmentary. Langhans* found in the cornea of the foetus of a cow, one inch and a quarter long, elongated and roundish cells, with not very sharply defined nuclei, lying in close apposition. In an embryo with a length of one inch and a half, the cells were irregularly roundish or angular in form. In an embryo two inches and a half long, a fibrous appearance was already visible in the teazed-out tissue ; the cells were large, and their form resembled more closely the corpuscles of the developed cornea. In the foetus of a Cow, the diameter of the eye of which amounted to about 0'6 of a millimeter, the cells were pale, elongated, and had from four to six processes. I have in my possession a series of meridianal sections of the embryoes of Sheep hardened in Muller's fluid, tinted with carmine, and imbedded in Peremeschko's solidifying mass. In these I can see that the cornea is originally composed of round cells in immediate contact with each other. Subsequently the cells appear to be flattened towards the surface of the cornea and lie superimposed one upon the other, like the cells in the upper layers of laminated tesselated epithelium. A. clear substance intervenes between these flattened cells, separating them from each other in the direction of the thickness of the cornea, so that appearances are already produced re- sembling those of the fully developed cornea. * Loc. cit., pp. 17 and 18. DEVELOPMENT OF THE PROPER TISSUE OF THE CORNEA. 423 This separation of the cells from one another does not occur uniformly in all the layers of the cornea. It commences near the anterior pole of the eye, affects the anterior layers first, and then extends progressively backwards towards the anterior chamber. At a certain period of development this layer is separated from the corneal layer with already fully developed intermediate substance by a layer of flattened cells superimposed one upon another, the innermost of which exactly resemble the cell layer corresponding to the endothelium of the membrane of Descemet. The membrane of Descemet is not as yet present. It occurs as a slender stria between the innermost cell layer and the cells forming plates superimposed one upon the other situated more externally. In the embryo of a Calf eight centimeters long, and in human embryoes of the second or third month, the membrane of Des- cemet presents, according to Donders,* the same structureless appearance as in adult animals, except that it is thinner. In the clear substance which, as mentioned above, separates the flattened cells of the developing tissue of the cornea, fine fibrils or fasciculi of fibrils occur at a very early period. The cells themselves appear to be provided with processes which radiate from them in all directions, and anastomose with the processes of neighbouring cells, but which, as is shown by teazed-out preparation and by sections, are never continuous with the substance of the fibrils.f The latter occur in the material occupying the interspaces of the granular protoplasm of the cells, in the same manner as the fibrils of the connective tissue in the development of the plexus 4 The histological processes taking place in the cornea of Rabbits after the anterior layers have been shaved off,§ and in the cornea of Man * Nederlandisch Lancet, August, 1851, p. 47. f See Wilckens, Ueber die Entwicklung der Hornhaut des Wirbelthie) - auges, (On the development of the cornea of the eye of vertebrate animals, ) Zeitschrift fur rationel. Medicin, 3 R., Band xi., p. 167. £ See this Manual, Vol. i., p. 84. § Bonders, HoUandische Beitrage zur Natur- uud Hellkunde, Band i., p. 387. De Gouvea, Archiv fur Augen- und Ohrcu-iicilkunde, Band i., p. 119. 424 THE CORNEA, BY ALEXANDER ROLLETT. after losses of substance,* and the regeneration of the tissue which has been observed to occur, likewise demand a more profound and searching investigation. THE EXTERNAL EPITHELIUM OF THE CORNEA. This epithelium is a laminated pavement epithelium, which in Man is O03 of a millimeter in thickness.f The characters of the external epithelium are very much alike in Man and Mammals. Its most superficial layers are composed of many layers of flattened cells, which are broader than those that are more deeply situated, and which, seen in situ, as in sections of hardened preparations, or in detached shreds of the epithelium, Fig. 388. Fig. 388. Ribbed and spinous cells from the middle cell layer of the external corneal epithelium of the Pig, isolated by maceration of the cornea in a ten per cent, solution of common salt, and subsequent treat- ment with water. present a polygonal form. In teazed-out specimens of epithe- lium prepared in iodine-serum, or for a longer period in a ten per cent, solution of common salt, and subsequently for a short time in water, these cells appear rough, slightly dentated, and as ribbed, spiny, or prickle cells, with their inequalities interlock- ing with each other (fig. 388). I have never been able to see any cells provided with such long processes (digitate cells) as ClelandJ states that he has isolated from the middle layers of * Bonders, Nederlandisch Lancet, 1848, p. 218. t Henle, loc. cit., p. 605. J Cleland, On the Epithelium of the Ox, Journal of Anatomy and Physiology, by Humphry and Turner, Vol. ii. , pp. 362, 364. Cambridge and London, 1868. EPITHELIUM OF THE CORNEA. 425 the corneal epithelium of the Ox by means of the bichromate of potash, and which he has depicted. The deepest cell layer resting directly on the corneal tissue is composed of cells that are vertically elongated. They are isolated, but rough in consequence of their detachment from the interdentations of the adjoining ones, and are seated with their broad bases upon the corneal tissue. They do not send off' any processes into this. When seen in profile, the base of the cells appears as a highly refractile line (basal hem or border). The round nucleus of these cells is somewhat nearer their outer than their inner extremity. It may be particularly well seen in sections stained with hsematoxylin, and rapidly hardened in alcohol, of the cornea of those animals that possess remarkably long cells, as for example in the Ox and Pig. Krause* states he has observed peculiar ellipsoidal cells to be sparingly distributed amongst the cells of these layers. In the Frog, the epithelium as seen in optical section, where the fresh cornea has fallen into folds, presents the appearances presented in fig. 378. I have convinced myself that here also maceration in a ten per cent, solution of common salt until the epithelium sepa- rates in shreds,f constitutes an excellent means of isolation. The cells of the outermost layers form a kind of mosaic, the areas of which are circumscribed by highly refractile branching- lines (cell contours with cement that blackens with nitrate of silver), and every polygonal cell contains a beautiful sharply defined granular nucleus (fig. 389, a). Rib • and prickle cells occur sparingly in the middle cell layers of the Frog. The cells there appear either polyhedric with smooth borders and surfaces, or, as may frequently be ob- served, they give off a limited number of longer or shorter pointed, and often very peculiarly formed, processes (fig. 389, 6). The innermost cell layer is here also composed of elongated cells, which, however, vary in length. Thus between shorter * Ueber das vordere Epithet der Cornea, (On the anterior epithelium of the cornea,) Gottinger gelehrte Nachrichten, 1870, No. 8 ; Reichert and Dubois-Reymond's Archiv, 1870, p. 232. t Schweigger-Seidel, loc. cit., p. 353. 426 THE CORNEA, BY ALEXANDER ROLLETT. cells of the form represented at c 1, fig. 389, longer ones are intercalated of the form seen in o 2, fig. 389, and the clavate form of cell may often be seen still more strongly expressed on account of the attenuation of the inner part of the cell, as in c 3, fig. 389. A highly refractile hem or border (fig. 389, c 1 2 3) exists at the point where the cells rest upon the corneal tissue, which in Fig. 389. Fig. 389. External epithelium of the cornea of the Frog, a, Cells from the outermost, 6, from the middle, andc, from the innermost layer. profile views recalls the smooth border that under some circum- stances certain columnar epithelial cells exhibit at their free margin. This border, which may be termed the basal border, usually appears to be expanded, and this is always the case with the clavate cells of the innermost layers. EPITHELIUM OF THE CORNEA. 427 The expanded basal borders of the cells are so applied to each other, or are so superimposed upon one another by their thin edges, that the borders of the several cells seen collectively in situ make a bright stria which forms the line of demarcation between the epithelium and the corneal tissue. Henle* men- tions this stria, but gives another interpretation of it. I have satisfied myself, as regards Man and Mammals, that the stria is due to the basal borders of the innermost cells. An accurate knowledge of the normal condition of the dif- ferent layers of the corneal epithelium is so much the more requisite, as this epithelium plays an important role in the investigations that have recently been made in regard to epithelial regeneration. J. Arnold, t who began the investigation, it is well known advanced a proposition of quite fundamental importance in admitting that the new epithelium filling an artificially produced abrasion of the epithelium arises from a blastema formed in the hollow. This, he thought, be- came converted at the border of the space into hyaline protoplasm, which divides into portions containing nuclei, i.e. into cells. The experiments on the external epithelium of the cornea made by Wadsworth and Eberth,;]; F. A. Hoffman§ and Heiberg,|| are however collectively opposed to the existence of Arnold's blastema. The regeneration occurs through the agency of daughter cells that arise by germination and fission of the epithelial cells forming the border of the cavity, or from the marginal cells of epithelial islands remaining intact in the cavity. F. A. HoffmanlF states that he never observed processes in the cells of the lowermost epithelial layers. This would indicate that the last-named layer had a definite position (see Cleland** and Krause).ff Heiberg,JJ however, opposes Hoffman's statements. But Heiberg lays too little stress on the peculiarity of the intact lowermost cell layer of the * Henle, loc. cit., p. 605, fig. 459. f Virchow's Archiv, Band xlvi. , p. 168. t Virchow's Archiv, Band li., p. 361. § Virchow's Archiv, Bandli., p. 373. || Medicinische JaJirbiicher der Gesellschaft der Aerzte in Wien, Jahrgang, 1871, p. 7. IF Hoffman, loc. cit., pp. 388 and 389. ** Cleland, loc. cit, p. 363. ft Krause, loc. cit., p. 235. U Heiberg, loc. cit., p. 19. 428 THE CORNEA, BY ALEXANDER ROLLETT. corneal epithelium. We have already seen that processes are present even in the normal condition in the cells of the middle layers. Heiberg* describes slow and gradual changes of form in the processes of the epithelium undergoing regeneration. F. A. Hoffinanf had pre- viously observed the protrusion and retraction of rounded processes in the cells of the anterior corneal epithelium in the vicinity of the eschar of the cornea caused by nitrate of silver. The regeneration of the epithelium in a cavity (the size of which is unfortunately not stated) caused by scratching the centre of the surface of the cornea with a cataract needle is accomplished in Frogs in about forty hours, or as a rule before the end of the third day, and in Mammals and Birds within twenty-four hours. After these periods had elapsed, the cavities were found to be completely filled up by cicatrisation.]: Migrating cells occur in the anterior corneal epithelium, just as in the corneal tissue, and such cells are also found between the two tissues (epithelial and subepithelial migrating cells).) Engelmann,[| J. Arnold,^ Wads worth and Eberth** F. A. HotTman,tf and Heiberg,}} consider it doubtful whether the migrating cells take any part in the regeneration of the epithelium after losses of its substance. THE NERVES OF THE CORNEA. The nerves of the cornea enter its margin at tolerably regu- lar distances from each other in the form of trunks of various size. The entrance of medullated nerves into the cornea has long been known to occur.§§ The number of such medullated nerves entering the cornea * Loc. cit., p. 12. t Ueber Contractilitatsvorgange im vorderen Epithel der Frosdiliomhaut. Diss. inaug. Berlin, 1861. J Heiberg, loc. cit., p. 10. § v. Recklinghausen, Virchow's Archiv, Band xxviii., p. 191. || Engelmann, loc. cit., p. 15. IF J. Arnold, loc. cit., p. 170, et seq. ** Wadsworth and Eberth, loc. cit., p. 370. ft F. A. Hoffman, loc. cit., p. 384. J$ Heiberg, loc. cit. , pp. 13 and 20. §§ Schlemm, Berliner Encyclopddie, Band iv., p. 22. Bochdalek, Bericht uber die Versammlung der Naturforscher in Prag im Jahr., 1837, Prag, 1838, p. 182. NERVES OF THE CORNEA. 429 varies in different animals. In Man the number is variously stated at from twenty to thirty,* twenty-four to thirty- six,-!- and forty to forty-five. J In the Rabbit, from twenty to thirty ; in the Ox and Sheep, from ten to twenty ; in the Fowl and Pigeon, from twelve to eighteen ;§ in the Guinea- pig, from fifteen to eighteen ;|| and in the Frog, on the average, fifteen^ have been counted. In the course of their dis- tribution in the substance of the cornea, the nerves form a plexus characterized by its numerous anastomoses, the fine branches of which run towards the anterior surface, where another plexus is found close beneath the epithelium, and just under the anterior structureless lamella.** The nerve plexus formed of non-medullated fibres presents the same appearance in Man and the most diverse animals,ff and in the Frog the fine extremities of the nerves distributed through the whole cornea are connected with the corneal corpuscles. JJ In Mammals, the fibres emanating from the outer parts of the nerve plexus may be followed into the anterior epi- thelium of the cornea. §§ The best insight into the mode of distribution and the termination of the nerves in the cornea, has been obtained by Cohnheim,||[| by the use of solution of chloride of gold, which is so admirably adapted for this pur- pose. His beautiful results have been in part corroborated both by Kolliker and by Engelmann. At a short distance from the margin of the cornea, the * Kolliker, Mikroskopische Anatomie, Band ii., p. 627. f Kolliker, Gewebelehre, p. 650. Leipzig, 1867. J Samisch, Beitrage zur normalen und pathologischen Anatomie desAuges. § Kolliker, Mikroskopische Anatomie, Band ii., p. 627. || Cohnheim, Virchow's Archiv, Band xxxviii., p. 354. *fT Kiihne, Untersuchungen uber das Protoplasma, etc. , p. 133. Leipzig, 1864. ** Kolliker, loc. cit., p. 627. ft His, Beitrage zur normalen und pathologischen Anatomie der Cornea, p. 60. J. Arnold, Bindehaut der Hornhaut. Samisch, loc. cit. Ciaccio, Quarterly Journal of Microscopical Science, July, 1863, p. 177. Kiihne, loc. cit. ££ Kiihne, loc. cit. §§ Hoyer, Reichert and Dubois-Reymdnd's Archiv, ]866, p. 180. || 1 1 Cohnheim, loc. cit., p. 343. 430 THE CORNEA, BY ALEXANDER ROLLETT. medullated nerve fibres suddenly lose their medullary sheath. The point at which this occurs is not constant (Cohnheim), sometimes occurring in the small entering trunklets, some- times in the branches of the first, second, or even the third order into which these break up. The nerves in their further course from this point are com- posed of a variable, but usually very large, number of extremely delicate non-medullated nerve fibres. These fasciculi of non- medullated fibres enclose long oval nuclei, which cannot, how- ever, be certainly shown to belong to any investing sheath. Fig. 390. Fig. 390, Nerves of the cornea of a Pig, as seen in a vertical section made from a specimen treated with chloride of gold. a a, Larger nerves ; b b, plexus beneath the anterior limiting layers of the cornea ; c c, subepithelial plexus ; d d, the terminal branches ascending through the epithelium. The individual medullated fibres often exhibit a very beautiful varicose appearance. These numerous fibres must obviously originate in a division or fibrillation of the axis cylinder (Max Schultze). The fibres just described as entering the corneal tissue then form, by their manifold branching, communications, and diver- gences, a rich plexus (fig. 390), which presents larger meshes, and is composed of stronger nerves in the deeper part of the NERVES OF THE CORNEA. 431 cornea, whilst towards the external surface the nerves become more and more delicate, and the meshes of the plexus smaller (fig. 390). The whole plexus in Mammals occupies essentially the two outer thirds of the thickness of the cornea. A few isolated fibres only supply those parts of the cornea that lie nearer the membrane of Descemet, and these run backwards from the marginal parts of the innermost portion of the anterior plexus formed by the largest nerve fibres. Kolliker states that in Rabbits he has observed the fine lines emanating from these fibres running in a horizontal direction along the membrane of Descemet, and at a short distance from it. Several subdivisions may be distinguished in the plexus oc- cupying the anterior parts of the cornea. For whilst the thicker nerves proceeding from the posterior parts of the cornea gently bend forward, they expand, together with finer branches, which for the most part run parallel to the surface at a short distance from the line of demarcation between the corneal tissue and the external epithelium (internal to the anterior limiting layer), to form a superficial plexus, enclosing uniform meshes. Emanating from this plexus, delicate vertical or slightly inclined branches (rami perforantes) run to the an- terior surface of the cornea and to the anterior epithelium, immediately subjacent to which they break up, either in the form of a brush, as in the Guinea-pig (Cohnheim), or in a stellate manner in a series of finer branches, which again form an exceedingly delicate superficially expanded web, termed the subepithelial plexus (391). From this again fine nerves run forwards at tolerably regular distances from each other between the inferior vertically elongated cells and the more superficially situated spheroidal cells of the epithelium. In this course they run at right angles to the surface. On arriving at the innermost layers of the superficial flattened cells, they give off on all sides their finest terminal fibres, which, after they have previously once or twice or repeatedly divided, often terminate with somewhat swollen extremities in the most superficial epithelial layers. Seen from the surface, the terminations of the fibres ascend- ing through the epithelium correspond to the nodal points in 432 THE CORNEA, BY ALEXANDER ROLLETT. which the terminal twigs converging from various directions unite. I have never been able to convince myself of the exist- ence of anastomoses of the various terminal twigs corresponding to such nodal points. Strieker recently showed me a fine plexus in the cornea of the Rabbit, first demonstrated by S. H. Chapman, who had satisfied himself that it was situated on the surface of the external epithelium. The preceding statements rest chiefly upon observations made on the cornere of the Pig and Ox, treated with chloride of Fig. 391. Fig. 391. Portion of the subepithelial nerve plexus of the cornea of the Pig, brought into view by. means of chloride of gold. gold. Similar appearances are, however, obtained, differing only in some points of detail, in the other Mammals that have been examined. The cornea of the Frog may also be employed in order to obtain extremely good gold preparations (fig. 392), and this possesses the further advantage, that after removal of the epi- thelium it may be brought under the microscope as a whole, whilst the thick cornese of the above-named animals, after im- pregnation with gold and the subsequent reduction of the metal, require to be cut into meridianal and surface slices. NERVES OF THE CORNEA. 433 Kuhne,* and still more completely, Engelmann,f have fol- lowed the distribution of the nerves in the cornea of the Frog examined in perfectly fresh aqueous humour. Trunklets composed of from five to fifteen or more medullated fibres enter the cornea at six or eight points of its periphery. At several points also isolated medullated fibres, or two together, penetrate its substance. The greater number of these fibres run at first in a straight direction, and for a distance of from ()-'2 to O5 of a millimeter towards the centre of the cornea; a few only are given off at right angles from the trunklets at the margin of the cornea, and these, after running for some distance parallel to the border, finally turn inwards. Fig. 392. Fig. 392. Portion of cornea of a Frog, prepared with chloride of gold, nn, Nerves. The nerves usually lose their medulla at a short distance from the corneal margin (0*3 to 0'5 of a millimeter) ; and then, undergoing repeated dichotomous division, form a wide-meshed plexus situated nearer to the posterior than to the anterior surface of the cornea. The occurrence of true anastomoses has not been demonstrated in this plexus of the Frog, any more than in that of Mammals. The presence of sheaths is indicated * Untersuchungen uber das Protoplasm, etc., p. 132. + Loc. cit., p. 15. VOL III. F F 434 THE CORNEA, BY ALEXANDER ROLLETT. both in the medullated as well as in the non-medullated fibres, by nuclei elongated in the direction of the axis of the nerve. As the nerves undergo progressive division, the nuclei become less and less numerous, till they are at length only found in the nodal points of the plexus, which they appear to distend. Ganglion-like structures are thus formed similar to those that have been observed in the corneal nerves of Mammals. Nei- ther in the Frog nor in the Mammal, however, have we to deal with true ganglia in the nodal points of the nervous tissue. From this plexus, which in the Frog lies almost entirely in one and the same plane, very fine branches are given off at various points, which, both in front and behind the coarse plexus (as far as to about the junction of the anterior with the two posterior thirds), form a close trellis-like nervous expansion in the substance of the cornea. It is doubtful whether any anas- tomoses exist in this trellis-work, but in the nodal points of its finest fasciculi nuclei are here and there scattered. Here again, however, there are no true ganglionic enlargements. The finest fibres are gradually lost in the corneal tissue, without its being possible to arrive at any definite conclusion of the exact mode. Engelmann* has differentiated the above-described nervous expansion from the nerves of the corneal epithelium, on the ground of its being placed in the proper substance of the cornea.f These last are branches of the above-described coarse plexus, which run vertically or nearly so to the external epi- thelium. Associated with these are a few fine non-medullated fibres, which pass directly forwards to the epithelium from the periphery. There are collectively from forty to sixty of these nerve trunks in each cornea. At the line of demarcation between the corneal tissue and the external epithelium these nerves give off a variable number of branches, which run in all direc- tions parallel to the surface, and ultimately, to some extent undivided, but in part also after frequent subdivision, reach the long cells of the deepest layer of the epithelium. A close plexus is thus again formed at this point, the terminal fibres proceed- ing from which reach those cell layers of the epithelium that * LOG. dt., p. 17. t Loc. cit.j p. 19. THE PERIPHERY OF THE CORNEA. 435 lie immediately beneath the superficial tesselated cells. Speci- mens prepared with chloride of gold corroborate all that lias just been placed before the reader in the most satisfactory manner. I have not observed the passage of the terminal fibres through the superficial layers of the epithelium. The connection stated by Kuhne to exist between the above- described corneal nerves and the corneal corpuscles does not, according to Engelmann, occur. I have sought in vain in a great number of extremely successful specimens of the cornea of the Frog, prepared witli chloride of gold, for the fine straight striae stated by Lip- mann* to occur between the finest nerve fibres of the cornea and the nucleoli of the corneal corpuscles in such gold preparations, as well as for the straight strise which are seen proceeding from the nucleoli of the endothelial cells of the membrane of Descemet. I must rather maintain, from the examination of these gold specimens, that the finest nerve fibres are always to be seen in the corneal tissue running past the corneal corpuscles and their processes, and that therefore no connection of the corneal corpuscles with nerves can be demonstrated. THE MARGIN OF THE CORNEA. (HornhautfaljB, Limbus Cornece.) This is a part to which special interest attaches on account of the transitions and connections that here occur between the above-described layers of the cornea and other tissues. The external epithelium (a a,' fig. 393) is thus continued with- out interruption into the epithelium of the conjunctiva (a f the propria, and end in peculiar terminal organs, which he * Wiirzburg, 1869. t Ueber terminate Korperchen, 1860. 454 CONJUNCTIVA AND SCLEROTIC. names ' terminal bulbs/ and in which he recognizes a connective- tissue sheath, with nuclei, an internal bulb of finely granular, dull-shining material, and in the interior of this a pale terminal fibre, with a somewhat bulbous thickened end. Krause was successful in discovering these terminal bodies in Man, but in only a few animals, as in the Horse, Ox, Sheep, and Pig. In these animals their number was also proportionately small, and their distribution highly dissimilar and irregular. He observes that in some instances not one of these terminal apparatuses can be discovered over a considerable extent of surface, whilst in others they may be found accumulated in large numbers, closely aggregated upon a few fibres radiating from a common centre. On account of their variations, no attempt was made to obtain their precise number, though on a rough estimate he concluded that, in the various animals, as in Man, the number of terminal bulbs present in the connective tissue appeared to be the same, and that consequently there was as remarkably small a total number of nervous terminal apparatus in the conjunctiva as in the skin of the last phalanges of the fingers. The form , presented by the terminal bulbs varies in Man, as well as in different animals. In the former, as in the Quadrumana, they . are rounded or almost spheroidal ; in other animals they have in general a more elongated, oval, or even well-marked cylindrical contour, and they are then either straight or slightly bent. In regard to their dimensions, he states that they usually stand in direct proportion to the size of the animal, and that they also increase to some extent with the growth of the body, since, though they present the same characters in young animals as in old, they are of somewhat smaller size. In regard to their minute anatomy, the sheaths of the terminal bulbs consist of delicate connective tissue, which is continuous with the neuri- lemma of the entering doubly contoured fibre, and in which are scattered numerous for the most part elongated nuclei. The internal bulb, which is the chief constituent of the whole organ, is finely granular; and the terminal fibre, which is the extremity of the doubly contoured fibril, is imbedded in its substance. At its distal extremity it exhibits a slight bulbous enlargement, and usually ends at some distance from the anterior boundary of the internal bulb. In Man, several terminal fibres are NERVES OF THE CONJUNCTIVA. 455 usually met with in the interior of each bulb, which sometimes form a series of coils, and in most instances originate from a single afferent fibre." The statement of Krause, resting on these observations, to the effect that the terminal bulbs constitute the only mode of termination of the conjurictival nerves, was energetically dis- puted by J. Arnold,* who, on the one hand, regarded the terminal bulbs of Krause as not pre-existent, but as artificial products, and ascribed their origin to the method of preparation adopted by Krause, whilst, on the other, he described as the true terminations of the nerves, a pale plexus of nerve fibres situated in the more superficial layers of the tissue. Owing to his mode of preparation, which consists in macerating the specimen in acetic acid, or in rendering it transparent by alkalies, Krause, he concluded, could not observe this plexus, since the first reagent would destroy the most superficial layer of the mucous mem- brane, whilst the second would render all the parts so trans- parent that these pale fibres could not be perceived. The terminal bulbs described by Krause might, he thought, arise through the rupture of the doubly contoured fibres, partly* effected in the act of preparing the specimen, but partly also occasioned by the reagents applied by Krause, which lead to an escape of myelin, and rolling up of the torn fibres. Both circumstances would occasion the illusory appearance of the internal bulb, the neurilemma of the torn fibres representing the connective-tissue sheath of the terminal bulbs, and the terminal fibre being represented by the axis cylinder. Every- where the distal prolongation of the fibre may be discovered, and it is also easy to discover ends and fragments of the nerve sheath at the periphery of the so-called terminal bulbs. The objections raised by Arnold have found opponents in Liidden and Frey, who again admit the existence of terminal bulbs as a certainly established fact. Helfreich gives the following details from his own researches : — The nerves destined for the conjunctiva pass to it from the inner and outer canthi, where the several branches are given off from the main trunks, and pursue a more or less sinuous * Virchow's Archiv, Band xxvi. 456 CONJUNCTIVA AND SCLEROTIC. course. It is, however, chiefly the trunk entering at the inner commissure that contains the principal portion of the fibres, and is hence remarkable for its size and the much larger num- ber of its branches. He was able to establish this type of aerve division in all the' specimens prepared from various animals that he examined ; the less important differences met with in a few instances, as, for example, a more or less superior point of entrance of the internally situated main trunk, are only incidentally mentioned. In consequence of the speedy division and subdivision of the two principal trunks, and especially of the inner one, a close and delicate plexus is formed, in which an exchange of a few fibres takes place bet ween the smaller branches. The principal portion of the branches constituting this plexus stretches toward the anterior half of the conjunctival sac; and to its palpebral portion, whilst the fornix contains but few small branches, and the visceral lamina of the same receives generally only a third or fourth part of the nerves passing to it. As has been already remarked, the number of the nerves entering at the inner commissure of the conjunctival sac is far greater than at the outer side, and this preponderance con- tinues to be so expressed (notwithstanding the large number of fibres given off for the supply of the membrana nictitans), in the further distribution of the nerves, so that the branches coming from the inner side pass beyond the antero-posterior median line of the conjunctival expansion, and thus only the smaller lateral portion of the sac is supplied with fibres coming from the outer commissure. Moreover, so far as regards another relation, namely, the proportion of nerves distributed to the upper and lower lids, some variations occur, in accordance with the special anatomical relations of the particular animal under examination. In the Frog, for example, where the membrana nictitans, by virtue of its peculiar arrangement and its large extent, not only represents the lower lid, but also fulfils the greater part of the functions which in other animals are per- formed by the upper lid, the richness of its supply of nerves may considerably exceed that of the latter. A modification again occurs in Birds, where the membrana nictitans is indeed present as an integral constituent of the conjunctival sac, but in which the lower lid surpasses the upper in anatomical extent NERVES OF THE CONJUNCTIVA. 457 and physiological importance. On the other hand, in regard to the higher animals, the Mammals, and Man himself, the opposite relation to that of the Frog holds, and the upper lid is more richly supplied with nerves than the lower. Finally, in regard to its origin, the internal medial trunk is to be regarded as one of the terminal branches of the infra- trochlearis, and the lateral as the termination of the nervus lachrymalis, both of which proceed from the first branch of the trigeminal nerve. After forming the coarse-meshed plexus in the subcoa- junctival, and in the deeper layers of the conjunctival tissue, the nerves, continually becoming smaller till they are com- posed of only a few fibres, gradually pass forwards. These branches never exhibit any plexiform anastomoses. The relation of the smallest trunks, which are still composed of from two to three doubly contoured fibres, is in some animals, as, for example, in the Frog, so regular that it may here be minutely described. After the trunks of the last order have extended as far as to the plane just beneath the last layers of the vascular capillary plexus, division once more occurs, owing to which the still doubly contoured fibres, as they part from each other, run in a direction nearly at right angles to that of the trunk, and may be followed for considerable distances, maintaining a perfectly straight course, or being but slightly sinuous. A system of more or less parallel doubly contoured fibres is thus produced, which lies beneath the capillaiy net- work. In other animals the course and mode of division of the ultimate trunklets composed of doubly contoured fibres is less regular ; and it is only necessary to state that, rising above the vessels in the most diverse vertical oblique direction, they gradually reach the surface, where, in the last division of the dark fibres, their transition into non-medullated fibrils takes place. An exception to this is met with in certain fibres which only gradually ascend, as Helfreich satisfied himself, not in surface preparations, but in a considerable number of vertical sections in various animals. In this case a single fibre proceeds from a trunklet that is still composed of a large number of doubly contoured fibrils, and runs nearly in the middle of the matrix of the conjunctiva ; the fibre at this point 458 CONJUNCTIVA AND SCLEROTIC. suddenly loses its medullary sheath, and, ascending vertically again, bends at right angles to its former course to enter the subepithelial plexus of pale fibres, in which it runs for some distance, as may be easily demonstrated in more obliquely made vertical sections. Reference must not be omitted to those pale fibres which enter the tissue on the same plane as the larger vascular and nervous trunks, and are characterised by a very sinuous course, and by preserving their original direction for a considerable distance. In consequence of this they only gradually pass for- wards, and then entering the general subepithelial nervous expansion, can no longer be separately followed. In this course they often come into relation with the larger vascular trunks, immediately around and on which they form numerous plexiform loops, and run, sometimes for long distances, upon the vessels themselves. But as these relations can only be ob- served in preparations of moderate size, we must often abandon the attempt to follow them out. Nevertheless, Helfreich was successful in a large number of cases in following them upwards towards the epithelium, and saw them enter the general plexus found beneath this. During their long course they exhibit numerous varicosities and many clusters of nuclei. As already mentioned, the trunklets of the last order are composed of two, or at most three, doubly contoured fibres. The latter lose their medullary sheath at the point of their ultimate division, but not previously, during their common course. A nucleus usually occupies the angle of division, and this shows also a slight varicose enlargement, at which point the pale fibres commence. These fibres are of extraordinary length, and a single fibril may often be followed through several fields of the microscope ; they usually run in a straight direction, and consequently only present slight and occasional loopings, or a gradually bending upwards to a higher level, crossing and interweaving with the t capillary plexus. The number of these non-medullated fibrils as they run upward through the capillary plexus is extraordi- narily great, so that the total number of the fibres running between the capillaries and immediately subjacent to the epithelium exceeds many times that of the fibres present in the STRUCTURE OF THE SCLEROTIC. 459 different trunks. It is self-evident that their number must be very different in the several regions of the conjunctiva, some- times being relatively small, so that a direct estimate of their number can be effected, and the several elements may be readily followed to their termination. Thus, as the result of the several larger fibrils running for long distances with continual subdivision, and their lateral branches repeating this process, a very dense plexus of large and also of extremely fine pale fibres is produced, which gradually extends through the layer of blood capillaries to the inferior surface of the epithelium. The fine fibrils found im- mediately beneath the epithelium have themselves also a very long course, give off innumerable fine branches at acute angles, and ultimately terminate close beneath the plane of the deepest cell layer, where they may easily, in preparations freed from the epithelium to which the account hitherto given applies, be discerned amongst the cells that here and there remain attached. Morano* has been engaged for several months, under Strieker's direction, in ascertaining the mode of termination of the nerves of the conjunctiva. The positive results obtained, however, are very few in number. They believe, though they are by no means certain, that they were able to follow the nerves in some instances upwards between the epithelial cells. These researches have, however, rendered it probable that more fortunate microscopists may be able to follow the nerves into the epithelial stratum. TUNICA SCLEROTICA. The scleroticf is bounded in front by the cornea, whilst pos- teriorly it is separated by a constriction from its continuation, the fibrous sheath of the optic nerve. Where the optic nerve enters the cavity of the sclerotic, the connective tissue investing its fasciculi joins the tissue of the sclerotic. This junction remains even after the optic-nerve fibres have been removed by * Centralblatt, April, 1871. •(• Briicke, Anatomische Beschreibung des menschlichen Augapfels, (Ana- tomical description of the human eye.) Berlin, 1847. 460 CONJUNCTIVA AND SCLEROTIC. maceration, in the form of a thin lamina perforated by many small holes, which is continuous with the internal surface of the sclerotic. This lamina is the so-called lamina cribrosa. The foramina correspond to the several fasciculi of the optic-nerve fibres which traverse it. Near its centre are two close together, of large size, through which the retinal vessels pass. The sclerotic becomes denser and more uniform in structure as we pass from without inwards. Irregularly shaped flat pigment cells, with clavate or radiating processes-, are deposited in the very dense tissue lining its smooth inner surface, and this is especially the case in dark eyes, giving to it, when they are present in large numbers, a brownish aspect. The arrangement of the fibres of the sclerotic was first described by Valentin.* Briicke was only able to support his statements so far as to say that, speaking generally, there were antero-posterior and circular fibres in the sclerotic, forming by their decussation a dense tissue, and that the fibres of the tendons of the recti muscles, after they have reached the sclerotic, spread out in a fan-like manner, and, dipping into the mesh- work of the sclerotic, essentially strengthen its anterior portion. That the sclerotic fibres are composed of connective tissue has already been shown at p. 79, vol. i. Cellular elements resembling the corpuscles of the cornea are distributed through the matrix. If a point of nitrate of silver be drawn across the sclerotic of a live Rabbit, the delicate lines of the serous canals may be seen in surface sections, when it is completely reduced. On the other hand, preparations made with chloride of gold give a positive to the negative images of the silver method. I have, indeed, only seen the latter in a preparation exhibited to me by Dr. Carmelt, of New York ; in this instance, how- ever, they were so sharply defined that no doubt of their pre- sence could exist. The cells that lie in these spaces contain, in many Mammals, pigment granules. f In Birds the sclerotic is composed of hyaline cartilage, in- vested both externally and internally by connective tissue. * Repertorium, Band i., Heft, iv., p. 301. f Leydig, loc. cit. STRUCTURE OF THE SCLEROTIC. 461 At the anterior margin of the sclerotic, and sometimes around the entrance of the optic nerve, there is in Birds a bony ring, composed of a series of plates. Hyaline cartilage is also present in the sclerotic of Amphibia and Fishes. Helfreich* took the opportunity, in his paper on the nerves of the sclerotic, to make a few observations upon the structure of the sclerotic of the Frog, which I shall here reproduce. The connective-tissue layer closely adhering by its inner sur- face to a slightly rose-coloured layer of cartilage, with extraordi- narily distinct and beautifully marked cells, appeared of a dark olive tint, composed of compact parallel and vertically arranged fibrous bands, to the outer side of which was applied, though separated by a sharp line of demarcation, the investing looser sheath of connective tissue. Antero -posterior sections of the sclerotic carried through its whole extent showed that the connective-tissue and cartilaginous layers vary in thickness at different points. The cartilaginous layer was thickest at the posterior pole of the globe of the eye, and diminished rapidly at the anterior part, terminating by a rounded edge just in front of the plane of insertion of the recti muscles. The connective-tissue layer exhibited the converse relation in regard to its thickness at various points. The cartilaginous layer was completely homogeneous, and never presented any interrup- tions or openings for the passage of vessels and nerves ; whilst in the connective-tissue layer these last presented the same clean aspect and elegance as in surface views. In the posterior parts of longitudinal sections the coarser trunks and doubly contoured fibres were visible, and towards the anterior por- tions, as far as to the border of the cartilaginous layer, and even beyond this, the fine light-blue violet-tinted axis cylinders were seen running for considerable distances either straight or with a slightly sinuous course. Here and there they exhibit slight varicose enlargements, and in regard to their course it was noticeable that they gradually approximated the line of demarcation between the connective-tissue and the cartilaginous layers. * Loc. cit. 462 CONJUNCTIVA AND SCLEEOTIC, The larger nerve trunks, everywhere composed of somewhat separated doubly contoured nerve fibres, exhibited after under- going manifold division, and after running for a greater or less extent forward, the most distinct connection with the already mentioned longitudinally running axis cylinders, with which they are continuous in such a manner that the ultimate trunk- lets, composed of two doubly contoured fibres, lose their medulla at the point of division. This suppression of the medullary sheath, as well as the course of the pale fibres towards the line of demar- cation of the connective-tissue and cartilaginous layers, could be satisfactorily demonstrated by altering the focussing. Owing to repeated division, there is a rapid increase in the number of the axis cylinders, just like that which has been already de- scribed as occurring in the subepithelial plexus of the conjunc- tiva. The fibres were observed to become progressively finer, and were ultimately lost, after pursuing a long course, and whilst of extremely small diameter, in the substance of the fibrous tissue very near the cartilage. In this course they frequently crossed one another, but never communicated, and thus formed a peculiar kind of plexus ; their extremities were marked, not by any increase in diameter, but rather by a diminution, since they simply ran out to a point. Through- out their whole course they were frequently seen to be in contact with the numerous connective-tissue corpuscles dis- tributed through the fibrous bands, but their extremities were never, in spite of the most careful examination, observed to be directly continuous with the processes of the latter. In the Pigeon and Fowl Helfreich found no traces of nerves having an analogous distribution to those above described in the Frog. Commencing from the plane of insertion of the recti muscles, however, were trunklets running forward throughout the whole circumference of the fibrous capsule ; but these, on ac- count of the absence of division, as well as on account of their relations generally, he regarded as nerves that are merely traversing the tissue on their way to the ciliary muscle, iris, cornea, etc. They had a similar destination in the sclerotic of the Mouse and Eat, in which animals the procurement of good specimens was rendered very difficult on account of the mani- fold and intimate connections between the sclerotic and choroid. NERVES OF THE SCLEROTIC. 463 At the same time the anterior distribution of the ciliary nerves was here very clearly brought into view. In his observations on the sclerotic of the Rabbit he always selected young albino animals, and here found that, quite in correspondence with the relations of the nerves entering the sclerotic of the Frog, there was a primary expansion of exactly the same kind, and a single division of the trunks, which were then speedily lost. The whole appearance of this expansion was neverthe- less so similar to the type of that above described in the Frog, that he had no hesitation in regarding the latter decisively as composed of nerves destined for the fibrous membrane ; and he had as little doubt that in the same animals the conjunc- tival nerves terminate immediately beneath the epithelium, although they only stain with gold as far as to the axis cylinders. IX. THE LACHEYMAL GLANDS. BY FRANZ BOLL. GENEEAL STEUCTUEE. — The lachrymal glands of Man and Mammals agree in all essential points of structure with the sali- vary glands (see chapter xiv., vol. i.), and belong, therefore, to the so-called acinous type of glands. Like the salivary glands, they are subdivided by a richly developed system of frequently decussating septa, which are given off from the capsule, and dip into the substance' of the organ, into a number of polyhe- dric bodies of the most diverse form, but in general of tolerably constant size ; and these septa, when examined under the micro- scope, are seen to be composed of loose fibrillar connective tissue. The principal portion of the polyhedric bodies, which in a strict sense we would characterise as the proper parenchyma of the gland, is seen in transverse sections to be almost exclusively composed of alveoli and bloodvessels. It is only in rare in- stances that we are fortunate enough to exhibit in one and the same section of a parenchymatous body the excretory duct together with the accompanying vessels and nerves. All these structures, the trunks of which enter at the hilus of the gland, run collectively imbedded in the loose connective tissue of the septa^ from whence they branch off usually at right angles into the parenchymatous bodies, accompanied for a short distance only by connective-tissue fibrils. Apart from these remains of the so-called interstitial tissues, the acini themselves contain no fibrillar connective tissue. 2. THE ALVEOLI.— The form and dimensions of these bodies, CELLS OF THE LACHRYMAL GLANDS. 465 which form the proper secreting parenchyma, present but slight variations. They form sacculi, in which we can distin- guish an investing membrane (membrana propria), and the secreting epithelium. The epithelial cells are of very various shape, but form polyhedric bodies of nearly equal size, that are bounded by a variable number of surfaces which come into apposition at dif- ferent angles, but almost always have sharply defined borders. Not unfrequently tolerably well-defined delicate grooves are met with upon the surfaces. None of the different diameters of the epithelial cells are especially developed at the expense of the others, so that they invariably appear in the form of irregular cubes. The spheroidal homogeneous nucleus, not always containing well-marked nucleoli, is in all instances excentric, being situated near the base of the cell which is turned towards the membrana propria. A tolerably strong and long bright process, staining deeply witli carmine, is, it would appear, constantly given off from the cell (Heidenhain), which seems to end by a free extremity at some distance from the cell, without forming any other connection. Its length may almost amount to the diameter of the body of the cell. The other angles of the cells are not unfrequently drawn out into long processes, the size of which is usually considerably less than that of the basal process. Not unfrequently, also, the nucleus of the cell exhibits a pointed process, which can never be followed beyond the limits of the cell, but which constantly runs in the direction of, and is sometimes contained within, the basal process itself. As Henle first demonstrated, and as Heidenhain has lately again pointed out, the acinous glands are divisible into those which contain mucus in their secretion, and into those in which it is absent .Certain histological characteristics of the secreting parenchyma correspond to these peculiarities of the secretion, especially in regard to the glandular epi- thelium, which, when no mucus is present, constantly remains protoplasmatic, whilst when it is present, the protoplasm undergoes a metamorphosis into mucus that is very easily demonstrable under the microscope. The lachrymal glands of Man and the other animals examined, as the Sheep, Ox, VOL. III. H H 466 THE LACHRYMAL GLANDS, BY FRANZ BOLL. and Horse, belong to the second kind. In the parenchyma of these glands not a single cell that has undergone mucous degeneration can be demonstrated. It may therefore be con- cluded with certainty that the secretion of the lachrymal glands never contains mucin.* According to the researches of Heidenhain, the so-called lunula, first described by Giannuzzi, is formed by a collection of protoplasmatic cells, usually appearing sickle-shaped on section, which are perhaps destined to supply the glandular epithelium that undergoes the mucous metamorphosis. It is obvious that as the lunula is only present in glands in which a mucous degeneration of the secretory elements occurs, we coukl not expect to meet with a lunula in the lachrymal gland, the cells of which, like the epithelial cells of the sub- maxillary gland of the Rabbit, remain permanently proto- plasmic. The alveoli are invested by a fine membrane, the so-called membrana propria, the structure of which is very peculiar. It is alwaj^s composed of flat stellate cells, which frequently inter- communicate by means of their often very largely developed processes, that run round the alveoli like hoops. These finely striated, more or less slender or broad processes which constantly lie flat on the curvature of the alveolus, proceed from the nucleated central portion of the cell ; they do not however form an interrupted investing membrane like basket-work to the alveolus, but appear in the form of thickened striae and ribs in a membrane firmly surrounding and enclosing the alveolus, composed of these stellate cells in a manner of which it is not very easy to give a clear description. The cells and their processes, in their relation to the substance of the membrana propria, may best be compared to the ribs of a leaf, or with toes between which a swimming membrane is expanded. We cannot however draw a completely sharp line of distinction between the ribs and the substance of the membrane, or show * The only analysis of the tears of Man hitherto published, that by Frerichs (in the article ' Tears,' in Wagner's Handworterbuch der Physio- logic, Band iii., Abtheil i., p. 618), certainly admits the existence of a small quantity of mucus. But in this instance the secretion of the Meibomian follicles was not excluded. MEMBRANA PROPPJA OF THE ALVEOLI. 467 that these stellate cells are anything different from the mem- brane. The whole thing constitutes an histological unity ; the stronger longitudinally striated ribs are distinguishable from the matrix of the membrane, but pass quite gradually and imperceptibly into the matrix, which last, usually on both sides of the ribs, becoming gradually fainter, exhibits a longi- tudinal striation parallel to the ribs. This description of the structure of the membrana propria, the correctness of which may be easily established by the examination of preparations of glands treated with iodine- serum and teased out with needles, or of sections of glands cautiously hardened in Muller's fluid and brushed out at their free borders, forms a most satisfactory explanation of the extremely various appearances which frequently occur in the same preparation, according to the more or less pro- longed maceration to which it has been subjected, or the greater or less facility with which the tissue breaks down. Owing to these causes, appearances may be obtained from the teasing out of glands macerated in diluted Muller's fluid of a variable and, as it would almost appear, a completely con- tradictory nature. Sometimes isolated alveoli are met with, the epithelial cells of which appear to be contained in a perfectly closed and for the most part strongly wrinkled homogeneous sac; sometimes, on the other hand, there are naked groups of epithelial cells which still preserve the form of the alveoli, and to which a few isolated stellate cells adhere. Then, again, perforated basket-work masses, composed exclu- sively of stellate cells and their processes, float in the fluid, and in the cavities of these a few secretory epithelial cells are usually discoverable. In addition to an innumerable number of isolated gland cells, isolated cells are also to be found of the same kind as those that form the membrana propria. The form and size of these are subject to considerable differences. In young animals (as may best be seen in the Calf) they are of larger size, not only in regard to the central mass, but their pro- cesses are more developed. Each cell is gibbous in form, the centre being sometimes protruded in the form of a vesicle ; and thus, when seen in profile, it often appears like a sickle, which in sections of the hardened gland not unfrequently encircles 2 468 THE LACHRYMAL GLANDS, BY FRANZ BOLL. the alveolus. If the fluid be moved by pressure on the covering glass, the transition of such a crescentic cell into a stellate multipolar cell may often be observed under the microscope. In young animals a small quantity of granular substance occupies the centre of the cell, surrounding the .usually round nucleus, which contains no distinct nucleolus. In older animals this small remains of protoplasm has almost entirely disappeared. The substance of the flat, frequently quite ribbon-like processes is pale, and sometimes finely longitu- dinally striated. They divide dichotomously at more or less acute angles, and not unfrequently a thick process may be seen suddenly breaking up into several branches. Some of the processes of these stellate cells penetrate, as may also be shown in isolation preparations, between the epi- thelial cells of the alveolus themselves. It was maintained by Pfliiger, who first accurately examined them in the salivary glands, that these processes are directly continuous with the processes of the secretory epithelial cells, and that from this connection with true epithelial structures the nervous nature of the stellate cells can be demonstrated. Although I am in possession of numerous specimens in which at first sight there appears to be a direct continuity bet ween the two cells,! have not been able to satisfy myself that such a connection really exists. 3. THE INTERSTICES OF THE ALVEOLI. — Whilst the inner sur- face of the membrana propria is lined by the epithelial cells of the alveolus, the external surface remains free, and during life forms the boundary of a space filled with lymph, which, in the case of each parenchymatous body of the gland, occupies the in- terval between the external wall of the capillaries and that of the alveoli, and the presence of which can be rendered evident by the most diverse methods, as by simple puncture injections, or by the production of artificial oedema in the gland, in Ludwig's method. The form and extent of these spaces in the secretory paren- chyma must obviously be extremely complicated. In sections of the several parenchymatous bodies, when injected, which is best accomplished with cold fluid Berlin blue, each alveolus of the gland, without exception, appears to be surrounded by a. LACUNAR SYSTEM OF THE ALVEOLI. 460 coloured ring. The alveoli themselves, uncoloured by the in- jection, lie separately on a coloured ground, an appearance that is often repeated with perfect regularity over a surface present- ing forty to fifty alveoli. If the bloodvessels have been coin- cidently injected with a different colour, as, for example, with vermilion, their irregular peculiarly inconstant division and red colour form a striking contrast to the very regular dispo- sition of the system of canals injected with blue. In fine sec- tions, the bloodvessels, running in the form either of straight or tortuous red lines, or, when seen in section, of red points only, are invariably surrounded by a blue-coloured space, identical in fact with that which surrounds each individual alveolus. These appearances, repeated with unvarying regu- larity in every section, admit of no other explanation than that an extraordinarily rich, freely intercommunicating system of fissures traverses the parenchyma of the entire gland, surround- ing every alveolus and every bloodvessel. It is not that there is a separate sheath for each alveolus and bloodvessel, consti- tuting a peri-alveolar or perivascular space, but a single, con- 'inuous, very complicated cavity surrounding every parenchy- matous body, which completely separates the bloodvessels from the alveoli, and which everything that the blood brings to the secreting parenchyma must first traverse before it can enter into the secretion. The already extremely complicated hlstological and topo- graphical relations of this cavity are rendered still more com- plicated by the circumstance that a very rich system of various- sized fibres, as well as of stellate cells, is stretched in its interior between the alveoli. On sections of the hardened gland these cells and their processes may be very easily demonstrated. They are to some extent in relation- with the stellate cells com- posing the membrana propria, whilst a few processes also run out to adjoining alveoli, fastening and attaching the walls more or less intimately together. Not unfrequently also cells are found which, lying between two alveoli, belong as much to the investing membrane of the one as the other, sending their pro- cesses into both. Cells are also frequently found lying almost perfectly free between the alveoli, or connected only very loosely by means of their processes. It is remarkable that these inter- 470 THE LACHRYMAL GLANDS, BY FRANZ BOLL. stitial connective-tissue cells join only with the external wall of the alveoli, and never with the capillaries, which do not in any instance possess a membrane corresponding to an adven- titia capillaris. Giannuzzi, the discoverer of this lacunar cavitary system in the secreting parenchyma, regards it as a true lymphatic space; that is to say, as standing in direct connection with, and injeet- ible from, real lymphatics, and as analogous with the spaces stated by Ludwig and Tomsa to surround the canaliculi and blood vessels, of the testis, the injection of which can actually be accomplished from the lymphatics of the cord. This, how- ever, has certainly not yet been satisfactorily effected in the case of the above-described space. Numerous attempts failed in consequence of the delicacy of the lymphatics emerging from the glands, and the resistance presented by their valves. Yet appearances are not unfrequently presented in specimens made by simple puncture injections, which at least render it probable that the spaces in the several parenchymatous bodies are in direct communication with true cylindrical lymphatics running in the loose connective tissue of the fissures separating the several parenchymatous bodies. In what mode, however, the cavity situated within the several parenchymatous bodies, and here sharply defined by the external surface of the mem- brana propria and of the blood capillaries, is shut off towards the larger trunks of the excretory ducts and bloodvessels, as well as towards the connective-tissue septa, has not as yet been clearly demonstrated. 4. THE EXCRETORY DUCTS.— The lachrymal ducts are lined by a single layer of low columnar epithelial cells. Where they enter the gland they speedily break up into numerous branches, which have a similar low columnar epithelial lining, and from these again are given off those ducts that Pfliiger has termed " salivary tubes " in the case of the salivary glands, and which may be most appropriately termed lachrymal tubes. Their internal diameter is usually small, and they are lined by elon- gated columnar cells, which are characterized by presenting a very distinct fibrillation at their basal extremity, which Pfliiger has described at great length, and has brought into THE EXCRETORY DUCTS. connection with the regeneration of the gland tissue. Lastly, from these tubes, lined by tall columnar cells, richly fibrillated at their base, and which appear to be present in all similarly constructed acinous glands, fine canals are given off' either by gradual or sudden transition of the epithelium. The canals are not much thicker than capillaries, and present characters which, both in regard to their size and in the dimensions of the cells composing the simple epithelial tubes, are similar to those of all the allied acinous glands. These cells are always much flattened, and are usually characterized by the presence of very substantial processes, which give them a fusiform appearance, or some form analogous to a spindle. They lie with their long axis parallel to the axis of the epithelial tube, and are frequently arranged in an imbricated manner. The canals are finally connected with the alveoli by means of short branches, which, being formed for the most part of from four to six epithelial cells, are prolonged into the interior of the alveoli, where they are invested almost circularly by the peculiar secreting epithelial cells. These last, and still more the former, cells of the excretory ducts, occupying almost the centre of the alveolus, penetrate by means of their processes between the secreting epithelial cells, and have been named by Langerhans (in the pancreas) ' centro-acinar ' cells. Whilst formerly a very simple form was attributed to the cavity situated in the interior of the alveolus, into which the secreting epithelial cells poured their secretion, investigations undertaken with improved methods of injection by Giannuzzi, Langerhans, Ewald, and Saviotti, have shown that the simple short and minute excretory duct of the alveolus breaks up into a very rich, much branched, and frequently anastomosing plexus of extremely fine cylindrical canals, which, in exactly the same mode as that given by Hering of the relations of the finest biliary ducts to to the hepatic cells, invests the individual epithelial cells, and includes them in its meshes. The canals lose their proper membrane, and beyond this point merely form sparingly distributed ducts situated between the variously formed polyhedric gland cells, which are in close apposition with each other, and are provided both along their borders and surfaces with grooves. 472 THE LACHRYMAL GLANDS, BY FEANZ BOLL. 5. THE NERVES. — The nerves of the lachrymal glands run constantly by the side of the branches of the bloodvessels and the excretory ducts. They are, even in the trunk of the lachrymal nerve, for the most part non-medullated. I have never been able to follow them quite satisfactorily beyond the salivary tubes, which they constantly accompany, and I can state nothing with certainty in regard to their termination or their anatomical relations to the secretory elements. No nerves exist in the interior of the parenchymatous bodies in the interstices between the alveoli; and if they are really in direct connection with the secretory epithelial cells, they must run to the alveoli with the finest excretory ducts.* 6. LITERATURE. — The histological literature of the lachrymal glands is identical with that of the acinous glands. Passing over the older works, I subjoin the complete literature since the important researches of Giannuzzi on this subject, which were made in Ludwig's laboratory, and the coincidentally made, and not less important, works of Pfliiger. LITERATURE. G. GIANNUZZI, Von den Folgen des beschleunigten Blutstroms fiir die Absonderung des Speichels. (On the consequences of accele- ration of the blood current upon the secretion of the saliva.) Sachsische academische Sitzungsber., mathem. phys. Cl., 27 Nov. 1865. E. F. W. PFLUGEK, Die Endigungen der Absonderungsnerven in den Speicheldriisen. (The termination of the secretory nerves in salivary glands.) Bonn, 1866. E. F. W. PFLUGEE, Die Endigungen der Absonderungsnerven in den Speicheldriisen und die Entwickelung der Epithelien. (The termination of the secretory nerves in the salivary glands, and the mode of development of epithelial cells.) SCHULTZE'S Archiv, Band v., 193. * The appearances which I have indicated in my first work, where non- medullated nerves run to the blunt end of the alveoli, can only occur at the margin of the parenchymatous body opposite the connective-tissue septa. LITERATURE. 473 E. F. W. PFLUGER, Die Encligungen der Absonderungsnerven in dem Pancreas. (The termination of the secretory nerves in the pancreas.) Idem, 199. The observations of Ewald are here given. E. F. W. PFLUGER, The salivary glands in this Manual, vol. i., p. 423. J. HENLE, Eingeweidelehre, 63 — 69. A. KOLLIKER, Handbuch der Gewebelehre. 5th edition, 1867, p. 357. R. HEIDENHAIN, Beitrage zur Lehre von der Speichelabsonderung. (Essays on the secretion of saliva.) Studien des physiol. Instituts zu Breslau, iv. 1868. F. BOLL, Ueber den Bau der Thranendriise. (On the structure of the lachrymal glands.) M. SCHULTZE'S Archiv, Band iv., 146. F. BOLL, Die Bindesubstanz der Driisen. (The connective tissue of glands.) Ebenda, v. 334. F. BOLL, Beitrage zur mikroskopischen Anatomie der acinosen Driisen. (Essays on the microscopic anatomy of the acinous glands.) Inaugural Dissertation. Berlin, 1868. P. LANGERHANS, Beitrage zur mikroskopischen Anatomie der Bauch- speicheldriise. (Essays on the microscopic anatomy of the pancreatic glands.) Inaugural Dissertation. Berlin, 1868. G. GIANNUZZI, Recherches sur la structure intime du Pancreas. (Researches on the minute anatomy of the pancreas.) Comptes rendus 1869, Mai, Ivii. 1280. G. SAVIOTTI, Untersuchungen iiber den feineren Bau des Pancreas. (Researches on the minute anatomy of the pancreas.) M. SCHULTZE'S Archiv, Band v., 203 and 404. CHAPTER XXXVII. UTERUS, PLACENTA, AND FALLOPIAN TUBES.* I. — UTERUS. BY DR. R. CHROBAK. THE peritoneum, which forms an extremely delicate membrane investing the uterus, reaches on its anterior surface a little below the constriction corresponding to the os internum, and on the posterior surface as far as to the attachment of the wall of the vagina to the cervix uteri.f Separating from it at these points, it forms the excavatio vesico- and recto-uterina. Ante- riorly as well as posteriorly it is firmly connected with the mus- cular tissue of the uterus by compact connective tissue, and is so attached that the boundary of that portion which covers the anterior surface, and which can only be detached with difficulty, if at all, forms an angle opening upwards, the apex of which is approxirnatively in the centre of the anterior surface of the uterus.J Laterally the intimate attachment of the peritoneum to the uterus only extends to about the distance of one centimeter below the Fallopian tube; beyond this point the peritoneal laminae separate from each other in order to permit the blood- vessels, lymphatics, and nerves to gain entrance into the sub- stance of the uterus. * The microscopic researches for this essay were made in the Physio- logical Institute of Vienna. t Luschka, Anatomie, Band ii., p. 360. £ Henle, Anatomie, Band ii., p. 486. MUSCULAR TISSUE OF THE UTERUS. 475 The principal portion of the substance of the uterus is com- posed of unstriated muscular fibres which are simply super- imposed on one another in a succession of layers ; but since even in the pregnant uterus it is not practicable to dissect off the several layers separately, considerable confusion prevails in regard to their arrangement and subdivision. If the development of the layers be followed, we may reduce the number of layers to three ; an internal, chiefly consisting of circular fibres; a middle, in which the fibres run for the most part longitudinally ; and an external accessory layer. The external layer, which is situated immediately beneath the peritoneum, and is intimately connected with it, is by far the thinnest, but at the same time is the most distinct and independent; it is prolonged upon the adnexa of the uterus. This external layer is chiefly formed of a fasciculus of longi- tudinal fibres on the posterior wall of the uterus arising from the margin of the cervix,* though these fibres pass to enter into its formation from the sides of the uterus, and it then spreads over the organ as far as to the round ligaments. The second layer, separated from the foregoing by many transverse fasciculi, is composed of numerous strong muscular fasciculi,")* extending from behind forward over the fundus; and these again, diverging anteriorly and posteriorly, decussate fre- quently with other short fibres. Near the middle of the fundus this muscular layer fuses to a certain extent with the superficial one.J Beneath this, which is the last distinctly recognizable layer, and which, like that above mentioned, does not cover the sides of the uterus, are a number of tolerably strong smooth and short fasciculi, pursuing for the most part a circular course, which decussate at the most diverse angles, give off a few processes to the ligaments, and run in such a manner that, speaking broadly, those which are superficial in front dip into the deeper part of the uterus posteriorly, and vice versa. This layer is by far the most important of all those of which * Helie, Recherches sur la disposition des Fibres musculaires de V Uterus. Paris, 1869. t Pappenheim, Vorlaufige Mittheilung. Korn and Wunderlich's Viertel jahrschrift, 3 Jahre, Heft. i. £ Helie, loc. cit. 476 UTERUS, BY DR. R. CHROBAK. the uterus is composed, and is recognized by its remarkably large and, during pregnancy, thick- walled vessels. The innermost layer, which, according to Luschka,* is to be regarded as the most important of all, since it exhibits traces of the early division of the uterus into two lateral halves, is essentially composed of circular fibres, which, proceeding from the circular fibre layer of the uterine portion of the Fallopian tubes, forms successively larger annuli that meet in the middle line, and not only form the foundation of the body of the uterus, but can be traced into the cervical region, and from thence into the vagina. (The so-called internal and external sphincters of the os uteri belong to this circular fibre layer.) Besides this well-marked circular layer, a triangular layer of longitudinal fibres is present on the anterior and posterior wall of the uterus, f the apex of the triangle being directed downwards ; from this delicate muscular fasciculi can be traced into the mucous membrane. The regular arrangement of the fibres described above is less observable in the cervical region of the uterus,J where they are grouped into about three layers (Henle). The circular fibres of the innermost layer of the body form by far the largest middle layer, which is bounded externally by longitu- dinal fibres that are in great part lost in the vicinity of the bladder, vagina, and urethra, whilst the innermost layer is likewise composed of longitudinal muscular fibres that sup- ply the mucous membrane with fibres, and interweave at the os externum and internum with the circular fibre layers forming the sphincters. According to Guyon,§ the sphincter of the os internum forms an isthmus three milli- meters in length. All these layers of the uterus are for the most part composed of contractile fibre cells, so firmly united into fasciculi and flat muscular expansions by means of a strong cementing material * Luschka, loc. cit. t Helie, loc. cit. J Retzius, Struldur des Uterus, in Froriep's Tagesbericht, in Canstatt's Jahresbericht, Band i. , p. 64, 1850. § Guy on, Etude sur la cavite de V Uterus a I'etat de vacuite, Journal de Physiologic, Tom. ii. MUSCULAR TISSUE OF THE UTERUS. 477 that it is only with great difficulty that they can be isolated. The fasciculi are again combined together by a large quantity of nucleated connective tissue and a few elastic fibres. The fibre cells of the uterus, as a rule, are fusiform, and often present very attenuated extremities ; in the pregnant condition, however, (besides the formation of new cells,) the contractile elements attain so great a development that their length, instead of 0'045 of a millimeter, becomes O660 of a millimeter, and their breadth, which was originally 0'009 — 0'014, increases to 0-074. Many of the muscular fibres have shovel-like, flat- tened, and dentated edges. The transverse section of the cells presents a rounded, ovoid, three to five-angled outline cor- responding to the several angles seen in surface views. The cell substance is only unclouded in the fresh condition, and during the first two-thirds of pregnancy ; it is at this period translucent, and allows the nucleus, which is never absent, and the granules, which are also constantly present at the two extremities, to be distinctly recognized * The nucleus, always single, is elliptical, fusiform, or rod- shaped, and varies from 0-002 to 0-015 of a millimeter in length, and from 0-001 to 0-003 of a millimeter in breadth,f (and these measurements also become nearly doubled in pregnancy.) In the greater number of cases it lies in the ventricose enlargement commonly found near the centre of the cell, but is often also excentric or attached to the walls. The brilliant granules occurring in the nucleus are still a subject of controversy .J The measurements above given do not hold for the muscular fibres of all the layers, but only for those which play an im- portant part in the expulsion of the foetus. The superficial fibre cells are shorter, more slender, and more cylindrical, like the muscular cells of the innermost layer, the length of which only amounts to 0*018 — 0'034 of a millimeter,§ and which do not present any remarkable hypertrophy during pregnancy. The mucous membrane lining the interior of the uterus * Arnold, see this Manual, 1868, p. 192. t Frankenhauser, Die Nerven der Gebarmutter. Jena, 1867. I Hessling, Gewebelehre, 1866. Frankenhauser, loc. cit. Arnold, loc. cit. § Kolliker, Zeitschrift fur wissenschqftliche Zoologie, Band i. 478 UTERUS, BY DR. R. CHROBAK. terminates at the upper end of the isthmus by a sharply defined border * In the virgin it presents the appearance of a grey or pale pink membrane having a thickness of from 1 to 1*8 milli- meters, but becoming thinner towards the cervix and the orifices of the Fallopian tubes. f Its separation from the subjacent mus- cular coat is not very distinctly marked, and it cannot in conse- quence be dissected off in large flakes. Its surface is smooth, except near the orifices of the tubse, where it exhibits very small folds (small papillse, Hennig)4 In health it is covered with a thin layer of a more or less grey, transparent, and rather gluti- nous fluid, possessing a feebly alkaline reaction, and containing in variable, but small proportions, columnar cells, spheroidal granule cells, secretion of the uterine glands, a few cilia, and very rarely perfect ciliated cells ; in older persons, cholesterin, monads, algae, free fat, etc., may be found. (Donne, Taylor, Smith, Scanzoni and Kolliker, Hennig, Schlossberger, Haus- mann, and many others.) The mucous membrane does not possess any definite connec- tive-tissue framework. § (Henle states that he has here and there, by pencilling out the tissue, discovered a fine plexus of pale fibres. He noticed this also in specimens treated with alkaline solution). It consists of the tubular glands of the uterus, which we shall immediately proceed to describe, between which are large numbers of apparently free nuclei, having a diameter of 0006 to O'OOS of a millimeter, of elongated or variously formed polyhedric flattened cells, of fibre cells in every stage of development, of a relatively large quantity of intermediate substance, and of muscular fasciculi running up to the base of the glands from the innermost layers of the muscularis. The glandulce utriculares, first pointed out by Malpighi,|| * Virchow, in Froriep's and Schleiden's Notizen ueber die Bildung der .Decidua, (On the formation of the decidua.) t Robin, Memoire pour servir a VHistoire anatomique de la Membrane muqueuse de V Uterus, Archives general, Juillet, 1847. I Hennig, Der Katarrh, etc. § Henle, loc. cit. || Malpighi, Opp. 1687, vol. ii., p. 220. GLANDS OF MUCOUS MEMBRANE OF UTERUS. 479 then demonstrated by v. Baer,* Burckhardt,f Eschricht and E. H. Weber, J and more recently described by Krause, § Sharpey, || Reichert,1[ Bischoff,** and especially by E. H. Weber, ff only present one form in Man, whilst in many animals there are two varieties, though this is still to some extent a moot point. JJ They form csecal tubes of various lengths, usually simple, but often giving off from their centre, or just below this point, two, or rarely several, branched tubes, which are either co- lumnar or somewhat inflated near their extremities, and open into the cavity of the uterus, upon the surface of the mucous membrane. Looking down upon the free extremity, the dia- meter of the opening of which is somewhat larger than that of the gland canal, the tubes often appear laterally compressed or triangular. §§ They are twisted in the most diverse direc- tions, and even form corkscrew-like coils, so that the total length of the gland tube often considerably exceeds the thick- ness of the mucous membrane. Taken collectively, however, they preserve a vertical position in regard to the membrane, especially at the lower part of the uterine cavity, and near the openings of the Fallopian tubes, whilst in the upper part of the body, and in the fundus, they assume an oblique and often nearly horizontal position. * v. Baer, Untersuchungen uber die Gefdssverbindung zwischen der Mutter und der Frucht, (Researches on the vascular connection between the mother and the offspring.) Leipzig, 1828. t Burckhardt, Observationes anatomicce, Kas., 1854 J Eschricht and E. H. Weber, Braunschweigen Naturforscher Versamm- lung. § Krause, Anatomie, 2nd edit., Band i. || Sharpey, see Canstatt's Jahresbericht, 1843, Band i., p. 106. IT Reichert, Miiller's Archiv, 1843. ** Bischoff, Entwicklungsgeschichte der Hunde-eies, and Miiller's Archiv, 1846. ft Weber, E. H., Zuscitze wim Bauz und der Verrichtung der Geschlechts- organe, 1846, (Additions to our knowledge of the structure and disposition of the sexual organs.) £t See Sharpey, loc. tit. ; Ercolani, Giamb. delle glandule otricolare, etc. , 1868 ; and Friedlander, Untersuchungen uber den Uterus, 1870. §§ Hennig, Katarrh der weibliche Geschlechtsorgane, 1870. 480 UTERUS, BY DR. R. CHROBAK. The substance of these glands can only be isolated with great difficulty in the healthy uterus. It is more easy to effect this during menstruation and pregnancy, though, on account of their numerous curvatures, it is very rarely that they can be seen throughout their whole length. They are composed of an extraordinarily thin structureless membrane, in the sub- stance of which, especially in the menstruating uterus, elon- gated oval nuclei are found, which are easily distinguishable from the muscle-nuclei that remain attached to the walls of the gland tubes when they are isolated. In regard to the epithelium of the glands, I shall here, in consequence of its importance, quote entire the account given by Gustav Lott.* As early as 1852, Leydigf made a communication in reference to an observation by Dr. Nylander, to the effect that the epithelium of the uterine glands of the Pig was a ciliated epithelium. Leydig, however, although at the end of this communication he stated as his opinion that similar epithelium might be found in other Mammals and in Man, has not since published any observations bearing on this point. KollikerJ simply corroborated Nylander's discovery. Leydig§ him- self, in his Manual of Histology, published five years after the above- mentioned communication, again only mentions the Pig; and Freyjl only does the same in his still more recent work. So far as the literature of the subject was accessible to Lott, no mention of this discovery is elsewhere made. Becker, II who investigated the generative organs of * See A. Rollett, Untersuchungen, Band ii. Leipzig, 1870. t Ueber Flimmerbewegung in den Uterindrusen des Schweins, (On the ciliary movement in the uterine glands of the Pig,) in Mtiller's Archiv fur Anat. und Physiologic, 1852, p. 375. I Handbuch der mik. Anat. 1852, Band ii., pp. 445, 446. § Lehrbuch der Histologie, 1857, p. 518. || H. Frey, Handbuch der Histologie und Histochemie des Menschen, 3rd edit. 1870, p. 539. IF Ueber Flimmerepithelium und Flimmerbewegung im Geschlechtsappa- rate der Sciugethiere und des Menschen, (On ciliary epithelium and ciliary movement in the sexual apparatus of Mammals and of Man,) in Mole- schott's Untersuchungen zur Naturlehre des Menschen und der Thiere, Band ii., p. 71. EPITHELIUM OF THE MUCOUS MEMBRANE. 481 Man and various animals for ciliary epithelium, does not mention the uterine glands at all, and Hennig* was even led to the conclusion, in regard to the glands he observed in the Fallopian tubes, that the principal difference between follicular organs and simple folds of the mucous membrane in the human Fallopian tubes depends on the pre- sence or absence of a deciduous ciliated investment on the mucous surface. Henle alsof expressly states that the columnar epithelium of the glands differs from that of the free surface of the uterine mucous mem- brane in the absence of cilia. The other statements in regard to this epithelium are very con- flicting. The majority of authors, indeed, ascribe the possession of columnar epithelium to Man and most Mammals, yet not to all. Differences of opinion exist even in regard to Man ; for whilst, for example, Weber, J Kolliker, § Leydig, || Henle, ^f Frey, ** and Hennig,tt describe a columnar epithelium, others, as Gerlach, jj Scanzoni,§§ and Schroder, |||| maintain that it is tesselated. Kolliker expressly terms it an ordinary, Henle and Hennig a ciliated columnar epithelium, whilst Leydig observes "that in all probability the epithelium of the glands exhibits as much ciliary movement as the rest of the internal surface of the uterus." The statements, again, that have been made in regard to various animals, are not quite in accordance with one another. LeydiglTIF ascribes to the glands of most Mammals (ciliated?) columnar * C. Hennig, Der Catarrh der inneren weiblichen Geschlechtsorgane 2 Aufl., 1870, p. 137- t J. Henle, Handbuch der systemat. Anatomie des Menschen, 1866, Band ii., p. 460. J E. H, Weber, Zusatze vom Bau und den Verrlchtungen der Geschlechts- organe, 1846, p. 33. § Loc. cit. || Lehrbuch der Histologie, p. 487. 1" J. Henle, Handbuch der systematischen Anatomie des Menschen, Band ii., p. 460. ** Loc. cit. ft Loc. cit., p. 13. U J. Gerlach, Handbuch der allgemeinen und speciellen Gewebelehre des Menschen, p. 352, 1850. §§ F. Scanzoni, Lehrbuch der Geburtshilfe, 4 Aufl., Band i., p. 50. Illl C. Schroder, Lehrbuch der Geburtshilfe, p. 22, 1870. 1HT Loc. cit., p. 518. VOL. III. I I 482 UTERUS, BY DK. K. CHROBAK. epithelium. According to Reichert* and Ercolani,f it is a pavement epithelium, which the latter author also maintains is the character of the epithelium lining the glands of the Dog and Mouse. In regard to the Pig, the Ruminants, and Solipedes, most observers agree in stating that their glands are lined by columnar epithelium. Very recently a treatise has been published by Friedlander,J in which the author makes mention of the " ciliated columnar epithelium " of the glands of the uterus (p. 25) and cervix (p. 45) in Man, and of the uterine glands in the Dog (p. 55). Friedlander appears to accept these as facts (though they are certainly not generally admitted), without further explanation. This is so much the more remarkable, as we may satisfy ourselves that the exhibition of the cilia of the cells in question is a matter of extreme difficulty in preserved specimens, as will be presently shown, and we are left quite in the dark as to the means by which Friedlander was successful in obtaining distinct evidence of the cilia. It would appear that he must have had preserved specimens under observation, and it would therefore be still more desirable to learn the method he adopted. Moreover, his statement that he observed ciliated epithelium in the cervix of girls not yet arrived at puberty, is not in accordance with observations of many others. Lott observed ciliary movement in the epithelium of the uterine glands as far as to their fundus, in fresh specimens taken from the Cow, Sheep, Pig, Babbit, Mouse, and a species of Bat. In four instances, examination of fresh specimens gave a negative result; these cases were those of the Calf, a very young Guinea-pig, a dissected Pig, and a Mare suffering from pyaemia. In a few cases he observed lively ciliary movement in the epithelium of the gland, when not only had all movement * Ueber die Bildung der Hinfdlligen Saute der Gebarmutter und deren Verhaltniss zur Placenta Uterina, (On the formation of the membrana decidua of the uterus, and their relation to the uterine placenta,) Mliller's Archiv fur Anatomie und Physiologie, 1848. p. 78. f G. B. Ercolani, Delle glandole otricolare delV utero e deW eryano glan- dolare di nuova formazione die nella gravidanza si sviluppa nell utero dell fern/mine dei mammiferi e nella specie umana, (On the utricular glands of the uterus and the new glandular organs that develop in the uterus of the female of Mammals and Man.) Bologna, 1868. 1 Physiologisch-Anatomisch Untersuchungen iiber den Uterus von Dr. Karl Friedlander. Leipzig, 1870. EPITHELIUM OF THE MUCOUS MEMBRANE. 483 ceased in the epithelium of the surface of the mucous mem- brane, but when no cilia were visible. He states that the best mode of observing the ciliary move- ment is to carefully break up with needles portions of the membrane excised with scissors, in iodized serum, aqueous humour, or a one per cent, solution of common salt. The vibrations of the cilia are usually extremely lively, though of very variable duration ; in the Mouse and Cat, for instance, ceasing after a few minutes, but persisting under similar conditions under a covering glass, in the Sheep, for an hour or more. The direction of the strokes of the cilia, as seen in optical longitudinal sections of the glands, is constantly from their fundus towards the orifice, whilst in optical transverse sections a vortex is formed, producing the appearance of a screwlike line. Observations of the appearances presented at different planes in one and the same tube are easily effected by proper focus- sing, especially in the Cow, on account of the numerous and often very sharp coils it makes in its course. In order to obtain separate cells with' quiescent but well-preserved cilia, Lott spread out a portion of the cornu of the uterus of the Sheep, either fresh or after being kept in iodized serum, in such a manner that he could scrape the surface rather firmly with a convex scalpel without cutting it. By this means the epithe- lial tubes of the glands can be squeezed out free from all sur- rounding connective tissue, and the cells may often be seen quite undisturbed in their position. Small fragments of the tube frequently appear in transverse section upon the slide, so that here also the most diverse sectional planes can be looked at coincidently. Such specimens should be examined either in iodized serum, or in a cold saturated solution of bichromate of potash, which renders the cells very transparent, and brings out the nuclei and contour lines with very sharp definition. He never observed vibration of the cilia in such preparations, nor in those macerated in iodized serum, and the quescient cilia had undergone some alterations, yet they were sufficiently dis- tinct to enable him to state that they were extremely short and fine, and that they stood in close apposition to one another. i i 2 484 UTERUS, BY DR. R. CHROBAK. In sections of uteri which had been macerated in Muller's fluid, or in a four per cent, solution of bichromate of potash, and then in alcohol, he was unable to recognize the presence of cilia, and he was not more successful with those that had been preserved in alcohol, in two per cent, solutions of chromic acid, in a O'OOl per cent, of chloride of palladium, or in a cold satu- rated solution of bichromate of potash. In such preparations he however always observed regularly closely arranged bud- like elevations on the inner margin of the epithelium, which gave a kind of striated appearance to it.* Nevertheless it is in hardened specimens that the form and disposition of these epithelial cells may best be studied, especially in very thin sections of preparations that have been hardened in Muller's fluid, and stained with carmine. In such specimens we can also examine in a very circumscribed space all conceivable real and optical sectional planes of the glands, and this whether longitudinal or transverse sections are made through the membrane. The cells are wedge-shaped, with hexangular cross section, the broad surface looking outwards, and the acute angle towards the lumen of the tube in such a manner that the edge cor- responds to the axis of the tube. In transverse sections of the gland, each cell has the form of an isosceles triangle, with a truncated apex directed inwards. The cells, differing in number with the size of the tube, which varies to a considerable extent, and with the species of the animal, form a ring surrounding the lumen. The narrower the lumen, and the fewer cells form the ring, by so much the more closely does their form approximate that of a triangle ; that is to say, so much the smaller is the inner border, and so much the more rapidly do these borders converge internally. * In the sixth volume of S. Th. v. Soemmering's treatise " On the Structure of the Human Body," edited by Henle, in 1841, at p. 246, Henle says of the cilia, that ' ' after death they appear in the form, of small spheroidal bodies, and then vanish entirely" See also Friedrich on the significance of the striation, in his essay " On the Structure of Columnar and Ciliated Epithelium " in the Archiv fur pathol. Anatomie und Physiologie, Band xv., p. 535. EPITHELIUM OF THE MUCOUS MEMBRANE. 485 The illustrations given by Henle* and Kolliker,f and especially those of the former, correspond to this description ; Kolliker only giving a couple of very wide tubes, in which the triangular form is of course a less marked feature. The appearances are differently represented by Hennig, J in whose drawing the cells float freely in the lumen of the gland. In longitudinal sections, on the other hand, the cells every- where present the form of a parallelogram, with their long diameter vertical to the membrane. Lott maintains this in opposition to several authors, who state that the epithelium is of the tesselated or pavement variety. (See, in regard to the Dog, Ercolani; § in regard to the Rabbit, Reichert|J and Ercolani; in regard to the Mouse, Ercolani ; and in regard to the human subject, Gerlach,1f Scanzoni,** and Schroder. ff Lott found the above-mentioned character to be everywhere present, though not with equal distinctness in all animals. The cells only undergo modifications of form at the points where the gland tubes make sharp curves. In longitudinal sections they here become pointed towards one side, so that on the convex side of the tube their pointed extremities are directed inwards, and on the concave side outwards. By means of corresponding changes of the focal distance we may also obtain a clear image of the cell boundaries on the external and internal surfaces of the tubes, and thus com- plete our conception of the form of these cells. On their ex- ternal surfaces the cells form a beautiful mosaic of tolerably regular hexagons (the bases of the wedges), whilst the internal surface exhibits a similar mosaic of hexagons elongated in the direction of the length of the tube, but appearing very slender in its transverse diameter (the acute border of the wedge). Such a mosaic is most distinctly seen in specimens preserved in Midler's fluid. * Loc. cit., figs. 538 and 539. f Kolliker, Handbuch der Gewebelehre, 5th edition, 1867. j Loc. cit., Taf. iii., fig. 10. § Loc. cit. ** Loc. cit. || LOG. cit. ft Loc. cit. IT Loc. cit. 486 UTERUS, BY DR. R. CHROBAK. Lott found the nucleus, which is usually of very large size (especially in the Dog), and always single, lying without ex- ception in the external portion of the cell, as Henle * and Kolliker f also depict it, whilst Hennig J describes it in Man as lying in a frequently clavate enlargement of the inner extremity of the cell, which Lott never observed. He however here and there found the nucleus so large that one portion of it projected into the internal segment of the cell. When fresh, it appeared coarsely granular, and much more highly refractile than the finely granular dull protoplasm. The cuneate cells bear the cilia on their slender internally directed extremities. Lott however is unable to state posi- tively whether they occur indiscriminately on all cells, though he regards this as being highly probable, both on account of the constancy of the form presented by the cells, and on ac- count of the invariable presence of the bud-like projections described above, which he considers to constitute the remains of the cilia. In addition to the animals already mentioned the uteri of other Mammals (as of the Cat, Dog, sexually mature Guinea- pig, Horse, and Man) were examined in hardened prepara- tions, and the agreement of the epithelial cells in all the characters mentioned above established. The epithelium of the mucous membrane undergoes per- petual replacement ;§ and it is more than probable that the epithelium is newly formed after each menstruation. That uncommonly rapid and uninterrupted changes take place in the epithelial structures of the uterus, is shown by the fact that the relative thickness of the parts composing the mucous membrane varies to an unusual extent according to its stage of development. In the normal state the mucous membrane measures from one millimeter to 1*8 millimeter in thickness, but at the men- strual period from four to six millimeters ; the glands which in the normal uterus are separated from one another by a * Loc. cit. * Loc. cit., p. 13. t Gewebelehre. § Kolliker, loc. cit. MUCOUS MEMBRANE OF THE CERVIX. 487 space of O03 to 01 of a millimeter, approximate at this period so closely that only quite narrow folds of the membrane in- tervene between them ; and their length, which ordinarily amounts at most to two millimeters, then rises to as much as seven millimeters ; their diameter in like manner increases from 0'05 of a millimeter to 01, and after conception to 0*240 of a millimeter; and even the epithelial cells which cover the mucous membrane and line the glands, and which in the normal state are from 0'015 to 0*04 of a millimeter in height, attain more than double this size in menstruation and preg- nancy. The mucous membrane of the cervix, which is separated from that of the body by a sharp line of demarcation, is much denser, firmer, and more transparent than that of the fundus. Its thickness varies from 0'25 to 3'00 millimeters. A special connective-tissue layer is found in the posterior wall between the mucous membrane and the muscular tissue. This layer extends over the os internum as far as to the body of the organ.* The internal surface of the cavity of the cervix covered with mucous membrane, shows upon its anterior as well as upon its posterior wall the well-known plicce palmatce, forming branching arborescent ridges, of which the anterior are placed somewhat to the right, and those of the posterior wall some- what to the left.f The substance of these ridges is composed of a dense tissue containing numerous connective-tinsue cor- puscles, a few muscular fibres, and a sparing amount of elastic fibres. The so-called " mucous follicles of the cervix " are imbedded in the substance of the ridges, excepting only in the lowermost smooth part of the cervical cavity. These sacs are usually spheroidal or flattened laterally, or, when partially filled, pressed together in a folded manner. Their size varies according to the thickness of the mucous * Rokitansky, Lehrbiich der patlwlogisclie Anatomie, Band iii. ; and Klob, Pathologische Anatomie der weibliche Sexualorgane, 1864. + Hjalmar Lindgren, Studier ofver lifmodrens byggnad hos menniskan, Canstatt's Jahresbericht, 1867, Band i., p. 25. 488 UTERUS, BY DR, R. CHROBAK. membrane, and they open on the free surface by orifices having a diameter of from O'l to 0'3 of a millimeter, or by a short broad excretory duct, through which their transparent, colour- less, slimy secretion, which possesses a strong alkaline reaction, and coagulates in alcohol, is discharged. Friedlander states that cup cells are present in this mucus. The statements made by the same author, to the effect that there are two kinds of glands, may be reduced to this, that the extremely small mucous sacs of the cervix in childhood become in the adult, by the growth of the mucous membrane, drawn out into tubules, and are still further elongated by their own growth at puberty. They are composed of a structureless membrane, which is so intimately fused with the connective tissue and the muscular fibres extending to the glands, that it is impossible to isolate it. The glands are lined by a nearly cubical epithelium, the nuclei of which are situated nearer the wall than the lumen. In the lower half of the cervix the mucous membrane be- tween the gland openings presents delicate slender papillse, O2 of a millimeter in height, covered with a ciliated epithelium, and each containing a vascular loop.* Hjalmar Lindgren mentions in addition a thin layer destitute of cells situated immediately beneath the epithelium, which is traversed by processes of the connective-tissue corpuscles. The epithelium of the mucous membrane lining the cervix is either throughout its whole extent, or only in its upper two- thirds, an actively moving columnar ciliated epithelium, the cells of which often appear to be filiform at their parietal extremity (Friedlander). Towards the os uteri externum it becomes, after exhibiting all the transitional forms, a simply laminated pavement epithelium. In addition to the above-described mucous glands, closed, colourless, and transparent or sherry-coloured vesicles — ovula Nabothi — are constantly met with, though varying in numbers and distribution, and extending in some instances as far as to * Kolliker, Gewebelehre. Hennig, Catarrh der weibliche Geschlechts- organe. Tyler Smith, Med. Chir. Transact., Vol. xxxv. NERVES OF THE UTERUS. 489 the outer surface of the vaginal portion. These have a dia- meter of from O3 to 0'5 of a millimeter, and often reach into the muscularis. They are considered to be partly primary neoplas- tic formations, and partly retention cysts. (Rokitansky,* Forster,f Hirsch,} Kolliker,^ Virchow,|| and others.) In pregnancy, and during the catamenial period, the mucous membrane of the cervix also shares in the general increase of thickness. The ridges disappear in proportion as the mucous sacs, which then attain a length of from 1* to 2*75 millimeters, enlarge, so that nothing remains of the mucous membrane ex- cept a thin trabecular framework three millimeters in thick- ness, whilst the mucous glands, the epithelium of which becomes larger and more succulent, secrete the consistent mucus that in pregnancy closes the os uteri. On the external surface of the vaginal portion of the cervix, neither folds nor glands are present. The glands of the portio vaginalis, described by Robing and Wagner,** have not, at least in the healthy woman, ff been observed by others ; on the other hand, the mucous membrane possesses a great many simple or compound papillae, each about 0'5 of a millimeter high, each containing a single vascular loop, and each invested with, in many instances, as many as ten layers of epithelial cells. The epithelium itself, very easily separable as a whole, is composed of columnar cells in its deepest layers, which become above flattened, clavate, elliptic, and spiny, till in the most superficial layers they only constitute small thin laminae connected by a relatively large quantity of cement. The nerves given off from the cervical and adjoining ganglia, and from the plexus hypogastricus, enter at the lateral border of the cervix, and by the ligamentum latum, in a horizontal direction, into the muscularis, and spread themselves horizon- * Rokitansky, loc. cit. t Forster, Handbuch der allgemeine pathol. Anatomic. £ Hirsch, Ueber Histologie und Formcii der Uteruspolypen. Dissert, inaug. Giessen, Canstatt's Jahresbericht, 1855, Band ii. § Kolliker, op. cit. j| Virchow, Krankhafte Geschwulste, Band i., p. 2G4. IT Robin, Gazette des Hopitaux, 1852, 11. ** E. Wagner, Archivfur physioloyische Heilkiuide, Band xv., p. 495. tt Friedliinder, loc. cit., p. 47. 490 UTERUS, BY DR. R. CHROBAK. tally, without in all instances following the course of the vessels to the anterior and posterior surfaces of the organ. Upon the whole, the cervix, in which nerve fibres may be followed as far as to the mucous membrane, appears to contain more nerves than the body (Kilian) ; * on the other hand, the fundus uteri appears to be more sensitive than any other part of the mucous membrane (Lazarewitsch f and others). In the uterus, doubly contoured and pale nerve fibres are found, as well as, according to the researches of Frankenhauser, J Koch,§ Kehrer,|| Luschka,1T Polle,** and others (at least in animals), ganglia in the submucosa, with each of which two or three pale nerve fibres are in connection. Further classification of the nerves is riot at present possible, since their mode of termination in the mucous membrane is not known. Kilian, Polle, and others, certainly describe the entrance of the nerve fibres into the papillae of the cervix, and Hjalmar Lindgren even finds a fine plexus of pale fibres with intercalated highly refractile and finely granular masses which, breaking up in a brush-like manner, extend to the epithelium. The nervous nature of these fibres is not, however, altogether beyond question. The distribution of the nerves in the muscular tissue of the uterus has frequently, of late years, been the subject of in- vestigation. According to Frankenhauser, ff pale fibres pro- ceeding from dark-edged fibres form plexuses around the mus- cles before they, becoming converted into nucleus- and then into node-bearing fibres terminate in the nuclei of the muscle cells. JJ * Kilian, Nerven des Uterus, Zeitschrift fur rationelle Medizin, 1851. t Lazarewitsch, the Lancet, 1867, No. 17. J Frankenhauser, Jenaische Zeitschrift, 1864, Heft. i. § Koch, Ueber das Vorkommen von Ganglienzellen an den Nerven des Uterus, (On the presence of ganglion cells on the nerves of the uterus.) Gottingen, 1865. || Kehrer, Beitrage zur G-eburtskunde, 1864. 1" Luschka, loc. cit., p. 378. ** Polle, die Nervenverbreitung in den weiblichen Genitalien. Gottingen, 1865. ft Frankenhauser, Nerven der Gebarmutter. JJ Arnold, loc. cit. VESSELS OF THE UTERUS. 491 There is an indubitable growth of the nerves also during pregnancy (W. Hunter, Tiedemann, Remak, and others), and, according to Kilian,the double-contoured nerves may be followed further in pregnancy than in the virgin state. The bloodvessels of the uterus proceed from the arterise uterina hypogastrica and uterina aortica (Luschka), and from the arteria spermatica externa. The veins unite to form two plexuses, the plexus uterinus, and the plexus pampiniformis. The two first-named arteries meet together upon the lateral surface of the uterus, forming an arch from which vessels of moderate size penetrate into the muscular layer, speedily branch, anastomose with the arteries of the opposite side,* surround the muscular fasciculi, and from thence extend to the mucous membrane. They form here, after surrounding the glands with capillaries, an irregular plexus of wider vessels in close proximity to the surface, from which thin- walled veins with- out valves arise. A much more regular arrangement of the vessels occurs in the cervix, and they here present disproportionately thick walls, so that the lumen only amounts to about one -third of the total diameter (Henle). Towards the cavity of the cervix the vessels run vertically to the surface in the septa between the mucous glands, and form a very superficial capillary plexus, from which a vascular loop ascends into each papilla. Externally, towards the labia, and extending through the muscularis as far as to the mucous membrane, are delicate, often slightly tortuous, or, in the upper parts, spirally twisted arteries, which form the capillary plexus immediately beneath the epithelium which supplies the papillae with loops, and from which the returning veins again take origin. The bloodvessels attain perfectly colossal dimensions after con- ception, which is principally owing to the hypertrophy and new formation of these contractile elements. The lymphatics form large plexuses in the peripheric layers immediately beneath the peritoneum in the pregnant uterus. The lymphatics proceeding from the body of the uterus ex- * Hyrtl, Topograph. Anatomie, 1860, Band ii.. n. 180. 492 UTERUS, BY DR. R. CHROBAK. tend to the plexus pampiniformis, in order to meet with the lymphatic glands of the lumbar region, whilst those arising from the cervix run to the lymphatic glands of the true pelvis. The lymphatics in the interior of the uterus are almost unknown. Hjalmar Lindgren describes the lymphatics in the collum as forming arches, from which csecal processes with sinuous margins extend towards the epithelium. METHODS OF RESEARCH. The coarse fibrillation of the uterus is best studied in the pregnant uterus, either in the fresh state, or hardened to some extent in alcohol, or macerated for a little while in a warmed mixture of 1 vol. of hydrochloric acid and 90 vols. of alcohol. In order to make good sections, the alcoholic preparations may be dried in air, or after previous boiling in dilute wood vinegar. For the purpose of isolating the muscular fibres, very diluted solutions of chromic acid, containing from O'l to O'Ol per cent., may be employed, or solutions of bichromate of potash, iodized serum, potash lye, or acetic acid containing one to two per cent, ; twenty per cent, solutions of nitric acid ; Moleschott's fluid ; a one- half per cent, solution of nitric acid heated to the boiling point ; wood vinegar alone, or this mingled with glycerine. To effect the hardening requisite to display the epithelium and nerves, chromic acid, bichromate of potash, alternately applied or mingled together, Miiller's fluid, and freezing, are well adapted ; but for the finest branches of the nerves the wood vinegar in glycerine is still the best. As colouring agents, carmine, anilin, picric acid, chloride of palladium, chloride of gold, may be used. But by far the most important is the investigation of preparations as fresh as possible, and merely moistened with solution of albumen or iodized serum. II. PLACENTA. This account has been furnished by Dr. Reitz, of St. Petersburg!!, who made the investigations bearing upon the subject under my directions. — STRICKER. THE placenta of the human subject is composed of a maternal and of a foetal portion; but from the fourth month of pregnancy these are intimately fused together. The maternal portion, the placenta uterina, which upon the average is from a quarter to half a millimeter thick, is composed chiefly of large cellular elements. The cells are very variously formed, and are for the most part thickly granulated, and exhibit a distinct large spheroidal nucleus, with one or several nucleoli ; occasionally two or more nuclei are present ; many cells are provided with one or several processes of various lengths. Between these cells, large vesicles, with numerous nuclei in their interior, are, according to Kolliker, to be here and there found.* The cells are usually arranged so closely that they form nearly the whole thickness of the placenta uterina ; but they are frequently arranged also in groups, and sometimes also in quite an isolated manner, imbedded in the matrix, which appears as a fibrous tissue, or in parts as a hyaline finely gra- nular mass. Between these cells If found colossal encapsuled cells with large vesicular nuclei and nucleoli. In consequence of their coarsely granular contents, nuclei and nucleoli, as * Kolliker, Entwickelungsgeschichte, 1861. t Sitzungsberichte d. K. Akad. der Wissenschaften, Mai-Heft. Wien,1868. 494 PLACENTA. well as their remarkable size and enclosure in capsules, they present a remarkable similarity to ganglion cells. The presence of smooth muscular fibres first described in the placenta uterina by Ecker,* and subsequently by Kamenew,t has been positively denied by all other inquirers. My own re- searches demonstrate the presence of smooth muscular fibres to be constant in the external layers of the placenta uterina. The fibres are tolerably abundant, and are frequently ar- ranged in a laminated manner in teased-out preparations, which, in accordance with the recommendations of Jassinski, J have been treated with hydrochloric acid; a distinct well- defined rod-like nucleus may be shown to exist in many of the cells. In addition a not inconsiderable number of fusiform cells, the characters of which could not be more closely investi- gated, are visible in the various layers of the placenta uterina. The processes of the placenta uterina, which like septa bound the cotyledons, and frequently divide and branch, penetrate deeply into the foetal part, without ever reaching, as Kolliker has pointed out, the innermost part of the foetal por- tion of the placenta. No direct passage of these processes into the foetal tissue exists, but they cease at the periphery of the cotyledons, so that in the centre of the secondary coty- ledons (Kamenew) no maternal tissue occurs between the villi. In the finer ramifications of these processes, which re- semble fibrous tissue, (the cellular) elements of the placenta uterina are but seldom found. In reference to the bloodvessels of the mature placenta, the researches of Kolliker, VirchowJ and others have shown that there is no plexus of capillaries between the arteries and veins ; but that a communication between these two sets of vessels is established by means of sinuous cavities. * Icones' Physiologicce. Explanation of Taf. xxviii. t Mikroskopische Untersuchungen der Blutgefasse des Muttertheils der Placenta, (Researches on the bloodvessels of the maternal portion of the placenta,) Medicinsky Westnik, 1864, No. 13. J Zur Lehre uber die Struktur der Placenta, Virchow's Archiv October Heft, 1867. § Ueber die Bildung der Placenta, Gesammelte Abhandlungen zur wissen- schqftliche Medicin. VILLI OF THE PLACENTA. 495 These sinuses, which traverse the whole placenta, and project freely into the foetal villi, are exclusively bounded by the placentary tissues. Kolliker and Bidder * were unable to dis- cover the presence of the thin membrane described by E. H. Weberf as forming an investment to the maternal cavities. The foetal portion — the placenta foetalis — is formed by the development of the villi of the chorion, in which are distributed branches of the two arteries and of the vena umbilicalis. The villi of the placenta foetalis have very recently been subjected to renewed examination by Jassinsky. He corro- borates the statement that the villi are invested by tesselated epithelium, and he even admits that the cells forming this layer may be covered by columnar epithelium ; for inasmuch as the villi project and penetrate into the uterine glands, the columnar epithelium of these glands may still remain adherent to the isolated villi. My own researches upon this point have led to the following results : Some villi really have an invest- ment of columnar cells, but in that case there is no subjacent layer of epithelium. The columnar cells bound the cavity of the villus in which the bloodvessels are contained. The young villi, on the other hand, are invested neither by columnar cells, nor by pavement cells, nor indeed by any well-defined cell bodies. They are rather composed of simple protoplasm, with numerous nuclei imbedded in its substance. The villi, as is well known, shoot out protoplasma-threads or knots from their substance. These elongate, and become thickened, and nuclei accumulate in them ; yet there are not here any well- defined cell groups, but merely a coherent mass of protoplasm. A cavity subsequently forms in the villus, but even then no epithelial cell walls can be brought into view by the silver method of staining. The villus however is soon invested by a layer of columnar cells, formed from this mass of protoplasm containing nuclei. At least, it is only in this way that the successive histological stages and phenomena can be explained. In the * Zur Histologij der Nachgeburt, (On the histology of the afterbirth,) Hoist's Beitrdge zur Gyndcologie und Geburtskunde, 1867, Heft ii. t R. Wagner, Physiologie, 3rd edition. ISC PLLCEXTA. first imtawy there are filiform solid villi ; these subsequ become thicker, then contain many nuclei then have a cavity in their interior, and finally have an investment of columnar cells smTounding the cavity. I must further remark, that I have in many instances seen the border bounding the villi externally, and describee Goodsir* and Schroder Tan der Kolkf as an independent membrane, raised up and isolated from the matrix; and in such cases I repeatedly saw the nuclei separated from the border bj a more or less thick layer of matrix. I do not know whether the limiting membrane exists during life. In fresh vifli no double contour is apparent, even when they are examined with the best microscopes. The membrane, which may be found partially detached when Jassmsky's method (maceration in "hydrochloric acid} is employed, may also be a product of the coagulation of the superficial layer of proto- plasm. It is moreover not probable that a membrane should form upon the threads protruded from the protoplasm, since one is subsequently seen investing the free extremities of the s"i r -r r£ : i;\l ; : LM n n xi : ••- 11 ^ The vessels of the villi are not in direct contact with the watt of the viflus. but rather float in a cavity of the villas, which may thus be termed a peri vascular space. This cavity is usually widest at the ends of the villi, and in the vilius- protrusions into which the vessels only just enter. Schroder van der Kolk was the first to demonstrate that the arteries and veins in the vifli do not form simple loops, but are connected by a dose capillary plexus. The connective tissue of the chorion penetrates with the vessels into the interior of the villi On the pedicles of the villi it exhibits a distinctly fibrous structure (Yireho w's mucous tissue), but near the extremities of the vifli it appears as structureless intercellular substance in which no indications of a fibrous structure are perceptible. Bound, fusiform, and stellate cells are distributed through + Am* m* ML A«fWi 1 VILLI OF THE PLACENTA. matrix of the villi, which are regarded by Kolliker as formative cells of the conne -ue. Besides these there are also nuclei which have no cell substance around them. The matrix: of the villi is directly continuous with the connec: :e matrix of the chorion. Between the chorion and the amnion there is still a gelati- nou- ^>called membrana intermedia, which, accord- ing to Bischoff's* researches, represents the remains of the fluid originally present between the chorion and amnios. X cellular elements or vessels are discoverable in this gelatinous * / Lthre wm den EihuHen des menteHichtn, Fcehu, (Eaaay on the membranes of the human fcetns,) 1851 (Kolliker. Bidder.) VOL. III. III. THE OVIDUCTS. (Fallopian Tubes.) The subjoined description of the Fallopian tubes has been executed by Mr. Griinwald, who has worked under my direction. — STBICKER. THE OVIDUCT. — The oviduct in Man is attached to the upper and lateral part of the uterus, behind and somewhat above the origin of the ligamentum teres. It runs outwards along the upper free border of the ligamentum latum, which constitutes a kind of mesentery for it,* and is partly straight and partly sinuous. The straight segment (isthmus, Barkow) is near the uterus, the looped part — ampulla (Henle) — is more external. The course of the Fallopian tubes varies in Mammals. They are sometimes looped immediately after their origin from the uterus, and then run straight towards the ovary, though some- times the reverse obtains. Sometimes they form a series of small curves along their whole extent, or they are contorted into a knot, and intertwine with one another as in the Rat,f the Simia silvanus, and to a still more marked extent in the Opossum.:}: The tubes are not always of equal length; sometimes the right and sometimes the left is the longer. The isthmus is * Henle, Lefirbuch der Anatomie. t Meyerstein, Henle and Pfeuffer's Zeitschrift, 3 Reihe, Band xxiii. , p. 63. Ueber die Eileiter einigen Saugethiere, (On the Fallopian tubes of some Mammals. J Blumenbach, Vergleichende Anatomie, p. 486. DIAMETER OF THE TUBA. always shorter than the ampulla, although the relative length of the two varies in different species of Mammals. In the Fowl, as in almost all Birds, only one oviduct is present, that, namely, of the left side. The rudiments of a pair of female sexual organs are, indeed, originally present, but in the course of development that of the right side usually disappears* This passes downwards, pursuing a more or less tortuous course in front of the left kidney, to the cloaca. At the lowest part it suddenly dilates, and becomes a uterus. It is fixed in its position by a peritoneal fold. In Amphibia the oviduct again becomes double. In Bufo cinereus it extends upwards over the root of the lung, and is at this its abdominal extremity, for about eight to ten millimeters, fastened by means of a peritoneal fold to the posterior abdominal wall. The upper part is very tortuous. At the lower end it becomes suddenly wider, and terminates in a vesicular dilatation which directly opens into the cloaca. The oviduct in Man and Mammals communicates by its narrow ostium uterinum with the cavity of the uterus. In Man this opening is at the upper part of the uterus, and is so small that it will scarcely permit the passage of a fine bristle. It enlarges as it approximates its external orifice — the ostium abdominale — but contracts again at the orifice itself. Haller maintained that after its dilatation it again underwent constriction near its middle, and Weber f held the same opinion. Meckelif gives the diameter of the ostium uterinum at half a millimeter, that of the ostium abdominale at three to four millimeters. Krauseg estimates the diameters of the ostium uterinum at one-fifth to one-fourth of a millimeter, and that of the widest portion in front of the ostium abdominale at two millimeters. Huschkej) gives as much as three to four milli- meters for the diameter of the tube at this latter point. In Man the Fallopian tube dilates to form a funnel at the * Stannius, Lehrbuch der veryleichenden Anatomic der Wirbelthiere, p. 333. t Band iii., p. 616. £ Band iv., p. 516. § Bandi., p. 559. || Loc. dt., p. 470. K K 2 500 THE OVIDUCTS. ostium abdominale, and the margins of the funnel are divided by deep radially arranged fissures into many lobes or fimbrise, which are sometimes pointed, and sometimes rounded. On the inner surface of these lobes, transverse and longitudinal folds are found, which are prolonged from the mucous membrane of the ampulla, and cannot be removed by stretching. One of the fimbrise considerably exceeds the others in length. This is the fmibria named ovarica by Henle, which is attached by its peritoneal surface to the sharp and free border of the ligamentum infundibulo-ovaricurn (Henle), itself a secondary fold of the ligamentum latum, extending between the lateral extremity of the ovary and the infundibulum. This fimbria ovarica reaches to the apex of the ovary, where its peritoneal investment fuses with the albuginea of the ovary. In many cases, however, it does not extend as far as to the ovary, and the ligament, inf. ovaricum then forms a groove or gutter. In the cases where an intervening space remains between the fimbria ovarica and the ovary, the intermediate sharp and naked border of the peritoneal fold is invested by ciliated epithelium. In the Fowl a furrow always intervenes between the ovary and oviduct, and I found that in this animal the ostium abdo- minale offers two relations. In three cases the oviduct terminated csecally, but presented an oblique incision near the apex, which opened into a thin- walled funnel. The incision was situated in the above-named furrow. This mode of termination, however, occurred in young animals that had as yet laid no eggs. The fourth was an old hen, and in this instance the ostium abdominale was infundibuliform, just as in the human subject. In Bufo cinereus the abdominal opening is situated at the upper attached extremity in a transverse fold of the peritoneum, and exhibits the same relations as in young Fowls. A transverse section of the Fallopian tube in Man and Mam- mals shows that the lumen is stellate, and the following layers may be distinguished from without inwards : — 1. The very vascular adventitia, composed of connective tissue. 2. The muscular layer, chiefly consisting of circular fibres, though longitudinal muscular laminae are interposed amongst them to a variable extent. 3. Lastly, the mucous membrane, which presents numerous folds that are partly STRUCTURE OF THE TUBA. 501 laminar, partly conical, or form low ridges. The epithelium consists of tolerably high columnar and ciliated cells. The matrix of the folds is a dense, very vascular fibrous plexus. The muscular layer of the mucous membrane is made up of longitudinal muscular fibres. At the ampulla the adventitia and muscular layer present the same relations, but the mucous membrane is beset with many complicated folds that suggest it has to perform a different function. These folds project farther into the lumen of the canal than in the isthmus, and often appear to, and sometimes actually dor coalesce with those of the opposite side. These folds often have secondary folds upon them, which again branch, giving to the whole an arborescent aspect. Simple unbranched folds also occur, arranged in close apposition with each other, which have led several authors (Bowman, Hennig) to admit the presence of glands in the mucous membrane of the oviduct. It may however easily be demonstrated in longitudinal sections that no glands exist in the oviducts of Man and Mammals. As regards the minute anatomy of the fimbria, they are composed of the same elements as the other parts of the oviduct, of which they are to be regarded as the direct con- tinuations. They are exceedingly vascular. In the Fowl the external investing membrane and the sub- jacent circular muscular layer are arranged as in Man. The folds of the mucous membrane throughout the whole length of the oviduct are unbranched, and consist of a finely fibrillated plexiform tissue, in which cells usually of a rounded form are distributed, and increase in numbers towards the epithelium. In the centre of the fold is a vascular trabecula of connective tissue, which gives off branches on all sides into the substance of the fold, producing by their intercommunications the above- mentioned finely fibrillated plexus. At the apex of the fold the connective-tissue trabecula disappears, having exhausted itself by giving off successive branches into the interior. The epithelium is composed of many tiers of columnar and ciliated cells. The folds vary in length. The structure of the oviduct in Bufo cinereus is quite differ- ent ; for whilst in Mammals and Birds glands are never present, 502 THE OVIDUCTS. tubular glands arranged vertically are found throughout the vjhole length, with the exception of the upper attached portion, of the oviducts of this species, and they are separated from one another only by thin layers of connective tissue proceeding from the mucous membrane. If the longitudinal folds of the mucous membrane that are met with throughout the whole length of the canal, and which attain their greatest height near the ostium abdominale, be separated from one another by means of needles, a fine velvety tissue, presenting minute openings, and resembling a honey- comb, may be seen, excepting only at the attached abdominal extremity, where the glands are less numerous. In transverse sections an investing membrane composed of connective tissue is seen; externally to this succeeds a thin layer of circular muscular fibres, on which the mucous mem- brane lies. The gland tubes are imbedded in this membrane, and, as already stated, they are only separated from one another by the vascular connective-tissue trabeculse given off by the tissue of the mucous membrane. The mucous membrane rises above these in numerous longitudinal folds, between which the openings of the gland tubes are visible. The tubes are lined by well-defined pavement cells. The folds of the mucous membrane in Man are moderately prominent, and are frequently branched. Their interior is occupied by a dense cord of connective tissue, in which bloodvessels and a few smooth muscular elements are contained. Externally they are coated by tall columnar and ciliated epithelial cells. In the further course of the oviduct the folds are unbranched. CHAPTER XXXVIII. DEVELOPMENT OF THE SIMPLE TISSUES. BY S. STKICKER. THE status nascens of a vertebrate animal is occasioned by, and coincident with, the impregnation of the female germ. The fecundated germ is a unicellular organism, which becomes by fission multicellular. When the process of division or fission has reached a certain point, the young cells form layers or laminae, and from these the different tissues are developed, the various organs of the body being again formed from the union of these tissues; coincidently with the appearance of the laminae, the differentiation of the tissues begins to take place, and it thus becomes intelligible why the account of the embryonal laminae is worked at with such care by histologists. Embryologists also understand by the term "embryonic laminae " the membranes by which the embryo subsequently becomes invested. These investments, however, do not stand in intimate relation to histogenesis ; they are really transitory organs, which, like all other organs, develop from the pri- mary laminae. A knowledge of the embryonic investments is therefore a part of the history of development of the several organs and the former cannot be discussed without sketching out the principal features of the latter. From these preliminary observations the line to be pursued in the following account is self-evident. The embryonic cell 504 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. layers will only so far be considered as may be requisite to render the histogenetic processes intelligible. An account of the unfecundated germ has already been given in vol. ii., p. 192 et seq. To this exhaustive treatise I have only to add a few observations in reference to the nomenclature. I shall systematically avoid the use of the expression "formative yolk" (Bildungsdotter) employed by Reichert, and that of "principal yolk" (Hauptdotter) used by His. Both expressions, as will presently be seen, are based upon erroneous assumptions, and as neither can claim the advantage of brevity, there is no good reason for discarding in their favour the word " germ," used by Remak. It will, in consequence of this, be further advantageous to term the investing membrane of the germ (the zona pellucida of Baer), not vitelline membrane (Dotterhaut), but blastoderm, germ- tunic, or investment (Keimhulle). I shall only call this tunic the vitelline tunic or vitelline membrane in those cases where the germ exists together with a vitellus (food yolk, Reichert ; secondary yolk, His) within one and the same membrane, as in the eggs of Birds, scaly Amphibia, and osseous Fishes. It is generally admitted that the fecundated germ is at first destitute of a nucleus.* This fact may best be demonstrated in Batrachia, if a pair of animals in coitu be examined, whilst some of the ova have been extruded, and others are still retained in the body of the parent. It may then be shown, either by tearing the fresh eggs in sunder, and examining the contents as they escape with low powers, or by section of the hardened ova, that each of the ova taken from the body of the mother possesses a vesicular nucleus (germinal vesicle), the membrane of which can, when fresh, be divided with needles, with the aid of a lens ; in the youngest fertilized ova, on the other hand, no nucleus can be distinguished. This fact is interesting, since it shows that the vertebrate animal begins as a non-nucleated mass. If such non-nucleated Batrachian germs be hardened, there * Precise statements to the effect that the germinal vesicle is persistent, and becomes transformed into the nucleus of the cleavage cells, has only been made by Johann Miiller, in the case of the Entoconcha mirabilis. Monateberichte der Berliner Akademie, September 1851. AMCEBOID MOVEMENTS OF THE YOLK. 505 may sometimes be perceived, when sections are made, a small cavity, corresponding in size to the formerly present nucleus. According to Remak, this is the nuclear cavity of v. Baer. This expression clearly indicates that on this view the cavity occupied by the nucleus still remains when, it has itself disappeared. If the fertilized germ be placed in favourable conditions, a fresh nucleus speedily makes its appearance in its sub- stance. In regard to this nucleus I can say nothing from my own experience, and it would scarcely serve any good purpose to adduce the concurrent testimony of others. As the ova are usually opaque under these circumstances, it is impossible to see the nucleus when fresh. If all observers have been in such complete agreement in regard to the formation of a new nucleus, this is essentially due to the fact that in the later cleavage products of the germ the nucleus is distinctly visible, whilst it may be shown in addition that it is homogeneous, and has exactly the ap- pearance of an oil drop. Reverting to the fact that the old nucleus disappears, it is thus rendered highly probable that we are here dealing with a new formation. Before the process of cleavage sets in in the germ, it undergoes " certain automatic changes of form. The amoe- boid movements of the Forella germ have already been de- scribed (vol. ii., p. 185). If the freshly deposited ova of Bufo cinereus be attentively watched, it may be seen that it has at first several facettes, and that it subsequently as- sumes a spherical shape. The occurrence of alterations of form in the ovum of the Bird before the commencement of cleavage, has only been deduced from a comparison in hardened preparations of sections made through germs at various stages of development. Here also attention may be called to the observation first made by Bischoff in the ovum of the Rabbit, that the yolk (germ, Keim) retracts from the zona pellucida before it divides. Whether the observation in regard to the rotation of the unseg- mented germ within the vitelline membrane, recorded in the same place, should also be here mentioned as belonging to these movements, 506 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. is doubtful. Bischoff only made the observation in one animal, and since that period nothing has been ascertained in regard to the occur- rence of rotation in the unsegmented ovum.* SEGMENTATION AND THE FORMATION OF LAMINA. (a.) In Batrachia. The segmentation of the ova in Batra- chia was discovered in the year 1824, by Prevost and Dumas,f and given in full detail by Rusconi,:£ in 1826. No material is so favourable as the ova of Batrachia for the observation of this process. With the return of the first days of spring the spawn may be obtained in large quantities ; and if the ova of various species are investi- gated, they may be repeatedly examined at intervals varying from a few days to several weeks. Another advantage is that the cleavage proceeds under our eyes, without the necessity of any interference on our part. It is only requisite to place a spawn chain (Bufo) or a mass of spawn (Rana) in water in a watch glass, and with the aid of a lens the whole process may be conveni- ently followed. The vitelline membrane is not visible (by direct light) by this mode of examination, and we obtain the impression that the germ itself undergoes cleavage upon its surface. If, however, we place a group of ova in a watch glass, and examine them by direct light with somewhat higher powers (as from forty to fifty linear) we may soon convince ourselves that the transparent membrane takes no part in the cleavage. The formation of the first grooves in the Batrachian ovum may best be rendered intelligible by taking a ball of modelling clay, and constricting it in the following manner. Place a thread in one meridian, and a second at right angles to it. Tighten the two threads so that the upper third of the spheroid is cut through by them. A third thread may now be placed parallel * Entwickelungsgeschichte des Kaninchens, (History of the development of the Rabbit,) 1842. At pp. 58 and 59 of this work the reader will find the literature bearing upon the rotation of the yolk. t Annales des Sciences, S^r. i., Tom. ii. t Developpement de la Grenouille. PROCESS OF CLEAVAGE IN BATRACHIAN OVA. 507 to the ^equator, about opposite the junction of the superior and middle third of the axis of the sphere, and this should be made to cut its way completely through. By this means, proceeding from the upper pole, the spherule is divided into four segments, whilst the larger inferior portion of the sphere remains un- divided, with the exception of the surface, where the two meridianal constrictions indicate the subsequent divisions. The formation of these three furrows proceeds gradually. It may occupy, at a temperature of 18°— 20° Cent. (64°— 68° Fahr.), from three to four hours from the period of the extrusion of the egg from the body of the parent. Before a groove is definitely formed, the surface becomes wrinkled, and then again smooth, and this change occurs several times consecutively. From the principal furrows numerous smaller secondary furrows proceed, which are only of a tran- sitory nature. Reichert has described these secondary furrows as the furrow crown (Faltenkranz), and Max Schultze* has shown that they are the expression of the movement of the germ. At the point where the first three furrows cut one another (that is to say, in what would be the upper half of the egg floating in water,) a cavity forms. From my own experience I am unable to say whether this coincides with the nucleus cavity or not. The cavity enlarges owing to the retraction and rounding off of the opposed angles of the segments. The further process of the cleavage is limited chiefly to the four upper segments. These become smaller by continual sub- division, whilst the cavity increases in size, till ultimately a spacious cavity is formed in the upper third of the ovum (F, fig. 399), that may be best comprehended with regard to the subsequent processes that take place in it by the following de- scription. It may be regarded as an apple so excavated in the upper third of its axis that only the rind remains. The lower and larger section of the apple would then be solid, whilst there would be a cavity in the upper segment that is only surrounded by a thin cortex. We designate the cavity in the ovum of the Frog Baer'^ * De ovorum ranarum Segmentatione, 1863. 508 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. cleavage cavity; the thin- walled dome surrounding it, and formed of small cleavage elements, or embryonal cells (rind of the apple), the roof (D); and the solid inferior half, the floor of the cleavage cavity. Whilst this cavity is forming, the cleavage of the inferior solid segment gradually progresses, though rather upon its sur- face than in its interior. Thus it happens that the whole ovum is very soon invested by a mantle of small cleavage segments or embryonal cells. The resemblance to a partially excavated apple is now still more striking. The rind of the apple corresponds to the mantle of small cells, and the solid substance of the lower part to those remains of the germ which only slowly undergo cleavage, and at the period when the mantle is divided off still consist of very large cleavage masses. The comparison, however, may be rendered complete if a circular piece be cut from the rind of the spheri- cal apple at its inferior pole, so as to expose the flesh ; for the progressive division (fission) of the superficial cells does not extend so far as to the inferior pole. At this point a small, and in the first instance irregular, but subsequently circular area (P) remains, the centre of which corresponds to the inferior pole, and which is composed of large polygonal facet tes. Whilst the external surface of the mantle of all Batrachian germs at this stage of development is of a dark-brown colour, this area remains whitish if the lower half of the ovum was so from the commencement (Bufo fuscus) ; or it becomes whitish if the lower half of the fresh-laid egg was brown (Rana tem- poraria, Bufo cinereus, and viridis). The large white cells that occupy the floor of the cleavage cavity, and are exposed at the inferior pole (z, fig. 399), were termed by Reichert the central vitelline mass (centrale Dotter- masse). Remak had already applied the term gland-germ to it (Driisen-keim), because he had found, in accordance with Rusconi, that in Batrachian ova there was no structure analo- gous to the vitellus. I cannot accept this nomenclature, be- cause the theory on which Remak arrived at it is not tenable. These cells are not exclusively devoted to the formation of the rudiments of the glands. At the same time they are not lami- nated cleavage elements from which the various tissues are PROCESS OF CLEAVAGE IN BATRACHIAN OVA. 509 developed. On this account I shall term them germ cells (Keim- zellen), and also point out that their ultimate destiny has not as yet been ascertained. At the point where the germ cells are exposed, they are at a very early period sharply separated from the outer brown mantle-zone of smaller cells by a semilunar fissure (N). This fissure is named after its discoverer, Rusconi's fissure.* It subsequently becomes completed into a circular groove, and the now still more perfectly circular and well-defined mass of large germ cells has been named by Eckerf the vitelline plug, Fig. 399. Fig. 399 represents a meridianal section of an egg of Bufo cinereus, the stage of development of which does not quite correspond to that described on this page. F, Cleavage cavity ; D, the roof ; P, white area at the inferior pole ; Z, germ cells on the floor of the cleavage cavity ; z, germ cells which project from the floor of the cavity towards the mantle ; N, section of Rusconi's furrow ; jR, dorsal half ; jB, abdominal half of the ovum. (Dotter-propf). I have named that half of the eggj where the semicircular furrow commences, the dorsal half, because it forms the dorsum of the embryo ; the longitudinal axis of the dorsum runs from the centre of this furrow to the superior pole. The opposite half I have termed the abdominal half. It was long ago known to v. Baer that the ova underwent in water a rotation of about 90°, so that the meridian became an * Developpement, etc. f Icones' Physiologicce. 1 Zeitschrift fur wisseiiscliaft. Zoologie, Band xi. 510 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKEll. ^equator. Owing to this rotation the now laterally placed dorsal half is turned outwards. This rotation is occasioned by the formation of a second cavity which extends along the dorsal half. By this means the centre of gravity of the ovum is displaced, and the rotation is a necessary consequence. This second cavity (N, fig. 401) was recognized by Rusconi * Golubewf has by historical inquiry discovered some erroneous references in the nomenclature of the two cavities, and has shown that the cavity of Baer is to be regarded as elliptic, but that of Rusconi as semilunar. Remak:}: was of opinion, on theoretical grounds, that the cavity of Rusconi originates from the furrow of the same name by an inversion. He considered that the germ of the Bird is composed of three cell layers or lamina?. The most superficial or most external he named the corneal or sexisorial lamina (Hornblatt oder sensorielles Blatt) ; the second, the middle or motor, or motor-germinal lamina (mittleres oder motorisches, auch motorisch gerrninatives Blatt), and the third the intestinal glandular lamina (Darmdriisenblatt). That the Avian germ is laminar, and curves downwards, has been known from the time of C. F. Wolf. Remak believed he could establish the analogy between the Avian and the Batrachian germ by the following observations. He sought the analogue of the sensory and motor laminae in the cover or roof of the cleavage cavity ; the analogue of the gland-layer of the Bird, on the other hand, in the white area at the inferior pole of the Batrachian ovum. The germ of the Frog, he remarked, is certainly not laminar, and therefore cannot curve inwards in the same manner as the Avian germ. On the other hand, the lower surface of the spherical Batrachian germ undergoes inversion, in order to become applied to the motor laminse, which he himself, as above stated, believed to be already completed at the inner surface of the mantle layer. I have § however shown that the Rusconian groove is produced * Mullens Archiv, 1836. t Hollett, Untersucihungen. Leipzig, 1870. £ Loc. cit. § Loc. cit. PROCESS OF CLEAVAGE IN BATRACHIAN OVA. 511 by the separation of the formed elements from one another, and not by an inversion. Proceeding from this groove, I also saw in transverse sections a trace of a division (Trennungs-spur) in one of the mantle surfaces extending upwards in a direction not quite parallel to the dorsal half. I therefore believe I am justified in considering this trace of division as the rudiment of the Rusconian cavity, and in maintaining that this arises not by an inversion, but by a separation of the morphological elements from one another. In regard to the question whether inversion or fission occurs, Golubew, who is the only author besides myself that has expressed himself definitely upon the point, is in favour of my view. Golubew* however states that my account of the mode of origin of the Rusconian cavity is not quite accurate. I cannot here enter into a controversy upon the subject, because, faithful to my project, I can only so far consider the anatomical details as may be necessary to render the formation of the layers intelligible. In regard to the relations of the fissure 'to the embryonic laminae there are no differences of opinion. Remak noticed that a group of white germ cells projects from the floor of the cleavage cavity, just at the margin where this is continuous with the roof of the cavity, for some distance towards the roof (z, fig. 399). If have further pointed out that this projecting mass of cells is of fundamental importance in the formation of the laminae. I have shown that the roof of the cleavage cavity (D, fig. 399) contains the rudiment of the sensorial lamina of Remak alone,* and that the analogues of those laminae termed by Remak the middle and gland laminae, are formed from the cells that are applied as new formations to the roof. When I found that these germ cells reached at first only a small distance towards the dorsal half, whilst they subsequently extended more and more, until they at length passed beyond the upper pole, the germ cells of the abdominal half at the same time similarly stretching upwards to the roof, and growing towards * Loc. cit., Taf. D, fig. 2. f Loc. cit. J The same fact has been subsequently pointed out by Gotte. See Max Schultze's Archiv, Band iv. 512 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. them ; and after I* had further discovered that the cells of the Batrachian germ were capable of spontaneously changing their form and position on the slide, I stated my opinion that these germ cells strove to pass outwards by spontaneous movements, in opposition to the laws of gravity. Golubewf is unable to adopt this view. He believes that the increase in height is due to cleavage processes. I am again unable to enter into any discussion in this place upon the different opinions we hold. The question whether the cells move from their position spontaneously, or as the result of progressive fission, is of interest in and by itself, but is of quite secondary importance in regard to the development of the laminae. It is here only important to notice that the cells generally suffer displacement in order to aid the formation of the embryonal laminae ; and this circumstance may again be regarded as admitted on all sides. It has been already pointed out that the fissure proceeding from the dorsally situated furrow of Rusconi runs upwards. When the semilunar fissure in the course of its upward ex- tension reaches the margin of the cleavage cavity, it meets with the above-mentioned white germ cells, which extend along the dorsal half from the floor of the cleavage cavity to the roof. The fissure penetrates these upward extending cells. If numerous horizontal sections, beginning from the inferior pole, are carried through the ovum, it is found that the fissure existing in the dorsal half is almost semilunar. It is bounded externally by the mantle layer composed of small cells, and internally by the white germ cells (z). The mantle zone is at this point much thicker than where it forms the roof of the cleavage cavity. In other words, the. fission of the large germ cells to form small ones has at this point progressed towards the axis of the ovum. That which now lies on the exterior of the fissure is no longer the analogue of the senso- rial lamina (Remak), but contains the rudiments of all the germ-laminae. From the fissure a part of the visceral cavity is subsequently formed, and that which lies more externally forms * Ueber die selbstdndigen Beivegungen, etc. , Wiener Sitzungsberichte, 1863. t Loc. cit. PROCESS OF DEVELOPMENT IN BATRACHIAX OVA. 513 the whole thickness of the back. Sufficiently thin sections of preparations hardened in chromic acid permit two layers of unequal thickness to be very distinctly seen in this part of the dorsum. The thinner external layer is composed of small cells, and is the analogue of the sensorial lamina of Remak ; the thicker internal layer is composed of large cells, but which are constantly becoming smaller than the large germ cells occupy- ing the centre of the floor of the cleavage cavity. From this internal and thicker layer an innermost unicellular layer separates (intestinal gland layer, Darmdriisenblatt, Remak), whilst the remainder forms the moderately thick middle or motor germinal lamina. Fig. 400. Fig. 400. Vertical enlarged section of an egg of Bufo cinereus. The cavity or fissure proceeding from N, and extending to z, is, for the sake of clearness, drawn throughout its whole extent as a broad fissure, which, however, in reality only holds good for the upper half ; D, roof ; z, floor of the cleavage cavity ; F, P, white area. The sickle-shaped (as seen on section) mass of cells (z) con- stantly rises towards the pole, and the (in horizontal sections) semilunar fissure extends in the same direction. But as the fissure penetrates into this newly developing mass of cells the portion external to the fissure forms a definite deposit upon the roof of the cleavage cavity, whilst the other part, which is the thinner of the two (D) remains as a septum between the fissure (N) and the cavity of Baer (F). If meridianal sections dividing the back into two halves be made through ova at this stage of development (fig. 401), it appears that those cells which have reached from the floor of VOL. III. L L 514 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STEICKER. the cleavage cavity to the roof, and which, after the forma- tion of the semilunar fissure, remain adherent to the roof, are continuous with those cells which were above described as be- longing to the internal thicker layer of the inferior segment of the back. In other words, that which subsequently adheres to the roof of the cleavage cavity is the rudiment of the motor and intestinal gland laminae. I have already mentioned that in the original roof of the cleavage cavity only the analogue of the sensorial lamina of Remak is to be looked for. This lamina, however, as I* and Fig. 401. Fig. 401. The illustration here reproduced was obtained from a remarkably successful preparation made in the year 1860. How far it is diagrammatic in its finer details I am unable to say, but the main features are undoubtedly as correct as possible. I have therefore no hesitation in giving it here, notwithstanding that the same relations have been excellently illustrated by Gotte, v. Bambeke, and Golubew. My figure appears to me to materially facilitate the understanding of the parts in question, and it is on this account that 1 give it. The letters D, F, P, Z, z, as in fig. 400 ; a, dorsum of the embryo ; s, septum between the food cavity, Nt and the cleavage cavity. v. Bambekef have shown, is composed of two layers in the Batrachia, of a superficial layer of brown cells forming one tier, and of a deeper layer of whitish cells, which in some parts form a single tier, and in others, many tiers. The external brown cells constitute the rudiments of the horny or corneal * Loc. cit. t Recherclies sur la developpement du Pelobates brun, Memoire publie par V Academic Belgique, Tom. xxxiv. PROCESS OF DEVELOPMENT IN BATRACHIAN OVA. 51. "3 investment of the animal, whilst the inner whitish cells form the proper sensorial lamina. In Birds and Mammals these two layers are so intimately connected that no difference can be demonstrated between them, even in the most successful transverse sections. Owing to this, Remak has regarded the two rudimentary structures as one, and has designated the whole lamina as the " sensorial lamina" (central portion), or " corneal lamina" (peripheric portion). He has, however, pointed out that there are theo- retical considerations that are opposed to the view that the corneal and nervous structures originate in one lamina. The fact is therefore of proportionate interest, that in Batrachia, and, as I shall subsequently sh*ow, in Fishes also, the corneal and nervous structures are already distinct at the earliest period of their development. Bearing in mind these circum- stances, I apply the term " corneal lamina" (Hornblatt) to the external layer of brown cells, and " nerve lamina " (Nerven- blatt) to the deeper whitish cell layer. In regard, however, to Birds and Mammals, and generally speaking, where it has become requisite from later investigations, I shall designate the external germ layer (Remak) as the " conjoined corneal and nervous lamina." To recapitulate, then, what we have just stated at length, it appears that the corneal and nervous lamina proceeds from an external mantle or investing layer of the spherical ovum, but that the motor and glandular layers originate in the large germ cells collected as a reserve store in the lower half of the ovum. The germ cells have in fact undergone this differentiation in their original position; that is to say, in the lower half of the ovum. But they must be in part also either actively or passively displaced from the inferior towards the superior pole, or, which comes to the same thing, from the caudal extremity of the future larva towards its capitate end. As soon as Rusconi's groove is completed into a circle, a fissure runs out from its abdominal half towards the upper pole. It scarcely, however, extends as far as one-fourth of th<> height of the germ cell layer (though its dimensions may vary in different species), and it dilates at the csecal extremity of the ovum. Remak has termed this cleft the anal cavity. L L 2 oil) DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. The cleft first visible on the dorsal half, and appearing semi- lunar in tiansverse section, is completed by the anal cavity. If a horizontal section be now carried through the inferior pole, the fissure is seen to be circular. Close to the inferior pole the circle becomes somewhat smaller, and ceases with the freely exposed groove of Rusconi. A funnel-shaped space thus com- mences at this groove, which is occupied by the plug composed of white germ cells (yolk plug, Dotter-propf, Ecker). As the canal in which the outermost portion of the cone sticks gradually contracts, the white area becomes so small as to be perceptible only as a white point. At a later period this also disappears, and there remains only a canal still recognizable in sections, and with high magnifying powers, which all authors have designated the anal opening. And now, when the extremely attenuated plug of white cells retracts or tears away, (as at least in all probability occurs in Bufo cinereus,) Rusconi's groove communicates with the anal cavity through- out its whole extent. A small annular swelling, visible even to the naked eye, on the outer wall of this cavity, still indicates the point where the yolk plug formerly interrupted ihe cavity, and the depression in the swelling is a guide to the spot where the section should be carried if it be desired to hit the canal at its embouchure. In the meanwhile the ovum has undergone its rotation ; the meridian has become its sequator; the anal opening has a lateral position, the dorsal half being superior, and the abdominal half, with the annulus of germ cells projecting strongly towards the food cavity, being inferior. In the latter, some remains of the cleavage cavity of Baer are long preserved. The ovum may still be regarded as a vesicle enclosed by laminated walls, except that in the lower half of the vesicle the innermost lamina is pushed inwards by a mass or hillock of gerrn cells. The various laminae, however, do not present the same thickness throughout. I must here draw this account to an abrupt conclusion, because these differences already con- stitute the beginnings of the rudimentary organs, which cannot in this work be further discussed. (&.) THE GERM OF THE FOWL.— In the egg of the Fowl, the PROCESS OF DEVELOPMENT IN AVIAN OVA. 517 so-called " tread," or cicatricula, constitutes the germ, which is enclosed in the same general investment as the yellow yolk. Pander * described the cicatricula as composed of two easily separable layers, of which one dips into the yellow yolk, whilst the other forms a layer upon its surface. The latter, he says, is a round disk, in and from which the foetus is formed, and which may therefore justly lay claim to the title of blastoderm (germ-membrane, Keimhaut). The former part was termed by Pander the nucleus of the cicatricula. This is a constituent of the so-called white yolk, which lies beneath, but is not con- nected with, the central transparent part of the germ-membrane. B Fig. 402. F N a P Z, as in the preceding figures ; kk, sections of. the annular swelling and margins of the anus. The- punctated line between k P, indicates the antecedent connection of the yolk plug with the germ-cell mass, z.. The ovum in this condition has already performed the rotation, the dorsum lying above, the abdomen below. The statement of Pander, that the embryo is developed exclusively from the germ disk, remains unshaken up to this time. Keichertf and His:}: have certainly endeavoured to show, from various points of view, that the morphological elements of the white yolk enter into the new animal body. His, on the ground of his own observations, has also designated the germ disk as the principal germ (Archiblast or Neuroblast), and the accompanying constituent of the white yolk as the * Beitrcige zur Entwickelungsgeschichte des Huhnchens, (Essays upon the history of the development of the Fowl.) Wiirzburg, 1817. t Entwickelungsleben im Wirbelthierereiche, 1840. £ Untersuchungen iiber die erste Anlage des Wirbelthierkibes, 1868. 518 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. secondary germ (Parablast or Hoemoblast). The account he has given has not, however, been sufficiently proved; and in the course of the subsequent description it will be shown that the observations from which it was drawn permit other significations to be given more conformable to general biological principles. The account given by Pander refers to the fertilized laid, but not incubated egg. The commencement of incubation certainly cannot be regarded as the beginning of the process of development. During the passage through the oviducts important processes, from my point of view, take place ; for the cleavage of the germ occurs .here, and the cleavage elements arrange themselves in layers. This lamination has progressed to various stages in different ova at the time of their being laid, and on this account alone it would be disadvantageous to ascribe a definite histological character to this period. The cleavage of the germ of the Fowl was first described by Coste * This, however, he did only so far as it can be observed to occur on -the surface. Oellacherf1 examined trans- verse sections of the yolks of eggs at various stages of cleavage, and in his essay we for the first time meet with an account of the very first traces of the chick. I feel myself compelled therefore to adhere to his statements. But inasmuch as his researches were conducted under my own inspection, the account here given is based in part upon my own observations. All the preparations here alluded to were obtained by the following means. The yolks of oviducal eggs, or of eggs obtained during the first day of incubation, were carefully freed from albumen, cautiously washed with dilute chromic acid, the albuminous precipitate as it formed being removed with forceps, and the clean yolk then placed in pure diluted solution of chromic acid. After a few days the segment of the yolk containing the germ membrane was removed, and care- fully placed in alcohol, where it was allowed to remain till the water was as far as possible removed. It was then imbedded. * See his Histoire du Developpement des Corps Organises. t Strieker's Studien, 1870. PROCESS OF DEVELOPMENT IN AVIAN OVA. 510 The proper method of imbedding is to make a little paper case, which is then half filled with a mixture of wax and oil. When the mixture has so far stiffened in the paper case that a pre- paration laid upon it will not sink in it, the specimen is placed in the desired position, and is again covered with the fluid mixture till the case is full. As soon as this second mass begins to stiffen, the position of the specimen is carefully noted, and when the stiffening is completed, the direction in which the section is to be made is marked. The proportion of the oil to the wax should be so chosen that the consistence of the mixture corresponds to that of the specimen and the convenience of the operator. I cannot allow this opportunity to pass without expressing my astonishment at the obstinacy with which even excellent micro- scopists overlook the advantages afforded by such a mixture as the above. The mixture of two bodies of such different consistence as wax and oil enables us to obtain all grades of consistence between those two extremes. For extremely delicate embryological specimens, such advantages are simply inestimable. I shall here incidentally remark, that where the specimens, as in the case of the ova of Frogs, enclose cavities in their interior, these must be opened to permit them to be filled with the mass. It is only in those instances .where the specimen and the mixture of wax and oil are everywhere in complete and accurate contact, that we can expect to obtain good preparations. The paper case should be sufficiently large to enable the operator to hold it securely. The knife should also be large, as sharp as possible, and on one side at least ground flat. When in use, its upper surface should be wetted with oil of turpentine. On completing the cut, the section should be floated off upon the slide by the aid of a little oil of turpentine. It can then be preserved in the usual way with oil of cloves, Dammar balsam, and a paper cushion. So far as sections of ova hardened in chromic acid permit us to speak positively in regard to the real form of the parts, the perfectly mature germ has the shape of a biconvex lens, which is somewhat concave at one pole, that, namely, which in the natural position is the inferior. Its diameter amounts to about half a millimeter ; its thickness is about 0*05 of a milli- meter at the concave, and O06 at the biconvex points. In such a sharply defined body the germ has to be sought. The vitel- line membrane is above it, and beneath is a finely granulated 520 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. mass, of which it cannot at present be stated whether it be- longs to the germ or not. Oellacher has not been able to recognize a germ- vesicle in sections made at this stage. The first groove in the germ was found in an egg that, ac- cording to the laying-time of the hen, had remained for twelve or fourteen hours in the oviduct. The body appearing to be the germ was in the already described position, but was some- what larger and thicker, a sinuous indication of fission of its substance extended somewhat obliquely downwards from the centre of its convex surface. The second groove was obtained from an ovum, the shell of which already presented some traces of calcification. And again, at the point at which the germ was to be sought, there was a somewhat concavo-convex disk, which however appeared to be thinner and larger than that of the earlier stage. Pro- ceeding from the surface, five clefts penetrated into the interior, splitting the disk into six areas on section. The two most external areas were the longest, but the four middle ones did not materially differ from each other. In this specimen it was impossible to state with certainty whether there were other, though less defined, morphological elements of the germ beneath the above areas. The next stage was taken from an eofff, the shell of which O OO7 was already consolidated, but was relatively \ery thin. The germ was here sharply separated from the yolk, and there was a distinctly perceptible cavity between the two. Sections through the centre showed that the germ was composed of polygonal areas, of which six could be counted between the surface and the cavity. The whole germ, and this term could now be applied with precision on account of the sharp definition of the mass below, always presented an approximation to the form of a biconvex lens, the upper surface of which was adherent to the vitelline membrane, but the under surface of which was irregularly bounded by the flat cavity existing between the germ and the yolk. The marginal areas were the largest, and were filled with larger granules than those more centrally situated. In a few of the areas a nucleus was distinctly visible. At a subsequent stage, in an ovum also taken from the ovi- PROCESS OF DEVELOPMENT IN AVIAN OVA. 521 duct, the process of cleavage had progressed to a marked extent. Large polygonal areas were only present at the margin. In the central parts were small granular morphological elements, loosely attached to one another, of which the upper ones were riner, whilst those in the deeper layers were more coarsely granular. In the peripheric parts the germ disk rested upon the yolk, but in the central parts the two were separated from each other by a flat cavity. A few morphological elements, resembling those of the lowermost layer of the germ disk, lay upon the floor of this cavity. Oviducal eggs of a still later stage presented little more that was worthy of notice. The cleavage had progressed to a some- what greater extent even at the marginal portions ; the mor- phological elements were in general smaller ; the whole disk was somewhat thinner, the cavity somewhat deeper, with a few- larger, spherical, strongly granular formed elements resting on its floor. Finally, in one oviducal egg a still more advanced stage of development was met with. The cleavage elements, or embryonal cells, as we may also term them, were partially separable into two laminae, of which the upper (S, fig. 403) was of closer texture, and was composed of smaller cells, whilst the lower (Z)) contained somewhat larger and more coarsely granular cells, so irregularly disposed that in some parts they only formed a single tier, whilst in others they were seen in section to be collected into heaps of from two to three cells deep, presenting in consequence projections at these points. In freshly laid ova the germ has sometimes undergone no development beyond that which has been already described, whilst in other instances the lower layer, composed of larger cells, is sharply separated from the upper throughout its whole extent. As a general rule, it may be said that, in freshly laid eggs, the separation of the germ into two layers is sometimes more, sometimes less well marked, but that the cleavage is not as yet quite completed. The morphological elements of the inferior layer are still tolerably large, and some very large cleavage spheroids (M, fig. 403) still occur, which project strongly down- ward towards the cavity, sometimes even touching its floor, so that the blastoderm appears in transverse section to be 522 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. supported on pillars. Sometimes such large elements rest upon the floor of the cavity without being in contact with the blasto- derm above; in such cases it must remain doubtful whether these elements have been detached during life, or have been separated by the action of reagents. The presence of such variously sized elements lying on the floor of the cavity is however so constant, that it is difficult to avoid the conclusion that they have been separated during life, or have remained adherent to the floor of the cavity when the blastoderm has been raised from it. Near the free border the blastoderm is thickened, chiefly owing to the large cleavage spheroids situated upon its lower surface, but beyond the thickening the border becomes thin and sharp. It rests with the thickening upon the yolk, and thus lies like a cover over a shallow depression in the latter. Fig. 403. Fig. 403. Section through the germ of a fresh-laid egg in the month of June. The cavity which is thus formed was termed by Remak the "Germ-cavity" (Keimhole). The wall bounding the cavity named by His the " Germ-wall" (Keimwall). This wall, how- ever, is by no means a constituent of the germ ; it belongs to the yolk, and the term germ- wall is consequently inappropriate. As the accounts of the layers of the embryo are associated with the last-mentioned stage, this is the place in which a sketch of the literature bearing upon the subject may be introduced. We are indebted to Caspar Friedrich Wolff* for the prevailing doctrine respecting the development of the Vertebrata from the so-called * De formatione intestinorum, 1768-69. Translated into German by Meckel, 1812. HISTORICAL ACCOUNT OF EMBRYOLOGY. 523 germinal laminae. According to his view, the entire composite system of the intestines is developed from a single lamina. His doctrines were enlarged and completed by Pander.* The blastoderm, he maintains, is composed of a layer of granules, which serves as the rudiment of the future inferior germ-layer. A second layer of similar granules develops upon this layer, even during the first hours of incubation, and constitutes the future superior layer, so that the blastoderm at the twelfth hour of incubation consists of two lamiiue, the upper one of which he named the serous, and the lower the mucous layer. Although he alludes also to the middle layer, under the term " vascular lamina," his description of it is deficient in clearness ; for, according to him, it is sometimes an independent struc- ture in which the vessels are developed, but in other instances it is a consequence of the development of the vessels. Nevertheless, he was perfectly aware of the fact that, after twenty-four hours' incubation, three layers, easily separable from one another, are recognizable in the blastoderm. Pander was also the first who endeavoured to sketch out a general plan showing the development of the organism, which he did by referring all the structures and organs that had been termed "animal" from the time of Bichat and Reil to the superior germ- lamina (or epiblast) ; to these belong the nervous system, with the organs of sense ; the muscular and the osseous system. The middle lamina (or mesoblast) he regarded as being simply a vascular lamina ; whilst the lower (endoblast) he considered to contain the rudiments of the intestinal system and its associated glands. The researches of v. Baer t corroborated those of Pander, and may be regarded as a continuation of them ; v. Baer described a layer in the non-incubated egg as the first rudiment of a blastoderm ; but, in opposition to Pander, he considered that in the course of the first few hours of incubation a second lamina was formed beneath, not above, this layer, which constituted the rudiment of the endoblast. The development of the mesoblast (vascular lamina) was described in a manner accordant with the account given by Pander, v. Baer con- siderably enlarged our views in respect to the general plan of development. He demonstrated the participation of the mesoblast in the formation 0f the fibrous ludiment of the intestine, as well as in that of the associated glands. He stated that the two layers origi- nating during the first hours of incubation, each divided again into two layers, of which the upper formed the integumental and muscular * LOG. cit. t Ueber die Entwickelungsgeschichte der Thiere, 1822, i. 524 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STEICKER. laminro ; the lower the mucous and intestinal fibrous lamina. The two upper layers he designated the animal ; the two lower the vegetative. Reichert* gave another account. He distinguished in the blasto- derm of the fecundated, but non-incubated ovum a layer of corpuscles, from which a membrane (the investing membrane) was developed during the first hours of incubation. The formation of this tunic Reichert regarded as being the first condition for the further develop- ment of the embryo, since the yolk cells assumed a laminated arrange- ment upon its inner surface. The rudiment of the nervous system, he maintained, first makes its appearance, then that of the middle lamina, which, on account of its position between the upper and lower germ layers, he termed the membrana intermedia. After the completion of the formation of this membrane the development of the lower layer commences, the yolk cells depositing themselves upon the lower sur- face of the former at a time when the embryo begins to be constricted off from the blastoderm. As regards the significance of the blastodermic layers in the further development of the embryo, he considered that the upper lamina takes no part in the formation of the embryo, and that it disappears during the embryonic life of the organism. In regard to the middle lamina, he was the first to show that a division of the lateral plates occurs, and. that the middle lamina participates in the formation of the walls of the body. He maintained also that the corneal layer of the integument, the glands of the skin, the muscular, osseous, and vascular systems, as well as the intestinal fibrous layer, with the associated glandular organs, are developed from this lamina. The lower lamina he regarded as representing simply the rudiment from which the epithelium of the digestive organs is developed. Remak first noticed that the blastoderm of the fertilized but non- incubated egg is composed of two layers. The next changes were referable, according to him, to the inferior layer, which becomes thicker, though it is always looser and less transparent than the upper one. Then follows an histological differentiation of its elements, a layer of cells becoming detached, and covering the inferior surface like an epithelium. As regards the relation of the germ layers to each other in the area of the germinal area (Fruchthof), the upper and middle appear to become thicker, and coalesce at a very early period in the centre of this area. The inferior layer, however, takes no part in this coalescence. With the exception of the middle part of the germinal area, all the three layers may be easily separated from each other throughout their whole extent, both in the vascular area, and in the * Loc. tit. HISTORICAL ACCOUNT OF EMBRYOLOGY. 525 peripheric parts of the germinal area. Rernak endeavoured at the same time with the anatomical independence of the germ layers to establish the relation to the various organs during the further develop- ment of the organism. The names that he applied to the lamina are self-explanatory. The upper lamina, as has been already stated, he termed the corneal or sensorial layer (Hornblatt oder Sinnes blatt) ; the middle, the motorio - germinal (motorisch - germrnatives) ; and the inferior lamina, lastly, the intestinal-glandular layer (Daruidriisen- blatt), since the epithelium of the intestinal system, with the associated glandular organs, is developed from it. His,* again, admitted the existence of only a single layer of corpuscles in the fertilized but non-incubated ovum, which constituted the rudiment of the upper germ layer (Archiblast or Neuro-blast). The inferior layer, he considered, develops during the first hours of incubation of the egg by the elongation and junction of the (subgerminal) processes which project from the inferior surface of the upper layer, and consist of one or several rows of cells. The lower layer, on this view, therefore is originally a production of the upper. From these two laminae the whole embryo, according to him, is formed, with the exception of the blood-vascular system and the group of the connective tissues which develop from the so-called white yolk. In the middle region of the germinal area, moreover, a layer separates from the upper, and one also from the lower lamina ; and lastly, an axial connecting band forms between the upper and lower germ layers. According to Hensen,f the division of the blastoderm into layers occurs at a later period than was admitted by Remak. Hensen also described, as forming at that period of the development of the embryo when the chorda dorsalis has developed in the centre of the germinal area, a "peculiar, consistent, non-nucleated membrane," to which he applied the name " membrana prima." It lies between the epi- and meso-blast, and is more closely adherent to the former than to the latter. He considers it to play an important part in the development of the embryo. According to Dursy,J the centre of the blastoderm (the embryonic shield) consists, at about the fifteenth hour of incubation, of two layers, and the inferior, he believes, may be regarded as the rudiment of the middle germ layer. The statement made by Remak, that the mesoblast is produced by a dilamination of this inferior layer of the blastoderm, * Loc. cit. t Yirchow's Archiv, Band xxx. ; Max Sclmltze's Archiv, Band iii. J Der Primitifstreif des Huhnchens. 526 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STEICKER. he considers to be not proven. The endoblast is perhaps developed subsequently on the vitelline side. Waldeyer,* on the other hand, returned again to the view of Eemak, that the mesoblast and the intestinal glandular layer proceed from the originally inferior lamina. Waldeyer, however, independently of Peremeschko, recognized that a great part of the cells subsequently existing in the rudiment of the embryo wandered between the blasto- dermic laminae. He was not, however, able to decide, so far at least as regards the cells on the floor of the germ cavity, whether they are descendants of the white yolk or are cleavage spheroids. That which His termed subgerminal processes he did not consider to be a production of the epiblast, but as primary descendants of the egg cells. I omit the statements of Peremeschkot and Oellacher,{ as they constitute the basis of the account I here subjoin. A comparison of my account with the historical review above given, shows that I, like Remak, consider the germ disk of the fresh -laid egg to be composed of two laminae. I would only add that the division into two is not always complete throughout the whole extent, the laminae being sometimes still intimately adherent, and the agency of the heat of incubation is required to perfect their separation. The cells of the lower lamina change their form and arrange- ment in the course of the first hours of incubation. They become flattened; and appear fusiform on section (D, fig. 404). After a few hours, thin sections of well-preserved specimens show with perfect clearness, that two, and only two, layers are present. The upper one is thicker and more compact, and is often composed of two, three, or more tiers of cells; the lower one consists of a number of flattened cells, appearing fusiform on section. The inferior lamina was indeed, in the first instance, after it had separated from the cloven germ, partially unicellular, though in some parts projecting masses of cells were visible in transverse section. I am unable to state what has in the mean- while become of these cell masses. * Zeitschrift fur rationelle Medicin, 1869. t Wiener Sitzungsberichte, 1868. 1 Loc. cit. PROCESS OF DEVELOPMENT IN AVIAN OVA. 527 Peremeschko, however, states that the large granular cells on the floor of the germ cavity augment considerably in num- ber in the course of the first hours of incubation. And, since with this increase in number there is no corresponding diminution in size, it becomes highly probable that the cells projecting downwards from the inferior lamina fall to the bottom of the cavity. This is the more likely, as it is obvious from the appearance above described, that a part of the cleavage elements lying in the lower segment of the germ remain lying upon the floor of the cavity when the germ rises in order to form this cavity. The lower of the two primary laminse is, in my opinion, therefore not identical with that which Eemak has described under the same designation. According to Remak, the middle and what is subsequently the inferior layer separate from this lower lamina. This, however, is not really an accurate state- ment of the case. The originally inferior lamina consists, at least before the middle one is formed over the germ cavity, of a layer of flat cells, and it preserves this structure long after the middle lamina is formed. The much thicker middle layer cannot arise by dilamination from this layer of flat cells. Peremeschko has met with the first traces of the middle lamina at about the seventeenth hour of incubation. The statement of the exact number of hours has only an approxima- tive value, since both the brooding temperature* and the con- dition of the ovum at the commencement of incubation must be taken into consideration. With this precautionary observa- tion I shall here follow the statements of Peremeschko. At about the seventeenth hour of incubation, then, coarsely granular elements occur here and there between the upper and lower laminse, which, both in regard to their size and contents, differ essentially from the cells of either of these laminae, but agree perfectly with those that lie on the floor of the cavity ; soon after this the rudiment of the central part of the middle lamina appears. In some preparations it may be observed that * I use a water bath for the purpose of incubation, maintained at a tolerably uniform temperature of 39° C. (102° Fahr.) by a self -regulating gas flame. 528 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. this rudiment consists already in part of the characteristic cells of the subsequent mesoblast, though in part also of the cha- racteristic coarsely granular large elements (M, fig. 404); the upper lamina appears to be tolerably sharply defined from the above-mentioned layer. The central portion of the meso- blast is thus developed at an earlier period than the rest. Preparations in which the central part was already developed, exhibited on both sides of it, in the space between the epiblast and endoblast, as far as to the periphery, and somewhat be- yond it, new-formed characteristic cells of the mesoblast, in the form of thin layers or small heaps, and sometimes between these, again, the large coarsely granular elements in which the transitional forms from the latter to the heaps of cells may be distinguished. From this observation it must be admitted that the mesoblast is developed from the large coarsely granular elements. Fig. 404. Fig. 404. Section of the germ of the Fowl on the first day of incu- bation. We thus see that certain morphological elements gradually diminish in number at one point (floor of the germ cavity), where they were previously abundant, whilst quite similar elements make their appearance in an adjoining cavity (between the 'epiblast and endoblast), and then augment in number, and become converted into collections of smaller cells. It therefore seems probable that a migration or displacement occurs, by means of which the granulated structures that pre- viously lay upon the floor of the cavity are introduced between the two first germ laminae. At about the twenty-third hour of incubation all three of the germ laminge are completely developed. The cells of each lamina possess such characteristic features, that they may easily PROCESS OF DEVELOPMENT IN AVIAN OVA. 529 be distinguished from each other. A description of the cells of the upper and lower germ laminse has already been given. Those forming the middle lamina are small round cells with uncommonly delicate outlines and elongated sharply defined nuclei. As regards the relation of the laminae amongst themselves they may be regarded as perfectly distinct, with the exception of the middle part of the blastoderm, where the separation of the middle from the upper lamina cannot be effected. Peremeschko has examined the variously named large ele- ments lying at the bottom of the cavity on the warmed stage. They change their form at a temperature of from 32° to 34° C. This alteration of form usually consists in a primary contrac- tion and loss of transparency, their form becoming oval or irregularly round ; they then begin again to increase in size, and to become more transparent. This alternate contraction and enlargement was several times repeated in one example. The changes in form were observable both in incubated and in non-incubated eggs, but took place with great slowness. The accuracy of Peremeschko 's observations have been corroborated by Oellacher. The perfectly unmistakable ap- pearances presented in similar specimens I have also myself so frequently seen, that I can entertain no doubt of the sub- stantial correctness of his statements. If we now compare the disposition of the cleavage elements in the germ of Batrachia with that of Fowls, it appears that in Batrachia the external germ lamina, or the sensorial lamina of Remak, is divided into two layers, whilst in the germ of the Fowl it is undivided. In both cases, however, it is developed from a superficial layer of cells v which is earlier differentiated than the deeper lamina ; from the latter two other laminae are developed, namely, the inferior and middle laminae. Thus at a Certain stage there exists an opposition common to both between an upper layer of smaller and a lower layer of larger cells. In Batrachia, as in Fowls, the larger and more slowly dividing cells experience a partial dislocation, passing into a cavity de- veloping coincidently with the process of cleavage. In the Batrachia the large germ cells are attached to the roof of the cleavage cavity, whilst in Fowls the large coarsely granular M M 530 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. elements fall down upon the floor of the cavity, and in order to penetrate between the superior and inferior laminae must necessarily undergo an active or passive migration. In both cases the more slowly cleaving large elements form the rudiments of the middle and gland laminae, and modifications only occur in the mode in which this end is attained. In the case of the Fowl, we know that the middle lamina is not com- pleted with the first rudiment of the embryo. I shall hereafter show that in the course of the second day of development a second migration of large coarsely granular elements occurs for the purpose of forming a rudiment of the vessels, the store of which on the floor of the germ cavity, as I may just state in passing, is not exhausted by the first migration. In the ova of Batrachia no analogue of the rudiment of the blood- vascular system completing the formation of the meso- blast is discoverable. This, however, may perhaps be referrible to the fact that nothing is at present known in regard to the origin of the bloodvessels in the ova of these animals. In the eggs of Batrachia, also, after the appearance of the rudiment of the mesoblast, a store of large cleavage elements remains behind (fig. 402), respecting the destination of which we know nothing. (c.) GERM OF THE FORELLA (TROUT). — For the purpose of com- parison, I shall here briefly give the facts that have been acquired in regard to the embryonal laminae in osseous Fishes. Rynek* has studied this subject under my inspection in the ova of the Forella, and his are the only researches which give the results of transverse sections. These show that the segmented germf lies originally in contact throughout its whole extent with the yolk, but that during the expansion of the germ the cavity already known through Lereboullet J is developed. This cavity is completely analogous with the germ cavity of the Fowl's egg. The germ is stretched over the cavity, and rests with a thickened border upon the yolk at the margin of the cavity. The part stretched over the cavity exhibits again, in * Max Schultze's Archiv, Band v. t The cleavage was first described by Rusconi in Mliller's Archiv for the year 1836. I Noui-elks Eecherches et Annales des Science Nat. Zoologie, Tom. ii., 1864. PROCESS OF DEVELOPMENT IN OVA OF FISH. 531 its inferior layer, large cells which are disposed, like those of the Fowl, in irregularly distributed heaps. By degrees the inferior surface becomes plane, and the part lying over the cavity then appears to be composed of two layers of uniformly small cells. The upper layer consists of a single tier of cells, but the lower is composed of two or three tiers of cells. Further research showed that the analogue of Remak's sensorial lamina was developed from these two layers. This is here, therefore, as in Batrachia, composed of two distinct rudiments. Large coarsely granular elements lie on the floor of the germ cavity. The origin of these elements can scarcely be a matter of doubt. The yolk of the egg of the Forella contains no mor- phological elements from which they can proceed. No other view can be held, therefore, than that they are the remains of the segmented germ which, on the elevation of the latter from the yolk, remain in part lying upon this, and have in part fallen down upon it from above. We thus see the parts around the germ cavity present relations analogous to those we have already met with in the germ of the Fowl. Fundamental differences, however, do exist, and in order to establish them I must enter into some comparative embryo- logical details. Coste* long ago called attention to the fact that the embryo of the Fish does not originate in the axis of the germ, as occurs in Fowls, but along a part of the thickened border. The relations that are here present may be readily understood by the following conception. Imagine a small sphere of wax placed upon a large wooden ball, and the former flattened out into a disk with a thickened border; the disk continues to expand, its thickened border constantly increasing in size till it reaches the sequator of the wooden ball. And now the wax cap may be conceived to enlarge still further, whilst the thick- ened border becomes constantly smaller, till when the opposite pole is reached it is reduced to the condition of a scarcely per- ceptible annulus. The ball will then be almost completely en- veloped by the wax cap. Relations exactly resembling the above exist between the germ and the yolk of the egg of the Forella. If the ova at various stages of development be hardened in chromic * Loc. cit. M M 2 532 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. acid, and the thick vitelline membrane be cautiously peeled off, the different stages of the process of investment may be fol- lowed with the naked eye. Before the cap covers the first third of the yolk sphere, it may be seen that the thickened border is particularly enlarged at one part. With a lens the dorsal groove may here be seen, which is directed towards the superior pole (the original position of the germ). As the cap enlarges, this rudiment of the embryo increases in size, forming a thickened cord or column of the cap extending from the thickened border towards the upper .pole. Finally, when the border is reduced to a slender ring, scarcely visible to the naked eye, it bears a relation to the embryo (the thick- ened cord) which recalls in a lively manner the relation in which Rusconi's anal aperture of the Batrachian ovum stands to the axis of the dorsal half. Rusconi has himself called attention to this resemblance. In the Batrachian ovum the dorsal furrow extends from the anal aperture towards the superior pole, though it does not quite reach to it. The thickened cord representing the dorsum of the embryo of the Forella has precisely the same relation to the annular remains of the thickened border which, as is self-evident, bounds a canal. In the egg of the Forella, how- ever, the yolk is exposed by means of this canal, whilst in the Batrachian ovum, in which there is no yolk, large cleavage cells are exposed. The whole remainder of the cap constitutes to some extent the wall of the body, but is in chief part a yolk sac.* The centre of the germ disk, which has thus been shown originally to lie over the germ cavity, is in Fowls the most important part, being in fact the proper embryo, whilst in Fishes it forms only the rudiment of the yolk sac. In both germs the deep-lying large cells fall upon the floor of the germ cavity. In Fowls, however, a layer remains behind to form the intestinal glan- dular layer. In the Forella all fall down, and scarcely any glandular lamina is formed in the centre. If now, at the time when the attenuated centre (S) of the * See my illustrations in the Sitzungsberichte der Wiener Akademie, Band li. PROCESS OF DEVELOPMENT IN MAMMALIAN OVA. .533 still but little expanded germ lies over the cavity, the larger cells lying on the floor of the cavity be followed towards the periphery, it may be seen that they are directly continuous with the deep layer of large cells which forms the lower layer of the thickened border, and, as it would further appear, the rudi- ment both of the motorial and intestinal glandular layer. This relation renders it highly probable that the large cells on the floor of the germ cavity migrate towards the periphery, in order to form or to strengthen the large-celled deposit there found. It is further to be remarked that a rich plexus of blood- vessels develops beneath the walls of the yolk sac, and that the large cells upon the floor of the cavity may fulfil some pur- pose in the development of this plexus. Fig. 405. Fig. 405. Section of the germ of Salmo fario. (d.) MAMMALS. — In regard to the first changes occurring in the germ of Mammals, I have scarcely myself made any observa- tions worthy of notice. In this domain I am therefore only a compiler. And, however valuable the literary material before me may be, I am still unable to make more than a limited use of it ; first, because I am unable to give here a history of the controversies by which the first positive facts were established ; and secondly, because the Mammalian ovum has scarcely been worked over during the most recent epoch of embryology. The older statements do not accord well with modern modes of expression, and I have no inclination to reconcile the differ- ences at the desk. I prefer to give a concise account, and at the same time to call attention to the fact that in the history of the development of the Mammalian ovum there is a rich field of inquiry to be worked over. Bischoff first gave an accurate account of the cleavage of the .534 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. Mammalian ovum, and in an historical point of view I must maintain this, though Bischoff * himself ascribes the first know- ledge of the process to Karl Ernst v. Baer. BischofF's description is really the first that stands on a level with our present know- ledge. In that description it is clearly stated that the germ (yolk) within its investing membrane, and independently of it, breaks up into smaller morphological elements. Thus the ovum of the Kabbit, he says in his excellent treatise, during the cleavage of the germ (}folk) into progressively smaller spheroids, and surrounded by a thick layer of albumen, passes from the oviduct into the uterus. The duration of its passage through the oviduct, from the concordant testimony of De Graaf, Cruikshank, Coste, Wharton Jones, Barry, and Bischoff, appears to be tolerably constantly two days and a half. The confidence that Bischoff 's illustrations inspire, leads us to believe that the cleavage of the Mammalian ovum is not equally uniform throughout its whole extent. Within the uterus a cavity is developed also in the Mammalian ovum, which gra- dually increases to such an extent that the cleavage elements compressed at the periphery form a very thin layer enclosing the cavity, or, as it may also be described, constitute the wall of a vesicle. In this condition the little ovum bad already been recognized by De Graaf. He described it as a minute vesicle composed of two membranes. The external membrane, as Bischoff has clearly shown, is the germ sheath (Keimhiille), but the internal is the proper germ membrane (Blastoderm, Keimhaut). Bischoff further described a dark mass, consisting of spheroids, attached to the germ vesicle at some point of its interior. These, he says, are spheroids which are obviously identical with the spheroids proceeding from the antecedent cleavage of the germ. They must thus in the process of cleav- age remain behind those that form the extremely thin and already very clear and transparent wall of the vesicle. Whether the place where these germ cells accumulate is identical with that at which the germinal vesicle subsequently becomes thickened, we must for the present allow to remain undecided. At this thickened spot ("germinal elevation," Keimhiigel of * Entwickelungsgeschichte des Kanincheneies, p. 66, 1842. PROCESS OF DEVELOPMENT IN MAMMALIAN OVA. 535 v. Baer, " embryonic stria," " embryonal spot " of Coste,) BischofF was again the first to observe the occurrence of a division into two laminae, and his description of the spot in question cor- responds exactly to the relations that we have now, with superior aids to research, ascertained to exist in the ova of Birds, Batrachia and Fish. The cells of the animal layer, in accordance with his description, form a dense membrane, whilst the cells of the vegetative lamina are still distinct, and are very delicate and pale. What signification we are to give to these two laminae, in the present state of our knowledge, I am unable to determine. A single tolerably clear section from the ovum of a Dog of corresponding age led me to think that the two laminae, of which the germinal vesicle external to the dorsal rudiment (germ elevation, Keimhugel) is composed, are to be regarded as the analogues of Remak's sensorial and glandular laminae. It is reserved for the future to give a more definite account, especially in regard to the relations existing at the germ elevation. I am unable to make any further statement respecting a third vascular lamina occurring between these two, which has been much discussed, and which was admitted by Bischoff. It is, in the first place, doubtful whether this middle lamina is really a vascular lamina, or merely corresponds to Remak's middle germinal lamina. The subject of the development of the middle germinal lamina in Mammals requires a fresh investigation. After the knowledge that has been gained by researches con- ducted on other classes, I cannot venture to reproduce here any of the opinions generally advanced. So far as this lamina really contains the rudiments of vessels, I shall hereafter have to refer to it again. (e.) MORPHOLOGICAL VALUE OF THE GERMINAL LAMINA. — It has already been stated that the external germinal lamina (epiblast) contains the rudiment of the central nervous system, of the nervous constituents of the organs of sense, and of the superficial cellular investment of the animal. It has also been explained why I have designated it the conjoined corneal and nervous lamina. In Batrachia, in which the corneal lamina is separated from the nervous lamina, the relations are extremely 536 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. clear. The corneal lamina is uniformly thin throughout its whole extent, except where the sucker of the larva originates. From it also develop the internal cellular lining of the central canal, the external cellular coat of the animal, and the cellular invest- ment of all the glands connected with that coat. I have more- over found that the nervous lamina, even at the earliest period, is thickened in the region where the brain subsequently makes its appearance. Proceeding outwards from this point, it be- comes gradually attenuated towards the caudal extremity (yolk plug), and rather quickly in all other directions. No special thickening exists for the rudiment of the retina, since this, as is well known, is developed from the brain (by a process of eversion). Special thickenings however occur for the olfactory, auditory, and gustatory organs.* I have no remark to make in regard to the rudiment of the tactile organ. J can only point out that the nerve lamina, like the corneal lamina, surrounds the entire periphery, and the relation that exists between the peripheric expansion and the tactile organ still remains, therefore, to be investigated. Notwithstanding the positive statements of Remak, I cannot consider it to be satisfactorily established that nervous struc- tures can also be developed from the middle germinal lamina. The subject still demands further careful investigation. Obser- vations made upon the tail of the larva of the Frog render it probable that the peripheric nerves proceeding from the axis to the periphery originally project as masses of protoplasm. Wherever, however, such protoplasmic masses occur, they may also develop cellular elements in their course and in their interior. As long as this theoretical consideration is not opposed by precise observations, we cannot regard this impor- tant question as settled in the sense held by Remak. The muscular and connective-tissue substances originate from the middle germinal laminae. This is so readily seen, that, notwithstanding the authority of those who deny it, I shall not enter into any discussion respecting it. In the first place, the chorda belongs to the connective-tissue substances. The * See the treatises of Schenk and Torok in the Wiener Sitzungsberichte, Bande 1. and liv. MORPHOLOGICAL VALUE OF THE GERMINAL LAMINA. 537 most simple section, however, shows that the chorda takes up the entire thickness of the middle germinal lamina ; being in contact above with the central nervous system, and below with the glandular lamina. The vertebrae are differentiated in a paired manner from those portions of the germinal lamina that bound the chorda laterally ; and again, the most element- ary sections show that these vertebrae, as Remak long ago demonstrated, undergo subdivision. A portion only of each prae vertebra is converted into bone ; a part certainly becomes muscle, and it may be presumed that a third part becomes the rudiment of the periosteum. I have further demonstrated* that at the point where the anterior segment of the cranium subsequently appears, bones and muscles are developed by the formation of boundary or limiting lines in an originally homogeneous material, and no doubt can therefore exist respecting the genesis of the connec- tive-tissue substances. Reichert, as has already been stated, first recognized the splitting of the middle germinal lamina for the formation of the pleural and peritoneal cavities. There is no great diffi- culty in demonstrating this fact by the means now adopted for displaying the development of the embryo; namely, by sections. It may be seen that the lateral portions bounding the ver- tebrae (lateral laminae, Seitenplatten, Remak) split just as Remak has stated, and become bilaminated, and that the serous cavities develop between them. The walls of these cavities are thus indubitably formed from the middle germinal lamina. For the rest I must refer to the clear description given by Remak, according to whom the upper of these two laminae applies itself to the conjoined nervous and horny lamina, and the lower to the glandular lamina, in order to form on the one hand the body wall, and on the other the intestinal tube. In the former case the horny lamina furnishes the external cel- lular investment and the cellular investment of the superficial glands, but in the latter case the intestinal glandular lamina forms the cellular investment of the cavity of the intestines, as * Reichert and Dubois-Reymond's ArcMv, 1864. 538 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. well as all the glandular organs that project from the intestine. The relations of the first rudiments of the urino-genital appa- ratus to the middle germinal layer have already been given by Waldeyer, see vol. ii., p. 192, et seq. DEVELOPMENT OF THE SIMPLE TISSUES IN THE EMBRYO. In regard to the origin of the cells, little remains to be added to that which has been already stated in vol. i., p. 35, of this Manual. I have, however, devoted much attention to the process of cell division, and have found that it may be observed with tolerable facility in inflamed tissues. It is only requisite to maintain the tissues under observation in conditions that are favourable to their vitality.* The results thus obtained by direct observation are identical with the conclusions that have long been arrived at theoretically. The account formerly given, however, does not appear to be quite accurate. It is not necessary that a cell should assume the form of a finger biscuit before it divides. It divides either with the constant performance of amoeboid movements, — the body of the cell, owing to these movements, separating into two masses, united by a thin thread which ultimately ruptures, — or the cell forms a ball-like mass, in which a line of division becomes visible, that sometimes disappears, and then again reappears, and so on, till finally the line becomes defined, in such cases we are led to the conviction that division has really taken place when one or both parts resume their amoeboid movements, and finally separate from each other. The cells, however, as a rule, do not part com- pany; they divide, and the cement existing between them alone indicates that the division is complete. The examination of the process of cell multiplication in inflamed tissues has led to certain modifications of the cell theory. It has demonstrated that cells which have already attained such an age that amoeboid movements can no longer be observed in them (fixed connective-tissue corpuscles) may under certain circumstances (as inflammation and its conse- * Strieker, Stndien. DEVELOPMENT OF THE SIMPLE TISSUES. 539 quences) again become capable of performing such movements. It has established, further, that this does not apply to old cells. It is found also that the external layers of the cells remain unchanged, and that the central portion alone retracts from the neighbouring parts ; so that the cell becomes con- verted into a vesicle, in the inteiior of which one or more amoeboid cells are contained. The account of endogenous cell formation given by Briicke (vol. i., p. 35) is in remarkable accordance with these facts, and the whole is completed by the observation of Oser,* that the endogenously formed cells escape through fissures in the maternal sheath. The development of the epithelia and endothelia, after the full description that has been given of them in this chapter, requires no further consideration. Rollett has detailed the development of the connective tissues in the second chapter of this work. I need only remark, as the subject is on the tapis, that I consider the origin of fibrillar connective tissue from cell processes to be demonstrated; and that, on the other hand, I think the splitting up of a homogeoeous matrix into fibrils has not been satisfactorily shown to occur. Our knowledge of the first traces of the embryonic blood- vessels has reference exclusively to the germ of the Fowl. C. F. Wolff was lonor a^o aware of the fact that the blood O O was developed in the form of islands in the germ disk of the Fowl, and Pander went a step further back when he showed that Wolff's blood islands proceeded from smaller dark islands which make their appearance both in the trans- parent area and in the area opaca. These islands, Pander remarks, elongate, become more slender, communicate with each other by their extremities, and form a reddish plexus with transparent meshes. Baer likewise mentioned Pander's islands, but gave rather a confused account of them, and subsequently Pander's observations fell into oblivion. After the appearance of Remak's works, that author was generally credited with the discovery of these facts; and though he * Ibidem, p. 83. 540 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. mistook the secondary for the primary stage, lie gave a very intelligible description of it. Remak regarded the completed blood-vascular plexus as the first trace of the system, and as he saw that the vessels were filled with blood, he explained the appearances pre- sented as follows: Cells, he says, coalesce to form cords and plexuses in such a manner that the peripheral elements of each cord coalesce to form a vascular wall, whilst the central ones become blood corpuscles. As a few years later, by means of the silver method, the cell boundaries could be rendered apparent even in the capillaries, the views of Remak appeared to be perfectly well founded. Some years ago the island-like rudiments of the blood- vessels were rediscovered by Affanasief, * and I may just mention that the research was conducted under my direction ; , for Affanasief has since stated that his discoveries were not quite satisfactorily made, in which I am unable to agree with him. M. His also soon afterwards expressed himself in favour of the island-like rudiments, and still more recently E. Kleinf has arrived at similar conclusions. Various points which remained doubtful in Affanasief 's researches have been satisfactorily explained by these authors ; and I now proceed to the description of the earliest stages of development of the bloodvessels with the consciousness of being able to treat the question as being finally settled from a morphological point of view. If a fresh germ disk be examined at the commencement of the second day of incubation, without any covering glass, with moderately strong powers, isolated cell elements may be per- ceived in the depths of the tissue, in various stages of develop- ment, till they ultimately form large bodies provided with vacuolse, or, in other words, constitute vesicular structures. In optical transverse section, each of these large vesicles gives the impression of being composed of fusiform cells. As the cell increases to form a vesicle, the nuclei in the wall of the vesicle increase also, project towards the cavity of the * Wiener Sitzungsberichte, 1866, Band liii. t Wiener Sitzungsberichte, 1871, Marz-Heft. DEVELOPMENT OF THE SIMPLE TISSUES. 541 vesicle, and ultimately as many fusiform cells appear to be present as nuclei are seen in optical transverse section. Klein has shown that these cells are constricted off from the inner wall of the vesicles, and falling into the cavity of the vesicle, become blood corpuscles. The isolated cell elements are also recognizable in sections of hardened specimens, and from these it appears that they must be regarded, for reasons that have already been given, like the cells of the middle lamina, as descendants of the cleavage mass, which however now migrate or wander into it. It further appears that in accordance with their definite position they must be regarded as belonging to the middle germ lamina. Thus we see that from a cleavage spheroid or an embryonal cell a blood-corpuscle-holding vesicle, or, as we may also say, a vessel constructed upon the type of the capillaries, but completely closed, is formed. The wall of the vesicle is composed of protoplasm, the nuclei of which have increased in number, and the cavity then originates, as vacuolse generally arise. According to the description given by Klein, blood corpuscles are developed endogenously in the cells, owing to buds pro- truding from the internal wall of the vesicle, which become constricted at the base, and fall into the cavity of the vesicle. But a second mode of endogenous blood formation also occurs, which is more analogous to the well-known endogenous forma- tion of cells. The central part of a large cell sometimes undergoes conversion into blood corpuscles, so that we have before us a cyst filled with blood corpuscles. Essentially both forms are alike, and in both cases closed and blood-corpuscle- containing vessels originate in single and isolated cells. The walls of such vesicles give off projections, which are at first solid, but subsequently become hollow. The free extre- mity of a bud of this kind may again grow out to form a vesicle of one form or the other, so that two cysts communicate with one another, or the buds of different vesicles may inter- communicate, or a bud may open into a vesicle, or the vesicles may open directly into each other, and thus a communicating vascular system originates. The formation of buds still con- tinues after the communicating plexus has been formed. In the tail of the Tadpole, where the new formation of vessels 542 DEVELOPMENT OF THE SIMPLE TISSUES, B\r S. STEICKEE. can be observed as soon as circulation has commenced, the formation of buds is so obvious that it cannot be overlooked by any careful observer. The vascular walls send out processes which augment in thickness, and unite with the processes of other vessels, or with other vessels directly ; as soon as these become hollow the communication is established. It is moreover probable that in the tail of Tadpoles free cells acquire processes, and attach themselves to a vessel in order to play the same part which, in accordance with the above description, 'is played by the vascular processes. My observation that in the tail of the Tadpole blood-containing fusiform cells, closed at both extre- mities, occur, has recently been corroborated by J. Arnold. These observations render it probable that even in the tail of the Tadpole an endogenous development of blood corpuscles takes place. It is moreover rendered certain, by researches that have been for some time past conducted in my laboratory, that blood can originate endogenously in the so-called vascu- larizing inflammatory foci (vascularisirenden Entzundungs- heerden) the walls of the cells becoming converted into vascular walls. No other mode of the new formation of vessels has as yet been observed. Originally all vessels, whether they subsequently form the heart, arteries, or veins, are constructed similarly to the capilla- ries ; that is to say, they have only a single nucleated wall, and this wall in the embryonic condition is composed of embryonic cell substance or protoplasm. The increased com- plexity of structure subsequently acquired by the heart, arte- ries, and veins, is the consequence of a secondary process in the external wall of the original tubular system, of which we have at present no information. The endothelia of the heart, arteries, and veins have thus the same genetic importance and value as the walls of the capillaries. Inasmuch as a system of brown lines can be brought into view by the action of nitrate of silver, exactly resembling those of completely developed capillaries, and continuous with the brown striae of cement of the endothelia both of the arteries and of the veins, we must admit that the striae of cementing substance must have formed subsequently through- DEVELOPMENT OF THE SIMPLE TISSUES. 543 out the whole system. This process is quite in accordance with the general principles of development. Moreover, in the first rudiments of the middle germinal layer no instance is known of cells coalescing to form a cellular structure. In all epithelia, as well as in all endothelia, we see cell division only so occurring that from one cell two or more cells arise ; these, however, never separate from one another, but cementing substances form between them, which indicates the discon- tinuity of the individual cells. The same views must be held in regard to the originally homogeneous protoplasmic tubes. I must once more adduce the example mentioned in the pre- face, that the vessels originally appear as if made like a cannon tube, but that they subsequently seem as if constructed on the plan of a chimney. We know very little as to the mode and place of origin of the blood in the embryo after the completion of the first rudi- ments of the vessels have been laid down. Reichert* main- tained that the blood is developed in the liver ; but no satis- factory evidence of this has been adduced. Again, the view entertained by Neumann and Bizzozero as to the origin of the blood in the cancellous spaces of bones cannot be held to ex- plain the origin of the blood during the earliest period of development, since such cancellous tissue is only formed at a later period. At present it is not known whether generally, and if so, how soon, the medullary spaces act as centres for the formation of the blood. For the earlier stages of develop- ment, lastly, we can scarcely regard the lymphatic glands as sources of the colourless blood corpuscles, since, as Sertoli •(• has shown, the first traces of these are only formed in embryoes at a later period of development. Before I proceed to describe the development of transversely striated muscular tissue, I must add a few words in regard to its structure, which did not find a place in chapter vi. Transversely striated muscular fibres are fusiform or cylin- drical, with blunt or pointed extremities. Their thickness varies to an extraordinary extent, being sometimes even visible * Entwickelunysyeschi-chte, etc. f Wiener Sitzungsberichte, Band liv., 18G6. 544 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. to the naked eye, though they are often very much smaller ; in short muscles they are equal in length to the muscle itself, but in long muscles they do not in general exceed four centi- meters (about one inch and three-quarters). Schwann discovered a sheath investing the fibres, which he termed the sarcolemma, and since his time it is customary to say that the sarcolemma is completely filled with the true muscular substance. The sheath cannot be seen in fresh fibres, but it comes into view when they are treated with water or diluted acetic acid, or, in short, with any reagent that exerts no action upon the sheath, but causes the muscular substance to swell. The sheath ultimately ruptures at some point, the muscular substance protrudes, and the ruptured canal of the sheath then comes distinctly into view. In such preparations, especially if the muscle examined be not fresh, but have been dead for about twenty-four hours, we may sometimes succeed in exhibiting considerable portions of the sheath : it then appears as a very thin, extremely transparent, and as seen with our instruments, structureless membrane. Schwann also discovered the nuclei of the muscular fibres ; these are the muscle corpuscles of authors ; and from the exact investigation of these, Max Schultze, as is well known, was led to make the first steps towards the reform of the old doctrines regarding cells. The muscle corpuscles lie for the most part on the surface of the muscular substance between this and the sarcolemma. Bonders* found that in the muscular fibres of the heart the muscle corpuscles occupied the interior of the fibre. Rollettf has further shown that muscle corpuscles are met with in the interior of the substance of the fibres of the muscles in Amphibia, Fishes, and Birds. Schwann, lastly, demonstrated the fibrils of muscular tissue, which he described as moniliform threads. He attributed the peculiar appearance on account of which these fibres are termed transversely striated to the regular collocation of the thicker and thinner parts of these fibres. For if such a fibre * Physiologie des Menschen, German translation by Theile. t Wiener Sitzungsberichte, 1857. STRUCTURE OF STRIATED MUSCLE. 545 be looked at from the surface, lighter and darker bands of a certain breadth are as a rule seen alternating with one another. These bands or zones, he thought, are caused by the regular juxtaposition of thicker and thinner segments of the fibrils. The muscular fibre was thus, as Valentin stated, a fasciculus of fibrils, and since then it has also been termed a primitive muscular fasciculus (Muskel-primitiv-biindel). Bowman maintained that the fibrils are not originally present in the fibre, but that they are the product of a process of disintegration. In some instances, he says, the fibres do not split in the longitudinal, but in the transverse direction, in consequence of which disks are formed . If a muscular fibre undergo division in both directions, — that is to say, if the whole length were divided into fibrils, and the whole thickness into disks, — minute particles, the " sarcous elements," would be obtained, of which the muscle is properly composed. Rollett objected to this view, that Bowman only described one kind of material, and had overlooked the connecting substance. Wharton Jones was the first to mention the alternate succession of two different substances in the longitudinal direction of the fibre ; namely, the disks and an intermediate substance. Dobie maintained that the fibrils themselves consisted of two different substances, and described them as composed of a linear series of alternating bright and dark bodies. Rollett assented to this view. He regarded the muscle-substance of the fibre as composed, in Schwann's sense, of a fascicu- lus of fibrils, each fibril being segmented by an alternation of two kinds of substances, to one of which, on account of its harder contours, he ascribed a greater refractive power than to the other. The stronger refracting substance he termed the chief substance (Haupt-substanz), the other the intermediate substance (Zwischen-substanz). Taking the fibre as a whole, disks of chief and intermediate substance alternate with each other, the latter corresponding to Bowman's disks. Looking at the fibrils alone, the chief substance corresponded to a sarcous element or a sarcous particle. Rollett might at that time already have been acquainted with Briicke's discovery, to the effect that the doubly refractile property was possessed by the VOL. III. N N 546 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. chief substance alone, but was absent in the intermediate substance. In regard to the internal arrangement of the fibrils, Rollett accepted the views of Leydig, chiefly resting on the examina- tion of transverse sections of firmly frozen ox hearts, according to which the primitive fasciculus is traversed by a lacunar sys- tem. He admitted this in consequence of the configuration of the areas which he obtained from transverse sections. On subjecting the sections to maceration for several days, they were found to present the transverse sections of the fibrils. Cohnheim* subsequently examined muscular fibres methodically by the freezing method, and showed that the transverse sec- tions of such fibres may be regarded as transverse sections through the living tissues. From such sections he has found the proper muscular substance to be composed of two quite different substances, one of which is of great transparency, and possesses a strong lustre, whilst the other is less transparent, and has a dull appearance, the relative quantity of the two being unequal. The highly refractile substance he describes as forming a dense trellis-work of slender lines, becoming wider at certain points only, and decussating at all angles ; the dull substance, on the contrary, being arranged in the form of a mosaic, with innumerable triangles, quadrangles, and pentagons, separated from one another by the slender bands of more transparent substance. At certain points the particles of the mosaic are separated to a greater distance from each other than elsewhere, owing to the accumulation of the refractile substance ; in the middle of these spots are the nuclei of the muscle. Cohnheim regarded the dull areas of the mosaic as the sections of the sarcous elements. He further maintained that the transverse section of the living muscular fibre so far corresponded to the longitudinal view, that in it also the sarcous elements make their appearance, surrounded and enclosed by another substance of a different nature. In regard to the con- sistence of the latter, Cohnheim states, upon the authority of Kiihne's researches, that it must be fluid. From this account an essentially novel view of muscular * Virchow's Archiv, Band xxxiv. STRUCTURE OF STRIATED MUSCLE. 547 structure was obtained, and it was concluded that sarcous elements, surrounded by a fluid intervening substance, and laminated (as disks) like the layers of bricks in a wall, com- posed the muscular substance. Kolliker* has however more recently opposed Cohnheim's description. He maintains that the areas described by Cohii- heim are the transverse sections of muscular columns, which he again regards as composed of smaller fasciculi of fibrils- His account therefore coincides with that given by Leydig and Rollett. From the description given by Kiihne (vol. i., p. 202, of this Manual), it appears that his opinion in regard to the internal structure is essentially the same as that which may be easily deduced from the account given by Cohnheim. Such was the state of our knowledge on this subject till the appearance, nearly coincidently, of the works of Krause and Hensen foreshadowed an essentially different explanation. Ac- cording to Hensen,f the structure of muscular fibre is some- what as follows : In the primitive fibre of a quiescent muscle, each transverse stria is divided into two halves by a dark line. This line is the expression of a fine disk (median disk). There is moreover, not simply an alternation of a highly refractile sub- stance, the intermediate substance, but after the first half of the transverse disk there follows a feebly refractile substance, the median disk ; then the second half of the transverse disk ; and lastly, the intermediate substance. KrauseJ gives a different explanation. Each fusiform fibre (muskel-spindel), according to him, consists, independently of the sarcolemma, of a very large number of muscular cases or compartments (Muskel-kastchen). Each muscle case contains a muscle prism, composed of anisotropal material, which almost entirely fills the muscle case. The form of the muscle prisms (sarcous elements) is that of a multangular 'column, transversely truncated above and below, the transverse diameter of which varies, whilst the height of the muscle prisms, like that of the * See his Manual of Histology, 1867, and the Zeitschrift fur u'ixstn- schaftliche Zooloyie, Band xvi. f Arbeiten aus dem Kiekr physioloyischen Institut, 1868. 1 Zcitschnft fur Bioloyie. N N 2 54S DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. muscle cases, is nearly constant throughout the whole vertebrate series. Both extremities of the prism are covered by a thin layer of fluid (muscle-case fluid). Between each two muscle cases is a basal membrane, by which the cases are separated from one enother. Each case, however, only possesses a single lateral membrane, investing it annularly, which fuses with the two terminal basal membranes. The muscle cases are arranged in the form of regular disks in the transverse direction of the spindles, which may be called muscular fibres. Each muscle compartment consists of a basal membrane, which appears in profile as a transverse line. Then in the longitudinal view of the muscle spindles there follows one half of a clear transverse band, a dark transverse band, then the half of the succeeding clear transverse band, then again the transverse line formed by the septum, and so on. The most noticeable difference in the signification which Hensen on the one hand, and Krause on the other, give to the appearances presented, is that Krause regards that as a muscle prism, and consequently as an anisotropal part, which Hensen holds to be intermediate substance, and an isotropal part. Heppner* has raised objections to the accounts given by Hensen and Krause. In his opinion, the refractile zone (muscle- case fluid of Krause, transverse disk of Hensen) is only the expression of total reflexion which occurs at the line of de- marcation between the chief and the intermediate substance. In support of his views he adduces the circumstance that the position of the refractile band, in relation to the limiting layer dividing it (median disk, Hensen — transverse line, Krause), can be altered by changing the position of the mirror, and that in certain positions of the mirror the bands may disappear al- together. He adduces also the appearances presented under polarised light. If the visual field be coloured by a Nicol's prism, both the refractile band and the dull disks constantly appear to be of the same colour. Both Hensen and Krause, however, maintain that only one of the two is anisotropal. So far as regards the explanation given by Krause and Hensen of the appearances first described by them, I must * Max Schultze's Archiv, Band v. STRUCTURE OF STRIATED MUSCLE. 549 declare myself in favour of Heppner 's views. I do not, how- ever, consider the matter to be finally settled. Since Heppner conducted his researches in my laboratory I have repeatedly and most carefully worked over the subject of the structure of muscular fibres, but have up to the present time arrived at no positive conclusion upon the point in question. My researches have been made exclusively upon fresh mus- cular fibres, which have been placed under the covering glass without the addition of any fluid, and compressed more or less gently by the insertion of a layer of cement between the margins of the cover and the slide. I have also not avoided the object which Hensen so strongly charges Heppner in a recent publication as having neglected ; but have for the most part used the muscles of Hydrophilus, because, as several distinguished fellow- workers have pointed out, the muscles of this animal are extremely favourable for this purpose. When examined with Hartnack's lens, No. 15, it may be seen, in cases in which the still living muscular fibres appear transversely striated, that the intermediate substances (in the sense of Rollett) are not homogeneous. It may in fact readily be shown, especially when they are not very slender, that dark granules lie in a clear matrix. In many cases I could only count two granules in the length of a single disk. Their arrangement in the clear matrix also varies: sometimes the whole intermediate substance appears in the form of a finely granular zone of protoplasm ; sometimes it is partially free from granules, or these are thinly and irregularly scattered. It has been stated by many observers, that the intermediate substance appears, according to the focussing, sometimes clear, sometimes dark ; but, so far as regards the appearances pre- sented with the No. 15 lens, I can state positively that the intermediate substance is always dark, when in perfect focus, at the point where the granulations are situated, whilst it is always clear where there are no granulations, clearer even than the chief substance. The chief substance remains rela- tively dull at all focuses. The appearances presented by the muscular fibres of Hydro- philus, so long as they still move actively, are extraordinarily variable. In those which only appear transversely striated, the 550 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKEB. chief and the intermediate substances alternate in breadth ; the form of the limiting surfaces of the two varies, so that the in- termediate substance sometimes exhibits a nodal point, some- times again an attenuation. The position of the disks, as regards the vertical line, also varies, being sometimes oblique, sometimes plane and vertical. Moreover, each zone does not implicate the whole surface or the whole area of a transverse section : displacements sometimes occur, giving the impression that one half of the fibre has been shifted about half the breadth of a disk, occasioning the limiting line between the chief and intermediate substance to be interrupted or to be angularly curved. Other fibres appear transversely and longitudinally striated, the longitudinal striation sometimes traversing both substances, and sometimes being limited to the chief substance. Other fibres, again, appear only longitudinally striated ; and others, again, neither longitudinally nor transversely striated. There is no doubt that all these conditions are presented by living fibres. The course of a fibre which is neither transversely nor longitudinally striated is rendered extraordinarily distinct, and it may also be clearly seen how such a fibre suddenly entirely or partially acquires transverse striation, and just as quickly loses it again. In order to make this intelligible, I can only refer to the image presented to the eye by a bird's- eye view of a corps of infantry whilst actively engaged in performing evolutions ; and as it sometimes inarches in more or less deep columns, and appears with transverse bands of variable breadth ; sometimes again formed into lines that are disposed vertically to the direction of the columns ; and some- times, lastly, form squares, in which the transverse and lon- gitudinal striation disappear in order to reappear, one or both, the next moment. Such appearances are, it is obvious, most in accordance with the view that muscle consists of small groups of disdiaclasts and a fluid intermediate substance. We must not at the same time forget that there are many considerations opposed to this view. It appears to me to be important to mention those work# that are chiefly occupied with the muscular tissue as it appears in the lowest forms of animals. Perhaps the works bearing STRUCTURE OF STRIATED MUSCLE. 551 on this subject may answer the questions that arise more de- cisively than is possible from researches upon Vertebrata and Arthropods. As I have made no personal observations upon the subject, I must base my account upon the latest published researches, those, namely, of Schwalbe,* to which I would also refer all those that are desirous of becoming better acquainted with the present state of our knowledge and with the litera- ture of the subject. I extract from this work the following statements which are of general importance. In the first place, that the lowest animals in which striated muscular fibres are met with are the Ccelenterata. Max Schultze, Briicke, and Virchow have seen distinct transverse striationin the muscular fibres of the swimming disk of Aurelia aurita, and Kolliker in that of Pelagia and Agalmopsis. Further, it is to be re- marked that, according to the observations of Schwalbe, in Ophiothrix fragilis (Echinodermata) the muscle cells between the ambulacral plates in the first place possess a sarcolemma, and, secondly, the muscular substance appears doubly striated. Such systems of lines, according to his statement, had already previously been observed by Mettenheimer in the muscles of Arenicola piscatorum and Nereis succinea. The same ap- pearance has also been observed in Mollusks. The circum- stance that the fibre cells of the muscles of Nematodes and Hirudinese are composed of a medullary substance surrounding the nucleus, and of a cortical substance splitting into fibrils, also seems to me to be of importance. This observation was made by G. Wagener in transverse sections of the dried mus- cular fibres of Aulosdoma nigrescens, and it was corroborated by Schwalbe in the Hirudo medicinalis. These observations seem to me of importance, because they correspond to a certain stage of development of muscle in the Vertebrata. Lastly, I shall adduce the fact that Weissmannf has divided the mus- cular fibres into muscle cells and primitive fasciculi, which division has been opposed by Wagener.J Wagener regarded the fibrils as the primitive elements of the muscular fibres. * Schultze's Archiv, Band v. + Zeitschrift fur rationelle Medizin, 1862 and 1864. I Archiv von Reichert, etc., 1863. 552 DEVELOPMENT OF THE SIMPLE TISSUES. BY S. STRICKER. I can now discuss but very briefly the development of the muscular fibres. So far as my observations extend in the embryoes of Rabbits, I must support the views of Kemak and those who agree with him, that a muscular fibre proceeds from a cell, which elongates and becomes fusiform, and at the same time increases in thickness; the nucleus then increases, and on its surface appears a mantle of longitudinal strise, which at the same time represents the cortex of a nucleated and granu- lar medullary substance. As soon as this mantle is formed, fibres may also be met with, in which the transverse striae are apparent. Up to this period it appears as if each fusiform cell were undergoing gradual conversion into muscular sub- stance from the periphery towards the centre. It is important to notice that the first traces of muscular substance in the fibre cells constantly appear to be fibrillar. It must, however, also be stated that it is impossible to investigate such fibres in a perfectly fresh condition. When they are removed from the living embryo, they rapidly die, and it is therefore not easy to determine whether the muscular substance is always fibrillar at its first appearance. In regard to the development of the sarcolemma, I must mention that I can discover no reason, from a study of its development, for considering it as a cell mem- brane. On the contrary, I have made observations which render it very probable that the sarcolemma is to be referred to cells which attach themselves to the muscle cells, and ultimately enclose them. For if a teased-out preparation be prepared from a trunk muscle of the foetus of a Rabbit at a time when the muscular fibres are still so imperfectly developed that they are either homogeneous, or are composed of cortex and medulla, it will be found that they lie enclosed in clusters of smaller cells. Moreover we find that more or less strongly projecting nucleated cells adhere to various points of the surface of the fibres when isolated. We may see also how the body of such a cell extends beyond the optical longitudinal section of the fibre as a thin extremely transparent marginal stria, which already presents the aspect of a section of the sarcolemma. With re- gard to the question of what now contributes to form Schwann's sheath ; with regard, further, to the fact that the sheath of Schwann and the sarcolemma are, sometimes continuous DEVELOPMENT OF THE NERVES. 553 with each other, it seems probable that the latter also proceeds from cells which apply themselves to the surface of the mus- cular fibres. It is to be remembered, however, that those muscle corpuscles that are found between the sarcolemma and the proper substance of the muscle proceed genetically from the latter. This view is based, first, upon the fact that the nuclei of young muscular fibres lie in the medulla ; secondly, that the cortex of the cells undergoes conversion into muscular substance ; and lastly, upon my observations of the relation of embryonal muscle cells to the smaller cells occurring upon their surface. From this point of view the superficial muscle corpuscles of the sarcolemma are perhaps to be regarded as connective-tissue corpuscles. I must also take this opportunity of mentioning that the muscular and connective tissues are to be referred genetically to one and the same origin, and that, consequent on my account of the superficial muscle corpuscles, it must be admitted that they may aid in the regeneration of the muscles. The researches of Babuchin have furnished the most recent information upon the development of the nervous system.* From his researches it appearsf that there is no essential differ- ence in minute structure between the axis-cylinder processes and the other processes of the nerve cells. It can nowhere be better shown than in embryonal cells that the axis-cylinder process does not communicate either with the nucleus or with the nucleolus; The embryonic nerve cells which have already fully developed axis-cylinder processes, possess a remarkably large nucleus, so that at first sight it appears as if it were quite naked, and was applied immediately to the extremity of the axis cylinder, like the head of a knitting-needle to the needle * The plan of the editor was to treat this question in connection with the description of the electric organs. Professor Babuchin undertook this article, and repeatedly visited the coasts of the Adriatic with a view of carrying on his investigations. Babuchin, however, has this year found it necessary to travel into Egypt for pursuing this very study. But as the completion of this work could not be postponed till his return, the editor has determined to stop at this point. The results of Babuchin's researches will appear as a special part supplementary to this work. t Centmlblatt, 1868. 554< DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. itself. By careful observation, however, and with good micro- scopic powers, a thin layer of protoplasm may already be dis- tinguished, which is sharply defined on all sides from the large nucleus, and gives origin to the axis cylinder. The axis cy- linder, which at its origin is relatively thick and conical for the most part, becomes attenuated as it passes outwards, without undergoing division, and is directly traceable into a very slender fibril. In this condition it emerges from the cranial cavity of the embryo, and extends to the most remote parts, where it not unfrequently breaks up into a fasciculus of extremely fine fibrils, only clearly visible with Hartnack's No. 15. APPENDIX. I. ON THE STRUCTURE OF THE SYNOVIAL MEMBRANES. BY EDWARD ALBERT. BICHAT long ago distinguished the synovial membranes from the true serous membranes, and divided them into two classes : (1) The capsules of the tendinous sheaths — synovial capsules ; and (2) the synovial membranes of the joints. No alteration has been made in this arrangement since his time by anatomists, and the only subject of inquiry has been whether the epithelial investment of the synovial membrane of the joints also covers the surfaces of the cartilages. The researches of H liter,* which appeared in 1866, first gave results that appeared to displace the synovial membranes from the position they so long maintained in the scheme of the membranes of the human body. From the results obtained by the silvering method, Hiiter denied the existence of an endothelium, and maintained that the synovial mem- brane was lined by a special modification of connective tissue, the iform of which sometimes resembled an endothelium, sometimes the gerous-canal markings of the cornea (epithelioid and keratoid con- nective tissue). The modification which the method of v. Reckling- hausen experienced at the hands of Schweigger-Seidelf has given results opposed to the statements of Hiiter, and Schweigger-Seidel has en- deavoured to prove the existence of an epithelium from the presence of nuclei which he finds to be regularly arranged upon the surface. * Virchow's Archiv, Band xxxvi.; and Klinik der Gelenk-Krankheiten, 1870. f Arbeiten aus der physiologischen Anstatt zu Leipzig, I860. 556 STKUCTURE OF THE SYNOVIAL MEMBRANES, BY E. ALBERT. In a provisional communication, Landzert * has strongly supported the view that the markings are due to the presence of an endothelium, and not to a serous-canal system. On the other hand, R. B6hm,f in his inaugural dissertation, has entirely accepted Hiiter's view in regard to the appearances brought into view by the action of silver; but adds that from the results of the investigation of fresh objects in salt and water, he believes he has recognised the innermost layer of the synovialis to be composed of a layer of non-nucleated cells. If a joint be opened and macerated for a few days in a solution of chromic acid (containing one part of the acid to 10,000 or to 5,000 of water) complete cells may be easily brought into view, forming the internal layer of the synovial membrane, and may be rendered still more distinct by staining with carmine. Under these circumstances a continuous layer of roundish or polygonal cells may be observed, which occa- sionally possess short processes, and of which each contains a distinct granulated rounded or oval nucleus with nucleoli. The nucleus sometimes occupies almost the whole of the interior of the cell, so that a small margin only represents the remainder of the cell. In other cases the nucleus is central and small, whilst the body of the cell is larger. It can be clearly demonstrated by this method of research that the deeper layer of the synovialis is coated with complete nucleated cells. In silvered specimens, again, it appears that two layers of markings can be perceived over large tracts of the synovial membrane. The upper layer presents appearances that essen- tially resemble the contour lines of the cells forming an endothelium, whilst the subjacent layer exhibits the charac- teristic markings of a vascular plexus of serous canals enclosing rhombic and quadratic meshes. If this account be compared with that given by Hiiter, the most noticeable difference appears to be that, according to Hiiter,J the epithelial markings lie in the same plane with the keratoid (serous canals). If it can be demonstrated from successful preparations that this is * Centralblatt fiir die medidnische Wissenschaften, 1867, No. 24. * Beitrcige zur Anatomie und Patholoyie der Gelenke, 1868. 1 Loc. cit.j p. 43. STRUCTURE OF THE SYNOVIAL MEMBRANES. 557 not the case, one might be easily induced to consider Hitter's view incorrect (Landzert), and to regard the synovial mem- branes as simple serous membranes. But the more the subject is investigated, the more do we become convinced that the sup- position of the superficial irregular (keratoid) markings being imperfectly brought-out endothelial markings is inadmissible. It may be shown that the markings resembling an endothelium occur indeed over the greater part of the synovial membrane, but that there are nevertheless tracts where they never occur, and in regard to these tracts Hiiter's description is undoubtedly perfectly accurate. We may also state in general terms where these tracts are situated. If the highest point of the head of a bone be taken, as, for example, that of the humerus, spheroidal cartilage cells are found around the pole, which in adults are separated by wide tracts of intercellular substance, but in children are in such close apposition that the intercellular substance only represents a slender trellis-work between the cells, giving the whole an epithelium-like appearance. As the sequator of the head of the bone is approximated, cells occur which exhibit angular contours and short isolated processes. Still further down the cartilage cells are stellate, the processes being relatively very long and occasionally branched, and forming anastomoses. On thus proceeding towards the inser- tion of the capsule, we arrive at a zone where the cartilage cells gradually pass into connective-tissue corpuscles.* This is the region of the synovial membrane, and we here meet with vessels that partly form arcades, and partly dip more deeply, and enclose the serous canals in their meshes. No superjacent layer of cells, however, can be perceived at this point. It is only still further down, where the synovial membrane extends as a free membrane from the glenoid cavity upon the head of the bone, that superficial endothelial-like markings become visible. * The importance of this fact in supplying an explanation of the serous canals has been clearly pointed out by Bohm. In opposition to Bohm, I have only to observe that the presence of stellate cartilage cells is associated with proximity to the insertion of the synovial membrane, and is not in relation with the mechanical relations of the cartilage, as freedom from friction, etc. 558 STRUCTURE OF THE SYNOVIAL MEMBRANES, BY E. ALBERT. In the synovial membrane, however, there is a zone, the zone of attachment, which in one direction is continuous with the cartilage, but in the opposite forms a serous membrane. The question now arises, whether on the other side of that zone, or, to speak more accurately, between the two zones of attach- ment (since the synovial membrane is extended between two lines of bone), the membrane preserves the character of a serous membrane in the strict sense of the term. It requires to be determined whether the difference is sufficiently well marked to cause a distinction to be made between the synovial and serous membranes. The differences are as follows : First, it may be seen in the most successful specimens that the trellis-work of the cementing material does not everywhere present such fine and uniformly broad lines as in the serous membranes ; and that the size and form of the cells, and the character of their nuclei, vary to a much more remarkable extent than in them. Secondly, villi are as a rule met with in most joints, as well as in many sheaths of tendons. I have even observed them in the joints of new-born children. Hiiter has also stated, as a farther point of distinction, that the vessels of the synovial membrane are naked. This feature would certainly be of great import- ance were Hiiter 's statement quite correct; but it may be shown that where the layer of investing cells covers the layer of serous canals the cells are also continued over the vessels. In the same way it appears to me that the cells in question are to be distinguished from the endothelia essentially by the circumstance that in the Frog, where the endothelia are so highly developed, such cells are not present on the inner side of the joint, but that there are others which in all these characters agree with the epithelioid cells of Mammals. Bohm, again, has declared that in the true serous mem- branes the epithelial layer is never extended over fat, where this occurs, as is the case with the synovial membranes ; and he has also further stated that the superficial cells cannot be pencilled away. But as regards the first point, it is to be borne in mind that in true serous membranes the endothelial markings do cover the fat cells. I thus maintain, in opposition to Hiiter, that the synovial membrane of the articulations possesses two STRUCTURE OF THE SYNOVIAL MEMBRANES. 559 layers, an investing cellular layer and a serous canal layer (Saftcanalchenschicht) ; in opposition to Bohm, that the investing cellular layer is nucleated; and, in opposition to Schweigger-Seidel, that the disposition and form of the nuclei in the investing layer corresponds only exceptionally to his drawings. The relations of the articular membranes are also remarkably different to the articular ligaments, as may be demonstrated in the articulation of the knee, shoulder, and hip. No ligaments have upon the side turned towards the articular cavity, on which we may admit the existence of a sy no vial membrane, any investment of epithelial cells, but their surface exhibits the same markings that are apparent upon the surface of the ten- dons, where they lie free in their synovial sheath. The state- ment that the cavity of the joint is coated throughout by a closed membrane is thus shown to be incorrect. The synovial membranes are characterised by the extra- ordinary richness of their serous canals. It may be de- monstrated by treatment with gold or chromic acid, though with difficulty, that this layer contains cells or nuclei. The form of the vessels presents many types. Bohm first maintained that the bloodvessels are directly continuous with the serous canals. In reality, however, it is the spaces that surround the bloodvessels which communicate with the serous canals. Hiiter states he has never been able to see any lymphatics, and that it is only in inflammatory states, in which the tension of the subsynovial lymphatics is increased, that they sometimes make their appearance. Landzert, on the other hand, declares that they can be distinctly brought into view by his method of silvering. I have myself been unsuccessful in accomplishing this. In one instance only, in the knee-joint of a Pig, I found distinct lymph cavities running off to a point, invested by an epithe- lial layer, and lined by an endothelium. Similarly shaped cavities are frequently also to be found in Man; but I have never been successful in finding an endothelium in them. It is possible that some of these were lymphatics ; but it is certain that the greater number of these clear spaces are only depres- 560 STRUCTURE OF THE SYNOVIAL MEMBRANES, BY E. ALBERT. sions between folds, into which the solution of silver has never gained access. The folds are rendered uncommonly distinct by the action of the nitrate of silver, and it may be shown that the clear spaces resembling lymphatics correspond to the folds that are visible even to the naked eye. The synovial sheaths of the tendons — objects well fitted for examination — have the following structure: — The matrix of the duplicatures is composed of fibrillar connective tissue, in which at certain points cartilage cells are constantly present. Superjacent to these are serous canals, similar in arrangement and form to those of the articular membranes. In some parts the framework of the matrix is so slender as to suggest the presence of epithelial structures. More careful observation, however, shows that the relations are here the same as in the zone of attachment of the articular synovial membrane. The structures in question lie upon the same plane as the most distinctly marked ramified structures ; and it is not difficult to follow the lines of the matrix widening out and becoming continuous with broad coloured areas. Putting aside the cartilage cells, the lamelke passing as meso-tendons to the tendons have the same structure as the above. Finally, the internal wall of the fibrous sheath has the same structure as the surface of the tendon ; and in regard to the latter I can only repeat what has been already stated by v. Recklinghausen. The internal wall of the typical mucous sacs or bursse, a few of which I have examined (in Man), exhibit the same structure, and the same may be said, though from the paucity of the observations, only with probability, of acquired bursse. As the latter obviously arise from spaces in the con- nective tissue, we have in the synovial cavities really a transi- tion from simple cavities in the connective tissue to cavities so organised that they stand next to the serous cavities. It OX THE XOX-PEDUNCULATED HYDATIDS. BY DR. ERNST FLEISCHL. So far as the results of a hitherto incomplete research can be put forward with the plea at least that only facts shall be advanced, the following account may be given. In the depression between the testis and the head of the epididymis in Man, there is an organ that at its maximum is about equal in size to two peas, but is never wholly absent ; it has been recognised by many observers, and has hitherto been described as the "non-pedunculated hydatids of Morgagni." By Krause it has been regarded as the analogue to one of the appendices epiploicre of the intestine. This structure, composed of richly nucleated connective tissue, tra versed by nerves, bloodvessels, and wide lymphatics, is invested with a layer of ciliated epithelium, which dips into the wide cascal depressions and involutions of the surface, which are so numerous at the 'apex of the organ. Running round the base of the organ is a circular, for the most part irregular, line, often perceptible even to the naked eye, which marks the boundary between the "true mucous epithelium" and the flat serous epithelium (endothelium) of the visceral lamina of the tunica vaginalis propria, just as a similar line at the free border of the ostium abdominale tuba?, and that at the base of the ovary, forms the sharply defined line of demarcation between the peritoneum and the germ epithelium. A canal commences near the base of the organ, which, however, I cannot aver to l>e constantly present, that extends towards the albuginea testis, 0 0 562 ON THE NON-PEDUNCULATED HYDATIDS, BY DR. E. FLEISCHL. and may occasionally penetrate for some distance into its sub- stance.* The walls of this canal are composed of the follow- ing layers : Most externally is a cylindrical sheath of densely interwoven, but for the most part circularly disposed, con- nective-tissue fibres. To this succeeds a thick layer of loose connective tissue, which forms closely arranged folds projecting strongly towards the lumen of the tube, their apices being almost in contact, and having deep depressions between ; and internal to this is a layer of columnar epithelium, which is probably also ciliated. The analogy of the whole apparatus with those parts of the female generative organs that develop from the upper layer of the germ-epithelium layer is obvious, and the microscopical aspect of transverse sections of the canal just described, and of the Fallopian tube of the female, bear a close resemblance. * I have made no mention of this canal in my provisional commu- nication on the " Non-pedunculated Hydatids," (Centralblatt fur die mecL Wissenschaften, 1871, No. 9,) although I was already aware of its existence. Soon after the publication of this communication Herr Prof. Waldeyer was kind enough to forward to me in a letter his views upon 'the significance of the organ in question, which he had in the meantime examined. This letter contains inter alia a complete and excellent description of the canal, and a well-founded suggestion of its nature. THE END. . INDEX. Abducens, origin of, ii. 490 Accessorius, origin of, ii. 505 Accessory tube (ear), iii. 75. Acini of the liver, ii. 5 Acinous glands of lower lip, i. 500 „ „ of larynx, ii. 41 „ vascular supply of, i. 591 Acusticus, origin of, ii. 496 Acusticus, distribution of, iii. 168 Adrenals, ii. 110 Adveiititia of arteries, i. 274 „ of capillaries, i. 67 „ of veins i. 278 Albuginea of ovary, ii. 168 „ of testis, ii. 133 Alimentary canal, vascular supply of, i. 586 Alveoli of lungs, ii. 51. Alveus communis, iii. 132 Amoeboid cells of the cornea, iii. 376 „ „ of connective tissue, i. 54 Ampullae of semicircular canals, iii. 108 „ of female generative organs, iii. 501 Amygdalae, i. 513 Anastomoses of ganglia, i. 186 Angulus vestibularis, iii. 142 Animal muscles, iii. 543 Annul! of Bottcher (ear), iii. 164 Aquseductus cochlese, iii. 143 Auiuvductus vestibuli, iii. 120, 133 Arches of Corti, iii. 151 Arrectores pili, ii. 240 Arterise helicinse, ii. 313 Arteries i. 267 Vasa vasorum and nerves, i. 266 Endothelium, i. 267 Adventitia, i. 274 Ela-stic internal coat, i. 268 Fenestrated membrane, i. 274 Internal fenestrated membrane, i. 267 Muscular coat, i. 270 External elastic coat and adventitia, i. 274 Arteriolse rectse, ii. 102 Arytenoid cartilage, ii. 37 AUDITORY ORGANS, iii. 27 Middle ear, iii. 51 Eustachian tube, iii. 67 Internal ear, iii. 85 Membranous labyrinth, iii. 85 Cochlea, iii. 131 Auerbach's plexus of nerves, i. 576, 579, 585 Axis-cylinder, its pre-existence, i. 154, ii. 335 Axis fibre, i. 149 Axis fibrils, i. 147 Bacillar layer of retina, *iii. 237 Bartholin's glands, ii. 321 Basilar membrane and processes of the organ of Corti, iii. 160 Bed of the nail, ii. 259 Bellini, tubes of, ii. 89, 106 Biliary cells, ii. 12 „ capillaries, ii. 13 „ ducts, ii. 20 Bladder, gall, ii. 23 „ urinary, ii. 125 Blood, i. 374 Blood crystals, i. 412 Plasma, i. 374 Red corpuscles, i. 375 „ „ form and colour of, i. 376 „ „ size, i. 380 „ ,, number, i. 383 „ ,, changes in from n - agents, i. 384 o o 2 564 INDEX. Red corpuscles, views in regard to the nature of, i. 406. „ „ haemoglobin crystals, i. 411 „ „ globulin and paraglo- buliii, i. 413 White 'Corpuscles, i. 414 Development of blood corpuscles, i. 419, iii. 539 Bloodvessels, histology of, i. 264 General structure, i. 265 Arteries, i. 267 Veins, i. 275 Capillaries, i. 279 Cavernous vessels, i. 289 Vascular plexuses, i. 292 Bloodvessels of the corium, ii. 224 „ of the intestinal canal, i. 586 Bone, i. 115 Structure of, i. 115 Matrix, i. 117 Cartilage, i. 117 Bone earth, i. 117 Constituents of bone, i. 118 Haversian canals, i. 119 Lamellse, i. 119 Fundamental lamellae, i. 119 Intercalated lamellae, i. 120 Bone corpuscles, i. 122 Canaliculi, i. 123 Primordial bones, i. 127 Secondary bones, i. 127 Sharpey's fibres, i. 126 Perforating fibres, i. 126 Development of the bones, i. 126 Bone growth, i. 142 Intra-cartilaginous, i. 137 Periosteal, i/136 Periosteum, i. 138 Intra-membranous, i. 142 Points of ossification, i. 128 Osteoblasts, i. 135 Bone medulla, red, i. 146 Bone medulla, yellow, i. 145 Myeloplaxes, i. 146 Of the penis, ii. 318 Bowman's glands, iii. 203 Bowman's lamellae of the cornea, iii 392 Bowman's disks and sarcous elements iii. 545 Brain, ii. 366 General structure of, ii. 369 Hemispheres of, ii. 378 Peduncles of, ii. 411 Origin of nerves from, ii. 479 Bronchia, ii. 52 Bruch's clusters, iii. 449 Briicke's method of employing electricity in microscopical research, i. xx. Briicke's behaviour of muscles in polar- ised light, i. 235 Brunner's glands, i. 568 Burdach'^ slender fasciculi, ii. 337 Canalis centralis medullaris, ii. 356 „ cechlearis, iii. 133 „ ganglionaris, iii. 140 „ intralobularis of the liver, ii. 13 „ Petiti, iii. 339 „ reuniens, iii. 121, 133 „ Schlemmii, iii. 340 Capillary vessels i. 279 Nucleated areas, i. 281 Stroma, i. 279 Cells of adventitia, i. 282 Escape of blood corpuscles from, i. 284 Stellate cells, i. 286 Capsule of Glisson, ii. 31 „ of the lens, iii. 370 „ of the teeth, Nasniyth's, i. 474 Caput gallinaginis, ii, 300 Carotid gland, i. 290 Cartilage, i. 95 „ true or hyaline, i. 96 „ cells, i. 96 fibre, i. 105 „ reticular, i. 106 „ cellular, i. 108 ,, development of, i. 109 „ matrix of, i. 109 „ calcification of, i. 114 Cavernous vessels, i. 289 Cement of the teeth, i. 475 Central nervous system, ii. 327 Cells, i. 1 General observations, i. 1 Ideal type of, i. 4 Independency of, i. 4 Physiological characters, i. 10 Movements of, i. 11, 98 Metamorphosis of, i. 14 Desintegration in, i. 25 Structure of, i. 27 Nucleus, i. 30 Origin of, i. 33 Forms of, i. 40 Connections of with others, i. 41 Division of, i. 43 Formative activity of, i. 45 Changes of cells in death, i. 45 Amoeboid, i. 54, iii. 376. Auditory, iii. 112, 160 Cartilage, i. 96 Cell clusters, ii. 551 Chalice, ii. 56 Ciliated, ii. 56, iii. 117, 481 INDEX. 565 Cells Colostrum, ii. 285 Columnar, i. 573, iii. 18, 113, 481 Connective -tissue, i. 53 Cup, ii. 56, i. 573, iii. 16 Egg, ii. 174 Elementary, i. 419 Endothelial, ii. 265 Epidermoid, ii. 227. Epithelial of small intestine, i. 573 Fat, i. 93. Forked, iii. 18 Fusiform, i. 60, iii. 114 Ganglion, i. 176, ii. 346, iii. 228 Goblet, i. 573, ii. 5-6, iii. 16 Granular, i. 55 Granule, ii. 169 Gustatory, iii. 10 Hair cells of the organ of Corti, iii. 1 51 Hair cells of the hair, ii, 249 Hepatic, ii. 12 Investing, iii, 19 Lymph, ii. 341 Lymphatic nerve, i.. 175< Migrating, i. 54 Muscle, i. 188 Muscle cells of the heart, i. 246 Myeloplaxes, i. 146 Nerve, ii. 346 Olfactory, iii. 205, 206 Pigment, i. 61, ii. 66, iii. 204 Pin or peg cells, iii. 11 Polar, ii. 199 Rod, iii. 11 Roof (ear), iii. 102. Salivary, i. 425 Seminal, ii. 138 Stellate of capillaries, i. 282 Stellate of connective tissue, i. 61 Supporting, iii. 152, 162. Tooth cells (ear), iii. 180 Twin or double cells of the organ of Corti, iii. 161 White blood, i. 414 Cerebellum, ii. 512 Cortex, ii. 513 Nuclei clentati, ii. 517 Roof nuclei, ii. 517 Medullary fibres, ii. 518 Brachia of the, ii. 518 Cerebrospinal nerves, origin of, ii. 399, 422, 443, 486 Cerebrum, iii. 367 Cerumen, iii. 29 Ckomlrin, i. 103 Chordae tendinese, i. 254 Chorda? vocales, i. 107, ii. 42 Choroid coat, iii. 299 Chorion, iii, 495 Chromatophores, i. 62 Chyle, i. 340 Chyle vessels, ii- 304 Cicatricula, ii. 181 Cilia of eyelids, iii. 442 Ciliary arteries, iii. 325 Ciliary processes, iii, 300* Ciliary vessels, iii. 321 Ciliaris Riolani, iii. 444 Ciliary muscle (eye), iii. 304 Ciliary muscle (lid), iii. 444 Ciliary nerves, iii. 307 Circulus iridis major, iii. 326 „ „ minor, iii. 327 Clarke's columns, ii. 354, 359 Clitoris, ii. 319 Coccygeal gland, Luschka's, i. 292 Cochlea, iii. 131 Cohnheim's areas, iii. 546 Colostrum corpuscles, iL 285 Colliculus seminalis, iL 300 Columnae Morgagni, i. 583 Commissura anterior, ii. 331, 343 „ posterior, iL 355 Conjunctiva, iii. 439 Cones of the retina, iii. 243 Connective tissue, i. 47 Fibrils of, i. 53 Cells of, i. 53 Amaeboid cells of, i. 54 Pigmented cells, L.61 Forms of, i. 52 Plexuses and trabeculse, L 63 Wharton's jelly, i. 64 Fibrillar form of, L.70 Elastic fibres, L 81 Distribution of fibrillar form of, i. 84 Development of, i. 84 Deposition of fat in, L 93 Subcutaneous, ii. 219 Coni vasculosi of the testis, ii. 134 Corium, ii. 221 Cornea, iii. 372 Proper tissue of the cornea, iii. 375 Migrating cells of the cornea, iii. 376 Corpuscles of the cornea, iii. 380 Fibrillar substance of the cornea, ih\ 391 Interfibrillarpartof the matrix, iii. 402 Vessels of the cornea, iii. 417 Membrane of Descemet, iiL 418 Development of the cornea, iii. 422 Nerves of the cornea, iii. 428 Marginal region of the cornea, iiL 429 Cornu Ammonis, ii. 393. Cornua ant. and post, of spinal cord, ii. 358 Corpora cavernosa clitoridis, ii. 319 INDEX. Corpora cavernosa penis, ii. 309 Corpora Malpighii of the spleen, i. 354 Corpus cavernosuin urethra?, ii. 311 Corpus ciliare, iii. 301 Corpus dentaturn of the cerebellum, ii. 517 Corpus geniculatum, ii. 436 Corpus iunominatum testis, ii. 132 Corpus Highmori of the testis, ii. 133 Corpuscles of blood, white, i. 414 red, i. 575 „ of bone, i. 122 „ of Reissner, ii. 233 of Pacini, i. 167, ii. 232 „ of Vater, i. 167 „ of Wagner, ii. 233 „ tactile, ii. 233 „ muscle, iii. 544 Corti's organ, iii. 143, 151 Costal cartilages, characters of, i. 105 Cowper's glands, ii. 305 Crista acustica, iii. 109 Crista spiralis, iii. 134, 143, 145 Crura cerebri, ii. 411 Crura cerebelli, ii. 518 Cumulus proligerus, ii. 172 Cutis, ii. 216 Corium, ii. 221 Epidermis, ii. 227 Nerves, ii. 231 Sebaceous follicles, ii. 236 Sweat glands, ii. 238 Hairs, ii. 241 Nails, ii. 258 Crypts of Lieberkiihn, i. 596 Cuticula of the teeth, i. 474 Cystic ula, iii. 131 Cystis fellea, ii. 23 Dartos, ii. 133 Decussatio pyramidum, ii. 528 Deiters, processes of, from nerve cells, i. 419, ii. 347 Demours, membrane of, iii. 418 Dentine, i. 466 „ development of, i. 488 Derma, ii. 221 Descemet, membrane of, iii. 418 Diaphyses, i. 129 Didyniis, ii. 131 Dilatator papillae, iii 312 Disks of muscle, iii. 545 Discus proligerus, ii. 174 Doyere's cones or eminences, i. 202, 230 Ductus biliferi, ii. 13 „ choledochus, ii. 24 „ cochlearis, iii. 133, 142 „ ejaculatorii, ii. 294 „ lactiferi, ii. 278 Ductus Mulleri, ii. 132 Duodenum, i. 560 Duverney, glands of, ii. 321 EAR. Auricle of, structure of, i. 106, iii 27 External Ear. Auricle, iii. 27 External auditory meatus, iii. 29 Hairs and ceruminous glands, iii. 29 Membrana tympani, iii. 30 Sulcus tympanicus, iii. 32 Layers of sulcus, iii. 32 Bloodvessels, iii/ 42 Lymphatics, iii 44 Nerves, iii. 46 Middle Ear. Tympanum iii. 51 Mucous membrane of, iii. 51 Fibrous layer of, iii. 52 Bloodvessels of, iii. 56 Lymphatics of, iii. 56. Nerves of, iii. 57 Peculiar cell-nuclei in, iii. 60 Ossicula, iii. 61 Periosteum of, iii. 61 Cells of mastoid process, iii. 62 Eustachian tube, iii. 66 Osseous portion of, iii. 67 Cartilaginous portion of, iii. 67 Muscular (membranous) portion of, iii. 69 Mucous membrane of, iii. 72 Safety tube of, iii. 75 Accessory fissure of, iii. 75 Nerves of, iii. 83 Vessels of, iii. 83 Internal ear. Membranous labyrinth, iii. 85 Lig. lab. canalic. et sacculorum, iii. 88 Wall, iii. 94 Vessels of, ir. 107 Nerves of, iii. 108 Epithelium of, iii. 108 Auditory hairs, iii. 117 Aquneductus vestibuli, iii. 120 Canalis reuniens, iii. 121 Otoliths, iii. 121 Fenestra ovalis, iii. 123 Articulation of stapes, iii. 126 Musculus fixator baseos Btapedis, iii. 127 Auditory Nerve and Cochlea. Origin of, ii. 496 Comparative investigation of, iii. 131 Developmental history of, iii. 136 Modiolus, iii. 133 Lamina spiralis, iii. 134 INDEX. Scala vestibuli et tympani, iii. 134 Helicotrerna, iii. 134 Structure of cochlea. Capsule of cochlea, iii. 140 Meuibrana propria of the ductus coch- learis, iii. 140 Ductus cochlearis, iii. 142. Reissner's membrane, iii. 142 Epithelium of the ductus cochlearis and organ of Corti, iii. 151 Basilar process, iii. 151 Membrana tectoria, iii. 152, 163 Lamina reticularis, iii. 164 Auditory nerve, and its relation to the organ of Corti, iii. 168 Comparative anatomical and physio- logical notes, iii. 186. Comparison between organ of Corti and retina, iii. 184. Ebur dentis, i. 466 Eichhorn's fibre, ii. 240 Elastic fibres of connective tissue, i. 81 „ cartilage, i. 106 „ matrix of spinal cord, ii. 333 „ tissue of the vessels, i. 267, 274, 276 Elastiu, i. 83 Electricity, action of on cartilarge cells, i. 98 Elementary cells, i. 419 Elements, sarcous, iii. 545 Electrical organs, nerves of, i. 164, 170 Enamel of the teeth, i. 471 „ „ development of. i. 479 Endocardium, i. 251 Endothelium of the heart, i. 251 ., of the bloodvessels, i. 268 End plates of the motor nerves, i. 202 Epidermis, ii. 227 Epididymis, ii. 134 Epiglottis, structure of, i. 106, ii. 35 Epithelium of alimentary canal, i. 504, 507, 515, 524, 529, 544, 573, 584 „ of biliary ducts, ii. 22 „ ef Eustachian tube, iii. 80 of lachrymal glands, iii. 465 of larynx, ii. 38 of lungs, ii. 56, 63 of lymphatics, i. 306 of skin, ii. 227 of teeth, i. 476 of tongue, iii. 10 of urinary tubules, ii. 92 of uterus, iii. 478, 481 of vessels, i. 267, 276 Erectori.s pili, ii. 241 Eustachian tube, iii. (Hi Eyelids, iii. 439 Skin, iii. 440 Hairs, iii. 442 Sweat glands, iii. 442 Ciliary muscle, iii. 444 Meibomian glands, iii. 445 Tarsus, iii. 445 Mucous glands, iii. 447 EYE. Retina. Nervous elements, iii. 221 Nerve-fibre layer, iii. 223 Ganglion-cell layer, iii. 228 Internal granulated layer, iii. 232 Internal granule layer, iii. 234 Intel-granule layer, iii. 236 External granule layer, iii. 236 Henle's external fibre layer, iii. 237 Cone and fibre layer, i. 166, iii. 237 External segments of cones and fibres, iii. 245 Internal segments, iii. 246 Retina of various animals, iii. 264 Pigmented layer of the retina, iii. 269 . Supporting connective-tissue frame- work of the retina, iii. 272 Limitans interna, iii. 272 Limitans externa, iii. 272 Radial fibres, iii. 272 Fibre plexuses, iii. 272 Macula lutea, iii. 280 Fovea centralis, iii. 280 Ora serrata, iii. 288 Pars ciliaris, iii. 290 Development of the retina, iii. 293 Clwroid and Iris (Tunica vascularls seu uvea), iii. 299 Choroid, iii. 299 Ciliary processes, iii. 300 Ciliary body, iii. 302 Lamina vitrea, iii. 303 Basement membrane, iii. 30 Vessels of the choroid, iii. 303 Tunica Ruyschiana, iii. 303 Tunica vasculosa Halleri, iii. 333 Ciliary muscle, iii. 304 Nerves of the choroid, iii. 307 Stroma of the choroid, iii. 309 Iris, iii. 310 Sphincter pupillso, iii. 311 Dilatator pupillae, iii. 312 Liganientum pectinatum iridis, i. 68, iii. 304 Vascular system of the Eye. Retinal vascular system, iii. 316 Arteriaet vena centralis retina, iii. 316 Zonula Zinnii or Halleri, iii. 317 Ciliary or choroidal vascular system, iii. 320 568 INDEX. Arterise et venae ciliares, iii. 327 Venae vorticosae, iii. 322 Arteria choroidea, iii. 324 Arteries of the ciliary body and iris, iii. 325 Veins of the choroid, iii. 327 Vessels of the corneal margin and of the connective tissue, iii. 331 Lymphatics of the Eye. Posterior lymphatics, iii. 334 Efferent vessels of choroid and scle- rotic, iii. 334 Perichoroidal space, iii. 335 Membrana suprachoroidea, iii. 385 Tenon's fascia and Tenon's cavity, iii. 336 Supravaginal cavity, iii. 337 Efferent lymphatics of the retina, iii. 337 Sub vaginal cavity, iii. 338 Anterior lymphatics, iii. 339 System of the anterior chamber of the eye, iii. 339 Canal of Petit, iii. 339 Canal of Fontana, iii. 339 Canal of Schlemm, iii. 340 Lymphatics of cornea, iii. 342 Lymphatics of conjunctiva, iii. 342 Vitreous. Membrana hyaloidea, iii. 346 Cells of the vitreous, iii. 352 ' Zonula Zinnii, iii. 354 Leas. Anterior epithelial layer, iii. 358 Fibres of lens, iii. 360 Capsule of lens, iii. 370 Cornea. Layers of the cornea, iii. 372 Proper tissue of the cornea, iii. 375 Migrating cells of cornea, iii. 376 Corneal corpuscles, iii. 380 Behaviour of corpuscles in inflamma- tion, iii. 389 Origin of migrating cells, iii. 389 Fibrillar substance of corneal tissue, iii. 391 Relations of cells of cornea to matrix, iii. 402 Interfibrillar part of matrix and its cavities, iii. 402 Vessels of the cornea, iii. 417 Membrane of Descemet, iii. 418 Endothelium, iii. 421 Development of the corneal layers belonging to connective tissue, iii. 422 External epithelium of cornea, iii. 424 Nerves of cornea, iii. 428 Margin of cornea, iii. 429 Conjunctiva palpebrarum, iii. 448 Plica semilunaris, iii. 440 Fornix conjunctivae, iii. 452 Conjunctiva bulbi, iii. 440 Papillae of the conjunctiva, iii. 449 Lymphatic follicles and vessels of, iii 449 Trachoma glands, iii. 450 Bruch's clusters, iii. 449 Nerves of the cornea, iii. 428 Eyelids. Tarsus, iii. 439, 445 Cilia, iii. 442 Sweat glands, iii. 442 Musculus sphincter orbicularis, iii. 444 Ciliaris Riolani, iii. 444 Meibomian and other glands, iii. 445 Tunica, Sderotica. Lamina cribrosa, iii. 400 Nerves of the sclerotic, iii. 459 Lachrymal Glands. Structure, iii. 464 Alveoli, iii. 464 Lunula, iii. 466 Membrana propria, iii. 467 Interstices of the alveoli, iii. 468 Exretory ducts, iii. 470 Nerves, iii. 472 Facial nerve, origin of, ii. 493 Fasciculus cuneatus, ii. 337 Fallopian tube, iii. 498 Fat cells of connective tissue, i. 93 Fenestra ovalis, iii. 123 Fenestra rotunda, membrane of, iii. 142 Fenestrated layer of arteries, i. 267 Fibres, elastic i. 81 „ organic muscular, i. 188 „ medullated nerve, i. 149 Fibrillar connective tissue, i. 70 Fibro- cartilage, i. 105 Fimbria ovarica, iii. 500 Follicle, Graafian, ii. 172 hair, ii. 241 lymph, iii. 449. Malpighian, i. 354 Peyer's, i. 565 sebaceous, ii. 236 solitary, i. 566 Fontana's cavity, iii. 339 Food yolk, ii. 175 Formative yolk, ii. 175 Fornix conjunctivae, iii. 452 Gall bladder, ii. 23 INDEX. Ganglia of nerves, i. 175, ii. 538 Ganglion cells, ii. 334, 346 Ganglion fibres, i. 155. Ganglion spirale, iii. 140 Gas chamber, construction of. i. viii. Generative organs, male, ii. 288 „ „ female, ii. 318 Genesis of cells, i. 33 „ of connective tissue, i. 84 ,, of elastic fibres, i. 92 „ of fat, i. 93 ,, of the tissxies generally, iii. 503 Giralde's, organ of, ii. 132, 205 Gland, Luschka's coccygeal, i. 292 Glandulae Brunnerianae, i. 568 Bartholini, ii. 321 Buccales, i. 503 Cowperi, ii. 305 lachry males, iii. 464 lenticulares, i. 548, 565 Lieberkuhnianae, i. 569, 577, 584 Littrii, ii. 302, 308, 324 lymphaticae, i. 329 Peyerianae, i. 565, 599 salivales, i. 423, 500, ii. 509 sebiferae, ii. 236 solitariae, i. 565 „ sudoriparse, ii. 238. ,, Tysonianse, ii. 317. „ utriculares, iii. 478 Glans penis, ii. 316 Glans clitoridis, ii. 319 Glisson's capsule, ii. 31 Globulin, i. 413 Glomeruli Malpighii, ii. 98 Glossopharyngeus, origin of, ii. 505 Goll's fasciculus cuneatus, ii. 337 Grey substance of the spinal cord, ii. 342 Graafian follicle, ii. 167, 172, 202 Granule of the ovum, ii. 180 Gums, i. 477 GUSTATORY ORGANS, iii. 1 Of Man and Mammals. Gustatory bulbs, iii. 1. Papillae circumvallatse, iii. 3 Papillae fungiformes, iii. 5 Gustatory cups, iii. 8 Investing and gustatory cells, i. 165, iii. 10 Nerves, iii. 12 Of Amphibia, iii. 14 Gustatory disks, iii. 14 Gustatory papilla?, iii. 14 Goblet cells, iii. 16 Columnar cells, iii. 18 Forked cells, iii. 18 Of Fishes, iii. 20 Hair, ii. 241 Hair follicle, ii. 241 Hair sac, ii. 242 Hair papilla, ii. 244 Root-sheaths, ii. 245 Shaft of the hair, ii. 247 Root of the hair, ii. 248 Huxley's sheath, ii. 250 Cuticula of the hair, ii. 247 Hair cells, ii. 249 Cortical substance, ii. 249 Medullary cord, ii. 247, 251 Development and succession of the hair, ii. 255 Sebaceous glands, ii. 236 Muscles of the hair follicle, erectores pili, ii. 240 Hairs, auditory, iii. 112, 117, 160 „ olfactory, i. 165, iii. 205 Haller's corona, iii. 317 Haemoglobin crystals, i. 412 Hartnack's lenses, i. v. Haversian canals, i. 119 Haversian lamellae, i. 1 21 Hearing, organ of, iii. 27 External and middle ear, iii. 27 Eustachian tube, iii. 66 Membranous labyrinth, iii. 85 Heart, i. 244 Musculature of, i. 244 Trabeculae carneae, i. 249 Fibrous rings of, i. 251 Endocardium, i. 251 Endothelium, i. 251 Muscle of the endocardium, i. 251 Purkinje's fibres, i. 252 Valves, i. 253 Chordae tendinese, i. 254 Pericardium, i. 255 Vessels of, i. 255 Lymphatics, i. 255 Nerves and ganglia, i. 256 Terminations of the nerves, i. 259 Helicotrema, iii. 134 Henle's loops (kidney), ii. 85 Henle's root-sheath of the hair, ii. 246 Henle's mucous cells of salivary glands, i. 428 Henle's albuminous cells of salivary glands, i. 428 Hensen's median disk in muscle, iii. 547 Hepatic lobules, ii. 5 Hepatic cells, ii. 12. Hepatic trabeculac, ii. 10 His's granule cell of the ovary, ii. 169 Humour, vitreous, iii. 345 Huxley's sheath of the hair, ii. 250 Hyaline cartilage, i. 96 Hyaloid membrane, iii. 346 570 INDEX. Hydatid of Morgagni, ii. 132, iii. 561 Hymen, ii. 321 Hypoglossus, origin of, ii. 509 Ideal type of cell, i. 4 Infundibula, ii. 50 Injection, preparation of tissues by, i. xxxiv. Imbedding, proper method of, iii. 519 Integumentum commune, ii. 217 Interlobular spaces, ii. 2 „ passages, ii. 2 „ vessels, ii. 3 Intestine, small, i. 560 Muscular coat, i. 560 Mucous membrane, i. 563 Villi of the small intestine, i. 564 Lymph follicles and Peyer's patches, i. 565 Brunner's and Lieberkiihnian glands, i. 568 Muscularis mucosse, i. 570 Epithelium of the mucous membrane, i. 573 Cup cells, i. 573 Nerves, i. 576 Intestine, large, i. 577 Mucous membrane, i. 577 Muscular layer, i. 579 Nerves, i. 579 Kectum, i. 579 Muscular coat, i. 580 Sphincter internus and externus, i. 582 Mucous membrane of, i. 582 Columnse Morgagni, i. 583 Bloodvessels of the alimentary canal, i. 586 Intra-cartilaginous ossification, i. 127 Intra-membranous ossification, i. 142 Intumescentia gangliformis, iii. 169. Isthmus faucium, i. 513 Kidney, ii. 83 Urinary tubules, ii. 85 Henle's loops, ii. 85 Primitive cones, ii. 88 Pyramids, ii. 89 Wall of urinary tubules, ii. 90 Bloodvessels, ii. 97 Lymphatics, ii. 105 Connective tissue, ii. 105 Nerves, ii 106 Krause's corpuscles, ii. 317, 321. iii. 453 „ muscle prism, iii. 547 Labia pudendi, ii. 318 Labyrinth, auditory, iii. 85 „ cartilage, in. 100 Lachrymal glands, iii. 464 „ alveoli, 464 Lacunae of bone, i. 122 Lacunae of Morgagni, ii. 306 Lacunar blood paths, i. 289 Lamellae of the bones, i. 116 Lamina cribrosa, iii. 460 „ modioli, iii. 134 ,, reticularis, iii. 164 „ spiralis, iii. 134, 143 Large intestine, i. 577 Larynx, ii. 34 Epiglottis, ii. 35 Thyroid cartilage, ii. 36 Cartilages of Wrisberg, ii. 36 Cartilage of Santorini, ii. 36 Arytenoid cartilages, ii. 37 Mucous membrane, ii. 38 Bulbous structures, ii. 39 Acinous glands, ii. 41 False vocal cords, ii. 42 True vocal cords, ii. 43 Vessels, ii. 45 Nerves, ii. 45 Latebra, or yolk cavity, ii. 182 Lens of the eye, iii. 358 Capsule of, iii. 370 Fibres of, iii. 360 Lenticular glands, i. 566 Lieberkuhn's crypts, i. 550, 569, 577, 584 Liquor folliculi, ii. 173 Littre's glands of the urethra, ii. 302, 308, 324 Ligamenta labyrinthi, iii. 88 Ligamentum ciliare, iii. 304 „ pectinatum iridis, i. 68 „ spirale, iii. 134, 142 Liquor folliculi, ii. 173 Liver, ii. 1 General structure of, ii. 1 Structure of the lobules, ii. 5 Hepatic cells, ii. 12 Intralobular biliary canal, ii. 13 Biliary ducts, ii. 20 Gall bladder, ii. 23 Bloodvessels of, ii. 25 Lymphatics, ii. 27 Connective tissue of, ii. 31 Capsule of Glisson, ii. 31 Nerves of, ii. 33 Lobules of the liver, ii. 5 Lobules of the lungs, ii. 59' Locus luteus, iii. 201 Lungs, ii. 49 Alveoli, ii. 51 Bronchia, ii. 52 External fibrous layer, ii. 53 Muscular layer, ii. 55 INDEX. 571 internal fibrous layer, or basal mem- brane, ii. 55 Epithelium, ii. 56, 63 Smallest bronchia, ii. 56 Vessels of, ii. 58 Nerves of, ii. 58 Alveoli, ii. 58 Infundibula, ii. 59 Lobules, ii. 59 Respiratory capillary plexus, ii. 61 Lymphatics, ii. 63 Of Birds, ii. 68 Of Reptiles and Amphibia, ii. 72 Swimming bladder of Fishes, ii. 78 Luschka's coccygeal gland, i. 292 Lymph and chyle, i. 340 Elementary corpuscles, i. 340 Lymph corpuscles, i. 341 Naked nuclei, i. 341 Pigmented cells, i. 341 Development of lymph corpuscles, i. 345 Serous transudate, i. 346 Lymph hearts, i. 300 Lymphatics, i. 297 Structure of, i. 299 Lymphatic capillaries, i. 301 Serous canals, i. 317 Perivascular space, i. 324 Of the retina, iii. 337 Of the skin, ii. 225 Of the uterus, iii. 491 Lymphatic follicles, i. 326, 565, iii. 449 Lymphatic glands, i. 329 ( lonnective tissue of, i. 65 Cortex, i. 330 Medullary substance, i. 330 Trabeculse, i. 332 Follicular cords, i. 333 Lymph paths, i 337 Macula acustica, iii. 109 Macula germinativa, ii. 175, 180, 207 Macula lutea, iii. 280 Malpighian corpuscles of spleen, i. 354 Glomerulus, ii. 98 Pyramids, ii. 89 Male sexual organs, ii. 288 Vas deferens, ii. 288 Vesiculse seminalis, ii. 293 Ductus ejaculatorii, ii. 294 Prostate gland, ii. 295 Colliculus seminalis, ii. 300 Urethra, ii. 301 Penis, ii. 309 Mammary glands, ii. 277 Lob ales, ii. 277 Stroma, ii. 278 Vesicles, ii. 278 Of male, ii. 281 Matrix of bone, i. 117 „ pili, ii. 244 „ of spinal cord, ii. 233 Meatus auditorius externus, iii. 29 Medulla oblongata, ii. 472 „ spinalis, ii. 327 Medullated nerve fibres, i. 149 Medulla of nerves, i. 51 Meibomian glands, iii. 445 Meidinger's method of warming the microscope stage, i. xiv. Meissner's corpuscles, i. 233 „ plexus, i. 576, 579, 585 Membrana basilaris, iii. 134, 143 „ capsulo-pupillaris, iii. 370 „ Cortii, iii. 163 „ Descemetii, iii. 437 ,, granulosa folliculi, ii. 172 „ Graafiani, ii. 172 „ hyaloidea, iii. 346 „ intermedia (placenta), 497 „ limitans, iii. 272, 275 „ nictitans, iii. 440 „ obturatoria stapedis, iii. 126 „ pigmenti, iii. 269 „ propria of the several organs. (See these.) „ Reissneri, iii. 142 „ Ruyschiana, iii. 303 ,, suprachoroidea, iii. 335 „ serosa, ii. 265 * „ synovialis, iii. 555. „ tectoria, iii. 148, 163. „ tympani, iii. 30 „ vitrea of hair, ii. 244 Membrane, serous, ii. 265 Endothelium, ii. 265 Basement membrane, ii. 269 Lymphatics, ii. 270 Bloodvessels, ii. 273 Nerves, ii. 274 Synovial membranes, iii. 555 Metamorphosis of cells, i. 25 Methods, general, of investigation, i. i. Micropyle, ii. 177 Migrating cells, i. 53 Milk, ii. 284 Middle coat of the arteries, i. 268 Modes of mounting objects, i. vii. „ of research with the microscope, i. 1 ,, of warming the stage of the microscope, i. xii. ., of applying electricity, i. xx. Preparation of tissue, i. xxv. By teasing, i. xxvii. „ section, i. xxvii. ,, staining, i. xxxii. 572 INDEX. By injection, i. xxxiv. „ self -injection, i. xxxvii. Modiolus, iii. 133 Moist chamber, i. vii. Morgagni, hydatid of, ii. 132, iii. 561 „ lacunae, ii. 306 Mouth, cavity of, i. 497 Lips, i. 497 Mucous membrane, i. 497 Epithelium, i. 498 Glands, i. 500 Musculature, i. 502 Frsenum, i. 504 Papilla of the mucoas, i. 504 Mucous layer, i. 504 Mucous membrane of the hard palate, i. 505 Soft palate, i. 506 Uvula, i. 506 Mucous membrane, i. 506 Glands, i, 509 Musculature, i. 511 Tonsils or amygdalse, i. 513 Miiller's duct, ii. 132 Muller's (H.) circular muscle of the eye, iii. 305 Muscles of the several organs. (See these.) Muscular tissue : — Smooth or unstriped form, i. 188 Form and general relation of, i. 188 Structure of, i. 190 Nucleus, i. 191 Connections and arrangement, i. 192 Vessels of, i. 194 Nerves of, i. 195 Distribution of. i. 198 ' Action of on polarised light, i. 205 Striated form, iii. 543 Transversely striated form in po- larised light, i. 205 Termination, i. 202 Sarcolemma, iii. 544 Nuclei, or muscle-corpuscles, iii. 544 , Disks and sarcous elements, iii. 545 Kollett's chief and intermediate substances, iii. 545 Cohnheim's areas, iii. 546 Hensen's median disk, iii. 547 Krause's muscle prisms, iii. 547 Strieker's views, iii. 549 In lower animals, iii. 550 Development of, iii. 552 Myelin drops of nerves, i. 151 Myeloplaxes, i. 146 Nabothian ovula iii. 488 Nail, ii. 258 „ root of, ii. 256 „ fold of, ii. 259 Nail, bed of, ii. 259 ,, bed, mucous layer of, ii. 260 „ matrix, ii. 262 „ development of, ii. 263 Nasmyth, persistent capsule of, i. 474 Nervi ciliares, iii. 307 NERVOUS SYSTEM, i. 147 Nervous tissue, i. 147 Morphological elements, i. 147 Nerve fibres, i. 147 Primitive nerve fibrils, i. 147 Deiter's protoplasmic processes, i. 149 Schultze's ramifying processes, i. 149 Schultze's axis-cylinder processes, i. 149 Primitive fibril fasciculi, i. 149 Medullary fibres, i. 149 Medullary sheath, i. 149 Nerve medulla, i. 151 Schwann's sheath (neurilemma), i. 152 Axis cylinder, i. 153 Non-medullated nerve fibres, i. 155 Varieties of nerve fibres, i. 157 Remak's sympathetic fibres, i. 155 Division of nerve fibres, i. 162 Termination of nerves in the cornea, i. 164 Termination of nerves in the con- junctiva, iii. 453 Termination of nerves in glands, i. 172, 433 Termination of nerves in muscles, i. 169, 195, 203 Termination of nerves in rete Mal- pighii, i. 187 Peripherie terminal organs, i. 165 Olfactory cells and hairs, i. 165 Gustatory cells, i. 165 Auditory cells, i. 166 Rods and cones, i. 166 Tactile corpuscles, i. 167 Pacinian corpuscles, i. 167 Krause's corpuscles, i. 168, iii. 453 Doye're's cones, i. 202 Terminal nerve plates, i. 169, 230 Terminal nerve bulbs, i. 168, 213 ; iii. 453 Electric terminal organs, i. 170 Origin of nerve fibres in the central organs, i. 172 Nerve cells, i. 172 Ganglia, i. 172, ii. 539 Spinal ganglia, i. 175 Sympathetic ganglia, i. 175 Processes of the ganglion cells, i. 176 Fibrillar ganglion cell substance, i. 178 Stilling's nuclei, i. 182 INDEX. 573 Small nerve cells of the cerebrum, i. 183 Anastomoses between ganglion cells, i. 186 Development of nerve tissue, iii. 553 Spinal cord, ii. 327 General structure, ii. 327 White substance, ii. 331 Connective-tissue matrix, ii. 331 Neuroglia, or nerve cement, ii. 332 Nerve fibres, ii. 335 Relative proportion of fibres to neu- roglia, ii. 338 Sulci longitudinalis ant. et post., ii. 331 Anterior white commissure, ii. 331, 340 Goll's cuneate cord, ii. 337, 340 Burdach's slender fascicxilus, ii. 337, 340 Grey substance of, ii. 342 Nerve fibres of, ii. 343 Plexus of, ii. 344 Nerve cells, ii. 346 Deiter's protoplasmic processes, ii. 349 Posterior grey commissure, ii. 355 Central canal, ii. 355 Anterior cornua, ii. 359 Median portion and Clarke's columns, ii. 359 Posterior cornea, ii. 361 Substantia gelatiiiosa of Rolando, ii. 361 Exit and entrance of nerves, ii. 363 Course of fibres in, ii. 363 Brain, ii. 367 General view of structure of, ii. 369 Four categories of grey masses, ii. 369 Projection system of, ii. 372 Cerebral hemispheres, ii. 374 Genetic succession of cerebral lobes, ii. 378 General or five-laminar type of cere- bral cortex, ii. 381 Type of occipital apex, ii. 390 Type of Sylvian fissure, ii. 391 Type of cornu Ammonis, ii. 393 Bulbus olfactorius, ii. 397 General arrangement of white fibres, ii. 402 Pes of the crus cerebri, and its gan- glia, ii. 411 Origin of pes from the cerebral cortex, ii. 411 Origin of pes from the nucleus cau- datus, ii. 412 Origin of pes from the nucleus lenti- fonnis, ii. 416 Grey substance of Soemmering, ii. 421 Tegunientum of the crus cerebri, ii. 421 Origin of the crusta from the optic thalami, ii. 422 Origin of the crusta from the cor- pora quadrigemina, ii. 435 Origin of the crusta from the corpus geniculatum, ii. 436 From the pineal gland, ii. 440 From a ganglion in the crus cerebri, ii. 451 Differences between the pes and crusta, ii. 453 Region of the interweaving of the cerebellar arms and projection system, ii. 454 The connection of the processus a cere- bello ad cerebrum with the me- dullary velum (valve of Vieus- seus), ii. 457 The connection of the processus a cere- bello ad pontem with the prolon-.. gation of the pes of the crus cerebri, ii. 461 The connection of the processus a cere- bello ad medullam with the prd- longation of the crusta, the in- ferior peduncle of the cerebel- lum, ii. 463 The posterior sectional area of the projection system, ii. 465 Origin of the olfactory nerve, ii. 399 optic nerve, ii. 422 oculomotor nerve, ii. 443 trochlearis, ii. 444 trigeminus, ii. 446, 486 abducens, ii. 490 facial, ii. 493 auditory, ii. 496 glossopharyngeal, ii. 505 vagus, ii. 505 accessory, ii. 505 hypoglossal, ii. 509 Cerebellum, ii. 512 Cortex of cerebellum, ii. 513 Deutated nucleus, ii. 517 Roof nucleus, ii. 517 Fibrse propriae, ii. 518 Arms of the cerebellum, ii. 518 Formation of the transit into the spinal cord, ii. 522 Shutting-off of the central canal, ii. 523 Decussation of the pyramids, ii. 528 Sympathetic nervous system, ii. 539 Ganglion cells, ii. 540 Structure of, ii. 540 574 INDEX. Nuclear communicating fibres, ii. 541 Nucleus, nueleolus, ii. 542 Processes of ganglion cells, straight and spiral, ii. 544 Development and regressive meta- morphosis of, ii. 550 Fibres of the sympathetic, ii. 551 Neurilemma, i. 152 Neuroglia, i. 65, ii. 335 Nose, iii. 201 Regio olfactoria, iii. 200 Locus luteus, iii. 200 Bowman's glands, iii. 203 Epithelium, iii. 205 Olfactory hairs, iii. 206 Olfactory nerves, iii. 210 Relations of the nerves in the epi- thelial layer, iii. 211 Nuclei dentati, ii. 517 Nueleolus of the sympathetic ganglia, ii. 542 Nucleus of cells, ii. 542 Nymphse, ii. 318 Oculomotorias, nucleus of, ii. 443 „ origin of, ii. 443 Odontoblasts, i. 476 (Esophagus, i. 528 Mucous membrane, i. 529 Muscular coat, i. 531 Connective-tissue coat, i. 532 Nerves and lymphatics, i. 532 Structure of, in the Dog, i. 533 „ Rabbit, i. 533 „ Horse, i. 535 „ Rat, i. 535 in Birds, i. 535 in Batrachia, i. 537 Vascular supply of, i. 592 Olfactory nerve, origin of, ii. 399 „ „ distribution of, iii. 211 Olfactory organ, iii. 201 Regio olfactoria, locus luteus, iii. 201 Bowman's glands, iii. 203 Olfactory cells and hairs, i. 165, iii 205 Epithelium, iii. 205 Olfactory nerve, i. 155, 162; iii. 210 Relations of the nerve-fibrils in the epithelial layer, iii. 211 Optic nerve, origin of, ii. 422 Ora serrata retinse, iii. 288 Oral cavity, i. 497 Orchides, ii. 131 Organ of Corti, iii. 151 Organ of Giralde"s, ii. 132, 205, 293 Organic muscles, i. 188 Form and general characteristics, i, 188 Structure of organic fibres, i. 190 Nucleus of the fibres, i. 190 Connection and arrangement of the fibres, i. 192 Vessels of, i. 194 Nerves of, i. 195 Distribution of organic muscles, i. 198 Methods of investigation, i. *200 Origin of cells, i. 33 „ nerve fibres in nerve centres, i. 172 ,, intra-cartilaginous, i. 127 „ iutra-membranous, i. 142 „ periosteal, i. 136 Ossification, points of, i. 128 Osteoblasts, i. 135 Otoliths, iii. 183 Ovary, ii. 164 Peritoneal investment, ii. 166 Medullary substance, ii. 167 Cortical substance, ii. 167 Stroma, ii. 168 Musculature, ii. 169 Vessels, lymphatics, and nerves, ii. 171 Graafian follicles, ii. 172 Liquor folliculi, ii. 173 Discus proligerus, ii. 174 Ovum, ii. 174 i Development of the ova, ii. 192 Parovarium, ii. 204 Ovarial tubules, ii. 196 Ovula Nabothi, iii. 488 Ovum, ii. 174 Structure of, ii. 174 Principal or formative yolk, ii. 175, 178 Secondary or food yolk, ii. 175 Zona pellucida or vitelline membrane, ii. 176 Micropyle, ii. 177 Nucleus, or germinal vesicle, ii. 178 Nueleolus, or germinal spot, ii. 180 Granule, ii. 130 Latebra of Purkinje, ii. 182 Ovum of the Bird, ii. 182 Of Sharks, ii. 185 Of Batrachia, ii. 185 Of Invertebrata, ii. 186 Development of, ii. 192 Pacinian corpuscles, i. 167, ii. 232, 298, 310, 321 Palate, hard, mucous membrane of, i. 505 Papilla) circumvallatse, i. 515, 589; iii. 3 „ filiformes, i. 514 „ fungiformes, i. 514, iii. 5 „ renales, ii. 83 „ of the hair, ii. 244 INDEX. 575 Papillae of the coriurn, ii. 224 „ of the mouth, i. 586 Paraglobulin, i. 413 Parovarium, ii. 203 Wolffian body, ii. 204 Rosenmuller's organ, ii. 205 Parenchyma-zone of the ovary, ii. 167 Parepididymis, ii. 132, 205, 293 Parotid gland, see salivary glands Penis, ii. 309 Perichorioidal space, iii. 335 Pericardium, i. 255 Periosteal ossification, i. 136 . Periosteum, i. 138 Periosteum, connective tissue of, i. 77 Peripherie nerve process of Deiters, i. 176 Peritoneum, i. 77, 83, 85 Perivascular spaces, i. 324 Pes of the crus cerebri, ii. 411 Petit, canal of, iii. 339 Peyer's glands, i. 565 ,, „ vascular supply of, i. 599 Phalanges of the organ of Corti, iii. 161 Pharynx, i. 523 Epithelium of its mucous membrane, i. 524 Vessels, i. 526, 592 Lymphatics, i. 525, 527 Muscles, i. 527 Glands, i. 527 Pia mater, ii. 331 Pigmented cells, i. 61 Pigment layer of the retina, iii. 969 Pili, ii. 241 Pillars of Corti, iii. 152 Placenta, iii. 493 Muscular fibres in, iii. 494 Bloodvessels of, iii. 494 Villi of, iii. 495 Plana semiluuaria, iii. Ill Planaria, movements of vitelline spheres of, i. 3 Plasma, i. 374 Plexus, vascular, i. 292 Plexus pampiniformis, iii. 491 Plexus promontorii, iii. 83 Plexus uterinus, iii. 491 Plicae palmatse, iii. 487 Plica semilunaris conjunctive, iii. 440 Pneumogastric nerve, origin of, ii. 505 Polarised light, action of muscles on, i. 235 Preparation of tissues for microscopic investigation, i. xxv. By teasing, i. xxvii. By section, i. xxvii. Primitive nerve fibrils, i. 148 Primordial ova, ii. 174 Principal yolk, ii. 175, 178 Processus ciliares, iii. 300 Prostate gland, ii. 295 Promontory, ii. 454 Protoplasm, i. 9 Protoplasmic processes of cells, i. 149 Pulpa dentis, i. 476 Pulpa lienis, i. 355 Pulpa pili, ii. 244 Pupilla, iii. 310 Purkinje's fibres of the endocardium i. 252 Pyramids of the kidneys, ii. 89 Pyramids, decussation of, ii. 528 Recessus labyrinthi, iii. 138 Rectum, i. 579 Muscular layers, i. 580 Mucous membrane, i. 582 Red corpuscles of blood, i. 374 Regio olfactoria, iii. 201 Reissner's membrane, iii. 134, 142 Remak's fibres, i. 155 Ren, ii. 83. Respiratory apparatus : — Larynx, framework, ii. 34 Connections of cartilages, ii. 3t> Soft parts of, ii. 38 Epithelium, ii. 39 Acinous glands, ii. 41 Vocal cords, ii. 42 Vessels of, ii. 45 Nerves, ii. 45 Trachea, ii. 46 Lungs, ii. 49 Bronchia, ii. 53 External fibrous layer, ii. 53 Muscular layer, ii. 55 Internal fibrous layer, or basal membrane, ii. 55 Epithelium, ii. 56 Smallest bronchi, ii. 56 Vessels of, ii. 58 Nerves of, ii. 58 Alveoli, ii. 58 Infundibula, ii. 59 Lobules of, ii. 59 Respiratory capillary plexus, ii. 61. Lymphatics of, ii. 63 Epithelium, ii. 63 Lungs of Birds, ii. 68 „ „ Reptilia, ii. 72 ,, „ Amphibia, ii. 72 „ and swimming bladder of Fishes, ii. 78 Rete Malpighii or mucosum, ii. 227 Reticular cartilage, i. 106 Reticulum of lymphatic glands, i. 65 Retiform connective tissue, i. 65 576 INDEX. Retina, iii. 218 Nervous constituents of, iii. 221 Nerve-fibre layer, iii. 223 Ganglion-cell layer, iii. 228 Internal granulated layer, iii. 232 Internal granule layer, iii. 234 External granule layer, iii. 236 Henle's external fibre layer, iii. 237 Rod and cone layer, iii. 237 External segments of rods and cones, iii. 245 Internal segments of rods and cones, iii. 246. Of various animals, iii. 264 Pigmented layer of the, iii. 269 Supporting connective tissue of, (in- cluding limitans externa and in- terna and fibrous plexus,) iii. 272 Macula lutea and fovea centralis, iii. 280 Ora serrata and pars ciliaris, iii. 288 Development of the retina, iii. 293 Rollett's chief and intermediate sub- stances (in muscle), iii. 545 Rolando's substantia gelatinosa of the spinal cord, ii. 361 Roof -cells, iii. 102 Rosenrnuller's organ, ii. 205 Ruysch's membrane, iii. 303 Saccular glands of mouth, i. 590 Sacculus, iii. 96, 131 Safety tube, iii. 74 Salivary glands, i. 423 General plan of structure, i. 423 Alveoli, i. 423 Cells of the alveoli, i. 426 Henle's mucous cells, i. 428. „ albuminous cells, i. 428 Excretory ducts, i. 429 Distribution of nerves in, i. 433 Regeneration of the glandular epithe- lium, i. 448 Morphological constituents of the sa- liva, i. 453 Changes in, coincident with func- tional activity, i. 455 Stroma of, i. 460 Methods of investigating, i. 461 Santorini, cartilage of, ii. 36 Sarcolemma, iii. 544 Sarcous elements, iii. 545 Scala media, iii. 134 „ tympani, iii. 134 „ vestibuli, iii. 134 Schultze's mode of warming the micro- scope stage, i. xii. Schultze's ramifying processes of cells, i. 149 Schwanu's sheath of the nerves, i. 1 49, ii. 336 Schweigger-Seidel on the heart, i. 244 Sclerotic coat of the eye, iii. 459 „ „ in Birds, iii. 460 „ „ in Amphibia and Fishes, iii. 461 „ „ nerves of, iii. 461 Scrotum, ii. 133 Sebaceous follicles, ii. 236 Secondary yolk, ii. 175 Section, preparation of tissues for, i. xxvii Self -injection, preparation of tissues by, i. xxxvii Septum cartilagineura (tongue), i. 515 Serous membranes, ii. 265 SEXUAL ORGANS (MALE), Testis. Tunica adnata, ii. 131 Tunica albuginea, ii. 133 Vaginalis propria, ii. 131 Corpus Highinori, ii. 133 Organ of Gil-aide's, ii. 132 Hydatids^of Morgagni, ii. 132 Duct of Miiller, ii, 132 Wolffian body, ii. 133 Septula testis, ii. 133 Cremaster interims, ii. 133 Tunica dartos, ii. 133 Septum scroti, ii. 134 Tubuli seminiferi. ii. 134 Rete testis, ii. 134 Coni vasculosi, ii. 134 Vas aberrans, ii. 134 Cellular contents of, ii. 138 Seminal corpuscles ii. 141 Of Invertebrata, ii. 142 Of Vertebrata, ii. 147 Development of, ii. 152 Vessels and nerves, ii. 162 Vas deferens, ii. 288 Mucous membrane of, ii. 288 Muscular coat of, ii. 289 Cremaster internus, ii. 291 Nerves and vessels, ii. 291 Cremaster medius, ii. 292 Parepididyniis, or organ of Giraldes, ii. 293 Vesiculse seminalis, ii. 293 Ductus ejaculatorii, ii. 294 Prostate gland, ii. 295 Muscular stroma, ii. 295 Structure of, ii. 296 Vessels and nerves of, ii. 298 Caput gallinaginis, ii. 301 Urethra, ii. 301 Mucous membrane of, ii. 301 Glands of Littre, ii. 302 INDEX. 577 Muscular coat of, ii. 302 \V.-s*.>ls and nerves of, ii. 303 <'o\vper's glands, ii. 305 Papilla of the mucous membrane of, ii. 307 Penis, ii. 209 Tunica albuginea of the corpora caver- nosa, ii. 309 Muscular fibres of, ii. 309 Bloodvessels, ii. 310 Mechanism of erection, ii. 313 Arteriae helicinse, ii. 313 Verne efferent es, ii. 314 Retia mirabilia, ii. 315 Glaus, ii. 316 Membrane of the prepuce, ii. 317 Test is, ii. 131 Tunica adnata, ii. 131 „ albuginea, ii. 133 Corpus Highmori, ii. 133 Giraldes' organ, ii. 132 Morgagni's hydatid, ii. 132, iii. 561 Muller's duct, ii. 132 Wolffian body, ii. 133, 204 Septula testis, ii. 133 Cremaster internus, ii. 133 Tunica dartos, ii. 133 F KM ALE. Ovary, ii. 164 Structure of, ii. 164 Germ epithelium of, ii. 166 Connective tissue and parenchy- niatous zone, ii. 167 Medullary substance, or vascular zone, ii. 167 Stroma, ii. 168 Albuginea, ii. 168 Ovarial tubes, ii. 168 Corpora lutea, ii. 167 Granule cells of His, ii. 169 Smooth muscular fibres, ii. 169 Vessels and nerves, ii. 171 (rraafian follicles, ii. 171 Cortical cells, ii. 172 Theca folliculi, ii. 172 Tunica fibrosa, ii. 172 Tunica propria, ii. 172 Membrana granulosa, or follicular epi- thelium, ii. 172 Discus or cumulus proligerus, ii. 172 Liquor folliculi, ii. 173 Omni, ii. 174 Size of, ii. 207 Epithelium of ovum, ii. 174 Primordial ova, ii. 174, 207 Formative or chief yolk, vitellus, ii. 175 Purkinje's germ vesicle, ii. 175, 207 G.M-minal spot, ii. 175, 180, 207 Vitelline membrane, or zona pellucida, ii. 175, 207 Food or secondary yolk, ii. 175 Basal membrane, or zona radiata, ii. 176 Micropyle, ii. 1V7 Various forms of ova, ii. 181 Development of the ovaries and ova, ii. 192 Parovarium, ii. 204 Wolffian body, ii. 204 Rosenmuller's organ, ii. 205 Mammary glands, ii. 277 General structure, ii. 277 Gland stroma, ii. 278 Area of the nipple, ii. 279 Excretory ducts, ii. 281 Vessels, ii. 282 Development and changes occurring in the gland, ii. 284 Milk, ii. 284 Vulva, ii. 318 Clitoris and vestibuhim, ii. 319 Bulbi vestibuli, ii. 320 Bartholin's glands, ii. 321 Hymen and vagina, ii. 321 Urethra, ii. 323 Glands of Littr^, ii. 324 Uterus, iii. 474 Peritoneal investment, iii. 474 Musculature, iii. 475 Mucous membrane, iii. 477 Secretion of uterine glands, iii. 478 Glandulse utriculares, iii. 478 Ciliated epithelium, iii, 482 Plicse palmatae, iii. 487 Mucous follicles of the cervix, iii. 487 Ovula Nabothi, iii. 488 Nerves of, iii. 489 Vessels of, iii. 491 Lymphatics of, iii. 491 Placenta, iii. 492 Placenta uterina, iii. 492 Muscular fibres of, iii. 494 Bloodvessels, iii. 494 Placenta fcotalis, iii. 495 Chorion, iii. 496 Vessels and villi of chorion, iii. 496 Oviduct, Fallopian tube, iii. 498. Isthmus, iii. 499 Ampulla, iii. 499 Ostium uterinum, iii. 499 Ostium abdominale, iii. 499 Fimbria, iii. 500 Coats of the oviduct, iii. 500 Sharpey's fibres, i. 126, 475 Sheath of Schwann, i. 152, ii. 336 Sinus rhomboidalis of Birds, i. 64 P P 578 INDEX. Skin, hair, and nails, ii. 217 Subcutaneous connective tissue, ii. 219 Corium, ii. 221 Papillae, ii. 224 Bloodvessels, ii. 224 Lymphatics, ii. 225 Epidermis, ii. 227 Rete Malpighii, ii. 229 Horny layer, ii. 229 Nerves, ii. 231 Pacinian corpuscles, ii. 232 Meissner's corpuscles, ii. 233 Sebaceous follicles, ii, 236 Sweat glands, ii. 238 Erectores pili, ii. 240 Hairs, ii. 241 Nails, ii. 258 Slender fasciculi of Burdach, ii 337 Small intestine, i. 560 Smell, organ of, iii. 201 Smooth muscular tissue, i. 188 Solitary glands, ii. 565 Spermatozoa, ii. 141 Sphincter ani, ii. 582 Sphincter oris, i. 502 Sphincter pupillte, iii. 311 Spinal cord, ii. 327 General structure ii. 327 White substance, ii. 331 Pia mater, ii. 331 Plexus of elastic tissue, ii. 333 Neuroglia, ii. 335 Nerve fibres, ii. 335 Course of the nerve fibres, ii. 340 Grey substance, ii. 343 Nerve cells, ii. 346 Origin of nerves in, ii. 350 Clarke's columns, ii. 354, 359 Grey commissure, ii. 355 Central canal, ii. 356 Anterior and posterior cornua, ii. 583 Substautia gelatinosa, ii. 361 Course of fibres in, ii. 363. Spleen, i. 338 Capsule, i. 352 Trabeculae, i. 352 Venous sheaths, i. 353 Arterial sheaths, i. 354 Malpighiau corpuscles, L 354 Pulp, i. 355 (Jells of, i. 356 Intermediate substance, i. 357 Bloodvessels of, i. 357. Intermediate blood paths, i. 358 Lymphatics, i. 359 Nerves, i. 360 I >i'\ elopment of, i. 360 Spiral fibres of the nerves, i. 175, ii. 546 Spiral lamina, iii. 134, 143 Staining, preparation of tissues by, i. xxxii., ii. 344 Stapes, iii. 123 Steinheil's lenses, i. iii. i Stomach, i. 543 Mucous membrane, i. 543 Lymphatics, i. 548 Bloodvessels, i, 594 Nerves of, i. 549 Muscular layers of, i. 547, 549 Tubular glands, i. 550 Of Dog, i. 661 Of Rabbit, i. 551 Of Rat, i. 522 Of Birds, i. 554 Of Frog, i. 558 Stomata, i. 307 Stratum bacillosum, iii. 327 „ granulosum, iii. 234 „ musculosum, i. 560 „ corneum, ii. 229 „ mucosum, ii. 229 Stria vascularis, iii. 142 Striated muscle, structure of, iii. 543 Strieker's moist chamber, i. viii. Strieker's method of heating the stage> i. xii. Stroma of the brain, ii. 383 „ „ choroid, iii. 303 „ heart, i. 251 „ liver, ii. 31 „ kidneys, ii 105 „ mammary glands, ii. 278 „ ovary, ii. 168 „ salivary glands, i. 460 „ spleen, i. 352 , , suprarenal capsules, ii. 1 1 8 Subiculum cornu Ammonis, ii. 394 Subcutaneous connective tissue, ii. 219 Sudoriparous glands, ii. 238, iii. 442 Supporting tissue of the retina, iii. 272 Substantia adamantina, i. 471 alba of the nerves, i. 151 cinerea of the nerves, i. 153 gelatinosa Rolandi, ii. 361 osteoidea, i. 117 vitrea, i. 471 Subvaginal space, iii. 338 Sulcus anterior and posterior of the spinal cord, ii. 327 Sulcus spiralis, iii. 134, 143 Supra vaginal space, iii. 337 Suprachorioidal membrane, iii. 385 Suprarenal capsules, ii. 110 Parenchyma, ii. Ill Cortex, ii. 112 Medulla, ii. 116 INDEX 579 Strum a, ii. 118 Vessels, ii. 120 Lymphatics, ii. 121 Nerves, ii. 121 Suspensorius duodeni, i. 561 Sweat glands, ii. 238 Swimming bladder of Fishes, ii. 78 Sympathetic fibres, non-medullated, ii. 551 Sympathetic nervous system, ii. 539 cells, ii. 540 „ fibres, ii. 551 Synovial membranes, iii. 555 Bichat's division, iii. 555 Endothelium, iii. 556 Serous vessels, iii. 559 Sheaths of tendons, iii. 560 Tactile corpuscles, i. 167 Tarsal cartilage of eyelids, iii. 44f> Taste, organs of, iii. 1 Gustatory bulbs, iii. 1, 8 Papilla circumvallatse, iii. 3 Papillae fungiformes, iii. f> Gustatory cells, iii. 10 Gustatory nerves, iii. 12 Of Amphibia, iii. 14 Gustatory disks, iii. 14 Of Fish, iii. 20 Teasing out, preparation of tissues by, i. xxvii. Teeth, i. 463 Dentine, i. 466 Dentinal canaliculi, i. 466 Dentinal fibres, i. 466, 469 Dentinal sheaths, i. 466 Interglobular spaces, i. 468 Enamel, i. 471 Enamel fibres or prisms, i. 472 Cuticula, i. 474 Cement, i. 475 Tooth pulp, or matrix, i. 476 Odoutoblasts, i. 476 Pulp, i. 476 Nerves of the teeth, i. 477 Gum, i. 477 Alveolar periosteum, i. 478 Development of the teeth, i. 479 Enamel organ, i. 479 Tooth sacculus, i. 480 „ furrow, or groove, i. 480 Knamel germ, i. 482 Dentine and cement, i. 488 Tegnientum of the crus cerebri, ii. 421 Tegmentuui vasculosum (ear), iii. 145 Tenon's facia and space, iii. 336 Termination of nerves in muscle, i. 202 Of Invertebrata, i. 205 . Of Amphibia, i. 209 Of Reptiles, i. 216 Of Man, i. 222 1 Testes, ii. 131 Tunica adnata, ii. 131 Tunica vaginalis propria, ii. 131 Tunica albuginea, ii. 133 Tunica vaginalis communis, ii. 13-i Corpus Highmori, ii. 133 Giraldes' organ, ii. 132 Piiratestis, ii. 132 Morgagni's hydatid, ii. 132 Muller's duct, ii. 132 Wolffian body, ii. 133, 204 Septula testis, ii. 133 Cremaster internus, ii. 133 Tunica dartos, ii. 133 Septum scroti, ii. 134 Structure of the seminiferous canals ii. 134 Rete testis, ii. 134 Coni vasculosi, ii. 134 Cell contents of the ducts, ii. 138 Various forms of the seminal cor- puscles, ii. 141 Structure of the spermatozoa, ii. 149 Movements of the spermatozoa, ii. 151 In Protozoa, ii. 142 In sponges, ii. 142 In Coeleuterata, ii. 142 In Echinodermata, ii. 142 In Vermes, ii. 1 42 In Annelida, ii. 143 In Cirripedia, ii. 143 In Ostracoda, ii. 143 In Phyllopoda, ii. 143 In Decapoda, ii. 144 In Amphipoda, ii. 144 In Arachnida, ii. 134 In Myriapoda, ii. 144 In Insecta, ii. 145 In Bryozoa, ii. 145 In Salpidse, ii. 145 In Lamellibranchiata, ii. 14f> In Cephalophora, ii. 146 In Gasteropoda, ii. 146 In Cephalopoda, ii. 147 In Pisces, ii. 147 In Amphibia, ii. 147 In Reptilia, ii. 148 In Mammalia, ii. 148 Development of the seminal corpus cles, ii. 152 Vessels and nerves of the testis, ii. 162 Theca folliculi, ii. 172 Thymus gland, i. 365 Follicles of, i. 367 Vessels of, i. 368 Physiological atrophy of, i. 369 580 INDEX. Thyroid cartilage, ii. 36 Thyroid gland, i. 370 Vesicles of, i. 370 Stroma of, i. 371 Vessels of, i. 372 Tongue, i. 514 Papillae filiformes, i. 514 Papillae fungiformes, i. 514 Papilla) circumvallatae, i. 515 Epithelium of tongue, i. 514 Septum cartilagineum, i. 515 Glands (Nuhn's), i. 516 Saccular lingual glands, i. 517 Foramen caecum, i. 518 Lymphatics of the tongue, i. 510 Muscles of the tongue, i. 51 9 Tonsilla pharyngea, i. 525 Tonsils, i. 513 Touch, organ of, ii. 217 External skin, ii. 217 Subcutaneous connective tissue, ii. 219 Corium, or cutis, ii. 221 Papillae of cutis, ii. 224 Bloodvessels and lymphatics of cutis, ii. 224 Epidermis, ii. 227 Stratum mucosum, or rete Malpighii, ii. 227 Corneal lamina, ii. 229 Nerves of the skin, ii. 231 Corpuscles of Pacini or of Vater, ii. 232 Corpuscles of Wagner or Meissner, ii. 233 Termination of non-medullated nerve fibres, ii. 235 Sebaceous glands, ii. 236 Sweat glands, ii. 238 Muscles of the skin, ii. 240 Hairs, ii. 241 Nails, ii. 258 Trabeculae cornea, iii. 393 Trabeculae lienis, i. 352 Trabecular connective tissue, i. 68 Trachea, ii. 46 Trachoma glands, iii. 450 Tread, or cicatricula, iii. 181 Trigeminus, origin of, ii. 446, 486 Trigonum Lieutodii, ii. 128 Trochlearis nerve, origin of, ii. 444 Tuba Eustachii, iii. 66 Tubae Fallopii, iii. 498 Tubuli uriniferi, ii. 85 Of Birds, ii. 96 Of Chelonia, ii. 96 Of Batrachia, ii. 96 Of Fish, ii. 97 Tunica adnata of the testis, ii. 131 Tunica adventitia of the vessels, i. 274 „ „ oviduct, iii. 500 albuginea testis, ii. 133 „ ovarii, ii. 167 conjunctiva, iii. 447 cornea, iii. 372 propria of ovary, ii. 172 ,, „ of the membranous la- byrinth, iii. 96. „ „ of tubuli uriniferi, ii. 92 ,, Ruyschiana, iii. 303 „ vaginalis communis, ii. 131 Type, ideal, of cell, i. 4 Tyson's glands, ii. 317 Ungues, ii. 258 Unstriated muscular tissue, i. 188 Ureters, ii. 129 Urethra, ii. 301 URINARY APPARATUS, ii. 83 Kidneys, ii. 83 Medullary substance, ii. 83 Cortical substance, ii. 83 Medullary rays, ii. 84 Pyramids, ii. 84 Labyrinth of the, ii. 84 Tubuli uriniferi, ii. 85 Capsule of the glomerulus, ii. 85 Henle's loops, ii. 85 Intermediate portion, ii. 87 Collecting tubes, ii. 87 Ductus papillares, ii. 88 Primitive cones, ii. 89 Structure of tubuli, ii. 90 Bloodvessels, ii. 97 Vessels of cortex, ii. 97 Arteriae interlobulares, ii. 97 Vasa afferentia, ii. 98 Vasa efferentia, ii. 98 Capillary plexus of the cortex, ii. 98 Vessels of the medulla, ii. 102 Arteriolae rectse, ii. 202 Capillary plexus of medulla, ii. 103 Vessels of the capsule, ii. 104 Lymphatics, ii. 105 Connective tissue, ii. 105 Nerves, ii. 106 Bladder, ii. 124 Epithelium of, ii. 125 Connective-tissue layer of, ii. 126 Muscular layer of, ii. 127 Vessels of, ii. 128 Nerves of, ii. 128 Uterus, iii. 474 Peritoneal relations, iii. 474 Musculature, iii. 475 Mucous membrane, iii. 477 Glandulae utriculares, iii. 478 Plicae palmatse, iii. 487 INDEX. 581 Mucous follicles of the cervix, iii. 487 Ovula Nabothi, iii. 488 Nerves of, iii. 489 Vessels and lymphatics, iii. 491 Utricular glands of uterus, iii. 478 Uvea, iii. 310 Uvula, i. 506 Vagina, ii. 321 Vagrant cells, i. 54 Vagus, origin of, ii. 505 Valves of Kerkringius, i. 563 Valvulse conniventes, i. 563 Vas deferens, ii. 134, 288 Vas spirale (ear), iii. 150 Vasa afferentia, ii 98 Vasa efferentia, ii. 98 Vasa vasorum, i. 226 Vascular plexuses, i. 289 Vater's corpuscles, i. 167, ii. 232 Veins, i. 275 Endothelium, i. 276 Elastic internal layer, i. 276 Internal fibrous layer, i. 276 Muscular layer, i. 277 Adventitia, i. 278 Valves of, i. 278 Vena centralis retinae, iii. 316 Venae interlobulares, ii. 24 „ intralobulares, ii. 24 „ ciliares, iii. 320 „ vorticosse, iii. 322 Ventriculus (stomach), i. 543 Vesica fellea, ii. 23 Vesicula germinativa, ii. 175 Vesicula prostatica, ii. 301 Vesiculae seminales, ii. 293 Vestibulum, ii. 319 Villi of the small intestine, i. 564 Vitellus, ii. 175 Vitreous humour, iii. 345 Vocal cords, true, ii. 43 „ „ false, ii. 42 Voluntary muscle, iii. 543 Vulva, ii. 318 Wagner's corpuscles, ii. 233 Wandering cells, i. 54 Warming the stage of the microscope, means of, i. xii. White corpuscles of blood, i. 414 White substance of spinal cord, i. 331 Wolffian bodies, ii. 133, 204 Wrisberg, cartilages of, ii. 36 Yolk, principal, ii. 174, 178 „ secondary, ii. 174 Zona denticulata, iii. 144 „ pectinata, iii. 144, 150 „ pellucida, ii. 175 „ radiata, ii. 176 Zonule of Zinn, iii. 345, 354 UNIT ?T \V.i»s. .n .-UK! 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